JPH0459873A - Silicone rubber composition for extrusion molding - Google Patents

Abstract

PURPOSE:To obtain the title compound excellent in storage stability at ca.room temperature, long in working life, high in heating cure rate, free from defects such as foaming, thus suitable for tubes, gaskets etc., by incorporating a specific organipolysiloxane raw rubber with a specified amount of silica fine powder, etc. CONSTITUTION:The objective composition can be obtained by incorporating (A) 100 pts.wt. of an organopolysiloxane raw rubber of the formula [R is (substituted) monovalent hydrocarbon; (a)=1.8-2.3] having at least two silicon atom-bound alkenyl groups in one molecule with (B) 10-100 pts.wt. of silica fine powder, (C) 0.1-10 pts.wt. of an organohydrogenpolysiloxane having at least two silicon atom-bound hydrogen atoms in one molecule, and (D) spherical fine particle catalyst 0.01-10mum in size, consisting of a silicone resin 50-250 deg.C in softening point containing >=0.01wt.%, in terms of platinum metal atom, of a platinum-based catalyst.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a silicone rubber composition for extrusion molding, and more specifically, it has excellent storage stability near room temperature and rapid heat curing properties, The present invention relates to a silicone rubber composition for extrusion molding that is suitably used for extrusion molding applications such as tubes, gaskets, and wire coatings.

[Prior art] Generally, the extrusion molding method for silicone rubber is a method of vulcanization and curing using an organic peroxide in a hot vulcanization furnace. Silicone rubber compositions are widely used because they have excellent storage stability near room temperature, have a long pot life, and are easy to handle. However, in this method, the decomposition products of organic peroxides pollute the working environment, making the working environment in a poor state. Moreover, there is a problem in that decomposition residues of this organic peroxide remain in silicone rubber molded products after vulcanization, and it is necessary to carry out post-vulcanization for an extremely long time to remove them. Ta. In recent years, in order to solve these problems, addition reaction type curable silicone rubber compositions that are cured using platinum-based catalysts have been studied for extrusion molding, and silicone rubbers obtained from these compositions are extremely effective. Because it is hygienic, it is used in tubes for food and medical materials. However, this type of addition reaction type curable silicone rubber composition has extremely poor storage stability and a pot life of only a few hours, making it extremely complicated to handle. In many cases, it could not be obtained as a molded product. In order to improve this storage stability, various catalyst activity inhibitors for platinum-based catalysts are being investigated. For example, a method has been proposed in which a platinum catalyst is used in combination with benzotriazole, an acetylene compound, a hydroperoxy compound, or the like. However, these methods not only fail to provide long-term storage stability of 6 months or more, but also have drawbacks such as a decrease in heating curing speed and the occurrence of foaming when curing in a hot vulcanization oven. .

[Problems to be Solved by the Invention] As a result of intensive research to solve the above problems, the present inventors have arrived at the present invention. An object of the present invention is to provide a silicone rubber composition for extrusion molding that has excellent storage stability near room temperature, has a long pot life, has a high heat curing rate, and is free from defects such as foaming.

[Means for solving the problem and their effects] The above purpose is (A) average compositional formula Ra5iO+4-s+7a (in the formula,
R is a substituted or unsubstituted monovalent hydrocarbon group, a is 1.8 to
The number is 2.3. ), 100 parts by weight of organopolysiloxane raw rubber having at least two silicon-bonded alkenyl groups in one molecule, (B) 10 to 100 parts by weight of fine silica powder, (C)
Organohydrodiene polysiloxane having at least two silicon-bonded hydrogen atoms in one molecule
0.1 to 10 parts by weight, (D) a spherical fine particle catalyst composed of a silicone resin containing 0.01% by weight or more of a platinum-based catalyst as platinum metal atoms (here, the softening point of the silicone resin is 50 to 250°C) This can be achieved by using a silicone rubber composition for extrusion molding characterized by comprising a catalytic amount (the particle diameter of the spherical fine particle catalyst is 0.01 to 10 μm).

To explain this, the organopolysiloxane (A) component used in the present invention is a main component of the composition of the present invention, and has at least two silicon-bonded alkenyl groups in one molecule. is necessary. In the above formula, R is a methyl group, an ethyl group,
Alkyl groups such as propyl group, butyl group, hexyl group, octyl group; Alkenyl groups such as vinyl group, allyl group, hexenyl group; Aryl group such as phenyl group;
3. 3. 3-) A monovalent hydrocarbon group exemplified by a substituted hydrocarbon group such as a refluoropropyl group, and a is 1.
The number is between 8 and 2.3.

The molecular structure of this organopolysiloxane is preferably linear, and may have a branched siloxane skeleton.

The degree of polymerization is not particularly limited, but it is within the range called organopolysiloxane raw rubber in the industry, which usually has a viscosity at 25°C of 107 centistokes or more and an average molecular weight of 25 x 10' or more, especially 40 x 104 or more. are preferably used.

The fine silica powder of component (B) has been conventionally used in silicone rubber, and examples include fumed silica and precipitated silica.

Among these, particles with a particle size of 50 mμ or less and a specific surface area of 10
Silica in the form of ultrafine powder with a particle size of 0 m'/g or more is preferred. Furthermore, surface-treated silica, such as finely powdered silica surface-treated with organosilane, organosilazane, diorganocyclopolysiloxane, etc., is more suitable. (B)
The blending amount of the component is 10 to 100 parts by weight of component (A).
The amount is 100 parts by weight, preferably 20 to 80 parts by weight.

In the present invention, the organopolysiloxane used as the component (C) is a crosslinking agent for the organopolysiloxane as the component (A). must have at least two silicon-bonded hydrogen atoms. Organic groups bonded to silicon atoms other than hydrogen atoms include the above-mentioned (A
) The same organopolysiloxanes as the component are exemplified. Only one type of this organic group may be present in one molecule, or two or more types may be present in a mixture. The molecular structure of this organohydrodiene polysiloxane may include a linear structure, a network structure, or a three-dimensional structure, and a single polymer or copolymer thereof or a mixture of two or more types of polymers can also be used. . The degree of polymerization of this organohydrodiene polysiloxane is usually such that the viscosity at 25°C is 0.
The range is 5 to 50,000 centipoise, preferably 1 to 10.000 centipoise. In addition, the blending amount is such that the molar ratio of the silicon-bonded hydrogen atom of this component to the silicon-bonded alkenyl group of component (A) is within the range of 0.5/1 to 10/1, and usually It is within the range of 0.1 to 10 parts by weight.

The spherical fine particle catalyst used in the present invention as component (E) is a component that characterizes the present invention.

Component (E) is a spherical fine particle catalyst made of a silicone resin containing 0.01% by weight or more of a platinum-based catalyst as platinum metal atoms.

This platinum-based catalyst is a platinum-based metal itself, a platinum-based compound, or a composition containing this platinum-based compound as a main component, which has a catalytic activity to promote the hydrosilylation reaction. Platinum-based catalysts for such hydrosilylation reactions include fine platinum powder,
Chloroplatinic acid, alcohol-modified chloroplatinic acid, complexes of platinum and diketones, complexes of chloroplatinic acid and olefins, complexes of chloroplatinic acid and alkenylsiloxane, and these supported on carriers such as alumina, silica, and carbon black. Things are exemplified. Among these, a complex of chloroplatinic acid and alkenylsiloxane is preferred because it has high catalytic activity as a catalyst for hydrosilylation whitening, and is particularly preferred as a complex of chloroplatinic acid and alkenylsiloxane.
Preferred are platinum alkenylsiloxane complexes such as those disclosed in Japanese Patent No. 22924.

The silicone resin used in the present invention has a softening point of 50 to 2.
It is necessary that the temperature be within a temperature range of 50°C. If the softening point is less than 50°C, the storage stability of the silicone rubber composition after it is added to a silicone rubber composition that is cured by a hydrosilylation reaction will decrease significantly, and if it exceeds 250°C, the catalytic activity will decrease. This is because the temperature at which the catalyst develops is too high, and it essentially ceases to function as a catalyst. From this point, the softening point of this silicone resin is 50
Preferably within the temperature range of ~200°C 70~1
More preferably, the temperature is within a temperature range of 50°C.

The molecular structure and chemical structure of this silicone resin are not particularly limited. However, it is necessary that this silicone resin does not permeate the platinum-based catalyst, and it is also necessary to select one that does not dissolve in the organopolysiloxane component in the silicone rubber composition.

Such a silicone resin has an average unit formula Ra5
A silicone resin represented by fO+4-s+/a (wherein R is a methyl group and a phenyl group, and a is a number from 0.8 to 1.8) is exemplified.

Component (E) used in the present invention is a spherical fine particle catalyst in which a platinum-based catalyst as described above is contained in a silicone resin as described above. The amount is preferably within the range of 0.01 to 5% by weight as platinum metal.

In addition, in order to sufficiently exhibit its catalytic activity and to maintain dispersion stability when added to a silicone rubber composition, its average particle diameter must be within the range of 0.01 to 10 μm. It is necessary for the shape to be spherical.

As a method for producing such a spherical fine particle catalyst, for example, a platinum-based catalyst and a silicone resin having a softening point of 50 to 250°C are dissolved in a solvent to form a solution, then the solution is sprayed into a hot air stream, and the It is manufactured by volatilizing the solvent and solidifying the silicone resin into fine particles in a sprayed state.

In addition, by emulsifying a solution consisting of a platinum-based catalyst, a silicone resin with a softening point of 50 to 250°C, and a solvent compatible therewith with an aqueous surfactant solution, and drying and removing the solvent from the emulsion, the platinum-based catalyst There is a method in which a silicone resin-containing spherical fine particle catalyst is produced, and then the platinum-based catalyst is dissolved, but the silicone resin is washed with a solvent that does not dissolve the silicone resin.

The amount of component (E) to be blended is usually in the range of 0.0000001 to 0.01 parts by weight as platinum metal atoms per 100 parts by weight of the organopolysiloxane of component (A), preferably 0.0000001 to 0.01 parts by weight as platinum metal atoms. It is within the range of 000001 to o, ooi parts by weight.

The composition of the present invention is a pressure molding silicone rubber composition comprising the above components (A) to (D).
In addition to component (D), if necessary, diorganopolysiloxane, organosilane, organosilazane, etc. endblocked with silanol groups at both terminals may be added to prevent crepe hardening, and improve storage stability and curing properties. In order to further improve the speed, additives conventionally known as inhibitors of platinum catalysts, such as benzotriazole, acetylene compounds, and hydroperoxy compounds, may be added. Depending on the purpose, various additives conventionally used in silicone rubber compositions, such as inorganic fillers, pigments, heat resistant agents, mold release agents, etc., may also be added.

Such additives include diatomaceous earth, quartz powder, calcium carbonate, mica, aluminum oxide, zinc oxide,
Examples include magnesium oxide, titanium oxide, carbon black, Bengara, etc., and examples of heat-resistant agents include rare earth oxides, cerium syralates, cerium fatty acid salts, etc.
Examples of the mold release agent include fatty acids such as stearic acid, zinc stearate, and calcium stearate, and metal salts thereof.

The composition of the present invention can be easily obtained by uniformly mixing the above components (A) to (D), but in particular, (A)
It is preferable that the component and the component CB) are first mixed uniformly, and then the component (C) and the component (D) are mixed.

The silicone rubber sheet for extrusion molding of the present invention as described above can be packaged in one package, and is extremely useful as a silicone rubber composition for extrusion molding of tubes, gaskets, wire coatings, and the like.

[Example] Next, the present invention will be explained by reference examples, examples, and comparative examples. In the examples, parts mean parts by weight, and the viscosity is 2.
The value is at 5°C, and Cst is centistokes.

In addition, in the examples, the heat curing properties of the silicone rubber composition,
Physical properties and injection molding properties were measured according to the following methods.

○Heat curing characteristics Curastmeter [Pour the silicone rubber composition into a Curastomer Model 3 manufactured by Toyo Baudouin Co., Ltd.,
Heating at 0°C, measuring the time from the time when heating started until the silicone rubber begins to harden (starts to behave as an elastic body), and this is defined as the curing start time (It),
Also, the time required for the torque to reach 90% of the maximum value (T
's) was measured.

Physical Properties of Silicone Rubber After O-curing The silicone rubber composition was placed in a mold and press-vulcanized at 150° C. for 5 minutes to obtain a silicone rubber sheet with a thickness of 2 mm. The physical properties of this sheet were measured according to JIS Kθ301.

Reference Example 1 Preparation of platinum vinyl siloxane complex composition 6 g of chloroplatinic acid aqueous solution (platinum content 33% by weight) and 16 g of 1,3-
Add 35 g of inpropyl alcohol to divinyltetramethyldisiloxane and stir at 70 to 80°C for 30 minutes in a suspended state.
It was allowed to react for 0 minutes. Isopropyl alcohol and water at pressure 5
Volatilized and removed under the conditions of 0 mm Hg and 45°C,
Platinum content 9.8% by weight by filtering the solid content
A 1,3-divinyltetramethyldisiloxane solution of the vinylsiloxane-coordinated platinum complex catalyst was prepared.

Reference Example 2 Preparation of thermoplastic silicone resin A solution prepared by diluting 332 g of phenyltrichlorosilane, 53 g of dimethyldichlorosilane, and 110 g of diphenyldichlorosilane with 150 g of toluene was mixed with 430 g of toluene, 142 g of methyl ethyl ketone, and 114 g of methyl ethyl ketone. It was dropped into a liquid consisting of water for hydrolysis.

The reaction mixture was washed with water to remove hydrogen chloride, and the organic phase was separated and further heated to remove methyl ethyl ketone. Next, 0.2 g of potassium hydroxide was added and heated, and the generated water was distilled off, followed by neutralization with acetic acid and repeated washing with water. Thereafter, the solvent was dried to obtain a thermoplastic silicone resin.

The glass transition point of this thermoplastic silicone resin is 65°C.
The softening point was 85°C.

Reference Example 3 Preparation of Spherical Fine Particle Catalyst 900 g of the thermoplastic silicone resin obtained in Reference Example 2, 500 g of toluene, and 4800 g of dichloromethane were charged into a glass container equipped with a stirrer and mixed uniformly. Next, platinum vinyl siloxane complex composition 44 obtained in Reference Example 1 was prepared.
4 g was added and mixed to obtain a homogeneous solution of platinum vinyl siloxane complex and thermoplastic silicone resin. This solution was then continuously sprayed using a fluid nozzle into a spray dryer bath with a hot stream of nitrogen gas. Here, the temperature of the hot air flow of nitrogen gas is 85°C at the inlet of the spray dryer tank, and 4°C at the outlet of the spray dryer tank.
5°C, and the hot air flow rate was 1.3 m"/min. After 1 hour of operation, 450 g
A silicone resin fine particle catalyst containing a platinum vinyl siloxane complex was collected. The average particle diameter of this particulate catalyst is 1.
1 μm, and the content of fine particle catalysts of 5 μm or more is 0
．． It was 5% by weight. Furthermore, when the shape of this particulate catalyst was observed using a scanning electron microscope, it was confirmed that this particulate catalyst was spherical.

Example 1 99.8 mol% dimethylsiloxane units, 0.2 mol% methylvinylsiloxane units, 100 parts dry organopolysiloxane raw rubber (degree of polymerization 5000), viscosity BOc
7.0 parts of silanol group-blocked dimethylpolysiloxane of ST and 45 parts of dry silica having a specific surface area of 300 m''/.g were placed in a kneader mixer and kneaded under heating until uniform. rubber base 10
The average molecular formula for 0 parts is (CHs)asio[(CBa)as10corea (
IIaCHSlO)sSl(CHa)a 0.40 parts of dimethylhydrodiene polysiloxane having a viscosity of 25 cst and 0.40 parts of the spherical fine particle catalyst obtained in Reference Example 3.
0.02 parts of silicone rubber and 0.001 parts of 1-ethynyl-1-cyclohexanol as a platinum catalyst inhibitor were mixed to prepare one-pack type silicone rubber composition 1.

For comparison, in the above, 0.05 part of the platinum vinyl siloxane complex composition obtained in Reference Example 1 was used instead of 0.02 part of the spherical fine particle catalyst obtained in Reference Example 3, and platinum catalyst inhibitor 1 was used. -ethynyl-1-cyclohexanol o. Silicone rubber composition 2 was prepared in the same manner as above except that 0.02 part of 1-ethynyl-1-cyclohexanol was mixed instead of the oot part (Comparative Example 1).

Silicone rubber tubes were manufactured by extrusion molding the silicone rubber composition 1 and silicone rubber composition 2 obtained above, and the characteristics of these silicone rubber tubes were investigated.

Here, the silicone rubber tube is made of a silicone rubber composition using an 85W extrusion mode to an inner diameter of 8. Owm■
, outer diameter 9. Extruded as ON■ tubular molded product,
This was manufactured by heat-treating it at 400° C. for 50 seconds in a hot air heating furnace. In addition, the silicone rubber physical properties, heat curing properties, and pot life of these silicone rubber first products were measured. The results of these measurements are shown in Table 1.

Table 1 Example 2 100 parts of organopolysiloxane raw rubber (degree of polymerization 5000) consisting of 89.8 mol% dimethylsiloxane units and 0.2 mol% methylvinylsiloxane units, dimethylpolysiloxane with silanol groups at both ends (viscosity 80cst) 8
．． 0 copies! : 20 parts of fumed silica with a specific surface area of 200 m"/g and wet silica with a specific surface area of 200 m"/g (
20 parts of Nip Seal LP (manufactured by Nippon Silikani Gyo Co., Ltd.) was put into a Negoo mixer and kneaded under heating until uniform. The average molecular formula for 100 parts of this silicone rubber base is IesSlo(IesSlo)s (ileH510)
Silicone rubber composition 8 was prepared by mixing 0.40 parts of dimethylhydrodiene polysiloxane represented by ssINes, 0.02 parts of platinum microcapsules obtained in Reference Example 1, and 0.001 parts of 1-ethynyl-1-cyclohexanol. Prepared. This composition 3 was extrusion molded in the same manner as in Example 1, and various properties of the silicone rubber 1 composition and the silicone rubber tube were measured in the same manner as in Example 1. These measurement results were as shown in Table 2. For comparison, 0.05 part of a platinum vinyl siloxane complex composition was used instead of the spherical fine particle catalyst containing a platinum compound catalyst, and 1-ethynyl as an inhibitor was used for comparison. Silicone rubber composition 4 was prepared by mixing 0.02 parts of -1-cyclohexanol. Regarding this composition, the curing properties and extrusion moldability were measured in the same manner as in Example 1.

These results are also listed in Table 2.

Table 2 Extrusion molding conditions and measurement results Example 3 80 parts of organopolysiloxane raw rubber (degree of polymerization 5000) consisting of 99.8 mol% dimethylsiloxane units and 0.2 mol% methylvinylsiloxane units, 98°4 dimethylsiloxane units 20 parts of organopolysiloxane raw rubber (degree of polymerization 5000) consisting of mol% and methylvinylsiloxane units o and e mol%, 13 parts of dimethylpolysiloxane (viscosity 80 cst) with silanol groups blocked at both ends, and a specific surface area of 200 m'/g. 55 parts of fumed silica was put into a kneader mixer and kneaded under heating until uniform. The average molecular formula for 100 parts of this rubber base is (fhc)ssio(CHsHSfO)nSf (CH
s) Mix 1.0 part of methylhydrodiene polysiloxane with a viscosity of 25 c s t, 0.06 part of the spherical fine particle catalyst obtained in Reference Example 1, and 0.003 part of 1-ethynyl-1-cyclohexanol. A one-pack silicone rubber composition 5 was prepared.

In addition, in the above, Reference Example 1 was used instead of the spherical fine particle catalyst.
The platinum vinyl siloxane complex composition obtained in 0. and the platinum catalyst inhibitor methyltris(methylbutynoxy)silane.
Two parts were mixed to prepare silicone rubber composition 6 (Comparative Example 3).

Electric wires coated with silicone rubber were manufactured by extrusion molding these compositions.

Here, this electric wire is made of a silicone rubber composition using an extrusion molding machine for silicone rubber-coated electric wires with an outer diameter of 1.0 m.
The core wire is coated with silicone rubber with a wall thickness of 0.5 m, and the molded product is extruded and heated in a hot air oven at 400°C.
It was manufactured by heat treatment for 15 seconds. Table 3 shows the characteristics of these silicone rubber coated wires.

Table 3 *1), 2) The values are measured after pulling out the core wire of the electric wire and using it as a pipe tube.

-7/ [Effects of the invention] The silicone rubber composition for pressure molding of the present invention consists of components (A) to (D), and especially contains a special spherical fine particle catalyst of component (D). It has excellent storage stability near room temperature, has a long pot life before molding, and has a fast heat curing speed (and has no drawbacks such as foaming).

Claims (1)

[Claims] (A) Average compositional formula RaSiO_(_4_-_a_)_/
_2 (wherein R is a substituted or unsubstituted monovalent hydrocarbon group,
a is a number from 1.8 to 2.3. ), 100 parts by weight of organopolysiloxane raw rubber having at least two silicon-bonded alkenyl groups in one molecule, (B) 10 to 100 parts by weight of fine silica powder, (C) at least two in one molecule. organohydrodiene polysiloxane having silicon-bonded hydrogen atoms of 0
．． 1 to 10 parts by weight, (D) 0.01% by weight of platinum-based catalyst as platinum metal atoms
A spherical fine particle catalyst composed of a silicone resin containing the above (here, the softening point of the silicone resin is 50 to 250
℃, and the particle size of the spherical fine particle catalyst is 0.01 to 10μ
It is m. ) A silicone rubber composition for extrusion molding, comprising a catalytic amount.