JP5976249B1 - Water dispersion and coating material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an aqueous dispersion having good storage stability and good physical properties, solvent resistance and discoloration of the resulting film. An aqueous dispersion of cellulose nanofibers (A) and a polyurethane resin (B) satisfying the following conditions, comprising at least a urethane prepolymer (b) solution and the cellulose nanofibers (A) An aqueous dispersion obtained by mixing an aqueous dispersion of the above and further subjecting the urethane prepolymer (b) to chain extension to obtain a polyurethane resin (B). (A-1) Number average fiber diameter of 2 nm to 500 nm (A-2) Average aspect ratio of 50 to 1000 (A-3) Cellulose I-type crystal structure (A-4) Anionic functional group is used . [Selection figure] None

Description

  The present invention relates to an aqueous dispersion and a coating material.

  In recent years, biodegradable biomass raw materials have attracted attention as environmentally friendly materials in recent years, which have biodegradable properties as environmentally friendly materials. Among these, materials in which the biomass raw material is in the form of fine fibers have attracted particular attention. Among them, cellulose nanofibers are expected to be applied as resin filler materials because of their high crystallinity. Water-based polyurethane resins are also widely used as environmentally friendly materials. (Patent Document 1).

Japanese Patent No. 5733761

  However, in the patent document resin composition, the strength of the film is not always sufficient. Then, this invention aims at providing the water dispersion which solves these subjects.

In order to solve the above problems, the present invention provides:
(1) An aqueous dispersion of cellulose nanofiber (A) and polyurethane resin (B) characterized by satisfying the following conditions,
At least after mixing the urethane prepolymer (b) solution and the aqueous dispersion of the cellulose nanofiber (A),
Furthermore, an aqueous dispersion obtained by chain-extending the urethane prepolymer (b) to obtain a polyurethane resin (B),
(A-1) Number average fiber diameter of 2 nm to 500 nm (A-2) Average aspect ratio of 50 to 1000 (A-3) Cellulose I-type crystal structure (A-4) Anionic functional group (2 The aqueous dispersion according to (1), wherein the mixing ratio (solid weight ratio) of the cellulose nanofiber (A) and the polyurethane resin (B) is 0.1 / 100 to 5/100,
(3) At least a step of mixing the urethane prepolymer (b) solution and the aqueous dispersion of cellulose nanofiber (A);
Thereafter, a method of producing an aqueous dispersion of cellulose nanofiber (A) and polyurethane resin (B) having a step of extending a urethane prepolymer to form a polyurethane resin (B),
(4) A coating material containing the aqueous dispersion described in (1) or (2).
About.

  According to the present invention, an aqueous dispersion having good storage stability and good physical properties, solvent resistance and discoloration of the resulting film can be obtained.

  Hereinafter, preferred embodiments of the present invention will be described.

The aqueous dispersion of this embodiment contains (A) and (B). An aqueous dispersion of cellulose nanofiber (A) and polyurethane resin (B) characterized by satisfying the following conditions, at least an aqueous dispersion of urethane prepolymer (b) solution and cellulose nanofiber (A) And a urethane prepolymer (b) is chain-extended to form a polyurethane resin (B).
(A-1) Number average fiber diameter of 2 nm to 500 nm (A-2) Average aspect ratio of 50 to 1000 (A-3) Cellulose I-type crystal structure (A-4) Anionic functional group

<Cellulose nanofiber (A)>
(A-1) Number average fiber diameter The cellulose nanofiber has a number average fiber diameter of 2 nm to 500 nm, preferably 2 nm to 150 nm, more preferably 2 nm to 100 nm, and particularly preferably 2 nm. More than 80 nm. If the number average fiber diameter is less than 2 nm, the elastic modulus of the film may decrease due to dissolution of cellulose nanofibers. When the number average fiber diameter exceeds 500 nm, the film is formed into a film. It becomes difficult to form a network of cellulose nanofibers, and the physical properties of the film may be reduced.

  The maximum fiber diameter of the cellulose nanofiber is preferably 1000 nm or less, particularly preferably 500 nm or less, from the viewpoint of dispersibility of the cellulose nanofiber. The number average fiber diameter and the maximum fiber diameter of the cellulose nanofiber can be measured, for example, as follows. That is, an aqueous dispersion of fine cellulose having a solid content of 0.05 to 0.1% by weight was prepared, and the dispersion was cast on a carbon film-coated grid that had been subjected to a hydrophilization treatment. (TEM) observation sample. In addition, when the fiber of a big fiber diameter is included, you may observe the scanning electron microscope (SEM) image of the surface cast on glass. Then, observation with an electron microscope image is performed at a magnification of 5000 times, 10000 times, or 50000 times depending on the size of the constituent fibers. At that time, an axis having an arbitrary vertical and horizontal image width is assumed in the obtained image, and the sample and observation conditions (magnification, etc.) are adjusted so that 20 or more fibers intersect the axis. Then, after obtaining an observation image that satisfies this condition, two random axes, vertical and horizontal, per image are drawn on this image, and the fiber diameter of the fiber that intersects the axis is visually read. In this way, images of at least three non-overlapping surface portions are taken with an electron microscope, and the fiber diameter values of the fibers intersecting with each of the two axes are read (thus, at least 20 × 2 × 3 = 120). Information on the fiber diameter of the book is obtained). The maximum fiber diameter and the number average fiber diameter are calculated from the fiber diameter data thus obtained.

(A-2) Average aspect ratio Although the average aspect-ratio of the said cellulose nanofiber is 50-1000, Preferably it is 100-1000, More preferably, it is 200-1000. If the average aspect ratio is less than 50, the physical properties of the film may be deteriorated.

The average aspect ratio of the cellulose nanofiber can be measured, for example, by the following method, that is, the cellulose nanofiber is cast on a carbon film-coated grid that has been hydrophilized and then negatively stained with 2% uranyl acetate. From the TEM image (magnification: 10,000 times), the number average fiber diameter and the fiber length of the cellulose nanofiber were observed. That is, the number average fiber diameter and fiber length were calculated according to the methods described above, and the average aspect ratio was calculated according to the following formula using these values.
Average aspect ratio = number average fiber length (nm) / number average fiber diameter (nm)

(A-3) Cellulose I-type crystal structure The cellulose nanofiber is a fiber obtained by refining a naturally-derived cellulose raw material having an I-type crystal structure. That is, in the process of biosynthesis of natural cellulose, nanofibers called microfibrils are first formed almost without exception, and these form a multi-bundle to form a higher order solid structure. The cellulose constituting the cellulose nanofiber has an I-type crystal structure, for example, in the diffraction profile obtained by wide-angle X-ray diffraction image measurement, in the vicinity of 2 theta = 14-17 ° and 2 theta = 22-23 °. It can be identified by having typical peaks at two nearby positions.

(A-4) Anionic functional group The cellulose nanofiber has an anionic functional group.

Although it does not restrict | limit especially as an anionic functional group of this invention, Specifically, a carboxyl group,
A phosphonium group and a sulfonium group are exemplified, and among these, a carboxyl group is preferred because of the ease of introduction of an anionic functional group into cellulose.

  As a method of introducing carboxyl into cellulose, a method of reacting at least one selected from the group consisting of a compound having a carboxyl group at the hydroxyl group of cellulose, an acid anhydride of a compound having a carboxyl group and derivatives thereof, a hydroxyl group of cellulose The method of converting into a carboalkyl group by oxidizing is mentioned.

  Although it does not specifically limit as a compound which has the said carboxyl group, Specifically, a halogenated acetic acid is mentioned, As a halogenated acetic acid, chloroacetic acid, bromoacetic acid, iodoacetic acid etc. are mentioned.

  The acid anhydride of the compound having a carboxyl group is not particularly limited, but acid anhydrides of dicarboxylic acid compounds such as maleic anhydride, succinic anhydride, phthalic anhydride, glutaric anhydride, adipic anhydride, itaconic anhydride, and the like. Can be mentioned.

  Although it does not specifically limit as a derivative | guide_body of the compound which has the said carboxyl group, The derivative of the acid anhydride of the compound which has a carboxyl group and the acid anhydride imidation of a compound which has a carboxyl group is mentioned.

  Although it does not specifically limit as an acid anhydride imidation thing of a compound which has a carboxyl group, Imidation thing of dicarboxylic acid compounds, such as maleimide, succinic acid imide, and phthalic acid imide, is mentioned.

  The acid anhydride derivative of the compound having a carboxyl group is not particularly limited. And those in which part of the hydrogen atoms are substituted with a substituent (eg, an alkyl group, a phenyl group, etc.).

The method for oxidizing the hydroxyl group of the cellulose is not particularly limited, and specifically, a method in which an N-oxyl compound is used as an oxidation catalyst and a cooxidant is allowed to act.
In the present invention, as a method for introducing a carboxyl group into cellulose, a method of oxidizing the hydroxyl group of cellulose is preferable because of excellent hydroxyl group selectivity on the fiber surface and mild reaction conditions. Hereinafter, cellulose having a carboxyl group introduced by oxidation of a hydroxyl group is referred to as oxidized cellulose.

The oxidized cellulose uses natural cellulose as a raw material, uses an N-oxyl compound as an oxidation catalyst in water, and reacts with a co-oxidant to oxidize the natural cellulose to obtain reactant fibers, removing impurities. Thus, it can be obtained by a production method including a purification step of obtaining a reactant fiber impregnated with water and a dispersion step of dispersing the reactant fiber impregnated with water in a solvent.

  It is preferable that the hydroxyl group at the C6 position of each glucose unit in the cellulose molecule of the cellulose nanofiber of the present invention is selectively oxidized and modified to be either an aldehyde group or a carboxyl group. The carboxyl group content (carboxyl group amount) is preferably in the range of 0.5 mmol / g or more and 2.5 mmol / g or less from the viewpoint of improving the elastic modulus and water resistance when cellulose nanofibers are formed into a film. The range is from 5 mmol / g to 2.0 mmol / g.

The measurement of the carboxyl group amount of the oxidized cellulose is, for example, preparing 60 ml of a 0.5 to 1% by weight slurry from a precisely weighed dry sample and adjusting the pH to about 2.5 with a 0.1 M aqueous hydrochloric acid solution. Then, 0.05M sodium hydroxide aqueous solution is dripped and electrical conductivity measurement is performed. The measurement is continued until the pH is about 11. The amount of carboxyl groups can be determined from the amount of sodium hydroxide consumed in the neutralization step of the weak acid with a slow change in electrical conductivity (V) according to the following formula.
Amount of carboxyl groups (mmol / g) = V (ml) × [0.05 / cellulose weight]
In addition, adjustment of a carboxyl group amount can be performed by controlling the addition amount and reaction time of the co-oxidant used at the oxidation process of a cellulose nanofiber so that it may mention later.

  The oxidized cellulose is preferably reduced with a reducing agent after the oxidative modification. As a result, part or all of the aldehyde group and the ketone group are reduced to return to the hydroxyl group. Note that the carboxyl group is not reduced. And by the said reduction | restoration, it is preferable that the total content of the aldehyde group and the ketone group by the measurement by the semicarbazide method of the said cellulose nanofiber shall be 0.3 mmol / g or less, Most preferably, it is 0-0.1 mmol / g. , Most preferably substantially 0 mmol / g. Thereby, the molecular weight fall of a cellulose nanofiber is suppressed and the high water resistance and the high elasticity modulus under the high humidity of a membrane | film | coat can be maintained for a long period of time.

The oxidized cellulose is oxidized using a co-oxidant in the presence of an N-oxyl compound such as 2,2,6,6-tetramethylpiperidine (TEMPO), and an aldehyde group generated by the oxidation reaction. It is preferable that the ketone group is reduced with a reducing agent because the cellulose nanofiber can be easily obtained. Also, reduction with the reducing agent, the is by hydrogenation sodium borohydride (NaBH _4), more preferable from the viewpoint.

  Measurement of the total content of aldehyde groups and ketone groups by the semicarbazide method is performed, for example, as follows. Specifically, 50 ml of a semicarbazide hydrochloride 3 g / l aqueous solution adjusted to pH = 5 with a phosphate buffer is accurately added to the dried sample, sealed, and shaken for 2 days. Next, 10 ml of this solution is accurately collected in a 100 ml beaker, 25 ml of 5N sulfuric acid and 5 ml of 0.05N potassium iodate aqueous solution are added and stirred for 10 minutes. Thereafter, 10 ml of 5% potassium iodide aqueous solution was added, and immediately titrated with a 0.1N sodium thiosulfate solution using an automatic titrator. From the titration amount and the like, according to the following formula (3), The amount of carbonyl groups (total content of aldehyde groups and ketone groups) can be determined. Semicarbazide reacts with an aldehyde group or a ketone group to form a Schiff base (imine), but does not react with a carboxyl group. Therefore, it is considered that only the aldehyde group and the ketone group can be quantified by the above measurement.

In the oxidized cellulose, the hydroxyl group at the C6 position of each glucose unit in the cellulose molecule on the fiber surface is selectively oxidized and modified to be either an aldehyde group or a carboxyl group. Whether the hydroxyl group at the C6 position of the glucose unit on the surface of the cellulose nanofiber is selectively oxidized can be confirmed by, for example, a ¹³ C-NMR chart. That is, a 62 ppm peak corresponding to the C6 position of the primary hydroxyl group of the glucose unit, which can be confirmed by a ¹³ C-NMR chart of cellulose before oxidation, disappears after the oxidation reaction, and instead a peak derived from a carboxyl group or the like (178 ppm) The peak of is a peak derived from a carboxyl group). In this way, it can be confirmed that only the C6 hydroxyl group of the glucose unit is oxidized to a carboxyl group or the like.

  Moreover, the detection of the aldehyde group in the oxidized cellulose can also be performed using, for example, a Fehring reagent. That is, for example, after adding a Fering reagent (a mixed solution of sodium potassium tartrate and sodium hydroxide and an aqueous solution of copper sulfate pentahydrate) to a dried sample, the supernatant is obtained when heated at 80 ° C. for 1 hour. When blue and cellulose nanofiber parts are amber, it can be judged that aldehyde groups have not been detected, and when the supernatant is yellow and cellulose fiber parts are red, it can be judged that aldehyde groups have been detected. it can.

<Polyurethane resin (B)>
In the present invention, the polyurethane resin is not particularly limited as long as it is a reaction product of a polyol and a polyisocyanate. For example, it can be produced by a conventionally known method, and is not particularly limited. For example, a polyol, an isocyanate compound and, if necessary, a hydrophilic group-containing compound are reacted, and a hydrophilic group contained if necessary. The urethane prepolymer (b) is obtained by neutralization or quaternization with a quaternizing agent, and is obtained by chain extension reaction with water or / and polyamine.

  In the present invention, the polyol is not particularly limited as long as it is a compound having two or more hydroxyl groups in the molecule. For example, a polyhydric alcohol, a polyether polyol, a polyester polyol, a polyether ester Molecular ends or molecules such as polyols, polycarbonate polyols, polyolefin polyols, polyacrylic polyols, polyacetal polyols, polybutadiene polyols, polysiloxane polyols, fluorine polyols Examples thereof include compounds having two or more hydroxyl groups. Although it does not specifically limit as polyhydric alcohol, For example, ethylene glycol, diethylene glycol, butanediol, propylene glycol, hexanediol, bisphenol A, bisphenol B, bisphenol S, hydrogenated bisphenol A, dibromobisphenol A, 1,4-cyclohexanedimethanol, dihydroxyethyl terephthalate, hydroquinone dihydroxyethyl ether, trimethylolpropane, glycerin, pentaerythritol -E.g. The polyether polyol is not particularly limited, and examples thereof include polyhydric alcohol alkylene derivatives, polytetramethylene glycol, polythioether polyol and the like. Polyester polyols and polyether ester polyols are not particularly limited. For example, polyhydric alcohols, polyhydric carboxylic acids, polyhydric carboxylic acid anhydrides, polyether polyols, polycarboxylic acid esters Esterified products, castor oil polyol, polycaprolactone polyol, and the like. The polyolefin polyol is not particularly limited, and examples thereof include polybutadiene polyol, polyisoprene polyol, and hydrogenated polyol thereof. Of these, polyester polyol and polyester polyol are preferred. Polycarbonate polyol is not preferred from the viewpoint of resistance to carbonate solvents. These can use 1 type, or 2 or more types. A hydroxyl group may be used in combination with one compound.

  In the present invention, the number average molecular weight of the polyol component is not particularly limited, but is preferably 50 to 10,000, more preferably 500 to 5,000 from the viewpoint of storage stability and physical properties.

  In the present invention, the polyisocyanate is not particularly limited, and examples thereof include organic polyisocyanates such as aromatic, aliphatic, alicyclic, and aromatic fats. Of these, organic polyisocyanates such as aliphatic, alicyclic, and aromatic fats, and their polydensates (dimers, trimers, etc.), or the reaction of organic polyisocyanates with water as described above The biuret modified body etc. which are produced | generated by are preferable. 4,4'-dicyclohexylmethane diisocyanate, isophorone diisocyanate, hydrogenated xylylene diisocyanate [bis (isocyanatemethyl) cyclohexane], hexamethylene diisocyanate, lysine diisocyanate -Organic polyisocyanates such as norbornane diisocyanate and xylylene diisocyanate, and modified products thereof are more preferred. Further, 4,4'-dicyclohexylmethane diisocyanate and isophorone diisocyanate are more preferable. These can use 1 type, or 2 or more types.

  In the present invention, the ratio of the isocyanate group and hydroxyl group (molar equivalent ratio) used for obtaining the urethane prepolymer (b) is not particularly limited as long as it is (isocyanate group: hydroxyl group =) 1.1 or more: 1. However, since the urethane prepolymer (b) can have a low viscosity and a stable emulsion can be obtained, 1.5 to 3.0: 1 is preferable, and 1.6 to 2.2: 1 is more preferable. preferable. Within these ranges, the film performance and storage stability are good.

  In the present invention, the average molecular weight of the urethane prepolymer (b) is preferably 5000 or less, and more preferably 4000 or less, from the viewpoints of emulsifying properties and emulsion stability. The average molecular weight here means a theoretical value calculated from the number average molecular weight of the charged raw materials.

  In the present invention, the hydrophilicity may be any of the anionic group, the cationic group, or the nonionic group, and is not particularly limited. Among these, from the viewpoint of storage stability and film performance, An anionic group or a nonionic group is preferred.

  The hydrophilic group compound to be introduced by incorporating the hydrophilicity is not particularly limited. For example, (di) alkanol carboxylic acid or sulfonic acid tertiary amine or alkali metal neutralized product, (methoxy) poly Examples include alkylene oxides, (di) alkanolamine organic / inorganic acid neutralized products, and quaternary ammonium salts obtained by reacting these with alkyl halides or dialkyl sulfuric acid. Of these, (di) neutralized products of alkanol carboxylic acids or sulfonic acids with tertiary amines or alkali metals, (di) neutralized products of alkanolamines with organic / inorganic acids, and reaction with alkyl halides or dialkyl sulfate Quaternary ammonium salts are preferred. The (methoxy) polyalkylene oxide may contain at least ethylene oxide as the alkylene oxide, and may contain other alkylene oxides such as propylene oxide and butylene oxide. An addition form (hydrophilic group introduction form) in the case of using (methoxy) polyalkylene oxide containing a plurality of types of alkylene oxides may be either block addition or random addition. .

The following can be illustrated as a compound which can introduce | transduce these hydrophilic groups.
For example, as anion type, dimethylolpropionic acid, dimethylolbutanoic acid,
Obtained by neutralizing carboxylic acid compounds such as lactic acid and glycine, and sulfonic acid compounds such as aminoethyl sulfonic acid and polyester diol composed of sulfoisophthalic acid and diol with tertiary alkanolamines such as triethylamine, NaOH and dimethylaminoethanol. The salt which can be mentioned can be mentioned. Of these, dimethylolpropionic acid, glycine, and sodium salt of aminoethylsulfonic acid are preferred from the viewpoints of storage stability and film performance.

  For example, as a cation type, a salt obtained by neutralizing an alkanolamine such as dimethylaminoethanol or methyldiethanolamine with an organic carboxylic acid such as formic acid or acetic acid, or an inorganic acid such as hydrochloric acid or sulfuric acid, or halogenation such as methyl chloride or methyl bromide Quaternized with dialkyl sulfuric acid such as alkyl and dimethyl sulfuric acid. Of these, a combination of methyldiethanolamine and an organic carboxylic acid and a combination of methyldiethanolamine and dimethylsulfuric acid are preferred because they are easy to produce industrially.

  The content of the hydrophilic group in the urethane prepolymer (b) is not particularly limited. For example, the content is preferably 0.07 to 2.10 mmol / g, more preferably 0.12 to 1.80 mmol / g, and still more preferably 0.17 to 1.60 mmol / g. If it is the said range, it is preferable from a viewpoint of storage stability and membrane | film | coat performance.

<Water dispersion>
The mixing ratio (solid content weight ratio) of the cellulose nanofiber (A) and the polyurethane resin (B) in the aqueous dispersion in the present invention is not particularly limited, but is preferably 0.1 / 100 to 5/100. More preferably, the ratio is 3/100 to 4/100, and more preferably 0.5 / 100 to 3.5 / 100. These ranges are preferable from the viewpoints of storage stability and film performance.

  Although it does not specifically limit as solid content of the cellulose nanofiber (A) in the aqueous dispersion in this invention, For example, 0.01-20 mass% is preferable with respect to an aqueous dispersion, 0.03-10 mass% Is more preferable, and 0.05-8 mass% is further more preferable. These ranges are preferable from the viewpoints of stability and workability. Although it does not specifically limit as solid content of the polyurethane resin (B) in the aqueous dispersion in this invention, For example, 1-60 mass% is preferable with respect to an aqueous dispersion, 3-55 mass% is more preferable, 4 -50 mass% is more preferable. These ranges are preferable from the viewpoints of stability and workability.

  Furthermore, various commonly used additives can be used in the aqueous dispersion of the present invention as necessary. Examples of such additives include weathering agents, antibacterial agents, antifungal agents, pigments, fillers, rust inhibitors, pigments, dyes, film-forming aids, inorganic crosslinking agents, organic crosslinking agents (for example, blocked isocyanates). -Based crosslinking agents, epoxy-based crosslinking agents, carbodiimide-based crosslinking agents, oxazoline-based crosslinking agents, melamine-based crosslinking agents), silane coupling agents, antiblocking agents, viscosity modifiers, leveling agents, antifoaming agents, dispersion stabilizers, light Stabilizers, antioxidants, ultraviolet absorbers, inorganic and organic fillers, plasticizers, lubricants, antistatic agents and the like can be mentioned.

<Method for producing cellulose nanofiber (A)>
Although it does not specifically limit as a cellulose nanofiber (A) for obtaining the water dispersion of this invention, It is preferable to use the water dispersion of a cellulose nanofiber (A). The aqueous dispersion of the cellulose nanofiber (A) is not particularly limited. For example, (I) an oxidation step for oxidizing cellulose, and (II) a purification step for adjusting the pH of the oxidized cellulose dispersion to 2 or less for purification. And (III) a neutralization step of neutralizing purified cellulose with an alkaline compound, and (IV) a dispersion step of dispersing the neutralized cellulose in the presence of a dispersion medium such as water. Is preferably produced by the following steps.

(I) Oxidation step After dispersing natural cellulose and N-oxyl compound in water (dispersion medium), a co-oxidant is added to start the reaction. During the reaction, a 0.5 M aqueous sodium hydroxide solution is added dropwise to maintain the pH at 10 to 11, and the reaction is regarded as completed when no change in pH is observed. Here, the co-oxidant is not a substance that directly oxidizes a cellulose hydroxyl group but a substance that oxidizes an N-oxyl compound used as an oxidation catalyst.

  The natural cellulose means purified cellulose isolated from a cellulose biosynthetic system such as a plant, animal, or bacteria-producing gel. More specifically, softwood pulp, hardwood pulp, cotton pulp such as cotton linter and cotton lint, non-wood pulp such as straw pulp and bagasse pulp, bacterial cellulose (BC), cellulose isolated from sea squirt, seaweed Cellulose isolated from can be mentioned. These may be used alone or in combination of two or more. Among these, soft wood pulp, hardwood pulp, cotton pulp such as cotton linter and cotton lint, and non-wood pulp such as straw pulp and bagasse pulp are preferable. The natural cellulose is preferably subjected to a treatment for increasing the surface area such as beating, because the reaction efficiency can be increased and the productivity can be increased. In addition, if the natural cellulose that has been stored after being isolated and purified and not dried (never dry) is used, the microfibril bundles are likely to swell. This is preferable because the number average fiber diameter after the crystallization treatment can be reduced.

  The dispersion medium of natural cellulose in the above reaction is water, and the concentration of natural cellulose in the reaction aqueous solution is arbitrary as long as the reagent (natural cellulose) can be sufficiently diffused. Usually, it is about 5% or less based on the weight of the reaction aqueous solution, but the reaction concentration can be increased by using a device having a strong mechanical stirring force.

  Examples of the N-oxyl compound include compounds having a nitroxy radical generally used as an oxidation catalyst. The N-oxyl compound is preferably a water-soluble compound, more preferably a piperidine nitroxyoxy radical, particularly 2,2,6,6-tetramethylpiperidinooxy radical (TEMPO) or 4-acetamido-TEMPO. preferable. The N-oxyl compound is added in a catalytic amount, preferably 0.1 to 4 mmol / l, more preferably 0.2 to 2 mmol / l.

  Examples of the co-oxidant include hypohalous acid or a salt thereof, hypohalous acid or a salt thereof, perhalogen acid or a salt thereof, hydrogen peroxide, a perorganic acid, and the like. These may be used alone or in combination of two or more. Of these, alkali metal hypohalites such as sodium hypochlorite and sodium hypobromite are preferable. And when using the said sodium hypochlorite, it is preferable to advance reaction in presence of alkali metal bromides, such as sodium bromide, from the point of reaction rate. The addition amount of the alkali metal bromide is about 1 to 40 times mol, preferably about 10 to 20 times mol for the N-oxyl compound.

  The pH of the aqueous reaction solution is preferably maintained in the range of about 8-11. The temperature of the aqueous solution is arbitrary at about 4 to 40 ° C., but the reaction can be performed at room temperature (25 ° C.), and the temperature is not particularly required to be controlled. In order to obtain a desired amount of carboxyl group and the like, the degree of oxidation is controlled by the amount of co-oxidant added and the reaction time. Usually, the reaction time is completed within about 5 to 120 minutes, at most 240 minutes.

(II) Purification step Next, purification is performed for the purpose of removing unreacted co-oxidant (such as hypochlorous acid) and various by-products. Specifically, the pH of the reaction mixture is adjusted to about 2 with various acids, and solid-liquid separation is performed with a centrifuge while sprinkling purified water to obtain cake-like oxidized cellulose. Solid-liquid separation is performed until the electric conductivity of the filtrate is 5 mS / m or less.

  As a purification method in the purification step, any apparatus can be used as long as it can achieve the above-described object, such as a method using centrifugal dehydration (for example, a continuous decanter). The aqueous dispersion of oxidized cellulose thus obtained is in the range of approximately 10% by mass to 50% by mass as the solid content (cellulose) concentration in a squeezed state. Considering the subsequent dispersion step, if the solid content concentration is higher than 50% by mass, it is not preferable because extremely high energy is required for dispersion.

(III) Neutralization Step Next, the purified oxidized cellulose is neutralized with an alkaline compound.
Specifically, it can be carried out by adding a dispersion medium such as water to an aqueous dispersion of oxidized cellulose to adjust the solid concentration of the predetermined oxidized cellulose, adding an alkaline compound, and stirring. In this case, the pH of the dispersion is preferably in the range of 5 to 10 (preferably in the range of 6 to 8). If the pH is less than the above range, the oxidized cellulose fibers are entangled by acid and are not easily loosened and cannot be dispersed at high pressure in the subsequent dispersion step. Conversely, if the pH exceeds the above range, the action of alkali This is because the viscosity decreases. The alkaline compound may be diluted with a dispersion medium such as water and added to the aqueous dispersion of oxidized cellulose.

  The solid content concentration of the oxidized cellulose is not particularly limited as long as the aqueous dispersion of oxidized cellulose can be stirred, but specifically, 0.1 mass% to 20 mass%, preferably 0.2 mass%. The amount is 5% by mass or less. If the solid content concentration of the oxidized cellulose is within the above range, an alkaline compound can be uniformly mixed, which is preferable. The stirring time is not particularly limited as long as the alkaline compound can be uniformly dispersed in the aqueous dispersion of oxidized cellulose.

(IV) Dispersing Step The dispersion of oxidized cellulose obtained in the neutralizing step is dispersed in water or a mixed solvent of water and the organic solvent. With the treatment, the viscosity increases, and a dispersion of cellulose nanofibers that has been refined can be obtained.

  Dispersers used in the above dispersion step include homomixers under high speed rotation, high pressure homogenizers, ultra high pressure homogenizers, ultrasonic dispersion processors, beaters, disc type refiners, conical type refiners, double disc type refiners, grinders, etc. Use of a powerful and beating-capable device is preferable in that more efficient and advanced downsizing is possible, and a viscous aqueous composition can be obtained economically advantageously. Examples of the disperser include a screw mixer, paddle mixer, disper mixer, turbine mixer, disper, propeller mixer, kneader, blender, homogenizer, ultrasonic homogenizer, colloid mill, pebble mill, and bead mill grinder. It can be used. Further, two or more types of dispersers may be used in combination.

The treatment conditions with the homogenizer of the present invention are not particularly limited, but the pressure conditions are 30 MPa or more, preferably 100 MPa or more, more preferably 140 MPa or more. In addition, prior to defibration / dispersion treatment with a high-pressure homogenizer, it is possible to pre-treat the oxidized cellulose using known mixing, stirring, emulsifying, and dispersing devices such as a high-speed shear mixer as necessary. is there. (V) Reduction step In the production of the oxidized cellulose, it is preferable to further perform a reduction reaction after the (I) oxidation step. Specifically, the reaction product fiber after the oxidation reaction is dispersed in purified water, the pH of the aqueous dispersion is adjusted to about 10, and the reduction reaction is performed with various reducing agents. As the reducing agent used in the present invention, a general reducing agent can be used, and preferred examples include LiBH ₄ , NaBH ₃ CN, NaBH _{4 and the} like. Among these, NaBH ₄ is preferable from the viewpoint of cost and availability.

  The amount of the reducing agent is preferably in the range of 0.1 to 4% by mass, particularly preferably in the range of 1 to 3% by mass, based on the oxidized cellulose. The reaction is usually carried out at room temperature or slightly higher than room temperature, usually 10 minutes to 10 hours, preferably 30 minutes to 2 hours.

  As the form of the cellulose nanofiber used as a raw material of the resin composition of the present invention, in consideration of the apparatus and the like, it is in a powder form (however, it is a powder form in which cellulose nanofibers are aggregated and does not mean cellulose particles), It can be arbitrarily selected from a suspension form (a visually transparent or opaque liquid).

  Examples of powdered cellulose nanofibers include, for example, a dried product obtained by directly drying an aqueous dispersion of cellulose nanofibers; a product obtained by pulverizing the dried product by mechanical treatment; A cellulose nanofiber aggregated by mixing with an aqueous solvent and the aggregate dried; an undried product of the aggregate; an aqueous dispersion of cellulose nanofiber pulverized by a known spray drying method; cellulose Examples thereof include a nanofiber aqueous dispersion powdered by a known freeze-drying method. The spray drying method is a method in which an aqueous dispersion of the cellulose nanofiber is sprayed in the air and dried.

  Further, as the suspension-like cellulose nanofiber, an aqueous dispersion of cellulose nanofiber can be used as it is, or a powdery cellulose nanofiber dispersed in an arbitrary medium can be used. . Such a medium is appropriately selected depending on a resin to be mixed and a mixing and molding method described later, and for example, water, alcohol or the like can be used.

<Method for producing urethane polymer (b)>
A known method can be used as a method for producing the urethane polymer (b) of the present invention, and is not particularly limited. For example, a polyol, an isocyanate compound, and, if necessary, a hydrophilic group-containing compound may be added at 30 to 130 ° C. The reaction is carried out under reaction conditions of about 5 hours to 10 hours, and if necessary, this is cooled to 5 ° C. to 45 ° C. to neutralize the contained hydrophilic groups or quaternize with a quaternizing agent. A prepolymer (b) is obtained. As the solvent, any organic solvent such as acetone, methyl ethyl ketone, tetrahydrofuran, dioxane, ethyl acetate, butyl acetate can be used.

<Method for producing aqueous dispersion>
The method for producing an aqueous dispersion of the present invention comprises at least a step of mixing a urethane prepolymer (b) solution and an aqueous dispersion of cellulose nanofiber (A), chain-extending the urethane prepolymer, and polyurethane resin (B). It has the process of.
In the present invention, the urethane prepolymer (b) solution and the cellulose nanofiber (A) are mixed and then chain-stretched, so that the storage stability is good and obtained as compared with those mixed after chain-stretching. The physical properties, solvent resistance and discoloration of the film are good. Although the reason for this is not clear, for example, a reason such as entanglement between polymers can be considered.

Although not specifically limited, it will be specifically described below.
As a step of mixing the urethane prepolymer (b) solution and the aqueous dispersion of cellulose nanofiber (A), the urethane prepolymer (b) solution obtained by the method for producing the urethane polymer (b) and cellulose nanofiber The aqueous dispersion (A) is added and emulsified. In addition, you may add water further as needed. As a total amount of water in the aqueous dispersion of cellulose nanofiber (A) and water to be added, it is preferable to add 100 to 900 parts by weight of water with respect to 100 parts by weight of the urethane polymer (b).

  As a step of chain-extending the urethane prepolymer to obtain a polyurethane resin (B), the water or, if necessary, polyamine is added to carry out a chain extension reaction. Thereby, a polyurethane resin (B) is obtained.

  Examples of the polyamine include, but are not limited to, aliphatic polyamines such as ethylenediamine, trimethylenediamine, propylenediamine, diethylenetriamine, and triethylenetetramine, aromatic polyamines such as metaxylenediamine, tolylenediamine, and diaminodiphenylmethane, piperazine, An alicyclic polyamine such as isophoronediamine, a polyhydrazide such as hydrazine, and adipic acid dihydrazide can be used. The said polyamine compound may be used independently and may use 2 or more types together.

<Physical properties>
The storage stability of the aqueous dispersion of the present invention according to the method described in the examples is preferably such that no separation is observed, and more preferably no separation is observed.

  The strength of the film obtained from the aqueous dispersion of the present invention is preferably improved with respect to the index 100 of the base urethane resin in the method described in the examples, and more preferably 110 or more.

  The elongation of the film obtained from the aqueous dispersion of the present invention is preferably in the method described in the examples, and more preferably 90 or more.

  As for the tensile stress of the film obtained from the aqueous dispersion of the present invention, the 100% modulus according to the method described in the examples is preferably improved with respect to the index 100 of the base urethane resin, and more preferably 110 or more.

The solvent resistance (area / mass increase rate) of the film obtained from the aqueous dispersion of the present invention to an ethyl acetate / toluene mixed solution (ethyl acetate / toluene = 50/50 (weight ratio)) is based on the method described in the examples. It is preferable to improve with respect to the index 100 of the urethane resin, and more preferably 80 or less.
The solvent resistance (area / mass increase rate) of the film obtained from the aqueous dispersion of the present invention to isopropyl alcohol (IPA) is preferably improved with respect to the index 100 of the base urethane resin in the method described in the examples. The following is more preferable.

  The discoloration of the film obtained from the aqueous dispersion of the present invention is preferably such that no discoloration is observed in the method described in the examples.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to these.

(Production Example 1 (Cellulose Fiber A1))
After adding 150 ml of water, 0.25 g of sodium bromide, and 0.025 g of TEMPO to 2 g of softwood pulp, and thoroughly stirring and dispersing, 13% sodium hypochlorite aqueous solution (co-oxidant) was added to 1.0 g of the above pulp. Was added so that the amount of sodium hypochlorite was 5.2 mmol / g, and the reaction was started. Since the pH decreased with the progress of the reaction, the reaction was continued until no change in pH was observed while dropping a 0.5N aqueous sodium hydroxide solution so that the pH was maintained at 10-11 (reaction time: 120 minutes). ). After completion of the reaction, 0.1N hydrochloric acid was added to adjust to pH 2, and then purified by repeating filtration and washing to obtain cellulose fibers having oxidized fiber surfaces. Pure water was added thereto to dilute to a cellulose fiber concentration of 2% by mass, and 10% sodium hydroxide was added to adjust the pH to 7. This was treated once at a pressure of 100 MPa using a high-pressure homogenizer (H11, manufactured by Sanwa Engineering Co., Ltd.) to prepare cellulose fiber A1.

(Production Example 2 (Cellulose Fiber A2))
Cellulose fiber A2 was obtained by the same production method as in Production Example 1 except that tetrabutylammonium hydroxide was used instead of sodium hydroxide in the neutralization step.

(Evaluation of cellulose fiber)
About the cellulose fiber obtained as mentioned above, each characteristic was evaluated according to the following reference | standard.

<Measurement of number average fiber diameter and average aspect ratio>
The number average fiber diameter and fiber length of the cellulose fibers were observed using a transmission electron microscope (TEM, JEM-1400 manufactured by JEOL Ltd.). That is, after each cellulose fiber was cast on a hydrophilized carbon film-coated grid and negatively stained with 2% uranyl acetate, the number average fiber diameter was determined according to the method described above. And fiber length were calculated. Furthermore, the average aspect ratio was calculated according to the following formula using these values.
Average aspect ratio = number average fiber length (nm) / number average fiber diameter (nm)
The number average fiber diameters of the cellulose fibers A1 and A2 were 58 and 50 nm, respectively. Further, the average aspect ratios were 127 and 135, respectively.

<Crystal structure>
Using an X-ray diffractometer (Rigaku Corporation, RINT-Utima3), the diffraction profile of cellulose fiber was measured, and typical at two positions, 2 theta = 14-17 ° and 2 theta = 22-23 °. When a typical peak was observed, the crystal structure (type I crystal structure) was evaluated as “present”, and when no peak was observed, it was evaluated as “none”.
Both cellulose fibers A1 and A2 were confirmed to have a cellulose I-type crystal structure.

(Production Example 3 (urethane prepolymer (b1))
The following raw materials were added to a four-necked flask equipped with a stirrer, reflux condenser, thermometer and nitrogen blowing tube, reacted at 75 ° C. for 4 hours, and free isocyanate group content to non-volatile content was 3.0%. A methyl ethyl ketone solution of a certain urethane prepolymer was obtained.
-Polyester polyol consisting of 1,4-butanediol and adipic acid Product name "Nipporan 4009" (Mw = 1,000, manufactured by Nippon Polyurethane Industry Co., Ltd.)
200 parts by weight of propylene oxide adduct of bisphenol A (polyether polyol)
Product name "Polyether BPX-11" (Made by ADEKA Mw = 360)
400 parts by weight, trimethylolpropane (low molecular weight polyol) 20 parts by weight, dimethylolpropionic acid (ionic group-containing compound) 40 parts by weight, hexamethylene diisocyanate (isocyanate compound) 340 parts by weight, methyl ethyl ketone 800 parts by weight The mixture was cooled to 40 ° C. and neutralized by adding 30 parts by weight of triethylamine to obtain a urethane prepolymer (b1).

(Production Example 4 (urethane prepolymer (b2))
The following raw materials were added to a four-necked flask equipped with a stirrer, reflux condenser, thermometer, and nitrogen blowing tube, reacted at 75 ° C. for 4 hours, and with a free isocyanate group content of 2.0% based on the nonvolatile content. A methyl ethyl ketone solution of a certain urethane prepolymer was obtained.
・ Polybutadiene polyol trade name “KRASOL LBH-3000” (Cray Valley Mw = 3,000) 750 parts by weight ・ Dimethylolpropionic acid (ionic group-containing compound) 40 parts by weight ・ Dicyclohexylmethane diisocyanate (isocyanate compound) 210 parts by weight Part / Methyl ethyl ketone 800 parts by weight The methyl ethyl ketone solution was cooled to 40 ° C. and neutralized by adding 30 parts by weight of triethylamine to obtain a urethane prepolymer (b2).

(Production Example 5 (urethane prepolymer (b3))
Polyester polyol A synthesis method: In a flask equipped with a dehydrator, 105 parts by weight of isophthalic acid and 105 parts by weight of terephthalic acid, 93 parts by weight of adipic acid as acid components, 62 parts by weight of ethylene glycol and 104 parts by weight of neopentyl glycol as diol components Polyester polyol A by adding 0.1 parts by weight of tetraisopropyl titanate as a reaction catalyst and then performing a condensation reaction at 220 ° C. until the acid value is 1.0 or less and the water content is 0.05% or less. Got. (Number average molecular weight: 2000, hydroxyl value: 56 mgKOH / g).
580 parts of polyester polyol A, 15 parts of trimethylolpropane and 667 parts of methyl ethyl ketone were added and dissolved with sufficient stirring, and then 300 parts of isophorone diisocyanate was added and reacted at 75 ° C. for 1 hour. After completion of the reaction, the mixture was cooled to 60 ° C., 105 parts of dimethylolpropionic acid and 59 parts of triethylamine (0.6 mol based on dimethylolpropionic acid) were added and reacted at 75 ° C. to end the NCO content at 1.0%. A urethane prepolymer (b3) having an isocyanate group was obtained.

Example 1
While stirring 1830 parts by weight of the urethane prepolymer (b1) obtained in Production Example 3 with a homogenizer, a mixture of 250 parts by weight of cellulose fiber A1 obtained in Production Example 1 and 2250 parts by weight of water was gradually added to emulsify and disperse. And stirred for 1 hour. The solvent was removed at 50 ° C. under reduced pressure to obtain an aqueous dispersion containing 30% by weight of polyurethane / cellulose fiber composite resin.

(Examples 2 and 3)
The composite ratio was obtained in the same manner as in Example 1 except that the composite ratio was changed as shown in Table 1.

Example 4
It was obtained by the same production method as in Example 1 except that A2 was used instead of cellulose fiber A1.

(Examples 5 and 6)
It was obtained by the same production method as in Example 1 except that (b2) or (b3) was used instead of the urethane prepolymer (b1).

(Comparative Example 1)
Cellulose fiber A1 was diluted to a solid content of 0.2% by mass to obtain Comparative Example 1.

(Comparative Example 2)
The following raw materials were added to a four-necked flask equipped with a stirrer, reflux condenser, thermometer and nitrogen blowing tube, reacted at 75 ° C. for 4 hours, and free isocyanate group content to non-volatile content was 3.0%. A methyl ethyl ketone solution of a certain urethane prepolymer was obtained.
-Polyester polyol consisting of 1,4-butanediol and adipic acid Product name "Nipporan 4009" (Mw = 1,000, manufactured by Nippon Polyurethane Industry Co., Ltd.)
200 parts by weight of propylene oxide adduct of bisphenol A (polyether polyol)
Product name "Polyether BPX-11" (Made by ADEKA Mw = 360)
400 parts by weight, trimethylolpropane (low molecular weight polyol) 20 parts by weight, dimethylolpropionic acid (ionic group-containing compound) 40 parts by weight, hexamethylene diisocyanate (isocyanate compound) 340 parts by weight, methyl ethyl ketone 800 parts by weight After cooling to 40 ° C. and neutralizing by adding 30 parts by weight of triethylamine, 2700 parts by weight of water was gradually added while stirring with a homogenizer, followed by stirring for 1 hour. The solvent was removed at 50 ° C. under reduced pressure to obtain an aqueous dispersion containing 30% by weight of a polyurethane resin.

(Comparative Example 3)
250 parts by weight of cellulose fiber A1 obtained in Production Example 1 was added to 6100 parts of the polyurethane resin aqueous dispersion prepared in the same manner as in Comparative Example 2 except that the amount of emulsified water was adjusted so that the mixing ratio in Table 1 was obtained. Obtained by stirring.

(Comparative Examples 4 and 6)
It was obtained by the same production method as Comparative Example 2 except that (b2) or (b3) was used instead of the urethane prepolymer (b1).

(Comparative Example 5)
It was obtained by the same production method as in Comparative Example 3 except that (b2) was used instead of the urethane prepolymer (b1).

(Storage stability)
The obtained water dispersion was observed visually at 20 ° C. for 3 days after standing. The case where no separation was observed was evaluated as ◯, the case where separation was slightly observed was evaluated as △, and the case where separation was complete was evaluated as ×.

(Film physical properties (strength, elongation, 100% modulus))
The obtained polyurethane resin aqueous dispersion was put into a Teflon (registered trademark) coating petri dish so as to have a film thickness of 200 μm and dried at 80 ° C. for 6 hours to prepare a film.
An evaluation sample was prepared by cutting the film into the size of a dumbbell-shaped test piece (No. 3). According to JIS-K-6301, tensile strength (N / mm ² ), elongation (%), 100% (N / mm ² ) modulus and the like were measured at a tensile speed of 100 mm / min. The evaluation was expressed as an index when the base urethane was 100. That is, in the case of Example 1, it was calculated as (actual value of Example 1) / (actual value of Comparative Example 2) × 100. The base urethane was set as Comparative Example 2 for Examples 1, 2, 3, 4 and Comparative Examples 1 and 3, as Comparative Example 4 for Examples 5 and 5, and as Comparative Example 6 for Example 6. .

(Solvent resistance)
As a test solution, an ethyl acetate / toluene mixed solution (ethyl acetate / toluene = 50/50 (weight ratio)) and isopropyl alcohol (IPA) were used. The test piece was immersed in each test solution for 24 hours, and the area increase rate with respect to the initial area (2 × 4 cm ² ) was obtained by the following formula, and expressed as an index when the base urethane was set to 100 as with the film properties. . The lower the area increase rate obtained, the better the water resistance.
Area increase rate (%) = (Area after immersion−Initial area) / Initial area × 100

(Discoloration of the film)
A film prepared by the same method as the film physical properties was visually observed for discoloration after 30 minutes in an environment of 150 ° C. The case where there was almost no discoloration was evaluated as ○, and the case where there was discoloration was evaluated as ×.

  As is apparent from Table 1, the aqueous dispersion of the present invention has good storage stability and good film properties, solvent resistance and discoloration obtained. On the other hand, it turns out that the comparative example which is outside the scope of the present invention is inferior. In particular, even when compared with a mixture of urethane and cellulose after chain extension, it can be seen that the film properties, solvent resistance, and discoloration are good.

  The aqueous dispersion of the present invention can be used as a coating material. In particular, since the storage stability is good and the resulting film has good physical properties, solvent resistance and discoloration, it can be suitably used in fields where these properties are required.

Claims (4)

An aqueous dispersion of cellulose nanofiber (A) and polyurethane resin (B) characterized by satisfying the following conditions,
At least the urethane prepolymer (b) solution and the cellulose nanofiber (A)
After mixing the aqueous dispersion of
Further, an aqueous dispersion obtained by chain-extending the urethane prepolymer (b) to obtain a polyurethane resin (B).
(A-1) Number average fiber diameter of 2 nm to 500 nm (A-2) Average aspect ratio of 50 to 1000 (A-3) Cellulose I-type crystal structure (A-4) Anionic functional group Mixing ratio of cellulose nanofiber (A) and polyurethane resin (B) (solid weight ratio)
The aqueous dispersion according to claim 1, wherein is 0.1 / 100 to 5/100. At least a step of mixing the urethane prepolymer (b) solution and the aqueous dispersion of cellulose nanofiber (A);
Then, the manufacturing method of the water dispersion of the cellulose nanofiber (A) which has the process of extending | stretching a urethane prepolymer and making it a polyurethane resin (B), and a polyurethane resin (B).   A coating material containing the aqueous dispersion according to claim 1.