JP4943490B2 - Conductive liquid silicone rubber composition - Google Patents

Description

  The present invention relates to a conductive liquid silicone rubber composition.

  Various conductive rubbers in which a conductive material such as carbon black is blended with a rubber-like substance that exhibits electrical insulation have been known in the past, and are applied in various fields by utilizing the properties and conductivity as a rubber-like substance. ing. On the other hand, silicone rubber, one of the electrically insulating rubbery substances, is excellent in heat resistance, cold resistance, weather resistance, etc. and is widely used as an electrically insulating rubber. By adding a conductive material such as black, it has been put to practical use as a conductive silicone rubber.

Examples of the conductive material added to the silicone rubber composition include various metal powders such as carbon black, graphite, silver, copper, and nickel. Among these, carbon black is often used as a conductive material because it can provide good conductivity to silicone rubber in addition to its low cost. For example, carbon black is 10 ³ Ω · m. In order to impart the following high conductivity, it is necessary to blend a relatively large amount of carbon black.

  As described above, when a relatively large amount of carbon black is blended in the silicone rubber composition, the polyorganosiloxane serving as the base polymer of the silicone rubber and the carbon black have no inherent affinity, and it is difficult to obtain a uniform mixed state. At the same time, there is a problem that the fluidity of the silicone rubber composition is lowered to adversely affect moldability and processability. In contrast, for example, Patent Document 1 discloses a conductive silicone rubber composition in which a phenyl group-containing organosilicon compound is blended in addition to a silicone base polymer and carbon black.

  Although the above-mentioned organosilicon compound containing a phenyl group is effective for improving the mixing state of the silicone base polymer and carbon black, an increase in the viscosity of the conductive silicone rubber composition due to the incorporation of carbon black can be avoided. However, this increase in viscosity leads to a decrease in moldability. In particular, it is important to maintain a low viscosity in a conductive liquid silicone rubber composition used for casting molding or the like, but in conventional phenyl group-containing organosilicon compounds, the viscosity of the conductive silicone rubber composition is kept low. There is a problem that the effect is insufficient. Further, even if the viscosity of the conductive silicone rubber composition at the beginning of mixing is somewhat low, an increase in viscosity over time during storage cannot be avoided.

Japanese Patent Publication No. 3-47663

  As described above, the conventional conductive liquid silicone rubber composition has a problem that an increase in viscosity is unavoidable due to poor dispersibility of carbon black in the silicone base polymer. Such a problem is not sufficiently improved even in a conductive silicone rubber composition using a conventional organosilicon compound-based treatment agent. In addition, even if the viscosity at the beginning of mixing is somewhat low, an increase in viscosity over time is unavoidable. Therefore, a conductive liquid silicone rubber composition that can maintain a fluidity, that is, a low viscosity, to which, for example, casting molding can be applied after adding a relatively large amount of carbon black to provide low resistance. Is required.

  The present invention has been made in order to cope with such problems, and a conductive liquid silicone rubber composition that achieves both low resistance and low viscosity by further increasing the affinity between the silicone base polymer and carbon black. The purpose is to provide goods.

（式中、Ｒ^１は同一または異なるアルキル基を、Ｒ^２はフェニル基又はα−メチルスチリル基から選ばれる一価基を、Ｒ^３ は一価炭化水素基であって、Ｒ^２がフェニル基の場合には炭素数が２以上のアルキル基を示し、ｎおよびｍはｎ＋ｍが５〜１０００の範囲の数である）で表され、かつ前記Ｒ^２基を含むＳｉＯ単位を少なくとも１０ｍｏｌ％含有するシリコーンオイル０．５〜３０質量部と、（Ｃ）比表面積が５００ｍ^２／ｇ以下で、かつＤＢＰ吸油量が２００ｍｌ／１００ｇ以下であるカーボンブラック５〜１００質量部と、（Ｄ）必要量の硬化剤と、を含有することを特徴としている。
また、本発明の流し込み成形用導電性液状シリコーンゴム組成物において、硬化剤としては、好ましくはオルガノハイドロジェンポリシロキサンと、白金系触媒との組み合わせである。 The conductive liquid silicone rubber composition for casting molding according to the present invention has (A) an addition reaction type polyorganosiloxane having a polymerization degree in the range of 100 to 2000 and 90 mol% or more of the side chain groups being methyl groups. And (B)

(Wherein, the R ¹ are the same or different alkyl group, a monovalent radical R ² is selected from phenyl or α- methylstyryl group, R ³ is a monovalent hydrocarbon group, R ² is a phenyl group In this case, it represents an alkyl group having 2 or more carbon atoms, n and m are represented by n + m in the range of 5 to 1000), and contains at least 10 mol% of SiO units containing the R ² group. (C) 5 to 100 parts by mass of carbon black having a specific surface area of 500 m ² / g or less and a DBP oil absorption of 200 ml / 100 g or less, and (D) a required amount And a curing agent.
In the conductive liquid silicone rubber composition for casting molding of the present invention, the curing agent is preferably a combination of an organohydrogenpolysiloxane and a platinum catalyst.

In the conductive liquid silicone rubber composition of the present invention, in addition to (A) component polyorganosiloxane, (C) component carbon black, and (D) component curing agent, (B) component (1) ) And a silicone oil containing at least 5 mol% of SiO units containing an R ² group. The silicone oil as component (B) improves the affinity between the silicone base polymer and carbon black, and further has excellent sustainability for improving the affinity. Therefore, the fluidity of the conductive liquid silicone rubber composition, It becomes possible to maintain the low viscosity which can exhibit the characteristic as a liquid composition.

  As described above, according to the present invention, a conductive liquid silicone that can maintain a low viscosity over a long period of time without impairing the fluidity as a liquid, for example, while imparting good conductivity with carbon black. A rubber composition can be provided stably. This greatly contributes to improving the moldability, reliability, storage stability, handleability, practicality, etc. of the conductive liquid silicone rubber composition.

Hereinafter, modes for carrying out the present invention will be described.
The conductive liquid silicone rubber composition of the present invention comprises (A) component polyorganosiloxane (silicone base polymer), (B) component silicone oil (silicone treatment agent), (C) component conductive carbon black, And the hardening | curing agent of (D) component is contained as an essential component.

  The polyorganosiloxane of component (A) serves as the base polymer of the conductive liquid silicone rubber composition of the present invention, and has a degree of polymerization in the range of 100 to 2000. When the degree of polymerization of the silicone base polymer exceeds 2000, the viscosity increases, and the fluidity required for the liquid silicone rubber composition, that is, the low viscosity cannot be obtained. On the other hand, when the degree of polymerization of the silicone base polymer is less than 100, the characteristics when the conductive liquid silicone rubber composition is cured deteriorates, and the original physical characteristics of the cured silicone product cannot be obtained. The degree of polymerization of the silicone base polymer (A) is more preferably in the range of 200 to 1,000.

  In the polyorganosiloxane of component (A) described above, 90 mol% or more of the side chain groups bonded to the silicon atoms constituting the main skeleton are methyl groups. Such polyorganosiloxane contributes to the maintenance of low viscosity as a liquid. In addition, various unsubstituted or substituted monovalent hydrocarbon groups can be applied to the side chain group other than the methyl group. In addition, the polyorganosiloxane molecular chain ends are blocked with hydrolyzable groups or hydroxyl groups, as with general silicone-based polymers, and with alkenyl groups such as vinyl groups depending on the curing reaction applied, etc. Applies. The alkenyl group may be used as part of the side chain group.

（式中、Ｒ^１は同一または異なるアルキル基を、Ｒ^２はフェニル基又はα−メチルスチリル基から選ばれる一価基を、Ｒ^３ は一価炭化水素基であって、Ｒ^２がフェニル基の場合には炭素数が２以上のアルキル基を示し、ｎおよびｍはｎ＋ｍが５〜１０００の範囲の数である）で実質的に表される組成を有し、かつ側鎖基としてＲ^２基を有するＳｉＯ単位を１０ｍｏｌ％以上含有するものである。 The component (B) silicone oil is a treatment agent that increases the affinity between the component (A) silicone base polymer and the component (C) carbon black,

(Wherein, the R ¹ are the same or different alkyl group, a monovalent radical R ² is selected from phenyl or α- methylstyryl group, R ³ is a monovalent hydrocarbon group, R ² is a phenyl group In the case of n, m represents an alkyl group having 2 or more carbon atoms, and n + m is a number in the range of n + m of 5 to 1000), and R ² as a side chain group It contains 10 mol% or more of SiO units having a group.

(1) As the R ¹ group in the formula, an alkyl group such as a methyl group, an ethyl group, or a propyl group is used. These side groups can be either identical or different.

R ² groups be those which characterize the component (B), Good phenyl beauty alpha - a methylstyryl group or al chosen monovalent group. Among these, it is preferable to apply an α-methylstyryl group in view of the above-described effect of improving affinity and its sustainability.

An alkyl group similar to the R ¹ group can be applied to the R ³ group, but when the R ² group is a phenyl group , an alkyl group having 2 or more carbon atoms is used. Examples of the alkyl group having 2 or more carbon atoms include ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, dodecyl and the like. Among these, it is particularly preferable to use an alkyl group having 6 or more carbon atoms. However, when the number of carbon atoms is too large, it becomes difficult to synthesize silicone oil, resulting in an increase in cost and a decrease in handleability. Therefore, an alkyl group having 20 or less carbon atoms is preferable.

  For the silicone oil as component (B), an organosiloxane having n + m in the range of 5 to 1000 in the above formula (1) is applied. When the value of n + m indicating the degree of polymerization of silicone oil is less than 5, the molecule is too small to sufficiently increase the affinity of carbon black for the silicone base polymer. On the other hand, when the value of n + m exceeds 1000, the molecule becomes too large, and the properties of the carbon black as a treating agent deteriorate. The value of n + m is more preferably in the range of 10 to 500.

Then, (B) a silicone oil as component shall contain at least 10 mol% or more in the range of SiO units having the ^{R 2} groups as described above. When the content of the R ² group-containing SiO unit is less than 10 mol%, the affinity between the silicone base polymer of the component (A) and the carbon black of the component (C) cannot be sufficiently increased, and the conductive liquid silicone The low viscosity of the rubber composition cannot be maintained. The SiO unit having an R ² group is more preferably contained in the range of 10 mol% or more in the silicone oil as the component (B) from the viewpoint of improving affinity and its sustainability. However, if the content is too large, not only the effect is not obtained, but also the synthesis becomes difficult industrially and the cost is increased. Therefore, the content of the SiO unit having R ² group is 80 mol%. It is preferable to make it less than.

As described above, the silicone oil of component (B) is a component that enhances the affinity between the carbon black of component (C) and the silicone base polymer of component (A).
By blending such a silicone oil of component (B) into a conductive liquid silicone rubber composition containing carbon black, a uniform mixed state can be stably obtained. Furthermore, since the silicone oil of component (B) has a high surface modification effect of carbon black and is excellent in its sustainability, the viscosity of the conductive liquid silicone rubber composition can be kept low, and can be stored. It is possible to suppress an increase in viscosity of the conductive liquid silicone rubber composition.

Here, the surface modification effect of carbon black by the silicone oil as the component (B) is obtained mainly based on the R ² group (a monovalent group selected from an aryl group and an aralkyl group). However, when the R ² group is an aryl group, the viscosity maintaining effect and the viscosity increase suppressing effect of the conductive liquid silicone rubber composition are insufficient, so that the R ³ group is an alkyl group having 2 or more carbon atoms. In particular, an alkyl group having 6 or more carbon atoms is applied. As a result, the viscosity of the conductive liquid silicone rubber composition can be kept low as described above. It is possible to suppress the increase in viscosity over time with good reproducibility. When an aralkyl group is applied as the R ² group, an unsubstituted or substituted monovalent hydrocarbon group similar to the R ¹ group including a methyl group can be used for the R ³ group.

  The blending amount of the silicone oil as the component (B) is in the range of 0.5 to 30 parts by mass with respect to 100 parts by mass of the silicone base polymer as the component (A). When the blending amount of the silicone oil as the component (B) is less than 0.5 parts by mass, the above-described affinity improvement effect cannot be sufficiently obtained. On the other hand, when the blending amount of the component (B) exceeds 30 parts by mass, the properties (eg, mechanical properties) of the cured product obtained by curing the conductive liquid silicone rubber composition may be deteriorated. (B) The compounding quantity of a component is more preferable to set it as the range of 1-10 mass parts with respect to 100 mass parts of (A) component.

The component (C), carbon black, is a component that imparts conductivity to the conductive liquid silicone rubber composition and the rubber-like elastic body obtained by curing the composition. Carbon black having a specific surface area of 500 m ² / g or less and a DBP oil absorption of 200 ml / 100 g or less is applied to the component (C). When the specific surface area of carbon black exceeds 500 m ² / g, the dispersibility in the silicone base polymer is lowered, leading to an increase in viscosity of the conductive liquid silicone rubber composition. The specific surface area of carbon black as the component (C) is more preferably 300 m ² / g or less.

The DBP (dibutyl phthalate) oil absorption is a characteristic value defined in JIS K 8221 (carbon black test method for rubber) and is an index indicating the degree of carbon structure development. When such DBP oil absorption exceeds 200 ml / 100 g, dispersibility in the silicone base polymer is lowered. The DBP oil absorption of carbon black as the component (C) is more preferably 150 ml / 100 g or less. That is, carbon black having a specific surface area of 500 m ² / g or less and a DBP oil absorption of 200 ml / 100 g or less is excellent in dispersibility in a silicone base polymer, and therefore, can suppress an increase in viscosity of the conductive liquid silicone rubber composition. Contribute. A specific example of such carbon black is acetylene black.

  The blending amount of the carbon black as the component (C) is in the range of 5 to 100 parts by mass with respect to 100 parts by mass of the polyorganosiloxane as the component (A). If the blending amount of carbon black is less than 5 parts by mass, sufficient conductivity may not be obtained. On the other hand, when the amount exceeds 100 parts by mass, the viscosity of the conductive liquid silicone rubber composition is likely to increase even when the silicone oil of component (B) is blended, and the mechanical properties of the resulting silicone rubber deteriorate. There is a fear. The blending amount of carbon black is more preferably in the range of 10 to 80 parts by mass, particularly in view of the balance between conductivity and mechanical properties.

  The component (D) curing agent is a variety of known curing agents capable of vulcanizing and curing the component (A) by utilizing a radical reaction or addition reaction usually applied to the curing of the silicone rubber composition. Can be appropriately selected and used, and is not particularly limited to the curing mechanism. Examples of such a curing agent include organic peroxides such as di-t-butyl peroxide and 2,5-dimethyl-2,5-di-t-butylperoxyhexane. Examples of the addition reaction type curing agent include a combination of an organohydrogenpolysiloxane (crosslinking agent) containing at least two hydrogen atoms bonded to silicon atoms in one molecule and a platinum catalyst. . Further, examples of the condensation reaction type curing agent include a combination of a crosslinking agent such as methyltris (methylethylketoxime) silane or trimethoxysilane and a catalyst such as a tin compound or organic titanate.

  The necessary amount of the curing agent described above may be blended as in the case of a normal silicone rubber composition. Specifically, for example, in the case of an organic peroxide, it is preferable to blend about 0.05 to 15 parts by mass with respect to 100 parts by mass of the (A) component polyorganosiloxane. In the case of an addition reaction type curing agent, the platinum catalyst is used in an amount of 1 to 1000 ppm in terms of platinum element with respect to 100 parts by mass of the polyorganosiloxane of component (A), and the crosslinking agent is contained in component (A). It is preferable to blend such an amount that 0.5 to 4.0 hydrogen atoms bonded to silicic group atoms in the crosslinking agent are added to one alkenyl group. In the case of a condensation reaction type curing agent, 0.5 to 20 parts by mass of a crosslinking agent and about 0.01 to 5 parts by mass of a catalyst may be blended with 100 parts by mass of the polyorganosiloxane of component (A). preferable.

  The conductive liquid silicone rubber composition of the present invention includes components other than the components (A) to (D) as necessary, that is, a silica-based filler or a quartz powder usually used in a silicone rubber composition. Fused quartz powder, diatomaceous earth, talc, calcium carbonate, titanium oxide, iron oxide, aluminum oxide, and the like may be added. Furthermore, a plasticizer, a heat resistance improver, a flame retardant imparting agent, a processing aid, a dispersant, a colorant, a solvent, and the like can be blended.

  The conductive liquid silicone rubber composition of the present invention can be obtained by uniformly dispersing and mixing the components (A) to (E) and additional components blended as necessary. . For example, (A) component silicone base polymer and (B) component silicone oil are charged into a universal kneader or kneader, and then (C) component conductive carbon black is added and mixed to uniformly disperse and mix Let At this time, the conductive carbon black may be added and mixed several times. In addition, it is allowed to pass these mixtures through three rolls or to heat knead. The conductive liquid silicone rubber composition of the present invention is obtained by adding the curing agent of component (D) to the mixture thus obtained and mixing it uniformly.

  The viscosity of the conductive liquid silicone rubber composition of the present invention is set according to the use application, etc., but considering the handleability and practicality as a liquid conductive silicone rubber composition, the viscosity Is preferably 1000 P or less. In consideration of characteristics after the conductive liquid silicone rubber composition is cured, the viscosity of the conductive liquid silicone rubber composition is preferably 10 P or more. The present invention makes it possible to maintain a viscosity capable of exhibiting the characteristics as a liquid as described above, after blending carbon black as a conductive material.

  The use of the conductive liquid silicone rubber composition of the present invention is not particularly limited, but the conductivity is required by utilizing the various properties inherent to the conductive silicone rubber composition and the properties as a liquid. It is preferably used as a casting material for silicone rubber. The conductive liquid silicone rubber composition applied to the casting molding material is required to have fluidity to such an extent that casting molding can be applied, and therefore preferably has a viscosity of about 10 to 1000 P described above. . However, the conductive liquid silicone rubber composition of the present invention is not limited to the viscosity, and the specific viscosity can be appropriately set according to the purpose of use.

  Next, specific examples of the present invention and evaluation results thereof will be described.

Example 1
First, a polydimethylsiloxane base polymer B having a molecular chain end blocked with a vinyl group, a degree of polymerization of 810, and a viscosity of 100 P, 50 mol% of α-methylstyryl group, the remaining group is a methyl group, and polymerization 60 degrees of silicone oil A and acetylene black (DENKA BLACK NC-75 (trade name, manufactured by Denki Kagaku Kogyo Co., Ltd.)) having a specific surface area of 28 m ² / g and a DBP oil absorption of 130 ml / 100 g as carbon black are prepared. did.

5 parts by mass of silicone oil A is added to 100 parts by mass of the above-mentioned siloxane base polymer B , and this is uniformly mixed at room temperature for 10 minutes. Kneaded uniformly. Thereafter, 1 part by mass of methyl hydrogen polysiloxane as a curing agent and 5 ppm (as platinum amount) of chloroplatinic acid as a curing catalyst were added and mixed uniformly to obtain a conductive liquid silicone rubber composition. This conductive liquid silicone rubber composition was subjected to the characteristic evaluation described later.

Example 2
Among the components prepared in Example 1 described above, the silicone oil A, full Eniru based on 30 mol%, wherein 30 mol% hexyl group, a remaining group is a methyl group, and a polymerization degree of 35 silicone oil B Instead of each , each component was prepared.

Except having mixed each component mentioned above with the compounding ratio shown in Table 1, it carried out similarly to Example 1, and produced the electroconductive liquid silicone rubber composition, respectively. These conductive liquid silicone rubber compositions were subjected to the characteristic evaluation described later .

Comparative Examples 1-6
A conductive liquid silicone rubber composition was prepared in the same manner as in Example 1 except that the components and compounding ratios shown in the comparative example column of Table 1 were used . This conductive liquid silicone rubber composition was subjected to the characteristic evaluation described later.
In addition, each component in the table is as follows.
Polydimethylsiloxane base polymer A: Polydimethylsiloxane base polymer whose molecular chain ends are blocked with hydroxyl groups, the degree of polymerization is 760, and the viscosity is 80P
Ketjen Black: Furnace Black (Ketjen Black EC-600JD (trade name, manufactured by Ketjen Black International)) with carbon black, specific surface area of 1270 m ² / g, DBP oil absorption of 495 ml / 100 g
Silicone oil C: Silicone oil containing 30 mol% of phenyl groups, the remaining groups being methyl groups, and a polymerization degree of 35 (silicone oil not corresponding to the component (B) of the present invention)
Silicone oil D: Silicone oil containing 3 mol% of α-methylstyryl groups, the remaining groups being methyl groups, and a polymerization degree of 65 (silicone oil not corresponding to the component (B) of the present invention)
In Comparative Examples 1 to 5, polydimethylsiloxane base polymer A was applied and methyltris (methylethylketoxime) silane and dibutyltin dilaurate were blended as curing agents. Applied and blended methylhydrogenpolysiloxane as a curing agent and chloroplatinic acid as a curing catalyst.

The characteristics of the conductive liquid silicone rubber compositions of Examples 1-2 and Comparative Examples 1-6 described above were evaluated as follows. First, the initial viscosity (initial viscosity) of each conductive liquid silicone rubber composition was measured. Then, after carrying out an acceleration test under the conditions of 70 ° C. × 5 days, the viscosity of each conductive liquid silicone rubber composition was measured. In addition, each conductive liquid silicone rubber composition was cured under conditions of 23 ° C. and 50% RH × 7 days for the condensation curable composition and 150 ° C. × 1 hour for the addition curable composition. The volume resistivity of was measured. In addition, regarding the measurement of volume resistivity, the silicone rubber was each produced using the composition at the beginning of preparation, and the composition after an acceleration test, and the volume resistivity of each of these silicone rubbers was measured. These measurement results are also shown in Table 1.

As is clear from Table 1, it can be seen that the conductive liquid silicone rubber compositions according to Examples 1 and 2 have a very low increase in viscosity even after being left for a long period of time in addition to a low initial viscosity. As described above, the conductive liquid silicone rubber composition of the present invention has both low resistance and low viscosity, and is excellent in storage stability as a liquid.

Claims (2)

(A) 100 parts by mass of an addition reaction type polyorganosiloxane having a polymerization degree in the range of 100 to 2000 and 90 mol% or more of the side chain groups are methyl groups;
(B)

(Wherein, the R ¹ are the same or different alkyl group, a monovalent radical R ² is selected from phenyl or α- methylstyryl group, R ³ is a monovalent hydrocarbon group, R ² is a phenyl group In this case, it represents an alkyl group having 2 or more carbon atoms, n and m are represented by n + m in the range of 5 to 1000), and contains at least 10 mol% of SiO units containing the R ² group. 0.5 to 30 parts by mass of silicone oil
(C) 5 to 100 parts by mass of carbon black having a specific surface area of 500 m ² / g or less and a DBP oil absorption of 200 ml / 100 g or less,
(D) a required amount of curing agent;
A conductive liquid silicone rubber composition for casting molding, characterized by comprising A conductive liquid silicone rubber composition for casting molding, wherein the curing agent is a combination of an organohydrogenpolysiloxane and a platinum catalyst.