JP7375319B2 - Method for producing fibrous cellulose-containing sheet - Google Patents

Description

The present invention relates to a method for manufacturing a fibrous cellulose-containing sheet.

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, in Patent Documents 1 to 3, methods for manufacturing sheets containing fine fibrous cellulose are discussed. In Patent Document 1, a polyimide resin and cellulose nanofibers are crosslinked to form a transparent composite film. Further, Patent Documents 2 and 3 disclose transparent substrates containing fine fibrous cellulose and a matrix material. In Patent Documents 1 to 3, a sheet that is a raw material for a sheet is filtered and then a film is formed into a sheet, but the filtration conditions and the like are not examined in detail.

JP2013-018931A Japanese Patent Application Publication No. 2011-001559 Japanese Patent Application Publication No. 2010-180416

Transparency is sometimes required for sheets containing fine fibrous cellulose. In such a transparent sheet, it is also important that foreign matter is not included in the sheet. Therefore, when forming a sheet from a slurry containing fine fibrous cellulose, it is required to control the manufacturing process so that no foreign matter is mixed in the sheet. On the other hand, when forming a sheet from a slurry containing fine fibrous cellulose, improving the production efficiency is also an issue.

Therefore, in order to solve the problems of the prior art, the present inventors conducted studies with the aim of providing a method for manufacturing a fine fibrous cellulose-containing sheet that has improved both foreign matter removal efficiency and production efficiency. I proceeded.

As a result of intensive studies to solve the above problems, the present inventors have discovered that in the process of passing a dispersion containing fine fibrous cellulose through a filter, by controlling the opening of the filter pores within a predetermined range. succeeded in achieving both high levels of foreign matter removal efficiency and production efficiency in the manufacturing process of sheets containing fine fibrous cellulose. Specifically, the present invention has the following configuration.

[1] A step of passing a dispersion containing fibrous cellulose with a fiber width of 1000 nm or less through a filter;
A method for producing a fibrous cellulose-containing sheet, comprising the step of forming a sheet from a dispersion liquid after passing through a filter,
A method for manufacturing a fibrous cellulose-containing sheet using a filter having filter pores of 12 μm or more and 100 μm or less in the step of passing through the filter.
[2] The method for producing a fibrous cellulose-containing sheet according to [1], wherein the filter is made of at least one member selected from the group consisting of resin, corrosion-resistant metal, and ceramics.
[3] The method for producing a fibrous cellulose-containing sheet according to [1] or [2], wherein a plurality of filters are arranged, and the plurality of filters are arranged in parallel.
[4] The method for producing a fibrous cellulose-containing sheet according to [1] or [2], wherein a plurality of filters are arranged, and the plurality of filters are arranged in series.
[5] The step of forming the sheet includes the step of paper-making the dispersion after passing through the filter, or the step of coating the dispersion on a base material [1] to [4]. Method of manufacturing sheets.

According to the manufacturing method of the present invention, both foreign matter removal efficiency and production efficiency can be improved in the manufacturing process of a fine fibrous cellulose-containing sheet.

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 manufacturing a sheet containing fine fibrous cellulose) The present invention comprises a step of passing a dispersion containing fibrous cellulose having a fiber width of 1000 nm or less through a filter, a step of forming a sheet from the dispersion after passing through the filter, The present invention relates to a method for producing a fibrous cellulose-containing sheet. Here, in the step of passing through the filter, a filter with filter pore openings of 12 μm or more and 100 μm or less is used. As described above, in the present invention, by setting the opening of the filter pores within a predetermined range in the process of passing through the filter, the production efficiency of the sheet can be improved while increasing the foreign matter removal efficiency in the manufacturing process of the fine fibrous cellulose-containing sheet. can be increased.
In addition, in this specification, fibrous cellulose having a fiber width of 1000 nm or less may be referred to as fine fibrous cellulose or CNF.

The opening of the filter pores of the filter used in the step of passing through the filter may be 12 μm or more, preferably 15 μm or more, and more preferably 20 μm or more. Further, the opening of the filter pores may be 100 μm or less, preferably 80 μm or less, and more preferably 65 μm or less. In addition, in this specification, the opening of the filter hole is, for example, if the shape of each opening of the filter hole is a square, the opening is the length of one side of the square. Furthermore, if the shape of each opening of the filter hole is a square, the length of the longest side corresponds to the length of the longest side, and if the shape of each opening is circular or elliptical, the diameter or major axis corresponds to the opening.

When forming a fine fibrous cellulose-containing sheet, the sheet is formed from a fine fibrous cellulose-containing dispersion (hereinafter also referred to as a dispersion or slurry). In the present invention, in the step of passing through the filter, a filter whose opening of the filter pores is within the above range is used. Contaminant foreign matter can be effectively removed. For example, it effectively removes cellulose fibers that remain in the process of manufacturing fine fibrous cellulose, aggregates of fine fibrous cellulose, and foreign substances such as metal pieces caused by raw materials and manufacturing equipment. be able to. Note that in the step of passing through the filter, foreign matter can be removed as described above, so the step of passing through the filter can also be called a foreign matter removal step or a filtration step.

Normally, when the opening of a filter is made smaller in order to increase the efficiency of removing foreign matter, the filter becomes clogged, resulting in a decrease in the liquid flow rate. However, in the present invention, by controlling the opening of the filter pores within the above-mentioned range, the drop in the liquid passing rate is suppressed while increasing the foreign matter removal efficiency. In the present invention, by suppressing a decrease in the liquid passing rate (rate of decrease in flow rate over a predetermined period of time), the production efficiency of the fine fibrous cellulose-containing sheet is increased as a result. In this way, the present invention has discovered the optimal conditions for passing a fine fibrous cellulose-containing dispersion through a filter, and has succeeded in achieving both foreign matter removal efficiency and production efficiency at a high level. .

In the method for producing a fibrous cellulose-containing sheet of the present invention, the rate of decrease in the flow rate of the dispersion after flowing for 10 minutes is preferably less than 30%, more preferably less than 20%, and less than 10%. More preferably, it is less than 5%, even more preferably less than 1%. Here, the rate of decrease in the flow rate of the dispersion liquid after 10 minutes of flowing is a value calculated by the following formula.
Flow rate reduction rate (%) = (starting flow rate (L/min) - flow rate after 10 minutes of liquid flow (L/min)) / starting flow rate (L/min) x 100 (%)
Note that each flow rate is measured by flowmeters installed before and after the filter. Further, each flow rate is also calculated by feeding the dispersion liquid to the filter with a metering liquid feeding pump and measuring the flow rate per unit time from the filter.
By setting the flow rate reduction rate within the above range, it becomes possible to increase the filtration rate of the dispersion, and as a result, the production efficiency of the fine fibrous cellulose-containing sheet is increased.

Furthermore, in the manufacturing process of the present invention, by controlling the opening of the filter pores within the above range, it is also possible to reduce the bubble content of the dispersion after passing through the filter. That is, by passing the fine fibrous cellulose-containing dispersion through a filter having a predetermined opening, the air bubbles contained in the dispersion can be captured in the filter. If the fine fibrous cellulose-containing dispersion contains air bubbles, the air bubbles will be trapped in the fine fibrous cellulose-containing sheet formed from the dispersion, resulting in problems such as deterioration in the appearance and strength of the sheet. It causes In the present invention, by controlling the opening of the filter pores within the above range, the air bubble content of the dispersion liquid after passing through the filter is reduced, resulting in a fine fibrous cellulose with excellent appearance and high strength. It becomes easier to obtain a containing sheet.

Note that the bubble content in the dispersion before and after passing through the filter can be calculated by measuring the density of the dispersion before and after passing through the filter, and calculating the degree of increase in density from that value. Specifically, the density increase degree is calculated as follows. First, the density before passing through the filter is determined by pouring the dispersion into a beaker (1 L) whose weight is known in advance, measuring the weight (g) with a balance, and passing 1/1000 of that value. Define the previous density (g/cm ³ ). The density after passing through the filter is determined by measuring the dispersion that has passed through the filter in the same manner as above. Then, from the density measured as described above, the density increase degree is calculated using the following formula.
Density increase rate = Density after passing through the filter (g/cm ³ )/Density before passing through the filter (g/cm ³ )
The degree of density increase is preferably 1.02 or more, more preferably 1.10 or more. Note that a large degree of increase in density means that the bubbles contained in the slurry disappeared or were captured by the filter when the slurry was passed through the filter.

The filter used in the step of passing through the filter is preferably made of at least one selected from the group consisting of resin, corrosion-resistant metal, and ceramics, and more preferably made of resin. preferable. That is, the filter is preferably a resin filter.

Specifically, examples of the resin constituting the filter include thermoplastic resins and thermosetting resins. 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. Note that it is also preferable to use a cartridge type filter. Cartridge type filters are easy to replace.

The filter is fixed to the filter housing, and it is preferable to use a member made of SUS as the fixing member at that time. By using a SUS member as the fixing member, corrosion due to the dispersion liquid can be avoided.

In the manufacturing process of the present invention, a plurality of filters may be arranged. For example, multiple filters may be arranged in parallel. In such a case, the processing speed of the dispersion can be effectively increased. In addition, when filters are arranged in parallel, if one filter becomes clogged and requires cleaning or replacement, or when performing maintenance, etc., the other filter can be used. The production process for cellulose-containing sheets can be operated without stopping.

Furthermore, when a plurality of filters are arranged in the manufacturing process of the present invention, the plurality of filters may be arranged in series. In such a case, the foreign matter removal performance can be improved more effectively. Further, when two filters are arranged in series, the openings of the filter holes of the first stage filter and the second stage filter may be different. For example, by using a filter with a large opening in the first stage filter and a filter with a smaller opening in the second stage filter, foreign matter removal performance can be more effectively enhanced. . Moreover, by using such a filter, clogging of the filter can also be suppressed. Note that in the manufacturing process of the present invention, three or more filters may be arranged in series.

In the manufacturing process of the present invention, the filters may be arranged in a combination of parallel arrangement and series arrangement. For example, a parallel arrangement and a series arrangement may be provided in this order.

<Sheeting process>
In the manufacturing process of the present invention, after the step of passing through the filter, a step of forming a sheet from the dispersion after passing through the filter is provided. 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 passing through the filter 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 vacuum thin film 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 dispersion)
The fine fibrous cellulose-containing dispersion used in the method for producing a fibrous cellulose-containing sheet of the present invention contains fibrous cellulose (fine fibrous cellulose) having a fiber width of 1000 nm or less. The fiber width of the fibrous cellulose is preferably 100 nm or less, more preferably 8 nm or less. As a result, when a fine fibrous cellulose-containing sheet is manufactured, the transparency of the sheet is increased, and in addition, the strength of the sheet is also increased.

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.

Anionic groups as ionic substituents include, for example, phosphorus oxo acid groups or substituents derived from phosphorus oxo acid groups (sometimes simply referred to as phosphorus oxo acid groups), carboxy groups or substituents derived from carboxy groups (simply referred to as carboxy groups). ), 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 It is called 1 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 based on the total mass of the fine fibrous cellulose-containing dispersion,
It is preferably 0.05% by mass or more, more preferably 0.1% by mass or more, and even more preferably 0.2% by mass or more. Further, the content of fibrous cellulose is preferably 50% by mass or less, more preferably 40% by mass or less, and 30% by mass or less based on the total mass of the fine fibrous cellulose-containing dispersion. It is more preferable that the amount is 20% by mass or less, and particularly preferably 20% by mass or less.

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

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. Typically, highly viscous solutions tend to slow down when passed through a filter and are more likely to entrap air bubbles. For this reason, it is not easy to increase the production efficiency of the sheet and keep the content of air bubbles trapped in the sheet low. However, in the manufacturing method of the present invention, in the process of passing through the filter, By using a filter with openings, it is possible to suppress a decrease in the speed when passing through the filter, and furthermore, it is possible to suppress the content of air bubbles to a low level. In addition, when measuring the viscosity of the fine fibrous cellulose-containing dispersion, the dispersion before passing through the filter 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.

<Production process of fine fibrous cellulose>
<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>
Preferably, the process for producing fine fibrous cellulose includes 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>
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 acid anhydrides of compounds having a carboxyl group include, but are not limited to, imidized 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 fine fibrous cellulose in this 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>
When producing fine fibrous cellulose, the fiber raw material may be subjected to alkali treatment between the ionic substituent introduction step and the defibration 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>
When producing fine fibrous cellulose, 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.

<Defibration treatment>
Fine fibrous cellulose is obtained by defibrating the ionic substituent-introduced fibers in the defibrating process. 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 fibrillation treatment step, it is preferable that, for example, the ionic substituent-introduced fibers are diluted 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.

(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. 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 1000 g/m ² or less, more preferably 800 g/m ² or less, and even more preferably 600 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.

[Manufacture example 1]
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 for 200 seconds in a hot air dryer at 165°C to introduce phosphoric acid groups into the cellulose in the pulp, thereby obtaining phosphorus oxo-oxidized pulp A.

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

[Neutralization treatment]
Next, the washed phosphorus oxo-oxidized pulp was neutralized 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 neutralized phosphorus oxo-oxidized pulp A. Next, the above-mentioned washing treatment was performed on the phosphorus oxo-oxidized pulp A after the neutralization treatment.

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

[Defibration processing]
Ion-exchanged water was added to the obtained phosphorus oxo-oxidized pulp A to prepare a slurry having a solid content concentration of 2% by mass. This slurry was treated twice at a pressure of 200 MPa with a wet atomizer (Starburst, manufactured by Sugino Machine Co., Ltd.) to obtain a fine fibrous cellulose dispersion A containing fine fibrous cellulose. It was confirmed by X-ray diffraction that this fine fibrous cellulose maintained cellulose type I crystals. Further, when the fiber width of the fine fibrous cellulose was measured using a transmission electron microscope, it was 3 to 5 nm. The amount of phosphorus oxo acid groups (first dissociated acid amount) measured by the measurement method described in [Measurement of phosphorus oxo acid group amount] described later was 1.45 mmol/g. Note that the total amount of dissociated acids was 2.45 mmol/g.

[Manufacture example 2]
As raw material pulp, softwood kraft pulp manufactured by Oji Paper (solid content 93% by mass, basis weight 245g/m ² sheet form, Canadian standard freeness (CSF) measured according to JIS P 8121 after disintegration is 700ml) It was used. This raw material pulp was subjected to phosphorus oxo oxidation treatment as follows. First, a mixed aqueous solution of phosphorous acid (phosphonic acid) and urea was added to 100 parts by mass (absolutely dry mass) of the raw material pulp, and 33 parts by mass of phosphorous acid (phosphonic acid), 120 parts by mass of urea, and 150 parts by mass of water were added. 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 250 seconds to introduce phosphorous acid groups into the cellulose in the pulp, thereby obtaining phosphorus oxo-oxidized pulp B.

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

[Neutralization treatment]
Next, the washed phosphorus oxo-oxidized pulp B was neutralized in the following manner. First, after diluting the washed phosphorus oxo-oxidized pulp B with 10 L of ion exchange water, a 1N aqueous sodium hydroxide solution is added little by little while stirring to obtain a phosphorus oxo-oxidized pulp slurry with a pH of 12 to 13. Ta. Next, the phosphorus oxo-oxidized pulp slurry was dehydrated to obtain a neutralized phosphorus oxo-oxidized pulp B. Next, the above-mentioned washing treatment was performed on the phosphorus oxo-oxidized pulp B after the neutralization treatment.

The infrared absorption spectrum of the phosphorus oxo-oxidized pulp B thus obtained 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 B 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.

[Defibration processing]
After adding ion-exchanged water to the obtained phosphite pulp, it was stirred to form a 2% by mass slurry. This slurry was treated three times at a pressure of 200 MPa using a wet atomizer (Ultimizer, manufactured by Sugino Machine Co., Ltd.) to obtain a fine fibrous cellulose dispersion B. It was confirmed by X-ray diffraction that this fine fibrous cellulose B maintained cellulose I type crystals. Further, the fiber width of the fine fibrous cellulose B was measured using a transmission electron microscope and was found to be 3 to 5 nm. Further, the amount of phosphorus oxo acid groups (first dissociated acid amount) measured by the measurement method described in [Measurement of phosphorus oxo acid group amount] described later was 1.51 mmol/g. Note that the total amount of dissociated acids was 1.54 mmol/g.

[Dissolution of polyvinyl alcohol]
Polyvinyl alcohol (manufactured by Kuraray Co., Ltd., Poval 105, degree of polymerization: 500, degree of saponification: 98-99 mol%) was added to ion-exchanged water at a concentration of 20% by mass, and the mixture was stirred at 95°C for 1 hour to dissolve. . Further, the mixture was diluted with ion-exchanged water so that the solid content concentration was 0.5% by mass to obtain a polyvinyl alcohol aqueous solution.

[Example 1]
[Preparation of sheet containing fine fibrous cellulose]
Fine fibrous cellulose dispersion A was diluted with ion-exchanged water so that the solid content concentration was 0.5% by mass. Next, 90 parts by mass of a polyvinyl alcohol aqueous solution was added to 10 parts by mass of the diluted fine fibrous cellulose dispersion A, and the mixture was stirred for 15 minutes at 3000 rpm using a Tornado manufactured by As One Corporation to prepare a sheet before passing through a filter. I got the raw material. Thereafter, the raw material for sheet production before passing through the filter was passed through a polypropylene filter (manufactured by Loki Techno Co., Ltd., 125L-SLS-200, opening 20 μm) set in a special filter housing to obtain a raw material for sheet production.
Next, the raw materials for sheet production were weighed so that the finished basis weight of the sheet would be 50 g/m ² , spread on a commercially available transparent acrylic plate, and dried in a constant temperature dryer at 50°C. Note that a damming frame (inner dimensions 100 mm x 100 mm, height 50 mm) was placed on the acrylic board so as to have a predetermined basis weight. Next, the dried sheet was peeled from the acrylic plate to obtain a fine fibrous cellulose-containing sheet.

[Example 2]
A fine fibrous cellulose-containing sheet was obtained in the same manner as in Example 1, except that a polypropylene filter (manufactured by Loki Techno, 125L-SLS-150, opening 15 μm) was used.

[Example 3]
Fine fibrous cellulose dispersion A was diluted with ion-exchanged water so that the solid content concentration was 0.5% by mass. Next, 40 parts by mass of a polyvinyl alcohol aqueous solution was added to 100 parts by mass of the diluted fine fibrous cellulose dispersion A to obtain a raw material for sheet production before passing through a filter. Except for this, a fine fibrous cellulose-containing sheet was obtained in the same manner as in Example 1.

[Example 4]
In Example 3, a fine fibrous cellulose-containing sheet was obtained in the same manner as in Example 3, except that fine fibrous cellulose dispersion B was used instead of fine fibrous cellulose dispersion A.

[Example 5]
A fine fibrous cellulose-containing sheet was obtained in the same manner as in Example 1, except that a nylon filter (manufactured by Loki Techno, 125L-SNP-200, opening 20 μm) was used.

[Example 6]
The same operation as in Example 1 was performed, except that a polypropylene filter (manufactured by Loki Techno, 125L-SLS-400, opening 40 μm) was used.

[Comparative example 1]
A fine fibrous cellulose-containing sheet was obtained in the same manner as in Example 1, except that the raw material for sheet production before passing through the filter was directly produced without passing through the filter.

[Comparative example 2]
A fine fibrous cellulose-containing sheet was obtained in the same manner as in Example 1, except that a polypropylene filter (manufactured by Loki Techno, 125L-SLS-020, opening 10 μm) was used.

[Comparative example 3]
A fine fibrous cellulose-containing sheet was obtained in the same manner as in Example 1, except that a polypropylene filter (manufactured by Loki Techno, 125L-SLS-12H, opening 120 μm) was used.

[Evaluation of foreign matter]
The sheets obtained in Examples and Comparative Examples were visually observed and evaluated based on the following criteria. In addition, when identifying a foreign body, a comparison was made with a foreign body specimen.
◎: There are no foreign objects with a diameter of 0.1 mm or more in the 100 cm ² sheet. ○: There are 1 or more foreign objects with a diameter of 0.1 mm or more in ^the 100 cm 2 sheet, but less than 10. △: There are no foreign objects with a diameter of 0.1 mm or more in the 100 cm ² sheet. 10 to less than 50 foreign objects with a diameter of 0.1 mm or more x: 50 or more foreign objects with a diameter of 0.1 mm or more in a 100 cm ² sheet

[Productivity]
The pressure on the pressure gauge installed in front of the filter was set to 1 MPa, and the initial flow rate was set to 2.0 L/min, and the dispersion liquid was fed to the filter. In order to measure the flow rate per unit time (1 minute) after passing through the filter, put it in a 2L or more container whose weight is known in advance, measure the weight (kg) with a balance, and calculate the value as the flow rate after passing through the filter ( L/min). Then, the flow rate reduction rate was calculated using the following formula.
Flow rate reduction rate (%) = (starting flow rate (L/min) - flow rate after 10 minutes of liquid flow (L/min)) / starting flow rate (L/min) x 100 (%)
◎: Decrease in flow rate after 10 minutes of flow is less than 1% ○: Decrease in flow rate after 10 minutes of flow is 1% or more and less than 5% △: Decrease in flow rate after 10 minutes of flow is 5% or more and less than 30% ×: The flow rate decreases by more than 30% after 10 minutes of flow.

[Density increase]
To determine the density before passing through the filter, put the dispersion liquid to 1 L in a beaker (1 L) whose weight is known in advance, measure the weight (g) with a balance, and calculate the density before passing through the filter by 1/1000 of that value. (g/cm ³ ). The density after passing through the filter was determined by measuring the dispersion that had passed through the filter in the same manner as above. From the density measured as described above, the density increase degree was calculated using the following formula. Note that a large degree of increase in density means that the bubbles contained in the slurry disappeared or were captured by the filter when the slurry was passed through the filter.
Density increase rate = Density after passing through the filter (g/cm ³ )/Density before passing through the filter (g/cm ³ )
○: Density increase is 1.10 or more △: Density increase is 1.02 or more and less than 1.10 ×: Density increase is less than 1.02

[Measurement of phosphorus oxoacid group amount]
The amount of phosphorus oxo acid groups in the fine fibrous cellulose is determined by diluting the fine fibrous cellulose dispersion containing the target fine fibrous cellulose with ion-exchanged water to a content of 0.2% by mass. The measurement was performed by treating a cellulose-containing slurry with an ion exchange resin and then titrating it with an alkali.
For the treatment with ion exchange resin, 1/10 of the volume of strongly acidic ion exchange resin (Amber Jet 1024; Organo Co., Ltd., conditioned) was added to the fibrous cellulose-containing slurry, and the mixture was shaken for 1 hour. The slurry was poured onto a mesh having an opening of 90 μm to separate the resin and the slurry.
In addition, titration using an alkali 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).

In the fine fibrous cellulose-containing sheets obtained in Examples, there were few foreign substances. Further, in the examples, the sheet productivity was also excellent.

Claims (4)

A step of passing a dispersion containing fibrous cellulose having a fiber width of 1000 nm or less through a filter;
A method for producing a fibrous cellulose-containing sheet, comprising the step of forming a sheet from a dispersion liquid after passing through a filter,
In the step of passing through the filter, a method for manufacturing a fibrous cellulose-containing sheet using a filter made of a resin having filter pore openings of 20 μm or more and 100 μm or less. The method for producing a fibrous cellulose-containing sheet according to claim 1 , wherein a plurality of the filters are arranged, and the plurality of filters are arranged in parallel. The method for producing a fibrous cellulose-containing sheet according to claim 1 , wherein a plurality of the filters are arranged, and the plurality of filters are arranged in series. The fibrous cellulose-containing sheet according to any one of claims 1 to 3 , wherein the step of forming the sheet includes a step of paper-making the dispersion after passing through the filter or a step of coating it on a base material. manufacturing method.