Patent Description:
Optical elements for optical equipment such as cameras, binoculars, microscopes, and semiconductor exposure devices optionally have a black light-shielding film outside their optically effective section to reduce stray light. This light-shielding film sufficiently absorbs stray light that reaches the periphery of a lens or any similar part of the optical element, reducing unnecessary lights, such as flares and ghosts.

A light-shielding film for an optical element is mainly a coating film formed on the surface of an optical component of the optical element, such as a glass component. The glass component can be a lens, a prism, or any other glass component for optical purposes.

The following describes the role of a light-shielding film for an optical element with reference to drawings. <FIG> is a schematic diagram illustrating an optical component that has a light-shielding film outside its optically effective plane. To be specific, <FIG> illustrates an example of a lens having a light-shielding film.

As illustrated in <FIG>, the light-shielding film <NUM> is located at the periphery <NUM> (an edge having very small irregularities) of an out-of-plane area <NUM> (any area outside the optically effective plane <NUM>) of the lens <NUM>. A ray of light that enters through the optically effective plane <NUM> and only travels in the lens like the light <NUM> passes through the lens <NUM> as transmitted light <NUM>. If no light-shielding film is provided (the lower side of the lens <NUM> in <FIG>), a ray of light that hits the periphery of the lens <NUM> and reflects off the inner surface goes out of the lens <NUM> as irrelevant internal reflection light <NUM>, causing a flare, a ghost, or any other event that affects the quality of the image. The light-shielding film <NUM> (the upper side of the lens <NUM> in <FIG>) decreases the amount of internal reflection light <NUM> that affects the quality of the image and prevents flares and ghosts by reducing the internal reflection of diagonal incident light <NUM>.

This light-shielding film is expected to reduce stray light that enters the light-shielding film from the inside of the optical element and is required to decrease the amount of internal reflection light <NUM>.

The wide variety of shapes of optical elements having a light-shielding film has made more common the situations where the light-shielding film is located to be seen by the user of the optical element. Besides the aforementioned reduction of internal reflection, good appearance of the interface between the optical element and the light-shielding film as viewed by the user from the optical element side is in demand.

Furthermore, the recent miniaturization and progress in performance of optical equipment has led to frequent use of high-refractive-index materials to make optical elements for optical systems. To be specific, materials such as glass materials having a refractive index of <NUM> to more than <NUM> are used.

Reducing the internal reflection of stray light incident on a high-refractive-index optical element requires increasing the refractive index of the light-shielding film accordingly. An example of a known method for this is to control the refractive index of a light-shielding film by introducing a high-refractive-index component into the film.

<CIT> discloses a light-shielding film for optical elements. To reduce internal reflection, this light-shielding film contains non-black inorganic fine particles that improve the refractive index and a dye that absorbs light. <CIT> discloses a light-shielding coating comprising a resin composition, a coloring agent and titania fine particles having an average primary particle diameter of <NUM> or more and <NUM> or less, and an organic solvent dissolving or dispersing the resin composition. <CIT> discloses a light-shielding coating comprising a cured substance at least containing an epoxy resin, titania fine particles, a dye, and an amine curing agent. <CIT> discloses a light-shielding coating comprising a resin, a coloring material, an inorganic fine particle, and a surfactant and/or an oil. <CIT> discloses a composition suitable for use as a hermetic varnish for wires or other electrical conductors, which comprises an aqueous solution of a water reducible epoxy adduct of an epoxy compound, an amino substituted aromatic carboxylic acid, an amine, an organic solvent and a crosslinking agent.

The light-shielding paint according to <CIT>, however, is disadvantageous when used to form a light-shielding film on the periphery <NUM> of an optical element made of a high-refractive-index material. Some areas of the interface between the optical element and the light-shielding film look like emitting white light when viewed from the optical element side (white spots), affecting the appearance of the element.

The following describes this problem. <FIG> is a cross-sectional view of the interface between an optical element <NUM> and a light-shielding film <NUM> on the periphery of the optical element <NUM>. As illustrated in <FIG>, many small cracks <NUM> are in the periphery (edge surface) of the optical element. Such cracks, developing while the edge surface is polished, are frequent when the optical element is made of a high-refractive-index glass material containing lanthanum or any similar element. The reason for the frequent occurrence of cracks in a high-refractive-index glass material should be that the lanthanum or other non-SiO<NUM> element added to the glass material as a refractive index enhancer affects the strength of intermolecular bonds (e.g., bonds between SiO<NUM> molecules), making the material more likely to crack when polished. Each crack usually measures <NUM> or less in width and <NUM> or less in length.

As illustrated in <FIG>, a light-shielding paint applied to an edge surface having small cracks <NUM> to form the light-shielding film <NUM> only insufficiently fills the inside of the cracks <NUM>, leaving air in the cracks <NUM>. The difference between the refractive index of the air in the cracks <NUM> and that of the optical element <NUM> causes incident light <NUM> to diffusely reflect and produce scattered light <NUM>. The resulting white spots on the interface between the optical element and the light-shielding film seen from the optical element side affect the appearance of the element. Worse yet, the high contrast between the black shielding film and the white spots makes the white spots conspicuous.

Made in light of such related art, an aspect of the present invention provides a light-shielding paint with which white spots on the interface between an optical element and a light-shielding film seen from the optical element side are prevented. Some other aspects of the present invention provide a light-shielding film, an optical element, and a method for producing an optical element that all ensure the prevention of white spots on the interface between an optical element and a light-shielding film seen from the optical element side.

The present invention in its first aspect provides a method for producing an optical element as specified in claims <NUM> to <NUM>.

The present invention in its second aspect provides a light-shielding paint as specified in claims <NUM> to <NUM>.

The present invention in its third aspect provides a light-shielding paint set as specified in claims <NUM> to <NUM>.

The present invention in its fourth aspect provides a method as specified in claims <NUM> or <NUM> for producing a light-shielding film.

The following describes some embodiments of the invention.

An optical element produced using a light-shielding paint according to an aspect of the invention sufficiently fills, as illustrated in <FIG>, cracks that form in a ground periphery of an optical element, preventing light from scattering at the cracks. This makes the optical element relate to a light-shielding paint that produces a light-shielding film with few white spots noticeable on the element-film interface (the interface between the light-shielding film and the optical element on which it has been formed) viewed from the optical element side as well as to such a light-shielding film, an optical element having such a light-shielding film, and a method for producing such an optical element.

The following describes some embodiments of the invention with reference to drawings.

A light-shielding paint according to an embodiment of the invention is first described.

The light-shielding paint according to the present invention is a light-shielding paint for optical elements that contains an epoxy resin, fine particles of titania, a dye, an organic solvent, an amine -based curing agent and inorganic fine particles other than the fine particles of titania.

According to the present invention the viscosity of the light-shielding paint is <NUM> mPa·s or more and <NUM> mPa·s or less. A viscosity of less than <NUM> mPa·s makes the light-shielding paint likely to move while drying, affecting its ease of application. A viscosity of more than <NUM> mPa·s of the light-shielding paint leads to poor filling in cracks that form in the periphery (edge) of an optical element, resulting in incomplete prevention of white spots.

The following describes materials contained in the light-shielding paint according to this embodiment. Epoxy resin.

Any one or two or more known epoxy resins can be used in the light-shielding paint according to this embodiment as long as they ensure the dispersibility of the fine particles of titania, are compatible with the dye, can be cured with the amine-based curing agent, will be stable in a coating, and allow the paint to adhere firmly to a substrate. Specific examples of epoxy resins that can be used include glycidyl-ether, glycidyl-ester, and glycidylamine epoxy resins, linear aliphatic epoxides, and alicyclic epoxides. In particular, it is preferred to use a bisphenol A epoxy resin.

The use of an epoxy resin having a high refractive index improves the refractive index of light-shielding films made from the light-shielding paint.

The epoxy resin content of the light-shielding paint according to this embodiment can be <NUM>% by mass or more and <NUM>% by mass or less, preferably <NUM>% by mass or more and <NUM>% by mass or less.

With their high refractive index, the fine particles of titania used in the light-shielding paint according to this embodiment allow easy adjustment of the refractive index of light-shielding films to the desired value. They are also widely available in the market at affordable prices with a sufficient degree of fineness.

The quantity of the fine particles of titania in the light-shielding paint according to this embodiment can be <NUM>% by mass or more and <NUM>% by mass or less, preferably <NUM>% by mass or more and <NUM>% by mass or less. The fine particles of titania insufficiently increase the refractive index of light-shielding films when being less than <NUM>% by mass. When being more than <NUM>% by mass, the fine particles of titania cause the films to be of insufficient quality for use as light-shielding films.

The average particle diameter of the primary particles of the fine particles of titania used in this embodiment can be <NUM> or more and <NUM> or less, preferably <NUM> or more and <NUM> or less. Fine particles of titania with an average particle diameter of less than <NUM> have extremely large surface areas, which make the fine particles very likely to aggregate and difficult to disperse well. Particles having an average particle diameter of more than <NUM> behave as light scatterers and cause films made from the paint to perform insufficiently as light-shielding films. The average primary particle diameter as mentioned herein refers to the equivalent spherical diameter of non-aggregated particles. The average primary particle diameter of the fine particles of titania is their number-average particle diameter.

Any known method, such as a vapor-phase or liquid-phase process, can be used to produce the fine particles of titania used in this embodiment. Examples include known methods such as synthesizing fine particles of titanium dioxide by burning a metal powder in a flame in an atmosphere containing at least oxygen and a sol-gel process in which a titanium alkoxide undergoes hydrolysis and condensation polymerization. Titania, known to have crystalline structures such as the rutile structure and anatase structure, exhibits a high refractive index as compared with that of amorphous structures. Any crystallographic form of titania, however, can be used as long as it has an intended refractive index.

Any known dye can be used in the light-shielding paint according to this embodiment as long as it has an absorption band in the visible range, is compatible with the epoxy resin, and ensures the dispersibility of the fine particles of titania. Besides the use of a single dye, it is possible to use a combination of dyes in different colors, such as black, red, yellow, and blue, to adjust the absorption wavelengths. Azo dyes are available in a wide variety of colors, and examples of other dyes that can be used include anthraquinone dyes, phthalocyanine dyes, stilbenzene dyes, pyrazolone dyes, thiazole dyes, carbonium dyes, and azine dyes. Dyes are more resistant to external influences such as light, water, and heat when containing chromium, cobalt, copper, or any similar metal than in their original form.

The dye content of the light-shielding paint according to this embodiment can be <NUM>% by mass or more and <NUM>% by mass or less, preferably <NUM>% by mass or more and <NUM>% by mass or less.

The organic solvent used in this embodiment may have a vapor pressure of <NUM> Pa or more and <NUM> Pa or less at a temperature of <NUM>. A vapor pressure of less than <NUM> Pa of the organic solvent at a temperature of <NUM> causes the light-shielding paint to move on the optical element to which it has been applied, making it difficult to form a uniform light-shielding film from the paint. A vapor pressure of more than <NUM> Pa of the organic solvent at a temperature of <NUM> causes a coating of the light-shielding paint applied to an optical element to dry into a light-shielding film too fast to sufficiently fill cracks in the edge surface of the optical element, making it more likely that white spots are noticeable on the element-film interface viewed from the optical element side.

The organic solvent used in this embodiment may be a mixture of a first organic solvent and a second organic solvent.

The first organic solvent used in the light-shielding paint according to this embodiment has a boiling point of <NUM> or more and <NUM> or less. A boiling point of less than <NUM> of the first organic solvent causes a coating of the light-shielding paint applied to an optical element to dry into a light-shielding film too fast to sufficiently fill cracks in the edge surface of the optical element, making it more likely that noticeable white spots are on the element-film interface viewed from the optical element side. When having a boiling point of more than <NUM>, the first organic solvent affects the chemical resistance of light-shielding films by remaining in the films.

The first organic solvent can be a solvent that dissolves the essential components of the paint, such as an epoxy resin and a dye, preferably with good compatibility with the fine particles of titania. Specific examples include benzyl alcohol (boiling point, <NUM>; vapor pressure at <NUM>, <NUM> Pa), <NUM>-ethyl-<NUM>-hexanol (boiling point, <NUM>; vapor pressure at <NUM>, <NUM> Pa), butyl cellosolve (boiling point, <NUM>; vapor pressure at <NUM>, <NUM> Pa), <NUM>-butoxy-<NUM>-propanol (boiling pint, <NUM>; vapor pressure at <NUM>, <NUM> Pa), and mixtures of these solvents.

The total quantity of the first organic solvent and the second organic solvent (described hereinafter) in the light-shielding paint according to this embodiment can be <NUM>% by mass or more and <NUM>% by mass or less, preferably <NUM>% by mass or more and <NUM>% by mass or less.

The second organic solvent can be propylene glycol monomethyl ether (boiling point, <NUM>; vapor pressure at <NUM>, <NUM> Pa).

The light-shielding paint according to this embodiment contains an amine-based curing agent with which the epoxy resin in the light-shielding paint is cured. Any known amine-based curing agent can be used as long as intended characteristics are ensured. Examples of amine-based curing agents that can be used include linear aliphatic ones, polyamide-based ones, alicyclic ones, and aromatic ones, as well as dicyandiamide, adipic acid dihydrazide, and so forth. Any one of these can be used alone, and it is also possible to use a mixture of two or more of these.

The amine-based curing agent content of the light-shielding paint according to this embodiment can be <NUM>% by mass or more and <NUM>% by mass or less of the light-shielding paint. An amine-based curing agent content of less than <NUM>% by mass causes the degree of hardening of light-shielding films to be so low that the adhesion of the films to their substrate is affected. An amine-based curing agent content of more than <NUM>% by mass leads to low optical characteristics.

According to the present invention the light-shielding paint contains inorganic fine particles other than the fine particles of titania, such as silica (hydrophobic silica, hydrophilic silica, or a mixture of them). The user can control the ease of application of the light-shielding paint by adding inorganic fine particles like silica. Such inorganic fine particles can also be used to form creases or irregularities on the surface of a light-shielding film that reduce the reflection of light at the interface between the film and the air.

The quantity of the inorganic fine particles in the light-shielding paint according to this embodiment can be <NUM>% by mass or more and <NUM>% by mass or less, preferably <NUM>% by mass or more and <NUM>% by mass or less. The inorganic fine particles often have insufficient effects on the ease of application of the paint and insufficiently reduce the reflection of light at the interface between a light-shielding film and the air when being less than <NUM>% by mass. When being more than <NUM>% by mass, the inorganic fine particles often cause films made from the paint to be of insufficient quality for use as light-shielding films.

The average primary particle diameter of the inorganic fine particles can be <NUM> or more and <NUM> or less, preferably <NUM> or more and <NUM> or less. Inorganic fine particles having an average primary particle diameter of less than <NUM> often have insufficient effects on the ease of application of the paint and insufficiently reduce the reflection of light at the interface between a light-shielding film and the air. Inorganic fine particles having an average particle diameter of more than <NUM> behave as light scatterers and cause films made from the paint to perform insufficiently as light-shielding films.

The light-shielding paint according to this embodiment may contain additives as long as the paint can be used for its intended purpose. Examples of additives that can be used include substances such as plasticizers, coupling agents, flame retardants (e.g., phosphates and melamines), surfactants (e.g., those based on aliphatic acid esters), antistatic agents such as alkyl sulfonates and glyceryl stearates, oxidation inhibitors, fungicides, and preservatives. Any one of these additives can be used alone, and it is also possible to use two or more of these in combination.

The additive content of the light-shielding paint according to this embodiment can be <NUM>% by mass or more and <NUM>% by mass or less, preferably <NUM>% by mass or more and <NUM>% by mass or less.

The following describes a light-shielding paint set according to an embodiment of the invention.

The light-shielding paint set according to this embodiment has two or more units including a unit having an epoxy resin and a unit having an amine-based curing agent. Mixing all units produces a light-shielding paint described above.

The light-shielding paint set according to the present invention is a light-shielding paint set for optical elements that has two or more units including a unit having an epoxy resin and a unit having an amine-based curing agent. The light-shielding paint set according to an embodiment contains an epoxy resin, at least fine particles of titania, inorganic fine particles other than the fine particles of titania, a dye, a first organic solvent, a second organic solvent, and an amine-based curing agent in any one or more of the units. The organic solvent in the light-shielding paint as a mixture of all units may have a vapor pressure of <NUM> Pa or more and <NUM> Pa or less at a temperature of <NUM>. According to the present invention the viscosity of the light-shielding paint as a mixture of all units in the light-shielding paint set is <NUM> mPa·s or more and <NUM> mPa·s or less.

The light-shielding paint set according to this embodiment can contain the materials described in "Light-shielding paint" in any unit so that mixing all units produces a light-shielding paint described above. Light-shielding film.

The following describes a light-shielding film according to an embodiment of the invention.

The light-shielding film according to this embodiment is produced through the application and subsequent curing of a light-shielding paint described above. The composition of the light-shielding film is the same as that of the light-shielding paint but excludes the organic solvent. The light-shielding film according to this embodiment therefore contains at least an epoxy resin, fine particles of titania, inorganic fine particles other than the fine particles of titania, a dye, and an amine-based curing agent, optionally with any other materials mentioned above for a light-shielding paint.

The thickness of the light-shielding film according to this embodiment is not limited. It can be <NUM> or more and <NUM> or less, preferably <NUM> or more and <NUM> or less.

The light-shielding film according to this embodiment may have an absorption coefficient of <NUM> or more and <NUM> or less and a refractive index (nd) of <NUM> or more. An absorption coefficient of less than <NUM> makes the light-shielding film insufficiently absorb light. An absorption coefficient of more than <NUM> leads to serious scattering, affecting the performance of the film in shielding light. When the light-shielding film is formed on a highly refractive optical element, a refractive index (nd) of less than <NUM> causes serious internal reflection to occur because of the difference between the refractive index of the optical element and that of the light-shielding film.

The following describes the quantities of the individual materials in the light-shielding film.

The epoxy resin content of the light-shielding film according to this embodiment can be <NUM>% by mass or more and <NUM>% by mass or less, preferably <NUM>% by mass or more and <NUM>% by mass or less.

The quantity of the fine particles of titania in the light-shielding film according to this embodiment can be <NUM>% by mass or more and <NUM>% by mass or less, preferably <NUM>% by mass or more and <NUM>% by mass or less. The fine particles of titania increase the refractive index of the resulting thin film only to a small extent, leading to large internal reflection, when being less than <NUM>% by mass.

The dye content of the light-shielding film according to this embodiment can be <NUM>% by mass or more and <NUM>% by mass or less, preferably <NUM>% by mass or more and <NUM>% by mass or less.

The amine-based curing agent content of the light-shielding film according to this embodiment can be <NUM>% by mass or more and <NUM>% by mass or less of the light-shielding paint. An amine-based curing agent content of less than <NUM>% by mass causes the degree of hardening of the light-shielding film to be so low that the adhesion of the film to its substrate is affected. An amine-based curing agent content of more than <NUM>% by mass leads to low optical characteristics.

The quantity of inorganic fine particles in the light-shielding film according to this embodiment other than the fine particles of titania can be <NUM>% by mass or more and <NUM>% by mass or less, preferably <NUM>% by mass or more and <NUM>% by mass or less.

The additive content of the light-shielding film according to this embodiment can be <NUM>% by mass or more and <NUM>% by mass or less, preferably <NUM>% by mass or more and <NUM>% by mass or less.

An optical element according to an embodiment of the invention has a lanthanum-containing glass substrate and a light-shielding film on part of the surface of the glass substrate. The light-shielding film is the aforementioned light-shielding film according to an embodiment of the invention.

The glass substrate can be a lens or a prism. The refractive index (refractive index at d line) can be <NUM> or more and <NUM> or less, preferably <NUM> or more and <NUM> or less.

The optical element according to this embodiment can be used as a lens, a prism, a reflector, a diffraction grating, or any other constitutive element of optical equipment. For example, the optical element according to this embodiment may be an optical element for any of cameras, binoculars, microscopes, and semiconductor exposure devices. In such equipment, the optical element can be used as an optical element having a light-shielding film outside its optically effective plane.

The optical element according to this embodiment has few white spots noticeable on the element-film interface viewed from the optical element side even when the lens or prism contains <NUM>% by number of cations or more and <NUM>% by number of cations or less. The optical element according to this embodiment has few white spots even when it has the light-shielding film on a ground periphery (edge surface) of the lens or prism.

A method according to an embodiment of the invention for producing an optical element is a method for producing an optical element having a lanthanum-containing glass substrate and a light-shielding film on part of the surface of the glass substrate. The method includes applying a light-shielding paint and curing the applied light-shielding paint. The light-shielding paint used in the method according to this embodiment for producing an optical element is a light-shielding paint described above. The method according to this embodiment for producing an optical element may include preparing the light-shielding paint before the application of the paint. The materials, conditions, and so forth mentioned above for an optical element can be used in the method according to this embodiment for producing an optical element. The following describes the individual steps.

The light-shielding paint used in the method according to this embodiment for producing an optical element may be prepared through the mixing and dispersion of the materials mentioned above for a light-shielding paint. Examples of mixing and dispersion methods that can be used include a ball mill, a bead mill, an impact disperser, a planetary mixer, a homogenizer, and a stirrer.

The fine particles of titania may be nano-dispersed before use. A specific example of a method for nano-dispersion is to disperse the fine particles into nanoparticles using equipment such as a bead mill or an impact disperser. Alternatively, the fine particles of titania may be synthesized as in the form of nanoparticles through a sol-gel process. It is also possible to use commercially available nano-dispersed particles. Application of the light-shielding paint.

The application of the light-shielding paint includes applying an aforementioned light-shielding paint according to an embodiment of the invention to part of the surface of a glass substrate.

The light-shielding paint can be applied using any known method selected in accordance with the intended shape of the coating, such as dipping, spin coating, slit coating, electrostatic coating, and the use of coating jigs such as a brush, sponge, and a bar coater.

The curing of the light-shielding paint includes curing the applied paint. The light-shielding paint can be cured through the drying of the applied paint. It is also possible to cure the light-shielding paint by firing the applied paint.

If the paint is dried, the temperature for drying can be <NUM> or more and <NUM> or less, preferably <NUM> or more and <NUM> or less, more preferably <NUM> or more and <NUM> or less. The duration of drying can be <NUM> minutes or more and <NUM> hours or less, preferably <NUM> minutes or more and <NUM> hours or less, more preferably <NUM> hour or more and <NUM> hours or less. If the paint is fired, the temperature for firing can be <NUM> or more and <NUM> or less, preferably <NUM> or more and <NUM> or less, more preferably <NUM> or more and <NUM> or less. The duration of firing can be <NUM> minutes or more and <NUM> hours or less, preferably <NUM> minutes or more and <NUM> hours or less.

The following describes certain aspects of the invention in more detail by providing examples and comparative examples. No aspect of the invention is limited to these examples. The inspection for white spots and the assessments for vapor pressure and ease of application of light-shielding paints in the Examples and Comparative Examples were conducted as follows.

A light-shielding film <NUM> was formed on a flat glass plate through the application of a light-shielding paint as illustrated in <FIG>. The white spots on the interface between the light-shielding film and the glass plate were imaged using a CCD camera <NUM> under light from the glass plate <NUM> side. The obtained image was processed using image analysis software (Media Cybernetics Image-Pro Plus), and spots that had an area of <NUM><NUM> or more and looked like emitting white light were counted in a field of <NUM><NUM>.

The criteria for the visual inspection were as follows. If the average number of white spots on the light-shielding film was <NUM> or less, the optical element was judged good in appearance (A). If the average number of white spots was <NUM> or more, the optical element was judged not to be sufficiently good in appearance (B or C).

The substrate for inspection samples was a flat plate of S-LAH66 glass material [trade name] (OHARA Inc. ), which contained <NUM>% lanthanum by number of cations. A rough surface of this flat glass plate was polished using a #<NUM> sanding material. A light-shielding paint was applied to the polished surface to a thickness that would be <NUM> after firing. After <NUM>-hour drying at room temperature, the coating was fired at <NUM> for <NUM> hours to form a light-shielding film.

Light-shielding paints for optical elements were assessed for the vapor pressure at <NUM> using the static method. The static method is a technique in which the equilibrium vapor pressure of a liquid is directly measured using a manometer at a constant temperature.

Light-shielding paints for optical elements were assessed for the viscosity at <NUM> through the measurement of viscosity using SV-<NUM> tuning-fork vibration viscometer [trade name] (A&D Co. ) at a constant temperature. Assessment of light-shielding paints for ease of application.

Light-shielding paints for optical elements were assessed for ease of application through the measurement of their displacement on a flat glass plate during drying. First, three strips of Kapton tape (<NUM> × <NUM> × <NUM> each) were attached in a stack to both ends of a flat glass plate (<NUM> × <NUM> × <NUM>) to make a sample with a difference in level (<NUM>) between the flat plate glass and the Kapton tape.

A light-shielding paint for optical elements was uniformly applied to a coating area (<NUM> × <NUM> × <NUM>) of the sample flat plate using a slide coater. After <NUM>-hour drying, the displacement of the paint was measured. If the displacement was <NUM> or less, the light-shielding paint was judged easy to apply (A). If the displacement was more than <NUM>, the paint was judged not to be sufficiently easy to apply (C) as it would be difficult to form a uniform film from the paint.

The following materials were stirred in a stirring vessel using HM-<NUM> planetary mixer [trade name] (Keyence) for <NUM> minutes: <NUM> of jER828 epoxy resin [trade name] (Mitsubishi Chemical), <NUM> of ND139 titania dispersion [trade name] (TAYCA Corporation; a dispersion of titania in PGME; titania concentration, <NUM>% by mass), <NUM> of VALIFAST-BLACK <NUM> [trade name] (dye (<NUM>); Orient Chemical Industries), <NUM> of VALIFAST-RED <NUM> [trade name] (dye (<NUM>); Orient Chemical Industries), <NUM> of VALIFAST-YELLOW <NUM> [trade name] (dye (<NUM>); Orient Chemical Industries), <NUM> of VALIFAST-BLUE <NUM> [trade name] (dye (<NUM>); Orient Chemical Industries), <NUM> of <NUM>-butoxy-<NUM>-propanol (an organic solvent; Kishida Chemical), <NUM> of Aerosil R972 [trade name] ((<NUM>) hydrophobic silica; Nippon Aerosil), <NUM> of Aerosil <NUM> [trade name] ((<NUM>) hydrophilic silica; Nippon Aerosil), and <NUM> of <NUM>-(<NUM>'-thiazolyl)benzimidazole [trade name] (SC Environmental Science). Nine grams of the resulting light-shielding paint was stirred with <NUM> of EH-<NUM> epoxy resin curing agent [trade name] (ADEKA) using HM-<NUM> planetary mixer [trade name] (Keyence) for <NUM> minutes.

The vapor pressure of the obtained light-shielding paint at <NUM> was measured to be <NUM> Pa under the above-described conditions.

Separately, the light-shielding paint was applied to the aforementioned rough surface of a flat glass plate to a thickness that would be <NUM> after firing. After <NUM>-hour drying at room temperature and <NUM>-hour firing at <NUM> in a thermostatic oven, the resulting film was inspected for white spots under the above-described conditions.

The light-shielding paint was also subjected to the aforementioned assessment for ease of application.

Data on this light-shielding paint are presented in Table <NUM>. The results of the visual inspection of the obtained light-shielding film and optical element for white spots and the assessment for ease of application are presented in Table <NUM>.

The vapor pressure of the obtained light-shielding paint for optical elements at <NUM> was measured to be <NUM> Pa under the above-described conditions.

The following materials were stirred in a stirring vessel using HM-<NUM> planetary mixer [trade name] (Keyence) for <NUM> minutes: <NUM> of jER828 epoxy resin [trade name] (Mitsubishi Chemical), <NUM> of ND139 titania dispersion [trade name] (TAYCA Corporation; a dispersion of titania in PGME; titania concentration, <NUM>% by mass), <NUM> of VALIFAST-BLACK <NUM> [trade name] (dye (<NUM>); Orient Chemical Industries), <NUM> of VALIFAST-RED <NUM> [trade name] (dye (<NUM>); Orient Chemical Industries), <NUM> of VALIFAST-YELLOW <NUM> [trade name] (dye (<NUM>); Orient Chemical Industries), <NUM> of VALIFAST-BLUE <NUM> [trade name] (dye (<NUM>); Orient Chemical Industries), <NUM> of <NUM>-ethyl-<NUM>-hexanol (an organic solvent; Kishida Chemical), <NUM> of Aerosil R972 [trade name] ((<NUM>) hydrophobic silica; Nippon Aerosil), <NUM> of Aerosil <NUM> [trade name] ((<NUM>) hydrophilic silica; Nippon Aerosil), and <NUM> of <NUM>-(<NUM>'-thiazolyl)benzimidazole [trade name] (SC Environmental Science). Nine grams of the resulting light-shielding paint was stirred with <NUM> of EH-<NUM> epoxy resin curing agent [trade name] (ADEKA) using HM-<NUM> planetary mixer [trade name] (Keyence) for <NUM> minutes.

The following materials were stirred in a stirring vessel using HM-<NUM> planetary mixer [trade name] (Keyence) for <NUM> minutes: <NUM> of jER828 epoxy resin [trade name] (Mitsubishi Chemical), <NUM> of ND139 titania dispersion [trade name] (TAYCA Corporation; a dispersion of titania in PGME; titania concentration, <NUM>% by mass), <NUM> of VALIFAST-BLACK <NUM> [trade name] (dye (<NUM>); Orient Chemical Industries), <NUM> of VALIFAST-RED <NUM> [trade name] (dye (<NUM>); Orient Chemical Industries), <NUM> of VALIFAST-YELLOW <NUM> [trade name] (dye (<NUM>); Orient Chemical Industries), <NUM> of VALIFAST-BLUE <NUM> [trade name] (dye (<NUM>); Orient Chemical Industries), <NUM> of butyl cellosolve (an organic solvent; Kishida Chemical), <NUM> of Aerosil R972 [trade name] ((<NUM>) hydrophobic silica; Nippon Aerosil), <NUM> of Aerosil <NUM> [trade name] ((<NUM>) hydrophilic silica; Nippon Aerosil), and <NUM> of <NUM>-(<NUM>'-thiazolyl)benzimidazole [trade name] (SC Environmental Science). Nine grams of the resulting light-shielding paint was stirred with <NUM> of EH-<NUM> epoxy resin curing agent [trade name] (ADEKA) using HM-<NUM> planetary mixer [trade name] (Keyence) for <NUM> minutes.

The following materials were stirred in a stirring vessel using HM-<NUM> planetary mixer [trade name] (Keyence) for <NUM> minutes: <NUM> of jER828 epoxy resin [trade name] (Mitsubishi Chemical), <NUM> of ND139 titania dispersion [trade name] (TAYCA Corporation; a dispersion of titania in PGME; titania concentration, <NUM>% by mass), <NUM> of VALIFAST-BLACK <NUM> [trade name] (dye (<NUM>); Orient Chemical Industries), <NUM> of VALIFAST-RED <NUM> [trade name] (dye (<NUM>); Orient Chemical Industries), <NUM> of VALIFAST-YELLOW <NUM> [trade name] (dye (<NUM>); Orient Chemical Industries), <NUM> of VALIFAST-BLUE <NUM> [trade name] (dye (<NUM>); Orient Chemical Industries), <NUM> of benzyl alcohol (an organic solvent; Kishida Chemical), <NUM> of Aerosil R972 [trade name] ((<NUM>) hydrophobic silica; Nippon Aerosil), <NUM> of Aerosil <NUM> [trade name] ((<NUM>) hydrophilic silica; Nippon Aerosil), and <NUM> of <NUM>-(<NUM>'-thiazolyl)benzimidazole [trade name] (SC Environmental Science). Nine grams of the resulting light-shielding paint was stirred with <NUM> of EH-<NUM> epoxy resin curing agent [trade name] (ADEKA) using HM-<NUM> planetary mixer [trade name] (Keyence) for <NUM> minutes.

The following materials were stirred in a stirring vessel using HM-<NUM> planetary mixer [trade name] (Keyence) for <NUM> minutes: <NUM> of jER828 epoxy resin [trade name] (Mitsubishi Chemical), <NUM> of ND139 titania dispersion [trade name] (TAYCA Corporation; a dispersion of titania in PGME; titania concentration, <NUM>% by mass), <NUM> of VALIFAST-BLACK <NUM> [trade name] (dye (<NUM>); Orient Chemical Industries), <NUM> of VALIFAST-RED <NUM> [trade name] (dye (<NUM>); Orient Chemical Industries), <NUM> of VALIFAST-YELLOW <NUM> [trade name] (dye (<NUM>); Orient Chemical Industries), <NUM> of VALIFAST-BLUE <NUM> [trade name] (dye (<NUM>); Orient Chemical Industries), <NUM> of hexamethylphosphoric triamide (an organic solvent; Showa Chemical), <NUM> of Aerosil R972 [trade name] ((<NUM>) hydrophobic silica; Nippon Aerosil), <NUM> of Aerosil <NUM> [trade name] ((<NUM>) hydrophilic silica; Nippon Aerosil), and <NUM> of <NUM>-(<NUM>'-thiazolyl)benzimidazole [trade name] (SC Environmental Science). Nine grams of the resulting light-shielding paint was stirred with <NUM> of EH-<NUM> epoxy resin curing agent [trade name] (ADEKA) using HM-<NUM> planetary mixer [trade name] (Keyence) for <NUM> minutes.

The following materials were stirred in a stirring vessel using HM-<NUM> planetary mixer [trade name] (Keyence) for <NUM> minutes: <NUM> of jER828 epoxy resin [trade name] (Mitsubishi Chemical), <NUM> of ND139 titania dispersion [trade name] (TAYCA Corporation; a dispersion of titania in PGME; titania concentration, <NUM>% by mass), <NUM> of VALIFAST-BLACK <NUM> [trade name] (dye (<NUM>); Orient Chemical Industries), <NUM> of VALIFAST-RED <NUM> [trade name] (dye (<NUM>); Orient Chemical Industries), <NUM> of VALIFAST-YELLOW <NUM> [trade name] (dye (<NUM>); Orient Chemical Industries), <NUM> of VALIFAST-BLUE <NUM> [trade name] (dye (<NUM>); Orient Chemical Industries), <NUM> of propylene glycol monomethyl ether (an organic solvent; Kishida Chemical), <NUM> of Aerosil R972 [trade name] ((<NUM>) hydrophobic silica; Nippon Aerosil), <NUM> of Aerosil <NUM> [trade name] ((<NUM>) hydrophilic silica; Nippon Aerosil), and <NUM> of <NUM>-(<NUM>'-thiazolyl)benzimidazole [trade name] (SC Environmental Science). Nine grams of the resulting light-shielding paint was stirred with <NUM> of EH-<NUM> epoxy resin curing agent [trade name] (ADEKA) using HM-<NUM> planetary mixer [trade name] (Keyence) for <NUM> minutes.

The following materials were stirred in a stirring vessel using HM-<NUM> planetary mixer [trade name] (Keyence) for <NUM> minutes: <NUM> of jER828 epoxy resin [trade name] (Mitsubishi Chemical), <NUM> of ND139 titania dispersion [trade name] (TAYCA Corporation; a dispersion of titania in PGME; titania concentration, <NUM>% by mass), <NUM> of VALIFAST-BLACK <NUM> [trade name] (dye (<NUM>); Orient Chemical Industries), <NUM> of VALIFAST-RED <NUM> [trade name] (dye (<NUM>); Orient Chemical Industries), <NUM> of VALIFAST-YELLOW <NUM> [trade name] (dye (<NUM>); Orient Chemical Industries), <NUM> of VALIFAST-BLUE <NUM> [trade name] (dye (<NUM>); Orient Chemical Industries), <NUM> of toluene (an organic solvent; Kishida Chemical), <NUM> of Aerosil R972 [trade name] ((<NUM>) hydrophobic silica; Nippon Aerosil), <NUM> of Aerosil <NUM> [trade name] ((<NUM>) hydrophilic silica; Nippon Aerosil), and <NUM> of <NUM>-(<NUM>'-thiazolyl)benzimidazole [trade name] (SC Environmental Science). Nine grams of the resulting light-shielding paint was stirred with <NUM> of EH-<NUM> epoxy resin curing agent [trade name] (ADEKA) using HM-<NUM> planetary mixer [trade name] (Keyence) for <NUM> minutes.

In Examples <NUM> to <NUM>, the light-shielding paints having a vapor pressure of <NUM> Pa or more and <NUM> Pa or less at <NUM> sufficiently filled cracks in an edge surface of the optical elements, preventing white spots from occurring on the light-shielding films formed through the application of the paints. The uniformity of the coatings of the light-shielding paints in Examples <NUM> to <NUM>, furthermore, allowed the production of light-shielding films with good appearance and preserved performance in shielding light and optical elements having them.

In Comparative Example <NUM>, however, white spots were few in number, and the paint did not form a uniform light-shielding film because of an increased displacement. Furthermore, residue of the organic solvent in the light-shielding film affected the chemical resistance of the film in Comparative Example <NUM>. In Comparative Examples <NUM> to <NUM>, the vapor pressure of the light-shielding paints at <NUM> as high as more than <NUM> Pa led to insufficient filling of cracks in an edge surface of the optical elements, resulting in a large number of white spots.

Optical elements according to an aspect of the present invention having a light-shielding film can be applied to optical equipment such as cameras, binoculars, and semiconductor exposure devices.

An aspect of the present invention provides a light-shielding paint that produces a light-shielding film with few white spots noticeable on the element-film interface (the interface between the light-shielding film and the optical element on which it has been formed) viewed from the optical element side. Some other aspects of the present invention provide such a light-shielding film and an optical element having such a light-shielding film.

Claim 1:
A method for producing an optical element having a lanthanum-containing glass substrate and a light-shielding film on part of a surface of the glass substrate, the method comprising:
applying a light-shielding paint on part of the surface of the glass substrate; and
curing the applied light-shielding paint,
the light-shielding paint at least containing:
an epoxy resin;
fine particles of titania;
a dye;
an organic solvent; and
an amine-based curing agent,
characterized in that
the light-shielding paint further comprises inorganic fine particles other than the fine particles of titania;
the light-shielding paint has a viscosity of <NUM> mPa·s or more and <NUM> mPa·s or less, and
the light-shielding paint has a vapor pressure of <NUM> Pa or more and <NUM> Pa or less at a temperature of <NUM>.