JP2001270935A - Polyester resin for can inner coating - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an organic-film-coated metal sheet which has a coating film excellent in adhesiveness, blister resistance, whitening resistance, flavor characteristics, etc., and can be formed into DI cans, DR cans, and DRD cans and to provide a polyester resin for a coating agent which can give the above coated metal sheet. SOLUTION: This polyester resin for can inner coating has such characteristics that terephthalic acid accounts for 60-100 mol% of the acid component and that propylene glycol accounts for 40-100 mol% of the glycol component.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyester resin for coating the inner surface of a can, and more particularly, to a polyester resin and can for an organic film-coated metal plate which can be formed into a two-piece can such as a drawn ironed can or a redrawn can. The present invention relates to an organic film coating for use.

[0002]

2. Description of the Related Art An organic coating for the inner surface of a metal can is used for the purpose of preventing corrosion of metal as a material of the can and not impairing the flavor and flavor of the contents.
It is required to have no toxicity, to withstand heat sterilization, to have a small mass of eluate, and to have good adhesiveness and workability.

[0003] Drink cans and food cans are classified into so-called three-piece cans and two-piece cans according to the method of making them. In recent years, two-piece cans have been increasing due to an increase in demand for beer, juice, carbonated beverages and the like. . Two-piece cans are called side seamless cans and are made by drawing a metal material such as an aluminum plate, tin plate, or tin-free steel plate.
Ironing etc. is performed, and it is molded into a cup consisting of a seamless trunk and a seamlessly integrated bottom,
Depending on the molding method, it can be divided into drawn iron cans (DI cans), drawn cans (DR cans), and redrawn cans (DRD cans). As a method of coating a two-piece can with an organic film, generally, a method of coating a molded can with a coating agent is often used, but recently, a synthetic resin film is preliminarily laminated on a metal material before molding. It is also known to use a method and a metal plate coated with a coating agent such as vinyl organosol, epoxy phenol or acrylic.

However, the former method requires a step of laminating a polyethylene terephthalate film with an adhesive, for example, and increases the cost, so that the latter method is desirable. However, since vinyl organosol-based coating agents are mainly composed of vinyl chloride polymers, problems of hygiene, can recycling, and environmental pollution have been pointed out. Epoxy-phenol-based and acrylic-based coating agents can not follow the elongation and deformation in the molding process during can-making, causing cracks and peeling in the coating film. There is a drawback that it is significantly reduced by processing.

[0005]

That is, DI cans and D cans
In the manufacturing process of the RD can, the coating film formed in advance is susceptible to mechanical damage, peeling of the coating film and decrease in adhesion are recognized, and this defect is remarkable in the heat sterilization process after filling the can contents. And cannot be used as food cans or beverage cans. Polyester resins have been studied for application to metal can inner surface coatings because of their excellent metal adhesion and few hygiene problems.However, they can withstand the severe molding process described above and have blister resistance during heat sterilization. At present, polyester resin-based coating agents having excellent whitening resistance have not yet been obtained. Accordingly, an object of the present invention is to provide a metal sheet coated with an organic film which is excellent in adhesion, blister resistance, whitening resistance, flavor and the like, and can be formed into a DI can, DR can, or DRD can. And to provide a polyester for a coating agent which makes it possible.

[0006]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies in order to solve the above-mentioned problems, and as a result, a system in which a specific polyester resin mainly containing terephthalic acid as an acid component and propylene glycol as a glycol component is blended. It has been found that the intended purpose can be achieved when a cured film is used as the coating agent of the present invention, and the present invention has been achieved. That is, according to the present invention, the acid component is terephthalic acid 60 to 100 mol%, and the glycol component is propylene glycol 40 to 10
It is a polyester resin for coating the inner surface of a can, which is 0 mol%.

Since the metal plate obtained in the present invention is covered with the above-mentioned specific organic cured film, it has excellent metal adhesion even after the can is formed, and also has a blister resistance during heat sterilization. And excellent whitening resistance.

The polyester resin (A) used in the present invention
Is terephthalic acid 60 to 100 as a dicarboxylic acid component
Mol%, preferably 65 to 100 mol%, more preferably 75 to 100 mol%, 0 to 40 mol%, preferably 0 to 35 mol%, more preferably 0 to 25 mol% of dicarboxylic acids other than terephthalic acid.

Examples of the dicarboxylic acid component other than terephthalic acid include aromatic dicarboxylic acids such as isophthalic acid, orthophthalic acid, 5-sodium sulfoisophthalic acid, and naphthalenedicarboxylic acid. Aliphatic dicarboxylic acids include succinic acid and adipic acid. , Azelaic acid, sebacic acid, dodecane dicarboxylic acid, dimer acid and the like, and alicyclic dicarboxylic acids such as hexahydroterephthalic acid and hexahydrophthalic anhydride.

The polyester resin (A) used in the present invention
In the case of less than 60 mol% of terephthalic acid and more than 40 mol% of dicarboxylic acid components other than terephthalic acid, the whitening resistance decreases. When an aliphatic dicarboxylic acid is used in combination as a dicarboxylic acid other than terephthalic acid, the content of the aliphatic dicarboxylic acid component is preferably within 30 mol%, more preferably within 20 mol%. The polyester resin (A) used in the present invention has a glycol component of 40 to 100 mol% of propylene glycol, preferably 60 to 9 mol%.
It consists of 9 mol% and 40 to 0 mol% of glycols other than propylene glycol, preferably 40 to 1 mol%.

The glycols other than propylene glycol include ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,3-butanediol, 1,5-pentanediol, 1,6-hexanediol, Pentyl glycol, diethylene glycol, dipropylene glycol, 1,4-cyclohexanedimethanol, p-xylylenediglycol, 2,2-
Dimethylol butane, 3,3-dimethylol heptane,
Examples include tricyclodecane dimethanol, 1,9-nonadiol, and an ethylene oxide or propylene oxide adduct of bisphenol A.

The polyester resin (A) used in the present invention
Means that the propylene glycol component is less than 40 mol% and the glycol components other than propylene glycol are 60 mol%
If it exceeds 3, the whitening resistance is lowered, and the object of the present invention cannot be achieved.

The polyester resin (A) used in the present invention
Is 3 other than the above-mentioned dicarboxylic acid component and glycol component.
It is preferable to copolymerize a polycarboxylic acid or polyol having a functionality of at least 0.1 to 3.0 mol% based on the total acid component or glycol component. Examples of the trifunctional or higher polycarboxylic acid include trimellitic anhydride and pyromellitic anhydride, and examples of the polyol include glycerin, trimethylolethane, trimethylolpropane, and pentaerythritol. 0.1 mol% of the above polycarboxylic acid or polyol component
If it is less, it is difficult to obtain a polyester resin having a high reduced viscosity,
If it exceeds 3 mol%, the coating film may become brittle.

The polyester resin (A) used in the present invention
Is preferably 0.3 or more. If the reduced viscosity is less than 0.3, the adhesion to metal is reduced, and a coating film with high elongation cannot be obtained, so that whitening resistance and corrosion resistance are significantly deteriorated. Further, the polyester resin in the present invention has a solubility parameter (SP value) of 10.5 or more,
A specific gravity of 1.25 or more is preferable because it is more effective for the use of the metal plate of the present invention.

In the present invention, it is preferable to use an alkyl etherified amino formaldehyde resin (B) in combination. Examples of the alkyl etherified aminoformaldehyde resin (B) include formaldehyde or paraformaldehyde alkylated with an alcohol having 1 to 4 carbon atoms such as methanol, ethanol, n-propanol, iso-propanol, and n-butanol. It is a condensation product with urea, N, N'-ethylene urea, dicyandiamide, aminotriazine and the like, and specifically, methoxylated methylol urea, methoxylated methylol-N, N'-ethylene urea, methoxylated methylol dicyandiamide, methoxy Methylol melamine, methoxylated methylol benzoguanamine, butoxylated methylol melamine, butoxylated methylol benzoguanamine, and the like. In particular, it is desirable to use a benzoguanamine compound.

In the present invention, the mixing ratio of the polyester resin (A) and the alkyl etherified amino formaldehyde resin (B) is 9 (polyester resin (A): alkyl etherified amino formaldehyde resin (B)).
It is preferably from 9: 1 to 70:30 (weight ratio), more preferably from 99: 1 to 75:25 (weight ratio), even more preferably from 99: 1 to 90:10 (weight ratio). This is the rate at which the elongation of the coating after the reaction with (B) becomes larger than that of the coating formed alone. If the compounding ratio of the alkyl etherified amino formaldehyde resin exceeds this range, the coating film becomes brittle, and not only is it difficult to draw and redraw or redraw, but also the flavor is poor, and a metal can with corrosion resistance cannot be obtained. There is. When the alkyl etherified aminoformaldehyde resin (B) is not used or when the amount used is too small, the strong elongation of the coating film may be reduced. Tensile rupture strength of cured film is 5
Kg / mm ² or more and tensile elongation at break are preferably 5% or more. By blending the alkyl etherified amino resin, the flavor property, for example, the amount of adsorbed D-limonene is reduced, and good results are obtained. That is, as described later (paragraph number 002)
Even in a severe D-limonene adsorption test as in 9), it is possible to achieve extremely excellent flavor such that the D-linen adsorption amount is 10 mg / g or less.

In the present invention, the polyester resin (A) and the aminoetherified aminoformaldehyde resin (B) are usually dissolved in an organic solvent, applied as a liquid coating agent to a metal plate, and dried or cured. Known organic solvents such as toluene, xylene, ethyl acetate, butyl acetate, methyl ethyl ketone, cyclohexanenone, isophorone, Solvesso # 100 and Solvesso # 150 can be used as the organic solvent, and are appropriately selected in consideration of solubility and evaporation rate.

The metal plate used in the present invention includes:
Surface-treated steel sheets, aluminum sheets, aluminum alloy sheets, etc., which have been subjected to surface treatments such as aluminum plating, zinc plating, tin plating, nickel plating, and chromic acid treatment, can be used. Use

In the present invention, the coating of the metal plate is carried out at least on the inner surface side of the metal plate by a known method such as a roll coating method, a spray coating method, a dip coating method and the like. 1 second ~
Dry or cure for 60 minutes. The thickness of the dried or cured coating film is not particularly limited, but is generally in the range of 3 to 50 μm, preferably 5 to 30 μm.

When a coating film is formed on one surface of a metal plate, it is formed on at least the inner surface. However, even if the coating film is the same on both surfaces (in a can, the inner and outer surfaces) of the same coating agent (coating composition), it is also different. It may be something. The coating agent used in the present invention can contain a known colorant or pigment for the purpose of hiding the metal plate or adjusting the mechanical strength of the coating film. For example, titanium dioxide, zinc white, Examples thereof include barium sulfate, calcium carbonate, talc, silica powder, aerosil, alumina, and carbon black. Examples of organic pigments include phthalocyanine green and toluidine red. These pigments can be blended in an amount of 0.1 to 200% by weight, particularly 0.5 to 150% by weight, based on the polyester resin.

The coating agent used in the present invention includes a surface smoothing agent for improving the smoothness of the coating film, an antifoaming agent and a surfactant for preventing pinholes and repelling of the coating film, and a slipperiness of the coating film. A slip agent, a curing catalyst, a thixotropic agent and the like for improving the viscosity.

In the step of obtaining the organic coated metal plate of the present invention, a primer layer such as a urethane-based, polyester-based, polyamide-based or epoxy-based primer may be provided for the purpose of improving the adhesion to the metal substrate.

Using the organic coated metal plate of the present invention, in a two-piece can, a step of punching into a disk having a size taking into account the drawing ratio and ironing rate, and then drawing and forming into a shallow drawn cup shape; Further, after the redrawing process or the redrawing process, the ironing process is performed to form a drawn ironed can or a redrawn can.

The can after molding is subjected to processing such as doming, neck-in, flange processing, printing and the like to obtain a two-piece can body. The drawing ratio and the ironing ratio may be determined in consideration of the type of the metal material, the shape of the can, and the like. In the above-mentioned processing, heating processing at an appropriate temperature may be appropriately performed in order to increase the formability of the organic film.

The drawn ironing can or redrawn can obtained from the coated metal sheet of the present invention is made of a specific polyester resin (A) obtained by copolymerizing terephthalic acid and propylene glycol as main components and trivalent polycarboxylic acid or polyol. Since it is molded from an organic coated metal plate coated with a film of a reaction product with the alkyl etherified formaldehyde resin (B),
It has excellent adhesiveness to metal and excellent corrosion resistance, and has sufficient resistance in the heat sterilization process, and has the advantage of eliminating the trouble of painting cans after molding. Can be used as

[0026]

EXAMPLES The present invention will be described in detail with reference to examples, but the present invention is not limited to the examples. In the examples, “parts” means “parts by weight”.

Preparation of Coating Agent 300 parts of various polyester resins shown in Tables 1 and 2 and cyclohexanone 700
Then, a predetermined amount of an alkyl etherified aminoformaldehyde resin, p-dodecylbenzenesulfonic acid as a curing catalyst and a surface smoothing agent were blended to prepare various coating agents for use in the present invention. Tables 3 and 4 show the compositions of the prepared coating agents.

[0028]

[Table 1] (Note) 1) The composition is the value analyzed by NMR analysis and gas chromatography by alcoholysis. 2) Glass transition temperature: value by DSC analysis. 3) Reduced viscosity: phenol / tetrachloroethane (6 /
(4 weight ratio) Measured value by solvent (0.1 g / 25 ml concentration, 30 ° C.).

[0029]

[Table 2] (Note) 1) The composition is the value analyzed by NMR analysis and gas chromatography by alcoholysis. 2) Glass transition temperature: value by DSC analysis. 3) Reduced viscosity: phenol / tetrachloroethane (6 /
(4 weight ratio) Measured value by solvent (0.1 g / 25 ml concentration, 30 ° C.).

[0030]

[Table 3]

[0031]

[Table 4]

Evaluation of Coating Film (Coating Film) of Molded Can (1) Appearance: The state of the coating film on the inner surface of the molded can was visually judged. (2) Adhesion: A test piece was cut out from a molded can and evaluated by a peeling test using a cellophane cellotape (registered trademark). (3) Whitening resistance and blister resistance: Visually determine the appearance of the coating film after treatment in steam at 130 ° C. for 30 minutes.
□: Almost good △: Slightly poor ×: Poor (4) Corrosion resistance: A carbonated beverage is rolled and filled in a molded can at 30 ° C.
The container was stored for one year under the conditions described above, and the corrosion state and leakage of the inner surface of the can were observed. ○: No abnormality △: Slight corrosion ×: Corrosion, leakage

(5) Flavor property: A coating agent is applied to a tin plate so as to have a dry film thickness of 50 μm.
After drying and curing at 0 ° C. for 60 seconds, the coating film is peeled off using mercury to form a film-like test piece (50 mm × 40 mm). The obtained film was immersed in a 95% aqueous solution of D-limonene and left at 37 ° C. for 10 days to measure the amount of D-limonene adsorbed (mg / g). (6) Tensile rupture elongation: A film-like test piece (15 mm × 30 mm) was obtained in the same manner as in the above (flavor property), and a tensile speed of 5 cm /
Measured in minutes.

Example 1 A coating agent No. shown in Tables 3 and 4 was applied to one side (inner side) of a tin-free steel metal plate having a thickness of 0.2 mm.
1 is roll-coated to a dry film thickness of 20 μm,
After drying and curing at 230 ° C. for 60 seconds, an organic coated metal plate used in the present invention was obtained. Apply palm oil to this coated metal plate,
After punching out into a disk, the plate was subjected to shallow drawing and redrawing according to a conventional method to obtain a redrawn can of the present invention having a cup diameter of 63 mm and a cup height of 100 mm. Table 5 shows the performance evaluation results of the obtained cans.

Examples 2 to 9 In the same manner as in Example 1, coating agents Nos. Using Nos. 2 to 9, a redrawn can of the present invention was obtained.
Tables 5 and 6 show the performance evaluation results of the obtained cans.

COMPARATIVE EXAMPLES 1-2 The coating agent Nos. Shown in Tables 3 and 4 were prepared in exactly the same manner as in Example 1. Using 10 to 11, a redrawn can was obtained. The results are shown in Tables 5 and 6.

[0037]

[Table 5]

[0038]

[Table 6]

[0039]

The organic coated metal plate obtained by the present invention contains terephthalic acid and propylene glycol as main components and has excellent adhesion to metal, so that the coating has high adhesion to metal, excellent corrosion resistance, and a heating step. And the complexity of painting the molded can is eliminated. In addition, since it is a polyester resin, the problem of hygiene is solved.

Claims (2)

[Claims] An acid component is terephthalic acid at 60 to 100 mol% and a glycol component is propylene glycol at 40 to 10 mol%.
A polyester resin for coating the inner surface of a can, which is 0 mol%. 2. A coated metal plate for a can, wherein a coating containing the polyester resin according to claim 1 is provided on at least an inner surface side.