JP6586892B2 - Fine cellulose fiber-containing sheet and method for producing the same - Google Patents

Description

  The present invention relates to a sheet containing fine cellulose fibers, having a small basis weight, and a small aspect ratio of tensile strength, and a method for producing the same.

  Active use of plant-derived resources is required. Plant fibers have many possibilities, but there are many cases where the performance is insufficient, and the development into fields such as automobiles, homes, and home appliances where the use of plant fibers is expected has not progressed sufficiently. Cellulose fiber-containing sheets are an effective utilization example of plant-derived resources, but paper products exhibiting higher performance are required.

In Patent Document 1, the basis weight is 15 to 65 g / m ² , the aspect ratio of the dry tensile strength defined in JIS P8113 is 2.0 or less, and the tensile breaking elongation defined in JIS P8113 is 14%. A paper sheet characterized by the following is described. Patent Document 2 describes paper characterized in that it is composed only of unbleached kraft pulp, and 80% by mass or more of the unbleached kraft pulp is softwood unbleached kraft pulp. Furthermore, Patent Document 3 describes an electrolytic paper that has low density and improved tensile strength and that does not shield inter-fiber voids. However, Patent Documents 1 to 3 do not describe the use of fine cellulose fibers.

In Patent Document 4, synthetic pulp and fibers having a glass transition temperature of 200 ° C. or higher are used as main raw materials, manufactured by wet papermaking, a basis weight of 30 g / m ² or more, and a dielectric breakdown voltage of 13 k∨ / mm or more. A sheet having a thickness standard deviation of 3.0 μm or less is described. Patent Document 5 uses a paper machine in which a plurality of paper meshes are combined, and at least one layer is made by a forward flow type net having a 90-mesh metal wire. A method for manufacturing a separator is described.

Patent Document 6 contains fine cellulose fibers having an average fiber width of 1000 nm or less, a specific surface area by nitrogen gas adsorption method of 30 to 210 m ² / g, an average pore diameter of 0.005 to 5 μm, and a basis weight of 5 to 5. A fine cellulose fiber-containing sheet that is 100 g / m ² is described. However, Patent Document 6 does not describe the aspect ratio of tensile strength and elastic modulus. Patent Document 7 describes a paper sheet-containing composite material characterized in that, in a composite material comprising at least a resin composition and a plurality of paper sheets, the paper sheet has a surface area of 30 cm ² or less. Patent Document 7 describes that the aspect ratio of the tensile strength of the paper sheet is preferably 3.0 to 6.0.

JP 2006-320625 A Japanese Patent Laying-Open No. 2015-1038 JP 2006-245629 A JP 2014-237915 A JP2015-53315A JP, 2014-163028, A JP 2012-158137 A

  In the manufacture of a paper sheet, it is desired to provide a paper sheet that has good pick-up when the wet paper is peeled from the wire in papermaking and has a good texture. This invention makes it the subject which should be solved to provide the sheet | seat with the favorable pick-up at the time of peeling wet paper from a wire in papermaking, and a favorable formation. Furthermore, this invention makes it the subject which should be solved to provide the manufacturing method of the said sheet | seat.

The present inventors diligently studied to solve the above problems, and adjusted the papermaking conditions when papermaking was performed using fine cellulose fibers as a raw material. As a result, the basis weight is 5 g / m ² or more and 30 g / m ² or less, the density is 0.3 g / m ³ or more and 1.0 g / m ³ or less, and the aspect ratio of the tensile strength defined in JIS P8113 is It has been found that a sheet of 2.5 or less can be produced. Furthermore, the present inventors have found that the pickup is good in the production of the sheet and the formation of the sheet is good, and the present invention has been completed.

That is, according to the present invention, the following inventions are provided.
(1) Contains fine cellulose fibers, has a basis weight of 5 g / m ² or more and 30 g / m ² or less, a density of 0.3 g / m ³ or more and 1.0 g / m ³ or less, and is defined in JIS P8113. A sheet having a tensile strength aspect ratio of 2.5 or less.
(2) The sheet according to (1), wherein the number average fiber width of the fine cellulose fibers is 1 μm or less.
(3) The sheet according to (1) or (2), wherein the fiber length of the fine cellulose fibers is 1 mm or less.
(4) The sheet according to any one of (1) to (3), wherein the aspect ratio of the elastic modulus defined in JIS P8113 is 3.0 or less.
(5) The sheet according to any one of (1) to (4), wherein the longitudinal and lateral tensile strengths defined in JIS P8113 are each independently 0.2 MPa or more and 3.0 MPa or less.
(6) The sheet according to any one of (1) to (5), wherein the longitudinal and lateral elastic moduli defined in JIS P8113 are each independently 2.0 GPa or more and 15.0 GPa or less.
(7) The sheet according to any one of (1) to (6), wherein the fine cellulose fiber is a cellulase-treated fine cellulose fiber.
(8) The sheet according to any one of (1) to (7), which is a circular net papermaking sheet.
(9) The manufacturing method of the sheet | seat as described in any one of (1) to (8) including the process of paper-making a fine cellulose fiber containing dispersion liquid.

  The sheet of the present invention has good pick-up when the wet paper is peeled from the wire in papermaking. Moreover, the formation of the sheet | seat of this invention is also favorable.

  Embodiments of the present invention will be described below. In this specification, the numerical range “X to Y” includes values at both ends unless otherwise specified.

[Fine cellulose fiber-containing sheet]
The sheet of the present invention contains fine cellulose fibers, has a basis weight of 5 g / m ² or more and 30 g / m ² or less, a density of 0.3 g / m ³ or more and 1.0 g / m ³ or less, JIS P8113. The aspect ratio of the tensile strength specified in 1 is 2.5 or less.

The basis weight of the sheet of the present invention is 5 g / m ² or more and 30 g / m ² or less, and preferably 6 g / m ² or more and 28 g / m ² or less. By making the basis weight 5 g / m ² or more, it is possible to suppress the occurrence of paper breaks and achieve a good pickup, and by making the basis weight 30 g / m ² or less, a good formation can be achieved. . If the basis weight is 30 g / m ² , the production efficiency is lowered.
The basis weight of the sheet can be measured according to JIS P8124.

The density of the sheet of the present invention is 0.3 g / m ³ or more and 1.0 g / m ³ or less, preferably 0.35 g / m ³ or more and 0.85 g / m ³ or less. By setting the density to 0.3 g / m ³ or more, the occurrence of paper breaks can be suppressed and a good pickup can be achieved. By setting the density to 1.0 g / m ² or less, resin impregnation into the sheet, molding Sex can be imparted.
The density of the sheet can be measured according to JIS-P-8118: 1998 “Paper and paperboard—Test method for thickness and density”.

  The aspect ratio of the tensile strength defined in JIS P8113 of the sheet of the present invention is 2.5 or less, preferably 2.0 or less, more preferably 1.8 or less, and further preferably 1.5 or less. More preferably, it is 1.3 or less. By setting the aspect ratio of the tensile strength within the above range, the strength anisotropy of the sheet can be reduced. Therefore, the sheet can be used without considering the anisotropy when used for industrial applications such as structural members. Can be used. Moreover, when producing a container with this invention sheet | seat, troubles, such as fracture | rupture in the direction where strength is inferior, can be avoided.

  The longitudinal and lateral tensile strengths defined in JIS P8113 of the sheet of the present invention are preferably independently 0.2 MPa or more and 3.0 MPa or less, more preferably 0.4 MPa or more and 2.6 MPa or less.

  The aspect ratio of the elastic modulus defined in JIS P8113 of the sheet of the present invention is preferably 3.0 or less, more preferably 2.5 or less, still more preferably 2.0 or less, and still more preferably. 1.5 or less. By setting the aspect ratio of the elastic modulus within the above range, when the sheet of the present invention is laminated to a structural member, the thermal contraction anisotropy of the member can be suppressed by reducing the elastic anisotropy. it can.

  The longitudinal and lateral elastic moduli defined in JIS P8113 of the sheet of the present invention are preferably independently 2.0 GPa or more and 15.0 GPa or less. The above elastic moduli are each independently more preferably 2.0 GPa or more and 10.0 GPa or less, further preferably 2.0 GPa or more and 7.0 GPa or less, and further preferably 2.0 GPa or more and 5.0 GPa or less. .

<Fine cellulose fiber>
The fine cellulose fiber can be obtained by refining a raw material containing cellulose (cellulose raw material). For example, as a method for producing fine cellulose fibers, there is a method in which a cellulose raw material is refined by wet pulverization utilizing a mechanical action. Examples of the wet pulverization method using a mechanical action include a method using a grinder (stone mill type pulverizer), a high-pressure homogenizer, an ultrahigh-pressure homogenizer, a high-pressure collision type pulverizer, a disk refiner, a conical refiner, and the like.

In addition, before the above-mentioned miniaturization, chemical treatment such as TEMPO (2,2,6,6-tetramethylpiperidine-1-oxy radical) oxidation, ozone treatment, enzyme treatment, introduction of ionic substituents, etc. is performed. Also good. The introduction of the ionic substituent will be described later.
It is also possible to obtain a cellulose raw material by pulverizing wood and then performing a process such as delignification.

  Examples of the cellulose raw material include paper pulp, cotton pulp such as cotton linter and cotton lint, non-wood pulp such as hemp, straw, and pagas, cellulose isolated from sea squirts and seaweed, etc., but are not particularly limited. . Among these, paper pulp is preferable in terms of availability, but is not particularly limited. Examples of the papermaking pulp include, but are not particularly limited to, non-wood pulp made from chemical pulp, semi-chemical pulp, mechanical pulp, cocoon, sardine, hemp, kenaf and the like, and deinked pulp made from waste paper. Examples of the chemical pulp include hardwood kraft pulp, softwood kraft pulp, sulfite pulp (SP), dissolved pulp (DP), and soda pulp (AP). Examples of hardwood kraft pulp include bleached kraft pulp (LBKP), unbleached kraft pulp (LUKP), and oxygen bleached kraft pulp (LOKP). Examples of softwood kraft pulp include bleached kraft pulp (NBKP), unbleached kraft pulp (NUKP), and oxygen bleached kraft pulp (NOKP). Semi-chemical pulp includes semi-chemical pulp (SCP), chemiground wood pulp (CGP), and the like. Examples of the mechanical pulp include groundwood pulp (GP) and thermomechanical pulp (TMP, BCTMP). Dissolving pulp can also be used. Examples of the dissolving pulp include a dissolving pulp produced by kraft cooking after prehydrolysis, a dissolving pulp produced by sulfite cooking, and the like. Among these, kraft pulp, deinked pulp, and sulfite pulp are preferable because they are more easily available, but are not particularly limited. A cellulose raw material may be used individually by 1 type, and may be used in mixture of 2 or more types.

  The number average fiber width of the fine cellulose fibers is preferably 1 μm or less, more preferably 2 nm to 1000 nm, and more preferably 2 nm to 800 nm.

  A cellulose fiber is an aggregate of cellulose molecules including a crystal part, and its crystal structure is type I (parallel chain). The number average fiber width of the cellulose fibers can be measured by observing with an electron microscope. When the average fiber width of the cellulose fibers is less than 2 nm, the physical properties (strength, rigidity, dimensional stability) as the fine fibrous cellulose are not expressed because the cellulose molecules are dissolved in water. Here, the fact that the fine fibrous cellulose has the I-type crystal structure is typical in two positions in the diffraction profile, ie, 2θ = 14 ° to 17 ° and 2θ = 22 ° to 23 °. It can be identified from having a strong peak. The above-mentioned diffraction profile is a diffraction profile obtained from a wide-angle X-ray diffraction photograph using CuKα (λ = 1.5418Å) monochromated with graphite.

  Measurement of the average fiber width of the cellulose fibers by electron microscope observation is performed as follows. An aqueous suspension of cellulose fibers 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 obtain a sample for TEM observation. 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 cellulose fibers is the average value of the fiber widths read in this way.

  Although the fiber length of a fine cellulose fiber is not specifically limited, 1 mm or less is preferable. The fiber length of the fine cellulose fibers is preferably 0.1 μm or more, more preferably 1 μm or more and 1000 μm or less, and further preferably 5 μm or more and 800 μm or less. When the fiber length is less than 0.1 μm, it is difficult to form a film (sheet). If it exceeds 1000 μm, the slurry viscosity of the cellulose fiber becomes very high, making it difficult to handle. The fiber length can be obtained as a length load average fiber length obtained by measurement with a fiber length measuring device “FiberLab”.

  The aspect ratio (axial ratio) (fiber length / fiber width) of the fiber is not particularly limited, but is preferably in the range of 20 or more and 10,000 or less, preferably in the range of 30 or more and 10,000 or less, and 50 or more and 10,000 or less. A range is more preferable. An aspect ratio of 20 or more is preferable in that a film can be easily formed during production. When the aspect ratio is 10,000 or less, it is preferable in that the slurry viscosity during the production of the film is lowered.

(Introduction of ionic substituents)
Although the cellulose fiber may have an ionic substituent, it is not specifically limited, It is not necessary to have an ionic substituent. The ionic substituent may be either anionic or cationic.

  Examples of anionic substituents include phosphate groups or substituents derived from phosphate groups, carboxy groups or substituents derived from carboxy groups, sulfate groups or substituents derived from sulfate groups, sulfonate groups or sulfonate groups. The substituent derived from is mentioned. A substituent derived from a phosphoric acid group or a phosphoric acid group is also referred to as a phosphoric acid-derived group. A carboxy group or a substituent derived from a carboxy group is also referred to as a group derived from a carboxylic acid. A sulfuric acid group or a substituent derived from a sulfuric acid group is also referred to as a sulfuric acid-derived group. A sulfonic acid group or a substituent derived from a sulfonic acid group is also referred to as a sulfonic acid-derived group.

The phosphoric acid group is a divalent functional group equivalent to the phosphoric acid obtained by removing the hydroxyl group. Specifically, it is a group represented by —PO ₃ H ₂ . The substituent derived from the phosphate group includes a substituent such as a group obtained by polycondensation of a phosphate group, a salt of a phosphate group, and a phosphate ester group. Moreover, the substituent derived from a phosphoric acid group or a phosphoric acid group may be represented by the following formula (1).

In formula (1), a, b, m and n each independently represent an integer (where a = b × m). α ⁿ (n = 1 to n) and α ′ each independently represent R or OR. R represents 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 aromatic group, or a derivative group thereof. β is a monovalent or higher cation composed of an organic substance or an inorganic substance.

  The anionic substituent is at least one selected from the group consisting of a group derived from phosphoric acid, a group derived from carboxylic acid, and a group derived from sulfuric acid, from the viewpoint of ease of handling and reactivity with fibers during production. It is preferable. These groups preferably form an ester or ether with the fiber, but are not particularly limited.

  Examples of the cationic substituent include groups derived from onium salts such as ammonium salts, phosphonium salts, and sulfonium salts. Specific examples include groups containing ammonium, phosphonium and sulfonium such as primary ammonium salt, secondary ammonium salt, tertiary ammonium salt and quaternary ammonium salt. The cationic substituent is preferably at least one of a group derived from a quaternary ammonium salt and a group derived from a phosphonium salt in view of ease of handling and reactivity with fibers during production.

  An ionic substituent is introduced into the cellulose fiber raw material to prepare an ionic substituent-introduced cellulose fiber, the ionic substituent-introduced cellulose fiber is refined to prepare an ionic substituent-introduced fine fibrous cellulose, and then In addition, a step of preparing a sheet can be performed.

(Step of obtaining ionic substituent-introduced cellulose fiber by introducing ionic substituent into cellulose fiber raw material)
A method for introducing an ionic substituent to the cellulose fiber is not particularly limited, and examples thereof include an oxidation treatment and a treatment with a compound capable of forming a covalent bond with a functional group in the cellulose fiber. The oxidation treatment is a treatment for converting a hydroxy group in cellulose fiber into an aldehyde group or a carboxy group. Examples thereof include TEMPO (2,2,6,6-tetramethylpiperidine 1-oxyl) oxidation treatment and treatment using various oxidizing agents (sodium chlorite, ozone, etc.).

  An example of the oxidation treatment is a method described in Biomacromolecules 8, 2485-2491, 2007 (Saito et al.), But is not particularly limited.

  The treatment with the compound capable of forming a covalent bond with the functional group in the cellulose fiber is performed by mixing the cellulose fiber raw material with a compound that reacts with the cellulose fiber raw material in the dry or wet fiber raw material. Can be implemented. In order to promote the reaction at the time of introduction, a heating method is particularly effective. The heat treatment temperature for introducing the substituent is not particularly limited, but it is preferably a temperature range in which thermal decomposition or hydrolysis of the fiber raw material hardly occurs. For example, the temperature is preferably 250 ° C. or lower from the viewpoint of the thermal decomposition temperature of the fiber, and is preferably heat-treated at 100 ° C. or higher and 170 ° C. or lower from the viewpoint of suppressing the hydrolysis of the fiber.

The compound that reacts with the cellulose fiber raw material is not particularly limited as long as it introduces an ionic substituent.
When a compound having a phosphoric acid-derived group is used as a compound that reacts with the cellulose fiber raw material, it is not particularly limited, but is composed of phosphoric acid, polyphosphoric acid, phosphorous acid, phosphonic acid, polyphosphonic acid, or a salt or ester thereof. It is at least one selected from the group. Among these, a compound having a phosphate-derived group is preferable because it is low-cost, easy to handle, and can further improve the refinement (defibration) efficiency by introducing a phosphate-derived group into the cellulose fiber raw material. However, it is not particularly limited.

  The compound having a phosphoric acid-derived group is not particularly limited, but phosphoric acid, lithium dihydrogen phosphate, dilithium hydrogen phosphate, trilithium hydrogen phosphate, trilithium phosphate, lithium pyrophosphate, lithium polyphosphate Can be mentioned. Furthermore, sodium dihydrogen phosphate, disodium hydrogen phosphate, trisodium phosphate, sodium pyrophosphate and sodium polyphosphate which are sodium salts of phosphoric acid are mentioned. Furthermore, potassium dihydrogen phosphate, dipotassium hydrogen phosphate, tripotassium phosphate, potassium pyrophosphate, and potassium polyphosphate which are potassium salts of phosphoric acid are mentioned. Further examples include ammonium dihydrogen phosphate, diammonium hydrogen phosphate, triammonium phosphate, ammonium pyrophosphate, and ammonium polyphosphate, which are ammonium salts of phosphoric acid.

  Of these, phosphoric acid, phosphoric acid sodium salt, phosphoric acid potassium salt, and phosphoric acid ammonium salt are preferred from the viewpoint of high efficiency of introduction of phosphoric acid-derived groups and easy industrial application. It is not limited. Among these, sodium dihydrogen phosphate and disodium hydrogen phosphate are more preferable, but not particularly limited.

  In addition, the compound is preferably used as an aqueous solution because of the uniformity of the reaction and the introduction efficiency of the group derived from phosphoric acid, but it is not particularly limited. The pH of the aqueous solution of the compound is not particularly limited, but is preferably 7 or less because of the high efficiency of introducing a phosphoric acid-derived group. From the viewpoint of suppressing the hydrolysis of the fiber, pH 3 or more and pH 7 or less are more preferable, but not particularly limited.

  The compound having a phosphate-derived group reacts with the fiber raw material together with one or more selected from urea, thiourea, biuret, phenylurea, benzylurea, dimethylurea, diethylurea, tetramethylurea, benzoleinurea, or hydantoin. You may let them. However, the present invention is not limited to this.

  When a compound having a carboxylic acid-derived group is used as the compound that reacts with the fiber raw material, the compound having a carboxylic acid-derived group, an acid anhydride of the compound having a carboxylic acid-derived group, and the like are not particularly limited. And at least one selected from the derivatives of

  The compound having a carboxylic acid-derived group is not particularly limited, but a dicarboxylic acid compound such as maleic acid, succinic acid, phthalic acid, fumaric acid, glutaric acid, adipic acid or itaconic acid, or a tricarboxylic acid compound such as citric acid or aconitic acid. Is mentioned.

  The acid anhydride of the compound having a carboxylic acid-derived group is not particularly limited, but acid anhydrides of dicarboxylic acid compounds such as maleic anhydride, succinic anhydride, phthalic anhydride, glutaric anhydride, adipic anhydride, itaconic anhydride, etc. Things.

  The derivative of the compound having a carboxylic acid-derived group is not particularly limited, and examples thereof include an acid anhydride imidized compound having a carboxylic acid-derived group and an acid anhydride derivative of a compound having a carboxylic acid-derived group. . The acid anhydride imidized compound having a carboxylic acid-derived group is not particularly limited, and examples thereof include imidized dicarboxylic acid compounds such as maleimide, succinimide, and phthalimide.

  The acid anhydride derivative of the compound having a carboxylic acid-derived group is not particularly limited. For example, at least some of the hydrogen atoms of the acid anhydride of the compound having a carboxylic acid-derived group, such as dimethylmaleic acid anhydride, diethylmaleic acid anhydride, diphenylmaleic acid anhydride, are substituted (for example, alkyl group, And those substituted with a phenyl group or the like.

  Among the compounds having a group derived from a carboxylic acid, maleic anhydride, succinic anhydride, and phthalic anhydride are preferred because they are easily applied industrially and easily gasified, but are not particularly limited.

  When a compound having a group derived from sulfuric acid is used as the compound that reacts with the cellulose fiber raw material, it is not particularly limited, but it is at least one selected from the group consisting of sulfuric anhydride, sulfuric acid and salts and esters thereof. Among these, sulfuric acid is preferable, but is not particularly limited because it is low cost and can improve the refinement (defibration) efficiency by introducing a sulfate group into the cellulose fiber raw material.

  The amount of the ionic substituent introduced when the ionic substituent is introduced is not particularly limited, but can be determined in consideration of the amount of the substituent introduced as a sheet. In the case of an anionic substituent, the amount of substituent introduced (by titration method) is preferably 0.005α to 0.11α, more preferably 0.01α to 0.08α per 1 g (mass) of fiber. If the introduction amount of the substituent is 0.005α or more, the fiber raw material can be easily refined (defibration). If the introduction amount of the substituent is 0.11α or less, dissolution of the fiber can be suppressed. However, (alpha) is the quantity (unit: mmol / g) by which the functional group which the compound which reacts with a fiber material can react, for example, a hydroxyl group and an amino group, is contained per 1 g of fiber materials. The amount of ionic substituent introduced can be measured by a conductivity titration method.

  When the introduced substituent is at least one selected from the group consisting of a phosphoric acid-derived group, a carboxylic acid-derived group and a sulfuric acid-derived group, the amount of substituent introduction is not particularly limited, but 0 It can be set to 0.001 mmol / g or more and 5.0 mmol / g or less. It may be 0.05 mmol / g or more and 4.0 mmol / g or less, and may be 0.1 mmol / g or more and 2.0 mmol / g or less.

  The cationic substituent can be introduced into the fiber raw material, for example, by adding a cationizing agent and an alkali compound to the cellulose fiber raw material and reacting them. As the cationizing agent, one having a quaternary ammonium group and a group that reacts with a hydroxy group of cellulose can be used. Examples of the group that reacts with the hydroxy group of cellulose include an epoxy group, a functional group having a halohydrin structure, a vinyl group, and a halogen group.

  Specific examples of the cationizing agent include glycidyltrialkylammonium halides such as glycidyltrimethylammonium chloride and 3-chloro-2-hydroxypropyltrimethylammonium chloride or halohydrin type compounds thereof.

  The alkali compound used in the cationization step contributes to the promotion of the cationization reaction. The alkali compound may be an inorganic alkali compound or an organic alkali compound.

Examples of inorganic alkali compounds include alkali metal hydroxides or alkaline earth metal hydroxides, alkali metal carbonates or alkaline earth metal carbonates, alkali metal phosphates or alkaline earth metal phosphoric acids. Salt.
Examples of the alkali metal hydroxide include lithium hydroxide, sodium hydroxide, and potassium hydroxide. Examples of the alkaline earth metal hydroxide include calcium hydroxide.

Examples of the alkali metal carbonate include lithium carbonate, lithium hydrogen carbonate, potassium carbonate, potassium hydrogen carbonate, sodium carbonate, and sodium hydrogen carbonate. Examples of the alkaline earth metal carbonate include calcium carbonate.
Examples of the alkali metal phosphate include lithium phosphate, potassium phosphate, trisodium phosphate, and disodium hydrogen phosphate. Examples of alkaline earth metal phosphates include calcium phosphate and calcium hydrogen phosphate.

Examples of the organic alkali compounds include ammonia, aliphatic amines, aromatic amines, aliphatic ammoniums, aromatic ammoniums, heterocyclic compounds and their hydroxides, carbonates, and phosphates. For example, ammonia, hydrazine, methylamine, ethylamine, diethylamine, triethylamine, propylamine, dipropylamine, butylamine, diaminoethane, diaminopropane, diaminobutane, diaminopentane, diaminohexane, cyclohexylamine, aniline, tetramethylammonium hydroxide, Tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, benzyltrimethylammonium hydroxide, pyridine, N, N-dimethyl-4-aminopyridine, ammonium carbonate, ammonium hydrogen carbonate, diammonium hydrogen phosphate, etc. Can be mentioned.
The said alkali compound may be single 1 type, and may combine 2 or more types.

  Among the above alkali compounds, sodium hydroxide and potassium hydroxide are preferable because the cationization reaction is more likely to occur and the cost is low. The amount of the alkali compound varies depending on the type of the alkali compound, and is, for example, in the range of 1% by mass or more and 10% by mass or less with respect to the pulp dry mass.

  Since the cationizing agent and the alkali compound can be easily added to the pulp, it is preferable to form a solution. The solvent used for the solution may be either water or an organic solvent, but a polar solvent (polar organic solvent such as water or alcohol) is preferable, and an aqueous solvent containing at least water is more preferable.

  In the present invention, it is preferable that the amount of solvent substance per 1 g of the pulp dry mass at the start of the cationization reaction is 5 mmol or more and 150 mmol or less. The substance amount of the solvent is more preferably 5 mmol or more and 80 mmol or less, and further preferably 5 mmol or more and 60 mmol or less. In order to bring the pulp content during the cationization reaction into the above range, for example, a pulp having a high content (that is, having a low water content) may be used. Moreover, it is preferable to reduce the amount of solvent contained in the solution of the cationizing agent and the alkali compound.

  The reaction temperature in the cationization step is preferably in the range of 20 ° C. or higher and 200 ° C. or lower, and more preferably in the range of 40 ° C. or higher and 100 ° C. or lower. If the reaction temperature is not less than the lower limit, sufficient reactivity can be obtained, and if the reaction temperature is not more than the upper limit, the reaction can be easily controlled. In addition, there is an effect of suppressing coloring of the pulp after the reaction. The time of the cationization reaction varies depending on the type of pulp and cationizing agent, pulp content, reaction temperature, and the like, but is usually in the range of 0.5 hours to 3 hours.

  The cationization reaction may be performed in a closed system or an open system. Further, the solvent may be evaporated during the reaction, and the amount of the solvent substance per 1 g of the pulp dry mass at the end of the reaction may be lower than that at the start of the reaction.

(Acid treatment or alkali treatment)
If necessary, an acid treatment or an alkali treatment can be performed after the step of obtaining the ionic substituent-introduced fiber. The acid treatment can be performed using, for example, one or more selected from the group consisting of hydrochloric acid, nitric acid and sulfuric acid. The alkali treatment can be performed using, for example, one or more selected from the group consisting of sodium hydroxide, potassium hydroxide, barium hydroxide, and calcium hydroxide.

  The acid treatment or alkali treatment method can be carried out, for example, by immersing the ionic substituent-introduced cellulose fiber in an acid solution or an alkali solution. As the solvent in the acid solution or the alkali solution, at least one of water and an organic solvent can be used. A polar one (polar organic solvent such as water or alcohol) is preferable, and an aqueous solvent containing water is more preferable. A particularly preferred example of the acid solution is hydrochloric acid, and a particularly preferred example of the alkaline solution is an aqueous sodium hydroxide solution or an aqueous potassium hydroxide solution.

  In the case of acid treatment, the pH of the acid solution at 25 ° C. can be appropriately determined, but is preferably 4 or less, more preferably 3.5 or less, and even more preferably 3 or less. In the case of the alkali treatment, the pH of the base solution at 25 ° C. can be appropriately determined, but is preferably 9 or more, more preferably 10 or more, and further preferably 11 or more.

  In order to reduce the amount of acid or alkali used, cellulose fibers having an ionic substituent may be washed before the acid treatment or alkali treatment step. For washing, at least one of water and an organic solvent can be used. In addition, after the acid treatment or the alkali treatment, the treated cellulose fiber having an ionic substituent may be washed with at least one of water and an organic solvent. In either case, the washing operation can be repeated.

(Step of obtaining ionic substituent-introduced fine fibrous cellulose by refining ionic substituent-introducing cellulose fiber)
The cellulose fiber raw material may be refined by subjecting it to a defibrating treatment, and fine fibrous cellulose having a number average fiber width of 2 nm to 1000 nm can be obtained by the refinement treatment. In the defibrating process, the fine fiber dispersion can be obtained by defibrating the raw material using a defibrating apparatus.

  During the refinement (defibration) process, the fibers are dispersed in a solvent. The type of the solvent is not particularly limited as long as it can be appropriately refined (sometimes referred to as defibration), but an aqueous solvent (water or a mixture of water and an organic solvent) can be used. Examples of the organic solvent include alcohols such as methanol, ethanol, n-propanol, isopropanol, n-butanol, and tbutyl alcohol. Further, ketones such as acetone and methyl ethyl ketone (MEK), ethers such as diethyl ether and tetrahydrofuran (THF), dimethyl sulfoxide (DMSO), dimethylformamide (DMF), dimethylacetamide (DMAc) and the like can be mentioned. Only one organic solvent may be used, or two or more organic solvents may be used.

  The dispersion concentration is preferably 0.05% by mass or more and 20% by mass or less, and more preferably 0.05% by mass or more and 10% by mass or less. This is because if the dispersion concentration is equal to or higher than the lower limit value, the processing efficiency is improved, and if the dispersion concentration is equal to or lower than the upper limit value, blockage in the defibrating apparatus can be prevented.

  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.

  The refinement treatment can be performed until a fiber having a desired average fiber width is obtained. A fine fiber dispersion (slurry) is obtained by the refining treatment. The obtained fine fiber dispersion may contain fibers having a fiber width of more than 1000 nm, but preferably does not contain fibers having a fiber width of more than 1000 nm. Although the density | concentration of a fine fiber here is not specifically limited, For example, they are 0.1 mass% or more and 20 mass% or less, and 0.5 mass% or more and 10 mass% or less may be sufficient.

<Fine cellulose fiber treated with cellulase>
The fine cellulose fiber may be a cellulase-treated fine cellulose fiber.
After diluting the cellulose fiber dispersion to an appropriate concentration, cellulase having endoglucanase activity is added in an amount of 1% by mass to 10% by mass with respect to the cellulose solid content, and a predetermined temperature (preferably 35 ° C. to 50 ° C., more preferably Can be processed at 40 ° C. to 50 ° C.). After the reaction, it is preferable to deactivate the enzyme, for example, by treating at 80 ° C. for 10 minutes.

<Other ingredients>
The sheet | seat of this invention may contain other components other than a fine cellulose fiber. Other components include inorganic particles, fillers, sizing agents, paper strength enhancers, yield improvers, colorants, bulking agents, freeness improvers, pH adjusters, fluorescent whitening agents, fluorescent decoloring agents, pitch control. Agents, slime control agents, antifoaming agents, water retention agents, dispersants, preservatives and the like. However, other components are not limited to the above, and any additive used in general papermaking can be used.

<Sheet type>
In the present invention, a sheet can be prepared from a dispersion (slurry) of cellulose fibers. Although the preparation method of a sheet | seat is not specifically limited, Typically, the papermaking method can be mentioned. That is, the sheet of the present invention is preferably a papermaking sheet. More preferably, the sheet of the present invention is a circular net paper sheet or a long net paper sheet, more preferably, the sheet of the present invention is a reverse flow net paper sheet or a forward flow net paper sheet, particularly preferably the present sheet. The sheet of the invention is a reverse flow net-making paper sheet.

[Method for producing fine cellulose fiber-containing sheet]
The present invention further relates to a method for producing the above-described sheet of the present invention, which comprises a step of papermaking the fine cellulose fiber-containing dispersion.

<Paper making>
The fine cellulose fiber-containing dispersion (slurry) is a continuous paper machine such as a long-mesh type, circular net type, or inclined type used in normal paper making, or a multi-layered paper making machine combining these, or hand-making, etc. Paper can be made into a sheet by a known paper making method. That is, after the fine cellulose fiber-containing dispersion is filtered and dehydrated on a wire to obtain a wet paper sheet, the sheet can be obtained by pressing and drying.

  The paper making is preferably performed using a circular net paper machine or a long net paper machine, more preferably using a reverse flow net paper machine or a forward flow net paper machine, and using a reverse flow net paper machine. Is particularly preferred.

  The jet wire ratio in the wire part of the paper machine is preferably 0.90 to 1.40, more preferably 1.0 to 1.4. By setting the jet wire ratio within the above range, it becomes easy to adjust the aspect ratio of the tensile strength defined in JIS P8113 of the manufactured sheet to 2.5 or less.

  The concentration of the fine cellulose fibers in the dispersion is not particularly limited, but is preferably 0.05% by mass or more and 5% by mass or less. If the concentration is too low, it takes a long time for filtration. Conversely, if the concentration is too high, a uniform sheet is obtained. Is not preferred because it cannot be obtained.

  When the dispersion is filtered and dehydrated, the filter cloth at the time of filtration is not particularly limited, but it is preferable that the cellulose fibers do not pass through and the filtration rate does not become 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.

<Dehydration and drying>
After papermaking or coating, at least one of dehydration and drying is performed as necessary to produce a sheet. Although it does not specifically limit as a dehydration method, The dehydration method normally used by manufacture of paper is mentioned, The method of dehydrating with a roll press after dehydrating with a long net, a circular net, an inclined wire, etc. is preferable. Further, the drying method is not particularly limited, and examples thereof include methods used in paper production. For example, methods such as a cylinder dryer, a Yankee dryer, hot air drying, and an infrared heater are preferable. The drying method is not particularly limited, and may be 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, 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 40 ° C. or higher and 120 ° C. or lower, and more preferably 40 ° C. or higher and 110 ° C. or lower. If the heating temperature is at least the lower limit value, the dispersion medium can be volatilized quickly, and if it is at most the upper limit value, the cost required for heating and the discoloration due to the heat of the fine fibers can be suppressed.

[Use of fine cellulose fiber-containing sheet]
The fine cellulose fiber-containing sheet of the present invention is used 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, and diapers. It can also be used for speaker diaphragm base paper.

  EXAMPLES Hereinafter, although an Example demonstrates this invention, the scope of the present invention is not limited by an Example.

  In Examples, the average fiber length and average fiber width of cellulose fibers, and the weight and density of sheets were measured by the following methods.

(1) Average fiber length of cellulose fiber “JAPAN TAPPI Paper Pulp Test Method No. 52: 2000 Pulp and Paper—Fiber Length Test Method—Optical Automatic Measurement Method” manufactured by Kajaani Co .: Fiber length measuring device “FiberLab” The length load average fiber length obtained by measurement was defined as the average fiber length.

(2) Average Fiber Width of Cellulose Fiber A surface obtained by casting a cellulose fiber aqueous suspension having a concentration of 0.05 to 0.1% by mass on glass was observed with a scanning electron microscope. At this time, when an axis having an arbitrary vertical and horizontal image width is assumed in the obtained image, the specimen and observation conditions (magnification, etc.) are set so that at least 20 fibers intersect the axis. With respect to an observation image that satisfies this condition, two random axes, vertical and horizontal, per image are drawn, and the fiber width of the fibers intersecting with the axis is visually read. In this way, images of at least three non-overlapping surface portions were observed with an electron microscope, and the fiber width values of fibers intersecting each other with two axes were read (at least 20 × 2 × 3 = 120 fiber widths). The value was measured.

(3) Basis weight of sheet Basis weight was measured according to JIS P8124. For papers that could not be picked up at the time of papermaking and sheets could not be obtained, the target basis weight was shown in parentheses in the table.

(4) Density of sheet Measured according to JIS-P-8118: 1998 “Paper and paperboard—Test method of thickness and density”.

Example 1
Water was added to and dispersed in softwood bleached kraft pulp (manufactured by Oji Paper Co., Ltd., water content: 50% by mass) to a concentration of 4.0% by mass, and then continuous circulation beating was performed with a double disc refiner for 5 hours. The obtained cellulose fibers had a length load average fiber length of 0.49 mm and an average fiber width of 350 nm. The cellulose fiber content concentration of the obtained cellulose fiber dispersion A was 3.95% by mass.

Cellulose fiber dispersion A was diluted to a concentration of 0.3% by mass, and papermaking was performed with a reverse flow type circular paper machine at a jet wire ratio of 1.23 to obtain a wet sheet. The wet sheet was dried with a Yankee dryer at a temperature of 110 ° C. to obtain a cellulose fiber sheet having a basis weight of 13.0 g / m ² and a density of 0.43 g / cm ³ .

(Example 2)
The cellulose fiber dispersion A of Example 1 was diluted to a concentration of 0.3% by mass, and papermaking was performed at a jet wire ratio of 1.24 using a forward flow circular net paper machine to obtain a wet sheet. The wet sheet was dried with a Yankee dryer at a temperature of 110 ° C. to obtain a cellulose fiber sheet having a basis weight of 16.0 g / m ² and a density of 0.48 g / cm ³ .

(Example 3)
The cellulose fiber dispersion A of Example 1 was diluted to a concentration of 0.3% by mass, and papermaking was performed with a reverse flow type circular net paper machine at a jet wire ratio of 1.21 to obtain a wet sheet. The wet sheet was dried with a Yankee dryer at a temperature of 110 ° C. to obtain a cellulose fiber sheet having a basis weight of 25.0 g / m ² and a density of 0.65 g / cm ³ .

(Example 4)
The cellulose fiber dispersion A of Example 1 was diluted to a concentration of 0.3% by mass, and papermaking was performed at a jet wire ratio of 1.25 using a forward flow circular net paper machine to obtain a wet sheet. The wet sheet was dried at 110 ° C. with a Yankee dryer to obtain a cellulose fiber sheet having a basis weight of 27.0 g / m ² and a density of 0.75 g / cm ³ .

(Example 5)
The cellulose fiber dispersion A of Example 1 was diluted to a concentration of 0.3% by mass, and papermaking was performed with a long-mesh paper machine at a jet wire ratio of 1.01 to obtain a wet sheet. The wet sheet was dried with a Yankee dryer at a temperature of 110 ° C. to obtain a cellulose fiber sheet having a basis weight of 18.0 g / m ² and a density of 0.68 g / cm ³ .

(Example 6)
The cellulose fiber dispersion A of Example 1 was diluted to a concentration of 0.3% by mass, and papermaking was performed with a long net paper machine at a jet wire ratio of 1.05 to obtain a wet sheet. The wet sheet was dried with a Yankee dryer at a temperature of 110 ° C. to obtain a cellulose fiber sheet having a basis weight of 25.0 g / m ² and a density of 0.72 g / cm ³ .

(Example 7)
Softwood bleached kraft pulp (manufactured by Oji Paper Co., Ltd., moisture 50% by mass) was added with water to a concentration of 4.0% by mass and dispersed, and then subjected to continuous circulation beating with a double disc refiner for 2.5 hours. . The obtained cellulose fibers had a length-weighted average fiber length of 0.62 ml and a fiber width of 720 nm. The cellulose fiber content concentration of the obtained cellulose fiber dispersion B was 3.8% by mass.

Cellulose fiber dispersion B was diluted to a concentration of 0.3% by mass, and papermaking was performed with a reverse flow circular net paper machine at a jet wire ratio of 1.25 to obtain a wet sheet. The wet sheet was dried with a Yankee dryer at a temperature of 110 ° C. to obtain a cellulose fiber sheet having a basis weight of 14.0 g / m ² and a density of 0.65 g / cm ³ .

(Example 8)
The cellulose fiber dispersion B obtained in Example 7 was diluted to a concentration of 0.3% by mass, and papermaking was performed with a forward-flow circular net paper machine at a jet wire ratio of 1.22, whereby a wet sheet was obtained. The wet sheet was dried with a Yankee dryer at a temperature of 110 ° C. to obtain a cellulose fiber sheet having a basis weight of 28.0 g / m ² and a density of 0.85 g / cm ³ .

Example 9
Cellulose fiber dispersion liquid B prepared in Example 7 was diluted to a concentration of 2% by mass, and subjected to a defibration treatment for 2 hours with Cleamix 11S manufactured by M Techniques, thereby obtaining a cellulose fiber dispersion liquid C. The obtained cellulose fibers had a length load average fiber length of 0.4 mm and a fiber width of 220 nm.

The obtained cellulose fiber dispersion C was diluted to a concentration of 0.3% by mass, and papermaking was performed at a jet wire ratio of 1.21 using a reverse flow circular net paper machine to obtain a wet sheet. The wet sheet was dried with a Yankee dryer at a temperature of 110 ° C. to obtain a cellulose fiber sheet having a basis weight of 6.0 g / m ² and a density of 0.35 g / cm ³ .

(Example 10)
The cellulose fiber dispersion C obtained in Example 9 was diluted to a concentration of 0.3% by mass, and papermaking was carried out at a jet wire ratio of 1.22 using a forward flow circular net paper machine to obtain a wet sheet. The wet sheet was dried with a Yankee dryer at a temperature of 110 ° C. to obtain a cellulose fiber sheet having a basis weight of 11.0 g / m ² and a density of 0.35 g / cm ³ .

(Example 11)
After the cellulose fiber dispersion B prepared in Example 8 was diluted to a concentration of 2% by mass, 2% by mass of cellulase having endoglucanase activity (Ecopulp 314-4093, manufactured by AB Enzyme) was added to the cellulose solid content. . After treatment at 45 ° C. for 1 hour, the enzyme was inactivated by treatment at 80 ° C. for 10 minutes. The solid content concentration of the obtained enzyme treatment liquid was 1.85% by mass. The enzyme-treated solution was defibrated for 2 hours with Cleamix 11S manufactured by M Techniques to obtain a cellulose fiber dispersion D having a solid content of 1.8% by mass. The obtained cellulose fibers had a length load average fiber length of 0.23 mm and a fiber width of 150 nm.

The obtained cellulose fiber dispersion D was diluted to a concentration of 0.3% by mass, and papermaking was performed with a reverse flow circular net paper machine at a jet wire ratio of 1.23 to obtain a wet sheet. The wet sheet was dried with a Yankee dryer at a temperature of 110 ° C. to obtain a cellulose fiber sheet having a basis weight of 6.0 g / m ² and a density of 0.38 g / cm ³ .

Example 12
The cellulose fiber dispersion D obtained in Example 11 was diluted to a concentration of 0.3% by mass, and papermaking was performed with a forward-flow circular net paper machine at a jet wire ratio of 1.22, whereby a wet sheet was obtained. The wet sheet was dried with a Yankee dryer at a temperature of 110 ° C. to obtain a cellulose fiber sheet having a basis weight of 13.0 g / m ² and a density of 0.5 g / cm ³ .

(Comparative Example 1)
Paper making of the cellulose fiber dispersion A obtained in Example 1 was attempted with a long web paper machine with a jet wire ratio of 1.01 and a basis weight of 12.0 g / m ² , but wet paper could not be picked up from the wire. Papermaking was impossible.

(Comparative Example 2)
Paper making of the cellulose fiber dispersion B obtained in Example 7 was attempted with a long net paper machine with a jet wire ratio of 1.05 and a basis weight of 9.0 g / m ² , but wet paper could not be picked up from the wire. Papermaking was impossible.

(Comparative Example 3)
Papermaking of the cellulose fiber dispersion C obtained in Example 7 was attempted with a long web paper machine with a jet wire ratio of 1.01 and a basis weight of 14.0 g / m ² , but wet paper could not be picked up from the wire. Papermaking was impossible.

(Comparative Example 4)
Softwood bleached kraft pulp (manufactured by Oji Paper Co., Ltd., water content: 50% by mass) was added with water to a concentration of 4.0% by mass and dispersed, and then treated once with a double disc refiner. The obtained cellulose fibers had a length load average fiber length of 1.2 mm and a fiber width of 15 μm. The cellulose fiber content concentration of the obtained cellulose fiber dispersion E was 3.98% by mass.

The cellulose fiber dispersion was diluted to a concentration of 0.3% by mass, and papermaking was performed at a jet wire ratio of 1.24 using a reverse flow circular paper machine to obtain a wet sheet. The wet sheet was dried with a Yankee dryer at a temperature of 110 ° C. to obtain a cellulose fiber sheet having a basis weight of 35.0 g / m ² and a density of 0.55 g / cm ³ .

(Comparative Example 5)
The cellulose fiber dispersion E obtained in Comparative Example 4 was diluted to a concentration of 0.3% by mass, and papermaking was performed at a jet wire ratio of 1.02 using a long paper machine to obtain a wet sheet. The wet sheet was dried with a Yankee dryer at a temperature of 110 ° C. to obtain a cellulose fiber sheet having a basis weight of 27.0 g / m ² and a density of 0.4 g / cm ³ .

(Comparative Example 6)
The cellulose fiber dispersion E obtained in Comparative Example 4 was diluted to a concentration of 0.3% by mass, and papermaking was performed with a forward-flow circular net paper machine at a jet wire ratio of 1.25 to obtain a wet sheet. The wet sheet was dried with a Yankee dryer at a temperature of 110 ° C. to obtain a cellulose fiber sheet having a basis weight of 22.0 g / m ² and a density of 0.6 g / cm ³ .

(Comparative Example 7)
The cellulose fiber dispersion E obtained in Comparative Example 4 was diluted to a concentration of 0.3% by mass, and papermaking was performed at a jet wire ratio of 1.02 using a long paper machine to obtain a wet sheet. The wet sheet was dried with a Yankee dryer at a temperature of 110 ° C. to obtain a cellulose fiber sheet having a basis weight of 20.0 g / m ² and a density of 0.5 g / cm ³ .

(Comparative Example 8)
A cellulose fiber sheet was made in the same manner as in Example 1 except that the basis weight was set to 3 g / m ² .

(Comparative Example 9)
A cellulose fiber sheet was made in the same manner as in Example 1 except that the paper machine was changed to an inclined wire type paper machine equipped with an inclined wire having an inclination angle of 10 °.

  The following evaluation was performed for each sheet of the above-described Examples and Comparative Examples. The evaluation results are listed in the table below.

(Evaluation methods)
Sampling properties were evaluated by sampling from the winding with the paper direction parallel to the paper traveling direction as "longitudinal" and the paper direction perpendicular to the paper traveling direction as "lateral" during paper machine production.

(Tensile modulus)
According to JIS P8113, the tensile modulus in the machine direction and the transverse direction of the sheet was measured.
(Tensile strength)
According to JIS P8113, the tensile strength in the machine and transverse directions of the sheet was measured.

(pick up)
When papermaking, when wet paper was peeled from the wire, it was transferred to a blanket and a sheet was obtained.

(Form)
Apply the transmitted light to the prepared paper, and evaluate the presence of foam formation (aggregates of thin portions of microcircular fibers) and scale (dropped portions of irregular fibers), and the aggregation of fibers according to the following criteria. went.
(Double-circle): There was no foam formation, scale, and fiber aggregation, and the surface quality was good.
○: Some of the foam texture, scale, and slight aggregation of fibers were observed, but the surface quality was generally good.
(Triangle | delta): Foam formation, scale, and aggregation of the fiber were seen in part, and surface quality was a little inferior.
X: Foam formation, scale, and aggregation of fibers were observed in several places and the surface quality was extremely inferior.
If the formation is ◎ or ○, it is practically acceptable.

  In papermaking aimed at low basis weight using the long paper machine of Comparative Examples 1 to 3, fine fibers bite into the wire, and the wet paper could not be peeled from the wire and a sheet could not be obtained. . On the other hand, in Examples 5 and 6, when the basis weight was increased from Comparative Examples 1 to 3, papermaking was possible even with a long net paper machine.

  Further, in Examples 1 to 12, it was better to use a circular net paper machine than a long paper machine, and the ratio of elastic modulus and strength tended to be low. Furthermore, the ratio of elastic modulus and strength tended to be lower when using a reverse flow type net paper machine than when using a forward flow type net paper machine.

When the fiber width was large as seen in Comparative Examples 4 to 7, the formation was poor and the ratio of elastic modulus and strength tended to be large.
Furthermore, in Comparative Example 8 having a basis weight of 3 g / m ² , there was a large amount of sheet slip, frequent paper breaks, and continuous production was impossible.
Further, in Comparative Example 9 using the inclined wire type paper machine, the number of sheet squeeze was very large, and paper breaks occurred frequently and continuous production was impossible.

Claims (7)

Containing fine cellulose fibers having a basis weight of at 5 g / ^{m 2} or more 30 g / ^{m 2} or less, a density of not more than 0.3 g / c ^{m 3} or more 1.0 g / c ^{m 3,} as defined in JIS P8113 A method for producing a sheet having a tensile strength aspect ratio of 2.5 or less, comprising a step of circular paper making a fine cellulose fiber-containing dispersion. The method according to claim 1, wherein the number average fiber width of the fine cellulose fibers is 1 μm or less. The method according to claim 1 or 2, wherein the fiber length of the fine cellulose fibers is 1 mm or less. The method according to any one of claims 1 to 3, wherein the aspect ratio of the elastic modulus defined in JIS P8113 of the sheet is 3.0 or less. The method according to any one of claims 1 to 4, wherein the longitudinal and lateral tensile strengths defined in JIS P8113 of the sheet are each independently 0.2 MPa or more and 3.0 MPa or less. The method according to any one of claims 1 to 5, wherein the longitudinal and lateral elastic moduli defined in JIS P8113 of the sheet are each independently 2.0 GPa or more and 15.0 GPa or less. The method according to any one of claims 1 to 6, wherein the fine cellulose fiber is a cellulase-treated fine cellulose fiber.