Bleaching and dyeing; fluid treatment and chemical modification – Dyeing process utilizing electric – magnetic – or wave energy;...
Reexamination Certificate
2001-02-23
2002-10-15
Einsmann, Margaret (Department: 1751)
Bleaching and dyeing; fluid treatment and chemical modification
Dyeing process utilizing electric, magnetic, or wave energy;...
C008S506000
Reexamination Certificate
active
06464733
ABSTRACT:
TECHNICAL FIELD
This invention relates to a method of tinting a plastic article; the invention is especially concerned with tinting plastic optical lenses, especially ophthalmic lenses, for use in spectacles and other eye wear, to provide a colour tint or ultraviolet (UV) light transmission inhibiting tint.
BACKGROUND ART
Tinting of optical lenses for spectacles and sunglasses is widely employed either to apply an aesthetic, fashion oriented coloured tint to eye wear or to apply a tint which functions to block or inhibit transmission of ultraviolet light in eye wear, while additionally providing a desired aesthetic or fashionable appearance.
Current techniques for tinting optical lenses involve immersing the lens in a bath comprising solution or dispersion of a tinting dye or pigment which is heated to a temperature typically of 75 to 85° C. and maintained well below boiling temperature. The heating is achieved by heat exchange, wherein pots containing the tinting dye or pigment are surrounded by a heat transfer fluid which may be a silicone oil or other heat transfer oil. Typically it takes about 60 minutes to heat the bath from room temperature to 75 to 85° C. by this conventional technique. The lenses are inserted into the hot bath, typically by means of a lens holder which maintains the lens in an upright or vertical disposition.
As the temperature of the lens rises in the hot bath, the surface pores of the lens open and dye or pigment penetrates to effect tinting. Opening of the surface pores and initial tinting typically takes 5 minutes, but in order to achieve a dark sunglass tint colour, the lens typically needs to be maintained immersed in the hot bath for 15 minutes or more, and in particular up to 45 minutes for a dark tint.
Different optical plastics are employed in lens manufacture. Some optical plastics are tintable, having surface pores which will receive a tinting dye or pigment, for example, diethylene glycol bis(allyl carbonate) known as CR-39. Other optical plastics such as polycarbonates are not-tintable or are difficult to tint.
In some cases optical lenses are provided with a thin, hard surface coating, typically about 2 microns, these hard surface coatings permit tinting but conventional tinting techniques require long tinting times, for example, several hours. Hard surface coatings may be, for example, of vinyl polyester or polysiloxane.
These hard surface coatings do permit tinting of optical lenses of non-tintable plastic, but as indicated above long tinting times are required. These hard surface coatings are also employed, in some cases, on otherwise tintable lenses such as CR-39 lenses, rendering such lenses more difficult to tint.
These prior techniques employ low energy dye pigments available for optical use, which pigments disintegrate within a few hours if exposed to temperatures of 95° C. or higher.
U.S. Pat. No. 5,560,751 describes another conventional technique in which a thin liquid coating of a tinting solution is formed on a surface of a lens by spinning the lens at 1000 to 2000 rpm while applying the tinting solution dropwise to the lens surface, whereafter the resulting coated lens is heated causing the dye in the coating to be absorbed.
Canadian Patent Specification 2,095,703 describes a method for producing a photochromic plastic lens in which the lens is immersed in a high boiling organic solvent bath containing the dye and exposed to microwave heating, typically for about 6 minutes, whereafter the lens was allowed to soak in the hot bath for about 15 minutes.
The use of organic solvents is costly and use of hot solvents requires special handling facilities and equipment to avoid or minimize escape of vapors of the hot solvents into the atmosphere with the consequent hazards to the environment and to personnel involved in the tinting operation.
It is thus desirable to develop tinting techniques which avoid the use of hot organic solvents, while at the same time shortening the time required for tinting and avoiding the need for special or costly equipment.
SUMMARY OF THE INVENTION
The invention seeks to provide a tinting method in which tinting is achieved in short times.
The invention further seeks to provide a tinting method which avoids the need for costly equipment or handling facilities and employs water-based materials.
In accordance with the invention there is provided a method of tinting a tintable plastic article comprising: i) immersing a tintable plastic article in an aqueous dispersion of a tinting agent; ii) exposing said aqueous dispersion with said immersed article to microwave radiation to bring said dispersion to ebullition; iii) maintaining said ebullition for a time period of at least about 2 seconds with transfer of tinting agent from said dispersion to said article to effect tinting, iv) removing the resulting tinted article from said dispersion; and v) rinsing the tinted article with water to remove residual dispersion.
DETAILED DESCRIPTION OF THE INVENTION
i) Plastic Articles
The invention is applicable to tintable plastic articles generally, especially small articles, but has particular application to plastic optical lenses employed in eye wear, more especially, spectacles, sunglasses and protective eye wear, such as eye shields and goggles.
It is to be understood that “tintable plastic articles” in the context of the invention, contemplates articles such as lenses which are either of a plastic which is itself tintable, or have a surface coating which is tintable.
The tinting method may be employed to provide a tint of a desired colour, for aesthetic or fashion reasons, or to provide a protective tint effective to reduce, inhibit or block transmission of ultraviolet light through the lens, or for both of these functions.
Typical plastics for eye wear are well established in the eye wear industry and include poly(methyl methacrylate), cellulose acetates, polyvinyl chloride, polyurethanes, polycarbonate and diethylene glycol bis(allyl carbonate).
Within this class of plastics, diethylene glycol bis(allyl carbonate) referred to in the trade as CR-39 is widely employed as a tintable optical lens, both for use in producing a tinted lens of a desired colour and shade, and also for producing lenses with a protective UV tint.
Polycarbonates are also widely employed as optical lens plastic.
ii) Tinting Method
a) Pretreatment
The method of the invention is applied to clean lenses and, if necessary, the lenses are subjected to a preliminary cleansing operation. If lenses are being re-tinted or it is desired to change an existing tint, the existing tint is first removed using a technique similar to that of the invention but with a water-based tint removal solution instead of the aqueous dispersion of dye.
In the tint removal operation the tinted lens is immersed in an aqueous solution of a surfactant effective for removal of the tint under the operating conditions.
The solution of surfactant is first exposed to microwave radiation until the solution boils quietly; the tinted lens is immersed in the hot boiling solution and boiling is maintained to liberate the tinting dye from the lens. The operation is continued until the dye is removed from the lens.
The lens is removed from the solution and washed and the aqueous solution containing liberated tinting agent is reused for removal of tint in other lenses or is discarded.
A clean lens which is to be tinted is suitably surface conditioned by immersing the lens in an aqueous solution of a surfactant which is effective to reduce or lower surface tension on the surfaces of the lens, such that the tinting dispersion uniformly coats the surfaces of the lens when the lens is immersed in the tinting dispersion.
One suitable surfactant for this purpose is that available under the Trade-mark KIRALON-OL from BASF, however, other suitable surfactants can be readily identified by trial and experiment.
The surface conditioning can be carried out at room temperature; suitably the lens is immersed in the aqueous solution of surfactant for 10 to 40, preferably 15 to 30 seconds, removed and
Bachman & LaPointe P.C.
Einsmann Margaret
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