JPH0675106A - Production of aspherical optical element - Google Patents

Abstract

PURPOSE:To improve a non-defective article rate by producing the aspherical optical element without degrading its accuracy. CONSTITUTION:The aspherical optical element is produced by (a) a first stage for preparing a mold 3 having the aspherical face reversed from a desired aspherical face and an element base material 1, (b) a second stage for holding a radiation curing type resin liquid 2a between the mold 3 and the element base material 1 to put the resin liquid 2a into the state of spreading the resin up to the outer side of the desired region, (c) a third stage for irradiating the resin liquid 2 with radiations via a mask 4 for shielding the outer side of this region, (d) a fourth stage for irradiating the resin liquid 2a including the part shielded by the mask 4 with the radiations and (e) a fifth stage for peeling the resulted aspherical face resin molding layer from the boundary with the mold 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an aspherical optical element comprising an aspherical resin molding layer and an element base material. Here, the "aspherical optical element" refers to, for example, an aspherical lens or a "blank of a reflecting mirror having an aspherical reflecting surface". When a reflective layer made of aluminum, silver or a multilayer optical thin film is formed on this blank, it becomes a reflecting mirror. An example of the element manufactured by the present invention is conventionally called a resin-bonded lens.

[0002]

2. Description of the Related Art Lenses used in optical products such as cameras and microscopes are mainly glass lenses. A glass lens is a glass block press-molded from molten glass (called a lens blank).
A lens having a desired curvature is manufactured by performing mechanical processing on the lens. A method of manufacturing a resin lens by a method such as press molding, injection molding, or casting using a resin instead of glass has been put into practical use. This method has a feature that the manufacturing cost is low because once a mold is manufactured, a large number of lenses can be mass-produced using the mold. But,
The resin lens has a fatal defect that its optical performance greatly changes due to changes in temperature and humidity, and is not used for precision lenses.

By the way, as the lens, there is an aspherical lens, and the surface shape is an aspherical surface. This aspherical surface is generally rotationally symmetrical about the optical axis. Aspherical lenses are widely used because they have excellent performance that cannot be obtained with spherical lenses. However, if an aspherical lens is manufactured in the same process as that for a spherical lens (grinding → polishing), it takes much time and labor. Therefore, the manufacturing cost is considerably higher than that of the spherical lens.

In order to solve this drawback, resin-bonded aspherical lenses as shown in FIGS. 6 and 7 have been developed. This is composed of a thin (for example, 5 to 100 μm) resin molding layer having an aspherical surface and a glass lens (element base material) as a main component. The element substrate has a spherical surface (see FIG. 6: JP-A-60-56544) or a rough aspherical surface (see FIG. 7: JP-A-63-157103). Both are available at low manufacturing costs. Such a resin-bonded aspherical lens is manufactured by, for example, a manufacturing method including the following first to sixth steps. See FIG. 8. (A) A first step of horizontally placing a mold (3) having an aspherical surface that is the opposite of the desired aspherical surface; (b) A predetermined amount of radiation-curable resin liquid (2a) in the center of the mold (3). ) Is dropped; (c) Third step of placing the glass lens (1) having a spherical surface or a rough aspherical surface on the mold (3); (d) Glass lens (1) and mold (3) A fourth step of bringing the distance between and to a predetermined value (at this time, the resin liquid spreads outside the effective diameter of the objective lens); (e) between the glass lens (1) and the mold (3) Fifth step of curing the resin liquid (2a) sandwiched between them by irradiating with radiation; and (f) the resin molding layer (2) obtained by curing the metal mold (3).
A sixth step of peeling from the interface with;

[0005]

In the conventional manufacturing method, the shape accuracy of the surface (aspherical surface) of the resin molding layer (2) is often low (particularly in the case of the resin thickness distribution as shown in FIG. 3), which is low. Since the product becomes a defective product, the conventional manufacturing method has a problem that the non-defective rate is low. An object of the present invention is to improve the non-defective rate by reducing the cases where the shape accuracy is low.

[0006]

Therefore, according to the present invention, (a) a die and an element base material having an aspherical surface which is the reverse of the desired aspherical surface (provided that at least one of the mold and the base material is exposed to radiation). (B) A radiation-curable resin liquid is sandwiched between the mold and the element base material so that the resin liquid spreads to the outside of a desired region. A second step of: (c) a third step of irradiating the resin liquid with radiation through a mask that shields the outside of the region; and (d) radiation of the resin liquid including the portion shielded by the mask. And (e) a fifth step of peeling the obtained aspherical resin molding layer from the interface with the mold; “aspherical resin molding layer and the element base material”. A method of manufacturing an aspherical optical element consisting of

[0007]

In the conventional manufacturing method, as shown in FIG. 5 (a), the entire resin liquid was irradiated with radiation. In that case, the thin portion S of the resin molding layer at the outer edge of the desired region (for example, near the effective diameter of the intended optical element) is cured before the thick portion T of the molding layer in the region. for that reason,
When the resin liquid in the thick portion T cures, this T
Even if the resin liquid of the part tries to shrink, there is no room to shrink because the surrounding resin liquid has already hardened. As a result, the resin liquid is peeled off from the mold, and the molding surface of the resin does not become a mirror surface as a lens.

On the other hand, in the present invention, in the third step, the resin liquid is irradiated with radiation while masking the outside of the region. Therefore, as shown in FIG. 5B, even if the thick portion T of the resin molding layer in the region hardens and shrinks,
The decrease in the volume of the resin due to the shrinkage is compensated by supplying the masked uncured resin liquid outside the region, so that the shrinkage amount can be suppressed. Therefore, it is possible to prevent the phenomenon that the resin layer is peeled off from the mold, and it is possible to suppress deterioration in shape accuracy.

Since the edge of the area shielded by the mask (the boundary with the irradiation area) makes a trace such as a step on the resin molding layer, this trace does not come within the intended effective diameter of the optical element. When avoiding it, it is necessary to appropriately set the region where the resin liquid is spread in the second step. For example,
If the resin liquid is spread to the outside of the effective diameter and the outside of the effective diameter is shielded by the mask, the traces do not affect the performance of the optical element. Further, when the aspherical expression of the aspherical surface portion (within the effective diameter of the optical element) is extended to the outside of the effective diameter of this optical element, the resin thickness becomes thin in the portion outside this diameter (see FIG. 5B). Indicated by U). With such a shape, a sufficient amount of resin may not be obtained even when the manufacturing method of the present invention is used. Therefore, in order to secure the supply amount of the resin, the shape is set so that a desired amount of the resin can be supplied (indicated by V in FIG. 5B), and this portion functions as a “resin reservoir”.

The mask that shields the light from the outside of the region is generally a light shield plate having an opening. When the surface of the base material (1) irradiated with radiation (the surface opposite to the resin molding surface) has a large radius of curvature, the mask may have a flat plate shape. On the other hand, when the radius of curvature of the surface irradiated with radiation is small,
A preferable result is obtained by bending a part of the mask (4) according to the radius of curvature of the substrate (1) as shown in FIG.

The diameter of the opening in the mask does not necessarily match the diameter of the desired area. After passing through the base material (1), the radiation is applied to the resin liquid. Therefore, the diameter of the luminous flux of the radiation applied to the resin liquid is affected by the curvature and the refractive index of the base material (1). Therefore, the diameter of the opening of the mask is set in consideration of these. When the maximum thickness of the resin molding layer is in the peripheral part within the effective diameter of the optical element, and assuming the maximum thickness to be 100%, the thickness of the resin layer at the edge position (outside the effective diameter) is 30%. % Is preferable. For more accuracy, when the resin amount near the maximum thickness is X and the shrinkage is 10%, calculate so that the resin amount of 0.1 X is supplied from outside the edge and calculate the edge position. The thickness of the resin layer may be set.

The element base material as the main component is preferably made of glass, but may be made of resin in some cases. The shape is
It may be set according to the target optical element, and may be a convex lens shape, a concave lens shape, a flat plate, or a rectangular parallelepiped. Generally, the substrate is a spherical lens made of glass. However, a glass lens having a rough aspherical surface may be used.
The rough aspherical surface has a rougher processing accuracy than the desired processing accuracy or surface accuracy (for example, 6 μm or less or 3 μm or less) and has the same or approximate aspherical surface as the desired aspherical surface. Since such a glass lens may be rougher than a desired processing accuracy, it is an aspherical lens, but the manufacturing cost is not so high. The manufacturing method of such an aspherical lens is already known, and can be easily manufactured by a commercially available grinding machine.

In order to improve the adhesive strength with the resin, it is preferable that the glass element base material is previously subjected to silane coupling treatment. Generally, the thickness of the resin molding layer is 1 at the center.
˜500 μm, preferably 5 to 100 μm. When the target element is a lens, the resin molding layer does not necessarily have to have the same refractive index as that of the element base material. This resin molding layer is formed as a result of curing the resin liquid by irradiating the radiation curable resin liquid with radiation. As a material of such a resin liquid, a thermosetting resin such as an epoxy resin, an unsaturated polyester, a polyurethane, a urethane acrylate, an ultraviolet curable resin or a modified acrylic resin is used. Examples of radiation include ultraviolet rays, electron beams, and γ
Rays, alpha rays, etc. are used.

Embodiments of the present invention will be described below with reference to the drawings, but the present invention is not limited thereto.

[0015]

EXAMPLE FIG. 2 is a vertical sectional view of a concave lens manufactured in this example. This lens is composed of a glass lens (1) as an element substrate and an aspherical resin molding layer (2) formed on the surface thereof. The glass lens (1) is a concave lens having a spherical surface, and has a diameter of 27 mm, a concave surface R _{1 has} a curvature radius of 11.170 mm, a convex surface R _{2 has} a curvature radius of 25.80 mm, and a center thickness of 1.5 m.
m. The surface of the glass lens (1) is previously subjected to silane coupling treatment in order to improve the adhesive force with the resin molding layer (2). As a silane coupling agent, here, KBM503 (trade name, manufactured by Shin-Etsu Chemical Co., Ltd.) was diluted with a 2 wt% ethanol solution and used. Resin molding layer (2)
Is on the convex surface R ₂ side, and its center thickness is about 30 μm.

The mold used for manufacturing has an aspherical surface with a radius of curvature of 28.8 mm on the side in contact with the resin. This mold is made of a stainless alloy, and the mold surface is nickel-plated. As the resin liquid, a urethane acrylate-based ultraviolet curable resin liquid was used. The shrinkage rate of the resin liquid is about 7%.

The mask has an opening diameter of φ = 18 mm. This aperture diameter is such that when ultraviolet rays are emitted from a point light source 110 mm away from the base lens and reach the resin liquid, the ultraviolet rays can irradiate a range slightly wider than a predetermined effective diameter. See FIG. Next, the manufacturing method of this embodiment will be described for each step with reference to FIG. (A) First step: the mold (3) having an aspherical surface that is the reverse of the desired aspherical surface and the lens (1) as an element substrate.
Prepared. (B) Second step: 70 mg of the ultraviolet curable resin liquid (2a) was dropped on the mold (3), and then the base lens (1)
Was pressed and sandwiched between the mold (3) and the base material (1). At this time, the center thickness of the resin layer was 30 μm,
The space between the mold (3) and the substrate (1) was set. As a result, the resin liquid (2a) was in a state of spreading outside the effective diameter of the target aspherical lens. (C) Third step: The mask (4) was placed on the base lens (1), and the resin liquid was irradiated with ultraviolet rays for 30 seconds through the mask (4). Ultraviolet rays are emitted from a xenon lamp (point light source) with an output of 150W. The point light source is 110 mm away from the base lens (1). The irradiation intensity is 30 mW / cm ² on the resin liquid.

During irradiation, the outside of the effective diameter is shielded by the mask (4). The thickness of the resin liquid (2a) at the boundary between the shaded portion and the shaded portion is 50 μm. This thickness is the maximum thickness of the resin liquid (2a) as shown in Fig. 1
It corresponds to about 50% of 80 μm. The position of the maximum thickness of the resin liquid is slightly inside the effective diameter of the lens. (D) Fourth step: The mask (4) was removed, and the entire resin liquid (2a) was irradiated with ultraviolet rays for 30 seconds under the same conditions. As a result, the resin liquid (2a) was cured to form the resin molding layer (2). (E) Fifth step: The obtained aspherical resin molding layer (2) was peeled from the interface with the mold to obtain the aspherical lens shown in FIG.

The mask (4) may be formed by applying a masking paint on the base lens (1) without using a separate member. Further, instead of the masking paint, a commonly used internal reflection preventing paint of a lens may be used. In these cases, in the fourth step, the point light source may be brought closer to the resin liquid (2a) instead of removing the mask (4). By doing so, the irradiation range of the ultraviolet rays is expanded to the area shielded by the paint, so that the entire resin liquid can be irradiated with the ultraviolet rays. Even when the mask (4) is used, the same effect can be obtained by bringing the point light sources close to each other without removing the mask (4) in the fourth step. This method is also included in the present invention. The manufacturing method of the present invention can also be applied to a lens as shown in FIG.

[0020]

According to the present invention, the number of cases in which the shape accuracy of the aspherical surface is lowered even after mass production is reduced, and the yield rate is improved.

[Brief description of drawings]

FIG. 1 is a conceptual diagram showing a vertical cross section of a lens (1) and the like in each step of a manufacturing method according to an embodiment of the present invention.

FIG. 2 is a schematic vertical sectional view of a resin-bonded aspherical lens manufactured in an example of the present invention.

FIG. 3 is a schematic diagram showing the thickness of the resin liquid in the radial direction of the base lens.

FIG. 4 is a schematic view showing an irradiation range of ultraviolet rays when the mask (4) is installed.

FIG. 5 is a schematic explanatory view comparing the manufacturing method of the present invention with a conventional manufacturing method.

FIG. 6 is a schematic vertical sectional view of a conventional resin-bonded aspherical lens.

FIG. 7 is a schematic vertical sectional view of a conventional resin-bonded aspherical lens.

FIG. 8 is a conceptual diagram showing a vertical cross section of the lens (1) and the like in each step of the conventional manufacturing method.

FIG. 9 is a schematic vertical sectional view of another resin-bonded aspherical lens.

[Explanation of symbols for main parts]

 1 glass lens or element base material or base lens 2 resin molding layer 2a UV curable resin liquid 3 mold 4 mask

Claims (1)

[Claims] 1. A method of preparing a die having an aspherical surface which is the opposite of a desired aspherical surface and an element substrate (provided that at least one of the die and the substrate is transparent to radiation). 1 step; (b) a second step in which the radiation curable resin liquid is sandwiched between the mold and the element substrate so that the resin liquid spreads to the outside of a desired region; (c) the region A third step of irradiating the resin liquid with radiation through a mask that shields the outside of the resin; (d) a fourth step of irradiating the resin liquid with radiation including the portion shielded by the mask; and (e) ) A fifth step of peeling the obtained aspherical resin molding layer from the interface with the mold; a "aspherical optical element comprising the aspherical resin molding layer and the element base material" is manufactured. how to.