Composition for light absorbing layer, optical filter, and method for producing composition for light absorbing layer

Abstract

To provide an optical filter with a light absorbing layer which has a prescribed thickness or less (e.g., 120 μm or less, or 80 μm or less), exhibits a desired transmittance property, and is advantageous in simplifying a manufacturing process of the optical filter, and to provide a light absorbing composition suitable for forming such light absorbing layer.SOLUTION: An optical filter (1a) provided herein has a thickness of 120 μm or less and satisfies conditions (i), (ii), (iii), and (iv) as follows: (i) an average transmittance is 74% or greater in a wavelength range of 450-600 nm; (ii) the maximum transmittance is 1% or less in a wavelength range of 750-1,080 nm; (iii) an infrared-side cutoff wavelength, representing a wavelength corresponding to a spectral transmittance of 50%, in a wavelength range of 550-700 nm is in a range of 600-680 nm; and (iv) an ultraviolet-side cutoff wavelength, representing a wavelength corresponding to a spectral transmittance of 50%, in a wavelength range of 350-500 nm is in a range of 350-420 nm.SELECTED DRAWING: Figure 1A

Description

[Technical field]

[0001] The present invention relates to optical filters and light absorbing compositions. [Background technology]

[0002] In an imaging device using a solid-state imaging element such as a CCD (Charge Coupled Device) or a CMOS (Complementary Metal Oxide Semiconductor), various optical filters are arranged in front of the solid-state imaging element in order to obtain an image with good color reproducibility. In general, a solid-state imaging element has a spectral sensitivity in a wide wavelength range from the ultraviolet region to the infrared region. Meanwhile, human visual sensitivity exists only in the visible light region. For this reason, a technique is known in which an optical filter that blocks infrared or ultraviolet light is arranged in front of the solid-state imaging element in order to bring the spectral sensitivity of the solid-state imaging element in the imaging device closer to the human visual sensitivity.

[0003] Conventionally, such optical filters generally use light reflection by a dielectric multilayer film to block infrared or ultraviolet rays. Meanwhile, in recent years, optical filters with a light absorbing layer containing a light absorbent have been attracting attention. Since the transmittance characteristics of optical filters with a light absorbing layer are not easily affected by the angle of incidence, good images with little change in color can be obtained even when light is obliquely incident on the optical filter in an imaging device. In addition, optical filters with a film containing a light absorbent are advantageous in terms of miniaturizing and thinning the imaging device.

[0004] For example, Patent Document 1 describes an optical filter having a UV-IR absorbing layer capable of absorbing infrared and ultraviolet rays, and having a predetermined transmittance characteristic. The UV-IR absorbing layer contains a UV-IR absorber formed of, for example, phosphonic acid and copper ions.

[0005] Furthermore, Patent Document 2 describes an infrared cut filter that includes an organic dye-containing layer that contains a specific organic dye, and a copper phosphonate-containing layer that contains copper phosphonate fine particles.

[0006] Patent Document 3 describes a method for producing a resin having copper salt particles dispersed therein. This production method includes steps A, B, and C. Step A is a step of washing a mixture containing near-infrared absorbing copper salt particles and a dispersant with a solvent, then precipitating the copper salt particles and removing the supernatant to obtain copper salt particles. Step B is a step of dispersing the copper salt particles obtained in step A in a dispersion medium to obtain a dispersion liquid. Step C is a step of mixing the dispersion liquid with a resin to obtain a resin having copper salt particles dispersed therein. At least a part of the near-infrared absorbing copper salt particles is a predetermined alkylphosphonic acid copper salt.

[0007] Patent Document 4 describes a method for producing a dispersion liquid containing a near-infrared absorbent. In this production method, a phosphonic acid compound, a specific phosphoric acid ester compound, and a copper salt are mixed in a solvent to obtain a reaction mixture containing a near-infrared absorbent. The solid content in the reaction mixture is allowed to settle, and the supernatant is removed. A purified near-infrared absorbent is obtained by drying the solid content. The purified near-infrared absorbent is dispersed in a dispersion medium.

[0008] Patent Document 5 describes a phthalocyanine compound that has high visible light transmittance and high near-infrared light blocking efficiency in the wavelength range of 850 to 950 nm.

[0009] Patent Document 6 describes an infrared absorbing material containing a specific copper phosphonate compound and a resin. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Patent No. 6232161 [Patent Document 2] Patent No. 6281023 [Patent Document 3] Patent No. 5738031 [Patent Document 4] Patent No. 5738014 [Patent Document 5] JP 2007-056105 A [Patent Document 6] International Publication No. 2009 / 123016 Summary of the Invention [Problem to be solved by the invention]

[0011] According to the examples of Patent Document 1, the thickness of the UV-IR absorbing layer is generally in the range of 130 to 220 μm. Patent Document 1 also describes an optical filter having a UV-IR absorbing layer with a thickness of 76 μm, but this optical filter has an infrared absorbing glass substrate, and a predetermined transmittance characteristic is obtained by combining the UV-IR absorbing layer and the infrared absorbing glass substrate.

[0012] In the technique described in Patent Document 2, the organic dye-containing layer and the copper phosphonate-containing layer must be formed separately, which tends to complicate the manufacturing process of the infrared cut filter.

[0013] It is unclear what kind of transmittance characteristics the near-infrared absorbing layer has when it is formed using the copper salt fine particle dispersed resin described in Patent Document 3. In addition, it is unclear what kind of transmittance characteristics the near-infrared absorbing layer has when it is formed using a dispersion liquid containing the near-infrared absorbent described in Patent Document 4.

[0014] The phthalocyanine compound described in Patent Document 5 has high visible light transmittance and high near-infrared light cutting efficiency in the wavelength range of 850 to 950 nm. On the other hand, when a near-infrared absorbing layer is formed using this phthalocyanine compound, it is unclear what kind of transmittance characteristics the near-infrared absorbing layer will have.

[0015] According to Patent Document 6, the spectral transmittance of a laminated glass obtained by sandwiching a 0.76 mm thick sheet formed of an infrared absorbing material containing a specific copper phosphonate compound and a resin between two glass slides is measured. The maximum transmittance of this laminated glass in the wavelength range of 750 nm to 1080 nm is relatively high.

[0016] Therefore, the present invention provides an optical filter having a light absorbing layer that has a desired transmittance characteristic even though it has a thickness of a predetermined thickness or less (for example, 120 μm or less or 80 μm or less) and is advantageous for simplifying the manufacturing process of the optical filter. The present invention also provides a light absorbing composition suitable for forming the light absorbing layer of such an optical filter. [Means for solving the problem]

[0017] The present invention relates to The present invention provides an optical filter having a light absorbing layer having a thickness of 120 μm or less and satisfying the following conditions (i), (ii), (iii), and (iv): (i) The average transmittance in the wavelength range of 450 nm to 600 nm is 74% or more. (ii) The maximum transmittance in the wavelength range of 750 nm to 1080 nm is 1% or less. (iii) The infrared cutoff wavelength, which is a wavelength showing a spectral transmittance of 50% in the wavelength range of 550 nm to 700 nm, is in the range of 600 nm to 680 nm. (iv) The ultraviolet cutoff wavelength, which is a wavelength showing a spectral transmittance of 50% in the wavelength range of 350 nm to 500 nm, is in the range of 350 nm to 420 nm.

[0018] The present invention also provides a method for producing a semiconductor device comprising the steps of: The present invention provides an optical filter having a light absorbing layer having a thickness of 80 μm or less and satisfying the following conditions (I), (II), (III), and (IV): (I) The average transmittance in the wavelength range of 450 nm to 600 nm is 74% or more. (II) The maximum transmittance in the wavelength range of 750 nm to 1080 nm is 5% or less. (III) The infrared cutoff wavelength, which is a wavelength showing a spectral transmittance of 50% in the wavelength range of 550 nm to 700 nm, is in the range of 600 nm to 680 nm. (IV) The ultraviolet cutoff wavelength, which is a wavelength showing a spectral transmittance of 50% in the wavelength range of 350 nm to 500 nm, is in the range of 350 nm to 420 nm.

[0019] Furthermore, the present invention provides a method for producing a The method includes the steps of: The concentration of the acid by-product in the production of the copper phosphonate is 1.0% by mass or less. A light absorbing composition is provided. Effect of the Invention

[0020] The light absorbing layer in the optical filter has a thickness equal to or less than a predetermined thickness but has a desired spectral transmittance, which is advantageous in simplifying the manufacturing process of the optical filter. In addition, the light absorbing composition is suitable for forming the light absorbing layer of the optical filter. [Brief description of the drawings]

[0021] [Figure 1A] FIG. 1A is a cross-sectional view of an optical filter according to an example of an embodiment of the present invention. [Figure 1B] FIG. 1B is a cross-sectional view of an optical filter according to another embodiment of the present invention. [Diagram 2] FIG. 2 is a cross-sectional view showing an imaging optical system including an optical filter according to an example of the embodiment of the present invention. [Diagram 3] FIG. 3 shows the transmittance spectrum of the optical filter according to the first embodiment. [Figure 4] FIG. 4 shows the transmittance spectrum of the optical filter according to the second embodiment. [Diagram 5] FIG. 5 shows the transmittance spectrum of the optical filter according to the third embodiment. [Figure 6] FIG. 6 shows the transmittance spectrum of the optical filter according to the fourth embodiment. [Figure 7]FIG. 7 shows the transmittance spectrum of the optical filter according to the fifth embodiment. [Figure 8] FIG. 8 shows the transmittance spectrum of the optical filter according to the sixth embodiment. [Figure 9] FIG. 9 shows the transmittance spectrum of the optical filter according to the seventh embodiment. [Figure 10] FIG. 10 shows the transmittance spectrum of the optical filter according to the eighth embodiment. [Figure 11] FIG. 11 shows the transmittance spectrum of the optical filter according to the ninth embodiment. [Figure 12] FIG. 12 shows the transmittance spectrum of the optical filter according to Comparative Example 1. As shown in FIG. [Figure 13] FIG. 13 shows the transmittance spectrum of the optical filter according to Comparative Example 2. As shown in FIG. [Figure 14] FIG. 14 shows the transmittance spectrum of the optical filter according to Comparative Example 3. As shown in FIG. [Figure 15] FIG. 15 shows the transmittance spectrum of the optical filter according to Comparative Example 4. As shown in FIG. [Figure 16] FIG. 16 shows the transmittance spectrum of the optical filter according to Comparative Example 5. As shown in FIG. [Figure 17] FIG. 17 shows the transmittance spectrum of a transparent glass substrate (manufactured by SCHOTT, product name: D263 T eco). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] Hereinafter, embodiments of the present invention will be described. Note that the following description is merely an example of the present invention, and the present invention is not limited to these.

[0023] 1A, the optical filter 1a includes a light absorbing layer 10. The light absorbing layer 10 has a thickness of, for example, 120 μm or less. In addition, the light absorbing layer 10 satisfies, for example, the following conditions (i), (ii), (iii), and (iv). (i) The average transmittance in the wavelength range of 450 nm to 600 nm is 74% or more. (ii) The maximum transmittance in the wavelength range of 750 nm to 1080 nm is 1% or less. (iii) The infrared cutoff wavelength, which is a wavelength showing a spectral transmittance of 50% in the wavelength range of 550 nm to 700 nm, is in the range of 600 nm to 680 nm. (iv) The ultraviolet cutoff wavelength, which is a wavelength showing a spectral transmittance of 50% in the wavelength range of 350 nm to 500 nm, is in the range of 350 nm to 420 nm.

[0024] When the light absorbing layer 10 satisfies the condition (i), the optical filter 1a is likely to have a sufficiently high transmittance in the visible light region, so that when the optical filter 1a is used together with a solid-state imaging device, visible light is likely to be incident on the solid-state imaging device with sufficient brightness.

[0025] By the light absorbing layer 10 satisfying the condition (ii), the optical filter 1a is likely to have a sufficiently low transmittance in the wavelength range of 750 nm to 1080 nm even if the optical filter 1a does not include a light absorbing layer other than the light absorbing layer 10 and a near-infrared reflective layer. Therefore, the optical filter 1a is likely to have a good light blocking property in the near-infrared region, and when the optical filter 1a is used together with a solid-state imaging element, it can cut light in the near-infrared region that cannot be detected by human vision. As a result, the characteristics of the optical filter 1a are likely to match the visual sensitivity of humans.

[0026] When the light absorbing layer 10 satisfies the conditions (iii) and (iv), the characteristics of the optical filter 1a tend to match the visual sensitivity of the human eye.

[0027] When the light absorbing layer 10 satisfies the conditions (i) to (iv), the lower limit of the thickness of the light absorbing layer 10 is not particularly limited, but is, for example, 70 μm or more.

[0028] The light absorbing layer 10 may have a thickness of 80 μm or less. In this case, the light absorbing layer 10 satisfies, for example, the following conditions (I), (II), (III), and (IV). (I) The average transmittance in the wavelength range of 450 nm to 600 nm is 74% or more. (II) The maximum transmittance in the wavelength range of 750 nm to 1080 nm is 5% or less. (III) The infrared cutoff wavelength, which is a wavelength showing a spectral transmittance of 50% in the wavelength range of 550 nm to 700 nm, is in the range of 600 nm to 680 nm. (IV) The ultraviolet cutoff wavelength, which is a wavelength showing a spectral transmittance of 50% in the wavelength range of 350 nm to 500 nm, is in the range of 350 nm to 420 nm.

[0029] When the light absorbing layer 10 satisfies (II), the optical filter 1a tends to have sufficient light shielding properties in the near infrared region.

[0030] When the light absorbing layer 10 satisfies the conditions (I) to (IV), the lower limit of the thickness of the light absorbing layer 10 is not particularly limited, but is, for example, 40 μm or more.

[0031] The transmittance of the light absorbing layer 10 at a wavelength of 700 nm is, for example, 15% or less. In this case, the optical filter 1a is likely to have high light shielding properties in the near-infrared region. As a result, the characteristics of the optical filter 1a are more likely to match the visual sensitivity of humans. The transmittance of the light absorbing layer 10 at a wavelength of 700 nm is preferably 12% or less, more preferably 10% or less, and even more preferably 5% or less.

[0032] The light absorbing layer 10 contains, for example, copper phosphonate and an organic dye. The organic dye typically has a maximum absorption wavelength of 720 nm to 780 nm. The maximum absorption wavelength of the organic dye can be determined, for example, from the absorption spectrum of a solution of the organic dye in methanol as a solvent.

[0033] The light absorption by copper phosphonate is based on the transition between d orbitals of the copper complex, and the transition of what is originally a forbidden transition occurs due to the disturbance of symmetry. Therefore, the absorbance due to the light absorption by copper phosphonate is low. Therefore, in order to improve the light absorption performance of the optical filter by the light absorption of copper phosphonate, it is necessary to increase the content of copper phosphonate in the light absorption layer. However, there is a limit to the amount of copper phosphonate that can be contained in a specific volume of resin, and in order to improve the light absorption performance of the optical filter, it is necessary to increase the thickness of the light absorption layer. On the other hand, there is a strong demand for thinner optical filters. Therefore, the present inventors attempted to prepare a single light absorption layer containing an organic dye that can exhibit high absorbance although it has a narrow absorption wavelength range, and copper phosphonate that does not easily exhibit high absorbance but has a wide absorption wavelength range. However, it was found that if copper phosphonate and an organic dye coexist in a single light absorption layer, the organic dye may not be able to fully exhibit its inherent light absorption performance. The present inventors thought that the organic dye may not be able to fully exhibit its inherent light absorption performance due to the influence of by-products in the production of copper phosphonate. Therefore, the present inventors, after much trial and error, developed a method for appropriately removing by-products in the production of copper phosphonate in a light-absorbing composition for forming a light-absorbing layer. Even if the light-absorbing layer 10 contains copper phosphonate and an organic dye, the organic dye can exhibit appropriate light-absorbing performance and has desired transmittance characteristics.

[0034] When the light absorbing layer 10 contains copper phosphonate and an organic dye, for example, the maximum absorption wavelength of the light absorbing layer 10 at wavelengths of 650 nm to 1000 nm is 700 nm to 900 nm.

[0035] The copper phosphonate is formed by phosphonic acid and copper ions. The phosphonic acid is not particularly limited. The phosphonic acid is, for example, a phosphonic acid having an alkyl group or an aryl group. The alkyl group may be a linear alkyl group or a branched alkyl group. The number of carbon atoms in the alkyl group is, for example, 2 to 10. The phosphonic acid is, for example, at least one selected from the group consisting of ethylphosphonic acid, propylphosphonic acid, butylphosphonic acid, pentylphosphonic acid, hexylphosphonic acid, heptylphosphonic acid, and octylphosphonic acid. To form the copper phosphonate, one type of phosphonic acid may be used, or multiple types of phosphonic acids may be used.

[0036] The organic dye is not particularly limited as long as its absorption maximum wavelength is 720 nm to 780 nm. The organic dye is, for example, at least one selected from the group consisting of phthalocyanine compounds, cyanine compounds, squarylium compounds, diimmonium compounds, naphthalocyanine compounds, and croconium compounds. The light absorbing layer 10 may contain one type of organic dye or multiple types of organic dyes.

[0037] The light absorbing layer 10 further contains, for example, a resin. In the light absorbing layer 10, the copper phosphonate and the organic dye are contained, for example, by a resin. The resin is not limited to a specific resin as long as it can contain, for example, copper phosphonate and the organic dye and has the desired durability. The resin is, for example, at least one selected from the group consisting of polyvinyl acetal resin, (meth)acrylic resin, polyester resin, polyolefin resin, polycarbonate resin, polyurethane resin, epoxy resin, and norbornene resin. Among them, polyvinyl acetal resin such as polyvinyl butyral resin can be preferably used as the resin contained in the light absorbing layer 10.

[0038] 1A, the optical filter 1a may further include a transparent substrate 20. The light absorbing layer 10 covers, for example, one of the main surfaces of the transparent substrate 20. The light absorbing layer 10 may be in contact with, for example, one of the main surfaces of the transparent substrate 20. The transparent substrate 20 has a transmittance of, for example, 80% or more in a wavelength range of 400 nm to 700 nm, desirably a transmittance of 85% or more, and more desirably a transmittance of 90% or more.

[0039] The material of the transparent substrate 20 is not limited to a specific material, but may be, for example, a certain glass or resin. When the material of the transparent substrate 20 is glass, the transparent substrate 20 is made of, for example, silicate glass such as soda-lime glass and borosilicate glass. The material of the transparent substrate 20 may be infrared-cutting glass. The infrared-cutting glass may be, for example, phosphate glass or fluorophosphate glass containing CuO.

[0040] When the material of the transparent substrate 20 is a resin, the resin is, for example, a cyclic olefin resin such as a norbornene resin, a polyarylate resin, an acrylic resin, a modified acrylic resin, a polyimide resin, a polyetherimide resin, a polysulfone resin, a polyethersulfone resin, a polycarbonate resin, or a silicone resin.

[0041] The light absorbing layer 10 can be formed, for example, by applying a composition for a light absorbing layer and curing the coating film formed. The composition for a light absorbing layer can be prepared by mixing a light absorbing composition in which light absorbing copper phosphonate is dispersed, a liquid containing an organic dye, and a resin. The liquid containing an organic dye can be prepared, for example, by adding the organic dye to a predetermined solvent such as cyclopentanone and stirring for a predetermined time. The resin is a resin exemplified as the resin contained in the light absorbing layer 10. The resin may be provided in a state in which it is dissolved in a predetermined solvent such as cyclopentanone in advance.

[0042] The light-absorbing composition contains, for example, the above-mentioned copper phosphonate in a dispersed state and an organic solvent. The copper phosphonate can be, for example, a copper phosphonate compound (copper phosphonate salt) produced by the reaction of the above-mentioned phosphonic acid with copper ions. The copper ions are provided by, for example, a copper salt. In this case, an acid derived from the copper salt is produced as a by-product with the production of the copper phosphonate. In the light-absorbing composition, the concentration of the acid, which is a by-product in the production of the copper phosphonate, is 1.0 mass% or less. This allows the organic dye to exhibit good light absorption performance in the light-absorbing layer 10 formed using the light-absorbing composition, and the light-absorbing layer 10 has the desired transmittance characteristics. In addition, the content of impurities contained in the light-absorbing composition is reduced. In addition, the copper phosphonate is less likely to aggregate, and the viscosity of the light-absorbing composition is easily maintained low. There is no particular limit to the method for specifying the concentration of the acid, which is a by-product, in the light-absorbing composition. The method can be, for example, capillary electrophoresis, liquid chromatography, or ion chromatography.

[0043] In the light absorbing composition, the concentration of acid, which is a by-product in the production of copper phosphonate, may be 1.0% by weight or less, or may be 0.7% by weight or less.

[0044] The copper phosphonate-containing layer obtained by applying a mixture of a light-absorbing composition not containing an organic dye and the above-mentioned resin to form a coating film and curing the coating film typically has a sufficiently low average transmittance at wavelengths of 780 nm to 1080 nm, preferably 5% or less, more preferably 1% or less.

[0045] The light-absorbing composition has a viscosity of 100 mPa·s or less after being stored for 72 hours in an atmospheric pressure environment at, for example, 20 to 25° C. In this manner, the light-absorbing composition can have good storage stability.

[0046] The average particle size of the copper phosphonate in the light-absorbing composition is, for example, 5 nm to 200 nm, may be 10 nm to 150 nm, or can be 15 nm to 125 nm. The average particle size of the copper phosphonate in the light-absorbing composition can be determined, for example, by dynamic light scattering.

[0047] The light-absorbing composition may contain a phosphoric acid ester compound as necessary. This makes it difficult for copper phosphonate to aggregate in the light-absorbing composition. The phosphoric acid ester compound is not particularly limited, but includes, for example, at least one of a phosphoric acid diester represented by the following formula (c1) and a phosphoric acid monoester represented by the following formula (c2). In the following formulas (c1) and (c2), R 21 , R 22 , and R3 are each -(CH2CH2O) n R is a monovalent functional group represented by R4, n is an integer of 1 to 25, and R4 is an alkyl group having 6 to 25 carbon atoms. 21 , R 22 and R3 are the same or different types of functional groups. [ka]

[0048] An example of a method for preparing a light-absorbing composition will be described. First, a copper salt is added to a predetermined solvent such as tetrahydrofuran (THF), stirred, and filtered as necessary to obtain a solution of the copper salt. The copper salt is, for example, copper acetate or a hydrate of copper acetate. The copper salt may be an anhydride or a hydrate of copper chloride, copper formate, copper stearate, copper benzoate, copper pyrophosphate, copper naphthenate, and copper citrate. For example, copper acetate monohydrate is represented as Cu(CH3COO)2·H2O, and one mole of copper acetate monohydrate supplies one mole of copper ions and two moles of acetic acid as a by-product. When anhydrides or hydrates of copper chloride, copper formate, copper stearate, copper benzoate, copper pyrophosphate, copper naphthenate, and copper citrate are used as the copper salt, hydrochloric acid, formic acid, stearic acid, benzoic acid, pyrophosphoric acid, naphthenic acid, and citric acid are produced as by-product acids, respectively.

[0049] Next, a phosphoric acid ester compound such as a phosphoric acid diester represented by formula (c1) and a phosphoric acid monoester represented by formula (c2) is added to the copper salt solution and stirred to prepare liquid A. The above phosphonic acid is also added to a predetermined solvent such as alcohol such as ethanol and methanol or tetrahydrofuran and stirred to prepare liquid B. Next, while stirring liquid A, liquid B is added to liquid A and stirred for a predetermined time to generate copper phosphonate, and liquid C is obtained. Liquid C is subjected to suction filtration to obtain a solid product of copper phosphonate. The obtained solid product of copper phosphonate is added to a predetermined solvent such as ethanol and stirred, and suction filtration is performed to obtain a solid product of purified copper phosphonate. Then, the purified copper phosphonate is added to a predetermined solvent such as toluene, hexane, and xylene and stirred to obtain liquid D. Next, a desolvation process is performed for a predetermined time while heating liquid D using an evaporator. This allows a light-absorbing composition to be obtained. The desolvation process may be performed in a state where the environment of liquid D is reduced pressure. In this case, the temperature of the desolvation process can be set low.

[0050] The optical filter 1a can be modified from various viewpoints. For example, the optical filter 1a may be modified to an optical filter 1b shown in FIG. 1B. The optical filter 1b has the same configuration as the optical filter 1a unless otherwise specified. The description of the optical filter 1a also applies to the optical filter 1b as long as there is no technical contradiction.

[0051] As shown in FIG. 1B, the optical filter 1b is composed of only the light absorbing layer 10. This makes it easy to make the optical filter 1b thinner. The optical filter 1b can be produced, for example, by applying the composition for a light absorbing layer on a predetermined substrate to form a coating film, curing the coating film, and peeling off the resulting light absorbing layer 10 from the substrate. The substrate can be a glass substrate, a resin substrate, a metal substrate, or a ceramic substrate. The substrate is preferably a substrate whose surface is coated with fluorine. In this case, the light absorbing layer 10 is easy to peel off from the substrate.

[0052] The optical filter 1a or 1b may further include at least one selected from the group consisting of a light absorbing layer other than the light absorbing layer 10, an infrared reflecting film, and an antireflection film, as necessary. The infrared reflecting film is, for example, a film in which a plurality of materials having different refractive indices are alternately laminated. The material forming the infrared reflecting film is, for example, an inorganic material such as SiO2, TiO2, and MgF2, or an organic material such as a fluororesin. The antireflection film is formed to form an interface between the optical filter and air, and is, for example, a film for reducing reflection of light in the visible light region. The antireflection film may be, for example, formed of a dielectric material such as a resin, an oxide, and a fluoride. The antireflection film may be a multilayer film formed by laminating two or more types of dielectric materials having different refractive indices. In particular, the antireflection film may be a dielectric multilayer film made of a low refractive index material such as SiO2 and a high refractive index material such as TiO2 or Ta2O5. In this case, Fresnel reflection at the interface between the optical filter and air is reduced, and the amount of light in the visible light region of the optical filter can be increased.

[0053] As shown in FIG. 2, for example, an imaging optical system 100 can be provided using an optical filter 1a. The imaging optical system 100 further includes, in addition to the optical filter 1a, for example, an imaging lens 3. The imaging optical system 100 is disposed in front of an imaging element 2 in an imaging device such as a digital camera. The imaging element 2 is, for example, a solid-state imaging element such as a CCD or a CMOS. As shown in FIG. 2, light from a subject is collected by the imaging lens 3, and enters the imaging element 2 after ultraviolet and infrared rays are cut by the optical filter 1a. Therefore, the spectral sensitivity of the imaging element 2 is close to the visual sensitivity of humans, and a good image with high color reproducibility can be obtained. The imaging optical system 100 may include an optical filter 1b instead of the optical filter 1a or in addition to the optical filter 1a. EXAMPLES

[0054] <Example 1> (Preparation of Light-Absorbing Composition) 5.86g of copper acetate monohydrate (Kanto Chemical) and 234.14g of ethanol (Kanto Chemical, EL grade for electronics industry) were mixed and stirred for 1 hour, then filtered through a filter (Merck Millipore, trade name: Milex, model number: SLLHH25NS, pore size: 0.45μm, diameter: 25mm) to obtain a copper acetate solution. Next, 2.572g of a phosphate ester compound (Daiichi Kogyo Seiyaku, product name: Plysurf A208N) was added to 200g of the copper acetate solution and stirred for 30 minutes to obtain a solution A. 40g of ethanol was added to 2.886g of n-butylphosphonic acid (Johoku Chemical Industry), and stirred for 10 minutes to obtain a solution B. Next, while stirring the solution A, solution B was added to the solution A, and the mixture was stirred at room temperature for 15 minutes to react, obtaining a solution C. In the liquid C, a solid matter (hereinafter referred to as a solid matter of copper phosphonate) containing phosphonic acid and copper ions and thought to have been produced by a reaction was precipitated. This liquid C was subjected to suction filtration to obtain a solid matter of copper phosphonate. The obtained solid matter of copper phosphonate was added to 200 g of ethanol, stirred at room temperature for 10 minutes, and then suction filtration was performed again to obtain a refined solid matter of copper phosphonate. This refined copper phosphonate was further added to 140 g of toluene and stirred at room temperature for 1 minute to obtain a liquid D. In the liquid D, the solid matter of copper phosphonate was not visible, and the copper phosphonate was in a dispersed state. From this, it is considered that the solid matter of copper phosphonate also contains a certain amount of phosphate ester, which has a dispersing effect, and that the phosphate ester contributes to the dispersion of copper phosphonate in toluene. The D solution was placed in a flask and heated in an oil bath (manufactured by Tokyo Rika Kikai Co., Ltd., model: OSB-2100) set at 105°C, while a solvent removal treatment was performed using a rotary evaporator (manufactured by Tokyo Rika Kikai Co., Ltd., model: N-1110SF). As a result, 94.606 g of a dispersion of copper butylphosphonate, which is a light-absorbing copper complex, was obtained as a light-absorbing composition. In this process, it is believed that the use of copper acetate produced acetic acid as a by-product along with the production of copper phosphonate. However, the obtained copper phosphonate and the dispersion of copper phosphonate did not have the odor characteristic of acetic acid, suggesting that acetic acid had been sufficiently removed.

[0055] (Evaluation of Light-Absorbing Composition) Pure water was added to the light-absorbing composition immediately after preparation to perform liquid-liquid extraction, and the aqueous layer was collected to prepare a measurement sample for capillary electrophoresis (CE). Using a CE device (manufactured by Agilent Technologies, product name: Agilent 1600), capillary electrophoresis was performed on the measurement sample for CE according to the indirect absorption method. Here, a 2,6-pyridinedicarboxylic acid-based electrophoretic solution (pH: 12) was used, and a capillary made of fused silica was used. As a result, the concentration of acetic acid in the light-absorbing composition immediately after preparation was 0.20% by mass.

[0056] The viscosity of the light-absorbing composition immediately after preparation was measured using a rotational viscometer (manufactured by Sekonic Corporation, product name: PR-10-L / VM-10A). As a result, the viscosity was 0.89 mPa·s. The average particle size of copper phosphonate in the light-absorbing composition immediately after preparation was measured according to a dynamic light scattering method using a particle size measuring system (manufactured by Otsuka Electronics Co., Ltd., product name: ELSZ-2000). As a result, the average particle size was 29 nm. The viscosity and the average particle size of copper phosphonate of the light-absorbing composition stored for 27 days in an atmospheric pressure environment at 20 to 25°C after preparation were similarly measured. As a result, the viscosity was 1.54 mPa·s, and the average particle size of copper phosphonate was 105 nm. In the light-absorbing composition stored for 27 days in an atmospheric pressure environment at 20 to 25°C after preparation, no precipitation or aggregation of copper phosphonate was observed at all, and it was confirmed that the light-absorbing composition maintained quality without any problem for forming an optical filter. On the other hand, when a part of the liquid C, which is a dispersion liquid of copper phosphonate, was stored as it is in an atmospheric pressure environment at 0 to 25°C, a highly viscous jelly-like substance was obtained 4 days after the start of storage. Even when this jelly-like substance was stirred, it did not return to its initial liquid state. In addition, in the liquid C immediately after the start of storage, no difference in appearance was observed compared to the above light-absorbing composition. It is considered that the removal of the by-product acetic acid in the liquid C was incomplete, and the copper phosphonate coagulated, causing the liquid C to change into a jelly-like substance.

[0057] (Preparation of organic dye-containing solution) Weigh out 0.1 g of an organic dye (manufactured by QCR Solutions, product name: NIR768A, maximum absorption wavelength: 768 nm), add 20 g of cyclopentanone, and stir for 30 minutes to obtain the “organic dye-containing liquid.” <1> The organic dye-containing liquid was prepared in the same manner as in Example 1, except that the type of organic dye and the amount of cyclopentanone added were adjusted as shown in Table 1. <1> Similarly, the organic dye-containing liquid <2> ~ <6> The following dyes were prepared. NIR740C is an organic dye manufactured by QCR Solutions, and DLS740D, DLS740E, DLS744A, and DLS745B are organic dyes manufactured by Crysta-Lyn Chemical. The maximum absorption wavelength of each organic dye was determined from the absorption spectrum of the methanol solution of the organic dye.

[0058] (Preparation of composition for light absorbing layer) 3 g of polyvinyl butyral resin (manufactured by Sekisui Chemical Co., Ltd., product name: S-LEC KS-10) and 30 g of cyclopentanone were mixed and stirred for 8 hours to obtain a "PVB solution." 0.2 g of the PVB solution and 0.2 g of the organic dye-containing solution <1> The mixture obtained by mixing 2 g of cyclopentanone and 1.5 g of toluene was stirred for 30 minutes. Then, 6.15 g of the above light absorbing composition was added to the mixture, and the mixture was stirred for another 10 minutes to obtain a composition for light absorbing layer according to Example 1. Table 2 shows the content of each component in the composition for light absorbing layer according to Example 1. In the composition for light absorbing layer according to Example 1, the ratio of the copper content to the organic dye content (copper content / organic dye content) was 102 by mass. In the composition for light absorbing layer according to Example 1, the ratio of the phosphonic acid content to the organic dye content (phosphonic acid content / organic dye content) was 189 by mass.

[0059] (Fabrication of optical filters) The composition for light absorbing layer according to Example 1 was applied by a dispenser to a range of 30×30 mm on a transparent glass substrate (manufactured by SCHOTT, product name: D263 T eco) made of borosilicate glass having dimensions of 76 mm×76 mm×0.21 mm to form a coating film, and the coating film was baked in a heating oven under conditions of 45° C. for 2 hours and then 85° C. for 0.5 hours to harden the composition for light absorbing layer, thereby obtaining an optical filter according to Example 1 having a light absorbing layer. The thickness of the light absorbing layer in the optical filter according to Example 1 was 81 μm. The thickness of the light absorbing layer was determined by measuring the distance between the surface of the light absorbing layer and the interface between the light absorbing layer and the glass substrate using a laser displacement meter LK-H008 manufactured by Keyence Corporation.

[0060] <Example 2> A composition for light absorbing layer according to Example 2 was obtained in the same manner as in Example 1, except that in the preparation of the composition for light absorbing layer, the amount of the PVB solution added was changed to 0.40 g.

[0061] 0.1g of Daikin Industries' Optool DSX (active ingredient concentration: 20%) and 19.9g of 3M's Novec 7100 (hydrofluoroether) were mixed and stirred for 5 minutes to produce a fluorine treatment agent (active ingredient concentration: 0.1%). The fluorine treatment agent was applied by spin coating at a rotation speed of 3000 rpm (revolutions per minute) to a transparent glass substrate (SCHOTT, product name: D263 T eco) made of borosilicate glass with dimensions of 76mm x 76mm x 0.21mm, and the coating was then left at room temperature for 24 hours to obtain a substrate with a fluorine film.

[0062] The composition for light absorbing layer according to Example 2 was applied onto the above-mentioned substrate with a fluorine film to form a coating film, and the coating film was baked in a heating oven under conditions of 45°C for 2 hours and then 85°C for 0.5 hours to harden the composition for light absorbing layer and obtain a light absorbing layer. Thereafter, the light absorbing layer was peeled off from the substrate with a fluorine film to obtain an optical filter according to Example 2 consisting of only the light absorbing layer. The thickness of the light absorbing layer of the optical filter according to Example 2 was 119 μm.

[0063] <Examples 3 to 8> In preparing the compositions for light absorbing layers, the types of organic dye-containing liquids and the contents of each component were adjusted as shown in Tables 1 and 2. Except for this, the compositions for light absorbing layers according to Examples 3 to 8 were obtained in the same manner as in Example 1.

[0064] In the preparation of the optical filters, the optical filters of Examples 3 to 8 were obtained in the same manner as in Example 1, except that the compositions for light-absorbing layers of Examples 3 to 8 were used instead of the composition for light-absorbing layer of Example 1.

[0065] <Example 9> (Preparation of Light-Absorbing Composition) 5.86g of copper acetate monohydrate and 234.14g of ethanol were mixed and stirred for 1 hour, and then filtered through a filter (Merck Millipore, product name: Milex, model number: SLLHH25NS, pore size: 0.45μm, diameter: 25mm) to obtain a copper acetate solution. Next, 2.572g of a phosphate ester compound (Daiichi Kogyo Seiyaku, product name: Plysurf A208N) was added to 200g of the copper acetate solution and stirred for 30 minutes to obtain solution A. 40g of ethanol was added to 2.296g of ethylphosphonic acid (Johnson Matthey) and stirred for 10 minutes to obtain solution B. Next, while stirring solution A, solution B was added to solution A, and the mixture was stirred at room temperature for 15 minutes to react and obtain solution C. Solution C contained phosphonic acid and copper ions, and solid copper phosphonate, which was thought to have been produced by the reaction, was precipitated. This solution C was subjected to suction filtration to obtain solid copper phosphonate. The obtained solid copper phosphonate was added to 200 g of ethanol, stirred at room temperature for 10 minutes, and then suction filtered again to obtain a purified solid copper phosphonate. The purified copper phosphonate was further added to 90 g of toluene and stirred at room temperature for 1 minute to obtain liquid D. In liquid D, the solid copper phosphonate was not visible, and the copper phosphonate was dispersed. From this, it is considered that the solid copper phosphonate also contains a certain amount of phosphoric acid ester with dispersing action, and the phosphoric acid ester contributes to the dispersion of copper phosphonate in toluene. Liquid D was placed in a flask and heated in an oil bath set at a temperature of 105 ° C., and a solvent removal treatment was performed using a rotary evaporator. As a result, a dispersion of ethyl copper phosphonate, which is a light-absorbing copper complex, was obtained as a light-absorbing composition of 82.080 g. As in the case of the dispersion of copper phosphonate and copper phosphonate according to Example 1, the dispersion of copper phosphonate and copper phosphonate according to Example 9 did not have the odor specific to acetic acid, suggesting that acetic acid had been sufficiently removed. The viscosity of the copper phosphonate dispersion according to Example 9 was 0.84 mPa·s.

[0066] (Preparation of composition for light absorbing layer) 3g of polyvinyl butyral resin (S-LEC KS-10) and 30g of cyclopentanone were mixed and stirred for 8 hours to obtain a "PVB solution." 0.2g of the PVB solution and 0.2g of the organic dye-containing solution <1> The mixture obtained by mixing 2 g of cyclopentanone and 1.5 g of toluene was stirred for 30 minutes. Then, 5.34 g of the above light absorbing composition was added to the mixture and stirred for another 10 minutes to obtain a composition for light absorbing layer according to Example 9. Table 2 shows the content of each component in the composition for light absorbing layer according to Example 9. In the composition for light absorbing layer according to Example 9, the ratio of the copper content to the organic dye content (copper content / organic dye content) was 102 by mass. In the composition for light absorbing layer according to Example 1, the ratio of the phosphonic acid content to the organic dye content (phosphonic acid content / organic dye content) was 150 by mass.

[0067] (Fabrication of optical filters) An optical filter according to Example 9 was obtained in the same manner as in Example 1, except that the composition for a light-absorbing layer according to Example 9 was used instead of the composition for a light-absorbing layer according to Example 1.

[0068] <Comparative Example 1> In preparing the composition for light absorbing layer, except that the light absorbing composition which is a dispersion liquid of copper phosphonate and toluene were not added, the composition for light absorbing layer according to Comparative Example 1 was prepared in the same manner as in Example 1. In producing an optical filter, except that the composition for light absorbing layer according to Comparative Example 1 was used instead of the composition for light absorbing layer according to Example 1, the optical filter according to Comparative Example 1 was obtained in the same manner as in Example 1.

[0069] <Comparative Example 2> In the preparation of the composition for the light absorbing layer, <1> A composition for a light absorbing layer according to Comparative Example 2 was prepared in the same manner as in Example 1, except that no light absorbing layer composition according to Example 1 was added. In producing an optical filter, an optical filter according to Comparative Example 2 was obtained in the same manner as in Example 1, except that a composition for a light absorbing layer according to Comparative Example 2 was used instead of the composition for a light absorbing layer according to Example 1. The thickness of the light absorbing layer of the optical filter according to Comparative Example 2 was 130 μm.

[0070] <Comparative Example 3> In the preparation of the composition for the light absorbing layer, <1> A composition for a light absorbing layer according to Comparative Example 3 was prepared in the same manner as in Example 1, except that the composition for a light absorbing layer according to Comparative Example 3 was used instead of the composition for a light absorbing layer according to Example 1 in the production of an optical filter, and an optical filter according to Comparative Example 3 was obtained in the same manner as in Example 1. The thickness of the light absorbing layer of the optical filter according to Comparative Example 3 was 96 μm.

[0071] <Comparative Example 4> A light-absorbing composition according to Comparative Example 4 was prepared in the same manner as in Example 1, except that the obtained copper phosphonate solid was added to 200 g of ethanol, and stirring was performed at room temperature for 10 minutes, and suction filtration was omitted. The concentration of acetic acid in the light-absorbing composition according to Comparative Example 4 immediately after preparation was determined by capillary electrophoresis in the same manner as in the light-absorbing composition according to Example 1. As a result, the acetic acid concentration of the light-absorbing composition according to Comparative Example 4 was 3.20 mass%. Thereafter, an optical filter according to Comparative Example 4 was obtained in the same manner as in Example 1, except that the light-absorbing composition according to Comparative Example 4 was used instead of the light-absorbing composition according to Example 1. The thickness of the optical filter according to Comparative Example 4 was 118 μm.

[0072] <Comparative Example 5> In preparing the composition for the light absorbing layer, 0.2 g of the organic dye-containing liquid <1> Instead of the organic dye-containing liquid, the amount of the organic dye-containing liquid in Table 2 was added. <7> A composition for a light absorbing layer according to Comparative Example 5 was prepared in the same manner as in Example 1, except that the composition for a light absorbing layer according to Comparative Example 5 was used instead of the composition for a light absorbing layer according to Example 1 in the production of an optical filter, and an optical filter according to Comparative Example 5 was obtained in the same manner as in Example 1. The thickness of the light absorbing layer of the optical filter according to Comparative Example 5 was 77 μm. S2084 is an organic dye manufactured by FEW Chemicals.

[0073] (Optical characteristics of optical filters) Using an ultraviolet-visible-near infrared spectrophotometer (manufactured by JASCO Corporation, product name: V670), the transmittance spectrum of the optical filters according to each Example and each Comparative Example was measured at an incident angle of 0°. In the optical filters according to Examples 1 to 9, the maximum transmittance in the wavelength range of 750 to 1080 nm was 5% or less, the maximum transmittance in the wavelength range of 800 to 950 nm was 5% or less, and the maximum transmittance in the wavelength range of 800 to 1000 nm was 5% or less. In addition, in the optical filters according to Examples 1 to 9, the maximum transmittance in the wavelength range of 1000 to 1100 nm was 4.28% or less, and the maximum transmittance in the wavelength range of 1100 to 1200 nm was 11.44% or less. Furthermore, in the optical filters according to Examples 1 to 9, the IR cutoff wavelength was 611 to 644 nm, and the UV cutoff wavelength was 362 to 394 nm. The absorption maximum wavelength of the light absorbing layer was 750 to 780 nm. The transmittance spectra of the optical filters according to Examples 1 to 9 are shown in Figs. 3 to 11, respectively. In addition, the transmittance spectra of the optical filters according to Comparative Examples 1 to 5 are shown in Figs. 12 to 16, respectively. Table 3 shows the characteristic values ​​that can be seen from the transmittance spectra shown in Figs. 3 to 16. The optical filters according to Examples 1 and 2 have good optical characteristics that satisfy the above requirements (i) to (iv), and it is suggested that they will exhibit good characteristics when used as light-absorbing optical filters. Table 4 shows the spectral transmittance of only the transparent glass substrate, and Fig. 17 shows the transmittance spectrum of the transparent glass substrate. In Example 1, taking into account the transmittance spectrum of only the transparent glass substrate, it is suggested that the light-absorbing layer in the optical filter according to Example 1 satisfies the above requirements (i) to (iv). The optical filters according to Examples 3 to 9 have good optical characteristics that satisfy the above requirements (I) to (IV), and it is suggested that they will exhibit good characteristics when used as light-absorbing optical filters. In addition, in Examples 3 to 9, taking into consideration the transmittance spectrum of only the transparent glass substrate, it was suggested that the light absorbing layers in the optical filters according to Examples 3 to 9 satisfied the above requirements (I) to (IV).

[0074] The optical filter according to Comparative Example 1 does not contain copper phosphonate as a light absorbent in its light absorbing layer, but contains only an organic dye, so that infrared rays in a wide wavelength range are not sufficiently absorbed, and the above requirements (ii) and (iv) cannot be satisfied. The optical filter according to Comparative Example 2 does not contain copper phosphonate as a light absorbent in its light absorbing layer, so that it has a thickness of 130 μm, but does not sufficiently absorb infrared rays in the wavelength range of 600 nm to 780 nm, and the above requirement (ii) cannot be satisfied. The optical filter according to Comparative Example 3 does not contain copper phosphonate as a light absorbing layer, so that it has a thickness of 96 μm, but does not sufficiently absorb infrared rays in the wavelength range of 600 nm to 780 nm, and the above requirement (ii) cannot be satisfied. The optical filter according to Comparative Example 5 contains an organic dye having its maximum absorption wavelength (669 nm) outside the wavelength range of 720 nm to 780 nm, and the above requirement (iii) cannot be satisfied.

[0075] A comparison of the acetic acid concentration of the light-absorbing composition according to Example 1 with that of the light-absorbing composition according to Comparative Example 4 suggests that the by-product acetic acid can be effectively removed by a purification treatment combining addition of ethanol to the solid copper phosphonate and filtration. In addition, the optical filter according to Comparative Example 4 did not satisfy the above requirement (i). This is presumably because the organic dye changed to a state having absorption in the visible range due to the effect of acetic acid remaining in the light-absorbing composition according to Comparative Example 4 during the preparation process of the composition for the light-absorbing layer or the heat treatment process after application to the substrate, whereby a part of the functional group of the organic dye was decomposed or the bonding state was changed.

[0076] [Table 1]

[0077] [Table 2]

[0078] [Table 3]

[0079]

Table 4

Claims

1. A composition for a light absorbing layer, comprising: The composition for a light absorbing layer includes a light absorbing composition and an organic dye, The light absorbing composition comprises a copper phosphonate, an organic solvent, and an acid; a concentration of the acid in the light-absorbing composition is 1.0% by mass or less; The organic dye has a maximum absorption wavelength of 740 nm to 780 nm. A composition for a light absorbing layer.

2. The copper phosphonate has an average particle size of 5 nm to 200 nm. The composition for a light absorbing layer according to claim 1 .

3. The light-absorbing composition has a viscosity of 100 mPa·s or less after being stored for 72 hours in an environment at atmospheric pressure and a temperature of 20 to 25°C. The composition for a light absorbing layer according to claim 1 or 2.

4. The organic dye is at least one selected from the group consisting of a phthalocyanine-based compound, a cyanine-based compound, a squarylium-based compound, a diimmonium-based compound, a naphthalocyanine-based compound, and a croconium-based compound. The composition for a light absorbing layer according to any one of claims 1 to 3.

5. In the transmission spectrum of the light absorbing layer obtained by curing the composition for a light absorbing layer, the minimum value of the transmittance in the wavelength range of 700 nm to 1100 nm exists in the wavelength range of 700 nm to 800 nm. The composition for a light absorbing layer according to any one of claims 1 to 4.

6. Obtaining a copper phosphonate; adding an organic solvent to the copper phosphonate to obtain a copper phosphonate dispersion; performing a solvent removal treatment on the copper phosphonate dispersion to obtain a light-absorbing composition having an acid concentration of 1.0 mass% or less; Obtaining an organic dye-containing liquid containing an organic dye; mixing the light absorbing composition, the organic dye-containing liquid, and a resin; The organic dye has a maximum absorption wavelength of 740 nm to 780 nm. A method for producing a composition for a light absorbing layer.

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