Process for making an abrasion resistant coating onto an...

Details Process for making an abrasion resistant coating onto an... Process for making an abrasion resistant coating onto an...

2000-06-29

2003-02-04

Pianalto, Bernard (Department: 1762)

Coating processes

Direct application of electrical, magnetic, wave, or...

Polymerization of coating utilizing direct application of...

C427S164000, C427S386000, C427S387000, C427S393500, C427S557000, C427S558000, C427S559000

Reexamination Certificate

active

06514574

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates, generally, to a process for forming an abrasion-resistant coating on solid substrates made of organic glasses such as ophthalmic lenses or other optical articles, and more particularly to a process for forming such an abrasion-resistant coating from a photochemically and thermally curable composition containing at least one epoxypolyalkoxysilane.
While ophthalmic lenses made of organic glasses benefit of ease of manufacture, lower cost than mineral glass, and being light in weight, they are easily scratched, therefore, requiring application of an abrasion-resistant coating to compete with abrasion resistance of mineral glass lenses;
Finished single vision lenses and semi-finished lenses quite often have an abrasion-resistant coating applied at the lens manufacturing site. In the case of the finished single vision lens, the optician or the laboratory needs only to edge the lenses for adjustment to the frame prior to dispensing. However, in the case of semi-finished lenses, the optician or the laboratory must surface the back of the lenses to prescription prior to edging and adjusting the lenses to the frames. This surfacing leaves the back or concave surface of the lenses uncoated. Opticians or dispensing laboratories may, of course, apply a UV curable composition on the back side of the lenses using a laboratory spin coater and then cure the composition using UV radiation. UV curing of these known UV curable compositions for making abrasion-resistant coatings is a relatively fast process, however, the resulting coatings although very scratch resistant suffer from a somewhat insufficient resistance to abrasion.
Polysiloxane “hard” coatings which exhibit very high abrasion resistance are also well known in the art. These coatings are typically formed by thermally curing a precursor composition including a hydrolysate of epoxyalkoxysilanes, silica and a thermal curing catalyst. Thermal curing is effected using thermal convection ovens with curing times that usually exceed 1 hour.
Compositions for making such polysiloxane “hard” coatings and the thermal curing thereof are disclosed, for example in U.S. Pat. No. 4,211,823.
In order to overcome the problem of long time curing associated with the above heat curable epoxyalkoxysilane based compositions, similar compositions curable by UV irradiation have been proposed, such as in document WO 94/10230. However, as indicated above, the resulting coatings exhibit abrasion resistances which are inferior than those of the thermally cured coatings.
Thus, one object of the present invention is to provide a process for curing an epoxyalkoxysilane based composition which results in an abrasion-resistant coating having abrasion-resistant properties as good as the classical thermally cured polysiloxane “hard” coatings but which needs a very short curing time compared to the usual thermal curing.
In particular, the process of the invention allows curing times of a few minutes and even of one minute or less while still resulting in a final abrasion-resistant coating as good as the classical thermally cured polysiloxane “hard” coatings.
A further object of the present invention is an epoxyalkoxysilane based composition specifically formulated for being cured according to the process of the invention.
SUMMARY OF THE INVENTION
According to the invention, there is provided a process for making an abrasion-resistant coating onto at least one surface of a substrate made of an organic glass which comprises:
(a) preparing a polymerizable composition containing a component A comprising at least one silane compound containing at least one epoxy group and at least two alkoxy groups directly bonded to the Si atom of the molecule or a hydrolysate thereof and a component B comprising fine particles of silica, an effective amount of at least one cationic photopolymerization initiator and an effective amount of at least one thermal polymerization catalyst;
(b) coating at least one surface of the substrate with the composition resulting from step (a);
(c) submitting the coated substrate to a photopolymerization step for pre-curing the coating layer; and thereafter,
(d) submitting the substrate with the pre-cured coating layer thereon to a thermal curing at a predetermined temperature and for a predetermined time to complete curing of the coating layer.
DETAILED DESCRIPTION OF THE INVENTION
The main components of the curable compositions for use in the process of the present invention are well known in the art and are disclosed in U.S. Pat. No. 4,211,823 and WO 94/10230.
These compositions contain as one of the main component a constituent A comprising an epoxyalkoxysilane or a mixture of epoxyalkoxysilanes or a hydrolysate thereof. The epoxyalkoxysilanes of the compositions of the instant invention contain at least one epoxy group and at least two alkoxy groups which are directly bonded to the silicon atom in the molecule.
The preferred epoxyalkoxysilanes are compounds of formula:
wherein R
1
is an alkyl or alkoxy alkyl group having 1 to 4 carbon atoms; R
2
is an alkyl or aryl group having 1 to 6 carbon atoms; R
3
is hydrogen or methyl group; m is 2 or 3; a is an integer from 1 to 6; and b is 0,1 or 2.
Among the preferred epoxyalkoxysilanes there may be cited &ggr;-glycidoxypropyltrimethoxysilane, &ggr;-glycidoxypropyltriethoxysilane, &ggr;-glycidoxypropylmethyldimethoxysilane, &ggr;-glycidoxypropylmethyldiethoxysilane and &ggr;-glycidoxyethoxypropylmethyldimethoxysilane. The most preferred epoxyalkoxysilane is &ggr;-glycidoxypropyltrimethoxysilane.
The amount of epoxyalkoxysilanes in the compositions generally ranges from 15 to 35% by weight.
The constituent A may also contain silane compounds or hydrolysates of silane compounds of formula:
R
4
c
R
5
d
SiZ
4−(c+d)
Wherein R
4
and R
5
are substituted or non substituted alkyl, alkenyl or aryl groups; Z is an alkoxy, alkoxyalkoxy or acyloxy group; c and d are 0,1 or 2; and c+d is 0,1 or 2.
Among these silane compounds there may be cited tetraalkoxysilanes such as methylsilicate, ethylsilicate, n-propylsilicate; trialkoxysilanes, trialkoxyalkoxysilanes and triacyloxy silanes such as methyltrimethoxysilane, methyltriethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, vinyltrimethoxyethoxysilane, vinyltriacetoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, &ggr;-chloropropyltrimethoxysilane, &ggr;-fluoropropyltrimethoxysilane, methacryloxypropyltrimethoxysilane and dialkoxysilanes such as dimethyldimethoxysilane, and methylphenyldimethoxysilane.
Hydrolysates of tetraalkoxysilanes and trialkoxysilanes or mixtures thereof are preferred.
The amount of these silanes in the compositions usually ranges from 15 to 35% by weight.
Hydrolysates are prepared by adding pure water or diluted aqueous hydrochloric acid, sulfuric acid, acetic acid, phosphoric acid or the like. Hydrochloric acid or sulfuric acid are preferred. Hydrolysis may be carried out with or without addition of solvent. Various solvents such as alcohol, ketones, halogenated hydrocarbon, aromatic hydrocarbon and mixtures thereof may be used.
Component A may also include other epoxy compounds such as polyglycidyl ethers and esters.
The second constituent B of the coating compositions comprises fine particles of silica, usually colloidal silica.
The amount of silica present in the compositions typically ranges from 2.5 to 50% by weight based on the total weight of the composition.
Typically, the colloidal silica used in this invention may have particle size of 1 nm to 1000 nm, preferably of 4 to 100 nm and more preferably of 10 to 60 nm. The silica may be dispersed in or have crystal-like particles in an aqueous or polar solvent or a combination of both. In general, the silica particles are dispersed in, preferably acidified, water, alcohol or water-alcohol mixtures. The preferred alcohols are methanol, ethanol, isopropanol, butanol, polyethylene glycol or combinations thereof.
The pH of the liquid coating composition is generally maintained between 3 and 5 to prevent g

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