Water-soluble photoradical polymerization initiator containing 1,4-dihydroxy-2-naphthoic acid amine salt

Abstract

To provide a compound which is useful as a water-soluble photo-radical polymerization initiator, exhibits activity even for ultraviolet light on long wavelength side of 365 nm or more and also has such a high solubility in water that the solubility in water at 25°C is 10 g / mL or more.SOLUTION: A photo-radical polymerization initiator is provided, containing 1,4-dihydroxy-2-naphthoic acid amine salt represented by the following general formula (1). (In the general formula (1), R1 represents a C1-10 alkyl group or a C1-10 hydroxyalkyl group; R2 and R3 each independently represent H, a C1-10 alkyl group, or a C1-10 hydroxyalkyl group; and X represents H or a C1-10 alkyl group.)SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a water-soluble photoradical polymerization initiator containing a 1,4-dihydroxy-2-naphthoic acid amine salt and a composition thereof. [Background technology]

[0002] Photopolymerization and curing systems are used in a variety of fields as clean curing methods and as fast curing methods because the curing reaction is completed in an extremely short time. For example, they are used in woodworking paints, metal coating materials, screen printing and offset printing inks, dry film resists used on electronic substrates, hologram materials, sealants, overcoats, stereolithography resins, adhesives, and more. They are particularly important in the production of resists that require high resolution and in printing that requires high speeds.

[0003] This photopolymerizable composition is mainly composed of a polymerizable compound and a polymerization initiator that initiates polymerization of the polymerizable compound by ultraviolet irradiation. Polymerization methods include radical polymerization, cationic polymerization, and anionic polymerization, of which radical polymerization has long been the most widely used. Radical polymerization includes thermal radical polymerization and photoradical polymerization. In the case of photoradical polymerization, a photoradical polymerization initiator is usually used together with a radically polymerizable compound, and radicals are generated from the photoradical polymerization initiator by irradiating the compound with energy rays, mainly ultraviolet rays, thereby initiating polymerization of the radically polymerizable compound.

[0004] Photoradical polymerization initiators are classified into intramolecular cleavage type and hydrogen abstraction type. Intramolecular cleavage type photoradical polymerization initiators absorb light of a specific wavelength, cleaving bonds at specific sites, generating radicals at the cleaved sites, which act as polymerization initiating species and initiate polymerization of radically polymerizable compounds. On the other hand, in the case of hydrogen abstraction type photoradical polymerization initiators, the photoradical polymerization initiator absorbs light of a specific wavelength and becomes excited, and the excited species undergo a hydrogen abstraction reaction from surrounding hydrogen donors, generating active radical species, which act as polymerization initiating species and initiate polymerization of radically polymerizable compounds.

[0005] Known intramolecular cleavage type photoradical polymerization initiators include alkylphenone-based photoradical polymerization initiators, aminoalkylphenone-based photoradical polymerization initiators, acylphosphine oxide-based photoradical polymerization initiators, and oxime ester-based photoradical polymerization initiators.

[0006] On the other hand, known hydrogen abstraction type radical polymerization initiators include benzophenone-based radical photopolymerization initiators and thioxanthone-based radical photopolymerization initiators.

[0007] Among these photoradical polymerization initiators, alkylphenone-based photoradical polymerization initiators are environmentally friendly, consisting only of oxygen, carbon, and hydrogen atoms, and do not contain atoms such as nitrogen and phosphorus, which are highly reactive to living organisms and pose safety concerns. These photoradical polymerization initiators have primarily been used with high-pressure mercury lamps (which have an emission spectrum extending to wavelengths shorter than 350 nm) as the energy beam irradiation source. However, with the advent of metal halide lamps and gallium-doped lamps, which emit light with longer wavelengths, alkylphenone-based photoradical polymerization initiators lack sufficient initiation ability in the wavelength range irradiated by high-pressure mercury lamps. Therefore, aminoalkylphenone-based, acylphosphine oxide-based, and even oxime ester-based photoradical polymerization initiators have been developed.

[0008] In recent years, LEDs (light-emitting diodes) have come to be used as the irradiation source in polymerization reactions that use ultraviolet light as an energy ray. Unlike high-pressure mercury lamps, LEDs have the advantage of generating less heat and having a long lifespan, which has led to an acceleration in the development of UV curing technology using LEDs. Typical LEDs are ultraviolet LEDs and blue LEDs. In particular, ultraviolet LEDs have been developed as a UV curing irradiation source for inkjet or semiconductor-related resists. LEDs with central wavelengths of 405nm, 395nm, 385nm, 375nm, and 365nm have been developed. As photoradical polymerization initiators suitable for these wavelengths, among the photoradical polymerization initiators listed above, 2-methyl-1-(4-methylthiophenyl)-2-morpholinopropan-1-one (trade name OMNIRAD907), 2-benzylmethyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1 (trade name OMNIRAD369), 2,4,6-trimethylbenzoyl-diphenylphosphine oxide (trade name OMNIRADDTPO), bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide (trade name OMNIRAD819), and the like are known to be highly sensitive (Patent Document 2).

[0009] However, these photoradical polymerization initiators contain nitrogen, sulfur, or phosphorus atoms as constituent elements in their molecular structures, which makes them highly active against living organisms and often raises safety concerns. Furthermore, photopolymerization initiators containing nitrogen or sulfur atoms can sometimes cause odor problems during operation or in the cured product. Furthermore, yellowing over time has also been noted.

[0010] Currently, photoradical polymerization initiators capable of initiating radical polymerization using LEDs or other devices emitting light in the 350 to 420 nm range are limited to acylphosphine oxide-based photoradical polymerization initiators, some oxime ester-based photoradical polymerization initiators, and thioxanthone-based photoradical polymerization initiators. All of these are limited to compounds containing nitrogen, sulfur, or phosphorus atoms. Few photoradical polymerization initiators active in this wavelength range are known, consisting solely of carbon, hydrogen, and oxygen atoms. In other words, in order to achieve high activity with energy rays containing light in the 350 to 420 nm wavelength range, they must contain nitrogen, sulfur, or phosphorus atoms. Therefore, there is a need for environmentally friendly photoradical polymerization initiators that are highly active with energy rays containing light in the 350 to 420 nm wavelength range and are composed solely of carbon, hydrogen, and oxygen atoms.

[0011] On the other hand, photopolymerizable compositions are generally composed of oil-soluble compounds, and many polymerization initiators are poorly soluble in water; water-soluble polymerization initiators are not widely known. However, with the recent rise in environmental awareness, aqueous photopolymerization systems using water as a solvent have attracted attention in the fields of UV printing inks and inkjet printing, reducing the amount of monomers used due to concerns about sensitization. While many water-soluble monomers are known, most photopolymerization initiators are oil-soluble. Commercially available water-soluble photoinitiators, such as 2-hydroxy-2-methyl-1-(4-hydroxyethoxy)phenylpropan-1-one, have a solubility of only 0.5% by mass in water and also exhibit low light absorption in the range of 365 nm or above, which is the main emission wavelength of high-pressure mercury lamps and the emission wavelength of LEDs, resulting in insufficient photosensitivity (Patent Documents 1 and 2). In this invention, water solubility is defined as a solubility of 1 g or more in 100 ml of water at 25°C, but by that definition, the photopolymerization initiator in question cannot be considered water-soluble.

[0012] Furthermore, acylphosphine oxide compounds are known as photopolymerization initiators that, although not sufficiently soluble in water, have excellent photocuring properties when irradiated with long-wavelength ultraviolet light and are less likely to discolor or discolor. Specifically, 2,4,6-trimethylbenzoyldiphenylphosphine oxide is exemplified (Patent Document 3). However, many phosphine compounds have concerns about their adverse effects on living organisms and the environment, limiting their applications.

[0013] Meanwhile, with regard to the compound having a 1,4-dihydroxy-2-naphthoic acid skeleton of the present invention, Patent Document 4 discloses a chain transfer agent having a condensed polycyclic aromatic skeleton, including the compound having a carboxylate group of the present invention, and lists 1,4-dihydroxy-2-naphthalenecarboxylic acid as an example thereof, along with its ester compounds, 2-methoxycarbonyl-1,4-dihydroxynaphthalene and 2-phenoxycarbonyl-1,4-dihydroxynaphthalene. It also discloses that by adding this compound together with a polymerization initiator to a radically polymerizable compound such as a general (meth)acrylic acid, (meth)acrylic acid ester, acrylic compound, aromatic vinyl compound, or substituted ethylene compound, it is possible to produce a polymer having a residue derived from the chain transfer agent having a condensed polycyclic aromatic skeleton at the end or part of the main chain of the resulting polymer. However, these compounds are poorly soluble in water, and there is no mention of salts of water-soluble 1,4-dihydroxy-2-naphthalenecarboxylic acid. The examples only include an example of adding 1,4-dihydroxy-2-naphthalenecarboxylic acid to methyl methacrylate, but no example of adding the water-soluble compound of the present invention to a water-soluble monomer. It is difficult to imagine the effect of the carboxylic acid dissociated as an anion on the electronic state of the naphthalene ring or the anion's radical scavenging. While this document describes the effects of carboxylic acids and their esters on the same level, it is unlikely that carboxylic acid anions have the same effect. Furthermore, the present invention claims that, among salts of 1,4-dihydroxy-2-naphthalenecarboxylic acid, sodium salts and ammonium salts are ineffective as initiators, and that only the amine salt exhibits photoradical polymerization initiator effects, but there is no mention or suggestion of their specificity.

[0014] Similarly, Patent Document 5 discloses that 1,4-dihydroxy-2-naphthoic acid compounds act as photopolymerization sensitizers, which is also clear from this disclosure. This document describes the promotion of photopolymerization of radically polymerizable compounds in the presence of 1,4-dihydroxy-2-naphthoic acid and its ester, 1,4-dihydroxy-2-naphthoic acid phenyl, and a photopolymerization initiator, an onium salt. Although the radically polymerizable compound is not water-soluble and the polymerization initiator is different from the initiator of the present invention, it is described as having a polymerization-promoting effect. However, the compound described in this document is also poorly soluble in water, and there is no mention of salts of 1,4-dihydroxy-2-naphthalenecarboxylic acid. Furthermore, there is no mention or suggestion of the unique feature of the present invention, in which only the amine salt of 1,4-dihydroxy-2-naphthalenecarboxylic acid exhibits the effect as a photoradical initiator. [Prior art documents] [Patent documents]

[0015] [Patent Document 1] Japanese Patent Application Publication No. 6-228218 [Patent Document 2] International Publication No. 86 / 05778 Brochure [Patent Document 3] Japanese Patent Application Laid-Open No. 2014-185319 [Patent Document 4] Japanese Patent Application Laid-Open No. 2014-91814 [Patent Document 5] Japanese Patent Application Laid-Open No. 2017-8269 Summary of the Invention [Problem to be solved by the invention]

[0016] An object of the present invention is to provide a compound useful as a water-soluble photoradical polymerization initiator, which exhibits activity even with ultraviolet light on the long wavelength side of 365 nm or more, and also has high solubility in water, with a solubility in water of 10 g / mL or more at 25°C. [Means for solving the problem]

[0017] The present inventors have conducted extensive research into compounds with a naphthalene skeleton for many years, and as a result have discovered that naphthalene compounds having a specific structure are water-soluble, and that these compounds generate radical species upon irradiation with light, which initiate the polymerization of water-soluble monomers, thereby completing the present invention.

[0018] That is, the first invention resides in a photoradical polymerization initiator containing an amine salt of 1,4-dihydroxy-2-naphthoic acid represented by the following general formula (1).

[0019] [ka]

[0020] In general formula (1), R 1 represents an alkyl group having 1 to 10 carbon atoms or a hydroxyalkyl group having 1 to 10 carbon atoms, and R 2 , R 3 each independently represents a hydrogen atom, an alkyl group having 1 to 10 carbon atoms or a hydroxyalkyl group having 1 to 10 carbon atoms, and X represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms.

[0021] A second invention resides in a radically polymerizable composition containing the photoradical polymerization initiator according to the first invention and a water-soluble monomer.

[0022] A third invention resides in the radically polymerizable composition according to the second invention, wherein the water-soluble monomer is at least one selected from the group consisting of 2-hydroxyethyl acrylate (2HEA), 6-hydroxyhexyl acrylate (HHA), 4-hydroxybutyl acrylate (4HBA), N-hydroxyethyl acrylamide (HEAA), and N-hydroxyethyl methacrylamide (HEMA).

[0023] A fourth invention resides in a polymerization method for polymerizing the radically polymerizable composition according to the second or third invention by irradiating it with energy rays containing light in the wavelength range of 300 nm to 470 nm.

[0024] A fifth invention resides in the polymerization method according to the fourth invention, wherein the irradiation source of light in the wavelength range of 300 nm to 470 nm is an ultraviolet LED or a semiconductor laser having a center wavelength of 365 nm, 375 nm, 385 nm, 395 nm, or 405 nm.

[0025] In the present invention, "(meth)acrylic" means acrylic or methacrylic, "(meth)acryloyl" means acryloyl or methacryloyl, and "(meth)acrylate" means acrylate or methacrylate, respectively.

[0026] In the present invention, the term "water-soluble" refers to a substance having a solubility in water of 1 g / 100 mL or more at 25°C. [Effects of the Invention]

[0027] The amine salt of 1,4-dihydroxy-2-naphthoic acid represented by the above general formula (1) of the present invention is a useful compound that has extremely high solubility in water and has the function of generating radical species when irradiated with light in the wavelength range of 300 nm to 470 nm, thereby initiating polymerization of water-soluble monomers. [Brief explanation of the drawings]

[0028] [Figure 1] 1 is a graph showing the amount of heat generated over time when a water-soluble radical polymerization composition containing an amine salt of 1,4-dihydroxy-2-naphthoic acid, a sodium salt of 1,4-dihydroxy-2-naphthoic acid, or an ammonium salt of 1,4-dihydroxy-2-naphthoic acid is irradiated with 405 nm light. DETAILED DESCRIPTION OF THE INVENTION

[0029] The present invention will now be described in detail.

[0030] (Photoradical polymerization initiator) The photoradical polymerization initiator of the present invention is an amine salt of 1,4-dihydroxy-2-naphthoic acid represented by general formula (1).

[0031] [ka]

[0032] In general formula (1), R 1 represents an alkyl group having 1 to 10 carbon atoms or a hydroxyalkyl group having 1 to 10 carbon atoms, and R 2 , R 3 each independently represents a hydrogen atom, an alkyl group having 1 to 10 carbon atoms or a hydroxyalkyl group having 1 to 10 carbon atoms, and X represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms.

[0033] In general formula (1), R 1 , R 2 , R 3 Examples of the alkyl group having 1 to 10 carbon atoms represented by the formula (I) include linear, branched, or cyclic alkyl groups such as methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, n-amyl, i-amyl, n-hexyl, n-heptyl, n-octyl, 2-ethylhexyl, n-nonyl, n-decyl, and cyclohexyl. Examples of the hydroxyalkyl group having 1 to 10 carbon atoms include 2-hydroxyethyl, 2-hydroxypropyl, 3-hydroxypropyl, 4-hydroxybutyl, 5-hydroxyamyl, 6-hydroxyhexyl, 7-hydroxyheptyl, 8-hydroxyoctyl, 9-hydroxynonyl, and 10-hydroxydecyl.

[0034] In general formula (1), examples of the alkyl group having 1 to 10 carbon atoms represented by X include linear, branched, and cyclic alkyl groups such as methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, n-amyl, i-amyl, n-hexyl, n-heptyl, n-octyl, 2-ethylhexyl, n-nonyl, n-decyl, and cyclohexyl.

[0035] Specific examples of the compound represented by general formula (1) include salts of 1,4-dihydroxy-2-naphthoic acid such as triethylamine, monoethylamine, diethylamine, trimethylamine, monomethylamine, dimethylamine, ethylenediamine, triethanolamine, tetramethylethylenediamine, pyrrolidine, piperidine, and pyridine; and salts of 1,4-dihydroxy-2-naphthoic acid such as monoethanolamine, diethanolamine, triethanolamine, monopropanolamine, dipropanolamine, tripropanolamine, triisopropanolamine, dimethylethanolamine, diethylethanolamine, dipropylethanolamine, dibutylethanolamine, methyldiethanolamine, ethyldiethanolamine, propyldiethanolamine, butyldiethanolamine, cyclohexyldiethanolamine, aminoethylethanolamine, hydroxyethylpiperidine, hydroxyethylmorpholine, 2-amino-2-methyl-1-propanol, methyldiethanolamine, ethyldiethanolamine, propyldiethanolamine, butyldiethanolamine, and cyclohexyldiethanolamine.Further examples include salts of 5-methyl-1,4-dihydroxy-2-naphthoic acid such as triethylamine, monoethylamine, diethylamine, trimethylamine, monomethylamine, dimethylamine, ethylenediamine, triethanolamine, tetramethylethylenediamine, pyrrolidine, piperidine, and pyridine; and salts of 1,4-dihydroxy-2-naphthoic acid such as monoethanolamine, diethanolamine, triethanolamine, monopropanolamine, dipropanolamine, tripropanolamine, triisopropanolamine, dimethylethanolamine, diethylethanolamine, dipropylethanolamine, dibutylethanolamine, methyldiethanolamine, ethyldiethanolamine, propyldiethanolamine, butyldiethanolamine, cyclohexyldiethanolamine, aminoethylethanolamine, hydroxyethylpiperidine, hydroxyethylmorpholine, 2-amino-2-methyl-1-propanol, methyldiethanolamine, ethyldiethanolamine, propyldiethanolamine, butyldiethanolamine, and cyclohexyldiethanolamine.Examples of the salts of 6-methyl-1,4-dihydroxy-2-naphthoic acid include triethylamine, monoethylamine, diethylamine, trimethylamine, monomethylamine, dimethylamine, ethylenediamine, triethanolamine, tetramethylethylenediamine, pyrrolidine, piperidine, and pyridine; and salts of 1,4-dihydroxy-2-naphthoic acid include monoethanolamine, diethanolamine, triethanolamine, monopropanolamine, dipropanolamine, tripropanolamine, triisopropanolamine, dimethylethanolamine, diethylethanolamine, dipropylethanolamine, dibutylethanolamine, methyldiethanolamine, ethyldiethanolamine, propyldiethanolamine, butyldiethanolamine, cyclohexyldiethanolamine, aminoethylethanolamine, hydroxyethylpiperidine, hydroxyethylmorpholine, 2-amino-2-methyl-1-propanol, methyldiethanolamine, ethyldiethanolamine, propyldiethanolamine, butyldiethanolamine, and cyclohexyldiethanolamine.

[0036] (Method for producing amine salts of 1,4-dihydroxy-2-naphthoic acid) The amine salt of 1,4-dihydroxy-2-naphthoic acid of the present invention can be produced by mixing and dissolving 1,4-dihydroxy-2-naphthoic acid and a roughly equivalent amount of the corresponding amine compound in a solvent such as deionized water. The resulting aqueous solution of the amine salt of 1,4-dihydroxy-2-naphthoic acid can be used as is, or it can be used after evaporating the water solvent to dryness and, if necessary, purifying by recrystallization or the like.

[0037] (Water-soluble monomer) The water-soluble monomer used in the present invention may be any water-soluble monomer, but from the viewpoint of being able to fully exert the effects of the photoradical polymerization initiator of the present invention, a hydroxyl group- and polar group-containing monomer is preferred, and as the hydroxyl group- and polar group-containing monomer, a hydroxyl group- and carboxylic acid group-containing monomer or a hydroxyl group- and amide group-containing monomer is preferred, and specific examples of the hydroxyl group- and carboxylic acid group-containing monomer include 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate, and specific examples of the hydroxyl group- and amide group-containing monomer include N-hydroxyethyl (meth)acrylamide, N-methyl-N-hydroxyethyl (meth)acrylamide, N-hydroxypropyl (meth)acrylamide, and N,N-bishydroxyethyl (meth)acrylamide. Particularly preferred are 2-hydroxyethyl acrylate (2HEA), 6-hydroxyhexyl acrylate (HHA), 4-hydroxybutyl acrylate (4HBA), N-hydroxyethyl acrylamide (HEAA), N-hydroxyethyl methacrylamide (HEMA), and the like.

[0038] The amount of the photoradical polymerization initiator in the present invention varies depending on the purpose, but is usually preferably 0.1 to 10 parts by weight, more preferably 0.2 to 5 parts by weight, per 100 parts by weight of the water-soluble monomer.

[0039] (Radical polymerizable composition) The radically polymerizable composition containing the photoradical polymerization initiator of the present invention may contain, in addition to the water-soluble monomer and polymerization initiator, other polymerizable compounds such as urethane (meth)acrylate. The radically polymerizable composition can be polymerized at a desired rate by irradiating it with light and / or heating it in the presence or absence of an aqueous solvent. In addition to water, the radically polymerizable composition of the present invention may also contain an organic solvent if necessary. While a water-soluble organic solvent is preferred, a non-water-soluble solvent can also be used as long as it dissolves in the photopolymerizable composition.

[0040] The radically polymerizable composition containing the photoradical polymerization initiator of the present invention may further contain a pigment and / or a dye. When a pigment is contained, it may also contain a dispersant therefor.

[0041] Both inorganic and organic pigments can be used as pigments. Examples of inorganic pigments include carbon blacks (CI Pigment Black 7) such as furnace black, lamp black, acetylene black, and channel black, as well as iron oxide and titanium oxide. Examples of organic pigments include azo pigments such as insoluble azo pigments, condensed azo pigments, azo lakes, and chelate azo pigments; polycyclic pigments such as phthalocyanine pigments, perylene and perinone pigments, anthraquinone pigments, quinacridone pigments, dioxane pigments, thioindigo pigments, isoindolinone pigments, and quinophthalone pigments; dye chelates (e.g., basic dye chelates, acid dye chelates, etc.); dye lakes (basic dye lakes, acid dye lakes); nitro pigments, nitroso pigments, aniline black, and daylight fluorescent pigments. These pigments can be used alone or in combination.

[0042] The dye is not particularly limited, and acid dyes, direct dyes, reactive dyes, and basic dyes can be used. The dyes can be used alone or in combination of two or more. Also, pigments and dyes can be used in combination.

[0043] The dispersant for dispersing the pigment is not particularly limited, and examples thereof include pigment dispersions such as polymer dispersants, etc. Specific examples thereof include those containing one or more of polyoxyalkylene polyalkylene polyamines, vinyl polymers and copolymers, acrylic polymers and copolymers, polyesters, polyamides, polyimides, polyurethanes, amino polymers, silicon-containing polymers, sulfur-containing polymers, fluorine-containing polymers, and epoxy resins as the main component.

[0044] Furthermore, other additives may be added as necessary within the range that does not impair the effects of the present invention, such as antioxidants, hindered amine light stabilizers, ultraviolet absorbers, antistatic agents, colorants, mold release agents, polymerization inhibitors, chain transfer agents, fillers, surfactants, plasticizers, dispersants, thixotropy-imparting agents, thickeners, and flame retardants.

[0045] (Polymerization method) A photocured product can be obtained by irradiating the radical polymerizable composition of the present invention with light to polymerize it. When irradiating the photopolymerizable composition with light to polymerize it and photocure it, the radical polymerizable composition can be molded into a film and then photocured, or it can be molded into a block and then photocured. It can also be polymerized in the form of a UV ink, with droplets applied to a substrate. When molded into a film and then photocured, the liquid photopolymerizable composition is applied to a substrate such as a polyester film using a bar coater or the like to a film thickness of 5 to 300 microns. Alternatively, it can be applied to a thinner or thicker film thickness using spin coating or screen printing.

[0046] The coating film made of the radical polymerizable composition thus prepared is irradiated with energy rays (ultraviolet rays) having a wavelength range of 300 nm to 470 nm at 1 to 1000 mW / cm 2A photocured product can be obtained by irradiating the material with light at an intensity of about 1000 nm. Examples of light sources that can be used include high-pressure mercury lamps, ultra-high-pressure mercury lamps, metal halide lamps, xenon lamps, gallium-doped lamps, black lights, 405 nm UV LEDs, 395 nm UV LEDs, 385 nm UV LEDs, 365 nm UV LEDs, semiconductor lasers, blue LEDs, white LEDs, and Fusion's D bulbs and V bulbs. Natural light such as sunlight can also be used. In particular, UV LEDs or semiconductor lasers with central wavelengths of 365 nm, 375 nm, 385 nm, 395 nm, or 405 nm, such as 405 nm UV LEDs, 395 nm UV LEDs, 385 nm UV LEDs, 375 nm UV LEDs, and 365 nm UV LEDs, are characterized by their sensitizing effect even with light in the long wavelength range of 365 nm to 405 nm. Preferred irradiation sources are ultraviolet LEDs or semiconductor lasers with central wavelengths of 365 nm, 375 nm, 385 nm, 395 nm, or 405 nm. [Example]

[0047] Examples of the present invention will be described below, but the present invention is not limited to these examples. In the examples, all "parts" indicate parts by weight.

[0048] <Optical DSC measurement> In this example, the polymerization initiation rate was measured by optical DSC measurement as follows: A Hitachi High-Technologies XDSC-7000 DSC measurement device was used, which was equipped with an optical DSC measurement unit so that DSC measurement could be performed while irradiating light.

[0049] The light source used for light irradiation was the LA-410UV manufactured by Hayashi Tokei Kogyo Co., Ltd. The light was emitted from the full wavelength of a high-pressure mercury lamp or 405 nm light extracted using a bandpass filter. The illuminance of the light was 50 mW / cm. 2 The light from the light source was guided to the top of the sample using a glass fiber, and the shutter of the light source was triggered so that DSC measurement could be performed simultaneously with the start of light irradiation.

[0050] For optical DSC measurements, approximately 1 mg of sample was precisely weighed into an aluminum pan and placed in the DSC measurement section, after which the optical DSC unit was attached. Nitrogen was circulated through the DSC measurement section at a rate of 100 mL / min, and measurements were performed under a nitrogen atmosphere. After the first measurement, the sample was measured again under the same conditions, and the measurement result for that sample was determined by subtracting the second measurement result from the first measurement result. Unless otherwise specified, results were compared in terms of the total heat generated per 1 mg of sample. Since heat is generated as the polymerization reaction progresses, the progress of the polymerization reaction can be determined by measuring the total heat generated.

[0051] Meanwhile, DSC measurements, which are used for thermal analysis, were also carried out. For DSC measurements, approximately 1 mg of sample was precisely weighed out in a nitrogen atmosphere in a sealed aluminum pan and placed in the DSC measurement section. Nitrogen was circulated through the DSC measurement section at a rate of 100 mL / min, and measurements were carried out in a nitrogen atmosphere. Unless otherwise stated, results were compared in terms of the total heat generated per 1 mg of sample. Heat is generated as the polymerization reaction progresses, so measuring the total heat generated makes it possible to determine the progress of the polymerization reaction. Measurements were carried out under temperature conditions, with the temperature rising from 30°C to 170°C at a rate of 5°C / min.

[0052] (Synthesis Example 1) Synthesis of 1,4-dihydroxy-2-naphthoic acid triethanolamine salt Under a nitrogen atmosphere, 1.0 g (4.9 mmol) of 1,4-dihydroxy-2-naphthoic acid, 0.8 g (5.4 mmol) of triethanolamine, and 3.2 g of ion-exchanged water were added to a 20 ml glass sample bottle containing a stir bar and stirred at room temperature. After stirring for 1 hour, it was confirmed that all of the raw materials had dissolved, yielding a dark brown 20% aqueous solution of 1,4-dihydroxy-2-naphthoic acid triethanolamine salt. A portion of the solution was then dried at room temperature under a nitrogen atmosphere for 20 hours.

[0053] (Synthesis Example 2) Synthesis of sodium salt of 1,4-dihydroxy-2-naphthoic acid Under a nitrogen atmosphere, 1.0 g (4.9 mmol) of 1,4-dihydroxy-2-naphthoic acid, 0.22 g (5.5 mmol) of sodium hydroxide, and 4.4 g of ion-exchanged water were added to a 10 ml glass sample bottle containing a stir bar and stirred at room temperature. After stirring for 1 hour, it was confirmed that all of the raw materials had dissolved, yielding a dark brown 20 wt% aqueous solution of 1,4-dihydroxy-2-naphthoic acid monosodium salt. A portion of the solution was then dried at room temperature under a nitrogen atmosphere for 20 hours.

[0054] (Synthesis Example 3) Synthesis of ammonium salt of 1,4-dihydroxy-2-naphthoic acid Under a nitrogen atmosphere, 1.0 g (4.9 mmol) of 1,4-dihydroxy-2-naphthoic acid, 0.38 g (5.6 mmol) of 25% aqueous ammonia, and 3.6 g of ion-exchanged water were added to a 10 ml glass sample bottle containing a stir bar and stirred at room temperature. After stirring for 1 hour, it was confirmed that all of the raw materials had dissolved, yielding a dark brown 20 wt% aqueous solution of ammonium salt of 1,4-dihydroxy-2-naphthoic acid. A portion of the solution was then dried at room temperature under a nitrogen atmosphere for 20 hours.

[0055] Example 1 A radically polymerizable composition was prepared by adding 3 parts by weight of the triethanolamine salt of 1,4-dihydroxy-2-naphthoic acid obtained in Synthesis Example 1 as a photoradical polymerization initiator to 100 parts by weight of N-hydroxyethyl methacrylamide (HEMA) as a water-soluble monomer. 1 mg of the radically polymerizable composition was precisely weighed into an aluminum pan and placed in the DSC measurement section, after which the photo-DSC unit was attached. The sample was irradiated with 405 nm light for 30 minutes under a nitrogen atmosphere. The calorific value was measured, and the results are plotted in Figure 1. In Figure 1, the solid line is the plot labeled "HEMA + DHNA-TEA 3 parts."

[0056] Furthermore, in order to investigate the water solubility of the photoradical polymerization initiator, the solubility of the triethanolamine salt of 1,4-dihydroxy-2-naphthoic acid obtained in Synthesis Example 1 in deionized water was measured at room temperature (25°C), and the solubility was found to be 20 g / 100 mL or more.

[0057] (Comparative Example 1) A radically polymerizable composition was prepared in the same manner as in Example 1, except that 15 parts by weight of a 20 wt % aqueous solution of the sodium salt of 1,4-dihydroxy-2-naphthoic acid obtained in Synthesis Example 2 was used instead of 3 parts by weight of the triethanolamine salt of 1,4-dihydroxy-2-naphthoic acid as the photoradical polymerization initiator. Polymerization was carried out in the same manner as in Example 1, and the amount of heat generated was measured. The results are plotted in Figure 1. In Figure 1, the dotted line is the plot labeled "15 parts of HEMA+DHNANa 20% aqueous solution." Although not shown in the figure, no heat generation was observed after 10 or 20 minutes.

[0058] (Comparative Example 2) A radically polymerizable composition was prepared in the same manner as in Example 1, except that 15 parts by weight of a 20 wt % aqueous solution of the ammonium salt of 1,4-dihydroxy-2-naphthoic acid obtained in Synthesis Example 3 was used instead of 3 parts by weight of the triamine salt of 1,4-dihydroxy-2-naphthoic acid as the photoradical polymerization initiator. Polymerization was carried out in the same manner as in Example 1, and the amount of heat generated was measured. The results are plotted in Figure 1. In Figure 1, the thick dotted line is the plot labeled "HEMA + DHNANH 4 20% aqueous solution 15 parts." Although not shown in the figure, no heat generation was observed after 10 or 20 minutes.

[0059] (Comparative Example 3) A radically polymerizable composition was prepared in the same manner as in Example 1, except that triethanolamine salt of 1,4-dihydroxy-2-naphthoic acid was not added as a photoradical polymerization initiator, and polymerization was carried out in the same manner as in Example 1. The amount of heat generated during polymerization was measured, and the results are shown in Table 1 and plotted in Figure 1. In Figure 1, the dashed line is the plot labeled "HEMABLANK." Although not shown in the figure, no heat generation was observed after 10 minutes or 20 minutes.

[0060] As is clear from Figure 1, by adding the photoradical polymerization initiator of the present invention, polymerization is initiated by irradiation with light of a long wavelength of 405 nm. On the other hand, even with salts having a similar structure, sodium salts and ammonium salts do not undergo polymerization at all, and it can be said that they have no effect of generating radical species by light irradiation.

Claims

1. A photoradical polymerization initiator containing an amine salt of 1,4-dihydroxy-2-naphthoic acid represented by the following general formula (1): 【Chemical 1】 (In general formula (1), R １ represents an alkyl group having 1 to 10 carbon atoms or a hydroxyalkyl group having 1 to 10 carbon atoms, R ２ , R ３ each independently represents a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, or a hydroxyalkyl group having 1 to 10 carbon atoms, and X represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms.

2. A radically polymerizable composition comprising the photoradical polymerization initiator according to claim 1 and a water-soluble monomer.

3. 3. The radical polymerizable composition according to claim 2, wherein the water-soluble monomer is at least one selected from the group consisting of 2-hydroxyethyl acrylate (2HEA), 6-hydroxyhexyl acrylate (HHA), 4-hydroxybutyl acrylate (4HBA), N-hydroxyethyl acrylamide (HEAA), and N-hydroxyethyl methacrylamide (HEMA).

4. A polymerization method for polymerizing the radically polymerizable composition according to claim 2 or 3 by irradiating it with energy rays containing light having a wavelength in the range of 300 nm to 470 nm.

5. 5. The polymerization method according to claim 4, wherein the irradiation source of light in the wavelength range of 300 nm to 470 nm is an ultraviolet LED or semiconductor laser having a center wavelength of 365 nm, 375 nm, 385 nm, 395 nm, or 405 nm.

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