JPH07290462A - Mold of bracelet lens made of synthetic resin - Google Patents

Abstract

PURPOSE:To accurately process a finely stepwise mirror surface and prolong the life of a mold in a mold of a bracelet lens made of a synthetic resin having a bracelet group finely stepwise changed in lens thickness as separating from an optical axis on at least one surface thereof. CONSTITUTION:A mold of a bracelet lens consists of a mold matrix 31 composed of a ferrous material and the nonferrous metal layer 32 formed on the matrix 31 and the surface on the side of the nonferrous metal layer 32 of the mold matrix 31 is composed of a smooth surface having no difference in level and the surface of the nonferrous metal layer 32 has a stepwise mirror surface corresponding to a bracelet group.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a synthetic resin single lens mold having a ring-shaped group of minute steps on at least one surface.

[0002]

2. Description of the Related Art Since chromatic aberration is difficult to correct with a single lens because it is determined by the characteristics of the material, it is necessary to correct chromatic aberration even in an optical system using a light source with a narrow wavelength width such as a semiconductor laser. In some cases, a glass combination lens was used. On the other hand, the present inventor (applicant) divides the refracting surface of the lens into an annular shape and corrects chromatic aberration by the diffraction effect, and can correct spherical aberration, coma aberration, and axial chromatic aberration with a single lens. Proposed a diffractive lens (a single lens for correcting chromatic aberration) (Japanese Patent Application No. 4-340562).
issue).

More specifically, this chromatic-aberration-correcting single lens is, more specifically, a diffractive lens surface in which at least one surface thereof is discretely shifted in a direction in which the lens thickness increases stepwise as the distance from the optical axis increases. It consists of
The diffractive lens is practically manufactured by injection molding of a plastic material. However, in this diffractive lens, it is difficult to manufacture the mold because the stepped unevenness of the ring zone is minute in wavelength order. For example, when the surface of the die is cut with a single crystal diamond bite, if the die is an iron-based material, the diamond bite wears quickly and it is difficult to perform fine mirror-finishing of minute step-like irregularities. On the other hand, when the mold is made of a non-ferrous metal material, cutting is easy and a good mirror surface can be obtained, but the strength is insufficient and the life is short when molding is repeated.

Further, in this diffractive lens, the boundary portion between the circular incident surface at the center of the surface having the stepped annular zone group and the annular zone,
It has been considered that it is preferable that the boundary between the zones and the zone is a cylindrical surface having the optical axis as an axis, but in the injection molding, it is considered that these boundaries are cylindrical surfaces having the optical axis as the axis. , It is difficult to transfer the shape of the sharp edge of the mold, the flow of the lens material may be obstructed by the part forming the step of the ring of the mold, and the birefringence may appear in the lens, the mold processing is difficult It turns out that there are problems such as

[0005]

It is an object of the present invention to directly form a molding die which does not cause the above problems in molding a chromatic aberration-correcting single lens proposed by the present applicant in Japanese Patent Application No. 4-340562 with a resin material. The purpose is to get.

[0006]

SUMMARY OF THE INVENTION The present invention is a molding die for a synthetic resin annular zone lens having an annular zone on at least one surface of which the lens thickness changes minutely in a stepwise manner with distance from the optical axis. The mold for molding the surface has a mold base material made of an iron-based material and a non-ferrous metal layer formed on the mold base material; the surface of the mold base material on the non-ferrous metal layer side is , Consisting of a smooth surface without steps, the surface of the non-ferrous metal layer is
It has a step-like mirror surface corresponding to the ring group.

In this molding die, the stepped mirror surface of the non-ferrous metal layer forms a boundary portion between the circular incident surface at the center of the molded lens and an outer ring zone, and a portion forming a boundary portion between adjacent ring zones, respectively. It is preferably composed of a part of a conical surface whose axis is the optical axis of the lens. By making it a conical surface,
A draft is obtained, the shape of the edge of the mold is easily transferred accurately, the step forming part of the ring zone of the mold does not hinder the flow of the lens material, and the mold processing becomes easy.

It is preferable that the non-ferrous metal layer has a thickness in which at least a step-like mirror surface corresponding to the ring group of the molded lens is formed only on the non-ferrous metal layer and not on the die base material.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below with reference to illustrated embodiments. FIG. 1 shows a diffractive chromatic aberration correction single lens proposed by the present applicant in Japanese Patent Application No. 4-340562, and a diffractive lens surface (a ring-shaped diffractive lens surface having a large number of stepped concentric minute steps on one surface thereof). A band surface 20a is provided to correct chromatic aberration by the diffraction effect. Ring surface 20a
Is provided with a large number of concentric orbicular zone incident surfaces rc sequentially outside the circular center incident surface cc.

The step (optical axis direction height) t in the optical axis direction between the circular center incident surface cc and the annular zone incident surface rc, and the adjacent annular zone incident surface rc are the surfaces for the light of the reference wavelength. Does not give a phase difference to the light incident on the other hand, on the other hand, for the light shifted from the reference wavelength, it gives the phase difference according to the shift of the wavelength and has the effect of giving divergence or convergence. . That is, divergence is given to light having a wavelength shorter than the reference wavelength as the wavelength becomes shorter, and converging is given to light having a wavelength longer than the reference wavelength as the wavelength becomes longer. In order to obtain this action, each ring-zone incident surface has an optical axis O
It is discretely shifted in the direction in which the lens thickness increases as the distance from the lens increases.

The present invention proposes a molding die 30 for molding the annular single lens 20 having such an annular surface 20a, and FIGS. 1 and 3 show an embodiment thereof. The molding die 30 includes a die base material 31 made of an iron-based material, and a non-ferrous metal layer 32 created on the die base material 31. As the iron-based material, for example, stainless steel, carbon tool steel, alloy tool steel, those heat-treated by heat treatment, etc. can be used, and as the non-ferrous metal, nickel,
An alloy obtained by adding a small amount of phosphorus to nickel, copper, a copper alloy, or an aluminum alloy can be used. Further, “creation” means to form the non-ferrous metal layer 32 on the mold base material 31 by electroless plating, vacuum deposition, chemical vapor deposition, or the like.

The surface 31a of the die base material 31 on the non-ferrous metal layer 32 side has a smooth curved surface having no step. The surface 31a can be a smooth curved surface macroscopically viewing the ring surface 20a, or can be a shape in which the inner edge or the outer edge of the boundary portion of the ring group is smoothly connected. In FIG. 1, the shape of the surface 31a of the die base material 31 on the non-ferrous metal layer side is the same as a curved surface 31a 'that smoothly connects the inner edge (the deepest portion) of the boundary portion of the ring group of the molded lens 20. Is set to. This surface 31a
Alternatively, the curved surface 31a 'may be offset in parallel so that the non-ferrous metal layer 32 has a uniform thickness.

On the surface of the non-ferrous metal layer 32, the annular lens 2
A step-like mirror surface corresponding to the step-like cross section of the ring zone surface 20a of 0 is formed. That is, a circular mold portion 32c corresponding to the center circular incident surface cc of the annular lens 20 and a plurality of circular mold portions 32c corresponding to a large number of annular incident surfaces rc of the annular lens 20 are sequentially formed on the outside of the circular mold portion 32c. Many ring-shaped parts 32r
It has and. A boundary portion (connection surface) between the circular die portion 32c and the outer annular die portion 32r, and the adjacent annular die portion 3
The boundary portions (connection surfaces) of 2r are each formed as a conical surface 32a whose axis is the optical axis of the annular lens 20. These are cut and formed by a diamond cutting tool of a numerically controlled lathe. The angle (inclination) of the conical surface 32a is determined so that it acts as a draft of the molding die 30. The annular lens 20 has the conical surface 3 of the molding die 30.
A conical surface 20a is formed according to 2a.

The thickness of the non-ferrous metal layer 32 is equal to that of the circular mold portion 32.
The c, the ring-shaped part 32r, and the conical surface 32a are all formed in the non-ferrous metal layer 32, and the die base material 31 is defined so as not to have these stepwise cross sections.

FIG. 3 shows how the amount of light is lost by the conical surface 20b. Of the light rays incident on the annular surface 20a as a parallel light flux parallel to the optical axis, the light rays incident on the conical surface 20b are refracted by the conical surface 20b and become loss light a outside the optical path. The lost light a causes a loss of light amount, but does not have an optical adverse effect.

The light loss of the conical surface 20a hardly changes as compared with the case where the conical surface 20a is replaced with a cylindrical surface having the optical axis as an axis. That is, the light amount loss is the same, or slightly even if the light amount loss increases. FIG. 4 shows such a situation. Since the light beam incident on the outer ring surface of the cylindrical surface 20b 'is refracted by the ring surface and reflected by the cylindrical surface 20b', the reflected light is lost light. a '. Comparing this loss light a ′ and the loss light a due to the conical surface 20 a, it can be seen that there is almost no difference between the two. Even if the width of the boundary portion (width of the orthographic projection of the conical surfaces 20a and 32a in the direction parallel to the optical axis) Wt is made wider, the increase of the loss light is slight.

Next, the diffractive chromatic aberration correction annular zone single lens 20
Specific numerical examples of Non-ferrous metal layer 3 of molding die 30
On the surface of No. 2, a step-like mirror surface will be formed according to this data. From this data, it is understood that the unevenness of the staircase-like mirror surface is the unevenness of the wavelength order.

Infinite system Working wavelength λ: 780 nm Focal length f: 3. Mold 30 mm Numerical aperture N. A. : 0.55 Lens refractive index: 1.53677 (for λ = 780 nm) Lens thickness t: 2.21 mm Thickness of disk 14 tD: 1.20 mm Disk refractive index nD: 1.51072

First Surface (Ring Zone Surface 20a) Shape The sag amount X (h) at a point at a distance h from the optical axis is expressed by the following equation 1
Given in. (In this expression 1, Δ _N is added to the ordinary aspherical expression form.)

[Formula 1] X (h) = h ² / r _N {1+ [1- (1 + K _N ) h ² / r _N ² ] ^1/2 } + A4 _N h ⁴ + A6
However _{^{N h 6 + A8 N h 8}} + A10 N h 10 + Δ N, N is the annular numbers belonging height h, the coefficients describing the aspheric surface is a function of N shown below. N = INT (4.71 × h ² +0.5) r _N = 2.126 + 5.09 × 10 ^-4 × NK _N = -0.3689 A4 _N = -1.470 × 10 ^-3 +1.45 × 10 ^-6 × N A6 _N = -2.180 × 10 ^-4 +8.72 × 10 ^-8 × N A8 _N = -1.000 × 10 ^-5 +4.36 × 10 ^-8 × N A10 _N = -1.400 × 10 ^-5 +3.49 × 10 ^-8 × N Δ _N = -0.001453 × N

Second surface shape (aspherical surface is the same as a normal surface) The sag amount X (h) at a point at a distance h from the optical axis is expressed by the following equation 2
Given in.

Formula 2 X (h) = h ² / r {1+ [1- (1 + K) h
^{2 / r 2] 1/2} +} A4h 4 + A6h 6 + A8h 8 +
A10h ¹⁰ r = -6.763 K = 0.000 A4 = 1.777 × 10 ^-2 A6 = -3.950 × 10 ^-3 A8 = 5.770 × 10 ^-4 A10 = -2.960 × 10 ^-5

[0021]

As described above, according to the present invention, in a mold for molding a lens having a ring-shaped group of minute steps on at least one surface with a resin material, a mold base material made of an iron-based material and this metal mold are used. A forming die is formed from the non-ferrous metal layer created on the die base material, and the surface of the die base material on the non-ferrous metal layer side is composed of a smooth surface with no steps. Since the step-like mirror surface corresponding to the band group is formed, it is possible to accurately process the minute step-like mirror surface and to extend the life of the molding die.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a molding die according to the present invention and a synthetic resin annular single lens molded by the molding die.

2A and 2B are a sectional view and a front view showing an example of an annular single lens targeted by the present invention.

FIG. 3 is an enlarged cross-sectional view of an annular zone and an annular zone boundary portion of the molding die and the annular zone single lens of FIG.

FIG. 4 is an enlarged cross-sectional view showing another example of the shape of the boundary portion between the ring zones of the single ring zone lens.

[Explanation of symbols]

 20 synthetic resin ring-shaped single lens 20a diffractive lens surface (ring-shaped surface) 20b conical surface (boundary) cc circular center incident surface rc ring-shaped incident surface 30 molding die 31 mold base material 32 non-ferrous metal layer 32a conical surface 32c Circular mold part 32r Ring-shaped mold part

Claims (3)

[Claims] 1. A molding die for a synthetic resin ring-shaped lens having a ring-shaped group in which the lens thickness changes in a minute stepwise manner with increasing distance from the optical axis, wherein the surface having the ring-shaped group is formed. The mold to be molded is composed of a mold base material made of an iron-based material and a non-ferrous metal layer formed on the mold base material.The surface of the mold base material on the non-ferrous metal layer side has a step. A molding die for a synthetic resin annular zone lens, characterized in that the surface of the non-ferrous metal layer has a stepped mirror surface corresponding to the annular zone group. 2. The step-like mirror surface of the non-ferrous metal layer according to claim 1, which forms a boundary between a circular incident surface at the center of the molded lens and an outer ring zone, and a boundary between adjacent ring zones. Mold for synthetic resin ring-shaped lens, each of which is composed of a part of a conical surface whose axis is the optical axis of the lens. 3. The non-ferrous metal layer according to claim 1 or 2, wherein at least a step-like mirror surface corresponding to the ring zone group of the molded lens is formed only on the non-ferrous metal layer, and formed on the die base material. Mold of synthetic resin ring-shaped lens with a thickness that is not protected.