JP2019090158A - Cellulose sheet - Google Patents

Abstract

[PROBLEMS] To provide a water resistant cellulose fiber capable of producing a cellulose sheet having high strength and Young's modulus in a wet state at low cost, and a method for producing the same.
A water-resistant cellulose fiber of the present invention is a cellulose fiber having an average fiber length of 2.0 mm or less and an average fiber width of 50 μm or less, and at least a part of hydroxy groups of cellulose molecules are converted to phosphate groups. And an aluminum ion is bound to the phosphate group. The cellulose sheet of the present invention contains the water resistant cellulose fiber.
【Selection chart】 None

Description

  The present invention relates to a water resistant cellulose fiber and a method for producing the same, a cellulose sheet and a method for producing the same.

Since cellulose fibers have a hydroxyl group, they have hydrophilicity, but when preparing a cellulose sheet such as paper or when using the sheet, the hydrophilicity may be a problem. For example, when the sheet is formed from an aqueous slurry of cellulose fibers if the hydrophilicity is high, the strength of the wet paper is not sufficient, and the wet paper may be broken when pressing for squeezing water, and the wet state Paper strength tends to decrease.
Therefore, polyamide epichlorohydrin, polyamine epichlorohydrin, polyamidoamine epichlorohydrin or their derivatives may be added as a wet strength agent to suppress strength reduction in the wet state (patented) Documents 1 to 4). In this method, it is supposed that the reduction in strength can be suppressed by crosslinking the pulp fibers via the wet paper strengthening agent.
Moreover, the method of chemically modifying a cellulose fiber is known as a method of suppressing the strength reduction in a wet state. For example, after adding nitroxyl radical and sodium bromide to a cellulose fiber, an aqueous solution of sodium hypochlorite is added to oxidize the hydroxy group of the cellulose fiber to an aldehyde group, and then an inter-fiber bonding material is added to form a sheet A method is disclosed (Patent Document 5). By heating in the sheet manufacturing process, it is said that a crosslinking reaction between cellulose or a crosslinking reaction between cellulose and an interfiber bonding material occurs from the aldehyde group as a starting point, and the strength reduction can be suppressed.

Unexamined-Japanese-Patent No. 2010-024608 Unexamined-Japanese-Patent No. 2003-239198 Unexamined-Japanese-Patent No. 2010-063418 Japanese Patent Application Laid-Open No. 2003-023880 JP, 2006-241601, A

In the methods described in Patent Documents 1 to 4, the paper drying step is essential for the expression of wet paper strength. However, when forming a sheet from an aqueous slurry of cellulose fibers, wet paper strength has not developed because it has not yet been heated. Therefore, the sheet tends to be broken when the pressing process is performed for squeezing water in the process of forming the sheet. In addition, the obtained cellulose sheet tended to have a low Young's modulus when it was rewet.
In the method described in Patent Document 5, the step of drying the paper is essential as in the methods described in Patent Documents 1 to 4. Therefore, wet sheet strength does not appear at the time of sheet formation, and oxidation reaction using a catalyst Although the aldehyde group is introduced, if the oxidation proceeds too much, the aldehyde group is converted to a carboxy group, and there is a disadvantage that the wet paper strength improvement effect is exhibited only within a limited range of substituent groups.

An object of the present invention is to provide a water resistant cellulose fiber which can be made water resistant without passing through a heating step, and can produce a cellulose sheet having high tensile strength and Young's modulus in the wet state, and a method for producing the same. I assume.
Another object of the present invention is to provide a cellulose sheet having high strength and Young's modulus in the wet state and a method for producing the same.

The present invention has the following aspects.
[1] A cellulose fiber having an average fiber length of 2.0 mm or less and an average fiber width of 50 μm or less, wherein a phosphate group is introduced into at least a part of hydroxy groups of cellulose molecules, and aluminum ions are attached to the phosphate group. Water resistant cellulose fiber bonded.
[2] A cellulose sheet containing the water resistant cellulose fiber according to [1].

[3] Phosphoric acid group introducing step of introducing phosphoric acid group into cellulose fiber to obtain phosphoric acid modified cellulose fiber, and phosphoric acid modified cellulose fiber, the average fiber length is 2.0 mm or less and the average fiber width is 50 μm or less Water resistance having a mechanical treatment step of obtaining mechanically treated phosphoric acid-modified cellulose fiber by fibrillation treatment or pulverization treatment as described above, and aluminum ion binding step of binding aluminum ion to the mechanical treatment phosphoric acid-modified cellulose fiber Method for producing cellulose fiber.
[4] The method for producing a water-resistant cellulose fiber according to [3], wherein the phosphate group introduction amount in the phosphate-modified cellulose fiber is 0.1 to 3.8 mmol / g in the phosphate group introducing step.
[5] A method for producing a cellulose sheet, comprising the step of making a water resistant cellulose fiber produced by the method for producing a water resistant cellulose fiber according to [3] or [4].

According to the present invention, it is possible to provide a water resistant cellulose fiber which can be made water resistant without passing through a heating step, and can produce a cellulose sheet having high tensile strength and Young's modulus in a wet state, and a method for producing the same.
The cellulose sheet of the present invention has both high strength and Young's modulus in the wet state.
According to the method for producing a cellulose sheet of the present invention, a cellulose sheet having the above effects can be easily produced.

<Water resistant cellulose fiber and method for producing the same>
(Water resistant cellulose fiber)
The water-resistant cellulose fiber is a cellulose fiber in which a phosphate group is introduced to at least a part of the hydroxy group of the cellulose molecule, and an aluminum ion is bonded to the phosphate group. That is, the water resistant cellulose fiber is an aluminum salt of cellulose fiber having a phosphate group.

[Fiber width]
The average fiber width of the water resistant cellulose fiber is cellulose having an average fiber width of 50 μm or less. The average fiber width of the water resistant cellulose fiber is preferably 2 nm to 40 μm, and more preferably 2 nm to 30 μm. When the average fiber width of the water resistant cellulose fiber exceeds the upper limit value, the tensile strength and the Young's modulus of the cellulose sheet obtained from the water resistant cellulose become low. On the other hand, when the average fiber width of the water resistant cellulose fiber is less than the lower limit value, it can no longer be said to be a fiber and is dissolved.
The average fiber width of the water-resistant cellulose fiber can be determined, for example, by measuring the fiber Width using a Kajaani fiber length measurement device (model FS-200) manufactured by Kajaani Automation. Moreover, it can also measure using a scanning electron microscope (SEM), a transmission electron microscope (TEM), etc. according to the width | variety of a fiber.

[Fiber length]
The average fiber length of the water resistant cellulose fiber is 2.0 mm or less, preferably 1.5 mm or less, and more preferably 1.2 mm or less. If the average fiber length of the water resistant cellulose fiber is equal to or less than the upper limit value, the tensile strength and Young's modulus of the cellulose sheet in the dry state can be made higher, and the tensile strength and Young's modulus of the cellulose sheet in the wet state are also Get higher.
The average fiber length can be determined, for example, by measuring the length-weighted average fiber length using a Kajaani fiber length measuring apparatus (model FS-200) manufactured by Kajaani Automation. Moreover, it can also measure using a scanning electron microscope (SEM), a transmission electron microscope (TEM), etc. according to the length of a fiber.

(Method of producing water resistant cellulose fiber)
The method for producing a water resistant cellulose fiber of the present invention comprises at least a phosphoric acid group introducing step, a mechanical treatment step and an aluminum ion bonding step.

[Phosphoric acid group introduction process]
The phosphate group introducing step is a step of introducing a phosphate group into the cellulose fiber raw material to obtain a phosphate-modified cellulose fiber.

The cellulose fiber raw material used in the phosphoric acid group introduction step has cellulose type I crystals. For example, pulp used in ordinary papermaking applications is used, but not particularly limited.
The pulp is selected from wood pulp, non-wood pulp and deinked pulp. As wood pulp, for example, hardwood kraft pulp (LBKP), softwood kraft pulp (NBKP), sulfite pulp (SP), soda pulp (AP), unbleached kraft pulp (UKP), oxygen bleached kraft pulp (OKP), etc. Chemical pulp (SCP), semi-chemical pulp such as chemiground wood pulp (CGP), mechanical pulp such as ground pulp (GP), thermomechanical pulp (TMP, BCTMP), etc. It is not limited. Examples of non-wood pulp include cotton-based pulp such as cotton linter and cotton lint, non-wood-based pulp such as hemp, straw, bagasse and the like, and cellulose isolated from ascidian and seaweed etc., but not particularly limited. Examples of the deinked pulp include, but not particularly limited to, deinked pulp using waste paper as a raw material. The pulp may be used singly or in combination of two or more. Among the above-mentioned pulps, wood pulps containing cellulose and deinked pulps are preferable in terms of availability.

As a method of introduce | transducing a phosphoric acid group into a cellulose fiber, the method of processing a cellulose fiber raw material with the compound or its salt containing a phosphoric acid group is mentioned.
In the treatment with a compound containing a phosphoric acid group or a salt thereof, a compound containing a phosphoric acid group or a salt thereof in at least a part of the hydroxy groups in the cellulose molecule is dehydrated to form a phosphoric acid group.

Examples of the compound containing a phosphoric acid group include phosphoric acid, metaphosphoric acid and polyphosphoric acid.
As a salt with the compound containing a phosphoric acid group, phosphoric acid, metaphosphoric acid, lithium salt of polyphosphoric acid, sodium salt, potassium salt, calcium salt, ammonium salt, organic alkali salt and the like can be mentioned.
The compound containing a phosphoric acid group or its salt may be used individually by 1 type, and may use 2 or more types together.
Among the above, at least one selected from the group consisting of phosphoric acid, sodium phosphate, potassium phosphate, and ammonium phosphate is preferable because it is easy to handle at low cost and the introduction efficiency of the phosphate group is enhanced.

  The mass ratio of the phosphate group-containing compound to the cellulose fiber raw material or the salt thereof is preferably 0.2 to 200 parts by mass as the phosphorus element amount of the phosphate group-containing compound or salt relative to 100 parts by mass of the cellulose fiber 1 to 100 parts by mass is more preferable, and 2 to 50 parts by mass is more preferable. If the ratio of the compound containing a phosphoric acid group or the salt thereof is equal to or more than the above lower limit value, the phosphoric acid group introduction rate becomes high. However, even if the above upper limit is exceeded, the effect of improving the phosphoric acid group introduction rate becomes a plateau, and only the compound or its salt containing the phosphoric acid group is wasted.

  As the heat treatment temperature, a temperature at which phosphoric acid groups can be efficiently introduced is selected while suppressing the thermal decomposition and hydrolysis reaction of the fiber. Specifically, the temperature is preferably 50 to 250 ° C., and more preferably 100 to 170 ° C., but is not particularly limited. In addition, a vacuum dryer may be used for heating.

  It is preferable that the chemical | medical solution containing the compound or its salt containing the phosphoric acid group used at a phosphoric acid group introduction process further contains urea. Urea swells the cellulose and can enhance the permeability of the drug solution.

  In the phosphate group introducing step, the phosphate group introduction amount in the phosphate-modified cellulose fiber is preferably 0.1 to 3.8 mmol / g, and more preferably 0.50 to 3.8 mmol / g. If the phosphoric acid group introduction amount is equal to or more than the lower limit value, the water resistance of the cellulose sheet can be further improved.

Here, about the introduction quantity to the textiles material of a phosphoric acid group, TAPPI T237 cm-08 (2008) can be computed and applied. Specifically, sodium hydrogencarbonate (NaHCO ₃ ) / sodium chloride (NaCl) of the test solution used in the above test method enables calculation of the introduction amount of the acidic group introduced into the fiber material to a wider range. A test solution in which 0.84 g / 5.85 g is dissolved and diluted in 1000 ml of distilled water is changed to a test solution in which 1.60 g of sodium hydroxide is dissolved and diluted in 1000 ml of distilled water. It calculates according to TAPPI T 237 cm-08 (2008) except having made the difference of a calculated value into substantial substitution introduction quantity.

  Moreover, since the said acidic group introduction | transduction amount calculation method is fundamentally the introduction | transduction amount calculation method of a monovalent | monohydric acid group (carboxy group), about calculation of the introduction | transduction amount of the phosphoric acid group which is a polyvalent acid group. The value obtained by dividing the substituent introduction amount obtained as the introduction amount of the monovalent acidic group by the acid value of the phosphate group is the introduction amount of the phosphoric acid group.

  The introduction amount of the phosphate group can be adjusted by the addition amount of the compound containing the phosphate group or the salt thereof, the addition amount of urea, the reaction temperature and the reaction time. In a suitable range, as the addition amount of the compound containing a phosphoric acid group or a salt thereof and urea is increased, and the reaction temperature is high and the reaction time is long, the introduced amount of phosphoric acid group is increased.

The phosphate-modified cellulose fiber may be subjected to an alkali treatment, if necessary.
Although it does not specifically limit as the method of alkali treatment, For example, the method of immersing a phosphoric acid modified cellulose fiber in an alkali solution is mentioned.
The alkali compound contained in the alkali solution may be an inorganic alkali compound or an organic alkali compound.
Examples of the inorganic alkali compound include lithium hydroxide, sodium hydroxide, potassium hydroxide and ammonia.
Examples of the organic alkali compound include tetramethyl ammonium hydroxide, tetraethyl ammonium hydroxide, tetrapropyl ammonium hydroxide, tetrabutyl ammonium hydroxide, phenylamine (aniline), diphenylamine, and triphenylamine.
The solvent in the alkaline solution may be either water or an organic solvent, but a polar solvent (a polar organic solvent such as water or alcohol) is preferable, and an aqueous solvent containing at least water is more preferable.
By performing the alkali treatment, the amount of energy required for the subsequent mechanical treatment process is reduced.

[Machine processing process]
The mechanical processing step is a step of fibrillating or refining the phosphate-modified cellulose fiber so as to have an average fiber length of 2.0 mm or less and an average fiber width of 50 μm or less to obtain a mechanically treated phosphate-modified cellulose fiber It is.
Here, fibrillation is to loosen and fluff fibers. Refinement is to finely grind or cut fibers. In the present specification, the fibrillation process and the micronization process may be collectively referred to as "machine process".
By increasing the number of phosphate groups exposed on the fiber surface by mechanical treatment, the effect of the aluminum ion bonding step described later is enhanced.

  Prior to mechanical treatment, the phosphate-modified cellulose fiber is preferably diluted with water to a dispersion having a cellulose concentration of 0.1 to 10% by mass. The cellulose concentration of the phosphoric acid-modified cellulose fiber dispersion is more preferably 0.2 to 5% by mass, and still more preferably 0.3 to 4% by mass. If the cellulose concentration of the phosphate-modified cellulose fiber is above the lower limit value, the fibrillation efficiency or the refining efficiency becomes high, and if it is below the above upper limit value, it is possible to prevent an increase in viscosity during processing.

  In the mechanical processing step, an apparatus or the like for wet grinding can be used as appropriate. Pulverizers include high-speed fibrillation machines, grinders (millers), high-pressure homogenizers and ultra-high pressure homogenizers, high-pressure collision crushers, ball mills, bead mills, disc refiners, conical refiners, twin screw kneaders, vibration mills, high speed A homomixer under rotation, an ultrasonic dispersion machine, a beater, etc. are mentioned.

  The phosphate group of the phosphate-modified cellulose fiber to be used in the mechanical treatment step is preferably neutralized with a monovalent cation. The monovalent cation includes lithium ion, sodium ion, potassium ion, ammonium ion, organic ammonium ion and the like. If the phosphate groups are neutralized with these ions, the osmotic and charge repelling effects increase the efficiency of the mechanical treatment.

[Aluminum ion bonding process]
The aluminum ion bonding step is a step of bonding aluminum ions to the phosphate group of the machine-treated phosphate-modified cellulose fiber.
Specifically, in the aluminum ion bonding step, a water-soluble aluminum salt is added to the aqueous dispersion of machine-treated phosphoric acid-modified cellulose fiber. In water, aluminum ions are generated from aluminum salts, and the aluminum ions react with the phosphate group of the mechanically treated phosphate-modified cellulose fiber to bind to the phosphate group to the aluminum ion.
By bonding an aluminum ion to a phosphate group, a water resistant cellulose fiber comprising an aluminum salt of a cellulose fiber having a phosphate group can be obtained.
The water resistant cellulose fiber obtained may be dewatered and dried as required.

Examples of the aluminum salt used as an aluminum ion source in the aluminum ion bonding step include aluminum sulfate, aluminum chloride, aluminum acetate, sodium aluminate and the like. Among these, aluminum sulfate and aluminum chloride are preferable.
An aluminum salt may be used individually by 1 type, and may use 2 or more types together.

  The addition amount of the aluminum ion to be bonded to the phosphate group of the mechanically treated phosphate-modified cellulose fiber is 0.2 P to 2.0 P [mol] with respect to the phosphate group amount P [mol] introduced to the phosphate-modified cellulose fiber ] Is preferable and 0.3P-1.8P [mol] are more preferable.

(Action effect)
Normal cellulose fibers have low water resistance because the hydroxyl groups of cellulose molecules tend to hydrogen bond with water molecules. Although the reason why the water resistant cellulose fiber of the present invention has high water resistance is not clear, the inorganic substance aluminum phosphate (AlPO ₄ ) has low hydrophilicity and is insoluble in water. Therefore, like aluminum phosphate, it is presumed that the phosphate-modified cellulose fiber in which an aluminum ion is bound to a phosphate group has low hydrophilicity and high water resistance.
Moreover, since the phosphate group introduce | transduced into cellulose is a bivalent anion and aluminum ion is a trivalent cation, it is also considered to be advantageous that there are many bonding contacts.
The cellulose sheet obtained from the water-resistant cellulose fiber of the present invention, which has high water resistance, is not only difficult to reduce the tensile strength even when it is wet, but also the Young's modulus does not easily decrease. This is because the general wet paper strength agent is randomly bonded to the cellulose fiber, whereas in the present invention, the cellulose fiber surface having a phosphate group introduced therein is more susceptible to mechanical treatment and more fibrillated. It is speculated that the aluminum phosphate structure is formed or concentrated and concentrated there to form a highly water resistant aluminum phosphate structure.
In the water resistant cellulose fiber of the present invention, it is not necessary to react the wet strength agent with the cellulose fiber by heating in order to improve the water resistance, and the range of the amount of substituents that can be introduced is wider. A great improvement in water resistance can be obtained.

<Cellulose sheet and method for producing the same>
(Cellulose sheet)
The cellulose sheet of the present invention is a sheet containing water resistant cellulose fibers.
The cellulose sheet may contain, in addition to the water resistant cellulose fiber, if necessary, fillers, sizing agents, paper additives, chemical additives such as retention aids, glues, and other fibers.

In the cellulose sheet of the present invention, the Young's modulus residual ratio in the wet state can be easily made 5% or more. Young's modulus is a value measured according to JIS P8135. The Young's modulus residual ratio is obtained by measuring the Young's modulus of the cellulose sheet before and after being wet with water, and [(Young's modulus of the cellulose sheet after wetting) / (Young's modulus of the cellulose sheet before wetting)] × 100% Is the value obtained by
When the Young's modulus residual ratio in the wet state is 5% or more, the decrease in Young's modulus when moistened is sufficiently suppressed.
Moreover, in the cellulose sheet of this invention, the tensile strength residual ratio in a wet state can be easily made 15% or more. The tensile strength is a value measured according to JIS P8135. The tensile strength residual ratio is obtained by measuring the Young's modulus of the cellulose sheet before and after being wetted with water, and [(the tensile strength of the cellulose sheet after the wetting) / (the tensile strength of the cellulose sheet before the wetting)] × 100% Is the value obtained by
If the tensile strength residual ratio in the wet state is 15% or more, the reduction in tensile strength upon wetting is sufficiently suppressed.

The density of the cellulose sheet is preferably 0.3 to 1.3 g / cm ³ . If the density of the cellulose sheet is within the above range, the Young's modulus residual ratio can be more easily 5% or more, and the tensile strength residual ratio can be more easily 15% or more.

(Method of producing cellulose sheet)
The method for producing a cellulose sheet of the present invention comprises the step of making the water resistant cellulose fiber.
Specifically, in the papermaking process, a slurry containing water resistant cellulose fibers is dewatered on a papermaking wire to obtain a wet sheet, and then the wet sheet is dried.
The slurry containing water resistant cellulose fibers is supplied to the papermaking wire such that the basis weight of the obtained cellulose sheet is preferably 5 to 200 g / m ² , more preferably 10 to 150 g / m ² . The obtained wet sheet can be easily exfoliated from a papermaking wire as basic weight of a cellulose sheet is more than the above-mentioned lower limit, and it is suitable for continuous production. On the other hand, dehydration time can be shortened as the basis weight of a cellulose sheet is below the said upper limit, and productivity can be made high.
The method for drying the wet sheet is not particularly limited. For example, a method of supplying the wet sheet to a hot air drying furnace and heating by hot air, applying a method of winding the wet sheet around the heated drum dryer, and the like are applied. Can.

  The above-mentioned paper making process can use a paper machine used in ordinary paper production. As a papermaking machine, continuous papermaking machines such as a long screen type, a circular net type, a tilting type and the like can be mentioned.

(Action effect)
Since the cellulose sheet of the present invention has water resistant cellulose fibers, its strength and Young's modulus are maintained even when it is wetted with water.
In the method for producing a cellulose sheet of the present invention, a cellulose sheet is produced by making water-resistant cellulose fibers, so there is no need to react the wet paper strengthening agent with the cellulose fibers by heating, and Because of the wide width, it is possible to obtain a cellulose sheet with greater water resistance.

  EXAMPLES The present invention will be specifically described below by showing Examples and Comparative Examples. However, the present invention is not limited to the following examples.

(Production Example 1)
An unrefined softwood kraft pulp (manufactured by Oji Paper Co., Ltd.) was impregnated with a chemical solution consisting of urea, sodium phosphate (molar ratio of phosphorus atom to sodium atom Na / P = 1.45), and water. Subsequently, it squeezed and the excessive chemical | medical solution was squeezed off and the chemical | medical solution impregnation pulp was obtained. The chemical-impregnated pulp contained 95 parts by mass of urea, 40 parts by mass of sodium phosphate as phosphorus atoms, and 120 parts by mass of water with respect to 100 parts by mass of the dry-dried pulp.
The chemical-impregnated pulp was dried and heated in an oven heated to 150 ° C. to introduce phosphoric acid groups into cellulose fibers of the pulp.
Ion-exchanged water is poured into a drug-impregnated pulp containing cellulose fibers into which phosphate groups have been introduced, stirred and dispersed uniformly, and then repeated operations of filtration dewatering to obtain a dewatered sheet are sufficient for excess drug solution. It was washed away. Subsequently, it diluted with ion exchange water so that a cellulose fiber density | concentration might be 2 mass%, 1N sodium hydroxide aqueous solution was added little by little, stirring, and the pulp slurry of pH 11-13 was obtained. Thereafter, the pulp slurry is dewatered to obtain a dewatered sheet, and then ion-exchanged water is poured again, and after stirring and dispersing uniformly, filtration dewatering to obtain a dewatered sheet is repeated to obtain excess water. The sodium oxide was thoroughly washed away to obtain phosphate-modified cellulose fiber A. The phosphate-modified cellulose fiber A had a introduced amount of phosphate groups of 0.804 mmol / g as determined by titration.
The above-mentioned phosphate-modified cellulose fiber A was diluted with ion-exchanged water so that the cellulose concentration would be 2% by mass, and then passed 5 times through a single disc refiner whose clearance was set to 50 μm to obtain machine-treated phosphate-modified cellulose fiber A . The length average fiber length obtained from the projected view of machine-treated phosphate-modified cellulose fiber A was 1.22 mm, and the average fiber width was 27.4 μm.

(Production Example 2)
In the same manner as in Production Example 1 above, a drug solution-impregnated pulp containing cellulose fibers into which phosphate groups were introduced was obtained.
Ion-exchanged water was poured into a drug solution-impregnated pulp containing cellulose fibers into which phosphate groups were introduced, and the mixture was stirred and dispersed uniformly. Next, after repeating the operation of obtaining the dewatered sheet by filtration and dehydration, the excess chemical solution was sufficiently washed away, and then diluted with deionized water so that the cellulose fiber concentration was 2 mass%. Subsequently, 1 N sulfuric acid aqueous solution was added little by little, stirring, and the pulp slurry of pH 2-3 was obtained. Thereafter, the pulp slurry was dewatered to obtain a dewatered sheet, and then ion-exchanged water was poured again and stirred to disperse uniformly. Next, the operation of obtaining dehydrated sheets by filtration dewatering was repeated to wash away excess sulfuric acid sufficiently, and then diluted with deionized water so that the cellulose fiber concentration became 2 mass%. Then, while stirring, 1 N aqueous ammonia solution was added little by little to obtain a pulp slurry having a pH of 11-12. Thereafter, the pulp slurry is dewatered to obtain a dewatered sheet, and then ion-exchanged water is poured again, and after stirring and dispersing uniformly, filtration ammonia is repeated to obtain a dewatered sheet, whereby excess ammonia is obtained. Was thoroughly washed away to obtain a cellulose fiber B. The phosphate-modified cellulose fiber B had a phosphate group introduction amount of 0.804 mmol / g, which was determined by a titration method.
The above-mentioned phosphate-modified cellulose fiber B was diluted with ion-exchanged water so that the cellulose concentration would be 2% by mass, and then passed through a single disc refiner whose clearance was set to 50 μm ten times to obtain machine-treated phosphate-modified cellulose fiber B . The length average fiber length obtained from the projected view of machine-treated phosphate-modified cellulose fiber B was 0.98 mm, and the average fiber width was 26.3 μm.

(Production Example 3)
Un-beaten softwood kraft pulp (manufactured by Oji Paper Co., Ltd.) was diluted with ion-exchanged water to a concentration of 1% by mass to form a slurry. Next, 1.6% by mass and 10% by mass of pulp mass of 2,2,6,6-tetramethyl-1-piperidine-N-oxyl (TEMPO) and sodium bromide, respectively, are added, and three minutes for 15 minutes. Stirred by a motor.
Then, the reaction was initiated by adding 3.8 mmol / g of a 0.75 M aqueous solution of sodium hypochlorite to 1 g of pulp. During the reaction, 0.5 M aqueous sodium hydroxide solution was added dropwise to keep the pH at about 10. Thereafter, the reaction product was separated by filtration, sufficiently washed with ion exchange water, and then added to an acetic acid buffer adjusted to pH 4.8 so that the pulp concentration was 1% by mass.
Next, sodium chlorite was added in an amount of 0.2 mmol / g to 1 g of pulp, and allowed to stand for 48 hours. The reaction product after standing was separated by filtration, and sufficiently washed with ion exchanged water to obtain a carboxylic acid-modified cellulose fiber. The carboxylic acid-modified cellulose fiber had a carboxy group introduction amount of 1.17 mmol / g as determined by titration.
The carboxylic acid-modified cellulose fiber was diluted with ion-exchanged water so that the cellulose concentration was 2% by mass, and then passed through a single disc refiner whose clearance was set to 50 μm five times to obtain a mechanically treated carboxylic acid-modified cellulose fiber. The length average fiber length obtained from the projected view of the machine-treated carboxylic acid-modified cellulose fiber was 0.97 mm, and the average fiber width was 27.0 μm.

Example 1
The machine-treated phosphoric acid-modified cellulose fiber A obtained in Production Example 1 was diluted with ion exchange water so that the cellulose concentration was 0.2 mass%, to obtain a slurry. The slurry was fractionated so that the sheet basis weight obtained was 20 g / m ^2, and the aqueous solution of aluminum sulfate diluted to 0.3% by mass was added to 8% by mass of the amount of aluminum sulfate based on the mass of cellulose fiber Was added at a rate of Then, after stirring, it was dewatered using a plastic wire (LL 70 E, manufactured by Nippon Filcon, filtration area 210 mm × 298 mm) as a filter medium, and paper was made to obtain a wet paper containing mechanically treated phosphate-modified cellulose fiber A .
Two sheets of absorbent paper were placed on the obtained wet paper, and the absorbent paper was rolled using a coach roll defined in JIS P 8222 to absorb excess water. Furthermore, the wet paper was sandwiched between fresh absorbent paper and dried with a cylinder drier at a surface temperature of 120 ° C. to obtain a cellulose sheet.

(Example 2)
A cellulose sheet was obtained in the same manner as in Example 1, except that the mechanically treated phosphoric acid modified cellulose fiber B was used instead of the mechanically treated phosphoric acid modified cellulose fiber A.

(Comparative example 1)
A wet paper web was obtained in the same manner as in Example 2 except that the aqueous solution of aluminum sulfate was not added to the slurry containing machine-treated phosphate-modified cellulose fiber B in Example 2. Two sheets of absorbent paper were placed on the obtained wet paper, and the absorbent paper was rolled using a coach roll specified in JIS P 8222 to try to absorb excess water. However, due to the pressure of the coating roll, the wet paper web breaks down and adheres to the absorbent paper, and the wet paper web of the mechanically treated phosphate-modified cellulose fiber B can not be peeled off, and a cellulose sheet can not be obtained.

(Comparative example 2)
In Example 2, instead of the aluminum sulfate aqueous solution, a cationic coagulant (FS-614 0.03% by mass aqueous solution manufactured by Arakawa Chemical Co., Ltd.) was added at a ratio of 500 ppm in terms of dry weight to cellulose fiber mass. The other procedures were the same as in Example 2 to obtain a wet paper.
Two sheets of absorbent paper were placed on the obtained wet paper, and the absorbent paper was rolled using a coach roll specified in JIS P 8222 to try to absorb excess water. However, due to the pressure of the coating roll, the wet paper web breaks down and adheres to the absorbent paper, and the wet paper web of the mechanically treated phosphate-modified cellulose fiber B can not be peeled off, and a cellulose sheet can not be obtained.

(Comparative example 3)
In Example 2, instead of the aluminum sulfate aqueous solution, 0.1 M hydrochloric acid was added until the pH of the slurry having a cellulose concentration of 0.2% by mass reached 4. The other procedures were the same as in Example 2 to obtain a wet paper. Two sheets of absorbent paper were placed on the obtained wet paper, and the absorbent paper was rolled using a coach roll specified in JIS P 8222 to try to absorb excess water. However, due to the pressure of the coating roll, the wet paper web breaks down and adheres to the absorbent paper, and the wet paper web of the mechanically treated phosphate-modified cellulose fiber B can not be peeled off, and a cellulose sheet can not be obtained.

(Comparative example 4)
In Example 2, instead of the aluminum sulfate aqueous solution, an aqueous calcium chloride solution diluted to 0.3% by mass was added at a ratio such that the amount of calcium chloride added was 8% by mass with respect to the mass of the cellulose fiber. The other procedures were the same as in Example 2 to obtain a wet paper. Two sheets of absorbent paper were placed on the obtained wet paper, and the absorbent paper was rolled using a coach roll specified in JIS P 8222 to try to absorb excess water. However, due to the pressure of the coating roll, the wet paper web breaks down and adheres to the absorbent paper, and the wet paper web of the mechanically treated phosphate-modified cellulose fiber B can not be peeled off, and a cellulose sheet can not be obtained.

(Comparative example 5)
In Example 2, instead of the aluminum sulfate aqueous solution, a magnesium chloride aqueous solution diluted to 0.3% by mass was added at a ratio such that the amount of magnesium chloride added was 8% by mass with respect to the mass of the cellulose fiber. The other procedures were the same as in Example 2 to obtain a wet paper. Two sheets of absorbent paper were placed on the obtained wet paper, and the absorbent paper was rolled using a coach roll specified in JIS P 8222 to try to absorb excess water. However, due to the pressure of the coating roll, the wet paper web breaks down and adheres to the absorbent paper, and the wet paper web of the mechanically treated phosphate-modified cellulose fiber B can not be peeled off, and a cellulose sheet can not be obtained.

(Comparative example 6)
In Example 2, instead of the aluminum sulfate aqueous solution, an aqueous calcium chloride solution diluted to 0.3% by mass was added at a ratio such that the amount of calcium chloride added was 16% by mass based on the mass of the cellulose fiber. The rest of the procedure was carried out in the same manner as in Example 2 to obtain a cellulose sheet.

(Comparative example 7)
In Example 2, instead of the aluminum sulfate aqueous solution, a magnesium chloride aqueous solution diluted to 0.3% by mass was added at a ratio such that the amount of magnesium chloride added was 20% by mass with respect to the mass of the cellulose fiber. The rest of the procedure was carried out in the same manner as in Example 2 to obtain a cellulose sheet.

(Comparative example 8)
In Example 2, instead of the aluminum sulfate aqueous solution, a wet paper strength agent (Arakawa Chemical Alafix 255) diluted to 0.3% by mass is added at a ratio of 0.5% by mass based on the mass of the cellulose fiber did. The other procedures were the same as in Example 2 to obtain a wet paper. Two sheets of absorbent paper were placed on the obtained wet paper, and the absorbent paper was rolled using a coach roll specified in JIS P 8222 to try to absorb excess water. However, due to the pressure of the coating roll, the wet paper web breaks down and adheres to the absorbent paper, and the wet paper web of the mechanically treated phosphate-modified cellulose fiber B can not be peeled off, and a cellulose sheet can not be obtained.

(Comparative example 9)
A cellulose sheet was obtained in the same manner as Example 1, except that the machine-treated carboxylic acid-modified cellulose fiber obtained in Production Example 3 was used instead of the machine-treated phosphate-modified cellulose fiber A.

(Comparative example 10)
In Example 1, in place of machine-treated phosphoric acid-modified cellulose fiber A, a beaten cellulose fiber (length average fiber length 0.46 mm, average fiber width 24.7 μm obtained from Oji Paper Co., Ltd. projection view, unmodified) is used. A cellulose sheet was obtained in the same manner as in Example 1 except that the aluminum sulfate aqueous solution was not added.

(Comparative example 11)
A cellulose sheet was obtained in the same manner as in Comparative Example 10 except that the aluminum sulfate aqueous solution diluted to 0.3% by mass was added at a ratio of 8% by mass with respect to the mass of the cellulose fiber.

(Comparative example 12)
Comparative Example except that a wet paper strength agent (Arakawa Chemical Arafix 255) diluted to 0.3% by mass was added instead of the aluminum sulfate aqueous solution at a ratio of 0.5% by mass with respect to the mass of cellulose fiber In the same manner as 10, a cellulose sheet was obtained.

<Measurement of paper quality>
The tensile strength and Young's modulus in the dry state of the sheet obtained in each Example and each Comparative Example are set to JIS
It measured based on P 8113.
The tensile strength and Young's modulus in the wet state of the sheet obtained in each example and each comparative example
It measured according to 8135.
The tensile strength residual ratio was determined from the formula [(tensile strength of wet cellulose sheet) / (tensile strength of wet cellulose sheet)] × 100%.
The Young's modulus residual ratio was determined from the formula [(Young's modulus of the cellulose sheet after wetting) / (Young's modulus of the cellulose sheet before wetting)] × 100%.
The tensile strength and Young's modulus of the cellulose sheet in a dry state, the tensile strength and Young's modulus of the cellulose sheet in a wet state, the tensile strength residual ratio and the Young's modulus residual ratio are shown in Tables 1 and 2.

In Examples 1 and 2 in which aluminum sulfate is added to the mechanically treated phosphoric acid-modified cellulose fiber, the tensile strength residual ratio and Young's modulus residual ratio of the obtained cellulose sheet are high, that is, the wet paper strength is high and the water resistance is excellent. The
In Comparative Example 1 in which aluminum sulfate was not added, the wet paper web was broken due to the pressure of the coating roll, and the paper stuck to the absorbent paper, so that a cellulose sheet could not be obtained. It is considered that the phosphate group of the phosphate-modified cellulose fiber is an ammonium salt and is highly hydrophilic.
In Comparative Example 2 in which a cationic coagulant was added instead of aluminum sulfate, the wet paper web was broken due to the pressure of the coating roll and adhered to the absorbent paper, so that a cellulose sheet could not be obtained. Since the phosphate group of the phosphate-modified cellulose fiber is an organic ammonium salt and is strongly hydrophilic, and the cationic coagulant has a large molecular weight, it is presumed that it can not sufficiently interact with the phosphate group.
In Comparative Example 3 in which hydrochloric acid was added until the slurry pH became 4 instead of aluminum sulfate, the wet paper broke due to the pressure of the coating roll, and the paper stuck to the absorbent paper, and a cellulose sheet could not be obtained. Although the slurry pH is lowered by the addition of aluminum sulfate, it is considered that lowering the slurry pH alone is still strongly hydrophilic.
In Comparative Example 4 in which calcium chloride is added at 8% by mass with respect to the fiber mass instead of aluminum sulfate, the wet paper web breaks down due to the pressure of the coating roll and adheres to absorbent paper, and a cellulose sheet can be obtained It was not.
In Comparative Example 5 in which 8% by mass of magnesium chloride is added to the fiber mass instead of aluminum sulfate, the wet paper web breaks down due to the pressure of the coating roll and adheres to the absorbent paper, and a cellulose sheet can be obtained. It was not.
In Comparative Example 6 in which calcium chloride was added in an amount of 16% by mass with respect to the fiber mass instead of aluminum sulfate, both the tensile strength residual ratio and the Young's modulus residual ratio of the obtained cellulose sheet were low.
In Comparative Example 7 in which 20% by mass of magnesium chloride was added with respect to the fiber mass instead of aluminum sulfate, both the tensile strength residual ratio and the Young's modulus residual ratio of the obtained cellulose sheet were low.
In Comparative Example 8 in which 0.5% by mass of a wet paper strengthening agent with respect to the fiber mass was added instead of aluminum sulfate, the wet paper broke due to the pressure of the coat roll and adhered to the absorbent paper, cellulose sheet Could not get. It is considered that the wet paper strengthening effect is not obtained because drying and heating processes have not been performed until the wet paper is obtained.
In Comparative Example 9 in which a carboxylic acid-modified cellulose fiber was used instead of the phosphoric acid-modified cellulose fiber, both the tensile strength residual ratio and the Young's modulus residual ratio of the obtained cellulose sheet were low.
In Comparative Examples 10 to 12 using cellulose fibers which were not phosphate-modified, both the tensile strength residual ratio and the Young's modulus residual ratio of the obtained cellulose sheet were low.

As described above, the cellulose sheets of Examples 1 and 2 not only have a high tensile strength residual rate, but also have a high Young's modulus residual rate and are excellent in wet strength. The maintenance of Young's modulus in the wet state was an effect not obtained by the addition of a wet strength agent.
Aluminum phosphate (AlPO ₄ ) is an insoluble substance which is insoluble in water, and it is presumed that when a similar structure to this substance is formed on the surface of cellulose fibers, the hydrophilicity will be low. Moreover, since the phosphate group introduced into cellulose is a divalent anion and the aluminum ion is a trivalent cation, there are many charge contacts. Therefore, it is presumed that the phosphate-modified cellulose fiber in which aluminum ions are bonded to the phosphate group has low hydrophilicity and high water resistance.
Moreover, it is estimated that the water resistance of a cellulose sheet became high by producing from the cellulose fiber with high water resistance.
In contrast, calcium phosphate (Ca ₃ (PO ₄ ) ₂ ), magnesium phosphate (Mg ₃ (PO ₄ ) ₂ ), and aluminum acetate (Al (COO) ₃ ) are slightly soluble in water. Also, compared to aluminum phosphate, there are fewer charge contacts. Therefore, when calcium ions are bound to the phosphate group, magnesium ions are bound to the phosphate group, and when aluminum ions are bound to the carboxy group, the hydrophilicity does not decrease and the water resistance decreases. It is guessed. Moreover, it is estimated that the water resistance of a cellulose sheet became low by having produced from a cellulose fiber with low water resistance.

Claims (3)

  Cellulose fibers having an average fiber length of 2.0 mm or less and an average fiber width of 50 μm or less, wherein at least a part of hydroxy groups of cellulose molecules are converted to phosphate groups, and aluminum ions are bonded to the phosphate groups A cellulose sheet containing water resistant cellulose fiber and having a Young's modulus residual ratio of 5% or more in a wet state.   Cellulose fibers having an average fiber length of 2.0 mm or less and an average fiber width of 50 μm or less, wherein at least a part of hydroxy groups of cellulose molecules are converted to phosphate groups, and aluminum ions are bonded to the phosphate groups A cellulose sheet containing water resistant cellulose fibers and having a residual tensile strength in a wet state of 15% or more.   The cellulose sheet according to claim 1 or 2, wherein the phosphoric acid group introduction amount in the cellulose fiber is 0.1 to 3.8 mmol / g.