GB2304922A

GB2304922A - Coating lens with ultraviolet blocking agent

Info

Publication number: GB2304922A
Application number: GB9602671A
Authority: GB
Inventors: Niall Patrick Mccrudden; Graham Smithers
Original assignee: Individual
Current assignee: Individual
Priority date: 1995-08-24
Filing date: 1996-02-09
Publication date: 1997-03-26
Also published as: IES66811B2; GB9602671D0; IES950645A2

Abstract

A lens, such as a spectacle lens, has an ultraviolet light (UV) blocking agent coated on it by cleaning the lens by immersing it in neutralising solution, e.g. diethylene glycol monoethyl ether, to clean the lens and to apply a positive charge to it, then bathing the lens in a bath containing UV blocking agent, a heat transferring solution and de-ionised water at between 90{C to 100{C, followed by dipping the lens in a volatile organic alcohol e.g. methylated spirits. The lens is preferably chamfered prior to treatment so that the edges define a smooth curve. After treatment, the spectacle lens may be mounted in a frame and sprayed with an anti-static substance.

Description

LENS COATING PROCESS The present invention relates to a process for coating optical lenses and in particular to a process for coating spectacle lenses.

Spectacle lenses are generally obtained by an optometrist from a supplier and are cut and matched to fit a patient's spectacle frames by a technician in the optometrist's own workshop. Various coatings are routinely applied to the lenses at this stage. For example, tint may be applied to control the colour of the lens or to adjust the light transmission properties of the lens.

Ultraviolet (W) light is known to cause damage to the eyes and consequently, it is not uncommon for a spectacle lens prescription to include a requirement for a ultraviolet filter coating to be applied to the lenses.

At present, there are many different UV blocking dyes on the market. Essentially these fall into three main groups, namely high risk (500-550nm), medium risk (400-500nm) and low risk (350-400nm).

Whilst the availability of standard dyes ensures that workshops can offer ultraviolet protective lens coatings to patients, no proper standardised technique for handling and preparing the lenses before and after the treatment exists. This is because at present, the UV dye is simply used like a tint, whereby the lens is left in solution for a set time, until the required colour develops.

As mentioned previously, it is generally regarded in medical circles that UV light in high doses can or will be harmful to the eyes over a period of time. The eyes, like the skin, have natural protective mechanisms that provide a degree of protection in normal everyday situations from the sun's UV rays. However, in view of environmental concerns, such as the reported depletion of the atmospheric ozone layer which shields the earth's surface from a deal of incident W rays, and in view of the lack of data on the affect of long-term UV exposure on the eyes, it is desirable to apply W protection to all spectacle lenses, whether prescription or otherwise.

Accordingly, the present invention provides a process for coating an optical lens with an ultraviolet light (UV) blocking agent, comprising: - cleaning a lens by immersing it in a neutralising solution containing an ionizing agent for a period sufficient to ensure that the surface of the lens is free of impurities and has a positive charge; - bathing the lens in a tinting bath containing a heat transferring fluid and a UV blocking agent dispersed in de-ionised water and heated to between 900C and 1000C, for a time sufficient to allow the blocking agent to be absorbed on to the lens surface; and - thereafter dipping the treated lens in a volatile organic alcohol to clean and degrease the lens surface.

Usually, the lens will be immersed in the neutralising solution for at least ten minutes.

Preferably, the lens is chamfered prior to coating to give its edges a curved smooth edge.

Conveniently, the tinting bath is heated to 970C +/- 20C and the volatile organic alcohol is methylated spirits.

Advantageously, the lens is a spectacle lens and the process includes mounting the lens in a spectacle frame after coating and optionally, spraying the mounted lens with an anti-static agent.

The invention also provides a lens coated with a UV blocking agent whenever prepared by the process as herein described.

Normally, once a lens has been cut, it is put into a special wheel to chamfer the edges. This is to ensure that it fits correctly into the frame. According to the invention described herein, this procedure is extended so that each lens has a "rolling edge". This means that the lens itself exhibits a fine curved smooth edge instead of a harsh angular one. The benefit of this in the UV coating process of the invention is that the solution will have a completely even adherence, uniform in its thickness throughout the lens. An angular chamfer often leads to irregularity at the edges, which in turn can lessen the optical performance of the lens.

The next step is systematically to clean the lens in neutralizing solution. One suitable neutralising solution is diethylene glycol monoethyl ether, supplied by B.P.I.

International. At least ten minutes immersion is required to ensure that the lens surface is completely devoid of any impurities. In prior art processes a mere wash in tap water was conducted prior to UV coating. The neutralising solution surrounds the lens in an ionizing agent that leaves a positive charge on the lens surface, ensuring even adherence of UV dye and a non-greasy surface. The lenses are laid on racks submerged in the neutralising solution for at least 10 minutes. For thicker lenses, a longer immersion is required to ensure the adequate treatment of the lens.

Once this procedure is complete, the lenses are ready for the W dye treatment, which is performed by bathing the lens in an appropriate UV dye solution until such time as the desired degree of dye is absorbed onto the lens surface. The tinting bath contains an aqueous solution of the W dye (usually anthraquinone derivatives and/or azodyes) and includes a heat transferring fluid such as B.P.I. International's HTF 90. Glycerine based heat transferring fluids may also be used, but are less satisfactory due to the generation of toxic fumes. The water used in the bath is de-ionised water rather than tap water as the letter can contain impurities which have an adverse effect on the coating process. The bath is heated to assist in effective transfer of dye on to the lenses in the bath. Suitably, the bath is heated to between 90 and 1000C, preferably 970C.The heat transferring fluid ensures that the tint stays at a fixed temperature and that no hot-spots develop in the tinting dyes which could cause uneven lens coating.

Stage three of the procedure is done after the lens is removed from the UV treatment bath. At this point in the prior known process, the lens would normally be washed again in tap water and then mounted into the spectacle frame. According to the present process, the lens is first dipped into a solution of methylated spirits for 10 seconds, then dried. The treatment with methylated spirits serves to remove any impurities from the surface of the lens by degreasing and removing any surface deposits such as marking inks. Any non-toxic volatile organic alcohol could be used in place of methylated spirits and this treatment also serves to add a key for the next step in the process so as to ensure that a uniform surface is ultimately obtained.Next, the lens is mounted into the frame, then finally sprayed with an anti-static spray such as Calotherm (trade mark) spray, Norville Optical, to keep the lens dust free. By way of quality control, the mounted lens is put under the spectrometer for its final testing of the UV blocking properties. The W transmission required from the coated lens is 0% transmission at 400 nm or longer UV wavelengths. The blocking obtained is a function of the particular dye chosen and the length of time that the lens if left in the tinting bath.

The process according to the invention is a carefully controlled one from start to finish to ensure that the optical qualities of the coated lens are as perfect as possible. Such quality control is not achievable in the prior known lens coating processes.

By the use of the process described herein, the optometrist can guarantee that the coating has been evenly applied to a lens that has no irregularities or imperfections, thereby ensuring maximum protection for the user.

It will of course be understood that the invention is not limited to the specific details described herein, which are given by way of example only, and that various modifications and alterations are possible within the scope of the invention as defined in the appended claims.

Claims

CLAIMS:

1. A process for coating an optical lens with an ultraviolet light (UV) blocking agent, comprising: - cleaning a lens by immersing it in a neutralising solution containing an ionizing agent for a period sufficient to ensure that the surface of the lens is free of impurities and has a positive charge; - bathing the lens in a tinting bath containing a heat transferring fluid and a UV blocking agent dispersed in de-ionised water and heated to between 900C and 1000C, for a time sufficient to allow the blocking agent to be absorbed on to the lens surface; and - thereafter dipping the treated lens in a volatile organic alcohol to clean and degrease the lens surface.

2. A process according to Claim 1, including chamfering the lens prior to coating to give its edges a curved smooth surface.

3. A process according to Claim 1 or Claim 2, in which the tinting bath is heated to 970C +/- 20C.

4. A process according to any of the preceding claims, in which the volatile organic alcohol is methylated spirits.

5. A process according to any of the preceding claims, in which the lens is immersed in the neutralising solution for at least 10 minutes.

6. A process according to any preceding claim, in which the lens is a spectacle lens and the process includes mounting the lens in a spectacle frame after coating and spraying the mounted lens with an anti-static agent.

7. A process for coating optical lenses with an ultraviolet light blocking agent according to any of the preceding claims, substantially as herein described.

8. A lens coated with an ultraviolet light blocking agent whenever prepared by a process according to any of the preceding claims.

9. A lens according to Claim 8, substantially as herein described.