JPH07126599A - Reactive hot-melt adhesive for food packaging composite laminate film - Google Patents

Abstract

PURPOSE:To obtain a solvent-free reactive hot-melt adhesive which contains an urethane prepolymer with a specific content of an isocyanate group, does not cause environmental pollution and has excellent adhesiveness to a metal foil, moisture resistance and coatability. CONSTITUTION:An urethane prepolymer with an isocyanate content of 0.5-5.0% obtd. by reacting a mixture of an alkoxysilane compd. having a group reactive with a polyisocyanate and a polyol with a polyisocyanate is used as a main component. It is pref. to add 1-50 pts. ester plasticizer to 100 pts. prepolymer to obtain excellent coatability.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composition of a reactive hot melt adhesive used as an adhesive for a food packaging composite laminate film, and particularly to a coating property of low thickness, adhesion to a metal foil and retort properties. It relates to a composition of excellent reactive hot melt adhesives.

[0002]

2. Description of the Related Art A composite packaging film for food packaging is made of various plastic films having a thickness of about 5 to 100 .mu.m.
And / or made of metal foil. Examples of the material are polyolefins such as polyethylene and polypropylene, copolymers with olefins, plastic films such as polyvinyl chloride, polyvinylidene chloride, polyester and polyamide, and metal foils such as aluminum and stainless steel.

These materials are characterized by strength, water resistance, moisture permeation resistance, oxygen permeation resistance, heat resistance, and the like, and by laminating two or more kinds of materials as required, a high film which cannot be obtained by a single film. It can be a high performance food packaging composite laminate film. At the time of its production, it is usual to use an adhesive agent, but as the adhesive agent for the conventional food packaging composite laminate film, solvent type one-component polyurethane is mainly used. However, the use of these solvent-based adhesives not only causes the organic solvent to volatilize in the bonding process and pollutes the work environment and the atmosphere, but it is inevitable that the solvent partially remains in the adhesive layer. There are drawbacks.

Although some liquid solvent-free one-component polyurethane adhesives without these defects have been put into practical use, the adhesive force immediately after lamination is extremely weak, and a process of forming a wound body after lamination. Further, during storage as a wound body, there is a defect that a gap between layers occurs, partial peeling occurs, and wrinkles easily occur. Furthermore, since the curing reaction is slow, 3
Curing in high temperature and high humidity was required for about 5 days, and the performance after curing was insufficient. For example, when used in a general retort food packaging laminate film consisting of polyester film / aluminum foil / unstretched polypropylene film, when it is subjected to retort treatment, the adhesive surface between the aluminum foil and the polypropylene film is pinned immediately after retort over time. There are drawbacks that holes are generated and the adhesive strength is significantly reduced. In addition, these conventional solventless liquid polyurethane adhesives have a limitation in material selection because they must be liquid at room temperature, for example, a polyether polyol as a main component or a polyester polyol having good adhesiveness. In the case of, it is difficult to use it alone, so it will be limited to an extremely limited composition

Furthermore, the conventional urethane-based reactive hot melt adhesives used for other purposes lack adhesion and moisture resistance to the metal foil surface, and are similar to solvent-free one-component polyurethane adhesives. When the retort treatment is applied, there is a drawback that the adhesive strength is reduced immediately after the retort.

[0006]

SUMMARY OF THE INVENTION The present invention solves the above problems and provides a necessary adhesive strength immediately after laminating without using a solvent that does not cause environmental pollution, and has an adhesive property, particularly a metal foil. It is intended to provide a reactive hot melt adhesive for a food packaging composite laminate film, which has excellent adhesiveness to a surface and moisture resistance, and further has excellent coatability as well as the conventionally used adhesive.

[0007]

The inventor of the present invention has achieved the present invention as a result of intensive studies to solve the above problems.

The following are used as the prepolymer of the main component. That is, polyisocyanate compounds (diphenylmethane diisocyanate, dimethyldiphenylmethane diisocyanate, dicyclohexylmethane diisocyanate, tolylene diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, P
-Phenylene diisocyanate, isophorone diisocyanate, etc.) and 2 or more, preferably 2 in one molecule.
One or more polyols having 3 to 3 active hydrogens (polyether polyols, polyester polyols, acrylic polyols, etc.) are appropriately selected so that the properties to be set can be obtained, and the compounding ratio is NCO / OH ratio of 1 ．
A polyurethane prepolymer is obtained by reacting in the range of 2 to 4.0, and more preferably in the range of 1.5 to 2.5 under heating at 60 to 130 ° C. for several hours. The urethane prepolymer has an alkoxysilane compound having one reactive group with polyisocyanate (γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, N-
β- (aminoethyl) -γ-aminopropyltrimethoxysilane, γ-ureidopropyltriethoxysilane,
γ-mercaptopropyltrimethoxysilane, γ-anilinopropyltrimethoxysilane, etc.) 0.1-5.0
Parts, more preferably 0.2 to 3.0 parts, and added to 60 to 1
It is a prepolymer obtained by reacting for several hours under heating at 30 ° C.

Alternatively, an alkoxysilane compound having one reactive group with polyisocyanate (γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, N-β- (aminoethyl) -γ-aminopropyltrimethoxysilane) , Γ-ureidopropyltriethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-anilinopropyltrimethoxysilane, etc.)
And a mixture of one or more polyols (polyether polyol, polyester polyol, acrylic polyol, etc.) having 2 or more, preferably 2 to 3 active hydrogens in one molecule, and a polyisocyanate compound (diphenylmethane diisocyanate). , Dimethyldiphenylmethane diisocyanate, dicyclohexylmethane diisocyanate, tolylene diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, P-phenylene diisocyanate, isophorone diisocyanate, etc.) are appropriately selected so as to obtain the characteristics to be set, and the compounding ratio is NCO. / OH ratio of polyol is in the range of 1.2 to 4.0, more preferably 1.5 to
It is a prepolymer obtained by reacting for several hours under heating at 60 to 130 ° C. in the range of 2.5.

In the above polyurethane prepolymer synthesis, the polyisocyanate compound and the polyol are NCO.
The / OH ratio is in the range of 1.2 to 4.0, and more preferably 1.
The reaction is conducted in the range of 5 to 2.5, which is NCO / OH.
This is because if the ratio is less than 1.2, the viscosity of the obtained prepolymer becomes too large, and if it exceeds 4.0, there is a drawback that foaming occurs remarkably during moisture curing.

Further, the NC of the functional group at the terminal of the prepolymer molecule is
The O / Si (OR) ₃ ratio is adjusted to a range of 1.0 to 99.0, more preferably 6.0 to 80.0, which has an NCO / Si (OR) ₃ ratio of 1. This is because if the ratio is less than 0, the reaction of the obtained adhesive will be delayed in reaction, and if it exceeds 99.0, the adhesiveness to the metal foil surface and the moisture resistance will be deteriorated.

Further, in order to provide a reactive hot melt adhesive having excellent coatability, as in the case of the conventional adhesive for a food packaging composite laminate film, an ester-based plasticizer is optionally used. It is advisable to add 1 to 50 parts of (diphenyl phthalate, dicyclohexyl phthalate, dimethyl cyclohexyl phthalate, ethyl phthalyl ethyl glycolate, triphenyl phosphate, diethylene glycol dibenzoate, trimethoxy propane, glycerol tribenzoate, glycerol trilaurate, etc.). This is because if the amount of the plasticizer added is less than 1 part, the effect of improving the coatability is small, and if it exceeds 50 parts, the adhesive strength, particularly the initial adhesive strength, decreases. Further, it is not preferable to reduce the molecular weight of the prepolymer or to add a tackifying resin in order to obtain excellent coatability, because the adhesive strength, particularly the initial adhesive strength is lowered.

If necessary, a thermoplastic polymer (polyurethane, polyester, polyether, ethylene-based copolymer, propylene-based copolymer, vinyl chloride-based copolymer, acrylic copolymer, various rubbers, etc.) may be added. Add.
Furthermore, compounding agents used for ordinary hot melt adhesives,
For example, tackifying resin (rosin resin, rosin ester resin, hydrogenated rosin ester resin, terpene resin, terpene phenol resin, hydrogenated terpene resin, petroleum resin, hydrogenated petroleum resin, coumarone resin, ketone resin, styrene resin, modified styrene resin , Xylene resin, epoxy resin, etc.),
And for the purpose of improving adhesive properties or coatability, fillers (silicic acid derivatives, talc, metal powder, calcium carbonate, clay,
Carbon black, etc.), as well as a catalyst (dibutyltin dilaurate, dibutyltin dioctate, dimethylcyclohexylamine, dimethylbenzylamine, etc.), pigment, antioxidant, UV absorber, surfactant, flame retardant, etc. Good, but not limited to the type of formulation.

Further, in the preparation of the adhesive of the present invention, the compounding ratio of the additive is usually 100 parts of the polyurethane prepolymer which is the main component, and 0 parts of the thermoplastic polymer.
-20 parts, 0-15 parts of tackifying resin, 0 of antioxidant
-10 parts, 0-3 parts of a surfactant, and other compounding agents in an appropriate amount range. These additives are dehydrated in advance by a method such as heating and vacuum drying. Mixing is performed by using a heatable mixer, for example, by purging nitrogen gas at 60 to 130 ° C. while blocking the air.

The reactive hot-melt adhesive obtained by such a procedure is semi-solid or solid at room temperature, but the adjustment of this state is necessary for the adhesive strength required immediately after the adhesion, as well as the coating workability and the heating. It is decided by comprehensively considering characteristics such as temperature, time during adhesion, durability after adhesion, and price. As the reactive hot melt adhesive for a food packaging composite laminate film, a semi-solid is desirable at room temperature.

When the reactive hot melt adhesive thus obtained is used for producing a food packaging composite laminate film, the reactive hot melt adhesive is supplied in a pail can or a tin can.

A roll coater having a heating device is used as a coating machine for coating the reactive hot-melt adhesive on the laminated base material, and the reactive hot-melt adhesive is coated at a coating temperature of 60 to 130.degree. Is coated on one surface of the base material and laminated on the other base material through a pair of laminating rolls. When three or more layers are laminated, they may be sequentially or simultaneously online. When at least one of the laminating rolls is heated to 60 to 130 ° C., sufficient adhesion can be obtained without inclusion of bubbles. The coating and laminating temperatures are determined according to the respective material characteristics, but are preferably 80 to 120 ° C. in view of viscosity, coatability and safety. The speed is usually 50 to 200 m / m in relation to the production amount.
It is coated and laminated in. The amount of the reactive hot melt adhesive applied on the surface of the laminated base material is about 1 to 10 g / m ² .

The food packaging composite laminate film adhered by the reactive hot melt adhesive can obtain the adhesive strength required for moving to the next step immediately after lamination. The adhesive strength at this stage is basically developed by cooling and solidification. In this respect, the conventional liquid 1,
This is different from the two-component polyurethane adhesive, and if a reactive hot melt adhesive is used, the process of forming a wound body after lamination and the occurrence of inter-layer displacement and wrinkles during storage as a wound body Can't be seen at all. Further, even if the slitting work is immediately performed, it is possible to perform the slitting with the normal rotating round teeth and the fixed teeth without any trouble. The curing reaction of the adhesive progresses due to the moisture in the air or the moisture present in the laminated base material, and most of the curing reaction is completed in one day in summer and in 3 to 5 days in winter, which is extremely reliable. A high-quality food packaging composite laminate film is completed.

[0019]

The reactive hot-melt adhesive has a solid or semi-solid polyurethane prepolymer as a main component at room temperature, and therefore, the adhesive strength is considerably obtained from the initial stage of the adhesion. In the curing reaction, the isocyanate group at the molecular end of the polyurethane prepolymer and the alkoxysilane react with water to become amine and silanol, and this amine and silanol are
Immediately, it reacts with another isocyanate group or alkoxysilane to form a urea bond, a urethane bond, or a siloxane condensation reaction, and polymerizes. During that time, the isocyanate group reacts with the generated urea bond or urethane bond to form a biuret reaction or an allophanate bond, respectively, to form a crosslinked structure. Through such a reaction, the adhesive strength becomes significantly higher than immediately after the adhesion, and contributes to the improvement of the reliability of the composite laminate film.

[0020]

EXAMPLES Next, examples will be described. "Part" in the example
"Parts by weight" means "parts by weight".

[0021]

Example 1 A polyester polyol (functional group number: 2.0, molecular weight: 2,000) containing adipic acid, isophthalic acid, 1.4-butanediol and 1.6-hexanediol as the main components, which had been dehydrated in advance by vacuum drying. Section and γ
-Mercaptopropyltrimethoxycin 0.5 parts and 8
The mixture was mixed at 0 ° C. for 15 minutes, and 16 parts of xylylene diisocyanate and 0.01 part of dibutyltin dilaurate were mixed and stirred in a N ₂ atmosphere at 100 ° C. for 4 hours to react to obtain a reactive hot melt adhesive. (Viscosity: 2,5
00 cps / 120 ° C.) was obtained. The Tg of this adhesive was semi-solid at room temperature at about 10 ° C., and the isocyanate content was 1.5%.

[0022]

Example 2 80 parts of a polyester polyol (functional group: 2.0, molecular weight: 2,000) having adipic acid, isophthalic acid and 1.4-butanediol as main components, which had been dehydrated in advance by vacuum drying, and γ-anilino 0.5 parts of propyltrimethoxysilane was mixed for 15 minutes at 80 ° C., 20 parts of diphenylmethane diisocyanate was added to the mixture, and the mixture was stirred in a N ₂ atmosphere while reacting at 100 ° C. for 4 hours to obtain a polyurethane prepolymer. Furthermore, 30 parts of diphenyl phthalate was added and mixed at 100 ° C. for 30 minutes to prepare a reactive hot melt adhesive (viscosity: 3,000 cp).
s / 120 ° C.) was obtained. This adhesive had a Tg of about 15 ° C. and was semi-solid at room temperature, and had an isocyanate content of 1.7.
%Met.

[0023]

Example 3 A polyester polyol containing adipic acid, isophthalic acid, sebacic acid, and 1.4-butanediol as the main components, which had been dehydrated by vacuum drying in advance (functional group:
2.0 molecular weight: 2,000) 84.5 parts and isophorone diisocyanate 15.5 parts were mixed and stirred in a N ₂ atmosphere and reacted at 100 ° C. for 4 hours to produce a polyurethane prepolymer (viscosity: 7,000 cps / 120 ° C.) and γ-aminopropyltriethoxysilane 0.5
Parts, 0.05 part of dibutyltin dilaurate and 10 parts of dicyclohexyl phthalate are added, and reacted for 30 minutes at 100 ° C. in a N ₂ atmosphere while mixing and stirring to obtain a reactive hot melt adhesive (viscosity: 3,500 cps / 120 ° C.). Got The Tg of this adhesive was semisolid at room temperature at about 5 ° C., and the isocyanate content was 1.3%.

[0024]

[Comparative Example 1] 80 parts of polyester polyol (functional group: 2.0, molecular weight: 2,000) containing adipic acid, isophthalic acid and 1.4-butanediol as the main components, which had been dehydrated in advance by vacuum drying, and 20 parts of diphenylmethane diisocyanate. Was added and reacted at 100 ° C. for 4 hours while mixing and stirring in an N ₂ atmosphere to obtain a reactive hot melt adhesive (viscosity: 7,000 cps / 120 ° C.). The adhesive had a Tg of about 15 ° C. and was semi-solid at room temperature.

[0025]

Comparative Example 2 Polyester polyol (functional group number: 2.0, molecular weight: 2,000) 84 containing adipic acid, isophthalic acid, 1.4-butanediol, and 1.6-hexanediol as main components, which had been dehydrated in advance by vacuum drying. Parts and 16 parts of xylylene diisocyanate were mixed and stirred in an N ₂ atmosphere at 100 ° C. for 4 hours to obtain a reactive hot melt adhesive (viscosity: 2,000 cps / 120 ° C.). The adhesive had a Tg of about 10 ° C. and was semi-solid at room temperature.

Using the reactive hot melt adhesives of the present invention obtained in Examples 1 to 3 and the conventional reactive hot melt adhesives obtained in Comparative Examples 1 and 2, the adhesive strength to an aluminum foil,
A heat resistance and retort resistance test was conducted.

The test method is as follows. Test sample: The reactive hot melt adhesive of the present invention obtained in Examples 1 to 3 and the conventional reactive hot melt adhesive obtained in Comparative Examples 1 and 2 were applied to a polyethylene terephthalate film at 120 ° C.
Adhesive coating amount 4 ~ by the roll coater heated to
5 g / m ² was applied, and the applied surface was combined with the surface of the aluminum foil and laminated with a pair of laminating rolls adjusted to 80 ° C. Further, the aluminum foil surface of this laminated film was coated with a roll coater, and the coated surface was laminated in the same manner as the corona-treated surface of the unstretched polypropylene film to obtain a composite laminated film consisting of three layers.

Immediately before the test, the above test sample was put in 200 mm × 1
It was cut to 5 mm. Using these test pieces, a T-type peeling test was carried out by a tensile tester at a pulling speed of 300 mm / min. Peel strength (kgf / 15mm) between unstretched polypropylene film and aluminum foil is 2
It was measured at 0 ° C. Temperature and humidity during storage are both 20 ° C x 6
It was set to 5% RH.

The laminate strengths of the reactive hot melt adhesives obtained in Examples 1 to 3 and the conventional reactive hot melt adhesives obtained in Comparative Examples 1 and 2 were measured at each elapsed time after lamination. Good adhesive strength could be obtained with any of the adhesives. (Laminate strength immediately after: about 0.5 kgf / 15 mm, laminate strength after one week of storage: about 1.0 kgf / 15 mm)

Next, after storage for 3 days, heat resistance and retort test were conducted. Heat resistance test: A test piece cut into 200 mm × 15 mm,
After being left at 120 ° C. for 30 minutes, a peeling test was performed at 120 ° C. Retortability test: A test piece cut into 200 mm × 15 mm is left in a pressure cooker of 125 ° C. × 100% steam for 30 minutes, and then immediately subjected to T in 20 ° C. × 65% RH.
A mold release test was conducted.

Measurement results of heat resistance and retort resistance tests of the reactive hot melt adhesives of the present invention obtained in Examples 1 to 3 and the conventional reactive hot melt adhesives obtained in Comparative Examples 1 and 2. Is shown in Table 1. As is clear from Table 1, in each of the reactive hot melt adhesives according to the present invention (Examples 1 to 3), the adhesive strength after retort did not decrease and was improved conversely.

[0032]

INDUSTRIAL APPLICABILITY As described above, according to the present invention, it is possible to obtain coatability with low thickness, moisture resistance, and adhesion to metal, which cannot be obtained with conventional reactive hot melt adhesives, and food packaging. By using the reactive hot melt adhesive of the present invention for the adhesion of the composite laminate film for use, it is possible to significantly improve the reliability of the composite laminate film for food packaging,
Furthermore, it has become possible to provide a reactive hot melt adhesive having a technology of great industrial value such that the required strength can be obtained immediately after bonding.

Claims (3)

[Claims] 1. A urethane prepolymer having an isocyanate content of 0.5 to 5.0%, which is obtained by reacting a mixture of an alkoxysilane compound having one reactive group with polyisocyanate and a polyol, and polyisocyanate. Reactive hot-melt adhesive for food packaging composite laminate film as a component. 2. An ester plasticizer in an amount of 1 to 50 parts per 100 parts of the prepolymer.
A reactive hot melt adhesive for a food packaging composite laminate film as described. 3. An ester plasticizer is added to 100 parts of a prepolymer obtained by preliminarily reacting a polyol with a polyisocyanate and then synthesizing the prepolymer and then reacting with an alkoxysilane compound having one isocyanate-reactive group. A reactive hot melt adhesive for a food packaging composite laminate film, characterized in that it comprises ˜50 parts.