JPH0411974A - Method for coating draw-ironing can - Google Patents

Abstract

PURPOSE:To obtain inner face coating film without any defect by applying coating material on the inner face of can body so that pencil hardness and coefficient of dynamic friction after hardening become the specific values and then printing on outer face of the can body after drying and baking. CONSTITUTION:The draw-ironing can (the following is shown as DI can) body 2 is put on a conveyor 3, and the inner face coating material 5 is injected onto the inside of DI can body 2 from multi-hole air blow nozzle type gun 4. This is dried and baked in a drying furnace 6 to obtain the inner face coating film Successively, the DI can body 2 is conveyed to a printing machine 10 with a pin conveyor 7, and a printed circular plate 13 is pressed on the outer face of DI can body 2 to apply multi-color printing. Then, this is shifted from a mandrel 12 to the pin conveyor and conveyed to a drying furnace 16. By this method, any defect of pin hole, etc., in the coating film on the inner face of can is not made to develop.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a method for coating the inner and outer surfaces of cans produced by drawing and ironing, which are used for filling various products such as beverages, foods, and cosmetics.

[Conventional technology]

Conventionally, the bodies of drawn and ironed cans (DI cans) have been produced by drawing a circular punched aluminum plate or tin plate to form a pot-shaped can body, and then ironing the side walls of the can body. After the DI can body formed in the shape of a pot is washed and dried, printing is applied to the outer surface using a printing machine 10 shown in FIG. This printing press 10 has a cylindrical mandrel 12 installed on the periphery of a rotatable circular table If at right angles to the rotating surface of the table 11.
This is a known printing machine as disclosed in Publication No. 2. Mount the DI can body 2 over the mandrel 12, rotate the circular table 11 and the mandrel 12, and
Printing is applied by pressing a printing disk 13 onto the outer surface of the can body 2. After printing, an overcoat is performed by a coating machine 15. The Dr can body 2 whose outer surface has been printed and painted is sent to a drying oven 8 by a bottle conveyor 7 shown in FIG. 4, for example, and the paint and ink are dried and baked while being placed on a bottle 7a. For example, the bottle conveyor 7 is manufactured by Japanese Patent Publication No. 62-26315.
It is disclosed in the publication No. Next, the inner surface is painted. Painting is done using a paint machine that rotates the can body at high speed, and an airless spray gun is used to spray the interior paint, followed by drying and baking. The coating machine is a known one as disclosed in Japanese Patent Publication No. 63-44026, for example. When the DI can body 2 whose inner and outer surfaces have been painted is subjected to neck-in processing and flange processing, the DI can body 2 is completed. The manufacturing process of the above-mentioned DI can body is described in section 7.7 Deep drawing ironing and can making of the Aluminum Technology Handbook edited by the Light Metals Association, and in the Steel Handbook ■ (-Following processing, surface treatment, heat treatment, (Welding) Section 7. SDI cans.

[Problem to be solved by the invention]

Mass production of these I-cans began about 20 years ago, but the production capacity per line has improved year by year due to faster machinery and equipment, and today there are lines with production capacity several times as large as at that time. It is used. However, as lines become faster, defects such as pinholes are more likely to occur in the coating on the inner surface of cans, and there is a need to reconsider the series of manufacturing processes. For example, the order in which cans are painted is the outside, then the inside.
It has not changed since mass production began. SUMMARY OF THE INVENTION An object of the present invention is to provide a method for coating drawn and ironed cans that is highly productive and provides a defect-free inner coating film.

[Means to solve the problem]

The inventors of the present invention have conducted extensive research to determine the cause of defects in the inner coating film, and have found that when the order of painting the inner and outer surfaces of the DI can is reversed, defects occur in the inner coating of the DI can that was painted first. I found out that it doesn't. This is thought to be due to dust and other foreign matter adhering to the unpainted inner surface of the can and scratches occurring during the exterior painting and associated transportation, drying, and baking, and the interior coating is then layered on top of it. Ru. Since the inner coating film is extremely thin, only a few micrometers, it is also affected by fine dust. That is, as shown in FIGS. 1 to 3, which correspond to embodiments, the method for coating a drawn and ironed can of the present invention to achieve the above object covers the inner surface of a can body 2 formed by drawing and ironing. In addition, baking was performed using paint 5 so that the pencil hardness of the cured coating film was 2H-4H- and the coefficient of dynamic friction was 0.04 to 0.10.
After coating, drying and baking, the outer surface of the can body 2 is printed and painted. As the paint used for painting the inner surface of the can body 2, for example, an epoxy-phenol paint can be used. The dry film hardness of the inner surface paint 5 is a value measured at 80°C using a paint film pencil scratch tester specified in JIS K 5401, and is preferably 2H-4H-. Paint film hardness is often determined by the resin that is the main component of the paint, but it can be adjusted by adding a soft or hard resin or a curing agent. resin, amine resin, acrylic resin, etc.), modify the epoxy resin,
It is adjusted by adding a polymeric epoxy resin (phenoxy resin) or the like, or by adding phosphoric acid as a reaction accelerating catalyst. If the coating hardness is less than 2H, the coating may be damaged in subsequent steps, and if it exceeds 4H-, there is a risk of processing cracks in the coating. The coefficient of dynamic friction of the inner paint 5 is ALTEC.
Steel ball diameter 16nu was tested using a three-point steel ball loading tester made by the company.
nφ, load 2kg, tensile speed 600m+m/min, 20℃
It is a value measured at 0.004 to 0.10. The coefficient of dynamic friction can be adjusted by adding, for example, lanolin, paraffin wax, microcrystalline wax, carnauba wax, polyethylene wax, or the like. If the coefficient of dynamic friction is less than 0.04, the coating film and the mandrel 12 may slip too much during external printing, resulting in printing misalignment, excess wax may build up on the mandrel 12 or the bottle 7a, or the contents may become distorted after filling. There is a risk of release. If it exceeds 0.10, use mandrel 1 in the outer coating process after inner coating.
The inner surface coating may be damaged by contact with 2 or the bottle 7a.

[Effect]

In the coating method of the present invention, the inner surface and outer surface of the DI can body 2 are coated in this order, and during the inner surface coating, the inner surface of the DI can 2 is kept in an extremely clean state by being washed and dried. . Therefore, defects in the coating film due to adhesion of dust and the like do not occur, and a uniform coating film is formed. The inner coating film has a pencil hardness of 2H-4H- and a dynamic friction coefficient of 0.04 to 0. Since it is set within the IO range, the coating film will not be damaged due to contact with other parts during transportation, and the coating film and mandrel 12 will not slip too much during external painting, causing printing misalignment. .

【Example】

Hereinafter, one embodiment of the present invention will be described in detail. Example 1 A resin mixture consisting of 80 parts by weight of a bisphenol A type epoxy resin with an average molecular weight of 3750 and 20 parts by weight of a phenol-formaldehyde resin obtained by reacting phenols and formaldehyde in the presence of an alkali metal hydroxide catalyst. , 0.5 parts by weight of microcrystalline wax (relative to 100 parts by weight of resin), and 0 parts by weight of phosphoric acid catalyst.
．． The added 5 parts by weight was dissolved in a mixed solvent consisting of 30% xylene, 20% n-butanol, 30% ethyl acetate, and 20% butyl acetate to prepare a paint for the inner surface of a DI can having a solid content of 20%. The viscosity of the obtained inner surface paint was 13 seconds (
Ford Cup No., 4720℃), surface tension is 25
It is dynes/cm. Next, apply this paint to the DI can body. A washed and dried tin DI can body 2 with a diameter of 66 W+m and a height of 123 mm is used as the test can. As shown in FIG. 1, the Dr can body 2 is placed on the conveyor 3, and the inner surface paint 5 is injected onto the inside of the DI can body 2 from the multi-hole air blower nozzle type gun 4. This is quickly dried in the drying oven 6.
Baking is performed to obtain an inner coating film with an average dry film thickness of 21 m. The DI can body 2 whose inner surface has been coated is conveyed to a printing machine 10 by a bin conveyor 7. As shown in FIG. 2, the printing press 10 has a cylindrical mandrel 12 mounted on the periphery of a rotatable circular table 11 at right angles to the rotating surface of the table 11. The can body 2 is removed from the bin 7a of the bottle conveyor 7 by the can supply device 9,
The six circular tables 11i3 and the mandrel 12, which are mounted and fixed so as to cover the mandrel 12, are rotated, and the DI
A printing disk 13 is pressed against the outer surface of the can body 2 to perform multicolor printing.The printing disk 13 is supplied with polyester resin/alkyd resin mixed thermosetting tinplate ink for outer surface printing from an ink supply device 14. be done. After printing, an overcoat (polyester clear paint) is applied by a coating machine 15. The DI can body 2 whose outer surface has been printed and painted is transferred from the mandrel 12 to the bin conveyor via a device similar to the can supply device 9 (not shown), and then transported to the drying oven 16 shown in FIG. . For drying and baking the outer surface, a bottleless drying oven I6 is used that dries and bakes the DI can body 2 while lying face down on the conveyor 3a. The dried and baked DI can body 2 is conveyed to the next processing step by a conveyor 3a, and subjected to neck-in processing and flange processing to complete the DI can body. The hardness of the inner coating film of DI can body 2 is determined according to JIS K 5401.
It was measured using a specified paint film pencil scratch tester, and the dynamic friction coefficient was measured using a three-point steel ball loading tester manufactured by ALTEC1.The measurement results are shown in Table 1 below. A copper sulfate solution was poured onto 100 of the DI cans that had been prepared, and they were allowed to stand at 25°C for 30 minutes to check for coating defects.The inner coating had defects such as pinholes, and the metal surface was exposed. If it is, copper precipitates in that area, indicating a coating defect.The test results are shown in Table 1.Example 2 The same resin as in Example 1 was used, and the mixing ratio was changed to bisphenol A epoxy. A DI can body was prepared and evaluated in the same manner as in Example 1, except that 90 parts by weight of the resin, 10 parts by weight of the phenol formaldehyde resin, and 0.4 parts by weight of only microcrystalline wax were added. The paint has a lower amount of phenol than the paint of Example 1, lowering the glass transition point and making the paint film softer. Example 3 The same resin as Example I was used, but the mixing ratio was changed to bisphenol A epoxy. 70 parts by weight of resin, 30 parts by weight of phenol formaldehyde resin, 0.4 parts by weight of microcrystalline wax, and 1.0 parts by weight of phosphoric acid catalyst.
A 01 can body was prepared and evaluated in the same manner as in Example 1 except that the parts by weight were changed. This inner surface coating contains an increased amount of phenol formaldehyde resin and phosphoric acid catalyst compared to the coating of Example 1 to advance the curing reaction, raise the glass transition point, and increase the hardness of the coating film. Comparative Example 1 A 01 can body was prepared and evaluated in the same manner as in Example 3, except that 0.3 parts by weight of Microcrystalline wax was used. Comparative Example 2 A 01 can body was prepared in the same manner as in Example 2, except that 95 parts by weight of bisphenol A epoxy resin, 5 parts by weight of phenol formaldehyde resin, and 0.5 parts by weight of only microcrystalline wax were added. We conducted an evaluation. Comparative Example 3 A 01 can body was prepared and evaluated in the same manner as in Example 1, except that a commercially available thermosetting vinyl paint (manufactured by Kansai Paint ■, 5J-6839-009C) was used as the inner surface paint. This paint is a mixture of vinyl chloride-vinyl acetate copolymer resin (molecular weight approximately 150,001), epoxy resin (molecular weight approximately 900), and urea formaldehyde resin in a ratio of 70 + 20 + 10. Comparative Example 4 As an internal paint, an average molecular weight of A 01 can body was prepared in the same manner as in Example 1, except that an epoxy urea paint (manufactured by Kansai Paint ■, XJ-K164D-2) consisting of 85 parts by weight of 3750 bisphenol A epoxy resin and 15 parts by weight of urea formaldehyde resin was used. Comparative Example 5 A commercially available epoxy phenol paint (manufactured by Kansai Paint ■) consisting of 80 parts by weight of bisphenol A type epoxy resin with an average molecular weight of 3750 and 20 parts by weight of phenol formaldehyde resin was used as an internal paint. A 01 can body was prepared and evaluated in the same manner as in Example 1, except that 28-L1511 was used. Comparative Example 6 An acrylic resin obtained by polymerizing styrene, ethyl acrylate, and methacrylic acid was mixed with bisphenol A. A 01 can body was prepared in the same manner as in Example 1, except that a commercially available epoxy acrylic paint consisting of 95 parts by weight of epoxy acnol resin obtained by reacting with a type epoxy resin and 5 parts by weight of a resol type phenolic resin was used as the inner surface paint. Table 1 shows the composition of the inner surface paint of each Example and Comparative Example and each evaluation result. (Leaving space below) 1. The evaluation criteria for surface inner surface coating defects are as follows. Yes. The quality is at the O8 practical level. △: Slightly lacking in the quality at the practical level. When the cans were manufactured, there were no defects on the inner surface, and none had holes due to deterioration or corrosion after filling. In addition, in the above example, one layer of coating was applied to both the inner and outer surfaces. Although a membrane is provided, in the case of cans that are applied to highly corrosive contents, especially steel DI cans, a top coat may be applied after flange processing to provide multiple layers of coating pressure.

【Effect of the invention】

As described above in detail, according to the method for coating drawn and ironed cans of the present invention, the inner and outer surfaces of cans manufactured by drawing and ironing can be coated efficiently and reliably, resulting in high productivity. Defects such as pinholes and scratches do not occur on the coating film on the inner surface of the can that comes into contact with the contents after commercialization.

[Brief explanation of the drawing]

Figure 1 is a schematic side view showing the process of painting the inner surface of a can according to the coating method of the present invention, Section 2 is a perspective view showing the process of painting the outer surface of the can, and Figure 3 shows the process of drying and baking the outer surface of the can. A schematic side view, FIG. 4 is a side view showing the conveyance state of cans in a conventional coating method. 2...DI can body 3.3a...Conveyor 4.
...Porous air blow nozzle type gun 5...Inner surface paint
6・8...Drying oven 7...Bin conveyor 7
a... Bin 9... Can feeding device 10... Printing machine 11... Circular table 12... Mandrel 1
3... Printing disk 14... Ink supply device 1
6...Pinless drying oven

Claims (1)

[Claims] 1. On the inner surface of the can body formed by drawing and ironing, the pencil hardness of the paint film after baking and hardening is 2H^--4H^-,
A method for coating drawn and ironed cans, which comprises applying a paint to a dynamic friction coefficient of 0.04 to 0.10, drying and baking, and then printing and painting the outer surface of the can body.