Method for producing organic cellulose fiber dispersion

Abstract

To provide a method for producing an organic dispersion of cellulose fibers, which enables production of the organic dispersion efficiently without losing cellulose fibers while maintaining properties of cellulose fibers, the organic dispersion having cellulose fibers dispersed in a dispersion medium in which a content ratio of a hydrophilic organic solvent exceeds 50 mass%.SOLUTION: A method for producing an organic dispersion of cellulose fibers comprises: dispersing mechanically fibrillated cellulose fibers in an aqueous dispersion medium to prepare an aqueous dispersion of cellulose fibers; thereafter adding a hydrophilic organic solvent to the aqueous dispersion of cellulose fibers; subsequently evaporating a mixed solvent of water and the hydrophilic organic solvent; and adjust a content ratio of the hydrophilic organic solvent in the dispersion medium so as to exceed 50 mass% by performing the solvent addition step and the solvent evaporation step at least once each.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for producing an organic dispersion of cellulose fibers. [Background technology]

[0002] It is known that fibers are added to various products such as paints to impart desired properties to the products. As such fibers, naturally occurring cellulose fibers have been considered as such fibers from the viewpoint of reducing the environmental load.

[0003] However, cellulose fibers are hydrophilic and difficult to disperse in organic solvents. Therefore, there are limitations on the products to which cellulose fibers can be applied. Therefore, it is desirable to disperse cellulose fibers in organic solvents.

[0004] For example, it has been proposed to add a hydrophilic solvent to an aqueous dispersion of cellulose fibers, and then deliquor the mixture to replace the aqueous dispersion with the hydrophilic solvent (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2011-6609 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, the deliquescence method described in Patent Document 1 involves filtration, squeezing, and centrifugation. When deliquescence is performed using such a deliquescence method, the cellulose fibers aggregate in the dispersion medium containing the hydrophilic solvent.

[0007] Therefore, in order to disperse cellulose fibers in a dispersion medium containing a hydrophilic solvent, very strong stirring is required, and there is a limit to how much the production efficiency of an organic dispersion of cellulose fibers can be improved.

[0008] Furthermore, in the draining method described in Patent Document 1, fine cellulose fibers may be mixed into the waste liquid removed by draining, which may result in the loss of cellulose fibers before and after draining.

[0009] The present invention provides a method for producing an organic cellulose fiber dispersion, in which cellulose fibers are dispersed in a dispersion medium having a hydrophilic organic solvent content exceeding 50% by mass, which can efficiently produce the organic cellulose fiber dispersion without losing the cellulose fibers while maintaining the properties of the cellulose fibers. [Means for solving the problem]

[0010] The present invention [1] is a method for producing an organic cellulose fiber dispersion in which cellulose fibers are dispersed in a dispersion medium containing a hydrophilic organic solvent, the method comprising: a preparation step of preparing an aqueous cellulose fiber dispersion in which mechanically defibrated cellulose fibers are dispersed in a dispersion medium containing water; a solvent addition step of adding the hydrophilic organic solvent to the aqueous cellulose fiber dispersion and mixing water and the hydrophilic organic solvent; and a solvent evaporation step of evaporating the mixed solvent of water and the hydrophilic organic solvent, the solvent addition step and the solvent evaporation step being carried out at least once each to adjust the content of the hydrophilic organic solvent in the dispersion medium to exceed 50 mass%.

[0011] The present invention [2] includes the method for producing an organic cellulose fiber dispersion described in the above [1], in which the solvent addition step and the solvent evaporation step are repeated multiple times.

[0012] The present invention [3] includes the method for producing an organic cellulose fiber dispersion described in [2] above, which includes a step in which the amount of the hydrophilic organic solvent added this time is the same as or greater than the amount of the hydrophilic organic solvent added last time. Effect of the Invention

[0013] According to the method for producing an organic cellulose fiber dispersion of the present invention, mechanically defibrated cellulose fibers are dispersed in an aqueous dispersion medium to prepare an aqueous cellulose fiber dispersion, a hydrophilic organic solvent is added to the aqueous cellulose fiber dispersion, and then the mixed solvent of water and the hydrophilic organic solvent is evaporated. The addition of the hydrophilic organic solvent and the evaporation of the mixed solvent are carried out at least once each to adjust the content of the hydrophilic organic solvent in the dispersion medium to exceed 50 mass%.

[0014] Therefore, aggregation of the cellulose fibers in the dispersion medium can be suppressed, and the properties of the cellulose fibers can be maintained while the cellulose fibers are not lost, and an organic cellulose fiber dispersion can be produced efficiently. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a graph showing the content ratio of the hydrophilic organic solvent contained in the mixed liquid relative to the total amount of the hydrophilic organic solvent added in Comparative Example 1 and Examples 2 to 5. [Diagram 2] FIG. 2 shows a graph of the viscosity of the cellulose fiber organic dispersion of Example 6 versus the rotation speed of a Brookfield viscometer. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] <Method of producing organic cellulose fiber dispersion> The method for producing an organic cellulose fiber dispersion includes a preparation process for preparing an aqueous cellulose fiber dispersion, a solvent addition process for adding a hydrophilic organic solvent to the aqueous cellulose fiber dispersion, and a solvent evaporation process for evaporating a mixed solvent of water and the hydrophilic organic solvent.

[0017] (1) Preparation process In the preparation step, the mechanically defibrated cellulose fibers are added to an aqueous dispersion medium and stirred and mixed, thereby preparing an aqueous cellulose fiber dispersion in which the mechanically defibrated cellulose fibers are dispersed in the aqueous dispersion medium.

[0018] Cellulose fibers are polysaccharide fibers having a β-1,4-glucan structure. Examples of cellulose fibers include plant-derived cellulose fibers, animal-derived cellulose fibers, and regenerated cellulose fibers.

[0019] Examples of plant-derived cellulose fibers include pulp fibers, specifically wood fibers, bamboo fibers, sugarcane fibers, seed hair fibers, zinc bark fibers, and leaf fibers.

[0020] An example of an animal-derived cellulose fiber is sea squirt cellulose.

[0021] Regenerated cellulose fibers include, for example, rayon and cellophane.

[0022] The cellulose fibers may be used alone or in combination of two or more kinds.

[0023] Among the cellulose fibers, preferably, plant-derived cellulose fibers are used, and more preferably, pulp fibers are used.

[0024] Such cellulose fibers are mechanically defibrated. The cellulose fibers may be mechanically defibrated without chemical defibration treatment, or may be mechanically defibrated after chemical defibration treatment.

[0025] Chemical defibration treatment chemically modifies the hydroxyl groups of cellulose fibers, and examples of chemical defibration treatments include the TEMPO oxidation method, the phosphoric acid esterification method, the sulfuric acid esterification method, and the sulfonation method.

[0026] Examples of mechanical fiberization methods include the grinder method, the homogenizer method, the underwater head-on collision method, the microfluidizer method, the freeze-pulverization method, and the ultrasonic fiberization method.

[0027] The cellulose fibers are preferably mechanically defibrated without chemical defibration treatment, since chemical defibration treatment of the cellulose fibers results in a relatively small diameter of the cellulose fibers, which may cause aggregation of the cellulose fibers in the organic dispersion of the cellulose fibers.

[0028] The diameter of the cellulose fibers is, for example, 5 nm or more, preferably 20 nm or more, and, for example, 20 μm or less, preferably 10 μm or less, more preferably 300 nm or less. In other words, the cellulose fibers are more preferably cellulose nanofibers.

[0029] The length of the cellulose fibers is, for example, 20 nm or more, preferably 500 nm or more, and, for example, 3 mm or less, preferably 500 μm or less. The diameter and length of the cellulose fibers can be measured by observation with a scanning electron microscope.

[0030] The aqueous dispersion medium contains at least water. The aqueous dispersion medium may contain a hydrophilic solvent, which will be described later, in addition to water. The aqueous dispersion medium is preferably composed of water.

[0031] The content of water in the aqueous dispersion medium exceeds 50% by mass, and is preferably 90% by mass or more, more preferably 95% by mass or more, and is, for example, 100% by mass or less.

[0032] The solid content concentration in the cellulose fiber aqueous dispersion is, for example, 0.1 mass % or more, preferably 1 mass % or more, and for example, 10 mass % or less, preferably 5 mass % or less.

[0033] When the solid content concentration in the cellulose fiber aqueous dispersion is equal to or less than the upper limit, irreversible aggregation of cellulose fibers in the cellulose fiber aqueous dispersion can be suppressed. In particular, when the solid content concentration in the cellulose fiber aqueous dispersion is equal to or less than 5 mass%, aggregation of cellulose fibers can be stably suppressed.

[0034] (2) Solvent addition process Next, the hydrophilic organic solvent is added to the cellulose fiber aqueous dispersion and mixed with stirring, whereby water and the hydrophilic organic solvent are mixed together.

[0035] The hydrophilic organic solvent is soluble in water. More specifically, the hydrophilic organic solvent exhibits both compatibility with water and resin. The solubility parameter δ of the hydrophilic organic solvent is the Hildebrand solubility parameter, and is, for example, 8.0 [cal / cm 3 ] (1 / 2) More than 10.0 [cal / cm 3 ] (1 / 2) For example, 15.0 [cal / cm 3 ] (1 / 2) Preferably, 13.0 [cal / cm 3 ] (1 / 2) The solubility parameter δ can be calculated using calculation software that uses known calculation means.

[0036] The hydrophilic organic solvent has at least one hydroxyl group. Examples of the hydrophilic organic solvent include monohydric alcohols and dihydric alcohols.

[0037] Examples of monohydric alcohols include alkyl alcohols, monoether monoalcohols, and polyether monoalcohols.

[0038] The alkyl alcohol has, for example, an alkyl group having a carbon number of 1 to 16. Specific examples of the alkyl alcohol include methanol, ethanol, propanol, isopropanol, n-butanol, isobutanol, s-butanol, t-butanol, and 2-ethylhexyl alcohol.

[0039] Examples of monoether monoalcohols include ethylene glycol monomethyl ether, ethylene glycol monoethyl ether (cellosolve), ethylene glycol monobutyl ether, ethylene glycol tertiary butyl ether, 3-methoxy-3-methyl-1-propanol, propylene glycol monomethyl ether, propylene glycol monoethyl ether, and propylene glycol monobutyl ether.

[0040] Examples of polyether monoalcohols include diethylene glycol monomethyl ether, diethylene glycol monoethyl ether (carbitol), diethylene glycol monobutyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, and dipropylene glycol monobutyl ether.

[0041] Dihydric alcohols include, for example, alkanediols and ether diols.

[0042] Examples of alkanediols include ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,3-butanediol, 1,2-butanediol, 1,5-pentanediol, and 1,6-hexanediol.

[0043] Examples of ether diols include diethylene glycol and dipropylene glycol.

[0044] The boiling point of the hydrophilic organic solvent is, for example, 55° C. or higher, preferably 75° C. or higher in consideration of the efficiency of solvent replacement, and, for example, 200° C. or lower, preferably 130° C. or lower in consideration of solvent removal during use.

[0045] The hydrophilic organic solvents can be used alone or in combination of two or more kinds.

[0046] Among the hydrophilic organic solvents, preferably, monohydric alcohols are used, more preferably, alkyl alcohols and monoether monoalcohols are used, further preferably, isopropanol and propylene glycol monomethyl ether (PGME) are used, and particularly preferably, PGME is used.

[0047] As will be described in detail later, the solvent addition step and the solvent evaporation step are preferably repeated multiple times.

[0048] In each solvent addition step, the amount of hydrophilic organic solvent added is, relative to 100 parts by mass of water contained in the cellulose fiber aqueous dispersion, for example, 10 parts by mass or more, preferably 20 parts by mass or more, more preferably 50 parts by mass or more, even more preferably 100 parts by mass or more, and for example, 1,000 parts by mass or less, preferably 550 parts by mass or less, more preferably 450 parts by mass or less, even more preferably 350 parts by mass or less, particularly preferably 250 parts by mass or less, and particularly preferably 200 parts by mass or less.

[0049] In addition, in each solvent addition step, the amount of hydrophilic organic solvent added is, relative to 100 parts by mass of the cellulose fiber aqueous dispersion, for example, 10 parts by mass or more, preferably 20 parts by mass or more, more preferably 50 parts by mass or more, and particularly preferably 100 parts by mass or more, and for example, 1,000 parts by mass or less, preferably 500 parts by mass or less, more preferably 400 parts by mass or less, even more preferably 300 parts by mass or less, particularly preferably 200 parts by mass or less, and particularly preferably 150 parts by mass or less.

[0050] When the amount of the hydrophilic organic solvent added is equal to or more than the lower limit, the content of water in the mixed solvent of water and the hydrophilic organic solvent can be smoothly reduced in the solvent evaporation step described below.When the amount of the hydrophilic organic solvent added is equal to or less than the upper limit, the amount of the hydrophilic organic solvent used can be reduced, the time required for the solvent evaporation step described below can be reduced, and the production efficiency of the cellulose fiber organic dispersion can be reliably improved.

[0051] Furthermore, when the solvent addition process is repeated, the total amount of hydrophilic organic solvent added is, for example, 200 parts by mass or more, preferably 300 parts by mass or more, and for example, 2000 parts by mass or less, preferably 1000 parts by mass or less, more preferably 500 parts by mass or less, and even more preferably 400 parts by mass or less, relative to 100 parts by mass of the cellulose fiber aqueous dispersion.

[0052] (3) Solvent evaporation process Next, the mixed solvent of water and the hydrophilic organic solvent is evaporated from the mixed liquid in which the hydrophilic organic solvent is added to the aqueous cellulose fiber dispersion.

[0053] The pressure in the solvent evaporation step is, for example, 0.1 kPa or more, preferably 1 kPa or more, and for example, normal pressure (101 kPa) or less, preferably 10 kPa or less.

[0054] The temperature in the solvent evaporation step is, for example, 40°C or more, preferably 50°C or more, and for example, 80°C or less, preferably 70°C or less.

[0055] In the solvent evaporation step, strong stirring (for example, a homogenizer) is not required to suppress aggregation of the cellulose fibers. When the mixed liquid is stirred in the solvent evaporation step, for example, a stirring blade or a rotary evaporator is used.

[0056] When the solvent addition step and the solvent evaporation step are repeated, the amount of evaporated mixed solvent is, for example, 50 parts by mass or more, preferably 90 parts by mass or more, more preferably 100 parts by mass, relative to 100 parts by mass of the hydrophilic organic solvent added in the immediately preceding solvent addition step. In other words, in the solvent evaporation step, more preferably, the same amount of the mixed solvent as the hydrophilic organic solvent added in the immediately preceding solvent addition step is evaporated.

[0057] The solids concentration of the mixed liquid at the end of the solvent evaporation step is, for example, 0.1 mass % or more, preferably 1 mass % or more, and 10 mass % or less, preferably 5 mass % or less.

[0058] When the solid content concentration in the mixed liquid at the end of the solvent evaporation step is equal to or less than the upper limit, irreversible aggregation of cellulose fibers in the mixed liquid can be suppressed. In particular, when the solid content concentration in the mixed liquid is equal to or less than 5 mass%, aggregation of cellulose fibers can be stably suppressed.

[0059] Then, the above-mentioned solvent addition step and the above-mentioned solvent evaporation step are each carried out at least once, so that the content ratio of the hydrophilic organic solvent in the dispersion medium is adjusted to exceed 50 mass %.

[0060] The above-mentioned solvent addition step and the above-mentioned solvent evaporation step are preferably performed multiple times, which can reliably improve the content of the hydrophilic organic solvent in the dispersion medium.

[0061] The number of times the solvent addition step and the solvent evaporation step are repeated is, for example, two or more times, and, for example, 20 or less times, preferably 15 or less times, more preferably 5 or less times, and particularly preferably 3 times.

[0062] When the number of times the solvent addition step and the solvent evaporation step are repeated is equal to or greater than the above lower limit, the content ratio of the hydrophilic organic solvent in the dispersion medium can be more reliably increased.When the number of times the solvent addition step and the solvent evaporation step are repeated is equal to or less than the above upper limit, the production efficiency of the cellulose fiber organic dispersion can be improved.

[0063] Furthermore, when the solvent addition process and the solvent evaporation process are repeated multiple times, the hydrophilic organic solvent is added again in the above-mentioned amount to the mixed liquid of the cellulose fiber aqueous dispersion and the hydrophilic organic solvent obtained in the previous solvent evaporation process, and the mixed solvent is then evaporated again under the above-mentioned conditions.

[0064] The repeatedly performed solvent addition step also includes a step in which the amount of hydrophilic organic solvent added this time is the same as or greater than the amount of hydrophilic organic solvent added last time.

[0065] In other words, the repeatedly performed solvent addition steps include a first step of adding a reference amount of hydrophilic organic solvent, a second step of adding the same amount of hydrophilic organic solvent as that added in the first step, and / or a third step of adding an amount of hydrophilic organic solvent greater than that added in the first step.

[0066] The order of steps is not particularly limited as long as the step 2 and / or the step 3 are carried out after the step 1. In addition, a step of adding a hydrophilic organic solvent in an amount smaller than that added in the step 1 may be carried out between the steps 1, 2, and 3.

[0067] The repeatedly performed solvent addition steps preferably include the first step, the second step, and the third step, and more preferably, the first step, the second step, and the third step are performed in sequence.

[0068] In this manner, a cellulose fiber organic dispersion is produced. In the cellulose fiber organic dispersion, cellulose fibers are dispersed in a dispersion medium containing a hydrophilic organic solvent. The dispersion medium of the cellulose fiber organic dispersion contains a hydrophilic organic solvent as a main component. The dispersion medium of the cellulose fiber organic dispersion may contain water as a secondary component.

[0069] The content of the hydrophilic organic solvent in the dispersion medium of the cellulose fiber organic dispersion is more than 50% by mass, preferably 80% by mass or more, more preferably 95% by mass or more, even more preferably 97% by mass or more, and for example, 100% by mass or less, preferably 99% by mass or less. When the content of the hydrophilic organic solvent in the dispersion medium is relatively low, the content of the hydrophilic organic solvent can be measured by gas chromatography. When the content of the hydrophilic organic solvent in the dispersion medium is relatively high, the content of the hydrophilic organic solvent can be calculated by subtracting the amount of moisture measured by a Karl Fischer moisture meter from the amount of moisture in the dispersion medium.

[0070] The water content in the dispersion medium of the cellulose fiber organic dispersion is, for example, 0 mass % or more, preferably 1 mass part or more, and less than 50 mass %, preferably 20 mass % or less, more preferably 5 mass % or less, and further preferably 3 mass % or less. The water content can be measured by a Karl Fischer moisture meter.

[0071] The solid content concentration in the cellulose fiber organic dispersion is, for example, 0.1 mass % or more, preferably 1 mass % or more, and for example, 10 mass % or less, preferably 5 mass % or less.

[0072] Such an organic dispersion of cellulose fibers can be mixed with various materials having hydrophobic properties.

[0073] Examples of materials having hydrophobic properties include hydrophobic organic solvents, reactive diluents, and resins.

[0074] Examples of hydrophobic organic solvents include aliphatic hydrocarbons, aromatic hydrocarbons, ketones, ethers, and esters.

[0075] Aliphatic hydrocarbons include, for example, n-hexane, n-heptane, and octane.

[0076] Aromatic hydrocarbons include, for example, benzene, toluene, and xylene.

[0077] Examples of ketones include acetone, methyl ethyl ketone, and methyl isobutyl ketone.

[0078] Examples of ethers include dimethyl ether, tetrahydrofuran, dioxane, and propylene glycol dimethyl ether.

[0079] Esters include, for example, ethyl acetate and butyl acetate.

[0080] In the mixture of the cellulose fiber organic dispersion and the hydrophobic organic solvent, the cellulose fibers can be well dispersed in the mixed solvent of the hydrophilic organic solvent and the hydrophobic organic solvent.

[0081] Also, the hydrophilic organic solvent of the cellulose fiber organic dispersion liquid can be replaced with a hydrophobic organic solvent. Specifically, the process of mixing the hydrophobic organic solvent with the cellulose fiber organic dispersion liquid and the process of evaporating the mixed solvent of the hydrophilic organic solvent and the hydrophobic organic solvent are carried out at least once each. In this case, the process is the same as the above-mentioned method for producing the cellulose fiber organic dispersion liquid, except that the hydrophobic organic solvent is mixed with the cellulose fiber organic dispersion liquid instead of the hydrophilic organic solvent.

[0082] The reactive diluent is, for example, a polymerizable monomer capable of reacting with a compound having an ethylenically unsaturated double bond. An example of the reactive diluent is styrene.

[0083] In the mixture of the cellulose fiber organic dispersion and the reactive diluent, the cellulose fibers can be well dispersed in the mixed solvent of the hydrophilic organic solvent and the reactive diluent. In addition, the hydrophilic organic solvent of the cellulose fiber organic dispersion can be replaced with the reactive diluent in the same manner as the hydrophobic organic solvent.

[0084] Examples of the resin include styrene resin, epoxy resin, rubber, and urethane resin.

[0085] In a mixture of an organic dispersion of cellulose fibers and a resin, the cellulose fibers can be well dispersed in the resin and can form a network structure.

[0086] <Action and effect> In the above-mentioned method for producing an organic cellulose fiber dispersion, mechanically defibrated cellulose fibers are dispersed in an aqueous dispersion medium to prepare an aqueous cellulose fiber dispersion, a hydrophilic organic solvent is added to the aqueous cellulose fiber dispersion, and then the mixed solvent of water and the hydrophilic organic solvent is evaporated. The addition of the hydrophilic organic solvent and the evaporation of the mixed solvent are carried out at least once each to adjust the content of the hydrophilic organic solvent in the dispersion medium to exceed 50 mass%.

[0087] Therefore, aggregation of the cellulose fibers in the dispersion medium can be suppressed, and the properties of the cellulose fibers can be maintained while the cellulose fibers are not lost, and an organic cellulose fiber dispersion can be produced efficiently. EXAMPLES

[0088] The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto. The specific numerical values ​​of the blending ratio (content ratio), physical property values, parameters, etc. used in the following description can be replaced with the upper limit values ​​(numerical values ​​defined as "less than or equal to" or "less than") or lower limit values ​​(numerical values ​​defined as "more than or equal to" or "exceeding") of the blending ratio (content ratio), physical property values, parameters, etc., described in the above "Form for carrying out the invention".

[0089] << comparison Example 1>> A cellulose fiber aqueous dispersion was prepared by dispersing mechanically defibrated cellulose fibers (diameter 30 to 200 nm, length 0.5 to 500 μm, product name Cellfim C-100, manufactured by Mori Machinery Co., Ltd.) in water without chemical defibration treatment. The solid content concentration in the cellulose fiber aqueous dispersion was 5 mass%.

[0090] Next, 400 parts by mass of PGME (hydrophilic organic solvent) was added to 100 parts by mass of the cellulose fiber aqueous dispersion and mixed with stirring (solvent addition step).

[0091] Next, the mixed solvent, in an amount equal to the amount of the added PGME, was evaporated from the mixed solution of the cellulose fiber aqueous dispersion and PGME under conditions of 5 kPa and 60° C. (solvent evaporation step).

[0092] Thus, a cellulose fiber organic dispersion liquid was prepared. The solid content concentration in the cellulose fiber organic dispersion liquid was 5 mass%. The content ratio of PGME in the mixed solvent at the end of the solvent evaporation process is shown in Table 1 and Figure 1.

[0093] <<Example 2>> comparison A cellulose fiber organic dispersion was prepared in the same manner as in Example 1. In Example 2, the addition of PGME and the evaporation of the mixed solvent were carried out three times. The amount of PGME added in the first step was 200 parts by mass relative to 100 parts by mass of the cellulose fiber aqueous dispersion. The amount of PGME added in the second and third steps was 100 parts by mass relative to 100 parts by mass of the mixed liquid obtained by the previous solvent evaporation step. The solid content concentration in the mixed liquid at the end of each solvent evaporation step was 5% by mass. The solid content concentration in the cellulose fiber organic dispersion was also 5% by mass.

[0094] <<Example 3>> comparison A cellulose fiber organic dispersion was prepared in the same manner as in Example 1. In Example 3, the addition of PGME and the evaporation of the mixed solvent were carried out three times. The amount of PGME added in the first step was 100 parts by mass relative to 100 parts by mass of the cellulose fiber aqueous dispersion. The amount of PGME added in the second step was 100 parts by mass relative to 100 parts by mass of the mixed liquid obtained by the first solvent evaporation step. The amount of PGME added in the third step was 200 parts by mass relative to 100 parts by mass of the mixed liquid obtained by the second solvent evaporation step. The solid content concentration of the mixed liquid at the end of each solvent evaporation step was 5% by mass. The solid content concentration in the cellulose fiber organic dispersion was 5% by mass.

[0095] <<Example 4>> comparisonA cellulose fiber organic dispersion was prepared in the same manner as in Example 1. In Example 4, the addition of PGME and the evaporation of the mixed solvent were carried out four times. The amount of PGME added in the first addition was 100 parts by mass relative to 100 parts by mass of the cellulose fiber aqueous dispersion. The amount of PGME added in the second to fourth additions was 100 parts by mass relative to 100 parts by mass of the mixed liquid obtained by the previous solvent evaporation step. The solid content concentration in the mixed liquid at the end of each solvent evaporation step was 5% by mass. The solid content concentration in the cellulose fiber organic dispersion was also 5% by mass.

[0096] <<Example 5>> comparison A cellulose fiber organic dispersion was prepared in the same manner as in Example 1. In Example 5, the addition of PGME and the evaporation of the mixed solvent were carried out 15 times. The amount of PGME added in the first addition was 20 parts by mass relative to 100 parts by mass of the cellulose fiber aqueous dispersion. The amount of PGME added in the second to fifteenth additions was 20 parts by mass relative to 100 parts by mass of the mixed liquid obtained by the previous solvent evaporation step. The solid content concentration of the mixed liquid at the end of each solvent evaporation step was 5% by mass. The solid content concentration in the cellulose fiber organic dispersion was also 5% by mass.

[0097] [Table 1]

[0098] <<Example 6>> A cellulose fiber organic dispersion was prepared in the same manner as in Example 3. The solid content of the cellulose fiber organic dispersion was 2% by mass. The content of PGME in the dispersion medium of the cellulose fiber organic dispersion was 99.0% by mass.

[0099] Next, the viscosity of the cellulose fiber organic dispersion obtained in Example 6 was measured at each rotation speed of a B-type viscometer (trade name Analog Viscometer LVT, manufactured by Brookfield) shown in Table 2. The viscosity was measured at 20°C with an LV-3 rotor, and the value at the fifth rotation from the start of the measurement was used. The results are shown in Table 2 and Figure 2. This confirmed the thixotropy of the cellulose fiber organic dispersion, and confirmed that the cellulose fibers were sufficiently dispersed in the cellulose fiber organic dispersion.

[0100] [Table 2]

[0101] <<Example 7>> A cellulose fiber organic dispersion was prepared in the same manner as in Example 3. In Example 7, PGME was replaced with isopropanol (IPA, a hydrophilic organic solvent). The solid content in the cellulose fiber organic dispersion was 5% by mass. The content of IPA in the dispersion medium of the cellulose fiber organic dispersion was 97.6% by mass.

[0102] Next, 50 parts by mass of styrene (reactive diluent) was added to 100 parts by mass of the cellulose fiber organic dispersion obtained in Example 7, and the mixture was stirred and mixed (solvent addition step).

[0103] Next, the same amount of mixed solvent (mixed solvent of styrene and IPA) as the amount of added styrene was evaporated from the mixed liquid of the cellulose fiber organic dispersion liquid and styrene under the conditions of 10 kPa and 50°C (solvent evaporation step). After that, the addition of styrene and the evaporation of the mixed solvent were repeated twice. In other words, the addition of styrene and the evaporation of the mixed solvent were carried out a total of three times.

[0104] In this way, a styrene-based dispersion of cellulose fibers was prepared. The solid content in the styrene-based dispersion of cellulose fibers was 5% by mass. The styrene content in the mixed solvent at the end of the solvent evaporation step is shown in Table 3.

[0105]

Table 3

Claims

[Claim 1] A method for producing an organic dispersion of cellulose fibers in which cellulose fibers are dispersed in a dispersion medium containing a hydrophilic organic solvent, comprising the steps of: A preparation step of preparing an aqueous cellulose fiber dispersion in which mechanically defibrated cellulose fibers are dispersed in a dispersion medium containing water; a solvent addition step of adding the hydrophilic organic solvent to the cellulose fiber aqueous dispersion and mixing water and the hydrophilic organic solvent; A solvent evaporation step of evaporating the mixed solvent of water and the hydrophilic organic solvent, The solvent addition step and the solvent evaporation step are repeated a number of times to adjust the content of the hydrophilic organic solvent in the dispersion medium to exceed 50% by mass; A method for producing an organic cellulose fiber dispersion, comprising a step in which the amount of the hydrophilic organic solvent added this time is the same as or greater than the amount of the hydrophilic organic solvent added last time.

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