JP2009282488A - Paint for optical element and optical element - Google Patents

Abstract

The present invention provides a coating material for an optical element having a sufficient inner surface antireflection effect even for a substrate having a refractive index of more than 1.70.
An optical element coating material includes an epoxy resin precursor having a refractive index of 1.65 or more, a curing catalyst, and black particles.
[Selection] Figure 1

Description

  The present invention relates to a coating material for an optical element such as a lens or a prism, and an optical element provided with a film that can be formed by the coating material.

  In an optical system configured by combining optical elements such as lenses and prisms, stray light is likely to be generated due to irregular reflection or scattering at the periphery, edge, ridge, or the like of each optical element. Particularly in an imaging optical system, stray light causes image ghosting and flare, which is one of the causes of image quality degradation. Therefore, in order to suppress such deterioration of the optical performance due to stray light, black ink for ink or glass is applied to a relatively large scattered processing surface present in the periphery, edge, ridge, etc. of the optical element. There are many cases.

  Recently, a material having a refractive index of more than 1.70 has been used as a material of an optical element due to a demand for reduction in size and weight of an optical system. Proposals have been made for new paints having prevention performance.

For example, JP-A-9-258005 discloses a black paint obtained by mixing a cardanol derivative and a polyisocyanate precursor with coal tar or coal tar pitch as a light absorber, and JP-A-7-82510 discloses A black paint containing black inorganic fine particles having a particle diameter of 0.1 μm or less and a refractive index of 1.5 or more is disclosed as a light absorber.
JP-A-9-258005 JP-A-7-82510

  However, coal tar and coal tar pitch used as light absorbers may not have sufficient durability against organic solvents used in the optical element cleaning process, and may cause problems such as discoloration. Since it contains carcinogenic substances such as pyrene, it is already prohibited to sell to general consumers.

  On the other hand, the black inorganic fine particles having a particle size of 0.1 μm or less have the property that it is difficult to uniformly disperse in the coating material, and the aggregation tends to occur. In other words, the particle diameter is enlarged, and there is a problem that desired antireflection characteristics cannot be obtained.

  Accordingly, the present invention provides an optical element provided with a film having a sufficient inner surface antireflection effect even on a substrate having a refractive index of 1.70 or more, and an optical element coating material suitable for forming the film. The task is to do.

  One aspect of the optical element provided by the present invention is an optical element having a base material and a film formed on the base material, and the film is an epoxy resin cured product having a refractive index of 1.67 or more. And black particles.

  Moreover, one aspect of the coating material for optical elements provided by the present invention is characterized by containing an epoxy resin precursor having a refractive index of 1.65 or more, a curing catalyst, and black particles.

  Another aspect of the optical element provided by the present invention is an optical element having a base material and a film formed on the base material, wherein the film has an index of refraction of 1.65 or more. It is a cured product of a coating material for an optical element containing a precursor, a curing catalyst, and black particles.

  The internal reflection of the optical element is reduced by forming a film on the surface of the base material because the light that oozes from the base material into the film is absorbed inside the film, and the return light to the base material side is reduced. by. For example, in the case of the optical element shown in FIG. 2, the light 6 incident on the interface between the substrate 1 and the coating 2 at an incident angle θ oozes from the substrate 1 to the coating 2 side by a distance d under the total reflection condition. 2 is absorbed, and the return light to the substrate 1 side is reduced.

  In order to reduce the return light from the coating 2 to the substrate 1, it is necessary to increase the light absorption amount per unit optical path length of the coating 2 or to increase the light bleed distance d into the coating 2. . The oozing distance d into the film 2 is obtained from the following formula (1) from physical optics.

d = λ / [2π (sin ² θ− (n ₂ / n ₁ ) ² ) ^1/2 ] (1)
Here, λ is the wavelength of light, θ is the incident angle, n ₁ is the refractive index of the substrate 1, and n ₂ is the refractive index of the coating 2.

From formula (1), it can be seen that the refractive index n ₂ of the film 2 should be close to the refractive index n ₁ of the substrate 1 in order to increase the oozing distance d into the film 2. That is, when the refractive index of the base material 1 is high, the refractive index of the film 2 may be increased.

In addition to this, if the refractive index n ₂ of the coating 2 is brought close to the refractive index n ₁ of the substrate 1, the critical angle θ _T of total reflection given by the equation (2) can be increased. The larger the critical angle θ _{T, the} narrower the incident angle range that satisfies the total reflection condition at the interface between the substrate 1 and the coating 2.

sin θ _T = n ₂ / n ₁ (2)
Here, n ₁ is the refractive index of the substrate 1, and n ₂ is the refractive index of the coating 2.

  In general, a coating used as an inner surface antireflection coating is composed of a vehicle component that determines adhesion to a substrate, hardness, scratch resistance, and the like, and a light absorbing material. In the conventional internal antireflection film, the refractive index of the vehicle component is less than 1.65, and it is not suitable for use as an internal antireflection film for a high refractive index substrate having a refractive index of 1.70 or more. It was enough.

  In the present specification, the refractive index refers to the refractive index of the d-line (587.6 nm) wavelength at 25 ° C. unless otherwise specified.

The inventor of the present invention increases the light seepage distance d into the film by increasing the refractive index of the vehicle component, and further increases the critical angle θ _T. It was speculated that a film having a high antireflection effect on the inner surface could be obtained without using black particles having a particle diameter of 0.1 μm or less. As a result of evaluating the characteristics of various resins as a vehicle component, a coating material containing an epoxy resin precursor having a refractive index of 1.65 or more, a curing catalyst, and black particles is applied on a substrate and cured. Thus, a film containing a cured epoxy resin having a refractive index of 1.67 or more and black particles can be formed, and such a film has an excellent inner surface even for a high refractive index substrate having a refractive index of 1.70 or more. It has been found that it has an antireflection effect.
[First embodiment]
1st Embodiment of this invention has the coating film which consists of the coating material for optical elements containing the epoxy resin precursor whose refractive index is 1.65 or more, a curing catalyst, and black particles, and the hardened | cured material of this coating material. The present invention relates to an optical element.

  Examples of the epoxy resin precursor having a refractive index of 1.65 or more suitable for the optical element paint of the first embodiment include bis [4- (2,3-epoxypropylthio) phenyl] sulfide, bis [4- (2 , 3-epoxypropylthio) phenyl] disulfide, 2,5-di (2,3-epoxypropylthio) -1,4-dithiane, 5,5′-di (2,3-epoxypropyloxy) -1, Examples include 1′-binaphthalene, 5,5′-di (2,3-epoxypropyloxy) -1,1′-diylcarbodiimide. These can be used alone or as a mixture of two or more.

  Among the epoxy resin precursors, bis [4- (2,3-epoxypropylthio) phenyl] sulfide is particularly easy to handle because it has a high refractive index of 1.67 and is a low viscosity liquid at room temperature. Since there is no unpleasant smell despite containing a large amount of sulfur atoms, it is suitable as the epoxy resin precursor of the first embodiment.

  The content of the epoxy resin precursor is 15% by weight or more and 60% by weight or less, more preferably 15% by weight or more and 45% by weight or less, and further preferably 20% by weight or more and 45% by weight or less of the total amount of the coating material. If the content of the epoxy resin precursor exceeds 60% by weight, the viscosity of the coating increases and the coating workability decreases. On the other hand, when the content of the epoxy resin precursor is less than 15% by weight, the adhesion properties of the coating material to the substrate, the properties of the film such as hardness, scratch resistance and the like are lowered.

  Suitable curing catalysts for the optical element coating material of the first embodiment include aliphatic tertiary amines, N, N ′, N′-trialkyl cyclic amidines, and the like. These curing catalysts can cure the above epoxy resin precursor at room temperature or under heating, particularly at a temperature of 80 ° C. or less, and have a refractive index of 1.67 or more because the shrinkage ratio upon curing is 3 to 5%. An epoxy resin cured product can be obtained. Moreover, it can be cured in air without oxygen inhibition of the coating surface, which is often a problem with acrylic resin coatings during curing.

  Specific examples of the aliphatic tertiary amine include benzyldimethylamine, 2- (dimethylaminomethyl) phenol, 2,4,6-tris (dimethylaminomethyl) phenol, triethanolamine, N, N′-dimethyl. Piperazine, 1,4-diazabicyclo [2.2.2] octane and the like can be mentioned. Of these aliphatic tertiary amines, 2,4,6-tris (dimethylaminomethyl) phenol is a trifunctional amine, and therefore has high reaction activity and can suppress the amount added, so that it is the first embodiment. Preferred as a curing catalyst.

  Specific examples of the N, N ′, N′-trialkyl cyclic amidine include 1,5-diazabicyclo [4.3.0] non-5-ene and 1,8-diazabicyclo [5.4.0]. ] Undec-7-ene, 2-methylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole and the like. Of these N, N ′, N′-trialkyl cyclic amidines, 1,8-diazabicyclo [5.4.0] undec-7-ene was added even though it was very basic. Since the paint has a long pot life at room temperature, it is preferable as the curing catalyst of the first embodiment.

  These curing catalysts can be used alone or in admixture of two or more. The blending amount of the curing catalyst with respect to the epoxy resin precursor is 0.1 to 5 parts by weight with respect to 100 parts by weight of the total amount of the epoxy resin precursor in order to cure at an appropriate speed without deteriorating the physical properties of the film. Part or less.

  Specific examples of black particles suitable for the optical element coating material according to the first embodiment include carbon black, acetylene black, graphite, nickel, silicon carbide, silicon nitride, and titanium black. Among these, carbon black Titanium black is particularly suitable because it has a high hiding power and can be easily dispersed. In addition to these black inorganic particles, black organic particles can be used in the same manner as long as they have sufficient elution resistance to the cleaning agent used for cleaning the optical element. Typical examples of the cleaning agent used for cleaning the optical element are isopropyl alcohol, perfluorobutyl methyl ether, n-propyl bromide, and the like, and the black inorganic particles have sufficient elution resistance against these. The above black inorganic particles and black organic particles can be used alone or as a mixture of two or more.

  The blending amount of the black particles is preferably 3% by weight or more and 30% by weight or less, more preferably 5% by weight or more and 20% by weight or less, and further preferably 5% by weight or more and 15% by weight or less. When the blending amount of the black particles exceeds 30% by weight, the viscosity of the coating is increased, the coating workability is deteriorated, and the black particles are easily aggregated to deteriorate the appearance of the film. On the other hand, when the blending amount of the black particles is less than 3% by weight, the light shielding property of the film is lowered, and stray light that penetrates the film from the outside and enters the inside of the optical element becomes a problem. The particle size of the black particles is preferably 0.3 μm or more and 10 μm or less so that aggregation does not easily occur and the appearance of the film is not impaired.

  The coating material containing the above epoxy resin precursor, curing catalyst, and black particles may be diluted with a solvent or the like as necessary. The type of solvent is not particularly limited as long as it does not interfere with the curing reaction of the epoxy resin precursor. Specifically, alkylbenzenes such as toluene, ethylbenzene, o-xylene, m-xylene and p-xylene, 2-methoxy Cellosolves such as ethanol and 2-ethoxyethanol, ethers such as tetrahydrofuran, tetrahydropyran, 1,4-dioxane and dimethoxyethane, ketones such as methyl ethyl ketone and cyclopentanone, ethyl acetate, n-propyl acetate, i-acetate Mention may be made of esters such as propyl, methyl propionate and ethyl propionate, and alcohols such as isopropyl alcohol, n-butyl alcohol, i-butyl alcohol and t-butyl alcohol. These can be used alone or as a mixture of two or more.

  Furthermore, the optical element coating material according to the first embodiment may contain additives for adjusting the storage stability, coating workability, and other physical properties of the coating material as necessary. Specifically, various dispersants such as pigment dispersants and anti-coloring agents for adjusting storage stability, sagging agents for adjusting coating workability, various thixotropic agents such as anti-settling agents, Surface adjusters such as water repellents, slip agents, leveling agents, defoaming and defoaming agents for adjusting physical properties, matting agents, rust inhibitors, fungicides, crosslinking agents, adhesion improvers, etc. is there.

  The coating material prepared by blending the above components can be applied to the surface of the substrate of the optical element and cured to form a film having an inner surface antireflection effect. As a coating method at this time, a commonly used coating method using a brush, a roller, a spray, or the like can be applied.

  The material of the base material of the optical element is not particularly limited and can be applied to various optical glasses and plastics. However, the optical element coating material of the first embodiment has a refractive index of 1.70 or more. When a base material is used, a remarkable effect is exhibited.

Since the optical element coating material of the first embodiment includes an epoxy resin precursor having a refractive index of 1.65 or more, a curing catalyst, and black particles, it is applied onto the substrate of the optical element and cured. Thus, a black film made of a cured epoxy resin having a refractive index of 1.67 or more can be formed on the substrate. Since such a film has a higher refractive index than a film formed by a conventional coating for an optical element, a light oozing distance from the substrate into the film is increased, and a substrate having a refractive index of 1.70 or more is used. Even if it is, the bleeding light can be absorbed efficiently. In addition, since the critical angle at the interface between the substrate and the film increases due to the high refractive index of the film, the incident angle range that satisfies the total reflection condition is narrowed, and the effect that the internal reflectance is further reduced can be obtained. it can. An optical element in which the above film is formed as an inner surface antireflection film on a base material having a refractive index of 1.70 or more has a high refractive index and a sufficiently low inner surface reflectance. By using it as an optical element constituting the system, it is possible to realize a high-performance optical system that is small and light and suppresses ghost and flare.
[Second Embodiment]
The optical element paint according to the second embodiment of the present invention is characterized in that the optical element paint according to the first embodiment further contains a bifunctional or higher aromatic polythiol.

  Bifunctional or higher aromatic polythiol acts as a curing agent in the curing reaction of the epoxy resin precursor. Aromatic polythiols are characterized in that they have a higher refractive index than acid anhydrides, aliphatic polyamines, and aliphatic polyamidoamines, have less odor than aliphatic polythiols, and have a long pot life when formulated as a paint. For this reason, if bifunctional or more aromatic polythiol is mix | blended with the coating material for optical elements, workability | operativity and sclerosis | hardenability can be improved, without reducing a refractive index.

  Specific examples of suitable aromatic polythiols in the second embodiment include 1,4-benzenethiol, 1,5-dimercaptonaphthalene, 4,4′-biphenyldithiol, 4,4′-thiobisbenzenethiol, 1,3,5-trimercaptobenzene and the like can be mentioned. These aromatic polythiols can be used alone or as a mixture of two or more.

  The blending amount of the aromatic polythiol is preferably 0.05 or more and 0.5 or less, more preferably 0.07 or more and 0.4 or less, in weight ratio with respect to the epoxy resin precursor. More preferably, it is 1 or more and 0.3 or less. When the blending ratio of the aromatic polythiol is smaller than 0.05, the curability at a temperature of 80 ° C. or lower is remarkably lowered, and when it exceeds 0.5, the crosslinking density becomes too high and the cured film becomes brittle.

  The same curing catalyst as in the first embodiment can be used as the curing catalyst in the second embodiment, but the blending amount of the curing catalyst in the second embodiment is the epoxy resin precursor and the aromatic polythiol. The total amount is preferably 0.1 parts by weight or more and 5 parts by weight or less with respect to 100 parts by weight.

  Except for the above, the optical element coating material of the second embodiment has the same configuration as the optical element coating material of the first embodiment, and therefore details on the epoxy resin precursor, the curing catalyst, the black particles, and the like. The detailed explanation is omitted.

  The optical element coating material of the second embodiment described above is excellent in internal reflection by being applied and cured on the surface of the optical element substrate in the same manner as the optical element coating material of the first embodiment. A film having a prevention performance can be formed. In addition to the composition of the optical element coating according to the first embodiment, the optical element coating according to the second embodiment further includes a bifunctional or higher aromatic polythiol as a curing agent. In addition to the characteristics of the optical element coating material according to the embodiment, it has a characteristic that it is further excellent in curability.

EXAMPLES The present invention will be described in more detail with reference to the following examples. However, these show examples of the embodiments of the present invention, and the scope of the present invention is not limited to the following examples.
(1) Preparation of sample As an epoxy resin precursor, bis [4- (2,3-epoxypropylthio) phenyl] sulfide (trade name MPG: manufactured by Sumitomo Seika) having a refractive index of 1.67 at the d-line is used. Using. To 100 parts by weight of this epoxy resin precursor, 5 parts by weight of carbon black (trade name Talker Black # 8500F: manufactured by Tokai Carbon) and 5 parts by weight of titanium black (trade name 13MC: manufactured by Mitsubishi Materials) are added as black particles. Furthermore, 90 parts by weight of a mixed solvent of toluene: 2-methoxyethanol = 2: 1 (volume ratio), and 15 parts by weight of ultrafine powder amorphous silica (trade name Fine Seal FM-30: manufactured by Tokuyama) as a matting agent are dispersed. As an agent, 5 parts by weight of a high molecular polyester acid amide amine salt (trade name: Disparon DA-7301: manufactured by Kashiwagi Chemical Co., Ltd.) was added, and the mixture was kneaded for 10 minutes with a high-speed revolving mixer.

  Next, 3 parts by weight of 2,4,6-tris (dimethylaminomethyl) phenol as a curing catalyst is added to the above mixture, and further 45 parts by weight of a mixed solvent of toluene: 2-methoxyethanol = 2: 1 (volume ratio). Added and stirred. Finally, the agglomerated particles were removed using a 200 mesh (12.7 μm) metal net to obtain paint A.

  A paint was prepared in the same manner as paint A except that 5 parts by weight of bis (2-mercaptoethyl) sulfide was added as an adhesion improver instead of the matting agent, and paint B was obtained.

  Next, paints D and E were prepared by the following steps. 20 parts by weight of 4,4′-thiobisbenzenethiol as a bifunctional or higher aromatic polythiol is added to 80 parts by weight of the bis [4- (2,3-epoxypropylthio) phenyl] sulfide, and the carbon black is used as black particles. And 5 parts by weight of titanium black, 90 parts by weight of the mixed solvent, 5 parts by weight of the ultrafine powdered amorphous silica, and 5 parts by weight of the high-molecular polyester acid amide amine salt are added for 10 minutes using a high-speed revolving mixer. Kneaded.

  In the same manner as paint A, 3 parts by weight of 2,4,6-tris (dimethylaminomethyl) phenol and 45 parts by weight of mixed solvent are added to the above mixture and stirred, and paint D is obtained through a 200 mesh metal net. It was.

  On the other hand, a paint was prepared by the same process as paint D, except that 20 parts by weight of 1,4-benzenethiol was added in place of 4,4′-thiobisbenzenethiol as the bifunctional or higher aromatic polythiol. E was obtained.

  In addition, as a comparative example for paints A to B and D to E, a commercially available epoxy paint C (trade name GT-7: manufactured by Canon Kasei) containing coal tar and a dye as a colorant was prepared.

The refractive index of the cured product when bis [4- (2,3-epoxypropylthio) phenyl] sulfide was cured alone was 1.71 at the wavelength of the d-line.
(2) Formation of coating As shown in FIG. 3, a plurality of triangular prisms 1 having the same shape are produced using optical glass having a refractive index of 1.87 at d-line and an Abbe number of 40, and (1 The coatings A to E prepared in the above were applied. Each triangular prism 1 coated with paint is cured by heating at 120 ° C. for paint A and B for 1 hour, for paint C at 40 ° C. for 40 minutes, and for paint D and E at 70 ° C. for 4 hours. Then, a film 2 was formed to obtain a sample 3 for evaluation.
(3) Evaluation Each sample for evaluation of paints A to E produced by the above method was immersed in 1 ml of isopropyl alcohol per 1 mg of the coating, and allowed to stand at room temperature for 15 hours. As a result, it was confirmed that the samples for evaluation of the paints A, B, D, and E were not colored with isopropyl alcohol and had sufficient solvent resistance. On the other hand, in the sample for evaluation of paint C, isopropyl alcohol was markedly colored, and it was considered that coal tar or dye was eluted from the film.

  Next, the internal reflectance of each sample for evaluation was measured using a spectrophotometer configured as shown in FIG. In FIG. 4, the monochromatic measuring light 7 emitted from the monochromator 4 is incident on one surface of the evaluation sample 3, passes through the evaluation sample 3, and enters the inclined surface on which the film 2 is formed from the inside. Then, the measurement light 7 reflected by the inclined surface on which the film 2 is formed passes through the evaluation sample 3 again and exits from the other surface. The measurement light 7 emitted from the evaluation sample 3 enters a detector 5 having an integrating sphere, and the amount of light is measured.

  As a reference sample for the internal reflectance, a triangular prism having the same material and shape as each evaluation sample and having no film formed on the slope is used. (Reflected light quantity of the evaluation sample) / (Reference sample The amount of reflected light) was defined as the internal reflectance of the sample for evaluation.

  FIG. 1 is a graph showing the internal reflectance of each evaluation sample measured by the above method. The internal reflectances of the samples for evaluation of the paints A to B and the paints D to E are all suppressed to 8% or less over the entire visible wavelength region, and even for a substrate having a high refractive index of 1.87. It was confirmed to have an excellent inner surface antireflection effect. In addition, the coatings D to E are more excellent in preventing internal reflection in the shorter wavelength region than the coatings A to B. In particular, the coating D reduces the internal reflectance to 3% or less in the wavelength region of 486 nm or less. Had possible performance. This is because the Abbe number of a cured product comprising 80 parts by weight of [4- (2,3-epoxypropylthio) phenyl] sulfide and 20 parts by weight of 4,4′-thiobisbenzenethiol is as small as 19, and in this wavelength region. This is probably because the refractive index greatly exceeded 1.75.

  On the other hand, the internal reflectance of the sample for evaluation of the commercially available paint C is higher than the internal reflectance of the samples for evaluation of the paints A to B and D to E over the entire visible region, particularly 8% on the short wavelength side. It became a high value exceeding.

  From the above evaluation results, the paints A to B and D to E have higher solvent resistance than the conventional paint C and have an excellent inner surface antireflection effect even for a high refractive index substrate. Was confirmed.

FIG. 1 is a graph showing the internal reflectance of an evaluation sample. FIG. 2 is an explanatory diagram of the internal reflection of the optical element. FIG. 3 is a schematic cross-sectional view showing the configuration of the evaluation sample. FIG. 4 is a schematic configuration diagram showing an internal reflectance measurement system.

Explanation of symbols

  1 .... Substrate 2 .... Coating 3 .... Sample for evaluation 4 .... Monochromator 5 .... Detector

Claims (17)

  An optical element having a base material and a film formed on the base material, wherein the film contains a cured epoxy resin having a refractive index of 1.67 or more and black particles.   An optical element, wherein the base material has a refractive index of 1.70 or more.   The optical element according to claim 1, wherein the cured epoxy resin is a cured product of bis [4- (2,3-epoxypropylthio) phenyl] sulfide.   The optical element according to any one of claims 1 to 3, wherein the black particles include at least one of carbon black and titanium black.   A paint for optical elements, comprising an epoxy resin precursor having a refractive index of 1.65 or more, a curing catalyst, and black particles.   6. The optical element paint according to claim 5, wherein the epoxy resin precursor is bis [4- (2,3-epoxypropylthio) phenyl] sulfide.   The optical element paint according to claim 5 or 6, wherein the curing catalyst contains at least one of an aliphatic tertiary amine and an N, N ', N'-trialkyl cyclic amidine.   8. The paint for optical elements according to claim 7, wherein the aliphatic tertiary amine is 2,4,6-tris (dimethylaminomethyl) phenol.   The optical element paint according to claim 7, wherein the N, N ', N'-trialkyl cyclic amidine is 1,8-diazabicyclo [5,4,0] undec-7-ene.   The optical element paint according to any one of claims 5 to 9, wherein the black particles include at least one of carbon black and titanium black.   11. The coating composition for an optical element according to claim 5, wherein the content of the epoxy resin precursor is 15% by weight or more and 60% by weight or less.   The optical element coating material according to any one of claims 5 to 11, wherein a content of the black particles is 3 wt% or more and 30 wt% or less.   The optical element paint according to any one of claims 5 to 12, further comprising a bifunctional or higher aromatic polythiol.   The optical element paint according to claim 13, wherein the aromatic polythiol is at least one of 4,4'-thiobisbenzenethiol and 1,4-benzenedithiol.   The optical element paint according to claim 13 or 14, wherein a weight ratio of the bifunctional or higher aromatic polythiol to the epoxy resin precursor is 0.05 or more and 0.5 or less.   An optical element having a base material and a film formed on the base material, wherein the film is made of a cured product of the coating for optical elements according to any one of claims 5 to 15. An optical element characterized by the above.   The optical element according to claim 16, wherein the base material has a refractive index of 1.70 or more.