Abstract:
A method and system for dyeing a plastic lens by printing a colored layer ( 2 ) on a print base body ( 3 ) with a dyeing solvent by using a printer ( 5 ) electrically controlled, the dyeing solvent containing a dissolved or fine-grained dispersed sublimatable dye, then, placing the print base body having the colored layer in a position where the colored layer faces a plastic lens ( 14 ) to be dyed without contact therewith, and heating the print base body in a vacuum to sublimate the dye from the colored layer and deposit the sublimated dye on the lens.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method of dyeing plastic lenses, in particular, spectacle lenses, and a dyeing system used in the dyeing method. 
     2. Description of Related Art 
     Heretofore, a dip dyeing method has been used in many cases to dye plastic lenses for spectacles. In this method, a dye solution is prepared by mixing dispersible dyes of three primary colors, i.e., red, blue, and yellow, and dispersing the mixture in water. The thus prepared dye solution is heated to about 90° C. A plastic lens is dipped in the heated dye solution, so that the lens is dyed. 
     As an alternative to the above dip dyeing method, a vapor deposition dyeing method has been proposed. This vapor-deposition dyeing method is carried out by heating a sublimatable dye to sublimate, thereby dyeing a plastic lens which is being heated. 
     In the above vapor-deposition dyeing method, the dyeing of lenses is effected by heating the sublimatable dye. As a result, a problem such as the disposal of waste solution after the dyeing will not arise. However, such the method has disadvantages that it is difficult to deposit dyes at a fixed quantity to adhere on a lens surface, to prepare dyes in desired density, and to dye lenses in a deep color. The hue or tint of a dye to be used is almost artificially prepared. As a result, the prepared dye is apt to be uneven in color, which will cause a large problem in quality control. 
     The conventional dip dyeing method mentioned above has also disadvantages that the interaction and condensation of the dispersible dyes cause variations and unevenness of hue or tint. This disables the stable provision of uniformly dyed objects. In addition, the dye solution after used has to be discharged finally, which causes a problem of disposal of waste solution and also prevents the effective use of dyes. In the dip dyeing method, furthermore, since the dye solution is heated, the dyeing work is carried out in the high-temperature and humidity environment, in which the foul smelling resulting from the dye is also present. The use of the dip dyeing method thus causes a deteriorated working environment. 
     SUMMARY OF THE INVENTION 
     The present invention has been made in view of the above circumstances and has an object to overcome the above problems and to provide a dyeing method capable of facilitating preparation of dyes in desired density and also dyeing plastic lenses with a stable hue or tint in every dyeing works, and improving a working environment thereof, and a dyeing system to be used for achieving the dyeing method. 
     Additional objects and advantages of the invention will be set forth in part in the description which follows and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims. 
     To achieve the purpose of the invention, there is provided a method of dyeing a plastic lens, including a first step of printing a print area on a print base body with a dyeing solvent by using a printer electrically controlled, the dyeing solvent containing a dissolved or fine-grained dispersed sublimatable dye, a second step of placing the print base body having the print area printed with the dyeing solvent in a position where the print area faces a plastic lens to be dyed without contact therewith, and a third step of heating the print base body in a vacuum to sublimate the dye and deposit the sublimated dye on the lens. 
     According to another aspect of the present invention, there is provided a system for dyeing a plastic lens, including a printer which is electrically controlled to print a print area on a print base body with a dyeing solvent containing a dissolved or fine-grained dispersed sublimatable dye, a deposition device for heating the base body in a vacuum to sublimate the dye and deposit the sublimated dye on the lens to be dyed, the lens being placed in a position where the lens faces the print area printed on the base body without contact therewith. 
     In the present invention, a print base body having a print area formed with the dyes which can be easily prepared in a desired density is used to dye plastic lenses, so that the plastic lenses can be dyed in a desired density and a stable hue. Since the dyeing operation is conducted in a dry environment, the dyeing working environment can be also improved as compared with a conventional wet environment. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are incorporated in and constitute a part of this specification illustrate an embodiment of the invention and, together with the description, serve to explain the objects, advantages and principles of the invention. 
     In the drawings, 
     FIG. 1 is a schematic view of a print base body constructed of a white sheet of paper and colored areas (layers) printed thereon, which is used in a first embodiment according to the present invention; 
     FIG. 2 is a schematic internal view of a vacuum vapor-deposition transfer device to be used in the first embodiment; 
     FIGS. 3A and 3B are sectional views of a part of a lens support plate with a (left) hole used in the first embodiment; 
     FIG. 4A is a cross sectional view of a dyeing jig used in a second embodiment according to the present invention; 
     FIG. 4B is a schematic view of a print base body used in the second embodiment; 
     FIG. 5 is a flow chart of a dyeing method in the first embodiment according to the present invention; 
     FIG. 6 is a schematic constructive view of a dyeing system for plastic lenses in the first embodiment according to the present invention; 
     FIGS. 7A to  7 D are schematic views of print base bodies produced in a fifth example; and 
     FIG. 8 is a graph showing the transmittance of lenses dyed using the print base bodies shown in FIGS.  7 A- 7 D. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A detailed description of preferred embodiments of a dyeing method and a dyeing system embodying the present invention will now be given referring to the accompanying drawings. In the following embodiments, the present invention is applied to spectacle plastic lenses. 
     In a first embodiment, the production of a print base body to be used for dyeing plastic lenses is first explained and then the dyeing of the plastic lenses is described. FIG. 5 shows a flow chart of the dyeing method in the first embodiment. FIG. 6 is a schematic view of the dyeing system including a dyeing device (jig) and others for carrying out the dyeing method shown in FIG.  5 . 
     (1) Production of Print Base Body 
     A print base body  3  shown in FIG. 1 is produced in the following manner. 
     As a dyeing solvent (a sublimatable dye), four colors of water-base dispersible dye inks (manufactured by Upepo Co. Ltd.), i.e., red, blue, yellow, and black inks are used. The ink is prepared by dissolving or fine-grain dispersing a sublimatable dye in a solvent. Those inks are filled in respective ink cartridges and mounted in an ink jet printer  5  which is a commercially available one (manufactured by MIJ Co. Ltd.). 
     Subsequently, for outputting a print in a desired color on the ink jet printer, a commercially available personal computer (referred to as “PC” hereinafter) is used to produce the hue and density of the inks (S 1 ). This production of hue is handled by a drawing software or computer color matching (CCM) in the PC. Accordingly, data on a desired color once produced can be stored in the PC, and prints in an identical color tone can be output a number of times if required. The color density is also digital-controlled by the PC, so that prints in an identical color density can also be output a number of times if required. 
     For a base body on which layers of the sublimatable dye are to be formed thereon, an A4-sized white paper  1  (high-quality PPC paper), commercially available, is used. This white paper  1  is set in the printer and subjected to the printing using the dye in the hue and density predetermined by the operation of the PC (S 2 ). On the paper  1 , circular colored layers  2  are formed as shown in FIG. 1. A print base body  3  is thus completed. In the present embodiment, two colored layers  2  are formed in pairs on the white paper  1 . This is because the previously formation in pairs is more convenient for dyeing a pair of spectacle lenses, i.e., for a right and left lenses. 
     The diameter of the colored layer  2  is preferably determined to have a slightly larger than that of the lens to be dyed actually. Because the dye may not fully spread over the whole coloring surface of the lens if the diameter of the colored layer  2  is smaller than the lens diameter. 
     (2) Dyeing of Plastic Lenses 
     With the base body  3  produced as above, the dyeing of plastic lenses is effected as follows, using a vacuum vapor-deposition transfer device shown in FIG. 2 which is a schematic internal view of the device seen from its front side. 
     The vacuum vapor-deposition transfer device  10  is provided, at its front upper portion, with an opening not shown through which the print base body  3  and plastic lenses  14  are inserted into the device  10  or removed therefrom. Reference number  11  denotes a support shaft which functions to move a support plate  12  for holding thereon the lenses  14  in a vertical direction and in a horizontal direction between the opening and a dyeing position. The movement of the support plate  12  by the support shaft  11  enables mounting or dismounting of the lenses  14  on or from the support plate  12  through the opening. The support plate  12  has two circular holes  12   a  disposed symmetrically with respect to the support shaft  11 , i.e., at a right and left sides thereof in FIG.  2 . The circular hole  12   a  is designed to have a larger diameter than that of the lens to be mounted thereon. On the underside of the support plate  12 , the print base body  3  (constructed of the white paper  1  with the colored layers  2  printed thereon) is attached so that the colored layers  2  are positioned on the upside of the body  3  and coaxially aligned with the holes  12   a  respectively, thereby to allow the dye of the colored layer  2  to sublimate toward the lens through the hole  12   a.    
     FIG. 3A is an enlarged view of a part of the support plate  12  with the hole  12   a  (a left one) in the first embodiment. A cylindrical lens holder  13  is joined with the support plate  12  so that the holder  13  is aligned with the hole  12   a . This lens holder  13  is provided with, as shown in FIG. 3A, a lens holding groove  13   a  formed in a shape capable of holding the lens  14  to prevent the fall thereof. When the edge of the lens  14  is set in the lens holding groove  13   a  of the holder  13  joined with the support plate  12 , the lens  14  can be held above the hole  12   a.    
     In the first embodiment, instead of the lens holder  13 , another lens holder  13 ′ having a different height shown in FIG. 3B may be used appropriately, whereby a distance from the print base body  3  to the lens  14  is changed, so that the dyeing density can be adjusted. In the present embodiment, six lens holders  13  of different heights are prepared so that the height can be adjusted in a range of 5-30 mm (in 5 mm steps). Even if the identical print base body  3  is used, for example, as the height of the lens holder  13  is higher, the amount of sublimated dye which will reaches the lens  14  is smaller. Accordingly, with the higher lens holder  13  selected, the lens  14  can be dyed in lighter (i.e., lower) color density. 
     The material of the plastic lens  14  is selected from polycarbonate resin (e.g., diethyleneglycol bis-allyl carbonate polymer (CR-39)), polyurethane resin, allyl resin (e.g., allyl diglycol carbonate and its copolymer, and diallyl phthalate and its copolymer), fumaric acid resin (e.g., benzyl fumarate copolymer), styrene resin, polymethyl acrylate resin, fibrid resin (e.g., cellulose propionate) and so on. 
     In the device  10 , a heater  15  is disposed below the lens support plate  12  and serves to sublimate the dye of the layers  2  printed on the white paper  1 . This heater  15  can be set to a desired temperature. The material of the heater  15  is aluminum which is high in thermal conductivity. By feeding current through a Nichrome wire not shown passing through the inside of the heater  15 , the surface temperature of the heater  15  is increased. This surface temperature is detected by a temperature sensor  16  as to whether or not the temperature reaches a preset value. 
     A rotary vacuum pump  17  is connected to the device  10  and used to produce an almost vacuum in the device  10  for a dyeing operation. Reference numeral  18  denotes a leak valve provided to the device  10 . This valve  18  is opened after the dyeing operation to take air into the device  10  maintained under vacuum, thereby to return it to an atmospheric pressure. 
     The vacuum vapor-deposition transfer device  10  configured as above is operated in the following manner to dye the plastic lens  14 . 
     First, the support shaft  11  is operated to move the support plate  12  upward and move horizontally toward the opening formed at the front side of the device  10 . Then, the print base body  3  produced in the above mentioned process (1) is inserted into the device  10  and attached, placing its print surface (with the colored layers  2 ) up, to the underside of the support plate  12  with an adhesive tape and the like so that the colored layers  2  are aligned with the two holes  12   a  of the support plate  12  respectively. After the attachment of the base body  3  to the support plate  12 , the lens holders  13  are fitted on the upside of the support plate  12 . 
     Subsequently, the plastic lenses  14  are set with the concave surface side down in the lens holders  13 . The heater  15  is then heated to a desired heating temperature. In the present embodiment, the heating temperature of the heater  15  is preset in a range of 100-200° C. If the heating temperature is less than 100° C., the dye printed on the print base body  3  will not sublimate easily. If it is higher than 200° C., to the contrary, there are possibilities of deteriorating the quality of the dye or deforming the lens. Accordingly, the heating temperature of the heater  15  is preferably set in a range of 100-200° C., and, more preferably, it is set at as high a temperature as possible within the range according to the material of the plastic lenses  14 . 
     The reason to set the heating temperature as high as possible for sublimation is that the higher temperature enables the reduction of the heating time needed for sublimating a dye in desired hue and density, and the increase of productivity in association therewith. 
     Next, the opening of the device  10  is closed and the rotary vacuum pump  17  is activated to produce a vacuum in the device  10 , namely, to reduce the internal pressure of the device  10  to about 1-50 mmHg. There is no problem even if reducing the pressure lower than 1 mmHg, but a high-performance exhauster is needed in such cases. To the contrary, as the internal pressure of the device  10  is higher, the temperature required for dye sublimation is higher. Accordingly, the upper limit of the pressure is preferably 50 mmHg. The more preferable range of the pressure is 10 to 30 mmHg. 
     When the sensor  16  detects that the heater  15  has been heated to the predetermined temperature, the support shaft  11  is operated to move the support plate  12  down until the plate  12  comes into contact with the heater  15  (S 3 ). 
     With the support plate  12  being held in contact with the heater  15 , the base body  3  attached to the underside of the support plate  12  is heated by the heater  15  for the predetermined duration, e.g., 1-20 min. from the contact (S 4 ). The sublimation of the dye applied on the base body  3  starts almost simultaneously with the contact to the heater  15 . If the heating duration is less than 1 min., the dye is not enough sublimated to dye the plastic lens  14  in a predetermined color density. If the heating duration exceeds 20 min., the plastic lens  14  is apt to be transformed by the heating. Accordingly, the heating duration is preferably in a range of 1 to 20 min. and more preferably 3 to 10 min. 
     Upon completion of the heating, the leak valve  18  is opened to return the pressure of the device  10  to normal. The support shaft  11  is operated to move the support plate  12  up to the opening of the device  10 , and the plastic lens  14  is taken out through the opening opened. The sublimated dye is deposited on the plastic lens  14 , but it is apt to come off if left as it is. To avoid this, the plastic lens  14  is further heated in an oven  35  as shown in FIG. 6 under normal pressure to fix the deposited dye on the lens  14  (S 5 ). Specifically, this process is carried out in the steps of first raising the temperature of the oven to a preset temperature which is as high as possible below the lens resistible temperature, heating the lens  14  in the oven  35  for the duration so predetermined as to provide the desired hue and density, and then taking the lens  14  out of the oven  35 . This heating temperature in the present embodiment is in a range of 50° C. to 150° C. and the heating duration is in a range of 30 to 60 min. 
     In the first embodiment, the plastic lens  14  is dyed from below with the sublimated dye heated from below in the vacuum vapor-deposition transfer device  10 . Alternatively, the lens  14  may be placed with the concave surface side up so that the concave surface is dyed from above with the sublimated dye. 
     This method of dyeing the lens from above is explained below in a second embodiment according to the present invention, referring to FIG.  4 A. FIG. 4A is a schematic front sectional view of a dyeing jig used in the second embodiment. Like elements corresponding to those in the first embodiment are indicated by like numerals. 
     Reference numeral  20  denotes a cylindrical support stand, on which a lens holder  13  provided with a lens holding groove  13   a  is mounted. As shown in FIG. 4A, the holder  13  holds a plastic lens  14  placed with the convex surface side down by fitting the edge of the lens  14  in the lens holding groove  13   a . The lens  14  is thus supported above the support stand  20 . 
     A print base body  33  constructed of a white paper  31  with a colored layer  32  printed thereon is easily produced by the use of a PC and a printer in the same manner as in the first embodiment. FIG. 4B is a plane view of the print base body  33 . Reference numeral  21  denotes a cylindrical support stand for supporting a print base body  33 , and  22  denotes a base body holder for securely holding the print base body  33  put on the upside of the support stand  21 , thereby preventing the displacement of the base body  33 . In this embodiment, the base body  33  is placed so that the surface on which the colored layer  32  is printed is on the underside to allow the dye of the layer  32  to sublimate downward. The plastic lens  14  is placed so that its concave surface side is not in contact with the lens holding groove  13   a . Accordingly, the whole concave surface of the lens  14  can be dyed. 
     Reference numeral  23  denotes a halogen lamp which is disposed in a vacuum deposition device not shown and heats the base body  33  from above to sublimate the dye of the colored layer  32  formed on the base body  33 . 
     Subsequently, with the above constructed dyeing jig, the following operation is carried out to sublimate the dye from the print base body  33  in a vacuum condition, similarly to the first embodiment, thereby to dye the plastic lens  14 . 
     First, the stand  20  is put in the vacuum deposition device not shown, and the lens holder  13  is mounted on the stand  20 . The plastic lens  14  is placed with the convex surface side down in the lens holding groove  13   a  of the lens holder  13 . Thereafter, the cylindrical support stand  21  is disposed so as to enclose the lens support stand  20 . The base body  33  is put on the support stand  21  as shown in FIG.  4 A. The base body holder  22  is fitted on the upside of the support stand  21  to securely hold the base body  33  on the support stand  21 , thereby preventing the displacement of the body  33 . 
     After the set of the plastic lens  14  and the print base body  33  in the dyeing jig in the above manner, a rotary vacuum pump is used in the same manner as in the first embodiment to reduce the pressure of the vacuum deposition device to a predetermined pressure in a range of about 1-50 mmHg, preferably, 10-30 mmHg. 
     After detection on the predetermined vacuum pressure of the vacuum deposition device, the halogen lamp  23  is turned on to heat the print base body  33  until the surface temperature of the base body  33  reaches a predetermined temperature in a range of 100 to 220° C. When the surface temperature reaches the predetermined temperature, the halogen lamp  23  is turned off to terminate the heating. It is to be noted that turning off the halogen lamp  23  at this time is because in general the heat of a halogen lamp efficiently travels by radiation to an element being heated, i.e., the print base body  33  in the embodiment, and therefore, the dye sublimates simultaneously when the surface temperature of the base body  33  reaches the predetermined temperature. 
     Upon completion of the heating to the base body  33 , the internal pressure of the vacuum deposition device is returned to normal, and the plastic lens  14  is taken out of the deposition device. Thereafter, the lens  14  is heated for the heating time, i.e., 30-60 min. and the heating temperature, i.e., 50-150° C., thereby to finish the fixing of the dye onto the plastic lens  14 . 
     As described above, in the first and second embodiments, the dyeing of plastic lenses can be carried out in a dry working environment, not in a wet working environment caused by the conventional dip dyeing method. According to the present embodiments, the working environment can be improved, and workability can be also extremely improved. In addition, the preparation of inks is conducted under digital-control by the PC, so that the dye can be printed to the print base body at the amount always controlled. Accordingly, the dyeing method and the dyeing system used therein in the embodiments can reduce unevenness in the hue and density and provide the excellent effect for productions which are low in the volume and wide in the variety. 
     Furthermore, since the density of the dye to be printed on the print base body is controlled by the PC, the lens can be dyed in a desired density gradient without color unevenness and color missing. 
     Next, description is made on various examples using the dyeing method and system in the first and second embodiments according to the present invention. 
     EXAMPLE 1 
     In Example 1, the vacuum vapor-deposition transfer device  10  in the first embodiment is used as a dyeing jig. A CR-39 lens is used as the plastic lens  14  to be dyed. For a sublimatable ink, a water-base dispersible dye manufactured by UPEPO Co. Ltd. is used. By the use of a drawing software in the PC, the color data is produced such that the hue of the dye is brown color (the combination ratio of red, blue, and yellow equals to 2-1-3) and the color density is 30% (in a light-shield rate). Thereafter, two circular colored layers  2  each having a slightly larger diameter than the diameter of a lens to be dyed are printed on the white paper  1  (high-quality PPC paper) based on the color data produced as above, thus completing the print base body  3 . 
     This print base body  3  is dried and then attached to the underside of the support plate  12  in the device  10  with an adhesive tape and the like. The lens holders  13  are mounted on the support plate  12  at respective positions of the holes  12   a . Then, the plastic lenses  14  (CR-39) are set one-by-one in the lens holders  13  so that the concave surface of the lens  14  is in the underside. The lens holder  13  having a height of 15 mm is used in the present example. The heater  15  is turned on and its temperature is sensed by the temperature sensor  16 . When the sensor  16  detects that the temperature of the heater  15  reaches 200° C., the rotary vacuum pump  17  is activated to reduce the internal pressure of the device 10 to 10 mmHg. Then, the support shaft  11  is operated to move the support plate  12  downward until the print base body  3  attached to the underside of the plate  12  comes into contact with the heater  15  to thereby start sublimation of the dye of the colored layers  2 . The contact time between the base body  3  and the heater  5 , i.e., the heating time, is 5 min. 
     After a lapse of the predetermined time (5 min.), the leak valve  18  is opened to return the pressure of the device  10  to a normal pressure. The dyed plastic lenses  14  are taken out of the device  10  and then put in the oven  35  at the heating temperature of 135° C. and for the heating time of 30 min., fixing the color (i.e., the deposited dye) on the plastic lenses  14 . After this fixing, the dyed lenses  14  are visually checked as to whether the dyed color agrees with a desired color without inferior appearance, color unevenness, color missing. As a result of the visual observation, there is no defect in the above points. 
     EXAMPLE 2 
     The dyeing operation is carried out to dye plastic lenses in a (half) density gradient in the same dyeing conditions as in the Example 1. 
     The color data is produced by the PC such that the density gradient is adjusted to have the light shield rate of 30% at a point of 10 mm distant from the geometrical center of the lens. In the same way as in the Example 1, two circular colored layers  2  are printed on a white paper  1  to form a print base body  3 . With this base body  3 , the plastic lenses  14  are dyed to have a predetermined density gradient. The final plastic lenses  14  are excellent in colored conditions and no defect is visually observed regarding color evenness and others. 
     EXAMPLE 3 
     The same dyeing as in the Example 2 is carried out at each dyeing density in a range of 10% to 90% other than 30% to provide a whole colored plastic lens and other colored ones having different density gradients. No color unevenness and others are found in a visual check. 
     EXAMPLE 4 
     The dyeing jig (see FIG. 4A) described in the second embodiment is put in a vacuum deposition device in general use. A plastic lens  14  made of the same material as in the first embodiment is used. A print base body  33  and the plastic lens  14  are placed in respective positions in the dyeing jig. The rotary vacuum pump  17  is activated to reduce the internal pressure of the deposition device 10 to 10 mmHg. Subsequently, a halogen lamp  23  is turned on to heat the print base body  33  until its surface temperature reaches 210° C. When the surface temperature reaches 210° C., the halogen lamp is immediately turned off. The dye is sublimated toward and deposited on the plastic lens. The pressure of the device is then returned to normal. The plastic lens  14  taken out of the device is put in an oven  35  at 135° C. and for about 30 min. to fix the color (dye). After the fixing, a visual check is made as to appearance defects such as color unevenness, color missing, and others and whether the dyed color agrees with a desired color. Consequently, no problem is found in the above visual observation points. 
     EXAMPLE 5 
     By using the dyeing system in the first embodiment and selecting a gradient pattern in a drawing software in the PC, four print base bodies  50 A- 50 D shown in FIGS. 7A-7D are produced, each having a colored layer printed in gradient (gradation) density on a white paper  40 . The color (a combination of red(R), green(G), and blue(B)) of the colored layer  41  to be printed is prepared in the drawing software in the PC so that the color index numbers of R,G,B are 0, 255, 255. 
     In this example, the color combination is determined to (R,G,B)=(0,255,255), but not limited thereto and it may be appropriately selected to suit the needs or preferences. 
     The print base body  50 A shown in FIG. 7A has a circular colored layer  41  printed on a white paper  40 , based on the gradient pattern selected in the drawing software. This selected pattern is of gradually changing gradient density over all. 
     The print base body  50 B shown in FIG. 7B has a substantially semicircular colored layer  42  on a white paper  40 , the colored layer  42  is wholly constant in density. Specifically, the brightness is 255, the hue is 180, the color saturation is 255, each of which is one of 256 steps including 0 to 255. 
     The print base body  50 C shown in FIG. 7C has a substantially semicircular colored layer  43  on a white paper  40 . The colored layer  43  is formed such that about two thirds of the layer  43  (corresponding to a colored layer  43   a ) is colored in constant density (the brightness is 255, the hue is 180, the color saturation is 255), and the remaining one-third (corresponding to a colored layer  43   b ) is colored in gradually changing gradient density. 
     The print base body  50 D shown in FIG. 7D has a substantially semicircular colored layer  44  on a white paper  40 . The colored layer  44  is formed such that about two thirds of the layer  44  (corresponding to a colored layer  44   a ) is colored in dark density (the brightness is 255, the hue is 180, the color saturation is 255) and the remaining one-third (corresponding to a colored layer  44   b ) is colored in light density(specifically, the darkness is about half as compared with the colored layer  44   a ). 
     With the use of those print base bodies  50 A- 50 D, plastic lenses  14  are dyed with the same dyeing jig as in the Example 4. The material of lenses and the dyeing conditions are the same as in the first embodiment. After dyeing, any color unevenness and other defects are not found in a visual check on the appearance of the lenses. 
     Furthermore, the transmittance of the plastic lenses  14  dyed using the print base bodies  50 A- 50 D are measured. This measurement is carried out by measuring the transmittance at several points in 5 mm steps on the diametrical line of the lens, starting from one point near the outer bound of the lens (for example, one point in the darkest dyed portion in FIG.  7 A). 
     A measurement device used in this example is MODEL 304 manufactured by ASAHI SPECTRA CO., LTD. The measurement result is shown in FIG. 8 graphing transmittance transitions by pattern. The horizontal axis of the graph indicates the distance from the measurement start point and the vertical axis indicates the transmittance measured at each measurement point. It is to be noted that, as the color density of the dyed lens is lower, the transmittance is higher. Four lines A to D indicate the results of the lenses dyed by the use of the print base body  50 A- 50 D, respectively. In the above manner, the plastic lenses  14  are dyed with respective gradient patterns by the use of the corresponding base body  50 A- 50 D. As shown in the graph, for example, with the base body  50 A, the lens  14  is dyed with the gradient pattern having a small part colored in dark density and providing a sudden change to light density. With the base bodies  50 B, 50 C, the lenses  14  are dyed with the gradient patterns having a constant density transition. With the base body  50 D, the lens  14  is dyed with the gradient pattern having a large part colored in dark density and providing a sudden change to light density. 
     Although it is very difficult to conduct the dyeing with the fine gradient patterns by the conventional method, the dyeing method in the above embodiments according to the present invention enables to dye lenses with the fine gradient patterns. 
     Specifically, according to the present invention, even if required gradient patterns are different by lens, a lens can be dyed with an optional gradient pattern selected from among those shown in FIGS. 7A-7D or a gradient pattern of halftone between those gradient patterns. 
     The present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. For instance, although a water-base ink is used in the above embodiments, an oil-base ink can provide the same effect. In the case of the oil-base ink, which is apt to be dried in the head portion of an ink cartridge and may cause clogging of the head, a piezoelectric-type ink jet printer is preferably used. 
     In the above embodiments, although the heating to the print base body is conducted from above or below the base body, it may be carried out from side of the base body to sublimate the dye therefrom. 
     Furthermore, the ink jet type printer is used in the above embodiment to print out the color data, i.e., the colored layer on the print base body. Alternately, instead of the sublimation type printer and ink cartridges, a laser printer using toner cartridges or an output device which outputs the data from a PC such as a plotter and the like may be used. 
     Furthermore, since the color density can be digital-controlled by the PC, the same color can be read if the color which is frequently ordered is assigned in advance to a management number of color data. This makes it possible to retain the stability of the color to be printed and also to efficiently conduct the dyeing work. 
     As described above in detail, according to the present invention, the adjustment of color density to be provided to a plastic lens can be facilitated, and the lens can be dyed in a stable hue. In addition, the dyeing work can be carried out in a comfortable working environment without deterioration therein. 
     The foregoing description of the preferred embodiment of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of the invention. The embodiment chosen and described in order to explain the principles of the invention and its practical application to enable one skilled in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto, and their equivalents.