JP2006264734A - Drink aluminum can internal face-coating method and drink aluminum can coated by the method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide, in terms of a drink aluminum container internal face-coating method, an excellently-corrosion-resistant drink aluminum container that is excellent in gas barrier properties, anti-corrosiveness, alcohol-proofness, and heat resistance and prevents degradation in the quality and flavor of a drink, and to provide the coating film formation method. <P>SOLUTION: In the drink aluminum container and its manufacturing method, an internal face coating (1), as a first layer coating, which is excellent in processibility is applied to the internal face of the metal base of the bottomed, cylindrical drink aluminum container, then the container is subject to a necking process and a flanging process or a screwing process (including a curling process), and thereafter an internal face coating (2), as a second layer coating, which is excellent in corrosion resistance is applied to the face coated with the internal face coating (1). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an aluminum bottle can for beverages or an inner surface coating method for aluminum cans. More specifically, the present invention is excellent in gas barrier properties, corrosion resistance, alcohol resistance, heat resistance, and does not deteriorate beverage quality and flavor. The present invention relates to an aluminum bottle can for beverages or an aluminum can excellent in corrosion resistance and a method for forming the coating film.

  As beverage containers, aluminum bottle cans or aluminum cans are characterized by their sealing properties, shielding from external light, water, gas, etc., ease of handling during transportation or transportation, and vending machines. With the widespread use of this, it is very frequently used. The inner surface of these beverage aluminum bottle cans or aluminum cans is usually protected by a paint to prevent the influence of contact between aluminum or an aluminum alloy and the beverage as a content. In recent years, beverages filled in beverage aluminum cans have also diversified, there are many beverages that require hot packs and heat sterilization, and more beverages that are heated and sold in stores are also growing. The applicability required for aluminum cans for use is diversified and sophisticated.

  As the resin component of these paints, epoxy resins such as epoxy / urea resin compositions, epoxy / phenol resin compositions, epoxy / acryl / melamine resin compositions, epoxy / acryl / phenol resin compositions, etc. are mainly used. Components, polyvinyl chloride / polyvinyl chloride vinyl acetate / propionic acid or maleic acid copolymer / epoxy / phenolic resin composition (see, for example, Patent Document 1), polyvinyl chloride vinyl acetate copolymer / epoxy / Vinyl resins such as urea, as well as polyvinyl chloride, phenol resin, epoxy resin and acrylic resin copolymer (for example, see Patent Document 2), epoxy resin / acrylic resin copolymer / phenoxy resin Resin component consisting of epoxy resin / acrylic resin / phenolic resin (for example, patent text) 3 reference), and the like. From these resin compositions, select a resin composition suitable for the properties of the beverage to be filled and the handling conditions after filling the beverage, etc., and apply and bake this resin composition on the inner surface of the metal container to form a coating film And the metal container for drinks is manufactured.

In the conventional resin composition described above, in the case of soft drinks, beer, teas, mineral water, etc., there is not much problem when the epoxy resin composition is coated, but sulfurous acid gas (SO ₂ ) The gas barrier property with respect to ₂ ) is inferior and the sorption property of the flavor component is high. For example, when a wine-based beverage or the like is filled, sulfurous acid gas (SO ₂ ) contained in the wine may pass through the coating film of these resin compositions and corrode the underlying aluminum surface. It may leak. This sulfurous acid gas reacts with the base aluminum to generate hydrogen sulfide (H ₂ S). This hydrogen sulfide (H ₂ S) is not only bad smell but also sulfurous acid gas (SO ₂ ) necessary for maintaining the quality of beverages. _{Since 2} ) is consumed, the quality of the beverage is deteriorated and the flavor is impaired. In addition, this resin composition easily sorbs components characterizing flavor in beverages, and is not sufficiently satisfactory for coating on the inner surface of aluminum beverage cans or aluminum cans for beverages.

On the other hand, when the vinyl resin composition is coated, the gas barrier property against sulfurous acid gas (SO ₂ ) and the like is poor as in the case of the epoxy resin composition, and there is still a risk of corrosion and leakage and a sensory problem. In addition, since the resin composition has poor heat resistance, it suffers from a loss of flavor when subjected to a high temperature retort treatment by heat sterilization after filling or when heated at a relatively high temperature for a long time in a vending machine. There is.

  Also, when coated with polyvinyl chloride / vinyl chloride vinyl acetate / propionic acid or maleic acid copolymer / epoxy / phenolic resin composition, it has excellent gas barrier properties and good corrosion resistance, and flavor components Therefore, when wine-based beverages and other beverages are filled, it is satisfactory in terms of sensuality and does not lead to leakage. However, since the vinyl chloride paint is not a water-based paint, a large amount of the solvent in the paint volatilizes, deteriorating the working environment. In addition, there is a problem because dioxins are generated when aluminum cans are recycled.

  In addition, aluminum bottle cans or aluminum cans usually have a bottomed cylindrical body coated with only one layer of corrosion-resistant paint. Necking processing (diameter reduction processing) and flanging processing (mouth expansion processing) such as three-stage necking, four-stage necking or smooth necking. ) Or aluminum bottle cans are required to be threaded. To increase the corrosion resistance of the paint, if the resin component of the paint is hard, the corrosion resistance will improve, but necking and flanging or threading will not be possible. When the coating film adhesion is not sufficient, the coating film cracks and peels, and if it is made of a soft resin component in order to maintain processability, it is inevitable that the corrosion resistance will be insufficient. In particular, as a container for contents that generate corrosive gas such as sulfurous acid gas generated from wine or the like, it is required to simultaneously solve both the workability and the corrosiveness caused by the contents in the diameter reduction treatment. .

Japanese Patent Publication No. 03-075419 Japanese Patent Application Laid-Open No. 07-232737 JP 2005008166 A

In the conventional coating method using an internal paint, when a paint made of a resin component having a composition compatible with highly corrosive wine containing sulfurous acid is used as the resin component in the vehicle, the necking portion and the flanging or screw processing are used. The coating film adhesion of the part could not be supported, the coating film was peeled off, the sulfurous acid gas generated from wine caused blistering of the coating film, the aluminum was corroded, the sulfurous acid gas and aluminum reacted to generate hydrogen sulfide, The flavor of wine is impaired.
An object of the present invention is to provide an aluminum bottle can or aluminum can in which a coating film without cracking or peeling of the coating film and excellent gas barrier properties is formed in necking processing, flanging processing or screw processing, and a coating method thereof. And

The present invention changes a part of the current aluminum bottle can or aluminum can manufacturing process line, and necks the bottomed cylindrical body after the coating of the first layer paint having excellent coating adhesion (workability) And an aluminum can or aluminum can that can withstand severe corrosive conditions by flanging or screwing, and then applying a second layer paint film with excellent gas barrier properties onto the paint film. Is. [1] After applying the inner surface coating (1) with excellent processability as the first layer coating to the inner surface of the aluminum can metal base for beverage with a bottomed cylindrical shape, and performing necking and flanging or screwing , An aluminum can for beverages or an aluminum can coated with an inner surface paint (2) having excellent corrosion resistance as a second layer paint on the painted surface,

[2] Inner surface of the first layer coating material excellent in processability comprising an epoxy resin having an average molecular weight of 8000 to 30000 containing 10 to 40 wt% of phenoxy resin having an average molecular weight of 30000 to 65000 and containing 3 to 10 wt% of a phenol resin The beverage aluminum bottle can or aluminum can according to [1], which is a paint (1),
[3] The above-mentioned [1] or [2], wherein the second layer paint having excellent corrosion resistance is an epoxy internal paint (2) containing an epoxy resin having an average molecular weight of 8000 to 30000 and containing 10 to 30 wt% as a phenol resin. ] Aluminum beverage cans or aluminum cans for beverages, and

    [4] A bottomed cylindrical aluminum can metal base for beverages (bottomed cylindrical body) is coated with an epoxy-based inner surface paint (1) mainly composed of an epoxy resin containing a phenoxy resin and containing a phenol resin, After performing necking, flanging, or screw processing (including curling), this coating surface is further coated with an epoxy-based inner surface paint (2) mainly composed of an epoxy resin containing a phenol resin, and cured. The above-mentioned problems have been solved by developing an aluminum bottle can for beverages or a method for coating the inner surface of an aluminum can.

  In the present invention, in order to improve the gas barrier property, corrosion resistance, and heat resistance of the inner surface coating of the aluminum bottle can, in particular, the inner layer coating (1) having excellent processability is applied as the first layer coating, and then the corrosion resistance after screw processing. By coating the inner surface paint (2) excellent in the above, an aluminum bottle can having an ERV for workability evaluation and an excellent corrosion resistance evaluation could be obtained.

Hereinafter, an example of an aluminum bottle can and an aluminum can manufacturing process according to the present invention will be described with reference to FIG. 1, but the present invention method can also be applied to other can manufacturing processes.
Aluminum bottle cans and aluminum cans are made by punching a circular blank from an aluminum plate or aluminum alloy plate coated with lubricating oil wound in a coil shape, forming a cup with a press, etc., and then drawing and ironing (DI processing) ) To form a bottomed cylinder.

  Next, the lubricating oil on the inner and outer surfaces of the can body is removed, and a chemical conversion treatment is performed to form a chemical conversion film on the inner and outer surfaces of the bottomed cylindrical body, followed by drying. Thereafter, the outer surface of the bottomed cylindrical body is subjected to a size coat and its baking step, printing / overcoat and its baking step, as necessary, to become a bottomed cylindrical aluminum can metal base for beverages with an unpainted inner surface. Usually, the inner surface of the metal substrate is painted and hardened in a baking and drying furnace, and after necking and flanging, or in bottle cans, it is cleaned and dried through screw processing (including trimming and skirt molding), and then aluminum. Can (afterwards filling the contents and making the product through lid attachment) or aluminum bottle can, but in the present invention, after coating and curing the inner surface paint (1) excellent in workability, it is necked In addition, in the flanging process or the bottle can, it is washed and dried through a threading process, and further, the inner surface paint (2) excellent in corrosion resistance is applied and cured to obtain an aluminum can or an aluminum bottle can.

  Aluminum bottle cans or aluminum cans are subjected to strict necking after inner surface coating, and further flanging, especially bottle cans, which are processed with greater deformation than screw processing. The surface will be subject to significant deformation. In addition, when the inner surface paint is damaged due to deformation, there is a risk of corrosion or metal elution when the metal portion comes into contact with the contents. For this reason, it was necessary to give lubricity of the processed part to the inner surface coating in the molding process.

In general, an aluminum can is usually coated on its inner surface with a paint containing a resin composition as described in Patent Document 1, Patent Document 2, or Patent Document 3. However, these paints have their merits and demerits, good coating film adhesion, excellent processability without cracks and peeling, and many of them have insufficient corrosion resistance, and are corrosive like wine and have a flavor. A paint having sufficient corrosion resistance for a beverage that is easily damaged is insufficient in processability, and there is a problem that the coating film is likely to be cracked or peeled off during the diameter reduction process.
In the present invention, this problem is surely overcome by using the inner paint (1) and the inner paint (2).

  That is, the inner surface coating (1) excellent in workability is applied to the inner surface of the metal base before necking, flanging or screw processing, and the inner surface coating excellent in corrosion resistance after necking, flanging or screw processing. (2) is applied.

  The inner surface paint (1) used in the present invention may be an epoxy resin paint that has been used conventionally, and can be used as long as it has excellent coating film adhesion and does not crack or peel off during diameter reduction. From the viewpoint of adhesion to the aluminum substrate, an aqueous epoxy / acrylic / phenolic resin composition that can improve the working environment is preferable. For example, as a preferable example, the blending ratio of the epoxy resin (A) having an average molecular weight of 8000 to 30000 and the acrylic resin (B) is in a range of (A) / (B) = 88/12 to 65/35, preferably An epoxy-acrylic copolymer formed in the range of 85/15 to 75/25 can be exemplified.

In this case, from the viewpoint of improving the workability of necking / flange processing or screw molding, the phenoxy resin having an average molecular weight of 30000-65000 is preferably 10-40 wt%, preferably 25-35 wt%, and the epoxy-acrylic copolymer 30- 60 wt%, preferably 40 to 50 wt%, and water based paint comprising an epoxy resin composition containing 3 to 10 wt% of a resol phenol resin having an average molecular weight of 300 to 1000 as a resin component from the viewpoint of improving adhesion to an aluminum substrate It is.
If the phenol resin is 3% by weight or less, the adhesion tends to be low, whereas if it is 10% by weight or more, the workability is lowered. Generally, as the phenol resin, a thermosetting resol resin having an average molecular weight of about 300 to 1000 obtained by reacting bisphenol A and formalin is used for an inner surface coating.

The vehicle in this case is composed of a dispersion medium composed of a resin component, an organic solvent, and water. Examples of the organic solvent component include n-butanol, isobutanol, butyl cellosolve, dimethylethanolamine and the like.
After the inner surface paint (1) is applied by spray coating or the like, the paint is cured in a baking and drying furnace.
Next, after necking, flanging or screw molding, on the inner surface (1) surface of the bottomed cylindrical body, in the case of bottle cans, the inner surface paint (2) is washed and dried by spray coating, etc. Apply, and then cure the baking paint in a baking oven.

  The inner surface coating (2) is not particularly limited as long as it has excellent corrosion resistance, since it is not necessary to consider the diameter reduction after coating, but it is a solvent-based or water-based inner surface coating that has been used conventionally. An epoxy / urea resin composition, an epoxy / phenol resin composition, an epoxy / acryl / melamine resin composition, an epoxy / acryl / phenol resin composition, or the like based on an epoxy resin can be used. .

  Unlike the paint (1), the paint (2) does not require the workability of the necking flange or screw molding. Therefore, the epoxy-acrylic copolymer is composed of the epoxy resin (A) having an average molecular weight of the epoxy resin of 8000-30000. An epoxy / acrylic copolymer comprising acrylic resin (B) in a weight ratio of (A) / (B) = 93/7 to 77/23, preferably 90/10 to 80/20 is used. An aqueous solution containing a resin composition containing 10 to 30 wt% of a thermosetting resol phenol resin having an average molecular weight of about 300 to 1000 based on the entire resin component of the paint without containing a phenoxy resin in order to improve corrosion resistance. It is a paint.

  If the phenolic resin is 10% by weight or less, the gas barrier property tends to be insufficient, and if it is 30% by weight or more, the inner coating film tends to break when the can and the lid are wound or the product falls, and the impact resistance is high. Is inferior. Unlike the first layer, the second layer does not require workability of necking / flange molding or screw molding. As the epoxy / acrylic copolymer, an epoxy resin having an average molecular weight of 8000 to 30,000 is used. Also in this case, an aqueous epoxy / acrylic / phenolic resin composition that improves the working environment is preferable.

In addition, when performing inner surface coating as the first layer coating material, the inner surface coating material (1) of the portion to be necked or screw processed has a coating thickness of 15 to 40 mg / dm ² , preferably 25 to 30 mg / dm ² , The inner coating (2) of the second layer is about 60 to 90 mg / dm ² as the total thickness of the first layer. The thicker the inner coating film, the better the corrosion resistance. However, if the inner coating film is too thick, there is a risk of foam blowing in the coating process during the baking process, so it is preferable that the maximum thickness be about 90 mg / dm ² .

(Examples 1-2)
Prepare a cylindrical body (outside surface printing and printing, baking, inner surface coating (1) coating, after baking) for an aluminum bottle can (3104 material) with an internal volume of 310 ml, wash it after necking and screwing Then, it was dried to obtain a bottle can container body and dried.
Next, as a resin component, 18 parts by weight of a resol phenol resin having an average molecular weight of 900, an epoxy resin (A) having an average molecular weight of 20000, and an acrylic resin (B) are epoxy having a weight ratio of (A) / (B) = 85/15・ Aqueous inner surface paint (2) containing 82 parts by weight of acrylic copolymer as a resin component is applied and baked. Using 48 cans as samples, coating thickness, conductivity and corrosion resistance to aqueous solution of potassium metabisulfite / salt The test was conducted. Table 1 shows the resin components of the inner coating (1) and the inner coating (2) used, and Table 2 shows the measurement results of various tests.

(Comparative Examples 1-4)
As a comparative example, a resin that does not contain a phenoxy resin in the epoxy resin is used as the inner surface coating (1), and when the inner surface coating (2) is not used as the comparative example 1, the comparative example 2 is almost an example. When the inner surface paint (2) similar to 1 is used, Comparative Example 3 shows an example using the inner surface paint (2) similar to Example 2.
In Comparative Example 4 using the same inner surface paint (1) containing phenoxy resin as in Example 1 or 2 and not using the inner surface paint (2), the ERV value of the workability evaluation is poor and the corrosion resistance evaluation result is not good. It was only a pass.

[Measuring method]
a. Inner surface coating thickness of the can body: Measured by ADMITTANCEGAUGE manufactured by HAYASHI ENGIHEERING.
b. ERV for workability evaluation: The amount of current that flows when a voltage of 6.2 V is applied via a 1 wt% saline solution.
c. Corrosion resistance evaluation: 1% by weight of potassium metabisulfite, 1% by weight of citric acid, 3% by weight of sodium chloride, 10% by weight of ethanol, and 85% by weight of purified water were filled in a can, and the lid was wrapped around, 37 ° C. After storage for 7 days, the state of corrosion was visually observed.

Aluminum bottle cans and aluminum cans for beverages that are the subject of the present invention are excellent in corrosion resistance, alcohol resistance, heat resistance of inner surface coating, and do not deteriorate the quality and flavor of beverages. Because it uses a hard resin with extremely high gas barrier properties against sulfurous acid gas (SO ₂ ), it can be used as a container for beverages such as general beer and soft drinks, and flavor (flavor) is emphasized. It is an excellent container for wine-based beverages. For example, even when a wine-based beverage or the like is filled, sulfurous acid gas (SO ₂ ) contained in the wine is completely blocked by the coating film of these resin compositions, and sulfurous acid gas necessary for maintaining the quality of the beverage (SO ₂ ) is not consumed, and the flavor important for wine is not impaired. For this reason, it is an extremely excellent product as a container for wine-based beverages that emphasize flavor.

Aluminum can manufacturing process line (schematic diagram)

Claims (4)

The inner surface paint (1) with excellent processability is applied as the first layer paint on the inner surface of the bottomed cylindrical aluminum bottle can or aluminum can metal base, and it is necked and flanged or screwed (curled) The aluminum bottle can for beverages or the aluminum can for which the coating surface is coated with an internal coating (2) having excellent corrosion resistance as the second layer coating. The first layer paint excellent in processability is composed mainly of an epoxy resin having an average molecular weight of 8000 to 30000 containing 10 to 40 wt% of a phenoxy resin having an average molecular weight of 30,000 to 65000, and an inner face paint containing 3 to 10 wt% of a phenol resin ( The beverage aluminum bottle can or aluminum can according to claim 1, which is 1). 3. The beverage according to claim 1, wherein the second layer paint having excellent corrosion resistance is an epoxy internal paint (2) containing an epoxy resin having an average molecular weight of 8000 to 30000 and containing 10 to 30 wt% as a phenol resin. Aluminum bottle can or aluminum can. A bottomed cylindrical aluminum can metal base for beverages (bottomed cylindrical body) is coated with an epoxy-based inner surface paint (1) containing an epoxy resin containing a phenoxy resin as a main component and a phenol resin, and necking. After performing flanging or screw processing (including curling), this paint surface is further coated and cured with an epoxy-based inner surface paint (2) mainly composed of an epoxy resin containing a phenol resin. A method for painting an inner surface of an aluminum bottle can for beverage or aluminum can.

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