ONE-PACK ADDITION CURABLE SILICONE COMPOSITION, METHOD FOR STORING SAME, AND METHOD FOR CURING SAME

Abstract

Provided are a one-pack addition curable silicone composition compatible with both a good long-term storage property at room temperature under conditions whereby air is blocked to a constant level and the advance of an addition curing reaction at room temperature by being applied in a thin film of 1500 m or less and exposed to air, which could not be obtained by conventional curable heat-dissipating grease, and a method for storing the same, and a method for curing this composition. A one-pack addition curable silicone composition having as essential ingredients: (A) organopolysiloxane having silicon-atom-bonded aliphatic unsaturated hydrocarbon groups and a specific kinematic viscosity; (B) one or more thermally conductive fillers selected from metals, metal oxides, metal hydroxides, metal nitrides, metal carbides, and allotropes of carbon; (C) organohydrogenpolysiloxane; and (D) a platinum group metal complex having an organic phosphorus compound represented by formula (1)

R.sup.1.sub.xP(OR.sup.1).sub.3-x (1)

(R.sup.1 is a monovalent hydrocarbon group, x is 0-3) as a ligand.

Claims

1. A method for storing a one-pack addition curable silicone composition comprising as essential components: (A) 100 parts by weight of an organopolysiloxane containing at least two silicon-bonded aliphatic unsaturated hydrocarbon groups per molecule and having a kinematic viscosity of 60 to 100,000 mm.sup.2/s at 25 C., (B) 100 to 3,000 parts by weight of at least one heat conductive filler selected from the group consisting of metals, metal oxides, metal hydroxides, metal nitrides, metal carbides, and carbon allotropes, (C) an organohydrogenpolysiloxane containing at least two silicon-bonded hydrogen atoms (i.e., SiH groups) per molecule in such an amount that the number of SiH groups divided by the total number of aliphatic unsaturated hydrocarbon groups in component (A) is 0.5 to 5, and (D) an effective amount of a platinum group metal complex coordinated with an organophosphorus compound represented by the general formula (1):
R.sup.1.sub.xP(OR.sup.1).sub.3-x (1) wherein R.sup.1 which may be the same or different is an optionally substituted monovalent hydrocarbon group of 1 to 20 carbon atoms, and x is an integer of 0 to 3, comprising the step of storing the one-pack addition curable silicone composition in a closed container made of a material having an oxygen permeability constant of up to 110.sup.12 cm.sup.3 (STP) cm/cm.sup.2.Math.s.Math.Pa, whereby the silicone composition develops a storage stability of at least 3 months at 25 C.

2. The method of claim 1, wherein the one-pack addition curable silicone composition further comprises (E) 1 to 200 parts by weight per 100 parts by weight of component (A) of a hydrolyzable organopolysiloxane compound having the general formula (2): ##STR00007## wherein R.sup.1 which may be the same or different is an optionally substituted monovalent hydrocarbon group of 1 to 20 carbon atoms, and m is an integer of 5 to 100.

3. The method of claim 1, wherein the one-pack addition curable silicone composition further comprises (F) 0.01 to 10 parts by weight per 100 parts by weight of component (A) of a hydrolyzable organosilane compound having the general formula (3):
R.sup.2Si(OR.sup.1).sub.3 (.sup.3) wherein R.sup.1 which may be the same or different is an optionally substituted monovalent hydrocarbon group of 1 to 20 carbon atoms, and R.sup.2 is an optionally substituted monovalent hydrocarbon group of 1 to 20 carbon atoms.

4. A method for curing the one-pack addition curable silicone composition comprising as essential components: (A) 100 parts by weight of an organopolysiloxane containing at least two silicon-bonded aliphatic unsaturated hydrocarbon groups per molecule and having a kinematic viscosity of 60 to 100,000 mm.sup.2/s at 25 C., (B) 100 to 3,000 parts by weight of at least one heat conductive filler selected from the group consisting of metals, metal oxides, metal hydroxides, metal nitrides, metal carbides, and carbon allotropes, (C) an organohydrogenpolysiloxane containing at least two silicon-bonded hydrogen atoms (i.e., SiH groups) per molecule in such an amount that the number of SiH groups divided by the total number of aliphatic unsaturated hydrocarbon groups in component (A) is 0.5 to 5, and (D) an effective amount of a platinum group metal complex coordinated with an organophosphorus compound represented by the general formula (1):
R.sup.1.sub.xP(OR.sup.1).sub.3-x (1) wherein R1 which may be the same or different is an optionally substituted monovalent hydrocarbon group of 1 to 20 carbon atoms, and x is an integer of 0 to 3, comprising the steps of applying the one-pack addition curable silicone composition as a thin film having a thickness of up to 1,500 m and exposing the film to air at room temperature for allowing addition cure reaction to take place at room temperature.

5. The method of claim 4, wherein the one-pack addition curable silicone composition further comprises (E) 1 to 200 parts by weight per 100 parts by weight of component (A) of a hydrolyzable organopolysiloxane compound having the general formula (2): ##STR00008## wherein R1 which may be the same or different is an optionally substituted monovalent hydrocarbon group of 1 to 20 carbon atoms, and m is an integer of 5 to 100.

6. The method of claim 4, wherein the one-pack addition curable silicone composition further comprises (F) 0.01 to 10 parts by weight per 100 parts by weight of component (A) of a hydrolyzable organosilane compound having the general formula (3):
R.sup.2Si(OR.sup.1).sub.3(3) wherein R.sup.1 which may be the same or different is an optionally substituted monovalent hydrocarbon group of 1 to 20 carbon atoms, and R.sup.2 is an optionally substituted monovalent hydrocarbon group of 1 to 20 carbon atoms.

Description

EXAMPLES

[0094] Examples and Comparative Examples are given below for further illustrating the invention although the invention is not limited thereto. Herein, the kinematic viscosity is as measured at 25 C. by an Ostwald viscometer of Ubbelohde type (Sibata Scientific Technology Ltd.). Room temperature (RT) is 25 C.

[0095] First, there were furnished the following components, from which one-pack addition curable silicone compositions within the scope of the invention were prepared.

Component (A)

[0096] A-1: dimethylpolysiloxane capped at both ends with dimethylvinylsilyl and having a kinematic viscosity of 600 mm.sup.2/s at 25 C. [0097] A-2: dimethylpolysiloxane capped at both ends with dimethylvinylsilyl and having a kinematic viscosity of 10,000 mm.sup.2/s at 25 C.

Component (B)

[0098] B-1: aluminum powder with an average particle size of 10.0 m (thermal conductivity 237 W/m.Math. C.) [0099] B-2: zinc oxide powder with an average particle size of 1.0 m (thermal conductivity 25 W/m.Math. C.)

Component (C)

[0100] C-1: methylhydrogenpolysiloxane having a kinematic viscosity of 90 mm.sup.2/s at 25 C., of the following formula

##STR00003##

[0101] C-2: methylhydrogenpolysiloxane having a kinematic viscosity of 12 mm.sup.2/s at 25 C., of the following formula

##STR00004##

Component (D)

[0102] D-1: platinum-trihexyl phosphite complex obtained in Synthesis Example 1 below

Synthesis Example 1

[0103] A 100-ml flask recovery flask was charged with 0.31 g (0.93 mmol) of trihexyl phosphite, 3.0 g (0.15 mmol of platinum atom) of a solution of platinum-divinyltetramethyldisiloxane complex in the same dimethylpolysiloxane as A-1 (platinum atom content: 1 wt % of platinum atom), and 6.7 g of toluene. The contents were stirred at RT for 3 hours, obtaining 9.8 g of colorless transparent platinum-trihexyl phosphite complex.

[0104] D-2: platinum-triphenyl phosphite complex obtained in Synthesis Example 2 below

Synthesis Example 2

[0105] A 100-ml flask recovery flask was charged with 0.29 g (0.93 mmol) of triphenyl phosphite, 3.0 g (0.15 mmol of platinum atom) of a solution of platinum-divinyltetramethyldisiloxane complex in the same dimethylpolysiloxane as A-1(platinum atom content: 1 wt % of platinum atom), and 6.7 g of toluene. The contents were stirred at RT for 3 hours, obtaining 9.8 g of colorless semi-transparent platinum-triphenyl phosphite complex.

[0106] D-3: solution of platinum-divinyltetramethyldisiloxane complex in the same dimethylpolysiloxane as A-1 (platinum atom content: 1 wt % of platinum atom)

Component (E)

[0107] E-1: trimethoxysilyl-containing dimethylpolysiloxane of the following formula

##STR00005##

Component (F)

[0108] F-1: decyltrimethoxysilane of the following formula

Chemical Formula 11

C.sub.10H.sub.21Si (OCH.sub.3).sub.3

Other Component

[0109] G-1: acetylene alcohol of the following formula

##STR00006##

Examples 1 to 8 and Comparative Examples 1 to 5

Preparation of One-Pack Addition Curable Silicone Compositions

[0110] One-pack addition curable silicone compositions were prepared by mixing components (A) to (F) and other component in the amounts shown in Tables 1 and 2 according to the following procedure. In Tables 1 and 2, SiH/SiVi designates a ratio of the total number of SiH groups in component (C) to the total number of alkenyl groups in component (A).

[0111] On a 5-L planetary mixer (Inoue Mfg., Inc.), components (A), (B), (E) and (F) were fed and mixed at 170 C. for 1 hour. The mixture was cooled to RT (25 C.), to which components (C), (D) and other component were added and mixed until uniform, obtaining a one-pack addition curable silicone composition.

[0112] Each of the compositions prepared by the above procedure was measured for viscosity and thermal conductivity and evaluated for RT storage stability and RT cure by the following methods. The results are also shown in Tables 1 and 2.

[Viscosity]

[0113] The absolute viscosity of each composition was measured at 25 C. using a Malcom viscometer (type PC-1T).

[Thermal Conductivity]

[0114] Each composition was wrapped with kitchen wrapping film and measured for thermal conductivity by meter TPA-501 (Kyoto Electronics Mfg. Co., Ltd.).

[RT Storage Stability]

[0115] Each composition was placed in a HDPE container (HDPE's oxygen permeability constant: 210.sup.13 cm.sup.3 (STP) cm/cm.sup.2.Math.s.Math.Pa) and, with the container sealed, stored at 25 C. The composition was rated good (O) when the time passed until cure was 3 months or longer and poor (X) when the time passed until cure was less than 3 months. As used herein, cure is defined as the state that measurement of absolute viscosity at 25 C. using a Malcom viscometer (type PC-1T) becomes impossible.

[RT Cure]

[0116] Each composition was applied onto an aluminum plate to a thickness of 120 m and then exposed to air at RT (252 C.). The composition was rated good (O) when a surface layer and the interior cured within 7 days, and poor (X) otherwise. As used herein, cure is defined as the state that when the composition is contacted with the finger, none is transferred to the finger.

TABLE-US-00001 TABLE 1 Example 1 2 3 4 5 6 7 8 Formulation A-1 100 100 100 100 100 100 100 (pbw) A-2 100 B-1 1,986 720 1,986 1,986 1,986 1,986 874 1,986 B-2 434 158 434 434 434 434 215 434 Total of fillers 2,420 878 2,420 2,420 2,420 2,420 1,089 2,420 C-1 4.2 1.4 1.4 14 4.2 4.2 4.2 C-2 4.1 D-1 0.7 0.7 0.7 0.7 0.7 0.7 0.7 D-2 0.7 D-3 E-1 100 50 100 100 100 100 100 F-1 6.0 6.0 G-1 Evaluation SiH/SiVi (number ratio) 1.5 1.5 1.5 0.5 5.0 1.5 1.5 1.5 results Viscosity (Pa .Math. s) 190 174 182 204 148 196 225 166 Thermal conductivity 5.7 2.6 5.6 5.7 5.3 5.6 4.0 5.5 (W/m .Math. C.) RT storage stability RT cure

TABLE-US-00002 TABLE 2 Comparative Example 1 2 3 4 5 Formulation A-1 100 100 100 100 100 (pbw) A-2 B-1 2,582 1,986 1,986 1,986 1,986 B-2 564 434 434 434 434 Total of fillers 3,146 2,420 2,420 2,420 2,420 C-1 4.2 1.1 16 4.2 4.2 C-2 D-1 0.7 0.7 0.7 D-2 D-3 0.3 0.3 E-1 100 100 100 100 100 F-1 G-1 0.3 Evaluation SiH/SiVi (number ratio) 1.5 0.4 5.7 1.5 1.5 results Viscosity (Pa .Math. s) did not 210 141 cured 198 Thermal conductivity (W/m .Math. C.) become 5.6 5.2 immediately 5.6 RT storage stability grease after X RT cure X X mixing of X components (C) and (D)

[0117] As seen from the results of Tables 1 and 2, the compositions of Examples 1 to 8 within the scope of the invention meet both RT storage stability under limited air-shutoff conditions and RT cure when it is applied as a thin film of up to 1,500 m and exposed to air. By contrast, the compositions of Comparative Examples 1 to 5 are difficult to meet both RT storage stability under limited air-shutoff conditions and RT cure when it is applied as a thin film of up to 1,500 m and exposed to air.

Examples 9 to 12 and Comparative Examples 6 to 7

[0118] Subsequently, the one-pack addition curable silicone composition was evaluated for RT storage stability in terms of the material of which the container for storing the silicone composition was made. Notably the one-pack addition curable silicone composition used herein was that of Example 1, and the RT storage stability was evaluated by the same procedure as mentioned above. Storage containers were made of the following five materials. The value in parentheses is an oxygen permeability constant. [0119] HDPE (210.sup.13 cm.sup.3 (STP) cm/cm.sup.2.Math.s.Math.Pa) [0120] PVC (310.sup.15 cm.sup.3 (STP) cm/cm.sup.2.Math.s.Math.Pa) [0121] PVDC (510.sup.16 cm.sup.3 (STP) cm/cm.sup.2.Math.s.Math.Pa) [0122] aluminum (0 cm.sup.3 (STP) cm/cm.sup.2.Math.s.Math.Pa) [0123] silicone rubber (610.sup.11 cm.sup.3 (STP) cm/cm.sup.2.Math.s.Math.Pa)

[0124] The one-pack addition curable silicone composition having the same formulation as in Example 1 was stored in containers of the above-described materials and evaluated for RT storage stability, with the results shown in Table 3.

TABLE-US-00003 TABLE 3 Comparative Example Example 9 10 11 12 6 7 Storage container HDPE * * material PVC * PVDC * aluminum * silicone rubber * Remarks not closed RT storage stability X X

[0125] As seen from the results of Table 3, the compositions of Examples 9 to 12 within the scope of the invention develop RT storage stability under limited air-shutoff conditions. By contrast, the composition of Comparative Example 6 is difficult to develop RT storage stability under limited air-shutoff conditions.

Examples 13 to 18 and Comparative Examples 8 to 9

[0126] Furthermore, the one-pack addition curable silicone composition was evaluated for RT cure in terms of the coating thickness of the silicone composition. Notably the one-pack addition curable silicone composition used herein was that of Example 1, and the RT cure was evaluated by the same procedure as mentioned above except that the coating thickness was changed.

[0127] The one-pack addition curable silicone composition having the same formulation as in Example 1 was coated to a varying thickness and evaluated for RT cure, with the results shown in Table 4.

TABLE-US-00004 TABLE 4 Comparative Example Example 13 14 15 16 17 18 8 9 Coating thickness 120 * (m) 300 * 700 * 1,000 * 1,300 * 1,500 * 1,700 * 2,000 * RT cure X X

[0128] As seen from the results of Table 4, in Examples 13 to 18 wherein a thin film of up to 1,500 m was coated and exposed to air, the one-pack addition curable silicone composition develops RT cure. By contrast, in Comparative Examples 8 and 9 wherein a film of more than 1,500 m was coated and exposed to air, the one-pack addition curable silicone composition is difficult to develop RT cure.

[0129] Accordingly, the results of Tables 1 to 4 demonstrate that the one-pack addition curable silicone composition within the scope of the invention meets both long-term storage stability at room temperature under limited air-shutoff conditions and the progress of addition cure reaction at room temperature when it is applied as a thin film of up to 1,500 m and exposed to air.

[0130] It is noted that the invention is not limited to the aforementioned embodiments. While the embodiments are merely exemplary, any embodiments having substantially the same construction as the technical concept set forth in the following claims and achieving equivalent functions and results are believed to be within the spirit and scope of the invention.