WO1997034708A1

WO1997034708A1 - Powder-coated plastic parts and method

Info

Publication number: WO1997034708A1
Application number: PCT/US1997/003970
Authority: WO
Inventors: Scott J. Balogh; Steven W. Balogh; Shenghe Lin
Original assignee: Mar-Bal, Inc.
Priority date: 1996-03-19
Filing date: 1997-03-13
Publication date: 1997-09-25
Also published as: AU2323797A

Abstract

A process is provided for producing a powder-coated plastic part. The process comprises providing a molded plastic substrate, depositing an essentially solventless powder onto at least a portion of a surface of the substrate, and melting and fusing the powder to form a coating. Preferably, the substrate is electrically conductive and the powder is electrostatically deposited onto the surface of the substrate. An appliance such as a kitchen range may be provided having powder-coated plastic parts and matching powder-coated metal parts, the same powder coating powder being used to coat both the plastic and the metal parts.

Description

POWDER-COATED PLASTIC PARTS AND METHOD

BACKGROUND OF THE INVENTION

The invention relates generally to coated plastic parts and more particularly to powder-coated plastic parts and a method of powder-coating plastic parts.

DESCRIPTION OF RELATED ART

It is known to mold plastic articles, such as thermoset plastic articles, for many uses, such as parts for appliances. These parts are typically of an integral material; that is, the material at the surface is substantially the same material and has substantially the same physical properties as the material in the middle. This leads to problems when specific properties are desired for the surface which are not provided by the integral material. For example, high temperature color stability may be desired for the surface, yet some internal mold release agents in the material cause the surface to yellow and/or color- shift at high temperature and the base material itself may have poor high temperature stability. High pigment loading may be desired for bright or stable surface color, yet high pigment loading of certain pigments in the base resin leads to excessive abrasiveness damaging to mixing equipment, processing machinery and molds and metal contamination from abraded metal particles can cause color shifts. Also, the extensive use of pigment to color the interior of the part is wasteful and hazardous to the environment to the extent pigments containing hazardous materials are used. Surface chemical resistance may not be economically achievable relying only on the properties of the integral material. Surface coating of plastic parts to address these problems is known, but these techniques generally rely on water or organic solvent as a carrier to carry the coating material to the surface and then volatilize, leading to environmental air quality problems and frequently failing to deposit an effective coating on the surface. There is a need for a method to more effectively coat plastic parts, yielding plastic parts with surface coatings having improved physical properties and which match adjacent powder-coated metal parts in an appliance.

SUMMARY OF THE INVENTION

A process is provided for producing a plastic-coated plastic part. The process comprises providing a molded plastic substrate, depositing an essentially solventless powder onto at least a portion of a surface of said substrate, and melting and fusing said powder to form a coating.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an elevational view of the back side of an oven door handle. FIG. 2 is a bottom view of the handle of FIG. 1. FIG. 3 is a front elevational view of a top trim piece for an oven door. FIG. 4 is a bottom view of the piece of FIG. 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

Percents are weight percent unless otherwise indicated or the context indicates otherwise. The plastic substrate is preferably a conductive, filled, glass fiber-reinforced, thermoset polyester plastic or resin. The preferred formulation is given in Table 1. TABLE 1 Less Even Less PreferredPreferredPreferredPreferred Weight Weight Weight Weight Component (lbs) Percent % Range % Range A. MR642 104 13.175 10-30 5-90 B. MR9600 10 1.267 0-5 0-50 C. NEULON T-Plus 56 7.094 3-15 1-20 D. TBIC-M75 Peroxide Catalyst 2 0.253 0.1-0.5 0.05-2 E. Styrene 2 0.253 0-2 0-4 F. Calcium stearate 6.4 0.811 0.7-1.5 0.6-3 G. Conductive carbon black 4 0.507 0.2-2 0.1-5 H. calcium carbonate filler 500 63.339 40-70 10-90 I. 1/4" chopped fiber glass 50 6.334 5-25 0-60 J. 1/2" chopped fiber glass 55 6.967 5-28 0-66 Component A is available from Ashland Chemical Co. as Prod. MR642 and is an unsaturated polyester resin having 75-80% unsaturated polyester resin (solids) and 20-25% vinyl toluene (a crosslinking monomer) . Component B is available from Ashland Chemical Co. as Prod. MR9600 and is an unsaturated polyester resin having 63-67% unsaturated polyester resin and 35% styrene (a crosslinking monomer) . It adds flexibility and crack resistance. Component C is available from Union Carbide as NEULON Polyester Modifier T-Plus and it has more than 20% polyvinyl acetate copolymer (typically 20 to 30%), more than 5% ester, epoxide, less than 60% styrene (typically 50 to 60%) , and less than 4% vinyl acetate (typically 1 to 4%) . It is a thermoplastic additive to control shrinkage and reduce cracking and is also a low profile additive. Component D is an organic peroxide initiator available from Elf Atochem as Lupersol TBIC-M75 and is 75% t-butyl peroxy isopropyl carbonate and 25% odorless mineral spirits. It is a high efficiency catalyst which leaves a minimum of residual free styrene and which is FDA approved for indirect food contact or indirect food additive. Preferably Component D is present at less than 0.4, more preferably less than 0.3, weight % of the formulation. Component E is styrene monomer, a crosslinking monomer. Component F is available from Witco as calcium stearate F (fine particle) , an internal mold release agent. Component G is available from Akzo Chemicals as Ketjenblack EC-600JD carbon black and makes the composition electrically conductive. Less preferably the formulation of Table 1 may be made nonconductive by eliminating Component G and slightly reducing Components A, C, D and F. Component H is available from ECC International, Sylacauga, AL as Snowflake P.E. and is a powder filler. Components I and J are available from PPG, Owens Corning, and Vetrotex Certainteed as chopped strand continuous filament fiber glass and is a reinforcing agent. This formulation is considered a bulk molding compound and is particularly suited for injection molding relatively long flow (15-30 inch) parts about 1/8 to 1 inch thick. Adjustments for other dimensions may be made as known in the art. This formulation is intended to release a minimum of gaε when heated during the coating process (specifically the bake cycle) to minimize bubbles which blemish the coating. Thus a minimum of catalyst is used, and no inhibitor is added other than the inhibitor put into the base resins by the manufacturer. The plastic substrate preferably uses as a base resin an unsaturated polyester resin, such as Components A and B above, less preferably the unsaturated polyester resins as known in the art for use in bulk, sheet, thick, and granular molding compounds. Less preferably an unsaturated vinylester resin may be used. The crosslinking monomers to be used may be any known in the art (such as styrene and vinyl toluene mentioned above and, less preferably, divinyl benzene, methyl methacrylate, hydroxypropyl acrylate, and other crosslinking agents for unsaturated polyester resins known in the art) . For Component C one may substitute in descending order of preferability other thermoplastic additives as follows: polyvinyl acetate, polymethyl methacrylate, polystyrene and copolymers, thermoplastic polyesters, KRATON thermoplastic elastomers, cellulose acetate and butyrate, polyethylene powder and polypropylene powder, polyvinyl chloride and copolymers, and polycaprolactone. These should be added in effective amounts to control shrinkage, reduce cracking, and act as a low profile additive. The formulation preferably contains at least 5, more preferably at least 7, weight % Component C; this thermoplastic additive has much reduced out-gassing compared with other thermoplastic additives; it causes nonuniform appearance (ie, mottling, streaking) but the part is then coated. For Component D one may substitute other peroxides or other initiators known in the art (e.g., azo compoundε and substituted dibenzyl compounds) in effective amounts for initiating the crosslinking reaction in the polyester resin system, but preferred are high efficiency catalysts which leave a minimum of residual free styrene and which are FDA approved for indirect food additive or indirect food contact. For Component E one may substitute other crosslinking monomers (as referenced in the preceding paragraph) in effective amounts to carry the initiator into the reaction system and to assist in the crosslinking. For Component F one may less preferably substitute metal or non-metal stearates such as zinc stearate and lithium stearate, other internal mold release agents known in the art, or one may use external mold release agents in the manner known in the art. The amount of internal mold release agent should be minimized so that adhesion of the coating to the substrate surface will, be maximized. The formulation of Table 1 preferably contains less than 0.85 or 0.80 weight % Component F. For Component G one may substitute in effective amounts to make the composition electrically conductive other electrical conductivity additives such as conductive carbon blacks, nickel-coated carbon fibers, and possibly other materials such as metal fibers or metal powders such as zinc, copper or iron. For Component H one may substitute other fillers such as other grades of CaC0₃, alumina trihydrate, calcium sulfate, clay, talc, glass, mica, barium sulfate, magnesium hydroxide, or other fillers known in the art. For Components I and J one may substitute (in size lengths known in the art and in effective reinforcing amounts) graphite fibers, carbon fibers, KEVLAR fibers, mineral reinforcing agents such as Franklin Fiber H30 from U.S. Gypsum (hemihydrate calcium sulfate) , wollastonite, organic fibers such as polyester or nylon fibers, and other reinforcing agents known in the art. In Table 1 Components A, B, C and E make up the resin or resin system of the formulation, and the resin or resin system is preferably 10-90 weight %, more preferably 14-40 weight %, of the formulation. The chopped fiber glass or other reinforcing fiber or reinforcing agent is preferably 0-60%, more preferably 5-25%, of the formulation. The filler is preferably 10-90%, more preferably 40-70%, of the formulation. The formulation of Table 1 is preferably combined in a double arm water-jacketed mixer or other mixing equipment known in the art as follows. Components A-H, plus l/ll of Component J, are typically mixed for about 20 min. or until the putty temperature reaches 85-95°F and until the composition is well blended and the powder is wetted out, then add the remaining components and mix for about 10 min. until the temperature reaches 95-105°F or until the glass fibers are fully dispersed. Then let the material rest for 2-3 days to fully wet out. The composition is then molded to form a plastic substrate. In a less preferred embodiment, the formulation of Table 1 is made nonconductive, this being achieved by modifying that formulation by reducing Component A from 104 to 98 lbs, reducing Component C from 56 to 54 pounds, reducing Component D from 2 to 1.9 lbs, reducing Component F from 6.4 to 6.2 lbs, and eliminating Component G. To this nonconductive formulation may be optionally added an antistatic agent as known in the art to facilitate coating. In substitution for the formulation of Table 1, one may use, in descending order of preferability, other bulk molding compounds, sheet molding compounds, pultrusion resins (to form pultrusion shapes using the pultrusion process) , thick molding compounds, and granular molding compounds, all as known in the art. The plastic substrate described above as a polyester thermoset may less preferably be other thermoset materials including polyamides, phenolics, epoxies, diallyl phthalate, melamine, ureas, and alkyds. Preferably these are able, after they are thermoset, to withstand without substantial deterioration 220°F, more preferably 250°F, more preferably 300°F, more preferably 350°F, more preferably 365°F, more preferably 380°F, more preferably 400°F, more preferably 430°F, more preferably 450°F, more preferably 500°F, such as encountered in the subsequent powder-coating procedure described hereinafter and for the time periods of such procedures. The plastic substrate may less preferably be thermoplastic materials including nylons, polyamides, polypropylene, ABS (acrylonitrile- butadiene-styrene) , polycarbonate, thermoplastic polyesters (including polybutylene terephthalate and polyethylene terephthalate) , polyethylene (including LDPE and HDPE) , polyphenylene sulfide, polyphthalamide, polystrene, and polyvinyl chloride. Preferably these are able, after they are molded, to withstand without deforming 200°F, more preferably 225°F, more preferably 250°F, more preferably 300°F, more preferably 350°F, more preferably 365°F, more preferably 380°F, more preferably 400°F, for time periods such as encountered in the subsequent powder-coating procedure. Additives as known in the art and./or as described above may be added to these base resins, such as fillers, reinforcing agents, mold release agents, electrical- conductivity aids, plasticizers, thermoplastic additives, etc. The plastic substrate is molded as known in the art for that particular plastic. With respect to the thermoset formulation of Table 1, the plastic substrate is molded as bulk molding compound is molded as is known in the art and also generally as follows. For injection molding, temperatures are preferably as follows: mold (cavity) - 220-400°F, preferably 310-330°F; mold (water-cooled manifold) - 90-240°F, preferably 120-140°F; in the mold (water-cooled nozzle/sprue bushing) - 90-240°F, preferably 120-140°F; barrel and nozzle of injection unit - 60-220°F, preferably 90-140°F. The injection pressures are preferably: clamp-varies depending on part configuration, 500 tons typical; boost (high pressure) - 400-2800 psi, preferably 900-1300 psi; hold (low pressure) - 200-2800 psi, preferably 400-1300, more preferably 600-1000, psi; back pressure - 0-300 psi, preferably 50-250 psi. The amount of time to open the clamp and to close the clamp is 0.1-120 sec, preferably 1-7 sec. The boost (high pressure) time is 0.1-25 sec, preferably 1-5 sec. The hold (low pressure) time is 0-200 sec, preferably 0.5-5 sec The cure time is 0.1-3600 sec, preferably 5-180 sec. Other molding and casting techniques as known in the art may be used, including compression and transfer molding. For compression molding, the mold (cavity) temperature, the clamp pressure, the clamp open and clamp close times, and cure time are the same as for injection molding, and the material loading time is 0.1-120 sec, preferably 2-20 sec. For transfer molding, the mold (cavity) temperature, the clamp open and clamp close times, and cure time are the same as for injection molding, the clamp pressure is typically 100-500 tons, the ram pressure(s) are 100-2200 psi, preferably 700-1100 psi, and the ram pressure time is 0.1-20 sec. , preferably 1-7 sec The molded plastic substrate is preferably rigid, free of voids (internal and external) , has a smooth surface finish, is free of cured material being forced through the mold, and is free of material buildup in the mold or on the surface of the part. The molded plastic substrate is powder-coated to produce the finished plastic-coated plastic part. In the powder coating process there is deposited an essentially solventless powder on a substrate, the powder then being melted and fused into a coating, such as a protective coating. The powder-coating process is preferably one of the well-known powder-coating processes to powder-coat metal parts; see U.S. Pats. 5,368,885; 4,315,845; 4,135,009; 4,436,890; 5,280,098; and 4,129,545 and Kirk-Othmer, Concise Encyclopedia of Chemical Technology (1985) pp. 944-5 (and the references cited therein) , the contents of all of which are incorporated by reference in their entirety. The powder is dry, particulate matter; the particles do not stick to each other. The electrically-conductive molded plastic substrate of the formulation of Table 1 is preferably powder-coated generally according to the electrostatic-spray powder-coating process, which is known in the art and is a process the steps of which occur at atmospheric pressure. The substrate is provided such as by placing it in an oven or in a spray booth. The part or substrate is preheated or heated so that the part, at the time of spraying, is 350-450°F, more preferably 375-425°F. The part is preferably maintained at about 380-450°F, more preferably 410- 420°F, for about 20 min. (preferably at least 5, more preferably at least 10, more preferably at least 20, minutes) before spraying, which is generally an effective amount of time to drive out gasses from the part or substantially all materials which could come out as gasses during the subsequent process steps and interfere therewith, such as coming out (after the powder coating is applied) during the bake cycle, when the gasses may come out as bubbles and cause surface imperfections, such as bubble blemishes. Bubble blemishes include a bubble, a bubble with a hole in its top or surface, and a dent or cavity or indentation resulting from a bubble having burst. The substrate being hot also facilitates the powder sticking thereto. As known in the art, the coating powder is dispersed in an air stream (preferable setting 10-80, more preferably 15-50, more preferable 25-30, psi) and passed through a high voltage field (preferable setting 30- 60, more preferable 45, kV) where the particles pick up an electrostatic charge. The charged particles are electrostatically attracted to and deposited on the grounded substrate, which is not in a mold at this time. The particles partially melt and stick to the hot substrate, covering all or part of the surface. The coated substrate is then baked in a bake cycle where the powder melts and forms a continuous coating, the separate particles melting and flowing and fusing together. If the powder coating material is a thermoset, the particles melt and fuse and the continuous coating is cured or set. In any event, the coating solidifies. The part is then cooled to ambient temperature, preferably free or substantially free of bubble blemishes. Optionally, the substrate may be deionized, using processes known in the art, before the substrate is powder coated. The finished coating on the substrate is preferably 0.5- 100, more preferably 1-50, more preferably 2-10, more preferably 3-4, mils thick. The coating material is not injected under pressure into a mold to surround a substrate in the mold. The powder coating plastic material is preferably polyester/TGIC powder coating powder such as Envirocron PCT 80165 (which is 30-40%_. titanium dioxide, 5-10% glycidtl isocyanurate, and 5-10% barium sulfate) and PCT 80166 (which is 30-40% titanium dioxide, 5-10% glycidtl isocyanurate, 1-5% silica, and 3-10% barium sulfate) from PPG, less preferably polyester (saturated) /urethane powder such as Envirocron PCT 80141 from PPG (which is 20-25% blocked isocyanate, 30-35% titanium dioxide, 5- 10% barium sulfate, and 30-35% film formers, resins, and additives) . The powder coating powder is preferably a thermoset and less preferably a thermoplastic Examples of thermoset (ther osettable) powder coating powders include polyester- urethane, polyester-TGIC, epoxy, hybrid, polyester amide, and acrylic. Examples of thermoplastic powder coating powders include polyvinyl chloride, polyamides (nylon 11 and 12) , LDPE, HDPE, EVA, and polypropylene. These and other powder coating powders are known in the art and are known for powder-coating metal parts. The particle size is preferably 5-300, more preferably 10-100, more preferably 20-80, preferably less than 90, microns. Different powder coating compounds may be selected, depending on the properties desired, such as color, gloss, adhesion, hardness, impact resistance, scratch resistance, chemical, heat, stain, and salt resistance, etc Preferably the adherent powder coating has or may have the following minimum film properties (determined using 2 to 3 mil film over iron phosphated, chrome rinse pretreated, 22 gauge, unpolished cold rolled steel) , with the property, test method, and value being listed: gloss - ASTM D-523-94 - 20-28 @ 60°; adhesion - ASTM D- 3359-95 - 100% (5B Pass) ; hardness - ASTM D-3363-92 - H Pencil (Eagle); impact resistance - ASTM D-2794-93 - 120 In.-Lb. Direct; conical mandrel - ASTM D-522-93 - 1/8" mandrel-1/2" tape off; salt spray resistance - ASTM B-117-94 - 500 hrs. less than 1/8" scribe creep - no blisters; humidity resistance - ASTM D-2247-94 - 500 hrs. less than 1/16" scribe creep - no blisters. Alternatively, the coating may have the following minimum film properties (determined using 1.5 mil dry film over iron phosphated pretreated 22 gauge cold rolled steel) : gloss - ASTM D-523-85 - 50 Min. @ 20°; adhesion - ASTM D-3359-83 - 100% (5B Pass) ; hardness - ASTM D-3363-74 - 3H pencil; impact resistance - ASTM D-2794-84 - 50 In.-Lb. Direct; conical mandrel - ASTM D-522- 85 - 1/8" mandrel - no cracking; salt spray resistance - ASTM B- 117-85 - 1000 Hrs. less than 1/8" scribe creep - no blisters; humidity resistance - ASTM D-2247-68 - excellent. To accommodate lower-melting or softening-point plastic substrates, powder coatings which may be baked on at lower temperatures are available, such as epoxy PCM90133 and acrylic PCC10108, both available from PPG and which may be baked on at 250°F and 285°F, respectively. The preferred time and temperature for the bake cycle for each specific powder coating powder is generally known in the art and is supplied by the manufacturer; the powder coating powder, after being applied to the substrate, is preferably baked at 200-500°F, more preferably 250-450°F, more preferably 300-400°F, more preferably 360-400°F, typically for about 5 to 30, more preferably 8 to 20, minutes. An advantage of the powder coating proceεε is that essentially zero volatile organic compounds (VOCs) are released into the atmosphere from the powder, and homogenous, firmly adherent, hard, typically non-electrically-conductive coatings are provided. Where the substrate is non-electrically-conductive (which is less preferred) , the same electrostatic-spray procedure may be followed, and the particles stick because the substrate is hot. Less preferably, other powder-coating processes known in the art may be used, such as the following. In the fluidized bed sintering method, a preheated (preferably above the sintering temperatures of the powder being used) substrate (which has had the gasses driven out as described above) is dipped into a bed of coating powder (typically 100-200 microns in size) which is kept suspended by a gentle flow of air through the porous bottom of the container; this process often includes a postheating step to provide a smooth cured coating. The immersion time depends on the thickness of the coating desired. The powder melts and sticks to the hot part. The substrate may or may not be electrically conductive. Typically, coatings of 5-50 mils can be obtained by this method. The electrostatic fluidized bed method is like the fluidized bed sintering method, except that the particles are charged and the substrate is grounded, although alternatively the substrate can be charged. Electrostatically the particles are attracted to the substrate. The substrate may or may not be hot when dipped, and a subsequent bake cycle may be provided. Very thin coating layers, such as 1-20 mil, can be obtained. In the electrostatic vibration powder coating method, the particles of the powder coating are electrostatically applied to the substrate connected to ground in a cloud of said particles electrostatically charged by supplying the same between a DC negative electrode and an AC electrode. In the electrostatic- spray method, the substrate may less preferably not be hot when sprayed. In these methods there is no primer coating or other coating or layer between the substrate and the powder-coating layer. The oven door handle of FIGS. 1-2 is part of the exterior surface of the oven and is about 29 inches long, about 1.25 inches wide at point A-A, and about 1 inch thick at point B-B. It is non-planar and not a sheet of plastic; what is being powder coated is more complicated than a simple flat surface. The top trim piece of FIGS. 3-4 is about 30 inches long, about 2.2 inches wide at point C-C, and about 1/8 inch thick at point D-D. These pieces would be quite suitable for production with a powder- coated surface in accordance with the invention, as would other parts which form some or all of the exterior surface of an appliance; these parts are well-known in the appliance art. The invention can be used to produce parts of any size and dimensions, but preferably for pieces of any length (preferably less than 48, more preferably less than 32, inches) and width (preferably less than 10, more preferably less than 5, more preferably less than 3, inches) with thickness range of 0.03-4, more preferably 0.1-1.5, inches. The invention has particular utility where the part is for an automobile (such as under-the- hood or in the passenger compartment) or an appliance, such as a toaster, microwave oven, refrigerator, freezer, washer, dryer, vacuum cleaner, dishwasher, air conditioner, toaster oven, waffle maker, blender, iron, griddle, skillet, hair dryer, hand dryer, sink basin, bathtub, shower stall, ashtray (automobile or free- standing) , etc. , such as when heat resistance of 300°F for 300 hours is needed and the part has a heat resistant non-yellowing powder coating, for example, plastic parts for an oven or kitchen range may have a powder coating which is heat resistant (particularly for the oven self-cleaning cycle) and which is stain-resistant and color matches the color of adjacent metal parts. Likewise, a plastic part or article that is exposed outdoors may be provided with a chemical resistant powder coating. The powder coating typically covers all of the exterior surface of the plastic part, but optionally may cover only some of the exterior surface, for example, the portion which shows. An advantage of the present invention is that, in an appliance such as those mentioned above, the finished plastic part can precisely match an adjacent metal part which has been powder- coated with the same powder used to powder coat the plastic part. The invention can be used to replace some or all powder-coated metal parts in an appliance with powder-coated plastic parts, with no change in surface coating or surface appearance, and generally identical surface performance. If fading occurs, the plastic and metal parts should fade the same, so the parts still match. The invention is further illustrated in the following Examples.

EXAMPLE 1

A formulation was made in accordance with the preferred weights of Components A-J of Table 1. A thermoset plastic substrate in the shape of the top trim piece of FIG. 3 was produced by injection molding in accordance with the injection molding procedure described above and as is known in the art. The electrically-conductive plastic substrate was subsequently heated or preheated at about 410-420°F for about 20 min. and was then coated with PPG Envirocron PCT 80141 powder coating powder via the electrostatic-spray powder-coating process. The powder adhered to the hot substrate because the powder partially melted and stuck and because the charged particles were attracted to the grounded substrate. The coated substrate was then baked at about 390°F for about 20 minutes; the powder melted and flowed and formed a continuous coating which crosslinked and cured as a thermoset. The cured coating was about 2-3 mils thick and had a good appearance; it only had insignificant surface blemishes or bubble blemishes. The surface coating was tested and had good adhesion, hardness, food stain resistance, grease resistance (after 168 hrs. exposure) , humidity resistance (after 500 hrs. exposure), water vapor resistance (after 250 hrs.) , detergent resistance (after 24 hrs.), UV resistance (after 168 hrs.), and high temperature resistance (exposure at 300°F for 300 hours with color shift of about 2.5 to 3.5 ΔE(Delta E) ) .

EXAMPLE 2

Example 1 was repeated except that the powder coating powder was PPG Envirocron PCT 80165. The results were the same, except that the 80165 coating had improved food stain resistance and grease resistance, and had excellent high temperature resistance (exposure at 300°F for 300 hours with color shift of about 1 to 1.5 ΔE) . Although the preferred embodiments of the invention have been shown and described, it should be understood that various modifications and rearrangements of the parts and steps may be resorted to without departing from the scope of the invention as disclosed and claimed herein.

Claims

WHAT IS CLAIMED IS:

1. A process for producing a plastic-coated plastic part comprising providing a molded plastic substrate, depositing an essentially solventless powder onto at least a portion of a surface of said substrate, and melting and fusing said powder to form a coating.

2. A process according to claim 1, wherein said substrate is electrically conductive and said powder is electrostatically deposited onto said surface of said substrate.

3. A process according to claim 1, further including the step of heating said substrate before said depositing step an effective amount to drive out materials which could come out as gasses during a subsequent bake cycle so that said coating is substantially free of bubble blemishes.

4. A process according to claim 2, further including the step of heating said substrate before said depositing step an effective amount to drive out materials which could come out. as gasses during a subsequent bake cycle so that said coating is substantially free of bubble blemishes.

5. A process according to claim 1, further including the step of heating said substrate before said depositing step so that said substrate is heated during said depositing step.

6. A process according to claim 1, said deposited powder being a thermosettable plastic, further including baking said deposited powder to form a continuous thermoset coating.

7. A process according to claim 1, said molded plastic substrate being an injection-molded plastic substrate.

8. A process according to claim 1, wherein said molded plastic substrate is the result of a molding of bulk molding compound.

9. A process according to claim 2, wherein said substrate is a reinforced polyester thermoset substrate.

10. A plastic-coated plastic part produced by the process of claim 1.

11. A plastic part according to claim 10, said part having a substrate portion, said substrate portion being a thermoset substrate.

12. A plastic part according to claim 11, said thermoset substrate being reinforced, said thermoset substrate having been produced from a polyester resin composition.

13. A plastic part according to claim 10, said part having a thermoset coating.

14. An appliance selected from the group consisting of an oven, kitchen range, washer, dryer, dishwasher, refrigerator, freezer, and air conditioner, said appliance having an exterior surface, a first portion of said appliance exterior surface being provided by an exterior surface of a plastic-coated plastic part produced by the process of claim 1, a second portion of said appliance exterior surface being provided by an exterior surface of a powder-coated metal part.

15. An appliance according to claim 14, said plastic part and said metal part having been powder-coated with the same powder coating powder.

16. A composition for producing a molded polyester thermoset part comprising an unsaturated polyester resin and effective amounts of (a) crosslinking monomer, (b) initiator, and (c) thermoplastic additive, said effective amounts being effective to provide a compound capable of being molded into a polyester thermoset part which is capable of being preheated for about 20 minutes at about 420°F and then, before cooling down, powder-coated by the electrostatic-spray powder-coating process to yield a coated part having a coating, said coating being substantially free of bubble blemishes.

17. A composition according to claim 16, further comprising an effective amount of reinforcing agent and an effective amount of an electrical conductivity additive.

18. A composition according to claim 17, further comprising an effective amount of filler and an effective amount of internal mold release agent.

19. A molded polyester thermoset part produced by molding a composition comprising an unsaturated polyester resin and effective amounts of (a) crosslinking monomer, (b) initiator, and (c) thermoplastic additive, said effective amounts being effective to yield said thermoset part such that said thermoset part is capable of being preheated for about 20 minutes at about 420°F and then, before cooling down, powder-coated by the electrostatic-spray powder-coating process to yield a coated part having a coating, said coating being substantially free of bubble blemishes.

20. A part according to claim 19, said composition further comprising an effective amount of reinforcing agent and an effective amount of an electrical conductivity additive.

21. A part according to claim 19, wherein said molded polyester thermoset part has a surface coating of a thermoset or thermoplastic material which is different from the material of the part.