Molded-article manufacturing method, mold, and optical element including fresnel lens

Abstract

A center-portion molding member having a center-portion transfer shape surface and a side wall surface is inserted and fitted in a frame-portion molding member having a frame-portion transfer shape surface to form a part of a cavity. The center-portion molding member has a groove portion in the side wall surface. The groove portion protrudes from the frame-portion transfer shape surface. Before injected resin transfers a shape of the center-portion transfer shape surface, the side wall surface of the center-portion molding member is sealed with the resin to form, between the center-portion transfer shape surface and the resin, a space in which gas is confined.

1 . A molded-article manufacturing method that transfers shapes provided in a cavity onto a resin by injecting gas and the resin into the cavity, the method comprising:
 inserting and fitting a center-portion molding member having a center-portion transfer shape surface and a side wall surface in a frame-portion molding member, the center-portion molding member or the frame-portion molding member having a frame-portion transfer shape surface to form a part of the cavity,   wherein the center-portion molding member has a groove portion on the side wall surface, the groove portion extending from the center-portion transfer shape surface and protruding from the frame-portion transfer shape surface.   
     
     
         2 . The molded-article manufacturing method according to  claim 1 , wherein a length of a portion, of the side wall surface, from the groove portion to the frame-portion transfer shape surface is within a range of 20 to 100 μm. 
     
     
         3 . The molded-article manufacturing method according to  claim 1 , wherein a width of the frame-portion transfer shape surface is more than a width of the groove portion. 
     
     
         4 . The molded-article manufacturing method according to  claim 1 , wherein a shape formed on the center-portion transfer shape surface is a Fresnel lens shape. 
     
     
         5 . An optical element having a Fresnel lens, the Fresnel lens manufactured by the molded-article manufacturing method according to  claim 1 . 
     
     
         6 . The optical element having the Fresnel lens according to  claim 5 , wherein a height difference between an upper surface of a frame portion and tops of grooves is within a range of 20 to 100 μm. 
     
     
         7 . The optical element having the Fresnel lens according to  claim 5 , wherein flatness unevenness among inclined portions of grooves is 10 nm or less.