Near-infrared transmissive black material

Abstract

The present invention provides a near-infrared-transmitting black material that sufficiently absorbs visible light and can sufficiently suppress the absorption of near-infrared rays.The present invention relates to a near-infrared-transmitting black material comprising an oxazine resin.

Description

Technical Field

[0001] The present invention relates to a near-infrared-transmitting black material that sufficiently absorbs visible light and can sufficiently suppress the absorption of near-infrared rays. Background Art

[0002] In recent years, the development of lasers, particularly semiconductor lasers, and laser-related sensors has led to a growing demand for functional pigments with optical properties not previously available in conventional pigments. For example, in the field of printing inks, there is a growing demand for infrared-transmitting pigments that can be used for printing with inks containing infrared-transmitting pigments and for reading information that is invisible to the naked eye using infrared readers, for example, for printing invisible barcodes and invisible 2D codes.

[0003] For example, Patent Document 1 describes an infrared-transmitting ink containing a magnetic material, a coloring pigment, and a varnish. Such an ink is considered to have excellent concealing properties.

[0004] However, the ink of Patent Document 1 has a problem in that the effect of suppressing the absorption of near-infrared rays is insufficient.

[0005] Infrared-transmitting pigments are also used in color filters. Color filters are essential components for solid-state imaging devices and liquid crystal displays. Color filters for solid-state imaging devices are particularly demanded to have improved color separation and color reproducibility.

[0006] As such a color filter, for example, Patent Document 2 describes a color filter composition containing a near-infrared-transmitting black colorant such as a bisbenzofuranone-based pigment. Such a composition is believed to have little noise derived from visible light components.

[0007] However, even the near-infrared transmitting black color material of Cited Document 2 has problems in that the visible light absorption effect is insufficient or the absorption of near-infrared rays cannot be sufficiently suppressed.

[0008] Prior art literature

[0009] Patent Literature

[0010] Patent Document 1: Japanese Patent Application Laid-Open No. 2015-196819

[0011] Patent Document 2: Japanese Patent Application Laid-Open No. 2014-130173 Summary of the Invention

[0012] Problems to be solved by the invention

[0013] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a near-infrared-transmitting black material that can sufficiently absorb visible light and sufficiently suppress the absorption of near-infrared rays.

[0014] Means used to solve problems

[0015] The present invention relates to a near-infrared-transmitting black material comprising an oxazine resin.

[0016] Hereinafter, the present invention will be described in detail.

[0017] The present inventors conducted intensive studies and found that oxazine resins exhibit high transmittance in the infrared region despite showing brown to black colors, thereby completing the present invention.

[0018] The near-infrared-transmitting black material of the present invention contains an oxazine resin.

[0019] By containing the oxazine resin, it is possible to achieve both absorption of visible light and suppression of absorption of near infrared rays.

[0020] As the oxazine resin, an aromatic oxazine resin having an aromatic ring is preferable.

[0021] Examples of the aromatic oxazine resin include benzoxazine resins having a benzene ring in the basic structure of the resin and naphthoxazine resins having a naphthalene ring.

[0022] Among them, naphthoxazine resins are preferred from the viewpoint of high absorption of visible light and higher blackness.

[0023] The benzoxazine resin may have a plurality of benzene rings in its repeating structure. Alternatively, the naphthoxazine resin may have a plurality of naphthalene rings in its repeating structure.

[0024] The oxazine resin is formed by ring-opening polymerization of oxazine, which is its precursor.

[0025] As the structure of the oxazine, an example of a partial structure of benzoxazine as an aromatic oxazine is shown in the following formula (1), and an example of a partial structure of naphthoxazine is shown in the following formulas (2) and (3).

[0026] [Chemical Formula 1]

[0027]

[0028] R in formula (1) 1 , R in formula (2) 2 , R in formula (3) 3 Each independently represents a hydrogen atom, a hydroxyl group, a halogen atom, an alkyl group or an alkoxy group.

[0029] Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom.

[0030] Examples of the alkyl group include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, and a tert-butyl group.

[0031] Examples of the alkoxy group include a methoxy group, an ethoxy group, an n-propoxy group, an isopropoxy group, an n-butoxy group, an isobutoxy group, and a tert-butoxy group.

[0032] The aromatic oxazine has a six-membered ring added to a benzene ring or a naphthalene ring, and the six-membered ring contains oxygen and nitrogen, which is the origin of the name.

[0033] Examples of the repeating structure of the oxazine resin obtained by the ring-opening polymerization of the aromatic oxazine are shown in the following formulas (4) to (6).

[0034] [Chemical Formula 2]

[0035]

[0036] R in formula (4) 4 , R in formula (5) 5 , R in formula (6) 6 Each independently represents a hydrogen atom, a hydroxyl group, a halogen atom, an alkyl group, or an alkoxy group.

[0037] Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom.

[0038] Examples of the alkyl group include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, and a tert-butyl group.

[0039] Examples of the alkoxy group include a methoxy group, an ethoxy group, an n-propoxy group, an isopropoxy group, an n-butoxy group, an isobutoxy group, and a tert-butoxy group.

[0040] The oxygen content of the oxazine resin is preferably 5.0 wt% or more, more preferably 10.0 wt% or more, and is preferably 50.0 wt% or less, and preferably 40.0 wt% or less.

[0041] The nitrogen content of the oxazine resin is preferably 0.5 wt% or more, more preferably 1.0 wt% or more, and is preferably 20.0 wt% or less, more preferably 10.0 wt% or less.

[0042] The oxygen content and nitrogen content can be measured by, for example, X-ray photoelectron spectroscopy.

[0043] The weight ratio of carbon to oxygen in the oxazine resin is preferably 1.0 or greater, more preferably 2.0 or greater, and is preferably 30.0 or less, more preferably 25.0 or less.

[0044] The carbon / nitrogen weight ratio in the oxazine resin is preferably 2.5 or greater, more preferably 5.0 or greater, and is preferably 100.0 or less, more preferably 50.0 or less.

[0045] The carbon / oxygen weight ratio and the carbon / nitrogen weight ratio can be measured by, for example, X-ray photoelectron spectroscopy.

[0046] Examples of methods for producing the oxazine resin include a method comprising reacting a mixed solution containing triazine, dihydroxynaphthalene, and a solvent; a method comprising reacting a mixed solution containing formaldehyde, an aliphatic amine, dihydroxynaphthalene, and a solvent; and the like. These methods can produce naphthoxazine resins.

[0047] In the above method, a benzoxazine resin can be produced by using phenols (for example, phenol, bisphenol, etc.) instead of dihydroxynaphthalene.

[0048] In the method for producing the naphthoxazine resin, the following mixed solutions are first prepared: a mixed solution containing triazine, dihydroxynaphthalene, and a solvent; a mixed solution containing formaldehyde, an aliphatic amine, dihydroxynaphthalene, and a solvent; and the like.

[0049] The above-mentioned formaldehyde is unstable, so it is preferable to use formalin as a formaldehyde solution. Formalin usually contains a small amount of methanol as a stabilizer in addition to formaldehyde and water. Regarding the formaldehyde used in the present invention, formalin can also be used as long as the formaldehyde content is clear.

[0050] In addition, paraformaldehyde is a polymerized form of formaldehyde. Although paraformaldehyde can also be used as a raw material, its reactivity is poor. Therefore, the above-mentioned formalin is preferably used.

[0051] The aliphatic amine is represented by the general formula R—NH 2 , wherein R is preferably an alkyl group having 5 or less carbon atoms. Examples of the alkyl group having 5 or less carbon atoms include methyl, ethyl, n-propyl, isopropyl, cyclopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, cyclobutyl, cyclopropylmethyl, n-pentyl, cyclopentyl, cyclopropylethyl, and cyclobutylmethyl.

[0052] The molecular weight is preferably reduced, and therefore, the substituent R is preferably a methyl group, an ethyl group, a propyl group, etc. As actual compound names, methylamine, ethylamine, propylamine, etc. can be preferably used. Methylamine, which has the smallest molecular weight, is most preferred.

[0053] The dihydroxynaphthalene has various isomers, for example, 1,3-dihydroxynaphthalene, 1,5-dihydroxynaphthalene, 1,6-dihydroxynaphthalene, 1,7-dihydroxynaphthalene, 2,3-dihydroxynaphthalene, 2,6-dihydroxynaphthalene, and 2,7-dihydroxynaphthalene.

[0054] Among them, 1,5-dihydroxynaphthalene and 2,6-dihydroxynaphthalene are preferred from the viewpoint of high reactivity, and 1,5-dihydroxynaphthalene is more preferred because it has the highest reactivity.

[0055] When using a method of adding formaldehyde and aliphatic amine without adding the above-mentioned triazine, the ratio of the three components of dihydroxynaphthalene, aliphatic amine and formaldehyde in the above-mentioned mixed solution is most preferably 1 mol of aliphatic amine and 2 mol of formaldehyde per 1 mol of dihydroxynaphthalene.

[0056] Depending on the reaction conditions, raw materials may be lost due to volatilization during the reaction. Therefore, the optimal mixing ratio is not exactly limited to the above ratio, but it is preferred to mix the aliphatic amine in a mixing ratio range of 0.8 to 2.2 mol and the formaldehyde in a mixing ratio range of 1.6 to 4.4 mol per 1 mol of dihydroxynaphthalene.

[0057] By setting the aliphatic amine content to 0.8 mol or more, sufficient oxazine ring formation is achieved, allowing for proper polymerization. Furthermore, by setting the content to 2.2 mol or less, formaldehyde required for the reaction is not consumed extraneously, allowing the reaction to proceed smoothly and yielding the desired naphthoxazine.

[0058] Similarly, by setting the formaldehyde content to 1.6 mol or more, oxazine rings can be sufficiently formed, allowing polymerization to proceed appropriately, while setting it to 4.4 mol or less is preferred because the occurrence of side reactions can be reduced.

[0059] The mixed solution contains a solvent for dissolving the two or three raw materials and reacting them.

[0060] Examples of the solvent include alcohols such as methanol, ethanol, and isopropyl alcohol; ketones such as acetone and methyl ethyl ketone; tetrahydrofuran, dioxane, chloroform, ethyl acetate, dimethylformamide, and dimethyl sulfoxide.

[0061] The solvent may be a single component or a mixture of two or more components. It is preferred that a solvent having a solubility parameter (SP value) of 9.0 or greater be used.

[0062] Examples of solvents having an SP value of 9.0 or greater include ethanol (12.7), methanol (14.7), isopropanol (11.5), cresol (13.3), ethylene glycol (14.2), phenol (14.5), water (23.4), DMF (N,N-dimethylformamide, 12.3), dimethyl sulfoxide (DMSO, 13.0), methyl ethyl ketone (9.3), dioxane (10.3), ethyl acetate (9.0), chloroform (9.4), and acetone (10.0).

[0063] The solvent having an SP value of 9.0 or higher is more preferably a solvent having an SP value of 9.0 to 15.0. When using a single solvent, the boiling point is preferably 50 to 150°C. It is further preferred to include a solvent having a boiling point of 50 to 130°C and an SP value of 9.0 or higher.

[0064] When the solvent is a mixed solvent composed of two or more solvents, the mixed solvent preferably contains a solvent with a boiling point of 150° C. or higher, and the content of the solvent with a boiling point of 150° C. or higher is 60% by volume or less. This allows a black material with a high average sphericity to be obtained.

[0065] A more preferred lower limit of the content of the solvent having a boiling point of 150° C. or higher is 45% by volume.

[0066] The amount of solvent added to the mixed solution is not particularly limited. When the raw materials (solute) comprising dihydroxynaphthalene, triazine, aliphatic amine, and formaldehyde are set to 100 parts by mass, it is usually preferably mixed with 300 to 200,000 parts by mass (equivalent to a molar concentration of the solute of 1.0 M to 0.001 M). By setting the amount to 300 parts by mass or more, the solubility of the solute increases, and by setting the amount to 200,000 parts by mass or less, the concentration becomes appropriate, thereby making the reaction easier to proceed.

[0067] In the method for producing the oxazine resin, the mixed solution is reacted to form the oxazine resin.

[0068] By continuing to heat during the above reaction, the produced oxazine ring opens, and the molecular weight increases during polymerization, thereby producing a so-called oxazine resin.

[0069] In addition, in order to make the making of particles evenly carried out, preferably the state of particle dispersion is used during reaction. As dispersion method, known methods such as stirring, ultrasonic wave, rotation can be utilized. In addition, in order to improve the dispersion state, suitable dispersant can be added.

[0070] The oxazine resin formation process proceeds slowly even at room temperature, but for efficient reaction, it is preferably carried out at a temperature of 50-150°C. The reaction time can be adjusted by the temperature, but is generally preferably 30 minutes to 20 hours. The reaction under these conditions yields spherical oxazine resin particles. The oxazine resin particles obtained in this process exhibit green, brown, or black colors, depending on the reaction conditions.

[0071] It should be noted that the particle size of the oxazine resin particles can be adjusted by parameters such as the concentration of the solution, the reaction temperature, the molar ratio of the raw materials, and the stirring conditions.

[0072] The ring-opening polymerization reaction of oxazine is accelerated by heating. Therefore, in order to fully proceed with the polymerization, it is preferable to perform a heat treatment at 100 to 300° C., more preferably 150 to 250° C., after the above reaction step. The heating time is preferably 30 minutes to 50 hours.

[0073] The atmosphere during heating is preferably an inert gas atmosphere such as nitrogen or argon, and is preferably performed in a sealed container to suppress evaporation.

[0074] The near-infrared-transmitting black material of the present invention may contain a binder resin, an ultraviolet absorber, a dispersant, and the like in addition to the above-mentioned oxazine resin.

[0075] The near-infrared-transmitting black material of the present invention preferably has an average transmittance of 20% or less in the visible light region with a wavelength of 400 to 800 nm.

[0076] By setting it as the said range, visible light can be fully absorbed and high blackness can be exhibited.

[0077] The average transmittance is more preferably 15% or less, and even more preferably 12% or less.

[0078] The average transmittance can be measured using, for example, a spectrophotometer equipped with an integrating sphere.

[0079] The near-infrared-transmitting black material of the present invention preferably has an average transmittance of 60% or more in the near-infrared region with a wavelength of 900 to 2500 nm.

[0080] By setting it as the said range, the transmittance|permeability of near infrared rays can be improved sufficiently.

[0081] The average transmittance is more preferably 70% or higher.

[0082] The average transmittance can be measured using, for example, a spectrophotometer equipped with an integrating sphere.

[0083] The zeta potential (surface potential) of the near-infrared-transmitting black material of the present invention is preferably -70 to +80 mV.

[0084] By setting the above range, black particles having excellent uniformity of particle size and good dispersibility in a solvent can be obtained.

[0085] The preferred lower limit of the zeta potential is -60 mV, and the preferred upper limit is +70 mV.

[0086] It should be noted that the above-mentioned zeta potential can be obtained, for example, as follows: using a microscope electrophoresis zeta potential measuring device, a solution containing dispersed black particles is injected into a measuring cell, a voltage is applied while observing with a microscope, and the potential when the particles become immobile (stationary) is measured.

[0087] The density of the near infrared ray-transmitting black material of the present invention is preferably 1.80 g / cm 3 the following.

[0088] By making the density 1.80 g / cm 3 The preferred lower limit of the density is 1.20 g / cm 3 The preferred upper limit is 1.70 g / cm 3 .

[0089] The volume resistivity of the near infrared ray transmissive black material of the present invention is preferably 1.0×10 7 Ω·cm or more.

[0090] By making the volume resistivity 1.0×10 7 Ω·cm or more, high insulation can be ensured. More preferably, it is 1.0×10 8 Ω·cm or more, more preferably 1.0×10 11 Ω·cm or more. In addition, the upper limit is preferably 1.0×10 18 Ω·cm.

[0091] When the near-infrared-transmitting black material of the present invention is measured by time-of-flight secondary ion mass spectrometry (TOF-SIMS), it is preferred that at least one of a mass spectrum derived from a benzene ring and a mass spectrum derived from a naphthalene ring be detected.

[0092] By having such a structure, highly dense particles can be obtained.

[0093] In the present invention, the mass spectrum derived from the benzene ring refers to a mass spectrum around 77.12, and the mass spectrum derived from the naphthalene ring refers to a mass spectrum around 127.27.

[0094] The above-mentioned measurement can be performed using, for example, a TOF-SIMS apparatus (manufactured by ION-TOF Corporation).

[0095] The shape of the near-infrared-transmitting black material of the present invention is not particularly limited, and may be a particle shape, a plate shape, a liquid shape, or the like. Among them, a particle shape is preferred.

[0096] When the near-infrared-transmitting black material of the present invention is in the form of particles, the average particle size is preferably 0.01 μm or more and preferably 10.0 μm or less.

[0097] By setting it as the said range, sufficient blackness and high dispersibility can be obtained.

[0098] The average particle size is more preferably 0.02 μm or larger, and more preferably 5.0 μm or smaller.

[0099] The coefficient of variation (CV value) of the particle size of the near-infrared-transmitting black material of the present invention is preferably 20% or less.

[0100] When the CV value of the above particle size is 20% or less, the monodispersity of the black material becomes good, and when used as a black pigment, the particles can be easily packed into the densest form. As a result, the shielding effect against visible light can be improved. The more preferred upper limit of the CV value of the above particle size is 15%. It should be noted that the lower limit is not particularly limited, but is preferably 0.5%.

[0101] The CV value (%) of the particle size is a value obtained by dividing the standard deviation by the average particle size and expressed as a percentage, and is a numerical value obtained by the following formula: A smaller CV value means smaller particle size variation.

[0102] CV value of particle size (%) = (standard deviation of particle size / average particle size) × 100

[0103] The average particle size and standard deviation can be measured using, for example, FE-TEM.

[0104] The near-infrared-transmitting black material of the present invention preferably has an average sphericity of 90% or more.

[0105] Thereby, the effect of the present invention can be enhanced.

[0106] A more preferred lower limit of the average sphericity is 95%.

[0107] It should be noted that the sphericity (minor diameter / major diameter) can be measured by analyzing an electron microscope photograph taken using a FE-TEM or FE-SEM using an image analysis device, and the average sphericity can be calculated by taking the average value of the sphericity of, for example, 100 particles arbitrarily selected from the electron microscope photograph.

[0108] The near-infrared-transmitting black material of the present invention preferably has a lightness L* value of 30 or less in the CIE LAB (L*a*b*) color system.

[0109] By setting it as the said range, high blackness can be exhibited.

[0110] The lightness L* is more preferably 25 or less, and even more preferably 20 or less.

[0111] The lightness L* can be measured using a spectrophotometer based on JIS Z 8722:2009, for example.

[0112] As a method for producing the near-infrared-transmitting black material of the present invention, for example, there can be mentioned the same method as the method for producing the oxazine resin described above.

[0113] The near-infrared-transmitting black material of the present invention can be used for coating films, black paints, near-infrared-transmitting inks such as anti-counterfeiting inks, near-infrared-transmitting filters such as black matrices for color filters, and near-infrared-transmitting films.

[0114] Furthermore, the above-mentioned near-infrared-transmitting ink and near-infrared-transmitting filter are also aspects of the present invention.

[0115] Effects of the Invention

[0116] According to the present invention, a near-infrared-transmitting black material that sufficiently absorbs visible light and can sufficiently suppress absorption of near-infrared rays can be provided. DETAILED DESCRIPTION

[0117] Hereinafter, although an embodiment of the present invention is described in more detail with reference to examples, the present invention is not limited to these examples.

[0118] (Example 1)

[0119] 1.20 g of 1,5-dihydroxynaphthalene (1,5-DHN, manufactured by Tokyo Chemical Industry Co., Ltd.) and 0.98 g of 1,3,5-trimethylhexahydro-1,3,5-triazine (manufactured by Tokyo Chemical Industry Co., Ltd.) were dissolved in 50 ml of ethanol to prepare an ethanol mixed solution.

[0120] The resulting mixed solution was then heated and stirred at 80°C for 5.0 hours (rotation speed: 300 rpm). The solution was filtered through a glass filter, washed three times with ethanol, and then vacuum-dried at 50°C for 3 hours. It was then further vacuum-heated at 200°C for 12 hours to obtain naphthoxazine resin particles as a near-infrared-transmitting black material.

[0121] 4 parts by weight of the obtained black material was dispersed in 40 parts by weight of polyvinyl butyral resin, applied on a slide glass to a thickness of 30 μm after drying, and dried at 100° C. for 2 hours to obtain a coating film.

[0122] (Example 2)

[0123] 1.0 g of 1,5-dihydroxynaphthalene (manufactured by Tokyo Chemical Industry Co., Ltd.), 0.5 g of 40% methylamine (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and 1.0 g of a 37% formaldehyde aqueous solution (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) were dissolved in this order in 500 ml of a mixed solution of isopropyl alcohol and water (weight ratio of isopropyl alcohol to water = 4:1).

[0124] The resulting mixed solution was then allowed to react overnight at 30°C and then heated and stirred at 80°C for 10 hours (rotation speed: 300 rpm). The particles were recovered, washed, vacuum-dried at 50°C for 3 hours, and further heat-treated at 220°C for 20 hours to obtain naphthoxazine resin particles serving as a near-infrared-transmitting black material.

[0125] A coating film was produced in the same manner as in Example 1 except that the obtained black material was used.

[0126] (Comparative Example 1)

[0127] A coating film was produced in the same manner as in Example 1 except that carbon black was used.

[0128] (Evaluation method)

[0129] (1) Average particle size, CV value and average sphericity

[0130] The average particle size was measured by analyzing FE-SEM images of the black materials obtained in Examples and the carbon black used in Comparative Examples using image analysis software (WINROOF, manufactured by Mitani Shoji Co., Ltd.).

[0131] In addition, for the black materials obtained in Examples, the standard deviation was calculated, and the coefficient of variation (CV value) of the particle size was calculated based on the obtained values.

[0132] Furthermore, for the black materials obtained in Examples, the sphericity was determined from the ratio of the minimum diameter to the maximum diameter of the particles, and the average sphericity was calculated.

[0133] (2) Average transmittance and lightness L*

[0134] For the coating films obtained in the examples and comparative examples, the reflectance spectra in the visible light region of 400 to 800 nm and the near-infrared region of 900 to 2500 nm were measured using a spectrophotometer with an integrating sphere (V-670 manufactured by JASCO Corporation). The geometric mean of the transmittance in each wavelength range was calculated, and the average transmittance was calculated as the average value of the transmittance in each wavelength range.

[0135] The coating films obtained in Examples and Comparative Examples were measured for lightness L* values ​​in the CIE LAB (L*a*b*) colorimetric system based on JIS Z 8722:2009 using a spectrophotometer with an integrating sphere (V-670 manufactured by JASCO Corporation).

[0136] [Table 1]

[0137]

[0138] Industrial applicability

[0139] According to the present invention, a near-infrared-transmitting black material that sufficiently absorbs visible light and can sufficiently suppress absorption of near-infrared rays can be provided.

Claims

1. A near-infrared-transmitting black material comprising an oxazine resin, The near-infrared-transmitting black material has an average transmittance of 20% or less in the visible light region with a wavelength of 400 nm to 800 nm and an average transmittance of 60% or more in the near-infrared region with a wavelength of 900 nm to 2500 nm.

2. The near-infrared-transmitting black material according to claim 1, wherein The oxazine resin is a naphthoxazine resin. 3 . The near-infrared-transmitting black material according to claim 1 , which is in the form of particles and has an average particle size of 0.02 μm to 10.0 μm. A near-infrared-transmitting ink comprising the near-infrared-transmitting black material according to any one of claims 1 to 3. A near-infrared-transmitting filter comprising the near-infrared-transmitting black material according to any one of claims 1 to 3.

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