JP7666768B1 - Method for separating and recovering plastic film, and method for producing recycled plastic pellets - Google Patents

Abstract

The method for separating and recovering a plastic film having at least an ink layer includes a step 1 of crushing the plastic film, a step 2 of immersing the plastic film in a cleaning liquid, and a step 3 of separating the ink layer from the plastic film by stirring the crushed plastic film in a rinsing liquid containing at least a water-soluble solvent. The present invention also provides a method for producing recycled plastic pellets, which comprises recovering the plastic crushed material separated by the methods of steps 1 to 3, melting the recovered material, and molding it with a molding machine.

Description

The present invention relates to a method for separating and recovering plastic films, and a method for producing recycled plastic pellets using crushed plastic material recovered by said method.

Currently, the recycling rate of plastic waste, which is separated and collected, is 9% of the plastic produced worldwide. Of the 91% of plastic that has become garbage, 12% has been incinerated, and 79% has been landfilled or leaked into the environment (Non-Patent Document 1). One of the reasons for this continued low recycling rate is the difficulty of the separation and collection system. In order to recycle plastic, it is necessary to separate and collect waste plastics that are integrated with different plastic materials such as polyethylene (PE) and polypropylene (PP) by material. However, many plastic products, including laminated films, are made of different plastic materials that are bonded and laminated, making it difficult to separate and collect them by material. Therefore, there is a strong demand for the construction of a recycling system that can easily separate and collect waste plastic.

In addition, recycled plastic products are difficult to turn into the same product from a cost perspective, and basically deteriorate every time they are recycled, so they are inevitably reborn as products of lower quality. One reason for the decline in quality of recycled plastic is that inks and pigments are mixed into the plastic as impurities. However, many plastic products have a printing process on their surface, making it difficult to decolorize them during the recycling process, and as a result, recycled plastic products are colored. Recycled plastics that contain pigments, inks, etc. not only have significantly lower commercial value due to the coloring, but the reality is that they only end up as plastic that has deteriorated physically due to the impurities, so there is a demand for recycling methods that can produce high-quality recycled plastic.

In response to these issues, Patent Document 1 proposes a recycling method in which the aluminum layer is dissolved from crushed multilayer film with alkali, the multilayer film is separated based on differences in specific gravity, and then the valuable components are separated and recycled by selectively melting the film in a solvent. Patent Document 2 proposes a process in which printed film is crushed, the ink is removed, and the film is rinsed and dried, but both processes are long and complicated.

Furthermore, Patent Document 3 provides a method for removing ink from a printed, rolled film using a solvent and a non-abrasive cloth, while Patent Document 4 provides a method for removing ink from a printed, rolled film using a solvent, a brush and a wiper blade, but these methods only produce an unprinted film by removing the ink from a rolled film.

In particular, in recent years, as packaging materials have become more diverse, there is an increasing demand for high functionality in packaging materials, improved adhesion of ink films to plastic substrates, and high design quality in printed matter. As a result, the types of packaging materials and inks have become more diverse, and at the same time, peeling off the ink layer has become more difficult. For example, in a laminate film in which multiple films are layered together, or in a laminate in which an ink layer is provided on a film and then laminated with another film, etc., via an adhesive layer, in the case of a laminate film in which an ink layer is provided between multiple films (reverse printing), peeling off the ink layer becomes more difficult because it is necessary to separate the multiple films to remove the ink layer. There is a need for a method that can peel off the ink layer from plastic films of such diverse configurations.

Science Advances 19 Jul 2017:Vol. 3, no. 7, e1700782

JP 2006-205160 A Special table 2015-520684 publication Special table 2016-509613 publication Special table 2018-514384 publication

In the conventional techniques, separation of laminated films involves a process of dry crushing the laminated film followed by an ink removal or separation process, which is a general process that is long and cumbersome. Furthermore, the conventional techniques make it difficult to recycle laminated films with a wide variety of compositions, which reduces the quality and commercial value of recycled plastics.

Therefore, the problem that this invention aims to solve is to provide a method for easily separating and recovering a wide variety of plastic films having at least an ink layer, and a method for producing high-quality recycled plastic pellets using the crushed plastic material recovered by this method.

As a result of extensive research into solving the above-mentioned problems, the inventors have discovered an easy method for regenerating plastic laminates into high-quality recycled raw materials, which comprises step 1 of crushing a plastic film, step 2 of immersing the plastic film in a cleaning liquid, and step 3 of separating the ink layer from the plastic film by agitating the crushed plastic film with a rinsing liquid.

That is, the present invention provides a method for separating and recovering a plastic film having at least an ink layer, comprising step 1 of crushing the plastic film, step 2 of immersing the plastic film in a cleaning liquid, and step 3 of separating the ink layer from the plastic film by stirring the crushed plastic film in a rinsing liquid containing at least a water-soluble solvent.

The present invention also provides a method for producing recycled plastic pellets, which comprises recovering the crushed plastic material separated by the method described above in single layers, melting the recovered material, and molding it using a molding machine.

According to the present invention, a wide variety of plastic films having at least an ink layer can be separated into single layers, and crushed single-layer films can be easily recovered, separated, and reused. According to the method of the present invention, not only plastic films in which the ink layer is exposed on the film surface (front-printed), but also plastic laminates of various configurations such as laminated films in which the ink layer is provided between multiple films (reverse-printed) can be separated into single layers, and the ink layer can be easily peeled off. In other words, regardless of the type of plastic laminate, the film can be separated into single layers, and the ink layer can be easily separated (peeled off), which makes it easier to separate and recover plastic laminates, and the recovered plastic can be reused as high-quality recycled plastic raw material.

<Regarding Step 1>
The method for separating and recovering a plastic film of the present invention includes a step 1 of crushing the plastic film. In the step 1, the method for crushing the plastic film is not particularly limited, and can be performed by a known method. The crushing may be performed in an air atmosphere in the absence of liquids such as a solvent, or in water or a cleaning solution. When crushing is performed in an air atmosphere, a dry crusher can be used. When crushing is performed in water or a cleaning solution, a wet crusher that can perform crushing and pressure feeding at the same time can be used. When a wet crusher is used, the plastic film can be efficiently crushed, and the laminated plastic film can be peeled off into each layer.

By crushing the plastic film in step 1, it becomes easier to completely peel off the plastic film into a single layer in steps 2 and 3 described below. In step 1, it is sufficient that the plastic film is crushed, and the crushed plastic film may be in a state where at least a part of the edge or the like is partially peeled off, or each layer may be completely peeled off, or each layer may not be peeled off.

The long sides of the plastic film crushed in step 1 are preferably 1 mm to 30 mm, more preferably 1 mm to 20 mm, and even more preferably 1 mm to 10 mm. If the length is within the above range, the time it takes for the treatment liquid to penetrate from the edge of the fluff to the center in step 2, in which the plastic film is immersed in the cleaning liquid, is shortened, making it easier to completely peel off the plastic film into a single layer.

In order to reduce the time it takes for the treatment solution to penetrate from the edge of the fluff to the center, it is more preferable for holes or slits to be made in the crushed plastic film. The diameter of the hole or the length of the slit is preferably 0.5 mm or more, more preferably 0.8 mm or more, and even more preferably 1.0 mm or more.

(Dry crusher)
The dry crusher used in step 1 is not particularly limited, and known techniques for crushing solids or cutting films can be applied, such as jaw crushers, impact crushers, cutter mills, stamp mills, ring mills, roller mills, jet mills, hammer mills, colloid mills, rotary cutters, mycolloiders, masscolloiders, ball mills, power mills, pin mills, airflow crushers (jet mills), shear friction crushers, cutter crushers, impact crushers (hammer mills, ball mills), roll crushers, homogenizers, ultrasonic crushers, etc. In order to prevent the substrate or ink layer from softening due to frictional heat during crushing and the cross section of the laminate from fusing, it is preferable to perform crushing or crushing in a cooled state of the laminate or crushing device.

The dry crusher can be preferably used for separating and recovering films in both plastic films in which the ink layer is exposed on the film surface (surface printing) and laminated films in which the ink layer is provided between multiple films (reverse printing). The ink layer applied to the plastic film is a printing ink layer for displaying the product name and the like and for providing decorativeness, and is often printed with organic solvent-based printing ink, water-based ink, or active energy ray curing ink using a gravure printing machine, flexographic printing machine, offset printing machine, inkjet printing machine, etc. In plastic films with such ink layers, the film and the printed surface are not completely separated when a dry crusher is used in step 1, but in the present invention, it is possible to completely separate the film and the printed surface in steps 2 and 3 described below. In the case of laminated films in which the ink layer is provided between multiple films (reverse printing), in addition to the dry crusher, it is preferable to use a wet crusher to improve the separation of the ink layer provided between the films.

(Wet crusher)
The wet crusher used in step 1 is not particularly limited, but is preferably a wet crusher that can crush, disperse, mix, and pump solids in a liquid at the same time. Specifically, it is preferable to use a crusher that has a mechanism for crushing solids in a liquid by shear force and/or friction force, and is also preferable to use a crusher that has a mechanism for crushing and pumping plastic films. Examples of such wet crushers include a wet crushing pump, a colloid mill, a grinder, and a beater.

(Wet fracturing pump)
The wet crushing pump preferably has a mechanism for crushing the solids using fixed blades and rotating blades while pumping the solids in the liquid, and a more preferred mechanism is a mechanism for crushing in three stages using a combination of four parts: cutting blades, a crushing impeller, a shroud ring, and a grid.

Plastic film is crushed in three stages by the wet crushing pump. The plastic film is roughly cut by the cutting blades of the fixed blades and the inlet edge of the rotating blade crushing impeller, then it is agitated and pumped by the axial flow crushing impeller, and some of the plastic film is cut when it hits the blades of the shroud ring of the fixed blade. The laminated film that passes through the crushing impeller is further crushed and agitated between the grids, passes through the grid, is pressurized by the pressurizing impeller, and is pumped to the next process.

The pumping speed is not particularly limited, but considering the peeling of the ink layer and the peeling and separation efficiency when separating the plastic film into each layer, it is preferably 0.03 ^m3 /min or more. There is no particular upper limit to the pumping speed, and even a standard operating speed of the device, for example 1.4 ^m3 /min, is sufficient to peel off the ink and separate the plastic film into single layers.

The grid shape is not particularly limited. Since the grid aperture affects the size of the laminated film after crushing, the grid aperture is preferably 0.1 to 50 mm, and taking into consideration the crushing efficiency and the size of the laminated film after crushing, it is more preferably 1 to 20 mm.

Specific examples of wet fracturing pumps include the KD series from Husqvarna Zenoah, the Suncutta series from Nikuni, the Disintegrator series from Furukawa Industrial Machinery Systems, the Incrusher series and Refiner from Aikawa Iron Works, the Scatter from Sanwa Hydrotech, and the Trigonal from Nippon Coke Company.

(Colloid Mill)
The colloid mill used in this invention is a machine used to reduce particle size in a dispersion system where particles are suspended in a liquid. A colloid mill consists of a rotor and a stator combination, where the rotor rotates at high speed against the fixed stator. The high speed rotation generates high levels of shear, which is used to reduce the particle size in the liquid.

The crushing section of the colloid mill consists of a toothed, truncated cone-shaped rotor and a stator, and the rotor and stator are tapered so that they narrow as they approach the discharge port. The laminated film is repeatedly subjected to powerful shearing, compression and impact in the ring-shaped gap that narrows as it approaches the discharge port, causing it to be crushed.

Specific colloid mills are not particularly limited as long as they are dispersion machines generally referred to as colloid mills, but examples include IKA's Colloid Mill MK series, Iwaki's WCM series, Mountec's PUC Colloid Mill series, and Eurotech's Cavitron.

(Grinder)
The grinding machine preferably has a mechanism for crushing solid matter placed between a pair of upper and lower millstones by shear or friction while rotating them in liquid, and is preferably capable of grinding solid matter into a fine powder while flowing water through it.

The size of the crushed material can be adjusted by adjusting the distance between the upper and lower stone mills, but it is usually finely ground to 500 μm or less, preferably 300 μm or less, and more preferably 200 μm or less. By reducing the size of the crushed material in this way, each layer of the plastic film is separated into a single layer, and the storage space for the crushed material can be reduced, making inventory management easier. In addition, when producing recycled plastic from the crushed material, it can be put into a kneader without going through a compressor, etc., so the process can be simplified. On the other hand, the lower limit of the size of the crushed material is preferably 10 μm or more, preferably 30 μm or more, and more preferably 50 μm or more in order to facilitate recovery.

There are no particular restrictions on rotation speed or water flow speed.

A specific example of a grinding machine is the Supermass Colloider manufactured by Masuko Sangyo Co., Ltd.

As mentioned above, the wet crusher can be preferably used when separating and recovering laminated plastic films in which an ink layer is provided between multiple films (reverse printing).

In most cases, reverse-printed laminated plastic films are provided with a printed ink layer for displaying product names and other information and for providing decorativeness, in addition to adhesives. The ink layer is often printed with organic solvent-based printing ink, water-based ink, or active energy ray curable ink using a gravure printer, flexo printer, offset printer, inkjet printer, etc. In plastic films provided with such an ink layer, the plastic film may be crushed in a cleaning solution containing a cleaning component or a peeling component in water in order to peel and remove the ink layer more efficiently. By crushing the plastic film in a cleaning solution containing a cleaning component or a peeling component in water, the ink layer provided on the plastic film can be peeled and removed and the plastic film can be separated into single layers at the same time. For example, the inks most commonly used for plastic laminated films, including those for food packaging, are gravure ink and flexo ink, but the wet crushing process using a cleaning solution is efficient because it can also peel off the printed ink layer. In addition, the laminated film may have a metal foil or vapor-deposited film such as aluminum laminated thereon, but in the present invention, the metal foil or vapor-deposited film can also be peeled off or dissolved. As already described above, the layers constituting the plastic film may be peeled off into single layers by crushing in water, or a part of the crushed plastic film may be partially peeled off. In addition, the ink layer provided on the plastic film does not need to be completely removed from the plastic film in step 1, and may be partially attached, or may not be removed from the ink layer.

When a wet crusher is used in step 1, crushing may be performed using water as a solvent, or a cleaning solution in which water contains a cleaning or peeling component such as an inorganic base or a surfactant, or other components. The cleaning solution may be water containing one or more of the following components in appropriate combination.

(Inorganic Base)
The aqueous cleaning solution usable in step 1 may be water containing an inorganic base. Specific examples of the inorganic base include sodium hydroxide and potassium hydroxide. These inorganic bases are contained in a concentration of 0.1 to 10% by weight, more preferably 0.1 to 5% by weight, based on the total amount of the aqueous cleaning solution. The pH is preferably 10 or higher.

(Surfactant)
Water containing a surfactant can be used as the aqueous cleaning liquid usable in step 1. The surfactant is not particularly limited, and any known surfactant can be used, including, for example, anionic surfactants, nonionic surfactants, amphoteric surfactants, and cationic surfactants.

Typical examples of nonionic surfactants include polyoxyalkylene alkyl ethers, polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene fatty acid esters, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene sorbitol fatty acid esters, glycerin fatty acid esters, polyoxyethylene glycerin fatty acid esters, polyglycerin fatty acid esters, sucrose fatty acid esters, polyoxyethylene alkylamines, polyoxyethylene fatty acid amides, fatty acid alkylol amides, alkyl alkanol amides, acetylene glycol, oxyethylene adducts of acetylene glycol, polyethylene glycol polypropylene glycol block copolymers, and the like. Among these, polyoxyethylene nonylphenyl ether, polyoxyethylene octylphenyl ether, polyoxyethylene dodecylphenyl ether, polyoxyethylene alkyl ethers, polyoxyethylene fatty acid esters, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, fatty acid alkylol amides, acetylene glycol, oxyethylene adducts of acetylene glycol, and polyethylene glycol polypropylene glycol block copolymers.

In the present invention, it is preferable that the aqueous cleaning liquid contains 50% by weight or more of water and 0.01% by weight to 5% by weight of a polyoxyalkylene alkyl ether surfactant containing at least one compound represented by general formula (1).

R ¹ -O-[CH ₂ -CH(X ¹ )-O]n ¹ -H (1)
In formula (1), ^R1 represents a linear or branched alkyl group, an alkenyl group or an octylphenol group, ⁿ¹ represents the average number of moles added, and ^X1 represents hydrogen or a short-chain alkyl group.

More preferably, ^R1 in formula (1) is a linear or branched alkyl or alkenyl group having 10 or more carbon atoms. The more carbon atoms there are, the better the ink removability, and this is preferred. Specific examples of the number of carbon atoms include a decyl group having 10 carbon atoms, a lauryl group having 12 carbon atoms, a tridecyl group having 13 carbon atoms, a myristyl group having 14 carbon atoms, a cetyl group having 16 carbon atoms, and an oleyl group and a stearyl group having 18 carbon atoms.

Specific examples of such products include the Noigen series, DSK NL-Dash series, and DKS-NL series manufactured by Daiichi Kogyo Seiyaku Co., Ltd., the Nonion series manufactured by NOF Corporation, the Emulgen series manufactured by Kao Corporation, and the Leox series, Leocol series, and Lionol series manufactured by Lion Corporation. Among these, the nonionic surfactants represented by the general formula (1) and having 10 or more carbon atoms represented by R ¹ are applicable, but are not limited thereto.

The HLB value of the polyoxyalkylene alkyl ether surfactant represented by the general formula (1) is not particularly limited. The HLB value here is a value that indicates the degree of affinity of the surfactant to water and oil (a water-insoluble organic compound), and is defined by the Griffin method (HLB value = 20 x sum of the formula weights of the hydrophilic parts / molecular weight).

Among the nonionic surfactants represented by the general formula (1), specific surfactants in which R ¹ has 10 or more carbon atoms and an HLB value of less than 12.5 are, by Dai-ichi Kogyo Seiyaku Co., Ltd., Noigen XL-41, Noigen LF-40X, Noigen TDS-30, Noigen TDS-50, Noigen TDS-70, Noigen TDX-50, Noigen SD-30, Noigen SD-60, DKS NL-15, DKS NL-30, DKS NL-40, DKS NL-50, DKS NL-60, DKS NL-70, Noigen ET-83, Noigen ET-102, DSK Dash400, DSK Dash403, DSK Dash404, DSK Dash 408, Noigen LP-55, Noigen LP-70, Noigen ET-65, Noigen ET-95, Noigen ET-115, Noigen ET-69, Noigen ET-89, Noigen ET-109, Noigen ET-129, Noigen ET-149, and NOF Corp. products include Nonion K-204, Persoft NK-60, Nonion P-208, Nonion P-210, Nonion E-202, Nonion E-202S, Nonion E-205, Nonion E-205S, Nonion S-202, Nonion S-207, Nonion EH-204, Nonion ID-203, Nonion HT-505, Nonion HT-507, Nonion H Examples of the antibacterial agents include, but are not limited to, T-510, Nonion HT-512, and those manufactured by Kao Corporation such as Emulgen 102KG, Emulgen 103, Emulgen 104P, Emulgen 105, Emulgen 106, Emulgen 108, Emulgen 210P, Emulgen 404, Emulgen 408, Emulgen 409PV, Emulgen 705, and Emulgen 707, and those manufactured by Lion Corporation such as Rheox CL-30, Rheox CL-40, Rheox CL-50, Rheox CL-60, Rheocol NL-30C, Rheocol TD-50, Rheocol TD-70, Rheocol SC-50, and Rheocol SC-70.

Among the nonionic surfactants represented by general formula (1), specific surfactants in which R1 represents a linear or branched alkyl or alkenyl group having 10 or more carbon atoms and an HLB value of 12.5 or more are listed by Daiichi Kogyo Seiyaku Co., Ltd. as NOIGEN XL-61, NOIGEN XL-6190, NOIGEN XL-70, NOIGEN XL-80, NOIGEN XL-100, NOIGEN XL-140, NOIGEN XL-160, XL-400D, NOIGEN XL-1 000, Noigen LF-60X, Noigen LF-80X, Noigen LF-100X, Noigen TDS-80, Noigen TDS-100, Noigen TDS-120, Noigen TDS-200D, Noigen TDS-500F, Noigen TDX-80, Noigen TDX-80D, Noigen TDX-100D, Noigen TDX-120D, Noigen SD-70, Noigen SD-80, Noigen SD-110, Noigen SD-150, DKS NL-80, DKS NL-90, DKS NL-100, DKS NL-110, DKS NL-180, DKS NL-250, DKS NL-450F, DKS NL-600F, NOIGEN ET-160, NOIGEN ET-170, NOIGEN ET-190, DSK Dash 410, Noigen LP-80, Noigen LP-100, Noigen LP-180, Noigen ET-135, Noigen ET-165, Noigen ET-159, Noigen ET-189, and NOF Corp. products include Nonion K-220, Nonion K-230, Nonion K-2100W, Persoft NH-90C, Persoft NK-100, Persoft NK-100C, Nonion P-210, Nonion P-213, and Nonion Nonion E-212, Nonion E-215, Nonion E-230, Nonion S-215, Nonion S-220, Nonion B-250, Nonion ID-206, Nonion ID-209, Dispanol TOC, Nonion HT-515, Nonion HT-518, and Kao's Emulgen 109P, Emulgen 120, Emulgen 123P, Emulgen 130K, Emulgen 147, Emulgen 150, Emulgen 22 0, Emulgen 320P, Emulgen 350, Emulgen 420, Emulgen 430, Emulgen 709, Emulgen 1108, Emulgen 1118S-70, Emulgen 1135S-70, Emulgen 1150S-60, Emulgen 4085, Emulgen 2020G-HA, Emulgen 2025G, and Lion Corporation's Leox CL-90, Leox CL-230, Leocol TD-90, Leocol Examples of the polyolefin resin include, but are not limited to, LEOCOL TD-90D, LEOCOL TDA-90-25, LEOCOL TDN-90-80, LEOCOL TD-120, LEOCOL TD-200, LEOCOL TDA-400-75, LEOCOL SC-80, LEOCOL SC-90, LEOCOL SC-120, LEOCOL SC-150, LEOCOL SC-200, LEOCOL SC-300, and LEOCOL SC-400.

When R ¹ in the general formula (1) is an octylphenol group, octylphenol ethoxylate is preferred.

Specific products include, but are not limited to, the TRITON (registered trademark) series from Dow Chemical, the Igepal CA series from Rhodia, the Nonidet P series from Shell Chemicals, and the Nikkol OP series from Nikko Chemicals.

Specifically, the amphoteric surfactant is preferably a betaine-type amphoteric surfactant, and more preferably, the amphoteric surfactant contains an alkylcarboxybetaine skeleton or an alkylamidecarboxybetaine skeleton containing at least one compound represented by the general formula (2a).

R1-R2-N ⁺ (CH ₃ ) ₂ CH ₂ COO ^- (2a)
In the general formula (2a), R1 represents hydrogen or C(═O)R3-NH- (R3 represents a linear or branched alkyl or alkenyl group), and R2 represents an alkylene group or an alkenylene group.
In formula (2a), R1 preferably represents a hydrogen atom.
The compound represented by formula (2a) is preferably an amphoteric surfactant having an alkylcarboxybetaine skeleton represented by formula (2a-1).

C _n H _2n+1 N ⁺ (CH ₃ ) ₂ CH ₂ COO ^- (2a-1)
(In general formula (2a-1), n represents the average number of moles added.)
In formula (2a-1), n is preferably 8 or more, more preferably 10 or more, and even more preferably 11 or more.

Specific products that fall under general formula (2a) include Nissan Anon BDF (registered trademark)-R, Nissan Anon BDF (registered trademark)-SF, Nissan Anon BDC-SF, and Nissan Anon BDL-SF manufactured by NOF Corporation, Amogen CB-H and Amogen HB-C manufactured by Daiichi Kogyo Seiyaku Co., Ltd., Rekabion B-200 and Rekabion B-300 manufactured by New Japan Chemical Co., Ltd., and Obazoline CAB-30 and Obazoline ISAB manufactured by Toho Chemical Industry Co., Ltd. Specific examples of products corresponding to the general formula (1a-1) include, but are not limited to, Amogene S, Amogene S-H, and Amogene K manufactured by Daiichi Kogyo Seiyaku Co., Ltd.; Amphitol 20BS, Amphitol 24B, and Amphitol 86B manufactured by Kao Corporation; Nissan Anon BF, Nissan Anon BL, and Nissan Anon BL-SF manufactured by NOF Corporation; Rekabion A-100, Rekabion A-200, and Rekabion A-700 manufactured by New Japan Chemical Co., Ltd.; and Obazoline LB and Obazoline LB-SF manufactured by Toho Chemical Co., Ltd.

In addition, the betaine-type amphoteric surfactant may be one having an imidazolinium betaine skeleton, and specific examples of such products include Nissan Anon GLM-R and Nissan Anon GLM-R-LV manufactured by NOF Corporation, and Amphitol 20Y-B manufactured by Kao Corporation, but are not limited to these.

The amphoteric surfactant may also be a surfactant represented by the following general formula (2b):

R4-(NHC ₂ H ₄ ) _nb -N(R5) ₂ (2b)
(In general formula (2b), R4 represents a linear or branched alkyl group or alkenyl group, nb represents an integer of 0 to 5, and R5 represents hydrogen, -CH ₂ COONa or -CH ₂ COOH, but two R5s may be the same or different, and at least one R5 represents -CH ₂ COONa.)
In general formula (2b), R4 preferably represents a linear alkyl group, and R4 preferably has 8 or more carbon atoms, more preferably 10 or more carbon atoms, and even more preferably 12 or more carbon atoms.

Specific products corresponding to general formula (2b) include Nissan Anon LG-R and Nissan Anon LA manufactured by NOF Corporation, but are not limited to these.

The amphoteric surfactant may also be an amine oxide type surfactant represented by the following general formula (2c):

R6-N ⁺ (CH ₃ ) ₂ O ^- (2c)
(In general formula (2c), R6 represents a linear or branched alkyl group or an alkenyl group.)
In general formula (2c), R6 is preferably a linear alkyl group, and in general formula (2b), R4 preferably has 8 or more carbon atoms, more preferably 10 or more carbon atoms, and even more preferably 12 or more carbon atoms.

Specific examples of products that fall under the general formula (2c) include Amogene AOL manufactured by Daiichi Kogyo Seiyaku Co., Ltd. and Amphitol 20N manufactured by Kao Corporation, but are not limited to these.

Specifically, the cationic surfactant is preferably a cationic surfactant having a quaternary ammonium skeleton, and more preferably, the cationic surfactant has a quaternary ammonium skeleton and contains at least one compound represented by the general formula (3a).

R1-N ⁺ (R2R3)-R4 (3a)
(In general formula (3a), R1 represents a linear or branched alkyl group, or a linear or branched alkenyl group, and -CH ₂ - in the alkyl or alkenyl group may be replaced by -C(═O)-, -NH-, or -C(═O)-NH-; R2 and R3 represent a hydrogen atom, a linear or branched alkyl group, or a linear or branched alkenyl group; R4 represents a hydrogen atom, a linear or branched alkyl group, a linear or branched alkenyl group, or a phenyl group, and the terminal -CH ₃ in the alkyl or alkenyl group may be replaced by a carboxy group or a phenyl group.)
In general formula (3a), R1 is preferably a long-chain alkyl group or alkenyl group in order to further enhance the releasability of the ink, specifically, it is preferably an alkyl group or alkenyl group having 8 to 30 carbon atoms, preferably an alkyl group having 10 to 25 carbon atoms, and preferably an alkyl group or alkenyl group having 12 to 22 carbon atoms. The alkyl group or alkenyl group may be linear or branched, but is preferably linear, and more preferably a linear alkyl group.

In R1, at least one or more -CH ₂ - in the alkyl group or alkenyl group may be substituted with -C(=O)-, -NH- or -C(=O)-NH-. Of these, it is preferable that at least one or more -CH ₂ - in the alkyl group or alkenyl group is substituted with -C(=O)-NH- or -NH-C(=O), it is preferable that one -CH ₂ - in the alkyl group is substituted with -C(=O)-NH- or -NH-C(=O), and it is more preferable that R1 has an amidopropyl skeleton.

R2 and R3 each preferably represent a linear or branched alkyl group or a linear or branched alkenyl group, and more preferably represent a linear or branched alkyl group. In particular, R2 and R3 each preferably represent a linear alkyl group having 1 to 3 carbon atoms, and more preferably represent a methyl group.

R4 is preferably a linear or branched alkyl group, a linear or branched alkenyl group, or a phenyl group, and more preferably a linear or branched alkyl group. In addition, the terminal _—CH3 in the alkyl or alkenyl group is preferably substituted with a carboxy group or a phenyl group.

R4 preferably has 1 to 8 carbon atoms, more preferably 1 to 5 carbon atoms, more preferably 1 to 3 carbon atoms, and more preferably 1 or 2 carbon atoms.

When R4 represents a methyl group, it is preferable that R2 and R3 also represent methyl groups and that general formula (3a) represents an alkyltrimethylammonium skeleton.

Furthermore, when R4 represents an ethyl group, the terminal —CH ₃ in the ethyl group is preferably substituted with a carboxy group or a phenyl group. In other words, it is preferable that R4 represents —CH ₂ —(C(═O)OH or represents a benzyl group.
The compound represented by formula (3a) is preferably a cationic surfactant having a quaternary ammonium skeleton represented by formula (3a-1).

C _n H _2n+1 N ⁺ (CH ₃ ) ₂ R4 (3a-1)
(In the general formula (3a-1), n represents the average number of moles added, and R4 has the same meaning as R4 in the general formula (3a) described in claim 3.)
In the general formula (3a-1a), the number of carbon atoms represented by n is preferably 8 or more. The greater the number of carbon atoms, exceeding 8, the better the ink removability, and this is preferred. Specific numbers of carbon atoms include an octyl group having 8 carbon atoms, a nonyl group having 9 carbon atoms, a decyl group having 10 carbon atoms, an undecyl group having 11 carbon atoms, a lauryl group having 12 carbon atoms, a tridecyl group having 13 carbon atoms, a myristyl group having 14 carbon atoms, a pentadecyl group having 15 carbon atoms, a cetyl group having 16 carbon atoms, and an oleyl group and a stearyl group having 18 carbon atoms.

The preferred groups for R4 are the same as those in formula (3a).
These cationic surfactants having a quaternary ammonium skeleton are preferably of the quaternary ammonium skeleton salt type which forms a salt with a halogen, and preferably form a salt with ^Cl- , more preferably form a salt with Br-, and even more preferably form a salt with ^{I- .} It is considered that the quaternary ammonium skeleton salt which forms a salt with a halogen promotes hydrolysis of the ink film due to the nucleophilic action of the halogen, and therefore improves the peelability of the ink.

Among these, alkyltrimethylammonium chloride type, dialkyldimethylammonium chloride type, and alkylbenzalkonium chloride type compounds are preferred.

Specific products corresponding to the general formula (3a) or (3a-1), manufactured by NOF Corporation, include Nissan Cation MA, Nissan Cation SA, Nissan Cation BB, Nissan Cation FB, Nissan Cation PB-300, Nissan Cation ABT2-500, Nissan Cation AB, Nissan Cation AB-600, Nissan Cation VB-M Flake, Nissan Cation VB-F, Nissan Cation 2-DB-500E, Nissan Cation 2-DB-800E, Nissan Cation 2ABT, Nissan Cation 2-OLR, Nissan Cation F _2-50R , Nissan Cation M ₂ Examples of the products manufactured by Daiichi Kogyo Co., Ltd. include Catiogen TML, Catiogen TMP, Catiogen TMS, Catiogen DDM-PG, Catiogen BC-50, and Catiogen TBB; examples of the products manufactured by Kao Corporation include Cortamine 24P, Cortamine 86P Conc, Cortamine 60W, Cortamine 86W, Sanisol C, and Sanisol B-50; and examples of the products manufactured by Lion Corporation include Lipoguard C-50, Lipoguard T-28, Lipoguard T-30, Lipoguard T-50, Lipoguard T-800, Lipoguard 16-29, Lipoguard 16-50E, and Lipoguard 18-63. , Lipoguard 22-80, Lipoguard CB-50, Lipoguard 210-80E, Lipoguard 2C-75, Lipoguard 2HP-75, Lipoguard 2HP flake, Lipoguard 2HT-75, Lipoguard 2HT flake, Lipoguard 20-751, Lipoguard 41-50, TMAC-50, TPAH-40, TBAB-50A, TBAB-100A, TBAH-40, Lipoguard PH-100, BTMAC-50, BTMAC-100A, BTEAC-50, BTEAC-100A, BTBAC-50A, and the like, but are not limited to these.

The cationic surfactant preferably contains at least one compound represented by a primary or secondary alkanolamine skeleton, and more preferably contains at least one compound represented by a monoalkanolamine skeleton.
The primary monoalkanolamine is preferably a lower alkanol having 1 to 4 carbon atoms, and specific examples thereof include monoethanolamine, 2-aminoisobutanol, etc., and the secondary monoalkanolamine is N-methylethanolamine, 2-ethylaminoethanol, isopropanolamine, etc., but substances other than those exemplified can also be used as appropriate. Furthermore, these monoalkanolamine compounds can be used alone or in appropriate combination of two or more, and can also be used by mixing with water.
These cationic surfactants having a monoalkanolamine skeleton are preferably of the monoalkanolamine salt type which forms a salt with a halogen, and preferably form a salt with ^Cl- .

These surfactants can be used alone or in combination of two or more. The amount of surfactant added is preferably 5% by weight or less, and more preferably 2% by mass or less, based on the total amount of the aqueous cleaning solution. There is no particular lower limit for the surfactant, and it may be 0% by mass, but when a surfactant is contained, it is preferably 0.1% by mass or more.

(non-water-soluble alcohol)
A cleaning liquid containing a water-insoluble primary alcohol can be used in step 1. The water-insoluble primary alcohol is preferably contained in an amount of 20% by weight or less relative to the water.

Examples of water-insoluble primary alcohols include butan-1-ol, pentan-1-ol, hexane-1-ol, heptan-1-ol, octan-1-ol, nonan-1-ol, decan-1-ol, undecane-1-ol, dodecane-1-ol, tridecane-1-ol, tetradecane-1-ol, pentadecane-1-ol, hexadecan-1-ol, heptadecane-1-ol, octadecane-1-ol, and nonadecan-1-ol. Examples of such amines include 1-methyl-1-phenylpropane, ...

(Non-water-soluble glycol ether organic solvent)
A water-insoluble glycol ether-based organic solvent may be contained in water as the cleaning liquid usable in step 1. It is preferable that the cleaning liquid is an aqueous cleaning liquid containing 20% by weight or less of the water-insoluble glycol ether-based organic solvent relative to the water.

Examples of water-insoluble glycol ether-based organic solvents include aromatic glycol ethers.

(Aromatic glycol ether solvent)
As a cleaning liquid that can be used in step 1, water containing an aromatic glycol ether solvent can be used. Examples of aromatic glycol ether solvents include ethylene glycol monophenyl ether (phenoxyethanol), ethylene glycol monobenzyl ether, ethylene glycol dibenzyl ether, diethylene glycol monophenyl ether, diethylene glycol diphenyl ether, and propylene glycol monophenyl ether. Examples of ester glycol ethers include ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, ethylene glycol mono-n-butyl ether acetate, diethylene glycol monoethyl ether acetate, propylene glycol monomethyl ether acetate, and dipropylene glycol monomethyl ether acetate. Among these, ethylene glycol monophenyl ether (phenoxyethanol) is more preferable.

(Water-soluble alcohol)
As a cleaning solution that can be used in step 1, a solution containing water-soluble primary alcohol can be used. Examples of water-soluble primary alcohol include methanol, ethanol, and propan-1-ol, and an arbitrary mixture of these can also be used as industrial alcohol. The water-soluble primary alcohol is preferably contained in an amount of 20% by weight or more relative to the water.

(Water-soluble glycol ether organic solvent)
A water-soluble glycol ether-based organic solvent may be contained in water as the cleaning liquid usable in step 1. It is preferable that the cleaning liquid is an aqueous cleaning liquid containing 20% by weight or more of the water-soluble glycol ether-based organic solvent relative to the water.

Examples of water-soluble glycol ether-based organic solvents include alkylene glycol alkyl ethers.

(Water-soluble alkylene glycol alkyl ether solvent)
R ¹ -O-[CH ₂ -CH(X)-O]n ¹ -R ² (4)
(In the general formula (4), ^R1 represents an alkyl group having one or more carbon atoms, ^R2 represents an alkyl group having one or more carbon atoms or hydrogen, ⁿ¹ represents an integer of 1 to 3, and X represents hydrogen or a methyl group.)
Among the alkylene glycol alkyl ethers represented by the general formula (4), water-soluble alkylene glycol alkyl ethers are more preferred.

Examples of the alkylene glycol alkyl ether represented by the general formula (4) include ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dipropyl ether, ethylene glycol methyl ethyl ether, ethylene glycol methyl propyl ether, ethylene glycol ethyl propyl ether, ethylene glycol monobutyl ether, ethylene glycol-tert-butyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol monobutyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dipropyl ether, diethylene glycol methyl ethyl ether, diethylene glycol methyl propyl ether, diethylene glycol ethyl propyl ether, triethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, propylene glycol dimethyl ether, and propylene glycol diethyl ether.
These alkylene glycol alkyl ethers can be used alone or in combination of two or more, and can also be mixed with water.There is no problem if the content of alkylene glycol alkyl ether is 20% by weight or more, but when water is the medium, it is preferably 30% by weight or more, and most preferably 40% by weight or more.On the other hand, the upper limit can be 100% by weight, but it is preferable to use water as the medium from the viewpoint of environmental impact and safety.

Among the water-soluble alkylene glycol alkyl ethers represented by general formula (4), the alkylene glycol monoalkyl ether represented by general formula (5) is more preferred.

R ² -O-[CH ₂ -CH(X)-O]n ² -H (5)
(In the general formula (5), ^R2 represents an alkyl group having one or more carbon atoms, ⁿ² represents an integer of 1 to 3, and X represents hydrogen or a methyl group.)
Examples of the water-soluble alkylene glycol alkyl ether represented by the general formula (5) include ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, ethylene glycol monobutyl ether, ethylene glycol-tert-butyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol monobutyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, and propylene glycol monobutyl ether.

Furthermore, in the aqueous cleaning liquid containing the water-soluble alkylene glycol alkyl ether represented by the general formula (5), from the viewpoint of maintaining strippability even in a composition in which the water content is much more than 50% by weight, it is preferable that R ² is an alkyl group having 3 or more carbon atoms, n ² is 1 to 3, and X ² is hydrogen or a methyl group.

Specific examples include ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, ethylene glycol tert-butyl ether, diethylene glycol monopropyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, etc. These alkylene glycol alkyl ethers can be used alone or in appropriate combination of two or more, and can also be used by mixing with water.

Furthermore, among these, diethylene glycol monobutyl ether, ethylene glycol mono-tert-butyl ether, and propylene glycol monopropyl ether are particularly preferred in terms of environmental characteristics, flammability, and antifoaming properties.

(Water-soluble monoalkanolamine organic solvent)
A water-soluble alkanolamine organic solvent may be contained in water as the cleaning liquid usable in step 1. The water-soluble alkanolamine organic solvent is preferably an aqueous cleaning liquid containing 20% by weight or more of the water.

Primary to secondary monoalkanolamines with a boiling point of 150 to 200°C can be contained in an amount of 10 to 50% by weight based on the total amount of the cleaning solution.

Examples of primary monoalkanolamines include monoethanolamine, 2-aminoisobutanol, and isopropanolamine, while examples of secondary monoalkanolamines include N-methylethanolamine, 2-ethylaminoethanol, and dimethylaminoethanol, but primary and secondary monoalkanolamines other than those exemplified can also be used as appropriate as long as they have a boiling point within the range of 150 to 200°C. Furthermore, these monoalkanolamine compounds can be used alone or in appropriate combinations of two or more, and can also be used by mixing with water.

(Antifoaming agent)
The water used in step 1 may contain a defoaming agent. In step 1, a large amount of bubbles may be generated during the stirring and crushing steps, and if the bubbles remain, they may overflow during the plastic film recovery step. In addition, in the plastic film crushing step, if a large amount of bubbles are entrained in the cleaning liquid, the plastic substrate may not be crushed to a desired size.

Compounds commonly used as defoaming agents include water-soluble organic solvents and nonionic surfactants with an HLB value in the range of 1 to 3, but silicone-based compounds are particularly preferred because of their high defoaming ability. Among these, emulsion-type and self-emulsifying silicone compounds are preferred.

Specific examples of self-emulsifying defoamers include X-50-1176, KS-530, and KS-537 manufactured by Shin-Etsu Chemical Co., Ltd., and emulsion types include KM-7750D, KM-7752, and KM-98 manufactured by Shin-Etsu Chemical Co., Ltd., and FS Antifoam 025, FS Antifoam 80, FS Antifoam 92, FS Antifoam 93, DKQ1-1183, and DKQ1-1247 manufactured by Nagase Chemspec Corporation, but are not limited to these.

The defoaming agent may be used alone or in combination of two or more kinds. The content of the defoaming agent in the cleaning solution usable in step 1 is preferably in the range of 0.01 to 5% by weight, more preferably in the range of 0.02 to 4% by weight, and even more preferably in the range of 0.03 to 3% by weight.

(liquid temperature)
The temperature of the water or cleaning solution used in step 1 is not particularly limited as long as the liquid state can be maintained, but it is usually preferable to carry out the step at a liquid temperature of 15 to 90° C. When using an aqueous cleaning solution in which a surfactant or the like has been added to water, it is preferable to adjust the liquid temperature depending on the type of surfactant. The optimal temperature at which the cleaning effect is excellent varies depending on the type of surfactant, but is, for example, preferably 40° C. or higher, preferably 65° C. or higher, and preferably 85° C. or higher.
On the other hand, when it is desired to improve the crushability of the plastic film, i.e., to crush the plastic film into smaller pieces, it is preferable that the liquid temperature is not too high, and therefore, it is preferably 40° C. or less, preferably 30° C. or less, and preferably 20° C. or less. Since the cross-sectional area increases as the size of the plastic film after crushing becomes smaller, it becomes easier for each layer constituting the plastic film to swell into a single layer in step 2.

<Regarding Step 2>
The method for separating and recovering plastic films of the present invention includes step 2 of immersing the plastic film crushed in step 1 in a cleaning solution. In step 2, each layer constituting the plastic film and the ink layer can be easily swollen.

(Soaking time)
In step 2, the immersion time is preferably a time for which the crushed plastic film is sufficiently swollen, and specifically, is preferably 30 minutes or more. More specifically, it is within the range of 30 minutes to 48 hours. If the lower limit is less than 30 minutes, it becomes difficult to achieve sufficient swelling in step 2. On the other hand, if the upper limit exceeds 48 hours, the separation and recovery of the present invention takes too much time. Note that swelling of the plastic film means that the ink layer provided on the plastic film, and if an adhesive layer is present, the adhesive layer and/or the ink layer swell, and the cross-sectional thickness of the plastic film increases.

The immersion time can be adjusted appropriately by combining the liquid temperature and agitation described below. The higher the liquid temperature, the shorter the immersion time. When constructing a practical recycling system, it is preferable to set the upper limit of the immersion time to about 4 hours while increasing the liquid temperature.
For example, when immersion is performed at room temperature, sufficient swelling can be achieved by immersion for 24 hours or more. When the liquid temperature is 40° C., sufficient swelling can be achieved by immersion for 16 hours. When the liquid temperature is 75° C., sufficient swelling can be achieved by immersion for 2 hours.

(temperature)
In step 2, the temperature of the cleaning liquid is not particularly limited as long as the liquid state can be maintained. If the liquid temperature is room temperature, heating is not required, which is preferable as it contributes to reducing _CO2 emissions. On the other hand, if efficiency is prioritized as a practical recycling system, a method of shortening the immersion time while heating the liquid temperature is also preferable. That is, it is usually preferable to carry out the process at a liquid temperature of 15 to 90°C. When using an aqueous cleaning liquid in which a surfactant or the like is added to water, it is preferable to adjust the liquid temperature according to the type of surfactant. The optimal temperature at which the cleaning effect is excellent varies depending on the type of surfactant, but is preferably 40°C or higher, preferably 50°C or higher, and preferably 60°C or higher. The upper limit of the liquid temperature is not particularly limited as long as the liquid state can be maintained, but is usually preferably 90°C or lower.

On the other hand, when it is desired to improve the crushability of the plastic film, i.e., to crush the plastic film into smaller pieces, it is preferable that the liquid temperature is not too high, and therefore it is preferably 40°C or less, more preferably 30°C or less, and more preferably 20°C or less. The smaller the size of the plastic film after crushing, the greater the cross-sectional area, which makes it easier for the layers constituting the plastic film to separate into single layers in step 3, and also makes it easier to peel off and decolorize the ink layer.

(Mixing)
In step 2, stirring is not essential but is optional, but stirring allows for more efficient swelling. It is preferable to keep the stirring speed at a level that does not easily cause foaming or the like even without the addition of an antifoaming agent.

The equipment and method for stirring are not particularly limited, and known methods can be used. Specific examples include a device equipped with a motor with stirring blades that can stir the cleaning liquid in a container, a device equipped with a device that generates ultrasonic waves, a device that can shake the container, a wet crusher, etc. The wet crusher may be the same as the crusher described in step 1.

(Cleaning solution)
The washing liquid used in step 2 may be the same as the washing liquid used when using the wet crusher in step 1. Specifically, it is preferable that the washing liquid contains water and the inorganic base described in step 1, and it is also preferable to use a washing liquid containing water and the inorganic base described in step 1 and further containing the surfactant described in step 1.

The cleaning solution used in step 2 preferably contains an appropriate amount of an organic solvent. As the organic solvent, for example, it is preferable to use a water-soluble solvent that is miscible with water, and specifically, the water-soluble solvent preferably contains one or more water-soluble alcohols or water-soluble solvents with a flash point of 21°C or higher. By using a water-soluble solvent in the cleaning solution, the hydroxide ions generated from the inorganic base contained in the cleaning solution are less likely to be hydrated, so the nucleophilicity of the hydroxide ions is increased, and the reaction of peeling the ink layer can be advanced in a hydrophobic field environment, which is effective in peeling the ink film.

Water-soluble solvents with a flash point of 21°C or higher are preferably water-soluble organic solvents that fall under the second and third petroleum categories defined in the Fire Service Act, such as diethylene glycol butyl ether, propylene glycol propyl ether, and 3-methoxy-3-methyl-1-butanol.

Examples of water-soluble alcohols include alcohols specified in the Fire Service Act. Specific examples of these include methanol, ethanol, 1-propyl alcohol, and 2-propyl alcohol, and these may be used alone or in combination.

The organic solvent may preferably contain the water-insoluble alcohol or water-insoluble glycol ether organic solvent described in step 1 above. Among these, butan-1-ol, benzyl alcohol, and ethylene glycol monophenyl ether (phenoxyethanol) are particularly preferred.

In step 2, the plastic film crushed in step 1 is sufficiently swelled, so that the plastic film can be easily peeled off completely into a single layer in step 3. In particular, when the plastic film has an ink layer, it can be difficult to decolorize the plastic depending on the type of ink and the structure of the plastic film. However, in the present invention, by carrying out steps 1 and 2, at least a portion of each layer of the plastic film is peeled off or a base that makes peeling easier is created, and in step 3 described below, the plastic film is separated into single layers and the ink layer is peeled off, so that the ink layer can be easily peeled off regardless of the type of ink or the structure of the plastic film.

In particular, from the viewpoint of the peelability of the ink layer, it is preferable that the cleaning solution used in step 2 contains a large amount of water-soluble solvent in the cleaning solution; specifically, the water-soluble solvent is preferably 30% by mass or more, preferably 40% by mass or more, preferably 50% by mass or more, preferably 60% by mass or more, preferably 70% by mass or more, preferably 80% by mass or more, preferably 90% by mass or more, and preferably 95% by mass or more.

In particular, the cleaning solution used in step 2 includes inorganic bases, specifically sodium hydroxide and potassium hydroxide. These inorganic bases are preferably contained at a concentration of 0.1 to 10% by weight, more preferably 0.1 to 5% by weight, based on the total amount of the ink cleaning solution. The pH is preferably 10 or more, more preferably 11 or more, and more preferably 12 or more. Since sodium hydroxide is poorly soluble in organic solvents, it is preferable to use a cationic surfactant in combination when sodium hydroxide is used. Specifically, a cleaning solution containing sodium hydroxide, a cationic surfactant, a water-insoluble aromatic glycol ether solvent, and a water-soluble alcohol or water-soluble alkanolamine solvent can be used. On the other hand, when potassium hydroxide is used, it is not necessary to use a cationic surfactant in combination because it is easily soluble in organic solvents. Specifically, a cleaning solution containing potassium hydroxide and a water-soluble alcohol or aromatic glycol ether solvent can be used.

In addition, the cleaning solution used in step 2 may contain water. By including water in the cleaning solution in step 2, the operational stability and environmental stability in step 2 can be improved.

Furthermore, the cleaning solution used in step 2 may contain a surfactant. The surfactant is not particularly limited, and known surfactants can be used, such as anionic surfactants, nonionic surfactants, amphoteric surfactants, cationic surfactants, etc. Specific types of these surfactants may be the same as those described as surfactants that can be contained in water in step 1.
In the cleaning solution of step 2, the surfactant may be used alone or in combination of two or more kinds. The amount of the surfactant added is preferably 5% by weight or less, and more preferably 2% by mass or less, based on the total amount of the cleaning solution. The lower limit of the surfactant is not particularly limited and may be 0% by mass, but when a surfactant is contained, it is preferably 0.01% by mass or more.

<Regarding step 3>
The method for separating and recovering plastic films of the present invention includes, after steps 1 and 2, a step 3 of agitating the crushed and swollen plastic film in a rinsing liquid to separate the plastic film.

(Rinse solution)
The rinse liquid used in step 3 contains at least a water-soluble solvent. Specifically, the water-soluble solvent preferably contains one or more water-soluble alcohols or water-soluble solvents having a flash point of 21° C. or higher. The use of a water-soluble solvent in the rinse liquid is effective in peeling off the ink film on the surface of the plastic film piece after step 3.

Water-soluble solvents with a flash point of 21°C or higher are preferably water-soluble organic solvents that fall under the second and third petroleum categories defined in the Fire Service Act. Specific examples of second and third petroleum categories include 3-methoxy-3-methyl-1-butanol, diethylene glycol monobutyl ether, and propylene glycol propyl ether.

Examples of water-soluble alcohols include alcohols specified in the Fire Service Act. Specific examples of alcohols include methanol, ethanol, 1-propyl alcohol, 2-propyl alcohol, etc., and industrial ethanol containing these may be used alone or in combination.

It may also contain the cleaning liquid used when using the wet crusher in step 1. For example, it may preferably contain the water-insoluble alcohol or water-insoluble glycol ether organic solvent described in step 1 as the organic solvent. Among these, butan-1-ol, benzyl alcohol, and ethylene glycol monophenyl ether (phenoxyethanol) are particularly preferred.

From the standpoint of the peelability of the ink layer, it is preferable that the rinsing liquid used in step 3 in particular contains a large amount of so-called water-soluble solvents, including alcohols, in the cleaning liquid; specifically, the water-soluble solvent is preferably 30% by mass or more, preferably 40% by mass or more, preferably 50% by mass or more, preferably 60% by mass or more, preferably 70% by mass or more, preferably 80% by mass or more, preferably 90% by mass or more, and preferably 95% by mass or more.

In step 3, when using a rinse solution that is mainly made of a water-soluble solvent, including alcohols that do not intentionally contain water, inorganic salts can be used.

(Inorganic salts)
The inorganic salt used in the present invention may be any salt that can be used as a grinding aid, and is not particularly limited. However, from the viewpoint of removing the inorganic salt in a later step, it is preferable that the inorganic salt is water-soluble to the extent that 10 g or more is dissolved in 100 g of water at room temperature. It is also preferable that the inorganic salt is insoluble to the extent that only 10 mg or less is dissolved in 100 g of the water-soluble organic solvent at room temperature, and it is more preferable that the inorganic salt is substantially insoluble in the organic solvent. Specifically, sodium chloride, potassium chloride, calcium chloride, sodium sulfate, potassium sulfate, aluminum sulfate, etc. are mentioned, and sodium chloride, potassium chloride, sodium sulfate, and potassium sulfate are more preferable. The inorganic salts mentioned above can be used alone or in combination of two or more kinds.

When an inorganic salt is used as a grinding aid, the amount of inorganic salt is preferably 100 to 2000% by mass, and more preferably 300 to 1500% by mass, relative to 100% of the plastic film. The amount of rinsing liquid is 5000 to 50,000% by mass, and preferably 10,000 to 40,000% by mass, relative to 100% of the plastic film. The more inorganic salt is used relative to the plastic film, the higher the peelability effect of the ink layer, and the smaller the amount of solvent used, the higher the effect.

When inorganic salts are used as grinding aids, the treatment temperature is preferably 1500°C or less, and more preferably 20 to 100°C. The treatment time is preferably about 10 minutes to 3 hours.

The device for kneading the mixture of plastic film pieces that have been through step 2, inorganic salt (grinding aid), and water-soluble organic solvent may be any device capable of mechanically grinding the plastic film pieces, a specific example being a kneader. In addition, it is also possible to use a paint shaker, a paint conditioner, a batch-type kneader such as Kawata's Super Mixer, Nippon Coke's FM Mixer, Attritor, or Inoue Seisakusho's Trimix, or a continuous kneader such as Asada Iron Works' KCK Mill. Other devices may also be used.

(Mixing)
In step 3, the equipment and method for stirring when stirring are not particularly limited, and known methods can be used. Specifically, examples include an apparatus equipped with a motor with stirring blades capable of stirring the cleaning liquid in a container, an apparatus equipped with a device that generates ultrasonic waves, an apparatus capable of shaking the container, a kneader, a wet crusher, etc. The wet crusher may be the same as the crusher described in step 1.

Step 3 preferably includes a step in which the plastic film crushed in step 1 passes through a clearance of 30 mm or less. The clearance is more preferably 20 mm or less, and even more preferably 10 mm or less. By passing through a clearance of 10 mm or less, a high shear force can be applied to the plastic film, which has the effect of, for example, rubbing off the ink from a plastic film with an exposed ink layer, or applying a shear stress to a plastic film with an ink layer provided between multiple films, thereby facilitating peeling of the laminate.

A wet crusher has a crushing mechanism using fixed and rotating blades, so the clearance can be easily controlled by the operating conditions. The narrower the clearance, the higher the shear force that can be applied to the plastic film. However, the narrower the clearance, the more likely it is that clogging of the plastic film will occur and the faster the temperature of the water or cleaning liquid will rise, so a clearance of 0.1 mm or more is preferable.

Specifically, the clearance through which the plastic film passes is set by a method of providing a clearance of a predetermined size or less and applying high shear. For example, the size gap between the inner tank wall of the treatment tank in which the plastic film and/or water is stirred and the stirring blade is controlled to a predetermined size or less, a baffle plate is installed at a distance of a predetermined size or less from the tank wall, the plastic film and/or water is designed to pass through a screen with holes of a diameter of a predetermined size or less, the plastic film and/or water is passed between two rolls with a gap of a predetermined size or less, the laminate is sandwiched between the media using a ball mill or the like to collide with each other, or, for example, a fixed blade is provided on the outside of the rotating blade as in a homogenizer, and the gap between the rotating blade and the fixed blade is controlled to a predetermined size or less.

The shear rate in step 3 is preferably 2,000 ^{s or} more. The higher the shear rate, the greater the effect of rubbing off the ink from the plastic film and the greater the effect of applying shear stress to the plastic film in which the ink layer is provided between multiple films, so there is no upper limit.

The shear rate (D) is defined by the following formula:
D = v / Δy
v: flow velocity (m/s), calculated as v = π × R × (n/60) π: circular constant R: diameter of the rotary blade (m)
n: Rotary blade rotation speed (rpm)
Δy: Clearance (m), here referring to the gap (m) between the rotary blade and the fixed blade.

The larger the diameter of the fixed blades of the wet crusher, the higher the flow rate, so the larger the fixed blades of the wet crusher, the more preferable it is, and the narrower the clearance, the higher the shear rate, so the narrower the clearance, the more preferable it is.

The blade design of the fixed blade and rotary blade is preferably such that at least some of the blades are arranged in a radial direction, and the blades arranged in a radial direction are preferably inclined at an angle of 2 to 60 degrees from the radial direction, more preferably 5 to 45 degrees.

When multiple blades are arranged on the rotary blade, it is preferable that the blade width of the rotary blade is 0.5 to 5.0 mm, the groove width between the blades is preferably 0.5 to 5.0 mm, and the blade height is preferably 1.0 to 5.0 mm.

The Froude number (Fr) of stirring in step 3 is preferably 10 or more. The faster the Froude number of stirring, the greater the effect of rubbing off the ink from the plastic film and the greater the effect of applying shear stress to the plastic film in which the ink layer is provided between multiple films, so there is no upper limit.

The Froude number (Fr) of stirring is defined by the following formula:
Fr={(n/60) ² }×R/g
n: Rotary blade rotation speed (rpm)
R: diameter of the rotary blade (m)
g: Gravitational acceleration = 9.8 (m/s ² )
Since step 3 is a step of peeling off adhesive and ink layers from the plastic film swollen in water, it is preferable to use a wet crusher that can obtain high shear force and/or high friction force. Examples of such wet crushers include the KD series from Husqvarna Zenoah, the Suncutter series from Nikuni, the Disintegrator series from Furukawa Industrial Machinery Systems, the Ink Crusher series and Refiner from Aikawa Iron Works, the Scatter from Sanwa Hydrotech, the Trigonal from Nippon Coke Company, the alkali cleaning/cleaning and deinking equipment from Nippon Seam, and the Scissors Cutter series cleaning and crushing machines.

Since the purpose of step 3 is to remove ink particles remaining on the surface of the plastic film, known dispersing equipment using media such as beads or rods can be used. Examples of dispersing equipment with media include dispersers, dispersing equipment with stirring blades such as turbine blades, paint shakers, roll mills, ball mills, vibration mills, attritors, sand mills, and bead mills.

The diameter of the media used is preferably 0.5 to 20 mm, more preferably 1 to 10 mm, and even more preferably 2 to 5 mm. Media materials include steel, zirconia, alumina, glass, etc., and can be appropriately selected depending on the properties of the rinsing liquid selected. If the media diameter is less than 0.2 mm, it is difficult to handle and recover the media, but if it exceeds 5 mm, it is easy to handle. The residence time in the disperser is preferably 1 to 30 minutes.

Examples of the media-equipped dispersing machine include Star Mill manufactured by Ashizawa Finetech Co., Ltd., MSC-MILL, SC-MILL, Attritor MA01SC manufactured by Mitsui Mining Co., Ltd., Apex Mill manufactured by Hiroshima Metal & Machinery Co., Ltd., Vibration Mill manufactured by Chuo Kakoki Co., Ltd., Nano Grain Mill, Pico Grain Mill, Pure Grain Mill, Mega Capper Grain Mill, Cera Power Grain Mill, Dual Grain Mill, AD Mill, Twin AD Mill, Basket Mill, Twin Basket Mill manufactured by Asada Iron Works, and Apex Mill, Ultra Apex Mill, and Super Apex Mill manufactured by Kotobuki Industries Co., Ltd.

The stirring time in step 3 is not particularly limited as long as the entire plastic film can be rinsed with the rinse solution. Although it varies depending on the stirring equipment and method used, in order to thoroughly rinse, 1 minute or more is preferable, 3 minutes or more is preferable, and 5 minutes or more is preferable. On the other hand, there is no particular upper limit to the stirring time, but 60 minutes or less is preferable, and 30 minutes or less is more preferable.

(Ink removal rate)
The ink removal rate of the plastic film after step 3 is preferably 50% or more, more preferably 75% or more, and particularly preferably 90% or more.

Ink removability is measured as follows:

After the third step, the film is washed and dried, and the ink removal rate of the printed portion is determined by calculating the area through image processing of a photograph taken with an optical microscope, and calculating the ink removal rate using the following formula: The ink removal rate is preferably 50% or more, more preferably 75% or more, and particularly preferably 90% or more.
Ink removal rate (%) = (1 - ink-adhered area after cleaning / ink-adhered area before cleaning) x 100
(Surface roughness)
The surface roughness of the plastic film pieces after step 3 is preferably 0.7 μm or more. By using the above-mentioned wet crushing equipment to make the surface roughness of the crushed material 0.7 μm or more, the plastic film laminate can be separated into single layers, and not only the ink layer provided on the surface of the plastic film laminate but also the ink layer provided between the laminates can be removed, so that the collected crushed material is suitable as a raw material for producing high-quality recycled plastic.

The surface roughness of the crushed material is preferably 0.7 μm or more, more preferably 0.8 μm or more, and even more preferably 0.9 μm or more. On the other hand, the upper limit is not particularly limited and can be appropriately adjusted depending on the conditions of the wet crushing equipment.

The surface roughness of the film is determined by measuring the surface roughness Sa of a 500 μm x 600 μm area using a white light interference microscope manufactured by Ryoka Systems Co., Ltd. Sa is not a value determined from a cross section like Ra, but is a value that indicates the entire area of the surface, so it has a wider evaluation range and can evaluate the overall surface roughness.

(Size of film piece)
The size of the plastic film pieces after step 3 is preferably 20 mm or less in the long side direction, more preferably 10 mm or less, and even more preferably 5 mm or less. Also, the length in the short side direction is preferably 20 mm or less, preferably 10 mm or less, preferably 5 mm or less, and preferably 3 mm or less. There is no particular lower limit for the size of the crushed material, but if it is too small, recovery properties will decrease, so the length in the long side direction is preferably 1 mm or more.
(Surface area ratio of film piece after step 1 and after step 3)
If the surface area of the film after step 1 is 1, the surface area after step 3 is preferably at least 1 or less, more preferably 0.9 or less, and even more preferably 0.8 or less. Since step 3 is a step for washing the film surface, the smaller the film is during washing than its original size, the better the film has been kneaded and washed.

(Collection equipment)
The crushed plastic material separated into single layers in step 3 can be collected as a single layer. The equipment and method for collecting the crushed plastic material are not particularly limited, but for example, a filter, a centrifuge, an automatic scraping bar screen, an inclined wire screen, a rotary drum screen, etc. can be used.

(Plastic film)
The plastic film separated and recovered by the present invention is a plastic film having at least an ink layer. Any plastic film can be separated and recovered, including plastic films with an ink layer exposed on the film surface (front-printed), laminated films with an ink layer between multiple films (reverse-printed), single-layer films and laminated films generally distributed as packaging materials for food packaging and daily necessities, and plastic films with various types of resin layers discarded by recycling. That is, the separation and recovery method of the present invention is characterized in that it does not require re-sorting and can be treated together.

In addition, shrink labels, which are laminated films formed into a cylindrical shape, are used on containers such as PET bottles to display product names and add decorative features. When recycling, consumers often peel off the shrink label and discard the PET bottle body and the shrink label separately. However, with the separation and recovery method of the present invention, even if the PET bottle body and the shrink label are integrated, the shrink label can be separated from the PET bottle body and the shrink label can be separated into each single-layer film.

A laminated film laminated with a reactive adhesive often has an adhesive layer made of the reactive adhesive laminated between at least two resin film layers or metal foil or vapor-deposited film layers. Specifically, in the laminated film, if the resin film layer is represented as (F), the metal foil layer of the metal foil or vapor-deposited film layer is represented as (M), and the adhesive layer of the reactive adhesive or the like is represented as (AD), the following configurations are considered as specific embodiments of the laminated film, but are of course not limited thereto.
(F)/(AD)/(F),
(F)/(AD)/(F)/(AD)/(F),
(F)/(AD)/(M)/(AD)/(F),
(F)/(AD)/(M),
(F)/(AD)/(M)/(F),
(F)/(AD)/(F)/(AD)/(M)/(AD)/(F),
(F)/(AD)/(M)/(AD)/(F)/(AD)/(F),
(M)/(AD)/(F)/(AD)/(M),
(AD)/(F)/(AD)/(M),
(AD)/(F)/(AD)/(F)/(AD), etc.

(Coat layer)
The outermost surface of the laminated film structure may have a functional coating layer. The coating layer may be colorless or colored. The coating layer may be provided in contact with the substrate, or may be provided via an inorganic deposition layer or the like in contact with the substrate. The coating layer may be in a form in which different coating layers are laminated. There is no particular restriction on the thickness of the coating layer, but it is preferably 0.1 μm or more and 100 μm or less, more preferably 0.1 μm or more and 10 μm or less, and even more preferably 1 μm or more and 5 μm or less.

Functional coating layers are formed for a variety of purposes. Typical functions are a wide range, including hard coating, silicone-based peeling, IR cut, waterproof and moisture-proof, antibacterial, UV cut, heat dissipation, photocatalysis, weather resistance, anti-fogging, fingerprint and stain resistance, self-repair, and water and oil repellency.

The laminated film that is the subject of this separation and recovery method may further have a paper layer, an oxygen absorbing layer, an anchor coat layer, an ink layer, a removable primer layer provided to facilitate the peeling of the ink, etc.

(Primer layer)
The printing ink is printed on a resin film that will be the base film layer (F1) of the laminated film, and then the reactive adhesive is applied to the printed surface, which is then laminated with another base film (F1), a sealant layer (F2), a metal foil, or a metal foil layer (M) of a vapor-deposited film layer to form a laminated film. In a laminated film having this layer structure, a primer layer can be preferably provided on the base film layer (F1) that will be the printed surface. The primer layer preferably contains a resin having an acidic group, since it is easily dissolved or hydrolyzed by an alkaline solution, and the laminated film that is printed with the ink and then laminated with the adhesive can be easily separated into a single layer film.

The primer may be applied on the sealant layer (F2) or on both F1 and F2. If primer is applied on both F1 and F2, it can be more easily separated into a single layer film.

For the primer layer, a resin having an acidic group or a low molecular weight compound can be used alone. A resin having an acidic group or a low molecular weight compound can also be mixed with a resin having no acidic group. Examples of resins having an acidic group include resins having an acid value such as rosin-modified maleic acid resins and rosin-modified fumaric acid resins, radical copolymers such as (meth)acrylic resins, styrene-(meth)acrylic resins, styrene-(anhydride)maleic acid resins, and terpene-(anhydride)maleic acid resins, which are copolymerized with polymerizable monomers having an acidic group, such as polymerizable monomers having a carboxyl group, such as acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, cinnamic acid, or their acid anhydrides, polymerizable monomers having a sulfonic acid group, such as sulfonated styrene, and polymerizable monomers having a sulfonamide group, such as vinylbenzenesulfonamide, and acid-modified polyolefin resins, which can be used singly or in combination.

The primer layer can also be made by mixing a resin with a low acid value and film-forming properties at room temperature with one or more low molecular weight compounds having acidic groups.

Examples of low molecular weight compounds having an acidic group include saturated fatty acids, unsaturated fatty acids, hydroxy acids, aromatic carboxylic acids, dicarboxylic acids, tricarboxylic acids, oxocarboxylic acids, carboxylic acid derivatives, and acid anhydrides, and these can be used singly or in combination.

Examples of saturated fatty acids include lauric acid, myristic acid, palmitic acid, margaric acid, and stearic acid. Examples of unsaturated fatty acids include oleic acid, linoleic acid, linolenic acid, arachidonic acid, eicosapentaenoic acid, docosahexaenoic acid, and sorbic acid. Examples of hydroxy acids include lactic acid, malic acid, and citric acid. Examples of aromatic carboxylic acids include benzoic acid, phthalic acid, isophthalic acid, terephthalic acid, salicylic acid, gallic acid, mellitic acid, and cinnamic acid. Examples of dicarboxylic acids include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, fumaric acid, and maleic acid. Examples of tricarboxylic acids include aconitic acid. Examples of oxocarboxylic acids include pyruvic acid and oxaloacetic acid. Examples of carboxylic acid derivatives include amino acids and nitrocarboxylic acids. Examples of acid anhydrides include trimellitic anhydride and pyromellitic anhydride. These can be used singly or in combination.

The resins capable of forming a film at room temperature include various synthetic resins, such as polyesters, polyvinyl chloride, copolymers of vinyl chloride and other unsaturated double bond-containing monomers, homopolymers of (meth)acrylic acid esters, copolymers of (meth)acrylic acid esters and other unsaturated double bond-containing monomers, copolymers of polystyrene or styrene monomers and other unsaturated double bond-containing monomers, ketone-formaldehyde condensates and hydrogenated products thereof, polyfunctional epoxy resins, polyvinyl acetals, polyurethanes, and the like. These can be used alone or in combination of one or more selected from these. Examples of polyfunctional epoxy compounds include bisphenol A novolac type epoxy resins, bisphenol F novolac type epoxy resins, bisphenol S novolac type epoxy resins, biphenyl type epoxy resins, and naphthalene type epoxy resins.

When using a single or multiple low molecular weight compounds having acidic groups mixed with the resin that has a low acid value and is capable of forming a film at room temperature, the amount added may be determined appropriately within a range that does not impair the printability or coatability of the primer solution, but the amount should generally be in the range of 0.5 to 50% by weight, and more preferably 1.0 to 30% by weight, based on the solids content of the primer solution.

When the substrate to be printed is, for example, polypropylene (PP), the film-forming resin is preferably at least one thermoplastic resin that is solid at 50° C. and is selected from the group consisting of ketone-formaldehyde condensates and hydrogenated products thereof, polyester, vinyl chloride-vinyl acetate copolymer, and polyvinyl acetal, which have good adhesion to PP by themselves. Examples of such ketone-formaldehyde condensates and hydrogenated products thereof include the TEGO (registered trademark) VariPlus series (SK, A) from Evonik Degussa Japan Co., Ltd.
P, etc.); polyesters include the Vylon (registered trademark) series (Vylon 200, etc.) manufactured by Toyobo Co., Ltd.; vinyl chloride-vinyl acetate copolymers include the Solvine (registered trademark) series (Solvine AL, etc.) manufactured by Nissin Chemical Industry Co., Ltd.; and polyvinyl acetals include the S-LEC (registered trademark) series (S-LEC KS-10, etc.) manufactured by Sekisui Chemical Co., Ltd.

To form a primer layer on a substrate, a solution prepared using the above components is applied to the substrate and dried. The amount of coating is about 0.1 to 5 μm (dry thickness), but if it is less than 0.1, it is difficult to apply uniformly, and if it exceeds 5 μm, it is uneconomical and not practical. Coating is performed using normal coating methods such as gravure, letterpress, flexography, roll coater, reverse coater, and spray method. The formation of the primer layer and printing on it can be performed continuously (in-line), or the formation of the primer layer and printing can be performed separately.

When printing is performed immediately after in-line primer coating using a roll-to-roll printer, the printed surface may stick to the back surface of the substrate, a phenomenon known as blocking, depending on the resolubility of the resin used in the primer layer in the ink solvent and the glass transition point (Tg) of the resin itself. To prevent this type of blocking, transparent particles with a particle size of 0.1 μm to 10 μm such as silica or titanium oxide may be mixed into the primer solvent as an anti-blocking agent at a rate of about 0.005 to 5% of the total amount of primer.

In addition, in order to prevent blocking, the resin solution with a high acid value used in the primer can be neutralized with ammonia or the like before application to prevent re-dissolution in the solvent contained in the printing ink.

The acid value of the compound having an acidic group is not particularly limited, but is preferably 50 mg KOH/g or more, more preferably 100 mg KOH/g or more, and even more preferably 150 mg KOH/g or more.

In laminated films using the aforementioned primer layer, if the printing design is based on white, the ink layer will mostly consist of white ink, and the film laminated with adhesive may be difficult to peel off at low temperatures or with a low-concentration alkaline solution. In such cases, the peelability of the ink layer can be improved by introducing a medium layer used in printing ink between the primer layer and the white ink layer, or between the white ink layer and the adhesive layer.

In the present invention, when the laminate film is a laminate film laminated with a reactive adhesive, it is preferable that the reactive adhesive contains a compound having an acidic group. Also, when the laminate film is a laminate film laminated with a reactive adhesive and has an ink layer and/or a primer layer, it is preferable that at least one layer of the reactive adhesive, the ink layer, and the primer layer contains a compound having an acidic group. If any one of the layers contains a compound having an acidic group, separation and recovery proceeds more easily.

Among them, it is preferable that one of the components of the reactive adhesive has an ester bond, since it is easily dissolved or hydrolyzed by an alkaline solution, and the adhesive can be easily separated into a monolayer film in a short time in steps 2 and 3. Specifically, one of the components of the reactive adhesive has an ester bond is a reactive adhesive containing either or both of a polyol composition having a polyol compound such as a polyester polyol, a polyether ester polyol, a polyester (polyurethane) polyol, or an acrylic polyol having an ester bond, or a polyisocyanate composition having a polyisocyanate compound that is a reaction product of the polyol compound having an ester bond and the various polyisocyanates.

In addition to the polyol composition and the polyisocyanate composition, a reactive adhesive to which a resin having an acidic group or a low molecular weight compound is added can also be preferably used. As the resin having an acidic group or the low molecular weight compound, any resin or low molecular weight compound can be used without any particular limitation as long as it can be easily mixed with the polyol composition or the polyisocyanate composition, which are the main components of the reactive adhesive (in this case, a solvent described below may be used as necessary), and has an acid value.

Examples of resins having acidic groups include resins having an acid value such as rosin-modified maleic acid resins and rosin-modified fumaric acid resins; radical copolymers such as (meth)acrylic resins, styrene-(meth)acrylic resins, styrene-maleic acid (anhydride) resins, and terpene-maleic acid (anhydride) resins, which are copolymerized with polymerizable monomers having acidic groups, such as polymerizable monomers having a carboxyl group, such as acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, cinnamic acid, or acid anhydrides thereof; polymerizable monomers having a sulfonic acid group, such as sulfonated styrene; and polymerizable monomers having a sulfonamide group, such as vinylbenzenesulfonamide; and acid-modified polyolefin resins, which may be used singly or in combination.

Examples of low molecular weight compounds having an acidic group include saturated fatty acids, unsaturated fatty acids, hydroxy acids, aromatic carboxylic acids, dicarboxylic acids, tricarboxylic acids, oxocarboxylic acids, carboxylic acid derivatives, and acid anhydrides, and these can be used singly or in combination.

Examples of saturated fatty acids include lauric acid, myristic acid, palmitic acid, margaric acid, and stearic acid. Examples of unsaturated fatty acids include oleic acid, linoleic acid, linolenic acid, arachidonic acid, eicosapentaenoic acid, docosahexaenoic acid, and sorbic acid. Examples of hydroxy acids include lactic acid, malic acid, and citric acid. Examples of aromatic carboxylic acids include benzoic acid, phthalic acid, isophthalic acid, terephthalic acid, salicylic acid, gallic acid, mellitic acid, and cinnamic acid. Examples of dicarboxylic acids include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, fumaric acid, and maleic acid. Examples of tricarboxylic acids include aconitic acid. Examples of oxocarboxylic acids include pyruvic acid and oxaloacetic acid. Examples of carboxylic acid derivatives include amino acids and nitrocarboxylic acids. Examples of acid anhydrides include trimellitic anhydride and pyromellitic anhydride. These can be used singly or in combination.

The acid value of the resin or low molecular weight compound having the acidic group is not particularly limited, but is preferably 150 mg KOH/g or more.

As mentioned above, the alkaline solution used in this separation and recovery method is presumed to act on the interface between the laminated film and the adhesive or printing ink, significantly reducing their adhesive strength, thereby causing interfacial peeling. Meanwhile, because the alkaline solution itself has high solubility, it also dissolves the non-crosslinked printing ink layer. Even if the printing ink layer itself is crosslinked, the present invention causes interfacial peeling, so it is presumed that efficient separation and recovery can be performed in a short time.

(Ink layer)
The ink layer is, for example, a printing ink printed with an organic solvent-based printing ink, a water-based ink, or an active energy ray-curable ink using a gravure printing machine, a flexographic printing machine, an offset printing machine, an inkjet printing machine, or the like. It may be an ink layer printed in multicolor using a plurality of ink types. In the present invention, the ink layer can be peeled off regardless of the type of ink by going through steps 1 and 2.

Printing inks to which resins or low molecular weight compounds having acidic groups have been added can also be preferably used. There are no particular limitations on the resins or low molecular weight compounds having acidic groups that can be easily mixed with the binder resin or organic solvent, which are the main components of the printing ink, and that have an acid value.

Resins and low molecular weight compounds having acidic groups can be used, such as the compounds described in the primer layer.

It is preferable that the printing ink contains a resin or low molecular weight compound having an acidic group. The amount of the compound added may be determined as appropriate within a range that does not impair the printability of the printing ink, but it is generally preferably in the range of 0.5 to 50% by weight, and more preferably in the range of 1.0 to 30% by weight, based on the solid content of the printing ink.

The location where the ink layer is provided is not particularly limited. For example, the ink layer may be provided on the outermost layer of the laminated film, or may be provided between the resin film layer (F) and the adhesive layer (AD). When the ink layer is provided between the resin film layer (F) and the adhesive layer (AD) (reverse printing), the ink layer and the adhesive layer are more strongly bonded, making peeling of the ink layer more difficult; however, the method of the present invention makes it possible to effectively peel off the ink layer even in a reverse printing configuration.

The ink layer may be a layer that displays any design, pattern, letter, symbol, etc., for the purpose of providing decoration or aesthetics, or displaying the contents, expiration date, and manufacturer or seller. The ink layer may be a solid ink layer that does not have a design, pattern, letter, symbol, etc. The method of forming the ink layer is not particularly limited, and it may be formed using a known pigment and/or dye. The ink layer may be preferably formed using a printing ink containing a pigment and/or dye. The ink layer may have a single layer structure or a multi-layer structure. The thickness of the ink layer is preferably 0.1 to 10 μm, more preferably 1 to 5 μm.

The ink layer may contain a pigment derivative and/or a resin-type dispersant as a dispersant for the colorant. These may be used alone, but using them in combination is preferable because it improves the dispersion stability and stability over time.

For example, when the plastic film has a structure of (F1)/INK/(AD)/(M)/(F2) or (F1)/INK/(AD)/(F2), the ink layer is present between the layers that make up the plastic film, and the ink layer and adhesive layer are more strongly bonded, making it difficult to separate them into a single layer and remove the ink layer. However, if the F2 film is partially peeled off in step 1, or F2 is crushed into a state that makes it easy to peel off, the remaining layer structure can be easily peeled off in step 2, and the ink layer can be removed.

The resin film layer (F) can be classified according to the role required of it, and functions as a base film layer (F1) or a sealant layer (F2) that serves as a heat-sealed portion when forming a packaging material.

Examples of resin films that can be used as the base film layer (F1) include polyolefin films such as low-density polyethylene, high-density polyethylene, linear low-density polyethylene, OPP (biaxially oriented polypropylene), and CPP (non-oriented polypropylene), polyester films such as polyethylene terephthalate (PET) and polybutylene terephthalate, polyamide films such as nylon 6, nylon 6,6, and metaxylene adipamide (N-MXD6), biodegradable films such as polylactic acid, polyacrylonitrile films, poly(meth)acrylic films, polystyrene films, polycarbonate films, saponified ethylene-vinyl acetate copolymer (EVOH) films, polyvinyl alcohol films, and K-coats such as polyvinylidene chloride, as well as films containing pigments. Transparent vapor-deposited films in which alumina or silica is vapor-deposited on these films may also be used.

In addition, various surface treatments such as flame treatment, corona discharge treatment, or chemical treatments such as desorption primers may be performed on the surface of the film material.

Preferred flexible polymer films for the sealant layer (F2) include polyethylene films, polypropylene films, polyolefin films such as ethylene-vinyl acetate copolymers, ionomer resins, EAA resins, EMAA resins, EMA resins, EMMA resins, and biodegradable resin films. Common names include CPP (non-oriented polypropylene) films, VMCPP (aluminum-deposited non-oriented polypropylene film), LLDPE (linear low-density polyethylene), LDPE (low-density polyethylene), HDPE (high-density polyethylene), VMLDPE (aluminum-deposited non-low-density polyethylene film), and films containing these pigments. The surface of the film may be subjected to various surface treatments such as flame treatment, corona discharge treatment, or chemical treatment using a desorption primer.

The thickness of the plastic film is preferably 5 μm or more and 200 μm or less, more preferably 10 μm or more and 100 μm or less, and even more preferably 10 μm or more and 50 μm or less.

From the viewpoint of reuse as a recycled substrate, the substrate preferably contains a polyolefin resin film such as polyethylene or biaxially oriented polypropylene.

Examples of the metal foil layer (M) include foils of metals with excellent ductility, such as gold, silver, copper, zinc, iron, lead, tin and alloys thereof, steel, stainless steel, and aluminum.

Examples of the paper layer include natural paper and synthetic paper. The first and second sealant layers may be formed from the same material as the sealant layer described above.

Other layers may contain known additives and stabilizers, such as antistatic agents, non-reactive adhesive layers, adhesion-enhancing coating agents, plasticizers, lubricants, antioxidants, etc.

<Particle size distribution of desorbed ink components>
The median diameter (D50) of the detached ink components is preferably 1 μm or more. By having the median diameter of the detached ink layer components be 1 μm or more, it is possible to suppress the detached ink components from reattaching to the substrate, and to obtain a colorless recycled material. The median diameter of the detached ink components is preferably 5 μm or more, more preferably 10 μm or more, even more preferably 15 μm or more, and particularly preferably 20 μm or more.

The span value A of the detached ink components represents the particle size distribution width of the detached ink layer components; the larger the value, the wider the particle size distribution width, and the more likely it is to contain fine ink layer components that are easily redeposited on the substrate. The span value A is preferably 10 or less, more preferably 8 or less, and even more preferably 5 or less. A span value of 10 or less is preferable because it can suppress redeposition of the detached ink layer.

In the present invention, the volume-based median diameter (D50) and span value A of the ink layer components detached from the plastic substrate layer are measured using a laser diffraction particle size distribution measuring device. The span value A is expressed by the following formula:

A=(D90-D10)/D50
D10: cumulative 10% diameter of volume-based particle size distribution obtained by laser diffraction particle size distribution measurement of the detached ink component D90: cumulative 90% diameter of volume-based particle size distribution obtained by laser diffraction particle size distribution measurement of the detached ink layer component <Method of manufacturing molding material>
The recycled plastic film pieces recovered by the above-mentioned method for producing recycled plastic film are melt-kneaded to produce molding pellets. In the melt-kneading process, various additives are added as necessary, and the mixture is mixed using a Henschel mixer, a tumbler, a disperser, or the like, and then mixed or dispersed using a kneader, a roll mill, a twin-screw extruder, a single-screw extruder, a rotor-type twin-screw kneader, or the like. This produces a recycled resin, which is a resin composition. The shape of the recycled resin is not particularly limited, and may be pellet-like, powder-like, granular, or bead-like. In the melt-kneading process, a twin-screw extruder is preferably used. The molding material may further contain a master batch. The master batch is not particularly limited as long as it has compatibility with the recycled resin, and generally, a mixture of a thermoplastic resin such as a polyethylene resin or a polypropylene resin and a colorant can be used. The thermoplastic resin contained in the master batch may be used alone or in combination of two or more types. The master batch may contain, within the scope not impairing the effects of the present invention, a metallic soap of an alkali metal, an alkaline earth metal, or zinc, hydrotalcite, a nonionic surfactant, a cationic surfactant, an anionic surfactant, an amphoteric surfactant, an antistatic agent, a flame retardant such as a halogen-based, phosphorus-based, or metal oxide, a lubricant such as ethylene bisalkyl amide, an antioxidant, an ultraviolet absorber, a filler, or a peroxide.

<Molded products>
Molded bodies can be obtained by hot-molding the molding material obtained by the above-mentioned manufacturing method. The hot-molding method is not particularly limited, and examples thereof include injection molding, extrusion molding, blow molding, and compression molding. Molded materials produced using the plastic substrate recovered by the separation and recovery method of the present invention are of high quality because the ink layer is detached and the reattachment of adhesive components is suppressed, and can be used in various fields such as home appliances, stationery, automobile parts, toys, sports goods, medical and building materials.

Additives that can be used in the manufacturing process of the recycled pellets obtained by the manufacturing method for recycled plastic film include at least one antioxidant selected from the group consisting of phenols and phosphorus-based antioxidants, at least one lubricant selected from fatty acid amides, alkylene fatty acid amides, metal soaps, and esters, hindered amine weather stabilizers, waxes having an acid value of 5 mg KOH/g or less, at least one antistatic agent selected from fatty acid sulfonates and fatty acid esters, and at least one peroxide selected from organic peroxides for modifying polypropylene.
Examples of phenol-based antioxidants include 2,6-di-t-butyl-p-cresol, butylated hydroxyanisole, 2,6-di-t-butyl-4-ethylphenol, 2,2'-methylene-bis-(4-methyl-6-t-butylphenol), 2,2'-methylene-bis-(4-ethyl-6-t-butylphenol), 4,4'-thiobis-(3-methyl-6-t-butylphenol), 4,4'-butylidene-bis-(3-methyl-6-t-butylphenol), 3,9-bis[{1,1-dimethyl-2-{β-(3-t-butyl-4-hydroxy-5-methyl tetrakis-{methylene-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate}methane, and bis{(3,3'-bis-4'-hydroxy-3'-t-butylphenyl)butyric acid}glycol ester.

Examples of phosphorus-based antioxidants include triphenyl phosphite, diphenyl isodecyl phosphite, phenyl diisodecyl phosphite, 4,4'-butylidene-bis-(3-methyl-6-t-butylphenyl-di-tridecyl) phosphite, cyclic neopentane tetrayl bis(octadecyl phosphite), trisdiphenyl phosphite, diisodecylpentaerythritol diphosphite, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, 10-(3,5-di-t-butyl-4-hydroxybenzyl)-9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, 10-decyloxy-9,10-dihydro-9-oxa-10-phosphaphenanthrene, cyclic neopentane tetrayl bis(2,4-di Examples of suitable phosphite include cyclic neopentanetetraylbis(2,6-di-t-methylphenyl)phosphite, cyclic neopentanetetraylbis(2,6-di-t-methylphenyl)phosphite, and 2,2-methylenebis(4,6-t-butylphenyl)octylphosphite.

These antioxidants may be used alone or in combination of two or more. The amount of antioxidant added is preferably 0.01 to 1 mass%, more preferably 0.03 to 0.5 mass%, based on the mass of the molding material. An amount of 0.01 mass% or more is preferred in terms of antioxidant properties, and an amount of 1 mass% or less is preferred in terms of processability.

Examples of fatty acid amide-based lubricants include aliphatic monocarboxylic acid amides such as lauric acid amide, palmitic acid amide, oleic acid amide, stearic acid amide, erucic acid amide, behenic acid amide, ricinoleic acid amide, and hydroxystearic acid amide; N-substituted aliphatic monocarboxylic acid amides such as N-oleyl oleic acid amide, N-oleyl stearic acid amide, and N-stearyl oleic acid amide; aliphatic biscarboxylic acid amides such as methylene bisstearic acid amide and ethylene bisstearic acid amide; N,N'-ethylene bis-oleyl amide, N,N'-ethylene bisstearic acid amide, and N,N'-methylene bisstearic acid amide.

Examples of metal soap-based lubricants include metal salts of higher fatty acids such as calcium stearate, magnesium stearate, barium stearate, zinc stearate, aluminum stearate, lithium stearate, calcium laurate, magnesium laurate, barium laurate, zinc laurate, aluminum laurate, and lithium laurate, as well as calcium hydroxystearate, magnesium hydroxystearate, barium hydroxystearate, zinc hydroxystearate, aluminum hydroxystearate, and lithium hydroxystearate.

These lubricants may be used alone or in combination of two or more. The amount of lubricant added is preferably 0.01 to 1 mass%, more preferably 0.03 to 0.5 mass%, based on the mass of the molding material. An amount of 0.01 mass% or more is preferred in terms of activity, and an amount of 1 mass% or less is preferred in terms of processability.

Examples of hindered amine weathering stabilizers include dimethyl succinate-1-(2-hydroxyethyl)-4-hydroxy-2,2,6,6-tetramethylpiperidine polycondensate, poly[{6-(1,1,3,3-tetramethylbutyl)amino-1,3,5-triazine-2,4-diyl}{(2,2,6,6-tetramethyl-4-piperidyl)imino}hexamethylene{{2,2,6,6-tetramethyl-4-piperidyl)imino}], N , N'-bis(3-aminopropyl)ethylenediamine-2,4-bis[N-butyl-N-(1,2,2,6,6-pentamethyl-4-piperidyl)amino]-6-chloro-1,3,5-triazine condensate, bis(2,2,6,6-tetramethyl-4-piperidyl)separate, and bis(1,2,2,6,6-pentamethyl-4-piperidyl)2-(3,5-di-t-4-hydroxybenzyl)-2-n-butylmalonate.

Examples of waxes with an acid value of 5 mgKOH/g or less include natural waxes and synthetic waxes. Examples of natural waxes include vegetable waxes such as carnauba wax, rice wax, and Japan wax; animal waxes such as beeswax, lanolin, and spermaceti; mineral waxes such as montan wax, ozokerite, and ceresin; and petroleum waxes such as paraffin wax, microcrystalline wax, and petrolatum. Examples of synthetic waxes include semi-synthetic waxes and fully synthetic waxes. Semi-synthetic waxes are natural waxes or natural wax-like materials that have been modified by chemical treatments such as esterification, amidation, and neutralization with acidic wax. Examples of synthetic waxes include synthetic hydrocarbons such as polyethylene waxes, polypropylene waxes, and polystyrene waxes.

These waxes having an acid value of 5 mgKOH/g or less may be used alone or in combination of two or more types. The amount of wax having an acid value of 5 mgKOH/g or less added is preferably 0.5 to 50 mass%, more preferably 1 to 30 mass%, based on the mass of the molding material. An amount of 0.5 mass% or more is preferred in terms of fluidity adjustment, and an amount of 50 mass% or less is preferred in terms of processability.

Examples of anionic surfactant-based antistatic agents include carboxylates such as alkali metal salts of higher fatty acids, sulfate ester salts such as higher alcohol sulfate ester salts and higher alkyl ether sulfate ester salts, sulfonate salts such as alkylbenzene sulfonate salts, alkyl sulfonate salts and paraffin sulfonate salts, and phosphate ester salts such as higher alcohol phosphate ester salts.

Examples of nonionic surfactants include polyethylene glycol-type nonionic surfactants such as higher alcohol ethylene oxide adducts, fatty acid ethylene oxide adducts, higher alkylamine ethylene oxide adducts, and polypropylene glycol ethylene oxide adducts; polyhydric alcohol-type nonionic surfactants such as fatty acid esters of polyethylene oxide or glycerin, fatty acid esters of pentaerythritol, fatty acid esters of sorbitol or sorbitan, alkyl ethers of polyhydric alcohols, and fatty amides of alkanolamines.

These antistatic agents may be used alone or in combination of two or more kinds.
The amount of the antistatic agent added is preferably 0.05 to 1 mass %, more preferably 0.1 to 0.5 mass %, based on the mass of the molding material. An amount of 0.05 mass % or more is preferable in terms of antistatic properties, and an amount of 1 mass % or less is preferable in terms of transparency and low bleeding properties.

Examples of organic peroxides include dicumyl peroxide, di(2-t-butylperoxyisopropyl)benzene, 2,5-dimethyl-2,5-bis(t-butylperoxy)hexane, and 2,5-dimethyl-2,5-bis(t-butylperoxy)hexyne-3.

These organic peroxides may be used alone or in combination of two or more types, or may be diluted with an inorganic filler.

In order to modify the physical properties of the recycled pellets obtained by the manufacturing method for recycled plastic film, they may be melt-kneaded with at least one of an acid-modified polypropylene and a thermoplastic elastomer having a melting point of 130°C or higher.

Modifying the physical properties of recycled pellets means changing the physical properties of the plastic pellets that are used as the raw material for plastic film before they are recycled.

The properties that can be modified are varied and include, but are not limited to, tensile strength, flexural strength, elongation at break, tensile modulus, flexural modulus, and yield stress.

Examples of commercially available acid-modified thermoplastic elastomers include maleic anhydride-modified isoprene rubber such as LIR-403 manufactured by Kuraray Co., Ltd., modified isoprene rubber such as LIR-410 manufactured by Kuraray Co., Ltd., carboxy-modified nitrile rubber such as Clynac 110, 221, and 231 manufactured by Polycer Co., Ltd., maleic anhydride-modified polybutene such as Nippon Oil Corporation's Nisseki Polybutene, ethylene methacrylic acid copolymers such as Nucrel manufactured by Mitsui DuPont Polychemicals Co., Ltd., ethylene methacrylic acid copolymers such as Yukalon manufactured by Mitsubishi Chemical Co., Ltd., maleic anhydride-modified ethylene-propylene rubber such as Tafmer M (MA8510) manufactured by Mitsui Chemicals Co., Ltd. and TX-1215 manufactured by Mitsui Chemicals Co., Ltd., and Examples of the maleic anhydride-modified ethylene-butene rubber include maleic anhydride-modified ethylene-butene rubber such as Tufmer M (MH7020) manufactured by I Chemicals, maleic anhydride-modified polyethylenes such as HPR series (maleic anhydride-modified EEA) manufactured by DuPont-Mitsui Polychemicals, Bondine (maleic anhydride-modified EEA) manufactured by Atofina, Tuftec (maleic anhydride-modified SEBS, M1943) manufactured by Asahi Kasei, Kraton (maleic anhydride-modified SEBS, FG1901X) manufactured by Kraton Polymers, Tufprene (maleic anhydride-modified SBS, 912) manufactured by Asahi Kasei, Septon (maleic anhydride-modified SEPS) manufactured by Kuraray, Rexpearl (maleic anhydride-modified EEA, ET-182G, 224M, 234M) manufactured by Japan Polyolefins, and Auroren (maleic anhydride-modified EEA, 200S, 250S) manufactured by Nippon Paper Chemicals.

A particularly suitable example of an acid-modified thermoplastic elastomer is a maleic anhydride-modified styrene-ethylene-butadiene-styrene copolymer. Commercially available acid-modified styrene-ethylene-butylene-styrene block copolymers include Tuftec M1911, Tuftec M1913, and Tuftec M1943 manufactured by Asahi Kasei Chemicals Corporation.

Examples of commercially available thermoplastic elastomers that are not acid-modified include ethylene methacrylic acid copolymers such as Nucrel manufactured by Mitsui DuPont Polychemicals, ethylene methacrylic acid copolymers such as Yukalon manufactured by Mitsubishi Chemical Corporation, α-olefin copolymers such as Tafmer manufactured by Mitsui Chemicals, SEBS such as Tuftec manufactured by Asahi Kasei Corporation, SBS manufactured by Kuraray such as Tufprene manufactured by Asahi Kasei Corporation, SEPS such as Septon, and EEA such as Rexpearl manufactured by Japan Polyolefins Co., Ltd.

For example, when a single-screw or twin-screw extruder is used in the melt-kneading process, general melt-kneading conditions can be used. The kneading temperature is preferably 180 to 260°C, more preferably 190 to 250°C, and even more preferably 200 to 240°C. If the temperature is below 180°C, melt-kneading is difficult, and if it is above 260°C, the physical properties of the recycled pellets produced will be significantly reduced. The screw rotation is preferably 50 to 500 rpm, more preferably 180 to 400 rpm, and even more preferably 100 to 300 rpm. If the rotation speed is too low, it is difficult to produce uniform recycled pellets during melting, and if it is too high, the heat generated during kneading will significantly reduce the physical properties of the recycled pellets produced.

The melt mass flow rate (MFR) of the recycled pellets is preferably 2 to 50 g/10 min, more preferably 3 to 40 g/10 min, and more preferably 5 to 30 g/10 min. By having a melt mass flow rate within the above range, it is possible to provide a regenerated mold material suitable for various molding processes such as injection molding and extrusion molding.

(Decolorization evaluation of recycled pellets)
The plastic film pieces that had been subjected to steps 1 to 3 in sequence were extruded at 200°C using a twin-screw extruder and pelletized to obtain recycled pellets. The recycled pellets were hot-pressed at 200°C using a heat press to produce a 1 mm thick press plate. The color values L ^* , a ^* , and b ^* of the press plate were measured using a spectrophotometer (X-rite, X-riteeXact). The raw material pellets of the plastic film were also similarly subjected to the hot-press process to produce a 1 mm thick press plate, and the color difference ΔE was calculated using the following formula.
ΔE = ((L ^* x - L ^* y) ² + (a ^* x - a ^* y) ² + (b ^* x - b ^* y) ² ) ^1/2
x: raw pellet y: recycled pellet ΔE is preferably 30 or less, more preferably 20 or less, more preferably 10 or less, and even more preferably 5 or less. The recycled pellets have been decolorized by the washing process to the extent that there is no color difference between the recycled pellets and the raw pellets, and are highly useful as recycled pellets. In addition, since many molded products are melt-kneaded with a master batch containing a colorant, a ΔE of 30 or less is sufficient for use as long as the desired color tone can be obtained.

When the recycled pellets are made into a film with a thickness of about 100 μm, the total light transmittance is preferably 30% or more, more preferably 50% or more, and even more preferably 70% or more. The higher the total light transmittance, the more the ink has been decolorized by the cleaning process, and the more useful the recycled pellets are.

(a mix of recycled and virgin pellets)
In the melt-kneading process of the plastic film from which the ink layer has been removed, it is possible to mix it with virgin plastic pellets at any ratio depending on the purpose. For example, the mixing ratio of recycled pellets to virgin pellets in terms of weight is 99.5:0.5 to 50:50. From the viewpoint of recyclability, it is preferable to make the ratio of recycled pellets as high as possible.

The virgin plastic pellets used in this case can be at least one type of polypropylene selected from block polymers, random polymers, and homopolymers. They can also be selected from acid-modified polypropylene, thermoplastic elastomers, and polyethylene using a metallocene catalyst, and at least one type of these can be mixed and used.

An example of a specific embodiment of the plastic film separation and recovery method of the present invention is described below.

(1) Process 1 of crushing plastic film
First, the plastic film is sequentially fed into a dry crusher or a wet crusher (hereinafter simply referred to as a crusher) to obtain crushed plastic material. At this time, the plastic film may be cut into plastic pieces, for example, about 20 cm square or 30 cm square, and then fed into the crusher. By passing through this cutting process, crushing in the crusher in the next process can be performed more efficiently. For cutting, a known crusher can be used, for example, an impact crusher such as a hammer crusher or a rotary crusher, a shredder, a cutter, etc. are included. The size and shape of the plastic film to be fed are not particularly limited, but the maximum length of the plastic pieces is, for example, preferably 50 cm or less, preferably 30 cm or less, preferably 20 cm or less, and preferably 10 cm or less.

When a screen or mesh is used in the dry crusher in step 1, the hole diameter is preferably 30 mm or less, more preferably 20 mm or less, and even more preferably 10 mm or less. When a 10 mm screen or mesh is used, the size of the crushed film pieces is 0.5 to 10 mm on the long side. The smaller the crushed film size is, the more effective the immersion in the cleaning solution in step 2 is, so the smaller the crushed film size in step 1, the more preferable it is.

When a wet crusher is used in step 1, the laminated film roll cut into pieces of about 20 cm square or 30 cm square is drawn into the crushing section by the suction of the crusher, crushed into pieces of about 1 to 20 mm or 5 to 20 mm, and pumped to the next step at 0.03 m ³ /min. At this time, the film fed in is subjected to high shear when crushed, which makes it easy for at least a part of each layer constituting the laminated film to be separated into single layers. If an ink layer is provided on the laminated film, the ink layer is also easily peeled off and removed from the film by the high shear caused by crushing, and it is preferable that at least a part of the ink layer is peeled off.

Even if the items to be shredded are not laminated film rolls but individual film bags collected from the market, they can be fed into the shredder in the same condition as they were collected.

When using an attritor as the crusher to pulverize the plastic film into powder form, it is preferable to use a laminated film roll cut into small pieces of about 5 mm square. The plastic film crushed by the attritor is pulverized to about 10 to 500 μm.

The crushing process in step 1 may be carried out once or in several separate steps.

(2) Step 2: Immersing the plastic film in a cleaning solution
In step 2, the plastic crushed material crushed in step 1 may be immersed in the cleaning solution by standing it still, or may be immersed and stirred as necessary using a known stirring device such as a homodisper or a wet crusher similar to that in step 1. If the crushed plastic film is a surface-printed film, the ink layer on the surface is made to swell sufficiently, and if it is a laminated film including a reverse-printed film, the ink layer and adhesive layer are made to swell completely.

The liquid temperature and stirring time when immersed in the cleaning solution are not particularly limited, and can be adjusted appropriately depending on various conditions such as the material of the cleaning solution used and the composition of the plastic film.

(3) A process of separating the crushed plastic film by stirring the crushed plastic film in a rinsing liquid.
After the plastic film is swollen by the steps 1 and 2, it is stirred in a rinsing liquid to separate the plastic film. After separation, the rinsing liquid contains the separated single layer films and residues of adhesives, printing inks, metal foils, etc., which are suspended or dissolved in the liquid. These are removed from the rinsing liquid and then separated and recovered.

As an example of a specific method, for example, in flotation separation, plastics with light specific gravity such as polyolefins such as polypropylene and polyethylene (floating matter) are separated from heavy materials such as condensation synthetic films such as polyester and nylon, which have a higher specific gravity than polyolefins, or metal foils, and the heavy materials are removed. Next, if necessary, the plastics recovered in a washing and dehydration process are washed and dehydrated, and plastics with different specific gravities are separated by centrifugation. For example, plastics can be separated into plastics containing vinyl chloride resins and polyethylene terephthalate, which have a specific gravity of 1 or more and sink in water, and plastics containing olefin-based resins such as polyethylene and polypropylene, which do not contain vinyl chloride resin. Further separation is possible by changing the specific gravity by appropriately changing the mixture ratio of the liquid used in the flotation separation, for example, water to an organic solvent or salt.

After rough separation and recovery using gravity separation, more advanced separation can be performed using electrostatic separation, which takes advantage of the inherent charging properties of plastics.

One specific example of a method is to separate a pre-charged plastic mixture by dropping it between parallel plate electrodes to which a voltage is applied. This makes it possible to separate combinations of plastics with small differences in specific gravity that are difficult to separate using gravity separation.

In step 3, known stirring devices such as a homodisper, wet crushers similar to those in step 1, as well as paint shakers, paint conditioners, mixers, kneaders, and other devices can be used. Other devices can also be used.

(4) Recovery and reuse of cleaning solution (Step 4)
The water, washing liquid, and rinsing liquid used in steps 1 to 3 are supplied to one or more recycle machines selected from a filter, a centrifuge, and an ultrafilter to recover them, and are reused after removing solid matter. While the wet crushing step and the gravity separation step are performed in steps 1 to 3, the water, washing liquid, or the step of reusing the washing liquid can be continuously operated to separate solid matter from the water, washing liquid, and rinsing liquid.

(5) Drying of plastic separation (step 5)
The plastic film recovered in step 3 is dried by one or more methods selected from reduced pressure heating drying, hot air drying, and pressurized compression drying to remove residual moisture. As a pre-treatment for producing recycled pellets, which will be described later, after or during drying of the recovered film pieces, a pressurized compression machine such as a Nippon Seam Co., Ltd. pressurized dehydrator, a pellet mill manufactured by Oike Iron Works, or a Stella or briquette machine manufactured by Elcom Co., Ltd. may be used to produce briquettes. When the plastic film is pulverized into powder form using a grinding machine as a wet crushing machine, the crushed material is pulverized to about 10 to 500 μm, and the density of the crushed material is high, so that the pressurized compression step can be omitted. The density varies depending on the material constituting the crushed material, but a higher density is preferable because it is easier to handle in a kneader. Specifically, in a dry state, it is preferably 0.03 kg or more, more preferably 0.05 kg or more, more preferably 0.2 kg or more, and even more preferably 0.3 kg or more.

(6) Preparation of recycled pellets (Step 6)
The film pieces or briquettes dried in step 5 are fed into a single-screw or twin-screw extruder to produce recycled pellets. When the film pieces are fed directly into the extruder without going through the pressurized compression step, a phenomenon called bridging, in which ink pieces clog the inlet, is likely to occur. To avoid bridging, the film pieces may be pressurized in the feeder section or pushed in with air. Also, the feeder section may use twin screws that rotate in opposite directions, or a side feeder may be used to push in. The kneader conditions are not particularly limited, but it is preferable to operate at 180 to 260°C in order not to significantly deteriorate the resin performance before recycling.

The contents and effects of the present invention will be described in more detail below with reference to examples. The films, printing inks, reactive adhesives, and organic solvents used as raw materials in each example and comparative example are also shown below.
(Film used in laminated film)
OPP: Biaxially oriented polypropylene film 20 μm
CPP: Non-oriented polypropylene film 35 μm
(Printing ink)
INK1: DIC Graphics Glossa 507 Primary Indigo S2
INK2: DIC Graphics Finart R507 Primary Blue INK3: DIC Graphics Finart R794 White S
(Reactive adhesive)
AD1: Solvent-based adhesive Dick Dry LX-401A and SP-60, two-liquid adhesive (ether-based adhesive)
AD2: Solvent-free adhesive Dikdry 2K-SF-400A and HA-400B, two-component adhesive (ester-based adhesive)
(Method of manufacturing laminated film)
The laminated film was produced by printing on the target film by the printing method described later, and then laminating the target film by the lamination method described later. The layer structure of the film, reactive adhesive, and printing ink were combined as shown in Table 1.

(Printing method)
For the gravure inks used for printing, each ink was applied to the film "Film 1" using a proofer.

(Lamination method)
The reactive adhesive "AD" was applied to the surface of the printing ink-applied film "Film1" using a laminator to a coating amount of 3 g/m2 solid content, and then laminated to the film "Film2". The laminated film was subjected to an aging reaction at 40°C for 72 hours. The laminated films "LAM1" to "LAM2" shown in Table 1 were obtained. Note that blanks indicate that no configuration was present.

(Step 1: Crushing step)
Print 1 and LAMs 1 and 2 were placed in a dry crusher equipped with a screen with a hole diameter of 10 mm, and crushed until the short side of the crushed film was about 5 to 10 mm and the long side was about 10 to 20 mm.

(Step 2: Immersion step)
PRO_A: gently immersed in the cleaning solution at 40° C. for 16 hours.
PRO_B: Placed in a cleaning solution at 75° C. for 120 minutes and stirred at 500 rpm using a three-one motor.

(Cleaning solution)
Water, a solvent shown in Table 2, and 2% by weight of potassium hydroxide were mixed to prepare the cleaning solution shown in Table 3. The cleaning solution composition was calculated by adding the ingredients vertically, and water was added to make up to 100% if the amount was less than 100%.

(Step 3 Stirring separation step)
PRO_V: 50 g of the plastic film obtained in step 2 was used in 1,000 mL of "diethylene glycol normal butyl ether" used as a rinsing liquid, and a vibration mill manufactured by Chuo Kakoki Co., Ltd. was used as the equipment. A stainless steel rod having a diameter of 19 mm was used as the media, and the rod filling rate was set to 30%, and the mill was operated for 10 minutes.
PRO_W: 10 g of the plastic film obtained in step 2 was used in 300 mL of city water, and the blender was a Mighty Blender manufactured by Osaka Gas Chemicals, which was operated at 19,000 rpm for 5 minutes.
PRO_X: 10 g of the plastic film obtained in step 2 was used in 300 mL of "normal propyl alcohol:water=60:40 liquid" used as a rinsing liquid, and the Mighty Blender manufactured by Osaka Gas Chemicals was used and operated at 19,000 rpm for 5 minutes.
PRO_Y: 10 g of the plastic film obtained in step 2 was used, and the equipment was operated for 30 minutes using a paint conditioner in 300 mL of "normal propyl alcohol containing 150 g of sodium chloride" used as a rinsing liquid.
PRO_Z: 10 g of the plastic film obtained in step 2 was used, and the device was operated for 30 minutes in a paint conditioner in a solution containing 100 mL of "diethylene glycol normal butyl ether" used as the rinsing liquid and 400 g of zirconia balls having a diameter of 4.8 mm.

(Decolorization evaluation of recycled pellets)
The results in Tables 4 to 6 show the state of ink removal from the plastic film. The pieces of plastic film that had been subjected to steps 1 to 3 in sequence were extruded at 200°C using a twin-screw extruder to produce recycled pellets. The recycled pellets obtained were hot-pressed at 200°C using a heat press to produce a pressed plate with a thickness of 1 mm. The color values L ^* , a ^* , and b ^* of the pressed plate were measured using a spectrophotometer (X-rite, X-riteeXact). The raw material pellets of the plastic film (non-recycled product, Prime Polymer F-300SP) were also subjected to the hot-press process in the same manner, and the color difference ΔE between them was determined.
⊚: ΔE is 10 or less. ◯: ΔE is 20 or less. △: ΔE is 30 or less. ×: ΔE is 31 or more. Furthermore, ⊚, ◯, and △ are in a range where there is no problem in practical use.

Comparative examples are shown in Table 6. Blank spaces in the table indicate that no implementation was performed.

From these results, it was shown that the embodiment of the present invention was able to peel off the plastic film and also peel off the ink layer present between the layers of the plastic film.

Claims (7)

A method for separating and recovering a plastic film having at least an ink layer, comprising:
A step 1 of crushing the plastic film;
A step 2 of immersing the plastic film in a cleaning solution;
A process 3 of separating the ink layer from the plastic film by stirring the crushed plastic film in a rinsing liquid containing at least a water-soluble solvent.
having
A method for separating and recovering plastic films , wherein the step 3 comprises agitating the plastic films using a medium that assists in grinding the plastic films . The method for separating and recovering a plastic film according to claim 1 , wherein the media is beads, rods, or inorganic salts that are present in an insoluble state in the rinse solution. 3. The method for separating and recovering a plastic film according to claim 1 or 2 , wherein the cleaning solution contains (a) a water-soluble solvent and (b) an inorganic base. The method for separating and recovering plastic films according to claim 1 or 2, wherein in step 2, the plastic film is immersed in a cleaning solution to swell the ink layer. The method for separating and recovering plastic films according to claim 1 or 2, wherein the plastic film is a laminate having at least a plastic film layer and another layer selected from a plastic film layer, a vapor deposition film layer, and a metal foil layer, and the ink layer is between the plastic film layer and the other layer. The method for separating and recovering plastic films according to claim 1 or 2, wherein in step 1, the long sides of the crushed plastic films are crushed to 1 mm or more and 30 mm or less. A method for producing recycled plastic pellets, comprising recovering the crushed plastic material separated by the method according to claim 1 or 2, melting the recovered material, and molding it with a molding machine.