JP2902268B2 - Moisture-proof optical material and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical material having an infrared transmitting or reflecting property and an excellent moisture-proof property, and a method for producing the same.

[0002]

2. Description of the Related Art Among conventional optical materials for measuring infrared rays, those which transmit infrared rays in a long wavelength range (400 cm ^{-1 to} 200 cm ^-1 ) include KBr, NaCl, CsI, KRS-5, KRS-6 and the like. There is. However, these optical materials, especially KBr, NaCl, CsI
Since deliquescence is extremely strong, it dissolves and the transmittance decreases over time, so it cannot be used in practice. For example,
The same applies to nonlinear optical materials such as LBO, DLAP, BBO, and KTP. In order to avoid such a problem, attempts have been made to provide a moisture-proof property by providing a coating of a fluorine resin or the like on the surface of an optical material such as KBr. However, this method is very complicated, and a satisfactory moisture-proof film cannot be obtained. Normally, the fluorine-based resin is very porous (a gap is opened so that water molecules can easily pass therethrough, that is, has a rough molecular structure) compared to the size of water molecules, so that the moisture permeability is large. (Moisture permeability: 1.
1 g / m ² × 24 hr). Therefore, when trying to impart moisture resistance using a fluororesin, the coating film thickness is, for example, 1.
Unless the thickness is about 0 μm, a satisfactory moisture-proof effect cannot be obtained. However, when the thickness of the fluorine resin moisture-proof film is increased, the infrared transmittance of the optical material is reduced by several tens% due to the infrared absorption based on the carbon-fluorine chemical bond near 1180 cm ^-1 , and the infrared transmission optical property is reduced. It cannot be used as a system optical material. Further, as a method of forming a fluorine-based resin, a vacuum deposition method (Japanese Patent Application Laid-Open No. 3-104857) and a plasma polymerization method (Japanese Patent Application Laid-Open No. 50-62652) have been proposed, but all are expensive and large-scale. In addition to the necessity of an apparatus, the formed film may be decomposed to generate hydrogen fluoride gas and corrode the apparatus. In addition, infrared reflective optical materials such as ZnSe, CaF ₂ (fluorite), SiO ₂ (quartz), Al ₂ O ₃ (sapphire), and glass are used for the substrate as the resonator mirror of the laser device. Water molecules adsorbed on these substrates absorb infrared rays in the 2.7 to 3.2 μm region, and the deposited film deposited on these substrates or the boundary between the substrates and the deposited films is heated, and the heat As a result, there is a problem that the substrate itself is destroyed.

[0003]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the above-mentioned problems and to provide an infrared optical material having excellent moisture-proof properties, which can be manufactured without requiring an expensive and large-scale apparatus, and a method for manufacturing the same. It is to provide.

[0004]

SUMMARY OF THE INVENTION The present invention provides a moisture-proof optical material obtained by applying a moisture-proof layer containing a vinylidene chloride copolymer having a crystalline region to an infrared optical material. In the present invention, a vinylidene chloride-based copolymer having a crystalline region is dispersed and dissolved in a tetrahydrofuran-containing mixed solvent, and the resulting solution is applied to an infrared optical material. An object of the present invention is to provide a method for producing a moisture-proof optical material in which a vinylidene-based copolymer film is formed by applying a vinylidene chloride-based copolymer-containing moisture-proof layer having a crystalline region to an infrared optical material, characterized by forming a vinylidene-based copolymer film.

The vinylidene chloride-based copolymer has a crystal structure, and its molecular spacing is very narrow, so that the penetration of water molecules can be blocked. By applying the composition to the surface of the optical material, an optical material having stable optical characteristics with respect to a change in humidity over time can be manufactured.

Hereinafter, the present invention will be described in detail. Examples of the infrared optical material used in the present invention include, but are not limited to, KBr,
NaCl, KCl, CsI, KRS-5, KRS-6, LBO, DLAP, BBO and
KTP can be mentioned, and ZnSe, CaF ₂ (fluorite), SiO ₂ (quartz), Al ₂ O ₃
(Sapphire) and glass. The vinylidene chloride-based copolymer used in the present invention is a copolymer of vinylidene chloride and a monomer copolymerizable therewith, for example, vinyl chloride, acrylate, acrylonitrile, etc. , 60: 40-7
0:30 is appropriate. Such a copolymer is commercially available, and examples thereof include Saran latex (manufactured by Asahi Kasei Corporation and Kureha Chemical Co., Ltd.).

In the present invention, the moisture-proof layer containing the crystalline vinylidene chloride copolymer preferably contains 70% by weight or more of the vinylidene chloride copolymer. The moisture-proof layer of the present invention,
Disperse the vinylidene chloride-based copolymer in an appropriate solvent to dissolve the amorphous region (and part of the crystalline region), and apply a liquid in which most of the crystalline region is in an undissolved state to the infrared optical material. Then, while heating, if necessary, the mixed solvent is evaporated to form a film. In this process, a vinylidene chloride-based copolymer film having a crystalline region existing in an undissolved state and a crystalline region formed by crystallization of a part of the dissolved vinylidene chloride-based copolymer is formed. Is done. Here, the “suitable solvent” refers to a solvent in which, when the vinylidene chloride-based copolymer is dispersed, its amorphous region is dissolved but its crystalline region is not substantially dissolved. Specifically, it is a solvent containing tetrahydrofuran, and more specifically, a mixed solvent composed of 10 to 90% by weight of tetrahydrofuran and 90 to 10% by weight of a diluting solvent. The diluting solvent may be any solvent that has little solubility of the vinylidene chloride copolymer and is well mixed with tetrahydrofuran, and examples thereof include ethyl acetate, toluene, dioxane, benzene, xylene, and a mixed solvent thereof. If the content of tetrahydrofuran in the mixed solvent is lower than 10% by weight, the solubility of the amorphous region of the vinylidene chloride copolymer is not sufficient, and
If it is higher than 0% by weight, the crystalline region of the vinylidene chloride copolymer is also dissolved, which is not preferable.

[0007] The crystalline region of the vinylidene chloride copolymer is
Semi-quantification by comparing the area intensity (A) of the infrared absorption peak (1040 cm ^-1 ) of carbon-chlorine with the area intensity (B) of the infrared absorption peak (1070 cm ^-1 ) specific to the crystal structure. Can be. That is, although A is constant, B varies according to the ratio of the crystal region, so that B / A
The ratio of the crystal region can be known from the value of. At this time, the area intensity of the infrared absorption peak (1070 cm ^-1 ) specific to the crystal structure of the vinylidene chloride homopolymer is defined as a crystallinity of 100%. The crystallinity of the powdery vinylidene chloride-based copolymer (mass of the crystal part with respect to the mass of the whole sample) thus obtained is 70 to 90% by weight, and is dissolved in an appropriate mixed solvent of the present invention. Next, the crystallinity of the coated vinylidene chloride-based copolymer formed by evaporating the solvent is 40 times that of the original vinylidene chloride-based copolymer.
６０60% by weight. The concentration of the vinylidene chloride copolymer in the coating solution is suitably from 1 to 30% by weight. When the coating is performed by dipping, the dipping may be performed at room temperature, and the dipping time is not particularly limited, but 1 to 10 seconds is sufficient. The speed of pulling the infrared optical material from the immersion liquid is 1 to 100 mm / m
in is appropriate. By adjusting the concentration of the vinylidene chloride copolymer in the immersion liquid and the pulling rate, the thickness of the moisture-proof film can be arbitrarily adjusted. In order to obtain a sufficient moisture-proof effect, the larger the film thickness, the better.
A suitable range is from 01 to 500 μm. Next, the solvent is evaporated while heating as required. Evaporation is generally 45-6
It is preferable to carry out the treatment at 0 ° C. for 4 to 48 hours.

In addition to the above immersion method, a liquid obtained by dispersing and dissolving a vinylidene chloride-based copolymer at a predetermined concentration in the above mixed solvent is applied to the surface of the infrared optical material by a spinner method, a spray method (spraying method), and a potting method (hanging). After the coating is performed to a desired film thickness by various methods such as (method), the mixed solvent is evaporated while heating under the above-described conditions, if necessary, to form a vinylidene chloride-based copolymer crystal-containing film. Good. As described above, an infrared optical material having stable optical characteristics with respect to humidity can be obtained. In addition,
It is desirable to provide a vinylidene chloride copolymer-containing moisture-proof film on the side of the infrared optical material where infrared light does not enter, to prevent water molecules from entering from the side.

[0009]

The infrared optical material of the present invention has a moisture-proof film made of a crystalline vinylidene chloride copolymer on its surface, and thus has optical characteristics stable against humidity. Further, it can be manufactured much more simply and at low cost (no capital investment is required) without requiring an expensive and large-scale device. further,
In addition to exhibiting better moisture-proof properties and optical characteristics than those provided with a conventional fluorine-based resin moisture-proof film, it is also effective in preventing the occurrence of mold, which often occurs in optical parts.
Further, the moisture-proof film containing the vinylidene chloride-based copolymer according to the present invention has a high moisture-proof property. Therefore, a far thinner film thickness is sufficient to obtain the same effect as the fluorine-based resin moisture-proof film. Therefore, the infrared absorption of the moisture-proof film itself is small, and the transmittance of the infrared-transmitting optical material is hardly affected. This is considered to be due to the fact that the infrared absorption intensity of the carbon-chlorine bond is smaller than that of the carbon-fluorine bond.

[0010]

Example 1 6 g of a powdery vinylidene chloride-acrylate copolymer ("Saran Latex" manufactured by Asahi Kasei Corporation) was dispersed and dissolved in 100 g of a mixed solvent of tetrahydrofuran and toluene (volume ratio 9: 1). A weight percent solution was prepared. Next, a KBr plate (diameter 30 mm, thickness 3 m)
m) was immersed in this solution at 20 ° C. for 2 to 3 seconds and pulled up at a pulling rate of 50 mm / min. Next, heat treatment was performed at 70 ° C. for 3 hours to completely volatilize the solvent. The thickness (after drying) of the moisture-proof film of the vinylidene chloride copolymer formed on the KBr surface was 0.05 μm. The infrared-transmitting optical material of the present invention provided with a vinylidene chloride-based copolymer moisture-proof film has an optical thickness of 175 nm on the transmission surface through which infrared light passes after drying, and has an infrared absorption of 1040 cm ^{-1 of} carbon-chlorine bond. Appears nearby. The magnitude of this absorption was smaller than the magnitude of infrared absorption of the carbon-fluorine bond of the fluororesin, and was about 5%. In addition, the average transmittance of the infrared transmitting optical material of the present invention in the range of the use wave number of 4000 cm ^{-1 to} 400 cm ^-1 was 90% or more, and it was found that the infrared transmitting optical material was sufficient as an optical material of the transmission optical system. This is because the molecular structure is very narrow due to the crystal structure, so that the intrusion of water molecules can be blocked. The moisture transmission value of the infrared transmitting optical material of the present invention provided with the moisture proof film is as described in JP-A-3-104857.
No. of about 1/10 of an infrared transparent optical material having a moisture-proof film of the fluorine-based resin described in JP (moisture permeation amount: 0.1g / m ² × ²
4 hr). Next, the results of the humidity resistance test will be described. The KBr plate provided with the vinylidene chloride copolymer moisture-proof film of the present invention was left for 3 hours in an atmosphere at a temperature of 30 ° C. and a humidity of 60%. Change in transmittance is less than 1% at 4000 cm ^-1, an average transmittance of 4000cm ^-1 ~400cm ^-1 is 90% or more, it can be seen that the moisture-proof effect is sufficient. On the other hand, in a KBr plate provided with a fluorine-based resin moisture-proof film, the change in transmittance is 10% or more at 4000 cm ⁻¹ ,
It does not satisfy the specification that the average transmittance of 4000 cm ^{-1 to} 400 cm ^-1 must be 90% or more. Therefore, it can be seen that the infrared-transmitting optical material provided with the moisture-proof film of the present invention has a superior moisture-proof effect as compared with the conventional optical material provided with the moisture-proof film. Although KBr is used in the above embodiment,
The present invention is not limited to this, and in addition, NaCl, KCl, CsI,
It can be applied to optical materials such as KRS-5 and KRS-6 and non-linear optical materials such as LBO, DLAP, BBO, and KTP. Can be.

[0011]

Embodiment 2 As a resonator mirror of a laser device of an Er: YAG laser, ZnSe, CaF ₂ (fluorite), SiO ₂ (quartz), Al ₂ O ₃ (sapphire),
Although infrared reflective optical materials such as glass are used,
Depending on the water molecules adsorbed on these substrates, 2.7 to 3.
There is a problem in that infrared rays in a region of 2 μm are absorbed, and a deposited film deposited on these substrates or a boundary portion between the substrates and the deposited film is heated, and the heat destroys the substrate itself. In this example, the following films were vacuum-deposited on a SiO ₂ (quartz) substrate, and a vinylidene chloride-based copolymer-containing moisture-proof layer was formed on the entire deposited optical material using an immersion method.

[0012] The reflectance of the quartz substrate, which had a reflectance of 99% in infrared light having a wavelength of 2.9 μm, was measured at a temperature of 30 ° C. and a humidity of 60%.
Even after being left in an atmosphere of 3% for 3 hours, it is still 99%,
There was no change. This indicates that the moisture-proof effect can be improved without impairing the characteristics of the resonator mirror itself due to water adsorption or the like.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G02B 1/10 G02B 13/14

Claims (4)

(57) [Claims] 1. A moisture-proof optical material obtained by applying a moisture-proof layer containing a vinylidene chloride copolymer having a crystal region to an infrared optical material. 2. The infrared optical material is KBr, NaCl, KCl, Cs
The moisture-proof optical material according to claim 1, wherein the material is selected from a group of infrared-transmitting optical materials consisting of I, KRS-5, KRS-6, LBO, DLAP, BBO, and KTP. 3. An infrared optical material selected from a group of infrared reflective optical materials consisting of ZnSe, CaF ₂ (fluorite), SiO ₂ (quartz), Al ₂ O ₃ (sapphire), and glass. The moisture-proof optical material according to claim 1, wherein: 4. A vinylidene chloride-based copolymer having a crystal region is dispersed and dissolved in a tetrahydrofuran-containing mixed solvent, and the resulting solution is applied to an infrared optical material. Then, the mixed solvent is evaporated to obtain a chloride having a crystal region. A method for producing a moisture-proof optical material, comprising forming a vinylidene-based copolymer film and forming a vinylidene chloride-based copolymer-containing moisture-proof layer having a crystal region on an infrared optical material.