Silicone gel composition and silicone gel cured product

Abstract

Provided are: a silicone gel composition providing a silicone gel cured product having excellent heat resistance at high temperatures; and a cured product (silicone gel) thereof. This silicone gel composition is an addition reaction-curable silicone gel composition containing, with respect to the total (mass) of the composition, 1-1,000 ppm of a niobium carboxylate and/or nickel carboxylate represented by the following formula (3).
(R.sup.3COO).sub.fM(3)
(In the formula, R.sup.3 is a homogeneous or heterogeneous monovalent hydrocarbon group, M is at least one metal selected from among nickel and niobium, and f is 2 when M is nickel and 4 or 5 when M is niobium).

Claims

1. A silicone gel composition comprising: (A) 100 parts by weight of an organopolysiloxane having at least one silicon-bonded alkenyl group per molecule, represented by the average compositional formula (1):
R.sub.aR.sup.1.sub.bSiO.sub.(4-a-b)/2(1) wherein R is independently alkenyl, R.sup.1 is independently a substituted or unsubstituted monovalent hydrocarbon group free of aliphatic unsaturation, a is a positive number of 0.0001 to 0.2, b is a positive number of 1.7 to 2.2, and the sum a+b is 1.9 to 2.4, (B) an organohydrogenpolysiloxane having at least two silicon-bonded hydrogen atoms per molecule, represented by the average compositional formula (2):
R.sup.2.sub.cH.sub.dSiO.sub.(4-c-d)/2(2) wherein R.sup.2 is independently a substituted or unsubstituted monovalent hydrocarbon group free of aliphatic unsaturation, c is a positive number of 0.7 to 2.2, d is a positive number of 0.001 to 0.5, and the sum c+d is 0.8 to 3, in such an amount as to give 0.01 to 3 silicon-bonded hydrogen atoms in component (B) per silicon-bonded alkenyl in the entire composition, (C) an effective amount of a platinum-based catalyst, and (D) a nickel carboxylate and/or niobium carboxylate having the formula (3):
(R.sup.3COO).sub.fM(3) wherein R.sup.3 which may be the same or different is a monovalent hydrocarbon group, M is at least one metal selected from nickel and niobium, f is 2 when M is nickel, and f is 4 or 5 when M is niobium, and the nickel carboxylate and/or niobium carboxylate as component (D) is present in an amount of 100 ppm to 500 ppm based on the total weight of the composition.

2. A silicone gel composition comprising: (A) 100 parts by weight of an organopolysiloxane having at least one silicon-bonded alkenyl group per molecule, represented by the average compositional formula (1):
R.sub.aR.sup.1.sub.bSiO.sub.(4-a-b)/2(1) wherein R is independently alkenyl, R.sup.1 is independently a substituted or unsubstituted monovalent hydrocarbon group free of aliphatic unsaturation, a is a positive number of 0.0001 to 0.2, b is a positive number of 1.7 to 2.2, and the sum a+b is 1.9 to 2.4, (B) an organohydrogenpolysiloxane having at least two silicon-bonded hydrogen atoms per molecule, represented by the average compositional formula (2):
R.sup.2.sub.cH.sub.dSiO.sub.(4-c-d)/2(2) wherein R.sup.2 is independently a substituted or unsubstituted monovalent hydrocarbon group free of aliphatic unsaturation, c is a positive number of 0.7 to 2.2, d is a positive number of 0.001 to 0.5, and the sum c+d is 0.8 to 3, in such an amount as to give 0.01 to 3 silicon-bonded hydrogen atoms in component (B) per silicon-bonded alkenyl in the entire composition, (C) an effective amount of a platinum-based catalyst, and (D) a niobium carboxylate having the formula (3):
(R.sup.3COO).sub.fM(3) wherein R.sup.3 which may be the same or different is a monovalent hydrocarbon group, M is niobium, f is 4 or 5, in an amount of 1 to 1,000 ppm based on the total weight of the composition.

3. The silicone gel composition of claim 1 or 2 which cures into a cured silicone gel having a penetration of 10 to 150 according to JIS K2220.

4. The silicone gel composition of claim 1 or 2 which cures into a cured silicone gel having a loss factor of 0.1 to 1.0 at 25 C. and shear frequency 1 Hz and a loss factor of 0.3 to 1.5 at 25 C. and shear frequency 10 Hz.

5. A cured silicone gel which is obtained by curing the silicone gel composition of claim 1 or 2.

6. A cured silicone gel which is obtained by curing the silicone gel composition of claim 3.

7. A cured silicone gel which is obtained by curing the silicone gel composition of claim 4.

Description

EXAMPLES

(1) Examples and Comparative Examples of the invention are given below by way of illustration and not by way of limitation. In Examples, parts and % are by weight. Vi stands for vinyl. The penetration is measured according to JIS K2220 with a cone, using an automatic penetrometer RPM-101 by Rigo Co., Ltd. The degree of polymerization or the number of repeating units is calculated from a number average degree of polymerization as analyzed by GPC versus polystyrene standards using toluene as developing solvent.

Example 1

(2) A silicone gel composition (Composition 1) was prepared by mixing 60 parts of both end dimethylvinylsiloxy-blocked dimethylsiloxane/diphenylsiloxane copolymer represented by the average molecular formula (4) and having a viscosity of 1,000 mPa.Math.s at 25 C., 40 parts of trimethylsiloxy and dimethylvinylsiloxy-blocked dimethylsiloxane/diphenylsiloxane copolymer represented by the average molecular formula (5) and having a viscosity of 700 mPa.Math.s at 25 C., 0.55 part of both end trimethylsiloxy-blocked dimethylsiloxane/methylhydrogensiloxane copolymer represented by the average molecular formula (6) and having a viscosity of 100 mPa.Math.s at 25 C., 5.6 parts of both end dimethylhydrogensiloxy-blocked dimethylpolysiloxane represented by the average molecular formula (7) and having a viscosity of 18 mPa.Math.s at 25 C. (to give 1.15 silicon-bonded hydrogen in component (B) per silicon-bonded alkenyl in the composition, that is, H/Vi ratio=1.15), 0.05 part of a dimethylpolysiloxane solution of chloroplatinic acid-vinylsiloxane complex (platinum concentration 1%), 0.02 part of ethynylcyclohexanol, and 0.05 part of nickel 2-ethylhexanoate (about 500 ppm based on the total weight of the composition) until uniform.

(3) ##STR00002## ##STR00003## ##STR00004##
The resulting Composition 1 was heat cured at 80 C. for 60 minutes, yielding a cured silicone gel having a penetration of 45.

Example 2

(4) Composition 2 was prepared as in Example 1 except that 0.01 part of niobium 2-ethylhexanoate (about 100 ppm based on the total weight of the composition) was used instead of 0.05 part of nickel 2-ethylhexanoate. Composition 2 was heat cured at 80 C. for 60 minutes, yielding a cured silicone gel having a penetration of 50.

Comparative Example 1

(5) Composition 3 (nickel carboxylate and/or niobium carboxylate content 0 ppm) was prepared as in Example 1 except that 0.05 part of nickel 2-ethylhexanoate was omitted. Composition 3 was heat cured at 80 C. for 60 minutes, yielding a cured silicone gel having a penetration of 40.

Comparative Example 2

(6) Composition 4 (iron content 120 ppm based on the total weight of the composition) was prepared as in Example 1 except that 0.15 part of a solution of a 2-ethylhexanoic acid salt composed mainly of iron (elemental iron content 8%) was used instead of 0.05 part of nickel 2-ethylhexanoate. Composition 4 was heat cured at 80 C. for 60 minutes, yielding a cured silicone gel having a penetration of 40.

Comparative Example 3

(7) Composition 5 was prepared as in Example 1 except that 0.15 part of nickel 2-ethylhexanoate (about 1,500 ppm based on the total weight of the composition) was used. Composition 5 was heat cured at 80 C. for 60 minutes, yielding a cured silicone gel having a penetration of 80.

Comparative Example 4

(8) Composition 6 was prepared as in Example 2 except that 0.15 part of niobium 2-ethylhexanoate (about 1,500 ppm based on the total weight of the composition) was used. Composition 6 was heat cured at 80 C. for 60 minutes, yielding a cured silicone gel having a penetration of 90.

(9) [Test]

(10) The cured silicone gels in Examples 1 and 2 and Comparative Examples 1 to 4 were examined by the following tests. The results are shown in Table 1.

(11) Evaluation of Volume Resistivity:

(12) The volume resistivity of the cured silicone gels in Examples and Comparative Examples was measured according to JIS K6249.

(13) Evaluation of Loss Factor:

(14) The silicone gel compositions in Examples and Comparative Examples were tested by the slit-shearing method using Rheogel E4000 (UBM Co., Ltd.). The cured silicone gels obtained by heat curing at 80 C. for 60 minutes were cooled to 25 C. and measured for a loss factor at 1 Hz and 10 Hz.

(15) Evaluation of Heat Resistance:

(16) Each of the cured silicone gels in Examples and Comparative Examples was measured for penetration after heat resistance tests of heating at 215 C. for 1,000 hours and at 250 C. for 200 hours. A sample with a penetration of more than 150 was rated failure. Also the silicone gels after the 215 C./1,000 hr test and 250 C./200 hr test were visually observed for cracks.

(17) TABLE-US-00001 TABLE 1 Example Comparative Example 1 2 1 2 3 4 Content of heat resistance-imparting 500 100 0 120 1,500 1,500 component in composition (ppm) H/Vi 1.15 1.15 1.15 1.15 1.15 1.15 Penetration @ cone 45 50 40 40 80 90 Volume resistivity (T .Math. m) 3.0 1.0 5.5 0.001 0.05 0.02 Loss factor (tan) 1 Hz 0.19 0.20 0.18 0.19 0.21 0.21 10 Hz 0.46 0.46 0.43 0.43 0.47 0.47 Heat 215 C./1,000 hr penetration 80 70 5 45 >150 >150 resistance (failure) (failure) cracks nil nil found nil nil nil 250 C./200 hr penetration 70 65 1 5 90 100 cracks nil nil found found nil nil
[Evaluation]

(18) The compositions of Examples 1 and 2 within the scope of the invention afforded cured silicone gels having good rubber properties. The cured silicone gels showed neither drops of penetration nor appearance anomalies such as cracks under long-term heating conditions at 215 C. or 250 C., demonstrating stability.

(19) By contrast, the compositions of Comparative Examples 1 and 2 which did not contain the key component (D), that is, did not meet the requirement of the invention to contain a nickel carboxylate and/or niobium carboxylate as an essential component in the inventive composition showed a lowering of heat resistance or a substantial drop of insulation. The compositions of Comparative Examples 3 and 4 which contained an excess of the key component (D), i.e., an amount of the nickel carboxylate and/or niobium carboxylate outside the range of the invention showed a significant loss of softness in the heat resistance test and a drop of insulation.

INDUSTRIAL APPLICABILITY

(20) Since the silicone gel composition of the invention cures into a cured silicone gel which maintains its characteristic properties such as low elastic modulus and low stress even after holding in an atmosphere at 200 C. for a long period of time, it is expected that the composition is improved in long-term durability in the protection of electronic parts such as ICs and hybrid ICs.