JPS637946B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a transparent laminate that has low permeability to gases such as oxygen, nitrogen, carbon dioxide, hydrogen, and helium, and low water vapor permeability, and can withstand steam sterilization treatment at 80° C. or higher. Conventionally, various transparent plastic materials with low gas permeability have been known, but when subjected to high-temperature steam sterilization treatment, the plastics undergo whitening, elution, cracking, etc., resulting in a decrease in gas barrier properties, making them unusable. It is. In particular, there was no transparent film that could withstand steam sterilization at temperatures above 130°C and had excellent gas barrier properties. However, retort packaging has been attracting attention as a form of food distribution in recent years, and current low-temperature and long-term sterilization (i.e. High-temperature, short-time sterilization (130-160°C x several minutes to several seconds) is more desirable than sterilization (120°C x 30 minutes), and there is a trend towards so-called high-retort sterilization. In view of the current situation, an object of the present invention is to provide a transparent packaging material that can withstand high temperature and steam sterilization and has excellent gas barrier properties. Membrane molded products made of polypropylene, polystyrene, polyvinyl chloride, polyester, polyamide, etc. have excellent mechanical properties and heat resistance, so they are widely used as packaging materials, but they have poor oxygen barrier properties, so they are not used for food packaging. Usually, it is necessary to laminate other films with good oxygen barrier properties. On the other hand, although film-like molded products made of polyvinyl alcohol have excellent oxygen barrier properties, they are extremely weak against moisture, and not only do their oxygen barrier properties drop significantly in an atmosphere of high relative humidity, but they also dissolve in boiling water. It's so much so that I end up with it. Therefore, it is used in combination with the hydrophobic resin mentioned above. However, in that case, there is a problem in that the adhesion between the hydrophilic polyvinyl alcohol film and the hydrophobic resin film is poor. Furthermore, even when used in bonded form, it still has insufficient water resistance and cannot withstand boiling water treatment. Known methods for improving the water resistance of polyvinyl alcohol include crystallization treatment by heating, copolymerization of hydrophobic monomers, and intramolecular or intermolecular crosslinking using chemical reactions of hydroxyl groups. However, boiling water resistance cannot be obtained by crystallization alone, and water resistance can be improved by copolymerization of hydrophobic monomers or chemical crosslinking, but when the content of hydroxyl groups in polyvinyl alcohol polymer decreases, It is also known in the industry that alcohol's inherently excellent oxygen barrier properties are rapidly degraded. Therefore, it has not been possible to simultaneously satisfy excellent gas barrier properties and water resistance. The present inventors have found a gas barrier laminate that simultaneously improves these problems, namely adhesion, water resistance, and gas barrier properties, and has excellent hot water resistance, resulting in the present invention. That is, the present invention uses silica, a polyvinyl alcohol polymer, methylolmelamine in which some or all of the methylol groups are alkyl etherified, and water as essential components, and the weight ratio of silica/polyvinyl alcohol polymer is 5/5. 95～
80/20, and the weight ratio of methylolmelamine compound/polyvinyl alcohol polymer is 2/98~
This invention relates to a laminate obtained by applying a 70/30 aqueous dispersion onto a film-like molded product made of a thermoplastic polymer and then heating the product. In the present invention, commercially available silica sols, hydrolysis products of tetraalkyl silicate, etc. can be effectively used as the silica source. Commercially available silica sol is a sol in which fine silica particles are finely dispersed in water and/or lower alcohol having an alcoholic hydroxyl group, and usually contains silica and alkali metal oxide, but SiO ₂ /M ₂ O (molar ratio ) [M is K, Na,
Li] is preferably 50 or more in the present invention. If necessary, a sol stabilized with NH ₄ ⁺ or a sol modified with Al ³⁺ can also be used. There is no particular restriction on the particle size of silica, but an average particle size of 100 mμ or less is preferable from the viewpoints of coating film properties, gas barrier properties, stability of an aqueous dispersion, and the like. The alkyl group of the tetraalkyl silicate is usually a C ₁ -C ₄ alkyl group, and tetraethyl silicate is particularly preferred. Further, tri- or di-alkoxysilane having a functional group (amino, vinyl, epoxy group, etc.) may be contained as a modifier. A polyvinyl alcohol polymer is usually a vinyl polymer containing 60 mol% or more of vinyl alcohol units, particularly polyvinyl alcohol with a saponification degree of 75 mol% or more and an average degree of polymerization of 300 to 5000, and 40 mol% or less of the total hydroxyl groups. Preferred examples include polyvinyl alcohol having an average degree of polymerization of 300 to 5,000, in which is acetalized, and copolymerized polyvinyl alcohol having 60 mol% or more of vinyl alcohol units. In the methylolmelamine used in the present invention, in which some or all of the methylol groups are alkyl etherified, at least some of the hydrogen atoms of the three amino groups bonded to the triazine ring are substituted with methylol groups. The number of methylol groups is generally 3 to 6, and some or all of the methylol groups are alkyl etherified. The alkyl moiety of the alkyl etherified methylolmelamine has 1 to 6 carbon atoms, preferably 1 to 3 carbon atoms.
It is a straight chain or branched chain. For example methyl, ethyl, n- or iso-propyl, n-,
iso- or tert-butyl, etc. Specific examples of methylolmelamine used in the present invention include hexakismethoxymethylmelamine, hexamethylolmelamine pentamethyl ether, hexamethylolmelamine tetramethyl ether, pentamethylolmelamine pentamethyl ether,
Examples include pentamethylol melamine tetramethyl ether, pentamethylol melamine trimethyl ether, tetramethylol melamine tetramethyl ether, tetramethylol melamine trimethyl ether, and trimethylol melamine trimethyl ether. Note that the methylolmelamine may partially contain a condensate such as a dimer. The medium of the aqueous dispersion solution in the present invention is a solvent containing water as an essential component, and the water/lower alcohol weight ratio is usually 100% water or 98/2 to 40/60.
Lower alcohols are usually alcoholic compounds having a linear or branched aliphatic group having 1 to 3 carbon atoms, and specific examples include methanol, ethanol, n- or iso-propyl alcohol, and ethylene glycol. It will be done. Methanol is particularly preferred, with a water/methanol (weight ratio) of 95/5 to
50/50 is preferred as the solvent used. Further, other organic solvents may be mixed within the range of being miscible with the solution system of the present invention. In addition, an aqueous dispersion solution is a polyvinyl alcohol-based polymer and a methylolmelamine-based compound.
This refers to a state in which fine silica particles are uniformly dissolved in the solvent and finely dispersed in the form of a sol. The aqueous dispersion of the present invention contains silica/polyvinyl alcohol polymer in a weight ratio of 5/95 to 80/20.
Included within the range of If this ratio is less than 5/95, the effect of silica on improving gas barrier properties and water resistance will be small, and if it is more than 80/20, the pinhole resistance and bending resistance of the coating will deteriorate, which is not preferred. Note that the amount of silica is shown as the amount of SiO ₂ . In the aqueous dispersion solution of the present invention, the weight ratio of silica/polyvinyl alcohol polymer is within the above range, and at the same time, the weight ratio of methylolmelamine compound/polyvinyl alcohol polymer is 2/98. ~
In the 70/30 range. If this ratio is smaller than 2/98, the effect of improving hot water resistance due to methylolmelamine crosslinking will be small, and if it is larger than 70/30, the stability of the aqueous dispersion will deteriorate, and the transparency of the coating film after drying and curing will decrease. It is not suitable because it deteriorates the gas barrier properties and the gas barrier properties. The pH of the aqueous dispersion of the present invention is usually in the range of 3-11.
If it is outside this range, the storage stability of the aqueous dispersion will deteriorate, and if left at room temperature, gelation or precipitate will form, which is not preferable. Further, the aqueous dispersion solution of the present invention may contain a curing catalyst. As a catalyst, ammonium chloride, ammonium nitrate, p-toluenesulfonic acid, and other curing accelerators for melamine resin can be effectively used. The amount used is 0.001 to 2% by weight based on the total solid content.
The total solids concentration of the aqueous dispersion of the present invention is preferably 2 to 30% by weight, usually 5 to 15% by weight. There are no restrictions on the method of preparing the aqueous dispersion solution, but the polyvinyl alcohol-based polymer is preliminarily mixed with a solvent at
It is desirable to mix the silica sol, methylolmelamine compound, or the solution after heating and dissolving at 95°C to make a homogeneous solution and cooling it to near room temperature. The aqueous dispersion solution of the present invention is coated onto a film-like molded article consisting essentially of a thermoplastic synthetic resin such as polypropylene, polystyrene, polyvinyl chloride, polyester, polyamide, or the like. Here, film-like molded products include films, sheets, drawn containers, tubular objects, bottles, etc. whose thickness is 3μ to 5mm (usually 5μ to 1mm).
mm), which of course includes those that have been stretched and heat treated. Further, the molded article may or may not be surface activated. Surface activation treatments include corona treatment, flame treatment, ultraviolet treatment, and various anchor coatings. For applying the aqueous dispersion solution to the molded article or surface, methods and devices normally used for applying solutions, such as coating, impregnation, and spraying methods, can be used. The molded article coated with the aqueous dispersion of the silica/polyvinyl alcohol polymer/methylol melamine compound of the present invention is then heat-cured at 80 to 200 DEG C. for less than one hour. Through this treatment, a silica/polyvinyl alcohol polymer/methylolmelamine composite with excellent water resistance can be obtained in a short period of time. The amount of lamination of the composite is usually 0.1 to 20 g/m ² ,
Preferably it is 2 to 10 g/ ^m2 . The polypropylene, polystyrene, and polyvinyl chloride used in the present invention may be copolymerized with other olefin compounds or may contain various additives to the extent that their thermal and mechanical properties are not significantly impaired. Polyamides include poly-ε-caprolactam, poly(hexamethylene adipamide),
There are poly(meta-xylene adipamide), poly(meta-phenylene isophthalamide), and modified polyamides containing these as main components. Polyester includes poly(ethylene terephthalate), poly(butylene terephthalate), polycarbonate,
Includes polyarylene esters and modified polyesters containing these as main components. The laminate of the present invention is used as a water-resistant gas barrier packaging material for bags, containers, etc., but a resin layer is also added on either side of the laminate of the present invention to impart heat-sealability and adhesive properties. or gas barrier layer,
Printing ink or the like may be laminated. One of the preferred embodiments is to print on the silica/polyvinyl alcohol/methylolmelamine coating of the laminate of the present invention,
Furthermore, a heat-sealable resin layer is laminated thereon. In addition, the aqueous dispersion of the silica/polyvinyl alcohol polymer/methylol melamine compound of the present invention may contain other modifiers (e.g. It may contain organic or inorganic compounds as crosslinking agents, ultraviolet absorbers, dyes, pigments, etc.). The laminate of the present invention can be used as a gas barrier packaging material with excellent water resistance and transparency. It can also be used for applications that utilize scratch resistance, weather resistance, and antifogging properties. The present invention will be described below with reference to Examples. In addition,
In these examples, the oxygen barrier properties are ASTM
Compliant with D1434-66, 30°C DRY and 30°C 80
Measured in %RH. The adhesion between the coating layer and the thermoplastic film was evaluated by a cellophane tape peel test according to a conventional method, and was expressed as the ratio of the area of the adhered part to the total area of the test surface. The water resistance of the coating film was evaluated based on its appearance after immersion in hot water at 90°C for 10 minutes. In addition, the oxygen permeability of the bag was determined by a qualitative test using the nosazurin reaction. This method takes advantage of the fact that when thioglycote, resazurin, and agar solution are placed in a bag, sealed, and then treated in boiling water at 100°C for 30 minutes and stored, the oxygen that passes through the packaging material reacts with nosazurin, causing it to turn red. This is what I did. Example 1 The following solutions and dispersions were prepared. A: The viscosity of a 4% aqueous solution at 20℃ is 35 to 43C.p.
S., and polyvinyl alcohol with a degree of saponification of 98.5 to 99.4 mol% was dissolved in water/methanol - 80/20 (weight ratio) to prepare a 10% solution. B 20% silica sol dispersion (Snowtex 0 manufactured by Nissan Chemical Industries, Ltd.) in water/methanol = 80/20
(weight ratio) to prepare a 10% dispersion. C 20% silica sol dispersion (Snowtex C manufactured by Nissan Chemical Industries, Ltd.) water/methanol = 80/20
(weight ratio) to prepare a 10% dispersion. D Alkyl etherified methylolmelamine (Sumimar M-30W manufactured by Sumitomo Chemical Co., Ltd.) was diluted with water/methanol = 80/20 (weight ratio) to prepare a 10% solution. Mix each of the above solutions in a predetermined weight ratio at room temperature,
A homogeneous aqueous dispersion solution was prepared. Next, each predetermined aqueous dispersion solution was coated on the corona-treated surface of biaxially stretched polyester film E5100 (25μ) manufactured by Toyobo Co., Ltd., and dried by heating in a hot air dryer at 140° C. for 10 minutes to produce a laminated film. The oxygen barrier properties, adhesive properties, and water resistance of each laminated film were evaluated, and the results are shown in Table 1.

[Table] Example 2 Laminated film No. 3 obtained in Example 1 and Comparative Example 1 were dry-laminated with a 60μ unstretched polypropylene film using a polyurethane adhesive on the coating layer side. These laminated films were treated in a pressurized steam oven at 130°C for 5 minutes and then stored at 20°C and 65% RH. One day later, the oxygen barrier properties of each laminated film were measured at 30° C. and 80% RH, and the results were as follows. Example (No. 3)/Unstretched PP laminate film 30c.c./m ² , 24hrs.atm Comparative example 1/Unstretched PP laminate film 480c.c./m ² 24hrs.atm Example 3 Example 2 Each laminated film was prepared in the same manner as the laminated film used in (length 25 cm, width 20 cm).
Fold it in half and stack it on top of each other, and make the two open sides 2
A bag was made by heat sealing a polypropylene layer over a length of cm. After sealing the agar solution containing the resazurin test reagent, the other side was heat-sealed under vacuum. When these samples were treated in boiling water at 100°C for 30 minutes, the barrier layer of Comparative Example 1 turned red immediately after treatment, but
The product prepared from Example 1 (No. 3) was only pink in color.

Claims (1)

[Scope of Claims] 1 The essential components are silica, a polyvinyl alcohol polymer, methylolmelamine in which some or all of the methylol groups are alkyl etherified, and water, and the weight ratio of silica/polyvinyl alcohol polymer is 5. /95 to 80/20, and an aqueous dispersion solution having a weight ratio of methylolmelamine compound/polyvinyl alcohol polymer of 2/98 to 70/30 was applied onto a film-like molded product made of a thermoplastic polymer. After that, the laminate obtained by heating. 2. The laminate according to claim 1, wherein the thermoplastic polymer forming the film-like molded product is substantially polyester or polypropylene.