JP2003147207A - Low-specific gravity liquid silicone rubber composition and molded product of low-specific gravity silicone rubber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a low-specific gravity liquid silicone rubber composition having excellent dimensional stability during molding and capable of affording a low-specific gravity silicone rubber having a small dimensional change by thermal expansion after curing and excellent dimensional stability when heated or cooled. SOLUTION: The low-specific gravity liquid silicone rubber composition comprises (A) a liquid diorganopolysiloxane containing at least 2 silicon atom- bound alkenyl groups in one molecule and having 100-100,000 mPa.s viscosity, (B) a hydrophobized reinforcing fine powdery silica filler, (C) an organopolysiloxane containing at least 2 silicon atom-bound hydrogen atoms in one molecule, (D) a platinum catalyst and (E) a hollow resin powder having a shell composed of a thermoplastic resin other than a silicone resin and encapsulating a gas and/or a volatile liquid therein and (F) water.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low specific gravity liquid silicone rubber composition which is cured by a hydrosilylation reaction, and more specifically, a low specific gravity silicone rubber molded article having excellent dimensional stability during heating and cooling. A specific gravity liquid silicone rubber composition and a low specific gravity silicone rubber molded product obtained by curing the same.

[0002]

2. Description of the Related Art Since low specific gravity silicone rubber has excellent heat resistance, weather resistance and light weight, its characteristics are utilized to make use of sealing material; packing; gasket; O-ring etc .; copiers, printers, fax machines, etc. It is used in a wide range of applications such as coating materials for rolls used in. Conventionally, as such a low specific gravity silicone rubber composition, a low specific gravity liquid silicone rubber composition in which a thermoplastic hollow powder that expands by heat is blended with a silicone rubber composition is known (see Japanese Patent Laid-Open No. 5-209080). .

However, the silicone rubber molded product obtained by curing this composition has a problem that the volume change of the molded product due to heating is extremely large due to the thermal expansion of the hollow body to be blended. Therefore, this composition is used for applications in which dimensional accuracy in heat molding using a mold or the like is required, and dimensional stability when heated or cooled is required, for example, copiers, printers, fax machines, etc. However, it was not satisfactory as a material for roll coating materials and automobile gaskets.

On the other hand, in a silicone rubber composition containing an inorganic hollow powder such as a glass hollow body, since the hollow body does not have thermal expansion, the volume change due to heating of the above silicone rubber molded product becomes small. However, when the inorganic hollow powder is blended in the composition, the hollow powder is easily broken, and the hardness of the obtained silicone rubber molded article becomes too high when blended in an amount sufficient for lowering the specific gravity, so that in a high temperature environment. When used for a long time, there is a problem that the hardness of the molded product tends to change significantly.

[0005]

The present inventors have arrived at the present invention as a result of extensive studies to solve the above problems. That is, the object of the present invention is a low specific gravity silicone rubber composition containing a hollow resin powder, which has excellent dimensional accuracy stability during molding, little dimensional change during heating and cooling of the molded product after curing, and is small and It is an object of the present invention to provide a low specific gravity liquid silicone rubber composition capable of forming a low specific gravity silicone rubber molded product having uniform cells.

[0006]

Means for Solving the Problems The above-mentioned object is “(A) Liquid diorganopolysiloxane containing at least two silicon-bonded alkenyl groups in one molecule and having a viscosity of 100 to 100,000 mPa · s. 100 parts by weight, (B) 1 to 50 parts by weight of hydrophobizing reinforcing fine powdery silica filler, (C) Organopolysiloxane containing at least 2 silicon atom-bonded hydrogen atoms in one molecule (in this component Amount in which the molar ratio of the silicon atom-bonded hydrogen atoms to the silicon atom-bonded alkenyl groups in the component (A) is (0.3: 1) to (5: 1)}, (D) Platinum catalyst {(A) An amount of 0.1 to 500 parts by weight as platinum metal with respect to 1 million parts by weight of the component}, (E) The outer shell is made of a thermoplastic resin other than a silicone resin, and contains a gas and / or a volatile liquid. Hollow resin powder 0.1 to 20 parts by weight and (F) water {amount in which the ratio of the volume of this component to the volume of (E) component is (0.01: 1) to (5: 1)}. A low specific gravity liquid silicone rubber composition, and a low specific gravity liquid silicone rubber composition obtained by blending 1 to 30 parts by weight of hollow powder (G) whose outer shell is made of an inorganic material into the low specific gravity liquid silicone rubber composition. And "a low specific gravity silicone rubber molded product obtained by curing the above low specific gravity liquid silicone rubber composition".

To explain this, it is used in the present invention.
The component (A) is used because the composition of the present invention cures to become rubber.
Is the main component of. Such liquid diorganopolysiloxane
Sun is the average unit formula: R_aSiO_{(4-a) / 2} (In the formula, R is a monovalent hydrocarbon group or a halogenated alkyl group.
And a monovalent hydrocarbon group such as a methyl group and an ethyl group.
Alkyl group such as vinyl group, propyl group; vinyl group, allyl group
Alkenyl groups such as; cycloalkyl such as cyclohexyl groups
Group; aralkyl group such as β-phenylethyl group; phenyl
An aryl group such as a ru group is exemplified. Halogenated alkyl group
As a 3-chloropropyl group, 3,3,3-triflu
An oropropyl group is exemplified. a is a number from 1.8 to 2.3
Is. ). Such an organopolyscillo
Xane usually has a viscosity of 100 to 10 at 25 ° C.
It is within the range of 2,000 mPa · s. Also its molecule
The structure is substantially linear, but part of the molecular chain is branched
May be. With such a diorganopolysiloxane
The end of the molecule chain is a dimethyl vinylsiloxy group-blocking dime
Chill polysiloxane, dimethyl vinyl silo at both ends of molecular chain
Xyl group-blocked dimethyl siloxane / methyl vinyl siloxa
Copolymer, dimethyl group with silanol groups at both ends of the molecular chain
Roxane / methyl vinyl siloxane copolymer, both molecular chains
Dimethylsiloxane with terminal dimethylvinylsiloxy groups blocked
-Methylphenyl siloxane copolymer, both ends of the molecular chain
Methyl vinyl siloxy group-blocked dimethyl siloxane / meth
Ruvinyl siloxane / methylphenyl siloxane copolymer
Body, molecular chain both ends dimethylvinylsiloxy group blocking dimethyl
Rusiloxane / diphenylsiloxane copolymer, molecular chain
Both ends dimethyl vinyl siloxy group blocked dimethyl siloxa
And methyl vinyl siloxane diphenyl siloxane
Polymer, molecular chain both ends dimethylvinylsiloxy group blocking di
Methyl siloxane / methyl (3,3,3-trifluoro
Propyl) siloxane copolymer, both ends of the molecular chain dimethyl
Vinylsiloxy group-blocked dimethyl siloxane / methyl vinyl
Rusiloxane methyl (3,3,3-trifluoropro
Pill) siloxane copolymers and two or more of these
The following mixture is exemplified.

The component (B) has a function of improving the physical strength of the low specific gravity silicone rubber molded product obtained by curing the composition of the present invention. Incidentally. Keeping the fluidity of the composition of the present invention,
In addition, the surface of this component needs to be hydrophobized in order to facilitate blending with the component (A). Examples of such a hydrophobicity-reinforcing fine powdery silica filler include a dry type such as fumed silica which is hydrophobized with an organosilicon compound such as organochlorosilane, organoalkoxysilane, hexaorganodisilazane, cyclodiorganopolysiloxane. Wet process silica such as process silica and precipitated silica is exemplified.
These hydrophobized reinforcing fine powder silica fillers may be used alone or in combination. In addition, when preparing the composition of the present invention, the surface of the silica filler may be hydrophobized while kneading the component (A), the untreated reinforcing fine powder silica filler and the above-mentioned surface treatment agent. Good. This component is B
The ET method specific surface area is preferably 50 m ² / g or more, and more preferably 100 m ² / g or more. The blending amount of this component is 100 parts by weight of the component (A).
It is in the range of 1 to 50 parts by weight, preferably 1 to 25 parts by weight, and more preferably 5 to 25 parts by weight. This is because if it is less than the lower limit of the above range, the mechanical strength of the molded product obtained by curing the composition of the present invention is insufficient, and if it exceeds the upper limit of the above range, it becomes difficult to mix it with the component (A). This is because the composition of the present invention may have an excessively high viscosity and may deteriorate the workability in handling.

The component (C) is a crosslinking agent, which will be described later.
(D) Silicon atom-bonded water of this component in the presence of a platinum-based catalyst
The elemental atom becomes a silicon atom-bonded alkenyl group in the component (A).
It cures by addition reaction. This component is low in one molecule
Having at least two silicon-bonded hydrogen atoms
is necessary. Here, the presence of other than silicon-bonded hydrogen atoms
Examples of the machine group are methyl group, ethyl group, and propyl group.
Alkyl group; exemplified by phenyl group and tolyl group
An aryl group is exemplified. The molecular structure of this component is linear
Any of linear, branched, linear, and mesh-like
Good. As such an organopolysiloxane,
Polymethyl high end blocked with trimethylsiloxy groups at both ends of the molecular chain
Drogen siloxane, trimethylsiloxy on both ends of the molecular chain
Si-group blocked dimethyl siloxane / methyl hydrogen
Roxane copolymer, dimethyl hydrogen at both ends of the molecular chain
Nyloxy group-blocked dimethylsiloxane, methylhydro
Gen siloxane copolymer, cyclic dimethyl siloxane
Methyl hydrogen siloxane copolymer, cyclic polymer
Cylhydrogen siloxane, formula: (CH₃)₃SiO
_{1 / 2}A siloxane unit represented by a unit, formula: (CH₃)₂H
SiO_1/2Siloxane unit represented by unit and formula: S
iO_4/2Organopo consisting of siloxane units represented by
Lisiloxane, formula: (CH₃)₂HSiO_1/2Expressed in units
Siloxane unit and formula: CH₃SiO_3/2Shown in units
Organopolysiloxa comprising siloxane units
, Formula: (CH₃)₂HSiO_1/2Shiroki expressed in units
Sun unit, formula: (CH₃)₂SiO_2/2Unit and formula: C
H₃SiO_3/2Unit consisting of siloxane units
Luganopolysiloxane, dimethylhydro at both molecular chain ends
Gensiloxy group-blocked polydimethylsiloxane, molecular chain
Both ends dimethyl hydrogen siloxy group blocked dimethyl
Siloxane / methylphenylsiloxane copolymer, molecule
Dimethy that blocks both ends of the chain with dimethyl hydrogensiloxy groups
Rusiloxane methyl (3,3,3-trifluoropro
Pill) siloxane copolymers and their organopoly
Illustrative is a mixture of two or more siloxanes. Book Olga
The viscosity of nopolysiloxane at 25 ° C is not particularly limited.
No range, but in the range of 2-100,000 mPa · s
Is preferred.

The blending amount of this component is such that the ratio of the number of moles of silicon atom-bonded hydrogen atoms in this component to the number of moles of silicon atom-bonded alkenyl groups in component (A) is (0.3: 1) to (5). :
It is the amount that becomes 1). This is because the ratio of this number of moles is (0.
If it is less than 3: 1), the crosslink density is too low and the cured product does not become a rubber-like elastic body, and if it exceeds (5: 1), non-uniform foam cells are generated due to the dehydrogenation reaction and the silicone after curing is cured. This is because the heat resistance of rubber may be reduced.

The component (D) is a catalyst for curing the composition of the present invention, and is used for the hydrosilylation reaction between the silicon atom-bonded alkenyl group in the component (A) and the silicon atom-bonded hydrogen atom in the component (C). It promotes, and known ones can be used. Such platinum-based catalysts include platinum fine powder,
Examples are platinum black, chloroplatinic acid, alcohol-modified chloroplatinic acid, olefin complexes of chloroplatinic acid, complexes of chloroplatinic acid and alkenylsiloxanes, and thermoplastic resin powders containing these platinum-based catalysts. Platinum-based catalysts are used as platinum metal in an amount of 0.1
It is preferably about 500 parts by weight.

The component (E) is an essential component for reducing the weight of the silicone rubber molded product like a foam. The thermoplastic resin as the outer shell of this component is selected from those other than silicone resin, polyethylene, polystyrene, polyvinyl acetate, polyvinyl chloride, polyvinylidene chloride, polyacrylonitrile, polymethacrylonitrile, polymethylmethacrylate, polybutadiene. , Vinyl polymers such as polychloroprene and copolymers thereof; nylon 6,
Examples thereof include polyamides such as nylon 66; polyesters such as polyethylene terephthalate and polybutylene terephthalate; polycarbonates, polyacetals and alloys thereof. The surface of this component may be treated with calcium carbonate, talc, titanium oxide or the like for the purpose of improving strength or improving dispersibility. The softening start temperature of the hollow resin powder is preferably in the range of 70 ° C to 200 ° C, and particularly preferably 70 to 160 ° C.

The substances contained in the hollow resin powder include substances that are gases at room temperature, such as air, nitrogen, and inert gases, as well as propane, butane, isobutane, pentane,
Hydrocarbons such as isopentane; alcohols such as methanol and ethanol; halogenated hydrocarbons such as dichloroethane, trichloroethane and trichloroethylene; volatile liquids having a low boiling point such as diethyl ether and isopropyl ether are exemplified.

The particle size of the hollow resin powder is 5 to 5 at room temperature.
It is preferably 300 μm, and particularly 5 to 100 μm.
It is preferably m. This is because when the content is less than the lower limit of the above range, the specific gravity of the silicone rubber does not become sufficiently small, and when it exceeds the upper limit of the above range, the strength of the hollow resin powder itself becomes low. This is because the outer shell may break when the molded product is molded. Such hollow resin powders are roughly classified into unexpanded products (true specific gravity of 0.1 to 1.3) and pre-expanded products (true specific gravity of 0.01 to 0.10). Expander (EX
PANCEL) or from Matsumoto Yushi-Seiyaku Co., Ltd. as Matsumoto Microspheres.

The blending amount of this component is 0.1 to 20 parts by weight, preferably 1 to 15 parts by weight, relative to 100 parts by weight of component (A), but the true specific gravity of this component is 0.10 to 1 part. When it is 0.30, it is 0.5 to 2 with respect to 100 parts by weight of the component (A).
It is preferably 0 parts by weight, and particularly preferably 0.5 to 15 parts by weight. Also, the true specific gravity of this component is 0.
When it is from 0 to 0.10, it is preferably 0.1 to 15 parts by weight, and particularly preferably 0.5 to 10 parts by weight, relative to 100 parts by weight of the component (A).

The component (F) is an essential component for improving the dimensional accuracy of the composition of the present invention during heating and molding and for reducing the dimensional change during heating and cooling of the molded product. The component (F) is preferably pure water, purified water, ion-exchanged water, or the like having high purity.

The blending amount of this component is the volume of this component and (E)
The ratio of the component to the volume is (0.01: 1) to (5: 1), but the true specific gravity of the component (E) is 0.10 to 1.
When it is 30, it is preferable that the ratio of the volume of this component to the volume of (E) component is (0.1: 1) to (5: 1), and the true specific gravity of (E) component is 0.01-0.10
When it is, it is preferable that the ratio of the volume of this component to the volume of the component (E) is (0.01: 1) to (1: 1).

Further, this component may be added to the composition of the present invention independently, but it is preferable to add it after previously mixing it with the component (E). This is because the component (F) is uniformly dispersed, and the component (E) is prevented from scattering during the production of the composition of the present invention to facilitate its handling.

The composition of the present invention comprises the above-mentioned components (A) to (F), and may further contain (G) a hollow powder having an outer shell containing a gas made of an inorganic material. By using this component in combination with component (E), it is possible to prevent deterioration of moldability such as surface roughness and cracking, and to further reduce the specific gravity of silicone rubber molded products without impairing dimensional stability. Can also respond. Examples of such hollow powders include glass balloons and shirasu balloons, but the types thereof are not particularly limited. Examples of the gas contained in the hollow powder include inert gases such as air, nitrogen and helium. The size of this hollow body is preferably 150 μm or less. This is because if it is larger than 150 μm, the strength of the hollow powder itself becomes low and it may be broken at the stage of producing the composition of the present invention or at the time of molding a silicone rubber molded article. The compounding amount of this component is 1 to 20 parts by weight with respect to 100 parts by weight of the component (A). If this is less than the lower limit of the above range,
The effect of reducing the specific gravity of the molded product obtained by curing the composition of the present invention is reduced, and if the above upper limit is exceeded, the hardness of the molded product obtained by curing the composition of the present invention becomes too high, or This is because the strength tends to be insufficient.

The composition of the present invention comprises, as an optional component, a silicone resin having an outer shell having a softening point of 40 to 200 ° C., containing air or an inert gas such as nitrogen gas or helium gas, and having an average particle diameter. May contain hollow silicone resin powder in the range of 0.1 to 500 μm. Such hollow silicone resin powder is produced, for example, by spraying a dispersion liquid of a silicone resin dissolved in a solvent and water into a hot air stream from a spray nozzle to scatter an organic solvent and powder the silicone resin. . The content of the hollow silicone resin powder is preferably 0.01 to 20 parts by weight with respect to 100 parts by weight of the component (A).

Other optional components include pyrogenic silica, manganese carbonate, aluminum hydroxide, aluminum oxide,
Quartz powder, diatomaceous earth, aluminosilicate, calcium carbonate, and other inorganic fillers; iron oxide, titanium dioxide, and other pigments; cerium oxide, cerium hydroxide, and other heat-resistant agents; carbon black, silver powder, and other metal powders, conductive materials A conductivity-imparting agent such as conductive zinc oxide or conductive aluminum oxide may be contained. These inorganic fillers may be untreated, and those whose surfaces are previously treated with a surface treating agent such as organoalkoxysilane, organochlorosilane, hexaorganosilazane, polyorganosiloxane, etc. are used. Good. Further, when preparing the composition of the present invention, the inorganic filler may be treated while kneading the component (A), the untreated inorganic filler and the surface treating agent.

In addition, the composition of the present invention contains 2-methyl-3-butyn-2-ol, 2-phenyl-3-butyn-2-ol, and 3-phenyl-3-butyn-2-ol in order to improve handling workability and storage stability. , 5-dimethyl-1-hexyn-3-ol, 1
-Ethynyl-1-cyclohexanol, 1,5-hexadiyne, 1,6-heptadiyne and other acetylenic compounds; 3,5-dimethyl-1-hexene-1-yne, 3-
Ene-in compounds such as ethyl-3-butene-1-yne and 3-phenyl-3-buten-1-yne; 1,3-divinyltetramethyldisiloxane, 1,3,5,7-tetravinyltetramethyl Cyclotetrasiloxane, 1,3-
Alkenylsiloxane oligomers such as divinyl-1,3-diphenyldimethyldisiloxane; methyltris (3
An ethynyl group-containing silicon compound such as -methyl-1-butyne-3-oxy) silane; a nitrogen-containing compound such as tributylamine, tetramethylethylenediamine, benzotriazole; a phosphorus-containing compound such as triphenylphosphine;
Others, sulfur-containing compounds, hydroperoxy compounds,
It is preferable to add a curing inhibitor such as a maleic acid derivative and a mixture of two or more kinds thereof.

The compounding amount of these curing inhibitors may be 0 to 3 parts by weight, usually 0.001 to 3 parts by weight, and preferably 0.01 to 1 part by weight, relative to 100 parts by weight of the component (A).
Parts by weight. Preferred curing inhibitors are the acetylene compounds specified above, and these exhibit sufficient balance and good curability in combination with the above-mentioned component (D).

The composition of the present invention further comprises a dimethylpolysiloxane endcapped with trimethylsiloxy groups at both ends of the molecular chain, a dimethylpolysiloxane endcapped with dimethylhydroxysiloxy groups at both ends of the molecular chain, and a dimethylsiloxane / methylphenylsiloxane endcapped with trimethylsiloxy groups at both ends of the molecular chain. Copolymers, dimethylsiloxy-diphenylsiloxane copolymers capped with trimethylsiloxy groups at both molecular chain ends, dimethylhydroxysiloxy groups-capped dimethylsiloxane / methylphenylsiloxane copolymers with molecular chain ends at both ends, trimethylsiloxy groups-capped dimethylsiloxane at both molecular chain ends A polyorganosiloxane having no silicon atom-bonded alkenyl groups and silicon atom-bonded hydrogen atoms, such as a methyl (3,3,3-trifluoropropyl) siloxane copolymer;
Silicone powder additives such as silicone rubber powder and silicone resin powder; stearic acid, calcium stearate,
Carboxylic acid or metal salt of carboxylic acid such as zinc stearate; Heat resistance improver such as cerium silanolate or cerium fatty acid salt; Surfactant or polyoxyalkylene-modified polyorganosiloxane may be added as a dispersant for water. .

The composition of the present invention is produced by adding the above-mentioned components (A) to (F) or components (A) to (G) and, if necessary, other components and mixing them uniformly. . Examples of the manufacturing apparatus at this time include various mixing apparatuses usually used for manufacturing a silicone rubber composition, such as a kneader mixer, a pressure kneader mixer, a Ross mixer, and a continuous kneading extruder.

The composition of the present invention can be obtained by uniformly mixing the above-mentioned components (A) to (F) or (A) to (G) and, if necessary, other optional components.
In order to improve the storage stability of the composition of the present invention near room temperature and to retain excellent curability when applied to a multicolor molding method after storage, it contains at least component (A) and component (D). , A composition containing no (C) component, and (A) component and
It is preferable that the two-component type silicone rubber composition comprises a composition containing at least the component (C) and a composition not containing the component (D).

When the composition of the present invention is cured, it becomes a low specific gravity silicone rubber. The temperature at this time is usually 8
It is 0 ° C. or higher, preferably in the range of 100 to 180 ° C. Although the addition curing reaction of the silicone rubber utilizing the hydrosilylation reaction proceeds even below the lower limit of the above temperature range,
In that case, it may take a long time for molding or the adhesive force may not be sufficiently exhibited when the composite component is produced by adhering it to another component.

As the molding method of the composition of the present invention, a molding machine and a molding method usually used for molding a liquid silicone rubber can be used, and in particular, injection molding using a mold, compression molding, transfer molding, dispenser and the like are used. Casting is suitable.

The composition of the present invention as described above is excellent in dimensional stability during molding, has little dimensional change due to thermal expansion after curing, and has a low specific gravity when heated and cooled. Therefore, in applications where such characteristics are required, for example, coating materials for rolls used in copiers, printers, fax machines, etc., especially fixing roll coating materials, automobile gaskets, aircraft gaskets, etc. It is useful as a material.

[0030]

EXAMPLES The present invention will now be described with reference to examples. In the examples, “parts” means “parts by weight”, and the viscosity is 25 ° C.
It is a value measured by using a rotational viscometer. “Method for producing test piece” Each composition was press-cured at 120 ° C. for 15 minutes and then heat-treated in an oven at 200 ° C. for 4 hours to obtain a sheet-like test piece having a thickness of 6 mm for measuring hardness and specific gravity. A cylindrical test piece having a diameter of 29 mm and a thickness of 12 mm for measuring the rate of change in thickness was obtained. The produced test piece was left for one day at room temperature and then used for evaluation. "Method of measuring hardness" Thickness 6m produced as described above
The hardness of the sheet-shaped test piece of m is asker C (ASKER
C) It measured using the hardness meter. "Method of measuring rate of change in thickness" The initial thickness of a cylindrical test piece having a thickness of 12 mm produced as described above was measured (t
₀ ), this was left in an oven at 200 ° C. for 4 hours, then taken out, allowed to cool at room temperature for 30 minutes, and the thickness of the test piece was measured by a non-contact thickness gauge (t). Based on the obtained measurement result, the rate of change in thickness was calculated by the following formula. Thickness change rate (%) = {(t−t ₀ ) / t ₀ } × 100

[0031]

Example 1 30 parts of a dimethylpolysiloxane having a viscosity of 40,000 mPa · s and a dimethylvinylsiloxy group blocked at both ends of the molecular chain (vinyl group content 0.08% by weight), a viscosity of 34
70 parts of 0 mPa · s molecular chain end-capped dimethylvinylsiloxy group-blocked methylvinyl-dimethylpolysiloxane copolymer (vinyl group content 0.90% by weight), BET specific surface area 130 m ² treated with hexamethyldisilazane /
g fumed silica 10 parts and outer shell of vinylidene chloride
Hollow resin powder made of acrylonitrile copolymer and containing isobutane ["Expansel 461DE" (EX
PANCEL461DE); purchased from Nippon Philite Co., Ltd .; softening start temperature 100 ° C., average particle size 40 μm,
3 parts of true specific gravity of 0.06] and 17 parts of water were mixed with a Ross mixer until uniform, to prepare a liquid silicone rubber base compound having fluidity. Then, to this liquid silicone rubber base compound, a methyl hydrogen siloxane / dimethyl siloxane copolymer (methyl silicon siloxane / dimethyl siloxane copolymer endblocked with dimethyl hydrogen siloxy groups at both ends) consisting of 40 mol% of methyl hydrogen siloxane units and 60 mol% of dimethyl siloxane units was added. Atomic bond hydrogen atom content 0.40% by weight) 4.9 parts (mol number of silicon atom bond hydrogen atom and mole number of vinyl group contained in vinyl group-containing diorganopolysiloxane in the above liquid silicone rubber base compound) Ratio of 0.80: 1), and a complex of chloroplatinic acid and 1,3-divinyltetramethyldisiloxane is used as the platinum metal to obtain 100 of vinyl group-containing diorganopolysiloxane in the liquid silicone rubber base compound. The amount is 20 parts for every 10,000 parts A liquid silicone rubber composition was prepared by adding 0.08 part of 1-ethynyl-1-cyclohexanol as a curing inhibitor and uniformly mixing the mixture. The viscosity of this composition is 64,
It was 000 mPa · s. Next, the specific gravity, hardness and rate of change in thickness of this composition were measured by the methods described above, and the results are shown in Table 1.

[0032]

Example 2 In Example 1, a liquid silicone rubber base compound was added to a glass balloon ("Glass Bubbles S38"; manufactured by Sumitomo 3M Ltd .; particle size: 75 μ).
m, true specific gravity 0.38) A liquid silicone rubber composition was prepared in the same manner as in Example 1 except that 10 parts were further added. The viscosity of this composition was 69,000 mPa · s. Then, the specific gravity, hardness and rate of change in thickness of this composition were measured in the same manner as in Example 1, and the results are shown in Table 1.

[0033]

Example 3 In Example 2, instead of blending the hollow resin powder (“Expansel 461DE”) and water, the hollow resin powder (“Expansel 461DE”; purchased from Nippon Philite Co., Ltd .; Softening start temperature 100 ° C,
A liquid silicone rubber composition was prepared in the same manner as in Example 2 except that 15 parts by weight of a mixture consisting of 15% by weight of average particle diameter 40 μm, true specific gravity of 0.06) and 85% by weight of water was blended. The viscosity of this composition was 82,000 mPa · s. Then, the specific gravity, hardness and rate of change in thickness of this composition were measured in the same manner as in Example 1, and the results are shown in Table 1.

[0034]

Example 4 Instead of blending the thermoplastic hollow resin powder (“Expancel 461DE”) and water in Example 2, a hollow resin whose outer shell is made of vinylidene chloride-acrylonitrile copolymer and which contains isobutane Powder ("
Matsumoto Microsphere F30E "; manufactured by Matsumoto Yushi-Seiyaku Co., Ltd .; softening start temperature 80 ° C, average particle diameter 40μ
m, true specific gravity 0.03; 15% by weight of this hollow resin powder and 8 water
A liquid silicone rubber composition was prepared in the same manner as in Example 2 except that 10 parts of a 5% by weight mixture) was added. The viscosity of this composition was 54,000 mPa · s. Then, the specific gravity, hardness and rate of change in thickness of this composition were measured in the same manner as in Example 1, and the results are shown in Table 1.

[0035]

COMPARATIVE EXAMPLE 1 In Example 1, without adding water, methylhydrogensiloxane unit 40 mol% and dimethylsiloxane unit 60 mol% both ends dimethylhydrogensiloxy group blocked methylhydrogensiloxane dimethylsiloxane. The copolymer (silicon atom-bonded hydrogen atom content 0.40% by weight) was added in an amount of 3.3 parts (the number of moles of the silicon atom-bonded hydrogen atom and the vinyl group-containing diorganopolysiloxane in the liquid silicone rubber base compound). A liquid silicone rubber composition was prepared in the same manner as in Example 1 except that the ratio with respect to the number of moles of vinyl groups contained in was 0.55: 1. The viscosity of this composition was 34,000 mPa · s. Then, the specific gravity, hardness and rate of change in thickness of this composition were measured in the same manner as in Example 1, and the results are shown in Table 1.

[0036]

COMPARATIVE EXAMPLE 2 In Example 2, water was not blended, and the methylhydrogensiloxane unit was 40 mol% and the dimethylsiloxane unit was 60 mol%. Both ends dimethylhydrogensiloxy group-blocked methylhydrogensiloxane-dimethylsiloxane. The copolymer (silicon atom-bonded hydrogen atom content 0.40% by weight) was added in an amount of 3.3 parts (the number of moles of the silicon atom-bonded hydrogen atom and the vinyl group-containing diorganopolysiloxane in the liquid silicone rubber base compound). A liquid silicone rubber composition was prepared in the same manner as in Example 2 except that the ratio to the number of moles of vinyl groups contained in was 0.55: 1. The viscosity of this composition was 60,000 mPa · s. Then, the specific gravity, hardness and change in thickness of this composition were measured in the same manner as in Example 1, and the results are shown in Table 1.

[0037]

[Table 1]

[0038]

Example 5 100 parts of a methylvinylpolysiloxane / dimethylpolysiloxane copolymer (vinyl group content 0.40% by weight) having a viscosity of 24,000 mPa · s and having trimethylsiloxy groups blocked at both ends of the molecular chain has methacrylic acid as the outer shell. Hollow resin powder [“Expansel 091-140 DU” (EXPANCEL091−, consisting of a methyl / acrylonitrile / methacrylonitrile copolymer and containing isobutane
140DU); purchased from Nippon Philite Co., Ltd .; softening temperature 120 ° C., average particle size 40 μm, true specific gravity 1.0
0] of 1.5 parts was blended and then kneaded at 170 ° C. to expand the hollow resin powder in the vinyl group-containing diorganopolysiloxane, and cooled to 40 ° C. or lower. 10 parts of fumed silica having a BET specific surface area of 130 m ² / g treated with hexamethyldisilazane and a thermoplastic silicone resin having an outer shell with a softening temperature of 80 ° C. (the number of moles of methylsiloxane unit: the number of moles of methylphenylsiloxane unit) = 22: 78), and 1 part of a hollow silicone resin powder having a mean particle size of 40 μm and containing nitrogen gas, and water.
A liquid silicone rubber base compound was prepared by placing 5 parts in a Ross mixer and mixing until uniform. Then, to this liquid silicone rubber base compound, dimethyl polysiloxane endcapped with dimethyl hydrogensiloxy groups at both molecular chain ends (silicon atom-bonded hydrogen atom content 0.20% by weight) 6.4 parts (moles of silicon atom-bonded hydrogen atom) The amount of which is 0.85: 1 with respect to the number of moles of vinyl groups in the vinyl group-containing diorganopolysiloxane in the liquid silicone rubber base compound), chloroplatinic acid and 1,3-divinyltetramethyldiene. The amount of the siloxane complex is platinum metal and the amount thereof is 20 parts with respect to 1 million parts of the vinyl group-containing organopolysiloxane in the liquid silicone rubber compound, and as a curing inhibitor.
A liquid silicone rubber composition was prepared by adding 0.08 part of 1-ethynyl-1-cyclohexanol and mixing them uniformly. The viscosity of this composition was 380000 mPa · s. Then, the specific gravity, hardness and rate of change in thickness of this composition were measured in the same manner as in Example 1, and the results are shown in Table 2.

[0039]

Comparative Example 3 A liquid silicone rubber composition was prepared in the same manner as in Example 5, except that the hollow silicone resin powder and water were not mixed. The viscosity of this composition is 250,000 mPa.s. It was s. Then, the specific gravity, hardness and change in thickness of this composition were measured in the same manner as in Example 1, and the results are shown in Table 2.

[0040]

[Table 2]

[0041]

The low specific gravity liquid silicone rubber composition of the present invention comprises the components (A) to (F) or (A).
Since it is composed of component (G), it has excellent dimensional stability during molding,
After curing, it has a feature that it can be a low specific gravity silicone rubber molded article having excellent dimensional stability when heated and cooled. Further, the rolls and various gaskets used in the copying machine, printer, fax, etc., which are made of the low specific gravity silicone rubber molded product of the present invention, are lighter in weight than conventional products, and are dimensionally stable when heated and cooled. It has the feature of excellent property.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ identification code FI theme code (reference) C08K 7/22 C08K 7/22 C08L 83/05 C08L 83/05 F16J 15/14 F16J 15/14 C F term (Reference) 4F074 AA37 AA49 AA90 AA91 AA95 AA98 AC01 AC32 AC34 AH01 CB62 CB85 DA39 DA59 4J002 AA013 BD103 BG103 CP04X CP12W CP14W DA117 DE029 DE177 DJ008 DJ016 DL008 FA103 FA108 GH00 GM00

Claims (5)

[Claims] 1. (A) 100 parts by weight of a liquid diorganopolysiloxane containing at least two silicon-bonded alkenyl groups in one molecule and having a viscosity of 100 to 100,000 mPa · s, (B) hydrophobizing Reinforcing fine powder silica filler 1 to 50 parts by weight, (C) Organopolysiloxane containing at least two silicon atom-bonded hydrogen atoms in one molecule {Silicon atom-bonded hydrogen atoms in this component and (A) Amount in which the molar ratio of silicon atom-bonded alkenyl groups in the component is (0.3: 1) to (5: 1)}, (D) Platinum-based catalyst {(A) Platinum relative to 1 million parts by weight of the component 0.1 to 500 parts by weight as metal}, (E) Hollow resin powder having an outer shell made of a thermoplastic resin other than a silicone resin and containing a gas and / or a volatile liquid 0.1 to 20 parts by weight Part and (F ) Water {amount in which the ratio between the volume of this component and the volume of component (E) is (0.01: 1) to (5: 1)}, which is a low specific gravity liquid silicone rubber composition . 2. The low specific gravity liquid silicone rubber composition according to claim 1, further comprising (G) 1 to 20 parts by weight of a hollow powder whose outer shell is made of an inorganic material. 3. A low specific gravity liquid silicone rubber according to claim 1, wherein the mixture of the component (E) and the component (F) is added in an amount of 1 to 70 parts by weight based on 100 parts by weight of the component (A). Composition 4. The low specific gravity liquid silicone rubber composition according to claim 1, which is for coating a fixing roll. 5. A low specific gravity silicone rubber molded product obtained by heat-curing the low specific gravity liquid silicone rubber composition according to claim 1.