JP2019218506A - Method for producing composition comprising cellulose nanofiber and polyvinyl alcohol-based polymer - Google Patents

Abstract

To provide a method for producing a composition comprising a cellulose nanofiber and a polyvinyl alcohol-based polymer having low viscosity and good handling.SOLUTION: There is provided a composition comprising a cellulose nanofiber and a polyvinyl alcohol-based polymer which is obtained by fibrillating a mixture of cellulose and a polyvinyl alcohol-based polymer, wherein the fibrillation is performed using a medium-agitation type disperser, a high pressure type disperser, or a rotation type disperser.SELECTED DRAWING: None

Description

  The present invention relates to a method for producing a composition containing cellulose nanofibers and a polyvinyl alcohol-based polymer.

  BACKGROUND ART Conventionally, polyvinyl alcohol-based resins have been widely used in various fields such as molded products such as adhesives, films, sheets, etc., as well as in dispersants, sizing agents for fibers, etc. by utilizing their water solubility and adhesiveness. Used. In recent years, polyvinyl alcohol-based resins having a relatively high degree of polymerization tend to be frequently used in order to improve the adhesive strength, film strength, barrier properties during paper processing, and the like.

  In such applications, the polyvinyl alcohol-based resin is often used as an aqueous solution, but as the degree of polymerization increases, the viscosity of the polyvinyl alcohol-based resin becomes extremely high. For example, the average degree of polymerization is 3000, and the average degree of saponification is 99 mol%. In the case of a 4% by weight aqueous solution of a polyvinyl alcohol-based resin, the viscosity (measured with a B-type viscometer) reaches about 100 cps (20 ° C.), and handling and coating operations are likely to be troublesome.

  On the other hand, in recent years, natural fibers or synthetic fibers having a diameter of about 1 to 100 nm are generally called nanofibers. Cellulose nanofibers, which are one of the nanofibers, have been used for various purposes such as complexing with a polyvinyl alcohol-based resin. It is expected to expand to various applications.

  As a method for obtaining cellulose nanofibers, there is known a method in which cellulose fibers are oxidized in water in the presence of an N-oxyl compound or the like, impurities are removed, and a dispersing force is applied (Patent Document 1). Usually, cellulose nanofibers are produced in the form of an aqueous dispersion, and are provided for complexation with other materials in the form of an aqueous dispersion.Heat-resistant water, a PVA-based polymer composition having excellent heat resistance, a film, A method for producing fibers and the like is known (Patent Document 2).

JP 2008-001728 A JP 2010-24203 A

  However, in the above-mentioned method, the aqueous dispersion may have a high viscosity and may be difficult to handle. For example, when coating a dispersion of a mixture of a polyvinyl alcohol-based polymer and a cellulose nanofiber dispersion, it is difficult to form a film because the viscosity is too high. Due to the high viscosity of the dispersion obtained by mixing the system polymer and the cellulose nanofiber dispersion, there has been a problem that both components are separated and a foreign defect is generated.

  Accordingly, an object of the present invention is to provide a method for producing a composition containing cellulose nanofiber and a polyvinyl alcohol-based polymer, which has low viscosity and good handling.

The present invention provides the following.
<1>
(A) a step of mixing cellulose and a polyvinyl alcohol-based polymer to obtain a mixture;
(B) a step of fibrillating the mixture to obtain a dispersion containing cellulose nanofibers and a polyvinyl alcohol-based polymer;
A method for producing a dispersion containing cellulose nanofibers and a polyvinyl alcohol-based polymer, comprising:
<2>
The method according to <1>, wherein the defibration is performed using a medium stirring type disperser, a high-pressure disperser, or a rotary disperser.
<3>
The method according to <1> or <2>, wherein a polyvinyl alcohol-based polymer is further added to the dispersion containing the cellulose nanofibers and the polyvinyl alcohol-based polymer.
<4>
The method according to any one of <1> to <3>, wherein the defibration is a process using an operating pressure of 1 MPa to 400 MPa using a high-pressure disperser.
<5>
The method according to any one of <1> to <4>, wherein the mixture contains 1 to 90 parts by mass of a polyvinyl alcohol-based polymer with respect to cellulose.
<6>
The method according to any one of <1> to <5>, wherein the cellulose is a chemically modified cellulose.

  According to the present invention, it is possible to provide a method for producing a composition containing cellulose nanofibers and a polyvinyl alcohol-based polymer, which has low viscosity and good handling. Further, the film produced from the composition has a uniform phase structure in the film, so that the occurrence of foreign defects is reduced.

  Hereinafter, the present invention will be described in detail.

<Cellulose nanofiber>
In the present invention, the cellulose nanofiber (hereinafter, sometimes referred to as CNF) is a fine fiber having a fiber width of about 1 to 500 nm, which is obtained by pulverizing a cellulose-based material such as pulp to a nanometer level. . The average fiber diameter and average fiber length of cellulose nanofibers are obtained by averaging the fiber diameter and fiber length obtained from the result of observing each fiber using an atomic force microscope (AFM) or a transmission electron microscope (TEM). Can be obtained by

  Cellulose nanofibers are obtained by mechanically applying pulp to micronization, or obtained by carboxylated cellulose (also called oxidized cellulose), carboxymethylated cellulose, or cellulose into which a phosphate group is introduced. It can be obtained by fibrillating modified cellulose such as anion-modified cellulose and cationized cellulose. The average fiber length and the average fiber diameter of the fine fibers can be adjusted by oxidation treatment and defibration treatment.

The average aspect ratio of the oxidized cellulose nanofiber is usually 50 or more. The upper limit is not particularly limited, but is usually 1,000 or less. The average aspect ratio can be calculated by the following equation:
Aspect ratio = average fiber length / average fiber diameter

<Cellulose>
Cellulose used in the present invention is not particularly limited. For example, plants (eg, wood, bamboo, hemp, jute, kenaf, agricultural waste, cloth, pulp (conifer unbleached kraft pulp (NUKP), conifer bleached kraft pulp ( NBKP), hardwood unbleached kraft pulp (LUKP), hardwood bleached kraft pulp (LBKP), softwood unbleached sulphite pulp (NUSP), softwood bleached sulphite pulp (NBSP) thermomechanical pulp (TMP), recycled pulp, used paper, etc. ), Animals (for example, ascidians), algae, microorganisms (for example, acetic acid bacteria (Acetobacter)), microorganism products, etc. The cellulose used in the present invention may be any of these, or may be two or more. , But preferably cellulose derived from plants or microorganisms (eg, A cellulose fiber), more preferably from plant-derived cellulose (e.g., cellulose fibers).

  The cellulose used in the present invention is preferably chemically modified cellulose obtained by subjecting cellulose to chemical modification such as anion modification or cation modification in order to efficiently perform defibration in the defibration step.

  The number average fiber diameter of cellulose used in the present invention is not particularly limited, but is about 30 to 60 μm in the case of softwood kraft pulp, which is a general pulp, and is about 10 to 30 μm in the case of hardwood kraft pulp. In the case of other pulp, those having undergone general purification are about 50 μm. For example, in the case of purifying a chip or the like having a size of several centimeters, it is preferable to perform a mechanical treatment with a disintegrator such as a refiner or a beater to adjust the diameter to about 50 μm.

<Chemically modified cellulose>
[Carboxymethylation]
In the present invention, when carboxymethylated cellulose is used as the modified cellulose, the carboxymethylated cellulose may be obtained by carboxymethylating the above cellulose raw material by a known method, or using a commercially available product. Is also good. In any case, it is preferable that the degree of carboxymethyl group substitution per anhydroglucose unit of cellulose is 0.01 to 0.50. An example of a method for producing such carboxymethylated cellulose includes the following method. Cellulose is used as the starting material, and 3 to 20 times by weight of water and / or lower alcohol as a solvent, specifically, water, methanol, ethanol, N-propyl alcohol, isopropyl alcohol, N-butanol, isobutanol, tertiary A single medium such as butanol, or a mixed medium of two or more kinds is used. The mixing ratio of the lower alcohol when the lower alcohol is mixed is 60 to 95% by mass. As the mercerizing agent, 0.5 to 20 moles of an alkali metal hydroxide, specifically, sodium hydroxide or potassium hydroxide, is used per anhydroglucose residue in the starting material. The bottom starting material, the solvent and the mercerizing agent are mixed, and the mercerizing treatment is performed at a reaction temperature of 0 to 70 ° C, preferably 10 to 60 ° C, and a reaction time of 15 minutes to 8 hours, preferably 30 minutes to 7 hours. Thereafter, a carboxymethylating agent is added in an amount of 0.05 to 10.0 times mol per glucose residue, the reaction temperature is 30 to 90 ° C, preferably 40 to 80 ° C, and the reaction time is 30 minutes to 10 hours, preferably 1 hour. Perform the etherification reaction for ~ 4 hours.

  In the present specification, `` carboxymethylated cellulose '', which is one type of chemically modified cellulose used for preparing chemically modified cellulose nanofibers, maintains at least a part of a fibrous shape even when dispersed in water. Means something.

[Carboxylation]
In the present invention, when a carboxylated (oxidized) cellulose is used as the modified cellulose, the carboxylated cellulose (also referred to as oxidized cellulose) can be obtained by carboxylating (oxidizing) the above-mentioned cellulose raw material by a known method. . Although not particularly limited, in the case of carboxylation, the amount of the carboxyl group is adjusted to be 0.6 to 2.0 mmol / g with respect to the absolute dry mass of the anion-modified cellulose nanofiber. It is more preferable to adjust so as to be 1.0 mmol / g to 2.0 mmol / g.

  As an example of the carboxylation (oxidation) method, a cellulose raw material is oxidized in water using an oxidizing agent in the presence of an N-oxyl compound and a compound selected from the group consisting of bromide, iodide or a mixture thereof. Methods can be mentioned. By this oxidation reaction, the primary hydroxyl group at the C6 position of the glucopyranose ring on the cellulose surface is selectively oxidized, and the cellulose fiber having an aldehyde group and a carboxyl group (—COOH) or a carboxylate group (—COO—) on the surface. Can be obtained. The concentration of cellulose during the reaction is not particularly limited, but is preferably 5% by mass or less.

  An N-oxyl compound refers to a compound that can generate a nitroxy radical. As the N-oxyl compound, any compound can be used as long as it promotes a target oxidation reaction. For example, 2,2,6,6-tetramethylpiperidine-1-oxy radical (TEMPO) and its derivative (for example, 4-hydroxy TEMPO) can be mentioned.

  The amount of the N-oxyl compound used is not particularly limited as long as it is a catalytic amount capable of oxidizing cellulose as a raw material. For example, the amount is preferably 0.01 to 10 mmol, more preferably 0.01 to 1 mmol, and still more preferably 0.05 to 0.5 mmol, based on 1 g of absolutely dried cellulose. Further, the amount is preferably about 0.1 to 4 mmol / L with respect to the reaction system.

  Bromide is a compound containing bromine, examples of which include alkali metal bromides that can dissociate and ionize in water. The iodide is a compound containing iodine, and examples thereof include an alkali metal iodide. The amount of bromide or iodide used can be selected within a range that can promote the oxidation reaction. The total amount of bromide and iodide is, for example, preferably 0.1 to 100 mmol, more preferably 0.1 to 10 mmol, and still more preferably 0.5 to 5 mmol, based on 1 g of absolutely dried cellulose.

  As the oxidizing agent, known agents can be used, and for example, halogen, hypohalous acid, halogenous acid, perhalic acid or salts thereof, halogen oxide, peroxide and the like can be used. Among them, sodium hypochlorite which is inexpensive and has a low environmental load is preferable. The amount of the oxidizing agent to be used is, for example, preferably 0.5 to 500 mmol, more preferably 0.5 to 50 mmol, still more preferably 1 to 25 mmol, and most preferably 3 to 10 mmol, based on 1 g of absolutely dried cellulose. Further, for example, 1 to 40 mol is preferable for 1 mol of the N-oxyl compound.

  The oxidation of cellulose allows the reaction to proceed efficiently even under relatively mild conditions. Therefore, the reaction temperature is preferably 4 to 40 ° C, and may be room temperature of about 15 to 30 ° C. Since a carboxyl group is generated in the cellulose as the reaction proceeds, a decrease in the pH of the reaction solution is observed. In order to allow the oxidation reaction to proceed efficiently, it is preferable to add an alkaline solution such as an aqueous solution of sodium hydroxide and maintain the pH of the reaction solution at about 8 to 12, preferably about 10 to 11. The reaction medium is preferably water because of its ease of handling and less occurrence of side reactions.

  The reaction time in the oxidation reaction can be appropriately set according to the degree of progress of the oxidation, and is usually 0.5 to 6 hours, for example, about 0.5 to 4 hours.

  Further, the oxidation reaction may be performed in two stages. For example, the oxidized cellulose obtained by filtration after the completion of the first-stage reaction is oxidized again under the same or different reaction conditions, so that the efficiency is improved without being inhibited by the salt produced as a by-product in the first-stage reaction. Can be oxidized well.

  As another example of the carboxylation (oxidation) method, there can be mentioned a method of oxidizing by contacting a gas containing ozone with a cellulose raw material. By this oxidation reaction, at least the hydroxyl groups at the 2- and 6-positions of the glucopyranose ring are oxidized, and the cellulose chain is decomposed. The ozone concentration in the gas containing ozone is preferably 50 to 250 g / m3, and more preferably 50 to 220 g / m3. The amount of ozone added to the cellulose raw material is preferably 0.1 to 30 parts by mass, more preferably 5 to 30 parts by mass, when the solid content of the cellulose raw material is 100 parts by mass. The ozone treatment temperature is preferably from 0 to 50 ° C, and more preferably from 20 to 50 ° C. The ozone treatment time is not particularly limited, but is about 1 to 360 minutes, preferably about 30 to 360 minutes. When the ozone treatment conditions are within these ranges, cellulose can be prevented from being excessively oxidized and decomposed, and the yield of oxidized cellulose is improved. After the ozone treatment, an additional oxidation treatment may be performed using an oxidizing agent. The oxidizing agent used in the re-oxidation treatment is not particularly limited, and examples thereof include chlorine compounds such as chlorine dioxide and sodium chlorite, oxygen, hydrogen peroxide, persulfuric acid, and peracetic acid. For example, these oxidizing agents may be dissolved in a polar organic solvent such as water or alcohol to prepare an oxidizing agent solution, and the cellulose material may be immersed in the solution to perform additional oxidation treatment.

  The amount of the carboxyl group of the oxidized cellulose can be adjusted by controlling the reaction conditions such as the amount of the oxidizing agent and the reaction time.

[Esterification]
Esterified cellulose can be used as the chemically modified cellulose. The cellulose is obtained by a method of mixing a powder or an aqueous solution of the phosphoric acid compound A with the above-mentioned cellulose-based material, or a method of adding an aqueous solution of the phosphoric acid compound A to a slurry of the cellulose-based material.

  Examples of the phosphoric acid compound A include phosphoric acid, polyphosphoric acid, phosphorous acid, phosphonic acid, polyphosphonic acid and esters thereof. These may be in the form of salts. Among these, compounds having a phosphate group are preferable because they are low-cost, are easy to handle, and can improve the defibration efficiency by introducing a phosphate group into cellulose of the pulp fiber. Compounds having a phosphate group include phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, trisodium phosphate, sodium pyrophosphate, sodium metaphosphate, potassium dihydrogen phosphate, dipotassium hydrogen phosphate, phosphorus Examples include tripotassium acid, potassium pyrophosphate, potassium metaphosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, triammonium phosphate, ammonium pyrophosphate, and ammonium metaphosphate. These can be used alone or in combination of two or more. Among them, phosphoric acid, sodium salt of phosphoric acid, potassium salt of phosphoric acid, phosphoric acid are preferred from the viewpoints of high efficiency of phosphate group introduction, easy defibration in the following defibration step, and easy industrial application. Are more preferred. Particularly, sodium dihydrogen phosphate and disodium hydrogen phosphate are preferable. In addition, the phosphoric acid-based compound A is preferably used as an aqueous solution because the uniformity of the reaction is increased and the efficiency of introducing a phosphate group is increased. The pH of the aqueous solution of the phosphoric acid compound A is preferably 7 or less from the viewpoint of increasing the efficiency of introducing a phosphate group, but is preferably from 3 to 7 from the viewpoint of suppressing the hydrolysis of pulp fibers.

  The following method can be mentioned as an example of the method for producing the phosphorylated cellulose. The phosphoric acid-based compound A is added to the dispersion of the cellulose-based raw material having a solid concentration of 0.1 to 10% by mass while stirring to introduce a phosphate group into the cellulose. When the cellulose-based material is 100 parts by mass, the amount of the phosphoric acid-based compound A is preferably 0.2 to 500 parts by mass, more preferably 1 to 400 parts by mass, as the amount of phosphorus element. . When the ratio of the phosphoric acid compound A is equal to or more than the lower limit, the yield of fine fibrous cellulose can be further improved. However, if the ratio exceeds the upper limit, the effect of improving the yield will level off, which is not preferable in terms of cost.

  At this time, in addition to the cellulose raw material and the phosphoric acid-based compound A, other powders or aqueous solutions of the compound B may be mixed. The compound B is not particularly limited, but a nitrogen-containing compound showing basicity is preferable. As used herein, "basic" is defined as the aqueous solution exhibiting a pink to red color in the presence of the phenolphthalein indicator, or the pH of the aqueous solution being greater than 7. The nitrogen-containing compound having basicity used in the present invention is not particularly limited as long as the effects of the present invention are exhibited, but a compound having an amino group is preferable. Examples include, but are not limited to, urea, methylamine, ethylamine, trimethylamine, triethylamine, monoethanolamine, diethanolamine, triethanolamine, pyridine, ethylenediamine, hexamethylenediamine, and the like. Among these, urea which is easy to handle at low cost is preferable. The amount of the compound B to be added is preferably 2 to 1000 parts by mass, more preferably 100 to 700 parts by mass, based on 100 parts by mass of the solid content of the cellulose raw material. The reaction temperature is preferably from 0 to 95C, more preferably from 30 to 90C. The reaction time is not particularly limited, but is about 1 to 600 minutes, more preferably 30 to 480 minutes. When the conditions of the esterification reaction are within these ranges, it is possible to prevent the cellulose from being excessively esterified and from being easily dissolved, and the yield of the phosphate esterified cellulose is improved. After dehydrating the obtained phosphated cellulose suspension, it is preferable to perform a heat treatment at 100 to 170 ° C from the viewpoint of suppressing hydrolysis of cellulose. Furthermore, it is preferable to heat at a temperature of 130 ° C. or lower, preferably 110 ° C. or lower while water is contained during the heat treatment, remove the water, and then heat-treat at 100 to 170 ° C.

  The phosphoric acid-substituted cellulose preferably has a phosphate group substitution degree per glucose unit of 0.001 to 0.40. By introducing a phosphate group substituent into cellulose, the celluloses repel each other electrically. For this reason, the cellulose into which the phosphate group has been introduced can be easily nanofibrillated. If the degree of substitution of the phosphate group per glucose unit is less than 0.001, nanofibrillation cannot be sufficiently performed. On the other hand, if the degree of substitution of the phosphate group per glucose unit is larger than 0.40, it may not be obtained as a nanofiber because of swelling or dissolution. In order to carry out defibration efficiently, it is preferable to wash the phosphoric acid-esterified cellulose-based material obtained above by boiling and then washing with cold water.

[Cationization]
As the chemically modified cellulose, cellulose obtained by further cationizing the above cellulose can be used. The cation-modified cellulose is obtained by adding a cationizing agent such as glycidyltrimethylammonium chloride, 3-chloro-2-hydroxypropyltrialkylammonium hydride or its halohydrin type to the cellulose raw material, and an alkali metal hydroxide as a catalyst ( Sodium hydroxide, potassium hydroxide, etc.) in the presence of water or an alcohol having 1 to 4 carbon atoms.

  The degree of cation substitution per glucose unit is preferably from 0.02 to 0.50. By introducing a cation substituent into the cellulose, the celluloses repel each other electrically. For this reason, the cellulose into which the cation substituent is introduced can be easily nano-defibrated. If the degree of cation substitution per glucose unit is smaller than 0.02, nanofibrillation cannot be sufficiently performed. On the other hand, if the degree of cation substitution per glucose unit is greater than 0.50, the swelling or dissolution may result in the inability to obtain a nanofiber. In order to perform defibration efficiently, the cation-modified cellulose-based material obtained above is preferably washed. The degree of cation substitution can be adjusted by the amount of the cationizing agent to be reacted and the composition ratio of water or an alcohol having 1 to 4 carbon atoms.

<Dispersion of cellulosic material>
In the process for dispersing cellulose of the present invention, the modified cellulose is usually dispersed in a solvent. The solvent is not particularly limited as long as the modified cellulose can be dispersed, and examples thereof include water, an organic solvent (for example, a hydrophilic organic solvent such as methanol), and a mixed solvent thereof. The solvent is preferably water because the cellulosic material is hydrophilic.

  The solid content concentration of the oxidized cellulose in the dispersion is usually 0.1% by weight or more, preferably 0.2% by weight or more, more preferably 0.3% by weight or more. This makes the liquid amount appropriate for the amount of the cellulose fiber raw material, which is efficient. The upper limit is usually 10% by weight or less, preferably 6% by weight or less. Thereby, fluidity can be maintained.

  Prior to the defibrating treatment, a preliminary treatment may be performed as necessary. The preliminary treatment may be performed using a mixing, stirring, emulsifying, or dispersing device such as a high-speed shear mixer.

<Polyvinyl alcohol polymer>
The polyvinyl alcohol-based polymer can be produced by polymerizing a vinyl ester-based monomer and saponifying the obtained vinyl ester-based polymer. Examples of vinyl ester monomers include, for example, vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl pivalate, vinyl versatate, and the like. Of these, vinyl acetate is preferred.

  The polyvinyl alcohol-based polymer (hereinafter, polyvinyl alcohol is sometimes referred to as PVA) used in the present invention is not particularly limited, but has a saponification degree of 70 to 100 mol%, preferably 80 to 99.8 mol%, A PVA-based polymer having a degree of 300 to 3000, preferably 500 to 2000 is suitably used.

  The degree of saponification of a PVA-based polymer indicates the ratio of units actually saponified to vinyl alcohol units among units that can be converted to vinyl alcohol units by saponification, and is measured according to JIS K6726 test method.

The degree of polymerization (Po) is a value measured according to the JIS K6726 test method. The intrinsic viscosity [η] (unit: deciliters) measured in water at 30 ° C. after re-saponifiing and purifying a PVA-based polymer. / G) by the following equation.
Po = ([η] × 103 / 8.29) (1 / 0.62)

  The polyvinyl alcohol-based polymer used in the present invention may be appropriately modified, and may be appropriately modified, such as a carboxyl-modified polyvinyl alcohol-based polymer, a silanol-modified polyvinyl alcohol-based polymer, a cation-modified polyvinyl alcohol-based polymer, and a terminal alkyl-modified polyvinyl alcohol. A system polymer or the like can be used.

  In the method for producing a composition according to the present invention, various additives, for example, a plasticizer, a surfactant, and a crosslinking agent can be blended according to the purpose and use. Here, the plasticizer is preferably a polyhydric alcohol, and examples thereof include ethylene glycol, glycerin, diglycerin, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, and trimethylolpropane. Species or a mixture of two or more can be used. Among these, ethylene glycol, glycerin and diglycerin are preferred.

<Composition>
The solvent in the composition of the present invention is preferably water, a water-soluble organic solvent, or a mixed solvent thereof. Considering the dispersibility of cellulose and cellulose nanofibers, the liquid medium is preferably water or a mixed solvent of water and a water-soluble organic solvent.

  A water-soluble organic solvent is an organic solvent that dissolves in water. Examples include methanol, ethanol, 2-propanol, butanol, glycerin, acetone, methyl ethyl ketone, 1,4-dioxane, N-methyl-2-pyrrolidone, tetrahydrofuran, N, N-dimethylformamide, N, N-dimethylacetamide, Dimethyl sulfoxide, acetonitrile, and combinations thereof. Among them, lower alcohols having 1 to 4 carbon atoms, such as methanol, ethanol, and 2-propanol, are preferable. From the viewpoint of safety and availability, methanol and ethanol are more preferable, and ethanol is still more preferable. The amount of the water-soluble organic solvent in the mixed solvent is preferably 70% by mass or less, more preferably 50% by mass or less, and even more preferably 10% by mass or more. Further, the liquid medium may contain a water-insoluble organic solvent to the extent that the effects of the invention are not impaired.

  In the present invention, when the cellulose and the polyvinyl alcohol-based polymer are mixed to obtain a mixture, the mixture contains 1 part by mass or more of the polyvinyl alcohol-based polymer with respect to 1 part by mass of the solid content of the cellulose. It is preferable from the viewpoint of improving. Further, the content is preferably 90 parts by mass or less, more preferably 70 parts by mass or less, and preferably 50 parts by mass or less, based on 1 part by mass of the solid content of cellulose. Is particularly preferred. By setting the polyvinyl alcohol-based polymer to 90 parts by mass or less with respect to 1 part by mass of the solid content of cellulose, an increase in viscosity due to the polyvinyl alcohol-based polymer can be suppressed, so that the defibration property during defibration is particularly good. It becomes.

<Method of fibrillating cellulose and polyvinyl alcohol-based polymer>
As a method of defibrating the cellulose nanofiber and the polyvinyl alcohol-based polymer, it is preferable to mix the two strongly, and as the PVA inhibits the network structure between the fibers exhibiting the viscosity of the cellulose nanofiber, the cellulose nanofiber is so degraded. It is preferable to use a combination of a device having a shearing force for making PVA and PVA uniformly dispersed.

<Apparatus used for defibration>
In the present invention, examples of an apparatus used for defibrating cellulose and a polyvinyl alcohol-based polymer include a medium stirring type disperser, a high pressure type disperser, and a rotary type disperser.

<Rotary dispersion machine>
The mixing by the rotary disperser is performed by using a rotary disperser having one or more rotary members serving as stirring means, and the peripheral speed of the blade tip of the rotary member (hereinafter referred to as “peripheral speed”) is 15 m / s. This is the processing method. The peripheral speed is 15 m / s or more, more preferably 20 m / s or more, and particularly preferably 22 m / s or more. Although there is no particular upper limit for the peripheral speed, it is preferably 100 m / s or less in view of economy and mechanical strength of the dispersing machine.

  The processing time can be appropriately set in relation to the peripheral speed, the capacity of the processing tank, the amount of processing at one time, and the like. For example, when the peripheral speed of the rotating body is 20 m / s, the capacity of the processing tank is 1 L, and 500 g of an aqueous dispersion having a solid concentration of 1% by mass is used, the processing time is about 1 to 120 minutes.

  The rotary type disperser is miniaturized by shearing force, impact force, and cavitation generated near a rotating rotating body. The rotating body is a known rotating body such as a stirring blade of various shapes, a rotating body itself, and the like.

  The rotary disperser is of a type in which the oxidized cellulose fiber to be processed is passed through the gap between the rotating body and the fixed portion to be dispersed, and the inside rotating body rotating in a certain direction and the outside of the inside rotating body are reversed. It is preferable to use a type that has an outer rotating body that rotates and that allows the oxidized cellulose fiber to be processed to pass through and be dispersed in the gap between the inner rotating body and the outer rotating body. Examples of the rotary dispersing machine include CLEARMIX of M Technique Co., Ltd., Milder of Taiyo Kiko Co., Ltd., TK Robomix of Primix Co., Ltd., and a comb-type high-speed rotary dispersing machine of Taiheiyo Kiko Co., Ltd. (Cavitron), a high-speed rotary disperser (Sharp Flow Mill) manufactured by Taiheiyo Kiko Co., Ltd., and a thin-film swirling high-speed rotary disperser (Filmix, manufactured by Primix Co., Ltd.).

  Since a high shear rate (unit: s-1) can be generated by passing through a narrow gap while rotating as described above, compared with a case of simply rotating (i.e., like a home juicer mixer, The fine processing can be performed effectively (compared to the case where mechanical means having a large gap and a low shear rate is used). The size of the void is preferably 5 mm or less, more preferably 3 mm or less, and still more preferably 2 mm or less.

  In addition, what is processed once by the rotary dispersing machine can be processed again. In the present invention, the first processing is performed in one pass, the first processing is performed, and then the second processing is performed in two passes. Performing the processing three times is referred to as three passes. The number of passes is preferably 1 to 20 passes from the viewpoint of productivity, and more preferably 1 to 10 passes.

<High-pressure disperser>
Examples of mixing using a high-pressure disperser include a high-pressure homogenizer (Invensys System Co., Ltd.), a nanomizer (Yoshida Kikai Kogyo Co., Ltd.), a microfluidizer (MFIC Corp.), and an ultimateizer system (Sugino Machine Co., Ltd.) ), A sound-less high-pressure emulsifying and dispersing apparatus (Biyaku Co., Ltd.) can be used. These devices are designed such that, when an inhaled treatment target (aqueous dispersion of oxidized cellulose fibers) is passed through a fine flow path at a high pressure, the fluid and the wall generated by the high shear force generated in the flow path and the device of the flow path The microfabrication process is performed by the impact force due to the collision of the fluids, the impact force between the fluids, or the cavitation generated when the fluid is discharged from a fine channel.

  The operating pressure is preferably 1 to 400 MPa, more preferably 5 to 350 MPa, and still more preferably 8 to 200 MPa. The high-pressure disperser treatment can be repeated 1 to 100 times. The processing (one or more processings) referred to herein means that the processing performed once by the high-pressure disperser is processed again. In the present invention, the processing performed once is performed in one pass and once. The second processing is called two passes, and the third processing in the same way is called three passes. The number of passes is preferably 1 to 20 passes, and more preferably 1 to 5 passes, from the viewpoint of productivity. As a processing method, there is also a method of performing a circulation process by directly returning the dispersion discharged from the high-pressure disperser sent from the raw material tank to the raw material tank.

<Medium stirring type dispersion machine>
As the mixing using the medium stirring type disperser, a medium stirring type disperser (media mill) can be applied. The media mill is a method of dispersing a processing liquid by flowing a medium filled in the mill by stirring or the like. For example, the following processing methods can be applied.

As a processing method,
(I) a batch processing method of injecting a processing liquid into a mill filled with media, performing processing for a predetermined time, and extracting the processing liquid;
(Ii) While the inside of the mill filled with the media is being stirred by the stirrer, the liquid to be treated in another tank is continuously supplied into the mill by a pump or the like, and the dispersed treatment liquid is returned to the original tank. Recirculation method,
(Iii) A dispersion treatment method by a pass method or the like in which all of the treatment liquid is received in another tank. The dispersion speed at the time of the dispersion treatment can be adjusted by the media particle size and filling rate, the stirring speed of the media mill, the supply speed, and the like.

  Examples of the media mill include a bead mill, a sand mill, a ball mill, and the like. Specifically, Visco Mill (manufactured by Imex Co., Ltd.), Tower Mill, DCP Superflow, Cosmo (manufactured by Nippon Eirich Co., Ltd.), Star Mill (Ashizawa)・ Finetech Co., Ltd.), Ultra Apex Mill (Kotobuki Kogyo Co., Ltd.), Pico Mill (Asada Tekko Co., Ltd.), SC Mill, MSC Mill, Attritor (Mitsui Mining Co., Ltd.) Known media mills.

  Examples of the material of the medium include high-hardness metals such as steel and chromium alloys, high-hardness ceramics such as alumina, zirconia, zircon, and titania, glass, and high-molecular materials such as ultrahigh molecular weight polyethylene and nylon.

  In the present invention, it is preferable to further add a polyvinyl alcohol-based polymer to a dispersion containing cellulose nanofibers obtained by defibration and a polyvinyl alcohol-based polymer. When the polyvinyl alcohol-based polymer is added, it is preferable to add the polyvinyl alcohol-based polymer so as to contain 1 part by mass or more of the polyvinyl alcohol-based polymer per 1 part by mass of the solid content of the cellulose nanofiber. In addition, it is preferable that the total amount of the polyvinyl alcohol-based polymer is added so as to contain 200 parts by mass or less with respect to 1 part by mass of the solid content of the cellulose nanofiber. It is particularly preferable to add so as to contain 120 parts by mass or less. By adding so that the total amount of the polyvinyl alcohol-based polymer is 200 parts by mass or less based on 1 part by mass of the solid content of the cellulose nanofiber, the miscibility of the cellulose nanofiber and the polyvinyl alcohol-based polymer obtained by the present invention is obtained. Is good, and an effect that defects are less likely to occur when a film or the like is formed is obtained.

  Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto.

<Production Example 1>
5.00 g (absolutely dry) of bleached unbeaten kraft pulp (85% whiteness) derived from conifers 39 mg of TEMPO (Sigma Aldrich) (0.05 mmol per 1 g of absolute dry cellulose) and 514 mg of sodium bromide (absolute dry) (1.0 mmol per 1 g of cellulose) was added to 500 ml of an aqueous solution, and the mixture was stirred until the pulp was uniformly dispersed. An aqueous solution of sodium hypochlorite was added to the reaction system so that the amount of sodium hypochlorite became 6.0 mmol / g, and an oxidation reaction was started. During the reaction, the pH in the system decreased, but the pH was adjusted to 10 by sequentially adding a 3M aqueous sodium hydroxide solution. The reaction was terminated when sodium hypochlorite was consumed and the pH in the system stopped changing. The mixture after the reaction was filtered through a glass filter to separate the pulp, and the pulp was sufficiently washed with water to obtain oxidized pulp (carboxylated cellulose). The pulp yield at this time was 90%, the time required for the oxidation reaction was 90 minutes, and the amount of carboxyl groups was 1.6 mmol / g. This was adjusted to 1.0% (w / v) with water.

<Measurement>
In the examples, each parameter was measured as follows.

(Measurement of carboxyl group content)
60 mL of a 0.5% by mass slurry (aqueous dispersion) of carboxylated cellulose was prepared, and a 0.1 M aqueous hydrochloric acid solution was added to adjust the pH to 2.5. The electrical conductivity was measured until the value became, and the amount of sodium hydroxide consumed in the neutralization stage of the weak acid having a gradual change in electrical conductivity (a) was calculated using the following formula: the amount of carboxyl groups [mmol / g carboxylated cellulose] = a [mL] × 0.05 / mass of carboxylated cellulose [g].

(Method of measuring average fiber diameter and aspect ratio)
The average fiber diameter and average fiber length of the carboxymethylated cellulose fibers are determined using an atomic force microscope (AFM) when the diameter is 20 nm or less, and using a field emission scanning electron microscope (FE-SEM) when the diameter is 20 nm or more. Analysis was performed on 200 randomly selected fibers.

<Example 1>
5. A 14% by mass solution of the carboxylated cellulose produced in Production Example 1 and a PVA-based polymer (JF-17 manufactured by Nippon Bi-Poval Co., Ltd.) was mixed with water to a solid content ratio of 1:10. It was adjusted to 4% (w / v) and treated three times with an ultra-high pressure homogenizer (20 ° C., 150 MPa) to obtain an aqueous dispersion containing cellulose nanofibers and a polyvinyl alcohol-based polymer. The obtained aqueous dispersion is diluted with water so that the cellulose nanofibers are 1.3% by mass and the solid content is 15.2% with respect to the polyvinyl alcohol, and then the solid polyvinyl alcohol (Nippon vinegar Bi-Poval) is diluted. JF-17) was added and stirred at 90 ° C. for 1 hour with a three-one motor. After stirring, the mixture was allowed to stand in a constant-temperature dryer at 90 ° C. for 2 hours. The B-type viscosity of the aqueous dispersion at 90 ° C. and 60 rpm was 4059 mPa · s.

<Example 2>
9. A 14% by mass solution of the carboxylated cellulose produced in Production Example 1 and a PVA-based polymer (JF-17, manufactured by Nippon Bi-Povar Co., Ltd.) was mixed with water so as to have a solid content ratio of 1:30. It was adjusted to 9% (w / v) and treated three times with an ultra-high pressure homogenizer (20 ° C., 150 MPa) to obtain an aqueous dispersion containing cellulose nanofibers and a polyvinyl alcohol-based polymer. The obtained aqueous dispersion is diluted with water so that the cellulose nanofibers are 1.3% by mass and the solid content is 15.2% with respect to the polyvinyl alcohol, and then the solid polyvinyl alcohol (Nippon vinegar Bi-Poval) is diluted. JF-17) was added and stirred at 90 ° C. for 1 hour with a three-one motor. After stirring, the mixture was allowed to stand in a constant-temperature dryer at 90 ° C. for 2 hours. The B-type viscosity of the aqueous dispersion at 90 ° C. and 60 rpm was 2369 mPa · s.

<Comparative Example 1>
The carboxylated cellulose produced in Production Example 1 was treated three times with an ultra-high pressure homogenizer (20 ° C., 150 MPa) to obtain a cellulose nanofiber dispersion. The resulting cellulose nanofiber dispersion is diluted with water so that the cellulose nanofibers are 1.3% by mass and the solid content is 15.2% with respect to polyvinyl alcohol, and then solid polyvinyl alcohol is added. The mixture was stirred at 90 ° C. for 1 hour with a motor. After stirring, the mixture was allowed to stand in a constant-temperature dryer at 90 ° C. for 2 hours. The B-type viscosity of the aqueous dispersion at 90 ° C. and 60 rpm was 5549 mPa · s.

[Production method of film and evaluation of defects]
60 g of the 10% by mass aqueous dispersion prepared in Production Examples 1 and 2 and Comparative Example 1 was put into a 9 cm-diameter plastic petri dish, and air-dried at room temperature to form a composite film of cellulose nanofiber and PVA having a thickness of 30 μm. Obtained. The foreign-state defects of these films were visually observed and evaluated.

〇: No defect in the form of foreign matter is observed. ×: A slight defect in the form of foreign matter is observed.

  From the results in Table 1, the compositions containing the cellulose nanofibers and the polyvinyl alcohol-based polymer of Examples 1 and 2 have a low viscosity when compared with Comparative Example 1 at the same concentration (excellent in handling properties). It can be seen that foreign matter-like defects hardly occur when formed into a film.

Claims (6)

(A) a step of mixing cellulose and a polyvinyl alcohol-based polymer to obtain a mixture;
(B) a step of fibrillating the mixture to obtain a dispersion containing cellulose nanofibers and a polyvinyl alcohol-based polymer;
A method for producing a dispersion containing cellulose nanofibers and a polyvinyl alcohol-based polymer, comprising: The method according to claim 1, wherein the defibration is performed using a medium stirring type disperser, a high-pressure disperser, or a rotary disperser. The method according to claim 1, wherein a polyvinyl alcohol-based polymer is further added to the dispersion containing the cellulose nanofibers and the polyvinyl alcohol-based polymer. The method according to any one of claims 1 to 3, wherein the defibration is a treatment using an operating pressure of 1 MPa to 400 MPa using a high-pressure disperser. The method according to any one of claims 1 to 4, wherein the mixture contains 1 to 90 parts by mass of a polyvinyl alcohol-based polymer with respect to cellulose. The method according to any one of claims 1 to 5, wherein the cellulose is a chemically modified cellulose.