Abstract:
An optical element molded between a first die and a second die which are jointed along a partition line, comprises a first optical surface on which a diffractive structure is provided; a second optical surface being a refractive surface opposite to the first optical surface; and a flange having a flange surface provided around a periphery of the optical element, a first edge portion of the flange surface adjoining to the first optical surface and a second edge portion of the flange surface adjoining to the second optical surface. The second edge portion is positioned at the partition line between the first die and second die.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to a manufacturing method of an optical element that forms the optical element through injection molding, and to the optical element.  
           [0002]    An example of the optical element is a plastic lens which is used for an optical system of an optical equipment such as an optical pickup device and a camera. As a plastic lens of this type, there is plastic lens  100  which has on its one side a surface of diffractive structure  100   a.    
           [0003]    For the manufacture of the plastic lens  100 , there is a method wherein resin is injected in a mold which is formed by metal mold  102  equipped with ejecting mechanism  101  for releasing a molding product and by metal mold  103  equipped with no ejecting mechanism as shown in FIG. 8, and then, the metal mold  102  equipped with ejecting mechanism  101  is moved for mold opening as shown in FIG. 9, and the ejecting mechanism  101  is actuated to eject the molding product representing plastic lens  100  to release it from the mold as shown in FIG. 10.  
           [0004]    In the manufacture of a plastic lens stated above, metal mold  103  equipped with no ejecting mechanism has mold surface  103   a  that forms a surface of diffractive structure  100   a  of plastic lens  100 . Therefore, if metal mold  102  equipped with ejecting mechanism  101  is deviated, even if the deviation is slight, in the direction perpendicular to the direction of its movement when the metal mold  102  is moved for mold opening, the diffractive structure  100   a  of the plastic lens  100  is sometimes deviated to be deformed in a moment of the mold opening.  
           [0005]    Because of a weight of the metal mold  102  equipped with ejecting mechanism  101 , it is not easy to restrain the deviation in the course of the mold opening, and this deviation sometimes makes the plastic lens  100  having the diffractive structure  100   a  to fail to obtain desired optical characteristics.  
         SUMMARY OF THE INVENTION  
         [0006]    The invention has been achieved in view of the problems mentioned above, and its object is to provide a manufacturing method of an optical element which is simple in structure and makes it possible to obtain accurate and desired optical characteristics and to provide the optical element.  
           [0007]    To solve the aforesaid problems and to attain the object, the invention is structured as follows.  
           [0008]    The invention described in ( 1 ) is a manufacturing method for an optical element having therein a metal mold on which a molding product remains when the mold is opened and a metal mold from which the molding product is released when the mold is opened, the metal mold on which a molding product remains when the mold is opened having thereon a mold surface that forms a microscopic step-wise surface like a diffractive structure on an optical element representing the molding product, a step of injecting resin in the mold formed by the metal mold on which a molding product remains when the mold is opened and a metal mold from which the molding product is released when the mold is opened, then, a step of opening the mold and thereby releasing the molding product representing the optical element from the metal mold on which the molding product remains when the mold is opened, and a step of manufacturing the optical element having on its one side a microscopic step-wise surface like a diffractive structure.  
           [0009]    In the invention described in ( 1 ), resin is injected into the mold formed by the metal mold on which a molding product remains when the mold is opened and a metal mold from which the molding product is released when the mold is opened, then, mold opening follows, and when the mold is opened, even when deviation is caused between metal molds, the mold surface on the metal mold on which the molding product remains when the mold is opened is not deviated from the microscopic step-wise surface like a diffractive structure on an optical element, and then, the molding product representing the optical element is released from the metal mold, thus, it is possible to manufacture an optical element having thereon a microscopic step-wise surface like a diffractive structure which makes it possible to obtain accurate and desired optical characteristics under the simple structure.  
           [0010]    The invention described in ( 2 ) is a manufacturing method for a plastic lens which has therein a metal mold equipped with an ejecting mechanism for releasing a molding product and a metal mold equipped with no ejecting mechanism, the metal mold equipped with an ejecting mechanism having thereon a mold surface that forms a microscopic step-wise surface like a diffractive structure on an optical element representing the molding product, a step of injecting resin in the mold formed by the metal mold equipped with an ejecting mechanism and a metal mold equipped with no ejecting mechanism, and a step of releasing the molding product representing the optical element by opening the mold and by actuating the ejecting mechanism, and manufactures the optical element having on its one side a microscopic stepwise surface like a diffractive structure.  
           [0011]    In the invention described in ( 2 ), resin is injected into the mold formed by the metal mold equipped with the ejecting mechanism and a metal mold equipped with no ejecting mechanism, then, mold opening follows, and when the mold is opened, even when deviation is caused between metal molds, the mold surface on the metal mold equipped with the ejecting mechanism is not deviated from the microscopic step-wise surface like a diffractive structure on an optical element. Then, the ejecting mechanism is actuated to eject and release the molding product representing the optical element, thus, it is possible to manufacture an optical element having thereon a microscopic step-wise surface like a diffractive structure which makes it possible to obtain accurate and desired optical characteristics under the simple structure.  
           [0012]    The invention described in ( 3 ) is the manufacturing method for an optical element described in Structure  1  or Structure  2  wherein the ejecting mechanism has on at least a part thereof a mold surface that forms a surface in a microscopic step-wise shape like a diffractive structure, and this ejecting mechanism is actuated to eject and release the molding product representing the optical element.  
           [0013]    In the invention described in ( 3 ), the ejecting mechanism has on at least a part thereof a mold surface that forms a surface of the optical element in a microscopic stepwise shape like a diffractive structure, and therefore, when this ejecting mechanism is actuated to eject and release the molding product representing the optical element, the total surface of the diffractive structure of the optical element is ejected, thereby, the surface of the diffractive structure is not deviated, and thus, it is possible to manufacture an optical element having thereon a microscopic step-wise surface like a diffractive structure which makes it possible to obtain more accurate and desired optical characteristics.  
           [0014]    The invention described in ( 4 ) is an optical element formed by the manufacturing method for an optical element described in either one of ( 1 )-( 3 ).  
           [0015]    The invention described in ( 4 ) is an optical element having on its one side a surface in a microscopic step-wise shape like a diffractive structure which makes it possible to obtain highly accurate and desired optical characteristics. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    [0016]FIG. 1 is a diagram showing the structure of a metal mold.  
         [0017]    [0017]FIG. 2 is a diagram showing the condition wherein resin is injected in a metal mold.  
         [0018]    [0018]FIG. 3 is a diagram showing mold opening of a metal mold,  
         [0019]    [0019]FIG. 4 is a diagram showing how an ejecting mechanism operates.  
         [0020]    [0020]FIG. 5 is a diagram showing a mold surface that forms a surface of a diffractive structure of a plastic lens and the surface of the diffractive structure of the plastic lens.  
         [0021]    [0021]FIG. 6 is a side view of a plastic lens having on its one side a surface of a diffractive structure.  
         [0022]    [0022]FIG. 7 is a side view of a conventional plastic lens having on its one side a surface of a diffractive structure.  
         [0023]    [0023]FIG. 8 is a diagram showing the structure of a conventional plastic lens and a metal mold.  
         [0024]    [0024]FIG. 9 is a diagram showing mold opening of a conventional metal mold.  
         [0025]    [0025]FIG. 10 is a diagram showing how a conventional ejecting mechanism operates. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0026]    Referring to the drawings, there will be explained the embodiment of the manufacturing method for an optical element in the invention and of the optical element, to which, however, the invention is not limited.  
         [0027]    [0027]FIG. 1 is a diagram showing the structure of the metal mold, FIG. 2 is a diagram showing how resin is injected in the metal mold, FIG. 3 is a diagram showing the opened metal mold, FIG. 4 is a diagram showing how the ejecting mechanism operates, FIG. 5 is a diagram showing the mold surface which forms a surface of the diffractive structure of a plastic lens and showing a surface of the diffractive structure of the plastic lens, and FIG. 6 is a side view of the plastic lens having on its one side a surface of the diffractive structure.  
         [0028]    A manufacturing apparatus of the present embodiment is one for manufacturing a plastic lens representing an optical element, and it is composed of metal mold  11  which is equipped with ejecting mechanism  10  that releases a molding product and is structured so that the molding product may remain thereon when the metal mold  11  is opened and of metal mold  12  which is not equipped with the ejecting mechanism and is structured so that the molding product may be released when the metal mold  12  is opened. The manufacturing apparatus is of the structure wherein the metal mold  12  is fixed and the metal mold  11  is moved, and it injection-molds plastic lens  1  which has on its one side a surface in a microscopic step-wise shape like a diffractive structure. The injection in the invention (injection molding) includes one for molding by injecting resin in a metal mold such as an injection compression molding.  
         [0029]    The plastic lens representing an optical element in the present embodiment has optical functional section  1   a  and flange section  1   b  that is formed on the outer circumference of the optical functional section  1   a . On the surface on one side of the optical functional section  1   a , there is formed diffractive structure  1   c  that is in a microscopic step-wise shape so that highly accurate and desired optical characteristics may be obtained. Incidentally, though the flange section  1   b  is provided on the outer circumference of the optical functional section  1   a  of the plastic lens  1  in the present embodiment, the lens does not need to have the flange section, and it may further be a disk-shaped lens without being limited to a circular lens. In addition, the optical element may be a light-conductive object, without being limited to a plastic lens.  
         [0030]    The metal mold  11  has mold surface  11   a  that forms flange section  1   b  of the plastic lens  1 . The ejecting mechanism  10  has mold surface  10   a  that forms a surface of diffractive structure  1   c  of the optical functional section  1   a  of the plastic lens  1  and has mold surface  10   b  that forms a part of an inner side of the flange section  1   b.    
         [0031]    Incidentally, with regard to the ejecting mechanism  10 , the total mold surface may also be made to be a mold surface that forms a surface of a diffractive structure of the optical functional section  1   a , without forming the mold surface  10   b  that forms a part of an inner side of the flange section  1   b.    
         [0032]    The metal mold  12  has mold surface  12   a  that forms optical functional section  1   a  of the plastic lens  1  and mold surface  12   b  that forms flange section  1   b.    
         [0033]    Resin is injected in a mold shown in FIG. 2 which is formed by the metal mold  11  equipped with the ejecting mechanism  10  and by the metal mold  12  equipped with no ejecting mechanism, and is cooled. This injection of resin is conducted from a runner which is an unillustrated channel for injecting resin, and a gate portion of the runner is formed to be integrally with flange section  1   b  and is cut off in the succeeding gate cutting process.  
         [0034]    After this cooling, the metal mold  11  equipped with ejecting mechanism  10  is moved to open the mold as shown in FIG. 3, and the ejecting mechanism  10  is actuated to eject and release a molding product representing plastic lens  1  as shown in FIG. 4.  
         [0035]    Further, the ejecting mechanism  10  has on at least a part thereof mold surface  10   a  that forms a surface of diffractive structure  1   c  of plastic lens  1 , and therefore, when this ejecting mechanism  10  is actuated to eject and release the molding product representing the plastic lens  1 , the total surface of the diffractive structure  1   c  of the plastic lens  1  is ejected, thereby, the surface of the diffractive structure  1   c  is not deviated, and thus, it is possible to manufacture the plastic lens  1  having thereon diffractive structure  1   c  which makes it possible to obtain more accurate and desired optical characteristics.  
         [0036]    Though the mold surface  10   a  that forms a surface of diffractive structure  1   c  of plastic lens  1  is formed to be in a serrated form in terms of a section as shown in FIG. 5, the invention does not need to be limited to the foregoing provided that the mold surface is in a shape that causes a diffraction phenomenon. Incidentally, it is preferable that a draft angle of the metal mold is zero (the direction of the serrated step of plastic lens  1  is in parallel with an optical axis of the plastic lens  1 ) as shown in FIG. 5, in view of the reduction of a loss of an amount of light, which offers an effect that the invention can further reduce a loss of an amount of light and can realize manufacture of that kind of plastic lens  1 .  
         [0037]    As stated above, resin is injected in a mold which is formed by metal mold  11  equipped with ejecting mechanism  10  and metal mold  12  equipped with no ejecting mechanism, and then, mold opening is conducted, and when the mold is opened, even when deviation is caused between metal molds, the mold surface  1   a  of the ejecting mechanism  10  is not deviated from the surface of diffractive structure  1   c  of plastic lens  1 . After that, the ejecting mechanism  10  is actuated to eject and release the plastic lens  1 , thus, it is possible to manufacture the plastic lens  1  having thereon a diffractive structure which makes it possible to obtain accurate and desired optical characteristics under the simple structure.  
         [0038]    Though a surface of diffractive structure  1   c  of plastic lens  1  is formed by mold surface  10   a  of ejecting mechanism  10 , and optical functional section  1   a  is ejected and released by ejecting mechanism  10  in the present embodiment, flange section  1   b  may also be ejected by the ejecting mechanism to be released without being limited to the foregoing, and in this case, the mold surface that forms a surface of diffractive structure  1   c  of the plastic lens  1  is formed on the metal mold  11  because the ejecting mechanism  10  and the metal mold  11  can be processed integrally.  
         [0039]    As stated above, in the invention described in ( 1 ), resin is injected into the mold formed by the metal mold on which a molding product remains when the mold is opened and a metal mold from which the molding product is released when the mold is opened, then, mold opening follows, and when the mold is opened, even when deviation is caused between metal molds, the mold surface on the metal mold on which the molding product remains when the mold is opened is not deviated from the microscopic step-wise surface like a diffractive structure on an optical element, and then, the molding product representing the optical element is released from the metal mold, thus, it is possible to manufacture an optical element having thereon a microscopic step-wise surface like a diffractive structure which makes it possible to obtain accurate and desired optical characteristics under the simple structure.  
         [0040]    In the invention described in ( 2 ), resin is injected into the mold formed by the metal mold equipped with the ejecting mechanism and a metal mold equipped with no ejecting mechanism, then, mold opening follows, and when the mold is opened, even when deviation is caused between metal molds, the mold surface on the metal mold equipped with the ejecting mechanism is not deviated from the microscopic step-wise surface like a diffractive structure on an optical element. Then, the ejecting mechanism is actuated to eject and release the molding product representing the optical element, thus, it is possible to manufacture an optical element having thereon a microscopic step-wise surface like a diffractive structure which makes it possible to obtain accurate and desired optical characteristics under the simple structure.  
         [0041]    In the invention described in ( 3 ), the ejecting mechanism has on at least a part thereof a mold surface that forms a surface of the optical element in a microscopic stepwise shape like a diffractive structure, and therefore, when this ejecting mechanism is actuated to eject and release the molding product representing the optical element, the total surface of the diffractive structure of the optical element is ejected, thereby, the surface of the diffractive structure is not deviated, and thus, it is possible to manufacture an optical element having thereon a microscopic step-wise surface like a diffractive structure which makes it possible to obtain more accurate and desired optical characteristics.  
         [0042]    The invention described in ( 4 ) is an optical element having on its one side a surface in a microscopic step-wise shape like a diffractive structure which makes it possible to obtain highly accurate and desired optical characteristics.