GB2140581A - Anti-static and/or anti-reflective abrasion-resistant ophthalmic lenses - Google Patents

Abstract

Organic polymeric plastic substrates of optical elements are made anti-static and abrasion-resistant by applying a conductive layer (4) to at least one surface of a plastic substrate (2) and overcoating the conductive layer with an abrasion-resistant layer (6). Other anti-static and/or anti-reflective optical elements may be produced by coating at least one surface of an organic polymeric plastic substrate with a protective organo-silica coating composition and then subjecting the coated plastic substrate to a glow discharge treatment. <IMAGE>

Description

SPECIFICATION Anti-static and/or anti-reflective abrasion-resistant ophthalmic lenses This invention relates to a novel anti-static, abrasion-resistant optical element, particularly a plastic ophthalmic lens having a conductive layer deposited on at least one surface and an abrasion-resistant coating adhered thereto, and to novel and improved methods of making such optical elements.

This invention also relates to methods of coating optical surfaces and in particular, to a new and useful process for coating an ophthalmic lens so that the finished lens has an anti-static and/or anti-reflective surface.

The term static electricity denotes the group of phenomena associated with the accumulation of electrical charges. Attraction of small particles by an electrically charged body is due to the induced charge. By approaching another insulator (dirt, ash, etc.) the negatively charged body repels the electrons at the surface of the particles. Thus their surface becomes positively charged and attraction results. After contact is established, the charge in the small particle is gradually neutralized; eventually the particle attains a negative charge and is repelled.

The build-up of static charge on plastic elements (especially plastic ophthalmic lenses coated with abrasion-resistant coatings) attracts dust and is unacceptable in many applications (e.g., polycarbonate safety lenses in steelmills, cotton mills and coal mines). In the case of eyewear, these dust particles cause light scattering or haze which can severely limit the visual acuity of the wearer and necessitates frequent cleaning.

Certain topical treatments are commercially available for the prevention of static charge build-up, but these topical treatments are short lived and must be continually repeated.

Another way of preventing the build-up of static charge on plastic lenses is to imbibe anti-static agents into the plastic materials. However, these anti-static agents are known eye irritants and may not be suitable for ophthalmic purposes. Furthermore, these anti-static agents are designed to migrate to the surface where they can interfere with the coating-substrate interface.

It is also often desirable in many applications to reduce the reflectance of an optical surface. By reducing the reflectance of light impinging upon the surface of an optical element, a greater percentage of incident light will be transmitted through the optical element.

When optical elements are moulded out of a polymeric plastic substrate, the reflectance is commonly reduced by vacuum deposition of single or multiple film layers which are designed and fabricated to reduce reflectance by interference effects. These layers require a high level of skill and complex equipment to manufacture on a large scale. Also, when some of these coatings are exposed to moist or otherwise hostile environments, they will deteriorate rapidly. Specifically, unless care is taken in the design and construction of such coatings, exposure to hostile environments may reduce the adherence of the coating to the substrate and the coating may be peeled or otherwise separated from the optical element.

There has been considerable use in recent years of an electrical discharge in order to form flexible thin films of solid organic material upon the surface of a susbtrate. Thin electrical discharge may be maintained in the sparking, corona or glow region of an electrial phenomenon.

A glow discharge may be defined as a silent discharge without sparks and having a space potential gradient in the vicinity of the cathode resulting in a potential difference near the cathode which is considerably higher than the ionization potential of the surrounding gas. The glow discharge is identified by a steep potential gradient at the cathode and operates primarily by electron liberation by positive ion bombardment at the cathode. In relation to a corona discharge, a glow discharge is characterized by a much lower potential or voltage and a higher current than a corona discharge. Unlike a corona discharge which is a reversible discharge situation, the glow discharge occurs after the sparking or breakdown potential is exceeded and is an irreversible change which has occurred in the electrical circuit.

Accordingly, it is the principal object of the present invention to prevent the build-up of static charge on optical elements.

It is a further object of the present invention to prevent the build-up of static charge on plastic ophthalmic lenses coated with abrasion-resistant coatings.

It is still a further object of the present invention to produce an anti-static abrasion-resistant optical element that is neither moisture nor wear sensitive.

It is another object of the invention to reduce the reflectance of and to prevent the build-up of static charge on the surface of plastic ophthalmic lenses coated with abrasion-resistant coatings.

It is a further object of the invention to reduce the reflectance of the surfaces of an optical element without causing any coatings on the optical element to peel or otherwise separate from the optical element.

The problems of the prior art are overcome by the discovery that novel anti-static, abrasion-resistant optical elements that are neither moisture nor wear sensitive can be produced by applying a conductive layer to at least one surface of an organic polymeric plastic substrate and overcoating said conductive layer with a protective layer.

If a semi-transparent conductive material known in the industry such as indium doped tin oxide (inn02) is used for the conductive layer, then after the conductive layer is deposited on at last one surface of the plastic substrate, the plastic substrate is preferably subjected to a glow discharge treatment before the abrasion-resistant coating is applied in order to convert the conductive layer to a fully transparent state.

Optionally, if such a transparent conductive layer is used, a silicon oxide (SiOx wherein x ranes from 1 to 2) prime coat may be applied to the surface of the plastic substrate before the conductive layer is applied, and another optical silicon oxide prime coat may be applied after the optional glow discharge process and before the application of the agrasion-resistant coating.

Other problems of the prior art are overcome by the discovery that novel anti-static and/or anti-reflective optical elements can be produced by coating at least one surface of organic polymeric plastic substrate with a protective organo-silica coating composition and then subjecting the coated plastic substrate to a glow discharge treatment.

Although ophthalmic lenses are the preferred optical elements of the invention, other optical elements of the invention may include solar panels, instrument covers and CRT display devices.

Reference is now made to the accompanying drawings, in which: Figure 1 is a side view of a lens manufactured in accordance with the present invention; Figure 2 is a graph showing charge decay time versus transmittance for a lens manufactured in accordance with the invention; Figure 3 is a graph showing nominal chromium thickness versus transmittance for a lens manufactured in accordance with the present invention; and Figure 4 is a graph illustrating the reflectance of an organo-silica coated CR-39 lens before and after a glow discharge treatment.

In one embodiment of the present invention, an anti-static abrasion-resistant optical element comprises: an organic polymeric plastic substrate; a conductive layer deposited on at least one surface of said plastic substrate; and a protective layer overcoating said conductive layer.

Any type of organic polymeric plastic substrate may be used, i.e., a polycarbonate susbtrate, more specifically a poly (2,2'-dihydroxyphenylpropane) carbonate substrate; an allyl substrate, more specifically a CR-39 substrate; or an acrylic substrate, more specifically a polymethyl methacrylate substrate. CR-39 is a polydiethylene glycol bis (allyl carbonate) obtained from PPG Industries, Inc. The plastic substrate must be transparent if the optical element of the invention is to be used for opthalmic purpsoes.

The conductive layer may comprise any metal or semiconductor. The type of material used for the conductive layer is dependent upon what type of optical element is being produced. For instance, gold would be a good candidate in many applications. Gold transmits light with a pleasing greenish colour and reflects infrared, therefore it is a good choice to be used in architectual glass or heat control. Gold, however, is expensive and does not generally adhere well. For ophthalmic use, factors such as maximizing the transmittance and achieving good adherence to the lens and overcoating are essential. Chromium is a good candidate for opthalmic applications because of its good adherence. Other similar metals would be nickel, nichrome (a nickel chromium alloy), and palladium.

If metal is used for the conductive layer of an ophthalmic element, the metal layer must be as thin as possible in order to maximize the transmittance, however, the metallayer must stil! be thick enough to form a continuous or quasi-continuous film in order to be conductive. For chromium, this optimum thickness was found to be about 30 A (Angstroms) +5An. When the thickness of the chromium layer is around.30 A the coating becomes conductive and the transmission for visible light of the coated lens still meets or comes very close to meeting the 89% ANSI requirement for plano safety lenses.If the percent transmission for visible light of a coated plano safety lens of this invention is at least 85%, it is believed that the advantages of such alens, i.e. the anti-static properties, outweigh the reduced transmittance. Thicker anti-static metal coatings with percent transmissions for visible light of at least 60% are quite useful for other eyewear and optical applications.

The conductive layer may be applied to at least one surface of the plastic substrate by any conventional means known in the art for producing a conductive layer of controlled thickness, such as by vacuum deposition or sputtering.

Figure 1 shows a ophthalmic lens 2 in which a layer of chromium metal 4 was deposited onto the front (convex) surface. The lens was then overcoated with an abrasion-resistant coating 6.

Even though the conductive metallayer is overcoated by a dielectric coating, the conductivity through the dielectric coating and along the metal coating is sufficient to cause a static charge applied to the surface to dissipate at a significantly faster rate than a similarly coated lens without the underlying metal film.

Table 1 describes the properties of an ophthalmic lens made in accordance with this invention having a poly (2,2'-dihydroxyphenylpropane) carbonate substrate, a chromium metal conductive layer, and an organo-silica layer (made in accordance with U.S. Patent 4,211,823, Suzuki et al, the teachings of which are incorporated herein).

TABLE 1 Chromium Metal Coating Visual transmittance 76.6% Charge Decay Time 3.6sec.

Material of conductive Layer Cr. Metal Coating thickness 35A The charge decay time of 3.6 seconds may be compared with times of tens or hundreds or minutes for polymer ophthalmic lenses or organo-silica coated polymer lenses under the same conditions but without the presence of the conductive layer.

Since a thin metal thickness is difficult to control accurately, a semi-transparent semiconductor which can be made transparent, such as indium doped tin oxide or zinc oxide, is the preferred material for the conductive layer of an opthalmic element. A form of indium doped tin oxide suitable for use is Patinal Substance a from E. M. Laboratories, Inc.

If a semi-transparent conductive material known in the industry, such as indium doped tin oxide, is used for the conductive layer, then after the conductive layer is applied to at least one surface of the plastic substrate by vacuum deposition, sputteringor any method known in the art for producing a conductive layer of controlled thickness, the plastic substrate is preferably subjected to a glow discharge treatment before the abrasion-resistant coating is applied. The purpose of the glow discharge treatment is to fully convert the semiconductor to the transparent state.Although the glow discharge treatment can take place under any conditions of pressure, voltage and current which will sustain a glow discharge, the semiconductor is preferably subjected to a glow discharge treatment of from 1-10 minutes, preferably 1-5 minutes, in an oxygen atmosphere under a pressure of between 0.05 and 0.150 Torr, at a voltage of 100 to 1500 VDC (Volts Direct Current) and an amperage of 100 to 800 mA.

The thickness o the semiconductor layer is not critical. For instance, it was found that an induim doped tin oxide layer thickness of 100 A was adequate. An indium doped tin oxide thickness of 100 A was found to be easily converted to a transparent state in a glow discharge of 1-5 minutes. This 100 A thickness gave sufficiently good conductivity with minimal optical absorbance. The only constraint on the thickness of the semiconductor coating is that a thicker coating is more difficult to fully convert to the transparent state.For example, using the glow discharge method to convert the indium doped tin oxide, if the thickness is greater than 150 A", it it may be necessary to deposit the coating in 100 A" increments followed by a glow discharge treatment after each increment to build up to the total thickness.

If a semi-transparent conductive material which can be made transparent, such as indium doped tin oxide, is used for the conductive layer, a silicon oxide (defined for purposes of this invention as SlOx wherein x ranges from 1 to < 2) prime coat is preferably applied to the surface of the plastic substrate that the conductive layer will be applied to before the conductive layer is applied, and another silicon oxide prime coat is preferably applied on top of the conductive layer after the optional glow discharge process and before the application of the abrasion-resistant coating. The silicon oxide prime coat layers are used to promote adhesion of the transparent conductive layer, i.e., indium doped tin oxide, to the plastic substrate and to the abrasion-resistant overcoating.

Table 2 gives standard durability test data results or ophthalmic lenses having poly (2,2'-dihydroxy phenylpropane) carbonate substrates, indium doped tin oxide conductive layers (fully converted to their transparent state through the use of a glow discharge treatment), and Suzuki et al overcoatings (Configuration 1), and ophthalmic lenses having the same components plus a silicon oxide layer applied to the polycarbonate substrate and a silicon oxide layer applied to the fully converted indium doped tin oxide layer (Configuration 2).

TABLE 2 Durability test data comparison Configuration 1: Poly (2,2'-dihydroxyphenylpropane) carbonate/lnSnO2/Suzuki et al Tape Test -Failed Life Test (Acidic Salt Solution soak - Failed Configuration 2: Poly (2,2'-dihydroxyphenylpropane) carbonate/SiO/lnSnO2/SiO/Suzuki et al Tape Test -Passed Cycle Humidity Plus Tape Test - Passed Boiling Water Pluse Tape Test - Passed Pad Abrasion Plus Tape Test - Passed Life Test - Passed Life Test Plus Tape Test - Few Small Tape Pulls Table 3 describes the properties of an ophthalmic lens made in accordance with this invention having a poly (2,2'-dihydroxyphenylpropane) carbonate substrate, a silicon oxide coating, an indium doped tin oxide conductive layer (fully converted to its transparent state through the use of a glow discharge treatment), another silicon oxide coating, and finally a Suzuki et al overcoating.

TABLE 3 InSnO2 Metal Oxide Coating Visual Transmittance 88.5% Charge Decay Time < 3sec Material of conductive layer InSnO2 Coating Thickness 100A The charge decay time of less than 3 seconds may be compared with times of tens or hundreds of minutes for polymer ophthalmic lenses or organo-silica coated polymer lenses under the same conditions without the presence of the conductive layer.

The abrasion-resistant layer of the optical element of the invention may comprise an organic layer, i.e.

melamine formaldehyde; an organo-silica layer, i.e. polyorgano siloxane or silica-polyorgano siloxane; or an inorganic layer, i.e. glass or SiO2, If an organo-silica layer is used, the thickness of the organo-silica layer is preferably between 1.5 and 7 microns. The silica-polyorgano siloxane coatings disclosed in U.S. Patent 4,211,823 (Suzuki et al) and U.S.

Patent 3,986,997 (Clark), the disclosures of which are incorporated herein, are the preferred organo-silica coatings of the invention.

The Suzuki et al coating composition includes (A) (1) hydrolysates of silane compounds containing at least one epoxy group and not less than two alkoxy groups which are directly bonded to Si atom in the molecule, and if necessary, (2) compounds containing silanol and/or siloxane groups in the molecule, and/or epoxy compounds; (B) fine silica particles having an average diameter of from about to about 100 mu; and (C) an aluminium chelate compound having the general formula AlXnY3 n, where X is OL (and L represents a lower alkyl group), Y represents one or more ligands produced from a compound selected from the group consisting of M'COCH2CO M2 a nd M3COCH2COOM4 where all of M', M2, M3 and M4 are lower alkyl groups, and wherein n is an integer comprising 0,1 or 2; and (D) a solvent comprising more than about 1 weight percent water, the amount of component b being about 1 to 500 parts by weight per 100 parts by weight of Component A, and the amount of Component C being about 0.01 to 50 parts by weight per 100 parts by weight of Component A.

The Clark coating composition is an aqueous coating composition comprising a dispersion of colloidal silica in lower alphatic alcohol-water solution of the partial condensate of a silanol of the formula RSi (OH)3 in which R is selected from the group consisting of alkyl radicals of 1 to 3 inclusive carbon atoms, the vinyl radical, the 3,3,3-trifluoropropyl radical, the gamma-glycidoxypropyl radical and the gammamethacryloxypropylradical, at least 70 weight percent of the silanol being CH3Si(OH)3, said composition containing 10 to 50 weight percent solids consisting essentially of 10 to 70 weight percent colloidal silica and 30 to 90 weight percent of the partial condensate, said composition containing sufficient acid to provide a pH in the range of 3.0 to 6.0.

This embodiment of the invention is better illustrated by the following nonlimiting examples.

Example 1 Atypical process for producing an ophthalmic lens in accordance with the present invention comprises the following steps: 1.Vacuum coat side 1 of a plastic substrate with 100 A silicon monoxide.

2. Flip the plastic substrate to the other side and vacuum coat side 2 with 100 A silicon monoxide.

3. Vacuum coat side 2 with 100 a of indium doped tin oxide (e.g. "Substance A" from E.M. Laboratories, Inc.).

4. Flip and vacuum coat side 1 with 100 A of indium doped tin oxide.

5. Glow discharge side 1 in oxygen at 0.070 Torr, 300mA, 350 + 50 VDC, for 1-5 minutes.

6. Flip and glow discharge side 2 as in step 5.

7. Vacuum coat side 2 with 100 A silicon monoxide.

8. Flip and vacuum coat side 1 with 100 A silicon monoxide.

9. Remove from vacuum coater and apply an organo-silica overcoating by any of the standard techniques such as dipping or spinning.

Example 2 Ophthalmic lenses comprising poly (2,2'-dihydroxyphenylpropane) carbonate substrates, vacuum deposited chromium metal layers on the plastic substrates and overcoatings of standard Suzuki et al material were produced. Tests were run in order to show the relationship of transmittance to anti-static behavior. Figure 2 is a graph showing the charge decay time versus transmittance. Figure 3 is a graph showing transmittance versus nominal chromium thickness.

It can be seen from Figure 2 that for percent transmittances from about 70 to about 89%, the charge decay time is approximately the same low amount, but for percent transmittances above 89%, there is a large increase in decay time. This increase in decay time is due to the fact that the chromium layer has become too thin to form a continuous film and is therefore less conductive. Figure 3 shows that there is a fairly close correlation between nominal chromium thickness and percent transmittance--as the chromium chromium layer gets thinner, the percent transmittance increases.

In another embodiment of the present invention, there is provided an optical element moulded from an organic polymeric plastic substrate wherein at least one surface of the plastic substrate is coated with a protective organo-silica coating composition which is then exposed to a vacuum glow discharge.

Any type of organic polymeric plastic substrate may be used, i.e., a polycarbonate substrate, more specifically a poly (2,2'-dihydroxyphenylpropane) carbonate substrate; an allyl substrate, more specifically a CR-39 substrate; or an acrylic substrate, more specifically polymethyl methacrylate. CR-39 is a polydiethylene glycol bis (allyl carbonate) obtained from PPG Industries, Inc.

The organo-silica coating composition may comprise, for example, the silica-polyorganosiloxane coating compositon of Clark, or the silica-polyorganosiloxane coating disclosed in Suzuki et al. The Suzuki et al coating is the preferred organo-silica coating of the invention. This coating not only is tintable and known to have excellent adherence even in hostile environments, but when the surfaces of an optical element of the invention are coated with this composition and then subjected to a glow discharge, the surfaces of the optical element become both anti-static and anti-reflective. Figure 4 illustrates the reflectance of a CR-39 monomer based lens with this coating before and after a glow discharge treatment.Line 10 represents the reflectance of such a coated lens before being subjected to a glow discharge treatment and line 12 represents the lower reflectance of the Suzuki et al coated lens after being subjected to a glow discharge treatment. When the surfaces of an optical element of the invention are coated with the Clark composition and then subjected to a glow discharge, the surfaces of the optical element do not become anti-reflective, but they do become quite anti-static.

As for the specifics of the glow discharge treatment, it was found that the method of producing the plasma was not important since DC, AC (60Hz) and RF plasmas all proved to be effective. The gas pressure was also found to be unimportant as any pressure capable of sustaining a plasma produced the desired results. Of course, there may be an optimum pressure and power (voltage and current) in case one wished to minimize the time required for the glow discharge treatment. For example, the time required for producing a surface with a lowered reficetance was found to be dependent on the power supplied. In the RF glow discharge, five minutes was sufficient, while with the DC glow discharge, times ranging from 5 to 15 minutes were required.

The one factor of the glow discharge treatment which did not seem to make a difference, especially in providing an anti-reflective surface, was the type of gas used. Although oxygen, air, helium and nitrogen all produced anti-static surfaces on both the Suzuki et al and Clark coatings, only gases containing oxygen (i.e., 2, air and a mixture of 02 and CF4) were effective in producing an anti-reflective surface and only on Suzuki et al coatings.

The invention is further illustrated by the following non-limiting examples.

Example 3 An optical element coated with the Suzuki et al coating composition was subjected to a DC glow discharge in oxygen at a pressure of 0.075 Torr, at a voltage of 300 VDC and at a current between 250 to 300 mA for 10 minutes. The optical element resulting from this process had an anti-reflective surface as well as an anti-static surface. Reflectance dropped from 6.5 percent before the glow discharge treatment to an average visual reflectance of 2 percent after the glow discharge treatment.

Example 4 Both sides of a Suzuki et al coated CR-39 lens were exposed to a DC glow discharge in airfor 15 minutes at a pressure of 0.07 Torr, at a current of 300 mA, and at a voltage of -300 VDC at a distance of about 5 cm from the cathode with the surface of the lens being parallel to that of the cathode. The charge decay rate (the time for initial surface charge created by a corona discharge to decay to 10 percent of its original value) was 17 minutes prior to the glow discharge exposure and less than 1 second after the exposure. As seen in the drawing, reflectance dropped from 6.8 percent before the treatment to an average visual reflectance of 4.2 percent after treatment.

Example 5 An optical element coated with the Suzuki et al coating composition was subjected to an RF (13.56 MHz) glow discharge in oxygen at a pressure of 0.5 to 0.6 Torr at 200 watts for 5 minutes. Once again, the optical element resulting from this process had an anti-reflective surface.

Example 6 A Sukuki et al coated optical element was subjected to the same RF glow discharge as in Example 5 except that the RF glow discharge treatment was performed in a nitrogen atmosphere instead of an oxygen atmosphere. The resulting optical element was found not to have an anti-reflective surface.

Example 7 A Suzuki et al coated optical element was subjected to the same RF glow discharge as in Example 5 except that the RF glow discharge treatment took place in air as opposed to in oxygen. The resulting optical element had a surface that was both anti-reflective and anti-static.

Example 8 A Suzuki et al coated optical element was subjected to an RF glow discharge as described in Example 5 except that the RF glow discharge took place in 02+CF4 instead of oxygen. The resulting optical element had an anti-reflective surface.

Example 9 An optical element coated with the Clark coating composition was subjected to the same RF glow discharge as in Example 5. The resulting optical element did not have an anti-reflective surface.

Example 10 A Clark coated optical element was subjected to the same RF glow discharge as in Example 6. The resulting optical element did not have an anti-reflective surface.

Example ii A Clark coated optical element was subjected to the same RF glow discharge as in Example 7. The resulting optical element had neither an anti-reflective nor an anti-static surface.

Example 12 An optical element coated with the Suzuki et al coating composition was subjected to an AC (60 Hz) glow discharge in air at a pressure of 1 mm Hg, and at a current of 25mA for 10 minutes. The optical element resulting from this process had an anti-satic surface.

Example 13 A Clark coated optical element was subjected to the same AC glow discharge as in Example 12. The optical element resulting from this process had an anti-static surface.

Although this invention has been described with reference to its preferred embodiment other embodiments can achieve the same results. Variations and modifications of the present invention will be obvious to those skilled in the art and it is intended to cover in the appended claims all such modifications and equivalents as follow in the true spirit and scope of this invention.

Claims (18)

1. An anti-static abrasion-resistant optical element comprising: a) an organic polymeric plastic substrate; b) a conductive layer on at least one surface of said plastic substrate; and c) an abrasion-resistant layer overcoating said conductive layer.

2. An optical element according to Claim 1 having a percent transmittance for visible light of at least 60%.

3. An optical element according to Claim 1 or 2 in which the abrasion-resistant layer is an organic layer.

4. An optical element according to Claim 1 or 2 in which the abrasion-resistant layer is a glass layer.

5. An optical element according to any of Claims 1 to 4 in which the conductive layer is a metal layer.

6. An optical element according to any of Claims 1 to 4 in which the conductive layer is a semiconductor layer.

7. An optical element according to Claim 6 wherein the semiconductor is indium doped tin oxide.

8. An optical element according to any of Claims 1 to 7 wherein there is a coating of silicon oxide between said plastic substrate and said conductive layer.

9. An optical element according to any of Claims 1 to 8 wherein there is a coating of silicon oxide between said conductive layer and said abrasion-resistant layer.

10. An optical element according to any of Claims 1 to 9 wherein the abrasion-resistant layer comprises an organo-silica layer.

11. An optical element substantially as herein described with reference to the accompanying drawings.

12. A method of producing an optical element comprising: a) applying a conductive layer to at least one surface of an organic polymeric plastic substrate; and b) overcoating organic coating.

13. A method of producing an anti-static optical element comprising: a) overcoating at least one surface of an organic polymeric plastic substrate with a protective organo-silica coating wherein said coating comprises an aqueous coating composition comprising a dispersion of colloidal silica in a lower aliphatic alcohol-water solution of the partial condensate of a silanol of the formula RSi (OH)3 in which R is selected from the group consisting of alkyl radicals of 1 to 3 inclusive carbon atoms, the vinyl radical, the 3,3,3-trifluoropropyl radical, the gamma-glycidoxypropyl radical and the gammamethacryloxypropyl radical, at least 70 weight percent of the silanol being CH3Si(OH)3, said composition containing 10 to 50 weight percent solids consisting essential of 10 to 70 weight percent colloidal silica and 30 to 90 weight percent of the partial condensate, said composition containing sufficient acid to provide a pH in the range of 3.0 to 6.0; and b) exposing said organo-silica coated plastic substrate to a vacuum glow discharge.

14. A method of producing an anti-static anti-reflective optical element comprising: a) overcoating at last one surface of an organic polymeric plastic substrate with an organo-silica coating comprising components A, B, C and D wherein Component A is a hydrolysate of a silane compound containing an epoxy group and not less than two alkoxy groups which are directly bonded to an Si atom in the molecule; Component B comprises fine particles of silica which particles have an average diameter of about 1 to 100 mu; Component C comprises an aluminium chelate compound having the formula AlXnY3r wherein X is OL (wherein L is a lower alkyl group), Y is at least one ligand produced from the group consisting of: (1)M1COCH2COM2 and (2)M3COCH2COOM4 wherein (M', M2, M3 and M4 are lower alkyl groups) and n is 1 or 2; and Component D comprises a solvent comprising more than about 1 weight percent water, the amount of Component B being about 1 to 500 parts by weight per 100 parts by weight of Component A, and the amount of Component C being about 0.01 to 50 parts by weight per 100 parts by weight of Component A; and b) exposing said organo-silica coated plastic substrate to a vacuum glow discharge.

15. A method according to Claim 13 or 14 wherein the coated plastic substrate is exposed to a vacuum glow discharge.

16. A method according to any of Claims 13 to 15 wherein the vacuum glow discharge is performed in a gas containing oxygen.

17. A method according to any of Claims 13 to 15 wherein the vacuum glow discharge is performed in a nitrogen atmosphere.

18. A method substantially as herein described with reference to the accompanying drawings.