JPH0213896B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a welded can body that uses a tinned steel plate as a can body member and has a protective resin coating layer on at least the inner surface of the can body, and has excellent corrosion resistance and suitability for contents. 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 coating layer is provided on the inner surface of the can, if the contents are filled and stored, corrosion or blisters are likely to occur under the protective coating layer, and the contents may discolor. 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/m ² or less is used, the above-mentioned problems are likely to occur. There are various possible causes for this, but one is that an alloy of tin and iron is formed in the lower layer of the tin-plated layer during the heating baking process such as painting and printing, which applies protective coating or printing to the inner and outer surfaces of the tin-plated steel plate. This is thought to be due to the fact that the amount of tin-iron alloy metal increases as the tin-plated layer progresses, and the protective effect of the tin-plated layer, which has a reduced amount of tin which has a large protective effect on the iron surface of the can stock, decreases. 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. In addition, as a method for producing a welded can body, after rolling the can material, stacking both ends together, passing the electrode wire between the electrode rolls with or without intervening the electrode wire, and passing a current under pressure to create an electrical resistance. A common method is to form a welded can body by welding, but in such a method, a tin-plated steel sheet whose tin-iron alloy layer has increased and the amount of tin has decreased in the pretreatment process described above is used to form a welded can body. When used as a can stock, not only the above-mentioned problems occur, but also the tin-iron alloy layer has a higher melting point than the base steel plate or tin, so it is difficult to weld, and the tin-iron alloy layer, which is a hard material, increases. On the other hand, since the melting point is low and the amount of tin is reduced in a soft material, in the electrical resistance welding method under pressure as described above, it is difficult for the welding electrode roll or wire electrode to sufficiently press against the tin-plated steel plate used as the can material. In addition, because of the side seam, it is difficult for the overlapped ends to come into close contact with each other, resulting in a reduction in the contact surface, which leads to an increase in contact resistance and locally causes poor welding. Moreover, in order to avoid such welding defects, it is necessary to increase the welding current or welding pressure, but when doing so, overwelding is likely to occur, spatters and voids occur at the weld joint, and the appearance of the joint becomes poor. Not only does this worsen, but it also becomes difficult to correct the coverage of the welded joints with ordinary paint. Therefore, in industrial manufacturing, it is difficult to set appropriate can-making conditions to continuously and stably manufacture good-quality welded cans, resulting in the production of welded cans of poor quality. The present inventors conducted studies to solve the above-mentioned problems that occur when a tin-plated steel plate with a small amount of tin coating is used as a can body member of a welded can, and as a result,
As a tinplate material, the amount of tin plating on the inside surface of the can is
In order to obtain a welded can body using a tin-plated steel plate of 0.5 to 1.7 g/ ^m2 , the composition of the tin-plated layer of the tin-plated steel plate to be used and the composition of the paint applied to the inner surface of the can are set appropriately in advance. After forming the welded can body, the tinned steel plate of the can body undergoes heat treatment during the can manufacturing process.
At the stage when the final can is formed, two layers are coated on the base steel plate: a tin-iron alloy layer with a tin content of 0.35 to 1.60 g/ ^m2 and a tin layer with a tin content of 0.10 to 1.35 g/ ^m2 . The welded can body has a structure in which at least the innermost layer in contact with the tin-plated steel plate is made of a thermosetting epoxy resin paint as a resin protective coating layer on the inner surface of the can body. As a result, there are no welding defects at the can body weld joints, and even when filled with various contents and stored, there is no corrosion of the can stock, no formation of blisters, and no quality deterioration such as discoloration or deterioration of flavor of the filled contents. The present invention was completed after discovering that welded cans of excellent quality can be obtained as can bodies for food cans, beverage cans, etc. Next, to explain the present invention in more detail, first, in the present invention, a tin-plated steel plate with a tin coating amount of 0.5 to 1.7 g/m ² is used as a can stock. After undergoing heat treatment in the normal can manufacturing process, such as heat treatment during the necessary painting and printing, the tin layer on the surface of the final can body has a tin content of 0.10 to 1.35 g/ ^m2 . Thickness (Hereinafter, the thickness of the tin layer is indicated by the amount of tin per unit volume.)
and the tin-iron alloy layer below it is equivalent to the tin content.
A tin-plated steel plate having a thickness of 0.35 to 1.60 g/m ² (hereinafter, the thickness of the tin-iron alloy layer is expressed in terms of tin content per unit area) can be used in advance. is necessary. Generally, welded cans are made by applying the desired paint and printing to the inner and outer surfaces of tin-plated steel plates with multiple can bodies, except for the parts to be welded, and then cutting them to the size of can body blanks, which are then rolled up using a known welding machine. A can body is formed by welding the side surfaces of the can body together using a can body, and after covering and correcting the exposed iron surface of the joint and the vicinity thereof, a flange is applied to the end of the can body, and a lid is seamed to one end of the can body.
Furthermore, if desired, it can be obtained by applying a correction coating or the like to the inner surface of the can body. Therefore, tin-plated steel sheets used for can manufacturing are used to protect the can material or to make it look beautiful during the process up to the can body.
Painted and printed several times, from 160℃
It undergoes heat treatment under temperature conditions exceeding 200℃, during which alloying of tin and iron progresses in the intermediate layer between the tin layer and the base steel sheet, and the tin-iron alloy layer, generally represented by FeSn ₂ , increases. However, the tin layer containing only tin decreases. This tendency varies depending on the composition of the tin-plated layer of the tin-plated steel sheet, which is the unpainted original sheet, especially the thickness of the alloy layer, the thickness of the tin layer, and the manufacturing conditions of the tin-plated steel sheet, but it depends on the can manufacturing process. Various heat treatments in the process, especially painting,
In the original plate before undergoing heat treatment in the printing process,
If a dense tin-iron alloy layer is formed in advance on the tin plating layer to be relatively thick (for example, 0.3 g/m ² or more), the increase in the tin-iron alloy layer due to heat treatment during the coating printing process will be 0.2 to 0.3 g. /m ² , but in a tin-plated steel plate in which almost no tin-iron alloy layer is formed, for example, the tin-iron alloy layer is 0.1 g/m ² or less, the tin-iron alloy layer is reduced to 0.4 g/m 2 by the heat treatment. ~0.6g/ ^m2
A large amount is formed, and the tin layer is greatly reduced. Moreover, the configuration of the tin layer and the tin-iron alloy layer of the tin plating layer is closely related to the weldability of the can material and the quality of the can after the can body is formed. In other words, it is necessary to have an appropriate tin-iron alloy layer and a certain thickness of the tin layer to avoid welding defects and to improve the corrosion resistance of the can body and its suitability for contents. If the structure of the layer and the tin-iron alloy layer is inappropriate, various problems will occur in terms of can manufacturing and can quality. In particular, in the case of the tin-plated steel sheet used in the present invention, which originally has a small amount of tin plating, the growth of the tin-iron alloy layer due to the heat treatment in the coating printing process leads to a relatively significant reduction in the tin layer. In such a can stock, the effect of the tin layer as described above can hardly be expected. In the present invention, a tin-plated steel plate with a tin coating amount of 0.5 to 1.7 g/ ^m2 is used, but at the stage where it is finally made into a can body through a heat treatment process such as a painting printing process,
The tin plating layer on the can body shall be formed of two layers: a tin layer with a tin content of 0.10 to 1.35 g/m ² and a tin-iron alloy layer with a tin content of 0.35 to 1.60 g/m ² . If the amount of tinning is less than 0.5g/ ^m2 , the original effect of tinning cannot be expected at all, and if the amount of tinning is less than 1.7g/ ^m2 ,
It may be handled in the same way as a so-called conventional tin-plated steel plate, and this is outside the scope of the present invention. In the present invention, at such a tin plating amount of 0.5 to 1.7 g/m ² ,
The configuration of the tin layer and tin-iron alloy layer with a limited tin weight as described above is desirable. If the tin layer is less than 0.1 g/ ^m2 , not only will weldability deteriorate, but also corrosion resistance and content resistance will deteriorate. descend. Also, as in the present invention, the amount of tin plating is
In tin-plated steel sheets of 0.5 to 1.7 g/m ² , even if the tin-iron alloy layer is 0.1 g/m ² or less at the original plate stage,
A tin-iron alloy layer grows during a heat treatment such as a painting printing process in a normal can manufacturing process, and usually becomes 0.35 g/m ² or more, and the tin layer does not become 1.35 g/m ² or more. However, the presence of an appropriate tin-iron alloy layer can be expected to improve the adhesion of the tin-plated layer to the base steel plate and provide corrosion protection for the base steel plate ^.
Preferably, a tin-iron alloy layer of 0.40 to 1.0 g/m ² is suitable. In order to obtain a can body with a tin-plated layer having such a structure, even if the tin-iron alloy layer grows in the heat treatment step of the can-making process, the tin layer and the tin-iron alloy layer do not remain in the tin-plated layer having the above-mentioned structure. It is necessary to use a tin-plated steel plate as the original plate, which is designed so that the amount of tin plating falls within the range of
0.5 to 1.7 g/ ^m2 , and the tin layer is 0.5 to 1.6
A tin-plated steel plate having ^{a tin-iron alloy layer of 0 to 1.2 g/m 2 is} suitable. Generally, the tin-iron alloy layer that makes up the plating layer of a tin-plated steel sheet is not evenly covered with the outer tin layer, and the tin-iron alloy layer and the base steel sheet may be exposed locally. The degree of this varies depending on the manufacturing method, etc. even with the same tin-iron alloy layer and tin layer thickness, and so-called no-reflow type tin-plated steel sheets tend to have less exposure of the tin-iron alloy layer than reflow type ones. In the present invention, a no-reflow type tin-plated steel plate with less exposure of the tin-iron alloy layer is preferred. In addition, in the case of ordinary tin-plated steel plates,
A very thin chromate layer is provided on the surface,
Such a chromate layer is thinner than the tin-plated layer and does not particularly affect the effect of the tin-plated layer of the present invention, so there is no problem in the present invention even if a conventional chromate layer is provided. There is no. 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 solder cans, welding cans, etc., and has a protective effect on the base steel sheet.
Since the effect of preventing iron elution into the contents is also reduced, in order to use it as food cans, beverage cans, etc., at least the surface of the tin-plated steel plate corresponding to the inner surface of the can should
It is extremely important to provide an appropriate resin protective coating layer in order to protect the can material from the contents to be filled into the can and to prevent discoloration and flavor deterioration of the contents due to elution of the can material. 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, , it is necessary to use a thermosetting epoxy resin paint, and a thermosetting epoxy phenol resin paint is particularly suitable.
In particular, a phenolic resin containing 65% by weight or more of a resol phenol type resin formed from bisphenol A and a bisphenol A type epoxy resin having a number average molecular weight of 1,400 to 7,000 are preferably mixed in a weight ratio of 50/50 to 5/95. A thermosetting paint containing 30/70 to 10/90 weight ratio is suitable. If a paint other than a thermosetting epoxy resin paint is used as the paint constituting the protective coating layer of the present invention, it is expected that the adhesion to the tin-plated layer with a small amount of tin, corrosion resistance, and the effect of preventing discoloration and flavor of the contents will be achieved. It is inappropriate to use it without being able to do so. Among the thermosetting epoxy resin paints (which are also preferred paint systems), the thermosetting epoxy phenol resin paints mentioned above are particularly suitable, but if the molecular weight of the epoxy resin used is too low or the bisphenol A
If the content of the resol-type phenolic resin formed from is less than 65% by weight, or if the ratio of phenolic resin to epoxy resin is outside the range of 50/50 to 5/95 weight ratio, the curability of the coating film will deteriorate. This is not preferable because adhesion, processability, etc. deteriorate, and from a practical standpoint, corrosion resistance, the effect of preventing iron elution into the contents, etc. decrease. Such thermosetting epoxy resin paints are usually used as solvent-based paints in which the resin component is dissolved in a solvent, but if necessary, solvent-soluble or insoluble resin components, curing agents, curing catalysts, etc. may be added as modifying components. Alternatively, inorganic components can be used. 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 tinned layer on the inner surface of a can body using the thermosetting epoxy resin paint of the present invention includes using the paint of the present invention.
Using an appropriate coating device such as a roll coater, paint the inner surface of the can body multi-piece tin-plated steel sheet, except for the weld joints, and bake it to form a can body blank. A method of producing a welded can body, or manufacturing a welded can body using an unpainted tin-plated steel plate on the inner side as a can body blank, and then applying the above paint to the inner side of the can body before or after attaching a lid to one end of the can body. Methods such as spray painting and baking may be mentioned, but the former method is preferable in terms of practical workability. Here, the protective coating layer can be used as a coating layer by further coating the same or different coating material on the coating film already formed before or after forming the can body and baking it dry. The suitable coating thickness for such a protective coating layer is 2 to 10 μm, 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 is suitable. 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 any measures to improve the quality by creating a layered coating film by layering or other methods, you can 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. Thus, the welded can body of the present invention has a reduced amount of tin plating.
A tin-plated steel plate with a tinned layer of 0.5 to 1.7 g/m ² is used, and when the final can is made, a tin-iron alloy layer and a tin layer with a tin content within a specified range are placed on the base steel plate. Since the can body is formed of two layers, and at least the innermost layer of the can body is protected with a resin protective coating layer made of epoxy resin paint, the amount of tin plating on the can body can be reduced. It is possible to use tin-coated steel sheets (so-called thin-coated tin plates) with low tint content, and has excellent can quality, making it suitable for a variety of contents, especially food,
It is suitable as a can for canning beverages. Examples will be described below, and parts represent parts by weight. In addition, 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 Civilization Specification and Examples were determined by JIS G3303 (electrolytic stripping method). It is. Comparative Example 1 75 parts of p-cresol and 25 parts of w-cresol were applied as paints to the inner surface of the can body of a tin-plated steel plate with a thickness of 0.22 mm and a tin-plated layer on both sides as shown. 15 parts of resol type phenolic resin obtained by reacting mixed phenol with formaldehyde in the presence of an ammonia catalyst and a number average molecular weight of approx.
Solid content: 30%, viscosity (Fc# ₄ , 25℃) obtained by dissolving 85 parts of 3000 bisphenol A type epoxy resin in a mixed solvent consisting of alcohol, ketone, ester, and aromatic organic solvents. Using epoxy/phenol resin paint (Paint ○A) for 40 seconds, apply margin painting with a roll coater, excluding the welded seams, and bake at 205℃ for 10 minutes.
A cured coating film with a film thickness of 5.2μ was formed. Next, acrylic resin white paint was applied to the outer surface of the can body, except for the welded joints, and baked at 190℃ for 10 minutes to form a white coating film.Printed on top of it at 160℃ After that, apply finishing varnish and bake at 175℃ for 10 minutes.
You can get a coated plate made by painting and printing on both sides of a tin-plated steel plate. This coated steel sheet is cut into the size of a 250g beverage can body blank, and is welded using a known welding machine that performs pressurized seam welding using an electrode roller via a copper electrode wire at a can making speed of 350 cans per minute. The side parts of the can body were welded together in an atmosphere to form a can body.
Next, the weld seam on the inner side of the can body and its vicinity were coated and corrected using a correction paint, flanges were applied to both ends of the can body, and an inner-coated aluminum lid was attached to one end by double seaming, and the can body containing 250 g was attached. Obtained. The results of various evaluations performed using the obtained painted plates, can bodies, and can bodies are shown in the attached table. From this result, in this comparative example, there were localized welding defects in the welded joints of the can body, and when welding was performed at a higher current value, there were more spatters, resulting in poor appearance, and it was difficult to correct the coating with correction paint. The weldability was poor due to insufficient welding. In addition, in actual can storage tests, corrosion was observed on the inner surface of the can body, and the iron content in the contents increased. Comparative Example 2 All comparative examples except for using a tin-plated steel plate with the configuration shown in the attached table (total amount of tin plating, tin layer, tin-iron alloy layer) of the tin-plated layer of the tin-plated steel plate before painting and printing. A painted steel plate, a can body, and a can body were prepared in the same manner as in 1, and various evaluations were performed. As a result, as shown in the attached table, the tin layer in the tin-plated layer structure in the can body after can body formation is reduced compared to the original plate before painting and printing, and the tin layer is The alloy layer has increased, and like the can body of Comparative Example 1, weldability is poor, and even in actual can storage tests, slight corrosion was observed on the inner surface of the can body, and the iron content in the contents was also slightly It was increasing. Example 1 A coated steel plate, a can body, and a can were prepared in the same manner as in Comparative Example 1, except that a tinned steel plate having the structure shown in the table below was used, with the composition of the tinned layer on the tinned steel plate before painting and printing. A body was created and various evaluations were conducted. As shown in the attached table, the welded seam of the can body of this example formed a good welded seam even under the same conditions as those of Comparative Example 1 where welding defects locally occurred. In addition, in the actual can storage test, only a slight amount of corrosion was observed, and the amount of iron leached into the contents was lower than that of Comparative Example 1.
It was less than that. Example 2 The composition of the tin-plated layer on a tin-plated steel plate before painting or printing uses a tin-plated steel plate as shown in the table below, and paint is applied to the surface of the steel plate that will become the inner surface of the can body. 20 parts of a resol type phenol resin obtained by reacting bisphenol A with formaldehyde in the presence of an ammonia catalyst and a number average molecular weight of
3410 bisphenol A type epoxy resin is dissolved in a mixed solvent to obtain a thermosetting epoxyphenol paint (Paint ○Ro) with a solid content of 29% and a viscosity (Fc # ₄ , 25℃) of 40 seconds. A coated steel plate, a can body, and a can body were prepared in the same manner as in Comparative Example 1 except for the use of these materials, and various evaluations were performed. As a result, as shown in the attached table, the welded seam of the can body of this example was in good condition with no defective joints or sputters, and the coating with the correction paint was also successful. In addition, in actual can storage tests, no corrosion was observed on the inner surface of the can body, and no iron was leached into the contents. Examples 3 to 6 Using tin-plated steel plates with different tin-plated layer compositions before painting and printing, the paint ○○ used in Example 2 was used as the paint to be applied to the inner surface of the can body. A painted steel plate, a can body, and a can body were prepared in the same manner as in Comparative Example 1, and various evaluations were performed. As shown in the attached table, the can body and can body using the tin-plated steel plate and paint of this example had good weldability, and good results were obtained in the actual can storage test after filling with contents. It was done.

[Table] This is the total amount of tin in the gold layer.
(*2) Cut a test piece from the body of an empty can and measure the composition of the tinned layer using the above-mentioned method. The amount of tin plating on the body of an empty can is the sum of the amount of tin in the tin layer and the amount of tin in the tin-iron alloy layer.
(*3) Judging the joint condition of the welded joint of the can body by visual inspection (microscopic observation) (carried out before inner coating correction).
◎Extremely good, ○Good, △There is no joint defect, but the appearance is poor and it is difficult to correct the coating, ×If the welding conditions are changed due to poor joint, spatter occurs frequently, and the appearance is poor.
(*4) Fill an empty can with milk coffee, seal it with a tin lid coated on the inside, sterilize it in a retort at 135℃ for 30 minutes, store it at 50℃ for 2 months, and then open the can. In addition to observing and determining the condition, the amount of iron eluted into the contents is measured and the flavor is determined.
◎ indicates no abnormality.
In addition, in the attached table, the amount of tin plating on the tin layer on the body of an empty can is different from the amount of tin plating on the original plate because the sampling position where the amount of tin was measured is different and it is based on actual measurements. .

Claims (1)

[Scope of Claims] 1. A welded can body in which both side edges of tin-plated steel plates are overlapped and welded together to form a can body, and at least a resin protective coating layer is provided on the inside of the can body, wherein the welded can The amount of tin plating on the tinned steel plate that forms the body of the can is
0.5 to 1.7 g/ ^m2 , and at least 0.35 in terms of tin content on the base steel plate at the stage of final can body.
~1.60g/ ^m2 tin-iron alloy layer and tin content 0.10~1.35g/
m ² of the tin layer in this order, and at least the innermost layer in contact with the tin-plated steel plate of the can body is a protective coating layer consisting of a thermosetting epoxy resin paint. A welded can body made of tin-plated steel plate characterized by the following. 2. The thermosetting epoxy resin paint comprises a phenolic resin containing 65% by weight or more of a resol type phenolic resin formed from bisphenol A;
It contains a bisphenol A type epoxy resin with a number average molecular weight of 1,400 to 7,000 in a weight ratio of 50/50 to 5/95, and the thickness of the resin protective coating layer formed by the paint is 2 to 10 μm. A welded can body using a tin-plated steel plate according to claim 1.