Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
1999-07-14
2002-09-10
Reddick, Judy M. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S563000, C524S570000, C524S579000
Reexamination Certificate
active
06448321
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to an aqueous dispersion of a thermoplastic resin which is capable of forming a coating exhibiting excellent water resistance, oil resistance, chemical resistance and adhesion to non-polar materials; its production method; a thermal transfer recording medium comprising a substrate, and a thermal transfer layer on the substrate comprising a binder derived from such aqueous dispersion and a colorant.
Aqueous dispersions of a thermoplastic resin of various types are known in the art. Aqueous dispersions have been used in a wide variety of fields since an aqueous dispersion prepared by using water as its dispersion medium is far more advantageous than the dispersions prepared by using an organic solvent for the dispersion medium in view of flammability, working environment, handling convenience, and the like. For example, when an aqueous dispersion is coated and dried on a surface of a substrate such as paper, fiber, wood, metal, or plastic molded article, the resin coating formed will provide the substrate with water resistance, oil resistance, chemical resistance, corrosion resistance and heat sealability.
Conventional aqueous dispersions of a thermoplastic resin have been produced either by a process wherein a polymerizable monomer which is the resin raw material is polymerized by emulsion polymerization in an aqueous medium in the presence of an emulsifying agent, or by a process wherein a molten thermoplastic resin and an aqueous medium, and optionally, a surfactant are agitated by applying shearing force. The former process is associated with the disadvantage of the limited number of the polymerizable monomers that can be used, and hence, in the limited number of the aqueous dispersion of the thermoplastic resin that can be produced, is limited. The former process also suffers from complicated control of the polymerization reaction as well as intricate equipment. On the other hand, the latter process is applicable to a wide variety of resins in a relatively simple equipment.
Many improvements are proposed for the latter process. For example, JP-A 51-12835 discloses a method wherein a thermoplastic resin is kneaded with a water-soluble high molecular weight compound, and then, dispersed in water. However, the coating obtained from the aqueous dispersion produced by such method suffered from insufficient mechanical strength and inferior water resistance due to the presence of the water-soluble high molecular weight compound.
JP-B 57-23703 discloses a method wherein polypropylene kneaded with a dispersing agent selected from; a surfactant, a water-soluble polymer, and a water-swellable polymer is dispersed in water. The particles in the aqueous dispersion produced by such method had a relatively large diameter, and use of a petroleum resin was necessary to reduce the particle diameter of such an aqueous dispersion. The coating obtained from such an aqueous dispersion then suffered from tackiness.
JP-A 56-2149 discloses a method wherein an aqueous dispersion is produced by kneading an olefinic resin and an aqueous solution of a partially saponified polyvinyl alcohol. The coating prepared therefrom also suffered from insufficient physical properties due to the presence of the water-soluble resin.
A different type of method is disclosed in JP-B 58-42207. In this method, a polyolefin melt kneaded with a carboxyl group-containing polyolefin is introduced in hot water containing a basic substance, and shearing force is applied to obtain the dispersion. The aqueous dispersion produced by this method is quite preferable since the dispersion is free from the water-soluble polymer and the water-swellable polymer, and the dispersion is prepared without using any petroleum resin. However, when a dispersion having a small particle diameter is desired, this type of aqueous dispersion suffers from the problem of the limited number of resins that can be used for the raw resin material. In addition, production of this type of dispersion required a pressure resistant reactor since the resin is dispersed at a high temperature and under a high pressure. In view of such situation, there is a demand for developing a method capable of producing an aqueous dispersion which is capable of using a wide variety of usage of polymer and which can be produced without using any water-soluble polymer or water-swellable polymer and without using the petroleum resin.
In consideration of such situation, the inventors of the present invention made an intensive study and found that when an olefinic resin and an olefinic polymer containing carboxyl group, its anhydride group or ester group are melt kneaded with a basic substance and an optional anionic surfactant in the presence of a limited amount of water, phase inversion, that is, an inversion of the phase wherein the water is converted to the dispersion medium phase and the solid content is converted to the dispersed particle phase apparently takes place to results in the aqueous dispersion of the solid, and that once such phase inversion has taken place, a large amount of water can be supplemented in or outside the system to enable the production of the aqueous dispersion having a wide range of water content (JP-A 61-123664, JP-B 7-8933).
Such aqueous dispersion, however, contained the olefinic polymer containing carboxyl group, its anhydride group or ester group as an essential component in addition to the olefinic resin, and the dispersion often failed to exhibit physical properties inherent to the olefinic resin. Increase in the olefinic resin content for the purpose of obviating such problem resulted in the decrease of the aqueous dispersion yield, and use of a surfactant resulted in the decrease of the water resistance of the coating.
Recently, thermal transfer recording systems are widely used as an output unit for facsimiles, personal computers, word processors and the like. In the printing using a thermal transfer recording system, a thermal transfer recording medium (an ink ribbon) having a thermal transfer layer comprising a colorant and a binder disposed on a substrate is used. The printing in such a thermal transfer recording system is accomplished by contacting a thermal head with the thermal transfer recording medium on the side of the substrate and heatingdots provided on the thermal head in correspondence with the information to be output to thereby melt or soften the thermal transfer layer of the positions corresponding to the heated dots and releasing the thermal transfer layer at such positions for transfer onto the surface of a paper or other transfer medium.
The binder used in such thermal transfer layer has been typically a wax such as carnauba wax. Such waxes, however, have suffered from insufficient cohesion to the thermal transfer layer itself due to the low molecular weight., and satisfactory results could not be obtained in the printing of season tickets and the like wherein durability is required.
In order to obviate such drawbacks, use of an ethylene-vinyl compound copolymer such as ethylene-vinyl acetate copolymer or ethylene-ethyl acrylate copolymer has been investigated. Use of such copolymeric resins was quite suitable for applications where durability is required owing to their capability of forming a strong thermal transfer layer. On the other hand, use of such copolymeric resin was associated with the problem of reduced workability in the hot melt coating, namely, reduced workability in the production of the thermal transfer recording medium when the resin had a high molecular weight, namely, when the resin had a high melt viscosity.
In view of such situation, there is proposed coating of an ethylene-vinyl compound copolymer onto the substrate after preparing an aqueous dispersion of such copolymer. In this method, workability is not reduced even in the coating of a copolymer having a molecular weight higher than that of the wax. Production of conventional copolymers, however, involved use of a low molecular weight surfactant, and the resulting coating suffered from poor wat
Mitsui Chemicals Inc.
Reddick Judy M.
Sherman & Shalloway
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