Optical element having cured film

Details Optical element having cured film Optical element having cured film

2000-03-30

2001-10-23

Dawson, Robert (Department: 1712)

Stock material or miscellaneous articles

Composite

Of silicon containing

C428S446000, C428S697000, C428S701000, C428S908800, C516S090000, C516S092000

Reexamination Certificate

active

06306513

ABSTRACT:

TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical element having a cured film coating, more precisely, to an optical element having a cured film coating (hereinafter simply referred to as a “cured film”), which has good scratch resistance, good moisture resistance and good weather resistance, and whose properties are little degraded even when further coated with a deposited film of an inorganic oxide.
RELATED AND BACKGROUND ART
Heretofore, in general, in order to make plastic moldings have scratch resistance, a method of providing a coating film with scratch resistance on the surface of the molding has been employed. Coating compositions proposed to be used for forming such a coating film, include, for example, a coating composition containing a colloidally-dispersed silica sol (Japanese Patent Laid-Open No. 111336/1978), a coating composition containing fine tin oxide particles coated with fine tungsten oxide particles (Japanese Patent Laid-Open No. 172369/1991), a coating composition containing a sol of tin oxide colloid particles modified with tin oxide-tungsten composite colloid particles (Japanese Patent Laid-Open No. 25603/1994), etc.
However, these prior coating compositions are all problematic in that, when they are coated, for example, on optical substrates, they could not form film coatings capable of making the coated substrates have good scratch resistance and good moisture resistance while also having an esthetic appearance (as used herein, esthetic appearance means that the coated substrates do not form interference fringes caused by a difference in the refractive index between the film coating and the substrate) and good weather resistance. Furthermore, even if an additional deposited film were provided thereon, the resulting coated substrates still could not have satisfactory scratch resistance and satisfactory moisture resistance while also having an esthetic appearance and good weather resistance.
The object of the present invention is therefore to solve the problems with the prior film coatings. Specifically, it is an object to provide an optical element having a cured film, which has good esthetic appearance, good weather resistance, good scratch resistance and good moisture resistance, and whose properties are little degraded even when further coated with a deposited film.
SUMMARY OF THE INVENTION
In accordance with the above objects, the present inventors have assiduously studied the problems of the prior art and developed an optical element having a cured film having good properties as described above. As a result, the inventors have found that, when a coating composition containing specific modified stannic oxide-zirconium oxide composition colloid particles and an organosilicon compound is coated on an optical substrate to form a cured film thereon, then the above objects can be attained.
Specifically, the present invention provides an optical element having a cured film on an optical substrate. The cured film is formed of a coating agent containing (A) modified stannic oxide-zirconium oxide composite colloid particles as prepared by coating at least a part of the surfaces of stannic oxide-zirconium oxide composite colloid particles with stannic oxide-tungsten oxide-silicon oxide composite colloid particles, and (B) an organosilicon compound.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The invention will now be described in detail with reference to certain preferred embodiments. The optical element having a cured film according to the present invention (hereinafter simply referred to as “optical element of the invention”) comprises an optical substrate and a cured film of a specific coating agent provided thereon. The coating agent of the invention comprises (A) modified stannic oxide-zirconium oxide composite colloid particles, and (B) an organosilicon compound.
The modified stannic oxide-zirconium oxide composite colloid particles of component (A) are prepared by coating all or a part of the surfaces of (1) stannic oxide-zirconium oxide composite colloid particles with (2) stannic oxide-tungsten oxide-silicon oxide composite colloid particles. The colloid particles of component (1) become the nuclei of the modified stannic oxide-zirconium oxide composite colloid particles. Preferably, the particles of component (1) are composed of stannic oxide colloid particles and zirconium oxide colloid particles bonded in a ratio by weight, ZrO
2
/SnO
2
, falling between about 0.02 and about 1.0, and have a particle size of from about 4 to about 50 nm, dependant on the properties of the coating agent to be prepared.
The stannic oxide-tungsten oxide-silicon oxide composite colloid particles of component (2) which coat all or a part of the surfaces of the colloid particles of component (1) have a ratio by weight, WO
3
/SnO
2
, falling between about 0.1 and about 100, and a ratio by weight, SiO
2
/SnO
2
, falling between about 0.1 and about 100, and have a particles size of from about 2 to about 7 nm, more preferably from about 2 to about 5 nm, dependant on the properties of the coating agent to be prepared.
In view of the stability and the properties of the coating agent containing them, the modified stannic oxide-zirconium oxide composite colloid particles of component (A) preferably have a particle size of from about 4.5 to about 60 nm.
According to the present invention, the modified stannic oxide-zirconium oxide composite colloid particles of the component (A) can be efficiently prepared, for example, according to a process comprising the following steps (a), (b), (c), (d) and (e).
Step (a):
Step (a) comprises mixing an aqueous stannic oxide sol with an aqueous solution or suspension of an oxyzirconium salt. Preferably, the aqueous stannic oxide sol contains stannic oxide colloid particles having a particle size of from about 4 to about 50 nm, and has an SnO
2
concentration of from about 0.5 to about 50% by weight, more preferably from about 1 to about 30% by weight. The aqueous stannic oxide sol may be prepared by any known method including, for example, an ion-exchanging method, a deflocculation method, a hydrolysis method, a reaction method, etc.
Examples of the ion-exchanging method include: processing a stannate such as sodium stannate or the like with a hydrogen-type cation exchange resin, processing a stannic salt such as stannic chloride, stannic nitrate or the like with a hydroxyl-type anion exchange resin, etc. Examples of the deflocculation method include: washing a stannic hydroxide gel prepared by neutralizing a stannic salt with a base or by neutralizing stannic acid with hydrochloric acid, followed by deflocculating the washed gel with an acid or a base, etc. Examples of the hydrolysis method includes: hydrolyzing a tin alkoxide, hydrolyzing a basic salt of stannic chloride under heat followed by removing the unnecessary acid from the resulting hydrolyzate, etc. Examples of the reaction method include: a method of reacting metal tin powder with an acid, etc.
The medium for the stannic oxide sol may be any of water, or hydrophilic organic solvents and their mixtures, but is preferably water to give an aqueous sol. In general, the pH of the sol preferably falls between about 0.2 and about 11, in view of the stability of the sol. Within a range not interfering with the objects of the invention, the stannic oxide sol may contain any optional components including, for example, an alkaline substance, an acidic substance, a hydroxy carboxylic acid and the like for stabilizing the sol.
The aqueous solution or suspension of an oxyzirconium salt preferably has an oxyzirconium salt concentration of from about 0.5 to about 50% by weight, more preferably from about 1 to about 30% by weight. The oxyzirconium salt includes, for example, zirconium oxychloride, zirconium oxynitrate, zirconium oxysulfate, oxyzirconium salts of organic acids such as zirconium oxyacetate, and also zirconium oxycarbonate, etc. Preferably, the oxyzirconium salts are used in the form of their aqueous solutions. However, when the aqueous stannic oxide

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