JPS6129873B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a composite biaxially stretched film, and more particularly to a composite biaxially stretched film for food packaging that has excellent hot water resistance and gas barrier properties, and a method for producing the same. The basic purpose of modern food packaging is to protect the enclosed food from deterioration and spoilage, with the hope that as a result it can be stored and preserved for as long as possible. Packaging materials must have high gas barrier properties and hot water resistance that can withstand high-temperature sterilization, and transparent flexible packaging has even higher commercial value. On the other hand, biaxially oriented films of polyesters, particularly polyethylene terephthalate (hereinafter abbreviated as PET), are widely used for packaging because of their excellent properties such as mechanical strength, heat resistance, and transparency. However, PET film alone is insufficient to meet the above-mentioned increasingly sophisticated demands. Therefore, in general, PET film is coated with polyvinylidene chloride resin (hereinafter referred to as PVDC type), which has excellent gas barrier properties, or a saponified product of ethylene-vinyl acetate copolymer (hereinafter referred to as EVAOH) is coated on PET film. Lamination has traditionally been a common practice.
However, the uses of PVDC systems are generally limited due to poor hot water resistance, browning occurs over time, and toxicity problems due to residual vinylidene monomers remain unresolved. Furthermore, unlike other thermoplastic resins, EVAOH has strong hydrogen bonds, the amount of work required for stretching does not change much depending on the stretching temperature, and it exhibits neck stretching, making it difficult to form into thin films. However, if a thick film is used as is, it is not only expensive, but also has poor strength in cold weather and poor hot water resistance. On the other hand, it is possible to make a thin film by impregnating EVAOH with water, but in this case, it cannot be highly oriented, so only a film with poor hot water resistance and gas barrier properties can be obtained. As a method to solve this problem,
Publication No. 6276 shows that it is possible to highly biaxially stretch an unstretched film of EVAOH and a thermoplastic resin such as polyester or acrylonitrile that can be biaxially stretched at high magnification after closely laminating the film. As a method to further improve hot water resistance, JP-A-52-
Publication No. 110781 describes a method of heat treating a laminated stretched film. Generally, the dry lamination method is used as a lamination method.
Possible methods include a coextrusion method, an extrusion lamination method, and a heat adhesion method. As mentioned above, as food packaging film,
The combination of PET and EVAOH is most preferred, and dry lamination is the method that provides a film with the most desirable physical properties for the application in question to obtain a composite film of this combination. That is, in the coextrusion method, it is not possible to stably coextrude EVAOH, which is easily thermally decomposed, with PET, which has a large difference in melting point, for a long period of time. On the other hand, for example, it would be good to increase the vinyl alcohol component of EVAOH to bring its melting point closer to that of PET, but the oxygen permeability at high humidity, which is a characteristic of EVAOH, would deteriorate, making it impossible to put it into practical use. The extrusion lamination method is not preferred because it requires expensive anchor coating equipment, which is the same as the dry lamination method, and the laminated film produced by the same method still has insufficient adhesive strength. Similarly, the heat adhesion method also fails to provide sufficient adhesive strength. Conventionally, organic solvent-based adhesives have been used as adhesives for dry lamination because of their excellent coating properties on substrates and the water resistance of the film. However, since organic solvents are used, there is inevitably a risk of explosion and flames, health hazards during handling, and air pollution problems. A further important problem is that it is unavoidable that the solvent remains on the adherend, and this residual solvent may deteriorate the quality of the food, which is not desirable from a safety standpoint. Furthermore, in recent years, pollution regulations and food safety regulations have become stricter, and there will be problems if we continue to use shared solvent adhesives in the future. The use of water-based adhesives can be considered to solve these drawbacks of organic solvent-based adhesives, but conventional water-based emulsion-based adhesives have poor affinity with plastic films and are generally colloidal, making it difficult to use adhesives. The coating properties were poor, and since it was non-crosslinked, the water resistance was insufficient. Moreover, even if it was a crosslinked type, only a product with poor coating properties could be obtained. The inventors of the present invention have made extensive studies to solve this problem, and as a result have arrived at the present invention. That is, the present invention relates to a composite biaxially stretched film comprising a biaxially stretched film of a saponified ethylene-vinyl acetate copolymer and a biaxially stretched polyester film, which are composited with an acrylic-epoxy resin water-based emulsion adhesive. The present invention will be explained in more detail below. PET in the present invention is not necessarily a homopolymer of polyethylene terephthalate, but a copolymer in which a part of the terephthalic acid component of the raw material is replaced with one or more of isophthalic acid, naphthalene dicarboxylic acid, adipic acid, or sebacic acid. , or a part of the ethylene glycol component is diethylene glycol, triethylene glycol,
Alternatively, it also includes a copolymer substituted with 1,4-butanediol or the like. In the present invention, EVAOH refers to a saponified ethylene-vinyl acetate copolymer, as well as a multi-component polymer obtained by copolymerizing ethylene-vinyl acetate with one or more other copolymerizable third components. All are suitably used. Oxygen barrier, transparency,
From the viewpoint of moisture resistance and extrusion moldability, etc.
Ethylene content in EVAOH is 26-45mo
←Those with a saponification degree of 96% or higher are suitable. The acrylic-epoxy resin aqueous emulsion adhesive in the present invention is an emulsion containing an acrylic resin, an epoxy resin, and water as essential components, and is an acrylic-epoxy resin obtained by coexisting an epoxy resin during emulsion polymerization of acrylic monomers. Resin water-based emulsion adhesive (), one-component acrylic-epoxy resin water-based emulsion adhesive () obtained by separately preparing acrylic emulsion and epoxy emulsion and then mixing the two;
Acrylic emulsion and epoxy emulsion, which are manufactured separately, are mixed at the time of use. It is a thermosetting water-based emulsion adhesive including a so-called two-component acrylic-epoxy resin water-based emulsion adhesive. There are two methods for manufacturing acrylic-epoxy resin water-based emulsion adhesives: one is to coexist with an epoxy resin emulsion during emulsion polymerization of acrylic monomers, and the other is to manufacture the acrylic resin water-based emulsion by emulsion polymerization and then continue. There is a method of emulsionizing an epoxy resin. The aqueous acrylic resin emulsion mentioned here is made from acrylic monomers such as acrylic esters and methacrylic esters, as well as other copolymerized monomers, and is processed by emulsion polymerization together with water, emulsifiers, initiators, and other additives as necessary. The resulting aqueous acrylic resin emulsion must have a functional group that can react with an epoxy group. Monomers that can be used in the production of acrylic resin aqueous emulsion include methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate,
n-decyl acrylate, n-dodecyl acrylate, methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n
- In addition to hexyl methacrylate, lauryl methacrylate, etc., acrylic acid, methacrylic acid, maleic acid, itaconic acid, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate,
Hydroxypropyl acrylate, hydroxypropyl methacrylate, acrylamide, N-
Examples include methylol acrylamide, cyacetone acrylamide, glycidyl methacrylate, diethylaminoethyl methacrylate, tert-butylaminoethyl methacrylate, and copolymerizable monomers such as styrene and vinyl acetate acrylonitrile. The acrylic component constituting the acrylic-epoxy resin aqueous emulsion adhesive of the present invention contains -
COOH, -OH, CH ₂ OH, -CH ₂ OR (in the formula, R represents a lower alkyl group such as -CH ₃ , -C ₂ H ₅ ), -
CONH ₂ , ―CONH (CH ₂ OH), ―CON
( _CH2OH ) ₂ ,

It is essential to contain a monomer having a functional group such as [Formula] as a copolymerization component. One or more copolymer components having these functional groups can be used together with acrylic esters and methacrylic esters. To manufacture a composite film, first, an adhesive is uniformly applied to a base film, ie, a PET film or an EVAOH film, using a bar coater, roll coater, or the like. PET film coated with adhesive after drying and dehydration or
A composite film can be obtained by laminating EVAOH films under pressure using heated rolls. In the drying step, the dehydrated emulsion particles are fused to form a film (film formation). In order for the emulsion particles to fuse together to form a film, the film forming temperature (film forming temperature) of the acrylic emulsion adhesive must be at least lower than the drying and baking temperature of this process. Furthermore, in order to obtain good adhesion during lamination, the adhesive layer must have tackiness (tackiness) or leveling (smoothness). For this reason, it is preferable that the minimum film forming temperature (MFT) of the aqueous acrylic-epoxy resin emulsion be lower. Aqueous acrylic-epoxy resin emulsions with low MFT generally have good tack properties. This acrylic-epoxy resin emulsion
MFT is mainly the Tg of the copolymer composition of acrylic resin.
The glass transition point) is preferably lower. Acrylic monomers suitably used for such purposes include ethyl acrylate, n-propyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, and lauryl methacrylate. Acrylic acid, methacrylic acid,
It is preferable to use a small amount of itaconic acid or the like to improve the stability of the emulsion. This not only serves to improve adhesiveness by introducing polar groups into the acrylic polymer, but also contributes to improved adhesive strength and hot water resistance through a crosslinking reaction with the epoxy resin. Furthermore, this carboxylic acid is neutralized,
By using a so-called alkali thickening type, significant improvements in coating properties and mixing stability with an aqueous epoxy resin emulsion are observed. Copolymerization components such as 2-hydroxyethyl methacrylate and N-methylolacrylamide are useful for improving the stability of emulsions and as functional groups for crosslinking. The other essential component of the aqueous acrylic-epoxy resin emulsion is an epoxy resin with a molecular weight of about 300 to 1000 containing on average one or more epoxy groups in each molecule, and bisphenol A. based epoxy resin,
In addition to glycidyl ether type epoxy resins derived from polynuclear polyhydric phenol compounds such as bisphenol F epoxy resins and novolac type epoxy resins, glycidyl ether type epoxy resins derived from mononuclear polyhydric phenol compounds, aromatic oxy Glycidyl ether-glycidyl ester type epoxy resins derived from acids, glycidyl ester type epoxy resins derived from aromatic or aliphatic polycarboxylic acids or their anhydrides, N-glycidyl type epoxy resins derived from aromatic amine compounds , various glycidyl ether type epoxy resins derived from aliphatic polyols, etc. A particularly preferred epoxy resin is a bisphenol A-based epoxy resin. When emulsifying the epoxy resin, it is prepared by appropriately combining general nonionic surfactants and emulsifying the mixture with a thickener, antifoaming agent, etc. using a homogenizer under heating. For the aqueous acrylic-epoxy resin emulsion used in the present invention, a water-soluble compound having a functional group that can react with the functional group contained in the acrylic-epoxy resin, such as ethanolamine, dicyandiamide, xylerin, is used as a third component. A curing agent for epoxy resin such as diamine, or a water-soluble resin or emulsion such as methylolated melamine resin, methylated methylolmelamine resin, or polyamide resin can be added as a crosslinking agent. Furthermore, water and other additives (surfactants, thickeners, antifoaming agents, protective colloids, antifungal agents, alcohols) may be added as necessary. The composition ratio of the acrylic polymer component and the epoxy resin component in the aqueous acrylic-epoxy resin emulsion is such that the equivalent ratio of epoxy groups to functional groups that can react with epoxy groups in the acrylic polymer is 0.1.
It is desirable to set the value to 10, preferably 0.5 to 2. When a large excess of epoxy resin is blended, adhesive performance can be improved by adding a curing agent component that can react with epoxy groups. The aqueous acrylic-epoxy resin emulsion of the present invention exhibits good wettability to PET-EVAOH film, and although it is aqueous, it exhibits good coating properties without repelling in thin film coating, and has a drying speed. The film that can be formed at a high speed has good transparency. When an aqueous acrylic resin emulsion is used alone, it exhibits fairly good coating properties, but its adhesive strength, water resistance, and hot water resistance are insufficient. In addition, epoxy resin aqueous emulsion has poor wetting properties for PET and EVAOH films, and even when used in combination with an epoxy curing agent, film forming properties are poor, and adhesion to the base material is not only poor. The resulting coating film is hard and unsuitable for film stretching. The concentration of the resin in the aqueous acrylic-epoxy resin emulsion of the present invention is usually 20 to 60%, and can be adjusted as appropriate by changing the amount of water. Various adhesive coating methods can be used, such as gravure roll coater, knife coater, air knife coater, revar roll coater, and Mayer bar coater, and are selected depending on the type of adhesive, coating speed, coating amount, etc. . Coating amount is usually 2μ to 60μ, preferably 4μ to 20μ
It is preferable to apply the coating to a film thickness of 1 to 15 g/m2, preferably ² to 15 g/m2 in dry coating amount.
~6 g/m ² is preferable. The film to be laminated is EVAOH film and
Although it is preferable to use an unstretched PET film, the PET film may be uniaxially or biaxially stretched. Such a laminated film is biaxially stretched in the longitudinal and transverse directions simultaneously or sequentially, and the conditions are 70~
At a temperature of 120°C, the longitudinal stretch ratio/horizontal stretch ratio is 0.5 to 2.0, and the product of the longitudinal and transverse stretch ratios is 8 to 8.
It is desirable to set it to 20. The laminated film obtained in this way is heated in the range from the crystallization initiation temperature of EVAOH to the melting temperature, that is, 140 to 220℃.
heat treatment at a temperature of, preferably 160-200°C. As described above, according to the present invention, a PET film with excellent mechanical properties, transparency, etc. and an EVAOH film with excellent gas barrier properties are dry-laminated and then stretched using an acrylic-epoxy resin water-based emulsion adhesive. It is possible to obtain a transparent film for food packaging with good hot water resistance using a water-based adhesive that does not cause pollution problems, which has been considered difficult. The present invention will be further explained below with reference to Examples, but it goes without saying that the present invention is not limited thereto. The measurement method used is described below. Solid content (nonvolatile content): Adhesive weight % after drying at 150°C for 2 hours Viscosity: BL type rotational viscometer (Tokyo Keiki Co., Ltd.)
The values are shown at 60 rpm and 30°C using a No. 1 rotor. Dry coating weight: The value obtained by subtracting the weight after the adhesive has been dissolved with a solvent from the weight after drying the adhesive is shown per ^1m2 . Adhesive strength: After lining both sides of the PET/EVAOH laminated film with biaxially stretched PET film (50μ), T-peel was performed at a sample size of 150 mm x 1 inch and a peeling speed of 100 mm/min. (Adhesive strength after boiling: A sample of the above size was boiled for 30 minutes in 100 °C water or 5% vinegar, and then subjected to a peel test.) Boil test (hot water resistance): The EVAOH side was corona-treated and a polyethylene film ( 60μ), then heat-seal two sets of films with sample widths of 60 x 70 mm with the polyethylene sides facing each other and three sides. This bag is filled with water or 5% vinegar and then made into a bag. Boil this in water at 100℃ for 30 minutes. Hot water resistance was judged based on the presence or absence of whitening, tunneling, or delamination. Oxygen permeability: Oxygen electrode isobaric method (OX-
Tran100: Measured by Modern Control Co., Ltd. at 25℃ and 65%RH. Below, methods for producing various adhesive emulsions used in Examples are shown. (1) Acrylic resin aqueous emulsion [A] Prepare the following raw material solutions (a) and (b). Raw material liquid (a) Ethyl acrylate 77.5 (parts) Methyl acrylate 8.5 Acrylic acid 4.0 Raw material liquid (b) Octyl phenyl polyoxyethylene ether 2.0 Sodium dodecylbenzenesulfonate 0.05 Ammonium persulfate 0.25 Ion exchange water 110 Dripping device, stirrer Blow nitrogen gas into a polymerization kettle equipped with a reflux condenser to form a sheet, and add the solution (b). While stirring, keep the internal temperature at 75℃ and add the solution (b).
was gradually added dropwise and emulsion polymerization was carried out for 4 hours, and the residual monomer was 1% or less. The resulting emulsion had a solids content of 45% and a viscosity of 110 cps. This acrylic resin aqueous emulsion is referred to as [A]. (2) Acrylic resin aqueous emulsion [B] Prepare the following raw material solutions (a) and (b). Raw material liquid (a) 2-ethylhexyl acrylate 100 (parts) Methyl acrylate 17 Acrylic acid 3.0 Raw material liquid (b) Polyoxyethylenonyl phenyl ether
2.0 Sodium dodecylbenzenesulfonate 0.05 Ammonium persulfate 0.25 Ion-exchanged water 80 Using the same reaction apparatus as in (1), conduct the reaction at 70℃ for 6
Polymerization was carried out in the same manner as in (1) except for changing the time. The resulting emulsion has a solids content of 60% and a viscosity of
It was 240cps. This aqueous acrylic resin emulsion is designated as [B]. (3) Acrylic-epoxy resin water-based emulsion [C] Prepare the following raw material solutions (a) and (b). Raw material liquid (a) Epoxy resin (epoxy equivalent 190, Epicote 828 (trade name, manufactured by Ciel Chemical Co., Ltd.) 7 (parts) Emulsifier; Polyoxyethylene nonyl phenyl ether 1.5 Emulgen A-500 Trade name, Kao Atlas Co., Ltd. 0.5 Epan 785 (trade name, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) 0.5 Ammonium persulfate 0.25 Sodium monohydrogen phosphate 0.20 Ion exchange water 110 Raw material solution (b) Methyl methacrylate 13 Butyl acrylate 5 2-ethylhexyl acrylate 70 Acrylic acid 2 Using the same reaction apparatus as in Example 1, prepare solution (a) in a nitrogen gas stream and heat to 75°C after sealing with nitrogen.
Mix while heating. Next, the mixture of solution (b) was gradually added dropwise, and polymerization was carried out while mixing. The residual monomer content was 1% or less 6 hours after the start of the reaction.
Thereafter, the reaction was completed by cooling. The resulting emulsion had a solids content of 45% and a viscosity of 40 cps.
The resulting aqueous acrylic-epoxy resin emulsion is designated as [C]. (4) Acrylic-epoxy resin water-based emulsion [D] Prepare the following raw material solutions (a) and (b). Raw material solution (a) Epoxy resin (epoxy equivalent 190, Epicote 828 (trade name), manufactured by Ciel Chemical Co., Ltd.) 5.0 (parts) Emulsifier; Polyoxyethylene nonyl phenyl ether 1.0 Emulgen A-500 (trade name, Kao Atlas 0.5 Epan 785 (Product name, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) 0.5 Silicone antifoam agent KM-85 (Product name, manufactured by Shin-Etsu Silicone Co., Ltd.) 0.16 Neopellex (Product name, manufactured by Kao Atlas Co., Ltd.) 0.1 Ion exchange water 140 Raw material solution (b) Ethyl acrylate 40 Methyl methacrylate 5.0 Methyl acrylate 9.0 Acrylic acid 1.0 Produced in the same manner as in the production of acrylic-epoxy resin aqueous emulsion [C]. The resulting emulsion had a solids content of 30% and a viscosity of 12 cps. This aqueous acrylic-epoxy resin emulsion is designated as [D]. Examples 1 to 4 Acrylic-epoxy resin aqueous emulsion adhesives having the compositions shown in Table 1 below were prepared.
EVAOH (ethylene content 35%, saponification degree 99.8
%) was melt extruded to obtain a 45μ amorphous film. Apply the adjusted adhesive to the film using a roll coater to a thickness of 8μ, and heat at 90°C.
It was heated and dried. Separately melt-extruded PET ([7]
= 0.62) 130μ unstretched film and the above EVAOH
The film was laminated using a laminating roll at the temperature shown in Table 1 and at a pressure of 5 kg/cm ² . The composite film was biaxially stretched 3 times in length and width at the temperature shown in Table 1.
Heat treatment was performed at 180°C for 30 seconds. The adhesive layer formed a smooth coating film without repelling, craters, etc., and a transparent composite film was obtained. Table 1 shows the adhesive strength of the obtained film.

[Table] Example 5 EVAOH (ethylene content 29 mol%, saponification degree
99.0%) was melt extruded to obtain a 60μ amorphous film. The film was coated with aqueous acrylic-epoxy resin emulsion [C] further diluted with ion-exchanged water to give a solid content of 30% using a Mayer bar coater, and then heated and dried at 90°C. A separately melt-extruded 100μ unstretched film of PET ([η] = 0.64) was laminated at 70°C, biaxially stretched 3.8 times in both length and width, and then heat treated at 170°C for 20 seconds to form a biaxially stretched film. Obtained. The mechanical strength of the obtained film was as follows: elongation MD95%/TD82%, Young's modulus 450Kg/ ^mm2 /490
Kg/mm ² , while the oxygen permeability coefficient is P=2.60×
10 ^-14 cc·cm/cm ² sec·cmHg, and had sufficient performance for practical use as a packaging film. The appearance of the film upon application of the adhesive was very uniform and no repellency was observed. Further, the adhesive strength of the stretched film was high, and it was found to be good with no tunneling phenomenon or delamination observed in the hot water resistance test. The results are shown in Table 2. Example 6 A similar experiment was conducted using an amorphous EVAOH film obtained in the same manner as in Example 5 and an aqueous acrylic-epoxy resin emulsion [D]. The results are shown in Table 2. Examples 7 to 10 Acrylic-epoxy resin mixed with 82 parts of acrylic resin water-based emulsion [A] and 12 parts of epoxy resin water-based emulsion Prizol L602 (trade name, manufactured by Dainippon Shikizai Co., Ltd.) as an adhesive. A composite film was obtained in the same manner as in Example 5, except that a water-based emulsion adhesive was used and the amount of water was changed to use the solid content shown in Table 2. The results are shown in Table 2.

【table】

Claims (1)

[Scope of Claims] 1. A composite biaxially stretched film in which a biaxially stretched film of a saponified ethylene-vinyl acetate copolymer and a biaxially stretched polyester film are combined with an acrylic-epoxy resin aqueous emulsion adhesive.2 Ethylene. - An unstretched film of the saponified vinyl acetate copolymer and a polyester film are composited using an acrylic-epoxy resin water-based emulsion adhesive, then biaxially stretched, and then melted from the crystallization initiation temperature of the saponified film. A method for producing a composite biaxially stretched film characterized by heat treatment at a temperature within a range of