Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF T~IE INVENTION
The allyl diglycol carbonate synthetic polymers are used
extensively for eyeglass lenses and other lenses in the optical
industry. Such polymeric lenses are advantageous since they can
be manufactured inexpensively by casting making it possible to
obtain thereby complicated surface configurations directly without
expensive grinding. While the allyl diglycol carbonate polymers
are substantially resistant to scratching as compared to lenses
made of methylmethacrylate polymers, it is desirable to further
increase the abrasion resistance of the allyl diglycol carbonate
lenses by applying thereto a hard transparent protective layer.
FIELD OF THE INVENTION
.. .. _ _
The invention relates to optical components such as
ophthalmic lenses af an allyl diglycol carbonate protected by an
abrasion resistant coating.
DESCRIPTION OF THE PRIOR ART
-- -- --
U.S. 3,404,426 rclates to the preparation of coated
organic polymer substrate having a surface film thereon obtained
by coating the surface of the polymer with a coating solution
comprising a polysilicic acid ester of an alcohol containing from
1 to 12 carbon atoms inclusive and having from 0.01 to 2.0 silicic
acid ester groups per silicon atom together with an organic poly-
meric material compatible with said ester in the solvent free film
and an organic solvent for the polymer the surface of which is
being coated. The patent discloses that condensation polyester
resins are among those polymer substrates which are adapted to
be coated by the process of the invention. The compatible organic
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polymer which is used in combination with the polysilicic acid
ester can be, for instance, a ureaformaldehyde or phenol-aldehyde
type polymer or can be a partially hydrolyzed polymer which
contains free alcohol or hydroxyl groups such as polyvinyl alcohol.
The allyl diglycol carbonate polymer composition chosen
as a polymer substrate in the process of the invention is
generally described as an addition type and not a condensation
type polymer. Fully hydrolyzed polyvinyl alcohol (about 90% to
100% hydrolyzed) is utilized in the coating process of the
invention to provide increased abrasion resistance over polysilicic
acid ester coatings containing partially hydrolyzed polyvinyl
alcohol (about 60 to about 85% hydrolyzed). The allyl diglycol
carbonate of the invention has generally good resistance to
abrasion such as by rubbing with emery paper but by the method
of the invention the surface can be upgraded further with respect
to resistance to such abrasion.
U.S. 3,484,157 relates to an abraison resistant trans-
parent plastic optical element prepared by the application of a
transparent base of organic material having a directly adhering
coating comprised of a vinyl polymer cross-linked with a dial-
dehyde cross-linking agent. There is disclosed that the process
of the patent can be used to upgrade a lens formed of allyl
diglycol carbonate.
U.S. 2,404,357 relates to a coated methylmethacrylate
polymer prepared by the application of a coating solution
comprising ethyl silicate hydrolyzed with at least 15% by weight
of water together with a partially hydrolyzed vinyl acetate
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polymer, said coating subsequent to application to the methyl-
methacrylate polymer surface is pressed against a rigid surface
at elevated temperature to cure the coating and properly bond the
coating to the surface of the methylmethacrylate polymer.
U.S. 3,700,487 discloses and anti-fog abrasion resistant
- coating of lightly cross-linked polyvinyl alcohol on a diallyl
glycol carbonate lens in which adequate bonding of the anti-fog
coating is obtained by first hydrolytically treating the polymer
surface by dipping in an aqueous or alcoholic solutions of caustic
such as sodium or potassium hydroxide.
SUMMARY OF THE INVENTION
A process for preparing an allyl diglycol carbonate
coated lens is disclosed comprising applying to said lens a
coating solution of an hydrolyzed polysilicic acid ester in combin-
ation with about 906 to 100% hydrolyzed polyvinyl alcohol. In the
process of the invention the coating is applied to at least one
surface of said lens, volatiles are allowed to escape from the
coating solution and the coating is then cured at elevated
temperature. Coated allyl diglycol carbonate lenses are obtained
by the process of the invention having improved abrasion
resistance over the uncoated lens. Adhesion of the coating can
be promoted by hydrolytically treating the surface of the polymer
lens by alkali treatment prior to coating.
DESCRIPTION OF THE PREFERRED EMBODI~ENTS
.. . .. _ . . _ .
The abrasion resistant allyl diglycol carbonate lens of
this invention includes a transparent base element formed in a
conventional manner by thermoforming, casting or the like.
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- In accordance with this invention the lens is provided
with a directly adhering, transparent, abrasion resistant surface
coating of polyvinyl alcohol comprising about 90~ to 99% hydro-
lyzed polyvinyl acetate in combination with an hydrolyzed poly-
silicie aeid ester of an alcohol containing from 1 to 12 carbon
atoms inelusive, said ester having up to 4 silicic ester groups
per silicon atom. The polyvinyl alcohol is conventionally
obtained by the hydrolysis of polyvinyl acetate.
The coating solution is prepared in the form of an aqueous
solution having a solids concentration of about 22% to about 26%
weight percent. The proportion of said polyvinyl alcohol to the
polysilicic acid ester is about 1 to about 7.
Silicic acid from which the polysilicic acid ester is
prepared contains hydroxyl groups attached to silicon. The esters
are hydrolyzed prior to application. Polysilicic acid esters are
characterized by the following structure:
OR where R is a
l ~(CH2)n -CH3
RO - Si OR
¦ radical and n is 0 to 11
OR
The polyvinyl alcohol solution utilized to coat the lens
is prepared as an aqueous solution by addition of the polyvinyl
alcohol to the desired amount of boiling demineralized water
which is under strong agitation at the time of the addition of the
polyvinyl aleohol. Strong agitation is maintained until eomplete
solution is obtained. After eomplete solution of the polyvinyl
alcohol, the desired amount of an aleohol having a earbon chain
length of Cl to C-4 is added as r~pidly as possible short of
causing precipitation of the polyvinyl alcohol and a small amount
of a wetting agent such as an alkyl phenoxy polyethoxy ethanol
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sold under the trademark "Triton X100" is added to increase the
wetting ability of the coating solution for the allyl diglycol
carbonate lens.
The surface treatment of the diallyl glycol carbonate lens
has been found to be an important step in improving the moisture - -
resistance of the coated assembly. Hydroxylation of the surface
of the diallyl glycol carbonate is preferably effected by the use
at 10C to 40C, preferably room temperature, of an aqueous
solu.ion of an alkali such as sodium hydroxide or potassium
hydroxide. The concentration of alkali is from about 2% by weight
to about 20% by weight. The treatment time is about 2 minutes to
about one hour. It is theorized that the alkali treatment of
diallyl glycol carbonate polymer splits ester groups on the polymer
chain and introduces one OH groups onto the chain.
The polysilicic acid ester can be hydrolyze~ with an
amount of water equal to at least 15% by weight of the ester, i.e.
ethyl silicate, which is commercially available as chiefly tetra-
e~hyl orthosilicate. Hydrolysis of the tetraethyl orthosilicate
is usually accomplished by adding this material to a solution of
freshly prepared polyvinyl alcohol at elevated temperature.
At least one side of the allyl diglycol carbonate base
lens element is coated with the coating solution in any conventional
manner, for instance the lens element can be dipped in the combined
solution to form a uniform coating following which the coated lens
can be heated at elevated temperature to dry the coating and remove
volatiles. During this heating process, the polysilicic acid
ester and polyvinyl alcohol combine in a condensation process to
form a directly adhering, transparent, cross-linked, abrasion
resistant coating on the lens element. The coating is heated to
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a temperature of between about 90C to about 125C for a period
of from 1 to 2 hours in order to dry and cure the abrasion resis-
tant coating. While a range of temperatures has been provided for
drying and curing the coated lens, it will be recognized by persons
skilled in the art that other temperatures higher and lower than
disclosed above can be used.
As an alternate coating method the lens can be spun and
the coating solution applied to at least one side of the spinning
lens. The coated lens is then air dried at elevated temperature
as before preferably between about 90C and about 125C. A dur-
able, abrasion resistant coating is obtained.
The following example illustrates specific embodiments
of the invention but is to be considered in no way as limiting
the scope of the invention since it will be apparent to one
skilled in the art that many variations are possible and are
encompassed within the scope of the subject disclosure. In the
speci~ication all solutions are described as being applied at room
temperature and in the specification and claims all proportions
are by weight and all temperatures are in degrees centigrade
unless otherwise indicated.
EXAMPLE 1
A coating solution was prepare~ by hydrolyzing tetra-
ethyl-orthosilicate and incorporating a polyvinyl alcohol as
internal plasticizer and cross-linking agent together therewith
in combination with water and ethanol as a solvents and alkyl
phenoxy polyethyoxy ethanol as a wetting agent.
A coating was prepared using the following amounts of
materials in grams:
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demineralized water 182 grams
polyvinyl alcohol
(sold under the trademark
"Elvanol 71-30") 8 grams
ethanol 112 grams
alkyl phenoxy polyethoxy ethanol 1 drop
0.5 normal hydrochloric acid 18 grams
tetraethyl orthosilicate 80 grams
The polyvinyl alcohol which was 99% to 100% hydrolyzed
was dissolved in the demineralized water by heating the water to
boiling prior to adding the polyvinyl alcohol with rapid agitation.
When the polyvinyl alcohol has completely dissolved the ethanol
is added rapidly but not so as to cause precipitation in the
polyvinyl alcohol. Next the alkyl phenoxy polyethoxy ethanol is
added in the amount of 1 drop followed by addition of the 0.5
normal hydrochloric acid and finally tetraethyl orthosilicate is
added.
The surface of the allyl diglycol carbonate lens is treated
to promote adhesion by hydrolyzing the lens in a 15 percent by
weight solution of sodium hydroxide for 15 minutes at 20C. The
lens is thereafter washed thoroughly and then immersed in demin-
eralized water prior to coating.
The surface treated lens of allyl diglycol carbonate is
placed in a chuck and spin coated with the above solution diluted
on an equal weight basis with a mixture of equal parts of isopro-
panol and demineralized water. In the process of applying the
solution to a spinning lens of allyl diglycol carbonate, the rate
of spin is set at 2200 to 2800 revolutions per minute. The
application of the coating is conducted in an enclosure in which
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the temperature is maintained at about 20 to 25C. Subsequent to
the application of the coating, the coated lenses are cured for
2 hours at 95C.
It has been found that the rate at which the lens is
spinning determines the coating thickness applied. For instance
at a spinning rate of about 2500 revolutions per minute, a final
coating thickness of 0.54 microns is applied to the lens. As the
rate of spin increases ordinarily a reduced amount of coating will
be applied.
Samples of allyl diglycol carbonate lenses coated using
the above procedure were evaluated for abrasion resistance by
an abrasion testing device which provides 72 strokes per minute t
at a stroke speed of 3.3 inches per second, a stroke distance of
l 3/8 inches and a load of 200 grams per square inch. Using an
abrasion surface of #600 Crystolin, a coated lens of 0.5 microns
thickness was evaluated together with a double coated lens and
crown glass. Results are as follows:
Coating % Haze
Example 1 - 1 coat (0.5 microns) 3 - 3.5
Example 1 - 2 coats~l.0 micron) 2.5 - 3
crown glass - none 1.1
The coated lenses prepared in Example l were placed in
a humidity test chamber maintained at 160F and 95% relative
humidity. Prior to testing in the humidity chamber, the samples
were conditioned at ambient temperature for 24 hours following
cure. The test conditions are as follows: Eight hours exposure
in the humidity chamber followed by 16 hours at ambient temperature
is equal to one cycle. Samples were exposed to a total of three
cycles. Results indicate no crazing of the coated lenses occurs.
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EXAMPLE 2
(comparative example)
~forming no part of this invention)
The process of Example 1 is repeated except that a
partially hydrolyzed grade of polyvinyl alcohol sold under the
trademark "Gelvatol 20-60" is used as a substitute for the so-
called fully hydrolyzed grade of polyvinyl alcohol used in
Example 1.
"Gelvatol 20-60" is 87-89% hydrolyzed.
Abrasion test results`are performed as described in
Example 1. It is found that abrasion is poor as compared wlth
results obtained in Example 1.
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