JP7264053B2 - Adhesive resin composition and protective film using the same - Google Patents

Description

TECHNICAL FIELD The present invention relates to an adhesive composition and a protective film having an adhesive layer comprising the same. Specifically, when the protective film is stored in a roll state and then unwound, the film does not partially stretch or deform, and has excellent processability, as well as adhesive strength and peelability to the adherend. It relates to a protective film having an adhesive resin composition and an adhesive layer thereof.

Conventionally, protective films are used for stacking and storing members such as prism sheets used for optical applications, synthetic resin plates, stainless steel plates, aluminum plates, decorative plywood, steel plates, and glass plates used for building materials. It has been used to protect against scratches during transportation and secondary operations such as bending and pressing. It has also been used to protect household appliances, precision instruments and automobile bodies from scratches during transportation in the manufacturing process.
Such a protective film should have good adhesiveness and be easily peeled off after use without contaminating the surface of the adherend with the adhesive.

In recent years, the variety of adherends has progressed, and a large number of adherends ranging from those with smooth surfaces to those with uneven surfaces can be seen.
Among them, the back surface of the prism sheet is smoother than the prism surface, which has large surface irregularities, but the back surface has fine surface irregularities. It has functions such as preventing interference by close contact and making appearance defects such as scratches less noticeable.

Therefore, the back surface of the prism sheet needs to have good adhesion to the back surface in order to be protected with a protective film when stacked and stored or transported.
However, when time elapses after the protective film is attached to the adherend, there arises a problem of an increase in adhesive strength (so-called increased adhesion), which makes it difficult to peel off. It is known that this is caused by exposure to high temperatures during transportation, storage, etc. of the product to which the protective film is adhered, and this becomes more conspicuous.

As a protective film for use on adherends with fine surface irregularities, a polymer block consisting mainly of aromatic alkenyl compound units, which are said to be relatively resistant to adhesion enhancement, is composed of continuous aromatic alkenyl compound units, and a conjugated It is known to use a copolymer consisting of an aromatic alkenyl-conjugated diene monomer copolymer block randomly containing diene monomer units and aromatic alkenyl compound units for the adhesive layer (for example, patent See Document 1, etc.), but although this has sufficient protective performance for the adherend, it does not satisfy both the ease of peeling from the adherend and the ease of unrolling the protective film from the roll state.

JP 2014-16934 A

An object of the present invention is to store a protective film in a roll state, and then when the film is unwound, the film does not partially stretch or deform, has excellent workability, and is like the back surface of a prism sheet. In addition, when attached to an adherend with fine surface irregularities, it has sufficient adhesive strength, and even if it is exposed to high temperatures during transportation and storage, the adhesive strength does not increase easily, and the protective film is peeled off. To maintain the function without leaving adhesive residue on an adherend afterward.

The present invention is a tacky resin composition containing a block copolymer that satisfies the following 1) and 2) as a main component and containing an α-methylstyrene resin and a terpene resin.
1) A block copolymer containing the following polymer block A and the following polymer block B and having a structural formula ABA and/or a structural formula AB.
Polymer block A: polymer block composed mainly of repeating units derived from aromatic alkenyl compound monomer units and mainly composed of units derived from aromatic alkenyl compound units Polymer block B: conjugated diene Aromatic alkenyl monomer-conjugated diene monomer copolymer block randomly containing units derived from monomer units and aromatic alkenyl compound monomer units 2) The conjugated diene in the polymer block B The hydrogenation rate of double bonds derived from monomer units is 90 mol % or more.

In this case, the conjugated diene monomer units are preferably butadiene monomer units.

Also, in this case, it is preferable that 1 to 50 parts by weight of the α-methylstyrene resin is contained with respect to 100 parts by weight of the block copolymer.

Furthermore, in this case, it is preferable that the terpene resin contains a terpene phenol resin.

Furthermore, in this case, it is preferable that 0.1 to 30 parts by weight of the terpene phenol resin is contained with respect to 100 parts by weight of the block copolymer.

Furthermore, in this case, it is preferable to contain an organic lubricant.

Furthermore, in this case, it is preferable to contain 0.1 to 2 parts by weight of an organic lubricant with respect to 100 parts by weight of the block copolymer.

Furthermore, in this case, the organic lubricant is preferably ethylenebisstearic acid amide and/or calcium stearate.

A protective film having an adhesive layer made of the adhesive resin composition and a substrate layer made of a polypropylene-based resin composition is suitable.

In this case, a protective film having a release layer on the side opposite to the adhesive layer is suitable.

In this case, the protective film is preferably used to protect the back surface of the prism sheet.

The pressure-sensitive adhesive resin composition of the present invention does not partially stretch or deform the protective film when the protective film is stored in a roll state and then unwound, and has excellent workability, and furthermore, it can be used as a prism sheet. When applied to an adherend with fine surface irregularities such as a back surface, it has sufficient adhesive strength, and even if it is exposed to high temperatures during transportation and storage, the adhesive strength does not increase easily and is protected. Even after peeling off the film, no adhesive residue is left on the adherend, and the function can be maintained.

(Block copolymer)
The block copolymer in the present invention is a block copolymer containing polymer block A and polymer block B below.
Polymer block A: polymer block composed mainly of repeating units derived from aromatic alkenyl compound monomer units, and composed mainly of units derived from aromatic alkenyl compound monomer units Polymer block B : Aromatic alkenyl compound monomer-conjugated diene monomer copolymer block randomly containing units derived from conjugated diene monomer units and aromatic alkenyl compound monomer units

The block copolymer of the present invention is a block copolymer containing polymer block A and polymer block B described above and having a structural formula ABA and/or AB.
The block copolymer of the present invention is an aromatic alkenyl compound monomer-conjugated diene monomer copolymer block randomly containing units derived from conjugated diene monomer units and aromatic alkenyl compound monomer units. By having a certain polymer block B, when the protective film is attached to an adherend having fine surface irregularities and is exposed to high temperatures during transportation and storage, compared to other block copolymers. However, it is difficult for adhesion to increase. Among them, it is preferable to use only the structural formula ABA in which polymer blocks A are present at both ends, because the increase in adhesion at high temperatures is further suppressed.

The content of units derived from aromatic alkenyl compound monomer units in the block copolymer is preferably 30% by weight or more.
If the content of units derived from the aromatic alkenyl compound monomer units is 30% by weight or more, the initial adhesive strength may be too strong, adhesive residue may occur, or the adhesive strength may be difficult to increase, and 40% by weight or more. is more preferred, and 45% by weight or more is even more preferred.
When the content of units derived from aromatic alkenyl compound monomer units is 60% by weight or less, the initial adhesive strength can be easily obtained, and 55% by weight or less is more preferable.
The unit content (St(A+B)) derived from the aromatic alkenyl compound monomer in the block copolymer represents a numerical value defined by the following formula.
The content of units derived from such aromatic alkenyl compound monomer units is determined by 1H-NMR. In addition, the content of units derived from such aromatic alkenyl compound monomer units can also be determined by an infrared spectroscopy method, and a value substantially equivalent to 1H-NMR is obtained.

St (A + B) = (mass of units derived from aromatic alkenyl compound monomer units in block copolymer) / (mass of all units derived from monomers in block copolymer) x 100 (% by weight) )

The block copolymer preferably has a weight average molecular weight of 30,000 to 200,000.
When the weight average molecular weight is 200,000 or less, it is easy to obtain adhesive strength to adherends having fine surface irregularities, the solubility in solvents and heat-melting properties are improved, and industrial processing into pellets and Film production by melt coextrusion may also be facilitated. More preferably, the weight average molecular weight of the block copolymer is 180,000 or less.
When the weight-average molecular weight is 30,000 or more, the polymer is less likely to adhere to production equipment or the like in the process of desolvating and drying the polymer, which may facilitate industrial production. The weight average molecular weight of the block copolymer is more preferably 100,000 or more, more preferably 130,000 or more.

The block copolymer preferably has a melt flow rate (MFR) value in the range of 0.1 to 20 g/min, more preferably 1 to 15 g/min. By setting the melt flow rate value in the range of 0.1 to 20 g/min, not only does it facilitate industrial production of the block copolymer, but it also provides excellent processability during film formation. be able to. When the melt flow rate value is less than 0.1 g/min, the solubility in the solvent during polymerization is deteriorated, the heat meltability is lowered, and it may be difficult to remove the polymer from the production equipment. This difficulty becomes a problem that may reoccur during film formation. More preferably, the melt flow rate value is 2 g/min or more, and even more preferably 3 g/min or more.
On the other hand, if the melt flow rate value is more than 20 g/min, the polymer adheres and remains inside the manufacturing equipment in the step of desolvating and drying the polymer, making it difficult to remove the polymer. This difficulty becomes a problem that may reoccur during film formation. More preferably, the melt flow rate value is 10 g/min or less, and even more preferably 6 g/min or less.

(Polymer block A)
The polymer block A in the present invention is composed mainly of repeating units derived from aromatic alkenyl compound monomer units, and is a polymer block mainly composed of units derived from aromatic alkenyl compound monomer units. However, the content of units derived from aromatic alkenyl compound monomer units in the polymer block A is preferably 80% by weight or more.
By making the unit derived from the aromatic alkenyl compound monomer unit in the polymer block A 80% by weight or more, the thermoplasticity of the adhesive resin composition can be suppressed, and the adhesive strength of the adhesive resin composition can be suppressed. There is an advantage that it becomes easier to suppress the change in . It is more preferable that the unit derived from the aromatic alkenyl compound monomer unit in the polymer block A is 90% by weight or more.

In addition, repeating units other than units derived from aromatic alkenyl compound monomer units may be contained in an amount of less than 20% by weight.
Examples of aromatic alkenyl compound monomer units include, but are not limited to, styrene, tert-butylstyrene, α-methylstyrene, p-methylstyrene, p-ethylstyrene, divinylbenzene, 1,1-diphenylethylene, Aromatic alkenyl monomeric units such as vinylnaphthalene, vinylanthracene, N,N-dimethyl-p-aminoethylstyrene, N,N-diethyl-p-aminoethylstyrene and vinylpyridine may be mentioned.
Among the aromatic vinyl alkenyl monomer units, styrene units are preferred because raw materials are readily available.
The repeating unit other than the unit derived from the aromatic alkenyl compound monomer is a repeating unit derived from a compound copolymerizable with the unit derived from the aromatic alkenyl compound monomer, such as a conjugated diene compound or A repeating unit derived from a (meth)acrylic acid ester compound can be mentioned. Among them, 1,3-butadiene and isoprene are preferred because they are highly copolymerizable with units derived from aromatic alkenyl compound units.

The content of polymer block A in the block copolymer must be 10% by weight or more. If the content of the polymer block A is less than 10% by weight, the initial adhesive strength may be too strong, resulting in adhesive residue or increased adhesive strength. On the other hand, the content of polymer block A in the block copolymer is preferably 50% by weight or less. If it exceeds 50% by weight, the initial adhesive strength may not be recognized. More preferably, it is 45% by weight or less, and still more preferably 40% by weight or less.

(Polymer block B)
Polymer block B in the present invention is an aromatic alkenyl monomer-conjugated diene monomer copolymer containing randomly units derived from conjugated diene monomer units and units derived from aromatic alkenyl compound monomer units. It is a polymer block. By randomly containing units derived from conjugated diene units and units derived from aromatic alkenyl compound units, the protective film using the adhesive resin composition of the present invention can be attached to an adherend having fine surface irregularities. After attachment, even when exposed to high temperatures during transportation and storage, adhesion is less likely to increase.
Here, the term "randomly" is interpreted in a broad sense, and the chain distribution of the conjugated diene units and the aromatic alkenyl compound units is a certain statistical rule obtained by simultaneously polymerizing the mixed conjugated diene and aromatic alkenyl compound. means to be in compliance with
Examples of aromatic alkenyl compound monomer units include, but are not limited to, styrene, tert-butylstyrene, α-methylstyrene, p-methylstyrene, p-ethylstyrene, divinylbenzene, 1,1-diphenylethylene, Aromatic vinyl monomeric units such as vinylnaphthalene, vinylanthracene, N,N-dimethyl-p-aminoethylstyrene, N,N-diethyl-p-aminoethylstyrene and vinylpyridine may be mentioned.
Among the aromatic vinyl monomer units, styrene units are preferred because raw materials are readily available.
The conjugated diene monomer unit in polymer block B in the present invention is not particularly limited, but examples include 1,3-butadiene, 1,2-butadiene, isoprene, 2,3-dimethyl-butadiene, 1,3- Pentadiene, 2-methyl-1,3-butadiene, 2-methyl-1,3-pentadiene, 1,3-hexadiene, 1,3-cyclohexadiene, 4,5-diethyl-1,3-octadiene, 3-butyl Mention may be made of diolefins such as -1,3-octadiene, myrcene and chloroprene.
Among diolefins, at least one unit selected from 1,3-butadiene units and isoprene units, which have high polymerization reactivity and easy availability of raw materials, is preferable. Furthermore, it is more preferable to select 1,3-butadiene units in order to obtain high mechanical strength.

From the viewpoint of heat resistance and weather resistance, the hydrogenation rate of the double bonds derived from the conjugated diene monomer units in the block copolymer B of the present invention is required to be 90 mol % or more. It is preferably 95 mol % or more, more preferably 98 mol % or more. If it is less than 90 mol %, the adhesive strength to an adherend having fine unevenness cannot be obtained, and there is concern about heat resistance and weather resistance.

The content of units derived from aromatic alkenyl compound monomer units in block copolymer B is preferably 10% by weight or more. If the content of units derived from the aromatic alkenyl compound monomer units is less than 10% by weight, the initial adhesive strength may be too strong, adhesive residue may occur, or the adhesive strength may increase easily. The content of units derived from aromatic alkenyl compound monomer units is more preferably 20% by weight or more, particularly preferably 30% by weight or more.
On the other hand, the content of units derived from aromatic alkenyl compound monomer units is preferably 80% by weight or less. If it exceeds 80% by weight, the initial adhesive strength may not be recognized. The content of units derived from aromatic alkenyl compound monomer units is more preferably 50% by weight or less, and particularly preferably 40% by weight or more.

(α-methylstyrene resin)
As a result of intensive studies, α-methylstyrene resin, in combination with a terpene resin, suppresses the increase in adhesion of the adhesive layer, and the surface of the base material layer opposite to the surface of the adhesive layer It has been found that it has the effect of improving the releasability from the adhesive and that a sufficient initial adhesive strength can be obtained. It is presumed that this is due to the diffusion of the α-methylstyrene resin into the polymer block B of the block copolymer. The content of units derived from the aromatic alkenyl compound monomer in the block copolymer simply having the structural formula ABA and/or AB and the content of the polymer block A in the block copolymer This is an effect that cannot be obtained simply by increasing the molecular weight of the block copolymer.
The α-methylstyrene resin used in the present invention includes α-methylstyrene homopolymer and/or α-methylstyrene as a main component, styrene and p-methylstyrene, p-chlorostyrene, chloromethylstyrene, Copolymers of two or more styrenic compounds such as tert-butylstyrene, p-ethylstyrene and divinylbenzene can be mentioned.
The α-methylstyrene resin may be a copolymer with an aliphatic monomer.
A molecular weight Mw of 4000 or more is preferable from the viewpoint of resin strength and bleeding out. A copolymer composed of two or more monomers may be a block copolymer or a random copolymer.
Among them, the α-methylstyrene resin preferably has a softening point of 100° C. or higher, more preferably 150° C. or higher. Specifically, Eastman Chemical Company, trade name "ENDEX155" (softening point 155 ° C., molecular weight Mz = 13850, Mw = 6950, Mn = 2400, Mw / Mn = 3.0, density = 1.04 g / ml , glass transition temperature = 99°C), "ENDEX 160" (softening point 160°C), and the like.

(Terpene resin)
In the present invention, terpene-based resins or hydrogenated products thereof are mentioned.
Terpene-based resins are obtained by cationic polymerization of terpene-based compounds (eg, α-pinene, β-pinene, limonene, etc.) collected from pine trees and orange peels as raw materials.
Terpene-based resins are roughly classified into polyterpene resins that are polymers of terpene monomers, aromatic modified terpene resins obtained by copolymerizing terpene monomers and aromatic monomers, terpene phenolic resins that are obtained by reacting terpene monomers and phenols, and further is classified as a hydrogenated terpene resin obtained by hydrogenating these.
If the resin is a hydrogenated terpene resin, it is possible to reduce concerns about discoloration due to high temperature or aging.
The above terpene-based resins may be used alone or in combination of two or more. A terpene resin having a glass transition temperature or softening point of 30° C. or higher is preferably used. If the temperature is 30° C. or higher, there is little fear of exudation at room temperature, and the handleability is excellent. The glass transition temperature or softening point of the terpene-based resin is preferably 50°C or higher, more preferably 65°C or higher, and particularly preferably 90°C or higher, in consideration of high-temperature acceleration.

A terpene-based resin, when combined with α-methylstyrene, can be expected to improve the adhesive strength and the suppression of the adhesion due to the effect of plasticizing the adhesive resin composition and the effect of inhibiting the molecular motion of the adhesive resin.
Among terpene-based resins, terpene phenol resins are preferred, and hydrogenated terpene phenol resins are particularly preferred. The phenol group of the terpene phenol resin has an electrical affinity with the adherend, so even if the product to which the protective film is attached is exposed to high temperatures during transportation and storage, its adhesive strength does not easily increase and it is stable. High adhesion is expected. A terpene phenol resin has a high softening point of about 130° C., and therefore, by combining it with an α-methylstyrene resin, it is possible to sufficiently exhibit the effect of suppressing the increase in adhesion and the initial adhesive strength.
Also in the case of terpene phenol resins, hydrogenation can reduce concerns about discoloration due to high temperature or aging.

(Adhesive resin composition)
The adhesive resin composition of the present invention contains the block copolymer described in paragraph 0020 as a main component, and contains an α-methylstyrene resin and a terpene resin. Here, the main component means that it is contained in the adhesive resin composition in an amount of 50% by weight or more.
At this time, it is preferable to contain 1 to 50 parts by weight of the α-methylstyrene resin with respect to 100 parts by weight of the block copolymer, more preferably 5 to 45 parts by weight, further preferably 10 to 40 parts by weight, and 15 to 15 parts by weight. 40 parts by weight is particularly preferred. If the α-methylstyrene resin is 1 part by weight or more relative to 100 parts by weight of the block copolymer, the increase in adhesion of the block copolymer is easily suppressed, and if it is 50 parts by weight or less, the adhesive strength to the adherend. is difficult to decrease. When the α-methylstyrene resin is 10 parts by weight or more relative to 100 parts by weight of the block copolymer, the increase in adhesion of the block copolymer is more likely to be suppressed, and when it is 40 parts by weight or less, the adhesion to the adherend increases. Power is less likely to decrease.
Further, at this time, it is preferable to contain 1 to 50 parts by weight of a terpene-based resin with respect to 100 parts by weight of the block copolymer. When the content of the terpene-based resin is 1 part by weight or more, the initial adhesive strength is improved. More preferably, it is 3 parts by weight or more, still more preferably 5 parts by weight or more, and particularly preferably 15 parts by weight or less.
When the content of the terpene-based resin is 50 parts by weight or less, the compatibility with the adhesive resin composition does not decrease, and the decrease in initial adhesive strength is hardly observed. More preferably, it is 40 parts by weight or less, still more preferably 30 parts by weight or less, and particularly preferably 25 parts by weight or less.

The adhesive resin composition of the present invention contains, in addition to the block copolymer, α-methylstyrene resin, and terpene resin described above, an organic lubricant, an antioxidant, a light stabilizer, and an ultraviolet absorber, if necessary. agents, fillers, pigments, styrenic block phase reinforcing agents, softening agents, anti-adhesion agents, olefin resins, silicone resins, liquid acrylic copolymers, phosphoric acid ester compounds, etc. You can Each is described below.

(organic lubricant)
The organic lubricant used in the present invention is preferably saturated fatty acid bisamide or fatty acid metal salt, considering excessive exudation at room temperature or high temperature. Specific examples include ethylenebisstearic acid bisamide and stearic acid metal salts. These may be used alone or in combination of two or more.

In the adhesive resin composition. It is preferable to contain 0.1 to 2 parts by weight of the organic lubricant with respect to 100 parts by weight of the block copolymer. An organic lubricant can be expected to have the effect of suppressing the increase in adhesive strength.
When the content of the organic lubricant is 0.1 parts by weight or more, it is easy to suppress the increase in adhesive strength at high temperature or over time, and it is more preferably 0.2 parts by weight or more.
When the content of the organic lubricant is 2 parts by weight or less, it is difficult to bleed out at high temperature or over time, and there is no fear of staining the adherend. Part by weight or less is particularly preferred.
The organic lubricant used in the present invention preferably has a high melting point in view of bleeding out at high temperatures and over time, and specific examples thereof include ethylenebisstearic acid amide and calcium stearate.

(Antioxidant)
Antioxidants used in the present invention are not particularly limited, and include, for example, commonly used phenolic (monophenolic, bisphenolic, polymeric phenolic), sulfur, and phosphorus antioxidants.

(light stabilizer)
The light stabilizer used in the present invention includes hindered amine compounds.

(Ultraviolet absorber)
The UV absorber used in the present invention is not particularly limited, and examples thereof include salicylic acid-based, benzophenone-based, benzotriazole-based, and cyanoacrylate-based.

(Softener)
The softening agent refers to a low melting point conjugated polymer having a melting point of 50° C. or less, a low melting point petroleum oil or a natural oil. Polybutadiene, paraffinic process oil, naphthenic process oil, aromatic process oil, castor oil, tall oil, natural oil, liquid polyisobutylene resin, polybutene, or hydrogenated products thereof can be used. These softeners may be used alone or in combination of two or more.

(filler)
Examples of fillers include calcium carbonate, magnesium carbonate, silica, zinc oxide and titanium oxide.

(Protective film)
The protective film according to the present invention is obtained by laminating an adhesive layer made of the adhesive resin composition on a substrate layer. Furthermore, a release layer may be provided on the substrate layer on the side opposite to the adhesive layer.
A detailed description will be given below.

(Adhesive layer)
The pressure-sensitive adhesive layer in the present invention is made of the pressure-sensitive adhesive composition described above, and has a thickness of usually about 1 to 30 μm, preferably 2 to 10 μm.

(Base material layer)
The substrate layer in the present invention can be formed from a polyolefin resin. The polyolefin resin contained in the substrate is not particularly limited, but ethylene homopolymer, ethylene-α-olefin copolymer, ethylene-(meth)acrylic acid copolymer, ethylene-(meth)acrylic acid ester copolymer. Polymers and polyethylene-based resins such as ethylene-vinyl acetate copolymers; polypropylene-based resins such as propylene homopolymers, propylene-α-olefin copolymers, and propylene-ethylene copolymers; butene homopolymers; butadiene and homopolymers or copolymers of conjugated dienes such as isoprene. Further, examples of the polyethylene-based resin include high-density polyethylene, medium-density polyethylene, and low-density polyethylene. The form of copolymerization may be random, block, or terpolymer form. The above polyolefin-based resins may be used alone, or two or more of them may be used in combination.

The polyethylene-based resin is obtained using ethylene as a main component. The proportion of structural units derived from ethylene is preferably 50% by weight or more, more preferably 70% by weight or more, and still more preferably 90% by weight or more in 100% by weight of all structural units of the polyethylene-based resin.

The polypropylene-based resin is obtained using propylene as a main component. The proportion of structural units derived from propylene is preferably 50% by weight or more, more preferably 70% by weight or more, and still more preferably 90% by weight or more in 100% by weight of all structural units of the polypropylene resin.
The substrate layer of the present invention is preferably composed mainly of a polypropylene-based resin in terms of heat resistance, weather resistance, or adhesion to the adhesive layer.

The thickness of the substrate layer in the present invention is preferably 10 μm or more, more preferably 100 μm or less. When the thickness of the substrate is 10 µm or more and 100 µm or less, the handleability of the protective film is further enhanced.

When the protective film according to the present invention is composed only of a substrate layer and an adhesive layer composed of the adhesive composition, the surface is provided with unevenness in order to suppress the peeling force between the surface of the substrate layer and the surface of the adhesive layer. It is preferable to reduce the contact area with the adhesive layer.
In this case, considering the resin composition of the adhesive layer of the present invention, the average surface roughness SRa of the surface of the release layer is preferably 0.40 μm or more. It is more preferable that the average surface roughness of the surface is 0.85 μm or less in SRa, and more preferably 0.50 μm or more and 0.70 μm or less.
By setting the average surface roughness SRa of the adhesive layer surface and the opposite surface of the adhesive layer of the base material layer to 0.40 μm or more, the adherend protection performance and peeling force can be improved. When the surface roughness of the release layer is less than 0.40 μm, the unreeling property of the film is deteriorated when the film is rolled. If the surface roughness of the base material layer is higher than 0.85 μm, the surface unevenness of the base material layer may be transferred to the surface of the adhesive layer, resulting in a significant decrease in adhesive strength.

In order to make the average surface roughness SRa 0.40 μm or more, it is preferable to add a resin incompatible with homopolypropylene or random polypropylene, or to use a propylene-ethylene block copolymer as the resin used for the base material layer. can be used for When a propylene-ethylene block copolymer is used, the uneven state is less likely to change due to changes in production equipment and melt-kneading conditions during film formation, and stable production is possible.
The average surface roughness SRa can be increased by increasing the molecular weight of the ethylene-propylene rubber in the propylene-ethylene block copolymer or by increasing the amount of ethylene. Further, by mixing an incompatible resin into the propylene-ethylene block copolymer, the average surface roughness SRa can be increased.
The average surface roughness SRa can also be increased by lowering the shear rate applied to the resin or lengthening the residence time in the extrusion step, which will be described later.
On the other hand, in order to reduce the average surface roughness SRa, it is effective to mix a propylene-ethylene block copolymer with a homopolypropylene resin.

As the resin incompatible with the propylene-ethylene block copolymer, α-olefin (co)polymers having 4 or more carbon atoms such as 4-methylpentene-1 (co)polymers can be suitably used. In addition, low-density polyethylene, high-density polyethylene, copolymer of ethylene and a small amount of α-olefin, copolymer of ethylene and vinyl acetate, polystyrene, alicyclic olefin resin, polyester resin, polyamide resin, etc. is mentioned. In particular, a 4-methylpentene-1 (co)polymer is preferable because it not only roughens the surface in a matt state, but also lowers the surface free energy of the film surface, thereby further reducing the peeling force.

The content of the α-olefin (co)polymer having 4 or more carbon atoms in the substrate layer (resin component constituting the substrate layer) is in the range of 0% by weight or more and 35% by weight or less. When the content of the α-olefin (co)polymer having 4 or more carbon atoms exceeds 35% by weight, the substrate layer and adhesive layer materials are co-extruded using a T-die or the like to laminate the substrate. The film formability of the layer deteriorates.

(release layer)
The release layer in the present invention can be provided on the substrate layer on the side opposite to the adhesive layer. As a result, by distributing the functions to the substrate layer and the release layer respectively, it is possible to respond to a wider range of applications.

In this case, it is preferable to reduce the contact area with the adhesive layer by imparting unevenness to the surface in order to suppress the peeling force between the surface of the release layer and the surface of the adhesive layer.
Considering the resin composition of the adhesive layer of the present invention, the average surface roughness SRa of the surface of the release layer is preferably 0.40 μm or more. It is more preferable that the average surface roughness of the surface is 0.850 μm or less in SRa, and more preferably 0.500 μm or more and 0.700 μm or less.

By setting the average surface roughness SRa of the surface of the release layer to 0.40 μm or more, it is possible to improve the protection performance of the adherend and the release force. When the surface roughness of the release layer is less than 0.40 μm, the film unreeling property is deteriorated when the film is rolled. If the surface roughness of the release layer is higher than 0.850 μm, the unevenness of the surface of the release layer may be transferred to the surface of the adhesive layer, resulting in a significant decrease in adhesive strength.

In order to make the average surface roughness SRa 0.40 μm or more, as the resin used for the release layer, it is preferable to add a resin incompatible with homopropylene or random polypropylene, or to use a propylene-ethylene block copolymer. can be used for When a propylene-ethylene block copolymer is used, the uneven state is less likely to change due to changes in production equipment and melt-kneading conditions during film formation, and stable production is possible.
The average surface roughness SRa can be increased by increasing the molecular weight of the ethylene-propylene rubber in the propylene-ethylene block copolymer or by increasing the amount of ethylene. Further, by mixing an incompatible resin into the propylene-ethylene block copolymer, the average surface roughness SRa can be increased.
The average surface roughness SRa can also be increased by lowering the shear rate applied to the resin or lengthening the residence time in the extrusion step, which will be described later.
On the other hand, in order to reduce the average surface roughness SRa, it is effective to mix a propylene-ethylene block copolymer with a homopolypropylene resin.

As the resin incompatible with the propylene-ethylene block copolymer, α-olefin (co)polymers having 4 or more carbon atoms such as 4-methylpentene-1 (co)polymers can be suitably used. Other examples include low-density polyethylene, high-density polyethylene, copolymers of ethylene and a small amount of α-olefin, copolymers of ethylene and vinyl acetate, polystyrene, polyester resins, polyamide resins, and the like. In particular, a 4-methylpentene-1 (co)polymer is preferable because it not only roughens the surface in a matt state, but also lowers the surface free energy of the film surface, thereby further reducing the peeling force.

The content of the α-olefin (co)polymer having 4 or more carbon atoms in the release layer (resin component constituting the release layer) is in the range of 0% by weight or more and 35% by weight or less. When the content of the α-olefin (co)polymer having 4 or more carbon atoms exceeds 35% by weight, the film formability of the base layer deteriorates when the base layer and the adhesive layer are laminated by co-extrusion.
The thickness of the release layer is not particularly limited. The thickness of the release layer is preferably 2 μm or more and preferably 10 μm or less. When the thickness of the release layer is 2 µm or more and 10 µm or less, the handleability of the protective film is further enhanced.

(Characteristics of protective film)
The initial adhesive strength of the protective film of the present invention is preferably 3 cN/25 mm or more and 20 cN/25 mm or less. When it is 3 cN/25 mm or more, it does not peel off or float during handling or transportation, and when it is less than 20 cN/25 mm, excessive force is not required when peeling it off. More preferably, it is 4 cN/25 mm or more and 15 cN/25 mm or less. More preferably, it is 5 cN/25 mm or more and 10 cN/25 mm or less.
The initial adhesive strength was measured as follows.
23±2° C. and a relative humidity of 50±5% RH so that the surface of the adhesive layer of the protective film is in contact with the back surface of the prism sheet. H. , a linear pressure of 15 kN/m was applied from the side opposite to the pressure-sensitive adhesive layer surface of the protective film, and the protective film was adhered at a speed of 2 m/min.
The resulting specimens were subjected to a temperature of 23±2° C. and a relative humidity of 50±5% RH. H. After being left in a room for 30 minutes, the 180-degree peel strength (unit: cN) at a width of 25 mm was measured at a peel rate of 300 mm/min according to JIS Z0237, and taken as the initial adhesive strength.

The protective film of the present invention preferably has an adhesion enhancement rate of 400% or less. When the adhesion rate is 400% or less, the peeling work can be performed under more constant conditions, and the work efficiency is improved. More preferably, it is 300% or less, still more preferably 200% or less.
The adhesion rate was calculated by the following formula using the initial adhesive strength and the time-dependent adhesive strength.
Adhesion rate = (adhesive strength over time/initial adhesive strength) x 100 (%)

The adhesive strength over time of the protective film of the present invention is preferably 3 cN/25 mm or more and 40 cN/25 mm or less. When it is 3 cN/25 mm or more, it does not peel off or float during handling and transportation, and when it is 40 cN/25 mm or less, excessive force is not required when peeling it off. More preferably, it is 4 cN/25 mm or more and 40 cN/25 mm or less. It is more preferably 5 cN/25 mm or more and 30 cN/25 mm or less, and particularly preferably 5 cN/25 mm or more and 20 cN/25 mm or less.
The adhesive strength over time was measured as follows.
A test piece was prepared under the same conditions as those for the prism sheet used to measure the adhesive strength over time. After being left for one week in an atmosphere of 65°C ± 2°C and a load of 6 kg/400 cm ² , the 180° peel strength at a width of 25 mm was measured at a peel speed of 300 mm/min in accordance with JIS Z0237, and was taken as the adhesive strength over time. .

The peeling force between the surface of the adhesive layer of the present invention and the surface of the base layer or the surface of the release layer on the opposite side of the adhesive layer is in the range of 10 cN / 25 mm or less at 23 ° C. When the protective film is in the form of a roll. is preferred from the viewpoint of film feedability. If the peel force exceeds 10 cN/25 mm, problems such as partial elongation or deformation of the protective film may occur when the protective film is rolled out. The peel force at 23° C. is more preferably 5 cN/25 mm or less, particularly preferably 3 cN/25 mm or less.
The lower limit of the peeling force of the protective film to the surface of the adhesive layer of the protective film and the surface of the base layer or release layer on the opposite side of the adhesive layer is about 1 cN/25 mm as a practical value, and further about 2 cN/25 mm. is preferred.

(Method of forming protective film)
The method for producing the protective film of the present invention includes, for example, introducing the pressure-sensitive adhesive composition and the polyolefin resin for the base layer into separate extruders and, if necessary, the polyolefin resin for the release layer, melting, A method of co-extrusion from a T-die and laminating, or a method of laminating another layer on the layer obtained by inflation molding by a lamination method such as extrusion lamination or extrusion coating, each layer being independently formed into a film. After that, there is a method of laminating each obtained film by dry lamination, but from the viewpoint of productivity, each material of the release layer, the base layer, and the pressure-sensitive adhesive layer is used in a multilayer extruder Co-extrusion molding is preferable, and T-die molding is more preferable from the viewpoint of thickness accuracy.

The protective film of the present invention is used to protect the surface of an adherend having a smooth surface or fine irregularities, and is particularly effective when the surface roughness is about 0.1 to 1.0 μm. is.

EXAMPLES The present invention will be described in more detail with reference to examples below, but the present invention is not limited to these examples.
The measurement method is shown below.

(1) Initial Adhesion The obtained surface laminated film was cut into a size of 150 mm length (winding direction during film production) x 25 mm width (perpendicular to the winding direction during film production) and used as a test piece. The pressure-sensitive adhesive layer surface was attached to the back surface of a 150 mm×35 mm prism sheet (acrylate polymer, SRa=0.24 μm) to prepare a test piece. Application was performed at 23±2° C. and 50±5% R.H. H. A linear pressure of 20 N/m was applied from the outside of the surface-laminated film (that is, the side opposite to the pressure-sensitive adhesive layer surface) under the environment of , and the film was adhered at a speed of 2 m/min. The following laminator was used for lamination.
Laminator manufacturer: Tester Sangyo Co., Ltd.
Model: SA-1010-S
Roll: Heat-resistant silicon rubber roll Roll diameter: Φ200
The resulting specimens were stored at 23±2° C. and 50±5% R.H. relative humidity. H. After being left in a room for 30 minutes, the 180-degree peel strength (unit: cN) at a width of 25 mm was measured at a peel rate of 300 mm/min according to JIS Z0237, and taken as the initial adhesive strength.

(2) Adhesive strength over time The resulting surface protective film was attached under the same conditions as the prism sheet used in the evaluation of the initial adhesive strength in (1), and subjected to an atmosphere of 65°C ± 2°C and a load of 6 kg/400 cm ² . After standing for 1 week, it was placed at 23±2° C. and 50±5% R.H. H. and the 180-degree peel strength at a width of 25 mm was measured at a peel rate of 300 mm/min according to JIS Z0237, and was taken as the adhesive strength over time.

(3) Rate of Adhesion Rise Using the initial adhesive strength and the time-dependent adhesive strength obtained in (1) and (2) above, the rate of change from the initial adhesive strength to the time-dependent adhesive strength (adhesion rate) was calculated by the following formula. .
Rate of change (adhesion rate) = (adhesive strength over time/initial adhesive strength) x 100

(4) Peeling force Two sheets of the obtained surface protective film are stacked and cut out to a size of 110 mm (winding direction at the time of film production) x 40 mm (direction perpendicular to the winding direction at the time of film production). Then, the top and bottom of it were sandwiched between copy papers, a weight of 60 kg was placed thereon, and the mixture was allowed to stand in a room at a temperature of 40° C. for 72 hours. After that, it was cooled to 23±2° C. and 50±5% R.H. H. 1 hour in a room, and using Shimadzu Corporation "Autograph (registered trademark)" (AGS-J), the resistance value when peeled 180 degrees at a speed of 300 mm / min was measured as peel force [cN /25 mm].
When measuring, prepare a polyester sheet with a thickness of 190 μm and a size of 40 mm × 170 mm as a gripping margin for the measurement sample, and attach it to the end of the 110 mm × 40 mm test piece with a cellophane tape with a width of 15 mm. It was used as a holding fee. The measurement was performed three times for one sample, and the average value was taken as the peel strength of that sample.

5) Elongation/deformation of the film when the film is unwound A film roll of 550 mm width and 500 m was obtained by slitting, and then stored in a roll state for 7 days in a light-shielding environment at a temperature of 23°C and a humidity of 75%. For this storage roll, immediately after 300m rewinding onto another plastic core (9 cm diameter), the film end was manually grasped and pulled to rewind 3m. A visual check was made to see if there was any partial stretching or deformation of the film upon unwinding. A sample with no partial elongation or deformation was rated as ◯ (good), and a sample with partial elongation or deformation was rated as x (bad).

6) Adhesive residue and transferred material after peeling from the adherend The obtained surface protective film was attached under the same conditions as the prism sheet used for the initial adhesive strength evaluation in (1), 65 ° C. ± 2 ° C., After being left for one week in an atmosphere with a weight of 6 kg/400 cm ² , it was placed at 23±2° C. and a relative humidity of 50±5%R. H. was allowed to stand in the room for 1 hour. Subsequently, the film was peeled off by hand, and the presence or absence of adhesive residue on the back surface of the prism sheet was visually checked. A case where there was no adhesive residue or transferred matter was rated as ◯ (good), and a case where there was even a little adhesive residue or transferred matter was rated as x (bad).

7) Surface roughness Evaluation of surface roughness on the side opposite to the adhesive layer of the obtained protective film is performed using a three-dimensional roughness meter (manufactured by Kosaka Laboratory Co., Ltd., model number ET-30HK), with a stylus pressure of 20 mg. , X-direction measurement length 1 mm, feed speed 100 μm/sec, Y-direction feed pitch 2 μm, number of recorded lines 99, height direction magnification 20000 times, cut-off 80 μm Measurement was performed, and conformed to JISB 0601 (1994). It was calculated according to the definition of arithmetic mean roughness described.
Arithmetic mean roughness (SRa) was evaluated by the average value of three trials.

8) Content of Aromatic Alkenyl Compound Unit in Block Copolymer Each raw material resin and mixed resin sample was dissolved in CDCl ₃ and 1H-NMR was measured.

9) Content of Block A in Block Copolymer The spectrum of homopolystyrene was compared with the infrared spectrum of each raw material resin and mixed resin sample, and the content of block A was calculated.

10) Weight Average Molecular Weight Each starting resin and mixed resin sample were dissolved in tetrahydrofuran (sample concentration: 0.05% by weight). After filtration through a 0.20 μm membrane filter, GPC analysis of the resulting sample solution was performed under the following conditions. The molecular weight was calculated in terms of standard polystyrene.
GPC apparatus conditions Apparatus: High performance liquid chromatograph HLC-8220 (TOSOH)
Column: TSKgel SuperHZM-H + SuperHZM-H + SuperHZ2000 (TOSOH)
Solvent: THF (tetrahydrofuran)
Flow rate: 0.35mL/min
Injection volume: 10 μL
Temperature: 40°C
Detector: RI
Data processing: GPC data processing system (TOSOH)

11) Hydrogenation rate of double bonds derived from conjugated diene monomer units in polymer block B The hydrogenation rate of double bonds derived from conjugated diene monomer units in polymer block B is The content of carbon-carbon double bonds derived from the conjugated diene compound monomer units in block B was measured by iodine value measurement, infrared spectrophotometer, ¹ H-NMR spectrum, etc. before and after hydrogenation. , can be obtained from the measured values.

Raw material resins used in the following examples and comparative examples are shown below.
(1) S1605: Product name “S1605”, hydrogenated styrene-butadiene copolymer, manufactured by Asahi Kasei Corporation, MFR = 3.5 g/10 min, double bond derived from conjugated diene unit of polymer block B Hydrogenation rate = 100 mol%, weight average molecular weight = 180700, density = 1.00 g/cc, content of aromatic alkenyl compound units = 66% by weight, content of polymer block A = 31% by weight, structural formula Mixtures of ABA and Structural Formula AB.

(2) S1606: Product name “S1606”, hydrogenated styrene-butadiene copolymer, manufactured by Asahi Kasei Corporation, MFR = 4.0 g/10 min, double bond derived from conjugated diene unit of polymer block B Hydrogenation rate = 100 mol%, weight average molecular weight = 169900, density = 0.96 g/cc, content of aromatic alkenyl compound units = 50% by weight, content of polymer block A = 25% by weight, structural formula ABA.

(3) H1221: Product name “H1221”, hydrogenated styrene-butadiene block copolymer, manufactured by Asahi Kasei Corporation, MFR = 4.5 g/10 minutes, hydrogenation rate of double bonds derived from conjugated diene units = 100 mol %, weight average molecular weight = 147600, density = 0.89 g/cc, content of aromatic alkenyl compound units = 12% by weight, content of polymer block A = 12% by weight, no polymer block B.

(4) UH115: trade name "UH115", hydrogenated terpene phenolic resin, manufactured by Yasuhara Chemical Co., glass transition temperature = 65°C

(5) TH130: Product name "TH130", terpene phenol resin, manufactured by Yasuhara Chemical Co., Ltd., glass transition temperature = 80°C

(6) ENDEX155: trade name “Endex (TM) 155 Hydrocarbon Resin, hydrocarbon polymer, manufactured by Eastman Chemical Co., softening point = 153°C

(7) EB-P: trade name “EB-P”, ethylenebisstearic acid amide, manufactured by Kao Corporation

(Example 1)
A pressure-sensitive adhesive composition comprising 70 parts by weight of S1606, 5 parts by weight of TH130, and 20 parts by weight of ENDEX155, and a polyolefin resin (trade name “WF836DG3”, propylene-ethylene random copolymer, Prime Polymer Co., Ltd.) as a raw material for the base material layer. , MFR = 4.5/10 min, melting point = 164°C, ethylene copolymerization amount = 0.3% by weight), and a polyolefin resin (trade name “BC3HF”, polypropylene-ethylene block copolymer) as a raw material for the release layer. (melting point = 171°C, ethylene content = 9% by weight) by Prime Polymer Co., Ltd.), the adhesive layer resin is extruded at a rate of 4 kg/hour by a 40 mm diameter single screw extruder, and the substrate layer resin is a 90 mm diameter single screw extruder. Using a screw extruder with a discharge rate of 32 kg / hour, the release layer resin is discharged with a 60 mm diameter single screw extruder with a discharge rate of 4 kg / hour, using a three-layer T die (lip width 850 mm, lip gap 1 mm), Each was co-extruded and cooled with a cooling roll to obtain a protective film having an adhesive layer, a substrate layer, and a release layer with thicknesses of 4 µm, 32 µm, and 4 µm, respectively, and a length in the width direction of 650 mm. Table 1 shows the above results.

(Examples 2-5, Comparative Examples 1-8)
A protective film was obtained in the same manner as in Example 1 except that the content of the raw material resin and additives of the adhesive layer, and the thickness and content of the adhesive layer were changed as shown in Table 1. Table 1 shows the above results.

The protective films of Examples 1 to 5 have sufficient adhesive strength when attached to the back surface of the prism sheet, and the adhesive strength does not easily increase even after one week at high temperature, and the peel strength is also good. It was an excellent control. In addition, the adhesive layer of the film and the surface on the opposite side have a large peeling force, and the film is difficult to stretch or deform.

On the other hand, the protective film of Comparative Example 1 exhibited too strong adhesion over time to the prism back surface.

The protective film of Comparative Example 2 had weak initial adhesion to the prism back surface and was easily peeled off. In addition, the adhesive strength over time increased significantly compared to the initial adhesive strength.

The protective film of Comparative Example 3 had an excessively strong adhesive force to the prism back surface over time and was difficult to peel off. In addition, the peeling force between the adhesive layer of the film and the surface on the opposite side is large, and the film is partially stretched or deformed.

The protective film of Comparative Example 4 was too strong in initial adhesive strength and adhesive strength over time to the prism back surface, and was difficult to peel off. In addition, the peeling force between the adhesive layer of the film and the surface on the opposite side is large, and the film is partially stretched or deformed.

The protective film of Comparative Example 5 had a very high initial adhesive strength to the prism back surface and a very high adhesive strength over time, and was difficult to peel off.

The protective film of Comparative Example 6 had a very high adhesion over time to the prism back surface and was difficult to peel off.

The protective film of Comparative Example 7 had weak initial adhesion to the prism back surface and was easily peeled off.

The protective film of Comparative Example 8 had a high initial adhesive strength to the prism back surface and was difficult to peel off. In addition, the adhesive layer of the film and the surface on the opposite side have a large peeling force, and the film tends to be partially stretched or deformed.

The pressure-sensitive adhesive composition of the present invention is industrially useful as the surface protective film of the present invention is suitably used for surface protection of prism sheets and the like, particularly for the back surface thereof.

Claims (9)

For 100 parts by weight of the block copolymer satisfying 1) and 2) below, 15 parts by weight or more and less than 50 parts by weight of α-methylstyrene resin satisfying 3) below, and 1 to 50 parts by weight of terpene resin Adhesive resin composition containing.
1) A block copolymer containing the following polymer block A and the following polymer block B and having a structural formula ABA and/or a structural formula AB.
Polymer block A: A weight composed mainly of repeating units derived from aromatic alkenyl compound monomer units and containing 80% to 100% by weight of units derived from aromatic alkenyl compound monomer units. Coalescing block polymer block B: Aromatic alkenyl monomer-conjugated diene monomer copolymer block randomly containing units derived from conjugated diene monomer units and aromatic alkenyl compound monomer units 2) above The hydrogenation rate of double bonds derived from the conjugated diene monomer units in the polymer block B is 90 mol % or more.
3) α-methylstyrene resin is α-methylstyrene homopolymer, or α-methylstyrene as a main component, styrene and p-methylstyrene, p-chlorostyrene, chloromethylstyrene, tert-butylstyrene, p- It is a copolymer consisting of one or more styrenic compounds selected from the range of ethylstyrene and divinylbenzene. 2. The adhesive resin composition according to claim 1, wherein said conjugated diene monomer units are butadiene units. The adhesive resin composition according to claim 1 or 2, wherein the terpene resin is a terpene phenol resin. The adhesive resin composition according to any one of claims 1 to 3, which contains an organic lubricant. 5. The adhesive resin composition according to claim 4, containing 0.1 to 2 parts by weight of an organic lubricant with respect to 100 parts by weight of the block copolymer. 6. The adhesive resin composition according to claim 4, wherein the organic lubricant is ethylenebisstearic acid amide and/or calcium stearate. A protective film having an adhesive layer made of the adhesive resin composition according to any one of claims 1 to 6 and a substrate layer made of a polypropylene resin composition. 8. The protective film according to claim 7, which has a release layer on the side opposite to the adhesive layer. 9. The protective film according to claim 7, which is used for protecting the back surface of a prism sheet.