Silicone Mixture and Method of Using It

This application, in general, relates to an improved silicone mixture and more particularly to an improved silicone rubber mixture having clay as an additive.

Silicone compounds, and in particular silicone rubbers, have been widely used in various environments. They are often used as insulating materials and in making various components. In general, the prior art silicone compounds have proved dissatisfactory since they are not as durable as some other materials. The prior art silicone compounds may often be easily abraded or torn.

On the other hand, silicone is known to have many desirable features. Silicone has good thermal characteristics that make it a desirable insulator for both electricity and heat. In addition, a silicone compound will produce a less toxic smoke when burned than most other prior art materials, such as nylon.

For this reason, it is desired to create an improved silicone mixture that will be more resistant to abrading and more durable than the prior art silicone compounds.

The present invention discloses an improved silicone mixture that resists abrading, is resilient, and is useful as material for insulation or forming various components.

In a disclosed embodiment of the present invention, the silicone mixture consists of a first known silicone compound that is mixed with a quantity of dried pulverized clay in order to result in a more flexible material that will provide better abrasion resistance to the final silicone mixture.

In a preferred embodiment of the present invention, the silicone compound is mixed with a dried pulverized clay and a quantity of powdered alumina-trihydrate is added to provide better burn resistance.

In one embodiment, a liquid silicone rubber is utilized as the silicone compound that is mixed with the clay. An example of a silicone rubber that may be utilized is available under the tradename Silastic.TM., available from Dow Chemical Company. This product consists of two compounds that are combined to initiate the setting up or curing of the product and is fully described in U.S. Pat. No. 3,445,420 entitled "Acetylenic Inhibited Platinum Catalyzed Organopolysiloxane Composition" issued to Kookoosedes, et al. In the first embodiment this silicone rubber is mixed with a clay that is dry, pulverized, and then sifted until very fine.

A particular clay that is utilized in a preferred embodiment consists of the following components:

20 to 30% Illite

10 to 15% Vermiculite

10 to 15% Kaolimite

10 to 15% Quartz

less than 5% Feltspars

5 to 10% Calcite

10 to 15% Dolomite

These are the volume percentages of the various materials found in the dry clay and not the original moist clay.

In one example, Silastic.TM. compound, weighing 1.84 pounds per pint was mixed with clay weighing 1.24 pounds per pint. A compound was arrived at by mixing 60% by volume of the Silastic.TM. compound and 30% by volume of the dry sifted clay with 10% by volume of the alumina-trihydrate.

The clay, the alumina-trihydrate and the two compounds that make up the Silastic.TM. compound were mixed and stored in a container that was maintained at 0.degree. F. for at least 24 hours. A vacuum was continuously applied to the container to remove air bubbles. The mixture was then ready for use.

A second embodiment of the mixture is formed by using a vulcanizing silicone rubber as the silicone compound. A silicone rubber sold under the tradename Sylgard.TM. and available from Dow Chemical Company, may be utilized in this second embodiment. The same clay utilized in the first embodiment is preferably utilized in the second embodiment. The Sylgard.TM. compound weighed 1.26 pound per pint.

The second embodiment of the mixture was arrived at by mixing 80% by volume of the Sylgard.TM. compound, 15% by volume of the dry sifted clay and 5% by volume of the alumina-trihydrate.

In preparing this second embodiment, the powdered clay and the powdered alumina-trihydrate are initially mixed. A small percentage of the Sylgard.TM. compound is then stirred into the powders to create a paste. The remainder of the Sylgard.TM. compound is then slowly stirred into the mixture. This mixture is exposed to some means for maintaining circulation while it is stored to prevent it from setting up.

The two mixtures are particularly advantageous for use as electric wire insulation and in particular for the outer insulating cover of electric cable. The mixtures may be coated upon the outer periphery of electric cable by a coating section that can consist of a series of chambers that each have the mixture circulating and a heated cable being drawn through the chamber. The coating will set-up on the cable due to the difference in temperature between the cable and the mixtures.

As should be clear this improved silicone mixture of this invention will have numerous other applications wholly outside electric insulator application. For instance, it is useful in forming floor tile or the like.

These and other features and objects of the present invention can be best understood from the following specification and appended drawings of which the following is a brief description thereof.

FIG. 1 shows an electric cable that may utilize the improved silicone mixture of the present invention.

FIG. 2 shows a first embodiment of a coating section for coating the improved silicone mixture upon an electric cable.

The present invention discloses an improved silicone mixture in which a base silicone compound is mixed with a dry pulverized clay to form a final mixture that is more resistant to abrasion and more durable than ordinary silicone compounds.

In one embodiment, a liquid silicone rubber is mixed with dry pulverized clay, and optionally, a quantity of alumina-trihydrate to provide better fire resistance.

The liquid silicone rubber that it utilized in this first embodiment may, for example, be Silastic.TM., available from Dow Chemical Company. Silastic.TM. consists of two compounds that are combined to initiate the setting up or curing of the final product. Silastic.TM. is described in U.S. Pat. No. 3,445,420 entitled "Acetylenic Inhibited Platinum Catalyzed Organopolysiloxane Composition", issued to Kookoosedes, et al.

Although it is preferred that dried pulverized sifted clay is mixed with the silicone compound, it is envisioned that an unrefined clay may also be utilized.

The clay that was utilized to make an example of the improved silicone compound consists of the following components;

20 to 30% Illite

10 to 15% Vermiculite

10 to 15% Kaolimite

10 to 15% Quartz

less than 5% Feltspars

5 to 10% Calcite

10 to 15% Dolomite

These are volume percentages measured from the dried sifted clay and not the original moist clay.

In making a second embodiment of the present invention, the silicone compound is a vulcanizing silicone rubber such as is available under the tradename Sylgard.TM. from Dow Chemical Company. Again, a powdered alumina-trihydrate may be added to increase burn resistance.

An example of the first embodiment was prepared by following the below described steps.

Silastic.TM. compound weighing 1.84 pounds per pint and the above identified clay weighing 1.24 pounds per pint were utilized to form the final improved silicone mixture. The final mixture contained 60% by volume of the Silastic.TM. compound and 30% by volume of the dry sifted clay. The final 10% of volume was powdered alumina-trihydrate which was added to improve burn resistance.

The clay, the alumina-trihydrate and the two compounds that make up the Silastic.TM. compound were mixed at ambient pressure and temperature. This mixing was continued until it was ensured that the four materials were all thoroughly interspersed.

The mixture was then stored in an airtight container that was maintained at 0.degree. F. for at least 24 hours. A vacuum was applied to this container to remove any air bubbles. At the end of the 24 hours the mixture was removed and was ready for use.

An example of the second embodiment was also prepared. Sylgard.TM. which weighed 1.26 pounds per pint was mixed with the above identified clay weighing 1.24 pounds per pint. This second mixture was arrived at by mixing 80% by volume of the Sylgard.TM. compound and 15% by volume of the dry sifted clay. 5% by volume of alumina-trihydrate was added, again for fire resistance.

The powdered clay and powdered alumina-trihydrate were initially mixed at ambient pressure and temperature. Once the two powders were thoroughly mixed, a small percentage of the Sylgard.TM. compound was stirred into the powders to create a paste. Once the paste had been established, the remainder of the Sylgard.TM. compound was stirred into the mixture. The mixture was then exposed to a means for maintaining circulation while the mixture was stored. The means for maintaining circulation prevented the mixture from setting up.

The improved silicone mixtures arrived at by the above two procedures have utility as electrical insulation materials.

FIG. 1 illustrates a cross-section of an electric cable 20 that utilizes the improved silicone mixture. A single strand of electric cable 20 has a central bare electric wire conductor 22 surrounded by wraps 24. An outer coating 30 of the improved silicone mixture is disposed around the wraps 24. Silicone impregnates an outer portion 28 of the wraps while an inner portion 26 remains free from silicone. By utilizing the improved silicone mixture, Applicant arrives at an improved electric cable in which the insulation will not abrade as easily as prior art cables. Also, Applicant arrives at an electric cable having a less toxic insulation that will not produce smoke as toxic as the prior art electric cable insulators.

A coating section 188 that may be utilized to coat the material upon the electric cable is illustrated in FIG. 2. This coating section 188 consists of a first coating portion 190, an intermediate cooling portion 192, and a second coating portion 194. First coating portion 190 consists of a chamber 196 that surrounds the electric cable and an inlet 198 that receives pressurized silicone mixture into chamber 196. The compound is circulated within chamber 196 to prevent it from setting up and eventually exits through exit 200.

The intermediate cooling section 192 consists of a chamber 202 that surrounds the cable and an inlet 204 that supplies cooling fluid to chamber 202. In a preferred embodiment of this invention, this cooling fluid may consist of water with an additive that has good thermal transfer characteristics, as an example, ordinary anti-freeze may be utilized. The cooling fluid circulates through chamber 202 and exists through port 206.

Second coating portion 194 has a chamber 208 surrounding the cable and a port 210 supplies the silicone mixture to the chamber 208. The fluid circulates within chamber 208 and exists through port 212.

Wire 78 enters coating portion 188 through port 213 and is coated within chamber 196. As the wire leaves chamber 196 it goes through guide port 214 separating first coating portion 190 from cooling portion 192. The size of the orifice at guide port 214 is chosen to be slightly larger than the orifice at opening 213 to accommodate the extra diameter of the wire due to the coating. As an example, it may be 0.015 inches larger in diameter.

Wire enters cooling chamber 202 through opening 215 and enters second coating portion 194. Cable is coated in second coating portion 194 and exits 80 through guide opening 218. Guide opening 218 is chosen to be slightly larger in diameter than opening 214 or 216, again to accommodate the extra diameter that the wire will now have due to the coating that has been applied in second coating portion 194.

The cable 80 is pulled through the coating section 188 by a force of approximately 150 foot pounds of tension. It is necessary to apply such a large force to pull the wire through coating section 188 since the guide openings 213, 214, 216 and 218 must be approximately the same diameter as the wire to ensure good sealing between the chamber 190, 192 and 194. Thus the improved silicone mixture of the present invention is coated onto an electric cable.

For further details of the coating of the improved silicone compound upon electric cable, and further embodiments of various types of coating sections attention is directed to the parent applications 07/330,008 and 07/329,927.

This material will have utility in a variety of applications. In particular, this material will be useful as an insulator for electric wire in all applications. In addition, this material may be useful as an insulator for welding cord and may also be useful for forming various components, such as automobile firewalls, automobile mufflers, protective clothing for fire fighters, high voltage insulated gloves, safety liners for bucket trucks doing high voltage electrical work, heat insulation pads for use in kitchens, truck bed liners and several other applications that will be obvious to one of ordinary skill in the art.

Preferred embodiments of the present invention have been disclosed, however a worker in the art would realize that certain modifications would be within the scope of this invention. Therefore, attention is directed to the following claims to determine the true scope of the present invention.