Die for press-molding optical element

A die for press-molding an optical element, comprising:

• a base material made of a material excellent in heat resistance, heat impact resistance and strength at high temperature;
• a thin film formed on the base material for enhancing adhesion strength between the base material and an intermediate layer formed on the thin film;
• said intermediate layer made of a Ni, Cu, Au, Pt, Pt-Au, Pt-Cu, Pt-Ni, Ni-P or Ni-B alloy thin film excellent in grinding machinability and cutting machinability;
• and a surface protective layer made of a metal thin film excellent in heat resistance and strength at high temperature and less reactive to a material of the optical element, formed on the intermediate layer.

A method of press-molding an optical element with a pair of dies by heating and pressing a material of the optical element between the pair of dies, wherein each of the dies comprises:

• a base material made of a material excellent in heat resistance, heat shock resistance and strength at high temperature;
• a thin film formed on the base material for enhancing adhesion strength between the base material and an intermediate layer formed on the thin film;
• the intermediate layer made of a Ni, Cu, Au, Pt, Pt-Au, Pt-Cu, Pt-Ni, Ni-P or Ni-P or Ni-B alloy thin film excellent in grinding machinability and cutting machinability;
• and a surface protective layer made of a metal thin film excellent in heat resistance and strength at high temperature and less reactive to the material of the optical element, formed on the intermediate layer.

A method for preparing a die for press-molding an optical element, provided with a press-molding part and a peripheral flange part which is positioned on the outside of the press-molding part, comprising the following step;

• (a) roughly machining a base material made of a material excellent in heat resistance, heat impact resistance and strength at high temperature into a shape approximated to the desired shape of the die;
• (b) forming an intermediate thin layer made of a Ni, Cu, Au, Pt, Pt-Au, Pt-Cu, Pt-Ni, Ni-P or Ni-B alloy excellent in grinding machinability and cutting machinability on the base materials;
• (c) precisely machining the intermediate layer into a desired shape of the die;
• (d) removing the peripheral flange part of the intermediate layer at the same time of the step (c) or thereafter;
• (e) forming a surface protective layer made of a metal thin film excellent in heat resistance and strength at high temperature and less reactive to a material of the optical element, on the press-molding part of the intermediate layer and the peripheral flange part of the base material in an uniform manner not to deform the desired shape precision.