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Title:
CONDUCTIVE COATING
Document Type and Number:
WIPO Patent Application WO/2005/019289
Kind Code:
A1
Abstract:
A conductive coating composition includes a conductive metal and a thermosetting copolymerizable composition. The thermosetting copolymerizable composition is formed from the reaction of an epoxy acrylate oligomer, a hydroxyalkyl (meth)acrylate, a vinyl-substituted aromatic compound, and a mono-ethylenically unsaturated alkyl or alicyclic compound. Coatings made from this composition provide excellent interface adhesion with thermoplastic substrates as well as most surface finishes and/or decorative top coatings.

Inventors:
Sizer, David (6602 Night Vista Drive, Parma, Oh, 44129, US)
Soulsby, Christopher (616 Sumatra Ave, Akron, Oh, 44305, US)
Mcbain, Douglas (233 Fixler Road, Wadsworth, Oh, 44281, US)
Application Number:
PCT/US2004/026756
Publication Date:
March 03, 2005
Filing Date:
August 17, 2004
Export Citation:
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Assignee:
OMNOVA SOLUTIONS INC. (175 Ghent Road, Fairlawn, Oh, 44333-3300, US)
Sizer, David (6602 Night Vista Drive, Parma, Oh, 44129, US)
Soulsby, Christopher (616 Sumatra Ave, Akron, Oh, 44305, US)
Mcbain, Douglas (233 Fixler Road, Wadsworth, Oh, 44281, US)
International Classes:
C08F299/02; C09D4/00; (IPC1-7): C08F290/14; C08F222/00; C08F299/02; C08J5/00; C09D4/00; C09D163/10
Foreign References:
US5614581A
US20030008934A1
Attorney, Agent or Firm:
Burleson, David (OMNOVA Solutions Inc, Legal Department 175 Ghent Roa, Fairlawn OH, 44333-3300, US)
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Claims:
CLAIMS What is claimed is:
1. A coating composition comprising: a) a conductive metal ; and b) a thermosetting copolymerizable composition that is formed from ingredients comprising an epoxy acrylate oligomer, a hydroxyalkyl (meth) acrylate, a vinylsubstituted aromatic compound, and a mono ethylenically unsaturated alkyl or alicyclic compound.
2. The coating composition of claim 1 comprising, on a weight percentage basis, from 35 to 65% of said conductive metal and from 65 to 35% of said thermosetting copolymerizable composition.
3. The coating composition of any of claims 1 to 2 wherein said thermosetting copolymerizable composition comprises the reaction product of a reaction mixture comprising, on a weight percentage basis, from about 25 to about 65% of said epoxy (meth) acrylate oligomer ; from about 5 to about 20% of said hydroxyalkyl (meth) acrylate ; from about 10 to about 35% of said vinyl substituted aromatic compound; and from about 1 to about 15% of said polymerized monoethylenically unsaturated alkyl or alicyclic compound.
4. The coating composition of any of claims 1 to 3 wherein said coating composition has a conductivity of 100 ohms/square or lower, based on a thickness of 25 Rm.
5. The coating composition of any of claims 1 to 4 wherein said epoxy (meth) acrylate oligomer is an epoxy diacrylate having acrylate double bonds on the terminal end portions of an epoxy intermediate and has a number average molecular weight from about 360 to about 2500; wherein said vinylsubstituted aromatic compound comprises styrene; and wherein said monoethylenically unsaturated alkyl or alicyclic compound comprises vinyl acetate.
6. The coating composition of any of claims 1 to 5 wherein said thermosetting copolymerizable composition further comprises at least one of a (meth) acrylic acid monomer and a low molecular weight diacrylate.
7. The coating composition of any of claims 1 to 6 further comprising one or more thermochromic and/or photochromic dyes.
8. The coating composition of any of claims 1 to 7 wherein a tactile surface characteristic is imparted to a coating derived from said coating composition by suspending a powder in said coating composition.
9. The coating composition of any of claims 1 to 8 wherein said thermosetting copolymerizable composition is cured using a free radical initiator and, optionally, an accelerator.
10. A process for applying a coating composition to a molded thermoplastic substrate and forming a coating thereon, comprising: a) into a die defining a mold cavity in which a molded substrate has been allowed to harden, injecting a metered amount of the coating composition of any of claims 1 to 9 and allowing said coating compo sition to contact at least a portion of a surface of said substrate; b) applying molding pressure to distribute said coating composition over said surface; c) maintaining said pressure while said material bonds to said surface and solidifies sufficiently to permit complete separation of said the component pieces of said die without disruption of the coating thus formed; and d) opening said die and removing said coated substrate from said cavity.
Description:
CONDUCTIVE COATING BACKGROUND INFORMATION [0001] This application claims the benefit of U. S. provisional patent application no. 60/496, 606, filed August 20,2003, the entire disclosure of which is incorporated by reference herein.

[0002] The invention relates to thermosetting conductive coatings for thermoplastic substrates.

[0003] For aesthetics, cost, and weight considerations, manufacturers of electronic equipment such as cellular phones and computers prefer that enclosures be made of plastic rather than metal. Unfortunately, plastic enclosures provide no electrostatic discharge (ESD), electromagnetic interference (EMI), or radio frequency (RF) shielding properties to contained objects. Accordingly, manufacturers have sought conductive coatings and paints to provide a conductive surface to the plastic. Thus, the demand for conductive coatings for the control of EMI in plastic enclosures is increasing steadily.

[0004] Various standards for electrostatic discharge control for electronic devices in different environments have been promulgated; see, e. g., ANSI/ESD S20.20-1990.

[0005] An example of a conductive, thermoset in-mold coating for molded fiber-reinforced plastic (FRP) parts is disclosed in U. S. Pat. No. 5,614, 581, the binder of which comprises at least one polymerizable epoxy-based oligomer having at least two acrylate groups and at least one copolymerizable ethylenically unsaturated monomer. Such a coating provides good flow and coverage during molding, good adhesion, uniform color, good surface quality, and good paintability. Other in-mold coatings include free radical peroxide-initiated thermosetting compositions that include an epoxy-based oligomer having at least two acrylate end groups and a hydroxy-or amide-containing monomer, as set forth in U. S. Pat. Nos. 5,391, 399; 5,359, 002; and 5,084, 353.

[0006] In injection molding processes used to make thermoplastic substrates, the molded part can be a finished article having many design details such as bosses, flanges, ribs, bushings, holes or other openings, various functional structures, decorative designs, and flat surfaces. Most molded substrates need

to be painted and need to adhere well to the applied surface coating. However, many desirable decorative or other finish surface coatings are difficult to adhere directly to thermoplastic substrates. Paint adhesion to molded thermoplastic substrates is frequently difficult to obtain with an applied finished top surface coating and often requires an intermediate primer coating to achieve adequate adhesion to a particular thermoplastic substrate. The primer coating provides adhesion to the substrate as well as interface adhesion with a surface coating.

Thus, for various reasons, an in-mold primer coating (IMPC) often is used in injection molding of thermoplastics.

[0007] An IMPC typically is sprayed into the mold cavity to coat the interior mold surfaces during the molding process to provide a primer surface coating integrally fused or adhered to the thermoplastic substrate being molded. In-mold coatings can be injected into a slightly opened mold, or under pressure into a closed mold, where the in-mold coating is applied to the mold cavity surfaces and/or applied over a molded or partially molded substrate, and then cured under heat and pressure in the mold cavity to form an integral thermoset cured surface coating on the molded substrate. An in-mold coating can be injected into the mold after the mold pressure is released or while the mold is opened infinitesi- mally to permit injection of the in-mold coating into the mold cavity. An IMPC can provide good adhesion to the thermoplastic substrate and an adherent surface for a subsequently applied surface topcoat.

[0008] In-mold polymeric epoxy acrylate coatings containing copolymerizable epoxy acrylates and/or ethylenically unsaturated monomers are disclosed in U. S.

Pat. Nos. 4,414, 173; 4,508, 785; 4,515, 710; 4,534, 888; 5,084, 353; 5,359, 002; 5,391, 399; 5,614, 581; and 5,132, 052.

SUMMARY OF THE INVENTION [0009] A conductive composition that includes a conductive metal and an epoxy-acrylate copolymer adapted to copolymerize with other ethylenically unsaturated components, including particularly a vinyl aromatic monomer, provides an IMPC with excellent adhesion to thermoplastic substrates, excellent interface adhesion with most surface finishes and/or decorative top coatings, and EMI and RF shielding properties.

[0010] Briefly, the invention provides a conductive thermosetting coating composition for injection and compression molded thermoplastic substrates that includes a conductive metal and a thermosetting copolymerizable composition.

The thermosetting composition includes an epoxy-acrylate oligomer, a hydroxyalkyl (meth) acrylate, a vinyl-substituted aromatic hydrocarbon, and a mono-ethylenically unsaturated alkyl or alicyclic compound.

[0011] In one illustrative embodiment, on a weight percentage basis, the IMPC includes from about 35 to about 65% conductive metal and from about 65 to about 35% thermosetting copolymerizable composition. A preferred IMPC includes from about 25 to about 65% of a low molecular weight epoxy acrylate oligomer having terminal (meth) acrylate groups and a number average molecular weight (Mn) of from about 360 to about 2500; from about 5 to about 20% of an hydroxylalkyl (meth) acrylate ; from about 10 to about 35% vinyl-substituted aromatic monomers; and from about 1 to about 15% of a polymerized mono- ethylenically unsaturated alkyl or alicyclic compound.

[0012] The IMPC is injected into the mold cavity after the thermoplastic substrate molding composition is at least partially cured. The injected IMPC composition is cured under heat and pressure to become a conductive IMPC that is integrally fused and adhered to the molded thermoplastic substrate surface.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS [0013] The thermosetting copolymerizable composition includes an epoxy (meth) acrylate oligomer, an hydroxyalkyl (meth) acrylate, a vinyl aromatic monomer, and a polymerized mono-ethylenically unsaturated alkyl or alicyclic compound. A conductive metal is added to the thermosetting composition to increase the conductivity of the coating to provide suitable EMI and RF shielding for commercial applications.

[0014] The conductive metal may be any metal used for conductive coating purposes. Preferred metals include Cu, Ni, Ag, and combinations thereof. Cu has excellent conductivity but is somewhat vulnerable to corrosion; Ag has excellent conductivity and corrosion resistance, but is expensive; Ni has relatively low conductivity, but excellent corrosion resistance. The total amount of metal in the coating can be from about 35 to about 75% by weight of the coating

composition. Such an amount provides adequate conductivity as well as EMI and RF shielding for most applications.

[0015] A general purpose conductive coating typically has a conductivity, as measured according to ASTM D257-99, of about 1x104 D/square or less (the resistance of a square of material is independent of the size of the square). The conductivity of a coating having a thickness of about 251lm (1 mil) typically is no more than about 100 0/square, depending on the amount of incorporated conductive metal. The thickness of the coating on the article is not critical, but must be sufficient so as to provide adequate conductivity to the coated article.

Typically, the thickness of the coating is from about 6 to about 125 um (0.25 to 5.0 mils).

[0016] The epoxy acrylate includes an epoxy-derived intermediate reacted with an unsaturated acid such as acrylic acid, methacrylic acid, or ethacrylic terminated epoxy acrylate having at least two epoxy intermediate can be an aromatic epoxy phenolic novalac epoxy, or an epoxy derived other diglycidyl functional resin. Bisphenol epoxy intermediates are preferred predominantly comprising the coreaction product of polynuclear dihydroxy phenols or bisphenois with halohydrins to produce epoxy resin intermediates containing at least one, predominantly two, and preferably two terminal epoxy functional groups per epoxy molecule.

[0017] The most common bisphenols are bisphenol-A, bisphenol-F, bisphenol-S and 4,4'-dihydroxy bisphenol-A. Useful halohydrins include epichlorohydrin, dichlorhydrin, dichlorohydrin-3-hydropropane, with the preferred being epichlorohydrin. A preferred epoxy resin intermediate, for example, comprises the reaction of excess equivalents of epichlorohydrin with lesser equivalents of a bisphenol-A to produce an epoxide group terminated linear chain comprising repeating units of diglycidyl ether of bisphenol-A. Ordinarily excess equivalents of epichlorohydrin are reacted with bisphenol-A where up to two molar equivalents of epichlorohydrin react with one molar equivalent of bisphenol-A to produce the diepoxide, although incomplete reaction is possible where some monoepoxide chains may be terminated at the other end with a bisphenol-A unit. Less preferred epoxy resins are predominantly bisphenol-A terminated and esterified with an acrylic acid to produce the epoxy-acrylate

oligomer. Particularly preferred epoxy intermediates include polyglycidyl ethers of bisphenol-A having two terminal 1,2-epoxide groups. Less preferred epoxy intermediate resins include epoxide-terminated epoxy novalac resins produced similar to bisphenol epichlorohydrin epoxies described above.

[0018] The epoxy-terminated intermediate, preferably a diepoxide, is further reacted with excess equivalents of an acrylic acid to provide an acrylate- terminated epoxy having acrylate double bonds essentially terminating each terminal end of the epoxy intermediate. The preferred epoxy acrylate is an epoxy diacrylate. Acrylic acids comprise acrylic acid (preferred) or a lower (e. g. , 1 to about 3 C atoms) alkyl-substituted acrylic acid such as methacrylic acid or ethacrylic acid. Epoxy acrylates preferably have a Mn of from about 360 to about 2500, more preferably from about 1000 to about 2000, as measured by GPC.

[0019] Epoxy acrylates are mixed with copolymerizable hydroxyalkyl (meth) - acrylates. Useful hydroxyalkyl (meth) acrylates include alkyl (meth) acrylates where the alkyl group contains from 1 to about 10, and preferably from 1 to about 5, C atoms. Useful alkyl groups include methyl, ethyl, propyl, butyl, and higher alkyl groups where propyl is the preferred alkyl chain and hydroxypropyl acrylate is the preferred hydroxy acrylate. Hydroxyalkyl (meth) acrylates comprise from about 5 to about 20% of the curable polymeric matrix. One or more hydroxyalkyl acrylates can be utilized.

[0020] Another component of the thermosetting IMPC composition is a vinyl- substituted aromatic hydrocarbon monomer including for example styrene, lower alkyl (e. g. , 1 to about 5 C atoms) substituted styrenes such as a-methyl and ethyl styrenes, vinyl toluene, halo-substituted styrenes such as a-chlorostyrene, and similar mono-vinyl aromatic monomers. On a weight basis, the copolymerizable IMPC composition contains from about 10 to about 35% by weight vinyl aromatic monomer.

[0021] The IMPC composition preferably contains minor amounts of copolymerizable other mono-ethylenically unsaturated alkyl or alicyclic monomer having a C-to-C double bond unsaturation including vinyl monomers, allylic monomers, acrylamide monomers, and similar monoethylenically unsaturated alkyl or alicylic monomers. Useful vinyl monomers include vinyl esters such as vinyl acetate, vinyl propionate, vinyl butyrates, vinyl isopropyl acetates and similar

vinyl alkyl esters, and vinyl alicyclic monomers such as cyclohexane. Useful acrylamide monomers include, for instance, methyl, ethyl, propyl, butyl, 2-ethyl hexyl, cyclohexyl, decyl, isodecyl, benzyl and similar lower alkyl (meth) acrylamide monomers. N-alkoxymethyl derivatives can also be used such as, for example, N-methylol, N-ethanol (meth) acrylamides. A preferred mono-ethylenically unsaturated alkyl or acylic copolymerizable polymer is polyvinyl acetate. On a weight basis, the in-mold coating can contain from 1 to about 15% by weight mono-ethylenically unsaturated alkyl or acylic copolymerizable polymer.

[0022] A minor amount of an unsaturated acid monomer selected from acrylic acid, methacrylic acid, ethacrylic acid, or mixtures thereof, may be included in the copolymerizable IMPC mixture. The inclusion of an acrylic acid component has been found to be particularly effective in providing adhesion to thermoplastic substrates such as polycarbonate and polycarbonate-based thermoplastic alloys.

The preferred acrylic acid is methacrylic acid. On a weight basis, the acrylic acid comprises from about 0 to about 5% of the polymeric matrix.

[0023] The IMPC composition can contain, if desired, a minor amount of an additional low molecular weight diacrylate such as (meth) acrylic diester of a diol.

The IMPC composition can contain, if any, from about 0.1 to about 5% by weight of such other low molecular weight diacrylate, if desired.

[0024] The IMPC can be copolymerized and thermoset under heat in the presence of a free radical initiator such as a peroxide. Useful peroxides include t- butyl peroxide, t-butyl perbenzoate, t-butyl peroctate, dibenzoyl peroxide, methyl ethyl ketone peroxide, diacetyl peroxide, t-butyl hydroperoxide, ditertiary butyl peroxide, benzoyl peroxide, t-butyl peroxypivalate ; 2, 4-dichlorobenzoyl peroxide, decanoylperoxide, propionyl peroxide, hydroxyheptyl peroxide, cyclohexanone peroxide, dicumyl peroxide, cumyl hydroperoxide, and similar free radical peroxide initiators. Azo free radical initiators can be useful including for instance azo bis-isobutyronitrile, dimethyl azobis-isobutyrate, and similar azo free radical initiators. A preferred initiator is t-butyl perbenzoate. Free radical peroxide or azo initiators are added to the copolymerizable IMPC composition at a level above about 0.5%, desirably from about 1 to about 5%, and preferably from about 1 to about 2%, by weight based on the weight of the copolymerizable thermosetting components.

[0025] In conjunction with the free radical initiator, a cure accelerator can be added. Examples include cobalt driers such as cobalt napthenate or octoate, or other metal napthenates such as zinc, lead, and manganese napthenates, or mixtures of such accelerators. Ordinarily minimal amounts of accelerator are used, if desired, at levels from about 0.01 to about 1 %, preferably from about 0.01 to about 0.5%, based on the weight of the copolymerizable thermosetting components in the IMPC composition.

[0026] Conversely, inhibitors, such as benzoquinone, hydroquinone, and methoxyhydroquinone can be added to control and delay cure times, if desired.

Inhibitors if used are added at very low levels, typically below 0. 1% to delay and properly control the copolymerization rate of the IMPC.

[0027] The IMPC composition can be compounded with other additives, known to the art and to the literature, such as opacifying pigments, tinting pigments or colorants, and inert fillers. Useful opacifying pigments include TiO2, ZnO, titanium calcium, while tinting pigments include a variety of oxides, chromium, cadmium, and other tinters. Small amounts of carbon black may also be used to provide a black or gray primer coating appearance. Useful fillers include clays, silicas, talc, mica, wood flour, BaS04, calcium and magnesium silicates, AI (OH) 3, and magnesium and calcium carbonates, where preferred fillers are talc and BaS04. Opacifying pigments, tinting pigments or colorants, and inert fillers can be used at a level from about 0 to about 80 weight parts per 100 weight parts of the thermosetting copolymerizable composition components.

Other dyes can be added as well including thermochromics or photochromics, such as spiro-naphthoxazines and naphthopyrans, which are special dyes that reversibly change color upon exposure to UV sources, such as sunlight.

[0028] Other useful additives can include lubricants and mold release agents such as zinc or calcium stearate, phosphoric acid esters, and zinc salts of fatty acids. Mold release agents can also be used to control the cure rate, where zinc fatty acids tend to moderately accelerate the cure time, while calcium fatty acids tend to moderately retard the cure time. Other lubricants can be added to impart a low coefficient of friction to the surface of the cured coating. A low profile additive, such as polyvinyl acetate, can be added if desired to avoid molding shrinkage of the IMPC.

[0029] Additional additives can be added to produce a functional coating or impart other desired qualities to the coating. Such additives can include various light and UV stabilizers, such as hindered amines, substituted benzophenones, substituted benzotriazoles, and the like. Other additives can include anti- bacterial agents, flame retardants, water proofing agents, buffers or other materials to impart acid resistance or other chemical resistance, hardeners to improve, e. g. , scratch resistance, thixotropes, such as silica, and adhesion agents, such as polyvinyl acetate.

[0030] Still other materials can be added either to the IMPC composition prior to curing or applied after coating formation as a surface treatment to impart other characteristics. Thus a reflective surface can be imparted to the coating by adding a reflective powder such as MgO or Al203 or a thin layer of metalized polyester. Similarly, non-skid or other tactile surface characteristics can be imparted with the use of various known additives. For example, texture can be added to the coating by suspending a non-skid powder in the IMPC composition.

Flocking may also be added to the coating as well.

[0031] The thermosetting conductive IMPC composition can be prepared by mixing the epoxy acrylate, hydroxyalkyl acrylate, vinyl aromatic monomer, and polymerized mono-ethylenically unsaturated alkyl or alicyclic compound components to form a uniform, fluid blend. Metal (s) can be added and dispersed in the blend. Free radical initiator also can be added at this point or can be added with one on the resinous components such as the aromatic monomer, along with accelerator if any, and inhibitor if any. Other compounding ingredients of pigments, colorants and fillers and other additives can be added as desired and mixed to form a uniformly dispersed IMPC composition.

[0032] The coating composition can be used on a variety of thermoplastic substrates. Suitable thermoplastics include, but are not limited to, various polyesters (optionally containing glass fiber reinforcement) such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), copolymers of PET and PBT, etc.; polyolefins including polyolefin homopolymers, copolymers of an olefin and another monomer, polyolefins grafted with functional groups such as (meth) acrylate, acids, halogens, etc, and blends thereof; acrylonitrile-butadiene- styrene copolymers (i. e. , ABS); polycarbonate; alloys of polycarbonate ; and

blends or mixtures of ABS and polycarbonate ; high impact polystyrene (HIPS) ; thermoplastic polyurethane, and the like.

[0033] One type of suitable thermoplastic is polycarbonate and alloys thereof.

Thermoplastic polycarbonates are primarily aromatic polyesters derived from reaction of carbonic acid derivatives with primarily an aromatic diol. Useful Mn of aromatic thermoplastic polycarbonates ordinarily are from about 10,000 to about 50,000, preferably from about 22,000 to about 35,000.

[0034] Polycarbonate polymeric blends or alloys with other thermoplastic polymers are likewise useful thermoplastic substrates. Such polycarbonate alloy blends include aromatic polycarbonate mixed with poly (butylene-terephthalate) known as PC/PBT, and aromatic polycarbonate blended with poly (ethylene terephthalate) known as PC/PET, as well as other polymeric alloy blends with aromatic polycarbonate. Such polycarbonate alloys ordinarily comprise a mixture of polycarbonate containing from about 40 to about 95 weight percent aromatic polycarbonate with the balance being the alloying secondary thermoplastic polymer or polymers. Additives to polycarbonates and alloy blends thereof can include tinting pigments, colorants, heat stabilizers, impact modifiers, lubricants, mold release agents, UV stabilizers, plasticizers, fibers, reinforcing materials, fillers, and other additives ordinarily added to injection molding thermoplastic substrate compounding resins as desired.

[0035] The thermosetting IMPC is particularly useful as an in-mold coating for molding of polycarbonate alloys comprising major amounts of polycarbonate mixed with minor amounts of nylon, ABS, PET, PBT, and/or HIPS. The polycarbonate and alloying c-polymer can be heated to make the two polymeric material miscible or partially miscible depending on the alloying polymer. The polymers may or may not interact, such as by ester interchange, during the heat alloying process. The polycarbonate ordinarily is the dominant matrix polymer but need not be. On a weight basis, polycarbonate alloys include by weight from about 40 to about 95% polycarbonate, preferably from about 50 to about 80% polycarbonate, with the balance being blend or alloying polymer (s). Examples of such polymers include nylons, ABS, PET, PBT, and HIPS ; these can be alloyed with polycarbonate and compounded with filler, pigments, and other additives similar to the compounding described previously.

[0036] Injection molding involves heating the resinous compounding composition to a temperature above the melting point of the compounding resin and injecting the heated resin melt into an injection mold cavity for molding a substrate part or article. The substrate resinous molding compound ordinarily is injected into the cavity of an injection mold and molded under heat and pressure to at least partially set the thermoplastic resin and form a molded substrate.

Substrate molding temperatures typically are from about 37° to about 150°C (100°-300°F) and preferably from about 65° to about 120°C (150°-250°F).

During the molding and cooling stage, the injection molding pressure preferably is partially released from the mold to permit injection of the IMPC composition into the minimally opened mold under reduced low pressure.

[0037] Alternatively, the substrate molding compound can be injection molded under high pressure followed by injecting the IMPC composition at a higher pressure into the mold maintained closed under pressure. A metered amount of the IMPC composition initiator, additives, and other compounding ingredients as desired is injected into a nozzle located within the parting line of the mold cavity and preferably disposed opposite from the thermoplastic substrate injection sprues. Pressure can be applied as needed and ordinarily can be from about 14 to about 34 MPa (2000-5000 p. s. i.), and preferably from about 20 to about 28 MPa (3000-4000 p. s. i.), but ordinarily at a pressure considerably less than that applied while molding the substrate resinous compound. The applied pressure can increase as the IMPC composition is injected between the partially molded substrate and the mold cavity surfaces.

[0038] The IMPC composition can be heat cured to copolymerize the epoxy acrylate oligomer, hydroxyalkyl acrylate, and the vinyl aromatic monomer to form a fully cured IMPC advantageously molded integrally with and fusion adhered to the fully formed thermoplastic substrate. IMPC curing temperatures can be from about 65° to about 150°C (150°-300°F) for a time sufficient to fully cure the IMPC, typically from about 30 to about 120 seconds and preferably from about 60 to about 90 seconds. The mold then is opened and the surface coated molded part or article can be removed from the mold cavity. The cured surface coating provides excellent adhesion to the polycarbonate based substrate as well as an

excellent primer surface amenable to good adhesion with a wide variety of top surface finish coatings.

[0039] The coating composition desirably is used to coat injection molded substrates. However, as discussed, the ordinarily skilled artisan recognizes that molded articles made by other known methods, such as resin or transfer molding, rotational molding, blow molding and thermoforming, likewise can be coated using the described process.

[0040] Injection of the thermoplastic used to form the substrate can be viewed as a three-stage process. The first stage is referred to as the filling stage; in this stage, an amount of thermoplastic is injected into the mold to nearly fill the mold cavity, preferably to at least about 75% of its capacity. The second stage is referred to as the packing stage; in this stage, additional thermoplastic is packed into the mold to fill the mold cavity, preferably to at least about 99% of its capacity. The third stage is referred to as the cooling stage; in this stage, the thermoplastic begins to solidify as it starts to cool.

[0041] For a typical thermoplastic, in the packing stage, packing pressure rises as a result of injecting more thermoplastic material into the mold and then is kept constant for a while to compensate for the material shrinkage caused by the temperature decrease as the thermoplastic begins to cool. During the cooling stage, the pressure in the mold cavity decreases as the thermoplastic continues to cool and begins to shrink. During the cooling stage, the IMPC composition is injected into the mold. One must wait until the surface of the substrate has sufficiently cooled and hardened such that the IMPC and the thermoplastic do not excessively intermingle. Also, the longer the period between the end of the thermoplastic filling and the coating composition injection, the lower the packing pressure needed to inject the coating composition and the easier the injection.

However, because the IMPC composition generally relies on the residual heat of the cooling thermoplastic to cure, one risks inadequate curing of the IMPC composition if the waiting period is too long. In addition, the thermoplastic needs to remain sufficiently molten to allow for sufficient adhesion between the IMPC composition and the substrate as well as to provide sufficient compressability to allow adequate flow of the IMPC composition around the surface of the substrate

in the mold. Thus, the ease of coating injection needs to be balanced with the need for sufficient residual heat to obtain an adequate curing of the IMPC.

[0042] After the resin has been injected into the mold cavity and the surface of the molded article to be coated has cooled below the melt point or otherwise reached a temperature or modulus sufficient to accept or support an IMPC but before the surface has cooled too much such that curing of the IMPC is inhibited, a predetermined amount of an IMPC composition is ready to be introduced into the mold cavity from a separate nozzle.

[0043] A supply pump can be utilized to supply the coating composition into the injector from a storage vessel. The coating composition is injected from the metering cylinder into the mold cavity through an orifice with a pressurizing device utilizing hydraulic, mechanical, or other pressure. When the coating injector is activated during injection mode, coating composition flows through the orifice and into the mold cavity between the surface of the thermoplastic substrate and the exterior of the molded article. The coating composition flows around the molded article and adheres to its surface.

[0044] As detailed above, the IMPC composition preferably is injected soon after the surface of the thermoplastic has cooled enough to reach its melt temperature. The determination of when the melt temperature is reached can be determined directly by observation of the internal mold temperature if the melt temperature of the specific thermoplastic is known, or indirectly by observation of the internal mold pressure. When the molded part reaches its melt temperature and begins to solidify, it contracts somewhat, thus reducing the pressure in the mold, which may recorded through the use of a pressure transducer in the mold.

[0045] In this process, the mold is generally not opened or undamped before the IMPC composition is applied. That is, the mold halves maintain a parting line and generally remain substantially fixed relative to each other while both the first and second compositions are injected into the mold cavity. The IMPC compo- sition spreads across the mold surface and coats a predetermined portion or area of the molded article. Immediately or very shortly after the IMPC composition is fully injected into the mold cavity, the nozzle valve or deactivation means of the second injector is engaged, thereby preventing further injection of the IMPC composition into the mold cavity.

[0046] After a predetermined amount of IMPC composition is injected into the mold cavity and covers or coats the predetermined area of the article or substrate, the coated substrate can be removed from the mold. However, before the mold halves are parted, the IMPC is typically cured by components present within its composition. The cure is optionally heat activated, from sources including the substrate or mold halves which are at or above the curing temper- ature of the IMPC composition. Cure temperature varies depending on the IMPC composition utilized. As mentioned above, it is important to inject the IMPC composition before the molded article has cooled to the point below where proper curing of the coating can be achieved. The IMPC composition requires a minimum temperature to activate the catalyst present therein which causes a cross-linking reaction to occur, thereby curing the composition and melt-bonding it to the thermoplastic substrate.

[0047] The IMPC composition of this invention is similarly useful for compression molded thermoplastic substrates. Thermoplastic molding materials for compression molding can be compounded in a manner similar to injection molding thermoplastic molding materials, typically supplied in the form of coarse granules often referred to as molding powder, which ordinarily comprises thermo- plastic resin, a filler or fillers, along with minor amounts of additives such as dye, colorant, and lubricants. Thermoplastic molding powders can be placed in a mold cavity and, on the application of heat and pressure, the thermoplastic resin melts and the compounding material flows to conform to the shape of the mold cavity and form into a molded part. The mold and molded part are then cooled to solidify and harden the molded part. IMPC compositions can be injected into the compression mold to form an in-mold cured thermoset surface coating on the molded part in a manner similar to injection molding.

[0048] The following examples further illustrate the merits and advantages of this invention, but are not intended to limit the scope of the invention.

[0049] Conductive IMPC was produced from the following materials. The thermosetting copolymerizable composition components are listed in Tablel.

Table 1 Ingredient Function Parts Wt. % bisphenol-A epoxy diacrylate1 crosslinking oligomer 125. 0 40. 36 hydroxypropyl methacrylate monomer 23.7 7.65 styrene monomer 51.26 16.55 PVA/styrene blend2 polymer 25.0 8.07 benzoquinone inhibitor 0.16 0.05 12% cobalt octoate accelerator 0.15 0.05 zinc stearate mold release 1.85 0.60 calcium stearate mold release 0.6 0.19 surfactant3 surfactant 2.065 talc filler 80 25.83 TOTAL 309. 7 100. 0

EbecrylTM 9125 resin (UCB Chemicals Corp.; Atlanta, Georgia), which contains 80% by weight epoxy diacrylate, 15% styrene and 5% hydroxypropyl methacrylate.

2 40% polyvinyl acetate and 60% styrene available as LP-90 (Dow Chemical Co.; Midland, Michigan) 3 Disperse Ayd-8 surfactant (Elementis Specialties, Inc. ; Hightstown, New Jersey) [0050] To 47.7% (by wt. ) of the thermosetting copolymerizable composition mixed in a dynamic mixer was added 52.3% (by wt.) Novamet 525 nickel (Novamet Specialty Products Corp.; Wyckoff, New Jersey) in a dynamic mixing head. The nickel containing mixture was added to an injection molding nozzle and then injected into a mold containing an article formed from Cycoloy MC8800 ABS/polycarbonate resin (GE Plastics; Pittsfield, Massachusetts). The coated article remained in the mold for approximately 2 minutes where it experienced temperatures of from about 100° to about 120°C.

[0051] The conductivity of the resulting coated molded article having a coating thickness of from 25 um (1.0 mils) was tested. The results (noted as Sample 1) are compared to those from an article coated using the same coating formulation without nickel (noted as Sample 2) are shown in Table 2. The Fluke meter readings were conducted using a Fluke multimeter machine according to ASTM D257-99.

Table 2 RANSBERG CONDUCTIVITY FLUKE METER Sample 1 pegged meter 20 Q/square Sample 2 pegged meter 140,000 Q/square

[0052] As can be seen from the results above, the presence of the nickel increased the conductivity of the coating several orders of magnitude and produced a laminate suitable for use in applications requiring ESD and EMI/RF shielding properties.