JPH05159759A - Manufacture of seal unit for alkaline battery - Google Patents

Abstract

PURPOSE:To provide a seal unit of excellent quality by providing a plurality of injection gates with a almost equal space in the peripheral location in a thin thickness part of the seal unit, so as to prevent improper connection of a weld part and breaking of a center part generated in the thin thickness part. CONSTITUTION:Injection gates 4, 4 opposed with the center part serving as a reference are provided in a peripheral part 8 from a thin thickness part 2 of a seal unit. Melted resin is pressurized to pass through the injection gates 4, 4 from a runner 6 and branch runners 5, 5 into a cavity. First, the resin flows into a large space in both sides next to reach thin thickness parts A, A. The resin is cooled a little in the thin thickness parts A, A to decrease an infiltrating speed with a flow detouring a little, and when a peripheral part of the thin thickness parts A, A is filled, the resin, increasing an internal pressure, flows into the center part first from right/left positions B, B which are parts of the highest fluidity. Here by the cavity internal pressure, the resin in a part of first reaching the thin thickness parts A, A also flows into the center part with a delay. After cooling the resin solidified, it is removed from a metal mold by cutting off a gate part.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a sealing body for an explosion-proof battery in a sealed alkaline battery.

[0002]

2. Description of the Related Art In a sealed alkaline battery, abnormal gas may be generated due to sudden discharge or charging due to a mistake in loading into a device, which may cause an explosion accident in the worst case. Therefore, a method of providing an explosion-proof valve is usually adopted. The present invention is directed to a sealing body made of a thermoplastic resin and having an extremely thin thin portion, and the thin portion is ruptured when the internal pressure of the battery exceeds a predetermined pressure to discharge gas to the outside. Is. This resin sealing body has a thin portion of 0.
The gas discharge function does not work unless it is made extremely thin to about 1 to 0.2 mm. The sealing body is usually manufactured by injection molding of a molten resin, but it has been extremely difficult to provide an excellent sealing body in the manufacturing method so far because of the existence of an extremely thin thin portion. ..

A method of manufacturing the resin sealing body will be described below. Conventionally, a method of manufacturing a resin sealing body having no thin portion and then forming the thin portion by cutting or ultrasonic processing has been performed. There is. In this case, there is a problem that a large amount of capital investment is required for the post-processing, and the product cost becomes high if the post-processing wage is included.

In order to solve the above-mentioned problems, a method has been adopted in which a molten resin is injection-molded at a time with a thin portion provided from the beginning. In the case of this injection molding method, there are roughly two methods at the position of the injection gate.
One is a method of locating the injection gate outside the thin portion, and another is a method of locating the injection gate on the inner center side of the thin portion.

As a method of locating the injection gate outside, a one-point gate method has been adopted so far. In this method, the molten resin to be filled hits the ring-shaped thin portion of the mold forming the thin portion, and the viscous resin is blocked here because the inflow space is extremely narrow. And
The flow of the molten resin in contact with the thin portion is temporarily stopped, heat is taken by the mold, and cooling and solidification starts rapidly. Especially in the thin portion where the resin from the injection gate first arrives, the flow tends to stop once, and the resin blocked here bypasses and flows into the outer periphery of the thin portion, When the outer peripheral portion is filled, the internal pressure of the cavity increases, and it passes through the thin portion from the opposite side of the injection gate, which is the portion having the highest fluidity.
Finally, the resin that has flowed into the central portion of the thin portion merges with the resin that has reached the thin portion first, but deep weld lines and defective joints occur at the merged portion.

Further, there is a press-fitting hole for the collector rod in the central portion of the sealing body, but the pressure loss of the filling pressure due to the partial solidification in the ring-shaped thin portion is large, and the resin density in the central portion may be lowered to cause a void. When a void is generated, the strength of that portion is reduced, and when the current collector rod is press-fitted, damage is likely to occur. As described above, the safety valve of the sealing body and the important function of the sealing property and the damage in the press-fitting of the current collector frequently occur, which is a serious obstacle to the quality stability.

Further, in the method of locating the injection gate at the inner central portion side of the thin portion, the injection gate is provided at the central portion of the sealing member so as to fill the resin from the inner side to the outer side through the thin portion. A method is used in which the resin is poured from the current collector rod press-fitting hole in the central portion by a film gate or by a pin gate on the boss end face forming the press-fitting hole. In this method, when the collector rod is assembled by press fitting into the press fitting hole, due to defects such as minute cracks and welds remaining on the cut surface of the injection gate, or flow orientation, and uneven strength of the resin near the injection gate. Since it is close to the collector rod press-fitting portion, it is known that the collector rod press-fit crack easily occurs even if a small deformation occurs. This occupies a great weight as a cause of frequent leakage of the content liquid.

[0008]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above-mentioned conventional circumstances, and a weld between a welded portion and a welded portion which is generated in a ring-shaped thin portion concentric with the center of a sealing body is not properly joined. Further, it provides a method for manufacturing a sealing body of excellent quality in strength, which secures important functions as a safety valve and sealing property of the sealing body by eliminating density reduction in the central part, strength reduction due to generation of voids, etc. It is a thing.

[0009]

In order to solve the above problems, the present invention is directed to the production of a thermoplastic resin sealing body for an alkaline battery having an annular thin portion concentric with the center of the sealing body by injection molding. In the method, a plurality of injection gates are provided at substantially equal intervals on the outer peripheral portion of the thin portion of the sealing body. Further, the injection gate is arranged at a position where the time difference from the time when the molten resin first reaches the thin portion to the time when the molten resin is filled outside the thin portion is minimized.

[0010]

EXAMPLES The present invention will be described based on examples. In FIGS. 1A and 1B showing the case of a two-point gate, the thin portion 2 (thickness 0.1 to 0.15 mm). The injection gates 4 and 4 are provided so as to face the outer peripheral portion 8 with the center portion as a reference. The case of this two-point gate will be described in detail below along with the flow of the molten resin.
6. From the branch runner (diameter 2.5 mm) 5 and 5, pass through the injection gate (injection diameter 0.7 mm) 4 and 4 and enter the cavity. Next, in FIG. 3 which is a plan view showing the filling process,
The filling is performed in the order of (a), (b), (c), and (d).
The left and right sides of the figure are the gate positions. First, as shown in (a), they flow into the wide space from both sides. Next, the first thin portions A, A of the molten resin are reached. Then, as shown in (c), the first thin portions A, A are slightly cooled and the invasion speed decreases, so that the flow slightly detours, and when the thin portion outer peripheral portion is filled, the internal pressure of the cavity increases and The left and right positions B and B in the figure, which are highly fluid parts, flow into the center first. At that time, due to the internal pressure of the cavity, the first thin portions A and the portions that have reached the first thin portions A also flow into the central portion with a delay. The state at that time is shown in (c). Finally, the center part is filled with molten resin (shown in FIG. 3D), cooled and solidified, and the gate part is cut and removed from the mold.

FIG. 4 shows the case of a three-point gate, where there are three gate positions, and first, as shown in (a), they flow into a wide space from three locations. Next, the first thin portions A, A, A of the molten resin are reached. And, as shown in (c),
The first thin portions A, A, A are slightly cooled and the invasion speed decreases, so that the flow is slightly diverted, and when the outer peripheral portion of the thin portion is filled, the internal pressure of the cavity increases, and this is the portion with the highest fluidity. B, B, B which is the middle part of A, A, A
It flows into the center first from the position. At that time, due to the internal pressure of the cavity, the first thin portions A, A, and the portions reaching A are also delayed and flow into the central portion. The state at that time is shown in (c). Finally, the center is filled with molten resin ((d) in Fig. 4).
), And solidify by cooling, and the gate part is cut and removed from the mold. In the case of the three-point gate, the filling is completed earlier than in the case of the two-point gate, so that the weld defect at the central portion is unlikely to occur.

In the case of the conventional single point gate, as shown in FIG. 2, the left end is at the gate position, and first, as shown in FIG. Next, it reaches the first thin portion (position A) of the molten resin. Then, as shown in (c), the first thin portion is cooled and the invasion speed is stopped, so that the flow is large and detours and merges to the opposite side of the gate position. Flow rate increases and flows into the center from the position B on the right in the figure, which is the most fluid part. This state is shown in FIG. Then, the central part is filled with the molten resin (shown in (e) of FIG. 3).
After that, the thin part (position A) and the position B that flowed in from the end
It is cooled and solidified at (the position in the thin portion), and the gate portion is cut and removed from the mold. In this case, since the time difference between the position A and the position B is large, there is a drawback that a weld joint defect is likely to occur.

In order to make the injection time from each gate uniform, the molten resin passes through the branch runner 6 to reach the gate 4 in order to make the injection time uniform from each gate. It is preferable that they are equal. FIG. 5 shows the flow path from the time when the molten resin reaches the first thin wall portion of the molten resin to the outside of the thin wall portion until the end of filling, and the longer this arrow line, the longer the time difference. ing. 5 (a), (b),
(C) shows the case where a gate is provided on the outermost periphery, (A) shows a one-point gate, (B) shows a two-point gate, and (C) shows a three-point gate. When this comparison is made, the preceding flow path a for reaching the first thin portion of the molten resin is the same, but the bypass flow path b becomes shorter as the number of gates increases, and in reality, there are four or more gates. Since the arrival time is faster, there is not much effect of cooling solidification. Particularly, in the case of the two-point gate of (b) and the three-point gate of (c), the time until the outside of the thin portion is filled is half or more than that of the one-point gate of (a). Since it is shortened to less than that, as shown in (c) of FIG. 3 and (c) of FIG. 4, the confluence position of the preceding flow path a and the bypass flow path b exceeds the thin part and enters the central part, and the thin part Never come to. 6 (a) and 6 (b) show the case where a gate is provided outside the thin portion, (a) shows a one-point gate, and (b) shows a two-point gate. Is. Since the gate is close to the thin portion in all cases, the flow passage a to the first thin portion of the molten resin is extremely short, and when the bypass flow passage b is provided with the gate at the outermost periphery at this time, It is shown that a large time difference occurs when compared. Therefore, it is preferable to provide the gate on the outermost periphery rather than on the outside near the thin portion. Also in this case, in the case of the two-point gate, the confluent position of the preceding flow path a and the bypass flow path b goes over the thin portion and enters the central portion (shown by an arrow in (b) of FIG. 6). ) Never come to the thin part.

[0014]

[Function] The sealing member made of resin requires a uniform thickness strength in the thin portion due to its structure, and has a high strength because the current collecting rod is press-fitted in the central portion.
A uniform strength is required on the outer periphery. Since the present invention uses the manufacturing method as described above, since no weld is formed in the thin portion, a uniform thickness and strength can be secured. In addition, the molten resin passes through the thin portion, and at the central portion, there are no minute cracks generated on the cut surface of the injection gate and no voids due to a decrease in density. The central portion occurs in the horizontal direction even if the weld joint failure occurs. The reason for this is that when the molten resin reaches the wide central cavity, it comes into contact with E shown in FIG. Then, the low-viscosity tip of the center of the molten resin hits the press-fitting hole side wall G and detours up and down F
Join at the position. This is because a weld is formed horizontally at this merging position (shown by K in FIG. 8B). Even if the collector rod is press-fitted through the press-fitting hole of the sealing body (the diameter of the collector rod is larger than the diameter of the press-fitting hole by about 20 percent, it is greatly expanded), but in the pulling direction (horizontal direction). Welds in) are not weak points in terms of strength. If a conventional method is adopted in which an injection gate is provided in the central portion, minute cracks and welds that always remain on the cut surface of the injection gate, and the injection gate.
There is a possibility that current collector rod press-in cracking is likely to occur due to non-uniform strength of the resin in the vicinity.

[0015]

EFFECTS OF THE INVENTION Since the present invention has the above-described structure, compared to the conventional manufacturing method, there are no welds and weld joint defects that occur in the ring-shaped thin portion of the product itself, and the ring-shaped thin portion safety valve It is safe because it does not interfere with the explosion-proof function. In addition, the density of the central part is not reduced, the generation of voids is eliminated, and the generation of cracks due to the press-fitting of the collector rod is eliminated. In particular, this product is an important part related to the human body that is supplied to alkaline batteries and is mass-produced, and a great effect can be expected in preventing the inclusion of defective products. Strict quality inspection is carried out with a huge number of inspection processes, and there is a case where the risk of contamination cannot be eliminated, but the ripple effects such as quality improvement, process reduction, and yield improvement are immeasurable. ..

[Brief description of drawings]

FIG. 1 is a plan view of the embodiment of the present invention, and FIG.

FIG. 2 is a schematic plan view showing a filling process in the case of a conventional one-point gate.

FIG. 3 is a schematic plan view showing the filling process in the case of the two-point gate of the present invention.

FIG. 4 is a schematic plan view showing the filling process in the case of the three-point gate of the present invention.

FIG. 5 shows the flow of resin, and (a) is a conventional single point game.
In the case of the two-point gate of the present invention,
Is a schematic plan view in the case of a two-point gate of the present invention.

FIG. 6 is a schematic plan view showing a case where a gate position is at an intermediate portion, where (a) is a one-point gate and (b) is a two-point gate.

FIG. 7 is a vertical sectional side view of a main part of an alkaline battery.

FIG. 8 (a) is a schematic vertical sectional side view in the central portion,
(B) is a perspective view.

[Explanation of sign]

 DESCRIPTION OF SYMBOLS 1 Sealing body 2 Thin part 3 Current collector rod press-fitting hole 4 Injection gate 5 Branch runner 6 Runner 7 Center part 8 Outer peripheral part 9 Current collector rod M Mold

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Susumu Watanabe 4-10-15 Toyomachi, Mibu-cho, Shimotsuga-gun, Tochigi Pref.

Claims (2)

[Claims] 1. A manufacturing method by injection molding of a thermoplastic resin sealing body for an alkaline battery, which has a ring-shaped thin portion concentric with the center of the sealing body, in a manufacturing method by injection molding. A method of manufacturing a sealing body for an alkaline battery, characterized in that a plurality of injection gates are provided in the arrangement. 2. The injection gate is arranged at a position where the time difference between the time when the molten resin first reaches the thin portion and the time when the molten resin is filled outside the thin portion is minimized. The method for producing a sealing body for an alkaline battery according to claim 1.