Manufacturing method for composite materials

Abstract

To provide a method for producing a composite material containing microfibrous cellulose and a rubber component which prevents the generation of agglomerates of the rubber component and has excellent strength.SOLUTION: There is provided a method for producing a composite material containing microfibrous cellulose and a rubber component, which comprises a mixing step of mixing a dispersion liquid of microfibrous cellulose and a dispersion liquid of rubber component and satisfies at least one requirements of (i) and (ii). (i) The mixing step comprises a step (A) of introducing the dispersion liquid of microfibrous cellulose and the dispersion liquid of rubber component into a mixing device and firstly mixing at a shear rate of 50 to 10000 [ / s]. (ii) The mixing step comprises a step (B) of introducing the dispersion liquid of microfibrous cellulose and the dispersion liquid of rubber component into the mixing device and firstly mixing at a shear rate of 10000 [ / s] or less and a step (C) of further mixing at a shear rate of 50 [ / s] or less. (Provided that a case where the shear rate of the step (B) is less than 50 [ / s] and the shear rate of the step (C) is more than 10000 [ / s] is excluded.)SELECTED DRAWING: None

Description

[Technical Field]

[0001] This disclosure relates to a method for manufacturing composite materials. [Background technology]

[0002] In recent years, materials made from renewable natural fibers have attracted attention due to the need for alternatives to petroleum resources and growing environmental awareness. Among natural fibers, fibrous cellulose with a fiber diameter of 10 μm to 50 μm, particularly fibrous cellulose (pulp) derived from wood, has been widely used, mainly in paper products.

[0003] Among fibrous celluloses, fine fibrous cellulose with an average fiber width of 1000 nm or less is also known. Fine fibrous cellulose is attracting attention as a new material, and its applications are diverse. For example, development is underway on sheets, resin composites, and thickeners containing fine fibrous cellulose. Furthermore, the creation of composite materials by combining fine fibrous cellulose with rubber components such as rubber latex is also being considered.

[0004] Patent Document 1 discloses a method for producing a masterbatch that includes the steps of (A) treating a cellulosic raw material with a phosphate compound to obtain modified cellulose, (B) defibrating and dispersing the modified cellulose to obtain cellulose nanofibers, (C) acidifying the cellulose nanofibers to obtain acidic cellulose nanofibers, and (D) mixing the acidic cellulose nanofibers with a rubber component. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2018-193465 [Overview of the project] [Problems that the invention aims to solve]

[0006] In the production of a composite material of microfibrillar cellulose and a rubber component, when mixing a dispersion of microfibrillar cellulose and a dispersion of the rubber component, if mixing is initially carried out at a high shear rate, agglomerates of the rubber component will occur, and regular cleaning (maintenance) of the mixing device will be required. Therefore, the inventors have found that not only is this disadvantageous in operation, but also the strength of the composite material decreases. On the other hand, when mixing is carried out only at a low shear rate during the above mixing, it has also been found that the microfibrillar cellulose and the rubber component are not uniformly mixed and the strength of the composite material decreases.

[0007] The present disclosure solves the above problems and provides a method for producing a composite material containing microfibrillar cellulose and a rubber component that prevents the generation of agglomerates of the rubber component and has excellent strength.

Means for Solving the Problems

[0008] As a result of investigations to solve the above problems, the inventors have found that the above problems can be solved by controlling the mixing conditions so that the shear rate [ / s] is within a specific range in the mixing step of mixing a dispersion of microfibrillar cellulose and a dispersion of the rubber component, and have completed the present invention.

[0009] That is, the present invention relates to the following [1] to [5]. [1] A method for producing a composite material containing microfibrillar cellulose and a rubber component, comprising: a mixing step of mixing the dispersion of the microfibrillar cellulose and the dispersion of the rubber component, and satisfying at least one of the following requirements (i) and (ii). (i) The mixing step includes a step (A) of introducing the dispersion of the microfibrillar cellulose and the dispersion of the rubber component into a mixing device and initially mixing at a shear rate of 50 [ / s] or more and 10,000 [ / s] or less. ​(ii) The mixing step includes: step (B) of introducing the dispersion of the microfibrous cellulose and the dispersion of the rubber component into a mixing device and first mixing them at a shear rate of 10,000 / s or less; and step (C) of further mixing them at a shear rate of 50 / s or more. (However, this does not include the case where step (B) is a step of mixing at a shear rate of less than 50 / s and step (C) is a step of mixing at a shear rate exceeding 10,000 / s). [2] The method for producing a composite material according to [1], which satisfies the requirement of (ii). [3] When step (B) is a step of mixing at a shear rate of b / s and step (C) is a step of mixing at a shear rate of c / s, the method for producing a composite material according to [2], wherein b < c. [4] The method for producing a composite material according to [3], wherein the shear rate c / s is 10,000 / s or more. [5] The method for producing a composite material according to any one of [1] to [4], wherein step (A) or step (B) is a step of mixing at a shear rate of 1,000 / s or less.

Advantages of the Invention

[0010] According to the present disclosure, it is possible to provide a method for producing a composite material containing microfibrous cellulose and a rubber component, which prevents the generation of agglomerates of the rubber component and has excellent strength.

Brief Description of the Drawings

[0011] [Figure 1] It is a schematic cross-sectional view of a mixing device having stirring blades. [Figure 2] It is a schematic cross-sectional view of a mixing device without stirring blades. [Figure 3] It is a graph showing the relationship between the amount of NaOH dropped and the pH of a slurry containing microfibrous cellulose having a phosphonooxy group. [Figure 4] It is a graph showing the relationship between the amount of NaOH dropped and the pH of a slurry containing microfibrous cellulose having a carboxy group.

Modes for Carrying Out the Invention

[0012] When a numerical range is expressed as "XX or greater and YY or less" or "XX to YY," unless otherwise specified, it means a numerical range that includes the lower and upper limits. When a numerical range is expressed in steps, the upper and lower limits of each range can be combined in any way.

[0013] [Manufacturing method for composite materials] One embodiment of the present disclosure, a method for manufacturing a composite material (hereinafter simply referred to as the "method for manufacturing a composite material"), is a method for manufacturing a composite material comprising fine fibrous cellulose and a rubber component, comprising a mixing step of mixing a dispersion of the fine fibrous cellulose and a dispersion of the rubber component, and satisfying at least one of the following requirements (i) and (ii). (i) The mixing step includes step (A) of introducing the dispersion of the fine fibrous cellulose and the dispersion of the rubber component into a mixing device and mixing them at a shear rate of 50 [ / s] or more and 10,000 [ / s] or less. (ii) The mixing step includes a step (B) of introducing the dispersion of the fine fibrous cellulose and the dispersion of the rubber component into a mixing device and mixing them first at a shear rate of 10,000 [ / s] or less, and a step (C) of further mixing them at a shear rate of 50 [ / s] or more. (However, this excludes cases where step (B) is a mixing step at a shear rate of less than 50 [ / s] and step (C) is a mixing step at a shear rate exceeding 10,000 [ / s].)

[0014] [Mixing process] The method for manufacturing the composite material includes a mixing step (hereinafter simply referred to as the "mixing step") in which a dispersion of fine fibrous cellulose and a dispersion of rubber components are mixed. The mixing step is the process of introducing the dispersion of fine fibrous cellulose and the dispersion of rubber components into a mixing device and mixing them.

[0015] The method for introducing the dispersion of fine fibrous cellulose and the dispersion of rubber components into the mixing device is not particularly limited. The dispersions may be introduced directly into the mixing device, using a hopper, or using a pump. However, the dispersions of fine fibrous cellulose and rubber components are not mixed before being introduced into the mixing device.

[0016] The mixing equipment used in the mixing process can be any known fluid mixing device, such as a disperser, homomixer, inline mixer, clear mixer, static mixer, or OHR mixer. Furthermore, the mixing equipment is not particularly limited as long as it is capable of mixing fluids. For example, fluid delivery devices such as screw pumps (mono pumps, twin-screw pumps) and dispersion devices such as wet atomizers can be used as mixing equipment in the mixing process because fluid mixing occurs during delivery or dispersion. The mixing device is preferably selected from a disperser, an inline mixer, a clear mixer, and a static mixer.

[0017] Shear rate, also known as shuffling speed, is the value obtained by dividing the speed at which one of two plates moves (V [m / s]) by the distance H [m] between the two plates when a fluid is sandwiched between them.

[0018] In this embodiment, if the mixing device used in the mixing process is a device having a stirring blade, such as a disperser, homomixer, inline mixer, or Creamix, the peripheral speed of the stirring blade corresponds to the speed V mentioned above. Also, the distance at which the gap between the tip of the stirring blade and the wall surface of the mixing device is minimized (see Figure 1) corresponds to the distance H mentioned above. When the mixing device is a device having a stirring blade, it is preferable that the cross-sectional shape of the mixing device in the direction perpendicular to the stirring axis is circular. The peripheral speed of the impeller can be calculated using the following equation (I). Peripheral speed of the impeller [m / s] = diameter of the impeller [m] × π × rotational speed of the impeller [rpm] / 60 (I)

[0019] In the case of a disperser, distance H corresponds to the distance between the tip of the stirring blade and the wall of the container into which the dispersion liquid is introduced, specifically the distance at which this distance is minimized. In the case of a homomixer, distance H corresponds to the distance at which the distance between the tip of the stirring blade (turbine) and the wall surface formed by the stator is minimized. In the case of inline mixers and Creamix, distance H corresponds to the minimum distance between the stirring blade (rotor) and the wall surface formed by the stator.

[0020] The stirring blades are preferably paddle blades, anchor blades, dissolution-type stirring blades, or helical ribbon blades. For mixing devices, dissolving type stirring blades or helical ribbon blades are preferred if the mixing device is a disperser, and helical ribbon blades are preferred if the mixing device is a homomixer. If the mixing device is an inline mixer or a clear mixer, it is preferable to use the rotor attached to the device as the stirring blade.

[0021] In this embodiment, if the mixing device used in the mixing process is a device in which the fluid is mixed by continuous transport within a pipe, such as a static mixer, an OHR mixer, or a wet atomizer, then the flow velocity of the dispersion in the mixing process corresponds to the aforementioned speed V. In the cross-section of the portion through which the dispersion passes during the mixing process, the distance between the point where the dispersion flow velocity is maximum (point X) and the point where the gap between the pipe wall is minimum (see Figure 2) corresponds to the aforementioned distance H. If the mixing device is a static mixer or an OHR mixer, 1 / 4 of the pipe diameter may be used as the aforementioned distance H.

[0022] In the case of static mixers and OHR mixers, the point indicated by H in the schematic cross-sectional diagram of the piping shown in Figure 2 corresponds to distance H. In the case of a wet atomization device, half the diameter of the chamber nozzle corresponds to the distance H.

[0023] In the method for manufacturing composite materials, by adjusting the shear rate to satisfy at least one of the requirements (i) and (ii) described above, the mixing conditions can be appropriately controlled, preventing the formation of aggregates of rubber components and enabling the production of composite materials with superior strength. Requirements (i) and (ii) are described below.

[0024] ·Requirement(i) If the method for manufacturing the composite material satisfies requirement (i), the mixing step includes a step (A) in which the materials are initially mixed at a shear rate of 50 [ / s] or more and 10,000 [ / s] or less. Here, the "initial mixing step" is the step in which both the dispersion of fine fibrous cellulose and the dispersion of the rubber component are introduced into the mixing apparatus and the two dispersions are initially mixed while they are present in the mixing apparatus. For example, the dispersion of fine fibrous cellulose and water may be introduced into the mixing apparatus and mixed without introducing the dispersion of the rubber component, but such a mixing step is not the "initial mixing step".

[0025] The lower limit of the shear rate in process (A) is 50[ / s] or more, preferably 60[ / s] or more, more preferably 70[ / s] or more, even more preferably 100[ / s] or more, and even more preferably 200[ / s] or more. The upper limit of the shear rate is 10000[ / s] or less, preferably 1000[ / s] or less, and more preferably 800[ / s] or less. The shear rate in process (A) is 50 to 10,000 [ / s], but it may also be 60 to 1,000 [ / s] or 70 to 800 [ / s].

[0026] If the shear rate in process (A) is less than 50 [ / s], the fine fibrous cellulose and rubber component are not uniformly mixed, resulting in a decrease in the strength of the composite material. Furthermore, if the shear rate in process (A) exceeds 10,000 [ / s], aggregates of the rubber component form, leading to a decrease in the strength of the composite material. The inventors believe the reason for this is as follows.

[0027] Rubber components have a tendency to solidify when exposed to air. When a dispersion containing fine fibrous cellulose and rubber components is initially mixed at a high shear rate exceeding 10,000 [ / s], the fine fibrous cellulose and rubber components are not uniformly mixed. This increases the frequency of contact between the air in the dispersion and the rubber components, which is thought to cause the rubber components to solidify and form aggregates. Alternatively, when a dispersion containing fine fibrous cellulose and rubber components is initially mixed at a high shear rate exceeding 10,000 [ / s], the rubber components are subjected to conditions similar to exposure to air, making solidification more likely. If the shear rate in step (A) is 10,000 [ / s] or less, the fine fibrous cellulose and rubber components are uniformly mixed without generating agglomerates. Once the mixture reaches this state, the movement of the rubber component molecules is suppressed by the fine fibrous cellulose, so even if it is subsequently stirred at a high shear rate exceeding 10,000 [ / s], it is thought that agglomerates will not form. Furthermore, if the shear rate is low (less than 50 [ / s]) and the fine fibrous cellulose and rubber components are not uniformly mixed, the rubber components reinforced by the fine fibrous cellulose and those that are not will be mixed together, resulting in an uneven strength distribution throughout the composite material, with some areas exhibiting lower strength. This is thought to reduce the strength of the composite material. In other words, if the shear rate in process (A) is within the above range, it is possible to achieve both uniform dispersion and suppression of agglomeration, resulting in a composite material with superior strength.

[0028] If the method for manufacturing the composite material satisfies requirement (i), the mixing step may consist only of step (A), or it may further include mixing steps other than step (A). Since process (A) is a mixing process at a shear rate of 50 [ / s] or higher, the fine fibrous cellulose and rubber components are uniformly mixed at the stage of process (A). In this case, even if the mixing process includes further mixing processes other than process (A), and the shear rate of those processes exceeds 10,000 [ / s], no aggregates of rubber components will be generated, and a composite material with superior strength can be manufactured.

[0029] • Requirement (ii) If the method for manufacturing the composite material satisfies requirement (ii), the mixing process includes a first mixing step (B) at a shear rate of 10,000 [ / s] or less, and a second mixing step (C) at a shear rate of 50 [ / s] or more. However, if step (B) is a mixing step at a shear rate of less than 50 [ / s] and step (C) is a mixing step at a shear rate greater than 10,000 [ / s], then this step is excluded from requirement (ii). The definition of "first mixing step" is the same as the definition in requirement (i).

[0030] The upper limit of the shear rate b[ / s] in process (B) is 10,000[ / s] or less, preferably 1,000[ / s] or less, and more preferably 800[ / s] or less. The lower limit of the shear rate b[ / s] is preferably 10[ / s] or more, and more preferably 50[ / s] or more. The shear rate b in process (B) may be, for example, 10 to 10000 [ / s], 10 to 1000 [ / s], or 50 to 800 [ / s].

[0031] If the shear rate b[ / s] in process (B) exceeds 10,000[ / s], aggregates of rubber components will form, leading to a decrease in the strength of the composite material. The reason for this is thought to be the same as described above in the explanation of process (A). On the other hand, even if the shear rate b[ / s] in process (B) is less than 50[ / s], the shear rate c[ / s] in process (C) is 50[ / s] or higher, allowing for uniform mixing of the fine fibrous cellulose and rubber component in process (C), thus enabling the production of a composite material with superior strength. The reason for this is considered to be the same as that described above in the explanation of process (A).

[0032] The lower limit of the shear rate c[ / s] in process (C) is 50[ / s] or more, preferably 100[ / s] or more, more preferably 1000[ / s] or more, and even more preferably exceeding 10000[ / s]. The upper limit of the shear rate c[ / s] is not particularly limited, but is usually 1,000,000[ / s] or less. The shear rate c in process (C) may be, for example, 50 to 100,000 [ / s], 1,000 to 100,000 [ / s], or 10,000 to 100,000 [ / s].

[0033] If the shear rate b[ / s] in process (B) is less than 50[ / s], and the shear rate c[ / s] in process (C) is also less than 50[ / s], the fine fibrous cellulose and rubber component will not be uniformly mixed, resulting in a decrease in the strength of the composite material. The reason for this is thought to be the same as described above in the explanation of process (A).

[0034] If the shear rate b[ / s] in process (B) is 50[ / s] or higher, the fine fibrous cellulose and rubber component are uniformly mixed at the stage of process (B). In this case, process (C) Even when the shear rate c[ / s] exceeds 10,000[ / s], no aggregates of rubber components are formed, and a composite material with superior strength can be manufactured. The reason for this is thought to be the same as described above in the explanation of process (A).

[0035] On the other hand, if the shear rate b[ / s] in process (B) is less than 50[ / s], the fine fibrous cellulose and rubber components will not be uniformly mixed at the stage of process (B). In this case, if the shear rate c[ / s] in process (C) exceeds 10,000[ / s], aggregates of the rubber components will form, resulting in a decrease in the strength of the composite material. In other words, from the viewpoint of suppressing the generation of aggregates of rubber components, requirement (ii) is excluded if the shear rate b[ / s] of process (B) is less than 50[ / s] and the shear rate c[ / s] of process (C) is greater than 10000[ / s].

[0036] The method for manufacturing the composite material preferably satisfies requirement (ii). When the method for manufacturing the composite material satisfies requirement (ii), the mixing step may be only two steps of step (B) and step (C), or may be a mixing step of three or more steps including steps other than step (B) and step (C). By including the two steps of step (B) and step (C) in the mixing step, the microfibrous cellulose and the rubber component can be uniformly mixed, and it becomes easy to manufacture a composite material having excellent strength. It is preferable that step (B) and step (C) are consecutive steps. That is, it is preferable that step (C) is a step of mixing the mixed liquid obtained in step (B).

[0037] When the method for manufacturing the composite material satisfies requirement (ii), it is preferable that the shear rate b [ / s] in step (B) and the shear rate c [ / s] in step (C) satisfy the relationship b <c. By b <c, the microfibrous cellulose and the rubber component can be uniformly mixed, and a composite material having excellent strength can be efficiently manufactured. More preferably, the shear rate c [ / s] is 10 times or more the shear rate b [ / s], and even more preferably 50 times or more.

[0038] The lower limit of the mixing time in step (A), step (B), and step (C) is not particularly limited, but is preferably 10 seconds or more, more preferably 15 seconds or more, and even more preferably 20 seconds or more. The upper limit of the mixing time is not particularly limited, but is usually 36000 seconds or less.

[0039] The mixing device used in step (A) is preferably a device selected from a disperser and a static mixer, the mixing device used in step (B) is preferably a device selected from a disperser, a static mixer, and an OHR mixer, and the mixing device used in step (C) is preferably a device selected from a disperser, a static mixer, an in-line mixer, and a clar mixer.

[0040] If the mixing device in process (A) is a disperser, the preferred peripheral speed of the stirring blade is 1.0 to 30.0 [m / s], the preferred distance H is 0.05 to 200 [cm], the preferred mixing time is 10 to 300 seconds, and the preferred shear rate is 60 to 1000 [ / s]. If the mixing device in process (B) is a disperser, the preferred peripheral speed of the stirring blade is 0.1 to 30.0 [m / s], the preferred distance H is 0.05 to 200 [cm], the preferred mixing time is 10 to 300 seconds, and the preferred shear rate is 5 to 1000 [ / s]. If the mixing device in process (C) is a disperser, the preferred peripheral speed of the stirring blade is 1.0 to 30.0 [m / s], the preferred distance H is 0.05 to 200 [cm], the preferred mixing time is 10 to 300 seconds, and the preferred shear rate is 60 to 5000 [ / s].

[0041] If the mixing device in process (A) is a static mixer, the preferred flow velocity of the mixed liquid is 0.50 to 4.00 [m / s], the preferred distance H is 0.2 to 3.0 [cm], the preferred mixing time is 1 to 10800 seconds, and the preferred shear rate is 60 to 1000 [ / s]. If the mixing device in process (B) is a static mixer, the preferred flow velocity of the mixed liquid is 0.12 to 30 [m / s], the preferred distance H is 0.2 to 3.0 [cm], the preferred mixing time is 1 to 10800 seconds, and the preferred shear rate is 5 to 1000 [ / s]. If the mixing device in process (C) is a static mixer, the preferred flow velocity of the mixed liquid is 0.12 to 30 [m / s], the preferred distance H is 0.2 to 3.0 [cm], the preferred mixing time is 1 to 10800 seconds, and the preferred shear rate is 60 to 1000 [ / s].

[0042] If the mixing device in process (B) is an OHR mixer, the preferred flow velocity of the mixed liquid is 0.05 to 30 [m / s], the preferred distance H is 0.2 to 3.0 [cm], the preferred mixing time is 1 to 10800 seconds, and the preferred shear rate is 5 to 1000 [ / s].

[0043] If the mixing device in process (B) is an in-line mixer, the preferred peripheral speed of the stirring blade is 0.6 to 60 [m / s], the preferred distance H is 0.002 to 0.2 [cm], the preferred mixing time is 1 to 100 seconds, and the preferred shear rate is 100 to 10000 [ / s]. If the mixing device in process (C) is an in-line mixer, the preferred peripheral speed of the stirring blade is 0.6 to 60 [m / s], the preferred distance H is 0.002 to 0.2 [cm], the preferred mixing time is 1 to 100 seconds, and the preferred shear rate is 100 to 100,000 [ / s].

[0044] If the mixing device in process (B) is a CreaMix, the preferred peripheral speed of the stirring blade is 1.5 to 45 [m / s], the preferred distance H is 0.01 to 0.3 [cm], the preferred mixing time is 1 to 100 seconds, and the preferred shear rate is 5000 to 10000 [ / s]. If the mixing device in process (C) is a CreaMix, the preferred peripheral speed of the stirring blade is 1.5 to 45 [m / s], the preferred distance H is 0.01 to 0.3 [cm], the preferred mixing time is 1 to 100 seconds, and the preferred shear rate is 5,000 to 500,000 [ / s].

[0045] In the mixing process, the lower limit of the solid content concentration of the dispersion of fine fibrous cellulose introduced into the mixing apparatus is preferably 0.2% by mass or more, more preferably 0.5% by mass or more, and even more preferably 0.7% by mass or more. The upper limit of the solid content concentration of the dispersion of fine fibrous cellulose is preferably 3.0% by mass or less, more preferably 2.5% by mass or less, and even more preferably 2.2% by mass or less. The solid content concentration of the dispersion of fine fibrous cellulose may be, for example, 0.2 to 3.0% by mass, 0.5 to 2.5% by mass, or 0.7 to 2.2% by mass.

[0046] In the mixing process, the lower limit of the solid content concentration of the rubber component dispersion introduced into the mixing apparatus is preferably 10% by mass or more, more preferably 15% by mass or more, and even more preferably 20% by mass or more. The upper limit of the solid content concentration of the rubber component dispersion is preferably 80% by mass or less, more preferably 75% by mass or less, and even more preferably 70% by mass or less. The solid content concentration of the rubber component dispersion may be, for example, 10 to 80% by mass, 15 to 75% by mass, or 20 to 70% by mass.

[0047] In the mixing process, after introducing the dispersion of fine fibrous cellulose and the dispersion of rubber components into the mixing apparatus, the lower limit of the solid content concentration of the mixture to be mixed (hereinafter simply referred to as "mixture") is preferably 0.5% by mass or more, more preferably 1.0% by mass or more, and even more preferably 3.0% by mass or more. The upper limit of the solid content concentration of the mixture is preferably 20.0% by mass or less, more preferably 15.0% by mass or less, and even more preferably 10.0% by mass or less. The solid content concentration of the mixture may be, for example, 0.5 to 20.0% by mass, 1.0 to 15.0% by mass, or 3.0 to 10.0% by mass.

[0048] If the solid content concentration of the dispersion of fine fibrous cellulose introduced into the mixing device, the solid content concentration of the rubber component, and the solid content concentration of the mixture after introduction into the mixing device are within the above range, the fine fibrous cellulose and rubber component can be uniformly mixed, making it easier to manufacture a composite material with superior strength. Furthermore, the amount of energy required to remove the solvent in the drying process after the mixing process can be reduced, and aggregation of the fine fibrous cellulose particles in the resulting composite material becomes less likely.

[0049] The solid content concentration can be calculated using the following formula (II) from the mass of the dried product obtained by drying a predetermined amount of dispersion (mixture) in a 105°C dryer until a constant weight is reached, and from the mass of the dispersion (mixture) used for drying. Solid content concentration [%] of the dispersion of the mixture = Mass of the dried material [g] / Mass of the dispersion (mixture) used for drying [g] × 100 (II)

[0050] In the mixture, the lower limit of the amount of fine fibrous cellulose solids per 100 parts by mass of rubber component solids is preferably 5 parts by mass or more, and more preferably 10 parts by mass or more. The upper limit of the amount of fine fibrous cellulose solids per 100 parts by mass of rubber component is preferably 500 parts by mass or less, and more preferably 50 parts by mass or less. By keeping the amount of fine fibrous cellulose solids per 100 parts by mass of rubber component within the above range, a sufficient reinforcing effect from the fine fibrous cellulose can be obtained, and the processability of the composite material can be improved. The amount of fine fibrous cellulose solids per 100 parts by mass of rubber component may be, for example, 5 to 500 parts by mass, 10 to 50 parts by mass, or 15 to 25 parts by mass.

[0051] [Heat drying process] The method for producing the composite material may include a step of further heating and drying the mixture containing the fine fibrous cellulose and rubber component obtained in the mixing step. Known heating and drying equipment can be used for the heating and drying step of the mixture, such as a hot air dryer, agitation dryer, rotary dryer, disc dryer, roll-type heating equipment, plate-type heating equipment, fluidized bed dryer, band-type dryer, filtration dryer, vibrating fluidized bed dryer, airflow dryer, vacuum dryer, infrared heating equipment, far-infrared heating equipment, microwave heating equipment, and high-frequency drying equipment.

[0052] [Other processes] The method for manufacturing composite materials may include steps other than the mixing step and the heating and drying step described above. An uncrosslinked rubber composition can be produced by adding a crosslinking agent to the dried product obtained in the heating and drying step and kneading it.

[0053] Mixing is the process of uniformly dispersing a crosslinking agent and other compounding agents in a masterbatch (in this invention, this refers to a composition containing rubber components and fine fibrous cellulose but without a crosslinking agent). Mixing may be carried out in known ways, for example, using a Banbury mixer, kneader, or open mixer. This can be carried out using a roll or similar device. Examples of crosslinking agents include sulfur and peroxides. Other compounding agents that can be used in the rubber field include sulfenamides (such as Nt-butyl-2-benzothiazole sulfenamide), vulcanization accelerators such as zinc oxide and stearic acid, reinforcing agents such as carbon black and silica, silane coupling agents, oils, cured resins, waxes, antioxidants, deconjugates, colorants, and pH adjusters. Alternatively, a rubber composition can be obtained by adding rubber components to the masterbatch along with the crosslinking agent and kneading, thereby diluting the cellulose nanofiber concentration.

[0054] After mixing is complete, molding may be performed as needed. Examples of molding equipment include die molding, injection molding, extrusion molding, hollow molding, and foam molding, and should be appropriately selected according to the shape, application, and molding method of the final product.

[0055] Regarding crosslinking, there are no particular restrictions on temperature as long as the conditions for the crosslinking reaction proceed, but generally, a crosslinked rubber composition is obtained by heating the uncrosslinked rubber composition obtained by kneading to crosslink it (also called vulcanization if sulfur is included). The heating temperature is preferably 140°C or higher, preferably 200°C or lower, and more preferably 180°C or lower. Therefore, the heating temperature is preferably around 140 to 200°C, and more preferably around 140 to 180°C. For crosslinking, vulcanization equipment such as mold vulcanization, can vulcanization, and continuous vulcanization can be used.

[0056] [Fine fibrous cellulose] The fine fibrous cellulose is not particularly limited, and known types may be used. The upper limit of the fiber width of the fine fibrous cellulose (hereinafter also simply referred to as "fine fibrous cellulose") used in the method for manufacturing composite materials is preferably 1000 nm or less, more preferably 100 nm or less, even more preferably 50 nm or less, even more preferably 20 nm or less, and particularly preferably 10 nm or less.

[0057] The average fiber width of the fine fibrous cellulose is, for example, 1000 nm or less. Preferably, the average fiber width of the fine fibrous cellulose is, for example, 2 nm to 1000 nm, more preferably 2 nm to 100 nm, even more preferably 2 nm to 50 nm, and particularly preferably 2 nm to 10 nm. The fine fibrous cellulose is, for example, monofilamentous cellulose.

[0058] The fiber width of fine fibrous cellulose is measured, for example, using an electron microscope as follows: First, an aqueous suspension of fine fibrous cellulose with a concentration of 0.05% to 0.1% by mass is prepared, and this suspension is cast onto a hydrophilic carbon film-coated grid to prepare a sample for TEM observation. If wide fibers are present, an SEM image of the surface cast on glass may be observed. Next, observation is performed using an electron microscope image at a magnification of 1000x, 5000x, 10000x, or 50000x, depending on the width of the fiber to be observed. However, the sample, observation conditions, and magnification should be adjusted to meet the following conditions.

[0059] (1) A straight line X is drawn at any point in the observed image, and 20 or more fibers intersect with this straight line X. (2) A line Y is drawn perpendicular to the line in the same image, and 20 or more fibers intersect with line Y.

[0060] For observation images that satisfy the above conditions, the width of the fibers intersecting lines X and Y is visually read. In this way, at least three sets of observation images of surface areas that do not overlap are obtained. Next, for each image, the width of the fibers intersecting lines X and Y is read. This allows for the reading of at least 20 × 2 × 3 = 120 fiber widths. The average of the read fiber widths is then taken as the number-average fiber width of the microfiber cellulose.

[0061] The fiber length of the fine fibrous cellulose is not particularly limited, but is preferably between 0.1 μm and 1000 μm, more preferably between 0.1 μm and 800 μm, and even more preferably between 0.1 μm and 600 μm. By keeping the fiber length within the above range, the fracture of the crystalline region of the fine fibrous cellulose can be suppressed. The fiber length of the fine fibrous cellulose can be determined, for example, by image analysis using TEM, SEM, or AFM.

[0062] It is preferable that the fine fibrous cellulose has a type I crystalline structure. Here, the presence of a type I crystalline structure in fine fibrous cellulose can be identified in the diffraction profile obtained from a wide-angle X-ray diffraction photograph using graphite-monochromatized CuKα (λ=1.5418Å). Specifically, it can be identified by the presence of typical peaks at two locations: around 2θ=14° to 17° and around 2θ=22° to 23°. The proportion of type I crystalline structure in the fine fibrous cellulose is preferably 30% or more, more preferably 40% or more, and even more preferably 50% or more. The degree of crystallinity can be determined by measuring the X-ray diffraction profile and analyzing its pattern using a conventional method (Seagal et al., Textile Research Journal, Vol. 29, p. 786, 1959).

[0063] The axial ratio (fiber length / fiber width) of the fine fibrous cellulose is not particularly limited, but is preferably 50 to 10,000, and more preferably 100 to 1,000. Setting the axial ratio above the lower limit makes it easier to form composite materials containing fine fibrous cellulose. Setting the axial ratio below the upper limit is preferable in that it makes handling easier, such as dilution, when handling the fine fibrous cellulose as a dispersion.

[0064] The fibrous cellulose in this embodiment, for example, has both crystalline and amorphous regions. A fibrous cellulose having both crystalline and amorphous regions and having an axial ratio within the above range can be realized by the method for producing fibrous cellulose described later.

[0065] In this embodiment, the fibrous cellulose preferably has an ionic substituent. The ionic substituent may include, for example, either an anionic group or a cationic group, or both. In this embodiment, it is particularly preferable that the ionic substituent has an anionic group. Furthermore, the ionic substituent is preferably a group introduced into the fibrous cellulose via an ester bond or an ether bond, and more preferably a group introduced into the fibrous cellulose via an ester bond. In this case, the ester bond is preferably formed by the dehydration condensation of the fibrous cellulose and the compound that will become the ionic substituent.

[0066] Examples of anionic groups as ionic groups include phosphorus oxoacid groups or substituents derived from phosphorus oxoacid groups (sometimes simply referred to as phosphorus oxoacid groups), carboxyl groups or substituents derived from carboxyl groups (sometimes simply referred to as carboxyl groups), sulfur oxoacid groups or substituents derived from sulfur oxoacid groups (sometimes simply referred to as sulfur oxoacid groups), xantate groups or substituents derived from xantate groups (sometimes simply referred to as xantate groups), phosphonone groups or substituents derived from phosphonone groups, phosphine groups or substituents derived from phosphine groups, sulfone groups or substituents derived from sulfone groups, carboxyalkyl groups, etc. In particular, it is preferable that the anionic group be at least one selected from the group consisting of phosphorus oxoacid groups, substituents derived from phosphorus oxoacid groups, carboxyl groups, sulfur oxoacid groups, substituents derived from sulfur oxoacid groups, carboxymethyl groups, carboxyethyl groups, and sulfone groups. More preferably, the anionic group is at least one selected from the group consisting of a phosphorus oxoacid group, a substituent derived from a phosphorus oxoacid group, a carboxyl group, a sulfur oxoacid group, and a substituent derived from a sulfur oxoacid group, and is particularly preferably a phosphorus oxoacid group. By introducing a phosphorus oxoacid group as an anionic group, the dispersibility of the fine fibrous cellulose can be further improved, for example, under alkaline or acidic conditions, and as a result, it becomes easier to obtain a high-strength and highly transparent sheet. Examples of cationic groups as ionic groups include ammonium groups, phosphonium groups, and sulfonium groups. Among these, ammonium groups are preferred as the cationic group.

[0067] A phosphorus oxoacid group or a substituent derived from a phosphorus oxoacid group is, for example, a substituent represented by the following formula (1). Multiple substituents represented by the following formula (1) may be introduced into each microfiber cellulose. In this case, the multiple substituents represented by the following formula (1) may be the same or different.

[0068] [ka]

[0069] In equation (1), a, b, and n are natural numbers, and m is any number (where a = b × m). Of the n α and α', at least one is O - The rest are R or OR. Note that all of each α and α' are O - It is acceptable for this to be the case. The n αs may all be the same, or they may all be different. β b+ It is a cation with one or more valencies, composed of organic or inorganic substances.

[0070] R is a hydrogen atom, a saturated linear hydrocarbon group, a saturated branched hydrocarbon group, a saturated cyclic hydrocarbon group, an unsaturated linear hydrocarbon group, an unsaturated branched hydrocarbon group, an unsaturated cyclic hydrocarbon group, an aromatic group, or a derivative thereof. In formula (1), n ​​is preferably 1.

[0071] Examples of saturated linear hydrocarbon groups include, but are not limited to, methyl, ethyl, n-propyl, or n-butyl groups. Examples of saturated branched hydrocarbon groups include, but are not limited to, i-propyl or t-butyl groups. Examples of saturated cyclic hydrocarbon groups include, but are not limited to, cyclopentyl or cyclohexyl groups. Examples of unsaturated linear hydrocarbon groups include, but are not limited to, vinyl or allyl groups. Examples of unsaturated branched hydrocarbon groups include, but are not limited to, i-propenyl or 3-butenyl groups. Examples of unsaturated cyclic hydrocarbon groups include, but are not limited to, cyclopentenyl or cyclohexenyl groups. Examples of aromatic groups include, but are not limited to, phenyl or naphthyl groups.

[0072] Furthermore, the derivative group in R is a carboxyl group or carboxylate group (-COO) attached to the main chain or side chain of the above-mentioned hydrocarbon groups. - ), hydroxyl group, amino group and ammonium Examples of functional groups include, but are not particularly limited to, functional groups in which at least one selected from functional groups such as ligaments is added or substituted. Furthermore, 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 within the above range, the molecular weight of the phosphorus oxoacid group can be set within an appropriate range, which facilitates penetration into the fiber raw material and can also increase the yield of fine fibrous cellulose. Note that if there are multiple Rs in formula (1) or if multiple substituents represented by formula (1) are introduced into fine fibrous cellulose, the multiple Rs may be the same or different.

[0073] β b+ β is a cation with one or more valencies composed of organic or inorganic substances. Examples of cations with one or more valencies composed of organic substances include organic onium ions. Examples of organic onium ions include organic ammonium ions and organic onium ions. Examples of organic ammonium ions include aliphatic ammonium ions and aromatic ammonium ions, and examples of organic onium ions include aliphatic phosphonium ions and aromatic phosphonium ions. Examples of cations with one or more valencies composed of inorganic substances include alkali metal ions such as sodium, potassium, or lithium, divalent metal ions such as calcium or magnesium, hydrogen ions, and ammonium ions. Note that β is included in formula (1). b+ If multiple β atoms are present, or if multiple substituents represented by formula (1) are introduced into the fine fibrous cellulose, then multiple β atoms will be present. b+ These may be the same or different. As a monovalent or more cation consisting of organic or inorganic material, β b+ Sodium or potassium ions are preferred because they do not easily yellow when the fiber raw material containing them is heated and are readily available for industrial use, but the material is not particularly limited.

[0074] Examples of the phosphooxo acid group or a substituent derived from the phosphooxo acid group include, more specifically, a phosphoric acid group (-PO3H2), a salt of the phosphoric acid group, a phosphorous acid group (phosphonic acid group) (-PO2H2), and a salt of the phosphorous acid group (phosphonic acid group). Further, the phosphooxo acid group or a substituent derived from the phosphooxo acid group may be a group in which phosphoric acid groups are condensed (for example, a pyrophosphoric acid group), a group in which phosphonic acids are condensed (for example, a polyphosphonic acid group), a phosphoric acid ester group (for example, a monomethyl phosphoric acid group, a polyoxyethylene alkyl phosphoric acid group), an alkyl phosphonic acid group (for example, a methyl phosphonic acid group), or the like.

[0075] In addition, the sulfur oxo acid group (sulfur oxo acid group or a substituent derived from the sulfur oxo acid group) is, for example, a substituent represented by the following formula (2). A plurality of types of the substituent represented by the following formula (2) may be introduced into each microfibrous cellulose. In this case, the substituents represented by the following formula (2) that are introduced in plurality may be the same or different from each other.

[0076] [Chemical formula]

[0077] In formula (2), b and n are natural numbers, p is 0 or 1, and m is an arbitrary number (however, 1 = b × m). When n is 2 or more, the plurality of p's may be the same number or different numbers. In formula (2), β b+ is a cation of one valence or more composed of an organic substance or an inorganic substance. Examples of the cation of one valence or more composed of an organic substance include an organic onium ion. Examples of the organic onium ion include, for example, an organic ammonium ion and an organic onium ion. Examples of the organic ammonium ion include, for Examples include aliphatic ammonium ions and aromatic ammonium ions, while examples of organic onium ions include aliphatic phosphonium ions and aromatic phosphonium ions. Examples of monovalent or greater cations consisting of inorganic materials include alkali metal ions such as sodium, potassium, or lithium, divalent metal ions such as calcium or magnesium, hydrogen ions, and ammonium ions. When multiple substituents represented by formula (2) are introduced into fine fibrous cellulose, multiple β atoms are present. b+ These may be the same or different. As a monovalent or more cation consisting of organic or inorganic material, β b+ Sodium or potassium ions are preferred because they do not easily yellow when the fiber raw material containing them is heated and are readily available for industrial use, but the material is not particularly limited.

[0078] The amount of ionic substituent introduced into the fine fibrous cellulose is preferably, for example, 0.10 mmol / g or more per 1 g (mass) of fine fibrous cellulose, more preferably 0.20 mmol / g or more, even more preferably 0.40 mmol / g or more, and particularly preferably 0.60 mmol / g or more. Furthermore, the amount of ionic substituent introduced into the fine fibrous cellulose is preferably, for example, 5.20 mmol / g or less per 1 g (mass) of fine fibrous cellulose, more preferably 3.65 mmol / g or less, even more preferably 3.00 mmol / g or less, even more preferably 2.50 mmol / g or less, even more preferably 2.00 mmol / g or less, even more preferably 1.50 mmol / g or less, and particularly preferably 1.00 mmol / g or less. Here, the denominator in the unit mmol / g is the amount of the counterion of the ionic substituent being a hydrogen ion (H + This indicates the mass of the fine fibrous cellulose when ). By keeping the amount of ionic substituents within the above range, it is possible to easily refine the fiber raw material and improve the stability of the fine fibrous cellulose.

[0079] The amount of ionic substituents introduced into fine fibrous cellulose can be measured after the cellulose fibers have been subjected to micronization treatment, for example, by neutralization titration. In measurement by neutralization titration, the amount introduced is determined by measuring the change in pH while adding an alkali such as an aqueous sodium hydroxide solution to the slurry containing the obtained fine fibrous cellulose.

[0080] Figure 3 is a graph showing the relationship between the amount of NaOH added to a slurry containing fine fibrous cellulose with phosphorus oxoacid groups and the pH. The amount of phosphorus oxoacid groups introduced into the fine fibrous cellulose can be measured, for example, as follows. First, ion-exchanged water is added to the target cellulose fibers to prepare a slurry with a solid content concentration of 0.2% by mass. This slurry is then processed four times at a pressure of 200 MPa using a wet atomization device (Starburst, manufactured by Sugino Machine Co., Ltd.) to obtain a fine fibrous cellulose dispersion (slurry) containing fine fibrous cellulose. Finally, the fine fibrous cellulose dispersion is treated with a strongly acidic ion-exchange resin. Next, the pH change is observed while adding an aqueous sodium hydroxide solution, and a titration curve like the one shown in the upper part of Figure 3 is obtained. In the titration curve shown in the upper part of Figure 3, the measured pH is plotted against the amount of alkali added, and in the titration curve shown in the lower part of Figure 3, the increment (derivative value) (1 / mmol) of pH with respect to the amount of alkali added is plotted. In this neutralization titration, two points are observed in the curve plotting the measured pH against the amount of alkali added where the increment (derivative value of pH with respect to the amount of alkali added) is maximum. Of these, the first maximum increment obtained after starting to add alkali is called the first endpoint, and the next maximum increment obtained is called the second endpoint. The amount of alkali required from the start of the titration to the first endpoint is equal to the amount of the first dissociated acid from the fine fibrous cellulose contained in the slurry used for titration, the amount of alkali required from the first endpoint to the second endpoint is equal to the amount of the second dissociated acid from the fine fibrous cellulose contained in the slurry used for titration, and the amount of alkali required from the start of the titration to the second endpoint is equal to the total dissociated acid from the fine fibrous cellulose contained in the slurry used for titration. This is equal to the amount of acid released. The amount of alkali required from the start of the titration to the first endpoint is divided by the amount of solids (g) in the slurry being titrated to obtain the amount of phosphorus oxoacid groups introduced (mmol / g). Note that when simply referring to the amount of phosphorus oxoacid groups introduced (or amount of phosphorus oxoacid groups), it refers to the amount of the first dissociated acid. In Figure 3, the region from the start of titration to the first endpoint is called the first region, and the region from the first endpoint to the second endpoint is called the second region. For example, if the phosphorus oxoacid group is a phosphate group and this phosphate group undergoes condensation, the amount of weakly acidic group in the phosphorus oxoacid group (also referred to as the amount of the second dissociated acid in this specification) appears to decrease, and the amount of alkali required in the second region becomes less than the amount of alkali required in the first region. On the other hand, the amount of strongly acidic group in the phosphorus oxoacid group (also referred to as the amount of the first dissociated acid in this specification) is equal to the amount of phosphorus atoms, regardless of whether condensation occurs or not. Also, if the phosphorus oxoacid group is a phosphite group, there is no weakly acidic group in the phosphorus oxoacid group, so the amount of alkali required in the second region becomes less, or in some cases, the amount of alkali required in the second region becomes zero. In this case, there is only one point on the titration curve where the pH increment is maximum.

[0081] The amount of phosphorus oxoacid groups introduced (mmol / g) mentioned above represents the amount of phosphorus oxoacid groups present in the acid-type microfibrous cellulose (hereinafter referred to as phosphorus oxoacid group amount (acid type)), since the denominator represents the mass of acid-type microfibrous cellulose. On the other hand, if the counterion of the phosphorus oxoacid group is substituted with an arbitrary cation C such that it is equivalent in charge, the amount of phosphorus oxoacid groups present in the microfibrous cellulose with cation C as the counterion (hereinafter referred to as phosphorus oxoacid group amount (C type)) can be determined by converting the denominator to the mass of microfibrous cellulose when cation C is the counterion. That is, it is calculated using the following formula. Phosphorus oxoacid group amount (C type) = Phosphorus oxoacid group amount (acid type) / {1 + (W - 1) × P / 1000} P[mmol / g]: Total amount of anions derived from the phosphorus oxoacid group in the fine fibrous cellulose (total amount of dissociated acids from the phosphorus oxoacid group) W: Formula weight per unit charge of the cation C (e.g., Na is 23, Al is 9)

[0082] Figure 4 is a graph showing the relationship between the amount of NaOH added to a fine fibrous cellulose dispersion having a carboxyl group as an ionic substituent and the pH. The amount of carboxyl group introduced into the fine fibrous cellulose can be measured, for example, as follows. First, ion-exchanged water is added to the target cellulose fibers to prepare a slurry with a solid content concentration of 0.2% by mass. This slurry is then processed four times at a pressure of 200 MPa using a wet atomization device (Starburst, manufactured by Sugino Machine Co., Ltd.) to obtain a fine fibrous cellulose dispersion (slurry) containing fine fibrous cellulose. Finally, the fine fibrous cellulose dispersion is treated with a strongly acidic ion-exchange resin. Next, the pH change is observed while adding an aqueous sodium hydroxide solution to obtain a titration curve as shown in the upper part of Figure 4. In the titration curve shown in the upper part of Figure 4, the measured pH is plotted against the amount of alkali added, while in the titration curve shown in the lower part of Figure 4, the increment (derivative value) (1 / mmol) of pH with respect to the amount of alkali added is plotted. In this neutralization titration, one point is identified in the curve plotting the measured pH against the amount of alkali added where the increment (derivative value of pH with respect to the amount of alkali added) is maximum, and this maximum point is called the first endpoint. Here, the region from the start of titration to the first endpoint in Figure 4 is called the first region. The amount of alkali required in the first region is equal to the amount of carboxyl groups in the dispersion used for titration. Then, the amount of alkali required in the first region of the titration curve (mmol) is divided by the solid content (g) in the dispersion containing the fine fibrous cellulose to be titrated to calculate the amount of carboxyl groups introduced (mmol / g).

[0083] Furthermore, the above-mentioned amount of carboxyl groups introduced (mmol / g) has the mass of acidic microfiber cellulose as the denominator, and therefore the amount of carboxyl groups contained in acidic microfiber cellulose (hereafter) This indicates the amount of carboxyl groups (referred to as the acid type). On the other hand, if the counterion of the carboxyl group is substituted with an arbitrary cation C such that it is equivalent in charge, the amount of carboxyl groups in the fine fibrous cellulose where the cation C is the counterion (hereinafter referred to as the amount of carboxyl groups (C type)) can be determined by converting the denominator to the mass of the fine fibrous cellulose when the cation C is the counterion. That is, it is calculated using the following formula. Carboxylate group weight (C type) = Carboxylate group weight (acid type) / {1 + (W - 1) × (Carboxylate group weight (acid type)) / 1000} W: Formula weight per unit charge of the cation C (for example, Na is 23, Al is 9)

[0084] In measuring the amount of ionic substituents by titration, if the amount of sodium hydroxide aqueous solution added is too large or the titration interval is too short, accurate values ​​may not be obtained, resulting in a lower-than-actual amount of ionic substituents. Appropriate titration volumes and intervals include, for example, titrating with 10-50 μL of 0.1N sodium hydroxide aqueous solution every 5-30 seconds. Furthermore, to eliminate the influence of carbon dioxide dissolved in the fine fibrous cellulose dispersion, it is desirable to blow an inert gas such as nitrogen gas into the slurry from 15 minutes before the start of titration until the end of the titration while performing the measurement.

[0085] Furthermore, the amount of sulfate ester groups and sulfone groups introduced into the fine fibrous cellulose is determined by wet ashing the obtained fine fibrous cellulose with perchloric acid and concentrated nitric acid, then diluting it to an appropriate ratio and measuring the sulfur content by ICP emission spectrometry. The amount of sulfur obtained by dividing this sulfur content by the oven-dry mass of the fine fibrous cellulose used in the experiment is defined as the amount of sulfur oxoacid groups / sulfone groups (unit: mmol / g).

[0086] To obtain fine fibrous cellulose with the ionic substituents described above, it is preferable to have an ionic substituent introduction step, a washing step, an alkali treatment step (neutralization step), and a defibration treatment step in this order, and an acid treatment step may be included instead of the washing step, or in addition to the washing step. Examples of ionic substituent introduction steps include a phosphorus oxo acid group introduction step, a carboxyl group introduction step, a sulfur oxo acid group introduction step, a xantate group introduction step, a phosphone group or phosphine group introduction step, and a sulfone group introduction step and a cationic group introduction step. Each of these will be described below.

[0087] <Phosphorus oxoacid group introduction process> When obtaining cellulose fibers having ionic substituents, it is preferable to include an ionic substituent introduction step before the micronization process. An example of an ionic substituent introduction step is a phosphorus oxoacid group introduction step. The phosphorus oxoacid group introduction step is a step in which at least one compound (hereinafter also referred to as "compound A") selected from compounds that can introduce phosphorus oxoacid groups by reacting with hydroxyl groups present in the cellulose-containing fiber raw material is reacted with the cellulose-containing fiber raw material. This step results in obtaining cellulose fibers having phosphorus oxoacid groups.

[0088] In the phosphorus oxoacid group introduction step according to this embodiment, the reaction of the cellulose-containing fiber raw material with compound A may be carried out in the presence of at least one selected from urea and its derivatives (hereinafter also referred to as "compound B"). Alternatively, the reaction of the cellulose-containing fiber raw material with compound A may be carried out in the absence of compound B.

[0089] One example of a method for reacting compound A with a fiber raw material in the presence of compound B is to mix compound A and compound B with the fiber raw material in a dry, wet, or slurry state. Of these, it is preferable to use a fiber raw material in a dry or wet state, and particularly preferable to use a fiber raw material in a dry state, due to the high uniformity of the reaction. The form of the fiber raw material is not particularly limited, but for example, it is preferable to be in the form of cotton or a thin sheet. Compound A and compound B can be added to the fiber raw material in powder form, as a solution dissolved in a solvent, or after being heated above their melting points to melt them. Of these, it is preferable to add them as a solution dissolved in a solvent, especially as an aqueous solution, because this provides high reaction uniformity. Compounds A and B may be added to the fiber raw material simultaneously, separately, or as a mixture. There are no particular limitations on the method of adding compounds A and B, but if compounds A and B are in solution form, the fiber raw material may be immersed in the solution to allow it to absorb the liquid and then removed, or the solution may be added dropwise to the fiber raw material. Alternatively, the required amount of compound A and compound B may be added to the fiber raw material, or excess amounts of compound A and compound B may be added to the fiber raw material separately, and then the excess compound A and compound B may be removed by pressing or filtration.

[0090] Compound A used in this embodiment may be any compound having a phosphorus atom and capable of forming an ester bond with cellulose, and is not particularly limited to, but includes phosphoric acid or its salts, phosphorous acid or its salts, dehydrated condensed phosphoric acid or its salts, and phosphoric anhydride (phosphorus pentoxide). As phosphoric acid, various purities can be used, for example, 100% phosphoric acid (orthophosphoric acid) or 85% phosphoric acid can be used. As phosphorous acid, 99% phosphorous acid (phosphonic acid) can be used. Dehydrated condensed phosphoric acid is obtained by condensing two or more molecules of phosphoric acid through a dehydration reaction, and examples include pyrophosphoric acid and polyphosphoric acid. Phosphates, phosphites, and dehydrated condensed phosphates include lithium salts, sodium salts, potassium salts, and ammonium salts of phosphoric acid, phosphorous acid, or dehydrated condensed phosphoric acid, and these can be neutralized to various degrees. Of these, phosphoric acid, sodium phosphoric acid, potassium phosphoric acid, ammonium phosphoric acid, or phosphorous acid, sodium phosphorous acid, potassium phosphorous acid, or ammonium phosphorous acid are preferred from the viewpoint of having high efficiency in introducing phosphate groups, easily improving the defibration efficiency in the defibration process described later, being low cost, and being easily applicable industrially. Phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, ammonium dihydrogen phosphate, or phosphorous acid or sodium phosphorous acid are more preferred.

[0091] 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 amount of phosphorus atoms, it is preferable that the amount of phosphorus atoms added to the fiber raw material (oven-dry mass) be 0.5% by mass or more and 100% by mass or less, more preferably 1% by mass or more and 50% by mass or less, and even more preferably 2% by mass or more and 30% by mass or less. By keeping 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 keeping the amount of phosphorus atoms added to the fiber raw material below the above upper limit, it is possible to balance the effect of improving yield with cost.

[0092] As described above, compound B used in this embodiment is at least one selected from urea and its derivatives. Examples of compound B include urea, biuret, 1-phenylurea, 1-benzylurea, 1-methylurea, and 1-ethylurea. From the viewpoint of improving the uniformity of the reaction, it is preferable to use compound B as an aqueous solution. Furthermore, 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.

[0093] The amount of compound B added to the fiber raw material (absolute dry weight) is not particularly limited, but is preferably 1% by mass or more and 500% by mass or less, more preferably 10% by mass or more and 400% by mass or less, and even more preferably 100% by mass or more and 350% by mass or less.

[0094] In the reaction of cellulose-containing fiber raw materials with compound A, in addition to compound B, other substances such as amides or amines may be included in the reaction system. Examples of amides include formamide. Examples include dimethylformamide, acetamide, and dimethylacetamide. Examples of amines include methylamine, ethylamine, trimethylamine, triethylamine, monoethanolamine, diethanolamine, triethanolamine, pyridine, ethylenediamine, and hexamethylenediamine. Among these, triethylamine is particularly known to act as a good reaction catalyst.

[0095] In the phosphorus oxoacid group introduction step, it is preferable to add or mix compound A or the like to the fiber raw material and then heat treat the fiber raw material. The heat treatment temperature is preferably selected to efficiently introduce phosphorus oxoacid groups while suppressing thermal decomposition and hydrolysis reactions of the fibers. The heat treatment temperature is preferably, for example, 50°C to 300°C, more preferably 100°C to 250°C, and even more preferably 130°C to 200°C. Furthermore, various heat transfer devices can be used for the heat treatment, such as agitation dryers, rotary dryers, disc dryers, roll-type heaters, plate-type heaters, fluidized bed dryers, band-type dryers, filtration dryers, vibrating fluidized bed dryers, airflow dryers, vacuum dryers, infrared heaters, far-infrared heaters, microwave heaters, and high-frequency dryers.

[0096] In the heat treatment according to this embodiment, for example, a method can be employed in which compound A is added to a thin sheet-like fiber raw material by impregnation or other methods, and then heated, or a method can be employed in which the fiber raw material and compound A are kneaded or stirred while heating. This makes it possible to suppress uneven concentration of compound A in the fiber raw material and to introduce phosphorus oxoacid groups more uniformly to the surface of the cellulose fibers contained in the fiber raw material. This is thought to be because, as water molecules move to the surface of the fiber raw material during drying, dissolved compound A is attracted to the water molecules by surface tension and similarly moves to the surface of the fiber raw material (i.e., uneven concentration of compound A is produced), and this can be suppressed.

[0097] Furthermore, the heating device used for the heat treatment is preferably one that can constantly discharge, for example, the moisture held in the slurry and the moisture generated by the dehydration condensation (phosphate esterification) reaction between compound A and hydroxyl groups contained in cellulose, etc., in the fiber raw material, to the outside of the device system. Examples of such heating devices include a forced-air oven. By constantly discharging moisture from the device system, it is possible to suppress the hydrolysis reaction of phosphate ester bonds, which is the reverse reaction of phosphate esterification, as well as the acid hydrolysis of sugar chains in the fibers. As a result, it becomes possible to obtain fine fibrous cellulose with a high axial ratio.

[0098] The heating time is preferably between 1 second and 300 minutes, more preferably between 1 second and 1000 seconds, and even more preferably between 10 seconds and 800 seconds, after substantially all moisture has been removed from the fiber raw material. In this embodiment, the amount of phosphorus oxoacid groups introduced can be kept within a preferred range by setting the heating temperature and heating time within an appropriate range.

[0099] The phosphorus oxoacid group introduction process only needs to be performed at least once, but it can also be repeated two or more times. By performing the phosphorus oxoacid group introduction process two or more times, a large number of phosphorus oxoacid groups can be introduced into the fiber raw material.

[0100] The amount of phosphorus oxoacid groups introduced into the fiber raw material is preferably 0.10 mmol / g or more per 1 g (mass) of cellulose fiber, more preferably 0.20 mmol / g or more, even more preferably 0.50 mmol / g or more, and particularly preferably 1.00 mmol / g or more. Furthermore, the amount of phosphorus oxoacid groups introduced into the fiber raw material is preferably 5.20 mmol / g or less per 1 g (mass) of cellulose fiber, more preferably 3.65 mmol / g or less, and 3.00 mmol / g or more. It is even more preferable that the amount is less than or equal to l / g. By keeping the amount of phosphorus oxoacid group introduced within the above range, the micronization of cellulose fibers in the micronization process can be facilitated, and the stability of the fine fibrous cellulose can be enhanced.

[0101] <Carboxyloid introduction process> The ionic substituent introduction step may include a carboxyl group introduction step. The carboxyl group introduction step is carried out by treating the cellulose-containing fiber raw material with an oxidation treatment such as ozono-oxidation, Fenton-type oxidation, or TEMPO oxidation treatment, or with a compound having a carboxylic acid-derived group or a derivative thereof, or with an acid anhydride or a derivative thereof of a compound having a carboxylic acid-derived group.

[0102] Compounds having a carboxylic acid-derived group are not particularly limited, but examples include dicarboxylic acid compounds such as maleic acid, succinic acid, phthalic acid, fumaric acid, glutaric acid, adipic acid, and itaconic acid, and tricarboxylic acid compounds such as citric acid and aconitic acid. Furthermore, derivatives of compounds having a carboxylic acid-derived group are not particularly limited, but examples include imidides of acid anhydrides of compounds having a carboxyl group, and derivatives of acid anhydrides of compounds having a carboxyl group. Imidides of acid anhydrides of compounds having a carboxyl group are not particularly limited, but examples include imidides of dicarboxylic acid compounds such as maleimide, succinimide, and phthalimide.

[0103] Acid anhydrides of compounds having a carboxylic acid-derived group are not particularly limited, but examples include acid anhydrides of dicarboxylic acid compounds such as maleic anhydride, succinic anhydride, phthalic anhydride, glutaric anhydride, adipic anhydride, and itaconic anhydride. Furthermore, derivatives of acid anhydrides of compounds having a carboxylic acid-derived group are not particularly limited, but examples include acid anhydrides of compounds having a carboxyl group, such as dimethyl maleic anhydride, diethyl maleic anhydride, and diphenyl maleic anhydride, in which at least some of the hydrogen atoms are substituted with substituents such as alkyl groups and phenyl groups.

[0104] In the carboxyl group introduction step, when performing TEMPO oxidation treatment, it is preferable to carry out the treatment under conditions where the pH is between 6 and 8. Such treatment is also called neutral TEMPO oxidation treatment. Neutral TEMPO oxidation treatment can be carried out, for example, by adding pulp as the fiber raw material, a nitroxyl radical such as TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl) as a catalyst, and sodium hypochlorite as a sacrificial reagent to a sodium phosphate buffer (pH=6.8). Furthermore, by including sodium chlorite, the aldehyde generated during the oxidation process can be efficiently oxidized to the carboxyl group. Alternatively, the TEMPO oxidation treatment may be carried out under conditions where the pH is between 10 and 11. Such treatment is also called alkaline TEMPO oxidation treatment. Alkaline TEMPO oxidation treatment can be carried out, for example, by adding a nitroxyl radical such as TEMPO as a catalyst, sodium bromide as a co-catalyst, and sodium hypochlorite as an oxidizing agent to pulp as the fiber raw material.

[0105] The amount of carboxyl groups introduced into cellulose fibers varies depending on the type of substituent, but for example, when introducing carboxyl groups by TEMPO oxidation, it is preferably 0.10 mmol / g or more per gram (mass) of cellulose fiber, more preferably 0.20 mmol / g or more, even more preferably 0.40 mmol / g or more, and particularly preferably 0.60 mmol / g or more. Furthermore, the amount of carboxyl groups introduced into cellulose fibers is preferably 3.65 mmol / g or less, more preferably 3.00 mmol / g or less, even more preferably 2.50 mmol / g or less, even more preferably 2.00 mmol / g or less, even more preferably 1.50 mmol / g or less, and particularly preferably 1.00 mmol / g or less. This is preferable. In addition, if the substituent is a carboxymethyl group, the amount of carboxyl group introduced may be 5.8 mmol / g or less per gram (mass) of cellulose fiber. By keeping the amount of carboxyl group introduced within the above range, the micronization of cellulose fibers in the micronization process can be facilitated and the stability of the fine fibrous cellulose can be improved.

[0106] <Sulfone group introduction process> The ionic substituent introduction step may include a sulfone group introduction step. In the sulfone group introduction step, a hydroxyl group present in the cellulose-containing fiber raw material reacts with a sulfur oxoacid to obtain cellulose fibers having sulfone groups (sulfone group-introduced fibers).

[0107] In the sulfone group introduction step, instead of compound A in the <phosphorus oxoacid group introduction step> described above, at least one compound (hereinafter also referred to as "compound C") selected from compounds that can introduce sulfone groups by reacting with hydroxyl groups present in the cellulose-containing fiber raw material is used. Compound C can be any compound having a sulfur atom and capable of forming an ester bond with cellulose, and examples include sulfuric acid or its salts, sulfite or its salts, and sulfuric acid amide, but is not particularly limited. Sulfuric acid of various purities can be used, for example, 96% sulfuric acid (concentrated sulfuric acid) can be used. As sulfite, 5% sulfurous acid water can be used. As sulfates or sulfites, examples include lithium salts, sodium salts, potassium salts, and ammonium salts of sulfates or sulfites, and these can be neutralized to various degrees. As sulfuric acid amide, sulfamic acid can be used. In the sulfone group introduction step, it is preferable to use compound B in the same manner as in the <phosphorus oxoacid group introduction step> described above.

[0108] In the sulfone group introduction step, it is preferable to mix the cellulose raw material with an aqueous solution containing sulfur oxoacid and urea and / or a urea derivative, and then heat-treat the cellulose raw material. The heat treatment temperature is preferably selected to efficiently introduce sulfone groups while suppressing thermal decomposition and hydrolysis reactions of the fibers. The heat treatment temperature is preferably 100°C or higher, more preferably 120°C or higher, and even more preferably 150°C or higher. Furthermore, the heat treatment temperature is preferably 300°C or lower, more preferably 250°C or lower, and even more preferably 200°C or lower.

[0109] In the heat treatment process, it is preferable to heat until substantially all moisture is removed. Therefore, the heat treatment time varies depending on the amount of moisture contained in the cellulose raw material, the amount of sulfur oxoacid and aqueous solution containing urea and / or urea derivatives added, but it is preferable to heat for 10 seconds or more and 10,000 seconds or less. Various heat transfer devices can be used for the heat treatment, such as hot air dryers, agitation dryers, rotary dryers, disc dryers, roll-type heaters, plate-type heaters, fluidized bed dryers, band-type dryers, filtration dryers, vibrating fluidized bed dryers, airflow dryers, vacuum dryers, infrared heaters, far-infrared heaters, microwave heaters, and high-frequency dryers.

[0110] The amount of sulfone groups introduced into the cellulose raw material is preferably 0.05 mmol / g or more, more preferably 0.10 mmol / g or more, even more preferably 0.20 mmol / g or more, even more preferably 0.40 mmol / g or more, and particularly preferably 0.50 mmol / g or more. Furthermore, the amount of sulfone groups introduced into the cellulose raw material is preferably 5.00 mmol / g or less, and more preferably 3.00 mmol / g or less. By keeping the amount of sulfone groups introduced within the above range, the micronization of cellulose fibers in the micronization process can be facilitated, and the stability of the fine fibrous cellulose can be improved.

[0111] <Oxidation process using chlorine-based oxidizing agent (second carboxyl group introduction process)> The ionic substituent introduction step may include an oxidation step using a chlorine-based oxidizing agent. In the oxidation step using a chlorine-based oxidizing agent, a carboxyl group is introduced into the fiber raw material by adding the chlorine-based oxidizing agent to a hydroxyl-containing fiber raw material in a wet or dry state and carrying out the reaction.

[0112] Examples of chlorine-based oxidizing agents include hypochlorous acid, hypochlorite, chlorous acid, chlorite, chloric acid, chlorate, perchloric acid, perchlorate, and chlorine dioxide. From the standpoint of substituent introduction efficiency, and consequently defibration efficiency, cost, and ease of handling, sodium hypochlorite, sodium chlorite, and chlorine dioxide are preferred as chlorine-based oxidizing agents. When adding a chlorine-based oxidizing agent, it may be added directly to the fiber raw material as a reagent (solid or liquid), or it may be dissolved in a suitable solvent before being added.

[0113] In the oxidation process using a chlorine-based oxidizing agent, the concentration of the chlorine-based oxidizing agent in the solution is preferably 1% by mass or more and 1,000% by mass or less, more preferably 5% by mass or more and 500% by mass or less, and even more preferably 10% by mass or more and 100% by mass or less, when converted to an effective chlorine concentration. The amount of chlorine-based oxidizing agent added per 100 parts by mass of fiber raw material is preferably 1 part by mass or more and 100,000 parts by mass or less, more preferably 10 parts by mass or more and 10,000 parts by mass or less, and even more preferably 100 parts by mass or more and 5,000 parts by mass or less.

[0114] The reaction time with the chlorine-based oxidizing agent in the oxidation step may vary depending on the reaction temperature, but is preferably, for example, 1 minute or more and 1,000 minutes or less, more preferably 10 minutes or more and 500 minutes or less, and even more preferably 20 minutes or more and 400 minutes or less. The pH during the reaction is preferably 5 or more and 15 or less, more preferably 7 or more and 14 or less, and even more preferably 9 or more and 13 or less. Furthermore, it is preferable to maintain a constant pH (for example, pH 11) at the start of the reaction and during the reaction by appropriately adding hydrochloric acid or sodium hydroxide. After the reaction, excess reaction reagents, by-products, etc. may be washed off with water by filtration or the like.

[0115] <Xantate group introduction process> The manufacturing process for fine fibrous cellulose may include a xantate group introduction step as an ionic substituent introduction step. The xantate group introduction step involves substituting the hydroxyl groups in the cellulose-containing fiber raw material with xantate groups represented by the following formula (3), thereby obtaining cellulose fibers having xantate groups (xantate group-introduced fibers). ―OCSS - M + ...(3) Here, M + is at least one selected from hydrogen ions, monovalent metal ions, ammonium ions, aliphatic or aromatic ammonium ions.

[0116] In the xantate group introduction process, first, the fiber raw material containing the cellulose is treated with an alkaline solution to obtain alkaline cellulose. Examples of alkaline solutions include aqueous alkali metal hydroxide solutions and alkaline earth metal hydroxide solutions. Among these, the alkaline solution is preferably an aqueous alkali metal hydroxide solution such as sodium hydroxide or potassium hydroxide, and is particularly preferably an aqueous sodium hydroxide solution. When the alkaline solution is an aqueous alkali metal hydroxide solution, the alkali metal hydroxide concentration in the aqueous alkali metal hydroxide solution is preferably 4% by mass or more, and more preferably 5% by mass or more. Furthermore, the alkali metal hydroxide concentration in the aqueous alkali metal hydroxide solution is preferably 9% by mass or less. By setting the alkali metal hydroxide concentration above the lower limit, the mercellation of cellulose can be sufficiently advanced, the amount of by-products generated during the subsequent xantate formation can be reduced, and as a result, the yield of xantate group-introduced fibers can be increased. This allows the defibration treatment described later to be carried out more effectively. Furthermore, by setting the alkali metal hydroxide concentration below the upper limit, mercellation can be advanced while the cellulose... Since the penetration of alkali metal hydroxide aqueous solution into the crystalline region can be suppressed, the crystalline structure of cellulose type I is more easily maintained, and the yield of fine fibrous cellulose can be further increased.

[0117] The alkaline treatment time is preferably 30 minutes or more, and more preferably 1 hour or more. Furthermore, the alkaline treatment time is preferably 6 hours or less, and more preferably 5 hours or less. By keeping the alkaline treatment time within the above range, the final yield can be increased, and productivity can be improved.

[0118] It is preferable to remove as much of the aqueous solution as possible from the alkali cellulose obtained by the above alkali treatment by solid-liquid separation. This reduces the water content during the subsequent xantate treatment and promotes the reaction. As for the solid-liquid separation method, general dehydration methods such as centrifugation or filtration can be used. It is preferable that the concentration of alkali metal hydroxide in the alkali cellulose after solid-liquid separation is 3% by mass or more and 8% by mass or less of the total mass of the alkali cellulose after solid-liquid separation.

[0119] In the xantate group introduction process, an alkali treatment is followed by a xantate treatment process. In the xantate treatment process, alkali cellulose is reacted with carbon disulfide (CS2) to form (-O - Na + )Based on (-OCSS - Na + ) A xantate group-introduced fiber is obtained using this group. In the above, the metal ions introduced into alkali cellulose are, representatively, Na + As described above, similar reactions proceed with other alkali metal ions.

[0120] In the xantate treatment, it is preferable to supply 10% by mass or more of carbon disulfide relative to the oven-dry mass of cellulose in the alkali cellulose. Furthermore, in the xantate treatment, the contact time between carbon disulfide and alkali cellulose is preferably 30 minutes or more, and more preferably 1 hour or more. Although xantate treatment proceeds rapidly upon contact of carbon disulfide with alkali cellulose, it takes time for the carbon disulfide to penetrate into the interior of the alkali cellulose, so it is preferable to set the reaction time within the above range. On the other hand, the contact time between carbon disulfide and alkali cellulose can be 6 hours or less, which allows sufficient penetration even into the dehydrated alkali cellulose mass, and almost complete the reactive xantate treatment.

[0121] The reaction temperature in the xantate treatment is preferably 46°C or lower. Keeping the reaction temperature within this range makes it easier to suppress the decomposition of alkali cellulose. Furthermore, keeping the reaction temperature within this range makes it easier to react uniformly, which suppresses the formation of by-products and also helps to suppress the removal of the generated xantate groups.

[0122] In the xantate group introduction process, the amount of xantate groups introduced is preferably 0.60 mmol / g or more per 1 g (mass) of fiber raw material, more preferably 0.70 mmol / g or more, even more preferably 0.80 mmol / g or more, even more preferably 1.00 mmol / g or more, and particularly preferably 1.20 mmol / g or more. Furthermore, the amount of xantate groups introduced is preferably 5.00 mmol / g or less per 1 g (mass) of fiber raw material, and more preferably 3.00 mmol / g or less. By keeping the amount of xantate groups introduced within the above range, it becomes easier to obtain a sheet with excellent transparency and excellent resistance to yellowing.

[0123] <Phosphozone group or phosphine group introduction process (phosphoalkylation process)> The ionic substituent introduction step may include a phosphone group or phosphine group introduction step (phosphoalkylation step). In the phosphoalkylation step, a compound having a reactive group and a phospho group or phosphine group (compound E) is used as an essential component. A ), alkalizing as an optional component By adding compound B, selected from the aforementioned urea and its derivatives, to a hydroxyl-containing fiber raw material in a wet or dry state and carrying out the reaction, a phosphone group or phosphine group is introduced into the fiber raw material.

[0124] Examples of reactive groups include alkyl halides, vinyl groups, and epoxy groups (glycidyl groups). Compound E AExamples include vinylphosphonic acid, phenylvinylphosphonic acid, and phenylvinylphosphinic acid. Compound E is chosen from the standpoint of substituent introduction efficiency, and consequently defibrillation efficiency, cost, and ease of handling. A It is preferable that it be vinylphosphonic acid. Furthermore, it is also preferable to use compound B from the <phosphorus oxoacid group introduction step> described above as an optional component, and the amount added is also preferably as described above.

[0125] Compound E A When adding the reagent, it may be added directly to the fiber raw material as a reagent (solid or liquid), or it may be added after being dissolved in a suitable solvent. It is preferable that the fiber raw material be alkali-cellulosed beforehand or simultaneously with the reaction. The method of alkali-cellulosed treatment is as described above.

[0126] The reaction temperature is preferably, for example, 50°C to 300°C, more preferably 100°C to 250°C, and even more preferably 130°C to 200°C.

[0127] Compound E A The amount added per 100 parts by mass of fiber raw material is preferably 1 part by mass or more and 100,000 parts by mass or less, more preferably 2 parts by mass or more and 10,000 parts by mass or less, and even more preferably 5 parts by mass or more and 1,000 parts by mass or less.

[0128] The reaction time may vary depending on the reaction temperature, but is preferably between 1 minute and 1,000 minutes, more preferably between 10 minutes and 500 minutes, and even more preferably between 20 minutes and 400 minutes. After the reaction, excess reaction reagents, by-products, etc., may be washed away with water by filtration or other means.

[0129] <Sulfone group introduction process (sulfoalkylation process) (second sulfone group introduction process)> The ionic substituent introduction step may include a sulfone group introduction step (sulfoalkylation step). In sulfoalkylation, a compound having a reactive group and a sulfone group (compound E) is used as an essential component. B ) and compound B, selected as an optional component from an alkaline compound, the aforementioned urea and its derivatives, are added to a hydroxyl-containing fiber raw material in a wet or dry state, and a reaction is carried out to introduce sulfone groups into the fiber raw material.

[0130] Examples of reactive groups include alkyl halides, vinyl groups, and epoxy groups (glycidyl groups). Compound E B Examples include sodium 2-chloroethanesulfonate, sodium vinylsulfonate, sodium p-styrenesulfonate, and 2-acrylamido-2-methylpropanesulfonic acid. Among these, compound E is considered to have the efficiency of substituent introduction, and consequently the efficiency of defibrillation, cost, and ease of handling. B It is preferable that it be sodium vinyl sulfonate. Furthermore, it is also preferable to use compound B from the <phosphorus oxoacid group introduction step> described above as an optional component, and the amount added is also preferably as described above.

[0131] Compound E B When adding the reagent, it may be added directly to the fiber raw material as a reagent (solid or liquid), or it may be added after being dissolved in a suitable solvent. It is preferable that the fiber raw material be alkali-cellulosed beforehand or simultaneously with the reaction. The method of alkali-cellulosed treatment is as described above.

[0132] The reaction temperature is preferably, for example, 50°C to 300°C, more preferably 100°C to 250°C, and even more preferably 130°C to 200°C.

[0133] Compound E BThe amount added per 100 parts by mass of fiber raw material is preferably 1 part by mass or more and 100,000 parts by mass or less, more preferably 2 parts by mass or more and 10,000 parts by mass or less, and even more preferably 5 parts by mass or more and 1,000 parts by mass or less.

[0134] The reaction time may vary depending on the reaction temperature, but is preferably between 1 minute and 1,000 minutes, more preferably between 10 minutes and 500 minutes, and even more preferably between 15 minutes and 400 minutes. After the reaction, excess reaction reagents, by-products, etc., may be washed away with water by filtration or other means.

[0135] <Carboxyalkylation process (third carboxyl group introduction process)> The ionic substituent introduction step may include a carboxyalkylation step. An essential component is a compound having a reactive group and a carboxyl group (compound E). C ) ) A carboxyl group is introduced into the fiber raw material by adding an alkaline compound, compound B selected from the aforementioned urea and its derivatives as an optional component, to a hydroxyl-containing fiber raw material in a wet or dry state and carrying out the reaction.

[0136] Examples of reactive groups include alkyl halides, vinyl groups, and epoxy groups (glycidyl groups). Compound E C From the viewpoint of substituent introduction efficiency, and consequently defibration efficiency, cost, and ease of handling, monochloroacetic acid, sodium monochloroacetate, 2-chloropropionic acid, 3-chloropropionic acid, sodium 2-chloropropionate, and sodium 3-chloropropionate are preferred. Furthermore, it is also preferable to use compound B from the <phosphorus oxoacid group introduction step> described above as an optional component, and the amount added is also preferably as described above.

[0137] Compound E CWhen adding the reagent, it may be added directly to the fiber raw material as a reagent (solid or liquid), or it may be added after being dissolved in a suitable solvent. It is preferable that the fiber raw material be alkali-cellulosed beforehand or simultaneously with the reaction. The method of alkali-cellulosed treatment is as described above.

[0138] The reaction temperature is preferably, for example, 50°C to 300°C, more preferably 100°C to 250°C, and even more preferably 130°C to 200°C.

[0139] Compound E C The amount added per 100 parts by mass of fiber raw material is preferably 1 part by mass or more and 100,000 parts by mass or less, more preferably 2 parts by mass or more and 10,000 parts by mass or less, and even more preferably 5 parts by mass or more and 1,000 parts by mass or less.

[0140] The reaction time may vary depending on the reaction temperature, but is preferably between 1 minute and 1,000 minutes, more preferably between 3 minutes and 500 minutes, and even more preferably between 5 minutes and 400 minutes. After the reaction, excess reaction reagents, by-products, etc., may be washed away with water by filtration or other means.

[0141] <Cationic group introduction process (cationization process)> As an essential component, a compound having a reactive group and a cationic group (compound E D ), optional components By adding compound B, selected from alkaline compounds, urea, and its derivatives as described above, to a hydroxyl-containing fiber raw material in a wet or dry state and carrying out the reaction, a cationic group is introduced into the fiber raw material.

[0142] Examples of reactive groups include alkyl halides, vinyl groups, and epoxy groups (glycidyl groups). Examples of cationic groups include ammonium groups, phosphonium groups, and sulfonium groups. Among these, ammonium groups are preferred as the cationic group. Compound E D As such, glycidyltrimethylammonium chloride, 3-chloro-2-hydroxypropyltrimethylammonium chloride, etc. are preferred in terms of substituent introduction efficiency, and consequently defibration efficiency, cost, and ease of handling. Furthermore, it is also preferable to use compound B from the <phosphorus oxoacid group introduction step> described above as an optional component. The amount added is also preferably as described above.

[0143] Compound E D When adding the reagent, it may be added directly to the fiber raw material as a reagent (solid or liquid), or it may be added after being dissolved in a suitable solvent. It is preferable that the fiber raw material be alkali-cellulosed beforehand or simultaneously with the reaction. The method of alkali-cellulosed treatment is as described above.

[0144] The reaction temperature is preferably, for example, 50°C to 300°C, more preferably 100°C to 250°C, and even more preferably 130°C to 200°C.

[0145] Compound E D The amount added per 100 parts by mass of fiber raw material is preferably 1 part by mass or more and 100,000 parts by mass or less, more preferably 2 parts by mass or more and 10,000 parts by mass or less, and even more preferably 5 parts by mass or more and 1,000 parts by mass or less.

[0146] The reaction time may vary depending on the reaction temperature, but is preferably between 1 minute and 1,000 minutes, more preferably between 5 minutes and 500 minutes, and even more preferably between 10 minutes and 400 minutes. After the reaction, excess reaction reagents, by-products, etc., may be washed away with water by filtration or other means.

[0147] <Washing process> In the process of obtaining cellulose fibers having ionic substituents, a washing step may be performed on the ionic substituent-introduced fibers as needed. The washing step is performed, for example, by washing the ionic substituent-introduced fibers with water or an organic solvent. Furthermore, the washing step may be performed after each of the steps described later, and the number of washing steps performed in each washing step is not particularly limited.

[0148] <Alkali treatment process> In the process of obtaining cellulose fibers having ionic substituents, an alkali treatment step may be provided between the ionic substituent introduction step and the micronization treatment step. The alkali treatment method is not particularly limited, but one example is immersing the ionic substituent-introduced fibers in an alkaline solution.

[0149] The alkali compound contained in the alkaline solution is not particularly limited and may be an inorganic alkali compound or an organic alkali compound. In this embodiment, it is preferable to use sodium hydroxide or potassium hydroxide as the alkali compound due to its high versatility. The solvent contained in the alkaline solution may be either water or an organic solvent. Among these, the solvent contained in the alkaline solution is exemplified by water or alcohol. It is preferable that the solution be a polar solvent, such as a polar organic solvent, and more preferably an aqueous solvent containing at least water. As for the alkaline solution, a sodium hydroxide aqueous solution or a potassium hydroxide aqueous solution is preferred due to its versatility.

[0150] The temperature of the alkaline solution in the alkaline treatment step is not particularly limited, but is preferably, for example, 5°C to 80°C, and more preferably 10°C to 60°C. The immersion time of the ionic substituent-introduced fiber in the alkaline solution in the alkaline treatment step is not particularly limited, but is preferably, for example, 5 minutes to 30 minutes, and more preferably 10 minutes to 20 minutes. The amount of alkaline solution used in the alkaline treatment is not particularly limited, but is preferably, for example, 100% by mass to 100,000% by mass, and more preferably 1,000% by mass to 10,000% by mass, relative to the absolute dry mass of the ionic substituent-introduced fiber.

[0151] To reduce the amount of alkaline solution used in the alkaline treatment process, the ionic substituent-introduced fibers may be washed with water or an organic solvent after the ionic substituent introduction process and before the alkaline treatment process. After the alkaline treatment process and before the micronization process, it is preferable to wash the alkaline-treated ionic substituent-introduced fibers with water or an organic solvent to improve handling.

[0152] <Acid treatment process> In the process of obtaining cellulose fibers having ionic substituents, an acid treatment step may be included between the ionic substituent introduction step and the micronization treatment step. For example, the ionic substituent introduction step, acid treatment, alkali treatment, and micronization treatment may be performed in this order.

[0153] The method of acid treatment is not particularly limited, but one example is immersing the fiber raw material in an acidic solution containing an acid. The concentration of the acidic solution used is not particularly limited, but is preferably 10% by mass or less, and more preferably 5% by mass or less. The pH of the acidic solution used is not particularly limited, but is preferably 0 to 4, and more preferably 1 to 3. Examples of acids that can be included in the acidic solution include inorganic acids, sulfonic acids, carboxylic acids, etc. Examples of inorganic acids include sulfuric acid, nitric acid, hydrochloric acid, hydrobromic acid, hydroiodic acid, hypochlorous acid, chlorous acid, chloric acid, perchloric acid, phosphoric acid, and boric acid. Examples of sulfonic acids include methanesulfonic acid, ethanesulfonic acid, benzenesulfonic acid, p-toluenesulfonic acid, and trifluoromethanesulfonic acid. Examples of carboxylic acids include formic acid, acetic acid, citric acid, gluconic acid, lactic acid, oxalic acid, and tartaric acid. Among these, the use of hydrochloric acid or sulfuric acid is particularly preferred.

[0154] The temperature of the acid solution in the acid treatment is not particularly limited, but is preferably 5°C to 100°C, and more preferably 20°C to 90°C. The immersion time in the acid solution in the acid treatment is not particularly limited, but is preferably 5 minutes to 120 minutes, and more preferably 10 minutes to 60 minutes. The amount of acid solution used in the acid treatment is not particularly limited, but is preferably 100% to 100,000% by mass, and more preferably 1,000% to 10,000% by mass, relative to the absolute dry mass of the fiber raw material.

[0155] <Fibroid Release Process> Fine fibrous cellulose can be obtained by defibrating fiber raw materials or ionic group-introduced fibers in a defibration process. Defibration is also called micronization. In the defibration process, for example, a defibration processing device can be used. The defibration processing device is not particularly limited, but examples include high-speed defibration machines, grinders (stone mill type pulverizers), high-pressure homogenizers and ultra-high-pressure homogenizers, high-pressure impact type pulverizers, ball mills, bead mills, disc type refiners, and Konica. A refiner, twin-screw kneader, vibrating mill, homomixer at high speed, ultrasonic disperser, or beater can be used. Among the above defibration processing devices, it is more preferable to use a high-speed defibration machine, high-pressure homogenizer, or ultra-high-pressure homogenizer, which have less influence from the pulverized media and less risk of contamination.

[0156] In the defibration process, it is preferable to dilute, for example, the fiber raw material or ionic group-introduced fiber with a dispersion medium to form a slurry. As the dispersion medium, one or more selected from water and organic solvents such as polar organic solvents can be used. The polar organic solvent is not particularly limited, but preferred examples include alcohols, polyhydric alcohols, ketones, ethers, esters, and aprotic polar solvents. Examples of alcohols include methanol, ethanol, isopropanol, n-butanol, and isobutyl alcohol. Examples of polyhydric alcohols include ethylene glycol, propylene glycol, and glycerin. Examples of ketones include acetone and methyl ethyl ketone (MEK). Examples of ethers include diethyl ether, tetrahydrofuran, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol mono-n-butyl ether, and propylene glycol monomethyl ether. Examples of esters include ethyl acetate and butyl acetate. Examples of aprotic polar solvents include dimethyl sulfoxide (DMSO), dimethylformamide (DMF), dimethylacetamide (DMAc), and N-methyl-2-pyrrolidinone (NMP).

[0157] The solid content concentration of the fine fibrous cellulose during the defibration process can be set as appropriate. Furthermore, the slurry obtained by dispersing the ionic group-introduced fibers in a dispersion medium may contain solid components other than the ionic group-introduced fibers, such as hydrogen-bonding urea.

[0158] <Substituent removal process> A method for producing fine fibrous cellulose may include a substituent removal step in which at least a portion of substituents are removed from fine fibrous cellulose having substituents and a fiber width of 1000 nm or less. In this specification, the step of removing at least a portion of substituents from the fine fibrous cellulose obtained in the above-described step is also referred to as the substituent removal step.

[0159] The substituent removal process includes steps such as heat treatment, enzymatic treatment, acid treatment, and alkali treatment of fine fibrous cellulose having substituents and a fiber width of 1000 nm or less. These may be performed individually or in combination. Among these, the substituent removal process is preferably a heat treatment or an enzymatic treatment. By going through the above treatment process, at least a portion of the substituents can be removed from fine fibrous cellulose having substituents and a fiber width of 1000 nm or less, and fine fibrous cellulose with a substituent introduction amount of less than 0.5 mmol / g can be obtained.

[0160] The substituent removal process is preferably carried out in slurry form. Specifically, the substituent removal process is preferably a process of heat treatment, enzymatic treatment, acid treatment, alkali treatment, etc., of a slurry containing fine fibrous cellulose having substituents and a fiber width of 1000 nm or less. By carrying out the substituent removal process in slurry form, it is possible to prevent the formation of coloring substances caused by heating during substituent removal, as well as the residue of added or generated acids, alkalis, salts, etc. This makes it possible to suppress the coloration of the fine fibrous cellulose obtained through process (B). Furthermore, if a salt removal process is carried out after substituent removal, it is possible to improve the efficiency of salt removal.

[0161] When a substituent removal treatment is performed on a slurry containing fine fibrous cellulose having substituents and a fiber width of 1000 nm or less, the concentration of fine fibrous cellulose in the slurry is 0 The concentration is preferably 0.05% by mass or more, more preferably 0.1% by mass or more, and even more preferably 0.2% by mass or more. Furthermore, the concentration of fine fibrous cellulose in the slurry is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less. By setting the concentration of fine fibrous cellulose in the slurry within the above range, the substituent removal process can be carried out more efficiently. Furthermore, by setting the concentration of fine fibrous cellulose in the slurry within the above range, it is possible to prevent the residue of coloring substances generated by heating during the substituent removal process, as well as added or generated acids, alkalis, salts, etc. This makes it possible to suppress the coloration of the fine fibrous cellulose obtained through step (B). In addition, when removing salts derived from the substituents removed after the substituent removal process, it is also possible to improve the efficiency of salt removal.

[0162] When the substituent removal process involves heat-treating fine fibrous cellulose having substituents and a fiber width of 1000 nm or less, the heating temperature in the heat treatment process is preferably 40°C or higher, more preferably 50°C or higher, and even more preferably 60°C or higher. Furthermore, the heating temperature in the heat treatment process is preferably 250°C or lower, more preferably 230°C or lower, and even more preferably 200°C or lower. In particular, when the substituents on the fine fibrous cellulose subjected to the substituent removal process are phosphorus oxoacid groups or sulfone groups, the heating temperature in the heat treatment process is preferably 80°C or higher, more preferably 100°C or higher, and even more preferably 120°C or higher.

[0163] If the substituent removal process is a heat treatment process, the heating equipment that can be used in the heat treatment process is not particularly limited, but may include hot air heaters, steam heaters, electric heaters, hydrothermal heaters, thermal heaters, infrared heaters, far-infrared heaters, microwave heaters, high-frequency heaters, stirring dryers, rotary dryers, disc dryers, roll-type heaters, plate-type heaters, fluidized bed dryers, band-type dryers, filtration dryers, vibrating fluidized bed dryers, airflow dryers, and vacuum dryers. From the viewpoint of preventing evaporation, heating is preferably carried out in a closed system, and from the viewpoint of increasing the heating temperature, it is preferable to carry out the heating in a pressure-resistant device or container. The heat treatment may be a batch process, a batch continuous process, or a continuous process.

[0164] If the substituent removal process involves enzymatically treating fine fibrous cellulose having substituents and a fiber width of 1000 nm or less, it is preferable to use phosphate hydrolase, sulfate hydrolase, etc., in the enzymatic treatment process.

[0165] In the enzyme treatment step, it is preferable to add enzymes so that the enzyme activity is 0.1 nkat or more per 1 g of fine fibrous cellulose, more preferably 1.0 nkat or more, and even more preferably 10 nkat or more. Furthermore, it is preferable to add enzymes so that the enzyme activity is 100,000 nkat or less per 1 g of fine fibrous cellulose, more preferably 50,000 nkat or less, and even more preferably 10,000 nkat or less. After adding enzymes to the fine fibrous cellulose dispersion (slurry), it is preferable to treat the material for 1 minute to 100 hours under conditions of 0°C to less than 50°C.

[0166] A step to deactivate the enzyme after the enzymatic reaction may be included. Methods for deactivating the enzyme include adding an acidic or alkaline component to the enzyme-treated slurry to deactivate the enzyme, or raising the temperature of the enzyme-treated slurry to 90°C or higher to deactivate the enzyme.

[0167] The substituent removal process removes substituents from fine fibrous material having a fiber width of 1000 nm or less. In the case of a step in which lurose is acid-treated, it is preferable to add an acid compound that can be used in the acid-treated step described above to the slurry during the acid-treated step.

[0168] If the substituent removal step is a step of alkali treatment of fine fibrous cellulose having substituents and a fiber width of 1000 nm or less, it is preferable to add an alkali compound that can be used in the alkali treatment step described above to the slurry during the alkali treatment step.

[0169] In the substituent removal process, it is preferable that the substituent removal reaction proceeds uniformly. To ensure uniform reaction, for example, the slurry containing fine fibrous cellulose may be stirred, or the specific surface area of ​​the slurry may be increased. Methods of stirring the slurry include applying external mechanical shear, or promoting self-stirring by increasing the slurry delivery rate during the reaction.

[0170] In the substituent removal process, spacer molecules may be added. These spacer molecules intersect between adjacent microfibrous cellulose molecules, thereby acting as spacers to create fine spaces between them. Adding such spacer molecules during the substituent removal process can suppress the aggregation of microfibrous cellulose after the removal process. This allows for more effective improvement of the aesthetic appeal and tensile properties of molded articles containing microfibrous cellulose.

[0171] The spacer molecule is preferably a water-soluble organic compound. Examples of the water-soluble organic compound include sugars, water-soluble polymers, urea, and the like. Specifically, trehalose, urea, polyethylene glycol (PEG), polyethylene oxide (PEO), carboxymethyl cellulose, polyvinyl alcohol (PVA), and the like can be mentioned. Further, as the water-soluble organic compound, alkyl methacrylate-acrylic acid copolymer, polyvinyl pyrrolidone, sodium polyacrylate, propylene glycol, dipropylene glycol, polypropylene glycol, isoprene glycol, hexylene glycol, 1,3-butylene glycol, polyacrylamide, xanthan gum, guar gum, tamarind gum, carrageenan, locust bean gum, quince seed, alginic acid, pullulan, carrageenan, pectin, cationized starch, raw starch, oxidized starch, etherified starch, esterified starch, starches such as amylose, glycerin, diglycerin, polyglycerin, hyaluronic acid, and metal salts of hyaluronic acid can also be used.

[0172] Also, known pigments can be used as the spacer molecule. For example, kaolin (including clay), calcium carbonate, titanium oxide, zinc oxide, amorphous silica (including colloidal silica), aluminum oxide, zeolite, sepiolite, smectite, synthetic smectite, magnesium silicate, magnesium carbonate, magnesium oxide, diatomaceous earth, styrene-based plastic pigment, hydrotalcite, urea resin-based plastic pigment, benzoguanamine-based plastic pigment, and the like can be mentioned.

[0173] <pH adjustment step>

[0174] When the substituent removal treatment step is performed in a slurry state, a step of adjusting the pH of the slurry containing microfibrillar cellulose may be provided before the substituent removal treatment step. For example, an anionic group is introduced into the cellulose fiber, and the counter ion of this anionic group is Na +In this case, the slurry containing the fine fibrous cellulose after defibration will be weakly alkaline. If heated in this state, monosaccharides, which are one of the causes of discoloration, may be generated due to the decomposition of cellulose, so it is preferable to adjust the pH of the slurry to 8 or less, and more preferably to 6 or less. Similarly, monosaccharides may also be generated under acidic conditions, so it is preferable to adjust the pH of the slurry to 3 or less. It is preferable to adjust it upwards, and more preferably to adjust it to 4 or higher.

[0175] Furthermore, if the substituted microfiber cellulose is a microfiber cellulose having a phosphate group, it is preferable that the phosphorus of the phosphate group is in a state that is easily susceptible to nucleophilic attack, from the viewpoint of improving the efficiency of substituent removal. Cellulose-OP(=O)(-OH) is susceptible to nucleophilic attack. + )(-O-Na + This represents a neutralization degree of 1, and to achieve this state, it is preferable to adjust the pH of the slurry to 3 or more and 8 or less, and more preferably to adjust the pH to 4 or more and 6 or less.

[0176] The means of adjusting the pH are not particularly limited, but for example, an acidic or alkaline component may be added to a slurry containing fine fibrous cellulose. The acidic component may be either an inorganic acid or an organic acid. Examples of inorganic acids include sulfuric acid, hydrochloric acid, nitric acid, and phosphoric acid. Examples of organic acids include formic acid, acetic acid, citric acid, malic acid, lactic acid, adipic acid, sebacic acid, stearic acid, maleic acid, succinic acid, tartaric acid, fumaric acid, and gluconic acid. The alkaline component may be an inorganic alkali compound or an organic alkali compound. Examples of inorganic alkali compounds include lithium hydroxide, sodium hydroxide, potassium hydroxide, lithium carbonate, lithium bicarbonate, potassium carbonate, potassium bicarbonate, sodium carbonate, and sodium bicarbonate. Examples of organic alkali compounds include ammonia, hydrazine, methylamine, ethylamine, diethylamine, triethylamine, propylamine, dipropylamine, butylamine, diaminoethane, diaminopropane, diaminobutane, diaminopentane, diaminohexane, cyclohexylamine, aniline, tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, benzyltrimethylammonium hydroxide, pyridine, and N,N-dimethyl-4-aminopyridine.

[0177] Furthermore, in the pH adjustment process, ion exchange treatment may be performed to adjust the pH. For ion exchange treatment, a strongly acidic cation exchange resin or a weakly acidic ion exchange resin can be used. By treating with an appropriate amount of cation exchange resin for a sufficient amount of time, a slurry containing fine fibrous cellulose at the desired pH can be obtained. In addition, the pH adjustment process may be combined with the addition of acidic or alkaline components and ion exchange treatment.

[0178] <Salt removal process> After the substituent removal process, it is preferable to remove salts derived from the removed substituents. Removing the substituent-derived salts makes it easier to obtain fine fibrous cellulose that can suppress discoloration. The means for removing substituent-derived salts are not particularly limited, but washing is one example. The washing is carried out by washing the fine fibrous cellulose aggregated in the substituent removal process with water or an organic solvent, for example. From the viewpoint of more effectively suppressing yellowing, the washing is preferably carried out by filtration dehydration, centrifugal dehydration, or centrifugation.

[0179] <Uniform Dispersion Processing> A method for producing fine fibrous cellulose may include a substituent removal step of removing at least some substituents from fine fibrous cellulose having substituents and a fiber width of 1000 nm or less, and a uniform dispersion step after the substituent removal step. The uniform dispersion step is a step of uniformly dispersing the fine fibrous cellulose obtained after the substituent removal step. The state in which the fine fibrous cellulose is uniformly dispersed in the uniform dispersion step means a state in which the fiber width of the fine fibrous cellulose is 100 nm or less. By going through the uniform dispersion step, it becomes easy to make the number-average fiber width of the fine fibrous cellulose 100 nm or less, preferably 50 nm or less, even though the amount of substituents introduced is low, less than 0.5 mmol / g.

[0180] In the process of uniform dispersion, for example, a high-speed defibrator, grinder (stone mill type grinder), high-pressure homogenizer, high-pressure impact grinder, ball mill, bead mill, disc refiner, conical refiner, twin-screw kneader, vibrating mill, homomixer under high-speed rotation, ultrasonic disperser, or beater can be used. Among the above uniform dispersion processing devices, the use of a high-speed defibrator and a high-pressure homogenizer is more preferable.

[0181] The processing conditions in the uniform dispersion process are not particularly limited, but it is preferable to increase the maximum movement speed of the fine fibrous cellulose during processing and the processing pressure. In a high-speed defibrator, the peripheral speed is preferably 20 m / sec or more, more preferably 25 m / sec or more, and even more preferably 30 m / sec or more. A high-pressure homogenizer can be used more preferably than a high-speed defibrator because it allows for a higher maximum movement speed of the fine fibrous cellulose during processing and a higher processing pressure. In high-pressure homogenizer processing, the processing pressure is preferably 1 MPa or more, more preferably 10 MPa or more, even more preferably 50 MPa or more, and particularly preferably 100 MPa or more. Furthermore, in high-pressure homogenizer processing, the processing pressure is preferably 350 MPa or less, more preferably 300 MPa or less, and even more preferably 250 MPa or less.

[0182] Furthermore, the aforementioned spacer molecules may be added during the uniform dispersion process. By adding such spacer molecules during the uniform dispersion process in step (B), the uniform dispersion of the fine fibrous cellulose can be performed more smoothly.

[0183] [Rubber components] For example, natural rubber (NR) or synthetic rubber can be used as the rubber component in the manufacturing method of composite materials.

[0184] Examples of synthetic rubbers include styrene-butadiene rubber (SBR), nitrile rubber (NBR), chloroprene rubber (CR), ethylene propylene rubber (EPDM), butyl rubber (IIR), chlorobutyl rubber (CIIR), acrylic rubber (ACM), silicone rubber (Q), fluororubber (FKM), butadiene rubber (BR), epoxidized butadiene rubber (EBR), epichlorohydrin rubber (CO,CEO), urethane rubber (U), and polysulfide rubber (T). Examples of nitrile rubbers include hydrogenated nitrile rubber; modified nitrile rubbers such as carboxyl group-modified nitrile rubber (XNBR), silicone-modified nitrile rubber, maleic acid-modified nitrile rubber, and hydroxyl group-modified nitrile rubber, or hydrogenated versions thereof; and acrylonitrile-butadiene-isoprene copolymers in which part of the butadiene is replaced with isoprene. Hydrogenated nitrile rubber (H-NBR) is sometimes called hydrogenated nitrile rubber or hydrogenated acrylonitrile-butadiene rubber. Hydrogenated nitrile rubber can be obtained by hydrogenating the double bonds contained in nitrile rubber.

[0185] Examples of natural rubber include natural rubber (NR), modified natural rubber such as epoxy-treated natural rubber (ENR), hydrogenated natural rubber, and deproteinized natural rubber. These rubber components may be used individually or in mixtures of two or more types. Furthermore, these rubber components may be pre-crosslinked raw materials without a crosslinked structure, or they may have a crosslinked structure.

[0186] In particular, the rubber component is preferably at least one selected from natural rubber, nitrile rubber, butadiene rubber, and styrene-butadiene rubber, and more preferably at least one selected from natural rubber and nitrile rubber, and natural rubber, carboxyl group modified nitrile It is even more preferable that it be at least one selected from rillgom.

[0187] Furthermore, the rubber component may be a pre-crosslinking raw material. For example, the rubber component is preferably at least one pre-crosslinking raw material selected from natural rubber and nitrile rubber, and more preferably at least one pre-crosslinking raw material selected from natural rubber and hydrogenated nitrile rubber. When the rubber component is a pre-crosslinking raw material, it is preferable that the rubber component is the latex of these rubber components. By using the above-mentioned rubber component, discoloration is suppressed, and it becomes easier to obtain a composite material with even better tensile properties. [Examples]

[0188] The features of the present invention will be further described below with reference to examples and comparative examples. The materials, amounts used, proportions, processing content, and processing procedures shown in the following examples can be modified as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be interpreted as being limited by the following specific examples.

[0189] <Manufacturing Example A1> [Phosphorylation] The raw material pulp used is softwood kraft pulp manufactured by Oji Paper Co., Ltd. (solids content 93% by mass, basis weight 245 g / m²). 2 A sheet-like material was used, which, when disintegrated, had a Canadian standard filtration efficiency (CSF) of 700 ml measured according to JIS P 8121-2:2012.

[0190] The raw pulp was subjected to phosphorus oxo-oxidation treatment as follows. First, a mixed aqueous solution of ammonium dihydrogen phosphate and urea was added to 100 parts by mass (oven-dry mass) of the raw pulp to adjust the mixture to 45 parts by mass of ammonium dihydrogen phosphate, 120 parts by mass of urea, and 150 parts by mass of water to obtain chemically impregnated pulp. Next, the obtained chemically impregnated pulp was heated in a hot air dryer at 165°C for 250 seconds to introduce phosphate groups into the cellulose in the pulp, thereby obtaining phosphorylated pulp.

[0191] Next, the obtained phosphorylated pulp was subjected to a washing treatment. The washing treatment was carried out by repeatedly adding 10 L of deionized water to 100 g (oven-dry mass) of phosphorylated pulp to obtain a pulp dispersion, stirring the mixture to ensure uniform dispersion of the pulp, and then filtering and dewatering it. The washing was terminated when the electrical conductivity of the filtrate fell to 100 μS / cm or less.

[0192] Next, the washed phosphorylated pulp was subjected to neutralization treatment as follows. First, the washed phosphorylated pulp was diluted with 10 L of deionized water, and then a 1N sodium hydroxide aqueous solution was gradually added while stirring to obtain a phosphorylated pulp slurry with a pH of 12 to 13. Next, the phosphorylated pulp slurry was dehydrated and washed to obtain phosphorylated pulp that had undergone neutralization treatment.

[0193] The obtained phosphorylated pulp was subjected to infrared absorption spectroscopy using FT-IR. The result showed that 1230 cm⁻¹ -1 Absorption based on the P=O of phosphate groups was observed in the vicinity, confirming that phosphate groups were added to the pulp. Furthermore, when the obtained phosphorylated pulp was analyzed using an X-ray diffractometer, typical peaks were observed at two locations: around 2θ = 14° to 17° and around 2θ = 22° to 23°, confirming the presence of type I cellulose crystals. The amount of phosphate groups (amount of first dissociated acid) measured by the measurement method described in [Measurement of Phosphorus Oxoacid Group Amount] below was 1.45 mmol / g. The total amount of dissociated acid was 2.45 mmol / g.

[0194] Deionized water was added to the obtained phosphorylated pulp to prepare a slurry with a solid content of 2.2% by mass. This slurry was then processed using a wet atomizing apparatus (Sugino Machine Co., Ltd., Starbur). The mixture was treated twice at a pressure of 200 MPa using a stoichiometric apparatus to obtain a dispersion of fine fibrous cellulose containing fine fibrous cellulose.

[0195] X-ray diffraction confirmed that the obtained fibrous cellulose maintained its type I cellulose crystal structure. Furthermore, the fiber width of the fibrous cellulose was measured using a transmission electron microscope and found to be 3–5 nm. The amount of phosphate groups (first dissociated acid) measured by the method described later in [Measurement of Phosphorus Oxoacid Groups] was 1.45 mmol / g. The total amount of dissociated acid was 2.45 mmol / g.

[0196] <Manufacturing example B1> [Phosphosphite] Except for using 33 parts by mass of phosphorous acid (phosphonic acid) instead of ammonium dihydrogen phosphate, the procedure was carried out in the same manner as in Production Example A1 to obtain a fine fibrous cellulose dispersion containing phosphorous pulp and fine fibrous cellulose.

[0197] The obtained phosphorylated pulp was subjected to infrared absorption spectroscopy using FT-IR. The result showed that at 1210 cm⁻¹ -1 Absorption based on P=O of the phosphonic acid group, a tautomer of the phosphite group, was observed in the vicinity, confirming that phosphite groups (phosphonic acid groups) were added to the pulp. Furthermore, when the obtained phosphite-oxidized pulp was analyzed using an X-ray diffractometer, typical peaks were observed at two locations: around 2θ = 14° to 17° and around 2θ = 22° to 23°, confirming the presence of type I cellulose crystals. The amount of phosphite groups (amount of first dissociated acid) measured by the method described in [Measurement of Phosphorus Oxoacid Group Amount] below was 1.51 mmol / g. The total amount of dissociated acid was 1.54 mmol / g.

[0198] X-ray diffraction confirmed that the obtained fibrous cellulose maintained its type I cellulose crystal structure. Furthermore, the fiber width of the fibrous cellulose was measured using a transmission electron microscope and found to be 3–5 nm. The amount of phosphorous phosphite groups (first dissociated acid) measured using the method described in [Measurement of Phosphorus Oxoacid Groups] below was 1.51 mmol / g. The total amount of dissociated acid was 1.54 mmol / g.

[0199] <Manufacturing example C1> [Sulfating] Except for using 38 parts by mass of sulfamic acid (amidosulfate) instead of ammonium dihydrogen phosphate and extending the heating time to 20 minutes, the procedure was carried out in the same manner as in Production Example A1 to obtain a fine fibrous cellulose dispersion containing sulfated pulp and fine cellulose.

[0200] The obtained sulfated pulp was subjected to infrared absorption spectroscopy using FT-IR. The results showed that the absorption spectrum was 1220-1260 cm⁻¹. -1 Absorption based on the S=O of the sulfate ester group was observed in the vicinity, confirming that sulfate ester groups were attached to the pulp. Furthermore, when the obtained sulfated pulp was analyzed using an X-ray diffractometer, typical peaks were observed at two locations: around 2θ = 14° to 17° and around 2θ = 22° to 23°, confirming the presence of cellulose type I crystals. The amount of sulfate ester group measured by the method described in [Measurement of Sulfate Ester Group Amount] below was 1.47 mmol / g.

[0201] X-ray diffraction confirmed that the obtained fine fibrous cellulose maintained its type I cellulose crystal structure. Furthermore, the fiber width of the fine fibrous cellulose was measured using a transmission electron microscope and found to be 3–5 nm. Further research on the obtained fine fibrous cellulose will be conducted later. The amount of sulfate ester groups measured by the measurement method described in [Measurement of Sulfate Ester Group Amount] was 1.47 mmol / g.

[0202] <Manufacturing Example D1> [TEMPO oxidation] As the raw material pulp, we used softwood kraft pulp (undried) manufactured by Oji Paper Co., Ltd. This raw material pulp was subjected to alkaline TEMPO oxidation treatment as follows.

[0203] First, the above raw material pulp, equivalent to 100 parts by mass (dry weight), 1.6 parts by mass of TEMPO(2,2,6,6-tetramethylpiperidine-1-oxyl), and 10 parts by mass of sodium bromide were dispersed in 10,000 parts by mass of water. Next, a 13% by mass sodium hypochlorite aqueous solution was added to a concentration of 10 mmol per 1.0 g of pulp to initiate the reaction. During the reaction, a 0.5 M sodium hydroxide aqueous solution was added dropwise to maintain the pH between 10 and 10.5, and the reaction was considered complete when no further change in pH was observed.

[0204] Next, the obtained TEMPO-oxidized pulp was subjected to a washing treatment. The washing treatment was carried out by dewatering the pulp slurry after TEMPO oxidation to obtain a dewatered sheet, adding 5000 parts by mass of deionized water, stirring to uniformly disperse the sheet, and then repeating the filtration and dewatering process. The washing was terminated when the electrical conductivity of the filtrate became 100 μS / cm or less.

[0205] The remaining aldehyde groups in this dehydrated sheet were subjected to further oxidation treatment as follows: 100 parts by mass of the above dehydrated sheet (equivalent to 100 parts by mass by dry weight) was dispersed in 10,000 parts by mass of 0.1 mol / L acetate buffer (pH 4.8). Then, 113 parts by mass of 80% sodium chlorite were added, and the mixture was immediately sealed. The mixture was then stirred at 500 rpm using a magnetic stirrer at room temperature for 48 hours to obtain a pulp slurry.

[0206] Next, the obtained oxidized TEMPO oxidized pulp was subjected to a washing treatment. The washing treatment was carried out by dewatering the pulp slurry after oxidization to obtain a dewatered sheet, adding 5000 parts by mass of deionized water, stirring to uniformly disperse the sheet, and then repeating the filtration and dewatering process. The washing was terminated when the electrical conductivity of the filtrate became 100 μS / cm or less.

[0207] The amount of carboxyl groups in the obtained TEMPO-oxidized pulp, as measured by the method described later, was 1.80 mmol / g. Furthermore, when the obtained TEMPO-oxidized pulp was analyzed using an X-ray diffractometer, typical peaks were observed at two locations: around 2θ = 14° to 17° and around 2θ = 22° to 23°, confirming the presence of type I cellulose crystals.

[0208] Deionized water was added to the obtained TEMPO-oxidized pulp to prepare a slurry with a solid content of 2.2% by mass. This slurry was processed twice at a pressure of 200 MPa using a wet atomizing device (Starburst, manufactured by Sugino Machine Co., Ltd.) to obtain a fine fibrous cellulose dispersion containing fine fibrous cellulose.

[0209] X-ray diffraction confirmed that the obtained fibrous cellulose maintained its type I cellulose crystal structure. Furthermore, the fiber width of the fibrous cellulose was measured using a transmission electron microscope and found to be 3–5 nm. The amount of carboxyl groups in the obtained fibrous cellulose, as measured by the method described later, was 1.80 mmol / g.

[0210] <Manufacturing example E1> [Hypochlorous acid oxidation] A sheet made from bleached coniferous kraft pulp (NBKP) (solid content concentration 90% by mass) Using a hand mixer (Osaka Chemical Co., Ltd., Lab Millser PLUS), the material was processed at a rotation speed of 20,000 rpm for 15 seconds to obtain cotton-like fluffy pulp (solid content concentration 90% by mass). Next, sodium hypochlorite pentahydrate was added to deionized water to prepare an aqueous solution with a sodium hypochlorite solid content concentration of 22% by mass. 9,000 parts by mass of the 22% by mass sodium hypochlorite aqueous solution was added to 100 parts by mass of the cotton-like fluffy pulp, and the mixture was reacted for 2 hours while adjusting the temperature to 30°C in a warm bath to obtain carboxyl group-introduced pulp. During the reaction, 1N sodium hydroxide aqueous solution was added as needed to maintain the pH at 11.

[0211] Next, the obtained carboxyl group-introduced pulp was subjected to a washing treatment. The washing treatment involved repeatedly adding deionized water to the obtained carboxyl group-introduced pulp to obtain a pulp dispersion, stirring the mixture to ensure uniform dispersion of the pulp, and then filtering and dewatering it. The washing was terminated when the electrical conductivity of the filtrate fell to 100 μS / cm or less.

[0212] The amount of carboxyl groups in the obtained carboxyl-introduced pulp, as measured by the method described later, was 0.70 mmol / g. Furthermore, when the obtained carboxyl-introduced pulp was analyzed using an X-ray diffractometer, typical peaks were observed at two locations: around 2θ = 14° to 17° and around 2θ = 22° to 23°, confirming the presence of type I cellulose crystals.

[0213] Deionized water was added to the obtained carboxyl group-introduced pulp to prepare a slurry with a solid content of 2.2% by mass. This slurry was processed twice at a pressure of 200 MPa in a wet atomizing apparatus (Starburst, manufactured by Sugino Machine Co., Ltd.) to obtain a fine fibrous cellulose dispersion containing fine fibrous cellulose.

[0214] X-ray diffraction confirmed that the obtained fibrous cellulose maintained its type I cellulose crystal structure. Furthermore, the fiber width of the fibrous cellulose was measured using a transmission electron microscope and found to be 3–5 nm. The amount of carboxyl groups in the obtained fibrous cellulose, as measured by the method described later, was 0.70 mmol / g.

[0215] <Manufacturing Example F1> [Maleic acid esterification] Sheets (solid content 90% by mass) made from bleached coniferous kraft pulp (NBKP) were processed using a hand mixer (Osaka Chemical, Lab Millser PLUS) at a rotation speed of 20,000 rpm for 15 seconds to obtain cotton-like fluffy pulp (solid content 90% by mass). 100 parts by mass of the cotton-like fluffy pulp and 50 parts by mass of maleic anhydride were packed into an autoclave and processed at 150°C for 2 hours to obtain carboxyl group-introduced pulp.

[0216] Next, the obtained carboxyl group-introduced pulp was subjected to a washing treatment. The washing treatment involved repeatedly adding deionized water to the obtained carboxyl group-introduced pulp to obtain a pulp dispersion, stirring the mixture to ensure uniform dispersion of the pulp, and then filtering and dewatering it. The washing was terminated when the electrical conductivity of the filtrate fell to 100 μS / cm or less.

[0217] The obtained carboxyl group-introduced pulp was subjected to infrared absorption spectrum measurements using FT-IR. The results showed absorption spectra at 1580 and 1720 cm⁻¹. -1 Absorption based on carboxyl groups was observed in the vicinity, confirming maleate esterification. The amount of carboxyl groups in the obtained carboxyl-introduced pulp, measured by the method described later, was 1.22 mmol / g. Furthermore, when the carboxyl-introduced pulp was analyzed using an X-ray diffractometer, typical peaks were observed at two locations: around 2θ = 14° to 17° and around 2θ = 22° to 23°, confirming the presence of type I cellulose crystals.

[0218] Deionized water was added to the obtained carboxyl group-introduced pulp to prepare a slurry with a solid content of 2.2% by mass. This slurry was processed twice at a pressure of 200 MPa in a wet atomizing apparatus (Starburst, manufactured by Sugino Machine Co., Ltd.) to obtain a fine fibrous cellulose dispersion containing fine fibrous cellulose.

[0219] X-ray diffraction confirmed that the obtained fibrous cellulose maintained its type I cellulose crystal structure. Furthermore, the fiber width of the fibrous cellulose was measured using a transmission electron microscope and found to be 3–5 nm. The amount of carboxyl groups in the obtained fibrous cellulose, as measured by the method described later, was 1.22 mmol / g.

[0220] <Manufacturing Example G1> [carboxyethylation] The raw material pulp used is softwood kraft pulp manufactured by Oji Paper Co., Ltd. (solids content 93% by mass, basis weight 245 g / m²). 2 A sheet-like material was used, which, when disintegrated, had a Canadian standard filtration efficiency (CSF) of 700 ml measured according to JIS P 8121-2:2012.

[0221] To 100 parts by mass (oven-dry mass) of this raw pulp, a chemical solution consisting of 250 parts by mass of 12N NaOH aqueous solution, 163 parts by mass of 2-chloropropionic acid, and 140 parts by mass of ion-exchanged water (total 553 parts by mass) was added to obtain chemical-impregnated pulp. Next, the obtained chemical-impregnated pulp was heated in a hot air dryer at 165°C for 10 minutes to introduce carboxyethyl groups (carboxyl groups) into the cellulose in the pulp, thereby obtaining carboxyl group-introduced pulp.

[0222] Next, the obtained carboxyl group-introduced pulp was subjected to a washing treatment. The washing treatment involved repeatedly adding deionized water to the obtained carboxyl group-introduced pulp to obtain a pulp dispersion, stirring the mixture to ensure uniform dispersion of the pulp, and then filtering and dewatering it. The washing was terminated when the electrical conductivity of the filtrate fell to 100 μS / cm or less.

[0223] Next, the carboxyl group-introduced pulp after washing was neutralized as follows. First, the carboxyl group-introduced pulp after washing was diluted with 10 L of ion-exchanged water, and then a 1N aqueous sodium hydroxide solution was added little by little while stirring to obtain a carboxyl group-introduced pulp slurry with a pH of 12 or more and 13 or less. Next, the carboxyl group-introduced pulp slurry was dehydrated and washed to obtain a carboxyl group-introduced pulp subjected to neutralization treatment.

[0224] Regarding the obtained carboxyl group-introduced pulp, the amount of carboxyl groups measured by the measurement method described later was 1.41 mmol / g. In addition, when the carboxyl group-introduced pulp was tested and analyzed with an X-ray diffractometer, typical peaks were confirmed at two positions around 2θ = 14° or more and 17° or less and around 2θ = 22° or more and 23° or less, and it was confirmed that it had cellulose I-type crystals.

[0225] Ion-exchanged water was added to the obtained carboxyl group-introduced pulp to prepare a slurry with a solid content concentration of 2.2% by mass. This slurry was treated twice at a pressure of 200 MPa with a wet atomization device (manufactured by Sugino Machine Limited, Starburst) to obtain a microfibrillated cellulose dispersion containing microfibrillated cellulose.

[0226] It was confirmed by X-ray diffraction that the obtained microfibrillated cellulose maintained cellulose I-type crystals. In addition, when the fiber width of the microfibrillated cellulose was measured using a transmission electron microscope, it was 3 to 5 nm. Regarding the obtained microfibrillated cellulose, the amount of carboxyl groups measured by the measurement method described later was 1.41 mmol / g.

[0227] <Production Example H1> [Carboxymethylation] As the raw material pulp, softwood kraft pulp (solid content 93% by mass, basis weight 245 g / m 2 Sheet-like, disintegrated, and the Canadian standard freeness (CSF) measured according to JIS P 8121-2:2012 was 700 ml) manufactured by Oji Paper Co., Ltd. was used.

[0228] To 100 parts by mass (dry mass) of this raw material pulp, 83 parts by mass of a 12N NaOH aqueous solution and a chemical solution (total 571 parts by mass) composed of 175 parts by mass of sodium monochloroacetate and 313 parts by mass of ion-exchanged water were added to obtain a chemically impregnated pulp. Next, the obtained chemically impregnated pulp was heated in a hot water bath at 95°C for 60 minutes to introduce carboxymethyl groups (carboxy groups) into the cellulose in the pulp, thereby obtaining a pulp with carboxy groups introduced.

[0229] Next, a washing treatment was performed on the obtained pulp with carboxy groups introduced. The washing treatment was carried out by repeating the operation of pouring ion-exchanged water into the obtained pulp with carboxy groups introduced, stirring the resulting pulp dispersion so that the pulp was uniformly dispersed, and then filtering and dehydrating. The washing was terminated when the electric conductivity of the filtrate reached 100 μS / cm or less.

[0230] Regarding the obtained pulp with carboxy groups introduced, the amount of carboxy groups measured by the measurement method described below was 1.21 mmol / g. Further, the pulp with carboxy groups introduced was tested and analyzed with an X When analyzed using an X-ray diffractometer, typical peaks were confirmed at two positions near 2θ = 14° or more and 17° or less and near 2θ = 22° or more and 23° or less, and it was confirmed that it had cellulose I-type crystals.

[0231] Ion-exchanged water was added to the obtained pulp with carboxy groups introduced to prepare a slurry with a solid content concentration of 2.2% by mass. This slurry was treated twice at a pressure of 200 MPa using a wet atomization device (manufactured by Sugino Machine, Ltd., Starburst) to obtain a microfibrillated cellulose dispersion containing microfibrillated cellulose.

[0232] It was confirmed by X-ray diffraction that the obtained microfibrillated cellulose maintained cellulose I-type crystals. Further, when the fiber width of the microfibrillated cellulose was measured using a transmission electron microscope, it was 3 - 5 nm. Regarding the obtained microfibrillated cellulose, the amount of carboxy groups measured by the measurement method described below was 1.21 mmol / g.

[0233] <Manufacturing Example I1> [Sulfoethylation] The raw material pulp used is softwood kraft pulp manufactured by Oji Paper Co., Ltd. (solids content 93% by mass, basis weight 245 g / m²). 2 A sheet-like material was used, which, when disintegrated, had a Canadian standard filtration efficiency (CSF) of 700 ml measured according to JIS P 8121-2:2012.

[0234] To 100 parts by mass (oven-dry mass) of this raw pulp, a chemical solution consisting of 180 parts by mass of 2N NaOH aqueous solution and 780 parts by mass of 25% by mass sodium vinyl sulfonate aqueous solution (total 960 parts by mass) was added to obtain chemical-impregnated pulp. Next, the obtained chemical-impregnated pulp was heated in a hot air dryer at 165°C for 16 minutes to introduce sulfoethyl groups (sulfone groups) into the cellulose in the pulp, thereby obtaining sulfoethyl group-introduced pulp (sulfone group-introduced pulp).

[0235] Next, the obtained sulfoethyl group-introduced pulp was subjected to a washing treatment. The washing treatment involved repeatedly adding deionized water to the obtained sulfoethyl group-introduced pulp to obtain a pulp dispersion, stirring the mixture to ensure uniform dispersion of the pulp, and then filtering and dewatering it. The washing was terminated when the electrical conductivity of the filtrate fell to 100 μS / cm or less.

[0236] The obtained sulfoethyl group-introduced pulp is measured by the measurement method described later. The amount of chill groups (sulfone groups) was 1.48 mmol / g. Furthermore, when pulp with introduced sulfoethyl groups was used and analyzed by X-ray diffraction, typical peaks were observed at two locations: around 2θ = 14° to 17° and around 2θ = 22° to 23°, confirming the presence of type I cellulose crystals.

[0237] Deionized water was added to the obtained sulfoethyl group-introduced pulp to prepare a slurry with a solid content of 2.2% by mass. This slurry was processed twice at a pressure of 200 MPa in a wet atomizing apparatus (Starburst, manufactured by Sugino Machine Co., Ltd.) to obtain a fine fibrous cellulose dispersion containing fine fibrous cellulose.

[0238] X-ray diffraction confirmed that the obtained fibrous cellulose maintained its type I cellulose crystal structure. Furthermore, the fiber width of the fibrous cellulose was measured using a transmission electron microscope and found to be 3–5 nm. The amount of sulfoethyl groups (sulfone groups) in the obtained fibrous cellulose, as measured by the method described later, was 1.48 mmol / g.

[0239] <Manufacturing Example J1> [Cationization] The raw material pulp used is softwood kraft pulp manufactured by Oji Paper Co., Ltd. (solids content 93% by mass, basis weight 245 g / m²). 2 A sheet-like material was used, which, when disintegrated, had a Canadian standard filtration efficiency (CSF) of 700 ml measured according to JIS P 8121-2:2012.

[0240] To 100 parts by mass (oven-dry mass) of this raw pulp, a chemical solution consisting of 180 parts by mass of 1N NaOH aqueous solution and 325 parts by mass of a cationizing agent (Catiomaster G, manufactured by Yokkaichi Gosei Co., Ltd., glycidyltrimethylammonium chloride, purity 73.1% by mass, moisture content 20.2% by mass) (total 505 parts by mass) was added to obtain chemical-impregnated pulp. Next, the obtained chemical-impregnated pulp was heated in a hot air dryer at 165°C for 12 minutes to introduce cationic groups into the cellulose in the pulp, thereby obtaining cationic group-introduced pulp.

[0241] Next, the obtained cation-introduced pulp was subjected to a washing treatment. The washing treatment involved repeatedly adding deionized water to the obtained cation-introduced pulp to obtain a pulp dispersion, stirring the mixture to ensure uniform dispersion of the pulp, and then filtering and dewatering it. The washing was terminated when the electrical conductivity of the filtrate fell to 100 μS / cm or less.

[0242] Next, the neutralization treatment of the cation group-introduced pulp after washing was carried out as follows. First, the cation group-introduced pulp after washing was diluted with 10 L of ion-exchanged water, and then 1 N hydrochloric acid was added little by little while stirring to obtain a cation group-introduced pulp slurry with a pH of 1 or more and 2 or less. Next, the cation group-introduced pulp slurry was dehydrated and washed to obtain a cation group-introduced pulp subjected to neutralization treatment.

[0243] For the obtained cation group-introduced pulp, trace nitrogen analysis was performed, and when the amount of cation groups was calculated by the following formula, it was 1.45 mmol / g. In addition, when the cation group-introduced pulp was tested and analyzed with an X-ray diffractometer, typical peaks were confirmed at two positions near 2θ = 14° or more and 17° or less and near 2θ = 22° or more and 23° or less, and it was confirmed that it had cellulose I-type crystals. (Amount of cation groups) [mmol / g] = (Amount of nitrogen) / 14 × 1000 / (Amount of cation group-introduced pulp tested)

[0244] Ion-exchanged water was added to the obtained cation group-introduced pulp to prepare a slurry with a solid content concentration of 2.2 mass%. This slurry was treated twice at a pressure of 200 MPa with a wet atomization device (manufactured by Sugino Machine Limited, Super Burst) to obtain a fine fibrous cellulose dispersion liquid containing fine fibrous cellulose. It was confirmed by X-ray diffraction that the obtained fine fibrous cellulose maintained cellulose I-type crystals. In addition, when the fiber width of the fine fibrous cellulose was measured using a transmission electron microscope, it was 3 to 5 nm. For the obtained fine fibrous cellulose, trace nitrogen analysis was performed, and when the amount of cation groups was calculated by the following formula, it was 1.45 mmol / g.

[0245] (Amount of cation groups) [mmol / g] = (Amount of nitrogen) / 14 × 1000 / (Amount of fine fibrous cellulose tested)

[0246] <Production Example K1> [Substituent removal treatment]​ In the fine fibrous cellulose dispersion obtained in Production Example A1, a 20% by mass aqueous citric acid solution was added to adjust the pH of the dispersion to 5.5. The resulting slurry was placed in a pressure vessel and heated at a liquid temperature of 160°C for 15 minutes until the phosphate group content reached 0.08 mmol / g. This procedure confirmed the formation of fine fibrous cellulose aggregates.

[0247] After heating, an equal amount of deionized water was added to the slurry to obtain a slurry with a solid content of approximately 1% by mass. The slurry was then stirred, and the filtration and dewatering process was repeated to wash the slurry. When the electrical conductivity of the filtrate fell below 10 μS / cm, deionized water was added again to obtain a slurry with a solid content of approximately 1% by mass, and the slurry was allowed to stand for 24 hours. The filtration and dewatering process was repeated again, and the washing was terminated when the electrical conductivity of the filtrate fell below 10 μS / cm once more. Deionized water was added to the obtained fine fibrous cellulose aggregates, and after substituent removal, a slurry was obtained. The solid content of this slurry was 1.7% by mass.

[0248] Deionized water was added to the obtained substituent-removed slurry to obtain a slurry with a solid content of 1.0% by mass. This slurry was then processed three times at a pressure of 200 MPa using a wet atomizing device (Starburst, manufactured by Sugino Machine Co., Ltd.) to obtain a dispersion of fine fibrous cellulose containing substituent-removed fine fibrous cellulose. The fiber width of the fine fibrous cellulose was measured using a transmission electron microscope and found to be 3-5 nm.

[0249] <Manufacturing example L1> [No denaturation] As the raw material pulp, softwood kraft pulp (undried) manufactured by Oji Paper Co., Ltd. was used to prepare a slurry with a solid content of 2.2% by mass. This slurry was processed 30 times at a pressure of 200 MPa in a wet pulverizer (Starburst, manufactured by Sugino Machine Co., Ltd.) to obtain a fine fibrous cellulose dispersion.

[0250] [Measurement of phosphorus oxoacid group content] In measuring the amount of phosphorus oxoacid groups (phosphate groups or phosphite groups) in microfibrous cellulose, first, deionized water was added to the target microfibrous cellulose to prepare a slurry with a solid content concentration of 0.2% by mass. The obtained microfibrous cellulose dispersion was then treated with an ion exchange resin, and the amount was measured by titration using an alkali. The ion exchange resin treatment was performed by adding 1 / 10 the volume of strongly acidic ion exchange resin (Amberjet 1024; Organo Corporation, conditioned) to the above-mentioned fine fibrous cellulose dispersion, shaking for 1 hour, and then pouring the mixture onto a mesh with a mesh size of 90 μm to separate the resin from the slurry. Furthermore, titration using alkali is performed on fine fibrous cellulose after treatment with ion exchange resin. The titration was performed by adding 10 μL of 0.1 N sodium hydroxide aqueous solution to the slurry at 5-second intervals, and measuring the change in the slurry's pH value. Nitrogen gas was blown into the slurry starting 15 minutes before the titration began. In this neutralization titration, two points were observed where the increment (the derivative of pH with respect to the amount of alkali added) was maximum on the curve plotting the measured pH against the amount of alkali added. Of these, the first maximum increment obtained after starting alkali addition is called the first endpoint, and the next maximum increment obtained is called the second endpoint (Figure 3). The amount of alkali required from the start of the titration to the first endpoint is equal to the amount of the first dissociated acid in the slurry used for the titration. Furthermore, the amount of alkali required from the start of the titration to the second endpoint is equal to the total amount of dissociated acid in the slurry used for the titration. The amount of alkali (mmol) required from the start of the titration to the first endpoint was divided by the solid content (g) in the slurry being titrated to determine the amount of phosphorus oxoacid groups (amount of first dissociated acid) (mmol / g). Furthermore, the amount of alkali (mmol) required from the start of the titration to the second endpoint was divided by the solid content (g) in the slurry being titrated to determine the total amount of dissociated acid (mmol / g).

[0251] [Measurement of carboxyl group content] The amount of carboxyl groups in microfibrous cellulose was measured by adding deionized water to a microfibrous cellulose dispersion containing the target microfibrous cellulose to adjust the content to 0.2% by mass, treating it with an ion exchange resin, and then performing a titration using an alkali. The ion exchange resin treatment was performed by adding 1 / 10 the volume of strongly acidic ion exchange resin (Amberjet 1024; manufactured by Organo Corporation, conditioned) to a slurry containing 0.2% by mass of fine fibrous cellulose, shaking for 1 hour, and then pouring the mixture onto a mesh with a mesh size of 90 μm to separate the resin from the slurry. Furthermore, the alkali titration was performed by adding a 0.1N sodium hydroxide aqueous solution to a fibrous cellulose-containing slurry after treatment with an ion exchange resin, and measuring the change in the pH value of the slurry. By observing the change in pH while adding the sodium hydroxide aqueous solution, a titration curve like the one shown in Figure 4 is obtained. As shown in Figure 4, in this neutralization titration, in the curve plotting the measured pH against the amount of alkali added, one point is observed where the increment (the derivative of pH with respect to the amount of alkali added) is maximum. This point of maximum increment is called the first endpoint. Here, the region from the start of titration to the first endpoint in Figure 4 is called the first region. The amount of alkali required in the first region is equal to the amount of carboxyl groups in the slurry used for titration. Then, the amount of carboxyl groups introduced (mmol / g) was calculated by dividing the amount of alkali (mmol) required in the first region of the titration curve by the solid content (g) in the fine fibrous cellulose-containing slurry being titrated.

[0252] [Measurement of sulfur oxoacid group content and sulfone group content] The amount of sulfur oxoacid groups or sulfone groups in fine fibrous cellulose was determined by pressurized heating and decomposition of the freeze-dried and pulverized sample in a sealed container using sulfuric acid, followed by appropriate dilution and measurement of sulfur content by ICP-OES. The value calculated by dividing by the oven-dry mass of the fine fibrous cellulose was defined as the amount of sulfur oxoacid groups or sulfone groups (mmol / g) of the fine fibrous cellulose.

[0253] <Example 1> The fine fibrous cellulose dispersion obtained in Production Example A1 was placed in a can container, and then deionized water was added to the can container so that the solid content concentration of the fine fibrous cellulose was diluted to 1.0% by mass. A tornado agitator (general-purpose high-speed agitator, PM-202, manufactured by AS ONE Corporation) was used as the agitator, and a 6-inch diameter agitator blade was attached, and the fine fibrous cellulose dispersion in the can container was stirred with the agitator at 1000 rpm for 5 minutes.

[0254] [Process (B)] A static mixer (1 / 2-N10-331-1, manufactured by Noritake Co., Ltd.) was used as the mixing device in process (B). A dispersion of fine fibrous cellulose with a concentration of 1.0% by mass was added to a static mixer so that the solid content of the fine fibrous cellulose was 100 parts by mass. Furthermore, an aqueous dispersion of natural rubber latex with a solid content of 61% by mass (Hyper HA, manufactured by Nomura Trading Co., Ltd.) was added to a static mixer so that the solid content of the rubber component was 500 parts by mass. The two dispersions were mixed under the conditions described in Table 1. After mixing, the presence or absence of aggregates of the rubber component was visually checked, but no aggregates were observed.

[0255] [Process (C)] A disperser (EUROSTAR20digital, manufactured by IKA Corporation, with a dissolving type stirring blade (40 mm in diameter)) was used as the mixing device in process (C). The same stirring blade was used in other examples where a disperser was used as the mixing device, other than Example 1. The mixture obtained in process (B) was mixed under the conditions described in Table 2. After mixing, the presence or absence of aggregated rubber components was visually checked, but no aggregated components were observed.

[0256] The resulting mixture was filtered under reduced pressure using a nylon mesh (100 mesh), and no filtrate was recovered. This indicated that the dispersion of fine fibrous cellulose and the dispersion of rubber components were uniformly mixed. The mixture was heated and dried in an oven set to 40°C for 18 hours to obtain a composite material of fine fibrous cellulose and rubber components.

[0257] <Examples 2-5> A composite material of fine fibrous cellulose and rubber components was obtained in the same manner as in Example 1, except that the mixture was mixed in step (B) under the conditions described in Table 1 and in step (C) under the conditions described in Table 2. No aggregates of the rubber component were observed after mixing, and no filtrate was recovered when the mixture was filtered under reduced pressure. In Example 2, step (B) used an OHR mixer (MX-F8, manufactured by OHR Fluid Engineering Laboratory Co., Ltd.) as the mixing device. In Example 4, step (C) used a Creamix (CLM2.2S, manufactured by M-Technique Co., Ltd.) as the mixing device. In Example 5, step (C) For the mixing device, we used an inline mixer (L5M-A inline verso, manufactured by Silverson Nippon Co., Ltd.).

[0258] <Example 6> A composite material of fine fibrous cellulose and rubber components was obtained in the same manner as in Example 1, except that the mixing was performed as in step (A) below, instead of steps (B) and (C). No aggregates of rubber components were observed after mixing, and no filtrate was recovered when the mixture was filtered under reduced pressure.

[0259] [Process (A)] A disperser (EUROSTAR20digital, manufactured by IKA Corporation, with a dissolving type stirring blade (40 mm in diameter)) was used as the mixing device in process (A). A dispersion of fine fibrous cellulose with a solid content concentration of 1.0% by mass was added to a container so that the solid content of fine fibrous cellulose was 100 parts by mass. Furthermore, an aqueous dispersion of natural rubber latex with a solid content concentration of 61% by mass (Hyper HA, manufactured by Nomura Trading Co., Ltd.) was added to the container so that the solid content of the rubber component was 500 parts by mass. The two dispersions were mixed under the conditions described in Table 1.

[0260] <Example 7> A composite material of fine fibrous cellulose and rubber components was obtained in the same manner as in Example 6, except that instead of an aqueous dispersion of natural rubber latex, carboxyl group-modified nitrile rubber (NA-13, manufactured by Nippon A&L Co., Ltd.) with a solid content of 47.5% was added so that the solid content of the rubber component was 500 parts by mass, and then mixed in step (A) under the conditions described in Table 1. No aggregates of the rubber component were observed after mixing, and no filtrate was recovered when the mixture was filtered under reduced pressure.

[0261] <Example 8> A composite material of fine fibrous cellulose and a rubber component was obtained in the same manner as in Example 4, except that the fine fibrous cellulose dispersion obtained in Production Example B1 was used instead of Production Example A1. No aggregates of the rubber component were observed after mixing, and no filtrate was recovered when the mixture was filtered under reduced pressure.

[0262] <Example 9> A composite material of fine fibrous cellulose and a rubber component was obtained in the same manner as in Example 4, except that the fine fibrous cellulose dispersion obtained in Production Example C1 was used instead of Production Example A1. No aggregates of the rubber component were observed after mixing, and no filtrate was recovered when the mixture was filtered under reduced pressure.

[0263] <Example 10> A composite material of fine fibrous cellulose and a rubber component was obtained in the same manner as in Example 4, except that the fine fibrous cellulose dispersion obtained in Production Example D1 was used instead of Production Example A1. No aggregates of the rubber component were observed after mixing, and no filtrate was recovered when the mixture was filtered under reduced pressure.

[0264] <Example 11> A composite material of fine fibrous cellulose and a rubber component was obtained in the same manner as in Example 4, except that the fine fibrous cellulose dispersion obtained in Production Example E1 was used instead of Production Example A1. No aggregates of the rubber component were observed after mixing, and no filtrate was recovered when the mixture was filtered under reduced pressure.

[0265] <Example 12> A composite material of fine fibrous cellulose and a rubber component was obtained in the same manner as in Example 4, except that the fine fibrous cellulose dispersion obtained in Production Example F1 was used instead of Production Example A1. No aggregates of the rubber component were observed after mixing, and no filtrate was recovered when the mixture was filtered under reduced pressure.

[0266] <Example 13> A composite material of fine fibrous cellulose and a rubber component was obtained in the same manner as in Example 4, except that the fine fibrous cellulose dispersion obtained in Production Example G1 was used instead of Production Example A1. No aggregates of the rubber component were observed after mixing, and no filtrate was recovered when the mixture was filtered under reduced pressure.

[0267] <Example 14> A composite material of fine fibrous cellulose and a rubber component was obtained in the same manner as in Example 4, except that the fine fibrous cellulose dispersion obtained in Production Example H1 was used instead of Production Example A1. No aggregates of the rubber component were observed after mixing, and no filtrate was recovered when the mixture was filtered under reduced pressure.

[0268] <Example 15> A composite material of fine fibrous cellulose and a rubber component was obtained in the same manner as in Example 4, except that the fine fibrous cellulose dispersion obtained in Production Example I1 was used instead of Production Example A1. No aggregates of the rubber component were observed after mixing, and no filtrate was recovered when the mixture was filtered under reduced pressure.

[0269] <Example 16> A composite material of fine fibrous cellulose and a rubber component was obtained in the same manner as in Example 4, except that the fine fibrous cellulose dispersion obtained in Production Example J1 was used instead of Production Example A1. No aggregates of the rubber component were observed after mixing, and no filtrate was recovered when the mixture was filtered under reduced pressure.

[0270] <Example 17> A composite material of fine fibrous cellulose and a rubber component was obtained in the same manner as in Example 4, except that the fine fibrous cellulose dispersion obtained in Production Example K1 was used instead of Production Example A1. No aggregates of the rubber component were observed after mixing, and no filtrate was recovered when the mixture was filtered under reduced pressure.

[0271] <Example 18> A composite material of fine fibrous cellulose and a rubber component was obtained in the same manner as in Example 4, except that the fine fibrous cellulose dispersion obtained in Production Example L1 was used instead of Production Example A1. No aggregates of the rubber component were observed after mixing, and no filtrate was recovered when the mixture was filtered under reduced pressure.

[0272] <Comparative Example 1> A composite material of fine fibrous cellulose and rubber component was obtained in the same manner as in Example 3, except that step (C) was omitted. No aggregates of the rubber component were observed after mixing, but when the mixture was filtered under reduced pressure, the filtrate was recovered as shown in Table 2.

[0273] <Comparative Example 2> A composite material of fine fibrous cellulose and rubber component was obtained in the same manner as in Example 2, except that step (C) was omitted. No aggregates of the rubber component were observed after mixing, but when the mixture was filtered under reduced pressure, the filtrate was recovered as shown in Table 2.

[0274] <Comparative Examples 3-5> A composite material of fine fibrous cellulose and rubber components was obtained in the same manner as in Comparative Example 1, except that the mixing was carried out under the conditions described in Table 1. No filtrate was recovered when the mixture was filtered under reduced pressure, but aggregates of the rubber component were observed after mixing. In Comparative Example 6, a wet atomizing device (Starburst, manufactured by Sugino Machine Co., Ltd.) was used as the mixing device, and the mixture was processed once at a pressure of 245 MPa.

[0275] [Tensile strength] The tensile strength was measured using the resulting composite material of fine fibrous cellulose and rubber components as a test specimen. Except for the length of the test specimen (80 mm) and the distance between chucks (50 mm), the procedure conformed to JIS P 8113:2006, and the maximum tensile load was measured using a Tensilon tensile testing machine (manufactured by A&D Co., Ltd.). The tensile strength (in MPa) was calculated by dividing this maximum tensile load by the cross-sectional area of ​​the test specimen (thickness × width [15 ± 0.1 mm]). For the measurement of the maximum tensile load, the test specimen was conditioned at 23°C and 50% relative humidity for 24 hours. The thickness of the test specimens was measured using a constant-pressure thickness gauge (TECLOCK CORPORATION, PG-02). Specifically, test specimens cut to a size of 50 mm square or larger were conditioned at 23°C and 50% relative humidity for 24 hours, and then the thickness of four arbitrary points was measured. The average value of these measurements was taken as the thickness of the test specimen.

[0276] [Table 1]

[0277] [Table 2]

[0278] As shown in Tables 1 and 2, in Examples 1 to 18, which satisfy at least one of requirements (i) and (ii), composite materials with superior strength were obtained compared to Comparative Examples 1 to 5, with no aggregates of rubber components observed. [Explanation of Symbols]

[0279] 11…Mixing device, 12…Agitator blade, 21…Static mixer piping

Claims

1. A method for producing a composite material containing fine fibrous cellulose and a rubber component, The process includes a mixing step of mixing the dispersion of the fine fibrous cellulose with the dispersion of the rubber component. A method for manufacturing a composite material that satisfies at least one of the following requirements (i) and (ii): (i) The mixing step includes step (A) of introducing the dispersion of the fine fibrous cellulose and the dispersion of the rubber component into a mixing apparatus and mixing them at a shear rate of 50 [ / s] or more and 10,000 [ / s] or less. (ii) The mixing step includes introducing the dispersion of the fine fibrous cellulose and the dispersion of the rubber component into a mixing device and first mixing them for 10 seconds or more at a shear rate of 10,000 [ / s] or less (B), and further mixing them for 10 seconds or more at a shear rate of 50 [ / s] or more (C), wherein step (B) is a mixing step at a shear rate b [ / s] and step (C) is a mixing step at a shear rate c [ / s], then b < c. (However, this excludes cases where step (B) is a mixing step at a shear rate of less than 50 [ / s] and step (C) is a mixing step at a shear rate exceeding 10,000 [ / s].)

2. A method for manufacturing a composite material according to claim 1, which satisfies the requirement of (ii) above.

3. The method for manufacturing a composite material according to claim 2, wherein the shear rate c[ / s] is 10,000[ / s] or more.

4. The method for manufacturing a composite material according to claim 1 or 2, wherein step (A) or step (B) is a step of mixing at a shear rate of 1000 [ / s] or less.

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