JPH0236386B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a polyester film with excellent gas barrier properties.

Polyester stretched molded products such as polyethylene terephthalate film and polyethylene terephthalate containers have excellent functional properties, dimensional stability, heat resistance,
It has excellent chemical resistance, transparency, gloss, moisture permeability, gas barrier properties, fragrance retention, safety and hygiene properties, and is being used not only for food but also as packaging for detergents, chemicals, etc. . Particularly in the food packaging field, polyethylene terephthalate has begun to be used not only for conventional general foods, but also for carbonated drinks, alcoholic drinks, fruit juice drinks, soybean oil, sauces, dressings, edible oils, etc., taking advantage of the properties of polyethylene terephthalate. . For these food applications, properties such as moisture permeability, oxygen gas barrier properties, carbon dioxide gas barrier properties, and aroma retention are important, and it is desired that these properties of current polyester stretch molded products be further improved. has been done.

Methods for improving the gas barrier properties of polyester stretched films include increasing the thickness of the film and forming multilayer polyester with resins other than polyester. One method is to apply vinylidene resin.
However, the adhesion between the polyester film and the vinylidene chloride resin is poor, and in particular, the water-dispersible vinylidene chloride resin contains a surfactant for stabilizing the emulsion, so the adhesion between the polyester film and the polyester film is poor. In order to improve such defects, for example, Japanese Patent Publication No. 49-37584, Japanese Patent Publication No. 50-28119, Japanese Patent Publication No. 50-28120, and Japanese Patent Publication No. 50-28120 provide an undercoat layer between the polyester film layer and the vinylidene chloride resin layer. Publication No. 50-35473 has been proposed. However, these methods use organic solvents as the solvent for the undercoat, which poses problems such as occupational safety and health, pollution control, resource and energy conservation, and residual solvent for food packaging applications. There is also the problem of high production costs due to the process of applying vinylidene chloride resin.

The present inventors conducted various studies to solve these drawbacks, and as a result, they arrived at the present invention. That is, the gist of the present invention is to produce a laminated polyester film by applying a coating liquid consisting of a water-dispersible polyester resin containing a sulfonic acid group and a water-dispersible vinylidene chloride resin to at least one side of a polyester film, and then stretching the coating solution. Exists on film.

The polyester constituting the base film in the present invention preferably has 90 mol% of its structural units.
The above are polyesters that are ethylene terephthalate.

Furthermore, the water-dispersible resin used in the present invention has various dispersion states depending on its molecular weight or the properties of the resin, and in some cases may be substantially dissolved in water. Therefore, the meaning of water dispersibility is not strict, and includes resins that are normally used in water as a medium.

The water-dispersible polyester resin having a sulfonic acid group in the present invention refers to Japanese Patent Publication No. 47-40873,
Examples include polyester resins known in JP-A-50-83497, JP-A-50-121336, and JP-A-52-155640, or polyester resins similar thereto. For example, the dicarboxylic acid component of the polyester resin includes aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, 2,5-naphthalene dicarboxylic acid, and ester-forming derivatives thereof, adipic acid, azelaic acid, sebacic acid, and esters thereof. Aliphatic dicarboxylic acids such as formable derivatives, oxymonocarboxylic acids such as oxybenzoic acid and ester-forming derivatives thereof, and the like can be used, but are not limited thereto.

Glycol components of polyester resin include ethylene glycol, 1,4-butanediol, diethylene glycol, triethylene glycol,
Aliphatic, alicyclic, aromatic diols such as 1,4-cyclohexanedimethanol, P-xylene diol, polyethylene glycol, polypropylene glycol, polytetraethylene glycol, etc. can be used, but are not limited to these. do not have.

The method for introducing a sulfonic acid group into a polyester resin uses a compound having an ester-forming sulfonic acid group together with the above-mentioned polyester forming component. Examples of compounds having a sulfonic acid group include metal salts such as sulfoisophthalic acid, sulfoterephthalic acid, 4-sulfonaphthalene-2,7-dicarboxylic acid and ester-forming derivatives thereof; As such, lithium, sodium, potassium, magnesium, etc. can be used, but the present invention is not limited to these. A very suitable compound having a sulfonic acid group is 5-sodiosulfoisophthalic acid or 5-sodiosulfodimethylisophthalate.

Another method for introducing sulfonic acid groups into polyester resins is to sulfonate the unsaturated groups of polyester containing an ester-forming aliphatic unsaturated compound as a copolymerization component with a sulfonating agent such as sodium bisulfite or sodium metabisulfite. It is also possible to exemplify a method of The amount of aromatic dicarboxylic acid in the dicarboxylic acid component of the polyester resin is preferably in the range of 50 mol% to 100 mol%. This is to increase the softening point or glass transition temperature of the polyester resin, improve blocking properties, and obtain mechanical strength.

The sulfonic acid group in the polyester resin must be present in the amount necessary to make the resin water-dispersible, and the dicarboxylic acid having the sulfonic acid group is used in the range of 2 mol% to 20 mol% of the dicarboxylic acid. It is preferable to do so. If the amount of sulfonic acid base is less than 2 mol%, the water dispersibility will be insufficient;
If the amount of sulfonic acid base is larger than that, there are problems such as water resistance of the coating layer and blocking due to moisture absorption.

Furthermore, as polyester resins, in addition to the saturated linear polyesters made of polyester-forming components mentioned above, polyesters made of compounds having trivalent or higher ester-forming components or polyesters having reactive unsaturated groups can also be used. can.

The water-dispersible vinylidene chloride resin in the present invention refers to vinylidene chloride and its copolymer. Examples of copolymers include vinylidene chloride-acrylonitrile copolymer, vinylidene chloride-vinyl chloride copolymer, and vinylidene chloride-vinylidene chloride copolymer. Acrylic acid ester copolymer, vinylidene chloride-methacrylic acid ester copolymer, or acrylic acid,
Examples include those copolymerized with methacrylic acid, crotonic acid, etc.

In the present invention, the blending amount of the polyester resin is 1% by weight or more as a solid content based on the total amount of the polyester resin and vinylidene chloride resin. If the polyester resin content is less than 1% by weight, the adhesiveness between the polyester molded layer and the coating layer will be insufficient. Gas barrier properties depend on the characteristics of the vinylidene chloride resin, the thickness of the coating layer, and the content of vinylidene chloride resin in the coating layer, so it is difficult to set an upper limit for the amount of polyester resin blended. However, it is preferably 50% by weight or less, more preferably 20% by weight or less. For gas barrier properties, it is preferable that the amount of polyester resin blended is small, but in order to provide heat sealability as well as gas barrier properties, it is preferable to increase the blend amount of polyester resin.

It is preferable to mix the polyester resin and the vinylidene chloride resin before applying.The method for applying the mixed aqueous dispersion to the polyester film is the reverse roll method described in Yuji Harasaki, "Cortein Method," Maki Shoten (1979). A coater, gravure coater, rod coater, air doctor coater, etc. can be used.

Application of water dispersion to polyester film is as follows:
A water dispersion is applied to a uniaxially stretched polyester film using a roll stretching method, and the polyester film is immediately stretched in a direction perpendicular to the previous stretching direction without drying, and then heat treated. However, the laminated biaxially stretched polyester film of the present invention can be produced. According to this method, it is possible to dry the coating layer at the same time as stretching.

For example, the coating solution of the present invention is applied to a uniaxially stretched polyester film stretched by about 3.5 times at about 95°C, and the coating solution of the present invention is applied at about 110°C by 3.7 times in a direction perpendicular to the stretching direction.
The film of the present invention can be produced by stretching the film to about twice the original length and then heat-setting it at a temperature of about 200° C. for about 10 seconds.

The thickness of the coating layer applied to the polyester stretched film is selected depending on the required gas barrier properties, but is usually about 0.5 to 20 microns, more preferably about 1 to 10 microns. In terms of weight, it is 0.5 to 25g/m ²
Preferably it is about 1 to 12 g/m ² .

The coating layer may contain pigments, dyes, lubricants, blocking improvers, plasticizers, antistatic agents, stabilizers, antifogging agents, and the like.

The polyester stretched molded product of the present invention thus obtained has good gas barrier properties, heat sealability, and transparency, and can be suitably used for food packaging.

The present invention will be explained below with reference to Examples. In addition, the measurement apex in Examples was measured by the following method.

(1) Adhesion A cellophane tape made by Nichiban Co., Ltd. with a width of 18 mm was applied to a length of 7 cm to prevent air bubbles from forming on the coated layer surface of the polyester stretched molding that had been left in an atmosphere of 20°C and 65% RH for 24 hours. A constant load is applied on top of this using a 3 kg manual loading roll. The adhesion between the coating layer and the polyester layer was evaluated by fixing the molded product, connecting one end of the cellophane tape to a 500 g weight, and starting a peel test in a 180° direction after the weight was allowed to fall naturally over a distance of 45 cm. Adhesiveness was evaluated using the following 5-level criteria, and a rating of 4 or higher was considered a pass.

Evaluation 5: No peeling at all on the cellophane tape surface.

Evaluation 4: Less than 10% peels off from the cellophane tape surface.

Evaluation 3: 10 to 50% of the area peels off to the cellophane tape side.

Evaluation 2: 50% or more of the part peels off to the cellophane tape side.

Evaluation 1: Completely peeled off to the cellophane tape side.

(2) Heat sealing strength 1Kg/cm ² between coated film layers at 120℃
Heat sealed for 1 second at a pressure of . After leaving this film in an atmosphere of 20℃ and 65% RH for 24 hours, it was tested at a tensile speed of 200mm/200mm using a tensile tester.
The heat seal strength was measured by peeling at a peel angle of 180°.

(3) Gas barrier properties Gas permeability at 30°C was measured according to ASTM D-1434-63.

(4) Transparency According to ASTM D-1005-52.

Comparative Example 1 The oxygen gas permeability of a biaxially stretched polyethylene terephthalate film with a thickness of 12 μ is 168 c.c./m ³ ,
It was 24 hours/ATM. One side of this film was coated with Kurehalon DOA (trade name), a water-dispersible vinylidene chloride resin manufactured by Kureha Chemical Industry Co., Ltd., and dried in a hot air dryer at 80°C for 1 minute and then at 130°C for 1 minute. . The thickness of the coating layer was approximately 4 g/m ² . The oxygen gas permeability of this film is ^51c.c./m2 .
24hr/ATM was good. However, the adhesion between the coating layer and the polyester film layer was rated 1 in a peel test using cellophane tape, and the heat seal strength was 69 g/cm, and the transparency of the film deteriorated after hot water treatment at 95°C, making it practical for practical use. It was not a film that could be used.

Example 1 95 parts of Krehalon DOA (trade name), a water-dispersible vinylidene chloride resin manufactured by Kureha Chemical Industry Co., Ltd. (solid weight, same hereinafter), 50 mol% of terephthalic acid component, isophthalic acid in dicarboxylic acid Ingredients 43 mol%,
7 mol% of 5-sodiosulfoisophthalic acid,
A coating solution consisting of 5 parts of a water-dispersible polyester resin in which the ratio of ethylene glycol, diethylene glycol, and triethylene glycol in glycol is about 2:1 was applied to one side of a uniaxially stretched polyethylene tetophthalate film that had been stretched 3.5 times at 95°C. The film was then stretched 3.7 times at 110°C in a direction perpendicular to the previous stretching direction, and then heat-set under tension at 210°C for 10 seconds. The base thickness of the polyester film of this biaxially stretched film was about 12 μm, and the coating layer was about 4 g/m ² . Peel test of this film with cellophane tape gave a rating of 5, heat seal strength 205 g/cm, oxygen gas permeability 65 c.c./m ^2.24 hr.
ATM, had good transparency, and could be put to practical use.

Example 2 80 parts of Deiophan 207DC (trade name), a water-dispersible vinylidene chloride resin manufactured by Mitsubishi Yuka-Verdate Co., Ltd., 10 parts of the water-dispersible polyester resin used in Example 1, and 10 parts of alkylol melamine. A film was obtained in the same manner as in Example 1, except that a coating solution consisting of 1.5 mmol. The obtained film had a good oxygen gas permeability of 43 c.c./m ² ·24 hr ·atm.

Example 3 80 parts of Deiophan 207DC (trade name), a water-dispersible vinylidene chloride resin manufactured by Mitsubishi Yuka-Verdate Co., Ltd., and a water-dispersible polyester containing a sulfonic acid group manufactured by Dainippon Ink and Chemicals Co., Ltd. 10 parts of Feintex ES-670 (trade name), a resin based on
8 parts of alkylol melamine, Tospar 120 (trade name), silicone particles manufactured by Toshiba Silicone Corporation
The procedure was the same as in Example 1, except that a two-part coating solution was used instead of the coating solution in Example 1, and the thickness of the base polyester film was 12μ, and the thickness of the coating layer was 1.2μ.
I got this film. The obtained film had a good oxygen gas permeability of 49 c.c./m ² .24 hr.atm.

Claims (1)

[Claims] 1 On at least one side of the polyester film,
A laminated polyester film obtained by applying a coating liquid comprising a water-dispersible polyester resin containing a sulfonic acid group and a water-dispersible vinylidene chloride resin, and then stretching the film.