Abstract:
A method for manufacturing a semi-finished blank for a varifocal liquid crystal lens includes coating the front of a first substrate and/or the rear of a second substrate with an adhesive agent, leaving an adhesive agent-free region that surrounds a liquid crystal holder; after said coating operation, reducing the pressure inside a sealed vessel that holds the first substrate and the second substrate, with respect to atmospheric pressure; affixing the second substrate over the front of the first substrate in the reduced pressure environment produced in said reducing the pressure operation; performing a standby operation including continuing the affixed state between the first substrate and the second substrate for a specific length of time in the reduced pressure environment produced in said reducing the pressure operation after the substrates have been affixed; and after said standby operation, restoring the pressure of the sealed vessel.

Description:
TECHNICAL FIELD 
     The present invention relates to a method for manufacturing a semi-finished blank for a high-quality varifocal lens. 
     BACKGROUND ART 
     In the past, a semi-finished blank for a varifocal lens was constituted so as to include a lower substrate whose front had a convex curved surface, and an upper substrate whose back had a concave curved surface and which was joined opposite this front. A varifocal section including a liquid crystal material was disposed between the upper and lower substrates. The refractive index of this varifocal section could be varied by applying voltage to the varifocal section, so the product could be used as a lens for bifocal eyeglasses, for example. 
     Patent Literature 1, for instance, discloses a method for manufacturing a semi-finished blank for a varifocal lens, in which, in the joining of an upper substrate and a lower substrate, the upper and lower substrates are stuck together and then an adhesive agent is introduced through one of two holes provided near the outer periphery of the upper substrate in a state in which the upper substrate has been pressed to the varifocal section via a pad, and air or the like is blown through the other hole so that the adhesive agent moves over all of both substrates. 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: US Laid-Open Patent Application 2009/256977 
     SUMMARY 
     However, with a conventional manufacturing method, there was the risk of decreasing the performance of the varifocal lens. 
     Specifically, with a conventional manufacturing method, the upper substrate was tightly pressed to the varifocal section side and the adhesive agent introduced so that the adhesive agent would not work its way into the varifocal section. Here, the local stress imparted to the varifocal section created problems such as damage to the lens and the generation of spaces within the varifocal section after pressure restoration, and there was the risk of decreasing the performance of the varifocal lens. 
     It is an object of the present invention to provide a method for manufacturing a semi-finished blank for a varifocal lens with which a decrease in the performance of the varifocal lens can be prevented. 
     To achieve the stated object, the method of the present invention for manufacturing a semi-finished blank for a varifocal lens is constituted such that a liquid crystal holder is disposed between the front of a first substrate and the rear of a second substrate that is opposite the first substrate, comprising an adhesive agent coating step, a pressure reduction step, an affixing step, a standby step, and a pressure restoration step. The adhesive agent coating step involves coating the front of a first substrate and/or the rear of a second substrate with an adhesive agent, leaving an adhesive agent-free region that surrounds the liquid crystal holder. The pressure reduction step involves reducing the pressure inside a sealed vessel that holds the first substrate and the second substrate, with respect to atmospheric pressure. The affixing step involves affixing the second substrate over the front of the first substrate in the reduced pressure environment produced in the pressure reduction step. The standby step involves continuing the affixed state between the first substrate and the second substrate for a specific length of time in the reduced pressure environment produced in the pressure reduction step after the substrates have been affixed. The pressure restoration step involves restoring the pressure of the sealed vessel after the standby step. 
     Also, it is preferable if the method of the present invention for manufacturing a semi-finished blank for a varifocal lens further comprises a liquid crystal coating step of coating the liquid crystal holder with a liquid crystal material by inkjet. 
     Also, it is preferable if the method of the present invention for manufacturing a semi-finished blank for a varifocal lens is such that the plurality of liquid crystal grains applied by inkjet in the liquid crystal coating step are applied spaced apart so as not to overlap each other. 
     Also, it is preferable if the method of the present invention for manufacturing a semi-finished blank for a varifocal lens is such that, in the liquid crystal coating step, the liquid crystal holder formed in a partial region on the front of the first substrate is coated with the liquid crystal material, and the coating amount is the amount in which the liquid crystal material is held on the liquid crystal holder by surface tension after the sealed vessel has been restored to atmospheric pressure. 
     Also, it is preferable if the method of the present invention for manufacturing a semi-finished blank for a varifocal lens is such that, in the adhesive agent coating step, the front of the first substrate and/or the rear of the second substrate is coated with the adhesive agent, with the plurality of adhesive agent grains spaced apart so as not to overlap each other and so as to surround the adhesive agent-free region. 
     Advantageous Effects 
     A decrease in the performance of a varifocal lens can be prevented with the present invention. 
     Specifically, when the second substrate is affixed over the front of the first substrate, a ring-shaped adhesive agent region is formed around the liquid crystal holder, with an adhesive agent-free region in between them. After this, pressure is restored to the sealed vessel, so that the adhesive agent is drawn in to the boundary at the outer periphery of the liquid crystal holder. That is, since the first substrate and second substrate are joined by packing the adhesive agent up to the boundary at the outer periphery of the liquid crystal holder without applying any pressing force on the liquid crystal holder, a decrease in the performance of the varifocal lens can be prevented without creating any problems such as damaging the liquid crystal holder or generating a space inside the liquid crystal holder. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is an oblique view of varifocal eyeglasses pertaining to an embodiment of the present invention; 
         FIG. 2  is a simplified exploded view of the first and second substrates constituting the semi-finished blank for a varifocal lens pertaining to an embodiment of the present invention; 
         FIG. 3  is a flowchart of some of the steps involved in the method for manufacturing the semi-finished blank for a varifocal lens in  FIG. 2 ; 
         FIG. 4   a  is an oblique view of the state when the first substrate of the semi-finished blank for a varifocal lens in  FIG. 2  is coated with a liquid crystal material, and  FIG. 4   b  is a detail cross section thereof; 
         FIG. 5   a  is an oblique view of the state when the first substrate of the semi-finished blank for a varifocal lens in  FIG. 2  is coated with an adhesive agent, and  FIG. 5   b  is a detail cross section thereof; 
         FIG. 6  is a simplified cross section showing the step of joining the first and second substrates of the semi-finished blank for a varifocal lens in  FIG. 2  inside a sealed vessel with reduced pressure; 
         FIG. 7   a  is a cross section showing the state in the standby step, which is one of the steps in the method for manufacturing the semi-finished blank for a varifocal lens in  FIG. 2 , and  FIG. 7   b  is a plan view thereof; and 
         FIG. 8   a  is a cross section showing the state in the pressure reduction step, which is one of the steps in the method for manufacturing the semi-finished blank for a varifocal lens in  FIG. 2 , and  FIG. 8   b  is a plan view thereof. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     The semi-finished blank for a varifocal lens of the present invention will now be described in detail along with the drawings.  FIG. 1  is a simplified diagram of varifocal eyeglasses  3  obtained by subjecting the semi-finished blank for a varifocal lens of this embodiment to surfacing, edging, or another such specific process. 
     A varifocal section  5  that includes a cholesteric liquid crystal material  39  is formed in the lower region slightly below the center of a varifocal lens  1 . Also, a circuit section  9  having a battery, a sensor circuit, etc., (not shown), is provided to an eyeglass frame  7 . For example, a sensor circuit featuring an acceleration sensor has the function of outputting an on/off signal according to the up and down angle of the head of the person wearing the varifocal eyeglasses  3 , and controls the voltage that is applied to the varifocal section  5 . 
     With the varifocal eyeglasses  3  constituted as above, the application of voltage to the varifocal section  5  is switched on the basis of a signal from the sensor circuit. This allows the varifocal eyeglasses  3  to function as bifocal eyeglasses by changing the apparent refractive index of the varifocal section  5 . 
     Next, the configuration of a varifocal lens semi-finished blank  11  will be described.  FIG. 2  is a simplified exploded view of a first substrate  13  and a second substrate  15  that is joined opposite the first substrate  13 . 
     As shown in  FIG. 2 , the first substrate  13  has a front with a convex curved surface, and a rear with a concave curved surface. A liquid crystal holder  19  is formed on the convex curved surface of the first substrate  13 . A Fresnel lens section  21  is formed on the surface of the liquid crystal holder  19 . A first transparent conductive film  23  and a first silicon dioxide film  25  are formed in that order, starting from the first substrate  13  side, on the convex curved surface of the first substrate  13 , and a first orientation film  27  is formed on the surface convex curved surface) of the first silicon dioxide film  25  in the region corresponding to the Fresnel lens section  21 . 
     The second substrate  15  has a front with a convex curved surface and a rear with a concave curved surface. A second transparent conductive film  31  and a second silicon oxide film  33  are formed in that order, starting from the second substrate  15  side, on the concave curved surface. A second orientation film  35  is formed in the region of the second silicon oxide film  33  that is opposite the Fresnel lens section  21 . 
     The first and second substrates  13  and  15  are made of thiourethane or another such plastic. 
     The varifocal lens semi-finished blank  11  with this constitution is manufactured as shown in the flowchart in  FIG. 3 . 
     In step  1 , which is a step of forming transparent conductive films, the first transparent conductive film  23  and the second transparent conductive film  31  are formed by sputtering over substantially the entire convex curved surface of the first substrate  13  and the concave curved surface of the second substrate  15 , respectively. The first and second transparent conductive films  23  and  31  are preferably formed in a thickness of 10 to 30 nm. Although this will not be described in detail, internal electrodes of the first and second transparent conductive films  23  and  31  are formed by spin coating and using a masking sheet, either directly before or directly after step  1 . The role of these internal electrodes is to improve contact between the transparent conductive films and external electrodes connected to the circuit section  9 . 
     In step  2 , which is an insulation layer formation step, the first and second silicon oxide films  25  and  33  are formed by sputtering. The first silicon dioxide film  25  and the second silicon oxide film  33  are formed by lamination over the first transparent conductive film  23  and the second transparent conductive film  31 , respectively. 
     In step  3 , which is an orientation film formation step, a first orientation film  27  is formed over the liquid crystal holder  19  of the first substrate  13 . A second orientation film  35  is then formed over the concave curved surface of the second substrate  15  so as to sandwich, along with the first orientation film  27 , the cholesteric liquid crystal material  39  applied over the liquid crystal holder  19  in step  4 . Specifically, the first orientation film  27  and the second orientation film  35  are laminated over the first silicon dioxide film  25  and the second silicon oxide film  33 , respectively, and are formed so as to be opposite one another. 
     In step  4 , which is a liquid crystal coating step, the cholesteric liquid crystal material  39  is applied toward the liquid crystal holder  19  with an inkjet  37 . More precisely, the first orientation film  27  formed on the Fresnel lens section  21  is coated with the cholesteric liquid crystal material  39 . The temperature and nozzle diameter can be suitably selected in applying the cholesteric liquid crystal material  39  with the inkjet  37 . In this embodiment, liquid crystal grains (300 pL per grain, 3% difference) of the cholesteric liquid crystal material  39  were applied using a nozzle with a diameter of 100 μm and at a nozzle tip temperature of 70 degrees. 
     The coating amount with the cholesteric liquid crystal material  39  is the amount in which the liquid crystal material  39  is held on the liquid crystal holder  19  by surface tension after the pressure restoration step (step  9 ) has ended. Also, the grains of the cholesteric liquid crystal material  39  are applied spaced apart so as not to overlap each other. The purpose of this is to prevent air bubbles from becoming admixed into the cholesteric liquid crystal material  39 . 
     Here, the cholesteric liquid crystal material  39  is preferably applied to the Fresnel lens section  21  on the surface of the liquid crystal holder  19  so that there is a slight excess. This suppresses manufacturing defects in the varifocal lens semi-finished blank  11  that would be caused by variance in the liquid crystal material coating state, and manufacturing variance in the first and second substrates  13  and  15  or the liquid crystal holder  19 . Specifically, even if such variance should cause a tiny deviation in the coating region of the cholesteric liquid crystal material  39 , the cholesteric liquid crystal material  39  that has been applied in excess can eventually spread out to cover the required area. 
       FIG. 4   a  shows the state when the inkjet  37  is used to apply the cholesteric liquid crystal material  39  toward the Fresnel lens section  21  of the first substrate  13 . More specifically, it shows the state when the cholesteric liquid crystal material  39  is applied over the first orientation film  27  formed on the Fresnel lens section  21 . The cholesteric liquid crystal material  39  is preferably not applied near the outermost peripheral portion of the Fresnel lens section  21 , as shown in  FIG. 4   b , taking into account the face that the material will eventually spread out over substantially the entire Fresnel lens section  21  after the second substrate  15  has been affixed to the surface of the first substrate  13 . 
     Step  5  is an adhesive agent coating step in which a jet dispenser  45  is used. As shown in  FIG. 5 , an adhesive agent  43  is applied to the convex curved surface of the first substrate  13 , leaving a specific spacing so that there is no overlap. As shown in  FIG. 7 , the adhesive agent  43  is applied so as to create a sealed space  53  around the liquid crystal holder  19  when adjacent drops of the adhesive agent  43  link up in the affixing step (step  7 ). The amount in which the adhesive agent  43  is applied here is set so that the adhesive agent  43  will spread out over substantially the entire convex curved surface of the first substrate  13 , except for the liquid crystal holder  19 , by the time the pressure restoration step (step  9 ) ends. 
     The adhesive agent  43  is applied so as to form a region that approximates a doughnut shape when seen from the front of the first substrate  13 . Specifically, an adhesive agent-free region  47  where no adhesive agent  43  is applied is provided to a specific region from near the liquid crystal holder  19  (the Fresnel lens section  21 ) and its periphery toward the outer periphery of the first substrate  13 . The adhesive agent-free region  47  is formed by taking into account the coating pattern and coating amount of the adhesive agent  43 , the final thickness of the adhesive agent layer, the size and shape of the liquid crystal holder  19 , the degree of pressure reduction (step  6 ), and so forth. Also, the area near the outer periphery of the first substrate  13  is not coated with the adhesive agent  43  in order to prevent the adhesive agent  43  from oozing out from the outer periphery of the first substrate  13 . 
     The adhesive agent  43  used in this embodiment has grains of about the same amount, but may instead be used as a linear adhesive agent. 
     The vacuum sealing step will now be described in detail. This vacuum sealing step consists of the pressure reduction step (step  6 ), the affixing step (step  7 ), the standby step (step  8 ), and the pressure restoration step (step  9 ). 
     As shown in  FIG. 6 , in step  6  a reduced pressure state (with respect to atmospheric pressure) is created with a vacuum pump  51  inside a sealed vessel  49 , which houses the first substrate  13  and the second substrate  15  coated with the cholesteric liquid crystal material  39  and the adhesive agent  43 . 
     Step  7  is a step of affixing the first substrate  13  and the second substrate  15  together. The first and second substrates  13  and  15  are fixed by a fixing member (not shown) so as to face each other with a gap in between, inside the sealed vessel  49 . The first substrate  13  is moved upward toward the second substrate  15 , and the fixing of the second substrate  15  is released at the point when it comes into contact with the first substrate  13 . Consequently, the surface of the first substrate  13  is pressed on by the weight of the second substrate  15 . 
     In step  8 , which is a standby step, the state in which the first substrate  13  and the second substrate  15  were affixed in step  7  is maintained for a specific length of time. As shown in  FIG. 7 , the adhesive agent  43  spreads out when the grains of the adhesive agent  43  are pressed under the weight of the second substrate  15  in the standby step, and the grains of the adhesive agent  43  link up as a result. This forms a sealed space  53 , which is independent from the exterior of the varifocal lens semi-finished blank  11 , in the adhesive agent-free region  47  by cutting the sealed space  53  off from the space to the outside of the adhesive agent  43 . Specifically, the adhesive agent-free region  47  is converted into the sealed space  53 , which is bound by the first substrate  13 , the second substrate  15 , and the adhesive agent  43 , and forms a ring-shaped adhesive agent region around the outer periphery of the sealed space  53 . 
     In this embodiment, this sealed space  53  is easily formed since the distance between the outer periphery of the adhesive agent-free region  47  and the outer periphery of the liquid crystal holder  19  is greater than the spacing at which the grains of the adhesive agent  43  are applied near the outer periphery of the adhesive agent-free region  47 . 
     In step  9 , the inside of the sealed vessel  49 , which was put under a reduced pressure environment in step  6 , is restored to atmospheric pressure. The adhesive agent-free region  47  around the liquid crystal holder  19  is bounded by the adhesive agent  43 , so the adhesive agent  43  is drawn in toward the sealed space  53  of the adhesive agent-free region  47 . Also, since the adhesive agent  43  is tacky, the speed at which it flows does not keep up with the pressure restoration speed. Accordingly, the inside of the sealed space  53  takes on a negative pressure. The second substrate  15  is pressed against the first substrate  13  by atmospheric pressure due to the negative pressure inside the sealed space  53 . As a result, the cholesteric liquid crystal material  39  goes all the way across the entire Fresnel lens section  21  of the liquid crystal holder  19 , and goes across the entire convex curved surface of the first substrate  13  except for the liquid crystal holder  19 , and the sealed space  53  is substantially eliminated as shown in  FIGS. 8   a  and  8   b.    
     The coating amount of the cholesteric liquid crystal material  39  here is the amount in which the liquid crystal material  39  is held on the liquid crystal holder  19  by surface tension on the second substrate  15  after the sealed vessel has been restored to atmospheric pressure. Accordingly, what is drawn to the adhesive agent-free region  47  is just the adhesive agent  43 , and not the cholesteric liquid crystal material  39 . Specifically, there is no mixing of the adhesive agent  43  and the cholesteric liquid crystal material  39 , so the bonding strength at the bonding layer can be raised. 
     The adhesive agent  43  is drawn into the sealed space  53  of the adhesive agent-free region  47  mainly in the pressure restoration step, but this space does not go under a perfect vacuum even in the pressure restoration step (step  6 ). Accordingly, this space is not necessarily completely filled by the adhesive agent  43 . Therefore, as shown in  FIG. 8 , extremely small air bubbles  55  are left behind near the outer peripheral part of the liquid crystal holder  19 . In  FIG. 8 , the air bubbles  55  are exaggerated and shown as larger points, but in reality these air bubbles  55  are extremely small. Furthermore, the air bubbles  55  lie along a boundary line between the varifocal section  5  and the rest of the region, so they are hard to see and pose no problem whatsoever to practical use. 
     It is predicted that the air bubbles  55  tend to occur at two points near the intersection between the outer periphery of the varifocal section  5  and the minor axis of the ellipse when the varifocal section  5  is substantially in the form of an ellipse, and tend to occur at one point on the outer periphery of the varifocal section  5  when the varifocal section  5  is substantially in the form of a circle. 
     Finally, in step  10 , which is an adhesive agent curing step, the region occupied by the adhesive agent  43  is irradiated with ultraviolet rays, visible light, or the like to cure the adhesive agent  43 . This step may, if needed, include a step of thoroughly spreading out the adhesive agent  43  between the upper and lower first substrate  13  and second substrate  15  for a specific length of time prior to the curing of the adhesive agent  43 . 
     In this embodiment, an example was given in which the cholesteric liquid crystal material  39  was applied over the liquid crystal holder  19 , but the present invention is not limited to this. For example, instead of this, or in addition to it, the region of the second substrate  15  that is opposite the liquid crystal holder  19 , namely, the second orientation film  35 , may be coated with the cholesteric liquid crystal material  39 . 
     Also, the liquid crystal holder  19  was formed on the front of the first substrate  13 , but may be formed on the rear of the second substrate  15 . 
     Also, in this embodiment an example was given in which the convex curved surface of the first substrate  13  was coated with the adhesive agent  43 , but the present invention is not limited to this. For example, the concave curved surface of the second substrate  15  may be coated with the adhesive agent  43 , or both surfaces may be coated. 
     Furthermore, in this embodiment an example was given in which the liquid crystal holder  19  was provided on a base that protrude into a partial region on the front of the first substrate  13 , but the present invention is not limited to this. For example, the configuration may be such that the base itself is not present on the front of the first substrate  13 , and the Fresnel lens section  21  is provided instead. In this case, the liquid crystal holder  19  is constituted by the Fresnel lens section  21 . Also, the configuration may be such that a concave portion is provided on the front of the first substrate  13  as the liquid crystal holder  19 . 
     As discussed above, in this embodiment the adhesive agent  43  is applied so as to form the sealed space  53  in the adhesive agent-free region  47  in the standby step under a reduced pressure environment. In the pressure restoration step, the adhesive agent  43 , which surrounds the sealed space  53  in a ring shape, is drawn to the sealed space  53  side. 
     Therefore, there is no need to press on the liquid crystal holder in order to join the first substrate and second substrate as with prior art, so there will be no problems such as damage to the lens or the generation of spaces within the liquid crystal holder. Thus, a varifocal lens semi-finished blank  11  can be manufactured without any decrease in performance. 
     Also, in this embodiment the cholesteric liquid crystal material  39  was applied only in the amount held on the liquid crystal holder  19  by surface tension at the stage of the pressure restoration step using the inkjet  37 . Consequently, the cholesteric liquid crystal material  39  is not drawn all the way into the sealed space  53 , and the adhesive agent  43  can be sent to the places where it is needed. 
     Furthermore, since there is no need to provide a hole in the upper substrate as with prior art, the entire blank can be effectively utilized in edging of the lens. 
     Industrial Applicability 
     The method for manufacturing a semi-finished blank for a varifocal lens pertaining to the present invention can be widely applied as a manufacturing method for optical parts such as eyeglass lenses and cameras. 
     Reference Signs List 
       1  varifocal lens 
       3  varifocal eyeglasses 
       5  varifocal section 
       7  eyeglass frame 
       9  circuit section 
       11  semi-finished blank for a varifocal lens 
       13  first substrate 
       15  second substrate 
       19  liquid crystal holder 
       21  Fresnel lens section 
       23  first transparent conductive film 
       25  first silicon dioxide film 
       27  first orientation film 
       31  second transparent conductive film 
       33  second silicon oxide film 
       35  second orientation film 
       37  inkjet 
       39  cholesteric liquid crystal material 
       43  adhesive agent 
       45  jet dispenser 
       47  adhesive agent-free region 
       49  sealed vessel 
       51  vacuum pump 
       53  sealed space 
       55  air bubble