WO2022191190A1

WO2022191190A1 - Method for producing coating of cellulose nano-fibers and/or chitin nano-fibers

Info

Publication number: WO2022191190A1
Application number: PCT/JP2022/010017
Authority: WO
Inventors: 昌浩森田; 啓吾渡部; 丈史中谷
Original assignee: 日本製紙株式会社
Priority date: 2021-03-09
Filing date: 2022-03-08
Publication date: 2022-09-15
Also published as: JP7367264B2; JPWO2022191190A1

Abstract

Provided is a method for forming a coating of anionic or cationic cellulose nano-fibers or chitin nano-fibers which are less uneven and uniform on an electroconductive substrate. A liquid dispersion of anionic cellulose nano-fibers or a liquid dispersion of cationic cellulose nano-fibers and/or chitin nano-fibers, an electroconductive substrate that is an object to be coated, and an electrode are placed in an electrolysis bath, an electric current is passed using the electroconductive substrate as a positive electrode when the anionic cellulose nano-fibers are used and using the electroconductive substrate as a negative electrode when the cationic cellulose nano-fibers and/or the chitin nano-fibers are used, and the nano-fibers are electrophoresed to the electroconductive substrate to coat the electroconductive substrate with the nano-fibers.

Description

Method for producing cellulose nanofiber and/or chitin nanofiber coating

The present invention relates to a method for producing a coating of cellulose nanofibers and/or chitin nanofibers. More particularly, it relates to a method of depositing anionic cellulose nanofibers, or cationic cellulose nanofibers and/or tin nanofibers on a conductive substrate to form a coating using the principle of electrophoresis.

Cellulose nanofibers obtained by introducing anionic or cationic groups into cellulose and defibrating using the charge repulsion of these introduced groups have a very fine fiber diameter and are generally It has been extensively studied because of its characteristics such as high homogeneity, various functionalities based on the introduced groups, and high strength. For example, as an anionic cellulose nanofiber obtained by introducing an anionic group into cellulose and defibrating it, some of the hydroxyl groups of cellulose are oxidized to carboxyl groups using the surface oxidation reaction of cellulose by an N-oxyl compound. oxidized cellulose nanofibers obtained by fibrillating and carboxymethylated cellulose nanofibers having a degree of carboxymethyl substitution of 0.01 to 0.30 and an average fiber diameter of 3 to 500 nm have been reported (patent References 1 and 2).

In addition, it has also been reported that chitin nanofibers are produced by a simple method from the shells and shells of crustaceans such as shrimp and crabs, which are usually discarded, and applied to coating compositions and the like (Patent Document 3).

Japanese Unexamined Patent Application Publication No. 2008-1728 WO2014/088072 WO2010/073758

These nanofibers have a long fiber length in spite of their small fiber diameter, generally have high elasticity, and exhibit high viscosity when dispersed. Methods of forming a nanofiber coating on a substrate using these nanofiber dispersions include a method of applying a nanofiber dispersion onto a substrate with a bar coater, and a method of applying a nanofiber dispersion onto a substrate. A method of spraying on the material can be considered. In these methods, the nanofibers are deformed and applied onto the substrate by applying a shearing force to the nanofibers in the dispersion. However, since nanofibers have high elasticity, a force is exerted to restore the original shape after coating, and unevenness tends to occur in the finally obtained nanofiber coating. In addition, the dispersion of nanofibers has pseudoplasticity, and the viscosity decreases while a shearing force is applied, but the viscosity recovers when the shearing force is released after being applied to the substrate. Leveling after application cannot be expected. Furthermore, the nanofiber dispersion has low affinity for metals and hydrophobic materials and poor wettability with respect to these substrates. Cheap. Therefore, it has been difficult to evenly coat the substrate with the above nanofibers. An object of the present invention is to provide a method capable of forming a uniform nanofiber coating on a substrate such as a metal with less unevenness.

As a result of intensive studies on the above object, the present inventors have found that by using the principle of electrophoresis, uniform cellulose nanofibers and/or chitin nanofibers with little unevenness can be produced on a conductive substrate such as metal. It has been found that coatings can be formed. Specifically, a dispersion of anionic or cationic cellulose nanofibers having an anionic or cationic group, a dispersion of chitin nanofibers, or a dispersion containing cationic cellulose nanofibers and chitin nanofibers. prepare. A conductive base material, which will be the base material for coating (object to be coated), is prepared and immersed in the dispersion. When anionic cellulose nanofibers are used, the conductive substrate is used as an anode, and when cationic cellulose nanofibers and/or chitin nanofibers are used, the conductive substrate is used as a cathode. This causes these nanofibers to migrate and deposit on the conductive substrate by the principle of electrophoresis, forming a coating of these nanofibers on the conductive substrate. As a result, the present inventors have found that a uniform nanofiber coating can be formed on a conductive substrate with little unevenness without being affected by the high elasticity of nanofibers and the pseudoplasticity of a nanofiber dispersion. In addition, the inventors have found that the nanofibers can be uniformly coated without being repelled because the nanofibers are densely adhered to the conductive substrate by electricity. The present invention includes the following.
[1] Putting a dispersion of anionic cellulose nanofibers in an electrolytic cell,
immersing a conductive base material and an electrode in the dispersion in the electrolytic bath; and energizing the conductive base material as an anode and the electrode as a cathode to transfer the anionic cellulose nanofibers to the conductive base material. A method of making a coating of anionic cellulose nanofibers, comprising coating the conductive substrate with the anionic cellulose nanofibers by electrophoresis to a substrate.
[2] placing a dispersion of cationic cellulose nanofibers and/or chitin nanofibers in an electrolytic cell;
immersing a conductive base material and an electrode in the dispersion in the electrolytic bath; and energizing the conductive base material as a cathode and the electrode as an anode to obtain the cationic cellulose nanofibers and/or chitin nanofibers. to the conductive substrate to coat the conductive substrate with the cationic cellulose nanofibers and/or chitin nanofibers. coating manufacturing method.
[3] The method according to [1], wherein the anionic cellulose nanofibers are oxidized cellulose nanofibers having carboxyl groups and/or carboxylate groups.
[4] The method according to [1], wherein the anionic cellulose nanofibers are carboxyalkylated cellulose nanofibers.
[5] The method according to [1], wherein the anionic cellulose nanofibers are phosphorylated cellulose nanofibers.
[6] The method according to [1], wherein the anionic cellulose nanofibers are sulfate-esterified cellulose nanofibers.
[7] The method according to any one of [1] to [6], wherein the conductive substrate is metal or carbon.

According to the present invention, anionic or cationic cellulose nanofibers or chitin nanofibers that form a dispersion with high elasticity and high pseudoplasticity are used to form a uniform coating with less unevenness and less peeling on a conductive substrate. will be able to form Since these nanofibers have high elasticity, when bar coating or spray coating is used, a force of returning to the original shape acts, and unevenness tends to occur in the finally obtained nanofiber coating. In addition, the dispersion of nanofibers has pseudoplasticity, and the viscosity decreases while a shearing force is applied. It was difficult to level (smooth) afterward, and the resulting irregularities tended to remain. Furthermore, the nanofiber dispersion has a low affinity for metals and hydrophobic materials, and poor wettability with respect to these substrates. The problem was that it was easy. On the other hand, in the present invention, the principle of electrophoresis is used to move the nanofibers to the conductive substrate and deposit/adhere them electrically. A coating can be formed thereon. This provides a uniform coating with few irregularities and wrinkles. In addition, since the nanofibers are tightly adhered to the base material by electricity, the nanofibers are not repelled on the base material and can be uniformly coated, and the problem of peeling of the coating is less likely to occur.

The present invention is a method for producing a coating of cellulose nanofibers (hereinafter, cellulose nanofibers will be referred to as “CNF”) or chitin nanofibers. A method comprising depositing anionic or cationic CNF or chitin nanofibers thereon to form a coating. In the present specification, anionic CNF, cationic CNF and chitin nanofibers may be collectively referred to simply as "nanofibers" or "NF". In the method of the present invention, first, the NF dispersion is placed in an electrolytic cell. Next, a conductive substrate and an electrode are immersed in this dispersion, and when anionic CNF is used, the conductive substrate is used as the anode, and when cationic CNF or chitin NF is used, the conductive group The material is used as a cathode and an electric current is applied. When energized, the NFs electrophoretically migrate toward the conductive substrate and deposit on the conductive substrate, forming a gel-like coating of NFs on the conductive substrate. This gel coating may be dried if desired. Drying may be performed using a normal method such as hot air drying after removing the conductive substrate having the gel-like coating from the electrolytic bath.

(Nanofiber)
In the present invention, nanofibers (NF) refer to anionic CNF, cationic CNF, or chitin NF having an average fiber diameter of less than 1 μm. The average fiber diameter is preferably about 3 nm to 500 nm, more preferably about 3 nm to 150 nm, still more preferably about 3 nm to 20 nm. The aspect ratio is 30 or more, preferably 50 or more, more preferably 100 or more. Although the upper limit of the aspect ratio is not limited, it is about 500 or less. The average fiber diameter and average fiber length of NF were randomly selected using an atomic force microscope (AFM) when the diameter was less than 20 nm and a field emission scanning electron microscope (FE-SEM) when the diameter was 20 nm or more. It can be measured by analyzing 200 fibers and calculating the average. Also, the aspect ratio can be calculated by the following formula:
Aspect ratio = average fiber length/average fiber diameter.

(Anionic CNF)
Anionic CNF is NF in which an anionic group is introduced into the molecular chain of cellulose. Anionic CNF can be obtained by defibrating anionic cellulose obtained by introducing an anionic group into the pyranose ring of cellulose so as to have an average fiber diameter of less than 1 μm.

The type of cellulose used as a raw material for anionic cellulose is not particularly limited. For example, bleached or unbleached mechanical pulp (e.g., thermomechanical pulp (TMP), groundwood pulp) and chemical pulp (e.g., sulfite pulp) made from softwood, hardwood, cotton, straw, bamboo, hemp, jute, kenaf, etc. , kraft pulp), dissolving pulp, regenerated cellulose, fine cellulose, microcrystalline cellulose excluding non-crystalline regions, and the like, and any of these can be used as the cellulose raw material.

An anionic cellulose can be produced by introducing an anionic group into such a cellulose raw material. The method for introducing the anionic group is not particularly limited, but examples include a method of directly oxidizing the hydroxyl group of the pyranose ring of cellulose to a carboxyl group, or a method of introducing an anionic group by an esterification reaction at the hydroxyl group portion of the pyranose ring. Anionic CNF can be obtained by fibrillating the obtained anionic cellulose so as to have an average fiber diameter of less than 1 μm. The defibration method is not particularly limited, and a known defibration device such as a high speed rotation type, a colloid mill type, a high pressure type, a roll mill type, and an ultrasonic type may be used. Among them, it is preferable to use a wet high-pressure or ultrahigh-pressure homogenizer.

(oxidized CNF)
An example of anionic CNF is oxidized CNF having a carboxyl group and/or a carboxylate group. As used herein, a carboxyl group refers to -COOH (acid form) and -COOM (metal salt form) (wherein M is a metal ion), and a carboxylate group refers to -COO ^- . Oxidized CNF having a carboxyl group and/or a carboxylate group (also referred to herein simply as "oxidized CNF") is obtained by obtaining oxidized cellulose using a known method of oxidizing the hydroxyl group of the pyranose ring of cellulose to a carboxyl group. and then fibrillating. As a method of oxidizing cellulose, for example, oxidation is performed in the presence of an N-oxyl compound such as 2,2,6,6-tetramethylpiperidine-1-oxy radical (TEMPO) and bromide and/or iodide. Examples include a method of oxidizing cellulose in water using an agent, and a method of oxidizing cellulose by bringing it into contact with a cellulose raw material using an ozone-containing gas as an oxidizing agent.

The total amount of carboxyl groups and carboxylate groups in the oxidized CNF is preferably 0.4 to 3.0 mmol/g, more preferably 0.6 to 2.0 mmol/g, relative to the absolute dry mass of the oxidized CNF. 0 to 2.0 mmol/g, more preferably 1.1 to 2.0 mmol/g. The amount of carboxyl groups and carboxylate groups in oxidized CNF can be adjusted by controlling reaction conditions such as the amount of oxidizing agent added and reaction time. The amount of carboxyl groups and carboxylate groups can be measured by the following methods:
Prepare 60 ml of 0.5% by mass slurry (aqueous dispersion) of oxidized CNF, add 0.1 M hydrochloric acid aqueous solution to adjust the pH to 2.5, and then drop 0.05 N sodium hydroxide aqueous solution to adjust the pH to 11. The electrical conductivity is measured until it becomes , and the amount of sodium hydroxide (a) consumed in the neutralization step of the weak acid, in which the change in electrical conductivity is gradual, is calculated using the following formula:
Carboxyl and carboxylate group amount [mmol/g oxidized CNF]=a [ml]×0.05/oxidized CNF mass [g].

(Carboxyalkylated CNF)
An example of an anionic CNF is a carboxyalkylated CNF having a carboxyalkyl group. As used herein, a carboxyalkyl group refers to -RCOOH (acid form) and -RCOOM (metal salt form). Here, R is an alkylene group such as a methylene group or ethylene group, and M is a metal ion. As the carboxyalkylated CNF having a carboxyalkyl group, carboxymethylated CNF having a carboxymethyl group in which R is a methylene group is most preferred (hereinafter "carboxymethyl" is referred to as "CM"). Carboxyalkylated CNF is obtained by obtaining carboxyalkylated cellulose using a known method of treating a cellulose raw material with a mercerizing agent and then treating it with a carboxyalkylating agent to introduce a carboxyalkyl group, and then defibrating it. Obtainable.

The degree of carboxyalkyl substitution per anhydroglucose unit of the carboxyalkylated CNF is preferably less than 0.40. Moreover, the lower limit of the degree of carboxyalkyl substitution is preferably 0.01 or more. Considering the workability, the degree of substitution is particularly preferably 0.02 or more and 0.35 or less, more preferably 0.10 or more and 0.35 or less, and 0.15 or more and 0.35 or less. is more preferable, and more preferably 0.15 or more and 0.30 or less. The anhydroglucose unit means an individual anhydroglucose (glucose residue) constituting cellulose, and the degree of carboxyalkyl substitution refers to the hydroxyl group (—OH) in the glucose residue constituting cellulose. The ratio of those substituted by groups (-ORCOOH or -ORCOOM) (the number of carboxyalkyl groups per glucose residue) is shown. The degree of carboxyalkyl substitution can be adjusted by controlling reaction conditions such as the amount of mercerizing agent and reaction time. The degree of CM substitution per glucose unit can be measured by the following method:
About 2.0 g of CM-modified CNF (absolute dry) is precisely weighed and placed in a 300 mL conical flask with a common stopper. Add 100 mL of a liquid obtained by adding 100 mL of special grade concentrated nitric acid to 900 mL of methanol and shake for 3 hours to convert the salt-type CM-CNF to the hydrogen-type CM-CNF. 1.5 g to 2.0 g of hydrogen-type CM-CNF (absolute dry) is accurately weighed and placed in a 300 mL conical flask equipped with a common stopper. Hydrogen-type CM-CNF is wetted with 15 mL of 80 mass % methanol, 100 mL of 0.1N NaOH is added, and shaken at room temperature for 3 hours. Excess NaOH is back-titrated with 0.1 N H ₂ SO ₄ using phenolphthalein as an indicator. The degree of CM substitution (DS) is calculated by the following formula:
A = [(100 × F'-(0.1 N H ₂ SO ₄ ) (mL) × F) × 0.1] / (absolute dry mass of hydrogen-type CM-CNF (g))
DS = 0.162 x A/(1 - 0.058 x A)
A: Amount of 1N NaOH (mL) required to neutralize 1 g of hydrogen-type CM-CNF
F: factor of 0.1N H ₂ SO ₄ F': factor of 0.1N NaOH The degree of substitution of carboxyalkyl groups other than CM groups can also be measured in the same manner as above.

(Phosphate esterified CNF)
Phosphate-esterified CNF can be mentioned as an example of anionic CNF. Phosphate-esterified CNF can be obtained by mixing the above-mentioned cellulose raw material with a phosphoric acid compound powder or aqueous solution, or by adding an aqueous solution of a phosphoric acid compound to a slurry of the cellulose raw material. It can be obtained by introducing an acid-based group into cellulose to obtain phosphate-esterified cellulose and defibrating it. Phosphoric acid compounds include phosphoric acid, polyphosphoric acid, phosphorous acid, hypophosphorous acid, phosphonic acid, polyphosphonic acid, and esters or salts thereof. Specifically, for example, but not limited to, phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, trisodium phosphate, sodium phosphite, potassium phosphite, sodium hypophosphite, potassium phosphite, sodium pyrophosphate, sodium metaphosphate, potassium dihydrogen phosphate, dipotassium hydrogen phosphate, tripotassium phosphate, potassium pyrophosphate, potassium metaphosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, triammonium phosphate, ammonium pyrophosphate, ammonium metaphosphate and the like. A phosphoric acid group derived from a phosphoric acid compound can be introduced into cellulose by using one or more of these in combination. As used herein, the phosphoric acid group derived from a phosphoric acid compound includes a phosphoric acid group, a phosphorous acid group, a hypophosphorous acid group, a pyrophosphate group, a metaphosphoric acid group, a polyphosphoric acid group, a phosphonic acid group, and polyphosphonic acid groups. Phosphate-esterified cellulose and phosphate-esterified CNF include those in which one or more of these phosphoric acid groups are introduced into the molecular chain of cellulose. When the cellulose raw material is reacted with the phosphoric acid compound, it is desirable to use the phosphoric acid compound in the form of an aqueous solution because the reaction can proceed uniformly and the efficiency of introduction of the above group increases. The pH is preferably pH 3-7. A nitrogen-containing compound such as urea may also be added.

The degree of substitution of a phosphate group per glucose unit in the phosphorylated CNF (hereinafter simply referred to as "degree of phosphate group substitution") is preferably 0.001 or more and less than 0.40. The degree of phosphate group substitution per glucose unit can be measured by the following method:
A slurry of phosphorylated CNF having a solids content of 0.2% by weight is prepared. To the slurry, 1/10 by volume of a strongly acidic ion exchange resin (Amberjet 1024; manufactured by Organo, conditioned) was added, shaken for 1 hour, and then poured onto a mesh with an opening of 90 μm to pour the resin. and the slurry are separated to obtain hydrogen-type phosphate-esterified CNF. Next, while adding 50 μL of 0.1N sodium hydroxide aqueous solution to the slurry after the treatment with the ion-exchange resin once every 30 seconds, the change in the electrical conductivity of the slurry is measured. Among the measurement results, by dividing the alkali amount (mmol) required in the region where the electrical conductivity sharply decreases by the solid content (g) in the slurry to be titrated, the hydrogen-type phosphate-esterified CNF per 1 g A phosphate group amount (mmol/g) is calculated. Furthermore, the degree of phosphate group substitution (DS) per glucose unit of the phosphorylated CNF is calculated by the following formula:
DS = 0.162 x A/(1 - 0.079 x A)
A: Phosphate group amount (mmol/g) per 1 g of hydrogen-type phosphate-esterified CNF.

(Sulfuric acid esterified CNF)
An example of anionic CNF is sulfated CNF. Sulfated CNF can be obtained by reacting the above-described cellulose raw material with a sulfuric acid-based compound to introduce a sulfuric acid-based group derived from the sulfuric acid-based compound into cellulose to obtain sulfated cellulose, which is defibrated. can be done. Examples of sulfuric acid compounds include sulfuric acid, sulfamic acid, chlorosulfonic acid, sulfur trioxide, and esters or salts thereof. Among these, sulfamic acid is preferably used because cellulose has low solubility and low acidity.

For example, when sulfamic acid is used as the sulfuric acid compound, the amount of sulfamic acid used can be appropriately adjusted in consideration of the amount of anionic groups to be introduced into the cellulose chain. For example, it can be used in an amount of preferably 0.01 to 50 mol, more preferably 0.1 to 3.0 mol, per 1 mol of glucose units in the cellulose molecule.

The amount of sulfate-based groups per glucose unit in the sulfated CNF (hereinafter simply referred to as "amount of sulfate groups") is preferably 0.1 to 3.0 mmol/g. The amount of sulfate groups per glucose unit can be measured by the following method:
The aqueous dispersion of sulfated CNF is subjected to solvent substitution in the order of ethanol and t-butanol, and then freeze-dried. 15 ml of ethanol and 5 ml of water are added to 200 mg of the obtained sample, and the mixture is stirred for 30 minutes. After that, 10 ml of 0.5N sodium hydroxide aqueous solution is added, and the mixture is stirred at 70° C. for 30 minutes and further stirred at 30° C. for 24 hours. Then, add phenolphthalein as an indicator, titrate with hydrochloric acid, and calculate using the following formula:
Sulfate group amount [mmol/g sample]=(5−(0.1×hydrochloric acid titration amount [ml]×2))/0.2.

(Cationic CNF)
Cationic CNF is cationic CNF in which a cationic group is introduced into the molecular chain of cellulose. Cationic CNF can be obtained by defibrating cationic cellulose obtained by introducing a cationic group into the pyranose ring of cellulose so as to have an average fiber diameter of less than 1 μm.

The type of cellulose used as a raw material for cationic cellulose is not particularly limited, and is the same as that described in the anionic CNF column. In addition, the method of fibrillating cationic cellulose to make cationic CNF is not particularly limited, and is the same as that described in the section on anionic CNF.

Cationic cellulose is prepared by adding a cationizing agent such as glycidyltrimethylammonium chloride, 3-chloro-2-hydroxypropyltrialkylammonium hydrate or its halohydrin type to the oxidized cellulose, and an alkali metal hydroxide (sodium hydroxide , potassium hydroxide, etc.) can be obtained by a known method of reacting in the presence of water or an alcohol having 1 to 4 carbon atoms, and the resulting cationic cellulose is fibrillated to obtain cationic CNF. can be done.

The degree of cation substitution per glucose unit in the cationic CNF is preferably 0.02-0.50. The degree of cation substitution can be adjusted by adjusting the amount of the cationizing agent to be reacted and the composition ratio of water or alcohol having 1 to 4 carbon atoms. The degree of cation substitution per glucose unit can be measured by the following method:
After drying the cationic CNF, the nitrogen content was measured using a total nitrogen analyzer (TN-10 manufactured by Mitsubishi Chemical Corporation), and the degree of cation substitution (mole of substituent per 1 mol of anhydroglucose unit) was determined by the following formula. Calculate the mean of the numbers):
Degree of cation substitution = (162 × N) / (1-151.6 × N)
N: nitrogen content.

(Chitin NF)
Chitin NF can be mentioned as cationic NF other than cationic CNF. Chitin is an aminopolysaccharide in which N-acetylglucosamine is linked in a chain form, and is industrially obtained from shrimp and crab shells and the like. Chitin derived from organisms such as shrimp and crab usually has a matrix such as protein and calcium carbonate around it, and is subjected to treatment to remove these matrices. A known alkali treatment method, proteolytic enzyme method, or the like can be used for the deproteinization treatment. Known methods such as acid treatment and ethylenediaminetetraacetic acid treatment can be used to remove ash such as calcium carbonate. Chitin NF can be obtained by fibrillating bio-derived chitin that has undergone deproteinization and deashing treatment using an apparatus such as a stone grinder or a high-pressure homogenizer. A method for producing chitin NF is described, for example, in WO2010/073758.

(NF dispersion)
A dispersion of anionic or cationic CNF or chitin NF as described above is prepared and placed in an electrolytic cell. The dispersion medium of the dispersion liquid is preferably water, but may contain a water-soluble organic solvent as long as it does not interfere with electrophoresis of NF. Examples of water-soluble organic solvents include methanol, ethanol, isopropanol, 2-propanol, butanol, glycerin, acetone, methyl ethyl ketone, 1,4-dioxane, N-methyl-2-pyrrolidone, tetrahydrofuran, N,N-dimethylformamide, N,N-dimethylacetamide, dimethylsulfoxide, acetonitrile, ethylene glycol, and combinations thereof. The proportion of water in the dispersion medium is preferably 80% by mass or more, more preferably 90% by mass or more, still more preferably 95% by mass or more, and most preferably 100% by mass (all water).

The solid content of NF in the dispersion is preferably 0.05 to 10.0% by mass, more preferably 0.1 to 7.5% by mass, in order to favorably advance electrophoresis during subsequent energization. .1 to 5.0% by mass is more preferable, and 0.1 to 3.0% by mass is more preferable.

The dispersion liquid preferably consists of water, which is a dispersion medium, and NF, but may contain substances other than NF as long as it does not interfere with the electrophoresis of NF. Examples of such substances include anionic polymers such as acrylic resins, carboxymethylcellulose, and uronic acid when anionic CNF is used. Moreover, when using cationic CNF and/or chitin NF, an alkylamine, an amine compound, a cationic polymer, etc. are mentioned. In addition, polyethylene glycol, silane coupling agents, carbodiimide group-containing polymers, and the like can be used in any case of anionic CNF, cationic CNF, and chitin NF. Electrolytes such as zinc chloride, aluminum chloride, magnesium chloride, sodium chloride, sodium hydroxide, acetic acid, and carbonic acid may be added to increase the electrical conductivity of the dispersion. The ratio of the solid content of NF to the total solid content in the dispersion is preferably 50% or more, more preferably 70% or more, still more preferably 80% or more, still more preferably 90% or more, further preferably 95% or more.

There are no particular restrictions on the electrolytic bath in which the dispersion liquid is placed, and any one that can cause electrophoresis of NF by energizing can be used. For example, an electrolytic bath used for electrodeposition coating can be used.

(Conductive base material, electrode)
After the dispersion of NF described above is placed in the electrolytic bath, the conductive substrate and the electrodes are immersed in the dispersion in the electrolytic bath. A conductive substrate is a substrate for forming a coating of NF thereon. The conductive substrate is not particularly limited as long as it is made of a material having conductivity. Examples include metals such as aluminum, copper, iron, zinc, titanium, nickel, lead, silver, platinum, tungsten, bismuth, stainless steel, brass, chromium, alloys thereof, or carbon. Moreover, it may be a material imparted with conductivity by containing one or more of these (for example, rubber to which carbon black is added).

The electrode is used as a counter electrode of the conductive base material when energized, and the type is not particularly limited. For example, an electrode or the like used as a counter electrode for an object to be coated in the field of electrodeposition coating can be used.

(energization)
After the conductive substrate and the electrodes are immersed in the NF dispersion, the NF is electrophoresed by energizing to form a NF coating on the conductive substrate. In the case of energization, when using anionic CNF, the conductive base material is used as the anode, and the electrode is used as the cathode. Moreover, when using cationic CNF and/or chitin NF, let a conductive base material be a cathode and let an electrode be an anode. This causes the NFs to migrate to and deposit on the conductive substrate, coating the conductive substrate.

The conditions for energization are not particularly limited, and may be appropriately adjusted according to the desired thickness of the coating. For example, the voltage range is preferably about 0.1 to 1000V, more preferably about 1 to 500V, more preferably about 5 to 500V, even more preferably about 5 to 100V, and even more preferably about 5 to 50V. The current density range is preferably about 0.1 to 10,000 mA/cm ² , more preferably about 1 to 10,000 mA/cm ² . The energization time is preferably about 1 to 100 minutes, more preferably about 2 to 60 minutes. In addition, if it is desired to increase the density of NF in the gel-like NF coating on the conductive substrate, the voltage during energization may be set higher within the above range, or the voltage may be increased during energization. You can change it higher. For example, such a high voltage is not particularly limited, but a voltage of about 50 to 1000 V, more preferably about 100 to 500 V can be mentioned. can be held for about 1 to 5 minutes.

After energization in the NF dispersion, the conductive substrate is placed in an electrolytic bath containing deionized water and allowed to stand while being energized for a certain period of time to wash the NF coating on the conductive substrate. you can go The voltage range in the energization during cleaning is not particularly limited, but is preferably about 0.1 to 1000 V, more preferably about 10 to 500 V, and the energization time is preferably about 1 to 100 minutes. , more preferably about 5 to 60 minutes.

(NF coating)
The energization described above forms a coating of NF on the conductive substrate. The coating obtained immediately after energization is a layer of transparent to translucent gel-like NF dispersion containing NF and dispersion medium. The conductive substrate with the gelled NF coating may be removed from the electrolytic bath and optionally dried to remove the dispersion in the gelled coating. The drying method in this case is not particularly limited, and examples thereof include natural drying, hot air/hot air drying, and vacuum drying.

The thickness of the gel-like NF coating on the conductive substrate can be adjusted by adjusting the NF solid content of the NF dispersion, the energization time, etc. For example, the thickness is about 0.1 to 10 mm. coating can be formed. The thickness of the coating obtained by drying (removing the dispersion medium from) the gel-like coating is not particularly limited, but is, for example, about 0.5 to 50 μm. After drying, the coating is a dense thin film consisting mainly of NF.

The ratio of the solid content of NF to the total solid content in the gel coating and the coating after drying is preferably 50% or more, more preferably 70% or more, more preferably 80% or more, and more preferably 90% or more. More preferably 95% or more.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

(Preparation of oxidized CNF)
500 g (absolute dry) of bleached unbeaten kraft pulp (85% whiteness) derived from softwood is added to 500 ml of an aqueous solution in which 780 mg of TEMPO (Sigma Aldrich) and 75.5 g of sodium bromide are dissolved, and the pulp is uniformly dispersed. Stir until done. An aqueous sodium hypochlorite solution was added to the reaction system so as to have a concentration of 6.0 mmol/g to initiate an oxidation reaction. The pH in the system decreased during the reaction, but was adjusted to pH 10 by successively adding 3M sodium hydroxide aqueous solution. The reaction was terminated when the 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 an oxidized pulp. The pulp yield at this time was 90%, and the time required for the oxidation reaction was 90 minutes. The oxidized pulp obtained in the above step is adjusted to 0.5% (w / v) with water, and defibration treatment is performed 5 times with an ultrahigh pressure homogenizer (20 ° C., 150 MPa) to obtain a dispersion of oxidized CNF. Obtained. The carboxyl group content of the obtained oxidized CNF was 1.42 mmol/g.

(Preparation of CM-CNF)
130 parts of water and 20 parts of sodium hydroxide dissolved in a mixed solvent of 10 parts of water and 90 parts of isopropanol (IPA) are added to a twin-screw kneader whose rotation speed is adjusted to 150 rpm, and hardwood pulp (Nippon Paper Industries ( LBKP manufactured by Co., Ltd.) was charged at 100° C. for 60 minutes in terms of dry weight. The mixture was stirred and mixed at 35° C. for 80 minutes for mercerization. Further, a mixed solvent of 23 parts of water and 207 parts of IPA and 40 parts of sodium monochloroacetate were added with stirring, and after stirring for 30 minutes, the temperature was raised to 70° C. and etherification treatment was performed for 90 minutes. After completion of the reaction, the mixture was neutralized with acetic acid until the pH reached 7, washed with water-containing methanol, deliquored, dried and pulverized to obtain a sodium salt of CM pulp. The degree of CM substitution in the obtained CM pulp was 0.17. The CM-modified pulp obtained in the above step was adjusted to 0.5% (w/v) with water, and defibrated three times with an ultrahigh-pressure homogenizer (20°C, 150 MPa) to obtain a CM-CNF dispersion. got

(Preparation of phosphorylated CNF)
100 g of hardwood pulp (LBKP, manufactured by Nippon Paper Industries Co., Ltd.) is immersed in 400 g of an aqueous solution of 120 g of urea and 45 g of ammonium dihydrogen phosphate, dried in an oven at 70 ° C. for 24 hours, and further at 150 ° C. for 10 minutes. heated. After that, it was washed with ion-exchanged water five times to obtain a phosphate-esterified pulp. When the amount of phosphate groups in the phosphate-esterified pulp was measured by the method described above, it was 0.87 mmol/g. The phosphate esterified pulp obtained in the above process is adjusted to 0.5% (w / v) with water, and defibrated three times with an ultrahigh pressure homogenizer (20 ° C., 150 MPa) to perform phosphate esterification. A dispersion of CNF was obtained.

(Preparation of sulfate esterified CNF)
After drying 100 g of hardwood pulp (LBKP, manufactured by Nippon Paper Industries Co., Ltd.) in an oven at 105° C. for 24 hours, 2000 g of a 60% aqueous sulfuric acid solution was added and stirred at 50° C. for 1 hour. After that, it was washed with ion-exchanged water five times to obtain sulfate-esterified pulp. The amount of sulfate groups in the sulfate-esterified pulp was measured by the method described above and found to be 0.79 mmol/g. The sulfated pulp obtained in the above step was adjusted to 0.5% (w / v) with water, and defibrated three times with an ultrahigh pressure homogenizer (20 ° C., 150 MPa) to produce sulfated CNF. A dispersion was obtained.

(Preparation of cationic CNF)
200 g of pulp (NBKP, manufactured by Nippon Paper Industries Co., Ltd.) in dry weight and 24 g of sodium hydroxide in dry weight are added to a pulper capable of stirring pulp, and water is added so that the solid content of the pulp becomes 15% by mass. added. Then, after stirring at 30° C. for 30 minutes, the temperature was raised to 70° C., and 200 g (converted to active ingredient) of 3-chloro-2-hydroxypropyltrimethylammonium chloride was added as a cationizing agent. After reacting for 1 hour, the reactant was taken out, neutralized and washed to obtain a cation-modified pulp having a degree of cation substitution per glucose unit of 0.05. The cationic pulp obtained in the above step was adjusted to 0.5% (w / v) with water, and defibration treatment was performed three times with an ultrahigh pressure homogenizer (20 ° C., 150 MPa), and the cationized CNF dispersion liquid got

(Preparation of chitin NF)
500 g of snow crab shells were allowed to stand in 5 L of a 20% aqueous sodium hydroxide solution for 24 hours, and washed with 5 L of deionized water three times. Then, it was allowed to stand in 5 L of 10% hydrochloric acid for 24 hours, and washed with 5 L of deionized water three times. After that, it was left standing in 2 L of ethanol and washed with 5 L of deionized water three times. A suspension of washed crab shells with a concentration of 0.5% (w/v) was adjusted to pH 6 with acetic acid, pulverized with a home-use mixer for 1 hour, and further milled with Homodisper (manufactured by Primix) at 6000 rpm for 5 hours. Preliminarily defibrated. This suspension was defibrated three times with an ultrahigh-pressure homogenizer (20° C., 150 MPa) to obtain an aqueous dispersion of chitin nanofibers.

(Test 1 Formation of coating by electrophoresis)
An aqueous dispersion of each NF prepared by the method described above was prepared. The solid content of NF in the dispersion is as described in Table 1. 500 mL of aqueous dispersion of each NF was placed in an electrolytic bath, the conductive substrate (25 cm ² ) listed in Table 1 and an aluminum plate (25 cm ² ) as a counter electrode were immersed in the dispersion, and the voltage was 18 with a rectifier. 5 V and a current value of 0.1 A or less, and energized for about 1 hour. After energization, each conductive substrate is taken out from the electrolytic cell, placed again in the separately prepared electrolytic cell containing deionized water, and left to stand for 1 hour under the same conditions as above while being energized. , the uniformity of the NF gel-like coating formed on the conductive substrate was evaluated by the method described below. In addition, the presence or absence of repelling of the coating on the base material was evaluated by the method described later.

After evaluating the uniformity and resilience, the conductive substrate with the NF gel-like coating was dried at 50°C to form a thin film. The coating obtained after drying was evaluated for the presence or absence of unevenness, the presence or absence of wrinkles, and the presence or absence of peeling by the methods described later. Table 1 shows the results.

(Test 2 Formation of coating by electrophoresis)
On the conductive substrate in the same manner as in Test 1, except that the NF aqueous dispersion and the conductive substrate described in Table 2 were used, the voltage was 30 V, the current value was 0.3 A or less, and the current was applied for 2 minutes. to form a gel-like coating of NF. The uniformity of the coating and the presence or absence of flipping on the substrate were evaluated in the same manner as in Test 1 by the method described below. After these evaluations, the conductive substrates with each coating were dried at 50°C. Regarding the coating after drying, the presence or absence of unevenness, the presence or absence of wrinkles, and the presence or absence of peeling were evaluated in the same manner as in Test 1 by the methods described below. Table 2 shows the results.

(Test 3 Formation of coating by electrophoresis)
A NF coating was formed and evaluated in the same manner as Test 2 except that the voltage was changed to 20V. Table 3 shows the results.

(Test 4 Formation of coating by electrophoresis)
A NF coating was formed and evaluated in the same manner as Test 2, except that the voltage was changed to 10V. Table 4 shows the results.

(Test 5 Formation of coating by electrophoresis)
A NF coating was formed and evaluated in the same manner as Test 2, except that the voltage was changed to 5V. Table 5 shows the results.

(Comparative test bar coat/spray coat)
As a comparative example, each NF dispersion liquid having the solid content shown in Table 6 was coated on each conductive substrate. Hand coated using a 40 wire bar (bar coat). Further, each NF dispersion liquid having the solid content shown in Table 6 was sprayed onto each conductive substrate using a two-fluid nozzle (spray coating). The uniformity of each coating obtained and the presence or absence of repelling on the substrate were evaluated by the methods described below in the same manner as in the Examples. After these evaluations, the conductive substrates with each coating were dried at 50°C. Regarding the coating after drying, the presence or absence of unevenness, the presence or absence of wrinkles, and the presence or absence of peeling were evaluated in the same manner as in Test 1 by the methods described below. Table 6 shows the results.

(Evaluation of uniformity)
In the state before drying, if the NF coating formed on the conductive substrate is visually smooth, the uniformity is evaluated as good (good). Uniformity was evaluated as poor (bad).

(Evaluation of presence/absence of flicking)
In the state before drying, the case where the NF coating remains without flowing is evaluated as not repelled (no), while the case where the coating locally aggregates over time or the surface of the conductive substrate is exposed It was evaluated that there is a rebound (yes) when it does.

(Evaluation of presence or absence of unevenness)
If the surface of the coating after drying is visually smooth, it is evaluated as having no unevenness (no), while if the surface is visually wavy or uneven in thickness, it is evaluated as having unevenness (yes). and evaluated.

(Evaluation of presence or absence of wrinkles)
Regarding the surface of the coating after drying, when it is visually glossy and uniform, it is evaluated as wrinkle-free (none), while when it is visually locally cloudy or locally rough, it is evaluated. It was evaluated as wrinkled (present).

(Evaluation of presence or absence of peeling)
Regarding the coating after drying, if the coating is visually not floating from the conductive substrate, it is evaluated as no peeling (no), while if the coating is visually floating from the conductive substrate, there is peeling ( Yes).

From the results in Table 6, when NF is coated on a substrate such as metal using conventional bar coating or spray coating, the uniformity is poor, and depending on the type of substrate, repelling occurs, and the coating after drying , it can be seen that unevenness, wrinkles, and peeling occur. On the other hand, according to the method of the present invention, in which each NF is deposited on a conductive substrate using the principle of electrophoresis to form a coating, the results in Tables 1 to 5 show that uniform and non-repelling on the conductive substrate. It can be seen that a coating can be formed, and even after drying, unevenness, wrinkles, and peeling do not occur.

Claims

placing a dispersion of anionic cellulose nanofibers in an electrolytic cell;
immersing a conductive base material and an electrode in the dispersion in the electrolytic bath; and energizing the conductive base material as an anode and the electrode as a cathode to transfer the anionic cellulose nanofibers to the conductive base material. A method of making a coating of anionic cellulose nanofibers, comprising coating the conductive substrate with the anionic cellulose nanofibers by electrophoresis to a substrate.
placing a dispersion of cationic cellulose nanofibers and/or chitin nanofibers in an electrolytic cell;
immersing a conductive base material and an electrode in the dispersion in the electrolytic bath; and energizing the conductive base material as a cathode and the electrode as an anode to obtain the cationic cellulose nanofibers and/or chitin nanofibers. to the conductive substrate to coat the conductive substrate with the cationic cellulose nanofibers and/or chitin nanofibers. coating manufacturing method.
The method according to claim 1, wherein the anionic cellulose nanofibers are oxidized cellulose nanofibers having carboxyl groups and/or carboxylate groups.
The method according to claim 1, wherein the anionic cellulose nanofibers are carboxyalkylated cellulose nanofibers.
The method according to claim 1, wherein the anionic cellulose nanofibers are phosphorylated cellulose nanofibers.
The method according to claim 1, wherein the anionic cellulose nanofibers are sulfate esterified cellulose nanofibers.
The method according to any one of claims 1 to 6, wherein the conductive substrate is metal or carbon.