Method for the manufacture of optical mold for reproducing curved surfaces having the same shape as an optical prototype

A sturdy optical mold for reproducing optical curved surfaces in the shape corresponding to that of an optical prototype comprising a resin layer formed on a base and a metallic layer formed on said resin layer, and a method for manufacturing an optical mold for reproducing optical curved surfaces in the shape corresponding to that of an optical prototype comprising forming layers of different metals on the surface of an optical prototype, dissolving one of said layers for releasing the other layer and fixing said released layer onto a base with a bonding agent.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an optical mold for replicating or 
reproducing curved optical surfaces having the corresponding shape to that 
of a prototype and manufacturing methods therefor. 
2. Description of the Prior Art 
In reproducing curved optical surfaces having the corresponding shape to 
that of an optical prototype by conventional method, such curved surfaces 
are reproduced on glass base directly from an optical prototype. Speaking 
more concretely with reference to FIG. 1 attached hereto, a curved optical 
surface is reproduced by forming a layer of release agent 2 on the surface 
of an optical prototype 1, further forming a layer 3 of photopolymerizable 
bonding agent or resin, bringing a base 4 made of glass into contact with 
said layer 3, thereafter hardening said layer 3 of bonding agent or resin 
(hardening photopolymerizable material by irradiating it with rays) and 
then detaching said layer from said optical prototype 1 to obtain the 
resin layer 3 having the curved surface corresponding to that of said 
optical prototype on the surface of said glass base. However, such a 
conventional manufacturing method has drawbacks that said optical 
prototype is made of glass and is therefore easily cracked, and that 
delicate care is required to release a reproduced optical surface from the 
prototype since both of said prototype and base are made of glass 
materials which have little difference in their coefficients of expansion. 
In addition, it is necessary to prepare numerous optical prototypes for 
reproducing a large number of optical curved surfaces. However, it is 
never easy to prepare numerous optical prototypes, for example, having a 
non-spherical surface for reproducing optical elements having 
non-spherical optical surfaces. As is understood from the above 
descriptions, the conventional method for reproducing optical curved 
surfaces directly from an optical prototype is disadvantageous for mass 
production. 
SUMMARY OF THE INVENTION 
A primary object of the present invention is to provide a sturdy optical 
mold which is reproduced from an optical prototype, and comprises a layer 
of a bonding agent and a protective layer of a metal both of which are in 
the shape corresponding to the curved surface of an optical prototype (in 
the same shape as the curved surface of an optical prototype for 
reproducing concave optical surfaces) on a base made of glass or the 
similar material. 
Another object of the present invention is to provide methods for 
manufacturing an optical mold comprising plating two layers of different 
metals consecutively on the surface of an optical prototype, dissolving 
and removing one of said metal layers, and bonding the other layer onto 
the surface of a base.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Now, the optical mold according to the present invention and methods for 
reproducing optical curved surfaces by using said mold will be described 
with reference to the accompanying drawings. 
In FIG. 2, the reference numeral 10 represents an optical mold according to 
the present invention comprising a base 11 made of glass on which a layer 
12 of bonding agent or resin is formed. Said layer 12 has a curved surface 
which corresponds to that of an optical prototype manufactured by the 
conventional method described with reference to FIG. 1. The reference 
numeral 13 designates a protective film of metal formed on the surface of 
said layer 12. The protective metallic film 13 may be formed, for example, 
by plating a layer of chromium directly onto the layer 12, or plating a 
layer of copper and further plating a layer of chromium over the surface 
of the layer 12. In order to reproduce optical curved surface by using the 
optical mold according to the present invention, a reproducing base 16 
coated with a layer 15 of bonding agent or resin is bonded to the surface 
of the optical mold 10, i.e., the surface of the protective film 13 with a 
release agent 14 disposed therebetween, and then said base is detached 
from the optical prototype 1. An optical curved surface which corresponds 
to that of the optical mold, i.e., optical curved surface of the prototype 
can be reproduced in this way. 
Now, a method for manufacturing an optical mold will be described below: 
FIG. 4A through FIG. 4D illustrate processes to manufacture an optical mold 
having a convex surface, whereas FIG. 5A through FIG. 5C show process to 
prepare an optical mold having a concave surface. In case where an optical 
concave surface is to be reproduced, an optical mold must have a convex 
surface. For manufacturing such an optical mold, a glass base 21 coated on 
the surface with a layer of bonding agent or resin 22 is pressed onto the 
optical prototype 1 with a release agent interposed therebetween, and then 
is detached in the procedures illustrated in FIG. 1 which are quite the 
same as the conventional ones. It is possible to manufacture an optical 
mold 20 on the surface of which the resin layer 22 having the shape 
corresponding to the optical prototype (FIG. 4B). After a layer 32 of a 
bonding agent or resin is formed on a base 31 having a convex surface and 
a layer 33 of chromium or copper + chromium is plated on said layer, said 
mold 20 is pressed onto said base to form a mold 30 having the convex 
surface which corresponds to the concave surface of said mold 20 and is 
therefore the same as the convex surface of the optical prototype. Optical 
concave surfaces can be reproduces by using said optical mold 30 in the 
same procedure as that illustrated in FIG. 3 (FIG. 4D). 
The reproducing processes for an optical convex surface will then be 
described with reference to FIG. 5A through FIG. 5C. On a base 41 having a 
concave surface, a layer 42 of bonding agent or resin is formed, and then 
another layer 43 is formed by plating chromium only or copper and chromium 
with a release agent interposed in the procedures similar to those 
illustrated in FIG. 4A through FIG. 4D. Then the base is pressed onto the 
optical prototype 1 so as to form an optical mold 40 having the concave 
surface corresponding to that of the optical prototype 1 (FIG. 5B). 
Optical surfaces as shown in FIG. 5C can be reproduced by using this 
optical mold. Now, another method for manufacturing the optical mold 
according to the present invention will be described below: 
FIG. 6A and FIG. 6B illustrate the processes for manufacturing an optical 
mold having a concave surface for manufacturing optical convex surfaces. 
In FIG. 6A, the reference numeral 1 represents the optical prototype, the 
reference numeral 51 designates a plated layer of metal, for example, 
copper, the reference numeral 52 denotes a plated layer of metal, for 
example chromium, different from said metal 51, and the reference numeral 
53 represents a layer of bonding agent or resin which serves to bond a 
base 54 consisting of a glass block having a concave surface to the plated 
layer 52. When the optical mold described above is dipped in a solution of 
sodium cyanide, the layer of copper 51 is dissolved and the upper layers 
are released. In this case, however, the layer of chromium 52 is not 
dissolved but is bonded by the bonding agent to the concave surface of the 
base 54 so as to form the concave surface corresponding to the convex 
surface of the optical prototype. An optical mold having a concave surface 
can be manufactured in this way. 
Then, processes for manufacturing an optical mold having a convex surface 
for reproducing optical concave surfaces will be described below: 
Though an optical prototype having a concave surface can be prepared by the 
procedures similar to those illustrated in FIG. 6A and FIG. 6B, it is very 
difficult to prepare an optical mold having a non-spherical concave 
surface under the present technical circumstaces. It is therefore obliged 
to use an optical prototype having a convex surface for reproducing 
optical concave surfaces. In FIG. 7A, the reference numeral 1 represents 
an optical prototype similar to that shown in FIG. 6A, on the convex 
surface of which a plated layer of copper 61 is formed first, and then a 
plated surface of chromium 62 is arranged. When the layer of copper 61 is 
dissolved by dipping the optical prototype shown in FIG. 7A in a solution 
of sodium cyanide, the upper layer of chromium 62 is released as shown in 
FIG. 7B. By bonding this layer of chromium to a base 64 with bonding agent 
63, an optical mold having a convex surface can be manufactured. 
Though copper and chromium are used in the embodiments described above, it 
is possible to select different pairs of metals so long as one is easily 
dissolved and the other is not. In such cases, when a metal M.sub.1 is 
brought in contact with an electrolytic solution, for example, sodium 
cyanide, in which direction the reaction to substitute said metal M.sub.1 
with ions M.sub.2 of different metal (M.sub.1 + M.sub.2.sup.+ 
.revreaction. M.sub.1.sup.+ + M.sub.2) proceeds or whether or not the 
reaction to dissolve said metal M.sub.1 with hydrogen (M.sub.1 + 
H.fwdarw.M.sub.1 ' + H) takes place is dependent on type of metal, type of 
solution and concentration of ions concerned in said solution. However, 
the most important parameter is the ionization tendency, and the 
above-mentioned reaction is apt to proceed in the rightward direction as 
M.sub.1 has higher ionization tendency. Further, metals having higher 
ionization tendency is selected as the metal to be dissolved or to be 
plated on an optical prototype. 
As is easily understood from the foregoing descriptions, the optical mold 
according to the present invention has a sturdy standard surface which is 
in the corresponding shape to that of an optical mold since said surface 
is coated with a protective metal layer. Further, said optical mold 
permits easily releasing reproduced optical surfaces since a large 
differences in expansion coefficient is obtained between the metal and 
glass forming the release layers. The optical mold according to the 
present invention is advantageous for mass production of optical curved 
surfaces. 
Furthermore, the present invention makes it possible to manufacture an 
optical mold having a precise surfacial metallic layer easily by forming 
two layers of different metals and dissolving one of said layers.