WO2025004985A1 - Inner surface antireflection coating material, inner surface antireflection coating film, and optical element - Google Patents

Abstract

To provide an inner surface antireflection coating material that has low impact on the environment, has excellent film-forming properties on base materials made of a resin, and can form an inner surface antireflection coating film excellent in adhesion to the base material and optical characteristics.　Provided is an inner surface antireflection coating material that contains a binder resin, a black pigment, an additive, and an aqueous medium, wherein the binder resin contains an acid-modified polyolefin resin and a polyurethane resin, the acid-modified polyolefin resin contains a propylene component and an ethylene component in a specific mass ratio, the content of the acid-modified polyolefin resin in the inner surface antireflection coating material is 60 mass% or more when the heating residue of the inner surface antireflection coating material at 105°C is taken to be 100 mass%, the black pigment is carbon black having a particle size (D90) of 200 nm or less, the carbon black is coated with a nonionic surfactant, and the additive is a urethane associative thickener.

Description

Inner surface anti-reflective paint, inner surface anti-reflective coating film, and optical element

The present invention relates to an internal anti-reflection paint, an internal anti-reflection coating film formed using the internal anti-reflection paint, and an optical element having the internal anti-reflection coating film.

In an optical system composed of a combination of optical elements such as lenses and prisms, when light is scattered around the edges, ridges, and edges of each optical element, generating stray light, ghosts and flares appear in the image formed by the optical system, causing a decrease in image quality. Therefore, in order to prevent the deterioration of image quality caused by such stray light, optical elements are used that suppress the occurrence of ghosts and flares by applying an internal anti-reflective paint to the peripheral parts of the optical elements and forming a black internal anti-reflective coating to prevent internal reflections.

In recent years, with the widespread use of resin lenses, there is a demand for internal anti-reflection paints that can be used effectively to coat not only glass but also optical elements made of resin.

Patent Document 1 proposes a light-shielding coating for resin lenses for optical elements, which is made of a cycloolefin polymer and is used to form a light-shielding film on the resin lenses.

Patent Document 2 proposes a water-based coating agent containing an acid-modified polyolefin resin that can form a coating film that has good adhesion and chemical resistance to cyclic polyolefin materials without the need for special surface treatment of the material.

JP 2013-250440 A JP 2014-237813 A

The light-shielding paint described in Patent Document 1 uses an organic solvent as a medium. However, in recent years, due to growing concern about the environment, there has been an increasing demand for environmentally friendly internal anti-reflection paints that use less volatile organic compounds (VOCs) in the paint. Therefore, there is room for improvement in the light-shielding paint described in Patent Document 1 from the perspective of its impact on the environment.

In order to reduce the emission of VOCs into the environment, it is possible to use an aqueous medium instead of an organic solvent as the paint medium. Patent Document 2 proposes a water-based coating agent that has good adhesion to resin materials, and it is possible to disperse black pigments, dyes, etc. in the water-based coating agent disclosed in Patent Document 2 to create an environmentally friendly internal reflection anti-paint. However, according to the inventors' studies, when a black pigment, dye, etc. is dispersed in a water-based coating agent containing an acid-modified polyolefin resin as disclosed in Patent Document 2 to create an internal reflection anti-paint, the film-forming properties and the adhesion of the formed coating film to the substrate may be reduced. In addition, the formation of aggregates in the paint may cause unintended thickening or gelation, which may lead to localization of the black pigment or dye in the coating film and the formation of an uneven coating film, resulting in a decrease in the optical properties of the coating film.

The present invention has been made in consideration of the above problems. That is, the object of the present invention is to provide an internal anti-reflection coating that has a small impact on the environment, has excellent film-forming properties on substrates made of resin, and is capable of forming an internal anti-reflection coating film that has excellent adhesion to the substrate and optical properties.

The internal reflection-preventive coating according to the present invention is an internal reflection-preventive coating containing a binder resin, a black pigment, a thickener, and an aqueous medium, the binder resin contains an acid-modified polyolefin resin and a polyurethane resin, the acid-modified polyolefin resin is composed of a propylene component and an ethylene component, the mass ratio of the propylene component to the ethylene component in the acid-modified polyolefin resin is in the range of propylene component:ethylene component=10:90 to 60:40, the content of the acid-modified polyolefin resin in the internal reflection-preventive coating is 60 mass% or more when the heating residue of the internal reflection-preventive coating at 105°C is taken as 100 mass%, the black pigment is carbon black having a particle size (D90) of 200 nm or less in a volume-based particle size distribution, the carbon black is coated with a nonionic surfactant, and the thickener is a urethane association type thickener.

The internal reflection anti-coating film according to the present invention is an internal reflection anti-coating film obtained by applying the above-mentioned internal reflection anti-coating paint.
Furthermore, the optical element according to the present invention has the above-mentioned internal antireflection coating film.

The present invention provides an internal anti-reflection coating that has a small impact on the environment, has excellent film-forming properties on substrates made of resin, and is capable of forming an internal anti-reflection coating film that has excellent adhesion to the substrate and excellent optical properties.

FIG. 2 is a diagram for explaining a method for measuring the internal reflectance in the examples.

Below, an embodiment of the present invention will be described. Hereinafter, the internal anti-reflective paint may be referred to simply as "paint" and the internal anti-reflective coating film may be referred to simply as "coating film."

In the present invention, the "heating residue of the anti-reflective coating at 105°C" refers to the solid components remaining after the anti-reflective coating is dried at 105°C. The "heating residue of the anti-reflective coating at 105°C" corresponds to the components that make up the anti-reflective coating, excluding the components that are lost in the process of forming the anti-reflective coating film using the anti-reflective coating. This portion may be simply referred to as the "solid content."

Conventionally, paints prepared by dispersing and dissolving each component in an organic solvent have been widely used, but in recent years, due to increasing concern about the environment, paints in which each component is dispersed and dissolved in an aqueous medium instead of an organic solvent are in demand. However, paints prepared by dispersing and dissolving each component in an aqueous medium generally have a problem in that it is difficult to achieve both film-forming properties and adhesion of the formed coating film on substrates made of resins, particularly resins with low polarity.
Patent Document 2 describes a water-based coating agent capable of forming a coating film having excellent adhesiveness and chemical resistance on the surface of a material made of a cyclic polyolefin having low polarity. Therefore, it is considered that an internal reflection-preventing coating material can be obtained by mixing a black pigment or other component other than an organic solvent among the components contained in the light-shielding coating material as disclosed in Patent Document 1, for example, with the water-based coating agent described in Patent Document 2. This is expected to provide a water-based coating material capable of forming an internal reflection-preventing coating film having excellent adhesiveness to resins having low polarity as well as excellent optical properties.

The inventors therefore investigated the possibility of dispersing black pigments, dyes, etc. in a water-based coating agent containing an acid-modified polyolefin resin as disclosed in Patent Document 2 to produce an internal reflection prevention coating. However, as mentioned above, there are cases where the film-forming properties and adhesion of the coating film to the substrate after formation are reduced, and cases where aggregates are generated in the coating, causing unintended thickening or gelation, etc., resulting in reduced optical properties of the coating film.

As a result of further investigation, the inventors have found that the above object can be achieved when the binder resin contains an acid-modified polyolefin resin containing an ethylene component and a propylene component in a specific ratio, and further contains a specific carbon black and a specific thickener.

That is, the internal reflection anti-coating according to the present invention is an internal reflection anti-coating containing a binder resin, a black pigment, a thickener and an aqueous medium, the binder resin contains an acid-modified polyolefin resin and a polyurethane resin, the acid-modified polyolefin resin is composed of a propylene component and an ethylene component, the mass ratio of the propylene component to the ethylene component in the acid-modified polyolefin resin is in the range of propylene component:ethylene component=10:90 to 60:40, and when the heating residue at 105° C. of the internal reflection anti-coating is taken as 100 mass%, the content of the acid-modified polyolefin resin in the internal reflection anti-coating is 60 mass% or more, the black pigment is carbon black having a particle size (D90) of 200 nm or less in a volume-based particle size distribution, the carbon black is coated with a nonionic surfactant, and the thickener is a urethane association type thickener.
The elements constituting the internal reflection preventing coating material according to the present invention will be described in detail below.

<Binder resin>
The internal reflection preventing coating material according to the present invention contains an acid-modified polyolefin resin and a polyurethane resin as binder resins.
By including a specific ratio or more of the acid-modified polyolefin resin in the coating film, it is possible to obtain good adhesion even to substrates made of low-polarity resins such as cyclic olefin resins (hereinafter sometimes referred to as "COP") and cyclic olefin copolymers. Furthermore, the present inventors have found that by making the composition of the olefin component, which is the main component of the acid-modified polyolefin resin, propylene and ethylene within a specific ratio range, it is possible to achieve both adhesion and film-forming properties. That is, it is believed that for resin compositions with low polarity, the propylene component mainly contributes greatly to improving adhesion, and the ethylene component has a high effect of improving film-forming properties. Therefore, it is believed that excellent film-forming properties and adhesion can be achieved by controlling their composition ratios.

An acid-modified polyolefin resin is a polyolefin resin that has been acid-modified with an unsaturated carboxylic acid component. Examples of the unsaturated carboxylic acid component include acrylic acid, methacrylic acid, maleic acid, maleic anhydride, itaconic acid, itaconic anhydride, fumaric acid, and crotonic acid. Of these, acrylic acid and maleic anhydride are preferred. The unsaturated carboxylic acid component may be copolymerized in the acid-modified polyolefin resin, and there are no limitations on its form. Specific examples of the copolymerization state include graft copolymerization.

The graft amount of the unsaturated carboxylic acid, the anhydride of the unsaturated carboxylic acid, and the derivative of the unsaturated carboxylic acid in the acid-modified polyolefin resin is preferably 0.5% by mass or more, and more preferably 1% by mass or more. When the graft amount is 0.5% by mass or more, it becomes easy to form an aqueous dispersion composition of the acid-modified polyolefin resin, and the adhesiveness of the aqueous dispersion composition to a polar substrate can be maintained. The graft amount is preferably 10% by mass or less. When the graft amount is 10% by mass or less, the generation of unreacted substances can be prevented, and the adhesion of the coating film to a resin with low polarity can be further improved.

The polyolefin resin used as the raw material for obtaining the acid-modified polyolefin resin contains at least one selected from the group consisting of a propylene component and an ethylene component. There are no particular limitations on the method for obtaining the polyolefin resin, but examples include a method of copolymerizing ethylene and propylene using a Ziegler-Natta catalyst or a metallocene catalyst as a polymerization catalyst. The raw polyolefin resin may be one type alone or a combination of two or more types. That is, the raw polyolefin resin may be a copolymer of ethylene and propylene alone, or a combination of polyethylene and polypropylene, or may be further combined with the above copolymer. The raw polyolefin resin is preferably a polyolefin resin obtained using a metallocene catalyst as a polymerization catalyst. Known metallocene catalysts can be used.

The acid-modified polyolefin resin is composed of a propylene component and an ethylene component derived from the raw material polyolefin resin. That is, the propylene component and the ethylene component constituting the acid-modified polyolefin resin are each modified with an acid.
When the heating residue at 105°C of the internal reflection anti-coating according to the present invention is taken as 100% by mass, the content of the acid-modified polyolefin resin in the internal reflection anti-coating is 60% by mass or more. In addition, the mass ratio of the propylene component to the ethylene component in the acid-modified polyolefin resin is in the range of propylene component:ethylene component = 10:90 to 60:40. In addition, the mass ratio of the propylene component to the ethylene component in the acid-modified polyolefin resin is preferably in the range of propylene component:ethylene component = 30:70 to 49:51. When the mass ratio of the propylene component in the acid-modified polyolefin resin is 10% or more, sufficient adhesion of the coating film to a substrate made of a resin with low polarity is obtained. In addition, when the mass ratio of the ethylene component in the acid-modified polyolefin resin is 40% or more, sufficient film-forming property is obtained on a substrate made of a resin with low polarity.

In the present invention, the heating residue (solid content) of the internal reflection prevention coating material at 105°C is the amount of the residue when the coating material is dried at 105°C for 60 minutes. The detailed measurement method is as follows. First, the weight of the aluminum cup is measured (measurement value A). Approximately 1.0 g of the measurement target (coating material) is weighed onto the aluminum cup (measurement value B) and air-dried for 30 minutes. After that, the sample is dried for 60 minutes in an electric furnace in an atmosphere of 105°C and then removed. The removed sample is aged for 2 hours in an environment of a temperature of 23±3°C and a relative humidity of 50±10%, and the weight of the heating residue including the aluminum cup is measured (measurement value C). The solid content (mass%) is calculated using the obtained measurement value according to the following formula.
Solid content (mass%)=100×(measured value C−measured value A)/measured value B

The internal anti-reflection coating material according to the present invention also contains a polyurethane resin as a binder resin. By including a polyurethane resin in the binder resin in addition to an acid-modified polyolefin resin, a coating film can be formed that has good adhesion even to substrates made of highly polar resins or glass.

Polyurethane resin is a polymer that has urethane bonds in the main chain, and is obtained, for example, by the reaction of a polyol compound with a polyisocyanate compound. From the viewpoint of improving adhesion to highly polar resins and glass, polyether-type polyurethane resins are preferred.

The polyol compound includes polyether polyol. Examples of polyether polyol include polyoxyethylene polyol such as polyethylene glycol, polyoxypropylene polyol such as polypropylene glycol, and polyoxyethylene/propylene polyol such as polytetramethylene ether glycol. Among them, polyether diol such as polyethylene glycol and polytetramethylene glycol is preferred because it is easily available, and polytetramethylene glycol is more preferred.
As polyols other than polyether polyols, 1,3-butanediol, 1,4-butanediol, 1,2-propanediol, 1,3-propanediol, 1,6-hexanediol, neopentyl glycol, 1,4-cyclohexanedimethanol, methyl-1,5-pentanediol, 1,8-octanediol, 2-ethyl-1,3-hexanediol, and the like may be used as long as the effects of the present invention are not impaired.

On the other hand, as the polyisocyanate compound constituting the polyurethane resin, one or a mixture of two or more aromatic, aliphatic or alicyclic diisocyanates can be used. Specific examples of diisocyanates include tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 1,3-phenylene diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, 1,5-naphthalene diisocyanate, isophorone diisocyanate, dimethyl diisocyanate, lysine diisocyanate, hydrogenated 4,4'-diphenylmethane diisocyanate, hydrogenated tolylene diisocyanate, dimer diisocyanate in which the carboxyl group of dimer acid is converted to an isocyanate group, and adducts, biurets and isocyanurates thereof. Among these, isophorone diisocyanate is preferred from the viewpoint of improving adhesion.

The content of polyurethane resin in the internal reflection prevention coating according to the present invention is not particularly limited, but when the heating residue of the coating at 105°C is taken as 100 mass%, the content of polyurethane resin is preferably 7.0 mass% or more and less than 17.0 mass%. Furthermore, the content of urethane resin is more preferably 9.0 mass% or more and less than 15.0 mass%. If the content of polyurethane resin in the coating is 7.0 mass% or more, a coating film having high adhesion to substrates made of highly polar resins or glass can be formed. Furthermore, if the content of polyurethane resin in the coating is less than 17.0 mass%, a coating film having high adhesion to substrates made of less polar resins can be formed.

The content ratio of the propylene component to the ethylene component in the binder resin and the content ratio of the ethylene component to the polyurethane can be calculated as follows. That is, the binder resin is measured by Fourier transform infrared spectroscopy (FT-IR), proton nuclear magnetic resonance (H-NMR), and gas chromatography mass spectrometry (GC-MS), and the respective values can be calculated using the obtained results.

<Black pigment>
The internal reflection preventing coating material according to the present invention contains carbon black having a particle size (D90) of 200 nm or less as a black pigment, and the carbon black is coated with a nonionic surfactant. In this specification, the particle size (D90) refers to the particle size (D90) in the volume-based particle size distribution.

By using carbon black with a particle size (D90) of 200 nm or less, it is possible to effectively suppress internal reflections over a wide range from the visible light region to the near infrared region (wavelengths of 400 nm to 1,500 nm). This allows for clearer imaging, for example, when the paint is applied to the optical elements that make up an imaging device, compared to using carbon black with a particle size (D90) of more than 200 nm.

The inventors have also discovered that by using carbon black coated with a nonionic surfactant, high adhesion and film-forming properties can be obtained, and unintended thickening and gelation of the coating liquid can be suppressed. This makes it possible to suppress localization of the black pigment in the coating film and deterioration of the optical properties of the coating film due to the formation of an uneven coating film. It is believed that by coating the carbon black with a nonionic surfactant, it is less susceptible to changes in pH and ionicity in paints that use aqueous media.

Nonionic surfactants are surfactants that have hydrophilic groups that do not ionize when dissolved in water, and are characterized by being less susceptible to the hardness of water or electrolytes. Nonionic surfactants that can be used in the present invention are not particularly limited, but include ester types (polyhydric alcohol types) that have a structure in which a polyhydric alcohol such as glycerin, sorbitol, or sucrose is ester-bonded to a fatty acid, ether types such as polyoxyethylene alkyl ether and polyoxyethylene alkylphenyl ether, ester-ether types that have both ester bonds and ether bonds in the molecule and are formed by adding ethylene oxide to an ester of a polyhydric alcohol such as glycerin or sorbitol and a fatty acid, and fatty acid alkanolamide types in which a hydrophobic group and a hydrophilic group are bonded by an amide bond. In the present invention, it is preferable to use the ether type, which can obtain a more stable dispersion state of the carbon particles.

The method for coating (treating) carbon black with a nonionic surfactant is not particularly limited, but an example is a method in which the carbon black particles are dispersed in water, the surfactant is added, and the mixture is mixed and stirred. From a manufacturing standpoint, it is simple and preferable to then add the mixture as is as a paint composition. In the present invention, it is preferable to prepare carbon black coated with a nonionic surfactant in advance and use this as one of the materials in preparing the paint.

The particle size (D90) of carbon black can be measured by dynamic light scattering. Specifically, for example, it can be measured using a particle size distribution measuring device (product name: Nanotrac WAVE-EZ150, manufactured by Microtrac Bell Co., Ltd.) as follows. The solution containing the carbon black to be measured is diluted to 0.05% by mass with ion-exchanged water, stirred and mixed with a stirrer for 1 minute, and then set in the measuring device to measure the particle size distribution.

In the present invention, the carbon black content in the internal anti-reflection coating is preferably 6.0% by mass or more and 12.0% by mass or less based on the solid content (coating film) of the internal anti-reflection coating. If the carbon black content in the coating film is 6.0% by mass or more, the effect of absorbing light in the near infrared region can be fully obtained, and the coating film can exhibit high internal anti-reflection performance. Furthermore, if the carbon black content in the coating film is 12.0% by mass or less, it is possible to suppress the scattering of internally reflected light caused by carbon black at the interface with the substrate. The carbon black content in the coating film is more preferably 8.0% by mass or more and 10.0% by mass or less based on the solid content of the paint. If the carbon black content in the coating film is 8.0% by mass or more and 10.0% by mass or less, the effect of absorbing light in the near infrared region and the effect of suppressing the scattering of internally reflected light described above can be more highly expressed.

The carbon black content can be measured, for example, by TG-DTA. Specifically, a solid material corresponding to the solid content defined in this invention is first prepared, and then TG-DTA measurement is performed using the solid material. The measurement conditions are as follows: First, the material is heated from 40°C to 600°C in a nitrogen atmosphere, and then the heating temperature is temporarily lowered to 400°C. Next, the atmospheric gas is switched from nitrogen to air, and the heating temperature is increased to 800°C. The weight loss when heated to 600°C in a nitrogen atmosphere corresponds to the amount of organic matter, and the weight loss when heated to 800°C after switching to an air atmosphere corresponds to the carbon black content.

<Thickener>
The internal reflection preventing coating material according to the present invention contains a urethane association type thickener. The association type thickener is a polymer having a molecular weight of several thousand to several tens of thousands, which is composed of a hydrophobic portion and a hydrophilic portion, and the hydrophobic portion of the thickener forms a network structure by associating with itself and with a hydrophobic substance such as a resin through hydrophobic interaction, thereby thickening the target liquid. The urethane association type thickener is a surfactant having a hydrophobic group at the molecular end and a urethane structure inside the molecule. The urethane association type thickener is also sometimes called hydrophobe modified ethoxylated urethane (HEUR).

In the present invention, by using a urethane association type thickener, a resin network structure is created in the paint, which effectively suppresses localization of the black pigment during the paint film formation process (drying) and deterioration of the optical properties of the paint film due to the formation of an uneven paint film. Therefore, compared to when no thickener is used, a paint film with excellent internal reflectance can be formed in a wide range from the visible light region to the near infrared region (wavelengths of 400 nm to 1,500 nm).

Commercially available urethane associative thickeners that can be used in the present invention include, for example, RHEOBYK-H3300VF and RHEOBYK-L1400VF (both manufactured by BYK Japan KK), ADEKA NOL UH-756VF and ADEKA NOL UH-450VF (both manufactured by ADEKA Corporation). Among these, RHEOBYK-H3300VF and RHEOBYK-L1400VF are preferably used from the viewpoint of long-term storage stability of the paint.

<Aqueous medium>
In the present invention, the aqueous medium refers to a medium containing water as a main component, such as ion-exchanged water, pure water, purified water, distilled water, etc. The aqueous medium may contain a water-soluble or water-miscible organic solvent, such as an alcohol solvent, an ester solvent, a ketone solvent, an amine solvent, or an amide solvent, as necessary.
In order to control the drying speed after application of the internal reflection preventing coating material, a mixture of a plurality of types of aqueous media may be used.
The ratio of the aqueous medium in the paint (dilution ratio) can be adjusted as desired according to the application. For example, the dilution ratio may be appropriately adjusted in the application method such as spray, dip, dispenser, and brush application, or in the case of controlling the thickness of the coating film according to the application. In addition, the dilution ratio may be appropriately changed to adjust the viscosity of the paint to the desired value.

<Viscosity>
The viscosity of the internal reflection anti-coating according to the present invention may be adjusted as appropriate depending on the desired film thickness or to prevent dripping after application, but is preferably 20 mPa·s or more and 1,000 mPa·s or less. If the viscosity of the internal reflection anti-coating is 20 mPa·s or more, dripping can be suppressed, and control of the film thickness of the coating film becomes easy. If the viscosity of the internal reflection anti-coating is 1,000 mPa·s or less, it is possible to suppress variation in film thickness and foaming.

<Other additives>
The internal reflection-preventive coating material according to the present invention may contain other additives as necessary within the range in which the internal reflection-preventive performance is maintained. Examples of other additives that the coating material may contain include defoamers, film-forming assistants, crosslinking agents, adhesion-imparting agents, leveling agents, preservatives, and mildew-proofing agents.

The binder resin in the paint of the present invention is an emulsion, so if the storage environment is high temperature, some of the emulsion may break down, causing the adhesion of the coating film to the substrate and anti-reflective performance to decrease. In response to this, by adding an appropriate amount of a known silicone-based or acetylene-based leveling agent to the paint, it is possible to suppress the collapse of the emulsion and improve the stability of performance even in a high-temperature storage environment.

In addition, a crosslinking agent for crosslinking the acid-modified polyolefin resin and/or polyurethane resin may be added to the coating material according to the present invention in order to improve adhesion. Examples of crosslinking agents include isocyanate compounds, melamine compounds, urea compounds, epoxy compounds, carbodiimide compounds, oxazoline group-containing compounds, hydrazide compounds, zirconium salt compounds, and silane coupling agents.

In the present invention, from the viewpoint of improving the adhesion of the coating film to the glass, it is preferable that the coating further contains at least one selected from the group consisting of a crosslinking agent and a silane coupling agent.

These additives may be used alone or in combination depending on the storage environment and application method.

<Method of manufacturing the internal anti-reflection coating>
The internal reflection preventing coating material according to the present invention can be produced by mixing a binder resin, a black pigment, a thickener, an aqueous medium, and other materials. The mixing can be carried out by a known method, for example, by using a magnetic stirrer, a propeller agitator, a ball mill, a paint shaker, a basket mill, a Dyno Mill, an Ultra Visco Mill, an annular type disperser, etc. The form of each material before mixing is not particularly limited, but a method in which each material is prepared in advance as an aqueous dispersion and then mixed is preferred.

[Inner surface anti-reflective coating]
The internal reflection anti-coating film according to the present invention is a coating film formed by using the internal reflection anti-coating material according to the present invention described above. That is, the internal reflection anti-coating film according to the present invention contains the above-mentioned binder resin, black pigment, and thickener.
The thickness of the internal reflection anti-coating film is preferably 0.5 μm or more and 100 μm or less. If the thickness of the internal reflection anti-coating film is 0.5 μm or more, the light that is incident from the opposite side of the surface of the substrate to which the paint is applied and then transmitted through the substrate can be effectively absorbed, and the effect of suppressing internal reflection and blocking light can be highly obtained. In addition, if the thickness of the internal reflection anti-coating film is 100 μm or less, the variation in the film thickness can be suppressed when the internal reflection anti-coating paint is formed.
The internal reflection preventing coating preferably has an internal reflectance of 3.0% or less for light with a wavelength of 400 nm to 1500 nm.
The adhesive strength of the inner-surface anti-reflection coating to the cyclic olefin resin (COP resin) is preferably 10 N or more.

<Method of manufacturing the internal anti-reflection coating film>
The internal reflection anti-coating film according to the present invention can be produced by applying the internal reflection anti-coating material according to the present invention described above to a substrate, and then drying the coating material.
The substrate on which the coating film is formed may be a known one such as glass or resin. The method for forming the coating film is not particularly limited, and any known coating method may be used. Examples of the coating method include spray, dispenser, brush, roller, roll coat, applicator, wire bar (bar coater), dip coating, sponge coating, etc.
The drying method may be any method that volatilizes the aqueous medium and then fuses the dispersed particles of the resin used to each other, and a known drying method may be selected according to the application and the required drying speed. Known drying methods include, for example, heating using an electric furnace, hot air, and far infrared rays. The drying temperature is not particularly limited, but a temperature of 80°C to 110°C is preferable because the dispersion state of the black pigment in the paint is unlikely to change during drying and the drying time is not long.

[Optical elements]
The optical element according to the present invention has the above-mentioned internal antireflection coating film according to the present invention. Specifically, for example, the optical element according to the present invention may have the internal antireflection coating film formed on the light-opaque surface of a lens.

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.
The materials used in each of the examples and comparative examples are shown in Table 1. In addition, Table 2 shows the types of substrates used as targets for coating with the internal reflection preventing coating material.
In Table 1, PP, PE, and PU indicate the mass-based content ratios of the propylene component, ethylene component, and polyurethane, respectively. Each content ratio was calculated from the measurement results of FT-IR, H-NMR, and GC-MS. The heating residue was calculated by preparing a solid matter according to the above definition of the solid matter and measuring its weight.

<Preparation of Inner Anti-Reflection Coating>
The materials were mixed in the ratios shown in Tables 3 and 4 to obtain the internal reflection preventing coating materials of Examples 1 to 24 and Comparative Examples 1 to 9.
The mixing conditions were as follows: a 5 L stainless steel stockpot and a propeller stirrer were used, and the mixture was mixed on a scale where the total liquid amount was 3.0 kg.
For Examples 1 to 15, 18, 19, and 24 and Comparative Examples 1 to 7, the binder resins were first mixed in the ratios shown in Tables 3 and 4, and stirred and mixed for 10 minutes. Then, a black pigment was added, and the mixture was stirred and mixed for an additional 10 minutes. Next, a leveling agent was added as an additive, and the mixture was stirred and mixed for an additional 10 minutes. Next, a thickener was added while stirring, and the mixture was stirred and mixed for an additional 10 minutes after the addition. Finally, the mixture was filtered through a nylon mesh (#100) to obtain an internal reflection preventing coating material.
In Examples 16 and 17, ion-exchanged water was added to the paint prepared in the same manner as in Example 1, and the paint was diluted to the viscosity shown in Table 7 to obtain an internal reflection preventing paint.
In Example 20, an internal reflection preventing coating material was obtained in the same manner as in Example 1, except that no leveling agent was added as an additive.
In addition, for Examples 21 to 23, the materials were mixed in the same order as in Example 1, and immediately before film formation, crosslinking agents 1 to 3 were added as other additives, respectively, and the mixture was stirred and mixed for 10 minutes to obtain an internal reflection prevention coating material.
In addition, in Comparative Example 8, since the thickener was in a paste form, an internal reflection preventing coating material was obtained in the same manner as in Example 1, except that a 10% by mass aqueous solution of the thickener was prepared in advance and then added, which was then used as a 10% by mass aqueous solution of the thickener.
In addition, in Comparative Example 9, since the thickener was in the form of a powder, an internal reflection preventing coating material was obtained in the same manner as in Example 1, except that a 1% by mass aqueous solution of the thickener was prepared in advance and used.

[Correction under Rule 26 16.07.2024]

<Preparation of Internal Antireflection Coatings A-1 and A-2>
The internal reflection antireflection coating material obtained by the above preparation of the internal reflection antireflection coating material was applied to a slide plate of a cyclic olefin polymer resin (COP) substrate using a wire bar (wet film thickness 12 μm), air-dried for 5 minutes, and then dried at 105° C. for 30 minutes to prepare an internal reflection antireflection coating film A-1. In addition, the drying temperature after air-drying was changed to 80° C. to prepare an internal reflection antireflection coating film A-2.

<Preparation of Internal Antireflection Coating Films B-1 and B-2>
Inner-surface antireflection coating films B-1 (drying temperature 105° C.) and B-2 (drying temperature 80° C.) were prepared in the same manner as for the inner-surface antireflection coating films A-1 and A-2, except that the type of substrate used was changed from a slide plate of a cycloolefin polymer resin (COP) substrate to a slide plate of a polycarbonate resin (PC).

<Preparation of Internal Antireflection Coatings C-1 and C-2>
A right-angled triangular prism (30 × 30 mm, t 15 mm, apex angle 90 °) was prepared as a substrate. First, all surfaces of the right-angled triangular prism were polished to a mirror surface using #2000 waterproof sandpaper. Next, the right-angled triangular prism was held using a jig in which the bottom surface (hypotenuse surface) of the right-angled triangular prism was the upper surface and horizontal, and the internal antireflection coating material obtained above was applied to the bottom surface of the right-angled triangular prism using a wire bar (wet film thickness 12 μm). Then, the film was dried at 105 ° C. for 30 minutes to prepare an internal antireflection coating film C-1. In addition, the drying temperature after air drying was changed to 80 ° C. to prepare an internal antireflection coating film C-2.

<Evaluation>
The internal reflection antireflection paints and internal reflection antireflection coating films A-1 to C-1 and A-2 to C-2 prepared in each of the Examples and Comparative Examples were evaluated as follows.

[Ingredients of internal anti-reflective paint]
The composition of each component (the ratio of each component on a mass basis) was calculated from the material composition shown in Table 1, and the results are shown in Tables 5 and 6.

[Correction under Rule 26 16.07.2024]

〔viscosity〕
The viscosity was measured using a TVB-15 viscometer (manufactured by Toki Sangyo Co., Ltd.) equipped with a THM type small sample adapter at a temperature of 23±1° C. The rotation speed of the rotor was appropriately adjusted to be optimal depending on the viscosity of the liquid to be measured.
The results of the measurements are shown in Tables 7 and 8. In Table 8, N.D. indicates that the paint gelled and therefore each measurement and evaluation could not be performed.

[Film-forming properties]
The film-forming properties were confirmed using the internal anti-reflection coating films A-1 and B-1. The surface condition of the internal anti-reflection coating film A was visually observed and evaluated as follows.
A: There is absolutely no repelling, cracking, or unevenness in film thickness with the substrate, and the surface condition is uniform.
B: There is no repelling or cracking from the substrate, but slight unevenness in film thickness is observed.
C: Cracks and repellency from the substrate, or significant unevenness in film thickness is observed.
The evaluation results are shown in Tables 7 and 8.

[Adhesion]
The adhesion between the internal reflection anti-coating film and the substrate was evaluated using the internal reflection anti-coating films A-1, A-2, B-1 and B-2 based on the cross-cut method (JIS K 5600-5-6:1999) as follows.
A: Cross-cut evaluation: "Classification: 0" or "Classification: 1"
B: Cross-cut evaluation: "Classification: 2" or "Classification: 3"
C: Cross-cut evaluation: "Classification: 4" or "Classification: 5"
The evaluation results are shown in Tables 7 and 8.

[Inner surface reflectance]
[Method for measuring internal reflectance]
The internal reflectance was measured using the internal reflection-preventive coating films C-1 and C-2. As shown in FIG. 1, a right-angled triangular prism provided with an internal reflection-preventive coating film 3 was placed in the sample placement section in the spectrophotometer. The light emitted from the light source 11 was passed through a polarizing plate 17 set to N-polarized light, and collected by a slit 18 (a rectangular aperture of 1 mm long x 3 mm wide) to obtain the incident light 12. The incident light 12 was refracted when it entered the right-angled triangular prism 10, entered the internal reflection-preventive coating film 3 at an incident angle θ, and was further reflected to emit the internally reflected light 13. The internally reflected light 13 was received by an integrating sphere 14 of φ60 mm equipped with a photodetector, and the light intensity at each wavelength was measured. The distance A from the vertical line (perpendicular line) 15 to the base surface of the right-angled triangular prism 10 to the tangent surface 16 of the integrating sphere entrance was 15·√2 mm, and the opening diameter B of the integrating sphere 14 was φ15 mm.
Without the right-angle triangular prism 10 installed, the internal reflection light intensity for light with wavelengths of 400 nm to 1500 nm was measured at 5 nm intervals in advance, and the light intensity for each wavelength was taken as 100% internal reflectance. Then, with the right-angle triangular prism 10 provided with the internal reflection prevention coating film 3 installed, the internal reflection light intensity for light with wavelengths of 400 nm to 700 nm was measured at 5 nm intervals, and the percentage of the internal reflection light intensity for each wavelength relative to the case where the right-angle triangular prism 10 was not installed was calculated. Next, the arithmetic mean value of the percentages obtained at each wavelength was taken, and this was taken as the internal reflectance (L) of the sample. Similarly, the internal reflection light intensity for light with wavelengths of 700 nm to 1500 nm was measured, and the arithmetic mean of the percentages was calculated, and this was taken as the internal reflectance (M) of the sample.
The internal reflection preventing performance was evaluated for the internal reflectance (L) in the visible light region (400 nm to 700 nm) obtained above according to the following criteria.
A: Internal reflectance (L) is 2.0% or less. B: Internal reflectance (L) is more than 2.0% and 3.0% or less. C: Internal reflectance (L) is more than 3.0%. Furthermore, the internal reflectance (M) in the near infrared region (700 nm to 1500 nm) obtained above was evaluated for internal reflection prevention performance according to the following criteria.
A: The internal reflectance (M) is 2.0% or less. B: The internal reflectance (M) is more than 2.0% and less than 3.0%. C: The internal reflectance (M) is more than 3.0%.

[COP adhesion]
The adhesive strength (COP adhesion) to a cyclic olefin resin (COP resin) was evaluated as follows.
The internal reflection prevention coatings according to each of the Examples and Comparative Examples were applied to a cyclic polyolefin (COP) film (ZEONOR film, thickness 100 μm, manufactured by Zeon Corporation) using a Mayer bar so that the thickness of the coating film after drying was 5 μm, and then dried at 100 ° C. for 1 minute. Then, the obtained laminates were pressed for 10 seconds at 120 ° C. and a seal pressure of 0.8 MPa in a heat press machine so that the coating surfaces of the laminates were in contact with each other. The pressed laminate was cut into a width of 15 mm and left for 1 day, and then the peel strength of the coating film was measured using a universal material testing machine (manufactured by A & D Co., Ltd.) at a tensile speed of 500 mm / min and a tensile angle of 180 degrees, and the measured value was evaluated as COP adhesion strength according to the following criteria.
A: COP adhesion is 15 N or more. B: COP adhesion is less than 15 N, 10 N or more. C: COP adhesion is less than 10 N. The evaluation results are shown in Tables 7 and 8.

〔comprehensive evaluation〕
The overall evaluation was performed using the evaluation results of the film-forming property, adhesion, internal reflectance, and COP adhesion according to the following criteria.
A: All evaluation results are "A".
B: At least one evaluation result is "B" and there is no "C".
C: At least one evaluation result is "C" or "ND."
The evaluation results are shown in Tables 7 and 8.

[Correction under Rule 26 16.07.2024]

The present invention is not limited to the above-described embodiment, and various modifications and variations are possible without departing from the spirit and scope of the present invention. Therefore, the following claims are appended to disclose the scope of the present invention.

This application claims priority based on Japanese Patent Application No. 2023-107234, filed on June 29, 2023, the entire contents of which are incorporated herein by reference.

3. Internal anti-reflection coating 10. Right-angle triangular prism 11. Light source 12. Incident light 13. Internally reflected light 14. Integrating sphere 15. Vertical line (perpendicular line) to the base of the right-angle triangular prism
16. Contact surface of integrating sphere entrance 17. Polarizing plate 18. Slit

Claims (9)

An internal anti-reflection coating material comprising a binder resin, a black pigment, a thickener and an aqueous medium,
the binder resin includes an acid-modified polyolefin resin and a polyurethane resin,
The acid-modified polyolefin resin comprises a propylene component and an ethylene component,
a mass ratio of the propylene component to the ethylene component in the acid-modified polyolefin resin (propylene component:ethylene component) is in the range of 10:90 to 60:40;
When the heating residue of the inner-surface reflection anti-reflection coating material at 105° C. is taken as 100% by mass, the content of the acid-modified polyolefin resin in the inner-surface reflection anti-reflection coating material is 60% by mass or more,
The black pigment is carbon black having a particle size (D90) of 200 nm or less in a volume-based particle size distribution,
The carbon black is coated with a nonionic surfactant,
The thickener is a urethane association type thickener.
Inner anti-reflective paint. The internal anti-reflection coating according to claim 1, wherein the mass ratio of the propylene component to the ethylene component in the acid-modified polyolefin resin is in the range of propylene component:ethylene component = 30:70 to 49:51. The anti-reflective coating according to claim 1 or 2, wherein the carbon black content in the anti-reflective coating is 6.0% by mass or more and 12.0% by mass or less, when the heat residue of the anti-reflective coating at 105°C is taken as 100% by mass. The internal anti-reflection coating according to any one of claims 1 to 3, wherein the viscosity of the internal anti-reflection coating is 20 mPa·s or more and 1,000 mPa·s or less. The internal anti-reflection coating according to any one of claims 1 to 4, further comprising at least one selected from the group consisting of a crosslinking agent and a silane coupling agent. An internal anti-reflective coating film formed by applying the internal anti-reflective coating material described in any one of claims 1 to 5. The internal anti-reflective coating according to claim 6, wherein the internal anti-reflective coating has an internal reflectance of 3.0% or less for light with a wavelength of 400 nm to 1500 nm. The internal anti-reflective coating according to claim 6 or 7, wherein the adhesive strength of the internal anti-reflective coating to the cyclic olefin resin is 10 N or more. An optical element having an internal anti-reflection coating according to any one of claims 6 to 8.

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