Low reflection film and camera module inspection cover using the same

Abstract

A low-reflection film with high transmittance over a wide bandwidth and capable of low-cost manufacturing is provided. The low-reflection film comprises: a transparent substrate made of resin, a first anti-reflection layer disposed on the outermost surface of one side of the transparent substrate, and a second anti-reflection layer disposed on the outermost surface of the other side of the transparent substrate. The wavelength of minimum reflectance of the first anti-reflection layer is in the range of 500–550 nm, the wavelength of minimum reflectance of the second anti-reflection layer is in the range of 400–450 nm, the transmittance of light with wavelengths of 450–650 nm is 98% or more, the average transmittance of light with wavelengths of 390–780 nm is 96% or more, and the transmittance of light with wavelengths of 405–425 nm and 770–790 nm are both 50% or more.

Description

Technical Field

[0001] The present invention relates to a low-reflection film capable of being used for inspection of camera modules and a camera module inspection cover using the low-reflection film. Background Technology

[0002] Figure 6 This is a schematic diagram illustrating the inspection method for the camera module.

[0003] The camera module 93 is inspected by illuminating it with light from a D65 light source and detecting the amount of light (current value). If the detected amount of light (current value) is above a predetermined threshold, it is considered a good product. To prevent foreign objects from adhering to the camera module 93 during inspection, such as... Figure 6 As shown, the camera module 93 is mounted on the inspection fixture 94 and further inspected while covered by a cover 90. The cover 90 includes a frame 92 with a window and a glass cover 91 that covers the window of the frame 92. Light from a light source passes through the glass cover 91 and enters the camera module 93, but is reflected at the interface between the glass cover 91 and the air when it enters the glass cover 91 and when it exits the glass cover 91.

[0004] When inspecting the camera module 93, the amount of light incident on the imaging element is predetermined. However, if the amount of light incident on the imaging element is less than the reference value due to reflection on the surface of the cover glass 91, the camera module 93, which should have been deemed a good product, is deemed a defective product. Therefore, in order to suppress the reduction in the amount of light incident on the imaging element, reflection prevention processing is performed on both sides of the cover glass 91.

[0005] Methods for forming the anti-reflection layer include: dry film formation methods such as sputtering or vapor deposition (for example, see Patent Document 1); and wet film formation methods using wet coating (for example, see Patent Document 2).

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent Application Publication No. 2014-224979

[0009] Patent Document 2: Japanese Patent Application Publication No. 2019-159202 Summary of the Invention

[0010] The problem to be solved by the present invention

[0011] For the inspection cover glass of the camera module, high transmittance across the entire bandwidth is required. As a method to achieve high transmittance across the bandwidth, multiple anti-reflection layers are generally stacked. However, even when using either dry or wet deposition methods, the manufacturing cost increases with the increase in deposition process.

[0012] Therefore, the object of the present invention is to provide a low-reflection film with high transmittance over a wide bandwidth and which can be manufactured at low cost.

[0013] Methods for solving problems

[0014] The low-reflection film of the present invention comprises: a transparent substrate made of resin, a first anti-reflection layer disposed on the outermost surface of one side of the transparent substrate, and a second anti-reflection layer disposed on the outermost surface of the other side of the transparent substrate. The wavelength of minimum reflectivity of the first anti-reflection layer is in the range of 500 to 550 nm, the wavelength of minimum reflectivity of the second anti-reflection layer is in the range of 400 to 450 nm, the transmittance of light with wavelengths of 450 to 650 nm is 98% or more, the average transmittance of light with wavelengths of 390 to 780 nm is 96% or more, and the transmittance of light with wavelengths of 405 to 425 nm and 770 to 790 nm are both 50% or more.

[0015] The camera module inspection cover of the present invention has the aforementioned low-reflection film.

[0016] The effects of the invention

[0017] According to the present invention, a low-reflection film with high transmittance over a wide bandwidth and which can be manufactured at low cost can be provided. Attached Figure Description

[0018] [ Figure 1 The diagram shows a cross-sectional view of the layer structure of the low-reflection film according to the first embodiment.

[0019] [ Figure 2 The diagram shows a cross-sectional view of the layer structure of the low-reflection film according to the second embodiment.

[0020] [ Figure 3 The diagram shows a cross-sectional view of the layer structure of the low-reflection film according to the third embodiment.

[0021] [ Figure 4 The reflection spectroscopic spectrum of the anti-reflection layer.

[0022] [ Figure 5 Transmission spectroscopic spectra of the low-reflection films involved in the examples and comparative examples.

[0023] [ Figure 6 This diagram illustrates the inspection method for the camera module.

[0024] Explanation of symbols

[0025] 1. 1a, 1b Transparent substrates

[0026] 2, 2a, 2b Hard coating

[0027] 3a, 3b low-reflection layers

[0028] 10, 20, 30 low-reflection films Detailed Implementation

[0029] (Layer Composition)

[0030] Figure 1 This is a cross-sectional view showing the layer structure of the low-reflection film according to the first embodiment.

[0031] The low-reflection film 10 is formed by bonding a laminated film consisting of a hard coating layer 2a and a low-reflection layer 3a stacked on one side of a transparent substrate 1a, and a laminated film consisting of a hard coating layer 2b and a low-reflection layer 3b stacked on one side of a transparent substrate 1b, via OCA (Optical Clear Adhesive) 4. In the low-reflection film 10, the transparent substrates 1a and 1b are bonded together via OCA 4. The low-reflection layer 3a is an anti-reflection layer disposed on the outermost surface of one side of the transparent substrate 1a or 1b, and the low-reflection layer 3b is an anti-reflection layer disposed on the outermost surface of the other side of the transparent substrate 1a and the other side of the transparent substrate 1b.

[0032] Figure 2 This is a cross-sectional view showing the layer composition of the low-reflection film according to the second embodiment.

[0033] The low-reflection film 20 is formed by laminating a hard coating 2a and a low-reflection layer 3a on one side of a transparent substrate 1, and laminating a hard coating 2b and a low-reflection layer 3b on the other side of the transparent substrate 1. The low-reflection layers 3a and 3b are anti-reflection layers respectively disposed on the outermost surface of one side and the outermost surface of the other side of the transparent substrate 1.

[0034] Figure 3 This is a cross-sectional view showing the layer structure of the low-reflection film according to the third embodiment.

[0035] The low-reflection film 30 is formed by laminating a hard coating 2 and a low-reflection layer 3a on one side of a transparent substrate 1, and laminating a low-reflection layer 3b on the other side of the transparent substrate 1. The low-reflection layers 3a and 3b are anti-reflection layers respectively disposed on the outermost surface of one side and the outermost surface of the other side of the transparent substrate 1.

[0036] In the above configurations, the transparent substrates 1a and 1b can be made of the same material or different materials. The hard coatings 2a and 2b can be made of the same material or different materials. Similarly, the low-reflection layers 3a and 3b can be made of the same material or different materials. It should be noted that the thickness of the low-reflection layers 3a and 3b will be described later.

[0037] (Transparent substrate)

[0038] The transparent substrate is a film that serves as the base for the low-reflection film, formed from a material with excellent visible light transmittance. Materials used to form the transparent substrate include: polyolefins such as polyethylene and polypropylene; polyesters such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate; polyacrylates such as polymethyl methacrylate; polyamides such as nylon 6 and nylon 66; transparent resins such as polyimide, polyarylate, polycarbonate, triacetyl cellulose, polyacrylate, polyvinyl alcohol, polyvinyl chloride, cyclic olefin copolymers, norbornene-containing resins, polyethersulfone, and polysulfone, or inorganic glass. The thickness of the transparent substrate is not particularly limited, but is preferably 10–200 μm. Furthermore, to improve transmittance, the transparent substrate preferably does not contain ultraviolet absorbers.

[0039] To improve adhesion to hard coatings or low-reflection layers, surface modification treatments can be applied to the surface of the transparent substrate. Examples of surface modification treatments include alkali treatment, corona treatment, plasma treatment, sputtering treatment, coating with surfactants, silane coupling agents, etc., and Si evaporation.

[0040] (Hard coating)

[0041] The hard coating layer imparts hardness to the low-reflection film and can be formed by coating a hard coating forming composition containing at least an active energy-curable resin, a photopolymerization initiator, and a solvent, and then curing it. The thickness of the hard coating layer is not particularly limited, but is preferably 2 to 10 μm. If the thickness of the hard coating layer is less than 2 μm, the hardness of the hard coating layer may be insufficient. If the thickness of the hard coating layer exceeds 10 μm, it is not conducive to the thinning of the low-reflection film and is therefore not preferred. However, the film thickness of the hard coating layer can be appropriately set according to the surface hardness and overall thickness required by the optical film. Furthermore, the hard coating layer may also contain metal oxide particles to adjust the refractive index and impart hardness.

[0042] Resin that is cured by active energy radiation is a resin that is polymerized and cured by irradiation with active energy radiation such as ultraviolet light or electron beams. For example, monofunctional, difunctional, or trifunctional (meth)acrylate monomers can be used. It should be noted that in this specification, "(meth)acrylate" is a general term for both acrylate and methacrylate, and "(meth)acryloyl" is a general term for both acryloyl and methacryloyl.

[0043] Examples of monofunctional (meth)acrylate compounds include: 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, glycidyl (meth)acrylate, acryloylmorpholine, N-vinylpyrrolidone, tetrahydrofurfuryl acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isobornyl (meth)acrylate, etc. Isodecyl acrylate, lauryl acrylate, tridecyl acrylate, hexadecyl acrylate, octadecyl acrylate, benzyl acrylate, 2-ethoxyethyl acrylate, 3-methoxybutyl acrylate, ethyl carbitol acrylate, methacrylate, ethylene oxide modified methacrylate, phenoxy acrylate, ethylene oxide modified phenoxy (meth)acrylate, propylene oxide modified phenoxy (Meth)acrylate, nonylphenol (meth)acrylate, ethylene oxide modified nonylphenol (meth)acrylate, propylene oxide modified nonylphenol (meth)acrylate, methoxydiethylene glycol (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, methoxypropylene glycol (meth)acrylate, 2-(meth)acryloyloxyethyl-2-hydroxypropyl phthalate, 2-hydroxy-3-phenoxypropyl phthalate, hydrogenated 2-(meth)acryloyloxyethyl phthalate, hydrogenated phthalic acid 2-(meth)acryloyloxypropyl ester, 2-(meth)acryloyloxypropyl hexahydrophthalic acid, 2-(meth)acryloyloxypropyl tetrahydrophthalic acid, dimethylaminoethyl (meth)acrylate, trifluoroethyl (meth)acrylate, tetrafluoropropyl (meth)acrylate, hexafluoropropyl (meth)acrylate, octafluoropropyl (meth)acrylate, 2-adamantane, and adamantane derivative mono(meth)acrylates such as adamantane alkyl acrylates having a monovalent mono(meth)acrylate derived from adamantane diol.

[0044] Examples of difunctional (meth)acrylate compounds include: ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, butanediol di(meth)acrylate, hexanediol di(meth)acrylate, nonanediol di(meth)acrylate, ethoxylated hexanediol di(meth)acrylate, propoxylated hexanediol di(meth)acrylate, diethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, ethoxylated neopentyl glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, and hydroxypentyl acid neopentyl glycol di(meth)acrylate, etc.

[0045] Examples of trifunctional or higher (meth)acrylate compounds include: trimethylolpropane tri(meth)acrylate, ethoxylated trimethylolpropane tri(meth)acrylate, propoxylated trimethylolpropane tri(meth)acrylate, tris(2-hydroxyethyl)isocyanurate tri(meth)acrylate, glycerol tri(meth)acrylate, etc.; and trifunctional (meth)acrylates such as pentaerythritol tri(meth)acrylate, dipentaerythritol tri(meth)acrylate, and di(trimethylolpropane)acrylate. Acrylates; polyfunctional (meth)acrylates such as pentaerythritol tetra(meth)acrylate, di(trimethylolpropane)tetra(meth)acrylate, dipentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, di(trimethylolpropane) penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, and di(trimethylolpropane) hexa(meth)acrylate; and polyfunctional (meth)acrylates formed by substituting a portion of these (meth)acrylates with alkyl groups or ε-caprolactones.

[0046] Alternatively, urethane (meth)acrylates can also be used as active energy ray-curable resins. Examples of urethane (meth)acrylates include those obtained by reacting a product obtained by reacting an isocyanate monomer or prepolymer with a polyester polyol with a (meth)acrylate monomer having hydroxyl groups.

[0047] Examples of urethane (meth)acrylates include: pentaerythritol triacrylate hexamethylene diisocyanate urethane prepolymer, dipentaerythritol pentaacrylate hexamethylene diisocyanate urethane prepolymer, pentaerythritol triacrylate toluene diisocyanate urethane prepolymer, dipentaerythritol pentaacrylate toluene diisocyanate urethane prepolymer, pentaerythritol triacrylate isophorone diisocyanate urethane prepolymer, and dipentaerythritol pentamethacrylate isophorone diisocyanate urethane prepolymer.

[0048] The aforementioned active energy ray-curable resin can be used in one or in combination of two or more. Furthermore, the aforementioned active energy ray-curable resin in the hard coating forming composition can be a monomer or a partially polymerized oligomer.

[0049] Photopolymerization initiators used in the hard coating forming composition can include, for example, 2,2-ethoxyacetophenone, 1-hydroxycyclohexylphenyl ketone, bibenzoyl, benzoin, benzoin methyl ether, benzoin ethyl ether, p-chlorobenzophenone, p-methoxybenzophenone, michalcone, acetophenone, 2-chlorothiaxanone, etc. One of these can be used alone or in combination of two or more.

[0050] In addition, solvents used in the hard coating forming composition include: ethers such as dibutyl ether, dimethoxymethane, dimethoxyethane, diethoxyethane, propylene oxide, 1,4-dioxane, 1,3-dioxolane, 1,3,5-trioxane, tetrahydrofuran, anisole, and phenethyl ether; ketones such as acetone, methyl ethyl ketone, diethyl ketone, dipropyl ketone, diisobutyl ketone, methyl isobutyl ketone, cyclopentanone, cyclohexanone, and methylcyclohexanone; esters such as ethyl formate, propyl formate, n-pentyl formate, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, n-pentyl acetate, and γ-butyrolactone; and cellosolvents such as methyl cellosolvent, cellosolvent, butyl cellosolvent, and cellosolvent acetate. These can be used alone or in combination of two or more.

[0051] In addition, the composition for forming a hard coating may also contain metal oxide particles in order to adjust the refractive index and impart hardness. Examples of metal oxide particles include: zirconium oxide, titanium oxide, niobium oxide, antimony trioxide, antimony pentoxide, tin oxide, indium oxide, indium tin oxide, zinc oxide, etc.

[0052] In addition, the composition for forming a hard coating may also contain any one of the following: silicon oxides that impart hydrophobicity and / or oleophobicity and improve antifouling properties; fluorinated silane compounds; fluoroalkylsilazanes; fluoroalkylsilanes; fluorinated silicon compounds; and silane coupling agents containing perfluoropolyether groups.

[0053] As other additives, leveling agents, defoamers, antioxidants, light stabilizers, photosensitizers, conductive materials, etc., can also be added to the composition for forming hard coatings.

[0054] (Low-reflective layer)

[0055] A low-reflection layer is an optical functional layer in which light reflected from the surface of a low-reflection layer is canceled out by interference with light reflected from the interface between the low-reflection layer and its inner layers, thereby reducing surface reflection. A low-reflection layer can be formed by coating a low-reflection layer forming composition containing at least an active energy-curable resin, a photopolymerization initiator, and a solvent, and then curing it. To adjust the refractive index, low-refractive-index microparticles can be added to the low-reflection layer forming composition. The refractive index of the low-reflection layer is preferably in the range of 1.31 or less. The lower the refractive index of the low-reflection layer, the higher the transmittance; therefore, it is preferable that the refractive index of the low-reflection layer be as low as possible.

[0056] There are no particular limitations on the active energy ray curable resin, photopolymerization initiator, and solvent used in the formation of the low-reflection layer; compounds exemplified as materials for hard coatings can be used.

[0057] As low-refractive-index microparticles, LiF, MgF, 3NaF·AlF, or AlF (all with a refractive index of 1.4) can be preferably used; or Na3AlF6 (cryolite, refractive index 1.33) microparticles; or silica microparticles with internal pores. Silica microparticles with internal pores allow the pore portion to have a refractive index similar to air (approximately 1), thus facilitating the reduction of the refractive index of the low-reflection layer 3. Specifically, porous silica particles can be shell-structured silica particles.

[0058] It should be noted that, depending on the requirements, various additives such as defoamers, leveling agents, antioxidants, ultraviolet absorbers, light stabilizers, polymerization inhibitors, and photosensitizers may also be added to the composition for forming the low-reflection layer.

[0059] In the low-reflection film of the present invention, the wavelength at which the reflectivity of either low-reflection layer 3a or 3b is minimized is in the range of 500 to 550 nm. Furthermore, the wavelength at which the reflectivity of the other low-reflection layer 3a or 3b is minimized is in the range of 400 to 450 nm. By making the reflective characteristics of low-reflection layers 3a and 3b different, the transmittance of light with wavelengths of 450 to 650 nm can be 98% or more, the average transmittance of light with wavelengths of 390 to 780 nm can be 96% or more, and the transmittance of light with wavelengths of 405 to 425 nm and 770 to 790 nm can both be 50% or more. The reasons for this will be explained below.

[0060] Figure 4 It is the reflection spectroscopic spectrum of the anti-reflection layer.

[0061] In the case of setting a single-layer low-reflection layer on the optical film, for example... Figure 4 As shown by the solid line, the reflectance spectrum of the optical film becomes a curve with a minimum value at a specific wavelength. That is, the reflectance of the optical film with a single anti-reflection layer is minimum at a specific wavelength in the visible light region (hereinafter, the wavelength where the reflectance is minimum is called the "bottom wavelength"), and increases with distance from the bottom wavelength. Therefore, in optical films with a single low-reflectance layer, it is difficult to widely obtain wavelength regions with low reflectance (i.e., wavelength regions with high transmittance) in the visible light region.

[0062] Conventional methods for reducing reflectivity over a wide bandwidth include, for example, multilayer films consisting of multiple layers with different refractive indices, such as a high-refractive-index layer, a medium-refractive-index layer, and a low-refractive-index layer, sequentially stacked from the transparent substrate side. However, increasing the number of layers constituting the anti-reflection layer leads to increased manufacturing costs.

[0063] Therefore, in this invention, by employing a layer structure with low-reflection layers (anti-reflection layers) on both sides, and making the reflection characteristics of the low-reflection layers different—with the bottom wavelength of one low-reflection layer set in the range of 500–550 nm and the bottom wavelength of the other low-reflection layer set in the range of 400–450 nm—a reduction in reflectivity over a wide bandwidth is achieved. The reflection spectroscopic spectrum varies depending on the thickness of the anti-reflection layer. For example, when the thickness of the anti-reflection layer decreases, the bottom wavelength shifts towards the lower wavelength side as shown by the dashed line; when the thickness of the anti-reflection layer increases, the bottom wavelength shifts towards the longer wavelength side as shown by the double-dotted line. With two low-reflection layers having different bottom wavelengths, the reflection of light in wavelength regions that cannot be suppressed by one low-reflection layer can be suppressed by the other low-reflection layer. That is, the reflection spectroscopic spectrum of the entire low-reflection film is approximately equivalent to the spectrum formed by synthesizing the reflection spectroscopic spectrum of the two low-reflection layers, and reflectivity can be suppressed throughout the entire bandwidth. By making the entire film low-reflective, transmittance can be improved. In addition, since two low-reflection layers can be stacked using a wet coating process, the manufacturing cost of the low-reflection film can be reduced compared to methods that use a wet coating process to stack three or more anti-reflection films, or methods that use a dry process to stack two or more anti-reflection films.

[0064] It should be noted that the average transmittance of light in the 390–780 nm range is preferably 98.4% or higher, more preferably 98.6% or higher. The transmittance of light in the 405–425 nm range is preferably 96.9% or higher, more preferably 97.1% or higher. Furthermore, the transmittance of light in the 770–790 nm range is preferably 97.0% or higher, more preferably 97.1% or higher.

[0065] In the above embodiments, a protective layer for protecting the low-reflection layer can be adhered to the anti-reflection layer on one side and the other side of the low-reflection film. The composition of the protective layer is not particularly limited; for example, an adhesive layer for adhering to the low-reflection layer can be laminated on one side of the resin film.

[0066] Furthermore, the low-reflection films described in the above embodiments can be used as inspection covers for camera modules. For example, as inspection covers for camera modules... Figure 6 As shown, an example can be provided: a hollow, box-shaped frame having a window on one side and an open, hollow box-like frame on the side opposite to the window; and a low-reflection film covering the window of the frame. When inspecting a camera module, a cover is used to cover the camera module to prevent dust adhesion. Light from a D65 light source passes through the low-reflection film covering the window of the cover and illuminates the camera module. As described above, the low-reflection film of the present invention suppresses reflection at the air interface and has high transmittance over a wide bandwidth, thus reducing the attenuation of the amount of light illuminating the camera module during inspection. Therefore, by using an inspection cover employing the low-reflection film of the present invention, high-precision inspection of the camera module can be performed.

[0067] Example

[0068] The following describes specific embodiments of the present invention.

[0069] As an example and comparative example, a device with... Figure 1 The low-reflection film is composed of the layers described. A 40 μm thick TAC film was used as the transparent substrate. A hard coating with a thickness of 5 μm and a refractive index of 1.525 was formed by coating a hard coating composition containing a UV-curable resin, a photopolymerization initiator, and a solvent onto the transparent substrate, drying it, and then polymerizing and curing the coating using UV irradiation. Next, a low-reflection layer with a refractive index of 1.295 was formed by coating a low-reflection layer coating liquid containing a UV-curable resin, low-refractive-index microparticles, a photopolymerization initiator, and a solvent onto the hard coating, drying it, and then polymerizing and curing the coating using UV irradiation. The thickness (physical film thickness) of the cured low-reflection layer was determined by the composition of the hard coating. Figure 1The low-reflection films described are designed such that the bottom wavelengths of the two reflective layers (low-reflection layers 1 and 2) are the values ​​listed in Table 1. Here, when the refractive index of the low-reflection layer is set to n and the bottom wavelength is set to λ, the physical film thickness d of the low-reflection layer is a value obtained by the formula nd = λ / 4. Specifically, when the refractive index of the low-reflection layer is 1.295, the physical film thicknesses at bottom wavelengths of 400 nm, 450 nm, 500 nm, and 550 nm are 77.2 nm, 86.9 nm, 96.5 nm, and 106.2 nm, respectively. The two laminated TAC films obtained are bonded together via OCA to obtain the low-reflection films involved in Examples 1, 2, and Comparative Examples 1 to 4.

[0070] The transmission spectrophotometer (Hitachi High-Technologies Corporation, U-4100) was used to measure the transmission spectrophotometer and the average transmittance of light from 390 to 780 nm of the low-reflection films involved in each example and comparative example. Figure 5 The transmission spectroscopic spectra of the low-reflection films involved in each embodiment and comparative example are shown.

[0071] Based on the measured transmission spectra, the minimum transmittance of light in the wavelength range of 405–425 nm and the minimum transmittance of light in the wavelength range of 770–790 nm with a transmittance of 98% or higher are calculated and evaluated according to the following criteria.

[0072] <Wavelength range with transmittance of 98% or higher>

[0073] ○: Includes the entire wavelength region from 450 to 650 nm.

[0074] ×: Does not include some or all of the wavelengths in the 450–650 nm range.

[0075] <Average transmittance of 390–780 nm>

[0076] ○: 96% or more

[0077] ×: Less than 96%

[0078] Minimum transmittance of light in the 405–425 nm range and minimum transmittance of light in the 770–790 nm range.

[0079] ○:More than 50%

[0080] ×: Less than 50%

[0081] Table 1 shows the bottom wavelength (wavelength at which reflectivity is minimum), wavelength range with transmittance of 98% or more, average transmittance of 390–780 nm, minimum transmittance of light of 405–425 nm, and minimum transmittance of light of 770–790 nm for each embodiment and comparative example of the low reflectance layer.

[0082] [Table 1]

[0083]

[0084] In Examples 1 and 2, the transmittance of light with wavelengths of 450–650 nm is 98% or more at any wavelength, the average transmittance of light with wavelengths of 390–780 nm is 96% or more, and the minimum transmittance of light with wavelengths of 405–425 nm and 770–790 nm is 50% or more. Therefore, a low-reflection film with high transmittance throughout the entire broadband band is obtained.

[0085] In contrast, the films involved in Comparative Examples 1-4 did not simultaneously satisfy the condition that the bottom wavelength of one low-reflection layer was in the range of 500-550 nm and the bottom wavelength of the other low-reflection layer was in the range of 400-450 nm. Therefore, the wavelength range in which the transmittance was 98% or higher was narrower than that of Examples 1 and 2. In other words, the minimum transmittance of the films involved in Comparative Examples 1-4 in the wavelength region of 450-650 nm could not reach 98% or higher, and were inferior to Examples 1 and 2 in the transmittance direction.

[0086] Industrial applicability

[0087] This invention can be used for covers and the like when inspecting camera modules.

Claims

1. A low-reflection film, comprising: Transparent substrate made of resin A first anti-reflection layer disposed on the outermost surface of one side of the transparent substrate, and A second anti-reflection layer is disposed on the outermost surface of the other side of the transparent substrate. The wavelength with the lowest reflectivity of the first anti-reflection layer is in the range of 500–550 nm. The wavelength with the lowest reflectivity of the second anti-reflection layer is in the range of 400–450 nm. The transmittance of light with wavelengths of 450–650 nm is over 98%. The average transmittance of light with wavelengths of 390–780 nm is over 96%. The transmittance of light with wavelengths of 405–425 nm and 770–790 nm is both above 50%. The refractive index n of the first anti-reflection layer and the second anti-reflection layer is in the range of 1.31 or less. When the refractive index of the first anti-reflection layer and the second anti-reflection layer is set to n, and the wavelength with the minimum reflectivity is set to λ, the physical film thickness d satisfies the condition nd = λ / 4.

2. The low-reflection film according to claim 1, further comprising a protective layer adhered to the surface of the first anti-reflection layer and the surface of the second anti-reflection layer.

3. A camera module inspection cover comprising the low-reflection film as described in claim 1.

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