Plastic and nonmetallic article shaping or treating: processes – Direct application of electrical or wave energy to work – Polymerizing – cross-linking – or curing
Reexamination Certificate
2000-10-31
2002-07-30
Berman, Susan W. (Department: 1711)
Plastic and nonmetallic article shaping or treating: processes
Direct application of electrical or wave energy to work
Polymerizing, cross-linking, or curing
C156S275500, C428S423100, C428S423900, C428S424800, C428S492000, C428S500000, C428S515000, C428S516000, C428S522000, C522S083000, C522S095000, C522S096000, C522S103000, C522S107000, C522S121000, C522S136000, C522S137000, C522S142000, C522S144000, C522S182000, C522S079000, C522S080000
Reexamination Certificate
active
06426034
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a radiation curable coating composition useful for coating thermoplastic substrates. More particularly, the invention is directed to a radiation curable resin consisting essentially of monomers, oligomers, or combinations thereof, each a mono or poly-ester of acrylic acid or methacrylic acid wherein each of the esters has a boiling point greater than 162° C. The invention is also directed to a method of reducing the gloss and increasing the scratch-resistance of the surface of a thermoplastic substrate by application of the coating composition, and a method of manufacturing such a thermoplastic substrate.
BACKGROUND AND SUMMARY OF THE INVENTION
Thermoplastic materials such as polyethylene, polypropylene, thermoplastic olefins, EPDM, rubber (ethylene/propylene/diene/monomer) vinyl, and various synthetic and natural rubbers have been developed which are useful in many applications, such as in the manufacture of automotive parts and accessories, furniture, and appliances, and in many other commercial applications.
Thermoplastic sheet materials are particularly useful for applications where it is desired to have an aesthetically pleasing surface that can be molded or laminated onto the functional part or assembly and have a leather-like feel. These thermoplastic sheet materials are particularly useful for automotive interior panels and trim pieces, such as dashboards, doorhandles, and other trim pieces, instrument panels, aircraft headliners, furniture armrests, appliance exteriors, bookbindings, briefcases, and the like.
It is often desirable to coat such thermoplastic sheet materials in order to protect the plastic material from marring, abrasion, and exposure to weather conditions such as sunlight, moisture, heat and cold in order to achieve more durable, longer-lasting parts. Furthermore, it is often desirable to give the thermoplastic sheet a leather-like feel. Additionally, in automotive interior applications, it is desirable to minimize the gloss of the coated article so that an undesirable and potentially dangerous glare does not cause visual impairment to the driver and other vehicle occupants.
Thermoplastic moldable sheet materials are particularly useful in that they can be molded onto a functional part using readily available processes known in the industry such as vacuum forming, thermoforming, or laminating. The application of coatings to flat thermoplastic sheets are simplified due to the lack of curvature of the sheets being coated. Conventional coating applications such as the various spray, roll coating, or curtain coating processes can be used with maximum transfer efficiency and at relatively high line speeds using automated equipment.
Thermoplastic substrates have widely varying surface properties including surface tension and roughness and may require extensive elongation during the molding process. These variations in surface properties has made it difficult to achieve adequate adhesion of the organic coating, particularly after the molding process.
A number of solutions to the problems with adhesion have been investigated including flame treatments, corona treatments, or plasma treatments to oxidize the plastic surface, and the application of various coating compositions containing chlorinated polyolefins, with or without the incorporation of polyhydroxylated polydiene polymers, to increase adhesion has also been investigated (see U.S. Pat. Nos. 4,683,264; 4,997,882; 5,258,444; 5,300,326; 5,319,032; 5,397,602; 5,585,192; 5,880,190; and 5,863,646). Thus, prior to the present invention, achieving adhesion to such difficult to paint substrates like thermoplastic olefins was limited to oxidation of the plastic substrate directly by flame, corona, or plasma treatment, or via the use of chlorinated polyolefins.
Oxidation of the thermoplastic surface by direct flaming poses hazards to the safety of workers as well as the potential for damage to the article being treated. Corona and plasma treatments require costly equipment, and often are not suitable for continuous operations. Additionally, corona and plasma treatments can result in inconsistent adhesion performance due to inconsistent levels of oxidation with resulting surface tension variations. The use of chlorinated polyolefins has generated environmental concerns due to limitations in the recycling of these thermoplastics, or in their disposal, since burning of chlorinated compounds may generate hydrochloric acid and other toxic and environmentally hazardous compounds.
The use of UV-curable formulations comprising a variety of acrylate oligomers and monomers for use on pressure sensitive adhesive tape consisting of polypropylene, polypropylene and thermoplastic olefins to provide a refastenable attachment zone for disposable diapers has been described (see U.S. Pat. No. 4,643,730). However, in contrast to the compositions of the present invention these UV-curable formulations have a limited service life.
As described in U.S. Pat. No. 5,585,415 most radiation-curable coating compositions are cured to glossy, cross-linked coatings, and the addition of conventional flatting pigments results in such high pigment to binder ratios that the binder is not able to hold the pigment and poor film performance results. The use of silica in photocurable coating compositions to improve the abrasion resistance in optical lenses used in eyeglasses is known (see U.S. Pat. No. 4,885,332). The use of a combination of powdered polyamino acid resin and silica in a non-photocurable coating composition composed mainly of a polyurethane resin to achieve a surface with a leather-like feel that is resistant to marring has also been described (see U.S. Pat. No. 5,258,446). However, there has been no description of using silica as a flatting pigment, either alone or in combination with insoluble polymeric beads, to achieve the low gloss radiation-curable coating compositions exhibiting excellent scratch-resistance that are provided in accordance with the present invention.
In one embodiment of the present invention a radiation curable composition is provided. The composition comprises about 20 to about 100 percent by weight free-radical curable resin components consisting essentially of monomers, oligomers, or combinations thereof, each a mono or poly-ester of acrylic acid or methacrylic acid, and each of said esters having a boiling point greater than 162° C. and a molecular weight of about 150 to about 10,000, about 0.1 to about 10 percent by weight of a free radical photoinitiator, and about 0 to about 60% by weight of an organic solvent. At least a portion of the esters in the radiation curable composition may be carboxy functional, may be an acrylic acid or methacrylic acid ester of a polyol containing at least 4 carbon atoms, may include a carbamate functionality, may be acrylic acid or methacrylic acid esters of isoborneol, and/or may be beta-carboxyethyl acrylate or beta-carboxyethyl methacrylate.
In an alternate embodiment of the invention the radiation curable composition may further comprise about 0 to about 50 percent by weight of polymeric beads or powder having a median particle size of about 1 to about 60 microns dispersed in the composition. The polymeric beads or powder may comprise polymers or copolymers of acrylic or methacrylic acid, esters thereof and styrene. Alternatively, the polymeric beads or powder may comprise a polyamide, a polyurethane, a urea/urea methanol condensate or polyurea.
In yet another embodiment of the invention the radiation curable composition may further comprise up to 30 percent silica by weight dispersed in the composition.
In another embodiment of the invention a method for reducing the gloss of the surface of a thermoplastic substrate is provided. The method comprises the steps of applying to the sheet stock a radiation curable composition as described above, irradiating the coated surface with UV radiation for a time sufficient to initiate polymerization of free radical curable components, and forming the thermoplastic sheet stock t
Clark Peter
McComas Jerry
Barnes & Thornburg
Berman Susan W.
Lilly Industries, Inc.
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