JPS6219459B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a heat-resistant heat sealant particularly useful for aluminum foil. Conventionally, laminated materials of aluminum foil and heat sealant resin have been used for various packaging materials, etc., and relatively heat-resistant heat sealant resins include vinyl chloride - vinyl acetate - maleic acid copolymer resin. accounts for the majority of them. The reason for this is that the above resin has good adhesion to aluminum foil and other resins and excellent blocking resistance, and the resulting laminated material is extremely flexible in processing. For example, this laminated material of resin and aluminum foil can be subjected to various types of squeezing processing. However, despite having the above-mentioned excellent performance, the above-mentioned copolymer resin is used to heat-seal aluminum foil, or aluminum foil and other materials, and this product cannot be heated to temperatures above 100°C. ,
In particular, when exposed to high-temperature atmospheres such as retort sterilization at 120°C, the resin softens and the heat-sealed part peels off even with the slightest force, immediately losing its value as a product. That is, it is not suitable for today's required heat-resistant seal applications such as retort containers. The present inventors have discovered that the above-mentioned copolymer resin has excellent properties as a heat sealant resin.
As a result of intensive studies to obtain a heat sealant resin composition for aluminum foil that has excellent peel strength in a high temperature atmosphere of about 120°C, we found that 100 parts by weight of vinyl chloride,
100 parts by weight of a resin copolymerized with 5 to 20 parts by weight of vinyl acetate and 0.3 to 3 parts by weight of maleic acid and polymethyl methacrylate having an average molecular weight of 200,000 to 500,000 are mixed in an organic solvent. The composition has excellent performance as a heat sealing agent composition for aluminum foil by compensating for the above-mentioned drawbacks,
Furthermore, when there are high requirements regarding thermal deterioration, even better properties can be obtained by adding 2 to 15 parts by weight of a bisphenol type epoxy resin with an epoxy equivalent of 200 to 1000 to the heat sealant composition. The inventors have discovered the following and arrived at the present invention. Vinyl chloride ~ vinyl acetate ~ used in the present invention
As the maleic acid copolymer resin, a resin in which 5 to 20 parts by weight of vinyl acetate and 0.3 to 3 parts by weight of maleic acid are added to 100 parts by weight of vinyl chloride is suitable. If the amount of vinyl acetate exceeds 30 parts by weight relative to vinyl chloride, the blocking resistance of the coating film obtained from this copolymer resin will deteriorate, and conversely, if the amount is less than 5 parts by weight, the resulting coating film will become hard. Becomes brittle and inflexible. Also, the amount of maleic acid, which is the third component, is
When the amount is less than 0.3 parts by weight and when it is more than 3 parts by weight, the adhesion to the aluminum foil becomes poor and it is unsuitable. Polymethyl methacrylate with an average molecular weight of 200,000 to 500,000 per 100 parts by weight of the above copolymer resin
A compound containing 30 parts by weight significantly increases the peel strength in a high temperature atmosphere of about 120°C without impairing the flexibility of the copolymer resin. Although there are various types of polymethacrylic acid ester-based and polyacrylic acid ester-based homopolymers or copolymer resins, only polymethyl methacrylate homopolymer is effective in the present invention. That is, the peel strength in a high-temperature atmosphere increases as the amount of polymethyl methacrylate added increases, but if it is less than 5 parts by weight, the effect is still insufficient, and if it exceeds 30 parts by weight, the resulting coating film is It becomes hard and brittle and lacks flexibility. When polymethyl methacrylate having an average molecular weight of 200,000 or less is used, the amount added must be more than 30 parts by weight in order to obtain sufficient peeling force in a high temperature atmosphere.
That is, in order to obtain a predetermined peeling force in a high-temperature atmosphere, a material with a lower average molecular weight requires a larger amount to be added, which is inappropriate. On the other hand, if the average molecular weight exceeds about 500,000, the viscosity becomes extremely high when dissolved in a solvent, making it practically impossible to use. Based on the relationship between the peel strength in a high-temperature atmosphere and the flexibility of the resulting coating film, the average molecular weight is between 250,000 and 40.
However, it is considered that the most appropriate amount is 10 to 20 parts by weight. Note that the average molecular weight used here is the average molecular weight calculated from the intrinsic viscosity of the polymer solution, and means the so-called viscosity average molecular weight. The solvent used in the present invention is vinyl chloride ~
A substance that is a good solvent for each of the vinyl acetate-maleic acid copolymer and polymethyl methacrylate may be used alone or in combination, or a substance that is a good solvent for each and a substance that is a good solvent for either one. It is used in combination with . For example, commonly used solvents include ethyl acetate, butyl acetate, methyl ethyl ketone, methyl isobutyl ketone, toluene, and the like. Of course, various pigments and fillers may be added to the extent that they do not adversely affect the performance of the resulting coating film. A mixed solution of vinyl chloride-vinyl acetate-maleic acid copolymer resin and polymethyl methacrylate is prepared using the above-mentioned solvent, and its concentration is suitably 30% or less. To apply the heat sealant composition thus obtained onto aluminum foil, a common method such as roll coating or gravure roll coating is used, and for drying, hot air, an infrared lamp, or a drum drying method is used alone. Or use them together as a heat source. The thickness of the resulting resin layer is 20μ after drying.
It is preferable to use up to a certain degree. As described above, the heat-sealing composition of the present invention is 120
By adding a bisphenol type epoxy resin to the above heat seal composition, the peel strength in a high temperature atmosphere of about ℃ is significantly increased.
The present inventors have found that this effect can be further enhanced, which will be described below. In other words, as mentioned above, the peel strength of the vinyl acetate-maleic acid copolymer resin of vinyl chloride decreases significantly in an atmosphere at a high temperature of about 120°C, and the copolymer fat itself deteriorates when heated in hot water. Especially when exposed to a high-temperature atmosphere for a long time, thermal deterioration may occur, and even when returned to room temperature, a significant decrease in peel strength may be observed compared to the peel strength before exposure to the high-temperature atmosphere. It is observed that the substance itself turns yellow. However, the present inventors have found that the above-mentioned copolymer resin has excellent peel strength in a high-temperature atmosphere without sacrificing its excellent properties as a heat sealing agent, as mentioned at the beginning, and also has no thermal deterioration and is particularly suitable for use in hot water or heat. As a result of intensive studies to obtain a heat-resistant heat sealing agent composition suitable for aluminum foil with stable sealing strength against heat, we found that 100 parts by weight of vinyl chloride, 5 to 20 parts by weight of vinyl acetate, and 0.3 to 3 parts by weight of maleic acid. 5 to 30 parts by weight of polymethyl methacrylate having an average molecular weight of 200,000 to 500,000 is added to 100 parts by weight of the copolymerized resin, and further bisphenol having an epoxy equivalent of 200 to 1000 is added. It has been found that when 2 to 15 parts by weight of Type A epoxy resin are mixed in a solvent, a heat sealant composition free of the various drawbacks as already explained can be obtained. The vinyl chloride-vinyl acetate-maleic acid copolymer resin and polymethyl methacrylate used here are as previously explained in detail, and the epoxy equivalent is
A compound containing 2 to 15 parts by weight of bisphenol A type epoxy resin with a molecular weight of 200 to 1000 suppresses thermal deterioration of the vinyl chloride-vinyl acetate-maleic acid copolymer resin, and prevents peeling before and after treatment even in high-temperature atmosphere treatment. A resin composition with stable strength was obtained. In this composition, if the amount of bisphenol type epoxy resin blended is 2 parts by weight or less with respect to 100 parts by weight of the above-mentioned copolymer resin blended with polymethyl methacrylate, the effect on thermal deterioration is not significant, and if it is 15 parts by weight or more. When it was added, there was no significant difference in the improvement effect on thermal deterioration of the resin, but rather it was seen that the peel strength in a high temperature atmosphere was reduced. Also, regarding epoxy equivalent
If the number is less than 200, the effect of addition is small and it is difficult to use, and if it is more than 1000, the compatibility with the above-mentioned copolymer resin becomes extremely poor and it is practically impossible to use. In actual use, the method for forming the heat-resistant heat-sealing agent is as described above, but when heat-sealing aluminum foil using the heat-sealing agent of the present invention, both foils are Alternatively, a film may be coated with the same heat sealing agent according to claim 1 or 2 to form an adhesive, or one of the foils or films may be coated with the heat sealing agent composition according to claim 1. to form an adhesive, and then apply 2
It goes without saying that whether or not to apply the heat sealant composition and form an adhesive layer can be arbitrarily selected depending on the convenience and purpose of implementation. Note that FIG. 1 is an enlarged sectional view showing an example of the structure of a laminated material for a sealed package such as a retort container or pouch according to the present invention, and FIG. It is a perspective view of a retort container consisting of. It is clear from the above description that a high-performance heat-resistant heat sealant composition can be obtained by the present invention. In order to further clarify the mode of implementation of the present invention, several examples are shown below, but it is clear that the present invention is not limited to these examples only. Examples 1 to 5 (Comparative Examples 1 to 3) Vinyl chloride consisting of 15 parts by weight of vinyl acetate and 1 part by weight of maleic acid to 100 parts by weight of vinyl chloride.
Polymethyl methacrylate having the average molecular weight and blending amount as shown in Table 1 is mixed with 100 parts by weight of vinyl acetate-maleic acid copolymer resin by the following method using a 1:1 solvent of methyl ethyl ketone and toluene. The concentration was adjusted to 10% to 30% to obtain a film thickness of . A coating agent having the above composition was coated on a 50μ aluminum foil using a 65 mesh gravure roll and dried at 180°C for 20 seconds to obtain a heat sealing agent layer with a film thickness of 5μ. The above aluminum foil was heated to 210℃, 3Kg/cm ²
Heat-seal the coated surfaces of the heat-sealing agent together for 1 second at a pressure of A peel test was conducted in an atmosphere and the results are shown below. At the same time, for the same composition, the concentration was changed from 15 to 15 to obtain a film thickness of 20μ using the same diluting solvent.
The coating agent having the above composition was coated on a 1 mm Teflon film using a 100 μ cord applicator and dried at 80° C. for 30 minutes to obtain a coating film with a thickness of 20 μ. This heat sealant layer was separated from the Teflon film and cut into pieces of 10 mm in width and 100 mm in length, and a tensile test was performed using an autograph at a tensile speed of 10 mm/min to demonstrate the flexibility of the resulting coating film. From Table 1, it is recognized that both cases have excellent peel strength and flexibility in a high-temperature atmosphere. As a comparative example, similar results were shown for the formulations shown in Table 2, but in this case they were inferior in either flexibility or peel strength in a high-temperature atmosphere.

【table】

[Table] Examples 6 to 8 (Comparative Examples 4 to 6) 100 parts by weight of vinyl chloride-vinyl acetate-maleic acid copolymer resin consisting of 15 parts by weight of vinyl acetate and 1 part by weight of maleic acid based on 100 parts by weight of vinyl chloride. 10 parts by weight of polymethyl methacrylate having an average molecular weight of 300,000 and the bisphenol A type epoxy resin shown in Table 3 were dissolved using a mixed solvent of methyl ethyl ketone and toluene in a ratio of 1:1. A heat sealing agent layer with a thickness of 5 μm was obtained on a 90 μm aluminum foil in the same manner as shown in 5. The above aluminum foil was heat-sifted in the same manner as in the above example, and the heat-sealed portion was cut into 15 mm width and 5 cm length. The test cut was immersed in boiling water for 60 minutes, and the peel strength before and after immersion was compared. I went there. It can be seen from Table 3 that the residual rate of peel strength was kept very high. Note that similar results were obtained when the bisphenol A type epoxy resin shown in Table 4 was used as a comparative example, but in the cases of Comparative Examples 4 and 5, the residual rate of peel strength was very low. , Comparative Example 6 has a very good residual rate, but 120
Peel strength deteriorates in a ℃ atmosphere, making it unsuitable.

【table】

【table】 [Brief explanation of the drawing]

FIG. 1 is an enlarged sectional view of a laminated material according to the present invention;
FIG. 2 is a perspective view of a retort container molded using the above laminated material. DESCRIPTION OF SYMBOLS 1... Aluminum foil, 2... Heat sealant coated film of the present invention, 3... Container body, 4... Lid.

Claims (1)

[Claims] 1 100 parts by weight of vinyl chloride, 5 to 20 parts by weight of vinyl acetate
100 parts by weight of a resin copolymerized with 0.3 to 3 parts by weight of maleic acid and 5 to 30 parts by weight of polymethyl methacrylate having an average molecular weight of 200,000 to 500,000.
A heat-resistant heat-sealing agent characterized by being made by mixing parts by weight in an organic solvent. 2 100 parts by weight of vinyl chloride, 5 to 20 parts by weight of vinyl acetate
100 parts by weight of a resin copolymerized with 0.3 to 3 parts by weight of maleic acid and 5 to 30 parts by weight of polymethyl methacrylate having an average molecular weight of 200,000 to 500,000.
1. A heat-resistant heat-sealing agent characterized by mixing parts by weight of a bisphenol type epoxy resin with an epoxy equivalent of 200 to 1000 in an organic solvent.