Patent Grant
10240063
Field of the Invention
The present invention relates to a light-shielding paint used for optical devices such as cameras, binoculars, and microscopes, a light-shielding paint set, a light-shielding film and a method for producing the light-shielding film, and an optical element and a method for producing the optical element.
Description of the Related Art
Light-shielding films used for optical elements or the like are mainly films disposed on the surface of glass. Such optical elements may be lenses, prisms, or other optical glasses. Hereafter, light-shielding films will be described using a lens as an example.
As illustrated in
The light-shielding film 1 for lenses is disposed at a position at which the light-shielding film 1 is visible when a lens user sees a lens barrel. Therefore, the light-shielding film 1 needs to have high-quality appearance for a long time. Specifically, a light-shielding film having appearance which is not easily changed is required even if being used in a high-temperature and high-humidity environment.
In recent years, there have been many glasses for optical elements such as lanthanum-based glasses, titanium-based glasses, alumina-based glasses, zirconia-based glasses, fluorine-based glasses, niobium-based glasses, tantalum-based glasses, and boron-based glasses, in addition to known silica-based glasses, for the purpose of providing characteristics in terms of refractive index, Abbe number, dispersion, and the like. When a light-shielding film is formed on each of these glasses and left in a high-temperature and high-humidity environment for a long time, white spots are generated at an interface between the glass and the light-shielding film, which may degrade the appearance.
WO2013125544A (hereafter referred to as “Patent Document 1”) discloses a light-shielding film formed by curing a light-shielding paint which contains an epoxy resin and an amine curing agent and in which, for example, the equivalent ratio of the active hydrogen equivalent of the amine curing agent and the epoxy equivalent of the epoxy resin is specified. Patent Document 1 discloses a light-shielding film that is less likely to be detached in a high-temperature and high-humidity environment and has resistance to a cleaning liquid, which is achieved by increasing the cross-linking density of the epoxy resin.
However, such an increase in the cross-linking density of the epoxy resin in the light-shielding film in Patent Document 1 has limitation in terms of preventing the detachment of a light-shielding film including the generation of white spots.
A light-shielding paint according to an embodiment of the present invention includes an epoxy group-containing compound, an inorganic fine particle, a coloring agent, and an amine curing agent, wherein a ratio (A′/A) of a mass (A′) of the amine curing agent to an active hydrogen equivalent (A) of the amine curing agent and a ratio (E′/E) of a mass (E′) of the epoxy group-containing compound to an epoxy equivalent (E) of the epoxy group-containing compound satisfy formula (1) below.
0.1≤[(A′/A)/(E′/E)]≤0.45 Formula (1)
A light-shielding paint set for an optical element according to an embodiment of the present invention includes two or more units which includes a unit containing an epoxy group-containing compound and a unit containing an amine curing agent, wherein the light-shielding paint set contains an inorganic fine particle and a coloring agent in any of the units, and a ratio (A′/A) of a mass (A′) of the amine curing agent to an active hydrogen equivalent (A) of the amine curing agent and a ratio (E′/E) of a mass (E′) of the epoxy group-containing compound to an epoxy equivalent (E) of the epoxy group-containing compound satisfy formula (1) below.
0.1≤((A′/A)/(E′/E))≤0.45 Formula (1)
A light-shielding film according to an embodiment of the present invention is produced from a light-shielding paint that contains an epoxy group-containing compound, an inorganic fine particle, a coloring agent, and an amine curing agent, wherein a ratio (A′/A) of a mass (A′) of the amine curing agent to an active hydrogen equivalent (A) of the amine curing agent and a ratio (E′/E) of a mass (E′) of the epoxy group-containing compound to an epoxy equivalent (E) of the epoxy group-containing compound satisfy formula (1) below.
0.1≤[(A′/A)/(E′/E)]≤0.45 Formula (1)
An optical element according to an embodiment of the present invention includes a light-shielding film disposed on a portion of a base made of an optical material, wherein the light-shielding film is produced from a light-shielding paint that contains an epoxy group-containing compound, an inorganic fine particle, a coloring agent, an amine curing agent, and a curing catalyst, and a ratio (A′/A) of a mass (A′) of the amine curing agent to an active hydrogen equivalent (A) of the amine curing agent and a ratio (E′/E) of a mass (E′) of the epoxy group-containing compound to an epoxy equivalent (E) of the epoxy group-containing compound satisfy formula (1) below.
0.1≤[(A′/A)/(E′/E)]≤0.45 Formula (1)
A method for producing a light-shielding film according to an embodiment of the present invention includes applying, onto a base, a light-shielding paint containing an epoxy group-containing compound, an inorganic fine particle, a coloring agent, and an amine curing agent and curing the applied light-shielding paint in an atmosphere of 20° C. or more and 200° C. or less, wherein a ratio (A′/A) of a mass (A′) of the amine curing agent to an active hydrogen equivalent (A) of the amine curing agent and a ratio (E′/E) of a mass (E′) of the epoxy group-containing compound to an epoxy equivalent (E) of the epoxy group-containing compound satisfy formula (1) below.
0.1≤((A′/A)/(E′/E))≤0.45 Formula (1)
A method for producing an optical element according to an embodiment of the present invention, the optical element including a light-shielding film disposed on a peripheral surface of a base made of an optical material, includes applying, onto the peripheral surface of the base, a light-shielding paint containing an epoxy group-containing compound, an inorganic fine particle, a coloring agent, and an amine curing agent and curing the applied light-shielding paint in an atmosphere of 20° C. or more and 200° C. or less, wherein a ratio (A′/A) of a mass (A′) of the amine curing agent to an active hydrogen equivalent (A) of the amine curing agent and a ratio (E′/E) of a mass (E′) of the epoxy group-containing compound to an epoxy equivalent (E) of the epoxy group-containing compound satisfy formula (1) below.
0.1≤((A′/A)/(E′/E))≤0.45 Formula (1)
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
In view of the foregoing background art, the present invention provides a light-shielding paint that suppresses, even in a high-temperature and high-humidity environment, the generation of white spots which are generated at an interface between a glass and a light-shielding film and cause appearance defects, a light-shielding film, and an optical element.
Hereafter, embodiments of the present invention will be described.
A light-shielding paint used for an optical element or the like according to an embodiment of the present invention suppresses white spots that cause appearance defects and provides a light-shielding film also having a function of reducing internal reflection.
First, a structure of the light-shielding film for reducing the internal reflection will be described. Then, a structure of the light-shielding film for suppressing the generation of white spots according to an embodiment of the present invention will be described. Then, a light-shielding paint, a light-shielding paint set, a light-shielding film, an optical element, a method for producing the light-shielding film, and a method for producing the optical element according to an embodiment of the present invention for achieving the foregoing will be described. Structure of light-shielding film for reducing internal reflection
The principle of internal reflection of an optical element will be described in detail with reference to
The first reflected light 9 can be reduced by bringing the refractive indices of the light-shielding film 1 and the lens 2 close to each other. The reason why the internal reflection is reduced by bringing the refractive indices close to each other is as follows. As shown in formula (2) below, the reflectance R at the interface between the light-shielding film 1 and the lens 2 is determined by the difference between the refractive index n1 of the light-shielding film 1 and the refractive index n0 of the lens 2 on the incident light 3 side, and the reflectance R decreases as the difference decreases.
The second reflected light 11 can be reduced by absorbing the transmitted light 10 that has passed through the light-shielding film. In order to efficiently absorb the transmitted light 10 into the film, the light-shielding film 1 can contain a coloring agent or the like so as to have a high degree of blackness.
Structure of Light-shielding Film for Suppressing Generation of White Spots in High-Temperature and High-Humidity Environment
The principle of the generation of white spots generated when the light-shielding film is left to stand in a high-temperature and high-humidity environment will be described. As illustrated in
As a result of thorough studies on the cause of the partial detachment (generation of white spots) after the light-shielding film is left to stand in a high-temperature and high-humidity environment, the present inventors have found that the partial detachment is caused by penetration of water, and thus the partial detachment can be suppressed by controlling the penetration of water.
Next, a method for suppressing the partial detachment of the light-shielding film in a high-temperature and high-humidity environment will be described.
The light-shielding film according to an embodiment of the present invention is formed by curing at least an epoxy group-containing compound, an amine curing agent, and a coloring agent. However, an unreacted amine group in the amine curing agent, in particular, a primary amine has high water absorbency. The amount of the unreacted amine having high water absorbency needs to be decreased to suppress the partial detachment of the light-shielding film. In an embodiment of the present invention, the amount of the unreacted amine group can be decreased by decreasing an equivalent ratio which is a ratio of the amount of the amine curing agent added per unit mass to the amount of a resin having an epoxy group per unit mass. Since the refractive index of the amine curing agent is generally low, the internal reflectance can be decreased by decreasing the amount of the amine curing agent added. Although such a decrease in the amount of the amine curing agent added reduces the cross-linking density of the light-shielding film, the reduction in the cross-linking density can be suppressed by any one of a method of high-temperature curing, a method of an increase in curing time, and a method of addition of a curing catalyst or a combined method thereof.
Light-shielding Paint
Next, materials for the light-shielding paint used for the optical element according to an embodiment of the present invention will be described. Hereafter, the contents of materials for the light-shielding paint are the contents of materials for the light-shielding paint containing a curing agent unless otherwise specified.
The light-shielding paint according to an embodiment of the present invention contains an epoxy group-containing compound, inorganic fine particles, a coloring agent, and an amine curing agent.
The ratio (A′/A) of the mass (A′) of the amine curing agent to the active hydrogen equivalent (A) of the amine curing agent indicates the number of active hydrogen atoms per unit mass. Furthermore, the ratio (E′/E) of the mass (E′) of the epoxy group-containing compound to the epoxy equivalent (E) of the epoxy group-containing compound indicates the number of epoxy groups per unit mass (epoxy equivalent). In the light-shielding paint according to an embodiment of the present invention, (A′/A)/(E′/E) satisfies formula (1).
0.1≤[(A′/A)/(E′/E)]≤0.45 Formula (1)
If (A′/A)/(E′/E) of the light-shielding paint is less than 0.1, the cross-linking density decreases and the solvent resistance degrades. If (A′/A)/(E′/E) is more than 0.45, the number of white spots generated after the light-shielding film is left to stand in a high-temperature and high-humidity environment increases.
Hereafter, the epoxy equivalent of the epoxy group-containing compound is measured in conformity with JIS K 7236 (2001). When an epoxy coupling agent is used, the epoxy equivalent of the epoxy group-containing compound indicates an equivalent including the coupling agent. The active hydrogen equivalent of the amine curing agent indicates a number obtained by dividing the molecular weight by the number of functional groups.
Epoxy Group-containing Compound
The epoxy group-containing compound of the light-shielding paint according to an embodiment of the present invention can be an epoxy resin or an epoxy coupling agent.
The epoxy resin of the light-shielding paint according to an embodiment of the present invention can be a bisphenol A epoxy resin, a bisphenol F epoxy resin, a polyfunctional epoxy resin, a flexible epoxy resin, a brominated epoxy resin, a glycidyl ester epoxy resin, a high-molecular-weight epoxy resin, or a biphenyl epoxy resin. These epoxy resins may be used alone or in combination of two or more as a mixture.
The content of the epoxy resin in the light-shielding paint according to an embodiment of the present invention is, for example, 5.0 mass % or more and 25.0 mass % or less. If the content of the epoxy resin is less than 5.0 mass %, the amount of a resin component in the light-shielding paint is small, which degrades the solvent resistance. If the content of the epoxy resin is more than 25.0 mass %, the refractive index decreases and thus the internal reflection increases.
The content of the epoxy coupling agent in the light-shielding paint according to an embodiment of the present invention is, for example, 0.5 mass % or more and 15.0 mass % or less. If the content of the epoxy coupling agent is less than 0.5 mass %, the adhesion with a base is decreased when the light-shielding film is formed. If the content of the epoxy coupling agent is more than 15.0 mass %, the adhesion with a base is decreased when the light-shielding film is formed. The epoxy coupling agent can be a commercially available silane coupling agent having an epoxy group or a synthesized silane coupling agent. Examples of the silane coupling agent include 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, and 3-glycidoxypropyltriethoxysilane.
Inorganic Fine Particle
The inorganic fine particles used for the light-shielding paint according to an embodiment of the present invention are, for example, silica fine particles or inorganic fine particles having a refractive index (nd) of 2.2 or more, or a mixture of the particles. The number-average particle size of the inorganic fine particles is preferably 5 nm or more and 1000 nm or less and more preferably 10 nm or more and 100 nm or less. If the number-average particle size is less than 5 nm, the stability of the light-shielding paint degrades, which increases the viscosity and easily causes gelation. If the number-average particle size of the inorganic fine particles is more than 1000 nm, an effect of suppressing the generation of white spots of the light-shielding film decreases.
When the silica fine particles are used, irregularities are formed on the surface of the light-shielding film and the reflection at the surface can be suppressed. The silica fine particles also have an effect of preventing sagging.
When the inorganic fine particles having a refractive index (nd) of 2.2 or more are used, the refractive index of the formed light-shielding film can be increased and thus the internal reflection is reduced. Examples of the inorganic fine particles having a refractive index (nd) of 2.2 or more include fine particles of titanium oxide, zirconium oxide, aluminum oxide, yttrium oxide, cadmium oxide, diamond, strontium titanate, and germanium. Among them, inorganic fine particles having a refractive index (nd) of 2.2 or more and 3.5 or less can be particularly used. If the refractive index of the inorganic fine particles is less than 2.2, an increase in the refractive index of the light-shielding film is small. The difference in refractive index between a base and the light-shielding film increases and thus the internal reflection is not effectively suppressed.
The number-average particle size of the inorganic fine particles having a refractive index (nd) of 2.2 or more is preferably 10 nm or more and 100 nm or less and more preferably 10 nm or more and 20 nm or less. The average particle size of the inorganic fine particles having a refractive index (nd) of 2.2 or more can be as small as possible, but it is substantially difficult to disperse the inorganic fine particles with a particle size of 10 nm or less. If the number-average particle size of the inorganic fine particles is more than 100 nm, scattering is easily caused. The average particle size of the inorganic fine particles is an actual size of particles present in the light-shielding film. For example, when the inorganic fine particles are aggregated, the average particle size of the inorganic fine particles is a size of aggregated particles.
The content of the inorganic fine particles in the light-shielding paint according to an embodiment of the present invention is preferably 2.5 mass % or more and 20.0 mass % or less and more preferably 5.0 mass % or more and 7.5 mass % or less. If the content is less than 2.5 mass %, an increase in the refractive index is small and the internal reflection increases. If the content is more than 20.0 mass %, the adhesion and durability of the film unfavorably degrade.
Coloring Agent
The coloring agent used for the light-shielding paint according to an embodiment of the present invention can be a dye, a pigment, or a mixture of dyes and pigments. Any dye may be used as long as the dye absorbs visible light having a wavelength of 400 nm to 700 nm and is soluble in a solvent. A single dye may be used or several dyes with colors such as black, red, yellow, and blue may be mixed with each other. Any pigment may be used as long as the pigment absorbs visible light having a wavelength of 400 nm to 700 nm. The pigment can be carbon black, titanium black, iron oxide, or a copper-iron-manganese composite oxide. The number-average particle size of the pigment is, for example, 5 nm or more and 200 nm or less. If the average particle size of the pigment is less than 5 nm, the stability of the light-shielding paint degrades. If the average particle size of the pigment is more than 200 nm, the internal reflection increases when the light-shielding film is formed.
The content of the coloring agent in the light-shielding paint according to an embodiment of the present invention is preferably 2.5 mass % or more and 15.0 mass % or less and more preferably 5.0 mass % or more and 7.5 mass % or less.
Amine Curing Agent
The light-shielding paint according to an embodiment of the present invention contains an amine curing agent for curing the epoxy group-containing compound contained in the light-shielding paint. The amine curing agent is not particularly limited as long as it satisfies desired characteristics, and a publicly known curing agent can be used. The amine curing agent can be a linear aliphatic amine curing agent, a polyamide-based amine curing agent, an alicyclic amine curing agent, an aromatic amine curing agent, dicyandiamide, or adipic dihydrazide. They may be used alone or in combination of two or more as a mixture.
The content of the amine curing agent in the light-shielding paint according to an embodiment of the present invention is, for example, 0.5 mass % or more and 13.0 mass % or less. If the content of the amine curing agent is less than 0.5 mass %, the degree of curing of the light-shielding film decreases, which degrades the adhesion of the light-shielding film to a base. Furthermore, if the content of the amine curing agent is more than 13.0 mass %, the optical properties degrade.
Organic Solvent
The light-shielding paint according to an embodiment of the present invention can contain an organic solvent because the viscosity can be controlled. The organic solvent used for the light-shielding paint according to an embodiment of the present invention is not particularly limited as long as the organic solvent satisfies the dispersibility of the inorganic fine particles and the solubility of the epoxy group-containing compound, the coloring agent, and the amine curing agent. Examples of the organic solvent include propylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, methyl ethyl ketone, methyl isobutyl ketone, xylene, toluene, isopropyl alcohol, acetone, and ethanol. These organic solvents may be used alone or in combination of two or more as a mixture.
The viscosity of the light-shielding paint is, for example, 10 mPa·s or more and 1000 mPa·s or less. If the viscosity of the light-shielding paint is less than 10 mPa·s, the light-shielding paint is not easily coated. If the viscosity is more than 1000 mPa·s, the light-shielding film may have thin portions after a coating process.
Curing Catalyst
The light-shielding paint according to an embodiment of the present invention can contain a curing catalyst for the purpose of increasing the cross-linking density of the epoxy group-containing compound when the light-shielding film is formed and thus improving the solvent resistance. The curing catalyst used in the present invention is, for example, a tertiary amine or an imidazole compound. Examples of the tertiary amine include benzyldimethylamine, 2-(dimethylaminomethyl)phenol, 2,4,6-tris(diaminomethyl)phenol, and tri-2-ethylhexanoate. Examples of the imidazole compound include 2-methylimidazole, 2-ethyl-4-methylimidazole, 2-undecylimidazole, 2-heptadecylimidazole, 2-phenylimidazole, 1-benzyl-2-methylimidazole, 1-cyanoethyl-2-methylimidazole, and 2,4-diamino-6-[2-methylimidazolyl-(1)]-ethyl-S-triazine.
The content of the curing catalyst in the light-shielding paint according to an embodiment of the present invention is, for example, 0.5 mass % or more and 2.5 mass % or less. If the content of the curing catalyst is less than 0.5 mass %, the solvent resistance of the formed light-shielding film degrades. If the content of the curing catalyst is more than 2.5 mass %, the cross-linking density of the formed light-shielding film increases and the toughness of the film sometimes decreases.
Additive
The light-shielding paint according to an embodiment of the present invention may contain an additive as long as the original purpose is not impaired. The additive is, for example, a fungicide or an antioxidant.
The content of the additive in the light-shielding paint according to an embodiment of the present invention is preferably 5.0 mass % or less and more preferably 3.0 mass % or less.
Light-shielding Paint Set
Next, a light-shielding paint set according to an embodiment of the present invention will be described.
The light-shielding paint set according to an embodiment of the present invention includes two or more units which include a unit containing an epoxy group-containing compound and a unit containing an amine curing agent. When all the units are mixed with each other, the above-described light-shielding paint is obtained.
The light-shielding paint set according to an embodiment of the present invention separately includes the unit containing an epoxy group-containing compound and the unit containing an amine curing agent, and thus has excellent shelf life. The light-shielding paint set according to an embodiment of the present invention contains the inorganic fine particles and the coloring agent in one or more of the units. That is, the inorganic fine particles and the coloring agent are contained in the unit containing an epoxy group-containing compound, the unit containing an amine curing agent, and/or a unit other than the foregoing units when the light-shielding paint set includes three or more units.
The ratio (A′/A) of the mass (A′) of the amine curing agent contained in the light-shielding paint set to the active hydrogen equivalent (A) of the amine curing agent and the ratio (E′/E) of the mass (E′) of the epoxy resin to the epoxy equivalent (E) of the epoxy group-containing compound satisfy formula (1) below.
0.1≤((A′/A)/(E′/E))≤0.45 Formula (1)
The light-shielding paint set according to an embodiment of the present invention contains, for example, a curing catalyst in any of the units. The curing catalyst is, for example, a tertiary amine or an imidazole compound.
The light-shielding paint according to an embodiment of the present invention can be obtained by mixing and dispersing the materials contained in all the units of the light-shielding paint set according to an embodiment of the present invention. The mixing and dispersing can be performed with a ball mill, a bead mill, an impact disperser, a planetary disperser, a homogenizer, or a stirrer.
Light-shielding Film
Next, a light-shielding film according to an embodiment of the present invention will be described.
The light-shielding film according to an embodiment of the present invention is a light-shielding film produced from the light-shielding paint containing the epoxy group-containing compound, the inorganic fine particles, the coloring agent, and the amine curing agent. In the light-shielding paint, the ratio (A′/A) of the mass (A′) of the amine curing agent to the active hydrogen equivalent (A) of the amine curing agent and the ratio (E′/E) of the mass (E′) of the epoxy group-containing compound to the epoxy equivalent (E) of the epoxy group-containing compound satisfy formula (1) below.
0.1≤[(A′/A)/(E′/E)]≤0.45 Formula (1)
Next, each component contained in the light-shielding film according to an embodiment of the present invention will be described. The materials contained in the light-shielding film are, for example, the materials described in the light-shielding film. The content of each material for the light-shielding film is as follows.
Epoxy Group-containing Compound
The content of the epoxy group-containing compound in the light-shielding film according to an embodiment of the present invention is preferably 5.0 mass % or more and 60.0 mass % or less and more preferably 5.0 mass % or more and 40.0 mass % or less. If the content of the epoxy group-containing compound is less than 5.0 mass %, the solvent resistance degrades. If the content of the epoxy group-containing compound is more than 60.0 mass %, the internal reflection increases.
Inorganic Fine Particle
The content of the inorganic fine particles in the light-shielding film according to an embodiment of the present invention is preferably 5.0 mass % or more and 40.0 mass % or less and 10.0 mass % or more and 15.0 mass % or less. If the content is less than 5.0 mass %, an increase in the refractive index is small and thus the internal reflection increases. If the content is more than 40.0 mass %, the adhesion and durability of the film are unfavorably degrade.
Coloring Agent
The content of the coloring agent in the light-shielding film according to an embodiment of the present invention is preferably 5.0 mass % or more and 30.0 mass % or less and more preferably 10.0 mass % or more and 15.0 mass % or less.
Amine Curing Agent
The content of the amine curing agent in the light-shielding film according to an embodiment of the present invention is preferably 1.0 mass % or more and 25.0 mass % or less. If the content of the amine curing agent is less than 1.0 mass %, the degree of curing of the light-shielding film decreases and thus the adhesion of the light-shielding film to a base degrades. If the content of the amine curing agent is more than 25.0 mass %, the optical properties degrade.
Curing Catalyst
The content of the curing catalyst in the light-shielding film according to an embodiment of the present invention is preferably 1.0 mass % or more and 5 mass % or less. If the content of the curing catalyst is less than 1.0 mass %, the solvent resistance of the formed light-shielding film degrades. If the content of the curing catalyst is more than 5.0 mass %, the cross-linking density of the formed light-shielding film increases and the toughness of the film sometimes decreases.
Additive
The content of the additive in the light-shielding film according to an embodiment of the present invention is preferably 15.0 mass % or less and more preferably 10.0 mass % or less.
Optical Element
Next, an optical element according to an embodiment of the present invention will be described.
In the optical element according to an embodiment of the present invention, the light-shielding film is disposed on a portion (peripheral surface) of a base formed of an optical material. The optical element according to an embodiment of the present invention includes the light-shielding film produced from the light-shielding paint containing the epoxy group-containing compound, the inorganic fine particles, the coloring agent, the amine curing agent, and the curing catalyst. In the light-shielding paint, the ratio (A′/A) of the mass (A′) of the amine curing agent to the active hydrogen equivalent (A) of the amine curing agent and the ratio (E′/E) of the mass (E′) of the epoxy group-containing compound to the epoxy equivalent (E) of the epoxy group-containing compound satisfy formula (1) below.
0.1≤[(A′/A)/(E′/E)]≤0.45 Formula (1)
The base is, for example, an optical lens or a prism. The difference in refractive index (nd) between the optical material and the light-shielding film is, for example, 0.0 or more and 0.2 or less in order to decrease the internal reflection.
The optical element according to an embodiment of the present invention can be used for optical devices such as cameras, binoculars, microscopes, and semiconductor exposure devices.
Method for Producing Light-shielding Film
Next, a method for producing the light-shielding film according to an embodiment of the present invention will be described.
The light-shielding film according to an embodiment of the present invention is produced by curing the light-shielding paint. The method for producing a light-shielding film according to an embodiment of the present invention includes applying, onto a base, a light-shielding paint containing an epoxy group-containing compound, inorganic fine particles, a coloring agent, and an amine curing agent and curing the applied light-shielding paint in an atmosphere of 20° C. to 200° C. In the light-shielding paint, the ratio (A′/A) of the mass (A′) of the amine curing agent to the active hydrogen equivalent (A) of the amine curing agent and the ratio (E′/E) of the mass (E′) of the epoxy group-containing compound to the epoxy equivalent (E) of the epoxy group-containing compound satisfy formula (1) below.
0.1≤((A′/A)/(E′/E))≤0.45 Formula (1)
In the step of applying the light-shielding paint, the light-shielding paint can be applied after being dispersed by a desired dispersion method. The dispersion can be performed with a ball mill, a bead mill, an impact disperser, a planetary disperser, a homogenizer, or a stirrer. In the step of applying the light-shielding paint, the light-shielding paint is applied using a brush or trace dispensing.
In the step of curing the light-shielding paint, the applied light-shielding paint is cured in an atmosphere of 20° C. or more and 200° C. or less and preferably in an atmosphere of 40° C. or more and 200° C. or less. If the light-shielding paint is cured at less than 20° C., the cross-linking density decreases and thus the solvent resistance degrades. If the light-shielding paint according to an embodiment of the present invention is cured at more than 200° C., the stress increases and the resulting light-shielding film is easily cracked.
The light-shielding paint used in the method for producing a light-shielding film according to an embodiment of the present invention desirably satisfy the above-described materials and conditions.
Method for Producing Optical Element
Next, a method for producing an optical element according to an embodiment of the present invention will be described.
The method for producing an optical element according to an embodiment of the present invention is a method for producing an optical element including a light-shielding film disposed on a peripheral surface of a base made of an optical material. The method for producing an optical element according to an embodiment of the present invention includes applying a light-shielding paint containing an epoxy group-containing compound, inorganic fine particles, a coloring agent, and an amine curing agent onto a peripheral surface of a base and curing the applied paint in an atmosphere of 20° C. or more and 200° C. or less. In the light-shielding paint used, the ratio (A′/A) of the mass (A′) of the amine curing agent to the active hydrogen equivalent (A) of the amine curing agent and the ratio (E′/E) of the mass (E′) of the epoxy group-containing compound to the epoxy equivalent (E) of the epoxy group-containing compound satisfy formula (1) below.
0.1≤((A′/A)/(E′/E))≤0.45 Formula (1)
The base made of an optical material may be a lens or a prism. The difference in refractive index (nd) between the optical material and the light-shielding film is, for example, 0.0 or more and 0.2 or less in order to reduce the internal reflection.
The method for producing an optical element according to an embodiment of the present invention desirably satisfies the conditions and the like described in the method for producing a light-shielding film.
Hereafter, Examples of the present invention will be described.
The preparation of a light-shielding paint, the production of a light-shielding film, the evaluation of optical properties, and the evaluation of appearance in Examples 1 to 16 were performed by the following methods.
Measurement of Average Particle Size
The average particle size of the inorganic fine particles was measured using a dynamic light scattering instrument (Zeta sizer Nano MPT-2, SYSMEX CORPORATION). A slurry diluted with propylene glycol monomethyl ether was inserted into a cell, and the average of 20 measurements at a voltage of 5 mV was detected. The average particle size was a particle size at a peak of the number distribution.
Evaluation of Optical Properties
Measurement Method of Internal Reflectance
As illustrated in
n=sin d/sin e Formula (3)
Subsequently, the light refracted by the triangular prism 14 is reflected at the bottom plane of the triangular prism 14 and emitted from the triangular prism 14. The intensity of the reflected light was detected with a detector in a visible region having a wavelength of 400 nm to 700 nm. A background sample was prepared by applying nothing to a bottom plane of the triangular prism 14 in which three planes of the bottom plane, an incidence plane, and a reflection plane were specular surfaces. A light-shielding film was formed on the bottom plane of the triangular prism 14 in which three planes of the bottom plane, an incidence plane, and a reflection plane were specular surfaces, and the internal reflectance was measured. The internal reflectance was the average of internal reflectances obtained by measuring internal reflection of visible light in a wavelength range of 400 nm to 700 nm at intervals of 1 nm.
Method for Evaluating Number of White Spots after Light-Shielding Film is Left to Stand in High-Temperature and High-Humidity Environment
The number of white spots after the light-shielding film was left to stand in a high-temperature and high-humidity environment was evaluated as follows. A glass for measurement was frosted with #240, had a diameter of 30 mm and a thickness of 1 mm, and was made of S-LAL 18. First, a light-shielding paint was applied onto a frosted surface of the glass using a sponge so as to have a thickness of 5.0 μm and cured by the above-described method for producing a light-shielding film. Then, the resulting product was left to stand in a furnace with an ambient temperature of 60° C. and a humidity of 90% for 250 hours to obtain a sample for evaluating white spots. The sample for evaluating white spots was photographed with a microscope. The number of white spots having a diameter of 0.02 mm or more was counted in the obtained image with a size of 6 mm2. The number of white spots generated was evaluated based on the criteria below. “A” is given to a light-shielding film having excellent appearance. “B” is given to a light-shielding film having good appearance. “C” is given to a light-shielding film having poor appearance.
The solvent resistance was evaluated by the following method. First, a light-shielding film having a thickness of 5.0 μm was formed on a freely selected ϕ30 mm glass by a method for forming a light-shielding film in each Example. The resulting light-shielding film was immersed in an isopropyl alcohol (hereafter referred to as “IPA”) solution for 10 minutes to observe whether the IPA was colored or not. “A” is given to a light-shielding film having excellent solvent resistance. “B” and “C” are given to a light-shielding film having good solvent resistance. “D” is given to a light-shielding film having poor solvent resistance.
Preparation of Light-shielding Paint
In Example 1, a light-shielding paint was prepared by the following method. That is, 42.9 g of propylene glycol monomethyl ether, a dispersant, and 14.3 g of titania fine particles having a refractive index (nd) of 2.2 or more were dispersed in a bead mill (Ultra Apex Mill, Kotobuki Industries Co., Ltd.) using ϕ50 μm beads. Thus, 57.2 g of a slurry in which the number-average particle size of the titania fine particles was 20 nm was obtained. Then, 57.2 g of the slurry obtained by using the bead mill, 21 g of an epoxy resin A, 1 g of a coupling agent, 13 g of a coloring agent, and 40 g of propylene glycol monomethyl ether were weighed and inserted into a ball mill pot. Then, five magnetic balls having a diameter of 20 mm were inserted into the ball mill pot. Titanium oxide (MT-05, TAYCA) was used as the inorganic fine particles having a refractive index (nd) of 2.2 or more. A polycondensate (Epicoat 828, Mitsubishi Chemical Corporation) of 4,4′-isopropylidenediphenol and 1-chloro-2,3-epoxypropane was used as the epoxy resin A. An epoxy-based silane coupling agent (KBM 403, Shin-Etsu Chemical Co., Ltd.) was used as the coupling agent. The ball mill pot containing the prepared paint and the magnetic balls was set on a roll coater and stirring was performed at 66 rpm for 48 hours to prepare a light-shielding paint of Example 1.
A mixture of a black dye, a red dye, a yellow dye, and a blue dye was used as an organic dye. For each dye, any of the dyes listed below was used.
The black dye was selected from VALIFAST BLACK 1821 (Orient Chemical Industries Co., Ltd.), VALRFAST BLACK 3810 (Orient Chemical Industries Co., Ltd.), Oil Black HBB (Orient Chemical Industries Co., Ltd.), and Aizen Spilon Black MHS-Liquid (Hodogaya Chemical Co., Ltd.).
The red dye was selected from VALIFAST RED 3320 (Orient Chemical Industries Co., Ltd.) and Aizen Spilon Red BEH S-Liquid (Hodogaya Chemical Co., Ltd.).
The yellow dye was selected from OIL YELLOW 129, VALIFAST YELLOW 3108, and Aizen Spilon Yellow RH S-Liquid (Hodogaya Chemical Co., Ltd.).
The blue dye was selected from VALIFAST BLUE 1605 (Orient Chemical Industries Co., Ltd.), VALIFAST BLUE 2650 (Orient Chemical Industries Co., Ltd.), VALIFAST BLUE 2606 (Orient Chemical Industries Co., Ltd.), and VALIFAST BLUE 2620 (Orient Chemical Industries Co., Ltd.).
Production of Light-shielding Film
In Example 1, a light-shielding film was produced by the following method. That is, 1.9 g of an amine curing agent A and 1 g of a curing catalyst A were added to 132.2 g of the light-shielding paint, and stirring was performed using a roll coater for 30 minutes. An aliphatic amine curing agent was used as the amine curing agent A (ADEKA Hardener EH6019, ADEKA Corporation), and 2,4,6-tris(diaminomethyl)phenol was used as the curing catalyst A. The stirring condition of the roll coater was 66 rpm. The epoxy equivalent of the epoxy resin A was 190 g/eq, the epoxy equivalent of the coupling agent was 236 g/eq, and (E′/E)=0.111+0.004=0.115. The active hydrogen equivalent of the amine curing agent A was 80 g/eq, and (A′/A)=0.011. As a result of the calculation based on the formula (1), the equivalent ratio (A′/A)/(E′/E) was 0.1.
The obtained light-shielding paint/curing agent solution was applied onto a glass substrate or a lens for evaluation so as to have a particular thickness and dried at room temperature for 60 minutes. After the light-shielding paint was dried, the light-shielding paint was cured in a thermostatic oven at 40° C. for 8 hours to produce a light-shielding film of Example 1.
In each of Examples 2 to 16, a light-shielding paint and a light-shielding film were produced in the same manner as in Example 1, except that the materials and conditions were changed to those shown in Tables 1 to 4.
Evaluation Results
Tables 5 to 8 show the evaluation results of the internal reflectance, the number of white spots after the light-shielding film was left to stand in a high-temperature and high-humidity environment, and the solvent resistance of the light-shielding paint and light-shielding film in Examples 1 to 16, the evaluation results being obtained by the above-described measurement methods.
In terms of good measurement results, the internal reflection is, for example, 20% or less. The number of white spots having a diameter of 0.02 mm or more after the light-shielding film is left to stand in a high-temperature and high-humidity environment is, for example, 100 or less in an image with a size of 6 mm2. The solvent resistance is, for example, at a level at which the tinge of the light-shielding film does not change after the immersion in IPA.
As shown in
Table 5 shows the physical properties of the light-shielding film formed of the light-shielding paint for optical elements in Example 2 in which the same light-shielding paint as in Example 1 was used except that the curing agent A was added so that the equivalent ratio was as large as 0.20. The internal reflectance was 17%, which was a good result. As a result of the evaluation of the number of white spots after the light-shielding film was left to stand in a high-temperature and high-humidity environment, the number of white spots having a diameter of 0.02 mm or more in an image with a size of 6 mm2 was 41 to 100, which was a good result. As a result of the evaluation of solvent resistance, IPA was not colored, which was a good result.
Table 5 shows the physical properties of the light-shielding film formed of the light-shielding paint for optical elements in Example 3 in which the same light-shielding paint as in Example 1 was used except that the curing agent A was added so that the equivalent ratio was as large as 0.45. The internal reflectance was 20%, which was a good result. As a result of the evaluation of the number of white spots after the light-shielding film was left to stand in a high-temperature and high-humidity environment, the number of white spots having a diameter of 0.02 mm or more in an image with a size of 6 mm2 was 41 to 100, which was a good result. As a result of the evaluation of solvent resistance, IPA was not colored, which was a good result.
Table 5 shows the physical properties of the light-shielding film formed of the light-shielding paint for optical elements in Example 4 in which the same light-shielding paint as in Example 1 was used except that the amount of the epoxy resin A added was 10 g, the amount of the epoxy-based silane coupling agent added was 12 g, and the amount of the curing agent A added was 0.85 g. The internal reflectance was 13%, which was a good result. As a result of the evaluation of the number of white spots after the light-shielding film was left to stand in a high-temperature and high-humidity environment, the number of white spots having a diameter of 0.02 mm or more in an image with a size of 6 mm2 was 41 to 100, which was a good result. As a result of the evaluation of solvent resistance, IPA was colored, but the tinge of the film did not change.
Table 6 shows the physical properties of the light-shielding film formed of the light-shielding paint for optical elements in Example 5 in which the same light-shielding paint as in Example 4 was used except that the curing agent A was added so that the equivalent ratio was as large as 0.2. The internal reflectance was 15%, which was a good result. As a result of the evaluation of the number of white spots after the light-shielding film was left to stand in a high-temperature and high-humidity environment, the number of white spots having a diameter of 0.02 mm or more in an image with a size of 6 mm2 was 41 to 100, which was a good result. As a result of the evaluation of solvent resistance, IPA was slightly colored, which was a good result.
Table 6 shows the physical properties of the light-shielding film formed of the light-shielding paint for optical elements in Example 6 in which the same light-shielding paint as in Example 4 was used except that the curing agent A was added so that the equivalent ratio was as large as 0.45. The internal reflectance was 18%. As a result of the evaluation of the number of white spots after the light-shielding film was left to stand in a high-temperature and high-humidity environment, the number of white spots having a diameter of 0.02 mm or more in an image with a size of 6 mm2 was 41 to 100, which was a good result. As a result of the evaluation of solvent resistance, IPA was not colored, which was a good result.
Table 6 shows the physical properties of the light-shielding film formed of the light-shielding paint for optical elements in Example 7 in which the same light-shielding paint as in Example 5 was used except that 2.4 g of a curing agent B was added. ADEKA Hardener EH551CH (manufactured by ADEKA Corporation), which is an aromatic amine curing agent, was used as the curing agent B. The internal reflectance was 13%, which was a good result. As a result of the evaluation of the number of white spots after the light-shielding film was left to stand in a high-temperature and high-humidity environment, the number of white spots having a diameter of 0.02 mm or more in an image with a size of 6 mm2 was 41 to 100, which was a good result. As a result of the evaluation of solvent resistance, IPA was slightly colored, which was a good result.
Table 6 shows the physical properties of the light-shielding film formed of the light-shielding paint for optical elements in Example 8 in which the same light-shielding paint as in Example 5 was used except that 1.7 g of a curing agent C was added. JEFFAMINE T-403 (manufactured by Mitsui Fine Chemicals, Inc.), which is a polyfunctional amine curing agent, was used as the curing agent C. The internal reflectance was 14%, which was a good result. As a result of the evaluation of the number of white spots after the light-shielding film was left to stand in a high-temperature and high-humidity environment, the number of white spots having a diameter of 0.02 mm or more in an image with a size of 6 mm2 was 41 to 100, which was a good result. As a result of the evaluation of solvent resistance, IPA was slightly colored, which was a good result.
Table 7 shows the physical properties of the light-shielding film formed of the light-shielding paint for optical elements in Example 9 in which the same light-shielding paint as in Example 5 was used except that the curing catalyst was not used. The internal reflectance was 9%, which was a good result. As a result of the evaluation of the number of white spots after the light-shielding film was left to stand in a high-temperature and high-humidity environment, the number of white spots having a diameter of 0.02 mm or more in an image with a size of 6 mm2 was 41 to 100, which was a good result. As a result of the evaluation of solvent resistance, IPA was colored, but the tinge of the film did not change.
Table 7 shows the physical properties of the light-shielding film formed of the light-shielding paint for optical elements in Example 10 in which the same light-shielding paint as in Example 5 was used except that the amount of the curing catalyst added was 1.0 g. The internal reflectance was 17%, which was a good result. As a result of the evaluation of the number of white spots after the light-shielding film was left to stand in a high-temperature and high-humidity environment, the number of white spots having a diameter of 0.02 mm or more in an image with a size of 6 mm2 was 41 to 100, which was a good result. As a result of the evaluation of solvent resistance, IPA was not colored.
Table 7 shows the physical properties of the light-shielding film formed of the light-shielding paint for optical elements in Example 11 in which the same light-shielding paint as in Example 5 was used except that the amount of the curing catalyst added was 3.0 g. The internal reflectance was 19%. As a result of the evaluation of the number of white spots after the light-shielding film was left to stand in a high-temperature and high-humidity environment, the number of white spots having a diameter of 0.02 mm or more in an image with a size of 6 mm2 was 41 to 100, which was a good result. As a result of the evaluation of solvent resistance, IPA was not colored.
Table 7 shows the physical properties of the light-shielding film formed of the light-shielding paint for optical elements in Example 12 in which the same light-shielding paint as in Example 5 was used except that the amount of the curing catalyst added was 4.0 g. The internal reflectance was 20%. As a result of the evaluation of the number of white spots after the light-shielding film was left to stand in a high-temperature and high-humidity environment, the number of white spots having a diameter of 0.02 mm or more in an image with a size of 6 mm2 was 41 to 100, which was a good result. As a result of the evaluation of solvent resistance, IPA was not colored. However, the film was slightly detached 1500 hours after the light-shielding film was left to stand in a high-temperature and high-humidity environment.
Table 8 shows the physical properties of the light-shielding film formed of the light-shielding paint for optical elements in Example 13 in which the same light-shielding paint as in Example 5 was used except that benzyldimethylamine was used as the curing catalyst. The internal reflectance was 15%, which was a good result. As a result of the evaluation of the number of white spots after the light-shielding film was left to stand in a high-temperature and high-humidity environment, the number of white spots having a diameter of 0.02 mm or more in an image with a size of 6 mm2 was 41 to 100, which was a good result. As a result of the evaluation of solvent resistance, IPA was slightly colored.
Table 8 shows the physical properties of the light-shielding film formed of the light-shielding paint for optical elements in Example 14 in which the same light-shielding paint as in Example 5 was used except that zirconia was used as the inorganic fine particles. The internal reflectance was 20%. As a result of the evaluation of the number of white spots after the light-shielding film was left to stand in a high-temperature and high-humidity environment, the number of white spots having a diameter of 0.02 mm or more in an image with a size of 6 mm2 was 41 to 100, which was a good result. As a result of the evaluation of solvent resistance, IPA was slightly colored.
Table 8 shows the physical properties of the light-shielding film formed of the light-shielding paint for optical elements in Example 15 in which the same light-shielding paint as in Example 5 was cured except that the curing temperature was changed to 20° C. and the curing time was changed to 24 hours. The internal reflectance was 17%, which was a good result. As a result of the evaluation of the number of white spots after the light-shielding film was left to stand in a high-temperature and high-humidity environment, the number of white spots having a diameter of 0.02 mm or more in an image with a size of 6 mm2 was 41 to 100, which was a good result. As a result of the evaluation of solvent resistance, IPA was colored, but the tinge of the film did not change.
Table 8 shows the physical properties of the light-shielding film formed of the light-shielding paint for optical elements in Example 16 in which the same light-shielding paint as in Example 5 was cured except that the curing temperature was changed to 200° C. and the curing time was changed to 0.5 hours. The internal reflectance was 12%, which was a good result. As a result of the evaluation of the number of white spots after the light-shielding film was left to stand in a high-temperature and high-humidity environment, the number of white spots having a diameter of 0.02 mm or more in an image with a size of 6 mm2 was 40 or less, which was a good result. As a result of the evaluation of solvent resistance, IPA was not colored.
The preparation of the light-shielding paint, the production of the light-shielding film, the evaluation of the optical properties, and the evaluation of the appearance for comparison were performed in the same manner as in Examples 1 to 16. The points different from those in Examples 1 to 16 will be described below.
Tables 9 and 10 show the types of epoxy resins, coupling agents, amine curing agents, curing catalysts, coloring agents, solvents, and inorganic fine particles constituting the light-shielding paint of each of Comparative Examples 1, 2, 3, 4, and 5 and the mixing ratio of the foregoing and the equivalent ratio.
Tables 11 and 12 show the results of the evaluation performed using the light-shielding paint of each of Comparative Examples 1, 2, 3, 4, and 5.
Table 11 shows the physical properties of the light-shielding film formed of the light-shielding paint for optical elements in Comparative Example 1 in which the same light-shielding paint as in Example 5 was used except that the curing agent A was added so that the equivalent ratio was as small as 0.05. The internal reflectance was 12%, which was a good result. As a result of the evaluation of the number of white spots after the light-shielding film was left to stand in a high-temperature and high-humidity environment, the number of white spots having a diameter of 0.02 mm or more in an image with a size of 6 mm2 was 101 or more, which was a poor result. As a result of the solvent resistance test, IPA was colored, the film was detached, and the tinge of the film changed.
Table 11 shows the physical properties of the light-shielding film formed of the light-shielding paint for optical elements in Comparative Example 2 in which the same light-shielding paint as in Example 5 was used except that the curing agent A was added so that the equivalent ratio was as large as 0.55. The internal reflectance was 23%, which was a poor result. As a result of the evaluation of the number of white spots after the light-shielding film was left to stand in a high-temperature and high-humidity environment, the number of white spots having a diameter of 0.02 mm or more in an image with a size of 6 mm2 was 101 or more, which was a poor result. As a result of the solvent resistance test, IPA was not colored.
Table 11 shows the physical properties of the light-shielding film formed of the light-shielding paint for optical elements in Comparative Example 3 in which the same light-shielding paint as in Example 1 was used except that the curing agent A was added so that the equivalent ratio was as small as 0.05. The internal reflectance was 14%, which was a good result. As a result of the evaluation of the number of white spots after the light-shielding film was left to stand in a high-temperature and high-humidity environment, the number of white spots having a diameter of 0.02 mm or more in an image with a size of 6 mm2 was 101 or more, which was a poor result. As a result of the solvent resistance test, IPA was colored, the film was detached, and the tinge of the film changed.
Table 11 shows the physical properties of the light-shielding film formed of the light-shielding paint for optical elements in Comparative Example 4 in which the same light-shielding paint as in Example 1 was used except that the curing agent A was added so that the equivalent ratio was as large as 0.55. The internal reflectance was 26%, which was a poor result. As a result of the evaluation of the number of white spots after the light-shielding film was left to stand in a high-temperature and high-humidity environment, the number of white spots having a diameter of 0.02 mm or more in an image with a size of 6 mm2 was 101 or more, which was a poor result. As a result of the solvent resistance test, IPA was not colored.
Table 12 shows the physical properties of the light-shielding film formed of the light-shielding paint for optical elements in Comparative Example 5 in which the same light-shielding paint as in Example 5 was used except that the curing agent A was added so that the equivalent ratio was as large as 1.10. The internal reflectance was 32%, which was a poor result. As a result of the evaluation of the number of white spots after the light-shielding film was left to stand in a high-temperature and high-humidity environment, the number of white spots having a diameter of 0.02 mm or more in an image with a size of 6 mm2 was 101 or more, which was a poor result. As a result of the solvent resistance test, IPA was not colored.
The light-shielding film according to an embodiment of the present invention can be used as a light-shielding film for optical elements used in optical devices such as cameras, binoculars, microscopes, and semiconductor exposure devices. In the light-shielding film according to an embodiment of the present invention, the number of white spots, which are appearance defects, generated after the light-shielding film is left to stand in a high-temperature and high-humidity environment is small. Therefore, the light-shielding film can be used for optical elements such as lenses and prisms.
The present invention can provide a light-shielding paint that has good optical properties and suppresses the generation of white spots, which are generated at an interface between the glass and a light-shielding film and degrades the appearance, even when the light-shielding film is used in a high-temperature and high-humidity environment for a long time. The present invention can also provide a light-shielding paint set, a light-shielding film, an optical element, a method for producing a light-shielding film, and a method for producing an optical element.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2014-163211, filed Aug. 8, 2014, which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2014-163211 | Aug 2014 | JP | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 5521262 | Patel | May 1996 | A |
| 20090226729 | Niimoto | Sep 2009 | A1 |
| 20090274844 | Scheibel | Nov 2009 | A1 |
| Number | Date | Country |
|---|---|---|
| 102879839 | Jan 2013 | CN |
| 2011164494 | Aug 2011 | JP |
| 2013054349 | Mar 2013 | JP |
| 2012161181 | Nov 2012 | WO |
| WO 2013021575 | Feb 2013 | WO |
| 2013-125544 | Aug 2013 | WO |
| Entry |
|---|
| Refractiveindex.info, Refractive index database https://refractiveindex.info/?shelf=main&book=TiO2&page=Devore-o (retrieved Apr. 13, 2017). |
| Sakai Chemical Industry Co., Ltd., Titanium Dioxide Product Details, http://www.sakai-chem.co.jp/en/products/product_01_01.html (retrieved Apr. 20, 2017). |
| Number | Date | Country | |
|---|---|---|---|
| 20160040031 A1 | Feb 2016 | US |
