Matting agent for aqueous coating, aqueous coating containing the same ad method for producing matting agent

Abstract

To provide a matting agent that is an aqueous matting agent containing wax, excellent in sedimentation stability in the aqueous coating, can suppress elution of wax into a solvent, and excellent in storage stability as powder, an aqueous solution containing the matting agent, and a producing method of the matting agent enabling to produce the matting agent.SOLUTION: The matting agent of the present invention is an aqueous matting agent for paint that contains wet silica particles and a wax that coats the surface of the wet silica particles. The wax has a melting point in the range of 85 to 120°C and a specific partial melting heat of 6% or less. Additionally, the matting agent has a BET specific surface area in the range of 50 to 250 m2 / g. The specific partial melting heat refers to the fraction of the melting heat calculated from the endothermic amount in the range of 40 to 60°C in relation to the total melting heat calculated from the endothermic peaks in the differential thermal analysis curve of the wax.SELECTED DRAWING: None

Description

[Technical Field]

[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. [Background technology]

[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 sedimentation stability of a paint while maintaining 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. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Special Publication No. 2020-530868 [Patent Document 2] Japanese Patent Application Publication No. 7-166091 [Patent Document 3] Japanese Patent Application Laid-Open No. 2002-97385 Summary of the Invention [Problem to be solved by the invention]

[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 are in place regarding their use, and these regulations have become stricter in recent years. In addition to their harmful effects on the human body, there is also growing interest in environmental considerations from the perspective of realizing a sustainable society. In light of 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 must be easy to redisperse by stirring the paint even after settling (high sedimentation stability).With the increasing demand for water-based paints mentioned above, the sedimentation stability of matting agents in water-based paints has become increasingly important in recent years.

[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 (such as an alcohol or glycol). When a wax-containing matting agent is incorporated into an aqueous paint, the wax may dissolve from 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 dissolution of the wax 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 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 dissolves from the matting agent into the solvent, or that matting agents stored as powder coagulate 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. [Means for solving the problem]

[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 an aqueous paint, comprising wet silica particles and a wax that coats the surfaces of the wet silica particles, 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 is 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 [1], having a specific partial heat of fusion of 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 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 any one of [1] to [4], wherein the elution rate of the wax is 40% or less. However, the wax elution rate is calculated using the following formula based on the amount of carbon in the matting agent before and after the test, by dispersing 5 parts by mass of matting agent in 100 parts by mass of toluene and leaving it to stand at 50°C for three days. 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 the 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] Matting agent is 2.5 x 10 -2 ~4.5×10 -2 cm 3 / m 2 The matting agent according to any one of [1] to [6], having 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 [1] to [6]. [8] The matting agent according to any one of [1] to [7], which has a DBA adsorption amount in the range of 100 to 320 mmol / kg. [9] The matting agent according to any one of [1] to [8], which 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 relative to 100 parts by mass of the wet silica particles; 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 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 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 the particle size distribution of 2.0 or less; Matting agent is 2.5 x 10 -2 ~4.5×10 -2 cm 3 / m 2 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 The matting agent has a DBA adsorption amount in the range of 100 to 320 mmol / kg, The matting agent has an oil absorption 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; The matting agent according to [1], wherein the wet silica particles are precipitated silica particles.

[13] [1] An aqueous paint containing 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 the 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: The above coating is applied when the BET specific surface area of ​​the matting agent is 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

[15] The manufacturing method according to

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

[16] The method according to

[14] or

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

[17] The method according to any one of

[14] to

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

[18] The method for producing silica particles according to any one of

[14] to

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

[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. DETAILED DESCRIPTION OF THE INVENTION

[0021] <Matting agent> The matting agent for aqueous paint of the present invention is a matting agent containing wet silica particles and a 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 "particular partial heat of fusion" means the ratio of the heat of fusion calculated from the endothermic amount in the range of 40 to 60°C to the total heat of fusion calculated from the entire endothermic peak in the differential thermal analysis curve of the wax, and is specifically calculated by 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 endothermic peak in the differential thermal analysis curve (total heat of fusion))] × 100 The matting agent of the present invention is obtained by coating wet-process silica particles with 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-process silica particles to improve the chemical resistance of the matting agent and the coating film containing it, while also providing a matting agent that has excellent sedimentation stability in aqueous paints, can inhibit elution of the wax into solvents, and has excellent storage stability as a powder.

[0022] <<Wax>> The matting agent of the present invention contains a wax that coats the surface of wet-process silica particles. A matting agent containing wax on the surface exhibits 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 can prevent the wax in the matting agent from unintentionally melting after coating the wet silica particles with the wax. For example, in the summer, the temperature inside a storage facility where the matting agent is stored can 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 can prevent 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 can prevent the wax from leaching into the solvent during heat drying of the coating film. This prevents the wax from floating out onto the coating film surface during heat drying, deteriorating the coating film's appearance and further changing the coating film's 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 it easier to handle. Furthermore, during storage of the matting agent, repeated melting and solidification of a portion of the wax due to changes in temperature in the storage cabinet can be suppressed, preventing the powdery matting agent from coagulating over time. From the perspective of further suppressing 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, or may be 0.01% or more, or may be 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) has a low heat of fusion ratio at 40 to 60°C and is a preferred material. 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 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] <<Matting agent properties>> The matting agent of the present invention is 50 to 250 m 2 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, in turn, 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, and 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 cumulative value from the bottom in the particle size distribution is 90%. The particle size distribution is measured by laser diffraction. Specific methods for measuring the particle size distribution are described in detail in the Examples section. When D50 is in the range of 3.0 to 10.0 μm and D90 / D50 is 2.0 or less, the matting agent can exhibit superior matting performance.

[0033] Specifically, by having a D50 of 3.0 μm or more, it is possible to easily avoid the problem of wet silica particles in the matting agent becoming embedded in the coating film, thereby achieving a more excellent matting effect. By having a D50 of 10.0 μm or less, it is possible to easily avoid the problem of the coating film surface becoming rough and impairing the design of the coating film, thereby achieving a more excellent matting effect. By having a D90 / D50 ratio of 2.0 or less, the amount of coarse powder in the matting agent is reduced, thereby suppressing the occurrence of so-called lumpy defects during coating. 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 2 It 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 with 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 that is not covered with wax is present, thereby improving wettability with water and aqueous solvents. Improved wettability of the matting agent helps to avoid the problem of wax floating on the coating film and damaging 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 making it less likely to form 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 the neutralization reaction of an alkali silicate aqueous solution (generally a sodium silicate aqueous solution) with an acid. Commercially available wet silica particles may also 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 and 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 solution) produces an alkaline silicate aqueous solution, which can then be neutralized with 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 silica particles used in the production of the matting agent of the present invention before wax coating preferably have a volume average particle diameter D50 in the particle size distribution in the range of 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 silica particles before wax coating within the above ranges makes it easier to control the D50 and D90 / D50 of the wet 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 silica particles are appropriately selected taking into account such a tendency for change in particle size distribution.

[0043] <Method of manufacturing 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 m².2 / g. As described 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>> The method for producing the matting agent of the present invention involves coating the surface of wet-processed silica particles with wax to obtain the matting agent. The wet-processed 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-processed silica particles and wax before wax coating as raw materials are the same as those described for 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 wet and dry methods. 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] <<Wet silica particle manufacturing process>> The manufacturing method of the present invention can further include producing wet-process 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-process silica particles. For example, the manufacturing method of the present invention can include mixing rice husk ash, sodium hydroxide, and water to produce an alkali silicate aqueous solution containing an alkali metal component, and neutralizing the alkali silicate aqueous solution with an acid to obtain wet-process silica particles.

[0051] <Water-based paint> The paint of the present invention is an aqueous paint containing the above-mentioned matting agent of the present invention. The matting agent of the present invention can be suitably used in commercially available aqueous paints. The aqueous paint may be an aqueous emulsion paint. The aqueous paint contains a water-soluble resin (binder) or emulsion and water, and further contains additives such as a water-soluble organic solvent and a coloring pigment, as necessary. 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 aqueous paints used to paint plastic products, wood products, metal products, concrete products, mortar products, and paper products.

[0052] When a matting agent is blended into an aqueous paint, for example, the matting agent is dispersed in water to prepare a matting agent dispersion having a concentration of about 10 to 20%, and this dispersion is 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 paint and solvent-based paint> 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 the water-based paint 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 done at 80-150°C for 5-30 minutes to improve productivity and 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. [Example]

[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 meaning of the wax numbers is 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 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 number is as follows: Gel silica 1: Product name NIPGEL AZ-200, manufactured by Tosoh Silica Corporation Gel Silica 2: Product 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 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 solution, 1.3 kg of 98.0 mass% concentrated sulfuric acid, and 0.674 kg of 30.0 mass% aluminum sulfate solution were simultaneously added dropwise to the solution over 200 minutes, maintaining the pH at 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 resulting silica cake was slurried using a reciprocating rotary agitator (Model: Ajiter AP04, Shimazaki Engineering Co., Ltd.), and the slurry was spray-dried using a disk-type spray dryer (Model: Spray Dryer AN-40R, Ashizawa Niro Atomizer Co., Ltd.) to obtain precipitated silica powder (Precipitated Silica 1).

[0062] Using an FM mixer (manufactured by Mitsui Mining Co., Ltd.), wax was applied to precipitated silica powder 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 set to 140°C, and the precipitated silica 1 and wax 1 were left to stand for 1 hour to fully warm up. The FM mixer was then operated at 1,600 rpm for 10 minutes. Thereafter, a jet mill (model: PJM-100NP, manufactured by Nippon Pneumatic Mfg. Co., Ltd.) was used to break down the wax-mediated agglomerations. Finally, a pneumatic classifier (model: Cruseal N-5, manufactured by Seishin Enterprise Co., Ltd.) was used to remove coarse particles from the crushed material and adjust 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 × 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 was changed to 25 parts by mass per 100 parts by mass of silica powder.

[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 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 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, thereby obtaining 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 × 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 the wax material was changed to Wax 5.

[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 × 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 properties> 1) Heat of fusion A TG-DTA measurement system (model: DTG-60, manufactured by 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 then placed in the system 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 sample 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 range of 40 to 60°C were calculated. The specific partial heat of fusion was then calculated according to the formula: [heat of fusion in the range of 40 to 60°C ÷ total heat of fusion] × 100.

[0085] 2) Melting point The melting points of the waxes were taken from catalog values ​​provided by the wax manufacturers.

[0086] <Matte agent properties> 1) BET specific surface area Measurements were carried out using a fully automatic specific surface area measuring device (Macsorb(R) HM model-1200, manufactured by Mountec Co., Ltd.) by the one-point method.

[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 Microtrack Bell), and the 50% value of the volume cumulative value (D50, volume average particle diameter) and the 90% value of the volume cumulative value (D90) were calculated based on the particle size distribution.

[0088] 3) DBA adsorption amount 250 mg of dried sample was weighed out, and 50 mL of N / 500 di-n-butylamine solution (petroleum benzine solvent) was added to this, and the mixture was left to stand at 20°C for approximately 2 hours. 5 mL of chloroform and 2 to 3 drops of indicator (crystal violet) were added to 25 mL of this supernatant, and the mixture was titrated with N / 100 perchloric acid solution (acetic anhydride solvent) until the purple color changed to blue, and the titration value at this point was recorded as A mL. Separately, 5 mL of chloroform and 2 to 3 drops of indicator (crystal violet) were added to 25 mL of N / 500 di-n-butylamine solution (petroleum benzine solvent), and the solution was similarly titrated with N / 100 perchloric acid solution (acetic anhydride solvent). The titration value at this time was designated as B mL. The amount of DBA adsorbed 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 porosimetry Using a mercury porosimeter "PASCAL440" manufactured by Thermo, the pore volume was measured when the pressure was increased from 0 MPa to 200 MPa.

[0090] 5) Oil absorption amount 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) Heating loss The heat loss was measured according to JIS K5101-15-1:2004 "Test methods for pigments - Part 15: Heat loss - Section 1: Volatile substances at 105°C".

[0092] 7) Bulk density The 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 in pure water (stirrer stirring) A powder wettability tester (model number: WET101P, manufactured by Rhesca) was used. 100 mL of water was placed in a tall beaker, and 0.01 g of the matting agent sample was added while stirring at 400 rpm. The change in laser light transmittance upon addition was measured. The time required for the laser light transmittance to decrease from 100% to 75% was measured. Evaluation criteria A: Less than 30 seconds B: 30 seconds or more but less than 60 seconds C: 60 seconds or more

[0094] 2) Wettability to aqueous solvents (static method, visual observation) 50 g of a 5 mass% n-butyl carbitol aqueous solution was weighed into a 200 mL disposable cup and allowed to stand. 1 g of the matting agent sample was then added to the cup all at once, and the time it took for the entire amount to soak into the solvent was measured. The measurement was performed three times, and the average of the three measurements was used as the result. Evaluation criteria A: Less than 10 minutes B: 10 minutes or more but less than 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 precipitate was redispersed by inverting the container upside down at a rate of once per second, and the number of inversions required to redisperse the precipitate was measured. A grade of B or higher was deemed to be the level at which the objective of the present invention was achieved. Evaluation criteria A: Once B: More than 2 times and less than 10 times C: 11 times or more

[0096] <Evaluation: Wax elution rate> A portion of the matting agent sample was taken for the elution test, and the elution test was carried out as described below. Toluene was used as the solvent for the elution test, as it is easy to see clear differences in a short time. It has been confirmed that the relationship between the wax elution rate of matting agents (i.e., the relative tendency of wax elution) is the same when using toluene as when using the aqueous solvent 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: Lavorution, manufactured by Primix Corporation). The top of the disposable cup was then covered with aluminum foil, and the cup was left to stand for three days while being heated in a 50°C water bath. After standing, the sample was transferred to a centrifuge tube and centrifuged in a centrifuge (Tabletop Centrifuge Model 2420, manufactured by Kubota Manufacturing Co., Ltd.) to produce a precipitate, and the toluene was discarded. To the centrifuge tube containing the remaining precipitate, the same volume of normal hexane as the discarded toluene was added, the centrifuge tube was capped, and the tube was shaken to thoroughly disperse the precipitate. Then, the tube was centrifuged again to produce a precipitate, the normal hexane was discarded, and a sample washed with normal hexane was obtained.

[0097] After the cleaning, the sample was dried at 80°C for at least 15 hours, and then the carbon content of the sample was measured. Separately, the carbon content of a sample that had not undergone the above-mentioned 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 was placed on top of a 0.02 g sample to measure the carbon content. The wax elution rate was calculated according to the following formula based on the carbon amount in the sample that underwent the elution test (carbon amount after the elution test) and the carbon amount in the sample that did not undergo the elution test (carbon amount before the elution test). The wax elution rate indicates the ratio of the carbon amount reduced by the elution test to the carbon amount before the elution test. If the wax elution rate is 45% or less, it is determined that the objective of the present invention has been achieved. Wax elution rate % = (Carbon amount before test - Carbon amount after test) ÷ (Carbon amount before test) × 100

[0098] <Evaluation: Compatibility with water-based paints> 20g of pure water and 4g of matting agent sample were placed in a 100mL disposable cup, and the solution was stirred at 1,000 rpm for 2 minutes using a high-speed mixer (model: Lavortion, manufactured by Primix Corporation) to create a slurry. 60g of water-based emulsion paint (product name: Burnock WE-301, manufactured by DIC Corporation) was placed in a 200mL disposable cup, and the previously prepared slurry was poured into the paint. The slurry was then stirred at 1,000 rpm for 5 minutes using a high-speed mixer to create a paint containing the matting agent. The degree of dispersion of the matting agent in the resulting paint containing the matting agent was measured using a 50 μm gauge in accordance with JIS K5600-2-5:1999 "General Test Methods for Paints - Part 2: Properties and Stability of Paints - Section 5: Dispersion." The paints prepared as described above were measured without dilution. In particular, the rate of change in the dispersion of the heated and compacted matting agent (Example 2, Comparative Example 4, Comparative Example 8) compared with the dispersion of the original matting agent (Example 1, Comparative Example 3, Comparative Example 7) is used as an indicator of storage stability. A rate of change of 15% or less is considered to be within the scope of the present invention.

[0099] <Evaluation: Paint properties> The paint containing the matting agent was applied to a commercially available ABS plate (100 mm × 200 mm, 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 Co., Ltd.) to form a paint film on the ABS plate. 1) Gloss value of the coating The 60° gloss value of the coating 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 matte performance.

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

[0101] Table 1: Physical properties of waxes and other waxes used in the 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 of Examples and Comparative Examples

[0102] [Table 1]

[0103] [Table 2]

[0104] [Table 3]

[0105] [Table 4]

[0106] [Table 5]

[0107] <Explanation of results> In the matting agents of Examples 1 to 9, the melting point of the wax is 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 is 6% or less, and the BET specific surface area of ​​the matting agent is 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] 〇Differences in types of wax When wet silica particles are coated with a wax having a specific partial heat of fusion of 6% or less (the ratio of the heat of fusion at 40 to 60°C to the total heat of fusion of the wax), sedimentation stability is improved, the wax is less likely to dissolve in solvents, and the chemical resistance of the coating film is improved (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 melting point of the wax is 85°C or higher, the wax is less likely to dissolve, and the wax dissolution rate is significantly improved (comparison between Example 1 and Comparative Example 3 or Example 8 and Comparative Example 5).

[0109] 〇Difference in wax amount When the amount of wax 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 amount of wax decreases (results of Examples 1, 3 to 5 and Comparative Example 9).

[0110] Differences between wax coating and non-wax coating The matting agent with a wax coating exhibits excellent sedimentation stability and chemical resistance in water-based paints (Compare Example 1 and Comparative Example 1).

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

[0112] ○When heated and compressed (assuming storage) The heated compaction 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 or without heated compaction indicates that the matting agent is resistant to coagulation in its powder state and has 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 approximately 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, maintaining its quality as a matting agent.

[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 compaction was approximately 26.3% (=(24-19) / 19x100) based on the results of Comparative Examples 3 and 4, and approximately 38.1% (=(29-21) / 21x100) based on the results of Comparative Examples 7 and 8. In these cases, the 60° gloss value decreased with heat compaction. The decrease in 60° gloss value indicates a change in the quality of the matting agent. This change is presumably due to the matting agent agglomerating as a result of some of the wax in the matting agent melting and solidifying due to heat compaction. 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 an aqueous paint, comprising wet silica particles and a wax that coats the surfaces of the wet silica particles, 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: Matting agent is 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. 2. The matting agent according to claim 1, wherein the specific partial heat of fusion is 5% or less.

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

4. 3. The matting agent according to claim 1, 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. 3. The matting agent according to claim 1 or 2, wherein the wax dissolution rate is 40% or less. However, the wax elution rate is calculated using the following formula based on the amount of carbon in the matting agent before and after the test, by dispersing 5 parts by mass of matting agent in 100 parts by mass of toluene and leaving it to stand at 50°C for three days. Wax elution rate % = [(carbon amount before test - carbon amount after test) ÷ (carbon amount before test)] x 100

6. 3. The matting agent according to claim 1, 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 2.5×10 -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. 3. The matting agent according to claim 1, wherein the matting agent has a DBA adsorption amount in the range of 100 to 320 mmol / kg.

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

10. 3. The matting agent according to claim 1, 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. 3. The matting agent according to claim 1, 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 relative to 100 parts by mass of the wet silica particles; The wax elution rate is 40% or less; the wax elution rate is calculated by dispersing 5 parts by mass of a 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 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)] x 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 the particle size distribution of 2.0 or less; The matting agent is 2.5×10 -2 ~4.5×10 -2 cm 3 / m 2 and 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 the matting agent has a DBA adsorption amount in the range of 100 to 320 mmol / kg; the matting agent has an oil absorption 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; 2. The matting agent according to claim 1, wherein the wet-process silica particles are precipitated silica particles.

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

14. A method for producing a matting agent, comprising coating the surface of wet silica particles with wax to obtain the 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: The coating is preferably formed by mixing a matting agent having a BET specific surface area 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

15. The method of claim 14, wherein the specific partial heat of fusion is 5% or less.

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

17. The method according to 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 according to claim 14 or 15, further comprising producing the wet-process silica particles from rice husk ash before the coating.

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