Laminated glazing unit

Abstract: A laminated glazing unit, comprises a first glass sheet, a second glass sheet and a plasticized polyvinyl chloride containing film therebetween. The first glass sheet is formed of a glass that, when at a thickness of about 2.2 mm, has an average transmittance of radiation having wavelengths in the range of 300 - 340 nm of less than about 20% and an average transmittance of radiation having wavelengths in the range of 340 - 500 nm of more than about 50%.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to laminated glazings having plasticized polyvinyl chloride resin interlayers. 2. Summary of Related Art Safety glass is a well known term for a glass sandwich composed of an interlayer bonding together two glass plates or sheets so that breaking the glass results in minimum dispersion of broken glass fragments. The interlayer must possess a number of properties, including the following: high impact energy adsorption to minimize concussive injury; shear and tear strength sufficient to prevent rupture of the interlayer by the broken glass; sufficient adhesion to the glass to inhibit laceration on contact with, and prevent dispersion of, broken glass; acceptable thermal heat stability and weatherability; and good optical quality. The interlayer must possess these properties over the wide range of temperatures in which these laminated glazings are used. It has been widely known to use a film of plasticized polyvinyl butyral as the interlayer material in safety glass for automobiles, air planes and building materials because of its high adhesiveness and superior light stability, transparency and low-temperature flexibility. However, the use of plasticized polyvinyl butyral films makes the production of laminated safety glass relatively expensive. The surface of plasticized polyvinyl butyral film is very tacky, and presents a problem of blocking at the time of windup after film formation. Thus, plasticized polyvinyl butyral film must be provided with some parting means if it is to be stored or transported in the form of stacks of die-cut blanks or in the form of rolls. Furthermore, the production of plasticized polyvinyl butyral films requires specialized equipment and, due to their sensitivity to moisture, plasticized polyvinyl butyral films must generally be handled under controlled atmosphere conditions during manufacture, storage and immediately prior to their incorporation into the laminated safety glass. This all adds to the expense of utilizing plasticized polyvinyl butyral films in laminated safety glass. Alternative interlayer materials have been proposed. For instance, U.S. Patent No. 4,277,538 to Beckmann et al discloses a laminated safety glass employing a sheet of plasticized polyvinyl chloride (PVC) as the interlayer. The use of PVC would be advantageous in that it may be produced on conventional equipment and would be much less expensive to manufacture and process into a laminated safety glass when compared with polyvinyl butyral. However, by itself, a PVC film will not adhere to glass. To increase the adhesion of the PVC to glass, Beckmann et al suggest the use of an organofunctional silane, either as a primer or uniformly dispersed within the PVC film. At least certain of the silicon-organofunctional silanes proposed by Beckmann et al are effective to increase the adhesion of a PVC interlayer to the glass sheets of a laminated safety glass. However, the laminated safety glass employing a PVC interlayer as taught by Beckmann et al does not possess all of the properties required of an interlayer for laminated safety glass, and therefore has not been placed into general use. For instance, the Beckmann et al interlayer has poor long term heat and light stability at service use temperatures. With only a few years of exposure to normal use levels of heat and light, the PVC interlayer tends to degrade to the point where it has visibly yellowed and is aesthetically unacceptable, and the haze has increased to the point that visibility through the glazing is significantly impaired. It would be advantageous to develop a laminated safety glass with a PVC interlayer wherein the interlayer exhibits a lower level of degradation over its useful life. SUMMARY OF THE INVENTION It is, therefore, the object of the present invention to provide a laminated glazing unit, comprising a first glass sheet, a second glass sheet and a plasticized polyvinyl chloride containing film therebetween, which has improved optical characteristics. This object according to the present invention is solved by the features of claim 1. Preferred embodiments of the laminated glazing unit according to the invention are defined in the subclaims. The laminated glazing unit according to the invention is defined in claim 1. It is characterized in that the first glass sheet is formed of a glass that, when at a thickness of about 2.2 mm, has an average transmittance of radiation having wavelengths in the range of 300 - 340 nm of less than 20% and an average transmittance of radiation having wavelengths in the range of 340 - 500 nm of more than 50%. According to a preferred embodiment the first glass sheet is formed of a glass that, when at a thickness of about 2.2 mm, has an average transmittance of radiation having wavelengths in the range of 300 - 340 nm of less than 5%, and preferably of less than 1%. According to a further embodiment the first glass sheet is formed of a glass that, when at a thickness of about 2.2 mm, has an average transmittance of radiation having wavelengths in the range of 340 - 500 nm of more than 60%, and preferably of 1% at a wavelength of 330 nm. Advantageously the first glass sheet is an outboard glass sheet and the second glass sheet is an inboard glass sheet, wherein the outboard glass sheet is formed of a glass that, when at a thickness of about 2.2 mm, has an average transmittance of radiation having wavelengths in the range of 300 - 340 nm which is lower than that of the inboard glass sheet when the inboard glass sheet is also at a thickness of about 2.2 mm. Appropriately the first glass sheet is formed of an ultraviolet radiation absorbing green glass. It has been found to be advantageous to incorporate the PVC containing film in a laminated safety glass wherein at least one of the glass sheets is formed of a glass which reduces the transmittance of UV radiation, by absorption, reflection, or a combination of both. Further, exposure to radiation in the range of 280 nanometers to 340 nanometers causes degradation and yellowing of a PVC containing interlayer. On the other hand, exposure to radiation in the range of 340 nanometers to 500 nanometers has a photobleaching effect on a PVC containing interlayer which acts counter to the yellowing effect. A glass sheet which permits the transmission of a relatively low amount of radiation in the range from 280 nanometers to 340 nanometers thus helps to prevent degradation and yellowing of the PVC containing interlayer, and the development of high haze in the glazing unit. It will also help to prevent degradation and yellowing of the PVC containing interlayer if this glass sheet permits the transmission of a relatively higher amount of radiation in the range from 340 nanometers to 500 nanometers. At least the outboard glass sheet has an average transmittance of radiation in the range of 300 to 340 nm of less than 20%. Below 300 nm, less than 1% of the radiation is transmitted through even a conventional clear glass sheet when at a thickness in the range of 1.5 mm to 2.7 mm. Preferably, the outboard glass sheet has an average transmittance of radiation in the range of 300 to 340 nm of less than 5%, and most preferably of less than 1% in this range. In addition, the glass sheets will also preferably have an average transmission in the range of 340 to 500 nm of at least 50%, and more preferably of at least 60%. The glass sheets of the laminated safety glass unit in accordance with the invention also preferably allow the transmittance of 50% or less of the radiation at 340 nm. More preferably, the glass sheets will allow the transmittance of 25% or less of the radiation at 330 nm, and most preferably only 1% or less of such radiation. Likewise, the glass sheets in the laminated unit in accordance with the invention will preferably allow the transmittance of 20% or less of the radiation at 330 nm. More preferably, the glass sheets will allow the transmittance of 5% or less of the radiation at 330 nm, and most preferably only 1% or less of such radiation. For such a laminated glazing unit embodied as an automotive windshield, the Illuminant A visible light transmittance must be greater than 70%. Compositions of a suitable glass having such a transmittance include, as examples, the infrared and ultraviolet absorbing green glasses described in the U.S. Patent Nos. 5,077,133 and 5,112,778. In a laminated glazing unit such an automotive windshield or an architectural window, it may be preferable to form only the outboard glass sheet of a glass sheet having a relatively low transmittance in the range of 300 to 340 nm, while the inboard glass sheet is formed from a glass sheet having a relatively higher transmittance in this range. Since most of the radiation passes through the interlayer before passing through the inboard glass sheet, forming the inboard glass sheet from a glass would be ineffective in reducing the radiation in this range which passes through the interlayer. Further, if the inboard glass sheet is formed of a glass sheet which reflects radiation in this range, the radiation will be reflected back through the interlayer, resulting in additional degradation. In addition, if the inboard glass sheet is somewhat less radiation absorbing, the outboard glass sheet can be formed with a greater absorption in this range without reducing the visible light transmittance to levels which are unacceptable in an automotive windshield. Thus, in a preferred embodiment, the outboard glass sheet is formed so as to have a lower average transmittance in the range of 300 to 340 nm than that of the inboard glass sheet. The following example is illustrative of the present invention and does not constitute any limitation with regard to the subject matter of the invention. All laminated samples were assembled as follows. Two glass sheets (0.088" thick) were cleaned with an ammonia solution, the air side of each piece of glass was wiped with adhesion promoter, and a piece of PVC film was placed between the two primed glass surfaces. After assembly, two different procedures were used for de-airing the glass/plastic assemblies. Windshield samples were de-aired using vacuum rings. The optical quality of the laminated samples was determined by measurement of transmitted distortion using a float glass distortion meter, and by visual inspection using both a shadowgraph and a gridboard background. Transmitted haze was measured with a Hazegard XL200 from Gardner/BYK. Flat laminates were formed from 2 feet by 3 feet sheets of glass and a film having the following formulation: Component phr 1300 PVC Resin 70 950 PVC Resin 30 DOZ 50 Drapex 6.8 3 KP-11 0,3 L-1960 1.5 Tinuvin 328 0.5 No. 5377 0.05 The laminates were formed using a 0.045" film formed of the above composition with two sheets each of a) an infrared and ultraviolet absorbing green glass sold commercially by Libbey-Owens-Ford Co. under the trademark EZ-KOOL® ; b) a lightly tinted green glass sold commercially by Libbey-Owens-Ford Co. under the trademark EZ-EYE® ; and c) a clear glass. The percent transmittance of radiation in the range of 300-400 nm was measured and is shown below for a 2.2 mm (0.088") thick sheet of each of these glasses: WAVELENGTH CLEAR GLASS EZ-EYE GLASS EZ-KOOL GLASS 300 0.23 0.0 0.0 305 1.43 0.0 0.01 310 5.36 0.0 0.01 315 13.42 0.0 0.00 320 25.70 0.09 0.04 325 39.69 0.73 0.04 330 53.47 3.83 0.02 335 64.81 11.60 0.02 340 73.11 23.93 0.02 345 79.16 38.10 0.13 350 83.42 51.49 1.97 355 85.76 61.63 10.06 360 87.31 69.48 24.75 365 88.47 74.47 40.63 370 88.65 77.05 51.30 375 88.92 75.26 54.71 380 88.46 73.45 54.77 385 88.86 76.39 60.40 390 89.57 80.81 67.06 395 90.19 83.26 71.89 400 90.48 84.58 74.48 The average transmittance for the range of 300 to 340 nm was 30.8% for the clear glass, 4.5% for the EZ-EYE glass, and 0.02% for the EZ-KOOL glass. The average transmittance for the range of 340 to 500 nm was 89.0% for the clear glass, 78.6% for the EZ-EYE glass, and 63.6% for the EZ-KOOL glass. These laminates were mounted so as to simulate installation in a vehicle and were placed outdoors in Arizona. After 34 months, the change in YIC for the clear glass laminates was measured to be about 7.3; the change in YIC for the EZ-EYE glass laminates was measured to be about 4.6; and the change in YIC for the EZ-KOOL glass laminates was measured to be about 1.2. A model developed to predict yellowing based solely on thermal effects predicted a change in YIC of about 5.2 after 34 months. The larger change in YIC measured for the clear glass laminates is believed to be due to the photodegradation caused by the radiation in the range of 280 to 340 nm. The smaller changes in YIC measured for both the EZ-EYE and EZ-KOOL glass laminates are believed to be due to the photobleaching effect of the radiation in the range of 330 to 500 nm, as well as the reduction or virtual elimination of the photodegradation effects of the radiation in the range of 280 to 340 nm.

Claims: A laminated glazing unit, comprising a first glass sheet, a second glass sheet and a plasticized polyvinyl chloride containing film therebetween, wherein said first glass sheet is formed of a glass that, when at a thickness of about 2.2 mm, has an average transmittance of radiation having wavelengths in the range of 300 - 340 nm of less than 20% and an average transmittance of radiation having wavelengths in the range of 340 - 500 nm of more than 50%. A laminated glazing unit as defined in claim 1, wherein said first glass sheet is formed of a glass that, when at a thickness of about 2.2 mm, has an average transmittance of radiation having wavelengths in the range of 300 - 340 nm of less than 5%. A laminated glazing unit as defined in claim 2, wherein said first glass sheet is formed of a glass that, when at a thickness of about 2.2 mm, has an average transmittance of radiation having wavelengths in the range of 300 - 340 nm of less than 1%. A laminated glazing unit as defined in claim 1, wherein said first glass sheet is formed of a glass that, when at a thickness of about 2.2 mm, has an average transmittance of radiation having wavelengths in the range of 340 - 500 nm of more than 60%. A laminated glazing unit as defined in claim 4, wherein said first glass sheet is formed of a glass that, when at a thickness of about 2.2 mm, has a transmittance of 1% or less of the radiation having a wavelength of 330 nm. A laminated glazing unit as defined in claim 1, wherein said first glass sheet is an outboard glass sheet and said second glass sheet is an inboard glass sheet, said outboard glass sheet being formed of a glass that, when at a thickness of about 2.2 mm, has an average transmittance of radiation having wavelengths in the range of 300 - 340 nm which is lower than that of said inboard glass sheet when said inboard glass sheet is also at a thickness of about 2.2 mm. A laminated glazing unit as defined in claim 1, wherein said first glass sheet is formed of an ultraviolet radiation absorbing green glass.

Inventors: HOLMES PAUL A, MACLACHLAN JULIA B, NEGISHI YASUO, PARKER ANTHONY A, PURVIS MICHAEL B, SCOTT JOHN R, STRICKLER DAVID A, HOLMES, PAUL A., MACLACHLAN, JULIA B., NEGISHI, YASUO, PARKER, ANTHONY A., PURVIS, MICHAEL B., SCOTT, JOHN R., STRICKLER, DAVID A.
Applicants: ACHILLES USA INC, LIBBEY OWENS FORD CO, PILKINGTON PLC, ACHILLES USA, INC., LIBBEY-OWENS-FORD CO.
Application year: 1995
Main classification: B32B17
IPC codes: B32B17