Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Particulate matter
Reexamination Certificate
1997-04-03
2001-03-13
Le, H. Thi (Department: 1773)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Particulate matter
C423S099000, C423S111000, C423S622000, C423S624000, C423S625000, C424S401000, C424S641000, C424S642000, C424S682000, C428S403000, C428S689000, C428S700000, C428S701000, C428S702000, C502S340000, C502S341000, C502S342000, C502S343000
Reexamination Certificate
active
06200680
ABSTRACT:
TECHNICAL FIELD
This invention relates to a process for producing zinc oxide-based fine particles which are useful as a raw material or an additive for rubber vulcanization accelerators, various coatings, printing inks, colors, glass, catalysts, medicines, pigments, ferrite, etc. and can also be made use of in electrophotographic photoreceptors, printing materials, platemaking materials, UV screens, UV absorbing materials, gas sensors, etc. It also relates to a process for producing zinc oxide-based fine particles which are useful as such an additive that has high light-transmitting properties in the visible region and high UV absorbing properties, i.e., a so-called transparent UV absorber in coating materials, varnishes, resins, paper, cosmetics, and the like.
The present invention relates to zinc oxide-based fine particles having high transparency in the visible region, excellent UV absorbing properties, and heat ray screening properties as well as the above-mentioned functions and uses, which are useful as a so-called transparent UV and heat ray screening agent, an electrically conducting agent or an antistatic agent that in coatings (e.g., coating agent, ink, etc.), resins, paper, cosmetics, etc.; a process for producing the same; and products containing the same, i.e., coatings, coated articles, resin compositions, resin molded articles, cosmetics, and paper.
The present invention relates to zinc oxide-based fine particles which have a unique higher-order structure in which the constituent primary particles (zinc oxide crystals) have a controlled size and therefore exhibit high light transmitting properties combined with excellent scattering properties in the visible region, that is, excellent diffuse transmission properties in addition to the above-described functions and uses. The fine particles are therefore useful as a light diffusing agent. The invention also relates to a process for producing such zinc oxide-based particles and products containing the same, such as coatings (e.g., coating agent, ink, etc.), coated articles, resin compositions, resin molded articles, cosmetics, and paper, typified by a medium for diffuse transmission, such as a diffuser film for back-lighting liquid crystal displays.
The present invention relates to zinc oxide-based fine particles which not only have the above-described functions and uses but have controlled crystal morphology and a unique agglomerated state (higher-order structure) and are therefore also excellent in antimicrobial properties and deodorizing properties; a process for producing the same; and products containing the same, such as coatings (e.g., coating agent, ink, etc.), coated articles, resin compositions, resin molded articles, cosmetics, and paper.
BACKGROUND ART
Zinc oxide fine particles, what we call zinc white, have been conventionally produced by (1) a method consisting of gas phase oxidation of zinc vapor (called a France process or a American process) or (2) a method comprising reacting a zinc salt and an alkali metal carbonate in an aqueous solution to obtain zinc carbonate powder and, after washing with water and drying, pyrolyzing the powder in air. Zinc oxide obtained by the method (1) appears to have a particle size of submicron order but undergoes strong secondary agglomeration during the production process. Dispersing the particles in coating compositions or resin compositions requires much mechanical labor and yet results in a failure of obtaining a homogeneous dispersion. Compared with the method (1), the method (2) provides such finer particles as have a primary particle size of 0.1 &mgr;m or smaller, but the effects expected from the fineness are not manifested sufficiently on account of the strong agglomerating force among primary particles. Under the present situation, it is still less achievable with these methods to obtain zinc oxide fine particles with strictly controlled morphology, such as particle size, shape and surface condition of the primary particles, and the state of dispersion or agglomeration, in agreement with the end use.
In recent years, development of zinc oxide-based fine particles practically having a particle size of not greater than 0.1 &mgr;m has been demanded for use as a weatherable and heat-resistant material which is highly transparent in the visible region and also capable of absorbing ultraviolet light, i.e., a so-called transparent UV absorber. Processes hitherto proposed for producing such fine particles include (3) a method comprising gas phase oxidation of zinc vapor and (4) a wet process, such as a process comprising hydrolysis of a zinc salt in an alkali aqueous solution (see JP-A-4-164813 and JP-A-4-357114, the term “JP-A” as used herein means an “unexamined published Japanese patent application”) and a process in which a mixed solution of an acidic salt of zinc and ammonium acetate and hydrogen sulfide are subjected to autoclaving to form zinc sulfide, which is then subjected to oxidation (see JP-A-2-311314). The fine particles as obtained by the method (3) are powder having undergone firm secondary agglomeration as stated above and, when added to plastic moldings, such as fiber, a plate or a film, or coatings for the purpose of imparting UV absorptivity or improving weatherability, fail to provide products having satisfactory transparency. Further, when the fine particles are dispersed in an appropriate solvent and, if necessary, mixed with a binder resin to prepare a coating agent, and the coating agent is applied to a transparent substrate, such as glass or a plastic film, for the purpose of imparting UV absorptivity, the resulting coating film has poor transparency and homogeneity. On the other hand, the wet processes (4) involve complicated steps and unavoidably incur high cost. Thus, a process for producing zinc oxide-based fine particles which manifest the functions and characteristics of fine particles to the full extent and still have general-purpose properties is unknown.
Since zinc oxide fine particles have excellent UV screening power (in absorbing or scattering), they are used in coating films or resin molded articles endowed with UV screening power. However, zinc oxide fine particles have low dispersibility due to their liability to agglomeration.
Light-diffusing compositions comprising transparent inorganic fine particles, e.g., calcium carbonate, silica or barium sulfate, as dispersed in a binder component capable of dispersing such fine particles (e.g., methacrylic resins) are known. The light-diffusing compositions are used as a coating composition to be applied to a transparent substrate to form a light-diffusing layer or as a molding material to be molded into a molded article having light-diffusing properties, to provide a diffuser. The diffusing properties of these diffusers are based on light scattering at the interface between the inorganic transparent fine particles and the binder component due to the difference in refractive index therebetween.
However, the inorganic transparent particles of calcium carbonate, silica, barium sulfate, and the like do not have a UV screening function. Further, these diffusers essentially have poor mechanical characteristics on account of low affinity between the inorganic transparent particles and the binder component. Furthermore, since the diffusers should contain a large quantity of the inorganic transparent particles for achieving high diffusing properties, they have a reduced percent transmission and further reduced mechanical characteristics.
There has recently been an increasing demand for antistatic treatment on glass products or plastic products (films and fibers) for use as window panes of a clean room, CRT screens, flooring, wall covering, clothing, and the like for the purpose of preventing adhesion of dust.
An insulator, such as resin, can be made electrically conductive by, for example, dispersing a conducting agent in resin or applying a coating composition having dispersed therein a conducting agent on a substrate to form an electrically conductive layer. Known conducting agents include
Matsuda Tatsuhito
Takeda Mitsuo
Le H. Thi
Nippon Shokubai Co. , Ltd.
Pendorf & Cutliff
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