JP2021181673A - Laminated sheet - Google Patents

Abstract

To provide a laminated sheet composed of a fiber layer containing fine fibrous cellulose and a resin layer, having high transparency and suppressed coloring.SOLUTION: A laminated sheet is composed of a fiber layer and a resin layer provided on at last one face of the fiber layer, wherein the fiber layer has a substituent group introduction amount of lower than 0.5 mmol/g and contains a fibrous cellulose having a fiber width of 1-10 nm.SELECTED DRAWING: Figure 1

Description

The present invention relates to a laminated 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. Fine fibrous cellulose is attracting attention as a new material, and its uses are wide-ranging. For example, sheets containing fine fibrous cellulose, resin complexes, and thickeners are being developed.

For example, Patent Document 1 describes (a) a step of introducing a substituent having electrostatic and / or steric functionality into a fine fiber raw material to obtain a substituent-introduced fiber, and (b) introducing a substituent. A step of mechanically treating the fiber and a step of (c) removing a part or all of the introduced substituent from the substituent-introduced fine fiber obtained in the step (b) to obtain a substituent-desorbed fine fiber. A method for producing the fine fibers having the same is disclosed. Further, Patent Document 2 describes a method for producing a desester compound, which comprises a step of heating a compound having an ester derived from phosphoric acid and / or an ester derived from carboxylic acid in the presence of a nitrogen-containing compound exhibiting basicity. It has been disclosed. In these documents, it is considered to eliminate the substituent introduced into the fine fiber.

Patent Document 3 describes, in the method for producing a fine fiber-containing sheet, at least (a) a step of introducing a substituent having electrostatic and / or steric functionality into a fiber raw material to obtain a substituent-introduced fiber. , (B) The step of mechanically treating the substituent-introduced fiber obtained in the step (a) to obtain the substituent-introduced fine fiber, and (c) a sheet from the substituent-introduced fine fiber obtained in the step (b). (D) A method for producing a fine fiber-containing sheet having a step of removing at least a part of the introduced substituent from the sheet obtained in the step (c) is disclosed. Here, a method of removing a substituent after forming a sheet from a fine fiber having a substituent is studied.

Further, Patent Documents 4 and 5 disclose a method for producing cellulose zantate nanofibers, which comprises defibrating cellulose zantate or a cationic substituent of cellulose zantate. In Patent Document 4, a method of returning cellulose zantate nanofibers to non-denatured cellulose by regenerating the cellulose zantate nanofibers as necessary is also studied. Further, Patent Document 5 discloses a derivative functional group-desorbed cellulose fine fiber-containing sheet having an average fiber diameter of 3 nm or more and 300 nm or less, in which a functional group is desorbed from the fine fibers of the cellulose derivative.

By the way, in recent years, the development of a complex containing a fine fibrous cellulose-containing sheet and a resin layer has also been promoted. In such a complex, for example, studies have been made to improve the adhesion between the fine fibrous cellulose-containing sheet (fiber layer) and the resin layer. For example, Patent Document 6 discloses a laminate having a fiber layer containing fine fibrous cellulose and a resin layer in contact with one surface of the fiber layer. Further, Patent Document 7 discloses a laminate including a fiber layer formed of fine fibrous cellulose, a resin layer, and an adhesive layer provided between the fiber layers and the resin layer. Patent Document 8 discloses a laminate in which a base material, an anchor layer, and a cellulose nanofiber layer are provided in this order.

International Publication No. 2013/176049 Japanese Unexamined Patent Publication No. 2015-098526 International Publication No. 2015/182438 International Publication No. 2017/111033 Japanese Unexamined Patent Publication No. 2019-7101 International Publication No. 2017/126432 Japanese Unexamined Patent Publication No. 2017-056715 Japanese Unexamined Patent Publication No. 2014-079383

The present inventors are conducting research on a laminated sheet having a sheet (fiber layer) containing fine fibrous cellulose and a resin layer, and when such a laminated sheet has reduced transparency or coloring. I found out that there is.

Therefore, in order to solve the problems of the prior art, the present inventors have a laminated sheet having a fiber layer containing fine fibrous cellulose and a resin layer, which has high transparency and suppresses coloring. We proceeded with the study for the purpose of providing the laminated sheet.

As a result of diligent studies to solve the above problems, the present inventors have replaced the fiber layer with a fiber layer in a laminated sheet having a fiber layer and a resin layer arranged on at least one surface of the fiber layer. By containing fibrous cellulose having a base introduction amount of less than 0.5 mmol / g and a fiber width of 1 to 10 nm, a laminated sheet having high transparency and suppressed coloring can be obtained. I found.
Specifically, the present invention has the following configurations.

[1] A laminated sheet having a fiber layer and a resin layer arranged on at least one surface of the fiber layer.
The fiber layer is a laminated sheet containing fibrous cellulose having a substituent introduction amount of less than 0.5 mmol / g and a fiber width of 1 to 10 nm.
[2] The laminated sheet according to [1], wherein the substituent is an anionic group.
[3] The laminated sheet according to [2], wherein the anionic group is a phosphoric acid group or a functional group derived from a phosphoric acid group.
[4] The laminated sheet according to any one of [1] to [3], wherein the fibrous cellulose has a carbamide group.
[5] The laminated sheet according to any one of [1] to [4], wherein the fiber layer has a thickness of 20 μm or more.
[6] The laminated sheet according to any one of [1] to [5], wherein the density of the fiber layer is 1.0 g / cm ^{3 or more.}
[7] The laminated sheet according to any one of [1] to [6], wherein the resin layer is directly laminated on the fiber layer.
[8] The laminated sheet according to any one of [1] to [7], wherein the resin layer contains at least one selected from a polycarbonate resin and an acrylic resin.
[9] The laminated sheet according to any one of [1] to [8], wherein the resin layer further contains an adhesion aid.
[10] The laminated sheet according to [9], wherein the adhesion aid is at least one selected from an isocyanate compound and an organosilicon compound.
[11] The adhesion aid is an isocyanate compound, and the content of the isocyanate compound is 10 parts by mass or more and 40 parts by mass or less with respect to 100 parts by mass of the resin contained in the resin layer, according to [9] or [10]. Laminated sheet.
[12] The laminated sheet according to any one of [1] to [11], wherein the YI value is 2.0 or less.
[13] The laminated sheet according to any one of [1] to [12], wherein the haze is 2.0% or less.
[14] The laminated sheet according to any one of [1] to [13], which is used for an optical member.
[15] A laminated body including the laminated sheet according to any one of [1] to [14] and an adherend.

According to the present invention, it is possible to obtain a laminated sheet having high transparency and suppressed coloring.

FIG. 1 is a cross-sectional view illustrating the configuration of the laminated 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.

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. In this specification, the numerical range represented by using "~" means a range including the numerical values before and after "~" as the lower limit value and the upper limit value.

(Laminated sheet)
The present invention relates to a laminated sheet having a fiber layer and a resin layer arranged on at least one surface of the fiber layer. Here, the fiber layer contains fibrous cellulose having a substituent introduction amount of less than 0.5 mmol / g and a fiber width of 1 to 10 nm.

FIG. 1 is a cross-sectional view illustrating the configuration of the laminated sheet of the present invention. As shown in FIG. 1, the laminated sheet 10 of the present invention has a resin layer 2 and a fiber layer 6. The resin layer 2 is directly laminated on the fiber layer 6, and the resin layer 2 and the fiber layer 6 are in contact with each other on either surface. The laminated sheet 10 of the present invention may have at least one resin layer 2 and at least one fiber layer 6, but may have two or more resin layers 2 and two or more fiber layers 6. It may be a thing. For example, the laminated sheet may have a structure in which a fiber layer, a resin layer, and a fiber layer are laminated in this order, or may have a structure in which a resin layer, a fiber layer, and a resin layer are laminated in this order.

Conventionally, it has been studied to increase the amount of a substituent of fine fibrous cellulose to be introduced in order to obtain a highly transparent sheet, thereby obtaining fine fibrous cellulose having a small fiber width. However, when fine fibrous cellulose having a high amount of substituents is blended in the sheet as described above, the sheet tends to be colored by being heated in the sheet manufacturing process or the usage environment. On the other hand, when the substituent introduction step was controlled to keep the amount of the substituent introduced low, the defibration of the fine fibrous cellulose was insufficient, and it was difficult to obtain a highly transparent sheet. Therefore, the present inventors have repeatedly studied the manufacturing process of fine fibrous cellulose, and have made the fiber width 1 to 1 even though the amount of substituents introduced is as low as less than 0.5 mmol / g. We succeeded in miniaturizing to the level of 10 nm. It has been found that the sheet containing the fibrous cellulose having a low amount of substituents and having a fiber width of 1 to 10 nm is highly transparent and the coloring is suppressed. When such a fine fibrous cellulose-containing sheet is laminated on the resin layer, the transparency of the resin layer is maintained without being impaired.

The total light transmittance of the laminated sheet is preferably 88% or more, more preferably 90% or more, further preferably 91% or more, and particularly preferably 91.5% or more. By setting the total light transmittance of the laminated sheet within the above range, it is possible to apply the laminated sheet of the present invention to applications to which transparent glass has been conventionally applied. Here, the total light transmittance is a value measured using a haze meter (HM-150 manufactured by Murakami Color Technology Research Institute) in accordance with JIS K 7631-1: 1997.

The haze of the laminated sheet is preferably 2.0% or less, preferably 1.5% or less, and even more preferably 1.0% or less. The lower limit of the haze of the laminated sheet is not particularly limited and may be 0%. Here, the haze is a value measured using a haze meter (HM-150 manufactured by Murakami Color Technology Research Institute) in accordance with JIS K 7136: 2000.

In the laminated sheet of the present invention, the interlayer adhesion between the fiber layer and the resin layer is also excellent. ^{Specifically, in accordance with JIS K 5400, 100 1 mm 2} crosscuts are placed on the surface of the laminated sheet on the fiber layer side, and cellophane tape (manufactured by Nichiban Co., Ltd.) is attached onto the surface, pressed, and then 90. When peeled in the ° direction, the number of cells peeled from the resin layer by the fiber layer is less than 5 points. In such a case, it can be determined that the interlayer adhesion between the fiber layer and the resin layer is good. The number of peeled cells is more preferably 3 points or less, further preferably 1 point or less, and particularly preferably 0 points.

The laminated sheet of the present invention has a fiber layer and a resin layer, and the fiber layer can also function as a layer for reinforcing the resin layer. Therefore, the strength of the laminated sheet itself is increased. Further, even when the laminated sheet is attached to an adherend such as another resin film or resin plate, the fiber layer functions as a layer for reinforcing the adherend. For example, by using a resin plate such as a polycarbonate plate as an adherend and attaching a laminated sheet to the resin plate, the mechanical strength of the resin plate can be reinforced. As described above, the laminated sheet having the fiber layer also has an effect of reinforcing the adherend.

For example, the reinforcing effect when the laminated sheet is attached to the adherend is 1.5 times or more the flexural modulus after the laminated sheet is attached to the adherend, compared with the flexural modulus of the adherend. When it is, it can be evaluated that an excellent reinforcing effect is exhibited. It is particularly preferable that the flexural modulus after the laminated sheet is attached to the adherend is 2.0 times or more the flexural modulus of the adherend. When laminating the adherend and the laminated sheet, the laminated sheet is produced by laminating the adherend and the laminated sheet and then heat-pressing the adherend to a glass transition temperature or higher.

The laminated sheet of the present invention itself has excellent mechanical strength. For example, the tensile elastic modulus of the laminated sheet at 23 ° C. and 50% relative humidity is preferably 2.5 GPa or more, more preferably 5.0 GPa or more, and even more preferably 10 GPa or more. The tensile elastic modulus of the laminated sheet at 23 ° C. and 50% relative humidity is preferably 30 GPa or less, more preferably 25 GPa or less, and even more preferably 20 GPa or less. The tensile elastic modulus of the laminated sheet is a value measured in accordance with JIS P 8113.

The total thickness of the laminated sheet is not particularly limited, but is preferably 30 μm or more, more preferably 40 μm or more, further preferably 50 μm or more, still more preferably 60 μm or more. , 70 μm or more is particularly preferable. Further, the total thickness of the laminated sheet is preferably 1000 μm or less. The thickness of the laminated sheet can be appropriately adjusted according to the intended use, but from the viewpoint of exerting the effect of reinforcing the adherend, the total thickness of the laminated sheet is preferably 50 μm or more.

The thickness of the fiber layer of the laminated sheet is preferably 5 μm or more, more preferably 10 μm or more, and further preferably 20 μm or more. The thickness of the fiber layer is preferably 500 μm or less, more preferably 200 μm or less, and even more preferably 100 μm or less. Here, the thickness of the fiber layer constituting the laminated sheet is measured by cutting out a cross section of the laminated sheet with Ultra Microtome UC-7 (manufactured by JEOL Ltd.) and observing the cross section with an electron microscope, a magnifying glass or visually. Value. When the laminated sheet contains a plurality of fiber layers, it is preferable that the total thickness of the fiber layers is within the above range.

The thickness of the resin layer of the laminated sheet is preferably 0.5 μm or more, more preferably 1 μm or more, further preferably 2 μm or more, and particularly preferably 3 μm or more. The thickness of the resin layer is preferably 15,000 μm or less, more preferably 5000 μm or less, and even more preferably 500 μm or less. Here, the thickness of the resin layer constituting the laminated sheet is measured by cutting out a cross section of the laminated sheet with Ultra Microtome UC-7 (manufactured by JEOL Ltd.) and observing the cross section with an electron microscope, a magnifying glass or visually. Value. When the laminated sheet contains a plurality of resin layers, it is preferable that the total thickness of the resin layers is within the above range.

The ratio of the thickness of the resin layer to the thickness of the fiber layer (thickness of the resin layer / thickness of the fiber layer) is preferably 10 or less, more preferably 5 or less, and further preferably 1 or less. Further, for example, when the resin layer is a coated layer formed by coating, the ratio of the thickness of the resin layer to the thickness of the fiber layer (thickness of the resin layer / thickness of the fiber layer) is 0.5 or less. It may be 0.2 or less, 0.15 or less, or 0.1 or less. In the laminated sheet, when there are a plurality of fiber layers, the thickness of the fiber layers is the total thickness of the fiber layers, and when there are a plurality of resin layers, the thickness of the resin layers is the total thickness of the resin layers. be.

In this embodiment, the YI value of the laminated sheet is preferably 2.0 or less, more preferably 1.5 or less. The lower limit of the YI value of the laminated sheet is not particularly limited, but is preferably 0.1 or more. Here, the YI value of the laminated sheet is a YI value measured in accordance with JIS K 7373: 2006. As the YI value measuring device, for example, Color Cutei (manufactured by Suga Test Instruments Co., Ltd.) can be used. Since the above-mentioned YI value is a YI value measured before heating the laminated sheet as described later, it may be referred to as an initial YI value.

In this embodiment, the YI value after heating the laminated sheet at 160 ° C. for 6 hours is preferably 20 or less, more preferably 15 or less, still more preferably 10 or less. The lower limit of the YI value of the laminated sheet after heating at 160 ° C. for 6 hours is not particularly limited, but is preferably 0.1 or more. The YI value after heating at 160 ° C. for 6 hours may be referred to as a YI value after heating.

The YI increase rate in the laminated sheet of the present embodiment is preferably 1500% or less, more preferably 1250% or less, further preferably 1000% or less, still more preferably 800% or less. , 600% or less is particularly preferable. The lower limit of the YI increase rate in the laminated sheet is not particularly limited, but is preferably 0.1% or more. Here, the YI increase rate of the laminated sheet is the increase rate of the YI value of the laminated sheet before and after heating the laminated sheet at 160 ° C. for 6 hours. Specifically, the YI increase rate is a value calculated by the following formula.
YI increase rate (%) = (YI value of laminated sheet after heating-YI value of laminated sheet before heating) / YI value of laminated sheet before heating × 100
In the above formula, the YI value of the laminated sheet is a YI value measured in accordance with JIS K 7373: 2006.

(Resin layer)
The laminated sheet has at least one resin layer. Here, the resin layer is directly laminated on the fiber layer, and the resin layer and the fiber layer are in contact with each other on either surface. The resin layer is preferably a resin layer (coated resin layer) formed by coating.

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 or 95% by mass or less.

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

As the synthetic resin, for example, at least one selected from polycarbonate resin, polyethylene terephthalate resin, polyethylene naphthalate resin, polyethylene resin, polypropylene resin, cyclic olefin resin, polyimide resin, polystyrene resin and acrylic resin is preferable. Among them, the synthetic resin is preferably at least one selected from the polycarbonate resin and the acrylic resin, and more preferably the polycarbonate resin. The acrylic resin is preferably at least one selected from polyacrylonitrile and poly (meth) acrylate.

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.

In the laminated sheet of the present invention, the resin layer preferably contains an adhesion aid. Examples of the adhesion aid include a compound containing at least one selected from an isocyanate group, a carbodiimide group, an epoxy group, an oxazoline group, an amino group, a silanol group and an alkoxysilyl group, and an organic silicon compound. Among them, the adhesion aid is preferably at least one selected from a compound containing an isocyanate group (isocyanate compound) and an organosilicon compound. Examples of the organosilicon compound include a silane coupling agent condensate and a silane coupling agent.

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). -4-Cyclohexene-1,2-dicarboxylate, 2,5-norbornan diisocyanate, 2,6-norbornan diisocyanate and the like can be mentioned.

Examples of the organosilicon compound include a compound having a siloxane structure and a compound that forms a siloxane structure by condensation. For example, examples of the organosilicon compound include a silane coupling agent or a condensate of a silane coupling agent. 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 embodiment 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, for example, 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.

As the silane coupling agent, one having an alkoxysilyl group may be used, or one having a silanol group after hydrolysis may be used. In this case, it is preferable that at least a part of the alkoxysilyl group and the silanol group is present even after laminating the fiber layer. Since the silanol group is a hydrophilic group, it is possible to more effectively enhance 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 laminated sheet is cut out by Ultramicrotome UC-7 (manufactured by JEOL). , 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. 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 surface of the resin layer on the fiber layer side may form a fine concavo-convex structure. Since the surface of the resin layer on the fiber layer side has a fine uneven structure, the adhesion between the fiber layer and the resin layer can be more effectively enhanced. When the surface of the resin layer on the fiber layer side has a fine concavo-convex structure, such a structure is formed by, for example, a processing step such as a blasting process, an embossing process, an etching process, a corona process, or a plasma discharge process. Is preferable. In the present specification, the fine concavo-convex structure means a structure in which the number of recesses existing on a straight line with a length of 1 mm drawn at an arbitrary position is 10 or more. When measuring the number of recesses, the laminated sheet is immersed in ion-exchanged water for 24 hours, and then the fiber layer is peeled off from the resin layer. After that, the measurement can be performed by scanning the surface of the resin layer on the fiber layer side with a stylus type surface roughness meter (Surfcoder series manufactured by Kosaka Research Institute). When the pitch of the unevenness is extremely small on the submicron and nano-order, the number of unevenness can be measured from the observation image of the scanning probe microscope (AFM5000II and AFM5100N manufactured by Hitachi High-Tech Science Co., Ltd.).

The resin layer may contain an arbitrary component other than the synthetic resin. Examples of the optional component include known components used in the field of resin films such as fillers, pigments, dyes, and ultraviolet absorbers.

(Fiber layer)
The fiber layer contains fibrous cellulose having a substituent introduction amount of less than 0.5 mmol / g and a fiber width of 1 to 10 nm. Usually, fibrous cellulose having a fiber width of 1000 nm or less is also referred to as fine fibrous cellulose or CNF. However, the fibrous cellulose contained in the fiber layer of the present invention is fine fibrous cellulose having a smaller fiber width.

In this embodiment, the density of the fiber layer ^{is preferably 1.0 g / cm 3} or more, more preferably 1.2 g / cm ³ or more, and further preferably 1.4 g / cm ³ or more. preferable. The density of the fiber layer is preferably 1.7 g / cm ³ or less, more preferably 1.65 g / cm ³ or less, further preferably 1.6 g / cm ³ or less. When the laminated sheet contains two or more fiber layers, it is preferable that the density of each fiber layer is within the above range.

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 laminated 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.

In this embodiment, the fiber layer is preferably 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).
Formula (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 cellulose.

In the present embodiment, the surface roughness of at least one surface of the fiber layer is preferably 50 nm or less, more preferably 30 nm or less, and further preferably 10 nm or less. It is also particularly preferable that the surface roughness of both sides of the fiber layer is within the above range. By setting the surface roughness within the above range, the transparency of the fiber layer can be further enhanced, and as a result, the transparency of the laminated sheet can also be enhanced. Specifically, the haze of the fiber layer and the laminated sheet can be made lower. Here, the surface roughness (arithmetic mean) of the fiber layer is the arithmetic average roughness of at least one surface of the fiber layer. The surface roughness (arithmetic mean) is a value obtained by measuring the arithmetic average roughness of 3 μm square using an atomic force microscope (NanoScope IIIa manufactured by Veeco).

In the present embodiment, the surface pH of the fiber layer is preferably 3 or more, more preferably 4 or more, and even more preferably 5 or more. The surface pH of the fiber layer is preferably 10 or less, more preferably 9 or less, and even more preferably 8 or less. By setting the surface pH of the fiber layer in the above range, the effect of suppressing yellowing can be easily obtained. In order to keep the surface pH of the fiber layer within the above range, it is preferable to appropriately adjust the pH of the fine fibrous cellulose dispersion obtained in the manufacturing process described later. When measuring the surface pH of the fiber layer, 10 μL of ion-exchanged water is dropped into a 1 cm square area on the surface of the fiber layer with a micropipette, and the pH of that portion is set to a flat pH composite electrode (6261-10C). Measured using HORIBA).

<Fine fibrous cellulose>
In the present embodiment, the amount of substituents introduced in the fine fibrous cellulose may be less than 0.5 mmol / g, preferably 0.4 mmol / g or less, and more preferably 0.3 mmol / g or less. It is more preferably 0.25 mmol / g or less, and particularly preferably 0.15 mmol / g or less. The amount of substituents introduced in the fine fibrous cellulose may be 0.0 mmol / g, but is preferably 0.03 mmol / g or more, more preferably 0.04 mmol / g or more. It is more preferably 0.05 mmol / g or more, and particularly preferably 0.07 mmol / g or more.

The fiber width of the fine fibrous cellulose may be 1 to 10 nm, preferably 1 to 9 nm, more preferably 1 to 8 nm, and even more preferably 1 to 7 nm. Here, the fiber width of the fine fibrous cellulose is measured as follows, for example, by observing with an electron microscope. First, the fine fibrous cellulose is dispersed in water so that the concentration of the cellulose is 0.01% by mass or more and 0.1% by mass or less, and cast on a hydrophilized carbon film-coated grid. After drying this, it is stained with uranyl acetate and observed with a transmission electron microscope (TEM, manufactured by JEOL Ltd., JEOL-2000EX). At that time, an axis having an arbitrary vertical and horizontal image width is assumed in the obtained image, and the magnification is adjusted so that 20 or more fibers intersect the axis. After obtaining an observation image satisfying this condition, two random axes in each of the vertical and horizontal directions are drawn for this image, and the fiber width of the fiber intersecting the axis is visually read. In this way, three non-overlapping observation images are taken, and the value of the fiber width of the fiber intersecting each of the two axes is read (20 or more × 2 × 3 = 120 or more).
(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.

For the fine fibrous cellulose contained in the fiber layer, the number average fiber width can be calculated from the fiber width obtained by the above method. The number average fiber width of the fibrous cellulose contained in the fiber layer is preferably 1 to 10 nm, more preferably 1 to 9 nm, further preferably 1 to 8 nm, and preferably 1 to 7 nm. Is particularly preferable. The fact that the number average fiber width of the fibrous cellulose contained in the fiber layer is within the above range means that the fiber layer does not substantially contain coarse cellulose fibers, and more than 70% of the fibers are fibers. It means that the fiber width of the cellulose is 10 nm or less. Of the total fibrous cellulose contained in the fiber layer, the proportion of fine fibrous cellulose having a fiber width of 10 nm or less is preferably 70% or more, more preferably 80% or more, still more preferably 90% or more.
Here, the ratio of the fine fibrous cellulose having a fiber width of 10 nm or less is a value represented by the following formula.
Percentage of fine fibrous cellulose having a fiber width of 10 nm or less (%) = (number of fine fibrous cellulose having a fiber width of 10 nm or less / number of total fibrous cellulose) × 100

The fiber width of the fine fibrous cellulose in the laminated sheet is measured as follows, for example, using an atomic force microscope observation. First, the fiber layer of the laminated sheet is observed with an atomic force microscope (NanoScope IIIa manufactured by Veeco). At that time, the image has a viewing angle of 500 nm. For the obtained image, two random axes are drawn vertically and horizontally for each image, 20 or more fibers intersecting the axes are randomly selected, and the fiber width is visually read. In this way, three non-overlapping observation images are taken and the value of the fiber width of the fiber intersecting each of the two axes is read. (20 or more x 2 x 3 = 120 or more)
(1) A straight line X is drawn at an arbitrary position in the observation image, and 20 or more intersecting fibers are randomly selected for the straight line X.
(2) A straight line Y that intersects the straight line perpendicularly to the straight line Y is drawn in the same image, and 20 or more intersecting fibers are randomly selected for the straight line Y.
When the fiber layer is not exposed in the laminated sheet, the laminated sheet is cut using an ultramicrotome or the like to cut out a cross section of the fiber layer and observed by the above method.

The fiber length of the fine 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 0.1 μm or more and 600 μm or less. More preferred. By setting the fiber length within the above range, it is possible to suppress the destruction of the crystal region of the fine fibrous cellulose. Further, it is possible to set the slurry viscosity of the fine fibrous cellulose in an appropriate range. The fiber length of the fine fibrous cellulose can be obtained by, for example, image analysis by TEM, SEM, or AFM.

The fine fibrous cellulose preferably has an I-type crystal structure. Here, the fact that the fine 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. 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 fine fibrous cellulose is not particularly limited, but is preferably 50 or more and 10000 or less, and more preferably 100 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 fine fibrous cellulose in the present embodiment has, for example, both a crystalline region and a non-crystalline region. The fine fibrous cellulose having both a crystalline region and a non-crystalline region and having an axial ratio within the above range is realized by a method for producing fine fibrous cellulose described later.

The cellulose component in fine fibrous cellulose can be classified into α-cellulose component and hemicellulose component. A lower ratio of hemicellulose is preferable because it is easy to obtain an effect of suppressing yellowing over time and yellowing by heating. The proportion of hemicellulose in the fine fibrous cellulose of the present invention is preferably less than 30%, more preferably less than 25%, still more preferably less than 20%.

Total amount of nitrogen contained in fine fibrous cellulose and free nitrogen contained in fine fibrous cellulose dispersion (hereinafter, "nitrogen amount", "nitrogen amount contained in fine fibrous cellulose" or "fine fibrous cellulose" The amount of nitrogen in the fiber) is preferably 0.08 mmol / g or less, more preferably 0.04 mmol / g or less, and even more preferably 0.02 mmol / g or less. The amount of nitrogen contained in the fine fibrous cellulose is preferably 0.001 mmol / g or more. The amount of nitrogen in the fine fibrous cellulose is a value measured by the following method. First, the dispersion liquid containing fine fibrous cellulose is adjusted to a solid content concentration of 1% by mass, and decomposed by the Kjeldahl method (JIS K 0102 2016 44.1). After decomposition, the amount of ammonium ions (mmol) is measured by cation chromatography and divided by the amount of cellulose (g) used for the measurement to calculate the nitrogen content (mmol / g). The amount of nitrogen is the amount of nitrogen bonded to fine fibrous cellulose by ionic bond and / or covalent bond, and free nitrogen dissolved in the dispersion liquid which is not bound to fine fibrous cellulose by ionic bond and / or covalent bond. The total amount.

In the present embodiment, the amount of the substituent introduced in the fine fibrous cellulose is less than 0.5 mmol / g, and the substituent referred to here is preferably an anionic group. That is, the fine fibrous cellulose of the present invention is obtained by subjecting the fine fibrous cellulose having an anionic group to a substituent removing treatment, and the fine fibrous cellulose of the present invention is a fine fibrous cellulose having a substituent removed. It is fibrous cellulose.

Examples of the anionic group 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 (sometimes referred to simply as a carboxy group), and the like. Examples include a sulfone group or a substituent derived from a sulfone group (sometimes simply referred to as a sulfone group), a zantate group or a substituent derived from a zantate group (sometimes simply referred to as a zantate group). 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 these, the anionic group is preferably at least one selected from a phosphorus oxo acid group or a substituent derived from a phosphorus oxo acid group, and a sulfone group or a substituent derived from a sulfone group, and is preferably a phosphorus oxo acid group or a substituent. More preferably, it is a substituent derived from a phosphoxoic acid group.

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 substituents represented by the following formula (1) may be introduced into each fine 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 the fine cellulose fiber 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 fine fibrous cellulose, the plurality of Rs present are the same. It may 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 onium ion. Examples of the organic ammonium ion include aliphatic ammonium ion and aromatic ammonium ion, and examples of the organic onium 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 fine fibrous cellulose, the plurality of β ^{b +} are present. They 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.

Further, the sulfone group (sulfo group or substituent derived from a sulfone group) is preferably a sulfur oxo acid group (sulfur oxo acid group or a substituent derived from a sulfur oxo acid group), for example, the following formula (2). It is preferably a substituent represented by. A plurality of substituents represented by the following formula (2) may be introduced into each fine 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 onium ion. Examples of the organic ammonium ion include aliphatic ammonium ion and aromatic ammonium ion, and examples of the organic onium 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 fine 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 anionic groups introduced into the fine fibrous cellulose can be measured, for example, by 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 sodium hydroxide solution to the obtained slurry containing the fine fibrous cellulose.

FIG. 2 is a graph showing the relationship between the amount of NaOH dropped and the pH with respect to a slurry containing fine fibrous cellulose having a phosphorus oxo acid group. The amount of the phosphorus oxo acid group introduced into the fine fibrous cellulose is measured, for example, as follows.
First, the slurry containing fine 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 was equal to the amount of first dissociated acid of the fine fibrous cellulose contained in the slurry used for titration, and was required from the first end point to the second end point. The amount of alkali is equal to the amount of second dissociating acid of the fine fibrous cellulose contained in the slurry used for titration, and the amount of alkali required from the start to the second end point of titration is contained in the slurry used for titration. Equal to the total amount of dissociated acid in the fibrous cellulose. 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 the phosphoric acid group causes condensation, the amount of weakly acidic groups in the phosphoric acid group (also referred to as the second dissociated acid amount in the present specification) is apparently. It decreases, and the amount of alkali required for the second region is smaller than the amount of alkali required for the first region. On the other hand, the amount of strongly acidic groups in the phosphorus oxo acid group (also referred to as the first dissociated acid amount in the present specification) is the same as the amount of phosphorus atoms 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 fine fibrous cellulose, the amount of the phosphorus oxo acid group contained in the acid-type fine fibrous cellulose (hereinafter, phosphorus oxo acid). It is called the base amount (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 to the mass of the fine fibrous cellulose when the cation C is a counterion. By doing so, the amount of phosphorus oxo acid groups (hereinafter, the amount of phosphorus oxo acid groups (C type)) possessed by the fine fibrous cellulose in which the cation C is a counter ion can be obtained.
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 fine fibrous cellulose (total dissociated acid amount of the phosphoric acid group)
W: Formulated amount of cation C per valence (for example, Na is 23, Al is 9).

In the measurement of the amount of anionic groups by the titration method, accurate values can be obtained, such as when the amount of one drop of sodium hydroxide aqueous solution is too large, or when the titration interval is too short, the amount of anionic groups is lower than originally intended. Sometimes not. 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 fine 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. ..

Further, the amount of the sulfone group introduced into the fine fibrous cellulose can be calculated by freeze-drying the slurry containing the fine fibrous cellulose and measuring the amount of sulfur in the crushed sample. Specifically, a slurry containing fine fibrous cellulose is freeze-dried, and the crushed sample is pressure-heated and decomposed with nitric acid in a closed container, diluted appropriately, and the amount of sulfur is measured by ICP-OES. do. The value calculated by dividing by the absolute dry mass of the fine fibrous cellulose tested is taken as the sulfone group amount (unit: mmol / g) of the fine fibrous cellulose.

The amount of the zantate group introduced into the fine fibrous cellulose can be measured by the following method by the Bredee method. First, add 40 mL of saturated ammonium chloride solution to 1.5 parts by mass (absolute dry mass) of fine fibrous cellulose, mix well while crushing the sample with a glass rod, leave it for about 15 minutes, and then GFP filter paper (GS manufactured by ADVANTEC). Filter with -25) and wash thoroughly with saturated ammonium chloride solution. Then, the sample is placed in a 500 mL tall beaker together with the GFP filter paper, 50 mL of 0.5 M sodium hydroxide solution (5 ° C.) is added, the mixture is stirred, and the mixture is left for 15 minutes. After adding the phenolphthalein solution until the solution turns pink, 1.5 M acetic acid is added, and the point at which the solution turns from pink to colorless is defined as the neutralization point. After neutralization, add 250 mL of distilled water, stir well, and add 10 mL of 1.5 M acetic acid and 10 mL of 0.05 mol / L iodine solution using a whole pipette. Then, this solution is titrated with a 0.05 mol / L sodium thiosulfate solution, and the amount of zantate group is calculated from the following formula from the titration amount of sodium thiosulfate and the absolute dry mass of the fine fibrous cellulose.
Zantate group amount (mmol / g) = (0.05 x 10 x 2-0.05 x sodium thiosulfate titration (mL)) / 1000 / absolute dry mass of fine fibrous cellulose (g)

In the present embodiment, the fine fibrous cellulose preferably has a carbamide group. In the present specification, the carbamide group is preferably a group represented by the following structural formula.

In the above structural formula, 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 group. A chain hydrocarbon group, an aromatic group, or an inducing group thereof. Above all, it is particularly preferable that R is a hydrogen atom.

The amount of carbamide group introduced in the fine fibrous cellulose is preferably 0.001 mmol / g or more. The amount of the carbamide group introduced in the fine fibrous cellulose is preferably 0.08 mmol / g or less, more preferably 0.04 mmol / g or less, and further preferably 0.02 mmol / g or less. preferable. Here, the amount of carbamide group introduced in the fine fibrous cellulose can be calculated by freeze-drying the slurry containing the fine fibrous cellulose and further crushing the sample by performing a trace nitrogen analysis. The amount of carbamide group introduced per unit mass of fine fibrous cellulose (mmol / g) is obtained by dividing the nitrogen content (g / g) per unit mass of fine fibrous cellulose obtained by trace nitrogen analysis by the atomic weight of nitrogen. Can be calculated by

In the present embodiment, when the fine fibrous cellulose used for forming the fiber layer is used as an aqueous dispersion having a concentration of 0.1% by mass and the nanofiber yield is calculated by the following formula, the nanofiber yield is 95% by mass or more. It is preferably present, and more preferably 96% by mass or more. The nanofiber yield may be 100% by mass.
Nanofiber yield [mass%] = C / 0.1 × 100
Here, C is the concentration of the fine fibrous cellulose contained in the supernatant obtained by centrifuging the aqueous dispersion having a fine fibrous cellulose concentration of 0.1% by mass under the conditions of 12000 G for 10 minutes. be.

Further, in the present embodiment, when the fine fibrous cellulose used for forming the fiber layer is used as an aqueous dispersion having a concentration of 0.2% by mass, the haze of the aqueous dispersion is preferably 5.0% or less. It is more preferably 4.0% or less, and further preferably 3.0% or less. The haze of the aqueous dispersion may be 0%. If the haze of the water dispersion having a concentration of 0.2% by mass is within the above range, it can be determined that the dispersion is transparent. Here, the haze of the aqueous dispersion is a value measured according to JIS K 7136: 2000 using a haze meter and a glass cell for liquid having an optical path length of 1 cm. The zero point measurement is performed with ion-exchanged water contained in the same glass cell. Further, the dispersion liquid to be measured is allowed to stand in an environment of 23 ° C. and a relative humidity of 50% for 24 hours before the measurement, and the liquid temperature of the dispersion liquid is set to 23 ° C.

In the present embodiment, when the fine fibrous cellulose used for forming the fiber layer is used as a dispersion liquid (water dispersion liquid) having a concentration of 1% by mass, the pH of the dispersion liquid is preferably 3 or more, preferably 4 or more. It is more preferable to have it, and it is further preferable to have 5 or more. The pH of the dispersion is preferably 10 or less, more preferably 9 or less, and even more preferably 8 or less. By setting the pH of the dispersion liquid in the above range, yellowing of the dispersion liquid and the sheet can be suppressed more effectively. In order to keep the pH of the dispersion in the above range, the same method as in the <pH adjustment step> described later can be taken.

In the present embodiment, when the fine fibrous cellulose used for forming the fiber layer is a dispersion liquid (water dispersion liquid) having a concentration of 0.4% by mass, the viscosity of the dispersion liquid at 23 ° C. is 100 mPa · s or more. It is preferably 1000 mPa · s or more, and even more preferably 2000 mPa · s or more. The viscosity of the dispersion at 23 ° C. is preferably 200,000 mPa · s or less, and more preferably 100,000 mPa · s or less. The viscosity of the dispersion having a fine fibrous cellulose concentration of 0.4% by mass can be measured using a B-type viscometer (analog viscometer T-LVT manufactured by BLOOKFIELD). The measurement conditions are 23 ° C., the rotation speed is 3 rpm, and the viscosity is measured 3 minutes after the start of measurement. Further, the dispersion liquid to be measured is allowed to stand in an environment of 23 ° C. and a relative humidity of 50% for 24 hours before the measurement, and the liquid temperature of the dispersion liquid is set to 23 ° C.

It is preferable that the amount of free nitrogen in the dispersion containing the fine fibrous cellulose used for forming the fiber layer is small. The amount of free nitrogen in the dispersion can be measured by measuring the nitrogen concentration in the filtrate when the fine fibrous cellulose dispersion is filtered. For example, the free nitrogen concentration in the dispersion having a fine fibrous cellulose concentration of 0.2% by mass is preferably 100 ppm or less, more preferably 80 ppm or less, further preferably 70 ppm or less, and even more preferably 60 ppm. It is more preferably less than or equal to, more preferably 50 ppm or less, further preferably 40 ppm or less, and particularly preferably 30 ppm or less. The nitrogen concentration in the dispersion having a fine fibrous cellulose concentration of 0.2% by mass may be 0 ppm. Since free nitrogen present in the dispersion liquid causes coloring, by keeping the nitrogen concentration in the filtrate within the above range, the yellowing of the dispersion liquid containing fine fibrous cellulose and the sheet is more effectively suppressed. can do. Here, the method for measuring the nitrogen concentration in the filtrate is as follows. First, distilled water is added so that the concentration of fine fibrous cellulose is 0.2% by mass, and after stirring for 24 hours, filtration is performed using a filter medium having a pore size of 0.45 μm to obtain a filtrate. Then, the nitrogen concentration (ppm) in the filtrate is measured by trace nitrogen analysis.

<Arbitrary ingredient>
The fiber layer may contain an arbitrary component other than fine fibrous cellulose. Examples of the optional component include spacer molecules, hydrophilic polymers, organic ions and the like, which will be described later. The hydrophilic polymer is preferably a hydrophilic oxygen-containing organic compound (however, the above-mentioned cellulose fibers are excluded). The oxygen-containing organic compound is preferably non-fibrous, and such non-fibrous oxygen-containing organic compound does not include fine fibrous cellulose or thermoplastic resin fiber.

The oxygen-containing organic compound is 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 oxygen-containing organic compound 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. Hydrophilic polymers such as acrylates, polyacrylamides, acrylic acid alkyl ester copolymers, urethane copolymers, cellulose derivatives (hydroxyethyl cellulose, carboxyethyl cellulose, carboxymethyl cellulose, etc.); hydrophilicity such as glycerin, sorbitol, ethylene glycol, etc. Sexual small molecules can be mentioned. Among these, polyethylene glycol, polyethylene oxide, polyvinyl alcohol, glycerin, and sorbitol are preferable from the viewpoint of improving the strength, density, chemical resistance, etc. of the fiber layer, and at least one selected from polyethylene glycol and polyethylene oxide. More preferably, it is more preferably at least one selected from polyethylene oxide, polyvinyl alcohol and polyethylene glycol.

The oxygen-containing organic compound is preferably an organic compound polymer having a molecular weight of 50,000 or more and 8 million or less. The molecular weight of the oxygen-containing organic compound is preferably 100,000 or more and 5 million or less, but for example, it may be a small molecule having a molecular weight of less than 1000.

The content of the oxygen-containing organic compound contained in the fiber layer is preferably 1 part by mass or more, more preferably 10 parts by mass or more, based on 100 parts by mass of the fine fibrous cellulose contained in the fiber layer. , 15 parts by mass or more is more preferable. The content of the oxygen-containing organic compound contained in the fiber layer is preferably 1000 parts by mass or less, and preferably 500 parts by mass or less, based on 100 parts by mass of the fine fibrous cellulose contained in the fiber layer. It is more preferably 100 parts by mass or less, and particularly preferably 50 parts by mass or less. By setting the content of the oxygen-containing organic compound within the above range, a laminated sheet having high transparency and strength can be formed.

Examples of the organic ion include tetraalkylammonium ion and tetraalkylphosphonium ion. 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.

Further, as the optional component, an antifoaming agent, a lubricant, an ultraviolet absorber, a dye, a pigment, a stabilizer, a surfactant, a preservative (for example, phenoxyethanol) and the like can be mentioned.

(Manufacturing method of fine fibrous cellulose)
The above-mentioned method for producing fine fibrous cellulose has a step (A) of removing at least a part of the substituent from the fine fibrous cellulose having a substituent and a fiber width of 1000 nm or less, and a step (A). After that, the step (B) of performing a uniform dispersion treatment is included. Here, the substituent contained in the fine fibrous cellulose used in the step (A) is preferably an anionic group, and more preferably a phosphoxoic acid group or a substituent derived from the phosphoxoic acid group. Further, the fine fibrous cellulose used in the step (A) preferably has a carbamide group.

(Step (A))
The step (A) is a step of removing at least a part of the substituent from the fine fibrous cellulose having a substituent and having a fiber width of 1000 nm or less. Hereinafter, a method for producing fine fibrous cellulose having a substituent and having a fiber width of 1000 nm or less (fine fibrous cellulose used in step (A)) will be described first.

<Fiber raw material>
The fine fibrous cellulose used in the step (A) 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 the 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 fine fibrous cellulose used in the step (A) has a substituent. Therefore, the process for producing the fine fibrous cellulose used in the step (A) preferably includes a substituent introduction step, and more preferably an anionic group introduction step. Examples of the anionic group introduction step include a phosphorus oxo 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”). Is preferable.

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 respect to the dry state, the wet state or the slurry-like fiber raw material. 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 powder, in the form of a solution dissolved in a solvent, or in the 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 phosphoric acid 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, Disodium hydrogen phosphate, ammonium dihydrogen phosphate, or phosphoric acid and sodium phosphite are 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 and the compound B 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 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. A drying device, a band type 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 acid 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 in the phosphorus oxo acid group introduction step is preferably 0.60 mmol / g or more, more preferably 0.70 mmol / g or more, and more preferably 0.80 mmol / g per 1 g (mass) of the fiber raw material. It is more preferably g or more, further preferably 1.00 mmol / g or more, and particularly preferably 1.20 mmol / g or more. The amount of the phosphorus oxo acid group introduced is, for example, preferably 5.20 mmol / g or less, more preferably 3.65 mmol / g or less, and 3.00 mmol / g or less per 1 g (mass) of the fiber raw material. It is more preferable to have. The fact that the amount of the phosphorus oxo acid group introduced in the phosphorus oxo acid group introduction step is within the above range means that the amount of the substituent of the fine fibrous cellulose provided in the step (A) is within the above range. do. By setting the introduction amount of the phosphoxoic acid group within the above range, the introduction amount of the substituent of the fine fibrous cellulose provided in the step (A) can be within the above range, and as a result, the final fiber width can be obtained. It becomes easy to produce fine fibrous cellulose having a thickness of 10 nm or less. In addition, the transparency of the dispersion liquid or sheet containing the fine fibrous cellulose of the present invention can be more effectively enhanced.

<Sulfone group (sulfur oxoacid group) introduction process>
The step of producing the fine fibrous cellulose provided in the step (A) may include a sulfone group introduction step as an anionic group introduction step. In the sulfone group introduction step, cellulose fibers having a sulfone group (sulfone group-introduced fiber) can be obtained by reacting the hydroxyl group of the fiber raw material containing cellulose with sulfonic acid.

In the sulfone group introduction step, at least one selected from compounds capable of introducing a sulfone group by reacting with the hydroxyl group of the fiber raw material containing cellulose instead of the compound A in the above-mentioned <phosphoroxo acid group introduction step>. A 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 sulfone group introduction step, it is preferable to use the compound B in the above-mentioned <phosphoroacid group introduction step> in the same manner.

In the sulfone group introduction step, it is preferable to mix the cellulose raw material with an aqueous solution containing sulfonic acid 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 sulfone 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 sulfonic acid and urea and / or a urea derivative, but is, for example, 10 seconds or more and 10,000 seconds or less. Is preferable. 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 sulfone group introduced in the sulfone group introduction step is preferably 0.60 mmol / g or more, more preferably 0.70 mmol / g or more, and 0.80 mmol / g or more per 1 g (mass) of the fiber raw material. It is more preferably 1.00 mmol / g or more, and particularly preferably 1.20 mmol / g or more. The amount of the sulfone group introduced is, for example, preferably 5.00 mmol / g or less, and more preferably 3.00 mmol / g or less per 1 g (mass) of the fiber raw material. The fact that the amount of the sulfone group introduced in the sulfone group introduction step is within the above range means that the amount of the substituent of the fine fibrous cellulose provided in the step (A) is within the above range. By setting the introduction amount of the sulfone group within the above range, the introduction amount of the substituent of the fine fibrous cellulose provided in the step (A) can be within the above range, and as a result, the fiber width is 10 nm or less. It becomes easy to produce fine fibrous cellulose. In addition, the transparency of the dispersion liquid or sheet containing the fine fibrous cellulose of the present invention can be more effectively enhanced.

<Zantate group introduction process>
The step of producing the fine fibrous cellulose used in the step (A) may include a zantate group introduction step as an anionic group introduction step. In the zantate group introduction step, a cellulose fiber having a zantate group (zantate group-introduced fiber) can be obtained by substituting the hydroxyl group of the fiber raw material containing cellulose with a zantate group represented by the following formula (2).
―OCSS ⁻ M ^＋ …… (2)
Here, M ⁺ is at least one selected from hydrogen ions, monovalent metal ions, ammonium ions, aliphatic or aromatic ammonium ions.

In the zantate group introduction step, first, the fiber raw material containing cellulose is treated with an alkaline solution to obtain alkaline cellulose. Examples of the alkaline solution include an aqueous solution of an alkali metal hydroxide and an aqueous solution of an alkaline earth metal hydroxide. Above all, the alkaline solution is preferably an aqueous solution of an alkali metal hydroxide such as sodium hydroxide or potassium hydroxide, and particularly preferably an aqueous solution of sodium hydroxide. When the alkaline solution is an alkaline alkali metal hydroxide aqueous solution, the alkali metal hydroxide concentration in the alkali metal hydroxide aqueous solution is preferably 4% by mass or more, and more preferably 5% by mass or more. Further, the alkali metal hydroxide concentration in the aqueous alkali metal hydroxide solution is preferably 9% by mass or less. By setting the alkali metal hydroxide concentration to the above lower limit or higher, the mercerization of cellulose can be sufficiently promoted, and the amount of by-products generated during the subsequent zantate formation can be reduced, and as a result, it is possible to reduce the amount of by-products. The yield of the zantate group-introduced fiber can be increased. As a result, the defibration treatment described later can be performed more effectively. Further, by setting the alkali metal hydroxide concentration to the above upper limit value or less, it is possible to suppress the permeation of the alkali metal hydroxide aqueous solution into the crystal region of cellulose while promoting mercerization, so that the cellulose I The crystal structure of the mold can be easily maintained, and the yield of fine fibrous cellulose can be further increased.

The time of the alkali treatment is preferably 30 minutes or more, and more preferably 1 hour or more. The alkali treatment time is preferably 6 hours or less, and more preferably 5 hours or less. By setting the alkali treatment time within the above range, the final yield can be increased and the productivity can be increased.

It is preferable that the alkaline cellulose obtained by the above alkaline treatment is then solid-liquid separated to remove the aqueous solution as much as possible. As a result, the water content in the subsequent zantate treatment can be reduced and the reaction can be promoted. As a solid-liquid separation method, a general dehydration method such as centrifugation or filtration can be used. The concentration of the alkali metal hydroxide contained in the alkali cellulose after solid-liquid separation is preferably 3% by mass or more and 8% by mass or less with respect to the total mass of the alkali cellulose after solid-liquid separation.

In the zantate group introduction step, the zantate treatment step is performed after the alkali treatment. The xanthate treatment process by reacting carbon disulfide (CS ₂₎ in the alkali cellulose, (- ^O - Na ⁺⁾ group (-OCSS ^- Na ⁺⁾ to obtain a xanthate group introduction fibers based on. In the above, the metal ion introduced into the alkali cellulose is represented by Na ⁺ , but the same reaction proceeds with other alkali metal ions.

In the zantate treatment, it is preferable to supply 10% by mass or more of carbon disulfide with respect to the absolute dry mass of the cellulose in the alkaline cellulose. Further, in the zantate treatment, the contact time between carbon disulfide and alkaline cellulose is preferably 30 minutes or more, and more preferably 1 hour or more. When carbon disulfide comes into contact with the alkaline cellulose, zantate formation proceeds rapidly, but it takes time for the carbon disulfide to penetrate into the inside of the alkaline cellulose, so the reaction time is preferably set within the above range. On the other hand, the contact time between carbon disulfide and alkaline cellulose may be as long as 6 hours or less, which allows sufficient penetration into the dehydrated alkaline cellulose lumps and almost all the reactionable zantate. Can be completed.

The reaction temperature in the zantate treatment is preferably 46 ° C. or lower. By setting the reaction temperature within the above range, it becomes easy to suppress the decomposition of alkaline cellulose. Further, by setting the reaction temperature within the above range, it becomes easy to react uniformly, so that the formation of by-products can be suppressed, and further, the removal of the formed zantate groups can be suppressed.

The amount of the zantate group introduced in the zantate group introduction step is preferably 0.60 mmol / g or more, more preferably 0.70 mmol / g or more, and 0.80 mmol / g or more per 1 g (mass) of the fiber raw material. It is more preferably 1.00 mmol / g or more, and particularly preferably 1.20 mmol / g or more. The amount of the zantate group introduced is, for example, preferably 5.00 mmol / g or less, and more preferably 3.00 mmol / g or less per 1 g (mass) of the fiber raw material. The fact that the amount of the zantate group introduced in the zantate group introduction step is within the above range means that the amount of the substituent of the fine fibrous cellulose provided in the step (A) is within the above range. By setting the introduction amount of the zantate group within the above range, the introduction amount of the substituent of the fine fibrous cellulose used in the step (A) can be within the above range, and as a result, the fiber width is 10 nm or less. It becomes easy to produce fine fibrous cellulose. In addition, the transparency of the dispersion liquid or sheet containing the fine fibrous cellulose of the present invention can be more effectively enhanced.

<Washing process>
In the step of producing the fine fibrous cellulose used in the step (A), a washing step can be performed on the anionic group-introduced fiber, if necessary. The washing step is performed by washing the anionic group-introduced fibers 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 step of producing the fine fibrous cellulose used in the step (A), the fiber raw material may be treated with an alkali between the step of introducing an anionic group and the step of the defibration treatment described later. The alkaline treatment method is not particularly limited, and examples thereof include a method of immersing the anionic group-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 or a polar organic solvent exemplified by alcohol, 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 anionic group-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 anionic group-introduced fiber. Is more preferable.

In order to reduce the amount of the alkaline solution used in the alkaline treatment step, the anionic group-introduced fiber may be washed with water or an organic solvent after the anionic group 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 anionic group-introduced fiber with water or an organic solvent from the viewpoint of improving handleability.

<Acid treatment process>
In the step of producing the fine fibrous cellulose used in the step (A), the fiber raw material may be acid-treated between the step of introducing an anionic group and the defibration treatment step described later. For example, the anionic group 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 liquid 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 liquid, 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.

<Nitrogen removal treatment>
The step of producing the fine fibrous cellulose provided in the step (A) may further include a step of reducing the amount of nitrogen introduced into the fibrous cellulose and the amount of nitrogen present in the system (nitrogen removal treatment step). By reducing the amount of nitrogen, it is possible to obtain fine fibrous cellulose that can further suppress coloring. The nitrogen removal treatment step may be provided after the uniform dispersion treatment step in the step (B) described later, but is preferably provided before the uniform dispersion treatment step in the step (B) described later. Further, it is preferably provided before the defibration treatment step in the step (A) described later.

In the nitrogen removal treatment step, it is preferable to adjust the pH of the slurry containing the anionic group-introduced fiber to 10 or more and perform the heat treatment. In the heat treatment, the liquid temperature of the slurry is preferably 50 ° C. or higher and 100 ° C. or lower, and the heating time is preferably 15 minutes or longer and 180 minutes or lower. When adjusting the pH of the slurry containing the anionic group-introduced fiber, it is preferable to add an alkaline compound that can be used in the above-mentioned alkali treatment step to the slurry.

After the nitrogen removal treatment step, a washing step can be performed on the anionic group-introduced fiber, if necessary. The washing step is performed by washing the anionic group-introduced fibers with, for example, water or an organic solvent. Further, the number of cleanings performed in each cleaning step is not particularly limited.

<Defibration treatment>
The step of producing the fine fibrous cellulose used in the step (A) includes a defibration treatment step. As a result, fine fibrous cellulose having a substituent and having a fiber width of 1000 nm or less can be obtained. 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 disk type refiner, a conical refiner, and a twin shaft. A kneader, a vibration mill, a homomixer under high speed rotation, an ultrasonic disperser, a beater, or the like 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.

The treatment conditions in the defibration treatment step are not particularly limited, but when a high-pressure homogenizer is used, for example, the pressure during the treatment is preferably 1 MPa or more and 350 MPa or less, more preferably 10 MPa or more and 300 MPa or less, and further preferably 50 MPa or more and 250 MPa or less.

In the defibration treatment step, for example, it is preferable to dilute the anionic group-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 anionic group-introduced fiber in a dispersion medium may contain a solid content other than the anionic group-introduced fiber such as urea having a hydrogen bond property.

The fiber width of the fine fibrous cellulose after the defibration treatment applied to the step (A) is preferably 1 to 50 nm, more preferably 1 to 25 nm, still more preferably 1 to 15 nm. It is particularly preferably 1 to 10 nm.

Further, when the fine fibrous cellulose used in the step (A) is used as an aqueous dispersion having a concentration of 0.1% by mass and the nanofiber yield is calculated, the nanofiber yield is preferably 90% by mass or more. , 93% by mass or more, more preferably 96% by mass or more. The nanofiber yield may be 100% by mass. Here, the nanofiber yield is such that the fine fibrous cellulose dispersion having a concentration of 0.1% by mass is centrifuged at 12000 G for 10 minutes using a cooling high-speed centrifuge (Kokusan Co., Ltd., H-2000B). , It is a value measured from the cellulose concentration of the obtained supernatant liquid based on the following formula.
Nanofiber yield (mass%) = supernatant cellulose concentration (mass%) /0.1 × 100

Further, when the fine fibrous cellulose used in the step (A) is used as an aqueous dispersion having a concentration of 0.2% by mass, the haze of the aqueous dispersion is preferably 10% or less, preferably 5.0% or less. Is more preferable, and 3.0% or less is further preferable. The haze of the aqueous dispersion may be 0%. Here, the haze of the aqueous dispersion of fine fibrous cellulose is a value measured according to JIS K 7136: 2000 using a haze meter (HM-150, manufactured by Murakami Color Technology Research Institute). At the time of measurement, a glass cell for liquid (manufactured by Fujiwara Seisakusho, MG-40, backlight path) having an optical path length of 1 cm is used. The zero point measurement is performed with ion-exchanged water placed in the same glass cell, and the dispersion liquid to be measured is allowed to stand in an environment of 23 ° C. and a relative humidity of 50% for 24 hours before measurement, and the liquid temperature of the dispersion liquid is measured. Is 23 ° C.

By setting the fiber width of the fine fibrous cellulose used in the step (A), the nanofiber yield of the fine fibrous cellulose dispersion and the haze within the above ranges, the fine fibrous cellulose obtained through the step (B) It is possible to more effectively enhance the transparency when the fiber is used as a slurry or a sheet.

<Substituent removal treatment>
The method for producing fine fibrous cellulose of the present invention includes a step (A) of removing at least a part of the substituent from the fine fibrous cellulose having a substituent and having a fiber width of 1000 nm or less. In the present specification, the step of removing at least a part of the substituent from the fine fibrous cellulose is also referred to as a substituent removing treatment step.

Examples of the substituent removing treatment step include a step of heat-treating fine fibrous cellulose having a substituent and a fiber width of 1000 nm or less, a step of enzymatic treatment, a step of acid treatment, a step of alkali treatment and the like. These may be performed alone or in combination. Above all, the substituent removing treatment step is preferably a heat treatment step or an enzyme treatment step. By going through the above treatment step, at least a part of the substituent is removed from the fine fibrous cellulose having a substituent and a fiber width of 1000 nm or less, and the amount of the substituent introduced is less than 0.5 mmol / g. Fibrous cellulose can be obtained.

The substituent removing treatment step is preferably performed in the form of a slurry. That is, the substituent removing treatment step is a step of heat-treating a slurry having a substituent and containing fine fibrous cellulose having a fiber width of 1000 nm or less, an enzyme treatment step, an acid treatment step, and an alkali treatment step. Etc. are preferable. By carrying out the substituent removing treatment step in the form of a slurry, it is possible to prevent the coloring substances generated by heating and the like during the substituent removing treatment and the residual of the acid, alkali, salt and the like added or generated. This makes it possible to suppress coloring when the fine fibrous cellulose obtained through the step (B) is used as a slurry or a sheet. Further, when the salt derived from the substituent removed after the substituent removal treatment is performed, the salt removal efficiency can be improved.

When a slurry containing a fine fibrous cellulose having a substituent and a fiber width of 1000 nm or less is subjected to a substituent removal treatment, the concentration of the fine fibrous cellulose in the slurry is determined.
It is preferably 0.05% by mass or more, more preferably 0.1% by mass or more, and further preferably 0.2% by mass or more. The concentration of the fine fibrous cellulose in the slurry is preferably 20% by mass or less, more preferably 15% by mass or less, and further preferably 10% by mass or less. By setting the concentration of the fine fibrous cellulose in the slurry within the above range, the substituent removing treatment can be performed more efficiently. Further, by setting the concentration of the fine fibrous cellulose in the slurry within the above range, it is possible to prevent the coloring substances generated by heating during the substituent removal treatment and the residual of the acid, alkali, salt and the like added or generated. can. This makes it possible to suppress coloring when the fine fibrous cellulose obtained through the step (B) is used as a slurry or a sheet. Further, when the salt derived from the substituent removed after the substituent removal treatment is performed, the salt removal efficiency can be improved.

When the substituent removing treatment step is a step of heat-treating fine fibrous cellulose having a substituent and a fiber width of 1000 nm or less, the heating temperature in the heat-treating step is preferably 40 ° C. or higher. , 50 ° C. or higher, more preferably 60 ° C. or higher. The heating temperature in the heat treatment step is preferably 250 ° C. or lower, more preferably 230 ° C. or lower, and even more preferably 200 ° C. or lower. Above all, when the substituent contained in the fine fibrous cellulose used in the substituent removing treatment step is a phosphoroxo acid group or a sulfone group, the heating temperature in the heat treatment step is preferably 80 ° C. or higher, preferably 100 ° C. or higher. It is more preferable that the temperature is 120 ° C. or higher.

When the substituent removal treatment step is a heat treatment step, the heating device that can be used in the heat treatment step is not particularly limited, but is not particularly limited, but is a hot air heating device, a steam heating device, an electric heat heating device, a water heat heating device, and a thermal heating device. , Infrared heating device, Far infrared heating device, Microwave heating device, High frequency heating device, Stirring drying device, Rotating drying device, Disk drying device, Roll type heating device, Plate type heating device, Flow layer drying device, Band type drying device , A filtration drying device, a vibration flow drying device, an air flow drying device, and a vacuum drying device can be used. From the viewpoint of preventing evaporation, heating is preferably performed in a closed system, and from the viewpoint of further increasing the heating temperature, it is preferably performed in a pressure-resistant device or a container. The heat treatment may be a batch treatment, a batch continuous treatment, or a continuous treatment.

When the substituent removing treatment step is a step of enzymatically treating fine fibrous cellulose having a substituent and having a fiber width of 1000 nm or less, in the enzymatic treatment step, a phosphate ester hydrolyzing enzyme or a sulfate ester hydrolysis is performed. It is preferable to use an enzyme or the like.

In the enzyme treatment step, it is preferable to add the enzyme so that the enzyme activity is 0.1 nkat or more, more preferably 1.0 nkat or more, and 10 nkat or more to 1 g of fine fibrous cellulose. It is more preferable to add the enzyme so that it becomes. Further, it is preferable to add the enzyme so that the enzyme activity is 100,000 nkat or less with respect to 1 g of the fine fibrous cellulose, and it is more preferable to add the enzyme so that the enzyme activity is 50,000 nkat or less. More preferred. After adding the enzyme to the fine fibrous cellulose dispersion (slurry), it is preferable to carry out the treatment under the conditions of 0 ° C. or higher and lower than 50 ° C. for 1 minute or longer and 100 hours or shorter.

After the enzymatic reaction, a step of inactivating the enzyme may be provided. As a method of inactivating the enzyme, a method of adding an acid component or an alkaline component to the slurry treated with the enzyme to inactivate the enzyme, or raising the temperature of the slurry treated with the enzyme to 90 ° C. or higher to inactivate the enzyme. There is a method of deactivating.

When the substituent removing treatment step is a step of acid-treating fine fibrous cellulose having a substituent and a fiber width of 1000 nm or less, the acid treatment step is an acid that can be used in the above-mentioned acid treatment step. It is preferred to add the compound to the slurry.

When the substituent removing treatment step is a step of alkali-treating fine fibrous cellulose having a substituent and having a fiber width of 1000 nm or less, the alkali-treating step is an alkali that can be used in the above-mentioned alkali-treating step. It is preferable to add the compound to the slurry.

In the substituent removal treatment step, it is preferable that the substituent removal reaction proceeds uniformly. In order to proceed the reaction uniformly, for example, the slurry containing fine fibrous cellulose may be stirred, or the specific surface area of the slurry may be increased. As a method of stirring the slurry, a mechanical share from the outside may be given, or self-stirring may be promoted by increasing the liquid feeding rate of the slurry during the reaction.

Spacer molecules may be added in the substituent removal treatment step. The spacer molecule penetrates between the adjacent fine fibrous celluloses, thereby acting as a spacer for providing a fine space between the fine fibrous celluloses. By adding such a spacer molecule in the substituent removing treatment step, aggregation of fine fibrous cellulose after the substituent removing treatment can be suppressed. This makes it possible to more effectively enhance the transparency of the dispersion liquid or the sheet containing the fine fibrous cellulose.

The spacer molecule is preferably a water-soluble organic compound. Examples of the water-soluble organic compound include sugars, water-soluble polymers, urea and the like. Specific examples thereof include trehalose, urea, polyethylene glycol (PEG), polyethylene oxide (PEO), carboxymethyl cellulose, polyvinyl alcohol (PVA) and the like. In addition, as water-soluble organic compounds, alkyl methacrylate / acrylic acid copolymer, polyvinylpyrrolidone, sodium polyacrylate, propylene glycol, dipropylene glycol, polypropylene glycol, isoprene glycol, hexylene glycol, 1,3-butylene glycol, polyacrylamide. , Xanthan gum, guar gum, tamarind gum, carrageenan, locust bean gum, quince seed, alginic acid, purulan, carrageenan, pectin, cationized starch, raw starch, oxidized starch, etherified starch, esterified starch, starches such as amylose, glycerin , Diglycerin, polyglycerin, hyaluronic acid, metal salts of hyaluronic acid can also be used.

Further, a known pigment can be used as the spacer molecule. For example, kaolin (including clay), calcium carbonate, titanium oxide, zinc oxide, amorphous silica (containing colloidal silica), aluminum oxide, zeolite, sepiolite, smectite, synthetic smectite, magnesium silicate, magnesium carbonate, magnesium oxide, diatomaceous earth, Examples thereof include styrene-based plastic pigments, hydrotalcites, urea resin-based plastic pigments, and benzoguanamine-based plastic pigments.

<pH adjustment process>
When the substituent removing treatment step is performed in the form of a slurry, a step of adjusting the pH of the slurry containing the fine fibrous cellulose may be provided before the substituent removing treatment step. For example, when an anionic group is introduced into a cellulose fiber and the counterion of the anionic group is Na ⁺ , the slurry containing the fine fibrous cellulose after defibration shows weak alkalinity. When heating is performed in this state, monosaccharides, which are one of the coloring factors, may be generated due to the decomposition of cellulose. Therefore, it is preferable to adjust the pH of the slurry to 8 or less, and it is more preferable to adjust it to 6 or less. preferable. Further, since monosaccharides may be generated under acidic conditions as well, it is preferable to adjust the pH of the slurry to 3 or more, and more preferably to 4 or more.

Further, when the fine fibrous cellulose having a substituent is a fine fibrous cellulose having a phosphoric acid group, the phosphorus of the phosphate group is vulnerable to a nucleophilic attack from the viewpoint of improving the removal efficiency of the substituent. Is preferable. The vulnerable to nucleophilic attack is a state of neutralization degree 1 represented by cellulose-O-P (= O) (-O-H ⁺ ) ( ^{-O-Na +).} The pH of the slurry is preferably adjusted to 3 or more and 8 or less, and more preferably 4 or more and 6 or less.

The means for adjusting the pH is not particularly limited, and for example, an acid component or an alkaline component may be added to a slurry containing fine fibrous cellulose. The acid component may be either an inorganic acid or an organic acid, and examples of the inorganic acid include sulfuric acid, hydrochloric acid, nitrate, and phosphoric acid. Examples of the organic acid include malic acid, acetic acid, citric acid, malic acid, lactic acid, adipic acid, sebacic acid, stearic acid, maleic acid, succinic acid, tartrate acid, fumaric acid, gluconic acid and the like. The alkaline component may be an inorganic alkaline compound or an organic alkaline compound. Examples of the inorganic alkaline compound include lithium hydroxide, sodium hydroxide, potassium hydroxide, lithium carbonate, lithium hydrogencarbonate, potassium carbonate, potassium hydrogencarbonate, sodium carbonate, sodium hydrogencarbonate and the like. Examples of organic alkaline compounds include ammonia, hydrazine, methylamine, ethylamine, diethylamine, triethylamine, propylamine, dipropylamine, butylamine, diaminoethane, diaminopropane, diaminobutane, diaminopentane, diaminohexane, cyclohexylamine, aniline, and tetramethyl. Examples thereof include ammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, benzyltrimethylammonium hydroxide, pyridine, N, N-dimethyl-4-aminopyridine and the like.

Further, in the pH adjusting step, an ion exchange treatment may be performed to adjust the pH. In the ion exchange treatment, a strongly acidic cation exchange resin or a weakly acidic ion exchange resin can be used. By treating with an appropriate amount of cation exchange resin for a sufficient time, a slurry containing fine fibrous cellulose having a desired pH can be obtained. Further, in the pH adjusting step, the addition of an acid component or an alkaline component may be combined with an ion exchange treatment.

<Salt removal treatment>
After the substituent removal treatment step, it is preferable to perform a substituent removal treatment for the removed substituent-derived salt. By removing the salt derived from the substituent, it becomes easy to obtain fine fibrous cellulose capable of suppressing coloring. The means for removing the salt derived from the substituent is not particularly limited, and examples thereof include a washing treatment. The washing treatment is performed by washing the fine fibrous cellulose aggregated in the substituent removing treatment with, for example, water or an organic solvent. From the viewpoint of more effectively suppressing yellowing, the washing treatment is preferably performed by filtration dehydration, centrifugal dehydration, or centrifugal separation.

(Step (B))
The method for producing fine fibrous cellulose of the present invention includes a step (A) of removing at least a part of the substituent from the fine fibrous cellulose having a substituent and a fiber width of 1000 nm or less, and a step (A). Followed by a step (B) of performing uniform dispersion processing. The step (B) for uniform dispersion treatment is a step for uniform dispersion treatment of the fine fibrous cellulose obtained through the substituent removal treatment in step (A). In the step (A), at least a part of the fine fibrous cellulose is aggregated by subjecting the fine fibrous cellulose to a substituent removing treatment. The step (B) is a step of uniformly dispersing the fine fibrous cellulose aggregated in this way. The state in which the fine fibrous cellulose is uniformly dispersed in the step (B) means a state in which the fiber width of the fine fibrous cellulose is 10 nm or less. As described above, the fine fibrous cellulose obtained by the production method of the present invention has a fiber width of 10 nm or less even though the amount of substituents introduced is as low as 0.5 mmol / g or less. ..

In the step (B) of uniform dispersion processing, for example, a high-speed defibrator, a grinder (stone mill type crusher), a high-pressure homogenizer high-pressure collision type crusher, a ball mill, a bead mill, a disc type refiner, a conical refiner, a twin-screw kneader, a vibration mill, etc. A homomixer, an ultrasonic disperser, a beater, or the like under high-speed rotation can be used. Among the uniform dispersion processing devices, it is more preferable to use a high-speed defibrator and a high-pressure homogenizer.

The treatment conditions in the step (B) for the uniform dispersion treatment are not particularly limited, but it is preferable to increase the maximum moving speed of the fine fibrous cellulose during the treatment and the pressure during the treatment. In the high-speed defibrator, the peripheral speed is preferably 20 m / sec or more, more preferably 25 m / sec or more, and further preferably 30 m / sec or more. The high-pressure homogenizer can be used more preferably than the high-speed defibrator because the maximum moving speed of the fine fibrous cellulose during the treatment and the pressure during the treatment are higher. In the high-pressure homogenizer treatment, the pressure at the time of treatment is preferably 1 MPa or more, more preferably 10 MPa or more, further preferably 50 MPa or more, and particularly preferably 100 MPa or more. Further, in the high-pressure homogenizer treatment, the pressure at the time of treatment is preferably 350 MPa or less, more preferably 300 MPa or less, still more preferably 250 MPa or less.

In the step (B), the above-mentioned spacer molecule may be newly added. By adding such a spacer molecule in the uniform dispersion treatment step of the step (B), uniform dispersion of the fine fibrous cellulose can be performed more smoothly. This makes it possible to more effectively enhance the transparency of the dispersion liquid or the sheet containing the fine fibrous cellulose.

(Manufacturing method of laminated sheet)
The method for producing a laminated sheet of the present invention includes a step of forming a fiber layer containing fibrous cellulose having a substituent introduction amount of less than 0.5 mmol / g and a fiber width of 1 to 10 nm, and a step of forming the fiber layer on the fiber layer. It is preferable to include a step of applying the resin composition. Further, in the method for producing a laminated sheet of the present invention, fine fibrous cellulose containing fibrous cellulose having a substituent introduction amount of less than 0.5 mmol / g and a fiber width of 1 to 10 nm on a resin layer is used. It may include a step of applying a dispersion liquid.

When applying the resin composition on the fiber layer or forming the resin layer, it is preferable to apply the resin composition containing the resin and provide a drying step after forming the coating film.

As a method for producing a laminated sheet, in addition to the above-mentioned method, a method in which a resin layer is placed on a fiber layer and heat-pressed can also be mentioned. Another method is to install a fiber layer in a mold for injection molding, inject a heated and melted resin into the mold, and bond the resin layer to the fiber layer.

The step of forming a fiber layer containing fibrous cellulose having a substituent introduction amount of less than 0.5 mmol / g and a fiber width of 1 to 10 nm is a fine fibrous cellulose dispersion (fine fibrous cellulose-containing slurry). It is preferable to include a step of coating the substrate on the substrate or a step of making a fine fibrous cellulose dispersion. Further, when a fine fibrous cellulose dispersion liquid containing fibrous cellulose having a fiber width of 1000 nm or less is coated on the resin layer, the base material may be changed to the resin layer and the coating method described later may be adopted. good.

The fine fibrous cellulose dispersion (slurry containing fine fibrous cellulose) may contain arbitrary components contained in the fiber layer, and the nanofiber yield, haze, pH, etc. of the fine fibrous cellulose dispersion may be contained. The viscosity, the amount of free nitrogen, and the like are preferably within the numerical ranges described in the item of <fine fibrous cellulose> described above.

<Coating process>
In the step of coating the fine fibrous cellulose dispersion liquid (fine fibrous cellulose-containing slurry) on the base material (hereinafter, also referred to as the coating step), the fine fibrous cellulose dispersion liquid is applied on the base material, and this is applied. This is a step of obtaining a sheet by peeling off the fine fibrous cellulose-containing sheet formed by drying. By using a coating device and a long base material, sheets can be continuously produced. The concentration of the fine fibrous cellulose dispersion to be coated is not particularly limited, but is preferably 0.05% by mass or more and 5% by mass or less.

The quality of the base material used in the coating process is not particularly limited, but a material having high wettability to the fine fibrous cellulose dispersion may suppress shrinkage of the sheet during drying, but is formed after drying. It is preferable to select a sheet that can be easily peeled off. Of these, a resin plate or a metal plate is preferable, but it is not particularly limited. For example, resin plates such as acrylic plates, polyethylene terephthalate plates, vinyl chloride plates, polystyrene plates and polyvinylidene chloride plates, metal plates such as aluminum plates, zinc plates, copper plates and iron plates, and those whose surfaces are oxidized, stainless steel. A plate, brass plate, etc. can be used.

In the coating process, when the viscosity of the fine fibrous cellulose dispersion is low and it develops on the base material, it is used for blocking on the base material in order to obtain a fine fibrous cellulose-containing sheet having a predetermined thickness and basis weight. The frame may be fixed and used. The quality of the dammed frame is not particularly limited, but it is preferable to select one in which the end portion of the sheet to be attached after drying can be easily peeled off. Of these, those obtained by molding a resin plate or a metal plate are preferable, but are not particularly limited. For example, resin plates such as acrylic plates, polyethylene terephthalate plates, vinyl chloride plates, polystyrene plates and polyvinylidene chloride plates, metal plates such as aluminum plates, zinc plates, copper plates and iron plates, and those whose surfaces are oxidized, stainless steel. Molded plates, brass plates, etc. can be used.

As the coating machine for applying the fine fibrous cellulose dispersion liquid, for example, a bar coater, a roll coater, a gravure coater, a die coater, a curtain coater, an air doctor coater and the like can be used. A bar coater, a die coater, a curtain coater, and a spray coater are preferable because the thickness can be made more uniform.

The coating temperature is not particularly limited, but is preferably 20 ° C. or higher and 45 ° C. or lower. When the coating temperature is at least the above lower limit value, the fine fibrous cellulose dispersion liquid can be easily applied, and when it is at least the above upper limit value, volatilization of the dispersion medium during coating can be suppressed.

In the coating step, it is preferable to coat the fine fibrous cellulose dispersion so that the finished basis weight of the sheet is 10 g / m ² or more and 100 g / m ^{2 or less.} By coating so that the basis weight is within the above range, a fiber layer having excellent strength can be obtained.

The step of manufacturing the fine fibrous cellulose-containing sheet preferably includes a step of drying the fine fibrous cellulose dispersion coated on the base material. The drying method is not particularly limited, but may be either a non-contact drying method or a method of drying while restraining the sheet, and these may be combined.

The non-contact drying method is not particularly limited, but a method of heating and drying with hot air, infrared rays, far infrared rays or near infrared rays (heat drying method) and a method of vacuum drying (vacuum drying method) are applied. Can be done. 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 can be performed using an infrared device, a far infrared device or a near infrared device, but is not particularly limited. The heating temperature in the heat drying method is not particularly limited, but is preferably 20 ° C. or higher and 150 ° C. or lower, and more preferably 25 ° C. or higher and 105 ° C. or lower. When the heating temperature is at least the above lower limit value, the dispersion medium can be rapidly volatilized, and when it is at least the above upper limit value, the cost required for heating can be suppressed and the discoloration of fine fibrous cellulose can be suppressed due to heat. ..

After drying, the obtained fine fibrous cellulose-containing sheet is peeled off from the base material. When the base material is a sheet, the fine fibrous cellulose-containing sheet and the base material are wound while being laminated to form fine fibers. The fine fibrous cellulose-containing sheet may be peeled off from the process substrate immediately before the use of the cellulose-containing sheet. In this way, a fine fibrous cellulose-containing sheet to be a fiber layer can be obtained.

In the step of applying the resin composition on the fiber layer, it is preferable to apply the resin composition to the surface of the fine fibrous cellulose-containing sheet on the side peeled from the base material. Thereby, the interlayer adhesion between the fiber layer and the resin layer can be further enhanced.

<Papermaking process>
The step of manufacturing the fine fibrous cellulose-containing sheet to be the fiber layer may include a step of making a papermaking of the fine fibrous cellulose dispersion. Examples of the paper machine in the paper making process 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, known papermaking such as hand papermaking may be performed.

In the papermaking process, the fine fibrous cellulose dispersion is filtered on a wire and dehydrated to obtain a wet paper sheet, which is then pressed and dried to obtain a sheet. The concentration of the fine fibrous cellulose dispersion is not particularly limited, but is preferably 0.05% by mass or more and 5% by mass or less. When the fine fibrous cellulose dispersion is filtered and dehydrated, the filter cloth at the time of filtration is not particularly limited, but it is important that the fine fibrous cellulose does not pass through and the filtration rate does not become too slow. The filter cloth is not particularly limited, but a sheet made of an organic polymer, a woven fabric, and a porous membrane are preferable. The organic polymer is not particularly limited, but non-cellulosic organic polymers such as polyethylene terephthalate, polyethylene, polypropylene, and polytetrafluoroethylene (PTFE) are preferable. Specific examples thereof include a porous membrane of polytetrafluoroethylene having a pore size of 0.1 μm or more and 20 μm or less, for example, 1 μm, polyethylene terephthalate having a pore diameter of 0.1 μm or more and 20 μm or less, for example, 1 μm, or a polyethylene woven fabric, but the present invention is not particularly limited.

The method for producing a sheet from the fine fibrous cellulose dispersion is not particularly limited, and examples thereof include a method using the production apparatus described in WO2011 / 013567. This manufacturing device discharges the fine fibrous cellulose dispersion onto the upper surface of the endless belt, squeezes the dispersion medium from the discharged fine fibrous cellulose dispersion to generate a web, and dries the web. It has a drying section to produce 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 that can be used in the present invention is not particularly limited, and examples thereof include a dehydration method that is normally used in the production of paper. Is preferable. Further, the drying method is not particularly limited, and examples thereof include methods used in the production of paper, and for example, methods such as a cylinder dryer, a Yankee dryer, hot air drying, a near infrared heater, and an infrared heater are preferable.

(Laminated body)
The present invention may relate to a laminated body formed by laminating the above-mentioned laminated sheet and an adherend. When the adherend is arranged on the resin layer side of the laminated sheet, the resin layer in the laminated sheet may function as an adhesive layer. Examples of the adherend include an organic film (hereinafter, also referred to as an organic layer) and an inorganic film (hereinafter, also referred to as an inorganic layer). Above all, the laminated body of the present invention is preferably a laminated body formed by laminating the above-mentioned laminated sheet and an organic film. Examples of the organic film include a resin film, a resin plate, a resin molded body, and the like.

A resin film, a resin plate, and a resin molded body (hereinafter, also simply referred to as a resin film) are layers 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 film. The content of the resin component 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 film. % Or more is particularly preferable. The content of the resin component may be 100% by mass with respect to the total mass of the resin film.

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

Examples of the synthetic resin include polyolefin resin, cyclic olefin resin, polycarbonate resin, polyethylene terephthalate resin, polyethylene naphthalate resin, polyimide resin, polystyrene resin, acrylic resin and the like. Among them, the synthetic resin is preferably a polyolefin resin, and preferably has at least one selected from a polyethylene resin and a polypropylene resin.

The method for forming the organic layer is not particularly limited, and examples thereof include a coating method, an injection molding method, and a heating and pressurizing method. In the coating method, it is preferable that the resin composition forming the organic layer is coated on the resin layer of the laminated sheet and then heat-cured or photo-cured. Further, in the heating and pressurizing method, it is preferable to heat-press the resin film in a state of being laminated on the resin layer of the laminated sheet. The heat pressing conditions at this time can be appropriately selected with reference to the glass transition temperature of the resin film and the like.

The substance constituting the inorganic layer is not particularly limited, and is, for example, aluminum, silicon, magnesium, zinc, tin, nickel, titanium; these oxides, carbides, nitrides, oxide carbides, oxide nitrides, or oxide carbides. Objects; or mixtures thereof. From the viewpoint that high moisture resistance can be stably maintained, silicon oxide, silicon nitride, silicon oxide carbide, silicon nitride, silicon oxide, aluminum oxide, aluminum nitride, aluminum oxide, aluminum nitride, or any of these. Mixtures are preferred.

The method for forming the inorganic layer is not particularly limited, and examples thereof include a chemical vapor deposition (CVD) and a physical vapor deposition (PVD). Specific examples of the CVD method include plasma CVD using plasma, catalytic chemical vapor deposition (Cat-CVD) for catalytically pyrolyzing a material gas using a heating catalyst, and the like. Specific examples of the PVD method include vacuum deposition, ion plating, sputtering and the like. Further, as a method for forming the inorganic layer, an atomic layer deposition method (ALD) can also be adopted. The ALD method is a method of forming a thin film in atomic layer units by alternately supplying the raw material gas of each element constituting the film to be formed to the surface on which the layer is formed.

(Use)
The laminated sheet of the present invention is a transparent laminated sheet having high mechanical strength and suppressed coloring. From the viewpoint of utilizing such excellent optical characteristics, it is suitable for optical members. For example, it can be used for various display devices, various solar cells, and other light-transmitting substrates. Further, the laminated 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.

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>
[Phosphorylation]
Hardwood pulp (dry sheet) made by Oji Paper was used as the raw material pulp. The raw material pulp was subjected to phosphorylation 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 chemical-impregnated pulp. Next, the obtained chemical-impregnated pulp was heated in a hot air drying device at 165 ° C. for 250 seconds to introduce a phosphate group into the cellulose in the pulp to obtain a phosphorylated pulp.

[Washing process]
Then, the obtained phosphorylated pulp was washed. The washing 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. went. When the electrical conductivity of the filtrate became 100 μS / cm or less, the washing end point was set.

[Neutralization treatment]
Next, the phosphorylated pulp after washing was neutralized 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 a phosphorylated pulp that had been neutralized. Next, the phosphorylated pulp after the neutralization treatment was subjected to the above washing treatment.

The infrared absorption spectrum of the resulting phosphorus oxo oxide pulp 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 processing]
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 with a wet atomizing device (manufactured by Sugino Machine Limited, Starburst) 6 times at a pressure of 200 MPa to obtain a fine fibrous cellulose dispersion containing fine fibrous cellulose. By X-ray diffraction, it was confirmed that this fine fibrous cellulose maintained the cellulose type I crystal. The amount of phosphoric acid group (first dissociated acid amount, strong acid group amount) measured by the measuring method described in the measurement of [phosphoroxo acid group amount] described later was 1.45 mmol / g. The total amount of dissociated acid was 2.45 mmol / g.

<Manufacturing example 2>
After the washing treatment and the neutralization treatment of the phosphorylated pulp, a fine fibrous cellulose dispersion containing the phosphorylated pulp and the fine fibrous cellulose was obtained in the same manner as in Production Example 1 except that the following nitrogen removal treatment was performed.

[Nitrogen removal treatment]
Ion-exchanged water was added to the phosphorylated pulp to prepare a slurry having a solid content concentration of 4% by mass. A 48% by mass sodium hydroxide aqueous solution was added to the slurry to adjust the pH to 13.4, and the slurry was heated at a liquid temperature of 85 ° C. for 1 hour. Then, the pulp slurry is dehydrated, and the pulp dispersion obtained by pouring 10 L of ion-exchanged water into 100 g (absolute dry mass) of phosphorylated pulp is stirred so that the pulp is uniformly dispersed, and filtered and dehydrated. The excess sodium hydroxide was removed by repeating. When the electrical conductivity of the filtrate became 100 μS / cm or less, the end point of removal was set.

The infrared absorption spectrum of the resulting phosphorus oxo oxide pulp 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, it was confirmed by X-ray diffraction that the obtained fine fibrous cellulose maintained the cellulose type I crystal. The amount of phosphate groups (first dissociated acid amount, strong acid group amount) measured by the measuring method described in [Measurement of phosphorus oxo acid group amount] described later was 1.35 mmol / g. The total amount of dissociated acid was 2.30 mmol / g.

<Manufacturing example 3>
[Subphosphorylation treatment]
The same operation 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 in the phosphorylation treatment, and the fine fibers containing phosphorous pulp and fine fibrous cellulose were used. A phosphorous acid dispersion was obtained.

The infrared absorption spectrum of the phosphorylated pulp thus obtained was measured using FT-IR. As a result, ^{P = O-based absorption of the phosphonic acid group, which is a metamorphic form of the phosphite group, was observed near 1210 cm -1} , and a (sub) phosphorous acid group (phosphonic acid group) was added to the pulp. It was confirmed that there was. Further, it was confirmed by X-ray diffraction that the obtained fine fibrous cellulose maintained the cellulose type I crystal. The (sub) phosphoric acid group amount (first dissociated acid amount) measured by the measuring method described in [Measurement of Phosphoric Acid Group Amount] described later is 1.51 mmol / g, and the total dissociated acid amount is. It was 1.54 mmol / g.

<Manufacturing example 4>
[Sulfation treatment]
In the phosphorylation treatment, 38 parts by mass of amide sulfuric acid (sulfamic acid) was used instead of ammonium dihydrogen phosphate, and the same operation as in Production Example 1 was carried out except that the heating time was extended to 19 minutes. A fine fibrous cellulose dispersion containing fine fibrous cellulose was obtained.

The infrared absorption spectrum of the sulfated pulp thus obtained was measured using FT-IR. As a result, ^{absorption based on a sulfate group (sulfone group) was observed in the vicinity of 1220-1260 cm-1} , and it was confirmed that a sulfate group (sulfone group) was added to the pulp. Further, it was confirmed by X-ray diffraction that the obtained fine fibrous cellulose maintained the cellulose type I crystal. The amount of sulfone groups measured by the measuring method described in [Measurement of Sulfone Group Amount] described later was 1.12 mmol / g.

<Manufacturing example 5>
The same operation as in Production Example 1 was carried out except that the following zantate treatment was performed instead of the phosphorylation treatment to obtain a fine fibrous cellulose dispersion containing the zantate pulp and fine fibrous cellulose.

[Zantate processing]
To 100 parts by mass (absolute dry mass) of raw material pulp (dissolving pulp of broadleaf tree (dry sheet) made by Oji Paper), 2500 parts by mass of 8.5 mass% sodium hydroxide aqueous solution was added, and the mixture was stirred at room temperature for 3 hours. Alkaline treatment was performed. The pulp after the alkali treatment was separated into solid and liquid by centrifugation (filter cloth 400 mesh, 3000 rpm for 5 minutes) to obtain a dehydrated product of alkaline cellulose. To 10 parts by mass (absolute dry mass) of the obtained alkaline cellulose, 3.5 parts by mass of carbon disulfide was added, and the sulfurization reaction was allowed to proceed at room temperature for 4.5 hours to carry out a zantate treatment.

By X-ray diffraction, it was confirmed that the obtained fine fibrous cellulose maintained the cellulose type I crystal. The amount of zantate group measured by the measuring method described in [Measurement of Zantate Group Amount] described later was 1.73 mmol / g.

<Manufacturing example 6>
Ion-exchanged water was added to the raw material pulp (hardwood pulp (dry sheet) made by Oji Paper Co., Ltd.) to prepare a slurry having a solid content concentration of 2% by mass. This slurry was treated 30 times at a pressure of 200 MPa with a wet atomizer (Sugino Machine Limited, Starburst) to obtain a cellulose dispersion containing coarse fibrous cellulose.

[measurement]
[Measurement of haze of dispersion]
To measure the haze of the dispersion, dilute the fibrous cellulose dispersion with ion-exchanged water to 0.2% by mass, and then use a haze meter (HM-150, manufactured by Murakami Color Technology Research Institute) to measure the optical path length. Measurements were made in accordance with JIS K 7136: 2000 using a 1 cm liquid glass cell (manufactured by Fujiwara Seisakusho, MG-40, backlit path). The zero point measurement was performed with ion-exchanged water contained in the same glass cell. The dispersion to be measured was allowed to stand in an environment of 23 ° C. and a relative humidity of 50% for 24 hours before the measurement. The liquid temperature of the dispersion liquid at the time of measurement was 23 ° C.

[Measurement of nanofiber yield]
The yield of nanofibers after centrifuging the fibrous cellulose dispersion was measured by the method described below. The nanofiber yield is an index of the yield of fine fibrous cellulose, and the higher the nanofiber yield, the higher the yield of fine fibrous cellulose. Each dispersion was adjusted to a cellulose concentration of 0.1% by mass, and centrifuged at 12000 G for 10 minutes using a cooling high-speed centrifuge (Kokusan Co., Ltd., H-2000B). The obtained supernatant was collected, and the cellulose concentration in the supernatant was measured. The yield of fine fibrous cellulose was determined based on the following formula.
Nanofiber yield (mass%) = supernatant cellulose concentration (mass%) /0.1 × 100

[Measurement of nitrogen content]
The total amount of nitrogen contained in the fibrous cellulose and free nitrogen contained in the fibrous cellulose dispersion was measured by the method described below. Each dispersion was adjusted to a solid content concentration of 1% by mass and decomposed by the Kjeldahl method (JIS K 0102: 2016 44.1). After decomposition, the amount of ammonium ions (mmol) was measured by cation chromatography and divided by the amount of cellulose (g) used for the measurement to calculate the nitrogen content (mmol / g).

<Example 1>
[Substituent removal treatment (high temperature heat treatment)]
A 20% by mass citric acid aqueous solution was added to the fine fibrous cellulose dispersion obtained in Production Example 1 to adjust the pH of the dispersion to 5.5. The obtained slurry was placed in a pressure-resistant container and heated at a liquid temperature of 160 ° C. for 15 minutes until the amount of phosphoric acid groups reached 0.08 mmol / g. The formation of fine fibrous cellulose aggregates was confirmed by this operation.

[Washing of slurry after removal of substituents]
The slurry was washed by repeating the operation of adding ion-exchanged water in the same amount as the slurry to make a slurry having a solid content concentration of about 1% by mass, stirring the slurry, and then filtering and dehydrating the slurry. .. When the electrical conductivity of the filtrate became 10 μS / cm or less, ion-exchanged water was added again to obtain a slurry of about 1% by mass, and the slurry was allowed to stand for 24 hours. The operation of further filtering and dehydrating was repeated from there, and the time when the electrical conductivity of the filtrate became 10 μS / cm or less was set as the washing end point. Ion-exchanged water was added to the obtained fine fibrous cellulose aggregate to remove substituents, and then a slurry was obtained. The solid content concentration of this slurry was 1.7% by mass.

[Uniform dispersion of slurry after removal of substituents]
Ion-exchanged water was added to the obtained slurry after removing the substituents to prepare a slurry having a solid content concentration of 1.0% by mass. This slurry had a pH of 5.5. The treatment was carried out three times at a pressure of 200 MPa with a wet atomizer (Sugino Machine Limited, Starburst) to obtain a substituent-removed fine fibrous cellulose dispersion containing a substituent-removed fine fibrous cellulose. The number average fiber width of the substituent-removed fine fibrous cellulose measured in [Measurement of fiber width] described later was 4 nm, and the ratio of the fiber width of 10 nm or less was 98%.

[Preparation of sheet 1]
Acetacetyl group-modified polyvinyl alcohol (Gosenex 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 was obtained.

The substituent-removed fine fibrous cellulose dispersion and the above polyvinyl alcohol aqueous solution were diluted with ion-exchanged water so that the solid content concentration was 0.6% by mass. Next, the diluted polyvinyl alcohol aqueous solution was mixed with 70 parts by mass of the diluted fine fiber-like cellulose dispersion to obtain 30 parts by mass to obtain a mixed solution. Further, the mixed solution was weighed so that the finished basis weight of the sheet was 37.5 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 from the acrylic plate to obtain a sheet containing fine fibrous cellulose from which substituents were removed. The thickness of the sheet was 25 μm. The surface pH of the fine fibrous cellulose-containing sheet from which the substituent was removed before laminating the resin layer was 4.8.

[Formation of resin layer]
100 parts by mass of an acrylic resin graft-polymerized with an acryloyl group having a hydroxyl group (Acryt 8KX-012C, manufactured by Taisei Fine Chemicals Co., Ltd., solid content concentration is 39% by mass) and 38 parts by mass of a polyisocyanate compound (manufactured by Asahi Kasei Chemicals Co., Ltd., TPA-100). And 100 parts by mass of methyl ethyl ketone were mixed to obtain a resin composition. Next, the resin composition was applied to one surface of the substituent-removed fine fibrous cellulose-containing sheet with a bar coater, and then heated at 100 ° C. for 1 hour to be cured, and the resin layer was laminated. Further, a resin layer was laminated on the other surface of the substituent-removed fine fibrous cellulose-containing sheet by the same procedure. The thickness of the resin layer was 5 μm per side. By the above procedure, a laminated sheet in which resin layers were laminated on both sides of a sheet containing fine fibrous cellulose from which substituents were removed was obtained.

<Example 2>
A laminated sheet was obtained in the same manner as in Example 1 except that the substituent removing treatment was carried out at a liquid temperature of 85 ° C. for 5 days. The surface pH of the fine fibrous cellulose-containing sheet from which the substituent was removed before laminating the resin layer was 4.7.

<Example 3>
The fine fibrous cellulose dispersion obtained in Production Example 1 was diluted to 0.7% by mass, subjected to a substituent removing treatment, and after a washing treatment step after removing the substituent, the obtained fine fibrous cellulose aggregate was obtained. A laminated sheet was obtained in the same manner as in Example 1 except that ion-exchanged water was added to the mixture to prepare a slurry having a solid content concentration of 1.0% by mass. The surface pH of the fine fibrous cellulose-containing sheet from which the substituent was removed before laminating the resin layer was 4.8.

<Example 4>
The substituent removal treatment was carried out at a liquid temperature of 160 ° C. for 40 minutes, and a laminated sheet was obtained in the same manner as in Example 1 except that the phosphate group amount was 0.05 mmol / g. The surface pH of the fine fibrous cellulose-containing sheet from which the substituent was removed before laminating the resin layer was 4.8.

<Example 5>
A laminated sheet was obtained in the same manner as in Example 1 except that the substituent removing treatment was carried out at a liquid temperature of 150 ° C. for 15 minutes until the amount of phosphate groups became about 0.21 mmol / g. The surface pH of the fine fibrous cellulose-containing sheet from which the substituent was removed before laminating the resin layer was 4.9.

<Example 6>
A laminated sheet was obtained in the same manner as in Example 1 except that the substituent removing treatment was carried out at a liquid temperature of 140 ° C. for 20 minutes until the amount of phosphate groups became about 0.40 mmol / g. The surface pH of the fine fibrous cellulose-containing sheet from which the substituent was removed before laminating the resin layer was 4.7.

<Example 7>
Laminated sheet in the same manner as in Example 1 except that the pH of the fine fibrous cellulose dispersion to be subjected to the substituent removal treatment was adjusted to 2.4, and the pH was adjusted to 5.5 after the cleaning treatment of the slurry after the substituent removal treatment. Got The amount of phosphoric acid group after removal of the substituent was 0.22 mmol / g. The surface pH of the fine fibrous cellulose-containing sheet from which the substituent was removed before laminating the resin layer was 4.7.

<Example 8>
The fine fibrous cellulose dispersion to be subjected to the substituent removal treatment was heat-treated without adjusting the pH, and after the substituent was removed and the slurry was washed, the pH was adjusted to 5.5, except that the pH was adjusted to 5.5. I got a sheet. The amount of phosphoric acid group after removal of the substituent was 0.29 mmol / g. The surface pH of the fine fibrous cellulose-containing sheet from which the substituent was removed before laminating the resin layer was 4.9.

<Example 9>
The uniform dispersion of the slurry after removing the substituents was carried out in the same manner as in Example 1 except that the slurry was uniformly dispersed for 180 minutes under the condition of a peripheral speed of 34 m / sec using a high-speed defibrator (Clearmix-11S manufactured by M-Technique). A laminated sheet was obtained. The surface pH of the fine fibrous cellulose-containing sheet from which the substituent was removed before laminating the resin layer was 4.8.

<Example 10>
A laminated sheet was obtained in the same manner as in Example 1 except that the substituent removal treatment was performed by the following enzyme treatment instead of the heat treatment, and the slurry was washed after the substituent removal by the following method. The surface pH of the fine fibrous cellulose-containing sheet from which the substituent was removed before laminating the resin layer was 4.8.

[Substituent removal treatment (enzyme treatment)]
A 20% by mass citric acid aqueous solution was added to the obtained fine fibrous cellulose dispersion to adjust the slurry to pH 5.5. Acid phosphatase (Sumiteam PM manufactured by Shin Nihon Kagaku Kogyo Co., Ltd.) was added to the obtained slurry so as to be 3 parts by mass with respect to 100 parts by mass of fine fibrous cellulose, and the enzyme was added to the obtained slurry in a hot water bath at 37 ° C. for 2.5 hours. Processing was performed. The formation of fine fibrous cellulose aggregates was confirmed by this operation.

[Washing treatment of slurry after removal of substituents by enzyme treatment]
The obtained slurry after removing the substituents contains a 1/5 volume of a strong basic ion exchange resin (Amberjet 4400; Organo Corporation, conditioned) and a weakly acidic ion exchange resin (Amberlite IRC76; Organo Corporation, conditioning). After adding (finished) and shaking for 1 hour, the slurry was washed by pouring it onto a mesh having an opening of 90 μm to separate the resin and the slurry.

<Example 11>
A laminated sheet was obtained in the same manner as in Example 1 except that the fine fibrous cellulose dispersion obtained in Production Example 2 was used instead of the fine fibrous cellulose dispersion obtained in Production Example 2. The surface pH of the fine fibrous cellulose-containing sheet from which the substituent was removed before laminating the resin layer was 4.7.

<Example 12>
A laminated sheet was obtained in the same manner as in Example 1 except that the fine fibrous cellulose dispersion obtained in Production Example 3 was used instead of the fine fibrous cellulose dispersion obtained in Production Example 3. The surface pH of the fine fibrous cellulose-containing sheet from which the substituent was removed before laminating the resin layer was 4.7.

<Example 13>
A laminated sheet was obtained in the same manner as in Example 1 except that the fine fibrous cellulose dispersion obtained in Production Example 4 was used instead of the fine fibrous cellulose dispersion obtained in Production Example 4. The surface pH of the fine fibrous cellulose-containing sheet from which the substituent was removed before laminating the resin layer was 4.8.

<Example 14>
Instead of the fine fibrous cellulose dispersion obtained in Production Example 1, the fine fibrous cellulose dispersion obtained in Production Example 5 was used. Further, instead of the substituent removing treatment (high temperature heat treatment), a substituent removing treatment (low temperature heat treatment) described later was performed. A laminated sheet was obtained in the same manner as in Example 1. The surface pH of the fine fibrous cellulose-containing sheet from which the substituent was removed before laminating the resin layer was 6.9.

[Removal of substituents (low temperature heat treatment)]
The obtained fine fibrous cellulose dispersion was heated at a liquid temperature of 40 ° C. for 45 minutes until the amount of zantate groups became less than 0.08 mmol / g.

<Example 15>
In [Formation of Resin Layer], a laminated sheet was obtained in the same manner as in Example 1 except that the resin layer was formed only on one surface of the substituent-removed fine fibrous cellulose-containing sheet. The surface pH of the fine fibrous cellulose-containing sheet from which the substituent was removed before laminating the resin layer was 4.8.

<Example 16>
In [Preparation of Sheet 1], polyethylene oxide diluted to a solid content concentration of 0.6% by mass instead of a polyvinyl alcohol aqueous solution having a solid content concentration of 0.6% by mass (manufactured by Sumitomo Seika Chemical Co., Ltd., PEO). -18; viscosity average molecular weight 4.3 million to 4.8 million) was used. A laminated sheet was obtained in the same manner as in Example 1. The surface pH of the fine fibrous cellulose-containing sheet from which the substituent was removed before laminating the resin layer was 4.8.

<Example 17>
A laminated sheet was obtained in the same manner as in Example 1 except that the procedure of [formation of the resin layer] was changed as follows. 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 to obtain a resin composition. Next, the resin composition was applied to one surface of the substituent-removed fine fibrous cellulose-containing sheet with a bar coater, and then heated at 100 ° C. for 1 hour to be cured, and the resin layer was laminated. Further, a resin layer was laminated on the other surface of the substituent-removed fine fibrous cellulose-containing sheet by the same procedure. The thickness of the resin layer was 5 μm per side. The surface pH of the fine fibrous cellulose-containing sheet from which the substituent was removed before laminating the resin layer was 4.8.

<Example 18>
In [Preparation 1 of Sheet], 40 parts by mass of the diluted polyvinyl alcohol aqueous solution was mixed with 40 parts by mass of the diluted substituent-removed fine fibrous cellulose dispersion liquid to obtain a mixed liquid. Further, the mixed solution was weighed so that the finished basis weight of the sheet was 35.0 g / m ² , and developed on a commercially available acrylic plate. A laminated sheet was obtained in the same manner as in Example 17. The thickness of the substituent-removed fine fibrous cellulose-containing sheet was 25 μm. The surface pH of the fine fibrous cellulose-containing sheet from which the substituent was removed before laminating the resin layer was 3.2.

<Example 19>
In [Preparation of Sheet 1], the diluted polyvinyl alcohol aqueous solution was mixed with 10 parts by mass of the diluted fine fiber-like cellulose dispersion liquid to obtain 90 parts by mass to obtain a mixed liquid. Further, the mixed solution was weighed so that the finished basis weight of the sheet was 31.0 g / m ² , and developed on a commercially available acrylic plate. A laminated sheet was obtained in the same manner as in Example 17. The thickness of the substituent-removed fine fibrous cellulose-containing sheet was 25 μm. The surface pH of the fine fibrous cellulose-containing sheet from which the substituent was removed before laminating the resin layer was 3.0.

<Example 20>
In [Preparation of Sheet 1], the mixed solution was weighed so that the finished basis weight of the sheet was 105.0 g / m ² , and laminated in the same manner as in Example 17 except that it was developed on a commercially available acrylic plate. I got a sheet. The thickness of the substituent-removed fine fibrous cellulose-containing sheet was 70 μm. The surface pH of the fine fibrous cellulose-containing sheet from which the substituent was removed before laminating the resin layer was 4.8.

<Example 21>
A laminated sheet was obtained in the same manner as in Example 20 except that the procedure of [formation of the resin layer] was changed as follows. 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, 0.75 methacryloxypropyltrimethoxysilane (SILQUEST A-174 SILANE, manufactured by Momentive Performance Materials Japan), which is an organosilicon compound (silane coupling agent), was added to the resin coating liquid as an adhesion aid. Parts were added by mass and mixed to obtain a resin composition. Next, the resin composition was applied to one surface of the substituent-removed fine fibrous cellulose-containing sheet with a bar coater, and then heated at 100 ° C. for 1 hour to be cured, and the resin layer was laminated. Further, a resin layer was laminated on the other surface of the substituent-removed fine fibrous cellulose-containing sheet by the same procedure. The thickness of the resin layer was 5 μm per side. The surface pH of the fine fibrous cellulose-containing sheet from which the substituent was removed before laminating the resin layer was 4.8.

<Comparative Example 1>
[Sheet preparation 1] is the same as the above [Sheet preparation 1] except that the fine fibrous cellulose dispersion obtained in Production Example 1 is used instead of the substituent-removing fine fibrous cellulose dispersion. The operation was carried out to obtain a fine fibrous cellulose-containing sheet. The surface pH of the fine fibrous cellulose-containing sheet before laminating the resin layer was 7.3.

<Comparative Example 2>
A fine fibrous cellulose-containing sheet was obtained in the same manner as in Comparative Example 1 except that the fine fibrous cellulose dispersion obtained in Production Example 3 was used. The surface pH of the fine fibrous cellulose-containing sheet before laminating the resin layer was 7.2.

<Comparative Example 3>
A fine fibrous cellulose-containing sheet was obtained in the same manner as in Comparative Example 1 except that the fine fibrous cellulose dispersion obtained in Production Example 4 was used. The surface pH of the fine fibrous cellulose-containing sheet before laminating the resin layer was 6.9.

<Comparative Example 4>
A fine fibrous cellulose-containing sheet was obtained in the same manner as in Comparative Example 1 except that the fine fibrous cellulose dispersion obtained in Production Example 5 was used. The surface pH of the fine fibrous cellulose-containing sheet before laminating the resin layer was 6.3.

<Comparative Example 5>
The substituent removal treatment was carried out at a liquid temperature of 140 ° C. for 10 minutes, and a laminated sheet was obtained in the same manner as in Example 1 except that the phosphate group amount was about 0.74 mmol / g. The surface pH of the fine fibrous cellulose-containing sheet from which the substituent was removed before laminating the resin layer was 4.9.

<Comparative Example 6>
A laminated sheet was obtained in the same manner as in Comparative Example 1 except that the cellulose dispersion liquid containing the coarse fibrous cellulose obtained in Production Example 6 was used. The surface pH of the coarse fibrous cellulose-containing sheet before laminating the resin layer was 5.8.

<Comparative Example 7>
A laminated sheet was obtained in the same manner as in Example 1 except that the slurry was not uniformly dispersed after the substituent was removed. The surface pH of the substituent-removed fibrous cellulose-containing sheet before laminating the resin layer was 4.8.

<Comparative Example 8>
A laminated sheet was obtained in the same manner as in Example 12 except that the slurry was not uniformly dispersed after the substituent was removed. The surface pH of the substituent-removed fibrous cellulose-containing sheet before laminating the resin layer was 4.6.

<Comparative Example 9>
A laminated sheet was obtained in the same manner as in Example 13 except that the slurry was not uniformly dispersed after the substituent was removed. The surface pH of the substituent-removed fibrous cellulose-containing sheet before laminating the resin layer was 4.5.

<Comparative Example 10>
A laminated sheet was obtained in the same manner as in Example 14 except that the slurry was not uniformly dispersed after the substituent was removed. The surface pH of the substituent-removed fibrous cellulose-containing sheet before laminating the resin layer was 6.8.

<Comparative Example 11>
In [Preparation of Sheet 1], a laminated sheet was obtained in the same manner as in Example 15 except that the fine fibrous cellulose dispersion obtained in Production Example 1 was used instead of the substituent-removed fine fibrous cellulose dispersion. rice field. The surface pH of the fine fibrous cellulose-containing sheet before laminating the resin layer was 7.3.

<Comparative Example 12>
In [Preparation of Sheet 1], a laminated sheet was obtained in the same manner as in Example 16 except that the fine fibrous cellulose dispersion obtained in Production Example 1 was used instead of the substituent-removed fine fibrous cellulose dispersion. rice field. The surface pH of the fine fibrous cellulose-containing sheet before laminating the resin layer was 7.2.

<Comparative Example 13>
In [Preparation of Sheet 1], a laminated sheet was obtained in the same manner as in Example 17 except that the fine fibrous cellulose dispersion obtained in Production Example 1 was used instead of the substituent-removed fine fibrous cellulose dispersion. rice field. The surface pH of the fine fibrous cellulose-containing sheet before laminating the resin layer was 7.3.

<Comparative Example 14>
In [Preparation of Sheet 1], a laminated sheet was obtained in the same manner as in Example 18 except that the fine fibrous cellulose dispersion obtained in Production Example 1 was used instead of the substituent-removed fine fibrous cellulose dispersion. rice field. The surface pH of the fine fibrous cellulose-containing sheet before laminating the resin layer was 6.9.

<Comparative Example 15>
In [Preparation of Sheet 1], a laminated sheet was obtained in the same manner as in Example 20 except that the fine fibrous cellulose dispersion obtained in Production Example 1 was used instead of the substituent-removed fine fibrous cellulose dispersion. rice field. The surface pH of the fine fibrous cellulose-containing sheet before laminating the resin layer was 7.2.

<Comparative Example 16>
In [Preparation of Sheet 1], a laminated sheet was obtained in the same manner as in Example 21 except that the fine fibrous cellulose dispersion obtained in Production Example 1 was used instead of the substituent-removed fine fibrous cellulose dispersion. rice field. The surface pH of the fine fibrous cellulose-containing sheet before laminating the resin layer was 7.2.

<Comparative Example 17>
A laminated sheet was obtained in the same manner as in Example 1 except that the following [ion exchange resin treatment of the slurry after removing the substituent] was performed instead of [cleaning treatment of the slurry after removing the substituent]. The surface pH of the fine fibrous cellulose-containing sheet from which the substituent was removed before laminating the resin layer was 2.4.

[Ion exchange resin treatment of slurry after removal of substituents]
Ion exchange water is added to the heated slurry obtained by [substituent removal treatment (high temperature heat treatment)] to make a slurry having a solid content concentration of about 1.1% by mass, and then it is strongly acidic at a volume ratio of 1/10. Add an ion exchange resin (Amberjet 1024; Organo Co., Ltd., conditioned) and a strong basic ion exchange resin (Amberjet 4400; Organo Co., Ltd., conditioned) with a volume ratio of 1/10, and shake for 1 hour. After that, the resin and the slurry were separated by pouring on a mesh having an opening of 90 μm. The obtained slurry had a pH of 3.1.

<Comparative Example 18>
A laminated sheet was obtained in the same manner as in Comparative Example 17 except that citric acid was not added in the [substituent removal treatment (high temperature heat treatment)] and 1/10 of the amount of urea of the fine fibrous cellulose dispersion was added. The surface pH of the fine fibrous cellulose-containing sheet from which the substituent was removed before laminating the resin layer was 2.4.

[evaluation]
The laminated sheets obtained in Examples and Comparative Examples were evaluated by the following methods.

[Measurement of fiber width]
The fiber width of the fibrous cellulose was measured by the following method. Each fibrous cellulose dispersion was diluted with water so that the concentration of cellulose was 0.01% by mass or more and 0.1% by mass or less, and cast onto a hydrophilized carbon film-coated grid. After drying this, it was stained with uranyl acetate and observed with a transmission electron microscope (TEM, manufactured by JEOL Ltd., JEOL-2000EX). At that time, an axis having an arbitrary vertical and horizontal image width was assumed in the obtained image, and the magnification was adjusted so that 20 or more fibers intersected the axis. After obtaining an observation image satisfying this condition, two random axes in each of the vertical and horizontal directions were drawn for this image, and the fiber width of the fibers intersecting the axes was visually read. Three non-overlapping observation images were taken for each dispersion, and the value of the fiber width of the fibers intersecting each of the two axes was read (20 or more × 2 × 3 = 120 or more). The number average fiber width was calculated from the fiber width obtained in this way. However, for Examples 1 to 21 and Comparative Examples 5 and 7 to 10, a substituent-removed fine fibrous cellulose dispersion was used, and for Comparative Examples 1 to 4 and 11 to 16, the fine fibrous cellulose dispersion was used. Measurements were made. Further, only for the coarse fibrous cellulose used in Comparative Example 6, the dispersion liquid was diluted with water so that the concentration of cellulose was 0.01% by mass or more and 0.1% by mass or less, cast onto a glass, and scanned. It was observed with an electron microscope (SEM).
Further, the proportion of fine fibrous cellulose having a fiber width of 10 nm or less was determined based on the following formula.
Percentage of fine fibrous cellulose having a fiber width of 10 nm or less (%) = (number of fine fibrous cellulose having a fiber width of 10 nm or less / number of total fibrous cellulose) × 100

[Measurement of phosphorus oxo acid group amount]
In measuring the amount of phosphorous acid group (phosphoric acid group or phosphorous acid group amount), first, ion-exchanged water is added to the target fine fibrous cellulose to prepare a slurry having a solid content concentration of 0.2% by mass. bottom. The obtained slurry was treated with an ion exchange resin and then titrated with an alkali for measurement.
For the treatment with the ion exchange resin, a strongly acidic ion exchange resin (Amberjet 1024; Organo Corporation, conditioned) with a volume of 1/10 is added to the fine fibrous cellulose-containing slurry, and the mixture is shaken for 1 hour. This was done by pouring onto a mesh with an opening of 90 μm to separate the resin and the slurry.
In the titration using alkali, the pH value indicated by the slurry is changed while adding 10 μL of 0.1 N sodium hydroxide aqueous solution to the fine fibrous cellulose-containing slurry treated with the ion exchange resin every 5 seconds. Was performed 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 was divided by the solid content (g) in the slurry to be titrated, and the value was defined as the amount of phosphoroxo acid groups (mmol / g).

[Measurement of sulfone group amount]
The amount of sulfone groups was measured as follows. The fine fibrous cellulose was frozen in a freezer and then dried in a freeze-dryer (FreeZone manufactured by Loveconco) for 3 days. The obtained freeze-dried product was pulverized at a rotation speed of 20,000 rpm for 60 seconds using a hand mixer (manufactured by Osaka Chemical Co., Ltd., Lab Miller PLUS) to form a powder. The sample after freeze-drying and pulverization treatment was decomposed by heating under pressure using nitric acid in a closed container. Then, it was diluted appropriately and the amount of sulfur was measured by ICP-OES. The value calculated by dividing by the absolute dry mass of the fine fibrous cellulose tested was taken as the amount of sulfate ester groups (unit: mmol / g).

[Measurement of Zantate group amount]
The amount of zantate group was measured by the Bredee method. Specifically, 40 mL of saturated ammonium chloride solution was added to 1.5 parts by mass (absolute dry mass) of fibrous cellulose, mixed well while crushing the sample with a glass rod, left for about 15 minutes, and then GFP filter paper (ADVANTEC). It was filtered with GS-25) manufactured by GS-25) and thoroughly washed with a saturated ammonium chloride solution. The sample was placed in a 500 mL tall beaker together with the GFP filter paper, 50 mL of 0.5 M sodium hydroxide solution (5 ° C.) was added, and the mixture was stirred. After leaving for 15 minutes, a phenolphthalein solution was added until the solution turned pink, and then 1.5 M acetic acid was added, and the point at which the solution turned from pink to colorless was defined as a neutralization point. After neutralization, 250 mL of distilled water was added and stirred well, and 10 mL of 1.5 M acetic acid and 10 mL of 0.05 mol / L iodine solution were added using a whole pipette. This solution was titrated with a 0.05 mol / L sodium thiosulfate solution. The amount of zantate group was calculated from the following formula from the titration amount of sodium thiosulfate and the absolute dry mass of fibrous cellulose.
Zantate group amount (mmol / g) = (0.05 × 10 × 2-0.05 × sodium thiosulfate titration (mL)) / 1000 / Absolute dry mass of fibrous cellulose (g)

[Measurement of total light transmittance of laminated sheet]
In accordance with JIS K 7631-1: 1997, the total light transmittance of the laminated sheet was measured using a haze meter (HM-150, manufactured by Murakami Color Technology Research Institute).

[Haze measurement of laminated sheet]
According to JIS K 7136: 2000, the haze of the laminated sheet was measured using a haze meter (HM-150 manufactured by Murakami Color Technology Research Institute).

[Measurement of yellowness before and after heating of laminated sheet]
According to JIS K 7373: 2006, the yellowness (YI value) of the laminated sheet before and after heating was measured using Color Cute i (manufactured by Suga Test Instruments Co., Ltd.). The YI value after heating was the YI value of the laminated sheet heated at 160 ° C. for 6 hours. In addition, the YI increase rate was measured by the following method.
YI increase rate (%) = (YI value of the sheet after heating-YI value of the sheet before heating) / YI value of the sheet before heating × 100

[Measurement of surface pH of sheet (CNF sheet) before laminating the resin layer]
10 μL of ion-exchanged water was dropped into a 1 cm square area on the sheet surface with a micropipette, and the pH of that portion was measured using a flat pH composite electrode (6261-10C; manufactured by HORIBA).

AC: Acrylic PIC: Polyisocyanate PC: Polycarbonate OSI: Organosilane

The laminated sheet obtained in the examples was highly transparent, and the YI after heating was low in addition to the YI before heating (Examples 1 to 21). On the other hand, when the substituent removal treatment was not performed or the removal treatment was insufficient, the obtained laminated sheet had a high YI after heating (Comparative Examples 1 to 5, 11 to 16). When unmodified coarse fibrous cellulose was used, the obtained laminated sheet was opaque (Comparative Example 6). When uniform dispersion was not performed after removing the substituent, the transparency of the laminated sheet was low (Comparative Examples 7 to 10).

<Example 101>
Two laminated sheets obtained in Example 20 trimmed to a 100 mm square were prepared. A polycarbonate plate having a size of 100 mm square and a thickness of 2 mm was sandwiched between the two laminated sheets, and further sandwiched between two stainless steel plates having a size of 200 mm square. Then, it was inserted into a mini test press (MP-WCH manufactured by Toyo Seiki Kogyo Co., Ltd.) set at room temperature, and the temperature was raised to 160 ° C. over 3 minutes under a press pressure of 0.2 MPa. After holding in this state for 30 seconds, it was cooled to 30 ° C. over 3 minutes. By the above procedure, a laminated body with a polycarbonate plate was obtained.

<Example 102>
A laminated body with a polycarbonate plate was obtained in the same manner as in Example 101 except that the laminated sheet obtained in Example 21 was used.

<Comparative Example 101>
A laminated body with a polycarbonate plate was obtained in the same manner as in Example 101 except that the laminated sheet obtained in Comparative Example 15 was used.

<Comparative Example 102>
A laminated body with a polycarbonate plate was obtained in the same manner as in Example 101 except that the laminated sheet obtained in Comparative Example 16 was used.

<Comparative Example 103>
In Example 101, the treatment with a mini test press was performed without sandwiching the polycarbonate plate between the two laminated sheets. This board was used for evaluation.

[evaluation]
The laminates and plates obtained in Examples and Comparative Examples were evaluated by the following methods.

[Measurement of flexural modulus]
A test piece having a size of 80 mm × 10 mm was cut out from the laminate and the plate, and a bending test was performed according to JIS K 7171: 2016, and the flexural modulus was measured.

[exterior]
According to JIS K 7373: 2006, the YI value of the laminate and the plate was measured using Color Cutei (manufactured by Suga Test Instruments Co., Ltd.). From the measurement results, the appearance was evaluated according to the following criteria.
A: YI is less than 10
B: YI is 10 or more

[exterior]
The laminate and the plate were heated at 90 ° C. for 720 hours. Then, in accordance with JIS K 7373: 2006, the YI values of the laminate and the plate were measured using Color Cute i (manufactured by Suga Test Instruments Co., Ltd.). From the measurement results, the appearance was evaluated according to the following criteria.
A: YI is less than 15
B: YI is 15 or more

The laminated sheet obtained in the examples had a low YI before and after heating and had a good appearance. Further, in the case of a laminated body, the flexural modulus was high, and the reinforcing effect of the resin material was also excellent (Examples 101 and 102). The laminated sheet that did not undergo the step of removing the substituent had a slightly low flexural modulus, and the appearance of the laminated sheet was also poor (Comparative Examples 101 and 102).

2 Resin layer 6 Fiber layer 10 Laminated sheet

Claims (15)

A laminated sheet having a fiber layer and a resin layer arranged on at least one surface of the fiber layer.
The fiber layer is a laminated sheet containing fibrous cellulose having a substituent introduction amount of less than 0.5 mmol / g and a fiber width of 1 to 10 nm. The laminated sheet according to claim 1, wherein the substituent is an anionic group. The laminated sheet according to claim 2, wherein the anionic group is a phosphoric acid group or a functional group derived from a phosphoric acid group. The laminated sheet according to any one of claims 1 to 3, wherein the fibrous cellulose has a carbamide group. The laminated sheet according to any one of claims 1 to 4, wherein the fiber layer has a thickness of 20 μm or more. The laminated sheet according to any one of claims 1 to 5, wherein the fiber layer has a density of 1.0 g / cm ^{3 or more.} The laminated sheet according to any one of claims 1 to 6, wherein the resin layer is directly laminated on the fiber layer. The laminated sheet according to any one of claims 1 to 7, wherein the resin layer contains at least one selected from a polycarbonate resin and an acrylic resin. The laminated sheet according to any one of claims 1 to 8, wherein the resin layer further contains an adhesion aid. The laminated sheet according to claim 9, wherein the adhesion aid is at least one selected from an isocyanate compound and an organosilicon compound. The laminate according to claim 9 or 10, wherein the adhesion aid is an isocyanate compound, and the content of the isocyanate compound is 10 parts by mass or more and 40 parts by mass or less with respect to 100 parts by mass of the resin contained in the resin layer. Sheet. The laminated sheet according to any one of claims 1 to 11, wherein the YI value is 2.0 or less. The laminated sheet according to any one of claims 1 to 12, wherein the haze is 2.0% or less. The laminated sheet according to any one of claims 1 to 13, which is for an optical member. A laminated body including the laminated sheet according to any one of claims 1 to 14 and an adherend.

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