KR100215023B1 - Polyester film for bonding to metal plate - Google Patents

Abstract

The present invention relates to a polyester film for exterior metal bonding molding processing that has no defects when bonding with a metal plate, has excellent molding processability when forming after joining, and hides the color of the metal plate on the outside, and has excellent clarity when printing with colored ink. And precrystallization of copolyester containing ethylene terephthalate and ethylene isophthalate as the main repeating unit, containing 0.005-0.2% by weight of phosphoric acid-based compound and 5-30 mol% of isophthalic acid in the total acid component. It is characterized by being obtained by biaxial orientation.

Description

Polyester film for metal bonding molding processing {POLYESTER FILM FOR BONDING TO METAL PLATE}

The present invention relates to a polyester film for metal bonding molding processing. More specifically, there is no defect in joining with the metal plate, it shows excellent molding processability in the can manufacturing process such as drawing after joining, and also conceals the appearance of the color of the metal plate on the outside, and is excellent in sharpness when printing with colored ink. It relates to a polyester film for molding processing.

Metal cans are widely used for coating metal surfaces by dissolving or dispersing various thermosetting resins such as epoxy and phenol in organic solvents for the purpose of preventing corrosion of the inner and outer surfaces. Recently, a method for obtaining corrosion protection without using an organic solvent has been developed for the purpose of streamlining the process, hygiene and environmental pollution. As one of the methods, the coating | covering of the metal plate with a thermoplastic resin film is tried. That is, a lot of researches have been conducted on a method of manufacturing a can by drawing a thermoplastic resin film after bonding a thermoplastic resin film to a metal plate such as tin, tin free steel, or aluminum. The use of polyolefin films and polyamide films as such thermoplastic resin films was attempted, but these films did not satisfy all of moldability and heat resistance, steering properties, and the like of product cans.

On the other hand, polyethylene terephthalate in polyester is chemically and physically stable and excellent in mechanical strength, heat resistance, chemical resistance, etc., and is widely used in medical and food packaging. In particular, it is widely used in place of glass containers, such as bottles for beverages and foods, and various cosmetic containers. In order to use such polyethylene terephthalate film in the exterior of a metal can, the following characteristics are required:

(1) excellent adhesion to the metal plate;

(2) no defects such as deformation, discoloration and deterioration should occur during thermal bonding with the metal plate;

(3) excellent moldability, and no defects such as pinholes after molding;

(4) the film does not peel off, crack or pinhole due to impact on the metal can;

(5) It should have proper concealment property to prevent the color of metal plate from appearing on the outside and enhance the printing effect.

On the other hand, when the co-polyester resin is dried under ordinary polyester resin drying conditions, fusion occurs between the resin and between the resin and the inner wall of the dryer. Therefore, it is necessary to precrystallize the copolyester resin before entering the drying. In addition, resin fusion does not occur in the precrystallization process.

Accordingly, an object of the present invention is to show good molding processability in the can manufacturing process such as drawing, and to conceal the appearance of the color of the metal plate on the surface, and to show the appearance of the metal plate on the surface of the can. It is to provide an ester film.

In order to achieve the above object, the present invention contains 0.01-0.5% by weight of a fluorescent brightener, 5-25% by weight of inorganic particles having an average particle diameter of 0.1-3.0 μm, and 5-30 mol% of isophthalic acid components among all acid components. The present invention provides a polyester film for metal bonding molding processing, which is obtained by pre-crystallizing a copolyester having ethylene terephthalate and ethylene isophthalate as a main repeating unit and then biaxially oriented.

Hereinafter, the present invention will be described in more detail.

In the present invention, the copolyester is a polycondensation of an aromatic dicarboxylic acid component and a glycol component. Specific examples of the aromatic dicarboxylic acid include terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid, diphenoxyethanedicarboxylic acid, diphenyldicarboxylic acid, diphenyletherdicarboxylic acid, and the like. Of these, terephthalic acid and isophthalic acid are particularly preferred. Specific examples of the glycol component include ethylene glycol, propanediol, butanediol, pentanediol, hexanediol, neopentylglycol and the like. Of these, ethylene glycol is particularly preferable.

In addition to the above-mentioned components, well-known additives such as a polycondensation catalyst, a dispersant, an electrostatic agent, a crystallization accelerator, a nucleating agent, an antiblocking agent and the like do not impair the effects of the present invention. You may add in the range.

In the present invention, the copolyester resin should be precrystallized without fusion. Under vacuum, which is a conventional method, it is bad in terms of efficiency because it requires a long time at low temperature to perform precrystallization without fusion occurrence. Therefore, in the present invention, precrystallization is carried out in water. Conditions for precrystallization are preferably to satisfy the following formula (1) and (2) simultaneously.

75 T 115

370 3 T + t 430

Where T is the precrystallization temperature (° C)

t: precrystallization time (min)

When T is 75 ° C. or lower, the time required for precrystallization becomes too long, resulting in poor efficiency. When T is above 115 ° C., fusion occurs between resins and between the resin and the inner wall of the apparatus. If t is smaller than the lower limit in Equation 2, sufficient crystallization does not occur, so that fusion occurs in the drying process, and if it is larger than the upper limit, no further crystallization occurs over time, which is not preferable in terms of time. .

Fluorescent whitening agent used in the present invention absorbs light energy in the ultraviolet region (330-380 nm), and the energy is displaced into the short wavelength region (400-450 nm) of visible light and emits light. It serves to increase the visible light short wavelength reflectance. Fluorescent whitening agents such as coumarin-based, pyrazole-in-based, imidazole-based, triazole-based, naphthimide-based, etc. may be used, but stilbene-based or oxazole-based dyes may have heat resistance required for polyester production. As it is most suitable. The amount of the optical brightener is preferably 0.01-0.5% by weight so that the reflectance at 440 nm, which is the short wavelength region of visible light, is 75% to 95%. If the dose is less than 0.01% by weight, the increase in reflectance at 440 nm hardly occurs, and if the dose is more than 0.5% by weight, the reflectance at 440 nm becomes too high, causing the film to become bluish-white, causing adverse effects.

Inorganic particles used in the present invention imparts concealability and whiteness to the film and serves to improve the printing effect. To improve concealment, light scattering effects must be maximized, and light scattering is influenced by the spacing and average size of inorganic particles. If the particles are too large or the spacing is too small, the diffraction hardly occurs. If the inorganic particles are too small, light does not recognize the inorganic particles and just passes through them. Therefore, it is preferable that the average particle diameter of the inorganic particles used is slightly smaller than 1/2 of the wavelength of the light to be scattered. Titanium dioxide is preferable as the inorganic particles.

The whiteness of the film is preferably about 80-110%, preferably about 85-105%. If the whiteness is less than 80%, the film has a yellow color, so the printing quality is poor. If the whiteness is more than 110%, the film surface has a blue color. The light transmittance of the film is preferably 0.5-1.0%.

Therefore, the amount of the inorganic particles may be changed depending on the thickness and the use of the polyester film, 5.0-25% by weight based on the copolyester is suitable. More preferably 5.0-15% by weight. If the amount of the inorganic particles exceeds 25% by weight, the mechanical properties such as the strength and flexibility of the film are lowered, and the whiteness and the light transmittance are almost constant due to the increased amount, so that the effect of the large amount cannot be seen. In addition, when the input amount is less than 5% by weight, the light transmittance is 1.0% or more, the concealment is inferior.

In the present invention, the isophthalic acid component is 5-30 mol% based on the total acid component of the copolyester. If the isophthalic acid content is less than 5 mol%, the thermal adhesiveness with the metal plate is inferior and the crystallinity of the polymer is too large, resulting in poor post-processability. In addition, when the isophthalic acid content exceeds 30 mol%, the heat resistance is lowered, so that it cannot withstand the heat applied during printing after the can is manufactured.

The present invention will be described in more detail with reference to the following examples. However, the present invention is not limited to the following examples. Various performance evaluation on the film and process produced in Examples and Comparative Examples of the present invention was carried out by the following method.

(1) strength

Tensile strength measurements of films by ASTM D882 using an Instron UTM Model-4206 type.

(2) dryness

After precrystallization or drying, fusion is observed between the resin and the inner wall of the device.

○: no fusion

×: fusion occurs

(3) reflectance

Measurement of reflectance at 440 nm in visible light wavelength using a light source color difference meter (Japan Color Industry Co., Ltd., Model: SZS-Σ80).

(4) light transmittance

ASTM D1003 (Diameter: 25 mm, Scattering Angle: 2.5。)

(5) heat adhesiveness

The tin-free steel was heated to 180-230 ° C. and then faced to the film prepared in Example between two silicone rubber molds, pressed and bonded at a pressure of 25 kg / m and a speed of 120 m / min, followed by cooling in air. I was. Adhesion was measured by 180 degree peeling test of this laminated board.

(6) laminate properties

Observation of the appearance of the laminated film film

○: Good appearance (no wrinkles, breaks, shrinkage, etc. of the film).

×: appearance defects (wrinkling, breaking, shrinkage, etc. of the film).

Example 1

After mixing 89 mole% of terephthalic acid and 11 mole% of isophthalic acid as the acid component and ethylene glycol as the glycol component with respect to the total acid component in a ratio of 1 to 2 equivalents, adding a transesterification catalyst to produce a monomer, the average particle diameter of 0.3 μm 15% by weight of titanium dioxide, 0.08% by weight of an oxazole dye (CIFluorescent Brightener 135) and a common polycondensation catalyst were added to complete the polycondensation reaction to prepare a copolyester resin having an intrinsic viscosity of 0.70 dl / g and 120 minutes at 100 ° C. After precrystallization, the sheet was dried, melted, and extruded by a conventional method to form a sheet, followed by stretching at a ratio of 3.2 to 3.5 times the longitudinal stretch ratio and the lateral stretch ratio, respectively, to prepare a biaxially stretched polyester film having a thickness of 25 µm. The film thus prepared has excellent physical properties such as film strength of 19 kg / mm ² , reflectance of 87%, light transmittance of 0.7%, and heat adhesion of 502 g / cm, as shown in Table 1, and good dryness and appearance when laminated. It was.

Example 2-3

It was carried out in the same manner as in Example 1 except that the content of isophthalic acid, the amount of additives and the precrystallization conditions were changed as shown in Table 1. The physical properties of the film thus prepared were good in overall physical properties and appearance as shown in Table 1.

Comparative Example 1-10

It was carried out in the same manner as in Example 1 except that the content of isophthalic acid, the amount of additives and the precrystallization conditions were changed as shown in Table 1. The physical properties of the film thus prepared were poor in overall physical properties and appearance as shown in Table 1.

As described above, the polyester film prepared in the present invention is excellent in workability during molding processing by bonding to a metal plate, concealing the appearance of the color of the metal plate on the outside, and excellent in vividness when printing with colored ink.

Claims (2)

A polyester film comprising ethylene terephthalate and ethylene isophthalate as the main repeating unit, comprising 5-30% by weight of ethylene isophthalate of all repeating units, 0.01-0.5% by weight of optical brightener and 0.005-0.2 phosphate compound A white polyester film for metal bonding molding processing, comprising a weight-based, pre-crystallized in water under a condition that satisfies the following equations (1) and (2) simultaneously. Equation 1 75 T 115 Equation 2 370 3T + t 430 Where T is the precrystallization temperature (° C.) t: precrystallization time (min) The method of claim 1, Phosphoric acid-based compound is a film, characterized in that the phosphate-based or phosphite-based compound.