JPH0368916B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a urethane adhesive for dry lamination. Conventional urethane adhesives for dry lamination have been known to be combinations of polyester polyols or polyether polyols and isocyanate compounds, but when used for food packaging materials that require boiling or retort high-temperature sterilization. There are many points of dissatisfaction in terms of performance. Adhesives whose main component is polyether polyol are
Adhesive strength is weaker than that of polyester polyol, and sufficient adhesive strength cannot be obtained particularly when the base material to be bonded is aluminum foil. An adhesive made of a polyester polyol and an isocyanate compound or an adhesive obtained from a polyester polyurethane polyol and an isocyanate compound obtained from a relatively low molecular weight polyester polyol and an isocyanate compound.
It has a strong initial adhesive strength and has been put into practical use in packaging materials that require high performance, such as for retort foods, but depending on the contents and base materials, deterioration of performance over time can be a problem. . For example, a typical laminate bag made of polyester film/aluminum foil/unstretched polypropylene film is filled with highly acidic foods such as vinegar, soybean oil, sauce, oily foods, or foods containing mixtures thereof. However, when retort treatment is applied, pinholes occur on the bonding surface of the aluminum foil and polypropylene film over time immediately after retorting, resulting in a significant decrease in bond strength. The present inventors have arrived at the present invention as a result of intensive studies to eliminate the above-mentioned drawbacks. That is, the present invention provides a dry laminating adhesive comprising a polyester composition containing a carboxyl group at the molecular end and an isocyanate compound, wherein the polyester composition has a molecular weight of 5,000 to 100,000 and has two or more hydroxyl groups at the end. Polyester (A)
The above-mentioned dry polyester (B) is characterized in that it contains a polyester (B) in which at least one terminal has been converted into a carboxyl group by reacting with an amount of anhydrous aromatic polyhydric carboxylic acid such that at least 30% of the terminal hydroxyl groups are consumed. This is an adhesive for laminating. In the present invention, polyester (A) is a starting material for polyester (B), has two or more hydroxyl groups at each terminal, and has a molecular weight of 5,000 to 5,000.
100,000, preferably in the range of 5,000 to 500,000. Polyester (A) is 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 polyvalent carboxylic acids include adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, maleic acid, fumaric acid, itaconic acid,
There are aliphatic or aromatic dicarboxylic acids such as phthalic acid, terephthalic acid, and isophthalic acid, and trivalent carboxylic acids such as trimellitic acid may also be combined with these. Examples of polyhydric alcohols include ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, 1,3-butylene glycol, tetramethylene glycol, hexamethylene glycol, trimethylolpropane, and pentaerythyl siltol. . 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 polyester (A) is a linear polyester having hydroxyl groups at both ends obtained from two or more dihydric carboxylic acids and two or more dihydric alcohols. In the present invention, polyester (B) contains at least 1
One terminal has one or two or more carboxyl groups via an aromatic ring. In order to introduce such carboxyl groups at both ends, it is preferable to react carboxylic anhydride with polyester (A). If an aromatic polycarboxylic acid that has not been anhydrified is used, the polyester (A) may be hydrolyzed by an acid catalyst and its molecular weight may decrease.
Furthermore, the esterification reaction tends to be slower than that of anhydrides, which is not preferable. Examples of the aromatic polycarboxylic anhydride include phthalic anhydride, trimellitic anhydride, and pyromellitic anhydride. The reaction between the polyester (A) and the aromatic polycarboxylic anhydride needs to be controlled at 220° C. or lower so that the main reaction is esterification by ring-opening reaction of the carboxylic anhydride. Regarding the reaction ratio between the two, the aromatic polycarboxylic anhydride is used in an amount such that at least 30% of the terminal hydroxyl groups of the polyester (A) are consumed. Here, "%" is based on the number of terminal hydroxyl groups. If the above value is less than 30%, the improvement in resistance to contents is not sufficient. Polyester (A)
It is also possible to use an amount of aromatic polyhydric carboxylic acid anhydride that is substantially 100% consumed with the terminal hydroxyl groups of . A particularly preferable range for improving content resistance is to use the aromatic polycarboxylic anhydride in an amount that consumes 50 to 95% of the terminal hydroxyl groups of the polyester (A). However, the terminal hydroxyl group of polyester (A)
If more than 100% of the aromatic anhydride polycarboxylic acid is added to the reaction, unreacted substances will remain in suspension in the polyester composition even after the reaction, which will ultimately affect the adhesive strength of the laminate. This is not preferable because it has an adverse effect on the physical properties of the material. Furthermore, when polyester (A) is reacted with aliphatic polycarboxylic anhydride, a carboxyl group can be similarly introduced at the terminal end, but such polyester has not been found to have good resistance to contents. When synthesizing a polyester, it is possible to obtain a polyester having a carboxyl group at the terminal in one step from a polyhydric carboxylic acid and a polyhydric alcohol. However, selecting only aromatic carboxylic acids as the carboxylic acid raw material for polyester has many problems in controlling the physical properties of polyester. Especially trivalent or 4
Polyhydric carboxylic acids impart branching to polyesters, and as a result, tend to gel, and cannot be used in large amounts.
In addition, aromatic polyhydric carboxylic acids have sublimation properties, so
During synthesis, these sublimates adhere to reaction vessels and dehydration equipment, causing various difficulties in production. In the present invention, a carboxyl group is introduced at the terminal using a polyester (A) synthesized in advance so as to obtain desired physical properties as a starting material, thereby eliminating the above-mentioned problems. The isocyanate compounds of the present invention include low molecular weight isocyanate compounds, polyurethane isocyanates obtained by reacting low molecular weight isocyanates with water or polyhydric alcohols, and low polymers that are dimers or trimers of low molecular weight isocyanates. . Examples of low molecular weight isocyanates include hexamethylene diisocyanate,
Phenyl diisocyanate, 2,4- or 2,6-tolylene 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-1,4-dimethylcyclohexane, and mixtures thereof. Examples of the polyhydric alcohol include those mentioned above as raw materials for polyester (A). The polyester composition and the isocyanate compound are blended such that the equivalent ratio of isocyanate groups in the isocyanate compound to the total of hydroxyl groups and carboxyl groups in the polyester composition is 1.0 to 5.0. The laminating base material for the dry laminating adhesive of the present invention includes 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, a commonly used method can be used, for example,
The adhesive may be applied to one side of one laminate base material by dry lamination, and after the solvent is volatilized, 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 substrate is about 1 to 10 g/m ² . The dry laminating adhesive of the present invention is
It is possible to obtain strong initial adhesive strength between laminated base materials, and there is no decrease in adhesive strength over time or occurrence of pinholes even when the contents are filled with highly acidic or oily foods as food packaging materials. , which can maintain strong adhesive strength over a long period of time. Examples will be described below. In the example, "part"
"parts by weight" are indicated. Synthesis of polyester (a) 48.5 parts of dimethyl terephthalate, 37.2 parts of ethylene glycol, 520 parts of neopentyl glycol and tetrabutyl orthotinetanate as a catalyst
0.027 part was charged into a reaction vessel and heated to 160 to 200°C with stirring under a nitrogen stream to carry out a transesterification reaction. 95% of the theoretical amount of methanol was distilled off in about 2 hours. Next, add 41.5% of isophthalic acid to this reaction vessel.
1 part and 73 parts of adipic acid were charged and an esterification reaction was carried out at 180 to 240°C. When the acid value becomes 20 or less, gradually reduce the pressure in the reactor to 1 mmHg or less, 240
Polyester a was polymerized under reduced pressure at ℃ for 3 hours to obtain polyester a having hydroxyl groups at both ends. The polyester (a) had a hydroxyl value of 10, an acid value of 0.5, and a molecular weight of about 11,000. Synthesis of polyester (b) 6.2 parts of trimellitic anhydride was added to the total amount of polyester (a) obtained above, and the mixture was reacted at 200°C for about 1 hour. After confirming the absence of unreacted trimellitic anhydride in the reaction system using a liquid chromatograph, the reaction system was taken out. This polyester (b) is obtained by reacting about 90% of the terminal hydroxyl groups of the polyester (a) with trimellitic anhydride. The acid value of polyester (b) was 17, and the hydroxyl value was 1.0 or less. Synthesis of polyester (c) Polyester (c) was obtained in the same manner as polyester (b), except that 3 parts of trimellitic anhydride was used with respect to the total amount of polyester (a) obtained in the above procedure. This polyester (c) is obtained by reacting 40% of the terminal hydroxyl groups of polyester (a) with trimellitic anhydride. Polyester (c) had an acid value of 7 and a hydroxyl value of 6.0. Synthesis of Polyester (d) Polyester (d) was obtained in the same manner as polyester (b) except that 4.8 parts of phthalic anhydride was used based on the total amount of polyester (a) obtained in the above operation. This polyester (d) has a terminal hydroxyl group of polyester (a).
90% is reacted with phthalic anhydride. The acid value of polyester (d) was 8, and the hydroxyl value was 1.0 or less. Synthesis of polyester (e) 58.2 parts of dimethyl terephthalate, 24.8 parts of ethylene glycol, 41.6 parts of neopentyl glycol,
A reaction vessel was charged with 31.8 parts of diethylene glycol and 0.029 parts of tetrabutyl orthotitanate as a catalyst, and the mixture was heated to 160 to 200° C. with stirring under a nitrogen stream to carry out a transesterification reaction. 95% of the theoretical amount of methanol was distilled off in about 2 hours. Next, 49.8 parts of isophthalic acid and 80.8 parts of sebacic acid were added to this reaction vessel.
A transesterification reaction was carried out at 180 to 240°C. When the oxidation level reached 20 or less, the pressure in the reaction vessel was gradually reduced and polymerization was carried out under reduced pressure at 240°C for 3 hours at a temperature of 1 mmHg or less, resulting in polyester having hydroxyl groups at both ends.
I got (e). The polyester (e) had a hydroxyl value of 10, an acid value of 0.3, and a molecular weight of about 11,000. Synthesis of polyester (f) 7.2 parts of trimellitic anhydride was added to the total amount of polyester (e) obtained in the above procedure, and the mixture was reacted at 200°C for about 1 hour. After confirming the absence of unreacted trimellitic anhydride in the reaction system using a liquid chromatograph, the reaction system was taken out. This polyester (f) is about 90% of the terminal hydroxyl group of polyester (e).
% was reacted with trimellitic anhydride.
The acid value of polyester (f) was 17, and the hydroxyl value was 1.0 or less. Synthesis of Polyester (g) Polyester (g) was obtained in the same manner as polyester (e) except that 3.7 parts of succinic anhydride was used based on the total amount of polyester (e) obtained in the above operation. This polyester (g) is obtained by reacting 90% of the terminal hydroxyl groups of polyester (e) with succinic anhydride. The acid value and hydroxyl value of polyester (g) was 1.0 or less. Example A 60% by weight ethyl acetate solution of polyester (a) to polyester (g) was blended with Coronate HL, a polyisocyanate compound (75% ethyl acetate solution manufactured by Nippon Polyurethane Co., Ltd., food name) as shown in Table 1. Adhesive No. 1 to Adhesive No. 8 were used.

[Table] Adhesive strength with aluminum foil, heat resistance, and food resistance tests were conducted using Adhesives 1 to 8. The test method is as follows. Peel test adherend: Polyethylene terephthalate film (thickness 12μ), aluminum foil (thickness 9μ), unstretched polypropylene (thickness 70μ) Adhesive application amount: 4 to 5 g/m ² Curing conditions: 40℃, 4 days test sample Each adhesive composition listed in Table 1 was first applied to a polyethylene terephthalate film using a dry laminator, and after the solvent was evaporated, the adhesive surface was aligned with the surface of the aluminum foil. After applying the same adhesive composition to the other side of the aluminum foil using a dry laminator, the solvent was evaporated and the adhesive side was aligned with the unstretched polypropylene film. Thereafter, the adhesive composition was cured. The above test sample was cut into a size of 200 mm x 25 mm. ASTMD1876−61 using these test pieces
The loading rate was determined by a tensile tester according to the test method of
A T-peel test was conducted at 300 mm/min. The peel strength (Kg/25mm) between the unstretched polypropylene film and the aluminum foil is shown as the average value of 10 test pieces. Heat Resistance and Food Resistance Test A bag having a multilayer structure of polyethylene terephthalate film-adhesive composition-aluminum foil-adhesive composition-unstretched polypropylene film was made in the same manner as the test sample used in the peel test.
This bag contains 3% acetic acid; salad oil; ketchup = 1:
1:1 soup and vinegar were each charged separately. After sterilizing this bag with hot water at 135℃ for 20 minutes under a pressure of 3.8Kg/ ^cm3 , the peeling condition between the aluminum foil and polypropylene film, the adhesive strength, and the peeling condition after storage at 60℃ for 2 weeks. I looked into it.
The test was conducted on 10 bags each. The results are shown in Table 2. As is clear from Table 2, the adhesives according to the present invention (No. 2, No. 3, No. 4, No. 6, and No. 7) all showed no decrease in adhesive strength during long-term storage after retorting. Ta. Further, no change was observed in the appearance of the inner surface of the bag immediately after retorting and after storage compared to before retorting. In contrast, a comparative product using polyester without carboxyl groups (

【table】

[Table] For both No. 1 and No. 5), the adhesive strength did not decrease immediately after retorting, but the adhesive strength decreased significantly after storage. In addition, in the case of the stored bag, small lumps were observed on the adhesive surface between the polypropylene film and the aluminum foil of the bag. Even in the comparative product (No. 8), which has a carboxyl group but whose modifier is not an aromatic polycarboxylic acid, No. 1 and No. 5
The results were similar.

Claims (1)

[Scope of Claims] 1. An adhesive for dry lamination consisting of a polyester composition containing a carboxyl group at the end of the molecule and an isocyanate compound, wherein the polyester composition has a molecular weight of 5,000 or more and has two or more hydroxyl groups at the end of the molecule. 100,000 polyester (A) with anhydrous aromatic polycarboxylic acid in an amount such that at least 30% of the terminal hydroxyl groups are consumed, thereby converting at least one terminal into a carboxyl group (B). An adhesive for dry lamination as described above, which is characterized by: 2. The adhesive for dry lamination according to claim 1, which is obtained by reacting anhydrous aromatic polycarboxylic acid in an amount such that 50 to 95% of the terminal hydroxyl groups of the polyester (A) are consumed. 3. The adhesive for dry lamination according to claim 1, wherein the aromatic carboxylic anhydride is a trivalent carboxylic acid.