JPH0531902B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a novel infrared absorbing composition,
More specifically, the present invention relates to an infrared absorbing composition that absorbs far-red light or near-infrared light with a wavelength of 700 to 1500 nm. (Prior Art) In addition to optical filter materials, infrared absorbers that selectively absorb far-red light with a wavelength of 700 to 1500 nm have various uses as described below. light →
Optical disk recording layer using thermal conversion effect. Thermosensitive color recording by laser. Inkjet printer ink using light absorption effect. Bar code ink. Antihalation agent soundtrack for photosensitive materials. Examples of applications include molds for infrared coupler photo sensors that form infrared absorbing dyes. Among these, the use of an aromatic dithiol-based nickel complex having a quaternary ammonium salt is disclosed in JP-A-58-16888 and JP-A-57-11090 as a light absorbent for laser recording films. Further, ink for inkjet printers uses a solvent such as ethyl cellosolve and a dye soluble in this organic solvent as an infrared absorber. In this case, this infrared absorber is a chemical substance that is useful for reading with an optical reading device that uses an infrared light source with a wavelength of 740 to 900 nm. Conventionally, infrared absorbers for such inkjet printers include nigrosine and chromium complex salts. Compounds such as those disclosed in JP-A-56-135568 are used. Next, silicon is mainly used in conventional photodetectors such as cameras and optical sensors such as optical image receptors, and photodiodes
MOS image sensor, CCD image sensor,
It is used in forms such as CID image sensors.
The spectral sensitivity of silicon is quite large for light in the infrared region of 700 to 1100 nm, and in order to make the spectral sensitivity curve similar to the specific luminous efficiency curve, noise in the infrared region must be cut out. Conventionally, this type of photodetection device uses inorganic glass,
Alternatively, an organic near-infrared absorber (see JP-A-58-9378) has been used. (Problems to be Solved by the Invention) However, aromatic dithiol-based nickel complexes containing quaternary ammonium salts have low solubility in organic media, and the concentration of the infrared absorber in the composition when coated on a substrate is low. There were disadvantages such as the inability to increase the temperature and the limitations on the media that could be used. In addition, even if nigrosine used in jet printer ink is initially solubilized, precipitates form when left for a long time.
Since chromium complex salts cannot be slightly dispersed or dissolved in organic solvents alone, it is necessary to further contain water or add a solubilizing agent containing nitrogen. Furthermore, the organic near-infrared absorber described in JP-A-58-9378 used in the photodetector has low solubility in organic solvents.
It had the disadvantage that the light resistance was not sufficiently high, and it was not satisfactory. The purpose of the present invention is to overcome the drawbacks of these infrared absorbing compositions and to provide an infrared absorbing composition that has high solubility in organic solvents and good compatibility with binders, etc. An object of the present invention is to provide an infrared absorbing composition that has a large ability to absorb near-infrared light and is robust against heat and light. (Means for Solving the Problems) As a result of various studies to achieve the above object, the present inventors found that certain quaternary phosphonium salts of aromatic dithiol-based nickel complexes are The inventors have discovered that the solubility in the infrared rays is extremely good, and the ability to absorb near-infrared light is extremely large.Based on this knowledge, the present invention has been completed. That is, the present invention has the general formula (In the formula, R ¹ to ^{R 4} represent an alkyl group or an aryl group, R represents a hydrogen atom or a methyl group, and n
represents an integer from 1 to 4. ) A quaternary phosphonium bis(1,2-benzenedithiolat)nitschelate derivative represented by ) and a binder are provided. . In the compound represented by the above general formula []
R ¹ to R ⁴ preferably represent an alkyl group having 1 to 20 carbon atoms, and examples of the alkyl group include methyl group, ethyl group, n-butyl group, iso-amyl group, n-dodecyl group, and n-octadecyl group. etc. can be given. In this case, the alkyl group may be further substituted with a phenyl group. Examples of the aryl group represented by R ¹ to ^{R 4} in the above general formula [] include a phenyl group and a p-tolyl group. Further, R ¹ to ^{R 4} may be a mixture of an alkyl group and an aryl group. In R ¹ to R ⁴ , one or more alkyl groups,
The number of aryl groups is preferably 3 or less. In the above general formula [], R ¹ to ^{R 4} are particularly preferably alkyl groups having 4 to 16 carbon atoms. As for the alkyl group, lower alkyl groups are preferred over long chain ones, straight chain alkyl groups are preferred over branched ones, and unsubstituted alkyl groups are preferred over substituted ones. The quaternary phosphonium bis(1,2-benzenedithiolat) nickelate derivative represented by the general formula [] can be produced as follows. A 1,2-benzenedithiol derivative is dissolved in absolute ethanol, and this is neutralized with KOH. An ethanol solution of a nickel salt is added to this solution, followed by a solution of a quaternary phosphonium salt, stirred in air (or while blowing oxygen), and the precipitate formed is filtered. By-product inorganic salt (potassium salt)
To remove this, crude crystals can be obtained by extracting with an organic solvent such as acetone and then distilling off the solvent. This is recrystallized from, for example, acetone-alcohol. Preferred examples of the compounds represented by the general formula [] are as follows, but it goes without saying that the present invention is not limited to these exemplified compounds. In addition, in the following formula, ⁿ C _x H _2x+1 means a linear alkyl group having x carbon atoms. The absorption maximum (λmax) and molar extinction coefficient (εmax, unit of 1·mol ⁻¹ ·cm ⁻¹ ) of these compounds are as follows.

[Table] The infrared absorbing composition of the present invention is a composition in which the compound represented by the above general formula [] is appropriately contained in a binder. There are no particular restrictions on the binder, and organic,
It can be used regardless of whether it is inorganic or not. Examples of such binders include polymeric materials such as plastics and inorganic materials such as glass. Further, if necessary, a smelter can be used in this binder. Preferred solvents include acetone, methyl ethyl ketone, methyl isobutyl ketone, chloroform, methylene chloride, methanol, ethanol,
Examples include organic solvents such as toluene, ethyl acetate, isoamyl acetate, acetonitrile, ethyl cellosolve, and dimethylformamide. Next, an embodiment in which the infrared absorbing composition of the present invention is used in an optical recording medium will be described. An optical recording medium basically consists of a substrate and a recording layer, but depending on the purpose, an undercoat layer can be provided on the substrate and a protective layer can be provided on the recording layer. Any known substrate can be used as long as it is transparent to the laser used. Typical examples include glass and plastic, and examples of plastic include acrylic, polycarbonate, polysulfone, polyimide, and polyester. Its shape can be various, such as a disk, card, sheet, or roll film. Guide grooves may be formed on the glass or plastic substrate to facilitate tracking during recording. Further, the glass or plastic substrate may be provided with a plastic binder or an undercoat layer such as an inorganic oxide or an inorganic sulfide. An undercoat layer having a lower thermal conductivity than the substrate is preferred. The recording layer is composed of an infrared absorber alone or a combination of it and other materials;
Alternatively, it can be divided into those composed of a reflective layer and a light absorption layer containing the infrared absorbing agent. The recording layer composed of the infrared absorber alone or in combination with other materials can be prepared by dissolving the infrared absorber in a solvent and applying it, by vapor depositing it on the substrate, or by mixing it with a resin solution and applying it. It is formed by a method of coating a mixed solution with other pigments, a method of dissolving it in a resin solution together with other pigments, and the like. Resins include PVA, PVP, polyvinyl butyral, polycarbonate, nitrocellulose,
polyvinyl formal, methyl vinyl ether,
Known materials such as maleic anhydride copolymer and styrene-butadiene copolymer are used, and the general formula [] for the resin in the infrared absorbing composition is used.
It is desirable that the weight ratio of the infrared absorbent expressed by is 0.01 or more. When using other dyes, such as triarylmethane dyes, merocyanine dyes, cyanine dyes, azo dyes, and anthraquinone dyes, which have absorption outside the wavelength range of semiconductor lasers, they can be used not only in semiconductor lasers but also in He-Ne lasers, etc. This is suitable because it can be recorded. One or more recording layers are provided. The thickness of the recording layer is usually in the range of 0.01 μm to 1 μm, preferably 0.08 to 0.8 μm. In the case of reflective readout, it is particularly preferably an odd multiple of 1/4 of the laser wavelength used for readout. When providing a reflective layer for a semiconductor laser or a He-Ne laser, it is possible to provide a reflective layer on the substrate and then provide a recording layer on the second reflective layer using the method described above, or to provide a recording layer on the substrate. There is one method of providing a recording layer and then providing a reflective layer thereon. The reflective layer can also be formed by other methods such as vapor deposition, sputtering, and ion plating. For example, a metal salt or metal complex salt is dissolved in a water-soluble resin (PVP, PVP, etc.), a reducing agent is further added, and a solution is applied to the substrate, and then heated and dried at 50°C to 150°C, preferably 60°C to 100°C. It is formed by The weight ratio of the metal salt or metal complex salt to the resin is 0.1 to 10, preferably 0.5 to 1.5. On this occasion,
The appropriate thickness of the recording layer is 0.01 to 0.1 .mu.m for the metal particle reflection layer and 0.01 to 1 .mu.m for the light absorption layer. As the metal salt or metal complex salt, silver nitrate, potassium silver cyanide, potassium gold cyanide, silver ammine complex, silver cyanide complex, gold salt, or gold cyanide complex can be used. Formalin is used as a reducing agent.
Tartaric acid, tartrates, reducing agents, hypophosphites, sodium borohydride, dimethylamine borane, etc. can be used. The reducing agent can be used in an amount of 0.2 to 10 mol, preferably 0.5 to 4 mol, per mol of metal salt or metal complex salt. In optical recording media, information is recorded by irradiating the recording layer with a spot-shaped high-energy beam such as a laser through the substrate or from the opposite side of the substrate, and the light absorbed by the recording layer is converted into heat. Pits (holes) are formed in the recording layer. Further, information is read by irradiating a laser beam with a low output power below a recording threshold energy, and detecting a change in the amount of reflected light from a pit portion and a portion where no pit is formed. In addition, when the infrared absorbing composition of the present invention is used for a sensor mold etc., for example, JP-A-57
This can be done by referring to the record in Publication No.-22209. Using at least one of the infrared absorbers of the present invention, acrylic or methacrylic resins, phenolic resins, modified phenolic resins, ketone resins, polyester resins, urethane resins,
A sensor mold can be formed by dissolving it in one or more silicone resins and applying the solution. The weight ratio of infrared absorber and resin is 1 part resin.
It is more preferably 0.01 to 0.2 parts than 0.001 to 0.5 parts, but this weight ratio is determined by the molecular extinction coefficient of the infrared absorber in the infrared region, the compatibility of the infrared absorber with the resin, and the coating thickness or molding thickness. be done. The solvent used is one that dissolves at least one of the infrared absorber and the resin. These include chlorinated solvents such as dichloromethane and chloroform, ester solvents such as ethyl acetate and isoamyl acetate, ester solvents such as acetone, methyl ethyl ketone, and methyl isobutyl ketone, alcohols such as ethyl alcohol and butyl alcohol, pyridine, dimethylformamide, These include nitrogen-containing solvents such as dimethylacetamide. Next, embodiments in which the infrared absorbing composition of the present invention is used in an inkjet ink will be described. Inkjet inks that use organic solvents as solvents are mainly used in electrostatic acceleration type and electrostatic air flow type, both of which require applying high-pressure pulses to the ink to enable ink flow or ink droplet formation. It won't happen. This problem involves not only the electrical properties of the ink but also the physical properties related to fluidity such as surface tension and viscosity.
It can be carried out according to the method described in JP-A-135568. The inkjet ink uses an infrared absorber, and the solvents include ethyl cellosolve, toluene, ethanol, n-butanol, ethyl methyl ketone, methyl isobutyl ketone, dichloromethane, triethanolamine, dimethylformamide, isoamyl acetate, etc. An organic solvent is used, and glycerin, metal soap, etc. are added to it to adjust the viscosity. The content has a viscosity of 10 cp or less at room temperature and a specific resistance of 1.
The composition ratio of the organic solvent and viscosity modifier is selected so that the resistance is ×10 ⁴ to 1 × 10 ¹¹ Ω·cm. The content ratio of the infrared absorber to the solvent is 0.01 to 0.8 parts of the infrared absorber per 1 part by weight of the solvent,
It should preferably be dissolved or at least finely dispersed to an average particle size of 0.8 μm or less at room temperature. In some cases, a dye that absorbs visible light may also be added to the ink. (Effect of the invention) In the present invention, quaternary phosphonium bis(1,2
-benzenedithiolat) nitschelate derivatives have excellent properties such as high solubility in organic solvents, good microdispersion or dissolution in printing vehicles, and high ability to absorb near-infrared light. Further, the infrared absorbing composition of the present invention has excellent heat resistance and light resistance. Furthermore, the quaternary phosphonium bis(1,2-benzenedithiolat) nickelate derivative of the present invention has excellent practical advantages in that it is easy to synthesize and can be produced at low cost. Therefore, the infrared absorbing composition of the present invention can be used not only as an ink for inkjet printers, but also as a material for thermosensitive coloring by laser using light->heat exchange, thermosensitive recording, and optical disk recording material. (Examples) Next, the present invention will be described in more detail based on Examples. In the following, "parts" means "parts by weight" unless otherwise specified. Reference Example 1 <Synthesis of Exemplified Compound (2)> 16 g of potassium hydroxide was dissolved in 200 ml of absolute ethanol, and 20 g of benzenedithiol was added to this solution, followed by stirring at room temperature for 10 minutes. Next, nickel chloride, hexahydrate (17 g) was added to this in absolute ethanol.
After adding the solution dissolved in 200ml, further boil at room temperature.
Stir for 30 minutes. Add 50g of tetra-n-butylphosphonium bromide to this solution in absolute ethanol.
Add 200 ml of the solution at room temperature. After the addition was completed, the mixture was further stirred at room temperature for 2 hours, and the precipitated dark green crystals were filtered, washed first with water and then with ethanol, and air-dried. This was recrystallized from hot acetone-ethanol to obtain exemplified compound (2). Yield 27g. Melting point 145~
148℃. Reference Example 2 <Synthesis of Exemplary Compound (3)> 36g of potassium hydroxide and 600ml of absolute ethanol
50 g of toluene-3,4-dithiol was added to this solution, and the mixture was stirred at room temperature for 10 minutes. Next, a solution of 36.8 g of nickel chloride hexahydrate dissolved in 400 ml of absolute ethanol was added thereto, and the mixture was further stirred at room temperature for 30 minutes. Add tetra-
A solution of 111 g of n-butylphosphonium bromide dissolved in 300 ml of absolute ethanol is added at room temperature.
After the addition was completed, the mixture was further stirred at room temperature for 2 hours, and then the dark green crystals precipitated were filtered, washed first with water and then with ethanol, and air-dried. This was recrystallized from hot acetone-ethanol to obtain exemplified compound (3).
Yield 50g. Melting point 142-144℃. Reference Example 3 <Synthesis of Exemplified Compound (6)> 36 g of potassium hydroxide was dissolved in 600 ml of absolute ethanol, and 50 g of toluene-3,4-dithiol was added to this solution, followed by stirring at room temperature for 10 minutes. Next, a solution of 36.8 g of nickel chloride hexahydrate dissolved in 400 ml of absolute ethanol was added thereto, and the mixture was further stirred at room temperature for 30 minutes. Add 230g of hexadecyltributylphosphonium bromide to this solution at 50°C.
Add the solution dissolved in 300 ml of absolute ethanol.
After the addition was completed, the mixture was further stirred at room temperature for 2 hours, and then the dark green crystals precipitated were filtered, washed first with water and then with ethanol, and air-dried. This was recrystallized from hot ethanol to obtain Exemplified Compound (6). Yield 43
g. Melting point 56-60℃. Reference Example 4 <Synthesis of Exemplified Compound (7)> 36 g of potassium hydroxide was dissolved in 600 ml of absolute ethanol, and 50 g of threene-3,4-dithiol was added to this solution, followed by stirring at room temperature for 10 minutes. Next, a solution of 36.8 g of nickel chloride hexahydrate dissolved in 400 ml of absolute ethanol was added thereto, and the mixture was further stirred at room temperature for 30 minutes. A solution of 127 g of benzyltributylphosphonium bromide dissolved in 360 ml of absolute ethanol is added to this solution at room temperature. After the addition was completed, the mixture was further stirred at room temperature for 2 hours, and then the dark green crystals precipitated were filtered, washed first with water and then with ethanol, and air-dried. This was recrystallized from hot acetone to obtain exemplified compound (7). Yield: 63g. melting point
213-215℃. Other exemplified compounds used in the present invention are also referred to in Reference Example 1.
It could be synthesized in the same manner as 4. Example 1 Exemplified compound (2) 1 part oil-soluble blue dye 0.7 parts ethyl cellosolve 5 parts 1,2-benzisothiazolone (mold inhibitor)
0.001 part Glycerin 3 parts The above ingredients are mixed homogeneously, and the resulting composition is:
It has a specific resistance of 10 ³ Ω・cm and a viscosity of 4 cp. This ink composition was applied to an inkjet recording device, and a good image was obtained, which could be read by a reading device using a semiconductor laser (830 nm) as a light source. Example 2 Isoamyl acetate 7 parts Exemplary compound (2) 0.5 parts Oil-soluble dye (Oil Black HBB) 0.5 parts Metal soap 0.05 parts The above components were mixed homogeneously, and the obtained ink composition had a specific resistance of 10 ⁷ Ω・A good image was obtained by applying it to an inkjet recording device with a viscosity of 5 cp.cm, which could be read by a reading device using a semiconductor laser (830 nm) as a light source. Example 3 Exemplified Compound (3) 1g Nitrocellulose 0.6g Dichloromethane 7ml A solution of the above composition was spin coated on a glass plate and heated at 40°C.
This was dried to obtain a recording layer with a thickness of 0.40 μm. wavelength
Reflectance and absorption at 780nm are respectively
They were 14% and 25%. A semiconductor laser with a wavelength of 780 nm, 4 mW on the irradiation surface, and a beam diameter of 1.6 μm was applied to the recording medium thus obtained.
When the signal was recorded at 1 MHz, a pit with a diameter of 1.0 μm was formed with irradiation for 0.4 μs (1.6 nJ/pit). This recording medium is stored at a temperature of 60℃, indoor light, and a humidity of 90℃.
% for one month, there was no change in the recording and reading characteristics. Example 4 Exemplified Compound (3) 1g Polycarbonate resin 1.0g CI Acid Blue 83 (CI42630) 1.2g 1,2-dichloroethane 20ml A solution of the above composition was spin-coated on a surface-hardened acrylic plate, dried at 60°C to a thickness of 0.4 A recording layer of μm was obtained. The reflectance and absorption at a wavelength of 800 nm were 15% and 19%, respectively. Also the wavelength
Absorption at 630nm is 13% and 60, respectively.
It was %. When a signal was recorded on this recording medium at 0.4 MHz using a semiconductor laser beam with a wavelength of 800 nm and a beam diameter of 1.6 μm at 6 mW on the irradiated surface, a pit with a diameter of 1.0 μm was formed with irradiation for 1.0 μs (6.0 nJ/pit). . In addition, a He-Ne laser was used for this recording medium, with a beam diameter of 1.6 μm and an energy of 5 mW on the recording surface.
When a 4 MHz signal was recorded, a pit with a diameter of 1.0 μm was formed with irradiation for 0.4 μs (1.6 nJ/pit). A storage test was conducted in the same manner as in Example 3, but there was no change in characteristics. Example 5 Exemplified compound (2) 1g Nitrocellulose 0.7g Dichloromethane 20ml A coating solution with the above composition was spin-coated on a glass plate,
It was dried at 0.degree. C. to obtain a recording layer with a thickness of 0.40 .mu.m. wavelength
Reflectance and absorption at 830nm are respectively
They were 15% and 65%. A semiconductor laser with a wavelength of 830 nm, 4 mW on the irradiation surface, and a beam diameter of 1.6 μm was applied to the recording medium thus obtained.
When the signal was recorded at 1 MHz, a pit with a diameter of 1.0 μm was formed with irradiation for 0.3 μs (1.6 nJ/pit). This recording medium is stored at a temperature of 60℃, indoor light, and a humidity of 90℃.
% for one month, there was no change in the recording and reading characteristics. Example 6 Exemplary compound (2) 1g Polycarbonate resin 0.7g CI Acid Blue 83 (CI42630) 1.2g 1,2-dichloroethane 12ml A solution of the above composition was spin-coated onto a surface-hardened acrylic plate, dried at 60°C to a thickness of 0.4 A recording layer of μm was obtained. The reflectance and absorption at a wavelength of 800 nm were 16% and 56%, respectively. Also the wavelength
Absorption at 630nm is 13% and 68 respectively
It was %. When a signal was recorded on this recording medium at 0.4 MHz using a semiconductor laser beam with a wavelength of 830 nm and a beam diameter of 1.6 μm at 6 mW on the irradiated surface, a pit with a diameter of 1.0 μm was formed with irradiation for 0.3 μs (1.8 nJ/pit). . In addition, a He-Ne laser was used for this recording medium, with a beam diameter of 1.6 μm and an energy of 5 mW on the recording surface.
When a 4 MHz signal was recorded, a pit with a diameter of 1.0 μm was formed with irradiation for 0.4 μs (1.6 nJ/pit). A storage test was conducted in the same manner as in Example 5, but there was no change in characteristics. Example 7 A liquid having the following composition was spin-coated onto a polycarbonate disk to obtain a subbing layer with a dry film thickness of 0.1 μm. Cellulose acetate butyrate 0.8 g Acetone 32 ml A liquid containing Exemplified Compound (2) with the following composition: Exemplified Compound (2) 1 g Polyvinyl formal 0.7 g Dichloromethane 10 g was spin-coated to form a recording layer with a dry film thickness of 0.4 μm. I got it. Furthermore, silver is vacuum-deposited on top of this to a thickness of 0.1μ,
A recording medium was prepared, the silver surfaces facing each other, spacers placed in the center and periphery of the discs, and two disc-shaped recording media joined together as a sandwich sandwich to obtain a recording medium. In addition, a wavelength of 830n is applied from the polycarbonate plate side.
A semiconductor laser beam with a beam diameter of 1.6 μm is irradiated at 6 mW on the irradiation surface for 0.7 μs (4.2 nJ/sec)
A pit with a diameter of 0.9 μm was formed. This recording medium was stored for two months at 80°C and 90% indoor light, but there was almost no deterioration in the recording and reading characteristics. Example 8 Exemplified Compound (2) 1.0g Polyvinyl formal 0.7g Dichloromethane 12ml A solution of the above composition was spin coated on a polycarbonate resin plate on which aluminum was vapor-deposited to a thickness of 0.08μm to obtain a light absorption layer with a thickness of 0.6μm. . The reflectance and absorption at a wavelength of 830 nm were 16% and 64%. A semiconductor laser with a wavelength of 830 nm is used for this recording medium, and the irradiation surface energy is 6 mW and the beam diameter is 1.6 μ.
When a 2MHz signal was recorded from the board side with m
Diameter 0.8μm at 0.5μsec irradiation time (3.0nJ/pit)
A pit was formed. Even after this recording medium was stored for one month at 60° C. and 90% humidity, the recording characteristics and the reproduction characteristics of the recorded pits did not deteriorate. Example 9 Nitrocellulose 0.4 g Dichloromethane 10 ml A liquid having the above composition was spin-coated on an acrylic plate to form an undercoat layer, and exemplified compound (2) was vacuum-deposited thereon to obtain a layer with a thickness of 0.2 μm. Gelatin 0.5 to this
Dissolve g in 10ml of water and spin coat it to a thickness of 0.5μ.
A protective layer of m was applied. A laser beam with a wavelength of 830 nm was irradiated from the substrate side in the same manner as in Example 5, and the
A pit with a diameter of 0.9 μm was formed by irradiation for seconds (2.0 nJ/pit). Store this recording medium in room light at a temperature of 60°C.
It was stored for one month at ℃ and 90% humidity, but there was no change in its characteristics. Example 10 2-anilino-3-methyl-6-N-cyclohexyl-N-methylaminofluorane 2.4 parts, 2
2.4 parts of -anilino-3-chloro-6-diethylaminofluorane (coloring agent: leuco dye) and 0.2 parts of Exemplified Compound (3) were dissolved in 24 parts of diisopropylnaphthalene to prepare a solution serving as a core material. Furthermore, 18 parts of xylylene diisocyanate/trimethylolpropane (3:1) adduct and 17 parts of methylene chloride were added and dissolved. Add this coloring agent solution to polyvinyl alcohol.
3.5 parts of gelatin, 1.7 parts of gelatin, and 2.4 parts of 1,4-di(hydroxyethoxy)benzene were added to an aqueous solution of 58 parts of water and emulsified and dispersed at a temperature of 20°C to form an emulsion with an average particle size of 3 μm. Obtained. water in emulsion
100 parts of the mixture was added and heated to 60° C. with stirring, and after 2 hours, a microcapsule liquid containing a color former, a color inhibitor, and an ultraviolet absorber in the core material was obtained. Separately, add 20 parts of bisphenol A as a color developer to 5
% polyvinyl alcohol aqueous solution and dispersed in a sand mill for about 24 hours to obtain a dispersion of bisphenol A with an average diameter of 3 μm. Five parts of the obtained microcapsule liquid and three parts of the bisphenol A dispersion were mixed to prepare a coating liquid.
This coating solution was applied to the surface of smooth high-quality paper (50 g/m ² ) and dried at a temperature of 40° C. for 30 minutes to provide a heat-sensitive recording layer having a dry weight of 7 g/m ² . In this way, a thermosensitive recording sheet A containing microcapsules was produced. Separately, a heat-sensitive recording sheet B was prepared without adding exemplified compound (3). Next, thermal recording was performed using each of the obtained thermal recording sheets. When the thermal recording sheets were loaded into a G-mode thermal printer (Panafax 7200, manufactured by Hitachi, Ltd.) and the thermal head was activated to record heat on the recording sheets, a black color appeared on each thermal recording sheet as shown below. A clear image was obtained. Thermal recording Thermal recording Sheet A Sheet B (With exemplified compound) (Without exemplified compound) Coloring density 1.20 1.09 Coloring (fogging) density 0.11 1.10

Claims (1)

[Claims] 1. General formula (In the formula, R ¹ to ^{R 4} represent an alkyl group or an aryl group, R represents a hydrogen atom or a methyl group, and n
represents an integer from 1 to 4. 1. An infrared absorbing composition (excluding an optical filter material) comprising a quaternary phosphonium bis(1,2-benzenedithiolat)nitschelate derivative represented by ) and a binder.