JP2001071376A - Production of packing for secondary cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make productivity excellent, to reduce a mold cost, and to extend a mold life by a method in which a fluorocarbon resin sheet is pressurized by using a die while being cooled, plastic-deformed into a three-dimensional form, and simultaneously or before/after the deformation, punched into a target size. SOLUTION: A shallow recession 11b is formed on the upper surface of a female mold 11a, and a longitudinal hole 11c penetrating it from the upper surface toward the lower surface is formed in the middle part of a main body part 11a. In a male mold 12, the first low projection part 12b is formed from the lower surface of the main body part 12a downward, and the second high projection part 12c is formed from the middle of the first projection part 12b downward. The projection part 12b is engaged with the recession 11b. The clearance between the inner circumference of the recession 11b and the outer circumference of the projection part 12b is designed to be 0.15 mm. The projection part 12c of the male mold 12 is well inserted into the hole 11c of the female mold 11 insertably/extractably.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a packing (gasket) made of a fluororesin used for an insulating seal of a secondary battery.
And a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, a very small packing has been used as an insulating material or a sealing material for a secondary battery represented by a lithium ion secondary battery. There are various shapes of the packing, and a typical one is a circular, oval or square dish with a through hole in the center. The following are known as packings for this purpose.

(1) First, the most widely used packing is made of a polypropylene injection molded product. However, this packing has difficulty in heat resistance and corrosion resistance as described later.

(2) Therefore, if a packing made of a fluorine-based resin having good heat resistance and no corrosion is used, it is expected that corrosion by the electrolytic solution is prevented and the sealing property is maintained for a long time. As a method of manufacturing the packing made of a fluororesin, a machining method and an injection molding method are considered.

(3) Japanese Patent Application Laid-Open No. Hei 11
Japanese Patent No. 16548 discloses that a material molded article made of a fluororesin is softened by heating it to a temperature higher than its softening temperature.
A method of manufacturing a packing for a secondary battery in which pressure is applied by a mold to deform into a three-dimensional softened three-dimensional molded product, and then cooled to a temperature lower than its softening temperature to form a target molded product is shown. .

[0006]

(1) A packing for a secondary battery has heat resistance, heat shock resistance (heat cycle shock resistance), and stress crack resistance (stress crack resistance) capable of withstanding a temperature of about 200 ° C. ), And anticorrosion properties against an electrolytic solution are required. However, although the packing made of the polypropylene injection molded product has good sealing properties, it lacks heat resistance, heat shock resistance and stress crack resistance are not necessarily sufficient, and the negative electrode of the secondary battery has a fluoride. When carbon is used, the eluted fluorine may attack the packing made of polypropylene and impair the sealability.Furthermore, during injection molding, a weld is formed where the flow of the molten resin divided into right and left joins, and the weld is formed. There is a problem that the mechanical strength of the part is inevitably lower than that of other parts. Therefore, the packing made of polypropylene has limitations on the types of secondary batteries that can be applied.

(2) Of the methods for obtaining a packing made of a fluorine-based resin, the machining method increases labor costs and causes variations in products, and thus cannot be said to be an industrially applicable method.

[0008] Among the methods for obtaining a packing made of a fluororesin, the injection molding method discharges a completely melted and fluidized fluororesin toward a mold, but has the following problems. have. (B) In general, a fluororesin having a melt flow index (at a temperature higher by 10 ° C. than the melting point) of less than about 5 g / 10 min has preferable characteristics, and a resin having a higher melt flow index has a heat cycle shock resistance. And stress crack resistance tend to be insufficient, but it is difficult to obtain a grade with a melt flow index of less than about 5 g / 10 min by the injection molding method. Injection molding must be carried out using a grade having a large size, which results in a problem that the characteristics of the obtained packing are not always preferable. (B) Since the packing for the secondary battery is extremely small, the ratio of sprue and runner is extremely large,
Moreover, since the sprue and runner cannot be reused (insulation performance is inferior if reused), the cost is considerably increased, and it is against the trend of resource saving. There are also disadvantages such as the need for trouble. (C) In addition, at the time of injection molding, a weld is generated at the place where the flows of the molten resin are separated from each other, and the mechanical strength at the weld is inevitably lower than at other places. There is a limit in nature.

(3) In this regard, the method for producing a packing made of a fluorine-based resin disclosed in Japanese Patent Application Laid-Open No. H11-16548 discloses a method of using a fluorine-based resin as a raw material and having a low melt flow index and good characteristics. Can be used to minimize the waste of expensive fluororesin, and to control burrs if strictly controlling the dimensions of the molded material used for the mold. Obtainable.

However, in this method, since a material molded article made of a fluororesin is heated to a temperature equal to or higher than its softening temperature to be softened and then cooled, a large amount of this type of packing must be produced. With that in mind,
It takes time in the process, and the productivity is not always good. In addition, since the mold is heated to a high temperature of about 300 ° C., the mold may be thermally deformed, which shortens the mold life and is disadvantageous in terms of energy. Since gas is generated, expensive metal with chemical resistance must be used as a mold.
In addition, issues remain in the work environment.

Under such a background, the present invention makes use of the advantages of the method of Japanese Patent Application Laid-Open No. H11-16548, which has been filed earlier, as it is, the productivity is remarkably improved, and the mold cost is reduced. In addition, it is possible to obtain a packing for a secondary battery, which is advantageous in terms of energy, has a favorable working environment, and has high reliability in terms of quality. It is intended to provide an efficient method.

[0012]

According to a method of manufacturing a packing for a secondary battery of the present invention, a fluororesin sheet is plastically deformed into a three-dimensional shape by pressurizing the sheet in a cold state using a mold. In addition, punching into a target size is performed simultaneously with or before or after the plastic deformation.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.

<Fluorine Resin and Sheet Thereof> As the fluorine resin, tetrafluoroethylene-perfluoroalkylvinylether copolymer (PFA) and tetrafluoroethylene-hexaene which are easily formed into a sheet and have required characteristic values are used. Fluoropropylene copolymer (F
EP) is important, and among them, PFA having excellent stress crack resistance and heat aging resistance is particularly important.

As the fluororesin, polytetrafluoroethylene (PTFE), ethylene-tetrafluoroethylene copolymer (ETFE), ethylene-chlorotrifluoroethylene copolymer (ECTFE) and the like can be used.

The sheet made of the above-mentioned fluororesin includes:
Although those having various melt flow indices are used, the melt flow
About 5g / 10min)
It is particularly preferable to be made of an extruded product of a fluororesin of a grade lower than that. This is because such grades are more advantageous in terms of heat cycle shock resistance and stress crack resistance.

A sheet made of a fluororesin can be obtained by any molding method. For example, in the case of PFA or FEP, a columnar body obtained by a direct pressure molding method is "skived". That is, a method of forming a sheet by slicing so as to peel the skin from the outer peripheral surface of the cylindrical body is particularly preferably employed in terms of thickness accuracy and productivity. In addition, a method of obtaining a sheet by extrusion molding, a method of forming a packing-like sheet obtained by slicing a round bar, and the like are also possible. When molding the fluororesin, coloring or shading can be achieved by adding various inorganic or organic additives as long as it does not adversely affect the plastic deformability due to cold pressing described below. It is also possible to improve properties such as heat resistance and chemical resistance.

The thickness of the sheet made of a fluororesin is set to a thickness required when the packing is used. In the case of a very small packing for a lithium ion secondary battery, for example, 0.25 to 1.2 mm, especially about 0.3 to 1.0 mm.

<Manufacture of packing> In the present invention, the above-mentioned sheet made of a fluororesin is plastically deformed into a three-dimensional shape by applying pressure in a cold state using a mold. Then, at the same time as the plastic deformation or before or after the plastic deformation, punching is performed to a target size. Thereby, the intended packing for the secondary battery is obtained.

More specifically, the cold pressing is performed by setting a sheet made of a fluororesin in a mold, applying pressure, and plastically deforming the sheet into a three-dimensional shape along the mold cavity. . It is also possible to perform cold pressing using upper and lower mold rolls instead of the mold.

The clearance between the inner periphery of the concave portion of the upper and lower molds (or the upper and lower mold rolls) and the outer periphery of the convex portion (FIG. 1)
The setting in (b) is important. If the clearance is too narrow, excessive shearing force is applied when plastically deforming into a three-dimensional shape, causing a decrease in strength of the vertical wall portion of the packing. On the other hand, if the clearance is too wide, the plastically deformed body removed from the mold returns to its original state over time, and the dimensional accuracy is impaired. According to a detailed study, this clearance is 0.15 to 0.35 d, particularly 0.2 to 0.3, where d is the thickness of the fluororesin sheet.
d is recommended.

When the sheet is plastically deformed into a three-dimensional shape, the step (height of the vertical wall, see the note in FIG. 1 (b)) is 0.5 to 0.9 d, especially 0.7 to the sheet thickness d. ~ 0.8d
It is preferable that When the height is too low, the packing does not satisfy the standard in many cases. On the other hand, when the height is too high, the strength of the step (vertical wall) or its vicinity is reduced.

The room temperature at the time of cold pressurization is sufficient,
The heat treatment may be performed at a lower temperature, or at a temperature somewhat higher than the normal temperature as long as the sheet does not soften. Usually 5
In the range of about 50 ° C, especially 10 to 40 ° C, especially 15
Pressurization is often performed at ３０30 ° C.

As a pressurizing method, a mechanism utilizing mechanical pressurization, hydraulic pressure, pneumatic pressure, or hydraulic pressure is employed. The pressure is suitably, for example, about 50 to 300 kg / cm ² .

Plastic deformation into a three-dimensional shape by cold pressing;
It is particularly preferred that the punching to the target size (size of the individual packings) be performed simultaneously or immediately after in the same mold. Even if it is performed immediately after, since the plastic deformation is performed almost instantaneously, the operation is practically the same as at the same time. Although there is a disadvantage in terms of productivity, it is also possible to transfer the plastically deformed sheet to another mold and perform punching, or to supply the previously punched sheet to the mold and subject it to plastic deformation. It is also possible.

The overall shape of the packing after punching is arbitrary, such as a circle, an oval, a square, or a rectangle in plan view.
At the time of punching, not only the whole punching but also a through hole can be provided together at an appropriate position in the central region thereof (a through hole can be provided before or after the whole punching). The number of through holes is not limited to one. The through hole is
In some cases, it may be provided on a sheet before cold pressing.

<Use> The packing obtained by the above method is a packing (gasket) made of a fluororesin used for an insulating seal of a secondary battery, especially a lithium ion secondary battery.
Useful as

[0028]

The present invention will be further described with reference to the following examples.

Example 1 FIG. 1 is an explanatory view showing an example of a manufacturing process of a packing for a secondary battery according to the present invention, and is shown in a vertical sectional end view.
FIG. 1B also shows the meanings of the clearance and the step.

FIG. 2 is an explanatory view showing an example of the product packing obtained by the process of FIG. 1, (a) is a plan view,
(B) is a cut end view, and (c) is a bottom view.

FIG. 3 is a photomicrograph of the portion A in FIG.

In FIG. 1, (1) is a mold, and a female mold (1
It consists of four blocks: 1), male type (12), lower fixed type (13), and upper fixed type (14). As shown in FIG. 1, the female mold (11)
A shallow depression (11b) is provided on the upper surface of the main body (11a),
Further, a vertical hole (11c) penetrating in the vertical direction from the upper surface to the lower surface is provided in the center of the main body (11a). On the other hand, male type (12)
Has a first convex portion (12b) having a lower height from the lower surface of the main body portion (12a) toward the lower side.
b) The second convex portion that is higher in height from the center of
(12c) is projected.

In the shallow recess (11b) of the female mold (11), the male mold (1
The first convex portion (12b) of the male mold (12) and the inner periphery of the shallow concave portion (11b) of the female mold (11) are fitted together with the first convex portion (12b) of the male mold (12). Is designed to be 0.15 mm (set to 0.3 d when the thickness of the sheet (S) is d (0.5 mm in this embodiment)). Also,
In the vertical hole (11c) of the female mold (11), the second convex portion (12c) of the male mold (12) is provided.
Is designed to fit almost perfectly within the range where it can be inserted and removed.

As a sheet (S) made of a fluororesin, 32
Wig off a cylindrical body of PFA with melt flow index of 2g / 10min at 0 ° C.
Then, a PFA sheet (a slightly opalescent transparent sheet) having a thickness d of 0.5 mm was prepared.

This sheet (S) is sandwiched between the lower fixed type (13) and the upper fixed type (14), and both fixed types (13) and (14) are tightened and fixed (FIG. 1 (a)). reference).

Then, the male mold (12) was lowered toward the female mold (11) under normal temperature conditions, and was pressed at a pressure of 100 kg / cm ² to plastically deform the sheet (S) into a three-dimensional shape. (See (b) of FIG. 1). Immediately thereafter, the female mold (11) and the male mold (12) are moved upward with the deformed sheet (S) sandwiched between both molds (11) and (12), thereby achieving the objective. A through hole (h) was formed at the same time as punching into a size (see (c) in FIG. 1).
Thereafter, the product packing of FIG. 2 as the target was taken out of the mold (1).

As a result, an oblong product packing having a peripheral wall (w) formed on the outer periphery on the left and right end sides of the upper surface of the packing body (p) and a through hole (h) in the center is obtained in plan view. Was done. The dimensions of this packing are shown in FIG.
mm). The step (height of the vertical wall) is relative to the sheet thickness d.
0.35 / 0.5 = 0.7d.

At the step formed by plastic deformation of the product packing, as shown in FIG. 3, microscopic observation shows a streak pattern when a film is produced by peeling a wig (skive). This indicates that the plastic deformation was performed. And it had good strength equivalent to that of the hot-pressed product including this step.

Embodiment 2 FIG. 4 is an explanatory view showing another example of the product packing.
(A) is a plan view, (B) is a cut end view, and (C) is a bottom view.

As the sheet (S) made of a fluororesin, 32
Wig off a cylindrical body of PFA with melt flow index of 2g / 10min at 0 ° C.
Then, a PFA sheet having a thickness d of 0.4 mm was prepared, and a product packing was manufactured under the same conditions as in Example 1. However, the pressure is 100 kg / cm ^2, and the clearance between the inner circumference of the shallow depression (11b) of the female mold (11) and the outer circumference of the first convex part (12b) of the male mold (12) is 0.25d. Set.

As a result, a peripheral wall (w) is formed all around the end of the upper surface of the packing body (p) and a through hole is formed in the center.
(h) A rectangular packing in a plan view was obtained.
The dimensions of this packing are shown in FIG. The step (height of the vertical wall) is 0.3 / 0.4 = 0.75d with respect to the sheet thickness d.
Met. The step formed by plastic deformation of this product packing had a slightly different microstructure from that obtained by hot pressing under microscopic observation.However, including the step, the same strength as the hot pressed product was obtained. Had.

Example 3 As a fluororesin sheet (S), a cylinder obtained by directly pressing FEP having a melt flow index of 2 g / 10 min at 270 ° C. and having a melt flow index of 0.5 g was obtained by stripping (skiving) a wig. Was prepared, and a product packing was manufactured under the same conditions as in Example 1. In this case, the same good product packing as in Example 1 was obtained.

[0043]

According to the present invention, a method of plastically deforming a sheet made of a fluorine-based resin into a three-dimensional shape by pressing the sheet in a cold state and punching the sheet into a target size is adopted to obtain a packing for a secondary battery. I have.

In the present invention, since a method of applying pressure at room temperature or at a temperature before or after room temperature is adopted, it is not necessary to heat or cool the mold. Therefore, when compared with the hot press method, ・ The process does not take much time, and the productivity is dramatically improved. ・ The degree of freedom in the material of the mold is great, and the mold life is extremely advantageous. And therefore, the cost of the mold can be reduced. ・ It is advantageous in terms of energy. ・ It does not generate gas during operation, so it is preferable in terms of the working environment. ing. In addition, despite the cold pressurization, the quality of the product packing is good and reliable.

In addition, the performance advantages of using a fluororesin can be used as it is, and a grade having a low melt flow index and good properties can be used as compared with the conventional injection molding method.・ Because there is no risk of burrs at the joint of the mold,
It does not require complicated processes for removing burrs. ・ No sprue or runner is generated, so waste of expensive fluorine-based resin is minimized, which is advantageous in terms of cost and is also a trend in resource saving. There are also advantages such as being attached.

Therefore, the present invention is extremely useful as an industrial method for producing packing for a secondary battery.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing one example of a manufacturing process of a packing for a secondary battery according to the present invention, and is shown in a vertical cross-sectional end view.

FIG. 2 is an explanatory view showing an example of a product packing obtained by the process of FIG. 1, (a) is a plan view, (b) is a cut end view, and (c) is a bottom view.

FIG. 3 is a micrograph of a portion A in FIG.

FIG. 4 is an explanatory view showing another example of the product packing; (A) is a plan view, (B) is a cut end view, and (C) is a bottom view.

[Explanation of symbols]

(1) ... mold, (11) ... female mold, (11a) ... main body, (11b) ... shallow depression, (11c) ... vertical hole, (12) ... male, (12a) ... main body, (12b) ... first convex portion, (12c) ... second convex portion, (13) ... lower fixed type, (14) ... upper fixed type, (S) ... sheet made of fluororesin, (p) ... packing Main body, (w) ... peripheral wall, (h) ... through-hole

Continued on front page F-term (reference) 4F202 AA16 AC03 AG01 AG05 AG13 AG19 AG24 AH13 AR12 CA17 CB01 CK11 CK84 CL02 CN30 CS10 4F208 AA16 AC03 AG01 AG05 AG13 AG19 AG24 AH13 AR12 MA05 MB01 MC03 MG01 MG11 MJ22 MW01 MW23

Claims (4)

[Claims] 1. A plastic resin sheet is plastically deformed into a three-dimensional shape by pressurizing it in a cold state using a mold, and simultaneously with or before or after the plastic deformation. A method for producing a packing for a secondary battery. 2. The method according to claim 1, wherein the plastic deformation and the punching are performed in the same mold simultaneously or immediately. 3. The clearance between the inner periphery of the concave portion of the upper and lower molds and the outer periphery of the convex portion is 0.15 to 0.35 d with respect to the sheet thickness d.
2. The method according to claim 1, wherein the method is set to: 4. The step (height of the vertical wall) when the sheet is plastically deformed into a three-dimensional shape is set to 0.5 to 0.5% of the sheet thickness d.
2. The method according to claim 1, wherein the value is set to 0.9 d.