Abstract:
It is an object of the present invention to provide a light diffusing lens production apparatus which makes it possible to efficiently produce a high-quality light diffusing lens having enhanced optical properties. 
     The light diffusing lens production apparatus includes: a pair of molds  15 , consisting of a fixed mold  16  and a movable mold  18 , which forms a final molded product cavity  22  that defines the shape of a light diffusing lens  14 ; a mold clamping apparatus  62  in which the pair of molds  15  is attached; a transport device  66 , having a chuck means capable of entering and exiting the space between the pair of molds  15  in an open state, which inserts a semifinished molded product  12  for the light diffusing lens  14  into the final molded product cavity  22 ; a heating device  68 , having a heating means capable of entering and exiting the space between the pair of molds  15  in an open state, which heats the fixed mold  16 -facing surface of the inserted semifinished molded product until the surface becomes a molten state; and an injection apparatus  64  which, after clamping of the pair of molds  15 , injects a molding material into the final molded product cavity  22  so that the molding material covers the molten surface of the semifinished molded product  12.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a production apparatus and a production method for producing a light diffusing sheet, e.g, for use in an automotive headlight, by injection molding. 
       BACKGROUND ART 
       [0002]    Injection-molded products include a molded product composed of a unified laminate of a plurality of resin layers (hereinafter referred to as a molded laminate product), for example, a molded product composed of resin layers of a combination of various colors and materials, or a molded product composed or a laminate of resin layers of the same material. 
         [0003]    Main conventional molding methods for producing such a molded laminate product include a multicolor molding method and an insert molding method. The multicolor molding method involves injecting a plurality of resin materials from different injection apparatuses into a cavity in a mold, thereby laminating a plurality of resin layers. The insert molding, method involves placing an injection-molded semifinished product as an insert in a cavity in a mold, and then injecting a resin material into the cavity to mold a laminate. 
         [0004]    These days optical parts, such as a plastic lens,are commonly produced by injection molding. While it is conventional practice to mold a plastic lens as a single-layer lens, there exist some thick plastic lenses, such as a light diffusing lens for use in outdoor lighting, an automotive headlight, etc. 
         [0005]    Such a thick light diffusing lens is required to be a homogeneous transparent body free of optical defects so that light will diffuse uniformly. In the case of molding a lens composed of a laminate of a plurality of resin layers, differences may be produced in physical properties, such as residual stress and internal distortion, between the resin layers even when the same molding material is used for the layers; therefore, it is difficult to mold a high-quality lens. Especially in the case of multicolor molding of a laminate, a difference will be produced in thermal history between the, resin layers. Therefore, multicolor molding is not suited to molding of a thick lens such as a light diffusing lens. Thus, at present, a light diffusing lens is usually produced as a single-layer molded product when the lens is produced by injection molding. 
         [0006]    However, in the case of injection molding of a single-layer light diffusing lens, defects such as sinks are likely to be formed in a thick portion. Therefore, in a pressure-keeping process, it is necessary to cool a molded product slowly over time. Accordingly, it takes a long time to mold such a lens. 
         [0007]    In order to shorten the time for molding a lens and increase the production efficiency, it is presently being studied to mold a lens, composed of not a single layer but a laminate of a plurality of layers, by employing the insert molding method. 
         [0008]    For example, PCT International Publication No. WO 2012/132597 has proposed a method which involves forming a plurality of cavities having different volumes in a mold, and repeating injection of a molten resin while sequentially transferring an intermediate molded product as an insert to a cavity having a larger volume than the intermediate molded product, thereby producing a molded laminate product. 
       SUMMARY OF THE INVENTION 
       [0009]    However, the lens molding method disclosed in the above patent document, which is based on insert molding, is solely intended to shorten the time for molding a thick lens and streamline the production process. In the case of insert molding, a molten resin is applied onto a cooled semifinished product, and therefore the temperature of the molten resin decreases and its fluidity becomes low. This results in low adhesion at the interface, leading to non-uniform internal stress in the final product. Thus, the conventional insert molding method can only produce a low-quality plastic lens having lower optical properties. 
         [0010]    The present invention has been made in view of the above problems in the prior art. It is therefore an object of the present invention to provide a light diffusing lens production apparatus and method which makes it possible to efficiently produce a high-quality light diffusing lens having enhanced optical properties. 
         [0011]    In order to achieve the object, the present invention provides an apparatus for producing a light diffusing lens by molding and laminating at least two resin layers, comprising: a pair of molds, consisting of a fixed mold and a movable mold, which forms a final molded product cavity that defines the shape of a light diffusing lens; a mold clamping apparatus in which the pair of molds is attached; a transport device, having a chuck means capable of entering and exiting the space between the pair of molds in an open state, which inserts a semifinished molded product for the light diffusing lens into the final molded product cavity; a heating device, having a heating means capable of entering and exiting the space between the pair of molds in an open state, which heats the fixed mold-facing surface of the inserted semifinished molded product until the surface becomes a molten state; and an injection apparatus which, after clamping of the pair of molds, injects a molding material into the final molded product cavity so that the molding material covers the molten surface of the semifinished molded product. 
         [0012]    The present invention provides also provides a method for producing a light diffusing lens by molding and laminating at least two resin layers, comprising: the insertion step of inserting a semifinished molded product for a light diffusing lens into a final molded product cavity, which defines the shape of the light diffusing lens and which is formed in a pair of molds consisting of a fixed mold and a movable mold, when the pair of molds is in an open state; the heating step of allowing a heating means to enter the space between the pair of molds in an open state, and heating the fixed mold-facing surface of the inserted semifinished molded product until the surface becomes a molten state; the mold clamping step of damping the pair of molds; the injection step of injecting a molding material into the final molded product cavity so that the molding material covers the molten surface of the semifinished molded product; and the molded product taking-out step of opening the pair of molds, and taking a final molded product out of the pair of molds. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIGS. 1A through 1C  are side views showing exemplary semifinished molded products and an exemplary light diffusing lens which are produced by a light diffusing lens production apparatus according to a first embodiment of the present invention; 
           [0014]      FIG. 2  is a cross-sectional view of a mold for use in the light diffusing lens production apparatus according to the first embodiment; 
           [0015]      FIG. 3  is a perspective view of the light diffusing lens production apparatus according to the first embodiment; 
           [0016]      FIG. 4  is a diagram illustrating a manner in which semifinished molded products and a light diffusing lens are taken out of a mold, and semifinished molded products are inserted into the mold and heated; 
           [0017]      FIGS. 5A through 5D  are diagrams illustrating process steps in a light diffusing lens production method according to the first embodiment; 
           [0018]      FIGS. 6A through 6C  are cross-sectional views showing a primary molded product, a secondary molded product and a light diffusing lens as a final molded product in a mold; 
           [0019]      FIG. 7  is a side view of a light diffusing lens having a four-layer laminate structure produced by the light diffusing lens production apparatus (method) according to the first embodiment of the present invention; 
           [0020]      FIG. 8  is a side view of a light diffusing lens having a five-layer laminate structure produced by the light diffusing lens production apparatus (method) according to the first embodiment of the present invention; 
           [0021]      FIG. 9  is a side view of a light diffusing lens having a two-layer laminate structure produced by a light diffusing lens production apparatus (method) according to a second embodiment of the present invention; 
           [0022]      FIG. 10  is a cross-sectional view of a mold for use in the light diffusing lens production apparatus (method) according to the second embodiment; 
           [0023]      FIGS. 11A through 11D  are diagrams illustrating process steps in the light diffusing lens production method according to the second embodiment; 
           [0024]      FIG. 12  is a cross-sectional view of a mold for use in a light diffusing lens production apparatus (method) according to a variation of the second embodiment; and 
           [0025]      FIGS. 13A through 13D  are diagrams illustrating process steps in the light diffusing lens production method according to the variation of the second embodiment. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0026]    Embodiments of a light diffusing lens production apparatus and method according to the present invention will now be described with reference to the drawings. 
       First Embodiment 
       [0027]      FIGS. 1A through 1C  are diagrams showing semifinished molded products and a light diffusing lens as a final molded is product, which are produced by a light diffusing lens production apparatus (method) according to a first embodiment. 
         [0028]      FIG. 1A  shows a primary molded product  10  which is a semifinished molded product composed solely of a first layer. The primary molded product  10  is finally molded into a light diffusing lens, composed of a laminate of e.g. three thermoplastic resin (molding material) layers, for use in outdoor lighting, an automotive headlight, etc. 
         [0029]      FIG. 1(B)  shows a secondary molded product (intermediate molded product)  12  which has been produced by placing the primary molded product  10  of  FIG. 1A  as an insert member in a mold, and forming a second layer on the surface of the primary molded product  10 . In the secondary molded product  12 , the lens portion is convex-curved. 
         [0030]      FIG. 1(C)  shows a tertiary molded product which has been produced by forming a third layer on the surface of the secondary molded product  12  of  FIG. 1B  as an insert member. In this embodiment the primary molded product  10  and the secondary molded product  12  are semifinished molded products which serve as insert members, and the tertiary molded product is a light diffusing lens  14  as a final molded product. 
         [0031]      FIG. 2  is a diagram showing a mold to be used in a mold clamping apparatus of an injection molding machine in order to mold the light diffusing lens  14 . The mold  15  includes a fixed mold  16  and a movable mold  18 . The fixed mold  16  is mounted to a fixed platen  17  of the mold damping apparatus, and the movable mold  18  is mounted to a movable platen  19 . 
         [0032]    The following three cavities are formed in the opposing surfaces of the fixed mold  16  and the movable mold  18 : a primary molded product cavity  20  for molding the primary molded product  10  shown in  FIG. 1A ; a secondary molded product cavity  21  for molding the secondary molded product  12  shown in  FIG. 1B ; and a final molded product cavity  22  for molding the final molded product, the light diffusing lens  14  shown in  FIG. 1C . 
         [0033]    Runners  23   a ,  23   b ,  23   c , which communicate with the primary molded product cavity  20 , the secondary molded product cavity  21  and the final molded product cavity  22 , respectively, are formed in the fixed mold  16  such that they branch from a sprue  25 . An injection nozzle  26  of the below-described injection apparatus is connected to the opening of the sprue  25  so that a molten resin (molding material) is injected into the mold. 
         [0034]    The molten resin is injected into the primary molded product cavity  20 , the secondary molded product cavity  21  and the final molded product cavity  22  either simultaneously or under control by a valve gate of a hot runner, whereby the primary molded product  10 , the secondary molded product  12  and the final molded product  14  are molded at a time. 
         [0035]    A production apparatus for performing a light diffusing lens molding method according to this embodiment will now be described with reference to  FIG. 3 . 
         [0036]    In  FIG. 3 , reference numeral  60  denotes the entire light diffusing lens production apparatus. The light diffusing lens production apparatus  60  includes a mold clamping apparatus  62 , an injection apparatus  64 , a first multi-axis robot  66  that operates as a transport device for placing a semifinished molded product for the light diffusing lens  14 , as an insert member, in a cavity of the mold  15 , and a second multi-axis robot  68  that operates as a heating device for heating the surface of the inserted semifinished molded product. 
         [0037]    The mold damping apparatus  62  includes a drive section  70  installed on a base  69  and having a not-shown toggle link mechanism for moving the movable platen  19  back and forth to open/close the mold, and clamping the mold after closing the mold. As shown in  FIG. 2 , the fixed mold  16  is mounted to the fixed platen  17 , and the movable mold  18  is mounted to the movable platen  19 . The mold  15 , consisting of the fixed mold  16  and the movable mold  18 , has the above-described construction. Reference numeral  71  denotes tie bars which are pulled by the toggle link mechanism after closing the mold and generate a mold clamping force. 
         [0038]    The injection apparatus  64  is movably installed on the base  69  via rails  72 . The injection apparatus  64  includes a barrel  73 , a screw  74  housed in the barrel  73 , a hopper  75  for feeding a resins as a molding material into the barrel  73 , and a drive  76  for rotating and moving back and forth the screw  73 . 
         [0039]    An injection nozzle  26  is provided at the front end of the barrel  73 . The injection apparatus  64  advances, and the injection nozzle  26  comes to connect with the fixed mold  16 , as shown in  FIG. 2 . When a molten resin has been weighed and accumulated in front of the screw  74  in the barrel  73 , the molten resin is injected from the injection nozzle  26  into the cavities in the mold  15  by advancing the screw  74 . 
         [0040]    The first multi-axis robot  66  and the second multi-axis robot  68  will now be described. 
         [0041]    The first multi-axis robot (transport device)  66  engages in the process steps of taking a primary molded product  10 , a secondary molded product  12  and a light diffusing lens  14  as a final molded product, as shown in  FIGS. 1A through 1C , out of the open mold  15 , and placing another primary molded product  10  and another secondary molded product  12  as insert members in the mold  15 . 
         [0042]    In this embodiment a light diffusing lens  14  as a final product, which has been taken out of the mold  15 , is carried to a transport conveyer  78  by the first multi-axis robot  66 . A primary molded product  10  and a secondary molded product  12 , which have been taken out of the mold  15 , are temporarily placed (stored) by the first multi-axis robot  66  on a temperature adjustment stage (storage section)  80 , disposed in a robot access area, where the temperatures of the primary molded product  10  and the secondary molded product  12  are adjusted to a predetermined temperature lower than the heat distortion temperature. 
         [0043]    As shown in  FIG. 4 , a plurality of primary molded products and  10  and a plurality of secondary molded products  12 , whose temperatures have been adjusted to a temperature lower than the heat distortion temperature, are arranged on the temperature adjustment stage  80 . The first multi-axis robot  66  takes a primary molded product  10  and a secondary molded product  12 , whose temperatures have reached a predetermined temperature (appropriate temperature), out of the temperature adjustment stage  80 , and set them as insert members in the movable mold  18 . The primary molded product  10  is set as an insert member in the secondary molded product cavity  21 , and the secondary molded product  12  is set as an insert member in the final molded product cavity  22 . 
         [0044]    In this embodiment, in addition to the first multi-axis robot  66  which performs the operation of taking semifinished products and a final product out of the mold, and inserting semifinished products into the mold, the second multi-axis robot (heating device)  68  is installed which performs the operation of heating a primary molded product  10  and a secondary molded product  12 , semifinished products that have been inserted into the movable mold  18 . An infrared heater  35  or the like is provided as a heating means at the front end of an arm of the second multi-axis robot  68 . 
         [0045]    Process steps in a light diffusing lens molding method, performed by the thus-constructed light diffusing lens production apparatus, will now be described in order with reference to  FIGS. 5A through 5D . 
         [0046]    In the light diffusing lens production method according to this embodiment, molding, of a primary molded product  10 , molding of a secondary molded product  12 , and molding of a light diffusing lens  14  as a final molded product are performed in parallel in order to streamline the production process. For easier understanding of the process steps, a description is started at a time when the immediately preceding cycle of molding of a primary molded product  10 , a secondary molded product  12  and a light diffusing lens  14  is completed. 
         [0047]    First,  FIG. 5A  illustrates the step of opening the movable mold  18  from the fixed mold  16  after completion of a pressure transmission step. At this time, the primary molded product  10 , the secondary molded product  12  and the light diffusing lens  14  remain in the movable mold  18 . 
         [0048]      FIG. 5B  illustrates the step of taking the primary molded product  10 , the secondary molded product  12  and the light diffusing lens  14  out of the movable mold  18 . In this embodiment the arm of the first multi-axis robot  66  has a o two-stage chuck  32 . The first-stage chuck  36  is a chuck for attracting and holding a primary molded product  10  and a secondary molded product  12  which have been placed on the temperature adjustment stage  80  and whose temperatures have been adjusted to a predetermined temperature. The second-stage chuck  37  is a chuck for attracting and holding a primary molded product  10 , a secondary molded product  12  and a light diffusing lens  14  as a final molded product which have been molded, and taking them out of the movable mold  18 . 
         [0049]    In this embodiment the first multi-axis robot  66 , while holding the temperature-adjusted primary molded product  10  and secondary molded product  12  with the first-stage chuck  36 , allows the chuck  32  to enter the space between the fixed mold  16  and the movable mold  18  of the open mold. The first multi-axis robot  56  then attracts and holds the primary molded product  10 , the secondary molded product  12  and the light diffusing lens  14  with the second-stage chuck  37 , and takes them out of the movable mold  18 . 
         [0050]    Next, as shown in  FIG. 5C , the first multi-axis robot  66  turns the chuck  32  by 180 degrees, and places the primary molded product  10  and the secondary molded product  12 , which have been held by the first-stage chuck  36 , in the secondary molded product cavity  21  and in the final molded product cavity  22 , respectively, as insert members. 
         [0051]    By using the chuck  32 , having the two front/back chucks, in the above-described manner, the taking-out of the semifinished molded products and the light diffusing lens  14  and the setting of the semifinished products as insert members in the movable mold  18  can be performed successively in the same process step. 
         [0052]    Thereafter, the primary molded product  10  and the secondary molded product  12  which have been taken out are transported to the temperature adjustment stage  80 , where their temperatures are adjusted to a predetermined temperature, and they wait until they are inserted into the mold  5 . When a polycarbonate (PC) resin is used as a molding material, the heat distortion temperature is 130° C. to 140° C. though it may somewhat vary depending on the quality and the grade of the resin. In the case of an acrylic resin (e,g. PMMA), the heat distortion temperature is 70° C. to 100° C. Depending on the type of the molding material, the temperatures of the primary molded product  10  and the secondary molded product  12  are adjusted to a temperature which is somewhat lower than the heat distortion temperature. 
         [0053]    In this embodiment the light diffusing lens  14  as a final molded product is sent to the transport conveyer  78  shown in  FIG. 3 . 
         [0054]      FIG. 5D  shows the step of heating semifinished molded products, the most important step in the light diffusing lens  14  production process according to this embodiment. The heating objects are the primary molded product  10  which has been placed as an insert member in the secondary molded product cavity  21 , and the secondary molded product  12  which has been placed as an insert member in the final molded product cavity  22 . 
         [0055]    The second multi-axis robot  68  shown in  FIG. 3  allows the infrared heater  35  or the like, provided as a (external) heating means at the front end of the arm, to enter the space between the fixed mold  16  and the movable mold  18  of the open mold. 
         [0056]    In the primary molded product  10  and the secondary molded product  12  as semifinished molded products, the portion to be heated is the surface to which a resin layer is to be laminated in the next step, i.e. the entire surface facing the fixed mold  16 . The surfaces of the primary molded product  10  and the secondary molded product  12  are heated to a temperature higher than the melting temperature of the resin as a molding material so that only the surfaces of the molded products become a molten state. The melting temperature is about 240° C. when the thermoplastic resin as a molding material is a polycarbonate (PC) resin, and about 160° C. in the case of an acrylic (PMMA) resin. The upper limit of the heating temperature is equal to the molding temperature. When the surfaces of the primary molded product  10  and the secondary molded product  12  have become a molten state, the second multi-axis robot  68  withdraws the infrared heater  35  from the mold  15 . 
         [0057]    Next, the mold  15  is closed and clamped. Thereafter, the injection apparatus  64  shown in  FIG. 3  is connected to the mold  15 , and the filling step (injection filling step) of injecting a resin (molding material) into the mold  15  is performed. 
         [0058]    In this embodiment, all the cavities in the mold  15 , i.e. the primary molded product cavity  20 , the secondary molded product cavity  21  and the final molded product cavity  22 , are simultaneously filled with a molten resin material by the filling step. In this embodiment the same resin is injected into the cavities from the single injection apparatus. 
         [0059]      FIG. 6A  shows a cross section of a primary molded product  10  in the primary molded product cavity  20 ,  FIG. 6B  shows a cross section of a secondary molded product  12  in the secondary molded product cavity  21 , and  FIG. 6C  shows a cross section of a light diffusing lens  14  in the final molded product cavity  22 . 
         [0060]    As shown in  FIG. 6A , the primary molded product  10  composed of a single resin layer is formed in the primary molded product cavity  20  by the filling of the molten resin. 
         [0061]    On the other hand, as shown in  FIG. 6B , the molten resin is filled into the secondary molded product cavity  21  in which the primary molded product  10  has been placed as an insert member; therefore, a second resin layer is laminated to the surface of the primary molded product  10 . Since the surface of the primary molded product  10  has been heated and has become a molten state, the injected molten resin can adhere to the interface with the primary molded product  10  in a homogeneously fused state. Further, there is no decrease in the temperature of the molten resin upon contact with the surface of the primary molded product  10 . Therefore, the molten resin is filled into the secondary molded product cavity  21  while maintaining good fluidity without partial solidification. 
         [0062]    The injected molten resin is thus filled into the secondary molded product cavity  21  while maintaining sufficient adhesion and fluidity at the interface with the primary molded product  10 . Accordingly, a pressure is transmitted uniformly within the molten resin. This can avoid the occurrence of the phenomenon of high residual stress in a portion, such as a portion near a gate, and low residual stress in the other portion. Therefore, in a pressure transmission step which is performed after the filling step and in which the molten resin is solidified while applying pressure to the resin, non-uniform residual stress can be prevented from remaining in the second layer, thereby achieving a uniform distribution of stress. 
         [0063]    Similarly, as shown in  FIG. 6C , the molten resin is filled into the final molded product cavity  22  in which the secondary molded product  12  has been placed as an insert member; a third resin layer is laminated to the surface of the secondary molded product  12 . 
         [0064]    Also in the final molded product cavity  22 , the surface of the secondary molded product  12  has been heated and has become a molten state, and therefore the injected molten resin can adhere to the interface with the secondary molded product  12  in a homogeneously fused state. The injected molten resin is thus filled into the tertiary molded product cavity  22  while maintaining sufficient adhesion and fluidity at the interface with the secondary molded product  12 . Accordingly, a pressure is transmitted uniformly within the molten resin. Therefore, in a pressure transmission step which is performed after the filling step and in which the molten resin is solidified while keeping the pressure, non-uniform residual stress can be prevented from remaining in the third layer, thereby achieving a uniform distribution of stress. 
         [0065]    The lamination of the light diffusing lens  14  is preferably performed in such a manner that, as in this embodiment, the protrusion of the convex curve of the lens increases stepwise from the primary molded product  10  which constitutes the bottom portion of the light diffusing lens  14 . Such a manner of lamination can stabilize the posture of a semifinished molded product when transporting it to the temperature adjustment stage  80 , and can facilitate placement of the semifinished molded product on the temperature adjustment stage  80 . 
         [0066]    Upon completion of the filling step, the process proceeds to the above-described pressure transmission step while keeping the pressure. 
         [0067]    After the molten resin in the primary molded product cavity  20 , the secondary molded product cavity  21  and the tertiary molded product cavity  22  is solidified, the mold opening step shown in  FIG. 5A  and the molded product taking-out step shown in  FIG. 5B  are performed. Subsequently, the same molding cycle is repeated successively. 
         [0068]    As described hereinabove, according to this embodiment, the surface of the primary molded product  10 , the first semifinished product, is heated into a molten state before the second layer is laminated to the primary molded product  10 , and the surface of the secondary molded product  12 , the next semifinished product, is likewise heated into a molten state before the third layer is laminated to the secondary molded product  12 . This makes it possible to mold the light diffusing lens  14 , the final molded product, which is a high-quality plastic lens having excellent optical properties and having a uniform stress distribution despite the large thickness. Further, the primary molded product  10 , the secondary molded product  12  and the light diffusing lens  14 , the final molded product, can be molded simultaneously in parallel by using the same mold  15 . Thus, the thick light diffusing lens  14  can be produced with high efficiency. 
         [0069]    Further, in this embodiment the primary molded product  10  and the secondary molded product  12  as semifinished molded products are temporarily placed (stored) on the temperature adjustment stage (storage section)  80  capable of temperature adjustment. This can prevent the primary molded product  10  and the secondary molded product  12  as semifinished molded products that are to serve as insert members from being completely solidified, thereby making it possible to smoothly perform heating in the later heating step. 
         [0070]    While the above-described embodiment relates to molding of the light diffusing lens  14  composed of a laminate of three layers, a light diffusing lens  14  composed of a laminate of four or five layers can also be molded by using a mold having cavities that define the shapes of molded products at various lamination stages. 
         [0071]      FIG. 7  shows a light diffusing lens  14  composed of a four-layer laminate. In the case of this light diffusing lens  14 , a secondary molded product  50  and a tertiary molded product  51  are intermediate molded products between the primary molded product  10  and the final molded product. Each semifinished molded product serves as an insert member in molding of a product at the next lamination stage: the primary molded product  10  serves as an insert member in molding of the secondary molded product  50 ; the secondary molded product  50  serves as an insert member in molding of the tertiary molded product  51 ; and the tertiary molded product  51  serves as an insert member in molding of the final molded product. 
         [0072]      FIG. 8  shows a light diffusing lens  14  composed of a five-layer laminate. In the case of this light diffusing lens  14 , a secondary molded product  50 , a tertiary molded product  51  and a quaternary molded product  52  are intermediate molded products between the primary molded product  10  and the final molded product. Each semifinished molded product serves as an insert member in molding, of a product at the next lamination stage: the primary molded product  10  serves as an insert member in molding of the secondary molded product  50 ; the secondary molded product  50  serves as an insert member in molding of the tertiary molded product  51 ; the tertiary molded product  51  serves as an insert member in molding of the quaternary molded product  52 ; and the quaternary molded product  52  serves as an insert member in molding of the final molded product. 
         [0073]    The foregoing is a description of a process for molding a light diffusing lens  14  composed of a laminate of three, four or five resin layers. The description is started at a time when the immediately preceding cycle of molding of semifinished products and a light diffusing lens  14  is completed. 
         [0074]    At the start of a first molding cycle, no semifinished molded product to be used as an insert member has yet been molded. Therefore, semifinished molded products are prepared in a preliminary molding process which is different from the above-described process for molding the final molded product, and are subjected to temperature adjustment performed in the above-described manner in advance of the first molding cycle. The first molding cycle starts by placing the thus-prepared semifinished molded products in the cavities for molding of products at the next lamination stage. 
       Second Embodiment 
       [0075]    In the above-described first embodiment, a final molded product  14 , which is a light diffusing lens composed of a laminate of three or more layers, is molded in such a manner that a secondary molded product  12  is lamination-molded using a primary molded product  10  as an insert member, and the secondary molded product  12  is then used as an insert member. 
         [0076]    On the other hand, in the below-described second embodiment, a light diffusing lens having a two-layer laminate structure is molded using a primary molded product  10  as an insert member. 
         [0077]      FIG. 9  shows a light diffusing lens  14  produced by a production apparatus (method) according to the second embodiment. As in the first embodiment, a primary molded product  10  which serves as an insert member constitutes the bottom portion of the lens: a convex-curved lens portion is formed by laminating a thermoplastic resin layer to the primary molded product  10 . 
         [0078]      FIG. 10  is a diagram showing a mold for use in molding of the light diffusing lens. The same reference numerals as used for the first embodiment shown in  FIG. 2  are used to refer to the same components, and a detailed description thereof is omitted. 
         [0079]    In the mold  40  shown in  FIG. 10 , a final molded product cavity  44 , which defines the shape of a light diffusing lens  14 , is formed by the opposing surfaces of a fixed mold  41  and a movable mold  42 . A runner  43  communicates with the final molded product cavity  44 . A primary molded product  10  is to be inserted into the final molded product cavity  44 . The primary molded product  10  has been molded in a different injection molding machine, and its temperature has been adjusted. 
         [0080]    A molding process using the mold  40  will now be described with reference to  FIGS. 11A through 11D . 
         [0081]      FIG. 11A  illustrates the step of opening the movable mold  42  from the fixed mold  41  after completion of the preceding molding cycle. A light diffusing lens  14  as a final molded product, produced in the preceding molding cycle, is waiting for its removal from the mold. 
         [0082]    Next, as shown in  FIG. 11B , the chuck  32  transports a primary molded product  10  from the temperature adjustment stage  80  shown in  FIG. 3  to between the fixed mold  41  and the movable mold  42  and, while holding the primary molded product  10 , attracts and holds the light diffusing lens  14  as a final molded product and takes it out of the movable mold  42 . Next, as shown in  FIG. 11C , the entire chuck  32  turns 180 degrees and places the primary molded product  10 , held by the first stage chuck  36 , as an insert member in the cavity  44 . Thereafter, the light diffusing lens  14  as a final molded product is transported to the transport conveyer  78 . 
         [0083]    Next, as shown in  FIG. 11D , the infrared heater  35  enters the space between the fixed mold  41  and the movable mold  42 , and heats the surface of the primary molded product  10  until it becomes a molten state. The mold is then closed and clamped. Thereafter, as shown in  FIG. 10 , the injection nozzle  26  of the injection apparatus  64  Is connected to the mold, and a molding material is filled into the cavity  44 . 
         [0084]    In the above-described embodiment, the primary molded product  10  which has been molded in a different molding apparatus is used as an, insert member. However, as in the first embodiment, a primary molded product  10  and a light diffusing lens  14  as a final molded product may be molded simultaneously using a mold as shown in  FIG. 12 . 
         [0085]    In the mold  50  shown in  FIG. 12 , a primary molded product cavity  53 , which defines the shape of a primary molded product  10 , and a final molded product cavity  54 , which defines the shape of a light diffusing lens  14 , are formed by the opposing surfaces of a fixed mold  51  and a movable mold  52 . Runners  56   a ,  56   b , which branch from a runner  55  and communicate with the primary molded product cavity  53  and the, final molded product cavity  54 , respectively, are formed in the fixed mold  51 . 
         [0086]    A molding process using the mold  50  will now be described with reference to  FIGS. 13A through 13D . 
         [0087]      FIG. 13A  illustrates the step of opening the movable mold  52  from the fixed mold  51  after completion of the preceding molding cycle. A primary molded product  10  and a light diffusing lens  14  as a final molded product, which have been produced in the preceding molding cycle, are waiting for their removal from the mold. 
         [0088]    Next, as shown in  FIG. 13B , the first-stage chuck  36  of the chuck  32  transports a temperature-adjusted primary molded product  10  from the temperature adjustment stage  80  to between the fixed mold  51  and the movable mold  52 , while the second-stage chuck  37  attracts and holds the light diffusing lens  14  as a final molded product and takes It out of the movable mold  52 . Next, as shown in  FIG. 13C , the entire chuck  32  turns 180 degrees and places the primary molded product  10 , held by the first-stage chuck  36 , as an insert member in the final molded product cavity  54 . Thereafter, the primary molded product  10  that has been molded and the light diffusing lens  14  as a final molded product are transported to the transport conveyer  78 . 
         [0089]    Next, as shown in  FIG. 13D , the infrared heater  35  enters the space between the fixed mold  51  and the movable mold  52 , and heats the surface of the primary molded product  10  until it becomes a molten state. The mold is then closed and clamped. Thereafter, as shown in  FIG. 12 , the injection nozzle  26  of the injection apparatus  64  is connected to the mold, and the same resin molding material is simultaneously filled into the primary molded product cavity  53  and the final molded product cavity  54 . In this manner, the primary molded product  10  as a semifinished molded product and the light diffusing lens  14  as a final molded product can be molded simultaneously in parallel. 
         [0090]    As described hereinabove, the surface of the primary molded product  10 , the first semifinished product, is heated into a molten state before the next, second layer is laminated to the primary molded product  10 . This makes it possible to mold the light diffusing lens  14 , the final molded product, as a high-quality plastic lens having excellent optical properties and having a uniform stress distribution. 
         [0091]    While a light diffusing lens production apparatus and method according to the present invention has been described with reference to preferred embodiments in which a lens, composed of a laminate of 2, 3, 4 or 5 resin layers is molded, the present invention can also be applied in a molding process which involves molding and laminating more than 5 resin layers to form a light diffusing lens.