GB1584231A - Method of coating lenses - Google Patents

Description

(54) METHOD OF COATING LENSES (71) We, AMERICAN OPTICAL CORPORATION, a corporation organised under the laws of the State of Delaware, United States of America, of 14 Mechanic Street, Southbridge, Massachusetts 01550, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to a method of coating lenses, such as ophthalmic lenses.

Various methods of improving the abrasion- and scratch-resistance of transparent polymeric materials are known. In particular, there are disclosed in U.S. Patent 3,986,997 certain abrasion-resistant coating compositions, particularly for optical elements, which comprise dispersions of colloidal silica in lower aliphatic alcohol-water solutions of the partial condensate of a silanol of the formula RSi(OH)3, in which R is an alkyl group having 1 to 3 carbon atoms, a vinyl group, a 3,3,3-trifluoropropyl group, a gamma-glycidoxy-propyl group or a gamma-methacryloxypropyl group, at least 70% by weight of the silanol being CH3Si(OH)3. These compositions, which are unpigmented, contain 10 to 50 /n by weight solids consisting essentially of 10 to 70% by weight colloidal silica and 90 to 30% by weight of the partial condensate, and contain an acid in an amount such that their pH is in the range 3.0 to 6.0.

We have now developed a tie coating suitable for use between the abrasionresistant coating compositions of the above-mentioned U.S. Patent and the lens to which such coating is applied, which tie coating requires less control of humidity conditions during coating than some of the tie coatings disclosed in the above U.S.

Patent.

According to the invention, there is provided a method of coating a lens formed of a polymer which is a polycarbonate or poly(diethylene glycol bis allyl carbonate) which comprises: (a) applying to the lens a tie coating comprising a silane of the formula: AR'Si(OR2)a (R3)b (OH)38b in which A is -NH2, -NHR2 or -NHR1NH2 when the polymer is a polycarbonate or

when the polymer is poly(diethylene glycol bis allyl carbonate), R' is an alkylene group having 2 to 10 carbon atoms, each of R2 and R3 is an alkyl group having 1 to 4 carbon atoms and each of a, b and a plus b is 0, 1 or 2; and (b) coating the tie coating with a pigment-free abrasion-resistant coating composition comprising a dispersion of colloidal silica in a lower aliphatic alcohol (as defined below)-water solution of a partial condensate of at least one silanol of the formula RSi(OH)3, in which R is an alkyl group having 1 to 3 carbon atoms, a vinyl group, a 3,3,3-trifluoropropyl group, a gamma-glycidoxypropyl group or a gamma-methacryloxypropyl group, at least 70 /,, by weight of the R groups being methyl, the dispersion containing 10 to 50 /" by weight solids consisting of 10 to 70% by weight colloidal silica and 90 to 30 /n by weight of the condensate. The term "lower aliphatic alcohol" is used herein to mean an aliphatic alcohol having 1 to 4 carbon atoms.

When the polymer constituting the lens is a polycarbonate, preferred silanes for use in the tie coating are gamma - aminopropyltriethoxysilane and N - beta aminoethyl - gamma - aminopropyltriethoxysilane, which are commercially available under the trade names A-1100 and Z-6020, respectively, from Dow Corning Corporation.

When the polymer constituting the lens is poly(diethylene glycol bis allyl carbonate), such as the polymer commercially available under the trade name CR39, the silane in the tie coating is preferably gammaglycidoxypropyltrimethoxysilane. This silane is commercially available from Union Carbide Corporation and Dow Corning Corporation under the trade names A-187 and Z-6040, respectively.

The tie coating may be applied in any conventional manner, such as by dipping in a dilute solution of the silane, preferably containing less than 20% by weight of the silane. A typical such solution consists of 10% by weight gammaaminopropyltriethoxysilane, 85% by weight ethanol and 5% by weight water. The immersion time in such a solution is, for example, about one minute or more, but the time is not particularly critical. It is believed that such treatment results in a tie coating from 1 to 10 molecules thick. The coating should not be so thick that it impairs transparency of the lens.

The lens is preferably rinsed with water after application of the tie coating in order to avoid haze in the lens, which is very objectionable in ophthalmic lenses.

However, if haze is not objectionable, for example, in sunglass lenses, the rinsing is not necessary.

The inverval between removal of the lens from the tie coating bath and rinsing is not critical and it is even possible to allow the lens to dry before rinsing.

However, if it is desired to rinse the lens, this should be done within about one day in order to avoid an unduly thick tie coating and/or undesirable haze.

The abrasion-resistant coating composition preferably has a pH of 3.0 to 6.0; such a composition is as described in the above-mentioned U.S. Patent and the reader is referred thereto for further details of the composition and its method of application. Typical compositions are available from Dow Corning Corporation under the trade names "ARC" and "C-Resin". These compositions are referred to in the November/December, 1976, issue of "Material News".

The abrasion-resistant coating is preferably applied by dipping in the composition and withdrawing at a rate of 1 to 20 inches per minute, more preferably 4 to 10 inches per minute. The rate of withdrawal is controlled in order to control the coating thickness.

In order that the invention may be more fully understood, the following Examples are given by way of illustration only: EXAMPLE 1 Ophthalmic quality injection-moulded polycarbonate lenses were immersed for one minute in a solution consisting of 10% by weight gamma-aminopropyl triethoxysilame, 85 /n by weight ethanol and 5% by weight of water, and, after removal from the solution, rinsed and dried.

The lenses were then dipped in a composition available from Dow Corning Corporation under the Trade name C-Resin (which composition was filtered before use) and withdrawn at a rate of 7t inches per minute.

After drying at room temperature, the coated lenses were cured for eight hours in an air-circulating oven for eight hours at 2500 F.

The resulting lens had good transparency, abrasion-resistance, haze and resistance to thermal shock.

EXAMPLE 2 Example 1 was repeated, except that the abrasion-resistant coating composition was replaced by a composition commercially available from Dow Corning Corporation under the trade name "ARC".

Similar results were obtained.

EXAMPLE 3 Ophthalmic quality lenses of a polymer commercially available under the Trade Mark CR-39 (a poly(diethylene glycol bis allyl carbonate), as mentioned above) were immersed for about one minute in a 10% by weight solution of gamma - glycidoxypropyltrimethoxy silane in a mixture of 17 parts by weight of ethanol and one part by weight of water, the solution having its pH adjusted to 3 to 5 by means of acetic acid.

An abrasion-resistant coating was applied to the resulting tie coated lens in exactly the same manner as in Example 2. Similar results were obtained.

The above examples show that careful control of humidity is not necessary in the method according to the invention. By way of comparison, if the tie coating was not used, it was necessary to dry the lenses thoroughly (for at least four hours in an air-circuiating oven at 2400 F) and to apply the abrasion-resistant coating in an environment having controlled relative humidity of 30% or less in order to obtain comparable results.

WHAT WE CLAIM IS: 1. A method of coating a lens formed of a polymer which is a polycarbonate or poly(diethylene glycol bis allyl carbonate) which comprises: (a) applying to the lens a tie coating comprising a silane of the formula: AR'Si(OR2)a (R3)b (OH)J-a--b in which A is -NH2, -NHR2 or -NHR1NH2 when the polymer is a polycarbonate or

qhen the polymer is poly(diethylene glycol bis allyl carbonate), R1 is an alkylene group having 2 to 10 carbon atoms, each of R2 and R3 is an alkyl group having 1 to 4 carbon atoms and each of a, b and a plus b is 0, 1 or 2; and (b) coating the tie coating with a pigment-free abrasion-resistant coating composition comprising a dispersion of colloidal silica in a lower aliphatic alcohol (as defined herein)-water solution of a partial condensate of at least one silanol of the formula RSi(OH)3, in which R is an alky group having 1 to 3 carbon atoms, a vinyl group, a 3,3,3 - trifluoropropyl group, a gamma - glycidoxypropyl group or a gamma - methacryloxypropyl group, at least 70% by weight of the R groups being methyl, the dispersion containing 10 to 50% by weight solids consisting of 10 to 70% by weight colloidal silica and 90 to 30% by weight of the condensate.

2. A method according to claim 1, in which the polymer is polycarbonate and the silane is gamma - aminopropyltriethoxy silane.

3. A method of coating a lens, substantially as herein described in any of Examples 1 to 3.

4. A coated polymeric lens when produced by the process claimed in any of the preceding claims.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (4)

**WARNING** start of CLMS field may overlap end of DESC **. Trade Mark CR-39 (a poly(diethylene glycol bis allyl carbonate), as mentioned above) were immersed for about one minute in a 10% by weight solution of gamma - glycidoxypropyltrimethoxy silane in a mixture of 17 parts by weight of ethanol and one part by weight of water, the solution having its pH adjusted to 3 to 5 by means of acetic acid. An abrasion-resistant coating was applied to the resulting tie coated lens in exactly the same manner as in Example 2. Similar results were obtained. The above examples show that careful control of humidity is not necessary in the method according to the invention. By way of comparison, if the tie coating was not used, it was necessary to dry the lenses thoroughly (for at least four hours in an air-circuiating oven at 2400 F) and to apply the abrasion-resistant coating in an environment having controlled relative humidity of 30% or less in order to obtain comparable results. WHAT WE CLAIM IS:

1. A method of coating a lens formed of a polymer which is a polycarbonate or poly(diethylene glycol bis allyl carbonate) which comprises: (a) applying to the lens a tie coating comprising a silane of the formula: AR'Si(OR2)a (R3)b (OH)J-a--b in which A is -NH2, -NHR2 or -NHR1NH2 when the polymer is a polycarbonate or

qhen the polymer is poly(diethylene glycol bis allyl carbonate), R1 is an alkylene group having 2 to 10 carbon atoms, each of R2 and R3 is an alkyl group having 1 to 4 carbon atoms and each of a, b and a plus b is 0, 1 or 2; and (b) coating the tie coating with a pigment-free abrasion-resistant coating composition comprising a dispersion of colloidal silica in a lower aliphatic alcohol (as defined herein)-water solution of a partial condensate of at least one silanol of the formula RSi(OH)3, in which R is an alky group having 1 to 3 carbon atoms, a vinyl group, a 3,3,3 - trifluoropropyl group, a gamma - glycidoxypropyl group or a gamma - methacryloxypropyl group, at least 70% by weight of the R groups being methyl, the dispersion containing 10 to 50% by weight solids consisting of 10 to 70% by weight colloidal silica and 90 to 30% by weight of the condensate.

2. A method according to claim 1, in which the polymer is polycarbonate and the silane is gamma - aminopropyltriethoxy silane.

3. A method of coating a lens, substantially as herein described in any of Examples 1 to 3.

4. A coated polymeric lens when produced by the process claimed in any of the preceding claims.