阅读说明：本技术 低粘度分散介质用高隐蔽性白色颜料及其制造方法 (High hiding white pigment for low viscosity dispersion medium and method for producing same ) 是由 胜山智祐 那须昭夫 森下正育 下村直敬 下村珠美 于 2020-01-30 设计创作，主要内容包括：本发明提供即使在水系分散介质那样的低粘度的分散介质中也不易沉降,并且,隐蔽性优异的以氧化钛作为主成分的表面被覆烧成颜料。本公开的以氧化钛作为主成分的表面被覆烧成颜料由具有表面突出形状的二次结构粒子构成,二次结构粒子由多个一次结构体连接而构成,二次结构粒子的表面被除氧化钛以外的无机材料被覆,并且,面积等效圆粒径为150nm以上且500nm以下。(The present invention provides a surface-coated fired pigment containing titanium oxide as a main component, which is less likely to settle even in a low-viscosity dispersion medium such as an aqueous dispersion medium and has excellent hiding properties. The surface-coated fired pigment mainly composed of titanium oxide is composed of secondary structure particles having a surface-protruding shape, the secondary structure particles are composed of a plurality of primary structures connected together, the surfaces of the secondary structure particles are coated with an inorganic material other than titanium oxide, and the area equivalent circle particle diameter is 150nm to 500 nm.)

1. A pigment comprising titanium oxide as a main component,

composed of secondary structure particles with surface protruding shapes,

the secondary structure particle is formed by connecting a plurality of primary structures,

the surface of the secondary structure particle is coated with an oxide layer of an inorganic material other than titanium oxide, and the area equivalent circle particle diameter is 150nm or more and 500nm or less.

2. The pigment according to claim 1, wherein the inorganic material is one or more than two kinds of oxides of elements selected from the group consisting of aluminum, silicon, zinc, titanium, zirconium, iron, cerium, and tin.

3. The pigment according to claim 1, wherein the inorganic material is at least one selected from the group consisting of silica and alumina.

4. The pigment according to any one of claims 1 to 3, wherein the shape of the primary structure is at least one selected from the group consisting of needle-like, granular, spindle-like, long-sized, straw-like, rod-like and cocoon-like shapes.

5. The pigment according to any one of claims 1 to 4, wherein the titanium oxide has an apparent bulk density of 600kg/m³The following.

6. The pigment according to any one of claims 1 to 5, wherein the titanium oxide has a specific surface area of 80m²The ratio of the carbon atoms to the carbon atoms is less than g.

7. The pigment of any one of claims 1 to 6, having a hiding power difference of 2.0 or more in a hiding power test.

8. The pigment of any one of claims 1 to 7, being of the rutile type.

9. The pigment according to any one of claims 1 to 8, which is for cosmetic use.

10. A pigment having an area equivalent circular particle diameter of 150nm or more and 500nm or less and selected from 600kg/m³Apparent bulk density of 80m²At least one kind of specific surface area of/g or less, and the surface is coated with an oxide layer of an inorganic material other than titanium oxide.

11. A composition comprising the pigment according to any one of claims 1 to 10 and a dispersion medium, and having a viscosity of 100 mPas or less at a shear rate of 1000/s.

12. The method for producing a pigment according to any one of claims 1 to 10, wherein a slurry containing secondary structure particles having a protruding shape on the surface, which are formed by connecting a plurality of primary structures, is prepared using a titanium oxide-forming solution, an inorganic material coating solution comprising an aqueous solution of an inorganic salt serving as a raw material of the coating agent is added to the slurry, and the secondary structure particles having the surface coated with an inorganic material are fired in air at 550 ℃ to 750 ℃.

Technical Field

The present disclosure relates to a surface-coated fired pigment containing titanium oxide as a main component, which is suitable for use in a low-viscosity dispersion medium, and a method for producing the same.

Background

In recent years, pigments containing titanium oxide having various particle shapes as a main component are blended into various dispersion media and used for various applications.

For example, patent document 1 discloses the use of hidden, unfired rutile titanium oxide aggregate particles for high-viscosity cosmetics, wherein the titanium oxide aggregate particles are formed by aggregating and/or binding together rod-like particles having a side size of 0.05 to 0.2 μm and a thickness direction of 0.02 to 0.1 μm, and fan-like rutile titanium oxide particles having a particle diameter of 0.1 to 5.0 μm and an average friction coefficient (MIU value) of 0.2 or more and less than 0.7 are further aggregated.

Patent documents 2 to 4 disclose that titanium oxide having a straw-like or long-like particle shape is used in a high-viscosity cosmetic.

Titanium oxide is widely used mainly for cosmetics, but is generally prone to aggregation and sedimentation because of its large Hamaker constant (Hamaker constant) which is an index of the strength of interaction.

In general, as an index of settleability of particles in a liquid medium, the stokes formula shown in the following formula 1 may be used:

[ number 1]

Wherein, V_sIs the sedimentation velocity, D_pMeans particle diameter, p_pRefers to the particle density, ρ_fRefers to the density of the medium, g refers to the acceleration of gravity, and η refers to the viscosity of the medium.

The average particle size of the pigment-grade titanium oxide is about 0.3. mu.m, and rutile which has a high refractive index and is advantageous in terms of hiding power is used as a crystal system of the pigment-grade titanium oxide in cosmetics. The rutile density was 4.27g/mL (Qingye, acidify チタン (titanium oxide), 1991). Since the sedimentation rate is proportional to the square of the particle diameter and the density difference and inversely proportional to the viscosity of the medium, for example, in a medium having a low viscosity such as an aqueous dispersion medium, the pigment-grade titanium oxide particles having a high density are liable to sediment. Therefore, even when such a pigment-grade titanium oxide is blended with a medium used for a relatively high-viscosity cosmetic or the like, it is not blended with a low-viscosity medium such as an aqueous dispersion medium without using a physical dispersion means such as stirring or shaking.

In addition, in order to exhibit a necessary concealing property, a general pigment-grade titanium oxide is often subjected to firing. However, since the density of the titanium oxide subjected to firing increases with a decrease in the porosity, the titanium oxide is more likely to settle than the titanium oxide not subjected to firing.

In a dispersion medium having a low viscosity, it is effective to reduce the particle size of titanium oxide to improve the sedimentation resistance. However, titanium oxide may not satisfy performance required as a material for cosmetics because the concealing property is lowered if the particle diameter is made small. Both sedimentation resistance and hiding property are required in a dispersion medium having a low viscosity.

Documents of the prior art

Patent document

Patent document 1: japanese patent No. 4684970

Patent document 2: japanese patent No. 6258462

Patent document 3: japanese patent No. 5096383

Patent document 4: japanese patent laid-open No. 2014-84251

Disclosure of Invention

Problems to be solved by the invention

The disclosed subject matter provides a surface-coated fired pigment containing titanium oxide as a main component, which is less likely to settle in a low-viscosity dispersion medium such as an aqueous dispersion medium and has excellent hiding properties.

Means for solving the problems

As a result of intensive studies on the dispersion of titanium oxide, the present inventors have found that a surface-coated fired pigment containing titanium oxide as a main component, which is excellent in sedimentation resistance and hiding properties in a low-viscosity dispersion medium, can be obtained by treating titanium oxide having a protruding shape as shown in fig. 1 with an aqueous solution of an inorganic salt serving as a raw material of a coating agent and firing the treated titanium oxide.

The surface-coated fired pigment containing titanium oxide as a main component of the present disclosure may be used in the form of a composition mixed with a dispersion medium.

Scheme 1

A pigment comprising titanium oxide as a main component and having secondary structure particles with a surface protruding shape, wherein the secondary structure particles are formed by connecting a plurality of primary structures, the surface of the secondary structure particles is coated with an inorganic material other than titanium oxide, and the area equivalent circle particle diameter is 150nm to 500 nm.

Scheme 2

The pigment according to claim 1, wherein the inorganic material is one or more oxides of elements selected from the group consisting of aluminum, silicon, zinc, titanium, zirconium, iron, cerium and tin.

Scheme 3

The pigment according to claim 1, wherein the inorganic material is at least one selected from the group consisting of silica and alumina.

Scheme 4

The pigment according to any one of claims 1 to 3, wherein the shape of the primary structure is at least one selected from the group consisting of needle-like shape, granular shape, spindle-like shape, long-like shape, straw bundle-like shape, rod-like shape and cocoon-like shape.

Scheme 5

The pigment according to any one of aspects 1 to 4, which has an apparent bulk density of 600kg/m³The following.

Scheme 6

The pigment according to any one of aspects 1 to 5, which has a specific surface area of 80m²The ratio of the carbon atoms to the carbon atoms is less than g.

Scheme 7

The pigment of any one of aspects 1 to 6, which has a hiding power difference of 2.0 or more in a hiding power test.

Scheme 8

The pigment according to any one of aspects 1 to 7, wherein the titanium oxide component is in a rutile type.

Scheme 9

The pigment according to any one of aspects 1 to 8, which is for cosmetic use.

Scheme 10

A pigment having an area equivalent circular particle diameter of 150nm or more and 500nm or less and selected from 600kg/m³Apparent bulk density of 80m²At least one kind of specific surface area of/g or less, and the surface of the titanium oxide-coated titanium oxide.

Scheme 11

A composition comprising the pigment according to any one of embodiments 1 to 10 and a dispersion medium, wherein the viscosity at a shear rate of 1000/s is 100 mPas or less.

Scheme 12

The method for producing a pigment according to any one of aspects 1 to 10, wherein,

preparing a slurry containing secondary structure particles having a surface-protruded shape, which are formed by connecting a plurality of primary structures, by using a solution for forming titanium oxide,

an inorganic material coating liquid comprising an aqueous solution of an inorganic salt which is a raw material of the coating agent is added to the slurry,

the secondary structure particles having the surface coated with an oxide layer of an inorganic material are fired in air at 550 ℃ to 750 ℃.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present disclosure, a surface-coated fired pigment containing titanium oxide as a main component, which is less likely to settle even in a low-viscosity dispersion medium such as an aqueous dispersion medium and has excellent hiding properties, can be provided.

Drawings

FIG. 1 is a transmission electron micrograph of titanium oxide whose surface was not coated and calcined.

FIG. 2 is a transmission electron microscope photograph after firing without titanium oxide coating on the surface.

Fig. 3 is a transmission electron microscope photograph after firing of a surface-coated fired pigment having titanium oxide as a main component, which is surface-coated with silicon oxide in one embodiment of the present disclosure.

Fig. 4 is a transmission electron microscope photograph after firing of a surface-coated fired pigment having titanium oxide as a main component, which is surface-coated with silicon oxide and aluminum oxide in another embodiment of the present disclosure.

Detailed Description

Hereinafter, embodiments of the present disclosure will be described in detail. The present disclosure is not limited to the following embodiments, and various modifications can be made within the scope of the present invention.

A surface-coated fired pigment containing titanium oxide as a main component according to one embodiment of the present disclosure is composed of secondary structure particles having a surface protruding shape as shown in fig. 3, the secondary structure particles being composed of a plurality of primary structures connected to each other, the surfaces of the secondary structure particles being coated with an inorganic material other than titanium oxide, and the area equivalent circle particle diameter being 150nm or more and 500nm or less.

For the pigments of the present disclosure, it is important that the secondary structure particles have a plurality of surface protrusion shapes. The pigment of the present disclosure has voids due to the protruding shape as shown in fig. 3, and therefore the apparent bulk density is reduced. Therefore, it is considered that the sedimentation rate is small even in a low-viscosity dispersion medium such as an aqueous dispersion medium, and the sedimentation is less likely to occur as compared with a general pigment-grade titanium oxide.

Such pigments have a specific apparent bulk density or specific surface area different from those of general pigment-grade titanium oxides and the like. It is considered that the pigment having such a specific apparent bulk density or specific surface area can exhibit the same effect.

The pigment of the present disclosure is obtained by applying a surface coating treatment to unfired titanium oxide having a specific morphology as shown in fig. 1 and then performing a firing treatment. As a result, unlike the pigment described in patent document 2 in which the surface of titanium oxide (fig. 2) that has been fired to change its surface shape is subjected to a surface coating treatment, the surface-coated fired pigment of the present disclosure can retain the specific form shown in fig. 3 and 4, that is, the form of secondary structure particles formed by connecting a plurality of primary structures. This is presumably because sintering of the primary structures is inhibited by forming a coating layer made of an inorganic material different from titanium oxide on the surface of the primary structures made of titanium oxide.

Further, the coating layer on the pigment surface is made of an inorganic material other than titanium oxide. Since hydroxyl groups are likely to be disposed on the surface of the coating layer made of an inorganic material, the aqueous dispersion medium is considered to have improved compatibility with titanium oxide and to be more easily dispersed than the aqueous dispersion medium.

Further, the coating layer on the pigment surface is improved in binding force with titanium oxide by firing, and the coating layer is prevented from peeling off, so that it is considered that the durability is improved as compared with the coating layer which is not fired.

The pigment of the present disclosure has an area equivalent circular particle diameter of 150nm or more and 500nm or less, is substantially the same as that of a general pigment-grade titanium oxide, and is fired after a surface coating treatment. As a result, the porosity of the pigment, particularly the porosity in the vicinity of the core inside the pigment which is not easily surface-coated, can be reduced as compared with the unfired surface-coated titanium oxide and the like described in patent documents 1,3, and 4, and thus it is considered that the concealing performance can be further improved.

Surface-coated fired pigment comprising titanium oxide as a main component

As the surface-coated fired pigment (may be simply referred to as "pigment") containing titanium oxide as a main component of the present disclosure, there can be used: a pigment composed of secondary structure particles having a surface-protruding shape of titanium oxide as a main component, the surface of which is coated with an inorganic material other than titanium oxide, has an area equivalent circular particle diameter of 150nm or more and 500nm or less, and is formed by connecting a plurality of primary structures; and/or have a molecular weight selected from 600kg/m³Apparent bulk density of 80m²A pigment containing titanium oxide as a main component and having at least one specific surface area of not more than g.

The titanium oxide component in the pigment may be any of anatase type, rutile type, and brookite type, but rutile type titanium oxide is preferable from the viewpoint of hiding property.

Characteristics of pigment

(area equivalent circle particle diameter)

The area equivalent circle particle diameter of the pigment may be converted to a particle diameter in the case of a circular particle having the same area as the projected area of the pigment observed with a transmission electron microscope, for example. Such an area equivalent circle particle diameter can be defined as an average value of 10 or more particles. The area equivalent circular particle diameter of the titanium oxide particles is preferably about 1/2 wavelengths of visible light, more preferably 150nm to 450nm, and particularly preferably 200nm to 400nm, in order to improve the scattering effect of visible light and enhance the concealing property.

(apparent bulk Density)

In order to make the settling velocity small, it is desirable that the apparent bulk density of the pigment of the present disclosure is 600kg/m³The following. The lower limit of the apparent bulk density is not particularly limited, and may be set to 100kg/m³The above. The apparent bulk density can be determined by, for example, using a specific volume tester and operating as described below.

(specific surface area)

From the viewpoints of hiding property, sedimentation resistance and the like, it is desirable that the specific surface area of the pigment of the present disclosure is 80m²The ratio of the carbon atoms to the carbon atoms is less than g. The specific surface area of titanium oxide can be determined by, for example, the BET method.

(concealment)

The pigment of the present disclosure can have a color difference (Δ E) that is an index of hiding property, for example, 30.0 or less, 27.0 or less, 25.0 or less, 24.0 or less, or 23.0 or less in a hiding property test described later. The lower limit of the color difference is not particularly limited, and may be, for example, 10.0 or more, 12.0 or more, or 15.0 or more.

In the hiding test described later, the hiding property of the pigment of the present disclosure can be evaluated by the difference in color difference (difference in hiding power) from other titanium oxide based on the color difference of titanium oxide which is not subjected to surface coating and firing treatment. The difference in hiding power can be defined as 2.0 or more. The upper limit value of the difference in hiding power is not particularly limited, and may be set to 20.0 or less, for example.

(crystallite diameter)

The pigment of the present disclosure desirably has a crystallite diameter of 8.0nm or more, and further desirably has a crystallite diameter of 25.0nm or less. The crystallite diameter of titanium oxide can be measured by a general X-ray diffraction method.

(shape)

As the pigment of the present disclosure, a pigment having a surface protruding shape formed by connecting a plurality of primary structures can be used.

The shape of the primary structure may be any shape as long as the sedimentation resistance and the concealing property can be obtained, and is not limited to the following shapes, and may be at least one selected from the group consisting of needle-like, granular, spindle-like, long-sized, straw-like, rod-like, and cocoon-like shapes, for example. Among them, the needle-like or rod-like shape as shown in fig. 3 and 4 is preferable.

The primary structures may be connected to each other so as to form a protruding shape on the surface of the secondary structure particle, and the connection structure is not particularly limited, and the primary structures may be connected to each other in a fan shape, a radial shape, or a random shape, and among these, the radial connection is preferable from the viewpoint of the sedimentation resistance and the concealing property.

Surface coating

The pigments of the present disclosure are coated on their surface with one or more inorganic materials other than titanium oxide. Such an inorganic material is not limited to the following materials, and examples thereof include a component containing an element selected from aluminum, silicon, zinc, zirconium, iron, cerium, and tin, and an oxide of the above element. Among these, silicon oxide and aluminum oxide are preferable, and silicon oxide is more preferable. From the viewpoint of concealing properties, the pigment having a surface coating layer is preferably composed mainly of titanium oxide, that is, 800g/kg or more of a titanium oxide component. The proportion of the surface coating layer in such titanium oxide may be 200g/kg or less, or 10g/kg or more, based on the mass of the pigment.

By coating the surface of the pigment of the present disclosure with an inorganic material other than titanium oxide, it is possible to reduce the shape change caused by sintering of the primary structure and to improve the dispersibility in a dispersion medium, particularly an aqueous dispersion medium.

Composition containing surface-coated calcined titanium oxide

The pigment containing titanium oxide as a main component of the present disclosure can be used in a composition together with a low-viscosity dispersion medium, particularly an aqueous dispersion medium.

Properties of composition

(viscosity)

Compositions comprising the pigments of the present disclosure may have a viscosity of 100 mPa-s or less at a shear rate of 1000/s. Such a viscosity can be measured, for example, by using a rheometer such as MCR-302 (manufactured by Anton-Paar), and the viscosity at a shear rate of 1000/s of the object to be measured at 32 ℃ under 1 atmosphere can be defined as 100 mPas or less, 50 mPas or less, or 10 mPas or less, and can be defined as 1 mPas or more, 2 mPas or more, or 3 mPas or more.

The static viscosity, i.e., shear rate, as a composition of the present disclosure is infinitely close to 0s^-1In the case of the above, for example, the viscosity at a shear rate of 1/s can be set to 1000 mPas or less, and further, can be set to 10 mPas or more. The static viscosity can also be measured at 32 ℃ under 1 atm using the above rheometer.

(resistance to sedimentation)

The composition of the present disclosure may be 90.0% or more, 93.0% or more, or 95.0% or more after 24 hours in the sedimentation resistance test described later, and may be 100% or less, less than 100%, or 99.0% or less.

(resistance to sedimentation)

The composition of the present disclosure may be 90.0% or more after 24 hours, and may be 85.0% or more after 90 hours in a sedimentation resistance test described later.

Blending amount of pigment

The amount of the pigment to be blended in the composition may be appropriately adjusted depending on the use application, and is not limited to the following amount, and for example, may be 50g/kg or more, 100g/kg or more, or 200g/kg or more, or may be 300g/kg or less, 270g/kg or less, or 250g/kg or less in the composition.

Dispersion medium

The dispersion medium is not particularly limited as long as it is a material capable of dispersing the pigment, and one or more known dispersion media such as an organic dispersion medium and an aqueous dispersion medium can be used. Among them, an aqueous dispersion medium is preferably used. Examples of the aqueous dispersion medium include water, various alcohols such as a lower alcohol and a polyhydric alcohol, and a mixture thereof.

Examples of the lower alcohol include ethanol, propanol, isopropanol, isobutanol, and tert-butanol.

Examples of the polyhydric alcohol include 2-membered alcohols (e.g., ethylene glycol, propylene glycol, 1, 3-propanediol, 1, 2-butanediol, 1, 3-butanediol, 1, 4-butanediol, 2, 3-butanediol, 1, 5-pentanediol, 2-butene-1, 4-diol, hexanediol, octanediol, etc.); 3-membered alcohols (e.g., glycerin, trimethylolpropane, etc.); 4-membered alcohols (e.g., pentaerythritol such as 1,2, 6-hexanetriol); 5-membered alcohols (e.g., xylitol, etc.); 6-membered alcohols (e.g., sorbitol, mannitol, etc.); polyol polymers (e.g., diethylene glycol, dipropylene glycol, triethylene glycol, polypropylene glycol, tetraethylene glycol, diglycerol, polyethylene glycol, triglycerol, tetraglycerol, polyglycerols, and the like); 2-membered alcohol alkyl ethers (e.g., ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol monophenyl ether, ethylene glycol monohexyl ether, ethylene glycol mono 2-methylhexyl ether, ethylene glycol isoamyl ether, ethylene glycol benzyl ether, ethylene glycol isopropyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, etc.); 2-membered alcohol alkyl ethers (e.g., diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol butyl ether, diethylene glycol methyl ethyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monobutyl ether, propylene glycol isopropyl ether, dipropylene glycol methyl ether, dipropylene glycol ethyl ether, dipropylene glycol butyl ether, etc.); 2-membered alcohol ether esters (e.g., ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, ethylene glycol monobutyl ether acetate, ethylene glycol monophenyl ether acetate, ethylene glycol diadipate, ethylene glycol disuccinate, diethylene glycol monoethyl ether acetate, diethylene glycol monobutyl ether acetate, propylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate, propylene glycol monopropyl ether acetate, propylene glycol monophenyl ether acetate, etc.); glycerol monoalkyl ethers (e.g., chimyl alcohol, selachyl alcohol, batyl alcohol, etc.); sugar alcohols (e.g., sorbitol, maltitol, maltotriose, mannitol, sucrose, erythritol, glucose, fructose, amylolytic sugar, maltose, xylitol, amylolytic sugar-reducing alcohol, etc.); グリソリッド, respectively; tetrahydrofurfuryl alcohol; POE-tetrahydrofurfuryl alcohol; POP-butyl ether; POP/POE-butyl ether; glyceryl tripropylene oxide ether; POP-glycerol ether; POP-glyceryl ether phosphoric acid; POP/POE-pentaerythritol ether, polyglycerol, etc.

Optional ingredients

The composition of the present disclosure may be appropriately blended with other components as needed, for example, a pigment other than titanium oxide, a dye, an ester, a humectant, a water-soluble polymer, an oil component, a higher alcohol, a binder, a dispersant, various salt components, a thickener, a surface tension reducer such as various surfactants, a skin film agent, an ultraviolet absorber, an ultraviolet scattering agent, a metal ion chelating agent, an amino acid, an organic amine, a polymer emulsion, a pH adjuster, a skin nutrient, a vitamin agent, an antioxidant aid, a perfume, a preservative, an anti-inflammatory agent, a whitening agent, an activator, an anti-seborrheic agent, various crude drug extracts, a medicament, and the like, within a range that does not impair the effects of the present disclosure. The pigment of the present disclosure can be used without a dispersant because of its excellent sedimentation resistance, but can be further improved in sedimentation resistance when a dispersant such as a polymer electrolyte is used.

Application

The surface-coated fired pigment containing titanium oxide as a main component of the present disclosure and the composition containing the pigment of the present disclosure can be suitably used in a wide range of applications such as cosmetics, paints, and inks.

Method for producing surface-coated calcined pigment containing titanium oxide as main component

The method for producing the surface-coated fired pigment mainly composed of titanium oxide of the present disclosure is not particularly limited. As for a method for producing the non-fired titanium oxide having no surface coating as shown in fig. 1, for example, patent document 1 discloses a method for producing the titanium oxide. Specifically, for example, a titanyl sulfate solution is used as a solution for forming titanium oxide, and the titanyl sulfate solution is subjected to alkali neutralization at a temperature of 10 ℃ or lower,hydrochloric acid is added to the obtained orthotitanic acid at a temperature of 10 ℃ or lower to completely dissolve the orthotitanic acid, and then hydrolysis is performed by heating, whereby unfired titanium oxide which is not surface-coated and has secondary structure particles in which needle-like primary structures are connected as shown in fig. 1 can be obtained. TiO in this case₂The concentration is 50g/L to 140g/L, preferably 60g/L to 120g/L, and the hydrochloric acid concentration is 70g/L to 170g/L, preferably 80g/L to 160 g/L. The hydrolysis temperature is 25 ℃ to 60 ℃, preferably 30 ℃ to 55 ℃.

The unfired titanium oxide which is not surface-coated as shown in fig. 1 may be obtained by hydrolyzing a titanium tetrachloride solution or an alkali salt of titanic acid obtained by treating metatitanic acid with an alkali, dissolved in hydrochloric acid, in addition to orthotitanic acid.

Further, unfired titanium oxide of secondary structure particles in which primary structures in the form of straw bundles, long strands, or the like are connected, which is not surface-coated, can be obtained by heating, firing, or the like as necessary, using the methods described in patent documents 3 and 4, for example, as appropriate.

The method of coating the surface of the unfired titanium oxide which is not surface-coated is not particularly limited, and for example, a slurry is prepared by adding the titanium oxide prepared as described above to ion-exchanged water. Then, the slurry is maintained at 70 ℃ and an inorganic material coating liquid comprising an aqueous solution of sodium silicate is slowly added while stirring, and after stirring for a predetermined time, an acid such as dilute hydrochloric acid or dilute sulfuric acid is added to adjust the pH to 5.0 to 8.0. By performing this operation 2 times or more, the layer composition or the coating amount of the surface coating layer can be adjusted. Further, the coating amount of the surface coating layer can be adjusted by adjusting the composition, concentration, blending amount, and the like of the inorganic material coating liquid.

The obtained slurry was filtered, washed with water, dried, and fired in a muffle furnace or a rotary kiln, which is a general firing furnace, to obtain a surface-coated fired pigment having titanium oxide as a main component in a shape as shown in fig. 3 and 4. Here, the firing temperature may be, for example, 500 ℃ to 800 ℃, more preferably 550 ℃ to 750 ℃, and the firing time may be 0.5 to 2.0 hours, more preferably 1.0 to 1.5 hours.

When the unfired titanium oxide which is not surface-coated is fired, the form generally changes from the form of fig. 1 to the form of fig. 2. However, when titanium oxide surface-coated with an inorganic material is fired, the particle shape of titanium oxide can substantially maintain the shape of fig. 1 as shown in fig. 3 and 4.

The properties of the pigment of the present disclosure, such as the retention of the surface protrusion shape, the sedimentation resistance, and the hiding property, can be controlled by appropriately adjusting the material of the surface coating layer, the firing temperature, and the firing time.

Examples

The present disclosure will be described in further detail below with reference to examples, but the present disclosure is not limited thereto. In the following, the blending amount is expressed in g/kg unless otherwise specified.

Examples 1 to 3 and comparative examples 1 to 5

The surface-coated fired pigment mainly composed of titanium dioxide obtained by the production method shown below was evaluated for area equivalent circle particle diameter, specific surface area, apparent bulk density, crystallite diameter, and hiding property. Further, with respect to the compositions obtained by the formulation and the manufacturing method of table 1 shown below, the viscosity and the sedimentation resistance were evaluated. In Table 1, SiO to be coated on unfired titanium dioxide which was not surface-coated₂The amount of (c) is expressed as "coating amount", and the case where the firing treatment is performed is expressed as "presence", and the case where the firing treatment is not performed is expressed as "absence".

Evaluation of pigment

The prepared pigment was subjected to various evaluations shown below, and the results are summarized in table 1.

(evaluation of area equivalent circle particle diameter)

The area equivalent circle particle diameter was evaluated as an average value of 10 titanium dioxide particles, enlarged to 100000 times using a transmission electron microscope type H7100 (manufactured by hitachi ハイテクノロジー).

(evaluation of specific surface area)

The specific surface area was evaluated by the BET method using Macsorb HMmodel-1208 (manufactured by Mountech).

(evaluation of apparent bulk Density)

About 10mL of pigment was added to a 20mL specific volume tube and weighed. The weighed test tube was tapped 200 times using a specific volume tester TAP-ONE TP01 (product of ヤマグチマイカ) to measure the volume, and the apparent bulk density was calculated. In addition, the apparent bulk density was evaluated by the following criteria.

A: apparent bulk density is less than or equal to 500kg/m³

B：500kg/m³The apparent bulk density is less than or equal to 600kg/m³

C：600kg/m³< apparent bulk Density

(evaluation of crystallite diameter)

The crystallite diameter of titanium dioxide was measured by an X-ray diffraction apparatus (Geigerflex, manufactured by ge motor corporation) and the average crystallite diameter was calculated by applying the scherrer equation.

(evaluation of concealment)

Titanium dioxide was mixed and stirred with nitrocellulose lacquer so that the proportion of pigment was 50g/kg, thereby preparing a slurry. Next, the slurry was applied to a black-and-white hiding ratio test paper described in JIS K5400 with a 0.101mm applicator and dried to obtain a test sample. The test samples were subjected to color measurement on the surfaces of the coating films on white and black papers using CM-2600d (manufactured by コニカミノルタ) as a spectrophotometer. The color difference (Δ E) in the Hunter Lab color space was calculated from the following equation 2, and the difference in color difference (hiding power difference) from each of the other pigments was calculated from the following equation 3 with reference to the color difference of titanium dioxide which was not subjected to surface coating and firing treatment, and the hiding performance was evaluated by the following criteria:

[ number 2]

Difference in hiding power (color difference of unfired titanium dioxide without surface coating and firing treatment) - (color difference of other pigments) … formula 3

The larger the difference in hiding power, particularly, if the difference in hiding power is 2.0 or more, the display hiding power is improved.

A: hiding power difference of 4.0 or less

B: the difference of hiding force is more than or equal to 2.0 and less than 4.0

C: the hiding power difference is less than 2.0

Evaluation of composition

The prepared compositions were subjected to various evaluations shown below, and the results are summarized in table 1.

(evaluation of viscosity)

The viscosity was evaluated by using MCR-302 (manufactured by Anton-Paar). Such a viscosity is a viscosity at a shear rate of 1000/s of the object to be measured at 32 ℃ under 1 atmosphere.

(evaluation of sedimentation resistance)

0.1g of a pigment was added to a 50mL colorimetric test tube, and then 30mL of ion-exchanged water was poured, followed by vigorous shaking to disperse titanium dioxide, thereby preparing a dispersion for evaluation. The ratio of the height of the sedimentation interface to the height of the water surface of the dispersion liquid was calculated as a percentage with respect to the sedimentation state of the pigment after a predetermined time had elapsed, and the results are summarized in table 1. The larger the value, particularly, the more 90.0% or more after 24 hours and 85.0% or more after 90 hours, the sedimentation resistance is excellent.

EXAMPLE 1

(Process for Forming unfired titanium dioxide without surface coating)

Washing metatitanic acid was dissolved in sulfuric acid, and the resulting titanyl sulfate solution was slowly dropped into 160g/L sodium carbonate solution so that the liquid temperature did not exceed 10 ℃, and when the pH became 10.0, dropping of titanyl sulfate was stopped. The obtained white precipitate was filtered by a conventional method and sufficiently washed to obtain orthotitanic acid.

Subsequently, the washed cake of orthotitanic acid was added to concentrated hydrochloric acid while cooling to 10 ℃ or lower, and stirred until the orthotitanic acid was completely dissolved. Then, with TiO₂The resulting mixture was adjusted so that the converted concentration became 60g/L and the hydrochloric acid concentration became 80g/L, and the mixture was heated while stirring to make the liquid temperature equal to 55 ℃ and stirred for 20 hours to hydrolyze the resulting mixture. The slurry thus obtained was neutralized, washed by a conventional method, and dried to obtain titanium dioxide a in the form of secondary structure particles in which needle-like primary structures are connected as shown in fig. 1.

(Process for Forming surface-coated fired pigment containing titanium dioxide as the Main component)

The obtained unfired titanium dioxide a, which was not surface-coated, was dispersed in ion-exchanged water to prepare a dispersion. Next, SiO was added to the dispersion containing titanium dioxide A while stirring₂The solution was stirred for 1 hour in terms of 50g/kg of sodium silicate aqueous solution, and then diluted hydrochloric acid was gradually added to adjust the pH to 5.0. Here, the amount of the sodium silicate solution is based on the mass of the titanium dioxide A before coating, and SiO₂The coating was used in an amount of 33 g/kg. The obtained dispersion was filtered, washed with water and dried by a conventional method to obtain surface-coated unfired titanium dioxide B.

Subsequently, the surface-coated unfired titanium dioxide B was fired in a muffle furnace at 550 ℃ for 1 hour to obtain surface-coated rutile-type fired titanium dioxide C. The particle shape of the obtained fired titanium dioxide C also exhibited a projected shape projected on the surface after firing, which was substantially the same as the shape of the unfired titanium dioxide a which was not surface-coated in fig. 1, as shown in fig. 3.

The calcined titanium dioxide C thus obtained was added to ion-exchanged water at the blending ratio shown in table 1 below, and the mixture was shaken vigorously to prepare a composition.

EXAMPLE 2

Mixing SiO₂A surface-coated calcined titania D was prepared in the same manner as in example 1, except that the amount of coating was changed from 33g/kg to 20g/kg, and the composition of example 2 was prepared in the same manner as in example 1 using the surface-coated calcined titania D.

EXAMPLE 3

Mixing SiO₂A surface-coated rutile-type calcined titania E was prepared in the same manner as in example 1, except that the amount of coating was changed from 33g/kg to 47g/kg, and the composition of example 3 was prepared in the same manner as in example 1 using this titania E.

Comparative example 1

Titanium dioxide a, which was not surface-coated or calcined, was prepared in the same manner as in the titanium dioxide formation step in example 1. Subsequently, the titanium dioxide a obtained was added to ion-exchanged water at the blending ratio shown in table 1 below, and shaken vigorously to prepare a composition of comparative example 1.

Comparative example 2

The titania a prepared in the same manner as in the step of forming titania not subjected to the surface treatment and the firing treatment in example 1 was fired at 550 ℃ for 1 hour in a muffle furnace to prepare fired titania F not subjected to the surface coating. Next, titanium dioxide F was added to ion-exchanged water at the blending ratio shown in table 1 below, and the mixture was vigorously shaken to prepare a composition of comparative example 2.

Comparative example 3

After surface coating was performed in the same manner as in the step of forming titanium dioxide without surface treatment and firing treatment and the step of forming surface-coated titanium dioxide in example 1, surface-treated titanium dioxide B without firing was prepared. Subsequently, the titanium dioxide B obtained was added to ion-exchanged water at the blending ratio shown in table 1 below, and shaken vigorously to prepare a composition of comparative example 3.

Comparative example 4

Pigment-grade rutile titanium dioxide TIPAQUE (trade name) CR-50 (manufactured by Shidai industries, Ltd.) having an amorphous particle shape was added to ion-exchanged water at a blending ratio shown in Table 1 below, and the mixture was vigorously shaken to prepare a composition of comparative example 4.

Comparative example 5

Rutile titanium dioxide TTO-55(A) (manufactured by Shidai corporation) having a needle-like particle shape was added to ion-exchanged water at a blending ratio shown in Table 1 below, and the mixture was vigorously shaken to prepare a composition of comparative example 5.

[ Table 1]

Results

As is clear from the results of examples 1 to 3 and comparative examples 1 to 3 in table 1, it was confirmed that the anti-settling property is improved if the surface of the titanium dioxide is coated with the inorganic material.

As is clear from the measurement results of examples 1 to 3 and comparative example 3, it is necessary to sinter titanium dioxide having a surface coated with an inorganic material in order to achieve a hiding power difference of 2.0 or more.

By coating titania with an inorganic material and further firing, titania having excellent resistance to sedimentation and having poor hiding power of 2.0 or more can be obtained.