JP7539637B2 - 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, ornaments, interior accessories, etc., that feature beautiful or pleasing designs. The designs on these base materials are made, for example, with water-based paint. The base material that has been painted with water-based paint is glazed and then fired to become a finished product.

Patent Document 1 discloses a technology related to the water-based paint used in this drawing, which is a water-based paint with a specified viscosity. Patent Document 1 states that the water-based paint composition can be used in the form of a viscous emulsion. One of the purposes of imparting viscosity to the water-based paint composition is to fix the water-based paint to the base material when drawing, and to prevent the water-based paint from dripping outward from the drawn area.

JP 2004-345882 A JP 2019-199671 A

However, water-based paints with excessively high viscosity tend to spread poorly when used for drawing. Poor spreadability leads to smearing of the drawn portion. In this case, for example, the smeared portion must be repainted to correct the desired drawing. However, this results in the drawn portion lacking in unity with the other drawn portions in terms of darkness, thickness, etc. The problem that the present invention aims to solve is to provide a water-based paint composition that does not drip easily and spreads well.

The aspects for solving the above problems are as follows.
(First aspect)
Contains a colored base material and cellulose nanofibers,
The Brookfield viscosity is 600 cP or more,
At a shear rate of 0.8 x ¹⁰⁵ (1/sec) or more, the minimum high shear viscosity is 3.5 cP or less.
1. An aqueous coating composition comprising:

When low-viscosity water-based paint is used to draw on a substrate, the surface tension causes the water-based paint to be repelled by the substrate at the interface between the substrate and the water-based paint, reducing the surface area. With a reduced surface area, the water-based paint will run along the substrate surface and drip outside the drawing. To draw the desired image on a substrate using water-based paint, it is preferable for the water-based paint to have a viscosity that makes it less likely to be repelled by the substrate.

The aqueous coating composition of this embodiment is viscous because it contains cellulose nanofibers. The viscosity can be evaluated, for example, by B-type viscosity. If the B-type viscosity is within the above-mentioned range, the aqueous coating composition is unlikely to be repelled by the substrate, will adhere well, and will not drip easily.

In addition, when drawing with one brush stroke without causing smearing as much as possible, it is preferable that the aqueous coating composition has good spreadability. In other words, while drawing along the surface of the substrate with a brush containing the aqueous coating composition, it is preferable that the viscosity of the aqueous coating composition is low. The inventors have found that the viscosity during drawing is related to the high-shear viscosity. The high-shear viscosity was measured by measuring the viscosity of cellulose nanofibers at a rotation speed of 550 to 8800 rpm and a shear rate of 1×10 ⁴ to 2×10 ⁵ (1/sec). It has been found that if the minimum value of the high-shear viscosity is within the above-mentioned range, the aqueous coating composition is less likely to smear and spreads well. In addition, it is presumed that the aqueous coating composition of this embodiment has cellulose nanofibers appropriately dispersed in the aqueous coating composition and the colored substrate attached to the cellulose nanofibers. Since the colored substrate is appropriately dispersed in the aqueous coating composition via the cellulose nanofibers, color unevenness is less likely to occur when drawing.

(Second Aspect)
The minimum high-shear viscosity of the cellulose nanofiber is 3.5 cP or less at a shear rate of 1 x 10 ⁵ to 2 x 10 ⁵ (1/sec).
The aqueous coating composition of the first embodiment.

Generally, artists paint with varying brush speeds. Most of the brush speeds fall within the range of about 1×10 ⁵ to 2×10 ⁵ (1/sec) when expressed in terms of shear rate. If the minimum high-shear viscosity is within the above-mentioned range within this shear rate range, the aqueous coating composition will have better spreadability, allowing artists to work without worrying about smearing.

(Third Aspect)
The cellulose nanofiber has a median diameter of a pseudo-particle size distribution of 5 to 60 μm, and has one peak value in a pseudo-particle size distribution curve, the peak value being within the range of 5 to 60 μm.
The aqueous coating composition according to the first aspect.

In this embodiment, the majority of the cellulose nanofibers fall within the aforementioned range, so there is little variation in size. Because there is little variation in size, there is little bias in the aqueous paint composition and it has good dispersibility. The cellulose nanofibers can be hydrogen bonded to each other through the hydroxyl groups of the cellulose, so the aqueous paint composition has a high viscosity overall. When shear force is applied, the hydrogen bonds are broken, so the high shear viscosity of the aqueous paint composition decreases. This results in an aqueous paint composition that has good adhesion, is less likely to drip, and has good spreadability.

(Fourth aspect)
The cellulose nanofiber is contained in an amount of 4% by mass or less,
The cellulose nanofibers contain 1 to 49% by mass of cellulose nanofibers obtained by defibrating chemical pulp.
The aqueous coating composition according to the first aspect.

Cellulose nanofibers can be obtained, for example, by defibrating mechanical pulp or chemical pulp. The inventors have found that chemical pulp is easy to defibrate because it has a low lignin content and a relatively high purity. If the purity is high, the variance in fiber diameter and fiber length when defibrated is small, i.e., the cellulose nanofibers have small variations in fiber diameter and fiber length. Cellulose nanofibers with small variations in fiber diameter and fiber length are excellent in dispersibility in aqueous paint compositions, and therefore form aqueous paint compositions with good adhesion, resistance to sagging, and good spreadability.

構造式（１）において、ａ，ｂ，ｍ，ｎは自然数である。
Ａ１，Ａ２，・・・，ＡｎおよびＡ’のうちの少なくとも１つはＯであり、残りはＲ、ＯＲ、ＮＨＲ、及び、なしのいずれかである。Ｒは、水素原子、飽和－直鎖状炭化水素基、飽和－分岐鎖状炭化水素基、飽和－環状炭化水素基、不飽和－直鎖状炭化水素基、不飽和－分岐鎖状炭化水素基、芳香族基、及びこれらの誘導基のいずれかである。αは有機物又は無機物からなる陽イオンである。 (Fifth aspect)
The cellulose nanofiber obtained by defibrating the chemical pulp is
A part of the hydroxyl groups is substituted with a functional group represented by the following structural formula (1) to introduce an ester of phosphorus oxoacid,
The amount of the functional group represented by the structural formula (1) introduced is more than 2.0 mmol per gram of the cellulose nanofiber.
The aqueous coating composition according to the fourth aspect.
[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 composed of an organic or inorganic substance.

Cellulose nanofibers that have been esterified with phosphorus oxoacid have high viscosity (see Patent Document 2). Therefore, aqueous paint compositions that contain this cellulose nanofiber are less likely to drip.

The present invention provides a water-based paint composition that is less likely to drip and has good spreadability.

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.

The following describes an embodiment of the present invention. Note that this embodiment is 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 in this embodiment contains a colored base material and cellulose nanofibers, and has a specified B-type viscosity and a specified high-shear viscosity.

Conventionally, when the aqueous paint composition used for painting on pottery bases (including pottery bases covered with a glaze layer) has a certain range of B-type viscosity, it is preferable because it adheres well to the pottery base and prevents dripping. However, when the painted pottery base is fired, cracks may occur in the painted area. One cause of these cracks is unclear, but it is presumed that it is probably due to uneven painting. Uneven painting refers to unevenness in the thickness of the paint film formed by painting the aqueous paint composition on the pottery base. When there is uneven painting, there are areas in the paint film where a lot of water evaporates during firing and areas where it does not. When the water evaporates, voids are generated in the areas where the water has evaporated, and the concentration of the colored base material changes. It is presumed that the degree of void generation and concentration change differs depending on the difference in the amount of water evaporated, which causes cracks.

Through extensive research, the inventors discovered that it is possible to produce an aqueous paint composition with a specific range of B-type viscosity and a specific range of high-shear viscosity from the materials listed below. This aqueous paint composition is described below.

(Colored substrate)
The coloring base material is a substance that colors the pottery base, and it exhibits various colors depending on the type of base material. There are two methods of painting the pottery base material with an aqueous paint composition having this coloring base material: overpainting and underpainting. Underpainting is painting before glazing, and can be performed by the following method as an example. A pattern is drawn on the bisque-fired pottery base material with an aqueous paint composition containing the coloring base material, and then glaze is applied and fired. Underpainting may be performed by firing multiple times, but if the secondary firing is not performed, it is less time-consuming and the manufacturing cost is low. Some coloring base materials such as pigments react with the glaze, such as by dissolving in the glaze. This reaction may cause the drawing to bleed or become blurred. By using a coloring base material of a metal chloride or nitric acid compound, which is a pigment that is difficult to react with the glaze, the above reaction can be suppressed, and bleeding and blurring can be avoided. In addition, there are also cases where the drawing is intentionally bled or blurred.

For example, overglazing can be performed by 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 layer formed body. A pattern is drawn on the surface of this glaze formed body with a brush or the like using a water-based paint composition. The pottery body with the pattern drawn on 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. The color of this pigment can be a variety of colors, such as red, blue, yellow, and other colors, as well as gold paint.

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

Ceramic pigments have excellent heat resistance, weather resistance, and chemical resistance, and are mainly 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 (Sn-V and Sn-Ti-V types, etc.), vanadium zirconium yellow, peacock, Victoria green, chrome green (Al-Cr type), Prussian blue, sea blue, Co-Zn-Si type, Co-Si type, vanadium zirconium blue, chrome tin lilac, lilac, chrome tin pink, ceramic red, salmon pink, chrome alumina pink, and fire red.

The average particle size of the colored substrate in this embodiment is, for example, 5 μm to 60 μm, preferably 5 μm to 40 μm. If it exceeds 60 μm, unevenness may occur in the painted area due to the colored substrate when the aqueous coating composition is applied thinly, and the color tone may not appear uniform. Also, if it is less than 5 μm, the dispersibility of the colored substrate in the aqueous coating composition may be insufficient, causing uneven coating.

When the main component of the pottery base, especially the surface, is silicic acid or a silicic acid compound (for example, glass or other solid solutions), the above-mentioned production of the glaze layer molded body may be omitted, and a pattern may be drawn on the pottery base with a brush or the like using an aqueous paint composition. In this case, the pottery base after the drawing is fired at a low temperature.

(Cellulose nanofiber)
Cellulose nanofibers increase the number of hydrogen bond 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.

As the raw pulp for cellulose nanofiber, one or more of the following can be selected and used: wood pulp made from broadleaf trees, coniferous trees, etc.; non-wood pulp made from straw, bagasse, cotton, hemp, bast fiber, etc.; and waste paper pulp (DIP) made from recycled waste paper, broke paper, etc. Note that the above various raw materials may be in the form of a pulverized material known as cellulose-based powder, for example.

However, in order to avoid the inclusion of impurities as much as possible, it is preferable to use wood pulp. As wood pulp, for example, one or more types can be selected from 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.

In particular, when an aqueous paint composition made of cellulose nanofibers made from mechanical pulp is used to paint on a subject (such as a ceramic base or glaze layer), the aqueous paint composition spreads well, adheres well to the subject, and is less likely to cause uneven coating. Some conventional aqueous paint compositions contain thickeners such as carboxymethylcellulose to improve adhesion. While carboxymethylcellulose increases the viscosity of the aqueous paint composition, it is a water-soluble thickener and dissolves in water when a glaze is applied, causing cracks after firing.

In addition, when the concentration of cellulose nanofibers in a dispersion liquid is increased, the B-type viscosity increases.

From the viewpoint of adhesion of the aqueous coating composition during drawing and baking, it is preferable to use mechanical pulp, and it is more preferable to use bleached mechanical pulp to bring out the original color of the colored substrate, and it is particularly preferable to use BTMP. If the aqueous coating composition has good adhesion when drawing, the aqueous coating composition is less likely to peel off from the object to be coated after drying, making it easier to carry out drawing work efficiently.

Cellulose nanofibers made from mechanical pulp have a relatively larger average fiber diameter and a relatively lower water retention and B-type viscosity than cellulose nanofibers made from other pulps. It is presumed that these physical properties improve the spread of aqueous paint compositions containing cellulose nanofibers made from mechanical pulp, making them less likely to cause uneven application. Therefore, it is presumed that small blisters that tend to form on the surface of a drawing after baking when drawing with conventional paints are less likely to form when drawing with the aqueous paint composition of this embodiment.

The cellulose nanofibers contained in the aqueous coating composition can be preferably obtained by defibrating mechanical pulp or chemical pulp. In addition, among chemical pulps, additives containing at least one of phosphorus oxoacids and phosphorus oxoacid metal salts may be added to cellulose fibers, and the cellulose fibers may be esterified with phosphorus oxoacids and then defibrated. These cellulose nanofibers are preferably contained in the aqueous coating composition at 2% by mass or more and 4% by mass or less, preferably 3% by mass or more and 4% by mass or less, based on the solid content. If the content exceeds 4% by mass, the concentration of the cellulose nanofibers is high, the interaction between the cellulose nanofibers is strong, and the high-shear viscosity is difficult to relatively lower, so that the elongation of the aqueous coating composition is insufficient, and it is difficult to paint with a uniform color. If the content is less than 2% by mass, the cellulose nanofibers are difficult to disperse throughout the aqueous coating composition, and the concentration of the cellulose nanofibers in the aqueous coating composition is likely to be non-uniform.

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 the cellulose nanofibers obtained by defibrating chemical pulp to the cellulose nanofibers obtained by defibrating mechanical pulp, the aqueous coating composition can have a relatively high B-type viscosity and a high-shear viscosity below a predetermined value.

When the aqueous coating composition contains cellulose nanofibers obtained by defibrating mechanical pulp and cellulose nanofibers obtained by defibrating chemical pulp, the mass ratio of the cellulose nanofibers obtained by defibrating mechanical pulp to the cellulose nanofibers obtained by defibrating chemical pulp is preferably 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 is used, which makes it easier for liquid to drip from the painted area and makes it easier for uneven coating to occur. If the mass ratio is below 1:1, the aqueous coating composition is less likely to drip outward from the painted area, but the concentration of cellulose nanofibers obtained by defibrating mechanical pulp is low, which weakens the effects of this cellulose nanofiber in improving fluidity and adhesion.

In addition, it is preferable that the cellulose nanofibers in the aqueous coating composition are 1 to 49% by mass, more preferably 10 to 30% by mass, of the cellulose nanofibers obtained by defibrating chemical pulp. Chemical pulp has excellent viscosity, so by including cellulose nanofibers obtained by defibrating chemical pulp in this range, an aqueous coating composition with the desired B-type viscosity is obtained. If the cellulose nanofibers obtained by defibrating chemical pulp exceed 49% by mass, the aqueous coating composition will become too viscous to achieve the desired high-shear viscosity and will not spread well. If the amount falls below 1% by mass, the aqueous coating composition may become prone to dripping.

Before defibrating the cellulose nanofibers, they can be pretreated by chemical methods. Examples of pretreatments by chemical methods 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 (including phosphite esterification) (chemical treatment).

By carrying out enzyme treatment, acid treatment, or oxidation treatment prior to defibration, it is possible to relatively reduce the water retention and increase the homogeneity. In this regard, 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, and the water molecules tend to aggregate and form droplets due to hydrogen bonds between them.

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

構造式（１）において、ａ，ｂ，ｍ，ｎは自然数である。
Ａ１，Ａ２，・・・，ＡｎおよびＡ’のうちの少なくとも１つはＯであり、残りはＲ、ＯＲ、ＮＨＲ、及び、なしのいずれかである。Ｒは、水素原子、飽和－直鎖状炭化水素基、飽和－分岐鎖状炭化水素基、飽和－環状炭化水素基、不飽和－直鎖状炭化水素基、不飽和－分岐鎖状炭化水素基、芳香族基、及びこれらの誘導基のいずれかである。αは有機物又は無機物からなる陽イオンである。このセルロースナノファイバーは光透過度及び粘度が極めて高いものである。 If esterification (chemical treatment) with phosphorus oxoacids such as phosphoric acid and phosphorous acid is performed prior to defibration, the fiber raw material can be refined, and the cellulose nanofibers produced have a large aspect ratio, excellent strength, and high light transmittance and viscosity. Esterification with phosphorus oxoacids can be performed by the method described in Patent Document 2 (JP Patent Publication 2019-199671). An example of a cellulose nanofiber esterified with phosphorus oxoacid is shown below. A part of the hydroxyl groups of the cellulose fiber is replaced with a functional group shown in the following structural formula (1) to introduce an ester of phosphorus oxoacid, and an example of a cellulose nanofiber in which the amount of the functional group shown in structural formula (1) introduced exceeds 2 mmol per 1 g of cellulose fiber can be given.
[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. This cellulose nanofiber has extremely high light transmittance and viscosity.

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

Examples of additives 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.

The amount of phosphorus oxoacid ester or phosphonic acid ester introduced is more than 2.0 mmol, preferably 2.1 mmol or more, more preferably 2.2 mmol or more, per 1 g of cellulose fine fibers. Also, it is 3.4 mmol or less, preferably 3.2 mmol or less, more preferably 3.0 mmol or less. If the amount introduced is 2.0 mmol or less, the viscosity of the aqueous coating composition may not be increased significantly. On the other hand, if the amount introduced exceeds 3.4 mmol, the cellulose fibers may dissolve in water.

Cellulose fibers esterified with phosphorus oxyacids can also include those in which some of the hydroxyl groups of the cellulose fibers have been replaced with carbamate groups, resulting in the introduction of carbamate.

(Carbamate Formation)
The additive used for substitution with a carbamate group includes at least one of urea and a urea derivative. For example, urea, thiourea, biuret, phenylurea, benzylurea, dimethylurea, diethylurea, tetramethylurea, etc. can be used as the additive. These ureas or urea derivatives can be used alone or in combination. However, it is preferable to use urea.

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

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

The raw pulp can be defibrated by beating the raw pulp using, for example, a homogenizer such as a beater, a high-pressure homogenizer, or a high-pressure homogenizer, a grinder, a mill-type friction machine such as a grinder, a single-shaft kneader, a multi-shaft kneader, a kneader refiner, a jet mill, or the like. However, it is preferable to use a refiner or a jet mill.

It is preferable to defibrate the raw pulp 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 are the desired values or evaluations as shown below.

The average fiber diameter (average fiber width; average diameter of a single fiber) of the cellulose nanofibers is preferably 1 to 200 nm, more preferably 1 to 100 nm, and particularly preferably 3 to 60 nm. If the average fiber diameter of the cellulose nanofibers is less than 1 nm, the water retention of the cellulose nanofibers may become too high, which may deteriorate the elongation of the aqueous coating composition.

On the other hand, if the average fiber diameter of the cellulose nanofiber exceeds 200 nm, the effect of increasing the number of hydrogen bond points may not be obtained.

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

The method for measuring the average fiber diameter of cellulose nanofibers is as follows.
First, 100 ml of an aqueous dispersion of cellulose nanofibers with a solid content concentration of 0.01 to 0.1% by mass is filtered through a Teflon (registered trademark) membrane filter, and the solvent is replaced once with 100 ml of ethanol and three times with 20 ml of t-butanol. Next, the sample is freeze-dried and osmium-coated to obtain a sample. This sample is observed using an electron microscope SEM image at a magnification of 3,000 to 30,000 times depending on the width of the fibers that constitute it. Specifically, two diagonal lines are drawn on the observed image, and three straight lines passing through the intersection of the diagonal lines are arbitrarily drawn. Furthermore, the widths of a total of 100 fibers that intersect 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 (length of a single fiber) of the cellulose nanofiber obtained from mechanical pulp is preferably 200 to 1300 μm, more preferably 200 to 1000 μm, and particularly preferably 200 to 800 μm. If the average fiber length of the cellulose nanofiber falls below 200 μm, it may be difficult for the cellulose nanofiber to be uniformly dispersed in the aqueous coating composition. A decrease in dispersibility causes problems in terms of resistance to sagging and good elongation.

On the other hand, when the average fiber length of the cellulose nanofiber 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 small, resulting in more easily scratched areas 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 manner as for the average fiber diameter, by visually measuring the length of each fiber. The median length of the measurements is taken as the average fiber length.

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

On the other hand, the water retention of the cellulose nanofibers should be, for example, 500% or less. If it exceeds 500%, the water retention of the cellulose nanofibers themselves is so high that water molecules will form droplets with each other, making it difficult to form a thin film with 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 nanofiber is measured in accordance with JAPAN TAPPI No. 26 (2000).

The median diameter in the pseudo particle size distribution of the cellulose nanofibers is preferably 5 to 60 μm, more preferably 5 to 40 μm. With a median diameter of the above size, the cellulose nanofibers are appropriately dispersed in the aqueous paint composition, and uniform drawing can be performed using the aqueous paint composition. If the median diameter exceeds 5 μm, it becomes difficult for the cellulose nanofibers to be uniformly dispersed in the aqueous paint composition. There are technical difficulties in the production of cellulose nanofibers with a median diameter of less than 5 μm.

The peak value in the pseudo particle size distribution curve of the cellulose nanofiber is preferably one peak. When there is one peak, the cellulose nanofiber defibrated from one or more types of pulp has high uniformity in fiber length and fiber diameter, and the dispersibility of the cellulose nanofiber in the aqueous paint composition is excellent. The peak value is a value measured in accordance with ISO-13320 (2009). It is preferable that the cellulose nanofiber has a single peak in the pseudo particle size distribution curve measured by a laser diffraction method in a water-dispersed state. In this way, cellulose nanofibers with one peak are sufficiently finely refined, can exhibit good physical properties as cellulose nanofibers, and are preferable because the resulting aqueous paint composition is uniformly drawn. The "pseudo particle size distribution curve" means a curve showing a volume-based particle size distribution measured using a particle size distribution measuring device (for example, Horiba's particle size distribution measuring device "LA-960S").

When the peak value in the pseudo-particle size distribution curve is in the range of 5 to 60 μm, the cellulose nanofiber has a uniform pseudo-particle size overall and is dispersed with little bias, which is preferable because it allows for drawing without color unevenness.

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

If necessary, the cellulose nanofibers obtained by defibration can be dispersed in an aqueous medium to form a dispersion liquid prior to mixing with the coloring base material. It is particularly preferable that the aqueous medium is entirely water (aqueous solution). However, the aqueous medium may also be a liquid that is partially compatible with water. As the other liquid, for example, lower alcohols having 3 or less carbon atoms can be used.

(Water-based paint composition)
In a paint containing cellulose nanofibers and a coloring substrate, it is presumed that the coloring substrate is attached to the cellulose nanofibers. Therefore, when the cellulose nanofibers are appropriately dispersed in the aqueous paint composition, the coloring substrate also has excellent dispersibility. For example, the cellulose nanofibers may be contained in an amount of 0.02 to 0.04 parts by mass, more preferably 0.03 to 0.04 parts by mass, per 1 part by mass of the coloring substrate. If the amount of cellulose nanofiber exceeds this range, the amount of cellulose nanofiber is too large relative to the coloring substrate, and the dispersibility of the coloring substrate in the entire paint is biased. If the amount of cellulose nanofiber is less than this range, the dispersibility of the coloring substrate in the entire paint is poor, which causes color unevenness when drawing.

The B-type viscosity of the aqueous coating composition is, for example, preferably 600 cP or more, more preferably 700 cP or more, and particularly preferably 800 cP or more. If the B-type viscosity is less than 600 cP, the aqueous coating composition may unexpectedly flow out from the area where it is drawn to areas other than the area. In addition, the B-type viscosity of the cellulose nanofiber is preferably 2000 cP or less. If the B-type viscosity exceeds 2000 cP, the paint will not spread well when drawing. In addition, interactions such as hydrogen bonds between the cellulose nanofibers will become stronger, and a large amount of energy will be required to disperse the cellulose nanofibers in the aqueous coating composition, which may lead to increased production costs.

The aqueous coating composition of this embodiment has a minimum high-shear viscosity of 3.5 cP or less at a shear rate of 0.8 x 10 ⁵ (1/sec) or more, preferably a minimum high-shear viscosity of 3.5 cP or less at shear rates of 1 x 10 ⁵ to 2 x 10 ⁵ (1/sec), more preferably a minimum high-shear viscosity of 3.3 cP or less at shear rates of 1 x 10 ⁵ to 2 x 10 ⁵ (1/sec), even more preferably a minimum high-shear viscosity of 3.0 cP or less at shear rates of 1 x 10 ⁵ to 2 x 10 ⁵ (1/sec), and preferably a maximum high-shear viscosity of 3.0 cP or less at shear rates of 1 x 10 ⁵ to 2 x 10 ⁵ (1/sec). If the minimum high-shear viscosity of the cellulose nanofiber exceeds 3.5 cP, the aqueous coating composition will not spread well when soaked in a brush and used for drawing, making it difficult to draw.

In addition to the coloring substrate and cellulose nanofiber, silica powder ( _SiO2 powder) and a thickener can be added to the coating composition. In particular, the thickener should not be added excessively because it increases the B-type viscosity and high-shear viscosity, but it is possible to increase the viscosity by adding an appropriate amount. As the thickener, a known thickener can be appropriately used, for example, carboxymethylcellulose (CMC), xanthan gum, guar gum, pectin, and carrageenan can be used. Depending on the type of coloring substrate and cellulose nanofiber, it is preferable that the thickener is contained in the aqueous coating composition in an amount of 20 to 30% by mass. However, the thickener does not necessarily have to be included in the aqueous coating composition.

(Ceramics base)
The pottery base is not particularly limited as long as it is a known base, and examples thereof 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 a glassware, for example, silicic acid, silicic acid 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 contain, for example, ash (fluxing agent), clay (adhesive), feldspar (adhesive, fluxing agent, glass raw material), and silica (glass raw material). Ash is mainly composed of calcareous substances such as calcium oxide, and has the function of melting at high temperatures to form a glass, and of making other components easier to melt as a fluxing agent, thereby increasing the fluidity of the glaze. Furthermore, if it contains color-producing components (such as copper or iron), it will produce a color-producing effect.

The chemical components of the glaze are 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 the fired glaze, and although it depends on the type of glaze, they account for approximately 45-80% of the glaze.

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

(Manufacturing)
<Glaze layer formation process>
The aqueous coating composition can be applied to a base material 11 that is the basis of finished products such as Japanese and Western tableware, ornaments, and interior accessories. The base material 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 base material whose surface is covered with a glaze layer (also called a glaze-layered base material) (manufacturing step 12). The firing conditions are, for example, heating to 950°C over 9 hours and 30 minutes, and then heating to 1250°C over 5 hours. The temperature of 1250°C is maintained for 30 minutes, and then naturally cooled. The finished product can be used as a ceramic product or an enamel product, for example.

Glazing can be applied to the entire surface of the base, or to just a part of it. Although crazing may occur, it is preferable to cover the entire surface of the base. Water is less likely to penetrate the glaze layer. Note that glazing also includes the case where glaze is dispersed in water and then poured onto the base.

If the base is for glassware, the glaze layer forming 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 paint composition, and then dried, for example, at 60 to 105° C. for 1 hour to obtain a drawn molded body (manufacturing step S13).

The drawn molded body is glazed (immersed), the design is glazed, and then it is dried again at 60 to 105°C for 1 hour (manufacturing step S21), and fired at 1220°C, so that the fired aqueous paint composition is coated with glaze and the glaze layer 20a is formed. That is, the glaze layer 20a is formed by coating the fired aqueous paint composition with glaze, and the drawn molded body is coated with the glaze layer 20a to form a glaze layer molded body (manufacturing step S22). The firing conditions are, for example, raising the temperature to 950°C over 9 hours and 30 minutes, and then raising the temperature to 1220°C over 5 hours. 1220°C is maintained for 30 minutes, and then naturally cooled. This glaze layer molded body can be used as a finished product, but it is also possible to manufacture a finished product consisting of multiple layers, in which one or more glaze layers are further layered on the glaze layer molded body.

If the base material is for glassware, the pattern 30a is drawn on the base material using a water-based paint composition, and then dried, for example, at 60 to 105°C for 1 hour to obtain a drawn molded product (manufacturing step S33).

The drawn molded body is glazed (immersed), the design is glazed, and then it is dried again at 60 to 105°C for 1 hour (manufacturing step S41), and fired at 580 to 780°C, so that the fired aqueous paint composition is coated with glaze to form the glaze layer 20a. That is, the glaze layer 20a is formed by coating the fired aqueous paint composition with glaze, and the drawn molded body is coated with the glaze layer 20a to form a glaze layer molded body (manufacturing step S42). The firing conditions are, for example, to raise the temperature to 550°C over 5 hours and 30 minutes, and then to 780°C over 5 hours. 780°C is maintained for 30 minutes, and then naturally cooled. This glaze layer molded body can be used as a finished product, but it is also possible to manufacture a finished product consisting of multiple layers, in which one or more glaze layers are further layered on the glaze layer molded body.

The main chemical composition of cellulose nanofiber is organic, with small amounts of inorganic matter also included. The organic content of cellulose nanofiber disappears 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 by the surface, and becomes hydrophilic after drying, making it easy to apply glaze. This makes it possible to apply the aqueous paint composition and then cover it with a glaze layer.

Overglaze painting is a known method for painting on the surface of a glaze layer, but because a glaze layer cannot be formed on the surface of the design, it is known to be less durable. For example, if the finished product is Japanese or Western tableware, it is known that the color will easily fade when repeatedly washed in the dishwasher.

(Preparation of Coating Composition)
A paint was produced by mixing 1.0 g of pigment (Nito Pigment Co., Ltd. Green M-142), BTMP cellulose nanofiber aqueous dispersion (bleached mechanical pulp product), LBKP cellulose nanofiber aqueous dispersion (bleached chemical pulp product derived from hardwood pulp), phosphorous esterified cellulose nanofiber, and water. The BTMP cellulose nanofiber was beaten with a Niagara beater or single disc refiner to obtain a treated product until the ratio of fine fibers was 80% or more, and the treated product was circulated 10 to 20 times in a high-pressure homogenizer for finer treatment, and the resulting product was concentrated to 3 to 4% by mass. The LBKP cellulose nanofiber was beaten with a Niagara beater or single disc refiner to obtain a treated product until the ratio of fine fibers was 80% or more, and the treated product was circulated 3 to 4 times in a high-pressure homogenizer for finer treatment. For the phosphorous-esterified cellulose nanofibers, chemical pulp was impregnated with water containing phosphorous acid and urea, and reacted for 2 hours at 170° C. to obtain a product. This product was washed with water and circulated 2 to 3 times in a high-pressure homogenizer for fine treatment and preparation.

<Test Example 1>
The composition of each substance in the aqueous coating composition of Test Example 1 is as follows.
・Pigment 1.0g
・2.0% BTMP cellulose nanofiber 0.07g
3.43g water
These substances were mixed together to obtain a water-based coating composition (Test Example 1).
<Test Example 2>
The composition of each substance in the aqueous coating composition of Test Example 2 is as follows.
・Pigment 1.0g
・3.0% BTMP cellulose nanofiber 0.06g
・2.0% LBKP cellulose nanofiber 0.01g
3.43g water
These substances were mixed together to obtain a water-based coating composition (Test Example 2).
<Test Example 3>
The composition of each substance in the aqueous coating composition of Test Example 3 is as follows.
・Pigment 1.0g
・2.5% BTMP cellulose nanofiber 0.07g
・2.0% LBKP cellulose nanofiber 0.02g
3.24g water
These substances were mixed together to obtain a water-based coating composition (Test Example 3).
<Test Example 4>
The composition of each substance in the aqueous coating composition of Test Example 4 is as follows.
・Pigment 1.0g
・2.0% BTMP cellulose nanofiber 0.06g
・2.0% LBKP cellulose nanofiber 0.02g
3.25g water
These substances were mixed together to obtain a water-based coating composition (Test Example 4).
<Test Example 5>
The composition of each substance in the aqueous coating composition of Test Example 5 is as follows.
・Pigment 1.0g
・2.0% BTMP cellulose nanofiber 0.05g
1.0% phosphite esterified cellulose nanofiber 0.01 g
3.45g water
These substances were mixed together to obtain a water-based coating composition (Test Example 5).
<Test Example 6>
The composition of each substance in the aqueous coating composition of Test Example 6 is as follows.
・Pigment 1.0g
・2.2% BTMP cellulose nanofiber 0.06g
・2.0% LBKP cellulose nanofiber 0.02g
3.56 g water
These substances were mixed together to obtain a water-based coating composition (Test Example 6).

(Evaluation test)
For Test Examples 1 to 6, the high-shear viscosity, B-type viscosity, degree of stretching during drawing, degree of dripping of the aqueous coating composition outside the drawn portion, and surface roughness of the coating film were measured and evaluated.

<High shear viscosity>
The high shear viscosity of each test example was measured by a high shear viscometer. The shear rate was gradually increased from 0 (1/sec) to 183580 (1/sec). Then, the shear rate was gradually decreased to 0 (1/sec). This imitates the process in which, when drawing, an artist brings a brush into contact with an object to be drawn, increases the speed of the brush while moving it along the object to be drawn until it reaches a predetermined speed, and then decreases the speed and then removes the brush from the object to be drawn. Here, although it cannot be said in general, the inventors have found that the speed at which an artist moves a brush corresponds to a range of approximately 183580 (1/sec) or less when expressed in terms of shear rate.

The measurement results of the high shear viscosity are shown in Table 1. In Table 1, the shear rate and the rotation speed are correlated. For each test example, the maximum and minimum values in Table 1 indicate the maximum and minimum values of the high shear viscosity measured by changing the shear rate. The final value in Table 1 indicates the high shear viscosity at 11470 (1/sec) when the shear rate is gradually decreased. The recovery rate in Table 1 indicates the value obtained by dividing the final value by the high shear viscosity at 11470 (1/sec) when the shear rate is gradually increased and multiplying the result by 100.

<B-type viscosity>
The Brookfield viscosity was measured in accordance with JIS-Z8803 (2011) "Method for measuring viscosity of liquids."

<Stretchability>
The spread of the aqueous coating composition was evaluated by drawing with a brush soaked in the aqueous coating composition on the surface of a ceramic base material that had been entirely covered with glaze. The evaluation criteria were as follows:
◯: The design drawn on the ceramic was not rubbed off and the paint was applied evenly.
×: The pattern drawn on the ceramic was scratched and uneven coating occurred.

<Drooping condition>
The degree of dripping of the aqueous coating composition was evaluated by drawing with a brush soaked in the aqueous coating composition on the surface of a ceramic base material entirely covered with glaze. The evaluation criteria were as follows:
◯: When the ceramic base on which the image was drawn was turned upside down so that the drawn area was facing down, the aqueous coating composition did not drip outside the drawn area.
×: When the painted ceramic base was turned upside down so that the painted part was facing down, the aqueous coating composition dripped outside the painted part.

<Surface roughness of coating film>
The aqueous coating composition was applied to a ceramic base and dried at 105°C, after which the surface roughness of the coating film of the applied aqueous coating composition was evaluated. The evaluation method was as follows. The surface roughness was evaluated by taking an image with an optical microscope (Keyence Corporation, product "VHX-6000") at a magnification of 500 times in 3D photography mode, and evaluating the height difference of the unevenness of the surface. Images with few areas where the paint protruded from the surface were judged to have good surface roughness.

The evaluation results of B type viscosity, elongation, sagging, and smoothness of the coating surface are shown in Table 2.

Test example 1 had a relatively low concentration of cellulose nanofibers, resulting in a low B-type viscosity and a tendency to drip. Test examples 2 and 3 had a relatively high high-shear viscosity and did not stretch well. Test examples 4 to 6 had good stretch and were not prone to dripping.

In particular, Test Example 5, which contains phosphorous-esterified cellulose nanofibers, had a relatively high B-type viscosity and a low high-shear viscosity, i.e., excellent thixotropy. This is presumably due to the following reasons. As described in Patent Document 2, phosphorous-esterified cellulose nanofibers have excellent viscosity, so even if the amount of phosphorous-esterified cellulose nanofiber used is relatively small, Test Example 5 has a predetermined B-type viscosity. In addition, the average fiber diameter of phosphorous-esterified cellulose nanofibers is about 3 nm, and the average fiber length is about 100 to 300 nm, which is relatively smaller than that of BTMP cellulose nanofibers and LBKP cellulose nanofibers. When the shear rate is high, the smaller the average fiber diameter and average fiber length, the smaller the interaction between the cellulose nanofibers in the aqueous paint composition, and therefore the smaller the high-shear viscosity. Therefore, Test Example 5 was less likely to droop outward from the painted area, and had good elongation.

The present invention is not limited to the above-described embodiment, 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, but organic solvents or other fluids can be used as appropriate.

(others)
- The high shear viscosity was measured at 25°C for the prepared aqueous coating composition using a high shear viscometer (SMT product PM-9000HV) and an E-bob at different shear rates. 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. By measuring the high shear viscosity, the viscosity of the non-Newtonian fluid according to the shear rate can be obtained.
The centrifuge used was a HITACH HI refrigerated centrifuge CR22N.
The average particle size of pigments and other particles is measured in accordance with JIS Z 8825:2013.
Room temperature refers to the temperature in an ordinary house, for example, 1 to 30°C, more preferably 15 to 25°C.
The B-type viscosity of the cellulose nanofiber dispersion is a value measured in accordance with JIS-Z8803 (2011) "Method for measuring viscosity of liquids." B-type viscosity is the resistance torque when the dispersion is stirred, and the higher the value, the more energy is required for stirring. B-type viscosity was measured at 25°C.

The present invention can be used as an aqueous coating composition for painting 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 Brookfield viscosity is 600 cP or more,
At a shear rate of 0.8×10 ⁵ (1/sec) or more, the minimum high shear viscosity is 3.5 cP or less;
The cellulose nanofiber is contained in an amount of 4% by mass or less,
The cellulose nanofibers contain 1 to 49% by mass of cellulose nanofibers obtained by defibrating chemical pulp.
1. An aqueous coating composition comprising: The minimum high shear viscosity is 3.5 cP or less at a shear rate of 1×10 ⁵ to 2×10 ⁵ (1/sec).
The aqueous coating composition according to claim 1. The cellulose nanofiber has a median diameter of a pseudo-particle size distribution of 5 to 60 μm, and has one peak value in a pseudo-particle size distribution curve, the peak value being within the range of 5 to 60 μm.
The aqueous coating composition according to claim 1. The cellulose nanofiber obtained by defibrating the chemical pulp is
A part of the hydroxyl groups is substituted with a functional group represented by the following structural formula (1) to introduce an ester of phosphorus oxoacid,
The amount of the functional group represented by the structural formula (1) introduced is more than 2.0 mmol per gram of the cellulose nanofiber.
The aqueous coating composition according to claim 1 .
[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 composed of an organic or inorganic substance.

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