JPH01272667A - Electrically conductive carbon black - Google Patents

Abstract

PURPOSE:To obtain the title carbon black having BET specific surface area being definite value or above, belonging to hard area, having amount of surface functional group and true specific gravity, etc., being in the definite range and capable of providing electrically conductive silicone rubber free from causing curing hindrance also in the area using the carbon black at high blend ratio. CONSTITUTION:The aimed carbon black having >=150m<3>/g BET specific surface area (N2SA), belonging to hard area and having (A) pH>9.0 and having (B) formula II in G value calculated from formula I and (C) formula III in T value calculated from the formula of pH/true specific gravity value. Furthermore, the aimed carbon black has preferably <0.5% volatile content (Vm).

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to conductive carbon black that can impart conductivity to silicone rubber without inhibiting vulcanization.

[Conventional technology]

Carbon black, especially hard type carbon black with a large particle specific surface area, is useful as a material that imparts electrical conductivity to silicone rubber. However, this type of carbon black has a strong surface activity, so during vulcanization, benzoyl peroxide, t-butyl peroxide,
In addition to inhibiting the crosslinking reaction caused by dicumyl peroxide and the like, it also has the disadvantage of impairing moldability (dimensional stability), reinforcing properties, etc.

In order to prevent such vulcanization inhibition, zinc white,
Measures have been taken to transfer 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, but the conductivity In terms of improvement, the use of these auxiliary agents is a negative factor.

In addition, as another solution, a proposal was made to reduce vulcanization inhibition by using carbon fiber as a conductivity imparting material and using it in combination with a 2,4-dichlorobenzoyl peroxide vulcanizing agent (Japanese Patent Laid-Open No. 49-33951). Public notice) has also been made, but
There is a disadvantage that the degree of improvement in conductive performance is inferior to that when carbon black is used.

[Problem to be solved by the invention]

As described above, although carbon black has excellent efficacy as a conductivity imparting material, there is an unresolved problem that it cannot be blended in large amounts because of the deterioration of moldability and reinforcing properties due to vulcanization inhibition. Therefore, if problems such as vulcanization inhibition can be solved in a high carbon black content range, it will be of great benefit in this field.

The present invention aims to solve the above problems from the viewpoint of the property structure of carbon black.

[Means to solve the problem]

That is, the conductive carbon black according to the present invention has B
It is characterized in that it has an ET specific surface area (N2SA) of 150 g/g or more, which belongs to the hard type region17, and has the following selective properties.

(1) pi (>9.0 filtration G value ≦0, 15g El/100g carbon black (3) T value calculated by the formula of pH/A specific gravity value>-4°54×10-2 (N2SA ) +13.38 Each characteristic value of carbon black applied to the present invention is a value determined by the following measurement method.

ASTM D3037-78 “5 standard M
methods orTest, in'g Carbon
Black-8urf'aee Area by Ni
trogen Adsorptlon' Meth
By od B. In addition, IRB"5 measured by this method
The value was 80.3rrr/f.

According to JIS K6221 (i982) Section 6.412.

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

However, A is the mass of the pycnometer, C is the mass of the pycnometer→-benzene, D is the quality of the pycnometer plus the carbon black sample 1, E is the mass of the pycnometer plus the carbon black sample + benzene, and d25 is the specific gravity of benzene. The true specific gravity value of IRB #4 measured by this method was 1.7780.

The conductive carbon black of the present invention having the above-mentioned properties is mainly characterized by a basic physical structure and rearranged crystallites.

First, the BET specific surface area < N 2 S A ) is 150
The hard type region of G/g or higher is a prerequisite characteristic item for imparting high conductivity to the rubber component.

The requirement for the pH to be 9.0 or higher is a factor that indicates that carbon black has become basic, and for example, the amount of O and H of surface functional groups involved in ion decomposition of organic peroxides such as quinone groups. It functions to prevent vulcanization inhibition together with the selection characteristic of G value (G value ≦0.15 gram equivalent/100 g CB) that regulates vulcanization.

The true specific gravity value is an index that expresses the rearrangement state of aggregate crystallites inside the carbon black aggregate, and the requirement that the T value is -4,54X10 (N2SA) + 13.38 or more means that the true specific gravity value is low at a constant pH level, i.e. This indicates that crystallite rearrangement is progressing. And constant B
By increasing the T value per ET specific surface area, appropriate reinforcing properties and structural characteristics advantageous for crosslinking reactions are imparted.

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

The conductive carbon black of the present invention has a BET specific surface area (
N2SA) It can be produced by subjecting ultrafine particle carbon black of t50rrf'/g or more to a thermal history. Thermal history is preferably carried out under high temperature and short-time conditions, such as holding at least 130 parts Celsius for about 30 minutes in an inert gas flow such as nitrogen or argon. Under low-temperature, long-term conditions such as processing at 1000°C or lower for 140 hours or more, strong surface functional groups such as quinone groups cannot be effectively removed, and sintering phenomenon occurs after crystallite rearrangement. This causes an increase in the true specific gravity value. Moreover, phenomena such as a decrease in BET specific surface area (N2SA) occur, and as a result, it becomes difficult to realize the selective characteristic range of the present invention.

[For production]

Generally, blending ultrafine particle carbon black with a large BET specific surface area (NSA) is effective for imparting high conductivity to silicone rubber, but on the other hand, its surface activity inhibits vulcanization due to peroxide crosslinking. It becomes a factor.

Carbon black that satisfies the property requirements of the present invention exhibits surface properties in which the surface activity is relatively sufficiently retracted, even though the BET specific surface area (N2SA) is located in an extremely large region. In addition, since the carbon black structural particles exhibit a structural form in which crystal rearrangement has progressed, these properties and structures act comprehensively, effectively preventing vulcanization inhibition and improving formability and reinforcing properties. Contribute.

〔Example〕

Furnace carbon black having a BET specific surface area (N2SA) of 150 and 7 g or more was given a thermal history under various conditions in a nitrogen stream. Table 1 shows the thermal history conditions and the properties of the carbon black after treatment.

Silicone rubber [manufactured by Shin-Etsu Chemical Co., Ltd.] was manufactured by using each carbon black having the above properties.

K E 520-U) 100 parts, t-butylperoxyhexane [vulcanizing agent, manufactured by Shin-Etsu Chemical, C-8A) 2
1 part and 50 parts of carbon black, and kneaded with rolls to form a sheet. Each sheet was then vulcanized at 165° C. for 40 minutes.

Table 2 shows the vulcanization conditions and the properties of the conductive silicone rubber obtained.

In the case of the examples of the present invention, normal vulcanization without foaming was performed, and a rubber composition having appropriate reinforcing properties and excellent conductive performance without impairing moldability was obtained. In all of the comparative examples that did not meet the property requirements, vulcanization and curing did not proceed, and significant foaming was observed.

[Effects of the Invention] As described above, the conductive carbon black provided by the present invention does not cause vulcanization inhibition even in the high blending range, which was considered extremely difficult in the past, and has a high level of conductive performance. It becomes possible to obtain conductive silicone rubber. Furthermore, the quality of the product is also improved because the reinforcing properties can be increased without impairing the moldability.

Patent applicant: Tokai Carbon Co., Ltd.

Claims (1)

[Claims] 1. BET specific surface area (N_2SA) is 150 m^2/g
A conductive carbon black that belongs to the above hard type field and has the following selective properties. (1) pH>9.0 (2) G value calculated by the formula O%/8+H% ≦0.
15g equivalent/100g carbon black (3) pH
/T value calculated by the formula of true specific gravity value>-4.54×1
0^-^2(N_2SA)+13.382, the conductive carbon black according to claim 1, having a volatile content (Vm) of less than 0.5%.