JP2014129195A - Inorganic material for optical element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inorganic material for an optical element and a component for an optical element having high infrared permeability, and a method for manufacturing the inorganic material for an optical element.SOLUTION: In an inorganic material for an optical element which mainly comprises a compound comprising zinc and sulfur, an element ratio of sulfur to zinc, (S/Zn), is 0.80 or more and 0.95 or less. Preferably a cubic polycrystalline material represented by ZnS(0<x≤0.2) is contained as a compound, and preferably the average crystal grain size of the cubic polycrystalline material is 0.5 μm or more and 20 μm or less. Preferably an amorphous material interposed between crystals of the cubic polycrystalline material is further contained as a compound.

Description

The present invention relates to an inorganic material for optical elements mainly composed of a compound composed of zinc and sulfur, an optical element component including the same, and a method for producing the inorganic material for optical elements.

Since ZnS (zinc sulfide) has good infrared transmission characteristics, it is frequently used as an optical element material such as a window material or a lens of an infrared sensor, an infrared image processing apparatus, an infrared laser or the like. Single crystal ZnS has very good translucency, but is difficult to increase in size. Therefore, the development of polycrystalline ZnS is in progress. As the method for producing the polycrystalline ZnS, the CVD (Chemical Vapor Deposition) method and the HP (Hot Press) method are mainly used. However, the CVD method has a low vapor deposition rate and high production cost. .

Under such circumstances, as a method for producing ZnS polycrystals using the HP method, the raw material powder has an average particle diameter of 0.1 to 5 μm and is sintered in vacuum at a temperature of 500 to 850 ° C. (Patent Document) 1), using a fine high-purity powder having a particle size of 5 μm or less as a raw material powder, and performing hot compression molding in vacuum under conditions of a temperature of 800 to 1050 ° C. and a pressure of 0.8 to 1.4 ton / cm ^2. (Refer to Patent Document 2), powder having an average particle diameter of 1 to 2 μm and a purity of 98% or more, and hot in a non-oxidizing atmosphere at a temperature of 900 to 1000 ° C. under a pressure of 150 to 800 kg / cm ^2. A compression molding method (see Patent Document 3) has been proposed. According to these methods, a ZnS polycrystal having a high infrared transmittance is obtained, but development of a material having a higher infrared transmittance is required as an optical element material for an apparatus using infrared rays. ing.

JP 2008-127236 A JP-A 61-205659 JP-A-11-295501

This invention is made | formed in view of this situation, and it aims at providing the manufacturing method of the inorganic material for optical elements with high infrared transmittance, components for optical elements, and such an inorganic material for optical elements.

Conventionally, when manufacturing a ZnS polycrystal for an optical element by a hot press method, it is said that by performing hot compression molding in a vacuum state, SOx remaining in the raw material is removed and the light transmittance is increased. (See Patent Document 1). However, the inventors have performed hot compression molding at a high temperature and in a high vacuum state in this manner, causing escape of Zn element and S element due to sublimation or decomposition of ZnS itself, which is a cause of lowering light transmittance. I found out that This escape is caused by a difference in boiling point of the single substance, so that S is larger than Zn. Therefore, the decrease of S (sulfur element) is remarkable with respect to Zn (zinc element). Thus, the inventors have found that the light transmittance of the obtained inorganic material can be increased by suppressing the relative decrease of the elemental sulfur in the production process from these findings, and have reached the present invention.

That is, the inorganic material for optical elements according to the first invention that meets the above object is an inorganic material for optical elements mainly composed of a compound consisting of zinc and sulfur, and the element ratio of sulfur to zinc (S / Zn) is 0. .80 or more and 0.95 or less.

According to the inorganic material for optical elements according to the first invention, by setting the element ratio of sulfur to zinc (element ratio in the entire inorganic material for optical elements) within the above range, high infrared transmittance can be exhibited. .

In the inorganic material for an optical element according to the first invention, the compound includes a cubic polycrystal represented by ZnS _1-x (0 <x ≦ 0.2), and the cubic polycrystal The average crystal grain size is preferably 0.5 μm or more and 20 μm or less. By including a cubic polycrystal having such a composition and crystal grain size, the infrared transmittance can be further improved.

In the inorganic material for an optical element according to the first invention, it is preferable that the compound further includes an amorphous body interposed between crystals of the cubic polycrystalline body. By interposing such an amorphous body, the infrared transmittance can be further increased, and the strength and the like can be increased.

In the inorganic material for an optical element according to the first invention, the maximum light transmittance at a thickness of 2 mm is preferably 62% or more and 75% or less in a wavelength range of 7 to 12 μm. The maximum light transmittance at a thickness of 2 mm is 34% to 45% in the 2.5 to 3 μm wavelength region, and 57% to 70% in the 4 to 6 μm wavelength region, and 43% or more in the 13 to 14 μm wavelength region. It is preferable that it is 60% or less. When the inorganic material for optical elements according to the first invention has such a high light transmittance, the utility value can be increased.

The inorganic material for optical elements according to the first invention preferably contains pores, and the average diameter of the pores is preferably 0.1 μm or more and 0.5 μm or less. Thus, infrared transmittance etc. can be further improved by making the average diameter of a pore into the said range.

In the inorganic material for an optical element according to the first invention, the three-point bending strength is preferably 80 MPa or more and 180 MPa or less. By having such a high three-point bending strength, the inorganic material for optical elements according to the first invention can exhibit high durability and the like.

The inorganic material for an optical element according to the first aspect of the present invention is a hot material of zinc sulfide cubic crystal particle powder under an atmospheric pressure set to 0.1 MPa or more by one or both of an inert gas and a non-oxidizing gas. It is preferably formed by compression molding. Since such an inorganic material for optical elements can be obtained from a general zinc sulfide cubic crystal particle powder, it is excellent in productivity.

Further, an optical element component according to the second invention that meets the above object comprises the optical element inorganic material according to the first invention, and an antireflection film laminated on the surface of the optical element inorganic material, The maximum light transmittance at a thickness of 2 mm is 75% or more and 90% or less in the wavelength range of 7 to 12 μm. The optical element component according to the second invention can thus exhibit excellent infrared transmission characteristics.

Furthermore, in the method for producing an inorganic material for an optical element according to the third aspect of the invention, the zinc sulfide cubic crystal particle powder is filled in a heat-resistant mold for hot pressing, and the atmospheric pressure (P1) is 0.1 Pa or less. The first step of heat degassing under,
While maintaining the atmospheric pressure (P1), the filling in the heat-resistant mold for hot pressing is heated to a temperature range (t2) of 850 ° C. or higher and 1100 ° C. or lower by hot pressing to a pressure range of 20 MPa or higher and 70 MPa or lower. The atmospheric pressure (P2) of 0.1 MPa or more by one or both of the inert gas and the non-oxidizing gas while maintaining the temperature range (t2) and the pressure range. (P2) It has the 3rd process of carrying out hot compression molding under.

According to the method for manufacturing an inorganic material for an optical element according to the third invention, the atmospheric pressure is increased by an inert gas and / or a non-oxidizing gas, contrary to the conventional method, during the hot compression molding in the third step. ing. By doing so, the escape of sulfur element can be suppressed, and an inorganic material for optical elements having high infrared transmittance can be obtained.

In the method for producing an inorganic material for optical elements according to the third invention, the purity of the zinc sulfide cubic crystal particle powder is 97% or more, and the element ratio of sulfur to zinc (S / Zn) is 0.99 or more. It is preferable that the average particle size is not more than 01 and the average particle size is not more than 10 μm. By using such a raw material, the infrared transmittance and the like of the obtained inorganic material can be further increased.

In the method for producing an inorganic material for an optical element according to the third invention, the heat deaeration in the first step is performed at a rate of 3 to 20 ° C./min from room temperature to a temperature range (t1) of 400 ° C. or more and less than 850 ° C. The temperature is increased, and then the temperature range (t1) is maintained for 1 to 4 hours,
The second step is performed at a rate of 2 to 10 ° C./min and pressurization is performed at a rate of 2.5 to 5.0 MPa / min,
The hot compression molding in the third step is preferably performed for 6 hours to 30 hours.

Moreover, in the manufacturing method of the inorganic material for optical elements according to the third invention, the hot compression molding in the third step is carried out from the zinc sulfide cubic crystal particle powder by adjusting the atmospheric pressure (P2). It is preferable to carry out while controlling the escape of elemental sulfur.

In the method for producing an inorganic material for optical elements according to the third invention, the infrared transmittance and the like of the obtained inorganic material for optical elements can be further improved by making the conditions of the first to third steps as described above. it can.

The inorganic material for optical elements according to the first invention and the optical element component according to the second invention have high infrared transmittance. Moreover, the manufacturing method of the inorganic material for optical elements which concerns on 3rd invention can obtain the inorganic material for optical elements which has high infrared transmittance.

4 is a graph showing the light transmittance of the inorganic material for optical elements having a thickness of 2 mm obtained in Example 1. 4 is a graph showing the light transmittance of the inorganic material for optical elements having a thickness of 4 mm obtained in Example 1. FIG. 2 is a field emission scanning electron micrograph of a cut surface of an inorganic material for optical elements obtained in Example 1. FIG. 2 is a field emission scanning electron micrograph of a fracture surface of an inorganic material for optical elements obtained in Example 1. FIG. 4 is a graph showing the light transmittance of an inorganic material for optical elements having a thickness of 4 mm obtained in Example 2. 6 is a graph showing the light transmittance of an inorganic material for optical elements having a thickness of 4 mm obtained in Example 3. 6 is a graph showing the light transmittance of an inorganic material for optical elements having a thickness of 4 mm obtained in Example 4. 6 is a graph showing the light transmittance of an inorganic material for optical elements having a thickness of 4 mm obtained in Example 5.

Next, an embodiment embodying the present invention will be described.

<Inorganic materials for optical elements>
The inorganic material for optical elements according to the first embodiment of the present invention is mainly composed of a compound consisting of zinc and sulfur. Here, the “compound composed of zinc and sulfur” refers to a compound represented by ZnS _y (y is an arbitrary positive number), and is not limited to so-called zinc sulfide represented by ZnS. Further, “mainly composed of this compound” means that this compound occupies the largest mass with respect to the entire inorganic material for optical elements, specifically, 80% by mass or more is preferable, and 90% by mass. The above is more preferable, and 99 mass% or more is still more preferable.

The element ratio (S / Zn) of sulfur to zinc in the inorganic material for an optical element (whole) according to the present embodiment is 0.80 or more and 0.95 or less, and preferably 0.80 or more and 0.85 or less. When this ratio is less than 0.80, infrared transmittance decreases due to precipitation of Zn alone. On the other hand, it is difficult for this production ratio to exceed 0.95 in the hot press method. In addition, let the element content rate in the whole inorganic material be the value measured by the ICP analysis method.

The inorganic material for an optical element according to the present embodiment may contain other components as a simple substance or a compound as long as the effects of the present invention are not impaired, in addition to the compound composed of zinc and sulfur. Examples of other components include an oxygen element and a hydrogen element.

The compound consisting of zinc and sulfur is usually contained in the inorganic material for optical elements as a polycrystal. The crystal structure of this polycrystal is preferably cubic. The crystal structure of a compound composed of zinc and sulfur (for example, ZnS) mainly includes a cubic system and a hexagonal system, but the cubic system has higher infrared transmittance than a hexagonal system. Therefore, infrared transmission can be improved by having a cubic crystal structure. In addition, as this crystal structure, crystal structures other than cubic systems, such as a hexagonal system, may be included in part.

In this polycrystal, the composition formula (chemical formula) is preferably represented by ZnS _1-x (0 <x ≦ 0.2), and x more preferably satisfies 0 <x ≦ 0.1. Thus, infrared transmittance can be improved by setting it as the composition by which the reduction | decrease of S in a crystal | crystallization was suppressed (x value is small). The element content (rate) in the polycrystal is a value measured by energy dispersive X-ray spectroscopy.

The average crystal grain size of this polycrystal is preferably 0.5 μm or more and 20 μm or less, and more preferably 1 μm or more and 15 μm or less. When the average crystal grain size is less than 0.5 μm, the infrared transmittance decreases due to an increase in light scattering caused by the crystal grain boundary. On the other hand, when the average crystal grain size exceeds 20 μm, the mechanical strength is reduced due to the coarsening of the crystal. The average crystal grain size is a value calculated by counting the number of crystals on any five line segments (one 50 μm) using a photograph of the surface taken with an electron microscope.

The compound composed of zinc and sulfur is preferably contained in the inorganic material for optical elements as an amorphous body interposed between the crystals in addition to the above-described polycrystalline body. By interposing such an amorphous body between crystals, infrared transmittance can be further increased, and strength and the like can be increased. The reason for this is not clear, but it is presumed that the amorphous body fills the gaps between the polycrystalline bodies to increase the infrared transmittance, and the amorphous body functions as a binder to increase the strength. In addition, it is guessed that this amorphous body is a compound formed by mixing zinc element and sulfur element in an arbitrary ratio.

The inorganic material for optical elements according to the present embodiment can usually contain pores. The average diameter of the pores is preferably 0.1 μm or more and 0.5 μm or less. Setting the average diameter of the pores to less than the lower limit is difficult in production and leads to an increase in production cost. Conversely, if the average diameter of the pores exceeds the upper limit, the infrared transmittance may be reduced. The average pore diameter is a value (Ferre diameter) calculated from the pore diameter existing in an arbitrary 50 μm square area using a photograph of the surface taken with an electron microscope.

In the inorganic material for optical elements according to the present embodiment, the maximum light transmittance at a thickness of 2 mm is preferably 62% or more and 75% or less, and more preferably 65% or more in the 7 to 12 μm wavelength region. Thus, the inorganic material for optical elements which concerns on this Embodiment can exhibit the high transmittance | permeability of infrared rays (7-12 micrometers wavelength range). The light transmittance is a value measured with a Fourier transform infrared spectrophotometer (FT-IR).

In the inorganic material for optical elements according to the present embodiment, the maximum light transmittance at a thickness of 2 mm is preferably 34% or more and 45% or less, and more preferably 40% or more in the 2.5 to 3 μm wavelength region. 57 to 70% is preferable in the 4 to 6 μm wavelength region, and 60% or more is more preferable. Moreover, 43 to 60% is preferable in a 13-14 micrometer wavelength range, and 50% or more is further more preferable. According to the inorganic material for an optical element according to the present embodiment, in addition to being able to increase the transmittance in the infrared region, the transmittance can be improved in a wide wavelength region before and after that, and the range of utilization is widened. Can do.

Further, the light transmittance at a thickness of 2 mm is 34% to 45% in the 2.5 to 3 μm wavelength region, and 57% to 70% in the 4 to 6 μm wavelength region, and 62% or more in the 7 to 12 μm wavelength region. 75% or less, preferably 43% or more and 60% or less in the 13 to 14 μm wavelength region. By setting the light transmittance in each wavelength region to such a range (the minimum transmittance is equal to or higher than the lower limit of the above range), the value as an optical material can be increased.

The maximum light transmittance at a thickness of 4 mm in the optical element inorganic material according to the present embodiment is 20% to 30% in the 2.5 to 3 μm wavelength region and 55% to 70% in the 4 to 6 μm wavelength region. Hereinafter, it is preferably 60% or more and 75% or less in the 7 to 12 μm wavelength region, and 40% or more and 50% or less in the 13 to 14 μm wavelength region. The light transmittance at a thickness of 4 mm in the inorganic material for optical elements according to the present embodiment is 15% to 30% in the 2.5 to 3 μm wavelength region and 40% to 70 in the 4 to 6 μm wavelength region. % Or less, 45 to 75% in the 7 to 12 μm wavelength region, and preferably 20 to 50% in the 13 to 14 μm wavelength region. Thus, the inorganic material for optical elements according to the present embodiment has a high light transmittance even when the thickness is 4 mm, and the utility value for optical element applications is increased.

The three-point bending strength of the optical element inorganic material according to the present embodiment is preferably 80 MPa or more and 180 MPa or less, and more preferably 100 MPa or more. By having such a high three-point bending strength, the inorganic material for optical elements according to the present embodiment can exhibit high durability and the like. The three-point bending strength is a value measured in accordance with JIS R1601 (a room temperature bending strength test method for fine ceramics).

The method for producing the inorganic material for optical elements according to the present embodiment is not particularly limited, but is a hot press method using a zinc sulfide cubic crystal particle powder to be described later, particularly any one of an inert gas and a non-oxidizing gas. One or both of them can be suitably obtained by hot compression molding of zinc sulfide cubic crystal particle powder under an atmospheric pressure of 0.1 MPa or more. However, the inorganic material for optical elements obtained by other methods such as CVD is not deviated from the first invention.

<Optical element parts>
An optical element component according to a second embodiment of the present invention includes the optical element inorganic material according to the first embodiment and an antireflection film laminated on the surface of the optical element inorganic material. .

The antireflection film is not particularly limited as long as it can reduce light reflection, and can be formed from a known material. Specific examples of the antireflection film include fluorides such as CeF ₃ and MgF ₂ and oxides such as TiO ₂ . These can be laminated on the surface of the inorganic material for optical elements by a known method such as vapor deposition or coating.

In the optical element component according to the present embodiment, the maximum light transmittance at 2 mm in thickness (transmittance when light is incident from the surface of the antireflection film) is 75% or more in the wavelength range of 7 to 12 μm. It is preferable that it is 90% or less. The optical element component according to the present embodiment can exhibit such excellent infrared transmission characteristics.

<Method for producing inorganic material for optical element>
In the method for producing an inorganic material for an optical element according to the third embodiment of the present invention, a zinc sulfide cubic crystal particle powder is filled in a heat-resistant mold for hot pressing, and the atmospheric pressure (P1) is 0.1 Pa or less. In the first step of heating and deaeration, the temperature in the heat-resistant mold for hot pressing is raised to a temperature range (t2) of 850 ° C. or higher and 1100 ° C. or lower by hot pressing while maintaining the atmospheric pressure (P1). A second step of pressurizing to a pressure range of 20 MPa or more and 70 MPa or less, and an atmospheric pressure of 0.1 MPa or more by one or both of an inert gas and a non-oxidizing gas while maintaining the temperature range (t2) and the pressure range. (P2) and has a third step of hot compression molding under the atmospheric pressure.

In the method of manufacturing an inorganic material for an optical element according to the present embodiment, during the hot compression molding in the third step, the atmospheric pressure is increased by a non-oxidizing gas or the like contrary to the conventional method, and the zinc sulfide cubic The escape of components (especially elemental sulfur) in the crystalline crystal particle powder is suppressed. By doing in this way, it is thought that the inorganic material for optical elements with a high infrared transmittance can be obtained by suppressing the fall of S content rate in the polycrystal body and by extension, the inorganic material for optical elements obtained. Hereinafter, each step will be described in detail.

(1) First Step In this step, first, zinc sulfide cubic crystal particle powder is filled in a heat-resistant mold for hot pressing, and the crystal particle powder is heated and deaerated under an atmospheric pressure (P1) of 0.1 Pa or less. .

As the zinc sulfide cubic crystal particle powder, a known powder can be used. The purity of the crystal particle powder is preferably 97% or more, and more preferably 98% or more. If a material with a purity of less than 97% is used, the amount of impurities in the resulting inorganic material for optical elements may increase, and the infrared transparency may decrease.

The element ratio of sulfur to zinc (S / Zn) in the zinc sulfide cubic crystal particle powder is preferably 0.99 or more and 1.01 or less, and more preferably 1. If this element ratio is out of the above range, the infrared transmittance and the like of the obtained inorganic material for optical elements may be lowered.

The average particle diameter of the zinc sulfide cubic crystal particle powder is preferably 10 μm or less, and more preferably 8 μm or less. When the average particle diameter of the crystal particle powder exceeds 10 μm, the infrared transmittance and the like of the obtained inorganic material for optical elements tend to be lowered. The lower limit of the average particle diameter is not particularly limited, but can be 0.1 μm, for example. The average particle diameter is a value measured by a laser diffraction method.

The heat-resistant mold for hot pressing is not particularly limited as long as it can withstand the heat and pressure during hot pressing, and for example, a mold made of a known material such as graphite or C / C composite can be used.

Specifically, the heat deaeration in the first step is performed by reducing the atmospheric pressure to an atmospheric pressure (P1) of 0.1 Pa or less, and then maintaining the atmospheric pressure (P1) to increase the temperature from room temperature to 400 ° C. to 850 ° C. The temperature is raised at a rate of 3 to 20 ° C./min to a temperature range of less than (t1), and then the temperature range (t1: 400 ° C. to less than 850 ° C.) is 1 hour to 4 hours (more preferably 1.5 hours). As described above, more preferably, it is preferably carried out for 2 hours or more. When the atmospheric pressure (P1) exceeds 0.1 Pa, deaeration is insufficient. In addition, although it does not specifically limit as a minimum of this atmospheric pressure (P1), For example, it can set to 10 ^<-4> Pa. When the lower limit of the temperature range (t1) is less than 400 ° C., the deaeration becomes insufficient, and bumping is likely to occur in the next step. When the upper limit is 850 ° C. or more, the deaeration is not sufficiently performed. Since sintering can proceed in this state, it is not preferable. The temperature range (t1) is more preferably 600 ° C. or higher and 820 ° C. or lower. Further, when the rate of temperature increase is less than 3 ° C./min, it takes time to increase the temperature and is inefficient, and when it exceeds 20 ° C./min, bumping is likely to occur. Further, when the holding time of the temperature range (t1) is less than 1 hour, there is a possibility that the deaeration is not sufficiently performed, and when it exceeds 4 hours, it becomes inefficient.

(2) Second step In this step, the filler in the heat-resistant mold for hot pressing is heated and pressurized by hot pressing while maintaining the atmospheric pressure (P1: 0.1 Pa or less). The pressurization at this time may be uniaxial pressurization or isotropic pressurization (HIP) using gas or the like.

The temperature increase in the second step is performed from the temperature range (t1) of the first step to a temperature range (t2) of 850 ° C. to 1100 ° C., and the pressurization is performed to a pressure range of 20 MPa to 70 MPa. When the lower limit of the temperature range (t2) in the second step is less than 850 ° C., sufficient crystal grain growth is difficult to proceed, and when the upper limit exceeds 1100 ° C., the phase transition to the hexagonal system proceeds. There is a possibility that the infrared transmittance is lowered or the grain growth is excessively advanced and the strength is lowered. The temperature range (t2) is more preferably 950 ° C. or higher and 1050 ° C. or lower, and further preferably 970 ° C. or higher and 1030 ° C. or lower. In addition, when the lower limit of the pressure range is less than 20 MPa, sufficient reaction (crystal grain growth, etc.) does not proceed and it is difficult to obtain an inorganic material having high infrared transparency, and when the upper limit exceeds 70 MPa, the pressure resistance of the heat resistant mold It is not preferable in terms of performance.

The temperature rise is preferably performed at a rate of 2 to 10 ° C./min, and the pressurization is performed at a rate of 2.5 to 5.0 MPa / min. When the rate of temperature increase is less than 2 ° C./min, it takes time and is inefficient, and when it exceeds 10 ° C./min, bumping is likely to occur. When the pressurization rate is less than 2.5 MPa / min, it takes time and is inefficient, and when it exceeds 5.0 MPa, there is a possibility that cracks or the like may occur due to sudden pressurization.

(3) Third step In this step, either or both of an inert gas and a non-oxidizing gas while maintaining the temperature range (t2) and pressure range after the temperature is raised and pressurized in the second step. Thus, the atmospheric pressure is set to an atmospheric pressure (P2) of 0.1 MPa or more, and hot compression molding is performed under the atmospheric pressure (P2). This hot compression molding is performed while controlling the escape of elemental sulfur from the zinc sulfide cubic crystal particle powder by adjusting the atmospheric pressure (P2) with one or both of an inert gas and a non-oxidizing gas. It is preferable. By doing in this way, the escape of the sulfur element from raw material powder is suppressed, and the inorganic material for optical elements with high infrared transmittance can be obtained. This escape occurs, for example, in the form of release of compounds such as SOx (x is usually 0.5 to 3.0), H ₂ S and the like.

The inert gas refers to a gas having no reactivity, and examples thereof include helium, argon, and nitrogen. A non-oxidizing gas refers to a gas that has reactivity but does not cause an oxidation reaction, and includes a reducing gas such as carbon monoxide. Among these, an inert gas is preferable.

When the atmospheric pressure (P2) is less than 0.1 MPa, it is difficult to control the escape of sulfur element from the raw material powder, and the infrared transmittance of the resulting inorganic material may be reduced. The atmospheric pressure (P2) is more preferably 0.3 MPa or more, and further preferably 0.4 MPa or more. In addition, although it does not restrict | limit especially as an upper limit of this atmospheric pressure (P2), For example, it can be 1 MPa.

Hot compression molding time (atmospheric pressure is set to 0.1 MPa or more (preferably 0.3 MPa or more, more preferably 0.4 MPa or more) by one or both of inert gas and non-oxidizing gas), and by hot press The time during which the heating and pressing state is maintained is preferably 6 hours or more and 30 hours or less, more preferably 12 hours or more, and further preferably 18 hours or more. When this time is less than 6 hours, sufficient shaping | molding is not performed and there exists a possibility that the infrared transmittance and intensity | strength of the inorganic material obtained may fall. On the other hand, when it exceeds 30 hours, it takes time and is inefficient.

(4) Fourth step The molded product obtained by hot compression molding in the third step is usually cooled to room temperature, then taken out from the heat-resistant mold for hot pressing, and subjected to processing such as grinding and polishing. Thus, the inorganic material for optical elements which concerns on 1st embodiment can be obtained.

The present invention is not limited to the above-described embodiment, and the configuration thereof can be changed without changing the gist of the present invention.

Hereinafter, the contents of the present invention will be described more specifically with reference to examples and comparative examples. In addition, this invention is not limited to a following example.

[Example 1]
200 g of zinc sulfide cubic crystal particle powder having a purity of 99.5% and an average particle size of 4.2 μm was filled in a graphite heat resistant mold for hot press having an inner diameter of 100 mm, and the pressure was reduced until the atmospheric pressure became 0.1 Pa or less. Next, the mold was heated to 800 ° C. at a rate of 10 ° C./min and held for 2 hours (first step). Next, while maintaining the atmospheric pressure, the hot press was pressurized to 65 MPa at a rate of 3.25 MPa / min while raising the temperature to 1000 ° C. at a rate of 5 ° C./min (second step). Thereafter, Ar gas was fed until the atmospheric pressure became 0.5 MPa (gauge pressure) while maintaining the heating and pressing state at 1000 ° C. and 65 MPa. Hot compression molding was performed by maintaining the hot press state (1000 ° C., 65 MPa) and the atmospheric pressure (0.5 MPa) for 24 hours (third step). Then, after cooling the obtained molding, it was taken out from the mold, surface-ground and polished, and an inorganic material for optical elements having a diameter of 100 mm and a thickness of 6 mm was obtained (fourth step).

(Evaluation)
Two types of optical property evaluation samples having a diameter of 30 mm, a thickness of 2 mm, and a thickness of 4 mm were cut out from the obtained inorganic material for optical elements, and 2 samples were obtained using a Fourier transform infrared spectrophotometer (FT / IR-6300, manufactured by JASCO Corporation). The light transmittance in the wavelength region of 5 μm to 14 μm was measured. FIG. 1 shows the measurement result of a sample having a thickness of 2 mm, and FIG. 2 shows the measurement result of a sample having a thickness of 4 mm.

As shown in FIG. 1, the light transmittance at a thickness of 2 mm is 34 to 43% in the 2.5 to 3 μm wavelength region, 57 to 67% in the 4 to 6 μm wavelength region, and 62 to 62 in the 7 to 12 μm wavelength region. It was 72% and 43 to 58% in the 13 to 14 μm wavelength region, and it was confirmed that the film had good translucency. Further, as shown in FIG. 2, the light transmittance at a thickness of 4 mm is 18 to 28% in the 2.5 to 3 μm wavelength region, 47 to 63% in the 4 to 6 μm wavelength region, and 51 in the 7 to 12 μm wavelength region. It was confirmed that the film had sufficient translucency at ˜70% and 25˜45% in the 13-14 μm wavelength region.

The obtained inorganic material for optical elements was subjected to elemental analysis by ICP, and the element ratio of Zn and S was calculated. S was 0.81 with respect to Zn (1: 0).

A cut surface sample piece in the thickness direction was cut out from the obtained inorganic material for optical elements, the vicinity of the center of the cut surface of the sample piece was polished by a cross section polisher, and this cut surface was observed with a field emission scanning electron microscope. A field emission scanning electron micrograph of this cut surface is shown in FIG. The observed pore diameter was in the range of 0.1 to 0.5 μm, and the average diameter was 0.3 μm. The crystal grain size was in the range of 2-10 μm, and the average crystal grain size was 6 μm. In addition, it is estimated that an amorphous substance exists in the crystal grain boundary (for example, white part) in the photograph of FIG.

The composition analysis of the portion surrounded by a square in FIG. 3 (inside the crystal) was performed by energy dispersive X-ray spectroscopy. From this analysis result, the element ratio of Zn and S was 0.92 for Zn (1: 0). Further, it was confirmed by an X-ray diffractometer that the crystal structure was cubic.

The three-point bending strength of the obtained inorganic material for optical elements was measured based on JIS R1601 (room temperature bending strength test method for fine ceramics). The measured 3-point bending strength was 110 MPa. A field emission scanning electron micrograph of the sample fracture surface after the bending strength test is shown in FIG. It can be seen that intergranular fracture and intragranular fracture occur together.

[Example 2]
An inorganic material for an optical element was obtained by the same production method as in Example 1, except that the holding time in the first step was 1 hour and the holding time (hot compression molding time) in the third step was 15 hours.

An optical property sample having a thickness of 4 mm was prepared, and the light transmittance in the wavelength region of 2.5 μm to 14 μm was measured in the same manner as in Example 1. The measurement results are shown in FIG.
The light transmittance is 1 to 2% in the 2.5 to 3 μm wavelength region, 13 to 41% in the 4 to 6 μm wavelength region, 45 to 62% in the 7 to 12 μm wavelength region, and 24 to 43% in the 13 to 14 μm wavelength region. It was confirmed that it has sufficient translucency.

[Example 3]
The holding time in the first step is 1 hour, the heating temperature in the second step and the holding temperature in the third step are 950 ° C., the holding time in the third step (hot compression molding time) is 6 hours, and the atmospheric pressure by Ar gas An inorganic material for optical elements was obtained by the same production method as in Example 1 except that the pressure was changed to 0.3 MPa (gauge pressure).

An optical property sample having a thickness of 4 mm was prepared, and the light transmittance in the wavelength region of 2.5 μm to 14 μm was measured in the same manner as in Example 1. The measurement results are shown in FIG.
The light transmittance is 0% in the 2.5-3 μm wavelength region, 0-6% in the 4-6 μm wavelength region, 0-21% in the 7-12 μm wavelength region, 10-18% in the 13-14 μm wavelength region, It was confirmed to have translucency.

[Example 4]
An inorganic material for optical elements was obtained by the same production method as in Example 1, except that the holding time in the first step was 1 hour and the holding time (hot compression molding time) in the third step was 6 hours.

An optical property sample having a thickness of 4 mm was prepared, and the light transmittance in the wavelength region of 2.5 μm to 14 μm was measured in the same manner as in Example 1. The measurement results are shown in FIG.
The light transmittance is 1 to 3% in the 2.5 to 3 μm wavelength region, 15 to 42% in the 4 to 6 μm wavelength region, 43 to 62% in the 7 to 12 μm wavelength region, and 23 to 44% in the 13 to 14 μm wavelength region. It was confirmed that it has translucency.

[Example 5]
The holding time in the first step is 1 hour, the heating temperature in the second step and the holding temperature in the third step are 1050 ° C., the holding time in the third step (hot compression molding time) is 6 hours, and the atmospheric pressure by Ar gas An inorganic material for optical elements was obtained by the same production method as in Example 1 except that the pressure was changed to 0.3 MPa (gauge pressure).

An optical property sample having a thickness of 4 mm was prepared, and the light transmittance in the wavelength region of 2.5 μm to 14 μm was measured in the same manner as in Example 1. The measurement results are shown in FIG.
The light transmittance is 0% in the 2.5-3 μm wavelength region, 0-2% in the 4-6 μm wavelength region, 0-22% in the 7-12 μm wavelength region, 14-23% in the 13-14 μm wavelength region, It was confirmed to have translucency.

[Comparative Example 1]
The temperature rise in the first step is up to 500 ° C., the holding time is 1 hour, the heating temperature in the second step and the holding temperature in the third step are 800 ° C., and the holding time in the third step (hot compression molding time) is 6 An inorganic material for optical elements was obtained by the same production method as in Example 1 except that the atmospheric pressure by Ar gas was 0.3 MPa (gauge pressure). A sample for evaluating optical characteristics was prepared in the same manner as in Example 1, and the maximum light transmittance in the 7 to 12 μm wavelength region was measured and found to be 1%.

The inorganic material for an optical element according to the present invention can be suitably used as a material for a window material or a lens of an apparatus using infrared rays such as an infrared sensor, an infrared image processing apparatus, and an infrared laser.

The present invention relates to an inorganic material for optical elements mainly composed of a compound comprising zinc and sulfur.

Since ZnS (zinc sulfide) has good infrared transmission characteristics, it is frequently used as an optical element material such as a window material or a lens of an infrared sensor, an infrared image processing apparatus, an infrared laser or the like. Single crystal ZnS has very good translucency, but is difficult to increase in size. Therefore, the development of polycrystalline ZnS is in progress. As the method for producing the polycrystalline ZnS, the CVD (Chemical Vapor Deposition) method and the HP (Hot Press) method are mainly used. However, the CVD method has a low vapor deposition rate and high production cost. .

Under such circumstances, as a method for producing ZnS polycrystals using the HP method, the raw material powder has an average particle diameter of 0.1 to 5 μm and is sintered in vacuum at a temperature of 500 to 850 ° C. (Patent Document) 1), using a fine high-purity powder having a particle size of 5 μm or less as a raw material powder, and performing hot compression molding in vacuum under conditions of a temperature of 800 to 1050 ° C. and a pressure of 0.8 to 1.4 ton / cm ^2. (Refer to Patent Document 2), powder having an average particle diameter of 1 to 2 μm and a purity of 98% or more, and hot in a non-oxidizing atmosphere at a temperature of 900 to 1000 ° C. under a pressure of 150 to 800 kg / cm ^2. A compression molding method (see Patent Document 3) has been proposed. According to these methods, a ZnS polycrystal having a high infrared transmittance is obtained, but development of a material having a higher infrared transmittance is required as an optical element material for an apparatus using infrared rays. ing.

JP 2008-127236 A JP-A 61-205659 JP-A-11-295501

The present invention has been made in view of such circumstances, and an object thereof is to provide an inorganic material for optical elements having high infrared transmittance.

Conventionally, when manufacturing a ZnS polycrystal for an optical element by a hot press method, it is said that by performing hot compression molding in a vacuum state, SOx remaining in the raw material is removed and the light transmittance is increased. (See Patent Document 1). However, the inventors have performed hot compression molding at a high temperature and in a high vacuum state in this manner, causing escape of Zn element and S element due to sublimation or decomposition of ZnS itself, which is a cause of lowering light transmittance. I found out that This escape is caused by a difference in boiling point of the single substance, so that S is larger than Zn. Therefore, the decrease of S (sulfur element) is remarkable with respect to Zn (zinc element). Thus, the inventors have found that the light transmittance of the obtained inorganic material can be increased by suppressing the relative decrease of the elemental sulfur in the production process from these findings, and have reached the present invention.

That is, the inorganic material for optical elements according to the present invention that meets the above object is an inorganic material for optical elements mainly composed of a compound consisting of zinc and sulfur, and the element ratio of sulfur to zinc (S / Zn) is 0.80. It is 0.95 or less, and includes, as the compound, a cubic polycrystalline body represented by ZnS _1-x (0 <x ≦ 0.2), and an average crystal grain size of the cubic polycrystalline body 0.5 μm or more and 20 μm or less, and the maximum light transmittance at a thickness of 2 mm is 34% or more and 45% or less in the 2.5 to 3 μm wavelength region, and 57% or more and 70% or less in the 4 to 6 μm wavelength region, 7 It is 62% or more and 75% or less in the ˜12 μm wavelength region, and 43% or more and 60% or less in the 13-14 μm wavelength region .

According to the inorganic material for optical elements according to the present invention, by setting the element ratio of sulfur to zinc (element ratio in the entire inorganic material for optical elements) within the above range, high infrared transmittance can be exhibited.

Inorganic materials for an optical element according to the present invention, by including a cubic polycrystal composed of such composition and crystal grain size, it is possible to further increase the infrared transparent.

In the inorganic material for an optical element according to the present invention, it is preferable that the compound further includes an amorphous body interposed between crystals of the cubic polycrystal. By interposing such an amorphous body, the infrared transmittance can be further increased, and the strength and the like can be increased.

Inorganic materials for an optical element according to the present invention, the maximum light transmittance at a thickness of 2mm is 75% or less 62% or more 7~12μm wavelength region, 45% or less 34% or more 2.5~3μm wavelength region, 4 to 6 [mu] m 70% 57% or more in the wavelength region below state, and are 60% or less 43% or more in 13~14μm wavelength region and having such a high light transmittance, it is possible to increase the utility value.

The inorganic material for optical elements according to the present invention contains pores, and the average diameter of the pores is preferably 0.1 μm or more and 0.5 μm or less. Thus, infrared transmittance etc. can be further improved by making the average diameter of a pore into the said range.

In the inorganic material for optical elements according to the present invention, the three-point bending strength is preferably 80 MPa or more and 180 MPa or less. By having such a high three-point bending strength, the inorganic material for optical elements according to the first invention can exhibit high durability and the like.

The inorganic material for optical elements according to the present invention is a hot compression molding of zinc sulfide cubic crystal particle powder under an atmospheric pressure of 0.1 MPa or more by one or both of an inert gas and a non-oxidizing gas. It is preferable that it is formed by. Since such an inorganic material for optical elements can be obtained from a general zinc sulfide cubic crystal particle powder, it is excellent in productivity.

The inorganic material for optical elements according to the present invention has high infrared transmittance.

4 is a graph showing the light transmittance of the inorganic material for optical elements having a thickness of 2 mm obtained in Example 1. 4 is a graph showing the light transmittance of the inorganic material for optical elements having a thickness of 4 mm obtained in Example 1. FIG. 2 is a field emission scanning electron micrograph of a cut surface of an inorganic material for optical elements obtained in Example 1. FIG. 2 is a field emission scanning electron micrograph of a fracture surface of an inorganic material for optical elements obtained in Example 1. FIG. 6 is a graph showing the light transmittance of the inorganic material for optical elements having a thickness of 4 mm obtained in Reference Example 1 . 6 is a graph showing the light transmittance of an inorganic material for optical elements having a thickness of 4 mm obtained in Reference Example 2 . 6 is a graph showing the light transmittance of an inorganic material for optical elements having a thickness of 4 mm obtained in Reference Example 3 . 10 is a graph showing the light transmittance of an inorganic material for optical elements having a thickness of 4 mm obtained in Reference Example 4 .

Next, an embodiment embodying the present invention will be described.

<Inorganic materials for optical elements>
The inorganic material for optical elements according to the first embodiment of the present invention is mainly composed of a compound consisting of zinc and sulfur. Here, the “compound composed of zinc and sulfur” refers to a compound represented by ZnS _y (y is an arbitrary positive number), and is not limited to so-called zinc sulfide represented by ZnS. Further, “mainly composed of this compound” means that this compound occupies the largest mass with respect to the entire inorganic material for optical elements, specifically, 80% by mass or more is preferable, and 90% by mass. The above is more preferable, and 99 mass% or more is still more preferable.

The element ratio (S / Zn) of sulfur to zinc in the inorganic material for an optical element (whole) according to the present embodiment is 0.80 or more and 0.95 or less, and preferably 0.80 or more and 0.85 or less. When this ratio is less than 0.80, infrared transmittance decreases due to precipitation of Zn alone. On the other hand, it is difficult for this production ratio to exceed 0.95 in the hot press method. In addition, let the element content rate in the whole inorganic material be the value measured by the ICP analysis method.

The inorganic material for an optical element according to the present embodiment may contain other components as a simple substance or a compound as long as the effects of the present invention are not impaired, in addition to the compound composed of zinc and sulfur. Examples of other components include an oxygen element and a hydrogen element.

The compound consisting of zinc and sulfur is usually contained in the inorganic material for optical elements as a polycrystal. The crystal structure of this polycrystal is preferably cubic. The crystal structure of a compound composed of zinc and sulfur (for example, ZnS) mainly includes a cubic system and a hexagonal system, but the cubic system has higher infrared transmittance than a hexagonal system. Therefore, infrared transmission can be improved by having a cubic crystal structure. In addition, as this crystal structure, crystal structures other than cubic systems, such as a hexagonal system, may be included in part.

In this polycrystal, the composition formula (chemical formula) is preferably represented by ZnS _1-x (0 <x ≦ 0.2), and x more preferably satisfies 0 <x ≦ 0.1. Thus, infrared transmittance can be improved by setting it as the composition by which the reduction | decrease of S in a crystal | crystallization was suppressed (x value is small). The element content (rate) in the polycrystal is a value measured by energy dispersive X-ray spectroscopy.

The average crystal grain size of this polycrystal is preferably 0.5 μm or more and 20 μm or less, and more preferably 1 μm or more and 15 μm or less. When the average crystal grain size is less than 0.5 μm, the infrared transmittance decreases due to an increase in light scattering caused by the crystal grain boundary. On the other hand, when the average crystal grain size exceeds 20 μm, the mechanical strength is reduced due to the coarsening of the crystal. The average crystal grain size is a value calculated by counting the number of crystals on any five line segments (one 50 μm) using a photograph of the surface taken with an electron microscope.

The compound composed of zinc and sulfur is preferably contained in the inorganic material for optical elements as an amorphous body interposed between the crystals in addition to the above-described polycrystalline body. By interposing such an amorphous body between crystals, infrared transmittance can be further increased, and strength and the like can be increased. The reason for this is not clear, but it is presumed that the amorphous body fills the gaps between the polycrystalline bodies to increase the infrared transmittance, and the amorphous body functions as a binder to increase the strength. In addition, it is guessed that this amorphous body is a compound formed by mixing zinc element and sulfur element in an arbitrary ratio.

The inorganic material for optical elements according to the present embodiment can usually contain pores. The average diameter of the pores is preferably 0.1 μm or more and 0.5 μm or less. Setting the average diameter of the pores to less than the lower limit is difficult in production and leads to an increase in production cost. Conversely, if the average diameter of the pores exceeds the upper limit, the infrared transmittance may be reduced. The average pore diameter is a value (Ferre diameter) calculated from the pore diameter existing in an arbitrary 50 μm square area using a photograph of the surface taken with an electron microscope.

In the inorganic material for optical elements according to the present embodiment, the maximum light transmittance at a thickness of 2 mm is preferably 62% or more and 75% or less, and more preferably 65% or more in the 7 to 12 μm wavelength region. Thus, the inorganic material for optical elements which concerns on this Embodiment can exhibit the high transmittance | permeability of infrared rays (7-12 micrometers wavelength range). The light transmittance is a value measured with a Fourier transform infrared spectrophotometer (FT-IR).

In the inorganic material for optical elements according to the present embodiment, the maximum light transmittance at a thickness of 2 mm is preferably 34% or more and 45% or less, and more preferably 40% or more in the 2.5 to 3 μm wavelength region. 57 to 70% is preferable in the 4 to 6 μm wavelength region, and 60% or more is more preferable. Moreover, 43 to 60% is preferable in a 13-14 micrometer wavelength range, and 50% or more is further more preferable. According to the inorganic material for an optical element according to the present embodiment, in addition to being able to increase the transmittance in the infrared region, the transmittance can be improved in a wide wavelength region before and after that, and the range of utilization is widened. Can do.

Further, the light transmittance at a thickness of 2 mm is 34% to 45% in the 2.5 to 3 μm wavelength region, and 57% to 70% in the 4 to 6 μm wavelength region, and 62% or more in the 7 to 12 μm wavelength region. 75% or less, preferably 43% or more and 60% or less in the 13 to 14 μm wavelength region. By setting the light transmittance in each wavelength region to such a range (the minimum transmittance is equal to or higher than the lower limit of the above range), the value as an optical material can be increased.

The maximum light transmittance at a thickness of 4 mm in the optical element inorganic material according to the present embodiment is 20% to 30% in the 2.5 to 3 μm wavelength region and 55% to 70% in the 4 to 6 μm wavelength region. Hereinafter, it is preferably 60% or more and 75% or less in the 7 to 12 μm wavelength region, and 40% or more and 50% or less in the 13 to 14 μm wavelength region. The light transmittance at a thickness of 4 mm in the inorganic material for optical elements according to the present embodiment is 15% to 30% in the 2.5 to 3 μm wavelength region and 40% to 70 in the 4 to 6 μm wavelength region. % Or less, 45 to 75% in the 7 to 12 μm wavelength region, and preferably 20 to 50% in the 13 to 14 μm wavelength region. Thus, the inorganic material for optical elements according to the present embodiment has a high light transmittance even when the thickness is 4 mm, and the utility value for optical element applications is increased.

The three-point bending strength of the optical element inorganic material according to the present embodiment is preferably 80 MPa or more and 180 MPa or less, and more preferably 100 MPa or more. By having such a high three-point bending strength, the inorganic material for optical elements according to the present embodiment can exhibit high durability and the like. The three-point bending strength is a value measured in accordance with JIS R1601 (a room temperature bending strength test method for fine ceramics).

The method for producing the inorganic material for optical elements according to the present embodiment is not particularly limited, but is a hot press method using a zinc sulfide cubic crystal particle powder to be described later, particularly any one of an inert gas and a non-oxidizing gas. One or both of them can be suitably obtained by hot compression molding of zinc sulfide cubic crystal particle powder under an atmospheric pressure of 0.1 MPa or more. However, the inorganic material for optical elements obtained by other methods such as the CVD method does not depart from the present invention.

<Optical element parts>
An optical element component according to a second embodiment of the present invention includes the optical element inorganic material according to the first embodiment and an antireflection film laminated on the surface of the optical element inorganic material. .

The antireflection film is not particularly limited as long as it can reduce light reflection, and can be formed from a known material. Specific examples of the antireflection film include fluorides such as CeF ₃ and MgF ₂ and oxides such as TiO ₂ . These can be laminated on the surface of the inorganic material for optical elements by a known method such as vapor deposition or coating.

In the optical element component according to the present embodiment, the maximum light transmittance at 2 mm in thickness (transmittance when light is incident from the surface of the antireflection film) is 75% or more in the wavelength range of 7 to 12 μm. It is preferable that it is 90% or less. The optical element component according to the present embodiment can exhibit such excellent infrared transmission characteristics.

<Method for producing inorganic material for optical element>
In the method for producing an inorganic material for an optical element according to the third embodiment of the present invention, a zinc sulfide cubic crystal particle powder is filled in a heat-resistant mold for hot pressing, and the atmospheric pressure (P1) is 0.1 Pa or less. In the first step of heating and deaeration, the temperature in the heat-resistant mold for hot pressing is raised to a temperature range (t2) of 850 ° C. or higher and 1100 ° C. or lower by hot pressing while maintaining the atmospheric pressure (P1). A second step of pressurizing to a pressure range of 20 MPa or more and 70 MPa or less, and an atmospheric pressure of 0.1 MPa or more by one or both of an inert gas and a non-oxidizing gas while maintaining the temperature range (t2) and the pressure range. (P2) and has a third step of hot compression molding under the atmospheric pressure.

In the method of manufacturing an inorganic material for an optical element according to the present embodiment, during the hot compression molding in the third step, the atmospheric pressure is increased by a non-oxidizing gas or the like contrary to the conventional method, and the zinc sulfide cubic The escape of components (especially elemental sulfur) in the crystalline crystal particle powder is suppressed. By doing in this way, it is thought that the inorganic material for optical elements with a high infrared transmittance can be obtained by suppressing the fall of S content rate in the polycrystal body and by extension, the inorganic material for optical elements obtained. Hereinafter, each step will be described in detail.

(1) First Step In this step, first, zinc sulfide cubic crystal particle powder is filled in a heat-resistant mold for hot pressing, and the crystal particle powder is heated and deaerated under an atmospheric pressure (P1) of 0.1 Pa or less. .

As the zinc sulfide cubic crystal particle powder, a known powder can be used. The purity of the crystal particle powder is preferably 97% or more, and more preferably 98% or more. If a material with a purity of less than 97% is used, the amount of impurities in the resulting inorganic material for optical elements may increase, and the infrared transparency may decrease.

The element ratio of sulfur to zinc (S / Zn) in the zinc sulfide cubic crystal particle powder is preferably 0.99 or more and 1.01 or less, and more preferably 1. If this element ratio is out of the above range, the infrared transmittance and the like of the obtained inorganic material for optical elements may be lowered.

The average particle diameter of the zinc sulfide cubic crystal particle powder is preferably 10 μm or less, and more preferably 8 μm or less. When the average particle diameter of the crystal particle powder exceeds 10 μm, the infrared transmittance and the like of the obtained inorganic material for optical elements tend to be lowered. The lower limit of the average particle diameter is not particularly limited, but can be 0.1 μm, for example. The average particle diameter is a value measured by a laser diffraction method.

The heat-resistant mold for hot pressing is not particularly limited as long as it can withstand the heat and pressure during hot pressing, and for example, a mold made of a known material such as graphite or C / C composite can be used.

Specifically, the heat deaeration in the first step is performed by reducing the atmospheric pressure to an atmospheric pressure (P1) of 0.1 Pa or less, and then maintaining the atmospheric pressure (P1) to increase the temperature from room temperature to 400 ° C. to 850 ° C. The temperature is raised at a rate of 3 to 20 ° C./min to a temperature range of less than (t1), and then the temperature range (t1: 400 ° C. to less than 850 ° C.) is 1 hour to 4 hours (more preferably 1.5 hours). More preferably, it is preferably carried out by maintaining for 2 hours or more. When the atmospheric pressure (P1) exceeds 0.1 Pa, deaeration is insufficient. In addition, although it does not specifically limit as a minimum of this atmospheric pressure (P1), For example, it can set to 10 ^<-4> Pa. When the lower limit of the temperature range (t1) is less than 400 ° C., the deaeration becomes insufficient, and bumping is likely to occur in the next step. When the upper limit is 850 ° C. or more, the deaeration is not sufficiently performed. Since sintering can proceed in this state, it is not preferable. The temperature range (t1) is more preferably 600 ° C. or higher and 820 ° C. or lower. Further, when the rate of temperature increase is less than 3 ° C./min, it takes time to increase the temperature and is inefficient, and when it exceeds 20 ° C./min, bumping is likely to occur. Further, when the holding time of the temperature range (t1) is less than 1 hour, there is a possibility that the deaeration is not sufficiently performed, and when it exceeds 4 hours, it becomes inefficient.

(2) Second step In this step, the filler in the heat-resistant mold for hot pressing is heated and pressurized by hot pressing while maintaining the atmospheric pressure (P1: 0.1 Pa or less). The pressurization at this time may be uniaxial pressurization or isotropic pressurization (HIP) using gas or the like.

The temperature increase in the second step is performed from the temperature range (t1) of the first step to a temperature range (t2) of 850 ° C. to 1100 ° C., and the pressurization is performed to a pressure range of 20 MPa to 70 MPa. When the lower limit of the temperature range (t2) in the second step is less than 850 ° C., sufficient crystal grain growth is difficult to proceed, and when the upper limit exceeds 1100 ° C., the phase transition to the hexagonal system proceeds. There is a possibility that the infrared transmittance is lowered or the grain growth is excessively advanced and the strength is lowered. The temperature range (t2) is more preferably 950 ° C. or higher and 1050 ° C. or lower, and further preferably 970 ° C. or higher and 1030 ° C. or lower. In addition, when the lower limit of the pressure range is less than 20 MPa, sufficient reaction (crystal grain growth, etc.) does not proceed and it is difficult to obtain an inorganic material having high infrared transparency, and when the upper limit exceeds 70 MPa, the pressure resistance of the heat resistant mold It is not preferable in terms of performance.

The temperature rise is preferably performed at a rate of 2 to 10 ° C./min, and the pressurization is performed at a rate of 2.5 to 5.0 MPa / min. When the rate of temperature increase is less than 2 ° C./min, it takes time and is inefficient, and when it exceeds 10 ° C./min, bumping is likely to occur. When the pressurization rate is less than 2.5 MPa / min, it takes time and is inefficient, and when it exceeds 5.0 MPa, there is a possibility that cracks or the like may occur due to sudden pressurization.

(3) Third step In this step, either or both of an inert gas and a non-oxidizing gas while maintaining the temperature range (t2) and pressure range after the temperature is raised and pressurized in the second step. Thus, the atmospheric pressure is set to an atmospheric pressure (P2) of 0.1 MPa or more, and hot compression molding is performed under the atmospheric pressure (P2). This hot compression molding is performed while controlling the escape of elemental sulfur from the zinc sulfide cubic crystal particle powder by adjusting the atmospheric pressure (P2) with one or both of an inert gas and a non-oxidizing gas. It is preferable. By doing in this way, the escape of the sulfur element from raw material powder is suppressed, and the inorganic material for optical elements with high infrared transmittance can be obtained. This escape occurs, for example, in the form of release of compounds such as SOx (x is usually 0.5 to 3.0), H ₂ S and the like.

The inert gas refers to a gas having no reactivity, and examples thereof include helium, argon, and nitrogen. A non-oxidizing gas refers to a gas that has reactivity but does not cause an oxidation reaction, and includes a reducing gas such as carbon monoxide. Among these, an inert gas is preferable.

When the atmospheric pressure (P2) is less than 0.1 MPa, it is difficult to control the escape of sulfur element from the raw material powder, and the infrared transmittance of the resulting inorganic material may be reduced. The atmospheric pressure (P2) is more preferably 0.3 MPa or more, and further preferably 0.4 MPa or more. In addition, although it does not restrict | limit especially as an upper limit of this atmospheric pressure (P2), For example, it can be 1 MPa.

Hot compression molding time (atmospheric pressure is set to 0.1 MPa or more (preferably 0.3 MPa or more, more preferably 0.4 MPa or more) by one or both of inert gas and non-oxidizing gas), and by hot press The time during which the heating and pressing state is maintained is preferably 6 hours or more and 30 hours or less, more preferably 12 hours or more, and further preferably 18 hours or more. When this time is less than 6 hours, sufficient shaping | molding is not performed and there exists a possibility that the infrared transmittance and intensity | strength of the inorganic material obtained may fall. On the other hand, when it exceeds 30 hours, it takes time and is inefficient.

(4) Fourth step The molded product obtained by hot compression molding in the third step is usually cooled to room temperature, then taken out from the heat-resistant mold for hot pressing, and subjected to processing such as grinding and polishing. Thus, the inorganic material for optical elements which concerns on 1st embodiment can be obtained.

The present invention is not limited to the above-described embodiment, and the configuration thereof can be changed without changing the gist of the present invention.

Hereinafter, the contents of the present invention will be described more specifically with reference to examples and comparative examples. In addition, this invention is not limited to a following example.

[Example 1]
200 g of zinc sulfide cubic crystal particle powder having a purity of 99.5% and an average particle size of 4.2 μm was filled in a graphite heat resistant mold for hot press having an inner diameter of 100 mm, and the pressure was reduced until the atmospheric pressure became 0.1 Pa or less. Next, the mold was heated to 800 ° C. at a rate of 10 ° C./min and held for 2 hours (first step). Next, while maintaining the atmospheric pressure, the hot press was pressurized to 65 MPa at a rate of 3.25 MPa / min while raising the temperature to 1000 ° C. at a rate of 5 ° C./min (second step). Thereafter, Ar gas was fed until the atmospheric pressure became 0.5 MPa (gauge pressure) while maintaining the heating and pressing state at 1000 ° C. and 65 MPa. Hot compression molding was performed by maintaining the hot press state (1000 ° C., 65 MPa) and the atmospheric pressure (0.5 MPa) for 24 hours (third step). Then, after cooling the obtained molding, it was taken out from the mold, surface-ground and polished, and an inorganic material for optical elements having a diameter of 100 mm and a thickness of 6 mm was obtained (fourth step).

(Evaluation)
Two types of optical property evaluation samples having a diameter of 30 mm, a thickness of 2 mm, and a thickness of 4 mm were cut out from the obtained inorganic material for optical elements, and 2 samples were obtained using a Fourier transform infrared spectrophotometer (FT / IR-6300, manufactured by JASCO Corporation). The light transmittance in the wavelength region of 5 μm to 14 μm was measured. FIG. 1 shows the measurement result of a sample having a thickness of 2 mm, and FIG. 2 shows the measurement result of a sample having a thickness of 4 mm.

As shown in FIG. 1, the light transmittance at a thickness of 2 mm is 34 to 43% in the 2.5 to 3 μm wavelength region, 57 to 67% in the 4 to 6 μm wavelength region, and 62 to 62 in the 7 to 12 μm wavelength region. It was 72% and 43 to 58% in the 13 to 14 μm wavelength region, and it was confirmed that the film had good translucency. Further, as shown in FIG. 2, the light transmittance at a thickness of 4 mm is 18 to 28% in the 2.5 to 3 μm wavelength region, 47 to 63% in the 4 to 6 μm wavelength region, and 51 in the 7 to 12 μm wavelength region. It was confirmed that the film had sufficient translucency at ˜70% and 25˜45% in the 13-14 μm wavelength region.

The obtained inorganic material for optical elements was subjected to elemental analysis by ICP, and the element ratio of Zn and S was calculated. For Zn (1. 00), S was 0.81.

A cut surface sample piece in the thickness direction was cut out from the obtained inorganic material for optical elements, the vicinity of the center of the cut surface of the sample piece was polished by a cross section polisher, and this cut surface was observed with a field emission scanning electron microscope. A field emission scanning electron micrograph of this cut surface is shown in FIG. The observed pore diameter was in the range of 0.1 to 0.5 μm, and the average diameter was 0.3 μm. The crystal grain size was in the range of 2-10 μm, and the average crystal grain size was 6 μm. In addition, it is estimated that an amorphous substance exists in the crystal grain boundary (for example, white part) in the photograph of FIG.

The composition analysis of the portion surrounded by a square in FIG. 3 (inside the crystal) was performed by energy dispersive X-ray spectroscopy. Element ratio from this analysis, Zn and S, compared Zn (1. 00), S is 0.92. Further, it was confirmed by an X-ray diffractometer that the crystal structure was cubic.

The three-point bending strength of the obtained inorganic material for optical elements was measured based on JIS R1601 (room temperature bending strength test method for fine ceramics). The measured 3-point bending strength was 110 MPa. A field emission scanning electron micrograph of the sample fracture surface after the bending strength test is shown in FIG. It can be seen that intergranular fracture and intragranular fracture occur together.

[ Reference Example 1 ]
An inorganic material for an optical element was obtained by the same production method as in Example 1, except that the holding time in the first step was 1 hour and the holding time (hot compression molding time) in the third step was 15 hours.

An optical property sample having a thickness of 4 mm was prepared, and the light transmittance in the wavelength region of 2.5 μm to 14 μm was measured in the same manner as in Example 1. The measurement results are shown in FIG.
The light transmittance is 1 to 2% in the 2.5 to 3 μm wavelength region, 13 to 41% in the 4 to 6 μm wavelength region, 45 to 62% in the 7 to 12 μm wavelength region, and 24 to 43% in the 13 to 14 μm wavelength region. It was confirmed that it has sufficient translucency.

[ Reference Example 2 ]
The holding time in the first step is 1 hour, the heating temperature in the second step and the holding temperature in the third step are 950 ° C., the holding time in the third step (hot compression molding time) is 6 hours, and the atmospheric pressure by Ar gas An inorganic material for optical elements was obtained by the same production method as in Example 1 except that the pressure was changed to 0.3 MPa (gauge pressure).

An optical property sample having a thickness of 4 mm was prepared, and the light transmittance in the wavelength region of 2.5 μm to 14 μm was measured in the same manner as in Example 1. The measurement results are shown in FIG.
The light transmittance is 0% in the 2.5-3 μm wavelength region, 0-6% in the 4-6 μm wavelength region, 0-21% in the 7-12 μm wavelength region, 10-18% in the 13-14 μm wavelength region, It was confirmed to have translucency.

[ Reference Example 3 ]
An inorganic material for optical elements was obtained by the same production method as in Example 1, except that the holding time in the first step was 1 hour and the holding time (hot compression molding time) in the third step was 6 hours.

An optical property sample having a thickness of 4 mm was prepared, and the light transmittance in the wavelength region of 2.5 μm to 14 μm was measured in the same manner as in Example 1. The measurement results are shown in FIG.
The light transmittance is 1 to 3% in the 2.5 to 3 μm wavelength region, 15 to 42% in the 4 to 6 μm wavelength region, 43 to 62% in the 7 to 12 μm wavelength region, and 23 to 44% in the 13 to 14 μm wavelength region. It was confirmed that it has translucency.

[ Reference Example 4 ]
The holding time in the first step is 1 hour, the heating temperature in the second step and the holding temperature in the third step are 1050 ° C., the holding time in the third step (hot compression molding time) is 6 hours, and the atmospheric pressure by Ar gas An inorganic material for optical elements was obtained by the same production method as in Example 1 except that the pressure was changed to 0.3 MPa (gauge pressure).

An optical property sample having a thickness of 4 mm was prepared, and the light transmittance in the wavelength region of 2.5 μm to 14 μm was measured in the same manner as in Example 1. The measurement results are shown in FIG.
The light transmittance is 0% in the 2.5-3 μm wavelength region, 0-2% in the 4-6 μm wavelength region, 0-22% in the 7-12 μm wavelength region, 14-23% in the 13-14 μm wavelength region, It was confirmed to have translucency.

[Comparative Example 1]
The temperature rise in the first step is up to 500 ° C., the holding time is 1 hour, the heating temperature in the second step and the holding temperature in the third step are 800 ° C., and the holding time in the third step (hot compression molding time) is 6 An inorganic material for optical elements was obtained by the same production method as in Example 1 except that the atmospheric pressure by Ar gas was 0.3 MPa (gauge pressure). A sample for evaluating optical characteristics was prepared in the same manner as in Example 1, and the maximum light transmittance in the 7 to 12 μm wavelength region was measured and found to be 1%.

The inorganic material for an optical element according to the present invention can be suitably used as a material for a window material or a lens of an apparatus using infrared rays such as an infrared sensor, an infrared image processing apparatus, and an infrared laser.

Claims (13)

In an inorganic material for optical elements mainly composed of a compound consisting of zinc and sulfur,
An inorganic material for optical elements, wherein the element ratio of sulfur to zinc (S / Zn) is 0.80 or more and 0.95 or less. In the inorganic material for optical elements according to claim 1,
The compound includes a cubic polycrystal represented by ZnS _1-x (0 <x ≦ 0.2), and the average crystal grain size of the cubic polycrystal is 0.5 μm or more and 20 μm or less. An inorganic material for optical elements. In the inorganic material for optical elements according to claim 2,
An inorganic material for optical elements, further comprising an amorphous body interposed between crystals of the cubic polycrystal as the compound. In the inorganic material for optical elements according to any one of claims 1 to 3,
An inorganic material for an optical element, wherein the maximum light transmittance at a thickness of 2 mm is 62% or more and 75% or less in a wavelength range of 7 to 12 μm. In the inorganic material for optical elements according to any one of claims 1 to 4,
Maximum light transmittance at a thickness of 2 mm is 34% to 45% in the 2.5 to 3 μm wavelength region, and 57% to 70% in the 4 to 6 μm wavelength region, and 43% to 60% in the 13 to 14 μm wavelength region. An inorganic material for optical elements, characterized by: In the inorganic material for optical elements according to any one of claims 1 to 5,
An inorganic material for optical elements, comprising pores, wherein the pores have an average diameter of 0.1 μm to 0.5 μm. In the inorganic material for optical elements according to any one of claims 1 to 6,
An inorganic material for optical elements, having a three-point bending strength of 80 MPa or more and 180 MPa or less. In the inorganic material for optical elements according to any one of claims 1 to 7,
It is formed by hot compression molding of zinc sulfide cubic crystal particle powder under an atmospheric pressure of 0.1 MPa or more by one or both of an inert gas and a non-oxidizing gas. Inorganic materials for devices. The inorganic material for optical elements according to any one of claims 1 to 8,
An antireflection film laminated on the surface of the inorganic material for optical elements,
A component for an optical element, wherein the maximum light transmittance at a thickness of 2 mm is 75% or more and 90% or less in a wavelength range of 7 to 12 μm. A first step of filling a zinc sulfide cubic crystal particle powder in a heat-resistant mold for hot pressing and heating and degassing under an atmospheric pressure (P1) of 0.1 Pa or less,
While maintaining the atmospheric pressure (P1), the filling in the heat-resistant mold for hot pressing is heated to a temperature range (t2) of 850 ° C. or higher and 1100 ° C. or lower by hot pressing to a pressure range of 20 MPa or higher and 70 MPa or lower. The atmospheric pressure (P2) of 0.1 MPa or more by one or both of the inert gas and the non-oxidizing gas while maintaining the temperature range (t2) and the pressure range. (P2) A method for producing an inorganic material for optical elements, comprising a third step of performing hot compression molding under (P2). In the manufacturing method of the inorganic material for optical elements of Claim 10,
The zinc sulfide cubic crystal particle powder has a purity of 97% or more, an element ratio of sulfur to zinc (S / Zn) of 0.99 to 1.01, and an average particle diameter of 10 μm or less. A method for producing an inorganic material for optical elements. In the manufacturing method of the inorganic material for optical elements of Claim 10 or 11,
In the first step, heat deaeration is performed at a rate of 3 to 20 ° C./minute from room temperature to a temperature range (t1) of 400 ° C. or more and less than 850 ° C., and then the temperature range (t1) is set for 1 to 4 hours. Done by keeping,
The second step is performed at a rate of 2 to 10 ° C./min and pressurization is performed at a rate of 2.5 to 5.0 MPa / min,
The method for producing an inorganic material for an optical element, wherein the hot compression molding in the third step is performed for 6 hours to 30 hours. In the manufacturing method of the inorganic material for optical elements of any one of Claims 10-12,
Inorganic for optical elements, wherein the hot compression molding in the third step is performed while controlling escape of sulfur element from the zinc sulfide cubic crystal particle powder by adjusting the atmospheric pressure (P2) Material manufacturing method.