Abstract:
Polycarbonate articles, especially eyeglass and optical lenses, are dyed in a dye solvent having a boiling point of at least 350° F. in which a dye is dissolved. The article to be dyed is retained in the solution maintained at 200° F. or more until sufficient dye has penetrated the polycarbonate, then removed, rinsed and dried. The dyeing operation does not unduly detract from impact resistance and the dyed product exhibits excellent ultraviolet light stability.

Description:
BACKGROUND OF THE INVENTION 
     Polycarbonate lenses of the type used in eyeglasses, camera lenses, optical instruments, eyeglass shields, goggles and other protective gear, cannot be dyed at temperatures of 212° F. or less, because of the high second order transition temperature (T g ) (250°-260° F.) of the polycarbonate. Aqueous dyeing under pressure at 265°-270° F. for 60-90 minutes is needed to obtain good coloration. However, this long heat treatment is costly and slow, and drastically reduces the impact resistance of the polycarbonate article. During the long heat treatment, the molding-related physical arrangements undergo changes which cause the loss of impact resistance. High impact resistance is a necessary requirement for all plastic lenses, and it is a special requirement for the military. 
     Thus, an object of this invention is to develop a rapid solvent dyeing process with uniform dye uptake without reducing the high impact resistance or changing the haze factor of dyed polycarbonate lenses. 
     Polycarbonate lenses are produced by placing liquid polycarbonate monomer (undyed) and an initiator, usually an organic peroxide, e.g., isopropyl peroxide, in a mold. After polymerization is completed, the lenses are polished and cleaned. Normally, lenses are dyed by adding organic dye to the monomer and initiator blend. These dyes must be compatible with both the monomer and initiator. This process requires a significant investment for dyes and an inventory of colored lenses to provide a full range of products. 
     Polycarbonate articles including lenses which contain tint or dye are required for optical and nonoptical uses, such as safety glasses and sunglasses, and for industrial and military applications such as helmets with protective face shields. 
     DESCRIPTION OF THE INVENTION 
     The present invention provides a dyeing process effective for dyeing polycarbonate lenses to obtain high retention of impact resistance, uniform dyeing, high UV stability (clarity) of the thus-colored lenses, no change in haze of the lens, and high productivity. 
     The effects of time and temperature of treatment on polycarbonate lens dyeing are shown below in Table III. Based on those tests, a dyeing process was developed to provide the advantages mentioned above. An outline of this process is as follows: 
     Polycarbonate lenses are dyed in a solution consisting of 0.1 to 1% of selected organic dye (see below) in white mineral oil. The oil is a naphthenic hydrocarbon, NF/USP pharmaceutical grade, and is referred to herein as &#34;white mineral oil&#34;. Dyeing is preferably conducted for 3 to 4 minutes at 268°-270° F. 
     Annealing is performed at about 80°-85° F. for 3-4 minutes. Excess solvent and dye are then scoured off as described below, and the lenses are then dried at room to warm air temperature. A hard siloxane can then be applied as a coating to improve the lenses&#39; scratch resistance. To avoid dye oxidation, oxygen-free gas, e.g., nitrogen, should be used above the dye and scouring baths; this is required if the dye solution is to be re-used. 
     The following nonionic, organic dyes have been found suitable for the process: 
     Crude Nonionic Dyes 
     Disperse Yellow 3 
     Disperse Orange 30 
     Disperse Red 55:1 
     Disperse Blue 56 
     Solvent Nonionic Dyes 
     Solvent Yellow 93 
     Solvent Orange 60 
     Solvent Red 52 
     Solvent Blue 59 
     Solvent 1:2 Premetalized Dyes 
     Solvent Yellow 83:1 
     Solvent Orange 54 
     Solvent Red 22 
     The process of this invention can be carried out at temperatures and times between 250° F. for 4 minutes and 380° F. for 30 seconds depending upon the dyeing media employed. Preferably, however, the process is carried out between 270° F. for 3 minutes and 290° F. for 2 minutes. The annealing time can vary between 2 and 4 minutes. 
     The process of the invention is conducted in the following manner: molded but otherwise untinted lenses are tinted or dyed by immersing the lens in a high-boiling solvent (specified in detail below) containing a tinctorial amount of at least one dye. The dyeing medium is maintained in a sealed container under an inert gas, nitrogen being convenient, to prevent dye oxidization. Dyeing is carried out at temperatures in the range of 250° F. to 380° F., preferably about 270° F. to 290° F. for 5 seconds up to 5  minutes depending on the depth of shade required. Temperature and time are inversely related, i.e., lower temperatures require longer exposure to the dyeing medium. 
     Next, the lens is given an after dyeing heat treatment or annealing, again in a nitrogen environment, to prevent dye oxidation. After annealing, any non-diffused dye and/or high boiling solvent remaining on the lens are removed in a solvent rinse or scour, for instance, in a fluorinated hydrocarbon scouring medium (e.g. Freon 113) optionally containing a small quantity of a solvent-soluble detergent. Three separate scourings of 15 to 30 seconds each with the fluorinated hydrocarbon scouring medium at slightly above room temperature (80° F. to 85° F.) are preferred. The dyed lens is then dried in warm air. Protective coatings or other finishes may be applied as required. 
     The process of this invention is described with emphasis on a lens, shield or other optically-related configuration; however, it will be understood that other forms of three-dimensional shaped articles made of polycarbonate may be similarly treated. 
     The total light transmittance of the dyed lenses varies with the depth of dyeing which, in turn, is a function of the materials and conditions employed. Approximately 20% to 25% light transmittance of the dyed lenses is preferable, e.g., for sunglasses. The process yields uniformly dyed lenses or articles with no visible change in haze (clarity) as compared with untreated lenses. 
     Suitable high-boiling organic media for the process of this invention are selected from those organic liquids having a boiling point above the operational temperature of the dyeing medium, compatible with the polycarbonate article to be dyed and in which the dye is soluble. Several types of solvents for dyeing and scouring media were screened to obtain optimum materials for processing as shown in Tables I and II, below. 
     
                                           TABLE 1__________________________________________________________________________Properties of Candidate Media for Dyeing Polycarbonate Lenses    Boiling        Viscosity at    Point        75° F.            270° F.                Cost                    UV    Depth of Dyeing at.sup.(e)Solvent  °F.        cps cps $/lb                    stability.sup.(d)                          270° F.                              300° F.                                  350° F.__________________________________________________________________________Diethylene glycol    470  80  15 0.40                    3-4   Low Med.                                  HighDow Corning200 Fluid.sup.(a)    380 500 180 2.80                    3-4   Low Med.                                  High510 Fluid    410 400 160 4.50                    3-4   Low Med.                                  High210H Fluid    800 180  45 9.50                    5     Low High                                  --710 Fluid    650 250  80 18.50                    3-4   Low High                                  --550 Fluid    480 500 180 8.90                    5     Low Med.                                  HighPolysulfolane    520 solid            30-50                1.70                    2-3   Low Med.                                  HighTEHM.sup.(b)    650 400 15-30                2.80                    3-4   Low High                                  --White Mineral    600 20-30            1-2 0.68                    5     High                              --  --Oil.sup.(c)__________________________________________________________________________ .sup.(a) Silicone fluid. .sup.(b) Tris(2ethylhexyltrimellitate). .sup.(c) Naphthenic hydrocarbon NF/USP pharmaceutical white mineral oil. .sup.(d) UV stability in AATCC Test 16E, using 60 hours of continuous xenon arc exposure. A rating of 5 is best, and indicates absence of a color break. .sup.(e) The test for depth of dyeing was conducted in a 0.5% solution of Solvent Blue 59 for 2 minutes at the specified temperatures. 
    
     
                       TABLE II______________________________________Properties of Candidate Media for ScouringDyed Polycarbonate Lenses                          Effect on        Solubility        Poly-        of White                Solubility                          carbonate        Mineral of Organic                          Lens        Oil     Dyes      Surface______________________________________Dimethyl sulfoxylate          Medium    High      SevereDimethylformamide          Medium    High      SevereMethylethyl ketone          Medium    Medium    SevereMethylethyl acetate          Medium    Medium    SeverePerchloroethylene          High      Medium    SevereTrichloroethylene          High      Medium    Severe1,1,1-Trichloroethane          High      Medium    SlightMethylene chloride          Medium    Medium    SevereFluorinated    High      Low/      Nonehydrocarbon (Freon 113)  Medium*______________________________________ *Solubility of dyes can be increased by addition of cationic detergent soluble in fluorinated hydrocarbon. 
    
     As shown by Table I, the dyeing media tested (with the exception of white mineral oil) provided a low depth of dyeing at 270° F., but demonstrated improved dyeing depths at higher temperatures. Impact resistance was least affected at lower treatment temperatures as shown by Table II. Thus, the preferred dyeing medium is white mineral oil, not only for the favorable depth of dyeing at lower temperatures, but also for the ultraviolet stability of the resulting product. An acceptable scouring medium will solubilize and remove the high boiling medium and solubilize the organic dye (at least to a reasonable extent while not extracting a significant portion of the dye diffused into the lens) while the polycarbonate lens surface should not be adversely affected. Fluorinated hydrocarbons are the preferred scouring agents for use in association with white mineral oil as the dyeing medium, as shown in Table II. 
     The invention will now be explained with reference to the following example in which all parts and percents are by weight unless otherwise indicated. 
    
    
     EXAMPLE 
     A series of 14 separate dye uptake studies were made in a 0.5% solution of Solvent Blue 59 in white mineral oil for two minutes under the times and temperatures specified, as shown in Table III. 
     
                                           Table III__________________________________________________________________________Effect of Treating Conditions on Polycarbonate Lens DyeingTest for Dye Uptake: Conducted in a 0.5% solution of Solvent Blue 59 inWhite MineralOil for 2 minutes at the specified temperatures.Dyeing            AnnealingExperiment Conditions  Time at 80° F.                     Dye   UV*  Impact**No.   Temp. °F.       Time Min.             Min.    Uptake                           Stability                                Resistance__________________________________________________________________________1     260   1     2       None  --   High2     260   2     2       Low   1    High3     260   4     2       Low   2    High4     270   1     2       Medium                           2-3  Med./High5     270   2     2       Med./High                           4-5  Med./High6     270   3     2       High  5    Med./High7     270   4     2       High  5    Med./High8     270   3     2       High  5    Med./High9     270   3     3       High  5    High10    270   3     4       High  5    High11    280   2     4       High  5    Low12    300   2     4       High  5    Low13    325   2     4       High  5    Low14    350   2     4       High  5    Low__________________________________________________________________________ *UV stability in AATCC TEST 16E, using 60 hours of continuous Xenon arc exposure. A rating of 5 is best, and indicates absence of a color break. **Qualitative judgment of cracking after dropping a 10 lb. weight from a height of one foot on lens specimens.