SILICONE PARTICLES WITH A CROSS-LINKED CORE AND PREPARATION THEREOF

Abstract

Particles P and methods of making the same. The particles P are composed of a core K comprising crosslinked silicone elastomer composition X and of a shell H of silica S. Where the core K includes a reinforcing filler F which is selected from pyrogenic or precipitated hydrophobic silicas having DIN 66131 BET surface areas of at least 50 m.sup.2/g and also from carbon blacks and activated carbons and silicone resins.

Claims

1-11. (canceled)

12. Particles P, comprising: wherein the particles P are composed of a core K comprising crosslinked silicone elastomer composition X and of a shell H of silica S; and wherein the core K comprises a reinforcing filler F which is selected from pyrogenic or precipitated hydrophobic silicas having DIN 66131 BET surface areas of at least 50 m.sup.2/g and also from carbon blacks and activated carbons and silicone resins.

13. The particles P of claim 12, wherein the silicone elastomer composition X is addition-crosslinking and comprises (A) at least one linear compound which contains radicals with aliphatic carbon-carbon multiple bonds, (B) at least one linear organopolysiloxane compound with Si-bonded hydrogen atoms, or, instead of (A) and (B), (C) at least one linear organopolysiloxane compound which contains SiC-bonded radicals with aliphatic carbon-carbon multiple bonds and Si-bonded hydrogen atoms, and (D) at least one hydrosilylation catalyst.

14. The particles P of claim 12, wherein the reinforcing filler F owing to surface treatment has a methanol number of greater than 40.

15. The particles P of claim 12, wherein the cores K comprise 5 to 200 parts by weight of reinforcing filler F per 100 parts by weight of the crosslinkable silicone elastomer composition X.

16. The particles P of claim 12, wherein the silica S is selected from pyrogenic or precipitated hydrophobic silicas having BET surface areas of at least 50 m.sup.2/g.

17. A method for producing particles P, comprising: in a first step, mixing a dispersion A comprising silica S and water with a mixture B comprising crosslinkable silicone elastomer composition X to give a continuous phase containing water and a discontinuous phase containing crosslinkable silicone elastomer composition X; in a second step, crosslinking the discontinuous phase to give the particles P; wherein the mixture B and the discontinuous phase comprise a reinforcing filler F.

18. The method of claim 17, wherein the continuous phase comprises at least 80 wt % of water.

19. The method claim 17, wherein in the first step, the total volume of mixture B and of the dispersion A is introduced initially, the initially introduced volume being made such that it comprises the total amount of required silica S and water.

20. The method of claim 17, wherein, in the first step, a catalyst is added for crosslinking the crosslinkable silicone elastomer composition X.

Description

EXAMPLES

Example 1: Preparation of an Aqueous Silica Dispersion A

[0173] 1300 g of a partially hydrophobic pyrogenic silica having a residual silanol content of 71% and a carbon content of 0.95%, obtained by reacting a hydrophilic starting silica having a specific BET surface area of 200 m.sup.2/g (available under the name HDK® N20 from Wacker-Chemie GmbH, Munich) with dimethyldichlorosilane in accordance with EP 1433749 A1, are incorporated in portions with stirring into 5200 g of fully demineralized (FD) water in a Labo-Top planetary dissolver from PC Laborsystem, CH, at 650 rpm. Following complete addition of the silica, dispersion is continued for a further 60 min at 650 rpm. This gives a high-viscosity dispersion with a solids content of 20% and a pH of 4.2.

Example 2: General Procedure for Mixing Dispersion A Comprising Silica S and Water with a Mixture B Using a Dissolver

[0174] Step 1: The silica dispersion described in Example 1 is weighed out into a suitable stirring vessel and agitated using a Labo-Top planetary dissolver from PC Laborsystem, CH, at 6000 rpm for 10 minutes. The viscosity of the dispersion goes down. Optionally FD water is added and mixed homogeneously. The mixed silicone oil component prepared according to one of Examples 5, 6 or 7 is added to the agitated silica dispersion and homogenized in the dissolver for 10 minutes at 6000 rpm with water coolant. During this time the temperature of the mixture ought not to rise above 35° C. The result is a white mass of high viscosity.

[0175] Step 2: The high-viscosity mass from method step 1 is diluted to 30% silicone oil content at 1000 rpm by addition of FD water in three equally sized portions. After each portion of FD water, stirring is carried out at 1000 rpm for 3 minutes. This gives a highly mobile, white O/W emulsion.

Example 3: General Procedure for Mixing Dispersion A Comprising Silica S and Water with a Mixture B Using an Ultra-Turrax

[0176] Step 1: The silica dispersion described in Example 1 is weighed out into a suitable 1000 m/I stainless steel vessel and agitated using an Ultra-Turrax T50, at 10000 rpm for 10 minutes. The viscosity of the dispersion goes down. Optionally FD water is added and mixed homogeneously. The mixed silicone oil component prepared according to one of Examples 5, 6 or 7 is added to the agitated silica dispersion and then homogenized using the Ultra Turrax for 10 min at 10000 rpm with ice cooling. During this time the temperature of the mixture ought not to rise above 35° C. The result is a white mass of high viscosity.

[0177] Step 2: The high-viscosity mass from step 1 is diluted to 30% silicone oil content by addition of FD water in three equally sized portions. After each portion of FD water, stirring is carried out at 6000 rpm for 3 minutes. This gives a highly mobile, white O/W emulsion.

Example 4: General Procedure for Producing Silica-Coated Silicone Elastomer Microparticles P of the Invention from Pickering Emulsions of Mixture B

[0178] 250 g of the Pickering emulsion amenable to polyaddition, prepared according to Example 2 or Example 3, are admixed using a paddle stirrer at 200 rpm with 20 ppm of Karstedt catalyst (based on the amount of platinum) in the form of a 1 wt % solution in polydimethylsiloxane containing vinyl groups with a viscosity of 1000 mm.sup.2/s (25° C.), in which both chain ends are blocked with a dimethylvinylsilyl group, and the mixture is stirred at 80° C. for 24 hours. The result is a white, highly mobile dispersion. For isolation, the particles P are removed by filtration and dried in a drying cabinet at 80° C. for 24 hours. This gives a fine, white powder.

Example 5: Silicon Resin-Reinforced Mixture B Amenable to Polyaddition

[0179] 375 g of a vinyldimethylsiloxy-terminated polydimethylsiloxane having a viscosity of 1 000 mm.sup.2/s (25° C.) and 264 g of a vinyldimethylsiloxy-terminated polydimethylsiloxane having a viscosity of 20 000 mm.sup.2/s (25° C.) were mixed homogeneously using a paddle stirrer. Then 274 g of a silicone resin containing vinyl groups with the composition [Me.sub.3SiO.sub.1/2].sub.26.65 [ViMe.sub.2SiO.sub.1/2].sub.3.72 [SiO.sub.4/2].sub.42.78 [HO.sub.1/2].sub.1.02 [EtO.sub.1/2].sub.5.93 (molecular weight by SEC (eluent, toluene): Mw=5300 g/mol; Mn=2560 g/mol) were added and the mixture was stirred until dissolution was complete. The base mass thus obtained was mixed homogeneously with 114 g of a copolymer made up of dimethylsiloxy, methylhydrogensiloxy and trimethylsiloxy units, having a viscosity of 40 mm.sup.2/s at 25° C. and an SiH content of 0.40%.

Example 6: Production of Silica-Coated, Silicone Resin-Reinforced Silicone Elastomer Particles P

[0180] 320 g of the mixture B of the invention from Example 5 and 240 g of the aqueous silica dispersion A from Example 1 were emulsified as in Example 2. Subsequently, as in Example 4, pulverulent silicone elastomer particles P were produced, having a mean particle size of d50=3.4 □m.

Example 7: Silica-Reinforced Mixture B Amenable to Polyaddition

[0181] Introduced initially in a commercial laboratory kneader were 917 g of a vinyldimethylsiloxy-terminated polydimethylsiloxane having a viscosity of 1000 mm.sup.2/s (25° C.), which were heated to 150° C. and admixed with 621 g of a hydrophobic pyrogenic silica having a specific surface area of 125 m.sup.2/g (measured by the BET method) and a carbon content of 1.6-2.0 wt %. This gave a high-viscosity mass, which was subsequently diluted with 618 g of the aforementioned polydimethylsiloxane. Kneading under reduced pressure (10 mbar) at 150° C. freed the resulting mass within an hour from water and excess residues of loading agent, especially volatile constituents. Then 123 g of a copolymer made up of dimethylsiloxy, methylhydrogensiloxy and trimethylsiloxy units, having a viscosity of 100 mm.sup.2/s at 25° C. and an SiH content of 0.47%, are added and homogeneously mixed.

Example 8: Production of Silica-Coated, Silica-Reinforced Silicone Elastomer Particles P

[0182] 156 g of the mixture B of the invention from Example 7 and 149 g of the aqueous silica dispersion A from Example 1 were emulsified as in Example 3. Subsequently, as in Example 4, pulverulent silicone elastomer particles P were produced, having a mean particle size of d50=12 □m.

Comparative Example C1: Silicone Elastomer Composition Amenable to Polyaddition, Without Reinforcing Filler

[0183] 1535 g of a polydimethylsiloxane containing vinyl groups with a viscosity of 1000 mm.sup.2/s (25° C.), in which both chain ends are blocked with a dimethylvinylsilyl group, were mixed homogeneously, using a paddle stirrer, with 123 g of a copolymer made up of dimethylsiloxy, methylhydrogensiloxy and trimethylsiloxy units with a viscosity of 100 mm.sup.2/s at 25° C. and an SiH content of 0.47%, without addition of a reinforcing additive.

Comparative Example C2: Production of Silica-Ccoated, Silicone Elastomer Particles Without Reinforcing Filler

[0184] 320 g of the silicone elastomer composition not in accordance with the invention, from comparative example C1, and 240 g of the aqueous silica dispersion from Example 1 were emulsified in accordance with Example 2. Subsequently, in accordance with Example 4, pulverulent silicone elastomer particles were produced, having a mean particle size of d50=18 □m.

Comparative Example C3: Silicone Elastomer Composition Amenable to Polyaddition, Without Reinforcing Filler

[0185] 479 g of a polydimethylsiloxane containing vinyl groups with a viscosity of 200 mm.sup.2/s (25° C.), in which both chain ends are blocked with a dimethylvinylsilyl group, were mixed homogeneously, using a paddle stirrer, with 21 wt % of a trimethylsilyl-terminated methylhydrosiloxane-dimethylsiloxane copolymer containing 0.73 wt % of Si-bonded hydrogen with a viscosity of 65 mm.sup.2/s (25° C.), without addition of a reinforcing additive.

Comparative Example C4: Production of Silica-Coated, Silicone Elastomer Particles Without Reinforcing Filler

[0186] 320 g of the silicone elastomer composition not in accordance with the invention, from comparative example C3, and 240 g of the aqueous silica dispersion from Example 1 were emulsified in accordance with Example 2. Subsequently, in accordance with Example 4, pulverulent silicone elastomer particles were produced, having a mean particle size of d50=9 □m.

Example 9: Sensory Evaluation of the Particles P

[0187] The sensory evaluation of the silica-coated silicone elastomer particles P of the invention from Examples 6 and 8, and also of the particles not in accordance with the invention, from comparative examples C2 and C4, was carried out by a trained team of five testers.

[0188] For the evaluation, the testers washed their hands and lower arms with soap and water. On the lower arm, a circular test area having a diameter of 4 cm was drawn on for each sample, and 0.04 g of the respective particles each time was applied and sprayed.

[0189] The parameters evaluated by the testers were the sensation of silkiness during spreading and skinfeel after spreading of the powders, on a scale from 0 (poor) to 4 (very good). The results are set out in Table 1.

TABLE-US-00001 TABLE 1 Example Silkiness Skin feel Example 6 4 3 Example 8 3 4 Comparative example C2* 1 2 Comparative example C4* 1 2 *not in accordance with the invention

Example 9: Mechanical Integrity of the Particles P

[0190] In contrast to Example 8 the testers spread the particles on the skin under strong pressure. The results for the silica-coated silicone elastomer particles P of the invention from Examples 6 and 8 were unchanged, whereas the particles not in accordance with the invention, from comparative examples C2 and C4, formed lumps during spreading, this being undesirable in cosmetic applications.

TABLE-US-00002 TABLE 2 Example Silkiness Skin feel Example 6 4 3 Example 8 3 4 Comparative example C2* 0 0 Comparative example C4* 0 0 *not in accordance with the invention

Example 11: Evaluation of the Mechanical Strength

[0191] The silica-coated silicone elastomer particles P of the invention from Examples 6 and 8, and also the particles not in accordance with the invention, from comparative examples C2 and C4, were each admixed with 100 wt % of a polydimethylsiloxane of viscosity 2 mm.sup.2/s (25° C.), with stirring. The particles swell and absorb the silicone oil completely.

[0192] The swollen particles were then tested on the skin in analogy to Example 9.

[0193] Surprisingly it was found that the silica-coated silicone elastomer particles of the invention, from Examples 6 and 8, exhibit a very good velvety-silky lubricious skinfeel after spreading, whereas the skinfeel of the particles not in accordance with the invention, from comparative examples C2 and C4, was much waxier and more sluggish after spreading.

TABLE-US-00003 TABLE 3 Example Silkiness Skin feel Example 6 4 4 Example 8 4 4 Comparative example C2* 3 0 Comparative example C4* 3 0 *not in accordance with the invention