Acid generator

Abstract

To provide an acid generator composed of biomass-derived materials, with non-photosensitivity and biodegradability, available for use in aqueous systems.SOLUTION: The present invention provides an acid generator that contains a cellulose nanofiber with a sulfate ester group as an active ingredient.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to an acid generator, and more particularly to an acid generator containing cellulose nanofibers having sulfate ester groups as an active ingredient. [Background technology]

[0002] Acid generators are used in fields such as photocurable resins, typically coating materials, adhesive materials, and molding materials, and photolithography materials.

[0003] A typical use of an acid generator is as a photopolymerization initiator. For example, Patent Document 1 discloses a photopolymerization initiator that reacts to high-energy rays such as ultraviolet rays, far ultraviolet rays, electron beams, X-rays, excimer lasers, gamma rays, or synchrotron radiation, and reacts with a compound represented by the general formula: HOCH2CH2CF2CF2SO3 - M + (In the formula, M + represents a lithium ion, a sodium ion, a potassium ion, an ammonium ion, or a tetramethylammonium ion. A photoacid generator for a chemically amplified resist material is disclosed, which generates a sulfonic acid represented by the formula:

[0004] Many photocationic polymerization initiators have an onium salt structure of an organic cation and an anion. Compounds in which the organic cation structure is a trivalent sulfonium ion are called sulfonium salts, and since the anion functions as an active species for polymerization, a counter anion of a Bronsted acid is used. Among these, aromatic sulfonium salts are used industrially as photocationic polymerization initiators with excellent stability. When excited by light, aromatic sulfonium salts decompose radically to generate cation radicals. The cation radicals abstract hydrogen from molecules such as monomers present in the system. Ultimately, aromatic sulfides and acids (H + X - The photodecomposition of aromatic sulfonium salts is completed by the formation of the compound (III). The decomposition process of aromatic sulfonium salts is shown below (Non-Patent Document 1).

[0005] [ka]

[0006] For example, Patent Document 2 discloses a composition containing 80% by mass or more of water and 0.1% by mass or more of an onium salt dissolved in the water, the onium salt being represented by the following general formula (I): [ka] The present invention discloses a photoacid generator composition characterized by comprising a sulfonium salt represented by the following formula: [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-7409 [Patent Document 2] Japanese Patent Application Laid-Open No. 2013-234320 [Non-patent literature]

[0008] [Non-Patent Document 1] Toshihiko Murai, "Development of Network Polymers by Photocationic Polymerization with Sulfonium Salts as the Main Component," Journal of Network Polymers, Vol. 40, No. 1, 2019, p. 37 Summary of the Invention [Problem to be solved by the invention]

[0009] From the perspective of reducing VOCs and moving away from petroleum, demand for water-based polymerizable polymers using acids as initiators and water-based cross-linked polymers using acids as initiators will continue to increase in the future.

[0010] However, for example, the photoacid generator disclosed in Patent Document 1 has a hydrophilic group, but also a skeleton containing a fluorine atom and a methylene group, which makes it difficult to disperse in an aqueous medium and makes it difficult to apply to coating agents and adhesives with aqueous compositions. Furthermore, since the photoacid generator is photosensitive, handling requires oblique light management and expensive equipment. Furthermore, the photoacid generator is not biodegradable, which poses a risk if it leaks into the environment.

[0011] Furthermore, the photoacid generator composition of Patent Document 2 is also photosensitive, so handling it requires oblique light management and expensive equipment. Furthermore, the photoacid generator is also not biodegradable, and there is a risk if it leaks into the environment.

[0012] Therefore, an object of the present invention is to provide an acid generator made of a biomass-derived material that is non-photosensitive and biodegradable and can be used in aqueous systems. [Means for solving the problem]

[0013] Due to growing environmental awareness, research aimed at the practical application of biomass-derived materials is underway worldwide. For example, cellulose is a component of plant cell walls and is the largest biomass resource on Earth. When using lignocellulosic biomass such as wood (wood chips, etc.), herbs, coconut shells, and nut shells as raw materials, if the components of cellulose, lignin, and hemicellulose could be fully utilized in industry, it would make a significant contribution to both recycling resource utilization and CO2 fixation.

[0014] Cellulose is attracting attention as a new, environmentally friendly material because it can be converted into nano-sized cellulose (also known as "nanocellulose") such as cellulose nanofibers (also known as "CNF") and cellulose nanocrystals (also known as "CNC"), which, when combined with resin, rubber, and even concrete, can lead to improvements in various physical properties such as strength, flexibility, and elongation.

[0015] As a result of extensive research into providing new uses for such nanocellulose, the inventors discovered that cellulose nanofibers containing sulfate ester groups have the effect of gradually eliminating the sulfate ester groups when thermal energy is applied, thereby generating sulfuric acid (H2SO4), particularly the effect of generating acid during the production of aqueous polymerizable polymers and / or aqueous crosslinked polymers, and thus completed the present invention.

[0016] That is, the gist of the present invention is as follows. (1) An acid generator containing, as an active ingredient, cellulose nanofibers having sulfate ester groups, The cellulose nanofibers have an average fiber width of 1 nm to 1000 nm, The sulfate ester group is represented by the following general formula (I): [ka] (In general formula (I), n is an integer of 1 to 3, and M n+ is an n-valent cation, and the wavy lines are the bonding sites to other atoms.) is expressed as The acid generator. (2) The acid generator according to (1), wherein the amount of sulfur introduced into the cellulose nanofibers due to the sulfate ester groups is 0.3 mmol / g to 3.0 mmol / g relative to the mass of the cellulose nanofibers. (3) The acid generator according to (1) or (2), further comprising one or more salts selected from metal salts and ammonium salts, wherein the content of the salt is 0.002 parts by mass to 10 parts by mass per 100 parts by mass of the cellulose nanofibers. (4) The acid generator according to any one of (1) to (3), further comprising water, the content of the water being 50% by mass or less relative to the total mass of the acid generator. (5) The acid generator according to any one of (1) to (4), further comprising water, the content of the water being 1,000 parts by mass or more per 100 parts by mass of the cellulose nanofibers. (6) The acid generator according to any one of (1) to (5), wherein when the acid generator and water are mixed to prepare an aqueous dispersion in which the concentration of the cellulose nanofibers is 0.3 mass% relative to the total mass of the aqueous dispersion, and the aqueous dispersion is heat-treated at 80°C for 24 hours, the pH of the aqueous dispersion after the heat treatment is reduced by 0.5 to 6.0 from the pH before the heat treatment. (7) The acid generator according to any one of (1) to (6), wherein when the acid generator is mixed with water to prepare an aqueous dispersion in which the concentration of the cellulose nanofibers is 0.3 mass% relative to the total mass of the aqueous dispersion, the viscosity of the aqueous dispersion measured at 2.6 rpm at 25°C is 500 mPa·s or more. (8) The acid generator according to any one of (1) to (7) above, for use in producing an aqueous polymerizable polymer and / or an aqueous crosslinked polymer. [Effects of the Invention]

[0017] The present invention provides an acid generator made of a biomass-derived material that is non-photosensitive and biodegradable and can be used in aqueous systems. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a graph showing the relationship between the amount of sulfur introduced and viscosity in Examples. [Figure 2] 1 is a graph showing the relationship between salt concentration and viscosity in an example. [Figure 3] 3 is a graph showing the salt concentration in FIG. 2 in logarithmic scale. [Figure 4] 1 is a graph showing the relationship between the amount of sulfur introduced and the pH change (pH before heat treatment - pH after heat treatment) in Examples. [Figure 5] 1 is a graph showing the relationship between salt concentration and pH change (pH before heat treatment - pH after heat treatment) in an example. [Figure 6] 6 is a graph showing the salt concentration in FIG. 5 in logarithmic scale. DETAILED DESCRIPTION OF THE INVENTION

[0019] Preferred embodiments of the present invention will now be described in detail. In this specification, the features of the present invention will be described with reference to the accompanying drawings as appropriate. The acid generator of the present invention is not limited to the following embodiments, and can be embodied in various forms including modifications and improvements that can be made by those skilled in the art without departing from the spirit and scope of the present invention.

[0020] In this specification, a range expressed as "a numerical value to a numerical value" means a range including the numerical value. For example, the term "1 nm to 1000 nm" means "1 nm or more and 1000 nm or less," that is, a range from 1 nm to 1000 nm, inclusive.

[0021] The present invention relates to an acid generator containing, as an active ingredient, cellulose nanofibers having sulfate ester groups.

[0022] Here, the acid generator refers to a composition containing a compound that has the property of generating an acid under specific conditions. The acid generator of the present invention is particularly a thermal acid generator that generates an acid upon input of thermal energy.

[0023] Cellulose is a polysaccharide in which glucose units are linked via β-1,4-glycosidic bonds (C6H 10 O5) n It is shown as follows.

[0024] Cellulose nanofibers are fibers made from cellulose.

[0025] The average fiber width (fiber diameter (equivalent circle diameter)) of the cellulose nanofibers is not limited, but is usually 1 nm to 1000 nm, preferably 2 nm to 200 nm. The average fiber length of the cellulose nanofibers is not limited, but is usually 0.05 μm to 6 μm, preferably 0.1 μm to 1 μm.

[0026] The average fiber width and average fiber length are not limited, but can be measured, for example, by using an atomic force microscope (SPM-9700HT, manufactured by Shimadzu Corporation) to measure the fiber width and fiber length of 50 arbitrarily selected fibers and calculating the arithmetic mean value for each.

[0027] Cellulose nanofibers having sulfate ester groups are also called sulfated cellulose nanofibers, and are cellulose nanofibers in which at least one of the OH groups in the cellulose constituting the cellulose nanofibers has been substituted with a sulfate ester group. The sulfate ester groups in cellulose nanofibers having sulfate ester groups are sulfate ester groups represented by the following formula (I):

[0028] [ka] (In general formula (I), n is an integer of 1 to 3, and M n+ is an n-valent cation, and the wavy lines are the bonding sites to other atoms.)

[0029] M in formula (I) n+ Examples of the monovalent to trivalent cations represented by the formula include hydrogen ions, metal ions, and ammonium ions. n+ When - is a divalent or trivalent cation, the cation forms an ionic bond with two or three -OSO3-.

[0030] Examples of metal ions include alkali metal ions, alkaline earth metal ions, transition metal ions, and other metal ions.

[0031] Here, examples of alkali metal ions include lithium ions, sodium ions, potassium ions, rubidium ions, and cesium ions. Examples of alkaline earth metal ions include calcium ions and strontium ions. Examples of transition metal ions include iron ions, nickel ions, palladium ions, copper ions, and silver ions. Examples of other metal ions include beryllium ions, magnesium ions, zinc ions, and aluminum ions.

[0032] The ammonium ion is NH4 + Not only NH4 + Examples include ammonium ions derived from various amines in which one or more hydrogen atoms are replaced by organic groups, such as NH4 + , quaternary ammonium cations, alkanolamine ions, pyridinium ions, etc.

[0033] M n+ In view of high processability, hydrogen ions, sodium ions, potassium ions, calcium ions, or quaternary ammonium cations are preferred as the cations represented by the formula (I). Any one of the above-listed cations may be used alone, or two or more may be used in combination.

[0034] In the cellulose nanofibers of the present invention having sulfate ester groups, the amount of sulfur introduced due to sulfate ester groups is not limited, but is typically 0.3 mmol / g to 3.0 mmol / g, preferably 1.0 mmol / g to 2.9 mmol / g or less, and more preferably 1.3 mmol / g to 2.7 mmol / g or less. The amount of sulfur introduced due to sulfate ester groups in cellulose nanofibers having sulfate ester groups is expressed as the sulfur content (mmol) due to sulfate ester groups per gram of cellulose nanofibers having sulfate ester groups. The amount of sulfur introduced due to sulfate ester groups can be set to any appropriate value within the above range depending on the amount of acid generated by the acid generator. The amount of sulfur introduced due to sulfate ester groups can be set to a desired range by adjusting the concentrations of reagents such as sulfuric acid and sulfamic acid, the amount of pulp relative to the reaction solution, and the reaction time.

[0035] The amount of sulfur introduced into cellulose nanofibers due to sulfate ester groups can be determined, for example, by combustion absorption-ion chromatography (IC). Alternatively, the amount of sulfur introduced into cellulose nanofibers due to sulfate ester groups can also be confirmed by infrared spectroscopy (IR). The amount of sulfur introduced into cellulose nanofibers due to sulfate ester groups can be measured, for example, by the following method.

[0036] Measurement method: Combustion absorption - IC Measurement equipment: ICS-1500 manufactured by Nippon Dionex Co., Ltd. Measurement conditions: 0.01 g of the sample (cellulose nanofibers with sulfate ester groups) was weighed onto a magnetic board and burned in a tube furnace (1350 °C) under an oxygen atmosphere (flow rate: 1.5 L / min). The generated gas components were absorbed in 3% hydrogen peroxide (20 ml) to obtain an absorbed solution. The resulting absorbed solution was diluted to 100 ml with pure water, and the diluted solution was subjected to ion chromatography. The amount of sulfate ions (mmol) per 1 g of cellulose nanofiber was calculated from the measurement results. Note that the detection limit of sulfate ion concentration based on cellulose using this method is 0.009 mmol / g. Therefore, the lower limit of quantification for sulfur content converted from sulfate ion concentration is 0.003 mmol / g. Therefore, cellulose nanofibers with sulfate ester groups and a sulfur content of less than 0.003 mmol / g can be considered unmodified (i.e., not modified by sulfate esterification).

[0037] The cellulose nanofibers of the present invention having sulfate ester groups may have other substituents in addition to the sulfate ester groups. When the cellulose nanofibers having sulfate ester groups have other substituents, the other substituents replace at least one of the OH groups in the cellulose constituting the cellulose nanofibers. Examples of other substituents include, but are not limited to, anionic substituents and their salts, ester groups, ether groups, acyl groups, aldehyde groups, alkyl groups, alkylene groups, aryl groups, and combinations of two or more of these. When two or more other substituents are used in combination, the content ratio of each substituent is not limited. Among the other substituents, anionic substituents and their salts, or acyl groups are preferred from the viewpoint of nano-dispersibility. As the anionic substituents and their salts, carboxyl groups, phosphate ester groups, phosphite ester groups, and xanthate groups are particularly preferred. When the anionic substituent is in the form of a salt, sodium salts, potassium salts, and calcium salts are particularly preferred from the viewpoint of nano-dispersibility. Furthermore, an acetyl group is a particularly preferred acyl group from the viewpoint of nano-dispersibility.

[0038] The average fiber diameter of the cellulose nanofibers having sulfate ester groups of the present invention is equivalent to the fiber diameter of the cellulose nanofibers defined above and is typically in the range of 1 nm to 1,000 nm. The average fiber diameter of the cellulose nanofibers is preferably 2 nm to 200 nm, more preferably 3 nm to 50 nm. If the average fiber diameter is less than 1 nm, performance aspects such as nanofiber strength may be reduced. If the average fiber diameter exceeds 1,000 nm, the large fiber diameter tends to make it difficult for the nanofibers to exhibit their performance. Note that the average fiber diameter is the value obtained by averaging 50 fibers randomly selected from atomic force microscope images, as with the cellulose nanofibers described above. The average fiber width and average fiber length can be set within the desired range by adjusting the concentration of reagents such as sulfuric acid, the amount of pulp relative to the reaction solution, and the reaction time.

[0039] The degree of crystallinity of the cellulose nanofibers having sulfate ester groups of the present invention can depend on the raw cellulose used. For example, cotton cellulose can have a higher intrinsic crystallinity than wood cellulose. That is, the degree of crystallinity of cellulose nanofibers varies depending on the raw cellulose used. However, the degree of crystallinity of cellulose nanofibers determines the performance of the cellulose nanofibers, such as homogenization with lignin-derived substances, processability, heat resistance, and reinforcing effect, and is therefore typically 20% to 99%, preferably 25% to 90%, more preferably 30% to 85%, and even more preferably 35% to 80%. If the degree of crystallinity is lower than 20%, the heat resistance and rigidity of the cellulose nanofibers may decrease.

[0040] An example of the cellulose nanofiber having sulfate ester groups of the present invention is as follows. [ka]

[0041] The method for producing cellulose nanofibers having sulfate ester groups of the present invention can be a method in which cellulose fibers such as pulp are treated with a defibrating solution consisting of dimethyl sulfoxide (DMSO), acetic anhydride, and sulfuric acid. Another method can be a method in which cellulose fibers such as pulp are treated with a defibrating solution prepared by dissolving sulfamic acid, urea, or a urea derivative in a solvent such as water.

[0042] Adjusting the sulfuric acid or sulfamic acid concentration is particularly effective as a factor for changing the amount of sulfur incorporated. When the sulfuric acid or sulfamic acid concentration in the defibration solution is less than 1% by mass, it is easy to adjust the amount of sulfur incorporated to less than 1.0 mmol / g. When the sulfuric acid or sulfamic acid concentration in the defibration solution is 1% to 3% by mass, it is easy to adjust the amount of sulfur incorporated to 1.0 mmol / g to 3.0 mmol / g. Furthermore, if the sulfuric acid or sulfamic acid concentration in the defibration solution is too high, the fiber length of the sulfated CNF tends to be short. Therefore, in order to obtain CNF with a long fiber length, it is effective to not increase the sulfuric acid or sulfamic acid concentration in the defibration solution too much and to extend the reaction time.

[0043] The cellulose nanofibers having sulfate ester groups in the present invention can be cellulose nanofibers having sulfate ester groups known in the art, and their manufacturing methods are also known. For example, the cellulose nanofibers having sulfate ester groups described in JP 2020-41255 A can be used as the cellulose nanofibers having sulfate ester groups.

[0044] The acid generator of the present invention may further contain one or more salts selected from metal salts and ammonium salts.

[0045] In the metal salt, the metal ion may be an alkali metal ion, an alkaline earth metal ion, a transition metal ion, or other metal ion.

[0046] Here, examples of alkali metal ions include lithium ions, sodium ions, potassium ions, rubidium ions, and cesium ions. Examples of alkaline earth metal ions include calcium ions and strontium ions. Examples of transition metal ions include iron ions, nickel ions, palladium ions, copper ions, and silver ions. Examples of other metal ions include beryllium ions, magnesium ions, zinc ions, and aluminum ions. Examples of counter anions to metal ions include anions of organic acids, such as carboxylate ions, for example, acetate ions, anions of inorganic acids, for example, sulfate ions, and halide ions, for example, fluoride ions (F - ), chloride ions (Cl - ), bromide ion (Br - ) and iodide ion (I - , I 3- ) etc.

[0047] In ammonium salts, the ammonium ion is NH4 + Not only NH4 + Examples include ammonium ions derived from various amines in which one or more hydrogen atoms are replaced by organic groups, such as NH4 + , quaternary ammonium cation, alkanolamine ion, pyridinium ion, etc. Counter anions of the ammonium ion include anions of organic acids such as carboxylate ions, for example, acetate ions, anions of inorganic acids such as sulfate ions, halide ions such as fluoride ions, chloride ions, bromide ions, and iodide ions.

[0048] The content of the salt is not limited, but is usually 0.002 to 10 parts by mass, and preferably 0.01 to 0.1 parts by mass, per 100 parts by mass of cellulose nanofibers having sulfate ester groups.

[0049] By including the salt in the above amount in the acid generator of the present invention, the viscosity of the acid generator and the amount of acid generated can be appropriately adjusted.

[0050] The acid generator of the present invention may further contain water.

[0051] The water content is usually 50% by mass or less, and preferably 20% by mass or less, relative to the total mass of the acid generator. Furthermore, the water content is usually 1,000 parts by mass or more, and preferably 5,000 parts by mass or more, relative to 100 parts by mass of the cellulose nanofibers having sulfate ester groups.

[0052] By ensuring that the water content is within the above range, the viscosity can be adjusted by the thickening effect of the cellulose nanofibers during production of the aqueous polymerizable polymer and / or aqueous crosslinked polymer, making it possible to control the degree of diffusion of the generated acid, and therefore an appropriate amount of acid generator can be provided during the production.

[0053] The acid generator of the present invention may further contain one or more additives.

[0054] The additives include various bases.

[0055] The content of the additive is not limited as it varies depending on the intended use of the additive, but is typically 0.001 to 5.0 parts by mass, and preferably 0.01 to 1.0 part by mass, per 100 parts by mass of cellulose nanofibers having sulfate ester groups.

[0056] The form of the acid generator of the present invention is not limited. The acid generator of the present invention may be in any shape, such as a solid or semi-solid form, such as a powder, a spherical, an ellipsoid, or a polygonal shape, or in the form of a dispersion in a solvent, such as water, alcohol, ethylene glycol monobutyl ether, formamide, or a mixture thereof. When alcohol, ethylene glycol monobutyl ether, or formamide is used as the solvent, it is preferable that the acid generator contains 50% by mass or more of water from the viewpoint of uniform dispersion.

[0057] When the acid generator of the present invention is mixed with water to prepare an aqueous dispersion in which the concentration of cellulose nanofibers is 0.3 mass % relative to the total mass of the aqueous dispersion, and the aqueous dispersion is heat-treated at 80°C for 24 hours, the pH of the aqueous dispersion after heat treatment is typically reduced by 0.5 to 6.0, preferably 1.0 to 4.0, from the pH before heat treatment.

[0058] Since the acid generator of the present invention has the above-mentioned pH lowering effect, it can be used as an acid generator during the production of an aqueous polymerizable polymer and / or an aqueous crosslinked polymer.

[0059] When the acid generator of the present invention is mixed with water to prepare an aqueous dispersion in which the concentration of the cellulose nanofibers is 0.3% by mass relative to the total mass of the aqueous dispersion, the viscosity of the aqueous dispersion measured at 2.6 rpm at 25°C is typically 500 mPa s or more, preferably 2,000 mPa s or more. The upper limit of the viscosity is not limited, but is typically 100,000 mPa s, preferably 50,000 mPa s.

[0060] In the production of aqueous polymerizable polymers or aqueous crosslinked polymers, it takes time for the water medium to dry. Therefore, if acid-induced polymerization or crosslinking is initiated and the reaction is completed before the polymer has dried sufficiently, the cured film may become non-uniformly porous. This is because, even after the reaction is completed, the water remaining in the coating film gradually evaporates over time, resulting in the formation of pores in the coating film derived from the remaining water. Therefore, when producing such polymers, particularly in thick films, an acid generator is required that has an acid-generating mechanism that disperses in the water medium during polymerization and crosslinking and gradually releases acid during the drying of the coating film, i.e., the process in which the water gradually dries from the coating film, thereby promoting polymerization and crosslinking.

[0061] For example, the photoacid generator composition of Patent Document 2 is a photoacid generator with an onium salt skeleton. Therefore, although this photoacid generator composition can rapidly generate acid by light energy, it is difficult to gradually release acid over a long period of time. Furthermore, if this photoacid generator composition is used to rapidly photocure a coating film before the water in the medium has sufficiently dried, curing will be completed with water remaining in the coating film. If moisture remains in the coating film, as described above, pores resulting from the remaining water will form in the resulting coating film, resulting in a porous coating. Therefore, this phenomenon is particularly pronounced when forming a thick coating film, which can make it difficult to form the desired dense film.

[0062] The acid generator of the present invention has the above viscosity, which makes it possible to control the diffusion rate of acid during the production of the aqueous polymerizable polymer and / or aqueous crosslinked polymer, thereby adjusting the polymerization rate of the aqueous polymerizable polymer and / or aqueous crosslinked polymer. For example, when the viscosity is increased by the acid generator of the present invention, the polymerization rate can be adjusted to be slow. If the polymerization rate can be adjusted to be slow, it is possible to prevent the coating film from becoming porous, which occurs when the aqueous polymerizable polymer and / or aqueous crosslinked polymer is coated in a thick film and polymerization or crosslinking is completed during drying of the coating film.

[0063] The acid generator of the present invention can be used as a curing agent for coating materials, adhesives, and molding materials of aqueous polymerizable polymers and / or aqueous crosslinked polymers. [Example]

[0064] The present invention will be described in more detail below using examples, but the technical scope of the present invention is not limited to these examples.

[0065] <Method for producing cellulose nanofibers with sulfate ester groups (sulfated CNF)> (Sample 1) 150 g of dimethyl sulfoxide (DMSO), 16.5 g of acetic anhydride, and 3.35 g of sulfuric acid (concentration in defibration solution: 1.97% by mass) were placed in a 300 ml sample bottle and stirred for approximately 30 seconds using a magnetic stirrer at room temperature of 23°C to prepare a defibration solution.

[0066] Next, 5.0 g of softwood kraft pulp (NBKP, manufactured by Nippon Paper Industries Co., Ltd.) was added to the defibrating solution and stirred for an additional 30 minutes at room temperature of 23°C to carry out a sulfuric acid esterification reaction. After stirring, 250 ml of distilled water was added to the cellulose-containing defibrating solution to stop the reaction, and then a 5% by mass aqueous solution of sodium hydroxide was added until the pH reached 7 to neutralize the sulfuric acid in the reaction solution. The supernatant was then removed by centrifugation (speed: 12,000 rpm, centrifugation time: 50 minutes).

[0067] An additional 1350 ml of distilled water and 1350 ml of ethanol were added and stirred until uniformly dispersed, after which the supernatant was removed by centrifugation under the same conditions as above. The same procedure was repeated for a total of three washings. After washing by centrifugation, distilled water was added and the total weight was diluted to 1000 g.

[0068] Next, the mixture was stirred for 3 minutes using a mixer (G5200, manufactured by Biolomix) to obtain a uniform aqueous dispersion of sulfated CNF with a concentration of 0.5% by mass and an incorporated sulfur content of 0.4 mmol / g.

[0069] Next, the obtained aqueous dispersion of sulfated CNF was frozen in a freezer at -18°C for 24 hours, and then dried for 72 hours using a freeze dryer (FDU-2110, manufactured by Tokyo Rikakikai Co., Ltd.) to obtain a dried sulfated CNF with a moisture content of 8%.

[0070] (Sample 2) 150 g of dimethyl sulfoxide (DMSO), 16.5 g of acetic anhydride, and 3.35 g of sulfuric acid (concentration in defibration solution: 1.97% by mass) were placed in a 300 ml sample bottle and stirred for approximately 30 seconds using a magnetic stirrer at room temperature of 23°C to prepare a defibration solution.

[0071] Next, 5.0 g of softwood kraft pulp (NBKP, manufactured by Nippon Paper Industries Co., Ltd.) was added to the defibrating solution and stirred for an additional 2 hours at room temperature of 23°C to carry out a sulfuric acid esterification reaction. After stirring, 250 ml of distilled water was added to the cellulose-containing defibrating solution to stop the reaction, and then a 5% by mass aqueous solution of sodium hydroxide was added until the pH reached 7 to neutralize the sulfuric acid in the reaction solution. The supernatant was then removed by centrifugation (speed: 12,000 rpm, centrifugation time: 50 minutes).

[0072] An additional 1350 ml of distilled water and 1350 ml of ethanol were added and stirred until uniformly dispersed, after which the supernatant was removed by centrifugation under the same conditions as above. The same procedure was repeated for a total of three washings. After washing by centrifugation, distilled water was added and the total weight was diluted to 1000 g.

[0073] Next, the mixture was stirred for 3 minutes using a mixer (G5200, manufactured by Biolomix) to obtain a uniform aqueous dispersion of sulfated CNF with a concentration of 0.5% by mass and an incorporated sulfur content of 1.5 mmol / g.

[0074] Next, the obtained aqueous dispersion of sulfated CNF was frozen in a freezer at -18°C for 24 hours, and then dried for 72 hours using a freeze dryer (FDU-2110, manufactured by Tokyo Rikakikai Co., Ltd.) to obtain a dried sulfated CNF with a moisture content of 5%.

[0075] (Sample 3) 150 g of dimethyl sulfoxide (DMSO), 16.5 g of acetic anhydride, and 3.35 g of sulfuric acid (concentration in defibration solution: 1.97% by mass) were placed in a 300 ml sample bottle and stirred for approximately 30 seconds using a magnetic stirrer at room temperature of 23°C to prepare a defibration solution.

[0076] Next, 5.0 g of softwood kraft pulp (NBKP, manufactured by Nippon Paper Industries Co., Ltd.) was added to the defibrating solution and stirred for an additional 2 hours at room temperature of 23°C to carry out a sulfuric acid esterification reaction. After stirring, 250 ml of distilled water was added to the cellulose-containing defibrating solution to stop the reaction, and then a 5% by mass aqueous solution of sodium hydroxide was added until the pH reached 7 to neutralize the sulfuric acid in the reaction solution. The supernatant was then removed by centrifugation (speed: 12,000 rpm, centrifugation time: 50 minutes).

[0077] An additional 1350 ml of distilled water and 1350 ml of ethanol were added and stirred until uniformly dispersed, after which the supernatant was removed by centrifugation under the same conditions as above. The same procedure was repeated for a total of three washings. After washing by centrifugation, distilled water was added and the total weight was diluted to 1000 g.

[0078] Next, the mixture was stirred for 3 minutes using a mixer (G5200, manufactured by Biolomix) to obtain a uniform aqueous dispersion of sulfated CNF with a concentration of 0.5% by mass and an incorporated sulfur content of 1.5 mmol / g.

[0079] Next, the obtained aqueous dispersion of sulfated CNF was frozen in a freezer at -18°C for 24 hours, and then dried for 24 hours using a freeze dryer (FDU-2110, manufactured by Tokyo Rikakikai Co., Ltd.) to obtain a dried sulfated CNF with a moisture content of 48%.

[0080] (Sample 4) 150 g of dimethyl sulfoxide (DMSO), 16.5 g of acetic anhydride, and 5 g of sulfuric acid (concentration in defibration solution: 2.92% by mass) were placed in a 300 ml sample bottle and stirred for approximately 30 seconds using a magnetic stirrer at room temperature of 23°C to prepare a defibration solution.

[0081] Next, 5.0 g of softwood kraft pulp (NBKP, manufactured by Nippon Paper Industries Co., Ltd.) was added to the defibrating solution and stirred for an additional 2 hours at room temperature of 23°C to carry out a sulfuric acid esterification reaction. After stirring, 250 ml of distilled water was added to the cellulose-containing defibrating solution to stop the reaction, and then a 5% by mass aqueous solution of sodium hydroxide was added until the pH reached 7 to neutralize the sulfuric acid in the reaction solution. The supernatant was then removed by centrifugation (speed: 12,000 rpm, centrifugation time: 50 minutes).

[0082] An additional 1350 ml of distilled water and 1350 ml of ethanol were added and stirred until uniformly dispersed, after which the supernatant was removed by centrifugation under the same conditions as above. The same procedure was repeated for a total of three washings. After washing by centrifugation, distilled water was added and the total weight was diluted to 1000 g.

[0083] Next, the mixture was stirred for 3 minutes using a mixer (G5200, manufactured by Biolomix) to obtain a uniform aqueous dispersion of sulfated CNF with a concentration of 0.5% by mass and an incorporated sulfur content of 2.8 mmol / g.

[0084] Next, the obtained aqueous dispersion of sulfated CNF was frozen in a freezer at -18°C for 24 hours, and then dried for 72 hours using a freeze dryer (FDU-2110, manufactured by Tokyo Rikakikai Co., Ltd.) to obtain a dried sulfated CNF with a moisture content of 6%.

[0085] (Sample 5) 150 g of dimethyl sulfoxide (DMSO), 16.5 g of acetic anhydride, and 3.35 g of sulfuric acid (concentration in defibration solution: 1.97% by mass) were placed in a 300 ml sample bottle and stirred for approximately 30 seconds using a magnetic stirrer at room temperature of 23°C to prepare a defibration solution.

[0086] Next, 5.0 g of softwood kraft pulp (NBKP, manufactured by Nippon Paper Industries Co., Ltd.) was added to the defibrating solution and stirred for an additional 2 hours at room temperature of 23°C to carry out a sulfuric acid esterification reaction. After stirring, 250 ml of distilled water was added to the cellulose-containing defibrating solution to stop the reaction, and then a 5% by mass aqueous solution of sodium hydroxide was added until the pH reached 7 to neutralize the sulfuric acid in the reaction solution. The supernatant was then removed by centrifugation (speed: 12,000 rpm, centrifugation time: 50 minutes).

[0087] Further, 1350 ml of distilled water and 1350 ml of ethanol were added and stirred until uniformly dispersed, and then the supernatant was removed by centrifugation under the same conditions as above. The same procedure was repeated for a total of three washings.

[0088] Next, 100 ml of distilled water was added to the washed solid matter, and the mixture was stirred for 5 minutes with a stirrer to prepare an aqueous dispersion, which was then frozen in a freezer at −18°C for 24 hours and then dried for 72 hours using a freeze dryer (FDU-2110, manufactured by Tokyo Rikakikai Co., Ltd.).

[0089] Next, 5 g of the freeze-dried solid was mixed with 1 g of an aqueous sodium acetate solution and 994 g of distilled water. Here, the aqueous sodium acetate solution was prepared by mixing 10 mg of sodium acetate with 100 g of distilled water.

[0090] Next, the mixture was stirred for 3 minutes using a mixer (G5200, manufactured by Biolomix) to obtain a uniform aqueous dispersion of sulfated CNF with a concentration of 0.5% by mass and an incorporated sulfur content of 1.5 mmol / g.

[0091] Next, the obtained aqueous dispersion of sulfated CNF was dried for 72 hours using a freeze dryer (FDU-2110, manufactured by Tokyo Rikakikai Co., Ltd.) to obtain a dried sulfated CNF with a water content of 3% and containing 0.002% by mass of sodium acetate relative to the sulfated CNF.

[0092] (Sample 6) 150 g of dimethyl sulfoxide (DMSO), 16.5 g of acetic anhydride, and 3.35 g of sulfuric acid (concentration in defibration solution: 1.97% by mass) were placed in a 300 ml sample bottle and stirred for approximately 30 seconds using a magnetic stirrer at room temperature of 23°C to prepare a defibration solution.

[0093] Next, 5.0 g of softwood kraft pulp (NBKP, manufactured by Nippon Paper Industries Co., Ltd.) was added to the defibrating solution and stirred for an additional 2 hours at room temperature of 23°C to carry out a sulfuric acid esterification reaction. After stirring, 250 ml of distilled water was added to the cellulose-containing defibrating solution to stop the reaction, and then a 5% by mass aqueous solution of sodium hydroxide was added until the pH reached 7 to neutralize the sulfuric acid in the reaction solution. The supernatant was then removed by centrifugation (speed: 12,000 rpm, centrifugation time: 50 minutes).

[0094] Further, 1350 ml of distilled water and 1350 ml of ethanol were added and stirred until uniformly dispersed, and then the supernatant was removed by centrifugation under the same conditions as above. The same procedure was repeated for a total of three washings.

[0095] Next, 100 ml of distilled water was added to the washed solid matter, and the mixture was stirred for 5 minutes with a stirrer to prepare an aqueous dispersion, which was then frozen in a freezer at −18°C for 24 hours and then dried for 72 hours using a freeze dryer (FDU-2110, manufactured by Tokyo Rikakikai Co., Ltd.).

[0096] Next, 5 g of the freeze-dried solid was mixed with 1 g of an aqueous sodium acetate solution and 994 g of distilled water. Here, the aqueous sodium acetate solution was prepared by mixing 0.5 g of sodium acetate and 99.5 g of distilled water.

[0097] Next, the mixture was stirred for 3 minutes using a mixer (G5200, manufactured by Biolomix) to obtain a uniform aqueous dispersion of sulfated CNF with a concentration of 0.5% by mass and an incorporated sulfur content of 1.5 mmol / g.

[0098] Next, the obtained aqueous dispersion of sulfated CNF was dried for 72 hours using a freeze dryer (FDU-2110, manufactured by Tokyo Rikakikai Co., Ltd.) to obtain a dried sulfated CNF with a water content of 4% and containing 0.1% by mass of sodium acetate relative to the sulfated CNF.

[0099] (Sample 7) 150 g of dimethyl sulfoxide (DMSO), 16.5 g of acetic anhydride, and 3.35 g of sulfuric acid (concentration in defibration solution: 1.97% by mass) were placed in a 300 ml sample bottle and stirred for approximately 30 seconds using a magnetic stirrer at room temperature of 23°C to prepare a defibration solution.

[0100] Next, 5.0 g of softwood kraft pulp (NBKP, manufactured by Nippon Paper Industries Co., Ltd.) was added to the defibrating solution and stirred for an additional 2 hours at room temperature of 23°C to carry out a sulfuric acid esterification reaction. After stirring, 250 ml of distilled water was added to the cellulose-containing defibrating solution to stop the reaction, and then a 5% by mass aqueous solution of sodium hydroxide was added until the pH reached 7 to neutralize the sulfuric acid in the reaction solution. The supernatant was then removed by centrifugation (speed: 12,000 rpm, centrifugation time: 50 minutes).

[0101] Further, 1350 ml of distilled water and 1350 ml of ethanol were added and stirred until uniformly dispersed, and then the supernatant was removed by centrifugation under the same conditions as above. The same procedure was repeated for a total of three washings.

[0102] Next, 100 ml of distilled water was added to the washed solid matter, and the mixture was stirred for 5 minutes with a stirrer to prepare an aqueous dispersion, which was then frozen in a freezer at −18°C for 24 hours and then dried for 72 hours using a freeze dryer (FDU-2110, manufactured by Tokyo Rikakikai Co., Ltd.).

[0103] Subsequently, 5 g of the freeze-dried solid, 0.4 g of sodium acetate, and 994.6 g of distilled water were mixed.

[0104] Next, the mixture was stirred for 3 minutes using a mixer (G5200, manufactured by Biolomix) to obtain a uniform aqueous dispersion of sulfated CNF with a concentration of 0.5% by mass and an incorporated sulfur content of 1.5 mmol / g.

[0105] Next, the obtained aqueous dispersion of sulfated CNF was dried for 72 hours using a freeze dryer (FDU-2110, manufactured by Tokyo Rikakikai Co., Ltd.) to obtain a dried sulfated CNF with a water content of 6% and containing 8% by mass of sodium acetate relative to the sulfated CNF.

[0106] (Sample 8) 150 g of dimethyl sulfoxide (DMSO), 16.5 g of acetic anhydride, and 3.35 g of sulfuric acid (concentration in defibration solution: 1.97% by mass) were placed in a 300 ml sample bottle and stirred for approximately 30 seconds using a magnetic stirrer at room temperature of 23°C to prepare a defibration solution.

[0107] Next, 5.0 g of softwood kraft pulp (NBKP, manufactured by Nippon Paper Industries Co., Ltd.) was added to the defibrating solution and stirred for an additional 2 hours at room temperature of 23°C to carry out a sulfuric acid esterification reaction. After stirring, 250 ml of distilled water was added to the cellulose-containing defibrating solution to stop the reaction, and then a 5% by mass aqueous solution of sodium hydroxide was added until the pH reached 7 to neutralize the sulfuric acid in the reaction solution. The supernatant was then removed by centrifugation (speed: 12,000 rpm, centrifugation time: 50 minutes).

[0108] Further, 1350 ml of distilled water and 1350 ml of ethanol were added and stirred until uniformly dispersed, and then the supernatant was removed by centrifugation under the same conditions as above. The same procedure was repeated for a total of three washings.

[0109] Next, 100 ml of distilled water was added to the washed solid matter, and the mixture was stirred for 5 minutes with a stirrer to prepare an aqueous dispersion, which was then frozen in a freezer at −18°C for 24 hours and then dried for 72 hours using a freeze dryer (FDU-2110, manufactured by Tokyo Rikakikai Co., Ltd.).

[0110] Next, 5 g of the freeze-dried solid was mixed with 1 g of an aqueous sodium sulfate solution and 994 g of distilled water. Here, the aqueous sodium sulfate solution was prepared by mixing 0.5 g of sodium sulfate and 99.5 g of distilled water.

[0111] Next, the mixture was stirred for 3 minutes using a mixer (G5200, manufactured by Biolomix) to obtain a uniform aqueous dispersion of sulfated CNF with a concentration of 0.5% by mass and an incorporated sulfur content of 1.5 mmol / g.

[0112] Next, the obtained aqueous dispersion of sulfated CNF was dried for 72 hours using a freeze dryer (FDU-2110, manufactured by Tokyo Rikakikai Co., Ltd.) to obtain a dried sulfated CNF with a water content of 8% and containing 0.1% by mass of sodium sulfate relative to the sulfated CNF.

[0113] (Sample 9) 150 g of dimethyl sulfoxide (DMSO), 16.5 g of acetic anhydride, and 3.35 g of sulfuric acid (concentration in defibration solution: 1.97% by mass) were placed in a 300 ml sample bottle and stirred for approximately 30 seconds using a magnetic stirrer at room temperature of 23°C to prepare a defibration solution.

[0114] Next, 5.0 g of softwood kraft pulp (NBKP, manufactured by Nippon Paper Industries Co., Ltd.) was added to the defibrating solution and stirred for an additional 2 hours at room temperature of 23°C to carry out a sulfuric acid esterification reaction. After stirring, 250 ml of distilled water was added to the cellulose-containing defibrating solution to stop the reaction, and then a 5% by mass aqueous solution of sodium hydroxide was added until the pH reached 7 to neutralize the sulfuric acid in the reaction solution. The supernatant was then removed by centrifugation (speed: 12,000 rpm, centrifugation time: 50 minutes).

[0115] Further, 1350 ml of distilled water and 1350 ml of ethanol were added and stirred until uniformly dispersed, and then the supernatant was removed by centrifugation under the same conditions as above. The same procedure was repeated for a total of three washings.

[0116] Next, 100 ml of distilled water was added to the washed solid matter, and the mixture was stirred for 5 minutes with a stirrer to prepare an aqueous dispersion, which was then frozen in a freezer at −18°C for 24 hours and then dried for 72 hours using a freeze dryer (FDU-2110, manufactured by Tokyo Rikakikai Co., Ltd.).

[0117] Next, 5 g of the freeze-dried solid was mixed with 1 g of an aqueous ammonium sulfate solution and 994 g of distilled water. Here, the aqueous ammonium sulfate solution was prepared by mixing 0.5 g of ammonium sulfate with 99.5 g of distilled water.

[0118] Next, the mixture was stirred for 3 minutes using a mixer (G5200, manufactured by Biolomix) to obtain a uniform aqueous dispersion of sulfated CNF with a concentration of 0.5% by mass and an incorporated sulfur content of 1.5 mmol / g.

[0119] Next, the obtained aqueous dispersion of sulfated CNF was dried for 72 hours using a freeze dryer (FDU-2110, manufactured by Tokyo Rikakikai Co., Ltd.) to obtain a dried sulfated CNF with a water content of 4% and containing 0.1% by mass of ammonium sulfate relative to the sulfated CNF.

[0120] (Sample 10) 150 g of dimethyl sulfoxide (DMSO), 16.5 g of acetic anhydride, and 3.35 g of sulfuric acid (concentration in defibration solution: 1.97% by mass) were placed in a 300 ml sample bottle and stirred for approximately 30 seconds using a magnetic stirrer at room temperature of 23°C to prepare a defibration solution.

[0121] Next, 5.0 g of softwood kraft pulp (NBKP, manufactured by Nippon Paper Industries Co., Ltd.) was added to the defibrating solution and stirred for an additional 2 hours at room temperature of 23°C to carry out a sulfuric acid esterification reaction. After stirring, 250 ml of distilled water was added to the cellulose-containing defibrating solution to stop the reaction, and then a 5% by mass aqueous solution of sodium hydroxide was added until the pH reached 7 to neutralize the sulfuric acid in the reaction solution. The supernatant was then removed by centrifugation (speed: 12,000 rpm, centrifugation time: 50 minutes).

[0122] Further, 1350 ml of distilled water and 1350 ml of ethanol were added and stirred until uniformly dispersed, and then the supernatant was removed by centrifugation under the same conditions as above. The same procedure was repeated for a total of three washings.

[0123] Next, 100 ml of distilled water was added to the washed solid matter, and the mixture was stirred for 5 minutes with a stirrer to prepare an aqueous dispersion, which was then frozen in a freezer at −18°C for 24 hours and then dried for 72 hours using a freeze dryer (FDU-2110, manufactured by Tokyo Rikakikai Co., Ltd.).

[0124] Next, 5 g of the freeze-dried solid was mixed with 1 g of an aqueous calcium acetate solution and 994 g of distilled water. Here, the aqueous calcium acetate solution was prepared by mixing 0.5 g of calcium acetate with 99.5 g of distilled water.

[0125] Next, the mixture was stirred for 3 minutes using a mixer (G5200, manufactured by Biolomix) to obtain a uniform aqueous dispersion of sulfated CNF with a concentration of 0.5% by mass and an incorporated sulfur content of 1.5 mmol / g.

[0126] Next, the obtained aqueous dispersion of sulfated CNF was dried for 72 hours using a freeze dryer (FDU-2110, manufactured by Tokyo Rikakikai Co., Ltd.) to obtain a dried sulfated CNF with a water content of 2% and containing 0.1% by mass of calcium acetate relative to the sulfated CNF.

[0127] (Sample 11) 0.13 mmol of 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO) and 10 mmol of sodium bromide were dissolved in water to obtain a 250 mL aqueous solution. 5 g of absolute dry softwood kraft pulp (NBKP, manufactured by Nippon Paper Industries Co., Ltd.) was added to this solution and stirred until the pulp was uniformly dispersed. After the mixture was cooled to 20°C, 32 mmol of aqueous sodium hypochlorite solution (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added to initiate the oxidation reaction. During the reaction, the temperature of the reaction system was maintained at 20°C, and the pH was maintained at 10 by gradually adding 3N aqueous sodium hydroxide solution. After the reaction was allowed to proceed for 3 hours, the resulting product was filtered through a glass filter, and the filter cake was thoroughly washed with water. This yielded oxidized pulp.

[0128] Ion-exchanged water was added to the oxidized pulp to adjust the solids concentration of the slurry to 0.5% by mass. The slurry was then processed three times at 140 MPa using an ultra-high-pressure homogenizer to obtain an aqueous dispersion of TEMPO-oxidized CNF. The resulting aqueous dispersion of CNF was then frozen in a freezer at -18°C for 24 hours. The dispersion was then placed in a freeze dryer (FDU-2110, Tokyo Rikakikai) and dried for 72 hours to obtain dried TEMPO-oxidized CNF with a moisture content of 5%.

[0129] (Sample 12) A phosphorylating reagent was prepared by dissolving 5 g of urea, 2.8 g of sodium dihydrogen phosphate dihydrate, and 2.1 g of disodium hydrogen phosphate in 5.5 g of water.

[0130] A dry sheet of softwood kraft pulp (NBKP, manufactured by Nippon Paper Industries Co., Ltd.) was processed using a cutter mill and a pin mill to obtain cotton-like fibers. A phosphate reagent was sprayed evenly onto 5 g of cotton-like fibers (bone-dry mass) and the fibers were kneaded by hand to obtain impregnated pulp. The impregnated pulp was then heat-treated for 80 minutes in a damper-equipped air dryer heated to 140°C. This process yielded phosphorylated pulp.

[0131] 500 mL of ion-exchanged water was added to 5 g of phosphorylated pulp and stirred until uniformly dispersed, and the dispersion was then filtered and dehydrated. The resulting sheet was stirred with 500 mL of ion-exchanged water until uniformly dispersed, and the dispersion was then filtered and dehydrated. The resulting sheet was treated once more in the same manner. Next, while stirring the resulting sheet and 500 mL of ion-exchanged water, 1 N aqueous sodium hydroxide solution was added little by little to obtain a pulp slurry with a pH of 12 to 13. This pulp slurry was dehydrated to obtain a sheet. The sheet was stirred with 500 mL of ion-exchanged water until uniformly dispersed, and the dispersion was then filtered and dehydrated. The resulting sheet was treated twice more in the same manner. The resulting sheet was mixed with ion-exchanged water to obtain a slurry containing 0.5 mass% phosphorylated pulp.

[0132] A slurry containing 0.5% by mass of phosphorylated pulp was defibrated for 180 minutes at 6,900 rpm using a defibration treatment device (Clearmix-11S, manufactured by M-Technique Co., Ltd.). Subsequently, ion-exchanged water was added to adjust the solids concentration of the slurry to 0.5% by mass, yielding an aqueous dispersion of phosphorylated CNF.

[0133] The resulting aqueous dispersion of CNF was then frozen in a freezer at −18°C for 24 hours, and then placed in a freeze dryer (FDU-2110, manufactured by Tokyo Rikakikai) and dried for 72 hours to obtain a phosphate-esterified CNF dry product.

[0134] (Sample 13: Photoacid generator described in JP 2013-234320 A) As a photoacid generator, exemplified compound 1 described in JP-A-2013-234320 is used. [ka] Sample 13 was prepared by the method described in Synthesis Example 1 of JP-A-2013-234320.

[0135] The amount of sulfur introduced into Samples 1 to 10 was determined using an infrared spectrometer (Nicolet iS 5N FT-IR, manufactured by Thermo Fisher Science) and an organic elemental analyzer (EA-3100, manufactured by JASCO).

[0136] The moisture content (%) of Samples 1 to 12 was measured in accordance with JIS P 8203. That is, the moisture content (%) was calculated based on the following formula. Moisture content (%) = ((mass of sample - mass of solids of sample) / mass of sample) x 100 (In the formula, the sample mass refers to the mass (g) of the sample used for measurement, i.e., the mass of the dried CNFs, and the solid mass of the sample refers to the solid matter remaining after drying an amount of the sample equivalent to that used for measurement in an atmosphere at 105°C for 2 hours until it reaches a constant mass, i.e., the mass (g) of the dried CNFs after drying them at 105°C for 2 hours until they reach a constant mass.)

[0137] The average fiber width of the CNFs in samples 1 to 12 was measured by measuring the fiber width of 50 randomly selected fibers using an atomic force microscope (SPM-9700HT, manufactured by Shimadzu Corporation) and calculating the arithmetic mean value. The evaluation samples were prepared using the following method.

[0138] 149.0 g of distilled water was added to 1.0 g of a 0.5% by mass uniform CNF aqueous dispersion, and the mixture was stirred for 3 minutes using a mixer (G5200, manufactured by Biolomix) to obtain a 0.003% by mass uniform CNF aqueous dispersion. Next, 30 μL of the 0.003% by mass uniform aqueous dispersion of Example Compound 1 was dropped onto a natural mica (natural muscovite) substrate (15 mm × 15 mm × 0.15 mm thick) using a micropipette, and the substrate was allowed to air dry for 0.5 hours to obtain a sample for fiber width evaluation.

[0139] <Method for preparing aqueous dispersion containing cellulose fibers and evaluation test method> [Example 1] Sulfated CNF of Sample 1 (sulfur content: 0.4 mmol / g) was mixed with water to prepare an aqueous dispersion in which the concentration of sulfated CNF of Sample 1 was 0.3 mass% relative to the total mass of the aqueous dispersion. The viscosity of the aqueous dispersion was then measured at 2.6 rpm at 25°C. Furthermore, the aqueous dispersion was heat-treated at 80°C for 1 hour, 5 hours, and 24 hours, and the pH change from before to after the heat treatment (pH before heat treatment - pH after heat treatment) was measured.

[0140] [Example 2] Sulfated CNF of Sample 2 (sulfur content: 1.5 mmol / g) was mixed with water to prepare an aqueous dispersion in which the concentration of sulfated CNF of Sample 2 was 0.3 mass% relative to the total mass of the aqueous dispersion. The viscosity of the aqueous dispersion was then measured at 2.6 rpm at 25°C. Furthermore, the aqueous dispersion was heat-treated at 80°C for 1 hour, 5 hours, and 24 hours, and the pH change from before to after the heat treatment (pH before heat treatment - pH after heat treatment) was measured.

[0141] [Example 3] Sulfated CNF of Sample 3 (sulfur content: 1.5 mmol / g) was mixed with water to prepare an aqueous dispersion in which the concentration of sulfated CNF of Sample 3 was 0.3 mass% relative to the total mass of the aqueous dispersion. The viscosity of the aqueous dispersion was then measured at 2.6 rpm at 25°C. Furthermore, the aqueous dispersion was heat-treated at 80°C for 24 hours, and the pH change from before to after the heat treatment (pH before heat treatment - pH after heat treatment) was measured.

[0142] [Example 4] Sulfated CNF of Sample 4 (sulfur content: 2.8 mmol / g) was mixed with water to prepare an aqueous dispersion in which the concentration of sulfated CNF of Sample 4 was 0.3 mass% relative to the total mass of the aqueous dispersion. The viscosity of the aqueous dispersion was then measured at 2.6 rpm at 25°C. Furthermore, the aqueous dispersion was heat-treated at 80°C for 1 hour, 5 hours, and 24 hours, and the pH change from before to after the heat treatment (pH before heat treatment - pH after heat treatment) was measured.

[0143] [Example 5] Sulfated CNF of Sample 5 (sulfur content: 1.5 mmol / g), water, and sodium acetate were mixed to prepare an aqueous dispersion in which the concentration of sulfated CNF of Sample 5 was 0.3 mass% relative to the total mass of the aqueous dispersion and the concentration of sodium acetate was 0.002 mass% relative to the total mass of the aqueous dispersion. The viscosity of the aqueous dispersion was then measured at 2.6 rpm at 25°C. Furthermore, the aqueous dispersion was heat-treated at 80°C for 1 hour, 5 hours, and 24 hours, and the pH change from before to after the heat treatment (pH before heat treatment - pH after heat treatment) was measured.

[0144] [Example 6] Sulfated CNF of Sample 6 (sulfur content: 1.5 mmol / g), water, and sodium acetate were mixed to prepare an aqueous dispersion in which the concentration of sulfated CNF of Sample 6 was 0.3 mass% relative to the total mass of the aqueous dispersion and the concentration of sodium acetate was 0.1 mass% relative to the total mass of the aqueous dispersion. The viscosity of the aqueous dispersion was then measured at 2.6 rpm at 25°C. Furthermore, the aqueous dispersion was heat-treated at 80°C for 1 hour, 5 hours, and 24 hours, and the pH change from before to after the heat treatment (pH before heat treatment - pH after heat treatment) was measured.

[0145] [Example 7] Sulfated CNF of Sample 7 (sulfur content: 1.5 mmol / g), water, and sodium acetate were mixed to prepare an aqueous dispersion in which the concentration of sulfated CNF of Sample 7 was 0.3 mass% relative to the total mass of the aqueous dispersion and the concentration of sodium acetate was 8 mass% relative to the total mass of the aqueous dispersion. The viscosity of the aqueous dispersion was then measured at 2.6 rpm at 25°C. Furthermore, the aqueous dispersion was heat-treated at 80°C for 1 hour, 5 hours, and 24 hours, and the pH change from before to after the heat treatment (pH before heat treatment - pH after heat treatment) of the aqueous dispersion was measured.

[0146] [Example 8] Sulfated CNF of Sample 8 (sulfur content: 1.5 mmol / g), water, and sodium sulfate were mixed to prepare an aqueous dispersion in which the concentration of sulfated CNF of Sample 8 was 0.3 mass% relative to the total mass of the aqueous dispersion and the concentration of sodium sulfate was 0.1 mass% relative to the total mass of the aqueous dispersion. The viscosity of the aqueous dispersion was then measured at 2.6 rpm at 25°C. Furthermore, the aqueous dispersion was heat-treated at 80°C for 1 hour, 5 hours, and 24 hours, and the pH change from before to after the heat treatment (pH before heat treatment - pH after heat treatment) of the aqueous dispersion was measured.

[0147] [Example 9] Sulfated CNF of Sample 9 (sulfur content: 1.5 mmol / g), water, and ammonium sulfate were mixed to prepare an aqueous dispersion in which the concentration of sulfated CNF of Sample 9 was 0.3% by mass relative to the total mass of the aqueous dispersion and the concentration of ammonium sulfate was 0.1% by mass relative to the total mass of the aqueous dispersion. The viscosity of the aqueous dispersion was then measured at 2.6 rpm at 25°C. Furthermore, the aqueous dispersion was heat-treated at 80°C for 1 hour, 5 hours, and 24 hours, and the pH change from before to after the heat treatment (pH before heat treatment - pH after heat treatment) of the aqueous dispersion was measured.

[0148] [Example 10] Sulfated CNF of Sample 10 (sulfur content: 1.5 mmol / g), water, and calcium acetate were mixed to prepare an aqueous dispersion in which the concentration of sulfated CNF of Sample 10 was 0.3 mass% relative to the total mass of the aqueous dispersion and the concentration of calcium acetate was 0.1 mass% relative to the total mass of the aqueous dispersion. The viscosity of the aqueous dispersion was then measured at 2.6 rpm at 25°C. Furthermore, the aqueous dispersion was heat-treated at 80°C for 1 hour, 5 hours, and 24 hours, and the pH change from before to after the heat treatment (pH before heat treatment - pH after heat treatment) of the aqueous dispersion was measured.

[0149] [Comparative Example 1] TEMPO-oxidized CNF of Sample 11 and water were mixed to prepare an aqueous dispersion in which the concentration of TEMPO-oxidized CNF of Sample 11 was 0.3% by mass based on the total mass of the aqueous dispersion. Subsequently, the viscosity of the aqueous dispersion measured at 2.6 rpm at 25°C was measured. Further, when the aqueous dispersion was heat-treated at 80°C for 1 hour, 5 hours, and 24 hours, the pH change (pH before heat treatment - pH after heat treatment) of the aqueous dispersion from before to after heat treatment was measured.

[0150] [Comparative Example 2] Phosphorylated CNF of Sample 12 and water were mixed to prepare an aqueous dispersion in which the concentration of phosphorylated CNF of Sample 12 was 0.3% by mass based on the total mass of the aqueous dispersion. Subsequently, the viscosity of the aqueous dispersion measured at 2.6 rpm at 25°C was measured. Further, when the aqueous dispersion was heat-treated at 80°C for 1 hour, 5 hours, and 24 hours, the pH change (pH before heat treatment - pH after heat treatment) of the aqueous dispersion from before to after heat treatment was measured.

[0151] <Evaluation Results of Aqueous Dispersion Containing CNF> Table 1 shows the results of Examples 1 to 10 and Comparative Examples 1 to 2. Figure 1 shows the relationship between the sulfur introduction amount and the viscosity. Figure 2 shows the relationship between the salt concentration and the viscosity. Note that Figure 3 is a graph in which the salt concentration in Figure 2 is shown in logarithmic scale. Figure 4 shows the relationship between the sulfur introduction amount and the pH change (pH before heat treatment - pH 24 hours after heat treatment). Figure 5 shows the relationship between the salt concentration and the pH change (pH before heat treatment - pH 24 hours after heat treatment). Note that Figure 6 is a graph in which the salt concentration in Figure 5 is shown in logarithmic scale.

[0152]

Table 1

[0153] From Table 1 and Figure 1, it was found that the viscosity of the aqueous dispersion can be adjusted by the sulfur introduction amount, that is, the introduction amount of sulfate groups. The viscosity of the aqueous dispersion leads to the adjustment of the diffusion rate, and as a result, leads to the adjustment of the acid release effect.

[0154] From Table 1, Figures 2 and 3, it was found that the viscosity of the aqueous dispersion can be adjusted to decrease by adding salt. The viscosity of the aqueous dispersion leads to the adjustment of the diffusion rate, and as a result, it leads to the adjustment of the acid release effect.

[0155] From Table 1 and Figure 4, it was found that when the sulfur introduction amount, that is, the introduction amount of the sulfate group, is large, the pH change (pH before heat treatment - pH after heat treatment) becomes large. Also, since there is a proportional relationship between the introduction amount of the sulfate group and the pH change, it was found that the target pH can be achieved by adjusting the introduction amount of the sulfate group.

[0156] From Table 1, Figures 5 and 6, it was found that the pH change (pH before heat treatment - pH after heat treatment) can be adjusted by adding salt. Also, it was found that a buffering effect can be obtained by using a weak acid salt as the salt.

[0157] <Preparation of a crosslinked film of a water-soluble polymer using a thermal acid generator composed of CNF> [Examples 11 to 20 and Comparative Examples 3 to 4] 5.0 g of polyvinyl alcohol (reagent special grade, manufactured by Fuji Film Wako Pure Chemical Industries, Ltd.) and 95.0 g of pure water were stirred at 80 °C for 5 hours with a three-one motor stirrer (BL300, manufactured by AS ONE Corporation) to obtain a polyvinyl alcohol aqueous dispersion having a solid content concentration of 5% by mass.

[0158] Using each of Samples 1 to 12, 0.6 g of the CNF dry body and 99.4 g of pure water were stirred with a three-one motor stirrer (BL300, manufactured by AS ONE Corporation) for 1 hour to obtain 12 kinds of CNF aqueous dispersions having a solid content concentration of 0.6% by mass.

[0159] 100 g of a polyvinyl alcohol aqueous dispersion having a solid content concentration of 5% by mass, 100 g of a CNF aqueous dispersion having a solid content concentration of 0.6% by mass, and 2.0 g of a 25% aqueous glutaraldehyde solution (Wako first grade, manufactured by Fuji Film Wako Pure Chemical Industries, Ltd.) as a crosslinking agent were added and stirred with a three-one motor stirrer (BL300, manufactured by AS ONE Corporation) for 1 hour to obtain a uniform reaction solution.

[0160] Subsequently, 23.7 g (1 cm wet film thickness) of the reaction solution was poured into a polystyrene petri dish with an inner diameter of 55 mm and dried in an oven (OFW-600SB, AS ONE Corporation) at 80°C for 24 hours to obtain a crosslinked water-soluble polymer film (Examples 11 to 20: Preparation of crosslinked water-soluble polymer films using Samples 1 to 10 as acid generators, respectively; Comparative Examples 3 and 4: Preparation of crosslinked water-soluble polymer films using Samples 11 and 12, respectively).

[0161] <Preparation of crosslinked water-soluble polymer films using photoacid generators> Comparative Example 5 5.0 g of polyvinyl alcohol (special reagent grade, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) and 95.0 g of pure water were stirred at 80°C for 5 hours using a three-one motor stirrer (BL300, manufactured by AS ONE Corporation) to obtain a polyvinyl alcohol aqueous dispersion with a solids concentration of 5% by mass.

[0162] 0.6 g of the photoacid generator sample 13 and 99.4 g of pure water were stirred with a stirrer for 1 hour to obtain an aqueous dispersion of the photoacid generator with a solid content concentration of 0.6 mass %.

[0163] 100 g of a polyvinyl alcohol aqueous dispersion with a solid content of 5% by mass, 100 g of a photoacid generator aqueous dispersion with a solid content of 0.6% by mass, and 2.0 g of a 25% aqueous glutaraldehyde solution (Wako Grade 1, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as a crosslinker were added and stirred for 1 hour with a Three-One Motor Stirrer (BL300, manufactured by AS ONE Corporation) to obtain a homogeneous reaction solution.

[0164] Next, 23.7 g of the reaction solution (wet film thickness 1 cm) was poured into a polystyrene dish with an inner diameter of 55 mm, and the reaction solution was measured under air at an illumination intensity of 50 mW / cm at 365 nm. 2 The film was irradiated with ultraviolet light for 5 seconds in an 80°C environment using a UV curing oven (UV PITARI LED, manufactured by Hisol Co., Ltd.), and then dried at 80°C for 24 hours to obtain a crosslinked film of the water-soluble polymer.

[0165] <Evaluation of crosslinking properties of crosslinked water-soluble polymer membranes> Using a dropper, 0.5 g of pure water was dropped onto the surface of the crosslinked water-soluble polymer film prepared in Examples 11 to 20 and Comparative Examples 3 to 5, and the film was left at room temperature for 24 hours. After leaving the film, the surface of the crosslinked water-soluble polymer film was observed with a magnifying glass (10x magnification, MG7173, manufactured by AS ONE Corporation) and evaluated according to the following criteria. 〇: The area where water was dropped is smooth, there are no dents or distortions on the film surface, and it can be said that the film is sufficiently cross-linked. ×: The area where water was dropped dissolved, causing depressions and distortions on the film surface, indicating that crosslinking was not performed or was insufficient.

[0166] <Evaluation of the prevention of porosity in crosslinked water-soluble polymer membranes> As an index of porosity of the crosslinked water-soluble polymer films prepared in Examples 11 to 20 and Comparative Examples 3 to 5, the haze value was measured using a haze meter (HZ-V3, manufactured by Suga Test Instruments Co., Ltd.) and evaluated using the following indexes. ◯: The haze value of the crosslinked film of the water-soluble polymer is less than 6% △: The haze value of the crosslinked film of the water-soluble polymer is 6% or more and less than 8% ×: The haze value of the crosslinked film of the water-soluble polymer is 8% or more.

[0167] <Evaluation results of crosslinked water-soluble polymer membranes> Table 2 shows the evaluation results of the crosslinked water-soluble polymer films prepared in Examples 11 to 20 and Comparative Examples 3 to 5.

[0168] [Table 2]

[0169] Table 2 shows that by using sulfated CNF as an acid generator in the crosslinking reaction of an aqueous polymer, it is possible to ensure the amount of acid required to form a crosslinked aqueous polymer film, i.e., crosslinkability, while also ensuring the sustained release of acid required to prevent the crosslinked aqueous polymer film from becoming porous, i.e., to achieve both the crosslinking reaction and the evaporation of water.

Claims

1. An acid generator containing, as an active ingredient, cellulose nanofibers having sulfate ester groups, The cellulose nanofibers have an average fiber width of 1 nm to 1000 nm, The sulfate ester group is represented by the following general formula (I): 【Chemistry 1】 (In general formula (I), n is an integer of 1 to 3, and M ｎ＋ is an n-valent cation, and the wavy lines are the bonding sites to other atoms.) is expressed as The acid generator.

2. 2. The acid generator according to claim 1, wherein the amount of sulfur introduced into the cellulose nanofiber due to the sulfate ester groups is 0.3 mmol / g to 3.0 mmol / g relative to the mass of the cellulose nanofiber.

3. The acid generator according to claim 1, further comprising one or more salts selected from metal salts and ammonium salts, wherein the content of the salt is 0.002 parts by mass to 10 parts by mass per 100 parts by mass of the cellulose nanofibers.

4. The acid generator according to claim 1 , further comprising water, the content of the water being 50% by mass or less based on the total mass of the acid generator.

5. The acid generator according to claim 1 , further comprising water, wherein the content of the water is 1,000 parts by mass or more per 100 parts by mass of the cellulose nanofibers.

6. The acid generator according to claim 1, wherein when the acid generator and water are mixed to prepare an aqueous dispersion in which the concentration of the cellulose nanofibers is 0.3 mass% relative to the total mass of the aqueous dispersion, and the aqueous dispersion is heat-treated at 80°C for 24 hours, the pH of the aqueous dispersion after the heat treatment is reduced by 0.5 to 6.0 from the pH before the heat treatment.

7. 2. The acid generator according to claim 1, wherein when the acid generator and water are mixed to prepare an aqueous dispersion in which the concentration of the cellulose nanofibers is 0.3 mass% relative to the total mass of the aqueous dispersion, the viscosity of the aqueous dispersion measured at 2.6 rpm at 25°C is 500 mPa s or more.

8. The acid generator according to any one of claims 1 to 7, for use in producing an aqueous polymerizable polymer and / or an aqueous crosslinked polymer.

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