Capped silicone film and method of manufacture thereof

A silicone film is attached to a surface by chemical bonding. The silicone film consists of chains of siloxane groups, each chain terminating in an end molecule which is either an ester, an ether, or a halogen. The end molecule is allowed to react with water to produce an OH group. The surface is then contacted with a capping agent which reacts with the OH group to produce a new end group which improves the properties of the film.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 This invention relates generally to silicone films, and more specifically
 to application of such films to glass and other surfaces.
 2. Description of the Prior Art
 Various methods exist for manufacturing easily cleanable, water repellent
 glass products, including shower doors, windshields, glass entry doors and
 glass partitions in restaurants. Two such methods are disclosed in U.S.
 Pat. No. 5,415,927 to Hirayama et et. and U.S. Pat. No. 4,263,350 to
 Valimont.
 In another method currently in use, the glass is coated with a film
 consisting of chains of silicone molecules, with each chain chemically
 bound at one end to the surface of the glass. Each chain contains from
 dozens to hundreds of dimethylsiloxane (DMS) units and is terminated at
 its free end by either a hydroxyl (OH) group or a chlorine attached to a
 silicon, which soon reacts with water vapor in the air to produce OH
 groups. This existing film is in use on a number of glass products as well
 as other silica-containing products such as granite, porcelain,
 earthenware and stoneware, and for the most part, has performed
 satisfactorily. However, the water-repellence of the film is limited to
 some extent by the presence of the terminal OH groups, which are highly
 water-attracting.
 Accordingly, it is an object of the present invention to improve the
 water-resistance of silicone films on glass, and to provide a support film
 for chemically active substances.
 Another object of the invention is to produce a family of silicone films
 for treating a variety of products such as the silica-containing products
 previously mentioned as well as organic substances including paper,
 cotton, nylon, leather, and wood, in order to improve the surface
 properties of those products.
 SUMMARY OF THE INVENTION
 Briefly, to achieve the desired objects of the instant invention in
 accordance with the preferred embodiments thereof, a silicone film is
 attached to a surface by chemical bonding. The silicone film consists of
 chains of siloxane groups, each chain terminating in an end molecule which
 is either an ester, an ether, or a halogen. The end molecule is allowed to
 react with water, either water vapor in the surrounding air or by covering
 the surface with liquid water, to produce an end OH group. The surface is
 then contacted with a capping agent which reacts with the OH group to
 produce a new end group which improves the properties of the film.
 The specific improvement in properties will depend on the siloxane groups
 used, as well as the composition of the capping agent. In general, the
 siloxane groups have the formula
 ##STR1##
 and the capping agent has the formula
 ##STR2##
 For water-repellent applications, R consists of nonpolar groups, and
 R.sup.1 consists of inert groups. For non-water-repellent applications, R
 consists of polar or nonpolar groups. In other applications, R.sup.1 could
 consist of chemically active groups, enabling the surface to be used as a
 solid state ion exchanger or an attachment point for chemically bound
 enzymes, chelating agents, dyes, chemical indicators or other substances.

DETAILED DESCRIPTION OF THE INVENTION
 Turning now to the drawings, attention is first directed to FIG. 1, which
 shows a surface G which has been treated with a water-repellent film using
 a prior art process. In the most widely-used application of the process,
 the surface G is glass, but the process may actually be used to treat any
 surface containing OH or nitrogen hydrogen bonds, such as
 silica-containing surfaces including granite, porcelain, earthenware and
 stoneware, as well as organic substances including cotton, paper, nylon,
 leather and others. The film comprises chains of dimethylsiloxane (DMS)
 groups. Each chain is chemically bonded at one end to an oxygen (O)
 molecule, which in turn is chemically bonded to the surface G. The
 opposite end of each chain includes either a hydroxyl (OH) group or a
 chlorine attached to silicone, which will soon react with water vapor in
 the surrounding air to produce an OH group.
 The process by which the film of FIG. 1 is created is as follows.
 Initially, the surface G is moistened. The moistened surface can be
 represented as shown in simplified form below:
 ##STR3##
 In reality, however, the number of H--O--H molecules at the surface would
 be much greater than the number of O--H groups on the surface (a ratio of
 about 100:1).
 Next, the surface is treated with dimethyldichlorosilane using Portable
 Vapor machines which may be adapted to fixed site chambers for large
 volume operations, or by using a wipe-on method or a dipping or spraying
 procedure. Where necessary, cyclohexylamine is used as a primer to ensure
 sufficient moisture for the chemical reaction to take place. After the
 dimethyldichlorosilane has been applied, a dimethyldichlorosilane molecule
 approaches an O--H group at the surface, as shown below:
 ##STR4##
 The ensuing reaction results in an anchor molecule which will chemically
 bond the film to the surface G, as shown below:
 ##STR5##
 The Si--Cl bond then reacts with water absorbed on the surface G as
 follows:
 ##STR6##
 resulting in the following structure:
 ##STR7##
 This structure then reacts with a DMS molecule as follows:
 ##STR8##
 resulting in the molecule shown below:
 ##STR9##
 The process of steps (c)-(f) above is repeated about 100 times until no
 more water remains for steps (c) and (d). The product has the formula:
 ##STR10##
 where n is around 100 or more. The groups in the brackets are highly water
 repellent. However, the chlorine atom at the end of the chain slowly
 reacts over several hours with water vapor in the air to result in a
 product having the formula:
 ##STR11##
 which is equivalent to the structure shown in FIG. 1. The Si--O--H group at
 the end of this final product is water-attracting, thus reducing the
 overall water repellence of the entire film, and creating a site for
 undesirable chemical reactions.
 In the improved process of the instant invention, a surface coated with the
 above film is then treated with trimethylchlorosilane, which reacts with
 the OH group at the end of the DMS chain to produce
 trimethylchlorosiloxane (TMS). The final product is a film having the
 formula:
 ##STR12##
 which is equivalent to the structure shown in FIG. 2. Because the TMS group
 at the end of the chain is chemically inert, the water-resistance of the
 film is much greater than that of the prior art film.
 The silicone film produced by the process of steps (a)-(i) above is one
 specific example of the invention, intended for water-repellent
 applications. In a more general case, the moistened surface G is first
 contacted with silane groups having the formula
 ##STR13##
 wherein R represents polar or nonpolar groups including hydrocarbons or
 halogenated hydrocarbons, and X is selected from the group consisting of
 esters, ethers, and halogens. The silane groups then react with the OH or
 nitrogen hydrogen bonds and water at the surface G to chemically bond the
 film to the surface G, in a process analogous to step (b) above. A series
 of reactions analogous to those shown in steps (b)-(f) above results in a
 polymer having the formula:
 ##STR14##
 were n is around 100 or more. The X atom at the end of the chain then
 reacts with water vapor in the surrounding air resulting in a molecule
 having the formula:
 ##STR15##
 The surface is then contacted with a capping agent having the formula:
 ##STR16##
 where R.sup.1 may include any combination of inert and reactive groups. The
 capping agent reacts with the OH group at the end of the chain, resulting
 finally in a chain having the formula:
 ##STR17##
 The properties of the film manufactured using this process will depend on
 the choice of R and R.sup.1, and to a lesser extent, X. Choosing X from
 the chloro group gives the lowest material cost and gives a faster
 reaction time, while esters and ethers are less reactive but produce less
 troublesome coproducts and require different processing conditions.
 In general, for water repellent applications, R consists of nonpolar groups
 and R.sup.1 consists of chemically inert groups. If R consists of
 approximately 50% methyl groups and 50% phenyl groups, the
 abrasion-resistance of the film is improved. The abrasion-resistance of
 the film can also be improved by connecting the DMS chains with
 methyltrichlorosilane (which causes branched chains and additional ends).
 The methyltrichlorosilane would cause the chains to be tied together in a
 three-dimensional structure, which would resist abrasion better than a
 two-dimensional structure.
 For non-water repellent applications, R consists of polar or nonpolar
 groups. If R.sup.1 is selected from chemically reactive groups, the end
 molecule can provide an attachment point for enzymes, chelating agents,
 ion exchange elements, chemical indicators and other substances.
 Various other modifications and variations to the embodiments herein chosen
 for purposes of illustration will readily occur to those skilled in the
 art. To the extent that such variations and modifications do not depart
 from the spirit of the invention, they are intended to be included within
 the scope thereof which is assessed only be a fair interpretation of the
 following claims.