Coating processes – Solid particles or fibers applied
Reexamination Certificate
2002-10-07
2004-08-17
Cameron, Erma (Department: 1762)
Coating processes
Solid particles or fibers applied
C427S387000, C427S421100, C427S426000
Reexamination Certificate
active
06777026
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to weatherable coatings applied on exterior surfaces of flexible substrate articles, particularly elastomeric or rubbery articles or substrates containing such materials. In addition to providing protective film properties, the coatings reduce heat buildup by directing heat away from the article (emissive). The coatings can be applied to an elastomeric substrate either before or after the substrate has been vulcanized.
BACKGROUND OF THE INVENTION
Engineered elastomeric products are designed to flex and bend, distort and recover, and/or dampen forces including absorbing torque or vibration repeatedly during their service life and are utilized in numerous industrial applications. For example, elastomeric materials are utilized in the manufacture of tires, hoses, seals, mountings such as engine mounts, dampers and insulating devices, and are designed to exhibit hysteretic losses, and withstand heat, to name a few design aspects. These and other articles shaped into myriad articles have many established uses such as industrial machines and parts for vehicles. Many elastomer products come into contact with heat from a variety of sources, such as from internal combustion engines. Recent increases in operating temperatures, and reduction of the size of vehicular engine compartments give rise to closer proximity between heat sources and such molded parts as rubber hoses, plastic housings, belts, various mounts, shrouds, seals, grommets, washers, spacers, covers, and housings, etc. Some of these articles are heat vulcanized, others are room temperature vulcanized and still others are cured in a different manner and exhibit characteristic flexing, elongation, rubbery elasticity, as thermoplastics or thermoset materials.
All polymeric materials degrade on account of exposure to heat, light, oxygen, ozone solvents, oils, and/or fuels. Elastomeric materials, and especially natural and/or synthetic vulcanized rubbers are particularly known to degrade when exposed to these agents, and there is a continuing search within industry to provide elastomer articles that are resistant to such degradative elements.
U.S. Pat. No. 6,022,626 discloses coatings suitable for covering engine mounts to protect the rubber substrate from oxygen, ozone and/or UV light, especially when reaching temperatures of 220° F./104° C., or more. The coatings taught provide a polymer barrier from chemical or UV intrusion. In exposure to hot environments, the polymers taught in U.S. Pat. No. 6,022,626 may provide an initial barrier against oxygen, ozone and UV radiation but lack durability to repeated flexure over long periods of time. Once adhesion fails or the coating is breached by cracks, degradative effects resume. Such coatings as taught in U.S. '626 also do not provide emissive properties and do not deflect heat.
U.S. Pat. No. 5,314,741 to Roberts, et. Al. entitled “Rubber Article Having Protective Coating” relates to polymeric articles which are coated with hydrogenated synthetic rubbers or polymers obtained by hydrogenating an unsaturated polymer which is a polymer of 1,3-butadiene and optionally one or more monoethylenically unsaturated polymers.
Conventional polymeric stabilizers, UV absorbers and the like are used for the rubber articles coated thereon, yet improved aging properties are desired even in light of more harsh operating conditions.
Achieving sufficient permanent adhesion to the underlying rubber which experiences repeated flexure or extension over long-term service life is further needing improvement.
Alkyd, urethane, and enamel metallic paint finishes are well known for providing sparkled metallic effects, are widely used as on automotive bodies. The substrates are mainly metal or rigid plastic parts where flexure is limited or the paints are expected to crack if impacted severely. Speckled-effect metallic coatings are commonly provided on metal body panels, whereby 1% or less metallic pigments are interspersed with coloring pigments, and overcoated with clear finish. Likewise, aluminized spray paints have been provided for applying to furniture, metal articles and the like, however the film forming materials utilized, cure to form a coating of very limited elongation, and would be unsuitable as coatings on flexible substrates such as engineered rubber articles due to flex cracking and loss of adhesion not long after placing the coating in service. Metal flake effect paints provide visual aesthetics for appearance parts but do not provide heat emissive properties to any extent useful for extending the useful long term service of engineered rubber products under hot environments.
One method of rendering elastomeric materials resistant to corrosive materials is to apply a protective coating to the elastomeric material. Various corrosion-resistant coatings previously utilized for both flexible substrates (e.g., elastomeric substrates) and rigid substrates (e.g., steel, stainless steel, aluminum or plastic) include polyurethanes, polysulfides and fluorocarbon elastomers. When applied to rigid substrates, traditional corrosion-resistant coatings such as fluorocarbon elastomers have been found to provide excellent resistance to oil and fuel. However, when applied to flexible elastomeric substrates comprising natural rubber and/or diene-type elastomers and mixtures, the fluorocarbon elastomers suffer from poor fatigue resistance, poor low temperature characteristics, and poor adhesion to these substrates.
Low molecular weight polyolefin or polyisoolefin based elastomers containing a low level of chemically bound functionality such as an hydroxyl or an amine bearing group are known for incorporation into urethane foams. Such elastomers can be blended with and cured by an unblocked or blocked polyisocyanate. For example, U.S. Pat. No. 4,939,184 discloses the preparation of flexible polyurethane foams made by reacting a low molecular weight polyisobutylene having two or three terminal hydroxy groups with a polyisocyanate in the presence of a blowing agent.
U.S. Pat. No. 4,136,219 to Odam relates to two methods or processes for applying polyurethane paint to vulcanized rubber parts.
U.S. Pat. No. 4,670,496 discloses tire sidewall striping paint as a coloring indicia of any color, such as a dye, and preferably metallic particles are disposed in a solution that contains unvulcanized diene rubber(s) and rubber vulcanization accelerator. Crosslinkable silicone and/or modified EPDM may also be disposed in the solution. The accelerator is essential for scavenging sulfur from the vulcanized rubber substrate to provide auto-vulcanizing of the coating rubber. In order to provide adequate adhesion for long term service as a coating for rubber articles, a diene polymer containing more than 10% residual unsaturation after curing will necessarily undergo degradation and embrittlement and will fail long before the underlying substrate fails.
Diisocyanate containing free isocyanate groups has also been previously proposed for curing copolymers of isobutylene and modified styrene containing tertiary aminoalcohol groups in EPA 325 997. EPA 325 997 discloses diisocyanate curing of polymers having a molecular weight of 700 to 200,000, and exemplifies blends of up to about 30,000 weight average molecular weight (Mw) and about 8,600 number average MW (Mn), as measured by gel permeation chromatography.
A variety of bulk isocyanate-cured rubbers and mastics have been disclosed in the 50′s and 60′s. Isocyanate reactive functional groups present in the elastomer readily cure with NCO groups of the diisocyanate. As an example, U.S. Pat. No. 6,087,454 discloses a process to produce a cured bulk elastomer comprising combining an elastomeric polymer, having an M
w
of 60,000 or more and containing hydroxyl and/or amine functional groups with a blocked polyisocyanate at a temperature below the temperature that will unblock the isocyanate. The mixture is cured by heating it to a temperature above the temperature that will unblock the polyisocyanate. This reaction can be
Caster Kenneth C.
Halladay James R.
Krakowski Frank J.
Troughton, Jr. Ernest Barritt
Cameron Erma
Dearth Miles B.
Lord Corporation
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