JPH0356981B2 - - Google Patents

Description

[Detailed description of the invention]

(Field of Application to which the Invention Pertains) The present invention relates to a method for manufacturing a welded can that has been subjected to a net-in process, and more particularly, it relates to a welded can that can be used for filling aerosol contents and that has excellent corrosion resistance in the processed part even after the net-in process. Relating to a method for manufacturing cans. (Prior art) Conventionally, the manufacturing method for can bodies is to cut a metal material for a can into a cylindrical shape, overlap the two end edges of the material, and then weld, glue, solder, etc. The most widely used method is to join them to form a seam. The side seam formed by this method is on the inner side of the can.
The cut edge of the material, that is, the cut edge, is always exposed, and it is extremely important to cover the cut edge of the material in order to prevent corrosion of the material and suppress metal elution into the contents. becomes. Various proposals have been made to cover and protect this seam, particularly the cut edge of the material. One of the most effective of these proposals is the
Publication No. 38140 discloses that the joint of a welded can consists of a continuous phase made of a thermosetting resin and a dispersed phase made of thermoplastic resin particles, and the thermoplastic resin particles are
The coating layer has a number average particle size of 80 microns and a ring and ball softening point of 50 to 300°C, and the thermosetting resin and the thermoplastic resin are present in a volume ratio of 95:5 to 25:75. It is proposed that a (Problems to be Solved by the Invention) Although the coating layer of the prior art is generally satisfactory in terms of adhesion to welded seams, barrier properties against corrosion-resistant components, and workability such as double seaming, it is still difficult to use aerosols. It has been found that the use of netquin cans has a number of problems. First, for aerosol cans, it is necessary to attach a small-diameter mounting cup and eyelid that support the nozzle to the top of the can, and the seamed part of the eyelid needs to protrude outward beyond the outer periphery of the can body. It is desirable from the viewpoint of the appearance and commercial value of the can to prevent this from occurring, and for this purpose, it is desirable to process the opening end of the can body, where the eyelet lid is attached, to have a small diameter. During this neck-in process, the metal material and organic resin coating that form the can body undergo plastic flow such that the circumferential dimension is reduced and the axial dimension is expanded. It cannot follow plastic flow sufficiently and tends to cause coating defects such as cracks during processing. Next, the aerosol contents are liquid glass polisher,
Often highly corrosive aqueous contents, such as laundry starch and shaving cream, tend to make welded seams more susceptible to corrosion. Since the degree of dissolution or diffusion of corrosive components into the coating increases as the internal pressure increases, seam corrosion in aerosol cans becomes an extremely serious problem. Therefore, an object of the present invention is to maintain excellent adhesion to the seam even when the coating layer on the welded seam is subjected to severe neck-in processing, and to prevent coating defects such as cracks and peeling during processing. An object of the present invention is to provide a method for manufacturing a net-in welded can that eliminates the occurrence of. Another object of the present invention is to provide a method for manufacturing a welded neck can particularly suited for use in filling aerosol contents. (Means for Solving the Problems) The present inventors have discovered that even when providing a hard and dense thermosetting resin-containing coating with excellent corrosion barrier properties to a welded seam with a considerably thick film thickness, the glass transition By selecting a material whose temperature dependence of Young's modulus is within a certain range in a temperature range lower than temperature (Tg), coating defects such as cracks and peeling can be avoided, and the relationship between seams and coating can be improved. It has been found that netuin processing is possible without reducing adhesion. According to the present invention, the process of manufacturing a can body by overlapping both end edges of metal materials to be joined and forming a joint by electric resistance welding, and applying a thermosetting resin-containing paint to the joint of the can body with a solid content of The thickness is 10mm
Apply to a thickness of 100μm, bake the paint,
The following formula R _E = E ₂₀ / E ₅₀ ...(1) In the formula, E ₂₀ represents the Young's modulus (Kg/mm ² ) of the coating at a temperature of 20°C, and E ₅₀ represents the Young's modulus (Kg/mm 2 ) of the coating at a temperature of 50°C. The temperature dependence of Young's modulus, defined as /mm ² ), is 1.3 to 3.0.
The step of forming a corrosion barrier thermosetting resin-containing coating with E ₂₀ ≧50Kg/mm ² is within the range of and subjecting it to at least one stage of neck-in processing at a low temperature.
A method of manufacturing a netquin welded can is provided. (Function) As already pointed out, the present invention has a Young's modulus (E ₂₀ ) of 50 Kg/mm ² or more at 20°C and a constant temperature dependence (R _E ) of the Young's modulus defined by the above formula (1). This is based on the knowledge that by providing a thermosetting resin-containing coating within the range of the above range to the welded seam, it becomes possible to perform neck-in processing of the seam-coated welded can without generating coating defects or reducing the adhesion between the seam and the coating. Although neck-in processing is a well-known processing method in the field of can manufacturing, there are special circumstances in which it is not easy to apply this processing method to seam-coated welded cans. The reasons for this are: firstly, the surface of the welded seam has a low adhesion to the coating due to the influence of the welding process, which is completely different from the metal material other than the seam; and secondly, the surface of the welded seam has low adhesion with the coating. The surface treatment effect of plating, electrolytic treatment, chemical treatment, etc. has been lost, and corrosion is likely to progress easily; thirdly, in order to prevent joint corrosion, it is necessary to improve the barrier properties against corrosive components. A dense thermosetting resin-containing coating with a large amount of heat must be applied to a considerable thickness, such that such a coating cannot withstand severe drawing operations. The present invention provides such a thermosetting resin-containing coating having an E ₂₀ ≧50 Kg/mm ² or more and a temperature dependence of Young's modulus ( _RE = E ₂₀ /E ₅₀ ) of 1. to 3.0, particularly 1.5. ~
2.5, and by subjecting such a seam-coated welded can body to net-in processing at a temperature of 50°C or higher and lower than the glass transition temperature (Tg) of the coating, the net-in processing can be performed in various ways. Not only is this possible without any trouble, but even if the manufacturer's welding can is filled with aerosol content, which is a highly corrosive aqueous content, welding seams and
This is based on the knowledge that it is possible to provide a welded can with excellent corrosion resistance without corrosion occurring from the necked-in portion. Among the above requirements related to the welded can manufacturing method of the present invention, E ₂₀ ≧50Kg/mm ² or more Young's modulus, and R _E
It goes without saying that selecting a resin-containing paint that can form a coating film within the range of 1.3 to 3.0 is important from the viewpoint of processing followability during NETSUIN processing, which will be described later, but there are other reasons as well. It is also important from the viewpoint of preventing corrosion of the seams of cans based on As will be explained in detail later, in cans equipped with a coating whose temperature dependence of Young's modulus (R _E ) is lower than the above range, cracks, peeling, etc. occur in the coating, and the adhesion to seams is extremely low, and R _E A can with a coating having a higher than the above-mentioned range has insufficient barrier properties against corrosive components, causing problems such as significant rusting at the seams. The reason for this is probably that only a resin coating that satisfies the above requirements can form a coating with a specific thickness that is dense, has high toughness, and has excellent adhesion to the base material. Next, the temperature conditions during neck-in processing, which is yet another requirement of the present invention, will be described. It has been known that thermosetting resins generally have a tendency to become soft when heated, even if they do not completely melt or soften, and this tendency is due to the glass transition point (Tg ) or is noticeable at temperatures above that temperature. The glass transition point (Tg) of a coating film containing a thermosetting resin refers to the temperature measured by the needle penetration method while changing the temperature of the coating film.
However, in the case of neck-in processing, if the resin is heated above its glass transition point, the coating itself will be damaged due to engagement between the coating and a tool, making it difficult to perform satisfactory processing. In the present invention, neck-in processing is performed in a temperature range in which the coating film during processing is sufficiently flexible and can sufficiently follow processing deformation, and the coating film is in contact with the tool during processing. This is carried out in a temperature range where sufficient recovery force can be maintained against deformation strain caused by temporary compression or stretching of the coating layer due to engagement or the like. From this point of view, in the method of the present invention, netquin processing is applied at a temperature of 50° C. or higher and lower than the glass transition temperature (Tg) of the coating resin. In other words, even if a film is formed using a paint that forms a thermosetting resin-containing coating with E ₂₀ ≧50Kg/mm ² and R _E in the range of 1.3 to 3.0, the above temperature during net-in processing is If the range requirements are not met, the coating film will not be able to follow the neck-in process and will not be able to exhibit sufficient corrosion barrier properties due to problems such as scratches on the coating film. The present invention will be explained in more detail below based on embodiments and the accompanying drawings, FIG. 1. Figure 1 of the accompanying drawings is a diagram showing the relationship between temperature and Young's modulus for various thermosetting resin-containing coatings, and curve A in Figure 1 shows the temperature dependence of the value of E ₂₀ and Young's modulus. Curve B is a coating whose R _E is within the range of the present invention, Curve _{C is a coating whose R E is} higher than the range of the present invention, and Curve D is a value of _E20 . This shows a coating film that is lower than the range of the present invention. For details of each of these coatings, please refer to Examples described later. Welded seams with these coatings can actually be heated to 50℃
Table 1 summarizes the results of measuring the state of coating, coating adhesion, exposed state of seam metal (current value by enamelator), and corrosion state of seams in actual cans for cans obtained by NETSUIN processing at temperatures of It is. The Young's modulus was measured as follows. Young's modulus measurement method Breaking strength and elongation of coating film Tensile speed: 10 mm/min Measurement temperature: variable Young's modulus was determined from the stress-strain curve obtained from a normal tensile test with a constant temperature bath. From these results, it can be seen that for cans with a coating whose temperature dependence of Young's modulus (R _E ) is lower than the above range,
Cracks, peeling, etc. occur in the coating, and the adhesion to the seams is significantly reduced _.
It is understood that cans with coatings having a higher than the above range have insufficient barrier properties against corrosive components, resulting in significant rusting at the seams. (Description of preferred embodiments of the invention) The present invention will be described in detail below. Welded can bodies The metal materials that make up the housing include, in addition to untreated steel plates (black plates), electrolytically plated or hot-dip plated steel plates such as tin, galvanized plates, chrome plated plates, and tin nickel plated plates, or chrome plated steel plates. Examples include steel plates chemically treated with acid, phosphoric acid, etc., and chemically treated steel plates such as electrolytic chromic acid treated steel plates.Furthermore, light metal plates such as aluminum plates can also be used. The formation of the side seam is preferably performed by electric resistance welding.The electric resistance welding of the side seam involves forming the can material into a cylindrical shape, and placing the formed overlapping portion between a pair of electrode rollers. This is done by making them communicate with each other, or by passing them between a pair of upper and lower electrode rollers via an electrode wire. At this time, the welding operation is performed in an inert atmosphere, and the atmosphere can be kept in an inert atmosphere until the surface temperature of the welded part drops to 550°C, and a porous metal oxide layer is formed on the outer surface of the joint. It is desirable to prevent this and improve the adhesion of protective coatings. As the inert atmosphere, nitrogen, argon, neon, hydrogen, carbon dioxide, etc. can be used. Although it is preferable to carry out the work while holding the welded joint in the above-mentioned inert gas flow, the work may also be carried out in a closed container filled with the above-mentioned gas. If a non-conductive protective film is formed on the surface of the metal material, such as electrolytic chromic acid-treated steel sheet (tain-free steel), remove these non-conductive layers from the overlapping area prior to electrical resistance welding. This can be done by removing the coating, or if the coating is thin, it can be carried out as is by using a tin-plated wire as an electrode. The width of the side seam of this welded can varies depending on the diameter of the can, but it can be relatively small, such as 0.2 to 1.2 mm. According to this seam formation method, the amount of can material used can be reduced. One of the notable advantages is that it can be done. Further, the thickness of the seam can vary from 2 times to 1.2 times the material thickness. That is, by pressing the overlapping part with high pressure during welding, the thickness of the seam can be reduced, thereby reducing the level difference between the joint part and other parts during double seaming.
This is an advantage of this welding method. Resin coating The thermosetting resin-containing coating used in the present invention exhibits excellent barrier properties against corrosive components, and has a temperature dependence of Young's modulus (R _E ) of 1.3 to 3.0, particularly 1.5.
Any resin coating can be used as long as it is within the range of 2.5 to 2.5. The temperature dependence of the Young's modulus of the resin coating ((R _E ) is
If the crosslinking density of the thermosetting resin is increased, it tends to be smaller, and conversely, if the crosslinking density is lowered, it tends to be larger. Furthermore, if the concentration of the aromatic skeleton in the thermosetting resin is increased, or even if the aromatic skeleton is the same, the degree (ratio) of para-directivity is increased, the temperature dependence of Young's modulus (R _E ) will be reduced. If you reverse the equation, R _E will have the opposite tendency. Furthermore, in composite coating systems containing both thermosetting resins and thermoplastic resins, the temperature dependence of Young's modulus (R _E ) tends to decrease as the content of thermosetting resin increases; If reversed, the opposite trend will occur. In the present invention, by adjusting the type of thermosetting resin, its degree of crosslinking, and the content ratio in the coating, it is possible to form a coating within the range of R _E on the seam. be. Thermosetting resins include phenol-formaldehyde resin, furan-formaldehyde resin,
xylene-formaldehyde resin, ketone-formaldehyde resin, urea formaldehyde resin,
Melamine-formaldehyde resin, alkyd resin, unsaturated polyester resin, epoxy resin, hismaleimide resin, triallyl cyanurate resin, thermosetting acrylic resin, silicone resin, oil-based resin, etc. alone or in combination of two or more, It is possible to use a coating in a cured state in which R _E falls within the above range. Among these thermosetting resins, epoxy-phenol paint resins and/or epoxy-amino paint resins have a high barrier property against corrosive components and are easy to set R _E within the above range. Examples include resin. In these coating resins, phenol resins and amino resins are generally components that increase crosslink density more, while epoxy resins give a much lower crosslink density than the former, so by selecting a combination of these, the optimum R _E can be achieved. It is possible to form a resin coating having the following properties. Generally, the ratio of epoxy resin component to phenolic resin component and/or amino resin component is 60:40.
The weight ratio is preferably in the range of 95:5 to 95:5, especially 70:30 to 90:10. As already pointed out, instead of using the thermosetting resin itself as a coating, a combination of a thermosetting resin and a thermoplastic resin can be used as the coating. As described in Japanese Patent Publication No. 59-38140, composite paints using thermoplastic resin as dispersed particles have excellent ability to be applied thickly to welded joints. Such thermoplastic resins include carbonyl groups (

Thermoplastic polymers containing [Formula]) in the main chain or side chain, especially those containing 12 to 12 carbonyl groups.
Mention may be made of thermoplastic polymers containing a concentration of 1400meq/100g polymer, in particular a concentration of 50 to 1200meq/100g polymer,
Suitable examples thereof include thermoplastic polyesters or copolymerized polyesters; polyamides or copolyamides; various acrylic resins; acid-modified olefin resins, and the like. In the case of this composite coating, the thermosetting resin and the thermoplastic resin are preferably used in combination in a weight ratio of 60:40 to 99:1, especially 70:30 to 96:4. The can body joint can be coated with a resin using these resins as a paint by a method known per se such as roller coating, spray coating, flow coating, dip coating, or the like. The formed coating film may be baked so that the temperature dependence of Young's modulus (R _E ) falls within the above-mentioned range. The thickness of the protective coating should be between 10 and 10 mm at the weld seam.
The thickness is preferably 100 μm, particularly within the range of 20 to 60 μm. Netlining Processing The seam-coated can bodies produced in this way are subjected to a single-stage or multi-stage netlining process using a netlining process known per se, for example the die process or the spin-necking process. The following formula Nr = R _L / R _S ...(2) In the formula, R _L represents the outer diameter of the can body before neck-in processing, and R _S represents the outer diameter of the can body at the neck-in processing part. The ratio is preferably in the range of 1.01 to 1.10, especially 1.02 to 1.07,
In the case of multi-stage neck-in processing, the overall
It is preferably within the range of 1.30, particularly 1.11 to 1.25. The neck-in process is preferably carried out at a temperature of 50° C. or higher and lower than the glass transition temperature (Tg) of the coating. In other words, temperatures above the coating's Tg are unfavorable because the coating itself will be damaged due to engagement between the coating and the tool, while temperatures lower than 50°C will cause the coating to follow the plastic flow of the metal material during neck-in processing. Therefore, coating defects such as peeling of the coating and occurrence of cracks are likely to occur. During neck-in processing, it is optional to apply a lubricant to the can body that comes into contact with the tool, or to form the tool surface that comes into contact with the can body from a material with excellent lubrication performance. The necked-in can body opening end is flanged and double-sealed to the can end to form the final can body. (Effects of the Invention) According to the present invention, the coating layer of a welded seam can withstand severe neck-in processing, maintain excellent adhesion to the joint, and prevent coating defects such as cracks and peeling during processing. We were able to provide a netzukin welding can that solved the problem. Furthermore, even when used as an aerosol can, it has become possible to prevent corrosion of welded seams due to the contents. (Example) The excellent effects of the present invention will be explained in more detail with the following example. The thermosetting paint used in the examples of the present invention is prepared by the method described below. (1) Epoxy/urea-based paint 75 parts of epoxy resin (Epicote 1007 manufactured by Ciel Co., Ltd.) with an average molecular weight of 2900, which is a condensation product of bisphenol A and epichlorohydrin, and 25 parts of butyl ether urea formaldehyde resin were mixed with ketones, esters, and hydrocarbons, respectively. An epoxy-urea paint (2) with a solid content of 25% is obtained by dissolving it in a mixed solvent consisting of the following. (2) Epoxy/phenol paint 0.5 mol of carbolic acid and 0.5 mol of p-cresol at 37
% formaldehyde aqueous solution 1.5 mol,
Add 0.15 mol of ammonia as a catalyst and react at 95°C for 3 hours. The reaction product is extracted with a mixed solvent consisting of ketones, alcohols, hydrocarbons, etc., washed with water, the aqueous layer is removed, a small amount of remaining water is removed by an azeotropic method, and the product is cooled to obtain a resol type phenol resin. Obtain a 30% solution of The above resol type phenolic resin solution and ketone in advance,
Mix a 30% solution of an epoxy resin with an average molecular weight of 2900 (Epicote 1007, manufactured by Ciel), which is a condensation product of bisphenol A and epichlorohydrin obtained by dissolving it in a mixed solvent consisting of ester, alcohol, hydrocarbon, etc. do. The weight ratio of phenolic resin and epoxy resin is
It's 30:70. This mixture is precondensed under reflux for 2 hours to obtain an epoxy-phenolic paint. Next, powder of nylon 12 (softening point 178°C by ring and ball method, carbonyl group concentration 508meq equivalent/100g) with an average particle size of 20μm obtained by freezing and crushing pellets in advance as a thermoplastic resin was added to the epoxy/phenol paint solid. The mixture was mixed so that the volume fraction of the thermoplastic resin in the mixture was 20%, and stirred and dispersed for 20 minutes using a high-speed mixer to obtain an epoxy/phenol paint (1). Next, the can body and the epoxy/urea paint mentioned above.
(2) and how to use epoxy/phenol paint (1) will be explained. Epoxy-urea paint (a mixture of epoxy resin and butyl ether urea formaldehyde resin in a weight ratio of 3:1) was applied to a regular tin plate with a thickness of 0.23 mm and a weight of 5.6 kg/ ^m2 at the seam of the can body. The margins were painted so that the film thickness after baking was 6 microns on the inner surface and 3 microns on the outer surface, except for the areas corresponding to the parts, and the margin dimensions were 2 mm wide on both sides. Then, the blank length of the coated board obtained by baking and hardening for 10 minutes in a hot air drying oven at 200°C was 206.4 mm.
Cut into a body blank with a blank height of 125.4mm. This can body blank was wrapped to a width of 0.4 mm using an ordinary seam resistance welding machine, and the welded can body (211
Obtain the diameter [outer diameter 65.8 mm]). Next, the various paints mentioned above were sprayed on the inner surface of the joint of the welded can body to a width of about 8 mm and a dry coating thickness of about 40 to 50 microns. At the same time, the outer surface was coated with a roll coat. Repair the epoxy ester paint with a width approximately equal to the width of the exposed metal part using the method so that the dry coating thickness is approximately 2 to 10 μm, and then bake it in a hot air drying oven at 220℃ for 3 minutes. A can body with the seam portion covered was obtained. Next, both sides of this can body are subjected to neck-in processing using a die method (the deformation amount of the neck processing at this time is from 211 diameter to 209 diameter). At this time, the can body is heated for approximately 10 seconds with heated air at a temperature of 200°C, so that the can temperature during netzin processing is 60°C. The can temperature is measured using a known surface thermometer. In addition, as another heating method, use an induction heater to adjust the heater current to 15A.
Heat the area around the netsukin processing area so that the temperature of the can during the netsukin processing reaches 60℃. Next, flange processing is performed when the can temperature does not drop below 50℃. Next, the neck and flange processing on the inner surface of the can body were observed with the naked eye, and the state of metal exposure at the inner seam was evaluated using the method described below (enamel letter test). Enamelator test Cut out the joint part of the can body to a width of 2 cm, and seal it with vinyl tape except for a part 5 mm wide in the direction perpendicular to this joint and 120 mm in the parallel direction to prepare a test piece. After immersing this test piece in an electrolyte of 3% saline at 25°C for 3 minutes, a carbon rod was used as a counter electrode.
Perform constant voltage electrolysis at a voltage of 100V for 10 seconds,
Measure the average current value flowing at that time. For each sample, the arithmetic mean value of the measurements of 20 specimens is taken as the result. The can body after flange processing has a nominal inner diameter of 63.4 mm with epoxy/urea coating on the inner and outer surfaces.
A tin lid for a can and a 62mm inner diameter eyelet with epoxy phenol paint on the inside and outside surfaces are double-sealed, and the resulting empty aerosol can is sealed using a conventional method.
Pack liquid glass polish, laundry paste and shaving cream, attach a mounting cup and store at 50℃ for 6 months, then open each can.
The state of corrosion at the can body joint was observed. Table 1 shows the results of the visual observation of the neck and flange portions described above, the enamellator test, and the observation results of the corrosion state of the cut portions (actual can test). In Table 1, the results using the epoxy/phenol paint (1) are shown as Example 1, and the results using the epoxy/urea paint (2) are shown as Example 2. Next, the glass transition point (Tg) was measured according to the following method. Glass transition temperature (Tg) of thermosetting resin-containing coating
In order to measure this, we used the previously described can body blank with unpainted inner and outer surfaces, and similarly repaired and baked only the inner surface of the welded and seamed areas to obtain a coated sample. This coated sample was cut out into a circular shape with a diameter of 5 mm and used as a sample for measurement. Tg refers to the temperature measured by the penetration method using a known measuring device and varying the temperature of the coating film. The thermosetting paint used in the comparative example is prepared by the method described below. (1) Comparative Example 1 70 parts of acrylic resin (acrylic copolymer consisting of acrylic ester, acrylonitrile, and methacrylic acid) and 20 parts of epoxy resin with an average molecular weight of 900, which is a condensation product of bisphenol A and epichlorohydrin. 10 parts of melamine resin, which is an addition condensate of melamine and formalin, is dissolved in a mixture of ketones, esters, alcohols, hydrocarbons, etc. to obtain an acrylic/epoxy paint (3) with a solid content of 30%. (2) Comparative Example 2 Average degree of polymerization of vinyl chloride and vinyl acetate copolymer
60 parts of 1000 vinyl chloride resin powder, hydrocarbon type, ether type, which does not dissolve the vinyl chloride resin,
It was obtained by dispersing it in an ester-based mixed solvent and further condensing it with 10 parts of an epoxy resin with an average molecular weight of 900, which is a condensation product of bisphenol A and epichlorohydrin, using bisphenol A, formalin, and ammonia as a catalyst. Vinyl organosol paint containing 5 parts of resol type phenol resin, 15 parts of acrylic resin of acrylic copolymer consisting of acrylic acid ester, acrylonitrile and methacrylic acid, and 10 parts of epoxidized soybean oil as a plasticizer. (4) is obtained. (3) Comparative Example 3 Bisphenol A was dissolved in formalin, reacted with an ammonia catalyst at a temperature of 95°C for about 3 hours, the reaction product was extracted with a mixed solvent of ketone, alcohol, and hydrocarbon, and dissolved in water. After washing with water, the aqueous layer was removed, and a small amount of remaining water was removed by an azeotropic method, and the mixture was cooled to obtain a resol type phenolic resin with a solid content of 30%. Next, bisphenol A type epoxy resin average molecular weight 3800 (Epicoat 1009, manufactured by Ciel)
The epoxy resin is dissolved in advance in a mixed solvent consisting of ketone, ester, alcohol, and hydrocarbon, and the solution with a solid content of 30% is mixed with the phenol resin. The weight ratio of phenolic resin and epoxy resin is
It's 50:50. This mixture is precondensed under reflux for 2 hours to obtain an epoxy-phenolic paint (5). For the test pieces and actual cans in which the paints of Comparative Examples 1, 2, and 3 were used for the can body joints, the can temperatures during net-in processing were applied to net-in processing at temperatures of 60°C, 55°C, and 60°C, respectively. Table 1 shows the results of the repair and evaluation performed in the same manner as in Example 1, except for the following. Comparative Examples 4 and 5 In the neck-in processing of can bodies, the can temperatures during processing were set at 93°C (Comparative Example 4) and 45°C (Comparative Example 5), respectively.
Table 1 shows the results of repair and evaluation in the same manner as in Example 1, using the same paint as that used in Example 1, except for the treatment.

【table】 [Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between temperature and Young's modulus for various thermosetting resin-containing coatings.

Claims (1)

[Claims] 1. Overlapping both end edges of metal materials to be joined,
A process of manufacturing a can body by forming a seam by electric resistance welding, and applying a thermosetting resin-containing paint to the can body joint so that the solid content is 10 to 100 μm.
After baking the paint, the following formula: R _E = E ₂₀ /E ₅₀ , where E ₂₀ represents the Young's modulus (Kg/mm ² ) of the coating at a temperature of 20°C, and E ₅₀ represents the Young's modulus of the coating at a temperature of 50°C. The temperature dependence of the Young's modulus, expressed as (Kg/mm ² ), is 1.3 to 3.0.
a step of forming a coating containing a corrosion barrier thermosetting resin having an E ₂₀ ≧50 Kg/mm ² within the range of at least 1 at lower temperatures
A method for manufacturing a welded net can, which comprises a step of adding to net-in processing of the steps.