JPH1135829A - Polyorganosiloxane composition and hardened substance thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject composition excellent in fluidity and tear strength after hardening by including polyorganosiloxane containing an alkenyl group, polyorganohydrogensiloxane, platinum-based compound, and hydrophobic silica fine powder having a particular specific surface area and bulk density. SOLUTION: This composition is obtained by including 100 pts.wt. of polyorganosiloxane having 2>= alkenyl groups each bonded to a silicon atom in one molecule, polyorganohydrogensiloxane having 3>= hydrogen atoms each bonded to a silicon atom in one molecule and 0.4 to 4 hydrogen atoms each bonded to the silicon atom based on one alkenyl group, 1 to 200 ppm platinum- based compound (e.g. platinum-vinylsiloxane complex) based on polyorganosiloxane in terms of platinum atom, and 1 to 40 pts.wt. of hydrophobic silica fine powder having 120 to 200 m<2> /g of BET specific surface area, 120 to 200 g/l of bulk density and its own surface treated with an organic silicon compound.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyorganosiloxane composition which cures to a rubber-like elastic material, and more particularly, to a polymer having a low apparent viscosity before curing and exhibiting a suitable fluidity. The present invention relates to a polyorganosiloxane composition suitable for obtaining a silicone rubber having excellent mechanical strength. The present invention also relates to a cured product obtained by curing such a polyorganosiloxane composition.

[0002]

2. Description of the Related Art Conventionally, silicone rubber has been widely used in various fields, taking advantage of its excellent heat resistance, cold resistance, and electrical properties. In particular, because of its good releasability, it has been used as a molding material for cultural properties, arts and crafts, and the like. In recent years, in the fields of electronic equipment, office machines, household appliances, and automotive parts, we have focused on the fact that prototype molding used at the product development stage and product sample creation is effective in improving the cost and required period. , Especially in terms of workability,
Liquid silicone rubber of the addition reaction type has come to be used frequently.

[0003] In order to obtain a large amount and elaborate copies of complicated shapes, silicone rubber for molding for such applications is required to have high strength in a mold obtained by curing. A high tear strength is required in order to mold from a prototype having a complicated shape. Also, because it is easy to use,
It is also required that the apparent viscosity in the uncured stage be low.

[0004] As an addition reaction type silicone rubber which meets such a demand, a method of compounding a reinforcing filler with a polyorganosiloxane having an alkenyl group at a molecular terminal, together with a compound having a Si-N bond in the molecule (particularly). JP-A-40-19178) and a method using hydrophobic silica and hexamethyldisilazane (JP-A-2-7075).
No. 5) is known. Further, as a part of the base polymer, an alkenyl group-containing linear polyorganosiloxane may be an MQ type polysiloxane comprising R ₃ SiO _0.5 unit (hereinafter, referred to as M unit) and SiO ₂ unit (hereinafter, referred to as Q unit), Alternatively, it further contains RSiO _1.5 units (hereinafter, referred to as T units) and / or R ₂ SiO units (hereinafter, referred to as D units) (wherein R represents a monovalent hydrocarbon group and at least two Is an alkenyl group.) It has been studied to incorporate a branched polyorganosiloxane such as an MTQ-type, MDQ-type, or MDTQ-type polyorganosiloxane. However, the tear strength is not enough to use for the reverse taper type mold release,
It is difficult to use as a mold having such a structure.

Further, such a high-strength silicone rubber composition for molding contains a large amount of a reinforcing filler, for example, fine silica powder such as fumed silica. Therefore, the viscosity of the composition in the uncured stage is significantly increased,
Poor workability due to poor fluidity.

[0006] Such a silica fine powder is often used to improve the flowability of the silicone rubber composition in the uncured stage and to reduce the aging of the silicone rubber composition during storage, so that dimethyldichlorosilane, trimethylchlorosilane and hexamethylsilane are often used. The surface is treated with an organosilicon compound such as disiloxane or polydimethylsiloxane.

However, even when the silica fine powder surface-treated with the organosilicon compound is used as a filler, the cured product has excellent fluidity before curing, and the cured product is a silicone rubber having a large tear strength. It cannot be obtained, and improvement of its tear strength has been further desired.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to form a silicone rubber having excellent fluidity before curing and having a high tear strength after curing, and is particularly suitable for a silicone rubber for molding. An object of the present invention is to provide a novel addition reaction type polyorganosiloxane composition and a cured product obtained by curing the composition.

[0009]

Means for Solving the Problems As a result of repeated studies to achieve the above object, the present inventors have conducted a hydrophobizing treatment on the surface with an organosilicon compound and have a BET specific surface area of 120 to 2
It has been found that the tear strength of a cured product of an addition reaction type polyorganosiloxane composition can be improved more than before by using a silica fine powder having a bulk density of 00 m ² / g and a bulk density of 120 to 200 g / l as a filler. Thus, the present invention has been completed.

That is, the polyorganosiloxane composition of the present invention comprises: (A) 100 parts by weight of a polyorganosiloxane having at least two alkenyl groups bonded to silicon atoms in one molecule; (B) hydrogen bonded to silicon atoms Polyorganohydrogensiloxane having three or more atoms in one molecule,
(A) an amount such that the number of hydrogen atoms bonded to silicon atoms per one alkenyl group in the component is 0.4 to 4; (C) a platinum compound; and (A) a platinum atom. Conversion 1
200 wt ppm; and (D) the surface is treated with an organosilicon compound, the BET specific surface area is 120 to 200 m ² / g, and the bulk density is 120 to 200.
The cured product of the present invention is characterized by containing 1 to 40 parts by weight of a hydrophobic silica fine powder having a g / l content and obtained by curing such a polyorganosiloxane composition.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The alkenyl group-containing polyorganosiloxane of the component (A) used in the present invention is a component serving as a base polymer in the composition of the present invention. This component (A) contains one alkenyl group bonded to a silicon atom.
Any material may be used as long as it has two or more molecules in the molecule and can form a network structure by an addition reaction.

The siloxane skeleton of the alkenyl group-containing polyorganosiloxane (A) may be linear or branched. In order to improve the mechanical properties of the cured composition and use it for molding of complex shapes, such as for prototypes, mix the above-mentioned linear polydiorganosiloxane with a branched polyorganosiloxane. It is preferable to use them. In order to increase the mechanical strength, particularly the tear strength and the elastic modulus of the cured product, the component (A) comprises M units and Q units, and if necessary, further comprises D units and / or T units. Of the organic group bonded to the compound is 2 to 50% by weight of a branched polyorganosiloxane in which at least two, and preferably three or more, of the organic groups are alkenyl groups, and the balance is linear and both ends are alkenyl groups. It is further preferred to use a mixture of polydiorganosiloxanes blocked by groups.

The alkenyl group includes vinyl, allyl,
A vinyl group is preferred because 1-butenyl and 1-hexenyl are exemplified, and the synthesis is easy, and a suitable addition reaction rate and storage stability are easily obtained.

Other organic groups bonded to the silicon atom of the component (A) include alkyl groups such as methyl, ethyl, propyl, butyl, pentyl, hexyl, octyl, decyl, dodecyl; aryl groups such as phenyl; Aralkyl groups such as phenylethyl and 2-phenylpropyl; chloromethyl, chlorophenyl, 3,3,3-trifluoropropyl, (2-perfluorobutyl) ethyl, (2
-Perfluorooctyl) ethyl, of the general formula:

Embedded image (Wherein, R ¹ represents a perfluoroalkyl group such as perfluoropropyl; a is an integer of 1 to 6), and is exemplified by a monovalent substituted hydrocarbon group such as a perfluoropolyoxypropylene substituted propyl group. You. Of these, a methyl group is most preferred because it is easy to synthesize and has an excellent balance of properties such as mechanical properties and fluidity before curing. When the cured product is required to have oil resistance, it preferably has a fluoro-substituted alkyl group and / or a perfluoropolyoxypropylene-substituted propyl group in addition to the methyl group.

The alkenyl group may be present at the terminal or midway of the molecular chain of the component (A), or may be present at both of them, but the cured composition has excellent mechanical properties. In order to provide, when it is linear, it is preferably present at least at both ends.

Such a linear component (A) can be arbitrarily selected from those having a degree of polymerization of from 70 to 10,000 according to the purpose. Particularly for applications such as molding, the following general formula:

Embedded image Wherein R ^f represents a fluoroalkyl group or a perfluoropolyoxypropylene-substituted propyl group;
M is an integer from 0 to 200, n + m is from 100 to 1,200; k is from 1 to 20
Are preferred.) Are preferred.

The component (A) has a viscosity at 25 ° C. of 10
It is arbitrarily selected from 0 to 30,000,000 cP according to the purpose. In particular, for use in applications such as molding, the composition before curing has good fluidity and workability, and the composition after curing has appropriate elasticity and mechanical properties. Those having 300 to 100,000 cP are preferred, and those having 2,000 to 20,000 cP are particularly preferred.

The polyorganohydrogensiloxane of the component (B) used in the present invention is prepared by subjecting the hydrosilyl group contained in the molecule to an addition reaction to the alkenyl group of the component (A) to give the component (A). It functions as a cross-linking agent, and has at least three hydrogen atoms bonded to silicon atoms in order to reticulate the cured product.

Examples of the organic group bonded to the silicon atom of the siloxane unit include the same organic groups other than the alkenyl group in the above-mentioned component (A). Among them, a methyl group is preferred because of its ease of synthesis. Is most preferred.

The siloxane skeleton in the component (B) may be linear, branched or cyclic. Moreover, you may use these mixtures.

The degree of polymerization of the component (B) is not particularly limited, but it is difficult to synthesize a polyorganohydrogensiloxane in which two or more hydrogen atoms are bonded to the same silicon atom. Is preferred.

The following are specific examples of the component (B). a. A branched polyorganohydrogensiloxane composed of (CH ₃ ) ₂ HSiO _1/2 units (hereinafter referred to as M ′ units) and Q units; b. The following formula:

Embedded image (Wherein p is an integer of 3 to 100; q is 0 to 100)
A linear polyorganohydrogensiloxane represented by the formula: and c. The following formula:

Embedded image (Wherein p is an integer of 1 to 100; q is 0 to 100)
A linear polyorganohydrogensiloxane represented by the formula:

The amount of component (B) is from 0.4 to 4, preferably from 1 to 4, hydrogen atoms bonded to silicon atoms in component (B) per alkenyl group in component (A). The quantity is such that there are three. The above hydrogen atom abundance ratio is 0.4
If the amount is less than the above, the curing is not completed completely, so that the mold obtained by curing the composition becomes tacky, and the mold releasability when molding the silicone rubber mold from the mother mold, and the mold removal. The releasability of the resulting duplicated product from the silicone rubber mold is reduced. Conversely, if the abundance is more than 4, foaming is liable to occur during curing, which is caused by the interface between the matrix and the silicone rubber mold and the copy obtained by molding with the silicone rubber mold. Not only does it accumulate at the interface, giving a mold or a replica with poor surface condition, but also the obtained silicone rubber mold becomes brittle, resulting in a decrease in the number of times of resin injection, that is, a decrease in the mold-making life, The mechanical strength is reduced.

The platinum compound as the component (C) used in the present invention is a catalyst for accelerating the addition reaction between the alkenyl group in the component (A) and the hydrosilyl group in the component (B).

Examples of the platinum compound include chloroplatinic acid, a reaction product of chloroplatinic acid and an alcohol, a platinum-olefin complex, a platinum-vinylsiloxane complex, and a platinum-phosphine complex. Among these, a reaction product of chloroplatinic acid and an alcohol, a platinum-vinylsiloxane complex, and the like are preferable from the viewpoint of good solubility in the component (A) and the component (B) and excellent catalytic activity.

The component (C) is used in an amount of 1 to 200 ppm, preferably 2 to 5 ppm in terms of platinum atom, based on the component (A).
It is 0 ppm. If the amount is less than 1 ppm, the curing speed is slow and the curing is not completely completed, so that the silicone rubber mold becomes tacky, and the mold releasability of the silicone rubber mold from the mother mold and the mold releasability from the silicone rubber mold. Decrease. 20
If it exceeds 0 ppm, the workability after blending each component is impaired because the curing speed is excessively increased, and it is uneconomical.

The hydrophobic silica fine powder of the component (D) used in the present invention is obtained by hydrophobizing the surface of a silica fine powder with an organosilicon compound. As the silica fine powder, fumed silica is preferably used. Examples of the organosilicon compound used for the surface treatment include dimethyldichlorosilane, trimethylchlorosilane, hexamethyldisilazane, and the like.The fluidity of the composition in the uncured stage is excellent, and the storage stability is excellent. Methyldisilazane is particularly preferred. The treatment is performed by adsorbing the organosilicon compound used for the treatment on the surface of the silica fine powder at room temperature or high temperature by a gas phase or a liquid phase using an inert solvent such as n-hexane, and heat-treating the silica. It can be carried out by organosilylating silanol groups on the surface of the fine powder. The silica fine powder having been subjected to such a surface treatment may be used after being pulverized by a pulverizing means such as a jet mill or a ball mill, if necessary.

The BET specific surface area of the component (D) used in the present invention thus obtained is 120 to ²⁰⁰ m ^2.
/ g. If it is less than 120 m ² / g, sufficient tear strength cannot be given to the cured product, and if it exceeds 200 m ² / g, the apparent viscosity of the composition before curing becomes extremely high and workability is impaired. .

The bulk density of the component (D) is from 120 to
It is 200 g / l. If the amount is less than 120 g / l, the apparent viscosity of the composition before curing becomes extremely high, and the tear strength of the cured product is not sufficient. On the other hand, even if the bulk density exceeds 200 g / l,
There is no effect of further reducing the apparent viscosity of the composition before curing, and the cured product has low tear strength and impairs transparency. The hydrophobic silica fine powder having such a bulk density can be obtained by physically aggregating silica fine powder which has been hydrophobized by an organosilicon compound.

The amount of the component (D) having such properties is 1 to 40 parts by weight, preferably 10 to 40 parts by weight, per 100 parts by weight of the component (A). If the amount is less than 1 part by weight, the uncured composition becomes excessively fluid and not only causes a sagging phenomenon but also cannot provide a cured product with sufficient mechanical strength. On the other hand, when the amount exceeds 40 parts by weight, the apparent viscosity of the uncured composition becomes excessive, and the composition does not flow.

If necessary, a coloring agent such as a pigment such as iron oxide, titanium oxide, or zinc oxide may be added to the composition of the present invention. When a particularly excellent release property is required for the cured product, a small amount of a polydiorganosiloxane such as silicone oil or silicone raw rubber may be further blended. As such a polydiorganosiloxane, non-reactive silicone oil or similarly non-reactive silicone raw rubber is used. The amount of such a polydiorganosiloxane is 25 parts by weight or less based on 100 parts by weight of the component (A).
Parts by weight are preferred.

In order to impart storage stability at room temperature to the polyorganosiloxane composition of the present invention and / or to improve the workability by extending the curing time, an acetylene compound, diallyl maleate, triallyl isocyanurate may be used. , A nitrile compound or a curing retarder such as an organic peroxide.

Further, additives such as a flame retardant, a plasticizer, a thixotropic agent, a bactericide, an antibacterial agent, and an adhesion improver can be added to the composition of the present invention. As the adhesion improver, a silane having a carbon functional group such as an amino group, an epoxy group, a mercapto group, or an ester bond bonded to a carbon atom is preferably used. In addition, as long as the object of the present invention is not impaired, it is not a problem to mix a filler other than the component (D).

The composition of the present invention comprises the components (A) to (D),
Further, other components to be blended as required can be uniformly kneaded by a mixing means such as a universal kneader, a kneader or the like. For stable long-term storage, the components (B) and (C) are separately stored in two containers so that the components (B) and (C) are in separate containers, and mixed immediately before use. It may be used after degassing under reduced pressure.

The cured product obtained by heating the polyorganosiloxane composition of the present invention to 20 to 80 ° C., for example, 60 ° C., can be used for a mold material and other uses. That is, the composition of the present invention can be poured into a matrix using its fluidity, heated to the above-described temperature and cured, and used as a mold for molding a duplicate.

[0036]

The polyorganosiloxane composition of the present invention has fluidity before curing and excellent workability, and the cured product is a rubber-like elastic material having excellent mechanical strength, especially tear strength. is there. Therefore, the composition of the present invention can be advantageously used for various types of molding, especially for duplicating complicated and sophisticated parts such as electric / electronic parts and automobile parts.

[0037]

The present invention will be described in more detail with reference to the following Examples and Comparative Examples. In these examples, parts indicate parts by weight, and viscosity indicates a viscosity at 25 ° C. The present invention is not limited by these examples.

Examples 1 to 4 and Comparative Examples 1 and 2 100 parts of polydimethylsiloxane having a molecular chain end blocked by a vinyldimethylsilyl group and having a viscosity of 5,000 cP were charged into a universal kneader. In addition to this, (CH ₃ ) ₃ SiO _0.5 unit (hereinafter referred to as M ^m unit), (CH ₂ CH) (CH
₃ ) ₂ SiO _0.5 unit (hereinafter referred to as ^Mv unit) and Q
Consists unit, a M ^m /Q=0.7 (molar ratio), 1
M ^v of vinyl groups per 00g corresponds to 0.1 moles
Type polymethylvinylsiloxane 10 containing units
And 30 parts of fumed silica having a BET specific surface area and a bulk specific gravity shown in Table 1 respectively, which were surface-treated with hexamethyldisilazane, and heated and kneaded at 150 ° C. for 4 hours. However, the silica fine powder used in Comparative Example 1 had a low bulk density, and the silica fine powder used in Comparative Example 2 had a low specific surface area and a low bulk density. After cooling to room temperature, chloroplatinic acid (20 ppm in terms of platinum atom) was added to the vinyl group-containing polysiloxane as an isopropanol solution, kneaded and dispersed.

The mixture obtained in this manner is composed of an MQ type poly (M ′ unit) having M ′ units, comprising M ′ units and Q units, wherein the amount of hydrogen atoms bonded to silicon atoms per gram corresponds to 1 mol. Three parts of methyl hydrogen siloxane were blended and uniformly mixed to obtain each composition.

The viscosity of each composition thus prepared was measured using a rotational viscometer. Further, each composition was cast to a thickness of 2 mm and cured by heating at 60 ° C. for 2 hours to prepare a sheet-like sample. The physical properties of the cured sample
When measured according to JIS K6301, the results shown in Table 1 were obtained.

[0041]

[Table 1]

Claims (4)

[Claims] (A) 100 parts by weight of a polyorganosiloxane having two or more silicon-bonded alkenyl groups per molecule; and (B) three or more silicon-bonded hydrogen atoms per molecule. Polyorganohydrogensiloxane,
(A) an amount such that the number of hydrogen atoms bonded to silicon atoms per one alkenyl group in the component is 0.4 to 4; (C) a platinum compound; and (A) a platinum atom. Conversion 1
200 wt ppm; and (D) the surface is treated with an organosilicon compound, the BET specific surface area is 120 to 200 m ² / g, and the bulk density is 120 to 200.
A polyorganosiloxane composition comprising 1 to 40 parts by weight of a fine powder of hydrophobic silica having a mass ratio of g / l. 2. The polyorganosiloxane composition according to claim 1, wherein (D) is a hydrophobic silica fine powder that has been hydrophobized with hexamethyldisilazane. 3. The viscosity of (A) at 25 ° C. is 300
The polyorganosiloxane composition according to claim 1, wherein the composition is １００100,000 cP. 4. A cured product obtained by curing the polyorganosiloxane composition according to claim 1.