JPS61209282A - Adhesive for dry lamination - Google Patents

Abstract

PURPOSE:To provice the titled adhesive for the lamination of different kinds of plastic films, etc., by reacting a polyester with an ethylenic unsaturated carboxylic acid (anhydride) and compounding the resultant modified polyester composition with a polyisocyanate compound. CONSTITUTION:The objective adhesive is produced by compounding (A) a modi fied polyester composition produced by reacting (i) 100pts.(wt.) of a polyester having a weight-average molecular weight of 500-100,000 with (ii) preferably 0.1-50pts. of an ethylenic unsaturated carboxylic acid (anhydride) [e.g. (meth) acrylic acid] in the presence of (iii) preferably 3-15pts. of a radical generator (e.g. benzoyl peroxide) with (B) a polyisocyanate compound (e.g. hexamethylene diisocyanate). USE:Lamination of a metallic foil and a plastic film.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a urethane-based dry laminating adhesive for laminating different types of plastic films or metal foils and plastic films.

(Conventional technology) Conventionally, urethane-based dry laminating adhesives include:
Combinations of polyester polyols or polyether polyols and polyisocyanate compounds are known, but when used as food packaging materials that require boiling or retort high-temperature sterilization, they are often unsatisfactory in terms of performance. Adhesives containing polyether polyol as a main component have weaker adhesive strength than polyester polyols, and in particular, cannot obtain sufficient adhesive strength when the substrate to be bonded is aluminum foil.

Adhesives made from polyester polyols and polyisocyanate compounds, or adhesives made from polyester polyurethane polyols and polyisocyanate compounds obtained from relatively low molecular weight polyester polyols and polyisocyanate compounds, have strong initial adhesive strength and are suitable for use in retort foods, etc. Although it has been put into practical use as a packaging material that requires high performance, deterioration of performance over time has sometimes been a problem depending on the contents and base materials. For example, a typical laminate bag made of polyester film/aluminum foil/unstretched polypropylene film is filled with highly acidic foods such as vinegar, soy sauce, sauces, oily foods, or foods containing a mixture of these. When the retort treatment was performed, pinholes were generated on the adhesive surface of the aluminum foil and the polypropylene film over time immediately after retorting, resulting in a significant decrease in adhesive strength.

(Problems to be Solved by the Invention) The present invention improves the food resistance of adhesives for dry lamination, particularly the decrease in adhesive strength over time after retort processing,
The present invention provides a practical dry laminating adhesive for all kinds of food contents.

[Structure of the invention]

(Means for solving the problem) That is, 1 the present invention has a weight average molecular weight of 500 to 1000
00 polyester (A) and an ethylenically unsaturated carboxylic acid or its acid anhydride.

A polyisocyanate compound (C
) is a dry laminating adhesive.

Polyester (A), which is the starting material for modified polyester (B) in the present invention, can be synthesized by an esterification reaction or transesterification reaction between a polyhydric carboxylic acid or its lower alkyl ester or anhydride and a polyhydric alcohol. .

Examples of polyhydric carboxylic acids include succinic acid.

Adipic acid, pimelic acid, speric acid, azelaic acid,
Aliphatic or aromatic dicarboxylic acids such as cepatic acid, maleic acid, fumaric acid, itaconic acid, phthalic acid, terephthalic acid, and isophthalic acid.

A trivalent carboxylic acid such as trimellitic acid may be used in combination with this. Examples of polyhydric alcohols include 1.

Ethylene glycol, diethylene glycol, triethylene glycol, 1.2-propylene glycol, 1,
3-butylene glycol, tetramethylene glycol,
Hexamethylene glycol.

These include neopentyl glycol, trimethylolpropane, and pentaerythritol.

Polyester (A) is synthesized by combining two or more polyhydric carboxylic acids and two or more polyhydric alcohols in order to obtain desirable basic physical properties such as flexibility.

A preferred example of the polyester (A) is a polyester having a molecular weight of 50 and having hydroxyl groups at both ends, obtained from two or more dihydric carboxylic acids and two or more dihydric alcohols.

There are ~100,000 linear polyesters. Furthermore, a polyester polyurethane polyol obtained by modifying a polyester containing a terminal hydroxyl group with a low molecular weight polyisocyanate and a low molecular weight polyol can also be used.

In the present invention, the modified polyester (B) is obtained by reacting the polyester (A) with an ethylenically unsaturated carboxylic acid or its acid anhydride in the presence of a radical generator to introduce a carboxyl group into the Beauriester molecule. .

Examples of ethylenically unsaturated carboxylic acids include monocarboxylic acids such as acrylic acid and methacrylic acid, dicarboxylic acids such as itaconic acid, maleic acid, and fumaric acid, and examples of ethylenically unsaturated carboxylic acid anhydrides include itaconic anhydride. , maleic anhydride, etc. Ethylenically unsaturated carboxylic acid or its acid anhydride is polyester (A) 10
0fi (0.1 to 50 parts by weight is used relative to part f. If the amount used is less than 0.1 part by weight, the specific effects of the present invention, that is, improvement in adhesive strength and food resistance, will not occur. ,
If the amount used is more than 50 parts by weight, the internal cohesive force of the adhesive layer decreases, and the adhesive force itself decreases. Examples of radical generators include peroxides such as benzoyl peroxide and azobis-based compounds such as azobisisobutyronitrile. A redox system in which these compounds are combined with a reducing agent can also be used. The amount of radical generator used is 0.1 to 100 parts by weight of polyester (A).
25 parts by weight, preferably 3 to 15 parts by weight.

If it is less than 0.1 part by weight, the ethylenically unsaturated carboxylic acid or its acid anhydride cannot react sufficiently, and if it is more than 25 parts by weight, the effect of the amount used will not be recognized.

Modified polyester (B) can be obtained by dissolving polyester (A) and ethylenically unsaturated carboxylic acid or its acid anhydride, preferably in an organic solvent, and sequentially adding a radical generator. . The reaction temperature is higher than the temperature necessary to generate radicals, and preferably 200° C. or lower in order to suppress the esterification reaction between the hydroxyl groups in the polyester and the carboxylic acid. It is preferable to proceed with the reaction under reflux of an organic solvent having an appropriate boiling point in order to keep the reaction temperature constant. Examples of organic solvents include aromatic hydrocarbons such as toluene and xylene, ketone solvents such as methyl ethyl ketone and cyclohexanone, ester solvents such as ethyl acetate and butyl acetate, and their derivatives such as 2-ethoxyethanol and 2-ethoxyethyl acetate. can be.

A mixed solvent of these may be used.

When obtaining the modified polyester (B) of the present invention, the polyester (A) may be modified by using an ethylenically unsaturated carboxylic acid or its acid anhydride as an essential component, and further adding other types of polymerizable additives. . Examples of the polymerizable polymer include (meth)acrylic acid alkyl esters such as methyl methacrylate and methyl acrylate, and styrene.

The polyisocyanate compound (C) of the present invention includes a low molecular weight diisocyanate compound, a polyurethane polyisocyanate obtained by reacting a low molecular weight polyisocyanate with water or a polyhydric alcohol, and a dimer or dimer of a low molecular weight polyisocyanate. There are low polymers that are

Examples of low molecular weight diisocyanates include hexamethylene diisocyanate, phenylene diisocyanate,
2,4- or 2,6-dolylene diisocyanate,
Diphenylmethane-4,4-diisocyanate 3.3
-dimethyl-4,4-biphenylene diisocyanate,
Dicyclohexylmethane-4,4-diisocyanate
Isophorone diisocyanate, ω, ω-diisocyanate 1,3-dimethylbenzene, ω, ω-diisocyanate 1,4-dimethylbenzene, ω, ω-diisocyanate 1,3-dimethylcyclohexane, ω, ω-diisocyanate 1. Examples include 4-dimethylcyclohexane and mixtures thereof.

As the polyhydric alcohol, raw material polyester (A)
Some of the constituent components are listed above.

The adhesive for dry lamination of the present invention is obtained by blending a polyisocyanate compound (C) into a modified polyester (B) composition containing the modified polyester (B) obtained by the method described above. here.

The modified polyester (B) composition may substantially contain a mixture of polyester (A) and modified polyester (B).

The polyisocyanate compound (C) is blended so that the equivalent ratio of isocyanate groups in the polyisocyanate compound to the total of hydroxyl groups and carboxyl groups in the modified polyester (B) composition is 1.0 to 5.0. be done.

The laminating base material for the dry laminating adhesive of the present invention is a polyethylene film.

There are plastic films such as polypropylene film, nylon film, polyester film, ethylene-vinyl alcohol resin film, and aluminum foil.

For adhesion processing using the adhesive for dry lamination of the present invention, nine commonly used methods are used, for example.

After applying the adhesive to one side of one laminate base material using a dry laminator and volatilizing the solvent, the adhesive may be bonded to the other laminate base material and cured at room temperature or under heating. The amount of adhesive applied to the surface of the laminate base material is about 1 to 10 g/nl.

Examples will be described below. In the examples, "parts" indicate "parts by weight."

(Example) Synthesis of polyester (a) 48.5 parts of dimethyl terephthalate, 37.21B of ethylene glycol, 52.0 parts of neopentyl glycol, and 0.02 parts of tetrabutyl orthotitanate as a catalyst.
Pour 7 parts into a reaction vessel and add 1 part while stirring under a nitrogen stream.
The transesterification reaction was carried out by heating to 60 to 200°C. 95% of the theoretical amount of methanol was distilled off in about 2 hours. Next, 41.5 parts of isophthalic acid and 73.0 parts of adipic acid were charged into this reaction vessel and an esterification reaction was carried out at 180 to 240°C.

When the acid value became 20 or less, the pressure in reaction vessel 9 was gradually reduced and polymerization was carried out under reduced pressure at 240° C. for 3 hours at a temperature of +1++ uwHg or less to obtain polyester (a) having hydroxyl groups at both ends of 9. Polyester <a> has a hydroxyl value of 10 and an acid value of 0.52.
The molecular weight was approximately 11.000.

Synthesis of polyester (b) 100 parts of polyester (a) obtained in the above procedure and 5 parts of maleic anhydride were dissolved in 250 parts of ethyl acetate at 80°C, and kept as such for about 180 minutes to prepare polyester (b).
) was obtained.

Synthesis of polyester (C) 100 parts of polyester (a) obtained by the above procedure was mixed with 25
0 parts of ethyl acetate at about 80°C, followed by 10 parts of ethyl acetate.
A 10% solution of benzoyl peroxide in ethyl acetate was added dropwise, and after completion of the addition, the mixture was kept at 80° C. for 60 minutes to obtain polyester (C).

Synthesis of polyester (d) 100 parts of polyester (a) obtained by the above procedure and 0.5 part of maleic anhydride were mixed in 250 parts of ethyl acetate at 80°C.
followed by 1 part of 0.5 part of benzoyl peroxide.
Add 0% ethyl acetate solution dropwise.

After completion, the temperature was kept at 80°C for 60 minutes to obtain polyester (d).

Synthesis of polyester (e) Polyester (e) was prepared in the same manner as polyester (d) except that 5 parts of maleic anhydride and 10 parts of benzoyl peroxide were used for 100 parts of polyester (a) obtained in the above procedure. Obtained.

Synthesis of polyester (f) Polyester (f) was prepared in the same manner as polyester (d) except that 10 parts of maleic anhydride and 1 part of benzoyl peroxide were used for 100 parts of polyester (a) obtained in the above procedure. Obtained.

Synthesis of polyester (g) Polyester (g) was prepared in the same manner as polyester (b) except that 5 parts of itaconic acid and 10 parts of benzoyl peroxide were used for 100 parts of polyester (a) obtained in the above procedure.
) was obtained.

Example A 60% by weight ethyl acetate solution of polyester (a) to polyester (g) was blended with the polyisocyanate compound Coronet) HL (trade name: 75% ethyl acetate solution manufactured by Nippon Polyurethane Co., Ltd.) as shown in Table 1. Adhesive No.: 1 part Adhesive No.: 7

Adhesive strength with aluminum foil using adhesives 1 to 7,
Heat resistance and food resistance tests were conducted.

The test method is as follows.

Peel test adherend: polyethylene terephthalate film (thickness 1
2 μ), aluminum foil (thickness 9 μ), 9 unstretched polypropylene (thickness 70 μ), adhesive coating amount: 4 to 5 g/rrr, curing conditions: 40°C, 4 days Test sample: Each adhesive composition listed in Table 1 was first applied to a polyethylene terephthalate film using a dry laminator, and the solvent was volatilized.

The adhesive surface was aligned with the surface of the aluminum foil. The same adhesive composition was applied to the other side of the aluminum foil using a dry laminator, and then the solvent was evaporated.

The adhesive surface was aligned with an unoriented polypropylene film. Thereafter, the adhesive composition was cured.

The above test sample was cut into a size of 200 mm x 25 mm. ASTMDI876 using these test pieces
A T-peel test was conducted using a tensile test Mlli at a loading rate of 300 mm/win according to the test method of No.-61. The peel strength (Kg/25 mm) between the unstretched polypropylene film and the aluminum foil was expressed as the average value of the IO test pieces.

Heat resistance and food resistance test Polyethylene terephthalate film - Adhesive composition -
A bag having a multilayer structure of aluminum foil-adhesive composition-unoriented polypropylene film was made in the same manner as the test sample used in the peel test.

In this bag, 3% acetic acid salad oil; ketchup = 1: ■ = 1
The soup and vinegar were separately filled. After sterilizing this bag in hot water at 135°C for 20 minutes under a pressure of 3.8 Kg/cal, the peeling state, adhesive strength, and 6
The state of peeling was examined after storage at 0°C for 2 weeks. The test was conducted on 10 bags each.

The results are shown in Table 2.

As is clear from Table 2, the adhesive according to the present invention (No. 4
．． No, 5. No, 6. No. 7) showed no decrease in adhesive strength during long-term storage after retorting.

Moreover, no significant change was observed in the appearance of the inner surface of the bag immediately after retorting and after storage compared to before retorting.

On the other hand, the comparative product (No. 1) using polyester not modified with carboxyl groups did not have a decrease in adhesive strength immediately after retorting.

After storage, the adhesive strength decreased significantly. In addition, those containing only either benzoyl peroxide or maleic anhydride (No, 2. No, 3) are unmodified (No,
It was the same as 1). Regarding the appearance after storage, for Nos. 1 to 3 which were in poor condition, small lumps and delamination were observed on the adhesive surface between the polypropylene film and the aluminum foil of the bag.

〔Effect of the invention〕

The adhesive for dry lamination of the present invention can obtain strong initial adhesive strength between plastic films or between plastic films and lamination substrates such as aluminum foil, and has excellent hygiene properties, so it is suitable for use in food packaging laminates. It is especially used as a film adhesive.

In addition, even when filled with highly acidic or oily foods, the adhesive strength does not decrease over time.
Foods can be stored stably for a long period of time.

Claims (1)

[Claims] 1. A modified polyester obtained by reacting a polyester (A) having a weight average molecular weight of 500 to 100,000 with an ethylenically unsaturated carboxylic acid or its acid anhydride in the presence of a radical generator. (B) An adhesive for dry lamination comprising a composition and a polyisocyanate compound (C). 2. The modified polyester (B) composition contains polyester (
The adhesive for dry lamination according to claim 1, wherein 0.1 to 50 parts by weight of an ethylenically unsaturated carboxylic acid or its acid anhydride is reacted with 100 parts by weight of A). 3. The modified polyester (B) composition contains polyester (
A) 0.1 to 2 radical generators per 100 parts by weight
Claim 1, which uses 5 parts by weight.
Adhesive for dry lamination according to items 1 to 2. 4. The modified polyester (B) composition contains polyester (
The adhesive for dry lamination according to claim 3, wherein 3 to 25 parts by weight of a radical generator is used per 100 parts by weight of A). 5. The adhesive for dry lamination according to claims 1 to 4, wherein the polyester (A) having a weight average molecular weight of 500 to 100,000 is a polyester containing terminal hydroxyl groups.