JPS62252457A - Silicone rubber composition - Google Patents

Abstract

PURPOSE:To provide the titled compsn. having excellent durable oil bleeding resistance over a long period of time, by blending a polyorgano(hydrogen) siloxane with a polydiorganosiloxane, an inorg. filler and a platinum catalyst. CONSTITUTION:100pts. (by weight; the same applies hereinbelow) polyorganosiloxane (A) having a viscosity of 500-100,000cp at 25 deg.C and at least two structural units of formula I [wherein R<1> is an alkenyl; R<2> is a (substd.) monovalent group having no aliph. unsaturated bond; a is a number of 1-2; b is a number of 0-2 and a+b is a number of 1-3] per molecule is blended with a polyorganohydrogensiloxane (B) having at least three H atoms attached to Si per molecule, composed of a structural unit of formula II [wherein R<3> is a (substd.) monovalent group; c is b; d is a and c+d is a number of 1-3] in such an amount as to give 0.5-4.0 H atoms attached to Si per R<1> group in the component A, 1-40pts. polydiorganosiloxane (C) composed of a structural unit of formula III (wherein R<4> is R<2>; and e is a number of 1.98-2.02) and having a viscosity of 0.5-2.0 times that of the component A, 5-200pts. inorg. filler (D) and 1-100ppm (in terms of Pt) of a platinum catalyst (E).

Description

Detailed Description of the Invention [Technical Field of the Invention] The present invention relates to a roller for fixing a toner powder image formed on a copy paper by applying pressure and heating in a dry type electrophotographic copying machine or a printer. Regarding silicone rubber compositions, in particular, silicone oil can be continuously bled onto the roll surface obtained by polishing,
This invention relates to a silicone rubber composition for rolls that can dramatically increase toner releasability and copy life.

[Technical background of the invention and its problems] Among OA equipment, the spread of copying machines using dry electrophotography is remarkable, but on the other hand, in addition to streamlining the manufacturing process, there are also improvements in resource saving, energy saving, and long life. Demand for such things as standardization is also becoming stronger. By the way, in such a dry type electrophotographic copying machine, a toner powder image is transferred from a drum developed with light and toner onto a support such as paper, and the image is pressed with a heated rubber roll and fixed by heating and fusing. . A so-called heated roll fixing method is commonly used. The rolls used for this have long been mainly made of silicone rubber, which has excellent heat resistance and mold release properties, but extending the lifespan of silicone rubber is now a major theme.

Heat-setting rubber rolls used for this purpose include heat-curing silicone rubber crosslinked with organic peroxide (for example, Japanese Patent Publication No. 36-1277 and Japanese Patent Application Laid-open No. 54-1
There are two types of liquid silicone rubbers: condensation-type liquid silicone rubbers that crosslink at room temperature through condensation reactions (for example, see JP-A No. 52-2439), and liquid silicone rubbers that undergo addition reactions. An addition-type liquid silicone rubber crosslinked by (see, for example, Japanese Patent Publication No. 6 L-4855) is known.

Rolls manufactured using heat-curing silicone rubber are
Although it has excellent strength, it has poor releasability against toner and does not have sufficient copy life.
A mechanism for continuously supplying and applying a mold release agent such as silicone oil to the surface during use is required, which poses the problem of complicating the apparatus. Furthermore, in the case of heat-curing silicone rubber, unvulcanized rubber is non-flowing, so it is necessary to use two rolls for catalyst mixing and dispensing, and the molding method is press molding or rolling. It is not suitable for automation or continuous production process because it requires manual work and increases the number of steps in roll manufacturing, such as having to rely on molding, and it is also difficult to remove decomposition products of organic peroxides. There are major problems in terms of productivity, such as the need for secondary vulcanization.

On the other hand, as mentioned above, there are two types of liquid silicone rubber for rolls: condensation reaction type and addition reaction type, due to differences in curing mechanism. The main advantages of using liquid silicone rubber compared to heat-curable silicone rubber are (1) advantages in terms of moldability or productivity since the raw material polymer is liquid; (2) ) Low viscosity silicone oil that does not participate in the crosslinking reaction can be added in advance to the liquid silicone rubber composition;
The two points are that silicone oil is allowed to bleed onto the roll surface during use, and light release properties or toner release properties can be significantly improved, thereby eliminating the need for a release agent application mechanism.

In the case of condensation type liquid silicone rubber, it is advantageous in terms of molding because it is liquid, but it requires several hours to several days to cure, resulting in significantly lower productivity.
There are problems in that by-products are generated during the curing reaction and a step is required to remove them after the reaction is completed. In contrast, so-called addition-type liquid silicone rubbers that use platinum or platinum compounds as catalysts have the advantage that the curing time can be adjusted from several seconds to several minutes depending on the heating temperature, and that the composition before curing is Since it is a liquid, it can be automatically and continuously produced using a simple injection molding machine. Furthermore, there is no need for polishing after roll forming, and since no reaction by-products are generated during curing, there is no need to remove them, and significant improvements are recognized in terms of moldability and productivity.

Next, with regard to easy releasability or toner releasability due to the addition of silicone oil, it is particularly necessary to add low-viscosity silicone oil to the above-mentioned condensation type liquid silicone rubber.

In other words, if the viscosity of the silicone oil to be added is high,
This is because the oil does not bleed sufficiently to the roll surface, making it impossible to obtain excellent mold release properties.

However, when low-viscosity silicone oil is used, it bleeds out extremely quickly during the pressurizing and heating process in practical use, so although the initial mold release property is excellent, it retains its mold release property over a long period of time. There is a big problem that it cannot be done.

On the other hand, addition-type liquid silicone rubber also uses low-viscosity silicone oil from the same point of view as condensation-type rubber, and therefore has the same problems as described above. To explain in more detail, addition-type rubber tends to be inferior to condensation-type rubber in terms of oil bleed properties, and especially for rolls whose surfaces are polished before use, the oil bleed properties fluctuate significantly. However, there is a drawback of poor reliability in practical use, and improvement of this problem is desperately needed.

[Object of the present invention] The present invention solves the above problems and provides a silicone rubber composition suitable as a material for heat fixing rolls used in dry electrophotographic copying machines, printers, etc.
In particular, by using addition-type liquid silicone rubber as a constituent component, silicone oil (polydiorganosiloxane) remains permanently on the surface when it is cured, molded, and finally polished to form a roll. The purpose of the present invention is to provide a silicone rubber composition for rolls that is useful for retaining releasability to toner and extending copy life when it bleeds.

[Structure of the Invention] The inventors of the present invention focused on the following points in order to improve the above-mentioned problems, especially the oil bleed property, and as a result 1
The present invention has now been completed.

That is, in the composition disclosed in the above-mentioned Japanese Patent Publication No. 61-4855, although the appropriate viscosity ranges of the two types of organopolysiloxanes, which are the rubber component and the oil component, partially overlap, overall, In particular, the upper limit values are significantly different, and the lower limit values are also low.
However, in the present invention, by reducing the difference in viscosity between polyorganosiloxane as a rubber component and polydiorganosiloxane as an oil component, and preferably making them substantially the same, the lower limit of their viscosity can be increased. By setting this, it is possible to continuously exhibit excellent oil bleed properties over a long period of time.

That is, the silicone rubber composition of the present invention.

(A) General formula.

(R”), (R2)bsi04-(6*b) (I
) (wherein, R1 represents an alkenyl group, R2 represents a substituted or unsubstituted monovalent group containing no aliphatic unsaturated bond; a represents 1 or 2; b represents 0, 1 or 2; Representation;
a+b represents 1.2 or 3) in the molecule, and the viscosity at 25°C is 500 to 100.000 cP
Polyorganosiloxane, ioo parts by weight; (B) General formula, (R3) Hd Si 04-(.+, 1)
(II) (wherein R3 represents a substituted or unsubstituted monovalent group; C represents 0, 1 or 2; d represents 1 or 2
c + d represents 1, 2 or 3) A polyorganohydrodiene siloxane having at least three hydrogen atoms bonded to a silicon atom in the molecule is used as the polyorganohydrogensiloxane of component (A). An amount such that the amount of hydrogen atoms bonded to silicon atoms is 0.5 to 4.0 per R1 group in the siloxane; (C) Inorganic filler, 5 to 200 parts by weight; (n)
General formula, (R')S 1o4-e (m) (wherein, R4 represents a substituted or unsubstituted monovalent group that does not contain an aliphatic unsaturated bond; e is 1.98 to 2.02 0.5 of component (A)
polydiorganosiloxane with a viscosity of ~2.0 times,
1 to 40 parts by weight; and (E) a platinum-based catalyst in an amount of 1 to 1100 pp as platinum atoms based on component (A).

The polyorganosiloxane as component (A) used in the present invention has at least two structural units represented by the general formula (I) in the molecule.

Examples of the fulkenyl group R1 in formula (1) include vinyl group, allyl group, 1-butenyl group, and 1-hexenyl group. A vinyl group is most preferable because of its superior properties.)12
Examples of substituted or unsubstituted monovalent groups that do not contain an aliphatic unsaturated group include alkyl groups such as methyl, ethyl, propyl, butyl, hexyl, and dodecyl; Aryl group; examples include aralkyl groups such as β-phenylethyl group and β-phenylpropyl group; furthermore, chloromethyl group, 313
Mention may also be made of substituted hydrocarbon groups such as the 3-triple oroprobyl group. Among these monovalent groups, 1
The degree of polymerization of polyorganosiloxane (
A methyl group is most preferred because it can provide a high viscosity (viscosity) and keep the viscosity of the polyorganosiloxane low before curing. Such a formula (I)
The structural unit represented by may be present either at the molecular chain end or in the molecular chain of the polyorganosiloxane, but in order to impart excellent mechanical properties to the cured product, at least one molecular chain end must be present. Preferably, it exists in

Further, the polyorganosiloxane as component (A) needs to have a viscosity of 500 to 100,000 cP at 25°C. When the viscosity is less than 500 cP, it is difficult to impart sufficient elongation and elasticity to the cured product;
If it exceeds 00.0OOcP, problems such as deterioration of workability during casting or processing will occur. Furthermore, especially when considering improvement of mechanical strength and oil bleed property, it is preferable that the viscosity is 2,500 to 100,000 cP. It can be used as a polymer or a mixture thereof.

The polyorganohydrodiene siloxane used in the present invention consists of a structural unit represented by the above general formula (■),
In the formula 0, which has at least 3 hydrogen atoms bonded to a silicon atom in the molecule, R3 is substituted or unsubstituted 1
Examples of the valent group include those similar to those exemplified for R2 in the structural unit represented by the general formula (I) above, but from the viewpoint of ease of synthesis, a methyl group is most preferred. In addition, this polyorganohydrodiene siloxane preferably has a viscosity of 1 to 10.000 cP at 25°C for ease of synthesis and handling. It can be used as a monobranched or cyclic polymer, or a mixture thereof.

The blending ratio of component (B) is such that the number of silicon-bonded hydrogen atoms in component (B) is 0.5 to 4.0 per fluorenyl group in component (A), Preferably 1.
The amount is 0 to 3.0. Number of hydrogen atoms is 0
．． If the number of hydrogen atoms is less than 5, the curing of the composition will not proceed sufficiently and the hardness of the composition after curing will be low. The physical properties of an object are reduced.

The inorganic filler, component (C), used in the present invention is one that makes the viscosity and fluidity of the composition appropriate, and imparts excellent mechanical strength, hardness, thermal conductivity, etc. to the cured product. . Examples of such inorganic fillers include fumed silica, precipitated silica, fused silica, fine quartz powder, diatomaceous earth, alumina, aluminum silicate, iron oxide, titanium oxide, zinc oxide, calcium carbonate, and carbon black. These can be used in combination of one or more types. In addition, these inorganic fillers can be coated with polyorganosiloxanes such as polydimethylsiloxane and octamethylcyclotetrasiloxane, such as hexamethyldisilazane and 1,1,3.3-tetramethyl-1°, if necessary. Silazane such as 3-divinyldisilazane:
and organosilanes such as vinyltriethoxysilane; and those treated with organosilicon compounds such as vinyltriethoxysilane can be used.

The blending ratio of component (C) is 5 to 200 parts by weight, preferably 10 to 100 parts by weight, per 100 parts by weight of component (A). If the blending ratio is less than 5 parts by weight, the mechanical strength, hardness and thermal conductivity of the cured product will be poor;
If the amount exceeds 1 part by weight, the fluidity of the composition will deteriorate and the cured product will also become brittle.

The polydiorganosiloxane of component CD) used in the present invention is composed of the constituent units represented by the above general formula (III). As the group, for example, the same groups as those exemplified for R2 in the structural unit represented by general formula (I) above can be mentioned, but the group is easy to synthesize and has excellent toner releasability. It is preferable that 60% or more of the polydiorganosiloxane is composed of methyl groups.The polydiorganosiloxane is most preferably composed of dimethylsiloxane units, but of course there are other commonly used polydiorganosiloxanes. Examples of diorganosiloxane units include dimethylsiloxane units, methylphenylsiloxane units, diethylsiloxane units, ethylmethylsiloxane units, ethylphenylsiloxane units, diphenylsiloxane units, methyl-3,3,3-trifluoropropylsiloxane units, Examples include ethyl-3,3,3-trifluoropropylsiloxane units and phenyl-3°3.3-)lifluoropropylsiloxane units, and one or more of these can be used.

In order to obtain a long copy life, the viscosity of the polyorganosiloxane needs to be in the range of 0.5 to 2.0 times the above-mentioned viscosity of the polyorganosiloxane of component (A).

If the viscosity is less than 0.5 times or more than 2.0 times, the object of the present invention cannot be fully achieved, and the viscosity of this component (D) is not particularly limited as long as it is within the above range. However, in order to improve the rubber strength when formed into a roll and the reliability in copying, it is necessary to
,000 cP, and more preferably as close as possible to the viscosity value of component (A).

Furthermore, this component CD) is a substantially linear polymer, and from the viewpoints of not participating in addition reactions during curing and improving oil bleed to the roll surface, hydroxyl groups are added to the molecular chain. It is preferable that the polydiorganosiloxane is a polydiorganosiloxane in which the molecular chain terminals are blocked with a trimethylsiloxy group, a dimethylphenylsiloxy group, or the like.

The blending ratio of component (D) is 1 to 40 parts by weight per 100 parts of component (A), and it is particularly preferable that the content in the composition is 2 to 20% by weight. If the amount is less than 1 part by weight, the object of the present invention cannot be fully achieved, and if it exceeds 40 parts by weight, oil bleed due to excess component (B) may occur when formed into a roll. A phenomenon in which the diameter of the roll becomes thinner occurs, impairing reliability during copying.

The (E) ja platinum-based catalyst used in the present invention is:

This is a component that promotes the addition reaction between the alkenyl group in component (A) and the hydrosilyl group in component CB. Examples of such platinum-based catalysts include simple platinum, chloroplatinic acid, platinum coordination compounds such as platinum-olefin complexes, and platinum-alcohol complexes.

The blending ratio of component (E) is 1 to 1100 pp, preferably 2 to 50 pp as platinum atoms, relative to component (A).
If the compounding ratio of p- is less than 1 ppm, the object of the present invention cannot be achieved, and even if it exceeds 100 PP, no further improvement in the curing rate can be achieved.

The composition of the present invention can be produced by uniformly mixing the five components (A) to (E) above. The specific steps in this case are not particularly limited, but
It is preferable to add component (C) to component (A) and disperse it as uniformly as possible before adding and mixing the other components. This is because the curing reaction starts immediately when they coexist. Therefore, it is preferable that component (A) and components (B) and (E) are coexisted immediately before casting or injection molding.In this case, in order to suppress the curing reaction, acetylene It is also possible to add addition reaction retarders such as olefin compounds, organic nitrogen compounds, and organic phosphorus compounds. Furthermore, mold release agents other than polydiorganosiloxane, antistatic agents, flame retardants, pigments, glass fibers, carbon fibers, and the like may be added to the composition of the present invention, if necessary.

[Examples] Hereinafter, the present invention will be described in further detail by presenting Examples and Comparative Examples. In addition, in Examples and Comparative Examples, "part"
All represent "parts by weight."

Example 1 100 parts of polydimethylsiloxane base oil with a viscosity of 3.000 cP at 25°C, both ends of the molecular chain capped with dimethylvinylsilyl groups, and 35 parts of Aerosil 200 (manufactured by Tegussa ■, trade name) as fumes silica. ,(
CH3) 2 parts of polyorganohydrodiene siloxane consisting of 2H9io units and 5i02 units, containing 1.02% by weight of hydrogen atoms bonded to silicon atoms, and having a viscosity of 21 cP at 25°C,
．． The present invention was prepared by mixing 15 parts of polydimethylsiloxane in which both ends of the molecular chain of 0OOcP are capped with trimethylsilyl groups and an isopropyl alcohol solution of chloroplatinic acid at 20 ppm based on the base oil as platinum atoms and uniformly dispersing each component. A composition was prepared.

Comparative Example 1 In Example 1, the viscosity at 25°C was 3.000c.
A comparative composition was produced in the same manner except that the polydimethylsiloxane capped with P's trimethylsilyl group was not used.

Comparative Example 2 In Example 1, the viscosity at 25°C was 3.000c.
A comparative composition was prepared in the same manner, except that 15 parts of polydimethylsiloxane, which had a viscosity at 25° C. of 100 cP and whose molecular chain was blocked at both ends of the molecular chain, was used instead of the polydimethylsiloxane blocked with trimethylsilyl groups of P. was manufactured.

Comparative Example 3 In Example 1, the viscosity at 25°C was 3.000c.
In place of polydimethylsiloxane blocked with trimethylsilyl groups of P, the viscosity at 25°C is 100,000.
A comparative composition was produced in the same manner except that 15 parts of polydimethylsiloxane in which both ends of the molecular chain were blocked with trimethylsilyl groups of cP was used.

The compositions obtained in the above Examples and Comparative Examples 1 to 3 were put into a chrome-plated mold, and the weight was 30 kg/ctll.
Press at 170°C for 10 minutes under the pressure of 2Ill
Silicone rubber sheets with a thickness of I11 and a thickness of 6 mm were obtained.

Next, this sheet was subjected to auto-vulcanization at 200° C. for 4 hours, and then mechanical properties were measured and a surface tack test was conducted at room temperature based on JIS K2SO3. The result is the first
The surface adhesion test shown in the table is based on Note 1.

Note 11: 1m2.5c layer on silicone rubber sheet, length 10c
10g of m tape (Sumitomo 3M Scotch 5490)
After crimping for about 5 hours at room temperature with a pressure of 7 cm, a 180° peel test was performed using an autograph at a peeling rate of 10 layers/layer, and the average load at that time was calculated based on the width of the tape.
The smaller the peeling force, expressed in terms of peeling force (unit: g/c layer), is the better the surface non-adhesion.

In addition, each composition was press-cured under the above conditions in a cylindrical mold into which a roll core metal treated with a primer was inserted, and after further auto-vulcanization at 200°C for 4 hours, it was polished and heat-fixed. I got a roll for it.

This roll was subjected to the Note 2 copy life test. The results are shown in Table 1.

Note 2 The fixing roll manufactured as described above was replaced with the attached fixing roll of the Toshiba Odry 7811 dry electrophotographic copying machine (product name: manufactured by Toshiba), and it was continuously operated under the following operating conditions. Copying was performed and the number of copies until stains (Macbeth density 1.0 or more) appeared on the fixing roll was defined as the copy life.

Fixing temperature: 180°C Fixing pressure: 4 kgf/crd Original Character document with image area ratio of approx. 30% Copying speed: 28 sheets/min Copy paper: For Toshiba RheoDry 7811 (made by Toshiba, product name) Size: A4 Toner used: For Toshiba RheoDry 7811 Toner (manufactured by Toshiba, trade name) Table 1 Example 2 100 parts of polydimethylsiloxane base oil with a viscosity of 10.000 cP at 25°C and whose molecular chains are blocked at both ends with dimethylvinylsilyl groups, Crystally VX
-3 (manufactured by Ryumori Co., Ltd., trade name) 40 parts, both terminals are blocked with trimethylsilyl groups, the hydrogen atom content bonded to silicon atoms is 0.8% by weight, and the viscosity at 25°C is 2.
0 cP linear polymethylhydrodiene siloxane 2
1 part, 20 parts of polydimethylsiloxane containing 5 mol % of diphenylsiloxane units, end-capped with trimethylsilyl groups and having a viscosity of 6,000 cP at 25°C, an isopropyl alcohol solution of chloroplatinic acid (as platinum based on base oil) l The composition of the present invention was prepared by mixing and uniformly dispersing Oppm.

Example 3 In Example 2, the viscosity at 25°C is 6.000 cP
Instead of polydimethylsiloxane, it contains 16 mol% of diphenylsiloxane units, the ends of the molecular chain are blocked with trimethylsilyl groups, and the viscosity at 25°C is 15.0%.
A composition of the present invention was prepared in the same manner except that 10 parts of 00 cP polydimethylsiloxane was used.

Juice Example 4 In Example 2, the viscosity at 25°C was 6.0OOc.
It contains 5 mol% of diphenylsiloxane units instead of polydimethylsiloxane in P, the molecular chain ends are blocked with trimethylsilyl groups, and the viscosity at 25°C is 2.000.
A comparative composition was prepared in the same manner except that 20 parts of cP polydimethylsiloxane was used.

Comparative Example 5 In Example 2, the viscosity at 25°C was 6.000c.
Instead of polydimethylsiloxane in P, the end of the molecular chain is blocked with a trimethyl group, and the viscosity at 25°C is 50.
A comparative composition was produced in the same manner except that 30 parts of cP polydimethylsiloxane was used.

Using each of the compositions obtained in Examples 2 and 3 and Comparative Examples 4 and 5, 2Il111 was prepared in the same manner as in Example 1.
A sheet with a thickness of 6+sm was obtained, and a heat fixing roll was obtained. Using the obtained sheet, mechanical properties were measured in the same manner as in Example 1, and a toner peeling test was conducted by the method shown in Note 3. In addition, a copy life test was conducted using a heat fixing roll according to the method shown in Note 2.

Note 31 A 2mm thick sheet that has been heated to room temperature after being heated is
Cut into two tanzag-shaped pieces of m x 130 m layers, and thoroughly polish the surface with sandpaper (No. 1,000). The edge of the polished surface of this sheet 30 Feng Cao xi
Toner EP310 (manufactured by Minolta ■, brand name) for the oo layer intestine
Apply evenly to the surface. Then, as shown in the drawing, 2
Place the toner-coated sides of the two sheets on top of each other and heat the sheets at 180℃ for 3
Crimp for 0 minutes (with a 1,000g weight on it). In addition, in the drawing, 1l = 30 layers, J12 = 100+s
The toner was then returned to room temperature and pulled in a 180° direction using a tensile tester with an automatic recorder, and the force required to peel off the crimped part was defined as the "toner peeling force." The smaller this value, the better the peeling property. represents something.

Table 2 [Effects of the Invention] As explained above, the composition of the present invention contains the polyorganosiloxane of component (A) used as its essential component;
By appropriately adjusting the viscosity range of the component D) polydiorganosiloxane and by setting a high lower limit of these viscosity, it can be used as a constituent material for heat fixing rolls used in dry type electrophotographic copying machines, printers, etc. In this case, it is possible to exhibit the most severe oil bleed property on the surface of the roll over a long period of time. Since it has such excellent oil bleed properties, it has excellent toner releasability and can dramatically extend copy life (see Tables 1 and 2).Furthermore, the present invention The composition described above is sufficiently satisfactory in terms of hardness and tensile strength of the cured product (see Tables 1 and 2). It is useful as a constituent material of a heat-fixing roll that is put into practical use after being polished.

[Brief explanation of drawings]

The drawings are diagrams showing the state of a sheet in a toner peeling test of an example of the present invention.

Claims (3)

[Claims] (1) (A) General formula, (R^1)_a(R^2)_bSiO_4_-_(_a
___+_b_)_/_2(I) (In the formula, R^1 represents an alkenyl group; R^2 represents a substituted or unsubstituted monovalent group that does not contain an aliphatic unsaturated bond; a is 1 or 2 b represents 0, 1 or 2; a+b represents 1, 2 or 3) in the molecule and has a viscosity of 500 to 100,000 cP at 25°C
100 parts by weight of polyorganosiloxane; (B) General formula, (R^3)_cHdSiO_4_-_(_c_+_d_
)_/_2(II) (wherein, R^3 represents a substituted or unsubstituted monovalent group; c represents 0, 1 or 2; d represents 1 or 2; c+d represents 1, 2 or 3) and has at least three hydrogen atoms bonded to silicon atoms in the molecule. (C) Inorganic filler, 5 to 200 parts by weight; (D) General formula, (R^ 4)_eSiO_4_−_e_/_2(III)(
In the formula, R^4 represents a substituted or unsubstituted monovalent group containing no aliphatic unsaturated bond; e represents a number from 1.98 to 2.02); A) component 0
．． 1 to 40 parts by weight of polydiorganosiloxane having a viscosity of 5 to 2.0 times; and (E) a platinum-based catalyst in an amount of 1 to 100 ppm as platinum atoms based on component (A); A silicone rubber composition. (2) The silicone rubber composition according to claim 1, wherein component (A) has a viscosity of 2,500 to 100,000 cP at 25°C. (3) The silicone rubber composition according to claim 1, wherein component (D) has a viscosity of 5,000 to 100,000 cP at 25°C.