Optics: eye examining – vision testing and correcting – Spectacles and eyeglasses – Ophthalmic lenses or blanks
Reexamination Certificate
1999-08-20
2001-06-26
Sugarman, Scott J. (Department: 2873)
Optics: eye examining, vision testing and correcting
Spectacles and eyeglasses
Ophthalmic lenses or blanks
C351S177000
Reexamination Certificate
active
06250760
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the field of transparent coatings for transparent objects such as eyeglass lenses.
BACKGROUND OF THE INVENTION
Eyeglass lenses and other transparent plastic materials are subject to becoming dull and hazy due to scratching and abrasion during use. Polycarbonate eyeglass lenses, for example, while strong and shatter-resistant, also have relatively soft surfaces that are susceptible to scratching.
Various coatings have been proposed for eyeglasses and other transparent plastic materials to reduce their propensity to become scratched and abraded. One such composition is shown in U.S. Pat. No. 4,378,250 (Treadway et al.), granted Mar. 29, 1983. This patent shows the use of a coating composition that has two basic components, one being an at least partially hydrolyzed epoxy-functional alklyalkoxysilane and the other a derivative of an amine-substituted alkyltrialkoxysilane, also at least partially hydrolyzed. The amine component is reacted with a carbonyl compound such as a ketone to form, for example, an imine structure which stabilizes this component. The coating composition itself is formed by mixing together the two components, permitting the mixture to stand for a period of time, and then using the resulting material to coat eyeglass lenses or the like.
U.S. Pat. No. 5,866,262 (Galic et al.), granted Feb. 2, 1999, discloses a coating composition that employs two components that appear to be substantially identical to the components employed in the Treadway et al. '250 patent except that it is said that the components are fully hydrolyzed. Galic et al. explain that “fully hydrolyzed” means that the hydrolysis reaction involving the three alkoxy groups pendant from the silicon has been conducted in the presence of at least a stoichiometrically sufficient amount of water to hydrolyze all of the alkoxy groups. The Galic et al. composition requires “bodying”, explained as a copolymerization reaction which occurs as the mixture of the two components is permitted to stand for a period of time. It has similarly been found that with the Treadway et al. '259 coating composition, if “bodying” is not carried out following mixing together of the two silane components, a coating of the material on a transparent substrate will tend to undergo “mudcracking” as the composition dries. Mudcracking refers to a phenomenon in which the coating itself develops a series of odd angled and completely unacceptable cracks similar in appearance to the cracked surface of dried mud flats. The appearance of mudcracking in coating compositions containing the hydrolysis products of an epoxy alkoxysilane and an imine derivative of an amino alkoxysilane does not appear to be dependent upon whether the compositions have been partially or fully hydrolyzed.
The necessary “bodying” procedure of a coating composition tends to substantially reduce the pot life of the composition—that is, the time the composition can be maintained at room temperature and optical lenses, for example, can be dipped or otherwise successfully coated with the material. If the bodying procedure could be avoided, the pot life of the coating composition could be substantially increased, and this would represent a substantial benefit by reducing the per lens cost of the coating material and reducing the frequency with which new batches of the coating composition need to be prepared.
SUMMARY OF THE INVENTION
I have found that the incorporation of one or more metal colloids in the coating composition resulting from blending hydrolyzed silane components enables the composition to be used immediately without the necessity of “bodying”, and without the appearance of mudcracking in the finished product, with the result of substantially extending the pot life of the composition.
Thus, in one embodiment, the invention relates to a coating composition comprising, in an organic solvent, a curable polymer precursor comprising, as a first component, a hydrolysis product of an epoxy-functional alkoxysilane and, as a second component, an imine derivative of a hydrolysis product of an amine-functional alkoxysilane. The composition includes one or more metal oxide colloids in a sufficient concentration as to prevent mudcracking, upon drying, of a coating of said composition freshly made by blending together said components.
The metal oxide colloid of the coating composition preferably includes silica at a solids concentration in the composition of not less than about 10% by weight.
The degree of hydrolysis of the alkoxysilane components can vary substantially. Either or both of the alkoxysilane components may be hydrolyzed by a sufficient amount of water to stoichiometrically hydrolyze all or one or more of the alkoxy groups. The percent hydrolysis referred to herein refers to the ratio, in percent, of the amount of water actually used for hydrolysis to the amount of water required stoichiometrically for complete hydrolysis of all of the alkoxy groups. Degrees of hydrolysis of at least about 30% and preferably at least about 70% are preferred.
The composition may include various other components a may be desired, including other epoxy-functional monomers or oligomers.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Compositions of the invention employ preferably an organic solvent, although small amounts of water may be tolerated as needed. The solvent may include a lower boiling alcohol such as a C
1
-C
4
alcohol (ethanol and isopropanol being preferred), and/or a ketone such as acetone, methyl ethyl ketone, methyl propyl ketone, methyl isobutyl ketone, or mixtures thereof. Low boiling organic solvents generally are preferred because they permit a thin coating of the composition to dry quickly. In some instances, it may be desired to employ one or more higher boiling solvents for the purpose of obtaining uniform, defect-free coatings, and solvents such as the glycol ethers (e.g., propylene glycol monomethyl ether) are appropriate for this purpose.
The coating composition results from mixing together two components shortly before using the composition, and it is a feature of the composition of the invention that one may immediately use the mixture without waiting for a pre-reaction, that is, “bodying”, to occur, thus extending the time that the coating composition may be used.
The first component for the coating composition comprises the partial or complete hydrolysis product of an epoxy-functional alkoxy silane and particularly the &ggr;-glycidoxyalkyl trialkoxy silanes of which &ggr;-glycidoxypropyl triethoxy silane is exemplary. Compounds of this type may have the formula
Q—R
1
—Si(R
2
)
m
—(OR
3
)
3−m
wherein R
1
is a C
1
-C
14
alkylene group, R
2
and R
3
independently are C
1
-C
4
alkyl groups and Q is a glycidoxy or epoxycyclohexyl group, and m is 0 or 1. During hydrolysis as discussed above, one or more of the alkoxy groups are hydrolyzed to form silanol groups with the release of an R
3
—OH alcohol. Some condensation of the resulting silanol groups may occur, but epoxy reactivity is preserved. Many epoxy-functional alkoxysilanes are suitable as hydrolysis precursors, including the following: glycidoxymethyl-trimethoxysilane, glycidoxymethyltriethoxysilane, glycidoxymethyl-tripropoxysilane, glycidoxymethyl-tributoxysilane, &bgr;-glycidoxyethyltnmethoxysilane, &bgr;-glycidoxyethyltriethoxysilane, &bgr;-glycidoxyethyl-tripropoxysilane, &bgr;-glycidoxyethyl-tributoxysilane, &bgr;-glycidoxyethyltrimethoxysilane, &agr;-glycidoxyethyl-triethoxysilane, &agr;-glycidoxyethyl-tripropoxysilane, &agr;-glycidoxyethyltributoxysilane, &ggr;-glycidoxypropyl-trimethoxysilane, &ggr;-glycidoxypropyl-triethoxysilane, &ggr;-glycidoxypropyl-tripropoxysilane, &ggr;-glycidoxypropyltributoxysilane, &bgr;-glycidoxypropyl-trimethoxysilane, &bgr;-glycidoxypropyl-triethoxysilane, &bgr;-glycidoxypropyl-tripropoxysilane, &bgr;-glycidoxypropyltributoxysilane, &agr;-glycidoxypropyl-trimethoxysilane, &agr;-glycidoxypropyl-triethoxysilane, &agr;-glycidoxypropyl-tripropoxysilane, &agr;-glycidoxypropyltributoxysilane, &ggr;-gl
Fredrikson & Byron PA
Sugarman Scott J.
The Walman Optical Company
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