JPH0248179B2 - KOKASEIORUGANOHORISHIROKISANSOSEIBUTSU - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a curable organopolysiloxane composition, particularly a curable organopolysiloxane composition that can be easily cured by relatively gentle heating and provides a silicone rubber with excellent low temperature properties. The present invention relates to siloxane compositions. (Prior art) Silicone oils, gels, and rubbers formed from dimethylpolysiloxane have excellent heat resistance and weather resistance, and are characterized by small changes in physical properties due to temperature changes. Even at low temperatures of -50°C or higher, the elastic modulus of silicone rubber changes by only a few percent. However, since this siloxane also has a crystallization point between -50 and -60°C, it becomes solid at temperatures below -50°C and loses its oil, gel, and rubber properties. This method has been tried, and the most common method currently is to introduce a phenyl group, but in this case, the movement of the phenyl group changes significantly depending on the temperature, so the phenyl group is formed. The disadvantage is that silicone oils, gels and rubbers are highly temperature dependent. (Structure of the Invention) The present invention relates to a curable organopolysiloxane composition that solves the above-mentioned disadvantages. α, ω with an average degree of polymerization of 50 or less and a ratio of weight average molecular weight to number average molecular weight of 1.5 or less, represented by
- 100 parts by weight of vinyldimethylpolysiloxane, (2)
general formula

[Formula] (where R is a hydrogen atom or the same or different unsubstituted or substituted saturated 1
valence hydrocarbon group, m = an integer of 3 to 6),
0.7 hydrogen atoms bonded to silicon atoms per vinyl group in the first component, which contains at least 3 hydrogen atoms bonded to silicon atoms in one molecule.
Cyclic siloxane in an amount giving ~5 pieces, (3) filler 0~
500 parts by weight, and (4) a catalytic amount of platinum or a platinum compound. That is, the present inventors investigated various ways to improve the low-temperature characteristics of dimethylpolysiloxane without introducing phenyl groups into the molecule, and as a result, we found that both ends of the molecular chain are blocked with vinyl groups as vinyldimethylpolysiloxane. In addition to selecting α,ω-vinyldimethylpolysiloxane, an organohydrodienepolysiloxane containing a hydrogen atom (≡SiH bond) bonded to a silicon atom to be subjected to an addition reaction with the vinyl group is used as a cyclic structure to carry out the reaction. It was discovered that by introducing a cyclic structure into the vinyl group site of vinyldimethylpolysiloxane, which serves as a cross-linking point, crystallization between the cross-linking points can be inhibited. There is a limit to the range of influence, including increasing the number of siloxane units between the bridging points by 50.
In addition, it is necessary to make the siloxane have a ratio of weight average molecular weight to number average molecular weight of 1.5 or less, so that the rubber obtained here will not have a melting point and its elastic modulus will be lower than that of glass. The present invention was completed by confirming that there is almost no change up to the dislocation temperature of about -100°C, and therefore a product with excellent low temperature properties can be obtained. α,ω-vinyldimethylpolysiloxane as the first component constituting the composition of the present invention has the general formula If the average degree of polymerization is 50 or more, this is a cyclic structure formed by the second component described below at the vinyl group site of dimethylsiloxane represented by the above general formula, which serves as a crosslinking point. The effect of inhibiting crystallization due to the introduction of
If the ratio w/n to n) is 1.5 or more, the molecular weight distribution will expand and there will be polymers with a higher degree of polymerization than the average degree of polymerization, and this portion will have a negative effect on low temperature properties. The average degree of polymerization must be 50 or less and the above w/n = 1.5 or less. In addition, as described above, the organosiloxane containing a hydrogen atom bonded to a silicon atom in its molecule as the second component introduces a cyclic structure into the site of the vinyl group that serves as a cross-linking point in the first component. General formula because it is a thing

[Formula], where R is a hydrogen atom, an alkyl group such as a methyl group, an ethyl group, a propyl group, a butyl group, an aryl group such as a phenyl group or a tolyl group, a cycloalkyl group such as a cyclohexyl group, or a cycloalkyl group such as a cyclohexyl group. The group is selected from chloromethyl groups, trifluoropropyl groups, cyanomethyl groups, etc. in which some or all of the hydrogen atoms bonded to the carbon atoms of the group are substituted with halogen atoms, cyano groups, etc., preferably 50% of which are methyl groups. It is a cyclic siloxane having at least three silicon-bonded hydrogen atoms (≡SiH bonds) in one molecule, which is the same or different kind of unsubstituted or substituted saturated monovalent hydrocarbon group. The first thing mentioned above is
Since the purpose is to generate a cured product through an addition reaction between the vinyl group in the component and this ≡SiH bond, it is necessary to provide only 0.7 to 5 ≡SiH bonds to one vinyl group in the first component. It is necessary to add it in quantity. Next, the filler as the third component in this composition is an optional component for adjusting the physical properties of the cured product obtained from this composition, and when it is added, the cured product has a lower mechanical strength. , resulting in a product with excellent thermal conductivity and flame retardancy. Examples of fillers used for this purpose include fumed silica, precipitated silica, aluminum silicate, quartz powder, fused silica powder, diatomaceous earth, calcium carbonate, titanium dioxide, and carbon black. Iron, zinc oxide, magnesium carbonate, etc. may also be blended. The amount of this filler to be blended is 100 parts by weight of the first component, because if it is blended in an excessive amount, the fluidity of the composition will deteriorate, and the cured product obtained from this composition will be hard and brittle. 500 parts by weight or less. The platinum compound as the fourth component in this composition is used as a catalyst for promoting the addition reaction between the first component and the second component, and includes platinum black, chloroplatinic acid, chloroplatinum Examples include complex salts of acids and olefins or aldehydes, alcohol-modified products of chloroplatinic acid, and the amount used may be increased or decreased as appropriate depending on the desired curing speed of this composition due to the reaction between the first component and the second component. Usually, the amount of platinum may be in the range of 0.1 to 50 ppm relative to the amount of the first component used. The composition of the present invention can be obtained by uniformly mixing predetermined amounts of the first to fourth components described above, but this composition may have a relatively low viscosity depending on the type and blending ratio of each component. Various compositions are obtained, from compositions with good fluidity to putty-like and non-flowable compositions. Therefore, various processing methods such as coating, impregnation, filling, and casting can be used to obtain molded products from this composition, but for example, gentle heating at about 80 to 150°C can be used. The molded product obtained in this way is an industrial product whose low-temperature properties do not change up to the glass transition point, such as -100℃, because crystallization between the crosslinking points is inhibited. advantage is given. Next, examples of the present invention will be given, where parts in the examples are parts by weight, and viscosity in the examples is a value measured at 25°C. Example 1, Comparative Example 1 Both ends of the molecular chain are blocked with vinyl dimethylsilyl groups, the viscosity is 19 cS, the average degree of polymerization is 24, w/
To 100 parts of dimethylpolysiloxane with Mn = 1.16, the formula

6.3 parts of tetramethylcyclotetrasiloxane represented by the formula, 5% of chloroplatinic acid
When 0.1 part of isopropyl alcohol solution was mixed and the mixture was placed in a mold with a depth of 2 mm and heated at 120°C for 10 minutes, a silicone rubber sheet measuring 2 x 100 x 100 mm was obtained. Next, a 2 x 3 x 30 mm test piece was cut out from this sheet and the temperature dependence of its elastic modulus was measured using a viscoelastic spectrometer (manufactured by Iwamoto Seisakusho), as shown in Table 1 below. The results were obtained, but for comparison, the measured values for the dimethylpolysiloxane used above with an average degree of polymerization of 52 and treated in the same manner as above are the first.
It was as listed in the table.

[Table] Example 2 Both ends of the molecular chain are blocked with vinyldimethylsilyl groups, viscosity is 3 cS, average degree of polymerization n = 5, w/
To 100 parts of dimethylpolysiloxane where n = 1.1, 25 parts of tetramethylcyclotetrasiloxane,
5% isopropyl alcohol solution of chloroplatinic acid
0.1 part was added and processed in the same manner as in Example 1 to make a sheet. A test piece was cut out and its elastic modulus was examined, and the results shown in Table 2 below were obtained.

[Table] Example 3 Dimethylpolysiloxane with a viscosity of 26 cS, average degree of polymerization n = 35, and w/n = 1.15, with both molecular chain ends capped with vinyldimethylsilyl groups.
100 parts of fumed silica 20 with a specific surface area of 200 m ² /g surface-treated with trimethylchlorosilane
4.4 parts of tetramethylcyclotetrasiloxane and 0.1 part of a 5% isopropyl alcohol solution of chloroplatinic acid were added and mixed to prepare a composition. Next, this composition was heated at 120℃ under a pressure of 100Kg/ ^cm2 .
When a sample piece of 2 x 3 x 30 mm was prepared by heat treatment for 10 minutes and the elastic modulus of this sample was measured, the results shown in Table 3 were obtained.

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Claims (1)

[Claims] 1 (1) General formula α,ω-vinyldimethylpolysiloxane with an average degree of polymerization of 50 or less and a ratio of weight average molecular weight to number average molecular weight of 1.5 or less, represented by 100
Part by weight (2) In one molecule, represented by the general formula [Formula] (where R is a hydrogen atom or the same or different unsubstituted or substituted saturated monovalent hydrocarbon group, m = an integer from 3 to 6) a cyclic siloxane (3) filler containing at least 3 hydrogen atoms bonded to silicon atoms in an amount that provides 0.7 to 5 hydrogen atoms bonded to silicon atoms per vinyl group in the first component; 0 to 500 parts by weight (4) A curable organopolysiloxane composition comprising a catalytic amount of platinum or a platinum compound.