Water-soluble radical polymerization retarder containing 1,4-dihydroxy-2-naphthoic acid salt

Abstract

To provide a water-soluble radical polymerization retarder that works in radical polymerization reaction of water-soluble monomers to inhibit unintended polymerization or level out heat of polymerization so as to control runaway reaction.SOLUTION: The water-soluble radical polymerization retarder contains a 1,4-dihydroxy-2-naphthoate represented by the general formula (1) or (2) in the figure, where X represents a hydrogen atom or C1-10 alkyl group, and Z represents alkali metal or ammonium.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Usually, a polymerization inhibitor or a polymerization retarder is used to prevent unintended polymerization during the production, purification, modification, storage, and polymerization of a polymerizable monomer. Among polymerizable monomers, the polymerization inhibitor or polymerization retarder used for a water-soluble monomer is one that dissolves in the aqueous layer, i.e., is water-soluble.

[0003] Conventionally, hydroquinones (Patent Documents 1 and 2), transition metal salts (Patent Document 3), piperidine-1-oxyls (Patent Document 4), and the like have been known as the above-mentioned water-soluble polymerization inhibitors.

[0004] Furthermore, a radical scavenger having a dihydroxynaphthalene skeleton is disclosed in Patent Document 5. This document discloses that naphthohydroquinone compounds, such as naphthohydroquinone sulfonate onium salts, have a radical scavenging effect even in the absence of oxygen, and have an excellent polymerization inhibiting effect on monomers in particular, and in the detailed description and examples, it describes that by adding naphthohydroquinone sulfonic acid and its salts to general monomers such as (meth)acrylic acid, (meth)acrylic acid esters, acrylic compounds, aromatic vinyl compounds, and substituted ethylene compounds, the generated radicals can be eliminated and stabilized, and the polymerization reaction can be prevented or inhibited.

[0005] However, naphthohydroquinone sulfonate itself is highly corrosive and contains sulfur atoms, which may produce harmful sulfur oxides when burned and cause problems for the environment and human health. Furthermore, since it is difficult to remove naphthohydroquinone sulfonate from the water-soluble monomer before polymerization, the polymer contains a strong acid component, making it difficult to use in electrical materials, metal coatings, and metal adhesives.

[0006] Although the document also describes the compound having a carboxylate group of the present invention, it does not provide any examples or working examples of the compound having a carboxylate group, and only states that the compound has a carboxylate group. Generally, sulfonate groups and carboxylate groups have extremely different degrees of acid dissociation, and it is thought that the electronic state of the naphthalene ring when the substituent is attached also differs greatly. Therefore, it is thought that the compound having a carboxylate group, even though it is exemplified as a sulfonate group, does not have the same effect.

[0007] Patent Document 6 discloses a chain transfer agent having a condensed polycyclic aromatic skeleton, including a compound having a carboxylate group according to the present invention. Examples of such agents include 1,4-dihydroxy-2-naphthalenecarboxylic acid, along with its ester compounds, such as 2-methoxycarbonyl-1,4-dihydroxynaphthalene and 2-phenoxycarbonyl-1,4-dihydroxynaphthalene. It also discloses that adding the compound, along with a polymerization initiator, to a radically polymerizable compound such as a typical (meth)acrylic acid, (meth)acrylic acid ester, acrylic compound, aromatic vinyl compound, or substituted ethylene compound can 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, there is no mention of a water-soluble salt of 1,4-dihydroxy-2-naphthalenecarboxylic acid, and 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 influence of the carboxylic acid on the electronic state of the naphthalene ring and the radical capture of the anion when the carboxylic acid is dissociated as an anion. This document describes that carboxylic acids and their esters have the same effects, but it is considered that carboxylic acid anions do not have the same effects.

[0008] This point is also clear from the disclosure in Patent Document 7 that a 1,4-dihydroxy-2-naphthoic acid compound acts as a photopolymerization sensitizer. This document describes the promotion of photopolymerization of a radically polymerizable compound in the presence of 1,4-dihydroxy-2-naphthoic acid and its ester, 1,4-dihydroxy-2-naphthoic acid phenyl, and an onium salt photopolymerization initiator. Although the radically polymerizable compound is not water-soluble and the polymerization initiator is different from the initiator of the present invention, the document describes a polymerization promoting effect rather than a polymerization retarding effect. This document neither describes nor suggests that when 1,4-dihydroxy-2-naphthoic acid becomes a salt, i.e., a carboxylate anion, it exhibits a polymerization retarding effect rather than a polymerization promoting effect. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Publication No. 54-14904 [Patent Document 2] Japanese Patent Application Publication No. 5-320095 [Patent Document 3] Japanese Patent Application Publication No. 10-218832 [Patent Document 4] Japanese Patent Application Publication No. 1-165534 [Patent Document 5] Japanese Patent Application Laid-Open No. 2008-239599 [Patent Document 6] Japanese Patent Application Laid-Open No. 2014-91814 [Patent Document 7] Japanese Patent Application Laid-Open No. 2017-8269 Summary of the Invention [Problem to be solved by the invention]

[0010] An object of the present invention is to provide a water-soluble radical polymerization retarder that prevents the unintended polymerization of water-soluble monomers. [Means for solving the problem]

[0011] The present inventors have conducted extensive research into compounds with a naphthalene skeleton for many years. As a result, they discovered that naphthalene compounds having a specific structure are water-soluble and that these compounds inhibit the polymerization of water-soluble monomers, leading to the completion of the present invention. That is, the first invention resides in a water-soluble radical polymerization retarder containing a 1,4-dihydroxy-2-naphthoate salt represented by the following general formula (1) or (2):

[0012] [ka]

[0013] In the general formula (1), X represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and Z represents an alkali metal or ammonium.

[0014] [ka]

[0015] In the general formula (2), X represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and Z represents an alkali metal or ammonium.

[0016] A second invention resides in a radically polymerizable composition containing the water-soluble radical polymerization retarder according to the first invention and a water-soluble monomer.

[0017] 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).

[0018] The fourth invention resides in a radical polymerizable composition characterized in that the radical polymerizable composition according to the second or third invention further contains a photopolymerization initiator.

[0019] A fifth invention resides in the radically polymerizable composition according to the fourth invention, wherein the photopolymerization initiator is an α-hydroxyalkylphenone-based photopolymerization initiator or an acylphosphine oxide-based photopolymerization initiator.

[0020] A sixth invention resides in a radically polymerizable composition characterized by further containing a thermal polymerization initiator in addition to the radically polymerizable composition according to the second or third invention.

[0021] A seventh invention resides in the radically polymerizable composition according to the sixth invention, characterized in that the thermal polymerization initiator is a water-soluble azo compound.

[0022] In the present invention, "(meth)acrylic" means acrylic or methacrylic, "(meth)acryloyl" means acryloyl or methacryloyl, and "(meth)acrylate" means acrylate or methacrylate, respectively.

[0023] 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]

[0024] The 1,4-dihydroxy-2-naphthoate salt of the present invention represented by the above general formula (1) or (2) has the effect of retarding the radical polymerization of water-soluble monomers, and is a useful compound that has the function of preventing unintended polymerization in the radical polymerization reaction of water-soluble monomers or leveling out the heat of polymerization, thereby controlling a runaway reaction. [Brief explanation of the drawings]

[0025] [Figure 1] 1 is a graph showing the amount of heat generated over time when a radical polymerization composition containing monosodium 1,4-dihydroxy-2-naphthoate or disodium 1,4-dihydroxy-2-naphthoate is irradiated with 405 nm light. [Figure 2] 1 is a graph showing the storage stability of a radical polymerization composition containing monosodium 1,4-dihydroxy-2-naphthoate or disodium 1,4-dihydroxy-2-naphthoate, measured with a rheometer. [Figure 3] NMR chart of monosodium 1,4-dihydroxy-2-naphthoate obtained in Synthesis Example 1. [Figure 4] NMR chart of disodium 1,4-dihydroxy-2-naphthoate obtained in Synthesis Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0026] The present invention will now be described in detail.

[0027] (Water-soluble radical polymerization retarder) The water-soluble radical polymerization retarder of the present invention is a salt of 1,4-dihydroxy-2-naphthoic acid represented by general formula (1) or (2).

[0028] A salt of 1,4-dihydroxy-2-naphthoic acid represented by general formula (1).

[0029] [ka]

[0030] In the general formula (1), X represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and Z represents an alkali metal or ammonium.

[0031] A salt of 1,4-dihydroxy-2-naphthoic acid represented by general formula (2).

[0032] [ka]

[0033] In the general formula (2), X represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and Z represents an alkali metal or ammonium.

[0034] In general formula (1) or (2), examples of the alkyl group having 1 to 10 carbon atoms represented by X 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.

[0035] In the general formula (1) or (2), examples of the alkali metal represented by Z include sodium and potassium.

[0036] Specific examples of the compound represented by general formula (1) include monosodium 1,4-dihydroxy-2-naphthoate, monopotassium 1,4-dihydroxy-2-naphthoate, monoammonium 1,4-dihydroxy-2-naphthoate, monosodium 5-methyl-1,4-dihydroxy-2-naphthoate, monopotassium 5-methyl-1,4-dihydroxy-2-naphthoate, monoammonium 5-methyl-1,4-dihydroxy-2-naphthoate, monosodium 6-methyl-1,4-dihydroxy-2-naphthoate, monopotassium 6-methyl-1,4-dihydroxy-2-naphthoate, monoammonium 6-methyl-1,4-dihydroxy-2-naphthoate, monosodium 5-ethyl 1,4-dihydroxy-2-naphthoate, and monoammonium 5-ethyl 1,4-dihydroxy-2-naphthoate. monopotassium hydroxy-2-naphthoate, monoammonium 5-ethyl 1,4-dihydroxy-2-naphthoate, monosodium 6-ethyl 1,4-dihydroxy-2-naphthoate, monopotassium 6-ethyl 1,4-dihydroxy-2-naphthoate, monoammonium 6-ethyl 1,4-dihydroxy-2-naphthoate, monosodium 5-butyl 1,4-dihydroxy-2-naphthoate, monopotassium 5-butyl 1,4-dihydroxy-2-naphthoate, monoammonium 5-butyl 1,4-dihydroxy-2-naphthoate, monosodium 6-butyl 1,4-dihydroxy-2-naphthoate, monopotassium 6-butyl 1,4-dihydroxy-2-naphthoate, monoammonium 6-butyl 1,4-dihydroxy-2-naphthoate, and the like.

[0037] Specific examples of the compound represented by general formula (1) include disodium 1,4-dihydroxy-2-naphthoate, dipotassium 1,4-dihydroxy-2-naphthoate, diammonium 1,4-dihydroxy-2-naphthoate, disodium 5-methyl-1,4-dihydroxy-2-naphthoate, dipotassium 5-methyl-1,4-dihydroxy-2-naphthoate, diammonium 5-methyl-1,4-dihydroxy-2-naphthoate, disodium 6-methyl-1,4-dihydroxy-2-naphthoate, dipotassium 6-methyl-1,4-dihydroxy-2-naphthoate, diammonium 6-methyl-1,4-dihydroxy-2-naphthoate, disodium 5-ethyl-1,4-dihydroxy-2-naphthoate, and 5-ethyl-1,4-dihydroxy dipotassium 5-ethyl-1,4-dihydroxy-2-naphthoate, diammonium 5-ethyl-1,4-dihydroxy-2-naphthoate, disodium 6-ethyl-1,4-dihydroxy-2-naphthoate, dipotassium 6-ethyl-1,4-dihydroxy-2-naphthoate, diammonium 6-ethyl-1,4-dihydroxy-2-naphthoate, disodium 5-butyl-1,4-dihydroxy-2-naphthoate, dipotassium 5-butyl-1,4-dihydroxy-2-naphthoate, diammonium 5-butyl-1,4-dihydroxy-2-naphthoate, disodium 6-butyl-1,4-dihydroxy-2-naphthoate, dipotassium 6-butyl-1,4-dihydroxy-2-naphthoate, diammonium 6-butyl-1,4-dihydroxy-2-naphthoate, and the like.

[0038] (Method for producing salts of 1,4-dihydroxy-2-naphthoic acid) The salt of 1,4-dihydroxy-2-naphthoic acid of the present invention can be produced by mixing and dissolving a 1,4-dihydroxy-2-naphthoic acid compound and a roughly equivalent amount of the corresponding alkali in a solvent such as deionized water. The resulting aqueous solution of the 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, recrystallization or other repurification.

[0039] (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 water-soluble radical polymerization retarder 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. 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. 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.

[0040] By incorporating the water-soluble radical polymerization retarder of the present invention into the water-soluble monomer, it is possible to prevent unintended polymerization during storage, etc., or during the production process, such as distillation purification, degassing, heating, etc. Furthermore, when the water-soluble monomer is radically polymerized in the presence of a radical polymerization initiator, by incorporating the water-soluble radical polymerization retarder of the present invention, it becomes possible to adjust the radical polymerization initiation time and level out the heat of polymerization.

[0041] The amount of the water-soluble radical polymerization retarder of the present invention to be added varies depending on the purpose, but is usually preferably 0.001 to 10 parts by weight, more preferably 0.01 to 5 parts by weight, per 100 parts by weight of the water-soluble monomer.

[0042] (Photopolymerization initiator) The water-soluble radical polymerization retarder of the present invention can be used together with a photopolymerization initiator to delay the initiation of radical polymerization. The photopolymerization initiator used in the present invention can be any compound that absorbs light energy and generates radical species, but an α-hydroxyalkylphenone-based photopolymerization initiator or an acylphosphine oxide-based photopolymerization initiator is preferred because it can be used to polymerize water-soluble monomers.

[0043] Examples of the α-hydroxyalkylphenone-based photoradical polymerization initiator include 2-hydroxy-2-methyl-1-phenylpropan-1-one (trade name OMNIRAD1173), 1-hydroxycyclohexyl phenyl ketone (trade name OMNIRAD184), 1-[4-(2-hydroxyethoxy)phenyl]-2-hydroxy-2-methyl-1-propan-1-one (trade name OMNIRAD2959), and 2-hydroxy-1-{4-[4-(2-hydroxy-2-methylpropionyl)benzyl]phenyl}-2-methylpropan-1-one (trade name OMNIRAD127).

[0044] Examples of acylphosphine oxide photopolymerization initiators include benzoyl-diphenylphosphine oxide, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, 2,3,5,6-tetramethylbenzoyl-diphenylphosphine oxide, 3,4-dimethylbenzoyl-diphenylphosphine oxide, 2,4,6-trimethylbenzoyl-phenylethoxyphosphine oxide, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, bis(2,6-dimethoxybenzoyl)-2,4,4-trimethyl-pentylphosphine oxide, bis(2,6-dimethylbenzoyl)-ethylphosphine oxide, etc. Commercially available acylphosphine oxide photoradical polymerization initiators include OMNIRADTPO, OMNIRADTPO-L, OMNIRAD819, etc.

[0045] The amount of the photopolymerization 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.

[0046] (thermal polymerization initiator) The water-soluble radical polymerization retarder of the present invention can be used together with a thermal polymerization initiator to delay the initiation of radical polymerization. Examples of the thermal polymerization initiator used in the present invention include water-soluble thermal polymerization initiators and redox polymerization initiators. Examples of the water-soluble thermal polymerization initiator include organic peroxides, hydrogen peroxide, and water-soluble azo compounds. Among these, water-soluble azo compounds are preferred because of their relatively easy handling. Examples of water-soluble azo compounds include 2,2'-azobis(2-methylpropionamidine) dihydrochloride, 2,2'-azobis[2-(2-imidazolin-2-yl)propane]disulfate dihydrate, 2,2'-azobis(2-methylpropionamidine) dihydrochloride, 2,2'-azobis[N-(2-carboxyethyl)-2-methylpropionamidine] tetrahydrate, and 2,2'-azobis[2-{1-(2-hydroxyethyl)-2-isopropyl] ... Examples of water-soluble azo compounds include 2,2'-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride, 2,2'-azobis[2-(2-imidazolin-2-yl)propane], 2,2'-azobis(1-imino-1-pyrrolidino-2-methylpropane) dihydrochloride, 2,2'-azobis[2-methyl-N-{1,1-bis(hydroxymethyl)-2-hydroxyethyl}propionamide], 2,2'-azobis[2-methyl-N-(2-hydroxyethyl)propionamide], etc. Examples of commercially available water-soluble azo compounds include VA-044, VA-046B, V-50, VA-057, VA060, VA-061, VA-067, VA-080, and VA-086 (manufactured by Wako Pure Chemical Industries, Ltd.).

[0047] The amount of the thermal 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.

[0048] (Radical polymerizable composition) The radically polymerizable composition containing the water-soluble radical polymerization retarder 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 solvent is preferred as the organic solvent, a non-water-soluble solvent can also be used as long as it dissolves in the radically polymerizable composition.

[0049] 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. [Example]

[0050] The present invention will be described in detail below with reference to examples, which are presented for illustrative purposes. That is, the following examples are not intended to be exhaustive or to limit the present invention to the precise form described. Therefore, the present invention is not limited to the following examples unless it exceeds the spirit of the present invention. Furthermore, unless otherwise specified, all parts and percentages are by weight.

[0051] (Material Identification) The compounds of the present invention were identified using the following equipment. Nuclear magnetic resonance apparatus (NMR): Manufactured by JEOL, model ECS-400

[0052] (Light curing measurement method) The transition of the complex viscosity of the radical polymerizable composition was measured with a photo-rheometer, and the storage stability was determined from the rate of increase in the viscosity. Measurement conditions: Measurement jig: Parallel plate (φ10 mm) Thickness: 20 μm Swing angle: 5.0% constant Frequency: 10Hz constant Temperature: constant 30℃ Measurement atmosphere: Air

[0053] (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.

[0054] 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.

[0055] 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.

[0056] 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 for measurement 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 the progress of the polymerization reaction can be determined by measuring the total heat generated.

[0057] (Synthesis Example 1) Synthesis of monosodium 1,4-dihydroxy-2-naphthoate 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.

[0058] (Synthesis Example 2) Synthesis of disodium 1,4-dihydroxy-2-naphthoate Under a nitrogen atmosphere, 1.0 g (4.9 mmol) of 1,4-dihydroxy-2-naphthoic acid, 0.43 g (10.8 mmol) of sodium hydroxide, and 4.8 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 disodium salt. A portion of the solution was then dried at room temperature under a nitrogen atmosphere for 20 hours.

[0059] (Synthesis Example 3) Synthesis of ammonium 1,4-dihydroxy-2-naphthoate 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.

[0060] In order to examine the water solubility of the salts of 1,4-dihydroxy-2-naphthoic acid synthesized in Synthesis Examples 1 to 3, the solubility in deionized water was measured at room temperature of 25° C., and the solubility was found to be 20 g / 100 mL or more.

[0061] Example 1 Storage Stability under Nitrogen A radically polymerizable composition was prepared by adding 100 parts by weight of N-hydroxyethyl methacrylamide (HEMA) as a water-soluble monomer, 4 parts by weight of the azo compound azobisisobutyronitrile (AIBN) as a thermal polymerization initiator, and 0.4 parts by weight of monosodium 1,4-dihydroxy-2-naphthoate as a water-soluble radical polymerization retarder. A 9 ml sample was placed in a glass bottle, the air space was purged with nitrogen, and the bottle was sealed and stored. The viscosity of the sample was measured after storage for a certain period of time, and the results are shown in Table 1.

[0062] Example 2 A radically polymerizable composition was prepared in the same manner as in Example 1, except that disodium 1,4-dihydroxy-2-naphthoate was used instead of monosodium 1,4-dihydroxy-2-naphthoate as the water-soluble radical polymerization retarder. 9 ml of the sample was placed in a glass bottle, the air space was purged with nitrogen, and the bottle was sealed and stored. The viscosity of the sample after storage for a certain period of time was measured, and the results are shown in Table 1.

[0063] (Comparative Example 1) A radically polymerizable composition was prepared in the same manner as in Example 1, except that hydroquinone (HQ), which is well known as a radical polymerization inhibitor and has a similar 1,4-dihydroxy structure, was used instead of monosodium 1,4-dihydroxy-2-naphthoate as the water-soluble radical polymerization retarder. 9 ml of the sample was placed in a glass bottle, the air space in the bottle was purged with nitrogen, and the bottle was sealed and stored. The viscosity of the sample after storage for a certain period of time was measured, and the results are shown in Table 1.

[0064] [Table 1]

[0065] In Table 1, "○" indicates that no increase in viscosity was observed, "△" indicates that the viscosity increased slightly, and "×" indicates that the viscosity increased and the material was almost solidified. In this experiment, radical species were intentionally generated by adding the thermal radical polymerization initiator azobisisobutyronitrile (AIBN) to the water-soluble monomer N-hydroxyethyl methacrylamide (HEMA), and the stability during storage was measured at an accelerated rate.

[0066] As is clear from Table 1, in the example where hydroquinone, an existing radical polymerization inhibitor, was added, an increase in viscosity was observed from the first day under these accelerated conditions, and the composition was almost completely hardened by the second day. On the other hand, under the same conditions, monosodium 1,4-dihydroxy-2-naphthoate and disodium 1,4-dihydroxy-2-naphthoate, which are water-soluble radical polymerization retarders of the present invention, did not harden even after 10 days, indicating excellent storage stability. In particular, disodium 1,4-dihydroxy-2-naphthoate did not even show an increase in viscosity even after 10 days, demonstrating extremely excellent storage stability.

[0067] (Example 3) Radical polymerization test by heating A radically polymerizable composition was prepared by adding 0.5 parts by weight of azobisisobutyronitrile (AIBN) as a thermal polymerization initiator and 10 parts by weight of a 20% by weight aqueous solution of monosodium 1,4-dihydroxy-2-naphthoate as a water-soluble radical polymerization retarder to 100 parts by weight of N-hydroxyethyl methacrylamide (HEMA) as a water-soluble monomer. The change in complex viscosity of the sample was measured using a rheometer while heating at 60°C, and the results are shown in Table 2 and Figure 2. In Figure 2, the plot indicated by the black square mark "DHNA-Na20%aq(10)" indicates no increase in complex viscosity during the measurement period.

[0068] Example 4 A radically polymerizable composition was prepared in the same manner as in Example 3, except that a 20 wt % aqueous solution of disodium 1,4-dihydroxy-2-naphthoate was used instead of monosodium 1,4-dihydroxy-2-naphthoate as the water-soluble radical polymerization retarder. The change in complex viscosity of the sample was measured using a rheometer at a gap of 0.02 mm under a nitrogen atmosphere at 60°C. The results are shown in Table 2 and Figure 2. In Figure 2, the plot indicated by the black triangle mark "DHNA-2Na20%aq(10)" shows no increase in complex viscosity during the measurement period.

[0069] (Comparative Example 2) A radically polymerizable composition was prepared in the same manner as in Example 3, except that 10 parts by weight of pure water was used instead of monosodium 1,4-dihydroxy-2-naphthoate as the water-soluble radical polymerization retarder. The change in complex viscosity of the sample was measured using a rheometer at 60°C under a nitrogen atmosphere, and the results are shown in Table 2 and Figure 2. In Figure 2, this is the plot marked with a cross "BLANK(PW(10))." The overlapping dashed line is an auxiliary line drawn to estimate the rise time of the graph.

[0070] [Table 2]

[0071] As is clear from Table 2 and Figure 2, in a blank experiment in which no water-soluble radical polymerization retarder was used, curing began after 2200 seconds under heating conditions at 60°C and was then completely cured. On the other hand, in the examples in which monosodium 1,4-dihydroxy-2-naphthoate and disodium 1,4-dihydroxy-2-naphthoate, which are water-soluble radical polymerization retarders of the present invention, were added, no increase in viscosity was observed even after 5000 seconds, demonstrating an extremely excellent radical polymerization inhibition effect.

[0072] Example 5 A radically polymerizable composition was prepared by adding 3 parts by weight of 1-hydroxycyclohexyl phenyl ketone (OMNIRAD 184) as a photopolymerization initiator to 100 parts by weight of N-hydroxyethyl methacrylamide (HEMA) as a water-soluble monomer, and 0.2 parts by weight of monosodium 1,4-dihydroxy-2-naphthoate as a water-soluble radical polymerization retarder. One milligram of the radically polymerizable composition was precisely weighed into an aluminum pan and placed in the DSC measurement section. The photo-DSC unit was then 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 shown in Table 3 and plotted in Figure 1. In Figure 1, the dashed line represents the plot labeled "HEMA + 184(3) + DHNANa(0.2)."

[0073] Example 6 A radically polymerizable composition was prepared in the same manner as in Example 5, except that disodium 1,4-dihydroxy-2-naphthoate was used instead of monosodium 1,4-dihydroxy-2-naphthoate as the water-soluble radical polymerization retarder, and the amount of heat generated was measured. The results are shown in Table 3 and plotted in Figure 1. In Figure 1, this is the plot indicated by the solid line "HEMA+184(3)+DHNA2Na(0.2)."

[0074] Example 7 A radically polymerizable composition was prepared in the same manner as in Example 5, except that monoammonium 1,4-dihydroxy-2-naphthoate was used instead of monosodium 1,4-dihydroxy-2-naphthoate as the water-soluble radical polymerization retarder, and the heat release rate was measured. The results are shown in Table 3 and plotted in Figure 1. In Figure 1, the dashed line represents the plot labeled "HEMA+184(3)+DHNANH4(0.2)."

[0075] (Comparative Example 3) A radically polymerizable composition was prepared in the same manner as in Example 5, except that monosodium 1,4-dihydroxy-2-naphthoate was not added as a water-soluble radical polymerization retarder, and the amount of heat generated was measured. The results are shown in Table 3 and plotted in Figure 1. In Figure 1, the dotted line is the plot labeled "HEMA+184(3)BLANK."

[0076] [Table 3]

[0077] As is clear from Table 3 and Figure 1, the addition of the water-soluble radical polymerization retarder of the present invention can delay the time at which polymerization starts. In particular, disodium 1,4-dihydroxy-2-naphthoate is highly effective.

Claims

1. A radical polymerizable composition containing a water-soluble radical polymerization retarder, a photopolymerization initiator, and a water-soluble monomer, wherein the photopolymerization initiator is an α-hydroxyalkylphenone-based photopolymerization initiator or an acylphosphine oxide-based photopolymerization initiator, and the water-soluble radical polymerization retarder is 1,4-dihydroxy-2-naphthoic acid salt represented by the following general formula (1) or (2): 【Chemical 1】 (In general formula (1), X represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and Z represents an alkali metal or ammonium.) 【Chemistry 2】 (In general formula (2), X represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and Z represents an alkali metal or ammonium.)

2. 2. The radical polymerizable composition according to claim 1, 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).

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