JPS6020573Y2 - metal can body - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a metal can body, and more particularly to a metal can body made of a tin-plated steel plate formed by a drawing-shido process with little iron exposed on the inner surface of the body wall.

The so-called two-piece can, which consists of a can body and a can lid formed by drawing and ironing tin-plated steel sheets, has recently been widely used for carbonated beverage cans such as cola and beer cans. However, if iron is leached into the liquid from the tin-plated steel plate that is the material, it will spoil the flavor of the liquid, so it is necessary to keep the amount of iron leached as low as possible.

Conventionally, measures have been taken to counter this problem, such as increasing the amount of tin plating on the surface of the tin-plated steel plate that is to become the inner surface of the can, or increasing the amount of coating on the inner surface.

However, all of these methods have the problem of increasing production costs.

The present invention aims to solve the problems of the prior art as described above.

The present inventors believe that in order to reduce the amount of iron elution,
The first priority is to reduce the amount of iron leached from the inner surface of the can body after ironing, but by using the ironing punch with a special surface profile that the present inventors proposed earlier, it is possible to reduce the amount of iron leached from the inside of the can body, which has been previously used. We arrived at this invention after finding out that the amount of exposed iron can be much reduced compared to the case of ironing punches.

The punch proposed earlier by the present inventors has an average roughness of 0.05 on most of the side surfaces in contact with the inner surface of the barrel wall of the can body.
It consists of a smooth part of less than μ wind and a groove line part having a V-shaped cross section with a depth of 0.5 to 5 μ9 and extending approximately in the circumferential direction. This ironing punch is characterized by being formed at average intervals and having a rounded boundary between the smooth portion and the groove line portion.

1 in FIG. 1 shows an example of the above-mentioned ironing punch, in which the groove line portion 2 is formed continuously in a spiral shape, the angle made with the circumferential direction is small, and it is almost circular. It extends in the circumferential direction.

The portion between the groove line portions 1 consists of a smooth portion 3.

FIG. 2 shows an example of the surface profile (in the axial direction) of the side main portion 1a of the punch of the type shown in FIG.

Between the punch 1 and the ironing die 4 as described above, the third
As shown in the figure, when the body wall 5 of the cup-shaped hollow body is ironed while moving along with the punch 1 in the direction of the arrow, a linear protrusion is formed on the inner surface of the body wall 5 at a position corresponding to the punch groove line 2. Yamabe 6 is under attack.

The protruding parts 6a and 6b are violently attacked from the inlet part to the outlet part of the die 4.

6, the height of the protruding portion 6 increases gradually, and the final height of the protruding portion 6 is approximately 0.5 to 3 μm.

Also, the average spacing between the protrusions 6 is about 0.0 mm, same as the groove line portion 2.
05~2rIr! It is n.

The gap between the groove line portion 2 and the protruding portions 6 (6a, 6b) is filled with the lubricant coolant 7 that is injected during the ironing process, and since the lubricant coolant 7 is incompressible, it searches for a place to escape. It is considered that the thin layer 8 is formed on the smooth portion 3 in the vicinity of the groove line portion 2.

FIG. 4 schematically shows the inner surface of the can body 9 that has been attacked in the manner described above, and shows a spiral-shaped continuous height extending approximately in the circumferential direction corresponding to the groove line portion 2 of the punch 1. The linear protrusion 6 with a diameter of about 0.5 to 3 μ9 is about 0.05 to 2 r
The average interval of rvn is rampant.

Fig. 5 shows a method of punching a tin-plated steel plate (the amount of tin plating on the inner surface of the can is 5.6 m) using the punch 1 having the surface profile shown in Fig. 2.
y/rrt) shows the profile (in the axial direction) of the inner surface of the barrel wall portion 5 of the can body 9 which has been iron-formed by ironing, and the protrusions 6 are formed at approximately equal intervals.

FIG. 6 shows a metal microscopic photograph (magnification: 100, horizontal direction is axial direction) of the inner surface.

The irregular roughness of the intermediate portion 10 between the protrusions 6 in FIG. 5 and the slight discontinuity of the protrusions 6 in FIG. It is presumed that this phenomenon (hereinafter referred to as linear) is caused by the roughness of the original tin-plated steel sheet used.

The can body 9 that has been ironed as described above is pulled out from the punch 1 with its open end being retained by a known stripper (not shown) during the return process of the punch 1.

FIG. 7 schematically shows the behavior during extraction, in which the barrel wall portion 5 of the can body 9 is stopped by the stripper and the punch 1 moves in the direction of the arrow.

At that time, the thickness of the trunk wall portion 5 is usually about 0.100 to 1.11.
Since it is extremely thin and flexible, the protrusion 6 can easily slide on the surface of the smooth part 3 of the punch 1.
The smooth part 3 of the groove line part 2 of the punch 1
The protrusion 6 easily slides over the surface of the punch 1, aided by the lubricating coolant 7 stored in the boundary radius 11 and the groove line 2, as well as by the aforementioned thin layer 8 of lubricating coolant. Therefore, the resistance to extracting the can body is much smaller than when a conventional punch with a smooth surface is used.

The inventors of the present invention have surprisingly found that the exposed iron on the inner surface of the body wall of the can body made of the tin-plated steel plate of the present invention obtained by ironing using a punch having the above-mentioned characteristics is different from that of the conventional can body. It has been found that the amount is much less than that of a can body obtained using a punch that is completely smooth.

The reason for this is not necessarily clear, but it can be assumed as follows.

Figure 8 shows the metallurgical microscopic structure (magnification: 100) of the inner surface of the barrel wall of a can body that has been ironed using a smooth punch.
As is clear from FIG. 9, which shows its surface profile (in the axial direction), the protrusion 6 as in FIG. 6 is not attacked.

Therefore, during extraction, slip occurs between the entire inner surface of the shell wall and the punch surface, and since there is almost no lubricating coolant between the inner surface of the shell wall and the punch surface, the slip occurs almost between the metals. This occurs in a state of contact, and therefore the tin layer is damaged over the entire inner surface of the shell wall, increasing the exposed area of iron on the original plate.

- In the case of the strength wood design, only the tip surface 6' (Fig. 7) of the protrusion 6 comes into contact with the punch surface, so the tin layer is damaged and the iron is exposed only at the tip surface 6'. Moreover, since there is plenty of lubricating coolant on the punch surface, the tip surface 6' can easily slide, and the exposed iron portion hardly spreads beyond the tip surface 6'.

Therefore, it is thought that the exposed area of iron on the inner surface of the body wall becomes smaller than when a conventional punch with a completely smooth surface is used.

As described above, the characteristics of the can body of the present invention are largely related to the characteristics of the ironing punch used in its manufacture.

The height of the linear protrusion 6 on the inner surface of the can body of the present invention is about 0.5 to 3 μm when the depth of the groove line of the punch is about 0.5 to 5 μm. The height of the protrusion 6 is approximately 0.5
This is because it is difficult to make it lower than μ skin and to make it higher than about 3μ skin.

In addition, making the depth of the groove line shallower than approximately 0.5μ skin
This is undesirable because it cannot function satisfactorily as a reservoir for lubricating coolant, which increases extraction resistance, and at the same time, the protrusion comes into metal-to-metal contact with the punch surface, increasing the exposed area of the iron.

Further, making the depth larger than about 5 μm means that the protrusion 6
It is undesirable to make the height of the can body larger than about 3 μm, since this increases the swelling resistance of the can body during extraction, resulting in a decrease in extraction performance and an increase in the exposed iron area of the protrusion.

Furthermore, if the groove lines do not extend substantially in the circumferential direction (therefore, the protrusion 6 also does not extend substantially in the circumferential direction), lubricating coolant tends to escape from the groove lines during ironing, and the thin layer 8 This is not preferable because it is difficult to form lubricity and therefore the exposed area of iron in the protrusion increases.

Furthermore, the average interval of the groove line parts (therefore, the average interval of the protruding parts 6)
If is smaller than about 0.05rrrIrL, the protrusion 6 will sink into the groove line when removing the can body, and will rise again many times, resulting in a large extraction resistance and at the same time, the exposed iron area of the protrusion will also increase. This is not desirable because it increases

On the other hand, if the lateral spacing is larger than about 2 mm, the amount of lubricating coolant sealed in the groove line portion will decrease, and metal-to-metal contact will likely occur between the protrusion 6 and the punch surface, which is difficult to extract. This is not preferable because the exposed area of iron on the tip surface 6' increases.

In addition, in the above embodiment, the protrusion 6 is continuous in a spiral shape, but it is formed using an ironing punch having discontinuous groove lines as proposed earlier by the present inventors. A can body having discontinuous linear protrusions 6 also has a similar effect.

When the drawn and ironed can body of the present invention made of tin-glued steel plate is pulled out from the ironing punch, only the tip end of the protrusion comes into contact with the ironing punch.

This is presumably because there is plenty of lubricant and coolant on the surface of the punch during extraction, but the iron exposure on the tip surface that occurs when the tip surface contacts the punch and slides is slight, so the inner surface The amount of iron exposure is small.

Furthermore, since there are protrusions, the adhesion of the coating film is also excellent.

Therefore, it has the advantage that the amount of iron leached into the contents after the inner surface is coated is small.

A specific example will be explained below.

Specific example Diameter of side main portion 1a (right cylindrical shape) in Fig. 1: 452.65
mm, height 115mm, height of shoulder 1b 9.5mm,
Diameter of reduced diameter part IC: 52.52TIrIn, height: 65rr
After polishing the side peripheral surface of the ironing punch 1 having a hardened alloy sleeve of rIrL with a 100-meter grindstone and lapping it smoothly using approximately 5μ bottle of diamond powder, the main side surface was polished while rotating the punch. A bamboo spatula coated with diamond powder (oil paste) with a skin diameter of approximately 100 μm is pressed on 1a and gradually moved in the axial direction to form a spiral groove line portion, and then the main side portion 1a is again coated with approximately 5 μm diameter. A punch having the surface profile shown in FIG. 2 (measured in the axial direction with a Tokyo Seimitsu stylus roughening tester, Surfcom 400A) on the main side surface 1a was manufactured by lapping with diamond powder.

Next, the plate thickness is 0.32mm, and the tin plating amount is 5.6F/yf (
The molded body obtained by drawing the tin-plated steel plate (both sides) into a cup shape was re-drawn and ironed using the punch described above.

In this case, the first scrubbing rate was 38.2%, the second scrubbing rate was 13.6%, and the third scrubbing rate was 39.4%, and a water emulsion of mineral oil was used as the lubricating coolant. used.

After the ironed can body was extracted using a stripper, the profile (in the axial direction) and microscopic structure of the inner surface of the body wall were examined, and the results shown in FIGS. 5 and 6 were obtained, respectively.

Regarding the above can body, an iron exposure amount test, a paint film adhesion test, and an iron elution amount test using a pack test were conducted using the following methods.

The results are shown in Table 1.

For comparison, the lap smooth finishing punch (
Conventional type, inner surface condition is shown in Figures 8 and 9)
The above test was also conducted on a can body prepared under the same conditions except that the following test was performed, and the results are shown in Table 1.

In addition, a punch with a maximum roughness of 3 μm on the main side surface was made by rough polishing, and the ironed can body was formed under the same conditions as above, but the opening end buckled when being pulled out with a stripper.
It was not possible to obtain a satisfactory can body.

(a) Iron exposure amount test: This was carried out according to the method described in Japanese Patent Application No. 105081/1983.

After injecting the following electrolyte into the cleaned can body for about 9 minutes,
Using a platinum electrode inserted into the can body approximately in the center to a depth that did not contact the bottom of the can as a counter electrode, electrolysis was carried out for 6 times at a potential of 1.3 volts with respect to a saturated silver chloride reference electrode, and the electrolytic current at that time was measured. .

The resulting electrolytic current is proportional to the exposed iron area.

Electrolyte: Soda carbonate 0.15M Soda bicarbonate 0.15M Chlorine ion 0.005M PH9.5 The above tests were conducted on m can bodies of the present invention and m can bodies of comparative examples, and the average values are shown in Table 1. Indicated.

(b) Paint film adhesion test: After washing and drying, apply 20% of epoxy area paint to the inner surface of the can body.
0mg (weight after drying) spray applied, 200℃ x 5
I baked it separately.

After that, I sprayed 200mg (weight after drying) of epoxyphenol paint and heated it to 200'C! Bake for 5 minutes.

Width 5mm and length 100mm from the open end of this can body
(in the axial direction) cut out small strip-shaped pieces, and as shown in Figure 10, coated with nylon 12.
An adhesion test piece was prepared by pressure welding at 3°C.

In Figure 10, the dimensions X, y, and 2 are 7-
15 pharynx and 3-.

Further, 14, 15, 16 and 17 are short pieces, an epoxyphenol coating, an epoxy phenol coating, and nylon 12, respectively.

Both ends of the T-shaped open portion of this test piece were pulled using a tensile testing machine, and coating film adhesion was evaluated based on the force required to pull it off.

All peeling occurred at the interface between the metal and the epoxy coating.

The above tests were performed on each of the five pieces, and the average value was calculated as the first
Shown in the table.

(c) Iron elution amount test Apply 20% of epoxy area paint to the inner surface of the can body after washing and drying.
0mg (weight after drying) Spray applied, 200℃ x 5
I baked it separately.

After that, apply 160mg of Polyvarnish Chill gloss varnish to the outside surface.
(Weight after drying) Roll coating was performed and baking was performed at 200° C. for 2 minutes.

The can body above is processed with a neck-in flange.
After packing the cola and clear carbonated drinks, the aluminum lid was rolled up.

After storing these at 37°C for 6 months, the cans were opened and the amount of iron eluted was measured.

The number of cans measured was 5 for each test lot, and the average value is shown in Table 1.

As described above, the can body of the present invention has a smaller exposed area of iron on the inner surface and superior coating film adhesion than the can body of the comparative example.

Therefore, it is clear that the amount of iron eluted into the content liquid after filling and sealing is small, and there is little risk of spoiling the flavor of the content liquid.

[Brief explanation of the drawing]

FIG. 1 is an explanatory front view of an example of the ironing punch used to manufacture the metal can body of the present invention, FIG. 2 is a diagram showing an example of the surface profile of the punch shown in FIG. 1, and FIG. 3
The figure is a schematic enlarged vertical cross-sectional view of the main part to explain the behavior of ironing using the punch shown in Fig. 4.
The figure is an explanatory longitudinal sectional view of an embodiment of the metal can body of the present invention, FIG. 5 is a line diagram showing an example of the inner surface profile of the can body of FIG. 4, and FIG. Fig. 7 is a schematic enlarged vertical cross-sectional view of the main part to explain the state when the ironed can body is extracted using the punch shown in Fig. 1, and Fig. 8 is a conventional A metallurgical micrograph of the inner surface of a metal can body that has been ironed using a smooth ironing punch, Figure 9 is a diagram showing the profile of the inner surface of the can body shown in Figure 8, and Figure 10 is a graph showing paint film adhesion. It is a perspective view of a test piece. 5... Trunk wall part, 6... Linear protrusion part, 9
...Metal can body.

Claims (1)

[Scope of utility model registration request] In a metal can body formed by drawing and ironing a tin-plated steel plate, there is a linear protrusion with a height of about 0.5 to 3μ extending approximately in the circumferential direction on the inner surface of the body wall of the container. A metal can body characterized in that it is formed at an average interval of .05 to 2 mm.