JP6560778B1 - Coating composition and method for producing the same - Google Patents

Abstract

To provide a coating composition excellent in storage stability, having few restrictions on components such as pigments to be blended and having excellent coating properties, and a method for producing the same. SOLUTION: Cellulose nanofibers satisfying the following conditions (A) to (E), a water-miscible organic solvent, water, and a pigment are contained, and the mass ratio of the content of the pigment and the content of the cellulose nanofiber is Pigment / cellulose nanofiber = 60 to 500. (A) Short width number average fiber width of 2 nm to 500 nm (B) Average aspect ratio of 50 to 1000 (C) Cellulose type I crystal structure (D) Anionic functional group (E) Organic concept Organic compound with an organic value of 450 or less in the figure is bound to an anionic functional group by ionic bond [Selection] None

Description

  The present invention relates to a coating composition and a method for producing the same.

  In recent years, biomass raw materials have attracted attention as environmentally friendly materials. Of these, materials made from biomass raw materials in the form of fine fibers are attracting particular attention. Among these, cellulose nanofibers are actively researched and developed as resin-reinforced materials, gas barrier films, thickeners, etc. The method used as is disclosed (Patent Document 1).

JP 2009-67910 A

  When cellulose nanofibers are used as a coating composition, there is a problem that a large amount of organic solvent cannot be blended due to the high hydrophilicity of cellulose nanofibers. For this reason, there existed a problem that the material to mix | blend was limited or the applicability | paintability was low and it was easy to make a nonuniformity. Moreover, there existed a problem that a cellulose hydrolyzes by storing for a long term, viscosity falls, and stability deteriorates.

  Accordingly, an object of the present invention is to provide a coating composition excellent in storage stability, having few restrictions on components such as pigments to be blended, and having excellent coating properties, and a method for producing the same.

The present invention provides the following [1] to [9].
[1] A cellulose nanofiber that satisfies the following conditions (A) to (E), a water-miscible organic solvent, water, and a pigment are contained, and the mass ratio of the content of the pigment and the content of the cellulose nanofiber is: pigment / cellulose nanofibers = 60 to 500 der is, the mass ratio of the content and the content of water-miscible organic solvent of the cellulose nanofibers cellulose nanofiber / water-miscible organic solvent = 0.001 coating composition characterized in <br/> that is.
(A) Short width number average fiber width of 2 nm to 500 nm (B) Average aspect ratio of 50 to 1000 (C) Cellulose type I crystal structure (D) Anionic functional group (E) Organic concept Organic compounds with organic values of 450 or less in the figure are bound to anionic functional groups by ionic bonds
[2] The coating composition according to [1], wherein the anionic functional group is a carboxyl group.
[3] The organic compound having an organic value of 450 or less in the organic conceptual diagram (E) is one or more selected from nitrogen-containing compounds and organic phosphorus compounds.
The coating composition according to [1] or [2].
[4] The organic compound having an organic value of 450 or less in the organic conceptual diagram (E) is one or more selected from ammonium and phosphonium [1] to [3] The coating composition according to any one of the above.
[5] The coating composition according to any one of [1] to [4], wherein the water-miscible organic solvent has a hydroxyl group.
[6] The coating composition according to any one of [1] to [5], wherein the pigment has an average particle size of 500 μm or less.
[7] The coating composition according to any one of [1] to [6], wherein the content of the cellulose nanofiber is 0.1% by mass or more and 2.0% by mass or less.
[8] (I) Oxidation step for oxidizing cellulose, (II) Purification step for adjusting the pH of the oxidized cellulose aqueous dispersion to 2 or less, (III) Organic value in the above organic conceptual diagram for purified cellulose [1] thru | or comprising the neutralization process neutralized with the organic compound whose is 450 or less, and (IV) the dispersion process which disperse | distributes the neutralized cellulose in presence of water and a water miscible organic solvent. [7] The method for producing a coating composition according to any one of [7].
[9] The method for producing a coating composition according to [8], wherein the dispersion condition in the dispersion step (IV) is a treatment with a high-pressure or ultrahigh-pressure homogenizer, and the treatment pressure is 30 MPa or more.

  The coating composition of the present invention is excellent in storage stability, has few restrictions on components such as pigments to be blended, and has an effect of being excellent in coating properties.

  Next, embodiments of the present invention will be described in detail.

The coating composition of the present invention contains a predetermined cellulose nanofiber.
(A) Number average fiber width of short width The number average fiber width of short width of the cellulose nanofiber is 2 nm or more and 500 nm or less, preferably 150 nm or less, more preferably 100 nm or less, particularly preferably 80 nm. It is as follows. When the number average fiber width of the short width is less than 2 nm, there is a possibility that sufficient thickening and dispersion stability may not be exhibited due to dissolution of the cellulose nanofiber, and the number average fiber width of the short width is 500 nm. When exceeding, since the surface area of a cellulose nanofiber becomes small and sufficient network structure of a nanofiber is not formed, there exists a possibility that it may be inferior to a viscosity increase and dispersion stability.

  The shortest maximum fiber width 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 short-width number average fiber width and the shortest maximum fiber width of the cellulose nanofiber can be measured, for example, as follows. That is, an aqueous dispersion of cellulose nanofibers 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. A sample for observation with a microscope (TEM) is used. 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 satisfying this condition, two random axes, vertical and horizontal, per image are drawn on this image, and the fiber width of the fibers crossing 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 width values of the fibers that intersect 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). Based on the fiber width data thus obtained, the shortest maximum fiber width and the short-width number average fiber width are calculated.

(B) 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 dispersion stability of the cellulose nanofiber may be lowered.

  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 width of the short width and the number average width of the long width of the cellulose nanofiber were observed. That is, according to the method described above, the number average width of the short width and the number average width of the long width were calculated, and the aspect ratio was calculated according to the following formula using these values.

Average aspect ratio = number average fiber width of long width (nm) / number average fiber width of short width (nm) (1)

(C) 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.

(D) Anionic functional group The cellulose nanofiber has an anionic functional group.

  The anionic functional group is not particularly limited, and specific examples include a carboxyl group, a phosphoric acid group, and a sulfuric acid group. Among these, a carboxyl group is used because of the ease of introduction of an anionic functional group into cellulose. Groups are preferred.

  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, but at least one of the acid anhydrides of the compound having a carboxyl group, such as dimethylmaleic anhydride, diethylmaleic anhydride, diphenylmaleic anhydride and the like. And those in which a part of the hydrogen atoms are substituted with a substituent (for example, 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 0.5 mmol / g or more, more preferably 1.5 mmol / g or more from the viewpoint of the ease of the dispersion process of oxidized cellulose and the uniformity of the fiber diameter of the obtained cellulose nanofibers. preferable. Moreover, 2.5 mmol / g or less is preferable and 2.0 mmol / g or less is more preferable.

  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 gentle change in electrical conductivity (V) according to the following formula (2).

Amount of carboxyl groups (mmol / g) = V (ml) × [0.05 / cellulose weight] (2)

  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 natural cellulose 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 reduction, the total content of aldehyde groups and ketone groups as measured by the semicarbazide method of the cellulose nanofiber is preferably 0.3 mmol / g or less, particularly preferably 0.1 mmol / g or less, Most preferably, it is substantially 0 mmol / g. Thereby, the molecular weight fall of a cellulose nanofiber is suppressed and dispersion stability can be maintained for a long 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.

Carbonyl group amount (mmol / g) = (D−B) × f × [0.125 / w] (3)
D: Sample titration (ml)
B: Titrate of blank test (ml)
f: Factor of 0.1N sodium thiosulfate solution (-)
w: Sample amount (g)

In the cellulose nanofiber, 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 said cellulose nanofabric can also be performed with a Faring reagent, for example. 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.

(E) Organic compound having an organic value of 450 or less in the organic conceptual diagram The cellulose nanofiber of the present invention has an organic value in the organic conceptual diagram (hereinafter sometimes simply referred to as an organic value) of 450 or less. The compound is bonded to the anionic functional group by an ionic bond.

  The organic conceptual diagram is described in, for example, “Organic conceptual diagram—Basics and applications” (Yoshio Koda, Sankyo Publishing, 1984). In other words, “organic conceptual diagram” means “organic” due to covalent bonds in the carbon region of all organic compounds and “inorganic” due to the influence of electrostatic properties present in substituents (functional groups). The “factor” is converted into a numerical value according to a predetermined rule, and the organic value is plotted on the X axis and the inorganic value is plotted on the Y axis. The above document states that the magnitude of the organic value in the organic conceptual diagram can be measured by the number of carbon atoms represented by the methylene group in the molecule of the organic compound. The organic value of one carbon atom is defined as 20 by taking an average boiling point increase of 20 ° C. by adding one carbon in the vicinity of 5 to 10 carbon atoms of the organic compound. .

  The organic value is 450 or less, preferably 400 or less, and more preferably 360 or less. If the organic value exceeds 450, the hydrophobicity is too high and the cellulose fibers may not be neutralized. The organic compound having an organic value of 450 or less in the organic conceptual diagram is preferably one or more selected from nitrogen-containing compounds and organic phosphorus compounds. Although it does not restrict | limit especially as said nitrogen-containing compound, Specifically, a primary amine, a secondary amine, a tertiary amine, a quaternary ammonium, etc. are mentioned.

  Among these nitrogen-containing compounds, preferably amines such as triethylamine, triethanolamine, dimethylbutylamine, dimethyloctylamine, monooctylamine, dimethylbenzylamine, triisopropanolamine, dimethyloctadecylamine, and tetramethylammonium hydroxide, tetraethyl Quaternary ammoniums such as ammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, benzyltrimethylammonium hydroxide, benzyltriethylammonium hydroxide, hexadecyltrimethylammonium hydroxide.

  Further, the organic phosphorus compound is not particularly limited, and specific examples thereof include quaternary phosphonium. Among these, tetramethylphosphonium hydroxide, tetraethylphosphonium hydroxide, tetrapropylphosphonium hydroxide, tetrabutyl are preferable. Phosphonium such as phosphonium hydroxide, benzyltrimethylphosphonium hydroxide, benzyltriethylphosphonium hydroxide, hexadecyltrimethylphosphonium hydroxide is preferable.

  Among these, the compound whose organic value is 400 or less includes dimethyloctadecylamine, and the compound whose organic value is 360 or less includes tetrabutylphosphonium hydroxide and tetrabutylammonium hydroxide.

  The coating composition of the present invention contains a water-miscible organic solvent.

  The water-miscible organic solvent is preferably an organic solvent that dissolves 50 g or more in 1 liter of ion-exchanged water at 25 ° C., and is not particularly limited. Specifically, as alcohols, monoalcohols such as methanol, ethanol, propanol, isopropanol Ethylene glycols such as ethylene glycol, diethylene glycol, thiodiethylene glycol, triethylene glycol, tetraethylene glycol, and polyethylene glycol as polyhydric alcohols such as butanol and acetylene alcohol; 2-methyl-1,3-propanediol, Propanediols such as 2-ethyl-1,3-propanediol and 3-methoxy-1,2-propanediol; 2-butene-1,4-diol, 1,3-butanediol, 2-methyl-1, 4- Butanediols such as tanger; 2-methyl-2,4-pentanediol, 1,5-pentanediol, 1,4-pentanediol, 3-methyl-1,3-pentanediol, 2,4-diethyl-1 Pentanediols such as 1,5-pentanediol; hexanediols such as 1,2-hexanediol; 1,2,6-trimethyl-1,7-heptanediol, 2,4,6-triethyl-1,7- Heptanediols such as heptanediol; octanediols such as 3,6-dithia-1,8-octanediol; other alkylene diols such as propylene glycol, dipropylene glycol, polypropylene glycol, butylene glycol; glycerin, hexanetriol , Thiodiglycol, trimethylolpro Examples of glycol derivatives such as polyols such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monomethyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, propylene glycol monomethyl ether , Propylene glycol monobutyl ether, dipropylene glycol monomethyl ether, triethylene glycol monomethyl ether, polyethylene glycol monomethyl ether, ethylene glycol monoisopropyl ether, triethylene glycol monobutyl ether, ethylene glycol monoisobutyl ether, di Ethylene glycol monoisobutyl ether, propylene glycol monopropyl ether, ethylene glycol diacetate, ethylene glycol monomethyl ether acetate, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, ethylene glycol monophenyl ether, etc., as amines such as ethanolamine, Diethanolamine, triethanolamine, N-methyldiethanolamine, N-ethyldiethanolamine, morpholine, N-ethylmorpholine, ethylenediamine, diethylenetriamine, triethylenetetramine, polyethyleneimine, tetramethylpropylenediamine, and other polar solvents such as formamide, N, N-dimethylformamide, N N-dimethylacetamide, dimethyl sulfoxide, sulfolane, 3-methylsulfolane, 3-sulfolene, bis (2-hydroxyethyl) sulfone, 2-pyrrolidone, N-methyl-2-pyrrolidone, N-vinyl-2-pyrrolidone, 2- Examples include pyrrolidone-5-carboxylic acid, 2-oxazolidone, 1,3-dimethyl-2-imidazolidinone, acetonitrile, acetone, diacetone alcohol, and 4-picoline. These may be used alone or in combination of two or more.

  Since the water-miscible organic solvent can form a hydrogen bond with a hydroxyl group of cellulose nanofiber, alcohols having a hydroxyl group are preferable.

  Although it does not restrict | limit especially as said alcohol, Specifically, methanol, ethanol, propanol, isopropanol, benzyl alcohol, ethylene diols, such as ethylene glycol, diethylene glycol, polyethyleneglycol, as a polyhydric alcohol; 2-methyl-1, Propanediols such as 3-propanediol, 2-ethyl-1,3-propanediol, 3-methoxy-1,2-propanediol; 2-butene-1,4-diol, 1,3-butanediol, 2 -Butanediols such as methyl-1,4-butanediol; 2-methyl-2,4-pentanediol, 1,5-pentanediol, 1,4-pentanediol, 3-methyl-1,3-pentanediol, 2,4-diethyl-1,5-pentanediol One or more selected pentane diols and the like. These may be used alone or in combination of two or more.

  The coating composition of the present invention contains a predetermined pigment.

  Examples of the pigment include inorganic pigments and organic pigments. These may be used alone or in combination of two or more. Examples of the inorganic pigment include carbon black, titanium oxide, zinc white, bengara, chromium oxide, iron black, cobalt blue, alumina white, iron oxide yellow, viridian, zinc sulfide, cadmium yellow, vermilion, cadmium red, yellow Lead, molybdate orange, zinc chromate, strontium chromate, white carbon, clay, talc, ultramarine, barite powder, lead white, bitumen, manganese violet, aluminum powder, brass powder and the like. Examples of the organic pigment include azo lake, insoluble azo pigment, chelate azo pigment, phthalocyanine pigment, perylene and perylene pigment, anthraquinone pigment, quinacridone pigment, dye lake nitro pigment, nitroso pigment and the like.

  The average particle diameter of the pigment is preferably 500 μm or less, and more preferably 100 μm or less. When the average particle diameter is 500 μm or less, there is an advantage that it is difficult to be uneven when coated and a uniform coating film can be easily obtained.

The coating composition of the present invention may contain a resin as necessary. The resin is preferably a resin emulsion, and the natural and / or synthetic resin emulsion includes a resin emulsion, a latex and the like. Among them, a synthetic resin aqueous emulsion is preferable.

  Examples of synthetic resin aqueous emulsions include vinyl acetate, urethane, acrylic, polyester, epoxy, and polyvinyl alcohol resin emulsions. Specifically, vinyl acetate resin emulsion, acrylic resin emulsion, styrene / Acrylic copolymer resin emulsion, ethylene, vinyl vinyl acetate, ethylenically unsaturated carboxylic acid, vinyl chloride, vinyl acetate copolymer copolymerized with vinyl acetate and (meth) acrylic acid alkyl ester, etc. . These may be used alone or in combination of two or more.

  The coating composition of the present invention can contain an optional component as long as it does not interfere with the effects of the present invention.

  The optional ingredients include lame, pearl, preservative, fragrance, plasticizer, antifoam, filler, antioxidant, UV absorber, curing agent, catalyst, solvent, surfactant, flame retardant, electrification Examples thereof include additives added for the purpose of preventing agents, heat stabilizers, thickeners, pigment dispersion, prevention of skinning, leveling, acceleration of drying, and the like.

  In the coating composition of the present invention, the content of cellulose nanofibers is preferably 0.05% by mass or more, and more preferably 0.1% by mass or more. Moreover, it is preferable that it is 2 mass% or less, and it is more preferable that it is 1.0 mass% or less. When the content is within the above range, a coating composition having excellent pigment dispersion stability and coating property can be obtained, which is preferable.

  In the coating composition of the present invention, the content of the water-miscible organic solvent is preferably 20% by mass or more, and more preferably 45% by mass or more. Moreover, 80 mass% or less is preferable, and 70 mass% or less is more preferable. When the content is within the above range, a coating composition having excellent pigment dispersion stability and coating property can be obtained, which is preferable.

  In the coating composition of the present invention, the content of the pigment is preferably 5% by mass or more, and more preferably 20% by mass or more. Moreover, 70 mass% or less is preferable, and 50 mass% or less is more preferable. When the content is within the above range, a coating composition having excellent pigment dispersion stability and coating property can be obtained, which is preferable.

The ratio of the pigment content and the cellulose nanofiber content in the coating composition of the present invention is pigment / cellulose nanofiber = 60 to 500 in terms of mass ratio, preferably 60 to 300, and more preferably 60 to 100. It is preferable in terms of long-term stability of the composition and coatability (rheological properties) that the content ratio is within the above range.

  The ratio of the cellulose nanofiber content to the water-miscible organic solvent content in the coating composition of the present invention is preferably cellulose nanofiber / water-miscible organic solvent = 0.001 to 0.1 in terms of mass ratio. 0025 to 0.005 is more preferable, and 0.006 to 0.0125 is more preferable. It is preferable in terms of long-term stability of the composition and coatability (rheological properties) that the content ratio is within the above range.

  The coating composition of the present invention comprises (I) an oxidation step for oxidizing cellulose, (II) a purification step for purification by adjusting the pH of the oxidized cellulose dispersion to 2 or less, and (III) an organic conceptual diagram of the purified cellulose. It is preferable to include a neutralization step of neutralizing with an organic compound having an organic value of 450 or less, and (IV) a dispersion step of dispersing the neutralized cellulose in the presence of water and a water-miscible organic solvent. Specifically, it is preferable to manufacture 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 initiate 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 has a solid content (cellulose) concentration in the range of about 10 wt% to 50 wt% in a squeezed state. Considering the subsequent dispersion step, if the solid content concentration is higher than 50% by weight, it is not preferable because extremely high energy is required for dispersion.

(III) Neutralization Step Next, the purified oxidized cellulose is neutralized with an organic compound having an organic value of 450 or less in the organic conceptual diagram. Specifically, the aqueous dispersion of oxidized cellulose is adjusted to a predetermined solid content concentration of water or water and the above water-miscible organic solvent, and an organic compound having an organic value of 450 or less is added. This can be done by stirring. In this case, the pH of the aqueous 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 is entangled by the acid, and it is difficult to unravel 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. An organic compound having an organic value of 450 or less may be diluted with water or a mixed solvent of water and the above organic solvent 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, it is preferable because an organic compound having an organic value of 450 or less can be uniformly mixed. The stirring time is not particularly limited as long as the organic compound having an organic value of 450 or less can be uniformly dispersed in the aqueous dispersion of reactant fibers.

(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 coating composition of the present invention, 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. Of 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 reactant fiber. 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.

  The coating composition of the present invention can be obtained by blending cellulose nanofibers, water, a water-miscible organic solvent, a pigment, and other additives such as a resin as necessary, followed by mixing treatment.

  More specifically, as the mixing treatment, for example, various homogenizers such as vacuum homomixer, disper, propeller mixer, kneader, various pulverizers, blender, homogenizer, ultrasonic homogenizer, colloid mill, pebble mill, bead mill pulverizer, Examples thereof include a mixing process using a high-pressure homogenizer, an ultrahigh-pressure homogenizer, or the like.

  Next, examples will be described together with comparative examples. However, the present invention is not limited to these examples. In the examples, “%” means mass basis unless otherwise specified.

[Manufacture of paint compositions]
[Example 1]
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 wt% sodium hypochlorite aqueous solution (co-oxidant) was added to the pulp 1. The reaction was started by adding sodium hypochlorite to 7.5 mmol / g with respect to 0 g. The temperature was kept at 20 ° C. during the reaction. 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 the pH to 2 or less, and then purification was repeated by filtration and washing with water.
Pure water was added thereto to adjust the solid content concentration to 2%. Thereafter, the pH of the slurry was adjusted to 10 with a 24% NaOH aqueous solution. The slurry was reduced to 30 ° C. by adding 0.2 mmol / g of sodium borohydride to the cellulose fiber and reacting for 2 hours. After the reaction, 0.1N hydrochloric acid was added to adjust the pH to 2 or less, and then purification was repeated by filtration and washing with water.
Pure water was added thereto so that the final concentration was 2% by mass of cellulose fibers and the balance was water. Tetrabutylphosphonium hydroxide (TBPH, organic value 340) was added thereto, and the pH was adjusted to 7. Cellulose nanofibers were prepared by treating this three times at a pressure of 100 MPa using a high-pressure homogenizer (manufactured by Sanwa Engineering, H11).
Ethanol (EtOH), pigment, and water were added to this so that the final concentration was the same as in Table 1, and the mixture was stirred with a homodisper (Primix, homodisper 2.5 type) at 4,000 rpm for 10 minutes, and the coating composition I got a thing.

[Examples 2 to 4]
Tetrabutylammonium hydroxide (TBAH, organic value 320), dimethylbenzylamine (DMBzA, organic value 180) instead of tetrabutylphosphonium hydroxide as neutralizing agent, 2-amino-2-methyl-1,3- A coating composition was prepared in the same manner as in Example 1 except that propanediol (AMPDOH, organic value 80) was used.

[Examples 5 to 7]
A coating composition was prepared in the same manner as in Example 2 except that the water-miscible organic solvent to be added was changed from ethanol to ethylene glycol (EG), isopropanol (IPA), and propylene glycol monomethyl ether (PGME).

[Examples 8 to 10]
A coating composition was prepared in the same manner as in Example 2 except that the blending amounts of cellulose nanofiber and water-miscible organic solvent were changed as shown in Table 1.

[Examples 11 to 13]
A coating composition was prepared in the same manner as in Example 2 except that the type of pigment was changed as shown in Table 1.

[Comparative Example 1]
Cellulose nanofibers and a coating composition were prepared in the same manner as in Example 1 except that the amount of sodium hypochlorite aqueous solution added was 1 mmol / g.

[Comparative Example 2]
Cellulose nanofibers and a coating composition were prepared in the same manner as in Example 1 except that sodium hydroxide was used instead of tetrabutylphosphonium hydroxide as a neutralizing agent.

[Comparative Example 3]
A coating composition was prepared in the same manner as in Example 2 except that ethanol was not added.

[Comparative Examples 4 and 5]
A coating composition was prepared in the same manner as in Example 2 except that the blending amounts of cellulose nanofiber, water-miscible organic solvent, and pigment were changed as shown in Table 1.

[Characteristic evaluation of coating composition]
The characteristics of the cellulose nanofibers and coating compositions described in Examples 1 to 13 and Comparative Examples 1 to 5 obtained as described above were evaluated according to the following criteria. The results are also shown in Table 1 below.

<Number average fiber width of short width>
The number average fiber width of cellulose was observed using a transmission electron microscope (TEM) (manufactured by JEOL Ltd., JEM-1400). That is, after each cellulose fiber was cast on a carbon film-coated grid that had been subjected to hydrophilization treatment, from a TEM image (magnification: 10000 times) that was negatively stained with 2% uranyl acetate, The average fiber width was calculated.

<Aspect ratio>
From the TEM image (magnification: 10000 times) of cellulose nanofibers cast on a hydrophilized carbon film-coated grid and then negatively stained with 2% uranyl acetate, the number average fiber width and length of cellulose nanofibers are short. The number average fiber width of the width was observed. That is, the number average fiber width of the short width and the number average fiber width of the long width were calculated according to the methods described above, and the aspect ratio was calculated according to the following formula using these values.

Average aspect ratio = number average fiber width of long width (nm) / number average fiber width of short width (nm) (1)

<Crystal structure>
Using an X-ray diffractometer (RINT-UltIma3, manufactured by Rigaku Corporation), the diffraction profile of each cellulose fiber was measured, and two positions of 2 theta = 14-17 ° and 2 theta = 22-23 ° were obtained. 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”.

<Dispersion stability>
25 ml of the obtained coating composition was transferred to a 25 ml graduated test tube and allowed to stand at 40 ° C. for 1 month. One month later, the sedimentation degree of the pigment was evaluated from the following formula (4).

Dispersion stability (%) = (25−amount of water separation (ml)) / 25 × 100 (4)

<Coating property>
The obtained coating composition was allowed to stand for 24 hours, and then applied to a PET film using a 12 μm bar coater. After drying at room temperature for 6 hours, the state of the coating film was visually observed and evaluated as follows.
3: There is no repelling or unevenness, and the coating film is uniform.
2: Although repellency and unevenness are partially observed, the coating film is almost uniform.
1: 80% or more of repelling, unevenness, etc. are seen in a coating area of 100%, and a uniform coating film cannot be created.

<Dispersibility of pigment>
The coating film of the coating composition obtained by the evaluation of the coating property was observed with an optical microscope (1,000 times magnification), and pigment aggregation was evaluated as follows.
3: Little pigment agglomeration is observed 2: 1 image shows 1-10 aggregates 1: 1 image shows 11-20 aggregates 0: 1 image 21 More than agglomerates

＊１：顔料種
・ＴｉＯ_２：タイペークＣＲ-５０（石原産業製）
・ＣＢ：カーボンブラックＭＡ―１００（三菱化学製）
・有機顔料１：ＬＩＯＮＯＧＥＮ ＢＬＵＥ ６５１０（トーヨーカラー製）
・有機顔料２：ＬＩＯＮＯＧＥＮ ＢＬＵＥ ６５１１（トーヨーカラー製）

* 1: Pigment type • TiO ₂ : Taipei CR-50 (Ishihara Sangyo)
・ CB: Carbon black MA-100 (Mitsubishi Chemical)
・ Organic Pigment 1: LIONOGEN BLUE 6510 (Toyo Color)
・ Organic pigment 2: LIONOGEN BLUE 6511 (Toyo Color)

  In all of the examples, the stability of the dispersion, the dispersibility of the pigment, and the coating property were high. Regarding Comparative Example 1, the shorter fiber width and the aspect ratio of the cellulose nanofiber are out of the claims, and the fiber is too thick, so that the stability of the dispersion, the dispersibility of the pigment, and the coatability are high. It was low. Regarding Comparative Example 2, since the cellulose nanofiber was a sodium salt, a uniform dispersion state could not be maintained in a state where the solvent was blended, and the stability of the dispersion was low. Furthermore, since the cellulose nanofibers aggregated, the dispersibility and coating property of the pigment were also low. Regarding Comparative Example 3, since no water-miscible organic solvent was blended, the wettability to the substrate was low, and the coating property was low. Regarding Comparative Example 4, the pigment / CNF blending ratio was smaller than the claims, the viscosity was too high, and the coating property was low. Regarding Comparative Example 5, the pigment / CNF blending ratio was larger than the claims, and the effect of suppressing the precipitation of the pigment in the dispersion with the cellulose nanofibers was not obtained, and the stability of the dispersion was low. Accordingly, the dispersion stability and coating property of the pigment were also low.

  The coating composition of the present invention can be suitably used in the field of coatings and inks such as automobiles, building materials, and stationery.

Claims (9)

Contains cellulose nanofibers that satisfy the following conditions (A) to (E), a water-miscible organic solvent, water, and a pigment,
And the content of the pigment, the mass ratio of the content of the cellulose nanofiber is a pigment / cellulose nanofibers = 60 to 500,
Weight ratio in content between the water-miscible organic solvent of the cellulose nanofibers are cellulose nanofibers / water-miscible organic solvent = 0.001,
The coating composition , wherein the water-miscible organic solvent is an alcohol .
(A) Short width number average fiber width of 2 nm to 500 nm (B) Average aspect ratio of 50 to 1000 (C) Cellulose type I crystal structure (D) Anionic functional group (E) Organic concept Organic compounds with organic values of 450 or less in the figure are bound to anionic functional groups by ionic bonds   The coating composition according to claim 1, wherein the anionic functional group is a carboxyl group.   3. The organic compound having an organic value of 450 or less in the organic conceptual diagram (E) is one or more selected from a nitrogen-containing compound and an organic phosphorus compound. The coating composition as described in 2.   4. The organic compound having an organic value of 450 or less in the organic conceptual diagram (E) is one or more selected from ammonium and phosphonium. 5. The coating composition as described in 2.   The coating composition according to any one of claims 1 to 4, wherein the water-miscible organic solvent has a hydroxyl group.   The coating composition according to any one of claims 1 to 5, wherein the pigment has an average particle size of 500 µm or less.   The coating composition according to any one of claims 1 to 6, wherein the content of the cellulose nanofiber is 0.1 mass% or more and 2.0 mass% or less. (I) an oxidation step for oxidizing cellulose,
(II) a purification step in which the pH of the aqueous dispersion of oxidized cellulose is adjusted to 2 or less and purified.
(III) A neutralization step of neutralizing the purified cellulose with an organic compound having an organic value of 450 or less in the organic conceptual diagram,
(IV) The method for producing a coating composition according to any one of claims 1 to 7, further comprising a dispersion step of dispersing the neutralized cellulose in the presence of water and a water-miscible organic solvent. The method for producing a coating composition according to claim 8, wherein the dispersion condition in the dispersion step (IV) is a treatment with a high-pressure or ultrahigh-pressure homogenizer, and the treatment pressure is 30 MPa or more.