JP7768148B2 - Negative radiation-sensitive sheets and patterned sheets - Google Patents

Description

The present invention relates to a negative-working radiation-sensitive sheet and a patterned sheet in which at least a portion of the unexposed areas of the negative-working radiation-sensitive sheet have been removed.

In the development of electronic devices, with the demand for finer and denser circuit configurations, there is a demand for substrates that allow for fine patterning.
Furthermore, with the growing awareness of the need to utilize renewable resources, the application of compounds derived from plant materials, such as cellulose nanofibers, to various applications is being considered.
Patent Document 1 discloses a fiber-reinforced composite material that contains fibers with an average fiber diameter of 4 to 200 nm and a matrix material, and has a light transmittance of 60% or more for wavelengths of 400 to 700 nm when converted into a 50 μm thickness, with the aim of providing a fiber-reinforced composite material that always maintains high transparency without being affected by temperature conditions, wavelength, etc., and that is imparted with various functions by combining the fibers with a matrix material.

Furthermore, Patent Document 2 discloses a photosensitive composite sheet that contains a photosensitive resin and a photosensitizer in a porous cellulose sheet, and that satisfies at least the following requirements.
Requirement 1: The air resistance of the cellulose porous sheet is 1 s/100 ml or more and 400,000 s/100 ml or less,
Requirement 2: the photosensitive resin contains at least one of a polymerizable compound, an alkali-soluble resin, and a resin in which a photofunctional group of the resin is protected with a protecting group,
Requirement 3: When the photosensitive composite sheet has a thickness of 50 μm, the light transmittance at wavelengths of 280 nm to 433 nm is 10% or more.

Japanese Patent Application Laid-Open No. 2005-60680 Japanese Patent Application Laid-Open No. 2018-132655

The sheet described in Patent Document 1 has a problem in that it is difficult to form a fine pattern, and the sheet described in Patent Document 2 has a problem in that it has low transparency.
An object of the present invention is to provide a negative-working radiation-sensitive sheet that is capable of forming a fine pattern and has excellent transparency, and a patterned sheet obtained by removing at least a portion of the unexposed areas of the negative-working radiation-sensitive sheet. Another object of the present invention is to provide a patterned sheet obtained by removing at least a portion of the radiation-sensitive composition in the unexposed areas of the negative-working radiation-sensitive sheet across the entire thickness direction.

The present inventors have found that the above-mentioned problems can be solved by a negative-working radiation-sensitive sheet containing a radiation-sensitive composition containing a specific compound and fine fibrous cellulose, and have thus completed the present invention.
That is, the present invention relates to the following items <1> to <12>.
<1> A negative-tone radiation-sensitive sheet containing at least a radiation-sensitive composition and fine fibrous cellulose having a fiber width of 1,000 nm or less, wherein the radiation-sensitive composition contains a compound (X) that contains a polymerizable unsaturated bond and has a Hansen solubility parameter (HSP) distance with water of 36 MPa ^0.5 or less and a polar term (dP) of 10 MPa ^0.5 or more.
<2> The negative radiation-sensitive sheet according to <1>, wherein the radiation-sensitive composition contains a photopolymerization initiator.
<3> The negative-working radiation-sensitive sheet according to <1> or <2>, wherein the content of the radiation-sensitive composition in the solid content of the negative-working radiation-sensitive sheet is 30% by mass or more.
<4> The negative radiation-sensitive sheet according to any one of <1> to <3>, wherein the compound (X) has at least one of a (meth)acryloyloxy group and a (meth)acrylamide group.
<5> The negative radiation-sensitive sheet according to any one of <1> to <4>, wherein the fine fibrous cellulose has an anionic group.
<6> The negative-working radiation-sensitive sheet according to any one of <1> to <5>, wherein the fine fibrous cellulose has a phosphorus oxo acid group or a group derived from a phosphorus oxo acid group.
<7> The negative radiation-sensitive sheet according to any one of <1> to <6>, wherein the radiation-sensitive composition is soluble in at least one of water, alcohol, and a mixed solvent thereof.
<8> The negative-working radiation-sensitive sheet according to any one of <1> to <7>, wherein the negative-working radiation-sensitive sheet has a total light transmittance of 70% or more.
<9> The negative-working radiation-sensitive sheet according to any one of <1> to <8>, wherein the negative-working radiation-sensitive sheet has a haze of 10% or less.
<10> A patterned sheet, in which at least a part of the unexposed area of the negative-working radiation-sensitive sheet according to any one of <1> to <9> has been removed.
<11> A patterned sheet, in which at least a portion of the radiation-sensitive composition in the unexposed areas of the negative-working radiation-sensitive sheet according to any one of <1> to <9> has been removed across the entire thickness direction.
<12> A radiation-sensitive composition used in the negative-working radiation-sensitive sheet according to any one of <1> to <9>.

The present invention provides a negative-type radiation-sensitive sheet that is capable of forming fine patterns and has excellent transparency, as well as a patterned sheet in which at least a portion of the unexposed areas of the negative-type radiation-sensitive sheet has been removed. Furthermore, the present invention provides a patterned sheet in which at least a portion of the radiation-sensitive composition in the unexposed areas of the negative-type radiation-sensitive sheet has been removed across the entire thickness direction.

FIG. 1 is a graph showing the relationship between the amount of NaOH dropped onto a slurry containing fibrous cellulose having phosphorus oxo acid groups and pH. FIG. 2 is a graph showing the relationship between the amount of NaOH dropped onto a slurry containing fibrous cellulose having a carboxy group and the pH.

[Negative radiation-sensitive sheet]
The negative-type radiation-sensitive sheet (hereinafter also simply referred to as "radiation-sensitive sheet" or "sheet") of the present invention contains at least a radiation-sensitive composition and fine fibrous cellulose (hereinafter also simply referred to as fine fibrous cellulose) having a fiber width of 1,000 nm or less, and the radiation-sensitive composition contains a compound (X) that contains a polymerizable unsaturated bond and has a Hansen solubility parameter (HSP) distance with water of 36 MPa ^0.5 or less and a polar term (dP) of 10 MPa ^0.5 or more.
According to the present invention, a radiation-sensitive sheet capable of forming a fine pattern and having excellent transparency can be obtained. Furthermore, according to the present invention, a patterned sheet can be obtained in which at least a portion of the radiation-sensitive composition in the unexposed areas has been removed across the entire thickness direction.
Although the detailed reasons why the above-mentioned effects are obtained are unclear, part of the reason is thought to be as follows. In the present invention, instead of providing a radiation-sensitive layer on a substrate, the radiation-sensitive sheet itself has excellent shape stability and functions as a substrate. When a radiation-sensitive layer is provided on a substrate, problems such as curling due to differences in the thermal expansion coefficient between the substrate and the radiation-sensitive layer and light reflection at the interface may occur, but in the present invention, such problems do not occur.
Furthermore, a sheet containing fine fibrous cellulose has extremely high transparency and, since the fiber width is 1,000 nm or less, it is believed that fine patterns can be formed thereon.
Furthermore, when a radiation-sensitive layer (resist) is provided on the substrate, after patterning, regions where the radiation-sensitive layer (resist) is present and regions where it is not present are generated, resulting in unevenness in the film thickness. On the other hand, in the present invention, after exposure, at least a portion of the exposed or unexposed portion of the radiation-sensitive composition is removed, but mainly only the radiation-sensitive composition is removed, and the fine fibrous cellulose remains in the sheet form as it is, so patterning can be performed without unevenness in the overall film thickness. Furthermore, by using a specific compound (X), the unexposed radiation-sensitive composition can be easily removed, and it can be removed over the entire thickness direction of the sheet. As a result, the removed portion becomes a front-to-back through-type pattern, and the composition is expected to be used as a sensor that effectively detects gases or liquids passing through the removed portion, or as a dye for a color filter or a conductive portion of a touch panel by dyeing the removed portion of the radiation-sensitive composition.
The present invention will be described in further detail below.

The terms used in this specification have the following meanings:
A range of values expressed as "to" means a range that includes both ends of the range.
"(Meth)acrylic" is a general term for "acrylic" and "methacrylic", and refers to acrylic and methacrylic individually. The same applies to "(meth)acryloyl", "(meth)acryloyloxy", "(meth)acrylic acid", "(meth)acrylate", and "(meth)acrylamide".

<Fine fibrous cellulose>
The radiation-sensitive sheet of the present invention contains fine fibrous cellulose.
The fine fibrous cellulose is a fibrous cellulose having a fiber width of 1,000 nm or less. The fiber width of the fibrous cellulose can be measured, for example, by observation using an electron microscope.
The fiber width of the fine fibrous cellulose is 1,000 nm or less. The fiber width of the fine fibrous cellulose is, for example, preferably 2 nm or more and 1,000 nm or less, more preferably 2 nm or more and 100 nm or less, even more preferably 2 nm or more and 50 nm or less, and particularly preferably 2 nm or more and 10 nm or less. By making the fiber width of the fine fibrous cellulose 2 nm or more, it is possible to suppress the dissolution of the cellulose molecules in water, and more easily realize the effects of the fine fibrous cellulose, such as improved strength, rigidity, and dimensional stability.

The average fiber width of the fine fibrous cellulose is, for example, 1,000 nm or less. The average fiber width of the fine fibrous cellulose is preferably 2 nm or more and 1,000 nm or less, more preferably 2 nm or more and 100 nm or less, even more preferably 2 nm or more and 50 nm or less, and particularly preferably 2 nm or more and 10 nm or less. By making the average fiber width of the fine fibrous cellulose 2 nm or more, it is possible to suppress the dissolution of the cellulose molecules in water, and more easily realize the effects of the fine fibrous cellulose, such as improved strength, rigidity, and dimensional stability. Note that the fine fibrous cellulose is, for example, single-filament cellulose.

The average fiber width of fine fibrous cellulose is measured, for example, using an electron microscope as follows. First, an aqueous suspension of fibrous cellulose with a concentration of 0.05% by mass or more and 0.1% by mass or less is prepared, and this suspension is cast onto a hydrophilically treated carbon film-coated grid to prepare a sample for TEM observation. When wide fibers are included, an SEM image of the surface cast onto glass may be observed. Next, electron microscope images are observed at magnifications of 1,000x, 5,000x, 10,000x, or 50,000x, depending on the width of the fibers to be observed. However, the sample, observation conditions, and magnification are adjusted to satisfy the following conditions.
(1) A line X is drawn at any point in the observed image, and 20 or more fibers intersect with the line X.
(2) Draw a line Y that intersects the line perpendicularly within the same image, and 20 or more fibers intersect the line Y.

For observation images that satisfy the above conditions, the width of the fibers that intersect with lines X and Y is visually read. In this way, three or more sets of observation images are obtained of at least the surface portions that do not overlap each other. Next, for each image, the width of the fibers that intersect with lines X and Y is read. In this way, the width of at least 20 fibers x 2 x 3 = 120 fibers is read. The average of the read fiber widths is then taken as the average fiber width of the fibrous cellulose.

The fiber length of the fine fibrous cellulose is not particularly limited, but is preferably 0.1 μm or more and 1,000 μm or less, more preferably 0.1 μm or more and 800 μm or less, and even more preferably 0.1 μm or more and 600 μm or less. By keeping the fiber length within the above range, destruction of the crystalline regions of the fine fibrous cellulose can be suppressed. It also becomes possible to keep the slurry viscosity of the fine fibrous cellulose within an appropriate range. The fiber length of the fine fibrous cellulose can be determined, for example, by image analysis using TEM, SEM, or AFM.

The fine fibrous cellulose preferably has a type I crystal structure. The fact that the fine fibrous cellulose has a type I crystal structure can be identified from a diffraction profile obtained from a wide-angle X-ray diffraction photograph using CuKα (λ=1.5418 Å) monochromated with graphite. Specifically, the cellulose can be identified from the presence of typical peaks at two positions, around 2θ=14° to 17° and around 2θ=22° to 23°.
The proportion of type I crystal structure in the fine fibrous cellulose is, for example, preferably 30% or more, more preferably 40% or more, and even more preferably 50% or more. This allows for even better performance in terms of heat resistance and low linear thermal expansion coefficient. The degree of crystallinity can be determined by measuring an X-ray diffraction profile and using the pattern in a conventional manner (Seagal et al., Textile Research Journal, Vol. 29, p. 786, 1959).

The axial ratio (fiber length/fiber width) of the fine fibrous cellulose is not particularly limited, but is preferably 20 to 10,000, and more preferably 50 to 1,000. By setting the axial ratio at or above the lower limit, it is easy to form a sheet containing the fine fibrous cellulose. Furthermore, sufficient viscosity is easily obtained when a solvent dispersion is prepared. Setting the axial ratio at or below the upper limit is preferable in that it makes handling, such as dilution, easier when handling the fine fibrous cellulose as an aqueous dispersion.

The fine fibrous cellulose in this embodiment has, for example, at least one of an ionic group and a nonionic group. From the viewpoint of improving the dispersibility of the fibers in the dispersion medium and increasing the defibration efficiency in the defibration treatment, it is more preferable that the fine fibrous cellulose has an ionic group. The ionic group may include, for example, either or both of an anionic group and a cationic group. Furthermore, the nonionic group may include, for example, an alkyl group and an acyl group. In this embodiment, it is particularly preferable that the ionic group include an anionic group.
The fine fibrous cellulose does not need to be subjected to a treatment for introducing ionic groups.

Examples of anionic groups as ionic groups include phosphorus oxoacid groups or substituents derived from phosphorus oxoacid groups (sometimes simply referred to as phosphorus oxoacid groups), carboxy groups or substituents derived from carboxy groups (sometimes simply referred to as carboxy groups), sulfur oxoacid groups or substituents derived from sulfur oxoacid groups (sometimes simply referred to as sulfur oxoacid groups), xanthate groups, phosphonic groups, phosphine groups, sulfonic groups, carboxyalkyl groups, etc. Among these, the anionic group is preferably at least one selected from the group consisting of phosphorus oxoacid groups, substituents derived from phosphorus oxoacid groups, carboxy groups, sulfur oxoacid groups, substituents derived from sulfur oxoacid groups, carboxymethyl groups, carboxyethyl groups, and sulfonic groups, more preferably at least one selected from the group consisting of phosphorus oxoacid groups, substituents derived from phosphorus oxoacid groups, carboxy groups, sulfur oxoacid groups, and substituents derived from sulfur oxoacid groups, and particularly preferably a phosphorus oxoacid group. By introducing a phosphorus oxoacid group as an anionic group, the dispersibility of fibrous cellulose can be further improved, for example, even under alkaline or acidic conditions, making it easier to obtain a high-strength, highly transparent sheet.
Examples of cationic groups as ionic groups include ammonium groups, phosphonium groups, sulfonium groups, etc. Among these, the cationic group is preferably an ammonium group.

The phosphorus oxo acid group or the substituent derived from the phosphorus oxo acid group is, for example, a substituent represented by the following formula (1). Multiple types of substituents represented by the following formula (1) may be introduced into each fibrous cellulose. In this case, the multiple introduced substituents represented by the following formula (1) may be the same or different.

In formula (1), a, b, and n are natural numbers, and m is an arbitrary number (where a = b × m). At least one of the n α and α' is ^O- , and the rest are R or OR. All of the α and α' may be ^O- . The n α may all be the same or different. ^{β b+} is a monovalent or higher cation made of an organic or inorganic substance.

Each R is a hydrogen atom, a saturated linear hydrocarbon group, a saturated branched hydrocarbon group, a saturated cyclic hydrocarbon group, an unsaturated linear hydrocarbon group, an unsaturated branched hydrocarbon group, an unsaturated cyclic hydrocarbon group, an aromatic group, or a derivative thereof. Furthermore, in formula (1), n is preferably 1.

Saturated linear hydrocarbon groups include, but are not limited to, methyl, ethyl, n-propyl, and n-butyl groups. Saturated branched hydrocarbon groups include, but are not limited to, i-propyl and t-butyl groups. Saturated cyclic hydrocarbon groups include, but are not limited to, cyclopentyl and cyclohexyl groups. Unsaturated linear hydrocarbon groups include, but are not limited to, vinyl and allyl groups. Unsaturated branched hydrocarbon groups include, but are not limited to, i-propenyl and 3-butenyl groups. Unsaturated cyclic hydrocarbon groups include, but are not limited to, cyclopentenyl and cyclohexenyl groups. Aromatic groups include, but are not limited to, phenyl and naphthyl groups.

Furthermore, the derivative group in R includes, but is not limited to, functional groups in which at least one functional group selected from the group consisting of a carboxy group, a carboxylate group (-COO-), a hydroxy group, an amino group, and an ammonium group is added to or substituted on the main chain or side chain of the above-mentioned hydrocarbon groups. The number of carbon atoms constituting the main chain of R is not particularly limited, but is preferably 20 or less, and more preferably 10 or less. By setting the number of carbon atoms constituting the main chain of R within the above range, the molecular weight of the phosphorus oxoacid group can be set within an appropriate range, facilitating penetration into the fiber raw material and increasing the yield of microfibrillated cellulose fibers. Furthermore, when multiple R groups are present in formula (1) or when multiple types of substituents represented by formula (1) are introduced into the fibrous cellulose, the multiple R groups may be the same or different.

β ^b+ is a monovalent or higher cation composed of an organic or inorganic substance. Examples of the monovalent or higher cation composed of an organic substance include organic onium ions. Examples of the organic onium ions include organic ammonium ions and organic phosphonium ions. Examples of the organic ammonium ions include aliphatic ammonium ions and aromatic ammonium ions, and examples of the organic phosphonium ions include aliphatic phosphonium ions and aromatic phosphonium ions. Examples of the monovalent or higher cation composed of an inorganic substance include ions of alkali metals such as sodium, potassium, or lithium, ions of divalent metals such as calcium or magnesium, hydrogen ions, and ammonium ions. Note that when multiple β ^b+ groups exist in formula (1) or when multiple types of substituents represented by formula (1) are introduced into the fibrous cellulose, the multiple β ^b+ groups may be the same or different. Examples of the monovalent or higher cation composed of an organic or inorganic substance include, but are not limited to, sodium or potassium ions, which are resistant to yellowing when a fiber raw material containing β ^b+ is heated and are easy to use industrially.

More specific examples of the phosphorus oxo acid group or a substituent derived from a phosphorus _oxo acid group include a phosphate group ( _-PO3H2 ), a salt of a phosphate group, a phosphorous acid (phosphonic acid) group ( _-PO2H2 ), and a salt of a phosphite (phosphonic acid) _group . Furthermore, the phosphorus oxo acid group or a substituent derived from a phosphorus oxo acid group may be a group in which a phosphate group is condensed (e.g., a pyrophosphate group), a group in which a phosphonic acid is condensed (e.g., a polyphosphonic acid group), a phosphate ester group (e.g., a monomethyl phosphate group, a polyoxyethylene alkyl phosphate group), an alkyl phosphonic acid group (e.g., a methylphosphonic acid group), or the like.

<Sulfur oxoacids>
The sulfur oxoacid group (a sulfur oxoacid group or a substituent derived from a sulfur oxoacid group) is, for example, a substituent represented by the following formula (2). A plurality of types of substituents represented by the following formula (2) may be introduced into each fibrous cellulose. In this case, the plurality of introduced substituents represented by the following formula (2) may be the same or different.

In the structural formula, b and n are natural numbers, p is 0 or 1, and m is any number (where 1 = b × m). When n is 2 or greater, the multiple p's may be the same or different. In the structural formula, β ^b+ is a monovalent or higher cation composed of an organic or inorganic substance. Examples of the monovalent or higher cation composed of an organic substance include organic onium ions. Examples of the organic onium ions include organic ammonium ions and organic phosphonium ions. Examples of the organic ammonium ions include aliphatic ammonium ions and aromatic ammonium ions, and examples of the organic phosphonium ions include aliphatic phosphonium ions and aromatic phosphonium ions. Examples of the monovalent or higher cation composed of an inorganic substance include ions of alkali metals such as sodium, potassium, or lithium, ions of divalent metals such as calcium or magnesium, hydrogen ions, and ammonium ions. When multiple types of substituents represented by the above formula (2) are introduced into the fibrous cellulose, the multiple β ^b+ may be the same or different. As the monovalent or higher cations consisting of organic or inorganic substances, sodium or potassium ions are preferred, as they are less likely to yellow when the fiber raw material containing β ^b+ is heated and are easy to use industrially, but there are no particular limitations.

The amount of ionic groups introduced into the fine fibrous cellulose is, for example, preferably 0.10 mmol/g or more per 1 g (mass) of fine fibrous cellulose, more preferably 0.20 mmol/g or more, even more preferably 0.50 mmol/g or more, and particularly preferably 1.00 mmol/g or more. Furthermore, the amount of ionic groups introduced into the fine fibrous cellulose is, for example, preferably 5.20 mmol/g or less per 1 g (mass) of fibrous cellulose, more preferably 3.65 mmol/g or less, even more preferably 3.50 mmol/g or less, and even more preferably 3.00 mmol/g or less. By setting the amount of ionic groups introduced within the above range, it is possible to facilitate the refinement of the fiber raw material and to improve the stability of the fine fibrous cellulose. Furthermore, by setting the amount of ionic groups introduced within the above range, it is possible to exhibit good properties in various applications, such as a thickener for fine fibrous cellulose.
Here, the denominator in the unit mmol/g indicates the mass of the fine fibrous cellulose when the counter ion of the ionic group is a hydrogen ion (H ⁺ ).

The amount of ionic groups introduced into the fibrous cellulose can be measured, for example, by neutralization titration, in which an alkali such as an aqueous sodium hydroxide solution is added to a slurry containing the obtained fibrous cellulose, and the amount introduced is measured by determining the change in pH.
FIG. 1 is a graph showing the relationship between the amount of NaOH dropped onto fibrous cellulose having phosphorus oxo acid groups and pH.

1 is a graph showing the relationship between the amount of NaOH added dropwise to a slurry containing fibrous cellulose having phosphorus oxo acid groups and pH. The amount of phosphorus oxo acid groups introduced into the fibrous cellulose is measured, for example, as follows.
First, a slurry containing fibrous cellulose is treated with a strongly acidic ion exchange resin. If necessary, the measurement object may be subjected to a defibration treatment similar to the defibration treatment step described below before the treatment with the strongly acidic ion exchange resin.
Next, the change in pH is observed while adding aqueous sodium hydroxide solution, and a titration curve such as that shown in the upper part of Figure 1 is obtained. The titration curve shown in the upper part of Figure 1 plots the measured pH against the amount of alkali added, while the titration curve shown in the lower part of Figure 1 plots the pH increment (derivative value) (1/mmol) against the amount of alkali added. In this neutralization titration, two points are identified in the curve plotting the measured pH against the amount of alkali added, where the increment (derivative value of pH with respect to the amount of alkali added) is maximized. Of these, the first maximum point of the increment after starting to add the alkali is called the first endpoint, and the next maximum point of the increment is called the second endpoint. The amount of alkali required from the start of titration to the first endpoint is equal to the amount of first dissociated acid of the fibrous cellulose contained in the slurry used for titration, the amount of alkali required from the first endpoint to the second endpoint is equal to the amount of second dissociated acid of the fibrous cellulose contained in the slurry used for titration, and the amount of alkali required from the start of titration to the second endpoint is equal to the total amount of dissociated acid of the fibrous cellulose contained in the slurry used for titration.The value obtained by dividing the amount of alkali required from the start of titration to the first endpoint by the solids content (g) in the slurry to be titrated is the amount of phosphorus oxo acid group introduced (mmol/g).Note that when simply referring to the amount of phosphorus oxo acid group introduced (or amount of phosphorus oxo acid group), it refers to the amount of first dissociated acid.
In FIG. 1 , the region from the start of titration to the first endpoint is referred to as the first region, and the region from the first endpoint to the second endpoint is referred to as the second region. For example, when the phosphorus oxoacid group is a phosphate group and this phosphate group undergoes condensation, the amount of weakly acidic groups in the phosphorus oxoacid group (also referred to herein as the second dissociated acid amount) appears to decrease, and the amount of alkali required in the second region is less than the amount of alkali required in the first region. On the other hand, the amount of strongly acidic groups in the phosphorus oxoacid group (also referred to herein as the first dissociated acid amount) corresponds to the amount of phosphorus atoms regardless of whether condensation occurs. Furthermore, when the phosphorus oxoacid group is a phosphite group, the phosphorus oxoacid group no longer contains weakly acidic groups, so the amount of alkali required in the second region is reduced or may even be zero. In this case, there is only one point on the titration curve where the pH increment is maximized.
The above-mentioned amount of introduced phosphorus oxoacid groups (mmol/g) indicates the amount of phosphorus oxoacid groups possessed by the acid-form fibrous cellulose (hereinafter referred to as the amount of phosphorus oxoacid groups (acid form)), since the denominator indicates the mass of the acid-form fibrous cellulose. On the other hand, when the counter ions of the phosphorus oxoacid groups are substituted with any cation C so as to be charge equivalent, the amount of phosphorus oxoacid groups possessed by the fibrous cellulose with the cation C as the counter ion (hereinafter referred to as the amount of phosphorus oxoacid groups (C form)) can be determined by converting the denominator to the mass of the fibrous cellulose when the cation C is the counter ion.
That is, it is calculated using the following formula.
Amount of phosphorus oxoacid group (C type)=Amount of phosphorus oxoacid group (acid type)/{1+(W−1)×A/1000}
A [mmol/g]: total amount of anions derived from phosphorus oxoacid groups in the fibrous cellulose (the sum of the amount of strongly acidic groups and the amount of weakly acidic groups in the phosphorus oxoacid groups)
W: Formula weight per valence of cation C (for example, Na is 23, Al is 9)

FIG. 2 is a graph showing the relationship between the amount of NaOH dropped onto fibrous cellulose having a carboxy group and pH.
The amount of carboxyl groups introduced into the fibrous cellulose can be measured, for example, as follows.
First, a slurry containing fibrous cellulose is treated with a strongly acidic ion exchange resin. If necessary, the measurement object may be subjected to a defibration treatment similar to the defibration treatment step described below before treatment with the strongly acidic ion exchange resin. Next, the change in pH is observed while adding a sodium hydroxide aqueous solution, and a titration curve such as that shown in FIG. 2 is obtained. If necessary, the measurement object may be subjected to a defibration treatment similar to the defibration treatment step described below.
As shown in Figure 2, in this neutralization titration, a single point is observed where the increment (the differential value of pH with respect to the amount of alkali added) is maximum on the curve plotting the measured pH against the amount of alkali added. This maximum increment is called the first end point. Here, the region from the start of titration to the first end point in Figure 2 is called the first region. The amount of alkali required in the first region is equal to the amount of carboxyl groups in the slurry used for titration. The amount of alkali introduced (mmol/g) was then calculated by dividing the amount of alkali (mmol) required in the first region of the titration curve by the solids content (g) in the fine fibrous cellulose-containing slurry to be titrated.
The above-mentioned amount of carboxyl groups introduced (mmol/g) indicates the amount of substituents per 1 g of fibrous cellulose mass when the counter ion of the carboxyl group is a hydrogen ion (H ⁺ ) (hereinafter referred to as the amount of carboxyl groups (acid type)).

The above-mentioned amount of carboxy groups introduced (mmol/g) indicates the amount of carboxy groups possessed by the acid-form fibrous cellulose (hereinafter referred to as the amount of carboxy groups (acid form)), since the denominator is the mass of the acid-form fibrous cellulose. On the other hand, when the counter ions of the carboxy groups are substituted with any cation C so as to be charge equivalent, the amount of carboxy groups possessed by the fibrous cellulose in which the cation C is the counter ion (hereinafter referred to as the amount of carboxy groups (C form)) (mmol/g) can be determined by converting the denominator to the mass of the fibrous cellulose when the cation C is the counter ion.
That is, it is calculated using the following formula.
Amount of carboxyl group (C type)=Amount of carboxyl group (acid type)/{1+(W−1)×(Amount of carboxyl group (acid type))/1000}
W: Formula weight per valence of cation C (for example, Na is 23, Al is 9)

The amount of sulfur oxoacid groups introduced into the fine fibrous cellulose is determined by wet ashing the obtained fibrous cellulose using perchloric acid and concentrated nitric acid, diluting it at an appropriate ratio, and measuring the amount of sulfur by ICP emission spectrometry.
The amount of sulfur divided by the bone dry mass of the fibrous cellulose sample is taken as the amount of sulfur oxoacid groups (unit: mmol/g).

In measuring the amount of substituents by titration, if too much sodium hydroxide aqueous solution is added or if the titration interval is too short, the amount of substituents may be lower than expected, and an accurate value may not be obtained. An appropriate amount of addition and titration interval, for example, is preferably a 0.1 N sodium hydroxide aqueous solution titrated at 10 to 50 μL intervals over 5 to 30 seconds. Furthermore, to eliminate the influence of carbon dioxide dissolved in the fibrous cellulose-containing slurry, it is preferable to perform measurements while blowing an inert gas such as nitrogen gas into the slurry, for example, from 15 minutes before the start of titration until the end of titration.
The measurement of the amount of ionic groups by the above-mentioned method is applied to fine fibrous cellulose having a fiber width of 1,000 nm or less. When measuring the amount of ionic groups in pulp fibers having a fiber width of more than 1,000 nm, the pulp fibers are first finely divided before measurement.

[Method for producing fine fibrous cellulose]
(cellulose-containing fiber materials)
Fine fibrous cellulose is produced from a fiber raw material containing cellulose.
The cellulose-containing fiber raw material is not particularly limited, but pulp is preferably used because of its ease of availability and low cost. Examples of pulp include wood pulp, non-wood pulp, and deinked pulp. Examples of wood pulp include, but are not limited to, chemical pulps such as hardwood kraft pulp (LBKP), softwood kraft pulp (NBKP), sulfite pulp (SP), dissolving pulp (DP), soda pulp (AP), unbleached kraft pulp (UKP), and oxygen bleached kraft pulp (OKP); semi-chemical pulps such as semi-chemical pulp (SCP) and chemi-ground wood pulp (CGP); and mechanical pulps such as groundwood pulp (GP) and thermomechanical pulp (TMP, BCTMP). Examples of non-wood pulp include, but are not limited to, cotton-based pulps such as cotton linters and cotton lint, and non-wood pulps such as hemp, straw, bamboo, and bagasse. The deinked pulp is not particularly limited, but may be, for example, deinked pulp made from recycled paper. The pulp of this embodiment may be one of the above types alone or a mixture of two or more types.
Among the above pulps, wood pulp and deinked pulp are preferred from the viewpoint of ease of availability. Furthermore, among wood pulps, chemical pulp is more preferred, and kraft pulp and sulfite pulp are even more preferred, from the viewpoint of a high cellulose content, a high yield of fine fibrous cellulose during defibration treatment, and small decomposition of cellulose in the pulp to obtain long-fiber fine fibrous cellulose with a large axial ratio. Note that the use of long-fiber fine fibrous cellulose with a large axial ratio tends to increase viscosity.
As a fiber raw material containing cellulose, for example, cellulose contained in sea squirts and bacterial cellulose produced by acetic acid bacteria can be used.
Furthermore, instead of fiber raw materials containing cellulose, fibers formed from linear nitrogen-containing polysaccharide polymers such as chitin and chitosan can also be used.

To obtain fine fibrous cellulose having ionic groups introduced therein, it is preferable to have an ionic group introduction step, in which ionic groups are introduced into the cellulose-containing fiber raw material, followed in this order by a washing step, an alkali treatment step (neutralization step), and a defibration step. Alternatively, an acid treatment step may be included instead of or in addition to the washing step. Examples of ionic group introduction steps include a phosphorus oxoacid group introduction step, a carboxyl group introduction step, a sulfur oxoacid group introduction step, a xanthate group introduction step, a phosphonic or phosphine group introduction step, and a sulfonic group introduction step. Each step is explained below.

(Ionic group introduction step)
- Phosphorus oxo acid group introduction step -
The phosphorus oxo acid group introduction step is a step in which at least one compound (hereinafter also referred to as "compound A") selected from compounds capable of introducing phosphorus oxo acid groups by reacting with hydroxyl groups in a cellulose-containing fiber raw material is allowed to act on the cellulose-containing fiber raw material, thereby producing a phosphorus oxo acid group-introduced fiber.
In the phosphate group introduction step according to this embodiment, the reaction of the cellulose-containing fiber raw material with compound A may be carried out in the presence of at least one selected from urea and its derivatives (hereinafter also referred to as "compound B"). Alternatively, the cellulose-containing fiber raw material may be reacted with compound A in the absence of compound B.
One example of a method for reacting compound A with a fiber raw material in the presence of compound B is a method in which compound A and compound B are mixed with a fiber raw material in a dry, wet, or slurry state. Among these methods, using a fiber raw material in a dry or wet state is preferred, as this provides high reaction uniformity, and using a fiber raw material in a dry state is particularly preferred. The form of the fiber raw material is not particularly limited, but is preferably in the form of a cotton or thin sheet. Compound A and compound B may be added to the fiber raw material in the form of a powder, a solution dissolved in a solvent, or a melted state heated to or above their melting point. Among these methods, adding compound A and compound B in the form of a solution dissolved in a solvent, particularly an aqueous solution, is preferred, as this provides high reaction uniformity. Compound A and compound B may be added to the fiber raw material simultaneously, separately, or as a mixture. The method for adding compound A and compound B is not particularly limited, but when compound A and compound B are in the form of a solution, the fiber raw material may be immersed in the solution to absorb the liquid and then removed, or the solution may be added dropwise to the fiber raw material. Alternatively, the required amounts of compound A and compound B may be added to the fiber raw material, or excess amounts of compound A and compound B may be added to the fiber raw material, and then the excess compound A and compound B may be removed by squeezing or filtration.

The compound A used in this embodiment may be any compound that has a phosphorus atom and can form an ester bond with cellulose, including, but not limited to, phosphoric acid or a salt thereof, phosphorous acid or a salt thereof, dehydrated condensed phosphoric acid or a salt thereof, and phosphoric anhydride (diphosphorus pentoxide). Phosphoric acid can be used with various purities, such as 100% phosphoric acid (orthophosphoric acid) or 85% phosphoric acid. Phosphorous acid can be, for example, 99% phosphorous acid (phosphonic acid). Dehydrated condensed phosphoric acid is a compound in which two or more molecules of phosphoric acid are condensed by a dehydration reaction, and examples thereof include pyrophosphoric acid and polyphosphoric acid. Phosphates, phosphites, and dehydrated condensed phosphates include lithium salts, sodium salts, potassium salts, and ammonium salts of phosphoric acid, phosphorous acid, or dehydrated condensed phosphoric acid, which can be neutralized to various degrees.
Among these, phosphoric acid, sodium salts of phosphoric acid, potassium salts of phosphoric acid, and ammonium salts of phosphoric acid are preferred, and phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, and ammonium dihydrogen phosphate are more preferred, from the viewpoints of high efficiency in introducing phosphate groups, easier improvement of defibration efficiency in the defibration step described below, low cost, and ease of industrial application.
The amount of compound A added to the fiber raw material is not particularly limited, but for example, when the amount of compound A added is converted into the amount of phosphorus atoms, the amount of phosphorus atoms added to the fiber raw material (bone dry mass) is preferably 0.5% by mass or more and 100% by mass or less, more preferably 1% by mass or more and 50% by mass or less, and even more preferably 2% by mass or more and 30% by mass or less. By setting the amount of phosphorus atoms added to the fiber raw material within the above range, the yield of fine fibrous cellulose can be further improved. On the other hand, by setting the amount of phosphorus atoms added to the fiber raw material to the above upper limit or less, a balance can be achieved between the yield improvement effect and costs.

As described above, the compound B used in this embodiment is at least one selected from urea and its derivatives. Examples of the compound B include urea, biuret, 1-phenylurea, 1-benzylurea, 1-methylurea, and 1-ethylurea.
From the viewpoint of improving the uniformity of the reaction, it is preferable to use an aqueous solution of compound B. Furthermore, from the viewpoint of further improving the uniformity of the reaction, it is preferable to use an aqueous solution in which both compound A and compound B are dissolved.
The amount of compound B added relative to the fiber raw material (bone dry mass) is not particularly limited, but is preferably, for example, 1 mass % or more and 500 mass % or less, more preferably 10 mass % or more and 400 mass % or less, and even more preferably 100 mass % or more and 350 mass % or less.

In the reaction of cellulose-containing fiber raw materials with compound A, in addition to compound B, the reaction system may contain, for example, amides or amines. Examples of amides include formamide, dimethylformamide, acetamide, and dimethylacetamide. Examples of amines include methylamine, ethylamine, trimethylamine, triethylamine, monoethanolamine, diethanolamine, triethanolamine, pyridine, ethylenediamine, and hexamethylenediamine. Of these, triethylamine in particular is known to act as a good reaction catalyst.

In the phosphorus oxo acid group introduction process, compound A or the like is preferably added to or mixed with the fiber raw material, and then the fiber raw material is subjected to a heat treatment. The heat treatment temperature is preferably selected so that the phosphorus oxo acid group can be efficiently introduced while suppressing thermal decomposition and hydrolysis of the fiber. The heat treatment temperature is preferably, for example, 50°C to 300°C, more preferably 100°C to 250°C, and even more preferably 130°C to 200°C. Furthermore, various types of equipment with heat transfer media can be used for the heat treatment, including, for example, agitator dryers, rotary dryers, disk dryers, roll-type heaters, plate-type heaters, fluidized-bed dryers, band dryers, filtration dryers, vibration fluidized-bed dryers, flash dryers, vacuum dryers, infrared heaters, far-infrared heaters, microwave heaters, and high-frequency dryers.

In the heat treatment according to this embodiment, for example, a method of adding compound A to a thin sheet-like fiber raw material by a method such as impregnation and then heating the material, or a method of heating the fiber raw material while kneading or stirring the fiber raw material and compound A in a kneader or the like, can be employed. This makes it possible to suppress unevenness in the concentration of compound A in the fiber raw material and to more uniformly introduce phosphate groups onto the surface of the cellulose fibers contained in the fiber raw material. This is thought to be because, when water molecules move to the surface of the fiber raw material as it is dried, the dissolved compound A is attracted to the water molecules by surface tension and is prevented from similarly moving to the surface of the fiber raw material (i.e., causing unevenness in the concentration of compound A).
Furthermore, the heating device used for the heat treatment is preferably one that can constantly discharge, to the outside of the device system, moisture retained in the slurry and moisture generated in the dehydration condensation (phosphorylation) reaction between compound A and hydroxyl groups contained in cellulose or the like in the fiber raw material. Examples of such heating devices include an oven using a blower system. Constantly discharging moisture from the device system can suppress the hydrolysis reaction of phosphate ester bonds, which is the reverse reaction of phosphate esterification, as well as acid hydrolysis of sugar chains in the fiber. This makes it possible to obtain fine fibrous cellulose with a high axial ratio.
The heat treatment time is, for example, preferably from 1 second to 300 minutes after the water content has been substantially removed from the fiber raw material, more preferably from 1 second to 1,000 seconds, and even more preferably from 10 seconds to 800 seconds. In this embodiment, by setting the heating temperature and heating time within appropriate ranges, the amount of phosphorus oxo acid groups introduced can be kept within a preferred range.

The phosphorus oxo acid group introduction process needs to be performed at least once, but can also be repeated two or more times. By performing the phosphorus oxo acid group introduction process two or more times, a large number of phosphorus oxo acid groups can be introduced into the fiber raw material. In this embodiment, a preferred example is when the phosphorus oxo acid group introduction process is performed two times.

The amount of phosphorus oxoacid groups introduced into the fiber raw material is preferably 0.10 mmol/g or more per 1 g (mass) of fine fibrous cellulose, more preferably 0.20 mmol/g or more, even more preferably 0.50 mmol/g or more, and particularly preferably 1.00 mmol/g or more. Furthermore, the amount of phosphorus oxoacid groups introduced into the fiber raw material is preferably 5.20 mmol/g or less per 1 g (mass) of fine fibrous cellulose, more preferably 3.65 mmol/g or less, and even more preferably 3.00 mmol/g or less. By keeping the amount of phosphorus oxoacid groups introduced within the above range, it is possible to facilitate the micronization of the fiber raw material and improve the stability of the fine fibrous cellulose.

-Carboxy group introduction step-
The carboxyl group introduction process is carried out by treating a fiber raw material containing cellulose with an oxidation treatment such as ozone oxidation, oxidation by the Fenton method, or TEMPO oxidation treatment, or with a compound having a carboxylic acid-derived group or a derivative thereof, or an acid anhydride of a compound having a carboxylic acid-derived group or a derivative thereof.
Examples of compounds having a group derived from carboxylic acid include, but are not limited to, dicarboxylic acid compounds such as maleic acid, succinic acid, phthalic acid, fumaric acid, glutaric acid, adipic acid, and itaconic acid, and tricarboxylic acid compounds such as citric acid and aconitic acid. Examples of derivatives of compounds having a group derived from carboxylic acid include, but are not limited to, imidized products of acid anhydrides of compounds having carboxy groups, and derivatives of acid anhydrides of compounds having carboxy groups. Examples of imidized products of acid anhydrides of compounds having carboxy groups include, but are not limited to, imidized products of dicarboxylic acid compounds such as maleimide, succinimide, and phthalimide.

Acid anhydrides of compounds having a carboxylic acid-derived group include, but are not limited to, acid anhydrides of dicarboxylic acid compounds such as maleic anhydride, succinic anhydride, phthalic anhydride, glutaric anhydride, adipic anhydride, and itaconic anhydride. Furthermore, derivatives of acid anhydrides of compounds having a carboxylic acid-derived group include, but are not limited to, acid anhydrides of compounds having carboxy groups such as dimethylmaleic anhydride, diethylmaleic anhydride, and diphenylmaleic anhydride, in which at least some of the hydrogen atoms have been substituted with substituents such as alkyl groups or phenyl groups.

When TEMPO oxidation treatment is performed in the carboxyl group introduction step, it is preferable to perform the treatment under conditions of a pH of 6 or higher and 8 or lower. This type of treatment is also called a neutral TEMPO oxidation treatment. The neutral TEMPO oxidation treatment can be performed, for example, by adding pulp as the fiber raw material, a nitroxy radical such as TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl) as a catalyst, and sodium hypochlorite as a sacrificial reagent to a sodium phosphate buffer solution (pH = 6.8). Furthermore, by adding sodium chlorite, aldehydes generated during the oxidation process can be efficiently oxidized to carboxyl groups.
The TEMPO oxidation treatment may be carried out under conditions of a pH of 10 to 11. Such a treatment is also called alkaline TEMPO oxidation treatment. The alkaline TEMPO oxidation treatment can be carried out, for example, by adding a nitroxy radical such as TEMPO as a catalyst, sodium bromide as a co-catalyst, and sodium hypochlorite as an oxidizing agent to pulp as a fiber raw material.
The amount of carboxyl groups introduced into the fiber raw material varies depending on the type of substituent, but for example, when carboxyl groups are introduced by TEMPO oxidation, the amount is preferably 0.10 mmol/g or more, more preferably 0.20 mmol/g or more, even more preferably 0.50 mmol/g or more, and particularly preferably 0.90 mmol/g or more per 1 g (mass) of fine fibrous cellulose. Also, the amount is preferably 2.5 mmol/g or less, more preferably 2.20 mmol/g or less, and even more preferably 2.00 mmol/g or less. Alternatively, when the substituent is a carboxymethyl group, the amount may be 5.8 mmol/g or less per 1 g (mass) of fine fibrous cellulose.

- Sulfur oxo acid group introduction step -
The process for producing fine fibrous cellulose may include, for example, a sulfur oxoacid group introduction step as an ionic substituent introduction step, in which hydroxyl groups in a cellulose-containing fiber raw material react with sulfur oxoacids to produce cellulose fibers having sulfur oxoacid groups (sulfur oxoacid group-introduced fibers).

In the sulfur oxo acid group introduction process, instead of compound A in the above-described <Phosphorus oxo acid group introduction process>, at least one compound (hereinafter also referred to as "compound C") selected from compounds capable of introducing sulfur oxo acid groups by reacting with hydroxyl groups in fiber raw materials, including cellulose, is used. Compound C may be any compound containing a sulfur atom and capable of forming an ester bond with cellulose, including, but not limited to, sulfuric acid or its salts, sulfurous acid or its salts, and sulfuric acid amides. Sulfuric acid of various purities can be used, such as 96% sulfuric acid (concentrated sulfuric acid). Sulfurous acid can be 5% aqueous sulfurous acid. Sulfates or sulfites include lithium, sodium, potassium, and ammonium salts of sulfates or sulfites, which can be neutralized to various degrees. Sulfamic acid or other sulfuric acid amides can be used. In the sulfur oxo acid group introduction process, it is preferable to use compound B in the above-described <Phosphorus oxo acid group introduction process>.

In the sulfur oxoacid group introduction process, the cellulose raw material is preferably mixed with an aqueous solution containing sulfur oxoacid and urea and/or a urea derivative, and then the cellulose raw material is subjected to a heat treatment. The heat treatment temperature is preferably selected so that sulfur oxoacid groups can be efficiently introduced while suppressing thermal decomposition and hydrolysis of the fiber. The heat treatment temperature is preferably 100°C or higher, more preferably 120°C or higher, and even more preferably 150°C or higher. The heat treatment temperature is also preferably 300°C or lower, more preferably 250°C or lower, and even more preferably 200°C or lower.

In the heat treatment process, it is preferable to heat until the moisture is substantially eliminated. Therefore, the heat treatment time varies depending on the moisture content of the cellulose raw material and the amount of aqueous solution containing sulfur oxoacid and urea and/or urea derivative added, but is preferably 10 seconds or more and 10,000 seconds or less. Heat treatment can be performed using equipment with various heat transfer media, such as agitator dryers, rotary dryers, disk dryers, roll-type heaters, plate-type heaters, fluidized-bed dryers, band dryers, filtration dryers, vibration fluidized-bed dryers, pneumatic dryers, reduced-pressure dryers, infrared heaters, far-infrared heaters, microwave heaters, and high-frequency dryers.

The amount of sulfur oxoacid groups introduced into the cellulose raw material is preferably 0.05 mmol/g or more, more preferably 0.10 mmol/g or more, even more preferably 0.20 mmol/g or more, even more preferably 0.50 mmol/g or more, and particularly preferably 0.90 mmol/g or more. Furthermore, the amount of sulfur oxoacid groups introduced into the cellulose raw material is preferably 5.00 mmol/g or less, more preferably 3.00 mmol/g or less. By keeping the amount of sulfur oxoacid groups introduced within the above range, it is possible to easily refine the fiber raw material and increase the stability of fibrous cellulose.

- Oxidation step using a chlorine-based oxidizing agent (second carboxyl group introduction step) -
The process for producing fine fibrous cellulose may include, for example, an oxidation step using a chlorine-based oxidizing agent as a step for introducing an ionic substituent. In the oxidation step using a chlorine-based oxidizing agent, the chlorine-based oxidizing agent is added to a wet or dry fiber raw material having a hydroxyl group to cause a reaction, thereby introducing a carboxyl group into the fiber raw material.

Examples of chlorine-based oxidizing agents include hypochlorous acid, hypochlorites, chlorous acid, chlorites, chloric acid, chlorates, perchloric acid, perchlorates, chlorine dioxide, etc. From the viewpoints of efficiency of introducing substituents, and therefore defibration efficiency, cost, and ease of handling, sodium hypochlorite, sodium chlorite, and chlorine dioxide are preferred.
The chlorine-based oxidizing agent may be added to the fiber raw material as a reagent as it is, or may be dissolved in an appropriate solvent and then added.

The reaction temperature in the oxidation process using a chlorine-based oxidizing agent is preferably, for example, 10°C or higher and 100°C or lower, more preferably 15°C or higher and 80°C or lower, and even more preferably 20°C or higher and 60°C or lower.

The concentration of the chlorine-based oxidizing agent in the solution in the oxidation step using the chlorine-based oxidizing agent is, for example, converted into an effective chlorine concentration, preferably 1% by mass or more and 1,000% by mass or less, more preferably 5% by mass or more and 500% by mass or less, and even more preferably 10% by mass or more and 100% by mass or less.
The amount of the chlorine-based oxidizing agent added per 100 parts by mass of the fiber raw material is preferably 1 part by mass or more and 100,000 parts by mass or less, more preferably 10 parts by mass or more and 10,000 parts by mass or less, and even more preferably 100 parts by mass or more and 5,000 parts by mass or less.

The reaction time with the chlorine-based oxidizing agent in the oxidation step using a chlorine-based oxidizing agent may vary depending on the reaction temperature, but is preferably, for example, from 1 minute to 1,000 minutes, more preferably from 10 minutes to 500 minutes, and even more preferably from 20 minutes to 400 minutes.
The pH during the reaction is preferably 5 or more and 15 or less, more preferably 7 or more and 14 or less, and even more preferably 9 or more and 13 or less. At the start of the reaction and during the reaction, the pH is preferably maintained constant (for example, pH 11) by appropriately adding hydrochloric acid or sodium hydroxide. After the reaction, excess reaction reagents, by-products, etc. may be washed with water and removed by filtration or the like.

-Xanthate group introduction step (xanthogen acid esterification step)-
The process for producing fine fibrous cellulose may include, for example, a xanthate group introduction process (hereinafter also referred to as a xanthation process) as an ionic substituent introduction process. In the xanthation process, carbon disulfide and an alkali compound are added to a wet or dry fiber raw material having a hydroxyl group to react with each other, thereby introducing xanthate groups into the fiber raw material. Specifically, carbon disulfide is added to a fiber raw material that has been converted into alkali cellulose by the method described below, and the reaction is carried out.

<Alkali cellulose>
When introducing ionic functional groups into a fiber raw material, it is preferable to convert the cellulose contained in the fiber raw material into alkali cellulose by treating the cellulose with an alkaline solution. This treatment causes ionic dissociation of some of the hydroxyl groups in the cellulose, thereby increasing the nucleophilicity (reactivity). The alkaline compound contained in the alkaline solution is not particularly limited and may be an inorganic alkaline compound or an organic alkaline compound. Due to their high versatility, it is preferable to use, for example, sodium hydroxide, potassium hydroxide, tetraethylammonium hydroxide, or tetrabutylammonium hydroxide. The conversion into alkali cellulose may be performed simultaneously with the introduction of ionic functional groups, before the introduction, or at both stages.

The solution temperature at the start of alkali cellulose conversion is preferably between 0°C and 50°C, more preferably between 5°C and 40°C, and even more preferably between 10°C and 30°C.

The alkaline solution concentration is preferably 0.01 mol/L or more and 4 mol/L or less, more preferably 0.1 mol/L or more and 3 mol/L or less, and even more preferably 1 mol/L or more and 2.5 mol/L or less. In particular, when the treatment temperature is less than 10°C, a concentration of 1 mol/L or more and 2 mol/L or less is preferable.

The alkali cellulose treatment time is preferably 1 minute or more, more preferably 10 minutes or more, and even more preferably 30 minutes or more. The alkali treatment time is preferably 6 hours or less, more preferably 5 hours or less, and even more preferably 4 hours or less.

By adjusting the type of alkaline solution, treatment temperature, concentration, and immersion time as described above, it is possible to suppress the penetration of the alkaline solution into the crystalline regions of cellulose, making it easier to maintain the crystalline structure of cellulose type I and increasing the yield of fine fibrous cellulose.

If the introduction of ionic functional groups and the conversion to alkali cellulose are not carried out simultaneously, it is preferable to remove water from the alkali cellulose obtained by alkali treatment by solid-liquid separation using a common deliquoring method such as centrifugation or filtration. This improves the reaction efficiency in the subsequent ionic functional group introduction step. The cellulose fiber concentration after solid-liquid separation is preferably 5% to 50%, more preferably 10% to 40%, and even more preferably 15% to 35%.

-Phosphonic or phosphine group introduction step (phosphoalkylation step)-
The process for producing fine fibrous cellulose may include, as an ionic substituent introduction step, a phosphonic or phosphine group introduction step (phosphoalkylation step). In the phosphoalkylation step, a compound having a reactive group and a phosphonic or phosphine group (compound E _A ) as an essential component, and an alkali compound and a compound B selected from the above-mentioned urea and its derivatives as optional components, are added to a wet or dry fiber raw material having a hydroxyl group and reacted to introduce a phosphonic or phosphine group into the fiber raw material.

Examples of the reactive group include a halogenated alkyl group, a vinyl group, and an epoxy group (glycidyl group).
Examples of the compound E _A include vinylphosphonic acid, phenylvinylphosphonic acid, phenylvinylphosphinic acid, etc. Vinylphosphonic acid is preferred from the viewpoints of the efficiency of introducing a substituent, and hence the defibration efficiency, cost, and ease of handling.
Furthermore, as an optional component, it is also preferable to use the compound B in the above-mentioned <Phosphorus oxo acid group introduction step> in the same manner, and the amount added is also preferably as described above.

Compound E _A may be added to the fiber raw material as a reagent directly or dissolved in a suitable solvent. The fiber raw material is preferably converted into alkali cellulose in advance or simultaneously with the reaction. The method for converting into alkali cellulose is as described above.

The reaction temperature is preferably, for example, 50°C or higher and 300°C or lower, more preferably 100°C or higher and 250°C or lower, and even more preferably 130°C or higher and 200°C or lower.

The amount of compound E _A added per 100 parts by mass of the fiber raw material is preferably 1 part by mass or more and 100,000 parts by mass or less, more preferably 2 parts by mass or more and 10,000 parts by mass or less, and even more preferably 5 parts by mass or more and 1,000 parts by mass or less.

The reaction time may vary depending on the reaction temperature, but is preferably, for example, from 1 minute to 1,000 minutes, more preferably from 10 minutes to 500 minutes, and even more preferably from 20 minutes to 400 minutes.
After the reaction, excess reaction reagents, by-products, etc. may be washed and removed by filtration or the like.

-Sulfonic acid group introduction step (sulfoalkylation step)-
The process for producing fine fibrous cellulose may include, for example, a sulfonic acid group introduction step (sulfoalkylation step) as an ionic substituent introduction step. In sulfoalkylation, a compound having a reactive group and a sulfonic acid group (compound E _B ) as an essential component, and an alkali compound and the above-mentioned compound B selected from urea and its derivatives as optional components, are added to a wet or dry fiber raw material having a hydroxyl group and reacted to introduce a sulfonic acid group into the fiber raw material.

Examples of the reactive group include a halogenated alkyl group, a vinyl group, and an epoxy group (glycidyl group).
Examples of compound E _B include sodium 2-chloroethanesulfonate, sodium vinylsulfonate, sodium p-styrenesulfonate, 2-acrylamido-2-methylpropanesulfonic acid, etc. Among these, sodium vinylsulfonate is preferred from the standpoints of the efficiency of introducing substituents, and therefore defibration efficiency, cost, and ease of handling.
Furthermore, as an optional component, it is also preferable to use the compound B in the above-mentioned <Phosphorus oxo acid group introduction step> in the same manner, and the amount added is also preferably as described above.

Compound E _B may be added to the fiber raw material as a reagent directly or dissolved in a suitable solvent. The fiber raw material is preferably converted into alkali cellulose in advance or simultaneously with the reaction. The method for converting into alkali cellulose is as described above.

The reaction temperature is preferably, for example, 50°C or higher and 300°C or lower, more preferably 100°C or higher and 250°C or lower, and even more preferably 130°C or higher and 200°C or lower.

The amount of compound E _B added per 100 parts by mass of the fiber raw material is preferably 1 part by mass or more and 100,000 parts by mass or less, more preferably 2 parts by mass or more and 10,000 parts by mass or less, and even more preferably 5 parts by mass or more and 1,000 parts by mass or less.

The reaction time may vary depending on the reaction temperature, but is preferably, for example, from 1 minute to 1,000 minutes, more preferably from 10 minutes to 500 minutes, and even more preferably from 15 minutes to 400 minutes.
After the reaction, excess reaction reagents, by-products, etc. may be washed and removed by filtration or the like.

-Carboxyalkylation step (third carboxy group introduction step)-
The process for producing fine fibrous cellulose may include, for example, a carboxyalkylation step as a step for introducing an ionic substituent. A compound having a reactive group and a carboxy group (compound E _C ) as an essential component, an alkali compound as an optional component, and the aforementioned compound B selected from urea and its derivatives are added to a wet or dry fiber raw material having a hydroxyl group and reacted to introduce a carboxy group into the fiber raw material.

Examples of the reactive group include a halogenated alkyl group, a vinyl group, and an epoxy group (glycidyl group).
As the compound E _C , monochloroacetic acid, sodium monochloroacetate, 2-chloropropionic acid, 3-chloropropionic acid, sodium 2-chloropropionate, and sodium 3-chloropropionate are preferred from the standpoints of the efficiency of introducing substituents, and therefore the defibration efficiency, cost, and ease of handling.
Furthermore, as an optional component, it is also preferable to use the compound B in the above-mentioned <Phosphorus oxo acid group introduction step> in the same manner, and the amount added is also preferably as described above.

Compound E _{and C} may be added to the fiber raw material as a reagent directly or dissolved in a suitable solvent. The fiber raw material is preferably converted into alkali cellulose in advance or simultaneously with the reaction. The method for converting into alkali cellulose is as described above.

The reaction temperature is preferably, for example, 50°C or higher and 300°C or lower, more preferably 100°C or higher and 250°C or lower, and even more preferably 130°C or higher and 200°C or lower.

The amount of compound E _C added per 100 parts by mass of the fiber raw material is preferably 1 part by mass or more and 100,000 parts by mass or less, more preferably 2 parts by mass or more and 10,000 parts by mass or less, and even more preferably 5 parts by mass or more and 1,000 parts by mass or less.

The reaction time may vary depending on the reaction temperature, but is preferably, for example, from 1 minute to 1,000 minutes, more preferably from 3 minutes to 500 minutes, and even more preferably from 5 minutes to 400 minutes.
After the reaction, excess reaction reagents, by-products, etc. may be washed and removed by filtration or the like.

-Cationic group introduction step (cationization step)-
A compound having a reactive group and a cationic group (compound E _D ) as an essential component, an alkaline compound as an optional component, and the aforementioned compound B selected from urea and its derivatives are added to a wet or dry fiber raw material having a hydroxyl group and reacted to introduce a cationic group into the fiber raw material.

Reactive groups include halogenated alkyl groups, vinyl groups, and epoxy groups (glycidyl groups).

As the compound E _D , glycidyl trimethyl ammonium chloride, 3-chloro-2-hydroxypropyl trimethyl ammonium chloride, etc. are preferred from the viewpoints of the efficiency of introducing substituents, and hence the defibration efficiency, cost, and ease of handling.

Furthermore, as an optional component, it is also preferable to use compound B in the above-mentioned <Phosphorus Oxo Acid Group Introduction Step>. The amount added is also preferably as described above.

Compounds E _{and D} may be added to the fiber raw material as reagents or may be dissolved in an appropriate solvent and then added. The fiber raw material is preferably converted into alkali cellulose in advance or simultaneously with the reaction. The method for converting into alkali cellulose is as described above.

The reaction temperature is preferably, for example, 50°C or higher and 300°C or lower, more preferably 100°C or higher and 250°C or lower, and even more preferably 130°C or higher and 200°C or lower.

The amount of compound E _D added per 100 parts by mass of the fiber raw material is preferably 1 part by mass or more and 100,000 parts by mass or less, more preferably 2 parts by mass or more and 10,000 parts by mass or less, and even more preferably 5 parts by mass or more and 1,000 parts by mass or less.

The reaction time may vary depending on the reaction temperature, but is preferably, for example, from 1 minute to 1,000 minutes, more preferably from 5 minutes to 500 minutes, and even more preferably from 10 minutes to 400 minutes.
After the reaction, excess reaction reagents, by-products, etc. may be washed and removed by filtration or the like.

(Cleaning process)
In the method for producing fine fibrous cellulose according to the present embodiment, the ionic group-introduced fibers may be subjected to a washing step as needed. The washing step is carried out by washing the ionic group-introduced fibers with water or an organic solvent, for example. The washing step may be carried out after each step described below, and the number of washing steps carried out in each washing step is not particularly limited.

(Alkali treatment step)
When producing fine fibrous cellulose, the fiber raw material may be subjected to an alkali treatment between the ionic group introduction step and the defibration step described below. The alkali treatment method is not particularly limited, but an example thereof is a method of immersing the ionic group-introduced fiber in an alkali solution.
The alkaline compound contained in the alkaline solution is not particularly limited and may be an inorganic alkaline compound or an organic alkaline compound. In this embodiment, it is preferable to use, for example, sodium hydroxide or potassium hydroxide as the alkaline compound because of their high versatility. The solvent contained in the alkaline solution may be either water or an organic solvent. Among these, the solvent contained in the alkaline solution is preferably water or a polar solvent including a polar organic solvent such as an alcohol, and more preferably an aqueous solvent including at least water. As the alkaline solution, for example, an aqueous sodium hydroxide solution or an aqueous potassium hydroxide solution is preferable because of their high versatility.
The temperature of the alkaline solution in the alkaline treatment step is not particularly limited, but is preferably, for example, from 5° C. to 80° C., and more preferably from 10° C. to 60° C. The immersion time of the ionic group-introduced fiber in the alkaline solution in the alkaline treatment step is not particularly limited, but is, for example, preferably from 5 minutes to 30 minutes, and more preferably from 10 minutes to 20 minutes. The amount of alkaline solution used in the alkaline treatment is not particularly limited, but is, for example, preferably from 100% by mass to 100,000% by mass, and more preferably from 1,000% by mass to 10,000% by mass, based on the absolute dry mass of the ionic group-introduced fiber.
When the fine fibrous cellulose has anionic groups, the alkali treatment may be a neutralization treatment and ion exchange treatment of the anionic groups. In this case, the temperature of the alkali solution is preferably room temperature.

In order to reduce the amount of alkaline solution used in the alkaline treatment step, the ionic group-introduced fiber may be washed with water or an organic solvent after the ionic group introduction step but before the alkaline treatment step. From the perspective of improving handleability, it is preferable to wash the alkaline-treated ionic group-introduced fiber with water or an organic solvent after the alkaline treatment step but before the defibration treatment step.

(Acid treatment step)
When producing fine fibrous cellulose, the fiber raw material may be subjected to an acid treatment between the step of introducing ionic groups and the defibration treatment step described below. For example, the ionic group introduction step, acid treatment step, alkali treatment step, and defibration treatment step may be performed in this order.
The acid treatment method is not particularly limited, but examples include a method of immersing the fiber raw material in an acid-containing acid solution. The concentration of the acid solution used is not particularly limited, but is preferably 10% by mass or less, and more preferably 5% by mass or less. The pH of the acid solution used is also not particularly limited, but is preferably 0 to 4, and more preferably 1 to 3. Examples of the acid contained in the acid solution include inorganic acids, sulfonic acids, and carboxylic acids. Examples of inorganic acids include sulfuric acid, nitric acid, hydrobromic acid, hydroiodic acid, hypochlorous acid, chlorous acid, chloric acid, perchloric acid, phosphoric acid, and boric acid. Examples of sulfonic acids include methanesulfonic acid, ethanesulfonic acid, benzenesulfonic acid, p-toluenesulfonic acid, and trifluoromethanesulfonic acid. Examples of carboxylic acids include formic acid, acetic acid, citric acid, gluconic acid, lactic acid, oxalic acid, and tartaric acid. Among these, hydrochloric acid or sulfuric acid is particularly preferred.
The temperature of the acid solution in the acid treatment is not particularly limited, but is preferably from 5° C. to 100° C., and more preferably from 20° C. to 90° C. The immersion time in the acid solution in the acid treatment is not particularly limited, but is preferably from 5 minutes to 120 minutes, and more preferably from 10 minutes to 60 minutes. The amount of the acid solution used in the acid treatment is not particularly limited, but is preferably from 100% by mass to 100,000% by mass, and more preferably from 1,000% by mass to 10,000% by mass, based on the absolute dry mass of the fiber raw material.
When the fine fibrous cellulose has cationic groups, the acid treatment may be a neutralization treatment/ion exchange treatment of the cationic groups. In this case, the temperature of the acid solution is preferably room temperature.

(Fibrillation process)
By subjecting the ionic group-introduced fibers to defibration treatment in a defibration treatment step, fine fibrous cellulose can be obtained.
In the defibration treatment step, for example, a defibration treatment device can be used. The defibration treatment device is not particularly limited, but examples that can be used include a high-speed defibrator, a grinder (stone mill-type grinder), a high-pressure homogenizer, an ultra-high-pressure homogenizer, a high-pressure collision grinder, a ball mill, a bead mill, a disk-type refiner, a conical refiner, a twin-screw kneader, a vibration mill, a homomixer under high-speed rotation, an ultrasonic disperser, or a beater. Among the above defibration treatment devices, it is more preferable to use a high-speed defibrator, a high-pressure homogenizer, or an ultra-high-pressure homogenizer, which are less affected by the grinding media and have less risk of contamination.

In the defibration process, it is preferable to dilute the ionic group-introduced fibers with a dispersion medium to form a slurry. The dispersion medium can be one or more selected from water and organic solvents such as polar organic solvents. Polar organic solvents are not particularly limited, but examples of preferred solvents include alcohols, polyhydric alcohols, ketones, ethers, esters, and aprotic polar solvents. Examples of alcohols include methanol, ethanol, isopropanol, n-butanol, and isobutyl alcohol. Examples of polyhydric alcohols include ethylene glycol, propylene glycol, and glycerin. Examples of ketones include acetone and methyl ethyl ketone (MEK). Examples of ethers include diethyl ether, tetrahydrofuran, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol mono-n-butyl ether, and propylene glycol monomethyl ether. Examples of esters include ethyl acetate and butyl acetate. Examples of aprotic polar solvents include dimethyl sulfoxide (DMSO), dimethylformamide (DMF), dimethylacetamide (DMAc), and N-methyl-2-pyrrolidinone (NMP).

The solid content concentration of the fine fibrous cellulose during the defibration treatment can be appropriately set.
The slurry obtained by dispersing the phosphorus oxo acid group-introduced fibers in a dispersion medium may contain solid components other than the phosphorus oxo acid group-introduced fibers, such as urea having hydrogen bonding properties.

From the viewpoint of transparency of the radiation-sensitive sheet and enabling the formation of fine patterns, the content of fine fibrous cellulose in the solid content of the radiation-sensitive sheet is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 15% by mass or more, and is preferably 70% by mass or less, more preferably 60% by mass or less, even more preferably 55% by mass or less, even more preferably 50% by mass or less, and particularly preferably 45% by mass or less.
As the fine fibrous cellulose, a fine fibrous cellulose containing an ionic group, which will be described later, and an unmodified fine fibrous cellulose may be used in combination.

<Radiation sensitive composition>
The negative-working radiation-sensitive sheet of this embodiment contains a radiation-sensitive composition.
In this embodiment, the radiation-sensitive composition contains a compound (X) that has a polymerizable unsaturated bond, a Hansen solubility parameter (HSP) distance with water of 36 MPa ^0.5 or less, and a polarity term (dP) of 10 MPa ^0.5 or more. In addition to the compound (X), the composition preferably contains a polymerization initiator, and more preferably a photopolymerization initiator.
The solubility of compound (X) in a solvent decreases when the radiation-sensitive compound is irradiated. That is, compound (X) has the property of polymerizing and/or crosslinking due to the action of reactive active species such as radicals generated from the radiation-sensitive compound upon irradiation. The radiation-sensitive compound imparts radiation-sensitivity to the radiation-sensitive composition.
The radiation-sensitive compound is a compound that generates reactive species upon exposure to radiation. Here, radiation includes at least visible light, ultraviolet light, far ultraviolet light, electron beams (charged particle beams), and X-rays. Among these, ultraviolet light is preferred. The radiation-sensitive compound is preferably an acid generator, a polymerization initiator, or a combination thereof, more preferably a polymerization initiator, and even more preferably a photopolymerization initiator.
When an acid generator is used, a negative radiation-sensitive composition can be obtained by adding other additive components.

[Compound (X)]
The compound (X) contains a polymerizable unsaturated bond, and has a Hansen solubility parameter (HSP) distance with water of 36 MPa ^0.5 or less and a polarity term (dP) of 10 MPa ^0.5 or more.
Examples of the polymerizable unsaturated bond include a carbon-carbon double bond (hereinafter also referred to as an ethylenically unsaturated bond) and a carbon-carbon triple bond, and among these, an ethylenically unsaturated bond is preferred.
The ethylenically unsaturated bond is preferably derived from a (meth)acryloyloxy group or a (meth)acrylamide group, more preferably derived from an acryloyloxy group or an acrylamide group, and even more preferably derived from an acrylamide group. That is, compound (X) preferably has at least one of a (meth)acryloyloxy group and a (meth)acrylamide group, more preferably has at least one of an acryloyl group and an acrylamide group, and even more preferably has an acrylamide group.
The number of polymerizable unsaturated bonds that compound (X) has in one molecule may be 1 or more, preferably 2 or more, and is preferably 8 or less, more preferably 6 or less, and even more preferably 4 or less.

(HSP distance and polarity terms)
In order to make the sheet transparent even when the content of the radiation-sensitive composition is increased, the radiation-sensitive composition must not only be water-soluble but also have extremely high affinity for water.
The Hansen solubility parameter (HSP) is widely used as an index of affinity with water. HSP expresses the solubility of a substance using three vectors: dispersion term (dD), polar term (dP), and hydrogen bond term (dH). The shorter the distance between these vectors, i.e., the closer the compatibility between substances with similar HSPs, the higher the compatibility. The HSP distance (Ra) between substance 1 and substance 2 is expressed by the following (Equation 1):
Ra={4×(dD ₁ −dD ₂ ) ² +(dP ₁ −dP ₂ ) ² +(dH ₁ −dH ₂ ) ² } ^0.5 (Formula 1)
Here, dD ₁ , dP ₁ , and dH ₁ represent the dispersion term, polar term, and hydrogen bond term of substance 1, respectively, and dD ₂ , dP ₂ , and dH ₂ represent the dispersion term, polar term, and hydrogen bond term of substance 2, respectively.
When substance 1 is water and substance 2 is compound (X), it can exhibit affinity for water.
The HSP distance is determined by determining the HSP of each substance using Hansen Solubility Parameters in Practice (HSPiP (software name)), 5th Edition, Ver. 5.2.07, and calculating according to (Equation 1). When substance 1 is water, dD ₁ = 15.6 MPa ^0.5 , dP ₁ = 16.0 MPa ^0.5 , and dH ₁ = 42.3 MPa ^0.5 .
In the radiation-sensitive sheet of the present invention, it is preferred that compound (X) has a high affinity for water, and the HSP distance of compound (X) to water is 36 MPa ^0.5 or less, preferably 35 MPa ^0.5 or less. The lower limit of the HSP is not particularly limited, but from the viewpoint of availability and molecular design of compound (X), it is preferably 20 MPa ^0.5 or more, more preferably 25 MPa ^0.5 or more, and even more preferably 30 MPa ^0.5 or more.
Furthermore, the polar term (dP) of the Hansen solubility parameter of compound (X) is 10 MPa ^0.5 or more, preferably 11 MPa ^0.5 or more, and more preferably 12 MPa ^0.5 or more. The upper limit of the polar term (dP) is not particularly limited, but from the viewpoint of availability and the molecular design of compound (X), it is preferably 30 MPa ^0.5 or less, more preferably 25 MPa ^0.5 or less, and even more preferably 20 MPa ^0.5 or less. The polar term of the Hansen solubility parameter of water is 16.0 MPa ^0.5 .

The compound (X) is not particularly limited as long as it has a polymerizable unsaturated bond and has the above-mentioned HSP distance and dP, but is preferably soluble in water, alcohol, or a mixed solvent thereof, more preferably soluble in water, methanol, or ethanol, and particularly preferably soluble in water.
When compound (X) is soluble in water, alcohol, or a mixed solvent thereof, it has high affinity with the fine fibrous cellulose dispersion and facilitates removal of the radiation-sensitive composition in the unexposed areas with a developer, thereby providing a patterned sheet from which the radiation-sensitive composition in the unexposed areas has been removed across the entire thickness direction.

The compound (X) includes not only compounds generally called polymers, but also lower molecular weight compounds, so-called oligomers and monomers.
That is, compound (X) is not particularly limited as long as it has a polymerizable unsaturated bond and has a predetermined HSP distance and dP, and is a compound whose solubility in a solvent decreases due to a reaction induced by reactive species such as radicals generated from the radiation-sensitive compound upon irradiation. Among these, compound (X) is preferably a compound whose solubility in a solvent decreases due to a polymerization reaction induced by radicals generated from the radiation-sensitive compound.

When compound (X) is a polymer compound, examples of the backbone structure thereof include polyalkylene glycols (polyethylene glycol, polypropylene glycol, etc.), cellulose derivatives (hydroxyethyl cellulose, carboxyethyl cellulose, carboxymethyl cellulose, etc.), casein, dextrin, polyvinyl alcohol, modified polyvinyl alcohols (acetoacetylated polyvinyl alcohol, ethylene-vinyl alcohol copolymer, ethylene oxide-modified polyvinyl alcohol, etc.), polyalkylene oxides (polyethylene oxide, etc.), polyvinylpyrrolidone, polyvinyl methyl ether, polyacrylates, polyacrylamide, acrylic acid ester copolymers, urethane copolymers, polyhydroxystyrene copolymers, polyalkyleneimines, etc. Among the above, structures containing polyethylene glycol, polyethylene oxide, polyvinyl alcohol, modified polyvinyl alcohol, polyacrylamide, acrylic acid ester copolymers, and polyalkyleneimines are particularly preferred.
When the compound (X) is a polymer, the compound (X) has a polymerizable unsaturated bond in addition to the above-described skeletal structure, and therefore the compound (X) is a compound that is polymerized via the polymerizable unsaturated bond.

As described above, the compound (X) used in the negative radiation-sensitive sheet has a polymerizable unsaturated group in addition to the above-mentioned skeleton structure.
Examples of the polymerizable unsaturated group include an acryloyloxy group, a methacryloyloxy group, an acrylamide group, and a methacrylamide group, and it is particularly preferable to use the group in combination with a photopolymerization initiator as the radiation-sensitive compound.
For example, when a portion of the radiation-sensitive sheet is irradiated with radiation, the non-irradiated portion of the sheet does not undergo a crosslinking reaction via polymerization of polymerizable unsaturated groups such as acryloyloxy groups, resulting in high solubility in a developer, etc. On the other hand, in the irradiated portion (exposed portion), radicals generated by the photoreaction of the photopolymerization initiator catalyze a crosslinking reaction via polymerization of polymerizable unsaturated groups, thereby suppressing solubility in a developer, etc. In other words, the radiation-sensitive sheet can usually exhibit negative radiation sensitivity.

When the radiation-sensitive sheet is a negative type, it is preferable to use an oligomer or monomer having a lower molecular weight as the compound (X).
From the viewpoint of obtaining a desired HSP distance, the compound (X) preferably has an ether bond, an amide bond, an ester bond, or an amino group (—NH—).
Suitable examples of compound (X) include the following compounds:

In this embodiment, when the radiation-sensitive sheet is a negative type, in addition to the compound (X), a polymerizable unsaturated compound (hereinafter also referred to as "another polymerizable unsaturated compound") that satisfies at least one of the following conditions: an HSP distance of more than 36 MPa ^0.5 and a polar term (dP) of less than 10 MPa ^0.5 may be used in combination.
The other polymerizable unsaturated compound is an unsaturated compound that polymerizes by irradiating the radiation-sensitive sheet with radiation in the presence of the radiation-sensitive compound in the radiation-sensitive composition. Such other polymerizable unsaturated compound is not particularly limited, but for example, a polyfunctional (meth)acrylic acid ester having two or more functional groups is preferred from the viewpoints of good polymerizability and improved strength of the radiation-sensitive sheet formed.
The other polymerizable unsaturated compounds may be used alone or in combination of two or more.

When the radiation-sensitive composition contains other polymerizable unsaturated compounds, the content of the other polymerizable compounds is preferably 100 parts by mass or less, more preferably 50 parts by mass or less, even more preferably 30 parts by mass or less, and even more preferably 10 parts by mass or less, per 100 parts by mass of compound (X).

Of the other polymerizable unsaturated compounds, examples of the bifunctional (meth)acrylic esters include ethylene glycol di(meth)acrylate, dipropylene glycol diacrylate, diethylene glycol di(meth)acrylate, tetraethylene glycol diacrylate, tetraethylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, and 1,9-nonanediol di(meth)acrylate. Commercially available examples of these compounds include Aronix (registered trademark) M-220 and M-240 (both manufactured by Toagosei Co., Ltd.), KAYARAD (registered trademark) HX-220 and R-604 (both manufactured by Nippon Kayaku Co., Ltd.), Viscoat 260 (manufactured by Osaka Organic Chemical Industry Ltd.), and Light Acrylate 1,9-NDA (manufactured by Kyoeisha Chemical Co., Ltd.).

Among the other polymerizable unsaturated compounds, examples of the tri- or higher functional (meth)acrylic acid esters include trimethylolpropane tri(meth)acrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, dipentaerythritol pentaacrylate, and dipentaerythritol hexaacrylate;
a mixture of dipentaerythritol pentaacrylate and dipentaerythritol hexaacrylate;
Ethylene oxide-modified pentaerythritol tetraacrylate, tri(2-(meth)acryloyloxyethyl)phosphate, succinic acid-modified pentaerythritol triacrylate, succinic acid-modified dipentaerythritol pentaacrylate, tripentaerythritol heptaacrylate, tripentaerythritol octaacrylate, isocyanuric acid EO-modified diacrylate, isocyanuric acid EO-modified triacrylate;
A mixture of an EO-modified isocyanuric acid diacrylate and an EO-modified isocyanuric acid triacrylate is exemplified.

Furthermore, among other polymerizable unsaturated compounds, examples of polyfunctional (meth)acrylic acid esters include polyfunctional urethane acrylate compounds obtained by reacting a compound having a linear alkylene group and an alicyclic structure and having two or more isocyanate groups with a compound having one or more hydroxyl groups and three, four, or five (meth)acryloyloxy groups in the molecule.
Examples of commercially available tri- or higher functional (meth)acrylic acid esters include, by trade name, Aronix (registered trademark) M-309, M-400, M-405, and M-450 (all manufactured by Toagosei Co., Ltd.), KAYARAD (registered trademark) TMPTA, KAYARAD DPHA, KAYARAD DPCA-20, KAYARAD DPCA-30, KAYARAD DPCA-60, and KAYARAD DPEA-12 (all manufactured by Nippon Kayaku Co., Ltd.), and Viscoat 295 (manufactured by Osaka Organic Chemical Industry Ltd.).

The molecular weight of compound (X) (weight average molecular weight when it has a molecular weight distribution) is not particularly limited, but from the viewpoint of enabling fine patterning and obtaining the desired HSP and dP, it is sufficient if it is 100 or more, preferably 120 or more, and more preferably 150 or more. Moreover, the molecular weight (weight average molecular weight) of compound (X) is preferably 100,000 or less, and more preferably 10,000 or less.
The weight average molecular weight can be measured, for example, by using GPC.

<Radiation sensitive compound>
In the present invention, the radiation-sensitive composition preferably contains a photopolymerization initiator as the radiation-sensitive compound.
[Photopolymerization initiator]
A photopolymerization initiator (hereinafter also simply referred to as "polymerization initiator") is a component that responds to radiation and generates active species capable of initiating polymerization of a polymerizable compound. By including a polymerization initiator, the radiation-sensitive composition of this embodiment can exhibit, for example, negative radiation sensitivity to alkaline developers. Examples of photopolymerization initiators include photoradical polymerization initiators. Photopolymerization initiators can initiate a crosslinking reaction of a compound having a polymerizable group upon exposure to radiation such as visible light, ultraviolet light, far ultraviolet light, electron beams, and X-rays. A preferred photopolymerization initiator is, for example, a photopolymerization initiator that generates the most radicals when exposed to ultraviolet light, particularly around 365 nm.
Examples of the photoradical polymerization initiator include O-acyloxime compounds, acetophenone compounds, biimidazole compounds, acylphosphine oxide compounds, etc. These compounds can be used alone or in combination of two or more.

Examples of O-acyloxime compounds include 1-[4-(phenylthio)-2-(O-benzoyloxime)], 1,2-octanedione-1-[4-(phenylthio)-2-(O-benzoyloxime)], ethanone-1-[9-ethyl-6-(2-methylbenzoyl)-9H-carbazol-3-yl]-1-(O-acetyloxime), 1-[9-ethyl-6-benzoyl-9H-carbazol-3-yl]-octan-1-one oxime-O-acetate, 1-[9-ethyl-6-(2-methylbenzoyl)-9H-carbazol-3-yl]-ethan-1-one oxime-O-benzoate, and 1-[9-n-butyl-6-(2-ethylbenzoyl)-9H-carbazol-3-yl]-ethan-1-one oxime-O-acetate. [0033] Examples thereof include ethanone-O-benzoate, ethanone-1-[9-ethyl-6-(2-methyl-4-tetrahydrofuranylbenzoyl)-9H-carbazol-3-yl]-1-(O-acetyloxime), ethanone-1-[9-ethyl-6-(2-methyl-4-tetrahydropyranylbenzoyl)-9H-carbazol-3-yl]-1-(O-acetyloxime), ethanone-1-[9-ethyl-6-(2-methyl-5-tetrahydrofuranylbenzoyl)-9H-carbazol-3-yl]-1-(O-acetyloxime), ethanone-1-[9-ethyl-6-{2-methyl-4-(2,2-dimethyl-1,3-dioxolanyl)methoxybenzoyl}-9H-carbazol-3-yl]-1-(O-acetyloxime).

Examples of the acetophenone compound include an α-aminoketone compound and an α-hydroxyketone compound.
Examples of the α-aminoketone compound include 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butan-1-one, 2-dimethylamino-2-(4-methylbenzyl)-1-(4-morpholin-4-yl-phenyl)-butan-1-one, and 2-methyl-1-(4-methylthiophenyl)-2-morpholinopropan-1-one.
Examples of α-hydroxyketone compounds include 1-phenyl-2-hydroxy-2-methylpropan-1-one, 1-(4-i-propylphenyl)-2-hydroxy-2-methylpropan-1-one, 4-(2-hydroxyethoxy)phenyl-(2-hydroxy-2-propyl)ketone, 1-hydroxycyclohexylphenyl ketone, 2-hydroxy-1-{4-[2-(2-hydroxyethoxy)ethoxy]phenyl}-2-methylpropan-1-one, and 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone.

Examples of biimidazole compounds include 2,2'-bis(2-chlorophenyl)-4,4',5,5'-tetraphenyl-1,2'-biimidazole, 2,2'-bis(2,4-dichlorophenyl)-4,4',5,5'-tetraphenyl-1,2'-biimidazole, and 2,2'-bis(2,4,6-trichlorophenyl)-4,4',5,5'-tetraphenyl-1,2'-biimidazole.
Examples of the acylphosphine oxide compound include 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide, phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, and lithium phenyl(2,4,6-trimethylbenzoyl)phosphinate.

Among these, the photopolymerization initiator is preferably an acetophenone compound, and more preferably an α-hydroxyketone compound, from the viewpoints of affinity with the fine fibrous slurry used in producing the radiation-sensitive sheet, solubility in the developer, and the like.
By including a photopolymerization initiator in the radiation-sensitive sheet, for example, when a part of the radiation-sensitive sheet is irradiated with radiation, the solubility of the irradiated part (exposed part) in a developer or the like can be reduced. In other words, the radiation-sensitive sheet can exhibit negative radiation sensitivity.

The content of the photopolymerization initiator in the radiation-sensitive composition of this embodiment is preferably 1 part by mass or more, more preferably 5 parts by mass or more, and preferably 40 parts by mass or less, more preferably 20 parts by mass or less, per 100 parts by mass of compound (X). Using a photopolymerization initiator in this range can impart excellent radiation sensitivity. Furthermore, by keeping the content of the photopolymerization initiator in this range, a radiation-sensitive sheet containing the radiation-sensitive composition of this embodiment can exhibit negative radiation sensitivity even at low exposure doses.

From the viewpoint of enabling fine patterning, the content of the radiation-sensitive composition in the solid content of the radiation-sensitive sheet is preferably 30% by mass or more, more preferably 40% by mass or more, even more preferably 45% by mass or more, even more preferably 50% by mass or more, and particularly preferably 55% by mass or more, and is preferably 95% by mass or less, more preferably 90% by mass or less, and even more preferably 85% by mass or less.

The radiation-sensitive composition is preferably dissolved in at least one of water, alcohol, or a mixed solvent thereof, which is preferable because it facilitates the coating or papermaking process described below.
The radiation-sensitive composition being soluble in at least one of water, alcohol, or a mixed solvent thereof means that 1 g or more of the radiation-sensitive composition is soluble in 100 g of water, an alcohol having from 1 to 6 carbon atoms (preferably an alcohol having from 1 to 4 carbon atoms, more preferably an alcohol having from 1 to 3 carbon atoms), or a mixed solvent of water and an alcohol having from 1 to 6 carbon atoms at 25°C and atmospheric pressure.
Dissolving the radiation-sensitive composition in at least one of water, alcohol, and a mixed solvent is preferred because it has high affinity with the fine fibrous cellulose, making it possible to prepare a uniform coating solution or papermaking slurry, and also because it makes it easy to remove the unexposed areas with a developer, making it possible to obtain a patterned sheet from which the radiation-sensitive composition has been removed across the entire thickness direction.

In order to provide a radiation-sensitive composition that dissolves in at least one of water, alcohol, or a mixed solvent thereof, the radiation-sensitive sheet of the present invention is preferably negative-type. By providing a negative-type radiation-sensitive sheet, it is possible to select a low-molecular-weight, hydrophilic monomer or oligomer as the radiation-sensitive composition, and to provide a radiation-sensitive composition that dissolves in water, alcohol, or a mixed solvent thereof.

<Other ingredients>
The radiation-sensitive sheet of the present invention may contain other components in addition to the above-mentioned fine fibrous cellulose, compound (X), and radiation-sensitive compound (for example, acid generator, photopolymerization initiator).
Examples of other components include hydrophilic polymers, monofunctional polymerizable unsaturated compounds, wet strength agents, organic ions, crosslinking agents, surfactants, coupling agents, inorganic layered compounds, inorganic compounds, leveling agents, preservatives, antifoaming agents, organic particles, lubricants, antistatic agents, UV absorbers, dyes, pigments, stabilizers, magnetic powders, orientation promoters, plasticizers, and dispersants.

(Hydrophilic polymer)
The radiation-sensitive sheet of the present invention may contain a hydrophilic polymer. The hydrophilic polymer refers to a polymer compound having a weight-average molecular weight of 5,000 or more and a solubility of 1 g or more in 100 mL of ion-exchanged water at normal pressure and 25°C.
The hydrophilic polymer does not include the above-mentioned resin for the radiation-sensitive composition, and does not have an acid-decomposable group or a radical-polymerizable group whose solubility in a solvent changes significantly due to an acid or radical generated by irradiating the radiation-sensitive compound with radiation.

The hydrophilic polymer is preferably a hydrophilic oxygen-containing organic compound (excluding the above-mentioned cellulose fiber). The hydrophilic oxygen-containing organic compound preferably has an SP value of 9.0 or more, for example.
Examples of hydrophilic polymers used in the present invention include polyalkylene glycols (polyethylene glycol, polypropylene glycol, etc.), cellulose derivatives (hydroxyethylmethylcellulose, hydroxypropylmethylcellulose, hydroxyethylcellulose, methylcellulose, carboxyethylcellulose, carboxymethylcellulose, etc.), proteins such as casein, starches (dextrin, cationized starch, raw starch, oxidized starch, etherified starch, esterified starch, amylose, etc.), polyvinyl alcohol, modified polyvinyl alcohol (acetoacetylated polyvinyl alcohol, ethylene-vinyl alcohol copolymer, ethylene oxidized polyvinyl alcohol, etc.), polyalkylene oxides (polyethylene oxy Examples of suitable polyols include polyvinylpyrrolidone, polyvinyl methyl ether, polyacrylates (sodium polyacrylate, etc.), polycations (polyacrylamide, polyethyleneimine, etc.), polyanions, amphoteric polymers, alkyl acrylate copolymers, urethane copolymers, thickening polysaccharides (xanthan gum, guar gum, tamarind gum, locust bean gum, quince seed, alginic acid, metal salts of alginic acid, pullulan, carrageenan, saccharin, pectin, etc.), polyesters, modified polyesters, modified polyimides, glycerins such as polyglycerin, hyaluronic acid, metal salts of hyaluronic acid, carboxyvinyl polymers, alkyl methacrylates, acrylic acid copolymers, and polyacrylates (sodium polyacrylate, etc.). Among the above, polyethylene glycol, polyethylene oxide, polyvinyl alcohol, and modified polyvinyl alcohol are particularly preferred.

The weight-average molecular weight of the hydrophilic polymer is not particularly limited as long as it is 5,000 or more, but from the viewpoint of the shape stability of the radiation-sensitive sheet and enabling fine patterning, it is preferably 10,000 or more, more preferably 15,000 or more, and even more preferably 20,000 or more. The weight-average molecular weight of the hydrophilic polymer is preferably 8 million or less, more preferably 5 million or less, even more preferably 1 million or less, and still more preferably 100,000 or less.
The weight average molecular weight can be measured, for example, by using GPC.

The content of the hydrophilic polymer in the solid content of the radiation-sensitive sheet is preferably 15% by mass or less, more preferably 13% by mass or less, and even more preferably 10% by mass or less, and 0% by mass or more, from the viewpoint of enabling shape stability of the radiation-sensitive sheet and fine patterning.
In one aspect of this embodiment, it is also preferable that the radiation-sensitive sheet does not contain a hydrophilic polymer.

(Monofunctional polymerizable unsaturated compound)
Examples of the monofunctional polymerizable unsaturated compound include (meth)acrylic acid esters, such as 2-hydroxyethyl (meth)acrylate, diethylene glycol monoethyl ether (meth)acrylate, ω-carboxypolycaprolactone monoacrylate, etc. Commercially available products of these compounds include, by trade name, Aronix (registered trademark) M-101A, M-111, M-113, and M-5300 (all manufactured by Toagosei Co., Ltd.).

(Wet strength agent)
Wet strength agents are chemicals that prevent the paper from losing strength when it gets wet. When added to pulp fibers that tend to loosen in water, they help maintain the bonds between the pulp fibers even when wet, making them less likely to loosen, thereby increasing the paper's strength.
Examples of wet strength agents include polyamine polyamide epihalohydrin, melamine formaldehyde resin, and urea formaldehyde resin.
Polyamine polyamide epichlorohydrin is synthesized by adding epichlorohydrin to a main chain formed by condensing a polyvalent acid and a polyethylene polyamine. Polyamine polyamide epichlorohydrin can be used over a wide pH range and can achieve high wet strength at low addition amounts.
Melamine formaldehyde resin is synthesized by adding formaldehyde to melamine and then acid condensing the mixture.
Urea-formaldehyde resin is synthesized by adding formaldehyde to urea and then partially crosslinking the resulting mixture.
Among these, polyamine polyamide epihalohydrin is preferred from the viewpoint of obtaining a sheet having low water absorption and linear thermal expansion coefficient and excellent transparency. Among polyamine polyamide epihalohydrins, polyamine polyamide epichlorohydrin is more preferred.

(organic ions)
Examples of organic ions include tetraalkylammonium ions and tetraalkylphosphonium ions. Examples of tetraalkylammonium ions include tetramethylammonium ion, tetraethylammonium ion, tetrapropylammonium ion, tetrabutylammonium ion, tetrapentylammonium ion, tetrahexylammonium ion, tetraheptylammonium ion, tributylmethylammonium ion, lauryltrimethylammonium ion, cetyltrimethylammonium ion, stearyltrimethylammonium ion, octyldimethylethylammonium ion, lauryldimethylethylammonium ion, didecyldimethylammonium ion, lauryldimethylbenzylammonium ion, and tributylbenzylammonium ion. Examples of tetraalkylphosphonium ions include tetramethylphosphonium ion, tetraethylphosphonium ion, tetrapropylphosphonium ion, tetrabutylphosphonium ion, and lauryltrimethylphosphonium ion. Examples of tetrapropylonium ions and tetrabutylonium ions include tetra-n-propylonium ion and tetra-n-butylonium ion, respectively.

<Method for producing radiation-sensitive sheet>
The radiation-sensitive sheet of the present invention can be obtained by preparing an aqueous dispersion (slurry) containing fine fibrous cellulose, a radiation-sensitive composition, and other components, and forming the dispersion into a sheet.
The method for forming the sheet is not particularly limited, but it is preferably obtained by a coating process in which the slurry is coated on a substrate, dried, and the formed sheet is peeled off from the substrate, or a papermaking process in which the slurry is made into paper. Alternatively, a radiation-sensitive sheet may be continuously produced by using a coating device and a belt-shaped substrate. Among these, it is more preferable to obtain the sheet by a coating process.

While there are no particular limitations on the material of the substrate used in the coating process, those with high wettability to the slurry are preferred in terms of preventing sheet shrinkage during drying, and those that allow the sheet formed after drying to be easily peeled off are also preferred. Resin films and plates and metal films and plates are preferred, but are not particularly limited. Specific examples include resin films and plates made of acrylic, polyethylene terephthalate, vinyl chloride, polystyrene, polypropylene, polycarbonate, polyvinylidene chloride, etc.; metal films and plates made of aluminum, zinc, copper, iron, etc.; and those with oxidized surfaces; stainless steel films and plates; and brass films and plates.

If the viscosity of the slurry is low during the coating process and it spreads on the substrate, a frame for blocking can be fixed to the substrate to obtain a radiation-sensitive sheet of the desired thickness and basis weight. The type of frame for blocking is not particularly limited, but it is preferable to select one that allows the edge of the sheet to be easily peeled off after drying. From this perspective, molded resin or metal plates are more preferable. In this embodiment, resin plates such as acrylic plates, polyethylene terephthalate plates, vinyl chloride plates, polystyrene plates, polypropylene plates, polycarbonate plates, and polyvinylidene chloride plates, metal plates such as aluminum plates, zinc plates, copper plates, and iron plates, and plates with their surfaces oxidized, as well as molded stainless steel plates and brass plates, can be used.

The coating machine used to apply the slurry to the substrate is not particularly limited, but examples that can be used include roll coaters, gravure coaters, die coaters, curtain coaters, and air doctor coaters. Die coaters, curtain coaters, and spray coaters are particularly preferred because they can produce a more uniform sheet thickness.

The slurry temperature and ambient temperature when applying the slurry to the substrate are not particularly limited, but are preferably between 5°C and 80°C, more preferably between 10°C and 60°C, even more preferably between 15°C and 50°C, and particularly preferably between 20°C and 40°C. If the application temperature is above the lower limit, the slurry can be applied more easily. If the application temperature is below the upper limit, evaporation of the dispersion medium during application and side reactions due to heat can be suppressed.

The method for drying the slurry coated on the substrate is not particularly limited, but examples include a non-contact drying method, a method in which the sheet is dried while being restrained, or a combination of these.
The non-contact drying method is not particularly limited, but for example, a method of drying by heating with hot air, infrared rays, far infrared rays, or near infrared rays (heat drying method), or a method of drying by vacuum (vacuum drying method) can be applied. Although the heat drying method and the vacuum drying method can be combined, the heat drying method is usually applied. Drying by infrared rays, far infrared rays, or near infrared rays can be carried out using, for example, an infrared device, a far infrared device, or a near infrared device, but is not particularly limited.
The heating temperature in the heat drying method is not particularly limited, but is preferably 20° C. or higher, more preferably 40° C. or higher, and preferably 150° C. or lower, more preferably 120° C. or lower, and even more preferably 100° C. or lower. If the heating temperature is equal to or higher than the above lower limit, the dispersion medium can be quickly volatilized. Furthermore, if the heating temperature is equal to or lower than the above upper limit, it is possible to reduce the cost required for heating and to suppress discoloration and side reactions of the fibrous cellulose due to heat.

The papermaking process is carried out by making paper from the slurry using a papermaking machine. The papermaking machine used in the papermaking process is not particularly limited, but examples include continuous papermaking machines such as Fourdrinier, cylinder, and tilting types, and multi-layer papermaking machines that combine these. In the papermaking process, known papermaking methods such as handmaking may also be used.
The papermaking process is carried out by filtering and dehydrating the slurry with a wire to obtain a wet sheet, and then pressing and drying the sheet. The filter cloth used to filter and dehydrate the slurry is not particularly limited, but it is more preferable that it does not allow fibrous cellulose, hydrophilic resin, and radiation-sensitive composition to pass through and does not slow the filtration rate too much. Such filter cloth is not particularly limited, but is preferably a sheet, woven fabric, or porous membrane made of an organic polymer. The organic polymer is not particularly limited, but is preferably a non-cellulose organic polymer such as polyethylene terephthalate, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), etc. In this embodiment, for example, a porous membrane made of polytetrafluoroethylene with a pore size of 0.1 μm to 20 μm, or a woven fabric made of polyethylene terephthalate or polyethylene with a pore size of 0.1 μm to 20 μm, etc.

In the papermaking process, a sheet can be produced from the slurry using a manufacturing device equipped with a water squeezing section in which the slurry is discharged onto the top surface of an endless belt and the dispersion medium is squeezed out of the discharged slurry to produce a web, and a drying section in which the web is dried to produce a sheet. An endless belt is disposed between the water squeezing section and the drying section, and the web produced in the water squeezing section is transported to the drying section while still on the endless belt.

The dehydration method used in the papermaking process is not particularly limited, but examples include dehydration methods commonly used in paper manufacturing. Among these, methods that involve dehydration using a Fourdrinier, cylinder, or inclined wire, followed by further dehydration using a roll press, are preferred. Furthermore, the drying method used in the papermaking process is not particularly limited, but examples include methods used in paper manufacturing. Among these, drying methods using a cylinder dryer, Yankee dryer, hot air dryer, near-infrared heater, infrared heater, etc. are more preferred.

<Characteristics of radiation-sensitive sheet>
From the viewpoint of shape stability and enabling fine patterning, the thickness of the radiation-sensitive sheet is preferably 10 μm or more, more preferably 20 μm or more, even more preferably 25 μm or more, and is preferably 1,000 μm or less, more preferably 500 μm or less, even more preferably 100 μm or less.
The coating amount and paper making amount may be adjusted appropriately so that the thickness of the radiation-sensitive sheet falls within the above range.

The radiation-sensitive sheet of the present invention preferably has excellent light transmittance, and the total light transmittance is preferably 70% or more, more preferably 80% or more, and even more preferably 90% or more, and is 100% or less, and from the viewpoint of ease of production, is preferably 99.5% or less.
The total light transmittance is measured using a haze meter in accordance with JIS K 7361-1:1997.

Furthermore, the radiation-sensitive sheet of the present invention preferably has excellent transparency, and the haze is preferably 10% or less, more preferably 3% or less, and even more preferably 2% or less, and is 0% or more, and from the viewpoint of ease of production, is preferably 0.1% or more.
The haze is measured using a haze meter in accordance with JIS K 7136:2000.

<Patterned Sheet>
The patterned radiation-sensitive sheet of the present invention is obtained by exposing the radiation-sensitive sheet of the present invention described above and removing (developing) the unexposed areas to form a pattern.
The radiation is usually irradiated by selectively exposing at least a portion of the radiation-sensitive sheet through a photomask or the like using, for example, a contact aligner, a stepper, or a scanner.
The light source for exposure is not particularly limited, and examples thereof include known exposure techniques such as a high-pressure mercury lamp, a metal halide lamp, an ultra-high-pressure mercury lamp, a KrF excimer laser, an ArF excimer laser, an EUV irradiation device, a soft X-ray irradiation device, an electron lithography device, etc. A post-exposure bake (PEB) step may be included.
Among the radiations to be irradiated to the radiation-sensitive sheet, radiation with a wavelength of 313 nm or more is preferred, and radiation containing 365 nm ultraviolet rays is particularly preferred. Therefore, as the exposure light source, high-pressure mercury lamps, metal halide lamps, and ultra-high-pressure mercury lamps, which can irradiate radiation with a wavelength of 313 nm or more including 365 nm ultraviolet rays, are more preferred. By using these exposure light sources, even sheets with a thickness of 10 μm or more can achieve relatively high transmittance in the wavelength range of 313 nm or more, and can fully expose the back side of the radiation-sensitive sheet without reducing the amount of light. In addition, the exposure dose is preferably 10 mJ/cm 2 or more to 1,000 mJ/cm ² or less, more preferably 100 mJ/cm ² or more to 800 mJ/cm ^{2 or less} , as measured by an illuminometer (OAI model 356, manufactured by OAI Optical Associates Inc.) at a wavelength of 365 nm.

As the developing method, for example, shower developing method, spray developing method, immersion developing method, puddle developing method, etc. may be adopted.
As the developer, an alkaline developer, water, or a water-miscible organic solvent can be used.
Examples of alkaline developers include aqueous alkaline solutions in which at least one alkaline compound such as sodium hydroxide, potassium hydroxide, sodium carbonate, sodium silicate, sodium metasilicate, aqueous ammonia, ethylamine, n-propylamine, diethylamine, di-n-propylamine, triethylamine, methyldiethylamine, ethyldimethylamine, triethanolamine, tetramethylammonium hydroxide (TMAH), pyrrole, piperidine, choline, 1,8-diazabicyclo-[5.4.0]-7-undecene, and 1,5-diazabicyclo-[4.3.0]-5-nonene is dissolved.
The alkaline developer is preferably a TMAH aqueous solution. The concentration of the alkaline developer is preferably 0.1% by mass or more and 2.38% by mass or less, and more preferably 0.4% by mass or less and 2.38% by mass or less.
Examples of water-miscible organic solvents include alcohols such as methanol, ethanol, 1-propanol, isopropyl alcohol (IPA), t-butanol, and 1-methoxy-2-propanol (PGME); polyhydric alcohols such as ethylene glycol and glycerin; ketones such as acetone; ethers such as tetrahydrofuran; esters such as ethyl acetate and methyl acetate; amides such as N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone; sulfoxides such as dimethyl sulfoxide, etc. These may be used alone or in combination of two or more.
As the water-miscible organic solvent, alcohols such as ethanol, IPA, and PGME are preferred.
The content of the organic solvent in the organic solvent developer is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 99% by mass or more. Examples of components other than the organic solvent in the organic solvent developer include water and silicone oil.
Of these, water is preferred as the developer, and pure water is more preferred.
After development, the formed pattern may be further rinsed (washed) with a rinse solution.

The patterned sheet has excellent transparency, and the radiation-sensitive composition has been removed throughout the entire thickness of the sheet. The removed areas form a front-to-back through-pattern, which is expected to enable applications as sensors that effectively detect gases or liquids passing through the removed areas, and by dyeing the removed areas of the radiation-sensitive composition, it can also be used as a dye for color filters or as the conductive parts of touch panels.

The features of the present invention are explained in more detail below with reference to examples and comparative examples. The materials, amounts used, ratios, processing details, processing procedures, etc. shown in the following examples can be modified as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be construed as being limited by the specific examples shown below.

<Production Example 1>
[Production of Fine Fibrous Cellulose Dispersion (1)]
The raw material pulp used was softwood kraft pulp manufactured by Oji Paper Co., Ltd. (solid content 93% by mass, basis weight 245 g/m ² , sheet form, Canadian Standard Freeness (CSF) measured after disintegration in accordance with JIS P 8121-2:2012 of 700 mL).
This raw pulp was subjected to phosphorus oxo-oxidation treatment as follows.
First, a mixed aqueous solution of ammonium dihydrogen phosphate and urea was added to 100 parts by mass (bone dry mass) of the raw pulp to adjust the composition to 45 parts by mass of ammonium dihydrogen phosphate, 120 parts by mass of urea, and 150 parts by mass of water, to obtain a chemical-impregnated pulp. The obtained chemical-impregnated pulp was then heated in a hot air dryer at 165°C for 250 seconds to introduce phosphorus oxo acid groups into the cellulose in the pulp, thereby obtaining phosphorus oxo-oxidized pulp 1.

Next, the resulting phosphorus oxo-oxidized pulp 1 was subjected to a washing treatment.
The washing treatment was carried out by repeatedly adding 10 L of ion-exchanged water to 100 g (bone dry weight) of phosphorus oxidized pulp to obtain a pulp dispersion, stirring the resulting solution to uniformly disperse the pulp, and then filtering and dehydrating the pulp. The washing was completed when the electrical conductivity of the filtrate reached 100 μS/cm or less.

Next, the washed phosphorus oxy-oxidized pulp was neutralized as follows.
First, the washed phosphorus oxidized pulp was diluted with 10 L of ion-exchanged water, and then a 1 N aqueous solution of sodium hydroxide was added little by little while stirring to obtain a phosphorus oxidized pulp slurry having a pH of 12 to 13. Next, the phosphorus oxidized pulp slurry was dehydrated to obtain a neutralized phosphorus oxidized pulp. Next, the neutralized phosphorus oxidized pulp was subjected to the above-mentioned washing treatment to obtain phosphorus oxidized pulp A.

The infrared absorption spectrum of the obtained phosphorus oxo-oxidized pulp A was measured using FT-IR, and the absorption due to P=O of the phosphate group was observed around 1230 cm ⁻¹ , confirming that the phosphate group had been added to the pulp.
Furthermore, when the obtained phosphorus oxo-oxidized pulp A was analyzed using an X-ray diffractometer, typical peaks were confirmed at two positions, around 2θ = 14° to 17° and around 2θ = 22° to 23°, confirming that it had a cellulose type I crystal structure.

Ion-exchanged water was added to the obtained phosphorus oxo-oxidized pulp A to prepare a slurry with a solids concentration of 2% by mass. This slurry was treated twice at a pressure of 200 MPa in a wet pulverization apparatus (Starburst, manufactured by Sugino Machine Co., Ltd.) to obtain a fine fibrous cellulose dispersion (1) containing fine fibrous cellulose.
X-ray diffraction confirmed that this fine fibrous cellulose maintained the cellulose type I crystal structure.
The fiber width of the fine fibrous cellulose was measured using a transmission electron microscope and found to be 2 to 5 nm. The amount of phosphorus oxoacid groups (amount of first dissociated acid) was 1.45 mmol/g. The total amount of dissociated acid was 2.45 mmol/g.

<Production Example 2>
[Production of fine fibrous cellulose dispersion (2)]
The same procedure as in Production Example 1 was carried out except that 33 parts by mass of phosphorous acid (phosphonic acid) was used instead of ammonium dihydrogen phosphate, to obtain phosphorus oxo-oxidized pulp B and fine fibrous cellulose dispersion (2).

The infrared absorption spectrum of the obtained phosphorus oxo-oxidized pulp B was measured using FT-IR. As a result, absorption due to P=O of the phosphonic acid group, which is a tautomer of the phosphorous acid group, was observed around 1210 cm ⁻¹ , confirming that a phosphorous acid group (phosphonic acid group) had been added to the pulp.

Furthermore, when the obtained phosphorus oxo-oxidized pulp B was tested and analyzed using an X-ray diffraction device, typical peaks were confirmed at two positions, around 2θ = 14° to 17° and around 2θ = 22° to 23°, confirming that it has a cellulose type I crystalline structure.

X-ray diffraction confirmed that the resulting fine fibrous cellulose maintained a cellulose type I crystal structure. Furthermore, the fiber width of the fine fibrous cellulose was measured using a transmission electron microscope and found to be 2 to 5 nm. Furthermore, for fine fibrous cellulose dispersion (2), the amount of phosphorous acid groups introduced into the cellulose (amount of first dissociated acid) and the total amount of dissociated acid were 1.51 mmol/g and 1.54 mmol/g, respectively.

<Production Example 3>
[Production of fine fibrous cellulose dispersion (3)]
The same operation as in Production Example 1 was carried out, except that 38 parts by mass of amidosulfuric acid was used instead of ammonium dihydrogen phosphate and the heating time in the hot air dryer was set to 19 minutes, to obtain a sulfated pulp and fine fibrous cellulose dispersion (3).

The infrared absorption spectrum of the obtained sulfated pulp was measured using FT-IR, and as a result, absorption due to sulfate groups was observed around 1220-1260 cm ⁻¹ , confirming that sulfate groups had been added to the pulp.

Furthermore, when the obtained sulfated pulp was tested and analyzed using an X-ray diffraction device, typical peaks were confirmed at two positions, around 2θ = 14° to 17° and around 2θ = 22° to 23°, confirming that it has a cellulose type I crystalline structure.

X-ray diffraction confirmed that the resulting fine fibrous cellulose maintained a cellulose type I crystal structure. Furthermore, the fiber width of the fine fibrous cellulose was measured using a transmission electron microscope and found to be 2 to 5 nm. Furthermore, the amount of sulfate groups introduced into the cellulose in fine fibrous cellulose dispersion (3) was 1.12 mmol/g.

<Production Example 4>
[Production of fine fibrous cellulose dispersion (4)]
The raw material pulp used was softwood kraft pulp (undried) manufactured by Oji Paper Co., Ltd. This raw material pulp was subjected to an alkaline TEMPO oxidation treatment as follows.
First, 100 parts by mass of the raw material pulp (dry mass equivalent), 1.6 parts by mass of TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl), and 10 parts by mass of sodium bromide were dispersed in 10,000 parts by mass of water. Next, 13 parts by mass of an aqueous sodium hypochlorite solution was added to 1.0 g of pulp to give a concentration of 3.8 mmol, to initiate the reaction. During the reaction, a 0.5 M aqueous sodium hydroxide solution was added dropwise to maintain the pH at 10 to 10.5, and the reaction was considered complete when no further change in pH was observed.

The resulting TEMPO oxidized pulp was then subjected to a washing treatment.
The washing treatment was carried out by dehydrating the pulp slurry after TEMPO oxidation to obtain a dehydrated sheet, pouring 5,000 parts by mass of ion-exchanged water into the sheet, stirring to uniformly disperse the pulp, and then filtering and dehydrating the sheet. The washing was completed when the electrical conductivity of the filtrate reached 100 μS/cm or less.

Furthermore, when the obtained TEMPO oxidized pulp was tested and analyzed using an X-ray diffraction device, typical peaks were confirmed at two positions, around 2θ = 14° to 17° and around 2θ = 22° to 23°, confirming that it has a cellulose type I crystalline structure.

Ion-exchanged water was added to the resulting TEMPO-oxidized pulp to prepare a slurry with a solids concentration of 2% by mass. This slurry was processed twice at a pressure of 200 MPa in a wet pulverization device (Starburst, manufactured by Sugino Machine Co., Ltd.) to obtain a fine fibrous cellulose dispersion (4) containing fine fibrous cellulose.

For fine fibrous cellulose dispersion (4), the amount of carboxyl groups introduced into the cellulose was 1.30 mmol/g.

<Method for measuring fiber width and ionic group content of fine fibrous cellulose>
[Measurement of fiber width]
The fiber width of the fine fibrous cellulose was measured by the following method. The supernatant of the fine fibrous cellulose dispersion was diluted with water so that the concentration of the fine fibrous cellulose was 0.01% by mass or more and 0.1% by mass or less, and the diluted solution was dropped onto a hydrophilized carbon grid membrane. After drying, the diluted solution was stained with uranyl acetate and observed under a transmission electron microscope (JEOL-2000EX, manufactured by JEOL Ltd.).

[Measurement of phosphorus oxoacid group content]
The amount of phosphorus oxoacid groups in the fine fibrous cellulose was measured by treating a fine fibrous cellulose-containing slurry with an ion exchange resin after diluting the dispersion containing the target fine fibrous cellulose with ion exchange water to a content of 0.2 mass % and then titrating the slurry with an alkali.
The treatment with ion exchange resin was carried out by adding 1/10 by volume of a strongly acidic ion exchange resin (Amberjet 1024; Organo Corporation, conditioned) to the above-mentioned fine fibrous cellulose-containing slurry, shaking the mixture for 1 hour, and then pouring the mixture onto a mesh with 90 μm openings to separate the resin from the slurry.
In addition, the alkali titration was performed by adding 10 μL of 0.1 N aqueous sodium hydroxide solution to the fine fibrous cellulose-containing slurry after treatment with an ion exchange resin at 5-second intervals, while measuring the change in the pH value of the slurry. Nitrogen gas was introduced into the slurry 15 minutes before the start of the titration. In this neutralization titration, two maximum points of increment (the differential value of pH with respect to the amount of alkali added) were observed on the curve plotting the measured pH against the amount of alkali added. Of these, the maximum point of increment obtained first after starting the addition of alkali is called the first endpoint, and the maximum point of increment obtained next is called the second endpoint (FIG. 1). The amount of alkali required from the start of the titration to the first endpoint is equal to the amount of first dissociated acid in the slurry used in the titration. Furthermore, the amount of alkali required from the start of the titration to the second endpoint is equal to the total amount of dissociated acid in the slurry used in the titration. The amount of alkali (mmol) required from the start of titration to the first endpoint was divided by the solid content (g) in the slurry to be titrated, and the value was taken as the amount of phosphate groups (mmol/g).

[Measurement of sulfur oxoacid group content]
The amount of sulfur oxoacid groups was determined by wet ashing the obtained fibrous cellulose with perchloric acid and concentrated nitric acid, diluting it at an appropriate ratio, and then measuring the amount of sulfur by ICP emission spectrometry.
The amount of sulfur divided by the bone dry mass of the fibrous cellulose sample was taken as the amount of sulfur oxoacid groups (unit: mmol/g).

[Measurement of Carboxy Group Amount]
The amount of carboxyl groups in the fine fibrous cellulose was measured in the same manner as in [Measurement of the amount of phosphorus oxoacid groups], except that 50 μL of 0.1 N aqueous sodium hydroxide solution was added once every 30 seconds to the fine fibrous cellulose-containing slurry after treatment with an ion exchange resin. The amount of carboxyl groups (mmol/g) was calculated by dividing the amount of alkali (mmol) required in the region corresponding to the first region shown in Figure 2 by the solid content (g) in the slurry to be titrated.

<Production Example 5>
[Production of Radiation-Sensitive Composition (1)]
A mixture of 1.0 part by mass of N,N'-{[(2-acrylamido-2-[(3-acrylamidopropoxy)methyl]propane-1,3-diyl)bis(oxy)]bis(propane-1,3-diyl)}diacrylamide (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., FOM-03006, Hansen solubility parameter polarity term dP 15.9 MPa ^0.5 , HSP distance to water 31.6 MPa ^0.5 ) and 0.1 part by mass of 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone (manufactured by Tokyo Chemical Industry Co., Ltd.) was dissolved in purified water to a concentration of 0.5% by mass. The mixture was then filtered through a Millipore filter with a pore size of 0.5 μm to prepare radiation-sensitive composition (1).

<Production Example 6>
[Production of Radiation-Sensitive Composition (2)]
A mixture of 1.0 part by mass of N,N',N"-triacryloyldiethylenetriamine (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., FOM-03007, Hansen solubility parameter polarity term dP 16.8 MPa ^0.5 , HSP distance to water 34.9 MPa ^0.5 ) and 0.1 part by mass of 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone (manufactured by Tokyo Chemical Industry Co., Ltd.) was dissolved in pure water to a concentration of 0.5% by mass. The mixture was then filtered through a Millipore filter with a pore size of 0.5 μm to prepare radiation-sensitive composition (2).

<Production Example 7>
[Production of Radiation-Sensitive Composition (3)]
A mixture of 1.0 part by mass of N,N'-diacryloyl-4,7,10-trioxa-1,13-tridecanediamine (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., FOM-03008, Hansen solubility parameter polarity term dP 12.7 MPa ^0.5 , HSP distance to water 34.0 MPa ^0.5 ) and 0.1 part by mass of 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone (manufactured by Tokyo Chemical Industry Co., Ltd.) was dissolved in pure water to a concentration of 0.5% by mass. The mixture was then filtered through a Millipore filter with a pore size of 0.5 μm to prepare radiation-sensitive composition (3).

<Production Example 8>
[Production of Radiation-Sensitive Composition (4)]
A mixture of 1.0 part by mass of N,N'-diacryloylethylenediamine (manufactured by Tokyo Chemical Industry Co., Ltd., E1086, Hansen solubility parameter polarity term dP 16.8 MPa ^0.5 , HSP distance to water 32.3 MPa ^0.5 ) and 0.1 part by mass of 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone (manufactured by Tokyo Chemical Industry Co., Ltd.) was dissolved in purified water to a concentration of 0.5% by mass. The mixture was then filtered through a Millipore filter with a pore size of 0.5 μm to prepare radiation-sensitive composition (4).

<Production Example 9>
[Production of Radiation-Sensitive Composition (5)]
A mixture of 1.0 part by mass of dipentaerythritol hexaacrylate (DPHA) (NK Ester A-DPH, manufactured by Shin-Nakamura Chemical Co., Ltd., having a Hansen solubility parameter polarity term dP of 1.3 MPa ^0.5 and an HSP distance to water of 36.6 MPa ^0.5 ) and 0.1 part by mass of 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone (manufactured by Tokyo Chemical Industry Co., Ltd.) was dissolved in 1-methoxy-2-propanol to a concentration of 0.5% by mass. The mixture was then filtered through a Millipore filter with a pore size of 0.5 μm to prepare radiation-sensitive composition (5).

Example 1
Ion-exchanged water was added to the fine fibrous cellulose dispersion (1) having a solid content concentration of 2.0% by mass to prepare a fine fibrous cellulose dispersion (A) having a solid content concentration of 0.5% by mass.
To 30 parts by mass of the obtained fine fibrous cellulose dispersion (A), 70 parts by mass of the radiation-sensitive composition (1) solution was added and stirred. The mixed solution was then weighed so that the finished sheet had a basis weight of 65 g/ ^m² , spread on a commercially available acrylic plate, and dried in a dryer at 50°C for 24 hours. A 150 mm square blocking plate was placed on the acrylic plate to achieve the desired basis weight. A radiation-sensitive sheet was obtained by the above procedure.
The thickness of the obtained radiation-sensitive sheet was 50 μm.

Example 2
A radiation-sensitive sheet was obtained in the same manner as in Example 1, except that the amount of the radiation-sensitive composition (1) solution was 80 parts by mass per 20 parts by mass of the fine fibrous cellulose dispersion (A).

Example 3
A radiation-sensitive sheet was obtained in the same manner as in Example 1, except that the amount of the radiation-sensitive composition (1) solution was 60 parts by mass relative to 40 parts by mass of the fine fibrous cellulose dispersion (A).

Example 4
Polyvinyl alcohol (PVA) (Poval 105, manufactured by Kuraray Co., Ltd., polymerization degree: 500, saponification degree: 98 to 99 mol%) was added to ion-exchanged water so as to have a concentration of 0.5 mass%, and the mixture was stirred at 95°C for 1 hour to dissolve, thereby obtaining an aqueous polyvinyl alcohol solution.

(Production of radiation-sensitive sheet)
A radiation-sensitive sheet was obtained in the same manner as in Example 1, except that the amount of the aqueous polyvinyl alcohol solution was 8 parts by mass, and the amount of the radiation-sensitive composition (1) solution was 70 parts by mass, relative to 22 parts by mass of the fine fibrous cellulose dispersion (A).

Example 5
A radiation-sensitive sheet was obtained in the same manner as in Example 1, except that the radiation-sensitive composition (2) was used instead of the radiation-sensitive composition (1).

Example 6
A radiation-sensitive sheet was obtained in the same manner as in Example 1, except that the radiation-sensitive composition (3) was used instead of the radiation-sensitive composition (1).

Example 7
A radiation-sensitive sheet was obtained in the same manner as in Example 1, except that the radiation-sensitive composition (4) was used instead of the radiation-sensitive composition (1).

Example 8
Ion-exchanged water was added to the fine fibrous cellulose dispersion (2) having a solid content concentration of 2.0% by mass to prepare a fine fibrous cellulose dispersion (B) having a solid content concentration of 0.5% by mass.
A radiation-sensitive sheet was obtained in the same manner as in Example 1, except that the fine fibrous cellulose dispersion (B) was used instead of the fine fibrous cellulose dispersion (A).

Example 9
Ion-exchanged water was added to the fine fibrous cellulose dispersion (3) having a solid content concentration of 2.0% by mass to prepare a fine fibrous cellulose dispersion (C) having a solid content concentration of 0.5% by mass.
A radiation-sensitive sheet was obtained in the same manner as in Example 1, except that the fine fibrous cellulose dispersion (C) was used instead of the fine fibrous cellulose dispersion (A).

Example 10
Ion-exchanged water was added to the fine fibrous cellulose dispersion (4) having a solid content concentration of 2.0% by mass to prepare a fine fibrous cellulose dispersion (D) having a solid content concentration of 0.5% by mass.
A radiation-sensitive sheet was obtained in the same manner as in Example 1, except that the fine fibrous cellulose dispersion (D) was used instead of the fine fibrous cellulose dispersion (A).

<Comparative Example 1>
A radiation-sensitive sheet was obtained in the same manner as in Example 1, except that the amount of the aqueous polyvinyl alcohol solution was 14 parts by mass, and the amount of the radiation-sensitive composition (5) solution was 50 parts by mass, relative to 36 parts by mass of the fine fibrous cellulose dispersion (A).

<Comparative Example 2>
A radiation-sensitive sheet was obtained in the same manner as in Example 4, except that the radiation-sensitive composition (5) was used instead of the radiation-sensitive composition (1).

<Comparative Example 3>
The radiation-sensitive composition (1) solution was applied onto a polyethylene terephthalate film (Lumirror U48, manufactured by Toray Industries, Inc., thickness 38 μm) using a bar coater, and dried in a dryer at 50° C. for 24 hours.
The thickness of the resulting laminate of the polyethylene terephthalate film and the radiation-sensitive composition (1) layer was 50 μm.

[Measurement method]
<Total light transmittance of sheet>
The total light transmittance of the radiation-sensitive sheet before exposure was measured using a haze meter (HM-150, manufactured by Murakami Color Research Laboratory Co., Ltd.) in accordance with JIS K 7361-1: 1997. The results are shown in Table 1.

<Sheet haze>
The haze of the radiation-sensitive sheet before exposure was measured using a haze meter (HM-150, manufactured by Murakami Color Research Laboratory Co., Ltd.) in accordance with JIS K 7136: 2000. The results are shown in Table 1.

<Patterning onto sheets>
A radiation-sensitive sheet or a laminate of a polyethylene terephthalate film and a radiation-sensitive composition (1) layer was placed in an exposure device equipped with a metal halide lamp (manufactured by iGraphics Co., Ltd., model number iGrandage ECS-4011GX/N, wavelength 200 to 450 nm). Next, a photomask (manufactured by Toppan Printing Co., Ltd., synthetic quartz, L/S = 400/400, 1,100/1,100 μm) was placed on the sheet. At this time, a shim tape (manufactured by Misumi Group Holdings Co., Ltd., thickness 500 μm, made of SUS) was used to ensure a gap of 500 μm between the substrate for pattern formation and the photomask.
Next, the intensity of the radiation at a wavelength of 365 nm was set to 500 mJ/cm ² using an illuminance meter (OAI model 356, manufactured by OAI Optical Associates Inc.), and then exposure was performed using an exposure device.

The exposed sheet was then developed by immersing it in pure water for 3 minutes.
As a result, a patterned sheet was obtained in which the resin for the radiation-sensitive composition had been removed only from the unexposed areas of the sheet.

Next, a pure solution of Acid Red 92 was dropped evenly onto one side of the sheet using a dropper, and after 3 minutes, the sheet was dipped in pure water for 3 minutes to wash.
As a result, a sheet was obtained in which Acid Red 92 was impregnated only in the area where the resin for the radiation-sensitive composition had been removed.

The sheet was observed under an optical microscope, and if a pattern was formed at both L/S = 400/400 μm and 1,100/1,100 μm, it was rated "A." If a pattern was not formed at L/S = 400/400 μm but a pattern was formed at L/S = 1,100/1,100 μm, it was rated "B." If a pattern was not formed at L/S = 400/400 μm or 1,100/1,100 μm, it was rated "C." The results are shown in Table 1.

<Dyeing depth of sheet>
This sheet was embedded in epoxy resin, and then cross-sectional sections were prepared using a microtome. Ten of these cross-sectional sections were prepared, and the depth of staining was observed under an optical microscope at 1,000x magnification. If an average of 90% or more of the thickness of the radiation-sensitive sheet or the laminate of the polyethylene terephthalate film and the radiation-sensitive composition (1) layer was stained, it was evaluated as "A." If an average of 50% to less than 90% of the thickness was stained, it was evaluated as "B." If an average of less than 50% was stained, it was evaluated as "C." The results are shown in Table 1.
In addition, in Examples 1 to 10, at least one of the ten pieces was dyed 100% relative to the thickness of the radiation-sensitive sheet, and the radiation-sensitive composition was removed throughout the entire thickness direction, whereas in Comparative Examples 1 to 3, not a single piece was dyed 100% relative to the thickness of the radiation-sensitive sheet or the laminate of the polyethylene terephthalate film and the radiation-sensitive composition (1) layer.

<Sheet curl>
This sheet is cut into a length of 100 mm and a width of 100 mm, and the four corners are designated "vertex A,""vertexB,""vertexC," and "vertex D." The four sides are designated "side AB,""sideBC,""sideCD," and "side DA."
When a sheet was placed on a glass substrate and sides BC and CD were fixed with tape, the distance from the glass substrate to vertex A was measured and designated _d1 . Similarly, when sides CD and DA were fixed with tape, the distance from the glass substrate to vertex B was measured and designated _d2 . When sides AB and DA were fixed with tape, the distance from the glass substrate to vertex C was measured and designated _d3 . When sides AB and BC were fixed with tape, the distance from the glass substrate to vertex D was measured and designated _d4 . When the average value of _d1 to _d4 was less than 10 mm, it was evaluated as "A." When it was 10 mm or more but less than 20 mm, it was evaluated as "B." When it was 20 mm or more, it was evaluated as "C." The results are shown in Table 1.

<Adhesion of Acid Red 92>
Adhesion was evaluated by the cross-cut method in accordance with JIS K 5600-5-6: 1999. If peeling of the cross-cut portion was less than 15%, it was rated "A", if it was 15% or more but less than 65%, it was rated "B", and if peeling was 65% or more or if the dyed portion could not be formed and the test itself could not be performed, it was rated "C".

According to the results of the Examples and Comparative Examples, the patterned sheets obtained in Examples 1 to 10 had high total light transmittance, low haze, and excellent transparency. They also had excellent patterning properties. Furthermore, an average of 50% or more of the radiation-sensitive composition in the unexposed areas was removed in the thickness direction, and at least a portion of the radiation-sensitive composition was removed across the entire thickness direction.
Furthermore, curling was suppressed and adhesion was excellent.
On the other hand, as exemplified in Comparative Examples 1 and 2, when a radiation-sensitive composition not specified in claim 1 was used, phase separation occurred between the cellulose and the sheet, resulting in high haze, and the low homogeneity of the sheet caused by the phase separation reduced the reproducibility of pattern formation (Comparative Example 2). This phase separation could be improved by reducing the amount of radiation-sensitive composition used, but at the same time, the amount of developable components (unexposed radiation-sensitive composition) was reduced, making it impossible to form a pattern all the way to the bottom of the sheet, resulting in a reduced dyeing depth (Comparative Example 1). Furthermore, as exemplified in Comparative Example 3, when the sheet did not contain a cellulose dispersion, all of the unexposed areas were developed, resulting in the problem of not being able to form dyed areas.

The present invention provides a radiation-sensitive sheet that can be finely patterned. The patterned sheet obtained by exposing and developing the radiation-sensitive sheet has excellent transparency. Furthermore, the radiation-sensitive composition is removed throughout the entire thickness of the sheet, and the removed areas form a front-to-back through-type pattern, which is expected to find applications as a sensor that effectively detects gases or liquids passing through the removed areas, or as a dye for color filters or conductive parts for touch panels by dyeing the removed areas of the radiation-sensitive composition.

Claims (11)

A negative-type radiation-sensitive sheet containing at least a radiation-sensitive composition and fine fibrous cellulose having a fiber width of 1,000 nm or less,
The radiation-sensitive composition contains a compound (X) that contains a polymerizable unsaturated bond and has a Hansen solubility parameter (HSP) distance with water of 36 MPa ^0.5 or less and a polarity term (dP) of 12 MPa ^0.5 or more.
Negative radiation-sensitive sheet. The negative-working radiation-sensitive sheet according to claim 1, wherein the radiation-sensitive composition contains a photopolymerization initiator. The negative-working radiation-sensitive sheet according to claim 1 or 2, wherein the content of the radiation-sensitive composition in the solid content of the negative-working radiation-sensitive sheet is 30% by mass or more. The negative-working radiation-sensitive sheet according to any one of claims 1 to 3, wherein the compound (X) has at least one of a (meth)acryloyloxy group and a (meth)acrylamide group. The negative-working radiation-sensitive sheet according to any one of claims 1 to 4, wherein the fine fibrous cellulose has anionic groups. The negative-type radiation-sensitive sheet according to any one of claims 1 to 5, wherein the fine fibrous cellulose has a phosphorus oxoacid group or a group derived from a phosphorus oxoacid group. The negative-type radiation-sensitive sheet according to any one of claims 1 to 6, wherein the radiation-sensitive composition is soluble in at least one of water, alcohol, and a mixed solvent thereof. The negative-type radiation-sensitive sheet according to any one of claims 1 to 7, wherein the negative-type radiation-sensitive sheet has a total light transmittance of 70% or more. The negative-working radiation-sensitive sheet according to any one of claims 1 to 8, wherein the haze of the negative-working radiation-sensitive sheet is 10% or less. A patterned sheet in which at least a portion of the unexposed areas of the negative-working radiation-sensitive sheet described in any one of claims 1 to 9 have been removed. A patterned sheet in which at least a portion of the radiation-sensitive composition in the unexposed areas of the negative-working radiation-sensitive sheet described in any one of claims 1 to 9 has been removed across the entire thickness direction.