Coating processes – With post-treatment of coating or coating material – Heating or drying
Reexamination Certificate
2000-12-04
2003-01-07
Szekely, Peter (Department: 1714)
Coating processes
With post-treatment of coating or coating material
Heating or drying
C427S393500
Reexamination Certificate
active
06503569
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a novel composition and process for applying a styrenic based adhesive, cement, coating, or paint to thermoplastic polymer surfaces, particularly to toy articles formed of elastomeric materials. Because the coating composition uses naturally occurring terpene solvents, it is safe for use as a coating or paint for toy articles which can be safely used by children.
BACKGROUND OF THE INVENTION
Children's toys and dolls, in particular, have a history dating back into antiquity. Generally, the technology surrounding the manufacture of dolls centers on creation of an attractive doll face, miniturized application of conventional clothes, manufacture of a doll body using plush or other sculptural techniques, and the simulation of the hair with sculptural elements, fibers, or other techniques. In the case of doll faces, the doll maker has a wide panoply of possible constructions and manufacturing techniques at his disposal. Traditional techniques involve the use of plaster-like or hard plastics material to cast a doll face. In time, however, soft rubber materials such as styrene-butadiene rubber (SBR) and syrene-butadiene-styrene block copolymer (Kraton) elastomers have come to replace plaster and hard plastics in the production of doll heads because of their realistic look and feel.
The soft rubber doll faces include all the normal features of a human figure simulated by the doll including the entire head, including well formed lips, teeth, cheeks, nose, chin, ears, and forehead. After the injection molding of an elastomeric doll face, it is finished by applying a dye or other similar material to give the face a natural skin color. Parts of the facial skin are often given a contrasting reddish color to improve the attractiveness of the face, as by using an air brush may be used to apply a patch of rosy hue to the cheeks.
Regardless of the type of paint used on a toy doll article, it has remained imperative that such materials be safe for young children. Safety requirements have evolved through the years as safety concerns have grown. Generally, safety requirements mandate that any material compositions used in a toy be odorless, nonirritating to the skin or eyes or the like, and be nontoxic if ingested. Additional requirements have been expected of materials used to coat or paint toy articles in that they must be non-peeling, requiring that the coating or paint tenaciously adhere to the toy item to avoid flaking or peeling and possible consumption by a child user. Accordingly, such paints should be resistant to oxidation and flaking, particularly as applied to elastomeric rubber surfaces of soft doll faces. And further the paint should be able to withstand the stretching and other physical abuse of a child so that the appearance of the painted surface is maintained. And above all the paint or coating composition must avoid the use of undesirable volatile organic solvents the residual presence of which can be dangerous due to the toxic effect of certain aromatic and chlorinated hydrocarbon solvents.
In view of the environmental, health and safety concerns in the use of organic solvents, less controversial solvents such as water or mineral spirits have been used to provide toy paint or coating compositions. The mineral spirits is less toxic and considered generally safe in coating applications for toys and, of course, water is completely safe and non odiferous as a coating solvent for any coating applications. However both solvents evaporate relatively slowly over a long period of time which detracts from the overall effectiveness of these coating compositions. For example, when applying a water based latex emulsion paint to a soft elastomeric item, a slower evaporation time delays set up of the paint coating composition and inhibits complete bonding between the joined surfaces of the applied coat and the article. As a result of an extended drying period, non-uniform and unstable coatings result leaving these coating vulnerable to use factors which generate peeling and splitting among other negative consequnces.
As indicated above, the class of the styrenic elastomeric materials commonly used to mold doll faces and other toy articles are A-B-A type block polymers such as styrene-butadienebutylene copolymer-styrene or styrene-butadiene-styrene, manufactured by Shell and sold under the trademark Kraton. The molded polymeric doll faces tend to be dull and unattractive and so are finished by application of a skin coating or paint to provide a good facial appearance to this facial piece. It has now been found that an elastomeric adhesive coating comprising a styrene based resin and a terpene solvent has particular advantages in forming tenaciously bonded adhesive coatings on styrenic resin molded items.
SUMMARY OF THE INVENTION
In accordance with the present invention, there is provided a resin coating composition particulary useful for toy article applications comprising a styrenic copolymer and a terpene solvent. The terpenes are naturally occuring, biodegradable compounds characterized by a very low level release of organic vapor and, accordingly, they are considered safe as solvents for coating or paint applications for toy items. The terpene solvents have also been found particularly effective in solubilizing styrenic copolymers and enhancing the bonding of the copolymers to form adhesive coatings on resinous substrate surfaces. Therefore compositions made in accordance with the present invention are completely non-toxic, environmentally and child safe, and result in an overall superior coating or paint product.
Of particular significance, styrenic copolymer/terpene coating compositions made in accordance with the present invention preliminarily dry in a rapid manner to provide a strong bond with polymeric substrate surfaces thereby engendering consequent use durability to the applied coat or film. The terpene solvent has been found capable of completely solubilizing styrene based resins, styrenic copolymers, pigments or other additives to provide a coating composition having a relatively high solids content up to 20% by weight of the total composition. Therefore while the resinous coating compositions made in accordance with the present invention can be viscous, they can be formulated to be poured and applied by hand, brush or other manipulative means for uniform coating application at ambient temperatures, while comprising a sufficient percentage of solids to avoid shrinkage following evaporation of the solvent.
The discovery of the present invention is that one may formulate a superior adhesive, cement, coating or paint composition by combining a styrenic copolymer and a terpene solvent in certain amounts to form a coating composition of completely unexpected character when applied to elastomeric substrate surfaces. While the coating composition is effective with any thermoplastic resin surface, the instant compositions are especially effective as a coating or adhesive for styrene based elastomers, those copolymers with a linear A-B-A configuration in which A is a polystyrene endblock. It is believed that the terpene solvent is particularly effective in solubilizing the styrene-based copolymer molecules of the substrate surface thereby takifying the elastomeric surface to generate a miscible interface with the applied coat resulting in an amalgam like bonding upon drying. The terpene solvent has been particularly effective with styrene based elastomeric copolymer surfaces having unsaturated block segments such as styrene-ethylene-butylene-styrene (SEBS) surfaces. Consequently the resulting coating is characterized by an exceptional durability, elongation and flexibility. Because the coating compositon employs certain naturally occuring terpene solvents, they are safe for use as paints for children's toys and are particularly useful in applications to the soft elastomeric materials used in doll facial structures where the paint coatings are expected to withstand the rigorous and hostile environment of child u
Mattel Inc.
Mulcahy Robert W.
Szekely Peter
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