ARTICLE COMPRISING A RIGID POLYMERIC SUBSTRATE AND A COATING, WITH A SILICATE-TITANATE COPOLYMER AS A PRIMER BETWEEN SAID POLYMERIC SUBSTRATE AND SAID COATING

Abstract: A silicate/titanate copolymer is disclosed for use as a primer in adhering rigid copolymer substrates to elastomeric interlayers or inorganic coatings.

Description: An article comprising a rigid polymeric substrate and a coating, with a silicate-titanate copolymer as a primer between said rigid polymeric substrate and said coating. The present invention relates generally to the art of adherence to plastics, and more particularly to an article comprising a rigid polymeric substrate and a coating, with a silicate-titanate copolymer as a primer between said rigid polymeric substrate and said coating. Various organic adhesives are known in the art to bond coatings to plastic substrates. US-A-36 19 255 discloses to adhere silicone rubber to metal or ceramic substrates by use of a solution of a silicate titanate copolymer dissolved in an appropriate inert solvent such as methylene chloride or toluene (column 4, lines 15 to 27). This is also exemplified by the working examples referring only to composite articles made of an elastomeric silicone rubber and a rigid substrate such as glass, steel, aluminum and/or filled polystyrene (examples 11, 13). Further, it is only generally stated that silicate/titanate copolymers adhere to any flexible or nonflexible solid surface (column 4, lines 60 to 62). Thus, this reference is completely silent on the subject matter presently claimed. In other words, the US-reference only discloses, and thus, only claims adhering of an elastomeric and a flexible or rigid material but not adhering of a rigid polymeric substrate and a specific other rigid material, namely a vinyl interlayer or a metal oxide interlayer, as called for in the present independent claims. BE-A-541 883 just as the US-reference deals with the adhering of an elastomeric material to a solid metallic, ceramic or polymeric material using a silicate/titanate copolymer solution in an inert organic solvent (claim 1, page 4, first paragraph). The working examples only disclose the adhering of an elastomeric layer and a metal- or PET-layer by the silicate/titanate copolymer primer. Again this reference is completely silent to the subject matter presently claimed. Thus, this reference only teaches to adhere to an elastomer and a material surface, but not the adhering of two rigid surfaces, i.e. a rigid polymeric surface and a specific other rigid surface namely a vinyl interlayer or a metal oxide interlayer as called for in the present independent claims. It is the object of the present invention to provide coated articles wherein the coating is adhered to a rigid polymeric substrate by a silicate/titanate copolymer primer. Thus, provided is an article comprising a rigid polymeric substrate and a coating, with a silicate/titanate copolymer as a primer between said rigid polymeric substrate and said coating. characterized in that said coating is a vinyl interlayer. Further, provided is an article comprising a rigid polymeric substrate and a coating, with a silicate-titanate copolymer as a primer between said rigid polymeric substrate and said coating, characterized in that said coating is a metal oxide film. According to a preferred embodiment of the present invention the silicate/titanate copolymer is a reaction product of an organosilicate and an organic titanium compound. Said organosilicate is more preferably selected from the group consisting of tetraethylorthosilicate and tetramethylorthosilicate. Said organic titanium compound is more preferably selected from the group consisting of titanium (IV) butoxide and titanium (IV) isopropoxide. According to a preferred embodiment of the present invention said silicate and said titanium compound are reacted in substantially equimolar ratio. According to a preferred embodiment of the present invention said rigid polymeric substrate is selected from the group consisting of polyacrylates and polycarbonates. The inorganic polymer primer of the present invention is useful in promoting adhesion of a film such as a vinyl interlayer to such surfaces as stretched acrylic or a metal oxide coated stretched acrylic substrate. The inorganic polymer of the present inventions is also useful in providing adhesion of inorganic coatings such as siloxanes to plastic surfaces. The inorganic polymer primer of the present invention comprises both silicate and titanate. A silicate/titanate primer in accordance with the present invention may be formulated simply by dissolving or partially hydrolysing appropriate silicate and titanate compounds, preferably silicon and titanium alkoxides, in a suitable solvent. Organic solvents such as alcohols are preferred, particularly isopropanol which contains up to about 0.2 percent water. A preferred primer in accordance with the present invention comprises tetraethylorthosilicate and titanium butoxide dissolved in 2-propanol. An equimolar mixture of tetraethylorthosilicate and titanium butoxide dissolved in 2-propanol at a concentration of about one half to one percent is a particularly preferred primer. A solution of silicate/titanate primer in accordance with the present invention may be applied to a substrate surface by any convenient means such as dipping or spraying. Flow coating is a preferred method of application. The primer of the present invention may be applied at ambient temperature. The solvent may be evaporated at ambient temperature, or evaporation may be accelerated by heating. However, heat curing of the silicate/titanate primer of the present invention is not necessary. While a silicate/titanate primer in accordance with the present invention may be obtained by simply mixing a silicate compound and a titanate compound together in an appropriate solvent, such a primer may be most effective only under conditions of low relative humidity, i.e. less than 50 percent, because of the moisture sensitivity of unhydrolyzed or unreacted titanate. At high relative humidity, adhesion promotion of the silicate/titanate primer may be compromised. In a particularly preferred embodiment of the present invention, a silicate/titanate primer is prepared in such a manner as to substantially reduce its moisture sensitivity. First, a silicate compound, preferably tetraethylorthosilicate, is partially hydrolyzed. The hydrolysis of tetraethylorthosilicate is preferably carried out in acidified alcohol, preferably 2-propanol containing an excess amount of water per mole of silicate, preferably a ratio of from 2 to 8 water per silicate. The hydrolyzing solution is preferably heated for about one hour at a temperature of about 50 to 80°C. A titanate compound, preferably titanium (IV) butoxide is then added and mixed into the hydrolysate. The molar ratio of silicate to titanate is preferably about equimolar. The resulting silicate/titanate primer is water insensitive and may be applied and used in high humidity environments. The present invention will be further understood from the description of the specific examples which follow. EXAMPLE I A stretched acrylic substrate is sprayed with a primer solution comprising 0.5 percent by weight of a mixture of equimolar amounts of tetraethylorthosilicate and titanium (IV) butoxide in isopropanol containing 0.2 percent water. The solvent is evaporated to yield a film of silicate/titanate copolymer. To the primed acrylic surface is laminated an interlayer of 1.5 millimeter (0.060 inch) thick vinyl containing 37.5 parts dibutyl sebacate plasticizer. The lamination is accomplished at about 99°C (210°F.) using pressure of 1.72 bar (25 pounds per square inch) for 90 minutes. The average peel strength of the resulting laminate is 7.14 kg/cm (about 40 ponds per lineal inch). EXAMPLE II An acrylic substrate is laminated to a vinyl interlayer as in the previous example. The acrylic surface is primed with silicate/titanate primer as in the previous example except that the primer solution contains 1.0 percent of the silicate/titanate primer, and is flow coated rather than sprayed onto the acrylic surface. The average peel strength is 9.82 to 10.71 kg/cm (about 55 to 60 pounds per lineal inch (pli)). EXAMPLE III A stretched acrylic substrate is coated with a conductive indium/tin oxide coating by magnetron sputtering. The indium/tin oxide conductive coating is deleted from an area about the periphery of the coated surface, and bus bars are applied. A silicate/titanate primer in. accordance with the present invention is prepared by dissolving 0.49 parts by weight of tetraethylorthosilicate in 98.7 parts isopropanol which contains at least about 0.04 percent water. The solution is heated to a temperature of about 60 to 70°C. To the solution is added 0.033 parts by weight additional water and 2 drops of hydrochloric acid per 100 grams of total weight. After heating at 60 to 70°C. for about one hour to hydrolyze the silicate, 0.76 parts by weight titanium (IV) butoxide is added. Heating at 60 to 70°C is continued for an additional 30 minutes. The resulting silicate/titanate primer solution is diluted with an equal volume of n-butanol resulting in a final concentration of about 0.5 percent silicate/titanate solids. The primer solution is sprayed over the entire surface, coated and coating deleted, of the acrylic substrate. The silicate/titanate primer polymerizes as the solvent evaporates to form a transparent primer film. A second stretched acrylic substrate is similarly coated with the silicate/titanate primer solution of the present invention, and the solvent is evaporated to yield a transparent primer film. The two primed acrylic surfaces are then laminated together with a sheet of 1.5 millimeter (0.060 inch) thick vinyl interlayer containing 37.5 parts DBS (dibutyl sebacate) plasticizer at about 99°C (210°F.) at 1.72 bar (25 pounds per square inch) for 90 minutes. The average peel strength is 16.07 to 20.05 kg/cm (90 to 115 pounds per lineal inch (pli)). EXAMPLE IV An indium/tin oxide coated acrylic substrate is laminated to another acrylic substrate with a vinyl interlayer as in Example III. The indium/tin oxide coated acrylic surface and the uncoated acrylic surface to be laminated are both primed with the silicate/titanate primer of Example III except that the primer is flow coated rather than sprayed. The average peel strength is 20.05 to 29.47 kg/cm (115 to 165 pounds per lineal inch). The above examples are offered only to illustrate the present invention. Various other silicate and titanate compounds such as tetramethylorthosilicate and titanium isopropoxide may be hydrolyzed and reacted in various concentrations and solvents to form silicate/titanate primers in accordance with the present invention. The primers of the present invention may be used in adhering a variety of materials in addition to acrylic substrates, vinyl interlayers and metal oxide films, such as polycarbonates, polysilicates and polysiloxanes. The scope of the present invention is defined by the following claims.

Claims: An article comprising a rigid polymeric substrate and a coating, with a silicate-titanate copolymer as a primer between said rigid polymeric substrate and said coating, characterized in that said coating is a vinyl interlayer. An article comprising a rigid polymeric substrate and a coating, with a silicate-titanate copolymer as a primer between said rigid polymeric substrate and said coating, characterized in that said coating is a metal oxide film. An article according to claims 1 or 2, wherein the silicate/titanate copolymer is a reaction product of an organosilicate and an organic titanium compound. An article according to claim 3, wherein said organosilicate is selected from the group consisting of tetraethylorthosilicate and tetramethylorthosilicate. An article according to claim 3, wherein said organic titanium compound is selected from the group consisting of titanium (IV) butoxide and titanium (IV) isopropoxide. An article according to claim 3, wherein said silicate and said titanium compound are reacted in substantially equimolar ratio. An article according to claims 1 or 2, wherein said rigid polymeric substrate is selected from the group consisting of polyacrylates and polycarbonates.

Inventors: LIN, CHIA-CHENG, RUKAVINA, THOMAS GEORGE
Applicants: PPG INDUSTRIES, INC.
Application year: 1986
Main classification: C09D201
IPC codes: C08J7, C09D183, C08G79, C08J5, C09D185, C09D4, C08G77, B32B15