JP2020165018A - Manufacturing method of sheet - Google Patents

Abstract

To provide a manufacturing method of sheets, capable of manufacturing sheets reduced in breaks and recesses.SOLUTION: A manufacturing method of sheets as a manufacturing method of sheets containing fibrous cellulose with a fiber width of 1,000 nm or less includes a step of adjusting a moisture content of sheets in a sheet-forming step to 10 pts.mass or more and 1,000 pts.mass based on 100 pts.mass of the fibrous cellulose.SELECTED DRAWING: None

Description

The present invention relates to a method for producing a sheet. Specifically, the present invention relates to a method for producing a sheet containing fine fibrous cellulose.

Conventionally, cellulose fibers have been widely used in clothing, absorbent articles, paper products and the like. As the 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 diverse. For example, development of sheets containing fine fibrous cellulose, resin composites, and thickeners is underway.

When forming a sheet containing fine fibrous cellulose, it has been studied to apply a slurry containing fine fibrous cellulose onto a substrate and then dry it to form a film-like sheet. For example, Patent Document 1 discloses a method for producing a cellulose nanofiber film containing fine fibrous cellulose. Here, after adding one or more additives selected from glycerin, sorbitol, and polyvinylacetamide-based compounds to a dispersion of cellulose nanofibers to obtain a coating liquid, the coating liquid is defoamed. , The resin base material is coated and dried to form a film.

Japanese Unexamined Patent Publication No. 2018-154699

When producing a sheet containing fine fibrous cellulose, a fine fibrous cellulose-containing dispersion is applied onto a base material and dried. However, it may be difficult to peel off the fine fibrous cellulose-containing sheet from the base material after drying. Further, even if the fine fibrous cellulose-containing sheet can be peeled off from the base material after drying, the sheet may have irregularities and the appearance of the sheet may be impaired.

Therefore, in order to solve the problems of the prior art, the present inventors have proceeded with studies on a method for producing a sheet in order to obtain a sheet containing fine fibrous cellulose having an excellent appearance.

As a result of diligent studies to solve the above problems, the present inventors set the water content of the sheet to 100 parts by mass of the fibrous cellulose within a predetermined range in the sheeting step of the fine fibrous cellulose-containing sheet. As a result, it was found that a fine fibrous cellulose-containing sheet having an excellent appearance can be obtained.
Specifically, the present invention has the following configuration.

[1] A method for producing a sheet containing fibrous cellulose having a fiber width of 1000 nm or less.
A method for producing a sheet, which comprises a step of adjusting the moisture content of the sheet to 10 parts by mass or more and 1000 parts by mass or less with respect to 100 parts by mass of fibrous cellulose during the sheet forming step.
[2] The sheet manufacturing method according to [1], wherein the humidity control step is a drying step or a hydration step.
[3] The humidity control step is a moisture addition step.
The method for producing a sheet according to [1] or [2], wherein in the water addition step, water is added so that the water content of the sheet is 10 parts by mass or more and 1000 parts by mass or less with respect to 100 parts by mass of fibrous cellulose. ..
[4] The method for producing a sheet according to [3], wherein the water-imparting step is a step of applying or spraying water.
[5] The method for producing a sheet according to [3] or [4], wherein the hydration step is provided after the drying step.

According to the production method of the present invention, a method for producing a fine fibrous cellulose-containing sheet having an excellent appearance is provided.

FIG. 1 is a graph showing the relationship between the amount of NaOH added dropwise and the pH of a fibrous cellulose-containing slurry having a phosphoric acid group. FIG. 2 is a graph showing the relationship between the amount of NaOH added dropwise to the fibrous cellulose-containing slurry having a carboxy group and the pH.

Hereinafter, the present invention will be described in detail. The description of the constituent elements described below may be based on typical embodiments or specific examples, but the present invention is not limited to such embodiments.

(Manufacturing method of fibrous cellulose-containing sheet)
The present invention relates to a method for producing a sheet containing fibrous cellulose having a fiber width of 1000 nm or less. The sheet manufacturing step of the present invention includes a step of adjusting the moisture content of the sheet to 10 parts by mass or more and 1000 parts by mass or less with respect to 100 parts by mass of fibrous cellulose during the sheet forming step. More specifically, the method for producing a sheet of the present invention includes a step of forming a dispersion liquid containing fibrous cellulose having a fiber width of 1000 nm or less into a sheet, and in the step of forming the sheet, the water content of the sheet is within the above range. Adjust to.
In the present specification, fibrous cellulose having a fiber width of 1000 nm or less may be referred to as fine fibrous cellulose or CNF. Further, in the present specification, the fine fibrous cellulose-containing sheet may be simply referred to as a sheet.

In the sheet manufacturing method of the present invention, a sheet having an excellent appearance can be manufactured. Specifically, in the sheeting step, the dried CNF sheet can be peeled off from the base material without cracking, and a sheet having an excellent appearance can be obtained when the sheet is not formed with irregularities. In addition, the sheet obtained by the method for producing a sheet of the present invention has high transparency. As described above, in the production method of the present invention, a sheet having high transparency and less unevenness can be obtained.

In the sheet manufacturing method of the present invention, the sheet has high peelability after the sheet forming step. Specifically, a dispersion liquid containing fibrous cellulose having a fiber width of 1000 nm or less is applied onto the base material, dried, and then the fine fibrous cellulose-containing sheet can be peeled off from the base material without cracking. .. Further, when peeling, the peeling stress is low, so that smooth peeling work is possible. Therefore, the production efficiency of the fine fibrous cellulose-containing sheet can be improved. Further, in the sheet manufacturing method of the present invention, cracking is suppressed in the sheet after peeling, and it can be said that the sheet is excellent in durability.

<Sheet process>
The sheet manufacturing process of the present invention includes a step of forming a dispersion liquid containing fibrous cellulose having a fiber width of 1000 nm or less into a sheet. In the step of making a sheet, a fine fibrous cellulose-containing sheet is formed by forming a wet sheet by papermaking or coating and then drying it. In addition, in this specification, a sheet-forming process may be referred to as a sheet-forming process.

-Papermaking process-
The papermaking process is performed by making a dispersion liquid with a paper machine. The paper machine used in the paper making process is not particularly limited, and examples thereof include continuous paper machines such as a long net type, a circular net type, and an inclined type, and a multi-layer paper making machine combining these. In the papermaking process, a known papermaking method such as hand-making may be adopted.

The papermaking process is performed by filtering and dehydrating the dispersion with a wire to obtain a wet paper sheet, and then pressing and drying the sheet. The filter cloth used for filtering and dehydrating the dispersion is not particularly limited, but it is more preferable that, for example, fine fibrous cellulose does not pass through and the filtration rate does not become too slow. Such a filter cloth is not particularly limited, but for example, a sheet made of an organic polymer, a woven fabric, or a porous membrane is preferable. The organic polymer is not particularly limited, but non-cellulosic organic polymers such as polyethylene terephthalate, polyethylene, polypropylene, and polytetrafluoroethylene (PTFE) are preferable. In the present embodiment, for example, a porous membrane of polytetrafluoroethylene having a pore size of 0.1 μm or more and 20 μm or less, polyethylene terephthalate having a pore size of 0.1 μm or more and 20 μm or less, a polyethylene woven fabric, or the like can be mentioned.

In the sheeting step, a method of producing a sheet from a dispersion is, for example, to discharge a dispersion containing fibrous cellulose onto the upper surface of an endless belt and squeeze a dispersion medium from the discharged dispersion to form a web. This can be done using a manufacturing apparatus that includes a water section and a drying section that dries the web to produce a sheet. An endless belt is arranged from the watering section to the drying section, and the web generated in the watering section is conveyed to the drying section while being placed on the endless belt.

The method for producing a sheet from the fine fibrous cellulose-containing dispersion is not particularly limited, and examples thereof include a method using the production apparatus described in WO2011 / 013567. This manufacturing device discharges a dispersion liquid containing fine fibrous cellulose onto the upper surface of an endless belt, and squeezes a dispersion medium from the discharged dispersion liquid to generate a web, and a water-squeezing section that dries the web to form a sheet. It has a dry section to produce. An endless belt is arranged from the watering section to the drying section, and the web generated in the watering 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, and examples thereof include a dehydration method that is usually used in the production of paper. A method of dehydrating with a long net, a circular net, an inclined wire, or the like, and then dehydrating with a roll press. Is preferable. The drying method is not particularly limited, and examples thereof include methods used in the production of paper. For example, a cylinder dryer, a yankee dryer, hot air drying, a near infrared heater, an infrared heater and the like are preferable. In the drying step, pressurization may be performed in parallel with drying.

-Coating process-
In the coating step, for example, a dispersion liquid containing fine fibrous cellulose is applied onto a base material, and the sheet formed by drying the dispersion is peeled off from the base material to obtain a sheet. 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 a material having high wettability to the dispersion may be able to suppress shrinkage of the sheet during drying, but the sheet formed after drying may be used. It is preferable to select one that can be easily peeled off. Of these, a resin film or plate or a metal film or plate is preferable, but is not particularly limited. For example, resin films and plates such as acrylic, polyethylene terephthalate, vinyl chloride, polystyrene, polypropylene, polycarbonate, and polyvinylidene chloride, metal films and plates of aluminum, zinc, copper, and iron plates, and their surfaces are oxidized. , Stainless film or plate, brass film or plate, etc. can be used.

In the coating process, if the viscosity of the dispersion is low and it develops on the base material, a dammed frame is fixed on the base material to obtain a sheet with a predetermined thickness and basis weight. You may. The frame for damming is not particularly limited, but it is preferable to select, for example, a frame in which the end portion of the sheet that adheres after drying can be easily peeled off. From this point of view, a resin plate or a metal plate molded is more preferable. In the present embodiment, for example, a resin plate such as an acrylic plate, a polyethylene terephthalate plate, a vinyl chloride plate, a polystyrene plate, a polypropylene plate, a polycarbonate plate, a polyvinylidene chloride plate, or a metal plate such as an aluminum plate, a zinc plate, a copper plate, or an iron plate. , And those whose surfaces are oxidized, stainless steel plates, brass plates and the like can be used.

The coating machine that coats the dispersion liquid on the base material is not particularly limited, and for example, a roll coater, a gravure coater, a die coater, a curtain coater, a spray coater, an air doctor coater, or the like can be used. A die coater, a curtain coater, and a spray coater are particularly preferable because the thickness of the sheet can be made more uniform.

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

As described above, the coating step includes a step of drying the dispersion liquid coated on the substrate. The step of drying the dispersion is not particularly limited, but is performed by, for example, 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, and for example, a method of heating and drying with hot air, infrared rays, far infrared rays or near infrared rays (heat drying method) or a method of vacuum drying (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 with infrared rays, far infrared rays or near infrared rays is not particularly limited, but can be performed by using, for example, an infrared device, a far infrared device or a near infrared device.

<Humidity control process>
In the sheet manufacturing process of the present invention, a humidity control step is provided in the sheet forming process as described above. The humidity control step is a step of adjusting the moisture content of the sheet to 10 parts by mass or more and 1000 parts by mass or less with respect to 100 parts by mass of fibrous cellulose during the sheet forming step. The water content of the sheet in the humidity control step may be 10 parts by mass or more, preferably 15 parts by mass or more, and more preferably 20 parts by mass or more with respect to 100 parts by mass of fibrous cellulose. The water content of the sheet in the humidity control step may be 1000 parts by mass or less, preferably 800 parts by mass or less, and more preferably 500 parts by mass or less with respect to 100 parts by mass of fibrous cellulose. It is preferably 100 parts by mass or less, and more preferably 100 parts by mass or less. By setting the water content of the sheet in the humidity control step within the above range, the appearance of the obtained sheet can be improved. Specifically, a sheet having high transparency and less unevenness can be obtained.

The water content of the sheet in the humidity control step is preferably 3% by mass or more, more preferably 5% by mass or more, and further preferably 8% by mass or more, based on the total mass of the sheet. It is particularly preferably 10% by mass or more. The water content of the sheet in the humidity control step is preferably 80% by mass or less, more preferably 60% by mass or less, and more preferably 50% by mass or less, based on the total mass of the sheet. More preferably, it is more preferably 30% by mass or less, and particularly preferably 20% by mass or less. By setting the water content of the sheet in the humidity control step within the above range, the appearance of the obtained sheet can be improved. Specifically, a sheet having high transparency and less unevenness can be obtained.

The humidity control step is preferably a drying step or a watering step. Above all, the humidity control step is preferably a moisture addition step of further adding moisture after the sheet is dried.

When the humidity control step is a drying step, in the drying step, the drying conditions are set so that the water content of the sheet is within the above range. Specifically, the drying conditions are controlled so that the sheet does not become too dry. The drying temperature in such a drying step is preferably 60 ° C. or higher, more preferably 80 ° C. or higher. The drying temperature in the drying step is preferably 200 ° C. or lower, more preferably 180 ° C. or lower. The drying time in the drying step is appropriately selected depending on the drying temperature, but is preferably 1 minute or longer, and more preferably 2 minutes or longer. The drying time in the drying step is preferably 180 minutes or less, more preferably 120 minutes or less. For example, when the drying temperature is 140 ° C., the drying time is particularly preferably 2 minutes or more and 100 minutes or less. When the drying temperature is 105 ° C., the drying time is particularly preferably 3 minutes or more and 120 minutes or less.

When the humidity control step is a moisture addition step, the moisture addition step is preferably a moisture addition step in which the sheet is dried and then further moisture is added. That is, the water addition step is preferably provided after the drying step. The water addition step is provided after the fine fibrous cellulose-containing dispersion is formed into a sheet, and the sheet is once dried to be in an overdried state. In this way, after the sheet-like material is once dried, moisture is added to the sheet-like material again to obtain the final form of the sheet. In the water addition step, by adding water to the overdried sheet, the water content of the sheet is set to 10 parts by mass or more and 1000 parts by mass or less with respect to 100 parts by mass of fibrous cellulose. The water content of the sheet at this time is preferably 15 parts by mass or more, and more preferably 20 parts by mass or more. The water content of the sheet is preferably 800 parts by mass or less, more preferably 500 parts by mass or less, and further preferably 100 parts by mass or less with respect to 100 parts by mass of fibrous cellulose.

The water addition step is preferably a step of coating or spraying water. In the step of applying the moisture, it is preferable to apply the moisture to the overdried sheet by using, for example, a roll coater, a gravure coater, a die coater, a curtain coater, a spray coater, an air doctor coater or the like. In the step of spraying the water, it is preferable to adopt a method such as mist spraying or heated steam spray to apply the water to the overdried sheet.

The amount of water added in the water addition step varies depending on the dry state of the sheet before the water addition step, but is preferably 0.1 g / m ² or more, more preferably 0.5 g / m ² or more, for example. It is preferably 1.0 g / m ² or more, and more preferably 1.0 g / m ² or more. The amount of water added in the water addition step is preferably 100 g / m ² or less, preferably 50 g / m ² or less, and preferably 30 g / m ² or less. By selecting the water content from the above range, it becomes easy to keep the water content of the sheet in the desired range in the humidity control step.

Before the humidity control step, a step of measuring the water content of the sheet may be provided. Then, in the sheet manufacturing process, it is preferable that a system for transmitting the measurement result of the water content to the humidity control process is provided. In this way, more precise control of the water content is possible by calculating the water content that needs to be controlled in the humidity control process from the water content of the sheet before the humidity control process. Examples of the moisture meter include an infrared moisture meter, a radiation moisture meter, a radio wave moisture meter, and the like.

<Other processes>
The sheet manufacturing method of the present invention may include other steps before and after the sheet forming step. Here, examples of other steps include a filtration step, a defoaming step, and the like. The filtration step is preferably provided before the sheeting step, and examples of the filtration step include a step of filtering using at least one selected from a screen, a cleaner and a filter. Further, it is preferable that the defoaming step is also provided before the sheeting step, and in the defoaming step, for example, a vacuum defoaming device, a centrifugal defoaming device, a decompression defoaming device, a rotation / revolution defoaming device, or the like may be used. it can. Then, after such a defoaming step, a step of transferring the dispersion liquid is usually provided, but the piping angle, the piping path, etc. are adjusted so that further defoaming is promoted in the transfer step as well. May be good.

A sheet winding step may be provided as a subsequent step of the sheet forming step. In the sheet winding step, after winding the sheet after the humidity control step, it is preferable that the sheet is sealed so that the humidity control conditions are maintained.

(Fine fibrous cellulose-containing dispersion)
In the method for producing a sheet of the present invention, a sheet is formed from a dispersion liquid (fine fibrous cellulose-containing dispersion liquid) containing fibrous cellulose having a fiber width of 1000 nm or less. The fiber width of the fibrous cellulose contained in the fine fibrous cellulose-containing dispersion may be 1000 nm or less, preferably 100 nm or less, and more preferably 8 nm or less. As a result, when a fine fibrous cellulose-containing sheet is produced, the transparency of the sheet is increased, and in addition, the strength of the sheet is also increased.

The fiber width of the fibrous cellulose can be measured, for example, by observation with an electron microscope. The average fiber width of the fibrous cellulose is, for example, 1000 nm or less. The average fiber width of the fibrous cellulose is, for example, 2 nm or more and 1000 nm or less, more preferably 2 nm or more and 100 nm or less, further preferably 2 nm or more and 50 nm or less, and 2 nm or more and 10 nm or less. Especially preferable. By setting the average fiber width of the fibrous cellulose to 2 nm or more, it is possible to suppress the dissolution of the fibrous cellulose as a cellulose molecule in water, and to make it easier to exhibit the effects of the fibrous cellulose on improving strength, rigidity and dimensional stability. it can. The fibrous cellulose is, for example, monofibrous cellulose. The average fiber width of the fibrous cellulose is preferably within the above range, but the fine fibrous cellulose-containing dispersion may contain coarse fibers having a fiber width of more than 1000 nm.

The average fiber width of fibrous cellulose is measured, for example, using an electron microscope as follows. First, an aqueous suspension of fibrous cellulose having a concentration of 0.05% by mass or more and 0.1% by mass or less is prepared, and this suspension is cast on a hydrophilized carbon film-coated grid to prepare a sample for TEM observation. And. If it contains wide fibers, an SEM image of the surface cast on the glass may be observed. Next, observation is performed using an electron microscope image at a magnification of 1000 times, 5000 times, 10000 times, or 50,000 times depending on the width of the fiber to be observed. However, the sample, observation conditions and magnification should be adjusted so as to satisfy the following conditions.
(1) A straight line X is drawn at an arbitrary position in the observation image, and 20 or more fibers intersect the straight line X.
(2) A straight line Y that intersects the straight line perpendicularly is drawn in the same image, and 20 or more fibers intersect the straight line Y.
The width of the fiber intersecting the straight line X and the straight line Y is visually read with respect to the observation image satisfying the above conditions. In this way, at least three sets of observation images of surface portions that do not overlap each other are obtained. Next, for each image, the width of the fiber intersecting the straight line X and the straight line Y is read. As a result, at least 20 fibers × 2 × 3 = 120 fibers are read. Then, the average value of the read fiber widths is taken as the average fiber width of the fibrous cellulose.

The fiber length of the fibrous cellulose is not particularly limited, but 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 further preferably 0.1 μm or more and 600 μm or less. preferable. By setting the fiber length within the above range, destruction of the crystal region of the fibrous cellulose can be suppressed. It is also possible to set the slurry viscosity of the fibrous cellulose in an appropriate range. The fiber length of the fibrous cellulose can be obtained by, for example, image analysis by TEM, SEM, or AFM.

The fibrous cellulose preferably has an I-type crystal structure. Here, the fact that the fibrous cellulose has an I-type crystal structure can be identified in the diffraction profile obtained from a wide-angle X-ray diffraction photograph using CuKα (λ = 1.5418 Å) monochromatic with graphite. Specifically, it can be identified by having typical peaks at two positions, 2θ = 14 ° or more and 17 ° or less and 2θ = 22 ° or more and 23 ° or less. The ratio of the type I crystal structure to the fine fibrous cellulose is, for example, preferably 30% or more, more preferably 40% or more, and further 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 crystallinity is determined by a conventional method from the X-ray diffraction profile measured and the pattern (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 20 or more and 10000 or less, and more preferably 50 or more and 1000 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 viscosity can be easily obtained when the solvent dispersion is produced. By setting the axial ratio to the above upper limit value or less, for example, when fibrous cellulose is treated as an aqueous dispersion, it is preferable in that handling such as dilution becomes easy.

The fibrous cellulose in the present embodiment has, for example, both a crystalline region and a non-crystalline region. In particular, fine fibrous cellulose having both a crystalline region and a non-crystalline region and having a high axial ratio is realized by a method for producing fine fibrous cellulose described later.

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 defibration efficiency in the defibration treatment, it is more preferable that the fibrous cellulose has an ionic substituent. The ionic substituent can include, for example, either one or both of an anionic group and a cationic group. Further, as the nonionic substituent, for example, an alkyl group and an acyl group can be included. In the present embodiment, it is particularly preferable to have an anionic group as the ionic substituent. The fibrous cellulose may not be subjected to a treatment for introducing an ionic substituent.

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

The phosphate group or the substituent derived from the phosphorus oxo acid group is, for example, a substituent represented by the following formula (1). The phosphorus oxo acid group is, for example, a divalent functional group obtained by removing a hydroxy group from phosphoric acid. Specifically, it is a group represented by −PO ₃ H ₂ . Substituents derived from a phosphorus oxo acid group include substituents such as a salt of a phosphorus oxo acid group and a phosphorus oxo acid ester group. The substituent derived from the phosphoric acid group may be contained in the fibrous cellulose as a group in which the phosphoric acid group is condensed (for example, a pyrophosphate group). Further, the phosphorous acid group may be, for example, a phosphorous acid group (phosphonic acid group), and the substituent derived from the phosphorous acid group may be a salt of the phosphorous acid group or the like.

In the formula (1), a, b and n are natural numbers, and m is an arbitrary number (where a = b × m). ^{α 1, α 2, ···,} a number of alpha ⁿ and alpha 'is O ^- a and the remainder is either R, the OR. It is also possible that all of each α ⁿ and α'are O ⁻ . R is a hydrogen atom, a saturated-linear hydrocarbon group, a saturated-branched chain hydrocarbon group, a saturated-cyclic hydrocarbon group, an unsaturated-linear hydrocarbon group, and an unsaturated-branched chain hydrocarbon, respectively. A hydrogen group, an unsaturated-cyclic hydrocarbon group, an aromatic group, or an inducing group thereof. Further, in the formula (1), n is preferably 1.

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

Further, as the inducing group in R, a functional group in which at least one of functional groups such as a carboxy group, a hydroxy group, or an amino group is added or substituted with respect to the main chain or side chain of the above-mentioned various hydrocarbon groups. The group is mentioned, but is not particularly limited. The number of carbon atoms constituting the main chain of R is not particularly limited, but is preferably 20 or less, and more preferably 10 or less. By setting the number of carbon atoms constituting the main chain of R to the above range, the molecular weight of the phosphorus oxo acid group can be set to an appropriate range, the penetration into the fiber raw material is facilitated, and the yield of the fine cellulose fiber is increased. You can also do it.

β ^{b +} is a monovalent or higher cation composed of an organic substance or an inorganic substance. Examples of monovalent or higher cations composed of organic substances include aliphatic ammonium or aromatic ammonium, and examples of monovalent or higher valent cations composed of inorganic substances include ions of alkali metals such as sodium, potassium, and lithium. Examples thereof include cations of divalent metals such as calcium and magnesium, hydrogen ions, and the like, but the present invention is not particularly limited. These may be applied alone or in combination of two or more. The monovalent or higher cation composed of an organic substance or an inorganic substance is preferably sodium or potassium ion which is hard to yellow when the fiber raw material containing β is heated and is easily industrially used, but is not particularly limited. Note that β ^{b +} may be an organic onium ion.

The amount of the ionic substituent introduced into the fibrous cellulose is, for example, 0.10 mmol / g or more, more preferably 0.20 mmol / g or more, and 0.50 mmol / g per 1 g (mass) of the fibrous cellulose. It is more preferably / g or more, and particularly preferably 1.00 mmol / g or more. The amount of the ionic substituent introduced into the fibrous cellulose is preferably 5.20 mmol / g or less per 1 g (mass) of the fibrous cellulose, and more preferably 3.65 mmol / g or less. It is more preferably .50 mmol / g or less, and particularly preferably 3.00 mmol / g or less. By setting the amount of the ionic substituent introduced within the above range, it is possible to facilitate the miniaturization of the fiber raw material and enhance the stability of the fibrous cellulose. Further, by setting the amount of the ionic substituent introduced within the above range, good properties can be exhibited in various applications such as a thickener for fibrous cellulose. Here, the denominator in the unit mmol / g indicates the mass of fibrous cellulose when the counter ion of the ionic substituent is a hydrogen ion (H ⁺ ).

The amount of the ionic substituent introduced into the fibrous cellulose can be measured by, for example, a neutralization titration method. In the measurement by the neutralization titration method, the introduction amount is measured by determining the change in pH while adding an alkali such as an aqueous sodium hydroxide solution to the obtained slurry containing fibrous cellulose.

FIG. 1 is a graph showing the relationship between the amount of NaOH added dropwise and the pH of a fibrous cellulose-containing slurry having a phosphoric acid group. The amount of the phosphorus oxo acid group introduced into the fibrous cellulose is measured, for example, as follows.
First, the slurry containing fibrous cellulose is treated with a strongly acidic ion exchange resin. If necessary, the same defibration treatment as the defibration treatment step described later may be performed on the measurement target before the treatment with the strongly acidic ion exchange resin.
Next, the 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 FIG. 1 plots the measured pH with respect to the amount of alkali added, and the titration curve shown in the lower part of FIG. 1 plots the pH with respect to the amount of alkali added. The increment (differential value) (1 / mmol) is plotted. In this neutralization titration, two points are confirmed in which the increment (differential value of pH with respect to the amount of alkali dropped) becomes maximum in the curve plotting the measured pH with respect to the amount of alkali added. Of these, the maximum point of the increment obtained first when alkali is added is called the first end point, and the maximum point of the 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 dissociating acid of the fibrous cellulose contained in the slurry used for titration, and the amount of alkali required from the first end point to the second end point. The amount is equal to the amount of the second dissociating acid of the fibrous cellulose contained in the slurry used for the titration, and the amount of alkali required from the start to the second end point of the titration is the fibrous cellulose contained in the slurry used for the titration. Is equal to the total amount of dissociated acid. 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 slurry to be titrated is the amount of phosphorus oxo acid group introduced (mmol / g). The amount of phosphorus oxo acid group introduced (or the amount of phosphorus oxo acid group) simply means the amount of the first dissociated acid.
In FIG. 1, the region from the start of titration to the first end point is referred to as a first region, and the region from the first end point to the second end point is referred to as a second region. For example, when the phosphoric acid group is a phosphoric acid group and the phosphoric acid group causes condensation, the amount of weakly acidic groups in the phosphoric acid group (also referred to as the second dissociated acid amount in the present specification) is apparently It decreases, and the amount of alkali required for the second region is smaller than the amount of alkali required for the first region. On the other hand, the amount of strongly acidic groups in the phosphorus oxo acid group (also referred to as the first dissociated acid amount in the present specification) is the same as the amount of phosphorus atoms regardless of the presence or absence of condensation. Further, when the phosphorous acid group is a phosphorous acid group, the weakly acidic group does not exist in the phosphorous acid group, so that 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, the titration curve has one point where the pH increment is maximized.

Since the denominator of the above-mentioned phosphorus oxo acid group introduction amount (mmol / g) indicates the mass of the acid-type fibrous cellulose, the phosphorus oxo acid group amount of the acid-type fibrous cellulose (hereinafter referred to as the phosphorus oxo acid group amount). (Called (acid type))). On the other hand, when the counterion of the phosphorus oxo acid group is replaced with an arbitrary cation C so as to have a charge equivalent, the denominator is converted to the mass of fibrous cellulose when the cation C is a counterion. This makes it possible to determine the amount of phosphorus oxo acid groups (hereinafter, the amount of phosphorus oxo acid groups (C type)) possessed by the fibrous cellulose in which the cation C is a counter ion.
That is, it is calculated by the following formula.
Phosphoric acid group amount (C type) = Phosphoric acid group amount (acid type) / {1+ (W-1) x A / 1000}
A [mmol / g]: Total amount of anion derived from phosphoric acid group of fibrous cellulose (total amount of dissociated acid of phosphoric acid group)
W: Formula amount per valence of cation C (for example, Na is 23, Al is 9)

FIG. 2 is a graph showing the relationship between the amount of NaOH added dropwise and the pH of a slurry containing fibrous cellulose having a carboxy group. The amount of the carboxy group introduced into the fibrous cellulose is measured, for example, as follows.
First, the slurry containing fibrous cellulose is treated with a strongly acidic ion exchange resin. If necessary, the same defibration treatment as the defibration treatment step described later may be performed on the measurement target before the treatment with the strongly acidic ion exchange resin.
Next, the 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 FIG. 2 plots the measured pH with respect to the amount of alkali added, and the titration curve shown in the lower part of FIG. 2 plots the pH with respect to the amount of alkali added. The increment (differential value) (1 / mmol) is plotted. In this neutralization titration, in the curve plotting the measured pH with respect to the amount of alkali added, one point was confirmed where the increment (differential value of pH with respect to the amount of alkali dropped) became maximum, and this maximum point was the first. Called one end point. Here, the region from the start of titration to the first end point in FIG. 2 is referred to as a first region. The amount of alkali required in the first region is equal to the amount of carboxy groups in the slurry used for titration. Then, the amount of alkali (mmol) required in the first region of the titration curve is divided by the solid content (g) in the slurry containing the fibrous cellulose to be titrated, so that the amount of carboxy group introduced (mmol / mmol /). g) is calculated.
The above-mentioned amount of carboxy group introduced (mmol / g) is the amount of substituents per 1 g of mass of fibrous cellulose when the counterion of the carboxy group is hydrogen ion (H ⁺ ) (hereinafter, the amount of carboxy group (acid). Type)).

In the measurement of the amount of phosphorus oxo acid groups and the amount of carboxy groups by the titration method, if the amount of one drop of the sodium hydroxide aqueous solution is too large or the titration interval is too short, the amount of phosphorus oxo acid groups or carboxy groups is lower than originally intended. Accurate values such as quantity may not be obtained. As an appropriate dropping amount and titration interval, for example, it is desirable to titrate 10 to 50 μL of a 0.1 N sodium hydroxide aqueous solution every 5 to 30 seconds. Further, in order to eliminate the influence of carbon dioxide dissolved in the fibrous cellulose-containing slurry, for example, it is desirable to measure while blowing an inert gas such as nitrogen gas into the slurry from 15 minutes before the start of titration to the end of titration.

The content of the fibrous cellulose is preferably 0.05% by mass or more, more preferably 0.1% by mass or more, and more preferably 0.2, based on the total mass of the fine fibrous cellulose-containing dispersion. It is more preferably mass% or more. The content of the fibrous cellulose is preferably 50% by mass or less, more preferably 40% by mass or less, and more preferably 30% by mass or less, based on the total mass of the fine fibrous cellulose-containing dispersion. It is more 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 further preferably 90% or more. 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 is determined by diluting the fine fibrous cellulose-containing dispersion with ion-exchanged water so that the fibrous cellulose content is 0.2% by mass, and then haze meter (Murakami color). It is a value measured in accordance with JIS K 7361 using a liquid glass cell (manufactured by Fujiwara Seisakusho, MG-40, backlit path) having an optical path length of 1 cm at HM-150) manufactured by Technical Research Institute. The zero point measurement is performed with ion-exchanged water contained in the glass cell. The dispersion to be measured is allowed to stand for 24 hours in an environment of 23 ° C. and 50% relative humidity before measurement.

The total light transmittance of the dispersion liquid described above is the total light transmittance of the dispersion liquid before defoaming, but the same total light transmittance as described above can be obtained even with the dispersion liquid after defoaming. preferable. That is, when the content of fibrous cellulose contained in the dispersion after defoaming is 0.2% by mass, the total light transmittance of the dispersion is preferably 80% or more, and is 85. It is more preferably% or more, and even 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 conforms to, for example, JIS K 7136, and is a haze meter (HM-150 manufactured by Murakami Color Technology Research Institute), and a glass cell for liquid with an optical path length of 1 cm (manufactured by Fujiwara Seisakusho, MG-). 40, a value measured using a back light path). The zero point measurement is performed with ion-exchanged water contained in the glass cell. The dispersion to be measured is allowed to stand for 24 hours in an environment of 23 ° C. and 50% relative humidity before measurement.

The fine fibrous cellulose-containing dispersion may contain an arbitrary component in addition to the fine fibrous cellulose. Examples of the optional component include hydrophilic polymers, hydrophilic low molecules, organic ions and the like. In addition, the fine fibrous cellulose-containing dispersion has optional components such as a surfactant, a coupling agent, an inorganic layered compound, an inorganic compound, a leveling agent, an antiseptic, an antifoaming agent, an organic particle, a lubricant, and an antistatic agent. , UV protection agents, dyes, pigments, stabilizers, magnetic powders, orientation promoters, plasticizers, dispersants, and cross-linking agents, which may contain one or more. The optional component is preferably added before the defoaming step.

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 modification. Distillate, polyvinyl alcohol, modified polyvinyl alcohol (acetoacetylated polyvinyl alcohol, etc.), polyvinylpyrrolidone, polyvinylmethyl ether, polyacrylates, acrylic acid alkyl ester copolymer, urethane-based copolymer, cellulose derivative (hydroxyethyl cellulose, carboxy) Ethyl cellulose, carboxymethyl cellulose, etc.) and the like.

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

Examples of the organic ion include tetraalkylammonium ion and tetraalkylphosphonium ion. Examples of the tetraalkylammonium ion include tetramethylammonium ion, tetraethylammonium ion, tetrapropylammonium ion, tetrabutylammonium ion, tetrapentylammonium ion, tetrahexylammonium ion, tetraheptylammonium ion, tributylmethylammonium ion, and lauryltrimethyl. Examples thereof 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 tetrapropyl onium ion and the tetrabutyl onium ion include tetra n-propyl onium ion and tetra n-butyl onium ion, respectively.

(Manufacturing process of fine fibrous cellulose)
<Fiber raw material>
Fine fibrous cellulose is produced from a fiber raw material containing cellulose. The fiber raw material containing cellulose is not particularly limited, but pulp is preferably used because it is easily available and inexpensive. Examples of pulp include wood pulp, non-wood pulp, and deinked pulp. The wood pulp is not particularly limited, and is, for example, broadleaf kraft pulp (LBKP), coniferous kraft pulp (NBKP), sulfite pulp (SP), dissolved 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 chemiground wood pulp (CGP), crushed wood pulp (GP) and thermomechanical pulp (TMP, BCTMP), etc. Examples include mechanical pulp. The non-wood pulp is not particularly limited, and examples thereof include cotton pulp such as cotton linter and cotton lint, and non-wood pulp such as hemp, straw and bagasse. The deinking pulp is not particularly limited, and examples thereof include deinking pulp made from used paper. As the pulp of the present embodiment, one of the above types may be used alone, or two or more types may be mixed and used. Among the above pulps, for example, wood pulp and deinked pulp are preferable from the viewpoint of availability. Further, among wood pulps, from the viewpoint of high cellulose ratio and high yield of fine fibrous cellulose during defibration treatment, long fiber fine fibrous cellulose having a small decomposition of cellulose in pulp and a large axial ratio can be obtained. From the viewpoint, for example, chemical pulp is more preferable, and kraft pulp and sulfite pulp are further preferable. When long fiber fine fibrous cellulose having a large axial ratio is used, the viscosity tends to increase.

As the fiber raw material containing cellulose, for example, cellulose contained in ascidians and bacterial cellulose produced by acetobacter can be used. Further, instead of the fiber raw material containing cellulose, a fiber formed by a linear nitrogen-containing polysaccharide polymer such as chitin or chitosan can also be used.

<Linoxo acid group introduction process>
The process for producing the fine fibrous cellulose-containing dispersion preferably includes an ionic substituent introduction step, for example, a phosphorus oxo acid group introduction step. In the phosphorus oxo acid group introduction step, at least one compound (hereinafter, also referred to as “compound A”) selected from compounds capable of introducing a phosphorus oxo acid group by reacting with a hydroxyl group of a fiber raw material containing cellulose is introduced into cellulose. It is a step of acting on a fiber raw material containing. By this step, a phosphorus oxo acid group-introduced fiber can be obtained.

In the phosphorus oxo acid group introduction step according to the present embodiment, the reaction between the fiber raw material containing cellulose and Compound A is carried out in the presence of at least one selected from urea and its derivatives (hereinafter, also referred to as “Compound B”). You may. On the other hand, the reaction of the fiber raw material containing cellulose with the compound A may be carried out in the absence of the compound B.

As an example of the method of allowing the compound A to act on the fiber raw material in the coexistence with the compound B, a method of mixing the compound A and the compound B with the fiber raw material in a dry state, a wet state or a slurry state can be mentioned. Of these, since the reaction uniformity is high, it is preferable to use a fiber raw material in a dry state or a wet state, and it is particularly preferable to use a fiber raw material in a dry state. The form of the fiber raw material is not particularly limited, but is preferably cotton-like or thin sheet-like, for example. Examples of the compound A and the compound B include a method of adding the compound A and the compound B to the fiber raw material in the form of a powder or a solution dissolved in a solvent, or in a state of being heated to a melting point or higher and melted. Of these, since the reaction uniformity is high, it is preferable to add the solution in the form of a solution dissolved in a solvent, particularly in the state of an aqueous solution. Further, the compound A and the compound B may be added to the fiber raw material at the same time, may be added separately, or may be added as a mixture. The method for adding the compound A and the compound B is not particularly limited, but when the compound A and the compound B are in the form of a solution, the fiber raw material may be immersed in the solution to absorb the liquid and then taken out, or the fiber raw material may be taken out. The solution may be dropped into the water. Further, the required amounts of Compound A and Compound B may be added to the fiber raw material, or after the excess amounts of Compound A and Compound B are added to the fiber raw material, respectively, the surplus Compound A and Compound B are added by pressing or filtering. It may be removed.

The compound A used in this embodiment may be a compound having a phosphorus atom and capable of forming an ester bond with cellulose, and may be phosphoric acid or a salt thereof, phosphoric acid or a salt thereof, dehydration-condensed phosphoric acid or a salt thereof. Examples thereof include salts and anhydrous phosphoric acid (diphosphorus pentoxide), but the present invention is not particularly limited. As the phosphoric acid, those having various puritys can be used, and for example, 100% phosphoric acid (normal phosphoric acid) or 85% phosphoric acid can be used. Examples of phosphorous acid include 99% phosphorous acid (phosphonic acid). The dehydration-condensed phosphoric acid is one in which two or more molecules of phosphoric acid are condensed by a dehydration reaction, and examples thereof include pyrophosphoric acid and polyphosphoric acid. Phosphates, phosphorous acids, dehydration-condensed phosphates include phosphoric acid, phosphorous acid or dehydration-condensed phosphoric acid lithium salts, sodium salts, potassium salts, ammonium salts, etc. It can be a sum. Of these, from the viewpoints that the introduction efficiency of phosphoric acid groups is high, the defibration efficiency is more likely to be improved in the defibration process described later, the cost is low, and it is easy to apply industrially, sodium phosphate and sodium phosphate A salt, a potassium salt of phosphoric acid, or an ammonium salt of phosphoric acid is preferable, and phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, or ammonium dihydrogen phosphate is more preferable.

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 the phosphorus atomic weight, the amount of phosphorus atom added to the fiber raw material (absolute dry mass) is 0.5% by mass or more. It is preferably 100% by mass or less, more preferably 1% by mass or more and 50% by mass or less, and further preferably 2% by mass or more and 30% by mass or less. By setting 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 setting the addition amount of the phosphorus atom to the fiber raw material to be equal to or less than the above upper limit value, the effect of improving the yield and the cost can be balanced.

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, 1-ethylurea and the like. From the viewpoint of improving the uniformity of the reaction, compound B is preferably used as an aqueous solution. Further, 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, and 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 between the fiber raw material containing cellulose and compound A, for example, amides or amines may be contained in the reaction system in addition to compound B. Examples of amides include formamide, dimethylformamide, acetamide, dimethylacetamide and the like. Examples of amines include methylamine, ethylamine, trimethylamine, triethylamine, monoethanolamine, diethanolamine, triethanolamine, pyridine, ethylenediamine, hexamethylenediamine and the like. Among these, triethylamine is known to act as a good reaction catalyst.

In the phosphorus oxo acid group introduction step, it is preferable to add or mix the compound A or the like to the fiber raw material and then heat-treat the fiber raw material. As the heat treatment temperature, it is preferable to select a temperature at which a phosphorus oxo acid group can be efficiently introduced while suppressing the thermal decomposition and hydrolysis reaction of the fiber. The heat treatment temperature is, for example, preferably 50 ° C. or higher and 300 ° C. or lower, more preferably 100 ° C. or higher and 250 ° C. or lower, and further preferably 130 ° C. or higher and 200 ° C. or lower. In addition, equipment having various heat media can be used for the heat treatment, for example, a stirring drying device, a rotary drying device, a disk drying device, a roll type heating device, a plate type heating device, a fluidized layer drying device, and an air stream. 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 the present embodiment, for example, a method of adding compound A to a thin sheet-shaped fiber raw material by a method such as impregnation and then heating, or a method of heating while kneading or stirring the fiber raw material and compound A with a kneader or the like. Can be adopted. This makes it possible to suppress uneven concentration of the compound A in the fiber raw material and more uniformly introduce the phosphorus oxo acid group onto the surface of the cellulose fiber contained in the fiber raw material. This is because when the water molecules move to the surface of the fiber raw material due to drying, the dissolved compound A is attracted to the water molecules by the surface tension and also moves to the surface of the fiber raw material (that is, the concentration unevenness of the compound A is caused. It is considered that this is due to the fact that it can be suppressed.

Further, the heating device used for the heat treatment always keeps the water content retained by the slurry and the water content generated by the dehydration condensation (phosphate esterification) reaction between the compound A and the hydroxyl group contained in the cellulose or the like in the fiber raw material. It is preferable that the device can be discharged to the outside of the device system. Examples of such a heating device include a ventilation type oven and the like. By constantly discharging the water in the apparatus system, it is possible to suppress the hydrolysis reaction of the phosphate ester bond, which is the reverse reaction of the phosphate esterification, and also to suppress the acid hydrolysis of the sugar chain in the fiber. it can. Therefore, it is possible to obtain fine fibrous cellulose having 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 the water is substantially removed from the fiber raw material. Is more preferable. In the present embodiment, the amount of the phosphorus oxo acid group introduced can be within a preferable range by setting the heating temperature and the heating time within an appropriate range.

The phosphorus oxo acid group introduction step may be performed at least once, but may be repeated twice or more. By performing the phosphorus oxo acid group introduction step two or more times, many phosphorus oxo acid groups can be introduced into the fiber raw material. In the present embodiment, as an example of a preferable embodiment, there is a case where the phosphorus oxo acid group introduction step is performed twice.

The amount of the phosphorus oxo acid group introduced into the fiber raw material is, for example, 0.10 mmol / g or more, more preferably 0.20 mmol / g or more, and 0.50 mmol / g / g per 1 g (mass) of fine fibrous cellulose. It is more preferably g or more, and particularly preferably 1.00 mmol / g or more. The amount of the phosphorus oxo acid group introduced into the fiber raw material is, for example, preferably 5.20 mmol / g or less per 1 g (mass) of fine fibrous cellulose, more preferably 3.65 mmol / g or less. It is more preferably 00 mmol / g or less. By setting the amount of the phosphorus oxo acid group introduced within the above range, it is possible to facilitate the miniaturization of the fiber raw material and enhance the stability of the fine fibrous cellulose.

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

The compound having a group derived from a carboxylic acid is not particularly limited, but for example, a dicarboxylic acid compound such as maleic acid, succinic acid, phthalic acid, fumaric acid, glutaric acid, adipic acid, itaconic acid, citric acid, aconitic acid and the like. Examples include tricarboxylic acid compounds. The derivative of the compound having a group derived from a carboxylic acid is not particularly limited, and examples thereof include an imide of an acid anhydride of a compound having a carboxy group and a derivative of an acid anhydride of a compound having a carboxy group. The imide of the acid anhydride of the compound having a carboxy group is not particularly limited, and examples thereof include an imide of a dicarboxylic acid compound such as maleimide, succinateimide, and phthalateimide.

The acid anhydride of the compound having a group derived from carboxylic acid is not particularly limited, but for example, a dicarboxylic acid compound such as maleic anhydride, succinic anhydride, phthalic anhydride, glutaric anhydride, adipic anhydride, and itaconic anhydride. Acid anhydride can be mentioned. The derivative of the acid anhydride of the compound having a group derived from carboxylic acid is not particularly limited, but for example, a compound having a carboxy group such as dimethylmaleic acid anhydride, diethylmaleic acid anhydride, diphenylmaleic acid anhydride and the like. Examples thereof include those in which at least a part of hydrogen atoms of the acid anhydride is substituted with a substituent such as an alkyl group or a phenyl group.

When the TEMPO oxidation treatment is carried out in the carboxy group introduction step, it is preferable to carry out the treatment under conditions of pH 6 or more and 8 or less, for example. Such a treatment is also referred to as a neutral TEMPO oxidation treatment. The neutral TEMPO oxidation treatment includes, for example, sodium phosphate buffer (pH = 6.8), pulp as a fiber raw material, TEMPO (2,2,6,6-tetramethylpiperidin-1-oxyl) as a catalyst, and the like. This can be done by adding a nitroxy radical and sodium hypochlorite as a sacrificial reagent. Further, by coexisting sodium chlorite, the aldehyde generated in the oxidation process can be efficiently oxidized to the carboxy group. Further, the TEMPO oxidation treatment may be carried out under the condition that the pH is 10 or more and 11 or less. Such a treatment is also referred to as an alkaline TEMPO oxidation treatment. The alkaline TEMPO oxidation treatment can be carried out, for example, by adding a nitroxy radical such as TEMPO as a catalyst, sodium bromide as a co-catalyst, and sodium hypochlorite as an oxidizing agent to pulp as a fiber raw material. ..

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

<Washing process>
In the method for producing fine fibrous cellulose in the present embodiment, a washing step can be performed on the ionic substituent-introduced fiber, if necessary. The washing step is carried out by washing the ionic substituent-introduced fiber with, for example, water or an organic solvent. Further, the cleaning step may be performed after each step described later, and the number of cleanings performed in each cleaning step is not particularly limited.

<Alkaline treatment process>
In the case of producing fine fibrous cellulose, an alkali treatment may be performed on the fiber raw material between the ionic substituent introduction step and the defibration treatment step described later. The alkaline treatment method is not particularly limited, and examples thereof include 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 alkaline compound or an organic alkaline compound. In the present embodiment, for example, sodium hydroxide or potassium hydroxide is preferably used as the alkaline compound because of its high versatility. Further, the solvent contained in the alkaline solution may be either water or an organic solvent. Among them, the solvent contained in the alkaline solution is preferably a polar solvent containing water or a polar organic solvent exemplified by alcohol, and more preferably an aqueous solvent containing at least water. As the alkaline solution, for example, an aqueous solution of sodium hydroxide or an aqueous solution of potassium hydroxide is preferable because of its high versatility.

The temperature of the alkaline solution in the alkaline treatment step is not particularly limited, but is preferably 5 ° C. or higher and 80 ° C. or lower, and more preferably 10 ° C. or higher and 60 ° C. or lower. The immersion time of the phosphorus oxo acid group-introduced fiber in the alkaline solution in the alkali treatment step is not particularly limited, but is preferably 5 minutes or more and 30 minutes or less, and more preferably 10 minutes or more and 20 minutes or less. The amount of the alkaline solution used in the alkaline 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 10000% by mass or less, based on the absolute dry mass of the phosphoric acid group-introduced fiber. Is more preferable.

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

<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 treatment step described later. For example, the ionic substituent introduction step, the acid treatment, the alkali treatment and the defibration treatment may be performed in this order.

The method of the acid treatment is not particularly limited, and examples thereof include a method of immersing the fiber raw material in an acidic liquid containing an acid. The concentration of the acidic liquid used is not particularly limited, but is preferably 10% by mass or less, and more preferably 5% by mass or less, for example. The pH of the acidic solution used is not particularly limited, but is preferably 0 or more and 4 or less, and more preferably 1 or more and 3 or less. As the acid contained in the acidic solution, for example, an inorganic acid, a sulfonic acid, a carboxylic acid or the like can be used. Examples of the inorganic acid include sulfuric acid, nitric acid, hydrochloric acid, hydrobromic acid, hydroiodic acid, hypochlorous acid, chloric acid, chloric acid, perchloric acid, phosphoric acid, boric acid and the like. Examples of the sulfonic acid include methanesulfonic acid, ethanesulfonic acid, benzenesulfonic acid, p-toluenesulfonic acid, trifluoromethanesulfonic acid and the like. Examples of the carboxylic acid include formic acid, acetic acid, citric acid, gluconic acid, lactic acid, oxalic acid, tartaric acid and the like. 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 5 ° C. or higher and 100 ° C. or lower, and 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 5 minutes or more and 120 minutes or less, and more preferably 10 minutes or more and 60 minutes or less. The amount of the acid solution used in the acid treatment is not particularly limited, but is preferably 100% by mass or more and 100,000% by mass or less, and 1,000% by mass or more and 10,000% by mass or less, for example, with respect to the absolute dry mass of the fiber raw material. Is more preferable.

<Fiber processing>
Fine fibrous cellulose can be obtained by defibrating the ionic substituent-introduced fiber in the defibration treatment step. In the defibration treatment step, for example, a defibration treatment apparatus can be used. The defibrating apparatus is not particularly limited, but for example, a high-speed defibrator, a grinder (stone mill type crusher), a high-pressure homogenizer or 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 twin shaft. A kneader, a vibration 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 crushed media and less likely to cause contamination.

In the defibration treatment step, for example, it is preferable to dilute the ionic substituent-introduced fiber with a dispersion medium to form a slurry. As the dispersion medium, one or more selected from water and an organic solvent such as a polar organic solvent can be used. The polar organic solvent is not particularly limited, but for example, alcohols, polyhydric alcohols, ketones, ethers, esters, aprotic polar solvents and the like are preferable. Examples of alcohols include methanol, ethanol, isopropanol, n-butanol, isobutyl alcohol and the like. Examples of polyhydric alcohols include ethylene glycol, propylene glycol, glycerin and the like. Examples of ketones include acetone, methyl ethyl ketone (MEK) and the like. Examples of ethers include diethyl ether, tetrahydrofuran, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol mono n-butyl ether, propylene glycol monomethyl ether and the like. Examples of the esters include ethyl acetate, butyl acetate and the like. Examples of the aprotic polar solvent include dimethyl sulfoxide (DMSO), dimethylformamide (DMF), dimethylacetamide (DMAc), N-methyl-2-pyrrolidinone (NMP) and the like.

The solid content concentration of the fine fibrous cellulose during the defibration treatment can be appropriately set. Further, the slurry obtained by dispersing the ionic substituent-introduced fiber in a dispersion medium may contain a solid content other than the phosphorus oxo acid group-introduced fiber such as urea having a hydrogen bond property.
Through the defibration treatment step, a dispersion liquid containing fibrous cellulose having a fiber width of 1000 nm or less is obtained. It is preferable that the solid content concentration of such a dispersion liquid is appropriately adjusted before being subjected to the defoaming step.

(Sheet containing fine fibrous cellulose)
The present invention may relate to a sheet produced by the method for producing a fine fibrous cellulose-containing sheet described above. The sheet of the present invention is a sheet containing fibrous cellulose having a fiber width of 1000 nm or less, and is highly transparent and has few irregularities.

The content of fibrous cellulose in the sheet is preferably 1% by mass or more, more preferably 2% by mass or more, and 5% by mass or more, based on the total mass of the fine fibrous cellulose-containing sheet. Is even more preferable. The content of the fibrous cellulose may be 100% by mass with respect to the total mass of the fine fibrous cellulose-containing sheet, but may appropriately contain any component that can be contained in the slurry.

The thickness of the fine fibrous cellulose-containing sheet produced by the steps described above is preferably 5 μm or more, more preferably 8 μm or more, and further preferably 10 μm or more. 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 (absolute dry basis weight) of the fine fibrous cellulose-containing sheet is preferably 5 g / m ² or more, more preferably 10 g / m ² or more, and further preferably 20 g / m ² or more. It is preferably 30 g / m ² or more, and particularly preferably 30 g / m ² . The basis weight (absolute dry 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 600 g / m ² or less. Is even more preferable. 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 (manufactured by Murakami Color Technology Research Institute, HM-150) 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 further 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 haze meter (HM-150, manufactured by Murakami Color Technology Research Institute) in accordance with JIS K 7361.

The features of the present invention will be described in more detail with reference to Examples and Comparative Examples. The materials, amounts used, ratios, treatment contents, treatment procedures, etc. shown in the following examples can be appropriately changed as long as they do not deviate from the gist of the present invention. Therefore, the scope of the present invention should not be construed as limiting by the specific examples shown below.

[Manufacturing Example 1]
As raw material pulp, softwood kraft pulp made by Oji Paper (solid content 93% by mass, basis weight 208 g / m ² sheet, dissociated and measured according to JIS P 8121, Canadian standard drainage degree (CSF) is 700 ml) It was used. The 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 (absolute dry mass) of the 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. To obtain a chemical-impregnated pulp. Next, the obtained chemical-impregnated pulp was heated in a hot air dryer at 165 ° C. for 200 seconds to introduce a phosphoric acid group into the cellulose in the pulp to obtain phosphoroxo-oxidized pulp A.

[Washing process]
Next, the obtained phosphorus oxo oxide pulp A was washed. The washing treatment is carried out by repeating the operation of pouring 10 L of ion-exchanged water into 100 g (absolute dry mass) of phosphorus oxo-oxidized pulp A, stirring the pulp dispersion liquid so that the pulp is uniformly dispersed, and then filtering and dehydrating the pulp. went. When the electrical conductivity of the filtrate became 100 μS / cm or less, the washing end point was set.

[Neutralization]
Next, the washed phosphorus oxo oxide pulp was neutralized as follows. First, the washed phosphorus oxo oxide pulp was diluted with 10 L of ion-exchanged water, and then a 1N aqueous sodium hydroxide solution was added little by little with stirring to obtain a phosphorus oxo oxide pulp slurry having a pH of 12 or more and 13 or less. .. Next, the phosphorus oxo oxide pulp slurry was dehydrated to obtain a neutralized phosphorus oxo oxide pulp A. Next, the phosphorus oxo oxide pulp A after the neutralization treatment was subjected to the above washing treatment.

The infrared absorption spectrum of the resulting phosphorus oxo-oxidized pulp was measured using FT-IR. As a result, absorption of the phosphate group based on P = O was observed around 1230 cm ^-1 , and it was confirmed that the phosphate group was added to the pulp. Further, when the obtained phosphorus oxo oxide pulp A was tested and analyzed by an X-ray diffractometer, two positions, 2θ = 14 ° or more and 17 ° or less and 2θ = 22 ° or more and 23 ° or less, were located. A typical peak was confirmed in, and it was confirmed that it had cellulose type I crystals.

[Defibering process]
Ion-exchanged water was added to the obtained phosphorus oxo oxide pulp A to prepare a slurry having a solid content concentration of 2% by mass. This slurry was treated twice with a wet atomizer (Starburst, manufactured by Sugino Machine Limited) at a pressure of 200 MPa to obtain a fine fibrous cellulose dispersion A containing fine fibrous cellulose. By X-ray diffraction, it was confirmed that this fine fibrous cellulose maintained the cellulose type I crystal. The fiber width of the fine fibrous cellulose was measured using a transmission electron microscope and found to be 3 to 5 nm. The amount of phosphorus oxo acid group (first dissociated acid amount) measured by the measuring method described in [Measurement of amount of phosphorus oxo acid group] described later was 1.45 mmol / g. The total amount of dissociated acid was 2.45 mmol / g.

[Manufacturing Example 2]
As raw material pulp, softwood kraft pulp made by Oji Paper (solid content 93% by mass, basis weight 245 g / m ² sheet, dissociated and measured according to JIS P 8121, Canadian standard drainage degree (CSF) is 700 ml) It was used. The raw material pulp was subjected to phosphorus oxo oxidation treatment as follows. First, a mixed aqueous solution of phosphorous acid (phosphonic acid) and urea is added to 100 parts by mass (absolute dry mass) of the raw material pulp to add 33 parts by mass of phosphorous acid (phosphonic acid), 120 parts by mass of urea, and 150 parts of water. The amount was adjusted to be parts by mass, and a chemical-impregnated pulp was obtained. Next, the obtained chemical-impregnated pulp was heated in a hot air dryer at 165 ° C. for 250 seconds to introduce a phosphite group into the cellulose in the pulp to obtain phosphorous oxide pulp B.

[Washing process]
Next, the obtained phosphorus oxo oxide pulp B was washed. The washing treatment is carried out by repeating the operation of pouring 10 L of ion-exchanged water into 100 g (absolute dry mass) of phosphorus oxo oxide pulp B, stirring the pulp dispersion liquid so that the pulp is uniformly dispersed, and then filtering and dehydrating the pulp. went. When the electrical conductivity of the filtrate became 100 μS / cm or less, the washing end point was set.

[Neutralization]
Next, the washed phosphorus oxo oxide pulp B was neutralized as follows. First, the washed phosphorus oxo oxide pulp B is diluted with 10 L of ion-exchanged water, and then a 1N aqueous sodium hydroxide solution is added little by little with stirring to obtain a phosphorus oxo oxide pulp slurry having a pH of 12 or more and 13 or less. It was. Next, the phosphorus oxo oxide pulp slurry was dehydrated to obtain a neutralized phosphorus oxo oxide pulp B. Next, the phosphorus oxo oxide pulp B after the neutralization treatment was subjected to the above washing treatment.

The infrared absorption spectrum of the phosphorus oxo oxide pulp B thus obtained was measured using FT-IR. As a result, absorption based on P = O of the phosphonic acid group, which is a tautomer of the phosphite group, was observed around 1210 cm ^-1 , and the phosphite group (phosphonic acid group) was added to the pulp. Was confirmed. Further, when the obtained phosphorus oxo oxide pulp B was tested and analyzed by an X-ray diffractometer, two positions, 2θ = 14 ° or more and 17 ° or less and 2θ = 22 ° or more and 23 ° or less, were located. A typical peak was confirmed in, and it was confirmed that it had cellulose type I crystals.

[Defibering process]
Ion-exchanged water was added to the obtained phosphorus oxo oxide pulp B and then stirred to obtain a 2% by mass slurry. This slurry was treated three times with a wet atomizing device (Ultimizer manufactured by Sugino Machine Limited) at a pressure of 200 MPa to obtain a fine fibrous cellulose dispersion B. By X-ray diffraction, it was confirmed that the fine fibrous cellulose B maintained the cellulose type I crystal. The fiber width of the fine fibrous cellulose B was measured using a transmission electron microscope and found to be 3 to 5 nm. The amount of phosphorus oxo acid group (first dissociated acid amount) measured by the measuring method described in [Measurement of phosphorus oxo acid group amount] described later was 1.51 mmol / g. The total amount of dissociated acid was 1.54 mmol / g.

[Preparation of aqueous polyvinyl alcohol solution]
Polyvinyl alcohol (manufactured by Kuraray Co., Ltd., Poval 105, degree of polymerization: 500, degree of saponification: 98 to 99 mol%) was added to ion-exchanged water so as to be 20% by mass, and the mixture was stirred at 95 ° C. for 1 hour to dissolve it. .. In this way, an aqueous polyvinyl alcohol solution was obtained.

<Example 1>
[Preparation of fine fibrous cellulose-containing sheet]
The fine fibrous cellulose dispersion A and the polyvinyl alcohol aqueous solution are mixed so that the solid content mass contained in the fine fibrous cellulose dispersion A is 100 parts by mass and the solid content mass contained in the polyvinyl alcohol aqueous solution is 40 parts by mass. Mixed. Next, the slurry A containing CNF was prepared by diluting with ion-exchanged water so that the total solid content concentration was 1.8% by mass. Next, the CNF-containing slurry A is weighed so that the absolute dry basis weight of the sheet is 34 g / m ² , and spread on a commercially available polyethylene terephthalate (PET) plate so as to have as uniform a thickness as possible and wet. A membrane was prepared. A dammed frame (inner dimensions 100 mm × 100 mm, height 50 mm) was arranged on the PET plate so as to have a predetermined basis weight.

The wet film formed on the PET plate is placed in a blower dryer set at 140 ° C. for 15 minutes to evaporate the water content to obtain a CNF sheet, and then the water content is sprayed to a water content of 4 g / m ^2. Granted. The basis weight of the CNF sheet thus obtained was 38 g / m ² , and the water content was 10.7 mass%. When the water content per 100 parts by mass of CNF (water content relative to CNF) was calculated from this water content, it was 17 parts by mass. The water content per 100 parts by mass of CNF was calculated from the following formula.
Moisture content compared to CNF (parts by mass) = Moisture weight in sheet (g / m ² ) / CNF weight in sheet (g / m ² ) x 100

<Comparative example 1>
In Example 1, a CNF sheet was obtained in the same manner as in Example 1 except that water was not added. The basis weight of the obtained CNF sheet was 35 g / m ² , and the water content was 4.5% by mass. The water content per 100 parts by mass of CNF (water content relative to CNF) was 7 parts by mass.

<Example 2>
A CNF sheet was prepared in the same procedure as in Example 1 except that the fine fibrous cellulose dispersion B was used instead of the fine fibrous cellulose dispersion A in Example 1. The basis weight of the obtained CNF sheet was 38 g / m ² , and the water content was 10.9 mass%. The water content per 100 parts by mass of CNF (water content relative to CNF) was 17 parts by mass.

<Example 3>
In Example 1, the fine fibrous cellulose dispersion A has a solid content of 10 parts by mass in the fine fibrous cellulose dispersion A and 90 parts by mass in the polyvinyl alcohol aqueous solution. And a polyvinyl alcohol aqueous solution were mixed, and a CNF sheet was prepared in the same procedure as in Example 1. The basis weight of the obtained CNF sheet was 38 g / m ² , and the water content was 2.5% by mass. The water content per 100 parts by mass of CNF (water content relative to CNF) was 26 parts by mass.

<Examples 4 to 6>
A CNF sheet was prepared in the same manner as in Example 1 except that the amount of water added in Example 1 was changed to the amount shown in Table 1. The basis weight, water content, and water content relative to CNF of the obtained CNF sheet are as shown in Table 1.

<Example 7>
In Example 1, ion-exchanged water was applied using a Mayer bar so that the amount of water added was 6 g / m ^2, and a CNF sheet was prepared in the same manner as in Example 1 except that water was applied. The basis weight of the obtained CNF sheet was 40 g / m ² , and the water content was 15.1% by mass. The water content per 100 parts by mass of CNF (water content relative to CNF) was 25 parts by mass.

<Example 8>
A sheet was prepared in the same manner as in Example 1 except that the temperature of the blower dryer was 105 ° C. and the drying time was 20 minutes. The basis weight of the obtained CNF sheet was 38 g / m ² , and the water content was 10.4% by mass. The water content per 100 parts by mass of CNF (water content relative to CNF) was 16 parts by mass.

<Comparative example 2>
The same operation as in Comparative Example 1 was performed except that the temperature of the blower dryer was 105 ° C. and the drying time was 20 minutes. The basis weight of the obtained CNF sheet was 35 g / m ² , and the water content was 4.7 mass%. The water content per 100 parts by mass of CNF (water content relative to CNF) was 7 parts by mass.

<Examples 9 to 11>
A CNF sheet was prepared in the same manner as in Example 8 except that the amount of water added in Example 8 was changed to the amount shown in Table 1. The basis weight, water content, and water content relative to CNF of the obtained CNF sheet are as shown in Table 1.

<Example 12>
In Example 8, ion-exchanged water was applied using a Mayer bar so that the amount of water added was 6 g / m ^2, and a CNF sheet was prepared in the same manner as in Example 6 except that water was applied. The basis weight of the obtained CNF sheet was 40 g / m ² , and the water content was 14.9 mass%. The water content per 100 parts by mass of CNF (water content relative to CNF) was 25 parts by mass.

<Example 13>
The same operation as in Comparative Example 1 was performed except that the drying time was set to 8 minutes. The basis weight of the obtained CNF sheet was 39 g / m ² , and the water content was 13.1% by mass. The water content per 100 parts by mass of CNF (water content relative to CNF) was 21 parts by mass.

<Comparative example 3>
The same operation as in Comparative Example 1 was performed except that the drying time was set to 5 minutes. The basis weight of the obtained CNF sheet was 304 g / m ² , and the water content was 88.9 mass%. The water content per 100 parts by mass of CNF (water content relative to CNF) was 1121 parts by mass.

<Example 14>
After the operation of Comparative Example 3, an additional 3 minutes of additional drying was performed in a blower dryer at 140 ° C. The basis weight of the obtained CNF sheet was 39 g / m ² , and the water content was 13.0% by mass. The water content per 100 parts by mass of CNF (water content relative to CNF) was 21 parts by mass.

(Measurement)
[Measurement of phosphorus oxo acid groups]
The amount of phosphorus oxo acid groups in the fine fibrous cellulose is a fibrous form prepared by diluting a fine fibrous cellulose dispersion containing the target fine fibrous cellulose with ion exchange water so that the content is 0.2% by mass. The measurement was carried out by treating the cellulose-containing slurry with an ion exchange resin and then performing titration with an alkali.
In the treatment with the ion exchange resin, a strongly acidic ion exchange resin (Amberjet 1024; Organo Corporation, which has been conditioned) with a volume of 1/10 is added to the fibrous cellulose-containing slurry, and the mixture is shaken for 1 hour. , The resin and the slurry were separated by pouring on a mesh having a mesh size of 90 μm.
For titration using alkali, the change in pH value indicated by the slurry is measured while adding 10 μL of a 0.1 N sodium hydroxide aqueous solution to the fibrous cellulose-containing slurry treated with an ion exchange resin every 5 seconds. I went by doing. The titration was carried out while blowing nitrogen gas into the slurry from 15 minutes before the start of the titration. In this neutralization titration, two points are observed in which the increment (differential value of pH with respect to the amount of alkali dropped) becomes maximum in the curve plotting the measured pH with respect to the amount of alkali added. Of these, the maximum point of the increment obtained first when alkali is added is called the first end point, and the maximum point of the increment obtained next is called the second end point (FIG. 1). The amount of alkali required from the start of the titration to the first end point is equal to the amount of the first dissociated acid in the slurry used for the titration. Further, the amount of alkali required from the start of titration to the second end point becomes equal to the total amount of dissociated acid in the slurry used for titration. The amount of alkali (mmol) required from the start of titration to the first end point divided by the solid content (g) in the slurry to be titrated was defined as the amount of first dissociating 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).

[Moisture content]
The water content of the sheet was measured as follows. First, the sheet was cut into a size of 10 cm × 10 cm, and the weight (1) was measured. Then, the sheet was sufficiently dried with a dryer, the weight (2) after drying was measured, and the water content was calculated by the following formula.
Moisture content (%) = (weight (1) -weight (2)) / weight (1) x 100

(Evaluation)
[Appearance evaluation]
The appearance of the CNF sheet was evaluated according to the following criteria.
◯: After manufacturing the CNF sheet, the CNF sheet can be peeled off from the PET plate without cracking, and further, no dents or marks are left due to the excess moisture contained in the sheet.
X: When the CNF sheet was peeled off from the PET plate in the manufacturing process of the CNF sheet, or when the CNF sheet was peeled off from the PET board after the production of the CNF sheet, the sheet was cracked or due to excess moisture contained in the sheet. It is dented or has marks.

[Evaluation of peelability]
The peelability of the CNF sheet was evaluated according to the following criteria.
◯: In the process of manufacturing the CNF sheet, the CNF sheet did not peel off from the PET plate, and after the production of the CNF sheet, the CNF sheet could be peeled off from the PET board without cracking.
X: In the process of manufacturing the CNF sheet, the CNF sheet was peeled off from the PET plate, or when the CNF sheet was peeled off from the PET board after the production of the CNF sheet, the sheet was cracked.

In the example, since the water content relative to CNF was kept within a predetermined range during the sheet forming step, a sheet having no cracks and few dents and having an excellent appearance was obtained. In Comparative Example 3, since it was in a wet paper state, it was impossible to peel it into a sheet.

Claims (5)

A method for producing a sheet containing fibrous cellulose having a fiber width of 1000 nm or less.
A method for producing a sheet, which comprises a step of adjusting the moisture content of the sheet to 10 parts by mass or more and 1000 parts by mass or less with respect to 100 parts by mass of the fibrous cellulose during the sheet forming step. The sheet manufacturing method according to claim 1, wherein the humidity control step is a drying step or a hydration step. The humidity control step is a moisture addition step.
The production of the sheet according to claim 1 or 2, wherein in the water addition step, water is added so that the water content of the sheet is 10 parts by mass or more and 1000 parts by mass or less with respect to 100 parts by mass of the fibrous cellulose. Method. The sheet manufacturing method according to claim 3, wherein the water-imparting step is a step of coating or spraying water. The method for producing a sheet according to claim 3 or 4, wherein the hydration step is provided after the drying step.