JP5835100B2 - Antistatic silicone rubber composition and method for inhibiting yellowing of cured antistatic silicone rubber - Google Patents

Description

  The present invention provides an antistatic silicone rubber composition that gives a cured product excellent in sufficient antistatic performance not only at room temperature but also at a high temperature, and yellowing of an antistatic silicone rubber cured product using the composition. It is related with the control method.

  Silicone rubber has excellent weather resistance, electrical properties, low compression set, heat resistance, cold resistance, and other properties, so it can be used in various fields including electrical equipment, automobiles, architecture, medical care and food. Widely used. For example, keypads used as rubber contacts for remote controllers, typewriters, word processors, computer terminals, musical instruments, etc .; gaskets for construction; anti-vibration rubber for audio devices, etc .; automotive parts such as connector seals, spark plug boots, etc. Applications include packing for compact discs used, bread and cake molds. Currently, the demand for silicone rubber is increasing, and the development of silicone rubber having excellent characteristics is desired.

  These silicone rubbers are generally supplied in the form of a composition containing a highly polymerized organopolysiloxane and a reinforcing filler. This composition is prepared by mixing a reinforcing filler and various dispersants with a raw material polymer using a mixing apparatus such as a dough mixer and a two-roller. Reinforcing fillers such as organopolysiloxane and silica are electrically insulating materials, and the silicone rubber composition obtained by blending them and the cured silicone rubber are charged by contact with various substances, resulting in static electricity. There are problems such as generation of dust and adsorption of dust in the air.

  Conventionally, an antistatic rubber has been used as an antistatic agent, such as a polyether (Patent Document 1: JP 2002-500237 A) or carbon black (Patent Documents 2: 3, JP 2002-507240 A, JP 2002/2002). -327122). When a polyether type is used, there is a problem that the polyether is decomposed at a high temperature and a sufficient antistatic effect is not exhibited. In particular, it was actually the case that the antistatic effect was almost lost even by performing a known post cure with a cured product of a thermosetting silicone rubber composition. When carbon black is used, there is a problem that it is difficult to maintain electrical insulation or it is limited to black.

  Japanese Patent Laying-Open No. 2003-82232 (Patent Document 4) proposes a silicone rubber composition for a semiconductive roller to which a lithium salt is added. In the semiconductive region, an electric wire that can be used only by an insulating material. There was a problem that it could not be applied to coatings or keypads. Further, when lithium salt is added, there is a problem that yellowing occurs when the cured product is exposed to a high temperature. In particular, yellowing is significant when cured with organic peroxides.

Special Table 2002-500237 Special table 2002-507240 gazette JP 2002-327122 A JP 2003-82232 A

  The present invention has been made in view of the above circumstances, and is an antistatic silicone rubber composition that does not turn yellow even when exposed to high temperatures and becomes a silicone rubber (cured product) that can maintain excellent antistatic properties. And a method for suppressing yellowing of the cured antistatic silicone rubber.

  As a result of intensive studies to achieve the above object, the present inventors have added a specific amount of an ion conductive antistatic agent of potassium salt to the thermosetting silicone rubber composition, while being electrically insulating, The inventors have found that an antistatic silicone rubber composition that is excellent in sufficient antistatic performance not only at room temperature but also at a high temperature and that can suppress yellowing of a cured product can be obtained, thereby completing the present invention.

That is, the present invention provides a method for suppressing yellowing of the antistatic silicone rubber composition and the cured antistatic silicone rubber described below.
[1]
An antistatic silicone rubber composition characterized by containing 0.0001 to 5 parts by mass of an ion conductive antistatic agent of KN (SO ₂ CF ₃ ) ₂ in 100 parts by mass of a thermosetting silicone rubber composition .
[ 2 ]
The antistatic silicone rubber composition according to [1] , wherein the thermosetting silicone rubber composition is an addition reaction curable type.
[ 3 ]
The antistatic silicone rubber composition according to [1] , wherein the thermosetting silicone rubber composition is an organic peroxide curable type.
[ 4 ]
The antistatic silicone rubber composition according to [1], wherein the thermosetting silicone rubber composition is a co-vulcanization type of addition reaction curing and organic peroxide curing.
[ 5 ]
[1] A method for suppressing yellowing of a cured antistatic silicone rubber comprising heating and curing the antistatic silicone rubber composition according to any one of [ 4 ] to obtain a cured silicone rubber.
[ 6 ]
The method for suppressing yellowing of the cured antistatic silicone rubber according to [ 5 ], wherein the antistatic silicone rubber composition is heat-molded at 80 to 400 ° C.
[ 7 ]
The method for suppressing yellowing of the cured antistatic silicone rubber according to [ 5 ] or [ 6 ], wherein the antistatic silicone rubber composition is further subjected to secondary vulcanization at 150 to 250 ° C.
[ 8 ]
The antistatic silicone rubber composition is molded by any one of extrusion molding, press molding, and injection molding, and yellowing of the antistatic silicone rubber cured product according to any one of [ 5 ] to [ 7 ] How to suppress.

  The cured product of the antistatic silicone rubber composition of the present invention has excellent antistatic properties, can maintain excellent antistatic properties even when exposed to high temperatures, and can suppress yellowing. Moreover, coloring can also be made freely.

Hereinafter, the present invention will be described in detail.
The antistatic silicone rubber composition of the present invention is characterized in that 0.0001 to 5 parts by mass of an ion conductive antistatic agent that is a potassium salt is contained in 100 parts by mass of a thermosetting silicone rubber composition. It is.
The antistatic silicone rubber composition of the present invention and the cured antistatic silicone rubber obtained by curing the composition are essentially electrically insulating.

The thermosetting silicone rubber composition is not particularly limited as long as it is a silicone rubber composition that cures by heating, but the organopolysiloxane (A) having at least two alkenyl groups in the molecule as a base polymer is used as a curing agent. (B) is preferably one using an addition reaction curing agent (B-1) and / or an organic peroxide curing agent (B-2). The shape may be a millable type or a liquid type.
In the present invention, typically, only the following components (A) and (B-1) are used as the thermosetting silicone rubber composition constituting the matrix in which the ion conductive antistatic agent that is a potassium salt is blended and dispersed. And an organic peroxide curable silicone rubber composition consisting only of the following components (A) and (B-2). Furthermore, the co-vulcanization type silicone rubber composition which uses only addition reaction hardening and organic peroxide hardening which consist only of the following (A) component, (B-1) component, and (B-2) component is mentioned.

[(A) Organopolysiloxane having at least two alkenyl groups in the molecule]
As the component (A), those represented by the following average composition formula (I) can be used.
R _a SiO _{(4-a) / 2} (I)
(Wherein R is the same or different from each other, an unsubstituted or substituted monovalent hydrocarbon group having 1 to 10 carbon atoms, and a is a positive number of 1.8 to 2.3.)

  Here, R is an unsubstituted or substituted monovalent hydrocarbon group having 1 to 10 carbon atoms, preferably 1 to 8 carbon atoms, which are the same or different from each other. Specifically, methyl, ethyl, propyl, isopropyl Group, butyl group, isobutyl group, tert-butyl group, pentyl group, neopentyl group, hexyl group, cyclohexyl group, octyl group, nonyl group, decyl group and other alkyl groups having 1 to 10 carbon atoms, phenyl group, tolyl group, Aryl groups having 6 to 10 carbon atoms such as xylyl group and naphthyl group, aralkyl groups having 7 to 10 carbon atoms such as benzyl group, phenylethyl group and phenylpropyl group, vinyl group, allyl group, propenyl group, isopropenyl group, Alkenyl groups having 2 to 10 carbon atoms such as butenyl group, hexenyl group, cyclohexenyl group and octenyl group, and some or all of hydrogen atoms of these groups Fluorine, bromine, halogen atom such as chlorine, those substituted with a cyano group or the like, such as chloromethyl group, chloropropyl group, bromoethyl group, trifluoropropyl group, cyanoethyl group and the like. Among these, a methyl group, a vinyl group, a phenyl group, and a trifluoropropyl group are preferable, and it is preferable that at least 50 mol%, particularly 80 mol% or more of R is a methyl group.

  In addition, at least two of R must be alkenyl groups (preferably having 2 to 8 carbon atoms, more preferably 2 to 6). The alkenyl group content in R is preferably 0.0001 to 20 mol%, particularly 0.001 to 10 mol%. This alkenyl group may be bonded to a silicon atom at the end of the molecular chain, may be bonded to a silicon atom in the middle of the molecular chain, or may be bonded to both.

  a is a positive number of 1.8 to 2.3, preferably 1.9 to 2.1, and this organopolysiloxane is basically linear, but partially within a range not impairing rubber elasticity. You may branch to.

The molecular weight is not particularly limited, and can be used from a low-viscosity liquid to a high-viscosity raw rubber that does not self-flow at room temperature (25 ° C). The polymerization degree is preferably 100 to 100,000, particularly 150 to 20,000, and more preferably 2,000 to 20,000.
In the present invention, the degree of polymerization can be determined, for example, as a weight average molecular weight (weight average degree of polymerization) in terms of polystyrene by gel permeation chromatography analysis using toluene as a developing solvent.

The liquid (oil-like) component (A) having self-fluidity at room temperature preferably has a viscosity at 25 ° C. of 100 to 1,000,000 mPa · s, particularly 50 to 100,000 mPa · s. .
The viscosity can usually be measured with a rotational viscometer (for example, BL type, BH type, BS type, cone plate type, etc.) at room temperature (25 ° C.) (hereinafter the same).

  As the component (A), the organopolysiloxane may be used alone or in combination of two or more having different molecular structures and polymerization degrees.

  Such an organopolysiloxane is subjected to ring-opening polymerization by a known method, for example, by (co) hydrolytic condensation of one or more of organohalogenosilanes, or by using a cyclic polysiloxane using an alkaline or acidic catalyst. Can be obtained.

[(B) Curing agent]
Examples of the (B) curing agent include (B-1) addition reaction curing agent and (B-2) organic peroxide curing agent as described above.

(B-1) Addition reaction curing agent (B-1) As the addition reaction curing agent, an organohydrogenpolysiloxane and a hydrosilylation catalyst are used in combination.

As organohydrogenpolysiloxane, if it contains 2 or more, preferably 3 or more, more preferably 3 to 200, and still more preferably about 4 to 100 SiH groups in one molecule, it is linear, It may be either cyclic or branched, and a known organohydrogenpolysiloxane can be used as a cross-linking agent for the addition reaction curable silicone rubber composition. For example, it is represented by the following average composition formula (II): Organohydrogenpolysiloxane can be used.
R ¹ _p H _q SiO _{(4-pq) / 2} (II)

In the above average composition formula (II), R ¹ represents an unsubstituted or substituted monovalent hydrocarbon group, which may be the same or different, and preferably excludes an aliphatic unsaturated bond. . Usually, those having 1 to 12 carbon atoms, particularly those having 1 to 8 carbon atoms are preferable. Specifically, alkyl groups such as methyl group, ethyl group and propyl group, cycloalkyl groups such as cyclohexyl group, phenyl groups, tolyl groups and the like. Aralkyl groups such as aryl group, benzyl group, 2-phenylethyl group and 2-phenylpropyl group, and groups in which part or all of hydrogen atoms of these groups are substituted with halogen atoms, for example, 3, 3, 3- Examples thereof include a trifluoropropyl group.
Note that p and q are 0 ≦ p <3, preferably 1 ≦ p ≦ 2.2, 0 <q ≦ 3, preferably 0.002 ≦ q ≦ 1, 0 <p + q ≦ 3, preferably 1.002 ≦. It is a positive number satisfying p + q ≦ 3.

  Organohydrogenpolysiloxane has 2 or more, preferably 3 or more, SiH groups in one molecule, which may be present at both ends of the molecular chain or in the middle of the molecular chain. Also good. Moreover, as this organohydrogenpolysiloxane, it is preferable that the viscosity in 25 degreeC is 0.5-10,000 mPa * s, especially 1-300 mPa * s.

Specific examples of such organohydrogenpolysiloxanes include 1,1,3,3-tetramethyldisiloxane, 1,3,5,7-tetramethylcyclotetrasiloxane, tris (hydrogendimethylsiloxy). ) Methylsilane, tris (hydrogendimethylsiloxy) phenylsilane, methylhydrogencyclopolysiloxane, methylhydrogensiloxane / dimethylsiloxane cyclic copolymer, both ends trimethylsiloxy group-blocked methylhydrogenpolysiloxane, both ends trimethylsiloxy group-blocked Dimethylsiloxane / methylhydrogensiloxane copolymer, dimethylhydrogensiloxy-blocked dimethylpolysiloxane at both ends, dimethylhydrogensiloxy-blocked dimethylsiloxane at both ends Methyl hydrogen siloxane copolymer, both ends trimethylsiloxy group blocked methyl hydrogen siloxane / diphenyl siloxane copolymer, both ends trimethyl siloxy group blocked methyl hydrogen siloxane / diphenyl siloxane / dimethyl siloxane copolymer, both ends trimethyl siloxy group Blocked methylhydrogensiloxane / methylphenylsiloxane / dimethylsiloxane copolymer, both ends dimethylhydrogensiloxy group blocked methylhydrogensiloxane / dimethylsiloxane / diphenylsiloxane copolymer, both ends dimethylhydrogensiloxy group blocked methylhydrogensiloxane・ Dimethylsiloxane ・ Methylphenylsiloxane copolymer, (CH ₃ ) ₂ HSiO _1/2 unit and (CH ₃ ) ₃ SiO _1/2 unit And copolymers comprising SiO _4/2 units, (CH _{3) 2} HSiO _1/2 consisting of units and SiO _4/2 units, and copolymers thereof, (CH _{3) 2} HSiO _1/2 units and SiO _{4 /} Copolymers composed of ₂ units and (C ₆ H ₅ ) ₃ SiO _1/2 units, etc., and those obtained by substituting some or all of the methyl groups with other alkyl groups, phenyl groups, etc. in the above exemplified compounds In addition, compounds having the following structural formulas can be exemplified.

（式中、ｋは２〜１０の整数、ｓ及びｔは０〜１０の整数である。）

(In the formula, k is an integer of 2 to 10, and s and t are integers of 0 to 10.)

  As for the compounding quantity of the said organohydrogen polysiloxane, 0.1-40 mass parts is preferable with respect to 100 mass parts of (A) component. In addition, it is appropriate that the ratio of hydrogen atoms bonded to silicon atoms (≡SiH groups) is 0.5 to 10 for one aliphatic unsaturated bond (alkenyl group, diene group, etc.) of component (A). There is an appropriate range of 0.7-5. If the number is less than 0.5, crosslinking may not be sufficient, and sufficient mechanical strength may not be obtained. If the number exceeds 10, the physical properties after curing will be deteriorated, and particularly heat resistance and compression set will be reduced. It may get worse.

The hydrosilylation catalyst is a catalyst that causes an addition reaction between the alkenyl group of component (A) and the silicon atom-bonded hydrogen atom (SiH group) of organohydrogenpolysiloxane.
Examples of the hydrosilylation catalyst include a platinum group metal catalyst, which includes a platinum group metal and a compound thereof, and conventionally known catalysts for addition reaction curable silicone rubber compositions can be used. For example, particulate platinum metal adsorbed on a carrier such as silica, alumina or silica gel, platinum chloride, chloroplatinic acid, chloroplatinic acid hexahydrate alcohol solution, palladium catalyst, rhodium catalyst, etc. Platinum or platinum compounds are preferred.

  The addition amount of the catalyst only needs to accelerate the addition reaction, and is usually used in the range of 1 mass ppm to 1 mass% with respect to the organopolysiloxane of the component (A) in terms of the amount of platinum-based metal. A range of ˜500 ppm by mass is preferred. If the addition amount is less than 1 mass ppm, the addition reaction may not be sufficiently promoted and curing may be insufficient. On the other hand, if it exceeds 1 mass%, the addition of more than this will have little effect on the reactivity. , It may be uneconomical.

(B-2) Organic peroxide curing agent (B-2) Examples of the organic peroxide curing agent include benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, p-methylbenzoyl peroxide, and o-methyl. Benzoyl peroxide, 2,4-dicumyl peroxide, 2,5-dimethyl-2,5-bis (t-butylperoxy) hexane, di-t-butyl peroxide, t-butyl perbenzoate, 1,6 -Hexanediol-bis-t-butyl peroxycarbonate and the like.

  The addition amount of the organic peroxide is preferably 0.1 to 10 parts by mass, particularly preferably 0.2 to 5 parts by mass with respect to 100 parts by mass of the component (A). If the blending amount is too small, curing may be insufficient, and if it is too large, the cured silicone rubber may turn yellow due to the decomposition residue of the organic peroxide.

In addition, (A) component was combined with (B-1) component and (B-2) component in the range of the said compounding amount, respectively, and addition reaction hardening and organic peroxide hardening were used together. A co-vulcanized silicone rubber composition can also be obtained.
A commercially available thermosetting silicone rubber composition may be used.

[(C) Reinforcing silica]
(C) Reinforcing silica can be blended with the antistatic silicone rubber composition of the present invention as needed in order to impart mechanical strength and the like.
Examples of (C) reinforcing silica include fumed silica and precipitated (wet) silica. These silicas preferably has a specific surface area by the BET method is 50 m ² / g or more, are preferred in particular 100 to 400 m ² / g.
Such silica may be used by treating the surface with a surface treatment agent such as organopolysiloxane, silazane, chlorosilane, alkoxysilane, or the like, if necessary. Further, when the fine powder silica is blended with the organopolysiloxane of the component (A), the surface treatment agent may be blended simultaneously.

  (C) Although the mixture of component is arbitrary, the compounding quantity is 0-100 mass parts with respect to 100 mass parts of organopolysiloxane of (A) component, Preferably it is 1-80 mass parts, Most preferably, it is 5-5. 50 parts by mass. If the amount is too small, sufficient rubber strength may not be obtained. Furthermore, in the case of millable rubber made from raw rubber, processability may be reduced. Moreover, when there are too many compounding quantities, it may be difficult to mix | blend and a rubber physical property may fall.

  In addition, when the addition reaction curing agent (B-1) is used as the component (B), the antistatic silicone rubber composition of the present invention has a curing rate in addition to the catalyst of the component (B-1). For the purpose of adjustment, an addition reaction control agent may be used as long as the object of the present invention is not impaired. Specific examples include acetylene alcohol-based control agents such as ethynylcyclohexanol and tetracyclomethylvinylpolysiloxane.

[Other ingredients]
In the antistatic silicone rubber composition of the present invention, a filler such as pulverized quartz, crystalline silica, diatomaceous earth, and calcium carbonate, and a colorant are added to the above components as long as the object of the present invention is not impaired. , Tear strength improvers, heat resistance improvers such as iron oxide and cerium oxide, flame retardant improvers such as titanium oxide and platinum compounds, acid acceptors, heat conductivity improvers such as alumina and boron nitride, mold release agents Known as thermosetting silicone rubber compositions such as various alkoxysilanes, particularly phenyl group-containing alkoxysilanes and hydrolysates thereof, diphenylsilanediol, carbon functional silane, silanol group-containing low molecular weight siloxanes as dispersants for fillers It is optional to add other fillers and additives.

  The thermosetting silicone rubber composition and other optional components can be obtained by mixing the above components with a known kneader such as a kneader, a Banbury mixer, a two-roller, etc., but the component (C) is blended. In this case, it is usually preferable to add the curing agent of the component (B) after mixing the organopolysiloxane of the component (A) and the reinforcing silica of the component (C).

  The antistatic agent contained in the antistatic silicone rubber composition of the present invention is not an electronic conductive material such as carbon black but an ion conductive antistatic agent of potassium salt. By using an ion conductive antistatic agent of potassium salt, excellent antistatic properties can be maintained even when the cured product of the antistatic silicone rubber composition is exposed to high temperatures, and yellowing is also suppressed. Is done.

などが例示される。これらは、１種単独で用いてもよく、２種以上を併用してもよい。 Specific examples of the potassium salt ion conductive antistatic agent include KBF ₄ , KClO ₄ , KPF ₆ , KAsF ₆ , KSbF ₆ , KSO ₃ CF ₃ , KN (SO ₂ CF ₃ ) ₂ , KN (SO ₂ C _{4 F 9) 2, KSO 3} C 4 F 9, KC (SO 2 CF 3) 3, KB (C 6 H 5) 4 and,

Etc. are exemplified. These may be used alone or in combination of two or more.

  Potassium salt ion conductive antistatic agent is especially paste with organopolysiloxane to improve dispersibility in millable (raw rubber-like) antistatic silicone rubber composition and exert stable effect It is preferable to make it. In this case, the organopolysiloxane may be the same as or different from the component (A), and may be raw rubber or oily (liquid). Preferred are dimethylpolysiloxane and methylvinylpolysiloxane. Moreover, in order to improve workability | operativity, you may add fillers, such as reinforcing silica and diatomaceous earth, to this paste.

The concentration of the potassium salt ion conductive antistatic agent in the paste is preferably 2 to 90% by mass, more preferably 5 to 80% by mass, and particularly preferably 10 to 50% by mass. If the concentration of the ionic conductive antistatic agent of the potassium salt is too low, the amount of paste added will increase, and the physical properties of the cured silicone rubber may decrease, and if it is too high, it may be difficult to make a paste. is there.
In preparing the paste, it is preferable to use three rolls in order to improve dispersibility.

  In addition, an ion conductive antistatic agent of potassium salt is preferably dissolved in a solvent and charged in order to improve dispersibility in a liquid antistatic silicone rubber composition at room temperature and to exhibit a stable effect. You may add as an inhibitor solution. As the solvent, alcohols such as methanol and ethanol, and esters such as aliphatic dicarboxylic acid esters such as adipic acid ester and sebacic acid ester are preferable.

  The concentration of the ion-conductive antistatic agent of potassium salt in the antistatic agent solution is preferably 1 to 90% by mass, more preferably 5 to 80% by mass, and particularly preferably 10 to 50% by mass. If the concentration of the ionic conductive antistatic agent of the potassium salt is too low, the amount of the solution added may increase, and the physical properties of the cured silicone rubber may decrease, and if it is too high, it may be difficult to dissolve. .

  The addition amount of the ion-conductive antistatic agent of potassium salt is 0.0001 to 5 parts by mass, preferably 0.0005 to 3 parts by mass with respect to 100 parts by mass of the thermosetting silicone rubber composition. Preferably it is 0.001-1 mass part, Most preferably, it is 0.001-0.5 mass part. When the amount is less than 0.0001 part by mass, the antistatic effect is insufficient. When the amount is more than 5 parts by mass, the physical properties and heat resistance of the silicone rubber are adversely affected.

  The potassium salt ion conductive antistatic agent may be added to the thermosetting silicone rubber composition at the time of preparation, or the thermosetting silicone rubber composition already prepared in advance. Or you may add at the time of this composition and other arbitrary component mixing manufacture.

  The antistatic silicone rubber composition of the present invention thus obtained becomes a silicone rubber having excellent antistatic properties by heat curing. As a molding method, a known molding method may be selected according to the shape and size of the target molded product. For example, methods such as injection molding, compression molding, injection molding, calendar molding, extrusion molding, coating, and screen printing are exemplified. The curing condition may be a known condition in the molding method, and is generally about 60 to 450 ° C., particularly 80 to 400 ° C., more preferably 120 to 200 ° C., for several seconds to 1 day. Further, for the purpose of reducing the compression set of the cured product, reducing the low-molecular siloxane component remaining in the silicone rubber, or removing the decomposition product of the organic peroxide, the temperature is 150 to 250 ° C. Preferably, post-curing (secondary vulcanization) may be performed in an oven at 200 to 250 ° C. for 1 hour or longer, preferably about 1 to 70 hours, and more preferably about 1 to 10 hours.

  As the antistatic performance of the obtained silicone rubber, static electricity was charged to the surface of the molded silicone rubber product by corona discharge using a static honestometer (manufactured by Sisid Electric Co., Ltd.), and then the charged voltage was It is preferable that the halving time (half life) is within 2 minutes, particularly within 1 minute.

  By curing the antistatic silicone rubber composition of the present invention by the above method, yellowing of the cured product can be suppressed. In particular, molding by any method of extrusion molding, press molding, injection molding, heat molding at 80 to 400 ° C., or secondary vulcanization at 150 to 250 ° C. can further suppress yellowing. An effect is obtained.

  EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated concretely, this invention is not restrict | limited to a following example. The degree of polymerization is a polystyrene-reduced weight average degree of polymerization by gel permeation chromatography analysis using toluene as a developing solvent, and the viscosity is measured with a rotational viscometer at room temperature (25 ° C.).

The amount of charge and the presence or absence of yellowing were measured by the following methods.
Using a static amount meter (Static Static Electricity Co., Ltd.), the surface of a 6 mm thick silicone rubber sheet after post-curing at 200 ° C. for 4 hours and after post-curing at 200 ° C. for 24 hours by corona discharge After charging 6 kV, the time when the charged voltage was halved was measured.

Measurement of presence or absence of yellowing by heat history Discoloration of 6 mm thick silicone rubber sheet after post-curing at 200 ° C. for 4 hours and after post-curing at 200 ° C. for 24 hours is indicated by a color difference meter (L, a, b). And measured according to the following criteria.
○: Good (no yellowing) (b value indicating yellow direction is in the range of +3 to -3)
Δ: Slightly yellow (b value indicating yellow direction exceeds +3 and less than +10)
X: Yellowing (b value indicating yellow direction is +10 or more)

An antistatic agent paste and an antistatic agent solution were prepared as follows.
[Preparation of antistatic paste 1]
An organic peroxide curable silicone rubber composition KE-541-U (manufactured by Shin-Etsu Chemical Co., Ltd.) is kneaded with 20 parts by mass of KN (SO ₂ CF ₃ ) ₂ as an antistatic agent for potassium salt. Then, an antistatic paste 1 was prepared.

[Preparation of Antistatic Agent Paste 2]
An antistatic agent paste 2 was prepared in the same manner as the antistatic agent paste 1 except that LiN (SO ₂ CF ₃ ) ₂ was used as the antistatic agent.

[Preparation of Antistatic Agent Solution 1]
An antistatic agent solution 1 was prepared by uniformly dissolving 20 parts by mass of KN (SO ₂ CF ₃ ) ₂ in 80 parts by mass of ethanol.

[Preparation of Antistatic Agent Solution 2]
An antistatic agent solution 2 was prepared in the same manner as the antistatic agent solution 1 except that LiN (SO ₂ CF ₃ ) ₂ was used as the antistatic agent.

[Example 1]
100 parts by mass of an organopolysiloxane raw rubber comprising 99.825 mol% of dimethylsiloxane units, 0.15 mol% of methylvinylsiloxane units, 0.025 mol% of dimethylvinylsiloxy units and having an average degree of polymerization of about 6,000, BET 45 parts by mass of fumed silica (Aerosil 200, manufactured by Nippon Aerosil Co., Ltd.) having a specific surface area of 200 m ² / g, a silanol group at both ends as a dispersant, an average polymerization degree of 15 and a viscosity at 25 ° C. of 30 mPa · 10 parts by mass of dimethylpolysiloxane as s was added, kneaded with a kneader, and heat-treated at 170 ° C. for 2 hours to prepare a composition (base compound).
0.25 parts by mass of the antistatic paste 1 and 2,5-dimethyl-2,5-bis (t-butylperoxy) hexane as a crosslinking agent with respect to 100 parts by mass of this composition (base compound) After adding a part by mass with two rolls and uniformly mixing to produce a raw rubber-like silicone rubber composition, the composition is press-cured for 10 minutes at 165 ° C. and 70 kgf / cm ² , 6 mm A thick sheet was produced. Next, post-curing for 4 hours and post-curing for 24 hours were performed in an oven at 200 ° C.
The silicone rubber was returned to room temperature, and the charge amount (half life) and the presence or absence of yellowing were measured. The results are shown in Table 1.

[Example 2]
The charge amount (half-life) and the presence or absence of yellowing were measured in the same manner as in Example 1 except that the addition amount of the antistatic agent paste 1 was changed to 0.5 parts by mass. The results are shown in Table 1.

[Example 3]
40 parts by mass of dimethylpolysiloxane blocked with dimethylvinylsiloxy group at both ends of a molecular chain having a viscosity of 1,000 mPa · s, 40 parts by mass of dimethylpolysiloxane blocked with dimethylvinylsiloxy at both ends of a molecular chain having a viscosity of 5,000 mPa · s, main chain A diorganosiloxane unit comprising 5 mol% of methyl vinyl siloxane units and 95 mol% of dimethyl siloxane units, and having a viscosity of 700 mPa · s and having a molecular chain at both ends trimethylsiloxy group-blocked dimethyl siloxane / methyl vinyl siloxane copolymer 20 parts by mass of coalescence, 20 parts by mass of hydrophobized fumed silica (R-972, manufactured by Nippon Aerosil Co., Ltd.) having a BET specific surface area of 110 m ² / g, both ends of a molecular chain having a viscosity of 50 mPa · s Trimethylsiloxy group-blocked methyl hydrogen polysiloxane Hydrogen atoms bonded to elementary atoms: 1.14% by mass) 5.0 parts by mass, molecular chain both ends dimethylhydrogen having a viscosity of 25 mPa · s and SiH groups in the middle of the molecular chain (side chain) Siloxy group-blocked dimethylsiloxane / methylhydrogensiloxane copolymer (hydrogen atom bonded to silicon atom: 0.54% by mass) 2.2 parts by mass [in the composition relative to the total of silicon atom-bonded vinyl groups in the composition The total molar ratio of SiH groups of SiH / SiVi = 3.7 mol / mol], 0.30 parts by mass of antistatic agent solution 1, 0.03 parts by mass of 1-ethynylcyclohexanol, chloroplatinic acid and divinyltetra A liquid silicone rubber composition in which a complex of methyldisiloxane is added in an amount of 15 ppm in terms of mass of platinum metal to the total of vinyl group-containing organopolysiloxane. It was prepared.
This composition was press-cured for 10 minutes under the conditions of 120 ° C. and 100 kgf / cm ² to prepare a 6 mm thick sheet. Next, post-curing for 4 hours and post-curing for 24 hours were performed in an oven at 200 ° C.
The silicone rubber was returned to room temperature, and the charge amount (half life) and the presence or absence of yellowing were measured. The results are shown in Table 1.

[Comparative Example 1]
Except for not adding the antistatic agent paste 1, the charge amount (half life) and the presence or absence of yellowing were measured in the same manner as in Example 1. The results are shown in Table 1.

[Comparative Example 2]
The amount of charge (half-life) and the presence or absence of yellowing were measured in the same manner as in Example 1 except that the antistatic agent paste 2 was used instead of the antistatic agent paste 1. The results are shown in Table 1.

[Comparative Example 3]
The amount of charge (half life) and the presence or absence of yellowing were measured in the same manner as in Example 3 except that the antistatic agent solution 1 was not added. The results are shown in Table 1.

[Comparative Example 4]
The amount of charge (half-life) and the presence or absence of yellowing were measured in the same manner as in Example 3 except that the antistatic agent solution 2 was used instead of the antistatic agent solution 1. The results are shown in Table 1.

Claims (8)

An antistatic silicone rubber composition characterized by containing 0.0001 to 5 parts by mass of an ion conductive antistatic agent of KN (SO ₂ CF ₃ ) ₂ in 100 parts by mass of a thermosetting silicone rubber composition . Thermosetting silicone rubber composition, antistatic silicone rubber composition according to claim 1, wherein the addition-curable. Thermosetting silicone rubber composition according to claim 1 antistatic silicone rubber composition wherein the organic peroxide curing type. Thermosetting silicone rubber composition, addition reaction curable organic peroxide antistatic silicone rubber composition of claim 1 wherein the co-vulcanizing with the curing. A method for suppressing yellowing of a cured antistatic silicone rubber product comprising heating and curing the antistatic silicone rubber composition according to any one of claims 1 to 4 to obtain a cured silicone rubber product. The method for suppressing yellowing of the cured antistatic silicone rubber according to claim 5 , wherein the antistatic silicone rubber composition is heat-molded at 80 to 400 ° C. The method for suppressing yellowing of the cured antistatic silicone rubber according to claim 5 or 6 , wherein the antistatic silicone rubber composition is further subjected to secondary vulcanization at 150 to 250 ° C. The antistatic silicone rubber composition according to any one of claims 5 to 7 , wherein the antistatic silicone rubber composition is molded by any one of extrusion molding, press molding, and injection molding. How to suppress.