JPH0827300A - Electrically conductive foamed rubber and its production - Google Patents

Abstract

PURPOSE:To easily obtain an electrically conductive foamed rubber by a specific method without increase in carbon black, thus it comprises fine, uniform and continuous foam and has low hardness, high conductivity, excellent shape restoration without bleedout. CONSTITUTION:One hundred parts by weight of an ethylidenenorbornene type EPDM having Mooney viscosity of >=60 (JIS-K-6300) at 100 deg.C are formulated with 10-40 pts.wt. of an electrically conductive carbon black having 500-200ml/100g DBP (dibutyl phthalate) absorption, a decomposition type foaming agent, vulcanizing agents and others and they are kneaded. Then, the resultant compound is charged into a mold cavity in an excessive amount more than its capacity and the primary vulcanization is carried out at a lower temperature than the decomposition point of the foaming agent under pressure at a lower than 1.1 foaming ratio. Subsequently, the secondary vulcanization is effected at a high temperature than the decomposition point of the foaming agent under normal pressure, and simultaneously, foaming is performed to produce a foamed rubber including open cells and closed cells mixed therein. Finally, the foamed rubber is compressed to break the closed cells to obtain the objective foamed rubber.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conductive foamed rubber which contains EPDM as a main component, has open cells, has a low hardness, and is excellent in conductivity and elastic recovery upon compression, and a method for producing the same. It is about.

[0002]

2. Description of the Related Art Foamed rubber containing EPDM as a main component is widely used in various fields such as office automation equipment such as copying machines and facsimiles and automobile parts because it is excellent in ozone resistance and weather resistance. . In the conventional foamed rubber containing EPDM as a main component, a compound of EPDM containing a decomposable foaming agent is filled into the concave portion of the mold and heated under a pressure higher than the decomposition temperature of the decomposable foaming agent. Then, the foaming reaction and the vulcanization reaction are terminated, and then the pressure is released to foam, which is so-called pressure foaming. Then, in the case of giving conductivity, carbon black was added to the above compound as a conductive agent.

However, the conventional foamed rubber made of EPDM has a poor electrical conductivity due to the high electric resistance of EPDM itself, and it is necessary to add a large amount of carbon black in order to impart the desired electrical conductivity to the foamed body. Occurs, in which case the viscosity of the compound increases and the expansion ratio decreases,
And the hardness increases and the contact pressure with other contact objects increases,
The contact could be destroyed. Addition of large amounts of plasticizer to solve this has resulted in plasticizer bleed-out, contaminating other parts. In addition, some rubbers have been added to reduce the hardness, but the Asker hardness (type JA) is too high at about 30 degrees, and the compression set (JIS K6382) is 20% or more. There is a problem that when used as a feed roller, the transportability deteriorates, and when used as a seal material, the sealability deteriorates.

[0004]

In order to solve these problems, the applicant of the present invention has previously proposed that 10 to 40 parts by weight of carbon black, 100 parts by weight of EPDM, one of calcium carbonate, silica and silicate should be used. A total of 20 to 80 parts by weight of one kind or two or more kinds, a decomposable foaming agent,
Vulcanizing agents, vulcanization accelerators, plasticizers and other necessary compounding ingredients are each mixed in appropriate amounts and kneaded, the resulting compound is filled in a mold, and the temperature is lower than the decomposition temperature of the decomposable foaming agent. Primary vulcanization is performed under pressure, then secondary vulcanization is performed under normal pressure at a temperature higher than the decomposition temperature of the decomposable foaming agent, and simultaneously foamed to form a foamed rubber in which continuous cells and closed cells are mixed, Next, a patent application was filed for a method of compressing the foamed rubber to destroy the closed cells (Japanese Patent Application No. 5-22).
5184).

This invention does not necessarily require the calcium carbonate, silica and silicate in the above-mentioned prior invention, and is composed of open cells of fine and uniform size without increasing the amount of carbon black. It is intended to provide a conductive foamed rubber that has high properties, is excellent in shape recovery, and does not cause bleed-out.

[0006]

The electrically conductive foam rubber of the first invention has a Mooney viscosity (JIS K-6300) of 100.
Echilidene norbornene type EPD below 60 ℃
10 to 40 parts by weight of conductive carbon black having a DBP (dibutyl phthalate) oil absorption of 500 to 200 mL / 100 g per 100 parts by weight of M and a decomposable foaming agent, a vulcanizing agent,
A vulcanization accelerator, a plasticizer, and other necessary compounding agents are each mixed in an appropriate amount, and the cell form is an open cell, the cell diameter is 800 μm or less, the resistivity is 1 × 10 ⁶ Ω or less, and the Asker hardness (Type F) 80 Degree or less, compression set (JIS K-
6382) 20% or less.

A second invention relates to the invention of the method for producing the conductive foamed rubber of the first invention, which has a Mooney viscosity (JIS).
DB-6 to 100 parts by weight of ethylidene norbornene type EPDM having K-6300) of 60 or less at 100 ° C.
(Bibutyl phthalate) Oil absorption 500 ~ 200mL / 10
10 to 40 parts by weight of conductive carbon black, a decomposable foaming agent, a vulcanizing agent, a vulcanization accelerator, a plasticizer and other necessary compounding agents are each mixed in an appropriate amount and kneaded, and the obtained compound is gold. The concave portion of the mold is filled with more than its volume, and primary vulcanization is performed under a pressure lower than the decomposition temperature of the decomposable foaming agent so that the expansion ratio is 1.1 times or less, and then the decomposable foaming described above. Secondary vulcanization is performed under normal pressure, which is higher than the decomposition temperature of the agent, and simultaneously foamed to form a foamed rubber in which open cells and closed cells are mixed, and then this foamed rubber is compressed to destroy the closed cells. Is characterized by.

The decomposable foaming agent used in the present invention has been conventionally used, and examples thereof include azodicarbonamide, dinitrosopentamethylenetetraamine and oxybisbenzothiazole. As the vulcanizing agent, the vulcanization accelerator and the plasticizer, those conventionally used can be used as they are. However, due to the problem of contamination such as bleed-out, it is not possible to use the paraffin plasticizer. preferable.

At the time of primary vulcanization, the compound obtained by kneading with the above-mentioned composition is filled in the concave portion of the mold a little more than the volume of the concave portion, preferably about 105% or less, and the vulcanization temperature is set. By setting the decomposition temperature to be lower than the decomposition temperature of the decomposition foaming agent, the vulcanization rate is adjusted, rapid foaming is suppressed under pressure, and the vulcanization speed and the decomposition rate of the foaming agent are easily balanced. The vulcanization temperature is lower than the decomposition temperature of the foaming agent, and is 100 to 140 ° C., particularly 110 to 13 ° C.
0 ° C. is preferable, and the vulcanization time is the vulcanization temperature (100 to 1
The expansion ratio when vulcanized and released at 40 ° C.) is 1.1 times or less. When the expansion ratio exceeds 1.1 times, the cells of the foam after the secondary vulcanization become almost independent cells, the cell diameter and its variation become large, and the compression set becomes excessive.

On the other hand, the secondary vulcanization is for completing vulcanization and foaming. The semi-vulcanized product obtained by the above primary vulcanization is placed under normal pressure to decompose the decomposition temperature of the above-mentioned decomposing foaming agent. It is heated at the above temperature and foamed under normal pressure. The secondary vulcanization temperature is preferably 140 to 180 ° C. The reaction time is preferably 5 to 60 minutes. The above decomposition temperature (including the time of primary vulcanization) is the actual decomposition temperature when the foaming agent is blended with EPDM together with other compounding agents, and the decomposition temperature is lowered by the addition of a foaming auxiliary agent or the like. , The reduced decomposition temperature.

In the second aspect of the invention, the semi-open cell foamed rubber obtained by the secondary vulcanization and having the closed cells and the open cells mixed therein is compressed, whereby the closed cells are destroyed to form open cells. Although it deforms, the compression means is
A method of passing the above-mentioned foam rubber between a pair of rollers which face each other with a constant gap and rotate is preferable.

[0012]

According to the second aspect of the present invention, during primary vulcanization, a compound containing a decomposable foaming agent as a main component is made of an EPDM of ethylidene norbornene type having a Mooney viscosity (JIS K-6300) of 60 or less at 100 ° C. In the primary vulcanization, foaming is suppressed and only vulcanization progresses because the vulcanization temperature is set to a temperature lower than the decomposition temperature of the decomposable foaming agent by filling a little more than the mold capacity. Then, at a temperature higher than the above decomposition temperature in a state where this vulcanization has progressed to the middle,
In addition, since the secondary vulcanization is performed under atmospheric pressure, a foamed rubber in which continuous cells and closed cells are mixed is obtained, and the foamed rubber is compressed to destroy the closed cells, so that the bubble diameter is 80
The electrically conductive foamed rubber of the first aspect of the present invention, which is uniformly provided with fine open cells of 0 μm or less, can be obtained.

The conductive foamed rubber of the first invention is the above-mentioned EP.
Since it is a foam of DM, it has excellent weather resistance and ozone resistance as in the past. And DBP oil absorption amount 500
Conductive carbon black of 200 mL / 100 g is blended and fine open cells having a bubble diameter of 800 μm or less are uniformly provided, so that the resistivity is 1 even though the blending amount of carbon black is relatively small. It is less than × 10 ⁶ Ωcm and excellent in conductivity. Further, since the blending amount of carbon black is relatively small, the viscosity before vulcanization becomes low, foaming becomes easy, and bubbles are uniformly formed. Moreover, since the cell form is continuous cells, the Asker hardness (type F) is reduced to 80 degrees or less and the compression set is 20% or less even if the amount of the plasticizer compounded is reduced.

However, when the content of the conductive carbon black is less than 10 parts by weight with respect to 100 parts by weight of EPDM, the resistivity becomes excessive, and when it exceeds 40 parts by weight, the hardness becomes excessive. On the other hand, when the amount of the mold filled during the primary vulcanization is too small and less than 100% of the concave volume of the mold, the charge is insufficient, resulting in voids in the rubber or defective foaming. If it exceeds 105% after that, filling becomes impossible. Also, if the temperature of the primary vulcanization is too low or the time is too short, the vulcanization is insufficient and the purpose of the primary vulcanization is not achieved, while the temperature of the primary vulcanization is too high. However, if the time is too long, the vulcanization proceeds too much, which makes foaming difficult during the secondary vulcanization. If the temperature during secondary vulcanization is too low or the time is too short,
Since the reaction of foaming and vulcanization has not ended, foaming does not occur, and on the contrary, when the temperature of the secondary vulcanization is too high, the reaction of vulcanization and foaming occurs rapidly, and the balance of foaming and The balance of sulfur is lost and foaming abnormality occurs.

[0015]

Example: Mooney viscosity (JIS K-6300) is 1
27 ethylidene norbornene type EPD at 00 ° C
DBP oil absorption of 370 mL / 100 with respect to 100 parts by weight of M
Compounds of Examples 1 to 6 and Comparative Examples 1 to 4 were obtained by kneading with a Banbury mixer while changing the compounding amount of the conductive carbon black of g variously. However, the compounding amount (parts by weight) of other compounding chemicals is 3 parts of stearic acid and 5 parts of zinc white.
Parts, plasticizer 40 parts (however, only 100 parts of Comparative Example 3),
15 parts decomposable foaming agent, 2 parts foaming aid, 3 parts vulcanization accelerator,
Unified to 2 parts sulfur. It should be noted that the decomposition foaming agent has a decomposition temperature of 2
An ADCA (azodicarbonamide) -based foaming agent at 20 ° C. was used together with a urea-based foaming auxiliary agent, and the decomposition temperature was lowered to about 145 ° C. before use.

The resulting compound was filled in a concave portion (width 250 mm, length 250 mm, depth 5 mm) of a primary vulcanization mold at 105% of its volume, and primary vulcanization was performed at 110 to 150 ° C. for 15 minutes. The obtained semi-vulcanized product was put into the concave portion (width 500 mm, length 500 mm, depth 15 mm) of the secondary vulcanization mold,
Secondary vulcanization was performed at 160 to 180 ° C. for 15 minutes under normal pressure to complete vulcanization and foaming. The foamed rubber obtained was passed between two parallel rollers (gap 1 mm) to break the closed cells, and almost all the bubbles were formed into continuous cells. The performance of the conductive foamed rubber thus obtained is shown in Tables 1 and 2 below together with the blending amount (parts by weight) of the conductive carbon black, the primary vulcanization temperature and the secondary vulcanization temperature.

Table 1 Example number 1 2 3 4 5 Carbon black (part) 15 25 35 25 25 Primary vulcanization temperature (° C) 120 120 120 130 110 Secondary vulcanization temperature (° C) 160 160 160 160 160 Electric resistance Rate (Ωcm) 5 × 10 ⁵ 5 × 10 ³ 5 × 10 ² 8 × 10 ³ 5 × 10 ³ Hardness (degree) 45 50 65 60 40 Bleed No No No No No Foaming degree Superior superior Superior superior Cellular form Continuous Continuous Continuous Continuous Continuous Continuous compression set (%) 15 9 15 10 8 Bubble diameter (mm) 0.5 0.4 0.5 0.3 0.7

Table 2 Comparative example number 1 2 3 4 Carbon black (part) 5 45 45 20 Primary vulcanization temperature (° C) 120 120 120 150 Secondary vulcanization temperature (° C) 160 160 160 180 Electrical resistivity (Ωcm) 5 × 10 ⁸ 5 × 10 ³ 8 × 10 ⁴ 5 × 10 ³ Hardness (degree) 65 95 80 80 Bleed No No Yes No No Foaming degree Good Yes Yes Yes Bubble morphology Continuous Independent Independent Independent Compression set (%) 25 78 85 68 Bubble diameter (mm) 0.8 0.5 0.4 0.7

In Tables 1 and 2 above, the hardness is Asker hardness (type F). The presence or absence of bleed was visually confirmed after placing in a gear oven at 70 ° C. for 360 hours. In addition, the foaming ratio is more than 8 times by volume ratio, 6
A ratio of 2 times or more was rated as good, and a value of 3 times or more was rated as good, and a material with almost no foam was rated as bad. Regarding the bubble morphology, those having a water absorption of about 100% were judged to be open cells, and 20% or less were judged to be closed cells. Also, compression set (JIS K-6382)
Put it in a gear oven at 70 ° C with 50% compression, 2
It was left for 2 hours, opened, and then measured for recovery after 30 minutes.

As is clear from Tables 1 and 2, in the examples in which an appropriate amount of conductive carbon black was blended and the degree of foaming was adjusted under the primary vulcanization conditions, the cell morphology was fine open cells, Low resistance and hardness, no bleed-out, excellent foaming degree and compression set. In particular, as can be understood from the comparison of Examples 2, 4, and 5, even if all the other conditions except the primary vulcanization temperature are the same, the bubble diameter depends on the primary vulcanization temperature, in other words, the vulcanization degree. In Example 4, in which the difference occurs and the primary vulcanization temperature is the highest, the bubble diameter is the minimum, and the resistivity, hardness, and compression set are respectively maximum. Therefore, by adjusting the primary vulcanization temperature according to the application, it is possible to change the bubble diameter and give the characteristics according to the application.

On the other hand, Comparative Example 1 having a small amount of conductive carbon black has a high electric resistance, and Comparative Example 2 having an excessive amount of the conductive carbon black is a bubble or a closed cell, which has an excessive hardness and is inferior in compression set. ing. In addition, Comparative Example 2
In Comparative Example 3 containing a large amount of the plasticizer, the bleeding out occurred although the hardness and the foaming degree were slightly improved. In Comparative Example 4, the composition is the same as in Example 2, but the primary vulcanization temperature is higher than the foaming temperature 145 ° C. of the decomposing foaming agent, so the cells become closed cells, and the compression set and the degree of foaming also decrease. did.

[0022]

As described above, the invention according to claim 1 has a Mooney viscosity (JIS K-6300) of 10 or less.
EP of ethylidene norbornene type of 60 or less at 0 ℃
Since it is a conductive foam rubber containing DM as a main component, it has excellent weather resistance and ozone resistance. And DBP oil absorption 5
Since conductive carbon black of 00 to 200 mL / 100 g is used and the cell diameter is 800 μm or less, high conductivity can be obtained with a relatively small amount of conductive carbon black, and hardness is low and compression set is low. Since it is small, it is suitable for high-performance parts such as automobile parts and office automation equipment.

According to a second aspect of the present invention, the above compounded rubber is used, and the compounded compound is kneaded, and the obtained compound is filled in the concave portion of the mold in an amount larger than the volume of the compounded foam. Primary vulcanization is performed under a pressure lower than the decomposition temperature of the agent so that the expansion ratio is 1.1 times or less, and then secondary vulcanization is performed under normal pressure at a temperature higher than the decomposition temperature of the decomposable foaming agent. This is a method of foaming simultaneously with vulcanization to form foamed rubber in which open cells and closed cells are mixed, and then compressing this foamed rubber to destroy the above-mentioned closed cells. By adjusting the time, the conductive foam rubber according to claim 1 can be easily obtained.

The invention described in claim 3 is the same as the invention described in claim 2, wherein the primary vulcanization temperature is 10
Since this is a method of setting the secondary vulcanization temperature to 0 to 140 ° C. and the secondary vulcanization temperature to 140 to 180 ° C., the above conductive foamed rubber can be obtained even more easily.

Claims (3)

[Claims] 1. Mooney viscosity (JIS K-6300)
10 to 40 parts by weight of a conductive carbon black having a DBP (dibutylphthalate) oil absorption of 500 to 200 mL / 100 g and a decomposable foaming agent to 100 parts by weight of ethylidene norbornene type EPDM of 100 or less at 100 ° C.
A vulcanizing agent, a vulcanization accelerator, a plasticizer and other necessary compounding agents are each mixed in an appropriate amount, and the cell form is an open cell having a cell diameter of 800 μm or less, a resistivity of 1 × 10 ⁶ Ω or less, and an Asker hardness ( Type F) 80 degrees or less, compression set (JI
SK-6382) 20% or less, a conductive foamed rubber. 2. Mooney viscosity (JIS K-6300)
10 to 40 parts by weight of a conductive carbon black having a DBP (dibutylphthalate) oil absorption of 500 to 200 mL / 100 g and a decomposable foaming agent to 100 parts by weight of ethylidene norbornene type EPDM of 100 or less at 100 ° C.
Vulcanizing agents, vulcanization accelerators, plasticizers and other necessary compounding agents are each mixed in appropriate amounts and kneaded, and the resulting compound is filled in the recesses of the mold in an amount greater than the volume of the decomposable foaming agent. Foaming ratio of 1.1 under pressure below decomposition temperature
Primary vulcanization is performed so that it becomes less than or equal to twice, and then secondary vulcanization is performed under normal pressure at a temperature higher than the decomposition temperature of the decomposable foaming agent and foamed at the same time as a foam rubber in which continuous cells and closed cells are mixed. Then, a method for producing a conductive foamed rubber, characterized in that the foamed rubber is then compressed to destroy the closed cells. 3. The method for producing a conductive foamed rubber according to claim 2, wherein the primary vulcanization temperature is set to 100 to 140 ° C. and the secondary vulcanization temperature is set to 140 to 180 ° C.