Matting agent for aqueous coating material, aqueous coating material comprising same, and method for producing said matting agent

Abstract

A matting agent for an aqueous coating material according to the present invention comprises wet silica particles and wax that covers the surfaces of the wet silica particles, wherein the wax has a melting point in the range of 85-120 °C and a specific partial heat of fusion of 6% or less, and the matting agent has a BET specific surface area in the range of 50 to 250 m2 / g. The specific partial heat of fusion denotes the ratio of the heat of fusion calculated from the endothermic amount in the range of 40-60 °C with respect to the total heat of fusion calculated from the entire endothermic peak in the differential thermal analysis curve of the wax. The present invention further provides an aqueous coating material comprising said matting agent, and a matting agent production method that enables the production of said matting agent.

Description

Matting agent for water-based paint, water-based paint containing the same, and method for producing the same

[0001] The present invention relates to a matting agent for aqueous paints, an aqueous paint containing the same, and a method for producing the matting agent. CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority from Japanese Patent Application No. 2024-023621, filed February 20, 2024, the entire disclosure of which is incorporated herein by reference.

[0002] Wet silica particles are used as a matting agent in paints for metal coatings, wood coatings, plastic coatings, paper coatings, etc. Wet silica particles are a general term for amorphous silica particles synthesized in water, and precipitated silica particles and gel silica particles are well known as powders. Wet silica particles are usually controlled to micron size by additional processes such as grinding and classification before being incorporated into paints.

[0003] Matting agents having specific functions are also known, which are obtained by coating the surfaces of wet silica particles with a coating agent such as wax and a surfactant.

[0004] For example, as described in Patent Document 1, a matting agent obtained by coating silica particles with wax can improve the chemical resistance of a coating film made from a paint containing the matting agent.

[0005] In addition, Patent Document 2 describes a matting agent obtained by coating precipitated silica particles with a certain amount of polyethylene wax in order to improve the settling stability of the paint while maintaining the matting performance. Patent Document 3 describes a matting agent obtained by surface-treating precipitated silica particles with wax, the surface treatment being carried out while the particles are in contact with air in a temperature range above the melting temperature and below the decomposition temperature.

[0006] Patent Document 1: Japanese Patent Publication No. 2020-530868 Patent Document 2: Japanese Patent Publication No. 7-166091 Patent Document 3: Japanese Patent Publication No. 2002-97385 The entire disclosures of Patent Documents 1 to 3 are incorporated herein by reference.

[0007] Solvent-based paints contain volatile organic compounds (VOCs) as solvents. VOCs are released into the atmosphere when the paint dries to form a coating, and small amounts of VOCs remaining in the coating are also released into the atmosphere over time. Because VOCs are known to have harmful effects on the human respiratory system, certain regulations govern their use, which have become increasingly strict in recent years. In addition to their harmful effects on the human body, there is growing interest in environmental considerations in order to realize a sustainable society. Given this situation, the paint industry is seeing a shift from solvent-based paints to water-based paints or solvent-free paints that use low-viscosity resins that do not contain VOCs.

[0008] Generally, when a matting agent is added to a paint, it tends to settle due to its own weight, so the matting agent is required to be easy to redisperse by stirring the paint even after settling (high sedimentation stability). In recent years, with the growing demand for water-based paints mentioned above, the sedimentation stability of matting agents in water-based paints has become increasingly important.

[0009] Therefore, the present inventors conducted extensive research to impart excellent sedimentation stability to wax-containing matting agents for aqueous paints. During this research, the present inventors discovered that aqueous solvents used in aqueous paints have the effect of dissolving wax. The term "aqueous solvent" as used herein refers to a solvent used in aqueous paints, specifically one whose main component is water and optionally contains a water-soluble organic solvent (e.g., alcohol or glycol). When a wax-containing matting agent is incorporated into an aqueous paint, the wax may leach out of the matting agent into the paint, causing the wax to float to the paint film surface, resulting in deterioration of the paint film properties. Therefore, it is desirable for a wax-containing matting agent to not only have excellent sedimentation stability in aqueous paints, but also to suppress wax leaching into the solvent.

[0010] Furthermore, the present inventors have found that when a matting agent containing wax is stored as a powder, a portion of the wax repeatedly melts and solidifies due to changes in the temperature in the storage facility, causing the powder matting agent to solidify over time. If the matting agent solidifies, the workability of blending the matting agent into a paint may deteriorate, and the physical properties of the paint film may also deteriorate. Therefore, it is desirable that the matting agent containing wax has excellent storage stability as a powder.

[0011] However, the prior art patent documents 1 to 3 fail to provide solutions to the problems of sedimentation stability in aqueous paints, elution of wax, and storage stability as powder.

[0012] The matting agent of Patent Document 1 is characterized by coating the surface of silica particles with a large amount of wax (e.g., 50% by weight of the matting agent) and filling the pores of the silica particles with wax to improve the chemical resistance of the coating film. However, when the surface of the silica particles is coated with such a large amount of wax, the matting agent becomes less wettable with water-based paint, which reduces the workability when blending the matting agent into the water-based paint and also reduces the stability in the water-based paint. Furthermore, Patent Document 1 does not teach that wax elutes from the matting agent into the solvent, or that the matting agent stored as a powder coagulates due to re-solidification of the wax.

[0013] Patent Document 2 focuses on the sedimentation stability of matting agents in solvent-based paints, but does not focus on the sedimentation stability of matting agents in water-based paints. Furthermore, Patent Document 2 does not teach that wax dissolves from the matting agent into the solvent, or that a matting agent stored as a powder coagulates due to re-solidification of the wax.

[0014] Patent Document 3 also focuses on the sedimentation stability of matting agents in solvent-based paints, but does not focus on the sedimentation stability of matting agents in water-based paints. Furthermore, Patent Document 3 does not teach that matting agents stored as powders will coagulate due to re-solidification of wax.

[0015] Therefore, an object of the present invention is to provide a matting agent for aqueous paints containing wax, which has excellent sedimentation stability in aqueous paints, can suppress elution of wax into solvents, and has excellent storage stability as a powder.

[0016] In another aspect, the present invention provides a water-based paint containing the matting agent. In another aspect, the present invention provides a method for producing the matting agent, which enables the production of the matting agent.

[0017] The present inventors have conducted extensive research to achieve the above object and have found that a matting agent obtained by coating wet-process silica particles with a wax having specific thermal properties and having a specific BET specific surface area is effective.

[0018] [1] A matting agent for aqueous paints, comprising wet silica particles and a wax coating the surface of the wet silica particles, wherein the wax has a melting point in the range of 85 to 120°C and a specific partial heat of fusion of 6% or less, the specific partial heat of fusion being calculated by the following formula, and the matting agent has a melting point of 50 to 250 m 2 / g. Specific partial heat of fusion % = [(heat of fusion between 40 and 60°C in a differential thermal analysis curve) ÷ (heat of fusion calculated from all endothermic peaks in a differential thermal analysis curve (total heat of fusion))] × 100 [2] The matting agent according to [1], wherein the specific partial heat of fusion is 5% or less. [3] The matting agent according to [1] or [2], wherein the melting point of the wax is 90°C or higher. [4] The matting agent according to any one of [1] to [3], wherein the wax content in the matting agent is 2 to 25 parts by mass per 100 parts by mass of wet silica particles. [5] The matting agent according to any one of [1] to [4], wherein the wax elution rate is 40% or less, provided that a test is conducted in which 5 parts by mass of the matting agent is dispersed in 100 parts by mass of toluene and allowed to stand at 50°C for three days, and the wax elution rate is calculated by the following formula based on the amount of carbon in the matting agent before and after the test. Wax elution rate % = [(carbon amount before test - carbon amount after test) ÷ (carbon amount before test)] × 100 [6] The matting agent according to any one of [1] to [5], wherein the matting agent has a volume average particle diameter D50 in a particle size distribution range of 3.0 to 10.0 μm and a D90 / D50 in the particle size distribution of 2.0 or less. [7] The matting agent according to any one of [1] to [5], wherein the matting agent has a volume average particle diameter D50 in a particle size distribution range of 3.0 to 10.0 μm and a D90 / D50 in the particle size distribution of 2.0 or less. -2 ~4.5×10 -2 cm 3 / m 2[8] The matting agent according to any one of [1] to [7], wherein the ratio of the total mercury pore volume to the BET specific surface area (mercury pore volume / BET specific surface area) is in the range of 100 to 320 mmol / kg. [9] The matting agent according to any one of [1] to [8], wherein the matting agent has an oil absorption in the range of 150 to 350 mL / 100 g.

[10] The matting agent according to any one of [1] to [9], wherein the matting agent has a heat loss at 105°C of 9.0% or less and a bulk density in the range of 0.05 to 0.30 g / mL.

[11] The matting agent according to any one of [1] to

[10] , wherein the wet silica particles are precipitated silica particles.

[12] The specific partial heat of fusion is 5% or less, the melting point of the wax is 90°C or higher, the content of the wax in the matting agent is 2 to 25 parts by mass per 100 parts by mass of wet silica particles, and the wax elution rate is 40% or less; the wax elution rate is calculated by dispersing 5 parts by mass of the matting agent in 100 parts by mass of toluene and leaving it to stand at 50°C for three days, and using the following formula based on the carbon amounts in the matting agent before and after the test: Wax elution rate % = [(carbon amount before test - carbon amount after test) ÷ (carbon amount before test)] × 100, the matting agent has a volume average particle diameter D50 in a particle size distribution range of 3.0 to 10.0 μm and a D90 / D50 in a particle size distribution of 2.0 or less, and the matting agent has a volume average particle diameter D50 of 2.5×10 -2 ~4.5×10 -2 cm 3 / m 2

[13] The matting agent according to [1], wherein the matting agent has a ratio of the total mercury pore volume to the BET specific surface area (mercury pore volume / BET specific surface area) in the range of 100 to 320 mmol / kg, the matting agent has a DBA adsorption amount in the range of 100 to 320 mmol / kg, the matting agent has an oil absorption amount in the range of 150 to 350 mL / 100 g, the matting agent has a heat loss at 105°C of 9.0% or less and a bulk density in the range of 0.05 to 0.30 g / mL, and the wet silica particles are precipitated silica particles.

[13] An aqueous paint comprising the matting agent according to any one of [1] to

[12] .

[14] A method for producing a matting agent, comprising coating the surface of wet silica particles with wax to obtain a matting agent, wherein the wax has a melting point in the range of 85 to 120°C and a specific partial heat of fusion of 6% or less, the specific partial heat of fusion being calculated by the following formula: 2 / g. Specific partial heat of fusion % = [(heat of fusion between 40 and 60°C in a differential thermal analysis curve) ÷ (heat of fusion calculated from all endothermic peaks in a differential thermal analysis curve (total heat of fusion))] × 100

[15] The manufacturing method according to

[14] , wherein the specific partial heat of fusion is 5% or less.

[16] The manufacturing method according to

[14] or

[15] , wherein the melting point of the wax is 90°C or higher.

[17] The manufacturing method according to any one of

[14] to

[16] , wherein the coating is carried out using wax in an amount ranging from 2 to 25 parts by mass per 100 parts by mass of silica.

[18] The manufacturing method according to any one of

[14] to

[17] , further comprising, before the coating, producing wet silica particles using rice husk ash as a raw material.

[0019] According to the present invention, it is possible to provide a matting agent for aqueous paints that contains wax, which has excellent sedimentation stability in aqueous paints, can suppress elution of wax into solvents, and has excellent storage stability as a powder.

[0020] In another aspect, the present invention can provide an aqueous paint containing the matting agent. Also, in another aspect, the present invention can provide a method for producing the matting agent, which enables the production of the matting agent.

[0021] <Matting Agent> The matting agent for aqueous paint of the present invention is a matting agent containing wet silica particles and wax that coats the surfaces of the wet silica particles, wherein the wax has a melting point in the range of 85 to 120°C and a specific partial heat of fusion of 6% or less, and the matting agent has a viscosity of 50 to 250 m 2 / g. In this specification, the "specific partial heat of fusion" refers to the ratio of the heat of fusion calculated from the endotherm in the range of 40 to 60°C to the total heat of fusion calculated from the entire endotherm peak in the differential thermal analysis curve of the wax, and is specifically calculated using the following formula: Specific partial heat of fusion % = [(heat of fusion between 40 and 60°C in the differential thermal analysis curve) ÷ (heat of fusion calculated from the entire endotherm peak in the differential thermal analysis curve (total heat of fusion))] × 100. The matting agent of the present invention is obtained by coating wet silica particles with a wax having specific thermal properties so as to have a specific BET specific surface area. This allows for the wax on the surface of the wet silica particles to improve the chemical resistance of the matting agent and the coating film containing it, while also providing a matting agent with excellent sedimentation stability in aqueous paints, suppressing elution of the wax into solvents, and excellent storage stability as a powder.

[0022] <<Wax>> The matting agent of the present invention contains wax that coats the surface of wet-process silica particles. Matting agents containing wax on the surface exhibit excellent chemical resistance. Silica particles not coated with wax tend to aggregate while forming a close-packed structure when precipitated in water, resulting in poor sedimentation stability. However, by coating wet-process silica particles with wax, the interaction between particles is weakened, improving sedimentation stability. The degree of wax coating on the surface of wet-process silica particles can be adjusted based on the BET specific surface area, which will be described later.

[0023] The melting point of the wax contained in the matting agent of the present invention is 85 to 120°C. Having a wax melting point of 85°C or higher prevents the wax in the matting agent from unintentionally melting after coating the wet silica particles with the wax. For example, during the summer, the temperature inside a storage facility where the matting agent is kept may temporarily rise to high temperatures (approximately 50°C) due to the influence of outside air. As a result of the day-night cycle, a portion of the wax repeatedly melts and solidifies, potentially causing the powdered matting agent to solidify over time. In the matting agent of the present invention, having a wax melting point higher than 50°C prevents the wax from solidifying during storage in the storage facility. Furthermore, for example, methods for drying water-based paints include natural drying and heat drying, which involves heating the paint to a temperature of 50 to 80°C. Having a wax melting point higher than this drying temperature prevents the wax from leaching into the solvent during heat drying of the paint film. This prevents the wax from floating out onto the surface of the paint film during heat drying, deteriorating the paint film's appearance and further changing its physical properties.

[0024] When the wax has a melting point of 120°C or less, the wax can be uniformly melted throughout when coating the wet silica particles with the wax. This prevents some of the wax from being applied to the surface of the wet silica particles without melting, resulting in an uneven coating thickness. In addition, when the wax has a melting point of 120°C or less, excessive energy is prevented from being required when melting the wax.

[0025] From the viewpoint of further improving unintended melting of the wax after wax coating and uniform melting of the wax during wax coating, the melting point of the wax is preferably 90 to 117°C, more preferably 93 to 116°C, even more preferably 96 to 115°C, and particularly preferably 98 to 114°C.

[0026] The wax contained in the matting agent of the present invention has a specific partial heat of fusion of 6% or less. The method for measuring the heat of fusion will be described in detail in the Examples. A specific partial heat of fusion of 6% or less can suppress melting of the wax at 40 to 60°C. This suppresses wax blocking and makes handling easier. Furthermore, during storage of the matting agent, changes in the temperature in the storage cabinet can prevent repeated melting and solidification of parts of the wax, which can lead to the powdery matting agent solidifying over time. To further suppress melting of the wax at 40 to 60°C, the specific partial heat of fusion is preferably 5% or less, 3% or less, or 2% or less, more preferably 1% or less, even more preferably 0.6% or less, and particularly preferably 0.4% or less. The lower limit of the specific partial heat of fusion is not particularly limited and may be 0% or more, 0.01% or more, or 0.05% or more.

[0027] The type of wax is not particularly limited as long as it has a melting point in the range of 85 to 120°C and a specific partial heat of fusion of 6% or less. Waxes are broadly divided into two types: natural waxes extracted from animals, plants, or petroleum, and synthetic waxes artificially produced by organic synthesis. Either type of wax can be used. Natural waxes include plant-derived carnauba wax, petroleum-derived paraffin wax, and microcrystalline wax. Synthetic waxes include polyethylene wax, polypropylene wax, and Fischer-Tropsch wax. The thermal properties of wax vary depending on its chemical structure and molecular weight. Therefore, by appropriately selecting or adjusting the chemical structure and molecular weight of the wax, a wax having the melting point and specific partial heat of fusion specified in the present invention can be selected.

[0028] As a result of studies by the present inventors, high-melting-point Fischer-Tropsch wax (FT wax) is a preferred material because it has a low heat of fusion ratio at 40 to 60°C. FT wax is a methylene polymer of saturated linear alkanes and is characterized by a high content of linear carbon chain components. FT wax is considered suitable for the present invention because it has high crystallinity and a sharp DTA curve peak near the melting temperature. That is, the wax used in the present invention is preferably an FT wax having a melting point of 85 to 120°C or an FT wax having a melting point of 90 to 117°C, more preferably an FT wax having a melting point of 93 to 116°C, even more preferably an FT wax having a melting point of 96 to 115°C, and particularly preferably an FT wax having a melting point of 98 to 114°C. Commercially available high-melting point FT waxes that can be used in the present invention include SX105 (melting point: 102°C), FNP-0090 (melting point: 90°C), and FT115 (melting point: 113°C) manufactured by Nippon Seiro Co., Ltd., and Sasol Wax H1 (melting point: 112°C) and Sasol Wax C105 (melting point: 117°C) manufactured by Sasol Corporation.

[0029] The wax content of the matting agent of the present invention can be adjusted appropriately to further improve sedimentation stability, wettability, storage stability, matting performance, and chemical resistance. By adjusting the wax content and controlling the ratio of wet silica particles in the matting agent, more appropriate matting performance can be achieved. In particular, the wax content of the matting agent of the present invention is preferably 2 to 25 parts by mass per 100 parts by mass of wet silica particles. By having a wax content of 2 parts by mass or more per 100 parts by mass of wet silica particles, sedimentation stability, wettability, storage stability, matting performance, and chemical resistance are further improved. By having a wax content of 25 parts by mass or less per 100 parts by mass of wet silica particles, wax elution is further suppressed, thereby further preventing deterioration of coating film properties and further improving workability when blending the matting agent into a paint. The wax content is preferably 5 to 20 parts by mass or 8 to 15 parts by mass, more preferably 9 to 12 parts by mass per 100 parts by mass of wet silica particles.

[0030] In the matting agent of the present invention, it is preferable that the wax elution rate into the solvent is low. In the present invention, the wax elution rate is preferably 40% or less. The wax elution rate is the ratio of the carbon content reduced by the elution test to the carbon content in the matting agent before the elution test, and is an indicator of the ease with which the wax dissolves from the matting agent into the solvent. The method for measuring the wax elution rate is explained in detail in the Examples section. A wax elution rate of 40% or less can prevent the wax from eluting from the matting agent into the paint during storage, thereby preventing a decrease in paint quality and sedimentation stability. Maintaining the quality of the paint during storage ensures that the appearance of the coating film produced using the paint is appropriate. The wax elution rate is preferably 35% or less or 30% or less, more preferably 25% or less, and even more preferably 20% or less. The lower limit of the wax elution rate is not particularly limited, as the lower the better, but a practical lower limit is about 5%, and it may be 8% or more, or 10% or more. The wax elution rate can be controlled by appropriately selecting the type of wax.

[0031] <<Physical Properties of Matting Agent>> The matting agent of the present invention has a viscosity of 50 to 250 m 2 / g. The BET specific surface area of ​​the matting agent of the present invention means the BET specific surface area of ​​the wet silica particles after being coated with wax. 2 / g or more, the exposed surface of the wet silica particles can be adequately secured even when coated with wax. This ensures adequate interaction between the silanol groups on the wet silica particle surface and water and aqueous solvents, improving sedimentation stability and ensuring sufficient wettability with water and aqueous solvents. 2 / g or less, the surface of the wet silica particles can be adequately coated with wax, improving the chemical resistance of the matting agent and, ultimately, the chemical resistance of the coating film containing the matting agent. In addition, the wax adequately inhibits the interaction between particles, improving sedimentation stability. From the viewpoint of further improving sedimentation stability, wettability, and chemical resistance, the BET specific surface area is 80 to 200 m 2 / g, and 85 to 180 m 2 / g, and more preferably 90 to 160 m 2 / g, more preferably 95 to 140 m 2 The BET specific surface area of ​​the matting agent can be controlled by appropriately adjusting the BET specific surface area of ​​the wet silica particles before wax coating and the amount of wax used during coating.

[0032] The matting agent of the present invention preferably has a volume average particle diameter (median diameter) D50 in the particle size distribution in the range of 3.0 to 10.0 μm, and a D90 / D50 (ratio of D90 to D50) in the particle size distribution of 2.0 or less. D90 refers to the particle diameter at which the volume-integrated cumulative value from the bottom of the particle size distribution is 90%. The particle size distribution is measured by laser diffraction. Specific methods for measuring the particle size distribution are explained in detail in the Examples section. By having a D50 in the range of 3.0 to 10.0 μm and a D90 / D50 of 2.0 or less, the matting agent can exhibit superior matting performance.

[0033] Specifically, a D50 of 3.0 μm or greater can easily avoid the problem of wet silica particles in the matting agent becoming embedded in the coating film, resulting in a more excellent matting effect. A D50 of 10.0 μm or less can easily avoid the problem of the coating film becoming rough and impairing the design of the coating film, resulting in a more excellent matting effect. A D90 / D50 ratio of 2.0 or less reduces the amount of coarse powder in the matting agent, thereby suppressing the occurrence of so-called "lumpy" defects during application. D50 is preferably in the range of 3.2 to 9.0 μm, more preferably in the range of 3.5 to 8.0 μm. D90 / D50 is preferably 1.9 or less, more preferably 1.8 or less. The lower limit of D90 / D50 is not particularly limited, but it may be, for example, 1.4 or more, or 1.6 or more. The D50 and D90 / D50 of the matting agent can be controlled by appropriately adjusting the D50 and D90 / D50 of the wet silica particles before wax coating and the amount of wax used during coating.

[0034] The matting agent of the present invention is 2.5×10 -2 ~4.5×10 -2 cm 3 / m 2It is preferable that the ratio (PV / SA) of the mercury pore volume (PV) to the BET specific surface area (SA) is in the range of 4.5×10. The PV / SA ratio, which indicates the size of the pore volume relative to the specific surface area, is an index of the density of the structure of the matting agent. The smaller the PV / SA ratio, the denser the structure of the matting agent, and the larger the PV / SA ratio, the more gaps there are in the structure of the matting agent. -2 cm 3 / m 2 When the PV / SA ratio is 4.5×10 or less, the matting agent structure has a moderate strength that is not too soft, making it easy to adjust the particle size. Generally, the larger the BET specific surface area, the larger the mercury pore volume tends to be, and it is difficult to control the BET specific surface area and the mercury pore volume independently of each other. -2 cm 3 / m 2 The matting agent with a PV / SA ratio of 2.5×10 or less has the advantage of being easy to manufacture. -2 cm 3 / m 2 By setting the PV / SA ratio at or above 2.8×10, the structure of the matting agent is not too dense and has a moderate strength that is not too hard, making it easy to adjust the particle size. Furthermore, it is possible to suppress unnecessary energy consumption during particle size adjustment, suppress a decrease in oil absorption, and ensure sufficient matting performance. The PV / SA ratio is preferably 2.8×10 -2 ~4.2×10 -2 cm 3 / m 2 and more preferably 3.0 × 10 -2 ~4.0×10 -2 cm 3 / m 2 The PV / SA ratio of the matting agent can be controlled by appropriately adjusting the PV / SA ratio of the wet silica particles before wax coating and the amount of wax used during coating.

[0035] The matting agent of the present invention preferably has a DBA adsorption amount in the range of 100 to 320 mmol / kg. The DBA adsorption amount is an indicator of the number of silanol groups on the matting agent surface that are not covered by wax. When the DBA adsorption amount is 320 mmol / kg or less, the matting agent surface is sufficiently covered with wax, thereby improving sedimentation stability and chemical resistance. When the DBA adsorption amount is 100 mmol / kg or more, a moderate amount of the matting agent surface is not covered by wax, thereby improving wettability with water and aqueous solvents. Improved wettability of the matting agent helps to avoid the problem of wax floating in the coating film and deteriorating the appearance of the coating film. The DBA adsorption amount is preferably 150 to 300 mmol / kg, more preferably 170 to 290 mmol / kg, even more preferably 190 to 280 mmol / kg, and particularly preferably 200 to 270 mmol / kg. The DBA adsorption amount of the matting agent can be controlled by appropriately adjusting the DBA adsorption amount of the wet silica particles before wax coating and the amount of wax used during coating.

[0036] The matting agent of the present invention preferably has an oil absorption in the range of 150 to 350 ml / 100g. An oil absorption of 150 ml / 100g or more provides better matting performance. An oil absorption of 350 ml / 100g or less minimizes the effect on paint viscosity, allowing the matting agent to be used in a wide range of paints. The oil absorption is preferably in the range of 200 to 300 ml / 100g, more preferably 210 to 280 ml / 100g. The oil absorption of the matting agent can be controlled by appropriately adjusting the oil absorption of the wet silica particles before wax coating and the amount of wax used during coating.

[0037] The matting agent of the present invention preferably has a heat loss at 105°C of 9.0% or less. The smaller the heat loss, the greater the silica content effective for matting, which is preferable. The heat loss is preferably 7.0% or less, more preferably 5.0% or less. The lower limit of the heat loss is not particularly limited, but may be, for example, 1.0% or more, or 1.5% or more. The heat loss of the matting agent at 105°C can be controlled by appropriately adjusting the heat loss at 105°C of the wet silica particles before wax coating and the amount of wax used during coating.

[0038] The matting agent of the present invention preferably has a bulk density in the range of 0.05 to 0.30 g / ml. Having a bulk density in this range has the advantage of improving the handling properties of the matting agent and reducing the likelihood of forming a hard cake upon settling. The bulk density is preferably in the range of 0.08 to 0.25 g / ml, more preferably 0.10 to 0.20 g / ml. The bulk density of the matting agent can be controlled by appropriately adjusting the bulk density of the wet silica particles before wax coating and the amount of wax used during coating.

[0039] <<Wet Silica Particles>> The matting agent of the present invention contains wet silica particles. Wet silica particles are a general term for amorphous silica particles synthesized in water, and may be either precipitated silica particles or gel silica particles. From the viewpoint of obtaining better wettability and chemical resistance of the matting agent, the wet silica particles are preferably precipitated silica particles. Wet silica particles can be produced by a neutralization reaction between an aqueous alkali silicate solution (generally an aqueous sodium silicate solution) and an acid. Commercially available wet silica particles may be used. Examples of wet silica particles that can be used in the matting agent of the present invention include Nipsil and NIPGEL manufactured by Tosoh Silica Corporation.

[0040] When producing wet silica particles, rice husk ash generated from biomass boilers or biomass power generation can be used instead of silica sand as a sustainable raw material. Dissolving rice husk ash in an alkaline aqueous solution (e.g., thorium hydroxide aqueous solution) produces an alkaline silicate aqueous solution, which can be neutralized with an acid to produce wet silica particles.

[0041] The wet silica particles used in the production of the matting agent of the present invention before being coated with wax have a thickness of 80 to 350 μm. 2 / g. When the BET specific surface area of ​​the wet silica particles before wax coating is in the above range, it becomes easy to control the BET specific surface area of ​​the wet silica particles (matting agent) after wax coating to be in the above range. Since the BET specific surface area of ​​the wet silica particles decreases after wax coating, the wet silica particles are appropriately selected taking this decrease into consideration.

[0042] The wet-process silica particles used in the production of the matting agent of the present invention preferably have a volume average particle diameter D50 in the particle size distribution ranging from 3.0 to 15.0 μm and a D90 / D50 in the particle size distribution of 2.5 or less. Having the D50 and D90 / D50 of the wet-process silica particles before wax coating within the above ranges makes it easier to control the D50 and D90 / D50 of the wet-process silica particles (matting agent) after wax coating within the above ranges. Generally, the particle size distribution shifts to a larger diameter before and after wax coating, i.e., the D50 and D90 increase before and after wax coating. In contrast, the change in the D90 / D50 ratio is small, or the D90 / D50 ratio remains almost unchanged. The wet-process silica particles are appropriately selected taking into account such trends in particle size distribution.

[0043] <Method for producing a matting agent> The method for producing a matting agent of the present invention comprises coating the surface of wet silica particles with wax to obtain a matting agent, wherein the wax has a melting point in the range of 85 to 120°C and a specific partial heat of fusion of 6% or less, and the coating is applied to a matting agent having a BET specific surface area of ​​50 to 250 m 2 / g. As mentioned above, the specific partial heat of fusion is the ratio of the heat of fusion in the range of 40 to 60°C to the total heat of fusion in the differential thermal analysis curve of the wax. The matting agent of the present invention can be produced by the method for producing the matting agent of the present invention.

[0044] <<Wet Silica Particles and Wax>> In the method for producing a matting agent of the present invention, the surface of wet silica particles is coated with wax to obtain the matting agent. The wet silica particles are powdery. The form of the wax is not particularly limited and can be powdery, granular, or lumpy. For ease of handling, the wax is preferably powdery or granular, and more preferably powdery. The melting point of the wax is preferably 90 to 117°C, and the specific partial heat of fusion is preferably 5% or less. Other details regarding the wet silica particles and wax before wax coating as raw materials are the same as those regarding the matting agent of the present invention.

[0045] <<Wax Coating>> In the manufacturing method of the present invention, the method for coating the wax is not particularly limited. Common coating methods include a wet method and a dry method. In the wet method, for example, wax coating can be performed by mixing a wax emulsion with a silica slurry containing wet silica particles to prepare a mixed slurry, and then granulating and drying the mixed slurry using a spray dryer or the like. In the dry method, wax coating can be performed by heating and mixing powdery wax and wet silica particles using a mixing device such as a Henschel mixer or a jet mill using superheated steam, and thoroughly mixing the molten wax and wet silica particles. Since the wax used in the present invention is solid at room temperature, wet silica particles can be coated using a dry method. The device for wax coating in the dry method is not particularly limited as long as it can sufficiently heat the wax and uniformly mix the wax and silica. It is preferable to use a high-speed mixer capable of high-speed stirring to prevent particle aggregation.

[0046] The heating temperature during wax coating by the dry method is preferably 20°C or more higher than the melting point of the wax in order to melt the wax uniformly. The heating temperature is, for example, in the range of 110 to 200°C, preferably 120 to 170°C, and more preferably 125 to 150°C.

[0047] The amount of wax used in the wax coating is adjusted so that the wax content in the matting agent falls within the aforementioned range. The amount of wax used in the wax coating roughly corresponds to the wax content in the matting agent, and is preferably 5 to 25 parts by mass per 100 parts by mass of silica. Other details regarding the wax amount are the same as those regarding the wax content in the matting agent of the present invention.

[0048] The mixture obtained by mixing wet silica particles and wax by a dry method or a wet method may contain agglomerates of wet silica particles agglomerated through reconsolidated wax. In order to break down the agglomerates through the wax, it is preferable to carry out a crushing treatment of the mixture after obtaining the mixture using a crusher such as a jet mill. The conditions of the crushing treatment can be appropriately adjusted to obtain a desired particle size distribution.

[0049] In the production method of the present invention, it is preferable to carry out a classification treatment to remove coarse particles from the wax-coated wet silica particles. By removing the coarse particles, the occurrence of lumpy defects when a coating film is formed can be further suppressed.

[0050] <<Process for Producing Wet Silica Particles>> The production method of the present invention can further include producing wet silica particles using rice husk ash as a raw material before coating with wax. Rice husk ash contains a large amount of silica and can be used as a raw material for wet silica particles. For example, the production method of the present invention can include mixing rice husk ash, sodium hydroxide, and water to produce an aqueous alkali silicate solution containing an alkali metal component, and neutralizing the aqueous alkali silicate solution with an acid to obtain wet silica particles.

[0051] <Water-based Paint> The paint of the present invention is a water-based paint containing the matting agent of the present invention described above. The matting agent of the present invention can be suitably used in commercially available water-based paints. The water-based paint may be a water-based emulsion paint. The water-based paint contains a water-soluble resin (binder) or emulsion and water, and optionally contains additives such as a water-soluble organic solvent and a coloring pigment. The solids concentration of the paint is adjusted to 10 to 50%, and the viscosity is adjusted to several tens to several thousands of centipoise. The matting agent of the present invention is particularly suitable for water-based paints used to coat plastic products, wood products, metal products, concrete products, mortar products, and paper products.

[0052] When a matting agent is incorporated into an aqueous paint, for example, the matting agent is dispersed in water to prepare a matting agent dispersion with a concentration of about 10 to 20%, and this dispersion is then added to the paint raw materials to obtain an aqueous paint containing the matting agent. The matting agent of the present invention is particularly suitable for use in aqueous paints because it has excellent wettability, dispersibility, and sedimentation stability in water or aqueous solvents.

[0053] <Difference between Water-Based Paints and Solvent-Based Paints> As mentioned above, the addition of a matting agent to a water-based paint is often carried out by, for example, dispersing the matting agent in water to prepare a matting agent dispersion in advance and then adding this dispersion to the paint. If a matting agent that does not have sufficient wettability to water-based paints is added directly to the paint, the matting agent will aggregate and not disperse in the paint, which can result in so-called lumpy defects.

[0054] Wet silica particles have high surface polarity due to the presence of surface silanol groups, and are more likely to be wetted by highly polar water than by low-polarity organic solvents. Therefore, when wet silica particles not coated with wax are added to water to make a dispersion, the water acts as a lubricant, causing strong interactions between the silica particles, making the wet silica particles prone to agglomeration. Furthermore, when such agglomerates settle, the particles tend to form a close-packed structure, which can easily lead to the formation of a hard cake. Coating wet silica particles with wax is useful to prevent the formation of a hard cake in a dispersion.

[0055] Water-based paints are often applied on-site, in which case they are dried slowly at room temperature. When applied in a factory, water-based paints are dried at temperatures of 50-80°C for 10 minutes to 2 hours. When drying water-based paints, applying temperatures above 100°C can cause defects in the paint film due to the effects of evaporated water vapor, so water-based paints are generally dried at temperatures below 80°C.

[0056] The main method of adding matting agents to solvent-based paints is to add them directly to the solvent-based composition. Drying after applying solvent-based paints is usually carried out in factories with VOC recovery equipment, and drying is often carried out at 80 to 150°C for 5 to 30 minutes to improve productivity and to cause a thermal reaction.

[0057] As described above, the method of applying the matting agent and the method of handling the paint differ between water-based paints and solvent-based paints, and therefore the properties required of the matting agent differ between water-based paints and solvent-based paints.

[0058] EXAMPLES The present invention will be described in detail below with reference to examples and comparative examples. However, the examples are merely illustrative of the present invention and are not intended to limit the scope of the present invention.

[0059] The meanings of the wax numbers are as follows: Wax 1: Fischer-Tropsch (FT) wax, product name SX105, manufactured by Nippon Seiro Co., Ltd. Wax 2: FT wax, product name FNP-0090, manufactured by Nippon Seiro Co., Ltd. Wax 3: FT wax, product name FT115, manufactured by Nippon Seiro Co., Ltd. Wax 4: Polyethylene (PE) wax, product name Hi-WAX 110P, manufactured by Mitsui Chemicals, Inc. Wax 5: Microcrystalline (MC) wax, product name Hi-Mic-1080, manufactured by Nippon Seiro Co., Ltd. Wax 6 (reference): FT wax, product name FT-0070, manufactured by Nippon Seiro Co., Ltd.

[0060] The meaning of the gel silica numbers is as follows: Gel silica 1: Trade name NIPGEL AZ-200, manufactured by Tosoh Silica Corporation Gel silica 2: Trade name NIPGEL BY-200, manufactured by Tosoh Silica Corporation

[0061] Example 1: 93.5 kg of hot water was prepared in a 240-liter jacketed stainless steel vessel equipped with a stirrer and a circulation pump. A sodium silicate aqueous solution (No. 3 sodium silicate) with a SiO concentration of 10.0% by mass and a SiO / NaO molar ratio of 3.2 was added to the hot water until the pH reached 10.5. The solution temperature was then raised to 86°C. Next, 66.5 kg of the same sodium silicate aqueous solution, 1.3 kg of 98.0 mass% concentrated sulfuric acid, and 0.674 kg of 30.0 mass% aluminum sulfate aqueous solution were simultaneously added dropwise to the solution over 200 minutes to maintain a pH of 10.0-11.0. The same concentrated sulfuric acid was then added dropwise to the solution until the pH reached 3, completely quenching the reaction and yielding a reaction solution. The resulting reaction solution was filtered through a filter press and washed with water to obtain a silica cake. The obtained silica cake was slurried using a reciprocating rotary agitator (model: Ajiter AP04, manufactured by Shimazaki Engineering Co., Ltd.), and the slurry was spray-dried using a disk-type spray dryer (model: Spray Dryer AN-40R, manufactured by Ashizawa Niro Atomizer Co., Ltd.) to obtain a precipitated silica powder (Precipitated Silica 1).

[0062] Wax was applied to precipitated silica powder using an FM mixer (Mitsui Mining Co., Ltd.) according to the following procedure. 100 parts by weight of precipitated silica 1 and 10 parts by weight of wax 1 were placed in the FM mixer, which was set to 140 °C. The precipitated silica 1 and wax 1 were allowed to stand for 1 hour to fully warm up. The FM mixer was then operated at 1,600 rpm for 10 minutes. A jet mill (model: PJM-100NP, Nippon Pneumatic Mfg. Co., Ltd.) was then used to break down wax-mediated agglomerates. Finally, a pneumatic classifier (model: Cruseal N-5, Seishin Enterprise Co., Ltd.) was used to remove coarse particles from the broken material and refine the particle size, thereby obtaining a matting agent.

[0063] Example 2: 15 g of the matting agent of Example 1 was placed in a 90 x 205 mm kraft envelope, and the matting agent was stuffed into the bottom. The envelope was then folded in half and wrapped in a plastic bag. A 5 kg load was placed on the entire folded envelope, and the envelope was left to stand in a constant temperature chamber at 50°C for 5 weeks to obtain a heated and compressed matting agent.

[0064] Example 3 A matting agent was obtained in the same manner as in Example 1, except that the amount of wax was changed to 5 parts by mass per 100 parts by mass of silica powder.

[0065] Example 4 A matting agent was obtained in the same manner as in Example 1, except that the amount of wax was changed to 15 parts by mass per 100 parts by mass of silica powder.

[0066] Example 5 A matting agent was obtained in the same manner as in Example 1, except that the amount of wax per 100 parts by mass of silica powder was changed to 25 parts by mass.

[0067] Example 6 A matting agent was obtained in the same manner as in Example 1, except that the wax material was changed to Wax 2.

[0068] Example 7 A matting agent was obtained in the same manner as in Example 1, except that the wax material was changed to Wax 3.

[0069] Example 8: 80 kg of warm water was prepared in the same clean container as in Example 1, and the same sodium silicate aqueous solution as in Example 1 was added to the warm water until the pH reached 11. The temperature of the solution was then raised to 80°C. Next, 2.0 kg of the same concentrated sulfuric acid as in Example 1 was added dropwise to the solution over 25 minutes. The temperature of the solution was then raised to 90°C, and another 2.0 kg of the same concentrated sulfuric acid was added dropwise to the solution over 65 minutes. Subsequently, 11.2 kg of the same sodium silicate aqueous solution and 0.55 kg of the same concentrated sulfuric acid were simultaneously added dropwise to the solution over 15 minutes. The same concentrated sulfuric acid was then added dropwise to the solution until the pH reached 3, completely quenching the reaction and obtaining a reaction solution.

[0070] The resulting reaction solution was treated in the same manner as in Example 1 to produce a precipitated silica powder (precipitated silica 2), and a matting agent was produced from this precipitated silica powder and wax 1 in the same manner as in Example 1. This matting agent had a higher BET specific surface area and a larger particle size than those of Example 1.

[0071] Example 9 A matting agent was obtained in the same manner as in Example 1, except that commercially available Gel Silica 1 was used as the silica powder to which the wax was applied.

[0072] Comparative Example 1 A precipitated silica powder (precipitated silica 1) was prepared in the same manner as in Example 1, and without adding wax, it was pulverized and classified to adjust the particle size to obtain a matting agent.

[0073] Comparative Example 2 A matting agent was obtained in the same manner as in Example 1, except that the wax material was changed to Wax 4.

[0074] Comparative Example 3 A matting agent was obtained in the same manner as in Example 1, except that the wax material was changed to Wax 5.

[0075] Comparative Example 4: 15 g of the matting agent of Comparative Example 3 was placed in a 90 x 205 mm kraft envelope, and the matting agent was stuffed into the bottom. The envelope was then folded in half and wrapped in a plastic bag. A 5 kg load was placed on the entire folded envelope, and the envelope was left to stand in a constant temperature chamber at 50°C for 5 weeks to obtain a heated and compressed matting agent.

[0076] Comparative Example 5 A matting agent was obtained in the same manner as in Example 8, except that Wax 5 was used as the wax material.

[0077] Comparative Example 6 A matting agent was obtained in the same manner as in Example 9, except that the wax material was changed to Wax 4.

[0078] Comparative Example 7 A matting agent was obtained in the same manner as in Example 9, except that the wax material was changed to Wax 4 and the amount of wax per 100 parts by mass of silica powder was changed to 25 parts by mass.

[0079] Comparative Example 8: 15 g of the matting agent of Comparative Example 7 was placed in a 90 x 205 mm kraft envelope, and the matting agent was stuffed into the bottom. The envelope was then folded in half and wrapped in a plastic bag. A 5 kg load was placed on the entire folded envelope, and the envelope was left to stand in a constant temperature chamber at 50°C for 5 weeks to obtain a heated and compressed matting agent.

[0080] Comparative Example 9 A matting agent was obtained in the same manner as in Example 9, except that the wax material was changed to Wax 4 and the amount of wax per 100 parts by mass of silica powder was changed to 42 parts by mass.

[0081] Comparative Example 10 A matting agent was obtained in the same manner as in Example 1, except that commercially available Gel Silica 2 was used as the silica powder to which the wax was applied.

[0082] Comparative Example 11 A matting agent was obtained in the same manner as in Example 1, except that commercially available Gel Silica 2 was used as the silica powder to which the wax was applied and Wax 4 was used as the wax material.

[0083] The physical properties of the waxes used in the Examples and Comparative Examples, and the physical properties of the matting agents prepared in the Examples and Comparative Examples, were measured or obtained by the methods described below. Furthermore, the matting agent samples prepared in the Examples and Comparative Examples were evaluated for wettability to water and aqueous solvents, sedimentation stability in water, elution rate of the wax into solvents, compatibility with aqueous paints, and chemical resistance when coating films were prepared, by the methods described below.

[0084] <Wax Physical Properties> 1) Heat of Fusion: A TG-DTA measurement device (Model: DTG-60, Shimadzu Corporation) was used. 10 mg of wax was weighed into an aluminum cell with a diameter of 6 mm and a height of 5 mm. The cell was placed in the device without a lid. The DTA curve was then measured at a heating rate of 5°C / min and an air flow rate of 20 mL / min, after which the wax was heated to 250°C. α-alumina was used as the reference material, and indium was used as the standard for the heat of fusion. Using the accompanying software, the total heat of fusion calculated from the entire endothermic peak of the DTA curve and the heat of fusion obtained from the endothermic heat in the 40-60°C range were calculated. The specific partial heat of fusion was then calculated according to the formula: [heat of fusion in the 40-60°C range ÷ total heat of fusion] × 100.

[0085] 2) Melting point The melting point of the wax was taken from the catalogue values ​​provided by the wax manufacturer.

[0086] <Physical Properties of Matting Agent> 1) BET Specific Surface Area Measurement was carried out by the one-point method using a fully automatic specific surface area measuring device (Macsorb(R) HM model-1200, manufactured by Mountec Co., Ltd.).

[0087] 2) Particle size distribution (D50 and D90) The particle size distribution was measured using a laser diffraction particle size distribution analyzer (model: SYNC, manufactured by Microtrac Bell), and the 50% value of the volume integrated cumulative value (D50, volume average particle diameter) and the 90% value of the volume integrated cumulative value (D90) were calculated based on the particle size distribution.

[0088] 3) DBA Adsorption Amount: 250 mg of dried sample was accurately weighed, and 50 mL of N / 500 di-n-butylamine solution (petroleum benzine solvent) was added. The mixture was then allowed to stand at 20°C for approximately 2 hours. 25 mL of the supernatant was added with 5 mL of chloroform and 2-3 drops of indicator (crystal violet). The mixture was titrated with N / 100 perchloric acid solution (acetic anhydride solvent) until the purple color changed to blue. The titer value at this point was recorded as A mL. Separately, 25 mL of N / 500 di-n-butylamine solution (petroleum benzine solvent) was added with 5 mL of chloroform and 2-3 drops of indicator (crystal violet). The mixture was similarly titrated with N / 100 perchloric acid solution (acetic anhydride solvent). The titer value at this point was recorded as B mL. The DBA adsorption amount was calculated using the following formula: DBA adsorption amount (mmol / kg) = 80 × (B - A) × f, where f is the factor of the N / 100 perchloric acid solution. The factor is the actual solution concentration divided by the target concentration (N / 100).

[0089] 4) Pore volume measured by mercury intrusion method Using a mercury porosimeter "PASCAL440" manufactured by Thermo Corporation, the pore volume was measured when the pressure was increased from 0 MPa to 200 MPa.

[0090] 5) Oil absorption The oil absorption was measured according to JIS K5101-13-2:2004 "Test methods for pigments - Part 13: Oil absorption - Section 2: Boiled linseed oil method".

[0091] 6) Heat loss Heat loss was measured in accordance with JIS K5101-15-1:2004 "Test methods for pigments - Part 15: Heat loss - Section 1: 105°C volatile substances."

[0092] 7) Bulk density Bulk density was measured according to "7.8.2 Constant mass method" in JIS K6220-1:2015 "Rubber compounding agents - Organic chemicals - Test methods - Part 1: General".

[0093] <Evaluation: Wettability to Water and Aqueous Solvents> 1) Wettability to Pure Water (Stirring) A powder wettability tester (Model: WET101P, manufactured by Rhesca) was used. 100 mL of water was placed in a tall beaker, and 0.01 g of matting agent sample was added while stirring with a stirrer at 400 rpm. The change in laser light transmittance upon addition was measured. The time required for laser light transmittance to change from 100% to 75% was measured. Evaluation criteria: A: Less than 30 seconds B: 30 to less than 60 seconds C: 60 seconds or more

[0094] 2) Wettability to aqueous solvents (static method, visual observation) 50g of 5 mass% n-butyl carbitol aqueous solution was weighed into a 200mL disposable cup and allowed to stand. Then, 1g of matting agent sample was poured into the cup all at once and the time until the entire amount was absorbed into the solvent was measured. The measurement was carried out three times, and the average of the three was used as the result. Evaluation criteria A: Less than 10 minutes B: 10 to 30 minutes C: 30 minutes or more

[0095] <Evaluation: Sedimentation Stability in Water> 40 g of water and 1 g of matting agent sample were placed in a 100 mL disposable cup, and the solution was stirred at 1,000 rpm for 5 minutes using a high-speed mixer (model: Lavorution, manufactured by Primix Corporation). The solution was then transferred to a 50 mL measuring cylinder and allowed to stand for 24 hours, after which the presence of precipitate was confirmed. The solution was inverted upside down at a rate of once per second to redisperse the precipitate, and the number of inversions required to redisperse the precipitate was measured. A score of B or higher was deemed to be a level at which the objective of the present invention was achieved. Evaluation criteria: A: 1 time; B: 2 to 10 times; C: 11 or more times.

[0096] <Evaluation: Wax Leaching Rate> A portion of the matting agent sample was removed for leaching testing, and the leaching test was performed as described below. Toluene was used as the solvent for the leaching test, as it quickly produces clear differences. The relationship between wax leaching rates among matting agents (i.e., the relative tendency of wax leaching) was confirmed to be similar when using toluene in aqueous solvents used in water-based paints. 150 g of toluene and 7.5 g of sample were placed in a 300 mL disposable cup, and the solution was stirred at 1,000 rpm for 5 minutes using a high-speed mixer (model: Lavortion, manufactured by Primix Corporation). The top of the disposable cup was then covered with aluminum foil and allowed to stand for three days while heating in a 50°C water bath. After standing, the sample was transferred to a centrifuge tube and centrifuged in a centrifuge (model: Tabletop Centrifuge Model 2420, manufactured by Kubota Manufacturing Co., Ltd.) to produce a sediment, and the toluene was discarded. To the centrifuge tube containing the remaining sediment, the same volume of normal hexane as the discarded toluene was added, the tube was capped, and the tube was shaken to thoroughly disperse the sediment. After that, centrifugation was performed again to generate a sediment, and the normal hexane was discarded to obtain a sample washed with normal hexane.

[0097] After drying the washed samples at 80°C for at least 15 hours, the carbon content of each sample was measured. Separately, the carbon content of a sample that had not undergone the elution test was measured in the same manner. The carbon content was measured using a carbon analyzer (Model C744, manufactured by LECO). Calcium carbonate was used as the standard sample, and 2.5 g of tin-plated copper (combustion improver) was placed on top of a 0.02 g sample. The wax elution rate was calculated using the following formula based on the carbon content of the sample that underwent the elution test (carbon content after the elution test) and the carbon content of the sample that did not undergo the elution test (carbon content before the elution test). The wax elution rate represents the ratio of the carbon content reduced by the elution test to the carbon content before the elution test. A wax elution rate of 45% or less was considered to be the level at which the objective of this invention was achieved. Wax elution rate (%) = (carbon content before the test - carbon content after the test) ÷ (carbon content before the test) × 100

[0098] <Evaluation: Compatibility with Water-Based Paints> 20 g of purified water and 4 g of matting agent sample were placed in a 100 mL disposable cup and stirred at 1,000 rpm for 2 minutes using a high-speed mixer (model: Lavlution, manufactured by Primix Corporation) to prepare a slurry. 60 g of water-based emulsion paint (product name: Burnock WE-301, manufactured by DIC Corporation) was placed in a 200 mL disposable cup, and the previously prepared slurry was added to the paint. The slurry was then stirred at 1,000 rpm for 5 minutes using a high-speed mixer to prepare a matting agent-containing paint. The dispersion of the matting agent in the resulting paint was measured using a 50 μm gauge in accordance with JIS K5600-2-5:1999 "General Test Methods for Paints - Part 2: Paint Properties and Stability - Section 5: Dispersion." The paint prepared as described above was measured without dilution. In particular, the rate of change in the dispersibility of the heated and compacted matting agent (Example 2, Comparative Example 4, Comparative Example 8) compared with the dispersibility of the original matting agent (Example 1, Comparative Example 3, Comparative Example 7) is used as an index of storage stability. If this rate of change is 15% or less, it is judged that the objective of the present invention has been achieved.

[0099] <Evaluation: Paint Properties> The matting agent-containing paint was applied to a commercially available ABS plate (100mm x 200mm, black, manufactured by Coating Tester Co., Ltd.) using a No. 20 bar coater, and the paint film was dried at 80°C for 2 hours using a dryer (Model: Perfect Oven SPH-102, manufactured by Espec Corporation) to form a paint film on the ABS plate. 1) Paint Film Gloss The 60° gloss value of the paint film on the ABS plate was measured using a gloss meter (Model: VG 7000, manufactured by Nippon Denshoku Industries Co., Ltd.). The lower the gloss value, the better the matting performance.

[0100] 2) Chemical resistance of the coating ABS sheet with a coating was immersed in a 5 mass% aqueous solution of sodium carbonate for 24 hours. The color coordinates of the coating before and after immersion were measured in the L*a*b* color system using a spectrophotometer (Model: CM-5, manufactured by Konica Minolta) and the rate of change in L* (lightness) was calculated. The smaller the rate of change in L*, the higher the chemical resistance of the coating. Evaluation criteria A: Less than 1.0% B: 1.0% to less than 3.0% C: 3.0% or more

[0101] Table 1: Physical properties of waxes and other waxes used in Examples and Comparative Examples Tables 2-3: Physical properties of matting agents in Examples and Comparative Examples Tables 4-5: Evaluation results of matting agents in Examples and Comparative Examples

[0102]

[0103]

[0104]

[0105]

[0106]

[0107] <Explanation of Results> In the matting agents of Examples 1 to 9, the melting point of the wax was 85 to 120°C, the ratio of the heat of fusion at 40 to 60°C to the total heat of fusion of the wax was 6% or less, and the BET specific surface area of ​​the matting agent was 50 to 250 m 2 / g, the matting agents of Examples 1 to 9 had excellent sedimentation stability in aqueous paints, the wax was less likely to dissolve in the solvent, and the storage stability as a powder was excellent. In addition, the matting agents of Examples 1 to 9 exhibited excellent wettability with aqueous paints, and coating films made with paints containing these matting agents exhibited excellent 60°C gloss values ​​and chemical resistance. More details are as follows.

[0108] Differences in wax type: When wet silica particles are coated with wax having a specific partial heat of fusion of 6% or less (the ratio of the heat of fusion at 40-60°C to the total heat of fusion of the wax), sedimentation stability improves, the wax is less likely to dissolve in solvents, and the chemical resistance of the coating film improves (comparison between Examples 1, 6, and 7 and Comparative Example 2). In particular, when the specific partial heat of fusion is 6% or less and the wax melting point is 85°C or higher, the wax is less likely to dissolve, and the wax dissolution rate improves significantly (comparison between Example 1 and Comparative Example 3 or Example 8 and Comparative Example 5).

[0109] Difference in wax amount When the wax amount is in the range of 2 to 25 parts by mass, good wettability of the matting agent to the aqueous solvent is obtained (results of Examples 1, 3 to 5). The wettability tends to improve as the wax amount decreases (results of Examples 1, 3 to 5 and Comparative Example 9).

[0110] Difference between presence and absence of wax coating The matting agent having a wax coating exhibits excellent sedimentation stability and chemical resistance in aqueous paint (Comparison between Example 1 and Comparative Example 1).

[0111] Differences in BET specific surface area The BET specific surface area of ​​matting agents is 50 to 250 m 2 When the content is in the range of 1 / g, the wettability of the matting agent to aqueous solvents, the sedimentation stability, and the chemical resistance of the coating film are improved (comparison between Examples 1 to 9 and Comparative Example 10).

[0112] When heated and compacted (assuming storage) The heated and compacted state simulates the state in which the matting agent is stored as a dense powder in a storage facility prone to high temperatures. The small change in the degree of dispersion of the matting agent with and without heated and compacted means that the matting agent is less likely to coagulate in its powder state, and is an indicator of its high storage stability.

[0113] In the present invention, the melting point of the wax is 85 to 120°C and the heat of fusion of a specific portion of the wax is 6% or less. The change in the degree of dispersion of the matting agent with or without heat consolidation was about 5.3% (= (20 - 19) ÷ 19 × 100) based on the results of Examples 1 and 2. The 60° gloss value hardly changed, because the particle size distribution (D50 and D90) of the matting agent did not change and its quality as a matting agent was maintained.

[0114] In the comparative examples that did not satisfy the wax requirements, the change in the degree of dispersion of the matting agent with and without heat consolidation was approximately 26.3% (= (24 - 19) ÷ 19 × 100) based on the results of Comparative Examples 3 and 4, and approximately 38.1% (= (29 - 21) ÷ 21 × 100) based on the results of Comparative Examples 7 and 8. In these cases, the 60° gloss value decreased with heat consolidation. The decrease in 60° gloss value indicates a change in the quality of the matting agent. This change is presumably due to the fact that some of the wax in the matting agent melted and solidified due to heat consolidation, causing the matting agent to aggregate. This can also be seen from the change in the particle size distribution (D50 and D90) of the matting agent.

[0115] The above results demonstrate that the matting agent of the present invention has high storage stability.

[0116] As explained above, the matting agent of the present invention has excellent sedimentation stability in aqueous paints, the wax is less likely to dissolve in the solvent, and has excellent storage stability as a powder, making it useful as a matting agent for aqueous paints. Furthermore, the matting agent of the present invention has excellent wettability with aqueous solvents, making it possible to provide a coating film with improved chemical resistance.

Claims

1. A matting agent for water-based paints, comprising wet silica particles and a wax that coats the surface of the wet silica particles, wherein the wax has a melting point in the range of 85 to 120°C and a specific partial heat of fusion of 6% or less, the specific partial heat of fusion being calculated by the following formula, and the matting agent has a viscosity of 50 to 250 m 2 / g, Specific partial heat of fusion % = [(heat of fusion between 40 and 60°C in the differential thermal analysis curve) ÷ (heat of fusion calculated from the entire endothermic peak in the differential thermal analysis curve (total heat of fusion))] × 100 2. The matting agent according to claim 1, wherein the specific partial heat of fusion is 5% or less.

3. The matting agent according to claim 1 or 2, wherein the melting point of the wax is 90°C or higher.

4. The matting agent according to claim 1 or 2, wherein the content of the wax in the matting agent is 2 to 25 parts by mass per 100 parts by mass of the wet silica particles.

5. The matting agent according to claim 1 or 2, wherein the wax elution rate is 40% or less: The wax elution rate is calculated by dispersing 5 parts by mass of the matting agent in 100 parts by mass of toluene, leaving the mixture at 50°C for three days, and then calculating the wax elution rate using the following formula based on the carbon content in the matting agent before and after the test: Wax elution rate (%) = [(carbon content before test - carbon content after test) ÷ (carbon content before test)] x 100 6. The matting agent according to claim 1 or 2, wherein the matting agent has a volume average particle diameter D50 in the particle size distribution in the range of 3.0 to 10.0 μm and a D90 / D50 in the particle size distribution of 2.0 or less.

7. The matting agent is 2.5 x 10 -2 ~4.5×10 -2 cm 3 / m 2 3. The matting agent according to claim 1, wherein the ratio of the total mercury pore volume to the BET specific surface area (mercury pore volume / BET specific surface area) is in the range of:

8. The matting agent according to claim 1 or 2, wherein the matting agent has a DBA adsorption amount in the range of 100 to 320 mmol / kg.

9. The matting agent according to claim 1 or 2, wherein the matting agent has an oil absorption in the range of 150 to 350 mL / 100 g.

10. The matting agent according to claim 1 or 2, wherein the matting agent has a heat loss at 105°C of 9.0% or less and a bulk density in the range of 0.05 to 0.30 g / mL.

11. The matting agent according to claim 1 or 2, wherein the wet silica particles are precipitated silica particles.

12. The specific partial heat of fusion is 5% or less, the melting point of the wax is 90°C or higher, the content of the wax in the matting agent is 2 to 25 parts by mass per 100 parts by mass of wet silica particles, and the wax elution rate is 40% or less; the wax elution rate is calculated by dispersing 5 parts by mass of the matting agent in 100 parts by mass of toluene and allowing the mixture to stand at 50°C for three days, and then calculating the wax elution rate based on the carbon amounts in the matting agent before and after the test using the following formula: Wax elution rate % = [(carbon amount before test - carbon amount after test) ÷ (carbon amount before test)] × 100, the matting agent has a volume average particle diameter D50 in a particle size distribution range of 3.0 to 10.0 μm and a D90 / D50 in a particle size distribution of 2.0 or less, and the matting agent has a volume average particle diameter D50 of 2.5×10 -2 ~4.5×10 -2 cm 3 / m 2 2. The matting agent according to claim 1, wherein the matting agent has a ratio of the total mercury pore volume to the BET specific surface area (mercury pore volume / BET specific surface area) in the range of 100 to 320 mmol / kg, wherein the matting agent has a DBA adsorption amount in the range of 100 to 320 mmol / kg, wherein the matting agent has an oil absorption amount in the range of 150 to 350 mL / 100 g, wherein the matting agent has a heat loss at 105°C of 9.0% or less and a bulk density in the range of 0.05 to 0.30 g / mL, and wherein the wet silica particles are precipitated silica particles.

13. A water-based paint containing the matting agent according to claim 1 or 2.

14. A method for producing a matting agent, comprising coating the surface of wet-process silica particles with a wax to obtain a matting agent, wherein the wax has a melting point in the range of 85 to 120°C and a specific partial heat of fusion of 6% or less, the specific partial heat of fusion being calculated by the following formula: 2 / g. Specific partial heat of fusion % = [(heat of fusion between 40 and 60°C in the differential thermal analysis curve) ÷ (heat of fusion calculated from the entire endothermic peak in the differential thermal analysis curve (total heat of fusion))] × 100 15. The method of claim 14, wherein the specific partial heat of fusion is 5% or less.

16. The method of claim 14 or 15, wherein the melting point of the wax is 90°C or higher.

17. The method of claim 14 or 15, wherein the coating is carried out using wax in an amount ranging from 2 to 25 parts by weight per 100 parts by weight of silica.

18. The method of claim 14 or 15, further comprising producing the wet-process silica particles using rice husk ash as a raw material before the coating.

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