SILICONE FOAM COMPOSITION

Abstract

This disclosure relates to silicone foam compositions for forming foamed silicone elastomers, the respective foamed silicone elastomers formed therefrom and to methods of making such compositions and foamed silicone elastomers. The silicone rubber foam composition comprises the (a) one or more organosilicon compounds having an average of at least two silicon bonded alkoxy groups per molecule selected from one or more silicone resins and/or silicone resin intermediates; (b) a Lewis acid catalyst; (c) one or more surfactants; and (d) one or more organopolysiloxane polymers having an average of at least two, alternatively at least three silicon bonded hydrogen groups per molecule.

Claims

1. A silicone rubber foam composition comprising: (a) one or more organosilicon compounds having an average of at least two silicon bonded alkoxy groups per molecule selected from one or more silicone resins and/or silicone resin intermediates; (b) a Lewis acid catalyst; (c) one or more surfactants; and (d) one or more organopolysiloxane polymers having an average of at least two, optionally at least three silicon bonded hydrogen groups per molecule.

2. The silicone rubber foam composition in accordance with claim 1, wherein component (a) has a weight average molecular weight of from 3,000 to 50,000 Da. determined in Daltons using triple-detector gel permeation chromatography and a single polystyrene standard.

3. The silicone rubber foam composition in accordance with claim 2, wherein component (a) is a silicone resin having a weight average molecular weight of from 300 to 3,000 Da. determined in Daltons using triple-detector gel permeation chromatography and a single polystyrene standard.

4. The silicone rubber foam composition in accordance with claim 1, wherein component (a) is a silicone resin comprising alkoxy groups present in an amount of from 2 to 50 wt. % of the silicone resin.

5. The silicone rubber foam composition in accordance with claim 1, wherein component (b) comprises one or more arylboranes or boron halides or a mixture thereof.

6. The silicone rubber foam composition in accordance with claim 5, wherein component (b) is selected from tris(pentafluorophenyl)borane, tris(3,5-bis(trifluoromethyl)phenyl)borane, bis(3,5-bis(trifluoromethyl)phenyl)(4-(trifluoromethyl)phenyl)borane, bis(3,5-bis(trifluoromethyl)phenyl)(2,4,6-trifluorophenyl)borane or a mixture thereof.

7. The silicone rubber foam composition in accordance with claim 1, wherein component (c) is or comprises a silicone fluorinated surfactant or an organic fluorinated surfactant.

8. The silicone rubber foam composition in accordance with claim 1, additionally comprising a physical blowing agent, a cure inhibitor or both a physical blowing agent and a cure inhibitor.

9. The silicone rubber foam composition in accordance with claim 8, wherein the cure inhibitor is present and is selected from one or more arylamines and/or alkylamines.

10. The silicone rubber foam composition in accordance with claim 9, comprising one or more cure inhibitors selected from triarylamines aniline, 4-methylaniline, 4-fluoroaniline, 2-chloro-4-fluoroaniline, diphenylamine, diphenylmethylamine, triphenylamine, 1-naphthylamine, 2-naphthylamine, 1-aminoanthracene, 2-aminoanthracene, 9-aminoanthracene, ?-aminostyrene, 1,3,5-hexatrien-1-amine, N,N-dimethyl-1,3,5-hexatrien-1-amine, 3-amino-2-propenal, 4-amino-3-buten-2-one, trimethylamine, triethylamine, tripropylamine, tributylamine, tripentylamine, trihexylamine, triheptalamine, trioctylamine and trinonylamine, butylamine, pentylamine, hexylamine, octylamine, dipropylamine, dibutylamine, dihexylamine, trimethylamine, triheptylamine, and/or mixtures thereof.

11. The silicone rubber foam composition in accordance with claim 1, comprising one or more additional additives selected from foam stabilizers, adhesion promoters; colorants, dyes and pigments; antioxidants; heat stabilizers; flame retardants; flow control additives and/or reinforcing and/or non-reinforcing fillers.

12. A silicone rubber foam which is a foamed and cured product of the composition in accordance with claim 1.

13. The silicone rubber foam in accordance with claim 12 having a density of less than 0.8 g/cm.sup.3.

14. A method of making a silicone rubber foam composition, the method comprising: mixing a silicone rubber foam composition comprising (a) one or more organosilicon compounds having an average of at least two silicon bonded alkoxy groups per molecule selected from one or more silicone resins and/or silicone resin intermediates; (b) a Lewis acid catalyst; (c) one or more surfactants; and (d) one or more organopolysiloxane polymers having an average of at least two, optionally at least three silicon bonded hydrogen groups per molecule; and causing foaming while the composition cures.

15. (canceled)

Description

EXAMPLES

[0107] Compositions were generated utilizing different types and amounts of components. These are detailed below. All amounts are in wt. % unless indicated otherwise. All viscosities are measured at 25? C. unless otherwise indicated. The viscosity of individual ingredients/components may be determined by any suitable method such as using a Brookfield? rotational viscometer with spindle LV-3 (designed for viscosities in the range between 200-400,000 mPa.Math.s) or a Brookfield? rotational viscometer with spindle LV-1 (designed for viscosities in the range between 15-20,000 mPa.Math.s) for viscosities less than 200 mPa.Math.s and adapting the speed according to the polymer viscosity.

[0108] A series of compositions for examples and a comparative example were prepared based on the compositions identified in Table 1a below (wt. % excluding catalyst solutions (Ex. 1-3) and/or catalyst/cure inhibitor complex solution (C.1)):

TABLE-US-00001 TABLE 1a Ingredient Ex. 1 Ex. 2 Ex. 3 C. 1 DOWSIL? US-CF-2403 10.5 Resin (wt. %) DOWSIL? 3074 3.3 Intermediate (wt. %) DOWSIL? 3037 9.8 Intermediate (wt. %) Tetraethyl orthosilicate 55.6 (TEOS) (wt. %) Surfactant (wt. %) 6 10 10 DOWSIL? MH 1107 Fluid 4.0 2.8 9.2 44.4 Dimethyl hydrogen terminated 79.5 polydimethylsiloxane (M.sup.HD.sub.97M.sup.H) (wt. %) Gelest? DMS-H31 (wt. %) 83.9 71.0

[0109] In C.1 N-methyldiphenylamine, (Ph.sub.2NCH.sub.3) was used as a cure inhibitor. It was prepared in a solution in toluene with the Lewis acid catalyst (b) with a 1:1 Lewis acid catalyst (b): cure catalyst molar ratio.

TABLE-US-00002 TABLE 1b Catalyst concentration introduced in toluene solution and ratio of Catalyst to inhibitor in Lewis Acid catalyst/cure inhibitor complex solution when N-methyldiphenylamine, (Ph.sub.2NCH.sub.3) was used as a cure inhibitor Ingredient Ex. 1 Ex. 2 Ex. 3 C. 1 Tris(pentafluorophenyl)borane, 400 1000 1000 400 B(C.sub.6F.sub.5).sub.3 ppm Catalyst:Cure Inhibitor molar ratio 1:1

[0110] Three methoxy functional silicone resins commercially available from Dow Silicones Corporation were used as methoxy resins in Table 1a:

[0111] DOWSIL? US-CF-2403 Resin is a methyl-methoxy functional, solventless and low molecular weight liquid siloxane. It has a viscosity of up to about 35 mPa.Math.s at 25? C. (datasheet) and a weight average molecular weight of less than 1000 Da (datasheet).

[0112] DOWSIL? 3074 Intermediate is a methoxy-functional, solventless liquid silicone resin. It has a 15 to 18 wt. % methoxy content, an average viscosity of about 120 mPa.Math.s at 25? C. and weight average molecular weight of between 1000 and 1500 Da (datasheet).

[0113] DOWSIL? 3037 Resin Intermediate is a methoxy-functional, solventless liquid silicone resin. It has a 15 to 18 wt. % methoxy content, an average viscosity of about 15 mPa.Math.s at 25? C. and weight average molecular weight of between 800 and 1300 Da (datasheet).

[0114] The surfactant used in the present examples was a commercial surfactant sold as DOWSIL? 3-9727 Profoamer by Dow Silicones Corporation of Midland, Michigan.

[0115] DOWSIL? MH 1107 Fluid is a trimethyl terminated polymethylhydrogen siloxane having a viscosity of about 30 mPa.Math.s at 25? C. (datasheet) commercially available from Dow Silicones Corporation.

[0116] Gelest? DMS-H31, is a dimethyl hydrogen terminated polydimethylsiloxane having a viscosity of 1,000 mPa.Math.s at 25? C. (Supplier information) from Gelest Inc;

[0117] In the case of the foams in Table 1a, Ex. 1 to 3 were all solely chemically blown to produce the resulting foams, whilst comparatives C.1 were chemically and physically blown.

[0118] In the examples of Table 1, catalyst (b) utilised, i.e., tris(pentafluorophenyl)borane, B(C.sub.6F.sub.5).sub.3 was introduced into the composition as a Lewis acid catalyst (b) solution in toluene in Ex. 1 to 3 and in a Lewis acid catalyst (b)/cure inhibitor complex solution for C.1.

[0119] The Lewis acid catalyst (b) solution was prepared by dissolving designated amounts of catalyst in toluene. The Lewis acid catalyst (b)/cure inhibitor complex solution was prepared by dissolving designated amounts of the selected catalyst and an optional cure inhibitor N-Methyldiphenylamine (Ph.sub.2NCH.sub.3) (often referred to as MDPA) in toluene in a Lewis acid catalyst: cure inhibitor molar ratio of 1:1. This enabled catalyst and cure inhibitor to interact and form a complex to inhibit catalytic activity until heated, before introduction into the composition.

Preparation of Ex. 1, 2 and 3 (Chemically Blown Foams)

[0120] For Ex. 1, 2 and 3, the organopolysiloxane polymers having an average of at least two, alternatively at least three silicon bonded hydrogen groups per molecule were first speed-mixed, and about 50 wt. % of the total composition of the resulting mixture was pre-heated in a 50? C. oven. The catalyst solution, surfactant, methoxy-functionalized silicone resin used, and room-temperature mixture of organopolysiloxane polymers having an average of at least two, alternatively at least three silicon bonded hydrogen groups per molecule mixture, and 50? C. mixture of same were added in sequence to a speedmix cup. The sample was subsequently speed-mixed at 3000 rpm for 30 seconds (s) and placed into a 50? C. water bath. 30 min after the cease of bubble generation, the sample was transferred to a 50? C. oven for complete cure.

Preparation of C.1 (ComparativeSurfactant-Free Chemically Blown Foam)

[0121] The catalyst solution, TEOS, and DOWSIL? MH 1107 Fluid were added in sequence to a speedmix cup, which was subsequently mixed using the speedmixer at 3000 rpm for 30 s. The sample was left at room temperature for foaming.

Measurement Information

[0122] The cure times of Ex. 1 to 3 were measured by a digital stopwatch and defined as the time when gas generation ceased and the sample stopped flowing.

Density Measurement

[0123] Foam densities were measured using a balance (Mettler-Toledo XS205DU) equipped with a density measurement kit based on Archimedes' principle. The weight of a sample (m.sub.0) in air was first measured, after which the balance was tared without removing the sample. The weight of the sample (?m.sub.1) in water (?.sub.0=1 g/cc) was then measured.

[00001]$?=\frac{m_0}{-m_1}?{?}_0$

TABLE-US-00003 TABLE 2 Cure Time and Properties of Foams Tested Property Ex. 1 Ex. 2 Ex. 3 C. 1 Cure time at 50? C. (min) 2.3 Instantaneous* 0.7 Density (g/cc) 0.40 0.44 0.25 0.29 Foam morphology (closed Mixed Mixed Mixed N/A or open cells) *The foaming process finished before timing started.

[0124] C.1 was prepared using DOWSIL? MH 1107 Fluid and tetraethyl orthosilicate (TEOS) using MDPA as a cure inhibitor to tune the reaction kinetics. However, unlike Ex. 1-3 herein comparative C.1 did not comprise a surfactant. The densities of resultant chemically blown silicone foams of Ex. 1 to 3 using tris(pentafluorophenyl)borane (B(C.sub.6F.sub.5).sub.3 as catalyst were comparable to those of C.1, but it was found that the use of a surfactant in each of Ex. 1-3 helped stabilize the cellular structure before the composition was fully cured and scanning electron microscope analysis (SEM) results indicated that Ex. 1, 2 and 3 had significantly improved regularity of the cell structure of their respective foams than comparative C.1. It was also found that increased viscosities of the compositions of Ex. 1, Ex. 2 and Ex. 3 were beneficial for tuning both cure kinetics and the cell structure with the working times of Ex. 1, 2 and 3 making the compositions easier to handle.

[0125] It will be appreciated that as alkanes are generated as chemical blowing agents for the Examples herein, the generation of the foam is safer than when using the previously preferred hydrogen gas as foaming agent because of the narrower explosive limits of alkanes. Furthermore, it will be appreciated that use of expensive platinum-based catalysts and hydrosilylation cure processes are avoided herein. Avoiding the need for such catalysts negates the need to use such expensive catalysts but also avoids discoloration and formation of colloidal platinum particles over time and the catalysts used herein do not suffer from being poisoned in the presence of impurities, such as nitrogen and sulfur-containing heterocyclics unlike platinum catalysts.