Near-infrared transmittance black material

Abstract

The present invention provides a near-infrared light transmitting black material which is capable of sufficiently suppressing absorption of near-infrared light, while sufficiently absorbing visible light. The present invention provides a near-infrared light transmitting black material which contains an oxazine resin.

Description

[Technical Field]

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

[0002] In recent years, with the development of lasers, particularly semiconductor lasers, and the sensors for them, there has been a demand in many fields for functional pigments with optical properties not found in conventionally used pigments. For example, in the printing ink field, there is a demand for infrared-transparent pigments that can be used for printing hidden barcodes and hidden two-dimensional codes, for example, by printing with ink containing infrared-transparent pigments and making it possible to read information that is indiscernible to the naked eye with an infrared reader. For example, Patent Document 1 describes an infrared-transmitting ink containing a magnetic material, a color pigment, and a varnish, and such ink is said to have excellent concealment properties. However, the ink of Patent Document 1 has a problem in that it is insufficient in its effect of suppressing absorption of near-infrared rays.

[0003] Infrared-transmitting pigments are also used in color filters, which are essential components of solid-state imaging devices and liquid crystal displays. In particular, color filters for solid-state imaging devices are required to have improved color separation and color reproducibility. As such a color filter, for example, Patent Document 2 describes a color filter composition containing a near-infrared transmitting black coloring material such as a bisbenzofuranone pigment, and such a composition is said to have less noise derived from visible light components. However, even the near-infrared transmitting black color material of Patent Document 2 has problems such as an insufficient effect of absorbing visible light and an inability to sufficiently suppress absorption of near-infrared light. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2015-196819 [Patent Document 2] Japanese Patent Application Laid-Open No. 2014-130173 Summary of the Invention [Problem to be solved by the invention]

[0005] 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 absorption of near-infrared light. [Means for solving the problem]

[0006] The present invention is a near-infrared transparent black material containing an oxazine resin. The present invention will be described in detail below.

[0007] As a result of extensive research, the present inventors have found that oxazine resins have high transmittance in the infrared region while exhibiting a brown to black color, and have thus completed the present invention.

[0008] The near-infrared transmitting black material of the present invention contains an oxazine resin. By including the oxazine resin, it is possible to achieve both absorption of visible light and suppression of absorption of near-infrared light.

[0009] The oxazine resin is preferably an aromatic oxazine resin having an aromatic ring. Examples of aromatic oxazine resins include benzoxazine resins having a benzene ring in the basic structure of the resin, and naphthoxazine resins having a naphthalene ring. Among these, naphthoxazine resins are preferred because they have high absorbency for visible light and exhibit a higher degree of blackness. The benzoxazine resin may have a plurality of benzene rings in the repeating structure, and the naphthoxazine resin may have a plurality of naphthalene rings in the repeating structure.

[0010] The oxazine resin is formed by ring-opening polymerization of its precursor, oxazine. As the structure of the above oxazine, an example of the partial structure of benzoxazine, which is an aromatic oxazine, is shown in the following formula (1), and an example of the partial structure of naphthoxazine is shown in the following formulas (2) and (3).

[0011] [ka]

[0012] R in formula (1) 1 , R in Equation (2) 2 , R in Equation (3) 3 each independently represents a hydrogen atom, a hydroxyl group, a halogen atom, an alkyl group, or an alkoxy group. Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom. 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 t-butyl group. 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 t-butoxy group.

[0013] The aromatic oxazines have a six-membered ring attached to a benzene or naphthalene ring, and the six-membered ring contains oxygen and nitrogen, hence the name.

[0014] Examples of the repeating structure of the oxazine resin obtained by ring-opening polymerization of the above aromatic oxazine are shown in the following formulas (4) to (6).

[0015] [ka]

[0016] R in equation (4) 4, R in Eq. (5) 5 , R in Equation (6) 6 each independently represents a hydrogen atom, a hydroxyl group, a halogen atom, an alkyl group, or an alkoxy group. Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom. 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 t-butyl group. 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 t-butoxy group.

[0017] The oxazine resin preferably has an oxygen content of 5.0% by weight or more, more preferably 10.0% by weight or more, and preferably 50.0% by weight or less, and more preferably 40.0% by weight or less. The oxazine resin preferably has a nitrogen content of 0.5% by weight or more, more preferably 1.0% by weight or more, and preferably 20.0% by weight or less, more preferably 10.0% by weight or less. The oxygen content and nitrogen content can be measured by, for example, X-ray photoelectron spectroscopy.

[0018] The carbon / oxygen weight ratio in the oxazine resin is preferably 1.0 or more, more preferably 2.0 or more, and is preferably 30.0 or less, more preferably 25.0 or less. The carbon / nitrogen weight ratio in the oxazine resin is preferably 2.5 or more, more preferably 5.0 or more, and is preferably 100.0 or less, more preferably 50.0 or less. The carbon / oxygen weight ratio and carbon / nitrogen weight ratio can be measured by, for example, X-ray photoelectron spectroscopy.

[0019] Examples of methods for producing the oxazine resin include a method having a step of reacting a mixed solution containing triazine, dihydroxynaphthalene, and a solvent, and a method having a step of reacting a mixed solution containing formaldehyde, an aliphatic amine, dihydroxynaphthalene, and a solvent. By the above methods, naphthoxazine resin can be produced. In addition, in the above method, a benzoxazine resin can be produced by using a phenol (for example, phenol, bisphenol, etc.) instead of dihydroxynaphthalene.

[0020] In the method for producing the naphthoxazine resin, first, a mixed solution such as a mixed solution containing triazine, dihydroxynaphthalene and a solvent, or a mixed solution containing formaldehyde, an aliphatic amine, dihydroxynaphthalene and a solvent is prepared.

[0021] Since formaldehyde is unstable, it is preferable to use formalin, which is a formaldehyde solution. Formalin usually contains a small amount of methanol as a stabilizer in addition to formaldehyde and water. The formaldehyde used in the present invention may be formalin as long as the formaldehyde content is clear. Furthermore, formaldehyde has a polymerized form called paraformaldehyde, which can also be used as a raw material, but since it has poor reactivity, it is preferable to use the above-mentioned formalin.

[0022] The aliphatic amine is preferably represented by the general formula R-NH, where R is an alkyl group having 5 or less carbon atoms. Examples of the alkyl group having 5 or less carbon atoms include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, a cyclopropyl group, an n-butyl group, an isobutyl group, an s-butyl group, a t-butyl group, a cyclobutyl group, a cyclopropylmethyl group, an n-pentyl group, a cyclopentyl group, a cyclopropylethyl group, and a cyclobutylmethyl group. Since it is preferable to have a small molecular weight, the substituent R is preferably a methyl group, an ethyl group, a propyl group, etc., and as actual compound names, methylamine, ethylamine, propylamine, etc. are preferably used. Methylamine, which has the smallest molecular weight, is the most preferred.

[0023] The dihydroxynaphthalene has many isomers, such as 1,3-dihydroxynaphthalene, 1,5-dihydroxynaphthalene, 1,6-dihydroxynaphthalene, 1,7-dihydroxynaphthalene, 2,3-dihydroxynaphthalene, 2,6-dihydroxynaphthalene, and 2,7-dihydroxynaphthalene. Among these, 1,5-dihydroxynaphthalene and 2,6-dihydroxynaphthalene are preferred due to their high reactivity, with 1,5-dihydroxynaphthalene being the most preferred due to its highest reactivity.

[0024] When the method of adding formaldehyde and an aliphatic amine without adding the triazine is used, the most preferable ratio of the three components of dihydroxynaphthalene, aliphatic amine, and formaldehyde in the mixed solution is 1 mole of aliphatic amine and 2 moles of formaldehyde per mole of dihydroxynaphthalene. Depending on the reaction conditions, raw materials may be lost due to evaporation or the like during the reaction, so the optimum blending ratio may not be exactly the above ratio, but it is preferable to blend 0.8 to 2.2 moles of aliphatic amine and 1.6 to 4.4 moles of formaldehyde per mole of dihydroxynaphthalene. By using 0.8 moles or more of the aliphatic amine, sufficient oxazine rings can be formed, and polymerization can proceed smoothly. By using 2.2 moles or less, the formaldehyde required for the reaction is not consumed excessively, and the reaction proceeds smoothly, allowing the desired naphthoxazine to be obtained. Similarly, by using 1.6 moles or more of formaldehyde, oxazine rings can be sufficiently formed and polymerization can proceed smoothly, while by using 4.4 moles or less, side reactions can be reduced, which is preferable.

[0025] The mixed solution contains a solvent for dissolving and reacting the two or three raw materials. Examples of the solvent include alcohols such as methanol, ethanol, and isopropanol; ketones such as acetone and methyl ethyl ketone; tetrahydrofuran, dioxane, chloroform, ethyl acetate, dimethylformamide, and dimethyl sulfoxide.

[0026] The solvent may be a single component or a mixture of two or more components. It is preferable to use a solvent having a solubility parameter (SP value) of 9.0 or more. Examples of solvents with an SP value of 9.0 or higher 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). The solvent having an SP value of 9.0 or more is preferably a solvent having an SP value of 9.0 to 15.0. When using only a single component of the solvent, it is preferable that the solvent has a boiling point of 50 to 150° C. It is even more preferable that the solvent contains a solvent having a boiling point of 50 to 130° C. and an SP value of 9.0 or more.

[0027] Furthermore, when the solvent is a mixed solvent composed of two or more solvents, it is preferable that the mixed solvent contains a solvent having a boiling point of 150° C. or higher, and the content of the solvent having a boiling point of 150° C. or higher is 60% by volume or less, thereby making it possible to obtain a black material with high average sphericity. A more preferable lower limit of the content of the solvent having a boiling point of 150° C. or higher is 45% by volume.

[0028] The amount of solvent added to the mixed solution is not particularly limited, but when the raw materials (solutes) containing dihydroxynaphthalene, triazine, aliphatic amine, and formaldehyde are 100 parts by mass, it is usually preferable to mix 300 to 200,000 parts by mass (corresponding to a molar concentration of the solute of 1.0 M to 0.001 M). By using an amount of 300 parts by mass or more, the solubility of the solute increases, and by using an amount of 200,000 parts by mass or less, the concentration becomes appropriate and the reaction proceeds more easily.

[0029] The method for producing the oxazine resin includes a step of reacting the mixed solution, and the oxazine resin is formed by allowing the reaction to proceed. In the above reaction, by continuing to heat, the produced oxazine ring opens, and polymerization occurs, increasing the molecular weight and forming a so-called oxazine resin. In order to produce particles uniformly, it is preferable that the particles are dispersed during the reaction. Dispersion methods that can be used include known methods such as stirring, ultrasonic waves, and rotation. To improve the dispersion state, a suitable dispersant may be added. In the step of forming the oxazine resin, the reaction proceeds slowly even at room temperature, but to ensure efficient reaction, it is preferably carried out at a temperature of 50 to 150°C. The reaction time can be adjusted by the temperature, and is usually preferably 30 minutes to 20 hours. The reaction under the above conditions yields spherical oxazine resin particles. The oxazine resin particles obtained in this step exhibit green, brown, or black color depending on the reaction conditions. 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.

[0030] Furthermore, since the ring-opening polymerization reaction of oxazine is accelerated by heating, in order to allow the polymerization to proceed sufficiently, after the above reaction step, heat treatment is preferably carried out at 100 to 300° C., more preferably at 150 to 250° C. The heating time is preferably 30 minutes to 50 hours. The heating atmosphere is preferably an inert gas atmosphere such as nitrogen or argon, and the heating is preferably carried out in a sealed container to prevent evaporation.

[0031] The near-infrared transmitting black material of the present invention may contain a binder resin, an ultraviolet absorber, a dispersant, etc. in addition to the oxazine resin.

[0032] 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. By setting the thickness within the above range, visible light can be sufficiently absorbed and a high level of blackness can be achieved. The average transmittance is more preferably 15% or less, and even more preferably 12% or less. The average transmittance can be measured, for example, using a spectrophotometer equipped with an integrating sphere.

[0033] 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. By setting the content within the above range, the transmittance of near-infrared rays can be sufficiently increased. The average transmittance is more preferably 70% or more. The average transmittance can be measured, for example, using a spectrophotometer equipped with an integrating sphere.

[0034] The near-infrared transmitting black material of the present invention preferably has a zeta potential (surface potential) of −70 to +80 mV. By setting the particle size within the above range, it is possible to obtain black particles having excellent uniformity of particle size and good dispersibility in a solvent. The preferred lower limit of the zeta potential is −60 mV, and the preferred upper limit is +70 mV. The zeta potential can be determined, for example, by using a microscope electrophoresis type zeta potential measurement device, injecting a solution in which black particles are dispersed into a measurement cell, applying a voltage while observing with a microscope, and measuring the potential when the particles stop moving (are stationary).

[0035] The near-infrared transparent black material of the present invention has a density of 1.80 g / cm 3 It is preferable that: Density is 1.80g / cm 3 A preferable lower limit of the density is 1.20 g / cm or less, thereby obtaining high dispersibility. 3 , the preferred upper limit is 1.70 g / cm 3 is.

[0036] The near-infrared transparent black material of the present invention has a volume resistivity of 1.0×10 7 It is preferable that the resistivity is Ω·cm or more. Volume resistivity is 1.0×10 7 High insulating properties can be ensured by a resistivity of Ω·cm or more. More preferably, it is 1.0×10 8 Ω·cm or more, more preferably 1.0×10 11 The preferred upper limit is 1.0×10 18 Ω·cm.

[0037] When the near-infrared transparent black material of the present invention is measured by time-of-flight secondary ion mass spectrometry (TOF-SIMS), it is preferable that at least one of a mass spectrum derived from a benzene ring and a mass spectrum derived from a naphthalene ring is detected. By having the above structure, highly dense particles can be obtained. In the present invention, the mass spectrum derived from the benzene ring refers to the mass spectrum around 77.12, and the mass spectrum derived from the naphthalene ring refers to the mass spectrum around 127.27. The above measurement can be carried out using, for example, a TOF-SIMS device (manufactured by ION-TOF).

[0038] The shape of the near-infrared transmitting black material of the present invention is not particularly limited, and examples thereof include particle, plate, and liquid shapes, with particle shape being preferred.

[0039] 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 10.0 μm or less. By setting the color in the above range, sufficient blackness and high dispersibility can be obtained. The average particle size is more preferably 0.02 μm or more and more preferably 5.0 μm or less.

[0040] The near-infrared transmitting black material of the present invention preferably has a coefficient of variation (CV value) of particle diameter of 20% or less. When the CV value of the particle diameter is 20% or less, the monodispersity of the black material is improved, and when used as a black pigment, the particles are easily packed closely together. As a result, it is possible to improve the visible light blocking effect. A more preferable upper limit of the CV value of the particle diameter is 15%. The lower limit is not particularly limited, but 0.5% is preferable. The CV value (%) of particle size is the standard deviation divided by the average particle size, expressed as a percentage, and is calculated using the following formula. A smaller CV value means smaller variation in particle size. CV value of particle size (%) = (standard deviation of particle size / average particle size) x 100 The average particle size and standard deviation can be measured, for example, using FE-TEM.

[0041] The near-infrared transmitting black material of the present invention preferably has an average sphericity of 90% or more. This can enhance the effects of the present invention. A more preferable lower limit of the average sphericity is 95%. The sphericity (minor diameter / major diameter) can be measured by analyzing an electron microscope photograph taken using an FE-TEM or FE-SEM using an image analyzer, and the average sphericity can be calculated by determining the average value of the sphericity for, for example, 100 particles randomly selected from the electron microscope photograph.

[0042] 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. By setting the color density within the above range, high blackness can be achieved. The lightness L* is more preferably 25 or less, and even more preferably 20 or less. The lightness L* can be measured, for example, using a spectrophotometer in accordance with JIS Z 8722:2009.

[0043] The near-infrared transmitting black material of the present invention can be produced, for example, by the same method as the above-mentioned method for producing the oxazine resin.

[0044] The near-infrared-transmitting black material of the present invention can be used for applications such as 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. The near-infrared transparent ink and near-infrared transparent filter are also part of the present invention. [Effects of the Invention]

[0045] According to the present invention, it is possible to provide a near-infrared transmitting black material that can sufficiently absorb visible light and sufficiently suppress absorption of near-infrared light. DETAILED DESCRIPTION OF THE INVENTION

[0046] The following examples will further illustrate the present invention, but the present invention is not limited to these examples.

[0047] Example 1 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 in that order to prepare an ethanol mixed solution. Next, the resulting mixed solution was heated and stirred (rotation speed: 300 rpm) at 80°C for 5.0 hours. The solution was filtered through a glass filter, washed three times with ethanol, vacuum dried at 50°C for 3 hours, and further vacuum heated at 200°C for 12 hours to obtain naphthoxazine resin particles as a near-infrared transparent black material. 4 parts by weight of the obtained black material was dispersed in 40 parts by weight of polyvinyl butyral resin, and the dispersion was applied to a slide glass so that the thickness after drying would be 30 μm, and dried at 100° C. for 2 hours to obtain a coating film.

[0048] Example 2 1.0 g of 1,5-dihydroxynaphthalene (Tokyo Chemical Industry Co., Ltd.), 0.5 g of 40% methylamine (Fujifilm Wako Pure Chemical Industries, Ltd.), and 1.0 g of 37% aqueous formaldehyde solution (Fujifilm Wako Pure Chemical Industries, Ltd.) were dissolved in 500 ml of a mixed solution of isopropanol and water (weight ratio of isopropanol to water = 4:1). The resulting mixed solution was then reacted overnight at 30°C, and then heated and stirred (rotation speed: 300 rpm) at 80°C for 10 hours. The particles were collected, washed, vacuum dried at 50°C for 3 hours, and further heat-treated at 220°C for 20 hours to obtain naphthoxazine resin particles as a near-infrared-transparent black material. A coating film was prepared in the same manner as in Example 1, except that the obtained black material was used.

[0049] (Comparative Example 1) A coating film was prepared in the same manner as in Example 1, except that carbon black was used.

[0050] (Evaluation method) (1) Average particle size, CV value and average sphericity The average particle size was measured by analyzing FE-SEM images of the black materials obtained in the examples and the carbon black used in the comparative examples using image analysis software (WINROOF, manufactured by Mitani Shoji Co., Ltd.). Furthermore, the standard deviation was calculated for the black materials obtained in the examples, and the coefficient of variation (CV value) of particle diameter was calculated from the obtained values. Furthermore, for the black materials obtained in the 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.

[0051] (2) Average transmittance and brightness L* For the coating films obtained in the examples and comparative examples, the reflectance spectra were measured in the visible light region of 400 to 800 nm wavelength and the near-infrared region of 900 to 2500 nm wavelength 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. Furthermore, the lightness L* value of the coating films obtained in the examples and comparative examples was measured using a spectrophotometer with an integrating sphere (manufactured by JASCO Corporation, V-670) in accordance with JIS Z 8722:2009 in the CIE LAB (L*a*b*) color system.

[0052] [Table 1] [Industrial Applicability]

[0053] According to the present invention, it is possible to provide a near-infrared transmitting black material that can sufficiently absorb visible light and sufficiently suppress absorption of near-infrared light.

Claims

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

2. The near-infrared transparent black material according to claim 1 , wherein the oxazine resin is a naphthoxazine resin.

3. 3. The near-infrared transmitting black material according to claim 1, which is in a particulate form and has an average particle diameter of 0.02 μm or more and 10.0 μm or less.

4. A near-infrared transparent ink comprising the near-infrared transparent black material according to any one of claims 1 to 3.

5. 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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