Antireflection film, stray light suppression film, and light receiving device

Abstract

Provided are an antireflection film having an antireflection layer that has an integrated reflectance of 1% or less in a wavelength band of 1530-1625 nm and has an uneven structure on the surface thereof, a stray light suppression film having at least the antireflection film and a light absorber, and a light receiving device having the stray light suppression film inside the device.

Description

Anti-reflection film, stray light suppression film, and light receiving device

[0001] The present invention relates to an anti-reflection film, a stray light suppression film, and a light receiving device. More specifically, the present invention relates to applications where the light output of a light source is large, particularly a member for suppressing stray light inside a light receiving device for optical communication, and a light receiving device using the same.

[0002] In recent years, in optical communication, the light output of light sources for signal transmission, particularly laser light sources, has been increasing. For example, according to Non-Patent Document 1, in 2011 it was about 20 [mW] (13 [dBm]), whereas in 2020 it was about 50 - 60 [mW] (17 - 18 [dBm]), an increase of 2.5 to 3 times. Thus, even if transmission loss occurs in the optical fiber, communication errors can be reduced by maintaining the light intensity and receiving signal information

[0003] Optical Transceivers for Datacom and Telecom Market and Technology 2023 (Yole)

[0004] However, when such a light source with a large light output is applied to conventional light receiving devices, it has been found that there is a problem of deterioration in the signal-to-noise ratio (S / N ratio). Although various factors contributing to the S / N ratio deterioration have been studied so far, as a result of detailed analysis, it has been found that stray light inside the device is the main factor. Also, the wavelength bands used in optical communication generally differ between short - to medium-distance applications (800 - 950 nm, O band: 1260 - 1360 nm) and long-distance applications. Stray light suppression is required in any wavelength band, but particularly in the C band (1530 - | 1565 nm) and L band (1565 - 1625 nm), which are wavelength bands for long-distance applications where light is transmitted through optical fibers of several tens of kilometers or more. Suppressing stray light in these bands is considered important, and the present invention was conceived.

[0005] An object of the present invention is to provide an anti-reflection film and a stray light suppression film that can be used as a member for suppressing stray light inside a light receiving device, and a light receiving device using the same.

[0006] To solve this problem, the present invention has the following configuration.

[0007] <1> An anti-reflective film having an anti-reflective layer having an integrated reflectance of 1% or less in the wavelength band of 1530 to 1625 nm and an anti-reflective layer having an uneven surface structure. <2> The anti-reflective film according to <1>, wherein the anti-reflective layer comprises particles that form protrusions and a binder. <3> The anti-reflective film according to <2>, wherein the particle size of the particles that form the protrusions is 400 to 800 nm. <4> The anti-reflective film according to <2> or <3>, wherein the particles that form the protrusions are not in contact with each other. <5> The anti-reflective film according to any one of <2> to <4>, wherein L is the distance between the vertices of adjacent protrusions and D is the particle size of the particles that form the protrusions, and L and D satisfy the following condition X. Condition X: 20 nm ≤ L-D ≤ 90 nm <6> An anti-reflective film according to any one of <2> to <5>, wherein a portion of the particles forming the protrusions is embedded in the binder, and the ratio of the length A of the portion of the particles embedded in the binder to the length B of the portion of the particles protruding from the binder is A:B = 3 to 6: 7 to 4. <7> An anti-reflective film according to any one of <1> to <6>, wherein the integrated reflectance of at least some wavelengths between 380 and 780 nm is 1% or more. <8> A stray light suppression film comprising at least an anti-reflective film according to any one of <1> to <7> and a light absorber. <9> A light receiving device having the stray light suppression film according to <8> inside the device. <10> An anti-reflective film according to any one of <2> to <6>, wherein the integrated reflectance in at least one of the wavelength bands of 800 to 950 nm and 1260 to 1360 nm is 1% or less, and the particle size of the particles forming the convex portion is 400 to 680 nm. <11> A stray light suppression film having at least the anti-reflective film according to <10> and a light absorber. <12> A light receiving device having the stray light suppression film according to <11> inside the device.

[0008] According to the present invention, it is possible to provide an anti-reflective film and a stray light suppression film that can be used as components for suppressing stray light inside a light receiving device, as well as a light receiving device using the same.

[0009] This is a schematic cross-sectional diagram showing an example of the anti-reflective film of the present invention. This is a schematic cross-sectional diagram showing an example of the anti-reflective layer of the present invention. This is a schematic cross-sectional diagram showing an example of the application of the anti-reflective layer of the present invention.

[0010] The anti-reflective film of the present invention will be described in detail below.

[0011] In this specification, numerical ranges expressed using "~" mean a range that includes the numbers before and after "~" as the lower and upper limits. In this specification, "identical" includes the error range that is generally accepted in the art. In this specification, when we say "all," "all," and "entire," we mean not only 100%, but also the error range that is generally accepted in the art, such as 99% or more, 95% or more, or 90% or more.

[0012] The anti-reflective film of the present invention has an integrated reflectance of 1% or less in the wavelength band of 1530 to 1625 nm, and is an anti-reflective film having an anti-reflective layer with an uneven surface structure. The anti-reflective film of the present invention will be described in detail below.

[0013] The anti-reflective layer described above preferably comprises particles that form protrusions and a binder. An example of a preferred embodiment of the anti-reflective film of the present invention is shown in Figure 1. The anti-reflective film 10 in Figure 1 comprises an anti-reflective layer 2 having an uneven structure and a substrate (support) 1. The anti-reflective layer has an uneven structure on the surface opposite to the substrate. The anti-reflective layer 2 comprises particles 3 that form protrusions and a binder 4. The particles 3 that form the protrusions do not come into contact with each other, and their particle size is in the range of 400 to 800 nm.

[0014] (Particle size) By making the particle size of the convex portion less than half the wavelength of the shortest wave in the wavelength band to be de-reflected, scattering and diffraction, which can be factors in diffuse reflection, can be suppressed. The particle size of the convex portion is preferably 400 to 800 nm (0.4 to 0.8 μm), and more preferably 450 to 650 nm (0.45 to 0.65 μm).

[0015] (Particle Shape) While spherical is the most preferred shape for the particles, irregular shapes or other non-spherical shapes are also acceptable. Furthermore, silica particles may be either crystalline or amorphous.

[0016] (Types of particles that form the protrusions) Examples of particles that form the protrusions include metal oxide particles, resin particles, and organic-inorganic hybrid particles having a metal oxide core and a resin shell, but metal oxide particles are preferred from the viewpoint of excellent film strength. Examples of metal oxide particles include silica particles, titania particles, zirconia particles, and antimony pentoxide particles, but silica particles are preferred from the viewpoint of being less likely to generate haze because their refractive index is close to that of many binders, and that they easily form an uneven structure. Examples of resin particles include polymethyl methacrylate particles, polystyrene particles, and melamine particles.

[0017] (Refractive index of particles) The refractive index of the above particles is preferably 1.35 to 1.65. If the refractive index is smaller than this, the particle size (particle diameter) needs to be larger in order to utilize interference, but as mentioned above, this can be a factor in increasing the diffuse reflection component due to scattering and diffraction. Conversely, if the refractive index is larger than this, the particles need to be smaller in order to utilize interference, but when the particles are small, aggregation is more likely to occur, and scattering by aggregated particles with a high refractive index can also be a factor in increasing the diffuse reflection component. The above refractive index is the refractive index of light at least a portion of the wavelengths between 850 and 1625 nm.

[0018] (Difference between the distance L between the vertices of adjacent protrusions and the particle size D) In ​​the anti-reflective film of the present invention, it is preferable that the particles forming the protrusions are not in contact with each other. It is preferable that the particles forming the protrusions are not in contact (not aggregated) because this increases the reflectivity reduction effect due to interference. In the anti-reflective film of the present invention, when L is the distance between the vertices of adjacent protrusions and D is the particle size of the particles forming the protrusions, it is preferable that L and D satisfy the following condition X. Condition X: 20 nm ≤ L - D ≤ 90 nm Within this range, the ratio of reflected light on the binder surface without particles to the reflected light on the top of the particles becomes approximately equal, and they interfere with each other to suppress reflected light. If it is smaller or larger than this range, the ratio changes, and the effect of suppressing reflected light due to interference decreases. It is more preferable that L - D is 30 to 80 nm. The vertex of a protrusion is the point at the highest position of that protrusion (for example, the highest position relative to the surface of the substrate or the surface of the binder). For example, if the anti-reflective layer comprises particles that form protrusions and a binder, the apex of the protrusion is the point on the particles that form the protrusion that is furthest from the surface of the binder.

[0019] (Ratio of the length A of particles embedded in the binder to the length B of particles protruding from the binder) In the anti-reflective film of the present invention, a portion of the particles forming the protrusions are embedded in the binder, and it is preferable that the ratio of the length A of the portion of the particle embedded in the binder to the length B of the portion of the particle protruding from the binder is A:B = 3 to 6:7 to 4. The length A of the portion of the particle embedded in the binder is the depth to which the particle is embedded in the binder, more specifically, the distance from the surface of the binder to the point on the particle that is at the deepest position toward the inside of the binder (see A in Figure 2). The length B of the portion of the particle protruding from the binder is the height to which the particle protrudes from the binder, more specifically, the distance from the surface of the binder to the point on the particle that is at the furthest position in the direction in which the particle protrudes (see B in Figure 2). A:By setting B within the above range, the particles function as a refractive index gradient layer where the refractive index gradually changes from the air layer to the binder layer, while maintaining the aforementioned interference-induced reflection suppression effect, thereby further reducing the reflectivity.

[0020] The particle size and distance (i.e., L, D, A, and B mentioned above) can be measured by cross-sectional SEM (Scanning Electron Microscope) observation of the anti-reflective film or by SEM observation from above. In cross-sectional SEM observation, the anti-reflective film sample may be cut with a microtome to obtain a cross-section and observed at an appropriate magnification (approximately 2500 to 5000 times). In SEM observation, the sample may be subjected to appropriate treatment such as carbon deposition or etching to facilitate observation. The particle size and distance (i.e., L, D, A, and B mentioned above) are calculated as the average value of 30 measurement points.

[0021] In the anti-reflective film of the present invention, the particles forming the protrusions of the uneven surface structure of the anti-reflective layer do not necessarily have to be in contact with each other. Here, "the particles forming the protrusions are not in contact with each other" does not strictly mean that there are absolutely no areas where the particles forming the protrusions are in contact with each other, but also includes cases where there are areas where they are in contact to some extent due to variations in industrial production, etc. Specifically, when the distance L between the vertices of adjacent protrusions and the particle size D satisfy the relationship L > D, it is considered that "the particles forming the protrusions are not in contact with each other." However, as mentioned above, L and D are the average values ​​obtained by measuring the lengths at 30 points, respectively.

[0022] The above particles may be surface-treated to improve dispersibility in the coating solution, improve film strength, and prevent aggregation. From the viewpoint of increasing film strength and improving scratch resistance, the particles may be treated with a compound having an unsaturated double bond on their surface. Specific examples and preferred examples of surface treatment methods are the same as those described in paragraphs

[0119] to

[0147] of Japanese Patent Application Publication No. 2007-298974.

[0023] (Binder resin for anti-reflective layer) The binder for the anti-reflective layer preferably contains a resin. The resin contained in the binder is also called the "binder resin". The binder resin for the anti-reflective layer is preferably obtained by curing a polymerizable compound (monomer) for binder resin formation. Examples of the above monomers include compounds having polymerizable functional groups (polymerizable unsaturated double bonds) such as (meth)acryloyl groups, vinyl groups, styryl groups, and allyl groups, and among these, compounds having a (meth)acryloyl group are preferred.

[0024] Specific examples of compounds having polymerizable functional groups include (meth)acrylic acid diesters of alkylene glycols, (meth)acrylic acid diesters of polyoxyalkylene glycols, (meth)acrylic acid diesters of alcohols, (meth)acrylic acid diesters of ethylene oxide or propylene oxide adducts, epoxy (meth)acrylates, urethane (meth)acrylates, polyester (meth)acrylates, and the like.

[0025] Among these, esters of alcohol and (meth)acrylic acid are preferred (for example, 2-hydroxyethyl methacrylate), and esters of polyhydric alcohol and (meth)acrylic acid are particularly preferred. Examples include pentaerythritol tetra(meth)acrylate, pentaerythritol tri(meth)acrylate, trimethylolpropane tri(meth)acrylate, ethylene oxide (EO) modified trimethylolpropane tri(meth)acrylate, propylene oxide (PO) modified trimethylolpropane tri(meth)acrylate, EO modified phosphate tri(meth)acrylate, trimethylolethane tri(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, dipentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, pentaerythritol hexa(meth)acrylate, 1,2,3-cyclohexanetetramethacrylate, urethane acrylate, polyester polyacrylate, caprolactone modified tris(acryloxyethyl) isocyanurate, and the like.

[0026] The above binder resin preferably includes a resin obtained by curing a compound having a (meth)acryloyl group with a molecular weight of 150 to 1600. The molecular weight of the compound having a (meth)acryloyl group is more preferably 170 to 1400, and even more preferably 200 to 1200. If the molecular weight of the compound having a (meth)acryloyl group is 150 or more, the strength of the anti-reflective layer can be sufficiently increased, and if it is 1600 or less, it is easier to form a textured structure. When the compound is a polymer, the above molecular weight is the mass-average molecular weight on a polystyrene basis measured by gel permeation chromatography.

[0027] The anti-reflective film of the present invention has an integrated reflectance of 1% or less in the wavelength band of 1530 to 1625 nm, but more preferably has an integrated reflectance of 1% or less in at least one of the wavelength bands of 800 to 950 nm and 1260 to 1360 nm, and more preferably has an integrated reflectance of 1% or less in the wavelength band of 800 to 950 nm and an integrated reflectance of 1% or less in the wavelength band of 1260 to 1360 nm. The anti-reflective film of the present invention has an integrated reflectance of 1% or less in at least one of the wavelength bands of 800 to 950 nm and 1260 to 1360 nm, and it is preferable that the particle size of the particles forming the protrusions is 400 to 680 nm.

[0028] (Method for Manufacturing Anti-Reflective Film) The anti-reflective film of the present invention can be manufactured by applying a composition containing second particles and a monomer for forming a binder resin onto a substrate, curing the coating film with heat or light, applying a composition containing particles for forming protrusions and a monomer for forming a binder resin onto the coating film, and curing the coating film with heat or light. The above composition may contain a solvent, a polymerization initiator, a particle dispersant, a leveling agent, an antifouling agent, etc. As for the solvent, it is preferable to select one with polarity close to that of the fine particles in order to improve dispersibility. Specifically, for example, if the fine particles are metal oxide fine particles, an alcohol-based solvent is preferred, such as methanol, ethanol, 2-propanol, 1-propanol, and butanol. Also, for example, if the fine particles are metal resin particles or resin particles with hydrophobic surface modification, a ketone-based, ester-based, carbonate-based, alkane, aromatic-based solvent is preferred, such as methyl ethyl ketone (MEK), dimethyl carbonate, methyl acetate, acetone, methylene chloride, and cyclohexanone. These solvents may be mixed in combination in a range that does not significantly worsen dispersibility. The particle dispersant can make it easier to uniformly arrange the particles by reducing the cohesive force between them. The dispersant is not particularly limited, but anionic compounds such as sulfates and phosphates, cationic compounds such as aliphatic amine salts and quaternary ammonium salts, nonionic compounds, and polymer compounds are preferred, with polymer compounds being more preferred due to the high degree of freedom in selecting both adsorption groups and steric repulsion groups. The leveling agent can stabilize the liquid after coating by reducing the surface tension of the coating liquid, making it easier to uniformly arrange particles and binder resins. For example, compounds described in Japanese Patent Publication No. 2004-331812 and Japanese Patent Publication No. 2004-163610 can be used. The antifouling agent can suppress the adhesion of dirt and fingerprints by imparting water-repellent and oil-repellent properties to the moth-eye structure. For example, compounds described in Japanese Patent Publication No. 2012-88699 can be used.

[0029] (Polymerization initiator) If the polymerizable compound for binder resin formation is a photopolymerizable compound, it is preferable to include a photopolymerization initiator. For example, compounds described in Japanese Patent Application Publication No. 2015-74087 can be used.

[0030] The method of applying the composition is not particularly limited, and known methods can be used. Examples include dip coating, air knife coating, curtain coating, roller coating, wire bar coating, gravure coating, and die coating.

[0031] From the viewpoint of easy uniform application, the solid content concentration of the above composition is preferably 10% by mass or more and 80% by mass or less, and more preferably 20% by mass or more and 60% by mass or less.

[0032] (Substrate) The anti-reflective film of the present invention preferably contains a substrate. The substrate is not particularly limited as long as it is a transparent substrate commonly used as a substrate for anti-reflective films, but plastic substrates and glass substrates are preferred. Various plastic substrates can be used, for example, cellulose resins; cellulose acylate (triacetate cellulose, diacetyl cellulose, acetate butyrate cellulose), etc., polyester resins; polyethylene terephthalate, etc., (meth)acrylic resins, polyurethane resins, polycarbonate, polystyrene, olefin resins, etc. From the viewpoint of easily creating a permeable layer, substrates containing cellulose acylate, polyethylene terephthalate, or (meth)acrylic resins are preferred, and substrates containing cellulose acylate are more preferred. As cellulose acylate, the substrate described in Japanese Patent Application Publication No. 2012-093723 can be preferably used.

[0033] The plastic substrate may have another resin layer on its surface. For example, it may have a hard coat layer to provide hard coating properties to the substrate, an easy-adhesion layer to provide adhesion to other layers, a layer to provide antistatic properties, and may have multiple such layers.

[0034] (Stray Light Suppression Film) The stray light suppression film of the present invention comprises at least the anti-reflective film described above and a light absorber.

[0035] (Light Absorber) The light absorber in this invention absorbs light transmitted through the anti-reflective film and suppresses stray light. It is not particularly limited as long as it absorbs the desired wavelength range, and known materials can be used. Examples include black pigments, carbon black, and black dyes. Films containing these materials or films coated with them can also be used.

[0036] The present invention will be described in more detail below with reference to examples. The materials, reagents, amounts and proportions of substances, and procedures shown in the following examples can be modified as appropriate, as long as they do not depart from the spirit of the present invention. Therefore, the scope of the present invention is not limited to the following specific examples.

[0037] (Example 1) (Preparation of coating solution for forming anti-reflective layer) Each component was placed in a mixing tank to obtain the following composition, stirred for 60 minutes, dispersed using an ultrasonic disperser for 30 minutes, and filtered through a polypropylene filter with a pore size of 5 μm to obtain coating solution TJ1 for forming an anti-reflective layer.

[0038] (Anti-reflective coating liquid TJ1) KE-P50 100.0 parts by mass A-TMMT 100.2 parts by mass DPHA 51.4 parts by mass Irgacure 127 6.5 parts by mass Leveling agent L1 0.3 parts by mass Ethanol 398.4 parts by mass

[0039] KE-P50: Amorphous silica particles with an average particle size of 0.5 μm: (manufactured by Nippon Shokubai Co., Ltd.) A-TMMT: Pentaerythritol tetraacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd.) DPHA: Dipentaerythritol penta and hexaacrylate (manufactured by Toagosei Co., Ltd.) Irgacure 127: Photoinitiator (manufactured by BASF Japan Ltd.) Leveling agent L1: The following compound (molecular weight 18,000). The content of each of the following repeating units is the content ratio (mass %) with respect to all repeating units.

[0040]

[0041] (Production of antireflection film) On a cellulose triacetate film, using a gravure coater, the coating solution TJ1 for forming an antireflection layer was wet-coated at a rate of about 3.5 ml / m ２ to form a coating film. After drying the above coating film at 120 °C for 5 minutes, while purging with nitrogen to create an atmosphere with an oxygen concentration of 100 ppm (parts per million) or less, it was irradiated with ultraviolet light at an irradiation dose of 300 mJ / cm ２ and cured to form an antireflection layer. In this way, the antireflection film FJ1 was produced.

[0042] (Example 2) Next, an antireflection layer-forming coating solution TJ2 was prepared in the same manner as in Example 1, except that silica particles with an average particle size of 0.75 μm were used instead of KE-P50 in the coating solution TJ1 for forming an antireflection layer, and it was coated on a cellulose acetate film to produce an antireflection film FJ2. The silica particles with an average particle size of 0.75 μm were prepared as follows. (Preparation of silica particles with an average particle size of 0.75 μm) Referring to Examples 3 and 24 of JP-A-2012-214340, silica particles were prepared as follows. A 100 ml flask was charged with methyl ethyl ketone: 25 ml, water: 2 ml, triethylamine: 1.0 ml, and tetramethoxysilane: 2.0 ml, stirred for 3 minutes, allowed to stand for 1 hour, and then the liquid was removed using an evaporator to obtain a white solid. As will be described later, it was confirmed from the observed image measured by SEM that particles with an average particle size of 0.75 μm were obtained.

[0043] (Example 3) Next, an antireflection layer-forming coating solution TJ3 was prepared in the same manner as in Example 1, except that the amount of A-TMMT used in the antireflection layer-forming coating solution TJ1 was changed to 75 parts by mass, and it was applied onto a cellulose acetate film to produce an antireflection film FJ3.

[0044] (Example 4) Next, an antireflection layer-forming coating solution TJ4 was prepared in the same manner as in Example 1, except that the amount of DPHA used in the antireflection layer-forming coating solution TJ1 was changed to 30 parts by mass, and it was applied onto a cellulose acetate film to produce an antireflection film FJ4.

[0045] (Example 5) Next, an antireflection layer-forming coating solution TJ5 was prepared in the same manner as in Example 1, except that the amount of KE-P50 used in the antireflection layer-forming coating solution TJ1 was changed to 75 parts by mass, and it was applied onto a cellulose acetate film to produce an antireflection film FJ5.

[0046] (Example 6) Next, an antireflection layer-forming coating solution TJ6 was prepared in the same manner as in Example 1, except that the amount of KE-P50 used in the antireflection layer-forming coating solution TJ1 was changed to 125 parts by mass, and it was applied onto a cellulose acetate film to produce an antireflection film FJ6.

[0047] (Comparative Example 1) Next, an antireflection layer-forming coating solution TH1 was prepared in the same manner as in Example 1, except that KE-P20 (average particle size: 0.2 μm, manufactured by Nippon Shokubai Co., Ltd.) was used instead of KE-P50 in the antireflection layer-forming coating solution TJ1, and it was applied onto a cellulose acetate film to produce an antireflection film FH1.

[0048] (Comparative Example 2) Next, an antireflection layer-forming coating solution TH2 was prepared in the same manner as in Example 1, except that silica particles with an average particle size of 1.5 μm were used instead of KE-P50 in the antireflection layer-forming coating solution TJ1, and it was applied onto a cellulose acetate film to produce an antireflection film FH2. The silica particles with an average particle size of 1.5 μm were prepared referring to Example 24 of JP-A-2012-214340. As will be described later in detail, the particle size was measured from the observation image by SEM.

[0049] (Comparative Example 3) Next, an anti-reflective layer forming coating solution TH3 was prepared in the same manner as in Example 1, except that the amount of A-TMMT used in the anti-reflective layer forming coating solution TJ1 was changed to 25 parts by mass. This solution was then applied to a cellulose acetate film to produce an anti-reflective film FH3.

[0050] (Comparative Example 4) Next, an anti-reflective layer forming coating solution TH4 was prepared in the same manner as in Example 1, except that the amount of DPHA used in the anti-reflective layer forming coating solution TJ1 was changed to 10 parts by mass. This solution was then applied to a cellulose acetate film to produce an anti-reflective film FH4.

[0051] (Comparative Example 5) Next, an anti-reflective layer forming coating solution TH5 was prepared in the same manner as in Example 1, except that the amount of KE-P50 used in the anti-reflective layer forming coating solution TJ1 was changed to 25 parts by mass. This solution was then applied to a cellulose acetate film to produce an anti-reflective film FH5.

[0052] (Comparative Example 6) Next, an anti-reflective layer forming coating solution TH6 was prepared in the same manner as in Example 1, except that the amount of KE-P50 used in the anti-reflective layer forming coating solution TJ1 was changed to 175 parts by mass. This solution was then applied to a cellulose acetate film to produce an anti-reflective film FH6.

[0053] (Evaluation of anti-reflective film) The various properties of the anti-reflective film were evaluated using the following method. The results are shown in Table 1. Although L-D is also listed in Table 1, for Comparative Example 2, "-" is indicated because L < D.

[0054]

[0055] (Integrated Reflectance) Each of the fabricated anti-reflective films was bonded to a black board via an adhesive (SK Dyne, manufactured by Soken Chemical Co., Ltd.) to eliminate back surface reflection. Using a spectrophotometer V-7200 (manufactured by JASCO Corporation), the integrated reflectance at an incident angle of 5° was measured in the wavelength regions of 1530-1625 nm and 380-780 nm, and the reflectance with the maximum value in each wavelength region was extracted.

[0056] (Evaluation of the anti-reflective layer) (Particle size D, and distance L between the vertices of adjacent protrusions) After carbon deposition was applied to the surface of the film sample, 10 fields of view were observed and photographed using a scanning electron microscope (SEM) at 2000x magnification. Particles were automatically identified from the obtained images (using the difference in brightness between the particle boundary and the area surrounding the particle), and the diameter of the particles was measured at 30 points, with the average value being defined as the particle size D. In addition, the center coordinates of each particle were determined from the obtained images, and the distance between the vertices of adjacent protrusions was measured at 30 points, with the average value being defined as the distance L between the vertices of adjacent protrusions.

[0057] (The ratio of the length A of the part of the particle embedded in the binder to the length B of the part of the particle protruding from the binder) A film sample was cut with a microtome to obtain a cross-section, and carbon was deposited on the cross-section and etched for 10 minutes. Twenty fields of view were observed and photographed using a scanning electron microscope (SEM) at 2000x magnification. From the obtained images, the depth to which the particle embedded in the binder (the distance from the binder surface to the point on the particle at the deepest position toward the binder) was measured at 30 points, and the average value was taken as the length A of the part of the particle embedded in the binder. Also, from the obtained images, the height of the particle protruding from the binder (the distance from the binder surface to the point on the particle at the furthest position in the direction of protrusion) was measured at 30 points, and the average value was taken as the length B of the part of the particle protruding from the binder. From the obtained A and B, the ratio of A to B (A:B) was calculated.

[0058] (S / N ratio) As shown in Figure 3, a sensor (photodiode power sensor S122C, manufactured by THORLABS) was surrounded by a black plate to which the anti-reflective films FJ1 to FJ6 of Examples 1 to 6 and the anti-reflective films FH1 to FH6 of Comparative Examples 1 to 6 were bonded with adhesive. A 1550 nm laser beam (small semiconductor laser module LDM1550, manufactured by THORLABS) was incident, and the S / N ratio was measured. Here, the S / N ratio is the measured amount of light I when incident from the front. ０ And the sum of the measured light quantities when incident at an oblique angle of 5 degrees I ５ The ratio (I ０ / I ５The following evaluations within the specified ranges are listed in Table 1: Good: S / N ratio = 100 or higher Fair: S / N ratio = 75 or higher, less than 100 Marginal: S / N ratio = 50 or higher, less than 75 Poor: S / N ratio = less than 50

[0059] As shown in the table above, the anti-reflective film of the embodiment of the present invention has a lower integrated reflectance in the wavelength band of 1530 to 1625 nm compared to the anti-reflective film of the comparative example, and also shows superiority in the signal-to-noise ratio, clearly indicating a high effect in suppressing stray light.

[0060] The anti-reflective film, stray light suppression film, and light receiving device of the present invention are suitably used for suppressing stray light in light receiving devices and sensors in the infrared region, particularly in the optical communication wavelength band.

[0061] Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention. This application is based on Japanese Patent Application No. 2024-158757 filed on 13 September 2024 and Japanese Patent Application No. 2025-038915 filed on 12 March 2025, the contents of which are incorporated herein by reference.

[0062] 10 Anti-reflective film 1 Substrate 2 Anti-reflective layer 3 Particles 4 Binder L Distance between the vertices of adjacent protrusions A Length of the part of the particle that is embedded in the binder B Length of the part of the particle that is protruding from the binder 5 Sensor 6 Blackboard 7 1550 nm laser light

Claims

1. An anti-reflective film having an integrated reflectance of 1% or less in the wavelength range of 1530 to 1625 nm, and having an anti-reflective layer with an uneven surface structure.

2. The anti-reflective film according to claim 1, wherein the anti-reflective layer comprises particles that form protrusions and a binder.

3. The anti-reflective film according to claim 2, wherein the particle size of the particles forming the protrusions is 400 to 800 nm.

4. The anti-reflective film according to claim 3, wherein the particles forming the protrusions are not in contact with each other.

5. The anti-reflective film according to claim 3, wherein L is the distance between the vertices of adjacent protrusions, and D is the particle size of the particles forming the protrusions, and L and D satisfy the following condition X: Condition X: 20 nm ≤ L - D ≤ 90 nm 6. The anti-reflective film according to claim 2, wherein a portion of the particles forming the protrusions are embedded in the binder, and the ratio of the length A of the portion of the particles embedded in the binder to the length B of the portion of the particles protruding from the binder is A:B = 3 to 6:7 to 4.

7. The anti-reflective film according to claim 1, wherein the integrated reflectance at least some wavelengths between 380 and 780 nm is 1% or more.

8. A stray light suppression film having at least an anti-reflective film according to any one of claims 1 to 7 and a light absorber.

9. A light receiving device having the stray light suppression film described in claim 8 inside the device.

10. An anti-reflective film according to any one of claims 2 to 6, wherein the integrated reflectance in at least one of the wavelength bands of 800 to 950 nm and 1260 to 1360 nm is 1% or less, and the particle size of the particles forming the protrusions is 400 to 680 nm.

11. A stray light suppression film having at least the anti-reflective film described in claim 10 and a light absorber.

12. A light receiving device having the stray light suppression film described in claim 11 inside the device.

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