JP2835447B2 - Heat-curable organopolysiloxane composition - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a heat-curable organopolysiloxane composition, and more particularly to an organopolysiloxane composition which gives a silicone rubber having excellent toughness (toughness) upon curing. .

[Prior Art] Silicone rubber has properties as a rubber elastic body having excellent properties in a wide temperature range, and thus is widely used in electric wire covering materials, keyboards, gaskets, packings, medical tubes, and the like. However, in general, silicone rubber has a disadvantage that it is inferior in toughness (toughness) as compared with other organic rubbers. Therefore, various methods have been proposed to improve this disadvantage. One of the attempts is to increase the tear strength of silicone rubber.For example, a high-molecular-weight organopolysiloxane having a low vinyl group content, a low-molecular-weight organopolysiloxane having a high vinyl group content, and silica fine powder as main components are used. Silicone rubber composition obtained by curing a silicone rubber composition to be cured with an organic peroxide to make the crosslink density extremely polar (see Japanese Patent Publication No. 48-10633), a mixture of a high molecular weight vinyl group-containing organopolysiloxane and an organohydrogen polymer There has been proposed a silicone rubber obtained by curing a silicone rubber composition containing siloxane and silica fine powder as main components with an organic peroxide (see JP-A-56-41252).

[Problems to be Solved by the Invention] However, the silicone rubber obtained by the above-described method has a high measured value of the tear strength itself as a mechanical property, but has a low modulus and is soft. It was of such a degree that it was damaged and cut by nails, and it could not be said that it was a silicone rubber having very excellent toughness.

The present inventors have conducted intensive studies to improve the disadvantages of the related art, and as a result, have reached the present invention.

An object of the present invention is to provide an organopolysiloxane composition which gives a silicone rubber having a high modulus and a high tear strength and excellent toughness after heat curing.

[Means and its effect for solving the problems] The present invention is (A) the general formula _{^{▲ R 1 3 ▼ SiO [▲}} R 2 2 ▼ SiO] nSi ▲ R 1 3 ▼ ( wherein, R ¹ represents a substituted or unsubstituted A substituted or unsubstituted monovalent hydrocarbon group or a hydroxyl group, and R ² is a substituted or unsubstituted monovalent hydrocarbon group.) Having a molecular weight of 500,000 or more as a weight average molecular weight; 100 parts by weight of an organopolysiloxane having an index in the range of 1.3 to 3.0, (B) R ₃ SiC _1/2 unit, R ₂ SiO unit, RSiO _3/2 unit (wherein,
Each R is a substituted or unsubstituted monovalent hydrocarbon group. )
And it consists organo km hexane units and SiO ₂ units selected from the group consisting of mixtures (where the molar ratio SiO ₂ units of the organosiloxane units is from 0.08 to 2.0
It is. ), 30 to 130 parts by weight of a reinforcing organopolysiloxane resin having a specific surface area of 200 m ² / g or more, and (C) a curing agent in an amount sufficient to cure the composition of the present invention. It relates to a siloxane composition.

Explaining this, the component (A) used in the present invention is one of the components that characterize the present invention, and forms a skeleton of silicone rubber by heat curing.

In the above formula (A), R ¹ is an alkyl group such as a methyl group, an ethyl group, or a propyl group; a cycloalkyl group such as a cyclohexyl group; an aralkyl group such as a β-phenylethyl group; And a substituted or unsubstituted monovalent hydrocarbon group or a hydroxyl group exemplified by a hydrogen atom of these groups substituted with a cyano group or the like, wherein R ² is the same as the substituted or unsubstituted R ¹ It is a substituted monovalent hydrocarbon group.

In the present invention, the molecular weight of the organopolysiloxane raw rubber of the component (A) is defined as a weight average molecular weight.
500,000 or more and its dispersion index (weight average molecular weight / number average molecular weight) needs to be in the range of 1.3 to 3.0.

This is because when the weight average molecular weight is less than 500,000, the degree of entanglement of the molecular chain of the organopolysiloxane raw rubber itself is low and the formation ratio of pseudo-crosslinking points is small, so that the modulus does not increase after heat curing, and the modulus is high. This is because a tough silicone rubber having a high tear property is not obtained, and only a silicone rubber having a high tear property can be obtained.

Here, the weight average molecular weight is measured by gel permeation chromatography according to a measuring method described later, and is calculated in terms of polystyrene.

The reinforcing organopolysiloxane resin of the component (B) used in the present invention is an essential component that characterizes the present invention, and functions to improve the toughness of the silicone rubber obtained by heat-curing the composition of the present invention. . Such (B)
The components are R ₃ SiC _1/2 unit, R ₂ SiO unit, RSiO _3/2 unit (wherein,
R is a substituted or unsubstituted monovalent hydrocarbon group. ) And the organopolysiloxane resin consisting of organosiloxane units and SiO ₂ units selected from the group consisting of mixtures. The amount of the organosiloxane units is an amount sufficient to hydrophobic reinforcing organopolysiloxane resin, the molar ratio of SiO ₂ units in the organosiloxane units is required to be within a range of 0.08 to 2.0, 0.20 It is preferably in the range of ~ 1.5. It has a molar ratio of 0.0
If it is less than 8, the mixing property will be reduced, while if it exceeds 2.0, the reinforcing property will be remarkably reduced and it will not be necessary as a reinforcing resin. Further, the shape is preferable in that the specific surface area is 200 m ² / g or more, preferably 300 m ² / g or more, in that the toughness of the obtained silicone rubber is increased.

Such a component (B) can be obtained, for example, by the method disclosed in Japanese Patent Publication No. 61-56255 or U.S. Pat. No. 4,418,165. According to these methods (B)
The component is usually obtained as a gel containing ammonia gas and a methanol solvent, and this gel can be directly blended as a reinforcing organopolysiloxane resin with the organopolysiloxane raw rubber of the component (A), It is also possible to remove the solvent and ammonia gas from the gel to obtain a powdery reinforcing organopolysiloxane resin, which can be blended with the organopolysiloxane raw rubber of the component (A).

In the present invention, the former method, that is, the above-mentioned gel-like substance is directly blended with the organopolysiloxa raw rubber of the component (A), and kneaded while removing the solvent and ammonia gas, and finally (A) The use of a mixture in which the reinforcing resin of the component (B) is uniformly dispersed in the organopolysiloxane raw rubber of the component can prevent molecular breakage of the organopolysiloxane raw rubber of the component (A), which easily occurs during kneading. This is a preferable means in terms of improving production efficiency.

In addition, the compounding amount is 30 parts by weight per 100 parts by weight of the component (A).
It is in the range of ~ 130 parts by weight, preferably in the range of 40-80 parts by weight.

The curing agent (C) used in the present invention is a catalyst for curing the composition of the present invention or a mixture of the catalyst and a crosslinking agent, and is used for curing a usual organopolysiloxane composition for silicone rubber. Can be used.

Examples of such a curing agent include a combination of an organic peroxide or a platinum compound catalyst and at least two silicon-bonded hydrogen atom-containing organohydrogenpolysiloxanes in one molecule.

Examples of the former organic peroxide include benzoyl peroxide, p-chlorobenzoyl peroxide,
Examples thereof include di-t-butylperoxide, 2,5-dimethyl-di-2,5-di (t-butylperoxy) hexane, and dicumyl peroxide.

Among the latter curing agents, examples of platinum compound catalysts include platinum black, chloroplatinic acid, platinum tetrachloride, olefin complexes of chloroplatinic acid, complexes of chloroplatinic acid with methylvinylsiloxane, rhodium compounds, and palladium compounds. And 1
Examples of the organohydrogenpolysiloxane containing at least two silicon-bonded hydrogen atoms in the molecule include a methylhydrogenpolysiloxane capped at both ends with trimethylsiloxy groups, a dimethylsiloxane / methylhydrogensiloxane copolymer capped at both ends with trimethylsiloxy groups, Examples thereof include a methylphenylsiloxane-methylhydrogensiloxane copolymer capped with dimethylphenylsiloxy groups at both ends, a cyclic methylhydrogenpolysiloxane, and a copolymer composed of dimethylhydrogensiloxy units and SiO _4/2 units.

In order to produce the composition of the present invention, for example, a base of silicone rubber was prepared by previously kneading the components (A) and (B) uniformly with a mixer such as a two-roll mill, a kneader mixer or a pressure kneader mixer. It can be easily obtained by blending the component (C) on two subsequent rolls. Here, in order to improve the workability of the composition of the present invention at the time of uncuring, and to improve the modulus and tear strength of the cured silicone rubber, a low molecular weight vinyl group-containing organopolysiloxane is used as a solvating agent. It is also possible to use as.

In the present invention, in addition to the above components (A) to (C), various inorganic fillers and pigments, for example, heat-resistant agents such as zinc oxide, titanium oxide, carbon black, red iron oxide, cerium oxide, and fatty acid salts of cerium. The addition may be made as long as the object of the present invention is not impaired.

The composition of the present invention thus obtained is characterized in that it becomes a tough silicone rubber having high modulus and high tearing properties after heat curing.

In other words, the mechanical properties have a tear strength (JIS A type) of 40 kg / cm or more Tear strength (JIS B type) of 40 kg / cm or more 50% modulus 15 kg / cm ² or more 100% modulus 30 kg / cm ² or more It is a tough silicone rubber.

Explaining this, the silicone rubber obtained by heat-curing the composition of the present invention is a silicone rubber having the above-mentioned mechanical properties, which, when measured according to the method specified in JIS K6301, usually has a tear strength of JIS. It is more than 40kg / cm when measured with A type, and even when measured with JIS B type
40 kg / cm or more. J for general silicone rubber
The measured value of the tear strength of the IS A type often indicates crack prevention performance, and a numerical value higher than the measured value of the JIS B type tends to be calculated. However, the silicone rubber obtained by heat-curing the composition of the present invention is characterized in that it shows a high value of 40 kg / cm or more even when measured by JIS B type. Normally, when this value is less than 40 kg / cm ² , there is a case where a sharp object such as a human nail is easily torn and does not have true toughness.

The modulus is important in this case in relation to the tear strength, especially the modulus at low elongations of 100% or less,
It is important in the relationship between tear strength and toughness. JIS K6301
50% modulus when measured according to the method prescribed in (tensile elongation tensile stress at 50%) is 15 kg / cm ² or more, 10
0% modulus (tensile stress when tensile elongation is 100%) is 30
kg / cm ² or more.

The composition of the present invention thus obtained has a feature that silicone rubber after heat curing has excellent toughness, and by utilizing such a feature, rubber for automobile wipers, various rubber belts, and a non-braided wire covering material. , Medical tubes, high-performance constant velocity joint boots, scuba diving equipment, and the like.

[Examples] Next, the present invention will be described with reference to examples and reference examples.
In the examples, “parts” means “parts by weight”, and the viscosity is
Value at 25 ° C. Further, the measurement of the molecular weight of the organopolysiloxane raw rubber and the measurement of the surface area of the reinforcing organopolysiloxane resin were performed according to the following methods.

<Measurement of Molecular Weight of Organopolysiloxane Raw Rubber> An organopolysiloxane raw rubber is dissolved in toluene to prepare a sample for gel permeation chromatography (hereinafter referred to as GPC). ]. The molecular weight was calculated based on a standard polyethylene sample. Accordingly, the molecular weight of the obtained organopolysiloxane raw rubber is a weight average molecular weight in terms of polyethylene.

<Measuring method of surface area of reinforcing organopolysiloxane resin> Specific surface area automatic measuring device Model 2200 [manufactured by Shimadzu Corporation]
Was measured according to the well-known BET method (continuous flow rate nitrogen adsorption method).

Reference Example 1 Preparation of Hydrophobizing Agent It was prepared as follows according to the method described in JP-B-61-56255.

Octamethylcyclotetrasiloxane 277 g, 1,3,5,
4.6 g of 7-tetramethyl-1,3,5,7-tetravinylcyclotetrasiloxane, 517 g of methyltrimethoxysilane and 0.43 g of potassium hydroxide as a catalyst are reacted at a temperature of 105 ° C. for about 2 hours to open and re-open the ring. An ordered organopolysiloxane was prepared. Here, potassium hydroxide was neutralized with carbon dioxide gas. Analysis of the resulting organopolysiloxane revealed that it was a linear organopolysiloxane containing 0.7 mol% of methylvinylsiloxy groups (hereinafter referred to as hydrophobizing agent A).

Also, 282 g of octamethylcyclotetrasiloxane,
517 g of methyltrimethoxysilane and 0.4 g of potassium hydroxide
Was reacted in the same manner as described above to obtain a linear organopolysiloxane containing no vinyl group (hereinafter referred to as hydrophobicizing agent B).
).

Reference Example 2 Synthesis of reinforcing organosiloxane resin Methanol 118, concentrated ammonia water 3
2 g and 39 g of the hydrophobizing agent A obtained in Reference Example 1 were added thereto, and the temperature of the reaction solution was adjusted to 30 ° C. to 40 ° C. while mixing with electromagnetic stirring.
Was heated. Then, while vigorously stirring the mixture, 96 g of methyl orthosilicate was added thereto at once. The reaction product became a gel after 20 seconds. Therefore, stirring was stopped, and the mixture was left to stand for one week in a sealed state to ripen.

After the obtained gel-like material (hereinafter, referred to as gel-like reinforcing resin A) is pulverized, it is put into an evaporator, and methanol and ammonia gas contained in the gel are removed under reduced pressure at a temperature of 90 ° C. Powdered reinforcing organopolysiloxane resin (hereinafter referred to as powdered reinforcing resin A)
I got The BET surface area of this product was determined.
It was 20 m ² / g. Similarly, a gel was obtained in the same manner as described above except that the hydrophobizing agent B was used instead of the hydrophobizing agent A (hereinafter, referred to as a gel-like reinforcing resin B).
Next, the gel-like material was treated in the same manner as above to obtain a powdery reinforcing organopolysiloxane resin (hereinafter, referred to as a powdery reinforcing resin B). It has a BET surface area of 6
It was 50 m ² / g.

Example 1 85 parts of a dimethylpolysiloxane raw rubber having a weight average molecular weight of 850,000 [vinyl group content 0.03% by weight, dispersity index 1.8], both ends of which are blocked with dimethylvinylsiloxy groups, and 85 parts of both ends of the molecular chains blocked with hydroxyl groups. Dimethylpolysiloxane having a weight average molecular weight of 450,000 [vinyl group content 2.20% by weight,
(Dispersion index 1.9, hereinafter referred to as high vinyl gum)] was placed in a kneader mixer. Next, 240 minutes of the gel-like reinforcing resin A (solid content: 25%) obtained in Reference Example 2 was dividedly charged, and the mixture was uniformly mixed while removing methanol at 90 ° C. This was further heated and mixed under reduced pressure at 180 ° C. for 2 hours to completely remove volatile components, thereby producing a silicone rubber base.
To 100 parts of this silicone rubber base, 1.4 parts of methyl hydrogen polysiloxane resin (silicon-bonded hydrogen atom content: 1.0% by weight) having a viscosity of 20 centistokes was blended, and then a complex salt of methylvinylpolysiloxane and chloroplatinic acid (platinum) 9 ppm as platinum metal
And mixed with two rolls to obtain a silicone rubber composition. The silicone rubber composition is heated to a temperature of 170
℃ pressure 30kg / cm compression 10 minutes molding under the conditions of ^2, a thickness of 2mm
Sheet. The physical properties of this sheet were measured according to the method specified in JIS K6301. The results were as shown in Table 1.

In the above, a specific surface area of 300 m ² /
The physical properties of the silicone rubber composition obtained in the same manner as above except that g of the fumed silica were used were measured in the same manner as above. The results are as shown in Table 1.

Example 2 85 parts of dimethylpolysiloxane raw rubber having a weight average molecular weight of 850,000 [vinyl group content 0.03% by weight, dispersion index 1.8], both ends of which are blocked with dimethylvinylsiloxy groups, 85 parts, both ends of which are blocked with hydroxyl groups Dimethylpolysiloxane having a weight average molecular weight of 450,000 [vinyl group content 2.20% by weight,
Dispersion index 1.9] and 2 parts of methylvinylpolysiloxane [vinyl group content 8% by weight] having a viscosity of 30,000 centistokes at 25 ° C. were put into a kneader mixer. Next, the gel-like reinforcing resin B obtained in Reference Example 2 was added thereto.
(Solid content 25%)
The mixture was uniformly mixed while being removed at 0 ° C. This was further heated and mixed under reduced pressure at 180 ° C. for 2 hours to completely remove volatile components, thereby producing a silicone rubber base. Based on 100 parts of this silicone rubber base, 1.4 parts of methyl hydrogen polysiloxane having a viscosity of 20 centistokes (content of silicon-bonded hydrogen atoms: 1.0% by weight) and a complex salt of methylvinyl polysiloxane and chloroplatinic acid (containing platinum) Amount 0.
(6% by weight) as platinum metal in an amount of 9 ppm and uniformly mixed with two rolls to obtain a silicone rubber composition. This was molded into a sheet under the same conditions as in Example 1 and its physical properties were measured. The results were as shown in Table 2.

Example 3 85 parts of dimethylpolysiloxane raw rubber having a weight-average molecular weight of 850,000 [vinyl group content 0.03% by weight, dispersity index 1.8], both ends of which are blocked with dimethylvinylsiloxy groups, and 85 parts of both ends of the molecular chains blocked with hydroxyl groups. Dimethylpolysiloxane having a weight average molecular weight of 450,000 [vinyl group content 2.20% by weight,
Dispersion index 1.9] and the powdered resin B obtained in Reference Example 2 were placed in a kneader mixer and uniformly mixed. Subsequently, 0.4 part of 2,5-dimethyl-2,5-di (t-butylperoxy) hexane was added to 100 parts of the mixture, and the mixture was uniformly mixed with two rolls to obtain a silicone rubber composition. This silicone rubber composition was compression molded for 10 minutes at a temperature of 170 ° C. and a pressure of 30 kg / cm ² to form a sheet having a thickness of 2 mm. The physical properties of this sheet were measured according to the method specified in JIS K6301. The results were as shown in Table 3.

Example 4 85 parts of dimethylpolysiloxane raw rubber having a weight average molecular weight of 850,000 [vinyl group content 0.03% by weight, dispersity index 1.8], both ends of which are blocked with dimethylvinylsiloxy groups, and 85 parts of both ends of the molecular chains blocked with hydroxyl groups. Dimethylpolysiloxane having a weight average molecular weight of 450,000 [vinyl group content 2.20% by weight,
Dispersion index 1.9] and the powdered resin B obtained in Reference Example 2 were placed in a kneader mixer and uniformly mixed. Then, 1.5 parts of methyl hydrogen polysiloxane resin (silicon-bonded hydrogen atom content: 1.0% by weight) and 3% by weight of chloroplatinic acid in isopropyl alcohol solution were added to 100 parts of the mixture in an amount of 10 ppm as platinum metal and uniformly mixed. Then, a silicone rubber composition was obtained. This silicone rubber composition was compression molded for 10 minutes at a temperature of 170 ° C. and a pressure of 30 kg / cm ² to form a sheet having a thickness of 2 mm. JIS K6 for this sheet
Physical properties were measured according to the method specified in 301. The results were as shown in Table 4.

[Effects of the Invention] The heat-curable organopolysiloxane composition of the present invention comprises the components (A) to (C), and in particular, the specific organopolysiloxane raw rubber of the component (A) and the specific reinforcing property of the component (B). Since it contains an organopolysiloxane resin, it has a high modulus after heat curing, and has the characteristic that it can be an unconventional silicone rubber having high tear strength and excellent toughness.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows the relationship between the tensile elongation and the tensile stress of the silicone rubber obtained in Example 1 of the present invention.

Claims (1)

(57) [Claims] 1. A (A) the general formula ^{_{R 1 3 SiO [R 2 2}} SiO] n SiR 1 3 ( wherein, R ¹ is a substituted or unsubstituted monovalent hydrocarbon group or a hydroxyl group, R ² is substituted Or an unsubstituted monovalent hydrocarbon group) having a molecular weight of 500,000 or more as a weight average molecular weight and a dispersion index of the molecular weight in the range of 1.3 to 3.0, 100 parts by weight of an organopolysiloxane raw rubber. , (B) R ₃ SiC _1/2 unit, R ₂ SiO unit, RSiO _3/2 unit (wherein,
Each R is a substituted or unsubstituted monovalent hydrocarbon group. )
And it consists organosiloxane units and SiO ₂ units selected from the group consisting of mixtures (where the molar ratio SiO ₂ units of the organosiloxane units is from 0.08 to 2.0
It is. ), 30 to 130 parts by weight of a reinforcing organopolysiloxane resin having a specific surface area of 200 m ² / g or more, and (C) a curing agent in an amount sufficient to cure the composition of the present invention. A siloxane composition, the silicone rubber after heat curing has a tear strength (JIS A type) of 40 kg / cm or more, a tear strength (JIS B type) of 40 kg / cm or more, and a 50% modulus of 15 kg. A heat-curable organopolysiloxane composition having a modulus of 100% / cm or more and a 100% modulus of 30 kg / cm or more.