Coating processes – Coating remains adhesive or is intended to be made adhesive
Reexamination Certificate
2001-12-28
2003-12-09
Pianalto, Bernard (Department: 1762)
Coating processes
Coating remains adhesive or is intended to be made adhesive
C427S385500, C427S393500, C446S268000
Reexamination Certificate
active
06660327
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a novel adhesive composition and process for applying a styrenic based adhesive and cement coatings to thermoplastic polymer surfaces, particularly to toy articles formed of resin materials. Specifically, the present invention relates to a cyanoacrylate adhesive composition having superior bonding and hot-cold cycle resistance characteristics, particularly suited for unfriendly toy play environments.
2. Description of the Related Art
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 styrene-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. Thereafter the soft rubbery doll's head must be joined to a body portion comprised of a torso and limbs to complete a full bodied toy doll item. This is generally accomplished by gluing, sealing or cementing the soft eleastomeric head potion to the headless body section generally composed of a hard or firm plastic. In selecting an adhesive for the purpose of affixing the dolls'head two considerations are important: (1) that the adhesive form a firm and effective bond and seal between the soft elastomer and the harder resin substrate surface and (2) that the adhesive composition be relatively quick drying so as to accommodate expeditious doll manufacturing processes. The principle outlined here can be applied to any toy parts requiring laminating or bonding affixation of parts. The present invention provides a cyanoacrylate adhesive which provides superior bonding and rapid curing or drying.
It is well known that alpha.-cyanoacrylate (also known as 2-cyanoacrylate) adhesives polymerize and cure rapidly in the presence of trace water absorbed on the surface of a material to be bonded, affording an extremely strong bond in a short time for almost all materials except some inert materials such as polyethylene and Teflon. Because of such a superior property, alpha-cyanoacrylate adhesives are widely used as instantaneous adhesives for a room temperature setting as one-part type adhesives for the bonding of metals, plastics, rubber, wood, etc. However, since the cyanoacrylate polymer is a brittle polymer, cyanoacrylate adhesives have the drawback that they are inferior in peeling bond strength and impact resistance. This problem has been generally remedied by modifying the cyanoacrylate adhesive compositions with various elastomers, core-shell polymers, adhesives and reinforcing agents. The present invention carries this modification concept one step further in employing styrene block co-polymers in adhesive applications for toy manufacturing.
As indicated above, the class of the styrenic elastomeric materials commonly used as the molding material for toy doll faces and the harder structural portions of toy articles are A-B-A type block polymers such as styrene-butadiene-butylene copolymer-styrene or styrene-butadiene-styrene, manufactured by Shell and sold under the trademark Kraton. In the case of a toy having a hard surface comprised of a rigid or semirigid A-B-A styrene based block copolymer, a compatible elastomeric A-B-A styrene copolymer in the form of styrene-ethylene-butylene-styrene, (SEBS, sold under the trademark Kraton-G) has been found to be an exceptional modifier of the alpha-cyanoacrylate adhesives to render them useful as glues, cements, or sealants to bond mechanical parts in in toy items.
For adhesives used to bond toy mechanical parts and like structures which are used in rugged or otherwise unfriendly environments it is considered necessary to have not only a high bond strength in the normal state of use but also a high adhesive force to endure the heavy handling of child's play. Moreover, the bonded mechanical parts must even be capable of withstanding extreme or sudden changes in temperature caused by leaving the toy item outdoors or immersing the toy item in hot and cold water, e.g. a child subjecting a doll to a sink bath. Conventional cyanoacrylate adhesive compositions are not generally satisfactory in meeting these demands as adhesives in toy items.
It has been found that a cyanoacrylate adhesive composition containing certain styrenic block copolymers and certain solvents results in an adhesive which not only possesses high shear adhesive force, peeling bond strength and impact adhesive force but also exhibits an outstanding hot-cold cycle resistance and heat resistance.
SUMMARY OF THE INVENTION
In accordance with the present invention, there is provided an improved cyanoacrylate adhesive composition particularly useful for toy article applications comprising (1) a styrenic elastomeric block copolymer, (2) a cyanoacrylate monomer, and (3) a solvent composition comprised of certain high evaporation rate organic solvents. More particularly, the cyanoacrylate adhesive composition is characterized by containing (a) up to 20% by weight of an alpha cyanoacrylate monomer, (b) a styrenic elastomeric block copolymer miscible or compatible with the cyanoacrylate monomer, and (c) an organic co-solvent mixture having solubility parameters compatible with the solubility parameter of the elastomeric phase of the block copolymer.
Specifically provided herein as a preferred embodiment is a cyanoacrylate adhesive comprises from about 2% up to 10% by weight of an alpha alkyl cyanoacrylate, a high molecular weight styrene-ethylene-butylene-styrene block copolymer, and an organic solvent having a solubility compatibility with both components. The solvents are certain organic liguids which (1) have relatively high evaporation rates, (2) are capable of solubilizing the cyanoacrylate, and (3) offer stability to the styrenic copolymer partner in the coating composition and in the elastomeric substrates to which they are applied in that the co-solvent is non-reactive with and non-destructive to the respective component materials.
High evaporation rate organic solvents and co-solvents within the purview of the present invention include isoprene, hexane, heptane, styrene liquid, xylene, toluene, methylcyclohexane, cyclohexane, 2,2-dichloropropane, methylene chloride, diisobutyl ketone, diisopropylketone, methyl isobutyl ketone, methyl isopropyl ketone, methyl cyclohexanone, cyclohexanone, isobutyl acetate, isopropyl acetate, butyl acetate, propyl acetate, ethyl acetate, diethyl ether, dimethyl ether, diethylene glycol, 2-ethylhexanol, and mixtures thereof. Any one or more of these solvents that is capable of solubilizing both the styrene phase and the elastomeric rubber portions of the styrenic block copolymer of the present cyanoacrylate adhesive composition will function effectively in the instant invention. In the case of the high molecular weight styrenic block SEBS, the solubility parameter (to be explained below) is about 7.9 from which it can be calculated that a solvent combination or blend having a solubility parameter of between 7.4 to 9.4 will be effective within the purview of the instant invention.
Mattel Inc.
Mulcahy Robert W.
Pianalto Bernard
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