JP2753676B2 - Conductive rubber foam and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conductive rubber foam having EPDM as a main component, having open cells, low hardness, and excellent conductivity, and a method for producing the same.

[0002]

2. Description of the Related Art EPDM is widely used in various fields because of its excellent heat resistance, chemical resistance, weather resistance and electrical properties. In recent years, however, there has been an increasing demand for rubber compositions having low hardness. Low hardness rubber compositions have been produced by various methods. In order to reduce the amount of the plasticizer used in reducing the hardness, conventionally, a compound containing a decomposable foaming agent is filled in the mold to fill the entire concave portion, and this is filled at a temperature higher than the decomposition temperature of the decomposable foaming agent. In general, the foaming reaction and the vulcanization reaction are completed by heating under pressure at the temperature described above, and then the pressure is released to cause foaming, that is, so-called pressure foaming. And when giving conductivity, the conductive agent was added to the said compound.

[0003]

However, the EPDM foam produced by the above-mentioned pressure foaming method has a high hardness and a poor shape recovery after compression since the foam is a closed cell. There was a problem. And when increasing the addition amount of carbon black to impart conductivity, the viscosity of the compound increases, foaming is suppressed, and when the plasticizer is increased to facilitate this foaming,
There is a problem that the obtained foam has tackiness and bleed out occurs.

According to the present invention, when the cells of the EPDM foam are made into open cells, the hardness is reduced and the shape recoverability is improved, and when calcium carbonate is used in combination with carbon black, the conductivity is improved without increasing the amount of carbon black. The conductive rubber foam, which is an open cell, has low hardness, high conductivity, and is excellent in shape recovery, does not cause bleed-out, and its production. It provides the law.

[0005]

That is, the conductive rubber foam according to the first invention comprises 10 to 40 parts by weight of carbon black per 100 parts by weight of EPDM, and one or more of calcium carbonate, silica and silicate. A total of 20 to 80 parts by weight of two or more types are blended, and the cell form is open cells, the hardness (Asker F hardness) is 80 degrees or less, and the resistivity is 1 × 10 ⁶ Ωcm or less. I do.

The method for producing a conductive rubber foam according to the second invention is characterized in that 10 to 40 parts by weight of carbon black and at least one of calcium carbonate, silica and silicate are added to 100 parts by weight of EPDM. Total 20
~ 80 parts by weight, decomposable foaming agent, vulcanizing agent, vulcanization accelerator, plasticizer and other necessary compounding agents are mixed in appropriate amounts and kneaded, and the obtained compound is filled in a mold, and Primary vulcanization is performed under pressure at a temperature lower than the decomposition temperature of the decomposable foaming agent, and then secondary vulcanization is performed at normal pressure at a temperature higher than the decomposition temperature of the decomposable foaming agent, and simultaneously foamed to open cells. And closed cells are mixed, and then the foamed rubber is compressed to destroy the closed cells.

The EPDM used in the present invention is not limited, and any commonly used EPDM can be used. Any carbon black can be used as long as it has a conductive effect, but it is preferable that the carbon black does not have too much oil absorption. In the present invention, any one or more of calcium carbonate, silica and silicate are used in combination with the above carbon black. Heavy and light calcium carbonate is used as the calcium carbonate, and wet silica and silica are used as the silica. Dry silica can be used, and silicates such as aluminum silicate and calcium silicate can be used.

[0008] The decomposable blowing agent has been conventionally used, and examples thereof include azodicarbonamide, dinitrosopentamethylenetetraamine, and oxybisbenzothiazole. As the vulcanizing agent, vulcanization accelerator and plasticizer, those conventionally used can be used as they are.

In the second invention, at the time of the primary vulcanization, the compound is filled into the entire concave portion of the mold, and the temperature is set lower than the decomposition temperature of the decomposable foaming agent, thereby controlling the vulcanization rate, It suppresses rapid foaming under pressure and balances the vulcanization rate and the decomposition rate of the foaming agent. The temperature is lower than the decomposition temperature of the foaming agent, particularly 90
~ 150 ° C is preferred. The vulcanization time at that time is 5
30 minutes is preferred. On the other hand, the secondary vulcanization is for completing vulcanization and foaming, and the semi-vulcanized product obtained by the above primary vulcanization is placed under normal pressure, and the temperature is lower than the decomposition temperature of the decomposable foaming agent. Heat at high temperature and foam under normal pressure. This secondary vulcanization temperature is higher than the above decomposition temperature, and particularly preferably 130 to 180 ° C. The reaction time is preferably 5 to 60 minutes. The above-mentioned decomposition temperature is an actual decomposition temperature in a state where EPDM is blended with other compounding agents. When the decomposition temperature is lowered by adding a foaming aid, the decomposition temperature refers to the lowered decomposition temperature. .

[0010] In the present invention, the semi-open-cell foamed rubber in which closed cells and open cells obtained by the secondary vulcanization are mixed is compressed, whereby the closed cells are broken and deformed into open cells. However, as the above-mentioned compression means, a method of passing the above-mentioned foamed rubber between a pair of rollers rotating opposite to each other with a certain gap is preferable.

[0011]

Since the conductive rubber foam of the first invention is an EPDM foam, it has excellent heat resistance, chemical resistance, weather resistance, etc. as in the prior art. Further, since one or more of calcium carbonate, silica and silicate are used in combination with carbon black, the resistivity is 1 × 10 ⁶ Ωcm or less despite the relatively small amount of carbon black. And has excellent conductivity. Further, since the compounding amount of carbon black is relatively small, the viscosity before vulcanization becomes low, foaming becomes easy, and bubbles are formed uniformly. In addition, since the cell form is open cells, even if the amount of the plasticizer is reduced, the hardness (ASKER F
Hardness) is reduced to 80 degrees or less, and the shape recoverability is improved.

However, when the compounding amount of the carbon black is less than 10 parts by weight based on 100 parts by weight of EPDM,
If the resistivity is too high, and if it exceeds 40 parts by weight, the hardness will be too high. On the other hand, when the amount of calcium carbonate, silica and silicate is less than 20 parts by weight, the electric resistance is insufficiently reduced, and the conductive effect, which is the object of the present invention, cannot be obtained. If so, the hardness increases and the degree of foaming decreases.

According to the second invention, the mold is filled with a compound mainly composed of EPDM and containing a decomposable foaming agent, and the primary vulcanization is performed at a temperature lower than the decomposition temperature of the decomposable foaming agent. In the vulcanization, foaming is suppressed and only vulcanization proceeds, and secondary vulcanization is performed at a temperature higher than the decomposition temperature in the state where this vulcanization has progressed halfway, so foaming in which open cells and closed cells are mixed A rubber is obtained, and the foamed rubber is compressed to break the closed cells, thereby obtaining an EPDM foam composed of open cells. In the above compound, calcium carbonate, silica, silicate and the like are used in combination with carbon black, so that the conductive rubber foam of the first invention is obtained.

However, if the temperature at the time of the primary vulcanization is too low or the time is too short, the purpose of the primary vulcanization cannot be achieved due to insufficient vulcanization. If the temperature is too high or the time is too long, vulcanization proceeds too much and foaming during secondary vulcanization becomes difficult. Also, if the temperature during the secondary vulcanization is too low or the time is too short, the reaction of foaming and vulcanization is not completed,
If foaming does not occur and the temperature of the secondary vulcanization is too high, the reaction of vulcanization and foaming occurs rapidly, and the balance between foaming and vulcanization is lost, resulting in abnormal foaming.

[0015]

EXAMPLE 100 parts by weight of EPDM were mixed with carbon black and other various additives in the mixing ratio (parts by weight) shown in Table 1 below, and kneaded with a Banbury mixer, a kneader, a roll, and the like. Compounds of Comparative Examples 1 to 4 were obtained. However, conductive carbon black was used as carbon black. An ADCA (azodicarbonamide) foaming agent having a decomposition temperature of 220 ° C. is used together with a urea foaming auxiliary as a foaming agent.
Lowered.

Table 1 Example 1 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 EPDM 100 100 100 100 100 Carbon black 20 20 20 50 50 Calcium carbonate 40 100 5 − − Stearic acid 3 3 3 3 3 Zinc white 5 5 5 5 5 Plasticizer 50 50 50 50 100 Degradable foaming agent 15 15 15 15 15 Foaming aid 2 2 2 2 2 Vulcanization accelerator 3 3 3 3 3 Sulfur 2 2 2 2 2

The obtained compound is 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 subjected to primary vulcanization at 110 ° C. for 15 minutes. The semi-vulcanized product is placed in the concave portion (width 5
00mm, length 500mm, depth 14mm) under normal pressure,
Secondary vulcanization was performed at 160 ° C. for 15 minutes to complete vulcanization and foaming. The obtained rubber foam was passed between two parallel rollers (gap of 1 mm) to break closed cells, and almost all the cells were formed into open cells. The performance of the conductive rubber foam thus obtained is shown in Table 2 below.

Table 2 Example 1 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Electric resistivity (Ωcm) 5 × 10 ³ 6 × 10 ³ 5 × 10 ⁶ 1 × 10 ³ 1 × 10 ⁴ Hardness (degree) 50 85 52 90 80 Bleed No No No No Yes Bubble degree Excellent Good Good Not good Possible Bubble form Continuous Continuous Continuous Independent Independent Shape recovery ○ ○ △ × ×

In Table 2 above, the hardness is a value measured by an Asker F hardness meter. The presence or absence of bleed was visually confirmed after being left in a gear oven at 70 ° C. for 360 hours. Also, the foaming degree is more than 8 times by volume ratio,
A value of at least 2 times was acceptable, and a value of at least 3 times was acceptable. Regarding the bubble form, those having a water absorption of almost 100% were determined to be open cells, and those having a water absorption of 20% or less were determined to be closed cells. The shape recoverability was determined by the recoverability after 30 minutes after being placed in a gear oven at 70 ° C. under 50% compression, left for 22 hours, and then opened. The recovery rate was 80% or more, Δ, 50% or more. Is rated as Δ, and less than 50% is rated as x.

As is clear from Tables 1 and 2 above, in Example 1 in which carbon black and calcium carbonate were blended in appropriate amounts, the cells were open cells, had low electric resistance and hardness, had no bleed-out, Excellent foaming degree and shape recovery. On the other hand, Comparative Example 1 with excessive calcium carbonate has excessive hardness and poor foaming degree, and Comparative Example 2 with small calcium carbonate has high electric resistance. Comparative Example 3, in which carbon black was increased and calcium carbonate was omitted, had excessive hardness, closed cells, poor foaming degree and poor shape recovery, and increased the amount of plasticizer in Comparative Example 3 above. In Comparative Example 4 in which the degree of foaming and the hardness were to be improved, although the hardness and the degree of foaming were slightly improved, bleed-out occurred. In addition,
Each of the compounds of Examples 1 and Comparative Examples 1 and 2 was filled in a mold for primary vulcanization, and foamed under pressure at a temperature (170 ° C.) higher than the decomposition temperature of the decomposable foaming agent in the same manner as before. Was carried out to complete the vulcanization reaction and the foaming reaction. Thereafter, when the foaming was carried out under normal pressure, the bubbles became closed cells and the shape recovery was poor.

In place of calcium carbonate in Example 1 above, wet silica (trade name “TOKUSEAL G” manufactured by Tokuyama Soda Co., Ltd.)
U ") was added, and the other procedure was the same as that of Example 1 to produce a conductive rubber foam of Example 2. In addition, aluminum silicate is used instead of the above calcium carbonate.
Example 3 was added in the same manner as in Example 1 except for adding 0 parts by weight.
Was produced. As shown in Table 3 below, the performance of the conductive rubber foams of Examples 2 and 3 was excellent as in Example 1.

Table 3 Example 2 Example 3 Electric resistivity (Ωcm) 3 × 10 ³ 2 × 10 ³ Hardness (degree) 55 50 Bleed No No Foaming degree Excellent Excellent Bubble morphology Continuous Continuous Shape recovery ○ ○

[0023]

As described above, the first aspect of the present invention is a conductive rubber foam made of EPDM, which is excellent in heat resistance, chemical resistance, weather resistance, and the like.
Since one or more of calcium carbonate, silica, and silicate are used in combination with carbon black, it has high conductivity despite the relatively small amount of carbon black, and before vulcanization. Has low viscosity, foaming is easy, bubbles are formed uniformly, and since the cells are open cells, the hardness is low, the shape recovery is good, and it is not necessary to use a large amount of plasticizer. .

The invention according to claim 2 is an EPD.
A required amount of 10 to 40 parts by weight of carbon black, 20 to 80 parts by weight in total of one or more of calcium carbonate, silica and silicate and a decomposable foaming agent and other additives is added to 100 parts by weight of M. And kneading, filling the obtained compound into a mold, performing primary vulcanization under pressure at a temperature lower than the decomposition temperature of the decomposable foaming agent, and then performing the primary vulcanization at a temperature lower than the decomposition temperature of the decomposable foaming agent. Performing secondary vulcanization under normal pressure at a high temperature and foaming at the same time to form a foamed rubber in which open cells and closed cells are mixed, and then compressing the foamed rubber to destroy the closed cells, The conductive rubber foam according to claim 1 can be easily manufactured.

Claims (2)

(57) [Claims] 1. A carbon foam is mixed with 10 to 40 parts by weight and a total of 20 to 80 parts by weight of one or more of calcium carbonate, silica and silicate based on 100 parts by weight of EPDM. It is an open cell with a hardness (Asker F hardness) of 80 degrees or less,
A conductive rubber foam having a resistivity of 1 × 10 ⁶ Ωcm or less. 2. 10 to 40 parts by weight of carbon black, 20 to 80 parts by weight of one or more of calcium carbonate, silica and silicate based on 100 parts by weight of EPDM, decomposable foaming agent, vulcanizing agent , A vulcanization accelerator, a plasticizer and other necessary compounding agents are each compounded in an appropriate amount and kneaded, and the obtained compound is filled in a mold and subjected to pressure under a temperature lower than the decomposition temperature of the decomposable foaming agent. Primary vulcanization, then secondary vulcanization under normal pressure at a temperature higher than the decomposition temperature of the decomposable foaming agent, and simultaneously foaming to form a foamed rubber in which open cells and closed cells are mixed, and then this foamed rubber A method for producing a conductive rubber foam, characterized in that the foam is compressed to break the closed cells.