Resin-coupled optical element and method of production

A resin-coupled lens has a resin layer on at least one surface of the lens and has a light-shielding membrane, wherein the edge surface of the outermost perimeter of the resin layer is covered by the light shielding membrane. A production method for the resin-coupled lens includes a resin layer formation process that forms a resin layer on at least one surface of the base material of the lens, a light-shielding membrane formation process that forms a light-shielding membrane on the edge surface of the outermost perimeter of the resin layer by applying a light-shielding coating, and a reflection-preventing membrane formation processes that forms a reflection-preventing membrane at least on the surface of the resin layer.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to optical elements having resin layers and 
methods of producing such elements, and more particularly, to a 
resin-coupled aspherical lens having a glass or plastic base material with 
a spherical surface or a rough aspherical surface and a resin layer with 
an aspherical surface, and the method of producing such a lens. 
2. Description of Related Art 
A known aspherical lens structure is shown in FIGS. 3 and 4. FIG. 3 shows a 
glass or plastic base material 1 having a spherical surface, and FIG. 4 
shows an example of such base material 1 having a rough aspherical 
surface, as disclosed in Japanese Laid-Open Patent Application No. 
63-157103. 
With the conventionally known aspherical surface, thin (5-100 .mu.m) resin 
layer 2 is layered on glass or plastic base material 1. With the method 
generally used for producing this kind of aspherical lens, resin layer 2 
is formed using ultraviolet-hardening resin. 
With this method of formation it is easy to obtain an aspherical lens 
having an optical surface of a desired shape, because the optical surface 
is formed using a malleable ultraviolet-hardening resin fluid. This method 
lends itself well to mass production. An example of this conventionally 
known method of producing resin-coupled aspherical lenses is shown in 
FIGS. 5A-5E for cases in which glass base material 1 possesses a spherical 
surface. 
First, the spherical glass lens (FIG. 5A) is produced using common base 
material production methods. Melted glass is shaped by pressing, and the 
resulting glass block is manufactured into a lens having the desired 
spherical surface by machine processing. Next, reflection-preventing 
membrane 4 is coated on one surface of the lens produced by the base 
material production process, by a reflection-preventing membrane formation 
process (FIG. 5B). Furthermore, by a resin layer formation process (FIG. 
5C), an ultraviolet-hardening resin fluid is coated on the surface of the 
base material on which reflection-preventing membrane 4 is formed by the 
reflection-preventing membrane formation process. The resin fluid coating 
forms resin layer 2. The surface on which resin layer 2 is formed will be 
referred to hereafter as the front surface of the lens. After formation of 
resin layer 2, reflection-preventing membrane 5 is coated on the front 
surface, on which resin layer 2 is formed, by a front surface 
reflection-preventing membrane formation process (FIG. 5D). Lastly, during 
a light-shielding membrane formation process (FIG. 5E), a light-shielding 
coating is applied so as to cover the outermost perimeter of the lens, 
that is, the rough edge area, and the outer perimeter of 
reflection-preventing membrane 5. The coating is baked on to form 
light-shielding membrane 3. When black ink is used as the light-shielding 
coating, it is not heated but rather is allowed to dry naturally. 
The edge of the lens produced using this method is shown in FIG. 2. With 
conventional methods of production, after resin layer 2 has been formed, 
reflection-preventing membrane 5 is coated onto the surface of resin layer 
2, following which light-shielding membrane 3 is formed on the outer 
perimeter, that is, the rough area, of the lens and the outermost 
perimeter of reflection-preventing membrane 5. Consequently, the edge of 
resin layer 2 is covered by the reflection-preventing membrane 5. 
However, with a resin-coupled aspherical lens produced using the described 
production process, edge surface 6 of the outermost perimeter of resin 
layer 2 shines in a ring-like manner when viewed from the back surface of 
the lens (the surface on which resin layer 2 is not formed). This 
condition is shown in FIGS. 8A-8C. Each of the FIGS. 8A-8C shows the area 
around the perimeter of a lens produced using conventional technology, as 
viewed from the back surface. FIG. 8A is magnified 10 times, FIG. 8B 20 
times and FIG. 8C 40 times. In addition, FIGS. 9A-9C are photographs of 
the area around the perimeter of a lens produced using conventional 
technology, the photograph being taken from the back surface. FIG. 9A is 
magnified 10 times, FIG. 9B 20 times and FIG. 9C 40 times. 
In both FIGS. 8A-8C and FIGS. 9A-9C, outer perimeter E of the lens, in 
which the edge surface of the outermost perimeter of resin layer 2 is 
reflective, and a ring-like region of light r are observable. With this 
ring-like region of light r, reflection is not uniform, as spots w are 
visible and form knots in the ring. This kind of ring-like and non-uniform 
reflection give a poor outer appearance, which, in some cases, is 
undesirable. When viewed through the lens, the reflection from edge 
surface 6 of the outermost perimeter of resin layer 2 is close to complete 
reflection and is seen as an extremely bright light. Furthermore, it is 
positioned in a place where reflection of the penetrating light stands out 
easily. 
SUMMARY OF THE INVENTION 
To address the above and other problems, it is an object of the present 
invention to provide a lens production method that will improve the 
quality of the outer appearance of the lens by decreasing the reflection 
of the edge surface of the outermost perimeter of the resin layer, without 
decreasing manufacturing capability. 
To achieve the above and other objects, an optical element according to an 
embodiment of the invention includes a base material, a resin layer 
disposed on at least one surface of the base material, and a 
light-shielding membrane disposed on at least a portion of the resin 
layer. The light-shielding membrane preferably covers an edge surface of 
an outermost perimeter of the resin layer. A reflection-preventing 
membrane preferably is disposed on at least a portion of the resin layer, 
so that the light-shielding membrane separates the reflection-preventing 
membrane from the edge surface of the outermost perimeter of the resin 
layer. 
According to another aspect of the invention, a method of producing a 
resin-coated optical element includes the steps of forming a resin layer 
on at least one surface of a base material of the optical element, forming 
a light-shielding membrane on at least a portion of the resin layer, and 
forming the reflection-preventing membrane on at least a portion of the 
resin layer. The step of forming the light-shielding membrane preferably 
includes the step of forming the light-shielding membrane on an edge 
surface of an outermost perimeter of the resin layer and also preferably 
includes the step of forming a portion of the light-shielding membrane on 
at least one surface of the base material. The step of forming the 
reflection-preventing membrane preferably includes the step of forming the 
reflection-preventing membrane on 1) the portion of the light-shielding 
membrane disposed on the surface of the base material and 2) the portion 
of the light-shielding membrane disposed on the portion of the resin layer 
.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
The outer perimeter of a lens according to the present invention is shown 
in FIG. 1. With the present invention, after resin layer 2 is formed, 
light-shielding membrane 3 is first formed on edge surface 6 of the 
outermost perimeter of the resin layer 2, following which 
reflection-preventing membrane 5 is formed. In this manner, it is possible 
to reduce the reflection of edge surface 6 of the outermost perimeter of 
resin layer 2. 
The present invention can be applied to a lens having resin layer 2 on the 
concave side of the base material, as shown in FIG. 3, or to a lens having 
resin layer 2 on the convex side, as shown in FIG. 4. In addition, the 
present invention is not limited to aspherical lenses having resin layer 2 
on either the concave or convex side of base material lens 1, but it can 
also be applied to a lens having resin layer 2 on both the convex and 
concave sides of base material lens 1, as shown, for instance, in FIG. 6. 
FIG. 1 is a cross-sectional view of an area near the outer perimeter of a 
lens according to an embodiment of the present invention. With this 
embodiment, edge surface 6 of the outermost perimeter of resin layer 2, 
which is formed on the front surface of glass base material lens 1, has a 
spherical surface and is covered by light-shielding membrane 3. The 
thickness of resin layer 2 is preferably in the range of 5-100 .mu.m at 
the center, for instance, but the present invention does not depend upon 
the thickness of resin layer 2. In addition, because lens 1 preferably is 
made of glass base material, a lens having an outer diameter of 15-40 mm 
and a center thickness of 1-10 mm may be used, but it is also possible to 
use a lens larger than this. In addition, it is possible to use a lens in 
which both surfaces have been polished into a spherical surface, but it is 
also possible to use a lens in which one of the surfaces or both of the 
surfaces are aspherical. Furthermore, the base material of the lens is not 
limited to glass. It is also possible to use plastic as the base material 
of the lens. 
According to the present embodiment of the invention, a resin-coupled lens 
having an aspherical surface is produced using the method described 
hereafter. The steps in production are shown in FIGS. 7A-7E. 
(1) According to this embodiment, a glass base material is used for lens 1, 
which has a diameter of 33 mm, a radius of curvature R1 for the convex 
surface of 89.5 mm, a radius of curvature R2 for the concave surface of 
19.0 mm, and a central thickness of 1.6 mm. Lens 1 has both surfaces 
polished into spherical surfaces. Opposite to the side of lens 1 coupled 
with resin layer 2, that is, on the side of lens 1 having a concave 
surface, a front surface reflection-preventing membrane 4 preferably 
already is formed. In addition, lens 1 preferably undergoes a silane 
coupling process on its front surface in order to enhance its adhesion 
with resin layer 2. As the silane coupling agent for the silane coupling 
process, KBM503 (produced by Shin-Etsu Chemical Co.), diluted in ethanol 
to a 2% concentration by weight, preferably is used. 
(2) Resin layer 2 is formed on lens 1, which preferably is formed of a 
glass base material. To form the aspherical surface of resin layer 2, 
metal mold 7 is prepared with an inverted aspherical surface. This 
aspherical surface preferably is dimensioned so that the curvature of the 
resin surface is 18.5 mm. To form resin layer 2, 60 mg of ultraviolet 
light-hardening resin fluid 2a is dripped into metal mold 7 (FIG. 7A). 
According to the present embodiment, a urethane acrylate resin preferably 
is used as the ultraviolet light-hardening resin to form resin layer 2. 
This resin preferably has an expansion/contraction ratio of about 7%. 
Subsequently, lens 1 is pressed against metal mold 7, into which resin 
fluid 2a has been dripped, so that resin fluid 2a fills the space between 
metal mold 7 and lens 1. The space between metal mold 7 and lens 1 is set 
so that the central thickness of the resin preferably is 70 .mu.m. Next, a 
150 W xenon lamp preferably is used, from the concave surface side of lens 
1, to illuminate resin layer 2 with ultraviolet rays 8 for 60 seconds 
(FIG. 7B). 
A lens with an aspherical surface similar to the one shown in FIG. 4 is 
thus obtained by removing the lens, with its aspherical surface resin 
layer 2 obtained in the manner described, from metal mold 7 (FIG. 7C). 
(3) Next, a light-shielding coating is applied to the rough area along the 
outer perimeter of the resulting lens and to the outer perimeter of resin 
layer 2, thereby forming light-shielding membrane 3 (FIG. 7D). 
Subsequently, the lens is baked preferably for one hour at 70.degree. C. 
in order to solidify this coating material. As a light-shielding coating 
that does not harm acrylic resin, an acrylic urethane resin coating, mixed 
with a silane coupling agent, preferably is used. 
(4) Lastly, reflection-preventing membrane 5 made of multiple inorganic 
membrane layers is coated onto the front surface of resin layer 2 (FIG. 
7E). 
The area near the outer perimeter of the resin-coupled lens, formed 
according to the invention in the manner described above, is shown in 
FIGS. 8D-8F. FIG. 8D is magnified 10 times, FIG. 8E times and FIG. 8F 40 
times. In addition, FIGS. 9D-9F are photographs of the area near the outer 
perimeter of a lens produced according to the invention, as viewed from 
the rear surface. FIG. 9D is magnified 10 times, FIG. 9E 20 times and FIG. 
9F 40 times. In FIGS. 8D-8F and FIGS. 9D-9F, perimeter E of the lens is 
shown. Even with the magnification in FIGS. 8D-8F and 9D-9F, the region of 
ring-shaped light r was only slightly apparent. With the resin-coupled 
lens according to the preferred embodiment, the reflection at edge surface 
6 of the outermost perimeter could not be observed by the naked eye, and 
the reflection did not have any detrimental effect on the quality of the 
external appearance of the lens. 
While this invention has been described in conjunction with specific 
embodiments thereof, it is evident that many alternatives, modifications 
and variations will be apparent to those skilled in the art. Accordingly, 
the preferred embodiments of the invention as set forth herein are 
intended to be illustrative, not limiting. Various changes may be made 
without departing from the spirit and scope of the invention as defined in 
the following claims.