JP6617843B1 - Sheet - Google Patents

Abstract

An object of the present invention is to provide a sheet capable of improving the balance between productivity and strength. The present invention provides a first cellulose fiber having a fiber width of 100 nm or less and having a phosphite group or a substituent derived from a phosphite group, and a second cellulose fiber having a fiber width of 1 μm or more and 100 μm or less. And wherein the content of the first cellulose fibers is 1% by mass or more and 30% by mass or less of the entire sheet. [Selection diagram] None

Description

  The present invention relates to a sheet.

  In recent years, materials that use reproducible natural fibers have attracted attention due to the substitution of petroleum resources and the growing environmental awareness. Among natural fibers, fibrous cellulose having a fiber diameter of 10 μm or more and 50 μm or less, in particular, fibrous cellulose (pulp) derived from wood has been widely used mainly as a paper product so far.

  As fibrous cellulose, fine fibrous cellulose having a fiber diameter of 5 μm or less is also known. In addition, a sheet composed of such fine fibrous cellulose, a composite sheet containing a fine fibrous cellulose-containing sheet and a resin, and a molded body have been developed. In the sheet | seat and molded object containing a fine fibrous cellulose, since the contact point of fibers increases remarkably, it is known that tensile strength etc. will improve large.

  For example, Patent Document 1 describes a nonwoven fabric obtained by papermaking cellulose fibers having an average fiber diameter of 0.1 to 20 μm and cellulose nanofibers having an average fiber diameter of less than 100 nm. Patent Document 2 discloses a first fiber having a number average fiber width of 2 nm or more and less than 1000 nm, a number average fiber width of 1000 nm or more and 100000 nm or less, and a number average fiber length of 0.1 to 20 mm. A composite in which a resin is contained in a nonwoven fabric containing fibers is described.

JP 2012-036517 A Japanese Patent Laying-Open No. 2015-025033

  The inventors of the present invention have made studies for the purpose of providing a fine fibrous cellulose-containing sheet having an excellent balance between productivity and strength.

[1] A sheet comprising a first cellulose fiber having a fiber width of 100 nm or less and having a phosphite group or a substituent derived from a phosphite group, and a second cellulose fiber having a fiber width of 1 μm to 100 μm. And the sheet | seat whose content rate of the said 1st cellulose fiber is 1 mass% or more and 30 mass% or less of the said whole sheet | seat.
[2] The sheet according to [1], wherein the first cellulose fiber has a fiber width of 8 nm or less.
[3] The sheet according to [1] or [2], comprising a polyamide polyamine epihalohydrin.
[4] The sheet according to any one of [1] to [3], wherein the second cellulose fiber includes softwood pulp and hardwood pulp.
[5] The second cellulose fiber includes softwood pulp and hardwood pulp,
The sheet according to any one of [1] to [4], wherein the value of N / L is 1 or more and 8 or less, where N is the content of softwood pulp and L is the content of hardwood pulp.
[6] The sheet according to [4] or [5], wherein the Canadian standard freeness of the mixture of softwood and hardwood pulp is 600 ml or less.
[7] The sheet according to [4] or [5], wherein the irregular freeness of the mixture of softwood pulp and hardwood pulp is 800 ml or less.
[8] The sheet according to any one of [1] to [7], wherein the increase rate of the specific tensile modulus calculated by the following formula is greater than 25%;
Rate of increase in specific tensile modulus (%) = (specific tensile modulus of sheet−specific tensile modulus of control sheet) / specific tensile modulus of control sheet × 100
Here, the control sheet is a sheet produced without blending the first cellulose fibers.

  According to the present invention, a fine fibrous cellulose-containing sheet having an excellent balance between productivity and strength can be obtained.

FIG. 1 is a graph showing the relationship between the amount of NaOH dropped and the pH with respect to a fibrous cellulose-containing slurry having a phosphorus oxo acid group.

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

(Sheet)
The present invention includes a first cellulose fiber having a fiber width of 100 nm or less and having a phosphite group or a substituent derived from a phosphite group, and a second cellulose fiber having a fiber width of 1 μm to 100 μm. Regarding the sheet. The content rate of the 1st cellulose fiber of the said sheet | seat is 1 mass% or more and 30 mass% or less of the whole sheet | seat. In the present specification, fibrous cellulose having a fiber width of 100 nm or less may be referred to as fine fibrous cellulose, and the sheet may be referred to as a fine fibrous cellulose-containing sheet.

  Since the sheet of the present invention has the above-described configuration, it has an excellent balance between productivity and strength. For this reason, it is particularly preferably used in industrial products where low cost and high strength are required.

The tensile strength of the sheet of the present invention is preferably 15 MPa or more, preferably 20 MPa or more, and more preferably 30 MPa or more. Moreover, although there is no restriction | limiting in particular in the upper limit of the tensile strength of a sheet | seat, For example, it can be 500 Mpa or less.
The tensile strength (unit: N / m) is measured using a tensile tester Tensilon (manufactured by A & D) according to, for example, JIS P8113. The tensile strength is divided by the thickness of the test piece to calculate the tensile strength (unit: MPa). In addition, when measuring tensile strength, what was conditioned for 24 hours at 23 degreeC and 50% of relative humidity is used as a test piece.

The tensile modulus of the sheet of the present invention is preferably 1.5 GPa or more, more preferably 2.0 GPa or more, and further preferably 3.0 GPa or more. Moreover, although there is no restriction | limiting in particular in the upper limit of the tensile elasticity modulus of a sheet | seat, For example, it can be 50 GPa or less.
The tensile elastic modulus can be measured using, for example, a tensile tester Tensilon (manufactured by A & D) based on JIS P8113. Here, the elastic modulus is a value calculated from the maximum positive slope value in the SS curve. Moreover, when measuring a tensile elasticity modulus, what was conditioned for 24 hours at 23 degreeC and 50% of relative humidity is used as a test piece.

The rate of increase in specific tensile modulus based on a control sheet prepared without blending the first cellulose fibers is preferably 25% or more, more preferably 30% or more, and 35% or more. Is more preferable. Note that the rate of increase in the specific tensile modulus is a value calculated by the following equation.
Rate of increase in specific tensile modulus (%) = (specific tensile modulus of sheet−specific tensile modulus of control sheet) / specific tensile modulus of control sheet × 100
Here, the control sheet is a sheet produced without blending the first cellulose fibers.

The specific tensile modulus of the sheet of the present invention is preferably larger than 8.0 kNm / g, more preferably larger than 8.5 kNm / g, still more preferably larger than 9.0 kNm / g. It is particularly preferred that it is greater than 0.0 kNm / g. The upper limit of the specific tensile modulus of the sheet of the present invention is not particularly limited, but can be set to, for example, 100 kNm / g. In the present specification, the specific tensile modulus is a value calculated by dividing the tensile modulus (GPa) of the sheet by the density (g / cm ³ ).

Interlayer strength of the sheet of the present invention is preferably 750 J / m ² or more, more preferably 1200 J / m ² or more, and still more preferably 1500 J / m ² or more. The upper limit of the interlayer strength of the sheet is not particularly limited, but can be, for example, 7000 J / m ² or less. In this specification, the interlayer strength of a sheet means the strength in the thickness direction of the sheet.
The interlayer strength can be measured using an internal bond tester (manufactured by Kumagaya Riki Kogyo Co., Ltd.) in accordance with, for example, JTAPPI 18-2. Further, when measuring the interlayer strength, a sheet conditioned for 24 hours at 23 ° C. and 50% relative humidity is used as a test piece.

  Sheet productivity can be increased, for example, by reducing the slurry dewatering time when the sheet is made. By shortening the slurry dehydration time, the production efficiency of the sheet is increased, and the sheet can be supplied at a lower cost. In addition, the productivity of the slurry is determined by flowing 250 g of slurry adjusted to a solid content concentration of 0.5% by mass on a wire (HT2525-30, manufactured by Haiku Wagner), and the time until water is drawn (pulp on the wire) It can be evaluated by measuring the time from when water is removed from the slurry and the gloss disappears from the pulp surface. The time until water is drawn is preferably less than 30 minutes, more preferably less than 10 minutes, even more preferably less than 1 minute, and particularly preferably not more than 30 seconds.

  Although the thickness of the sheet | seat of this invention is not specifically limited, It is preferable that it is 5 micrometers or more, It is more preferable that it is 10 micrometers or more, It is further more preferable that it is 15 micrometers or more. Moreover, the upper limit of the thickness of the sheet is not particularly limited, but can be, for example, 1000 μm or less. In addition, the thickness of a sheet | seat can be measured with a stylus type thickness meter (Maltron 1202D by Marl).

The basis weight of the sheet of the present invention is preferably 6 g / m ² or more, more preferably 13 g / m ² or more, and further preferably 19 g / m ² or more. The basis weight of the sheet is preferably 500 g / m ² or less, and more preferably 300 g / m ² or less. Here, the basis weight of the sheet can be calculated in accordance with JIS P 8124.

The density of the sheet of the present invention is preferably 0.1 g / cm ³ or more, and more preferably 0.2 g / cm ³ or more. The density of the sheet of the present invention is preferably 5 g / cm ³ or less. Here, the density of the sheet can be calculated in accordance with JIS P 8118: 2014.

(First cellulose fiber)
The sheet of the present invention includes first cellulose fibers having a fiber width of 100 nm or less and having a phosphite group or a substituent derived from a phosphite group. In the present specification, the first cellulose fiber is also referred to as fine fibrous cellulose or fine cellulose fiber. In the present invention, from the viewpoint of improving strength, the fiber width of the first cellulose fiber is particularly preferably 8 nm or less.

  As above-mentioned, content of a 1st cellulose fiber is 1 mass% or more with respect to the total mass of a sheet | seat, It is more preferable that it is 2 mass% or more, It is further more preferable that it is 5 mass% or more. In addition, from the viewpoint of further improving the strength, the content of the first cellulose fiber can be 15% by mass or more based on the entire sheet. Moreover, content of a 1st cellulose fiber is 30 mass% or less with respect to the total mass of a sheet | seat, and it is more preferable that it is 25 mass% or less. Moreover, from a viewpoint of improving productivity, content of a 1st cellulose fiber can also be 18 mass% or less with respect to the whole sheet | seat.

  Although it does not specifically limit as a fibrous cellulose raw material for obtaining a fine fibrous cellulose, It is preferable to use a pulp from the point of being easy to acquire and cheap. Examples of the pulp include wood pulp, non-wood pulp, and deinked pulp. Examples of wood pulp include hardwood kraft pulp (LBKP), softwood kraft pulp (NBKP), sulfite pulp (SP), dissolved pulp (DP), soda pulp (AP), unbleached kraft pulp (UKP), oxygen bleached craft Chemical pulps such as pulp (OKP) are listed. Moreover, semi-chemical pulps such as semi-chemical pulp (SCP) and chemi-ground wood pulp (CGP), mechanical pulps such as ground wood pulp (GP), and thermomechanical pulp (TMP, BCTMP) are exemplified, but not particularly limited. Non-wood pulp includes cotton pulp such as cotton linter and cotton lint, non-wood pulp such as hemp, straw, and bagasse, cellulose isolated from sea squirts and seaweed, chitin, chitosan, etc., but is not particularly limited. . The deinking pulp includes deinking pulp made from waste paper, but is not particularly limited. The pulp of this embodiment may be used alone or in combination of two or more. Among the above pulps, wood pulp containing cellulose and deinked pulp are preferable in terms of availability. Among wood pulps, chemical pulp has a large cellulose ratio, so the yield of fine fibrous cellulose is high at the time of fiber refinement (defibration), and the degradation of cellulose in the pulp is small and the fineness of long fibers with a large axial ratio is high. It is preferable at the point from which fibrous cellulose is obtained. Of these, kraft pulp and sulfite pulp are most preferably selected. When long fibrous fine fibrous cellulose having a large axial ratio is used, a high-strength sheet tends to be obtained.

  The average fiber width of the first cellulose fibers is 100 nm or less as observed with an electron microscope. The average fiber width is preferably 2 nm or more and 100 nm or less, more preferably 2 nm or more and 50 nm or less, and further preferably 2 nm or more and 10 nm or less, but is not particularly limited. When the average fiber width of the first cellulose fibers is less than 2 nm, the physical properties (strength, rigidity, dimensional stability) as fine fibrous cellulose tend to be difficult to be expressed because cellulose molecules are dissolved in water. . The fine fibrous cellulose is monofilamentous cellulose having a fiber width of 100 nm or less, for example.

  Measurement of the average fiber width of the fine fibrous cellulose by electron microscope observation is performed as follows. An aqueous suspension of fine fibrous cellulose having a concentration of 0.05% by mass or more and 0.1% by mass or less is prepared, and the suspension is cast on a carbon film-coated grid subjected to a hydrophilic treatment to prepare a sample for TEM observation. To do. When a wide fiber is included, an SEM image of the surface cast on glass may be observed. Observation with an electron microscope image is performed at a magnification of 1000 times, 5000 times, 10000 times, or 50000 times depending on the width of the constituent fibers. However, the sample, observation conditions, and magnification are adjusted to satisfy the following conditions.

(1) One straight line X is drawn at an arbitrary location in the observation image, and 20 or more fibers intersect the straight line X.
(2) A straight line Y perpendicular to the straight line is drawn in the same image, and 20 or more fibers intersect the straight line Y.

  The width of the fiber that intersects with the straight line X and the straight line Y is visually read from the observation image that satisfies the above conditions. In this way, at least three sets of images of the surface portion that do not overlap each other are observed, and the width of the fiber intersecting with the straight line X and the straight line Y is read for each image. Thus, at least 20 × 2 × 3 = 120 fiber widths are read. The average fiber width of the fine fibrous cellulose is an average value of the fiber widths read in this way.

  The fiber length of the first cellulose fiber is not particularly limited, but is preferably 0.1 μm or more and 1000 μm or less, more preferably 0.1 μm or more and 800 μm or less, and particularly preferably 0.1 μm or more and 600 μm or less. By making the fiber length within the above range, the destruction of the crystalline region of the fine fibrous cellulose can be suppressed, and the slurry viscosity of the fine fibrous cellulose can be made an appropriate range. The fiber length of the fine fibrous cellulose can be determined by image analysis using TEM, SEM, or AFM.

The fine fibrous cellulose preferably has an I-type crystal structure. Here, the fact that the fine fibrous cellulose has a type I crystal structure can be identified in a diffraction profile obtained from a wide-angle X-ray diffraction photograph using CuKα (λ = 1.5418Å) monochromatized with graphite. Specifically, it can be identified by having typical peaks at two positions of 2θ = 14 ° to 17 ° and 2θ = 22 ° to 23 °.
The proportion of the I-type crystal structure in the fine fibrous cellulose is preferably 30% or more, more preferably 50% or more, and further preferably 70% or more. In this case, further superior performance can be expected in terms of heat resistance and low linear thermal expansion coefficient. The degree of crystallinity is obtained by measuring an X-ray diffraction profile and determining the crystallinity by a conventional method (Seagal et al., Textile Research Journal, 29, 786, 1959).

The fine fibrous cellulose has a phosphite group or a substituent derived from a phosphite group (also simply referred to as a phosphite group). In the present invention, the phosphite group or the substituent derived from the phosphite group is, for example, a substituent represented by the following formula (2).

  In Formula (2), b is a natural number, m is an arbitrary number, and b × m = 1. α is a hydrogen atom, a saturated-linear hydrocarbon group, a saturated-branched hydrocarbon group, a saturated-cyclic hydrocarbon group, an unsaturated-linear hydrocarbon group, an unsaturated-branched hydrocarbon group. An unsaturated-cyclic hydrocarbon group, an aromatic group, or a derivative group thereof. Among these, α is particularly preferably a hydrogen atom. Note that α in the formula (2) does not include a group derived from a cellulose molecular chain.

  Examples of the saturated-linear hydrocarbon group represented by α in Formula (2) include, but are not particularly limited to, a methyl group, an ethyl group, an n-propyl group, and an n-butyl group. Examples of the saturated-branched hydrocarbon group include i-propyl group and t-butyl group, but are not particularly limited. Examples of the saturated-cyclic hydrocarbon group include, but are not particularly limited to, a cyclopentyl group or a cyclohexyl group. Examples of the unsaturated-linear hydrocarbon group include, but are not particularly limited to, a vinyl group or an allyl group. Examples of the unsaturated-branched hydrocarbon group include i-propenyl group and 3-butenyl group, but are not particularly limited. Examples of the unsaturated-cyclic hydrocarbon group include, but are not limited to, a cyclopentenyl group and a cyclohexenyl group. Examples of the aromatic group include, but are not limited to, a phenyl group or a naphthyl group.

  In addition, the derivative group in α is a functional group in which at least one of functional groups such as a carboxy group, a hydroxy group, or an amino group is added or substituted to the main chain or side chain of the above-mentioned various hydrocarbon groups. Although group is mentioned, it is not specifically limited. Further, 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 phosphite group can be set within an appropriate range, and the penetration into the fiber raw material can be facilitated, and the yield of fine cellulose fibers can be reduced. It can also be increased.

Β ^{b +} in the formula (2) is a monovalent or higher cation composed of an organic substance or an inorganic substance. Examples of the monovalent or higher cation made of an organic substance include aliphatic ammonium or aromatic ammonium. Examples of the monovalent or higher cation made of an inorganic substance include ions of alkali metals such as sodium, potassium, or lithium, Examples include, but are not particularly limited to, a cation of a divalent metal such as calcium or magnesium, or a hydrogen ion. These can be applied alone or in combination of two or more. The monovalent or higher cation composed of an organic substance or an inorganic substance is preferably a sodium ion or potassium ion which is not easily yellowed when heated to a fiber raw material containing β and is industrially easily used, but is not particularly limited.

  In addition to the phosphite group or the substituent derived from the phosphite group, the fine fibrous cellulose may further have a phosphate group or a group derived from the phosphate group. The group derived from a phosphoric acid group or a phosphoric acid group is, for example, a substituent represented by the following formula (1) or (3). The phosphoric acid group or the group derived from the phosphoric acid group may be a condensed phosphorus oxo acid group represented by the following formula (3).

In formula (1), a and b are natural numbers, and m is an arbitrary number (provided that a = b × m). Of α and α ′, a is O ⁻ and the rest is OR. Here, R is a hydrogen atom, a saturated-linear hydrocarbon group, a saturated-branched hydrocarbon group, a saturated-cyclic hydrocarbon group, an unsaturated-linear hydrocarbon group, an unsaturated-branched chain. It is a hydrocarbon group, an unsaturated-cyclic hydrocarbon group, an aromatic group, or a derivative group thereof. In addition, α in the formula (1) may be a group derived from a cellulose molecular chain.

In formula (3), a and b are natural numbers, m is an arbitrary number, and n is a natural number of 2 or more (provided that a = b × m). Of α ¹ , α ² ,..., α ⁿ and α ′, a is O ⁻ and the rest is either R or OR. Here, R is a hydrogen atom, a saturated-linear hydrocarbon group, a saturated-branched hydrocarbon group, a saturated-cyclic hydrocarbon group, an unsaturated-linear hydrocarbon group, an unsaturated-branched chain. It is a hydrocarbon group, an unsaturated-cyclic hydrocarbon group, an aromatic group, or a derivative group thereof. In addition, α in the formula (3) may be a group derived from a cellulose molecular chain.

Specific examples of each group in formulas (1) and (3) are the same as the specific examples of each group in formula (2). Further, the formula (1) and specific examples beta ^{b +} a in (3) are the same as specific examples of beta ^{b +} in equation (2).

The fact that fine fibrous cellulose has a phosphite group as a substituent means that an infrared absorption spectrum of a dispersion containing fine fibrous cellulose is measured and a tautomer of a phosphite group is present in the vicinity of 1210 cm ^−1. This can be confirmed by observing the absorption based on P = O of a certain phosphonic acid group. Further, the fact that fibrous cellulose has a phosphate group as a substituent means that an infrared absorption spectrum of the dispersion containing fibrous cellulose is measured, and absorption based on P = O of the phosphate group is around 1230 cm ^−1. This can be confirmed by observation. The fact that fibrous cellulose has a phosphorous acid group or a phosphoric acid group as a substituent can also be confirmed by a method of confirming a chemical shift using NMR or a method of combining titration with elemental analysis.

<Phosphorous acid group introduction process>
In the phosphite group introduction step, at least one selected from a compound having a phosphite group and a salt thereof (hereinafter referred to as “phosphorylation reagent” or “compound A”) is applied to the fiber raw material containing cellulose. It can be performed by reacting. Such a phosphorylation reagent may be mixed in a powder or aqueous solution with a dry or wet fiber raw material. As another example, a phosphorous reagent powder or an aqueous solution may be added to the fiber raw material slurry.

  The phosphite group introduction step is carried out by reacting a fiber raw material containing cellulose with at least one selected from a compound having a phosphite group and a salt thereof (phosphorylation reagent or compound A). it can. This reaction may be carried out in the presence of at least one selected from urea and derivatives thereof (hereinafter referred to as “compound B”).

  As an example of a method for causing compound A to act on a fiber raw material in the presence of compound B, a method of mixing powder or an aqueous solution of compound A and compound B with a dry or wet fiber raw material can be mentioned. Another example is a method of adding powders and aqueous solutions of Compound A and Compound B to a fiber raw material slurry. Among these, since the uniformity of the reaction is high, a method of adding an aqueous solution of Compound A and Compound B to a dry fiber material, or a powder or an aqueous solution of Compound A and Compound B to a wet fiber material The method is preferred. Moreover, the compound A and the compound B may be added simultaneously, or may be added separately. Moreover, you may add the compound A and the compound B first used for reaction as aqueous solution, and remove an excess chemical | medical solution by pressing. The form of the fiber raw material is preferably cotton or thin sheet, but is not particularly limited.

  Compound A used in this embodiment is at least one selected from a compound having a phosphite group and a salt thereof. Examples of the compound having a phosphite group include phosphorous acid, and examples of phosphorous acid include 99% phosphorous acid (phosphonic acid). Examples of the salt of the compound having a phosphite group include lithium salt, sodium salt, potassium salt, and ammonium salt of phosphorous acid, and these can have various degrees of neutralization. Of these, phosphorous acid and phosphorous acid are introduced from the viewpoint that the introduction efficiency of the phosphorus oxo acid group is high, the fibrillation efficiency is easily improved in the fibrillation process described later, the cost is low, and the industrial application is easy. The sodium salt of acid, the potassium salt of phosphorous acid, or the ammonium salt of phosphorous acid is preferably used.

  In addition, compound A is preferably used as an aqueous solution because the uniformity of the reaction is enhanced and the efficiency of introducing a phosphite group is increased. The pH of the aqueous solution of Compound A is not particularly limited, but is preferably 7 or less because the efficiency of introducing phosphite groups is increased, and more preferably pH 3 or more and pH 7 or less from the viewpoint of suppressing hydrolysis of pulp fibers. The pH of the aqueous solution of Compound A may be adjusted by, for example, using a compound having a phosphite group in combination with a compound that exhibits acidity and a compound that exhibits alkalinity, and changing the amount ratio thereof. The pH of the aqueous solution of Compound A may be adjusted by adding an inorganic alkali or organic alkali to a compound having a phosphorous acid group and showing acidity.

  The amount of compound A added to the fiber raw material is not particularly limited, but when the amount of compound A added is converted to phosphorus atomic weight, the amount of phosphorus atom added to the fiber raw material (absolute dry mass) is 0.5 mass% to 100 mass%. Or less, more preferably 1% by mass or more and 50% by mass or less, and most preferably 2% by mass or more and 30% by mass or less. If the amount of phosphorus atoms added to the fiber raw material is within the above range, the yield of fine fibrous cellulose can be further improved. By making the amount of phosphorus atoms added to the fiber raw material 100% by mass or less, it is possible to balance the effect of improving the yield and the cost. On the other hand, a yield can be raised by making the addition amount of the phosphorus atom with respect to a cellulose fiber more than the said lower limit.

  Examples of the compound B used in this embodiment include urea, biuret, 1-phenylurea, 1-benzylurea, 1-methylurea, 1-ethylurea and the like.

  Compound B is preferably used as an aqueous solution in the same manner as Compound A. Moreover, since the uniformity of reaction increases, it is preferable to use the aqueous solution in which both compound A and compound B are dissolved. The amount of Compound B added to the fiber raw material (absolute dry mass) is preferably 1% by mass or more and 500% by mass or less, more preferably 10% by mass or more and 400% by mass or less, and 100% by mass or more and 350% by mass or less. More preferably, it is more preferably 150% by mass or more and 300% by mass or less.

  In addition to Compound A and Compound B, amides or amines may be included in the reaction system. Examples of amides include formamide, dimethylformamide, acetamide, dimethylacetamide and the like. Examples of amines include methylamine, ethylamine, trimethylamine, triethylamine, monoethanolamine, diethanolamine, triethanolamine, pyridine, ethylenediamine, hexamethylenediamine, and the like. Among these, triethylamine is known to work as a good reaction catalyst.

  In the phosphite group introduction step, it is preferable to perform heat treatment after adding or mixing the compound A or the like to the fiber raw material. As the heat treatment temperature, it is preferable to select a temperature at which phosphite groups can be efficiently introduced while suppressing thermal decomposition and hydrolysis reaction of the fiber. Specifically, it is preferably 50 ° C. or higher and 300 ° C. or lower, more preferably 100 ° C. or higher and 250 ° C. or lower, and further preferably 130 ° C. or higher and 200 ° C. or lower. In addition, equipment having various heat media can be used for the heat treatment. For example, stirring and drying apparatus, rotary drying apparatus, disk drying apparatus, roll heating apparatus, plate heating apparatus, fluidized bed drying apparatus, air flow A drying device, a vacuum drying device, an infrared heating device, a far infrared heating device, a microwave heating device, or a high-frequency drying device may be used.

  During the heat treatment, while water is contained in the fiber raw material slurry to which compound A is added, if the time for allowing the fiber raw material to stand still becomes long, the compound A dissolved with water molecules moves to the fiber raw material surface with drying. To do. Therefore, the concentration of the compound A in the fiber raw material may be uneven, and the introduction of phosphite groups to the fiber surface may not proceed uniformly. In order to suppress the occurrence of unevenness in concentration of Compound A in the fiber material due to drying, a very thin sheet-like fiber material is used, or the fiber material and Compound A are kneaded or stirred with a kneader or the like and dried by heating or reduced pressure. The method should be taken.

  The heating device used for the heat treatment is preferably a device that can always discharge the moisture retained by the slurry and the moisture generated by the addition reaction to the hydroxyl groups of the fibers such as phosphite groups, for example, with a blower system. An oven or the like is preferable. If water in the system is always discharged, the hydrolysis reaction of the phosphate ester bond, which is the reverse reaction of the esterification, can be suppressed, and the acid hydrolysis of the sugar chain in the fiber can also be suppressed. A fine fiber having a high axial ratio can be obtained.

  The heat treatment time is also affected by the heating temperature, but it is preferably 1 second or more and 300 minutes or less, preferably 1 second or more and 1000 seconds or less after moisture is substantially removed from the fiber raw material slurry. Preferably, it is 10 seconds or more and 800 seconds or less. In the present invention, the amount of phosphite group introduced can be within the preferred range by setting the heating temperature and the heating time within an appropriate range.

  The phosphite group introduction step may be performed at least once, but may be repeated a plurality of times. In this case, more phosphite groups are introduced, which is preferable. In the present invention, for example, it is also a preferred embodiment to perform the phosphite group introduction step twice.

  The amount of phosphite group introduced is preferably 0.10 mmol / g or more, more preferably 0.20 mmol / g or more per 1 g (mass) of fine fibrous cellulose, and 0.50 mmol / g or more. More preferably, it is more preferably 1.00 mmol / g or more. The amount of phosphite group introduced is preferably 5.20 mmol / g or less, more preferably 3.65 mmol / g or less, and 3.00 mmol / g per 1 g (mass) of fine fibrous cellulose. More preferably, it is as follows. By making the introduction amount of the phosphite group within the above range, the fiber raw material can be easily refined and the stability of the fine fibrous cellulose can be enhanced. In addition, when the amount of the phosphite group introduced is within the above range, good characteristics can be exhibited as a thickener for a battery separator coating liquid. In addition, in this specification, content of the phosphite group which fine fibrous cellulose has (introduction amount of phosphite group) is the amount of strongly acidic groups of phosphite groups which fine fibrous cellulose has as described later. Is equal to

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

FIG. 1 is a graph showing the relationship between the amount of NaOH dropped and the pH with respect to a fibrous cellulose-containing slurry having a phosphorus oxo acid group. For example, the introduction amount of the phosphorus oxo acid group into the fibrous cellulose is measured as follows.
First, the slurry containing fibrous cellulose is treated with a strongly acidic ion exchange resin. In addition, you may implement the fibrillation process similar to the fibrillation process mentioned later with respect to a measuring object before the process by strong acidic ion exchange resin as needed.
Next, the pH change is observed while adding an aqueous sodium hydroxide solution to obtain a titration curve as shown in the upper part of FIG. In the titration curve shown in the upper part of FIG. 1, the measured pH is plotted against the amount of added alkali, and in the titration curve shown in the lower part of FIG. The increment (derivative value) (1 / mmol) is plotted. In this neutralization titration, two points where the increment (differential value of pH with respect to the amount of alkali dropped) is maximized in the curve plotting the measured pH against the amount of alkali added. Among these, the maximum point of increment obtained first after adding alkali is called the first end point, and the maximum point of increment obtained next is called the second end point. The alkali amount required from the start of titration to the first end point is equal to the first dissociated acid amount of fibrous cellulose contained in the slurry used for titration, and the alkali required from the first end point to the second end point Fibrous cellulose whose amount is equal to the second dissociated acid amount of fibrous cellulose contained in the slurry used for titration, and whose alkali amount required from the start of titration to the second end point is contained in the slurry used for titration Is equal to the total dissociated acid amount. Then, the value obtained by dividing the alkali amount required from the start of titration to the first end point by the solid content (g) in the titration target slurry is the amount of introduced phosphorus oxoacid group (mmol / g). In addition, when it is simply referred to as a phosphorus oxo acid group introduction amount (or a phosphorus oxo acid group amount), it represents the first dissociated acid amount.
In FIG. 1, a region from the start of titration to the first end point is referred to as a first region, and a region from the first end point to the second end point is referred to as a second region. For example, when the phosphorus oxo acid group is a phosphate group, and this phosphate group undergoes condensation, the amount of weakly acidic groups in the phosphorus oxo acid group (also referred to as the second dissociated acid amount in this specification) is apparent. The amount of alkali required for the second region is reduced compared to the amount of alkali required for the first region. On the other hand, the strongly acidic group amount (also referred to as the first dissociated acid amount in the present specification) in the phosphorus oxo acid group coincides with the amount of phosphorus atoms regardless of the presence or absence of condensation. Further, when the phosphorus oxo acid group is a phosphite group, the weakly acidic group does not exist in the phosphorus oxo acid group, so that the alkali amount required for the second region is reduced or the alkali amount required for the second region is reduced. May be zero. In this case, in the titration curve, there is one point where the increment of pH becomes maximum.

The above-mentioned introduction amount (mmol / g) of the phosphorus oxo acid group indicates the mass of the acid type fibrous cellulose in the denominator, so that the amount of the phosphorus oxo acid group possessed by the acid type fibrous cellulose (hereinafter, the amount of the phosphorus oxo acid group) (Referred to as (acid type)). On the other hand, when an arbitrary cation C is substituted so that the counter ion of the phosphorus oxo acid group has a charge equivalent, the denominator is converted to the mass of fibrous cellulose when the cation C is the counter ion. Thus, the amount of the phosphorus oxo acid group (hereinafter, the amount of the phosphorus oxo acid group (C type)) possessed by the fibrous cellulose whose cation C is the counter ion can be determined.
That is, it calculates with the following formula.
Phosphooxo acid group amount (C type) = Phosphooxo acid group amount (acid type) / {1+ (W−1) × A / 1000}
A [mmol / g]: A total amount of anion derived from a phosphorus oxo acid group in fibrous cellulose (total amount of dissociated acid of a phosphorus oxo acid group)
W: Formula weight per cation C (for example, Na is 23, Al is 9)

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

  In addition to phosphorous acid group, whether phosphorous oxoacid detected when it contains either phosphoric acid group or condensed phosphoric acid group or both is derived from phosphorous acid, phosphoric acid or condensed phosphoric acid As a method of distinguishing, for example, a method of performing the above-mentioned titration operation after performing a treatment of cutting a condensed structure such as acid hydrolysis, or a method of converting a phosphite group to a phosphate group such as an oxidation treatment Examples thereof include a method of performing the above-described titration operation.

<Alkali treatment>
When manufacturing a fine fibrous cellulose, you may perform an alkali treatment between a phosphite group introduction | transduction process and the fibrillation process mentioned later. Although it does not specifically limit as a method of an alkali treatment, For example, the method of immersing a phosphite group introduction | transduction fiber in an alkaline solution is mentioned.
The alkali compound contained in the alkali solution is not particularly limited, but may be an inorganic alkali compound or an organic alkali compound. The solvent in the alkaline solution may be either water or an organic solvent. The solvent is preferably a polar solvent (polar organic solvent such as water or alcohol), and more preferably an aqueous solvent containing at least water.
Of the alkaline solutions, a sodium hydroxide aqueous solution or a potassium hydroxide aqueous solution is particularly preferred because of its high versatility.

Although the temperature of the alkali solution in an alkali treatment process is not specifically limited, 5 to 80 degreeC is preferable and 10 to 60 degreeC is more preferable.
The immersion time in the alkaline solution in the alkali treatment step is not particularly limited, but is preferably 5 minutes or longer and 30 minutes or shorter, and more preferably 10 minutes or longer and 20 minutes or shorter.
Although the usage-amount of the alkaline solution in an alkali treatment is not specifically limited, It is preferable that it is 100 mass% or more and 100,000 mass% or less with respect to the absolute dry mass of a phosphite group introduction | transduction fiber, and it is 1000 mass% or more and 10000 mass% or less. More preferably.

  In order to reduce the amount of alkaline solution used in the alkali treatment step, the phosphite group-introduced fiber may be washed with water or an organic solvent before the alkali treatment step. After the alkali treatment, in order to improve handleability, it is preferable to wash the alkali-treated phosphite group-introduced fiber with water or an organic solvent before the defibrating treatment step.

<Defibration processing>
The phosphite group-introduced fiber is defibrated in the defibrating process. In the defibrating process, the fiber is usually defibrated using a defibrating apparatus to obtain a fine fibrous cellulose-containing slurry, but the processing apparatus and the processing method are not particularly limited.
As the defibrating apparatus, a high-speed defibrator, a grinder (stone mill type pulverizer), a high-pressure homogenizer, an ultra-high pressure homogenizer, a high-pressure collision type pulverizer, a ball mill, a bead mill, or the like can be used. Alternatively, as the defibrating apparatus, a wet type pulverizer such as 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 should be used. You can also. The defibrating apparatus is not limited to the above. Preferable defibrating treatment methods include a high-speed defibrator, a high-pressure homogenizer, and an ultra-high pressure homogenizer that are less affected by the grinding media and less worried about contamination.

  In the defibrating treatment, it is preferable to dilute the fiber raw material with water and an organic solvent alone or in combination to form a slurry, but there is no particular limitation. As the dispersion medium, in addition to water, a polar organic solvent can be used. Preferable polar organic solvents include alcohols, ketones, ethers, dimethyl sulfoxide (DMSO), dimethylformamide (DMF), dimethylacetamide (DMAc), and the like, but are not particularly limited. Examples of alcohols include methanol, ethanol, n-propanol, isopropanol, n-butanol, and t-butyl alcohol. Examples of ketones include acetone and methyl ethyl ketone (MEK). Examples of ethers include diethyl ether and tetrahydrofuran (THF). The dispersion medium may be one type or two or more types. Further, the dispersion medium may contain a solid content other than the fiber raw material, such as urea having hydrogen bonding property.

  In the present invention, the fibrillation treatment may be performed after the fine fibrous cellulose is concentrated and dried. In this case, the concentration and drying methods are not particularly limited, and examples thereof include a method of adding a concentrating agent to a slurry containing fine fibrous cellulose, a generally used dehydrator, a press, and a method using a dryer. Moreover, a well-known method, for example, the method described in WO2014 / 024876, WO2012 / 107642, and WO2013 / 121086 can be used. Further, the concentrated fine fibrous cellulose may be formed into a sheet. The sheet can be pulverized to perform a defibrating process.

  The equipment used for pulverization of fine fibrous cellulose includes high-speed defibrator, grinder (stone mill type pulverizer), high-pressure homogenizer, ultra-high pressure homogenizer, high-pressure collision type pulverizer, ball mill, bead mill, disk type refiner, conical An apparatus for wet pulverization such as a refiner, a twin-screw kneader, a vibration mill, a homomixer under high-speed rotation, an ultrasonic disperser, a beater, and the like can be used, but is not particularly limited. The treatment conditions are not particularly limited as long as a preferable degree of polymerization is obtained.

(Second cellulose fiber)
The sheet | seat of this invention contains a 2nd cellulose fiber. The second cellulose fiber is a cellulose fiber having a fiber width of 1 μm to 100 μm. The second cellulose fiber is preferably a cellulose fiber having a fiber width of more than 1000 nm and not more than 100 μm. In the present specification, the second cellulose fiber is also referred to as coarse cellulose fiber or coarse fibrous cellulose.

  In the present embodiment, for example, the pulp exemplified above as the fibrous cellulose raw material can be used as the second cellulose fiber. Thereby, manufacturing cost can be further suppressed. The fiber width of the pulp is, for example, 15 μm or more, and is preferably 20 μm or more from the viewpoint of improving productivity. On the other hand, the fiber width of the pulp is, for example, 100 μm or less.

  The fiber width of the pulp fiber can be measured using a Kajaani fiber length measuring instrument (FS-200 type) manufactured by Kajaani Automation. Here, the fiber width of the pulp fiber is a fiber width in the trunk fiber of the cellulose fiber. For example, when the pulp fiber is a fibril cellulose fiber, the fiber width of the trunk fiber constituting the main axis is referred to as the fiber width of the pulp fiber, not the fiber width of the fiber fibrillated and branched.

  The content of the second cellulose fiber is preferably 50% by mass or more, more preferably 65% by mass or more, and further preferably 75% by mass or more with respect to the total mass of the sheet. In addition, from a viewpoint of improving productivity more, content of a 2nd cellulose fiber can also be 85 mass% or more with respect to the whole sheet | seat. Moreover, content of a 2nd cellulose fiber is 99 mass% or less with respect to the total mass of a sheet | seat, and it is more preferable that it is 95 mass% or less. Further, from the viewpoint of improving the strength, the content of the second cellulose fiber can be 85% by mass or less with respect to the entire sheet.

The second cellulose fibers preferably include softwood pulp and hardwood pulp. Furthermore, in the sheet of the present invention, when the content (parts by mass) of softwood pulp is N and the content (parts by mass) of hardwood pulp is L, the value of N / L is preferably 1 or more, It is more preferably 1.5 or more, further preferably 2 or more, and particularly preferably 3 or more. Further, the value of N / L is preferably 8 or less, and more preferably 7 or less. In the sheet of the present invention, the specific tensile elastic modulus of the sheet is effectively increased by making the content of the hardwood pulp with the conifer pulp within the above range and further mixing the fine fibrous cellulose therein.
In the sheet of the present invention, the ratio of the content of the softwood pulp and the content of the hardwood pulp is determined, for example, by quantifying the fibers dissociated from the sheet and dyed under a microscope in accordance with JIS P 8120: 1998. Can be sought.

  The Canadian standard freeness of the mixture of softwood and hardwood pulp is preferably 600 ml or less, more preferably 550 ml or less, and even more preferably 500 ml or less. The lower limit of the Canadian standard freeness of the mixture of coniferous and hardwood pulp is not particularly limited, but is preferably 50 ml or more. The Canadian standard freeness is a freeness measured by a Canadian standard freeness method according to JIS P 8121-1995.

  Also, the irregular freeness of the mixture of coniferous pulp and hardwood pulp may be 800 ml or less. In this case, the irregular freeness of the mixture of softwood pulp and hardwood pulp is preferably 700 ml or less, and more preferably 650 ml or less. The irregular freeness of the mixture of softwood pulp and hardwood pulp is preferably 200 ml or more. A pulp fiber having an irregular freeness in the above range can be said to be a high beaten pulp, and an example of such a pulp is glassine pulp. Since the freeness of high beat pulp is difficult to measure by the general Canadian standard freeness method, irregular freeness is measured. The irregular freeness is changed by changing the pulp concentration from 0.3% by mass to 0.03% by mass and changing from JIS standard screen plate to 80 mesh wire in the Canadian Standard Freeness Method specified in JIS P 8121-1995. The measured freeness.

  When the sheet | seat of this invention contains highly beaten pulp, this can improve the intensity | strength of a sheet | seat more effectively. The fiber width of the highly beaten pulp is, for example, 1 μm or more, and preferably 5 μm or more from the viewpoint of improving productivity. On the other hand, the fiber width of the high beaten pulp is, for example, less than 15 μm.

  The beating of the pulp can be performed using, for example, a defibrating apparatus. The defibrating apparatus is not particularly limited. For example, a high-speed defibrator, a grinder (stone mortar-type pulverizer), a high-pressure homogenizer, an ultrahigh-pressure homogenizer, a CLEARMIX, a high-pressure collision-type pulverizer, a ball mill, a bead mill, a disk type refiner, and a conical refiner can be used. In addition, a wet pulverizing apparatus such as a twin-screw kneader, a vibration mill, a homomixer under high-speed rotation, an ultrasonic disperser, and a beater can be used as appropriate.

(ratio)
When the content of the first cellulose fiber is C1 and the content of the second cellulose fiber is C2, C1 / (C1 + C2) is preferably 0.01 or more, more preferably 0.05 or more. It is preferably 0.08 or more. On the other hand, C1 / (C1 + C2) is preferably 0.3 or less, and more preferably 0.25 or less. Thereby, the balance between the productivity and strength of the sheet can be improved more effectively.
Here, the first cellulose fibers in the sheet can be observed, for example, with a scanning electron microscope (manufactured by Hitachi High-Technologies Corporation, S-3600N). The second cellulose fiber can be observed with, for example, a high-resolution field emission scanning electron microscope (manufactured by Hitachi, Ltd., S-5200). Through such observation, the mass ratio may be calculated from the volume ratio of each fiber. However, the mixing ratio of each cellulose fiber in the sheet manufacturing process as described later is equivalent to the ratio of the first cellulose fiber and the second cellulose fiber in the sheet.

(Polyamide polyamine epihalohydrin)
The sheet of the present invention can further contain, for example, polyamine polyamide epihalohydrin. Thereby, the strength of the sheet can be further improved. Polyamine polyamide epihalohydrin is a cationic thermosetting resin obtained by synthesizing a polyamidopolyamine by heat condensation of an aliphatic dibasic carboxylic acid or a derivative thereof and a polyalkylene polyamine, and then reacting the polyamidopolyamine with the epihalohydrin. It is. Since polyamine polyamide epihalohydrin is an aqueous resin, polyamine polyamide epihalohydrin can also be added as an aqueous solution to the slurry for sheet formation.

  Examples of the polyamine polyamide epihalohydrin include polyamine polyamide epichlorohydrin, polyamine polyamide epibromohydrin, polyamine polyamide epiiohydrin, and the like.

  The content of the polyamine polyamide epihalohydrin is preferably 0.05% by mass or more, more preferably 0.1% by mass or more, and 0.3% by mass or more with respect to the total mass of the sheet. Is more preferable.

(Other fibers)
The sheet | seat of this invention may contain the other cellulose fiber other than the 1st cellulose fiber and the 2nd cellulose fiber. Examples of other cellulose fibers include high beating pulp in which the second cellulose fibers are beaten to make the fiber width greater than 100 nm and less than 1000 nm. Here, the fiber width of the other fibers is a fiber width in the trunk fiber of the cellulose fiber. For example, when the other fiber is a fibrillated cellulose fiber, the fiber width of the trunk fiber is referred to as the fiber width of the other fiber, not the fiber width of the fiber fibrillated and branched.

  The beating of other cellulose fibers can be performed using, for example, a defibrating apparatus. The defibrating apparatus is not particularly limited. For example, a high-speed defibrator, a grinder (stone mortar-type pulverizer), a high-pressure homogenizer, an ultrahigh-pressure homogenizer, a CLEARMIX, a high-pressure collision-type pulverizer, a ball mill, a bead mill, a disk type refiner, and a conical refiner can be used. In addition, a wet pulverizing apparatus such as a twin-screw kneader, a vibration mill, a homomixer under high-speed rotation, an ultrasonic disperser, and a beater can be used as appropriate.

(Optional component)
The sheet of the present invention may contain an optional component other than the components described above. Optional components include, for example, hydrophilic resins, preservatives, antifoaming agents, lubricants, ultraviolet absorbers, dyes, pigments, stabilizers, surfactants, sizing agents, yield improvers, bulking agents, and drainage improvers. , PH adjusters, fluorescent brighteners, pitch control agents, slime control agents, antifoaming agents, water retention agents, dispersants and the like.

  Moreover, a thermoplastic resin emulsion, a thermosetting resin emulsion, a photocurable resin emulsion, or the like may be added to the sheet of the present invention. Specific examples of the thermoplastic resin emulsion, the thermosetting resin emulsion, and the photocurable resin emulsion include those described in JP2009-299043A.

(Sheet manufacturing method)
The manufacturing process of the sheet has a fiber width of 100 nm or less, a first cellulose fiber having a phosphite group or a substituent derived from a phosphite group, a second cellulose fiber having a fiber width of 1 μm to 100 μm, The process of obtaining the slurry containing this, the process of apply | coating this slurry on a base material, or the process of paper-making a slurry are included. The most preferable production process of the present invention is a method of obtaining a sheet from a slurry by papermaking from the viewpoint of productivity.

  In the step of obtaining the slurry, it is preferable to include a step of mixing softwood pulp and hardwood pulp as the second cellulose fiber, and it is preferable to include a step of adding and mixing the first cellulose fiber thereafter. In the step of mixing the conifer pulp and the hardwood pulp, it is preferable to provide a beating treatment step as necessary. In the beating treatment step, it is preferable to beat the pulp fibers so as to obtain a desired freeness.

<Coating process>
The coating step is a step of obtaining a sheet by coating a slurry containing first cellulose fibers and second cellulose fibers on a base material, and drying the formed slurry from the base material. It is. By using a coating apparatus and a long base material, sheets can be continuously produced.

  The material of the base material used in the coating process is not particularly limited, but the one having higher wettability with the slurry may be able to suppress the shrinkage of the sheet during drying, but the sheet formed after drying is easier. It is preferable to select one that can be peeled off. Among them, a resin plate or a metal plate is preferable, but not particularly limited. For example, resin plates such as acrylic plates, polyethylene terephthalate plates, vinyl chloride plates, polystyrene plates, polyvinylidene chloride plates, metal plates such as aluminum plates, zinc plates, copper plates, iron plates, etc., and those whose surfaces are oxidized, stainless steel A plate, a brass plate or the like can be used.

  In the coating process, when the slurry has a low viscosity and spreads on the base material, a damming frame may be fixed on the base material to obtain a sheet having a predetermined thickness and basis weight. Good. The quality of the damming frame is not particularly limited, but it is preferable to select one that can easily peel off the edge of the sheet attached after drying. Among them, a resin plate or a metal plate is preferable, but not particularly limited. For example, resin plates such as acrylic plates, polyethylene terephthalate plates, vinyl chloride plates, polystyrene plates, polyvinylidene chloride plates, metal plates such as aluminum plates, zinc plates, copper plates, iron plates, etc., and their surfaces oxidized, stainless steel A plate, a brass plate or the like can be used.

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

  The coating temperature is not particularly limited, but is preferably 20 ° C or higher and 45 ° C or lower, more preferably 25 ° C or higher and 40 ° C or lower, and further preferably 27 ° C or higher and 35 ° C or lower. If the coating temperature is not less than the above lower limit value, the slurry can be easily applied, and if it is not more than the above upper limit value, volatilization of the dispersion medium during coating can be suppressed.

In the coating step, it is preferable to apply the slurry so that the finished basis weight of the sheet is 6 g / m ² or more and 500 g / m ² or less, preferably 19 g / m ² or more and 300 g / m ² or less. By coating so that the basis weight is within the above range, a sheet having excellent strength can be obtained.

  It is preferable that a coating process includes the process of drying the slurry apply | coated on the base material. Although it does not specifically limit as a drying method, Either a non-contact drying method or the method of drying while restraining a sheet | seat may be sufficient, and these may be combined.

  The non-contact drying method is not particularly limited, but a method of drying by heating with hot air, infrared rays, far infrared rays or near infrared rays (heating drying method) or a method of drying in vacuum (vacuum drying method) is applied. Can do. Although the heat drying method and the vacuum drying method may be combined, the heat drying method is usually applied. Although drying by infrared rays, far infrared rays, or near infrared rays can be performed using an infrared device, a far infrared device, or a near infrared device, it is not particularly limited. The heating temperature in the heat drying method is not particularly limited, but is preferably 20 ° C. or higher and 150 ° C. or lower, and more preferably 25 ° C. or higher and 105 ° C. or lower. If the heating temperature is not less than the above lower limit value, the dispersion medium can be volatilized quickly, and if it is not more than the above upper limit value, it is possible to suppress the cost required for heating and to prevent the fine fibrous cellulose from being discolored by heat. .

<Paper making process>
The manufacturing process of a sheet | seat may also include the process of papermaking the slurry containing a 1st cellulose fiber and a 2nd cellulose fiber. Examples of the paper machine in the paper making process include a continuous paper machine such as a long-mesh type, a circular net type, and an inclined type, and a multi-layered paper machine combining these. In the paper making process, known paper making such as hand making may be performed.

  In the papermaking process, the slurry is filtered and dehydrated on a wire to obtain a wet paper sheet, and then the sheet is obtained by pressing and drying. When the slurry is filtered and dehydrated, the filter cloth at the time of filtration is not particularly limited, but it is important that fine fibrous cellulose and other components do not pass through and the filtration rate is not too slow. Although it does not specifically limit as such a filter cloth, The sheet | seat, fabric, and porous film which consist of organic polymers are preferable. The organic polymer is not particularly limited, but non-cellulosic organic polymers such as polyethylene terephthalate, polyethylene, polypropylene, polytetrafluoroethylene (PTFE) and the like are preferable. Specific examples include a porous film of polytetrafluoroethylene having a pore size of 0.1 μm to 20 μm, for example, 1 μm, polyethylene terephthalate or polyethylene woven fabric having a pore size of 0.1 μm to 20 μm, for example, 1 μm, but is not particularly limited.

  Although it does not specifically limit as a method of manufacturing a sheet | seat from a slurry, For example, the method of using the manufacturing apparatus of WO2011 / 013567, etc. are mentioned. This manufacturing apparatus discharges a slurry containing fine fibrous cellulose onto the upper surface of an endless belt, squeezes a dispersion medium from the discharged slurry, generates a web, and dries the web to dry the fiber sheet. And a drying section to produce. An endless belt is disposed from the squeezing section to the drying section, and the web generated in the squeezing section is conveyed to the drying section while being placed on the endless belt.

  The dehydration method that can be employed is not particularly limited, and examples include a dehydration method that is normally used in paper manufacture. A method of dehydrating with a long net, circular net, inclined wire, etc., and then dehydrating with a roll press is preferable. Further, the drying method is not particularly limited, and examples thereof include methods used in paper manufacture. For example, methods such as a cylinder dryer, a Yankee dryer, hot air drying, a near infrared heater, and an infrared heater are preferable.

(Laminated sheet)
The present invention also relates to a laminated sheet further having a coating layer on at least one surface side of the above-described sheet. The coating layer is preferably laminated directly on at least one surface of the above-described sheet.

The coating layer may contain a binder, a pigment, and the like. Moreover, various auxiliary agents normally used, such as a dispersing agent, a water retention agent, an antifoamer, and a coloring agent, can be used as needed.
Examples of binders that can be used in the present invention include water-soluble polymers such as casein, starch, modified starch, and polyvinyl alcohol, or polyester resins, polyurethane resins, styrene-butadiene resins, vinyl acetate resins, ethylene-vinyl acetate resins. Resins, acrylonitrile-butadiene resins, polyethylene resins, polypropylene resins, carboxymethyl cellulose resins, polyamide resins, vinyl chloride resins, vinylidene chloride resins, fluorine resins, silicone resins and the like can be used.
Examples of pigments that can be used in the present invention include kaolin, calcium carbonate, magnesium carbonate, magnesium oxide, aluminum hydroxide, alumina, silica, magnesium aluminosilicate, calcium silicate, white carbon, bentonite, zeolite, sericite, smectite, calcium sulfate, and sulfuric acid. Inorganic pigments such as barium, synthetic mica, titanium dioxide, and zinc oxide, and polydienes such as polyisoprene, polyneoprene, and polybutadiene, polyalkenes such as polybutene, polyisobutylene, and polypropylene, vinyl acetate, styrene, (meth) acrylic acid , (Meth) acrylic acid alkyl ester, (meth) acrylamide, polymers and copolymers of vinyl monomers such as methyl vinyl ether, polyurethane resins, polyester resins Examples include various solid pigments such as polyamide resins, urea resins, melamine resins, and benzoguanamine resins, and organic pigments such as hollow or through-hole type particles. One or more pigments should be used. Can do.

The basis weight of the coating layer is not particularly limited, it is preferably 0.05 g / m ² or more, more preferably 0.1 g / m ² or more, 0.2 g / m ² or more More preferably. The upper limit value of the basis weight of the coating layer is not particularly limited, but can be, for example, 10 g / m ² or less.

The coating layer is impregnation treatment, spray treatment, etc., and generally known coating equipment such as size press coater, blade coater, air knife coater, roll coater, reverse roll coater, bar coater, curtain coater, slot die coater, gravure coater. For example, a champlex coater, a brush coater, a slide bead coater, a two-roll or metering blade type size press coater, a bill blade coater, a short dwell coater, a gate roll coater, and a nip coater using a calendar are appropriately used.
As long as the effect of this invention is not impaired, the sheet | seat of this invention may perform a smoothing process as needed. The smoothing process can be performed using a normal smoothing apparatus such as a super calendar, a gloss calendar, or a soft calendar.

(Use)
The sheet of the present invention, the sheet containing fine cellulose fibers of the present invention alone or in combination with other materials, various paper products such as printing paper, filters, separators, particle-carrying sheets, packaging materials, cardboard, It can also be used for wet, dry nonwoven fabrics, diapers, household appliances, various vehicles, building interior materials, exterior materials, and the like.

The features of the present invention will be described more specifically with reference to examples and comparative examples. The materials, amounts used, ratios, processing details, processing procedures, and the like shown in the following examples can be appropriately changed without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be construed as being limited by the specific examples shown below. In the following, Examples 1 to 4 are to be read as Reference Examples 1 to 4, respectively.

[Example 1]
<Production of first cellulose fiber (1)>
Oji Paper's softwood kraft pulp as raw material pulp (solid content 93% by weight, basis weight 245g / m ² sheet, Canadian standard freeness (CSF) measured according to JIS P 8121 after disaggregation is 700ml) It was used.

  The raw material pulp was subjected to phosphorus oxo oxidation treatment as follows. First, a mixed aqueous solution of phosphorous acid (phosphonic acid) and urea is added to 100 parts by mass (absolute dry mass) of the above raw pulp, and 33 parts by mass of phosphorous acid (phosphonic acid), 120 parts by mass of urea, and 150 parts of water. It prepared so that it might become a mass part, and obtained the chemical | medical solution impregnation pulp. Next, the obtained chemical-impregnated pulp was heated with a hot air dryer at 165 ° C. for 250 seconds to introduce a phosphite group into cellulose in the pulp to obtain a phosphorylated pulp.

  100 g of the obtained phosphorylated pulp was separated by pulp mass, poured with 10 L of ion exchange water, stirred and dispersed uniformly, and then subjected to filtration and dehydration to obtain a dehydrated sheet twice. Next, the obtained dehydrated sheet was diluted with 10 L of ion-exchanged water, and a 1N sodium hydroxide aqueous solution was added little by little while stirring to obtain a pulp slurry having a pH of 12 or more and 13 or less. Thereafter, the pulp slurry was dehydrated to obtain a dehydrated sheet, and then 10 L of ion exchange water was added. The step of stirring and dispersing uniformly, followed by filtration and dehydration to obtain a dehydrated sheet was repeated twice.

An infrared absorption spectrum of the obtained phosphorylated pulp was measured using FT-IR. As a result, absorption based on P = O of a phosphonic acid group, which is a tautomer of a phosphorous acid group, was observed near 1210 cm ⁻¹ , and a phosphorous acid group (phosphonic acid group) was added to the pulp. Was confirmed. Moreover, when the obtained phosphorylated pulp was tested and analyzed with an X-ray diffractometer, two positions of 2θ = 14 ° to 17 ° and 2θ = 22 ° to 23 ° were found. A typical peak was confirmed, and it was confirmed to have cellulose type I crystals. In addition, about the obtained phosphorous-ized pulp, the amount of phosphite groups (1st dissociated acid amount) measured by the measuring method as described in [Measurement of the amount of phosphite groups] described later was 1.51 mmol / g. It was. The total dissociated acid amount was 1.54 mmol / g.

<Machine processing>
Ion exchanged water was added to the dehydrated sheet of the obtained phosphorylated pulp to prepare a slurry having a solid content concentration of 2% by mass. This slurry is treated three times at a pressure of 245 MPa with a wet atomization apparatus (manufactured by Sugino Machine Co., Ltd., an optimizer), and contains a first cellulose fiber (1) which is fine fibrous cellulose. (1) was obtained. In addition, the fiber width of the 1st cellulose fiber (1) was about 3 nm.

<Preparation of second cellulose fiber (1)>
As the second cellulose fiber (1), softwood kraft pulp was used. The fiber width of the second cellulose fiber (1) was about 30 μm.

<Sheet>
The first cellulose fiber dispersion (1), the second cellulose dispersion (1), and polyamine polyamide / epichlorohydrin were mixed to obtain a papermaking slurry. The slurry for papermaking is 10 parts by weight of the first cellulose fiber (1), 90 parts by weight of the second cellulose fiber (1), polyamine polyamide / epichlorohydrin (manufactured by Seiko PMC Co., Ltd., wet paper strength agent WS4030). An aqueous dispersion containing 0.5 parts by mass and having a solid content concentration of 0.3% by mass was obtained.
The papermaking slurry was paper-made and dehydrated on a wire using a square handmaking device to obtain a wet sheet. The wet sheet was dried with a Yankee dryer at a temperature of 110 ° C. to prepare a sheet having a basis weight of 30 g / m ² .

[Example 2]
As a papermaking slurry used in the sheet forming step, 20 parts by mass of the first cellulose fiber (1), 80 parts by mass of the second cellulose fiber (1), polyamine polyamide / epichlorohydrin (manufactured by Seiko PMC Co., Ltd., A sheet forming step was performed in the same manner as in Example 1 except that a wet paper strength agent WS4030) containing 0.5 part by mass was used to obtain a sheet.

Example 3
As the papermaking slurry used in the sheet forming step, the one containing 20 parts by mass of the first cellulose fiber (1), 80 parts by mass of the second cellulose fiber (1) and not containing polyamine polyamide / epichlorohydrin is used. A sheet was obtained in the same manner as in Example 1 except that the sheet was obtained.

Example 4
<Creation of second cellulose fiber (2)>
Water was added to disperse the softwood bleached kraft pulp so as to have a concentration of 4.0% by mass, and then dispersed, and then treated once with a double disc refiner to obtain a second cellulose fiber (2). The fiber width of the second cellulose fiber (2) was about 10 μm.

<Sheet making process>
As a papermaking slurry, 10 parts by mass of the first cellulose fiber (1), 90 parts by mass of the second cellulose fiber (2), polyamine polyamide / epichlorohydrin (manufactured by Seiko PMC Co., Ltd., wet paper strength agent WS4030) A sheet forming step was performed in the same manner as in Example 1 except that a material containing 0.5 part by mass was used to obtain a sheet.

[Comparative Example 1]
As a papermaking slurry used in the sheet forming step, 100 parts by mass of the first cellulose fiber (1) and 0.5 parts by mass of polyamine polyamide / epichlorohydrin (manufactured by Seiko PMC Co., Ltd., wet paper strength agent WS4030) A sheet forming step was performed in the same manner as in Example 1 except that a material containing no second cellulose fiber was used.

[Comparative Example 2]
As a papermaking slurry used in the sheet forming step, 100 parts by mass of the second cellulose fiber (1) and 0.5 parts by mass of polyamine polyamide / epichlorohydrin (manufactured by Seiko PMC Co., Ltd., wet paper strength agent WS4030) A sheet was obtained by carrying out the sheeting process in the same manner as in Example 1 except that a material containing no first cellulose fiber was used.

[Comparative Example 3]
As a papermaking slurry used in the sheet forming step, 100 parts by mass of the second cellulose fiber (2) and 0.5 parts by mass of polyamine polyamide / epichlorohydrin (manufactured by Seiko PMC Co., Ltd., wet paper strength agent WS4030) A sheet was obtained by carrying out the sheeting process in the same manner as in Example 1 except that a material containing no first cellulose fiber was used.

[Comparative Example 4]
<Creation of unmodified fine cellulose fiber>
Water was added to disperse the softwood bleached kraft pulp so as to have a concentration of 4.0% by mass, and then continuous circulation beating was performed with a double disc refiner for 5 hours to obtain unmodified fine cellulose fibers. The fiber width of the obtained unmodified fine cellulose fiber was about 350 nm.

<Sheet making process>
As a papermaking slurry used in the sheet forming step, 20 parts by mass of unmodified fine cellulose fibers, 80 parts by mass of second cellulose fibers (1), polyamine polyamide / epichlorohydrin (manufactured by Seiko PMC Co., Ltd., wet paper) A sheet was obtained in the same manner as in Example 1 except that 0.5 parts by mass of the force agent WS4030) and no first cellulose fiber were used.

Example 101
<Preparation of second cellulose fiber (3)>
As the second cellulose fiber (3), a mixture of 80 parts by weight of softwood kraft pulp (NBKP) and 20 parts by weight of hardwood kraft pulp (LBKP) was used. The average fiber width of the second cellulose fiber (3) was about 30 μm, and the Canadian standard freeness was 450 ml.

<Sheet>
The first cellulose fiber dispersion (1), the second cellulose dispersion (3), and polyamine polyamide / epichlorohydrin were mixed to obtain a papermaking slurry. The slurry for papermaking is 20 parts by mass of the first cellulose fiber (1), 80 parts by mass of the second cellulose fiber (3), and polyamine polyamide / epichlorohydrin (manufactured by Seiko PMC Co., Ltd., wet paper strength agent WS4030). An aqueous dispersion containing 0.5 parts by mass and having a solid content concentration of 0.5% by mass was obtained.
The papermaking slurry was paper-made and dehydrated on a wire using a square handmaking device to obtain a wet sheet. The wet sheet was dried with a Yankee dryer at a temperature of 110 ° C. to prepare a sheet having a basis weight of 20 g / m ² .
In addition, as a control sheet of Example 101, a sheet was prepared in the same manner as described above from a papermaking slurry containing 100 parts by mass of the second cellulose fiber (3) and 0.5 parts by mass of polyamine polyamide / epichlorohydrin. did.

Example 102
<Preparation of second cellulose fiber (3)> In the same manner as in Example 101 except that the mixing ratio of NBKP and LBKP was 60:40 (NBKP: LBKP) and the second cellulose fiber (4) was used. Got. The average fiber width of the second cellulose fiber (4) was about 30 μm.
In addition, as a control sheet of Example 102, a sheet was produced in the same manner as described above from a papermaking slurry containing 100 parts by mass of the second cellulose fiber (4) and 0.5 parts by mass of polyamine polyamide / epichlorohydrin. did.

Example 103
<Preparation of second cellulose fiber (3)> In the same manner as in Example 101 except that the mixing ratio of NBKP and LBKP was 50:50 (NBKP: LBKP) and the second cellulose fiber (5) was used. Got. The average fiber width of the second cellulose fiber (5) was about 30 μm.
In addition, as a control sheet of Example 103, a sheet was produced in the same manner as described above from a papermaking slurry containing 100 parts by mass of the second cellulose fiber (5) and 0.5 parts by mass of polyamine polyamide / epichlorohydrin. did.

Example 104
<Production of second cellulose fiber (6)>
After adding water and dispersing so that the total concentration of 60 parts by weight of softwood bleached kraft pulp and 40 parts by weight of hardwood bleached kraft pulp is 4.0% by weight, it is treated once with a double disc refiner, and high beaten pulp A slurry was prepared. This highly beaten pulp slurry was designated as the second cellulose fiber (6). The average fiber width of the second cellulose fiber (6) was about 15 μm, and the irregular freeness was 570 ml. The irregular freeness is changed from the JIS standard screen plate to 80 mesh wire by changing the pulp concentration from 0.3% by mass to 0.03% by mass in the Canadian Standard Freeness Method stipulated in JIS P 8121-1995. It is the freeness measured.

<Sheetization> In the papermaking slurry, water containing 20 parts by mass of the first cellulose fiber (1), 80 parts by mass of the second cellulose fiber (6), and 0.5 parts by mass of polyamine polyamide / epichlorohydrin. A sheet having a basis weight of 20 g / m ² was obtained in the same manner as in Example 101 except that the dispersion was used.
In addition, as a control sheet of Example 104, a sheet was prepared in the same manner as described above from a papermaking slurry containing 100 parts by mass of the second cellulose fiber (6) and 0.5 parts by mass of polyamine polyamide / epichlorohydrin. did.

Example 105
<Sheetization> In the papermaking slurry, 10 parts by mass of the first cellulose fiber (1), 90 parts by mass of the second cellulose fiber (6), polyamine polyamide / epichlorohydrin (manufactured by Seiko PMC Co., Ltd., wet) A sheet having a basis weight of 20 g / m ² was obtained in the same manner as in Example 104 except that the aqueous dispersion containing 0.5 part by mass of the paper strength agent WS4030) was used.
The control sheet of Example 105 was the control sheet of Example 104.

〔Measuring method〕
<Measurement of substituent amount>
The amount of phosphorous acid group of the fine fibrous cellulose is a fiber prepared by diluting a fine fibrous cellulose dispersion containing the target fine fibrous cellulose with ion-exchanged water so that the content becomes 0.2% by mass. It measured by performing the titration using an alkali, after processing with an ion exchange resin with respect to the slurry containing a cellulose.
In the treatment with the ion exchange resin, 1/10 by volume of the strongly acidic ion exchange resin (Amberjet 1024; Organo Corporation, conditioned) is added to the fibrous cellulose-containing slurry, and the mixture is shaken for 1 hour. The mixture was poured onto a mesh having an opening of 90 μm to separate the resin and the slurry.
In addition, titration using an alkali measures the change in the pH value of the slurry while adding 10 μL of a 0.1 N sodium hydroxide aqueous solution every 5 seconds to the fibrous cellulose-containing slurry after treatment with an ion exchange resin. It was done by doing. The titration was performed while blowing nitrogen gas into the slurry 15 minutes before the start of titration. In this neutralization titration, two points at which the increment (differential value of pH with respect to the amount of alkali dropped) is maximized in a curve plotting the measured pH against the amount of alkali added. Among these, the maximum point of increment obtained first after adding alkali is called the first end point, and the maximum point of increment obtained next is called the second end point (FIG. 1). The amount of alkali required from the start of titration to the first end point is equal to the amount of first dissociated acid in the slurry used for titration. Further, the amount of alkali required from the start of titration to the second end point becomes equal to the total amount of dissociated acid in the slurry used for titration. In addition, the value which remove | divided the alkali amount (mmol) required from the titration start to the 1st end point by the solid content (g) in a titration object slurry was made into the amount of phosphite groups (mmol / g).

<Measurement of fiber width>
The fiber widths of the first cellulose fiber and the second cellulose fiber were measured by the following method.
The supernatant of the fine fibrous cellulose dispersion was diluted with water so that the concentration was 0.01% by mass or more and 0.1% by mass or less, and dropped onto a hydrophilic carbon grid membrane. After drying, it was stained with uranyl acetate and observed with a transmission electron microscope (JEOL-2000EX, manufactured by JEOL Ltd.).

<Freeness>
The Canadian standard freeness is a value measured by the Canadian standard freeness method according to JIS P 8121-1995. The free beating pulp's freeness was measured by the anomalous freeness measurement method because it was difficult to measure by the general Canadian standard freeness method. Specifically, in the Canadian Standard Freeness Method stipulated in JIS P 8121-1995, the pulp concentration was changed from 0.3% by mass to 0.03% by mass, and the JIS standard screen plate was changed to 80 mesh wire. The freeness measured was taken as the irregular freeness.

[Evaluation]
The sheets produced in each of the examples and comparative examples were evaluated according to the following evaluation methods.

<Productivity>
The time from when 250 g of papermaking slurry (solid content concentration: 0.5% by mass) flows on the wire (HT2525-30, manufactured by Haiku Wagner) until water is drawn (pulp slurry on the wire) Time until water disappears and the gloss disappears from the pulp surface). Productivity was evaluated based on the following criteria. In addition, productivity becomes high, so that the time until water is drawn is short.
A: 30 seconds or less B: 30 seconds or more and less than 1 minute C: 1 minute or more and less than 30 minutes D: 30 minutes or more

<Tensile strength>
Based on JIS P8113, tensile strength (unit: N / m) was measured using a tensile tester Tensilon (manufactured by A & D). The tensile strength was divided by the thickness of the test piece, and the tensile strength (unit: MPa) was calculated. In addition, when measuring tensile strength, what was conditioned for 24 hours at 23 degreeC and 50% of relative humidity was used as a test piece.
From the measurement results, the tensile strength was evaluated based on the following criteria.
A: 25 MPa or more B: 20 MPa or more and less than 25 MPa C: 15 MPa or more and less than 20 MPa D: less than 15 MPa

<Tensile modulus>
In accordance with JIS P 8113, the tensile modulus was measured using a tensile tester Tensilon (manufactured by A & D). The elastic modulus is a value calculated from the maximum positive slope value in the SS curve. When measuring the tensile modulus, a specimen conditioned at 23 ° C. and 50% relative humidity for 24 hours was used as a test piece.
From the measurement results, the tensile elastic modulus was evaluated based on the following criteria.
A: 2.5 GPa or more B: 2.0 GPa or more and less than 2.5 GPa C: 1.5 GPa or more and less than 2.0 GPa D: Less than 1.5 GPa

<Specific tensile modulus>
The tensile modulus was measured using a tensile tester Tensilon (manufactured by A & D) in accordance with JIS P 8113 except that the length of the test piece was 80 mm and the distance between chucks was 50 mm. The elastic modulus is a value calculated from the maximum positive slope value in the SS curve. When measuring the tensile modulus, a specimen conditioned at 23 ° C. and 50% relative humidity for 24 hours was used as a test piece. Thereafter, the specific tensile modulus was calculated using the following formula. In addition, the density of a test piece is measured based on JISP8118: 2014.
Specific tensile modulus (kNm / g) = sheet tensile modulus (GPa) / density (g / cm ³ ) Further, the specific tensile modulus was evaluated according to the following criteria.
A: Over 10 kNm / g B: Over 8.5 kNm / g at 10 kNm / g or less C: Over 7 kNm / g at 8.5 kNm / g or less D: 7 kNm / g or less

[Rate of increase in specific tensile modulus]
The increase rate of the specific tensile modulus was calculated using the following formula.
Rate of increase in specific tensile modulus (%) = (specific tensile modulus of sheet−specific tensile modulus of control sheet) / specific tensile modulus of control sheet × 100
The control sheet is a sheet prepared without blending the first cellulose fibers. For example, in Example 101, a sheet formed from a slurry in which 80 parts by mass of NBKP and 20 parts by mass of LBKP are mixed serves as a control sheet.
Furthermore, the rate of increase in specific tensile modulus was evaluated according to the following criteria.
A: 35% or more B: 35% or less and 25% or more C: 25% or less and 15% or more D: 15% or less

<Interlayer strength>
In accordance with J TAPPI 18-2, internal bond tester No. The interlayer strength (strength in the thickness direction of the sheet) of the sheet was measured using 2085 (manufactured by Kumagai Riki Kogyo KK). When measuring the interlaminar strength, a specimen conditioned at 23 ° C. and 50% relative humidity for 24 hours was used as a test piece.
From the measurement results, the interlayer strength was evaluated based on the following criteria.
A: 1500 J / m ² or more B: 1200 J / m ² or more and less than 1500 J / m ² C: 750 J / m ² or more and less than 1200 J / m ² D: less than 750 J / m ²

In the examples, excellent productivity and tensile strength were realized. In any of the examples, good results were obtained in the evaluation of tensile modulus and interlayer strength.
On the other hand, in Comparative Example 1, since the second cellulose fiber was not included and a large amount of the first cellulose fiber was included, the result was inferior in productivity as compared with the Example. In Comparative Examples 2 to 4, since the first cellulose fiber was not included, the tensile strength and the tensile elastic modulus were inferior to those of Examples. Moreover, in Comparative Examples 2-3, the interlayer strength was inferior to that of the Examples.

  In particular, in Examples 101 to 105, the specific tensile modulus was high and the rate of increase in the specific tensile modulus was high.

Claims (6)

A first cellulose fiber having a fiber width of 100 nm or less and having a phosphite group or a substituent derived from a phosphite group;
A second cellulose fiber having a fiber width of 1 μm to 100 μm;
A sheet including
Ri der content of 30 mass% or less than 1 wt% of the whole sheet of the first cellulose fibers,
The second cellulose fiber includes softwood pulp and hardwood pulp,
The sheet | seat whose value of N / L is 1 or more and 8 or less when content of the said conifer pulp is set to N and content of the said hardwood pulp is set to L.   The sheet | seat of Claim 1 whose fiber width of a said 1st cellulose fiber is 8 nm or less.   The sheet according to claim 1 or 2, comprising a polyamide polyamine epihalohydrin. The sheet according to any one of claims 1 to 3, wherein a Canadian standard freeness of the mixture of the softwood pulp and the hardwood pulp is 600 ml or less. The sheet | seat of any one of 1-3 whose irregular freeness of the mixture of the said conifer pulp and the said hardwood pulp is 800 ml or less. The sheet according to any one of claims 1 to 5 , wherein an increase rate of the specific tensile modulus calculated by the following formula is greater than 25%;
Rate of increase in specific tensile modulus (%) = (specific tensile modulus of sheet−specific tensile modulus of control sheet) / specific tensile modulus of control sheet × 100
Here, the control sheet is a sheet produced without blending the first cellulose fibers.

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