METHOD OF MANUFACTURING A FORMED GLASS SHEET WITH PAINT THEREON

Abstract: A method of forming a glass sheet with ceramic paint thereon is disclosed. The method has the following general steps. A first ceramic paint (12) is applied to and dried on a glass sheet (10). The first ceramic paint includes a low temperature melting glass frit as a component thereof. A second ceramic paint (16) is applied over at least a portion of the dried first ceramic paint. The second ceramic paint includes as a component thereof a high temperature melting glass frit. The high temperature melting glass frit melts at a temperature higher than that temperature at which the low temperature melting glass frit melts at. In another embodiment a single layer of ceramic paint is applied to the glass sheet, said paint including a high temperature melting glass frit and a low temperature melting glass frit. The glass sheet is heated to a temperature which softens the glass sheet sufficiently so that the glass sheet can be formed. The heated glass sheet is engaged by a fiberglass covered forming die to form the glass sheet into a desired shape. The formed glass sheet is removed from the forming die, the second ceramic paint being effective to prevent sticking of any ceramic paint to the fiberglass covered forming die.

Description: This invention is directed to a method of manufacturing a formed glass sheet having a paint on a portion thereof. It is common in certain applications to have curved or formed glass sheets with an opaque border portion. The border portion is commonly a paint that is applied to the glass sheet prior to the glass sheet being heated so that it can be formed by a forming die. A problem in the art has been the sticking of the painted surface to the forming die during the forming process. Commonly the paints used are ceramic paint compositions generally well known to the skilled artisan. These ceramic paint compositions can be used, for example, to form borders around the edges of glass sheets which are used as windshields, sidelites and backlites in motor vehicles. Such ceramic paints usually include a mixture of metal oxides which together act as a coloring agent for the ceramic paint. The metal oxides are nonreactive with one another and nonreactive with any elements or compounds they come in contact with while being heated to temperatures up to 704°C (1300°F). The mixture of metal oxides can be controlled so as to get a selected color from the ceramic paint composition. Normally, in automotive applications, the selected color is black although shades of gray are now becoming popular. Such ceramic paint compositions also include a glass frit which melts generally at a temperature well below 732°C (1350°F). The glass frit is the material which bonds the mixture of metal oxides to the glass sheet and ensures that the mixture of metal oxides remains after the glass sheet has been cooled back to room temperature. A vehicle is normally mixed with the metal oxides and glass frit to allow the ceramic paint composition to be applied in a paint application process. For example, if the paint application process is a silk screen printing operation, the vehicle can be an oil-base or a UV-base organic medium for carrying the other materials during the silk screen printing operation. In US-A-4,596,590 which issued on June 24, 1986 there is disclosed a method of forming a glass sheet with a ceramic paint thereon. This patent contains a discussion of a problem encountered in the sticking of ceramic paint to a forming die covered by fiberglass when the forming die engages a heated glass sheet with ceramic paint thereon. US-A-4,596,590 discloses a method of forming a glass sheet with a ceramic paint thereon which has the following steps. A ceramic paint is applied to the glass sheet. The ceramic paint includes normal ceramic paint components along with, as a new component thereof, a metal oxide having at least a low valance oxidation state and a high valance oxidation state. The metal oxide is in its low valance state when applied to the glass sheet as part of the ceramic paint. The glass sheet is heated to a temperature which softens the glass sheet sufficiently so that the glass sheet can be formed. The glass sheet and the ceramic paint thereon are engaged with a fiberglass covered forming die to form the heated glass sheet to a desired shape. The forming die is removed from engagement with the glass sheet. The metal oxide addition to the ceramic paint in its low valance state is credited with being effective to prevent sticking of any of the ceramic paint to the forming die. The glass sheet is cooled to obtain a formed glass sheet with a ceramic paint thereon. In both U.S. patent application Serial No. 936,575, filed December 1, 1986, now U.S. patent 4,684,388, entitled "Method of Forming a Glass Sheet with a UV-Base Ceramic Paint Thereon, and U.S. application Serial No. 936,576, filed December 1, 1986, now U.S. patent 4,684,389, entitled "Method of Forming a Glass Sheet with an Oil-Base Ceramic Paint Thereon", there is disclosed that the method proposed in US-A-4,596,590, when using stannous oxide as the metal oxide having at least a low valance oxidation state and a high valance oxidation state, did have some drawbacks. It is found that in a UV-gase system, when stannous oxide is present in the paint in an amount greater than 20% by weight or so, there is some tendency for the paint to stick to fiberglass when a relatively high pressure is applied to the painted glass sheet in a bending operation. When working with an oil-base ceramic paint, it is also found that the use of stannous oxide as the metal oxide having at least a low valance oxidation state and a high valance oxidation state also had some drawbacks. It is found that stannous oxide did, in some cases, oxidize too rapidly when subjected to a heating operation. This rapid oxidation caused a fine, white dust to be generated. This dust has a tendency to move over the surface of the glass sheet during the bending operation. The loose dust, at an elevated temperature, can cause marking and/or indentation of the glass sheet, which results in a scrappage thereof. In US application Serial No. 936,575, now U.S. patent 4,684,388 there is disclosed a method of forming a glass sheet with a UV-base ceramic paint thereon, the method having the following steps. A UV-base ceramic paint is applied to the glass sheet. The UV-base ceramic paint includes normal ceramic paint components along with, as a new component thereof, finely divided zinc metal powder. The glass sheet is subjected to UV radiation and then heated to a temperature which softens the glass sheet sufficiently so that the glass sheet can be formed. The glass sheet and the ceramic paint thereon are engaged with a fiberglass covered forming die to form the heated glass sheet to a desired shape. The forming die is removed from engagement with the glass sheet. The finely divided zinc metal powder addition to the ceramic paint is credited with being effective to prevent sticking of any of the ceramic paint to the forming die. The glass sheet is cooled to obtain a formed glass sheet with a ceramic paint thereon. In US application Serial No. 936,576, now U.S. patent 4,684,389 there is disclosed a method of forming a glass sheet with an oil-base ceramic paint thereon, the method having the following steps. An oil-base ceramic paint is applied to the glass sheet. The oil-base ceramic paint includes normal ceramic paint components along with, as a new component thereof, finely divided zinc metal powder. The glass sheet is heated to a temperature which softens the glass sheet sufficiently so that the glass sheet can be formed. The glass sheet and the ceramic paint thereon are engaged with a fiberglass covered forming die to form the heated glass sheet to a desired shape. The forming die is removed from engagement with the glass sheet. The finely divided zinc metal powder addition to the ceramic paint is credited with being effective to prevent sticking of any of the ceramic paint to the forming die. The glass sheet is cooled to obtain a formed glass sheet with a ceramic paint thereon. Despite the methods that have been described above, there are situations where paint sticking still occurs when high pressures are applied on a ceramic paint by a fiberglass covered die in which there is a high degree of bend over a relatively short distance. Under such conditions, it is found that even though zinc powder is added to the ceramic paint, a degree of sticking of the ceramic paint to the fiberglass cloth will take place in the areas of bending where high pressures over small areas are used between the fiberglass covered forming die and the painted glass sheet. It is a principal object of the method of this invention to provide a method of forming a glass sheet with ceramic paint thereon which can be carried out at high contact pressures between a fiberglass covered forming die and ceramic paint without the sticking of ceramic paint to the fiberglass. The method disclosed herein has been successfully developed for forming glass sheets with ceramic paint thereon under high pressure over small areas of such glass sheets without any sticking of ceramic paint to the fiberglass covered forming dies. According to the present invention there is provided a method of manufacturing a formed glass sheet with ceramic paint thereon, which method comprises the steps of, applying a first ceramic paint on said glass sheet, said first ceramic paint including a glass frit as a component thereof, drying said first ceramic paint on said glass sheet, applying a second ceramic paint over at least a portion of said dried first ceramic paint, said second ceramic paint including a glass frit as a component thereof, the glass frit of said second paint melting at a temperature higher than that temperature at which the glass frit of said first paint melts, heating said glass sheet to a temperature which softens said glass sheet sufficiently so that said glass sheet can be formed, engaging said glass sheet with said first and said second ceramic paints thereon with a fiberglass covered forming die to form said heated glass sheet to a desired shape, and removing said forming die from engagement with said glass sheet, said second ceramic paint including finely divided zinc metal which reduces the sticking of ceramic paint to fiberglass.. It is preferred that both ceramic paints have finely zinc metal material which reduces the sticking of ceramic paints to fiberglass. It is also preferred that the second ceramic paint have a greater percent by weight of the fiberglass sticking reduction material therein that does the first ceramic paint. A preferred method of forming a glass sheet with ceramic paint thereon in accordance with the invention has the following steps. A first ceramic paint is applied to the glass sheet. The first ceramic paint includes a low temperature melting glass frit, a fiberglass sticking reduction material, and an application vehicle as components thereof. The first ceramic paint is dried on the glass sheet. A second ceramic paint is applied over at least a portion of the dried first ceramic paint. The second ceramic paint includes: a high temperature melting glass frit, a fiberglass sticking reduction material, and an application vehicle as components thereof. The high temperature melting glass frit melts at a temperature higher than the temperature at which the low temperature melting glass frit melts. The glass sheet is heated to a temperature which softens the glass sheet sufficiently so that the glass sheet can be formed. The glass sheet with the first and the second ceramic paints thereon is engaged with a fiberglass covered forming die to form the heated glass sheet to a desired shape. The forming die is removed from engagement with the glass sheet. The second ceramic paint and the fiberglass sticking reduction material contained in both ceramic paints being effective to prevent sticking of any of the ceramic paint to the forming die. The glass sheet is then cooled to obtain a formed glass sheet with ceramic paint thereon. If the glass sheet is cooled rapidly, the final glass sheet is tempered by the rapid cooling process. The invention will now be described further, by way of example, with reference to the accompanying drawings, in which : Figure 1 is a front elevation view of a glass sheet having ceramic paint thereon formed in accordance with the method of the invention, Figure 2 is a rear elevation view of the glass sheet of Figure 1, and Figure 3 is a cross-sectional view taken along line III-III of Figure 2 showing the glass sheet in a formed condition with ceramic paint thereon being shown in an exaggerated condition. The following description is what I consider to be a preferred embodiment of the method of my invention of forming a glass sheet with ceramic paint thereon. The following description also sets forth what I now contemplate to be the best mode of carrying out my inventive method. The description is not intended to be a limitation upon the broader principles of this method, and while preferred materials are used in teaching the method of my invention in accordance with the requirements of the laws, it does not mean that other materials cannot be used in my method. In the drawings there is shown a glass sheet 10 formed of soda/lime silica glass. Such a glass sheet may be cut from a glass sheet manufactured by a float glass process. In this particular case, the glass sheet is one which is installed in a motor vehicle between the backlite and the last glass window associated with a vehicle door. This glass sheet is generally called a quarter lite. The glass sheet 10, as viewed in Figure 1, has an opaque ceramic band 12 therearound as well as a plurality of opaque ceramic dots therearound of varying sizes, generally identified by the numeral 14. As seen in Figure 1, this is the surface of the glass sheet which would be viewed by someone standing on the outside of a vehicle when the glass sheet is installed in that vehicle. The ceramic band and ceramic dots are used to form an aesthetically pleasing way of camouflaging the back of retaining clips and other upholstering items which otherwise could be viewed therethrough. Such camouflaging on automotive glass is in wide use today. The ceramic band 12 and ceramic dots 14 are applied by applying a first ceramic paint to what is to be the inside surface of the glass sheet 10. The first ceramic paint includes a low melting glass frit as a component thereof. In accordance with the preferred embodiment of the method of my invention, the low melting glass frit melts at a temperature in a range of 538-662°C (1100-1224°F). As is disclosed in my aforementioned U.S. patent 4,596,590 and is known to the art, the ceramic paint is made up of several other ingredients besides the glass frit. The ceramic paint composition also includes as an element thereof a mixture of metal oxides which together act as a coloring agent for the ceramic paint. The mixture of metal oxides are nonreactive with one another and nonreactive with any elements or compounds they come in contact with while being heated to a temperature in a range up to 704°C (1300°F). A vehicle is also mixed with the metal oxides and the low melting point glass frit to form all of the mentioned materials into a ceramic paint which can be applied to the glass surface in a process such as a silk screen printing operation. In accordance with the teachings of the method of my invention, the first ceramic paint applied to the glass sheet 10 can form both the ceramic band 12 and the ceramic dots 14. In my preferred embodiment, I use Drakenfeld paint composition 24-2247 in a 1718 UV curable medium. In the preferred embodiment, the first ceramic paint contains, on a weight percent basis: 32% metal oxide mixture of iron, manganese, chrome and nickel; 43% of glass frit which melts at a temperature in a range from 621 to 649°C (1150 to 1200°F).and 25% of the 1718 organic vehicle. As will be described below, one can also add a material to the ceramic paint composition which reduces the sticking of ceramic paint to fiberglass. The first ceramic paint may be applied to the glass sheet through a 255 mesh screen. The first ceramic paint is dried on the glass sheet 10. If the vehicle used to make the ceramic paint is an oil-base vehicle, then the first ceramic paint is dried by heating the glass sheet to a temperature sufficient to volatilize the oil-base vehicle, leaving behind the other materials of the paint which are not volatile. If the vehicle of the ceramic paint is a UV cross-linkable material, as it is in the preferred embodiment, the first ceramic paint is dried by UV curing the vehicle by the application of UV energy as is well known in the art. As seen in Figure 2, which depicts the reverse side of the glass sheet 10 of Figure 1, there is shown a second ceramic band 16. In the preferred embodiment, the second ceramic band 16 is shown formed over the first ceramic band 12, basically being positioned about a 1/4 inch inside the outboard edges of the first ceramic band. This second ceramic band 16 is developed by applying a second ceramic paint over at least a portion of the dried first ceramic paint. The second ceramic paint includes a high temperature melting glass frit as a component thereof. The high temperature melting glass frit melts at a temperature higher than the temperature at which the low temperature melting glass frit melts at. In the preferred embodiment disclosed herein, the high temperature melting glass frit melts at a temperature in a range of 1275-1350°F. For the second ceramic paint, I used Drakenfeld paint composition 24-2276 in a 900 oil base vehicle. In this preferred embodiment, the second ceramic paint contains, on a weight percent basis: 35% metal oxide mixture of iron, manganese, chrome, nickel and cobalt; 40% of glass frit which melts at a temperature in a range from 691-718°C (1275 to 1325°F) and 25% of the 900 organic vehicle. A material which reduces ceramic paint sticking to fiberglass may also be included in the second ceramic paint composition as will be set forth below. The second ceramic paint composition may be printed through a 305 mesh screen. The next step in my method is that of heating the glass sheet 10 to a temperature which softens the heated glass sheet sufficiently so that the glass sheet can be formed. Normally this softening temperature of the glass sheet is a temperature in a range of 538-649°C (1000-1200°F), preferably 593°C (1100°F). The heated glass sheet 10, with the first and the second ceramic paints thereon, is engaged with a fiberglass covered forming die to form the heated glass sheet to a desired shape. Thereafter, the forming die is removed from engagement with the glass sheet. The second ceramic paint, which is fused to the glass sheet by the low melting glass frit of the first ceramic paint, is effective to prevent the sticking of the ceramic paint to the forming die. I believe this occurs because the higher melting point glass frit of the second ceramic paint does not soften sufficiently to stick to the fiberglass covered forming die and therefore acts as a protective barrier. In accordance with more detailed teachings of the method of my invention, the second ceramic paint includes as a component thereof a material which reduces the sticking of ceramic paint to fiberglass. As mentioned previously, prior patent applications of mine have disclosed that finely divided zinc metal powder and finely divided stannous oxide powder are suitable nonstick materials. The material which reduces the sticking of ceramic paint to fiberglass may also be included in the first ceramic paint. In accordance with still further preferred teachings of the method of my invention, the first ceramic paint includes 10-30% by weight of the finely divided nonstick material and the second ceramic paint includes 30-60% by weight of the finely divided fiberglass sticking reduction material. In accordance with the teachings of a preferred embodiment of the method of my invention, the first 12 and second 16 ceramic bands have a thickness in a range of about .002 - .003cm (0.0008-0.0012 inch).

Claims: 1. A method of manufacturing a formed glass sheet with ceramic paint thereon, which method comprises the steps of, appying a first ceramic paint on said glass sheet, said first ceramic paint including a glass frit as a component thereof, drying said first ceramic paint on said glass sheet, applying a second ceramic paint over at least a portion of said dried first ceramic paint, said second ceramic paint including a glass frit as a component thereof, the glass frit of said second paint melting at a temperature higher than that temperature at which the glass frit of said first paint melts, heating said glass sheet to a temperature which softens said glass sheet sufficiently so that said glass sheet can be formed, engaging said glass sheet with said first and said second ceramic paints thereon with a fiberglass covered forming die to form said heated glass sheet to a desired shape, and removing said forming die from engagement with said glass sheet, said second ceramic paint including finely divided zinc metal which reduces the sticking of ceramic paint to fiberglass. 2. A method as claimed in claim 1, wherein both said first and said second ceramic paints include finely divided zinc metal which reduces the sticking of ceramic paint to fiberglass. 3. A method as claimed in claim 2, wherein said second ceramic paint has a greater percent by weight of finely divided zinc metal therein than does said first ceramic paint. 4. A method as claimed in any one of claims 1 to 3, wherein each of said first and second paints includes application vehicle or component thereof. 5. A method as claimed in claim 4, wherein said application vehicle of said first ceramic paint is a UV curable material, and wherein said first ceramic paint is dried by the application of UV energy thereon. 6. A method as claimed in claim 4, wherein said application vehicle of said first ceramic paint is an oil based material, and wherein said first ceramic paint is dried by the application of heat. 7. A method as claimed in claim 3, wherein said finely divided zinc metal is 10 to 30% by weight of said first ceramic paint and said finely divided zinc metal is 30 to 60% by weight of said second ceramic paint. 8. A method as claimed in any one of the preceding claims wherein said first and said second ceramic paints each have a thickness in a range from 0,002 cm (0.0008 inches) to 0.003 cm (0.0012 inches). 9. A method as claimed in any one f the preceding claims wherein said low temperature melting glass frit melts at a temperature in a range of 593°C (1100°F) to 663°C (1225°F), and said high temperature melting glass frit melts at a temperature in a range from 691°C (1275°F) to 732°C (1350°F).

Inventors: BOAZ, PREMAKARAN T.
Applicants: FORD FRANCE S. A., FORD MOTOR COMPANY LIMITED, FORD-WERKE AKTIENGESELLSCHAFT
Application year: 1988
Main classification: C03C17
IPC codes: C03B23, C03C17, C03C8, B60J1