JP2012246373A - Paint for preventing internal reflection of optical element, and optical element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To decrease internal reflection even in a lens with a higher refractive index.SOLUTION: A paint 4 for preventing internal reflection of an optical element contains at least one of nanoparticles of titanium oxide and niobium oxide, and carbon black.

Description

  The present invention relates to an inner reflection preventing paint for optical elements and an optical element such as a lens or a prism to which the paint is applied.

  In optical elements such as lenses and prisms, part of the light incident on the optical element is internally reflected on the outer peripheral surface of the optical element, which causes flare, ghost, and the like. The internal reflection increases as the refractive index of the optical element increases. In particular, the optical element formed of high refractive index glass has a problem due to harmful light such as flare and ghost.

  In order to prevent this internal reflection, a method of applying an internal antireflection coating to the outer peripheral surface of the optical element is known. The internal antireflection coating is generally a coating that has carbon black as a main pigment and has a blackness, but the refractive index of the coating itself is relatively low at about 1.5. For this reason, when the refractive index of the glass constituting the optical element is higher than the refractive index of the inner surface antireflection paint, the difference in refractive index between the two becomes large, and the reflectance at the interface between the optical element and the inner surface antireflection paint is high. Become. As the reflectivity increases, internal reflection increases, and damage due to harmful light becomes significant.

  In Patent Document 1, as an internal reflection preventing coating capable of suppressing internal reflection of a lens using a glass having a high refractive index, zirconium oxide nanoparticles, aluminum oxide nanoparticles having a refractive index of 1.5 or more are used. A material containing non-black inorganic nanoparticles and a black pigment is described. Thereby, internal reflection is also reduced in combination with glass having a refractive index of 1.76.

JP-A-7-82510

  However, in the technique of Patent Document 1, in a lens using a glass having a refractive index of 1.8 or more, the difference in refractive index between the lens and the inner surface antireflection coating becomes large, and the effect of preventing internal reflection is low. Failures such as ghosts will occur.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an inner surface antireflection coating having a high inner surface antireflection effect even in a lens having a higher refractive index.

In order to achieve the above object, the present invention provides the following means.
The inner surface antireflection coating for optical elements of the present invention is characterized by containing at least one of titanium oxide and niobium oxide nanoparticles and carbon black.

  The content of at least one of the titanium oxide and niobium oxide nanoparticles may be 20 wt% or more and 80 wt% or less.

  Moreover, it is preferable that the internal reflection preventing coating for optical elements of the present invention does not contain titanium black.

  The optical element of the present invention is characterized in that the inner reflection preventing paint for optical elements of the present invention is applied.

In the optical element of the present invention, a value obtained by dividing the surface area per 100 μm square by the area of 10,000 μm ^{2 on} the surface on which the inner reflection preventing paint for optical elements is applied may be 1.8 or less.

  The surface on which the inner reflection preventing paint for optical elements is applied may be a surface formed by press-molding a heat-softened glass material with a molding die.

  According to the inner surface antireflection coating for an optical element of the present invention, it is formed of high refractive index glass having a refractive index of 1.8 or more by including at least one of titanium oxide and niobium oxide nanoparticles and carbon black. Also in the optical element, the reflectance can be suppressed and long-term use is possible.

It is sectional drawing of the optical element which apply | coated the inner surface antireflection coating of embodiment of this invention.

Hereinafter, the inner surface antireflection coating of the first embodiment of the present invention will be described.
FIG. 1 is a cross-sectional view of an optical element to which an inner surface antireflection coating according to an embodiment of the present invention is applied.
The optical element 1 is a lens made of glass, and includes an optical surface 2 and an outer peripheral surface 3. An inner surface antireflection coating 4 is applied to the outer peripheral surface 3. The incident light 5 to the optical element 1 becomes reflected light 6 and refracted light (not shown) at the interface with the inner surface antireflection coating 4, and the refracted light is absorbed by the inner surface antireflection coating 4.

The inner surface antireflection coating 4 comprises a toluene dispersion containing titanium oxide nanoparticles which are non-black inorganic nanoparticles, a thinner solution containing carbon black which is a black pigment and a resin component, and titanium black which is a black pigment. A liquid in which toluene is added as a solvent by mixing with the contained toluene dispersion is used as a raw material. The inner surface antireflection coating 4 is obtained by applying the above raw material to the outer peripheral surface 3 of the optical element 1 and then heat-curing it. That is, the inner surface antireflection coating 4 has titanium oxide nanoparticles dispersed in a resin and contains carbon black and titanium black.
As the resin used in the coating material, resins generally used in coating materials such as acrylic resin, epoxy resin, melamine resin, alkyd resin and modified products thereof, and mixtures thereof can be used. Also, these resins are cured (polymerized) by adding and heating a curing agent to form a paint. Here, the resin before curing is used as the resin component.

  Titanium oxide is a component having a high refractive index in the transparent oxide, so that the inner surface antireflection coating 4 has a high refractive index by being contained in the inner surface antireflection coating 4. The transparent oxide particles having a high refractive index are not limited to nanoparticles of titanium oxide, and for example, niobium oxide nanoparticles can be used, but titanium oxide having a high refractive index is more preferable. The particle diameter of the particles is preferably 50 nm or less, and the titanium oxide of the present embodiment has a particle diameter of 15 nm.

Carbon black is a component for providing blackness to the inner surface antireflection coating 4.
Here, since both titanium oxide and niobium oxide have photocatalytic activity, these nanoparticles have a function of deteriorating surrounding paint agents by absorbing ultraviolet rays. In the inner surface antireflection coating 4 of this embodiment, since carbon black absorbs ultraviolet rays, the photocatalytic activity of titanium oxide and niobium oxide can be suppressed.

  The content of titanium oxide is preferably 20 wt% or more and 80 wt% or less, and more preferably 30 wt% or more and 50 wt% or less. If the content is as small as, for example, 20 wt% or less, the inner surface antireflection coating 4 cannot have a high refractive index. On the other hand, if the content is as high as 80 wt% or more, for example, the coating is deteriorated due to photocatalytic activity, and the resistance of the coating is deteriorated. That is, by setting the content of titanium oxide in the above range, it is possible to prevent deterioration due to long-term use while keeping the refractive index of the inner surface antireflection coating 4 high.

  Moreover, it is preferable that the inner-surface antireflection coating 4 has a configuration not containing titanium black. This is because titanium black is more likely to transmit ultraviolet light than carbon black, so the photocatalytic activity of titanium oxide or niobium oxide cannot be sufficiently suppressed, and the resistance of the internal antireflection coating 4 may be insufficient. It is. That is, by adopting a configuration that does not contain titanium black, the resistance of the inner surface antireflection coating 4 can be further improved.

The surface of the outer peripheral surface 3 of the optical element 1 on which the inner surface antireflection coating 4 is applied is a value obtained by dividing (dividing) the surface area per 100 μm square (a square region having a side of 100 μm) by an area of 10,000 μm ² (surface area / Area) is 1.8 or less. That is, when the surface area per 100 μm square is 10,000 μm ² , that is, when the surface is completely flat (mirror surface), the above value is 1.
This value indicates the state of unevenness on the outer peripheral surface 3, and the larger the value, the greater the unevenness. In addition, the presence of irregularities on the surface of the outer peripheral surface 3 means that the interface between the outer peripheral surface 3 (optical element 1) and the inner surface antireflection coating 4 has an irregular shape.

  The optical element 1 is formed by press-molding a heat-softened glass material with a mold. That is, the outer peripheral surface 3 to which the inner surface antireflection coating 4 is applied is also formed by press molding.

As described above, when the unevenness of the interface is 1.8 or less (when close to a mirror surface), scattering of reflection of incident light is reduced. That is, there is little change in the intensity of incident light, and stronger light is reflected, and the effect of the inner surface antireflection coating 4 becomes greater.
Specifically, when the optical element 1 is formed by press molding, the unevenness at the interface becomes small, and thus the effect of the inner surface antireflection coating 4 is more exhibited. Furthermore, the man-hour for manufacturing the optical element 1 can be reduced.

  In manufacturing the optical element 1, the outer peripheral surface 3 as well as the optical surface 2 are formed by press molding. However, the present invention is not limited to this, and the outer peripheral surface may be polished by performing a conventional centering process. The above-described embodiment in which the outer peripheral surface 3 is formed by press molding realizes a reduction in the number of manufacturing steps of the optical element 1, and at a lower cost by applying the high refractive index inner surface antireflection coating 4 to the outer peripheral surface 3. The optical element 1 can be manufactured.

Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited thereto.
The production method, the glass surface evaluation method, and the paint evaluation method of the inner surface antireflection coating 4 used in the examples and comparative examples are as follows.

(Preparation method and coating method)
[Examples 1 to 6, Comparative Example 1]
(1) Carbon black-containing solution (Origin Electric Co., Ltd. Lens Black B No. 3 20 wt% thinner solution)
(2) Titanium oxide (particle size 15 nm) -containing solution (CIK Nanotech Co., Ltd. TiO ₂ 15 wt% toluene dispersion)
(3) Titanium black-containing solution (Mitsubishi Materials Corporation Titanium Black Toluene Dispersion)
The above three solutions were mixed at the blending ratio shown in Table 1.
That is, in Examples 1 to 5, (1) a carbon black-containing solution and (2) a titanium oxide-containing solution were mixed. In Example 6, the above (1), (2) and (3) titanium black-containing solution were mixed. In the comparative example 1, it was set as the internal-surface antireflection coating 4 containing only (1).
Furthermore, toluene was appropriately added as a solvent and stirred well. The particle diameter of titanium oxide is 15 nm.

The following four types of glass flat plates were used as the glass flat plates to which the inner surface antireflection coating 4 was applied.
<1> Glass flat plate having a refractive index of 1.516 (Ohara L-BSL7)
<2> Glass flat plate with a refractive index of 1.694 (OHARA L-LAL13)
<3> Glass flat plate with a refractive index of 1.806 (Ohara L-LAH53)
<4> Glass flat plate with a refractive index of 1.851 (Optical Glass Co., Ltd. Q-LASFH18S)
On the above four types of glass flat plates (30 mm square, 5 mm thickness), the inner surface antireflection coating 4 was applied to a thickness of 20 μm using a bar coater, and heat cured at 110 ° C. for 1 hour.

[Example 7, Comparative Example 2]
(3) One surface of the glass flat plate having a refractive index of 1.806 was polished so that the surface area / area = 2.0, and the other surface was mirror-finished. Next, the inner surface antireflection coating 4 was applied to the polished surface. The solution constituting the inner surface antireflection coating 4 was mixed at the blending ratio shown in Table 1.
That is, in Example 7, the solutions (1) and (2) were mixed, and in Comparative Example 2, the inner surface antireflection coating 4 containing only (1) was obtained. Except this, it was the same as Example 2 and Comparative Example 1.

[Comparative Example 3]
(4) Epoxy resin (Mitsubishi Chemical Corporation Epicoat 828)
Two solutions of (2) titanium oxide-containing solution and (3) titanium black-containing solution described above were added to the epoxy resin so as to have a blending ratio shown in Table 1, and stirred well.

  Next, the same amount of curing agent as the epoxy resin (ADEKA ADEKA HARDNER EH551CH) was added and stirred well. The inner surface antireflection coating 4 was applied so as to have a thickness of 20 μm.

(Glass surface evaluation method)
The surface area per 100 μm square was measured using a laser microscope (OLYMPUS LEXT OLS3500) without applying the inner surface antireflection coating 4. Table 2 shows values (surface area / area) obtained by dividing the measured surface area by an area of 10,000 μm ² . That is, in Examples 1 to 6 and Comparative Examples 1 and 3, a glass plate having a surface area / area = 1.0 is used, and in Example 7 and Comparative Example 2, a surface area / area = 2.0 is provided. A glass flat plate was used.

(Internal reflection prevention paint evaluation method)
1. Reflectance Evaluation Using a lens reflectometer (Olympus USPM-RU), the wavelength of visible light was changed in the range of 380 to 780 nm, and the reflectance of the interface between the glass flat plate / inner surface antireflection coating was measured. Table 2 shows the average values at wavelengths of 380 to 780 nm.

2. Tolerance Evaluation After irradiating ultraviolet light with an illuminance of 200 mW / cm ² for 4 hours, the reflectance was measured again. The evaluation method is “impossible” when the average value of the reflectance at a wavelength of 380 to 780 nm is higher than 0.1% as compared with that before irradiation with ultraviolet light, 0.1% or less, 0.05 If the change was more than 1%, it was judged as “OK”, and if the change was less than 0.05%, it was judged as “good”. The evaluation results are shown in Table 3.

As is clear from Table 2, when the content of titanium oxide nanoparticles contained in Examples 1 to 5, that is, the inner surface antireflection coating 4, is 15 wt% or more and 90 wt% or less, the glass having a high compression ratio. The Example using a flat plate (refractive index 1.8 or more) has low reflectance compared with the comparative example 1 in which the titanium oxide nanoparticle is not contained. In particular, in Examples 2 to 5, since the content of the titanium oxide nanoparticles is 20 wt% or more, the refractive index can be further suppressed.
That is, internal reflection can be prevented even in a lens using a glass plate having a high refractive index.

As is apparent from Table 3, in Example 5, the content of titanium oxide nanoparticles exceeds 80 wt%, and thus the resistance is slightly deteriorated. This seems to be due to deterioration of the paint due to the photocatalytic activity of the titanium oxide nanoparticles.
In Example 6, since the inner surface antireflection coating 4 contains titanium black, the resistance is slightly deteriorated. This seems to be because the photocatalytic activity of titanium oxide is not suppressed because titanium black transmits ultraviolet rays.

  Further, as is apparent from Table 2, in Comparative Example 1, since the titanium oxide nanoparticles are not included in the inner surface antireflection coating 4, particularly when a glass plate having a refractive index of 1.8 or more is used, the reflection is reduced. The rate will be high.

In Example 7 and Comparative Example 2, one surface of the glass flat plate was set to have a surface area / area = 2.0, and the inner surface antireflection coating 4 was applied to this surface.
When Example 7 and Comparative Example 2 are compared, in Example 7, the inner surface antireflection coating 4 contains titanium oxide nanoparticles to increase the refractive index, but the reflectivity is not significantly reduced. That is, when the inner surface antireflection coating 4 is applied to the uneven interface with the surface area / area = 2.0, the effect of the inner surface antireflection coating 4 does not increase as compared with the case where the unevenness is small.

  In Comparative Example 3, since only black was used as a black pigment and carbon black was not included, the resistance of the inner surface antireflection coating 4 was poor. That is, after irradiating with ultraviolet rays for 4 hours, the reflectivity increased beyond 0.1%.

DESCRIPTION OF SYMBOLS 1 ... Optical element, 3 ... Outer peripheral surface (surface to which inner surface antireflection coating is applied), 4 ... Inner surface antireflection coating

Claims (6)

  An inner surface antireflection coating for an optical element, comprising at least one of titanium oxide and niobium oxide nanoparticles and carbon black.   2. The inner surface for an optical element according to claim 1, wherein the content of at least one of the titanium oxide and niobium oxide nanoparticles is 20 wt% or more and 80 wt% or less. Anti-reflective paint.   The inner reflection preventing paint for optical elements according to claim 1 or 2, which does not contain titanium black.   An optical element, wherein the optical element inner surface antireflection coating according to any one of claims 1 to 3 is applied. 5. The optical element according to claim 4, wherein a value obtained by dividing a surface area per 100 μm square by an area of 10,000 μm ² is 1.8 or less on the surface on which the inner reflection preventing paint for an optical element is applied. Optical element.   6. The optical element according to claim 5, wherein the surface on which the inner reflection preventing paint for an optical element is applied is a surface formed by press-molding a heat-softened glass material with a molding die. An optical element.

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