JP6607327B1 - Sheet - Google Patents

Abstract

An object of the present invention is to provide a sheet containing pulp and fine fibrous cellulose and having an elastic modulus improved by the addition of fine fibrous cellulose. The present invention includes a softwood pulp, a hardwood pulp, and a fibrous cellulose having a fiber width of 1000 nm or less and having a phosphite group or a substituent derived from a phosphite group. When the content of N is N and the content of hardwood pulp is L, the value of N / L relates to a sheet having a value of 1 to 8. [Selection figure] None

Description

  The present invention relates to a sheet. Specifically, the present invention relates to a sheet containing pulp and fine fibrous cellulose.

  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 and a composite sheet containing a fine fibrous cellulose-containing sheet and a resin have been developed. In the sheet | seat 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 Documents 1 and 2 describe paper in which cellulose nanofibers are internally added. Here, it is considered to improve the strength and various properties of paper by internally adding cellulose nanofibers. Patent Document 3 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. Since such a nonwoven fabric is also excellent in air permeability, it has been studied to use it as a separator or a filter for a storage element.

JP 2009-263849 A Japanese Patent Application Laid-Open No. 2006-094680 JP 2012-036517 A

As described above, it has been studied to increase the strength and the like of paper by internally adding cellulose nanofibers (fine fibrous cellulose). However, depending on the application, there is a case where further improvement in elastic modulus or the like is required.
Therefore, the present inventors proceeded with studies for the purpose of effectively improving the elastic modulus of the sheet by adding cellulose nanofibers (fine fibrous cellulose).

[1] Softwood pulp, hardwood pulp, and fibrous cellulose having a fiber width of 1000 nm or less and having a phosphite group or a substituent derived from a phosphite group,
A sheet having a value of N / L of 1 or more and 8 or less, where N is the content of softwood pulp and L is the content of hardwood pulp.
[2] The sheet according to [1], wherein the content of fibrous cellulose is 1% by mass or more and 30% by mass or less with respect to the total mass of the sheet.
[3] The sheet according to [1] or [2], wherein the fiber width of the fibrous cellulose is 8 nm or less.
[4] The sheet according to any one of [1] to [3], wherein the Canadian standard freeness of the mixture of softwood and hardwood pulp is 600 ml or less.
[5] The sheet according to any one of [1] to [3], wherein the irregular freeness of the mixture of softwood pulp and hardwood pulp is 800 ml or less.
[6] The sheet according to any one of [1] to [5], wherein the increase rate of the specific tensile modulus calculated by the following formula is 25% or more;
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 having a fiber width of 1000 nm or less and prepared without blending fibrous cellulose having a phosphite group or a substituent derived from a phosphite group.

  According to this invention, it is a sheet | seat containing a pulp and a fine fibrous cellulose, Comprising: The sheet | seat with which the elasticity modulus improved by adding fine fibrous cellulose 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 relates to a sheet comprising softwood pulp, hardwood pulp, and fibrous cellulose having a fiber width of 1000 nm or less and having a phosphite group or a substituent derived from a phosphite group. In the sheet of the present invention, when N is the content of softwood pulp and L is the content of hardwood pulp, the value of N / L is 1 or more and 8 or less. In the present specification, fibrous cellulose having a fiber width of 1000 nm or less may be referred to as fine fibrous cellulose, 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, an improvement in the elastic modulus of the sheet is achieved. Specifically, the tensile elastic modulus is improved in the sheet of the present invention, and the rate of increase in the specific tensile elastic modulus based on a control sheet prepared without blending fine fibrous cellulose is high. As described above, in the sheet of the present invention, the specific tensile elastic modulus is effectively increased by setting the content of the softwood pulp and the hardwood pulp to an appropriate range, and further mixing the fine fibrous cellulose therein. Successful.

The rate of increase in specific tensile modulus based on a control sheet prepared without blending fine fibrous cellulose 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 having a fiber width of 1000 nm or less and prepared without blending fibrous cellulose having a phosphite group or a substituent derived from a phosphite group. The ratio of the content of softwood pulp and hardwood pulp in the control sheet is the same as the ratio in the sheet.

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 ).

  The tensile elastic modulus (GPa) of the sheet is a value measured according to JIS P 8113, except that the length of the test piece is 80 mm and the distance between chucks is 50 mm. When measuring the tensile modulus, a specimen conditioned at 23 ° C. and 50% relative humidity for 24 hours is used as a test piece. The tensile elastic modulus of the sheet can be measured using, for example, a tensile tester Tensilon (manufactured by A & D). The tensile elastic modulus of the sheet is preferably 3.0 GPa or more, more preferably 3.5 GPa or more, and further preferably 4.0 GPa or more. In addition, although the upper limit of the tensile elasticity modulus of a sheet | seat is not specifically limited, For example, it can be 50.0 GPa.

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.

Interlayer strength of the sheet of the present invention is preferably 300 J / m ² or more, more preferably 750 J / m ² or more, more preferably 1200 J / m ² or more, at 1500 J / m ² or more It is particularly preferred. 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.

  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.

  The sheet of the present invention is also excellent in productivity. 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, and particularly preferably less than 5 minutes. Thus, since the sheet of the present invention is excellent in productivity, it is particularly preferably used in industrial products where low cost and high strength are required.

(Fine fibrous cellulose)
The sheet of the present invention contains fibrous cellulose having a fiber width of 1000 nm or less and having a phosphite group or a substituent derived from a phosphite group. In the present specification, fibrous cellulose having a fiber width of 1000 nm or less is also referred to as fine fibrous cellulose. In the present invention, from the viewpoint of improving strength, the fiber width of the fibrous cellulose is more preferably 100 nm or less, and further preferably 8 nm or less.

  The content of the fine fibrous cellulose is preferably 1% by mass or more, more preferably 2% by mass or more, and further preferably 5% by mass or more with respect to the total mass of the sheet. In addition, from the viewpoint of further improving the strength, the content of fine fibrous cellulose can be 15% by mass or more based on the entire sheet. Moreover, it is preferable that it is 30 mass% or less with respect to the total mass of a sheet | seat, and, as for content of a fine fibrous cellulose, it is more preferable that it is 25 mass% or less.

  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 during fiber refinement (defibration) is high, 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 fine fibrous cellulose is preferably 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 fine fibrous cellulose is less than 2 nm, the physical properties (strength, rigidity, dimensional stability) as the fine fibrous cellulose tend to be difficult to be expressed because the cellulose molecules are dissolved in water. . The fine fibrous cellulose is preferably 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 observation with an electron microscope 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 fine fibrous cellulose is not particularly limited, but is preferably 0.1 μm or more and 1000 μm or less, more preferably 0.1 μm or more and 800 μm or less, and 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. Note that 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 axial ratio (fiber length / fiber width) of the fine fibrous cellulose is not particularly limited, but is preferably 20 or more and 10,000 or less, and more preferably 50 or more and 1,000 or less, for example. By setting the axial ratio to be equal to or more than the above lower limit value, it is easy to form a sheet containing fine fibrous cellulose. By setting the axial ratio to be equal to or less than the above upper limit value, for example, when handling the second cellulose fiber as an aqueous dispersion, it is preferable in terms of easy handling such as dilution.

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

The fine fibrous cellulose in this embodiment 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 a cyclopentyl group and a cyclohexyl group, but are not particularly limited. 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 useful, 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.

The amount of phosphite groups introduced into the fine fibrous cellulose is, for example, preferably 0.10 mmol / g or more, more preferably 0.20 mmol / g or more per 1 g (mass) of the fine fibrous cellulose. More preferably, it is at least 50 mmol / g, particularly preferably at least 1.00 mmol / g. Further, the amount of ionic substitution introduced into the fine fibrous cellulose is preferably 3.65 mmol / g or less, more preferably 3.50 mmol / g or less per 1 g (mass) of the fine fibrous cellulose, More preferably, it is 3.00 mmol / g or less. By making the introduction amount of the phosphorous acid group within the above range, the fiber raw material can be easily refined, and the stability of the fibrous cellulose can be enhanced. Here, the denominator in the unit mmol / g indicates the mass of the fibrous cellulose when the counter ion of the phosphite group is a hydrogen ion (H ⁺ ).

  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 introduction of the phosphorus oxo acid 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 phosphoric acid group and this phosphate group undergoes condensation, the amount of the weakly acidic group in the phosphorus oxo acid group (also referred to as the second dissociated acid amount in this specification) apparently appears. 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.

<Phosphorous acid group introduction process>
The production process of fine fibrous cellulose includes a phosphite group introduction process. In the phosphite group introduction step, at least one compound selected from compounds capable of introducing a phosphite group by reacting with a hydroxyl group of a fiber raw material containing cellulose (hereinafter also referred to as “compound A”) is used. It is the process of making it act on the fiber raw material containing a cellulose. By this step, a phosphite group-introduced fiber is obtained.

  In the phosphite group introduction step according to this embodiment, the reaction between the fiber raw material containing cellulose and compound A is carried out in the presence of at least one selected from urea and its derivatives (hereinafter also referred to as “compound B”). You may go. On the other hand, in the state where compound B does not exist, the fiber raw material containing cellulose and compound A may be reacted.

  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 compound A and compound B with a dry, wet, or slurry fiber raw material can be mentioned. Among these, since the uniformity of the reaction is high, it is preferable to use a fiber raw material in a dry state or a wet state, and it is particularly preferable to use a fiber raw material in a dry state. Although the form of a fiber raw material is not specifically limited, For example, it is preferable that it is a cotton form or a thin sheet form. The compound A and the compound B may be added to the fiber raw material in the form of a powder or a solution dissolved in a solvent, or heated to a melting point or higher and melted. Among these, since the uniformity of the reaction is high, it is preferable to add in the form of a solution dissolved in a solvent, particularly in the form of an aqueous solution. Compound A and Compound B may be added simultaneously to the fiber raw material, may be added separately, or may be added 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, they may be taken out after dipping the fiber raw material in the solution and absorbing the fiber raw material. The solution may be added dropwise. In addition, a necessary amount of Compound A and Compound B may be added to the fiber raw material, or after adding an excessive amount of Compound A and Compound B to the fiber raw material, respectively, excess compound A and Compound B may be added by pressing or filtration. It may be removed.

  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.

  The amount of compound A added to the fiber raw material is not particularly limited. For example, 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% by mass or more. It is preferably 100% by mass or less, more preferably 1% by mass or more and 50% by mass or less, and further preferably 2% by mass or more and 30% by mass or less. By making the addition amount of the phosphorus atom with respect to the fiber raw material within the above range, the yield of the fine fibrous cellulose can be further improved. On the other hand, when the amount of phosphorus atoms added to the fiber raw material is set to the upper limit value or less, the effect of improving the yield and the cost can be balanced.

  Compound B used in this embodiment is at least one selected from urea and derivatives thereof as described above. 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, the compound B is preferably used as an aqueous solution. From the viewpoint of further improving the uniformity of the reaction, it is preferable to use an aqueous solution in which both compound A and compound B are dissolved.

  The amount of compound B added to the fiber raw material (absolute dry mass) is not particularly limited, but is preferably 1% by mass or more and 500% by mass or less, and more preferably 10% by mass or more and 400% by mass or less, More preferably, it is 100 mass% or more and 350 mass% or less.

  In the reaction of the fiber raw material containing cellulose and Compound A, in addition to Compound B, for example, 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 heat-treat the fiber raw material 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. The heat treatment temperature is, for example, preferably 50 ° C. or higher and 300 ° C. or lower, more preferably 100 ° C. or higher and 250 ° C. or lower, and further preferably 130 ° C. or higher and 200 ° C. or lower. In addition, equipment having various heat media can be used for the heat treatment. For example, 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 can be used.

  In the heat treatment according to this embodiment, for example, compound A is added to a thin sheet-like fiber raw material by a method such as impregnation, and then heated, or heated while kneading or stirring the fiber raw material and compound A with a kneader or the like. The method to do can be adopted. Thereby, it is possible to suppress the concentration unevenness of the compound A in the fiber raw material and introduce the phosphite group more uniformly on the surface of the cellulose fiber contained in the fiber raw material. This is because when the water molecules move to the fiber raw material surface with drying, the dissolved compound A is attracted to the water molecules by the surface tension and similarly moves to the fiber raw material surface (that is, the concentration unevenness of the compound A is reduced). This can be attributed to the fact that it can be suppressed.

  In addition, the heating device used for the heat treatment, for example, always retains the moisture retained by the slurry and the moisture generated in the dehydration condensation (phosphate esterification) reaction between the compound A and the hydroxyl group contained in the cellulose or the like in the fiber raw material. It is preferable that the apparatus can be discharged out of the apparatus system. As such a heating device, for example, a blower type oven or the like can be cited. In addition to being able to suppress the hydrolysis reaction of the phosphate ester bond, which is the reverse reaction of phosphate esterification, by constantly discharging the water in the apparatus system, it is also possible to suppress the acid hydrolysis of sugar chains in the fiber. it can. For this reason, it becomes possible to obtain fine fibrous cellulose having a high axial ratio.

  The time for the heat treatment is, for example, preferably from 1 second to 300 minutes after moisture is substantially removed from the fiber raw material, more preferably from 1 second to 1000 seconds, and more preferably from 10 seconds to 800 seconds. More preferably. In the present embodiment, the amount of phosphite groups introduced can be within a preferred range by setting the heating temperature and the heating time to appropriate ranges.

  The phosphite group introduction step may be performed at least once, but may be repeated twice or more. By performing the phosphite group introduction step twice or more, a large number of phosphite groups can be introduced into the fiber raw material. In this embodiment, the case where a phosphorous acid group introduction | transduction process is performed twice as an example of a preferable aspect is mentioned.

<Washing process>
In the manufacturing method of the fine fibrous cellulose in this embodiment, a washing process can be performed with respect to the fiber which introduce | transduced the phosphorous acid group as needed. The washing step is performed, for example, by washing the phosphite group-introduced fiber with water or an organic solvent. In addition, the cleaning process may be performed after each process described later, and the number of times of cleaning performed in each cleaning process is not particularly limited.

<Alkali treatment process>
When manufacturing a fine fibrous cellulose, you may perform an alkali process with respect to a fiber raw material 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.

  Although the temperature of the alkali solution in an alkali treatment process is not specifically limited, For example, it is preferable that they are 5 degreeC or more and 80 degrees C or less, and it is more preferable that they are 10 degreeC or more and 60 degrees C or less. The immersion time of the phosphite group-introduced fiber in the alkali solution in the alkali treatment step is not particularly limited, but is preferably, for example, from 5 minutes to 30 minutes, and more preferably from 10 minutes to 20 minutes. The amount of the alkali solution used in the alkali treatment is not particularly limited. For example, it is preferably 100% by mass or more and 100000% by mass or less, and 1000% by mass or more and 10000% by mass with respect to the absolute dry mass of the phosphite group-introduced fiber. The following is more preferable.

  Although the temperature of the alkali solution in an alkali treatment process is not specifically limited, For example, it is preferable that they are 5 degreeC or more and 80 degrees C or less, and it is more preferable that they are 10 degreeC or more and 60 degrees C or less. The immersion time of the phosphite group-introduced fiber in the alkali solution in the alkali treatment step is not particularly limited, but is preferably, for example, from 5 minutes to 30 minutes, and more preferably from 10 minutes to 20 minutes. The amount of the alkali solution used in the alkali treatment is not particularly limited. For example, it is preferably 100% by mass or more and 100000% by mass or less, and 1000% by mass or more and 10000% by mass with respect to the absolutely dry mass of the phosphite group-introduced fiber. The following is more preferable.

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

<Acid treatment process>
When manufacturing a fine fibrous cellulose, you may acid-treat with respect to a fiber raw material between the process of introduce | transducing a phosphorous acid group, and the fibrillation process process mentioned later. For example, the phosphite group introduction step, acid treatment, alkali treatment, and defibration treatment may be performed in this order.

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

  Although the temperature of the acid solution in an acid treatment is not specifically limited, For example, 5 to 100 degreeC is preferable and 20 to 90 degreeC is more preferable. The immersion time in the acid solution in the acid treatment is not particularly limited, but is preferably, for example, 5 minutes to 120 minutes, and more preferably 10 minutes to 60 minutes. Although the usage-amount of the acid solution in an acid treatment is not specifically limited, For example, 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 fiber raw material, and it is 1000 mass% or more and 10000 mass% or less. Is more preferable.

<Defibration processing>
The phosphite group-introduced fiber is subjected to a defibrating process in a defibrating process, whereby fine fibrous cellulose is obtained.
In the defibrating process, for example, a defibrating apparatus can be used. The defibrating apparatus is not particularly limited, but for example, a high-speed defibrator, a grinder (stone mill type pulverizer), a high-pressure homogenizer or an ultrahigh-pressure homogenizer, a high-pressure collision type pulverizer, a ball mill, a bead mill, a disk type refiner, a conical refiner, biaxial A kneader, a vibration mill, a homomixer under high-speed rotation, an ultrasonic disperser, or a beater can be used. Among the above-described defibrating apparatuses, it is more preferable to use a high-speed defibrator, a high-pressure homogenizer, or an ultrahigh-pressure homogenizer that is less affected by the pulverizing media and has less risk of contamination.

In the defibrating process, for example, it is preferable to dilute the phosphite group-introduced fiber with a dispersion medium to form a slurry. As a dispersion medium, 1 type, or 2 or more types selected from water and organic solvents, such as a polar organic solvent, can be used. The polar organic solvent is not particularly limited, but alcohols, polyhydric alcohols, ketones, ethers, esters, aprotic polar solvents, and the like are preferable. Examples of alcohols include methanol, ethanol, isopropanol, n-butanol, and isobutyl alcohol. Examples of the polyhydric alcohols include ethylene glycol, propylene glycol, glycerin and the like. 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, propylene glycol monomethyl ether, and the like. Examples of the esters include ethyl acetate and butyl acetate. Examples of the aprotic polar solvent include dimethyl sulfoxide (DMSO), dimethylformamide (DMF), dimethylacetamide (DMAc), N-methyl-2-pyrrolidinone (NMP) and the like.
The solid content concentration of the fine fibrous cellulose during the defibrating treatment can be set as appropriate. The slurry obtained by dispersing the phosphite group-introduced fiber in the dispersion medium may contain solids other than the phosphite group-introduced fiber such as urea having hydrogen bonding properties.

(Pulp fiber)
The sheet of the present invention includes softwood and hardwood pulp. In the present specification, pulp (pulp fiber) is cellulose fiber having a fiber width of more than 1000 nm. In the present specification, pulp (pulp 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 pulp fiber. The fiber width of the pulp fiber may be larger than 1 μm, preferably 10 μm or more, more preferably 15 μm or more, and particularly preferably 20 μm or more. On the other hand, the fiber width of the pulp fiber is preferably 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 pulp fiber is preferably 70% by mass or more, and more preferably 75% by mass or more with respect to the total mass of the sheet. Moreover, it is preferable that it is 99 mass% or less with respect to the total mass of a sheet | seat, and, as for content of a pulp fiber, it is more preferable that it is 98 mass% or less, and it is further more preferable that it is 95 mass% or less. In addition, from a viewpoint of improving strength, the content of the pulp fiber can be 85% by mass or less with respect to the entire sheet.

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 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 prescribed in JIS P 8121-1995. The measured freeness.

  When the sheet | seat of this invention contains highly beaten pulp, the elasticity modulus of a sheet | seat can be improved more effectively by this. The fiber width of the high beaten pulp is preferably, for example, larger than 1 μm and 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 fine fibrous cellulose is C1, and the content of pulp fibers is C2, C1 / (C1 + C2) is preferably 0.01 or more, more preferably 0.05 or more, It is especially preferable that it is 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 fine fibrous cellulose in the sheet can be observed, for example, with a scanning electron microscope (manufactured by Hitachi High-Technologies Corporation, S-3600N). The pulp fibers 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 described later is equivalent to the ratio of fine fibrous cellulose and pulp fiber in the sheet.

(Optional component)
The sheet of the present invention may contain an optional component other than the components described above. Optional ingredients include, for example, hydrophilic resins, paper strength enhancers, preservatives, antifoaming agents, lubricants, UV absorbers, dyes, pigments, stabilizers, surfactants, sizing agents, yield improvers, bulking agents. , Freeness 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.

  Examples of the paper strength enhancer include a dry paper strength agent and a wet strength paper strength agent. Examples of the dry paper strength agent include cationized starch, polyacrylamide (PAM), carboxymethylcellulose (CMC), acrylic resin, and the like. Examples of the wet paper strength agent include polyamide epihalohydrin, urea, melamine, and heat crosslinkable polyacrylamide. Especially, it is preferable that the sheet | seat of this invention contains polyamine polyamide epihalohydrin.

  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 optional component contained in the sheet is preferably 50% by mass or less, more preferably 40% by mass or less, and preferably 30% by mass or less with respect to the total mass of the sheet. Further preferred.

(Sheet manufacturing method)
The sheet manufacturing process includes obtaining a slurry containing softwood pulp, hardwood pulp, and fibrous cellulose having a fiber width of 1000 nm or less and having a phosphite group or a substituent derived from a phosphite group. And a step of coating the slurry on a base material, or a step of paper-making the slurry. In addition, when the content of softwood pulp in the slurry is N and the content of hardwood pulp is L, the value of N / L is 1 or more and 8 or less.

  The step of obtaining the slurry preferably includes a step of mixing the coniferous pulp and the hardwood pulp, and thereafter, the fiber width is 1000 nm or less, and the fibrous form having a phosphite group or a substituent derived from the phosphite group It is preferable to include a step of adding and mixing cellulose. In the step of mixing the coniferous pulp and the hardwood pulp, it is preferable to provide a beating treatment step as necessary, and in the beating treatment step, it is preferable to beaten the pulp fibers so as to obtain a desired freeness.

  The step of forming the sheet is preferably a step of papermaking the slurry. Thereby, it becomes possible to raise production efficiency more.

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

  The paper making process is performed by filtering and dewatering the slurry with a wire to obtain a wet paper sheet, and then pressing and drying the sheet. The filter cloth used when the slurry is filtered and dehydrated is not particularly limited, but it is more preferable that, for example, fibrous cellulose does not pass through and the filtration rate does not become too slow. Such a filter cloth is not particularly limited, but for example, a sheet made of an organic polymer, a woven fabric, and a porous film 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. In this embodiment, for example, a porous film of polytetrafluoroethylene having a pore diameter of 0.1 μm or more and 20 μm or less, a polyethylene terephthalate or polyethylene fabric having a pore diameter of 0.1 μm or more and 20 μm or less, and the like can be mentioned.

  In the sheet forming step, a method for producing a sheet from the slurry includes, for example, discharging a slurry containing cellulose fibers onto the upper surface of the endless belt, and squeezing the dispersion medium from the discharged slurry to generate a web; and It can be carried out using a production device comprising a drying section that dries the web to produce a sheet. 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.

In the paper making process, it is preferable to make 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 making paper so that the basis weight falls within the above range, a sheet having excellent strength can be obtained.

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

<Coating process>
In the coating process, for example, a sheet can be obtained by coating a slurry (coating liquid) containing cellulose fibers on a substrate, and drying the formed sheet to release the sheet formed from the substrate. Moreover, a sheet | seat can be continuously produced by using a coating device and a elongate base material.

  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 film or plate or a metal film or plate is preferable, but is not particularly limited. For example, a film or plate of a resin such as polypropylene, acrylic, polyethylene terephthalate, vinyl chloride, polystyrene, polycarbonate, or polyvinylidene chloride, a metal film or plate of aluminum, zinc, copper, or iron plate, and the surface thereof oxidized Stainless steel films and plates, brass films and plates, and 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 is fixed on the base material to obtain a sheet having a predetermined thickness and basis weight. May be. The damming frame is not particularly limited, but for example, it is preferable to select one that can easily peel off the edge of the sheet attached after drying. From such a viewpoint, a molded resin plate or metal plate is more preferable. In the present embodiment, for example, a resin plate such as a polypropylene plate, an acrylic plate, a polyethylene terephthalate plate, a vinyl chloride plate, a polystyrene plate, a polycarbonate plate, or a polyvinylidene chloride plate, or a metal plate such as an aluminum plate, a zinc plate, a copper plate, or an iron plate And those obtained by oxidizing these surfaces, stainless steel plates, brass plates and the like can be used.
Although it does not specifically limit as a coating machine which coats a slurry on a base material, For example, a roll coater, a gravure coater, a die coater, a curtain coater, an air doctor coater etc. can be used. A die coater, a curtain coater, and a spray coater are particularly preferable because the thickness of the sheet can be made more uniform.

  The slurry temperature and the atmospheric temperature when applying the slurry to the substrate are not particularly limited, but are preferably 5 ° C. or more and 80 ° C. or less, more preferably 10 ° C. or more and 60 ° C. or less, and more preferably 15 ° C. The temperature is more preferably 50 ° C. or lower and particularly preferably 20 ° C. or higher and 40 ° C. or lower. If the coating temperature is equal to or higher than the lower limit, the slurry can be applied more easily. If coating temperature is below the said upper limit, 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.

  A coating process includes the process of drying the slurry coated on the base material as above-mentioned. The step of drying the slurry is not particularly limited, and is performed by, for example, a non-contact drying method, a method of drying while restraining the sheet, or a combination thereof.

  The non-contact drying method is not particularly limited. For example, 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 is not specifically limited, For example, it can carry out using an infrared device, a far-infrared device, or a near-infrared device.

  The heating temperature in the heat drying method is not particularly limited, but is preferably 20 ° C. or higher and 150 ° C. or lower, and more preferably 25 ° C. or higher and 105 ° C. or lower. If the heating temperature is at least the above lower limit, the dispersion medium can be volatilized quickly. Moreover, if heating temperature is below the said upper limit, the suppression of the cost which heating requires and the suppression of discoloration by the heat | fever of a cellulose fiber are realizable.

(Laminated sheet)
The present invention may relate to a laminate in which another layer is further laminated on the above-described sheet. As another layer, a coating layer can be mentioned, for example. 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, and (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 Chanplex 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 alone or in combination with other materials, various paper products such as printing paper, filters, separators, particle-carrying sheets, packaging materials, cardboard, wet, dry nonwoven fabrics, diapers, and home appliance components It can be used for various vehicles and building interior and exterior materials.

  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 changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be construed as being limited by the specific examples shown below.

[Example 1]
<Production of pulp components>
Water was added and dispersed so that the concentration of softwood bleached kraft pulp (NBKP) was 2% by mass, and then beaten with a beater. The same operation was performed on hardwood bleached kraft pulp (LBKP). Each pulp was mixed so that solid content mass ratio might be set to 80:20 (NBKP: LBKP), and NBKP80 / LBKP20 pulp slurry was obtained. The Canadian standard freeness of a mixture having a solid mass ratio of NBKP to LBKP of 80:20 was 450 ml. The Canadian standard freeness is a value measured by the Canadian standard freeness method defined in JIS P 8121-1995.

<Preparation of fine fibrous cellulose>
Oji Paper's softwood kraft pulp as raw material pulp (solid content 93% by weight, basis weight 245g / m ² sheet, disaggregated and measured according to JIS P 8121, Canadian standard freeness (CSF) 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.

The obtained phosphorylated pulp was subjected to infrared absorption spectrum measurement 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.

  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 was processed three times at a pressure of 245 MPa with a wet atomization apparatus (manufactured by Sugino Machine Co., Ltd., an optimizer) to obtain a fine fibrous cellulose-containing dispersion containing fine fibrous cellulose. The fiber width of the fine fibrous cellulose was about 3 nm.

<Sheet>
The NBKP80 / LBKP20 (freeness 450 ml) pulp slurry and the fine fibrous cellulose-containing dispersion are mixed so that the solid content of the pulp mixture is 80 parts by mass and the solid content of the fine fibrous cellulose is 20 parts by mass. 0.5 parts by mass of polyamide / epichlorohydrin (manufactured by Seiko PMC Co., Ltd., wet paper strength agent WS4030) was added to obtain a papermaking slurry. The solid content concentration of the papermaking slurry was 0.5% by mass.
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 thickness of 50 μm and a basis weight of 20 g / m ² .
In addition, the sheet | seat was produced by the method similar to the above from the slurry for papermaking containing 100 mass parts of NBKP80 / LBKP20 pulp slurry and 0.5 mass part of polyamine polyamide and epichlorohydrin as a control sheet of Example 1.

[Example 2]
<Preparation of pulp component> A sheet was obtained in the same manner as in Example 1 except that the mixing ratio of NBKP and LBKP was 60:40 (NBKP: LBKP).
In addition, the sheet | seat was produced by the method similar to the above from the slurry for papermaking containing 100 mass parts of NBKP60 / LBKP40 pulp slurries and 0.5 mass part of polyamine polyamide and epichlorohydrin as a control sheet of Example 2.

Example 3
<Manufacture of pulp components> A sheet was obtained in the same manner as in Example 1 except that the mixing ratio of NBKP and LBKP was 50:50 (NBKP: LBKP).
In addition, the sheet | seat was produced by the method similar to the above from the slurry for papermaking containing 100 mass parts of NBKP50 / LBKP50 pulp slurry and 0.5 mass part of polyamine polyamide * epichlorohydrin as a control sheet of Example 3.

Example 4
Water was added and dispersed so that the total concentration of NBKP 60 parts by mass and LBKP 40 parts by mass was 4% by mass, and then beaten with a double disc refiner to obtain NBKP60 / LBKP40 high beating pulp slurry. The irregular freeness of the high beating pulp having a solid mass ratio of NBKP and LBKP of 60:40 was 570 ml. In addition, 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.

NBKP60 / LBKP40 (an irregular freeness 570 ml) high beating pulp slurry and a fine fibrous cellulose-containing dispersion so that the solid content of the high beating pulp mixture is 80 parts by mass and the solid content of the fine fibrous cellulose is 20 parts by mass. Further, 0.5 parts by mass of polyamine polyamide / epichlorohydrin (manufactured by Seiko PMC Co., Ltd., wet paper strength agent WS4030) was added to obtain a papermaking slurry. The solid content concentration of the papermaking slurry was 0.5% by mass.
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 thickness of 40 μm and a basis weight of 20 g / m ² .
In addition, as a control sheet of Example 4, a sheet was prepared in the same manner as described above from a papermaking slurry containing 100 parts by mass of NBKP60 / LBKP40 high beating pulp slurry and 0.5 parts by mass of polyamine polyamide / epichlorohydrin. .

Example 5
NBKP60 / LBKP40 (an irregular freeness 570 ml) high beating pulp slurry and a fine fibrous cellulose-containing dispersion so that the solid content of the high beating pulp mixture is 90 parts by mass and the solid content of the fine fibrous cellulose is 10 parts by mass. Further, 0.5 parts by mass of polyamine polyamide / epichlorohydrin (manufactured by Seiko PMC Co., Ltd., wet paper strength agent WS4030) was added to obtain a papermaking slurry. The solid content concentration of the papermaking slurry was 0.5% by mass.
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 thickness of 40 μm and a basis weight of 20 g / m ² .
In addition, as a control sheet of Example 5, a sheet was produced in the same manner as described above from a papermaking slurry containing 100 parts by mass of NBKP60 / LBKP40 high beating pulp slurry and 0.5 parts by mass of polyamine polyamide / epichlorohydrin. .

[Comparative Example 1]
<Production of pulp component> A sheet was obtained in the same manner as in Example 1 except that LBKP was not mixed.
In addition, the sheet | seat was produced by the method similar to the above from the slurry for papermaking containing 100 mass parts of NBKP pulp slurries and 0.5 mass part of polyamine polyamide and epichlorohydrin as a control sheet of the comparative example 1.

[Comparative Example 2]
<Preparation of pulp component> A sheet was obtained in the same manner as in Example 1 except that the mixing ratio of NBKP and LBKP was 90:10 (NBKP: LBKP).
In addition, the sheet | seat was produced by the method similar to the above from the slurry for papermaking containing 100 mass parts of NBKP90 / LBKP10 pulp slurries, and 0.5 mass part of polyamine polyamide * epichlorohydrin as a control sheet of the comparative example 2.

[Comparative Example 3]
<Production of pulp components> A sheet was obtained in the same manner as in Example 1 except that the mixing ratio of NBKP and LBKP was 40:60 (NBKP: LBKP).
In addition, the sheet | seat was produced by the method similar to the above from the slurry for papermaking containing 100 mass parts of NBKP40 / LBKP60 pulp slurry and 0.5 mass part of polyamine polyamide * epichlorohydrin as a control sheet of the comparative example 3.

[Comparative Example 4]
In <Production of Pulp Component>, a sheet was obtained in the same manner as in Example 1 except that NBKP was not mixed.
In addition, the sheet | seat was produced by the method similar to the above from the slurry for papermaking containing 100 mass parts of LBKP pulp slurries and 0.5 mass part of polyamine polyamide and epichlorohydrin as a control sheet of the comparative example 4.

[Comparative Example 5]
Water was added and dispersed so that the concentration of 100 parts by mass of NBKP was 4% by mass, followed by beating with a double disc refiner to obtain NBKP100 high beating pulp slurry. The irregular freeness of high beaten pulp of NBKP100 was 330 ml.

NBKP100 (an irregular freeness 330 ml) high beating pulp slurry and a fine fibrous cellulose-containing dispersion are mixed so that the solid content of the high beating pulp is 80 parts by mass and the solid content of the fine fibrous cellulose is 20 parts by mass, 0.5 parts by mass of polyamine polyamide / epichlorohydrin (manufactured by Seiko PMC Co., Ltd., wet paper strength agent WS4030) was added to obtain a papermaking slurry. The solid content concentration of the papermaking slurry was 0.5% by mass.
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 thickness of 20 μm and a basis weight of 20 g / m ² .
In addition, the sheet | seat was produced by the method similar to the above from the slurry for papermaking containing 100 mass parts of NBKP high beating pulp slurries and 0.5 mass part of polyamine polyamide and epichlorohydrin as a control sheet of the comparative example 5.

(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 width of the fine fibrous cellulose was measured by the following method.
The supernatant of the fine fibrous cellulose dispersion was diluted with water so that the concentration 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)
[Specific tensile modulus]
The tensile modulus was measured using a tensile tester Tensilon (manufactured by A & D Co.) according to 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) = tensile modulus (GPa) / density (g / cm ³ ) of sheet
Furthermore, 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
In addition, a control sheet is a sheet | seat produced without mix | blending the fibrous cellulose which has a fiber width which is 1000 nm or less and has a substituent derived from a phosphorous acid group or a phosphorous acid group. For example, in Example 1, 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

[productivity]
250 g of slurry for handmaking (solid content concentration: 0.5% by mass) is run on a wire (HT2525-30, manufactured by Haiku Wagner), and the time until water is drawn (water is drained from the pulp slurry on the wire, The time until the gloss disappears from the pulp surface was measured and evaluated according to the following criteria.
A: Less than 5 minutes B: 5 minutes or more and less than 30 minutes C: 30 minutes or more

  In the examples, the specific tensile modulus was high and the rate of increase in the specific tensile modulus was high. Thus, when softwood pulp and hardwood pulp were blended in a specific ratio, it was found that the specific tensile modulus was significantly increased by the addition of fine fibrous cellulose.

Claims (6)

Softwood pulp, hardwood pulp, and fibrous cellulose having a fiber width of 1000 nm or less and having a phosphite group or a substituent derived from a phosphite group,
A sheet having a value of N / L of 1 or more and 8 or less, where N is the content of the softwood pulp and L is the content of the hardwood pulp.   The sheet according to claim 1, wherein the content of the fibrous cellulose is 1% by mass or more and 30% by mass or less with respect to the total mass of the sheet.   The sheet according to claim 1 or 2, wherein a fiber width of the fibrous cellulose is 8 nm or less.   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 according to any one of claims 1 to 3, wherein the irregular freeness of the mixture of the softwood pulp and the 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 25% or more.
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 having a fiber width of 1000 nm or less and prepared without blending fibrous cellulose having a phosphite group or a substituent derived from a phosphite group.

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