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  Sheet molding compound having improved surface characteristicsUSPTO Application #: 20060219346Title: Sheet molding compound having improved surface characteristics Abstract: A composite part made from a sheet molding compound is disclosed as having improved characteristics over traditional sheet molding compound composite parts. The composite part may be made from a unique sheet molding compound material having a resin impregnated filamentized fiber layer and a resin impregnated fiber layer prior to compaction. The resin impregnated filamentized fiber layer side prevents the movement of partially filamentized or unfilamentized fibers to the visible surface of the composite part when the part is molded. The resin impregnated filamentized fiber layer may be contain a conductive filamentized fiber such that the surface of a sheet molding compound may be conductive and be capable of being electrostatically sprayed. (end of abstract) Agent: Owens Corning - Granville, OH, US Inventor: Michael H. Jander USPTO Applicaton #: 20060219346 - Class: 156062200 (USPTO) Related Patent Categories: Adhesive Bonding And Miscellaneous Chemical Manufacture, Methods, Surface Bonding And/or Assembly Therefor, With Formation Of Lamina By Bulk Deposition Of Discrete Particles To Form Self-supporting Article The Patent Description & Claims data below is from USPTO Patent Application 20060219346. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS-REFERENCE TO RELATED APPLICATIONS [0001] The present invention claims priority from Provisional Application Ser. No. 60/328,860 entitled "Sheet Molding Compound Having Improved Characteristics, filed Oct. 12, 2001, which is incorporated herein by reference. TECHNICAL FIELD AND INDUSTRIAL APPLICABILITY OF THE INVENTION [0002] The present invention relates generally to reinforced fiber composites and more specifically to sheet molding compounds having improved conductive and/or surface characteristics. BACKGROUND OF THE INVENTION [0003] In the manufacture of fiber reinforced resin products, sheet molding compounds are frequently used. Sheet molding compounds offer an appealing solution for the production of Class A surface parts compared to steel both in terms of cost and coefficients of thermal expansion. [0004] Sheet molding compounds consist of a mixture of a liquid thermosetting resin, particulate filler and chopped reinforcement fibers, such as glass fibers. In most cases, the resin and chopped fibers are sandwiched between films of plastic material to form a laminated sheet that is wound in rolled form or festooned for storage. The laminated sheet is stored under conditions that will not result in final curing of the resin, but will allow the paste to thicken to a desired molding viscosity range, typically between 30,000 and 50,000 centipoise (MilliPascal seconds). At the time of use, the protective carrier film is removed and the laminated sheet is cut into blanks, or plies, of a desired shape and size. The plies are then molded to form a cured composite part. In most applications, multiple plies of the laminated sheets are used in the composite structure and typically comprise between 25 and 50% of the die/tool's surface area. When the laminated sheets are molded, the resin and glass flow within the mold under heat and pressure to cover the entire surface of the mold. Sheet molding compounds are used in a variety of applications that require aesthetic appeal, corrosion resistance, lighter weight dimensional control and high strength. [0005] One deficiency with currently available sheet molding compounds is that the charge typically does not form a Class A type surface parts when cured. This is due to the fact that the chopped fibers move to the surface of the sheet molding compound to form surface imperfections. Further, the fiber used in some sheet molding compounds typically does not flow well in the mold, and this creates surface imperfections such as surface pores. Thus, sheet molding compounds require sanding and polishing, or otherwise reworking to be used in applications requiring a desired surface appearance. [0006] Yet another problem with surface characteristics occurs when these composite parts formed from the sheet molding plies are painted. Paint pops may be caused by the release of volatile liquids (such as water, styrene or di-vinyl benzene monomer) from the sheet molding paste or by the release of moisture or solvents contained within fiber bundles during the curing process are quite common, typically affecting 5-10% or more of painted SMC composite parts. This leads to substantial cost in terms of rework and waste. [0007] In addition, to allow a long and uniform flow that will produce a wavefree surface, the fibers used in sheet molding compounds are typically provided by the glass manufacturer as bundles or "splits" of multiple filaments. The act of impregnating the bed of chopped fibers between two layers of sheet molding compound paste often leaves air trapped within the composite sheet, most often besides the bundles where small differences in surface tension adversely affects the wetting of the bundles or splits. Unfortunately, this bundling may also include entrapped air which, when released during the flow, produces tiny bubbles which travel slowly under a pressure gradient. To evacuate these bubbles, it is useful to have the molding compound flow to fill out the tool to allow the action of the pressure gradients to move those air bubbles towards the edge of the flow front and thus towards the edge of the part. Such large flow typically calls for loading the tool by a charge representing 50% or less of the area of the part [0008] It is therefore highly desirable to improve the surface characteristics of sheet molding compound. This would allow sheet molding compound parts to be used in a wider variety of composite applications wherein surface quality is a concern. SUMMARY OF THE INVENTION [0009] It is thus an object of the present invention to improve the physical and surface characteristics and electrostatic sprayability of composites parts made of sheet molding compound composite sheets. [0010] The present invention addresses the above object and comprises a composite part may be made from a unique sheet molding compound composite sheet having a thin resin surface layer, a resin impregnated filamentized fiber layer, a resin impregnated unfilamentized or partially filamentized fiber layer, and a second resin paste layer. The resin impregnated filamentized fiber layer side acts as a barrier to prevent the movement of partially filamentized or unfilamentized fibers into the thin resin surface layer of the composite part when the part is compacted, molded and cured. This presents a visible surface that is resin rich and porous free, which is shown to improve surface characteristics of the composite part without adversely affecting strength and stiffness characteristics. [0011] Other objects and advantages of the present invention will become apparent upon considering the following detailed description and appended claims, and upon reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS [0012] FIG. 1A is a cross-sectional view of a sheet molding compound having improved surface characteristics according to one preferred embodiment of the present invention; [0013] FIG. 1B is a cross-sectional view of a prior art sheet molding compound; [0014] FIG. 2A is a schematic diagram for making the sheet molding compound of FIGS. 1A and 1B; [0015] FIG. 2B is an alternate schematic diagram for making the sheet molding compound of FIGS. 1A and 1B; [0016] FIG. 2C is a close-up view of the funnel shaped dispensing device of FIG. 2B; [0017] FIG. 2D is an enlarged partial cross sectional view of the funnel shaped dispensing device shown in FIG. 2B. DETAILED DESCRIPTION AND PREFERRED EMBODIMENTS OF THE INVENTION [0018] Referring now to FIG. 1A, a sheet molding compound made in accordance with a preferred embodiment of the present invention is generally shown as 10 prior to compaction. The sheet molding composite (SMC) sheet 10, from top to bottom, is shown having an upper carrier film layer 12, a top resin paste layer 14, a resin impregnated unfilamentized or partially filamentized fiber layer 16, a resin impregnated filamentized fiber layer 18 (including paste 18' and filamentized fibers 57) and a bottom carrier film layer 20. Of course, the order of the layering from top to bottom for a finished composite part made from this sheet molding compound is reversed, as the resin impregnated filamentized fiber layer 18 forms the class A surface side desired when the SMC sheet 10 is made into a finished part. The process for forming the SMC sheet 10 of FIG. 1A is shown below in FIGS. 2A and 2B. Additionally, the cross-section of FIG. 1B maybe made using this device, provided the paste 18' does not include filamentized fibers 57, and therefore the shown bottom layer 13 of FIG. 1B does not include these fibers as does the layer of paste 18 of FIG. 1A (one skilled in the art appreciates that the layer of paste 18 (and the paste 18') in the remaining figures could be replaced by a nonfilamentized paste, or layer of nonfilamentized paste 13, where appropriate). Continue reading... Full patent description for Sheet molding compound having improved surface characteristics Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Sheet molding compound having improved surface characteristics patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. 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