JP2752904B2 - Method for producing conductive silicone rubber sponge - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a conductive silicone rubber sponge for obtaining a conductive silicone rubber sponge having fine cells. The silicone rubber sponge obtained by the method of the present invention is particularly effective for a conductive sponge roll for office equipment.

[0002]

Technical Background of the Invention and Problems There have been known various conductive rubbers in which a conductive material is blended with a rubber-like substance having electrical insulation properties. For example, conductive rubber such as conductive carbon black is blended as a conductive material. In addition, conductive rubber having an electric resistance in the range of 10 ⁵ to 10 Ω · cm has been applied in a wide range of fields. On the other hand, silicone rubber, which is one of the electrically insulating rubber-like substances, has excellent heat resistance, cold resistance, and weather resistance, and is widely used as an electrically insulating rubber. A conductive silicone rubber is also put into practical use by adding a conductive material of the formula (1), and a conductive silicone rubber foam which is foamed and cured by further adding a foaming agent is also known. In this case, as the conductive material to be added to the conductive silicone rubber, for example, various metal powders such as carbon black, graphite, silver, nickel, and copper, various non-conductive powders, and the surface of short fibers are treated with a metal such as silver. which was, carbon fibers, those such as a mixture of metal fibers, ¹⁰ 10 volume resistivity of the silicone rubber depending on the type and loading of the conductive material without impairing the peculiar characteristics with silicone rubber
To 10 ^-3 Omega · are frequently used since it may reduce to approximately cm, and particularly when obtaining highly conductive silicone rubber below 10 ⁵ Ω · cm, of these, carbon black, silver, nickel And the like, particularly carbon black is frequently used from the viewpoint of cost. However, when a conductive silicone rubber composition using carbon black such as acetylene black as a conductive material is to be molded (vulcanized) into a sponge such as a sealing material, a gasket material, or a roll material by extrusion molding or the like, The vulcanization system is very limited, and it has been difficult to obtain a conductive silicone rubber sponge having a fine cell structure. On the other hand,
In order to obtain a silicone rubber sponge containing no carbon black, a silicone rubber composition is prepared by adding an azobisisobutyronitrile as a foaming agent, an acyl peroxide such as 2,4-dichlorobenzoyl peroxide as a curing agent, and dicumyl. It was common to use an alkyl-based peroxide such as a peroxide at the same time and foam by hot air vulcanization. However, in silicone rubber containing carbon black, a sponge having a fine cell structure could not be obtained because the acyl peroxide was not vulcanized. Japanese Patent Publication No. 62-49895 discloses a method using peroxyketal as a vulcanizing agent, and Japanese Patent Application Laid-Open Nos. 5-25393 and 5-43802 propose a method using percarbonate. However, in the method of simply foaming and curing in hot air or the method of foaming in a mold, partial foaming proceeds before the rubber is cured due to the influence of moisture in the conductive silicone rubber,
There is a problem that a fine cell cannot be obtained. These sponges, which are not fine cells, are unsuitable as conductive rolls for office use, such as charging rolls, transfer rolls, developing rolls, and fixing rolls, because precise copying is not performed in large cell portions. A conductive silicone rubber sponge having the following has been desired.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to solve the problems of the prior art and to provide a conductive silicone rubber sponge having fine cells and suitable as a conductive roll for office use. .

[0004]

The present inventors have conducted intensive studies to achieve the above object, and as a result, have found that a conductive silicone rubber sponge having fine cells can be obtained by employing a specific method. It was completed. That is, the present invention provides a composition containing (a) a conductive silicone rubber containing conductive carbon black, (b) a curing agent and (c) a foaming agent, in which the reaction rate of the crosslinking group is in the range of 1 to 80%. After being vulcanized under pressure at a temperature of 90 to 170 ° C., it is removed from the mold, and further subjected to foaming and the remaining crosslinking reaction in a larger mold or hot air at a temperature of 140 to 300 ° C. This is a method for producing a conductive silicone rubber sponge.

Hereinafter, the present invention will be described in detail. The (a) carbon black-containing conductive silicone rubber of the present invention comprises an organopolysiloxane and a conductive carbon black, and is not particularly limited as an organopolysiloxane, but may be an organopolysiloxane represented by the following general formula (1). Is common. R ¹ _a SiO _{(4-a) / 2} (1) In the formula, R ¹ is an alkyl group such as a methyl group, an ethyl group, a propyl group, or a butyl group; an alkenyl group such as a vinyl group, an allyl group, or a butaniel group; Chloromethyl, chloropropyl, and 3,3,3-triyl groups in which part or all of the hydrogen atoms bonded to the carbon atoms of aryl groups such as The same or different unsubstituted or substituted monovalent hydrocarbon groups selected from fluoropropyl group, 2-cyanoethyl group and the like, preferably having 1 to 10 carbon atoms, more preferably 1 to 8 carbon atoms,
a is a positive number between 1.90 and 2.05. It is preferable that the compound has a linear molecular structure, but there is no problem even if the molecule contains a partially branched compound. In addition, this may be one in which the molecular chain end is blocked with a triorganosilyl group or a hydroxyl group. Examples of the triorganosilyl group include a trimethylsilyl group, a dimethylvinylsilyl group, a methylphenylvinylsilyl group, and a methyldiphenylsilyl group. Group, methyldivinylsilyl group, trivinylsilyl group and the like. In this case, in order to further reduce the surface tack, both ends of the molecular chain are (CH ₂ = CH) ₂ RSi-, (CH ₂ = C
It is preferable to use a polyfunctional group such as H) ₃ Si- (R has the same meaning as R ¹ ). Although the degree of polymerization is not particularly limited, those having a viscosity at 25 ° C. of 300 cSt or more are preferable. Moreover R ¹ is 0.01 to 1.0 mole percent vinyl group as a crosslinking group, an allyl group, it preferably contains an alkenyl group such as Butanieru group.

[0006] As the conductive carbon black, usually,
Those commonly used in conductive rubber compositions can be used.
For example, acetylene black, conductive furnace black (CF), superconductive furnace black (SCF), extra conductive furnace black (XCF), conductive channel black (CC), furnace black or channel black heat-treated at a high temperature of about 1500 ° C. Can be mentioned. Specific examples of acetylene black include Denka acetylene black (manufactured by Denki Kagaku) and Shaunigan acetylene black (manufactured by Shaunigan Chemical Co., Ltd.). Specific examples of conductive furnace black include Continex CF (Continental Carbon Stocks). And Vulcan C (Cabot Co., Ltd.). Specific examples of superconductive furnace black include Continex SCF (Continental Carbon Co., Ltd.) and Vulcan SC (Cabot Co., Ltd.). Asahi HS-500 (manufactured by Asahi Carbon Co., Ltd.), Vulcan XC-72 (manufactured by Cabot Co., Ltd.), etc., and as a conductive channel black, Kolux L (degussa stock) Company, Ltd.) are exemplified, also, Ketjen black EC and Ketjen black EC-600JD, which is a type of furnace black
(Made by Ketjen Black International)
Can also be used. Among these, acetylene black is particularly excellent in conductivity because it has a low impurity content and has a developed secondary structure, and is particularly preferably used in the present invention. Furthermore,
Ketjen Black EC and Ketjen Black EC-600JD, which have excellent specific surface area and exhibit excellent conductivity even at a low filling amount, can also be preferably used. The addition amount of the conductive carbon black is preferably 3 to 100 parts by weight, particularly preferably 5 to 70 parts by weight, based on 100 parts by weight of the organopolysiloxane component. If the amount is less than 3 parts by weight, desired conductivity may not be obtained. If the amount exceeds 100 parts by weight, the cured product may have poor mechanical strength.

The curing agent (b) may be either an organic peroxide or an addition reaction curing agent. Organic peroxides include 2,4,4-trimethylpentylperoxy-2
-Ethylhexanoate, t-arylperoxy-2-
Ethylhexanoate, t-butylperoxy-2-ethylhexanoate, t-butylperoxy-isobutyrate, di-t-butylperoxy-hexahydroterephthalate, 1,1-t-butylperoxy-3, 3,5 −
Trimethylcyclohexane, 1,1-t-butylperoxycyclohexane, 1,6-bis (t-butylperoxycarboniloxy) hexane, diethylene glycol-bis (t-butylperoxycarbonate), di-t-butyl peroxide , 2,5-dimethyl-2,5-di (t-
Butylperoxy) hexane, 2,5-dimethyl-2,5-
Di- (t-butylperoxy) hexane, 2,5-dimethyl-2,5-di- (t-butylperoxy) hexene, dicumyl peroxide, 1,3-bis- (t-butylperoxy- Isopropyl) -benzene, 2,2-di (t-butylperoxy) butane, t-butylperoxybenzoate and the like. The amount of the organic peroxide is based on 100 parts by weight of the conductive silicone rubber (a).
A range of 0.05 to 15 parts by weight is preferred. If the compounding amount of the organic peroxide is less than 0.05 parts by weight, the vulcanization is not sufficiently performed, and if the compounding amount exceeds 15 parts by weight, not only there is no further special effect, but also the physical properties of the obtained silicone rubber are reduced. May have adverse effects.

The addition reaction curing agent is a curing catalyst such as a platinum catalyst such as chloroplatinic acid, platinum olefin complex, platinum vinyl siloxane complex, platinum black, and platinum triphenylphosphine complex. Polyorganosiloxanes having an average of at least two hydrogen atoms bonded to silicon atoms per molecule are used. Among the curing agents of the component (b), the amount of the curing catalyst is preferably in the range of 1 to 1000 ppm in terms of the amount of platinum element with respect to the conductive silicone rubber of the component (a). If the amount of the curing catalyst is less than 1 ppm in terms of platinum element, the curing will not proceed sufficiently, and if it exceeds 1000 ppm, no particular improvement in the curing speed can be expected. The amount of the crosslinking agent is
(A) Alkenyl group of polyorganosiloxane in component (1)
Hydrogen atoms bonded to silicon atoms in the crosslinking agent
The amount is preferably 0.5 to 4.0, more preferably 1.0 to 3.0. If the amount of hydrogen atoms is less than 0.5, curing of the composition will not proceed sufficiently, and the hardness of the composition after curing will be low. The physical properties and heat resistance of the composition are reduced. Further, the curing agent (b) is preferably a combination of two or more organic peroxides or a combination of one or more organic peroxides and an addition reaction curing agent. More preferably, at least one of the curing agents used in combination is selected from alkyl peresters, peroxyketals, and percarbonates having a one-minute half-life temperature of 110 to 160 ° C. in order to obtain finer cells. It is effective for These organic peroxides include 1,1-di-t-butylperoxy-3,3,5-trimethylcyclohexane,
1,1-di-t-butylperoxycyclohexane, t-
Butylperoxy-2-ethylhexanoate, t-butylperoxy-isobutyrate, t-butylperoxy-3,5,5-trimethylhexoate, 1,6-bis (t
-Butylperoxycarbonyloxy) hexane, diethylene glycol-bis (t-butylperoxycarbonate) and the like.

As the foaming agent (c), azobisisobutyronitrile, dinitropentamethylenetetramine, P,
P'-oxybis (benzenesulfonyl hydrazide), N,
It consists of a decomposition gas generating type organic foaming agent such as N'-dinitroso-N, N'-dimethylterephthalamide, azodicarbonamide, or a plastic micro hollow body which expands by heat in which a volatile substance is included in a plastic shell. A foaming agent or the like can be used. As organic foaming agents,
Preferably, a combination of azodicarbonamide and a decomposition aid such as urea or a plastic micro hollow body is effective for obtaining a fine cell structure. The addition amount of the foaming agent is preferably in the range of 0.5 to 10 parts by weight based on 100 parts by weight of the conductive silicone rubber (a). If the amount is less than 0.5 part by weight, a sufficiently foamed sponge cannot be obtained. If the amount exceeds 10 parts by weight, the obtained sponge is brittle, and the heat resistance is lowered due to the remaining foaming agent and decomposition residue.

[0010] The conductive silicone rubber of the above-mentioned component (A) may optionally contain a dispersing agent such as a low-molecular-weight siloxane having a degree of polymerization of 100 or less, a silane containing a silanol group, a silane containing an alkoxy group, iron oxide, oxidized Heat-resistant improvers such as cerium and iron octylate, pigments, etc., as well as fumed silica, wet silica, fumed silica or wet silica with a hydrophobic surface, quartz fine powder, diatomaceous earth, etc. Fine powdered silica may be blended, and furthermore, for the purpose of imparting processability and moldability to the composition, a saturated aliphatic hydrocarbon such as an isoparaffin solvent, and other additives added to the usual silicone rubber composition. It may be added. These compositions may be blended and kneaded with a conventionally used apparatus such as a kneader, a Banbury mixer, and a mixing roll, but the kneading temperature may be equal to or lower than the decomposition temperature of the curing agent or the foaming agent. Required.

In order to obtain a conductive silicone rubber sponge having a fine cell structure from the conductive silicone rubber composition obtained here, the primary vulcanization is performed so that the reaction rate of the crosslinking group is 1 to 80%. The mold was completely filled in a mold at 90 to 170 ° C. and kept under pressure for 3 to 40 minutes to allow a part of the curing reaction to proceed, and then removed from the mold.
It can be obtained by carrying out foaming and a sufficient curing reaction in a larger mold at 0 to 300 ° C. or in hot air. The characteristic feature of the present invention is that a part of the crosslinking reaction of the silicone rubber is performed in a state where the generation of bubbles due to a foaming agent or moisture in the pressurizing mold is prevented, the viscosity of the rubber is increased, and then the foam is removed from the mold and foamed. This is to prevent uneven foaming. For this purpose, it is necessary to perform 1 to 80% of the crosslinking reaction in the primary vulcanization, and more preferably 5 to 70%. In order to carry out 1 to 80% of the crosslinking reaction, the temperature of the primary vulcanization is preferably 100 to 150 ° C, more preferably 110 to 150 ° C.
140 ° C. If the temperature is lower than 90 ° C., the primary vulcanization hardly proceeds, and a fine cell sponge cannot be obtained. The temperature of the secondary vulcanization is preferably from 140 to 250 ° C, more preferably from 150 to 200 ° C, when foaming and curing are performed in the mold. When foaming and curing are performed in hot air, the temperature of the hot air is preferably set to 1
The temperature is preferably from 50 to 300 ° C, more preferably from 170 to 250 ° C. If the temperature is lower than 140 ° C, sufficient foam hardening is not performed, and 300
If the temperature is higher than ℃, there is a problem that the curing progresses rapidly and the expansion ratio is lowered. The conductive silicone rubber sponge manufactured by such a method has an unprecedented fine cell structure, and since there is no generation of a large cell partially like a pinhole, a conductive sponge roll for office equipment or the like is used. When used, precise copying can be performed, which is effective.

[0012]

Next, the present invention will be described specifically with reference to examples and comparative examples, but the present invention is not limited to the following examples. In the following examples, all parts are parts by weight. Example 1 Conductive silicone rubber (XE manufactured by Toshiba Silicone Co., Ltd.)
23-A4707) 100 parts of t-butylperoxy-
0.5 parts of 2-ethylhexanoate, 2,5-dimethyl-2,
1.0 part of 5-di-t-butylperoxyhexane and 3 parts of an azodicarbonamide-based blowing agent (Cermic CAP-500, manufactured by Sankyo Chemical Co., Ltd.) were blended with a two-roll mill to prepare a composition. This composition is placed in a mold (10cm × 10cm × 1cm)
The mixture was completely filled and press vulcanized at 120 ° C. for 10 minutes. Thereafter, it was taken out and placed in a mold (12 cm × 12 cm × 1.5 cm) and kept at 170 ° C. for 20 minutes to obtain a silicone rubber sponge. The hardness, expansion ratio,
The number of cells having a diameter of 0.5 mm or more per 1 cm ^{2 of the} cut surface was measured. The ratio of residual vinyl groups was measured at two points after primary vulcanization and after secondary vulcanization before vulcanization. The measurement was carried out by adding KOH in a closed vessel at 300 ° C. and measuring the gas generated by thermal decomposition by gas chromatography. Table 1 shows the results
Shown in Example 2 In Example 1, the secondary vulcanization was carried out in hot air at 200 ° C. to perform foam curing, and the same evaluation was performed. Table 1 shows the results. Example 3 A vinylidene chloride / acrylonitrile copolymer micro-hollow body containing isobutane instead of the azodicarbonamide-based blowing agent in Example 1 (WU, manufactured by Expancel Co., Ltd.)
# 642) The foaming and curing were performed in the same manner except that 3 parts were blended, and the evaluation was performed similarly. Table 1 shows the results. Comparative Example 1 In Example 1, preliminary molding was performed in a mold at 25 ° C. without performing primary vulcanization, foaming and curing were performed in the same manner after secondary vulcanization, and the same evaluation was performed. Table 1 shows the results. Comparative Example 2 In Example 2, preliminary molding was performed in a mold at 25 ° C. without performing primary vulcanization, foaming and curing were similarly performed after secondary vulcanization, and the same evaluation was performed. Table 1 shows the results. Example 4 In Example 1, instead of 2,5-dimethyl-2,5-di-t-butylperoxyhexane, the molecular chain end was blocked with a trimethylsilyl group, and 50
%, And 3 parts of methylhydrogenpolysiloxane having a polymerization degree of 20 consisting of 50% of methylhydrogensiloxane units, 1 part of triallyl isocyanurate, and 0.001 part of chloroplatinic acid were similarly evaluated. Table 1 shows the results. Comparative Example 3 In Example 4, preliminary molding was performed in a mold at 25 ° C. without performing primary vulcanization, foaming and curing were similarly performed after secondary vulcanization, and the same evaluation was performed. Table 1 shows the results. Comparative Example 4 Foaming and curing were performed in the same manner as in Comparative Example 2, except that 3 parts of azoisobutyronitrile was blended instead of the azodicarbonamide-based blowing agent, and the same evaluation was performed. Table 1 shows the results.

Comparative Example 5 In Example 1, the primary vulcanization was performed at 155 ° C. for 10 minutes, and after the secondary vulcanization, foaming and curing were performed in the same manner, and the same evaluation was performed. Table 1 shows the results.

[0014]

[Table 1]

Claims (4)

(57) [Claims] 1. A composition comprising (a) a conductive silicone rubber containing conductive carbon black, (b) a curing agent and (c) a foaming agent, wherein the reaction rate of the crosslinking group is in the range of 1 to 80%. After being vulcanized under pressure at a temperature of 90 to 170 ° C., it is removed from the mold, and further subjected to foaming and the remaining crosslinking reaction in a larger mold or hot air at a temperature of 140 to 300 ° C. Of producing a conductive silicone rubber sponge. 2. The method for producing a conductive silicone rubber sponge according to claim 1, wherein the foaming agent is azodicarbonamide. 3. The method for producing a conductive silicone rubber sponge according to claim 1, wherein the foaming agent is a plastic micro hollow body which expands by heat. 4. A curing agent having a one-minute half-life temperature of 110 to 110.
The method for producing a conductive silicone rubber sponge according to claim 1, wherein the alkyl perester at 150 ° C is used in combination with another organic peroxide or an addition reaction catalyst.