JP7346874B2 - Method for producing a dispersion containing fine fibrous cellulose and method for producing a sheet containing fine fibrous cellulose - Google Patents

Description

The present invention relates to a method for manufacturing a dispersion containing fine fibrous cellulose and a method for manufacturing a sheet 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

Dispersions containing fine fibrous cellulose have a wide variety of uses, and depending on the use, high transparency may be required. Further, a dispersion containing fine fibrous cellulose may be processed into a sheet, and such a sheet may also be required to have high transparency. In such highly transparent dispersions and sheets, residual foreign matter poses a problem because it significantly impairs the appearance.
Therefore, an object of the present invention is to provide a method for producing a fine fibrous cellulose-containing dispersion and a fine fibrous cellulose-containing sheet with excellent appearance.

As a result of intensive studies to solve the above problems, the present inventors have discovered that fine fibrous cellulose with excellent appearance can be obtained by providing a step for removing metal foreign matter in the manufacturing process of a fine fibrous cellulose-containing dispersion. It has been found that a containing dispersion and a fine fibrous cellulose containing sheet can be obtained.
Specifically, the present invention has the following configuration.

[1] A method for producing a fine fibrous cellulose-containing dispersion including a step of removing metal foreign matter.
[2] The method for producing a fine fibrous cellulose-containing dispersion according to [1], further comprising a defibration treatment step.
[3] The method for producing a fine fibrous cellulose-containing dispersion according to [2], which includes a defibration treatment step after the metal foreign matter removal step.
[4] In the metal foreign matter removal step, a process using a combination of a metal detector and a solution discharge mechanism is performed, or a process using a magnet is performed, and the fine particles according to any one of [1] to [3] are A method for producing a fibrous cellulose-containing dispersion.
[5] The method for producing a fine fibrous cellulose-containing dispersion according to [4], wherein the metal foreign matter removal step is performed using a combination of a metal detector and a solution discharge mechanism.
[6] In the metal foreign matter removal process, a process using a combination of a metal detector and a solution discharge mechanism, or a process using a magnet, and at least one selected from a screen, a cleaner, and a filter. The method for producing a fine fibrous cellulose-containing dispersion according to [4] or [5], further comprising:
[7] A method for producing a fine fibrous cellulose-containing sheet, comprising a step of forming a sheet from a fine fibrous cellulose-containing dispersion obtained by the manufacturing method according to any one of [1] to [6].

According to the present invention, a method for producing a fine fibrous cellulose-containing dispersion and a fine fibrous cellulose-containing sheet with excellent appearance is provided.

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

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 dispersion containing fine fibrous cellulose) The present invention relates to a method for producing a dispersion containing fine fibrous cellulose, which includes a step of removing metal foreign substances. Since the method for producing a fine fibrous cellulose-containing dispersion of the present invention includes a step of removing metal foreign matter, a fine fibrous cellulose-containing dispersion having an excellent appearance can be obtained. Further, a sheet with excellent appearance can also be formed from the fine fibrous cellulose-containing dispersion thus obtained. In addition, in this specification, fibrous cellulose with a fiber width of 1000 nm or less is referred to as fine fibrous cellulose. Further, in this specification, a metal foreign object refers to a metal foreign object having a maximum width of 0.1 mm or more.

In this specification, the appearance of the fine fibrous cellulose-containing dispersion or the fine fibrous cellulose-containing sheet can be visually observed and determined by the presence or absence of a foreign body sensation. For example, when no foreign matter is contained, the fine fibrous cellulose-containing dispersion becomes a uniform solution, and the surface of the fine fibrous cellulose-containing sheet has a smooth texture and feel.

The method for producing a fine fibrous cellulose-containing dispersion of the present invention further includes a defibration treatment step. Although the above-mentioned metal foreign matter removal step may be provided after the fibrillation treatment step, it is preferably provided before the metal foreign material removal step. That is, it is preferable that a fibrillation treatment step is provided after the metal foreign matter removal step. Thereby, it is possible to prevent troubles such as clogging of nozzles during the defibration treatment process, and it is possible to more effectively increase the production efficiency of the fine fibrous cellulose-containing dispersion and the fine fibrous cellulose-containing sheet. In addition, in the manufacturing method of the present invention, the metal foreign matter removal step may be provided in both the pre-process and post-defibration 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. Note that when long fiber fine fibrous cellulose with a large axial ratio is used, the viscosity tends to increase.

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 preferably includes a step of introducing an ionic substituent group, for example, a step of introducing a phosphorus oxoacid 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. In this embodiment, as an example of a preferable aspect, a case where the phosphorus oxoacid group introduction step is performed twice is mentioned.

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.

<Carboxy group introduction step>
The manufacturing process of the fine fibrous cellulose-containing dispersion may include a carboxy group introduction process as an ionic substituent introduction process. In the carboxy group introduction step, the fiber raw material containing cellulose is subjected to oxidation treatment such as ozone oxidation, oxidation by the Fenton method, TEMPO oxidation treatment, a compound having a group derived from a carboxylic acid or a derivative thereof, or a compound having a group derived from a carboxylic acid. This is carried out by treating the compound with an acid anhydride or a derivative thereof.

Compounds having carboxylic acid-derived groups include, but are not particularly limited to, dicarboxylic acid compounds such as maleic acid, succinic acid, phthalic acid, fumaric acid, glutaric acid, adipic acid, and itaconic acid, and citric acid and aconitic acid. Examples include tricarboxylic acid compounds. Further, derivatives of compounds having a carboxylic acid-derived group include, but are not particularly limited to, for example, imidized acid anhydrides of compounds having a carboxy group, and derivatives of acid anhydrides of compounds having a carboxy group. Examples of imidized products of acid anhydrides of compounds having a carboxyl group include, but are not limited to, imidized products of dicarboxylic acid compounds such as maleimide, succinimide, and phthalic acid imide.

Acid anhydrides of compounds having carboxylic acid-derived groups include, but are not particularly limited to, dicarboxylic acid compounds such as maleic anhydride, succinic anhydride, phthalic anhydride, glutaric anhydride, adipic anhydride, and itaconic anhydride. Examples include acid anhydrides. In addition, acid anhydride derivatives of compounds having a group derived from carboxylic acid include, but are not particularly limited to, for example, dimethylmaleic anhydride, diethylmaleic anhydride, diphenylmaleic anhydride, and the like. Examples include acid anhydrides in which at least some of the hydrogen atoms are substituted with substituents such as alkyl groups and phenyl groups.

In the carboxyl group introduction step, when TEMPO oxidation treatment is performed, it is preferable to perform the treatment under conditions where the pH is 6 or more and 8 or less, for example. Such treatment is also referred to as neutral TEMPO oxidation treatment. Neutral TEMPO oxidation treatment involves, for example, adding pulp as a fiber raw material and TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl) or the like as a catalyst in a sodium phosphate buffer (pH = 6.8). This can be done by adding nitroxy radicals and sodium hypochlorite as a sacrificial reagent. Furthermore, by coexisting sodium chlorite, aldehyde generated during the oxidation process can be efficiently oxidized to carboxy groups. Further, the TEMPO oxidation treatment may be performed under conditions where the pH is 10 or more and 11 or less. Such treatment is also referred to as alkaline TEMPO oxidation treatment. Alkaline TEMPO oxidation treatment can be performed, for example, by adding a nitroxy radical such as TEMPO as a catalyst, sodium bromide as a cocatalyst, and sodium hypochlorite as an oxidizing agent to pulp as a fiber raw material. .

The amount of carboxy groups introduced into the fiber raw material varies depending on the type of substituent, but for example, when introducing carboxy groups by TEMPO oxidation, it is preferably 0.10 mmol/g or more per 1 g (mass) of fine fibrous cellulose. , more preferably 0.20 mmol/g or more, even more preferably 0.50 mmol/g or more, particularly preferably 0.90 mmol/g or more. Moreover, it is preferably 2.5 mmol/g or less, more preferably 2.20 mmol/g or less, and even more preferably 2.00 mmol/g or less. In addition, when the substituent is a carboxymethyl group, the amount may be 5.8 mmol/g or less per 1 g (mass) of fine fibrous cellulose.

<Cleaning process>
In the method for producing a fine fibrous cellulose-containing dispersion according to the present embodiment, the ionic substituent-introduced fibers can be subjected to a washing step, if necessary. The washing step is performed by washing the ionic substituent-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 ionic substituent 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 ionic substituent-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 oxoacid group-introduced fibers may be washed with water or an organic solvent after the ionic substituent introduction step and before the alkali treatment step. After the alkali treatment step and before the fibrillation treatment step, the ionic substituent-introduced fibers subjected to the alkali treatment are preferably washed with water or an organic solvent from the viewpoint of improving handling properties.

<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 an ionic substituent and the defibration step described below. For example, the ionic substituent 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.

<Metal foreign matter removal process>
The method for producing a fine fibrous cellulose-containing dispersion of the present invention includes a step of removing metal foreign matter. Although the metal foreign matter removal step may be provided after the defibration treatment step, it is preferably provided before the metal foreign material removal step. That is, it is preferable that a fibrillation treatment step is provided after the metal foreign matter removal step. This can prevent the occurrence of troubles such as clogging of nozzles during the defibration treatment process, and can more effectively increase the production efficiency of the fine fibrous cellulose-containing dispersion.

In the metal foreign matter removal process, it is preferable to perform processing using a combination of a metal detector and a solution discharge mechanism, or to perform processing using a magnet. Among these, in the metal foreign matter removal process, it is more preferable to perform processing using a combination of a metal detector and a solution discharge mechanism. By discharging the dispersion fraction containing foreign metal particles in this way, it becomes possible to remove metal foreign substances at a high level from the dispersion liquid containing fibrous cellulose or fine fibrous cellulose. Here, when performing processing using a combination of a metal detector and a solution discharge mechanism as the metal foreign matter removal process, examples of the metal detector include a minute metal detector (manufactured by Nikka Densoku Co., Ltd.), a metal detector (manufactured by System Square Co., Ltd.), etc. can be used. The solution discharge mechanism is a mechanism for discharging a dispersion liquid fraction containing metal foreign matter detected by a metal detector. Examples of such mechanisms include, for example, a mechanism for discharging and collecting the dispersion fraction containing foreign metal particles as waste liquid, a mechanism for scooping up the dispersion fraction containing foreign metal substances, and a mechanism for discharging and collecting the dispersion liquid fraction containing foreign metal substances. Examples include a mechanism for sending liquid to a branch pipe. The solution discharge mechanism functions to discharge a dispersion liquid fraction containing a specific metal foreign substance when a metal foreign substance is detected in the metal detector. In this way, it is preferable that the metal detector and the solution discharge mechanism are linked mechanisms.

When a process using a magnet is performed as the metal foreign matter removal step, for example, a magnetic iron removal device (Nikka Densoku Co., Ltd., Magnetic Filter) or the like can be used. It is preferable to use a magnet with a low natural demagnetization rate.

The solid content concentration of the dispersion liquid to be subjected to the metal foreign matter removal step is preferably 0.1% by mass or more, more preferably 0.5% by mass or more. Further, the solid content concentration of the dispersion liquid to be subjected to the metal foreign matter removal 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 metal foreign matter removal step within the above range, it becomes possible to increase the production efficiency of the fine fibrous cellulose-containing dispersion liquid while increasing the metal foreign body removal efficiency.

In the metal foreign matter removal process, in addition to a process using a combination of a metal detector and a solution discharge mechanism, or a process using a magnet, a process using at least one selected from a screen, a cleaner, and a filter is further performed. It's okay. Screens and filters are divided into components based on the shape and size of the cellulose fibers. Further, the cleaner is processed by, for example, centrifugation, and each component is separated depending on the difference in specific gravity with respect to cellulose fibers. In this way, by further performing a process using at least one selected from a screen, a cleaner, and a filter, it is possible to not only increase the efficiency of removing metal foreign substances but also to remove other foreign substances other than metal foreign substances. Become. The opening of at least one selected from screens and filters is preferably 0.01 mm or more, more preferably 0.05 mm or more, and even more preferably 0.10 mm or more. Further, the opening of at least one selected from screens and filters is preferably 1.00 mm or less, more preferably 0.80 mm or less, and even more preferably 0.60 mm or less. Note that the opening in this specification is, for example, when the shape of each opening constituting at least one mesh portion selected from a screen and a filter is square, the opening is the length of one side of the square. . Further, if the shape of each opening is a square, the length of the longest side corresponds to the length, and if the shape of each opening is circular or elliptical, the diameter corresponds to the opening.

At least one selected from the screen and filter is preferably composed of at least one selected from the group consisting of resin, corrosion-resistant metal, and ceramics, and is preferably composed of resin. It is more preferable. Examples of the resin constituting at least one selected from the screen and the filter include thermoplastic resins, thermosetting resins, electron beam curable resins, and the like. Among these, thermoplastic resins are preferably used, and examples of the thermoplastic resins include polypropylene resins, polyester resins, polyamide resins, polycarbonate resins, ABS resins, and nylon resins. Among these, at least one selected from polypropylene resin and nylon resin is preferably used as the resin constituting the filter. By using such a resin filter, foreign matter removal efficiency and production efficiency can be more effectively increased.

When a metal detector is used in the metal foreign matter removal process, the processing speed of the dispersion liquid is preferably 60 m/min or less. By controlling the processing speed of the dispersion liquid within the above range, the removal efficiency of metal foreign matter can be further improved.

<Defibration treatment>
The method for producing a fine fibrous cellulose-containing dispersion of the present invention further includes a defibration treatment step. It is preferable that the fibrillation treatment step is provided after the metal foreign matter removal step. This can prevent the occurrence of troubles such as clogging of nozzles during the defibration treatment process, and can more effectively increase the production efficiency of the fine fibrous cellulose-containing dispersion. For example, if the number of times the pressure is increased in the defibration process is small (eg, 2 times or less per 1 ton of throughput), it can be determined that the occurrence of clogging troubles of nozzles, etc. in the defibration process is suppressed.

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, for example, diluted ionic substituent-introduced fibers with a dispersion medium to form a slurry. 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 ionic substituent-introduced fibers in a dispersion medium may contain solids other than the phosphorus-oxo acid group-introduced fibers, such as urea having hydrogen bonding properties.

The metal foreign matter concentration in the fine fibrous cellulose-containing dispersion obtained through the above-mentioned metal foreign matter removal step and fibrillation treatment step is preferably 0.01 pieces/L or less, and 0.001 pieces/L or less. It is more preferable that In addition, it is particularly preferable that the concentration of metal foreign substances in the fine fibrous cellulose-containing dispersion is 0 pieces/L.

(Fine fibrous cellulose-containing dispersion)
The fine fibrous cellulose-containing dispersion obtained by the production method of the present invention contains fibrous cellulose (fine fibrous cellulose) with 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. As a result, when a fine fibrous cellulose-containing sheet is produced from a fine fibrous cellulose-containing dispersion, the transparency of the sheet is increased, and in addition, the strength of the sheet is also increased. Furthermore, when a fine fibrous cellulose-containing sheet is manufactured from the fine fibrous cellulose-containing dispersion obtained by the manufacturing method of the present invention, a sheet with excellent appearance without any foreign matter remaining can be obtained.

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. Although the average fiber width of the fibrous cellulose is preferably within the above range, the fine fibrous cellulose-containing dispersion may contain coarse fibers with a fiber width exceeding 1000 nm.

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.

The fibrous cellulose may have at least one of an ionic substituent and a nonionic substituent. From the viewpoint of improving the dispersibility of the fibrous cellulose in the dispersion medium and increasing the fibrillation efficiency in the fibrillation process, it is more preferable that the fibrous cellulose has an ionic substituent. The ionic substituent can include, for example, one or both of an anionic group and a cationic group. Further, the nonionic substituent may include, for example, an alkyl group and an acyl group. In this embodiment, it is particularly preferable to have an anionic group as the ionic substituent. Note that the fibrous cellulose does not need to be subjected to a treatment for introducing ionic substituents.

Examples of the anionic group as an ionic substituent include a phosphorus oxoacid group or a substituent derived from a phosphorus oxoacid group (sometimes simply referred to as a phosphorus oxoacid group), a carboxy group or a substituent derived from a carboxyl group (simply a carboxy group) ), and a sulfone group or a substituent derived from a sulfone group (sometimes simply referred to as a sulfone group). Among these, the anionic group is more preferably at least one selected from a phosphorus oxo acid group and a carboxy group, and particularly preferably a phosphorus oxo acid group. By introducing a phosphoric acid group such as a phosphoric acid group or a phosphorous acid group as an anionic group, for example, the dispersibility of fibrous cellulose can be further improved even under alkaline or acidic conditions. When a sheet is formed from a cellulose-containing dispersion, the strength of the fine fibrous cellulose-containing sheet can be increased. Further, by introducing a phosphoric acid group such as a phosphoric acid group or a phosphorous acid group, the transparency of the sheet obtained can be more effectively improved.

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 ionic substituent introduced into the fibrous cellulose is preferably 0.10 mmol/g or more, more preferably 0.20 mmol/g or more, and 0.50 mmol/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 ionic substituents introduced into fibrous cellulose is preferably 5.20 mmol/g or less, more preferably 3.65 mmol/g or less, and 3.65 mmol/g or less per 1 g (mass) of fibrous cellulose. It is more preferably at most .50 mmol/g, particularly preferably at most 3.00 mmol/g. By controlling the amount of the ionic substituent to be introduced within the above range, it is possible to easily refine the fiber raw material and improve the stability of the fibrous cellulose. Furthermore, by introducing the amount of ionic substituent within the above range, it is possible to exhibit good properties in various uses such as a thickener for fibrous cellulose. Here, the denominator in the unit mmol/g indicates the mass of the fibrous cellulose when the counter ion of the ionic substituent is a hydrogen ion (H ⁺ ).

The amount of ionic substituents 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.

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. The amount of carboxy 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. 2 is obtained. The titration curve shown in the upper part of Figure 2 plots the measured pH against the amount of alkali added, and the titration curve shown in the lower part of Figure 2 plots the pH measured against the amount of alkali added. Increment (differential value) (1/mmol) is plotted. In this neutralization titration, one point where the increment (differential value of pH with respect to the amount of alkali dropped) becomes maximum is confirmed on the curve plotting the measured pH against the amount of alkali added, and this maximum point is This is called the 1st 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 dispersion 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 dispersion containing the fibrous cellulose to be titrated, the amount of carboxy group introduced (mmol) is calculated. /g).
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).

The content of fibrous cellulose is preferably 0.05% by mass or more, more preferably 0.1% by mass or more, and 0.2% by mass or more, based on the total mass of the fine fibrous cellulose-containing dispersion. More preferably, it is at least % by mass. 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.

Note that the total light transmittance of the dispersion liquid mentioned above is the total light transmittance of the dispersion liquid before it passes through the filter, but the total light transmittance of the dispersion liquid after passing through the filter also has the same total light transmittance as above. is preferably obtained. That is, when the content of fibrous cellulose contained in the dispersion after passing through the filter is 0.2% by mass, the total light transmittance of the dispersion is preferably 80% or more, and 85%. % or more, more preferably 90% or more.

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. Note that the total light transmittance haze of the dispersion liquid is the haze of the dispersion liquid before passing through a filter, but it is preferable that the same haze as described above is obtained even in the dispersion liquid after passing through a filter.

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 mPa·s 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, alignment promoters, plasticizers, dispersants, 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 does not slow down the filtration rate too much. Such filter cloth is not particularly limited, but is preferably, for example, a sheet, woven fabric, or porous membrane made of an organic polymer. 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 between the step of removing metal foreign matter and the step of forming the sheet. More preferably, it is provided. 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.

(Fine fibrous cellulose-containing sheet)
The present invention may also relate to a fine fibrous cellulose-containing sheet manufactured by the method for manufacturing a fine fibrous cellulose-containing sheet described above. In the fine fibrous cellulose-containing sheet, residual foreign matter is suppressed, and in particular, residual metallic foreign matter is suppressed. Therefore, it can be said that it is a fine fibrous cellulose-containing sheet with excellent appearance. Furthermore, in the sheet of the present invention, residual foreign matter is suppressed, and in particular, residual metallic foreign matter is suppressed, so that the sheet has an excellent tactile feel.

The content of fibrous cellulose is preferably 1% by mass or more, more preferably 2% by mass or more, and preferably 3% by mass or more with respect to the total mass of the fine fibrous cellulose-containing sheet. More preferred. Further, the content of fibrous cellulose may be 100% by mass based on the total mass of the fine fibrous cellulose-containing sheet, but optional components that may be included in the dispersion may be included as appropriate.

The thickness of the fine fibrous cellulose-containing sheet produced by the above-described production method is preferably 5 μm or more, more preferably 8 μm or more, and even more preferably 10 μm or more. Further, the thickness of the fine fibrous cellulose-containing sheet is preferably 1000 μm or less, more preferably 800 μm or less, and even more preferably 600 μm or less.

The basis weight of the fine fibrous cellulose-containing sheet is preferably 10 g/m ² or more, more preferably 30 g/m ² or more, even more preferably 50 g/m ² or more, and 100 g/m ² It is particularly preferable that it is above. Further, the basis weight of the fine fibrous cellulose-containing sheet is preferably 500 g/m ² or less, more preferably 400 g/m ² or less, and even more preferably 300 g/m ² or less. Here, the basis weight of the fine fibrous cellulose-containing sheet is a value calculated in accordance with JIS P 8124:2011.

The haze of the fine fibrous cellulose-containing sheet is, for example, preferably 2% or less, more preferably 1.5% or less, and even more preferably 1% or less. On the other hand, the lower limit of the haze of the fine fibrous cellulose-containing sheet is not particularly limited, and may be, for example, 0%. Here, the haze of the fine fibrous cellulose-containing sheet is a value measured using a haze meter (HM-150, manufactured by Murakami Color Research Institute) in accordance with JIS K 7136.

The total light transmittance of the fine fibrous cellulose-containing sheet is, for example, preferably 80% or more, more preferably 85% or more, and even more preferably 90% or more. On the other hand, the upper limit of the total light transmittance of the fine fibrous cellulose-containing sheet is not particularly limited, and may be, for example, 100%. Here, the total light transmittance of the fine fibrous cellulose-containing sheet is a value measured using a hazemeter (HM-150, manufactured by Murakami Color Research Institute) in accordance with JIS K 7361.

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]
<Preparation of phosphorus oxo oxidized pulp>
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 phosphorus oxo-oxidized pulp with 10 L of ion exchange water, a 1N sodium hydroxide aqueous solution was added little by little while stirring to obtain a phosphorus oxo-oxidized pulp slurry with a pH of 12 to 13. . 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 phosphoric acid groups was observed near 1230 cm ⁻¹ , confirming 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.

<Metal foreign matter removal 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 passed through a minute metal detector (metal detector) (manufactured by Nikka Densoku Co., Ltd., NT3P-2.0S+BV) equipped with a solution discharge mechanism to remove metal foreign substances. When 1 ton of slurry was passed through, metal foreign matter was detected three times.

<Defibration treatment>
<Metallic foreign matter removal treatment> The slurry obtained through the process was treated four times at a pressure of 200 MPa using a wet atomization device (manufactured by Sugino Machine Co., Ltd., Starburst) to form a fine fibrous material containing fine fibrous cellulose. A cellulose-containing dispersion was obtained. During the defibration process, the number of times the pressure was increased to 210 MPa or higher was zero.

It was confirmed by X-ray diffraction that the fine fibrous cellulose in the fine fibrous cellulose-containing dispersion 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. Further, the amount of phosphorus oxo acid groups (first dissociated acid amount) measured by the measurement method described below was 1.45 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. After performing a treatment step with an ion exchange resin on a fibrous cellulose-containing slurry prepared by diluting the target fine fibrous cellulose-containing dispersion with ion-exchanged water to a content of 0.2% by mass. , was measured by titration with 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 slurry, 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, and the phosphorus oxo acid group was converted to the acid form.
In addition, titration using an alkali is performed by adding 10 μL of 0.1N sodium hydroxide aqueous solution every 5 seconds to the fibrous cellulose-containing slurry after treatment with an ion exchange resin, and measuring the change in the pH value of the slurry. It was done by doing. 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).

[Example 2]
In <metallic foreign matter removal treatment> of Example 1, the sample was placed in a flat screen manufactured by Kumagai Riki Kogyo before being passed through a micrometal detector. The screen used had an opening of 0.25 mm. The dispersion liquid that had passed through the screen was collected, and the recovered liquid was subjected to the same treatment as <Metal foreign matter removal treatment> in Example 1 to obtain a dispersion liquid subjected to metal foreign matter removal treatment. In the <metallic foreign matter removal process> of Example 2, metallic foreign matter was detected twice. Other procedures were the same as in Example 1 to obtain a fine fibrous cellulose-containing dispersion. During the defibration process, the number of times the pressure was increased to 210 MPa or higher was zero.

[Example 3]
<Chemical treatment>
Except for using 33 parts by mass of phosphorous acid (phosphonic acid) instead of ammonium dihydrogen phosphate, the same operation as <Preparation of phosphorus oxo oxidized pulp> of Example 1 was performed to obtain phosphorus oxo oxidized pulp 2.

The infrared absorption spectrum of the thus obtained phosphorus oxo-oxidized pulp 2 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 phosphorus oxo-oxidized pulp 2 was analyzed using an X-ray diffraction device, two positions were found: 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.

<Metal foreign matter removal treatment>
Ion-exchanged water was added to the obtained phosphorus oxo-oxidized pulp 2 to prepare a slurry having a solid content concentration of 2% by mass. This slurry was passed through a minute metal detector (NT3P-2.0S+BV, manufactured by Nikka Densoku Co., Ltd.) equipped with a solution discharge mechanism to remove metal foreign substances. When 1 ton of slurry was passed through, metal foreign matter was detected three times.

<Defibration treatment>
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 containing fine fibrous cellulose. During the defibration process, the number of times the pressure was increased to 210 MPa or higher was zero.

It was confirmed by X-ray diffraction that the fine fibrous cellulose in the fine fibrous cellulose-containing dispersion maintained cellulose type I crystals. Further, the fiber width of the fine fibrous cellulose measured by the same measuring method as in Example 1 was 3 to 5 nm. Further, the amount of phosphorus oxo acid groups (first dissociated acid amount) measured in <Measurement of amount of phosphorus oxo acid groups> described above was 1.51 mmol/g.

[Comparative example 1]
In Example 1, <metallic foreign matter removal treatment> was not performed. A fine fibrous cellulose-containing dispersion was obtained in the same manner as in Example 1 except for the above. During the defibration process, the pressure was increased to 210 MPa or more three times.

<Evaluation>
Sheets were formed using the fine fibrous cellulose-containing dispersions obtained in Examples and Comparative Examples, and their appearance was inspected.

<Method of forming sheet>
The concentration of the fine fibrous cellulose-containing dispersion was adjusted by adding ion-exchanged water so that the solid content concentration was 0.5% by mass. Next, 20 parts by mass of a 0.5% by mass aqueous solution of polyethylene oxide (manufactured by Sumitomo Seika Co., Ltd., PEO-18) was added to 100 parts by mass of this fine fibrous cellulose-containing dispersion to obtain a coating liquid. . The coating solution was measured so that the finished basis weight of the resulting sheet (layer composed of solid components of the above coating solution) was 50 g/m ² , and coated on a commercially available acrylic plate. It was dried in a constant temperature and humidity chamber at a humidity of 15%. In addition, a metal frame for damming (a metal frame with internal dimensions of 180 mm x 180 mm) was placed on the acrylic board so as to have a predetermined basis weight. Thereby, a sheet containing fine fibrous cellulose and having a thickness of 33 μm was obtained.

<Appearance inspection>
A visual appearance inspection was conducted on the sheet formed by the method described above.
○: The presence of foreign matter cannot be confirmed, and the result is extremely good.
×: The presence of foreign matter was confirmed, and the appearance was poor.

In the fine fibrous cellulose-containing sheets obtained in Examples, the presence of foreign matter was not confirmed, and sheets with excellent appearance were obtained. Further, in the examples, no pressure increase was observed during the defibration process, and productivity was also excellent.

Claims (5)

Including metal foreign matter removal process,
The metal foreign object removal step is a step of removing metal foreign objects having a maximum width of 0.1 mm or more,
In the metal foreign matter removal step, a process is performed using a combination of a metal detector and a solution discharge mechanism,
A method for producing a fine fibrous cellulose-containing dispersion having a metal foreign matter concentration of 0.01 pieces/L or less . The method for producing a fine fibrous cellulose-containing dispersion according to claim 1, further comprising a defibration treatment step. The method for producing a fine fibrous cellulose-containing dispersion according to claim 2, comprising a defibration treatment step after the metal foreign matter removal step. The method for producing a fine fibrous cellulose-containing dispersion according to any one of claims 1 to 3, wherein in the metal foreign matter removal step, a treatment using at least one selected from a screen, a cleaner, and a filter is further performed. . A method for producing a sheet containing fine fibrous cellulose, comprising the step of forming a sheet from a dispersion containing fine fibrous cellulose obtained by the method according to any one of claims 1 to 4 .