POLYVINYL BUTYRAL LAMINATES

Abstract: Polyvinyl butyral laminates with polyethylene tereph­ thalate having an abrasion-resistant silanol coating and their preparation.

Description: TITLE POLYVINYL BUTYRAL LAMINATES BACKGROUND OF THE INVENTION Polyvinyl butyral is widely used in combination with one or more layers of glass or other glazing material to provide a laminate which is resistant to shattering. In recent years, effort has been directed to the preparation of other composites which can be used in combination with glass to provide not only resistance to shattering but protection against abrasion and scratching when used as a component of a glazing material. The preparation of laminates for use in automotive windshields presents unusually stringent requirements. In addition to the basic requirements noted above, an automotive windshield must provide high impact resistance and excellent optical clarity. Beyond this, for improved fuel efficiency, these characteristics should desirably be provided at a minimum weight. Previously, attempts to provide this combination of properties have often resulted in a laminate that performed well at ambient conditions, but crazed when exposed to especially high or low temperatures or humidity. Summary¯of the Invention The present invention provides an improved process for the production of polymeric laminates !sèful in conjunction with glazing material, as well as he resulting products, which are characterized by ¯outstanding abrasion resistance, clarity and adhesion to zit glazing' material. Specifically, the instant invention provides a process for preparing a polymeric laminate comprising: a) treating both sides of a biaxially oriented, dimensionally stable, polyethylene terephthalate film having a thickness of about 2-7 mils and a haze level of less than about 1.0%, to enhance the ability of the film to adhere to other materials; b) coating at least one surface of the resulting polyethylene terephthalate film to a thickness of about 1-20 microns with an organic silanol coating composition comprising: (i) about 5-50 weight percent solids, the solids complementally comprising about 10-70 weight percent silica; about 1-20 weight percent of a partially polymerized epoxy functional silanolt and about 30-90 weight percent of a partially polymerized organic silanol of the general formula RSi(OH)3, wherein R is selected from methyl and up to about 40% of a radical selected from the group consisting of vinyl and phenyl, and (ii) about 95-50 weight percent solvent, the solvent comprising about 10-90 weight percent water and about 90-10 weight percent lower aliphatic alcohol and containing about 0.01-1.0% non-ionic surfactant; the coating composition having a pH of about 6.2-6.5; c) bonding the polyethylene terephthalate film at elevated heat and pressure to a sheet of plasticized polyvinyl butyral to provide a laminate in which the surface of the polyethylene terephthalate not bonded to the polyvinyl butyral is coated with the organic silanol composition. The instant invention further provides a polymeric laminate comprising, a) a sheet of plasticized polyvinylbutyral, b) a biaxially oriented, dimensionally stable, polyethylene terephthalate film bonded to the polyvinyl butyral and having a thickness of about 2-7 mils and a haze level of less than about 1.0%, the polyethylene terephthalate film having been treated on both sides to enhance the ability of the film to adhere to other materials and, c) a coating on the polyethylene terephthalate film having a thickness of about 1-20 microns, the coating having been produced from an organic silanol composition comprising: (i) about 5-50 weight percent solids, the solids complementally comprising about 10-70 weight percent silica; about 1-20 weight percent of a partially polymerized epoxy functional silanol; and about 30-90 weight percent of a partially polymerized organic silanol of the general formula RSi(OH)3, wherein R is selected from methyl and up to about 40% of a radical selected from the group consisting of vinyl and phenyl, and (ii) about 95-50 weight percent solvent, the solvent comprising about 10-90 weight percent water and about 90-10 weight percent lower aliphatic alcohol and containing about 0.01-1.0% non-ionic surfactant; the coating composition having a pH of about 6.2-6.5; and in which at least the surface of the polyethylene terephthalate film not bonded to the polyvinyl butyral bears coating (c). Preferably, the polyethylene terephthalate film is flame treated on both sides to enhance the ability of the film to adhere to other materials. Detailed Description of the Invention The present invention is based on the discovery that in the preparation of a laminate of polyvinyl butyral and polyethylene terephthalate having an abrasion resistant coating, the selection of specific components and process variables will result in a laminate particularly suitable for use with glazing materials which exhibits outstanding optical properties, integrity, resistance to crazing at extreme temperatures and humidity, abrasion resistance and adhesion to glazing materials. In addition, the laminates provide glazing materials with markedly improved penetration resistance. The polyethylene terephthalate sheeting used in the present invention is biaxially oriented by stretching at least about 2.5 times in each of the longitudinal and transverse directions in the plane of the film. An important feature of the polyethylene terephthalate films used in the present invention is that they exhibit a haze level of less than about 1.0t, as measured according to ANSI/ASTM D 1003-61, using the hazemeter specified in that test. This haze level is attained by the absence of filler and uniform surface characteristics resulting from processing conditions described in Alles, U.S. Patent 2,779,684, hereby incorporated by reference. In addition, the film is dimensionally stabilized, for example, by heating under tension as described in the Alles patent. This dimensional stabilization should be carried out at a temperature at least equal to the temperature of intended use. Both surfaces of the polyethylene terephthalate film are conditioned to enhance their ability to adhere to other materials. The surfaces are preferably conditioned by direct contact with a gas flame for a period of time sufficient to alter the surface characteristics of the treated material, but not for so long a period as to change the bulk properties of the film. Flame treating techniques previously known which can be used in the present invention include those described in Kreidl U.S. Patent 2,632,921, Kritchever U.S. Patent 2,648,097, Kritchever U.S. Patent 2,683,894 and Kreidl U.S. Patent 2,704,382, all of which are hereby incorporated by reference. Preferably a reducing flame having a high fuel to oxygen ratio is used. Other electrical and chemical surface conditioning treatments known to improve adhesion of polymeric films can also be used in the instant invention. In addition, combinations of treatments can be used to enhance the ability of the polyethylene terephthalate film to adhere. For example, one surface of the film can be flame treated and the second surface coated with an adhesion promoting material, such as the water-permeable colloid described in the Alles patent to which reference is made above. The polyethylene terephthalate film, after conditioning to improve adhesion, is flext coated on at least one conditioned side with an abrasion resistant coating of the composition indicated above. The coating is generally present in a final coating thickness of about 1-20 microns. The silica and organic silanol components and the general preparation of these coating compositions are described in detail in Ubersax U.S. Patent 4,177,315, hereby incorporated by reference. However, in addition to the silica and organic silanolkdescribed in that patent, the present coating composition furthercomprises, as about 1-20 percent of the solids in the coating composition, an epoxy functional silanol. Epoxy functional silanes which can be used to provide the silanols in the present invention include, for example, gamma-glycidoxypropyl-trimethoxysilane as well as beta-(3,4-epoxycyclohexyl)-ethyltrimethoxy-silane. These compositions are commercially available from Union Carbide Corporation as A-187 and A-186, respectively. Other epoxy functional silanes known in the art can also be used. The coating solution, in accordance with the present invention, also contains about 0.01-1.0%, by weight of the solvent, of a non-ionic surfactant. A wide variety of such surfactants is commercially available, including, for example, fluorosurfactants available from E. I. du Pont de Nemours and Company as Zonyl non-ionic fluorosurfactants, and from 3M as Fluorad non-ionic fluorosurfactants. Particularly preferred because of compatibility with the other components of the coating solution are silicone surfactants. Such silicone surfactants include, for example, polyalkylene oxide methylpolysiloxanes, such as those commercially available from Union Carbide as Silwet Surface Active Copolymers and those commercially available from Dow Corning Corporation as silicone glycol copolymer fluids. One such silicone surfactant found to be particularly useful is the polyethyleneoxide methyl siloxane commercially available from Union Carbide Corporation as Silwet L-720. The coated polyethylene terephthalate film is next laminated, under typical conditions of elevated temperature and pressure, to a plasticized polyvinyl butyral resin sheet. The lamination is carried out to provide a polyethylene terephthalate film surface coated with the abrasion resistant coating opposite to the surface of the film bonded to the polyvinyl butyral. The preparation of such polyvinyl butyral sheeting is described, for example, in VanDless U.S. Patent 2,720,501, Stamatoff U.S. Patent 2,400,957, and Woodworth U.S. Patent 2,739,080, all hereby incorporated by reference. The polyvinyl butyral can contain a wide variety of plasticizers, as known in the art, including, for example, triethylene glycol di-2-ethylbutyrate, dihexyl adipate, triethylene glycol di-n-heptanoate, tetraethylene glycol di-n-heptanoate, propylene oxide oligomers and mixtures of these and other plasticizers. Particularly satisfactory polyvinyl butyral sheeting is that commerically available as "Butacite" plasticized polyvinyl butyral resin sheeting from E. I. du Pont de Nemours and Company. The polyvinyl butyral used in the present invention should exhibit a satisfactorily high level of adhesion to glazing materials. This level of adhesion is attained by minimizing the adhesion control additives, for example, used in the polyvinyl butyral sheeting. A maximum of about 400 parts per million of potassium based adhesion control additives can be used in polyvinyl butyral plasticized with tetraethylene glycol di-n-heptanoate. The level of adhesion control additives should be such as te provide a peel force between the polyvinyl butyral sheeting and the polyester film or glass of at least about 5 pounds per inch. The polyvinyl butyral surface of the present laminates can be bonded to glass using elevated heat and pressure in conventional laminating techniques. The resulting structure exhibits excellent optical characteristics, abrasion resistance, and penetration resistance. In addition, the laminates show exceptional resistance to crazing at extremely high and low temperatures and high humidity. The invention is further illustrated in the following examples, in which parts and percentages are by weight unless otherwise indicated. Examples 1-3 and Comparative Examples A-D In Examples 1 and 2, 550 parts of a 30 percent aqueous solution of colloidal silica was added to a reaction vessel. The pH of the solution was adjusted to 5.0 by the addition of glacial acetic acid. 350 parts of methyltrimethoxysilane and 43.7 parts of gamma-glycidoxypropyl trimethoxy silane primer (commercially available from Union Carbide Corporation as "A-187") were added, and the solution was mixed for 6 hours at room temperature. 1250 parts of a 2/1 isopropanol/water mixture was then added along with 0.8 parts of silicone surfactant, resulting in a final pH of the solution of 6.2. A 4-mil biaxially oriented, heat relaxed polyethylene terephthalate film having a haze level of less than 1% was flame-treated by contact with a reducing flame to improve the adhesion characteristics. The film was then coated on both sides with the silane solution prepared above. Excess solution was allowed to drain from the polyester film, which was then placed in an oven with a circulating air flow maintained at about 1000C for 3 minutes in Example 1 and at about 1500C for thirty minutes in Example 2. The dried thickness of the coating was about 4 microns in each case. In Example 3, the procedure of Example 2 was repeated, except that the epoxy silane was replaced with beta-(3, 4-epoxycyclohexyl)-ethyltrimethoxy- silane (commercially available from Union Carbide Corporation as "A-186"). In Comparative Examples A and B, the procedure of Examples 1 and 2 was repeated, except that the epoxy silane was eliminated from the coating applied to the flame-treated polyethylene terephthalate film. In Comparative Examples C and D the procedure of Comparative Examples A and B was repeated, except that the polyehylene terephthalate film was treated by an electrical corona discharge instead of the reducing flame and the polyethylene terephthalate film was primed by application of a solution of the primer directly to the film instead of incorporating the primer into the coating solution. The primer solution was prepared by adding 2 parts of gamma-glycidoxypropyl trimethoxy silane to 98 parts of butanol in a mixing vessel. The polyethylene terephthalate film was first corona discharge treated, and then coated on both sides with the primer solution. Excess solution was allowed to drain from the polyethylene terephthalate film, which was then placed in an oven with a circulating air flow maintained at about 1200C for 30 minutes. The primed polyethylene terephthalate film was then coated on both sides with the silane solution of Comparative Examples A and B. Excess solution was allowed to drain from the polyethylene terephthalate film which was then placed in an oven maintained at about 100 C for 3 minutes in Comparative Example C and at about 1500C for 30 minutes in Comparatve Example D. The coated films of Examples 1-3 and Comparative Examples A-D were tested for adhesion of the coating to the polyethylene terephthalate film as-produced and after at least 3 days in a chamber maintained at about 53"C and at about 100% relative humidity. The coating adhesion was determined by the tape adhesion parallel cut method (ASTM D 3002-71). A pressure-sensitive tape was applied to a 3-by-3 pattern of 9 squares of about 1/8-inch sides scribed through the coating on the polyethylene terephthalate film. The tape was then quickly removed and the fraction of film surface within the squares still covered by the coating was estimated. The coating of Examples 1-3, in which primer was incorporated into the coating solution, was superior to that of the Comparative Examples in adhesion and coating retention. The results are summarized in the following Table I. TABLE I ADHESION OF COATING TO POLYETHYLENE TEREPHTHALATE FILM TAPE PEEL TEST Coating Remaining on Substrate (%) Example Description As-Produced After 3 days/53 C/100% R.H. 1Flame-treated PET; 100 90 A-187 epoxy-silane added; 3-minute cure at 1000C 2 Flame-treated PET: 100 100 A-187 epoxy silane added; 30-minute cure at 150C 3 Flame-treated PET; 100 98 A-186 epoxy-silane added; 30-minute cure at 1500C A Flame-treated PET; 30 0 No epoxy-silane added; 3-minute cure at l000C B Flame-treated PET; 100 0 No epoxy-silane added; 30-minute cure at 150-C C Corona discharge 0 treated PET Primed with A-187; No epoxy silane added to coating solution; 3-minute cure at 1500C D Corona discharge 0 treated PET Primed with A-187; No epoxy silane added to coating solution; 30-minute cure at 1500C The coated films of Example 1 and Comparative Example A were compared for abrasion resistance on the coated surface. An additional film, designated as Example E, was also tested for abrasion resistance. The film of Comparative Example E was prepared according to the procedure of Example I except that the polyethylene terephthalate film was not coated with any solution. The abrasion resistance was 3etermined by the Taber Abraser method described in ANSI Z 26.1-1977 Section 5.17. An integrating sphere, photoelectric photometer was used to measure the light scattered by the samples before and after being exposed to 100 revolutions of an abrasive wheel carrying a load of 500 grams. The coated films of this invention were at least as abrasion resistant as those of the Comparative Examples. The results are summarized in the following Table II. TABLE II ABRASION RESISTANCE TABER ABRASER TEST Change in Percent Haze Example Description After 100 Cycles 1 Flame-treated PET; 0.5 A-187 epoxy-silane added; 3-minute cure at lO00C A Flame-treated PET; 1.2 No epoxy-silane added; 3-minute cure at 1000C E Flame-treated PET; 34 No coating Example 4 and Comparative Examples F and G In Example 4 and Comparative Examples F and G, craze resistance of the polyethylene terephthalate film was evaluated. In Example 4, the procedure of Example 1 was repeated, except that the polyethylene terephthalate film was heated under tension at a temperature equal to or exceeding any subsequent processing or exposure temperature. In particular the film was heated under tension at about 150 C. The coated film was laminated to polyvinyl butyral sheeting having a hydroxyl content of about 23%, a potassium-based adhesion control additive content of about 250 ppm, a thickness of 30 mils and plasticized with about 28% of tetraethyleneglycol di-n-heptanoate. This composite was then further laminated to a sheet of 3/32-inch thick glass. The films were laminated at a pressure of 225 pounds per square inch and a temperature of about 1490C for a period of 90 minutes to provide a unitary structure with excellent clarity. In Comparative Example F the procedure of Example 4 was repeated, except that the polyethylene terephthalate film was heated under tension at about 1200C In Comparative Example G, the procedure of comparative Example F was repeated, except that the flame treated polyethylene terephthalate film was replaced with a polyethylene terephthalate film coated with an adhesion-promoting water-permeable colloid as described in Alles, U.S. Patent 2,779,684 and which is commercially available from E. I. du Pont de Nemours and Company as CRONARE P-42. The laminates of Example 4 and Comparative Examples F and G were compared for integrity or lack of crazing or cracking after exposure to environmental extremes. The laminates were compared as-made, after exposure to about 53"C and 100% relative humidity for 1 week and after exposure to about -54-C for 12 hours. The results are summarized in the following Table III. TABLE III CRAZE RESISTANCE OF COATED POLYETHYLENE TEREPHTHALATE FILM CONDITION AFTER EXPOSURE TO: Room 530C Example Temp. -540C 100% R.H. 4 Flame-treated Clear Clear Clear PET, 150 C relaxation F Flame-treated Clear Crazed Clear PET: 120 C relaxation G Gel-coated PET; Clear -- Crazed 120 C relaxation Comparative Examples H and I The penetration resistance of glass laminates of the present invention was compared with laminates not containing the coated polyethylene terephthalate. In Comparative Example H, the procedure of Example 4 was repeated, except that the coated film was omitted. In Comparative Example I, a polyvinyl butyral film of the type used in Example 4 was laminated between two layers of 3/32-inch (90 mils) glass. The laminates of Example 4 and Comparative Examples H and I were compared for penetration resistance. The penetration resistance was determined by a changing height staircase method of dropping a 5-pound steel ball onto the 12-inch square laminates. The laminates of Example 4 were clamped in the support frame to insure failure by penetration and the laminates of Example 4 and Comparative Example H were contacted by the ball on the polymeric side of the laminate. The results obtained are summarized in the following Table IV. TABLE IV PENETRATION RESISTANCE OF LAMINATES Example Description Mean Support Height (Feet) 4 PET/PVB/GLASS Laminate 31.7 H PVB/GLASS Laminate 11.3 I GLASS/PVB/GLASS Laminate 21.0

Claims: CLAIMS: 1. A process for preparing a polymeric laminate comprising: a) treating both sides of a biaxially oriented, dimensionally stable, polyethylene terephthalate film having a thickness of about 2-7 mils and a haze level of less than about 1.0%, to enhance the ability of the film to adhere to other materials; b) coating at least one surface of the resulting polyethylene terephthalate film to a thickness of about 1-20 microns with an organic silanol coating composition comprising: (i) about 5-50 weight percent solids, the solids complementally comprising about 10-70 weight percent silica; about 1-20 weight percent of a partially polymerized epoxy functional silanol; and about 30-90 weight percent of a partially polymerized organic silanol of the general formula RSi(OH)3, wherein R is selected from methyl and up to about 40% of a radical selected from the group consisting of vinyl and phenyl, and ii) about 95-50 weight percent solvent, the solvent comprising about 10-90 weight percent water and about 90-10 weight percent lower aliphatic alcohol and containing about 0.01-1.0% non-ionic surfactant; the coating composition having a pH of about 6.2-6.5; c) bonding the coated polyethylene terephthalate film at elevated heat and pressure to a sheet of plasticized polyvinyl butyral to provide a laminate in which the surface of the polyethylene terephthalate not bonded to the polyvinyl butyral is coated with the organic silanol composition. 2. A process of Claim 1 wherein the epoxy functional silanol in the coating solution consists essentially of gamma-glycidoxypropyl-trimethoxysilanol. 3. A process of Claim 1 wherein the epoxy functional silanol consists essentially of beta-(3,4,-epoxycyclohexyl)-ethyltrimethoxy-silanol. 2 or 3, 4. A process of Claim l,jwherein the non-ionic surfactant is a silicone surfactant. anv one of to 4 5. A process of/Claims 1/wherein the polyvinyl butyral contains less than about 400 parts Per million of potassium based adhesion control agent. anv one of to 5 - - 6. A process¯of/Claims l/wherein the polyethylene terephthalate film is treated on both sizes with a reducing gas flame to enhance the abilitv of the film to adhere to other materials. any one of to 6 7. A process of/Claims l/wherein one side of the polyethylene terephthalate film is coated with the coating composition and the polyvinyl butyral sheeting is bonded to the uncoated side of the polyethylene terephthalate film. any once of to 7 8. A process of/Claims l/further comprising bonding at least one sheet of glass to the surface of the plasticized polyvinyl butyral. 9. A polymeric laminate comprising, a) a sheet of plasticized polyvinylbutyral b) a biaxially oriented, dimensionally stable, polyethylene terephthalate film bonded to the polyvinyl butyral and having a thickness of about 2-7 mils and a haze level of less than about 1.096, the polyethylene terephthalate film having been treated on both sides to enhance the ability of the film to adhere to other materials and, (c) a coating on the polyethylene terephthalate film having a thickness of about 1-20 microns, the coating having been produced from an organic silanol composition comprising: (i) about 5-50 weight percent solids, the solids complementally comprising about 10-70 weight percent silica; about 1-20 weight percent of a partially polymerized epoxy functional silanol; and about 30-90 weight percent of a partially polymerized organic silanol of the general formula RSi(OH)3, wherein R is selected from methyl and up to about 40% of a radical selected from the group consisting of vinyl and phenyl, and (ii) about 95-50 weight percent solvent, the solvent comprising about 10-90 weight percent water and about 90-10 weight percent lower aliphatic alcohol and containing about 0.01-1.0% non-ionic surfactant: the coating composition having a pH of about 6.2-6.5; and in which at least the surface of the polyethylene terephthalate not bonded to the polyvinyl butyral bears coating (c). 10. A laminate of Claim 9 wherein the epoxy functional silanol in the coating solution consists essentially of gamma-glycidoxypropyl-trimethoxysilanol. 11. - A laminate of Claim 9 wherein the epoxy functional silanol consists essentially of beta-(3,4,-epoxycyclohexyl)-ethyltrimethoxy-silanol. 12. A laminate of Claim 9,)2wherein the non-ionic surfactant is a silicone surfactant. anv one of to 1 13. A laminate or/Clairrs 9/wherein the polyvinyl butyral contains less than about 400 parts per million of potassium based adhesion control aqent. arw one of to 13 14. A laminate of/Clains 9/wherein the polyethylene terephthalate film is treated on both sides with a reducing gas flame to enhance the ability of the film to adhere to other materials. anv one of to 14 15. A laminate of/Claims 9/wherein one side of the polyethylene terephthalate film is coated with the coating composition and the polyvinyl butyral sheeting is bonded to the uncoated side of the polyethylene terephthalate film any one of to 15 16. A laminate /Claims 9/further comprising at least one sheet of glass bonded to the surface of the plasticized polyvinyl butyral.

Inventors: KWIATKOWSKI, CHARLES THOMAS
Applicants: E.I. DU PONT DE NEMOURS AND COMPANY
Application year: 1984
Main classification: B32B17
IPC codes: B32B27, C08J7, B32B17, C09D183