JP7129946B2 - Internal anti-reflection black coating, internal anti-reflection black coating and optical elements - Google Patents

Description

TECHNICAL FIELD The present invention relates to an internal antireflection black paint, an internal antireflection black coating film, and an optical element.

In an optical system constructed by combining optical elements such as lenses and prisms, an image formed by the optical system when light scatters around the edges, ridges, edges, etc. of each optical element and causes stray light. This can cause ghosts and flares to occur in the image, resulting in lower image quality.

Therefore, in order to suppress the degradation of image quality due to such stray light, the periphery of the optical element is coated with a black internal anti-reflection paint to form an internal anti-reflection black coating film, which suppresses the occurrence of ghosts and flares. optical elements are used.

Patent Document 1 describes an internal antireflection coating for optical glass containing coal tar or coal tar pitch and a vinylidene chloride copolymer which is a copolymer of vinyl ester or acrylonitrile.

Japanese Patent Publication No. 58-4946

The coating film formed using the internal antireflection coating for optical glass described in Patent Document 1 is excellent in the performance of preventing internal reflection in the optical element, but it has solvent resistance and long-term use in a high temperature and high humidity environment. There is still room for improvement in anti-reflection performance over long-term use.
Specifically, in the production of optical elements, the coating film formed by applying the internal antireflection coating for optical glass described in Patent Document 1 is washed with a solvent to remove coal tar in the coating film. In some cases, the pitch melts out and contaminates the surface of the optical element. In addition, when an optical element having a coating film formed by applying the internal antireflection coating for optical glass described in Patent Document 1 is used for a long time in a high-temperature and high-humidity environment, the coating film and the optical In some cases, microscopic speckles were generated on the interface of the element, which degraded the antireflection performance.

Accordingly, it is an object of the present invention to provide an internal antireflection black paint that has high solvent resistance and is capable of forming a coating film with excellent internal antireflection performance even when used for a long period of time in a high-temperature, high-humidity environment. aim.
A further object of the present invention is to provide an internal antireflection black coating film formed using the internal antireflection black paint, and an optical element having the internal antireflection black coating film.

The above objects are achieved by the present invention described below. That is, the internal antireflection black paint according to one aspect of the present invention is an internal antireflection black paint containing a binder resin, coal tar pitch, a dye, and a solvent, wherein the coal tar pitch has a toluene-insoluble content of 20 mass. % or more.
Further, an internal antireflection black coating film according to another aspect of the present invention is an internal antireflection black coating film containing a binder resin, coal tar pitch and a dye,
The coal tar pitch is characterized by having a toluene insoluble content of 20% by mass or more.
Furthermore, an optical element according to another aspect of the present invention is characterized by having the internal antireflection black coating film.

According to the present invention, it is possible to provide an internal antireflection black paint that has high solvent resistance and is capable of forming a coating film with excellent internal antireflection performance even when used for a long period of time in a high-temperature, high-humidity environment. can.
Further, according to the present invention, it is possible to provide an internal antireflection black coating film and an optical element which are excellent in operability and internal antireflection performance.

FIG. 4 is a schematic diagram for explaining the internal reflection preventing function of the optical element according to the present invention. It is a schematic diagram for explaining the internal reflection in the optical element according to the present invention. FIG. 4 is a schematic diagram of a right-angle prism used for measuring the intensity of internally reflected light. FIG. 4 is a schematic diagram for explaining a method of measuring the intensity of internal specularly reflected light; FIG. 2 is a schematic diagram of an apparatus for measuring the intensity of internal diffusely reflected light.

DETAILED DESCRIPTION OF THE INVENTION Embodiments for carrying out the present invention will be described below. Hereinafter, the internal antireflection black paint may be simply referred to as "paint", and the internal antireflection black coating film may be simply referred to as "coating film".

An internal antireflection black paint according to one aspect of the present invention contains a binder resin, coal tar pitch, a dye and a solvent.
Each component contained in the paint is described in detail below.

(coal tar pitch)
The coal tar pitch contained in the internal antireflection black paint according to one aspect of the present invention has a toluene-insoluble content of 20% by mass or more.
Coal tar pitch is obtained using coal tar produced when coal is carbonized in a coke oven as a starting material. Coal tar pitch is the residue obtained by distillation after removal of sludge and aqueous ammonia contained in coal tar, or treatment combining distillation and heat treatment by a special process. Coal tar pitch can be adjusted in the toluene-insoluble content by subjecting it to secondary treatments such as thermal reforming and vacuum distillation.
The ratio of toluene-insoluble matter in coal tar pitch can be determined according to JIS K2425:2006 14.2.

Coal tar pitch, which has a low toluene-insoluble content, is conventionally used for paints from the viewpoint of dissolving it in the paint at the molecular level. The present inventors dared to use coal tar pitch, which has a toluene insoluble content of 20% by mass or more and has low solubility in a solvent, as a paint component. Furthermore, the inventors have found that the problems in the prior art can be solved. In other words, the coating film formed by the coating material exhibits excellent solvent resistance and excellent maintenance of internal antireflection performance in long-term use under high-temperature and high-humidity environments.

The coal tar pitch used for the paint preferably has a toluene-insoluble content of 25% by mass or more and 50% by mass or less. When the toluene-insoluble matter is 25% by mass or more, the resulting coating film can have higher solvent resistance. In addition, when the toluene-insoluble content is 50% by mass or less, the effect of maintaining the internal antireflection performance can be further enhanced when the resulting coating film is used for a long period of time in a high-temperature, high-humidity environment.

The toluene-insoluble content when using a combination of multiple types of coal tar pitch can be calculated as follows. For example, when 10 g of coal tar pitch A (20% insoluble in toluene) and 10 g of coal tar pitch B (40% insoluble in toluene) are used together, (20% x 10 g + 40% x 10 g)/20 g = 30%.

The content of coal tar pitch used in the paint is preferably 20% by mass or more and 50% by mass or less with respect to the total solid content in the paint.
When the content of coal tar pitch is 20% by mass or more, the resulting coating film can have higher solvent resistance. In addition, since the content of coal tar pitch is 50% by mass or less, when the obtained coating film is used for a long time in a high-temperature and high-humidity environment, the effect of maintaining the internal antireflection performance can be further enhanced. be able to.
The content of coal tar pitch used in the paint is more preferably 25% by mass or more and 40% by mass or less with respect to the total solid content in the paint.

In the present invention, it is considered that at least a portion of the coal tar pitch in the paint is particulate and dispersed. That is, it is preferable that the paint has a degree of dispersion of 5 μm or more and 50 μm or less as determined by grit gauge measurement. Grain gauge measurement can be performed according to JIS K5600-2-5.
When the degree of dispersion is 5 µm or more, the coatability of the paint and the matting effect on the surface of the resulting coating film are improved. Further, when the dispersion degree is 50 μm or less, when the obtained coating film is used for a long period of time in a high-temperature and high-humidity environment, it is possible to obtain a higher effect of maintaining the internal antireflection performance. It is more preferable that the paint has a dispersion degree of 10 μm or more and 30 μm or less as determined by grain gauge measurement.
Coal tar pitch may be pulverized prior to mixing with other materials, or coal tar may be ground during the process of dispersion treatment after mixing with other materials, in order to ensure that the degree of dispersion of the paint is an appropriate value. You can grind the pitch.

(dye)
It is preferable that the dye has an absorption coefficient of 10 L/(g·cm) or more for light having a wavelength of 555 nm. Thereby, a coating film having high internal antireflection performance can be obtained. Here, the absorption coefficient corresponds to the absorbance measured with a light path length of 1 cm for a solution obtained by dissolving 1 g of a dye in 1 L of a solvent, and can be obtained according to the Lambert-Beer law.
As the dye, commercially available ones can be used. Examples of dyes that can be used include azo dyes, anthraquinone dyes, phthalocyanine dyes, triallylmethane dyes, indigo dyes and metal complex dyes.

Specific dyes include, but are not limited to, C.I. Solvent Yellow 2, 13, 14, 16, 21, 25, 29, 33, 56, 60, 88, 89, 93, 104, 105, 112, 113, 114, 157, 160, 163, C.I. Solvent Red 3, 18, 22, 23, 24, 27, 49, 52, 60, 111, 122, 125, 127, 130, 132, 135, 149, 150 , 168, 179, 207, 214, 225, 233, C.I. 197, C.I. Solvent Black 3, 5, 7, 27, 28, 29, 34, C.I. Solvent Violet 8, 13, 31, 33, 36, C.I. Solvent Orange 11, 55, 60, 63, 80, 99, 114, C.I.Solvent Brown 42, 43, 44, C.I.Solvent Green 3, 5, 20, C.I.Acid Yellow42, C.I.Acid Black1, 52, C.I.Basic Red1, 1:1, C.I.Basic Violet1, 10, 17, C.I.Basic Blue7, C.I.Direct Blue87, etc. In addition, commercially available dyes not assigned a C.I. No. can also be used.

The dye content in the paint is preferably 3% by mass or more and 20% by mass or less with respect to the total solid content. When the content of the dye is 3% by mass or more, a coating film having high inner surface diffuse antireflection performance can be obtained. Moreover, when the content of the dye is 20% by mass or less, a coating film having high solvent resistance can be obtained.
More preferably, the dye content in the paint is 5% by mass or more and 15% by mass or less with respect to the total solid content.

(binder resin)
The binder resin is not particularly limited as long as it adheres to the surface of an object to be coated, such as an optical element, and can ensure the strength of the coating film to the extent that it does not adversely affect the use of the object to be coated.
Specific binder resins include, for example, epoxy resins, polyurethane resins, acrylic resins, vinyl resins, polyester resins, silicone resins, fluorine resins, phenol resins, nitrocellulose, and the like. Among them, epoxy resins, polyurethane resins and acrylic resins are preferred, and epoxy resins are more preferred.

Epoxy resin is a general term for compounds having two or more oxirane rings (epoxy groups) in the molecule, and is usually cured in combination with a curing agent.
Examples of epoxy resins include the following. Bisphenol A type epoxy resin, bisphenol F type epoxy resin, brominated epoxy resin, bisphenol S type epoxy resin, diphenyl ether type epoxy resin, hydroquinone type epoxy resin, naphthalene type epoxy resin, biphenyl type epoxy resin, fluorene type epoxy resin, bisphenol A type novolak epoxy resin, phenol novolac type epoxy resin, ortho-cresol novolac type epoxy resin, dicyclopentadiene phenol type epoxy resin, trishydroxyphenylmethane type epoxy resin, trifunctional epoxy resin, tetraphenylolethane type epoxy resin, 4 Functional epoxy resin, hydrogenated bisphenol A epoxy resin, bisphenol A nucleated polyol epoxy resin, polypropylene glycol epoxy resin, glycidyl ester epoxy resin, glycidylamine epoxy resin, glyoxal epoxy resin, alicyclic epoxy resin , alicyclic polyfunctional epoxy compounds, and heterocyclic epoxy resins such as triglycidyl isocyanate (TGIC).

Examples of curing agents include amine-based curing agents, acid or acid anhydride-based curing agents, basic active hydrogen compounds, and active hydrogen compounds such as imidazoles. As a curing agent, a latent curing agent such as ketiminized amine, boron trifluoride-amine complex, dicyandiamide, organic acid hydrazide, etc. can be used, and this latent curing agent is used to ensure the paint pot life. is preferred. Among them, ketiminated amines are particularly preferred.

Examples of amine-based curing agents include the following. Aliphatic polyamines such as ethylenediamine, diethylenetriamine and triethylenetetramine; Alicyclic polyamines such as isophoronediamine and 1,3-bisaminomethylcyclohexane; Aromatic polyamines such as diaminodiphenylmethane and diaminodiphenylsulfone; Linear diamines and tetramethyl secondary or tertiary amines such as guanidine, triethanolamine, piperidine, pyridine and benzyldimethylamine; polyamidoamines obtained by reacting dimer acid with polyamines such as diethylenetriamine and triethylenetetramine.

Examples of acid or acid anhydride curing agents include the following. Polycarboxylic acids such as adipic acid, azelaic acid, trimellitic acid, pyromellitic acid, decanedicarboxylic acid; phthalic anhydride, trimellitic anhydride, pyromellitic anhydride, 3,3′,4,4′-benzophenonetetracarboxylic acid Aromatic anhydrides such as acid anhydrides; cyclic aliphatic acid anhydrides such as maleic anhydride, succinic anhydride, tetrahydrophthalic anhydride, and methyltetrahydrophthalic anhydride; polyadipic anhydride, polyazelaic anhydride, polysebacic acid Aliphatic acid anhydrides such as anhydrides, dodecenylsuccinic anhydride, poly(ethyl)octadecanedioic anhydride.

Examples of basic active hydrogen compounds include organic acid dihydrazides.
Examples of imidazoles include 2-methylimidazole, 2-ethyl-4-methylimidazole, 2-heptanedecylimidazole and the like.

In addition to curing agents, catalysts may be used to control the rate of the curing reaction.
Examples of catalysts include tertiary amines, imidazoles, boron trifluoride-amine complexes, organic acid compounds, phenols, and organometallic compounds.

A polyurethane resin is cured by using a compound (polyol) having two or more hydroxyl groups and a compound (isocyanate compound) having two or more isocyanate groups as a curing agent. At this time, a catalyst may be used to control the curing reaction rate.

Isocyanate compounds undergo a curing reaction with active hydrogen compounds having functional groups such as amino groups, mercapto groups, and carboxyl groups in addition to hydroxyl groups. Therefore, for example, by using a polyol and these active hydrogen compounds together, or by introducing these active hydrogen functional groups into the polyol molecule, the strength of the coating film after curing and the stability of the coating can be adjusted.

The isocyanate compound may be allowed to coexist with the polyol in the paint by masking the isocyanate group with a blocking agent in advance so that it can be cured by heating when forming the paint film. Alternatively, an isocyanate compound having a large molecular weight may be used to slow down the curing reaction and cure by reacting with moisture in the atmosphere.

Examples of polyols include the following.
Polyhydric alcohols such as relatively low-molecular-weight 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, ethylene glycol, propylene glycol, glycerin, and trimethylolpropane, and relatively high-molecular-weight polypropylene Glycol, polytetramethylene glycol, condensed polyester polyol, lactone polyester polyol, polycarbonate polyol, polybutadiene polyol, hydrogenated polybutadiene polyol, acrylic polyol, phosphorus-containing polyol, castor oil polyol, hydrogenated castor oil polyol, phenolic polyol.

Among the polyols listed above, preferred are addition polymers with propylene glycol, condensation polyester polyols, lactone polyester polyols, acrylic polyols, polycarbonate polyols, and phenol polyols. Moreover, these polyols may be used in combination of two or more, if necessary.

The isocyanate compound is not particularly limited as long as it is a compound having two isocyanate groups in one molecule, and examples thereof include the following.
Aliphatic diisocyanates such as hexamethylene diisocyanate (HMDI) and trimethylhexamethylene diisocyanate (TMDI); Alicyclic diisocyanates such as isophorone diisocyanate (IPDI); Aromatic-aliphatic diisocyanates such as xylylene diisocyanate (XDI); Aromatic diisocyanates such as tolylene diisocyanate (TDI) and 4,4-diphenylmethane diisocyanate (MDI); dimer acid diisocyanate (DDI), hydrogenated TDI (HTDI), hydrogenated XDI (H6XDI), hydrogenated MDI (H12MDI) Hydrogenated diisocyanates such as; Dimers, trimers, tetramers or higher polyisocyanates thereof; Additions of these with polyhydric alcohols such as trimethylolpropane, water or low molecular weight polyester resins etc.

The polyol and isocyanate compound have a short pot life because the urethane curing reaction starts when they are mixed in the paint. In order to prolong the pot life, a blocked isocyanate compound obtained by blocking the reactive group (isocyanate group) of the isocyanate compound with a suitable blocking agent may be used.

The blocking agent is not particularly limited, and examples thereof include the following.
Oxime blocking agents such as methyl ethyl ketoxime, acetoxime, cyclohexanone oxime, acetophenone oxime, and benzophenone oxime; phenolic blocking agents such as m-cresol and xylenol; methanol, ethanol, butanol, 2-ethylhexanol, cyclohexanol, ethylene glycol monoethyl alcohol blocking agents such as ether; lactam blocking agents such as ε-caprolactam; diketone blocking agents such as diethyl malonate and acetoacetate; mercaptan blocking agents such as thiophenol; urea blocking agents such as thiourea; imidazole-based blocking agents; carbamic acid-based blocking agents; Among them, lactam blocking agents, oxime blocking agents, alcohol blocking agents, and diketone blocking agents are preferred.

Acrylic resins can be used as (meth)acrylate polymers and copolymers thereof. In this specification, "(meth)acrylate" means acrylate and/or methacrylate.

Examples of (meth)acrylates include the following. Alkyl (meth)acrylates such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate; hydroxymethyl (meth)acrylate, hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate hydroxyalkyl (meth)acrylates such as acrylates, hydroxybutyl (meth)acrylate and hydroxypentyl (meth)acrylate;

(solvent)
Solvents are used to ensure the fluidity of paints, and generally known solvents used for paints can be applied. Specific solvents include the following.
Chain hydrocarbons such as neopentane, n-hexane, n-heptane, Solvesso; aromatic hydrocarbons such as toluene and xylene; halogenated hydrocarbons such as trichlorethylene and perchlorethylene; methanol, ethanol, isopropanol, n-butanol, etc. ketones such as acetone, methyl ethyl ketone and methyl isobutyl ketone; esters such as ethyl acetate and n-butyl acetate; ethers such as cellosolve, butylsolve and cellosolve acetate; mineral spirits (hydrocarbon oils).
In addition, the said solvent may be used individually by 1 type, or may use 2 or more types together by arbitrary combinations of arbitrary ratios.

(Silica fine particles)
It is preferable that the paint further contains silica fine particles in a proportion of 3% by mass or more and 25% by mass or less with respect to the total solid content. Thereby, the viscosity of the paint can be suitably adjusted, and the matting effect of the surface of the resulting coating film can be enhanced. That is, if the content of silica fine particles is 3% by mass or more, the viscosity of the paint is sufficiently high, it is difficult to sag during coating, and the coating film has a certain thickness or more. Since there is no need to reapply, it is possible to prevent a decrease in work efficiency. Moreover, if the content of the silica fine particles is 25% by mass or less, the viscosity does not increase excessively, and the occurrence of film thickness unevenness due to coating streaks can be suppressed.

More preferably, the paint contains silica fine particles in a proportion of 5% by mass or more and 20% by mass or less with respect to the total solid content. When the content of the silica fine particles is 5% by mass or more, the coatability is further improved, and the surface matting effect of the resulting coating film can be further enhanced. Moreover, when the content of the silica fine particles is 20% by mass or less, the storage stability of the paint can be improved.

The particle diameter of the silica fine particles contained in the paint is preferably 5 nm or more and 50 nm or less. Here, the particle size of the silica fine particles is the volume-average primary particle size. If the particle diameter of the silica fine particles is 5 nm or more, the viscosity of the coating does not increase excessively depending on the amount of silica fine particles added, and the viscosity of the coating can be easily adjusted. Further, if the particle diameter of the silica fine particles is 50 nm or less, it is possible to suppress an increase in the inner surface diffuse reflectance of the resulting coating film due to the addition of the silica fine particles.

(Silane coupling agent)
The paint may further contain a silane coupling agent. By containing the silane coupling agent, even when the optical element according to the present invention is stored for a long period of time in a high-temperature and high-humidity environment, it is possible to suppress deterioration in the internal antireflection performance of the resulting coating film. .

When an optical element having an internal antireflection black coating film is stored for a long period of time in a high-temperature and high-humidity environment, minute spots with a size of about 1 μm to 50 μm may occur at the interface between the coating film and the optical element. Microscopic speckles can be observed. These minute spots are considered to be due to peeling at minute interfaces, and the places where these spots are generated do not have an internal anti-reflection function, and cause an increase in the internal reflectance as a whole.

Therefore, a silane coupling agent is used for the purpose of increasing the adhesion between the coating film and the optical element in order to suppress peeling at the minute interface even when stored for a long period of time in a high-temperature, high-humidity environment. is preferred. Also, the silane coupling agent preferably has at least one active hydrogen group or electron-withdrawing group as a reactive functional group.

Active hydrogen groups include hydroxyl groups, amino groups and mercapto groups, and electron-withdrawing groups include isocyanate groups, epoxy groups, (meth)acryl groups, styryl groups and vinyl groups.

These silane coupling agents form a chemical bond with the surface of the optical element through a coupling reaction, especially when forming a coating film on an optical element made of glass. form a bond. This chemical bond between the two forms a continuous chemical bond from the inside of the coating film to the surface of the optical element. The occurrence of spots can be suppressed.

Examples of hydroxyl group-containing silane coupling agents include the following. N,N-bis(2-hydroxyethyl)-3-aminopropyltriethoxysilane, 2,2-bis(3-triethoxysilylpropoxymethyl)butanol, N-(2-hydroxyethyl)-N-methylaminopropyl trimethoxysilane.

Examples of amino group-containing silane coupling agents include the following. 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-(2-aminoethylamino)propyltrimethoxysilane, 3-(2-aminoethylamino)propylmethyldimethoxysilane, 3-phenylaminopropyltri methoxysilane, bis(trimethoxysilylpropyl)amine, n-butylaminopropyltrimethoxysilane, N-methylaminopropyltrimethoxysilane, ketiminesilane.

Mercapto group-containing silane coupling agents include, for example, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropylmethyldimethoxysilane, and 3-mercaptopropyltriethoxysilane.

Examples of isocyanate group-containing silane coupling agents include 3-isocyanatopropyltrimethoxysilane and 3-isocyanatopropyltriethoxysilane.

Examples of epoxy group-containing silane coupling agents include the following. 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycid xypropyltriethoxysilane.

(Meth)acrylic group-containing silane coupling agents include, for example, the following. 3-methacryloyloxypropylmethyldimethoxysilane, 3-methacryloyloxypropyltrimethoxysilane, 3-methacryloyloxypropylmethyldiethoxysilane, 3-methacryloyloxypropyltriethoxysilane, 3-acryloyloxypropyltriethoxysilane.

Examples of styryl group-containing silane coupling agents include p-styryltrimethoxysilane, and examples of vinyl group-containing silane coupling agents include vinyltrimethoxysilane and vinyltriethoxysilane.

In addition to these monomer type silane coupling agents, a silicone alkoxy oligomer containing an alkoxy group in a relatively low-molecular-weight silicone skeleton may be used as the silane coupling agent. Specific examples of such silicone alkoxy oligomers include the following. X-40-2651 (product name, containing amino group), X-41-1805 (product name, containing mercapto group), X-41-1818 (product name, containing mercapto group), X-41-1810 (product name , containing a mercapto group), X-41-1053 (product name, containing an epoxy group), X-41-1059A (product name, containing an epoxy group), X-40-2655A (product name, containing a methacrylic group), KR- 513 (product name, acrylic group-containing) (both manufactured by Shin-Etsu Chemical Co., Ltd.). The alkoxy group content in the molecule of these silicone alkoxy oligomers is preferably 5% by mass or more and 80% by mass or less, and the active group equivalent weight is preferably 100 g/eq or more and 1000 g/eq or less.

The paint preferably contains the silane coupling agent at a ratio of 0.5% by mass or more and 10.0% by mass or less with respect to the entire paint. When the amount is 0.5% by mass or more, even when the optical element is stored for a long period of time in a high-temperature and high-humidity environment, a high effect of lowering the internal antireflection performance of the resulting coating film can be obtained. Further, if it is 10.0% by mass or less, it is possible to prevent the occurrence of "sagging" caused by the unreacted coupling agent remaining in a liquid state for a while after the solvent is evaporated.

One type of these silane coupling agents may be used, or two or more types may be used simultaneously.

(Other additives)
The paint may contain various additives in addition to the above-mentioned materials as long as the effects of the present invention are not impaired. Various additives can be used, for example, to adjust the viscosity of the paint, improve the adhesion of the resulting coating film to the substrate, improve the leveling property of the obtained coating film, make the surface matte of the resulting coating film, adjust the black color tone, and It is used to improve the light resistance, anti-mold and anti-corrosion of the coating film.

Thickeners such as bentonite, silicone elastomers, thickening polysaccharides and glycols, and diluent solvents may be used to adjust the viscosity of the paint.
In order to improve the adhesion of the resulting coating film to the substrate, in addition to the above silane coupling agents, silicone coupling agents, aluminate coupling agents, titanate coupling agents, and the like may be used.
In order to improve the leveling property of the resulting coating film, a leveling agent such as silicone oil or surfactant may be used.
Resin particles, glass powder, quartz powder, mica powder, mica powder, and the like having a size of about 0.1 μm to 20 μm may be used to improve the matteness of the surface of the resulting coating film.
In order to adjust the color tone of black, a dye, an organic pigment, or an inorganic pigment may be used as a complementary color.
In order to improve the light resistance of the resulting coating film, benzophenone-based, salicylate-based, triazine-based benzotriazole-based, etc., zinc oxide fine particles, titanium oxide fine particles, etc. may be used as UV absorbers.
An antifungal agent may be used to prevent mold, and an antirust agent may be used to prevent rust.

FIG. 1 is a schematic diagram for explaining the internal reflection preventing function of the optical element according to the present invention. In FIG. 1, a lens 1 as an optical element according to the present invention has an inner antireflection black coating 2 according to the present invention on its edge portion. The inner antireflection black coating film 2 is a coating film formed using the inner antireflection paint according to one aspect of the present invention. That is, the inner antireflection black coating film 2 contains a binder resin, coal tar pitch and dye, and the coal tar pitch has a toluene-insoluble content of 20% by mass or more.

The inner anti-reflection black coating film 2 provided on the edge of the lens 1 suppresses/prevents light (stray light) 4 that reaches the edge and is internally reflected from the incident light 3 entering the lens 1 from the outside. As a result, it is possible to suppress the occurrence of ghosts and flares in the image formed by the optical system composed of the lens 1 .

FIG. 2 is a schematic diagram for explaining internal reflection in the optical element according to the present invention. Of the incident light 3 coming from outside the lens 1, light (stray light) 4 that reaches the edge portion and is internally reflected can be divided into two types: internal regular reflection light 4a and internal diffuse reflection light 4b. The inner surface specularly reflected light 4a is light reflected inside the lens 1 at the same angle (incident angle) as the light incident on the inside of the lens 1 reaches the edge of the lens 1. FIG. In addition, the inner surface diffusely reflected light 4b is light that bounces back at various angles different from the incident angle. Here, the intensity of the internal specularly reflected light 4a tends to increase as the incident angle increases (the incident angle approaches 90°). On the other hand, the intensity of the inner surface diffusely reflected light 4b tends to increase as the incident angle decreases (the incident angle approaches 0°).

Internal specularly reflected light has a great influence on the occurrence of abnormal images such as ghosts and flares in images mainly captured by cameras. On the other hand, the diffusely reflected light from the inner surface causes not only the occurrence of abnormal images due to flare, but also a loss of aesthetics in that the jet-blackness of the anti-reflection coating cannot be obtained when the camera lens is viewed from the outside. .

The degree of suppression of the internal specularly reflected light is determined by measuring the intensity of the internal specularly reflected light by the measurement method shown in FIG. can be evaluated by

That is, the light emitted from the light source 6 is passed through the polarizing plate 12 set to N-polarized light, and the incident light 7 condensed by the slit 13 is inserted into the rectangular prism 5 and internally reflected by the coating film 2. . Subsequently, the internal specularly reflected light 8 emitted from the rectangular prism 5 is received by an integrating sphere 9 provided with a light receiver 14, and the light intensity is measured. At this time, attention should be paid to the following conditions because they affect the measured value of the internal specular reflected light 8 . The orientation of the polarizing plate 12, the degree of convergence of the incident light 7 by the slit 13, the size of the rectangular prism 5, the distance A from the vertical line (perpendicular) 10 to the bottom surface of the prism to the tangent surface 11 to the entrance of the integrating sphere, the integrating sphere 9 and the size B of the opening diameter.

In the rectangular prism 5 without the coating film 2, the critical angle of total reflection of the incident light 7 on the bottom surface of the rectangular prism 5 is obtained by the following equation A according to Snell's law.
θ=sin ⁻¹ (sin90°/n) Formula A
Here, n is the refractive index of the rectangular prism 5, .theta. is the angle formed by the vertical line (perpendicular line) 10 with respect to the bottom surface of the prism, and the refractive index of air is 1.0.

That is, for example, in the rectangular prism 5 with n=1.8,
θ=sin ⁻¹ (sin90°/1.8)≈33.7°
is the critical angle for total reflection, and the incident light 7 undergoes total reflection within the incident angle range of 33.7° to 90°.

In order to narrow the range of angles in which such total reflection occurs, it is effective to make the refractive index of the coating film 2 closer to or higher than the refractive index of the rectangular prism 5 .

Further, the degree of suppression of the inner surface diffusely reflected light can be evaluated by measuring the intensity of the light based on the inner surface diffusely reflected light using the apparatus shown in FIG. 5, for example.

That is, first, an integrating sphere 9 having a light receiving section 15 and a light trap section 17, and having an incident light aperture 19, a specular reflection light trap aperture 20, and a sample installation aperture 21 is installed in a spectrophotometer. Subsequently, a disc-shaped glass plate 18 having the coating film 2 is placed outside the sample placement opening 21 . At this time, the disk-shaped glass plate 18 is placed with the surface opposite to the surface having the coating film 2 in contact with the integrating sphere. As a result, the incident light 22 from the light source 6 enters the disk-shaped glass plate 18 from the surface opposite to the surface having the coating film 2, reaches the coating film 2, and is internally reflected. At this time, the internal specularly reflected light 23 is absorbed by the specularly reflected light trap 16 , and the internal diffusely reflected light 24 is emitted and accumulated inside the integrating sphere 9 , and the light intensity at each wavelength is measured by the light receiving section 15 .

EXAMPLES The present invention will be described in more detail below with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

(Example 1)
First, the following materials were prepared.
・ Binder resin A (product name: jER828, manufactured by Mitsubishi Chemical Corporation, epoxy resin): 32.0 g
・ Curing agent A (product name: jER Cure H3, manufactured by Mitsubishi Chemical Corporation): 22.5 g
· Coal tar pitch A (product name: MCP-110, JFE Chemical Co., Ltd., toluene insoluble content 30% by mass): 35.0 g
・ Dye A (product name: VALIFAST BLACK 3810, manufactured by Orient Chemical Industry Co., Ltd., absorption coefficient for light with a wavelength of 555 nm: 31 L / (g cm)): 10.0 g
・ Silica fine particles (product name: Aerosil #200, manufactured by Nippon Aerosil Co., Ltd.): 12.0 g
・ Silane coupling agent A (product name: KBM-403, manufactured by Shin-Etsu Chemical Co., Ltd., 3-glycidoxypropyltrimethoxysilane): 11.0 g
・ 1-Methoxy-2-propanol as a solvent (solvent A): 50.0 g
- Toluene as a solvent (solvent B): 50.0 g
All of the above materials except curing agent A were weighed and placed in a 1.5 L ball mill pot together with 30 magnetic balls of 20 mm in diameter. After that, the ball mill pot was placed on a pot mill rotating gantry and stirred at 60 rpm until a suitable degree of dispersion was obtained.
Subsequently, the curing agent A was added to the mixed solution after stirring, and the mixture was further stirred for 5 minutes to obtain a coating material according to Example 1.

(Examples 2 to 27, Comparative Examples 1 and 2)
In Example 1, the types and amounts of materials used to prepare the paint were changed as shown in Table 1. Except for this, the coatings of Examples 2 to 27 and Comparative Examples 1 and 2 were obtained in the same manner as in Example 1.
Here, materials other than the above used in Examples and Comparative Examples are as follows.
・Binder resin B (product name: NIPPOLAN 983, manufactured by Tosoh Corporation, polyol)
・ Curing agent B (product name: Duranate TPA-100, manufactured by Asahi Kasei Corporation)
・ Coal tar pitch B (product name: PK-U, manufactured by JFE Chemical Co., Ltd., toluene insoluble content 20% by mass)
・ Coal tar pitch C (product name: MCP-150, manufactured by JFE Chemical Co., Ltd., toluene insoluble content 40% by mass)
・ Coal tar pitch D (product name: MCP-250, manufactured by JFE Chemical Co., Ltd., toluene insoluble content 65% by mass)
・ Coal tar pitch E (product name: MCP-350, manufactured by JFE Chemical Co., Ltd., toluene insoluble content 82% by mass)
・ Coal tar pitch F (product name: PK-QL, manufactured by JFE Chemical Co., Ltd., toluene insoluble content 10% by mass)
・ Dye B (product name: VALIFAST BLUE 603, manufactured by Orient Chemical Industry Co., Ltd., absorption coefficient for light with a wavelength of 555 nm: 9.5 L / (g cm))
・ Dye C (product name: ORASOL BROWN 324, manufactured by BASF, absorption coefficient for light with a wavelength of 555 nm: 10 L / (g cm))
・ Dye D (product name: OIL BLACK HBB, manufactured by Orient Chemical Industry Co., Ltd., absorption coefficient for light with a wavelength of 555 nm: 55 L / (g cm))
・Silane coupling agent B (product name: KBE-9007N, manufactured by Shin-Etsu Chemical Co., Ltd., 3-isocyanatopropyltrimethoxysilane)
・1-Methoxy-2-propanol as (solvent A) ・Toluene as (solvent B)

In the examples and comparative examples, the degree of dispersion was adjusted as follows. Materials other than the curing agent were placed in a ball mill pot together with magnetic balls, and then stirred at 60 rpm until the degree of dispersion shown in Table 2 was achieved. 5 g of the mixed solution was sampled from the inside of the ball mill pot and the degree of dispersion was measured. When the measurement result was greater than the desired degree of dispersion, additional stirring was performed, and 5 g of the mixed solution was sampled again to measure the degree of dispersion. The dispersity measurements with additional stirring and sampling were repeated until the desired dispersity was obtained. When the dispersity became too much smaller than the predetermined value, each material was put back into the ball mill pot, additional stirring time was set shorter, and the dispersity measurement by stirring and sampling was repeated. The amount of the curing agent added was adjusted so as to achieve the weight ratio shown in Table 1 for each example and comparative example.

In addition, the toluene-insoluble matter and content of coal tar pitch contained in the paints obtained in the above Examples and Comparative Examples, the degree of dispersion, the absorption coefficient and content of the dye for light with a wavelength of 555 nm, and the content of silica fine particles are summarized. are shown in Table 2.

[evaluation]
(Internal specular reflectance)
A rectangular prism for evaluation (product name: S-LAH53, manufactured by OHARA, n = 1.8, length of two sides sandwiching the right angle is 30 mm each) with all surfaces polished in advance to a mirror surface, with the bottom facing upward and horizontally It was set on the rotary table of the spin coater so that Subsequently, the paints according to each example and comparative example were applied to the entire bottom surface by spin coating so as to form a uniform film thickness. Then, after drying at room temperature for 30 minutes, it was cured in an electric furnace at 140° C. for 1 hour to obtain a sample for evaluating internal regular reflectance as shown in FIG. The thickness of the coating film was adjusted to be 10 µm or more at which the transparency of the coating film was lost.

Subsequently, a rectangular prism 5 without the coating film 2 is installed in the spectrophotometer, and the internal specular reflection light intensity for light with a wavelength of 400 nm to 700 nm is measured in advance at intervals of 5 nm by the measurement method shown in FIG. It was measured.

Next, a rectangular prism 5 (internal regular reflectance evaluation sample) having a coating film 2 is installed, and the internal regular reflection light intensity for light with a wavelength of 400 nm to 700 nm is measured at intervals of 5 nm by the measurement method shown in FIG. It was measured. The internal regular reflectance of the sample for evaluating the internal regular reflectance was obtained by setting the light intensity at each wavelength measured in advance by the rectangular prism 5 without the coating film 2 in the spectrophotometer as 100% of the internal regular reflectance. The arithmetic average value of the internal regular reflectance at each wavelength was taken as the internal regular reflectance of the sample. Evaluation was made according to the following criteria from the internal regular reflectance values obtained for the samples according to each example and comparative example.
A: Less than 35% B: 35% or more and less than 45% C: 45% or more and less than 55% D: 55% or more Table 3 shows the results.

(Internal diffuse reflectance)
One side of a disk-shaped glass plate (product name: S-LAH53, manufactured by Ohara, n = 1.8, φ 30 mm, thickness 1.5 mm) optically polished on both sides with the paint according to each example and comparative example , was coated in the same manner as in the preparation of the sample for evaluating the internal specular reflectance. After that, the coating film was dried and cured in the same manner as the preparation of the inner surface specular reflectance evaluation sample to prepare an inner surface diffuse reflectance evaluation sample.

Subsequently, using the apparatus shown in FIG. 5, the inner surface diffuse reflectance was measured.
First, a standard white plate was placed as a disk-shaped glass plate 18 in the sample installation opening 21, and the internal diffuse reflection light intensity for light with a wavelength of 400 nm to 700 nm was measured at intervals of 5 nm. The ratio was set to 100%. Subsequently, the inner diffuse reflectance evaluation sample prepared above was placed as a disk-shaped glass plate 18, and the inner diffuse reflected light intensity for light with a wavelength of 400 nm to 700 nm was measured at intervals of 5 nm to obtain the inner diffuse reflectance. . The arithmetic average value of the internal diffuse reflectance at each wavelength was taken as the internal diffuse reflectance of the sample. From the values of the inner surface diffuse reflectance obtained for the samples according to each example and comparative example, evaluation was made according to the following criteria.
A: Less than 0.20% B: 0.20% or more and less than 0.25% C: 0.25% or more and less than 0.30% D: 0.30% or more Table 3 shows the results.

(long-term storage durability under high temperature and high humidity environment)
Frosting is performed on one side of a disk-shaped glass flat plate (product name: S-LAH53, manufactured by Ohara, n = 1.8, φ30 mm, thickness 1.5 mm) (count # 600), and the frosted surface , was coated in the same manner as the preparation of the inner surface regular reflectance evaluation sample. After that, the composition was heat-cured at 90° C. for 1 hour to prepare a sample for evaluation of long-term storage durability under a high-temperature and high-humidity environment. Subsequently, the obtained durability evaluation sample was placed in a high-temperature and high-humidity environment (temperature 60° C., humidity 90%) for 200 hours, and then a 4 mm ² area of the interface between the glass and the coating film was observed with a microscope. , the number of white spots with a diameter of 0.02 mm or more was counted. The obtained results were evaluated according to the following criteria.
A: 10 or less B: 11 or more and 30 or less C: 31 or more and 50 or less D: 51 or more The results are shown in Table 3.

(solvent resistance)
A sample similar to the sample for evaluation of long-term storage durability under a high-temperature and high-humidity environment was prepared, and the obtained sample was immersed in 50 g of methyl ethyl ketone for 3 minutes. After that, the colored state of methyl ethyl ketone was visually observed. The obtained results were evaluated according to the following criteria.
A: Almost no coloring B: Slightly yellowish coloring C: Slightly blackish coloring D: Strongly blackish coloring The results are shown in Table 3.

1 lens 2 internal antireflection black coating 3, 7, 22 incident light 4 internal reflected light (stray light)
4a, 8, 23 Inner specular reflected light 4b, 24 Inner diffuse reflected light 5 Rectangular prism 6 Light source 9 Integrating sphere 10 Plumb line (perpendicular line) to the bottom surface of the prism
11 Contact surface with integrating sphere entrance 12 Polarizing plate 13 Slit 14 Light receiver 15 Light receiving part 16 Regular reflection light trap 17 Light trap part 18 Glass plate 19 Incident light opening 20 Regular reflection light trap opening 21 Sample setting opening

Claims (6)

An internal antireflection black paint containing a binder resin, coal tar pitch, a dye and a solvent,
The coal tar pitch has a toluene insoluble content of 20% by mass or more and 50% by mass or less ,
An internal antireflection black paint, wherein the dispersion degree of the internal antireflection black paint obtained by grain gauge measurement is 5 μm or more and 50 μm or less . 2. The internal antireflection black paint according to claim 1, wherein the coal tar pitch content is 20% by mass or more and 50% by mass or less based on the total solid content. 3. The internal antireflection black paint according to claim 1, wherein the dye has an absorption coefficient of 10 L/(g·cm) or more for light having a wavelength of 555 nm. 4. The internal antireflection black paint according to any one of claims 1 to 3 , further comprising silica fine particles in a proportion of 3% by mass or more and 25% by mass or less relative to the total solid content. An internal antireflection black coating containing a binder resin, coal tar pitch and a dye,
An internal antireflection black coating film, which is obtained by applying the internal antireflection black paint according to any one of claims 1 to 4 . An optical element comprising the inner antireflection black coating according to claim 5 .

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