Abstract:
A method for coating glass, and specifically to a method for manufacturing perfluoroalkoxy copolymer coated glass. The method includes placing a glass substrate on an electrically grounded support and cleaning the substrate with a solvent to remove impurities and prepare the surface of the substrate to be coated. The method also includes coating the surface with a primer and an electro-conductive enhancer, which is uniformly applied to the primer so that the surface of the glass substrate is wet, but not uneven. The method includes powder spraying the perfluoroalkoxy copolymer on the electro-conductive enhancer while the enhancer is still wet. The method includes securing the perfluoroalkoxy copolymer to the glass substrate by evaporating the electro-conductive enhancer.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates in general to coated glass, and specifically to perfluoroalkoxy copolymer coated glass and a method of manufacturing perfluoroalkoxy copolymer coated glass. 
     Coatings have been applied to glass to change one or more characteristics of the glass. One such coating is perfluoroalkoxy copolymer (“PFA”) which is one of the compounds sold by E.I. Du Pont de Nemours and Company under the trademark Teflon®. PFA is most commonly used as a non-stick coating on cookware such as pots and pans. PFA has also been used to coat glass such as automobile windshields and light bulbs. 
     The structure of PFA makes it highly resistive to sticking or adhering to other substances. In particular, the structure of perfluoroalkoxy copolymer is a copolymer of tetrafluoroethylene (CF2=CF2) with a perfluoroalkoxy vinyl ether [F(CF2)m CF20CF—CF2]. The resultant polymer contains the carbon-fluorine backbone chain typical of polytetrafluoroethylene with perfluoroalkoxy side chains. The side chains are connected to the carbon-fluorine backbone of the polymer through flexible oxygen linkages. The fluorine atoms in the chain resist almost any other atom or molecule, even other fluorine atoms. As a result, the fluorine atoms in PFA resist adhering to or even being near other molecules. Thus, molecules at the surface of PFA repel the other molecules and almost anything else that attempts to adhere or come close to the PFA molecule. Additionally, the bond between the carbon and fluorine atoms is extremely strong. The bond is so stable that little to almost nothing will react with it. Thus, PFA is a desirable coating to coat glass products because it is a material, which minimally reacts with other compounds. PFA also includes very strong bonds between its atoms which enables the coating to withstand extreme temperature and pressure conditions. 
     However, there are certain problems with known PFA coated glass. One known problem is that although the PFA coats the glass, it does not form a strong bond with or strongly adhere to the glass because of its highly resistive nature with respect to other molecules. Thus, when a glass substrate or glass product coated with PFA shatters or breaks, certain of the glass shards or pieces break away from the PFA coating. In some coated glass products such as coated light bulbs, the PFA coating is applied to the outside of the light bulb. When the light bulb coated with PFA breaks, the glass pieces remain inside the light bulb because the PFA layer creates a closed container such that the glass pieces are contained inside the light bulb. However, other glass products such as laboratory beakers are open glass containers. Therefore, the glass shards in these products can become loose and break away from the surfaces of these products. The glass shards are unsafe and may cause injury or severe injuries to users of these glass products. 
     Accordingly, there is a need for glass-coated materials and glass products that are coated with a material that has a very high bond strength and which strongly adheres to glass. Additionally, there is a need for a glass-coated materials and products that maintain the structural integrity of the surfaces of the glass materials and products. 
     SUMMARY OF THE INVENTION 
     The present invention relates in general to coated glass, and specifically to perfluoroalkoxy copolymer coated glass and a method of manufacturing perfluoroalkoxy copolymer coated glass. 
     One embodiment of the perfluoroalkoxy copolymer or PFA coated glass of the present invention includes a glass substrate, which may be any suitable glass substrate, a layer of primer applied to the surface of the glass substrate being coated, an electro-conductive enhancer applied to the primer and a layer of PFA applied to the electro-conductive enhancer to form the coated glass substrate, wherein the electro-conductive enhancer is evaporated to secure the PFA to the surface of the glass substrate. 
     In one presently preferred embodiment of the method of the present invention, a glass substrate is positioned on an electrically conductive support. The surface of the glass substrate being coated is cleaned with a cleaner such as a solvent. In one embodiment, the solvent is methyl ethyl ketone (“MEK”). This solvent cleans and removes impurities which may be present on the surface of the glass substrate. In this step, the solvent may be manually applied or mechanically applied to the glass substrate as desired by the manufacturer. Alternatively, the substrate may be pre-cleaned and the coating method may be performed in a suitable “clean room” where the cleaning step is not necessary. 
     In the next step, a layer of primer is applied to the surface of the substrate. The primer is applied as a mist or atomized spray so that a cloudy or opaque appearance does not form on the surface of the glass substrate. After the primer is applied, the primer is cured using a suitable curing process. The curing process dries the primer and strengthens the bonds between the primer and the surface of the glass substrate. In a presently preferred embodiment, the primer is cured at a temperature of approximately 500° F. (260° C.) for approximately five minutes. It should be appreciated that other suitable curing processes may be employed in accordance with the present invention. 
     When the primer has been properly cured, an electro-conductive enhancer is applied on the primer on the surface of the glass substrate. In the presently preferred embodiment, the enhancer is a highly polar solvent which is electrically conductive. When the solvent is applied, the glass substrate becomes electrically grounded. By grounding the glass substrate, the solvent becomes charged and thereby attracts oppositely charged particles. In one presently preferred embodiment, the solvent is a water soluble solvent such as N-methyl-2-pyrrolidone (NMP). In a presently preferred embodiment, the NMP layer is sprayed or applied to the surface as a fog or mist so as to completely wet the surface of the glass substrate. However, the NMP layer is preferably applied so as to avoid forming a thick layer and avoid drippings which might detract from the bonding ability of the coatings. 
     While the solvent or NMP layer is still wet, a layer of PFA in powder form is sprayed over the wet NMP. The PFA particles have a charge which is opposite to the charge of the NMP. Thus, the PFA particles are attracted to the NMP on the surface of the glass substrate. As a result, the PFA particles uniformly coat the surface of the NMP on the glass substrate. The PFA is applied to the NMP until the coatings on the surface of the glass substrate achieve a desired thickness. In one presently preferred embodiment, the desired thickness is approximately 0.002 and 0.003 inches. Other suitable thickness ranges may be used as desired by the manufacturer for other types of glass substrates or glass products. 
     Once the PFA layer is applied to the surface of the glass substrate, the NMP and PFA layers are heated, to evaporate the solvent or NMP from the surface of the glass substrate and cure the PFA. In one embodiment, the NMP and PFA layers are heated to a temperature of approximately 800° F. (427° C.) for approximately twenty minutes. The heating process evaporates the NMP and cures the PFA layer which directly adheres to the primer on the surface of the glass substrate. Because the PFA was applied to the wet solvent, the PFA is tightly packed and forms a uniform coating on the surface of the glass substrate. As a result, the coated glass substrate is clearer or more transparent and translucent. 
     It should be appreciated that the method of manufacturing or forming the PFA coated glass may be performed as described above by applying or spraying the coatings on to the surface of a glass substrate or glass product. Alternatively, the coatings may be applied using other suitable coating methods. In one embodiment, the NMP layer is applied by dipping the glass substrate in the NMP solvent. This coating process ensures that the surface of the glass substrate is completely coated with the solvent. 
     It is therefore an advantage of the present to provide PFA coated glass and a method for manufacturing the PFA coated glass that maintains the structural integrity of the glass. 
     Another advantage of the present invention is to provide a method for manufacturing coated glass which enables a perfluoroalkoxy copolymer coating to adhere to a glass substrate. 
     A further advantage of the present invention is to provide a method of manufacturing coated glass that forms a strong bond between a perfluoroalkoxy copolymer and a glass substrate. 
     Another advantage of the present invention is to provide a coated glass substrate and a method of manufacturing same that can be used on a wide variety of glass substrates and products. 
     Additional features and advantages of the present invention are described in and will be apparent from, the following Detailed Description of the Invention and the Figures. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1A  is an enlarged fragmentary side view of a coated glass substrate of one embodiment of the present invention. 
         FIG. 1B  is an enlarged fragmentary cross-sectional view of the coated glass substrate of FIG.  1 A. 
         FIG. 2  is a flowchart illustrating one embodiment of the coating method of the present invention. 
         FIG. 3A  is an enlarged fragmentary side view of a coated glass substrate of one embodiment of the present invention illustrating the coated glass substrate before the solvent layer is evaporated. 
         FIG. 3B  is an enlarged fragmentary cross-sectional view of the coated glass substrate of FIG.  3 A. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to  FIGS. 1A ,  1 B,  2 ,  3 A and  3 B, one embodiment of the coated glass product or substrate of the present invention is illustrated. The coated glass substrate or glass product  100  includes a glass substrate  102 , a layer of primer  104  applied to at least one portion, area or surface of the glass substrate and a layer of PFA  108  applied to the primer layer on the surface of the glass substrate  102 . This combination creates a very strong bond between the PFA and the primer on the surface of the glass substrate and thereby enables the PFA layer to adhere to and stretch with the glass substrate, which substantially holds the glass substrate in tact. Additionally, the strong bond formed between the PFA and the glass substrate enables the coated glass substrate to withstand extreme conditions such as extreme temperatures and pressures. It should be appreciated that the glass substrate  102  may be any suitable type of glass substrate. Additionally, the glass substrate  102  may also be any suitable shape or configuration. 
     Referring now to  FIGS. 2 ,  3 A and  3 B, in one presently preferred embodiment of the method of the present invention, the glass substrate is positioned on an electrically grounded support or holder as indicated by block  200 . In one embodiment, the grounded support is made of an electrically conductive material such as metal and contacts and supports the glass substrate. In another embodiment, the grounded support includes a grounding plate or surface which supports and contacts a surface of the glass substrate. It should be appreciated that any suitable grounding support may be used to support and ground the glass substrate. 
     Before any coatings are applied to the glass substrate, one or more surfaces of the glass substrate  102  such as the outer surface of a glass beaker, are cleaned using a suitable cleaner to remove all or a substantial portion of the impurities from the surface of the glass substrate as indicated in block  201 . In the presently preferred embodiment, the cleaner is a solvent such as methyl ethyl ketone (“MEK”). The cleaning of the surface of the glass substrate may be performed manually or mechanically such as by a machine. It should be appreciated that other suitable cleaning methods and cleaners may be used to clean the surface of the glass substrate. It should also be appreciated that the surface of the glass substrate does not have to be cleaned prior to applying the primer. For example, the glass substrate itself may be clean or substantially free of impurities prior to applying the layers to the glass substrate. The layers are then applied to the substrate in a clean room or a room virtually free from impurities. It should be appreciated that the glass substrate could also be manufactured in a clean room. It should further be appreciated that the glass substrate may be cleaned by a separate cleaning process or in a separate cleaning area prior to positioning the glass substrate on the grounded support. 
     A layer of primer  104  is applied to the cleaned surface of the glass substrate as indicated by block  202 . The primer may be any suitable primer such as the 1200 clear primer manufactured by the Dow Corning Corporation. In a presently preferred embodiment, the primer is a clear primer and is applied or sprayed onto the surface of the glass substrate as a mist or atomized spray. It should be appreciated that the primer may be applied using other suitable coating processes such as dipping the substrate into a container of the primer. In this embodiment, the purpose of applying the primer as a mist is to avoid or reduce the chances of the surface of becoming wet or saturated with the primer. If the surface is wet or saturated with the primer, the appearance of the final coated glass substrate might appear cloudy or obscured due to the pooling of the primer on the surface of the glass substrate. Therefore, the pooling of the primer may also cause the surface to be uneven and inhibit light from passing through or cause refraction of the light through the coated glass substrate. The obscure nature of the glass substrate may also inhibit a user from being able to see through the substrate. Therefore, a fine mist or atomized spray is preferably applied to the substrate in relatively small quantities over the surface of the substrate. The primer adheres to the surface of the glass substrate being coated and acts as a bonding agent for subsequent coating layers. Once the primer is applied to the surface of the glass substrate, the primer is cured using a suitable curing process as indicated by block  204 . In one embodiment, the primer is cured in an oven or other suitable heater. In another embodiment, the primer is air-dried to cure the primer. It should be appreciated that any suitable curing process or method may be used to cure the primer in accordance with the present invention. In the presently preferred embodiment, the primer is cured by heating the primer with an oven or kiln to a temperature of approximately 500° F. (260° C.) for approximately five minutes. 
     After the primer has properly cured, an electro-conductive enhancer is applied to the primer as indicated by block  206 . In the presently preferred embodiment, the enhancer is a highly polarized solvent which is electrically conductive. When the solvent is applied to the primer the glass substrate becomes grounded. As a result, the solvent and the glass substrate develop a charge which attract materials or particles having an opposite charge. In one embodiment, the solvent is a water soluble solvent. In another embodiment, the solvent is N-methyl-2-pyrrolidone (NMP), which is water soluble. In the presently preferred embodiment, the NMP solvent is applied as a fog spray onto the primer layer  104  of the surface of the glass substrate  102 . This process continues until the surface of the glass substrate is wet or completely coated with the NMP. 
     While the layer of NMP is still wet, a layer of PFA is applied to the wet NMP layer. In the presently preferred embodiment, the PFA is applied as particles which have an opposite charge from the NMP layer. As described above, the glass substrate is grounded, which promotes the flow of electric charge from the PFA layer to the solvent layer. The voltage differential causes the NMP layer to attract the oppositely charged PFA particles to the NMP as indicated by block  208 . This process causes the PFA layer to uniformly coat the NMP layer without pooling or forming drips. Once the particles coat the solvent or NMP layer, the particles act as an insulator against further particles accumulating on the NMP layer. In a presently preferred embodiment, the PFA layer  108  is powder sprayed and electrically attracted to the wet NMP layer until the thickness of the coatings on the glass substrate achieves a desired thickness. Specifically, the desired thickness of the coatings is approximately 0.002 to 0.003 inches. Once the PFA layer  108  is applied, the coated glass substrate includes three coating layers  104 ,  106  and  108  as illustrated in  FIGS. 3A and 3B . It should be appreciated that any suitable thickness may be implemented with the present method based on the desire of the manufacturer. Additionally, the PFA layer  108  may include any suitable PFA coating such as 532-5010 or 5011 PFA manufactured by E.I. Du Pont de Nemours and Company. 
     After the PFA layer  108  has been applied to the NMP layer  106  on the surface of the glass substrate, the coated substrate is heated to evaporate the solvent layer and secure or adhere the PFA layer  108  to the primer  104  on the surface of the glass substrate as indicated by block  210 . It should be appreciated that any suitable evaporation method may be employed to evaporate the solvent. It should also be noted that the solvent evaporates at a temperature of 400° F. (204° C.) and the PFA particles or layer begins to melt and cure at 500° F. (260° C.). In a presently preferred embodiment, the layer is heated at a temperature of approximately 800° F. (427° C.) for approximately twenty minutes. Because the solvent evaporates at 400° F., the solvent evaporates first as the coated substrate is heated. Once the solvent evaporates from the surface of the coated glass substrate, the PFA remains and begins to melt and cure on the surface of the glass substrate. 
     The PFA layer is tightly packed due to application of the PFA to the wet layer of solvent. As a result, the PFA layer adheres directly to the primer on the surface of the glass substrate when the solvent (NMP) evaporates from the surface of the glass substrate. This enables the final PFA coated glass substrate to have a much clearer appearance. Therefore, a user can see through the coated glass substrate and light is able to pass through the coated glass substrate. These transparent and translucent characteristics of the coated glass substrate of the present invention enable the coated glass substrate and method of the present invention to be used for several commercial and industrial applications such as light bulbs, home glassware, laboratory glassware, windows and windshields. Once the curing process is complete, the coated glass substrate is transferred to another manufacturing area for further processing. 
     The method of the present invention creates very strong bonds between the PFA and the primer on the surface of the glass substrate  102 . As a result, the PFA layer conforms to the glass and stretches to hold the glass surface together even when the glass shatters into several pieces. This prevents the glass from breaking up and falling away from the glass surface. Therefore, the coated glass substrates and products produced according to the present invention are very durable and resistant breaking apart, which makes the coated glass substrate of the present invention suitable for several different applications. For example, the PFA coated glass substrate may be used for laboratory glassware such as a test tube or beaker. The strength of the bonds created between the PFA layer  108  and the surface of the glass substrate  102  enables the glass surface of the laboratory glassware to substantially maintain its structural integrity upon shattering or breaking. This is very important for safety purposes because injuries or potentially serious injuries can be minimized or prevented. Also, the strength of the PFA bonds enables the coated glass to withstand high pressure and temperature cleaning systems found in laboratories and hospitals. 
     It should be understood that various changes and modifications to the presently preferred embodiments described herein will be apparent to those skilled in the art. Such changes and modifications can be made without departing from the spirit and scope of the present invention and without diminishing its intended advantages. It is therefore intended that such changes and modifications be covered by the appended claims.