SPONGE-FORMING SILICONE RUBBER COMPOSITION AND SILICONE RUBBER SPONGE

Abstract

A sponge-forming silicone rubber composition is disclosed. The sponge-forming silicone rubber composition comprises: (A) an organopolysiloxane having at least two alkenyl groups per molecule; (B) an organopolysiloxane having at least two silicon atom-bonded hydrogen atoms per molecule; (C) water; (D) a thickener; (E) a surfactant; (F) a silane compound having silicon atom-bonded alkoxy groups, or a partially hydrolyzed condensate thereof; and (G) a hydrosilylation reaction catalyst. The sponge-forming silicone rubber composition forms a silicone rubber sponge. In general, the silicone rubber sponge has excellent water absorption and water retentivity.

Claims

1. A sponge-forming silicone rubber composition comprising: (A) 100 parts by mass of an organopolysiloxane having at least two alkenyl groups per molecule; (B) an organopolysiloxane having at least two silicon atom-bonded hydrogen atoms per molecule, in an amount such that the silicon atom-bonded hydrogen atoms in this component are 0.4 to 20 mols with respect to one mol of the alkenyl groups in component (A); (C) 20 to 1000 parts by mass of water; (D) 0.01 to 15 parts by mass of a thickener with respect to 100 parts by mass of component (C); (E) 0.1 to 15 mass parts of a surfactant; (F) 0.1 to 20 parts by mass of a silane compound having silicon atom-bonded alkoxy groups, or a partially hydrolyzed condensate thereof; and (G) a hydrosilylation reaction catalyst in a sufficient amount to crosslink the composition.

2. The sponge-forming silicone rubber composition according to claim 1, wherein component (A) consists of: (A-1) 10 to 90 mass % of a diorganopolysiloxane having on an-average two alkenyl groups at molecular chain terminals and having no alkenyl group at a molecular side chain; and (A-2) 10 to 90 mass % of a diorganopolysiloxane having at least two alkenyl groups at a molecular side chain; provided the total of components (A-1) and (A-2) is 100 mass % of component (A).

3. The sponge-forming silicone rubber composition according to claim 1, wherein component (D) is at least one thickener selected from a group consisting of: an inorganic thickener, cellulose fibers, an aqueous polymer, a water-absorbing polymer, a hydrophilic composite consisting of the inorganic thickener and the aqueous polymer, and a hydrophilic composite consisting of the inorganic thickener and the water-absorbing polymer.

4. The sponge-forming silicone rubber composition according to claim 3, wherein component (D) comprises or is smectite clay.

5. The sponge-forming silicone rubber composition according to claim 1, wherein component (E) consists of: (E-1) a nonionic surfactant having an HLB value of 3 or more; and (E-2) a nonionic surfactant having an HLB value of less than wherein a mass ratio of component (E-1) to component (E-2) is at least 1.

6. The sponge-forming silicone rubber composition according to claim 1, wherein component (F) comprises or is methyltrimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-g lycidoxypropyltrimethoxysilane, methylsilicate, or ethylsilicate.

7. The sponge-forming silicone rubber composition according to claim 1, further comprising: (H) 0.001 to 5 parts by mass of a hydrosilylation reaction inhibitor with respect to 100 parts by mass of component (A).

8. The sponge-forming silicone rubber composition according to claim 7, further comprising: (I) greater than 0 to 40 parts by mass of reinforcing silica fine powder with respect to 100 parts by mass of component (A).

9. A silicone rubber sponge obtained by crosslinking the sponge-forming silicone rubber composition according to claim 1 and then removing water from the silicone rubber.

10. The sponge-forming silicone rubber composition according to claim 1, further comprising: (I) greater than 0 to 40 parts by mass of reinforcing silica fine powder with respect to 100 parts by mass of component (A).

Description

EXAMPLES

[0080] The sponge-forming silicone rubber composition and silicone rubber sponge according to the present invention will be described in further detail by way of more examples. Note that the viscosity in the examples is the value at 25° C.

[0081] <Density>

[0082] The density of the silicone rubber sponge was measured in accordance with JIS K 6268.

[0083] <Hardness (Asker C)>

[0084] The hardness of the silicone rubber sponge was measured in accordance with a test method using the type C hardness tester stipulated in JIS K 7312. Note that for the measurement, two silicone rubber sponge test pieces having a thickness of 6 mm were laminated and used.

[0085] <Tensile Strength, Elongation>

[0086] The tensile strength and elongation according to the silicone rubber sponge were measured in accordance with JIS K 6251.

[0087] <Air Bubble State>

[0088] The cross section of the silicone rubber sponge test pieces was visually observed and evaluated as: [0089] uniform when the air bubble state was uniform over the entire cross section; and [0090] nonuniform when excessive air bubbles were partially recognized.

[0091] <Average Air Bubble Diameter>

[0092] The central part obtained by cutting the silicone rubber sponge test pieces with a razor blade was observed with a scanning electron microscope to measure the air bubble diameter.

[0093] <Water Absorption and Water Retentivity>

[0094] A strip shaped test piece having a width of 15 mm and a length of 100 mm was created from a molded sheet having a thickness of 2 mm, then left to stand at 25° C. for 24 hours in a 300 cc container having 100 cc water such that 20 mm of the lower side of the strip shaped test piece was in contact with water. The test piece was removed after 24 hours, after which the height to which water was sucked up was measured and used as an index of water absorption. When the entire test piece absorbed water, it was 100 mm, so 100 mm was the maximum value.

[0095] Moreover, the increase in the mass of the test piece after absorbing water to the initial mass of the test piece was expressed as a percentage in accordance with the following equation to obtain the value used as an index of water retentivity.

[00001]$\begin{array}{cc}\mathrm{Water}\mathrm{retentivity}\left(\%\right)=\frac{\mathrm{Mass}\left(g\right)\mathrm{after}\mathrm{water}\mathrm{supply}-\mathrm{initial}\mathrm{mass}\left(g\right)}{\mathrm{Initial}\mathrm{mass}\left(g\right)}\times 100& \left[\mathrm{Equation}1\right]\end{array}$

Examples 1 to 5 and Comparative Examples 1 and 2

[0096] In the below-mentioned silica masterbatch, components (A), (C), (D), (E), and (F), and other components were added into a homomixer (produced by Tokushu Kika Kogyo Co., Ltd.) at the blending ratio of Table 1, then uniformly mixed at 25° C. Subsequently, component (B) was blended in the obtained mixture and degassed to prepare a sponge-forming silicone rubber composition. Note that in the silicone rubber composition, the molar ratio of silicon atom-bonded hydrogen atoms in the component corresponding to component (B) to the total of 1 mol of vinyl groups in the component corresponding to component (A) was 3.

[0097] The obtained sponge-forming silicone rubber composition was crosslinked and cured under conditions of 90° C/10 minutes using a compression molding machine to make a silicone rubber test piece in a water-containing state. Subsequently, this test piece was left to stand in an open system at 150° C. for four hours to remove water in the test piece and obtain a silicone rubber sponge test piece. Using this silicone rubber sponge test piece, the density, hardness, tensile strength, elongation, air bubble state, air bubble diameter, water absorption, and water retentivity were measured, the results of which are indicated in Table 1.

[0098] As the silica masterbatch, a silica masterbatch was used which was obtained by adding, into a Ross mixer, 100 parts by mass of a dimethylpolysiloxane blocked at both molecular chain terminals with dimethylvinylsiloxy groups and having a viscosity of 40 Pa.Math.s (content of vinyl groups=0.09 mass %), 50 parts by mass of fumed silica having a BET specific surface area of 225 m.sup.2/g, 10 parts by mass of hexamethyldisilazane, 2 parts by mass of water, and 0.2 parts by mass of a dimethylsiloxane-methylvinylsiloxane copolymer blocked at both molecular chain terminals with dimethylhydroxysiloxy groups and having a viscosity of 20 mPa.Math.s (content of vinyl groups=approximately 10.9 mass %), uniformly mixing them at room temperature, and then heating at 200° C. for two hours under reduced pressure.

[0099] The following components were used as component (A-1).

[0100] Component (a-1): a dimethylpolysiloxane blocked at both molecular chain terminals with dimethylvinylsiloxy groups and having a viscosity of 9 Pa.Math.s (content of vinyl groups: 0.14 mass %)

[0101] Component (a-2): a dimethylpolysiloxane blocked at both molecular chain terminals with dimethylvinylsiloxy groups and having a viscosity of 2 Pa.Math.s (content of vinyl groups: 0.23 mass %)

[0102] The following components were used as component (A-2).

[0103] Component (a-3): a dimethylmethylvinylpolysiloxane blocked at both molecular chain terminals with trimethylsiloxy groups and having a viscosity of 40 Pa.Math.s (content of vinyl groups=0.50 mass %).

[0104] Component (a-4): a dimethylsiloxane-methylvinylsiloxane copolymer blocked at both molecular chain terminals with dimethylvinylsiloxy groups and having a viscosity of 350 mPa.Math.s (content of vinyl groups: approximately 1.17 mass %).

[0105] Component (a-5): a dimethylsiloxane-methylvinylsiloxane copolymer blocked at both molecular chain terminals with trimethylsiloxy groups and having a viscosity of 40 Pa.Math.s (content of vinyl groups: 0.13 mass %).

[0106] As component (B), a dimethylsiloxane-methylhydrogensiloxane copolymer blocked at both molecular chain terminals with trimethylsiloxy groups and having a viscosity of 63 mPa.Math.s (content of silicon atom-bonded hydrogen atoms: approximately 0.70 mass %) was used.

[0107] Ion exchanged water was used as component (C), smectite clay (organic polymer composite refined bentonite produced by HOJUN Co., Ltd.; pH of 6.5) was used as component (D), and 0.85 parts by mass of smectite clay and 99.15 parts by mass of ion exchanged water were added into a homomixer, then uniformly mixed and prepared at room temperature to prepare a mixture of water and smectite clay.

[0108] The following components were used as component (E).

[0109] Component (e-1): a nonionic surfactant of HLB of 4.3 (sorbitan fatty acid ester, RHEODOL SP-010V produced by Kao Corporation).

[0110] Component (e-2): a nonionic surfactant of HLB of 1.8 (sorbitan fatty acid ester, RHEODOL SP-030V produced by Kao Corporation).

[0111] The following components were used as component (F).

[0112] Component (f-1): 3-methacryloxypropyltrimethoxysilane

[0113] Component (f-2): 3-glycidoxypropyltrimethoxysilane

[0114] Component (f-3): methylsilicate (SILICATE 40 produced by Tama Kogyo K.K.)

[0115] As component (G), a 1,3-divinyltetramethyldisiloxane solution of a 1,3-divinyltetramethyldisiloxane complex of platinum (content of platinum metal: approximately 4000 ppm) was used.

[0116] The following components were used as component (H).

[0117] Component (h-1): a dimethylsiloxane-methylvinylsiloxane copolymer blocked at both molecular chain terminals with dimethylhydroxysiloxy groups and having a viscosity of 20 mPa.Math.s (content of vinyl groups=approximately 10.9 mass %).

[0118] Component (h-2): a mixture of 2 parts by mass of 1-ethynyl-1-cyclohexanol and 98 parts by mass of a dimethylpolysiloxane blocked at both molecular chain terminals with dimethylvinylsiloxy groups and having a viscosity of 10 Pa.Math.s (content of vinyl groups: 0.13 mass %).

[0119] As a pigment masterbatch, a mixture of 40 parts by mass of red iron oxide (trade name: Bayferrox, produced by Bayer) and 60 parts by mass of a dimethylpolysiloxane blocked at both molecular chain terminals with dimethylvinylsiloxy groups and having a viscosity of 10 Pa.Math.s (content of vinyl groups: 0.13 mass %) was used.

TABLE-US-00001 TABLE 1 Example Comparative Example Example Example Example Example Example Comparative Comparative 1 2 3 4 5 Example 1 Example 2 Silica masterbatch 19.3 19.3 19.3 54.6 34.7 19.3 54.8 Component (A) Component (A-1) Component (a-1) 32.7 32.7 32.7 25.3 10.0 32.6 25.4 Component (a-2) — — — 10.9 — — — Component (A-2) Component (a-3) — — — — 19.2 — — Component (a-4) 31.5 31.5 31.5 29.8 49.3 31.4 29.7 Component (a-5) 23.3 23.3 23.3 — — 23.3 — Component (B) 7.2 7.2 7.2 6.3 10.9 7.5 6.5 Component (C) 247 247 247 422 411 248 410 Component (D) 2.1 2.1 2.1 3.6 3.5 2.1 3.5 Component (E) Component (e-1) 3.6 6.0 3.6 4.2 5.2 3.7 4.2 Component (e-2) 0.3 0.3 0.3 0.1 0.3 0.3 0.1 Component (F) Component (f-1) 4.2 — — — — — — Component (f-2) — 4.2 — — — — — Component (f-3) — — 4.2 4.7 4.6 — — Component (G) 0.4 0.4 0.4 0.4 0.3 0.4 0.3 Component (H) Component (h-1) 0.5 0.5 0.5 — 0.5 0.5 — Component (h-2) — — — 0.35 — — 0.40 Pigment masterbatch 7.5 7.5 7.5 5.5 6.7 7.5 5.5 Density (g/m.sup.3) 0.39 0.39 0.42 0.29 0.34 0.40 0.29 Hardness (Asker C) 18 19 19 19 24 18 19 Tensile strength (MPa) 0.24 0.26 0.17 0.16 0.11 0.25 0.30 Elongation (%) 78 70 90 52 30 79 50 Air bubble state Uniform Uniform Uniform Uniform Uniform Uniform Uniform Air bubble diameter (μm) 3-5 3-5 3-5 3-5 3-5 3-5 3-5 Water absorption (mm) 100 100 97 100 65 33 20 Water retention (%) 169 169 140 258 131 52 5

INDUSTRIAL APPLICABILITY

[0120] The sponge-forming silicone rubber composition according to the present invention can form a silicone rubber sponge having excellent water absorption and water retentivity, making it suitable for the application of forming a silicone rubber sponge which is used under the harsh environments of a heat insulating material, sound absorbing material, cushion, packing, gasket, pad, etc.