JPH0132068B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a laminated polyester film for food containers, and particularly to a material for beverage containers. Traditionally, food containers, especially beverage containers, have been made of glass bottles, metal cans such as aluminum or steel, plastic bottles, and paper containers made of laminated polyethylene.However, changes in consumer lifestyles and food distribution routes have led to the use of packaging. The form of containers is changing, and there are new requirements, especially for light weight, ease of packaging, and ease of disposing of used containers. Among the food containers mentioned above, paper containers laminated with polyethylene are lightweight, and empty containers can be easily reduced in volume after use, and can be easily incinerated in household garbage incinerators. While it has its advantages, it can absorb the aroma of the contents of the container, such as beverages such as juice, cola, soda water, and alcohol, as well as seasonings such as soy sauce and sauce, which can change the aroma and taste of the contents. This may be due to the action of a small amount of catalyst residue used during polyethylene polymerization, the high content of low molecular weight polyethylene, or the resin being heated and melted during the molding process of the container material, resulting in decomposition and oxidation of the resin. This is due to a variety of reasons, including being exposed to water and producing a bad odor. In particular, extrusion lamination of polyethylene is carried out at a high temperature of 300 to 330 DEG C. in order to improve the adhesiveness of the polyethylene, and as a result, bad odors are often produced due to decomposition and oxidation of the resin. As a result of intensive research to solve the above problems, the inventors of the present invention have found that they are lightweight and have excellent gas barrier properties.
To provide a food container material that hardly changes the aroma or taste of the contents and allows easy disposal of the container after use. In other words, this invention has a film density of 1.355.
g/ ^cm3 or less, the maximum value of the refractive index in the film plane direction is
A laminated film consisting of a polyester film with a tan δ of 1.590 or less, a flexible polymer material with a tan δ of 0.05 or more laminated as necessary on one side of the polyester film, and a poorly gas permeable material further laminated on that side. Therefore, the amount of oxygen permeation at 20°C in the dry state of the laminated film is 30 c.c./m2, ²⁴ hours, atmospheric pressure or less, and the sealing strength when heat-sealing the polyester film is 1000 g/15 mm (20
℃) or more. Polyester film is formed by melt-extruding polyester obtained by reacting dibasic acids and glycols, and a wide range of known dibasic acids and glycols can be used.
Examples of polyesters with good flavor resistance that do not easily absorb scents include polyethylene terephthalate, polyethylene isophthalate, polyethylene terephthalate/ethylene isophthalate copolymer, polytetramethylene terephthalate, polytetramethylene isophthalate, and polytetramethylene terephthalate/tetramethylene. Isophthalate copolymers are preferred. In addition, a polyester copolymer obtained from terephthalic acid, ethylene glycol, and propylene glycol or an ethylene oxide adduct of bisphenol A as a third component can also be used. Generally useful polyesters have an intrinsic viscosity of at least 0.2 dl/g, particularly preferably 0.5 to 30 dl/g, as measured at 25-30°C using orthochlorophenol or a 6:4 mixed solvent of phenol:tetrachloroethane. It is 1.3dl/g. In the present invention, it is important that the density of the polyester film be 1.355 g/cm ³ or less, and that the maximum value of the refractive index in the direction of the film surface be 1.590 or less. The density and maximum refractive index of the film are increased by heating the film to crystallize it or by stretching it. A substantially amorphous, non-oriented, transparent polyethylene terephthalate film obtained by melt-extruding polyester from a die and immediately quenching it has a density of 1.336 g/cm ³ , a maximum in-plane refractive index of the film of 1.576, and For polyethylene terephthalate/ethylene isophthalate copolymer films containing 40 mol% or less of isophthalate components, the density is 1.333 to 1.335.
g/cm ³ , the maximum value of the film's in-plane refractive index is 1.573, and for polyethylene isophthalate film, the density is 1.325 g/cm ³ , and the maximum value of the refractive index is 1.571.
It is. On the other hand, the density and in-plane refractive index of a commonly used stretched polyethylene terephthalate film (manufactured by Toyobo Co., Ltd., packaging film) are 1.4018 g/cm ³ and 1.6684, respectively. The maximum values of the density and refractive index of the polyester film are correlated to the heat seal strength of the polyester film, and the heat seal strength of the polyester film is greater when it is within the range of the above values, that is, when it is amorphous and unoriented. In a commonly used stretched film, the density and refractive index become larger than the above numerical range, and while the strength of the film is improved, the heat sealing strength is reduced.
The heat seal strength of polyester film is 20
It is important that it is 1000g/15mm or more at °C.
When the heat seal strength is less than 1000g/15mm,
When transporting a food container filled with food, vibrations or shocks can cause the heat seal to open, causing food to spill out or bacteria to enter through the opening. The above polyester film has greater stiffness and poor flexibility than conventional polyethylene, polypropylene, etc., which have heat sealability. Therefore, when packaging heavy items, problems may arise in pinhole resistance and bending fatigue resistance. In order to solve this problem, in this invention, one side of the polyester film is heated at 20°C.
This involves laminating flexible polymer materials with a tan δ of 0.05 or more. The tan δ of the above polymer material represents the dynamic properties and is the number obtained by dividing the loss modulus by the storage modulus. tan δ is the ratio of the viscous term and the elastic term in the viscoelastic properties of the material, and the viscosity It is a standard measure. Tanδ is also a measure of the amount of energy dissipated as heat during dynamic deformation and reflects the micro-Brownian motion of amorphous materials. this
tan δ shows a peak when the polymer material is at the glass transition temperature. The present inventors have discovered that tan δ is correlated with heat sealability. These polymer materials include polyethylene, polypropylene, 1,2-polybutadiene, natural rubber,
Polymer elastomers such as synthetic rubber, polyurethane, and polyether ester elastomer, as well as Teflon and paper, are used. After laminating a polymeric material on one side of the above polyester film, or without laminating it, a poorly gas-permeable material is laminated, and the oxygen permeation rate in a dry state at 20°C is 30 c.c./m ^2.24 hours and atmospheric pressure.
These poorly gas permeable materials include polyvinyl alcohol, saponified ethylene/vinyl acetate copolymer, polyvinylidene chloride, polyamide and modified products thereof, metal foil such as aluminum,
Plastic films such as metallized polyester and polyamide are used. When the poorly gas permeable material is a resin, it can be formed into a film and laminated, or the resin can be melt-extruded to perform extrusion lamination. Furthermore, a resin emulsion may be applied. Furthermore, in the case of a film in which the poorly gas-permeable material is metalized, a thin film of aluminum, zinc, etc. can be formed by vacuum evaporation, spackle ring, ion plating, or the like. The above-mentioned polyester film, polymer material, and poorly gas permeable material can be laminated using an adhesive, or polyester and polymer material can be coextruded and then extruded and laminated to a difficult gas permeable material. You can also do this. Furthermore, if necessary, a polyethylene film, biaxially oriented polypropylene, or polyester film can be laminated on the surface of the poorly gas permeable material for surface protection and aesthetics. Further, the surface may be appropriately printed. The laminated polyester film of this invention can be heated at 20°C.
It is important that the amount of oxygen permeation in the dry state of the container is below ^30c.c./m2/24 hours/atmospheric pressure, but the required amount of oxygen permeation varies depending on the type of food packed in the container. . An example is shown in Table 1 below.

[Table] The above oxygen permeation amount is adjusted by the type and thickness of the poorly gas permeable material, and examples of combinations thereof are shown in Table 2.

【table】

[Table] In Table 2, the ethylene/vinyl acetate copolymer is
The ethylene content is 33 mol%, and the aluminum-deposited polyester film has an ethylene content of 0.03 to 0.03% on the biaxially oriented polyethylene terephthalate film.
It has a 0.1 micron aluminum layer deposited on it. In the table, the thickness is in microns and the oxygen permeation rate is in
cc/m ² / 24 hours / atmospheric pressure unit. The oxygen permeation amount in Table 2 is 10,000 for low density polyethylene with a thickness of 12 microns, and 10,000 for polypropylene.
This is much smaller than 3000. The laminated polyester film according to this invention is
It has excellent heat sealing properties, high sealing strength, and good gas barrier properties, making it an excellent material for food containers. Foods packaged with this material are prevented from oxidative discoloration, fat oxidation, vitamin oxidation, etc., and have good aroma and flavor retention. This material also reduces packaging costs, is easy to handle, and is disposable. Furthermore, since it can be packaged compactly, it is easy to transport, and since the unfilled empty container is flat, it is easy to store. In addition, containers made of polyester film laminated with aluminum foil or metallized film as a material with low gas permeability have poor thermal conductivity when filled with beverages or foods and heat-sealed for heat sterilization or retort processing. Very good and
Compared to solid containers such as canned goods, the rate of temperature rise of the contents is more than twice as fast, the time required to sterilize food is shortened, and the fresh flavor of the contents can be preserved. Convenient packaging containers such as standing pouches made of the material of this invention can be used for curries, stews, sauces such as Tomigura sauce and meat sauce, soups such as potage, consommé, and corn mash, boiled beans, mousses, oden, and vegetables. It is used for retort foods such as stews, grain bean paste, chestnuts, zenzai, soybean vegetables, Chinese dishes such as eight treasures and sweet and sour pork, as well as for food containers such as vinegared jellyfish and bamboo shoots. It can also be used as a flexible beverage container for carbonated drinks such as cola and Sprite, soft drinks such as soy milk, fruit drinks, and lactic acid drinks, as well as alcoholic drinks such as sake, grape sake, Yomeishu, shochiyu, and whisky. can. Furthermore, it can be used as a container material for processed livestock products such as ham and sausage, processed seafood products such as kamaboko, salmon roe, and salted fish, and other general foods. Next, a method for measuring physical properties and a processing method in this invention will be explained. (1) Density: A density gradient tube was used in accordance with JIS-K7112, and the temperature of the gradient tube was measured at 30°C. (2) Refractive index: Measured based on ASTM-D542 using an Atsbe refractometer type I (manufactured by Atago Corporation) at a temperature of 20° C. using methylene iodide as the filling liquid. (3) tanδ: Using a solid viscoelasticity measuring device (viscoelastic spectrometer VES-S type, manufactured by Iwamoto Seisakusho),
Measurements were made at a temperature of 20°C and a frequency of 60Hz. (4) Oxygen permeation rate: Automatic oxygen permeability measuring device (Ox
−Tran100 type, manufactured by Mo Con), 20
The measurement was carried out at ℃ and in a dry state (0% RH). The samples were left in a desiccator containing dry silica gel for 24 hours before measurement. (5) Heat sealing: Using a tabletop automatic sealing machine (Automini AM-250R model, manufactured by Shiga Packaging Machinery Co., Ltd.),
The heating time and stop time knobs were set to 4 and sealed at each temperature. (6) Sealing strength: The width of the heat-sealed film
Cut into 15 mm strips and use a universal tensile tester (Tensilon UTM type, manufactured by Toyo Baldwin)
Measurement was carried out using a T-shaped peel in an atmosphere of 20° C. and 65% humidity at a peeling rate of 200 mm/min. (7) Retort processing: Dyeing processing machine (HUHT212/
The film was placed in a wire mesh bag and treated in flowing hot water at 120°C for 30 minutes to prevent the film from floating. In order to prevent the sealant from adhering, paper was sandwiched between the films. (8) Boil treatment: The film was placed in a wire mesh bag and submerged in boiling water to prevent it from floating and treated for 30 minutes. In order to prevent the sealants from fusing together, paper was sandwiched between the sealants. (9) Resin odor: After a certain period of time, the product was opened and smelled. The judgment was made by five people who are sensitive to odors. (10) Taste: A mouthful of the contents was placed in the mouth to examine the taste. ◎ mark is the best, △ mark is poor. (11) Polymer intrinsic viscosity and reduced specific viscosity: Using a mixed solvent of phenol/tetrachloroethane (3/2), dissolve 80 mg of polymer in 20 c.c. of solvent and use an Ubbelohde capillary viscometer. Measured at 30°C. Examples of the present invention will be described below. Example 1 Dimethyl terephthalate, dimethyl isophthalate, and a mixture thereof, with 40 mmol% zinc acetate and 30 mmol% antimony trioxide as catalysts.
was added, and a transesterification polycondensation reaction with ethylene glycol was carried out in a conventional manner to produce polyesters of polyethylene terephthalate, polyethylene isophthalate homopolymers, and polyethylene terephthalate/ethylene isophthalate copolymer. After drying, it was melt-extruded at 280-290℃ and rapidly solidified on a casting drum kept at 25℃ to a thickness of 50℃.
Unstretched films of micron and 600 micron were obtained. For comparison, the above unstretched film with a thickness of 600 microns was stretched in the longitudinal direction at 3.3 times at 80°C using a roll stretching machine, and then stretched at 95°C using a tenter.
It was stretched in the transverse direction at 3.7 times and then heat set at 130-200°C to obtain a sequentially biaxially stretched polyester film with a thickness of 49 microns. A flexible polymer material with tan δ of 0.1 or more was laminated on the above polyester film. This flexible polymer material is polypropylene film (trade name: Toyobo Pylene Film, unstretched P1120, thickness 40
micron) and a polyester resin film (a 40 micron thick film made by melt-extruding Toyobo Vylon GM900 (trade name) at 170°C). Then, a dry laminating adhesive (manufactured by Toyo Morton Co., Ltd., product names: AD300A and AD300D mixed in a 1:1 ratio and diluted 1.3 times with a diluent) was applied to the polyester film using a gravure coater. After drying at °C, the above-mentioned Pyrene film and Vylon film were pressed and laminated. Apply a dry laminating adhesive (manufactured by Toyo Morton Co., Ltd., trade name:
A solution prepared by mixing AD-1010 and AD-RTI in a ratio of 100:7 and diluting it 1.5 times with the diluent BTS-500) was applied using a gravure coater, dried through a drying zone at 60℃, and then heated to 70℃. Aluminum foil with a thickness of 12 microns was passed between the heated metal roll and the rubber roll for pressure, overlapping the surface coated with the adhesive, and the foil was laminated and wound up. Furthermore, on the top surface of the aluminum foil, a thickness of one side is printed in the same manner as above.
A 12 micron biaxially stretched film of polyethylene terephthalate (manufactured by Toyobo Co., Ltd., trade name: Polyester Film T4100) was laminated under pressure, and the resulting laminated polyester film was aged at 35° C. for 20 hours. The results of the performance tests of these laminated films are shown in Table 3. For comparison, a film in which a polymer material and aluminum foil were laminated on the biaxially stretched polyester film in the same manner as in the examples, and a film in which a polyethylene film was laminated instead of the polyester film were tested.

【table】

[Table] The sensory test for resin odor and taste in Table 3 was conducted using the above laminated film to create a standing pouch measuring 16 cm in length and 10 cm in width, and after filling the pouch with 170 c.c. of sake and sealing it. The samples were left in a room at 40°C for two weeks, and then a sensory test was conducted. ◎ indicates that there is no resin odor, and △ indicates that the sample is defective. Further, the reduced specific viscosity of sample number 1-1 in Table 3 indicates the intrinsic viscosity. Example 2 In addition to terephthalic acid and ethylene glycol,
Propylene glycol (PG) or ethylene oxide adduct of bisphenol A (BPA) was blended as the third component and polycondensed by a conventional method to produce a copolymerized polyester. On the other hand, a biaxially stretched polyethylene terephthalate film with a thickness of 12 microns (trade name Toyobo Ester Film No. E5100),
Alternatively, a metallized film is produced by vacuum-depositing aluminum to a thickness of 50 mm on the surface of a low-density polyethylene film, and the above copolyester is melt-extruded onto the metallized film at 270°C to a thickness of 50 mm. Micron copolymerized polyester films were extruded and laminated.
For comparison, a polyester film was used in which an unstretched copolymerized polyester having a thickness of 175 microns was uniaxially stretched in the longitudinal direction at 80° C. to a ratio of 3.5 times as in the comparative example of Example 1 above. For comparison, an unstretched polypropylene film was used instead of the copolymerized polyester film. The results of the performance test of Example 2 are shown in Table 4.

【table】

[Table] For the sensory test, a standing pouch similar to that in Example 1 was made, and orange juice 170 c.c.
The test was conducted after filling and sealing the container and leaving it in a tank at 40°C for 4 hours. Example 3 An unstretched copolymerized polyester film with a thickness of 50 microns obtained from the copolymerized polyester film copolymerized with isophthalic acid in Example 1,
An unstretched film with a thickness of 15 microns made of saponified ethylene vinyl acetate copolymer (manufactured by Kuraray Co., Ltd., trade name: EVAL F) as a material with low gas permeability without using a flexible polymer material, and printing. A laminated polyester film was produced by laminating the processed biaxially stretched polyethylene terephthalate film (trade name: Toyobo Ester Film No. E5100) with a thickness of 12 microns by a dry lamination method. For comparison, a 50 micron thick unstretched film obtained from an ionomer resin (manufactured by Mitsui Polychemical Co., Ltd., trade name: Himilan No. 1650) was used instead of the copolymerized polyester film. The results of the performance test of Example 3 are shown in Table 5.

[Table] In the above sensory test, 170 c.c. of wine was sealed in a standing pouch made in the same manner as in Example 1.
The test was carried out after being left at the actual temperature for one month.

Claims (1)

[Claims] 1. A polyester film having a film density of 1.355 g/cm ³ or less and a maximum refractive index in the direction of the film surface of 1.590 or less, and a tan δ of 0.05 laminated on one side of the polyester film as necessary. A laminated film made of the above flexible polymeric material and a poorly gas permeable material further laminated on its surface, the laminated film has an oxygen permeation rate of 30 c.c./m ² at 20°C in a dry state. - A laminated polyester film for food containers, characterized in that the temperature is below 24 hours and atmospheric pressure, and the sealing strength when heat-sealing the polyester film is 1000 g/15 mm (20°C) or more. 2 Polyester consists of a dibasic acid and a glycol, where the dibasic acid is terephthalic acid, isophthalic acid and a mixture of these acids, and the glycol is an ethylene oxide adduct of ethylene glycol and propylene glycol or bisphenol A as a third component. A laminated polyester film for food containers according to claim 1. 3. The laminated polyester film for food containers according to claim 1 or 2, wherein the poorly gas permeable material is an aluminum foil or a metalized aluminum film. 4. The laminated polyester film for food containers according to any one of claims 1 to 3, wherein the flexible polymeric material is polyethylene, polypropylene, polyetherester elastomer, paper, or the like. 5. Claim 1, in which a biaxially stretched polyester film is laminated on the surface of a material with low gas permeability.
The laminated polyester film for food containers according to any one of items 1 to 4. 6. According to any one of claims 1 to 5, each layer or some of the layers of the polyester film, flexible polymeric material, and poorly gas permeable material are adhesively laminated using an adhesive. Laminated polyester film for food containers. 7. Claim 1, in which the layers or some of the layers of the polyester film, flexible polymeric material, and poorly gas permeable material are laminated by coextrusion.
The laminated polyester film for food containers according to any one of items 6 to 6.