JPH0631362A - Manufacture of multi-drawing can made of laminated steel sheet with high adhesion - Google Patents

Abstract

PURPOSE:To secure can manufacturing workability and quality in can body by carrying out during a canning process the measures of improving adhesion that is deteriorated through multi-drawing process, in reference to the manufacture of two piece cans made of laminated steel sheet especially such as DRD cans or DTR cans. CONSTITUTION:Multi-drawing is performed by using as the base material a steel sheet laminated with an organic resin film with thermoplastic resin as an adhesion layer. During the multidrawing, the softening point of the thermoplastic resin layer or a heating process for temperatures above the melting point is set. It is desirable that the laminated steel sheet to be laminated is provided with a two layer construction, that the adhesion layer with the steel sheet is composed of a thermoplastic resin with a low melting point and a small crystaliizability, that the non-adhesion layer is of higher melting point than the adhesion layer and is composed of a thermoplastic resin with a large crystallizability. Polyolefin, polyamide, polyester, etc., are available as the resin, but a film in the series of thermoplastic saturated polyester resin is desirable in point of heat resistance, mechanical property, anti-corrosion performance, flavor and other aspects of general performance.

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 so-called canned food containers such as natural foods and beverages.

Currently, metal containers for food cans mainly consist of a three-piece can in which a can body is formed by welding, bonding, etc. and a top and bottom lid is wound and a two-piece can in which a can body and a bottom lid are integrally formed. Has become. The present invention is directed to the method for manufacturing a two-piece can of these, and uses an organic resin film laminated steel sheet having a thermoplastic resin as an adhesive layer on at least one surface of the steel sheet as a material.

[0003]

2. Description of the Related Art The main body of the current two-piece can is DI (Draw & Draw) manufactured by a combination of drawing and ironing.
Ironing cans and DRD (Draw & Re-Drawing) cans manufactured by multi-stage drawing.

In the case of a DI can, a tin-plated steel plate or an aluminum plate is used as a material, and after the DI processing, degreasing and chemical conversion treatment, the inside and outside of the can are painted and printed to ensure corrosion resistance to the contents.

On the other hand, in the case of a DRD can, in many cases, a coated steel sheet having a thick vinyl chloride film is subjected to multistage drawing to form a can body. At that time, in order to reduce the material cost, stretch processing is performed after drawing, and DTR processing (Draw &
The Thin-reDrawing method has been developed and put into practical use.

Since the processing conditions of the DTR can are more severe than those of the DRD can, the adhesion of the coating film is deteriorated by the processing in the conventional PVC-coated steel sheet, and when the multistage drawing is performed, the coating film is cracked during the processing in the later steps. Tends to enter, resulting in a can body having poor coating film adhesion. As a result, there is concern about corrosion resistance, and it can only be used for contents that are weakly corrosive.

On the other hand, the DTR can-making method has many advantages over the DI can-making method, such as low equipment cost, small equipment area, small operating personnel, and improved working environment. There is. Therefore, in order to utilize this can-making method, for example,
New proposals have been made such as a polyester resin film laminated steel sheet described in JP-B-60-47103, a coated metal plate for a squeezing can and a squeezing can described in JP-A-3-101930.

[0008]

Problems to be Solved by the Invention DTR can or DI
The reduction of the plate thickness is 20-70 due to the strength processing like a can.
In the case of processing up to 100%, many cracks occur in the conventional thermosetting can coating material, and practical corrosion resistance cannot be obtained.

In the case of a laminated steel sheet in which a thermoplastic resin film is laminated on the surface of a steel sheet, it is possible to design a film that can withstand strong processing by selecting a film having good processability. However, this film must be firmly adhered to the surface of the steel plate during the entire processing process, and if film peeling occurs at the interface between the steel plate and the organic film even partially, the film around it will be broken and It will be a defect to reach.

The present invention relates to a two-piece can manufacturing process, especially DR
It is an object of the present invention to provide a method for producing a two-piece can that dramatically improves the adhesion of an organic film in the D and DTR can making steps and can exhibit excellent corrosion resistance to any content. .

[0011]

The gist of the present invention is as follows.

In a method for producing a deep-drawn can by multi-stage drawing using an organic resin film laminated steel sheet having a thermoplastic resin as an adhesive layer, a heating step to a temperature not lower than the softening point or melting point of the thermoplastic adhesive resin layer is performed. A method for manufacturing a multi-stage drawn can made of a laminated steel sheet having excellent adhesion, which is characterized in that it is provided between multi-stage drawing processes.

The above-mentioned adhesion characterized in that an organic resin film having a two-layer structure in which the resin of the layer adhered to the steel plate has a lower melting point and a smaller crystallinity than the resin of the non-adhesive layer is laminated A method of manufacturing a multi-stage squeezer made of laminated steel sheet with excellent properties.

A method for producing a multi-stage squeezed can made of a laminated steel sheet having excellent adhesiveness as described in (1), which comprises laminating an organic resin film made of a saturated polyester resin.

[0015]

In the present invention, a steel plate in which an organic resin film having a thickness of 10 μm or more is laminated on at least one surface of the steel plate is used. As the steel plate, a surface-treated steel plate such as tin-plated, nickel-plated, chrome-plated or the like which is currently used as a steel plate for containers is used. The presence of an appropriate chromate film is desirable to improve the adhesion of the resin film.

As the resin film to be laminated, a thermoplastic resin such as polyolefin, polyamide or polyester resin is used. Among them, the thermoplastic saturated polyester resin film is preferable in terms of heat resistance, mechanical properties, anticorrosion performance, flavor property, and other comprehensive performance. These resin films are directly heat-bonded to the steel plate surface without using a thermosetting adhesive or the like. Since the adhered resin film is heated and melted in the can making process, it is desirable that the resin film has a two-layer structure. The adhesive layer to the steel sheet is a resin with a low melting point and low crystallinity, and has a composition with good adhesion and solubility, and the non-adhesive layer does not melt during the dissolution treatment of the lower layer resin, and can holder in the heat treatment furnace It is desirable to use a resin having a higher melting point and a stronger crystallinity than the lower layer resin in order to prevent adhesion to the resin. The melting point temperature difference between the lower layer and the upper layer is 10 ° C or more,
It is preferably 20 ° C. or higher.

Such a resin film is laminated on both sides or one side of a steel plate. In the case of a one-sided laminate, the other side is uncoated or a conventional thermosetting can coating material is applied.

The method of the present invention will be described below by taking a DTR can as an example.

The resin film laminated steel sheet firmly adhered to the steel sheet is subjected to the first drawing. Although it depends on the size of the final product, a drawing ratio of 1.
A drawing process of about 5 to 1.8 is performed. At this stage,
Large shear stress acts on the adhesive interface of the laminate film, resulting in a decrease in adhesion. Further, the chromate film on the surface of the steel plate forming the side wall of the can body is also destroyed, and a considerable amount of iron base material is exposed. This effect tends to appear more clearly on the upper side of the squeeze cup.

In the usual case, the squeezing cup having the film with the adhesion thus reduced is subsequently subjected to stretch molding. Stretch molding has a redraw ratio of 1.
It is performed using a die having a very small radius of curvature of about 20 mm to about 1.60, for example, 0.4 mm. This stretch forming is performed a number of times depending on the final product size, and the die is designed so that it is 10 to 20% thinner than the original plate thickness each time. Multiple stretch forming deteriorates the adhesion of the laminate film, and may cause film peeling at the cut end in the subsequent trimming process of the top of the can, or lifting of the film when performing retort sterilization treatment after filling the contents. .

In the present invention, heat treatment is performed between the multi-stage drawing steps in order to prevent such a decrease in adhesion and enable smooth processing in the subsequent steps. A film having a thermoplastic resin as an adhesive layer is softened by heat treatment, and a new bond is formed again in the temperature range exceeding the softening point or the melting point to restore the adhesiveness. Usually, the material temperature exceeds 100 ° C. immediately after processing due to heat generation and friction heat of the material due to processing, but it does not rise to such a degree that the resin is melted. In addition to this processing heat, by heating for a short time to a temperature above the softening point or melting point of the resin forming the adhesive layer by high-frequency induction heating, radiant heating, hot air heating, or the like, the adhesive strength is rapidly recovered. This has a function of causing a new bond between the surface of the resin and the steel plate, and also softening the resin layer by thermally destroying the resin layer molecularly oriented by the processing, thereby preventing a decrease in the adhesive strength in the next processing step. It is a thing.

When performing processing by multi-stage drawing, it is possible to partially omit the heat treatment depending on the distribution of the processing degree. For example, when the drawing ratio of the first drawing is small and the adhesiveness that can withstand the first redrawing remains, the heat treatment is omitted and the first redrawing is directly performed. Then, heat treatment is performed after the first redrawing process to prepare for the second redrawing process.

The crystallinity, softening point and melting point of the resin used in the present invention are defined as follows. The melting point is obtained by using a differential scanning calorimeter and the maximum endothermic temperature for crystal melting observed when heating is performed at a heating rate of 5 ° C./min. The crystallinity is determined by heating the resin at a temperature of the melting point + 30 ° C. obtained by the above method for 10 minutes and then rapidly cooling it to 5 ° C. or less, using a differential scanning calorimeter as in the melting point measurement, and heating rate of 5 ° C. The size is checked by the amount of heat of crystal fusion per unit mass calculated from the endothermic peak area of crystal fusion observed when heating at a heating rate of 1 / min. The softening point is determined by measuring the lowest temperature at which the film is fused to the steel plate surface when the film is pressed against the heated steel plate surface at 100 g / cm ² .

When the heat treatment is carried out in the can making process, the can body must be held and conveyed by some method, and as described above, the two-layer structure film is most suitable. Only the inner layer (the surface that is bonded to the steel plate) is melted, the outer layer is not melted and the inner layer is protected. The outer layer film needs to be a resin having a high melting point and high crystallinity so that it does not stick even when it comes into contact with the can holder. In the case of a double-sided laminated steel plate, it is desirable that the inner and outer surfaces are made of the same resin.

[0025]

EXAMPLES Examples of the present invention will be shown below.

[0026]

Example 1 A polyester-based two-layer film containing terephthalic acid, isophthalic acid and ethylene glycol as main components was prepared. This two-layer film has a melting point of the adhesive layer of 225 ° C. and a heat of fusion of 2.4 cal / g (thickness of 5.0).
μ), melting point of outer layer 248 ° C., heat of fusion 5.1 cal / g
The copolymerization amount of isophthalic acid was adjusted to be (thickness 20.0μ). This film was T-die extruded and then biaxially stretched to obtain a stretched film having a degree of orientation of 0.133.

On a steel plate having a plate thickness of 0.186 mm and having a surface of metallic chromium and a hydrated chromium oxide film, the orientation of the lower layer (adhesive layer) was completely destroyed at 230 ° C. by a heat fusion laminating method, and substantially Bonded as an amorphous film. Melting point 24
The outer layer film at 8 ° C. was laminated without breaking the stretched orientation.

Using a laminated steel sheet having this coating on both sides, it is drawn with a blank diameter of 175 mm and a drawing ratio of 1.56, and the drawing cup is placed in a heating furnace before redrawing.
Heated to 30 ° C. After cooling to 100 ° C. or less, the first re-drawing process was performed at a re-drawing ratio of 1.37, and the cup after re-drawing was heated again to 230 ° C. in the heating furnace. Furthermore, in order to perform the second redrawing process, after cooling to 100 ° C or less,
A second redrawing process was performed at a redrawing ratio of 1.29 to form a cup having a final can diameter.

In this molding step, there was no problem in the adhesion of the laminate film, and the working degree (thinning rate) of the can body was about 35%. The cup thus formed was subjected to doming, necking, and flanging processing by a known method to obtain a can body.

[0030]

Example 2 Using the same laminated steel sheet as in Example 1,
The first drawing was carried out with a blank diameter of 175 mm and a drawing ratio of 1.45, and then the first redrawing was carried out with a redrawing ratio of 1.42. After that, heat treatment at 230 ℃,
After cooling to 100 ° C. or lower, the second redrawing was performed at a redrawing ratio of 1.31. The total degree of processing was set in the same manner as in Example 1, but the number of heat treatments could be once.

In this molding step, there was no problem with the adhesion of the laminate film, and the degree of processing (thinning rate) of the can body was about 35%. The cup thus formed was subjected to doming, necking, and flanging processing by a known method to obtain a can body.

[0032]

Example 3 A polyester-based two-layer film containing terephthalic acid, isophthalic acid and ethylene glycol as the main ingredients was prepared. This two-layer film has a melting point of the adhesive layer of 220 ° C. and a heat of fusion of 2.2 cal / g (thickness of 10.0).
μ), melting point of outer layer 245 ° C., heat of fusion 5.0 cal / g
The copolymerization amount of isophthalic acid was adjusted so that the thickness was 15.0 μm. This film was T-die extruded and then biaxially stretched to obtain a stretched film having an orientation degree of 0.148.

A steel plate having a plate thickness of 0.186 mm and a metal chromium and hydrated chromium oxide film on the surface was laminated at 250 ° C. by a heat fusion laminating method, and all layers were adhered as a substantially amorphous film. .

A steel sheet having this coating on both sides was subjected to drawing with the same drawing ratio distribution as in Example 2. The radius of curvature of the drawing die was adjusted so that the workability (thinning rate) of the body of the can was about the same. 5
The mold was set so as to be 3%. The heat treatment between the first and second redrawing steps was set to 220 ° C. to improve the adhesion.

In this molding step, there was no problem in the adhesion of the laminated film, and the molded cup was subjected to doming, necking and flanging processing by a known method to obtain a can body.

[0036]

[Comparative Example 1] A laminated steel sheet and a processing method similar to those of Example 1 were processed without heat treatment between processing steps.
A slight film peeling occurred at the upper end of the cup in the second redrawing process. After that, in the second redrawing, a considerably severe film peeling occurred on the outer surface of the can, and subsequent doming, necking, flanging, etc. could not be performed, and a satisfactory can body could not be manufactured.

[0037]

[Comparative Example 2] A laminated steel sheet and a processing method similar to those of Example 3 were processed without heat treatment between processing steps.
Although slight peeling was observed at the upper end of the outer surface of the can in the second redrawing process, the portion was removed by trimming and subjected to doming, necking, flanging, etc. to manufacture a can body. In this can body, the adhesion of the coating was significantly deteriorated in the retort test after filling with water, and the can body had no practical performance.

The cans obtained in Examples 1 to 3 are 12
Even in a retort test of 0 ° C. × 1 hour or a heating test to 200 ° C., it had excellent adhesion and had sufficient corrosion resistance.

[0039]

According to the present invention, the DT having a high degree of sidewall processing
The R can can be efficiently manufactured, the cost competitiveness is strong, and the two-piece can having excellent quality as a can can be obtained.

Claims (3)

[Claims] 1. A method for producing a deep-drawn can by multi-stage drawing using an organic resin film-laminated steel sheet having a thermoplastic resin as an adhesive layer, comprising heating the thermoplastic adhesive resin layer to a temperature above its softening point or melting point. A method for producing a laminated steel multi-stage drawn can with excellent adhesion, characterized by having steps between the multi-stage drawing steps. 2. An organic resin film having a two-layer structure in which a resin of a layer adhered to a steel sheet has a melting point lower than that of a resin of a non-adhesive layer and is made of a thermoplastic resin having a small crystallinity is laminated. Item 2. A method for producing a multi-stage drawn can made of a laminated steel sheet having excellent adhesion according to Item 1. 3. An organic resin film made of a saturated polyester resin is laminated, and the organic resin film is laminated.
A method for producing a multi-stage squeezed can made of a laminated steel sheet having excellent adhesion.