Coating processes – Direct application of electrical – magnetic – wave – or... – Electrostatic charge – field – or force utilized
Reexamination Certificate
2001-09-13
2003-09-16
Parker, Fred J. (Department: 1762)
Coating processes
Direct application of electrical, magnetic, wave, or...
Electrostatic charge, field, or force utilized
C427S458000, C427S475000, C427S485000
Reexamination Certificate
active
06620463
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an improved method of electrostatically coating substrates which are made of polymers, polymer composites, or other electrically non-conductive materials.
BACKGROUND OF THE INVENTION
The use of electrostatic powder coating techniques to paint electrically conductive substrates, such as metals, is well known and successfully employed. Using this method, a powder coating material is statically charged or ionized to a positive polarity or negative polarity, and then sprayed or blown onto a grounded, conductive article to which it adheres. The electrostatic attraction between the paint and the grounded article results in a more efficient painting process with less wasted material, and a thicker, more consistent paint coverage, particularly on articles that have a complex shape. Once coated, the article is then baked. In electrostatic painting, a powder coating material is statically charged and applied using standard powder coating equipment. With electrically conductive substrates, a static electric potential is generated between the paint and the substrate to be painted resulting in an attraction of the paint to the object.
When articles fabricated from metals are painted, the metal, which is inherently conductive, is easily grounded and efficiently painted.
However, in recent years, there has been an emphasis on the use of polymeric materials in the manufacture of articles, particularly in applications requiring reductions in weight and improved corrosion resistance, such as automotive applications. However, polymers typically used in such processes are insufficiently conductive to efficiently obtain satisfactory paint thickness and coverage when the article is electrostatically painted.
On poor electrical conductors such as polymeric materials, the conventional electrostatic coating techniques are not as successful because an electric charge potential must exist between both the substrate and the paint. If an object has poor electrical conductivity, it cannot be efficiently electrostatically charged and cannot, therefore, be efficiently electrostatically painted. Furthermore, on non-conductive surfaces, low humidity levels can have a negative impact on the quality of the bond of the powder coating to the surface.
Even so, electrostatic painting techniques are still desirable for use due to the benefits, especially for large scale commercial operations, including less loss of paint than with the use of other painting techniques such as spraying a liquid paint, and the quality of the coating is quite good because the method allows for a uniform distribution of paint without the entire surface being easily accessible. Materials having little or no conductivity such as plastics, may first be coated with a conductive primer or “prep” coating, and then electrostatically painted.
Some specific examples of methods of applying an electrostatic charge to surface having little or no conductivity include the addition of conductive fillers to polymers, for instance, application of a conductive primer such as a quaternary amine, However, the conductivity from these treatments, as well as the physical and/or surface characteristics may be less than desirable for certain applications.
The use of conductive primer compositions to prime the article in order to increase its conductivity is also known. However, depending on the particular primer employed, the cured primer may have adhesion, surface smoothness, hydrolytic stability, and durability characteristics, which are less than desirable for a particular application. Additionally, such primers compositions may contain volatile organic solvents, the emission of which during the priming process may be undesirable, as well as environmentally unfriendly. Further, each of the treatments described above can be expensive.
SUMMARY OF THE INVENTION
The present invention relates to an improved surface treatment for inducing conductivity in a substrate which has little or no conductivity which includes at least one halogen or halogen complex.
The present invention further relates to a method of treating a substantially non-conductive surface to improve the adhesion of an electrostatic powder coating to the surface. The method involves application of a surface treatment composition which includes a halogen, halogen complex, or hypohalite to the surface of a substrate. In some embodiments, the surface treatment composition includes iodine or iodine complex. In other embodiments, the surface treatment composition includes sodium hypochlorite, or bleach.
More specifically, the present invention relates to a method of electrostatically coating substrates having poor electrical conductivity including the steps of priming the substrate by applying a surface treatment composition which includes at least one halogen, halogen complex, or hypohalite induce conductivity in an otherwise substantially nonconductive material, applying a charge to the surface treated substrate, and electrostatically coating the substrate. In some particular embodiments, the halide is iodine. In some embodiments, the substrate comprises at least one polymeric material.
The present invention further relates to articles electrostatically coated according to the present invention. In some embodiments, the articles comprise at least one polymeric material.
The process of the present invention finds utility for use on any article that may be electrostatically coated or painted. For example, articles for the automotive industry, appliances, equipment parts and machine components, furniture, articles for outdoor activities including hunting, fishing and camping, and so forth. The process of the invention finds a preferred application in connection with the coating of radiators, car bodies and automotive accessories, machine components, compressors, shelving units, office furniture and comparable industrial products.
Examples of articles useful for outdoor activities include, but are not limited fishing rods, fishing lures, archery bows, cookware, and so forth.
The method of the present invention is economical, and has minimal impact on the environment.
DETAILED DESCRIPTIONS OF THE PREFERRED EMBODIMENTS
The present invention relates to an improved method of electrostatically coating substrates which have little or no electrical conductivity including, for example, polymeric substrates and polymer composite substrates, wood and wood products, and to an improved surface treatment composition for use therein.
The composition of the present invention suitable for use as surface treatment is desirably a liquid composition including at least one halogen, halogen complex, a halide salt, hypohalite, hypohalate, perhalate, and so forth, or mixture thereof, and a liquid carrier or solvent. Examples of suitable carriers include, but are not limited to, water, alcohol such as ethanol, isopropanol and methanol, acetone, ethers such as diethyl ether, toluene, p-xylene, benzene, carbon disulfide, chloroform, carbon tetrachloride, glycerol, alkaline iodide solutions, and so forth, and mixtures thereof. Some carriers are more preferable than others due to the varying levels of toxicity or environmental concern, with water being a preferred solvent. Water in combination with another carrier, such as an alcohol, is also suitably used.
Any of the halogens find utility herein including iodine, bromine, chlorine, and fluorine. Iodine and chlorine are more suitable for use, with iodine being most suitable.
“Halophors” including bromophors, chlorophors, iodophors, fluorophors, and so forth, also find utility herein. As used herein, the term “halophor” is used to refer to complexes of halogens with solubilizers or carriers which are typically polymers such as polyvinyl pyrrolidone or polyethylene glycol, or certain types of surface active agents including those that have detergent properties. Complexes of halogens are readily known.
The hypohalites include hypochlorite, hypoiodite, hypobromite, hypofluorite, hypoastatite, and mixtures thereof. Hypochlorite is su
Matthews, Inc.
Parker Fred J.
Vidas Arrett & Steinkraus
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