JPH0542647A - Production of film laminate steel plate for can for foods - Google Patents

Abstract

PURPOSE:To obtain a method for producing a film laminate steel plate, which is suprior in corrosion resistance and molding properties and suitable for can for packing foods, with a high productivity by using a very thin thermoplastic resin film. CONSTITUTION:When a nylon film is laminated on a tinned steel belt through an adhesive, temperatures of the steel belt and the adhesive are controlled to be in an optimum range, and the static electricity of the film is removed. In this manner, the extremely thin film can be continuously and stably laminated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a film-laminated steel sheet for a food can, which has excellent corrosion resistance and can reduce the production cost, and particularly, to produce a good film-laminated steel sheet using an extremely thin thermoplastic resin film. It is possible to achieve a great resource saving effect and economic effect.

[0002]

2. Description of the Related Art As food cans, there are many two-piece cans which are composed of a body and a bottom-integrated part and a lid. This two-piece can is manufactured by the following steps. A tin-plated steel strip is cut into sheets of a predetermined size to obtain tinplate sheets.

Next, a thermosetting resin is applied to one side of the sheet and baked in a baking oven. At this time, the sheet is heat-treated with the unpainted surface leaning against the support. As the thermosetting resin, a resin containing a phenolic resin, a urea resin, an ester resin, etc. as a curing agent based on an epoxy resin is generally used. The temperature condition in a baking furnace is 180 to 220 ° C. × 10 to 20 minutes. When the painting / baking of one surface is completed in this manner, the painting / baking of the other surface is similarly performed.

Next, printing / baking is performed on a surface corresponding to the outer surface of the can. This printing / baking is performed in the same manner as the above-mentioned painting / baking. Next, press working, DP (Drawing an
d Pressing, DRD (Drawing)
and Redrawing) processing, DTR (Dra
Wing and Thin Drawing) or the like is performed to obtain a can body in which the can body and the can bottom are integrated.

After filling the contents with this, a lid manufactured separately is attached.

[0006]

As described above, the tin plate is coated with thermosetting resin at 180 to 220 ° C x 10
Heat treatment (baking) is performed for a long time of ~ 20 minutes.
At this time, the coating film has a three-dimensional network structure and is excellent in permeation resistance (barrier property) with respect to the filling material and exhibits corrosion resistance, but there is a problem in workability. That is, when a forming process such as press working is performed, a fine crack may be generated or damaged in the coating film, or the coating film may be peeled off, and as a result, corrosion resistance may not be sufficiently exhibited. Was often there. Specifically, when a highly corrosive content is filled, blackening (SnS) or black spots (Fe
S) may occur. In particular, when liquid or gel foods are stored, even if there is one coating film defect on the inner surface of the can, corrosion of the metal material of the can proceeds from this part,
In addition to lowering the flavor and storability of foods, heat sterilization and hot water treatment will make the product even worse and lose its commercial value.

In addition, during coating, as described above, since heat treatment is performed for each tinting sheet and for each front and back surfaces for a long time, there is a problem that productivity is extremely poor.
The present invention has been made in view of the above problems of the prior art, corrosion resistance using an ultrathin thermoplastic resin film, a film-laminated steel sheet for food can excellent in formability excellent for food can It is an object of the present invention to provide a method for producing a film laminated steel sheet.

A method for producing a coated metal structure in which a thermoplastic polyester resin film is adhered to a metal surface instead of the thermosetting resin layer is disclosed in JP-A-52-65588.
However, there is no suggestion regarding the technique of sticking an ultrathin thermoplastic resin film to a metal surface continuously in a good state in this prior art example. It is said that specifying the crystallinity is the essence.

Further, JP-A-1-145137 and JP-A-1-192545 disclose a method for producing a composite steel sheet in which a polyester film is thermocompression-bonded to a tin plate under a specific temperature condition, and further, JP-A-1-180336. In the above No. 1, there is proposed a method for manufacturing a composite steel sheet in which a polybutylene terephthalate film is heat-bonded and then rapidly cooled. The technology for pasting is not disclosed.

[0010]

According to the present invention, the tin deposition amount is 0.
Bake size paint on 5 ~ 2.8 g / m ² tinned steel sheet,
Next, the steel sheet previously held at 20 to 40 ° C. is coated with an adhesive whose temperature is adjusted to 25 to 35 ° C., and then static electricity is removed from the film when the thermoplastic resin film is coated.

[0011]

The present inventors considered that the problems of the above-mentioned prior art are due to the use of a thermosetting resin as a paint. That is, in order to obtain corrosion resistance, it is necessary to react the unreacted functional groups in the polymer of the thermosetting resin to form a three-dimensional network structure in the molecular structure by crosslinking between the polymers, and for that reason Requires heat treatment. It was considered that the thermosetting by this baking treatment deteriorates the workability and makes it easy for defects such as cracks to occur. Therefore, the present inventors have conceived to use a thermoplastic resin instead of the conventional thermosetting resin. Since this thermoplastic resin does not need to be thermoset, the processability does not deteriorate. Moreover, since it is provided in the form of a film, it is not necessary to cut the surface-treated steel strip into a sheet in advance, and since the film can be continuously attached to the steel strip using an adhesive, the productivity can be greatly improved. Become.

Further details will be described below. In order to maintain high corrosion resistance even after forming such as pressing and deep drawing, it is necessary to increase the adhesive strength of the film against tint. Therefore, in the present invention, the size coating material is first applied to the tin plate, and then the adhesive is applied onto the tin plate, and then the film is attached. This size paint can enhance the adhesive strength of the film.

As the size paint, epoxy-amino resin, thermosetting vinyl, polyester melamine resin or the like is selected according to the application. For example, vinyl is used for ultra deep drawing, epoxy-amino resin is used for higher heat resistance, and polyester melamine resin is used for ultra deep drawing that requires higher heat resistance. To be selected. The size paint may be applied only to the surface corresponding to the inner surface of the can.

As the adhesive, a thermosetting resin dissolved in a diluent is used, and as the resin, one kind or two or more kinds of a phenol resin, an epoxy resin and a urethane resin may be used. A thermoplastic resin film (hereinafter referred to as a laminated film) is used as the film. Nylon resin is suitable as the laminate film. To explain the reason, the properties required for the laminated film are as follows. First of all, since it undergoes a forming process, a large elongation is required. Also, in the case of food cans, they are sterilized at high temperature (110-140 ° C) after filling the contents, and they are stored in a refrigerator, so they have excellent heat resistance and strength at low temperatures, and cans collide with each other. Even so, the collision strength must be great so that it does not crack or break. Nylon-based resins are preferred in the present invention because nylon-based resins can exhibit the above properties.

As the thermoplastic resin film, polyethylene terephthalate (PE
T) Films are well known. This PET film has excellent barrier properties and exhibits a good anticorrosion effect on various contents. However, on the other hand, this film has poor moldability,
When subjected to severe processing such as in a two-piece can, the film is likely to crack, and the workability is limited. In this respect, nylon film has an elongation of 300-400% (ASTM
-D882) is also available, and can withstand severe molding processing.

When manufacturing the film-laminated steel sheet for food cans of the present invention, first, while rewinding the tin plate coil, the size paint is applied to one surface and baking is performed for a short time. Next, after applying the adhesive on both sides and immediately drying and curing in a drying oven, a laminate film is attached,
Aging treatment is performed at a temperature of 20 to 180 ° C to improve the adhesive properties. The film is cured by this aging treatment, but it is not cured at less than 20 ° C, and the upper limit was set to 180 ° C from the viewpoint of heat resistance. After the aging treatment, it is cooled to be a film-laminated steel plate for food cans.

Since it can be manufactured through the above steps, it is not necessary to carry out coating one by one in a sheet form,
It is possible to manufacture continuously and it is possible to greatly improve the productivity. The thickness of the above-mentioned laminate film is generally 50 to 100 μm, which is generally manufactured. However, as long as the corrosion resistance can be ensured, the thinner one is preferable. However, if it is too thin, the work of continuously attaching the film becomes difficult. The reason is that if the film is very thin, wrinkles are more likely to occur when the film is applied, and if the film is applied as it is, it will become double adhesion. In order to prevent the generation of wrinkles, it is conceivable that the film is attached in a state in which a large tension is applied, but in that case, the film shrinks after being dried by the tension only after drying. In addition, since the laminated film thickness of the steel sheet becomes non-uniform due to the non-uniform shrinkage over the entire surface, it is not practically used because it is greatly damaged during the subsequent press forming process.

Therefore, the inventors of the present invention have conducted extensive studies on the cause of wrinkles in a thin film, and in the process, for example, the static electricity on the film surface immediately after rewinding a 20 μm-thick laminated film wound in a coil shape. Is 1
It has been found that as much as 5 KV can be reached, and that wrinkles are formed on the thin film surface due to this charging. Then, it was clarified that if this static electricity is removed and the amount of charge on the film surface is set to 2 KV or less, even a thin film having a thickness of 20 μm can be continuously applied without wrinkles, and the present invention has been completed.

Various methods can be applied to remove static electricity. For example, a static electricity removing method using corona discharge or a method using a static electricity removing tape is effective, and in particular, a combination method using both of them is preferably the above-mentioned charge amount 2
It was recognized that conditions below KV could be achieved. In the former corona discharge method, positive and negative ions are generated by a corona discharge device, and static electricity is removed by hitting the laminate film surface as an ion wind with an air flow. This method also has the advantage that dust can be removed at the same time as static electricity is removed from the film surface by ionic wind. The latter static electricity removing tape method uses a composite tape of a conductive cloth and a conductive rubber made of metal short fibers having good conductivity and synthetic fibers. When this is brought into contact with the charged film surface, corona discharge is generated between the two and the film surface is discharged.

Further, it has been found that, in addition to the above-mentioned generation of wrinkles due to electrostatic charging, minute air bubbles caused by air entrained at the time of applying an adhesive can also be a factor that prevents uniform application of a very thin film. .. That is, when the above-mentioned thermosetting resin is diluted with a solvent and applied to a steel plate surface with a roll coater or the like, and immediately dried and cured in a drying oven, air is entrapped in the adhesive coating film to cause minute bubble defects. Occurs. As a result, the thickness of the adhesive coating film becomes uneven.
This air entrapment phenomenon is due to the viscosity of the adhesive, and the release of the entrained bubbles can be promoted by increasing the amount of the diluent added to reduce the viscosity. However, if a large amount of diluent is used, the prescribed adhesive coating film thickness cannot be obtained, and the adhesiveness of the laminated film to be subsequently applied,
Problems occur in both workability and corrosion resistance.
Therefore, the adhesive used in the present invention needs to be adjusted to have a high concentration and a low viscosity.

Therefore, in the present invention, as a means for obtaining a prescribed adhesive coating film thickness without causing bubble defects, the temperatures of both the steel sheet and the adhesive are appropriately adjusted in advance before the adhesive is applied. To control. The temperature control range is 20 to 40 ° C. for the steel plate and 25 to 35 ° C. for the adhesive. If the temperature is lower than the lower limit temperature, the viscosity of the adhesive increases and bubbles are likely to be generated during application. On the other hand, if the upper limit temperature is exceeded,
The viscosity of the adhesive becomes too small to obtain the specified film thickness.

Therefore, the production of the film-laminated steel sheet for food cans of the present invention is carried out through the following steps. First, size paint is applied to a tin-plated steel sheet having a tin deposit of 0.5 to 2.8 g / m ² and baked for a short time in a drying oven. 20 in advance
An adhesive whose temperature is adjusted to 25 to 35 ° C is applied to the steel plate kept at -40 ° C, and immediately dried and cured in a drying furnace. The surface of the steel sheet is unwound from a roll and passed through a static eliminator to remove the static electricity, and a thermoplastic resin film is applied to cover the surface of the steel sheet for aging.

Thus, according to the method for producing a film-laminated steel sheet for food cans of the present invention, an extremely thin laminate film having a thickness of 20 μm, which was conventionally impossible, can be continuously applied on an industrial scale. became. Moreover, since the film quality is stable and has no defects, not only the film thickness but also the tin weight per unit area of the tin plate itself can be significantly reduced. By the way, in the conventional case, tin tint of 5.6 g / m ² and 8.4 g / m ² was used in order to supplement the corrosion resistance of the coating film, but in the present invention, sufficient corrosion resistance can be achieved. Therefore, the weight per unit area of expensive tin can be reduced to 0.5 to 2.8 g / m ² , and its resource saving effect and economic effect are very large.

[0024]

[Example] A cold-rolled steel sheet having a thickness of 0.13 mm was tin-plated with a halogen type electric tin-plating line to finish a tin plate. Three types with different plating amounts were used. The plating conditions are shown in Table 1.

[0025]

[Table 1]

To the thus finished tin plate, 3.0 g / m ^{2 of} thermosetting vinyl was applied as a size paint and baked at a high temperature of 210 ° C. × 15 seconds for a short time. Next, apply an adhesive of the following composition to a dry weight of 5 g / m ^2, and apply 170 ° C ×
It was dried under the condition of 30 seconds and immediately unstretched nylon 6 film (manufactured by Toray Synthetic Film Co., Ltd., Rayfan NOT-1)
401) was attached and wound into a coil. The thickness of the film used is 20μm, 30μm, 40μm and 50μm
Each of the samples was prepared by sticking them separately. The above-mentioned nylon film was adhered after the static electricity was removed by using a corona discharge type static eliminator and a static eliminator tape before pasting.

[Adhesive] Main agent: polyester resin,
Epoxy resin Curing agent: Aliphatic polyisoamide Mixing ratio: Main agent: Curing agent = 15: 2 After that, the coil was covered with a heat-retaining box for aging treatment to finish, and various evaluation items described below were evaluated.

The tinting temperature at the time of applying the adhesive is 25
There were two types, ℃ and 35 ℃. The temperature of the adhesive was 30 ° C. On the other hand, for comparison, the adhesive temperature during adhesive application
We prepared 20 ° C and 40 ° C samples, and test materials with tint temperatures of 15 ° C and 45 ° C different from the above. Table 2 shows the results of measuring the amount of adhered adhesive, the presence or absence of air bubbles in the adhesive layer, the amount of charge on the laminate sheet, the state of wrinkles, and the film adhesive strength for each of these test materials. Regarding the film adhesive strength, those peeled with almost no resistance when holding the edge of the film were judged to be insufficient in strength, and those in which resistance was felt to be peeled were judged to be high in strength.

[0029]

[Table 2]

Among the materials shown in Table 2, the following quality evaluations were carried out for the materials in which no bubbles were observed in the adhesive layer, the film was attached without wrinkles, and the film adhesive strength was high. 1) Cross-cut Erichsen test 11x11 cross-cut scratches were made on the surface of the test material at intervals of approximately 1 mm, and a 4 mm overhang process was performed using an Erichsen tester to bond to the swollen portion. The tape was attached and peeled off, and the peeled state was evaluated as shown in Table 3.

[0031]

[Table 3]

2) 1T bending test Using a DuPont impactor, a weight of 2.3 Kg was applied to the test material 3 times.
The test piece was bent by dropping it from a height of 0 cm, the processed test piece was immersed in a 3% NaCl aqueous solution together with an electrode (cathode), and a voltage of 6 V was applied for 4 seconds to evaluate the current value. If there is an exposed metal portion, a current proportional to the exposed area flows, so that the degree of damage to the coating film or film layer can be determined.

3) Workability evaluation A disk having a diameter of 80 mm was punched out from the test material and processed into a cylinder with a drawing ratio of 2.0. This cylinder was subjected to a retort sterilization treatment at 130 ° C. for 30 minutes, and the inner and outer surfaces were visually observed. As a result, if there was even one flaw or the film was peeled off, it was rejected.

4) Enamelator test In the can body obtained in the above item 3), 3% N was added as an electrolytic solution.
The electrode was immersed in an aCl aqueous solution and the can body was used as an anode, and a constant voltage of 6 V was applied for 4 seconds, and the area of the metal exposed portion was evaluated by the current value flowing at this time. 5) Actual can test The contents of commercially available tuna oil pickles were repacked in the can body, the can lid was attached by double winding, and after retort sterilization treatment at 130 ° C x 30 minutes, it was kept at 50 ° C for 12 months. After that, the cans were opened and the flavor evaluation of the contents, the corrosion state, and the adhesion state of the film etc. were investigated.

Table 4 shows the results of the above evaluation tests.

[0036]

[Table 4]

According to the present invention, good results were obtained despite severe test evaluation. Among the comparative examples, those which were not subjected to static elimination (Comparative Examples 1, 8, 10, 12) had many wrinkles in the laminated film attached, and the evaluation was poor. In addition, although it was applied to the tin plate in the above-mentioned embodiment, it can also be applied to a chrome-plated steel sheet.

The film-laminated steel sheet for food cans of the present invention is not limited to two-piece cans, but can be applied to three-piece cans. Further, it can also be applied to those in which a film is attached to both front and back surfaces.

[0039]

According to the present invention, when a thermoplastic resin film is attached to a tin plate with an adhesive, the temperature of the tin plate and the temperature of the adhesive are kept at an optimum temperature at which no bubbles are generated in the adhesive coating film. At the same time, since the static electricity of the thermoplastic resin film is removed in advance, the occurrence of wrinkles is prevented,
It becomes possible to attach an extremely thin thermoplastic resin film that could not be used in the past, and as a result, productivity can be significantly improved compared to the conventional one. In addition, the amount of tin weight can be greatly reduced, and the corrosion resistance and workability are very excellent.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshikatsu Kato 1 Kawasaki-cho, Chiba-shi, Chiba Inside the Kawasaki Steel Co., Ltd. (72) Inventor Tomohiko Akiyama 1 Kawasaki-cho, Chiba-shi Kawasaki Steel Co., Ltd. Chiba Inside the Steel Works (72) Inventor Hiroshi Narumi 1 Kawasaki-cho, Chiba City, Chiba Prefecture Inside the Kawasaki Steel Co., Ltd. Chiba Works (72) Inventor Makoto Tanaka 1 Kawasaki-cho, Chiba City Chiba Works (72) Inventor Mitsuyoshi Nakatani 1 385 Shiota-cho, Chiba City, Chiba Prefecture Kawakawa Steel Plate Co., Ltd. Chiba Plant

Claims (1)

[Claims] 1. A tin-plated steel sheet having a tin deposition amount of 0.5 to 2.8 g / m ² is baked with a size paint, and then the steel sheet previously held at 20 to 40 ° C. is coated with an adhesive whose temperature is adjusted to 25 to 35 ° C. A method for producing a film-laminated steel sheet for food cans, which comprises applying static electricity and then removing static electricity from the film when the thermoplastic resin film is coated.