JP7751787B2 - Water-soluble radical polymerization retarder containing 1,4-dihydroxy-2-naphthoic acid salt - Google Patents

Description

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

Polymerization inhibitors and polymerization retarders are usually used to prevent unintended polymerization during the production, purification, modification, storage, and polymerization of polymerizable monomers. For water-soluble polymerizable monomers, polymerization inhibitors and polymerization retarders that dissolve in the aqueous phase, i.e., water-soluble polymerization inhibitors and polymerization retarders, are used.

Conventionally, known examples of water-soluble polymerization inhibitors such as those described above include hydroquinones (Patent Documents 1 and 2), transition metal salts (Patent Document 3), and piperidine-1-oxyls (Patent Document 4).

Furthermore, Patent Document 5 discloses a radical scavenger having a dihydroxynaphthalene skeleton. This document discloses that naphthohydroquinone compounds, including naphthohydroquinone sulfonate onium salts, have a radical scavenging effect even in the absence of oxygen, and are particularly effective in inhibiting polymerization of monomers. The detailed description and examples state that adding naphthohydroquinone sulfonic acid and its salts to common monomers such as (meth)acrylic acid, (meth)acrylic acid esters, acrylic compounds, aromatic vinyl compounds, and substituted ethylene compounds scavenges and stabilizes the radicals that are generated, effectively preventing or inhibiting polymerization reactions.

However, naphthohydroquinone sulfonate itself is highly corrosive, and because it contains sulfur atoms, there are concerns that when it is burned and disposed of, it will produce harmful sulfur oxides, which could be harmful to the environment and the human body. Furthermore, because it is difficult to remove naphthohydroquinone sulfonate from the water-soluble monomer before polymerization, the polymer contains strong acid components, making it difficult to use in electrical materials, metal coatings, or metal adhesives.

While the document also describes compounds of the present invention having a carboxylate group, it does not provide any examples or working examples of the compounds having a carboxylate group; it simply states that the compounds have a carboxylate group. In general, sulfonate groups and carboxylate groups have extremely different degrees of acid dissociation, and it is believed that the electronic state of the naphthalene ring when the substituent is attached also differs significantly. Therefore, it is unlikely that compounds having a carboxylate group will have the same effect, even if they are exemplified as sulfonate groups.

Furthermore, Patent Document 6 discloses a chain transfer agent having a condensed polycyclic aromatic skeleton, including a compound having a carboxylate group of the present invention. Examples of such an agent 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 this 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 residues 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 electronic state of the naphthalene ring when carboxylic acid dissociates as an anion, or the effect of the anion on radical capture, and this document describes the effects of carboxylic acids and their esters on the same level, so it is unlikely that carboxylic acid anions have the same effect.

This point is also clear from the disclosure in Patent Document 7 that 1,4-dihydroxy-2-naphthoic acid compounds act as photopolymerization sensitizers. The document describes promoting the 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 an onium salt photopolymerization initiator. While the compound is not a water-soluble radically polymerizable compound and the polymerization initiator is different from the initiators of the present invention, the document describes a polymerization-promoting effect rather than a polymerization-retarding effect. The document neither mentions 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.

Japanese Unexamined Patent Publication No. 54-14904 Japanese Patent Application Publication No. 5-320095 Japanese Patent Application Publication No. 10-218832 Japanese Unexamined Patent Publication No. 1-165534 Japanese Patent Application Laid-Open No. 2008-239599 JP 2014-91814 A Japanese Patent Application Laid-Open No. 2017-8269

The object of the present invention is to provide a water-soluble radical polymerization retarder that prevents unintended polymerization of water-soluble monomers.

The inventors have conducted extensive research into naphthalene-based compounds for many years. As a result, they discovered that naphthalene compounds with 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. Specifically, the first invention resides in a water-soluble radical polymerization retarder containing 1,4-dihydroxy-2-naphthoic acid salt represented by the following general formula (1) or (2):

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.

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.

The second invention resides in a radically polymerizable composition containing the water-soluble radical polymerization retarder described in the first invention and a water-soluble monomer.

A third invention resides in the radically polymerizable composition according to the second invention, in which 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).

The fourth invention resides in a radically polymerizable composition characterized by further containing a photopolymerization initiator in addition to the radically polymerizable composition described in the second or third invention.

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.

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

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.

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

In addition, in the present invention, "water-soluble" refers to a substance whose solubility in water is 1 g/100 mL or more at 25°C.

The 1,4-dihydroxy-2-naphthoic acid salts of the present invention represented by the above general formula (1) or (2) have the effect of retarding the radical polymerization of water-soluble monomers, and are useful compounds that function to prevent unintended polymerization in radical polymerization reactions of water-soluble monomers or to level out the heat of polymerization and control runaway reactions.

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. 1 is a graph showing the storage stability of radical polymerization compositions containing monosodium 1,4-dihydroxy-2-naphthoate or disodium 1,4-dihydroxy-2-naphthoate, measured with a rheometer. NMR chart of monosodium 1,4-dihydroxy-2-naphthoate obtained in Synthesis Example 1. NMR chart of disodium 1,4-dihydroxy-2-naphthoate obtained in Synthesis Example 2.

The present invention is described in detail below.

(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 the general formula (1) or (2).

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

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

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.

In general formula (1) or general formula (2), examples of alkali metals represented by Z include sodium and potassium.

Specific examples of compounds 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 monosodium 5-ethyl 1,4-dihydroxy-2-naphthoate. Examples include 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, and monoammonium 6-butyl 1,4-dihydroxy-2-naphthoate.

Specific examples of compounds 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 Examples include dipotassium 1,4-ethyl-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, and diammonium 6-butyl-1,4-dihydroxy-2-naphthoate.

(Method for producing a salt 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 substantially 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, recrystallizing it.

(Water-soluble monomer)
The water-soluble monomer used in the present invention may be any water-soluble monomer. From the viewpoint of being able to fully exert the effects of the water-soluble radical polymerization retarder of the present invention, however, a hydroxyl group- and polar group-containing monomer is preferred. 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.

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

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

(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.

Examples of α-hydroxyalkylphenone-based photoradical polymerization initiators 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).

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, and bis(2,6-dimethylbenzoyl)-ethylphosphine oxide. Commercially available acylphosphine oxide photoradical polymerization initiators include OMNIRADTPO, OMNIRADTPO-L, and OMNIRAD819.

The amount of photopolymerization initiator used in the present invention varies depending on the purpose, but is typically preferably 0.1 to 10 parts by weight, and more preferably 0.2 to 5 parts by weight, per 100 parts by weight of water-soluble monomer.

(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 commercially available water-soluble azo compounds include VA-044, VA-046B, V-50, VA-057, VA-060, VA-061, VA-067, VA-080, and VA-086 (manufactured by Wako Pure Chemical Industries, Ltd.).

The amount of thermal polymerization initiator used in the present invention varies depending on the purpose, but is typically preferably 0.1 to 10 parts by weight, and more preferably 0.2 to 5 parts by weight, per 100 parts by weight of water-soluble monomer.

(Radical polymerizable composition)
The radical 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 radical 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 radical 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 radical polymerizable composition.

Furthermore, other additives may be added as needed, provided they do not impair the effects of the present invention. Examples of additives include antioxidants, hindered amine light stabilizers, UV absorbers, antistatic agents, colorants, mold release agents, polymerization inhibitors, chain transfer agents, fillers, surfactants, plasticizers, dispersants, thixotropic agents, thickeners, and flame retardants.

The present invention will now be described in detail with reference to the following examples, which are presented for illustrative purposes only. In other words, 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, provided that the spirit of the present invention is not exceeded. Furthermore, unless otherwise specified, all parts and percentages are by weight.

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

(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: 30°C constant Measurement atmosphere: air atmosphere

(Photo-DSC measurement)
In this example, the polymerization initiation rate was measured by optical DSC measurement as follows: The DSC measurement device used was an XDSC-7000 manufactured by Hitachi High-Tech Corporation, and an optical DSC measurement unit was attached to it so that DSC measurement could be performed while irradiating light.

The light source used for light irradiation was an LA-410UV manufactured by Hayashi Watch Co., Ltd. The irradiation light was either the full wavelength of a high-pressure mercury lamp or 405 nm light extracted using a bandpass filter. The illuminance of the light was adjusted to 50 mW/ ^cm2 . 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 trigger-controlled so that DSC measurement could be performed simultaneously with the start of light irradiation.

For optical DSC measurements, approximately 1 mg of sample was accurately weighed into an aluminum pan for measurement, placed in the DSC measurement section, and then 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 without modification, and the measurement result for that sample was determined by subtracting the result of the second measurement from the result of the first measurement. Unless otherwise specified, 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 degree of progress of the polymerization reaction can be determined by measuring the total heat generated.

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 measurement 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 taken 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 degree of progress of the polymerization reaction can be determined by measuring the total heat generated.

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 placed in a 10 ml glass sample bottle containing a stirrer, and the mixture was 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 monosodium 1,4-dihydroxy-2-naphthoate. A portion of the solution was then dried at room temperature under a nitrogen atmosphere for 20 hours.

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 placed in a 10 ml glass sample bottle containing a stirrer, and the mixture was 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 disodium 1,4-dihydroxy-2-naphthoate. A portion of the solution was then dried at room temperature under a nitrogen atmosphere for 20 hours.

(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 placed in a 10 ml glass sample bottle containing a stirrer, and the mixture was 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 1,4-dihydroxy-2-naphthoate. A portion of the solution was then dried at room temperature under a nitrogen atmosphere for 20 hours.

To investigate the water solubility of the salts of 1,4-dihydroxy-2-naphthoic acid synthesized in Synthesis Examples 1 to 3, their solubility in deionized water was measured at room temperature (25°C), and they showed a solubility of over 20 g/100 mL.

Example 1 Storage Stability Under Nitrogen A radically polymerizable composition was prepared by adding 4 parts by weight of azobisisobutyronitrile (AIBN), an azo compound, 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 to 100 parts by weight of N-hydroxyethyl methacrylamide (HEMA) as a water-soluble monomer. 9 ml of the sample was placed in a glass bottle, and the air space was replaced with nitrogen, after which 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.

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.

(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.

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-hydroxyethylmethacrylamide (HEMA), and storage stability was measured at an accelerated rate.

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 mixture was nearly completely hardened by the second day. In contrast, under the same conditions, monosodium 1,4-dihydroxy-2-naphthoate and disodium 1,4-dihydroxy-2-naphthoate, the water-soluble radical polymerization retarders of the present invention, did not harden even after 10 days, demonstrating excellent storage stability. In particular, disodium 1,4-dihydroxy-2-naphthoate showed no observed increase in viscosity even after 10 days, demonstrating its extremely excellent storage stability.

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 wt % 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 is marked with a black square and labeled "DHNA-Na 20% aq (10)." No increase in complex viscosity was observed within the measurement time.

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, and the results are shown in Table 2 and Figure 2. In Figure 2, the plot indicated by the black triangle mark "DHNA-2Na 20% aq (10)" shows no increase in complex viscosity during the measurement time.

(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.

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 2,200 seconds under heating conditions of 60°C and was then completely cured. On the other hand, in the examples in which the water-soluble radical polymerization retarders of the present invention, monosodium 1,4-dihydroxy-2-naphthoate and disodium 1,4-dihydroxy-2-naphthoate, were added, no increase in viscosity was observed even after 5,000 seconds, demonstrating their extremely excellent radical polymerization inhibition effect.

Example 5
A radically polymerizable composition was prepared by adding 3 parts by weight of 1-hydroxycyclohexyl phenyl ketone (trade name OMNIRAD184) 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. 1 mg of the radically polymerizable composition was precisely weighed into an aluminum pan for measurement, placed in the DSC measurement section, and then attached to a photo-DSC unit. 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, this is the plot labeled "HEMA + 184 (3) + DHNANa (0.2)."

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 as the solid line "HEMA + 184(3) + DHNA2Na(0.2)."

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 amount of heat generated was measured. The results are shown in Table 3 and plotted in Figure 1. In Figure 1, the dashed line is the plot labeled "HEMA + 184 (3) + DHNANH4 (0.2)."

(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."

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 (2)

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 a 1,4-dihydroxy-2-naphthoate salt represented by the following general formula (1) or (2):

(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.)
(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. 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 ).