Stock material or miscellaneous articles – Composite – Of polycarbonate
Reexamination Certificate
2002-05-31
2004-04-13
Boykin, Terressa (Department: 1711)
Stock material or miscellaneous articles
Composite
Of polycarbonate
C428S412000, C428S423300, C428S451000, C528S196000
Reexamination Certificate
active
06720076
ABSTRACT:
FIELD OF THE INVENTION
The invention pertains to in-mold coatings for thermoplastic substrates and more particularly to reactive epoxy-acrylates copolymerizable with other ethylenically unsaturated components to provide a thermosetting in-mold primer coating for thermoplastic substrates including polycarbonates and polycarbonate alloy substrates.
BACKGROUND OF THE INVENTION
Thermoplastic substrates ordinarily are based on converting thermoplastic resins, powders, granules, pellets and similar forms of thermoplastic resinous material under heat and pressure to form useful molded articles. Injection molding processes for molding thermoplastic resinous materials typically comprise heating the molding compound to form a viscous flowable melt, injecting the heated melt under high pressure into a relatively cool closed mold cavity, cooling the melt to form a solid shape molded substrate conforming to the interior configuration of the mold cavity, and then ejecting the molded part from the mold cavity. Thermoplastic compression molding ordinarily comprises thermoplastic resin compounded with fillers, colorants, lubricant and other processing additives to form granular or palletized thermoplastic particles known as molding powder. On the application of heat and pressure, the compounded molding resin flows under pressure into a heated mold to conform to the shape of the mold cavity. The mold is closed and the heat and pressure is maintained for sufficient dwell time to fully form the intended plastic article. The mold and formed plastic article are cooled to harden the molded plastic article, whereupon the mold can be opened and the molded article removed. In thermoplastic molding processes, 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 obtain good adhesion to the applied surface coating. However, many desirable decorative or other finish surface coatings are difficult to adhere directly to thermoplastic substrates, especially polycarbonates and polycarbonate alloy plastics. Paint adhesion to molded thermoplastic substrates is frequently difficult to obtain with an applied finished top surface coating and invariably requires an intermediate primer coating to achieve the necessary adhesion with the particular thermoplastic substrate. The primer coating must provide adhesion to the substrate as well as interface adhesion with the finished surface coatings. Thus, for various reasons, an in-mold primer coating is often used in injection molding of thermoplastics to enable subsequent adhesion of a wide variety of surface top coatings regardless of the substrate thermoplastic resin composition. It is particularly difficult to obtain adhesion with surface coatings on thermoplastic polycarbonates and polycarbonate plastic alloys.
In-mold coatings typically are 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 have been found to be particularly advantageous for molded parts or articles to provide a functional surface coating similar to post-mold process such as paint, as well as avoid surface imperfections in the molded part such as surface porosity, sink marks, surface waviness, and similar surface defects and imperfections which frequently require additional labor and costs to rework and post finish such moldings. In addition, in-mold primer coatings must provide adhesion to the substrate along with interface adhesion with most any type of finish surface coating. 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 infinitesimally to permit injection of the in-mold coating into the mold cavity. For instance, U.S. Pat. No. 5,902,534 discloses a method of injecting molding resin into a mold, followed by injecting an in-mold coating into the mold cavity between the molded substrate and the mold cavity surfaces, then compressing and curing the in-mold coating while in contact with the mold cavity surface, and then cooling the molded substrate to provide interface adherence of the cured in-mold coating to the molded substrate surface. Similarly, U.S. Pat. No. 4,668,460 suggests a method of in-mold coating a molded substrate contained within a closed mold by first molding the substrate under pressure and then injecting an in-mold coating into the closed mold at a pressure higher than the molding pressure. In-mold coatings are primarily directed to producing smooth surfaces free of surface defects and imperfections, while in-mold primer coatings additionally provide good adhesion to the specific thermoplastic substrate and an adherent surface for the subsequently applied surface topcoat.
In-mold polymeric epoxy acrylate coatings containing copolymerizable epoxy acrylates and/or ethylenically unsaturated monomers are disclosed in U.S. Pat. No. 4,414,173, U.S. Pat. No. 4,508,785, U.S. Pat. No. 4,515,710, U.S. Pat. No. 4,534,888, U.S. Pat. No. 5,084,353, U.S. Pat. No. 5,359,002, U.S. Pat. No. 5,391,399, U.S. Pat. No. 5,614,581, and U.S. Pat. No. 5,132,052.
It now has been found that an in-mold primer coating comprising an epoxy-acrylate copolymer adapted to addition copolymerize with other ethylenically unsaturated components, including particularly minor amounts of a copolymerizable acrylic acid selected from acylic, methacrylic or ethacrylic acids, provides an excellent in-mold primer coating for difficult adhesion substrates, such as thermoplastic polycarbonates and polycarbonate based alloy molding compounds. The in-mold primer coating of this invention further provides excellent interface adhesion with most surface finishes and/or decorative top coatings. The cured in-mold primer coating produces smooth primer surfaces free of surface defects and imperfections, which enables direct finish coat painting without intervening costly refinishing or reworking of the molded part. These and other advantages of this invention will become more apparent by referring to the detailed description of the invention and the illustrative examples herein.
SUMMARY OF THE INVENTION
Briefly, the invention pertains to thermosetting in-mold primer coatings for injection and compression molded thermoplastic substrates, especially polycarbonates and polycarbonate plastic alloys, to provide molded thermoplastic parts or articles with a cured in-mold primer coating integrally fused with the surface of the thermoplastic molded substrate. The in-mold primer coating of this invention comprises on a weight percentage basis from about 25% to about 65% or about 74% or about 75% of a low molecular weight epoxy acrylate oligomer having terminal acrylate or methacrylate groups and a number average molecular weight from about 360 to about 2,500, from about 15% to about 40% of an hydroxyl alkyl acrylate or methacrylate, from about 10% to about 35% vinyl substituted aromatic hydrocarbon monomers and from about 1% to about 10% of an acrylic acid.
On a weight parts basis, the in-mold primer coating comprises 100 weight parts of the epoxy-acrylate oligomer, from about 30 to about 70 weight parts of an hydroxyl alkyl acrylate or methacrylate, from about 30 to about 80 weight parts of a vinyl aromatic monomer, and from about 2 to about 20 weight parts of an acrylic acid monomer, where the basis is 100 weight parts of the epoxy-acrylate oligomer. The in-mold primer coating is injected into the mold cavity after the thermoplastic substrate molding compositio
Boykin Terressa
Burleson David G.
Fay, Sharpe, Minnich, & Mckee LLP
OMNOVA Solutions Inc.
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