JPH0373348B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention provides a beverage that has excellent can quality with extremely little iron elution even after long-term storage after filling, and no deterioration in the quality of the contents or flavor.
This invention relates to a method for manufacturing a welded can suitable for canning food. Conventionally, soldered cans, seamed cans, etc. have been used as food or beverage cans, but in recent years, welded cans have also come into practical use. As the can material for such welded cans, tin-plated steel plate (tinplate material) or stain-free steel is used. Among these, the tin-plated steel sheets used are those conventionally used in solder cans, and the amount of tin plating is as high as 2.8 g/m ² or more because of the need to maintain so-called solderability. Recently, due to tin resource issues, consideration has been given to the practical application of tin-plated steel sheets with a small amount of tin plating, and application to welded cans is also being considered, but in general, tin-plated steel sheets with a small amount of tin plating are When steel plates are used, even if a protective resin coating layer is provided on the inner surface of the can, if the contents are filled and stored, corrosion and blisters are likely to occur under the protective resin coating layer. Discoloration and flavor changes are likely to occur. In particular, when a tin-plated steel plate (so-called thinned tin plate material) with a tin coating amount of 1.2 g/cm ² or less is used, the above-mentioned problems are likely to occur. There are various possible causes for this, but one is that the surface treatment of the tin-plated steel plate is inappropriate, resulting in tin plating during the heating baking process such as painting and printing, which applies protective coating or printing to the inside and outside surfaces. This is thought to be because alloying of tin and iron progresses in the lower layer, the tin-iron alloy layer increases, and the tin layer, which has a large protective effect on the iron surface of the can stock, becomes thinner, reducing the protective effect of the tin-plated layer. It will be done. Next, the method for producing a welded can body is to roll up the can stock, stack both ends together, pass it between electrode rolls with or without an electrode wire, and apply current under pressure to generate an electric current. A common method is to form a welded can body by resistance welding, but when welding by a method similar to the above-mentioned tin-plated steel plate, the tin layer, which is a soft material with a low melting point, is reduced in the pre-treatment process as described above. Therefore, the welding electrode roll or wire electrode cannot be sufficiently pressed against the tin-plated steel plate used as the can material, reducing the contact surface, and the side seams make it difficult for the overlapped ends to come into close contact with each other. The surface area decreases, leading to an increase in the contact resistance value and causing local weld joint failure. Therefore, in industrial manufacturing, it is difficult to set appropriate can-making conditions to continuously and stably manufacture good welded can bodies. The reason for this may be that it is difficult. Another possible cause is that the resin protective coating layer provided on the tin-plated steel plate is defective or is inappropriate as a protective coating for the tin-plated steel plate. On the other hand, even if sufficient consideration is given to the problems of the material of the can body, the resin protective coating layer itself, and the problems during the painting process, the quality after long-term storage is not necessarily constant. Quality control is required to select only welded can bodies that are suitable for long-term storage. As one type of quality control, we have traditionally carried out accelerated tests to determine the quality of cans made of coated steel sheets filled with contents and stored for long periods of time.
The under-cutting corrosion test (so-called UCC test) is used, but the test results vary widely and do not match the can quality after long-term storage of welded can bodies, and are therefore insufficient. There is no suitable means for accurately and early grasping the quality of cans with an emphasis on long-term storage stability of cans filled with contents, and it is difficult to obtain cans with excellent long-term storage stability after filling with contents. Ta. The present applicant previously disclosed in Japanese Patent Laid-Open No. 58-177448 that a can material used for a can body formed by overlapping and welding both side edges has a tin plating amount of 0.5 to 1.7 g/m ² . Yes, on the base steel plate, at least in terms of tin content.
Tin-iron alloy layer of 0.35-1.60g/ ^m2 and tin content 0.10-1.35
Using a tin-plated steel plate having two layers with a tin content of 65 g/m ² in this order, a resol type phenol resin formed from bisphenol A is added to the hardening type epoxy resin paint applied to the inner surface of the can body. phenolic resin containing more than % by weight and a number average molecular weight of 1400~
7000 bisphenol A type epoxy resin and 50/
We proposed a tin-plated steel plate with a coating containing a coating material in a weight ratio of 50 to 5/95 and a resin protective coating layer having a thickness of 2 to 10 μm. As a result of extensive studies, the inventors of the present invention found that even if the tin content of the steel plate used for the can body is 0.2 to 1.2 g/ ^m2 , which is even lower than that of the tin-plated steel plate proposed above, the can quality remains the same as proposed above. In addition to achieving can quality equivalent to that of tin-plated steel sheets, it also prevents welding defects at the welded joints of the side seams of the can body, improving weldability, and improving corrosion resistance of the can material and rust resistance during storage of the can body. We have found that it is possible to improve In other words, cans for beverages and food cans are made of welded can bodies made of coated steel sheets with a protective resin coating on tin-plated steel sheets, which have a tin content of 0.2 to 1.2 g/ ^m2 , which is lower than that of conventional tinplate materials. When used as a body, a tin-plated steel plate with a specific surface treatment and a tin-plated layer thereon, which becomes the specific tin-plated layer after applying a protective resin coating. using a specific resin protective coating layer,
By manufacturing a welded can body using a coated steel sheet as a can body member whose corrosion characteristic value is below a specified value as detected by a prescribed test, it has excellent long-term storage stability as a can body for canned beverages and food. It has been found that a can body can be obtained. The purpose of the present invention is to provide a base steel plate with a nickel content of 0.01 to 0.01.
A coating layer made of a thermosetting epoxy resin paint is applied to a tin-plated steel plate ^{, which has a tin-plated layer with a tin content of 0.2 to 1.2 g/m 2 formed} on the upper layer that has been nickel-plated with a concentration of 0.2 g/m 2. It is an object of the present invention to provide a welded can body which uses a coated steel plate and has excellent long-term storage stability after being filled with contents. Another object of the present invention is that the tin content is 0.2 to 1.2 g/
We have established a method to quickly and accurately determine the quality of cans when welded can bodies with internal coatings made of surface-treated steel sheets as small as ^2.0 m2 are filled with contents such as beverages and food and stored for long periods of time. By regulating the contents, even if the contents are filled with highly corrosive contents such as natural or synthetic beverages and stored for a long period of time, the quality of the contents will not deteriorate due to pitting corrosion or iron elution, and the contents of the can and the contents of the beverage can be maintained. An object of the present invention is to provide a welded can body whose inner surface is coated using a tin-containing surface-treated steel plate whose quality can be guaranteed for a long period of time. That is, the gist of the present invention is that the amount of tin is 0.2~
For cans of beverages and food, the can body is made by welding a coated steel plate with a resin protective coating layer made of thermosetting epoxy resin paint on a tin-plated steel plate with a tinned layer of 1.2 g/ ^m2 . In the method for manufacturing a welded can body, the tin-plated steel plate is a base steel plate with the tin-plated layer formed thereon, and the tin-plated layer is formed after the resin protective coating layer is formed. Tin content 0.15~1.19g/ ^m2 Tin alloy layer and tin amount 0.01~
1.05 g/m ² It is a steel plate equipped with a tinned layer consisting of two tin layers, and the resin protective coating layer is a phenolic resin containing 65% by weight or more of a resol type phenolic resin formed from bisphenol A. , a film thickness of 2 consisting of a thermosetting epoxyphenol resin paint containing bisphenol A type epoxy resin with a number average molecular weight of 1400 to 7000 in a weight ratio of 50/50 to 5/95.
The coated steel plate, which has a resin coating layer of ~10μ and forms the can body, is cut with two cuts of 20 mm in length at a depth reaching the base steel plate from the coating layer forming surface so as to intersect at right angles, and the intersection point is 5mm with a convex surface with a radius of 10mm from the back side of the surface with the cut line in the center.
Extrude to form a convex surface, and apply citric acid to a radius of 25 mm centered on the intersection of the notches at the apex of the convex surface.
Contains 0.071 mole and 0.26 mole of salt in caustic soda
After adjusting the pH to 3.0 and contacting an aqueous solution heated to 95℃, slowly cooling to 70℃ for 30 minutes and then holding at 70℃ for 20 hours, the peeling area of the resin protective coating layer from the base steel plate due to corrosion was measured. The corrosion characteristic value, defined as the value measured and expressed in square millimeters, is
200 or less. Next, the present invention will be explained in more detail as follows. The tin-plated steel plate used in the present invention needs to have excellent weldability and the effect of protecting the base steel plate by the tin-plated layer. Generally, welded can bodies are produced by applying the desired paint and printing to the inner and outer surfaces of tin-plated steel plates made of multiple can bodies, excluding the parts to be welded, and then cutting them into can body blank sizes, which are then rolled up and welded using known welding techniques. A can body is formed by welding the sides of the can body together using a machine, and after covering and correcting the exposed iron surface of the joint and its vicinity, a flange is applied to the end of the can body, and a lid is seamed to one end. Furthermore, if desired, it can be obtained by applying a correction coating or the like to the inner surface of the can body. For this reason, the tin-plated steel sheets used for can making are painted and printed several times in order to protect and beautify the can material during the process up to the can body.
During heat treatment under temperature conditions ranging from °C to over 200 °C, alloying of tin and iron progresses in the intermediate layer between the tin layer and the base steel sheet, forming a tin-iron alloy layer generally represented by FeSn _2. increases and the tin layer decreases. This type of tin plating layer has a close relationship with the weldability of the can material and the quality of the can after the can body is formed, and a certain thickness of the tin layer improves weldability, corrosion resistance of the can body, and suitability for contents. It is necessary to In the present invention, a tin-plated steel plate with a small tin content of 0.2 to 1.2 g/m ² is used, but the base steel plate is pre-treated with nickel plating with a nickel content of 0.01 to 0.2 g/m ² . , the amount of tin in the upper layer is 0.2
A tin-plated layer with a tin content of ~1.2 g/m ² is formed, and after a protective resin coating described later is applied, the tin-plated layer becomes a tin-iron alloy with a tin content of 0.15-1.19 g/m ² . A tin-plated steel sheet comprising a tin alloy layer made of a tin-nickel alloy or the like, and a tin layer with a tin content of 0.01 to 1.05 g/m ² is suitable. Applying nickel plating treatment to the above tin-plated steel sheets prevents welding defects at the weld joints of the can body side seams, improves weldability, and improves the corrosion resistance of the can material during storage. 0.01~ before tin plating, as it has the effect of improving rust resistance, etc.
It is provided within the range of 0.2 g/m ² . Furthermore, if the tin plating amount of the tin plating layer provided on the base steel plate or nickel treatment is less than 0.2 g/m ² , the original effect of tin plating cannot be expected at all;
g/m ² or more, it is similar to a so-called conventional tin-plated steel plate and is not a thin-plated tin plate, which is the object of the present invention. In addition, in tin-plated steel sheets that have been subjected to nickel plating, the base steel sheet is not uniformly coated with the nickel plating formed on the upper surface of the base steel sheet, and in particular, in the thin plating treatment, the base steel sheet is not uniformly coated with the nickel plating treatment formed on the upper surface of the base steel sheet. Since the surface of the base steel plate is exposed, when tin plating is performed on top of nickel plating, a tin-containing alloy layer containing a tin-iron alloy and a tin-nickel alloy and a tin layer are formed. The tin alloy layer formed in this way increases further after forming the subsequent resin protective coating layer as described above, but the tin alloy layer is formed on the base steel plate or nickel layer. The tin alloy layer has a tin content of 0.15 to 1.19 g/ ^m2 ,
Further, the upper tin layer having a tin content of 0.01 to 1.05 g/m ² is suitable in terms of adhesion to the base steel plate, corrosion resistance, etc. In addition, the tin-plated steel sheet of the present invention may be subjected to surface treatment with chromium hydrated oxide similar to conventional tinplate materials, but it is preferable to provide a chromium/chromium hydrated oxide layer from sergeant melting. This is desirable because corrosion resistance can be improved at any time without impairing weldability. The tin-plated steel sheet of the present invention has a smaller amount of tin plating than the tin-plated steel sheet conventionally used for welded cans, etc., and has a protective effect on the base steel sheet,
The effect of preventing iron elution into the contents will also decrease,
To be used as food cans, beverage cans, etc., at least the surface of the tin-plated steel plate corresponding to the inner surface of the can must be protected from the contents to be filled into the can, and must be protected against elution of the can material. It is extremely important to provide an appropriate resin protective coating layer for the purpose of preventing the discoloration and flavor deterioration of the contents caused by this. As such a resin protective coating layer, a single coating layer or a protective coating layer consisting of multiple coating layers using the same or different types of paint is used, but as the coating that constitutes the innermost layer in contact with the tinned layer, , thermosetting epoxy phenolic resin paints are suitable, especially phenolic resins containing 65% by weight or more of resol type phenolic resins formed from bisphenol A, and paints with a number average molecular weight of 1400.
~7000 bisphenol A type epoxy resin and 50/
50-5/95 weight ratio, more preferably 30/70-10/
A thermosetting paint containing 90% by weight is preferred. If a paint other than the thermosetting epoxy phenol resin paint with the above structure is used as the paint constituting the protective coating layer of the present invention, the adhesion to the tinned layer with a small amount of tin, corrosion resistance, discoloration and flavor of the contents will be reduced. It is inappropriate because no preventive effect can be expected. Furthermore, in the thermosetting epoxy phenol resin paint, the molecular weight of the epoxy resin used is too low, the content of resol type phenol resin formed from bisphenol A in the phenol resin is 65% by weight or less, and If the ratio of phenolic resin and epoxy resin is outside the range of 50/50 to 5/95 weight ratio, the curing properties, adhesion, processability, etc. of the coating film will deteriorate, and in practical terms, corrosion resistance and infiltration into the contents will deteriorate. This is not preferable because it reduces the effect of preventing iron elution. Such thermosetting epoxy phenol resin paints are usually used as solvent-based paints by dissolving the resin component in a solvent, but if necessary, solvent-soluble or insoluble resin components, curing agents, curing catalysts, etc. may be added as modifying components. can use inorganic components. In the case of thermosetting epoxyphenol paints, which are suitable paints for the present invention, phenoxy resins, etc. are used in combination, aminoplasts such as urea resins are used as curing agents, and solvent-insoluble thermoplastic resins or hardened resins are used in combination. It is possible to use the resin powder in combination with dispersion. The content of such modifying components is preferably 30% by weight or less based on the resin solid content of the paint. A method for forming a protective coating layer on the tin-plated steel plate using the thermosetting epoxy phenol resin paint of the present invention includes using the paint of the present invention and using an appropriate coating device such as a roll coater.
Paint the inside surface of the can body multi-piece tin-plated steel sheet, except for the weld joints, and bake it.
After that, a can body plank is made and a welded can body is made by a welding machine, or a welded can body is manufactured using an unpainted tin-plated steel plate on the inner side as a can body plank, and then a lid is attached to one end of the can body. There is a method in which the paint is later applied to the inner surface of the can body by a method such as spray painting and then baked, but the former method is preferable in terms of practical workability. Here, the protective coating layer can be used as a multilayer by further coating the same or different type of paint on the coating film already formed before or after forming the can body, and baking and drying it, if necessary. The suitable coating thickness for such a protective coating layer is 2 to 10μ, and in the case of a protective coating layer formed by overcoating, etc., the thickness of the protective coating layer made of thermosetting epoxy resin paint should be A suitable thickness is 2 to 7 microns. If the thickness of the protective coating layer is less than 2μ, it cannot be expected to protect the can material, and if it is more than 10μ, the processability of the coating will be poor.
When the lid is attached by seaming after filling with the contents, a processing defect occurs in the seaming part, and if the contents are filled and stored, this part will corrode, which is undesirable. In particular, when the thermosetting epoxy phenol resin paint is used as the paint for forming the protective coating layer of the present invention, the same or different paint is applied by roll coating, spray coating, etc. on the previously formed coating film. Even if you do not take measures to improve the quality by creating a multi-layered coating film by overcoating, etc., it is possible to sufficiently cover and protect the can material with a relatively thin film of 2 to 7μ, especially 3 to 7μ, in one coat. is possible and particularly preferred. In addition, in the present invention, on the outer surface side of the can stock,
Painting or printing can be applied for protection or decoration as appropriate, except for the welded joints. According to the present invention, a welded can body obtained by using a tin-plated steel plate having a structure including the above-mentioned nickel plating layer and a tin-plating layer and a coated steel plate having the above-mentioned resin protective coating is used to hold the content of the beverage. In order to have can quality with excellent long-term shelf life, the coated steel plate used as the can body member must have a corrosion characteristic value of 200 or less as determined by the test described below. Corrosion characteristic value
For cans made of coated steel sheets higher than 200, if stored for a long period of time after filling with contents, coating corrosion will occur and the amount of iron leached will increase, resulting in a decrease in the quality and flavor of the contents, which is a practical problem. This is not desirable. Here, to explain in detail the corrosion characteristic values of the coated steel plate, FIGS. 1 and 2 are illustrations of a test piece 1 for measuring the corrosion characteristic values. Two cut lines 2 of length 20 mm intersecting at right angles are made on the tin-plated steel plate at a depth that reaches the base steel plate from the coating forming surface of the coated steel plate piece on which the resin coating has been applied. Using an Erichsen testing machine or the like, extrude the inserted surface by 5 mm from the back side using a convex member with a radius of 10 mm, using the intersection point of the cut line 2 as the apex, and create a test piece with the relevant part 3 protruding approximately 5 mm from the front side on the convex surface. shall be. Figure 3 shows an apparatus for determining corrosion characteristic values using the test piece 1. An aqueous solution 4 in which 0.26 mol of common salt and 0.071 mol of citric acid are dissolved is adjusted to pH 3.0 using caustic soda and heated to 95°C. After that,
About 100 ml was placed in a glass container 5 with an inner diameter of 50 mm and a content capacity of 150 ml, and the test piece 1 was placed with the convex portion 3 facing inward.
At the container mouth 5, so that the intersection of the score lines 2 is at the center,
Place the container 5 through an O-ring packing 6 and fix it with a clampable jig 7 so as not to leak even if the container 5 is turned over.Then, the apparatus is turned over and the test aqueous solution 4 is placed on the convex surface 3 of the test piece 1. and slowly cooled to 70°C over about 30 minutes, then held at 70°C for 20 hours. After a predetermined period of time has elapsed, the test piece 1 is taken out, the resin protective coating layer that has been lifted off the base steel plate due to corrosion under the resin protective coating layer is removed using adhesive tape, and the area peeled off due to corrosion from the base steel plate is measured and squared. Corrosion characteristic value expressed in millimeters.
The corrosion characteristic values obtained by this method are characteristic values related to the integrity of the metal can stock and the resin protective coating layer used, and are applicable to welded cans made of the same coated steel plate as the test piece used. The quality of cans when filled with contents and stored for a long period of time is closely related to, for example, the state of corrosion that occurs under the protective resin coating layer. Figure 4 shows welded cans with different corrosion characteristics using tin-plated steel plates with different surface treatment conditions, thermosetting epoxy resin paints and film thickness conditions, etc., and filled with milk coffee. This is an example of the relationship between the occurrence of corrosion on the inner surface of a can and the corrosion characteristic value when stored for two months in a welded can using a coated steel plate with a corrosion characteristic value of 200 or less. It is clear that this does not occur. The actual can storage test results shown in FIG. 4 were visually evaluated according to the following evaluation criteria. 1...No abnormalities on the inside of the can and its contents. 3...Corrosion occurred on the inside of the can, but the effect on the contents was small. 5...Corrosion on the inside of the can was significant and had a large effect on the contents. The can bodies of the present invention thus obtained have excellent can quality and are suitable as cans for canning various contents, especially foods and beverages. The test examples will be explained below, and parts are by weight. In addition, the measurements of the amount of tin plating in the tin-plated steel sheets, the amount of tin in the surface tin layer, and the tin content in the tin-iron alloy layer in this civil specification and test examples were determined by JIS G3303 (electrolytic stripping method). For tin-plated steel sheets that have been subjected to nickel plating treatment, the tin content in the alloy layer is determined by fluorescent X-ray method using a calibration curve prepared in advance after dissolving the tin layer with alkali. It is. -Test Example- In test numbers 1 and 4, a tin-plated steel plate with a thickness of 0.22 mm and a tin-plated layer on both sides was configured as shown in test numbers 1 to 8 on the inside surface of the can body. 75 parts of p-cresol and 25 parts of m-cresol as paint
15 parts of a resol type phenol resin obtained by reacting 1 part of mixed phenol with formaldehyde in the presence of an ammonia catalyst and 85 parts of a bisphenol A type epoxy resin with a number average molecular weight of about 3000 are mixed into alcohol-based, ketone-based, ester-based and Epoxy/phenol resin paint (paint ○A) with a solid content of 30% and a viscosity (Fc ₄ #, 25°C) of 40 seconds obtained by dissolving it in a mixed solvent consisting of aromatic organic solvents, and test number 2. , 3, 5, 6, 7, and 8, 30 parts of a resol type phenol resin obtained by reacting bisphenol A with formaldehyde in the presence of an ammonia catalyst and a bisphenol A type epoxy resin having a number average molecular weight of 3410 were used as coatings. Solid content obtained by dissolving 70 parts in a mixed solvent: 29
%, viscosity (Fc ₄ #, 25℃) for 40 seconds using a thermosetting epoxy phenol paint (paint ○○), except for the weld seam, apply margin coating with a roll coater, and bake at 205℃ for 10 minutes. A protective resin coating layer with a thickness of 5.2 μm was formed. Next, apply white acrylic resin paint to the outer surface of the can body, except for the welded seams.
Baked at 190℃ for 10 minutes to form a white coating, printed on top of that, baked at 160℃ for 10 minutes, and then applied finishing varnish to 175℃ for 10 minutes.
A tin-plated steel plate with coating and printing on both sides was obtained. This coated steel plate is 250
The can bodies are cut to the size of can body blanks for cans containing 3-g beverages, and the cans are welded in an inert gas atmosphere at a can-making speed of 350 cans per minute using a known welding machine that performs pressurized seam welding using copper electrode wires and electrode rollers. The side parts of the can body were welded together to form a can body. Next, the weld seam on the inner surface of the can body and its vicinity are coated and corrected using a correction paint,
Both ends of the can body were flanged, and an internally painted aluminum lid was attached to one end by double seaming to obtain a can body containing 250 g. Using the obtained coated steel plates, the corrosion characteristic values were measured for each of test numbers 1 to 8, and welded cans formed from each coated steel plate were filled with various contents and stored at 50°C for 2 months. The quality of the cans was evaluated. The results are shown in the attached table. The results show that can bodies using coated steel sheets with a corrosion characteristic value of 200 or more had poor can quality in actual can storage tests, but can bodies with a corrosion characteristic value of 200 or less had good quality. Incidentally, Test No. 3 is different from the steel sheet of the present invention disclosed in Japanese Patent Application Laid-Open No. 177448/1983 proposed by the applicant prior to the present invention, that is, a tin-plated single layer without a nickel-plated layer ( A tin-plated steel plate with a tin content of 0.5 to 1.7 g/m ² is used. In addition, as shown in test numbers 5, 6, 7, and 8, the surface treatment conditions of the tin-plated steel plate and the resin protective coating layer used were within the preferred range of the present invention, and the corrosion property value was 200 or less for a long period of time. Although cans have good quality during storage, even if the surface treatment conditions and/or resin protective coating layer are within the preferred range of the present invention, cans with a corrosion characteristic value of 200 or more may not have good can quality during long-term storage. Nakatsuta. As is clear from the table, although the tin content range of the tin plating layer applied to the steel plate is 0.2 to 1.2 g/ ^m2 , which is smaller than that of the conventional can body, the can body obtained by the method of the present invention is As for quality, the tin content range of the tin plating layer is 0.5 ~
It was at the same level as 1.7g/ ^m2 steel plate. Also,
Test number 5 of the present invention having a nickel plating layer,
Nos. 6, 7, and 8 showed a tendency for the corrosion characteristic values to be lower than those with only a tinned layer. Therefore, when applying a tin plating layer to a steel plate, by applying a nickel plating layer in advance, weld joint defects at the weld joint of the side seam of the can body can be prevented.
It was confirmed that this method improves weldability, and also improves the corrosion resistance of the can stock and the rust resistance during storage of the can body.

[Table] ○: Good, △ Fairly good, × Poor bonding or poor appearance, making it difficult to correct the coating.
*2) Fill an empty can with milk coffee, paint the inside, seal it with a tin lid, retort sterilize it at 125℃ for 30 minutes, store it at 50℃ for 2 months, and observe the condition of the inside after opening the can. At the same time, the amount of iron eluted into the contents is measured and the flavor is determined.
○: Good, △: Slightly good, ×: Poor due to occurrence of corrosion under the coating, large amount of iron elution, and change in flavor.

[Brief explanation of drawings]

Fig. 1 is a perspective view of a test piece used in the test of the present invention, Fig. 2 is a sectional view taken along the line - - of Fig. 1, Fig. 3 is a longitudinal sectional view showing the test device of the present invention, and Fig. 4 is an actual It is a diagram showing the results of a can storage test.

Claims (1)

[Claims] 1 A coated steel plate with a protective resin coating layer made of a thermosetting epoxy resin paint is welded onto a tin-plated steel plate having a tin-plated layer with a tin content of 0.2 to 1.2 g/m ² and used as a can body. In the manufacturing method of welded can bodies for canned beverages and food, the first tin-plated steel plate is a base steel plate plated with nickel with a nickel content of 0.01 to 0.2 g/cm ³ and a first tin-plated layer formed on the upper layer. and the tin-plated layer has a tin content of at least 0.15 to 1.19 after forming the resin protective coating layer.
A steel plate with ^{a tin-plated layer consisting of two layers: a tin alloy layer with a tin content of 0.01 to 1.05 g/m 2 ;}
The resin protective coating layer comprises a phenolic resin containing 65% by weight or more of a resol type phenolic resin formed from bisphenol A, and a number average molecular weight of 1400 to 1,400.
7000 bisphenol A type epoxy resin 50/50
It is a resin coating layer with a film thickness of 2 to 10 μm consisting of a thermosetting epoxy phenol resin paint containing in a weight ratio of ~5/95, and the coated steel plate forming the can body is attached to the base steel plate from the coating layer forming surface. Make two cuts with a length of 20 mm at right angles to the depth reached, and from the back side of the surface with the cut lines, extrude 5 mm from a member with a convex surface with a radius of 10 mm, forming a convex surface. An area with a radius of 25 mm centered around the intersection of the apexes of the cut was brought into contact with an aqueous solution containing 0.071 mol of citric acid and 0.26 mol of salt, adjusted to pH 3.0 with caustic soda and heated to 95°C for 30 minutes.
After slowly cooling to 70℃ and then holding at 70℃ for 20 hours,
Manufacture of welded can bodies for canned beverages and food, characterized by having a corrosion characteristic value of 200 or less, which is defined as a numerical value expressed in square millimeters, measured by measuring the peeling area of a resin protective coating layer from a base steel plate due to corrosion. Method.