Abstract:
A method for finishing a repaired surface is described. The method includes wiping a sealer on the repaired surface to seal microporosity in the repaired surface, the sealer consisting essentially of a mixture of polymer, at least one filler, solvent, and optionally microspheres; and applying a top coat to the sealed surface without sanding the sealed surface, the top coat being free of visible pinholes. Sealers and tools for applying surface sealers are also described.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates generally to smoothing composite surfaces, such as repaired surfaces. 
     When a plastic part, such as an automobile panel, is repaired, a material, such as unsaturated polyester resins, primers, fillers, adhesives, or putties, is used to resurface and reshape the damaged areas. The repaired composite material is sanded to obtain a smooth surface. However, sanding creates small imperfections and pinholes in the surface which are visible when a top coat is applied. These pinholes must be sealed before the top coat is applied. The top coat is typically a multilayer coating including a primer, base coat/color, and a clearcoat. 
     Conventional methods of sealing the pinholes involve several steps and are very time consuming. For example, in one method, a liquid or paste sealer is dispensed onto an applicator, such as a squeegee or a spreader knife. The applicator is then used to wipe the sealer onto the porous surface. This method usually results in an excess film build of the sealer which must be removed before the next step in the process. The excess material is removed by wiping and sanding the residue. 
     Therefore, there is a need for improved sealers, tools for applying sealers, and methods of repairing pinholes and imperfections in composite materials. 
     SUMMARY OF THE INVENTION 
     The present invention meets this need. One aspect of the invention involves a method for finishing a repaired surface. In one embodiment, the method includes wiping a sealer on the repaired surface to seal microporosity in the repaired surface, the sealer consisting essentially of a mixture of about 10 to about 30 wt % polymer, about 10 to about 55 wt % of at least one filler, about 5 to about 30 wt % microspheres, and about 25 to about 45 wt % solvent; and applying a top coat to the sealed surface without sanding the sealed surface, the top coat being free of visible pinholes. 
     Another aspect of the invention involves a sealer for sealing a repaired surface. In one embodiment, the sealer consists essentially of about 10 to about 30 wt % polymer; about 10 to about 55 wt % of at least one filler; about 5 to about 30 wt % microspheres; and about 20 to about 45 wt % solvent. 
     Another aspect of the invention relates to a tool for applying a surface sealer. In one embodiment, the tool includes an applicator impregnated with a dry sealer for sealing microporosity on a surface, the dry sealer consisting essentially of a mixture of a polymer, at least one filler, and optionally microspheres, the dry sealer being dissolvable in a solvent. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A sealer is applied to a repaired surface to seal microporosity in the repaired surface. The sealer typically includes about 10 to about 30 wt % polymer, about 10 to about 55 wt % of at least one filler, 0 to about 30 wt % microspheres, and about 20 to about 45 wt % solvent. The sealer can be applied without excess material being deposited. Therefore, there is no need to sand the surface before applying the top coat. The top coat typically includes a primer, a base coat/color, and a clear coat, although other types of top coats could also be used. 
     Suitable polymers include, but are not limited to, cellulose polymers, such as nitrocellulose polymers and cellulose acetate butyrate, acrylic polymers (including methacrylic polymers) polyester polymers, urethane polymers, and epoxies, and combinations thereof. The polymer is generally present in an amount of about 10 to about 30 wt %, or about 15 to about 30 wt %, or about 20 to about 30 wt %, or about 15 to about 25 wt %. 
     The polymer composition includes one or more fillers. Suitable fillers include, but are not limited to, talc, titanium dioxide, clay, calcium carbonate, silica, and the like. The filler is generally present in an amount of about 10 to about 55 wt %, or about 10 to about 35 wt %, or about 10 to about 25 wt %, or about 10 to about 20, or about 10 to about 15 wt %. 
     Microspheres can optionally be included, if desired. It is believed that microspheres fill pin holes more efficiently than other types of fillers because of their larger size (particle size range 5-200 microns). With a composition using only other types of fillers (typical particle size 2-15 microns), the application may need to be repeated several times to fill larger pin holes because of the small size of the filler, while a composition including microspheres may only require one pass. Microspheres are generally present in an amount of 0 to about 30 wt %, or about 5 to about 30 wt %, or about 10 to about 30 wt %, or about 15 to about 30 wt %, or about 20 to about 30 wt %. 
     The appropriate solvent will depend on the polymer used. For example, acetone can be used with acrylic polymers, nitrocellulose polymers, polyesters, epoxies, and urethanes. Suitable solvents include, but are not limited to, acetone, xylene, ethylene glycol monobutyl ether, methoxy propyl acetate, isopropyl alcohol, isobutyl acetate, toluene, dimethyl carbonate, or combinations thereof. The solvent is generally present in an amount of about 20 to about 40 wt %, or about 25 to about 40 wt %, or about 30 to about 40 wt %. 
     The composition can include small amounts of other materials typically used, such as dispersants, stabilizers, colorants, and the like. 
     In one embodiment, an applicator is impregnated by dispensing the sealer in liquid form onto the applicator at the time of use. The wet applicator is then used to wipe the material onto the surface to fill in the pinholes and microporosity. The sealer does not leave a residue that interferes with the top coat adhesion and surface profile. 
     In another embodiment, the sealer is applied to the applicator, which is then dried, leaving the solids of the composition impregnated in the applicator. The applicator can be manufactured and sold with the dry sealer impregnated for ease of use. Suitable polymers for this embodiment are any polymers which can change from a liquid state to a solid state and act as a sealer. The polymers discussed above are suitable for this embodiment as well. 
     In this embodiment, the polymer composition remains solid until the applicator is wetted with a solvent. The solvent causes the sealer to become soluble, allowing the polymer, filler, and optional micro spheres to transfer onto the porous surface with hand pressure and a wiping motion in order to fill the microporosity. The applicator picks up the excess residue at the same time, eliminating the need to sand the surface or remove the excess material in a separate step. The excess residue dries in the applicator tool and can be reused in a later application. The solvent used to wet the applicator can be the same solvent used in making the sealer, or it can be different. 
     The applicator should be absorbent to allow for impregnation. It should also be solvent resistant to maintain its physical integrity during the life of the product. Suitable materials for the applicator tool include, but are not limited to, foams and absorbent toweling. Suitable foams include, but are not limited to open cell polyurethane foams. 
     EXAMPLE 1 
     Resin and fillers were mixed with acetone as the solvent in the quantities indicated in Table 1. Foam material was placed in the dispersion and impregnated with the mixture. The impregnated foam was dried at 50C until all of the solvent was evaporated, typically about 2-3 hrs. Before use, the applicator with the dry sealer was wetted out with acetone to dissolve the polymer and other materials and allow it to flow from the foam to the treated surface and fill the pin holes. 
     
       
         
               
               
             
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
             
             
               
                   
                   
               
               
                   
                 Component 
               
             
          
           
               
                   
                 A 
                 B 
                 C 
                 D 
                 E 
                 F 
                 G 
               
               
                   
                   
               
             
          
           
               
                 Polyester (Epotuf 91-314) 
                 10 
                 20 
                 30 
                   
                   
                   
                   
               
               
                 Epoxy (Epotuf 38-505) 
                   
                   
                   
                 10 
               
               
                 Acrylic (Paraloid B-84) 
                   
                   
                   
                   
                 10 
                 20 
               
               
                 Unsaturated polyester 
                   
                   
                   
                   
                   
                   
                 10 
               
               
                 (Fine-Clad M-8100) 
               
               
                 Talc (Nicron 554) 
                 25 
                 20 
                 10 
                 25 
                 25 
                 20 
                 25 
               
               
                 Calcium carbonate 
                 30 
                 20 
                 15 
                 30 
                 30 
                 20 
                 30 
               
               
                 (Camel White) 
               
               
                 Acetone 
                 35 
                 40 
                 45 
                 35 
                 35 
                 40 
                 35 
               
               
                   
               
             
          
         
       
     
     EXAMPLES 2 and 3 
     The resin, fillers, and microspheres were mixed with solvent as indicated in Tables 2 and 3. The liquid high solids polymer composition was then applied to the applicator. 
     
       
         
               
               
             
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                   
                 TABLE 2 
               
             
             
               
                   
                   
               
               
                   
                 Component 
               
             
          
           
               
                   
                 A 
                 B 
                 C 
                 D 
                 E 
                 F 
               
               
                   
                   
               
             
          
           
               
                 Polyester resin 
                 10 
                 20 
                 20 
                 20 
                 20 
                 25 
               
               
                 (Epotuf D808-XD-71) 
               
               
                 Solvent (Xylene) 
                 15 
                 12 
                 9 
                 9 
                 5 
                 6 
               
               
                 Solvent (Ethylene glycol 
                 3 
                 3 
                   
                   
                 7 
                 8 
               
               
                 monobutyl ether) 
               
               
                 Solvent 
                   
                   
                   
                   
                   
                 7 
               
               
                 (Methoxy propyl acetate) 
               
               
                 Solvent (Isopropyl alcohol) 
                 4 
                 3 
                 4 
                 4 
               
               
                 Dispersant (BYK 410) 
                   
                   
                   
                   
                   
                 0.8 
               
               
                 Resin/solvent (CAB 
                   
                   
                 18 
                   
                 18 
               
               
                 (Cellulose Acetate Butyrate) 
               
               
                 30% solution in 
               
               
                 methoxy propyl acetate 
               
               
                 Resin/solvent (CAB 30% 
                 18 
                 18 
                   
                 18 
               
               
                 solution in isobutyl acetate) 
               
               
                 Talc (Nicron 554) 
                 24.7 
                 22.7 
                 24.7 
                 21.7 
                 20 
                 21.2 
               
               
                 Calcium carbonate 
                 25 
                 21 
                 20 
                 20 
                 22.7 
                 24.7 
               
               
                 (Camel White) 
               
               
                 Microspheres (PQ 7040S) 
                   
                   
                   
                 5 
                 4 
                 4 
               
               
                 Microspheres (S 22) 
                   
                   
                 3 
                 2 
                 3 
                 3 
               
               
                 Colorant (Black iron oxide) 
                 0.3 
                 0.3 
                 0.3 
                 0.3 
                 0.3 
                 0.3 
               
               
                   
               
             
          
         
       
     
     
       
         
               
               
             
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                   
                 TABLE 3 
               
             
             
               
                   
                   
               
               
                   
                 Component 
               
             
          
           
               
                   
                 A 
                 B 
                 C 
                 D 
                 E 
                 F 
               
               
                   
                   
               
             
          
           
               
                 Polyester resin 
                 20 
                 18 
                 20 
                 20 
                 20 
                 20 
               
               
                 (Epotuf D808-XD-71) 
               
               
                 Solvent (Xylene) 
                 9.5 
                 6 
                 9.8 
                 9.8 
                 8 
                 6.5 
               
               
                 Solvent (Ethylene glycol 
                 6 
                 6 
                 8 
                 8 
                 8 
                 6 
               
               
                 butyl ether) 
               
               
                 Solvent (Methoxy propyl 
                 2 
                 6 
                 7.5 
                 7.5 
                 7.5 
                 7 
               
               
                 acetate) 
               
               
                 Resin/solvent (CAB 30% 
                 19 
                 18 
                 19 
                 20 
                 19 
                 19 
               
               
                 solution in methoxy 
               
               
                 propyl acetate) 
               
               
                 Silica (Aerosil 200) 
                 1.8 
                   
                 1.2 
                 1.2 
                 1.2 
                 1.2 
               
               
                 Talc (Nicron 554) 
                 24 
                 16.1 
                 10 
                 14 
                 10 
                 10 
               
               
                 Calcium carbonate 
                 17.4 
                 18.5 
               
               
                 (Camel White) 
               
               
                 Microspheres (PQ 
                   
                 6.5 
                 24 
                 11 
               
               
                 7040S) 
               
               
                 Microspheres (25P45) 
                   
                 4.6 
                   
                 8 
               
               
                 Microspheres 
                   
                   
                   
                   
                 26 
                 30 
               
               
                 (Extendospheres TG) 
               
               
                 Colorant (Black iron 
                 0.3 
                 0.3 
                 0.5 
                 0.5 
                 0.3 
                 0.3 
               
               
                 oxide) 
               
               
                 Viscosity B@ 5 rpm 
                  26K 
                   6K 
                 4.4K 
                   6K 
                   4K 
                 5.2K 
               
               
                 viscosity B@ 50 rpm 
                 5.4K 
                 2.5K 
                 1.5K 
                 1.8K 
                 1.2K 
                 1.8K 
               
               
                 TI 
                 4.8 
                 2.4 
                 2.9 
                 3.3 
                 3.3 
                 2.9 
               
               
                   
               
             
          
         
       
     
     The surface to be repaired was treated by applying the applicator in a wiping motion on one half and the other half is left untreated for comparison. 
     Repairs of surfaces exhibiting pinholes and microporosity were made using the sealers shown in Tables 1-3. Several one square foot areas were repaired. Each repair had pinholes created naturally and also some created artificially for control purposes. The sealer was used/applied to one half of the repair panel(s). Top coats (acrylic urethane primer, polyester base coat/color, and polyurethane clearcoat) were applied over the sealer using standard automotive spray equipment and processes. After top coat application, pinholes were visible in the un-treated area. Pinholes where not visible where the sealer was applied. 
     Compositions C-F (containing microspheres) in Table 2 had improved results compared to Compositions A-B (without microspheres). 
     Based on the results of Example 2, the amount of microspheres was increased for the compositions in Table 3. Composition A in Table 3 required at least three applications, and the surface had to be cleaned with a solvent. Compositions B-F displayed good application, and no solvent wipe was required to remove excess sealer. 
     Having described the invention in detail and by reference to specific embodiments thereof, it will be apparent that modifications and variations are possible without departing from the scope of the invention defined in the appended claims. More specifically, although some aspects of the present invention are identified herein as preferred or particularly advantageous, it is contemplated that the present invention is not necessarily limited to these preferred aspects of the invention.