JPH0136519B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing metal cans, particularly beverage metal cans, and more specifically, it relates to a method for manufacturing metal cans, particularly beverage metal cans, and more specifically, it is possible to produce beverage metal cans from coated metal materials with a high drawing ratio and excellent corrosion resistance and flavor characteristics. and a method for producing the same with degreasing and cleaning properties. Metal containers for beverages are made by deep-drawing or drawing-ironing a metal material such as aluminum or tin to form a pot-shaped can body with a flange, which is then double-sealed with a can lid. A two-piece can or the above-mentioned material is pressed to produce a cup-shaped lower body with a bottom and a cup-shaped upper body with a spout. A bottle-shaped container is used by overlapping and joining the parts. In this drawing or pressing process, it is recommended to provide an organic coating film on the metal material before processing, in terms of drawing processability and workability.
It is also advantageous in that it does not require the trouble of painting the can body after processing, but the following drawbacks still occur when attempting to deep draw a coated metal material by several stages of press working. In other words, known coated metal materials have a certain drawing limit, and if this drawing limit is exceeded, the material tends to break at the head or flange, and therefore beverage cans with a large height-to-diameter ratio are It becomes difficult to manufacture. In addition, when the drawing ratio becomes large during this pressing process, coating defects such as peeling, breakage, cracks, and pinholes are likely to occur in the coating film on the material, and metal leaching into the contents (especially iron leaching) and canning. Corrosion such as pitting corrosion on the body becomes more likely to occur. Furthermore, it may be possible to improve the drawing processability by applying a known lubricant on the paint film, but in this case, it becomes difficult to degrease the lubricant on the paint film, and the lubricant remaining on the paint film may A fatal drawback is that the lubricant tends to spoil the flavor of the beverage, which relies on a delicate flavor. The present inventors have discovered that when an oil-in-water aqueous emulsion containing a liquid glyceride having a fatty acid component having 8 to 24 carbon atoms, ethanol, and a nonionic surfactant is applied to the coating surface of a painted metal material, excellent results can be obtained. It has been found that a combination of drawability and excellent degreasing and cleaning properties can be obtained, and a metal can for beverages can be obtained in which all of the above-mentioned drawbacks are eliminated. That is, an object of the present invention is to provide a method for molding metal cans, particularly beverage metal cans, which eliminates the above-mentioned drawbacks. Another object of the present invention is to provide a method for molding metal beverage cans that significantly improves the drawing limit and the degreasing and cleaning properties compared to conventional molding methods. Still another object of the present invention is to be able to uniformly and uniformly apply a lubricating component to the coating surface of a painted metal material, and to perform high-level drawing processing without causing defects in the coating on the material. An object of the present invention is to provide a method for manufacturing a metal beverage can. According to the present invention, in a method for producing a metal can by subjecting a metal material on which an organic resin coating film has been formed in advance to several stages of drawing processing, liquid glyceride having a fatty acid component having 8 to 24 carbon atoms is completely extracted. Hit 3~
An oil-in-water aqueous emulsion containing 50% by weight, 1 to 20% by weight of ethanol as a water-miscible organic solvent, and 0.5 to 10% by weight of a nonionic surfactant, based on glyceride, was applied to the organic coating of the material. Provided is a method for producing metal cans, which comprises uniformly coating the film surface, subjecting the coated material to drawing forming, and subjecting the can obtained by drawing forming to warm washing with an aqueous medium. be done. The present invention will be explained in detail below. In FIG. 1 showing the cross-sectional structure of a metal material to be press-formed, the metal material 1 for forming includes a metal substrate 2 made of an aluminum plate, tinplate, etc., an organic coating 3a provided on both surfaces of the substrate, It consists of 3b. In the present invention, liquid glyceride having a fatty acid component having 8 to 24 carbon atoms, ethanol, and a nonionic surfactant are added to the surfaces of these organic coatings 3a and 3b in a specific quantitative ratio prior to press working. This method is characterized in that the layers 4a and 4b of the oil-in-water aqueous emulsion are uniformly applied. BACKGROUND ART Conventionally, it is generally known to use a lubricant in the form of an aqueous emulsion when press-molding metal materials. However, this aqueous emulsion type lubricant is based on mineral oil, and when applied to the coated surface of a painted metal material, this water-based lubricant blends firmly with the coated surface and is difficult to wash with hot water, etc. With this simple method, it is difficult to degrease the coated surface of the can body after molding. Moreover, it is difficult to apply this water-based emulsion uniformly to the coating surface, and even if a good lubrication effect can be obtained in areas where the water-based emulsion layer exists, the coating film will be damaged in water-repellent areas. Damage etc. will inevitably occur. In the present invention, by selecting glyceride as a lubricating component and using this glyceride in the form of an aqueous emulsion emulsified with a nonionic surfactant, the can body after molding can be washed with an aqueous medium at a warm temperature. The coating film surface can be effectively and completely degreased and cleaned by an extremely simple operation of applying it. In addition, by mixing a small amount of ethanol into this aqueous emulsion, the wettability of the coating film surface is significantly improved, and a uniform thin layer of the aqueous emulsion is uniformly maintained on the coating film surface, making it easier to press mold. It provides excellent lubrication and cooling protection for the coating film. Among various water-miscible organic solvents, ethanol used in the present invention is particularly excellent in improving the wettability of coating films, and is also excellent in flavor retention of foods. Although the exact reason why the glyceride used in the present invention exhibits excellent degreasing and cleaning properties and processability during press working of coated metal materials is unclear, it is thought to be as follows. That is, this glyceride has a chemical structural feature of having a nonpolar group (lipophilic group) derived from a fatty acid and a polar group derived from glyceride (glycerin ester). Due to this chemical structural feature, during press processing,
Uniform to the coating surface with similar polar groups,
It is believed that this forms a continuous lubricating surface with a high oil film strength. Furthermore, due to the action of the nonionic emulsifier contained in the aqueous emulsion and the chemical structure characteristics mentioned above, such a lubricating film is easily re-emulsified and dispersed in hot water during washing, resulting in excellent degreasing performance. recognized as a thing. The fatty acid component in the glyceride used in the present invention is
It is also important to have a carbon number of 8 to 24, especially 12 to 24. If this carbon number is lower than the above range, the oil film strength will be low and satisfactory lubrication performance will not be obtained. On the other hand, if this carbon number is higher than the above range, the above-mentioned re-emulsification and dispersion becomes difficult and the degreasing performance deteriorates. The fatty acids that make up glycerides include caprylic acid, capric acid, lauric acid, myristic acid,
In addition to saturated fatty acids such as palmitic acid, margaric acid, stearic acid, arachic acid, behenic acid, lignoceric acid, and cerotic acid, 2-octenoic acid, caproleic acid, 2-lauroleic acid, myristoleic acid, palmitoleic acid, and petroselin Examples include unsaturated fatty acids such as oleic acid, elaidic acid, gondotic acid, erucic acid, ceracoleic acid, linoleic acid, linoleaidic acid, eleostearic acid, linolenic acid, arachidonic acid, and culpanodonic acid. These fatty acids are generally used for the purpose of the present invention in the form of triglycerides, provided that the triglycerides are liquid at room temperature.
It can be a single fatty acid glyceride or a mixed fatty acid glyceride. Suitable examples of triglycerides are: Tricaprylin, 1-oleo-2,3-dicaprin, 1-capryl-2,3
-Diolein, 1-lauro-2,3-diolein, 1-lauro-2,3-dilinolein, 1-myrist-2,3-dilinolein, 1-palmitote-
2,3-dilinolein, 1-stearo-2,3-
Girino Rain. Of course, this triglyceride is derived from safflower oil,
soybean oil, sunflower oil, corn oil, cottonseed oil,
It may be a mixed glyceride based on edible vegetable oils such as sesame oil, rapeseed oil, rice oil, pumpkin oil, peanut oil, olive oil, palm oil, coconut oil, etc. In the present invention, it is desirable to use the above-mentioned triglycerides, but if desired, it is also possible to use those mixed with diglycerides or monoglycerides. In the present invention, the liquid glyceride described above is used in the form of an aqueous emulsion. In terms of lubricating performance, this aqueous emulsion should contain at least 3% by weight, especially at least 5% by weight, of glycerides, while in terms of degreasing performance and cooling effect, the amount of glycerides in the emulsion should be 50% by weight. In particular, the content should be 40% by weight or less. In the present invention, a nonionic surfactant is used as an emulsifying and dispersing agent for liquid glycerides. That is, nonionic surfactants, compared to other surfactants,
It has the advantage that it has particularly good degreasing and cleaning properties on the surface of the coating film, and therefore the formed painted squeeze can has excellent flavor characteristics. As the nonionic surfactant, sorbitan fatty acid ester, polyoxyethylene alkyl phenyl ether, polyoxyethylene fatty acid amide ether, polyoxyethylene sorbitan fatty acid partial ester, triethanolamine fatty acid ester, etc. may be used alone or in combination of two or more. used in These surfactants are preferably used in an amount of 0.5 to 10% by weight based on glyceride. It is extremely important for the aqueous emulsion used in the present invention to contain a small amount of ethanol in order to improve wetting of the coating surface. However, satisfactory coating properties and lubricity cannot be obtained. Among various water-miscible organic solvents, ethanol has particularly excellent safety and hygienic properties. Ethanol is preferably used in an amount of 1 to 20% by weight, especially 2 to 15% by weight, based on the aqueous emulsion. In addition to the above-mentioned essential ingredients, the aqueous emulsion of the present invention contains ingredients known per se, such as rust preventives,
Sequestering agents, antifoaming agents, antioxidants, and the like can be added according to known formulations. One of the advantages of the present invention is that a remarkable effect can be obtained with a significantly small amount of the aqueous emulsion applied to the organic coating surface of the material.For example, generally speaking, based on non-volatile components, Satisfactory results are obtained with application amounts of 5 to 200 mg/m ² , especially 5 to 150 mg/m ² . If the amount applied is less than the above range, the lubrication performance will be unsatisfactory, while if it is more than the above range, the degreasing operation will be burdensome, which will likely be disadvantageous in terms of economy and flavor characteristics. In the present invention, the aqueous emulsion is applied to the coating surface by means known per se, such as roller coating, spray coating, dip coating, and foam coating. The coated metal materials used in the present invention are known per se. Examples of the metal materials include untreated steel plates (black plates), various surface-treated steel plates, such as tin-plated steel plates (tin plate), galvanized steel plates, Plated steel sheets such as aluminized steel sheets and chrome-plated steel sheets; electrolytically treated steel sheets such as electrolytic chromic acid treated steel sheets; chemically treated steel sheets such as phosphoric acid and/or chromic acid treated steel sheets, light metal sheets such as aluminum, or composite materials thereof. be done. Suitable metal materials include rolled aluminum materials made of pure aluminum or aluminum alloys, which generally have a diameter of 0.15 to 0.80 mm, although they differ depending on the drawing conditions and purpose.
It is especially used in material thicknesses of 0.17 to 0.50 mm. Other suitable metal materials are those having a tin loading, ie pounds of tin per base box, in the range 0.1 to 1.0, especially 0.15 to 0.75. This tin plating layer may be a no-reflow board (matte board) that has been electrolytically plated, or may be a reflow board (bright board) in which the electrolytically plated layer has been heat-melted. The base plate thickness used is generally in the range of 0.15 to 0.5 mm, particularly in the range of 0.15 to 0.35 mm. On the other hand, the protective coatings include any protective coatings made of thermosetting and thermoplastic resins; for example, modified epoxy coatings such as phenol-epoxy paints and amino-epoxy paints; for example, vinyl chloride-vinyl acetate copolymers, vinyl chloride-acetic acid copolymers, etc. Vinyl or modified vinyl paints such as partially saponified vinyl copolymers, vinyl chloride-vinyl acetate-maleic anhydride copolymers, epoxy-modified, epoxyamino-modified, or epoxyphenol-modified vinyl resin paints; acrylic resin paints; Synthetic rubber paints such as styrene-butadiene copolymers may be used alone or in combination of two or more. These paints can be applied to metal materials in the form of organic solvent solutions such as enamel or lacquer, or in the form of aqueous dispersions or solutions, in the form of roller coating, spray coating, dip coating, electrostatic coating, electrophoretic coating, etc. Apply in advance. Of course, if the resin paint is thermosetting, the paint may be baked if necessary. These organic coatings generally have a thickness of 2 to 30 μm, particularly 3 to 30 μm, from the viewpoint of preventing corrosion and improving drawing workability.
It is desirable to have a thickness (dry state) of 20 μm. According to the present invention, as shown in FIG. 2, the painted metal material 10 coated with an aqueous emulsion is
The cup is pressed between a punch 12 and a die 13 that are relatively movable in the axial direction, and is formed into a seamless cup with a bottom. At this time, it is possible to apply press processing after drying the aqueous emulsion layer, but in general, since the amount of coating is extremely small and the subsequent degreasing operation is easy,
It is preferable to press the applied emulsion layer as it is, that is, in a wet state. In the present invention, press working is performed several times while gradually reducing the diameter of the punch and die until the desired shape and desired height/diameter ratio are obtained. At this time, the drawing ratio defined by the following formula: Drawing ratio = Diameter before processing / Diameter after processing is 1.20 in one press processing.
to 2.10, especially 1.30 to 1.90, and the overall aperture ratio to 1.50 to 3.00, especially 1.80.
It is desirable to do this so that the ratio is between 2.70 and 2.70. A significant advantage of the invention is that by subjecting the cans thus formed to warm cleaning with an aqueous medium, the glycerides used for lubrication are very effectively degreased. The temperature during washing is generally in the range of 40 to 80°C, and washing at such a warm temperature significantly promotes re-emulsification and dispersion of glycerides. After washing, the cans are dried and used for subsequent can manufacturing operations. In other words, in a normal deep-drawn can with a two-piece structure,
If necessary, neck-in processing and flange processing are performed, and after filling with contents, the can body is double-sealed with the can lid. Further, in the case of a bottle-shaped metal container having a circumferential side seam, a lower body 20 consisting of a bottomed cup shown in FIG. 3 and an upper body 21 consisting of an inverted cup with an opening are formed, As shown in FIG. 4, these two pieces are overlapped and bonded via the adhesive layer 22 to form a bottle-shaped container. The invention is illustrated by the following example. The method for preparing the aqueous emulsion and the evaluation method for the metal container used in the following specific examples are as follows. [Preparation of aqueous emulsion] Rapeseed oil (Table 1 shows the fatty acid composition determined by gas chromatography using the glyceride decomposition methyl esterification method using sodium methoxide-methanol/boron fluoride-methanol)
A mixed liquid of 10% by weight, 89.8% by weight of water, and 0.2% by weight of sorbitan monolaurate was uniformly stirred using a homogenizer to obtain an aqueous emulsion. Next, 5% by weight of ethanol is added to the emulsion and stirred uniformly. The aqueous emulsion thus obtained is designated as E-1. Aqueous emulsions E-2 to E-7 were prepared using the same method as preparing E-1, except for changing the glyceride (oil and fat) and its content (the total content of glyceride and water was kept at 99.8%). . Table 1 shows E-2 to E
The content of the glycerides (oils and fats) used in -7, their fatty acid compositions, and glycerides (oils and fats) are shown. [Evaluation of Metal Containers] In the following Examples and Comparative Examples, metal containers were evaluated in accordance with the method described below. (a) Paint film damage A metal container was filled with a 1% aqueous sodium chloride solution, a voltage of 7V was applied, and the current value (mA) that flowed at that time was evaluated. Ten pieces of each were measured, and their arithmetic mean value was used as the result. (b) Metal Elution A metal container was filled with a synthetic carbonated beverage, and after 3 months at room temperature, the amount of metal eluted was measured by atomic absorption spectrometry. Ten pieces of each were measured, and their arithmetic mean value was used as the result. (c) Flavor test A metal container was filled with a synthetic carbonated beverage, and after 3 months at room temperature, a flavor test was conducted by a panel of 20 people. The results are evaluated on a 5-point scale, with a score of 5 (good).
Indicated as ~1 (bad). Example 1 Modified vinyl paint was applied to the inner and outer surfaces of an aluminum plate (3004H19 material) with a base thickness of 0.23 mm, and the total coating amount was
After coating and baking to give a concentration of 150mg/dm ² and 60mg/dm ² , the aqueous emulsion [symbol E-1] shown in Table 1 was applied to the inner and outer vinyl coating surfaces at room temperature. It was applied uniformly to 80 mg/m ² using a roll method. After that, it was punched into a disc with a diameter of 250 mm, and drawn using normal press processing so that the total drawing ratio was 2.26. After forming a cup with an inner diameter of 110.6 mm at the edge of the joint, it was further subjected to multi-stage press processing. An upper body having a spout with a diameter of 30 mm in the center was manufactured. On the other hand, a painted plate coated with the same liquid lubricant was drawn with a total drawing ratio of 2.26 similar to the upper body, and the outside diameter of the joint edge was further reduced by a netting process.
The lower body was made to have a diameter of 110.6 mm. Thereafter, both parts were spray-washed at a common temperature (70°C), and then dried in an oven. The upper body and the lower body were heat-bonded using a heat-sealing adhesive to produce a metal beverage container with a capacity of about 2. In the process of producing these metal containers, press formability was evaluated, and on the other hand, the amount of lubricant remaining after warm washing was measured. In addition, after filling the synthetic carbonated beverage into this metal container, the spout was tightly closed, sterilized at 62℃ for 10 minutes, and left at room temperature for 3 months to measure the amount of metal eluted and evaluate the flavor. Summer. The results are shown in Table 2. Examples 2 to 5 Same as Example 1 except that the aqueous emulsions [symbols E-2, E-3, E-4, E-5] shown in Table 1 were applied to the coating surface as liquid lubricants. Multistage press molding was performed to produce a metal container with a capacity of approximately 2. Table 2 shows the evaluation results of these press moldability, residual amount of lubricant, amount of metal elution, and flavor. In the method using the aqueous emulsions used in Examples 1 to 5, good evaluations were obtained for all properties. In particular, it showed excellent properties in terms of degreasing and cleaning properties and flavor, demonstrating the superiority of producing metal containers using the method of the present invention. Comparative Examples 1 to 4 For comparison, as shown in Table 1, two types of aqueous emulsions [symbols E-6, E-7], an aqueous emulsion using mineral oil as a base oil [symbol E-8], and rapeseed oil Four types of lubricants (symbol E-9) were prepared. Multi-stage press molding was carried out in the same manner as in Example 1 except that these lubricants were applied to the surface of the coated aluminum material, and after degreasing and washing, a metal container with a capacity of about 2 was produced. This manufacturing process improves press formability, degreasing and
The washability was evaluated, and the contents were then filled and each characteristic was evaluated. The results are shown in Table 2, and it was found that all four types had significantly poorer degreasing and cleaning properties than those using the aqueous emulsions of Examples 1 to 5, and were difficult to apply to containers. In particular, aqueous emulsions with mineral oil as the base oil [symbol E
-8] and rapeseed oil [symbol E-9], it was found that warm washing alone was not sufficient to degrease and wash the oil, and the flavor was significantly impaired. Example 6 Epoxy paint was applied to the inner and outer surfaces of a tin-plated steel plate (tinplate material, plating amount #25/25, temper T-2) with a base plate thickness of 0.20 mm, with a total coating amount of 100 mg/each.
Press molding was carried out using the same aqueous emulsion as in Example ¹ , except that coating and baking were carried out so that the emulsion was 50 mg/dm ² , and the press moldability, degreasing, The washability and characteristics as a metal container were evaluated. As a result, even in the case of tin-plated steel sheets coated with epoxy paint, according to the forming method for forming an aqueous emulsion of the present invention, not only press formability but also
Degreasing/cleaning properties, metal elution and flavor
It was found that an excellent container was obtained without any abnormality in terms of.

【table】

【table】

[Table] Example 6 and Comparative Example 5 Modified vinyl paint was applied to the inner and outer surfaces of an aluminum plate (3004H19 material) with a base thickness of 0.23 mm, and the total coating amount was
After coating and baking to give a concentration of 150mg/dm ² and 60mg/dm ^{2 ,} 80mg of the aqueous emulsion shown in Table 3 was applied onto the inner and outer vinyl coating surfaces at room temperature using a roll method. / ^m2 . After that, it was punched into a disc with a diameter of 250 mm, and drawn using normal press processing so that the total drawing ratio was 2.26. After forming a cup with an inner diameter of 110.6 mm at the edge of the joint, it was further subjected to multi-stage press processing. An upper body having a spout with a diameter of 30 mm in the center was manufactured. On the other hand, a painted plate coated with the same liquid lubricant was drawn with a total drawing ratio of 2.26 similar to the upper body, and the outer diameter of the joint edge was reduced to 110.6 by netting processing.
The lower body was made to have a diameter of mm. Thereafter, both parts were spray-washed at a common temperature (70°C), and then dried in an oven. The upper body and the lower body were heat-bonded using a heat-sealing adhesive to produce a metal beverage container with a capacity of about 2. After filling the synthetic carbonated beverage into this metal container, the spout was sealed, and the container was sterilized at 62°C for 10 minutes, and then the flavor was evaluated. In addition, some of the samples were left at room temperature for one month and then evaluated for flavor. Flavor evaluation was performed by a panel of 20 people, and the results were evaluated on a 5-point scale and expressed as 5 (good) to 1 (bad). The composition of the aqueous emulsion and the flavor test results are shown in Table 3. As is clear from these results, it was difficult to degrease the coating film after processing in the aqueous emulsion using fatty acid as an alkali metal soap emulsifier, and the resulting cans had poor flavor characteristics.

【table】 [Brief explanation of drawings]

Fig. 1 is a sectional view showing the structure of a metal material subjected to press forming, Fig. 2 is a sectional view illustrating the drawing process of the metal material, and Figs. 3 and 4 are illustrative of the press forming method according to the present invention. 1 is a diagram illustrating a specific example of a metal container for use in storage, in which reference numeral 1 is a metal material, 2 is a metal substrate, 3a,
3b is an organic coating film, 4a and 4b are liquid lubricant solution layers, 10 is a painted metal material, 11 is a wrinkle suppressor, 12
13 is a punch, 20 is a lower body, 21 is an upper body, 22 is an adhesive layer, and 23 is a joint edge.

Claims (1)

[Claims] 1. A method for producing metal cans by subjecting a metal material on which an organic resin coating has been formed in advance to several stages of drawing processing, in which a liquid glyceride having a fatty acid component having 8 to 24 carbon atoms is produced. 3 to 50% by weight of total, 1 to 20% of ethanol by weight, and 0.5 to 10% of nonionic surfactant by weight of glyceride.
The oil-in-water aqueous emulsion contained therein is uniformly applied onto the organic coating surface of the material, the material after application is subjected to drawing forming, and the can obtained by drawing forming is warm washed with an aqueous medium. A method for manufacturing a metal can, characterized by subjecting it to a metal can. 2. The method according to claim 1, wherein the liquid glyceride is an edible vegetable oil. 3. The method according to claim 1, wherein the aqueous emulsion is applied to the organic coating surface of the material in an amount of 5 to 200 mg/m ² based on non-volatile components.