JP2006119526A - Optical material, method for molding optical element, optical element and optical system unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical material which inhibits crystallization and is molded at room temperature, a method for molding an optical element, the optical element, and an optical system unit. <P>SOLUTION: The optical material comprises at least N-vinylcarbazole, vinyl benzoate and a photopolymerization initiator. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical material, a method for molding an optical element, an optical element, and an optical system unit. The optical material has a large refractive index dispersion and can be applied to optical elements such as lenses, filters, mirrors, refractive optical elements, and diffractive optical elements. About.

  Conventionally, in an optical system constituted only by a refractive system, chromatic aberration is reduced by combining glass materials having different dispersion characteristics. For example, in an objective lens such as a telescope, a glass material with small dispersion is used as a positive lens and a glass material with high dispersion is used as a negative lens, and these are used in combination to correct chromatic aberration appearing on the axis. For this reason, there are cases where the chromatic aberration cannot be sufficiently corrected when the configuration and number of lenses are limited or when the glass materials used are limited.

  Non-Patent Document 1 discloses a method of reducing chromatic aberration by using a diffractive optical element provided with a diffraction grating having a diffractive action on a lens surface or a part of an optical system, in contrast to a method of reducing chromatic aberration by combining glass materials. Yes.

  This utilizes a physical phenomenon that the chromatic aberration for a light beam having a certain reference wavelength appears in the opposite direction between the refracting surface and the diffractive surface in the optical system.

  Further, such a diffractive optical element can have an aspherical lens effect by changing the period of the periodic structure of the diffraction grating, and has a great effect in reducing aberrations.

  Here, when compared in terms of the refracting action of light rays, one light ray on the lens surface is still one light after refraction, whereas when one light ray is diffracted on the diffractive surface, the light is in each order. Divided into multiple.

  Therefore, when a diffractive optical element is used as the lens system, it is necessary to determine the grating structure so that the light beam in the used wavelength region is concentrated on a specific order (hereinafter also referred to as a step order). When the light is concentrated at a specific order, the intensity of the other diffracted light beams is low, and when the intensity is 0, the diffracted light does not exist.

  Therefore, in order to have the above characteristics, it is necessary that the diffraction efficiency of the light beam of the designed order is sufficiently high. In addition, when there is a light beam having a diffraction order other than the design order, the light is imaged at a place different from the light beam of the design order, so that it becomes flare light.

  Patent Document 1, Patent Document 2, Patent Document 3, and Patent Document 4 present a configuration that can reduce the decrease in diffraction efficiency. This is a configuration having high diffraction efficiency in a wide wavelength range by optimally selecting dispersion of different materials and each grating thickness.

  Specifically, a diffractive optical element is disclosed in which a plurality of optical materials (layers) are stacked on a substrate, and a relief pattern, a staircase shape, a kinoform, etc. are formed on at least one of the boundary surfaces of different optical materials. ing.

  In any of Patent Document 1, Patent Document 2, Patent Document 3, and Patent Document 4, in order to obtain a structure having high diffraction efficiency in a wide wavelength range, a relatively low refractive index material and a high refractive index dispersion A combination of materials is used. Specifically, in the case of Patent Document 1, BMS81 (nd = 1.64, νd = 60.1: manufactured by OHARA) and plastic optical material PC (nd = 1.58, νd = 30.5: manufactured by Teijin Chemicals Ltd.) In the case of Patent Document 2, LaL14 (nd = 1.6968, νd = 55.5: manufactured by OHARA), acrylic resin (nd = 1.49, νd = 57.7), Cytop (nd = 1.34149) , Νd = 93.8: manufactured by Asahi Glass Co.), PC (nd = 1.58, νd = 30.5: manufactured by Teijin Chemicals Ltd.), Patent Document 3 and Patent Document 4, C001 (nd = 1.5250, νd = 50.8: manufactured by Dainippon Ink Co.), plastic optical material PC (nd = 1.58, νd = 30.5: manufactured by Teijin Chemicals Ltd.), PS (nd = 1.5918, νd = 31.1) , PMMA (nd = 1.4917, νd = 57.4), B S81 (nd = 1.64, νd = 60.1: manufactured by Ohara Inc.), and the like are used.

  In order to further improve the optical performance, optical materials that are commercially available or researched and developed as optical materials were examined, and the distribution was as shown in FIG.

The materials of the laminated diffractive optical elements described in Patent Document 1 and Patent Document 3 also fall within the distribution of FIG.
JP-A-9-127321 JP-A-9-127322 Japanese Patent Laid-Open No. 11-04808 Japanese Patent Laid-Open No. 11-044810 SPIE Vol. 1354 International Lens Design Conference (1990)

  However, in the case of an optical element such as a diffractive optical element, when the incident angle (field angle) of light is large due to its shape, there arises a problem that flare light or ghost is generated due to the light being scattered. Therefore, in order to widen the angle of view, it is necessary to use a material having a larger refractive index dispersion than conventional optical materials. Therefore, it is considered that one of effective methods is to use poly (N-vinylcarbazole) (νd = 17.8). At that time, by photopolymerizing N-vinylcarbazole, it becomes possible to form a diffractive optical element or the like into an arbitrary shape, but this is generally due to replica molding performed at room temperature. It is inconvenient to use N-vinylcarbazole that crystallizes as it is.

  In other words, replica molding is one of the molding techniques for optical elements that has been characterized by its excellent large area moldability and high transferability, and is suitable for mass production due to the ease of the molding technique. is there. In this replica molding technology, a photocurable resin is dropped onto a mold surface having a reverse shape of a desired optical shape, and a lens blank is crimped and spread out from the mold surface. When the material that crystallizes at room temperature is used, it is usually performed at room temperature. Crystallization occurs when the lens is dropped into the mold or during the pressure bonding of a lens blank such as glass, which causes inconvenience in obtaining a desired shape.

  In order to suppress crystallization, a method of setting the mold temperature to be equal to or higher than the crystallization temperature is conceivable. However, when the mold is constrained for molding, free expansion does not occur and the mold linearly expands freely. Absent. It is even more difficult if the mold has a temperature distribution. That is, it is preferable to design a mold at room temperature that easily reaches temperature equilibrium and to mold at room temperature. Moreover, it is difficult to manufacture a mold that allows for expansion due to temperature due to the complexity of shapes such as free-form surfaces and lattice shapes in recent optical element shapes. In particular, the lattice shape on a free-form surface is even more difficult.

  Therefore, the present invention solves the above-mentioned problems, an optical material having a larger refractive index dispersion that can suppress crystallization even during molding at room temperature, a method for molding an optical element using the optical material, An object of the present invention is to provide an optical element molded by the molding method and an optical system unit having the optical element.

  In order to achieve the above object, the present invention provides an optical material configured as in the following (1) to (11), a method for molding an optical element using the optical material, an optical element molded by the molding method, And an optical system unit having the optical element.

  (1) An optical material comprising at least N-vinylcarbazole, vinyl benzoate, and a photopolymerization initiator.

  (2) The optical material as described in (1) above, comprising at least N-vinylcarbazole and poly (N-vinylcarbazole), vinyl benzoate, and a photopolymerization initiator.

(3) The composition of the optical material is
Poly (N-vinylcarbazole): 10-30 wt%
Vinyl benzoate: 10-30 wt%
The optical material as described in (1) or (2) above, wherein

  (4) In an optical element molding method for molding an optical element with a molding die, the optical material according to any one of (1) to (3) is used as a molding material for the optical element. Molding method.

  (5) When molding an optical element using the optical material, the optical material is placed in the mold and photopolymerized to mold the optical element. Optical element molding method.

  (6) The method for molding an optical element according to (4) or (5), wherein the viscosity of the optical material is adjusted in a range of 50 mPa · s to 5000 mPa · s.

  (7) A diffractive optical element in which the optical element is formed by laminating at least two types of layers made of materials having different dispersions on a plurality of layered substrates so as to increase the diffraction efficiency of a specific order (design order) over the entire use wavelength range. The method for molding an optical element according to any one of (4) to (6), wherein the optical element is an element.

  (8) An optical element molded by the optical element molding method according to any one of (4) to (7).

  (9) An optical system unit comprising the optical element according to (8).

  (10) The optical system unit according to (9), wherein the optical system unit is a photographing optical system unit.

  (11) The optical system unit according to (9), wherein the optical system unit is a projection optical system unit.

  Optical material capable of suppressing crystallization and molding at room temperature by using an optical material comprising at least N-vinylcarbazole, vinyl benzoate, and a photopolymerization initiator, and method for molding optical element An optical element and an optical system unit can be provided.

  Refractive index dispersion that can suppress crystallization even in molding at room temperature by applying the above configuration and configuring an optical material composed of N-vinylcarbazole, vinyl benzoate, and a photopolymerization initiator. Larger optical material, an optical element molding method using the optical material, an optical element molded by the molding method, and an optical system unit having the optical element can be realized.

  N-vinylcarbazole is a molecule having a large π electron conjugated system. As a result, π-π electron bonds between molecules occur and crystallize at room temperature. In order to suppress this crystallization, the π-π electron bond is inhibited by adding another compound, and the crystallization temperature is lowered by adding a substance having an interaction between the compound and N-vinylcarbazole. be able to. The vinyl benzoate used here has the same effect, and can lower the crystallization temperature of N-vinylcarbazole.

  Since the material of the present invention is an optical material, transparency is required. Therefore, the compound added to suppress crystallization must be transparent after polymerization. Poly (N-vinylcarbazole) alone is transparent. However, when other compounds are added, depending on the compatibility of the polymers after molding by photopolymerization, phase separation occurs, and the mixture becomes cloudy and causes optical scattering. As a result of intensive studies by the inventors, vinyl benzoate is transparent after polymerization even when added in a larger amount than other compounds. By adding vinyl benzoate within a range of 30 wt% or less, an optical element free from optical scattering can be formed. Further, by adding 10 wt% or more of vinyl benzoate, the crystallization temperature can be lowered to around room temperature.

  Poly (N-vinylcarbazole) can also suppress crystallization and lower the crystallization temperature of N-vinylcarbazole as in the case of adding vinyl benzoate.

  Moreover, it melt | dissolves in the melt of N-vinyl carbazole, is excellent in compatibility, and shows moderate viscosity. The viscosity in the replica molding used here is preferably in the range of 50 mPa · s to 5000 mPa · s. By using a viscosity in this range, the amount of dripping can be stably controlled by a dispenser. When the pressure is 50 mPa · s or less, it is difficult to drop a small amount, and a phenomenon that the liquid scatters from the dropping nozzle occurs. Further, at a viscosity of 5000 mPa · s or more, the optical material of the present invention has the yarn property, so that there is a possibility that the yarn is pulled from the nozzle port and adhered to other than the desired portion.

  Moreover, it is preferable that the ratio of poly (N-vinyl carbazole) is 10 wt% or more and 30 wt% or less.

  If it is the said range, it can adjust to the viscosity range preferable for replica molding.

  Examples of the present invention will be described below, but the present invention is not limited by them.

  First, the outline of the optical element molding method in the present embodiment will be described with reference to the schematic view of FIG. In FIG. 2, a photocurable resin 22 is dropped on a mold 21 having a reverse shape of a desired optical shape, and a lens blank 23 is crimped and spread out from above the mold 21. The light-curing resin 22 is cured by irradiating light from the resin, and molding is performed by releasing it.

Example 1
Optical materials of Experimental Examples 1 to 9 and Comparative Experimental Example 1 used in this example were prepared. In the optical materials of each experimental example, the following compounds were mixed at the ratio shown in Table 1. Mixing was performed as follows. N-vinyl carbazole (manufactured by Tokyo Chemical Industry Co., Ltd.) and Irgacure 184 (manufactured by Ciba Specialty Chemicals) as a photopolymerization initiator were mixed and dissolved by heating at 80 ° C. for 2 hours. Furthermore, after sufficiently stirring, after mixing vinyl benzoate (manufactured by Shin-Etsu Vinyl Acetate Co., Ltd.) and poly (N-vinylcarbazole) (manufactured by ACROSS), the mixture was sufficiently stirred and dissolved at 80 ° C. The optical material of each experimental example of the example was obtained.

  The crystallization temperature was measured by DSC for the materials of each experimental example of this example. The DSC chart of Comparative Experimental Example 1 is shown in FIG. 3, and the crystallization temperature and melting temperature of each experimental example are shown in FIG.

  In Comparative Experimental Example 1, the crystallization temperature was about 40.9 ° C. The crystallization temperature in Experimental Example 1 was 30.5 ° C., and a decrease in crystallization temperature was observed, but did not decrease to room temperature. In other experimental examples, the crystallization temperature was 25 ° C. or lower.

  Next, each optical material of this example was molded using a flat mold. About 0.04 g of the optical material of this example kept at 80 ° C. was discharged onto a flat mold at 25 ° C. using a dispenser. The mold temperature is controlled within ± 1.0 ° C. by temperature control. The material of Comparative Experimental Example 1 was instantly crystallized and could not be molded. Since crystallization did not occur for other materials, a 50 μm spacer was placed on the mold, a glass plate (BK7) was placed on the discharge liquid, and the liquid was filled between the glass and the mold. Furthermore, it was cured by irradiating ultraviolet rays having a center wavelength of 365 nm from the glass plate direction at 40 mW for 300 seconds. The said hardened | cured material was peeled from the metal mold | die and the molding using the optical material of a present Example was obtained. The molded products obtained in Experimental Examples 7, 8, and 9 were measured for transmittance. The transmittance measurement results are shown in FIG.

  In Experimental Example 9 in which 30 wt% of vinyl benzoate was added, there was some scattering, but sufficient transmittance was shown.

  Next, the refractive index was measured for the materials of Experimental Examples 4, 7, 8, and 9 of this example. A sample for refractive index measurement was prepared as follows. About 0.04 g of the optical material of each experimental example kept at 80 ° C. was discharged onto a glass plate S-TIH53 (manufactured by OHARA INC.) Placed on a hot plate at 25 ° C. using a dispenser.

  The temperature is controlled within ± 1.0 ° C. by temperature control. A 50 μm spacer was placed on the glass plate, another glass plate (BK7) was placed on the discharge liquid, and the liquid was filled between the glass plates.

  Further, UV light having a central wavelength of 365 nm was irradiated at 40 mW for 250 s and cured. The cured product was cut into two with a slicer to obtain a molded product using the optical material of this example. Refractive index measurement was performed on the cut molded sample. FIG. 6 shows the refractive index of the d-line, and FIG. 7 shows the result of the Abbe number. Addition of vinyl benzoate decreases the refractive index and increases the Abbe number, but an optical material having a sufficiently low Abbe number compared to commercially available optical materials could be obtained.

(Example 2)
The configuration of the diffractive optical element in Embodiment 2 of the present invention will be described with reference to FIG. In FIG. 8, the diffractive optical element of this embodiment is designed in accordance with the materials of the optical elements 1 and 2 so that the light beams in the wavelength region of 400 nm to 700 nm are concentrated in the design order. The pitch between each grating is 200 μm. In this example, Experimental Example 7 (Nd: 1.697, νd: 17.7) described in Example 1 which is an optical material of the present invention was used as the optical element 1. The grating height d1 is 4.00 μm. For the optical element 2, RC-C001 (manufactured by Dainippon Ink & Chemicals, Inc.), which is a photocurable resin, was used. The grating height d2 is 6.45 μm. Using the designed mold, each of these optical elements was formed by replica molding.

  After molding, an antireflection film is formed on the side of the glass plate opposite to the replica molding surface so as to obtain a large light transmittance (diffraction efficiency) in the used wavelength range. After forming the antireflection film, the replica molding surfaces of these optical elements are faced to each other, the positions of the grating tips are aligned so as to be symmetrical, and the elements are bonded in parallel so as to have an interval of 1.5 μm. The element is obtained.

  The optical element in this example was molded as follows. About 0.04 g of the optical material of Experimental Example 7 described in Example 1 kept at 80 ° C. was discharged onto a 25 ° C. mold using a dispenser. The mold temperature is controlled within ± 1.0 ° C. by temperature control. After a glass plate (BK7) at 25 ° C. is slowly in contact with the discharge liquid, it is pressure-bonded and slowly spread out so that no bubbles enter. Between.

  Furthermore, it was cured by irradiating ultraviolet rays having a central wavelength of 365 nm at 40 mW for 500 s from the glass plate direction. The said hardened | cured material was peeled from the metal mold | die and the optical element 1 shape | molded using the optical material of a present Example was obtained.

  Similarly, RC-C001 is cured using the mold of the optical element 2 in the same manner as the optical element 1, after being wetted, pressure-bonded and filled, and irradiated with UV light having a central wavelength of 365 nm from the glass plate direction at 40 mW for 500 s. Peeling optical element 2 was obtained. In both the optical elements 1 and 2, an antireflection film was provided on the glass plate side, and the diffractive optical element of this example in which the optical element 1 and the optical element 2 were bonded in parallel was obtained. FIG. 9 shows the results of measuring the diffraction efficiency of the diffractive optical element of this example. A diffractive optical element having sufficient diffraction efficiency could be obtained.

Optical glass, refractive index of polymer, and Abbe number distribution Schematic diagram of the molding method of Example 1 The figure which shows the DSC chart of the comparative experiment example 1 of Example 1 (A) The figure which shows the crystal melting temperature of Example 1, (b) The figure which shows the crystallization temperature of Example 1. The figure which shows the transmittance | permeability of Experimental example 7, 8, 9 of Example 1. The figure which shows the refractive index (Nd) of Experimental example 4, 7, 8, 9 of Example 1. The figure which shows the Abpe number ((nu) d) of Experimental example 4,7,8,9 of Example 1. FIG. Schematic diagram of diffractive optical element of Example 2 The figure which shows the diffraction efficiency of the optical element of Example 2

Explanation of symbols

21 Mold 22 Optical material (photo curable resin)
23 Lens blank (glass plate)
24 Light source

Claims (11)

  An optical material comprising at least N-vinylcarbazole, vinyl benzoate, and a photopolymerization initiator.   The optical material according to claim 1, comprising at least N-vinylcarbazole and poly (N-vinylcarbazole), vinyl benzoate, and a photopolymerization initiator. The composition of the optical material is
Poly (N-vinylcarbazole): 10-30 wt%
Vinyl benzoate: 10-30 wt%
The optical material according to claim 2, wherein the optical material falls within the range.   In the molding method of the optical element which molds an optical element with a mold, the optical material according to any one of claims 1 to 3 is used as a molding material of the optical element.   5. When molding an optical element using the optical material, the optical element is molded by placing the optical material in the mold and performing photopolymerization. Method.   The method for molding an optical element according to claim 4, wherein the viscosity of the optical material is adjusted to a range of 50 mPa · s to 5000 mPa · s.   The optical element is a diffractive optical element in which at least two layers made of materials with different dispersions are stacked on a multi-layer substrate to increase the diffraction efficiency of a specific order (design order) over the entire wavelength range to be used. The method for molding an optical element according to any one of claims 4 to 6, wherein:   An optical element formed by the method for molding an optical element according to claim 4.   An optical system unit comprising the optical element according to claim 8.   The optical system unit according to claim 9, wherein the optical system unit is a photographing optical system unit.   The optical system unit according to claim 9, wherein the optical system unit is a projection optical system unit.

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