JP2832091B2 - Method of forming conductive elastic body - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a conductive elastic body, and more particularly to a method for forming an elastic body having a stable electric resistance in a medium resistance region.

In detail, a molding material in an unsolidified state is press-fitted into a cavity of a molding die such as injection molding or transfer molding, and the molding material is solidified in the cavity to form a conductive elastic body. The present invention relates to a method for forming an elastic body.

[0003]

2. Description of the Related Art In general, a conductive elastic material has a predetermined electric resistance obtained by dispersing a conductive material such as carbon black, metal oxide, or metal powder in an elastic material as a base material. Like that.

[0004] This conductive elastic body is formed into a product by injection molding, transfer molding, compression molding, or the like, and then through post-processing such as polishing and cutting as necessary.

[0005] The conductive elastic body is used for various applications, and particularly when used for precision parts, various characteristics are required.

[0006] Among these properties, the electrical properties are particularly:
It is easily affected by the surface property, and therefore, when the surface roughness of the surface of the conductive elastic body is not uniform, it is difficult to obtain a uniform electric resistance value. In particular, the electric resistance value is 1 × 10 ^{3 to} 1 ×
This tendency is remarkable in a medium resistance region of 10 ¹⁰ Ω.

When the conductive elastic body has a parting line (hereinafter, referred to as "PL") due to the mold structure at the time of molding on its surface, the electrical characteristics are reduced at the PL part. It is necessary to remove the PL by polishing the surface.

However, the hardness of the conductive elastic body is determined by JI
In the case of a relatively low hardness of 60 ° or less in SA, even if the surface is polished, the surface roughness becomes only about Rz = 10 μm,
If a higher surface roughness is required, it has been difficult to cope with the surface polishing.

For these measures, for example, a method of molding using a molding die having a structure having no PL such as a cylindrical shape and using no polishing is adopted. In this case, the molding material in an unsolidified state is used. Since the molding material is injected into the cavity through the gate, the molded product is greatly affected by the flow of the molding material, the pressure retention, and the depressurization method when passing through the gate and in the cavity. In addition, the electrical resistance partially varies within the same molded product. Especially as you get closer to the gate,
The variation in the electrical resistance value was large, so that stable electrical characteristics could not be obtained. In addition, this method has a structure in which air and reactive gas tend to accumulate in the molding die, and it is difficult to absorb the rubber expansion due to heat.Therefore, defects such as chips, cracks, air, etc. May have occurred. Therefore, in this method, after molding a product that is considerably larger than the actual size, it is necessary to cut and use a portion having less variation in electrical resistance in the same molded product in accordance with the product size, which complicates the process and Was wasting a lot of material.

[0010]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method of forming a conductive elastic body which can solve the above-mentioned various problems.

That is, an object of the present invention is to provide a method for forming a conductive elastic body that does not generate PL.

It is another object of the present invention to provide a method for forming a conductive elastic body having stable electric characteristics by further suppressing variation in electric resistance value within the same molded article.

It is a further object of the present invention to provide a method for forming a conductive elastic body which does not require post-processing such as polishing and cutting, reduces waste of material, stabilizes electrical characteristics, and the like.

Still another object of the present invention is to provide a method for forming a conductive elastic body having an arbitrary surface roughness (Rz).

[0015]

According to the method for molding a conductive elastic body of the present invention, a molding material in an unsolidified state is press-fitted into a cavity of a molding die, and the molding material is solidified in the cavity. In a method for molding a conductive elastic body for molding a body, molding is performed using a molding die having an injection gate portion for injecting the molding material into the cavity and an outflow gate portion for releasing the molding material from inside the cavity. By doing so, the above object is achieved.

According to the method for molding a conductive elastic body of the present invention, a molding material in an unsolidified state is press-fitted into a cavity of a molding die, and the molding material is solidified in the cavity to form a conductive elastic body. The method of molding a viscoelastic body includes a step of press-fitting a molding material into a cavity through an injection gate and a step of releasing a part of the molding material press-fit from the injection gate from the inside of the cavity through an outflow gate. The above object is achieved by the features described above.

The variation in the electric resistance value in the same molded product is such that when an unsolidified molding material is pressed into a cavity via an injection gate during molding, the molding material has strong elasticity against shear stress. In addition, when flowing at a specific shear rate, it is molded with internal strain, so due to these effects, the uneven distribution, orientation, structural change or It is generally considered to appear because it causes destruction and the like.

On the other hand, in the method for molding a conductive elastic body of the present invention, a molding having an injection gate for injecting an unsolidified molding material into a cavity and an outflow gate for allowing the molding material to escape from the cavity are provided. It is molded using a mold, that is, the unsolidified molding material is press-fitted into the cavity via the injection gate, and in the press-fitting process, a part of the molding material press-fitted from the injection gate is removed from inside the cavity. Evacuation through the outflow gate makes it possible to make the flowability of the molding material uniform and dissipate internal strains, so that the pressure distribution of the molding material in the cavity can be made relatively uniform. it is conceivable that.

Accordingly, in the molded elastic body, the uneven distribution, orientation, structural change, destruction and the like of the conductive substance in the elastic body do not occur or decrease, so that the electric resistance value in the same molded article is reduced. Was able to be suppressed as compared with the conventional one not using the outflow gate portion.

When the total of the cavity-side cross-sectional area of the injection gate portion in the mold is S _ENT and the total of the cavity cross-sectional area of the outflow gate portion is S _EXT , S _ENT and S _ENT
The relationship with _EXT is preferable because the maximum value of the electric resistance value can be made 5 times or less with respect to the minimum value by satisfying the following condition S _EXT / S _ENT = 0.08 to 1.2. Further, when the following condition S _EXT / S _ENT = 0.2 to 0.8 is satisfied, the above magnification can be further reduced, which is more preferable.

The sum total of the cross-sectional area on the cavity side of the injection gate portion according to the present invention refers to the cavity 6 of the molding die formed by the injection-side die 1, the outflow-side die 2 and the die body 3 shown in FIG. This is the area of the opening of the injection gate portion 4 facing, and when there are a plurality of injection gate portions 4, it is a numerical value obtained by summing the areas of the openings. Similarly, the sum of the cross-sectional areas on the cavity side of the outflow gate portion refers to the area of the opening of the outflow gate portion 5 facing the cavity 6, and the outflow gate 5
Is a numerical value obtained by summing the areas of the openings.

The shapes of the injection gate and the outflow gate according to the present invention are not particularly limited, and are arbitrarily set according to the shape of the molded product.

As the conductive substance contained in the conductive elastic body according to the present invention, a conventionally known material that is a conductive fine powder such as carbon black, metal oxide or metal powder can be used. .

Examples of the elastic material include synthetic rubbers having a conventionally known rubber-like elasticity such as synthetic rubbers such as olefin-based, organosilicon-based, diene-based, polysulfide-based, fluorine-containing, urethane-based and vinyl-based rubbers. Can be used.

As a method for molding the conductive elastic body, a molding method in which an unsolidified molding material is pressed into a cavity through an injection gate, such as injection molding including reaction injection molding or transfer molding, can be used. .

As the molding material, a material obtained by dispersing the above-mentioned conductive material as a fine powder in an unsolidified elastic molding material is used.

The molding material in an unsolidified state refers to a material in a fluidized state in which a thermoplastic resin is heated and softened or in a fluidized (plasticized) state before the thermosetting resin is solidified. The unreacted or in-reaction thermoplastic resin in a state where the thermoplastic resin is cooled and loses its flow due to cooling, or in a fluidized state, undergoes a chemical reaction due to the action of a curing agent, catalyst or heat. Hardened (solidified).

The molding die used in the molding method of the present invention has a surface finished by polishing in accordance with the surface roughness (Rz) of the molded product to obtain the surface constituting the cavity of the molding die. Use

In the molding method of the present invention, the hardness is JIS A
By adjusting the surface finishing accuracy of the surface constituting the cavity of the above-mentioned mold even for an elastic body of 60 ° or less, the surface roughness is not less than Rz = 10 μm,
can be smaller than μ.

The electric resistance of the conductive elastic body according to the present invention is a value measured by the following method.

The conductive elastic body is heat-treated in an atmosphere of 150 ° C. for 4 hours, left to stand for one day, and closely adhered to a 10 mm-wide aluminum box around the outer periphery of the roller.
Apply a voltage of 50 V to the tester (HIROKI 31
16 DEGITAL MΩ HI TESTER).

The surface roughness of the conductive elastic body according to the present invention is:
It is a value measured according to JIS B-0601.

[0033]

The present invention will be specifically described below with reference to examples and comparative examples.

Example 1 Polyolefin Synthetic Rubber E
100 parts by weight of PDM PX-007 (trade name of Mitsui Petrochemical Industry Co., Ltd.), 10 parts by weight of Ketjen Black EC (trade name of Lion, Akzo Co., Ltd.) Liquid paraffin PW-380 for industrial use (Idemitsu Kosan Co., Ltd. (1) Composition 1 was prepared using 30 parts by weight of two rolls.

Then, silicone rubber KE 520u
(Shin-Etsu Chemical Co., Ltd. product name) was used as composition 2, and the mixing ratio of composition 1 and composition 2 was composition 1 / composition 2 = 50/5.
Then, 1.6 parts by weight of dicumyl peroxide was added to the mixture so as to be 0 to prepare a compound (hereinafter, silicone rubber).

On the other hand, as the molding die, FIG. 2 and Table 1 show a longitudinal sectional view of the molding die of FIG. 1 and an arrow view of the injection piece 1 alone in the molding die of FIG. Injection mold 1 having an injection gate 4 and a core holder 7, and an outlet piece 2 having an outlet gate 5 and a core holder 7.
And a mold body 3 having a cylindrical cavity 6 formed by the injection-side piece mold 1, the outflow-side piece mold 2, and the mold body 3.
And the shape of the inflow gate 5 was the gate shape shown in Table 1.

After the stainless steel cylindrical core is held in the molding die by the injection molding piece 1 and the outflow side molding die 2 by transfer molding using the compound, the molding is performed. A cylindrical roller (conductive elastic body) having an outer diameter of 12 mm, a core diameter of 6 mm, and a length of 230 mm having an elastic body around the core was formed.

This roller was rolled at 150 ° C. in an atmosphere of 4 ° C.
After heat treatment for 1 hour, let the electric resistance of the roller be 10m
When measured for each m, 3.5 × 10 ^{4 to} 9.5 × 10 ⁴
And the maximum value was 2.71 times the minimum value.

(Comparative Example 2) The same procedure as in Example 1 was performed except that the gate shape shown in Comparative Example 1 in Table 1 was used. Excess rubber was allowed to escape naturally from the mating part of the mold. The electric resistance of the roller was measured by using this mold to measure 2.5 × 10 ^{3 to} 8.2 × 10 ⁵ Ω, and the maximum value was 3.3 × 10 ² times the minimum value. Rollers were obtained.

Example 2 The procedure of Example 1 was repeated except that the gate shape shown in Example 2 of Table 1 was used, and the electric resistance of the roller was measured to be 2.3 × 10 ⁴ .
1.0 × 10 ⁵ Ω, and the maximum value is 4.3 with respect to the minimum value
A 5-fold roller was obtained.

[0041] (Example 3) Table except 1 that using the gate shape shown in Example 3 was made in the same manner as in Example 1, was measured and the electric resistance of the roller 7.2 × 10 ³ ~
1.3 × 10 ⁵ Ω, and the maximum value is 1.
An 8 × 10 roller was obtained.

[0042] (Example 4) Table except 1 that using the gate shape shown in Example 4 was made in the same manner as in Example 1, was measured and the electric resistance of the roller 8.3 × 10 ⁵ ~
4.0 × 10 ⁶ Ω, and the maximum value is 4.0 with respect to the minimum value.
An 82 times roller was obtained.

[0043] (Example 5) Table except 1 that using the gate shape shown in Example 5 was made in the same manner as in Example 1, was measured electrical resistance of the roller 1.1 × 10 ⁶ ~2.
1 × 10 ⁸ Ω, and the maximum value is 1.9 ×
10 ² times the roller was obtained.

[0044]

[Table 1]

[0045]

According to the method for molding a conductive elastic body of the present invention, a molding die having an injection gate for injecting an unsolidified molding material into a cavity and an outflow gate for releasing the molding material from the cavity. The following effects can be obtained because the molding is performed by using the molding method.

A conductive elastic body in which PL does not occur on the surface can be formed.

In the same molded article, it is possible to mold a conductive elastic body in which the variation of the electric resistance value is suppressed as compared with the conventional method of molding without using the outflow gate.

It is possible to form a conductive elastic body having stable electric characteristics without performing post-processing such as polishing and cutting, and reducing waste of materials.

A conductive elastic body having an arbitrary surface roughness (Rz) and a surface can be formed.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a mold used for using the conductive elastic body of the present invention.

FIG. 2 is an arrow view of the molding die as viewed from the direction A of the inflow-side piece die alone of the molding die of FIG. 1;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Injection piece type 2 Outflow side piece type 3 Mold body 4 Injection gate part 5 Outflow gate part 6 Cavity

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁶ , DB name) B29C 45/00-45/84 B29C 33/00-33/76

Claims (5)

(57) [Claims] In a method for molding a conductive elastic body, a molding material in an unsolidified state is press-fitted into a cavity of a mold, and the molding material is solidified in the cavity. A method for molding a conductive elastic body, comprising: molding using a molding die having an injection gate portion for injecting the molding material into the inside and an outflow gate portion for releasing the molding material from inside the cavity. 2. A method of forming a conductive elastic body by press-fitting a molding material in an unsolidified state into a cavity of a mold and solidifying the molding material in the cavity. A step of press-fitting the molding material into the cavity through the portion and a step of releasing a part of the molding material press-fitted from the injection gate portion from the cavity through the outflow gate portion. Molding method. 3. When the sum of the cavity-side cross-sectional areas of the injection gate portion is S _ENT and the sum of the cavity-side cross-sectional areas of the outflow gate portion is S _ENT , the relationship between S _ENT and S _EXT is as follows: 3. The method according to claim 1, wherein _EXT / S _ENT satisfies 0.08 to 1.2. 4. When the sum of the cross-sectional areas in the cavity of the injection gate portion is S _ENT and the sum of the cross-sectional areas in the cavity of the outflow gate portion is S _ENT , the relationship between S _ENT and S _EXT is as follows: 3. The method for forming a conductive elastic body according to claim 1, wherein _EXT / _SENT = 0.2 to 0.8 is satisfied. 5. An electric resistance value of 1 × 10 ^{3 to} 1 × ^{10 10}
2. An electrically conductive elastic body of .OMEGA. Is formed.
5. The method for forming a conductive elastic body according to any one of items 4 to 4.