JPH0134862B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a lock seam can in which the body is joined by a lock seam (so-called burst seam), and more specifically, the can has excellent corrosion resistance on the inner surface and the lock seam is hermetically sealed with solder. Regarding the rectangular lock seam can with attached.

All-lock seam cans such as conventional 9 and 18 square cans (refers to cans that do not include a wrap part in the lock seam formed at the corner of the body.The side lock seam part of round cans, etc. is usually at the end. serves as a lap part, which prevents a large step from forming at the seam after the lid is double-sealed.In this specification, all-lock seam cans are referred to as lock-seam cans.) , Regular tinplate (both sides tin-plated steel plate)
If the corrosion resistance of the inner surface of the can is particularly a problem, mold the lockseam can body from a tin blank that has been painted and baked, leaving only the portion of the inner surface of the can that is to become the lockseam part as an unpainted part. After the plate and the bottom plate are double-sealed, the lock seam portion and the double-sealed portion are soldered to ensure the strength and airtightness of the seam portion. However, if the inner surface is composed of a thin baked coating film (for example, a 5 μm thick phenol epoxy coating film) on top of the tinned layer, the contents may be neutral or weak, such as liquid detergent or boiled bamboo shoots. When filled with an alkaline material, tin is easily eluted from scratches in the coating film and contaminates the contents. Further, as mentioned above, there is a problem in that the painting process is complicated because the part that should become the lock seam part is left unpainted.
Recently, for example, in order to solve such problems,
No. 53-141786 proposes a can body made of a steel plate coated with a polyolefin film whose side joints are thermally bonded with an organic adhesive. In this case, too, if tinplate is used as the base plate, and cracks occur in the polyolefin film near the double seaming part where the degree of processing is high during the can manufacturing process, or at the embossed part on the body surface (polyolefin film is used in the laminating process or When slowly cooled during the can manufacturing process, etc., it crystallizes and becomes brittle, which causes the problem of tin elution as described above. Especially in this case, even if there is only one micropore in the film, tin will be eluted one after another from that hole, and for example, if the content is neutral detergent, the tin leaching area will expand to about 10 to 20 cmφ in 3 months. Then, the film in that area floated up.
Moreover, a black tin-iron alloy layer remains on the surface of the base metal after tin is eluted, and this black part is visible through the colorless transparent film, making defects more noticeable. The base plate is made of stain-free steel (electrolytic chromic acid treated steel plate. In other words, on both sides,
This problem can be solved by using a surface-treated steel sheet (which is a surface-treated steel sheet with an electrolytic chromic acid treatment film that has a hydrated chromium oxide layer on top of which the main layer is a metallic chromium layer). In this case, as mentioned above, the side seams of the can body must be thermally bonded using an organic adhesive, which requires special equipment and complicated operations, and it is easy to ensure high bonding strength and complete airtightness. The problem is that it is not. Similar problems occur when using films other than polyolefin resin, such as linear polyester resin or polyamide resin films.

The present invention has been made in view of the problems of the prior art as described above, and an object of the present invention is to provide a lock seam can having a lock seam portion with high bonding strength and airtightness without tin elution on the inner surface of the can. That's true.

The present inventors have developed a lock seam can for which the outer surface of the can is tin-plated, and the inner surface is made of a thin steel plate with a polyolefin film pasted on a tin-iron alloy layer. It has been found that the above object can be achieved by forming a solder layer on the part.

That is, the present invention uses a steel plate in which a tinned layer is formed on the surface that is to become the outer surface of the can, a tin-iron alloy layer is formed on the surface that is to be the inner surface, and a polyolefin film is pasted on the alloy layer. This is a rectangular lock seam can having lock seam portions formed at the corners of the body, which has excellent corrosion resistance, characterized in that at least the opposing tinned layers of the lock seam portions are joined by solder. The company provides lock seam cans.

The present invention will be explained below.

FIG. 1 shows the external appearance of a lock seam rectangle 1, in which 2 is a lock seam formed at the corner of the body, 3 and 4 are 2 parts of a top plate 5, a bottom plate 6, and a body 7, respectively. Shows the heavily seamed part. Note that 8 is an embossed portion. The lock seam can of the present invention is a surface-treated steel plate in which a tin-plated layer and a tin-iron alloy layer are formed on the surface that is to become the outer surface of the can, and a polyolefin film is pasted on the tin-iron alloy layer on the surface that is to become the inner surface. 9 forms a body portion 7, a top plate 5, and a bottom plate 6. Therefore, a schematic sectional view of the side lock seam portion 2 before soldering is as shown in FIG. 2-a.
That is, the surface-treated steel sheet 9 has, from the outside, a tin layer 10, a tin-iron alloy layer 11, a low carbon thin steel sheet 12, and a tin-iron alloy layer 1.
3 and a polyolefin film 14.

The surface of the tin layer 10 is usually coated with a very thin chromate film and an oil film. The present invention also includes a case where a coating film or a printed film is formed on the tin layer except for the lock seam portion. tin layer 1
It is preferable that the thickness of 0 is 1 to 12 g/m ² .
This is because if it is thinner than 1 g/m ² , solder penetration will be poor and corrosion resistance and rust resistance will decrease. 12 again
This is because even if it exceeds g/m ² , no particular improvement in quality can be expected, but rather increases in cost. Tin-iron alloy layer (Fe
The thickness of the material (based on Sn ₂ ) 11 may be that of ordinary tinplate, that is, 0.05 to 1.0 g/m ² .
The low carbon thin steel plate 12, which is the substrate, is made of a standard plate for tinplate, and its thickness is usually about 0.1 to 0.4 mm. A tin-iron alloy layer (Fe Sn ₂
From the viewpoint of corrosion resistance, it is preferable that the material (mainly composed of) 13 be dense and have no underlying iron exposed. Such a tin-iron alloy layer can be formed into a dense layer by, for example, tin plating using a weakly acidic bath with a low tin ion concentration or a known alkaline bath under conditions that generate a large amount of hydrogen gas during tinning. After the tin plating layer is formed, electricity is applied to the substrate to raise the temperature of the low carbon steel plate 12 and the tin plating layer by resistance heating, induction heating, etc. to melt the tin for a short time to perform melting diffusion. or by solid state diffusion at a temperature just below the melting point of tin. The former is mainly carried out in an electric tinning line, and the latter is mainly carried out in a polyolefin film bonding line, which will be described later. It is preferable that no undiffused tin layer remains on the tin-iron alloy layer 13 from the viewpoint of corrosion resistance to the contents. In other words, when a pinhole exists in a polyolefin film, the tin around the pinhole is eluted one after another by the content liquid (e.g., weakly alkaline) through the pinhole, and the polyolefin film floats up. This is because it has excellent corrosion resistance, so the above phenomenon is unlikely to occur. The thickness of the tin-iron alloy layer 13 is preferably 0.05 to 1.0 g/m ² in terms of tin. If it is thinner than 0.05g/m ² , corrosion resistance will decrease, while if it is thicker than 1.0g/m ² , workability will decrease and cracks will occur in the processed area, impairing the corrosion resistance of that area, and corrosion resistance in non-processed areas is also particularly expected. This is because it is not possible, and furthermore, it will cause an increase in the cost of tin. In order to increase the adhesive strength of adhesive for polyolefin film, tin-iron alloy layer 1
It is more preferable to coat the top of the layer 3 with an extremely thin hydrated chromium oxide layer (chromate film) of about 0.005 to 0.05 g/m ² (chromium equivalent) (not shown).
In this case, if it is thinner than 0.005g/ ^m2 , corrosion resistance will decrease.
If it is thicker than 0.05 g/m ² , flat plate adhesion strength tends to decrease. Such a hydrated chromium oxide layer is formed by a known method, for example, by cathodic treatment using a sodium dichromate bath used for post-treatment of electroplating.

Although illustration of the adhesive layer is omitted, the polyolefin film 14 is usually adhered onto the tin-iron alloy layer 13 via the adhesive layer. There are no particular restrictions on the adhesive, but for example, bisphenol A type epoxy resin proposed in JP-A No. 52-130832, vinyl chloride-vinyl acetate, etc.
one consisting of a maleic acid copolymer resin, an amine curing agent, and a propylene-acrylic acid copolymer resin;
Or an olefin copolymer resin having a carboxyl group proposed in JP-A No. 53-133242,
Those made of epoxy resin and its curing agent are preferably used. The thickness of the adhesive layer is usually 8 to 100 μm.
It is. As a polyolef in film, about 10
~200 μm thick low density polyethylene, medium density polyethylene, high density polyethylene, polypropylene, polybutylene, ethylene-propylene random copolymer, ethylene-propylene block copolymer, ethylene-1-butene copolymer, ethylene-propylene -Butadiene terpolymers, etc., copolymers obtained by graft-modifying these resins with polar groups such as carboxyl groups, ionomers, or mixtures thereof may be used as desired depending on the purpose of use. Further, a mixture of these with a light stabilizer, a heat stabilizer, a flame retardant, a lubricant, a coloring agent, etc. may also be used.

As is clear from FIG. 2-a, in the lock seam portion 2, of the contact portions at both ends of the blank, the tin layers 9 are in contact with each other in the can outer surface side portion 2a, and the polyolefin film 14 is in contact with the can inner surface side portion 2b. are in contact with each other. On the other hand, at the intermediate contact portion 2c, the tin layer 9 and the polyolefin film 14 are in contact. Therefore, if the lock seam part 2 is immersed in a solder bath in the presence of a suitable flux, or if solder is dripped or applied to the preheated outer surface contact area 2a of the lock seam part 2, as shown in FIG. 2-b. , 2a, the solder penetrates between the opposing tinned layers to form a solder joint 15, and the tin of the tinned layer is integrated with the solder. That is, the opposing tinned layers are joined by solder. Penetration of solder usually stops before the intermediate contact portion 2c. All-tin solder (melting point 232
℃) 60% Sn-40% Pb solder (melting point 190℃) is used. Therefore, during soldering, the temperature of the lock seam increases to over 200°C. On the other hand, the melting point of polyolefin resin is approximately 110°C for low density polyethylene,
High-density polyethylene has a temperature of about 130°C, and polypropylene has a temperature of about 165°C. Therefore, during soldering work,
Normally, the polyolefin films 14 on both sides of the inner surface contact portion 2b are thermally fused to form a fused portion 16, as shown in FIG. 2-b. Therefore, airtightness of the lock seam portion to the outside and the inside is ensured by the solder joint portion 15 and the heat-sealed portion 16, respectively.
Therefore, the liquid content enters from the inner surface contact portion 2b and acts on the end surface 2d, corroding the base iron 12 and the tin layer 10,
Eventually, the solder of the solder joint 15 is also corroded,
This prevents the occurrence of troubles such as leakage of the liquid content. If the organic film on the inner surface is a baked coating of paint, or is made of polyethylene terephthalate resin (melting point approximately 260°C) or polyamide resin (melting point approximately 250°C for nylon 6.6), which has a relatively high melting point, the above effects will be achieved. I can't wait.

FIG. 3 shows a schematic cross-sectional view of the double seam portion 3. In this figure, the reference numeral 12' indicates the tin-iron alloy layer 11, the low carbon thin steel plate 12, and the tin-iron alloy layer 13.
Parts with the same reference numerals as in FIG. 2-b indicate the same parts, except for those shown representatively of the layers consisting of the same parts. It is clear that the solder joint part 15 and the heat-sealed part 16 are formed also in this part, and the same effect as in the case of FIG. 2-b can be obtained.

Further, high bonding strength at the lock seam portion is also ensured by the solder joint portion 15 and the heat-sealed portion 16.

The lock seam can of the present invention is manufactured, for example, as follows.

After degreasing and pickling the low carbon steel strip, it is tin-plated on one side (tin-iron alloy layer 13 side) and tin-plated on the other side (tin-iron alloy layer 13 side) under conditions that generate a large amount of hydrogen gas during tinning as described above. The differential thickness plating on the layer 10 side) is performed to a predetermined thickness. However, in this case (for example, when using an alkaline bath), the current effect is low, so if you do not like the fact that it takes a long time to thicken,
After thinning to a predetermined thickness on both sides under the above conditions, only one side (the tin layer 10 side) is tinned to a predetermined thickness in a normal tinning bath. After washing with water, a reflow treatment is performed by heating to a temperature just above the melting point of tin for a time necessary to convert all the tin on the diluted side into a tin-iron alloy. More preferably, chromate treatment and oiling are performed. Next, an adhesive is applied and heated on the tin-iron alloy surface, and then a polyolefin film is attached while being heated. Incidentally, the tin-iron alloy layer may be grown during application heating of the adhesive and/or heating and adhesion of the polyolefin film. Next, the surface-treated steel sheet produced in this way is cut into blanks of a specified size, and a lock seam can body is formed by a conventional method.
A top plate and a bottom plate previously formed on this can body are double-sealed to form a lock seam can such as 18 cans, and the side lock seam portions and the bottom double seam portion are soldered by a conventional method. Thereafter, after filling the contents, the container is sealed with a cap 17.

Since a tin layer is formed on the surface of the blank that is to be the outer surface of the lock seam can of the present invention, solder penetrates into the contact portion on the outer surface of the can among the contact portions at both ends of the blank in the lock seam portion, facilitating solder jointing. part is formed. On the other hand, since the blank surface, which is to become the inner surface of the can, is covered with a polyolefin resin film whose melting point is lower than that of the solder, a heat-sealed part of the polyolefin resin is formed at the contact area on the inner surface of the can during the soldering work. Ru. Therefore, even if the contents filled in the can are weakly alkaline tin or liquid detergent that easily dissolves solder, the liquid detergent will penetrate inside the lock seam and dissolve the tin layer and solder joints. There is no risk of perforation or leakage. Furthermore, the joint strength of the lock seam portion is comparable to that of a regular tin can (the lock seam portion is soldered) which is made of a tin layer on the inner surface due to the solder joint portion and the heat-sealed portion. Furthermore, since the inner surface is coated with a chemically inert polyolefin film, it is possible to fill the inner surface with highly corrosive contents that cannot be protected by ordinary paint baking. Furthermore, a tin-iron alloy layer with excellent adhesion and corrosion resistance, especially alkali resistance, is interposed between the low carbon steel plate and the polyolefin film, so when liquid detergent etc. is filled, pin holes may be formed in the polyolefin film. Even if corrosion occurs, corrosion will not spread. Therefore, as seen when there is a tin layer on the tin-iron alloy layer 13 (when ordinary tinplate is used), the elution of tin under the polyolefin film progresses one after another starting from the pinholes. There is a peeled part of the film with a diameter of approximately 5 to 20 cm, and there is a black tin-iron alloy layer underneath that part (the tin-iron alloy layer remaining due to surface tin elution appears black when wet, but the present invention It has the advantage that it does not cause defects such as those formed densely (which have a grayish-white appearance when the polyolefin film is in close contact with the polyolefin film) to be seen through and make defects more conspicuous. Furthermore, since the amount of expensive tin used is extremely small on one side, the cost is lower and economically advantageous compared to the case where the base plate is a normal tin plate plated on both sides.

Examples will be described below.

Example: A low carbon steel strip with a thickness of 0.32 mm and a hardness (Rockwell 30T) of 61 was degreased and pickled using a conventional method, and then heated in an acidic tin plating bath with the following composition at a bath temperature of 45°C and a current density.
Both sides were tinned at 0.08 g/m ² under the condition of 7 A/dm ² .

Tin plating bath composition; tin sulfate 40g/phenolsulfonic acid (as 60% liquid)
40 g/ ethoxylated α-naphthol sulfonic acid 5 g/ subsequently in a bath of the same composition at a bath temperature of 45°C and a current density of
Tin plating of 11.2 g/m ² was carried out on one side only at 30 A/dm ² . Then, after washing with water, the
It was heated for 0.6 seconds at a temperature just above the melting point of tin, subjected to reflow treatment, and then rapidly cooled in water. By this heat treatment, all the tin on the thinner side was changed to a tin-iron alloy, and the thickness of the alloy layer on the thicker side was 0.09 g/m ² (in terms of tin). Subsequently, cathodic treatment was performed at a temperature of 50°C in a dichromic acid aqueous solution with a concentration of 30 g/dm at a current density of 10 A/dm ² to form a hydrated chromium oxide layer of 0.015 g/m ² (chromium equivalent) on the surface. and on top of that 4.0
mg/m ² of cottonseed oil was applied electrostatically.

100mg/g of adhesive having the composition below was applied onto the tin-iron alloy layer of the tamped steel plate manufactured as described above using a metal roll with a grain pattern and a rubber roll.
It was reverse coated to a thickness of dm ² , dried and baked at 200°C for 30 seconds, and cooled to room temperature.

Adhesive composition: Part by weight Propylene-maleic anhydride graft copolymer powder (particle size 200 μm or less) 90 Bisphenol A type epoxy resin 10 Amine curing agent 1 Solvent (toluene-MIBK-cyclohexanone)
200 Next, the above strip was heated at 180° C. for 30 seconds, and then a 50 μm thick polypropylene film was attached with a roll and heated at 200° C. for 30 seconds, followed by water cooling.

From the sheets obtained by cutting the polypropylene adhesive strips described above, 18 can bodies were manufactured by a conventional method so that the tinned surface was the outer surface. On the other hand, a polypropylene adhesive strip obtained by treating a low carbon steel strip with a thickness of 0.32 mm and a hardness of 53 in the same manner as above was cut to make a top plate and a bottom plate with the tinned layer facing the outside. . This top plate and bottom plate were double-sealed to the can body. Thereafter, the double seam portion and the lock seam portion were run at a speed of 27 m/min using filamentous solder and a tin solder bath to form a solder joint. obtained in this way
After filling 18 cans with commercially available liquid detergent and sealing them,
960 cans were stored at room temperature for 6 months, but there were no abnormalities such as metal elution or leakage into the contents. Cans manufactured in the same manner were also subjected to leakage tests and pressure tests in accordance with JIS-Z-1602-6, but no abnormalities were found.

Comparative Example A commercially available product was produced in exactly the same manner as in the example except that a tin plated layer with a thickness of 11.2 g/m ² was formed on the tin-iron alloy layer on the inner surface of the can was used as the original plate for attaching the polyolefin film. 18 cans filled and sealed with liquid detergent were manufactured. When 960 of these cans were stored at room temperature for 6 months, significant tin elution (100 to 150 ppm) was observed in the liquid content of 18 of them, and examination of the inside of the cans showed that these cans had a diameter of approximately 5 to 15 cm. It was observed that the tin elution area was developed under the film. It was confirmed that the origin of these defects was minute cracks that occurred in processed areas such as double seams and embossed areas.

[Brief explanation of drawings]

FIG. 1 is a perspective view of a lock seam square can which is an embodiment of the present invention, and FIGS. 2-a and 2-b are schematic cross-sectional views taken along the line - in FIG. 1, respectively, before soldering. FIG. 3 is a schematic sectional view taken along the - line of the can in FIG. 1 after soldering. DESCRIPTION OF SYMBOLS 1... Lock seam can, 2... Lock seam part, 10... Tin plating layer, 12... Steel plate, 13...
...Tin-iron alloy layer, 14...Polyolefin film, 15...Solder joint, 16...Polyolefin heat-sealed part.

Claims (1)

[Claims] 1. A tinned layer is formed on the surface that should become the outer surface of the can, and a tin-iron alloy layer is formed on the surface that should become the inner surface,
A rectangular lock seam can made of a steel plate with a polyolefin film adhered to the alloy layer and having lock seam portions formed at the corners of the body, wherein at least the tinned layer opposite the lock seam portions is A lock seam can with excellent corrosion resistance that is bonded with solder. 2. A lock seam can with excellent corrosion resistance according to claim 1, wherein opposing polyolefin films of the lock seam portion are heat-sealed to each other.