JPH04245910A - Photothermal converting fiber and photothermal fusible fiber - Google Patents

Abstract

PURPOSE:To obtain fiber, converting near infrared rays in sunlight into heat, having heat insulating and storing properties and capable of instantaneously fusing mutual fibers with the near infrared rays and producing nonwoven fabrics. CONSTITUTION:The following fiber is provided. The fiber is obtained by including a product of reaction between a thiourea derivative and a copper compound as a near infrared ray absorbent in synthetic fiber by a method for mixing diphenylthiourea with copper stearate in a resin such as polyethylene terephthalate, melt spinning the resultant mixture, etc. Furthermore, the fiber is prepared by mixing the product of the reaction between the thiourea derivative with the copper compound as the near infrared absorbent in a resin to be a sheath part of fiber having a sheath-core structure and including the above- mentioned reaction product in the aforementioned sheath part.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to photothermal conversion fibers and photothermal fusion fibers that have the function of absorbing light in the near-infrared region of sunlight and converting it into heat, and utilizes its heat storage and heat retention properties. Winter sports clothing such as ski wear,
It can be used primarily as a material for nonwoven fabrics by utilizing the melt adhesive properties of the fiber surface.

0002

[Prior Art] Heat storage and insulation fibers include fibers with ceramics such as zirconium carbide sealed in the center, fibers with a nylon fabric fused to a film containing zirconium carbide, and fibers coated with zirconium carbide. There is.

[0003] These absorb light in the near-infrared region of sunlight and convert it into heat, while at the same time storing far-infrared rays emitted from the human body as heat inside the clothing.

[0004] However, zirconium carbide, which is the mainstream heat-insulating material, has a deep black color, and fibers containing it have a dark, dull color, so fashionability that requires bright or subtle colors There were some difficulties in using it for clothing that emphasizes.

[0005] In addition, nonwoven fabrics, whose uses have been expanding in recent years, are manufactured through a process of web formation, web adhesion, and finishing.In the spunbond method and the melt blow method, high strength nonwoven fabrics can be obtained by the adhesion that occurs during the web formation process. It will be done. However, webs formed by other methods cannot obtain sufficient strength unless they are bonded again. Methods include dipping or printing adhesive such as latex,
Methods such as a method of dissolving part of the fiber using a solvent, a mechanical method using a needle punch, and a thermal bond method (melt fusion method) are known, but in order to obtain sufficient strength with these methods, However, it requires post-processes such as drying and solvent recovery, and has disadvantages such as crushing the fibers, which impairs functionality and aesthetics.

[0006]

[Problem to be solved by the invention] In view of the above-mentioned current situation, the present inventors have considered the use of a near-infrared absorbing material that is a material that can absorb light and convert it into heat, and has less coloration in the visible region. . However, near-infrared absorbing materials used in optical recording media such as optical disks and electrophotographic photoreceptors do not have sufficient heat resistance to be uniformly incorporated into plastic fibers that are melt-spun by heat. There is no visible coloration, and the amount used is small and the chemical structure is complex, making it expensive, making it unreasonable to use it as an additive to general synthetic fibers. Furthermore, in the near-infrared absorbing materials developed for the above-mentioned applications, there were no fibers with broad absorption in the near-infrared region, and the conversion efficiency was poor because only a specific narrow range of near-infrared rays could be used. .

[0007] Therefore, the present invention focuses on
A photothermal conversion fiber that absorbs uniformly in the entire near-infrared region, has little visible coloring, and has excellent durability, and can be fused with light because it can be bonded in a short time without contact. The challenge was to provide photothermal bondable fibers that could be bonded with light and heat.

[0008]

[Means for Solving the Problems] The object of the present invention is to provide synthetic fibers with the general formula (1)◎

[0009]

[Chemical 3]

(In the formula, R1, R2, R3 are hydrogen,
Represents a monovalent group selected from the group consisting of an alkyl group, a cycloalkyl group, an aralkyl aryl group, and a 5- or 6-membered heterocyclic residue, each group having one or more substituents. R1 and R2 or R2 and R3 may be connected to form a ring).
The present invention has been completed based on the discovery that the problem can be solved by incorporating a reaction product of a certain thiourea derivative and at least one copper compound as a near-infrared absorbing material.

[0011] As the near-infrared absorbing material used in the present invention, all those discovered by the present inventors and disclosed in JP-A-2-3493 can be used, but compounds that can be preferably used in the present invention are can be selected mainly by considering the following conditions.

[0012] A material that fully reacts to become a near-infrared absorbing material at a temperature required in the process of synthesizing resin as a fiber raw material or in the process of fiberizing the obtained synthetic resin. It provides a near-infrared absorbing material that is stable at this reaction temperature. The obtained near-infrared absorbing material is stable over time under normal environmental conditions. Both raw materials and near-infrared absorbing material are highly safe. The resulting near-infrared absorbing material has little coloration in the visible region. Something that has absorption throughout the near-infrared region. Cheap and industrially available. The following compounds can be exemplified as thiourea derivatives that meet these conditions. Thiourea◎ 1-ethylthiourea◎ 1-phenylthiourea◎ 1-m-nitrophenylthiourea◎ 1-p-aminophenylthiourea◎ 1,1-diphenylthiourea◎ 1,3-dimethylthiourea◎ 1,3-dicyclohexylthiourea◎1 ,3-distearylthiourea◎ 1,3-dibehenylthiourea◎ 1,3-diphenylthiourea◎ 1,3-di-m-chlorophenylthiourea◎1,3-
Bis(2-hydroxyethyl)thiourea◎1-methyl-3-p-hydroxyphenylthiourea◎1-ethyl-3-phenylthiourea◎1-ethyl-3-p-chlorophenylthiourea◎1-ethyl-3-(2- Hydroxyethyl)thiourea◎ 1-phenyl-3-p-chlorophenylthiourea◎1
-Phenyl-3-p-methoxyphenylthiourea◎1
-p-hydroxyphenyl-3-phenylthiourea◎ 1-p-bromophenyl-3-phenylthiourea◎1
-p-aminophenyl-3-phenylthiourea◎1-
p-Nitrophenyl-3-phenylthiourea◎1-(
2-thiophenyl)-3-phenylthiourea◎1-(
2-thiazolyl)-3-phenylthiourea◎1,1-
Dibenzyl-3-phenethylthiourea ◎ Ethylenethiourea Further, as preferred copper compounds, the following compounds can be exemplified. Copper stearate, copper palmitate, copper oleate, copper laurate, copper benzoate, copper paratoluate, copper p-tert-butylbenzoate, copper parachlorobenzoate, copper p-phenylbenzoate, o-benzoylbenzoic acid Copper, copper p-nitrobenzoate, copper aminobenzoate, copper diethyldicarbamate, copper alkylbenzenesulfonate, copper p-toluenesulfonate, copper naphthalenesulfonate, copper dodecylbenzenesulfonate. In addition, copper salts of phthalic acid derivatives, which were invented by the present inventors and described in the specification filed as Japanese Patent Application No. 1-250863, can be used. Specifically, the following phthalic acid derivatives can be used. acid (
Preferred examples include copper salts of meth)acryloyl esters. (meth)acryloyloxyethyl copper phthalate ◎(meth)acryloyloxy-2-propyl copper phthalate ◎(meth)acryloyloxy-2-butyl copper phthalate ◎(meth)acryloyloxy-2-acyl phthalate A copper salt near-infrared absorbing material can be easily produced by mixing these thiourea derivatives with a copper compound and reacting the mixture at a temperature of 80°C or higher, preferably 90°C to 300°C. Since normal fiber manufacturing processes include steps at temperatures above this temperature regardless of the spinning method, it is extremely easy to incorporate the near-infrared absorbing material of the present invention into fibers.

[0013] Therefore, in order to incorporate a near-infrared absorbing material into synthetic fibers, the thiourea derivative and the copper compound are added separately or as a mixture during the fiber manufacturing process.
A near-infrared absorbing material obtained by reacting at a temperature of 0° C. or higher or by reacting a thiourea derivative and a copper compound in advance may be simply added at an appropriate point during the fiber manufacturing process. The fiber manufacturing process usually involves the production of raw material resin,
It includes the steps of producing granules such as chips or pellets, spinning, and post-processing, but some of these steps may be omitted.

The spinning process includes wet spinning, dry spinning, melt spinning, and direct spinning, and the present invention can be applied to any of these spinning methods. Among these spinning methods, the melt spinning method of the present invention is easy to use in that a temperature sufficient to generate the near-infrared absorbing material is satisfied without requiring any special steps, and therefore, the raw material resin can also be melt-spun. Those suitable for this method can be preferably used in the present invention.

In this case, either thiourea and the copper compound are contained unreacted in the raw material resin, or granules such as pellets or chips containing a near-infrared absorbing material prepared in advance are melt-spun, or the raw material resin is It is easy to use a method in which thiourea and a copper compound are mixed as they are, or a near-infrared absorbing material prepared in advance is added and mixed in a hopper etc. in which the thiourea and copper compound are melted.

The synthetic resin that can be used in the present invention is not particularly limited as long as it can be made into fibers by the above-mentioned known methods. Materials suitable for wet spinning include aromatic polyamide, acrylic, modacrylic, vinylon, etc. Materials suitable for dry spinning include acrylic, vinyl chloride, vinylon, polyurethane, aromatic polyamide, etc. Examples of the material include nylon, alicyclic polyamide, polyester, vinylidene chloride, polyethylene, polypropylene, and polyurethane.

The polyester polymer is an ordinary fiber-forming polyester, and is not particularly limited, but preferably polyethylene terephthalate, which has terephthalic acid or its ester as the main dicarboxylic acid component and ethylene glycol as the main glycol component. A part of this terephthalic acid or its ester is replaced with a dicarboxylic acid or its ester such as adipic acid or sebacic acid, or an oxycarboxylic acid or its ester such as p-oxybenzoic acid or p-β-oxyethoxybenzoic acid. Alternatively, a part of the ethylene glycol component can be replaced with a glycol such as tetramethyl glycol, 1,4-bis(β-oxyethoxy)benzene, bisglycol ether such as bisphenol A, or polyalkylene glycol.

The addition ratio of the reaction product of the thiourea derivative and the copper compound to the synthetic fiber raw material resin is 0.01 to 20 parts by weight, preferably 0.0 parts by weight per 100 parts by weight of the resin.
It is 5 to 10 parts by weight. The ratio of the thiourea derivative to the copper compound is preferably about 0.01 to 6 copper atoms in the copper compound to 1 sulfur atom in the thiourea derivative, particularly 0.01 to 6 copper atoms in the copper compound.
．． 1 to 3 are preferred.

In addition to the thiourea derivative and the copper compound, the synthetic fiber of the present invention contains an antioxidant, a stabilizer, a dispersion aid, an antibacterial agent,
Modifiers and functional agents such as deodorants, flame retardants, colorants, and ultraviolet absorbers may also be contained.

[0020]Furthermore, the fibers of the present invention may be single fibers or composite fibers, and the cross-sectional shape may be round, hollow, or irregularly shaped. Composite fibers are made of two or more resin components, and depending on how the components are arranged, there are bimetal type (side-by-side type), sheath-and-core type (core-sheath type), kidney type, matrix type, multilayer bonded type, etc. Any type of conjugate fiber known in the art can be utilized as the fiber of the present invention.

[0021] In the case of a composite fiber, it can be made into a photothermal bondable fiber by incorporating a near-infrared absorbing material made of the above-mentioned thiourea and a copper compound into one component having a low melting point.

In the case of a bimetal type or a multilayer bonding type, a near-infrared absorbing material is contained in the component with the lowest melting point that melts to produce adhesive properties, and a sheath-and-core type, kidney type, or matrix type is used. In this case, a resin component that melts at a low melting point to produce adhesive properties is used for the outer layer, and a near-infrared absorbing material is contained in this outer layer component. When this composite fiber is irradiated with light containing enough near-infrared light to melt the surface of the low-melting point component, the near-infrared absorbing material absorbs the near-infrared light and converts it into heat, and the generated heat causes the component resin to melt. Melts and produces adhesive properties.

[0023] Conventional fusing of heat-fusible fibers required direct contact with a heating element or heated air, and in some cases also required pressure, making it impossible to fuse them in a short time without contact. However, the present invention The photothermal fusible fibers can be instantaneously photofused by irradiation from an appropriate light source.

The photofusion fiber of the present invention thus obtained can be effectively used in the production of nonwoven fabrics. In other words, there is no need for special adhesives or pressure equipment to bond fibers together, so there are fewer restrictions on the process, and since the fibers can be fused together without contact, it is bulky and has excellent aesthetics and strength. It becomes a non-woven fabric.

[0025] For example, the photothermal adhesive fibers are fibers of 1 to 8 deniers, and in the case of dry nonwoven fabrics, long cut fibers,
In the case of wet-processed nonwoven fabrics, a shortcut is sufficient. Also,
Using the spunlace method, rayon, polyethylene terephthalate, and pulp can be wet-processed into a nonwoven fabric using a hydroentangling device.

[0026] Non-woven fabrics using photo-bonding fibers are used not only for general purposes such as various filters and facing materials for disposable diapers and sanitary products, but also for medical purposes, futons, quilting padding, etc., where the light-to-heat conversion properties can be effectively utilized. Can be used for

[0027] Also, sheath and core type, kidney type,
Heat retention can be further enhanced by using an infrared emitting substance such as zirconium carbide for the inner component (core) of the matrix-type composite fiber and covering the outside with a polymer containing the near-infrared absorbing material of the present invention.

The same applies to composite fibers containing an infrared radioactive substance in the inner component and light-to-heat converting fibers containing the near-infrared absorbing material of the present invention, or composite fibers made by twisting the fibers together. Can be used. Such fibers are suitable as materials for cold-resistant clothing.

Infrared radioactive substances are conventionally known materials such as carbide ceramics, oxide ceramics, and nitride ceramics, but among them, oxide-based zirconia (ZrO
2), silica (SiO2), and alumina (Al2O3) can be preferably used, but particularly preferred is high-purity zirconia carbide.

[0030] These photothermal conversion fibers and photothermal fusion fibers can be woven or knitted alone or together with general fibers that do not contain near-infrared absorbers to make fabrics or knitted fabrics with good heat retention, or they can be combined with non-woven fabrics. can do.

The light used in the present invention may be sunlight, a halogen lamp, a xenon lamp, a mercury lamp, a laser beam, etc., as long as it includes wavelengths in the near-infrared region.
For photothermal conversion fibers, a relatively weak light source such as sunlight is preferable.
It is desirable to use a strong light source such as a halogen lamp, xenon lamp, mercury lamp, or laser light for the photothermal fused body and fibers.

[0032]

[Action] The near-infrared absorbing material obtained by converting a thiourea derivative into a copper compound and reacting them has no adverse effect on the fiber manufacturing process even if it is included in the fiber manufacturing process, and it also contains a near-infrared absorbing material. It does not adversely affect the physical properties such as the strength of the fibers. The photothermal conversion fiber is a near-infrared absorbing reaction product from a thiourea derivative and a copper compound that absorbs in the wavelength range of 800 to 2600 nm.
The fiber absorbs light in a wide range of near-infrared rays and efficiently converts it into heat, warming the fiber itself, and the photothermal fusion fiber absorbs near-infrared light in the light irradiated by the near-infrared absorbing material. It instantly and efficiently converts into heat, and the generated heat melts some of the fibers and bonds them together. The photothermal fused body and fiber of the present invention are produced by irradiating strong light (light in the near-infrared region), and the near-infrared-absorbing reaction product absorbs the light.
Converts into heat above °C, melts the binder polymer and instantly fuses it. Fibers, films and adhesives are possible.

[0033]

EXAMPLES The present invention will be explained in more detail below using examples. In the following Examples and Comparative Examples, all parts are parts by weight.

Example 1 ◎ 0.4 part of diphenylthiourea and 0.2 part of copper stearate
100 parts of polyethylene terephthalate polymer were blended into an extruder and led to a spinneret device at 28 parts.
Spinning was carried out at 3°C. The spun yarn was air-cooled and oiled according to a conventional method, and then taken off and bundled at 680 m/min. This undrawn yarn was heated at 25°C and 65% R. H. The fibers were seasoned for 20 hours under the following conditions, stretched four times at 90 m/min using a stretching machine, crimped the fibers, cut and spun the resulting fibers, and then produced circular knits. After irradiating this knitted fabric with near-infrared rays using a halogen lamp, the temperature of the fibers and the infrared radiation energy emitted from the fibers were measured to evaluate the photothermal conversion characteristics and infrared radiation characteristics.

Comparative Example 1 ◎ A circular knit for comparison was produced in the same manner as in Example 1 except that 0.4 part of diphenylthiourea and 0.2 part of copper stearate were not added.
Table 1 ◎ Fiber heating temperature Infrared radiant energy ◎
Example 1 23.4°C 0.21m
J/cm2 ◎ Comparative example 1
6.9°C 0.08mJ/cm2
As shown in Table 1, when irradiated with a halogen lamp, the temperature of the fiber is higher than that of the comparative example, the infrared radiant energy is also high, the near-infrared rays are effectively absorbed and converted into heat, and the fiber has an excellent heat retention effect. It shows that.

Fiber temperature measurement method: Instead of sunlight, 30
A 0W halogen lamp was irradiated for 10 seconds from a distance of 20 cm, and a thermoelectron couple sensor installed on the back of the knitted fabric measured the temperature change in the fiber. Infrared radiant energy measurement method:
After irradiating with a halogen lamp for 10 seconds, infrared radiation energy was measured from a position 1 cm from the surface of the irradiated knitted fabric using a laser power energy meter (manufactured by TEMco., LTD.).

Example 2 ◎ In Example 1, thiourea and copper compounds shown in Table 2 were used in place of diphenylthiourea and copper stearate at various blending ratios, and PMMA or the like was used in place of polyethylene terephrate as the fiber polymer. Each circular knitted fabric was produced using the resin shown on the front side and performing the same operation. The heat conversion properties and infrared radiation properties of these knitted fabrics were evaluated in the same manner as in Example 1.

[0038]
Table 2◎ NO Thiourea compound Copper compound Resin Mixing ratio Fiber heating temperature◎ 1 ClPTU STCu
PMMA 0.4:0.1:100 40°C◎ 2 DPTU PTCu
PMMA 0.4:0.1:100 38°C◎ 3 ClPTU STCu
PET 0.3:0.1:100 39
゜C◎ 4 DLTU BACu
HDPE 0.4:0.1:100 37
゜C◎ 5 -
- PMMA 0:0:100
5゜C◎◎ ClPTU: 1,3-di-m-chlorophenylthiourea ◎ DPTU: 1,
3-Diphenylthiourea ◎
ClPTU: 1,3-dilaurylthiourea ◎ STC
u: Copper stearate◎ PTCu: Copper palmitate◎ BACu: Copper benzoate◎
PMMA: Polymethacrylic resin ◎
PET: Polyethylene terephthalate◎
HDPE: High density polyethylene
Example 3 ◎ Two parts of zirconium carbide were mixed with 100 parts of polyethylene terephthalate polymer to form a fiber core composition. The outer sheath material of the fiber was blended with 0.5 parts of diphenylthiourea and 0.3 parts of copper stearate into 100 parts of polyethylene terephrate polymer and fed into an extruder so that the composition was different in the center and outside. The resulting material was introduced into a double spinneret device with a concentric core-sheath structure and spun at 283°C. The spun yarn was air-cooled and oiled according to a conventional method, and then taken off and bundled at 680 m/min. This undrawn yarn is
5°C, 65%R. H. Seasoned for 20 hours under the conditions of The heat conversion properties and infrared radiation properties of the fabric were evaluated in the same manner as in Example 1.

Comparative Example 2 ◎ A comparative fabric was produced in the same manner as in Example 3, except that diphenylthiourea and copper stearate were not added.

[0040]
Table 3 ◎ Fiber heating temperature Infrared radiant energy ◎
Example 3 25.4°C 0.2
7mJ/cm2◎ Comparative example 3
9.8°C 0.13mJ/cm2
As shown in Table 3, the fiber of Example 3 containing the near-infrared absorbing material of the present invention in the sheath portion is different from that of Comparative Example 2 containing no near-infrared absorbing material.
The heating temperature and infrared radiant energy of the fiber were higher than that of the fiber, indicating that the outside of the fiber was first efficiently warmed by light from the outside, and then the inside of the fiber was further kept warm by the infrared radiation of the core. Example 4 ◎ Core component is polyethylene terephthalate polymer 100
In this section, 100 parts of polyethylene, 0.6 parts of diphenylthiourea, and 0.4 parts of copper stearate were mixed as a sheath component and fed to an extruder to form a concentric core-sheath with different compositions in the center and outside. The structure is guided into the double spinneret device 2.
Spun at 83°C. The spun yarn was air-cooled and oiled according to a conventional method, and then taken off and bundled at 680 m/min. This undrawn yarn was heated at 25°C and 65% R. H. Seasoned for 20 hours under the conditions of
The fibers were stretched twice, crimped, and the resulting fibers were cut and spun to produce circular knits. A light-fused fiber with a concentric core-sheath structure containing polyester as a core component was obtained.

When this fiber was irradiated with a strobe flash light of 50.8 WS from a distance of 1 cm, the sheath portion of the fiber instantaneously melted in the portion that was hit by the light, and the sheath portions joined together. The optically fused fibers had an excellent appearance, and a sheet with appropriate bulkiness and strength was obtained.

Comparative example 3
◎Example 4 except that 0.6 parts of diphenylthiourea and 0.4 parts of copper stearate are not added to 100 parts of polyethylene as sheath components.
Comparative fibers were obtained in the same manner. This fiber was irradiated with light in the same manner as in Example 4, but no photofusion occurred.

Example 5 ◎ 0.5 parts of diphenylthiourea in 100 parts of polypropylene
and 0.3 parts of copper stearate are mixed and fed into an extruder and extruded into filaments to form a dry web. This dry web was irradiated with a 500 W halogen lamp for 3 seconds and bonded by photothermal fusion. A nonwoven fabric with superior appearance, bulkiness, etc., was obtained than a nonwoven fabric simply fused during extrusion or subjected to calender pressure and heat treatment.

Comparative Example 4 ◎ In Example 5, 0.5 part of diphenylthiourea and 0.3 part of copper stearate were used as a sheath component and polyethylene 100%
Comparative fibers were obtained in the same manner as in Example 5, except that the fibers were not added. This fiber was irradiated with light in the same manner as in Example 5, but
There was no photofusion at all.

[0045]

Effects of the Invention As described above, the fibers of the present invention contain a reaction product of a thiourea compound and a copper compound in the synthetic fibers, so they are inexpensive, have little coloring, and can absorb near-infrared light when irradiated. It was possible to provide a photothermal conversion fiber that absorbs and converts it into heat and has a heat-retaining effect using the heat, and a photothermal fusion fiber that instantaneously fuses the outside of the fiber with the heat. In addition, when this fiber is used in winter sportswear and swimwear, it not only absorbs near-infrared rays in sunlight to retain heat and store thermal energy, but also by irradiating it with near-infrared light, which is more powerful than the above-mentioned light. Using the heat generated by the conversion, the fibers are instantly fused together, resulting in a highly bulky nonwoven fabric with a unique finish.

Claims

[Claims] Claim 1: The synthetic fiber has the general formula (1)◎ [Formula 1] (wherein R1, R2, and R3 are hydrogen, an alkyl group,
Represents a monovalent group selected from the group consisting of a cycloalkyl group, an aryl group, an aralkyl group, and a 5- or 6-membered heterocyclic residue; each group may have one or more substituents. A reaction product of at least one thiourea derivative selected from R1 and R2 or R2 and R3 may be connected to form a ring) and at least one copper compound is used as a near-infrared absorbing material. Photothermal conversion fiber containing as. 2. The light-to-heat converting fiber according to claim 1, which is prepared by melt-spinning polyester resin, nylon, polyolefin resin, vinylidene chloride resin, and polyurethane. Claim 3: Infrared emissivity at 40°C for wavelengths 6 to 1
A composite material obtained by spinning a synthetic resin containing an infrared radioactive substance having an average infrared radiation characteristic of 70% or more in a 4 μm area and a synthetic resin containing the near-infrared absorbing material according to claim 1. Photothermal conversion fiber. Claim 4: Infrared emissivity at 40°C for wavelengths 6 to 1
A composite obtained by blending or twisting an infrared emitting fiber containing an infrared emitting substance having infrared emitting characteristics of 70% or more on average in a 4 μm area and the photothermal conversion fiber according to claim 1. Photothermal conversion fiber. 5. The fiber raw material has a composite composition of two or more types of synthetic resins, and the near-infrared absorbing material according to claim 1 is contained in the synthetic resin that becomes the outer side when spun. A photothermal bonding fiber. 6. A woven fabric, nonwoven fabric, or knitted fabric using the fibers according to claims 1 to 5. [Claim 7] General formula (1)◎ [Formula 2] (wherein R1, R2, R3 are hydrogen, an alkyl group,
Represents a monovalent group selected from the group consisting of a cycloalkyl group, an aryl group, an aralkyl group, and a 5- or 6-membered ring heterocyclic residue, each group may have one or more substituents,
R1 and R2 or R2 and R3 may be linked to form a ring) and at least one copper compound. A method for producing a light-to-heat converting fiber, which involves kneading and incorporating the near-infrared absorbing composition with a raw material resin for synthetic fibers, and then melt-spinning at a temperature sufficient for the near-infrared absorbing composition to react and become a near-infrared absorbing material. .