Method for Providing Objects with a Protective Coating of Silicone Elastomer

Abstract

The present invention relates to a method for providing objects with a protective coating of silicone elastomer. The present invention further relates to silicon coated objects obtainable by the method of present invention. The method of present invention can be used for the thin, protective and durable coating and production of environmental friendly consumer products.

Claims

1. A method for providing an object with a protective coating of silicone elastomer, wherein the method comprises the steps of a) providing a liquid composition comprising room temperature vulcanisation (RTV) silicone elastomers, wherein said liquid composition comprising RTV silicone elastomer has a viscosity of between 2500 mPa.Math.s to 10000 mPa.Math.s, b) spraying a first layer of said liquid composition on the surface of said object, thereby coating the surface of the object with the liquid composition, wherein the object is comprised of polymeric foam selected from the group consisting of polyurethane, polyether, silicone, natural latex, polystyrene, polyethylene, polypropylene, or mixtures thereof, preferably polyurethane, and wherein spraying is performed at an air pressure of at least 3 bar, c) allowing polymerization of the first layer of RTV silicone elastomers, and d) optionally, providing on said first layer at least one additional layer of said composition comprising a silicon elastomer.

2. The method according to claim 1, wherein the first layer covering the surface of the object, has a thickness of at most 1 mm.

3. The method according to claim 1, wherein polymerization is allowed for about 1 to 120 minutes.

4. The method according to claim 1, wherein the at least one additional layer is provided during the gel time of the RTV silicone elastomer of the first layer, wherein the gel time is about 1 to 30 minutes.

5. The method according to claim 1, wherein the object has a temperature of preferably between about 15 C. to 25 C.

6. The method according to claim 1, wherein said composition comprising RTV silicone elastomer is obtained by an addition reaction of hydrogen siloxane with vinyl siloxane in the presence of a catalyst and optionally a filler.

7. The method according to claim 6, wherein said catalyst is platinum.

8. The method according to claim 6, wherein said filler is a silicium oxide or iron oxide, preferably silicium dioxide.

9. The method according to claim 1, wherein the composition further comprises between 0.01% to 10% w/w of a thixotropic additive based on the total weight of the composition.

10. The method according to claim 1, wherein the method is free of volatile organic compounds (VOC's).

11. The method according to claim 1, wherein the composition does not comprise a solvent.

12. The method according to claim 1, wherein polymerisation is allowed at a temperature of at least 30 C.

13. A silicon coated object obtainable by the method according claim 1, wherein the object is comprised of polymeric foam selected from the group consisting of polyurethane, polyether, silicone, natural latex, polystyrene, polyethylene, and polypropylene.

14. Silicon The silicon coated object according to claim 13, wherein said object is coated with at least a first layer covering the surface of the object, wherein said at least first layer has a thickness of at most 1 mm.

15. The silicon coated object according to claim 13, wherein the coating is comprised of a RTV silicone elastomer is obtained by an addition reaction of hydrogen siloxane with vinyl siloxane in the presence of a catalyst and optionally a filler.

Description

[0014] Specifically, the above object, amongst other objects, is met, according to a first aspect, by the present invention by a method for providing an object with a protective coating of silicone elastomer, wherein the method comprises the steps of [0015] a) providing a liquid composition comprising room temperature vulcanisation (RTV) silicone elastomers, wherein said liquid composition comprising RTV silicone elastomer has a viscosity of between 2500 mPa.Math.s to 10000 mPa.Math.s, [0016] b) spraying a first layer of said liquid composition on the surface of said object, thereby coating the surface of the object with the liquid composition, wherein the object is comprised of polymeric foam selected from the group consisting of polyurethane, polyether, silicone, natural latex, polystyrene, polyethylene, polypropylene, or mixtures thereof, preferably polyurethane, and wherein spraying is performed at an air pressure of at least 3 bar, [0017] c) allowing polymerization of the first layer of RTV silicone elastomers, and [0018] d) optionally, providing on said first layer at least one additional layer of said composition comprising a silicon elastomer.

[0019] To provide the liquid composition of step a), components A and B are mixed in a mixing chamber, preferably using a static mixer for the continuous mixing of the two component. One component (e.g. component A) contains a platinum complex which is mixed with the second component, preferably a hydride- and a vinyl-siloxane polymer. When components A and B are mixed, a polymerization reaction (curing) is initiated and the viscosity of the liquid composition will increase over time. When the silicon elastomer is allowed to cure, adherence of the first layer into the object (e.g. a foam object) is provided by mechanical binding of the silicon elastomer to the object. In step c) the provided first layer of silicone elastomer is allowed to polymerize. Polymerization time depends on various conditions, such as temperature (of the air and of the object) and humidity, and can be influenced by the addition of additives (such as a retarder) or the presence of impurities in the liquid composition mixture. The first layer provides the basis of further coating of the object. Further coating in step d may be performed using the composition comprising the silicone elastomer, however also different coatings can be used.

[0020] The present invention relates to the method, wherein spraying is performed at an air pressure of at least 3 bar, preferably at least 5 bar, more preferably at least 7 bar. When the liquid composition is sprayed using air pressure, i.e. mist-spraying said composition on the surface of the object to be coated, the liquid composition covers the surface of the object, but in addition and due to the air pressure that is applied, the composition partially penetrates the object. For instance, when an object to be coated is comprised of polymeric foam, the liquid composition comprising the silicon elastomer will, due to the air pressure spraying, penetrate partially into the pores of the foam. When the silicon elastomer is allowed to cure, adherence of the first layer into the foam is provided by mechanical binding of the silicon elastomer to the foam.

[0021] The present invention relates to the method, wherein the object is comprised of polymeric foam selected from the group consisting of polyurethane, polyether, silicone, natural latex, polystyrene, polyethylene, polypropylene, preferably polyurethane. The present invention relates to the method, wherein the object can further be comprised of textile, wood or stone. The method of present invention includes the penetration of the composition comprising silicon elastomer into the object to be coated. This penetration depends on the properties of the composition itself, i.e. the viscosity, but also on the properties of the object to be coated. Preferably the object is comprised of material that contains pores in which the liquid composition can flow into or forced into the object during pressure spraying of the object.

[0022] The liquid composition comprising RTV silicone elastomer in the method of present invention has a viscosity of between 2500 mPa.Math.s to 10000 mPa.Math.s, preferably between 3000 mPa.Math.s to 7500 mPa.Math.s, more preferably between 4000 mPa.Math.s to 6000 mPa.Math.s, most preferably between 4500 mPa.Math.s to 5500 mPa.Math.s. It is important that the liquid composition remains low enough in viscosity that it can still be easily applied/sprayed as a coating on the surface of the object and to obtain a thin first coated layer.

[0023] According to a preferred embodiment, the present invention relates to the method, wherein the first layer covering the surface of the object, has a thickness of at most 1 mm, preferably at most 2 mm, more preferably at most 2.5 mm, most preferably at most 25 mm. A thin first layer is sprayed on the surface of the object to be coated, providing preferably a sealed surface of the object. The first layer adheres by mechanical binding of the silicon elastomer into the pores of the object. The first layer provides the basis of further coating of the object and may serve as a basis layer for further coating, e.g. by providing a finishing layer. The coatings may provide a textured layer resulting in a more mat finish as coating, by addition of an additive such as a thixotropic agent to the silicone elastomer composition. Also, metallic's may be added to the composition to provide a silicone elastomer composition with improved conductive properties.

[0024] According to another preferred embodiment, the present invention relates to the method, wherein polymerization is allowed for about 1 to 120 minutes, preferably 2 to 60 minutes, more preferably 5 to 15 minutes.

[0025] According to another preferred embodiment the present invention relates to the method, wherein the at least one additional layer is provided during the gel time of the RTV silicone elastomer of the first layer. The gel time (or pot life) can be determined, i.e. when it is observed that the first (preceding) layer applied on the surface of the object starts to become more viscous, stringy and gel-like, though not quite fully cured. For the method of present invention, it is not necessary to await a fully cured first layer in order to proceed with providing the coated object with an additional layer of the composition comprising a silicon elastomer. For optimal adhesion of the at least one additional layer, said additional layer is preferably provided on the first (or preceding) layer within the gel time of the composition of the first layer.

[0026] According to another preferred embodiment, the present invention relates to the method, wherein the gel time is about 1 to 30 minutes, preferably 5 to 15 minutes, more preferably 6 to 8 minutes. Depending on the further additives in the liquid composition comprising silicon elastomer, such as the addition of a retarder or thixotropic agent, the gel time may be affected.

[0027] According to a preferred embodiment, the present invention relates to the method, wherein the object has a temperature of preferably between about 15 C. to 25 C., preferably about 17 C. to 19 C. Preferably the method of present invention is performed at room temperature, preferably between about 15 C. to 25 C.

[0028] In step b) the provided liquid composition is sprayed on the surface of the object that is coated, using a spraying device. The liquid composition is transported through the spraying device towards the spray nozzle under pressure (material pressure of between 0.5-2.5 bar) of at least 3 to 7 bar of air pressure, depending on the desired degree of penetration of the silicone coating in the object.

[0029] According to a preferred embodiment, the present invention relates to the method, wherein said composition comprising RTV silicone elastomer is obtained by an addition reaction of hydrogen siloxane with vinyl siloxane in the presence of a catalyst, pigments and optionally a filler.

[0030] According to yet another preferred embodiment, the present invention relates to the method, wherein said catalyst is platinum.

[0031] According to a preferred embodiment, the present invention relates to the method, wherein said filler is a silicium oxide or iron oxide, preferably silicium dioxide.

[0032] According to another preferred embodiment, the present invention relates to the method, wherein the composition further comprises between 0.01% to 10% w/w, preferably between 0.05% to 5% w/w, most preferably between 0.1% to 0.5% w/w of a thixotropic additive based on the total weight of the composition. An example of suitable thixotropic agent that can be used in the method of present invention is polyglycol. In many cases it is desirable for the liquid composition comprising silicon elastomer to flow sufficiently to form a uniform layer (coating), then to resist further flow, thereby preventing sagging on a vertical surface. Also the viscosity of the composition comprising silicone elastomer should be such that it is able to penetrate into the object that is coated, using the method of present invention. A thixotropic agent can increase the viscosity and reduce the flowability of silicone elastomers for use in coatings, without adversely affect the physical properties of the silicone coating, when cured. Also, in case materials are used that have smaller pores than e.g. PU foam, such as wood, the use of less thixotropic agent may be required to reduce viscosity and to increase the penetration of the coating into the material to be coated, when spraying the first layer on the surface of the object.

[0033] According to yet another preferred embodiment, the present invention relates to the method, wherein the method is free of volatile organic compounds (VOC's).

[0034] According to another preferred embodiment, the present invention relates to the method, wherein the composition does not comprise a solvent. Depending on the working conditions, a lower viscosity may be desired and usually solvents are therefore used. However most solvents adversely affect the physical properties of the silicone elastomer after curing is finished. With the addition of a solvent or diluent to the silicone elastomer mixture also the curing time is often prolonged, the hardness and tensile strength are considerably decreased, which are all characteristics that can be maintained in the method of coating of present invention.

[0035] According to a preferred embodiment, the present invention relates to the method, wherein polymerisation is allowed at a temperature of at least 30 C., preferably at least 45 C., more preferably at least 60 C. Polymerisation is preferably allowed at room temperature, however higher temperatures to speed up the process may be applied, e.g. by heating the object that is coated or by increasing the environment temperature. Curing may proceed more quickly at a temperature form about 30 C. to 150 C.

[0036] The present invention, according to a second aspect, relates to a silicon coated object obtainable by the method of present invention, wherein the object is comprised of polymeric foam selected from the group consisting of polyurethane, polyether, silicone, natural latex, polystyrene, polyethylene, polypropylene, preferably polyurethane. Using the method of present invention objects with difficult angles and double curved corners can be more easily silicon coated.

[0037] According to a preferred embodiment, the present invention relates to the silicon coated object, wherein said object is coated with at least a first layer covering the surface of the object, wherein said at least first layer has a thickness of at most 1 mm, preferably at most 2 mm, more preferably at most 2.5 mm, most preferably at most 25 mm.

[0038] The present invention relates to the silicon coated object, wherein a silicon coating penetrates into said object for at least between 0.01 mm, preferably at least 0.5 mm, more preferably at least 1 mm, most preferably at least 5 mm.

[0039] According to a preferred embodiment, the present invention relates to the silicon coated object, wherein the coating is comprised of a RTV silicone elastomer is obtained by an addition reaction of hydrogen siloxane with vinyl siloxane in the presence of a platinum catalyst and optionally a filler. The filler is preferably silicium dioxide.

[0040] The present invention will be further detailed in the following figure wherein:

[0041] FIG. 1: A) shows a foam object coated with a silicon elastomer composition according to the method of present invention; [0042] B) shows the surface of a foam object that is coated with approximately 1 mm thick single layer of silicon elastomer according to the method of present invention; [0043] C) shows a cross section of the silicone coated foam object of B according to the method of present invention. The penetration of the thin silicone layer into the pores of the material is clearly observed, providing a mechanical binding of the