JPH0919733A - Method for forming two piece can drum - Google Patents

Abstract

PURPOSE: To provide a producing method of a two piece can drum which prevents the generation of hair. CONSTITUTION: At least, the face to be made to the internal side of a can of a metal sheet is covered preliminarily with a thermoplastic resin, this resin covered metal sheet is drawn and a cup is made, the peripheral circumference of this cup is treated with heat, the chip of thermoplastic resin which is generated with drawing and extended from the cup upper end part to the outside is contracted with heat, an exposed metal face without existing of the thermoplastic resin on the cup opening part is formed, further after the resin contracted with heat is molten, redrawing or redrawing and ironing are executed and the generation of hair of the thermoplastic resin cover is prevented, this is the method for forming two piece can drum.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention provides a method for manufacturing a two-piece can body in which the resin coating on the peripheral portion of the edge of the cup is prevented from peeling and hair is prevented from occurring.

[0002]

2. Description of the Related Art A metal plate (at least the surface on the inside of a can) is coated with a thermoplastic resin in advance, and this resin-coated metal plate is drawn to form a cup, and this cup is redrawn or redrawn. When forming a two-piece can body by ironing, if they are formed by dropout,
The resin around the edge of the cup peels off to form a filamentous hair, which adheres to the drawing die, the ironing die, the bottom molding die, and the like, resulting in defective molding during continuous molding. Therefore, the cans must be frequently stopped to remove the hairs generated, continuous cans cannot be made, and the productivity is remarkably poor, so it has not been put to practical use until now. Hair is width
The thickness is about 10 to 10 times the thickness of the thermoplastic resin, the length is the cup circumference length (or the length cut into several pieces), and it is a thread-like shape.

[0003]

PROBLEM TO BE SOLVED: To provide a method for molding a two-piece can body by suppressing the generation of hair during the manufacturing of the can body, having a good appearance, a good resin coating property on the inner surface, and a high productivity.

[0004]

MEANS FOR SOLVING THE PROBLEMS The present invention provides "1. A thermoplastic resin is coated on at least a surface of a metal plate which is to be an inner side of a can in advance, the resin-coated metal plate is drawn to form a cup, and an end of the cup is formed. A piece of thermoplastic resin that extends outward from the upper end of the cup generated by heat treatment of the peripheral edge portion of the edge is heat-shrinked to form an exposed metal surface free of the thermoplastic resin in the cup opening, and A method for forming a two-piece can body which prevents the occurrence of hair of a thermoplastic resin coating, which comprises re-drawing or re-drawing and ironing after fusing a heat-shrinked resin. 2. A thermoplastic resin is coated on at least the surface of the metal plate that is to be the inside of the can in advance, and this resin-coated metal plate is drawn to form a cup, and the drawing is performed to substantially cover the resin around the edge of the cup. Peel off, and Stretch the thermoplastic resin piece that extends outward from the upper edge of the cup, and then heat-treat the periphery of the edge of the cup to shrink the thermoplastic resin piece that extends outward from the upper edge of the cup. Thermoplastic resin characterized by forming an exposed metal surface free of thermoplastic resin in the cup opening, and fusing the heat-shrinkable resin, and then redrawing or redrawing and ironing A method for forming a two-piece can body that prevents the occurrence of resin-coated hair 3. A thermoplastic resin that substantially peels off the resin coating around the edge of the cup and extends outward from the upper edge of the cup 3. A method of forming a two-piece can body in which the generation of hair of the thermoplastic resin coating described in item 2 is prevented, in which the method of stretching the resin piece is a combination of drawing and ironing. Heat treatment temperature around the edge Of at least the melting point of the thermoplastic resin, and a method for forming a two-piece can body in which the thermoplastic resin coating described in any one of items 1 to 3 is prevented from generating hair. 5. The heat treatment of the peripheral portion of the edge of the cup includes the first step at a temperature of the thermoplastic resin melting point −50 ° C. to the thermoplastic resin melting point + 30 ° C. and the second step at a temperature equal to or higher than the thermoplastic resin melting point. 2. A method for forming a two-piece can body in which the generation of hair of the thermoplastic resin coating described in any one of items 1 to 4 is prevented, which is characterized by two stages. The kind of resin is a polyester resin, and the generation of hair of the thermoplastic resin coating described in any one of items 1 to 5 is prevented.
A method of forming a piece can body. 7. The metal plate is a tin-plated steel plate, a tin-free steel plate, an aluminum alloy plate, 1
Item 7. A method for forming a two-piece can body in which the thermoplastic resin-coated hair described in any one of items 1 to 6 is prevented from being generated. 8. The width of the exposed metal surface where the thermoplastic resin does not exist is 5
The method for forming a two-piece can body in which the generation of hair of the thermoplastic resin coating described in any one of items 1 to 3 is prevented, which is characterized in that it is 0 μm or more. About.

[0005]

The function of the present invention will be described first with respect to the cause of hair generation and defective molding caused by hair. Next, the countermeasures will be described to clarify the constitution of the present invention and explain the operation.

Mechanism of Hair Generation The present invention relates to a method for producing a two-piece can of drop-out type, such as drawing and drawing and ironing. In the cup edge portion of the first drawing cup, the edge of the thermoplastic resin is at substantially the same position as the edge of the metal surface, or is in a state of being stretched slightly outward by the first drawing process. In redrawing, as the draw forming progresses, the area of the upper part of the cup in contact with the wrinkle holding tool becomes smaller, so the wrinkle holding load per unit area gradually increases, resulting in a gap between the thermoplastic resin and the wrinkle holding die. Friction force increases, the thermoplastic resin is stretched outward from the metal cut surface, the thermoplastic resin is cut by the metal edge at the final stage of drawing, and hair is generated at a part of the cup edge. In order to improve this, it has been attempted to prevent the wrinkle holding pressure from becoming too high at the final stage of squeezing, but it was possible to eliminate hair altogether when multi-stage redrawing was performed. Absent. Ironing is a method of ironing (compressing) the cup in contact with the punch with an ironing die in contact with the outer surface of the cup. Both the metal and thermoplastic resin of the cup are compressed and deformed toward the top of the cup. . At this time, since the thermoplastic resin has a smaller deformation resistance than the metal, the thermoplastic resin is extruded to the outside of the cup particularly at the edge above the cup, and is easily protruded. That is, even if the thermoplastic resin surface and the metal surface of the cup edge before starting the ironing are in the same position, the thermoplastic resin surface is more likely to be extruded to the outside of the cup due to the ironing process, and the molding and compression of the metal at the cup edge is performed. Due to the force, the stretched resin piece is cut and hair is generated.

Molding failure due to hair When hair occurs, the following molding failure occurs. When the hair is caught between the outer surface or inner surface of the cup body and the mold, the cup breaks during molding. By molding the hair by biting it between the outer surface of the cup body and the mold, discoloration or deformation such as push marks can be created on the outer surface of the cup and the appearance will deteriorate (outer surface of the cup body, bottom outer surface). By pinching the hair between the molds and molding, a metal pinhole (hereinafter referred to as a can barrel pinhole) in the cup body is generated. When the hair is bitten between the inner surface of the cup body and the mold, the thermoplastic resin on the inner surface of the cup becomes defective, the metal is exposed on the inner surface of the cup, and it becomes a starting point of can corrosion. Hair is mixed into the inner surface of the cup and foreign matter is mixed in.

Prevention of Hair Generation As a result of various investigations on these measures for hair generation, the thermoplastic resin edge of the cup edge before redrawing is made to be about 50 μm or more lower than the metal edge of the cup edge.
It was revealed that the generation of hair can be eliminated.
The lower side means below the cup edge when the cup is set up. In other words, the cup edge of the surface on which the thermoplastic resin is disposed (the inner surface of the cup) is about 50 μm.
It was found that the generation of resin hair can be eliminated by exposing the metal in the width and not allowing the thermoplastic resin to exist in that portion. It is considered that the reason why the metal exposure of the cup edge is effective is that even if the thermoplastic resin is stretched by ironing or redrawing, it does not reach the edge of the metal and is not cut by the metal edge.

The present inventor has researched a method for realizing metal exposure of the cup edge, and has revealed that the metal is exposed by peeling the thermoplastic resin of the cup edge of the first squeezing cup from the cup and shrinking the heat. did. In the drawing process, the material of the cup side wall is deformed by compressing and deforming both the metal and the thermoplastic resin in the circumferential direction and extending in the cup height direction. At this time, since the metal and the thermoplastic resin have different deformability, the thermoplastic resin is relatively easily peeled off due to the processing, especially at the cup edge. The degree of this peeling is larger when the drawing ratio is larger. Further, even if the strain due to processing is the same, the smaller the adhesion between the thermoplastic resin and the metal, the larger the peeling width. Further, even if the cup edge is not completely peeled off, the cup edge has a smaller adhesiveness and is easily peeled off by the subsequent heat treatment. When the cup edge in this state is heated at a temperature equal to or higher than the melting point of the thermoplastic resin, the strained thermoplastic resin thermally shrinks, exposing the metal to the cup edge, gathering downward (lower side of the cup) and melting, Fuse to metal. If the heating temperature of the cup edge is lower than the melting point of the thermoplastic resin, the melting is insufficient, the contracted thermoplastic resin surface does not become smooth, and the adhesion between the metal and the thermoplastic resin is not sufficient, and the subsequent processing At times, the contracted resin comes off and becomes hair (generally shorter), and the effect is insufficient. The heat treatment at a temperature equal to or higher than the melting point requires more time to reach this state as the temperature difference from the melting point is smaller. If the temperature difference from the melting point is too large, the thermoplastic resin will start to decompose, so it is necessary to treat it in a short time. High-frequency induction heating is effective for processing in a short time.

At this time, the heat shrinkage of the thermoplastic resin is the first stage, and the melting and fusing of the thermoplastic resin is the second stage.
Cup edge heating in two stages is more effective. In the first stage, the heating temperature is changed from the melting point of the thermoplastic resin −50 ° C. to the melting point of the thermoplastic resin + 30 ° C., and in the second stage, the heating temperature is equal to or higher than the melting point of the thermoplastic resin. By doing so, the thermoplastic resin is sufficiently heat-contracted and then melted and fused, so that the exposed metal surface can be obtained every other day.

The exposed metal width of the cup edge after the heat treatment must be 50 μm or more. After the heat treatment, when the processing amount is large due to ironing or the like, it is desirable that the thickness be 200 μm or more. The exposed metal width of the cup edge obtained by heat shrinkage is larger as the adhesiveness between the thermoplastic resin and the metal is smaller, and is larger as the thickness of the thermoplastic resin is larger.

As the method for heat treating the cup edge, any of high frequency induction heating, oven heating and the like can be used. What is important is the temperature and time of the cup edge thermoplastic. In the high frequency induction heating process, when only the cup edge is processed, the high frequency induction heating coil should be installed above the cup edge. However, it may be installed around the side wall of the cup. Alternatively, a high-frequency induction heating coil may be installed so as to act on a part of the cup edge, and the cup may be rotated to heat the entire circumference of the cup edge. Anyway, any method can be adopted as long as the cup edge can be treated to a certain degree at a required temperature and time.

The resin used in the present invention is required to be a resin which shrinks by heating. That is, it needs to be a thermoplastic resin. However, since the melting point of the thermoplastic resin varies depending on the type of the resin, the proper temperature for cup edge heating naturally varies. The temperature of the cup edge heating needs to be equal to or higher than the melting point of the resin. When this resin is a thermosetting resin, a large resin film defect occurs due to the molding of the two-piece can body, and is not suitable for practical use as a can. The method of laminating the resin on the metal plate includes a method of directly laminating on the metal plate with a T-die, a method of thermally bonding an unstretched film, a method of thermally bonding a biaxially stretched film,
Either method can be used. Also, a double-sided laminated material in which a thermoplastic resin is laminated on both sides of a metal plate has the same effect. As the metal plate, any tin material such as tin plate, TFS (tin-free steel), and aluminum can be used.

Although it has been described that the first squeezing cup is used for the heat treatment, when squeezing is performed in multiple stages,
The cup heating process and the cup ironing process may be performed on the cups after the second drawing. Further, it is more effective to subject the cup edge part to an ironing process before the cup edge heating process after the first draw forming. The purpose of this treatment is to stretch the cup edge to increase the heat shrinkability of the thermoplastic resin and to reduce the substantial adhesion between the thermoplastic resin and the metal. When the drawing ratio of the first squeeze is considerably small, the substantial decrease in the adhesiveness between the thermoplastic resin and the metal is insufficient, and hair may be generated even if the cup edge heat treatment is performed. In such a case, if the cup edge portion is subjected to a process such as ironing, the substantial adhesion between the thermoplastic resin and the metal is sufficiently lowered, and the hair can be prevented by the cup edge heat treatment.

Further, as the blanking state, it is preferable that the thermoplastic resin of the blank edge does not stick out from the cut surface, or that the thermoplastic resin of the blank edge is inside the cut surface. For this purpose, when there is a burr on the side opposite to the thermoplastic resin surface, it is effective to make the cutter clearance proper and reduce the burr. Further, it is more preferable that the burrs are formed on the side of the thermoplastic resin so that the thermoplastic resin of the blank edge is inside the metal cut surface. If the protrusion from the metal cutting surface of the thermoplastic resin of the blank edge is too large,
This is because when the cup edge is heated, heat shrinkage of the resin does not easily occur, and at the time of the first squeezing, a part of the cup edge tends to become hair, which makes it difficult to prevent hair.

[0016]

【Example】

Example 1 Thickness 30 of crystalline polyester resin (polyethylene terephthalate / isophthalate system) having a melting point of 235 ° C.
An unstretched film of μm is heat-coated on one side of a tin plate with a plate thickness of 0.245 mm and a plating amount of 2.8 / 2.8. Using this one-side resin-coated tin plate, the resin-coated surface is the inner surface of the can. Blanking with a blank diameter of 142 mm,
Mold a squeeze cup with a first squeeze ratio of 1.6 and at the same time 30%
The cup was ironed by the amount of ironing. This cup
High temperature induction heating reaches the cup edge temperature of 300 ° C 1.
After the cup edge heat treatment for 0 seconds, redrawing with a drawing ratio of 1.3 and three steps of ironing forming are performed continuously to obtain a can barrel diameter of 65.8.
mm, can body metal thickness 80 μm, neck metal thickness 135
A cup having a size of μm was formed, trimmed to a cup height of 123 mm, degreased and washed, and then dried in an oven at 200 ° C. to obtain a squeezed and ironed cup. The cup was evaluated. The conditions and evaluation are shown in Table 1.

Example 2 A metal used was an aluminum 3004 alloy having a plate thickness of 0.300 mm, and a drawn ironing cup having a can body metal thickness of 100 μm and a neck metal thickness of 160 μm. 230 ° C for 1.0 second, second
A squeezed and ironed cup was obtained in the same manner as in Example 1 except that the cup edge heat treatment in the step was 300 ° C. for 1.0 second. The conditions and evaluation are shown in Table 1.

Example 3 Thickness 30 of crystalline polyester resin (polyethylene terephthalate / isophthalate system) having a melting point of 235 ° C.
μm biaxially stretched film with 0.26 mm thick TFS
Is heat-coated on both sides, and using this double-sided resin-coated TFS plate,
Blanking with a blank diameter of 179 mm was performed to form a squeezing cup with a first squeezing ratio of 1.6, and at the same time, squeezing was performed with a 30% squeezing amount. This cup is subjected to a high-frequency heating, a cup edge reaching temperature of 300 ° C., a cup edge heating treatment of 1.0 second, and further drawn and drawn in two steps to obtain a can body diameter of 65.8 mm and a can body metal thickness of 2000 μm. And was heat-treated in an oven at 200 ° C. and trimmed to a cup height of 123 mm to obtain a multistage squeezing cup. The cup was evaluated. The conditions and evaluation are shown in Table 1.

Example 4 A non-stretched film of polypropylene having a melting point of 170 ° C. and a thickness of 30 μm was used, except that the high frequency induction heating was performed at a cup edge reaching temperature of 200 ° C. for 1.0 second. In the same manner as in Example 1, a squeezed ironing cup was obtained. The conditions and evaluation are shown in Table 1. The drying temperature after degreasing and washing at this time was 150 ° C.

Example 5 A drawn and ironed cup was prepared in the same manner as in Example 1 except that the first drawing ratio was 1.8, no cup ironing was performed, and the redrawing ratio was 1.2. Got The conditions and evaluation are shown in Table 1.

Comparative Example 1 The same procedure as in Example 1 was carried out except that the cup-shaped first drawn cup was not subjected to the cup edge heating treatment.
I got a squeezed ironing cup. The conditions and evaluation are shown in Table 1.

[0022]

[Table 1]

(Note) 1. Cup heating conditions The first diaphragm cup is placed upright and a high frequency induction heating coil is installed above the cup so that high frequency magnetic flux is applied to the cup edge. The high frequency induction heating coil was installed at a position 3 mm from the cup edge. The high frequency output was adjusted to control the temperature of the cup edge. The temperature of the cup edge was evaluated by discoloring by applying several kinds of temperature-indicating paint to the resin surface on the inner surface of the cup. 2. Cup ironing condition When the original plate thickness (including the thermoplastic resin) is A and the drawing ratio of the first cup is B, the wall thickness C of the cup edge after drawing is C
Was calculated by the following formula. C = B ^0.5 × A The cup ironing amount R was calculated as follows, where D is the cup edge thickness after cup ironing. R = ((C−D) × 100) / C The drawing ratio B of the first cup was determined as follows. Drawing ratio = blank diameter / cup diameter after drawing Cup ironing was performed immediately after the first drawing, by making an ironing part under the R part of the drawing die and ironing with the same drawing punch stroke. 3. Number of cups with can body pinholes Squeezing ironing cups obtained under the conditions shown in Examples and Comparative Examples,
Alternatively, the number of cups with a can body pinhole was investigated for 1000 cups of the multi-stage squeezing cup. The inspection was performed with a light tester that detects the light passing through the pinhole. 4. Number of bottom dented cups Squeezing ironing cups obtained under the conditions shown in Examples and Comparative Examples,
Alternatively, with respect to 1000 cups of the multi-stage drawn cup, the number of cups having a recess in the bottom portion was investigated. The inspection was done visually. 5. ERV of cup after molding Squeezed ironing cup obtained under the conditions shown in Examples and Comparative Examples,
Or about 100 cups of multi-stage squeezing cup, ER
V was measured. The ERV was evaluated by a current value when a voltage of 6.3 V was applied using a 1% sodium chloride aqueous solution as an electrolytic solution, an inner surface of the cup as an anode, and a stainless steel rod as a cathode. The unit is mA. The average value of 100 cups was used as the score. From Examples 1 to 5, the generation of hair coated with a thermoplastic resin was prevented. In order to obtain a two-piece can body that has good appearance, good resin coatability on the inner surface, and high productivity, a thermoplastic resin is coated on at least the inner surface of the metal plate in advance, and this resin-coated metal plate is A cup is formed by drawing, and the periphery of the edge of this cup is heat-treated to heat-shrink a piece of thermoplastic resin that extends outward from the upper edge of the cup to expose the cup opening to the absence of thermoplastic resin. It can be seen that a manufacturing method characterized by performing redrawing or redrawing and ironing after forming the metal surface is effective. It can be seen from Comparative Example 1 that the occurrence of hair cannot be prevented when the cup edge heat treatment is not performed with the first squeezing cup.

[0024]

EFFECTS OF THE INVENTION According to the present invention, it is possible to prevent hair from being generated during molding of a can body and to carry out continuous can manufacturing.

Claims (8)

[Claims] 1. A thermoplastic resin is coated on at least a surface of a metal plate, which is to be an inner side of a can, and the resin-coated metal plate is formed by drawing to form a cup. A piece of thermoplastic resin that extends outward from the upper edge of the cup generated by processing is heat-shrunk to form an exposed metal surface free of thermoplastic resin at the cup opening, and the heat-shrinked resin is fused. And then redrawing and ironing. Then, a method for forming a two-piece can body in which the occurrence of hair of a thermoplastic resin coating is prevented. 2. A thermoplastic resin is coated on at least a surface of a metal plate which is to be an inner side of a can in advance, and the resin-coated metal plate is drawn to form a cup, and a resin coating is applied to a peripheral portion of an edge of the cup by the drawing process. To substantially exfoliate and stretch the thermoplastic resin piece that extends outward from the upper edge of the cup, and then heat-treat the peripheral portion of the edge of the cup to extend the heat that extends outward from the upper edge of the cup. Form an exposed metal surface where no thermoplastic resin is present in the cup opening where a piece of plastic resin is heat shrunk, and fuse the heat shrunk resin, and then redraw or redraw and iron Characterized by that
A method for molding a two-piece can body that prevents the generation of hair covered with a thermoplastic resin. 3. A method of substantially peeling off the resin coating around the edge of the cup and stretching the thermoplastic resin piece extending outward from the upper edge of the cup is a method of drawing and ironing. A method of forming a two-piece can body, which is a combination, in which the generation of hair of the thermoplastic resin coating according to claim 2 is prevented. 4. The heat treatment temperature around the edge of the cup is equal to or higher than the melting point of the thermoplastic resin.
A method for forming a two-piece can body in which the thermoplastic resin-coated hair described in any one of 1 to 3 is prevented from generating hair. 5. The heat treatment of the peripheral portion of the edge of the cup includes a first stage at a temperature of a melting point of the thermoplastic resin of −50 ° C. to a melting point of the thermoplastic resin + 30 ° C. and a second stage at a temperature equal to or higher than the melting point of the thermoplastic resin. 2. The method according to claim 1, wherein the number of steps is two.
5. A method for molding a two-piece can body in which the occurrence of hair of the thermoplastic resin coating described in any one of items 1 to 4 is prevented. 6. A two-piece can in which the thermoplastic resin-coated hair according to any one of claims 1 to 5 is characterized in that the type of the thermoplastic resin is a polyester resin. How to mold the body. 7. The thermoplastic resin-coated hair according to claim 1, wherein the metal plate is a tin-plated steel plate, a tin-free steel plate, or an aluminum alloy plate. A method for forming a two-piece can body that prevents the occurrence. 8. The width of the exposed metal surface on which the thermoplastic resin is not present is 50 μm or more.
A method for forming a two-piece can body in which the thermoplastic resin-coated hair described in any one of 1 to 3 is prevented from generating hair.