Curable silicone rubber composition

Abstract

The present disclosure provides a curable silicone rubber composition containing 0.1 to 15 mass % of a biuret compound represented by the general formula: ##STR00001##
wherein R.sup.1 represents the same or different alkyl groups having 1 to 6 carbons, R.sup.2 represents the same or different alkyl groups having 1 to 3 carbons, R.sup.3 represents the same or different alkylene groups having 2 to 6 carbons, and “a” represents the same or different integers of from 0 to 2. The curable silicone rubber composition may be cured by a condensation reaction, an addition reaction, or the like. The curable silicone rubber composition generally has good adhesion to plastics, metals, and the like.

Claims

1. A curable silicone rubber composition containing 0.1 to 15 mass % of a biuret compound represented by the general formula: ##STR00010## wherein R.sup.1 represents the same or different alkyl groups having 1 to 6 carbons, R.sup.2 represents the same or different alkyl groups having 1 to 3 carbons, R.sup.3 represents the same or different alkylene groups having 2 to 6 carbons, and “a” represents the same or different integers of from 0 to 2.

2. The curable silicone rubber composition according to claim 1, wherein the biuret compound is a reaction product of an aminoalkyl alkoxysilane represented by the general formula:
NH.sub.2—R.sup.3—SiR.sup.1.sub.a(OR.sup.2).sub.(3-a) wherein R.sup.1 is an alkyl group having 1 to 6 carbons, R.sup.2 is an alkyl group having 1 to 3 carbons, R.sup.3 is an alkylene group having 2 to 6 carbons, and “a” is an integer from 0 to 2; and an isocyanate alkyl alkoxysilane represented by the general formula:
O═C═N—R.sup.3—SiR.sup.1.sub.a(OR.sup.2).sub.(3-a) wherein R.sup.1 represents the same alkyl groups as described above or different alkyl groups having 1 to 6 carbons, R.sup.2 represents the same alkyl groups as described above or different alkyl groups having 1 to 3 carbons, R.sup.3 represents the same alkylene group as described above or different alkylene group having 2 to 6 carbons, and “a” represents the same integers as described above or different integer of from 0 to 2.

3. The curable silicone rubber composition according to claim 2, wherein the biuret compound is a reaction product with a molar ratio of 1:1.5 to 1:3 of the aminoalkyl alkoxysilane and the isocyanate alkyl alkoxysilane.

4. The curable silicone rubber composition according to claim 1, wherein the curable silicone rubber composition is in the form of a condensation reaction curable silicone rubber composition.

5. The curable silicone rubber composition according to claim 4, wherein the condensation reaction curable silicone rubber composition comprises: (A) a biuret compound represented by the general formula: ##STR00011## wherein R.sup.1 represents the same or different alkyl groups having 1 to 6 carbons, R.sup.2 represents the same or different alkyl groups having 1 to 3 carbons, R.sup.3 represents the same or different alkylene groups having 2 to 6 carbons, and “a” represents the same or different integers of from 0 to 2, in an amount of from 0.1 to 15 mass % in the composition; (B.sub.1) a diorganopolysiloxane capped at both molecular terminals with silicon atom-bonded hydroxyl groups or silicon atom-bonded hydrolyzable groups; (B.sub.2) a silane crosslinking agent having a silicon atom-bonded hydrolyzable group, in an amount sufficient to crosslink component (B.sub.1); and (B.sub.3) a condensation reaction promotion catalyst for promoting a condensation reaction of the composition.

6. The curable silicone rubber composition according to claim 1, wherein the curable silicone rubber composition is in the form of an addition reaction curable silicone rubber composition.

7. The curable silicone rubber composition according to claim 6, wherein the addition reaction curable silicone rubber composition comprises: (A) a biuret compound represented by the general formula: ##STR00012## wherein R.sup.1 represents the same or different alkyl groups having 1 to 6 carbons, R.sup.2 represents the same or different alkyl groups having 1 to 3 carbons, R.sup.3 represents the same or different alkylene groups having 2 to 6 carbons, and “a” represents the same or different integers of from 0 to 2, in an amount of from 0.1 to 15 mass % in the composition; (C.sub.1) an organopolysiloxane having at least two silicon atom-bonded alkenyl groups in each molecule; (C.sub.2) an organohydrogenpolysiloxane having at least two silicon atom-bonded hydrogen atoms in each molecule, in an amount sufficient to cros slink component (C.sub.1); and (C.sub.3) a platinum group metal-based catalyst in an amount sufficient to promote an addition reaction of the composition.

Description

EXAMPLES

(1) The curable silicone rubber composition of the present invention will be described in detail hereinafter using examples. Note that in the examples, the viscosity is a value at 25° C.

Reference Example 1

(2) First, 14.2 g (79 mmol) of 3-aminopropyl trimethoxysilane was charged into a 100 cc flask, and 25.8 g (126 mmol) of 3-isocyanatepropyl trimethoxysilane was added dropwise over the course of 60 minutes and reacted while stirring at room temperature. Upon completion of the drop-wise addition, they were further stirred for 60 minutes to obtain a reaction mixture containing 54 mass % of a biuret compound represented by the formula:

(3) ##STR00007##
and 46 mass % of a urea compound represented by the formula:

(4) ##STR00008##

Reference Example 2

(5) First, 21 g (117 mmol) of 3-aminopropyl trimethoxysilane was charged into a 100 cc flask, and 19 g (93 mmol) of 3-isocyanatepropyl trimethoxysilane was added dropwise over the course of 60 minutes and reacted while stirring at room temperature. Upon completion of the drop-wise addition, they were further stirred for 60 minutes to obtain a reaction mixture containing 80 mass % of a urea compound represented by the formula:

(6) ##STR00009##
and 20 mass % of unreacted 3-aminopropyltrimethoxysilane.

Reference Example 3

(7) First, 100 parts by mass of a polydimethylsiloxane capped at both molecular terminals with dimethylhydroxysiloxy groups and having a viscosity of 16,500 mPa.Math.s, and 70 parts by mass of stearic acid-treated calcium carbonate having a BET specific surface area of 21 m.sup.2/g were charged into a Ross mixer, mixed until uniform at room temperature, and then degassed under reduced pressure to prepare a silicone rubber base.

Reference Example 4

(8) First, 100 parts by mass of a dimethylpolysiloxane capped at both molecular terminals with dimethylvinylsiloxy groups having a viscosity of 40,000 mPa.Math.s, 40 parts by mass of fumed silica having a BET specific surface area of 400 m.sup.2/g, 7 parts by mass of hexamethyldisilazane, and 1.7 parts by mass of water were charged into a Ross mixer, mixed until uniform at room temperature, and then heat-treated for two hours at 200° C. under reduced pressure to prepare a silicone rubber base having fluidity.

Reference Example 5

(9) First, 85 parts by mass of a dimethylsiloxane.methylvinylsiloxane copolymer capped at both molecular terminals with trimethylsiloxy groups and having a viscosity of 40,000 mPa.Math.s (vinyl group content=0.13 mass %) and 15 parts by mass of acetylene black (Denka Black: manufactured by Denki Kagaku Kogyo K.K.) were charged into a Ross mixer, mixed until uniform at room temperature, and passed five times through a three-roll mill to prepare a pigment paste having fluidity.

Reference Example 6

(10) First, 72 parts by mass of dimethylpolysiloxane capped at both molecular terminals with trimethylsiloxy groups and having a viscosity of 9,800 mPa.Math.s, and 28 parts by mass of acetylene black (Denka Black: manufactured by Denki Kagaku Kogyo K.K.) were charged into a Ross mixer, mixed until uniform at room temperature, and passed five times through a three-roll mill to prepare a pigment paste having fluidity.

Example 1 and Comparative Examples 1 to 5

(11) Condensation reaction curable silicone rubber compositions were prepared with the compositions shown in Table 1 using the following components.

(12) The following was used as a silicone rubber base.

(13) Silicone rubber base (1): silicone rubber base prepared in Reference Example 3

(14) The following were used as pigment pastes.

(15) Pigment paste (1): pigment paste prepared in Reference Example 5

(16) Pigment paste (2): pigment paste prepared in Reference Example 6

(17) The following was used as a silane crosslinking agent.

(18) Silane crosslinking agent: 1,6-bis(trimethoxysilyl)hexane

(19) The following were used as condensation reaction catalysts.

(20) Condensation reaction catalyst (1): dimethyltin dineodecanoate

(21) Condensation reaction catalyst (2): dimethyltin dineodecanoate dispersed in dimethylpolysiloxane capped at both molecular terminals with trimethylsiloxy groups and having a viscosity of 100 mm.sup.2/s.

(22) The following were used as adhesion promoters.

(23) Adhesion promoter (1): reaction mixture prepared in Reference Example 1

(24) Adhesion promoter (2): reaction mixture prepared in Reference Example 2

(25) Adhesion promoter (3): 3-aminopropyl trimethoxysilane

(26) Adhesion promoter (4): 3-isocyanatepropyl trimethoxysilane

(27) Adhesion promoter (5): 3-aminopropyl triethoxysilane

(28) The initial adhesion and heat-resistant adhesion of the curable silicone rubber compositions prepared in Example 1 and Comparative Examples 1 to 5 were evaluated as follows, and the results are shown in Table 1. Note that in Comparative Examples 4 and 5, the adhesion promoter also served as a silane crosslinking agent.

(29) <Initial Adhesion>

(30) After the curable silicone rubber composition was applied to a thickness of 1 mm between two polycarbonate resin adherends (50 mm×50 mm×5 mm), the composition was left to cure for 30 minutes in a 60° C. oven. The composition was heated for 30 minutes at 60° C., and the curing state and adhesion was observed. Cases in which the composition cured with good adhesion was evaluated as “∘”; cases in which peeling was observed was evaluated as “Δ”, and compositions that did not cure was evaluated as “x”.

(31) <Heat-Resistant Adhesion>

(32) After the initial adhesion was confirmed for the compositions exhibiting good initial adhesion in the initial adhesion evaluation described above, the composition was immediately placed in an oven at 130° C. and heated for 10 days. The composition was then cooled to room temperature, and the adhesive state was observed. Compositions exhibiting sufficient adhesion was evaluated as “∘”; and cases in which gas pockets was observed at the interface between the adherend and the rubber layer or cases in which peeling was observed was evaluated as “x”.

(33) TABLE-US-00001 TABLE 1 Segment Comparative Example Present Comp. Comp. Comp. Comp. Comp. Invention Exam. Exam. Exam. Exam. Exam. Items Example 1 1 2 3 4 5 Composition Silicone rubber base (1) 100 100 100 100 100 100 of curable Pigment paste (1)     3.1 —     3.1     3.1 — — silicone rubber Pigment paste (2) — 0.5 — —     0.5     0.5 composition Silane crosslinking agent     2.1 3.9     2.1     2.1 — — (parts by mass) Condensation reactive      0.06 —      0.03      0.06 — — catalyst (1) Condensation reactive — 8.1 — —     8.1     8.1 catalyst (2) Adhesion promoter (1)     2.0 — — — — — Adhesion promoter (2) — —     2.0 — — — Adhesion promoter (3) — — —     0.7 — — Adhesion promoter (4) — — —     1.3     3.9 — Adhesion promoter (5) — — — — —     3.9 Initial adhesion ∘ Δ ∘ Δ x ∘ Heat-resistant adhesion ∘ — x — — x

Example 2 and Comparative Example 6

(34) Addition reaction curable silicone rubber compositions were prepared with the compositions shown in Table 2 using the following components.

(35) The following was used as a silicone rubber base.

(36) Silicone rubber base (2): silicone rubber base prepared in Reference Example 4

(37) The following was used as a viscosity adjusting agent.

(38) Viscosity adjusting agent: dimethylsiloxane.methylvinylsiloxane copolymer capped at both molecular terminals with dimethylvinylsiloxy groups and having a viscosity of 350 mPa.Math.s (vinyl group content=1.17 mass %)

(39) The following was used as a crosslinking agent.

(40) Crosslinking agent: organopolysiloxane having a dynamic viscosity of 12 mm.sup.2/s and represented by the following average unit formula:
[(CH.sub.3).sub.3SiO.sub.1/2].sub.2[(CH.sub.3).sub.2SiO.sub.2/2].sub.7[(CH.sub.3)HSi.sub.2/2].sub.12(CH.sub.3SiO.sub.3/2).sub.1
(silicon atom-bonded hydrogen atom content=approximately 0.83 mass %)

(41) The following was used as a platinum group metal-based catalyst.

(42) Curing catalyst: 1,3-divinyltetramethyldisiloxane solution of a 1,3-divinyltetramethyldisiloxane complex of platinum (platinum metal content=approximately 7,000 ppm)

(43) The following was used as a reaction inhibitor.

(44) Reaction inhibitor: a mixture of 2 parts by mass of 1-ethynylcyclohexan-1-ol and 98 parts by mass of a dimethylpolysiloxane capped at both molecular terminals with dimethylvinylsiloxy groups and having a viscosity of 10,000 mPa.Math.s (vinyl group content=approximately 0.13 mass %)

(45) The following was used as an adhesion promoter.

(46) Adhesion promoter (1): reaction mixture prepared in Reference Example 1

(47) The curability and adhesion of the curable silicone rubber compositions prepared in Example 2 and Comparative Example 6 were evaluated as follows, and the results are shown in Table 2.

(48) <Curability>

(49) The following vulcanization characteristics of the curable silicone rubber composition were measured at 130° C./3 minutes using a Curelastomer III type (manufactured by JSR) in accordance with JIS K6300. T10: Time required for the vulcanization to progress 10% from the start of heating (that is, until the torque reaches 10% of the maximum torque value MH in the vulcanization curve) (=vulcanization starting point) T90: Time required for the vulcanization to progress 90% from the start of heating (that is, until the torque reaches 10% of the maximum torque value MH in the vulcanization curve) (=optimum vulcanization point)
<Adhesion>

(50) The curable silicone rubber composition was applied to a thickness of 1 mm to a 25 mm×75 mm×1 mm adherend (polycarbonate resin: PC, acrylonitrile butadiene styrene copolymer resin: ABS, polyethylene terephthalate resin: PET, polybutylene terephthalate resin: PBT, stainless steel: SUS), and after the composition was heated for 10 minutes in an oven at 130° C., the composition was cooled and the adhesive state of the silicone rubber was observed. The composition in which the rubber layer exhibited cohesive failure was evaluated as “∘”, and composition which exhibited peeling at the interface with the adherend was evaluated as “x”.

(51) TABLE-US-00002 TABLE 2 Comparative Present Example Invention Comparative Example 2 Example 6 Composition of Silicone rubber base (2) 100 100 curable silicone Viscosity adjusting agent 20 20 rubber composition Crosslinking agent 2.2 2.2 (parts by mass) Curing catalyst 0.08 0.08 Reaction inhibitor 1.5 1.5 Adhesion promoter (1) 1.24 0 Curability T10 39 36 T90 90 63 Adhesion PC ∘ x ABS ∘ x PET ∘ x PBT ∘ x SUS ∘ x

INDUSTRIAL APPLICABILITY

(52) The curable silicone rubber composition of the present invention has good adhesion to plastics such as polycarbonate resins, metals, and the like, and can therefore be suitably used as an adhesive, a sealing agent, or a coating agent.