Microfibrillated cellulose–containing sheet, laminated sheet, and laminate

Abstract

An objective of the present invention is to provide a laminate with excellent strength of the laminate as a whole and excellent adhesive strength between layers. A further objective of the present invention is to provide a microfibrillated cellulose–containing sheet and a laminated sheet to be used in the laminate.　A microfibrillated cellulose–containing sheet according to the present embodiment has: a microfibrillated cellulose–containing layer 1A containing microfibrillated cellulose with a fiber width of 1,000 nm or less and a hydrophilic polymer 1A; and a microfibrillated cellulose–containing layer 1B containing microfibrillated cellulose with a fiber width of 1,000 nm or less and a hydrophilic polymer 1B, wherein the hydrophilic polymer 1A and the hydrophilic polymer 1B have hydroxyl groups, and provided that OHV_1A (mg KOH / g) is the hydroxyl value of the hydrophilic polymer 1A and OHV_1B (mg KOH / g) is the hydroxyl value of the hydrophilic polymer 1B, the following expression (I) is satisfied.　(I): OHV_1A < OHV_1B

Description

Fine fibrous cellulose-containing sheet, laminated sheet and laminate

[0001] The present invention relates to a fine fibrous cellulose-containing sheet, a laminated sheet, and a laminate.

[0002] In recent years, materials using renewable natural fibers have been attracting attention due to the need to replace petroleum resources and growing environmental awareness. Among natural fibers, fibrous cellulose with a fiber width of 10 μm to 50 μm, particularly wood-derived fibrous cellulose (pulp), has been widely used, primarily in paper products. As fibrous cellulose, fine fibrous cellulose with a fiber width of 1,000 nm or less is also known. Furthermore, sheets composed of such fine fibrous cellulose, as well as composite sheets and molded articles containing fine fibrous cellulose and resin, have been developed. It is known that sheets and molded articles containing fine fibrous cellulose have significantly increased fiber-to-fiber contact points, resulting in significantly improved tensile strength and other properties. Patent Document 1 discloses a polycarbonate resin / cellulose fiber laminate comprising a polycarbonate resin layer and a cellulose fiber layer, in which the thickness of the polycarbonate resin layer is 1.4 times or more the thickness of the cellulose fiber layer, with the aim of providing a composite that has high transparency, high elasticity, a low linear expansion coefficient, a good balance of properties such as impact resistance, and is also easy to produce by laminating a polycarbonate resin layer and a cellulose fiber layer.

[0003] Patent No. 4985573

[0004] Because fine fibrous cellulose-containing sheets have excellent mechanical strength, such as tensile strength, and also have excellent transparency, they can be combined with resin plates or resin films to form laminates, which can be used in various display devices, optical components such as various solar cells, and window materials for various vehicles and buildings. When used in such applications, it is desirable for the laminate to have improved interlayer adhesive strength compared to conventional laminates in order to further improve product quality. Therefore, an object of the present invention is to provide a laminate that has excellent overall strength and excellent interlayer adhesive strength. Another object of the present invention is to provide a fine fibrous cellulose-containing sheet and a laminate sheet to be used in the laminate.

[0005] The present inventors have found that in a fine fibrous cellulose-containing sheet having a fine fibrous cellulose-containing layer 1A containing fine fibrous cellulose having a fiber width of 1,000 nm or less and a hydrophilic polymer 1A, and a fine fibrous cellulose-containing layer 1B containing fine fibrous cellulose having a fiber width of 1,000 nm or less and a hydrophilic polymer 1B, the above-mentioned problems can be solved by having hydrophilic polymers 1A and 1B contain hydroxyl groups and by making the hydroxyl value of hydrophilic polymer 1A and the hydroxyl value of hydrophilic polymer 1B have a specific relationship.

[0006] That is, the present invention relates to the following items <1> to <22>. <1> A fine fibrous cellulose-containing sheet having a fine fibrous cellulose-containing layer 1A containing fine fibrous cellulose having a fiber width of 1,000 nm or less and a hydrophilic polymer 1A, and a fine fibrous cellulose-containing layer 1B containing fine fibrous cellulose having a fiber width of 1,000 nm or less and a hydrophilic polymer 1B, wherein the hydrophilic polymer 1A and the hydrophilic polymer 1B have hydroxyl groups, and when the hydroxyl value of the hydrophilic polymer 1A is OHV_1A (mg KOH / g) and the hydroxyl value of the hydrophilic polymer 1B is OHV_1B (mg KOH / g), the fine fibrous cellulose-containing sheet satisfies the following formula (I): OHV_1A<OHV_1B (I) <2> The fine fibrous cellulose-containing sheet according to <1>, wherein the hydrophilic polymer 1A is a nonionic water-soluble cellulose ether. <3> The fine fibrous cellulose-containing sheet according to <2>, wherein the hydrophilic polymer 1A has at least one functional group selected from the group consisting of an alkoxy group and a hydroxyalkoxy group. <4> The fine fibrous cellulose-containing sheet according to any one of <1> to <3>, wherein the hydrophilic polymer 1B is polyvinyl alcohol or a modified product thereof having a saponification degree of 80 or more. <5> The fine fibrous cellulose-containing sheet according to any one of <1> to <4>, wherein the following formula (II) is satisfied: 1200 mg KOH / g ≧ OHV_1B - OHV_1A ≧ 450 mg KOH / g (II). <6> The fine fibrous cellulose-containing sheet according to any one of <1> to <5>, wherein the fine fibrous cellulose has an anionic group. <7> The fine fibrous cellulose-containing sheet according to <6>, wherein the anionic group of the fine fibrous cellulose is a phosphorus oxo acid group or a functional group derived from a phosphorus oxo acid group. <8> The fine fibrous cellulose-containing sheet according to <6> or <7>, wherein the content of anionic groups in the fine fibrous cellulose is less than 0.5 mmol / g. <9> The fine fibrous cellulose-containing sheet according to any one of <1> to <8>, wherein the ratio of the thickness of the fine fibrous cellulose-containing layer 1A to the thickness of the fine fibrous cellulose-containing layer 1B (fine fibrous cellulose-containing layer 1A:fine fibrous cellulose-containing layer 1B) is more than 5.0:5.0 and not more than 9.0:1.0.<10> The fine fibrous cellulose-containing sheet according to any one of <1> to <9>, wherein the total thickness of the fine fibrous cellulose-containing layer 1A and the fine fibrous cellulose-containing layer 1B is 20 μm or more and 300 μm or less. <11> A laminate sheet, comprising the fine fibrous cellulose-containing sheet according to any one of <1> to <10>, an adhesive layer 1A on the side of the fine fibrous cellulose-containing layer 1A opposite to the side having the fine fibrous cellulose-containing layer 1B, and an adhesive layer 1B on the side of the fine fibrous cellulose-containing layer 1B opposite to the side having the fine fibrous cellulose-containing layer 1A. <12> The laminate sheet according to <11>, wherein the adhesive layer 1A and the adhesive layer 1B contain at least one resin selected from the group consisting of a polycarbonate-based resin, an acrylic-based resin, and a polyester-based resin. <13> The laminate sheet according to <11> or <12>, wherein the adhesive layer 1A and the adhesive layer 1B are formed from an adhesive composition containing an isocyanate compound. <14> The laminate sheet according to any one of <11> to <13>, which has a resin film 1 on a surface of the adhesive layer 1B of the laminate sheet opposite to a surface having the fine fibrous cellulose-containing layer 1B. <15> The laminate sheet according to <14>, in which the thickness of the resin film 1 is 30 μm or more and 500 μm or less. <16> A laminate according to any one of <11> to <15>, further comprising a core resin plate on a surface of the adhesive layer 1A of the laminate sheet opposite to a surface having the fine fibrous cellulose-containing layer 1A. <17> The laminate according to <16>, in which the thickness of the core resin plate is 500 μm or more and 4,500 μm or less. <18> The laminate according to <16> or <17>, in which the core resin plate contains at least one resin selected from the group consisting of polycarbonate resins and acrylic resins.<19> The laminate according to any one of <16> to <18>, wherein the surface of the core resin plate opposite to the surface having the adhesive layer 1A is provided, in this order from the core resin plate, with an adhesive layer 2A, a fine fibrous cellulose-containing layer 2A containing fine fibrous cellulose having a fiber width of 1,000 nm or less and a hydrophilic polymer 2A, a fine fibrous cellulose-containing layer 2B containing fine fibrous cellulose having a fiber width of 1,000 nm or less and a hydrophilic polymer 2B, an adhesive layer 2B, and a resin film 2, wherein the hydrophilic polymer 2A and the hydrophilic polymer 2B have hydroxyl groups, and when the hydroxyl value of the hydrophilic polymer 2A is OHV_2A (mg KOH / g) and the hydroxyl value of the hydrophilic polymer 2B is OHV_2B (mg KOH / g), the following formula (I') is satisfied: OHV_2A<OHV_2B (I') <20> The laminate according to any one of <16> to <19>, wherein the haze is 2.0% or less. <21> The laminate according to any one of <16> to <20>, which has a total light transmittance of 85% or more. <22> The laminate according to any one of <16> to <21>, which has a yellow index (YI value) of 2.50 or less.

[0007] According to the present invention, a laminate having excellent overall strength and excellent interlayer adhesive strength is provided. Also provided are a fine fibrous cellulose-containing sheet and a laminate sheet for use in the laminate.

[0008] Fig. 1 is a graph showing the relationship between the amount of NaOH dropped onto a slurry containing fibrous cellulose having a phosphorus oxo acid group and pH. Fig. 2 is a graph showing the relationship between the amount of NaOH dropped onto a slurry containing fibrous cellulose having a carboxy group and pH.

[0009] Hereinafter, embodiments of the present invention will be described. In this specification, the range "X to Y" means "X or more and Y or less." In this specification, the upper and lower limits of the numerical ranges can be combined arbitrarily. In this specification, the components contained or may be contained in each layer constituting the laminate may be used alone or in combination of two or more.

[0010] [Fine fibrous cellulose-containing sheet, laminated sheet, and laminate] The fine fibrous cellulose-containing sheet of the present embodiment has a fine fibrous cellulose-containing layer 1A containing fine fibrous cellulose having a fiber width of 1,000 nm or less and a hydrophilic polymer 1A, and a fine fibrous cellulose-containing layer 1B containing fine fibrous cellulose having a fiber width of 1,000 nm or less and a hydrophilic polymer 1B, wherein the hydrophilic polymer 1A and the hydrophilic polymer 1B have hydroxyl groups, and when the hydroxyl value of the hydrophilic polymer 1A is OHV_1A (mg KOH / g) and the hydroxyl value of the hydrophilic polymer 1B is OHV_1B (mg KOH / g), the following formula (I) is satisfied: OHV_1A<OHV_1B (I) The laminate sheet of this embodiment has an adhesive layer 1A on the surface of the fine fibrous cellulose-containing sheet opposite to the surface having the fine fibrous cellulose-containing layer 1B of the fine fibrous cellulose-containing layer 1A, and an adhesive layer 1B on the surface of the fine fibrous cellulose-containing layer 1B opposite to the surface having the fine fibrous cellulose-containing layer 1A. The laminate sheet preferably has a resin film 1 on the surface of the adhesive layer 1B opposite to the surface having the fine fibrous cellulose-containing layer 1B. Furthermore, the laminate of this embodiment has a core resin plate on the surface of the adhesive layer 1A of the laminate sheet opposite to the surface having the fine fibrous cellulose-containing layer 1A. The laminate of this embodiment has excellent strength and adhesiveness as a whole, and further has the additional effect of high total light transmittance and low haze and YI value.

[0011] Although the detailed mechanism by which the above-mentioned effect is obtained is unknown, a laminate having an adhesive layer, a fine fibrous cellulose-containing layer, an adhesive layer, and a resin film on one side of a core resin plate in this order from the core resin plate has excellent strength as a whole due to the presence of the fine fibrous cellulose-containing layer. However, when the laminate was cut, peeling from the edge was sometimes observed. When this peeling was investigated, it was found that peeling occurred between the adhesive layer on the resin film side and the fine fibrous cellulose-containing layer. Therefore, in consideration of improving adhesion with the adhesive layer, the fine fibrous cellulose-containing layer was made into two layers, and a hydrophilic polymer with a higher hydroxyl value was used for the fine fibrous cellulose-containing layer on the adhesive layer side, and it was found that the above-mentioned problem was solved. Note that the above-mentioned mechanism is speculation and is not limited thereto.

[0012] The laminate of this embodiment preferably has, on one side of the core resin plate, an adhesive layer 1A, a fine fibrous cellulose-containing layer 1A containing fine fibrous cellulose with a fiber width of 1,000 nm or less and a hydrophilic polymer 1A, a fine fibrous cellulose-containing layer 1B containing fine fibrous cellulose with a fiber width of 1,000 nm or less and a hydrophilic polymer 1B, and an adhesive layer 1B, in this order, and further has a resin film 1 in this order on the surface of adhesive layer 1B opposite to the surface having fine fibrous cellulose-containing layer 1B, and more preferably has at least an adhesive layer 2 and a resin film 2 in this order on the surface of the core resin plate opposite to the surface having adhesive layer 1A, thereby improving the strength of the laminate. From this viewpoint, it is preferable that the surface of the core resin plate opposite to the surface having the adhesive layer 1A of the core resin plate is laminated in this order from the core resin plate on which the adhesive layer 2A, the fine fibrous cellulose-containing layer 2A containing fine fibrous cellulose and the hydrophilic polymer 2A having a fiber width of 1,000 nm or less, the fine fibrous cellulose-containing layer 2B containing fine fibrous cellulose and the hydrophilic polymer 2B having a fiber width of 1,000 nm or less, the adhesive layer 2B, and the resin film 2, wherein the hydrophilic polymer 2A and the hydrophilic polymer 2B have hydroxyl groups, and when the hydroxyl value of the hydrophilic polymer 2A is OHV_2A (mg KOH / g) and the hydroxyl value of the hydrophilic polymer 2B is OHV_2B (mg KOH / g), the following formula (I') is satisfied: OHV_2A<OHV_2B (I') Hereinafter, this embodiment will be described in more detail.

[0013] [Core Resin Plate] The laminate of this embodiment has a core resin plate. The core resin plate preferably contains at least one selected from the group consisting of polycarbonate-based resins and acrylic-based resins. "Polycarbonate-based resin" refers to a resin containing a moiety in which structural units are repeatedly bonded via carbonate groups (-O-(C=O)-O-). Furthermore, "acrylic-based resin" refers to a resin having structural units derived from (meth)acrylic acid or a (meth)acrylic acid ester. The core resin plate more preferably contains a polycarbonate-based resin or an acrylic-based resin, and even more preferably contains a polycarbonate-based resin. From the viewpoint of improving the strength and transparency of the laminate, the total content of the polycarbonate-based resin and the acrylic-based resin in the core resin plate is preferably 70% by mass or more, more preferably 75% by mass or more, even more preferably 80% by mass or more, even more preferably 85% by mass or more, even more preferably 90% by mass or more, and even more preferably 95% by mass or more, and 100% by mass or less. When the core resin plate contains a polycarbonate resin, it may contain, in addition to the polycarbonate resin, for example, an acrylonitrile butadiene styrene copolymer or a polymethyl methacrylate resin. When the core resin plate contains an acrylic resin, it may contain, in addition to the acrylic resin, for example, an acrylonitrile butadiene styrene copolymer or a polycarbonate resin.

[0014] <Thickness> The thickness of the core resin plate in this embodiment is preferably 200 μm or more and 5,000 μm or less, more preferably 500 μm or more, even more preferably 700 μm or more, still more preferably 900 μm or more, and more preferably 4,500 μm or less, even more preferably 4,000 μm or less, still more preferably 3,500 μm or less, and even more preferably 3,200 μm or less. The thickness of the core resin plate is preferably adjusted appropriately depending on the application of the laminate.

[0015] [Adhesive Layers 1A, 1B, 2, 2A, 2B] As described above, the laminate sheet of this embodiment has an adhesive layer 1A on the side of the fine fibrous cellulose-containing sheet opposite to the side having the fine fibrous cellulose-containing layer 1B of the fine fibrous cellulose-containing layer 1A, and an adhesive layer 1B on the side of the fine fibrous cellulose-containing layer 1B opposite to the side having the fine fibrous cellulose-containing layer 1A. Furthermore, as described above, the laminate of this embodiment preferably has adhesive layers 1A and 1B on one side of the core resin plate and adhesive layer 2 on the other side of the core resin plate, more preferably adhesive layers 2A and 2B. The components contained and the components that can be contained in each of the adhesive layers 1A, 1B, 2, 2A, and 2B may be the same or different, but are preferably the same. The preferred forms of the components contained and the components that can be contained in each of the adhesive layers 1A, 1B, 2, 2A, and 2B are the same. Hereinafter, adhesive layers 1A, 1B, 2, 2A, and 2B will also be collectively referred to simply as "adhesive layers."

[0016] Examples of adhesives constituting the adhesive layer include polycarbonate resins, acrylic resins, polyester resins, vinyl chloride resins, vinyl acetate resins, urethane resins, silicone resins, epoxy resins, ethylene / vinyl acetate copolymer resins, polyvinyl alcohol resins, ethylene-vinyl alcohol copolymer resins, and rubber emulsions such as SBR and NBR. One or more selected from the group consisting of polycarbonate resins, acrylic resins, and polyester resins are preferred, and polycarbonate resins are more preferred. Examples of polycarbonate resins that can be used include the polycarbonate copolymers described in JP 2008-24919 A.

[0017] The adhesive layer is preferably formed from an adhesive composition containing an adhesive aid (formed using an adhesive composition containing an adhesive aid). Examples of the adhesive aid include compounds containing at least one selected from an isocyanate group, a carbodiimide group, an epoxy group, an oxazoline group, an amino group, and a silanol group. Among these, compounds containing an isocyanate group (isocyanate compounds) are preferred as the adhesive aid from the viewpoint of excellent adhesion to the fine fibrous cellulose-containing layer.

[0018] The adhesive composition preferably contains an adhesive and an adhesive aid, more preferably contains one or more resins selected from the group consisting of polycarbonate-based resins, acrylic-based resins, and polyester-based resins, and an isocyanate compound, and even more preferably contains a polycarbonate-based resin and an isocyanate compound.

[0019] In the adhesive composition, the content of the adhesive aid relative to 100 parts by mass of the adhesive is preferably 5 parts by mass or more and 30 parts by mass or less, more preferably 10 parts by mass or more, even more preferably 15 parts by mass or more, and more preferably 25 parts by mass or less, even more preferably 20 parts by mass or less, from the viewpoint of improving adhesiveness.

[0020] The adhesive composition preferably contains an organic solvent, such as toluene, methylene chloride, tetrahydrofuran, tetraglyme, dimethyl carbonate, methyl ethyl ketone, ethyl acetate, dimethylacetamide, and styrene.

[0021] From the viewpoints of coatability and solvent removal, the solids concentration of the adhesive composition is preferably 1% by mass or more and 25% by mass or less, more preferably 4% by mass or more, even more preferably 7% by mass or more, and more preferably 20% by mass or less, even more preferably 15% by mass or less.

[0022] [Fine fibrous cellulose-containing layers 1A, 1B, 2A and 2B] The fine fibrous cellulose-containing sheet of this embodiment has a fine fibrous cellulose-containing layer 1A and a fine fibrous cellulose-containing layer 1B. Furthermore, the laminate sheet of this embodiment has a fine fibrous cellulose-containing layer 1A and a fine fibrous cellulose-containing layer 1B, and preferably has an adhesive layer 1A on the side of the fine fibrous cellulose-containing layer 1A opposite to the side having the fine fibrous cellulose-containing layer 1B, an adhesive layer 1B on the side of the fine fibrous cellulose-containing layer 1B opposite to the side having the fine fibrous cellulose-containing layer 1A, and a resin film 1 on the side of the adhesive layer 1B opposite to the side having the fine fibrous cellulose-containing layer 1B. Furthermore, the laminate of this embodiment, as described above, has fine fibrous cellulose-containing layers 1A and 1B containing fine fibrous cellulose with a fiber width of 1,000 nm or less on one side of the core resin plate. In addition, the laminate of this embodiment preferably has fine fibrous cellulose-containing layers 2A and 2B containing fine fibrous cellulose having a fiber width of 1,000 nm or less on the other side of the core resin plate. The components contained in the fine fibrous cellulose-containing layer 1A and the components that can be contained therein, as well as the thickness, basis weight and density of the fine fibrous cellulose-containing layer 1A, and the components contained in the fine fibrous cellulose-containing layer 2A and the components that can be contained therein, as well as the thickness, basis weight and density of the fine fibrous cellulose-containing layer 2A may be the same or different, but are preferably the same. Similarly, the components contained in the fine fibrous cellulose-containing layer 1B and the components that can be contained therein, as well as the thickness, basis weight and density of the fine fibrous cellulose-containing layer 1B, and the components contained in the fine fibrous cellulose-containing layer 2B and the components that can be contained therein, as well as the thickness, basis weight and density of the fine fibrous cellulose-containing layer 2B may be the same or different, but are preferably the same. The preferred forms described below are the same for the fine fibrous cellulose-containing layer 1A and the fine fibrous cellulose-containing layer 2A, and are also the same for the fine fibrous cellulose-containing layer 2A and the fine fibrous cellulose-containing layer 2B. Hereinafter, the fine fibrous cellulose-containing layers 1A, 1B, 2A, and 2B will also be collectively referred to simply as "fine fibrous cellulose-containing layers."

[0023] <Fine fibrous cellulose> Fine fibrous cellulose is fibrous cellulose having a fiber width of 1,000 nm or less. The fiber width of fibrous cellulose can be measured, for example, by observation under an electron microscope. The fiber width of fine fibrous cellulose is 1,000 nm or less. The fiber width of fine fibrous cellulose is preferably 2 nm or more and 1,000 nm or less, more preferably 2 nm or more and 100 nm or less, even more preferably 2 nm or more and 50 nm or less, and even more preferably 2 nm or more and 10 nm or less. By making the fiber width of fine fibrous cellulose 2 nm or more, dissolution of cellulose molecules in water can be suppressed, and the effect of improving strength and dimensional stability due to fine fibrous cellulose can be more easily achieved.

[0024] The average fiber width of the fine fibrous cellulose is, for example, 1,000 nm or less. The average fiber width of the fine fibrous cellulose is preferably 2 nm or more and 1,000 nm or less, more preferably 2 nm or more and 100 nm or less, even more preferably 2 nm or more and 50 nm or less, and even more preferably 2 nm or more and 10 nm or less. By making the average fiber width of the fine fibrous cellulose 2 nm or more, it is possible to suppress the dissolution of the cellulose molecules in water, and to more easily achieve the effects of the fine fibrous cellulose, such as improving strength and dimensional stability. The fine fibrous cellulose is, for example, monofilament cellulose.

[0025] The number-average fiber width of fine fibrous cellulose is measured, for example, using an electron microscope as follows. First, an aqueous suspension of fine fibrous cellulose with a concentration of 0.01% by mass to 0.1% by mass is prepared, and this suspension is cast on a hydrophilically treated carbon film-coated grid to prepare a sample for transmission electron microscope (TEM) observation. When wide fibers are included, a scanning electron microscope (SEM) image of the surface cast on glass may be observed. Next, electron microscope images are observed at magnifications of 1,000x, 5,000x, 10,000x, or 50,000x, depending on the width of the fibers to be observed. However, the sample, observation conditions, and magnification are adjusted to satisfy the following conditions: (1) A line X is drawn at any location within the observed image, and 20 or more fibers intersect with line X. (2) A line Y is drawn within the same image, perpendicular to line X, and 20 or more fibers intersect line Y.

[0026] For observation images that satisfy the above conditions, the widths of fibers intersecting with lines X and Y are visually read. In this way, three or more sets of observation images of at least the surface portions that do not overlap each other are obtained. Next, for each image, the widths of fibers intersecting with lines X and Y are read. In this way, the widths of at least 20 fibers x 2 x 3 = 120 fibers are read. The average of the read fiber widths is then taken as the number-average fiber width of the fibrous cellulose.

[0027] The fiber length of the fine fibrous cellulose is not particularly limited, but is preferably 0.1 μm or more and 1,000 μm or less, more preferably 0.1 μm or more and 800 μm or less, and even more preferably 0.1 μm or more and 600 μm or less. By setting the fiber length within the above range, destruction of the crystalline regions of the fine fibrous cellulose can be suppressed. It also becomes possible to set the slurry viscosity of the fine fibrous cellulose within an appropriate range. The fiber length of the fine fibrous cellulose can be determined by image analysis using, for example, TEM, SEM, or atomic force microscope (AFM).

[0028] The fine fibrous cellulose preferably has a type I crystal structure. The fact that the fine fibrous cellulose has a type I crystal structure can be identified by a diffraction profile obtained from a wide-angle X-ray diffraction photograph using CuKα (λ=1.5418 Å) monochromated with graphite. Specifically, it can be identified by the presence of typical peaks at two positions: near 2θ=14° to 17° and near 2θ=22° to 23°. The proportion of type I crystal structure in the fine fibrous cellulose is, for example, preferably 30% or more, more preferably 40% or more, and even more preferably 50% or more. This can be expected to provide even better performance in terms of the expression of a low linear thermal expansion coefficient. The degree of crystallinity can be determined by measuring the X-ray diffraction profile and using a conventional method from the pattern (Seagal et al., Textile Research Journal, Vol. 29, p. 786, 1959).

[0029] The axial ratio (fiber length / fiber width) of the fine fibrous cellulose is not particularly limited, but is preferably, for example, 20 to 10,000, and more preferably 50 to 1,000. By setting the axial ratio to the above lower limit or more, a sheet containing the fine fibrous cellulose can be easily formed. By setting the axial ratio to the above upper limit or less, it is preferable in that, for example, when the fine fibrous cellulose is used as an aqueous dispersion, handling such as dilution becomes easier.

[0030] The fine fibrous cellulose in this embodiment preferably has at least one of an ionic substituent and a nonionic substituent. From the viewpoint of improving the dispersibility of fibers in a dispersion medium and increasing the defibration efficiency in the defibration treatment, it is more preferable that the fine fibrous cellulose has an ionic substituent. The ionic substituent may include, for example, either an anionic group or a cationic group, or both. Furthermore, the nonionic substituent may include, for example, an alkyl group and an acyl group. In this embodiment, it is particularly preferable that the ionic substituent has an anionic group. Furthermore, the ionic substituent is preferably a group that is introduced into the fine fibrous cellulose via an ester bond or an ether bond, and more preferably a group that is introduced into the fine fibrous cellulose via an ester bond. In this case, the ester bond is preferably formed by dehydration condensation between the fine fibrous cellulose and a compound that becomes the ionic substituent. Note that the fine fibrous cellulose does not need to be subjected to a treatment to introduce an ionic substituent.

[0031] Examples of anionic groups as ionic substituents include phosphorus oxo acid groups or substituents derived from phosphorus oxo acid groups (sometimes simply referred to as phosphorus oxo acid groups), carboxy groups or substituents derived from carboxy groups (sometimes simply referred to as carboxy groups), sulfur oxo acid groups or substituents derived from sulfur oxo acid groups (sometimes simply referred to as sulfur oxo acid groups), xanthate groups or substituents derived from xanthate groups (sometimes simply referred to as xanthate groups), phosphonic groups or substituents derived from phosphonic groups, phosphine groups or substituents derived from phosphine groups, sulfonic groups or substituents derived from sulfonic groups, and carboxyalkyl groups. Among these, the anionic group is preferably at least one selected from the group consisting of phosphorus oxoacid groups, substituents derived from phosphorus oxoacid groups, carboxy groups, carboxymethyl groups, carboxyethyl groups, sulfur oxoacid groups and sulfur oxoacid groups, xanthate groups, and sulfonic acid groups. It is more preferably at least one selected from the group consisting of phosphorus oxoacid groups, substituents derived from phosphorus oxoacid groups, carboxy groups, sulfur oxoacid groups, and sulfur oxoacid groups. It is more preferably at least one selected from the group consisting of phosphorus oxoacid groups, substituents derived from phosphorus oxoacid groups, carboxy groups, sulfur oxoacid groups, and sulfur oxoacid groups. It is particularly preferably a phosphorus oxoacid group. By introducing a phosphorus oxoacid group as an anionic group, the dispersibility of fibrous cellulose can be further improved, even under alkaline or acidic conditions, resulting in a high-strength, highly transparent fine fibrous cellulose-containing layer. Examples of cationic groups as ionic substituents include ammonium groups, phosphonium groups, sulfonium groups, etc. Among these, the cationic group is preferably an ammonium group.

[0032] The phosphorus oxo acid group or the substituent derived from the phosphorus oxo acid group is, for example, a substituent represented by the following formula (1). A plurality of substituents represented by the following formula (1) may be introduced into each fine fibrous cellulose. In this case, the plurality of introduced substituents represented by the following formula (1) may be the same or different.

[0033]

[0034] In formula (1), a, b, and n are natural numbers, and m is an arbitrary number (where a=b×m). At least one (preferably a) of n α and α′ is O. － and the rest are R or OR. Note that all of α and α' are O － The n α's may all be the same or may be different. ｂ＋ is a monovalent or higher cation composed of an organic or inorganic substance. R is each a hydrogen atom, a saturated linear hydrocarbon group, a saturated branched hydrocarbon group, a saturated cyclic hydrocarbon group, an unsaturated linear hydrocarbon group, an unsaturated branched hydrocarbon group, an unsaturated cyclic hydrocarbon group, an aromatic group, or a group derived from any of these. In addition, α in formula (1) may be a group derived from a cellulose molecular chain. In addition, in formula (1), n ​​is preferably 1.

[0035] Examples of saturated linear hydrocarbon groups 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 saturated branched hydrocarbon groups include, but are not limited to, an i-propyl group, an t-butyl group, and the like. Examples of saturated cyclic hydrocarbon groups include, but are not limited to, a cyclopentyl group, an cyclohexyl group, and the like. Examples of unsaturated linear hydrocarbon groups include, but are not limited to, a vinyl group, an allyl group, and the like. Examples of unsaturated branched hydrocarbon groups include, but are not limited to, an i-propenyl group, an 3-butenyl group, and the like. Examples of unsaturated cyclic hydrocarbon groups include, but are not limited to, a cyclopentenyl group, an cyclohexenyl group, and the like. Examples of aromatic groups include, but are not limited to, a phenyl group, an naphthyl group, and the like. In addition, the derivative group in R may be a carboxy group, a carboxylate group (-COO), or the like, which is bonded to the main chain or side chain of the above-mentioned various hydrocarbon groups. －), a hydroxy group, an amino group, and the like. Examples of functional groups include, but are not limited to, functional groups to which at least one type of functional group selected from the group consisting of an alkyl group, a hydroxy group, and an amino group is added or substituted. Furthermore, the number of carbon atoms constituting the main chain of R is not particularly limited, but is preferably 20 or less, and more preferably 10 or less. By setting the number of carbon atoms constituting the main chain of R within the above range, the molecular weight of the phosphorus oxoacid group can be set within an appropriate range, facilitating penetration into the fiber raw material and increasing the yield of fine fibrous cellulose. When multiple Rs are present in formula (1) or when multiple types of substituents represented by formula (1) are introduced into the fine fibrous cellulose, the multiple Rs present may be the same or different.

[0036] β ｂ＋ is a monovalent or higher cation made of an organic or inorganic substance. Examples of the monovalent or higher cation made of an organic substance include organic onium ions. Examples of the organic onium ions include organic ammonium ions and organic phosphonium ions. Examples of the organic ammonium ions include aliphatic ammonium ions and aromatic ammonium ions, and examples of the organic phosphonium ions include aliphatic phosphonium ions and aromatic phosphonium ions. Examples of the monovalent or higher cation made of an inorganic substance include, but are not limited to, ions of alkali metals such as sodium, potassium, or lithium, ions of divalent metals such as calcium or magnesium, hydrogen ions, ammonium ions, etc. These can be used alone or in combination of two or more types. Note that β in formula (1) ｂ＋ When a plurality of β ｂ＋ may be the same or different. The monovalent or higher cations made of organic or inorganic substances include β ｂ＋ Sodium or potassium ions are preferred because they are less likely to yellow when the fiber raw material containing the cation is heated and are easy to use industrially, but there is no particular limitation.

[0037] More specifically, the phosphorus oxo acid group or a substituent derived from a phosphorus oxo acid group is a phosphate group (-PO ３ H ２ ), salts of phosphate groups, phosphite groups (phosphonic acid groups) (-PO ２ H ２ and salts of phosphorous acid groups (phosphonic acid groups). The phosphorus oxo acid group or the substituent derived from the phosphorus oxo acid group may be a group in which a phosphoric acid group is condensed (e.g., a pyrophosphate group), a group in which a phosphonic acid is condensed (e.g., a polyphosphonic acid group), a phosphate ester group (e.g., a monomethyl phosphate group, a polyoxyethylene alkyl phosphate group), an alkyl phosphonic acid group (e.g., a methyl phosphonic acid group), or the like.

[0038] The sulfur oxoacid group (a sulfur oxoacid group or a substituent derived from a sulfur oxoacid group) is, for example, a substituent represented by the following formula (2). A plurality of types of substituents represented by the following formula (2) may be introduced into each fine fibrous cellulose. In this case, the plurality of introduced substituents represented by the following formula (2) may be the same or different.

[0039]

[0040] In formula (2), 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, multiple p's may be the same number or different numbers. In formula (2), β ｂ＋is a monovalent or higher cation composed of an organic or inorganic substance. Examples of the monovalent or higher cation composed of an organic substance include organic onium ions. Examples of the organic onium ions include organic ammonium ions and organic phosphonium ions. Examples of the organic ammonium ions include aliphatic ammonium ions and aromatic ammonium ions, and examples of the organic phosphonium ions include aliphatic phosphonium ions and aromatic phosphonium ions. Examples of the monovalent or higher cation composed of an inorganic substance include ions of alkali metals such as sodium, potassium, or lithium, ions of divalent metals such as calcium or magnesium, hydrogen ions, ammonium ions, etc. Note that when multiple types of substituents represented by the above formula (2) are introduced into the fine fibrous cellulose, the multiple β ｂ＋ may be the same or different. The monovalent or higher cations made of organic or inorganic substances include β ｂ＋ Sodium or potassium ions are preferred because they are less likely to yellow when the fiber raw material containing the cation is heated and are easy to use industrially, but there is no particular limitation.

[0041] The amount of ionic substituent introduced into the fine fibrous cellulose is, for example, preferably 0.05 mmol / g or more per 1 g (mass) of fine fibrous cellulose, more preferably 0.10 mmol / g or more, even more preferably 0.20 mmol / g or more, even more preferably 0.50 mmol / g or more, and particularly preferably 1.00 mmol / g or more. Furthermore, the amount of ionic substituent introduced into the fine fibrous cellulose is, for example, preferably 5.20 mmol / g or less per 1 g (mass) of fibrous cellulose, more preferably 3.65 mmol / g or less, even more preferably 3.50 mmol / g or less, and even more preferably 3.00 mmol / g or less. By setting the amount of ionic substituent (preferably anionic group) introduced within the above range, it is possible to facilitate the micronization of the fiber raw material and to increase the stability of the fine fibrous cellulose. Here, the denominator in the unit mmol / g is calculated based on the fact that the counter ion of the ionic substituent is a hydrogen ion (H ＋ ) indicates the mass of the fine fibrous cellulose when

[0042] Furthermore, the amount of ionic substituents (preferably anionic groups) introduced into the fine fibrous cellulose is, from the viewpoint of the water absorption of the laminate, preferably less than 0.50 mmol / g per 1 g (mass) of fine fibrous cellulose, more preferably 0.40 mmol / g or less, even more preferably 0.30 mmol / g or less, even more preferably 0.25 mmol / g or less, and particularly preferably 0.15 mmol / g or less, and from the viewpoint of the total light transmittance and haze of the laminate, preferably 0.01 mmol / g or more, more preferably 0.02 mmol / g or more, and even more preferably 0.03 mmol / g or more. Such low-substituent amount fine fibrous cellulose may be obtained, for example, by subjecting the fine fibrous cellulose to a treatment for removing substituents, as described below.

[0043] The amount of ionic substituents introduced into the fine fibrous cellulose can be measured, for example, by neutralization titration, in which an alkali such as an aqueous sodium hydroxide solution is added to a slurry containing the obtained fine fibrous cellulose, and the amount introduced is measured by determining the change in pH.

[0044] FIG. 1 is a graph showing the relationship between the amount of NaOH added dropwise to a slurry containing fibrous cellulose having phosphorus oxo acid groups and pH. The amount of phosphorus oxo acid groups introduced into fibrous cellulose is measured, for example, as follows. First, a slurry containing fibrous cellulose is treated with a strongly acidic ion exchange resin. If necessary, the measurement target may be subjected to a defibration treatment similar to the defibration treatment process described below before treatment with the strongly acidic ion exchange resin. Next, the change in pH is observed while adding aqueous sodium hydroxide solution, and a titration curve such as that shown in the upper part of FIG. 1 is obtained. The titration curve shown in the upper part of FIG. 1 plots the measured pH against the amount of alkali added, while the titration curve shown in the lower part of FIG. 1 plots the pH increment (differential value) (1 / mmol) against the amount of alkali added. In this neutralization titration, two points at which the increment (differential value of pH with respect to the amount of alkali added) is maximized are identified on the curve plotting the measured pH against the amount of alkali added. Of these, the first maximum point of the increment obtained after starting the addition of alkali is called the first endpoint, and the next maximum point of the increment is called the second endpoint. The amount of alkali required from the start of titration to the first endpoint is equal to the amount of first dissociated acid of the fibrous cellulose contained in the slurry used for titration, the amount of alkali required from the first endpoint to the second endpoint is equal to the amount of second dissociated acid of the fibrous cellulose contained in the slurry used for titration, and the amount of alkali required from the start of titration to the second endpoint is equal to the total amount of dissociated acid of the fibrous cellulose contained in the slurry used for titration. The value obtained by dividing the amount of alkali required from the start of titration to the first endpoint by the solids content (g) in the slurry to be titrated is the amount of phosphorus oxo acid group introduced (mmol / g). Note that when simply referring to the amount of phosphorus oxo acid group introduced (or amount of phosphorus oxo acid group), it refers to the amount of first dissociated acid. 1, the region from the start of titration to the first endpoint is referred to as Region 1, and the region from the first endpoint to the second endpoint is referred to as Region 2. For example, when the phosphorus oxoacid group is a phosphate group and this phosphate group undergoes condensation, the amount of weak acid groups in the phosphorus oxoacid group (also referred to herein as the second dissociated acid amount) appears to decrease, and the amount of alkali required in Region 2 becomes smaller than the amount of alkali required in Region 1.On the other hand, the amount of strong acid groups in the phosphorus oxoacid group (also referred to herein as the amount of first dissociated acid) is equal to the amount of phosphorus atoms, regardless of whether condensation occurs or not. Furthermore, when the phosphorus oxoacid group is a phosphorous acid group, the phosphorus oxoacid group does not contain any weakly acidic groups, so the amount of alkali required for the second region may be reduced or even zero. In this case, the titration curve will have only one point at which the pH increment is maximized. The above-mentioned amount of introduced phosphorus oxoacid groups (mmol / g) indicates the amount of phosphorus oxoacid groups in the acid-form fibrous cellulose (hereinafter referred to as the amount of phosphorus oxoacid groups (acid form)), since the denominator indicates the mass of the acid-form fibrous cellulose. On the other hand, when the counter ions of the phosphorus oxoacid groups are substituted with any cation C so as to be charge equivalent, the amount of phosphorus oxoacid groups possessed by the fibrous cellulose when the cation C is the counter ion (hereinafter referred to as the amount of phosphorus oxoacid groups (type C)) can be determined by converting the denominator to the mass of the fibrous cellulose when the cation C is the counter ion. That is, it is calculated using the following formula: Amount of phosphorus oxoacid groups (type C) = Amount of phosphorus oxoacid groups (acid type) / {1 + (W - 1) × A / 1000}, where A [mmol / g] is the total amount of anions derived from phosphorus oxoacid groups possessed by the fibrous cellulose (the sum of the amount of strongly acidic groups and the amount of weakly acidic groups in the phosphorus oxoacid groups), and W is the formula weight per valence of the cation C (for example, 23 for Na and 9 for Al).

[0045] FIG. 2 is a graph showing the relationship between the amount of NaOH added to carboxyl-containing fine fibrous cellulose and pH. The amount of carboxyl groups introduced into fine fibrous cellulose is measured, for example, as follows. First, a slurry containing fine fibrous cellulose is treated with a strongly acidic ion exchange resin. If necessary, the measurement object may be subjected to a defibration treatment similar to the defibration treatment process described below before treatment with the strongly acidic ion exchange resin. Next, the change in pH is observed while adding aqueous sodium hydroxide, and a titration curve such as that shown in FIG. 2 is obtained. If necessary, the measurement object may be subjected to a defibration treatment similar to the defibration treatment process described below. As shown in FIG. 2, in this neutralization titration, a single point is observed where the increment (the differential value of pH with respect to the amount of alkali added) is maximized on the curve plotting the measured pH against the amount of alkali added. This maximum increment point is called the first endpoint. Here, the region from the start of titration to the first endpoint in FIG. 2 is called the first region. The amount of alkali required in the first region is equal to the amount of carboxyl groups in the slurry used in the titration. The amount of alkali (mmol) required in the first region of the titration curve was divided by the solid content (g) in the fine fibrous cellulose-containing slurry to be titrated to calculate the amount of carboxyl groups introduced (mmol / g). Note that the amount of carboxyl groups introduced (mmol / g) was calculated based on the case where the counter ions of the carboxyl groups were hydrogen ions (H ＋ ) (hereinafter referred to as the amount of carboxy groups (acid type)) per 1 g of mass of fibrous cellulose.

[0046] The above-mentioned amount of carboxy groups introduced (mmol / g) indicates the amount of carboxy groups possessed by the acid-form fibrous cellulose (hereinafter referred to as the amount of carboxy groups (acid form)), since the denominator is the mass of the acid-form fibrous cellulose. On the other hand, when the counter ions of the carboxy groups are substituted with any cation C so as to be charge equivalent, the amount of carboxy groups possessed by the fibrous cellulose in which the cation C is the counter ion (hereinafter referred to as the amount of carboxy groups (C form)) (mmol / g) can be determined by converting the denominator to the mass of the fibrous cellulose when the cation C is the counter ion. That is, it is calculated using the following formula: Amount of carboxy groups (C form) = Amount of carboxy groups (acid form) / {1 + (W - 1) × (Amount of carboxy groups (acid form)) / 1,000} W: Formula weight per valence of cation C (for example, 23 for Na, 9 for Al)

[0047] In measuring the amount of substituents by titration, if too much sodium hydroxide aqueous solution is added or if the titration interval is too short, the amount of substituents may be lower than expected, and an accurate value may not be obtained. An appropriate amount of addition and titration interval, for example, is preferably a 0.1 N sodium hydroxide aqueous solution titrated at 10 to 50 μL intervals over 5 to 30 seconds. Furthermore, to eliminate the influence of carbon dioxide dissolved in the fibrous cellulose-containing slurry, it is preferable to perform measurements while blowing an inert gas such as nitrogen gas into the slurry, for example, from 15 minutes before the start of titration until the end of titration.

[0048] The amount of sulfur oxoacid groups or sulfonic groups introduced into fibrous cellulose can be calculated by freeze-drying a slurry containing fibrous cellulose and then pulverizing the sample to measure the amount of sulfur. Specifically, a slurry containing fibrous cellulose is freeze-dried, and the resulting pulverized sample is subjected to pressure-heat decomposition using nitric acid in a sealed container, after which the sample is appropriately diluted and the amount of sulfur is measured by ICP-OES. The value calculated by dividing the value by the bone dry mass of the fibrous cellulose tested is taken as the amount of sulfur oxoacid groups or sulfonic groups (unit: mmol / g) of the fibrous cellulose.

[0049] <<Method for Producing Fine Fibrous Cellulose>> (Cellulose-Containing Fiber Raw Material) Fine fibrous cellulose is produced from a cellulose-containing fiber raw material. The cellulose-containing fiber raw material is not particularly limited, but pulp is preferably used because it is easily available and inexpensive. Examples of pulp include wood pulp, non-wood pulp, and deinked pulp. Examples of wood pulp include, but are not particularly limited to, chemical pulp such as hardwood kraft pulp (LBKP), softwood kraft pulp (NBKP), sulfite pulp (SP), dissolving pulp (DP), soda pulp (AP), unbleached kraft pulp (UKP), and oxygen-bleached kraft pulp (OKP), semi-chemical pulp such as semi-chemical pulp (SCP) and chemi-groundwood pulp (CGP), and mechanical pulp such as groundwood pulp (GP) and thermomechanical pulp (TMP, BCTMP). Non-wood pulps include, but are not limited to, cotton-based pulps such as cotton linters and cotton lint, and non-wood pulps such as hemp, straw, and bagasse. Deinked pulps include, but are not limited to, deinked pulp made from recycled paper. The pulps of this embodiment may be used alone or in combination. Among the above pulps, wood pulp and deinked pulp are preferred from the viewpoint of availability. Furthermore, among wood pulps, chemical pulps are more preferred, with kraft pulp and sulfite pulp being even more preferred, because they have a high cellulose content, resulting in a high yield of fine fibrous cellulose during defibration, and because cellulose decomposition in the pulp is minimal, resulting in the production of long-fiber fine fibrous cellulose with a high axial ratio. Using long-fiber fine fibrous cellulose with a high axial ratio tends to increase viscosity. Cellulose-containing fiber raw materials include, for example, cellulose contained in sea squirts and bacterial cellulose produced by acetic acid bacteria. Furthermore, instead of fiber raw materials containing cellulose, fibers formed from linear nitrogen-containing polysaccharide polymers such as chitin and chitosan can also be used.

[0050] In order to obtain the fine fibrous cellulose into which the above-mentioned ionic substituents have been introduced, it is preferable to have an ionic substituent introduction step for introducing an ionic substituent into the above-mentioned cellulose-containing fiber raw material, a washing step, an alkali treatment step (neutralization step), and a defibration treatment step in this order, and instead of or in addition to the washing step, an acid treatment step may be included. Examples of the ionic substituent introduction step include a phosphorus oxo acid group introduction step, a carboxy group introduction step, a sulfur oxo acid group introduction step, a xanthate group introduction step, a phosphonic or phosphine group introduction step, a sulfonic group introduction step, and a cationic group introduction step. Each of these steps will be explained below.

[0051] (Ionic Substituent Introduction Step) - Phosphorus Oxo Acid Group Introduction Step - The phosphorus oxo acid group introduction step is a step of reacting a cellulose-containing fiber raw material with at least one compound (hereinafter also referred to as "compound A") selected from compounds capable of introducing phosphorus oxo acid groups by reacting with hydroxyl groups possessed by the cellulose-containing fiber raw material. This step results in a fiber into which phosphorus oxo acid groups have been introduced. In the phosphorus oxo acid group introduction step according to this embodiment, the reaction of the cellulose-containing fiber raw material with compound A may be carried out in the presence of at least one selected from urea and its derivatives (hereinafter also referred to as "compound B"). Alternatively, the cellulose-containing fiber raw material may be reacted with compound A in the absence of compound B. One example of a method for reacting compound A with a fiber raw material in the coexistence of compound B is a method in which compound A and compound B are mixed with a dry, wet, or slurried fiber raw material. Of these, using a dry or wet fiber raw material is preferred because it results in high reaction uniformity, and using a dry fiber raw material is particularly preferred. The form of the fiber raw material is not particularly limited, but is preferably, for example, in the form of a cotton or thin sheet. Compound A and compound B can be added to the fiber raw material in the form of a powder, a solution dissolved in a solvent, or a melted state obtained by heating to or above their melting point. Of these, adding them in the form of a solution dissolved in a solvent, particularly an aqueous solution, is preferred because it results in high reaction uniformity. Compound A and compound B may be added to the fiber raw material simultaneously, separately, or as a mixture. The method for adding compound A and compound B is not particularly limited, but when compound A and compound B are in solution form, the fiber raw material may be immersed in the solution to absorb the liquid and then removed, or the solution may be added dropwise to the fiber raw material. Alternatively, the required amounts of compound A and compound B may be added to the fiber raw material, or excess amounts of compound A and compound B may be added to the fiber raw material, and then the excess compound A and compound B may be removed by squeezing or filtration.

[0052] The compound A used in this embodiment may be any compound that has a phosphorus atom and can form an ester bond with cellulose, including, but not limited to, phosphoric acid or a salt thereof, phosphorous acid or a salt thereof, dehydrated condensed phosphoric acid or a salt thereof, and phosphoric anhydride (diphosphorus pentoxide). Phosphoric acid can be used with various purities, such as 100% phosphoric acid (orthophosphoric acid) or 85% phosphoric acid. Phosphorous acid can be, for example, 99% phosphorous acid (phosphonic acid). Dehydrated condensed phosphoric acid is a compound in which two or more molecules of phosphoric acid are condensed by a dehydration reaction, and examples thereof include pyrophosphoric acid and polyphosphoric acid. Phosphates, phosphites, and dehydrated condensed phosphates include lithium salts, sodium salts, potassium salts, and ammonium salts of phosphoric acid, phosphorous acid, or dehydrated condensed phosphoric acid, which can be neutralized to various degrees. Among these, phosphoric acid, sodium salt of phosphoric acid, potassium salt of phosphoric acid, or ammonium salt of phosphoric acid is preferred from the viewpoints of high efficiency of introduction of phosphorus oxoacid groups, easier improvement of defibration efficiency in the defibration step described below, low cost, and ease of industrial application, and phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, or ammonium dihydrogen phosphate is more preferred. The amount of compound A added to the fiber raw material is not particularly limited, but for example, when the amount of compound A added is converted into the amount of phosphorus atoms, the amount of phosphorus atoms added per 100 parts by mass of fiber raw material (bone dry mass) is preferably 0.5 parts by mass or more and 100 parts by mass or less, more preferably 1 part by mass or more and 50 parts by mass or less, and even more preferably 2 parts by mass or more and 30 parts by mass or less. By setting the amount of phosphorus atoms added to the fiber raw material within the above range, the yield of fine fibrous cellulose can be further improved. On the other hand, by setting the amount of phosphorus atoms added to the fiber raw material to the above upper limit or less, a balance between the yield improvement effect and cost can be achieved.

[0053] As described above, compound B used in this embodiment is at least one selected from urea and its derivatives. Examples of compound B include urea, biuret, 1-phenylurea, 1-benzylurea, 1-methylurea, and 1-ethylurea. From the viewpoint of improving the uniformity of the reaction, compound B is preferably used as an aqueous solution. Furthermore, from the viewpoint of further improving the uniformity of the reaction, it is preferable to use an aqueous solution in which both compound A and compound B are dissolved. The amount of compound B added per 100 parts by mass (bone dry mass) of the fiber raw material is not particularly limited, but is, for example, preferably 1 part by mass or more and 500 parts by mass or less, more preferably 10 parts by mass or more and 400 parts by mass or less, and even more preferably 100 parts by mass or more and 350 parts by mass or less.

[0054] In the reaction of a fiber raw material containing cellulose with compound A, the reaction system may contain, in addition to compound B, for example, amides or amines. Examples of amides include formamide, dimethylformamide, acetamide, and dimethylacetamide. Examples of amines include methylamine, ethylamine, trimethylamine, triethylamine, monoethanolamine, diethanolamine, triethanolamine, pyridine, ethylenediamine, and hexamethylenediamine. Among these, triethylamine is known to function as a particularly good reaction catalyst.

[0055] In the phosphorus oxo acid group introduction step, it is preferable to add or mix compound A or the like to or with the fiber raw material, and then heat-treat the fiber raw material. The heat treatment temperature is preferably selected so that the phosphorus oxo acid group can be efficiently introduced while suppressing thermal decomposition and hydrolysis of the fiber. The heat treatment temperature is, for example, preferably 50°C or higher and 300°C or lower, more preferably 100°C or higher and 250°C or lower, and even more preferably 130°C or higher and 200°C or lower. Various types of equipment having heat transfer media can be used for the heat treatment, including, for example, a stirring dryer, a rotary dryer, a disk dryer, a roll-type heater, a plate-type heater, a fluidized-bed dryer, a band-type dryer, a filtration dryer, a vibration fluidized-bed dryer, a flash dryer, a reduced-pressure dryer, an infrared heater, a far-infrared heater, a microwave heater, and a high-frequency dryer.

[0056] In the heat treatment according to this embodiment, for example, compound A may be added to a thin sheet-like fiber raw material by impregnation or other methods, followed by heating, or heating while kneading or stirring the fiber raw material and compound A in a kneader or the like. This suppresses unevenness in the concentration of compound A in the fiber raw material, enabling phosphorus oxoacid groups to be more uniformly introduced onto the surface of the cellulose fibers contained in the fiber raw material. This is thought to be due to the fact that, when water molecules move to the surface of the fiber raw material as it dries, the dissolved compound A is attracted to the water molecules by surface tension and is prevented from migrating to the surface of the fiber raw material (i.e., causing unevenness in the concentration of compound A). Furthermore, it is preferable that the heating device used in the heat treatment is a device that can constantly discharge, to the outside of the device system, moisture retained in the slurry and moisture generated by the dehydration condensation (phosphate esterification) reaction between compound A and hydroxyl groups contained in cellulose or the like in the fiber raw material. Examples of such heating devices include a blower oven. By constantly draining the water from the apparatus, it is possible to suppress the hydrolysis of phosphate ester bonds, which is the reverse reaction of phosphate esterification, and also to suppress acid hydrolysis of sugar chains in the fibers. This makes it possible to obtain fine fibrous cellulose with a high axial ratio. The heat treatment time is, for example, preferably 1 second to 300 minutes, more preferably 1 second to 1,000 seconds, and even more preferably 10 seconds to 800 seconds, after the water has been substantially removed from the fiber raw material. In this embodiment, the amount of phosphorus oxo acid groups introduced can be kept within a preferred range by setting the heating temperature and heating time within appropriate ranges.

[0057] The amount of phosphorus oxoacid groups introduced into the fiber raw material is, for example, preferably 0.05 mmol / g or more per 1 g (mass) of fine fibrous cellulose, more preferably 0.10 mmol / g or more, even more preferably 0.20 mmol / g or more, even more preferably 0.50 mmol / g or more, and particularly preferably 1.00 mmol / g or more. The amount of phosphorus oxoacid groups introduced into the fiber raw material is, for example, preferably 5.20 mmol / g or less per 1 g (mass) of fine fibrous cellulose, more preferably 3.65 mmol / g or less, and even more preferably 3.00 mmol / g or less. By keeping the amount of phosphorus oxoacid groups introduced within the above range, it is possible to facilitate the micronization of the fiber raw material and improve the stability of the fine fibrous cellulose.

[0058] -Carboxy Group Introduction Process- The carboxyl group introduction process is carried out by treating a cellulose-containing fiber raw material with an oxidation process such as ozone oxidation, oxidation by the Fenton method, or TEMPO oxidation, or with a compound having a carboxylic acid-derived group or a derivative thereof, or an acid anhydride of a compound having a carboxylic acid-derived group or a derivative thereof. Examples of compounds having a carboxylic acid-derived group include, but are not limited to, dicarboxylic acid compounds such as maleic acid, succinic acid, phthalic acid, fumaric acid, glutaric acid, adipic acid, and itaconic acid, and tricarboxylic acid compounds such as citric acid and aconitic acid. Examples of derivatives of compounds having a carboxylic acid-derived group include, but are not limited to, imidized products of acid anhydrides of compounds having a carboxyl group, and derivatives of acid anhydrides of compounds having a carboxyl group. Examples of imidized products of acid anhydrides of compounds having a carboxyl group include, but are not limited to, imidized products of dicarboxylic acid compounds such as maleimide, succinimide, and phthalimide.

[0059] The acid anhydride of a compound having a group derived from carboxylic acid is not particularly limited, but examples thereof include acid anhydrides of dicarboxylic acid compounds such as maleic anhydride, succinic anhydride, phthalic anhydride, glutaric anhydride, adipic anhydride, itaconic anhydride, etc. Furthermore, the derivative of an acid anhydride of a compound having a group derived from carboxylic acid is not particularly limited, but examples thereof include acid anhydrides of compounds having carboxy groups such as dimethylmaleic anhydride, diethylmaleic anhydride, diphenylmaleic anhydride, etc. in which at least some of the hydrogen atoms have been substituted with substituents such as alkyl groups or phenyl groups.

[0060] When TEMPO oxidation treatment is performed in the carboxyl group introduction step, it is preferable to perform the treatment under conditions of pH 6 or higher and 8 or lower. This type of treatment is also referred to as neutral TEMPO oxidation treatment. Neutral TEMPO oxidation treatment can be performed, for example, by adding pulp as the fiber raw material, a nitroxy radical such as TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl) as a catalyst, and sodium hypochlorite as a sacrificial reagent to a sodium phosphate buffer solution (pH = 6.8). Furthermore, by adding sodium chlorite, aldehydes generated during the oxidation process can be efficiently oxidized to carboxyl groups. The TEMPO oxidation treatment may also be performed under conditions of pH 10 or higher and 11 or lower. This type of treatment is also referred to as alkaline TEMPO oxidation treatment. The alkaline TEMPO oxidation treatment can be performed, for example, by adding a nitroxy radical such as TEMPO as a catalyst, sodium bromide as a co-catalyst, and sodium hypochlorite as an oxidizing agent to pulp as the fiber raw material. The amount of carboxy groups introduced into the fiber raw material varies depending on the type of substituent. For example, when carboxy groups are introduced by TEMPO oxidation, the amount is preferably 0.05 mmol / g or more per 1 g (mass) of fine fibrous cellulose, more preferably 0.10 mmol / g or more, even more preferably 0.20 mmol / g or more, even more preferably 0.50 mmol / g or more, and particularly preferably 0.90 mmol / g or more. The amount is preferably 3.65 mmol / g or less, more preferably 3.00 mmol / g or less, even more preferably 2.50 mmol / g or less, even more preferably 2.20 mmol / g or less, and particularly preferably 2.00 mmol / g or less. Furthermore, when the substituent is a carboxymethyl group, the amount may be 5.8 mmol / g or less per 1 g (mass) of fine fibrous cellulose. By setting the amount of carboxy groups introduced within the above range, it is possible to facilitate the refinement of cellulose fibers in the refinement treatment step and improve the stability of the fine fibrous cellulose.

[0061] -Sulfur oxoacid group introduction step- The process for producing fine fibrous cellulose may include, for example, a sulfur oxoacid group introduction step as an ionic substituent introduction step. In the sulfur oxoacid group introduction step, hydroxyl groups in a fiber raw material containing cellulose are reacted with sulfur oxoacids to obtain cellulose fibers having sulfur oxoacid groups (sulfur oxoacid group-introduced fibers).

[0062] In the sulfur oxo acid group introduction step, instead of compound A in the above-described <Phosphorus oxo acid group introduction step>, at least one compound (hereinafter also referred to as "compound C") selected from compounds capable of introducing sulfur oxo acid groups by reacting with hydroxyl groups in a fiber raw material containing cellulose is used. Compound C may be any compound containing a sulfur atom and capable of forming an ester bond with cellulose, including, but not limited to, sulfuric acid or a salt thereof, sulfurous acid or a salt thereof, and sulfuric acid amide. Sulfuric acid of various purities can be used, for example, 96% sulfuric acid (concentrated sulfuric acid). Examples of sulfurous acid include 5% aqueous sulfurous acid. Examples of sulfates or sulfites include lithium, sodium, potassium, and ammonium salts of sulfates or sulfites, which can be neutralized to various degrees. Examples of sulfuric acid amides include sulfamic acid. In the sulfur oxo acid group introduction step, it is preferable to use compound B in the above-described <Phosphorus oxo acid group introduction step> as well.

[0063] In the sulfur oxoacid group introduction step, it is preferable to mix a cellulose raw material with an aqueous solution containing a sulfur oxoacid and urea and / or a urea derivative, and then heat-treat the cellulose raw material. The heat-treatment temperature is preferably selected so that sulfur oxoacid groups can be efficiently introduced while suppressing thermal decomposition and hydrolysis of the fiber. The heat-treatment temperature is preferably 100°C or higher, more preferably 120°C or higher, and even more preferably 150°C or higher. The heat-treatment temperature is preferably 300°C or lower, more preferably 250°C or lower, and even more preferably 200°C or lower.

[0064] In the heat treatment step, heating is preferably performed until substantially no moisture is present. Therefore, the heat treatment time varies depending on the amount of moisture contained in the cellulose raw material and the amount of aqueous solution containing sulfur oxoacid and urea and / or a urea derivative added, but is preferably, for example, 10 seconds to 10,000 seconds. For the heat treatment, various devices having a heat medium can be used, such as an agitator dryer, rotary dryer, disk dryer, roll-type heater, plate-type heater, fluidized-bed dryer, band-type dryer, filtration dryer, vibration fluidized dryer, flash dryer, reduced-pressure dryer, infrared heater, far-infrared heater, microwave heater, and high-frequency dryer.

[0065] The amount of sulfur oxoacid groups introduced into the cellulose raw material is preferably 0.05 mmol / g or more, more preferably 0.10 mmol / g or more, even more preferably 0.20 mmol / g or more, even more preferably 0.50 mmol / g or more, and particularly preferably 0.90 mmol / g or more. The amount of sulfur oxoacid groups introduced into the cellulose raw material is preferably 5.00 mmol / g or less, more preferably 3.00 mmol / g or less. By keeping the amount of sulfur oxoacid groups introduced within the above range, it is possible to easily pulverize the fiber raw material and improve the stability of the fibrous cellulose.

[0066] - Oxidation step using a chlorine-based oxidizing agent (second carboxyl group introduction step) - The ionic substituent introduction step may include an oxidation step using a chlorine-based oxidizing agent. In the oxidation step using a chlorine-based oxidizing agent, a chlorine-based oxidizing agent is added to a wet or dry fiber raw material having a hydroxyl group to cause a reaction, thereby introducing a carboxyl group into the fiber raw material.

[0067] Examples of chlorine-based oxidizing agents include hypochlorous acid, hypochlorites, chlorous acid, chlorites, chloric acid, chlorates, perchloric acid, perchlorates, and chlorine dioxide. From the viewpoints of the efficiency of introducing substituents, and therefore the defibration efficiency, cost, and ease of handling, the chlorine-based oxidizing agent is preferably sodium hypochlorite, sodium chlorite, or chlorine dioxide. When adding a chlorine-based oxidizing agent, it may be added to the fiber raw material as a reagent (solid or liquid) as is, or may be dissolved in an appropriate solvent and added.

[0068] The concentration of the chlorine-based oxidizing agent in the solution in the oxidation step using the chlorine-based oxidizing agent is, for example, preferably 1 to 1,000 mass %, more preferably 5 to 500 mass %, and even more preferably 10 to 100 mass %, calculated as an effective chlorine concentration. The amount of the chlorine-based oxidizing agent added per 100 parts by mass of the fiber raw material is preferably 1 to 100,000 parts by mass, more preferably 10 to 10,000 parts by mass, and even more preferably 100 to 5,000 parts by mass.

[0069] The reaction time with the chlorine-based oxidizing agent in the oxidation step using the chlorine-based oxidizing agent may vary depending on the reaction temperature, but is preferably, for example, from 1 minute to 1,000 minutes, more preferably from 10 minutes to 500 minutes, and even more preferably from 20 minutes to 400 minutes. The pH during the reaction is preferably from 5 to 15, more preferably from 7 to 14, and even more preferably from 9 to 13. At the start of the reaction, the pH during the reaction is preferably maintained constant (for example, pH 11) by appropriately adding hydrochloric acid or sodium hydroxide. After the reaction, excess reaction reagents, by-products, etc. may be washed and removed with water by filtration or the like.

[0070] -Xanthate group introduction step (xanthogenic acid esterification step)- The ionic substituent introduction step may include, for example, a xanthate group introduction step (hereinafter also referred to as a xanthation step). In the xanthation step, carbon disulfide and an alkali compound are added to a wet or dry fiber raw material having a hydroxyl group and reacted to introduce a xanthate group into the fiber raw material. Specifically, carbon disulfide is added to a fiber raw material that has been converted into alkali cellulose by the method described below, and the reaction is carried out.

[0071] ((Alkali Cellulose Formation)) When introducing an ionic substituent into a fiber raw material, it is preferable to convert the cellulose contained in the fiber raw material into alkali cellulose by treating the cellulose with an alkaline solution. This treatment causes ionic dissociation of some of the hydroxyl groups of the cellulose, thereby increasing the nucleophilicity (reactivity). The alkaline compound contained in the alkaline solution is not particularly limited, and may be an inorganic alkaline compound or an organic alkaline compound. Due to their high versatility, it is preferable to use, for example, sodium hydroxide, potassium hydroxide, tetraethylammonium hydroxide, or tetrabutylammonium hydroxide. The conversion into alkali cellulose may be carried out simultaneously with the introduction of the ionic substituent, before the introduction, or at both the same time.

[0072] The solution temperature at the start of alkali cellulose formation is preferably 0°C or higher and 50°C or lower, more preferably 5°C or higher and 40°C or lower, and even more preferably 10°C or higher and 30°C or lower.

[0073] The alkali concentration in the alkaline solution is preferably 0.01 mol / L or more and 4 mol / L or less, more preferably 0.1 mol / L or more and 3 mol / L or less, and even more preferably 1 mol / L or more and 2.5 mol / L or less, in terms of molar concentration. In particular, when the treatment temperature in alkali cellulose formation is less than 10° C., the alkali concentration is preferably 1 mol / L or more and 2 mol / L or less.

[0074] The treatment time for alkali cellulose formation is preferably 1 minute or more, more preferably 10 minutes or more, and even more preferably 30 minutes or more, and the alkali treatment time is preferably 6 hours or less, more preferably 5 hours or less, and even more preferably 4 hours or less.

[0075] By adjusting the type of alkaline solution, treatment temperature, concentration, and immersion time as described above, it is possible to suppress penetration of the alkaline solution into the crystalline regions of cellulose, making it easier to maintain the cellulose type I crystal structure and increasing the yield of fine fibrous cellulose.

[0076] When the introduction of ionic substituents and the conversion to alkali cellulose are not carried out simultaneously, the conversion to alkali cellulose is preferably carried out before the introduction of ionic substituents. In this case, the alkali cellulose obtained by the conversion to alkali cellulose treatment is preferably subjected to solid-liquid separation by a common deliquoring method such as centrifugation or filtration to remove moisture. This improves the reaction efficiency in the subsequent ionic substituent introduction step. The cellulose fiber concentration after solid-liquid separation is preferably 5% to 50%, more preferably 10% to 40%, and even more preferably 15% to 35%.

[0077] - Phosphonic or Phosphine Group Introduction Step (Phosphoalkylation Step) - The ionic substituent introduction step may include a phosphonic or phosphine group introduction step (phosphoalkylation step). In the phosphoalkylation step, a compound having a reactive group and a phospho or phosphine group (compound E) is used as an essential component. Ａ ), and an optional component, an alkali compound, and a compound B selected from the above-mentioned urea and its derivatives are added to a wet or dry fiber raw material having a hydroxyl group, and the reaction is carried out to introduce a phosphonic group or a phosphine group into the fiber raw material.

[0078] Examples of the reactive group include a halogenated alkyl group, a vinyl group, and an epoxy group (glycidyl group). ＡExamples of the compound include vinylphosphonic acid, phenylvinylphosphonic acid, and phenylvinylphosphinic acid. In terms of the efficiency of introducing substituents, and therefore the defibration efficiency, cost, and ease of handling, Compound E Ａ is preferably vinylphosphonic acid. Furthermore, as an optional component, it is also preferable to use the compound B in the above-mentioned <Phosphorus oxo acid group introduction step> in the same manner, and the amount added is also preferably as described above.

[0079] Compound E Ａ When adding, the reagent (solid or liquid) may be added directly to the fiber raw material, or may be dissolved in an appropriate solvent and added. The fiber raw material is preferably converted into alkali cellulose in advance or simultaneously with the reaction. The method for converting into alkali cellulose is as described above.

[0080] The temperature during the reaction is, for example, preferably 50°C or higher and 300°C or lower, more preferably 100°C or higher and 250°C or lower, and even more preferably 130°C or higher and 200°C or lower.

[0081] Compound E Ａ The amount of addition per 100 parts by mass of the fiber raw material is preferably 1 part by mass or more and 100,000 parts by mass or less, more preferably 2 parts by mass or more and 10,000 parts by mass or less, and even more preferably 5 parts by mass or more and 1,000 parts by mass or less.

[0082] The reaction time may vary depending on the reaction temperature, but is preferably from 1 minute to 1,000 minutes, more preferably from 10 minutes to 500 minutes, and even more preferably from 20 minutes to 400 minutes. After the reaction, excess reaction reagents, by-products, etc. may be washed and removed with water by filtration or the like.

[0083] - Sulfonic acid group introduction step (sulfoalkylation step) - The ionic substituent introduction step may include a sulfonic acid group introduction step (sulfoalkylation step). In the sulfoalkylation, a compound having a reactive group and a sulfonic acid group (compound E) is used as an essential component. Ｂ) and, as an optional component, an alkali compound and a compound B selected from the above-mentioned urea and its derivatives are added to a wet or dry fiber raw material having a hydroxyl group and reacted to introduce a sulfonic acid group into the fiber raw material.

[0084] Examples of the reactive group include a halogenated alkyl group, a vinyl group, and an epoxy group (glycidyl group). Ｂ Examples of suitable acrylic acid esters include sodium 2-chloroethanesulfonate, sodium vinylsulfonate, sodium p-styrenesulfonate, and 2-acrylamido-2-methylpropanesulfonic acid. Among these, compound E is particularly preferred in terms of the efficiency of introducing substituents, and therefore the defibration efficiency, cost, and ease of handling. Ｂ is preferably sodium vinyl sulfonate. Furthermore, as an optional component, it is also preferable to use the compound B in the above-mentioned <Phosphorus oxo acid group introduction step> in the same manner, and the amount added is also preferably as described above.

[0085] Compound E Ｂ When adding, the reagent (solid or liquid) may be added directly to the fiber raw material, or may be dissolved in an appropriate solvent and added. The fiber raw material is preferably converted into alkali cellulose in advance or simultaneously with the reaction. The method for converting into alkali cellulose is as described above.

[0086] The temperature during the reaction is, for example, preferably 50°C or higher and 300°C or lower, more preferably 100°C or higher and 250°C or lower, and even more preferably 130°C or higher and 200°C or lower.

[0087] Compound E Ｂ The amount of addition per 100 parts by mass of the fiber raw material is preferably 1 part by mass or more and 100,000 parts by mass or less, more preferably 2 parts by mass or more and 10,000 parts by mass or less, and even more preferably 5 parts by mass or more and 1,000 parts by mass or less.

[0088] The reaction time may vary depending on the reaction temperature, but is preferably, for example, from 1 minute to 1,000 minutes, more preferably from 10 minutes to 500 minutes, and even more preferably from 15 minutes to 400 minutes. After the reaction, excess reaction reagents, by-products, etc. may be washed and removed with water by filtration or the like.

[0089] -Carboxyalkylation Step (Third Carboxy Group Introduction Step)- The ionic substituent introduction step may include a carboxyalkylation step. As an essential component, a compound having a reactive group and a carboxy group (compound E Ｃ ), and an optional component, an alkaline compound, and a compound B selected from the above-mentioned urea and its derivatives are added to a wet or dry fiber raw material having a hydroxyl group and reacted to introduce a carboxyl group into the fiber raw material.

[0090] Examples of the reactive group include a halogenated alkyl group, a vinyl group, and an epoxy group (glycidyl group). Ｃ As the compound, monochloroacetic acid, sodium monochloroacetate, 2-chloropropionic acid, 3-chloropropionic acid, sodium 2-chloropropionate, and sodium 3-chloropropionate are preferred from the viewpoints of the efficiency of introducing the substituent, and therefore the defibration efficiency, cost, and ease of handling. Furthermore, it is also preferred to use, as an optional component, the compound B in the above-mentioned <Phosphorus oxoacid group introduction step> in the same manner, and the amount added is also preferably as described above.

[0091] Compound E Ｃ When adding, the reagent (solid or liquid) may be added directly to the fiber raw material, or may be dissolved in an appropriate solvent and added. The fiber raw material is preferably converted into alkali cellulose in advance or simultaneously with the reaction. The method for converting into alkali cellulose is as described above.

[0092] The temperature during the reaction is, for example, preferably 50°C or higher and 300°C or lower, more preferably 100°C or higher and 250°C or lower, and even more preferably 130°C or higher and 200°C or lower.

[0093] Compound EＣ The amount of addition per 100 parts by mass of the fiber raw material is preferably 1 part by mass or more and 100,000 parts by mass or less, more preferably 2 parts by mass or more and 10,000 parts by mass or less, and even more preferably 5 parts by mass or more and 1,000 parts by mass or less.

[0094] The reaction time may vary depending on the reaction temperature, but is preferably, for example, from 1 minute to 1,000 minutes, more preferably from 3 minutes to 500 minutes, and even more preferably from 5 minutes to 400 minutes. After the reaction, excess reaction reagents, by-products, etc. may be washed and removed with water by filtration or the like.

[0095] -Cationic group introduction step (cationization step)- As an essential component, a compound having a reactive group and a cationic group (compound E Ｄ ), and an optional component, an alkaline compound, and a compound B selected from the above-mentioned urea and its derivatives are added to a wet or dry fiber raw material having a hydroxyl group and reacted to introduce a cationic group into the fiber raw material.

[0096] Examples of reactive groups include halogenated alkyl groups, vinyl groups, and epoxy groups (glycidyl groups). Examples of cationic groups include ammonium groups, phosphonium groups, and sulfonium groups. Among these, the cationic group is preferably an ammonium group. Compound E Ｄ As the compound, glycidyl trimethyl ammonium chloride, 3-chloro-2-hydroxypropyl trimethyl ammonium chloride, etc. are preferred from the viewpoints of the efficiency of introducing the substituent, and therefore the defibration efficiency, cost, and ease of handling. Furthermore, it is also preferable to use, as an optional component, the compound B in the above-mentioned <Phosphorus oxo acid group introduction step> in the same manner. The amount added is also preferably as described above.

[0097] Compound E Ｄ When adding, the reagent (solid or liquid) may be added directly to the fiber raw material, or may be dissolved in an appropriate solvent and added. The fiber raw material is preferably converted into alkali cellulose in advance or simultaneously with the reaction. The method for converting into alkali cellulose is as described above.

[0098] The temperature during the reaction is, for example, preferably 50°C or higher and 300°C or lower, more preferably 100°C or higher and 250°C or lower, and even more preferably 130°C or higher and 200°C or lower.

[0099] Compound E Ｄ The amount of addition per 100 parts by mass of the fiber raw material is preferably 1 part by mass or more and 100,000 parts by mass or less, more preferably 2 parts by mass or more and 10,000 parts by mass or less, and even more preferably 5 parts by mass or more and 1,000 parts by mass or less.

[0100] The reaction time may vary depending on the reaction temperature, but is preferably from 1 minute to 1,000 minutes, more preferably from 5 minutes to 500 minutes, and even more preferably from 10 minutes to 400 minutes. After the reaction, excess reaction reagents, by-products, etc. may be washed and removed with water by filtration or the like.

[0101] (Washing step) In the method for producing fine fibrous cellulose in this embodiment, a washing step can be carried out on the ionic substituent-introduced fibers as needed. The washing step is carried out by washing the ionic substituent-introduced fibers with water or an organic solvent, for example. The washing step may be carried out after each step described below, and the number of washings carried out in each washing step is not particularly limited.

[0102] (Alkali Treatment (Neutralization Treatment) Step) When producing fine fibrous cellulose, an alkali treatment (neutralization treatment) may be performed on the fiber raw material between the ionic substituent introduction step and the defibration treatment step described below. The alkali treatment method is not particularly limited, and for example, a method of immersing the ionic substituent-introduced fibers in an alkaline solution may be used. 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. The solvent contained in the alkaline solution may be either water or an organic solvent. Among these, the solvent contained in the alkaline solution is preferably water or a polar solvent including a polar organic solvent such as an alcohol, and more preferably an aqueous solvent containing at least water. As the alkaline solution, for example, an aqueous sodium hydroxide solution or an aqueous potassium hydroxide solution is preferable because of its high versatility. The temperature of the alkaline solution in the alkali treatment step is not particularly limited, and is preferably, for example, from 5°C to 80°C, and more preferably from 10°C to 60°C. The immersion time of the ionic substituent-introduced fiber in the alkaline solution in the alkaline treatment step is not particularly limited, but is preferably, for example, from 5 to 30 minutes, and more preferably from 10 to 20 minutes. The amount of the alkaline solution used in the alkaline treatment is not particularly limited, but is, for example, preferably from 100 to 100,000% by mass, and more preferably from 1,000 to 10,000% by mass, based on the bone dry mass of the ionic substituent-introduced fiber.

[0103] In order to reduce the amount of alkaline solution used in the alkali treatment step, the ionic substituent-introduced fiber may be washed with water or an organic solvent after the ionic substituent-introducing step and before the alkali treatment step. From the viewpoint of improving handleability, it is preferable to wash the alkali-treated ionic substituent-introduced fiber with water or an organic solvent after the alkali treatment step and before the defibrating step.

[0104] (Acid Treatment Step) When producing fine fibrous cellulose, an acid treatment may be performed on the fiber raw material between the step of introducing an ionic substituent and the defibration treatment step described below. For example, the ionic substituent introduction step, acid treatment step, alkali treatment step, and defibration treatment step may be performed in this order. The acid treatment method is not particularly limited, but an example is a method of immersing the fiber raw material in an acid-containing acidic solution. The concentration of the acidic solution used is not particularly limited, but is preferably 10% by mass or less, and more preferably 5% by mass or less. The pH of the acidic solution used is also not particularly limited, but is preferably 0 to 4, and more preferably 1 to 3. Examples of acids that can be used in the acidic solution include inorganic acids, sulfonic acids, and carboxylic acids. Examples of inorganic acids include sulfuric acid, nitric acid, hydrobromic acid, hydroiodic acid, hypochlorous acid, chlorous acid, chloric acid, perchloric acid, phosphoric acid, and boric acid. Examples of sulfonic acids include methanesulfonic acid, ethanesulfonic acid, benzenesulfonic acid, p-toluenesulfonic acid, and trifluoromethanesulfonic acid. Examples of carboxylic acids include formic acid, acetic acid, citric acid, gluconic acid, lactic acid, oxalic acid, and tartaric acid. Among these, 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, for example, from 5°C to 100°C, and more preferably from 20°C to 90°C. The immersion time in the acid solution in the acid treatment is not particularly limited, but is, for example, preferably from 5 minutes to 120 minutes, and more preferably from 10 minutes to 60 minutes. The amount of the acid solution used in the acid treatment is not particularly limited, but is, for example, preferably from 100% by mass to 100,000% by mass, and more preferably from 1,000% by mass to 10,000% by mass, based on the bone dry mass of the fiber raw material.

[0105] (Defibrillation Treatment Step) Fine fibrous cellulose is obtained by defibrillating the ionic substituent-introduced fibers in the defibrillation treatment step. In the defibrillation treatment step, for example, a defibrillation treatment device can be used. The defibrillation treatment device is not particularly limited, and examples that can be used include a high-speed defibrillator, a grinder (stone mill-type grinder), a high-pressure homogenizer, an ultra-high-pressure homogenizer, a high-pressure collision grinder, a ball mill, a bead mill, a disk-type refiner, a conical refiner, a twin-screw kneader, a vibration mill, a homomixer under high-speed rotation, an ultrasonic disperser, or a beater. Among the above defibrillation treatment devices, it is more preferable to use a high-speed defibrillator, a high-pressure homogenizer, or an ultra-high-pressure homogenizer, which are less affected by the grinding media and have less risk of contamination.

[0106] In the defibration process, it is preferable to dilute the ionic substituent-introduced fibers with a dispersion medium to form a slurry. The dispersion medium can be one or more selected from water and organic solvents such as polar organic solvents. The polar organic solvent is not particularly limited, but examples thereof include alcohols, polyhydric alcohols, ketones, ethers, esters, and aprotic polar solvents. Examples of alcohols include methanol, ethanol, isopropanol, n-butanol, and isobutyl alcohol. Examples of polyhydric alcohols include ethylene glycol, propylene glycol, and glycerin. Examples of ketones include acetone and methyl ethyl ketone (MEK). Examples of ethers include diethyl ether, tetrahydrofuran, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol mono-n-butyl ether, and propylene glycol monomethyl ether. Examples of esters include ethyl acetate and butyl acetate. Examples of aprotic polar solvents include dimethyl sulfoxide (DMSO), dimethylformamide (DMF), dimethylacetamide (DMAc), and N-methyl-2-pyrrolidinone (NMP).

[0107] The solids concentration of the fine fibrous cellulose during the defibration treatment can be appropriately set. The slurry obtained by dispersing the phosphorus oxo acid group-introduced fibers in a dispersion medium may contain solids other than the phosphorus oxo acid group-introduced fibers, such as urea, which has hydrogen bonding properties.

[0108] (Nitrogen Removal Treatment) The process for producing fine fibrous cellulose may further include a step of reducing the nitrogen content (nitrogen removal treatment step). By reducing the nitrogen content, fine fibrous cellulose that can further suppress discoloration can be obtained. The nitrogen removal treatment step is preferably performed before the defibration treatment step.

[0109] In the nitrogen removal treatment step, it is preferable to adjust the pH of the slurry containing the substituent-introduced fibers to 10 or more and then perform a heat treatment. In the heat treatment, the liquid temperature of the slurry is preferably 50°C or more and 100°C or less, and the heating time is preferably 15 minutes or more and 180 minutes or less. When adjusting the pH of the slurry containing the substituent-introduced fibers, it is preferable to add an alkali compound that can be used in the above-mentioned alkali treatment step to the slurry.

[0110] After the nitrogen removal treatment step, the substituted fiber may be subjected to a washing step as needed. The washing step is carried out by washing the ionic substituent-introduced fiber with, for example, water or an organic solvent. The number of washing steps to be carried out in each washing step is not particularly limited.

[0111] (Substituent Removal Treatment) The method for producing fine fibrous cellulose may include a step of removing at least a portion of the substituents from fine fibrous cellulose having a substituent and a fiber width of 1,000 nm or less. By undergoing such a step, it is possible to obtain fine fibrous cellulose having a small fiber width but a low amount of introduced substituents. In this specification, the step of removing at least a portion of the substituents from the fine fibrous cellulose is also referred to as a substituent removal treatment step.

[0112] Examples of the substituent removal treatment step include a step of heat treating a fine fibrous cellulose having a substituent and a fiber width of 1,000 nm or less, an enzyme treatment step, an acid treatment step, an alkali treatment step, etc. These may be performed alone or in combination. Among these, the substituent removal treatment step is preferably a heat treatment step or an enzyme treatment step. By undergoing the above treatment step, at least a portion of the substituents are removed from the fine fibrous cellulose having a substituent and a fiber width of 1,000 nm or less, and fine fibrous cellulose having an introduction amount of less than 0.5 mmol / g can be obtained. By forming a fine fibrous cellulose-containing layer using such fine fibrous cellulose, a laminate with better water resistance can be obtained.

[0113] The substituent removal treatment step is preferably carried out in the form of a slurry. That is, the substituent removal treatment step is preferably a step of subjecting a slurry containing a substituent-containing fine fibrous cellulose having a fiber width of 1,000 nm or less to a heat treatment, an enzyme treatment, an acid treatment, an alkali treatment, or the like. By carrying out the substituent removal treatment step in the form of a slurry, it is possible to prevent the residue of colored substances generated by heating or the like during the substituent removal treatment, and added or generated acids, alkalis, salts, etc. This makes it possible to suppress coloration of the fine fibrous cellulose-containing layer. Furthermore, when a treatment is carried out to remove salts derived from the substituents removed after the substituent removal treatment, it is also possible to increase the salt removal efficiency.

[0114] When a substituent removal treatment is performed on a slurry containing fine fibrous cellulose having a substituent and a fiber width of 1,000 nm or less, the concentration of the fine fibrous cellulose in the slurry is preferably 0.05% by mass or more and 20% by mass or less, more preferably 0.1% by mass or more, even more preferably 0.2% by mass or more, and more preferably 15% by mass or less, and even more preferably 10% by mass or less. By controlling the concentration of the fine fibrous cellulose in the slurry within the above range, the substituent removal treatment can be performed more efficiently. Furthermore, by controlling the concentration of the fine fibrous cellulose in the slurry within the above range, it is possible to prevent the residue of colored substances caused by heating during the substituent removal treatment, and added or generated acids, alkalis, salts, etc. This can suppress coloration of the fine fibrous cellulose-containing layer. Furthermore, when a treatment is performed to remove salts derived from the substituents removed after the substituent removal treatment, it is also possible to improve the salt removal efficiency.

[0115] When the substituent removal treatment step is a step of heat-treating fine fibrous cellulose having a substituent and a fiber width of 1,000 nm or less, the heating temperature in the heat treatment step is preferably 40° C. or higher and 250° C. or lower, more preferably 50° C. or higher, even more preferably 60° C. or higher, more preferably 230° C. or lower, and even more preferably 200° C. or lower. In particular, when the substituent in the fine fibrous cellulose subjected to the substituent removal treatment step is a phosphorus oxo acid group, the heating temperature in the heat treatment step is preferably 80° C. or higher, more preferably 100° C. or higher, and even more preferably 120° C. or higher.

[0116] 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, and examples that can be used include a hot air heater, a steam heater, an electric heater, a hydrothermal heater, a thermal heater, an infrared heater, a far-infrared heater, a microwave heater, a high-frequency heater, a stirring dryer, a rotary dryer, a disk dryer, a roll-type heater, a plate-type heater, a fluidized bed dryer, a band-type dryer, a filtration dryer, a vibration fluidized dryer, a flash dryer, and a reduced-pressure dryer. From the viewpoint of preventing evaporation, the heating is preferably carried out in a closed system, and from the viewpoint of further increasing the heating temperature, it is preferably carried out in a pressure-resistant device or container. The heat treatment may be a batch process, a batch continuous process, or a continuous process.

[0117] When the substituent removal treatment step is a step of enzymatically treating fine fibrous cellulose having substituents and a fiber width of 1,000 nm or less, it is preferable to use a phosphate ester hydrolase, a sulfate ester hydrolase, or the like in the enzymatic treatment step depending on the type of substituent.

[0118] In the enzyme treatment step, the enzyme is preferably added so that the enzymatic activity per 1 g of fine fibrous cellulose is 0.1 nkat or more, more preferably 1.0 nkat or more, and even more preferably 10 nkat or more. Furthermore, the enzyme is preferably added so that the enzymatic activity per 1 g of fine fibrous cellulose is 100,000 nkat or less, more preferably 50,000 nkat or less, and even more preferably 10,000 nkat or less. After adding the enzyme to the fine fibrous cellulose dispersion (slurry), it is preferable to carry out treatment under conditions of 0°C or higher and lower than 50°C for 1 minute to 100 hours.

[0119] After the enzymatic reaction, a step of deactivating the enzyme may be performed. Examples of the method for deactivating the enzyme include a method of adding an acid component or an alkali component to the enzymatically treated slurry to deactivate the enzyme, and a method of increasing the temperature of the enzymatically treated slurry to 90°C or higher to deactivate the enzyme.

[0120] When the substituent removal treatment step is a step of acid-treating fine fibrous cellulose having a substituent and a fiber width of 1,000 nm or less, it is preferable to add an acid compound that can be used in the acid treatment step described above to the slurry in the acid treatment step.

[0121] When the substituent removal treatment step is a step of alkali treating fine fibrous cellulose having a substituent and a fiber width of 1,000 nm or less, it is preferable to add an alkali compound that can be used in the alkali treatment step described above to the slurry in the alkali treatment step.

[0122] In the substituent removal treatment step, it is preferable that the substituent removal reaction proceeds uniformly. To proceed with the reaction uniformly, for example, the slurry containing the fine fibrous cellulose may be stirred, or the specific surface area of ​​the slurry may be increased. As a method for stirring the slurry, external mechanical shear may be applied, or self-stirring may be promoted by increasing the liquid feed rate of the slurry during the reaction.

[0123] In the substituent removal treatment step, spacer molecules may be added. The spacer molecules penetrate between adjacent fine fibrous cellulose particles, thereby acting as spacers to create fine spaces between the fine fibrous cellulose particles. Adding such spacer molecules in the substituent removal treatment step can suppress aggregation of the fine fibrous cellulose particles after the substituent removal treatment. This can more effectively increase the transparency of the fine fibrous cellulose-containing layer.

[0124] The spacer molecule is preferably a water-soluble organic compound. Examples of water-soluble organic compounds include sugars, water-soluble polymers, and urea. Specific examples include trehalose, urea, polyethylene glycol (PEG), polyethylene oxide (PEO), carboxymethyl cellulose, and polyvinyl alcohol (PVA). Furthermore, examples of water-soluble organic compounds that can be used include 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, pullulan, carrageenan, pectin, cationized starch, raw starch, oxidized starch, etherified starch, esterified starch, and starches such as amylose; glycerin, diglycerin, polyglycerin, hyaluronic acid, and metal salts of hyaluronic acid.

[0125] Also, known pigments can be used as spacer molecules, such as kaolin (containing 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, styrene-based plastic pigments, hydrotalcite, urea resin-based plastic pigments, and benzoguanamine-based plastic pigments.

[0126] (pH Adjustment Step) When the above-mentioned substituent removal treatment step is carried out in the form of a slurry, a step of adjusting the pH of the slurry containing the fine fibrous cellulose may be carried out before the substituent removal treatment step. For example, an ionic substituent is introduced into the cellulose fiber, and the counter ion of this ionic substituent is Na. ＋In this case, the slurry containing the defibrated fine fibrous cellulose exhibits a weak alkaline pH. If the slurry is heated in this state, monosaccharides, which are one of the causes of discoloration, may be generated due to the decomposition of cellulose, so it is preferable to adjust the pH of the slurry to 8 or less. Similarly, monosaccharides may be generated under acidic conditions, so it is preferable to adjust the pH of the slurry to 3 or more.

[0127] Furthermore, when the substituted fine fibrous cellulose is a fine fibrous cellulose having a phosphate group, it is preferable that the phosphorus of the phosphate group is in a state susceptible to nucleophilic attack, from the viewpoint of improving the efficiency of removing the substituent. The phosphorus susceptible to nucleophilic attack is cellulose -O-P(=O)(-O-H ＋ ) (-O-Na ＋ To achieve this state, the pH of the slurry is preferably adjusted to 3 or more and 8 or less, and more preferably adjusted to 4 or more and 6 or less.

[0128] The means for adjusting the pH is not particularly limited, and for example, an acid component or an alkali component may be added to a slurry containing fine fibrous cellulose. The acid component may be either an inorganic acid or an organic acid. Examples of inorganic acids include sulfuric acid, hydrochloric acid, nitric acid, and phosphoric acid. Examples of organic acids include formic acid, acetic acid, citric acid, malic acid, lactic acid, adipic acid, sebacic acid, stearic acid, maleic acid, succinic acid, tartaric acid, fumaric acid, and gluconic acid. The alkali component may be an inorganic alkali compound or an organic alkali compound. Examples of inorganic alkali compounds include lithium hydroxide, sodium hydroxide, potassium hydroxide, lithium carbonate, lithium bicarbonate, potassium carbonate, potassium bicarbonate, sodium carbonate, and sodium bicarbonate. Examples of the organic alkali compound include ammonia, hydrazine, methylamine, ethylamine, diethylamine, triethylamine, propylamine, dipropylamine, butylamine, diaminoethane, diaminopropane, diaminobutane, diaminopentane, diaminohexane, cyclohexylamine, aniline, tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, benzyltrimethylammonium hydroxide, pyridine, and N,N-dimethyl-4-aminopyridine.

[0129] In addition, in the pH adjustment step, 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 the desired pH can be obtained. Furthermore, in the pH adjustment step, the addition of an acid component or an alkali component may be combined with the ion exchange treatment.

[0130] (Salt Removal Treatment) After the substituent removal treatment step, it is preferable to perform a treatment to remove salts derived from the removed substituents. Removing the salts derived from the substituents makes it easier to obtain fine fibrous cellulose that can suppress coloration. The means for removing the salts derived from the substituents is not particularly limited, and examples thereof include a washing treatment and an ion exchange treatment. The washing treatment is performed by washing the fine fibrous cellulose that has aggregated in the substituent removal treatment with, for example, water or an organic solvent. In the ion exchange treatment, an ion exchange resin can be used.

[0131] (Uniform Dispersion Treatment) After the substituent removal treatment step, a step of uniformly dispersing the fine fibrous cellulose obtained through the substituent removal treatment may be provided. By subjecting the fine fibrous cellulose to the substituent removal treatment, at least a portion of the fine fibrous cellulose is aggregated. The uniform dispersion treatment step is a step of uniformly dispersing the aggregated fine fibrous cellulose.

[0132] In the uniform dispersion treatment step, for example, a high-speed defibrator, grinder (stone mill type grinder), high-pressure homogenizer, high-pressure collision type grinder, ball mill, bead mill, disk type refiner, conical refiner, twin-screw kneader, vibration mill, homomixer under high-speed rotation, ultrasonic disperser or beater can be used. Among the above-mentioned uniform dispersion treatment devices, it is more preferable to use a high-speed defibrator or high-pressure homogenizer.

[0133] The treatment conditions in the uniform dispersion treatment step are not particularly limited, but it is preferable to increase the maximum movement speed of the fine fibrous cellulose during treatment and the pressure during treatment. In a high-speed defibrator, the peripheral speed is preferably 20 m / sec or more, more preferably 25 m / sec or more, and even more preferably 30 m / sec or more. A high-pressure homogenizer is more preferably used because it has a higher maximum movement speed of the fine fibrous cellulose during treatment and a higher pressure during treatment than a high-speed defibrator. In high-pressure homogenizer treatment, the pressure during treatment is preferably 1 MPa or more and 350 MPa or less, more preferably 10 MPa or more and 300 MPa or less, and even more preferably 50 MPa or more and 250 MPa or less.

[0134] In the uniform dispersion treatment step, the above-mentioned spacer molecules may be newly added. By adding such spacer molecules in the uniform dispersion treatment step, the fine fibrous cellulose can be dispersed more uniformly and smoothly. This makes it possible to more effectively improve the transparency of the fine fibrous cellulose-containing layer.

[0135] In the fine fibrous cellulose-containing layer of this embodiment, the content of fine fibrous cellulose in the fine fibrous cellulose-containing layer 1A on the core resin plate side and the content of fine fibrous cellulose in the fine fibrous cellulose-containing layer 2A are preferably 30% by mass or more and 90% by mass or less, more preferably 55% by mass or more, even more preferably 60% by mass or more, still more preferably 65% ​​by mass or more, and more preferably 85% by mass or less, even more preferably 80% by mass or less, and still more preferably 75% by mass or less, from the viewpoint of improving the strength of the laminate. Furthermore, the content of fine fibrous cellulose in the fine fibrous cellulose-containing layer 1B on the resin film side and the content of fine fibrous cellulose in the fine fibrous cellulose-containing layer 2B are preferably 5% by mass or more and 90% by mass or less, more preferably 10% by mass or more, more preferably 85% by mass or less, even more preferably 80% by mass or less, and still more preferably 75% by mass or less, from the viewpoint of adhesion to the resin film.

[0136] In this embodiment, the fine fibrous cellulose may be a combination of fine fibrous cellulose containing ionic groups and unmodified fine fibrous cellulose. Furthermore, in addition to the fine fibrous cellulose, coarse cellulose fibers having a fiber width exceeding 1 μm may also be contained. In the following description, fine fibrous cellulose and coarse cellulose fibers are collectively referred to as "cellulose fibers." The fiber width of the coarse cellulose fibers is not particularly limited as long as it is 1 μm or more, but is preferably 1 μm or more and 100 μm or less, more preferably 5 μm or more, even more preferably 10 μm or more, and more preferably 50 μm or less, and even more preferably 40 μm or less. The fiber width of the coarse cellulose fibers can be determined using a fiber length distribution measuring device (for example, an FS5 manufactured by Valmet or an L&W Fiber Tester Plus manufactured by ABB).

[0137] The coarse cellulose fibers may have ionic substituents to improve dispersibility in the fine fibrous cellulose-containing layer. Preferred embodiments of the ionic substituents are the same as those for the fine fibrous cellulose, and the preferred ranges of the type and amount of the substituents are also the same. The coarse cellulose fibers are preferably obtained by introducing ionic groups into the fiber raw material and then gently defibrating the raw material. Examples of defibrators used for the gentle defibration process include refiners such as disk refiners and conical refiners.

[0138] When coarse cellulose fibers are contained, the preferred content of fine fibrous cellulose in the above-mentioned fine fibrous cellulose-containing layer is the preferred range of the total content of fibrous cellulose, i.e., fine fibrous cellulose and coarse cellulose fibers. When coarse cellulose fibers are contained, the content of coarse cellulose fibers per 100 parts by mass of fibrous cellulose (total of fine fibrous cellulose and coarse cellulose fibers) is preferably 1 part by mass or more and 80 parts by mass or less, more preferably 3 parts by mass or more, even more preferably 5 parts by mass or more, and preferably 60 parts by mass or less, more preferably 40 parts by mass or less, and even more preferably 20 parts by mass or less. When the content of coarse cellulose fibers is within the above range, coarse cellulose fibers can be produced more cheaply than fine fibrous cellulose, so the laminate can be produced more cheaply.

[0139] <Hydrophilic Polymer> The fine fibrous cellulose-containing layer in this embodiment contains a hydrophilic polymer from the viewpoint of ease of production of the fine fibrous cellulose-containing layer and adhesion of the laminate. A hydrophilic polymer generally refers to a polymer compound that is easily dissolved, swelled, or wetted in water. Examples of the hydrophilic polymer include polymer compounds having ionic groups such as carboxyl groups, sulfone groups, or amino groups in the molecular structure, and polymer compounds having nonionic hydrophilic groups such as hydroxyl groups, amide groups, ether groups, polyoxyethylene groups, and polyoxypropylene groups. Examples of hydrophilic polymers include carboxyvinyl polymers; polyvinyl alcohol; alkyl methacrylate-acrylic acid copolymers; polyvinylpyrrolidone; polyvinyl methyl ether; polyacrylates such as sodium polyacrylate; alkyl acrylate copolymers; urethane copolymers; modified polyesters; modified polyimides; polyalkylene glycols such as polyethylene glycol, polyethylene oxide, and polypropylene glycol; polycations such as polyacrylamide and polyethyleneimine; polyanions; amphoteric polymers; xanthan gum, guar gum, tamarind gum, carrageenan, locust bean gum, and crumbly gum. Can be mentioned thickening polysaccharides such as inseed, alginic acid, metal salt of alginic acid, pullulan, sakuran and pectin; cellulose derivatives such as carboxymethylcellulose, carboxyethylcellulose, methylcellulose, hydroxypropylmethylcellulose, hydroxyethylmethylcellulose and hydroxyethylcellulose; starches such as cationized starch, raw starch, oxidized starch, etherified starch, esterified starch, dextrin and amylose; glycerins such as polyglycerin; hyaluronic acid, metal salt of hyaluronic acid; protein such as casein.Also, it can be copolymer of these hydrophilic polymers.

[0140] In this embodiment, the fine fibrous cellulose-containing layer 1A on the core resin plate side contains a hydrophilic polymer 1A, and the fine fibrous cellulose-containing layer 2A contains a hydrophilic polymer 2A. Furthermore, the fine fibrous cellulose-containing layer 1B on the resin film side contains a hydrophilic polymer 1B, and the fine fibrous cellulose-containing layer 2B contains a hydrophilic polymer 2B. Here, the hydrophilic polymer 1A and the hydrophilic polymer 1B have hydroxyl groups, and when the hydroxyl value of the hydrophilic polymer 1A is OHV_1A (mg KOH / g) and the hydroxyl value of the hydrophilic polymer 1B is OHV_1B (mg KOH / g), the following formula (I) is satisfied: OHV_1A<OHV_1B (I) Furthermore, it is preferable that the hydrophilic polymer 2A and the hydrophilic polymer 2B have hydroxyl groups, and when the hydroxyl value of the hydrophilic polymer 2A is OHV_2A (mg KOH / g) and the hydroxyl value of the hydrophilic polymer 2B is OHV_2B (mg KOH / g), the following formula (I') is satisfied. OHV_2A<OHV_2B (I') That is, it is preferable that the hydroxyl value of the hydrophilic polymer contained in the fine fibrous cellulose-containing layer on the resin film side is larger than the hydroxyl value of the hydrophilic polymer contained in the fine fibrous cellulose-containing layer on the core resin plate side. By adopting the above-mentioned configuration, the adhesion between the fine fibrous cellulose-containing layer and adhesive layer 1B or 2B is improved, and peeling of the laminate is suppressed, which is preferable.

[0141] The hydrophilic polymers 1A and 2A are preferably nonionic water-soluble cellulose ethers. Nonionic water-soluble cellulose ethers are preferred because they are highly transparent and can produce laminates with excellent strength. "Water-soluble" means that 1 g or more dissolves in 100 g of water at any temperature between 0°C and 100°C. "Polymer" means that the average molecular weight (weight average molecular weight when the molecular weight distribution is present) is 1,000 or more, preferably 1,500 or more, and more preferably 2,000 or more. The nonionic water-soluble cellulose ether preferably has at least one functional group selected from an alkoxy group and a hydroxyalkyl group. The number of carbon atoms in the alkoxy group and the hydroxyalkyl group is preferably 1 to 6, more preferably 1 to 4, and even more preferably 1 to 3. Examples of nonionic water-soluble cellulose ethers include methyl cellulose, ethyl cellulose, propyl cellulose, hydroxyethyl cellulose, hydroxyethyl methyl cellulose, hydroxypropyl cellulose, and hydroxypropyl methyl cellulose. The nonionic water-soluble cellulose ether may be appropriately selected from commercially available products. Hydroxyethyl cellulose is commercially available from Daicel Chemical Industries, Ltd. as the HEC SE series (e.g., SE400, SE600, SE850, SE900). Methylcellulose is commercially available from Shin-Etsu Chemical Co., Ltd. as the Metolose SM series and from Matsumoto Yushi Seiyaku Co., Ltd. as the Marborose series. Hydroxypropyl cellulose is commercially available from Nippon Soda Co., Ltd. as the NISSO HPC series. Hydroxypropyl methylcellulose is commercially available from Shin-Etsu Chemical Co., Ltd. as the Metolose 60SH, Metolose 65SH, and Metolose 90SH series. Hydroxyethyl methylcellulose is commercially available from Shin-Etsu Chemical Co., Ltd. as the Metolose SEB and Metolose SNB series. The degree of substitution of alkoxy groups and / or hydroxyalkyl groups may be appropriately selected depending on the desired hydroxyl value described below.

[0142] In this embodiment, among these, hydroxypropyl methylcellulose is preferred as hydrophilic polymer 1A and 2A. The degree of substitution of methoxy group is preferably 1.0 or more and 2.5 or less, more preferably 1.2 or more, even more preferably 1.4 or more, even more preferably 1.6 or more, and more preferably 2.4 or less, even more preferably 2.2 or less, and even more preferably 2.0 or less. In addition, the molar substitution number of hydroxypropoxy group (average molar number of hydroxypropoxy group added per unit to anhydroglucose of cellulose) is preferably 0.05 mol or more and 1.00 mol or less, more preferably 0.08 mol or more, even more preferably 0.10 mol or more, even more preferably 0.12 mol or more, and more preferably 0.80 mol or less, even more preferably 0.60 mol or less, even more preferably 0.40 mol or less, and even more preferably 0.30 mol or less.

[0143] Hydrophilic polymers 1B and 2B are preferably polyvinyl alcohol or modified products thereof having a saponification degree of 80 or more. Polyvinyl alcohol or modified products thereof having a saponification degree of 80 or more have a high hydroxyl value, resulting in a laminate with excellent adhesion to adhesive layers 1B and 2B. Modified polyvinyl alcohol (hereinafter also referred to as modified polyvinyl alcohol) is not particularly limited, and examples include polyvinyl alcohol modified with a hydrophilic functional group and polyvinyl alcohol modified with a hydrophobic functional group. Polyvinyl alcohol modified with a hydrophilic functional group is preferred. Examples of hydrophilic functional groups include acetyl groups, carboxy groups, sulfo groups, phosphate groups, phosphonic groups, acetoacetyl groups, polyalkylene oxide groups, and polypropylene oxide groups. Examples of hydrophobic functional groups include alkyl groups such as ethylene groups and propylene groups. Among these, acetoacetyl group-modified polyvinyl alcohol is preferred from the standpoints of transparency and strength. Acetoacetyl group-modified polyvinyl alcohol is preferred because the crosslinking reaction proceeds even under mild conditions, resulting in good adhesive properties.

[0144] From the viewpoint of obtaining a high hydroxyl value, the degree of saponification of the polyvinyl alcohol and the modified polyvinyl alcohol is preferably 80 or more, more preferably 85 or more, even more preferably 90 or more, still more preferably 95 or more, and even more preferably 97 or more, and the upper limit is not particularly limited, but is 100 or less.

[0145] The hydroxyl values ​​of hydrophilic polymers 1A and 2A are preferably 50 mgKOH / g or more and 500 mgKOH / g or less, more preferably 100 mgKOH / g or more, more preferably 250 mgKOH / g or more, even more preferably 300 mgKOH / g or more, and more preferably 450 mgKOH / g or less, even more preferably 400 mgKOH / g or less, from the viewpoint of adhesion to adhesive layer 1A and adhesive layer 2A and from the viewpoint of obtaining a preferable difference from the hydroxyl values ​​of hydrophilic polymers 1B and 2B. Furthermore, from the viewpoint of adhesion to adhesive layer 1B and adhesive layer 2B and from the viewpoint of obtaining a preferable difference from the hydroxyl value of hydrophilic polymers 1A and 2A, the hydroxyl value of hydrophilic polymers 1B and 2B is preferably 900 mgKOH / g or more and 1,273 mgKOH / g or less, more preferably 950 mgKOH / g or more, even more preferably 1,000 mgKOH / g or more, still more preferably 1,100 mgKOH / g or more, even more preferably 1,200 mgKOH / g or more, and preferably 1,270 mgKOH / g or less.

[0146] The difference between OHV_1B (mgKOH / g), which is the hydroxyl value of hydrophilic polymer 1B, and OHV_1A (mgKOH / g), which is the hydroxyl value of hydrophilic polymer 1A, preferably satisfies the following formula (II): 1200 mgKOH / g ≥ OHV_1B - OHV_1A ≥ 450 mgKOH / g (II) The difference between OHV_1B and OHV_1A (OHV_1B - OHV_1A) is more preferably 1100 mgKOH / g or less, even more preferably 1000 mgKOH / g or less, still more preferably 950 mgKOH / g or less, and more preferably 500 mgKOH / g or more, even more preferably 550 mgKOH / g or more, and still more preferably 600 mgKOH / g or more. When the difference between the hydroxyl value of the hydrophilic polymer 1B and the hydroxyl value of the hydrophilic polymer 1A is within the above range, the toughness of the fine fibrous cellulose-containing layer is excellent, and the adhesion between the adhesive layer 1B and the fine fibrous cellulose-containing layer 1B is also excellent, and the adhesion between the fine fibrous cellulose-containing layer 1A and the fine fibrous cellulose-containing layer 1B is also excellent, which is preferable. The difference between the hydroxyl value of the hydrophilic polymer 1B and the hydroxyl value of the hydrophilic polymer 1A can be adjusted to a desired range by selecting an appropriate hydrophilic polymer. For example, if a polyvinyl alcohol or modified polyvinyl alcohol with a high degree of saponification is used as the hydrophilic polymer 1B, a high hydroxyl value can be obtained. Furthermore, if a nonionic water-soluble cellulose with a high degree of alkoxy group substitution is used as the hydrophilic polymer 1A, the hydroxyl value tends to be low, and if a nonionic water-soluble cellulose with a high degree of hydroxyalkyl group substitution is used, the hydroxyl value tends to be low.

[0147] Furthermore, it is preferable that the difference between OHV_2B (mgKOH / g), which is the hydroxyl value of hydrophilic polymer 2B, and OHV_2A (mgKOH / g), which is the hydroxyl value of hydrophilic polymer 2A, satisfies the following formula (II'): 1200 mgKOH / g ≥ OHV_2B - OHV_2A ≥ 450 mgKOH / g (II') The difference between OHV_2B and OHV_2A (OHV_2B - OHV_2A) is more preferably 1100 mgKOH / g or less, even more preferably 1000 mgKOH / g or less, still more preferably 950 mgKOH / g or less, and is more preferably 500 mgKOH / g or more, even more preferably 550 mgKOH / g or more, and still more preferably 600 mgKOH / g or more. When the difference between the hydroxyl value of the hydrophilic polymer 2B and the hydroxyl value of the hydrophilic polymer 2A is within the above range, the adhesive properties between the adhesive layer 2A and the fine fibrous cellulose-containing layer 2A are excellent, and the adhesive properties between the adhesive layer 2B and the fine fibrous cellulose-containing layer 2B are also excellent. Furthermore, the adhesive properties between the fine fibrous cellulose-containing layer 2A and the fine fibrous cellulose-containing layer 2B are also excellent. The difference between the hydroxyl value of the hydrophilic polymer 2B and the hydroxyl value of the hydrophilic polymer 2A can be adjusted to a desired range by selecting an appropriate hydrophilic polymer. For example, a high hydroxyl value can be obtained by using a polyvinyl alcohol or modified polyvinyl alcohol with a high degree of saponification as the hydrophilic polymer 2B. Furthermore, the hydroxyl value tends to be low when a nonionic water-soluble cellulose with a high degree of alkoxy group substitution is used as the hydrophilic polymer 2A, and the hydroxyl value tends to be low when a nonionic water-soluble cellulose with a high degree of hydroxyalkyl group substitution is used.

[0148] In the fine fibrous cellulose-containing layer of this embodiment, the content of hydrophilic polymer 1A in the fine fibrous cellulose-containing layer 1A on the core resin plate side and the content of hydrophilic polymer 2A in the fine fibrous cellulose-containing layer 2A are preferably 10% by mass or more and 70% by mass or less, more preferably 15% by mass or more, even more preferably 20% by mass or more, even more preferably 25% by mass or more, and more preferably 45% by mass or less, even more preferably 40% by mass or less, and even more preferably 35% by mass or less, from the viewpoint of improving adhesion and film-forming properties. Also, the content of hydrophilic polymer 1B in the fine fibrous cellulose-containing layer 1B on the resin film side and the content of hydrophilic polymer 2B in the fine fibrous cellulose-containing layer 2B are preferably 10% by mass or more and 95% by mass or less, more preferably 15% by mass or more, even more preferably 20% by mass or more, even more preferably 25% by mass or more, and even more preferably 90% by mass or less, from the viewpoint of adhesion to the resin film.

[0149] In the fine fibrous cellulose-containing layer of this embodiment, the sum of the content of fine fibrous cellulose and the content of hydrophilic polymer in the solid content of the fine fibrous cellulose-containing layer is, from the viewpoint of improving the rigidity of the laminate, preferably 80% by mass or more, more preferably 85% by mass or more, even more preferably 90% by mass or more, and even more preferably 95% by mass or more, and is 100% by mass or less.

[0150] In the laminate of this embodiment, the "fine fibrous cellulose-containing layer content (%)" (100 x total thickness (μm) of fine fibrous cellulose-containing layers 1 (fine fibrous cellulose-containing layer 1A and fine fibrous cellulose-containing layer 1B) and 2 (fine fibrous cellulose-containing layer 2A and fine fibrous cellulose-containing layer 2B) / thickness (μm) of laminate) is, from the viewpoint of improving the strength of the laminate, preferably 16.0% or less, more preferably 14.0% or less, even more preferably 12.0% or less, still more preferably 10.0% or less, and is preferably 0.6% or more, more preferably 0.9% or more, even more preferably 1.2% or more, and still more preferably 1.5% or more.

[0151] <Other Components> The fine fibrous cellulose-containing layer of this embodiment may contain components (other components) other than the fine fibrous cellulose having a fiber width of 1,000 nm or less and the hydrophilic polymer. Examples of other components include the above-mentioned fibrous cellulose having a fiber width of more than 1,000 nm, hydrophilic low-molecular-weight compounds, paper strength agents, thermoplastic resins, surfactants, organic ions, coupling agents, inorganic layered compounds, inorganic compounds, leveling agents, preservatives, antifoaming agents, organic particles, lubricants, antistatic agents, UV protection agents, dyes, pigments, stabilizers, magnetic powders, orientation promoters, plasticizers, dispersants, color inhibitors, polymerization inhibitors, pH adjusters, and crosslinking agents. In addition, in the fine fibrous cellulose-containing layer of this embodiment, the total content of "other components" in the solid content of the fine fibrous cellulose-containing layer can be, for example, 5% by mass or less, 3% by mass or less, 1% by mass or less, or even 0% by mass.

[0152] <Thickness> The thickness of the fine fibrous cellulose-containing layer 1 in this embodiment, i.e., the total thickness of the fine fibrous cellulose-containing layer 1A and the fine fibrous cellulose-containing layer 1B, is preferably 20 μm or more and 300 μm or less, more preferably 25 μm or more, even more preferably 30 μm or more, and more preferably 250 μm or less, and even more preferably 200 μm or less. The preferred range of the thickness of the fine fibrous cellulose-containing layer 2 in this embodiment is the same as the above-mentioned thickness range. It is preferable to adjust the thickness of the fine fibrous cellulose-containing layer appropriately depending on the application of the laminate.

[0153] The ratio of the thickness of the fine fibrous cellulose-containing layer 1A to the thickness of the fine fibrous cellulose-containing layer 1B (fine fibrous cellulose-containing layer 1A:fine fibrous cellulose-containing layer 1B) is preferably greater than 5.0:5.0 and not more than 9.0:1.0, more preferably 5.5:4.5 or more, even more preferably 6.0:4.0 or more, even more preferably 6.5:3.5 or more, and more preferably 8.5:1.5 or less, even more preferably 8.0:2.0 or less, and even more preferably 7.5:2.5 or less, from the viewpoint of obtaining a laminate having excellent strength and adhesiveness. By making the thickness of the fine fibrous cellulose-containing layer 1A thicker than that of the fine fibrous cellulose-containing layer 1B, a laminate having excellent strength and transparency can be obtained, which is preferable. Furthermore, the thickness of the fine fibrous cellulose-containing layer 1B is preferably within the above-mentioned range from the viewpoint of improving adhesion to the adhesive layer 1B. In this embodiment, the preferred range of the ratio between the thickness of the fine fibrous cellulose-containing layer 2A and the thickness of the fine fibrous cellulose-containing layer 2B is the same as the range described above.

[0154] <Basis Weight> The basis weight of the fine fibrous cellulose-containing layer 1 in this embodiment, i.e., the sum of the basis weight of the fine fibrous cellulose-containing layer 1A and the basis weight of the fine fibrous cellulose-containing layer 1B, is preferably 25 g / m ２ More than 400g / m ２ More preferably, it is 30 g / m or less. ２ More preferably, 35 g / m ２ More preferably, 40 g / m ２ More preferably, it is 300 g / m or more. ２ More preferably 200 g / m or less ２ More preferably, 100 g / m or less ２ The preferred range of the basis weight of the fine fibrous cellulose-containing layer 2 in this embodiment is the same as the above-mentioned range of basis weight. The basis weight of the fine fibrous cellulose-containing layer is preferably adjusted appropriately depending on the application of the laminate.

[0155] <Density> The density of the fine fibrous cellulose-containing layer 1 in this embodiment is preferably 0.6 g / cm ３ 2.5g / cm or more３ or less, more preferably 0.8 g / cm ３ More preferably, 1.0 g / cm ３ More preferably, 1.2 g / cm ３ More preferably, it is 2.0 g / cm or more. ３ More preferably, 1.8 g / cm or less ３ More preferably, 1.6 g / cm or less ３ The preferred range of the density of the fine fibrous cellulose-containing layer 2 in this embodiment is the same as the above-mentioned density range. The density of the fine fibrous cellulose-containing layer is calculated by dividing the basis weight of the fine fibrous cellulose-containing layer by its thickness.

[0156] [Resin Films 1 and 2] As described above, the laminate of this embodiment preferably has a resin film 1 on the side of the laminate sheet opposite the side of the adhesive layer 1B having the fine fibrous cellulose-containing layer 1B, and preferably has a core resin plate on the side of the adhesive layer 1A opposite the side of the core resin plate having the fine fibrous cellulose-containing layer 1A. It is preferable to have a laminate sheet on the side of the core resin plate opposite the side having the adhesive layer 1A so that the adhesive layer 2A is in contact with the core resin plate, and to have a resin film 2 on the side of the adhesive layer 2B of the laminate sheet opposite the side having the fine fibrous cellulose-containing layer 2B. The components contained or may be contained in resin film 1, and the thickness of resin film 1, and the components contained or may be contained in resin film 2, and the thickness of resin film 2 may be the same or different, but are preferably the same. Hereinafter, resin films 1 and 2 will be collectively referred to simply as "resin films."

[0157] The resin constituting the resin film preferably contains at least one selected from the group consisting of polycarbonate and polyethylene terephthalate, more preferably polycarbonate or polyethylene terephthalate, and even more preferably polycarbonate. The total content of polycarbonate and polyethylene terephthalate in the resin constituting the resin film is preferably 85% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more, and 100% by mass or less.

[0158] <Thickness> The thickness of the resin film 1 in this embodiment is preferably 30 μm or more and 500 μm or less, more preferably 80 μm or more, even more preferably 120 μm or more, still more preferably 160 μm or more, and more preferably 450 μm or less, even more preferably 400 μm or less, still more preferably 350 μm or less, and even more preferably 300 μm or less. The preferred range of the thickness of the resin film 2 in this embodiment is the same as the above-mentioned thickness range. It is preferable to adjust the thickness of the resin film appropriately depending on the application of the laminate.

[0159] [Laminate Properties] [Total Light Transmittance] The total light transmittance of the laminate of this embodiment is preferably 80% or more, more preferably 83% or more, and even more preferably 85% or more. Meanwhile, the upper limit of the total light transmittance of the laminate may be, for example, 100%. The total light transmittance of the laminate can be controlled by the fiber width of the fine fibrous cellulose, the type of ionic group, the amount of ionic group introduced, the type of hydrophilic polymer, the type of resin constituting the resin film, the content of the fine fibrous cellulose and hydrophilic polymer in the fine fibrous cellulose-containing layer, the thickness of each layer constituting the laminate, and the like. The total light transmittance of the laminate is a value measured in accordance with JIS K 7361-1:1997.

[0160] [Haze] The haze of the laminate of this embodiment is preferably 6.0% or less, more preferably 5.0% or less, even more preferably 4.0% or less, even more preferably 3.0% or less, even more preferably 2.0% or less, and even more preferably 1.0% or less. The lower limit of the haze of the laminate may be, for example, 0%. The haze of the laminate can be controlled by the fiber width of the fine fibrous cellulose, the type of ionic group, the amount of ionic group introduced, the type of hydrophilic polymer, the type of resin constituting the resin film, the content of the fine fibrous cellulose and hydrophilic polymer in the fine fibrous cellulose-containing layer, the thickness of each layer constituting the laminate, and the like. The haze of the laminate is a value measured in accordance with JIS K 7136:2000.

[0161] [Yellow Index] The yellow index (YI value) of the laminate of this embodiment is preferably 8.00 or less, more preferably 6.00 or less, even more preferably 4.00 or less, even more preferably 3.00 or less, and even more preferably 2.50 or less, with no particular lower limit. The YI value of the laminate can be controlled by the fiber width of the fine fibrous cellulose, the type of ionic group, the amount of ionic group introduced, the type of hydrophilic polymer, the type of resin constituting the resin film, the content of the fine fibrous cellulose and hydrophilic polymer in the fine fibrous cellulose-containing layer, the thickness of each layer constituting the laminate, etc. The YI value of the laminate is a value measured in accordance with JIS K 7373:2006.

[0162] [Thickness] The thickness of the laminate of this embodiment is preferably 800 μm or more, more preferably 1,000 μm or more, and even more preferably 1,200 μm or more, and is preferably 6,000 μm or less, more preferably 5,000 μm or less, and even more preferably 4,000 μm or less. It is preferable to adjust the thickness of the laminate appropriately depending on the application.

[0163] [Method for producing laminate] The laminate of this embodiment can be produced, for example, by the following steps: Step 1: a step of obtaining a fine fibrous cellulose-containing layer (fine fibrous cellulose-containing sheet) 1 by laminating a fine fibrous cellulose-containing layer 1A and a fine fibrous cellulose-containing layer 1B; Step 2: a step of providing an adhesive layer 1A on the fine fibrous cellulose-containing layer 1A of the fine fibrous cellulose-containing layer 1, and a step of providing an adhesive layer 1B on the fine fibrous cellulose-containing layer 1B, to obtain a laminated sheet 1; Step 3: a step of obtaining a fine fibrous cellulose-containing layer (fine fibrous cellulose-containing sheet) 2 by laminating a fine fibrous cellulose-containing layer 2A and a fine fibrous cellulose-containing layer 2B; Step 4: a step of providing an adhesive layer 2A on the fine fibrous cellulose-containing layer 2A of the fine fibrous cellulose-containing layer 2, and a step of providing an adhesive layer 2B on the fine fibrous cellulose-containing layer 2B, to obtain a laminated sheet 2. Step 5: A step of laminating the resin film 1, laminate sheet 1, core resin plate, laminate sheet 2, and resin film 2 in the following stacking order: resin film 1 / adhesive layer 1B / fine fibrous cellulose-containing layer 1B / fine fibrous cellulose-containing layer 1A / adhesive layer 1A / core resin plate / adhesive layer 2A / fine fibrous cellulose-containing layer 2A / fine fibrous cellulose-containing layer 2B / adhesive layer 2B / resin film 2, and then heating and pressurizing. Steps 1 and 2 are performed in this order, and steps 2 and 4 are performed in this order. Furthermore, steps 1 to 4 are performed before step 5. Note that the method for producing the laminate of this embodiment is not limited to this. An example of a method for producing the laminate of this embodiment is described below.

[0164] [Preparation of fine fibrous cellulose-containing sheet 1 and laminate sheet 1] A coating liquid for the fine fibrous cellulose-containing layer 1A containing fine fibrous cellulose and hydrophilic polymer 1A, and a coating liquid for the fine fibrous cellulose-containing layer 1B containing fine fibrous cellulose and hydrophilic polymer 1B are prepared. When preparing the coating liquid, for example, it is preferable to prepare an aqueous solution of a hydrophilic polymer in advance and mix it with a fine fibrous cellulose dispersion to prepare the coating liquid. The fine fibrous cellulose-containing layer 1A and the fine fibrous cellulose-containing layer 1B are obtained by heating and drying the above-mentioned coating liquid. Specifically, a method of applying the coating liquid to a substrate and then heating and drying is exemplified. A coating liquid for the fine fibrous cellulose-containing layer 1A is applied to a substrate and heated and dried to prepare the fine fibrous cellulose-containing layer 1A. Then, a coating liquid for the fine fibrous cellulose-containing layer 1B is applied to the obtained fine fibrous cellulose-containing layer 1A and heated and dried to obtain a fine fibrous cellulose-containing layer (fine fibrous cellulose-containing sheet) 1 in which the fine fibrous cellulose-containing layer 1A and the fine fibrous cellulose-containing layer 1B are laminated. The order of coating is not limited to this; the fine fibrous cellulose-containing layer 1B may be prepared first, and then the fine fibrous cellulose-containing layer 1A may be laminated. The material of the substrate is not particularly limited, but it is preferable to select one that can be easily peeled off after drying. Resin films are preferably plates, and metal films and plates are preferred. Furthermore, if the substrate unfolds, a blocking frame may be fixed to the substrate to obtain a fine fibrous cellulose-containing layer of the desired thickness and basis weight. A substrate with a batt-shaped blocking frame formed thereon may also be used. The blocking frame is not particularly limited, but it is preferable to select one that can be easily peeled off after drying. From this viewpoint, a molded resin plate or metal plate is more preferable. The coating machine for applying the coating liquid to the substrate is not particularly limited, and examples thereof include a roll coater, a gravure coater, a die coater, a curtain coater, and an air doctor coater. When the solid rubber composition is a sheet-shaped rubber mixture, a die coater, a curtain coater, and a spray coater are particularly preferable because they can make the thickness of the sheet more uniform.The solid content concentration of the coating liquid is, for example, 0.1 to 5.0% by mass, and more preferably 0.3 to 3.0% by mass.

[0165] Next, a resin coating liquid (adhesive composition) is applied to the obtained fine fibrous cellulose-containing layer 1, and the adhesive composition is dried and cured by heating, thereby obtaining a laminate sheet 1 (layer structure: adhesive layer 1A / fine fibrous cellulose-containing layer 1A / fine fibrous cellulose-containing layer 1B / adhesive layer 1B). The heating temperature is preferably 50°C or higher and 120°C or lower, more preferably 65°C or higher and 105°C or lower. The heating time is preferably 5 minutes or higher and 6 hours or lower, more preferably 15 minutes or higher and 3 hours or lower, and even more preferably 20 minutes or higher and 2 hours or lower. A similar procedure is followed to obtain a laminate sheet 2 (layer structure: adhesive layer 2A / fine fibrous cellulose-containing layer 2A / fine fibrous cellulose-containing layer 2B / adhesive layer 2B). Furthermore, additional heating treatment of sheet 1 or sheet 2 can further strengthen the adhesion between the adhesive layer and the fine fibrous cellulose-containing layer. The heating temperature is preferably 50°C or higher and 120°C or lower, more preferably 70°C or higher and 100°C or lower. The heating time is preferably 5 hours or more and 150 hours or less, and more preferably 15 hours or more and 100 hours or less.

[0166] [Laminate Formation] Laminate sheet 1 is placed on one side of a core resin plate so that adhesive layer 1A contacts the core resin plate, and resin film 1 is placed so that it contacts adhesive layer 1B. Sheet 2 is placed on the other side of the core resin plate so that adhesive layer 2A contacts the core resin plate, and resin film 2 is placed so that it contacts adhesive layer 2B. The laminate precursor thus obtained is heated from room temperature (e.g., 23°C) to 130-190°C over a period of preferably 15 seconds to 30 minutes, more preferably 30 seconds to 20 minutes, while being pressurized at 0.5 to 10 MPa. The temperature is then maintained at 15 seconds to 15 minutes, more preferably 30 seconds to 10 minutes, and the laminate is then cooled to 20-40°C over a period of preferably 15 seconds to 30 minutes, more preferably 30 seconds to 15 minutes, to obtain the laminate of this embodiment. In this embodiment, the laminate sheet 1 may be prepared as a laminate sheet 1' in advance, in which the adhesive layer 1B and the resin film 1 are in contact with each other. Similarly, the laminate sheet 2 may be prepared as a laminate sheet 2' in which the adhesive layer 2B and the resin film 2 are in contact with each other. The laminate sheet 1' may be arranged on one side of the core resin plate so that the adhesive layer 1A of the laminate sheet 1' is in contact with the core resin plate, and the laminate sheet 2' may be arranged on the other side so that the adhesive layer 2A of the laminate sheet 2' is in contact with the core resin plate. The resulting laminate precursor may then be heated and pressed in the same manner as described above to obtain a laminate.

[0167] [Applications] The fine fibrous cellulose-containing sheet and laminate sheet of this embodiment are suitable for applications such as various display devices, optical components such as various solar cells, substrates for electronic devices, separators for electrochemical devices, components for home appliances, window materials for various vehicles and building materials, interior and exterior materials, and packaging materials. In particular, the laminate sheet may be used for the above applications as is, or a resin layer may be laminated on the laminate sheet. Furthermore, the laminate of this embodiment is suitable for optical components such as various display devices and various solar cells. It is also suitable for applications such as substrates for electronic devices, separators for electrochemical devices, components for home appliances, window materials for various vehicles and buildings, interior and exterior materials, and packaging materials. The laminate of this embodiment may also be subjected to heat bending. Since the laminate of this embodiment has excellent adhesiveness, peeling between the layers of the laminate is suppressed even during heat bending, making it suitable for applications requiring heat bending.

[0168] The features of the present invention will be explained in more detail below with reference to examples and comparative examples. The materials, amounts used, ratios, treatment details, treatment procedures, etc. shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be interpreted as being limited by the specific examples shown below. Unless otherwise specified, the following operations were carried out at room temperature (23°C) and a relative humidity of 50%.

[0169] <Production of Fine Fibrous Cellulose> (Phosphorylation Treatment) Hardwood dissolving pulp (dry sheet) manufactured by Oji Paper Co., Ltd. was used as the raw material pulp. This raw material pulp was subjected to a phosphorylation treatment as follows. First, a mixed aqueous solution of ammonium dihydrogen phosphate and urea was added to 100 parts by mass (bone dry mass) of the raw material pulp to adjust the composition to 45 parts by mass of ammonium dihydrogen phosphate, 120 parts by mass of urea, and 150 parts by mass of water, thereby obtaining a chemical-impregnated pulp. Next, the obtained chemical-impregnated pulp was heated in a hot air dryer at 165°C for 250 seconds to introduce phosphate groups into the cellulose in the pulp, thereby obtaining a phosphorylated pulp.

[0170] (Washing Treatment) The resulting phosphorylated pulp was then washed. The washing treatment was carried out by repeatedly adding 10 L of ion-exchanged water to 100 g (bone dry mass) of phosphorylated pulp to obtain a pulp dispersion, stirring the resulting pulp to uniformly disperse the pulp, and then filtering and dehydrating the pulp. The washing was completed when the electrical conductivity of the filtrate reached 100 μS / cm or less.

[0171] (Neutralization Treatment) Next, the washed phosphorylated pulp was neutralized as follows. First, the washed phosphorylated pulp was diluted with 10 L of ion-exchanged water, and then a 1 N aqueous sodium hydroxide solution was added little by little while stirring to obtain a phosphorylated pulp slurry having a pH of 12 to 13. Next, the phosphorylated pulp slurry was dehydrated to obtain a neutralized phosphorylated pulp. Next, the neutralized phosphorylated pulp was subjected to the above-mentioned washing treatment.

[0172] (Nitrogen Removal Treatment) Ion-exchanged water was added to phosphorylated pulp to prepare a slurry with a solids concentration of 4% by mass. A 48% by mass aqueous solution of sodium hydroxide was added to the slurry to adjust the pH to 13.4 and heated at 85°C for 1 hour. The pulp slurry was then dehydrated, and 10 L of ion-exchanged water was added per 100 g (bone dry mass) of phosphorylated pulp to obtain a pulp dispersion. The pulp was stirred to uniformly disperse, and the filtration and dehydration were repeated to remove excess sodium hydroxide. The removal was terminated when the electrical conductivity of the filtrate reached 100 μS / cm or less. The amount of carbamide groups introduced, calculated from the nitrogen content measured by the measurement method described below, was 0.01 mmol / g.

[0173] The infrared absorption spectrum of the phosphorus oxy-oxidized pulp thus obtained was measured using FT-IR. －１Absorption due to the P=O of the phosphate group was observed near the peak, confirming that phosphate groups had been added to the pulp. Furthermore, when the obtained phosphorylated pulp was analyzed using an X-ray diffractometer, typical peaks were observed at two positions, near 2θ = 14° to 17° and near 2θ = 22° to 23°, confirming that cellulose type I crystals were maintained. The amount of phosphate groups (amount of first dissociated acid) measured by the measurement method described below was 1.45 mmol / g. The total amount of dissociated acid was 2.45 mmol / g.

[0174] (Defibrillation Treatment) Ion-exchanged water was added to the obtained phosphorylated pulp to prepare a slurry with a solid content of 2% by mass. This slurry was treated six times in a wet pulverization device (Starburst, manufactured by Sugino Machine Co., Ltd.) at a pressure of 200 MPa to obtain a fine fibrous cellulose dispersion containing fine fibrous cellulose.

[0175] (Substituent Removal Treatment (High-Temperature Heat Treatment)) A 20% by mass aqueous citric acid solution was added to the obtained fine fibrous cellulose dispersion, and the pH of the dispersion was adjusted to 5.5. Thereafter, the dispersion was placed in a pressure-resistant container and heated at a liquid temperature of 160°C for 15 minutes until the amount of phosphate groups reached 0.08 mmol / g. The production of fine fibrous cellulose aggregates was confirmed by this operation.

[0176] (Washing treatment of slurry after removal of substituents) The same amount of ion-exchanged water as the slurry was added to the heated slurry to obtain a slurry with a solids concentration of approximately 1% by mass. The slurry was stirred and then filtered and dehydrated. This procedure was repeated to wash the slurry. When the electrical conductivity of the filtrate reached 10 μS / cm or less, ion-exchanged water was added again to obtain a slurry with a solids concentration of approximately 1% by mass, and the mixture was allowed to stand for 24 hours. The filtration and dehydration procedure was then repeated, and the end point of the washing was determined when the electrical conductivity of the filtrate again reached 10 μS / cm or less. Ion-exchanged water was added to the obtained fine fibrous cellulose aggregates to obtain a slurry after removal of substituents. The solids concentration of this slurry was 1.7% by mass.

[0177] (Uniform dispersion of the slurry after removal of substituents) Ion-exchanged water was added to the obtained slurry after removal of substituents to make a slurry with a solid content of 1.0 mass%, and then the slurry was treated three times at a pressure of 200 MPa with a wet pulverization device (Starburst, manufactured by Sugino Machine Co., Ltd.) to obtain a dispersion liquid (A) of the substituent-removed fine fibrous cellulose containing the substituent-removed fine fibrous cellulose. Furthermore, the fiber width of the fine fibrous cellulose was measured using a transmission electron microscope and found to be 4 nm.

[0178] (Measurement of phosphorus oxo acid group content) The phosphorus oxo acid group content (equal to the phosphorus oxo acid group content of phosphorus oxo-oxidized (phosphorylated or phosphorous) pulp) was measured by adding ion-exchanged water to a fine fibrous cellulose dispersion containing the target fine fibrous cellulose to prepare a slurry with a fine fibrous cellulose content of 0.2% by mass. The resulting slurry was treated with an ion-exchange resin and then titrated with an alkali. The ion-exchange resin treatment was performed by adding 1 / 10 by volume of a strongly acidic ion-exchange resin (Amberjet 1024; manufactured by Organo Corporation, conditioned) to the fine fibrous cellulose-containing slurry, shaking for 1 hour, and then pouring the mixture onto a mesh with 90 μm openings to separate the ion-exchange resin from the slurry. In addition, the alkali titration was performed by adding 10 μL of 0.1 N sodium hydroxide aqueous solution to the fine fibrous cellulose-containing slurry after treatment with an ion exchange resin every 5 seconds, while measuring the change in the pH value of the slurry. Nitrogen gas was blown into the slurry 15 minutes before the start of the titration. In this neutralization titration, two maximum points of increment (differential value of pH with respect to the amount of alkali added) were observed on the curve plotting the measured pH against the amount of alkali added. Of these, the maximum point of increment obtained first after starting the addition of alkali is called the first endpoint, and the maximum point of increment obtained next is called the second endpoint (Figure 1). The amount of alkali required from the start of the titration to the first endpoint is equal to the amount of first dissociated acid in the slurry used in the titration. Furthermore, the amount of alkali required from the start of the titration to the second endpoint is equal to the total amount of dissociated acid in the slurry used in the titration. The amount of alkali (mmol) required from the start of titration to the first endpoint divided by the solid content (g) in the slurry to be titrated was taken as the amount of phosphorus oxo acid groups (mmol / g). The amount of alkali (mmol) required from the start of titration to the second endpoint divided by the solid content (g) in the slurry to be titrated was taken as the total amount of dissociated acid (mmol / g). The amount of phosphorus oxo acid groups (amount of phosphorus oxo acid groups introduced) (mmol / g) is calculated by dividing the amount of alkali (mmol) required from the start of titration to the second endpoint by the solid content (g) in the slurry to be titrated. ＋ ) and the amount of substituents per 1 g of the fine fibrous cellulose.

[0179] (Measurement of carbamide group amount) The amount of carbamide groups in the fine fibrous cellulose was measured by subjecting the freeze-dried and pulverized sample to a trace total nitrogen analyzer TN-110 manufactured by Mitsubishi Chemical Analytech Co., Ltd. Note that ionic nitrogen was removed during the neutralization and washing processes. The amount of carbamide groups introduced per unit mass of the fine fibrous cellulose (mmol / g) was calculated by dividing the nitrogen content (g / g) per unit mass of the fine fibrous cellulose obtained by trace nitrogen analysis by the atomic weight of nitrogen.

[0180] <Dissolution of Cellulose Ether> Hydroxypropyl methylcellulose (Metolose 65SH-1500, manufactured by Shin-Etsu Chemical Co., Ltd., weight average molecular weight: 2.2 × 10), which is a non-ionic water-soluble cellulose ether, was dissolved in ion-exchanged water. ５ A cellulose ether aqueous solution having a concentration of 2% by mass was obtained by dissolving cellulose ether having a substitution degree (methoxy group): 1.8, a molar substitution number (hydroxypropoxy group): 0.15, and a hydroxyl value of 340 mg KOH / g to 360 mg KOH / g (calculated value: 343 mg KOH / g).

[0181] <Dissolution of Polyvinyl Alcohol> Acetoacetyl group-modified polyvinyl alcohol (hereinafter also referred to as "polyvinyl alcohol (A)"; manufactured by Mitsubishi Chemical Corporation, Gohsenx) was dissolved in ion-exchanged water. ＴＭ Z-300, saponification degree 98.0 to 99.0 mol%, hydroxyl value ≈ 1200 to 1250 mgKOH / g) was added to the solution to give a concentration of 12% by mass, and the solution was stirred at 95°C for 1 hour to dissolve. By the above procedure, an aqueous solution of polyvinyl alcohol (A) was obtained. In addition, an acetoacetyl group-modified polyvinyl alcohol (hereinafter also referred to as "polyvinyl alcohol (B)", manufactured by Mitsubishi Chemical Corporation, Gohsenx ＴＭAn aqueous polyvinyl alcohol solution (B) was obtained in the same manner as above, except that a polyvinyl alcohol (Z-200, saponification degree 99.0 mol% or more, hydroxyl value ≒ 1235 to 1275 mgKOH / g) was used instead of the polyvinyl alcohol (A). Furthermore, an aqueous polyvinyl alcohol solution (C) was obtained in the same manner as above, except that a polyvinyl alcohol (C) containing an antifoaming agent (Kuraray Poval PVA 22-88SB, manufactured by Kuraray Co., Ltd., saponification degree 87.0 to 89.0 mol%, hydroxyl value ≒ 985 to 1025 mgKOH / g) was used instead of the polyvinyl alcohol (A).

[0182] Example 1 (Preparation of a sheet containing fine fibrous cellulose) The fine fibrous cellulose dispersion, the cellulose ether aqueous solution, and the polyvinyl alcohol aqueous solution (A) were each diluted with ion-exchanged water to a solids concentration of 0.5% by mass. Next, 70 parts by mass of the diluted fine fibrous cellulose dispersion were mixed with 30 parts by mass of the diluted cellulose ether aqueous solution to obtain a mixed solution (A1). Also, 70 parts by mass of the diluted fine fibrous cellulose dispersion were mixed with 30 parts by mass of the diluted polyvinyl alcohol aqueous solution (A) to obtain a mixed solution (B1). The finished basis weight of the sheet was 35 g / m ２ The mixed solution (A1) was weighed out so that the mixed solution (A1) would have a final weight of 15 g / m² and was spread on a commercially available acrylic plate. A damming frame (inner dimensions: 250 mm x 250 mm, height: 5 cm) was placed on the acrylic plate to achieve a predetermined weight. This was dried in a dryer at 100°C for 1 hour, and then a 15 g / m² sheet was placed on top of it. ２ The mixed solution (B1) was spread so that the resultant sheet was dried again and peeled off from the acrylic plate, thereby obtaining a fine fibrous cellulose-containing sheet having two laminated fine fibrous cellulose-containing layers each containing a different hydrophilic polymer.

[0183] (Formation of Adhesive Layer) 8.5 parts by mass of modified polycarbonate resin (Iupizeta FPC-2136, manufactured by Mitsubishi Gas Chemical Company, Inc.), 60 parts by mass of toluene, and 30 parts by mass of methyl ethyl ketone were mixed to obtain a resin coating liquid. Next, 1.5 parts by mass of an isocyanate compound (Duranate TPA-100, manufactured by Asahi Kasei Chemicals Corporation) was added as an adhesion aid to the resin coating liquid and mixed. This resin coating liquid was applied to one side of a fine fibrous cellulose-containing sheet (the side containing cellulose ether that had been in contact with the acrylic plate) using a bar coater. Thereafter, the resin coating liquid was cured by heating at 100°C for 1 hour, forming an adhesive layer A. Next, a resin coating liquid was applied to the opposite side of the fine fibrous cellulose-containing sheet using the same procedure, and then heated at 70°C for 30 minutes to cure the resin coating liquid, forming an adhesive layer B, and a laminate sheet was obtained. Furthermore, the obtained laminate sheet was subjected to an additional heat treatment by heating at 80°C for 80 hours. The thickness of the adhesive layer formed by the above steps was 3 μm per side.

[0184] (Manufacture of laminate) The fine fibrous cellulose-containing sheet provided with the above-mentioned adhesive layer was cut with a cutter to prepare a sheet of 50 mm × 50 mm. Next, one commercially available polycarbonate plate (core resin plate (PC)) with a thickness of 1 mm was cut into a size of 100 mm × 100 mm, and two commercially available polycarbonate films (resin films) with a thickness of 0.2 mm were cut into a size of 50 mm × 50 mm, and polycarbonate film / adhesive layer B / fine fibrous cellulose-containing sheet (fine fibrous cellulose-containing layer containing polyvinyl alcohol (A) / fine fibrous cellulose-containing layer containing cellulose ether) / adhesive layer A / polycarbonate plate / adhesive layer A / fine fibrous cellulose-containing sheet (fine fibrous cellulose-containing layer containing cellulose ether / fine fibrous cellulose-containing layer containing polyvinyl alcohol (A)) / adhesive layer B / polycarbonate film were superimposed. At this time, the polycarbonate film and the fine fibrous cellulose-containing sheet were placed at the center of the polycarbonate plate. This was sandwiched between stainless steel plates with a thickness of 1 mm and dimensions of 200 mm x 200 mm and inserted into a mini test press (MP-WCH, manufactured by Toyo Seiki Seisakusho Co., Ltd.) set at room temperature. The mini test press was heated to 150 ° C over 3 minutes under a press pressure of 1 MPa, held at this state for 5 minutes, and then cooled to 30 ° C over 5 minutes. The stainless steel plates used had a release agent (Teflerise, manufactured by Odec Co., Ltd.) applied to the sandwiching surface. By the above procedure, a laminate of a fine fibrous cellulose-containing sheet and polycarbonate was obtained.

[0185] Example 2 In the (preparation of a fine fibrous cellulose-containing sheet) of Example 1, 40 parts by mass of the diluted fine fibrous cellulose dispersion was mixed with 60 parts by mass of the diluted aqueous polyvinyl alcohol solution (A) to obtain a mixed solution (B2). A laminate was obtained in the same manner as in Example 1, except that the mixed solution (B2) was used instead of the mixed solution (B1).

[0186] Example 3 A mixed solution (B3) was obtained by using the polyvinyl alcohol aqueous solution (B) instead of the polyvinyl alcohol aqueous solution (A) in Example 1. A laminate was obtained in the same manner as in Example 1, except that the mixed solution (B3) was used instead of the mixed solution (B1).

[0187] Example 4 A laminate was obtained in the same manner as in Example 1, except that the aqueous polyvinyl alcohol solution (C) was used instead of the aqueous polyvinyl alcohol solution (A) in Example 1, and in (preparation of a fine fibrous cellulose-containing sheet), a mixed solution (B4) was used in which 90 parts by mass of the diluted aqueous polyvinyl alcohol solution (C) was mixed with 10 parts by mass of the diluted fine fibrous cellulose dispersion.

[0188] Example 5 A laminate was obtained in the same manner as in Example 1, except that a commercially available polymethyl methacrylate plate (core resin plate (PMMA)) having a thickness of 1 mm was used instead of a commercially available polycarbonate plate (core resin plate (PC)) having a thickness of 1 mm.

[0189] Comparative Example 1 A fine fibrous cellulose-containing sheet was produced and an adhesive layer was provided in the same manner as in Example 1. Thereafter, in (production of laminate), a laminate was obtained in the same manner as in Example 1, except that the layers were laminated in the following order: polycarbonate film / fine fibrous cellulose-containing sheet provided with an adhesive layer / polycarbonate plate / fine fibrous cellulose-containing sheet provided with an adhesive layer / polycarbonate film, so that the fine fibrous cellulose-containing layer containing polyvinyl alcohol (A) as a hydrophilic polymer was on the polycarbonate plate side, and the fine fibrous cellulose-containing layer containing cellulose ether as a hydrophilic polymer was on the polycarbonate film side.

[0190] Comparative Example 2 A fine fibrous cellulose-containing sheet was produced and an adhesive layer was provided in the same manner as in Example 2. Thereafter, in (production of laminate), a laminate was obtained in the same manner as in Example 2, except that the layers were laminated in the order of polycarbonate film / fine fibrous cellulose-containing sheet provided with an adhesive layer / polycarbonate plate / fine fibrous cellulose-containing sheet provided with an adhesive layer / polycarbonate film, so that the fine fibrous cellulose-containing layer containing polyvinyl alcohol (A) as a hydrophilic polymer was on the polycarbonate plate side and the fine fibrous cellulose-containing layer containing cellulose ether as a hydrophilic polymer was on the polycarbonate film side.

[0191] Comparative Example 3 A fine fibrous cellulose-containing sheet was produced and an adhesive layer was provided in the same manner as in Example 3. Thereafter, in (production of laminate), a laminate was obtained in the same manner as in Example 3, except that the layers were laminated in the order of polycarbonate film / fine fibrous cellulose-containing sheet provided with an adhesive layer / polycarbonate plate / fine fibrous cellulose-containing sheet provided with an adhesive layer / polycarbonate film, so that the fine fibrous cellulose-containing layer containing polyvinyl alcohol (B) as a hydrophilic polymer was on the polycarbonate plate side and the fine fibrous cellulose-containing layer containing cellulose ether as a hydrophilic polymer was on the polycarbonate film side.

[0192] Comparative Example 4 In Example 1 (production of a fine fibrous cellulose-containing sheet), only a mixed solution (A1) containing 70 parts by mass of a fine fibrous cellulose dispersion and 30 parts by mass of a diluted cellulose ether aqueous solution was used. ２ The mixed solution (A1) was weighed out so that the thickness was 100°C and spread on a commercially available acrylic plate. The mixture was then dried in a dryer at 100°C for 1 hour and peeled off from the acrylic plate to obtain a fine fibrous cellulose-containing sheet. The thickness of the sheet was 34 μm. The other procedures were the same as in Example 1 to obtain a laminate.

[0193] Comparative Example 5 A fine fibrous cellulose-containing sheet was produced and an adhesive layer was formed in the same manner as in Comparative Example 4. A laminate was obtained in the same manner as in Comparative Example 4, except that in (formation of laminate), the side of the fine fibrous cellulose-containing sheet that had been in contact with the acrylic plate was placed on the polycarbonate film side.

[0194] Comparative Example 6 A laminate was obtained in the same manner as in Comparative Example 4 (production of a fine fibrous cellulose-containing sheet), except that the mixed liquid (B1) was used instead of the mixed liquid (A1).

[0195] Comparative Example 7 A laminate was obtained in the same manner as in Comparative Example 4 (production of a fine fibrous cellulose-containing sheet), except that the mixed liquid (B3) was used instead of the mixed liquid (A1).

[0196] <Comparative Example 8> A laminate was obtained in the same manner as in Comparative Example 4 (preparation of a sheet containing fine fibrous cellulose), except that the composition of the mixed solution was changed so that the diluted fine fibrous cellulose dispersion contained 70 parts by mass of the diluted aqueous cellulose ether solution and the diluted aqueous polyvinyl alcohol solution (A) contained 15 parts by mass.

[0197] <Comparative Example 9> In Comparative Example 8 (production of a fine fibrous cellulose-containing sheet), a laminate was obtained in the same manner as in Comparative Example 8, except that the composition of the mixed solution was changed so that the diluted fine fibrous cellulose dispersion liquid contained 70 parts by mass of the diluted cellulose ether aqueous solution and the diluted polyvinyl alcohol aqueous solution (A) contained 21 parts by mass and 9 parts by mass, respectively.

[0198] <Measurement and Evaluation> (Thickness of Fine Fibrous Cellulose-Containing Sheet) In Examples 1 to 4 and Comparative Examples 1 to 3, the thickness of the fine fibrous cellulose-containing sheet before the adhesive layer was provided was measured using a stylus thickness meter (Millitron 1202D, manufactured by Mahl Co., Ltd.). Furthermore, the thickness of each layer was calculated taking into account the ratio of the assumed finished basis weight. In Comparative Examples 4 to 9, the thickness of the fine fibrous cellulose-containing sheet before the adhesive layer was provided was measured.

[0199] (Thickness of adhesive layer) In all examples and comparative examples, the thickness of adhesive layer A was calculated by first subtracting the thickness of the fine fibrous cellulose-containing layer measured by the method described above from the thickness of the fine fibrous cellulose-containing sheet provided with adhesive layer A. In addition, the thickness of adhesive layer B was calculated by subtracting the total thickness of adhesive layer A and the fine fibrous cellulose-containing layer from the thickness of the fine fibrous cellulose-containing sheet provided with adhesive layers A and B.

[0200] (Evaluation of sheet strength (ease of sheet cracking)) When the sheet was cut with a cutter, the frequency of edge cracking was evaluated using the following four levels: A: Edge cracking hardly occurs B: Edge cracking occurs occasionally C: Edge cracking occurs D: Edge cracking occurs significantly

[0201] (Transparency of Laminate) The total light transmittance of the laminate was evaluated using a haze meter (HM-150, manufactured by Murakami Color Research Laboratory Co., Ltd.) in accordance with JIS K 7361-1: 1997. The haze of the laminate was also evaluated in accordance with JIS K 7136: 2000.

[0202] (Yellowness Index of Laminate) The yellowness index (yellow index, YI value) of the laminate was measured in accordance with JIS K 7373:2006 using Colour Cute i (manufactured by Suga Test Instruments Co., Ltd.).

[0203] (Evaluation of Adhesion Strength) The interlayer adhesive strength of the laminate was evaluated by the following method. Cutter evaluation: A 10 mm x 10 mm cut was made in the surface of the laminate, and this area was peeled off. Peel evaluation: The polycarbonate film at the edge of the laminate was grasped and peeled off. The adhesive strength was evaluated according to the following criteria. A: Peeling was not possible, or if forced peeling was attempted, the polycarbonate film broke and the interface was disrupted. B: A large force was required to peel, and the interface was disrupted after peeling. C: Force was required to peel, but the interface was smooth after peeling. D: The force required for peeling was small, and the interface was smooth after peeling. E: Peeling proceeded with just a small impact.

[0204] (Identification of peeling interface) In the evaluation of adhesive strength, ion-exchanged water was dropped with a dropper onto the peeled polycarbonate film side and the polycarbonate plate side, and after 10 seconds, the water droplets were wiped off. If the water droplets bled, it was determined that a fine fibrous cellulose-containing sheet was present, and the peeling interface was assumed as follows based on the position of the water droplets. If the bleed occurred on the peeled polycarbonate film: Peeling occurred at the interface between the adhesive layer (adhesive layer A) in contact with the polycarbonate plate and the fine fibrous cellulose-containing sheet (CNF layer). If the bleed occurred on the polycarbonate plate side: Peeling occurred at the interface between the adhesive layer (adhesive layer B) in contact with the polycarbonate film and the fine fibrous cellulose-containing sheet (CNF layer).

[0205] (Evaluation of Processing Suitability) Assuming secondary processing of the laminate, the laminate was cut with a slide saw and the presence or absence of peeling from the edge was observed.

[0206]

[0207] As can be seen from Table 1, the laminates of Examples 1 to 5 had excellent adhesive strength, and when cut with a cutter, edge cracking was suppressed, resulting in excellent strength. Furthermore, when cut with a slide saw, peeling from the edges was suppressed, demonstrating excellent processability. On the other hand, as in Comparative Examples 1 to 3, when the hydroxyl value of the hydrophilic polymer contained in the fine fibrous cellulose-containing layer A on the polycarbonate plate side, which is the core resin plate, was greater than the hydroxyl value of the hydrophilic polymer contained in the fine fibrous cellulose-containing layer B on the polycarbonate film side, which is the resin film, the laminates had poor adhesive strength and poor processability. Furthermore, as in Comparative Examples 4 and 5, when a single layer of a fine fibrous cellulose-containing layer containing hydroxypropylmethylcellulose, in which the hydroxyl value of the hydrophilic polymer was relatively low, was used, the sheet strength and optical properties were excellent, but sufficient adhesive strength could not be obtained, and the processability was also poor. As in Comparative Examples 6 and 7, when a single layer of a fine fibrous cellulose-containing layer containing polyvinyl alcohol, in which the hydroxyl value of the hydrophilic polymer is relatively high, was used, the adhesive strength was excellent and the processability was good, but the sheet strength was poor and the optical properties were also poor. As in Comparative Examples 8 and 9, when a single layer of a fine fibrous cellulose-containing layer containing hydroxypropyl methylcellulose, which has a relatively low hydroxyl value, and polyvinyl alcohol, which has a relatively high hydroxyl value, was used as the hydrophilic polymer, the adhesive strength was not sufficient and the processability was also poor.

Claims

1. A fine fibrous cellulose-containing sheet having a fine fibrous cellulose-containing layer 1A containing fine fibrous cellulose having a fiber width of 1,000 nm or less and a hydrophilic polymer 1A, and a fine fibrous cellulose-containing layer 1B containing fine fibrous cellulose having a fiber width of 1,000 nm or less and a hydrophilic polymer 1B, wherein the hydrophilic polymer 1A and the hydrophilic polymer 1B have hydroxyl groups, and when the hydroxyl value of the hydrophilic polymer 1A is OHV_1A (mg KOH / g) and the hydroxyl value of the hydrophilic polymer 1B is OHV_1B (mg KOH / g), the following formula (I) is satisfied: OHV_1A<OHV_1B (I) 2. The fine fibrous cellulose-containing sheet according to claim 1, wherein the hydrophilic polymer 1A is a non-ionic water-soluble cellulose ether.

3. The fine fibrous cellulose-containing sheet according to claim 2, wherein the hydrophilic polymer 1A has at least one functional group selected from the group consisting of an alkoxy group and a hydroxyalkoxy group.

4. A fine fibrous cellulose-containing sheet according to claim 1, wherein the hydrophilic polymer 1B is polyvinyl alcohol having a saponification degree of 80 or more or a modified product thereof.

5. The fine fibrous cellulose-containing sheet according to claim 1, which satisfies the following formula (II): 1200 mg KOH / g ≧ OHV_1B − OHV_1A ≧ 450 mg KOH / g (II) 6. The fine fibrous cellulose-containing sheet according to claim 1, wherein the fine fibrous cellulose has anionic groups.

7. A fine fibrous cellulose-containing sheet according to claim 6, wherein the anionic group possessed by the fine fibrous cellulose is a phosphorus oxo acid group or a functional group derived from a phosphorus oxo acid group.

8. The fine fibrous cellulose-containing sheet according to claim 6, wherein the content of anionic groups in the fine fibrous cellulose is less than 0.5 mmol / g.

9. A fine fibrous cellulose-containing sheet according to claim 1, in which the ratio of the thickness of the fine fibrous cellulose-containing layer 1A to the thickness of the fine fibrous cellulose-containing layer 1B (fine fibrous cellulose-containing layer 1A:fine fibrous cellulose-containing layer 1B) is greater than 5:5 and not greater than 9:

1.

10. A fine fibrous cellulose-containing sheet according to claim 1, wherein the total thickness of the fine fibrous cellulose-containing layer 1A and the fine fibrous cellulose-containing layer 1B is 20 μm or more and 300 μm or less.

11. A laminated sheet comprising the fine fibrous cellulose-containing sheet of any one of claims 1 to 10, having an adhesive layer 1A on the side of the fine fibrous cellulose-containing layer 1A opposite to the side having the fine fibrous cellulose-containing layer 1B, and having an adhesive layer 1B on the side of the fine fibrous cellulose-containing layer 1B opposite to the side having the fine fibrous cellulose-containing layer 1A.

12. The laminate sheet according to claim 11, wherein adhesive layer 1A and adhesive layer 1B contain at least one resin selected from the group consisting of polycarbonate-based resins, acrylic-based resins, and polyester-based resins.

13. The laminate sheet according to claim 11, wherein adhesive layer 1A and adhesive layer 1B are formed from an adhesive composition containing an isocyanate compound.

14. The laminate sheet according to claim 11, which has a resin film 1 on the surface of the adhesive layer 1B of the laminate sheet opposite to the surface having the fine fibrous cellulose-containing layer 1B.

15. The laminate sheet according to claim 14, wherein the thickness of the resin film 1 is 30 μm or more and 500 μm or less.

16. A laminate further comprising a core resin plate on the surface of the adhesive layer 1A of the laminate sheet according to claim 14 opposite to the surface having the fine fibrous cellulose-containing layer 1A.

17. The laminate according to claim 16, wherein the thickness of the core resin plate is 500 μm or more and 4,500 μm or less.

18. The laminate according to claim 16, wherein the core resin plate contains at least one resin selected from the group consisting of polycarbonate resin and acrylic resin.

19. The laminate according to claim 16, wherein the surface of the core resin plate opposite to the surface having adhesive layer 1A is provided with, in this order from the core resin plate, adhesive layer 2A, fine fibrous cellulose-containing layer 2A containing fine fibrous cellulose having a fiber width of 1,000 nm or less and hydrophilic polymer 2A, fine fibrous cellulose-containing layer 2B containing fine fibrous cellulose having a fiber width of 1,000 nm or less and hydrophilic polymer 2B, adhesive layer 2B, and resin film 2, wherein hydrophilic polymer 2A and hydrophilic polymer 2B have hydroxyl groups, and the following formula (I') is satisfied when the hydroxyl value of hydrophilic polymer 2A is OHV_2A (mg KOH / g) and the hydroxyl value of hydrophilic polymer 2B is OHV_2B (mg KOH / g): OHV_2A<OHV_2B (I').

20. The laminate of claim 16, having a haze of 2.0% or less.

21. The laminate according to claim 16, having a total light transmittance of 85% or more.

22. The laminate according to claim 16, having a yellow index (YI value) of 2.50 or less.

Images