Stock material or miscellaneous articles – Composite
Reexamination Certificate
2001-09-28
2002-12-24
Boykin, Terressa M. (Department: 1711)
Stock material or miscellaneous articles
Composite
C524S430000, C428S412000, C428S423100, C428S423500, C428S423700, C428S426000
Reexamination Certificate
active
06497958
ABSTRACT:
BACKGROUND ART
The present invention relates to a coating composition for forming a transparent film on the surfaces of plastic lenses, the transparent film exhibiting excellent abrasion resistance, resistance against chemicals and weather-proof property, and to a method of producing the same.
Owing to their features such as small weight, safety, easy machinability and fashionableness which are not found in the glass lenses, plastic lenses have been widely used in recent years. However, a diethylene glycol bisallyl carbonate resin lens that is generally used has a refractive index of 1.50 which is smaller than that of the glass, and the outer circumference of the lens tends to become thick. In the field of plastic lenses, therefore, efforts have been made to reduce the thickness by developing highly refractive plastic lenses.
The plastic lenses, however, are subject to be easily scratched and it is a widely accepted practice to apply a silicone coating film onto the surfaces of the plastic lenses. The silicone coating film is usually formed by applying a coating composition (hereinafter also referred to as lowly refractive coating composition) comprising chiefly a fine silica powder, a polymerizable organosilane compound, a polymerizing catalyst, an acidic aqueous solution and a solvent onto the surfaces of the plastic lenses, followed by heating to cure the composition and to vaporize the solvent as disclosed in, for example, Japanese Examined Patent Publication (Kokoku) No. 2735/1982.
When a highly refractive plastic lens having a refractive index of not smaller than 1.54 is coated with a lowly refractive coating composition, however, there occur interference stripes due to a difference in the refractive index between the plastic lens and the coated film deteriorating the appearance.
In order to solve this problem, Japanese Unexamined Patent Publication (Kokai) No. 264805/1993 discloses a coating composition in which a fine silica powder which is a component of the coating composition is substituted by a composite metal oxide such as of Sb, Ti, Zr or Sn having a highly refractive index. Further, Japanese Unexamined Patent Publication (Kokai) No. 245523/1998 discloses a coating composition using a composite metal oxide such as of Ti, Ce or Sn, and Japanese Unexamined Patent Publication (Kokai) No. 306258/1998 teaches a coating composition using a composite metal oxide of Ti, Sn or Zr. Moreover, Japanese Patent No. 2577486, discloses a coating composition using a metal oxide which is an oxide of tungsten coated with a tin oxide. A coating composition using a metal oxide having a refractive index higher than that of the fine silica powder is hereinafter referred to as highly refractive coating composition.
When preserved for extended periods of time, however, the above highly refractive coating composition no longer exhibits the initial property of the coated film due probably to that the initial composition changes by the reaction among the components in the composition while being preserved.
DISCLOSURE OF THE INVENTION
It is an object of,the present invention to provide a highly refractive coating composition which can be stably preserved without losing the initial properties even after preserved for extended periods of time.
In order to solve problems inherent in the prior art, the present inventors have conducted keen study and have discovered the fact that the preservation stability is affected by an organoamine compound which is contained as a dispersant in a metal oxide suspension that is a starting material and is, hence, inevitably contained in the conventional highly refractive coating composition. A further study revealed that upon suppressing the content of the organoamine compound within a particular range, preservation stability of the coating composition could be markedly improved, and the inventors have thus completed the invention.
That is, the present invention is concerned with a coating composition containing a metal oxide, a polymerizable alkoxysilane compound, a polymerization catalyst, an acidic aqueous solution and a solvent, wherein an organoamine compound is contained in an amount of from 0.05 to 1.3% by weight with respect to the metal oxide.
The invention is further concerned with a method of producing a coating composition by mixing a metal oxide suspension containing an organoamine compound in an amount of not smaller than 1.3% by weight with respect to the metal oxide, a polymerizable alkoxysilane compound, a polymerization catalyst, an acidic aqueous solution and a solvent, wherein the organoamine compound is removed so that the amount thereof is from 0.05 to 1.3% by weight with respect to the metal oxide contained in said metal oxide suspension.
In the above production method of the invention, the organoamine compound is favorably removed by bringing the metal oxide suspension containing the organoamine compound in an amount of not smaller than 1.3% by weight with respect to the metal oxide into contact with a cation exchanger, or by bringing a mixture of said metal oxide suspension and at least one of other components into contact with the cation-exchange member.
BEST MODE FOR CARRYING OUT THE INVENTION
The coating composition of the invention contains a metal oxide, a polymerizable alkoxysilane compound, a polymerization catalyst, an acidic aqueous solution and a solvent.
There is no particular limitation on the metal oxide used for the coating composition of the present invention provided it is an oxide of a metal. There can be used any known metal oxide that: has heretofore been used for the lowly refractive or highly refractive coating compositions. Among these metal oxides, it is desired to use oxides of one or two or more kinds of metals selected from Al, Ti, Fe, In, Zr, Au, Ag, Sn, Sb, W and Ce, or a metal oxide containing composite oxides of these metals and, particularly, to use oxides of at least one or two or more kinds of metals selected from Al, Ti, Fe, Zr, Sn, Sb and W from the standpoint of abrasion resistance and large refractive index of the obtained coated film. It is also allowable to use these metal oxides in combination with silicon dioxide from the standpoint of adjusting the refractive index. In this case, the blending amount may be determined depending upon a desired refractive index of the coated film.
Though there is no particular limitation, it is desired that the metal oxide used in the present invention has an average particle diameter of from 1 to 300 nm so will not to impair the transparency of the obtained coated film. The metal oxide having such particle diameters is usually used being dispersed in a dispersing medium such as water, alcohol or any other organic solvent just like in the conventional coating composition. Generally, the metal oxide is colloidally dispersed to prevent the particles from being coagulated.
The amount of the metal oxide blended in the coating composition of the present invention is suitably determined depending upon the kind of the metal oxide and use of the coated film that is finally obtained, and is desirably from 20 to 70% by weight of the weight (mass) of the coated film that is finally formed. When the blending amount of the metal oxide on the above basis is smaller than 20% by weight, the coated film fails to exhibit abrasion resistance to a sufficient degree. When the blending amount exceeds 70% by weight, the coated film tends to be cracked. The weight of the coated film that is finally formed is substantially the weight of the metal oxide plus the weight of the polymerizable alkoxysilane compound that is polymerized and condensed as will be described later.
As the polymerizable alkoxysilane compound used for the coating composition of the present invention, there can be used, without limitation, any known alkoxysilane compound that has heretofore been used in the lowly refractive and highly refractive coating compositions as taught in, for example, Japanese Examined Patent Publication (Kokoku) N. 38419/1989 and Japanese Unexamined Patent Publication (Kokai) No. 116843/1999.
Abe Takashi
Kanou Kenichiro
Boykin Terressa M.
Sherman & Shalloway
Tokuyama Corporation
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