JP2001062974A - Multilayer polyester film for hot laminating - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a film of superior bonding force even in the case of being placed under a hot and wet environment and suitable for the use to be stuck on a metal plate used for an aqueous content such as, for example, a beverage can. SOLUTION: A multilayer polyester film is formed of a plurality of layers, and at least one surface is constituted of a polyester layer provided with hot gluing properties, and the reflective index of the polyester layer is 1.580 or less and the equilibrium moisture content is 1500 ppm or less. Also the thickness of the polyester layer is 1 μm or less, and the polyester layer is composed of a polyester in which 10-35 molar % of the total ester unit is a 1,4- cyclohexanedimethylene terephthalate unit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyester film used as a composite material bonded to other materials such as plastic, metal, paper, cloth and wood.

[0002]

2. Description of the Related Art Polyester films are widely used as composite materials by laminating with various materials. For example,
In the field of beverage cans, there is an example of processing a laminated metal plate on which a polyester film is bonded as an organic coating for improving the corrosion resistance of a metal to obtain a can.

Conventionally, an adhesive, particularly a non-aqueous adhesive, has been generally used for bonding a polyester film to another material. However, from the viewpoint of refraining from using a large amount of an organic solvent, a polyester film is used. In many cases, thermal adhesion is imparted to a substrate, and the substrate is directly bonded to an adherend. Polyethylene terephthalate, which is the most widely used polyester as a film material, does not have sufficient thermal adhesiveness. Therefore, a general method is to impart thermal adhesiveness by copolymerizing other components such as isophthalic acid. However, in any case, the polyester is amorphous at the laminate interface.

[0004] Amorphized polyester is liable to be plasticized by water absorption, and when it is used as a case of contact with liquid water, for example, a laminate material coating layer used for beverage cans, the polyester film coating layer peels off. So-called feathering that does not break according to the score shape at the time of opening may occur. In particular, it is heated and stored at the time of distribution, such as coffee and tea, and the danger increases.

[0005]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an excellent adhesive force even when placed in a humid environment. An object of the present invention is to provide a film suitable for use in bonding to a metal plate used for a container of contents.

[0006]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies in view of the above problems, and as a result, have found that a multilayer film having a specific layer structure can easily solve the above problems, and have completed the present invention. I came to. That is, the gist of the present invention is a multilayer polyester film composed of a plurality of layers, at least one surface of which is composed of a polyester layer having a thermal adhesive property, the polyester layer has a refractive index of 1.580 or less, and equilibrium water content. Rate is not more than 1500 ppm in the multilayer polyester film for thermal lamination.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
The polyester in the present invention is a polymer in which repeating units are polycondensed with an ester bond. The repeating unit may have an ester bond. Rather, many of widely used polyesters use a condensate of a dicarboxylic acid and a diol as a repeating ester unit.

Examples of the dicarboxylic acids include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, phthalic acid, 2,6-naphthalenedicarboxylic acid and 2,7-naphthalenedicarboxylic acid, adipic acid, azelaic acid and sebacic acid. And the like. Examples of the diol include ethylene glycol, trimethylene glycol, tetramethylene glycol, 1,4-cyclohexanedimethanol, polyethylene glycol, polytetramethylene glycol, and the like.

In addition to these dicarboxylic acids and diols, those capable of forming an ester unit alone, for example, p-hydroxybenzoic acid and the like may be polycondensed. Moreover, the structure of the ester repeating unit obtained by condensing polyhydric carboxylic acids, such as trimellitic acid and pyromellitic acid, or polyhydric alcohols, such as glycerin, may be sufficient. The film of the present invention is composed of a polyester layer having at least one surface having thermal adhesiveness. The term "thermal adhesion" as used herein refers to the method of applying pressure and adhesion to a target adherend, for example, a metal at a temperature sufficiently higher than the glass transition temperature, so that the adhesive adheres to the adherend even after the temperature is lowered to room temperature. This is the characteristic that the state where the operation is continued. Specific examples of polyesters having thermal adhesiveness include copolymerized polyesters obtained by copolymerizing the above-mentioned various dicarboxylic acids or diols. For example, 90 to 60 mol% of the total acid component is terephthalic acid, 10 to 40 mol%.
Copolymerized polyethylene terephthalate in which mol% is isophthalic acid and the diol component is ethylene glycol can be exemplified.

[0010] The refractive index of the heat-adhesive polyester layer constituting at least one surface of the film of the present invention must be 1.580 or less. Refractive index is 1.
If it exceeds 580, even if it is amorphous, an oriented structure exists, and the fluidity at the time of heating decreases. Therefore, extra heat or pressure must be applied in order to increase the wetted area on the metal surface during bonding, which is not suitable because it may cause bonding failure.

The thermoadhesive polyester layer of the film of the present invention must have an equilibrium water content of 1500 ppm or less. If the equilibrium water content exceeds 1500 ppm, the heat-adhesive polyester layer tends to be deformed by moisture absorption at the bonding interface in a humid environment, and may be separated when a force is applied for some reason, which is not appropriate. . As an example of a material having thermal adhesiveness and an equilibrium water content of 1500 ppm or less, an ester unit in which terephthalic acid and 1,4-cyclohexane dimethanol are condensed, that is, 1,4-cyclohexane dimethylene terephthalate is 10% of all ester units And copolymerized polyethylene terephthalate which occupies ~ 35 mol%. Note that the equilibrium water content of the polyester does not substantially change after the raw material stage and processing into a film.

Since the heat-adhesive polyester layer of the film of the invention is amorphous, it is preferable to have a structural layer having a high molecular orientation structure and further an oriented crystal structure in order to have practical strength. . It is desirable that such a structural layer has a thickness of 80% or more of the total thickness, depending on the degree and thickness of the orientation. As a preferable standard for the orientation of the structural layer, 1.60 regardless of the refractive index of the film surface in any direction.
0 or more. The polyester constituting the structural layer is not particularly limited.However, when the heat-adhesive polyester layer is melt-amorphized by a heat treatment in the film manufacturing process, the heat-adhesive polyester is used so that the orientation is not lost and the crystals are not melted. It is desirable that the melting point is higher by at least 10 ° C. than that of the layer. Further, such a structure layer may be composed of a plurality of layers. For example, according to a three-layer structure in which a skin layer containing lubricant particles is laminated on a particle-free layer and a heat-adhesive polyester layer is provided on the side opposite to the skin layer, it is blended into the structural layer. It is preferable because it is possible to suppress a decrease in transparency due to lubricant particles and to form a highly transparent coating layer having a haze of less than 0.8%.

The thickness of the heat-adhesive polyester layer of the film of the present invention is preferably 1 μm or less. It is difficult to completely eliminate the moisture content of the heat-adhesive polyester layer, and plasticization due to a certain amount of water content is inevitable. Even in this case, the thickness of the layer that can be softened and deformed by plasticization is 1
By limiting the thickness to not more than μm, peeling can be made difficult.

The heat-adhesive polyester layer of the present invention may be a mixture of a plurality of polyesters. For example,
A polymer blend of polycyclohexane dimethylene terephthalate and polyethylene terephthalate comprising only 1,4-cyclohexane dimethylene terephthalate unit may be used in which the thermal adhesion and the equilibrium water content are within predetermined ranges.

Further, the crystallization rate of the heat-adhesive polyester layer of the present invention is preferably low. Even if it is amorphous at the film stage, in the bonding process,
This is because, when left in a temperature range where crystallization is possible for a long time, if the crystallization speed is not sufficiently low, crystallization may cause a decrease in adhesive strength. As a guide, if the melt which has completely lost its amorphous structure at 300 ° C. is cooled at a cooling rate of −10 ° C./min while noting the decrease in molecular weight due to hydrolysis, if the temperature does not drop and crystallize, It is enough.

As a method of reducing the crystallization rate, there is a method of reducing the crystallinity by increasing the copolymer composition ratio. However, if the copolymer composition ratio cannot be set high due to the demand for characteristics, the catalyst residue serving as a crystal nucleating agent is removed. By reducing, it is possible to reduce the crystallization rate to some extent. In this case, the amount of the catalytic metal element is desirably 10 ppm or less, and a titanium compound such as tetrabutyl titanate or tetrapropyl titanate is used as a main polymerization catalyst in order to enable polymerization with such a low catalyst system. Is recommended.

Various organic compounds and inorganic compounds can be added to the film of the present invention as long as its properties are not impaired. For example, inorganic particles such as silica, alumina, titanium oxide, kaolin, calcium carbonate, calcium phosphate, and clay, and organic materials containing styrene, acrylic acid, and the like are used as nuclei of surface protrusions formed for imparting slipperiness. Particles such as particles may be added. In addition, dye
A coloring agent such as a pigment, an antistatic agent, a plasticizer, and an ultraviolet absorber may be added.

[0018]

EXAMPLES Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited to the following examples unless it exceeds the gist. In the following examples, “parts” means parts by weight. (1) In-plane refractive index of film An Abbe refractometer manufactured by Atago was used. Methylene iodide was mounted and the sample film was adhered to the prism, and the in-plane refractive index was measured using monochromatic sodium D-ray as a light source. The prism is brought into close contact with the side opposite to the heat-adhesive polyester layer. (2) Equilibrium water content [ppm] Excluding the target layer was removed by plasma ashing to obtain only the layer to be measured, and 1.000 g of the layer was measured at room temperature 23 ° C., relative humidity 50%, and atmospheric pressure for 2 days. It was left and conditioned. Water vaporized from the sample was collected and quantified at 230 ° C. for 10 minutes under a flow rate of dry nitrogen of 300 cc / min, and the weight ratio of water to the original sample was defined as the equilibrium water content. The measurement was performed using a trace moisture meter VA-05 manufactured by Mitsubishi Chemical Corporation. (3) Adhesive layer thickness [μm] After providing a film of about 100% gold on both sides of the film, the one embedded in epoxy resin is cut into thin pieces with an ultramicrotome, and the cross section is observed with a scanning electron microscope and bonded. The layer thickness was determined. (4) Ester composition ratio [mol%] A sample is dissolved in a deuterium trifluoroacetate solvent, and H-NMR measurement is performed using GX-270 manufactured by JEOL Ltd. to obtain an integral curve of each peak. The composition ratio of each ester unit was determined from the integral curve. (5) Melting point of each layer [° C.] Excluding the target layer was removed by plasma ashing to obtain only the layer to be measured. 10 mg of the obtained sample was measured by MDSC2920 manufactured by TA Instruments.

That is, after equilibrating at 300 ° C., a sample was taken out, immersed in liquid nitrogen and quenched.
The measurement was performed at a temperature rising rate of 3 ° C./min in the range of 00 ° C., and the peak temperature of the crystal melting endothermic peak was defined as the melting point. (6) Adhesiveness The sample film was bonded with a table laminator VA-700 made by Taisei Laminator at a bonding speed of 1 m / min at a nip roll temperature of 170 ° C. and a nip roll air pressure of 0.3 M.
As Pa, it was press-contacted to both surfaces of an aluminum plate having a thickness of 200 μm and a width of 200 mm. The obtained sample was subjected to a heat treatment at 230 ° C. for 2 minutes in a nitrogen atmosphere in a hot air oven to obtain a laminate.

In a DuPont impact tester manufactured by Tester Sangyo,
Dent was formed on the laminated material with the tip R having a 3/16 inch, a falling weight of 500 g, and a falling distance of 30 cm. This was sealed together with 300 ml of pure water in a pressure-resistant tube having an inner volume of 350 ml, immersed in an oil bath and heated at 121 ° C. for about 2 hours.
The retort treatment was performed for 30 minutes while maintaining the internal pressure of the atmospheric pressure. The laminated material after the retort was taken out, and the adhesiveness was classified into the following three levels according to the state of film peeling at the dents.

：: The film at the dents portion was not peeled at all. Δ: The film was peeled at a part of the dents portion. X: The film was peeled over the entire surface of the dents portion. [Production of Polyester] Polyester A 100 parts of dimethyl terephthalate , Ethylene glycol 6
After charging 0 parts and purging with nitrogen, 225 mol of titanium tetrabutoxide was added as a titanium element amount, and the temperature was raised to 240 ° C. over 2 hours in a nitrogen atmosphere, and further 2 hours.
After transesterification by holding at 40 ° C. for 1 hour, an ethylene glycol slurry containing amorphous silica was added, and further, an equimolar mixture of ethyl phosphate and diethyl phosphate was added in an amount of 440 mol as a phosphorus element amount. Then, 370 mol of cobalt acetate tetrahydrate was added as an elemental amount of cobalt, and 300 mol of germanium dioxide was added as an elemental amount of germanium.

Thereafter, the pressure of the system was reduced to 1 mmHg in 1 hour and 25 minutes, and the temperature was raised from 20 minutes after the start of the pressure reduction, and finally the polymerization reaction was carried out at 270 ° C. The polymerization was completed 3 hours and 16 minutes after the start of the pressure reduction, and polyester A was obtained. The silica content was 600 ppm. Polyester B (Ti-based CHDM 15 mol%) 100 parts of dimethyl terephthalate, ethylene glycol 6
0 parts and 1,4-cyclohexanedimethanol 1
A polyester B was obtained in the same manner as the polyester A except that 1.1 parts were charged.

Polyester C (Ti-based CHDM 30 mol%) The charge amount of 1,4-cyclohexanedimethanol was 1
Polyester B except that 22.3 parts were used instead of 1.1 parts
Polyester C was obtained in the same manner as described above. Polyester D (Ti-based IPA 30 mol%) Polyester D was obtained in the same manner as Polyester A except that 70 parts of dimethyl terephthalate and 30 parts of dimethyl isophthalate were used instead of 100 parts of dimethyl terephthalate.

Example 1 Polyester A and polyester B were melt-extruded at 280 ° C. using different extruders, and were merged and extruded in a T-die at a discharge ratio of 17: 1. The extruded molten sheet was quenched below the glass transition temperature on a cast drum to form a substantially amorphous sheet. Subsequently, the amorphous sheet was 3.6 mm long at 85 ° C.
Double stretching was performed to obtain a uniaxially stretched film. This uniaxially stretched film was placed in a transverse direction at 100 ° C. 4.0 with a tenter stretching machine.
The film was double-stretched, heat-fixed at 240 ° C. while the width was fixed, relaxed 5% in the width direction at 200 ° C., cooled to room temperature, and wound up to obtain a film having a total thickness of 9 μm.

Example 2 A film having a total thickness of 9 μm was obtained in the same manner as in Example 1 except that a mixed polyester prepared by mixing equal parts of polyester A and polyester C was used instead of polyester B. Comparative Example 1 A film having a total thickness of 9 μm was obtained in the same manner as in Example 1 except that the heat setting temperature was changed to 210 ° C. instead of 240 ° C.

Comparative Example 2 A film having a total thickness of 9 μm was obtained in the same manner as in Example 2 except that polyester D was used instead of polyester C in the mixed polyester of polyester A and polyester C. Example 3 A film having a total thickness of 9 μm was obtained in the same manner as in Example 1 except that the discharge amount ratio between the polyester A and the polyester B was 2: 1.

The results obtained are summarized in Table 1 below.
Shown in

[0028]

[Table 1] Table 1 ──────────────────────────────────── contact adhesive layer structure layer adhesion Refractive index Equilibrium thickness Copolymer composition ratio Melting point Refractive index Thickness Melting point Water content μm Component ℃ ℃ ──────────────────────────────実 施 Example 1 1.576 1300 0.5 x 15 220 1.655 8.5 255 ○ Example 2 1.574 1400 0.5 x 15 230 1.655 8.5 255 ○ Example 3 1.575 1400 3.0 x 15 230 1.649 6.0 255 △ Comparative Example 1 1.621 1300 0.5 x 15 230 1.655 8.5 255 × Comparative Example 2 1.575 3000 0.5 y 15 230 1.655 8.5 255 × ───────────────────────────── ─────── (copolymer components other than ethylene terephthalate) x: 1,4-dichlorohexane dimethylene terephthalate y: ethylene isophthalate

[0029]

The polyester film for heat lamination of the present invention has excellent adhesive strength even when placed in a humid environment, and is used, for example, for bonding to a metal plate used for containers for aqueous contents such as beverage cans. And its industrial value is high.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4F100 AK41A AK41B AK41C BA02 BA03 BA07 BA10B BA10C EH20 GB90 JL12 JL12B JL12C JN18B JN18C YY00B YY00C

Claims (3)

[Claims] 1. A multilayer polyester film comprising a plurality of layers, at least one surface of which is composed of a polyester layer having thermal adhesiveness, wherein the polyester layer has a refractive index of 1.580 or less and an equilibrium water content of 1500 ppm.
A multilayer polyester film for thermal lamination characterized by the following. 2. The multilayer polyester film for thermal lamination according to claim 1, wherein the thickness of the polyester layer having thermal adhesiveness is 1 μm or less. 3. The polyester layer having thermal adhesiveness according to claim 1, wherein 10 to 35 mol% of the total ester units are polyesters of 1,4-cyclohexane dimethylene terephthalate unit. The multilayer polyester film for heat lamination according to the above.