JPH0742408B2 - Conductive silicone rubber composition - Google Patents

Description

TECHNICAL FIELD The present invention relates to a conductive silicone rubber composition capable of imparting conductivity to silicone rubber without inhibiting vulcanization.

[Conventional technology]

As a material for imparting conductivity to silicone rubber, carbon black, particularly carbon black in a hard region having a large particle specific surface area, is useful. However, since this type of carbon black has strong surface activity, benzoyl peroxide, t-butyl peroxide,
In addition to inhibiting the cross-linking reaction due to dicumyl peroxide, it has the drawback of impairing moldability (dimensional stability) and reinforcing properties.

In order to prevent such vulcanization inhibition, zinc white,
Means for migrating the filler component to the base side by adding a vulcanization aid selected from metal oxides such as magnesium oxide or organic amines such as triethanolamine and diphenylguanidine have been taken. From the standpoint of improvement, the use of these auxiliaries is a negative factor.

Further, as another solution, a carbon fiber is used as a conductivity-imparting material, and it is proposed to use it together with a 2,4-dichlorobenzoyl peroxide vulcanizing agent to reduce vulcanization inhibition (JP-A-49-33951). However, there is a drawback in that the degree of improvement in conductive performance is inferior to the case where carbon black is used.

[Problems to be Solved by the Invention]

As described above, although carbon black has an excellent effect as a conductivity-imparting material, there is an unsolved problem that it cannot be blended in a large amount due to deterioration of moldability and reinforcing property due to inhibition of vulcanization. Therefore, when blended with silicone rubber in a high blending range of carbon black,
If problems such as vulcanization inhibition can be resolved, there will be great benefits in this field.

The present invention is intended to solve the above problems from the aspect of the property structure of carbon black.

[Means for Solving the Problems]

That is, in the conductive silicone rubber composition according to the present invention, furnace carbon black having a BET specific surface area (N ₂ SA) of 150 m ² / g or more is used in an inert gas stream at a temperature of 1300 to 1500 ° C.
A constitutional feature is that the conductive carbon black having the following selective characteristics, which is modified by applying a short heat history within a time period, is blended with a silicone rubber.

(1) pH> 9.0 (2) O% / 8 + H% calculated G value ≦ 0.15 gram equivalent / 100g carbon black (3) pH / true specific gravity calculated T value> −4.54 × 10 ^-2 (N ₂ SA) + 13.38 (4) Volatile content (Vm) is less than 0.5% Each characteristic value of carbon black applied to the present invention is
The value is based on the following measurement method.

BET Specific Surface Area (N ₂ SA) ASTM D3037-78 “Standard Methods of Testin′g Carb
on Black-Surface Area by Nitrogen Adsorption "Meth
by od B. The value of IRB ^# 5 measured by this method is 8
It was 0.3 m ² / g.

pH According to JIS K6221 (1982) 6.4.2.

True specific gravity value Drop the carbon black sample into a crucible with a lid, 650 ± 2
After deaeration at a temperature of 5 ° C for 5 minutes, the measurement is carried out in accordance with the method B described in "Industrial Chemistry Magazine" Vol. 66, No. 12 (1963), page 1758. That is, an appropriate amount of the degassed sample is weighed in a pycnometer, immersed in a small amount of benzene, and then degassed under reduced pressure under a vacuum of 2 to 5 mmHg until no bubbles are observed. Then, the pycnometer is filled with benzene, kept in a constant temperature water bath of 25 ± 0.1 ° C. for 30 minutes, and then weighed. The true specific gravity value is calculated by the following formula.

Where A is the mass of the pycnometer, C is the mass of the pycnometer + benzene, D is the mass of the pycnometer + carbon black sample, E is the mass of the pycnometer + carbon black sample + benzene, and ▲ d ²⁵ ₄ ▼ is of the benzene. It is specific gravity. The true specific gravity of IRB ^# 4 measured by this method was 1.7780.

The conductive carbon black of the present invention having the above characteristics is characterized mainly in that its characteristic structure is basic and crystallites are rearranged.

First, the hard system region having a BET specific surface area (N ₂ SA) of 150 m ² / g or more is a prerequisite characteristic item for imparting a high degree of conductivity to the rubber component.

The requirement of pH of 9.0 or more is an element showing that carbon black has shifted to basicity, and for example, O of the surface functional group involved in the ionic decomposition of organic peroxide such as quinone group.
And H value regulated G value (G value ≤ 0.15 gram equivalent / 100
It functions to prevent the inhibition of vulcanization together with the selective characteristics of gCB).

The true specific gravity is an index showing the rearrangement state of the aggregate crystallites inside the carbon black aggregate, and the requirement that the T value is −4.54 × 10 ⁻² (N ₂ SA) + 13.38 or more is low at a certain pH level. Specific gravity, that is, the fact that crystallite rearrangement is in progress. By increasing the T value per constant BET ratio surface, appropriate reinforcing properties and structural characteristics advantageous for the crosslinking reaction are imparted.

As another additional requirement, if the volatile content (Vm) of carbon black is maintained at less than 0.5%, the effect of preventing vulcanization is further improved.

The conductive carbon black of the present invention has a BET specific surface area (N ₂ S
A) It can be produced by applying a thermal history to furnace carbon black of ultrafine particles of 150 m ² / g or more.
The thermal history is 1300 ~ in an inert gas stream such as nitrogen or argon.
It is necessary to perform it at a temperature of 1500 ° C for a short time within 1 hour. For example, it is not possible to effectively remove strong surface functional groups such as quinone groups under conditions of low temperature and long time such as treating this at 1000 ° C. or lower for 140 hours or more, and the compaction phenomenon after crystallite rearrangement This causes an increase in the true specific gravity value. In addition, phenomena such as inducing a decrease in BET specific surface area (N ₂ SA) occur, and as a result, it becomes difficult to realize the selective characteristic range of the present invention.

Further, when heat history is applied at a temperature exceeding 1500 ° C., the true specific gravity becomes high because the graphitization of the furnace carbon black progresses, and the T value requirement is not satisfied.

The conductive carbon black subjected to heat history is blended with silicone rubber to obtain the conductive silicone rubber composition of the present invention. The compounding amount of the conductive carbon black is in the range of 40 to 150 parts by weight with respect to 100 parts by weight of the silicone rubber, and kneading may be carried out together with a commonly used vulcanizing agent, vulcanization accelerator and other additives as required.

[Action]

Generally, the addition of ultrafine carbon black having a large BET specific surface area (N ₂ SA) is effective for imparting a high degree of conductive performance to silicone rubber, but it is vulcanized by peroxide crosslinking due to its surface activity. It becomes an obstacle.

The carbon black satisfying the characteristic requirements of the present invention has a surface property in which the surface activity is relatively recessed despite being located in a region where the BET specific surface area (N ₂ SA) is extremely large. In addition, since the carbon black structure particles show a structural morphology in which the crystal rearrangement has progressed, these property structures act comprehensively to prevent vulcanization inhibition during the compounding of silicone rubber, improve moldability and reinforcement, etc. Effectively contribute to.

〔Example〕

Furnace carbon black having a BET specific surface area (N ₂ SA) of 150 m ² / g or more was given a thermal history under various conditions in a nitrogen stream. Table 1 shows the thermal history conditions and the property characteristics of the carbon black after the treatment.

Silicone rubber (KE520-U, manufactured by Shin-Etsu Chemical Co., Ltd.) 100 was prepared by using each of the carbon blacks having the above properties.
Parts, t-butylperoxyhexane [vulcanizing agent, manufactured by Shin-Etsu Chemical Co., Ltd., C-8A] 2 parts, and carbon black 50 parts, and roll kneaded to form a sheet. Then, each sheet was vulcanized at 165 ° C. for 40 minutes.

The vulcanization status and the properties of the obtained conductive silicone rubber are shown in Table 2.

In the case of the examples of the present invention, normal vulcanization without foaming was performed, and a silicone rubber composition having a suitable reinforcing property and excellent conductive performance without impairing moldability was obtained. In each of the comparative examples which did not satisfy the characteristic requirement of No. 3, the vulcanization and curing did not proceed, and remarkable foaming was recognized.

〔The invention's effect〕

As described above, according to the present invention, it is possible to obtain a normal conductive silicone rubber composition having a high level of conductive performance without causing vulcanization inhibition even in a high compounding use range which has been conventionally considered difficult. . Moreover, since the reinforcing property can be increased without impairing the moldability, the product quality is improved.

Claims (1)

[Claims] 1. A furnace carbon black having a BET specific surface area (N ₂ SA) of 150 m ² / g or more was modified by subjecting it to a heat history in an inert gas stream at a temperature of 1300 to 1500 ° C. for a short time within 1 hour. A conductive silicone rubber composition, characterized in that a conductive carbon black having the following selective characteristics is blended with a silicone rubber. (1) pH> 9.0 (2) O% / 8 + H% calculated G value ≦ 0.15 gram equivalent / 100g carbon black (3) pH / true specific gravity calculated T value> −4.54 × 10 ^-2 (N ₂ SA) + 13.38 (4) Volatile content (Vm) is less than 0.5%