JP7395836B2 - Method for producing fine fibrous cellulose-containing dispersion - Google Patents

Description

The present invention relates to a method for producing a dispersion containing fine fibrous cellulose.

Conventionally, cellulose fibers have been widely used in clothing, absorbent articles, paper products, and the like. As cellulose fibers, in addition to fibrous cellulose having a fiber diameter of 10 μm or more and 50 μm or less, fine fibrous cellulose having a fiber diameter of 1 μm or less is also known. Fine fibrous cellulose is attracting attention as a new material, and its uses are wide-ranging. For example, sheets, resin composites, and thickeners containing fine fibrous cellulose are being developed.

For example, Patent Document 1 includes a foreign matter removal step in which a cellulose fiber raw material dispersion containing a cellulose fiber raw material is treated to remove foreign matter, and a micronization step in which a cellulose fiber raw material dispersion that has been subjected to a foreign matter removal treatment is subjected to a finer treatment. , discloses a method for producing fine cellulose fibers. Further, Patent Document 2 discloses a method for filtering a cellulose nanofiber dispersion, which includes a step of filtering the cellulose nanofiber dispersion under pressure or reduced pressure.

Japanese Patent Application Publication No. 2014-125689 International Publication No. 2017/078084

When producing a dispersion containing fine fibrous cellulose, a filtration process may be provided to remove foreign substances and the like. However, when a dispersion containing fine fibrous cellulose is subjected to filtration treatment, clogging of the filter medium tends to occur, which causes a problem in that the filtration efficiency decreases.
Therefore, an object of the present invention is to provide a method for producing a fine fibrous cellulose-containing dispersion having a filtration treatment step with excellent filtration efficiency.

As a result of intensive studies to solve the above problems, the present inventors have discovered that a phosphorus oxoacid group or a substituent derived from a phosphorus oxoacid group It has been found that the filtration efficiency can be improved by using a dispersion containing fibrous cellulose having the following properties and using at least one selected from a filter medium and a filter aid in the filtration process.
Specifically, the present invention has the following configuration.

[1] A method for producing a fibrous cellulose-containing dispersion comprising a step of filtering a dispersion containing fibrous cellulose having a fiber width of 1000 nm or less and having a phosphorus oxo acid group or a substituent derived from a phosphorus oxo acid group. There it is,
A method for producing a fibrous cellulose-containing dispersion, wherein in the filtration step, at least one selected from a filter medium and a filter aid is used.
[2] The method for producing a fibrous cellulose-containing dispersion according to [1], wherein a filter is used as a filter medium in the filtration process.
[3] The method for producing a fibrous cellulose-containing dispersion according to [2], wherein the filter is composed of at least one member selected from the group consisting of resins, metals, and ceramics.
[4] The method for producing a fibrous cellulose-containing dispersion according to [2] or [3], wherein the opening of the filter is 0.1 μm or more and 5 mm or less.
[5] The method for producing a fibrous cellulose-containing dispersion according to any one of [1] to [4], wherein a filter medium and a filter aid are used in the filtration process.

According to the present invention, there is provided a method for producing a fine fibrous cellulose-containing dispersion having a filtration treatment step with excellent filtration efficiency.

FIG. 1 is a graph showing the relationship between the amount of NaOH added dropwise to a fibrous cellulose-containing dispersion having phosphorus oxoacid groups and pH. FIG. 2 is a graph showing the relationship between the amount of NaOH dropped and pH for a dispersion containing fibrous cellulose having a carboxy group.

In the following, the present invention will be explained in detail. Although the constituent elements described below may be explained based on typical embodiments and specific examples, the present invention is not limited to such embodiments.

(Method for producing a fine fibrous cellulose-containing dispersion) The method for producing a fibrous cellulose-containing dispersion of the present invention is to produce a fibrous cellulose-containing dispersion having a fiber width of 1000 nm or less and having a phosphorus oxoacid group or a substituent derived from a phosphorus oxoacid group. The method includes a step of filtering a dispersion containing cellulose. Here, in the filtration process, at least one selected from a filter medium and a filter aid is used. In this specification, fibrous cellulose having a fiber width of 1000 nm or less is also referred to as fine fibrous cellulose or CNF. Moreover, the process of performing filtration treatment is also referred to as a filtration treatment process.

In the method for producing a fine fibrous cellulose-containing dispersion of the present invention, fibrous cellulose having a phosphorus oxo acid group or a substituent derived from a phosphorus oxo acid group is used, and further, in the filtration treatment step, a fibrous cellulose is selected from a filter medium and a filter aid. By using at least one of these, the filtration efficiency in the filtration process can be increased. By increasing the filtration efficiency, as a result, the production efficiency of the fine fibrous cellulose-containing dispersion also increases. Thus, according to the production method of the present invention, a fine fibrous cellulose-containing dispersion can be efficiently produced.

The method for producing a fine fibrous cellulose-containing dispersion of the present invention further includes a defibration treatment step. The above-mentioned filtration process is provided after the fibrillation process.
Below, a method for producing a fine fibrous cellulose-containing dispersion will be specifically explained.

<Fiber raw materials>
Fine fibrous cellulose is produced from a fibrous raw material containing cellulose. The fiber raw material containing cellulose is not particularly limited, but it is preferable to use pulp because it is easily available and inexpensive. Pulps include, for example, wood pulp, non-wood pulp, and deinked pulp. Examples of wood pulp include, but are not limited to, hardwood kraft pulp (LBKP), softwood kraft pulp (NBKP), sulfite pulp (SP), dissolving pulp (DP), soda pulp (AP), and unbleached kraft pulp (UKP). ) and chemical pulp such as oxygen bleached kraft pulp (OKP), semi-chemical pulp such as semi-chemical pulp (SCP) and chemical ground wood pulp (CGP), ground wood pulp (GP) and thermomechanical pulp (TMP, BCTMP), etc. Examples include mechanical pulp. Examples of the non-wood pulp include, but are not particularly limited to, cotton-based pulps such as cotton linters and cotton lint, and non-wood-based pulps such as hemp, wheat straw, and bagasse. Deinked pulp is not particularly limited, but includes, for example, deinked pulp made from waste paper. The pulp of this embodiment may be used alone or in combination of two or more of the above. Among the above-mentioned pulps, wood pulp and deinked pulp are preferable from the viewpoint of easy availability. In addition, among wood pulps, the cellulose ratio is high and the yield of fine fibrous cellulose during fibrillation treatment is high, and the decomposition of cellulose in the pulp is small and long fiber fine fibrous cellulose with a large axial ratio can be obtained. From this point of view, for example, chemical pulp is more preferred, and kraft pulp and sulfite pulp are even more preferred.

As the fiber raw material containing cellulose, for example, cellulose contained in sea squirts or bacterial cellulose produced by acetic acid bacteria can also be used. Further, instead of the fiber raw material containing cellulose, fibers formed from linear nitrogen-containing polysaccharide polymers such as chitin and chitosan can also be used.

<Phosphorus oxoacid group introduction step>
The manufacturing process of the fine fibrous cellulose-containing dispersion includes a process of introducing a phosphorus oxo acid group or a substituent derived from a phosphorus oxo acid group. In this specification, the step of introducing a phosphorus oxo acid group or a substituent derived from a phosphorus oxo acid group is also referred to as a step of introducing a phosphorus oxo acid group. In the step of introducing phosphorus oxoacid groups, at least one compound selected from compounds capable of introducing phosphorus oxoacid groups (hereinafter also referred to as "compound A") is added to cellulose by reacting with hydroxyl groups possessed by fiber raw materials containing cellulose. This is a process of acting on fiber raw materials containing. Through this step, fibers introduced with phosphorus oxo acid groups are obtained.

In the phosphorus oxoacid group introduction step according to the present embodiment, a reaction between a cellulose-containing fiber raw material and compound A is performed in the presence of at least one selected from urea and its derivatives (hereinafter also referred to as "compound B"). It's okay. On the other hand, the cellulose-containing fiber raw material and compound A may be reacted in the absence of compound B.

An example of a method for causing compound A to act on a fiber raw material in the coexistence of compound B includes a method of mixing compound A and compound B with respect to a fiber raw material in a dry state, a wet state, or a slurry state. Among these, it is preferable to use dry or wet fiber raw materials, and it is particularly preferable to use dry fiber raw materials, since the reaction uniformity is high. The form of the fiber raw material is not particularly limited, but it is preferably cotton-like or thin sheet-like, for example. Compound A and compound B may be added to the fiber raw material in the form of a powder, a solution dissolved in a solvent, or a melted state by heating to a temperature higher than the melting point. Among these, it is preferable to add them in the form of a solution dissolved in a solvent, particularly an aqueous solution, since the reaction is highly uniform. Moreover, compound A and compound B may be added to the fiber raw material simultaneously, may be added separately, or may be added as a mixture. The method of adding Compound A and Compound B is not particularly limited, but if Compound A and Compound B are in the form of a solution, the fiber raw material may be immersed in the solution and taken out after absorption; The solution may be added dropwise. Alternatively, the necessary amounts of Compound A and Compound B may be added to the fiber raw material, or after adding excessive amounts of Compound A and Compound B to the fiber raw material, excess Compound A and Compound B may be removed by compression or filtration. May be removed.

The compound A used in this embodiment may be any compound having a phosphorus atom and capable of forming an ester bond with cellulose, such as phosphoric acid or its salt, phosphorous acid or its salt, dehydrated condensed phosphoric acid or its salt. Examples include salts, phosphoric anhydride (diphosphorus pentoxide), etc., but are not particularly limited. Phosphoric acid of various purity can be used, for example, 100% phosphoric acid (orthophosphoric acid) or 85% phosphoric acid. Examples of phosphorous acid include 99% phosphorous acid (phosphonic acid). Dehydrated condensed phosphoric acid is one in which two or more molecules of phosphoric acid are condensed through a dehydration reaction, and examples include pyrophosphoric acid and polyphosphoric acid. Examples of phosphates, phosphites, and dehydrated condensed phosphates include lithium salts, sodium salts, potassium salts, and ammonium salts of phosphoric acid, phosphorous acid, or dehydrated condensed phosphoric acid, which are It can be made into peace. Among these, phosphoric acid, sodium phosphate Salt, potassium salt of phosphoric acid, or ammonium salt of phosphoric acid is preferred, and phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, or ammonium dihydrogen phosphate is more preferred.

The amount of compound A added to the fiber raw material is not particularly limited, but for example, when the amount of compound A added is converted to phosphorus atomic weight, the amount of phosphorus atoms added to the fiber raw material (absolute dry mass) is 0.5% by mass or more. The content is preferably 100% by mass or less, more preferably 1% by mass or more and 50% by mass or less, and even more preferably 2% by mass or more and 30% by mass or less. By controlling the amount of phosphorus atoms added to the fiber raw material within the above range, the yield of fine fibrous cellulose can be further improved. On the other hand, by controlling the amount of phosphorus atoms added to the fiber raw material to be equal to or less than the above upper limit, it is possible to balance the yield improvement effect and cost.

Compound B used in this embodiment is at least one selected from urea and its derivatives as described above. Examples of compound B include urea, biuret, 1-phenylurea, 1-benzylurea, 1-methylurea, and 1-ethylurea. From the viewpoint of improving the uniformity of the reaction, compound B is preferably used as an aqueous solution. Moreover, from the viewpoint of further improving the uniformity of the reaction, it is preferable to use an aqueous solution in which both compound A and compound B are dissolved.

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

In the reaction of the cellulose-containing fiber raw material and compound A, in addition to compound B, for example, amides or amines may be included in the reaction system. Examples of amides include formamide, dimethylformamide, acetamide, dimethylacetamide, and the like. Examples of amines include methylamine, ethylamine, trimethylamine, triethylamine, monoethanolamine, diethanolamine, triethanolamine, pyridine, ethylenediamine, and hexamethylenediamine. Among these, triethylamine is known to act as a particularly good reaction catalyst.

In the phosphorus oxoacid group introduction step, it is preferable to heat-treat the fiber raw material after adding or mixing compound A and the like to the fiber raw material. As the heat treatment temperature, it is preferable to select a temperature at which phosphorus oxo acid groups can be efficiently introduced while suppressing thermal decomposition and hydrolysis reactions of the fibers. The heat treatment temperature is, for example, preferably 50°C or more and 300°C or less, more preferably 100°C or more and 250°C or less, and even more preferably 130°C or more and 200°C or less. In addition, for the heat treatment, equipment having various heat media can be used, such as a stirring dryer, a rotary dryer, a disc dryer, a roll-type heating device, a plate-type heating device, a fluidized bed dryer, an air flow dryer, etc. A drying device, a vacuum drying device, an infrared heating device, a far-infrared heating device, a microwave heating device, and a high frequency drying device can be used.

In the heat treatment according to this embodiment, for example, the compound A is added to a thin sheet-like fiber raw material by a method such as impregnation, and then heated, or the fiber raw material and compound A are heated while kneading or stirring with a kneader or the like. A method can be adopted. This makes it possible to suppress uneven concentration of compound A in the fiber raw material and more uniformly introduce phosphorus oxoacid groups onto the surface of the cellulose fibers contained in the fiber raw material. This is because when water molecules move to the surface of the fiber raw material during drying, the dissolved compound A is attracted to the water molecules by surface tension and similarly moves to the surface of the fiber raw material (in other words, the concentration unevenness of compound A is reduced). This is thought to be due to the fact that this can be suppressed.

In addition, the heating device used for the heat treatment constantly removes, for example, the water retained in the slurry and the water generated due to the dehydration condensation (phosphate esterification) reaction between Compound A and hydroxyl groups contained in cellulose, etc. in the fiber raw material. Preferably, the device is capable of being discharged outside the device system. Examples of such a heating device include a blower type oven and the like. By constantly draining water from the equipment system, it is possible to suppress the hydrolysis reaction of phosphate ester bonds, which is the reverse reaction of phosphoric acid esterification, and also to suppress acid hydrolysis of sugar chains in fibers. can. Therefore, it becomes possible to obtain fine fibrous cellulose with a high axial ratio.

The heat treatment time is preferably 1 second or more and 300 minutes or less, more preferably 1 second or more and 1000 seconds or less, and 10 seconds or more and 800 seconds or less after water is substantially removed from the fiber raw material, for example. It is more preferable that In this embodiment, by setting the heating temperature and heating time within appropriate ranges, the amount of phosphorus oxo acid groups introduced can be within a preferable range.

The step of introducing a phosphorus oxoacid group may be carried out at least once, but it can also be carried out twice or more. By performing the phosphorus oxo acid group introduction step twice or more, a large number of phosphorus oxo acid groups can be introduced into the fiber raw material.

The amount of phosphorus oxo acid groups introduced into the fiber raw material is preferably 0.10 mmol/g or more, more preferably 0.20 mmol/g or more, and 0.50 mmol/g per 1 g (mass) of fine fibrous cellulose. It is more preferably at least 1.00 mmol/g, particularly preferably at least 1.00 mmol/g. Further, the amount of phosphorus oxo acid groups introduced into the fiber raw material is preferably 5.20 mmol/g or less, more preferably 3.65 mmol/g or less, for example, per 1 g (mass) of fine fibrous cellulose. More preferably, it is 00 mmol/g or less. By introducing the amount of phosphorus oxo acid groups within the above range, it is possible to easily refine the fiber raw material and improve the stability of the fine fibrous cellulose. Moreover, by controlling the amount of introduced phosphorus oxo acid groups within the above range, the filtration efficiency in the filtration treatment process can be increased.

<Cleaning process>
In the method for producing a fine fibrous cellulose-containing dispersion according to the present embodiment, the phosphorus oxo acid group-introduced fibers can be subjected to a washing step, if necessary. The washing step is carried out by washing the phosphorus oxo acid group-introduced fiber with water or an organic solvent, for example. Further, the cleaning step may be performed after each step described below, and the number of times of cleaning performed in each cleaning step is not particularly limited.

<Alkali treatment process>
In the method for producing a fine fibrous cellulose-containing dispersion, the fiber raw material may be subjected to alkali treatment between the phosphorus oxo acid group introduction step and the defibration treatment step described below. The alkali treatment method is not particularly limited, but includes, for example, a method of immersing the phosphorus oxo acid group-introduced fiber in an alkaline solution.

The alkaline compound contained in the alkaline solution is not particularly limited, and may be an inorganic alkali compound or an organic alkali compound. In this embodiment, it is preferable to use, for example, sodium hydroxide or potassium hydroxide as the alkaline compound because of its high versatility. Moreover, the solvent contained in the alkaline solution may be either water or an organic solvent. Among these, the solvent contained in the alkaline solution is preferably a polar solvent containing water or a polar organic solvent such as alcohol, and more preferably an aqueous solvent containing at least water. The alkaline solution is preferably, for example, a sodium hydroxide aqueous solution or a potassium hydroxide aqueous solution because of its high versatility.

The temperature of the alkaline solution in the alkali treatment step is not particularly limited, but is preferably, for example, 5°C or more and 80°C or less, and more preferably 10°C or more and 60°C or less. The immersion time of the phosphorus oxo acid group-introduced fibers in the alkaline solution in the alkali treatment step is not particularly limited, but is preferably, for example, 5 minutes or more and 30 minutes or less, and more preferably 10 minutes or more and 20 minutes or less. The amount of alkaline solution used in the alkali treatment is not particularly limited, but is preferably 100% by mass or more and 100,000% by mass or less, and 1000% by mass or more and 10,000% by mass or less based on the absolute dry mass of the phosphorus oxo acid group-introduced fiber. It is more preferable that

In order to reduce the amount of alkaline solution used in the alkali treatment step, the phosphorus oxo acid group-introduced fibers may be washed with water or an organic solvent after the phosphorus oxo acid group introduction step and before the alkali treatment step. After the alkali treatment step and before the fibrillation treatment step, from the viewpoint of improving handling properties, it is preferable to wash the alkali-treated phosphorus acid group-introduced fiber with water or an organic solvent.

<Acid treatment process>
In the method for producing a fine fibrous cellulose-containing dispersion, the fiber raw material may be subjected to acid treatment between the step of introducing phosphorus oxo acid groups and the defibration step described below. For example, the phosphorus oxoacid group introduction step, acid treatment, alkali treatment, and fibrillation treatment may be performed in this order.

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

The temperature of the acid solution in the acid treatment is not particularly limited, but is preferably, for example, 5°C or higher and 100°C or lower, more preferably 20°C or higher and 90°C or lower. The immersion time in the acid solution in the acid treatment is not particularly limited, but is preferably, for example, 5 minutes or more and 120 minutes or less, and more preferably 10 minutes or more and 60 minutes or less. The amount of acid solution used in the acid treatment is not particularly limited, but for example, it is preferably 100% by mass or more and 100,000% by mass or less, and 1000% by mass or more and 10,000% by mass or less based on the absolute dry mass of the fiber raw material. is more preferable.

<Defibration treatment>
The method for producing a fine fibrous cellulose-containing dispersion of the present invention further includes a defibration treatment step. In the defibration processing step, for example, a defibration processing device can be used. The defibration processing equipment is not particularly limited, but includes, for example, a high-speed defibrator, a grinder (stone mill-type crusher), a high-pressure homogenizer, an ultra-high-pressure homogenizer, a high-pressure collision type crusher, a ball mill, a bead mill, a disc-type refiner, a conical refiner, and a biaxial refiner. A kneader, a vibratory mill, a homomixer under high speed rotation, an ultrasonic disperser, or a beater can be used. Among the above-mentioned defibration processing devices, it is more preferable to use a high-speed defibrator, a high-pressure homogenizer, and an ultra-high-pressure homogenizer, which are less affected by the crushing media and have less risk of contamination.

In the defibration treatment step, it is preferable to perform the defibration treatment on a slurry obtained by diluting, for example, phosphorus oxo acid group-introduced fibers with a dispersion medium. As the dispersion medium, one or more types selected from water and organic solvents such as polar organic solvents can be used. The polar organic solvent is not particularly limited, but preferably includes alcohols, polyhydric alcohols, ketones, ethers, esters, aprotic polar solvents, and the like. Examples of alcohols include methanol, ethanol, isopropanol, n-butanol, and isobutyl alcohol. Examples of polyhydric alcohols include ethylene glycol, propylene glycol, and glycerin. Examples of ketones include acetone and methyl ethyl ketone (MEK). Examples of the ethers include diethyl ether, tetrahydrofuran, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol mono-n-butyl ether, and propylene glycol monomethyl ether. Examples of esters include ethyl acetate and butyl acetate. Examples of the aprotic polar solvent include dimethylsulfoxide (DMSO), dimethylformamide (DMF), dimethylacetamide (DMAc), and N-methyl-2-pyrrolidinone (NMP).

The solid content concentration of the fine fibrous cellulose during the defibration treatment can be set as appropriate. Further, the slurry obtained by dispersing the phosphorus oxo acid group-introduced fibers in a dispersion medium may contain solid content other than the phosphorus oxo acid group introduced fibers, such as urea having hydrogen bonding properties.

<Filtration process>
The method for producing a fine fibrous cellulose-containing dispersion of the present invention includes a filtration treatment step. The filtration process is provided after the fibrillation process. In this way, by performing the filtration treatment on the dispersion containing fine fibrous cellulose having phosphorus oxo acid groups, the filtration efficiency of the filtration treatment step can be increased. Thereby, the production efficiency of the fine fibrous cellulose-containing dispersion can also be improved.

In the filtration process, at least one selected from a filter medium and a filter aid is used. In the filtration treatment step, it is preferable to use at least a filter medium, and it is preferable to use a filter as the filter medium.

When a filter is used as a filter medium, the filter is preferably composed of at least one selected from the group consisting of resin, metal, and ceramics, and preferably composed of at least one selected from resin and metal. It is more preferable that it be made of metal, even more preferably that it is made of metal, and particularly preferably that it is made of stainless steel. By employing a filter made of such a material, the filtration efficiency of the filtration process can be more effectively increased.

When using a filter as a filter medium, the opening of the filter is preferably 0.1 μm or more, more preferably 1 μm or more, even more preferably 5 μm or more, and particularly preferably 10 μm or more. Further, the opening of the filter is preferably 5 mm or less, more preferably 1 mm or less, and even more preferably 100 μm or less.

It is also preferable to use a filter medium and a filter aid in the filtration process. By performing filtration treatment using a combination of a filter medium and a filter aid, filtration efficiency can be more effectively increased. Furthermore, the transparency of the fine fibrous cellulose-containing dispersion obtained after the filtration process can be increased and the content of foreign substances can be reduced.

Examples of filter aids include inorganic compounds and organic compounds. More specifically, examples of filter aids include diatomaceous earth, perlite, powdered cellulose, and activated carbon. Among these, it is particularly preferable that the filter aid is diatomaceous earth. Diatomaceous earth has silica as its main component, but may also contain alumina, iron oxide, alkali metal oxide, etc. in addition to silica.

Preferably, the filter aid is granular. In this case, the average particle diameter of the filter aid is preferably 1 to 150 μm, more preferably 10 to 100 μm. By setting the average particle diameter of the filter aid within the above range, filtration efficiency can be more effectively increased.

When using a filter aid in the filtration process, there is pre-coat filtration in which a layer of filter aid is formed on the filter medium, and body feed filtration in which the filter aid and fine fibrous cellulose-containing dispersion are mixed in advance and filtered. Various filtration methods can be employed, such as filtration. Among these, filtration efficiency can be more effectively increased by performing filtration processing by combining precoat filtration and body feed filtration.

The filtration rate in the filtration treatment step is preferably 10 L/h or more, more preferably 30 L/h or more, even more preferably 50 L/h or more, and particularly preferably 80 L/h or more. . In the method for producing fine fibrous cellulose of the present invention, since a dispersion containing fine fibrous cellulose having a phosphorus oxo acid group or a substituent derived from a phosphorus oxo acid group is used, the filtration treatment was performed at the above-mentioned filtration rate. It is possible to suppress clogging of the filter medium even in the case of

The filtration efficiency in the filtration process can be determined, for example, by measuring the degree of clogging of the filter medium used in the filtration process. The degree of blockage of the filter medium is determined by measuring the pressures upstream and downstream of the filter medium, and if the pressure difference is small, it can be determined that the blockage of the filter medium is suppressed. That is, the pressure difference before and after the filter medium is calculated, and if the pressure difference is small, it can be determined that the blockage of the filter medium is suppressed. Note that the pressure in the process can be measured with pressure gauges attached before and after the filter. It is preferable that the pressure difference before and after the filter is 0.1 MP or less, and in such a case, it can be determined that clogging of the filter medium is suppressed.

Moreover, the filtration efficiency in the filtration treatment process can also be evaluated by the filtrate recovery rate. The filtrate recovery rate is calculated by measuring the amount of filtrate that has passed through the filter and using the following formula. Note that the amount of filtrate that has passed through the filter is the amount of filtrate that is collected by reducing the pressure to 0.05 MPa using an aspirator.
Filtrate recovery rate (%) = Amount of fine fibrous cellulose-containing dispersion (filtrate) after filtration (L) / Amount of fine fibrous cellulose-containing dispersion subjected to filtration (L) x 100
The filtrate recovery rate is preferably 80% or more, more preferably 85% or more, and even more preferably 90% or more.

The solid content concentration of the fine fibrous cellulose-containing dispersion to be subjected to the filtration process is preferably 0.1% by mass or more, more preferably 0.5% by mass or more. Further, the solid content concentration of the fine fibrous cellulose-containing dispersion to be subjected to the filtration treatment step is preferably 10% by mass or less, more preferably 5% by mass or less. By setting the solid content concentration of the dispersion liquid to be subjected to the filtration treatment step within the above range, it is possible to increase the filtration efficiency and the production efficiency of the fine fibrous cellulose-containing dispersion liquid.

After the filtration treatment step, a step of concentrating the fine fibrous cellulose-containing dispersion may be provided as necessary. Thereby, a dispersion liquid with an increased content of fine fibrous cellulose-containing dispersion liquid can be obtained. Alternatively, it may be a solid fine fibrous cellulose-containing material. Alternatively, a fine fibrous cellulose-containing sheet may be produced by forming a fine fibrous cellulose-containing dispersion into a sheet.

(Fine fibrous cellulose-containing dispersion)
The fine fibrous cellulose-containing dispersion produced by the production method of the present invention contains fibrous cellulose (fine fibrous cellulose) having a fiber width of 1000 nm or less. The fiber width of the fibrous cellulose is preferably 100 nm or less, more preferably 8 nm or less.

The fiber width of fibrous cellulose can be measured, for example, by electron microscopic observation. The average fiber width of fibrous cellulose is, for example, 1000 nm or less. The average fiber width of the fibrous cellulose is, for example, preferably 2 nm or more and 1000 nm or less, more preferably 2 nm or more and 100 nm or less, even more preferably 2 nm or more and 50 nm or less, and 2 nm or more and 10 nm or less. Particularly preferred. By setting the average fiber width of fibrous cellulose to 2 nm or more, dissolution of cellulose molecules in water can be suppressed, and the effects of improving strength, rigidity, and dimensional stability due to fibrous cellulose can be more easily expressed. can. Note that the fibrous cellulose is, for example, monofilament cellulose.

The average fiber width of fibrous cellulose is measured using, for example, an electron microscope as follows. First, an aqueous suspension of fibrous cellulose with a concentration of 0.05% by mass or more and 0.1% by mass or less is prepared, and this suspension is cast onto a hydrophilic carbon film-coated grid to provide a sample for TEM observation. shall be. If wide fibers are included, a SEM image of the surface cast on glass may be observed. Next, observation using an electron microscope is performed at a magnification of 1000 times, 5000 times, 10000 times, or 50000 times, depending on the width of the fiber to be observed. However, the sample, observation conditions, and magnification should be adjusted to satisfy the following conditions.
(1) Draw a straight line X at any location in the observed image, and 20 or more fibers intersect with the straight line X.
(2) Draw a straight line Y that intersects the straight line perpendicularly within the same image, and 20 or more fibers intersect with the straight line Y.
For an observed image that satisfies the above conditions, visually read the width of the fibers that intersect the straight lines X and Y. In this way, at least three sets of observation images of surface portions that do not overlap with each other are obtained. Then, for each image, the width of the fibers intersecting the straight lines X and Y is read. In this way, the width of at least 20 x 2 x 3 = 120 fibers is read. Then, the average value of the read fiber widths is defined as the average fiber width of the fibrous cellulose.

The fiber length of the fibrous cellulose is not particularly limited, but for example, it is preferably 0.1 μm or more and 1000 μm or less, more preferably 0.1 μm or more and 800 μm or less, and even more preferably 0.1 μm or more and 600 μm or less. preferable. By setting the fiber length within the above range, destruction of the crystalline region of fibrous cellulose can be suppressed. Furthermore, it is also possible to set the viscosity of the fibrous cellulose dispersion within an appropriate range. Note that the fiber length of fibrous cellulose can be determined, for example, by image analysis using TEM, SEM, or AFM.

It is preferable that the fibrous cellulose has a type I crystal structure. Here, the fact that fibrous cellulose has a type I crystal structure can be identified in the diffraction profile obtained from a wide-angle X-ray diffraction photograph using CuKα (λ=1.5418 Å) monochromated with graphite. Specifically, it can be identified because it has typical peaks at two positions: around 2θ=14° or more and 17° or less and around 2θ=22° or more and 23° or less. The proportion of type I crystal structure in the fine fibrous cellulose is, for example, preferably 30% or more, more preferably 40% or more, and still more preferably 50% or more. As a result, even better performance can be expected in terms of heat resistance and low coefficient of linear thermal expansion. The degree of crystallinity is determined by measuring an X-ray diffraction profile and using the pattern in a conventional manner (Seagal et al., Textile Research Journal, Vol. 29, p. 786, 1959).

The axial ratio (fiber length/fiber width) of the fibrous cellulose is not particularly limited, but is preferably, for example, 20 or more and 10,000 or less, more preferably 50 or more and 1,000 or less. By setting the axial ratio to the above lower limit value or more, it is easy to form a sheet containing fine fibrous cellulose. In addition, sufficient thickening properties are easily obtained when a solvent dispersion is prepared. It is preferable that the axial ratio be equal to or less than the above upper limit because handling such as dilution becomes easier when handling fibrous cellulose as an aqueous dispersion, for example.

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

Fibrous cellulose has a phosphorus oxoacid group or a substituent derived from a phosphorus oxoacid group. The phosphorus oxo acid group or the substituent derived from the phosphorus oxo acid group is, for example, a substituent represented by the following formula (1). A phosphorus oxoacid group is a divalent functional group, for example, equivalent to phosphoric acid with a hydroxyl group removed. Specifically, it is a group represented by -PO ₃ H ₂ . The substituents derived from the phosphorus oxo acid group include substituents such as salts of the phosphorus oxo acid group and phosphorus oxo acid ester groups. Note that the substituent derived from the phosphorus oxoacid group may be included in the fibrous cellulose as a group (for example, a pyrophosphate group) in which a phosphoric acid group is condensed. Further, the phosphorus oxo acid group may be, for example, a phosphorous acid group (phosphonic acid group), and the substituent derived from the phosphorus oxo acid group may be a salt of a phosphorous acid group.

In formula (1), a, b, and n are natural numbers, and m is an arbitrary number (a=b×m). a of α ¹ , α ² , . . . , α ⁿ and α′ are O ⁻ , and the rest are either R or OR. Note that all of α ⁿ and α′ may be O ⁻ . R is a hydrogen atom, a saturated linear hydrocarbon group, a saturated branched hydrocarbon group, a saturated cyclic hydrocarbon group, an unsaturated linear hydrocarbon group, or an unsaturated branched hydrocarbon group, respectively. A hydrogen group, an unsaturated cyclic hydrocarbon group, an aromatic group, or a group derived from these. Further, in formula (1), n is preferably 1.

Examples of the saturated linear hydrocarbon group include a methyl group, an ethyl group, an n-propyl group, an n-butyl group, and the like, but are not particularly limited. Examples of the saturated-branched hydrocarbon group include i-propyl group and t-butyl group, but are not particularly limited. Examples of the saturated cyclic hydrocarbon group include a cyclopentyl group and a cyclohexyl group, but are not particularly limited. Examples of the unsaturated linear hydrocarbon group include a vinyl group and an allyl group, but are not particularly limited. Examples of the unsaturated branched hydrocarbon group include an i-propenyl group and a 3-butenyl group, but are not particularly limited. Examples of the unsaturated cyclic hydrocarbon group include a cyclopentenyl group and a cyclohexenyl group, but are not particularly limited. Examples of the aromatic group include a phenyl group and a naphthyl group, but are not particularly limited.

In addition, the derivative group in R is a functional group in which at least one functional group such as a carboxy group, a hydroxy group, or an amino group is added or substituted to the main chain or side chain of the various hydrocarbon groups mentioned above. Examples include, but are not particularly limited to, groups. Further, the number of carbon atoms constituting the main chain of R is not particularly limited, but is preferably 20 or less, more preferably 10 or less. By setting the number of carbon atoms constituting the main chain of R within the above range, the molecular weight of the phosphorus oxo acid group can be set in an appropriate range, facilitating penetration into the fiber raw material and increasing the yield of fine cellulose fibers. You can also do that.

β ^b+ is a monovalent or higher cation consisting of an organic substance or an inorganic substance. Examples of monovalent or more valent cations made of organic substances include aliphatic ammonium or aromatic ammonium, and examples of monovalent or more valent cations made of inorganic substances include ions of alkali metals such as sodium, potassium, or lithium, Examples include cations of divalent metals such as calcium or magnesium, hydrogen ions, etc., but are not particularly limited. These can also be applied singly or in combination of two or more. As monovalent or higher cations made of organic or inorganic substances, sodium or potassium ions are preferred, but are not particularly limited, as they do not easily yellow when β-containing fiber raw materials are heated and are easy to use industrially. Note that β ^b+ may be an organic onium ion.

The amount of phosphorus oxoacid group introduced into fibrous cellulose is preferably 0.10 mmol/g or more, more preferably 0.20 mmol/g or more, and 0.50 mmol/g per 1 g (mass) of fibrous cellulose. It is more preferably at least 1.00 mmol/g, particularly preferably at least 1.00 mmol/g. Further, the amount of phosphorus oxo acid groups introduced into the fibrous cellulose is preferably 5.20 mmol/g or less, more preferably 3.65 mmol/g or less, for example, per 1 g (mass) of fibrous cellulose. It is more preferably 50 mmol/g or less, particularly preferably 3.00 mmol/g or less. By controlling the amount of phosphorus oxo acid groups introduced within the above range, it is possible to easily refine the fiber raw material and improve the stability of the fibrous cellulose. Moreover, by controlling the amount of introduced phosphorus oxo acid groups within the above range, the filtration efficiency in the filtration treatment process can be increased. Here, the denominator in the unit mmol/g indicates the mass of the fibrous cellulose when the counter ion of the phosphorus oxoacid group is a hydrogen ion (H ⁺ ).

The amount of phosphorus oxoacid groups introduced into fibrous cellulose can be measured, for example, by neutralization titration. In the measurement by neutralization titration, the amount introduced is measured by adding an alkali such as an aqueous sodium hydroxide solution to the resulting dispersion containing fibrous cellulose and determining the change in pH.

FIG. 1 is a graph showing the relationship between the amount of NaOH added dropwise to a fibrous cellulose-containing dispersion having phosphorus oxoacid groups and pH. The amount of phosphorus oxoacid groups introduced into fibrous cellulose is measured, for example, as follows.
First, a dispersion containing fibrous cellulose is treated with a strongly acidic ion exchange resin. Note that, if necessary, a defibration process similar to the defibration process described below may be performed on the measurement target before the treatment with the strongly acidic ion exchange resin.
Next, a change in pH is observed while adding an aqueous sodium hydroxide solution, and a titration curve as shown in the upper part of FIG. 1 is obtained. The titration curve shown in the upper part of Figure 1 plots the measured pH against the amount of alkali added, and the titration curve shown in the lower part of Figure 1 plots the pH measured against the amount of alkali added. Increment (differential value) (1/mmol) is plotted. In this neutralization titration, two points at which the increment (differential value of pH with respect to the amount of alkali dropped) becomes maximum are confirmed on a curve in which the measured pH is plotted against the amount of alkali added. Among these, the maximum point of increment obtained first after starting to add the alkali is called the first end point, and the maximum point of increment obtained next is called the second end point. The amount of alkali required from the start of titration to the first end point is equal to the amount of first dissociated acid of the fibrous cellulose contained in the dispersion used for titration, and the amount of alkali required from the first end point to the second end point is The amount of alkali becomes equal to the amount of second dissociated acid of fibrous cellulose contained in the dispersion used for titration, and the amount of alkali required from the start of titration to the second end point is contained in the dispersion used for titration. It is equal to the total amount of dissociated acids in fibrous cellulose. Then, the value obtained by dividing the amount of alkali required from the start of titration to the first end point by the solid content (g) in the dispersion to be titrated becomes the amount of phosphorus oxo acid group introduced (mmol/g). In addition, when it is simply referred to as the amount of phosphorus oxo acid groups introduced (or the amount of phosphorus oxo acid groups), it refers to the amount of the first dissociated acid.
In FIG. 1, the region from the start of titration to the first end point is called the first region, and the region from the first end point to the second end point is called the second region. For example, when the phosphorus oxo acid group is a phosphoric acid group and this phosphoric acid group causes condensation, the amount of weak acid groups (also referred to herein as the second dissociated acid amount) in the phosphorus oxo acid group appears to be The amount of alkali required in the second region is smaller than the amount of alkali required in the first region. On the other hand, the amount of strong acid groups in the phosphorus oxo acid group (also referred to as the first dissociated acid amount in this specification) matches the amount of phosphorus atoms regardless of the presence or absence of condensation. In addition, when the phosphorus oxo acid group is a phosphorous acid group, there is no weakly acidic group in the phosphorus oxo acid group, so the amount of alkali required for the second region is reduced, or the amount of alkali required for the second region is reduced. may be zero. In this case, in the titration curve, there is one point where the pH increment becomes maximum.

Note that the above-mentioned amount of phosphorus oxo acid groups introduced (mmol/g) has a denominator indicating the mass of acid type fibrous cellulose. (called the acid form). On the other hand, if the counter ion of the phosphorus oxo acid group is substituted with any cation C so as to have a charge equivalent, convert the denominator to the mass of the fibrous cellulose when the cation C is the counter ion. By doing so, the amount of phosphorus oxo acid groups (hereinafter referred to as the amount of phosphorus oxo acid groups (C type)) that the fibrous cellulose having the cation C as a counter ion can be determined.
That is, it is calculated using the following calculation formula.
Amount of phosphorus oxo acid groups (C type) = Amount of phosphorus oxo acid groups (acid type)/{1+(W-1)×A/1000}
A [mmol/g]: Total amount of anions derived from phosphorus oxo acid groups possessed by fibrous cellulose (total amount of dissociated acids of phosphorus oxo acid groups)
W: formula weight per valence of cation C (for example, 23 for Na, 9 for Al)

In addition, when measuring the amount of phosphorus oxo acid groups using the titration method, if the amount of one drop of sodium hydroxide aqueous solution dropped is too large, or if the titration interval is too short, the amount of phosphorus oxo acid groups may be lower than originally expected, resulting in inaccurate values. Sometimes you can't get it. As for an appropriate dropping amount and titration interval, for example, it is desirable to titrate a 0.1N aqueous sodium hydroxide solution at a rate of 10 to 50 μL every 5 to 30 seconds. In addition, in order to eliminate the influence of carbon dioxide dissolved in the fibrous cellulose-containing dispersion, measurements may be performed while blowing an inert gas such as nitrogen gas into the dispersion from 15 minutes before the start of titration until the end of titration. desirable.

The content of fibrous cellulose is based on the total mass of the fine fibrous cellulose-containing dispersion,
It is preferably 0.05% by mass or more, more preferably 0.1% by mass or more, and even more preferably 0.2% by mass or more. Further, the content of fibrous cellulose is preferably 50% by mass or less, more preferably 40% by mass or less, and 30% by mass or less based on the total mass of the fine fibrous cellulose-containing dispersion. It is more preferable that the amount is 20% by mass or less, and particularly preferably 20% by mass or less.

The total light transmittance of the fine fibrous cellulose-containing dispersion is preferably 80% or more, more preferably 85% or more, and even more preferably 90% or more. Note that the total light transmittance of the fine fibrous cellulose-containing dispersion may be 100%. The total light transmittance of the fine fibrous cellulose-containing dispersion was determined by diluting the fine fibrous cellulose-containing dispersion with ion-exchanged water so that the fibrous cellulose content was 0.2% by mass, and then using a hazemeter (Murakami Color). This is a value measured in accordance with JIS K 7361 using a liquid glass cell (manufactured by Fujiwara Seisakusho, MG-40, reverse light path) with an optical path length of 1 cm. Note that the zero point measurement is performed using ion-exchanged water placed in the same glass cell. Moreover, the dispersion liquid to be measured is left standing in an environment of 23° C. and 50% relative humidity for 24 hours before measurement.

The haze of the fine fibrous cellulose-containing dispersion is preferably 2% or less, more preferably 1.5% or less, and even more preferably 1% or less. The haze of the fine fibrous cellulose-containing dispersion can be measured, for example, in accordance with JIS K 7136 using a haze meter (HM-150, manufactured by Murakami Color Research Institute) and a glass cell for liquids with an optical path length of 1 cm (manufactured by Fujiwara Seisakusho, MG-150). 40, reverse optical path). Note that the zero point measurement is performed using ion-exchanged water placed in the same glass cell. Moreover, the dispersion liquid to be measured is left standing in an environment of 23° C. and 50% relative humidity for 24 hours before measurement.

The viscosity of the fine fibrous cellulose-containing dispersion measured at 23° C. and a rotation speed of 0.3 rpm is preferably 10,000 mPa·s or more, more preferably 50,000 mPa·s or more, and 100,000 mPa·s or more. It is more preferable that it is, and it is especially preferable that it is 300,000 mPa·s or more. The viscosity of the fine fibrous cellulose-containing dispersion measured at 23° C. and a rotational speed of 0.3 rpm is preferably 4,000,000 or less. When measuring the viscosity of a fine fibrous cellulose-containing dispersion, the dispersion is defoamed for 30 minutes using Awatori Rentaro ARE-310 manufactured by Shinky Co., Ltd., and then the measurement is performed. A B-type viscometer (manufactured by BLOOKFIELD, analog viscometer T-LVT) is used to measure the viscosity. The measurement conditions are a rotational speed of 0.3 rpm, and the viscosity value 3 minutes after the start of the measurement is taken as the viscosity of the dispersion. Further, the dispersion liquid to be measured is left standing for 24 hours in an environment of 23°C and relative humidity of 50% before measurement, and the temperature of the dispersion liquid at the time of measurement is 23°C.

The fine fibrous cellulose-containing dispersion may contain optional components in addition to the fine fibrous cellulose. Examples of optional components include hydrophilic polymers, hydrophilic low molecules, and organic ions. In addition, the fine fibrous cellulose-containing dispersion may optionally contain a surfactant, a coupling agent, an inorganic layered compound, an inorganic compound, a leveling agent, a preservative, an antifoaming agent, an organic particle, a lubricant, and an antistatic agent. , ultraviolet protection agents, dyes, pigments, stabilizers, magnetic powders, orientation promoters, plasticizers, dispersants, preservatives, and crosslinking agents.

The hydrophilic polymer is preferably a hydrophilic oxygen-containing organic compound (excluding the above-mentioned cellulose fibers), and examples of the oxygen-containing organic compound include polyethylene glycol, polyethylene oxide, casein, dextrin, starch, and modified Starch, polyvinyl alcohol, modified polyvinyl alcohol (acetoacetylated polyvinyl alcohol, etc.), polyvinylpyrrolidone, polyvinyl methyl ether, polyacrylates, acrylic acid alkyl ester copolymers, urethane copolymers, cellulose derivatives (hydroxyethylcellulose, carboxylic acid) ethyl cellulose, carboxymethyl cellulose, etc.).

The hydrophilic low molecule is preferably a hydrophilic oxygen-containing organic compound, and more preferably a polyhydric alcohol. Examples of polyhydric alcohols include glycerin, sorbitol, ethylene glycol, and the like.

Examples of organic ions include tetraalkylammonium ions and tetraalkylphosphonium ions. Examples of the tetraalkylammonium ion include tetramethylammonium ion, tetraethylammonium ion, tetrapropylammonium ion, tetrabutylammonium ion, tetrapentylammonium ion, tetrahexylammonium ion, tetraheptylammonium ion, tributylmethylammonium ion, and lauryl trimethyl. Examples include ammonium ion, cetyltrimethylammonium ion, stearyltrimethylammonium ion, octyldimethylethylammonium ion, lauryldimethylethylammonium ion, didecyldimethylammonium ion, lauryldimethylbenzylammonium ion, and tributylbenzylammonium ion. Examples of the tetraalkylphosphonium ion include tetramethylphosphonium ion, tetraethylphosphonium ion, tetrapropylphosphonium ion, tetrabutylphosphonium ion, and lauryltrimethylphosphonium ion. Further, examples of the tetrapropylonium ion and the tetrabutylonium ion include a tetra n-propyl onium ion and a tetra n-butylonium ion, respectively.

(Method for producing a sheet containing fine fibrous cellulose) The present invention provides a process for forming a sheet from a dispersion containing fine fibrous cellulose obtained by the above-described method for producing a dispersion containing fine fibrous cellulose. It may also relate to a method of manufacturing a containing sheet. The step of forming the sheet preferably includes a step of making paper from the dispersion or a step of applying the dispersion to a base material. In the step of forming a sheet, a fine fibrous cellulose-containing sheet is obtained by forming a wet sheet by papermaking or coating and then drying it. Note that in this specification, the process of forming a sheet may be referred to as a sheet-forming process.

<Paper making process>
The paper making process is performed by making paper from the dispersion using a paper machine. The paper machine used in the paper making process is not particularly limited, but examples include continuous paper machines such as Fourdrinier type, cylinder type, and inclined type, and multilayer paper machines combining these. In the paper-making process, a known paper-making method such as hand-making may be employed.

The papermaking process is carried out by filtering and dewatering the dispersion using a wire to obtain a wet paper sheet, and then pressing and drying this sheet. The filter cloth used for filtering and dehydrating the dispersion is not particularly limited, but it is more preferable to use one that does not allow fine fibrous cellulose to pass through and that does not slow down the filtration rate too much. Such filter cloth is not particularly limited, but for example, sheets, textiles, and porous membranes made of organic polymers are preferable. The organic polymer is not particularly limited, but non-cellulose organic polymers such as polyethylene terephthalate, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), etc. are preferred. In this embodiment, for example, a porous membrane of polytetrafluoroethylene with a pore diameter of 0.1 μm or more and 20 μm or less, a polyethylene terephthalate or polyethylene fabric with a pore diameter of 0.1 μm or more and 20 μm or less, and the like.

In the sheet-forming process, a method for manufacturing a sheet from a dispersion liquid is, for example, a squeezing method in which a dispersion liquid containing fibrous cellulose is discharged onto the upper surface of an endless belt, and a dispersion medium is squeezed from the discharged dispersion liquid to form a web. This can be done using manufacturing equipment that includes a water section and a drying section that dries the web to produce sheets. An endless belt is disposed from the water squeezing section to the drying section, and the web produced in the water squeezing section is conveyed to the drying section while being placed on the endless belt.

A method for manufacturing a sheet from a fine fibrous cellulose-containing dispersion is not particularly limited, but includes, for example, a method using a manufacturing apparatus described in WO2011/013567. This manufacturing equipment includes a water squeezing section that discharges a dispersion containing fine fibrous cellulose onto the upper surface of an endless belt, squeezes out the dispersion medium from the discharged dispersion to produce a web, and a water squeezing section that produces a web by drying the web and forming a sheet. It is equipped with a drying section to produce. An endless belt is disposed from the water squeezing section to the drying section, and the web produced in the water squeezing section is conveyed to the drying section while being placed on the endless belt.

The dehydration method that can be used in the present invention is not particularly limited, but includes dehydration methods commonly used in paper manufacturing, such as dehydration using a fourdrinier, cylinder screen, inclined wire, etc., followed by dehydration using a roll press. is preferred. Further, the drying method is not particularly limited, but includes methods used in paper manufacturing, such as cylinder dryers, Yankee dryers, hot air drying, near-infrared heaters, and infrared heaters.

Examples of methods for drying the dispersion to form a sheet include heating drying, blow drying, and reduced pressure drying. Pressure may be applied in parallel with drying. The heating temperature is preferably about 50°C to 250°C. When the temperature is within the above range, drying can be completed in a short time and discoloration and discoloration can be suppressed. Pressure is preferably 0.01 MPa to 5 MPa. When the pressure is within the above range, the occurrence of cracks and wrinkles can be suppressed and the density of the fine fibrous cellulose-containing sheet can be increased.

<Coating process>
In the coating step, a sheet can be obtained by, for example, coating a dispersion containing fine fibrous cellulose on a substrate, drying it, and peeling the formed sheet from the substrate. Further, by using a coating device and a long base material, sheets can be continuously produced.

The material of the base material used in the coating process is not particularly limited, but materials with higher wettability to the dispersion liquid are better because they can suppress shrinkage of the sheet during drying. It is preferable to select one that can be easily peeled off. Among these, resin films and plates and metal films and plates are preferred, but they are not particularly limited. For example, films and plates made of resin such as acrylic, polyethylene terephthalate, vinyl chloride, polystyrene, polypropylene, polycarbonate, and polyvinylidene chloride; films and plates made of metal such as aluminum, zinc, copper, and iron; and those whose surfaces have been oxidized. , stainless steel film or plate, brass film or plate, etc. can be used.

In the coating process, if the viscosity of the dispersion liquid is low and it spreads on the base material, a dam frame may be fixed on the base material in order to obtain a sheet with a predetermined thickness and basis weight. You may. The damming frame is not particularly limited, but it is preferable to select one that allows the edges of the sheet to be easily peeled off after drying, for example. From this point of view, it is more preferable to use a molded resin plate or metal plate. In this embodiment, for example, resin plates such as acrylic plates, polyethylene terephthalate plates, vinyl chloride plates, polystyrene plates, polypropylene plates, polycarbonate plates, and polyvinylidene chloride plates, and metal plates such as aluminum plates, zinc plates, copper plates, iron plates, etc. , and those whose surfaces have been oxidized, stainless steel plates, brass plates, etc. can be used.

The coating machine for coating the base material with the dispersion is not particularly limited, and for example, a roll coater, gravure coater, die coater, curtain coater, air doctor coater, etc. can be used. A die coater, a curtain coater, and a spray coater are particularly preferred because they can make the sheet thickness more uniform.

The temperature of the dispersion and the ambient temperature when applying the dispersion to the substrate are not particularly limited, but are preferably, for example, 5°C or more and 80°C or less, more preferably 10°C or more and 60°C or less, The temperature is more preferably 15°C or more and 50°C or less, and particularly preferably 20°C or more and 40°C or less. If the coating temperature is equal to or higher than the above lower limit, the dispersion can be coated more easily. If the coating temperature is below the above upper limit, volatilization of the dispersion medium during coating can be suppressed.

As described above, the coating step includes the step of drying the dispersion coated on the substrate. The step of drying the dispersion liquid is not particularly limited, and may be performed, for example, by 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 for example, a method of drying by heating with hot air, infrared rays, far infrared rays, or near infrared rays (heat drying method), or a method of drying under 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. Drying using infrared rays, far infrared rays, or near infrared rays is not particularly limited, and can be performed using, for example, an infrared device, a far infrared device, or a near infrared device. The heating temperature in the heating drying method is not particularly limited, but is preferably, for example, 20°C or higher and 150°C or lower, more preferably 25°C or higher and 105°C or lower. If the heating temperature is equal to or higher than the above lower limit, the dispersion medium can be quickly volatilized. Moreover, if the heating temperature is below the above-mentioned upper limit, it is possible to suppress the cost required for heating and suppress discoloration of the fibrous cellulose due to heat.

<Other processes>
The method for producing a fine fibrous cellulose-containing sheet of the present invention may further include a defoaming step in addition to the steps described above. When the manufacturing method of the present invention includes a defoaming step, the defoaming step is preferably provided before the step of forming the sheet described above, and is preferably provided between the step of filtering and the step of forming the sheet. is more preferable. Thereby, defoaming efficiency can be improved and a fine fibrous cellulose-containing sheet with a low bubble content can be formed.

In the defoaming step, it is preferable to remove air bubbles from the dispersion using a defoaming device. Examples of the defoaming device include a vacuum defoaming device, a centrifugal defoaming device, a vacuum defoaming device, a rotation-revolution defoaming device, and the like. After degassing is performed in such an apparatus, the dispersion liquid is sent to the sheet forming process through a liquid delivery pipe or the like.

EXAMPLES The features of the present invention will be explained in more detail below with reference to Examples and Comparative Examples. The materials, usage amounts, proportions, processing details, processing procedures, etc. shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be interpreted as being limited by the specific examples shown below.

[Example 1]
<Chemical treatment>
As raw material pulp, softwood kraft pulp manufactured by Oji Paper (solid content 93% by mass, basis weight 208 g/m ² sheet form, Canadian standard freeness (CSF) measured according to JIS P 8121 after disintegration is 700 ml) It was used.

This raw material pulp was subjected to phosphorus oxo oxidation treatment as follows. First, a mixed aqueous solution of ammonium dihydrogen phosphate and urea is added to 100 parts by mass (absolutely dry mass) of the above raw material pulp to obtain 45 parts by mass of ammonium dihydrogen phosphate, 120 parts by mass of urea, and 150 parts by mass of water. A pulp impregnated with a chemical solution was obtained. Next, the resulting chemical solution-impregnated pulp was heated in a hot air dryer at 165° C. for 200 seconds to introduce phosphoric acid groups into the cellulose in the pulp, thereby obtaining phosphorus oxo-oxidized pulp.

Next, the obtained phosphorus oxo-oxidized pulp was subjected to a washing treatment. The washing treatment was performed by pouring 10 L of ion-exchanged water into 100 g (absolutely dry mass) of phosphorus oxo-oxidized pulp, stirring the resulting pulp dispersion so that the pulp was evenly dispersed, and then repeating the process of filtering and dehydrating the pulp. went. The washing end point was determined when the electrical conductivity of the filtrate became 100 μS/cm or less.

Next, the washed phosphorus oxo-oxidized pulp was subjected to alkali treatment as follows. First, after diluting the washed phosphoric acid oxidized pulp with 10 L of ion-exchanged water, a 1N aqueous sodium hydroxide solution is added little by little while stirring to form a phosphorus oxo oxidized pulp slurry with a pH of 12 to 13. Obtained. Next, the phosphorus oxo-oxidized pulp slurry was dehydrated to obtain a phosphorus oxo-oxidized pulp subjected to alkali treatment. Next, the phosphorus oxo-oxidized pulp after the alkali treatment was subjected to the above-mentioned washing treatment.

The infrared absorption spectrum of the phosphorus oxo-oxidized pulp thus obtained was measured using FT-IR. As a result, absorption based on P=O of phosphoric acid groups was observed near 1230 cm ⁻¹ , and it was confirmed that phosphoric acid groups were added to the pulp. In addition, when the obtained phosphorus oxo-oxidized pulp was sampled and analyzed using an X-ray diffraction device, it was found that there were two positions near 2θ = 14° or more and 17° or less and 2θ = 22° or more and 23° or less. A typical peak was confirmed, and it was confirmed that cellulose type I crystals were present.

<Defibration treatment>
Ion-exchanged water was added to the obtained phosphorus oxo-oxidized pulp to prepare a slurry having a solid content concentration of 2% by mass. This slurry was treated four times at a pressure of 200 MPa using a wet atomizer (Starburst, manufactured by Sugino Machine Co., Ltd.) to obtain a fine fibrous cellulose-containing dispersion A containing fine fibrous cellulose. It was confirmed by X-ray diffraction that this fine fibrous cellulose maintained cellulose type I crystals. Further, the fiber width of the fine fibrous cellulose measured by the measuring method described below was 3 to 5 nm. The amount of phosphorus oxo acid groups (first amount of dissociated acids) of the fine fibrous cellulose measured by the measurement method described below was 1.45 mmol/g, and the total amount of dissociated acids was 2.45 mmol/g.

<Measurement of phosphorus oxo acid group amount>
The amount of phosphorus oxo acid groups in the fine fibrous cellulose was measured by neutralization titration. A treatment process using an ion exchange resin was performed on a fibrous cellulose-containing dispersion prepared by diluting the target fine fibrous cellulose-containing dispersion with ion-exchanged water to a content of 0.2% by mass. Afterwards, it was measured by titration using an alkali.
In the treatment step with an ion exchange resin, 1/10 of the volume of a strongly acidic ion exchange resin (Amber Jet 1024; Organo Co., Ltd., conditioned) was added to the fine fibrous cellulose-containing dispersion, and the mixture was shaken for 1 hour. After that, the slurry was poured onto a mesh having an opening of 90 μm to separate the resin and the slurry, thereby converting the phosphorus oxo acid group into the acid form.
In addition, titration using an alkali is performed by adding 10 μL of a 0.1N sodium hydroxide aqueous solution every 5 seconds to the fibrous cellulose-containing dispersion after treatment with an ion exchange resin, and measuring the change in the pH value of the slurry. This was done by measuring. Note that the titration was performed while blowing nitrogen gas into the slurry 15 minutes before the start of the titration.
In this neutralization titration, on a curve in which the measured pH is plotted against the amount of alkali added, two points are observed where the increment (differential value of pH with respect to the amount of alkali added) becomes maximum. Among these, the maximum point of increment obtained first after starting to add the alkali is called the first end point, and the maximum point of increment obtained next is called the second end point (FIG. 1). The amount of alkali required from the start of titration to the first end point is equal to the amount of first dissociated acid in the slurry used for titration. Further, the amount of alkali required from the start of titration to the second end point is equal to the total amount of dissociated acid in the slurry used for titration. Note that the value obtained by dividing the amount of alkali (mmol) required from the start of titration to the first end point by the solid content (g) in the slurry to be titrated was defined as the first amount of dissociated acid (mmol/g). Further, the value obtained by dividing the amount of alkali (mmol) required from the start of titration to the second end point by the solid content (g) in the slurry to be titrated was defined as the total amount of dissociated acid (mmol/g).

<Measurement of fiber width>
The fiber width of the fine fibrous cellulose was measured by the following method. The supernatant liquid of the above-mentioned fine fibrous cellulose-containing dispersion obtained by processing in a wet atomization device is diluted with water so that the concentration of fine fibrous cellulose is 0.01% by mass or more and 0.1% by mass or less. The solution was diluted with water and dropped onto a hydrophilized carbon grid membrane. After drying this, it was stained with uranyl acetate and observed using a transmission electron microscope (manufactured by JEOL, JEOL-2000EX).

<Filtration treatment>
10 L of the obtained fine fibrous cellulose-containing dispersion A was passed through a metal filter (manufactured by Loki Techno Co., Ltd., opening 20 μm) using a pump (Mono Pump, manufactured by Heishin Gijutsu Co., Ltd.). The flow rate was 120 L/h. The differential pressure before and after the filter was 0.03 MPa. The temperature of the fine fibrous cellulose-containing dispersion A was 23°C.

[Example 2]
<Chemical treatment>
Except for using 33 parts by mass of phosphorous acid (phosphonic acid) instead of ammonium dihydrogen phosphate, the same operation as in Example 1 was performed to obtain phosphorous oxo-oxidized pulp.

The infrared absorption spectrum of the obtained phosphorous pulp was measured using FT-IR. As a result, an absorption based on P=O of a phosphonic acid group, which is a tautomer of a phosphorous acid group, was observed near 1210 cm ^-1 , indicating that a phosphorous acid group (phosphonic acid group) was added to the pulp. was confirmed. In addition, when the obtained phosphorous pulp was sampled and analyzed using an X-ray diffraction device, two positions were detected: around 2θ = 14° or more and 17° or less, and around 2θ = 22° or more and 23° or less. A typical peak was observed, and it was confirmed that cellulose type I crystals were present.

<Defibration treatment>
Ion-exchanged water was added to the obtained phosphite pulp to prepare a slurry having a solid content concentration of 2% by mass. This slurry was treated four times at a pressure of 200 MPa using a wet atomizer (Starburst, manufactured by Sugino Machine Co., Ltd.) to obtain a fine fibrous cellulose-containing dispersion B containing fine fibrous cellulose.
It was confirmed by X-ray diffraction that this fine fibrous cellulose B maintained cellulose I type crystals. Further, the fiber width of the fine fibrous cellulose B measured by the same measuring method as in Example 1 was 3 to 5 nm. The amount of phosphorous acid groups (first amount of dissociated acid) of the fine fibrous cellulose measured by the measurement method described above was 1.51 mmol/g, and the total amount of dissociated acid was 1.54 mmol/g.

<Filtration treatment>
The obtained fine fibrous cellulose-containing dispersion B was filtered in the same manner as in Example 1, except that the flow rate was 108 L/h. The differential pressure before and after the filter was 0.04 MPa. The temperature of the fine fibrous cellulose-containing dispersion A was 23°C.

[Comparative example 1]
<Chemical treatment>
As the raw material pulp, softwood kraft pulp (undried) manufactured by Oji Paper was used. This raw material pulp was subjected to alkaline TEMPO oxidation treatment as follows.
First, the above raw material pulp equivalent to 100 parts by mass of dry mass, 1.6 parts by mass of TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl), and 10 parts by mass of sodium bromide were added to 10,000 parts by mass of water. It was distributed to different departments. Next, a 13% by mass aqueous sodium hypochlorite solution was added in an amount of 3.8 mmol per 1.0 g of pulp to start the reaction. During the reaction, a 0.5M aqueous sodium hydroxide solution was added dropwise to maintain the pH at 10 or more and 10.5 or less, and the reaction was considered complete when no change in pH was observed.

Next, the obtained TEMPO oxidized pulp was subjected to a washing treatment. The cleaning treatment was carried out by dehydrating the pulp slurry after TEMPO oxidation to obtain a dehydrated sheet, pouring 5000 parts by mass of ion-exchanged water, stirring to uniformly disperse it, and repeating the process of filtration and dehydration. Ta. The washing end point was determined when the electrical conductivity of the filtrate became 100 μS/cm or less. This dehydrated sheet was subjected to additional oxidation treatment to remove remaining aldehyde groups as follows.

The above-mentioned dehydrated sheet corresponding to 100 parts by mass of dry mass was dispersed in 10,000 parts by mass of 0.1 mol/L acetate buffer (pH 4.8). Next, 113 parts by mass of 80% sodium chlorite was added, and the mixture was immediately sealed and reacted for 48 hours at room temperature while stirring at 500 rpm using a magnetic stirrer to obtain a pulp slurry.

Next, the obtained additionally oxidized TEMPO oxidized pulp was subjected to a washing treatment. The cleaning process was carried out by dehydrating the pulp slurry after additional oxidation to obtain a dehydrated sheet, pouring 5000 parts by mass of ion-exchanged water, stirring to uniformly disperse it, and repeating the process of filtration and dehydration. Ta. The washing end point was determined when the electrical conductivity of the filtrate became 100 μS/cm or less. In addition, when the obtained TEMPO oxidized pulp was sampled and analyzed using an X-ray diffraction device, it was found that there were two positions near 2θ = 14° or more and 17° or less and 2θ = 22° or more and 23° or less. A typical peak was confirmed, and it was confirmed that cellulose type I crystals were present.

<Defibration treatment>
Ion-exchanged water was added to the obtained dehydrated sheet to prepare a slurry having a solid content concentration of 2% by mass. This slurry was treated four times at a pressure of 200 MPa using a wet atomizer (Starburst, manufactured by Sugino Machine Co., Ltd.) to obtain a fine fibrous cellulose-containing dispersion C. The carboxy group content of the fine fibrous cellulose measured by the measuring method described below was 1.30 mmol/g.

<Measurement of carboxy group amount>
The amount of carboxy groups in the fine fibrous cellulose was measured by neutralization titration. The amount of carboxy groups in the fine fibrous cellulose is determined by adding ion-exchanged water to a fine fibrous cellulose-containing dispersion containing the target fine fibrous cellulose to make the content 0.2% by mass, and then treating it with an ion exchange resin. After that, the measurement was performed by titration using an alkali.
The treatment with an ion exchange resin was performed by adding 1/10 of the volume of a strongly acidic ion exchange resin (Amber Jet 1024; manufactured by Organo Co., Ltd., conditioned) to a dispersion containing 0.2% by mass of fine fibrous cellulose. After shaking for a period of time, the slurry was poured onto a mesh having an opening of 90 μm to separate the resin and the slurry.
In addition, titration using an alkali was performed by measuring the change in pH value of the slurry while adding a 0.1N aqueous sodium hydroxide solution to the fibrous cellulose-containing dispersion after treatment with an ion exchange resin. Ta. Observing the change in pH while adding an aqueous sodium hydroxide solution, a titration curve as shown in FIG. 2 is obtained. As shown in Figure 2, in this neutralization titration, in the curve plotting the measured pH against the amount of alkali added, there is one point where the increment (differential value of pH with respect to the amount of alkali added) is maximum. Observed. The maximum point of this increment is called the first end point. Here, the region from the start of titration to the first end point in FIG. 2 is referred to as a first region. The amount of alkali required in the first region is equal to the amount of carboxy groups in the slurry used for titration. Then, by dividing the amount of alkali (mmol) required in the first region of the titration curve by the solid content (g) in the fine fibrous cellulose-containing dispersion to be titrated, the amount of carboxy group introduced (mmol/ g) was calculated.
Note that the above-mentioned amount of carboxy groups introduced (mmol/g) is the amount of substituents per 1 g of mass of fibrous cellulose when the counter ion of the carboxy group is a hydrogen ion (H ⁺ ) (hereinafter referred to as the amount of carboxy groups (acid) type).

<Filtration treatment>
The obtained fine fibrous cellulose-containing dispersion C was filtered in the same manner as in Example 1, except that the flow rate was 60 L/h. The pressure difference before and after the filter was 0.2 MPa. The temperature of the fine fibrous cellulose-containing dispersion A was 23°C.

In Examples 1 and 2, when the same amount of fine fibrous cellulose-containing dispersion was treated, the pressure difference before and after the filter was suppressed. That is, in Examples 1 and 2, it was found that clogging of the filter was suppressed.

[Example 3]
A fine fibrous cellulose-containing dispersion A was obtained in the same manner as in Example 1. The obtained fine fibrous cellulose-containing dispersion A was subjected to filtration treatment in the following manner.

<Filtration treatment>
A nylon mesh (manufactured by NYTAL, opening 1 μm) was attached to a filter holder (manufactured by ADVANTEC, filtration area 38 cm ² ). As a filter aid, 3.8 g of diatomaceous earth (Radiolite 3000, manufactured by Showa Kagaku Kogyo) was collected and dispersed in 500 mL of water to form a filter aid layer. After 1 g of diatomaceous earth was mixed with 1 L of the fine fibrous cellulose-containing dispersion A, it was filtered under reduced pressure. In the vacuum filtration process, the pressure was reduced to 0.05 MPa using an aspirator, and the filtrate recovery rate after 3 minutes of filtration time was 95%.
The filtrate recovery rate was calculated by measuring the amount of filtrate that passed through the filter and using the following formula.
Filtrate recovery rate (%) = Amount of fine fibrous cellulose-containing dispersion (filtrate) after filtration (L) / Amount of fine fibrous cellulose-containing dispersion subjected to filtration (L) x 100

[Example 4]
A fine fibrous cellulose-containing dispersion B was obtained in the same manner as in Example 2. The obtained fine fibrous cellulose-containing dispersion B was filtered in the same manner as in Example 3. In the vacuum filtration process, the pressure was reduced to 0.05 MPa using an aspirator, and the filtrate recovery rate after 3 minutes of filtration time was 93%.

[Comparative example 2]
A fine fibrous cellulose-containing dispersion C was obtained in the same manner as in Comparative Example 1. The obtained fine fibrous cellulose-containing dispersion C was filtered in the same manner as in Example 3. In the vacuum filtration process, the pressure was reduced to 0.05 MPa using an aspirator, and the filtrate recovery rate after 3 minutes of filtration time was 70%.

In the treatments of Examples 3 and 4, the filtrate recovery rate was high. On the other hand, in Comparative Example 2, there was a tendency for the filtrate recovery rate to be inferior. This is considered to be due to the high dispersibility of the fine fibrous cellulose in the examples.

Claims (5)

A fiber comprising the step of filtering a dispersion containing fibrous cellulose having a fiber width of 1000 nm or less and having a phosphorus oxoacid group or a substituent derived from a phosphorus oxoacid group to obtain a fibrous cellulose-containing dispersion as a filtrate. A method for producing a dispersion containing cellulose, comprising:
In the filtration process, at least one selected from a filter medium and a filter aid is used,
A method for producing a fibrous cellulose-containing dispersion , wherein the filtrate recovery rate calculated by the following formula in the filtration step is 80% or more.
Filtrate recovery rate (%) = Amount of fine fibrous cellulose-containing dispersion (filtrate) after filtration (L) / Amount of fine fibrous cellulose-containing dispersion subjected to filtration (L) x 100 The method for producing a fibrous cellulose-containing dispersion according to claim 1, wherein a filter is used as a filter medium in the filtration process. The method for producing a fibrous cellulose-containing dispersion according to claim 2, wherein the filter is made of at least one member selected from the group consisting of resin, metal, and ceramics. The method for producing a fibrous cellulose-containing dispersion according to claim 2 or 3, wherein the filter has an opening of 0.1 μm or more and 5 mm or less. The method for producing a fibrous cellulose-containing dispersion according to any one of claims 1 to 4, wherein a filter medium and a filter aid are used in the filtration step.