JP2012162814A - Cellulose fiber sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cellulose fiber sheet with high strength obtained by allowing cellulose fiber to contain a specific cationic polyacrylamide-based resin.SOLUTION: A cellulose fiber sheet is obtained by using cellulose fiber comprising: a cationic polyacrylamide-based resin having a viscometric average molecular weight measured by an intrinsic viscosity method of 5,000,000 or more and a cationic charge density of 0.5 to 1.5 meq/g; and a cationic polyacrylamide-based resin having a cationic charge density of 1.5 to 3.0 meq/g.

Description

  The present invention relates to a cellulose fiber sheet applicable as a reinforcing fiber for structural members such as automobiles, houses, home appliances, and furniture, and relates to a cellulose fiber sheet containing a specific cationic polyacrylamide resin.

  In recent years, the use of biomass resources, which are recyclable and recyclable resources, has attracted attention due to the growing awareness of global environmental issues. Plant fiber, one of the biomass resources, has many possibilities, but its performance is often not satisfied, so it is expected to be used in large markets such as automobiles, houses, and household appliances. Development is not progressing. Paper sheets, on the other hand, are a long-lasting material that has been recycled, but in the long history, weight reduction and strength improvement have progressed, but the degree of improvement has never been so great that it can be used only for paper products that take advantage of strength. The fact is that development is not progressing.

  When making pulp fiber, it has been performed since the birth of papermaking technology to beat the pulp and strengthen the bond between pulp fibers. There are several properties imparted to pulp fibers by beating, and among these, fibrillation of fibers, which has an important influence on interfiber bonding, can be mentioned. In general, fibrillation is considered that fine fibers (microfibrils) partially generated in pulp fibers contribute to an increase in fiber surface area and formation of a bond network between fibers, and strengthen the bond between pulp fibers. However, as another phenomenon that occurs simultaneously with fibrillation at the time of beating, a shortening phenomenon called pulp fiber cutting occurs, causing a reduction in paper strength. For this reason, as a method for enhancing the paper strength, there is a method of making a fine fiberized pulp and adding it to the pulp slurry before paper making to enhance the paper strength. Since energy is required, provision of an efficient manufacturing method is strongly demanded.

  For example, Patent Document 1 attempts to refine a pulp aqueous suspension by a medium agitating mill or a vibration mill, but this method takes time to refine and requires a great deal of energy.

  Patent Documents 2 and 3 propose a method of further refinement of a pulp slurry that has been beaten in advance with a high-pressure homogenizer, but during the final high-pressure homogenizer treatment, a pulp slurry liquid accelerated at high speed by pressure is used. Since it collides and refines | miniaturizes, a slurry viscosity rises rapidly in the process of refinement | miniaturization, there exists a possibility that piping etc. may be clogged, and it is not efficient. Moreover, since it is processed by excessive force, it is easy to shorten the fiber, and it is difficult to obtain the effect of increasing the strength of the fiber sheet.

  In Patent Document 4, after the cellulose fiber is oxidized, it is mechanically processed with a high-speed rotary disperser in the first stage, and mechanically processed with a high-pressure disperser such as a high-pressure homogenizer in the second stage. A production method for obtaining a cellulose fiber dispersion is disclosed. Cellulose fine oxidized cellulose can be obtained by this method. However, when paper was made with a plastic wire used in a normal paper machine, the fine fiber fell off the wire, and the cellulose fiber sheet could not be produced efficiently.

  Patent Document 5 proposes a method for producing a high tensile strength nonwoven fabric made of fine cellulose fibers, but the tensile strength is insufficient to reinforce a structural member that requires strength. In addition, since isobutyl alcohol is used for papermaking, there is a problem that special equipment with an explosion-proof function is necessary for papermaking.

JP-A-8-188980 Japanese Patent No. 2967804 Japanese Patent No. 4302794 JP 2009-161893 JP 2008-274525 A

  The present invention provides a cellulose fiber sheet having a significantly improved strength compared to conventional paper even when paper is made with a plastic wire normally used in papermaking by blending a specific cationic polyacrylamide resin into a cellulose fiber-containing slurry. The issue is to provide.

The present invention includes the following inventions.
(1) A cationic polyacrylamide resin having a viscosity average molecular weight of 5 million or more and a cationic charge density of 0.5 to 1.5 meq / g and a cationic charge density of 1.5 to 3. This is a cellulose fiber sheet containing a cationic polyacrylamide-based resin of 0 meq / g.

(2) The cellulose fiber sheet according to (1), wherein the cationic polyacrylamide resin is a copolymer of acrylamide and a monomer represented by the following formula (I).

（式（Ｉ）中、Ｒ_１、Ｒ_２、Ｒ_３はそれぞれ独立して、Ｈ、メチル基、エチル基又はベンジル基；Ｒ_４はＨ又はメチル基；ＸはＣｌ⁻、Ｂｒ⁻を表す。）

(In formula (I), R ₁ , R ₂ and R ₃ each independently represent H, a methyl group, an ethyl group or a benzyl group; R ₄ represents H or a methyl group; X represents Cl ⁻ or Br ⁻ . )

(3) 0.1 to 2 parts by mass of the cationic polyacrylamide resin having a cation charge density of 0.5 to 1.5 meq / g and 100 parts by mass of the cation charge density with respect to 100 parts by mass of the cellulose fiber. It is a cellulose fiber sheet as described in (1) or (2) which contains 0.1-2 mass parts of cationic polyacrylamide type-resins which are 0.5-3.0 meq / g.

(4) The aspect ratio of the tensile strength measured according to JIS P8113: 1998 of the cellulose fiber sheet is 3.0 or more, and the geometric average of the longitudinal strength and the transverse strength is 120 to 300 MPa (1) It is a cellulose fiber sheet given in any 1 paragraph of-(3).

  ADVANTAGE OF THE INVENTION According to this invention, a high strength cellulose fiber sheet can be provided simply with the plastic wire used with a normal paper machine.

Hereinafter, the present invention will be described in detail.
(Raw material for cellulose fiber)
Although it does not specifically limit as a raw material for cellulose fibers of this invention, Plant origin cellulose, animal origin cellulose, bacteria origin cellulose, etc. are mentioned. More specifically, chemical pulp fibers obtained by digesting conifers and hardwoods using the craft method, sulfite method, soda method, polysulfide method, etc .; Thereafter, semichemical pulp fibers pulped by mechanical force; or waste paper pulp fibers can be exemplified, and they can be used in an unbleached (before bleaching) or bleached (after bleaching) state, respectively. Examples of non-wood fibers produced from herbs include fibers obtained by pulping cotton, manila hemp, flax, mitsumata, straw, bamboo, bagasse, kenaf, and the like in the same manner as wood pulp.

  The tree species used as pulp are bay pine, red pine, black pine, todomatsu, spruce pine, beech pine, larch, fir, tsuga, cedar, cypress, larch, syringe, spruce, hiba, douglas fir, hemlock, white fur, spruce, balsam fur. And conifers such as cedar, pine, merck pine, and radiata pine, and broadleaf trees such as beech, birch, alder, nara, tub, shii, birch, boxwood, poplar, tamo, dragonfly, eucalyptus, mangrove, and lawan.

(Preparation of pulp suspension)
When performing the preliminary beating as a pretreatment using the pulp fiber, a conventional beating machine conventionally used for papermaking can be used, for example, beater, Jordan, conical refiner, single disc refiner, double disc Any beating machine such as a refiner can be used. The pulp slurry concentration at the time of preliminary beating is preferably in the range of 4 to 20% by mass. More preferably, it is 5-10 mass%. If it is less than 4% by mass, the dispersion concentration of the pulp fiber is low, and the beating efficiency is lowered. On the other hand, if it exceeds 20% by mass, the viscosity of the slurry will increase during the beating, and the beating efficiency will similarly decrease. The dispersion medium used may be water, an organic solvent, or a mixture thereof, but water is preferred.
Since the processing efficiency of the above-described pulp beater is very high, it is preferable to keep the Canadian standard freeness (hereinafter referred to as CSF) of JIS P 8121-1995 as small as possible in the preliminary beating process. In any case of short fiber pulp, beating is performed so that the CSF is 20 ml or less to obtain a pulp suspension. The pulp suspension has a CSF of preferably 15 ml or less, and more preferably 10 ml or less. When the CSF is 10 ml or less, the measurement error increases. In this case, the irregular CSF can be measured by diluting the concentration of the pulp suspension (for example, diluting to 0.1% by mass). In the case of 0.1% by mass irregular CSF, the range is preferably 10 to 400 ml, more preferably 50 to 350 ml.

(Microfibrillation)
The concentration of the pulp suspension in which CSF was beaten to 20 ml or less was adjusted to 4% by mass or less, preferably 0.2 to 3.5% by mass, and more preferably 0.7 to 2.8% by mass. Thereafter, the weight-weighted average fiber length is 0.30 mm to 0.80 mm, and the average fiber width is treated with a high-speed rotary disperser so that the average fiber width is 25 μm or less, and the aqueous suspension of cellulose fibers used in the present invention. Obtain a liquid. The cellulose fibers preferably have a weight weighted average fiber length of 0.40 to 0.70 mm, an average fiber width of 0.05 to 10 μm, more preferably a weight weighted average fiber length of 0.45 to 0.65 mm, Microfilrillation is performed so that the average fiber width is 0.1 to 3 μm. When the weight-weighted average fiber length is smaller than 0.30 mm, the pulp itself is short, so that the strength of the obtained cellulose fiber sheet is small. If the average fiber width exceeds 0.80 mm or the average fiber width exceeds 25 μm, microfibrillation of the cellulose fibers is insufficient, so that the obtained cellulose fiber sheet can obtain only the same strength as ordinary paper. The weight-weighted average fiber length and the average fiber width of the present invention are those of JAPAN TAPPI Paper Pulp Test Method No. 52: 2000, a value measured using a fiber length measuring device (FS-200) manufactured by KAJANI.

  In the present invention, the cellulose fibers are preferably microfibrillated using a high-speed rotary disperser. The microfibrillation treatment by the high-speed rotating disperser uses a high-speed rotating disperser having one or two or more rotating bodies serving as stirring means as a mechanical process, and the peripheral speed ( (Hereinafter referred to as “peripheral speed”) is a method of processing at 10 m / s or more. The peripheral speed is preferably 12 m / s or more, more preferably 15 m / s or more, and particularly preferably 20 m / s or more. The upper limit of the peripheral speed is not particularly limited, but is preferably 100 m / s or less in view of economy and mechanical strength of the disperser.

In a high-speed rotating disperser, kinetic energy is applied to the pulp suspension by a rotor that rotates at high speed, and the suspension passes at high speed through the screen slit, but at the same time, a jet flow is generated intermittently, and the speed interface The microfibrillation of the pulp fiber is promoted by the shearing force. At this time, the pulp fiber hardly has a tensile force that cuts the fiber in the length direction, so that the fiber is hardly cut. Unlike a high-pressure disperser such as a high-pressure homogenizer, the pulp fiber has a characteristic that it is difficult to shorten the fiber. . Further, the recovery rate of microfibrillated cellulose fibers is high. Examples of the rotating body include well-known and publicly-used ones such as various shapes of stirring blades and those in which the tank itself rotates.
The high-speed rotating disperser is of a type in which the pulp suspension to be treated is passed through the gap between the rotating body and the fixed part to disperse the inner rotating body that rotates in a fixed direction and the outside of the inner rotating body. There is an outer rotating body that rotates in reverse, and there is a type in which the object to be treated is passed through and dispersed in the gap between the inner rotating body and the outer rotating body. In the present invention, the latter is used because of the efficiency of microfibrillation. These types are preferred. Examples of high-speed rotary dispersers include `` CLEAMIX '' manufactured by M Technique, `` Milder '' manufactured by Taiyo Koki Co., `` Sharp Flow Mill '', `` Cabitron '' manufactured by Eurotech, TK robot mix "," fill mix "and the like.

Since a high shear rate (unit s ⁻¹ ) can be generated by passing through a narrow gap while rotating at a high speed in this way, a high-speed rotation (for example, a general commercially available homomixer with a large gap and a low shear rate) ), The microfibrillation treatment can be effectively performed. The size of the gap is preferably 5 mm or less, more preferably 3 mm or less, and still more preferably 2 mm or less.

  The processing time for microfibrillation can be appropriately set in relation to the peripheral speed, the processing amount of one pulp suspension, the capacity of the processing tank, and the like. For example, when the peripheral speed of the rotating body is 18 m / s, the capacity of the treatment tank is 1 L, and the pulp suspension having a concentration of 2.5 mass% is 500 g, the treatment time is about 5 to 100 minutes.

(Manufacture of cellulose fiber sheet)
In this invention, although the manufacturing method of the fiber sheet containing the said cellulose fiber is not specifically limited, For example, it is possible to manufacture with the following method.
(A) Method of making a sheet by making a cellulose fiber-containing raw material pulp slurry by a normal paper making method (B) Cellulose fibers formed by coating a cellulose fiber-containing raw material pulp slurry on a substrate and drying it The method of peeling a layer from a base material and making it into a sheet | seat etc. is mentioned.

  The method (A) is not only a continuous paper machine such as a long-mesh type, a circular net type, an inclined type, etc., in which a cellulose fiber-containing raw pulp slurry is used in ordinary paper making, but also a multi-layered paper making machine combining these, Paper is made by a known paper making method such as paper making, and can be made into a sheet by the same method as general paper. That is, after a cellulose fiber containing raw material pulp slurry is dehydrated on a wire to obtain a wet paper sheet, the fiber sheet can be obtained by pressing and drying. Of course, if necessary, the surface can be smoothed by a machine calender or a super calender and densified to improve the strength.

In the present invention, the cellulose fiber-containing raw material pulp slurry has a cationic polyacrylamide resin having a viscosity average molecular weight of 5 million or more by an intrinsic viscosity method and a cationic charge density of 0.5 to 1.5 meq / g, and a cationic charge density. Paper making or coating is carried out by containing a cationic polyacrylamide resin of 1.5 to 3.0 meq / g. If the polyacrylamide has a cationicity of 3.0 meq / g or more, the fine cellulose fibers are excessively aggregated to deteriorate the texture when paper is produced, and the strength is lowered. On the other hand, when the polyacrylamide has a cationic property of 0.5 meq / g or less, fine cellulose fibers fall out of the wire during papermaking. When the molecular weight is 5 million or less, it is insufficient for bonding fine cellulose fibers by hydrogen bonding.
Furthermore, a cationic polyacrylamide resin having a viscosity average molecular weight of 5 million or more by an intrinsic viscosity method and a cationic charge density of 0.5 to 1.5 meq / g and a cationic charge density of 1. By containing two kinds of cationic polyacrylamide resins of 5 to 3.0 meq / g, it is possible to prevent the fine fibers from coming out of the wire during paper making and to obtain a high strength cellulose fiber-containing sheet. Of the two types of cationic polyacrylamides, fine fibers are gently agglomerated with high cationic polyacrylamide to prevent fine fibers from coming off during paper making, and cellulose fibers with low cationic polyacrylamide. This is because the gap is firmly bonded by hydrogen bonding.
Moreover, the addition amount with respect to the cellulose fiber of cationic polyacrylamide type resin has preferable 0.1-2 mass parts. If the addition amount is 0.1% or less, the fine fibers are not sufficiently aggregated and fall off when paper is made. On the other hand, when the addition amount exceeds 2% by mass, the viscosity of the cellulose fiber-containing slurry at the time of paper making increases, and the paper making speed becomes slow.

  The cationic polyacrylamide resin is preferably a copolymer of acrylamide and a monomer represented by the following formula (I).

（式（Ｉ）中、Ｒ_１、Ｒ_２、Ｒ_３はそれぞれ独立して、Ｈ、メチル基、エチル基又はベンジル基；Ｒ_４はＨ又はメチル基；ＸはＣｌ⁻、Ｂｒ⁻を表す。）

(In formula (I), R ₁ , R ₂ and R ₃ each independently represent H, a methyl group, an ethyl group or a benzyl group; R ₄ represents H or a methyl group; X represents Cl ⁻ or Br ⁻ . )

In the (meth) acryloyloxyethylammonium salt of the structural formula (I), R ₁ , R ₂ and R ₃ are preferably all methyl groups, or R ₁ , R ₂ are methyl groups, and R ₃ is preferably a hydrogen atom, Particularly preferred are all methyl groups. X is preferably Cl ⁻ or Br ⁻ , and R ₄ may be either a hydrogen atom or a methyl group.
Specific examples of the monomer of the structural formula (I) include (meth) acryloyloxyethyltrimethylammonium salt and (meth) acryloyloxyethyldimethylammonium salt.

  The (meth) acryloyloxyethyltrimethylammonium salt of the structural formula (I) is obtained by reacting dimethylaminoethyl (meth) acrylate with a quaternizing agent, for example, an alkyl halide such as methyl chloride. (Meth) acryloyloxyethyldimethylammonium salt is obtained by reacting dimethylaminoethyl (meth) acrylate with an acid such as hydrochloric acid, bromic acid, sulfuric acid, nitric acid, acetic acid and the like. It is sulfuric acid.

  In the method (B), a cellulose fiber-containing raw material pulp slurry is applied onto a substrate, and the cellulose fiber-containing layer formed by drying the slurry is peeled from the substrate to obtain a sheet made of cellulose fibers. Is the method. By using a coating apparatus and a long substrate, sheets made of cellulose fibers can be continuously produced. The material of the base material that has higher wettability to the cellulose fiber-containing raw material pulp slurry may be able to suppress shrinkage of the fiber sheet during drying, but the fiber sheet formed after drying can be easily peeled off You have to choose one. Among them, it is preferable to use a suitable one alone or laminated among resin plates or metal plates. For example, resin plates such as acrylic plates, polytetrafluoroethylene plates, polyethylene terephthalate plates, vinyl chloride plates, polystyrene plates, polyvinylidene chloride plates, metal plates such as aluminum plates, zinc plates, copper plates, iron plates, and their surfaces Oxidized ones, stainless steel plates, brass plates and the like can be used. In order to apply the cellulose fiber-containing raw material pulp slurry onto the base material, various coaters capable of applying a predetermined amount of slurry to the base material may be used. For example, roll coater, gravure coater, die coater, curtain coater, spray coater, blade coater, rod coater, air doctor coater, etc. can be used, among them coating methods such as die coater, curtain coater, spray coater, air doctor coater, etc. Is effective for uniform application. For drying, hot air drying, infrared drying, vacuum drying and the like are effective. By forming a cellulose fiber-containing sheet with a coater using a long winding plate on the substrate, it becomes possible to produce a continuous sheet. The cellulose fiber-containing sheet formed on the substrate is wound together with the substrate and used at the time of use. The cellulose fiber-containing sheet may be peeled off before the substrate is wound, and the substrate and the fiber sheet may be wound up.

Regardless of the production method of (A) and (B), the basis weight of the cellulose fiber sheet of the present invention is not particularly limited, but 10 to 500 g / m ² is preferable. More preferably, it is 20-300 g / m < ² >. If it is 10 g / m ² or less, the fiber sheet is easily cut during the production process of the cellulose fiber sheet, and if it is 500 g / m ² or more, the production efficiency is lowered regardless of the production methods (A) and (B).

In order to further improve the strength of the cellulose fiber sheet, it is preferable to add a paper strength agent. For example, urea formaldehyde resin, melamine formaldehyde resin, polyamide polyamine epichlorohydrin resin, vegetable gum, latex, polyethyleneimine, glyoxal, gum, mannogalactan, polyacrylamide resin, polyvinyl alcohol, starch, carboxymethylcellulose, guar gum, urea resin, etc. Examples include force enhancers.
Although the addition method of a paper strength agent is not specifically limited, It is preferable that the addition amount contains 0.1-10 mass parts with respect to 100 mass parts of said pulps. More preferably, it contains 0.5 to 5 parts by mass. If the amount is less than 0.1 parts by mass, the effect of increasing the paper strength is small.

  In addition, when a raw material pulp slurry, which is a cellulose fiber-containing suspension, is applied to paper or a base material to produce a sheet, a filler, a pH adjuster, an antifoaming agent, a thickening agent are used as required. It is possible to add an agent or the like.

It is possible to obtain a higher-density fiber sheet by sufficiently pressing the cellulose fiber sheet in the wet paper state obtained by the production method of (A) and (B), and as a result, a high-strength cellulose fiber A sheet can be obtained. After pressing, it is dried by general drying equipment. Thereafter, the density can be improved by using a machine calendar or a super calendar to further increase the strength. The cellulose fiber sheet density is preferably in the range of 0.90 to 1.20 g / cm ³ .

The aspect ratio of the tensile strength (measured according to JIS P 8113: 1998) of the cellulose fiber sheet used in the present invention is 3.0 or more, and the geometric mean of the longitudinal strength and the transverse strength is 120 MPa or more. preferable. Accordingly, when a composite material with a resin or the like is produced as an application of the paper sheet of the present invention, the composite material has high strength.
When the aspect ratio of the tensile strength of the cellulose fiber sheet is less than 3.0, or when the geometric average of the tensile strength in the longitudinal direction and the tensile strength in the transverse direction is less than 120 MPa, the obtained composite material of cellulose fiber sheet and resin Insufficient strength. In order to efficiently produce using the production methods such as (A) and (B), the aspect ratio of the tensile strength of the cellulose fiber sheet is preferably 3.0 to 6.0, and preferably 3.0 to 4.0. Particularly preferred. To increase the geometric mean value of the longitudinal strength and lateral strength of cellulose fiber sheet, it is possible to add paper strength agent to some extent, but sheet strength is further improved by further refinement of pulp fiber It is easy to get the effect. From the viewpoint of production efficiency and cost, the geometric mean of the strength in the vertical direction and the strength in the horizontal direction is preferably 120 to 300 MPa, and particularly preferably in the range of 120 to 200 MPa.

  Since the cellulose fiber sheet of the present invention has a very high strength compared to conventional fiber sheets, it is one of important applications to use the fiber sheet as a composite material by impregnating the fiber sheet with a thermoplastic or thermosetting resin. It is. Specifically, it can be used for structural members such as automobiles, houses, home appliances, and furniture, but is not limited thereto.

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. However, the present invention is not limited to these examples.

<Preparation of pulp raw material>
Softwood bleached kraft pulp (NBKP) was beaten with a double disc refiner until the irregular freeness reached 100 ml.

<Example 1>
NBKP having an irregular freeness of 100 ml was prepared so as to have a concentration of 0.5%, and fibrillation treatment with mechanical force was performed for 30 minutes with CLEARMIX 2.2S manufactured by M Technique Co., Ltd. to obtain a pulp slurry. At this time, the weight weighted average fiber length was 0.62 mm, and the average fiber width was 19.3 μm.
Acrylamide-dimethylaminoethyl acrylate copolymer as a cationic polyacrylamide resin (100 parts by mass (solid content)) (viscosity average molecular weight by the intrinsic viscosity method: 14 million, cationic charge density: 2.36 meq / 0.1 parts by mass (solid content) of g) and 0.1 mass of acrylamide-dimethylaminoethyl acrylate copolymer (viscosity average molecular weight by the intrinsic viscosity method: 13 million, cationic charge density: 1.08 meq / g) Part (solid content) was blended to prepare a papermaking pulp slurry having a concentration of 0.2% by mass.
The cellulose pulp sheet of the present invention was manufactured by using the paper pulp slurry and making paper using a long paper machine. LL-70E (manufactured by Nippon Filcon) was used as the wire for paper making. The basis weight of the cellulose fiber sheet was 105 g / m ² .

<Example 2>
The fibrillation treatment by mechanical force is 60 minutes, and acrylamide-dimethylaminoethyl acrylate copolymer as a cationic polyacrylamide resin (viscosity average molecular weight by the intrinsic viscosity method: 14 million, cationic charge density: 2.36 meq / g) 0.1 part by mass (solid content) and 1.5 parts by mass of acrylamide-dimethylaminoethyl acrylate copolymer (viscosity average molecular weight by the intrinsic viscosity method: 13 million, cationic charge density: 1.08 meq / g) A cellulose fiber sheet was produced in the same manner as in Example 1 except that. The weight-weighted average fiber length of the pulp slurry after the fibrillation treatment by mechanical force was 0.61 mm, and the average fiber width was 19.6 μm. Moreover, the basic weight of the cellulose fiber sheet was 98 g / m ² .

<Example 3>
The fibrillation treatment by mechanical force is 90 minutes, and acrylamide-dimethylaminoethyl acrylate copolymer as a cationic polyacrylamide resin (viscosity average molecular weight by the intrinsic viscosity method: 13 million, cationic charge density: 1.08 meq / g) 1.5 parts by mass and 0.1 part by mass (solid content) of acrylamide-dimethylaminoethyl acrylate copolymer (viscosity average molecular weight by the intrinsic viscosity method: 8 million, cationic charge density: 2.85 meq / g) A cellulose fiber sheet was produced in the same manner as in Example 1 except that. The weight-weighted average fiber length of the pulp slurry after the fibrillation treatment by mechanical force was 0.60 mm, and the average fiber width was 19.4 μm. Moreover, the basic weight of the obtained fiber sheet was 102 g / m ² .

<Example 4>
A cellulose fiber sheet was produced in the same manner as in Example 1 except that the fibrillation treatment by mechanical force was 120 minutes and the treatment concentration was 1%. The weight-weighted average fiber length of the pulp slurry after the fibrillation treatment by mechanical force was 0.53 mm, and the average fiber width was 19.2 μm. The basis weight of the resultant fiber sheet was 98 g / ^{m 2.}

<Example 5>
A cellulose fiber sheet was produced in the same manner as in Example 1 except that the fibrillation treatment by mechanical force was 120 minutes and the treatment concentration was 2%. The weight-weighted average fiber length of the pulp slurry after the fibrillation treatment by mechanical force was 0.55 mm, and the average fiber width was 18.7 μm. The basis weight of the resultant fiber sheet was 105 g / ^{m 2.}

<Comparative Example 1>
Softwood bleached kraft pulp (NBKP) was beaten with a double disc refiner until the irregular freeness reached 300 ml, and a fibrillation treatment by mechanical force was performed in the same manner as in Example 1. The weight-weighted average fiber length of the pulp slurry at this time was 0.85 mm, and the average fiber width was 21.0 μm. Further, a cellulose fiber sheet was produced in the same manner as in Example 1 except that the paper was made without adding the cationic polyacrylamide resin. The basis weight of the obtained fiber sheet was 71 g / m ² .

<Comparative example 2>
Example 1 except that 1.5 parts by mass (solid content) of Mannich-modified polyacrylamide (viscosity average molecular weight by intrinsic viscosity method: 600,000, cationic charge density: 2.4 meq / g) was added as a cationic polyacrylamide resin. A cellulose fiber sheet was produced in the same manner as described above. The basis weight of the obtained fiber sheet was 90 g / m ² .

<Comparative Example 3>
A copolymer of dimethylaminoethyl methacrylate, acrylamide and acrylic acid as an amphoteric polyacrylamide resin instead of a cationic polyacrylamide resin during papermaking (viscosity average molecular weight by limiting viscosity method: 8 million, cationic charge density: 0 A cellulose fiber sheet was prepared in the same manner as in Example 1 except that 0.8 parts by mass (solid content) of .18 meq / g) was added.

<Comparative example 4>
Example 1 except that 1.2 parts by mass (solid content) of Hoffman-modified polyacrylamide (viscosity average molecular weight by intrinsic viscosity method: 800,000, cationic charge density: 0.90 meq / g) was added as a cationic polyacrylamide resin. A cellulose fiber sheet was produced in the same manner as described above.

<Comparative Example 5>
Example 1 except that 0.6 parts by mass (solid content) of Hoffman-modified polyacrylamide (viscosity average molecular weight by intrinsic viscosity method: 700,000, cationic charge density: 0.34 meq / g) was added as a cationic polyacrylamide resin. A cellulose fiber sheet was produced in the same manner as described above.

[Evaluation method]
<Tensile strength of sheet>
Measured according to JIS P 8113: 1998, the tensile strength per unit area was expressed in MPa.

<Measurement of irregular freeness>
Except for measuring the solid content concentration of the pulp suspension to be measured at 0.1% by mass, it conformed to JIS P 8121-1995.

<Measurement of charge density of acrylamide resin>
Measurement was performed using Charge Analyzer II (manufactured by Rank Brothers).

<Yield>
It calculated | required with the following formula.
Yield (%) = Wire drop concentration / Paper slurry concentration for papermaking (%) × 100

As apparent from Table 1, in Examples 1 to 5, cellulose fiber sheets having high yield and high tensile strength were obtained. On the other hand, in Comparative Example 1, only the yield was small and the tensile strength was small. Moreover, in Comparative Examples 2-5, although the fiber sheet with a high yield was obtained, only the thing with small tensile strength was obtained.

Claims (4)

  A cationic polyacrylamide-based resin having a viscosity average molecular weight of 5 million or more by an intrinsic viscosity method and a cationic charge density of 0.5 to 1.5 meq / g and a cationic charge density of 1.5 to 3.0 meq / A cellulose fiber sheet comprising a cationic polyacrylamide-based resin which is g. The cellulose fiber sheet according to claim 1, wherein the cationic polyacrylamide resin is a copolymer of acrylamide and a compound of the following formula (I).

(In formula (I), R ₁ , R ₂ and R ₃ each independently represent H, a methyl group, an ethyl group or a benzyl group; R ₄ represents H or a methyl group; X represents Cl ⁻ or Br ⁻ . )   0.1 to 2 parts by mass of the cationic polyacrylamide resin having a cationic charge density of 0.5 to 1.5 meq / g and the cationic charge density of 1.5 to 100 parts by mass with respect to 100 parts by mass of the cellulose fiber. The cellulose fiber sheet according to claim 1 or 2, comprising 0.1 to 2 parts by mass of a cationic polyacrylamide resin having a concentration of 3.0 meq / g.   The aspect ratio of the tensile strength measured according to JIS P 8113: 1998 of the cellulose fiber sheet is 3.0 or more, and the geometric mean of the strength in the longitudinal direction and the strength in the transverse direction is 120 to 300 MPa. The cellulose fiber sheet according to any one of claims 1 to 3.