COMPOSITION AND METHOD FOR TEXTURING THE SURFACE OF ARTICLES

Abstract: Novel one and two-part silicone dispersions are described which are suitable for applying a durable textured silicone surface on both silicone and non-silicone articles. The non-blocking surface is obtained by dip-coating a final layer over an article wherein the dispersion used for the final layers comprises a unique hydrophilic silica filler having a specific surface area of about 75-200 m<2> per gram, at least one crosslinkable polysiloxane and a crosslinking agent. The silica particles, securely imbedded within the final layer of silicone with portions thereof extending outwardly beyond the new outer silicone surface of the article, present a non-blocking, non-allergenic textured surface.

Description: COMPOSITION AND METHOD FOR TEXTURING THE SURFACE OF ARTICLES BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a composition and method f making a silicone article that has a textured non-blocking surfac 2. Prior Art As is well known in the art, silicone articles may formed by dipping or otherwise depositing a dispersion of silico on an appropriate form. The dispersion may also contain vulcanizing agent along with accelerators and other additive After each layer of dispersion is deposited on the form, the lay is permitted to cure and the process is repeated until the out shell of the article reaches the required thickness. A smooth untreated elastomer surface has the physic characteristic of blocking; that is, the characteristic of sticki to itself and other surfaces. For some applications blocking undesirable. For example, blocking is undesirable in late silicone and other elastomer gloves because it makes them difficul to don. Various lubricants and release agents have been dusted o otherwise applied to gloves to improve performance and overco blocking. The shedding of these lubricants can cause undesirabl side-effects, such as contamination, infection and foreign bod reactions due to powders from gloves entering the wound durin surgical procedures. As a result, much of the early work o textured surfaces was performed on latex surgical gloves. U.S. Patent No. 3,761,965, discloses a sanitary glove having a textured surface provided by a granular vinyl chloride polymer imbedded on the surface of the film from which the glove is manufactured. This glove is suitable for donning without the use of a lubricant such as powder. However, this type of glove has the same type of problem as talc-dusted gloves in that particulates may enter a wound causing an adverse foreign body reaction. Dusted gloves are, therefore, not generally suitable for surgical procedures. U.S. Patent No. 1,983,963 discloses a method of providing a textured surface on a rubber glove which subjects the vulcanized surface of the glove to the action of a rubber solvent or swelling agent such as naphtha, benzol, or gasoline either by immersion of by subjecting the surfaces to the fumes of these chemicals. This process, which is similar to etching, has not enjoyed widespread use and is not adaptable to silicone. U.S. Patent No. 4,143,109, issued to Stockum, describes a method of dip-coating a first layer of natural rubber latex onto a glove form, the form having the general contour of a human hand, followed by dip-coating a second layer containing particulates which are randomly distributed throughout dispersion. After curing, the glove is inverted and may be donned without the use of lubricants. The general method developed by Stockum for latex articles haas not been transferrable to silicone articles becau the particulates taught by Stockum for use with latex would weak the outermost layers of silicone substantially. The foregoing inventions have been developed for lat articles. U.S. Patent no. 4,061,709 to Miller, et al., describ a method for manufacturing silicone rubber gloves with a no blocking surface by repeatedly dipping a form in a solve dispersion of uncured silicone rubber to build up a plurality layers and then forming a layer of liquid droplets on the surfa of the article thereby forming an irregular or textured surface the solvent evaporates. Utilization of this method for physical altering the exterior uniformly from lot to lot requires a high controlled manufacturing environment which is difficult a expensive to maintain. The present invention utilizes a uniq dispersion which produces a uniformly textured, non-blocki surface. There are other areas where a non-organic, no contaminating, non-blocking, non-allergenic, texturized surfa with low reflectivity and high diffusivity would be highl advantageous. Some space applications demand low reflectivity o high diffusivity in paints and coatings. Epoxies, and almost al organic coatings other than silicone, are not durable enough t withstand the highly oxidizing atmospheres that satellites mus endure. For example, an anti-blocking silicone surface i necessary in a bellows or in rolled solar array to facilitat separation of adjacent surfaces during deployment. Until now prior art silicone technology has not been able to produc contaminant-free silicone anti-blocking, low reflectivity, hig diffusivity outer layers which are sufficiently durable t withstand the physical and chemical properties of these extrem environments. SUMMARY OF THE PRESENT INVENTION The invention general contemplates providing a new an improved composition and process which enables both silicone an non-silicone articles to be coated with silicone and textured in situ. Texturizing is brought about by the incorporation of hydrophilic silica in a silicone dispersion used for a final coating or texturing dip. In the final dispersion of the dipping process, the silica particles are incorporated within the outermost layer and stand up away from the surface providing a textured unblocking surface, while, at the same time, not substantially weakening the article or permitting delamination of the textured final layer. It is an object of the invention to provide a composition for making a silicone article having an integral textured non- blocking outer surface, which surface is formed in situ; and to provide a method for making the same. It is yet another object of this invention to provide composition and method useful for applying a textured silicon coating to both silicone and non-silicone articles. It is yet a further object of the invention to provide composition for applying a contaminant-free outer surface to a article. It is still a further object of the invention to provid a composition for applying a textured, non-allergenic outer surface to an article. DESCRIPTION OF PREFERRED EMBODIMENTS This invention teaches the addition of hydrophilic silica preferably in the size range of 2-10 microns, to elastomer dispersion to provide a textured non-blocking silicone surface coating on articles dipped therein. Dipping articles in elastomer dispersions is well known in the art of applying elastomer coatings. Suitable silicone dispersions for applying smooth, non- textured coatings to articles are also well known in the art. What has been unknown in the art until the invention thereof by the present inventor is the addition of hydrophilic silica to a silicone dispersion to render a textured surface to articles coated therewith. The addition of colloidal silica to elastomer dispersions is also well known in the art. The function of added colloidal silica is to strengthen the elastomer upon curing. Colloidal silica, which is hydrophobic (organophilic) , is obtained by the surface treatment of silica with organic moieties to generate a particulate species capable of colloidal dispersion. While the addition of colloidal silica to a silicone dispersion strengthens the resultant elastomer layer, the dispersion is inoperative for providing a textured surface to an article coated therewith. Surprisingly, adding hydrophilic silica, preferably in the size range 2-10 microns, to a dispersion does provide a textured surface to an article coated therewith. Colloidal silica is too dense for the particles to "float" to the surface while the layer is curing. It is important that the silica particles have a large specific surface area and a density such that the hydrophilic silica particles "float" in an elastomer dispersion thereby migrating to the surface of a layer coated with such dispersion. Example 1: FIRST PREFERRED EMBODIMENT The present invention is directed to the task of improving the surface morphology of articles, including silicone articles, to provide a textured surface which has a lower coefficient of friction than a smooth surface and which is suitable for coating articles such as surgical gloves which presently require lubricants to enable donning. In accordance with the invention, the surface morpholo of articles is substantially improved by bonding to the surface silicone coating comprising the reaction product of a compositi comprising: (1) at least one crosslinkable polysiloxane; ( silica filler; (3) crosslinking catalyst; (4) a crosslinking agen The coating may be applied to the surface from a liquid vehicl preferably a volatile organic solvent, followed by heating to dri off the organic solvent or other liquid vehicle and to effe crosslinking. The manner of application, whether by dippin flowing, spraying, etc. is a matter of individual choice and per comprises no part of this invention. An example of a two-part silicone dispersion which, wh combined and applied to the surface of an article, and allowed cure, produces a durable textured, non-blocking surface on sai article, is as follows: The coating composition of this invention is readily prepared by mixing the ingredients under ambient temperature and pressure. The surface may then be coated by per se known techniques, dipping in the coating solution being more e ficacious. Crosslinking, as well as solvent removal, is effected by heating at a temperature and for a time to effect complete cure as well as solvent removal. Since there is a time-temperature relationship to effect cure, the time and temperature are not susceptible to precise quantitative statements. On a bench scale, heating at about 150°C for about 30 minutes is effective. Example 2: SECOND PREFERRED EMBODIMENT A second system which is suitable for using as a final coat dispersion for producing textured surfaces on silicone and non-silicone articles is a one-part system similar to the two-part system described in Example 1. The one-part system utilizes, for example, dimethyl polysiloxane (0-100%) , Dimethyl diphenyl polysiloxane (30-0%) , hydrophilic silica having a specific surface area between 75-200 square meters per gram (0-20%) , tri (methylethyl ketoximo) methylsilane (<10%) and a catalyst (organo tin complex) in naphtha. Before the above dispersion is suitabl for a final application, the percentage of texturing silica (e.g Degussa TS-100) must be adjusted to fall within the range of abou 0-20% by solids weight. Solvent for the final dilution runs fro 0-70% by solids weight.

Claims: CLAIMS What I claim is : 1. In a one or two part dispersion of a silicone elastomer in a organic solvent, the improvement comprising the addition of hydrophilic silica to said dispersion to provide a textured surface to an article coated with said dispersion. 2. The improved dispersion of Claim 1 wherein the hydrophilic silica has a particle size of 2-10 micrometers and a specific surface area of 75-200 square meters per gram. 3. The improved dispersion of Claim 1 wherein said silicone elastomer is a copolymer comprising dimethyl polysiloxane. 4. The improved dispersion of Claim 1 wherein said elastomer is a copolymer comprising dimethyl diphenyl polysiloxane. 5. The improved dispersion of Claim 2 wherein said silicone elastomer is a copolymer comprising dimethyl polysiloxane. 6. The improved dispersion of Claim 2 wherein said elastomer is a copolymer comprising dimethyl diphenyl polysiloxane. 7. An article having a textured outer surface made by the process comprising (a) coating the article in a dispersion of silicone elastomer in an organic solvent to which dispersion hydrophilic silica has been added; and (b) curing the coating.

Inventors: NASH BRIAN, NASH, BRIAN
Applicants: NUSIL TECHNOLOGY
Application year: 1992
Main classification: C08L83
IPC codes: A41D19, C08K3, C09D183