LIQUID SILICONE RUBBER COMPOSITION

Abstract

A liquid silicone rubber (LSR) composition, and articles and coatings made therewith are disclosed. Also disclosed is a process to provide for the composition, and a process to coat on textile.

Claims

1. A liquid silicone rubber composition comprising: (i) a liquid silicone rubber base comprising a reinforcing filler; (ii) a hydrophobic silica aerogel in an amount of from 3 to 8 weight percent (wt %) of the composition, where the hydrophobic silica aerogel is different from the reinforcing filler of the liquid silicone rubber base (i); (iii) an elastomeric powder in an amount of from 3 to 8 wt % of the composition; and (iv) a volatile solvent; wherein the weight ratio of the hydrophobic silica aerogel (ii) to the elastomeric powder (iii) is from 0.8:1 to 2:1.

2. The liquid silicone rubber composition according to claim 1, wherein the liquid silicone rubber base (i) comprises at least one liquid alkenyl-containing polydiorganosiloxane (A), at least one organohydrogenpolysiloxane (B), at least one reinforcing filler (C), and at least one hydrosilylation catalyst (D).

3. The liquid silicone rubber composition according to claim 1, wherein the hydrophobic silica aerogel (ii) has a surface area of from 500 to 1200 m.sup.2/g using the BET method.

4. The liquid silicone rubber composition according to claim 1, wherein the hydrophobic silica aerogel (ii) has a particle size of from 5 to 1000 m as measured by laser light scattering.

5. The liquid silicone rubber composition according to claim 1, wherein the elastomeric powder (iii) has a particle size of from 0.1 to 1000 m as measured by a laser diffraction type particle size distribution analyzer.

6. The liquid silicone rubber composition according to claim 1, wherein the weight ratio of the hydrophobic silica aerogel (ii) to the elastomeric powder (iii) is from 0.8:1 to 1.5:1.

7. The liquid silicone rubber composition according to claim 1, wherein the volatile solvent (iv) is selected from the group consisting of silicone based volatile solvents, hydrocarbon based volatile solvents, and mixtures thereof.

8. The liquid silicone rubber composition according to claim 1, wherein the liquid silicone rubber base (i) is a silicone textile printing ink.

9. A method for preparing the liquid silicone rubber composition according to claim 1, the method comprising mixing ingredients (i) to (iv) at ambient temperature.

10. A method for coating a textile, the method comprising: coating the textile with a liquid silicone rubber composition; and curing the composition to form a coating; wherein the liquid silicone rubber composition comprises: (i) a liquid silicone rubber base comprising a reinforcing filler; (ii) a hydrophobic silica aerogel in an amount of from 3 to 8 weight percent (wt %) of the composition, where the hydrophobic silica aerogel is different from the reinforcing filler of the liquid silicone rubber base (i); (iii) an elastomeric powder in an amount of from 3 to 8 wt % of the composition; and (iv) a volatile solvent; wherein the weight ratio of the hydrophobic silica aerogel (ii) to the elastomeric powder (iii) is from 0.8:1 to 2:1.

11. The method according to claim 10, wherein the textile is selected from the group of leather or natural fibers and/or synthetic fibers.

12. The method according to claim 11, wherein the textile comprises natural fibers selected from the group consisting of cellulosic fibers, wool, and/or silk.

13. The method according to claim 10, wherein the composition is applied by screen printing.

14. A textile coated with the liquid silicone rubber composition in accordance with claim 1 or a cured coating thereof.

15. An article cured from the liquid silicone rubber composition in accordance with claim 1.

16. A composite part comprising a silicone elastomer cured from the liquid curable silicone rubber composition in accordance with claim 1 on a substrate.

15. (canceled)

16. (canceled)

17. (canceled)

18. (canceled)

17. A method to impart a mattifying effect to a silicone elastomer article or composite part, wherein the silicone elastomer article or composite part is obtained from curing a liquid silicone rubber composition comprising a combination of hydrophobic silica aerogel and elastomeric powder, where the ratio of hydrophobic silica aerogel to elastomeric powder is from 0.8:1 to 2:1.

Description

EXAMPLES

[0159] Gloss test method: the coating composition provided in the present invention and the comparative compositions were applied on a piece of textile fabric, and left to cure, providing for a coating of 0.05 mm thickness (typically 3 layers of composition applied). In each instance three different types of fabric were used as alternative substrates for the sake of comparison, namely cotton, lycra and polyester, unless otherwise indicated the gloss values were the same irrespective of the substrate used. The resulting coating was measured for gloss at an angle of 60, using a BYK micro-TRI-Gloss glossmeter.

[0160] Gloss of commercial available materials is currently 0.8 (at 60 angle).

[0161] Hand feel evaluation is run in comparison with standard samples from current commercial coatings, with 10 panelists. Satisfactory handfeel is considered when the 10 panelists confirm the improved feel for 1 sample over the comparative sample.

[0162] Discolouration was assessed by visual inspection.

[0163] The liquid silicone rubber base as disclosed in Table 1 was used in the following working examples. All viscosities were measured at 25 C. relying on the cup/spindle method of ASTM D 1084 Method B, using an appropriate spindle for the viscosity range unless otherwise indicated.

TABLE-US-00001 TABLE I Liquid silicone rubber base 1 Alkenyl-containing mixture of alkenyl Vinyl-terminated polydiorganosiloxane polydimethylsiloxane having the viscosity of 55 Pa .Math. s at 25 C. and Vinyl-terminated polydimethylsiloxane having the viscosity of 2 Pa .Math. s at 25 C. Organohydrogen Mixture of Trimethylsiloxy-terminated polysiloxane polydimethyl-methylhydrogensiloxane containing 0.12% by weight of hydrogen atom bonded to silicon and the viscosity of 0.005 Pa .Math. s at 25 C. and Hydrogendimethylsiloxy-terminated polydimethylsiloxane having the viscosity of 0.011 Pa .Math. s at 25 C. Inhibitor Mixture of Methylvinyl cyclosiloxane (MeViSiO).sub.n (n < 6) and 1-Ethynyl-1-cyclohexanol Reinforcing filler Hydrophobic treated fumed silica having the surface area of 225 m.sup.2/g (BET Method) Hydrosilylation A catalyst, which was a solution catalyst composed of 0.2 percent by weight of platinum-siloxane complex prepared from platinum dichloride and 1,3-divinyltetramethyldisiloxane according to method described in U.S. Pat. No. 5,175,325, and 98 percent by weight of vinyldimethylsiloxy-terminated polydimethylsiloxane having the viscosity of 0.19 Pa .Math. s at 25 C. and 1.8 percent by weight of 1,3-divinyltetramethyldisiloxane, to have platinum content of 1000 ppm.

Examples 1 to 7

[0164] Each example and comparative example was prepared by mixing the ingredients and applying the resulting composition onto a cotton, a lycra and a polyester fabric substrate surface. Samples were cured for a period of 2 minutes at a temperature of 140 C. and the resulting cured elastomeric product was analysed for gloss, hand feel and discoloration. Examples 1 to 7, disclosed in Table 2, indicate the matt evolution upon the combination of the aerogel and elastomeric powder, when used in conjunction. Additionally, the Examples having the lower gloss maintain a good feel, as desired for the function.

TABLE-US-00002 TABLE 2 Parts by Example Example Example Example Example Example Example weight 1 2 3 4 5 6 7 Liquid silicone 94 94 94 94 94 94 94 rubber base 1 Black pigment 10 10 10 10 10 10 10 Hydrophobic 0.5 1 2 3 3.5 4 5 silica aerogel Elastomeric powder 1 2 3 4 4.5 5 6 Solvent 20 20 20 20 20 20 40 (silicone based) GLOSS (60 degree) 0.9 0.9 0.7 0.6 0.5 0.4 0.3 Feel Rubbery Rough Rough Good Good Soft Soft feel Discolouration No No No No No No No Observed?

[0165] It was found that Examples 6 and 7 successfully met all requirements in that no discolouration was noted, they had a soft feel and a gloss of <0.5. Of these example 6 was preferred given it had a lower viscosity. Indeed additional solvent (iv) was added into composition of example 7 than might have originally been intended but even then the viscosity was deemed too high to be used as a practical ink. Examples 4 and 5 also gave pretty good results but unfortunately their gloss values were slightly higher than preferred.

Comparative Examples 1 to 5

[0166] Comparative Examples 1 to 5 are disclosed in Table 3.

[0167] Comparative Example 1 represents the liquid silicone rubber composition free of hydrophobic silica aerogel and elastomeric powder. Gloss is not satisfying with a value of 1.

[0168] Comparative Examples 2 to 4 provide for comparison with additional hydrophobic filler having a surface area of 200-240 mm.sup.2/g (BET method), also free of hydrophobic silica aerogel and elastomeric powder. Gloss is reduced with increasing amount of hydrophobic silica, but color discoloration was noticed, which is not acceptable in the field of textile coating. Furthermore, the viscosity of comparative example 4 was too high for use in a printing ink application as well as showing discolouration.

[0169] Comparative Example 5 features a known mattifying ingredient Expancel DET 40, from Akzo Nobel, that is, dry microspheres composed of a thermoplastic shell encapsulating a gas, which expand upon heating. Although gloss is reduced to a commercially acceptable level of 0.7, hand feel remains unsatisfactory. Additionally, the composition is not easy to mix because of very low bulk density.

TABLE-US-00003 TABLE 3 Parts by Comparative Comparative Comparative Comparative Comparative weight Example 1 Example 2 Example 3 Example 4 Example 5 Liquid silicone 94 94 94 94 94 rubber base 1 Black pigment 10 10 10 10 10 Hydrophobic 0 3 7 14 0 silica - non aerogel (surface area 200-240 m.sup.2/g) Expancel 0 0 0 0 0.5 DET 40 Solvent 0 20 20 20 20 GLOSS (60 degree) 1 0.9 0.8 0.4 0.7 Feel Rubbery Rough Good Good Rubbery Discoloration Yes Yes Yes Observed?

Example 8 and Comparative Example 6

[0170] Example 8 and Comparative Example 6, disclosed in Table 4, are based on an alternative liquid silicone rubber composition 2 approved for textile coating.

[0171] Example 8 has a lower gloss at 0.4, taking advantage of the combined presence of the hydrophobic silica aerogel and elastomeric powder, which both are absent of Comparative Example 6. However, it was found that upon cure the elastomeric product of Example 8 was not sufficiently adhesive to the respective substrates to which it was applied.

Liquid silicone rubber base 2 was a commercial curable LSR from Dow Silicones Corporation, Dowsil LCF 9800 Textile Printing Ink.

TABLE-US-00004 TABLE 4 Parts by weight Comparative Example 6 Example 8 Liquid silicone rubber base 2 94 94 Black pigment 10 10 Hydrophobic silica aerogel 0 3 Elastomeric powder 0 4 Solvent 0 10 GLOSS (60 degree) 0.8 0.4 Feel Rubbery Good

Comparative Examples 7-8

[0172] Comparative Examples 7 and 8, disclosed in Table 5, illustrate the requirement of the combined presence of the hydrophobic silica aerogel and elastomeric powder to achieve a satisfactory level of gloss. When the hydrophobic silica aerogel is used alone, gloss is only reduced to a value of 0.7. When the elastomeric powder is used alone, gloss in increased to 1.7.

[0173] It is therefore surprising that adding the elastomeric powder to the hydrophobic silica aerogel would further decrease gloss, rather than cancelling the mattifying effect of the hydrophobic silica aerogel.

TABLE-US-00005 TABLE 5 Comparative Comparative Parts by weight Example 7 Example 8 Liquid silicone rubber base 94 94 Black pigment 10 10 Hydrophobic silica aerogel 4.5 0 Elastomeric powder 0 5.6 Solvent 22.5 22.5 GLOSS (60 degree) 0.6 1.7 Feel Rough Rubbery

[0174] Given the excellent results of Example 6 in Table 2 the physical properties of this composition were further analysed to indicate its suitability for use as a printing ink. Results showed that this was a suitable material and had sufficiently good physical properties for use as a printing ink.

TABLE-US-00006 TABLE 6 Post Cure Physical Properties Property Test Method Result Durometer hardness (Shore A) ASTM D2240 40 Tensile Strength (MPa) ASTM D412 4.2 Elongation at break (%) ASTM D412 400

[0175] These results indicate that the use of the aerogel and elastomeric powders in combination provided decreased gloss results of <0.5 but did not substantially negatively affect the standard physical properties of the cured elastomeric silicone rubber materials.

[0176] Likewise, it was seen that the gloss values were not affected by the substrate to which these materials had been applied, in that in each case the gloss values were noted to be 0.4 as can be seen in Table 7 below.

TABLE-US-00007 TABLE 7 Gloss value on different Fabric Substrates Fabric type Gloss (60) Lycra 0.4 Polyester cotton blend 0.4 Cotton 0.4

Wash Fastness

[0177] As a measure of the adhesion of the elastomeric product s on the different fabric substrates above samples of fabrics to which the elastomeric product resulting from the cured elastomer made from the composition of Example 6 above were washed and analysed in accordance with AATCC Test Method 61-2003 Test No. 1A. Samples were washed 25 times and subsequent to each wash the samples were assessed for the loss of elastomer from the fabric substrate (wash off) during the wash. Table 8 below shows that no wash off was observed.

TABLE-US-00008 TABLE 8 Wash Fastness Fabric type Wash Fastness (25 washes) Lycra No wash off Observed Polyester cotton blend No wash off Observed Cotton No wash off Observed

[0178] A further advantage of the coating made from the ink made from the formulation of example 6 above is that there were no visible signs of fibre deterioration (fibrillation) after cure, i.e. the apparent worn out appearance was not observed on the substrates utilised.