Abstract:
A process for making a fastener having a shank with a head and a flat tip. A polymeric coating is applied to the tip of the fastener. The coating forms a parabolic bubble and is subsequently cured. The bubble prevents damage to a decorative coating of a vehicle during installation of a component in which the fastener is utilized. The disclosure is further directed to the fastener which is produced by the process.

Description:
RELATED APPLICATION 
     This application claims priority to and all the benefits of co-pending U.S. Provisional Patent Application Ser. No. 60/119,741 entitled “Anti-Scratch Coating For Automotive Fasteners”, which was filed on Feb. 12, 1999. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention pertains to automotive fasteners. More particularly, the present invention pertains to automotive fasteners having a parabolic shaped coating adhered to the tip of the fastener to prevent scratching during installations and the process of producing the same. 
     2. Prior Art 
     There exists the need for an automotive fastener that can be used to attach automotive components to a vehicle without damaging the decorative coating that has been applied to the body of the vehicle. 
     During the assembly process, fasteners of the general type disclosed in this invention are welded to a bracket, such as a bumper mounting bracket, to allow attachment of various components to a vehicle body. The mounting bracket assemblies are commonly treated to prevent corrosion by processing with caustic and acid washes, with a subsequent electrodeposited paint coating. 
     During installation of the bracket assembly, the tips of the fasteners have been known to damage the decorative coating of the vehicle body. The damage is predominantly caused when a person attempts to install the bracket assembly at an angle other than perpendicular to a mounting hole. When attempting to install the bracket assembly at an angle, the fastener tip may be dragged across the vehicle body thereby scratching the decorative coating. 
     It is an object of this invention to provide a fastener having a parabolic shaped coating applied to the tip of the fastener to prevent scratching of the decorative coating of a vehicle during installation. It is a further object of this invention to provide a fastener having a parabolic shaped coating applied to the tip of the fastener, where the coating can withstand the welding and corrosion treatment outlined above. 
     Various fasteners having coatings are known, U.S. Pat. No. 4,692,080 entitled “Self Drilling Fasteners And Process For Making The Same”, discloses a self-drilling screw having a frangible polymer coating on the screw tip. The coating is applied prior to applying a corrosion resistant plating to the screw for preventing the plating from being deposited upon the tips of the fasteners. The coating comprises a triallyl cyanurate which is ultra-violet or infrared curable. The coating breaks away from the fastener during the installation process, to expose the sharp self-drilling tip of the disclosed fastener. 
     The fastener of the above referenced patent does not provide a fastener having a parabolic shaped coating on the tip that will not break off during the installation process, thereby preventing the scratching of the decorative coating of the vehicle body. 
     U.S. Pat. No. 4,713,855 entitled “Process For Making Self-Drilling Fasteners”, discloses a process for manufacturing the fasteners outlined in the previously referenced U.S. Pat. No. 4,692,080. The patent discloses a process for applying the frangible coating to the self-tapping screw tip which includes dipping the tip into a triallyl cyanurate polymer bath and subsequently curing the polymer using ultra-violet or infrared light. 
     The process of the above referenced patent does not provide a process for applying a coating to the tip of a fastener, to produce a parabolic shaped coating on the tip. 
     It is therefore, the purpose of the present invention to cure those deficiencies outlined above by providing a fastener and the process for producing the same, whereby the tip of the fastener has a parabolic shaped coating adhered to the tip of the fastener to prevent scratching of the decorative coating of a vehicle during installation. 
     SUMMARY OF THE INVENTION 
     Thus, in accordance with the present invention, there is provided a process for making a fastener having a shank with a head and a flat tip. A polymeric coating is applied to the flat tip to form a parabolic bubble on the tip of the fastener. The bubble is cured to prevent the tip of the fastener from damaging a decorative coating on a vehicle, such as during installation of the fastener. 
     The invention includes the several steps and the relationship of the several steps with respect to each other. The invention also includes the article produced by the process and its properties as disclosed in the following Detailed Description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side view of a fastener having a parabolic shaped coating on a tip; 
     FIG. 2 is a side view of the fastener with an applicator for applying a paint bubble to the tip. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to the Figures, wherein like numerals indicate like or corresponding parts throughout the several views, a fastener for securing a component to a vehicle (not shown) is generally illustrated at  10  in FIG.  1 . The component may be any suitable exterior trim piece or body panel which is secured to the vehicle. In addition, the component may be formed of plastic or metal as is desired. 
     The fastener  10  comprises a shank  12  having first  14  and second  16  ends. The shank  12  may be of any desired length or diameter as needed for a particular application. A head  18  is disposed on the first end  14  with the second end  16  terminating at a flat tip  20 . The head  18  may be of any suitable shape and size such as circular or oval. 
     A majority of the shank  12  has a plurality of threads  22  extending between the head  18  and the tip  20 . The threads  22  work in concert with a bolt or other like device (not shown) to secure the component to the vehicle. The entire fastener  10  is preferably formed of a metal material, such as steel, which can withstand typical oven temperatures. As appreciated, the threads  22  may be substituted for locking projections or the like. The important feature is that the fastener  10  adequately secures the component part to the vehicle. 
     The fastener  10  is characterized by a polymeric coating  24  disposed on the flat tip  20 . The polymeric coating  24  forms a parabolic bubble  24  on the flat tip  20  for preventing scratching of the vehicle by the fastener  10  during installation of the component. In particular, the parabolic shaped coating  24  prevents the tip  20  from contacting the decorative coating of a vehicle body. The decorative coating is primarily the painted exterior body panel of the vehicle. 
     The thickness (or height) of the parabolic shaped coating  24  is directly proportional to the angle the fastener  10  can approach the vehicle body without the tip  20  scratching the decorative coating. For example, a 0.5 mm coating thickness prevents the tip  20  from contacting the vehicle body at a 24.5 degree approach, while a 2.5 mm thickness prevents the tip  20  from contacting the vehicle body at a 66.3 degree approach. A range of coating thickness can be applied to obtain a desired approach angle, whereby the tip  20  will not contact and scratch the decorative coating. The determined range includes: 
     
       
         
               
               
               
             
           
               
                   
                   
               
               
                   
                 Thickness 
                 Approach angle 
               
               
                   
                   
               
             
             
               
                   
                 0.5 mm 
                 24.5 degrees 
               
               
                   
                 0.75 mm  
                 34.5 degrees 
               
               
                   
                 1.0 mm 
                 42.4 degrees 
               
               
                   
                 1.5 mm 
                 53.8 degrees 
               
               
                   
                 2.0 mm 
                 61.2 degrees 
               
               
                   
                 2.5 mm 
                 66.3 degrees 
               
               
                   
                   
               
             
          
         
       
     
     The parabolic shaped coating  24  is formed from a paint mixture comprising at least four components. The first component is a high solid polyurethane polymer dispersed in dispersing solvents Methyl ethyl Ketone, N-Butyl Acetate, and Methyl Amyl-Ketone. However, other dispersing solvents may be used as required. The polyurethane polymer can be purchased from Cardinal Industrial Finishes and is sold as High Solids Polyurethane. 
     The second component is a polyurethane catalyst. The catalyst comprises Hexamethane Diisocyanate, a free monomer, dispersed in dispersing solvent N-butyl acetate. However, other dispersing solvents may be used as required. The Hexamethane Diisocyanate causes the polyurethane to crosslink while curing in a bake oven. The catalyst can be purchased from Cardinal Industrial Finishes and is sold as  340 HP Catalyst. 
     The third component is a pigment paste for adding color and inhibiting corrosion. Various pigments have been contemplated for use to meet various color requirements. A pigment known to meet color and corrosion requirements is Zinc Oxide. Zinc Oxide is wetted with Toluene and Aliphatic Naphtha forming the third component. This pigment can be purchased from Tremulad. 
     The fourth component is a hardening agent having Isopropanol. A higher concentration of the hardening agent in the final product hardens the coating and improves adhesion. The hardening agent reduces the affect of gravitational forces which cause the paint to flow during curing. Thus, a higher concentration of the hardening agent will yield a thicker (higher) coating. The hardening agent can be purchased from Sheffield Bronze Inc., and is known as Japan Dryer. 
     The preferred composition range for the four components is: 
     
       
         
               
               
               
             
           
               
                   
                   
               
               
                   
                 Component 
                 Range 
               
               
                   
                   
               
             
             
               
                   
                 One 
                 46%-66% 
               
               
                   
                 Two 
                 18%-34% 
               
               
                   
                 Three 
                 10%-20% 
               
               
                   
                 Four 
                 2%-8% 
               
               
                   
                   
               
             
          
         
       
     
     The preferred target for operation for each component is: 
     
       
         
               
               
               
             
           
               
                   
                   
               
               
                   
                 Component 
                 Range 
               
               
                   
                   
               
             
             
               
                   
                 One 
                 65% 
               
               
                   
                 Two 
                 20% 
               
               
                   
                 Three 
                 10% 
               
               
                   
                 Four 
                  5% 
               
               
                   
                   
               
             
          
         
       
     
     Another example of a target composition for the four components is: 
     
       
         
               
               
               
             
           
               
                   
                   
               
               
                   
                 Component 
                 Amount 
               
               
                   
                   
               
             
             
               
                   
                 One 
                 70% 
               
               
                   
                 Two 
                 15% 
               
               
                   
                 Three 
                 12% 
               
               
                   
                 Four 
                  3% 
               
               
                   
                   
               
             
          
         
       
     
     Still another example of a target composition is: 
     
       
         
               
               
               
             
           
               
                   
                   
               
               
                   
                 Component 
                 Amount 
               
               
                   
                   
               
             
             
               
                   
                 One 
                 60% 
               
               
                   
                 Two 
                 25% 
               
               
                   
                 Three 
                 10% 
               
               
                   
                 Four 
                  5% 
               
               
                   
                   
               
             
          
         
       
     
     Still another example is: 
     
       
         
               
               
               
             
           
               
                   
                   
               
               
                   
                 Component 
                 Amount 
               
               
                   
                   
               
             
             
               
                   
                 One 
                 55% 
               
               
                   
                 Two 
                 20% 
               
               
                   
                 Three 
                 20% 
               
               
                   
                 Four 
                  5% 
               
               
                   
                   
               
             
          
         
       
     
     The paint mixture requires a three part blending process prior to application to the tip  20 . First, components three and four are mixed together forming a first pre-mix. Second, components one and two are mixed together forming a second pre-mix. Shortly thereafter, the first pre-mix is blended with the second pre-mix over a two to five minute period under medium speed agitation forming the paint mixture. 
     Referring to FIG. 2, an applicator  26  for applying the coating  24  is shown. The applicator  26  includes an infeed line  28  leading from an application tank (not shown). The applicator has a hole through  30  which is formed in a flat base  32 . The applicator  26  preferably has a closed cylindrical configuration with the hole  30  disposed at the opposite end of the infeed line  28 . 
     During application, the paint mixture is loaded into the application tank and maintained under agitation. A plurality of paint lines  28  lead from the application tank. 
     Each paint line  28  connects with a corresponding applicator  28  having a hole  30  through a flat base  32 . While under pressure, the paint mixture is forced through the hole  30  which is in close proximity to the tip  20  forming a bubble on the tip  20 . Prior to application, the tips  20  are cleaned via a solvent wipe. A plurality of fasteners  10  are held in a processing fixture (not shown) during paint application. 
     After application, the processing fixture is installed into a preheated oven for curing the paint and forming the bubble shaped coating  24 . The oven curing cycle ranges from two hours at 450 degrees Fahrenheit to eight hours at 300 degrees Fahrenheit. While in the oven, the paint bubble cures into the parabolic shape of the coating  24 . A higher oven temperature will yield a harder coating  24 . The preferred oven curing cycle associated with the preferred range of operation includes oven curing for four hours at 425 degrees Fahrenheit. 
     The invention has been described in an illustrative manner, and it is to be understood that the terminology which has been used is intended to be in the nature of words of description rather than of limitation. Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.