JP2021185278A - Sheet and sheet manufacturing method - Google Patents

Abstract

To provide a laminated sheet in which a fiber layer containing fine fibrous cellulose and a resin layer are laminated and which has high transparency.SOLUTION: The present invention relates to a sheet having a fiber layer and a resin layer on both sides of the fiber layer, wherein the fiber layer contains fibrous cellulose with a fiber width of 1000 nm or less, and the surface roughness (Ra) of both sides of the sheet is 12.0 nm or less.SELECTED DRAWING: Figure 1

Description

The present invention relates to a sheet and a method for manufacturing the sheet. Specifically, the present invention relates to a sheet containing fine fibrous cellulose and a method for producing the sheet.

In recent years, due to the substitution of petroleum resources and increasing environmental awareness, materials using reproducible natural fibers have been attracting attention. Among natural fibers, fibrous cellulose having a fiber diameter of 10 μm or more and 50 μm or less, particularly fibrous cellulose (pulp) derived from wood, has been widely used mainly as paper products.

As the fibrous cellulose, fine fibrous cellulose having a fiber diameter of 1 μm or less is also known. Further, a sheet composed of such fine fibrous cellulose and a composite containing a fine fibrous cellulose-containing sheet and a resin layer have been developed. It is known that in a sheet or a complex containing fine fibrous cellulose, the contact points between the fibers are remarkably increased, so that the tensile strength and the like are greatly improved. It is also known that the transparency is greatly improved by making the fiber width shorter than the wavelength of visible light.

When forming a complex containing a fine fibrous cellulose-containing sheet and a resin layer, it has been considered to include an additive or the like in each layer in order to improve the adhesion between the fine fibrous cellulose-containing sheet and the resin layer. There is. For example, in Patent Document 1, it is studied to add a polycarboxylic acid-based polymer to a fine fibrous cellulose-containing sheet. Further, Patent Document 2 proposes that a polycarbonate sheet is heat-fused to a fine fibrous cellulose-containing sheet to form a laminated body. Here, the fine fibrous cellulose-containing sheet and the polycarbonate sheet, which have been previously impregnated with a primer treatment liquid such as an acrylic primer, are heat-fused to form a laminate.

Patent Document 3 proposes to improve the adhesion between the resin layer and the fine fibrous cellulose-containing sheet by blending a silane coupling agent in the fine fibrous cellulose-containing sheet. Further, in Patent Document 4, in a laminate having a fiber layer containing fine fibrous cellulose and a resin layer in contact with one surface of the fiber layer, the resin layer contains a adhesion aid to form a fiber layer and a resin. It is being studied to improve the adhesion of the layers.

Japanese Unexamined Patent Publication No. 2014-223737 Japanese Unexamined Patent Publication No. 2010-023275 International release WO2011 / 118360 International release WO2017 / 126432

There are various uses for a laminated sheet in which a fiber layer containing fine fibrous cellulose and a resin layer are laminated, but depending on the use, the laminated sheet may be required to have high transparency. However, in the conventional laminated sheet in which the fiber layer containing fine fibrous cellulose and the resin layer are laminated, there is room for improvement in the transparency of the laminated sheet.
Therefore, in order to solve the problems of the prior art, the present inventors provide a laminated sheet in which a fiber layer containing fine fibrous cellulose and a resin layer are laminated, and has high transparency. We proceeded with the study for the purpose of this.

As a result of diligent studies to solve the above problems, the present inventors have laminated resin layers on both sides of a fiber layer containing fibrous cellulose having a fiber width of 1000 nm or less, and further laminated each layer. It has been found that a sheet having high transparency can be obtained by setting the surface roughness (Ra) of both sides of the sheet to 12.0 nm or less.
Specifically, the present invention has the following configurations.

[1] A sheet having a fiber layer and resin layers on both sides of the fiber layer.
The fiber layer contains fibrous cellulose having a fiber width of 1000 nm or less, and contains.
A sheet having a surface roughness (Ra) of 12.0 nm or less on both sides of the sheet.
[2] The sheet according to [1], wherein the thickness of each resin layer is 10 μm or less.
[3] The sheet according to [1] or [2], wherein the fibrous cellulose has an ionic substituent.
[4] The sheet according to [3], wherein the ionic substituent is a phosphate group or a substituent derived from a phosphate group.
[5] The sheet according to any one of [1] to [4], wherein the refractive index of the fiber layer is 1.51 to 1.60.
[6] The sheet according to any one of [1] to [5], wherein the fiber layer further contains a hydrophilic polymer.
[7] The sheet according to [6], wherein the hydrophilic polymer is polyvinyl alcohol.
[8] The sheet according to [7], wherein the degree of saponification of polyvinyl alcohol is 99.9% or less.
[9] The sheet according to any one of [1] to [8], wherein the resin layer contains an amorphous resin.
[10] The sheet according to any one of [1] to [9], wherein the resin layer is a solvent-coated layer.
[11] The sheet according to any one of [1] to [10], wherein the fiber layer has a thickness of 10 to 1000 μm.
[12] The sheet according to any one of [1] to [11], wherein the resin layer contains an isocyanate compound.
[13] The sheet according to any one of [1] to [12], wherein the haze value is less than 0.5%.
[14] The sheet according to any one of [1] to [13], which has a moisture content of 12% by mass or less.
[15] The sheet according to any one of [1] to [14], which has a tensile elastic modulus of 2.5 GPa or more at 23 ° C. and a relative humidity of 50%.
[16] The sheet according to any one of [1] to [15], which is used for an optical member.
[17] The sheet according to any one of [1] to [16], wherein the refractive index ratio of the fiber layer to the resin layer calculated by the following formula is 0.98 or more and 1.02 or less.
Refractive index ratio = Refractive index of fiber layer / Refractive index of resin layer [18] The sheet according to any one of [1] to [17], wherein the refractive index of the fiber layer is 1.51 to 1.54.
[19] A method for producing a sheet, which comprises a step of forming a resin layer on both sides of a fiber layer containing fibrous cellulose having a fiber width of 1000 nm or less.
A method for manufacturing a sheet, wherein the surface roughness (Ra) on both sides of the sheet is 12.0 nm or less.
[20] The method for producing a sheet according to [19], wherein the thickness of the resin layer is 10 μm or less.
[21] The step of forming the resin layer is a step of applying a resin coating liquid on both sides of the fiber layer to form the resin layer.
The resin coating liquid contains a solvent and contains
The method for producing a sheet according to [19] or [20], wherein the viscosity of the resin coating liquid is 100 cps or less.
[22] The method for producing a sheet according to [21], wherein the solid content in the resin coating liquid is 12% by mass or less.

According to the present invention, a sheet containing a fiber layer containing fine fibrous cellulose and having high transparency can be obtained.

FIG. 1 is a cross-sectional view illustrating the structure of the sheet of the present invention. FIG. 2 is a graph showing the relationship between the amount of NaOH dropped and the pH with respect to the fibrous cellulose-containing slurry having a phosphorus oxo acid group. FIG. 3 is a graph showing the relationship between the amount of NaOH dropped and the pH with respect to the fibrous cellulose-containing slurry having a carboxy group.

Hereinafter, the present invention will be described in detail. The description of the constituent elements described below may be based on typical embodiments and specific examples, but the present invention is not limited to such embodiments.

(Sheet)
The present invention relates to a fiber layer and a sheet having resin layers on both sides of the fiber layer. Here, the fiber layer contains fibrous cellulose having a fiber width of 1000 nm or less, and the surface roughness (Ra) of both surfaces of the sheet is 12.0 nm or less. In the present specification, fibrous cellulose having a fiber width of 1000 nm or less may be referred to as fine fibrous cellulose or CNF.

FIG. 1 is a cross-sectional view illustrating the structure of the sheet of the present invention. As shown in FIG. 1, the sheet 10 of the present invention has a fiber layer 2 containing fine fibrous cellulose and a resin layer 6 containing a resin as a main component on both sides of the fiber layer 2. As shown in FIG. 1, since the sheet 10 of the present invention is a sheet having a laminated structure, it may be referred to as a laminated sheet. In the structure of the resin layer 6 / fiber layer 2 / resin layer 6 in the sheet 10, each layer is directly laminated in a state of being in contact with each other.

The surface roughness (Ra) of both sides of the sheet of the present invention may be 12.0 nm or less, preferably 11.0 nm or less, more preferably 10.0 nm or less, and 9.0 nm or less. It is more preferably 8.0 nm or less, and particularly preferably 8.0 nm or less. The lower limit of the surface roughness (Ra) on both sides of the sheet is not particularly limited, but is preferably 1.0 nm or more, for example. In the present invention, it is preferable that the surface roughness (Ra) of both sides of the sheet is within the above range. That is, the surface roughness (Ra) of both the sheet surface on which one resin layer (first resin layer) is provided and the sheet surface on which the other resin layer (second resin layer) is provided on the sheet. ) Is preferably within the above range. The surface roughness (Ra) of the surface on the first resin layer side and the surface on the second resin layer side may be the same value, or may be different values within the range of 12.0 nm or less. good.

The surface roughness (Ra) of the sheet is a value measured by a light interference type non-contact surface shape measuring machine according to JIS B 0601: 1994. As the optical interferometry non-contact surface shape measuring machine, for example, a non-contact surface / layer cross-sectional shape measuring system VertScan2.0, R5500GML manufactured by Ryoka System Co., Ltd. can be used. The surface roughness is measured using a × 10 objective lens in a measurement range of 470 μm × 350 μm, and the arithmetic average roughness (Ra) is calculated from the average value.

Since the sheet of the present invention has the above-mentioned structure, it has high transparency. It is known that the transparency of the sheet having fine fibrous cellulose is higher than that of the sheet containing coarse cellulose fiber, but the sheet of the present invention is achieved in the conventional sheet containing fine fibrous cellulose. It has achieved a high level of transparency that was not obtained. As described above, since the sheet of the present invention is an extremely highly transparent sheet, it is useful as, for example, an optical member or an optical member bonding sheet. Further, it is suitable for applications that require high transparency in addition to applications for optical members.

The transparency of the sheet can be evaluated by measuring the haze of the sheet. Here, the haze of the sheet is a value measured using a haze meter in accordance with JIS K 7136: 2000. As the haze meter, for example, HM-150 manufactured by Murakami Color Technology Research Institute can be used. In the present specification, it can be evaluated that the transparency of the sheet is high when the haze of the sheet is less than 0.5%.

The total light transmittance of the sheet is preferably 85% or more, more preferably 90% or more. Here, the total light transmittance of the sheet is a value measured using a haze meter in accordance with JIS K 7631-1: 1997. As the haze meter, for example, HM-150 manufactured by Murakami Color Technology Research Institute can be used.

The tensile elastic modulus of the sheet at 23 ° C. and 50% relative humidity is preferably 2.5 GPa or more, more preferably 5 GPa or more, further preferably 7 GPa or more, and further preferably 9 GPa or more. It is preferably 10 GPa or more, and particularly preferably 10 GPa or more. The tensile elastic modulus of the sheet at 23 ° C. and 50% relative humidity is preferably 30 GPa or less. The tensile modulus of the sheet is a value measured in accordance with JIS P 8113: 2006, and the tensile modulus is a value calculated from the maximum positive inclination value in the SS curve (stress-strain curve). ..

The sheet of the present invention can exhibit excellent water resistance. As described above, the sheet of the present invention is a sheet having both high transparency and water resistance. The water resistance of the sheet can be evaluated by the water contact angle of the surface of the sheet. Specifically, the water contact angle of both surfaces of the sheet is preferably 75 ° or more, and more preferably 80 ° or more. That is, the water contact angles of both the sheet surface on which one resin layer (first resin layer) is provided and the sheet surface on which the other resin layer (second resin layer) is provided are set. It is preferably within the above range. Here, the water contact angle on the surface of the sheet is the water contact angle 30 seconds after dropping 4 μL of distilled water onto the surface of the sheet. A dynamic water contact angle tester is used for the measurement. As the dynamic water contact angle tester, for example, 1100 DAT manufactured by Fibro can be used.

In the sheet of the present invention, the fiber layer and the resin layer show excellent interlayer adhesion. Here, the interlayer adhesion can be evaluated by the number of peeled masses of the resin layer. Specifically, in accordance with JIS K 5400: 1990, ^{100 1 mm 2} crosscuts are placed on the surface of the resin layer, and cellophane tape (manufactured by Nichiban Co., Ltd.) is attached on it to obtain 1.5 kg / cm ² . Press with a load. Then, the cellophane tape is peeled off in the 90 ° direction, and the adhesion between the fiber layer and the resin layer is evaluated based on the number of peeled cells. The number of peeled cells is preferably less than 10 points, more preferably less than 5 points, and particularly preferably 0 points.

The total thickness of the sheet of the present invention is not particularly limited, but is preferably 10 μm or more, more preferably 20 μm or more, and further preferably 30 μm or more. The total thickness of the sheet is preferably 1000 μm or less, more preferably 800 μm or less, and even more preferably 600 μm or less. It is preferable that the thickness of the sheet is appropriately adjusted according to the intended use.

The total basis weight of the sheet ^{is preferably 10 g / m 2} or more, more preferably 20 g / m ² or more, and even more preferably 30 g / m ² or more. The total basis weight of the sheet is not particularly limited, ^{but is preferably 5000 g / m 2} or less, more preferably 2500 g / m ² or less, and 1000 g / m ² or less. It is more preferably 500 g / m ² or less, and particularly preferably 500 g / m 2. The basis weight of the sheet is measured according to JIS P 8124: 2011.

Overall density of the sheet is preferably at 1.00 g / cm ³ or more, more preferably 1.20 g / cm ³ or more, more preferably 1.30 g / cm ³ or more, 1.40 g It is particularly preferable that it is / cm ^{3 or more.} The density of the sheet is calculated by dividing the basis weight of the sheet by the thickness. The thickness of the sheet can be measured with a stylus type thickness gauge (Millitron 1202D manufactured by Marl Co., Ltd.).

The water content (moisture content) of the sheet is preferably 15% by mass or less, more preferably 12% by mass or less, further preferably 10% by mass or less, and 5% by mass or less. It is particularly preferable to have. Here, the moisture content of the sheet can be evaluated as follows. Specifically, the sheet is cut out into a test piece of 5 cm × 5 cm, the test piece is humidity-controlled at 23 ° C. and a relative humidity of 50% for 24 hours, and then dried in a constant temperature machine at 105 ° C. until it becomes completely dry. The weight of the test piece after humidity control is W (g), the weight of the test piece after drying is D, and the value calculated by (WD) / W × 100 is the moisture content (mass%) of the sheet. And. By keeping the moisture content of the sheet within the above range, tensile properties such as tensile elastic modulus can be improved.

The refractive index of the resin layer constituting the sheet is preferably 1.30 or more, more preferably 1.40 or more, and further preferably 1.50 or more. The refractive index of the resin layer is preferably 1.70 or less, more preferably 1.65 or less, further preferably 1.60 or less, and further preferably 1.57 or less. It is preferably 1.55 or less, and particularly preferably 1.55 or less. Here, the refractive index of the resin layer is a value measured using an Abbe refractive index meter in accordance with JIS K 7142: 2008. As the Abbe refractive index meter, for example, NAR-3T manufactured by ATAGO Co., Ltd. can be used. When measuring the refractive index of the resin layer, 0.5 mL of the resin coating liquid is applied onto a glass substrate (2 cm × 2 cm) for Abbe measurement and heated at 100 ° C. for 1 hour to form the resin layer. The resin layer formed on the glass substrate is not peeled off from the glass substrate and is used as it is for measuring the refractive index.

The refractive index of the fiber layer constituting the sheet is preferably 1.51 or more, and more preferably 1.53 or more. The refractive index of the fiber layer is preferably 1.60 or less, more preferably 1.58 or less, further preferably 1.56 or less, and particularly preferably 1.54 or less. preferable. Here, the refractive index of the fiber layer is a value measured by using an Abbe refractive index meter in accordance with JIS K 7142: 2008. As the Abbe refractive index meter, for example, NAR-3T manufactured by ATAGO Co., Ltd. Can be used.

It is preferable that the refractive index of the fiber layer and the refractive index of the resin layer are close to each other. At this time, the refractive index ratio between the fiber layer and the resin layer (refractive index of the fiber layer / refractive index of the resin layer) is preferably 0.50 or more, preferably 0.80 or more, and 0.95. The above is more preferable, 0.97 or more is further preferable, and 0.98 or more is particularly preferable. The refractive index ratio between the fiber layer and the resin layer (refractive index of the fiber layer / refractive index of the resin layer) is preferably 1.50 or less, more preferably 1.20 or less, and 1.10. It is more preferably 1.02 or less, and particularly preferably 1.02 or less.

Above all, by setting the refractive index ratio between the fiber layer and the resin layer (refractive index of the fiber layer / refractive index of the resin layer) to 0.98 or more and 1.02 or less, optical interference occurs when the sheet is used as an optical member. It is also possible to suppress the occurrence of ripple (rainbow unevenness) caused by. In particular, when the refractive index of the fiber layer is 1.51 to 1.54 and the refractive index ratio (refractive index of the fiber layer / refractive index of the resin layer) is 0.98 or more and 1.02 or less, the ripple The outbreak can be suppressed more effectively.

(Resin layer)
The resin layer is a layer containing a natural resin or a synthetic resin as a main component. Here, the main component refers to a component contained in an amount of 50% by mass or more with respect to the total mass of the resin layer. The content of the resin is preferably 60% by mass or more, more preferably 70% by mass or more, further preferably 80% by mass or more, and 90% by mass, based on the total mass of the resin layer. The above is particularly preferable. The content of the resin may be 100% by mass.

In the present invention, the thickness of each resin layer is preferably 10 μm or less, more preferably 8 μm or less, further preferably 6 μm or less, further preferably 5 μm or less, and further preferably 4 μm or less. Is particularly preferred. The thickness of each resin layer is preferably 0.1 μm or more. It is preferable that the values of both the first resin layer and the second resin layer are within the above range. Here, the thickness of the resin layer constituting the sheet is a value measured by cutting out a cross section of the sheet with Ultra Microtome UC-7 (manufactured by JEOL Ltd.) and observing the cross section with an electron microscope, a magnifying glass or visually. Is.

Examples of the natural resin include rosin-based resins such as rosin, rosin ester, and hydrogenated rosin ester.

Examples of the synthetic resin include polycarbonate resin, polyester resin, polyethylene naphthalate resin, polyethylene resin, polypropylene resin, polyimide resin, polystyrene resin, urethane resin, acrylic resin, fluororesin and the like. Among them, the synthetic resin is preferably an amorphous resin, more preferably at least one selected from the group consisting of a polycarbonate resin, a urethane resin, an acrylic resin and a fluororesin, and more preferably a polycarbonate resin. Especially preferable. The acrylic resin also includes a urethane acrylic resin.

Examples of the polycarbonate resin constituting the resin layer include aromatic polycarbonate-based resins and aliphatic polycarbonate-based resins. These specific polycarbonate-based resins are known, and examples thereof include the polycarbonate-based resins described in JP-A-2010-023275.

The resin layer preferably contains a hydrophobic resin. In the present specification, the hydrophobic resin is defined as a resin having a contact angle with water of 60 degrees or more in a dry state. Here, "in a dry state" means excluding a state in which the hydrophobic resin has an affinity for water, for example, when it is in an emulsion state.

The resin layer may contain an adhesion aid. Examples of the adhesion aid include a compound containing at least one selected from the group consisting of an isocyanate group, a carbodiimide group, an epoxy group, an oxazoline group, an amino group and a silanol group, and an organic silicon compound. Examples of the organosilicon compound include a silane coupling agent condensate and a silane coupling agent. Among them, the adhesion aid is preferably a compound containing an isocyanate group (isocyanate compound), and the resin layer is preferably one containing an isocyanate compound.

Examples of the isocyanate compound include polyisocyanate compounds and polyfunctional isocyanates. Specific examples of the polyisocyanate compound include aromatic polyisocyanates having 6 or more and 20 or less carbon atoms excluding carbon in the NCO group, aliphatic polyisocyanates having 2 or more and 18 or less carbon atoms, and 6 or more and 15 or less carbon atoms. Examples thereof include alicyclic polyisocyanates, aralkyl-type polyisocyanates having 8 or more and 15 or less carbon atoms, modified products of these polyisocyanates, and mixtures of two or more of these. Of these, an alicyclic polyisocyanate having 6 or more and 15 or less carbon atoms, that is, isocyanurate is preferably used.

Specific examples of the alicyclic polyisocyanate include isophorone diisocyanate (IPDI), dicyclohexylmethane-4,4'-diisocyanate (hydrogenated MDI), cyclohexylene diisocyanate, methylcyclohexylene diisocyanate, and bis (2-isocyanatoethyl). Examples thereof include -4-cyclohexene-1,2-dicarboxylate, 2,5-norbornan diisocyanate, and 2,6-norbornan diisocyanate.

Examples of the organosilicon compound include a compound having a siloxane structure and a compound that forms a siloxane structure by condensation. For example, a silane coupling agent or a condensate of a silane coupling agent can be mentioned. The silane coupling agent may have a functional group other than the alkoxysilyl group, or may have no other functional group. Examples of the functional group other than the alkoxysilyl group include a vinyl group, an epoxy group, a styryl group, a methacrylox group, an acryloxy group, an amino group, a ureido group, a mercapto group, a sulfide group, an isocyanate group and the like. The silane coupling agent used in the present invention is preferably a silane coupling agent containing a methacryloxy group.

Specific examples of the silane coupling agent having a methacryloxy group in the molecule include methacryloxypropylmethyldimethoxysilane, methacryloxypropyltrimethoxysilane, methacryloxypropylmethyldiethoxysilane, and methacryloxypropyltriethoxysilane. Examples thereof include 1,3-bis (3-methacryloxypropyl) tetramethyldisiloxane. Among them, at least one selected from methacryloxypropyltrimethoxysilane, methacryloxypropyltriethoxysilane and 1,3-bis (3-methacryloxypropyl) tetramethyldisiloxane is preferably used. The silane coupling agent preferably contains 3 or more alkoxysilyl groups.

In the silane coupling agent, it is preferable that silanol groups are generated after hydrolysis, and at least a part of the silanol groups is present even after laminating the fiber layer. Since the silanol group is a hydrophilic group, it is possible to improve the adhesion between the resin layer and the fiber layer by increasing the hydrophilicity of the surface of the resin layer on the fiber layer side.

The adhesion aid may be contained in a state of being uniformly dispersed in the resin layer. Here, the state in which the adhesion aid is uniformly dispersed in the resin layer means that the concentrations of the following three regions ((a) to (c)) are measured and the concentrations of any of the two regions are compared. A state in which there is no difference of 2 times or more.
(A) Region from the surface of the resin layer on the fiber layer side to 10% of the total thickness of the resin layer (b) 10 of the total thickness of the resin layer from the surface opposite to the surface of the resin layer on the fiber layer side Region up to% (c) Region of ± 5% (total 10%) of the total thickness from the central surface in the thickness direction of the resin layer

Further, the adhesion aid may be unevenly distributed in the region on the fiber layer side of the resin layer. For example, when the organosilicon compound is used as the adhesion aid, the organosilicon compound may be unevenly distributed in the region on the fiber layer side of the resin layer.
Here, the state of being unevenly distributed in the region on the fiber layer side of the resin layer means that the two concentrations of the following regions ((d) and (e)) are measured and the difference between these concentrations is more than twice. It means the state where it comes out.
(D) Region from the surface of the resin layer on the fiber layer side to 10% of the total thickness of the resin layer (e) Region of ± 5% (total 10%) of the total thickness from the central surface in the thickness direction of the resin layer. Here, the concentration of the adhesion aid is a numerical value measured by an X-ray electron spectroscope or an infrared spectrophotometer, and a cross section of a predetermined region of the sheet is cut out by Ultramicrotome UC-7 (manufactured by JEOL). It is a value obtained by measuring the cross section with the device.

An organosilicon compound-containing layer may be provided on the surface of the resin layer on the fiber layer side, and such a state is also included in the state where the organosilicon compound is unevenly distributed in the region on the fiber layer side of the resin layer. Is done. The organosilicon compound-containing layer may be a coating layer formed by applying an organosilicon compound-containing coating liquid.
When the organosilicon compound-containing layer is provided on the surface of the resin layer on the fiber layer side, in the above region (d), the “surface on the fiber layer side of the resin layer” is the “organosilicon compound-containing layer”. It shall be read as "exposed surface", and "thickness of the entire resin layer" shall be read as "total thickness of the resin layer and the organosilicon compound-containing layer".

The content of the adhesion aid is preferably 0.1 part by mass or more, and more preferably 0.5 part by mass or more with respect to 100 parts by mass of the resin contained in the resin layer. The content of the adhesion aid is preferably 40 parts by mass or less, and more preferably 35 parts by mass or less, with respect to 100 parts by mass of the resin contained in the resin layer.
When the adhesion aid is an isocyanate compound, the content of the isocyanate compound is preferably 10 parts by mass or more, more preferably 15 parts by mass or more, based on 100 parts by mass of the resin contained in the resin layer. It is more preferably 18 parts by mass or more. The content of the isocyanate compound is preferably 40 parts by mass or less, more preferably 35 parts by mass or less, and more preferably 30 parts by mass or less with respect to 100 parts by mass of the resin contained in the resin layer. More preferred.
When the adhesion aid is an organosilicon compound, the content of the organosilicon compound is preferably 0.1 part by mass or more, and 0.5 part by mass or more with respect to 100 parts by mass of the resin contained in the resin layer. It is more preferable to have. The content of the organosilicon compound is preferably 10 parts by mass or less, and more preferably 5 parts by mass or less, based on 100 parts by mass of the resin contained in the resin layer.
By setting the content of the adhesion aid within the above range, the adhesion between the fiber layer and the resin layer can be enhanced more effectively.

When the adhesion aid is an isocyanate compound, the content of the isocyanate group contained in the resin layer is preferably 0.5 mmol / g or more, more preferably 0.6 mmol / g or more, and 0.8 mmol or more. It is more preferably / g or more, and particularly preferably 0.9 mmol / g or more. Further, the content of the isocyanate group contained in the resin layer is preferably 3.0 mmol / g or less, more preferably 2.5 mmol / g or less, and further preferably 2.0 mmol / g or less. It is preferably 1.5 mmol / g or less, and particularly preferably 1.5 mmol / g or less.

The surface of the resin layer on the fiber layer side may be surface-treated. Examples of the surface treatment method include corona treatment, plasma discharge treatment, UV irradiation treatment, electron beam irradiation treatment, flame treatment and the like. Above all, the surface treatment is preferably at least one selected from the corona treatment and the plasma discharge treatment. The plasma discharge process is preferably a vacuum plasma discharge process.

The resin layer may contain an arbitrary component other than the synthetic resin as long as the effect of the present invention is not impaired. Examples of the optional component include known components used in the field of resin films such as fillers, pigments, dyes, and ultraviolet absorbers.

In the present invention, the resin layer may be an ultraviolet curable resin layer or a solvent-coated layer. Above all, the resin layer is preferably a solvent-coated layer. That is, the resin layer is preferably a layer formed by applying a resin coating liquid containing a solvent on the fiber layer and curing it. By using the resin layer as the solvent-coated layer in this way, it is possible to efficiently manufacture a sheet exhibiting high transparency.

When the resin layer is an ultraviolet curable resin layer, it is preferable that the resin coating liquid contains a photopolymerization initiator. For example, the resin layer can be formed by applying a resin coating liquid containing a solvent and a photopolymerization initiator on the fiber layer, volatilizing the solvent by heating and drying, and then irradiating with ultraviolet rays. The irradiation amount of ultraviolet rays is arbitrary as long as the photopolymerization initiator generates radicals.

(Fiber layer)
The fiber layer contains fibrous cellulose (fine fibrous cellulose) having a fiber width of 1000 nm or less. The content of the fine fibrous cellulose is preferably 10% by mass or more, more preferably 50% by mass or more, still more preferably 60% by mass or more, more preferably 70% by mass, based on the total mass of the fiber layer. It is more preferably mass% or more.

The thickness of the fiber layer is preferably 10 μm or more, more preferably 15 μm or more, and further preferably 20 μm or more. The thickness of the fiber layer is preferably 1000 μm or less, more preferably 800 μm or less, and even more preferably 600 μm or less. Here, the thickness of the fiber layer constituting the sheet is a value measured by cutting out a cross section of the sheet with an ultramicrotome UC-7 (manufactured by JEOL Ltd.) and observing the cross section with an electron microscope, a magnifying glass or visually. Is.

The density of the fiber layer ^{is preferably 1.0 g / cm 3} or more, more preferably 1.1 g / cm ³ or more, and even more preferably 1.2 g / cm ³ or more. The density of the fiber layer ^{is preferably 1.8 g / cm 3} or less, more preferably 1.7 g / cm ³ or less, and even more preferably 1.6 g / cm ³ or less.

The density of the fiber layer is calculated according to JIS P 8118: 2014 from the basis weight and thickness of the fiber layer. The basis weight of the fiber layer can be calculated by cutting with Ultra Microtome UC-7 (manufactured by JEOL Ltd.) so that only the fiber layer of the sheet remains, and in accordance with JIS P 8124: 2011. When the fiber layer contains an arbitrary component other than the fine fibrous cellulose, the density of the fiber layer is a density containing an arbitrary component other than the fine fibrous cellulose.

The present invention is also characterized in that the fiber layer is a non-porous layer. Here, the fact that the fiber layer is non-porous means that the density of the entire fiber layer is 1.0 g / cm ³ or more. When the density of the entire fiber layer is 1.0 g / cm ³ or more, it means that the porosity contained in the fiber layer is suppressed to a predetermined value or less, and it is distinguished from the porous sheet or layer. ..
The non-porous fiber layer is also characterized by a void ratio of 15% by volume or less. The porosity of the fiber layer referred to here is simply obtained by the following formula (a).
Equation (a): Porosity (% by volume) = {1-B / (M × A × t)} × 100
Here, A is the area of the fiber layer (cm ² ), t is the thickness of the fiber layer (cm), B is the mass of the fiber layer (g), and M is the density of the solid content constituting the fiber layer.

<Fine fibrous cellulose>
The fiber layer contains fibrous cellulose having a fiber width of 1000 nm or less. The fiber width of the fibrous cellulose is preferably 100 nm or less, more preferably 8 nm or less. As a result, the dispersibility in the solvent can be enhanced more effectively, and a high-strength and highly transparent fiber layer can be easily obtained.

The fiber width of the fibrous cellulose can be measured, for example, by observation with an electron microscope. The average fiber width of the fibrous cellulose is, for example, 1000 nm or less. The average fiber width of the fibrous cellulose is, for example, preferably 2 nm or more and 1000 nm or less, more preferably 2 nm or more and 100 nm or less, further preferably 2 nm or more and 50 nm or less, and 2 nm or more and 10 nm or less. Especially preferable. By setting the average fiber width of the fibrous cellulose to 2 nm or more, it becomes easy to suppress the dissolution of the cellulose molecule in water. The fibrous cellulose is, for example, monofibrous cellulose.

The average fiber width of fibrous cellulose is measured, for example, using an electron microscope as follows. First, an aqueous suspension of fibrous cellulose having a concentration of 0.05% by mass or more and 0.1% by mass or less is prepared, and this suspension is cast on a hydrophilized carbon film-coated grid to be a sample for TEM observation. And. If it contains wide fibers, an SEM image of the surface cast on the glass may be observed. Next, observation is performed using an electron microscope image at a magnification of 1000 times, 5000 times, 10000 times, or 50,000 times depending on the width of the fiber to be observed. However, the sample, observation conditions and magnification should be adjusted so as to satisfy the following conditions.
(1) A straight line X is drawn at an arbitrary position in the observation image, and 20 or more fibers intersect the straight line X.
(2) A straight line Y that intersects the straight line perpendicularly is drawn in the same image, and 20 or more fibers intersect the straight line Y.
The width of the fiber intersecting the straight line X and the straight line Y is visually read with respect to the observation image satisfying the above conditions. In this way, at least three sets of observation images of surface portions that do not overlap each other are obtained. Next, for each image, the width of the fiber intersecting the straight line X and the straight line Y is read. As a result, at least 20 fibers × 2 × 3 = 120 fibers are read. Then, the average value of the read fiber widths is taken as the average fiber width of the fibrous cellulose.

The fiber length of the fibrous cellulose is not particularly limited, but is preferably 0.1 μm or more and 1000 μm or less, more preferably 0.1 μm or more and 800 μm or less, and further preferably 0.1 μm or more and 600 μm or less. preferable. By setting the fiber length within the above range, it is possible to suppress the destruction of the crystal region of the fibrous cellulose. It is also possible to set the slurry viscosity of the fibrous cellulose in an appropriate range. The fiber length of the fibrous cellulose can be obtained by, for example, image analysis by TEM, SEM, or AFM.

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

The axial ratio (fiber length / fiber width) of the fibrous cellulose is not particularly limited, but is preferably 20 or more and 10000 or less, and more preferably 50 or more and 1000 or less. By setting the axial ratio to the above lower limit value or more, it is easy to form a sheet containing fine fibrous cellulose. By setting the axial ratio to the above upper limit value or less, it is preferable in that handling such as dilution becomes easy when, for example, fibrous cellulose is treated as a dispersion liquid.

The fibrous cellulose in this embodiment has, for example, both a crystalline region and a non-crystalline region. In particular, fine fibrous cellulose having both a crystalline region and a non-crystalline region and having a high axial ratio is realized by the method for producing fine fibrous cellulose described later.

The fibrous cellulose preferably has an ionic substituent. When the fibrous cellulose has an ionic substituent, the dispersibility of the fibrous cellulose in the dispersion medium can be improved, and the defibration efficiency in the defibration treatment can be improved. The ionic substituent may include, for example, one or both of an anionic group and a cationic group. In this embodiment, it is particularly preferable to have an anionic group as the ionic substituent.

Examples of the anionic group as an ionic substituent include a phosphate group or a substituent derived from a phosphorusoxo acid group (sometimes referred to simply as a phosphorusoxo acid group), a carboxy group or a substituent derived from a carboxy group (simply a carboxy group). (Sometimes), a sulfone group or a substituent derived from a sulfone group (sometimes simply referred to as a sulfone group), a zantate group, a phosphon group, a phosphine group, a carboxyalkyl group (including a carboxymethyl group), etc. can. When a sulfone group or a substituent derived from a sulfone group is introduced via an ester bond, the substituent is referred to as a sulfur oxo acid group or a substituent derived from a sulfur oxo acid group (simply referred to as a sulfur oxo acid group). There is also). Among them, the anionic group is composed of a phosphorus oxo acid group, a substituent derived from a phosphorus oxo acid group, a carboxy group, a substituent derived from a carboxy group, a carboxymethyl group, a sulfur oxo acid group and a substituent derived from a sulfur oxo acid group. It is preferably at least one selected from the above group, and is derived from a phosphorus oxo acid group, a substituent derived from a phosphorus oxo acid group, a carboxy group, a substituent derived from a carboxy group, a sulfur oxo acid group and a sulfur oxo acid group. It is more preferably at least one selected from the group consisting of substituents, and particularly preferably a phosphorusoxo acid group. By introducing a phosphorus oxo acid group as an anionic group, for example, the dispersibility of fibrous cellulose can be further enhanced even under alkaline or acidic conditions, resulting in a high-strength and highly transparent fiber layer. It will be easier to get rid of.

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

In the 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. It is also possible that all of each α and α'are O ^−. The n αs may all be the same or different from each other. β ^{b +} is a monovalent or higher cation composed of an organic substance or an inorganic substance.

R is a hydrogen atom, a saturated-linear hydrocarbon group, a saturated-branched chain hydrocarbon group, a saturated-cyclic hydrocarbon group, an unsaturated-linear hydrocarbon group, and an unsaturated-branched chain hydrocarbon, respectively. A hydrogen group, an unsaturated-cyclic hydrocarbon group, an aromatic group, or an inducing group thereof. Further, in the formula (1), n is preferably 1.

Examples of the saturated-linear hydrocarbon group include, but are not limited to, a methyl group, an ethyl group, an n-propyl group, an n-butyl group and the like. Examples of the saturated-branched chain hydrocarbon group include an i-propyl group and a t-butyl group, but the group is not particularly limited. Examples of the saturated-cyclic hydrocarbon group include, but are not limited to, a cyclopentyl group, a cyclohexyl group and the like. Examples of the unsaturated-linear hydrocarbon group include, but are not limited to, a vinyl group, an allyl group and the like. Examples of the unsaturated-branched chain hydrocarbon group include an i-propenyl group and a 3-butenyl group, but the group is not particularly limited. Examples of the unsaturated-cyclic hydrocarbon group include, but are not limited to, a cyclopentenyl group, a cyclohexenyl group and the like. Examples of the aromatic group include, but are not limited to, a phenyl group, a naphthyl group and the like.

As the derivative groups in R, to the main chain or side chain of the various hydrocarbon group, a carboxy group, a carboxylate group (-COO ^-), hydroxy group, selected from the functional groups such as an amino group and an ammonium group Examples thereof include functional groups in which at least one of them is added or substituted, but the functional group is not particularly limited. 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 to the above range, the molecular weight of the phosphorus oxo acid group can be set to an appropriate range, the penetration into the fiber raw material is facilitated, and the yield of fibrous cellulose is increased. You can also do it. When a plurality of Rs are present in the formula (1) or when a plurality of types of substituents represented by the above formula (1) are introduced into the fibrous cellulose, the plurality of Rs present are the same. It may or may not be different.

β ^{b +} is a monovalent or higher cation composed of an organic substance or an inorganic substance. Examples of monovalent or higher cations composed of organic substances include organic onium ions. Examples of the organic onium ion include an organic ammonium ion and an organic phosphonium ion. Examples of the organic ammonium ion include aliphatic ammonium ion and aromatic ammonium ion, and examples of the organic phosphonium ion include aliphatic phosphonium ion and aromatic phosphonium ion. Examples of monovalent or higher cations composed of inorganic substances include alkali metal ions such as sodium, potassium, and lithium, divalent metal ions such as calcium and magnesium, hydrogen ions, and ammonium ions. When a ^{plurality of β b +} are present in the formula (1) or when a plurality of types of substituents represented by the above formula (1) are introduced into the fibrous cellulose, the plurality of β ^{b +} are present respectively. It may be the same or different. The monovalent or higher cation composed of an organic substance or an inorganic substance is preferably sodium or potassium ion which is hard to yellow when the fiber raw material containing ^{β b + is heated and is easily industrially used, but is not particularly limited.} ..

Specific examples of the phosphoric acid group or the substituent derived from the phosphoric acid group include a phosphoric acid group (-PO ₃ H ₂ ), a salt of a phosphoric acid group, and a phosphite group (phosphonic acid group) (-PO). ₂ H _2), and salts of phosphorous acid (phosphonic acid group). Further, the phosphoric acid group or the substituent derived from the phosphoric acid group includes a group in which a phosphoric acid group is condensed (for example, a pyrophosphate group), a group in which a phosphonic acid is condensed (for example, a polyphosphonic acid group), and a phosphoric acid ester group (for example, a phosphoric acid ester group). For example, it may be a monomethyl phosphate group, a polyoxyethylene alkyl phosphate group), an alkylphosphonic acid group (for example, a methylphosphonic acid group), or the like.

The sulfur oxoacid group (sulfur oxoacid group or a substituent derived from the 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 substituents represented by the following formula (2) to be introduced may be the same or different.

In the above structural formula, b and n are natural numbers, p is 0 or 1, and m is an arbitrary number (where 1 = b × m). When n is 2 or more, a plurality of ps may be the same number or different numbers. In the above structural formula, β ^{b +} is a monovalent or higher cation composed of an organic substance or an inorganic substance. Examples of monovalent or higher cations composed of organic substances include organic onium ions. Examples of the organic onium ion include an organic ammonium ion and an organic phosphonium ion. Examples of the organic ammonium ion include aliphatic ammonium ion and aromatic ammonium ion, and examples of the organic phosphonium ion include aliphatic phosphonium ion and aromatic phosphonium ion. Examples of monovalent or higher cations composed of inorganic substances include alkali metal ions such as sodium, potassium, and lithium, divalent metal ions such as calcium and magnesium, hydrogen ions, and ammonium ions. When a plurality of types of substituents represented by the above formula (2) are introduced into the fibrous cellulose, the plurality of β ^{b +} may be the same or different. The monovalent or higher cation composed of an organic substance or an inorganic substance is preferably sodium or potassium ion which is hard to yellow when the fiber raw material containing ^{β b + is heated and is easily industrially used, but is not particularly limited.} ..

The amount of the ionic substituent introduced into the fibrous cellulose is, for example, preferably 0.10 mmol / g or more, more preferably 0.20 mmol / g or more, and 0.50 mmol / g per 1 g (mass) of the fibrous cellulose. It is more preferably / g or more, and particularly preferably 1.00 mmol / g or more. The amount of the ionic substituent introduced into the fibrous cellulose is, for example, preferably 5.20 mmol / g or less per 1 g (mass) of the fibrous cellulose, and more preferably 3.65 mmol / g or less. It is more preferably .50 mmol / g or less, and even more preferably 3.00 mmol / g or less. By setting the amount of the ionic substituent to be introduced within the above range, it is possible to facilitate the miniaturization of the fiber raw material and enhance the stability of the fibrous cellulose. Here, the denominator in the unit mmol / g indicates the mass of the fibrous cellulose when the counterion of the ionic substituent is a hydrogen ion (H ^+).

The amount of the ionic substituent introduced into the fibrous cellulose can be measured by, for example, a neutralization titration method. In the measurement by the neutralization titration method, the introduction amount is measured by determining the change in pH while adding an alkali such as an aqueous solution of sodium hydroxide to the obtained slurry containing fibrous cellulose.

FIG. 2 is a graph showing the relationship between the amount of NaOH titrated and the pH of a fibrous cellulose-containing slurry having a phosphoric acid group as an ionic substituent. The amount of the phosphorus oxo acid group introduced into the fibrous cellulose is measured, for example, as follows.
First, the slurry containing fibrous cellulose is treated with a strongly acidic ion exchange resin. If necessary, the same defibration treatment as the defibration treatment step described later may be performed on the measurement target before the treatment with the strong acid ion exchange resin.
Next, the change in pH is observed while adding an aqueous sodium hydroxide solution, and a titration curve as shown in the upper part of FIG. 2 is obtained. The titration curve shown in the upper part of FIG. 2 plots the measured pH with respect to the amount of alkali added, and the titration curve shown in the lower part of FIG. 2 plots the pH with respect to the amount of alkali added. The increment (differential value) (1 / mmol) is plotted. In this neutralization titration, two points are confirmed in which the increment (differential value of pH with respect to the amount of alkaline drop) becomes maximum in the curve plotting the measured pH with respect to the amount of alkali added. Of these, the maximum point of the increment obtained first when alkali is added is called the first end point, and the maximum point of the increment obtained next is called the second end point. The amount of alkali required from the start of titration to the first end point is equal to the amount of first dissociated acid of the fibrous cellulose contained in the slurry used for titration, and the amount of alkali required from the first end point to the second end point. The amount is equal to the amount of the second dissociated acid of the fibrous cellulose contained in the slurry used for the titration, and the amount of alkali required from the start to the second end point of the titration is the fibrous cellulose contained in the slurry used for the titration. Is equal to the total amount of dissociated acid. Then, the value obtained by dividing the amount of alkali required from the start of titration to the first end point by the solid content (g) in the slurry to be titrated is the amount of phosphorus oxo acid group introduced (mmol / g). The amount of phosphorus oxo acid group introduced (or the amount of phosphorus oxo acid group) simply means the amount of the first dissociated acid.
In FIG. 2, the region from the start of titration to the first end point is referred to as a first region, and the region from the first end point to the second end point is referred to as a second region. For example, when the phosphoric acid group is a phosphoric acid group and this phosphoric acid group causes condensation, the amount of weakly acidic groups (second dissociated acid amount) in the phosphoric acid group apparently decreases, and the first region The amount of alkali required for the second region is smaller than the amount of alkali required for the second region. On the other hand, the amount of the strongly acidic group (the amount of the first dissociated acid) in the phosphorus oxo acid group is the same as the amount of the phosphorus atom regardless of the presence or absence of condensation. When the phosphorous acid group is a phosphorous acid group, the weakly acidic group does not exist in the phosphorous acid group, so that the amount of alkali required for the second region is reduced or the amount of alkali required for the second region is reduced. May be zero. In this case, there is only one point on the titration curve where the pH increment is maximum.

Since the denominator of the above-mentioned phosphorus oxo acid group introduction amount (mmol / g) indicates the mass of the acid-type fibrous cellulose, the phosphorus oxo acid group amount of the acid-type fibrous cellulose (hereinafter referred to as the phosphorus oxo acid group amount). (Called (acid type))). On the other hand, when the counterion of the phosphorus oxo acid group is replaced with an arbitrary cation C so as to have a charge equivalent, the denominator is converted into the mass of fibrous cellulose when the cation C is a counterion. This makes it possible to determine the amount of phosphorus oxo acid groups (hereinafter referred to as the amount of phosphorus oxo acid groups (C type)) possessed by the fibrous cellulose in which the cation C is a counter ion.
That is, it is calculated by the following formula.
Amount of phosphorus oxo acid group (C type) = Amount of phosphorus oxo acid group (acid type) / {1+ (W-1) × A / 1000}
A [mmol / g]: Total anion amount derived from the phosphoric acid group of the fibrous cellulose (total dissociated acid amount of the phosphoric acid group)
W: Formulated amount per valence of cation C (for example, Na is 23, Al is 9)

FIG. 3 is a graph showing the relationship between the amount of NaOH dropped and the pH of a dispersion liquid containing fibrous cellulose having a carboxy group as an ionic substituent. The amount of the carboxy group introduced into the fibrous cellulose is measured, for example, as follows.
First, the dispersion liquid containing fibrous cellulose is treated with a strongly acidic ion exchange resin. If necessary, the same defibration treatment as the defibration treatment step described later may be performed on the measurement target before the treatment with the strong acid ion exchange resin.
Next, the change in pH is observed while adding an aqueous sodium hydroxide solution, and a titration curve as shown in the upper part of FIG. 3 is obtained. The titration curve shown in the upper part of FIG. 3 plots the measured pH with respect to the amount of alkali added, and the titration curve shown in the lower part of FIG. 3 plots the pH with respect to the amount of alkali added. The increment (differential value) (1 / mmol) is plotted. In this neutralization titration, in the curve plotting the pH measured with respect to the amount of alkali added, one point was confirmed where the increment (differential value of pH with respect to the amount of alkali dropped) became maximum, and this maximum point was the first. Called one end point. Here, the region from the start of titration to the first end point in FIG. 3 is referred to as a first region. The amount of alkali required in the first region is equal to the amount of carboxy groups in the dispersion used for titration. Then, the amount of alkali (mmol) required in the first region of the titration curve is divided by the solid content (g) in the dispersion containing the fibrous cellulose to be titrated, so that the amount of carboxy group introduced (mmol). / G) is calculated.

Since the denominator of the above-mentioned carboxy group introduction amount (mmol / g) is the mass of the acid type fibrous cellulose, the carboxy group amount of the acid type fibrous cellulose (hereinafter, the carboxy group amount (acid type)). ) Is shown. On the other hand, when the counterion of the carboxy group is replaced with an arbitrary cation C so as to have a charge equivalent, the denominator is converted to the mass of fibrous cellulose when the cation C is a counterion. Therefore, the amount of carboxy group (hereinafter, the amount of carboxy group (C type)) possessed by the fibrous cellulose in which the cation C is a counter ion can be obtained. That is, it is calculated by the following formula.
Carboxy group amount (C type) = Carboxy group amount (acid type) / {1+ (W-1) x (carboxy group amount (acid type)) / 1000}
W: Formulated amount per valence of cation C (for example, Na is 23, Al is 9)

In the measurement of the amount of ionic substituents by the titration method, if the amount of one drop of sodium hydroxide aqueous solution is too large, or if the titration interval is too short, the amount of ionic substituents will be lower than it should be. It may not be obtained. As an appropriate dropping amount and titration interval, for example, it is desirable to titrate 10 to 50 μL of a 0.1 N sodium hydroxide aqueous solution every 5 to 30 seconds. Further, in order to eliminate the influence of carbon dioxide dissolved in the fibrous cellulose-containing slurry, for example, it is desirable to measure while blowing an inert gas such as nitrogen gas into the slurry from 15 minutes before the start of titration to the end of titration.

The amount of sulfone group introduced into fibrous cellulose is determined by wet ashing fibrous cellulose with perchloric acid and concentrated nitric acid, diluting it at an appropriate magnification, and measuring the amount of sulfur by ICP emission analysis. Can be calculated. The value obtained by dividing the amount of sulfur by the absolute dry mass of the fibrous cellulose tested is the amount of sulfone groups (unit: mmol / g).

<Manufacturing process of fine fibrous cellulose>
<Fiber raw material>
Fine fibrous cellulose is produced from a fiber raw material containing cellulose. The fiber raw material containing cellulose is not particularly limited, but pulp is preferably used because it is easily available and inexpensive. Examples of pulp include wood pulp, non-wood pulp, and deinked pulp. The wood pulp is not particularly limited, but is, for example, broadleaf kraft pulp (LBKP), coniferous kraft pulp (NBKP), sulfite pulp (SP), dissolved pulp (DP), soda pulp (AP), and unbleached kraft pulp (UKP). ) And chemical pulp such as oxygen bleached kraft pulp (OKP), semi-chemical pulp such as semi-chemical pulp (SCP) and chemiground wood pulp (CGP), crushed wood pulp (GP) and thermomechanical pulp (TMP, BCTMP), etc. Examples include mechanical pulp. The non-wood pulp is not particularly limited, and examples thereof include cotton pulp such as cotton linter and cotton lint, and non-wood pulp such as hemp, straw and bagasse. The deinking pulp is not particularly limited, and examples thereof include deinking pulp made from recycled paper. As the pulp of this embodiment, one of the above may be used alone, or two or more of them may be mixed and used. Among the above pulps, for example, wood pulp and deinked pulp are preferable from the viewpoint of availability. Further, among wood pulps, it is possible to obtain long-fiber fine fibrous cellulose having a large cellulose ratio and a high yield of fine fibrous cellulose during defibration treatment, and having a small decomposition of cellulose in the pulp and a large axial ratio. From the viewpoint, for example, chemical pulp is more preferable, and kraft pulp and sulfite pulp are further preferable. It should be noted that the viscosity tends to be high when the fine fibrous cellulose of long fibers having a large axial ratio is used.

As the fiber raw material containing cellulose, for example, cellulose contained in ascidians and bacterial cellulose produced by acetic acid bacteria can also be used. Further, instead of the fiber raw material containing cellulose, a fiber formed by a linear nitrogen-containing polysaccharide polymer such as chitin or chitosan can also be used.

<Linoxo acid group introduction process>
The process for producing fine fibrous cellulose preferably includes an ionic substituent introduction step, and examples of the ionic substituent introduction step include a phosphoxoic acid group introduction step. In the phosphorus oxo acid group introduction step, at least one compound (hereinafter, also referred to as “compound A”) selected from compounds capable of introducing a phosphorus oxo acid group by reacting with a hydroxyl group of a fiber raw material containing cellulose is used as cellulose. It is a step of acting on a fiber raw material containing. By this step, a phosphorus oxo acid group-introduced fiber can be obtained.

In the phosphorus oxo acid group introduction step according to the present embodiment, the reaction between the fiber raw material containing cellulose and compound A is carried out in the presence of at least one selected from urea and its derivatives (hereinafter, also referred to as “compound B”). You may. On the other hand, the reaction of the fiber raw material containing cellulose with the compound A may be carried out in the absence of the compound B.

As an example of the method of allowing the compound A to act on the fiber raw material in the coexistence with the compound B, there is a method of mixing the compound A and the compound B with the fiber raw material in a dry state, a wet state or a slurry state. Of these, since the reaction uniformity is high, it is preferable to use a fiber raw material in a dry state or a wet state, and it is particularly preferable to use a fiber raw material in a dry state. The form of the fiber raw material is not particularly limited, but is preferably cotton-like or thin sheet-like, for example. Examples of the compound A and the compound B include a method of adding the compound A and the compound B to the fiber raw material in the form of a powder or a solution dissolved in a solvent, or in a state of being heated to a melting point or higher and melted. Of these, since the reaction uniformity is high, it is preferable to add the solution in the form of a solution dissolved in a solvent, particularly in the state of an aqueous solution. Further, the compound A and the compound B may be added to the fiber raw material at the same time, may be added separately, or may be added as a mixture. The method for adding the compound A and the compound B is not particularly limited, but when the compound A and the 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 taken out, or the fiber raw material may be taken out. The solution may be dropped into the water. Further, a required amount of compound A and compound B may be added to the fiber raw material, or an excess amount of compound A and compound B may be added to the fiber raw material, respectively, and then the surplus compound A and compound B may be added by pressing or filtering. It may be removed.

The compound A used in this embodiment may be any compound having a phosphorus atom and capable of forming an ester bond with cellulose, and may be phosphoric acid or a salt thereof, phosphoric acid or a salt thereof, dehydration condensed phosphoric acid or a salt thereof. Examples thereof include salts and anhydrous phosphoric acid (diphosphoric pentoxide), but the present invention is not particularly limited. As the phosphoric acid, those having various puritys can be used, and for example, 100% phosphoric acid (normal phosphoric acid) or 85% phosphoric acid can be used. Examples of phosphorous acid include 99% phosphorous acid (phosphonic acid). The dehydration-condensed phosphoric acid is one in which two or more molecules of phosphoric acid are condensed by a dehydration reaction, and examples thereof include pyrophosphoric acid and polyphosphoric acid. Examples of the phosphate, sulphate, and dehydration-condensed phosphate include phosphoric acid, sulphite, or lithium salt of dehydration-condensed phosphoric acid, sodium salt, potassium salt, ammonium salt, and the like. It can be a sum. Of these, from the viewpoints of high efficiency of introducing phosphoric acid group, easy improvement of defibration efficiency in the defibration process described later, low cost, and easy industrial application, phosphoric acid and sodium phosphate Salt, potassium salt of phosphoric acid, ammonium salt or phosphoric acid of phosphoric acid, sodium salt of phosphoric acid, potassium salt of phosphoric acid, ammonium salt of phosphoric acid are preferable, and phosphoric acid, sodium dihydrogen phosphate, Phosphoric acid disodium hydrogen phosphate, ammonium dihydrogen phosphate, or phosphoric acid, sodium phosphite, sodium hydrogen phosphite is more preferred.

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 to the phosphorus atomic weight, the amount of phosphorus atom added to the fiber raw material (absolute dry mass) is 0.5% by mass or more. It is preferably 100% by mass or less, more preferably 1% by mass or more and 50% by mass or less, and further preferably 2% by mass or more and 30% by mass or less. By setting the amount of phosphorus atom 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 addition amount of the phosphorus atom to the fiber raw material to be equal to or less than the above upper limit value, the effect of improving the yield and the cost can be balanced.

The compound B used in this embodiment is at least one selected from urea and its derivatives as described above. Examples of compound B include urea, biuret, 1-phenylurea, 1-benzylurea, 1-methylurea, 1-ethylurea and the like. From the viewpoint of improving the uniformity of the reaction, compound B is preferably used as an aqueous solution. Further, 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 to the fiber raw material (absolute dry mass) is not particularly limited, but is preferably 1% by mass or more and 500% by mass or less, and more preferably 10% by mass or more and 400% by mass or less. It is more preferably 100% by mass or more and 350% by mass or less.

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

In the phosphorus oxo acid group introduction step, it is preferable to add or mix the compound A or the like to the fiber raw material and then heat-treat the fiber raw material. As the heat treatment temperature, it is preferable to select a temperature at which a phosphorus oxo acid group can be efficiently introduced while suppressing the thermal decomposition and hydrolysis reaction of the fiber. The heat treatment temperature is, for example, preferably 50 ° C. or higher and 300 ° C. or lower, more preferably 100 ° C. or higher and 250 ° C. or lower, and further preferably 130 ° C. or higher and 200 ° C. or lower. In addition, equipment having various heat media can be used for the heat treatment, for example, a stirring drying device, a rotary drying device, a disk drying device, a roll type heating device, a plate type heating device, a fluidized layer drying device, and a band. A mold drying device, a filtration drying device, a vibration flow drying device, an air flow drying device, a vacuum drying device, an infrared heating device, a far infrared heating device, a microwave heating device, and a high frequency drying device can be used.

In the heat treatment according to the present embodiment, for example, a method of adding compound A to a thin sheet-shaped fiber raw material by a method such as impregnation and then heating, or a method of heating while kneading or stirring the fiber raw material and compound A with a kneader or the like. Can be adopted. This makes it possible to suppress unevenness in the concentration of compound A in the fiber raw material and to more uniformly introduce the phosphoric acid group onto the surface of the cellulose fiber contained in the fiber raw material. This is because when the water molecules move to the surface of the fiber raw material due to drying, the dissolved compound A is attracted to the water molecules by the surface tension and also moves to the surface of the fiber raw material (that is, the concentration unevenness of the compound A is caused. It is considered that this is due to the fact that it can be suppressed.

Further, the heating device used for the heat treatment always keeps the water content retained by the slurry and the water content generated by the dehydration condensation (phosphate esterification) reaction between the compound A and the hydroxyl group contained in the cellulose or the like in the fiber raw material. It is preferable that the device can be discharged to the outside of the device system. Examples of such a heating device include a ventilation type oven and the like. By constantly discharging the water in the apparatus system, it is possible to suppress the hydrolysis reaction of the phosphate ester bond, which is the reverse reaction of the phosphate esterification, and also to suppress the acid hydrolysis of the sugar chain in the fiber. can. Therefore, it is possible to obtain fine fibrous cellulose having a high axial ratio.

The heat treatment time is preferably 1 second or more and 300 minutes or less, more preferably 1 second or more and 1000 seconds or less, and 10 seconds or more and 800 seconds or less after the water is substantially removed from the fiber raw material. Is more preferable. In the present embodiment, the amount of the phosphorus oxo acid group introduced can be within a preferable range by setting the heating temperature and the heating time within appropriate ranges.

The phosphorus oxo acid group introduction step may be performed at least once, but may be repeated twice or more. By performing the phosphorus oxo acid group introduction step two or more times, many phosphorus oxo acid groups can be introduced into the fiber raw material.

The amount of the phosphorus oxo acid group introduced into the fiber raw material is, for example, preferably 0.10 mmol / g or more, more preferably 0.20 mmol / g or more, and 0.50 mmol / g per 1 g (mass) of fine fibrous cellulose. It is more preferably g or more, and particularly preferably 1.00 mmol / g or more. The amount of the phosphorus oxo acid group introduced into the fiber raw material is, for example, preferably 5.20 mmol / g or less per 1 g (mass) of fine fibrous cellulose, more preferably 3.65 mmol / g or less. It is more preferably 00 mmol / g or less. By setting the amount of the phosphorus oxo acid group introduced within the above range, it is possible to facilitate the miniaturization of the fiber raw material and enhance the stability of the fine fibrous cellulose.

<Carboxy group introduction process>
The process for producing fine fibrous cellulose may include, for example, a carboxy group introduction step as an ionic substituent introduction step. The carboxy group introduction step has an oxidation treatment such as ozone oxidation, oxidation by the Fenton method, TEMPO oxidation treatment, a compound having a group derived from carboxylic acid or a derivative thereof, or a group derived from carboxylic acid with respect to the fiber raw material containing cellulose. It is carried out by treatment with an acid anhydride of a compound or a derivative thereof.

The compound having a group derived from a carboxylic acid is not particularly limited, and for example, a dicarboxylic acid compound such as maleic acid, succinic acid, phthalic acid, fumaric acid, glutaric acid, adipic acid, and itaconic acid, citric acid, aconitic acid and the like. Examples include tricarboxylic acid compounds. The derivative of the compound having a group derived from a carboxylic acid is not particularly limited, and examples thereof include an acid anhydride derivative of the compound having a carboxy group and an acid anhydride derivative of the compound having a carboxy group. The imide of the acid anhydride of the compound having a carboxy group is not particularly limited, and examples thereof include an imide of a dicarboxylic acid compound such as maleimide, succinic acidimide, and phthalic acidimide.

The acid anhydride of the compound having a group derived from carboxylic acid is not particularly limited, but for example, a dicarboxylic acid compound such as maleic anhydride, succinic anhydride, phthalic anhydride, glutaric anhydride, adipic anhydride, and itaconic anhydride. Acid anhydride is mentioned. The derivative of the acid anhydride of the compound having a group derived from carboxylic acid is not particularly limited, but for example, a compound having a carboxy group such as dimethylmaleic acid anhydride, diethylmaleic acid anhydride, diphenylmaleic acid anhydride and the like. Examples thereof include those in which at least a part of the hydrogen atom of the acid anhydride is substituted with a substituent such as an alkyl group or a phenyl group.

When the TEMPO oxidation treatment is performed in the carboxy group introduction step, it is preferable to perform the treatment under conditions of pH 6 or more and 8 or less, for example. Such a treatment is also referred to as a neutral TEMPO oxidation treatment. The neutral TEMPO oxidation treatment includes, for example, sodium phosphate buffer (pH = 6.8), pulp as a fiber raw material, TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl) as a catalyst, and the like. This can be done by adding a nitroxy radical and sodium hypochlorite as a sacrificial reagent. Further, by coexisting with sodium chlorite, the aldehyde generated in the oxidation process can be efficiently oxidized to the carboxy group. Further, the TEMPO oxidation treatment may be carried out under the condition that the pH is 10 or more and 11 or less. Such a treatment is also referred to as an alkaline TEMPO oxidation treatment. The alkaline TEMPO oxidation treatment can be performed, 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 carboxy group introduced into the fiber raw material varies depending on the type of substituent, but for example, when a carboxy group is introduced by TEMPO oxidation, it is preferably 0.10 mmol / g or more per 1 g (mass) of fine fibrous cellulose. , 0.20 mmol / g or more, more preferably 0.50 mmol / g or more, and particularly preferably 0.90 mmol / g or more. Further, it is preferably 2.5 mmol / g or less, more preferably 2.20 mmol / g or less, and further preferably 2.00 mmol / g or less. In addition, when the substituent is a carboxymethyl group, it may be 5.8 mmol / g or less per 1 g (mass) of fine fibrous cellulose.

<Sulfur oxoacid group introduction process>
The process for producing fine fibrous cellulose may include, for example, a sulfur oxoacid group introduction step as an ionic substituent introduction step. In the sulfur oxoacid group introduction step, a cellulose fiber having a sulfur oxoacid group (sulfur oxoacid group-introduced fiber) can be obtained by reacting the hydroxyl group of the fiber raw material containing cellulose with sulfur oxoacid.

In the sulfur oxoacid group introduction step, instead of compound A in the above-mentioned <phosphooxoacid group introduction step>, a compound capable of introducing a sulfur oxoacid group by reacting with a hydroxyl group of a fiber raw material containing cellulose is selected. At least one compound (hereinafter, also referred to as "Compound C") is used. The compound C may be any compound having a sulfur atom and capable of forming an ester bond with cellulose, and examples thereof include sulfuric acid or a salt thereof, sulfurous acid or a salt thereof, and sulfate amide, but the compound C is not particularly limited. As the sulfuric acid, those having various puritys can be used, and for example, 96% sulfuric acid (concentrated sulfuric acid) can be used. Examples of sulfurous acid include 5% sulfurous acid water. Examples of the sulfate or sulfite include lithium salts, sodium salts, potassium salts and ammonium salts of sulfates or sulfites, and these can have various neutralization degrees. As the sulfuric acid amide, sulfamic acid or the like can be used. In the sulfur oxoacid group introduction step, it is preferable to use the compound B in the above-mentioned <phosphooxoacid group introduction step> in the same manner.

In the sulfur oxoacid group introduction step, it is preferable to mix the cellulose raw material with an aqueous solution containing sulfur oxoacid and urea and / or a urea derivative, and then heat-treat the cellulose raw material. As the heat treatment temperature, it is preferable to select a temperature at which the sulfur oxoacid group can be efficiently introduced while suppressing the thermal decomposition and hydrolysis reaction 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 preferably 300 ° C. or lower, more preferably 250 ° C. or lower, and even more preferably 200 ° C. or lower.

In the heat treatment step, it is preferable to heat until the water content is substantially eliminated. Therefore, the heat treatment time varies depending on the amount of water contained in the cellulose raw material and the amount of the aqueous solution containing sulfur oxoacid and urea and / or a urea derivative, but is, for example, 10 seconds or more and 10,000 seconds or less. It is preferable to do so. Equipment having various heat media can be used for the heat treatment, for example, a hot air drying device, a stirring drying device, a rotary drying device, a disk drying device, a roll type heating device, a plate type heating device, and a fluidized layer drying device. , Band type drying device, filtration drying device, vibration flow drying device, air flow drying device, vacuum drying device, infrared heating device, far infrared heating device, microwave heating device, high frequency drying device can be used.

The amount of the sulfur oxoacid group introduced into the cellulose raw material is preferably 0.10 mmol / g or more, more preferably 0.20 mmol / g or more, still more preferably 0.50 mmol / g or more. It is particularly preferably 1.00 mmol / g or more. The amount of sulfur oxoacid group introduced into the cellulose raw material is preferably 5.00 mmol / g or less, and more preferably 3.00 mmol / g or less. By setting the amount of sulfur oxoacid group introduced within the above range, it is possible to facilitate the miniaturization of the fiber raw material and enhance the stability of the fibrous cellulose.

<Oxidation by chlorine-based oxidant>
The step of producing the fine fibrous cellulose may include, for example, an oxidation step with a chlorine-based oxidizing agent as a step of introducing an ionic substituent. In the oxidation step using a chlorine-based oxidant, a carboxy group is introduced into the fiber raw material by adding the chlorine-based oxidant to a wet or dry fiber raw material having a hydroxyl group and carrying out a reaction.

Examples of the chlorine-based oxidizing agent include hypochlorite, hypochlorite, chloric acid, chlorate, chloric acid, chlorate, perchloric acid, perchlorate, chlorine dioxide and the like. Sodium hypochlorite, sodium chlorite, and chlorine dioxide are preferable from the viewpoints of introduction efficiency of substituents, defibration efficiency, cost, and ease of handling.

The chlorine-based oxidizing agent may be added by adding the reagent to the fiber raw material as it is, or by dissolving it in an appropriate solvent.

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

The concentration of the chlorine-based oxidant in the solution in the oxidation step using the chlorine-based oxidant is, for example, preferably 1% by mass or more and 1000% by mass or less, more preferably 5% by mass or more and 500% by mass or less in terms of effective chlorine concentration. It is more preferably 10% by mass or more and 100% by mass or less. The amount of the chlorine-based oxidizing agent added to the fiber raw material is preferably 1% by mass or more and 100,000% by mass or less, more preferably 10% by mass or more and 10,000% by mass or less, and further preferably 100% by mass or more and 5000% by mass or less.

The reaction time with the chlorine-based oxidizing agent in the oxidation step using the chlorine-based oxidizing agent may vary depending on the reaction temperature, but is preferably 1 minute or more and 1000 minutes or less, more preferably 10 minutes or more and 500 minutes or less, and 20 minutes or more. 400 minutes or less is more preferable. The pH at the time of reaction is preferably 5 or more and 15 or less, more preferably 7 or more and 14 or less, and further preferably 9 or more and 13 or less. Further, at the start of the reaction, it is preferable that the pH during the reaction is kept constant (for example, pH 11) while appropriately adding hydrochloric acid or sodium hydroxide. Further, after the reaction, excess reaction reagents, by-products and the like may be washed and removed by filtration or the like.

<Zantate formation (xanthate esterification)>
The step of producing the fine fibrous cellulose may include, for example, a zantate step as the step of introducing an ionic substituent. In the zantate formation step, a zantate group is introduced into the fiber raw material by adding carbon disulfide and an alkaline compound to a wet or dry fiber raw material having a hydroxyl group and carrying out a reaction. Specifically, carbon disulfide is added to the fiber raw material which has been made into alkali cellulose by the method described later, and a reaction is carried out.

<Alkaline celluloseization>
When introducing an ionic functional group into a fiber raw material, it is preferable to allow an alkaline solution to act on the cellulose contained in the fiber raw material to convert the cellulose into alkaline cellulose. By this treatment, a part of the hydroxyl group of cellulose is ionically dissociated, and the nucleophilicity (reactivity) can be enhanced. The alkaline compound contained in the alkaline solution is not particularly limited, and may be an inorganic alkaline compound or an organic alkaline compound. Since it is highly versatile, it is preferable to use, for example, sodium hydroxide, potassium hydroxide, tetraethylammonium hydroxide, or tetrabutylammonium hydroxide. Alkaline celluloseization may be performed at the same time as the introduction of the ionic functional group, may be performed as a pre-stage thereof, or may be performed at both timings.

The solution temperature at the start of alkaline cellulose formation is preferably 0 ° C. or higher and 50 ° C. or lower, more preferably 5 ° C. or higher and 40 ° C. or lower, and further preferably 10 ° C. or higher and 30 ° C. or lower.

The molar concentration of the alkaline solution 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 further preferably 1 mol / L or more and 2.5 mol / L or less. In particular, when the treatment temperature is less than 10 ° C., it is preferably 1 mol / L or more and 2 mol / L or less.

The treatment time for alkali celluloseization is preferably 1 minute or longer, more preferably 10 minutes or longer, and even more preferably 30 minutes or longer. 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, treatment temperature, concentration, and immersion time of the alkaline solution as described above, the penetration of the alkaline solution into the crystalline region of cellulose can be suppressed, the crystalline structure of cellulose type I can be easily maintained, and the cellulose is in the form of fine fibers. The yield of cellulose can be increased.

When the introduction of ionic functional groups and the formation of alkaline cellulose are not performed at the same time, the alkaline cellulose obtained by the alkaline treatment is separated into solid and liquid by a general liquid removal method such as centrifugation or filtration to remove water. It is preferable to keep it. This improves the reaction efficiency in the subsequent ionic functional group introduction step. The cellulose fiber concentration after solid-liquid separation is preferably 5% or more and 50% or less, more preferably 10% or more and 40% or less, and further preferably 15% or more and 35% or less.

<Phosphoralkylation>
The step of producing fine fibrous cellulose may include, for example, a phosphoalkylation step as an ionic substituent introduction step. In the phosphoalkylation step, as an essential component, a compound having a reactive group and a phospho group or a phosphine group (Compound E _A ), as an optional component, an alkaline compound, the above-mentioned compound B selected from urea and its derivatives, and a reaction. A phosphon group or a phosphine group is introduced into the fiber raw material by adding the compound C as an auxiliary agent to the wet or dry fiber raw material having a hydroxyl group and carrying out the reaction.

Examples of the reactive group include an alkyl halide group, a vinyl group, an epoxy group (glycidyl group) and the like.

The compound E _A, e.g. vinyl phosphoric acid, phenyl vinyl phosphonic acid, and phenyl vinyl phosphinic acid. Vinyl phosphoric acid is preferable from the viewpoint of introduction efficiency of substituents, defibration efficiency, cost, and ease of handling.

Further, as an optional component, it is also preferable to use the compound B in the above-mentioned <phosphoric acid group introduction step> in the same manner, and C may be further added. It is preferable that the addition amount is also as described above.

Compound E _A is to reagents may be added directly to the fiber raw materials may be added dissolved in a suitable solvent. It is preferable that the fiber raw material is made alkaline cellulose in advance or is made alkaline cellulose at the same time as the reaction. The method of alkali celluloseization is as described above.

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

Amount for fiber material of Compound _{E A} is preferably 1 mass% to 100,000% by mass, more preferably at most 2 mass% or more 10000 wt%, more preferably 1000% by mass or more and 5 mass% or less.

The reaction time may vary depending on the reaction temperature, but is preferably 1 minute or more and 1000 minutes or less, more preferably 10 minutes or more and 500 minutes or less, and further preferably 20 minutes or more and 400 minutes or less. After the reaction, excess reaction reagents, by-products, etc. may be washed and removed by filtration or the like.

<Sulfonalkylation>
The step of producing the fine fibrous cellulose may include, for example, a sulfoalkylation step as the step of introducing an ionic substituent. In sulfoalkylated, as essential components, a compound having a reactive group and a sulfonic group (Compound E _B), an alkaline compound as an optional component, described above, the compound selected from urea and its derivatives B, as a reaction aid By adding the compound C of the above compound C to a wet or dry fiber raw material having a hydroxyl group and carrying out a reaction, a sulfone group is introduced into the fiber raw material.

Examples of the reactive group include an alkyl halide group, a vinyl group, an epoxy group (glycidyl group) and the like.

The compound E _B, 2-sodium chloroethane sulfonate, sodium vinyl sulfonate, p- sodium styrenesulfonate, 2-acrylamido-2-methylpropane sulfonic acid. Of these, sodium vinylsulfonate is preferable from the viewpoints of introduction efficiency of substituents, defibration efficiency, cost, and ease of handling.

Further, as an optional component, it is also preferable to use the compound B in the above-mentioned <phosphoric acid group introduction step> in the same manner, and C may be further added. It is preferable that the addition amount is also as described above.

Compound E _B is to reagents may be added directly to the fiber raw materials may be added dissolved in a suitable solvent. It is preferable that the fiber raw material is made alkaline cellulose in advance or is made alkaline cellulose at the same time as the reaction. The method of alkali celluloseization is as described above.

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

Amount for fiber material compound _{E B} is preferably 1 mass% to 100,000% by mass, more preferably at most 2 mass% or more 10000 wt%, more preferably 1000% by mass or more and 5 mass% or less.

The reaction time may vary depending on the reaction temperature, but is preferably 1 minute or more and 1000 minutes or less, more preferably 10 minutes or more and 500 minutes or less, and further preferably 20 minutes or more and 400 minutes or less. Further, after the reaction, excess reaction reagents, by-products and the like may be washed and removed by filtration or the like.

<Carboxyalkylation>
The step of producing the fine fibrous cellulose may include, for example, a carboxyalkylation step as the step of introducing an ionic substituent. As essential components, a compound having a reactive group and a carboxy group (Compound E _C), alkaline compound as an optional component, described above, the compound selected from urea and its derivatives B, wetting or compound C as a reaction aid A carboxy group is introduced into the fiber raw material by carrying out the reaction in addition to the fiber raw material having a hydroxyl group in a dry state.

Examples of the reactive group include an alkyl halide group, a vinyl group, an epoxy group (glycidyl group) and the like.

The compound E _C, introduction efficiency of the substituents, and thus solution繊効rate, cost, ease of handling monochloroacetic acid in terms of sodium monochloroacetate, 2-chloropropionic acid, sodium 2-chloropropionic acid is preferred.

Further, as an optional component, it is also preferable to use the compound B in the above-mentioned <phosphoric acid group introduction step> in the same manner, and C may be further added. It is preferable that the addition amount is also as described above.

Compound E _C is to reagents may be added directly to the fiber raw materials may be added dissolved in a suitable solvent. It is preferable that the fiber raw material is made alkaline cellulose in advance or is made alkaline cellulose at the same time as the reaction. The method of alkali celluloseization is as described above.

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

Amount for fiber material compound _{E C} is preferably 1 mass% to 100,000% by mass, more preferably at most 2 mass% or more 10000 wt%, more preferably 1000% by mass or more and 5 mass% or less.

The reaction time may vary depending on the reaction temperature, but is preferably 1 minute or more and 1000 minutes or less, more preferably 10 minutes or more and 500 minutes or less, and further preferably 20 minutes or more and 400 minutes or less. Further, after the reaction, excess reaction reagents, by-products and the like may be washed and removed by filtration or the like.

<Washing process>
In the method for producing fine fibrous cellulose in the present embodiment, a washing step can be performed on the ionic substituent-introduced fiber, if necessary. The washing step is performed by washing the ionic substituent-introduced fiber with, for example, water or an organic solvent. Further, the cleaning step may be performed after each step described later, and the number of cleaning steps performed in each cleaning step is not particularly limited.

<Alkaline treatment process>
In the case of producing fine fibrous cellulose, the fiber raw material may be treated with an alkali between the step of introducing an ionic substituent and the step of defibration treatment described later. The alkaline treatment method is not particularly limited, and examples thereof include a method of immersing the ionic substituent-introduced fiber in an alkaline 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 its high versatility. Further, the solvent contained in the alkaline solution may be either water or an organic solvent. Among them, the solvent contained in the alkaline solution is preferably a polar solvent containing water, a polar organic solvent exemplified by alcohol, and the like, and more preferably an aqueous solvent containing at least water. As the alkaline solution, for example, an aqueous solution of sodium hydroxide or an aqueous solution of potassium hydroxide is preferable because of its high versatility.

The temperature of the alkaline solution in the alkaline treatment step is not particularly limited, but is preferably 5 ° C. or higher and 80 ° C. or lower, and more preferably 10 ° C. or higher and 60 ° C. or lower. The immersion time of the ionic substituent-introduced fiber in the alkaline solution in the alkaline treatment step is not particularly limited, but is preferably 5 minutes or more and 30 minutes or less, and more preferably 10 minutes or more and 20 minutes or less. The amount of the alkaline solution used in the alkaline treatment is not particularly limited, but is preferably 100% by mass or more and 100,000% by mass or less, and 1000% by mass or more and 10,000% by mass or less, for example, with respect to the absolute dry mass of the ionic substituent-introduced fiber. The following is more preferable. When the fibrous cellulose has an anionic group, the alkaline treatment may be carried out to neutralize the anionic group and / or to perform an ion exchange treatment. In this case, the temperature of the alkaline solution is preferably room temperature.

In order to reduce the amount of the alkaline solution used in the alkaline treatment step, the ionic substituent-introduced fiber may be washed with water or an organic solvent after the ionic substituent introduction step and before the alkaline treatment step. After the alkali treatment step and before the defibration treatment step, it is preferable to wash the alkali-treated ionic substituent-introduced fiber with water or an organic solvent from the viewpoint of improving handleability.

<Acid treatment process>
In the case of producing fine fibrous cellulose, the fiber raw material may be acid-treated between the step of introducing an ionic substituent and the defibration treatment step described later. For example, the ionic substituent introduction step, the acid treatment, the alkali treatment and the defibration treatment may be performed in this order.

The method of the acid treatment is not particularly limited, and examples thereof include a method of immersing the fiber raw material in an acidic liquid containing an acid. The concentration of the acidic liquid used is not particularly limited, but is preferably, for example, 10% by mass or less, and more preferably 5% by mass or less. The pH of the acidic solution used is not particularly limited, but is preferably 0 or more and 4 or less, and more preferably 1 or more and 3 or less. As the acid contained in the acidic solution, for example, an inorganic acid, a sulfonic acid, a carboxylic acid or the like can be used. Examples of the inorganic acid include sulfuric acid, nitric acid, hydrochloric acid, hydrobromic acid, hydroiodic acid, hypochlorous acid, chloric acid, chloric acid, perchloric acid, phosphoric acid, boric acid and the like. Examples of the sulfonic acid include methanesulfonic acid, ethanesulfonic acid, benzenesulfonic acid, p-toluenesulfonic acid, trifluoromethanesulfonic acid and the like. Examples of the carboxylic acid include formic acid, acetic acid, citric acid, gluconic acid, lactic acid, oxalic acid, tartaric acid and the like. Among these, it is particularly preferable to use hydrochloric acid or sulfuric acid.

The temperature of the acid solution in the acid treatment is not particularly limited, but is preferably 5 ° C. or higher and 100 ° C. or lower, and more preferably 20 ° C. or higher and 90 ° C. or lower. The immersion time in the acid solution in the acid treatment is not particularly limited, but is preferably 5 minutes or more and 120 minutes or less, and more preferably 10 minutes or more and 60 minutes or less. The amount of the acid solution used in the acid treatment is not particularly limited, but is preferably 100% by mass or more and 100,000% by mass or less, and 1000% by mass or more and 10,000% by mass or less, for example, with respect to the absolute dry mass of the fiber raw material. Is more preferable. When the fine fibrous cellulose has a cationic group, the acid treatment may be carried out by a neutralization treatment and / or an ion exchange treatment of the cationic group. In this case, the temperature of the acid solution is preferably room temperature.

<Defibration treatment>
Fine fibrous cellulose can be obtained by defibrating the ionic substituent-introduced fiber in the defibration treatment step. In the defibration treatment step, for example, a defibration treatment apparatus can be used. The defibration processing device is not particularly limited, but for example, a high-speed defibrator, a grinder (stone mill type crusher), a high-pressure homogenizer or an ultra-high pressure homogenizer, a high-pressure collision type crusher, a ball mill, a bead mill, a disc type refiner, a conical refiner, and a twin shaft. A kneader, a vibration mill, a homomixer under high speed rotation, an ultrasonic disperser, or a beater can be used. Among the above-mentioned defibration processing devices, it is more preferable to use a high-speed defibrator, a high-pressure homogenizer, and an ultra-high-pressure homogenizer, which are less affected by crushed media and have less risk of contamination.

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

The solid content concentration of the fine fibrous cellulose during the defibration treatment can be appropriately set. Further, the slurry obtained by dispersing the ionic substituent-introduced fiber in a dispersion medium may contain a solid content other than the ionic substituent-introduced fiber such as urea having a hydrogen bond property.

<Arbitrary ingredient>
The fiber layer may contain an arbitrary component other than fine fibrous cellulose. Examples of the optional component include hydrophilic polymers, hydrophilic low molecules, organic ions and the like. Above all, the fiber layer is preferably a layer further containing a hydrophilic polymer.

The hydrophilic polymer is preferably a hydrophilic oxygen-containing organic compound (however, the above-mentioned cellulose fibers are excluded). In this case, the oxygen-containing organic compound is particularly preferably a hydrophilic organic compound. Hydrophilic oxygen-containing organic compounds can improve the strength, density, chemical resistance and the like of the fiber layer. The hydrophilic oxygen-containing organic compound preferably has, for example, an SP value of 9.0 or more. Further, the hydrophilic oxygen-containing organic compound is preferably one in which 1 g or more of the oxygen-containing organic compound is dissolved in 100 ml of ion-exchanged water, for example.

Examples of the hydrophilic polymer include polyethylene glycol, polyethylene oxide, casein, dextrin, starch, modified starch, polyvinyl alcohol, modified polyvinyl alcohol (acetoacetylated polyvinyl alcohol, etc.), polyethylene oxide, polyvinylpyrrolidone, polyvinylmethyl ether, and poly. Examples thereof include acrylates, polyacrylamide, acrylic acid alkyl ester copolymers, urethane-based copolymers, cellulose derivatives (hydroxyethyl cellulose, carboxyethyl cellulose, carboxymethyl cellulose, etc.). Above all, from the viewpoint of improving the strength, density, chemical resistance and the like of the fiber layer, the hydrophilic polymer is preferably at least one selected from the group consisting of polyethylene glycol, polyethylene oxide and polyvinyl alcohol, and polyvinyl is preferable. Alcohol is particularly preferred.

When polyvinyl alcohol is blended in the fiber layer, the saponification degree of polyvinyl alcohol is preferably 99.9% or less, more preferably 99% or less, still more preferably 95% or less. The saponification degree of polyvinyl alcohol is preferably 85% or more. By containing polyvinyl alcohol having a saponification degree within the above range in the fiber layer, the transparency of the fiber layer can be more effectively enhanced, and as a result, a sheet having higher transparency can be obtained.

The weight average molecular weight of the hydrophilic polymer may be 10,000 or more, preferably 50,000 or more, and more preferably 100,000 or more. The weight average molecular weight of the hydrophilic polymer is preferably 8 million or less, more preferably 5 million or less.

The content of the hydrophilic polymer is preferably 5% by mass or more, more preferably 10% by mass, still more preferably 15% by mass or more, more preferably 20% by mass, based on the total mass of the fiber layer. It is particularly preferable that it is by mass or more. The content of the hydrophilic polymer is preferably 95% by mass or less, more preferably 90% by mass or less, and further preferably 80% by mass or less, based on the total mass of the fiber layer. preferable. By setting the content of the hydrophilic polymer within the above range, a high-strength and highly transparent sheet can be formed.

Examples of the hydrophilic low molecule include glycerin, sorbitol, ethylene glycol and the like. Moreover, as an organic ion, a tetraalkylammonium ion and a tetraalkylphosphonium ion can be mentioned. Examples of the tetraalkylammonium ion include tetramethylammonium ion, tetraethylammonium ion, tetrapropylammonium ion, tetrabutylammonium ion, tetrapentylammonium ion, tetrahexylammonium ion, tetraheptylammonium ion, tributylmethylammonium ion and lauryltrimethyl. Examples thereof include ammonium ion, cetyltrimethylammonium ion, stearyltrimethylammonium ion, octyldimethylethylammonium ion, lauryldimethylethylammonium ion, didecyldimethylammonium ion, lauryldimethylbenzylammonium ion and tributylbenzylammonium ion. Examples of the tetraalkylphosphonium ion include tetramethylphosphonium ion, tetraethylphosphonium ion, tetrapropylphosphonium ion, tetrabutylphosphonium ion, and lauryltrimethylphosphonium ion. Further, examples of the tetrapropyl onium ion and the tetrabutyl onium ion include tetra n-propyl onium ion and tetra n-butyl onium ion, respectively.

<Surface treatment>
The surface of the fiber layer on the resin layer side may be surface-treated. Examples of the surface treatment method include corona treatment, plasma discharge treatment, UV irradiation treatment, electron beam irradiation treatment, flame treatment and the like. Above all, the surface treatment is preferably at least one selected from the corona treatment and the plasma discharge treatment. The plasma discharge process is preferably a vacuum plasma discharge process.

(Sheet manufacturing method)
The method for producing a sheet includes a step of forming a resin layer on both sides of a fiber layer containing fibrous cellulose having a fiber width of 1000 nm or less. The surface roughness (Ra) on both sides of the sheet thus produced is 12.0 nm or less.

The step of forming the resin layer on both sides of the fiber layer may be a step of laminating a resin film or a resin sheet on both sides of the fiber layer, but a resin coating liquid is applied to both sides of the fiber layer to make a resin. It is preferably a step of forming a layer. Here, the resin coating liquid preferably contains a solvent, and the resin layer formed on both sides of the fiber layer is preferably a solvent coating layer.

The viscosity of the resin coating liquid containing the solvent is preferably 100 cps or less, more preferably 80 cps or less, and further preferably 60 cps or less. Here, the viscosity of the resin coating liquid is a value measured by a B-type viscometer. The measurement conditions are a rotation speed of 60 rpm, and the viscosity value 1 minute after the start of measurement is the viscosity of the resin coating liquid. As the B-type viscometer, for example, an analog viscometer T-LVT manufactured by BLOOKFIELD Co., Ltd. can be used. By setting the viscosity of the resin coating liquid within the above range, it becomes easy to control the surface roughness of the sheet within a predetermined range, and as a result, the transparency of the sheet can be more effectively improved.

The solid content in the resin coating liquid is preferably 12% by mass or less, more preferably 10% by mass or less, and further preferably 8% by mass or less. Here, the solid content content in the resin coating liquid is mainly the content of the resin component contained in the resin coating liquid, but any component such as an adhesion aid as described later in the resin coating liquid. If is included, the content will be the content including any components.

The resin coating liquid may contain an optional component such as an adhesion aid, if necessary. As the adhesion aid, the above-mentioned adhesion aid can be preferably exemplified.

The step of applying the resin coating liquid to both sides of the fiber layer to form the resin layer can be carried out by using a known coating device. Examples of the coating device include a blade coater, an air knife coater, a roll coater, a bar coater, a gravure coater, a micro gravure coater, a rod blade coater, a lip coater, a die coater, a curtain coater and the like. At this time, it is preferable to apply the resin coating liquid so that the resin layers having a thickness of 10 μm or less are formed on both surfaces of the fiber layer.

The sheet manufacturing method preferably includes a step of forming a fiber layer containing fibrous cellulose having a fiber width of 1000 nm or less as a pre-step of a step of forming a resin layer on both sides of the fiber layer. Here, the step of forming the fiber layer is a step of obtaining a fibrous cellulose-containing composition having a fiber width of 1000 nm or less (hereinafter, also referred to as a slurry or a coating liquid) and a step of obtaining the fibrous cellulose-containing composition on a substrate. Includes a coating step of coating the fiber or a papermaking step of making the fibrous cellulose-containing composition. As a result, the above-mentioned fiber layer can be obtained. The fibrous cellulose-containing composition is preferably a composition containing a hydrophilic polymer as described above.

<Coating process>
In the coating step, for example, a fibrous cellulose-containing composition (slurry) containing fibrous cellulose is applied onto a base material, and the fiber sheet formed by drying the coating is peeled off from the base material to form a fiber layer. Obtainable. Further, by using the coating device and the long base material, the fiber sheet to be the fiber layer can be continuously produced.

The material of the base material used in the coating process is not particularly limited, but a material having high wettability to the fibrous cellulose-containing composition (slurry) may suppress shrinkage of the fiber sheet during drying. It is preferable to select a fiber sheet that can be easily peeled off after drying. Of these, a resin film or plate or a metal film or plate is preferable, but is not particularly limited. For example, resin films and plates such as polypropylene, acrylic, polyethylene terephthalate, vinyl chloride, polystyrene, polycarbonate, and polyvinylidene chloride, metal films and plates of aluminum, zinc, copper, and iron plates, and their surfaces are oxidized. , Stainless film or plate, brass film or plate, etc. can be used.

In the coating process, when the viscosity of the slurry is low and it develops on the base material, a dammed frame is fixed on the base material to obtain a fiber sheet with a predetermined thickness and basis weight. You may. The frame for damming is not particularly limited, but it is preferable to select, for example, a frame in which the end portion of the fiber sheet adhering after drying can be easily peeled off. From this point of view, a resin plate or a metal plate molded is more preferable. In the present embodiment, for example, a resin plate such as a polypropylene plate, an acrylic plate, a polyethylene terephthalate plate, a vinyl chloride plate, a polystyrene plate, a polycarbonate plate, a polyvinylidene chloride plate, or a metal plate such as an aluminum plate, a zinc plate, a copper plate, or an iron plate. , And those whose surfaces are oxidized, stainless steel plates, brass plates and the like can be used.
The coating machine for coating the slurry on the substrate is not particularly limited, and for example, a roll coater, a gravure coater, a die coater, a curtain coater, an air doctor coater, or the like can be used. A die coater, a curtain coater, and a spray coater are particularly preferable because the thickness of the fiber sheet can be made more uniform.

The slurry temperature and the atmospheric temperature when the slurry is applied to the substrate are not particularly limited, but are preferably, for example, 5 ° C. or higher and 80 ° C. or lower, more preferably 10 ° C. or higher and 60 ° C. or lower, and 15 ° C. It is more preferably 50 ° C. or higher, and particularly preferably 20 ° C. or higher and 40 ° C. or lower. When the coating temperature is equal to or higher than the above lower limit, the slurry can be coated more easily. When the coating temperature is not more than the above upper limit, the volatilization of the dispersion medium during coating can be suppressed.

In the coating process, the slurry is prepared so that the finished basis weight of the fiber sheet is preferably 10 g / m ² or more and 100 g / m ² or less, and more preferably 20 g / m ² or more and 60 g / m ² or less. It is preferable to apply it to the base material. By coating so that the basis weight is within the above range, a fiber sheet having higher strength can be obtained.

As described above, the coating step includes a step of drying the slurry coated on the substrate. The step of drying the slurry is not particularly limited, but is performed by, for example, a non-contact drying method, a method of drying while restraining the fiber sheet, or a combination thereof.

The non-contact drying method is not particularly limited, and for example, a method of heating and drying with hot air, infrared rays, far infrared rays or near infrared rays (heat drying method) or a method of vacuum drying (vacuum drying method) is applied. can do. Although the heat drying method and the vacuum drying method may be combined, the heat drying method is usually applied. Drying with infrared rays, far infrared rays or near infrared rays is not particularly limited, but can be performed by using, for example, an infrared device, a far infrared device or a near infrared device.

The heating temperature in the heat-drying method is not particularly limited, but is preferably 20 ° C. or higher and 150 ° C. or lower, and more preferably 25 ° C. or higher and 105 ° C. or lower. When the heating temperature is equal to or higher than the above lower limit, the dispersion medium can be rapidly volatilized. Further, when the heating temperature is not more than the above upper limit value, it is possible to suppress the cost required for heating and suppress the discoloration of the fibrous cellulose due to heat.

<Papermaking process>
The papermaking process is performed by making a slurry with a paper machine. The paper machine used in the paper making process is not particularly limited, and examples thereof include continuous paper machines such as a long net type, a circular net type, and an inclined type, and a multi-layer paper making machine combining these. In the papermaking process, a known papermaking method such as hand-making may be adopted.

The papermaking process is performed by filtering and dehydrating the slurry with a wire to obtain a fiber sheet in a wet paper state, and then pressing and drying the fiber sheet. The filter cloth used for filtering and dehydrating the slurry is not particularly limited, but it is more preferable that, for example, fibrous cellulose does not pass through and the filtration rate does not become too slow. The filter cloth is not particularly limited, but for example, a fiber sheet made of an organic polymer, a woven fabric, or a porous membrane is preferable. The organic polymer is not particularly limited, but non-cellulosic organic polymers such as polyethylene terephthalate, polyethylene, polypropylene, and polytetrafluoroethylene (PTFE) are preferable. In the present embodiment, for example, a porous membrane of polytetrafluoroethylene having a pore size of 0.1 μm or more and 20 μm or less, polyethylene terephthalate having a pore size of 0.1 μm or more and 20 μm or less, a polyethylene woven fabric, or the like can be mentioned.

The method for producing a fiber sheet from a slurry is, for example, a watering section in which a slurry containing fibrous cellulose is discharged onto the upper surface of an endless belt and a dispersion medium is squeezed from the discharged slurry to generate a web, and the web is dried. It can be carried out using a manufacturing apparatus including a drying section for producing a fiber sheet. An endless belt is disposed from the watering section to the drying section, and the web generated in the watering section is conveyed to the drying section while being placed on the endless belt.

The dehydration method used in the papermaking process is not particularly limited, and examples thereof include a dehydration method normally used in the production of paper. Among these, a method of dehydrating with a long net, a circular net, an inclined wire, or the like and then further dehydrating with a roll press is preferable. The drying method used in the papermaking process is not particularly limited, and examples thereof include methods used in the production of paper. Among these, a drying method using a cylinder dryer, a Yankee dryer, hot air drying, a near infrared heater, an infrared heater, or the like is more preferable.

(Use)
The sheet of the present invention has high transparency and excellent optical properties. From the viewpoint of utilizing the excellent optical characteristics, the sheet of the present invention is preferably used for an optical member. More specifically, the sheet of the present invention is suitable for applications of light transmissive substrates such as various display devices and various solar cells. Further, the sheet of the present invention is also suitable for applications such as substrates of electronic devices, members of home appliances, window materials of various vehicles and buildings, interior materials, exterior materials, packaging materials and the like.

(Laminated body)
The present invention may relate to a laminate in which another layer is laminated on the above-mentioned sheet. For example, in the structure of the resin layer / fiber layer / resin layer of the sheet, another layer may be laminated on the surface side of the resin layer where the fiber layer is not in contact to form a laminated body. Examples of the other layer include a cycloolefin polymer film and a polyimide film.

Hereinafter, the features of the present invention will be described in more detail with reference to Examples and Comparative Examples. The materials, amounts used, ratios, treatment contents, treatment procedures, etc. shown in the following examples can be appropriately changed as long as they do not deviate from the gist of the present invention. Therefore, the scope of the present invention should not be construed as limiting by the specific examples shown below.

<Manufacturing example 1>
(Manufacturing of phosphorylated pulp)
As the raw material pulp, Oji Paper's softwood kraft pulp (solid content 93% by mass, basis weight 208 g / m ² sheets, separated and measured according to JIS P 8121: 2012) has a Canadian standard drainage degree (CSF). 700 mL) was used. The raw material pulp was subjected to phosphorus oxo oxidation treatment as follows. First, a mixed aqueous solution of ammonium dihydrogen phosphate and urea is added to 100 parts by mass (absolute dry mass) of the raw material pulp to obtain 45 parts by mass of ammonium dihydrogen phosphate, 120 parts by mass of urea, and 150 parts by mass of water. To obtain a drug-impregnated pulp. Next, the obtained chemical-impregnated pulp was heated in a hot air dryer at 165 ° C. for 200 seconds to introduce a phosphate group into the cellulose in the pulp to obtain a phosphorylated pulp.

Then, the obtained phosphorylated pulp was washed. The cleaning treatment is carried out by repeating the operation of pouring 10 L of ion-exchanged water into 100 g (absolute dry mass) of phosphorylated pulp, stirring the pulp dispersion liquid so that the pulp is uniformly dispersed, and then filtering and dehydrating the pulp. gone. When the electrical conductivity of the filtrate became 100 μS / cm or less, the washing end point was set.

Next, the phosphorylated pulp after washing was subjected to alkali treatment (neutralization treatment) as follows. First, the washed phosphorylated pulp was diluted with 10 L of ion-exchanged water, and then a 1N aqueous sodium hydroxide solution was added little by little with stirring to obtain a phosphorylated pulp slurry having a pH of 12 or more and 13 or less. .. Next, the phosphorylated pulp slurry was dehydrated to obtain phosphorylated pulp subjected to alkali treatment (neutralization treatment).

Next, the phosphorylated pulp after the neutralization treatment was subjected to the above washing treatment. The infrared absorption spectrum of the phosphorylated pulp thus obtained was measured using FT-IR. As a result, absorption ^{of the phosphate group based on P = O was observed near 1230 cm-1} , and it was confirmed that the phosphate group was added to the pulp. Further, when the obtained phosphorylated pulp was tested and analyzed by an X-ray diffractometer, it was found at two positions, 2θ = 14 ° or more and 17 ° or less and 2θ = 22 ° or more and 23 ° or less. A typical peak was confirmed, and it was confirmed that it had cellulose type I crystals.

(Defibration treatment)
Ion-exchanged water was added to the obtained phosphorylated pulp to prepare a slurry having a solid content concentration of 2% by mass. This slurry was treated four times with a wet atomizing device (manufactured by Sugino Machine Limited, Starburst) at a pressure of 200 MPa to obtain a fine fibrous cellulose dispersion (A) containing fine fibrous cellulose.

By X-ray diffraction, it was confirmed that this fine fibrous cellulose maintained the cellulose type I crystal. Moreover, when the fiber width of the fine fibrous cellulose was measured using a transmission electron microscope, it was 3 to 5 nm. The amount of phosphate group (first dissociated acid amount) measured by the method for measuring the amount of phosphoroxo acid group described later was 1.45 mmol / g. The total amount of dissociated acid was 2.45 mmol / g.

<Manufacturing example 2>
(Manufacturing of subphosphorylated pulp)
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 phosphorous oxide pulp.

The infrared absorption spectrum of the subphosphorylated pulp thus obtained was measured using FT-IR. As a result, ^{absorption based on P = O of the phosphonic acid group, which is a metamorphic form of the phosphorous acid group, was observed near 1210 cm-1} , and the phosphorous acid group (phosphonic acid group) was added to the pulp. Was confirmed. Further, when the obtained subphosphorylated pulp was tested and analyzed by an X-ray diffractometer, two positions were found, 2θ = 14 ° or more and 17 ° or less and 2θ = 22 ° or more and 23 ° or less. A typical peak was confirmed in, and it was confirmed that it had cellulose type I crystals.

(Defibration treatment)
Ion-exchanged water was added to the obtained subphosphorylated pulp to prepare a slurry having a solid content concentration of 2% by mass. This slurry was treated four times with a wet atomizing device (manufactured by Sugino Machine Limited, Starburst) at a pressure of 200 MPa to obtain a fine fibrous cellulose dispersion (B) containing fine fibrous cellulose. By X-ray diffraction, it was confirmed that this fine fibrous cellulose maintained the cellulose type I crystal. Moreover, when the fiber width of the fine fibrous cellulose was measured using a transmission electron microscope, it was 3 to 5 nm. The amount of phosphorous acid group (first dissociated acid amount) measured by the method for measuring the amount of phosphorous acid group described later was 1.51 mmol / g. The total amount of dissociated acid was 1.54 mmol / g.

<Manufacturing example 3>
(Manufacturing of TEMPO oxide pulp)
As the raw material pulp, softwood kraft pulp (undried) manufactured by Oji Paper Co., Ltd. was used. The raw material pulp was subjected to alkaline TEMPO oxidation treatment as follows. First, the above-mentioned raw material pulp equivalent to 100 parts by mass of dry mass, 1.6 parts by mass of TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl), and 10 parts by mass of sodium bromide are added to 10,000 parts by mass of water. It was dispersed in the department. Then, a 13 mass% sodium hypochlorite aqueous solution was added to 1.0 g of pulp so as to be 3.8 mmol, and the reaction was started. During the reaction, a 0.5 M aqueous sodium hydroxide solution was added dropwise to keep the pH at 10 or more and 10.5 or less, and the reaction was considered to be completed when no change was observed in the pH.

Then, the obtained TEMPO oxide pulp was washed. The washing treatment is carried out by dehydrating the pulp slurry after TEMPO oxidation to obtain a dehydrated sheet, pouring 5000 parts by mass of ion-exchanged water, stirring and uniformly dispersing the pulp slurry, and then repeating the operation of filtering and dehydrating. rice field. When the electrical conductivity of the filtrate became 100 μS / cm or less, the washing end point was set.

With respect to the TEMPO oxide pulp thus obtained, the amount of carboxy group measured by the measuring method described later was 1.30 mmol / g. Further, when the obtained TEMPO oxide pulp was tested and analyzed by an X-ray diffractometer, it was found at two positions, 2θ = 14 ° or more and 17 ° or less and 2θ = 22 ° or more and 23 ° or less. A typical peak was confirmed, and it was confirmed that it had cellulose type I crystals.

(Defibration treatment)
Ion-exchanged water was added to the obtained TEMPO oxide pulp to prepare a slurry having a solid content concentration of 2% by mass. This slurry was treated four times with a wet atomizing device (manufactured by Sugino Machine Limited, Starburst) at a pressure of 200 MPa to obtain a fine fibrous cellulose dispersion (C) containing fine fibrous cellulose. By X-ray diffraction, it was confirmed that this fine fibrous cellulose maintained the cellulose type I crystal. Moreover, when the fiber width of the fine fibrous cellulose was measured using a transmission electron microscope, it was 3 to 5 nm. The amount of carboxy group measured by the method for measuring the amount of carboxy group described later was 1.30 mmol / g.

<Manufacturing example 4>
(Manufacturing of sulfated pulp)
The same procedure as in Production Example 1 was carried out except that 38 parts by mass of amide sulfuric acid was used instead of ammonium dihydrogen phosphate to obtain sulfated pulp. However, the heating time in the hot air dryer was set to 20 minutes.

The infrared absorption spectrum of the sulfated pulp thus obtained was measured using FT-IR. As a result, ^{absorption based on the sulfate group was observed near 1220-1260 cm-1} , and it was confirmed that the sulfate group was added to the pulp.

(Defibration treatment)
Ion-exchanged water was added to the obtained sulfated pulp and then stirred to make a 2% by mass slurry. This slurry was treated four times with a wet atomizing device (manufactured by Sugino Machine Limited, Starburst) at a pressure of 200 MPa to obtain a fine fibrous cellulose dispersion (D) containing fine fibrous cellulose. By X-ray diffraction, it was confirmed that this fine fibrous cellulose maintained the cellulose type I crystal. 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 sulfuric acid group measured by the method for measuring the amount of sulfur oxoacid group described later was 1.47 mmol / g.

<Measurement>
(Measurement of phosphorus oxo acid group amount)
The amount of phosphoric acid group in the fine fibrous cellulose (equal to the amount of the phosphoric acid group in the phosphoric oxide pulp) is adjusted by adding ion-exchanged water to the fine fibrous cellulose dispersion containing the target fine fibrous cellulose. The content was 0.2% by mass, and the measurement was performed by treatment with an ion exchange resin and then titration with an alkali.
For the treatment with the ion exchange resin, a strongly acidic ion exchange resin (Amberjet 1024; manufactured by Organo Corporation, conditioned) with a volume of 1/10 is added to the fine fibrous cellulose-containing slurry and shaken for 1 hour. After that, it was poured onto a mesh having an opening of 90 μm to separate the resin and the slurry.
In the titration using an alkali, the pH value indicated by the slurry is changed by adding 10 μL of a 0.1 N sodium hydroxide aqueous solution to the fine fibrous cellulose-containing slurry treated with an ion exchange resin every 5 seconds. It was done by measuring. Titration was performed while blowing nitrogen gas into the slurry from 15 minutes before the start of titration. In this neutralization titration, two points are observed where the increment (differential value of pH with respect to the amount of alkaline drop) becomes maximum in the curve plotting the measured pH with respect to the amount of alkali added. Of these, the maximum point of the increment obtained first when alkali is added is called the first end point, and the maximum point of the increment obtained next is called the second end point (FIG. 2). The amount of alkali required from the start of titration to the first end point is equal to the amount of first dissociated acid in the slurry used for titration. Further, the amount of alkali required from the start of titration to the second end point becomes equal to the total amount of dissociated acid in the slurry used for titration. The amount of alkali (mmol) required from the start of titration to the first end point divided by the solid content (g) in the slurry to be titrated is the amount of phosphorus oxo acid groups (first dissociated acid amount) (mmol / g). ). Further, the value obtained by dividing the amount of alkali (mmol) required from the start of titration to the second end point by the solid content (g) in the slurry to be titrated was taken as the total amount of dissociated acid (mmol / g).

(Measurement of carboxy group amount)
The carboxy group amount of the fine fibrous cellulose (equal to the carboxy group amount of the TEMPO oxide pulp) is set to 0 by adding ion-exchanged water to the fine fibrous cellulose dispersion containing the target fine fibrous cellulose. The measurement was made at 2% by mass, treated with an ion exchange resin, and then titrated with an alkali.
The treatment with an ion exchange resin is performed by adding a strongly acidic ion exchange resin (Amberjet 1024; manufactured by Organo Corporation, conditioned) with a volume of 1/10 to a slurry containing 0.2% by mass of fine fibrous cellulose for 1 hour. After the shaking treatment, the resin and the slurry were separated by pouring onto a mesh having an opening of 90 μm.
In addition, titration using alkali was performed by measuring the change in the pH value indicated by the slurry while adding 0.1 N sodium hydroxide aqueous solution to the fibrous cellulose-containing slurry treated with the ion exchange resin. .. By observing the change in pH while adding the aqueous sodium hydroxide solution, a titration curve as shown in FIG. 3 is obtained. As shown in FIG. 3, in this neutralization titration, there is one point in which the increment (differential value of pH with respect to the amount of alkaline drop) becomes maximum in the curve plotting the measured pH with respect to the amount of alkali added. Observed. The maximum point of this increment is called the first end point. Here, the region from the start of titration to the first end point in FIG. 3 is referred to as a first region. The amount of alkali required in the first region is equal to the amount of carboxy groups in the slurry used for titration. Then, the amount of alkali (mmol) required in the first region of the titration curve is divided by the solid content (g) in the fine fibrous cellulose-containing slurry to be titrated, so that the amount of carboxy group introduced (mmol / g). ) Was calculated.
The above-mentioned amount of carboxy group introduced (mmol / g) is the amount of substituents per 1 g of mass of fibrous cellulose when the ^{counterion of the carboxy group is hydrogen ion (H +) (hereinafter, the amount of carboxy group (acid).} Type)) is shown.

(Measurement of sulfur oxoacid group amount)
The obtained fibrous cellulose was wet-ashed with perchloric acid and concentrated nitric acid, diluted at an appropriate magnification, and the amount of sulfur was measured by ICP emission analysis. The value obtained by dividing this amount of sulfur by the absolute dry mass of the fibrous cellulose tested was taken as the amount of sulfate groups (unit: mmol / g).

<Example 1>
(Dissolution of polyvinyl alcohol)
Acetacetyl group-modified polyvinyl alcohol (Gosenex ^TM Z-200, manufactured by Mitsubishi Chemical Corporation) was added to ion-exchanged water in an amount of 12% by mass, and the mixture was stirred at 95 ° C. for 1 hour to dissolve. By the above procedure, an aqueous polyvinyl alcohol solution (A) was obtained.

(Formation of fiber layer)
The fine fibrous cellulose dispersion (A) and the polyvinyl alcohol aqueous solution (A) were each diluted with ion-exchanged water so that the solid content concentration was 0.6% by mass. Then, the diluted polyvinyl alcohol aqueous solution was mixed with 70 parts by mass of the diluted fine fibrous cellulose dispersion so as to be 30 parts by mass to obtain a mixed solution. Further, the mixed solution was weighed so that the finished basis weight of the fiber sheet was 35 g / m ² , and developed on a commercially available acrylic plate. A dammed frame (inner dimensions 250 mm × 250 mm, height 5 cm) was placed on the acrylic plate so as to have a predetermined basis weight. Then, it was dried in a dryer at 70 ° C. for 24 hours and peeled off from the acrylic plate to form a fiber layer (fine fibrous cellulose-containing layer). The thickness of the fiber layer was 25 μm.

(Formation of resin layer)
A modified polycarbonate resin (manufactured by Mitsubishi Gas Chemical Company, Limited, Iupizeta FPC-2136) was mixed with 8.5 parts by mass, 60 parts by mass of toluene, and 30 parts by mass of methyl ethyl ketone to obtain a resin coating liquid. Next, 1.5 parts by mass of an isocyanate compound (Duranate TPA-100, manufactured by Asahi Kasei Chemicals Co., Ltd.) was added to the above resin coating liquid as an adhesion aid and mixed. The viscosity of the resin coating liquid measured by the measuring method described later was 30 cps. This resin coating liquid was applied to one surface of the fiber layer (the surface in contact with the acrylic plate) with a bar coater. Then, the resin coating liquid was cured by heating at 100 ° C. for 1 hour to form a resin layer (first resin layer). Next, a resin layer (second resin layer) was formed on the opposite surface of the fiber layer by the same procedure. The thickness of the resin layer was 3 μm per side. By the above procedure, a laminated sheet in which a resin layer was laminated on both sides of a fiber layer (a layer containing fine fibrous cellulose) was obtained.

<Example 2>
In Example 1 (formation of fiber layer), the mixing amount of the diluted fine fibrous cellulose dispersion (A) was changed to 40 parts by mass, and the mixing amount of the diluted polyvinyl alcohol aqueous solution was changed to 60 parts by mass. In the same manner as in Example 1, a laminated sheet was obtained.

<Example 3>
In Example 1 (formation of fiber layer), the finished basis weight of the fiber sheet ^{was changed to 70 g / m 2} , and the same procedure as in Example 1 was obtained except that a fiber layer having a thickness of 50 μm was obtained to obtain a laminated sheet. ..

<Example 4>
In Example 2 (formation of fiber layer), the finished basis weight of the fiber sheet ^{was changed to 70 g / m 2} , and a laminated sheet was obtained in the same manner as in Example 2 except that a fiber layer having a thickness of 50 μm was obtained. ..

<Example 5>
In Example 1 (formation of fiber layer), the finished basis weight of the fiber sheet ^{was changed to 140 g / m 2} , and a laminated sheet was obtained in the same manner as in Example 1 except that a fiber layer having a thickness of 100 μm was obtained. ..

<Example 6>
In Example 2 (formation of fiber layer), the finished basis weight of the fiber sheet ^{was changed to 140 g / m 2} , and a laminated sheet was obtained in the same manner as in Example 2 except that a fiber layer having a thickness of 100 μm was obtained. ..

<Example 7>
In Example 6 (formation of fiber layer), the mixing amount of the diluted fine fibrous cellulose dispersion (A) was set to 20 parts by mass, and the mixing amount of the diluted polyvinyl alcohol aqueous solution was changed to 80 parts by mass. In the same manner as in Example 6, a laminated sheet was obtained.

<Example 8>
In Example 7 (formation of fiber layer), the mixing amount of the diluted fine fibrous cellulose dispersion (A) was changed to 10 parts by mass, and the mixing amount of the diluted polyvinyl alcohol aqueous solution was changed to 90 parts by mass. In the same manner as in Example 7, a laminated sheet was obtained.

<Example 9>
In Example 4 (formation of the fiber layer), a laminated sheet was obtained in the same manner as in Example 4 except that the fine fibrous cellulose dispersion liquid (B) was used.

<Example 10>
In Example 4 (formation of the fiber layer), a laminated sheet was obtained in the same manner as in Example 4 except that the fine fibrous cellulose dispersion liquid (C) was used.

<Example 11>
In Example 4 (formation of the resin layer), a laminated sheet was obtained in the same manner as in Example 4 except that the thickness of each resin layer was changed to 1 μm.

<Example 12>
In Example 4 (formation of the resin layer), a laminated sheet was obtained in the same manner as in Example 4 except that the thickness of each resin layer was changed to 4.5 μm.

<Example 13>
In Example 1 (dissolution of polyvinyl alcohol), a polyvinyl alcohol aqueous solution (B) in which a modified polyvinyl alcohol having a hydrophilic ethylene oxide group (Gosenex ^{TM WO-320N manufactured by Mitsubishi Chemical Corporation) was dissolved was used.} Other procedures were the same as in Example 4 to obtain a laminated sheet.

<Example 14>
In Example 1 (dissolution of polyvinyl alcohol), a polyvinyl alcohol aqueous solution (C) in which polyvinyl alcohol having a degree of polymerization of 500 (manufactured by Kuraray Co., Ltd., Poval 105, saponification degree: 98 to 99 mol%) was dissolved was used. Other procedures were the same as in Example 4 to obtain a laminated sheet.

<Example 15>
In Example 1 (dissolution of polyvinyl alcohol), an aqueous polyvinyl alcohol solution (D) in which polyvinyl alcohol having a degree of polymerization of 1,700 (manufactured by Kuraray Co., Ltd., Poval 117, degree of saponification: 98 to 99 mol%) was dissolved was used. .. Other procedures were the same as in Example 4 to obtain a laminated sheet.

<Example 16>
In Example 1 (dissolution of polyvinyl alcohol), polyvinyl alcohol having a degree of polymerization of 1,700 (manufactured by Kuraray Co., Ltd., Poval 217, degree of polymerization: 1,700, degree of saponification: 87 to 89 mol%) was dissolved. An aqueous solution (E) was used. Other procedures were the same as in Example 4 to obtain a laminated sheet.

<Example 17>
In Example 3 (formation of resin layer), 100 parts by mass of an acrylic resin (Acryt 8KX-012C manufactured by Taisei Fine Chemical Co., Ltd., manufactured by Asahi Kasei Chemicals Co., Ltd.) in which an acryloyl group having a hydroxyl group was graft-polymerized, and a polyisocyanate compound (TPA manufactured by Asahi Kasei Chemicals Co., Ltd.). −100) 38 parts by mass and 100 parts by mass of methyl ethyl ketone were mixed to obtain a resin coating liquid. The viscosity of the resin coating liquid measured by the measuring method described later was 50 cps. Other procedures were the same as in Example 3 to obtain a laminated sheet.

<Example 18>
In Example 4 (formation of resin layer), 100 parts by mass of urethane acrylic resin (Acryt 8UA-347A manufactured by Taisei Fine Chemical Co., Ltd.) having a urethane unit / acrylic unit mass ratio of 2/8, a polyisocyanate compound (Asahi Kasei). 9.7 parts by mass of Duranate TPA-100) manufactured by Chemicals Co., Ltd. was mixed to obtain a resin coating liquid. The viscosity of the resin coating liquid measured by the measuring method described later was 36 cps. Other procedures were the same as in Example 4 to obtain a laminated sheet.

<Example 19>
In Example 4 (formation of the resin layer), a laminated sheet was obtained in the same manner as in Example 4 except that a polyester resin coating liquid (manufactured by Unitika Ltd., Elitel UE-3320) was used. The viscosity of the resin coating liquid measured by the measuring method described later was 40 cps.

<Example 20>
In Example 4 (formation of the resin layer), a laminated sheet was obtained in the same manner as in Example 4 except that a fluororesin coating liquid (manufactured by Asahi Glass Co., Ltd., Cytop) was used. The viscosity of the resin coating liquid measured by the measuring method described later was 43 cps.

<Example 21>
A laminated sheet was obtained in the same manner as in Example 4 except that (dissolution of polyvinyl alcohol) and (formation of resin layer) were changed as follows.

(Dissolution of polyvinyl alcohol)
Acetacetyl group-modified polyvinyl alcohol (Gosenex ^TM Z-300, manufactured by Mitsubishi Chemical Corporation) was added to ion-exchanged water in an amount of 12% by mass, and the mixture was stirred at 95 ° C. for 1 hour to dissolve. By the above procedure, an aqueous polyvinyl alcohol solution (F) was obtained.

(Formation of resin layer)
Modified polycarbonate resin adjusted to have a refractive index of 1.52 by incorporating a low refractive index monomer into the polymerization (adjusted based on Iupizeta FPC-2136 manufactured by Mitsubishi Gas Chemicals Co., Ltd.) 8.5 parts by mass, toluene 60 A resin coating liquid was obtained by mixing 30 parts by mass and 30 parts by mass of methyl ethyl ketone. Next, 1.5 parts by mass of an isocyanate compound (Duranate TPA-100, manufactured by Asahi Kasei Chemicals Co., Ltd.) was added to the above resin coating liquid as an adhesion aid and mixed. The viscosity of the resin coating liquid measured by the measuring method described later was 32 cps. This resin coating liquid was applied to one surface of the fiber layer (the surface in contact with the acrylic plate) with a bar coater. Then, the resin coating liquid was cured by heating at 100 ° C. for 1 hour to form a resin layer (first resin layer). Next, a resin layer (second resin layer) was formed on the opposite surface of the fiber layer by the same procedure. The thickness of the resin layer was 3 μm per side.

<Example 22>
In Example 21 (formation of a resin layer), a modified polycarbonate resin (manufactured by Mitsubishi Gas Chemical Company, Inc., Iupizeta FPC-2136) prepared by incorporating a low refractive index monomer into the polymerization and adjusting the refractive index to 1.53 is used. A laminated sheet was obtained in the same manner as in Example 21 except that (adjusted to the base) was used. The viscosity of the resin coating liquid measured by the measuring method described later was 34 cps.

<Example 23>
In Example 21 (formation of a resin layer), a modified polycarbonate resin (manufactured by Mitsubishi Gas Chemical Company, Inc., Iupizeta FPC-2136) prepared by incorporating a low refractive index monomer into the polymerization and adjusting the refractive index to 1.55 is used. A laminated sheet was obtained in the same manner as in Example 21 except that (adjusted to the base) was used. The viscosity of the resin coating liquid measured by the measuring method described later was 32 cps.

<Example 24>
In Example 21 (Formation of Resin Layer), an acrylic polymer resin coating liquid (manufactured by Aika Kogyo Co., Ltd., Aika Aitron) prepared by incorporating a low refractive index monomer into the polymerization and adjusting the refractive index to 1.49. A laminated sheet was obtained in the same manner as in Example 21 except that (adjusted based on Z-815-4L) was used. The viscosity of the resin coating liquid measured by the measuring method described later was 37 cps.

<Example 25>
In Example 21 (Formation of Resin Layer), an acrylic polymer resin coating liquid (manufactured by Aika Kogyo Co., Ltd., Aika Aitron) prepared by incorporating a low refractive index monomer into the polymerization and adjusting the refractive index to 1.51. A laminated sheet was obtained in the same manner as in Example 21 except that (adjusted based on Z-815-4L) was used. The viscosity of the resin coating liquid measured by the measuring method described later was 35 cps.

<Example 26>
In Example 21 (Formation of Resin Layer), an acrylic polymer resin coating liquid (manufactured by Aika Kogyo Co., Ltd., Aika Aitron) prepared by incorporating a low refractive index monomer into the polymerization and adjusting the refractive index to 1.52. A laminated sheet was obtained in the same manner as in Example 21 except that (adjusted based on Z-815-4L) was used. The viscosity of the resin coating liquid measured by the measuring method described later was 38 cps.

<Example 27>
A laminated sheet was obtained in the same manner as in Example 21 except that (formation of the resin layer) was changed as follows.

(Formation of resin layer)
UV curable acrylic resin coating liquid (manufactured by Aica Kogyo Co., Ltd., Aica Aitron Z-773-5MLT; containing a photopolymerization initiator) is applied to one surface of the fiber layer (the surface in contact with the acrylic plate) with a bar coater. After coating at 80 ° C., the mixture was heated at 80 ° C. for 1 minute. Further, using a UV conveyor device (ECS-4011GX manufactured by Eye Graphics Co., Ltd.) ^{, ultraviolet rays are irradiated so that the integrated light amount becomes 150 mJ / cm 2,} and the resin coating liquid is cured to cure the resin layer (No. 1). 1 resin layer) was formed. Next, a resin layer (second resin layer) was formed on the opposite surface of the fiber layer by the same procedure. The thickness of the resin layer was 3 μm per side. By the above procedure, a laminated sheet in which a resin layer was laminated on both sides of a fiber layer (a layer containing fine fibrous cellulose) was obtained. The viscosity of the resin coating liquid measured by the measuring method described later was 36 cps.

<Example 28>
In Example 4 (formation of the fiber layer), a laminated sheet was obtained in the same manner as in Example 4 except that the fine fibrous cellulose dispersion liquid (D) was used.

<Comparative Example 1>
In Example 3, (formation of the resin layer) was not performed, and a sheet of the fiber layer alone was obtained.

<Comparative Example 2>
In Example 4, (formation of the resin layer) was not performed, and a sheet of the fiber layer alone was obtained.

<Comparative Example 3>
In Example 3 (formation of the resin layer), a laminated sheet was obtained in the same manner as in Example 3 except that the resin layer (second resin layer) was provided only on the surface of the fiber layer not in contact with the acrylic plate. rice field.

<Comparative Example 4>
In Example 4 (formation of the resin layer), a laminated sheet was obtained in the same manner as in Example 4 except that the resin layer was provided only on the surface of the fiber layer not in contact with the acrylic plate.

<Comparative Example 5>
In Example 3 (formation of the resin layer), a laminated sheet was obtained in the same manner as in Example 3 except that the thickness of the resin layer was 10 μm.

<Comparative Example 6>
In Example 4 (formation of the resin layer), a laminated sheet was obtained in the same manner as in Example 4 except that the thickness of the resin layer was 10 μm.

<Comparative Example 7>
(Dissolution of polyethylene oxide)
Polyethylene oxide (manufactured by Sumitomo Seika Chemical Co., Ltd., PEO-18) was added to ion-exchanged water in an amount of 12% by mass and dissolved. By the above procedure, an aqueous polyethylene oxide solution was obtained.

(Formation of fiber layer)
The fine fibrous cellulose dispersion (A) and the above polyethylene oxide aqueous solution were each diluted with ion-exchanged water so that the solid content concentration was 0.6% by mass. Then, the diluted polyethylene oxide aqueous solution was mixed with 83 parts by mass of the diluted fine fibrous cellulose dispersion so as to be 17 parts by mass to obtain a mixed solution. Further, the mixed solution was weighed so that the finished basis weight of the fiber sheet was 50 g / m ² , and developed on a commercially available acrylic plate. A dammed frame (inner dimensions 250 mm × 250 mm, height 5 cm) was placed on the acrylic plate so as to have a predetermined basis weight. Then, it was dried in a dryer at 70 ° C. for 24 hours and peeled off from the acrylic plate to form a fiber layer. The thickness of the fiber layer was 33 μm.

(Formation of resin layer)
A modified polycarbonate resin (manufactured by Mitsubishi Gas Chemical Company, Limited, Iupizeta FPC-2136) was mixed with 15 parts by mass, 57 parts by mass of toluene, and 28 parts by mass of methyl ethyl ketone to obtain a resin coating liquid. Next, 2.25 parts by mass of an isocyanate compound (Duranate TPA-100, manufactured by Asahi Kasei Chemicals Co., Ltd.) was added to the resin coating liquid as an adhesion aid and mixed. The viscosity of the resin coating liquid measured by the measuring method described later was 40 cps. This resin coating liquid was applied to one surface of the fiber layer with a bar coater. Then, the resin coating liquid was cured by heating at 100 ° C. for 1 hour to form a resin layer. Next, a resin layer was formed on the opposite surface of the fiber layer by the same procedure. The thickness of the resin layer was 3 μm. By the above procedure, a laminated sheet in which a resin layer was laminated on both sides of a fiber layer (a layer containing fine fibrous cellulose) was obtained.

<Measurement>
(Thickness of resin layer)
A cross section of the sheet was cut out by an ultramicrotome UC-7 (manufactured by JEOL, UC-7), and the cross section was observed with an electron microscope, a magnifying glass or visually, and the measured value was taken as the thickness of the resin layer.

(Viscosity of resin coating liquid)
The viscosity of the prepared resin coating liquid was measured with a B-type viscometer (analog viscometer T-LVT manufactured by BLOOKFIELD Co., Ltd.). The measurement conditions were a rotation speed of 60 rpm, and the viscosity value 1 minute after the start of the measurement was taken as the viscosity of the resin coating liquid.

<Evaluation>
(Adhesion)
In accordance with JIS K 5400: 1990, ^{100 1 mm 2} crosscuts were placed on the surface of the resin layer, cellophane tape (manufactured by Nichiban Co., Ltd.) was attached onto it, and the resin layer was pressed with a load of ^{1.5 kg / cm 2.} Then, the cellophane tape was peeled off in the 90 ° direction. The adhesion between the fiber layer (fine fibrous cellulose-containing layer) and the resin layer was evaluated according to the following criteria based on the number of cells peeled off. Since the evaluation sheets of Comparative Examples 1 and 2 do not have a resin layer, this evaluation was not performed.
A: The number of peeled cells is 0 points B: The number of peeled cells is 1 point or more and less than 5 points C: The number of peeled cells is 5 points or more and less than 10 points D: The number of peeled cells is 10 points or more

(water resistant)
In accordance with JIS R 3257: 1999, using a dynamic water contact angle tester (1100DAT manufactured by Fibro Co., Ltd.), 4 μL of ion-exchanged water was dropped on the surfaces of both sides of the laminated sheet, and the water contact angle after 30 seconds was determined. It was measured.
A: The contact angle of both sides of the laminated sheet is 80 ° or more and B: The contact angle of both sides of the laminated sheet is 75 ° or more and less than 80 °, or the contact angle of at least one surface of the laminated sheet is 75 ° or more and less than 80 °. The contact angle of the other surface of the laminated sheet is 80 ° or more. C: The contact angle of at least one surface of the laminated sheet is less than 75 °.

(Refractive index)
In accordance with JIS K 7142: 2008, the refractive index of the fiber layer before laminating was measured using an Abbe refractive index meter (NAR-3T, manufactured by ATAGO Co., Ltd.). When measuring the refractive index of the resin layer, 0.5 mL of a resin coating solution was applied onto a glass substrate (2 cm × 2 cm) for Abbe measurement and heated at 100 ° C. for 1 hour to obtain a resin layer. The resin layer formed on the glass substrate was not peeled off from the glass substrate and was used as it was for measuring the refractive index.

(Surface roughness)
Compliant with JIS B 0601: 1994, using an optical interferometry non-contact surface shape measuring machine (Non-contact surface / layer cross-section shape measuring system VertScan2.0, R5500GML manufactured by Ryoka System Co., Ltd.) on both sides of the laminated sheet. The surface roughness was evaluated. The surface roughness was calculated with a measurement range of 470 μm × 350 μm with a × 10 objective lens.

(transparency)
The haze of the laminated sheet was evaluated using a haze meter (HM-150, manufactured by Murakami Color Technology Research Institute) in accordance with JIS K 7136: 2000. In addition, transparency was evaluated according to the following criteria based on the haze value.
A: Haze is less than 0.5% B: Haze is 0.5% or more and less than 1% C: Haze is 1% or more

(Tension modulus)
The tensile elastic modulus of the laminated sheet was measured using a tensile tester Tencilon (manufactured by A & D Co., Ltd.) in accordance with JIS P 8113: 2006. The elastic modulus is a value calculated from the maximum positive slope value in the SS curve. When measuring the tensile elastic modulus, a test piece prepared at 23 ° C. and a relative humidity of 50% for 24 hours was used.

(Moisture percentage)
The laminated sheet was cut out to form a test piece of 5 cm × 5 cm, and the test piece was humidity-controlled at 23 ° C. and a relative humidity of 50% for 24 hours, and then dried in a thermostat at 105 ° C. until it became completely dry. The weight of the test piece before and after drying was measured, and the moisture content of the laminated sheet was calculated by the following formula.
Moisture content (mass%) of laminated sheet = (WD) / W × 100
Here, W is the weight (g) of the test piece after humidity control, and D is the weight (g) of the test piece after absolute drying.

The sheet (laminated sheet) obtained in the examples had high transparency. In addition, the sheet (laminated sheet) obtained in the examples was also excellent in water resistance. On the other hand, in the sheet obtained in the comparative example, the transparency was inferior.

Further, in particular, in Examples 21 to 27, the appearance of the obtained sheet (laminated sheet) tended to suppress the generation of ripple (rainbow unevenness) due to optical interference.

2 Fiber layer 6 Resin layer 10 Sheet

Claims (22)

A sheet having a fiber layer and resin layers on both sides of the fiber layer.
The fiber layer contains fibrous cellulose having a fiber width of 1000 nm or less.
A sheet having a surface roughness (Ra) of 12.0 nm or less on both sides of the sheet. The sheet according to claim 1, wherein the thickness of each of the resin layers is 10 μm or less. The sheet according to claim 1 or 2, wherein the fibrous cellulose has an ionic substituent. The sheet according to claim 3, wherein the ionic substituent is a phosphate group or a substituent derived from a phosphorusoxo acid group. The sheet according to any one of claims 1 to 4, wherein the refractive index of the fiber layer is 1.51 to 1.60. The sheet according to any one of claims 1 to 5, wherein the fiber layer further contains a hydrophilic polymer. The sheet according to claim 6, wherein the hydrophilic polymer is polyvinyl alcohol. The sheet according to claim 7, wherein the degree of saponification of the polyvinyl alcohol is 99.9% or less. The sheet according to any one of claims 1 to 8, wherein the resin layer contains an amorphous resin. The sheet according to any one of claims 1 to 9, wherein the resin layer is a solvent-coated layer. The sheet according to any one of claims 1 to 10, wherein the fiber layer has a thickness of 10 to 1000 μm. The sheet according to any one of claims 1 to 11, wherein the resin layer contains an isocyanate compound. The sheet according to any one of claims 1 to 12, wherein the haze value is less than 0.5%. The sheet according to any one of claims 1 to 13, wherein the moisture content is 12% by mass or less. The sheet according to any one of claims 1 to 14, wherein the tensile elastic modulus at 23 ° C. and a relative humidity of 50% is 2.5 GPa or more. The sheet according to any one of claims 1 to 15, which is for an optical member. The sheet according to any one of claims 1 to 16, wherein the refractive index ratio of the fiber layer to the resin layer calculated by the following formula is 0.98 or more and 1.02 or less.
Refractive index ratio = Refractive index of fiber layer / Refractive index of resin layer The sheet according to any one of claims 1 to 17, wherein the refractive index of the fiber layer is 1.51 to 1.54. A method for producing a sheet, which comprises a step of forming a resin layer on both sides of a fiber layer containing fibrous cellulose having a fiber width of 1000 nm or less.
A method for manufacturing a sheet, wherein the surface roughness (Ra) on both sides of the sheet is 12.0 nm or less. The method for manufacturing a sheet according to claim 19, wherein the thickness of the resin layer is 10 μm or less. The step of forming the resin layer is a step of applying a resin coating liquid to both surfaces of the fiber layer to form the resin layer.
The resin coating liquid contains a solvent and contains
The method for producing a sheet according to claim 19 or 20, wherein the viscosity of the resin coating liquid is 100 cps or less. The method for producing a sheet according to claim 21, wherein the solid content in the resin coating liquid is 12% by mass or less.

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