JP7802292B2 - water-based paint composition - Google Patents

Description

The present invention relates to an aqueous coating composition.

Traditionally, there have been traditional crafts, Japanese and Western tableware, decorative items, interior accessories, and other items that feature beautiful or pleasing designs. These designs are applied to the ceramic base using, for example, an aqueous paint composition. After the design is applied with the aqueous paint, the ceramic base is glazed and fired to become the finished product.

When an artist paints, for example, they pour an appropriate amount of the aqueous coating composition into a mortar and soak a brush in it to paint. This aqueous coating composition contains a coloring base material such as a pigment. If the aqueous coating composition poured into the mortar is left standing, the coloring base material will settle in the aqueous coating composition due to gravity, resulting in separation into a coloring base phase and an aqueous phase. When painting with the separated aqueous coating composition, color unevenness or uneven application may occur. To prevent this, for example, the artist frequently stirs the aqueous coating composition thoroughly with a pestle to make it uniform.

One way to make an aqueous paint composition less susceptible to separation is to add a thickener. Patent Document 1 describes a technique for adding a thickener. In Patent Document 1, a thickener (rheology control agent) that is effective in small amounts is added to the aqueous paint composition to ensure the desired viscosity. However, when a highly viscous aqueous paint composition is applied to a brush and used to paint on a ceramic base (the object to be painted), the aqueous paint composition does not spread well, making it difficult to paint.

One way to improve spreadability is to dilute the water-based paint composition with water or an organic solvent, but this dilutes the concentration of the thickener and reduces the viscosity, causing the diluted water-based paint composition to separate over time.

JP 2014-132091 A Japanese Patent Application Laid-Open No. 2019-1876 Japanese Patent Application Laid-Open No. 2019-199671

The problem that this invention aims to solve is to provide an aqueous coating composition that prevents the colored substrate from settling even after a period of time.

The inventors conducted extensive research and discovered that cellulose nanofibers esterified with phosphorus oxoacid have extremely high dispersibility and maintain a dispersed state for a long period of time. They discovered that by including this cellulose nanofiber in an aqueous coating composition, the colored substrate can be maintained in a dispersed state for a long period of time. Based on this discovery, the following aspects solve the problem.
(First Aspect)
The present invention comprises a coloring base material and cellulose nanofibers having an ester group of phosphorous acid introduced therein,
The concentration index of the liquid surface after standing for 24 hours is 90 or more.
1. A water-based coating composition comprising:

Cellulose nanofibers modified with ester groups of phosphorus oxoacid have excellent viscosity, and therefore remain dispersed without settling. Furthermore, the colored substrate remains dispersed by adhering to the cellulose nanofibers or remaining in the gaps formed between the cellulose nanofibers. Therefore, the aqueous coating composition of this embodiment allows the colored substrate to remain dispersed for an extended period of time without settling.

(Second Aspect)
The cellulose nanofibers are contained in an amount of 2 to 4% by mass,
The cellulose nanofibers have cellulose nanofibers obtained by defibrating chemical pulp,
The cellulose nanofibers obtained by defibrating the chemical pulp have cellulose nanofibers (A) in which some of the hydroxy groups of the cellulose fibers have been substituted with functional groups represented by the following structural formula (1) and an ester of a phosphorus oxoacid has been introduced:
Water-based paint composition.
[Structural formula (1)]
In structural formula (1), a, b, m, and n are natural numbers.
At least one of A1, A2, ..., An and A' is O, and the rest are R, OR, NHR, or none. R is a hydrogen atom, a saturated linear hydrocarbon group, a saturated branched hydrocarbon group, a saturated cyclic hydrocarbon group, an unsaturated linear hydrocarbon group, an unsaturated branched hydrocarbon group, an aromatic group, or a group derived from any of these. α is a cation made of an organic or inorganic substance.

Cellulose nanofibers can be obtained, for example, by defibrating mechanical pulp or chemical pulp. The inventors have found that chemical pulp, in particular, is easy to defibrate because it has a low lignin content and relatively high purity. High purity pulp results in cellulose nanofibers with small variance in fiber diameter and fiber length after defibration, i.e., small variations in fiber diameter and fiber length. Cellulose nanofibers with small variations in fiber diameter and fiber length are highly dispersible in aqueous paint compositions, resulting in aqueous paint compositions with good adhesion, resistance to sagging, and good spreadability. Furthermore, because cellulose nanofiber (A) has a relatively high viscosity, it maintains a dispersed state and is resistant to settling. Therefore, the colored substrate also maintains a stably dispersed state without settling for an extended period of time.

(Third Aspect)
A part of the hydroxy groups of the cellulose fibers is substituted with carbamate groups to introduce carbamate.
Water-based paint composition.

The cellulose nanofibers of this embodiment include those into which an ester of phosphorus oxoacid has been introduced and those into which a carbamate has been introduced. The interaction between the ester of phosphorus oxoacid and the carbamate increases the shear force of the aqueous coating composition, improving viscosity. The high viscosity makes it difficult for the cellulose nanofibers dispersed in the aqueous coating composition to settle, maintaining excellent dispersibility for an extended period of time.

(Fourth Aspect)
The cellulose nanofibers (A) are cellulose fibers in which two or more of the hydroxy groups are substituted with functional groups represented by the structural formula (1) and an ester of a phosphorus oxoacid is introduced.
Water-based paint composition.

Since the ester group of phosphorus oxoacid is polar, it is presumed that hydrogen bonding occurs easily. In a hydrogen-bonded state, the free movement of cellulose nanofibers is restricted, making them less likely to settle. In this embodiment, because two or more phosphorus oxoacid esters are introduced, there are relatively more sites where hydrogen bonding can occur, further restricting the free movement of cellulose nanofibers.

(Fifth Aspect)
In a pseudo particle size distribution measured by a laser diffraction method, the ratio (D50/D90) of the cumulative 50% diameter (D50) to the cumulative 90% diameter (D90) on a volume basis is 0.50 to 1.
Water-based paint composition.

The closer the ratio (D50/D90) is to 1, the less variation there is in the pseudo-particle size of the entire solid content contained in the aqueous paint composition, and the more uniform the pseudo-particle size of the entire solid content. The more uniform the pseudo-particle size of the entire solid content, the longer the solid content will remain dispersed.

This invention results in an aqueous coating composition in which the colored substrate is less likely to settle even after time has passed.

This is an explanatory diagram of the base material, the glaze layer covering this base material, and the drawing. 1A to 1C are diagrams illustrating a manufacturing procedure. 1A to 1C are diagrams illustrating a manufacturing procedure. FIG. 1 is a diagram showing particle size distribution. FIG. 10 is a diagram showing the results of a test on the degree of sedimentation. FIG. 10 is a diagram showing the results of a test on the degree of sedimentation. FIG. 10 is a diagram showing the results of a test on the degree of sedimentation. FIG. 10 is a diagram showing the results of a test on the degree of sedimentation. FIG. 10 is a diagram showing the results of a test on the degree of sedimentation.

The following describes an embodiment of the present invention. Note that this embodiment is merely an example of the present invention. The scope of the present invention is not limited to the scope of this embodiment.

The aqueous coating composition of this embodiment comprises a colored substrate and cellulose nanofibers, the cellulose nanofibers comprising cellulose nanofibers (A) into which an ester of a phosphorus oxoacid has been introduced, and which have a single peak in a pseudo-particle size distribution curve measured by laser diffraction. Each composition is described in detail below.

(Colored base material)
A coloring base material is a substance that colors the pottery base and exhibits various colors depending on the type of base material. Methods for decorating pottery base materials with an aqueous coating composition include overglazing and underglazing. Underglazing involves painting a design on a bisque-fired pottery base using an aqueous coating composition containing a coloring base material, followed by application of a glaze and firing. Underglazing can involve multiple firings, but omitting a secondary firing reduces the labor and manufacturing costs. Some coloring base materials, such as pigments, react with the glaze, such as by dissolving in the glaze. This reaction can cause the image to bleed or blur. Using a coloring base material made of a metal chloride or nitrate compound, which is a pigment that is less reactive with the glaze, suppresses the reaction and prevents bleed or blur. In some cases, the image may be intentionally bled or blurred.

Overglaze painting can be performed, for example, using the following method. First, a glaze is applied to a bisque-fired pottery body, which is then fired at a high temperature to form a glaze layer. The pottery body with this glaze layer is called a glaze-layered body. A design is painted onto the surface of this glaze-layered body using a brush or other tool with an aqueous paint composition. The painted pottery body is then fired at a low temperature. When firing at a low temperature, it is preferable to use a colored pigment as the coloring base. This pigment can be in a variety of colors, such as red, blue, yellow, and other colors, as well as gold.

In addition to the color pigments listed above, the coloring base material can include silica, alumina, silica-alumina composites with metal oxides in solid solution, or composite compounds of these. Examples of metal oxides include, but are not limited to, cobalt oxide, iron oxide, copper oxide, manganese oxide, chromium oxide, nickel oxide, and tin oxide. Examples of coloring base materials include zirconium, silicon, praseodymium, vanadium, titanium, antimony, zinc, manganese, cobalt, nickel, aluminum, copper, lead, cadmium or its compounds, and chromium or its compounds (e.g., chromium oxide, viridian, and cobalt turquoise). The coloring base material can also include ceramic pigments.

Ceramic pigments have excellent heat resistance, weather resistance, and chemical resistance, and are primarily composed of oxides, composite oxides, silicates, etc. However, they are not limited to these. Examples of ceramic pigments include spinel-based solid solutions, antimony tin gray, zircon gray, praseodymium yellow, vanadium tin yellow (including Sn-V and Sn-Ti-V), vanadium zirconium yellow, peacock, Victoria green, chrome green (Al-Cr), Prussian blue, sea blue, Co-Zn-Si, Co-Si, vanadium zirconium blue, chrome tin lilac, lilac, chrome tin pink, ceramic red, salmon pink, chrome alumina pink, and fire red.

The average particle diameter of the colored substrate in this embodiment is, for example, 1 μm to 20 μm, preferably 5 μm to 10 μm. If it exceeds 20 μm, unevenness may occur in the painted area when the aqueous coating composition is applied thinly, resulting in an uneven appearance of the color tone. Furthermore, if it is less than 1 μm, the colored substrate may not disperse sufficiently in the aqueous coating composition, causing uneven coating. Furthermore, to ensure that the colored substrate is adequately dispersed in the aqueous coating composition via the cellulose nanofibers, it is preferable that the particle size distribution of the colored substrate and the pseudo-particle size distribution of the cellulose nanofibers are similar. If the particle size is above or below the range of 1 μm to 20 μm, the difference with the diameter of the cellulose nanofiber becomes significant, resulting in poor dispersibility and the aqueous coating composition being more susceptible to separation into two phases.

If the main component of the ceramic body, especially the surface, is silicic acid or a silicic acid compound (for example, glass or other solid solutions), the production of the glaze layer molded body described above can be omitted, and a design can be painted onto the ceramic body with a brush or other device using an aqueous paint composition. In this case, the ceramic body after painting is fired at a low temperature.

(Cellulose nanofiber)
Cellulose nanofibers increase the number of hydrogen bonding points in cellulose fibers, thereby improving the strength of molded articles. Cellulose nanofibers can be obtained by defibrating (refining) raw pulp, and can be produced by known processing methods such as chemical processing and mechanical processing.

The raw pulp for cellulose nanofibers can be selected from one or more of the following: wood pulp made from hardwoods, softwoods, etc.; non-wood pulp made from straw, bagasse, cotton, hemp, bast fibers, etc.; and recycled paper pulp (DIP) made from recycled waste paper, broke, etc. The above raw materials may also be in a pulverized state, such as cellulose powder.

However, to minimize the inclusion of impurities, it is preferable to use wood pulp. Examples of wood pulp that can be used include chemical pulps such as hardwood kraft pulp (LKP), softwood kraft pulp (NKP), sulfite pulp (SP), and dissolving pulp (DP), and mechanical pulp (TMP).

As mechanical pulp, one or more types can be selected and used from, for example, stone ground pulp (SGP), pressed stone ground pulp (PGW), refiner ground pulp (RGP), chemi-ground pulp (CGP), thermo-ground pulp (TGP), ground pulp (GP), thermo-mechanical pulp (TMP), chemi-thermomechanical pulp (CTMP), refiner mechanical pulp (RMP), bleached thermo-mechanical pulp (BTMP), etc.

Before defibrating cellulose nanofibers, they can also be pretreated by chemical methods. Examples of chemical pretreatments include hydrolysis of polysaccharides with acid (acid treatment), hydrolysis of polysaccharides with enzymes (enzyme treatment), swelling of polysaccharides with alkali (alkali treatment), oxidation of polysaccharides with an oxidizing agent (oxidation treatment), reduction of polysaccharides with a reducing agent (reduction treatment), oxidation with a TEMPO catalyst (oxidation treatment), and phosphate esterification (chemical treatment).

By carrying out enzyme treatment, acid treatment, or oxidation treatment prior to defibration, it is possible to reduce water retention relatively and increase homogeneity. However, if the water retention of cellulose nanofibers is too high, the aqueous paint composition will not spread well. This is probably because the aqueous paint composition contains a lot of water, which makes it easier for the water molecules to aggregate and form droplets due to hydrogen bonding between them.

When raw pulp is treated with enzymes, acids, or oxidation, the amorphous regions of hemicellulose and cellulose contained in the pulp are broken down, resulting in a reduction in the energy required for the refining process and improved uniformity and dispersibility of the cellulose fibers. Dispersibility of cellulose fibers contributes to improving the homogeneity of the molded product, for example. However, since pretreatment reduces the aspect ratio of the cellulose nanofibers, excessive pretreatment is preferably avoided.

In particular, when an aqueous paint composition containing cellulose nanofibers obtained by defibrating mechanical pulp is used to paint on an object (for example, a glaze-coated base where a ceramic base is covered with a glaze layer, or a ceramic base), the aqueous paint composition spreads well, adheres well to the object, and is less likely to produce uneven paint. Some conventional aqueous paint compositions contain thickeners such as carboxymethyl cellulose to increase viscosity and improve adhesion. Carboxymethyl cellulose increases the viscosity of the aqueous paint composition, but because it is water-soluble, it dissolves when the glaze is applied, causing cracks after firing.

Cellulose nanofibers can be mixed and dispersed in liquids such as water or organic solvents to form a dispersion.

From the standpoint of adhesion and spread of the aqueous paint composition during painting, it is preferable to use mechanical pulp, and to bring out the original color of the colored substrate, it is more preferable to use bleached mechanical pulp, with BTMP being particularly preferable. The aqueous paint composition has good adhesion when painting. If the aqueous paint composition has good adhesion when painting, it will be less likely to peel off from the substrate after drying, making it easier to carry out painting work efficiently.

The cellulose nanofibers contained in the aqueous coating composition can be suitably obtained by defibrating mechanical pulp or chemical pulp. In particular, chemical pulp may be obtained by adding an additive containing at least one of phosphorus oxoacids and phosphorus oxoacid metal salts to cellulose fibers, and defibrating pulp in which some of the hydroxy groups of the cellulose fibers have been esterified with phosphorus oxoacids; by defibrating pulp in which some of the hydroxy groups of the cellulose fibers have been substituted with carbamate groups to introduce carbamate; or by defibrating pulp in which some of the hydroxy groups of the cellulose fibers have been esterified with phosphorus oxoacids and some of the other hydroxy groups have been substituted with carbamate groups to introduce carbamate.

These cellulose nanofibers should be included in the aqueous coating composition at 2 to 4 mass %, preferably 3 to 4 mass %, based on the solids content. If the content exceeds 4 mass %, the concentration of cellulose nanofibers will be high, and the interactions between the cellulose nanofibers will be strong, resulting in high viscosity and insufficient spreadability of the aqueous coating composition. If the content is below 2 mass %, although sedimentation will be less likely to occur over a long period of time, there is a risk that the aqueous coating composition may drip outward from the drawn area when painting.

The inventors have found that when comparing a dispersion of cellulose nanofibers obtained by defibrating chemical pulp with a dispersion of cellulose nanofibers obtained by defibrating mechanical pulp, the latter has a higher viscosity. By adjusting the ratio (mass ratio) of cellulose nanofibers obtained by defibrating chemical pulp to cellulose nanofibers obtained by defibrating mechanical pulp, it is possible to create an aqueous coating composition with a relatively high viscosity.

When the aqueous coating composition contains cellulose nanofibers obtained by defibrating mechanical pulp and cellulose nanofibers obtained by defibrating chemical pulp, a preferred embodiment is one in which the mass ratio of the cellulose nanofibers obtained by defibrating mechanical pulp to the cellulose nanofibers obtained by defibrating chemical pulp is 1 to 9:1, and particularly 1 to 3:1. If the mass ratio exceeds 9:1, a relatively large amount of cellulose nanofibers obtained by defibrating mechanical pulp will be used, resulting in increased costs. If the mass ratio is below 1:1, the aqueous coating composition will be less likely to drip outward from the painted area, but the concentration of cellulose nanofibers obtained by defibrating mechanical pulp will be low, weakening the dispersibility effect of this cellulose nanofiber.

Esterification (chemical treatment) with phosphorus oxoacid prior to defibration can refine the fiber raw material, resulting in cellulose nanofibers with a large aspect ratio, excellent strength, and high light transmittance and viscosity. Esterification with phosphorus oxoacid can be carried out by the method described in Patent Document 3 (JP 2019-199671 A). An example of cellulose nanofiber (A) esterified with phosphorus oxoacid is shown below. An example of a cellulose nanofiber (A) esterified with phosphorus oxoacid is shown below. A portion of the hydroxy groups of the cellulose fiber is esterified with phosphorus oxoacid by substitution with a functional group shown in structural formula (1) below. An example of such a cellulose nanofiber is one in which the amount of the functional group shown in structural formula (1) introduced exceeds 2 mmol per gram of cellulose fiber. The upper limit of the amount of the functional group introduced is 3.4 mmol per gram of cellulose fiber. Exceeding this upper limit may result in the cellulose nanofiber becoming more soluble in water.
[Structural formula (1)]
In structural formula (1), a, b, m, and n are natural numbers.
At least one of A1, A2, ..., An and A' is O, and the rest are R, OR, NHR, or none. R is any of a hydrogen atom, a saturated linear hydrocarbon group, a saturated branched hydrocarbon group, a saturated cyclic hydrocarbon group, an unsaturated linear hydrocarbon group, an unsaturated branched hydrocarbon group, an aromatic group, and derivatives thereof. α is a cation made of an organic or inorganic substance.

The cellulose nanofibers (A) may also be those in which two or more of the hydroxyl groups of the cellulose fibers have been substituted with the functional group shown in structural formula (1) and an ester of phosphorus oxoacid has been introduced. The viscosity is improved by interactions between the cellulose nanofibers through hydrogen bonds, etc.

Cellulose fibers have a structure in which multiple β-glucose units are polymerized, with β-glucose being one structural unit. In one polymerized cellulose fiber, the ester group of the phosphorus oxoacid may be substituted with a specific β-glucose and not with another β-glucose. Furthermore, the ester group of the phosphorus oxoacid may be introduced and substituted at multiple positions in a specific β-glucose.

Cellulose nanofibers esterified with this phosphorus oxoacid have extremely high light transmittance and viscosity.

The esterification reaction with phosphorus oxoacids proceeds by adding a solution of additive (A) containing at least one of phosphorus oxoacids and phosphorus oxoacid metal salts, with a pH of less than 3.0, to cellulose fibers, heating them, and defibrating them.

Examples of additives (A) that can be used include phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, triammonium phosphate, ammonium pyrophosphate, ammonium polyphosphate, lithium dihydrogen phosphate, trilithium phosphate, dilithium hydrogen phosphate, lithium pyrophosphate, lithium polyphosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, trisodium phosphate, sodium pyrophosphate, sodium polyphosphate, potassium dihydrogen phosphate, dipotassium hydrogen phosphate, tripotassium phosphate, potassium pyrophosphate, potassium polyphosphate, phosphorous acid, sodium hydrogen phosphite, ammonium hydrogen phosphite, potassium hydrogen phosphite, sodium dihydrogen phosphite, sodium phosphite, lithium phosphite, potassium phosphite, magnesium phosphite, calcium phosphite, triethyl phosphite, triphenyl phosphite, and phosphorous acid compounds such as pyrophosphorous acid. These additives can be used alone or in combination. However, it is preferable to use phosphonic acids as part or all of the phosphorus oxoacids. The use of phosphonic acids prevents yellowing of cellulose fibers, resulting in an aqueous coating composition that retains the original color of the colored substrate.

The cellulose nanofibers incorporating an ester of phosphorus oxoacid should be present in the aqueous paint composition at 2 to 4 mass %, preferably 3 to 4 mass %, based on the solids content. If the content exceeds 4 mass %, the concentration of cellulose nanofibers will be high, and the interactions between the cellulose nanofibers will be strong, resulting in high viscosity and insufficient spread of the aqueous paint composition, making it difficult to paint with a uniform color. If the content is below 2 mass %, although sedimentation will be less likely to occur over a long period of time, there is a risk that the aqueous paint composition may drip outward from the painted area when painting.

(Carbamate formation)
The cellulose fibers esterified with phosphorus oxoacid may also include those in which some of the hydroxy groups of the cellulose fibers have been substituted with carbamate groups to introduce carbamate groups.

The additive (B) used to substitute with a carbamate group includes at least one of urea and a urea derivative. Examples of this additive include urea, thiourea, biuret, phenylurea, benzylurea, dimethylurea, diethylurea, and tetramethylurea. These ureas or urea derivatives can be used alone or in combination. However, urea is preferred.

When the additive (B) is heated, it decomposes into isocyanic acid and ammonia, as shown in reaction formula (1) below. Isocyanic acid is highly reactive and forms hydroxyl groups in cellulose and carbamate, as shown in reaction formula (2) below. Therefore, adding additive (B) to cellulose fibers promotes the introduction of carbamate.

The amount of additive (B) added is preferably 0.01 to 100 mol, more preferably 0.2 to 20 mol, per 1 mol of additive (A). If the amount added is less than 0.01 mol, the introduction of carbamate may not proceed smoothly. On the other hand, if the amount added exceeds 100 mol, the effect of adding urea may plateau.

NH ₂ -CO-NH ₂ → HN=C=O+NH ₃ ...(1)
Cell-OH+H-N=C=O → Cell-O-CO-NH ₂ ...(2)
Note that Cell refers to a cellulose molecule.

There are no particular limitations on the type of pulp that can be used to introduce esters or carbamates using phosphorus oxoacids, and any known pulp can be used as appropriate. However, bleached softwood kraft pulp or bleached hardwood kraft pulp is preferably used, with bleached softwood kraft pulp being preferred. Bleached softwood kraft pulp and bleached hardwood kraft pulp are easily decomposed by hemicellulase enzymes, and subsequent defibration processing is also easy.

Hemicellulase enzymes that can be used include, for example, xylanase, an enzyme that breaks down xylan, mannase, an enzyme that breaks down mannan, and arabanase, an enzyme that breaks down araban. Pectinase, an enzyme that breaks down pectin, can also be used.

Cellulose fibers can be defibrated using one or more of the following means: homogenizers such as high-pressure homogenizers and high-pressure homogenizers; grinders, millstone-type friction machines such as attritors; refiners such as conical refiners and disc refiners; and various bacteria. However, defibration of cellulose fibers is preferably carried out using a device or method that uses a water flow, particularly a high-pressure water flow, to refine the fibers. This device or method results in extremely uniform dimensions and uniform dispersion of the resulting cellulose fine fibers. In contrast, using a grinder that grinds the fibers between rotating grindstones, for example, makes it difficult to uniformly refine the cellulose fibers, and in some cases, there is a risk that some undisintegrated fiber clumps may remain.

Grinders used to defibrate cellulose fibers include, for example, the Masscolloider manufactured by Masuko Sangyo Co., Ltd. Furthermore, devices that use high-pressure water flow to pulverize the fibers include, for example, the Starburst (registered trademark) manufactured by Sugino Machine Co., Ltd. and the Nanovater (registered trademark) manufactured by Yoshida Kikai Kogyo Co., Ltd. Furthermore, high-speed rotary homogenizers used to defibrate cellulose fibers include the Clearmix-11S manufactured by M Technique Co., Ltd.

The inventors have found that when cellulose fibers are defibrated using both a method of grinding between rotating grindstones and a method of refining with a high-pressure water jet, and the resulting fibers are observed under a microscope, the fibers obtained using the method of refining with a high-pressure water jet have a more uniform fiber width.

Defibration using a high-pressure water stream is preferably carried out by pressurizing a cellulose fiber dispersion using a pressure intensifier to, for example, 30 MPa or more, preferably 100 MPa or more, more preferably 150 MPa or more, and particularly preferably 220 MPa or more (high-pressure conditions), spraying it from a nozzle with a pore diameter of 50 μm or more, and then reducing the pressure to, for example, 30 MPa or more, preferably 80 MPa or more, and more preferably 90 MPa or more (reduced-pressure conditions). The pulp fibers are defibrated by the cleavage phenomenon caused by this pressure difference. If the pressure under the high-pressure conditions is low or the pressure difference from the high-pressure conditions to the reduced-pressure conditions is small, the defibration efficiency decreases, and repeated defibration (spraying from the nozzle) becomes necessary to achieve the desired fiber width.

A high-pressure homogenizer is preferably used as the device for defibrating using a high-pressure water stream. A high-pressure homogenizer is one that is capable of spraying a cellulose fiber slurry at a pressure of, for example, 10 MPa or more, preferably 100 MPa or more. When cellulose fibers are treated with a high-pressure homogenizer, collisions between the cellulose fibers, pressure differences, microcavitation, and other factors act to effectively defibrate the cellulose fibers. This means that the number of defibration treatments can be reduced, and the production efficiency of cellulose microfibers can be improved.

It is preferable to use a high-pressure homogenizer that causes cellulose fiber slurry to collide in a straight line. Specifically, for example, a counter-impingement type high-pressure homogenizer (MICROFLUIDIZER (registered trademark), wet jet mill) is used. In this device, two upstream flow paths are formed so that the pressurized cellulose fiber slurry collides in a counter-impingement manner at the confluence. The cellulose fiber slurry collides at the confluence, and the collided cellulose fiber slurry flows out from the downstream flow path. The downstream flow path is arranged perpendicular to the upstream flow path, and the upstream and downstream flow paths form a T-shaped flow path. Using such a counter-impingement type high-pressure homogenizer maximizes the conversion of energy imparted by the high-pressure homogenizer into collision energy, allowing for more efficient defibration of cellulose fibers.

The raw material pulp is preferably defibrated so that the average fiber diameter, average fiber length, water retention, peak value of the pseudo-particle size distribution, and B-type viscosity of the aqueous coating composition of the resulting cellulose nanofibers reach the desired values or evaluations shown below.

An aqueous coating composition in which the ratio (D50/D90) of the cumulative 50% diameter (D50) to the cumulative 90% diameter (D90) on a volume basis in the pseudo particle size distribution is 0.5 to 1 is preferred because the colored substrate is less likely to settle and remains dispersed.

The average fiber diameter (average fiber width; average diameter of a single fiber) of cellulose nanofibers is 1 to 200 nm, preferably 2 to 100 nm, more preferably 3 to 80 nm, and especially preferably 3 to 60 nm. Cellulose nanofibers with an average fiber diameter of less than 1 nm are expensive to produce. On the other hand, if the average fiber diameter of cellulose nanofibers exceeds 200 nm, the effect of increasing the number of hydrogen bonding points may not be achieved. Cellulose nanofibers in a dispersion gel and have viscosity. In particular, if the average fiber diameter is 100 nm or less, the gelled cellulose nanofibers have a relatively high static viscosity, which inhibits sedimentation, and the colored substrate also inhibits sedimentation.

The average fiber diameter of cellulose nanofibers can be adjusted, for example, by selecting the raw pulp, pre-treating it, defibrating it, etc.

The average fiber diameter of cellulose nanofibers was measured as follows.
First, 100 ml of an aqueous dispersion of cellulose nanofibers with a solid content of 0.01 to 0.1% by mass is filtered through a Teflon (registered trademark) membrane filter and solvent-substituted once with 100 ml of ethanol and three times with 20 ml of t-butanol. The sample is then freeze-dried and osmium-coated to obtain a sample. This sample is then observed using an SEM electron microscope at a magnification of 3,000x to 30,000x depending on the width of the fibers constituting it. Specifically, two diagonal lines are drawn on the observed image, and three straight lines are arbitrarily drawn passing through the intersections of the diagonal lines. Furthermore, the widths of a total of 100 fibers intersecting with these three straight lines are visually measured. The median diameter of the measured values is then taken as the average fiber diameter.

The average fiber length (single fiber length) of the cellulose nanofibers is preferably 200 to 1,300 μm, more preferably 200 to 1,000 μm, and particularly preferably 200 to 800 μm. If the average fiber length of the cellulose nanofibers is less than 200 μm, it may be difficult for the cellulose nanofibers to disperse uniformly in the aqueous coating composition. Decreased dispersibility can cause problems with sagging resistance and spreadability.

On the other hand, if the average fiber length of the cellulose nanofibers exceeds 1,300 μm, the fibers tend to become entangled with each other, and it is presumed that the degree of adhesion between the fibers and the colored substrate is relatively low, resulting in more likely smearing when drawing with the aqueous paint composition.

The average fiber length of cellulose nanofibers can be adjusted, for example, by selecting the raw pulp, pre-treating it, defibrating it, etc.

The average fiber length of cellulose nanofibers is measured in the same way as for the average fiber diameter: the length of each fiber is measured visually. The median length of the measured values is taken as the average fiber length.

Cellulose nanofibers should have an aspect ratio of 100 to 300, preferably 100 to 250, and more preferably 100 to 200. Cellulose nanofibers with an aspect ratio within this range are long and thin, and are presumed to maintain a dispersed state (i.e., a three-dimensional network) by sterically entangling with each other or by hydrogen bonding. If the aspect ratio exceeds 300, the cellulose nanofibers will be highly entangled with each other, resulting in an aqueous coating composition with poor spreadability. If the aspect ratio is below 100, it will be difficult to maintain the so-called three-dimensional network structure over the long term, and there is a risk that the colored substrate will settle within a short period of time.

The water retention of cellulose nanofibers should be, for example, 150% or higher, preferably 200%, more preferably 220%, and even more preferably 250%. If the water retention of cellulose nanofibers is below 150%, the dispersibility of the cellulose nanofibers will deteriorate, which may in turn deteriorate the dispersibility of the colored substrate attached to the cellulose nanofibers.

On the other hand, the water retention of cellulose nanofibers should be, for example, 500% or less. If it exceeds 500%, the water retention capacity of the cellulose nanofibers themselves will be so high that water molecules will form droplets, making it difficult to form a thin film of the aqueous coating composition on the base or glaze layer.

The water retention of cellulose nanofibers can be adjusted, for example, by selecting the raw pulp, pre-treating it, defibrating it, etc.

The water retention of cellulose nanofibers was measured in accordance with JAPAN TAPPI No. 26 (2000).

The cumulative 50% diameter (hereinafter referred to as D50, median diameter) on a volume basis in the pseudo-particle size distribution of cellulose nanofibers should be 1 to 20 μm, more preferably 5 to 15 μm. A median diameter of this size allows the cellulose nanofibers to be adequately dispersed in the aqueous paint composition, enabling uniform drawing with the aqueous paint composition. If the median diameter exceeds 20 μm, it becomes difficult for the cellulose nanofibers to be uniformly dispersed in the aqueous paint composition. There are technical difficulties in producing cellulose nanofibers with a median diameter of less than 1 μm.

When the median diameter of the pseudo-particle size distribution of cellulose nanofibers obtained by defibrating mechanical pulp and the median diameter of the pseudo-particle size distribution of cellulose nanofibers esterified with phosphorus oxoacid are both 5 to 20 μm, the pseudo-particle size of the cellulose nanofibers as a whole is roughly uniform, and the cellulose nanofibers as a whole are dispersed with little bias, which is preferable as it allows for drawing without color unevenness.

The pseudo-particle size distribution curve of the aqueous coating composition of this embodiment preferably has a single peak. When there is a single peak, the cellulose nanofibers defibrated from one or more types of pulp have high uniformity in fiber length and fiber diameter, resulting in excellent dispersibility of the cellulose nanofibers in the aqueous coating composition. The peak value is a value measured in accordance with ISO-13320 (2009). It is preferable that the cellulose nanofibers have a single peak in the pseudo-particle size distribution curve measured by laser diffraction in an aqueous dispersion state. Cellulose nanofibers with a single peak are sufficiently refined and can exhibit good physical properties as cellulose nanofibers, resulting in uniform drawing with the resulting aqueous coating composition. The term "pseudo-particle size distribution curve" refers to a curve showing the volumetric particle size distribution measured using a particle size distribution analyzer (e.g., Horiba's LA-960S particle size distribution analyzer).

An aqueous paint composition having a configuration that has a single peak in the pseudo-particle size distribution curve is preferred. In this configuration, there is little variation in particle size across the solids contained in the aqueous paint composition (specifically, the colored substrate and cellulose nanofibers). It is presumed that the small particle size variation makes it difficult for the cellulose nanofibers to be unevenly distributed within the aqueous paint composition, making them easier to disperse throughout the aqueous paint composition.

An aqueous paint composition containing cellulose nanofibers obtained by defibrating mechanical pulp and carboxylated cellulose microfibers exhibits multiple peaks in its pseudo-particle size distribution curve. When this aqueous paint composition is prepared and allowed to stand for an extended period of time, it separates into a colored substrate phase and a liquid phase. The mechanism by which this aqueous paint composition separates into two phases is unclear, but is presumed to be as follows: carboxylated cellulose microfibers are formed by selectively modifying the hydroxyl group at the C6 position of glucose, a structural unit of cellulose fiber, to an aldehyde group and a carboxy group, resulting in an imbalance in the charge of the glucose. This also leads to an imbalance in the interactions between the cellulose fibers, making it difficult to maintain uniform dispersion.

In contrast, cellulose nanofibers esterified with phosphorus oxoacids have one or more of the six carbon atoms of glucose, a structural unit of cellulose fibers, randomly esterified with phosphorus oxoacids. This reduces the charge imbalance across the esterified glucose groups. As a result, uniform dispersion is maintained for a long period of time.

The mode of particle size and the median diameter of the pseudo-particle size distribution of cellulose nanofibers can be adjusted, for example, by selecting the raw pulp, pre-treating it, defibrating it, etc.

If necessary, the cellulose nanofibers obtained by defibration can be dispersed in an aqueous medium to form a dispersion prior to mixing with the coloring substrate. It is particularly preferable that the aqueous medium is entirely water (aqueous solution). However, the aqueous medium may also contain other liquids, some of which are compatible with water. Examples of other liquids that can be used include lower alcohols with 3 or fewer carbon atoms.

(viscosity)
Cellulose nanofiber dispersions have the property of dispersing throughout the liquid. However, when cellulose nanofiber dispersions are left for a while, they separate into a cellulose nanofiber phase and an aqueous phase, and an interface between the two phases appears, and this interface may drop. It is believed that viscosity is involved in this phase separation phenomenon. Cellulose nanofiber dispersions have viscosity. Viscosity varies depending on the raw materials, processing methods, physical properties, etc. of the cellulose nanofibers.

For example, it has been found that cellulose nanofibers obtained by defibrating mechanical pulp have a relatively low viscosity, while cellulose nanofibers obtained by defibrating chemical pulp have a relatively high viscosity. Furthermore, cellulose nanofibers into which phosphorus oxoacid esters or carbamates have been introduced have localized charge imbalances, which facilitate the formation of hydrogen bonds with water and organic solvents in the dispersion, and are therefore thought to have a high viscosity.

Furthermore, even for cellulose nanofiber dispersions obtained from specific raw materials using the same manufacturing process, the viscosity will vary depending on the concentration of cellulose nanofibers, with higher concentrations resulting in higher viscosity. Viscosity can be evaluated using Type B viscosity.

(Water-based paint composition)
In the aqueous coating composition of this embodiment, it is assumed that the colored substrate is attached to the cellulose nanofiber. Therefore, by adequately dispersing the cellulose nanofiber in the aqueous coating composition, the colored substrate also exhibits excellent dispersibility. Furthermore, imparting high viscosity by cellulose nanofibers incorporating a phosphorus oxoacid ester is effective in maintaining the dispersion of the colored substrate for a long period of time. For example, a mixing ratio of the colored substrate to the cellulose nanofibers incorporating a phosphorus oxoacid ester can be 1:0.005-0.045, preferably 1:0.010-0.045. If the cellulose nanofibers incorporating a phosphorus oxoacid ester are present at a ratio greater than this, the amount of cellulose nanofiber relative to the colored substrate will be too high, resulting in uneven dispersibility of the colored substrate in the overall coating. Furthermore, if the cellulose nanofibers incorporating a phosphorus oxoacid ester are present at a ratio less than this, the cellulose nanofibers will be too low, resulting in poor dispersibility of the colored substrate in the overall aqueous coating composition, which can cause color unevenness when painting.

The B-type viscosity of the cellulose nanofibers that make up the aqueous paint composition is, for example, 600 cP or more, more preferably 700 cP or more, and particularly preferably 800 cP or more, in a dispersion with a solids concentration of 2.0% by mass. If the B-type viscosity is less than 600 cP, the aqueous paint composition may unexpectedly flow out of the area where it is applied to other areas. It is also recommended that the B-type viscosity of the aqueous paint composition be 2000 cP or less. If the B-type viscosity exceeds 2000 cP, the paint will not spread well when applied to a drawing, causing uneven application and peeling. Water was used as the solvent for the dispersion.

The cellulose nanofibers constituting the aqueous coating composition of this embodiment, in a dispersion with a solids concentration of 2.0% by mass, have a minimum high-shear viscosity of 3.5 cP or less, preferably 3.3 cP or less at a shear rate of 1 x ¹⁰ to 2 x ¹⁰ (1/sec), more preferably 3.0 cP or ^less at a shear rate of 1 x 10 to 2 x ¹⁰ (1/sec), and even more preferably 3.5 cP or less at a shear rate of 1 x ¹⁰ to 2 x ¹⁰ (1/sec). If the minimum high-shear viscosity exceeds 3.5 cP, the aqueous coating composition will not spread well when applied to a brush for drawing, making it difficult to draw. Water was used as the solvent for the dispersion.

In addition to the coloring substrate and cellulose nanofibers, silica powder ( _SiO2 powder) and thickeners can be added to the coating composition. Thickeners, in particular, should not be added in excess because they increase B-type viscosity and high-shear viscosity, but adding an appropriate amount can supplementarily increase viscosity. Known thickeners can be used as appropriate, including carboxymethylcellulose (CMC), xanthan gum, guar gum, pectin, and carrageenan. Depending on the type of coloring substrate and cellulose nanofiber, a thickener content of 20 to 30% by mass in the aqueous coating composition is preferred. However, a thickener does not necessarily need to be included in the aqueous coating composition.

(Ceramic base)
The pottery base is not particularly limited as long as it is a known base, and examples include pottery, porcelain, glassware, enamel, earthenware, and unglazed pottery. For example, clay, silica stone, feldspar, and mixtures thereof can be used as raw materials for the pottery base. When the pottery base is glassware, for example, silicic acid, silicate compounds, boric acid, boric acid compounds, phosphoric acid, phosphoric acid compounds, titanic acid, titanic acid compounds, tellurium, tellurium compounds, alumina, alumina compounds, and compounds and mixtures thereof can be used to make the glassware.

(glaze)
Glazes are vitreous and contain known compositions, but may also contain, for example, ash (a melting agent), clay (an adhesive), feldspar (an adhesive, melting agent, and glass raw material), and silica (a glass raw material). Ash is primarily composed of calcareous substances such as calcium oxide, and melts and vitrifies at high temperatures, and as a melting agent, it facilitates the dissolution of other components, thereby increasing the fluidity of the glaze. Furthermore, the inclusion of color-producing components (such as copper and iron) enhances the color-producing effect.

The chemical components of glazes include silicic acid and silicic acid compounds, alumina and alumina compounds, potassium oxide and potassium oxide compounds, potassium oxide and potassium oxide compounds, sodium oxide and sodium oxide compounds, iron oxide and iron oxide compounds, and may also contain cadmium and cadmium compounds, lead and lead compounds, etc. In other words, silicic acid and silicic acid compounds are the main components of fired glazes, accounting for approximately 45-80% of the glaze, depending on the type of glaze.

Glazes can have the following composition, for example, but are not limited to: 35.4 wt% Fukushima feldspar, 18.6 wt% limestone, 17 wt% Korean kaolin, and 29 wt% silica are mixed with an equal amount of water and stirred in a ball mill. The mixture is then sieved to remove iron, and water is added to adjust the specific gravity. This gives Glaze A. 3 g of CMC is then added to 297 g of this Glaze A and dissolved, giving Glaze B.

A preferred embodiment is one in which the concentration index of the liquid surface portion after standing for 24 hours is 90 or more, preferably 95 or more. If the concentration index of the liquid surface portion is less than 90, the dispersion stability is lacking, and appropriate stirring is required to prevent separation of the composition within the prepared aqueous coating composition. The liquid surface portion refers to the aqueous coating composition located within a depth range of 5 mm from the liquid surface, particularly 3 mm from the liquid surface, when 30 mL of the aqueous coating composition is prepared in the polyvinyl chloride bottle used in the examples.

(Manufacturing)
<Glazed layer formation process>
The aqueous coating composition can be applied to a substrate 11, which serves as the base for finished products such as Japanese and Western tableware, decorative items, and interior accessories. The substrate 11 is glazed (i.e., glazed), dried at room temperature to 105°C (manufacturing step S11), and fired at 1200 to 1300°C to obtain a substrate with a glaze layer (also referred to as a glazed substrate) (manufacturing step S12). The firing conditions include, for example, raising the temperature to 950°C over 9 hours and 30 minutes, and then raising the temperature to 1250°C over 5 hours. The temperature is maintained at 1250°C for 30 minutes, followed by natural cooling. The finished product can be used, for example, as a ceramic product or an enamel product.

Glazing can be applied to the entire surface of the base, or to just a portion of it. Although crazing may occur, it is preferable to cover the entire surface. Water is less likely to penetrate the glaze layer. Note that glazing also includes pouring a glaze dispersed in water or other liquid onto the base.

If the base is for glassware, the glaze layer formation process described above can be omitted and production can begin with the drawing process.

<Drawing process>
A pattern 30a is drawn on the obtained glaze layer molded body using an aqueous coating composition, and then dried, for example, at 60 to 105° C. for 1 hour to obtain a drawn molded body (manufacturing step S13).

The patterned molded body is glazed (immersed), the design is glazed, and the body is then dried again, for example, at 60-105°C for one hour (manufacturing step S21). The glaze is then fired at 1220°C, coating the fired aqueous paint composition with the glaze to form the glaze layer 20a. That is, the glaze layer 20a is formed by coating the fired aqueous paint composition with the glaze. The patterned molded body is then coated with the glaze layer 20a to form a glaze-layered molded body (manufacturing step S22). The firing conditions are, for example, to raise the temperature to 950°C over 9 hours and 30 minutes, then to 1220°C over 5 hours. The temperature is maintained at 1220°C for 30 minutes, and then the body is allowed to cool naturally. While this glaze-layered molded body can be used as a finished product, a multi-layered finished product can also be produced by layering one or more glaze layers on top of the glaze-layered molded body.

If the substrate is for glassware, the pattern 30a is drawn on the substrate using an aqueous coating composition, and then dried, for example, at 60 to 105°C for 1 hour to obtain a drawn molded product (manufacturing step S33).

The patterned molded body is glazed (immersed), the glaze is applied to the design, and then it is dried again, for example, at 60-105°C for one hour (manufacturing step S41). Then, it is fired at 580-780°C, whereby the fired aqueous paint composition is coated with the glaze, forming a glaze layer 20a. That is, the glaze layer 20a is formed by coating the fired aqueous paint composition with the glaze, and the patterned molded body is coated with the glaze layer 20a, forming a glaze-layered molded body (manufacturing step S42). The firing conditions are, for example, to raise the temperature to 550°C over 5 hours and 30 minutes, then to 780°C over 5 hours. 780°C is maintained for 30 minutes, and then the body is allowed to cool naturally. This glaze-layered molded body can be used as a finished product, or a multi-layered finished product can be produced by layering one or more glaze layers on top of the glaze-layered molded body.

Cellulose nanofiber is primarily composed of organic matter, with traces of inorganic matter also present. The organic components of cellulose nanofiber are lost during the firing process.

Conventionally, the surface of a glaze layer molded body, i.e., the surface of the glaze layer, is very smooth, and even if an aqueous paint composition is applied to this surface, the surface repels the aqueous paint composition, making it difficult for the aqueous paint composition to adhere to the surface. However, paint containing cellulose nanofibers adheres easily to the surface, is less likely to be repelled, and becomes hydrophilic after drying, making it easy to apply a glaze. This makes it possible to apply the aqueous paint composition and then coat it with a glaze layer.

Overglaze painting is a known method of painting on the surface of a glaze layer, but because it does not form a glaze layer on the surface of the design, it is less durable. For example, if the finished product is Japanese or Western tableware, it is known that the color will easily fade after repeated washing in the dishwasher.

(Preparation of aqueous coating composition)
Aqueous coating compositions, Comparative Examples 1 to 5 and Examples 1 to 3, were prepared by mixing 1.0 g of pigment (Nittoh Pigment Co., Ltd. Green M-142), a cellulose nanofiber dispersion, and water. The cellulose nanofiber dispersions were prepared by mixing one or more selected from the group consisting of a BTMP cellulose nanofiber aqueous dispersion (bleached mechanical pulp), an LBKP cellulose nanofiber aqueous dispersion (bleached chemical pulp derived from hardwood pulp), a phosphite-esterified cellulose nanofiber, and a carboxylated cellulose fine fiber in varying amounts. The amounts of each composition were as shown in Table 1. The BTMP cellulose nanofibers were beaten in a Niagara beater or single-disc refiner to obtain a treated product with a fine fiber content of 80% or more. This treated product was then circulated 10 to 20 times in a high-pressure homogenizer for micronization, and the resulting product was diluted with water to a concentration of 3 to 4% by mass. For LBKP cellulose nanofibers, a processed product was obtained by beating using a Niagara beater or single-disc refiner until the proportion of fine fibers was 80% or more, and the processed product was then circulated through a high-pressure homogenizer 3 to 4 times for refinement. For phosphite-esterified cellulose nanofibers, chemical pulp was impregnated with water containing phosphorous acid and urea, and the product was reacted at 170°C for 2 hours to obtain a product. This product was washed with water and circulated through a high-pressure homogenizer 2 to 3 times for refinement. The phosphite-esterified cellulose nanofibers are cellulose nanofiber dispersions produced by the phosphite esterification method.

(Evaluation test)
Evaluation tests were conducted on the sedimentation state, solids concentration at the liquid surface, and particle size distribution for Comparative Examples 1 to 6 and Examples 1 to 3. The results are shown in Figures 4 to 9. Comparative Example 1 is labeled a1, Comparative Example 2 a2, Comparative Example 3 a3, Comparative Example 4 a4, Comparative Example 5 a5, Comparative Example 6 a6, Example 1 b1, Example 2 b2, and Example 3 b3.

<Sedimentation status 1>
30 mL of each of Comparative Examples 1 to 4 and Examples 1 to 3 was prepared using a 100 mL beaker or a poly bottle ("Labolan screw cap" product of AS ONE Corporation, 30 mL capacity, 30 mm inner diameter x 65 mm length). These Test Examples and Examples were left to stand at room temperature, and the degree of sedimentation at the interface of the colored substrate was evaluated after 10 minutes, 60 hours, and 130 hours. The results are shown in Figure 5 for the state of sedimentation after 10 minutes, Figure 6 for the state of sedimentation after 60 hours, and Figure 7 and Table 2 for the state of sedimentation after 130 hours. The evaluation criteria are as follows:
◯: The aqueous coating composition consisted of only the colored substrate phase 50, and neither the foam phase 51 nor the liquid phase 52 was observed.
Δ: The water-based coating composition separated into a colored substrate phase 50 and a foam phase 51 and/or a liquid phase 52, and an interface of the colored substrate phase 50 was formed less than 5 mm below the liquid surface of the water-based coating composition.
×: The aqueous coating composition separated into a colored substrate phase 50 and a foam phase 51 and/or liquid phase 52, with the interface of the colored substrate phase 50 occurring 5 mm or more below the liquid surface of the aqueous coating composition.
The aqueous coating composition has a pigmented base phase 50, a foam phase 51, and a liquid phase 52.

After 10 minutes of standing, a foam phase 51 was observed near the liquid surface in Comparative Examples 1 to 4, indicating separation from the colored substrate phase 50. No foam phase 51 was observed in Examples 1 to 3. After 60 hours of standing, the foam phase 51 had changed to a liquid phase 52 in Comparative Examples 1 to 4, and an interface had formed between the colored substrate phase 50 and the liquid phase 52. Note that the colored substrate phase 50 was the lower phase, and the liquid phase 52 was the upper phase. After 130 hours of standing, the colored substrate phase 50 had separated from the liquid phase 52 in Comparative Examples 1 to 4, forming an interface. In Example 1, the colored substrate phase 50 had slightly separated from the liquid phase 52, forming an interface. It is unlikely that an aqueous coating composition would be placed in a mortar or palette and left to stand for 130 hours during painting work, and it is likely that the painting work would be completed before 130 hours had elapsed. Therefore, it can be said that Example 1 maintains a dispersed state of the colored substrate for a long period of time.

<Sedimentation condition 2>
Comparative Example 5 and Example 2 were each prepared in the same plastic bottle. These test examples and examples were left standing at room temperature for 16 hours, and the degree of sedimentation at the interface of the colored substrate was evaluated. The results are shown in Figure 8 and Table 5. The evaluation criteria were the same as those in <Sedimentation Level Part 1>.

After 16 hours of standing, in Example 5, an interface had formed between the colored substrate phase 50 and the foam phase 51.

<Sedimentation status 3>
Test Example c1, which was a 1:1 dilution of Example 2 and water, Test Example c2, which was a 1:2 dilution of Example 2 and water, and Test Example c3, which was a 1:3 dilution of Example 2 and water, were left at room temperature for 24 hours and the degree of sedimentation at the interface of the colored substrate was evaluated. The results are shown in Figure 9 and Table 6. The evaluation criteria were the same as those for <Sedimentation Level Part 1>.

In test examples c2 and c3, an interface was formed between the colored substrate phase 50 and the foam phase 51.

< Concentration index >
The aqueous coating compositions prepared in the above-mentioned polyethylene bottles were measured for the solids concentration of each of Comparative Examples 1 to 4 and Examples 1 to 3. The solids concentration was measured immediately after preparation and after 24 hours at room temperature by inserting the tip of a pipette to a depth of 3 mm from the liquid surface without disturbing the liquid surface. The solids concentration was measured in accordance with JIS P 8225:2003. The solids concentration of the aqueous coating compositions immediately after preparation and after 24 hours of standing, as well as the concentration index of the liquid surface after 24 hours of standing, are shown in Table 3. The concentration index of the liquid surface refers to the solids concentration of the aqueous coating composition prepared in the polyethylene bottle and after 24 hours of standing, where the solids concentration of the liquid surface immediately after preparation of the aqueous coating composition is set to 100. The concentration index is calculated using the following formula (1):
[Formula (1)]
Concentration index of the liquid surface portion after standing for 24 hours = (solids concentration (mass%) of the liquid surface portion of the aqueous coating composition after standing for 24 hours / solids concentration (mass%) of the liquid surface portion of the aqueous coating composition immediately after preparation) × 100

<Particle size distribution>
The particle size distribution was measured for the comparative example and the example, and the results are shown in Figure 4 and Table 4.

In Figure 4, a1 represents Comparative Example 1, a3 represents Comparative Example 3, a5 represents Comparative Example 5, a6 represents Comparative Example 6, and b2 represents Example 2. The frequency (%) on the vertical axis of Figure 4 represents the number (%) of particles with a specific particle diameter (μm) in Comparative Example 1, assuming that the total number of particles in Comparative Example 1 is 100%, for example. The frequency (%) is the same for Comparative Examples 3, 5, 6, and Example 2.

In Table 4, the cumulative 10% diameter of the pseudo particle size distribution is represented as D10, the cumulative 50% diameter as D50, and the cumulative 90% diameter as D90.

In Comparative Example 5, there were two peak values.

The present invention is not limited to the above-described embodiments, and various modifications are possible without departing from the spirit of the present invention.

The cellulose nanofibers can be in any form, such as powder, paste, or slurry, and the medium for dispersing the cellulose nanofibers is not limited to water; organic solvents or other fluids can also be used as appropriate.

(others)
- The high shear viscosity of the prepared aqueous coating composition was measured at a temperature of 25°C using a high shear viscometer (SMT, product "PM-9000HV") and an E-bob, while varying the shear rate. The high shear viscosity was measured by subjecting the sample to a specific shear rate and measuring the value at which it stabilized. High shear viscosity refers to the viscosity (cP) of a fluid flowing at a specific shear rate (1/sec). Non-Newtonian fluids generally have the property that their viscosity varies depending on the shear rate (shear rate). By measuring the high shear viscosity, the viscosity of the non-Newtonian fluid corresponding to the shear rate can be obtained.
The centrifuge used was a Hitachi refrigerated centrifuge CR22N.
The average particle size of pigments and other particles is a value measured in accordance with JIS Z 8825:2013.
Room temperature refers to the temperature in a typical house, for example, 1 to 30°C, more preferably 15 to 25°C.
The B-type viscosity (solid content concentration is adjusted as appropriate) is a value measured in accordance with JIS-Z8803 (2011) "Method for measuring viscosity of liquids." The B-type viscosity is the resistance torque when stirring a dispersion (or aqueous dispersion), and the higher the value, the more energy is required for stirring. The B-type viscosity was measured at 25°C.

The present invention can be used as an aqueous coating composition for painting on traditional crafts, Japanese and Western tableware, decorative items, interior accessories, etc.

10 Finished product 11 Base 20a Glaze layer 21 Glaze layer 30a First design

Claims (4)

Contains a colored base material and cellulose nanofibers,
The cellulose nanofibers contain cellulose nanofibers obtained by defibrating mechanical pulp and cellulose nanofibers into which a phosphorous acid ester group has been introduced,
The cellulose nanofibers into which ester groups of phosphorous acid have been introduced are those into which carbamate groups have been introduced by substituting some of the hydroxy groups of the cellulose fibers with carbamate groups,
The concentration index of the liquid surface after standing for 24 hours is 90 or more.
1. A water-based coating composition comprising: The cellulose nanofibers having phosphorous acid ester groups introduced therein are obtained by defibrating chemical pulp,
the mass ratio of the cellulose nanofibers obtained by defibrating the mechanical pulp to the cellulose nanofibers having phosphorous acid ester groups introduced therein is 1 to 9:1;
The aqueous coating composition according to claim 1. the mixing ratio of the colored base material to the cellulose nanofibers having phosphorous acid ester groups introduced therein is 1:0.005 to 0.045;
The aqueous coating composition according to claim 1. In a pseudo particle size distribution measured by a laser diffraction method, the ratio (D50/D90) of the cumulative 50% diameter (D50) to the cumulative 90% diameter (D90) on a volume basis is 0.5 to 1.
The aqueous coating composition according to claim 1.