Silica, paint, and method for producing silica

Abstract

This silica exhibits excellent matting properties when used as a paint matting agent, and can suppress the occurrence of cloudiness. The silica is characterized by having an aggregate structure obtained by aggregation of primary particles, and in that the particle ratio R indicated in formula (1) below is 4.3-5.2, the absorbance of 700nm light by a 1.48 mass% concentration aqueous dispersion is less than or equal to 0.6, and the particle density measured with a He pycnometer is greater than or equal to 2.18g / cm3. Formula (1) R = LD50 / CD50 (in formula (1), LD50 represents the volume-based cumulative 50% particle diameter (μm) of the silica, measured on the basis of laser diffraction scattering, and CD50 represents the volume-based cumulative 50% particle diameter (μm) of the silica, measured on the basis of the Coulter counter method.)

Description

Technical Field

[0001] The present invention relates to silica, paint, and a method for manufacturing silica.

Background Art

[0002] Silica produced by flame pyrolysis of chlorosilane is fine silica having a specific surface area of about 50 m 2 / g to 500 m 2 / g, and is generally called fumed silica. This fumed silica is mainly used as a filler and reinforcing agent for transparent resins, a thickening agent, and a fluidizing agent for powders, and has excellent dispersibility. For this reason, fumed silica is particularly well used as a filler for silicone rubber, a thickening agent for polyester resins, a fluidizing agent for toner, and the like.

[0003] However, when applying fumed silica as a matting agent for paint, this good dispersibility becomes a demerit. That is, fumed silica disperses to a size below the wavelength of visible light in the paint even if the dispersing power is weak. For this reason, generally, fumed silica cannot be used as it is as a matting agent for paint. Therefore, as a matting agent for paint, silica obtained by pulverizing and classifying wet silica (silica produced in a solvent such as water) having a large particle diameter is used. However, it is hard to say that sufficient matting performance is always obtained even when silica produced from wet silica is used as a matting agent.

[0004] On the other hand, a technique for using fumed silica, which cannot be used as a matting agent as it is, as a matting agent has been proposed. For example, Patent Document 1 proposes a technique of using silica in an aerogel-like structure obtained by blending 5 to 50% by weight of water with fumed silica and drying the resulting powdery mixture as a matting agent. In addition, techniques that employ an approach significantly different from the technique described in Patent Document 1 have also been proposed. For example, Patent Document 2 proposes a technique of using textured-coated silica obtained by spraying water and a thermoplastic elastomer onto fumed silica while mixing in a mixing container, then pulverizing, and subsequently drying this mixture as a matting agent.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] The inventor further examined the technique described in Patent Document 1 among the techniques described in Patent Documents 1 and 2, which have significantly different technical approaches. As a result, it was confirmed that even when the silica obtained by using the technique described in Patent Document 1 is used as a matting agent for paint, sufficient matting properties are not necessarily obtained.

[0007] The present invention has been made in view of the above circumstances, and an object thereof is to provide silica that exhibits high matting properties and can suppress the occurrence of cloudiness when used as a matting agent for paint, a paint using the silica, and a method for producing the silica.

Means for Solving the Problems

[0008] The above problems are achieved by the following present invention. That is, The silica of the present invention has an aggregated structure in which primary particles are aggregated, the particle size ratio R represented by the following formula (1) is 4.3 to 5.2, the absorbance of an aqueous dispersion with a concentration of 1.48% by mass with respect to light with a wavelength of 700 nm is 0.6 or less, and the particle density measured by a He pycnometer is 2.18 g / cm 3 or more. · Formula (1) R = L D50 / C D50 〔In the above formula (1), L D50 represents the volume-based cumulative 50% particle size (μm) of the silica measured based on the laser diffraction scattering method, C D50 represents the volume-based cumulative 50% particle size (μm) of the silica measured based on the Coulter counter method.〕

[0009] One embodiment of the silica of the present invention is that the volume-based cumulative 50% particle size L D50 is preferably 1.7 μm or more.

[0010] Another embodiment of the silica of the present invention preferably has a bulk density of 35 g / L or more.

[0011] Another embodiment of the silica of the present invention is preferably used as a matting agent for paints.

[0012] Another embodiment of the silica of the present invention is preferably such that the paint containing the silica of the present invention is any paint selected from the group consisting of a clear paint and a black paint.

[0013] The paint of the present invention contains at least a matting agent and a resin, and the matting agent has an aggregated structure in which primary particles are aggregated, the particle size ratio R represented by the following formula (1) is 4.3 to 5.2, the absorbance of an aqueous dispersion with a concentration of 1.48% by mass with respect to light with a wavelength of 700 nm is 0.6 or less, and the particle density measured by a He pycnometer is 2.18 g / cm 3 or more. · Formula (1) R = L D50 / C D50 〔In the above formula (1), L D50 represents the volume-based cumulative 50% particle size (μm) of the silica measured based on the laser diffraction scattering method, C D50 represents the volume-based cumulative 50% particle size (μm) of the silica measured based on the Coulter counter method.〕

[0014] One embodiment of the paint of the present invention is preferably any one selected from the group consisting of a clear paint and a black paint.

[0015] The method for producing silica of the present invention includes a basic aqueous solution addition step of adding a basic aqueous solution containing a basic substance at a concentration of 5 N or more in a range of 4 parts by mass to 13 parts by mass with respect to 100 parts by mass of fumed silica having an absorbance of 0.14 or less with respect to light with a wavelength of 700 nm in an aqueous dispersion having a concentration of 1.48% by mass and a bulk density of 40 g / L to 110 g / L, and a drying step of heating and drying the wet mixture to which the basic aqueous solution is added to the fumed silica at a temperature equal to or higher than the boiling point of the basic substance, and producing silica through at least these steps.

[0016] One embodiment of the method for producing silica of the present invention is preferably aqueous ammonia in which the basic aqueous solution has a concentration of 5 N or more.

[0017] Another embodiment of the method for producing silica of the present invention further includes a pulverization step of pulverizing the silica obtained through the drying step using a pulverization device selected from the group consisting of a jet mill and a pin mill. In the pulverization step, the volume-based cumulative 50% particle size C D50 of the silica measured based on the Coulter counter method after the pulverization treatment is preferably pulverized until it becomes 3.5 μm or less.

Advantages of the Invention

[0018] According to the present invention, it is possible to provide silica that exhibits high matting properties and can suppress the occurrence of cloudiness when used as a matting agent for paints, a paint using the silica, and a method for producing the silica.

Embodiments for Carrying Out the Invention

[0019] 1. Silica The silica of this embodiment has an aggregated structure in which primary particles are aggregated, <1> the particle size ratio R shown in the following formula (1) is 4.3 to 5.2, <2> the absorbance of an aqueous dispersion with a concentration of 1.48% by mass with respect to light with a wavelength of 700 nm (hereinafter, this absorbance may be referred to as τ700) is 0.6 or less, and <3> the particle density measured by a He pycnometer is 2.18 g / cm 3 or more. · Formula (1) R = L D50 / C D50 〔In formula (1), L D50 represents the volume-based cumulative 50% particle size (μm) of silica measured based on the laser diffraction scattering method, C D50 represents the volume-based cumulative 50% particle size (μm) of silica measured based on the Coulter counter method.〕

[0020] In the silica of this embodiment, when used as a matting agent for paints, by satisfying any of the conditions <1> to <3> shown above, it becomes easy to improve matting properties and / or suppress cloudiness. And when the conditions <1> to <3> are satisfied simultaneously, high matting properties can be exhibited and the occurrence of cloudiness can also be suppressed. Hereinafter, each of <1> the particle size ratio R, <2> τ700, and <3> the particle density will be described in detail.

[0021] <1> Particle size ratio R The particle size shown in formula (1) L In the laser diffraction scattering method used for measuring D50, scattering occurs at the outermost surface of each individual particle to be measured. For this reason, the particle size measured by the laser diffraction scattering method is a value extremely close to the particle size of the particles observed by, for example, SEM (scanning electron microscope) or the like. In contrast, the particle size shown in formula (1)C In the Coulter counter method used for measuring D50, the size of particles is measured based on the change in electrical resistance when the particles pass through the aperture. Therefore, when the particles to be measured have a porous structure, the voids in the particles are filled with the electrolyte used as the dispersion solvent for the measurement (for example, Isoton II, which will be described later, used for measuring the particle size C D50). At this time, since an electric current will flow through the voids, in the case of particles having a porous structure, compared with the particle size measured by the laser diffraction scattering method or SEM, the particle size C D50 will show a significantly smaller value. Therefore, it can be said that the particle size ratio R shown in formula (1) is an index for evaluating the degree of voids in the particles to be measured.

[0022] The silica of the present embodiment has a particle size ratio R shown in formula (1) of 4.3 to 5.2 as described above. Therefore, the primary particles are gently bonded and have a bulky aggregated structure (a porous structure with a high porosity). Therefore, since the silica of the present embodiment has a structure with large irregularities on the surface of each silica particle, light diffused reflection is likely to occur on the silica particle surface, and it becomes easy to improve the matting property of the paint. In addition, since the number of silica particles contained per unit weight also becomes larger, it is also easy to exhibit an excellent matting effect even when the addition amount of the silica of the present embodiment to the paint is small. Further, along with the improvement of the matting property, it also becomes easy to suppress the clouding of the coating film. Furthermore, when a clear paint or a black paint using the silica of the present embodiment is applied to a substrate with a dark coating surface (dark substrate), along with the exhibition of the matting effect, it also becomes easy to form a coating film having excellent jet blackness.

[0023] From the perspective of further enhancing the effect of improving the matting property, the lower limit value of the particle size ratio R is preferably 4.5 or more, more preferably 4.7 or more. On the other hand, the larger the particle size ratio R, the more bulky the aggregated structure of the silica particles will be. Therefore, if such an aggregated structure can be maintained as it is even in the paint, further improvement in the matting property is expected. However, when the particle size ratio R is too large, the bulky aggregated structure is likely to collapse due to the shear force applied to the silica particles during stirring and mixing during paint preparation. As a result, the matting property deteriorates and cloudiness is likely to occur. Therefore, the particle size ratio R needs to be 5.2 or less, preferably 5.0 or less.

[0024] For reference, it should be noted that in silica particles having an aggregated structure in which primary particles are aggregated, the oil absorption amount is generally used as an index for evaluating the porosity and bulkiness of the silica particles. However, the oil absorption amount may include not only the amount of oil absorbed in the voids formed within each silica particle but also the amount of oil present in the gaps between the silica particles. In addition, as described above, the voids formed within the silica particles are closely related to the matting property, but the gaps between the silica particles have no relation to the matting property. Therefore, the oil absorption amount does not exactly correspond to the size of the voids of each silica particle, and compared with the particle size ratio R, it is a parameter with a relatively lower correlation with the matting property.

[0025] <2>τ700 In addition, for the silica of the present embodiment, the absorbance (τ700) of an aqueous dispersion with a concentration of 1.48% by mass with respect to light with a wavelength of 700 nm is 0.6 or less. By setting τ700 to 0.6 or less, the dispersibility of silica particles in the paint is improved, and the effective area of the silica particle surface that diffusely reflects light can be made larger. Therefore, it becomes easier to improve the matting property, and along with the improvement of the matting property, it also becomes easier to suppress the cloudiness of the coating film. Furthermore, when a clear paint or a black paint using the silica of the present embodiment is applied to a substrate with a dark coating surface (dark substrate), along with the exhibition of the matting effect, it also becomes easier to form a coating film having excellent jet blackness. Also, when the silica of the present embodiment is used in a paint containing a solvent, by setting τ700 to 0.6 or less, it becomes easier to apply to the substrate, and it also becomes easier to obtain a paint that is not likely to drip after application. Note that τ700 is preferably 0.5 or less, and more preferably 0.4 or less. Also, the lower limit value of τ700 is not particularly limited, but in practical terms, the lower limit value of τ700 is preferably 0.25 or more, and more preferably 0.30 or more.

[0026] <3>Particle density In addition, for the silica of the present embodiment, the particle density measured with a He pycnometer is 2.18 g / cm 3 or more. This makes it easy to suppress the cloudiness of the coating film. Furthermore, along with the suppression of cloudiness, the glossiness of the coating film also decreases more or less, and as a result, it also becomes easier to improve the matting property. The reason why setting the particle density to 2.18 g / cm 3 or more makes it easy to suppress cloudiness and the like is as follows.

[0027] First, the refractive index of pure amorphous silica (theoretical refractive index) is 1.46. In contrast, the refractive index of urethane resin, which is widely used as a resin component in paints, is about 1.5. Also, the refractive indices of various resins for paints other than urethane resin are generally greater than 1.46. Here, when fine voids exist inside each primary particle constituting the aggregated structure of silica particles, the refractive index of the silica particles decreases in proportion to the presence of the voids. Therefore, when a coating film is formed with a paint using such silica particles, the refractive index difference between the resin and the silica particles constituting the paint becomes large, and the coating film becomes cloudy due to such a refractive index difference. Therefore, it is preferable that the refractive index of the silica particles is as close as possible to 1.46, which is the theoretical refractive index. For this purpose, it is better that the voids inside each primary particle constituting the aggregated structure of the silica particles are less. Here, the fact that there are few voids inside the primary particles means that the particle density of the primary particles is high. Therefore, in the silica of the present embodiment, the particle density is 2.18 g / cm 3 or more.

[0028] Incidentally, for reference, when measuring the particle density with a He pycnometer, as a measurement sample, a compressed product obtained by compressing silica particles under high pressure to break the aggregated structure is used. Therefore, the particle density measured by the He pycnometer substantially corresponds to the density of the primary particles constituting the silica particles.

[0029] The particle density is preferably 2.185 g / cm 3 or more, and more preferably 2.19 g / cm 3 or more. The upper limit value of the particle density is not particularly limited, but in practical use, it is preferably 2.21 g / cm 3 or less, which is close to the true density of amorphous silica, and may be 2.205 g / cm 3 or less.

[0030] In addition, in order for the silica of this embodiment to exhibit matting properties, it is necessary to have a size that does not transmit visible light at least minimally. Therefore, its average particle size only needs to be larger than the wavelength range of visible light (about 0.4 μm to 0.76 μm). Note that the matting property is exhibited by scattering the light incident from the outside by the portion of the silica particles that protrudes with respect to the coating film surface among the silica particles partially buried in the coating film surface. That is, only the portion slightly smaller than the portion corresponding to the actual particle size among the silica particles (the portion where the silica particles protrude with respect to the coating film surface) contributes to light scattering. Therefore, also considering this point, in order to more surely exhibit the matting property, the particle size of the silica of this embodiment is preferably somewhat larger than the wavelength range of visible light. Specifically, the particle size L is preferably 1.7 μm or more in terms of D50, more preferably 3.0 μm or more, and even more preferably 5.0 μm or more. The particle size L The upper limit value of D50 is not particularly limited, but in practical use, it is preferably 25.0 μm or less.

[0031] The pH of the silica of this embodiment is not particularly limited, but usually shows a pH in the vicinity of weakly acidic to weakly basic. When the silica of this embodiment is dispersed in water and measured, the pH value is in the range of about 5.5 to 9.5. Details of the pH measurement method will be described later.

[0032] The bulk density of the silica of this embodiment is not particularly limited, but its lower limit value is preferably 35 g / L or more, more preferably exceeding 36 g / L, and even more preferably 43 g / L or more. On the other hand, the upper limit value is not particularly limited, but in practical use, it is preferably 70 g / L or less, and more preferably 65 g / L or less. By setting the bulk density to 35 g / L or more, when dispersing the matting agent composed of the silica of this embodiment in the resin composition for paint, it is possible to prevent the silica from not being uniformly dispersed, or to easily shorten the time required for the silica to be uniformly dispersed.

[0033] 2. Paint The silica of the present embodiment can be used in various applications, but it is particularly suitable for use as a matting agent for paints. In this case, the paint of the present embodiment contains at least a matting agent (the silica of the present embodiment) and a resin. Further, the paint of the present embodiment may be a colored paint containing coloring materials such as pigments and dyes, a clear paint containing no coloring materials (colorless and transparent), or a slightly colored clear paint containing a small amount of coloring materials within a range that does not impair the transparency of the coating film. Furthermore, when the paint of the present embodiment is in a liquid state, the paint further contains a solvent such as water or an organic solvent. Also, the paint of the present embodiment may contain various additives other than the silica of the present embodiment used as a matting agent.

[0034] The paint of the present embodiment can be used in the form of solvent-based paints, ultraviolet (UV) curable paints, powder paints, etc. Specifically, it can be used in the form of water-based paints, oil-based paints, nitrocellulose paints, alkyd resin paints, amino alkyd paints, vinyl resin paints, acrylic resin paints, epoxy resin paints, polyester resin paints, chlorinated rubber-based paints, etc. Among these, the paint of the present embodiment is preferably a vinyl chloride paint or a urethane paint used as a paint for synthetic leather.

[0035] As the resin constituting the paint, any resin used in paints can be used without particular limitation. For example, one or more of rosin, ester gum, penta resin, coumarone-indene resin, phenolic resin, modified phenolic resin, maleic resin, alkyd resin, amino resin, vinyl resin, petroleum resin, epoxy resin, polyester resin, styrene resin, acrylic resin, silicone resin, rubber-based resin, chlorinated resin, urethane resin, polyamide resin, polyimide resin, fluorine-based resin, natural or synthetic lacquer, etc. can be mentioned.

[0036] In the case of ultraviolet curable paints, usually, high solid resins such as UV curable acrylic resins, epoxy resins, vinyl urethane resins, acrylic urethane resins, polyester resins, etc. are used alone or in combination of two or more. In powder paints, in addition to thermoplastic resins such as polyamide, polyester, acrylic resin, olefin resin, cellulose derivative, polyether, vinyl chloride resin, etc., epoxy resins, epoxy / novolak resins, isocyanates or epoxy-cured polyester resins, etc. are blended.

[0037] When the paint of this embodiment is a solvent-based paint, an organic solvent is used as the solvent. Examples of the organic solvent include aromatic hydrocarbon solvents such as toluene and xylene; aliphatic hydrocarbon solvents such as n-heptane, n-hexane, and Isopar; alicyclic hydrocarbon solvents such as cyclohexane; ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; alcohol solvents such as ethanol, propanol, butanol, and diacetone alcohol; ether solvents such as tetrahydrofuran and dioxane; cellosolve solvents such as ethyl cellosolve and butyl cellosolve; ester solvents such as ethyl acetate and butyl acetate; aprotic polar solvents such as dimethylformamide, dimethylacetamide, and dimethyl sulfoxide, etc.

[0038] When the silica of this embodiment is blended into the paint as a matting agent, the blending amount is appropriately set based on various physical properties required for the paint. Usually, 5 to 33 parts by mass, more preferably 10 to 30 parts by mass, is preferable with respect to 100 parts by mass of the solid content contained in the paint. By setting the blending amount to 5 parts by mass or more, it becomes easier to exhibit the matting property, and by setting it to 33 parts by mass or less, it becomes easy to ensure the strength of the paint film and suppress cloudiness.

[0039] The paint of this embodiment can be used as various types of paints as described above. In particular, it is preferably used as a clear paint or a black paint. When a paint film is formed by using the paint of this embodiment as a clear paint or a black paint on a coated surface of a dark-colored substrate (dark-colored substrate), a paint film with high jet blackness can also be obtained.

[0040] Note that as the dark-colored substrate, the material is not particularly limited as long as the coated surface is a dark-colored substrate such as black, navy blue, deep red, deep green, etc. For example, a substrate made of synthetic leather is suitable. Also, when using the paint of this embodiment as a clear paint, a small amount of a black pigment such as carbon black or aniline black can be added to the paint of this embodiment as long as the transparency of the paint film is not impaired. In this case, the jet blackness of the paint film can be further enhanced.

[0041] When the dark-colored substrate is made of synthetic leather, the paint of this embodiment used as a clear paint or a black paint is preferably a vinyl chloride paint or a urethane paint as described above. Generally, as urethane paints, aromatic urethane paints are relatively inexpensive and have high weather resistance, but in terms of appearance such as jet blackness, aliphatic urethane paints are usually used. However, if a urethane paint containing an aromatic urethane resin with silica added as a matting agent in this embodiment is used, it is easy to obtain a paint film with jet blackness comparable to that of a conventional urethane paint containing an aliphatic urethane resin with silica added as a matting agent.

[0042] 3. Method for manufacturing silica The silica of the present embodiment is not particularly limited as long as it is produced through a process of aggregating raw material particles. These raw material particles correspond to the particles that form the primary particles of the aggregated structure in the silica of the present embodiment. Here, fumed silica is usually used as the raw material particles. Fumed silica is produced by hydrolyzing a silica precursor such as a silane compound in a flame. Since fumed silica is treated at an extremely high temperature during its production, it is distinguished from wet silica that forms silica in an aqueous medium. Any fumed silica can be used, but it is preferable to use fumed silica that has not been surface-treated with a surface treatment agent such as a hydrophobizing agent.

[0043] However, from the perspective of easily obtaining the silica of the present embodiment, the manufacturing method of the silica of the present embodiment is such that the absorbance of a 1.48 mass% aqueous dispersion at a wavelength of 700 nm is 0.14 or less, and the bulk density is 40 g / L to 110 g / L. For 100 parts by mass of fumed silica, a basic aqueous solution containing a basic substance at a concentration of 5 N or more is added in the range of 4 parts by mass to 13 parts by mass in a basic aqueous solution addition step, and a wet mixture in which the basic aqueous solution is added to the fumed silica is heated and dried at a temperature equal to or higher than the boiling point of the basic substance in a drying step. It is particularly preferable that silica is produced through at least these steps. After passing through the drying step, usually, in order to obtain silica having a desired particle size and particle size distribution, it is preferable to appropriately perform a pulverization step and a classification step. The details of each step will be described below.

[0044] In the basic aqueous solution addition step, fumed silica having an absorbance (τ700) at a wavelength of 700 nm of a 1.48 mass% aqueous dispersion of 0.14 or less and a bulk density of 40 g / L to 110 g / L is used as the raw material particles. By using fumed silica that satisfies the above conditions, the silica of the present embodiment can be easily produced.

[0045] Note that the particle density of the fumed silica used as the raw material particles (measured value by a He pycnometer) is usually 2.20 g / cm3 ~2.21 g / cm 3 Thus, it is easy to control the particle density of silica (aggregates of primary particles) produced using fumed silica as raw material particles to 2.18 g / cm 3 or higher.

[0046] Also, by setting the bulk density of fumed silica to 40 g / L to 110 g / L, it becomes easier to control the particle size ratio R of the resulting silica within the range of 4.3 to 5.2. Note that the bulk density is preferably 50 g / L to 100 g / L. Also, by setting τ700 of fumed silica to 0.14 or less, it becomes easy to control τ700 of the resulting silica to 0.6 or less. Note that τ700 is preferably 0.13 or less, and the lower limit is not particularly limited, but is preferably 0.06 or more for practical use.

[0047] In general, for many commercially available fumed silicas, τ700 is 0.14 or less. Such silica has a small particle size and good dispersibility in an aqueous medium, so the value of τ700 is considerably smaller compared to the silica of the present embodiment.

[0048] Also, when using fumed silica with a bulk density of less than 40 g / L as raw material particles, when aggregating the raw material particles by adding a basic Water solution, it is necessary to use a large-volume processing apparatus. In addition to this, the bulk density of the produced silica also becomes low. And when using silica with a low bulk density as a matting agent, during dispersion in a resin composition for paint, the dispersion of silica into the resin composition is significantly inhibited while remaining floating on the resin composition, and it takes time to uniformly disperse into the resin composition, or in some cases, it may not disperse into the resin composition at all. Furthermore, by using fumed silica with a bulk density of less than 40 g / L as raw material particles, the cost of the manufacturing apparatus increases, and the filling weight when packing the produced silica decreases, making it easy for the transportation cost to increase.

[0049] Generally, fumed silica has an extremely low bulk density. When attempting to treat fumed silica with a low bulk density using a basic aqueous solution, a large amount of the basic aqueous solution is required. And when a large amount of the basic aqueous solution is added to the fumed silica, in the subsequent drying process, when the basic aqueous solution evaporates and dries, the silica produced is likely to undergo significant shrinkage, making it difficult to obtain silica having a bulky aggregated structure. Therefore, from such a perspective, it is also preferable to set the bulk density to 40 g / L or more. When the bulk density of the obtained fumed silica is less than 40 g / L, the fumed silica can be compressed using a degassing press or the like, and the one adjusted to be within the range of 40 g / L to 110 g / L in bulk density can be used in the basic aqueous solution Add in the process.

[0050] Also, the fumed silica used as the raw material particles usually preferably has a specific surface area of about 190 m 2 / g to 500 m 2 / g, and particularly preferably 220 m 2 / g to 400 m 2 / g. On the other hand, the specific surface area of the silica in this embodiment tends to be smaller than that of the fumed silica used as the raw material particles because dissolution occurs on the surface of the raw material particles due to the action of the added basic aqueous solution, and usually is 180 m 2 / g to 350 m 2 / g. Further, the fumed silica used as the raw material particles preferably has few coarse particles, and particularly preferably has a sieve residue of 0.01% by weight or less with a mesh opening of 45 μm according to the Moka sieving method.

[0051] In the basic aqueous solution addition step, with τ700 being 0.14 or less as described above, a basic aqueous solution containing a basic substance at a concentration of 5 N or more is added in the range of 4 parts by mass to 13 parts by mass with respect to 100 parts by mass of fumed silica having a bulk density of 40 g / L to 110 g / L. The preferable addition amount of the basic aqueous solution is 4.5 parts by mass to 8 parts by mass.

[0052] By setting the addition amount of the basic aqueous solution to 4 parts by mass or more, it becomes easier to uniformly treat the fumed silica used as the raw material particles, so that the silica of the present embodiment can be stably obtained. In addition, it also becomes easier to control the particle size ratio R to 4.3 or more. Further, by setting the addition amount of the basic aqueous solution to 13 parts by mass or less, in the drying step which is the next step, energy required for drying treatment can be saved and / or the drying time can be shortened. For this reason, it is possible to suppress strong aggregation of the raw material particles treated with the basic aqueous solution, and as a result, the silica of the present embodiment can be stably obtained. Also, the particle density of the silica of the present embodiment empirically tends to be slightly lower than the particle density of the fumed silica used as the raw material particles, and particularly, when a large amount of a high-concentration basic aqueous solution is used, the decrease in particle density tends to be remarkable. Therefore, from such a viewpoint as well, it is preferable to set the addition amount of the basic aqueous solution to 13 parts by mass or less. Although the details of the reason for the decrease in particle density are unclear, it is presumed that one of the reasons is that the surface of the fumed silica is dissolved by the action of the base, and the raw material particles with a slightly modified structure constitute the primary particles of the silica (aggregate).

[0053] In the raw material particles to which the basic aqueous solution is added, the surface thereof is dissolved by the action of the base, and a part of the surface where dissolution has occurred binds to other raw material particles to form aggregates. Since such aggregation is not very strong, silica having a bulky and loose aggregation structure can be obtained.

[0054] Note that when the basic aqueous solution is added to the raw material particles and the raw material particles are wetted with the basic aqueous solution, heat treatment may be carried out at a temperature lower than the boiling point of water.

[0055] In addition, as the basic aqueous solution, a solution containing a basic substance at a concentration of 5N or more is used. By setting the concentration to 5N or more, the above-described dissolution and aggregate formation are sufficiently promoted, and as a result, the silica of the present embodiment can be stably obtained. In addition to this, it becomes particularly easy to control τ700 to 0.6 or less. The concentration is preferably 7N or more, more preferably 10N or more. On the other hand, from a practical viewpoint, the upper limit of the concentration is preferably 20N or less.

[0056] As the basic substance, from the viewpoint of being easily removable from the surface of the aggregate of the raw material particles by heat treatment in the drying step which is the next step, ammonia or water-soluble amines such as methylamine, dimethylamine, ethylenediamine, tetramethylammonium, tetraethylammonium are preferable, and ammonia is particularly preferable. For example, if the basic aqueous solution is 10 mass% aqueous ammonia, the concentration of ammonia as the basic substance is about 5.6N. Considering ease of acquisition and preparation, etc., as the basic aqueous solution, aqueous ammonia having a concentration of 5N or more is preferable, and in terms of the concentration in terms of ammonia content (mass%), aqueous ammonia of 9.8 mass% or more is preferable, aqueous ammonia of 10 mass% or more is more preferable, and aqueous ammonia of 20 mass% or more is even more preferable.

[0057] When adding the basic aqueous solution, it is preferable to spray the basic aqueous solution in a state where the raw material particles in the container are stirred with a stirring blade or gas flow is caused, etc., so that the basic aqueous solution comes into contact with the raw material particles uniformly. At the time of spraying, addition with a one-fluid nozzle, a two-fluid nozzle or an ultrasonic spray is simple and preferable. At this time, it is more preferable to select the average particle diameter of the spray liquid to be 100 μm or less. Further, the basic aqueous solution may be intermittently supplied or continuously supplied into the reactor container containing the raw material particles.

[0058] Considering appropriately causing dissolution on the surface of raw material particles and aggregation between raw material particles, since the reaction temperature needs to be in the range where the basic aqueous solution remains in a liquid state, generally it is preferably about 15°C to 85°C. Also, if the reaction time is too short, dissolution etc. is difficult to occur, and if it is too long, aggregation tends to progress too much. Therefore, it is preferably carried out in the range of 0.4 hours to 3 hours. Here, the reaction time referred to is the time from the point when the basic aqueous solution is added to the raw material particles until the heating starts for carrying out the drying process, which is the next process. The pressure during the contact treatment between the basic aqueous solution and the raw material particles is not particularly limited and can be appropriately selected within the range from under negative pressure to under pressure. Also, the contact treatment may be carried out batchwise or continuously.

[0059] In the basic aqueous solution addition step, after finishing the contact treatment between the basic aqueous solution and the fumed silica used as the raw material particles, a drying step is carried out. In the drying step, the wet mixture with the basic aqueous solution added to the fumed silica is heated and dried at a temperature above the boiling point of the basic substance. However, when the boiling point of the basic substance contained in the basic aqueous solution used is lower than the boiling point of water, it is necessary to heat at a temperature above the boiling point of water in the drying step. For example, when the basic substance is ammonia (boiling point at atmospheric pressure is about -33°C) and the drying step is carried out at atmospheric pressure, the drying step is carried out by heating to a temperature above the boiling point of water (100°C at atmospheric pressure). By performing such heat treatment, the basic substance can be quickly and sufficiently removed from the surface of the aggregate of the raw material particles. Also, thereby, it is possible to suppress the progress of excessive aggregation in the drying step. Therefore, even when the basic aqueous solution addition step using a basic aqueous solution containing a basic substance with a concentration of 5N or more is carried out, the particle size ratio R of the silica obtained is 4.3 to 5.2, τ700 is 0.6 or less, and the particle density is 2.18 g / cm 3 It becomes easier to control within the above range. And as a result, it becomes easy to stably obtain the silica of the present embodiment.

[0060] When the boiling point of the basic substance contained in the basic aqueous solution to be used is lower than the boiling point of water, when the drying step is carried out under atmospheric pressure, the heating temperature may be 100 °C or higher, preferably 150 °C or higher. By setting the heating temperature to 100 °C or higher, the drying time can be reduced, and the removal of the basic substance can be sufficiently carried out. When the drying step is carried out under a pressure other than atmospheric pressure, the heating temperature may be equal to or higher than the boiling point of water under that pressure, preferably equal to or higher than the boiling point of water under that pressure + 50 °C. In addition, the upper limit value of the heating temperature during the drying treatment is not particularly limited, but considering the physical heat resistance of the heating device used for the drying treatment, it is preferably 300 °C or lower. Further, during the drying treatment, the temperature increase to the target heating temperature is preferably carried out at a temperature increase rate of 100 °C / hr or lower. Also, during the drying treatment, it is preferable to carry out the drying treatment in an inert gas atmosphere by supplying an inert gas such as nitrogen gas.

[0061] For the silica obtained through the drying step (an aggregate in which the primary particles corresponding to the raw material particles are aggregated), in order to adjust the particle size and particle size distribution, it is usually preferable to carry out a pulverization step. As the pulverization device, it is preferable to use a pulverization device in which compression of the powder to be pulverized, such as a jet mill or a pin mill, is unlikely to occur, and a jet mill is particularly preferable. Also, when pulverizing the silica after the drying treatment using such a pulverization device, the particle size C D50 and Particle size ratio There is a loose correlation with R, and as the particle size C D50 decreases, the particle size ratio R tends to increase.

[0062] In this case, generally, if the pulverization treatment is carried out until the particle size C D50 becomes 4.0 μm or less, it becomes easy to control the particle size ratio R to 4.3 or more. In order to more reliably control the particle size ratio R to 4.3 or more, the pulverization treatment is carried out based on the particle size at the end of the pulverization treatment CIt is more preferable to carry out the process until D50 becomes 3.5 μm or less, still more preferable until it becomes 2.6 μm or less, and particularly preferable until it becomes 1.8 μm or less. On the other hand, from a practical point of view such as avoiding a decrease in productivity due to a long pulverization treatment time, the pulverization treatment is carried out until the particle size C at the end of the pulverization treatment is preferably in the range where D50 is 0.8 μm or more, more preferably in the range where it is 1.1 μm or more, and still more preferably in the range where it is 1.2 μm or more. In view of the circumstances in the manufacturing process as described above, as a result, the particle size C of the silica in the present embodiment, D50 is preferably 1.1 μm to 3.5 μm, more preferably 1.2 μm to 2.6 μm, and still more preferably 1.2 μm to 1.8 μm.

[0063] Further, for the silica obtained through the drying process or the silica obtained through the pulverization process, a classification process may be carried out as necessary to remove coarse particles contained in the silica. Also, prior to the basic aqueous solution addition step, a stirring and mixing step of stirring and mixing raw material particles using a Henschel mixer or the like may be carried out.

Examples

[0064] Examples are given below to explain the present invention in detail, but the present invention is not limited to these examples. The measurement methods of various physical property values and characteristic values in the examples and comparative examples described later are as follows.

[0065] I. Evaluation of various physical property values The various physical properties of the fumed silica used as raw material particles in each example and comparative example, and the silica incorporated in the paint were measured as follows.

[0066] 1. Specific surface area The specific surface area was measured by the nitrogen adsorption BET one-point method using a specific surface area measuring device (SA-1000) manufactured by Shibata Rikagaku Co., Ltd.

[0067] 2. Absorbance (τ700) of the aqueous dispersion with a concentration of 1.48 mass% with respect to light with a wavelength of 700 nm The measurement of τ700 was carried out by the measurement method disclosed in r Journal of Ceramic Society e of Japan 101[6], 707 - 712 (1993). Specifically, a glass sample tube (manufactured by AS ONE Corporation, internal volume 30 ml, outer diameter approximately 28 mm) was filled with 0.3 g of the powder sample and 20 ml of distilled water. Next, the probe tip of an ultrasonic cell disruptor (Digital Sonifier Model 250 manufactured by BRANSON, probe: 1 / 4 inch microtip) was placed at a position 10 mm below the water surface of the mixture of 0.3 g of the powder sample filled in the sample tube and distilled water. In this state, by ultrasonic stirring under the conditions of an output of 39% (30 W) and a dispersion time of 180 seconds, an aqueous dispersion in which 0.3 g of the powder sample was finely dispersed in distilled water (powder sample concentration: 1.48 mass%) was obtained. Subsequently, the absorbance of the obtained aqueous dispersion with respect to light with a wavelength of 700 nm was measured using a spectrophotometer (V - 530 manufactured by JASCO Corporation). As the measurement cell used for the absorbance measurement, a quartz cell with a side made of ground glass and an optical path length of 10 mm was used.

[0068] 3. Bulk density (ρ) The measurement of the bulk density was carried out according to the following procedure. First, after placing a resin volumetric cylinder with a capacity of 1 L on an electronic balance and taring, approximately 1 L of the powder sample was filled into the resin volumetric cylinder and the weight M (g) was recorded. Then, with the tapping height (falling distance) set to 10 cm, the volume V (ml) after performing tapping by hand 30 times was measured, and the bulk density ρ was calculated based on the following formula (2). ルを (This seems to be an incorrect or incomplete Japanese term. It's hard to accurately translate without more context. Maybe it should be something like "the loop" or similar, but for now it remains as is.) · Formula (2) Bulk density ρ = 1000×M / V (g / L) · Formula (2) Bulk density ρ = 1000×M / V (g / L)

[0069] 4. Volume - based cumulative 50% diameter ( L D50) Particle size LD50 was measured using a laser diffraction / scattering particle size distribution analyzer (manufactured by Horiba, Ltd., LA950V2). The internal settings of LA950V2 were set to Circulation 5, Agitation 7, and UltraSonic 4. Also, during the measurement, 0.1 g of dried silica powder was directly put into the apparatus for measurement.

[0070] 5. Volume-based cumulative 50% particle size C D50 Particle size C The measurement of D50 was carried out according to the following procedure. First, an alcohol dispersion was prepared by dispersing a mixture of 50 g of methanol and 0.2 g of silica powder for 3 minutes using an ultrasonic cleaner (manufactured by Nippon Emerson Co., Ltd., B1510J-MT). Next, the particle size of the silica particles dispersed in the alcohol dispersion was measured using a particle size distribution analyzer (manufactured by Coulter, TA II type) with an aperture tube of 50 μm. Isoton II was used as the electrolyte for the particle size distribution analyzer.

[0071] 6. Particle density by He pycnometer The measurement of particle density was carried out according to the following procedure. First, a powder sample to be measured was filled into a cemented carbide press die (diameter 50 mm × height 75 mm), and then the powder sample to be measured was compression molded (uniaxial pressing) under a pressure of 15 tons using a press apparatus (manufactured by MASADASEISAKUSHO, MH-15TON press (ram diameter 55 mm)). After applying pressure for about 2 seconds, the compressed powder sample was taken out of the die. Next, the compressed silica was dried in a vacuum dryer at a temperature of 200 °C and a pressure of -0.095 PaG or less for 8 hours, and then allowed to cool to room temperature under reduced pressure in the vacuum dryer to obtain a measurement sample.

[0072] The obtained measurement sample was measured using a dry-type automatic densitometer (AccuPyc1330 type, manufactured by Shimadzu Corporation) with a 10 ml sample insert and He gas at a pressure of 0.16 Pa. The measurement temperature of the densitometer during density measurement was maintained at 25 °C by a constant temperature water circulation.

[0073] 7. pH The pH was measured according to the following procedure. First, 100 ml of degassed pure water was added to 5 g of the powder sample and stirred with a stirrer for 10 minutes to prepare a slurry for pH measurement. Next, the pH of this slurry was measured using a PH meter F-52 type manufactured by Horiba. Standard solutions of pH 4 and pH 9 were used for calibration of the pH meter.

[0074] 8. Dibutyl phthalate (DBP) oil absorption The DBP oil absorption of the silica powder was measured based on JIS K6217-4 using an oil absorption measuring device H5000 type manufactured by Asahi Riken Co., Ltd. Absorb

[0075] II. Evaluation of various physical property values and characteristic values of paints and coatings To evaluate various physical property values and characteristic values of paints and coatings, paints and coatings were prepared according to the following procedure.

[0076] <Preparation of paint> A mixture of 50 g of a resin composition for paint (Leatheroid LU-1500, manufactured by Dainichi Kasei Co., Ltd., aromatic urethane paint resin solid content 20%), 33.3 g of MEK (methyl ethyl ketone), 16.7 g of DMF (dimethylformamide), and 2.5 g of silica powder of each example and comparative example was dispersed using a homomixer at 8000 rpm (peripheral speed 11.7 m / S) for 6 minutes to prepare a paint (clear paint). ro

[0077] <Preparation of coating film> ​​The above paint was applied to a urethane synthetic leather with a black painted surface using a bar coater No. 14. Subsequently, after application, it was dried at 60 °C for 1 hour and then left at room temperature for 12 hours to obtain a urethane synthetic leather with a coating film formed on the painted surface. The L * value of the painted surface of the urethane synthetic leather used for forming the coating film was 25.0, and the gloss value (gloss value at an incident angle of 60 degrees) was 3.5%. The L * value and the gloss value of the painted surface of the urethane synthetic leather are values measured by the measurement method described below.

[0078] 9. Granularity gauge value The granularity gauge value was measured using a 100 μm granularity gauge for the paint based on JIS K 5600-2-5.

[0079] 10. Viscosity and TI The viscosity was measured for the paint left in a constant temperature water bath at 25 °C for 2 hours using a BL type rotational viscometer at 25 °C under the conditions of 60 rpm and 6 rpm. In Tables 3 and 4, the viscosity measured at 60 rpm is shown. Also, the value obtained by dividing the viscosity at 6 rpm by the viscosity at 60 rpm was determined as TI (thixotropy index).

[0080] 11. L * value L * The L value of the surface on which the coating film was formed of the urethane synthetic leather with the coating film formed was measured using a spectrophotometer (manufactured by Konica Minolta, CM-5 type). As the color system, L * a * b * (CIE1976) was used, and the L value was measured with SCI (value including regular reflected light) with a measurement diameter of 8 mm. This L * value is an index of blackness. *

[0081] 12. Gloss value The gloss value was measured on the surface of the urethane synthetic leather on which the coating was formed, in accordance with JIS Z 8741. A gloss meter (RHOPINT, IQ3 model) was used for the measurement, and the gloss (gloss value) was evaluated at an incidence angle of 60 degrees.

[0082] 13. Visual evaluation The surface of the urethane synthetic leather on which the coating film was formed was visually observed and evaluated. The evaluation criteria were as follows: A: Even better jet blackness than the B rating below. B: No white areas are found throughout the entire surface, and the surface has a sufficiently matte finish and jet black color. C: Partial clouding is observed. D: Overall opacity is observed.

[0083] Example 1 The raw material particles have a specific surface area of ​​300m 2 / g, τ700 is 0.084, bulk density is 75g / L, and particle density is 2.209g / cm 3 The raw material particles were placed in a 300L Henshion flask containing 5 kg of fumed silica. ェ (This seems to be an incorrect or incomplete Japanese term. It's hard to accurately translate without more context. Maybe it should be something like "work" or similar, but for now it remains as is.) The raw material particles were put into a tubular mixer, stirred and mixed, and the atmospheric gas in the mixer was replaced with nitrogen gas by introducing nitrogen gas into the mixer. Next, with the temperature in the mixer heated to 80°C, 250 ml of ammonia water with a concentration of 25% by mass was supplied into the mixer using a one-fluid nozzle at a flow rate of 500 ml / hr to obtain a wet mixture in which the raw material particles were wetted with ammonia water. The fumed silica used as the raw material particles in Example 1 was not surface-treated. This point was the same for the fumed silica used as the raw material particles in the other Examples and Comparative Examples.

[0084] Subsequently, while continuing to stir the wet mixture, nitrogen was supplied into the mixer at 40 L / hr, and the temperature was raised to 180°C at 100°C / hr. Then, by holding the inside of the mixer at 180°C for 1 hour, dried silica powder was obtained. Next, the dried silica powder was pulverized by a jet mill (manufactured by Seishin Enterprise Co., Ltd., model STJ315), and the particle size C was adjusted so that D50 became 1.4 μm, thereby obtaining the silica powder of Example 1. Regarding the jet mill used in the Examples and Comparative Examples described below, unless otherwise specified, the one manufactured by Seishin Enterprise Co., Ltd., model STJ315 was used.

[0085] (Example 2) In the pulverization step, the silica powder of Example 2 was obtained by carrying out the same process as in Example 1, except that it was pulverized by a jet mill so that the particle size C D50 became 2.6 μm.

[0086] (Example 3) Using fumed silica with a specific surface area of 300 m 2 / g, τ700 of 0.084, a bulk density of 61 g / L, and a particle density of 2.209 g / cm 3 , the silica powder of Example 3 was obtained by carrying out the same process as in Example 1, except that 340 ml of 18 mass% aqueous ammonia was added to the raw material particles as the basic aqueous solution.

[0087] (Example 4) Using fumed silica with a specific surface area of 250 m 2 / g, τ700 of 0.114, a bulk density of 85 g / L, and a particle density of 2.205 g / cm 3 , the silica powder of Example 4 was obtained by carrying out the same process as in Example 1, except that 223 ml of 25 mass% aqueous ammonia was added to the raw material particles as the basic aqueous solution.

[0088] (Example 5) The concentration of aqueous ammonia used as the basic aqueous solution added to the raw material particles was 9.8% by mass, and the addition amount of aqueous ammonia to the raw material particles was 600 ml. The basic aqueous solution addition step and the drying step were carried out in the same manner as in Example 1 except for this. Then, the silica after the drying treatment was C pulverized by a jet mill so that the D50 of the particle size became 1.3 μm, and the silica powder of Example 5 was obtained.

[0089] (Example 6) As the raw material particles, the specific surface area was 300 m 2 / g, τ700 was 0.084, the bulk density was 100 g / L, and the particle density was 2.209 g / cm 3 The basic aqueous solution addition step and the drying step were carried out in the same manner as in Example 1 except that fumed silica was used. Then, the silica after the drying treatment was C pulverized by a jet mill so that the D50 of the particle size became 1.1 μm, and the silica powder of Example 6 was obtained.

[0090] (Example 7) As the raw material particles, the specific surface area was 380 m 2 / g, τ700 was 0.067, the bulk density was 55 g / L, and the particle density was 2.210 g / cm 3 The basic aqueous solution addition step and the drying step were carried out in the same manner as in Example 1 except that fumed silica was used. Then, the silica after the drying treatment was C pulverized by a jet mill so that the D50 of the particle size became 1.2 μm, and the silica powder of Example 7 was obtained.

[0091] (Example 8) The silica after the drying treatment was C pulverized by a jet mill so that the D50 of the particle size became 3.5 μm, and the silica powder of Example 8 was obtained by carrying out the same process as in Example 1 except for this.

[0092] (Example 9) As the raw material particles, the specific surface area was 225 m 2 / g, τ700 was 0.128, the bulk density was 110 g / L, and the particle density was 2.203 g / cm 3Using fumed silica, a basic aqueous solution addition step and a drying step were carried out in the same manner as in Example 1, except that 500 ml of aqueous ammonia with a concentration of 14% by mass was added to the raw material particles as the basic aqueous solution. Thereafter, the silica after the drying treatment was ground by a jet mill so that the particle size C D50 became 3.3 μm, thereby obtaining the silica powder of Example 9.

[0093] (Example 10) As the raw material particles, fumed silica with a specific surface area of 220 m 2 / g, τ700 of 0.130, a bulk density of 40 g / L, and a particle density of 2.203 g / cm 3 was used, and a basic aqueous solution addition step and a drying step were carried out in the same manner as in Example 1, except that 650 ml of aqueous ammonia with a concentration of 10% by mass was added to the raw material particles as the basic aqueous solution. Thereafter, the silica after the drying treatment was ground by a jet mill so that the particle size C D50 became 3.0 μm, thereby obtaining the silica powder of Example 10.

[0094] (Example 11) In Example 1, the silica powder of Example 11 was obtained by carrying out the same process as in Example 1, except that the temperature during and after nitrogen substitution in the mixer was maintained at room temperature (20°C).

[0095] (Comparative Example 1) The silica powder of Comparative Example 1 was obtained by carrying out the same process as in Example 1, except that the concentration of the aqueous ammonia used as the basic aqueous solution was 2% by mass and the addition amount of the aqueous ammonia to the raw material particles was 400 ml.

[0096] (Comparative Example 2) As the raw material particles, fumed silica with a specific surface area of 300 m 2 / g, τ700 of 0.084, a bulk density of 25 g / L, and a particle density of 2.209 g / cm 3Using fumed silica, the basic aqueous solution addition step and the drying step were carried out in the same manner as in Example 1, except that 1000 ml of aqueous ammonia with a concentration of 0.15% by mass was added to the raw material particles as the basic aqueous solution. After that, the silica after the drying treatment was C pulverized with a jet mill so that the D50 became 2.2 μm, thereby obtaining the silica powder of Comparative Example 2.

[0097] (Comparative Example 3) Using fumed silica with a specific surface area of 200 m 2 / g, τ700 of 0.157, bulk density of 75 g / L, and particle density of 2.200 g / cm 3 and carrying out the same process as in Example 1, the silica powder of Comparative Example 3 was obtained.

[0098] (Comparative Example 4) The basic aqueous solution addition step and the drying step were carried out in the same manner as in Example 1, except that 1500 ml of a basic aqueous solution (pH 10.8) obtained by diluting sodium silicate No. 3 specified in JIS K 1408 to a concentration of 1% by mass was added to the raw material particles. After that, the silica after the drying treatment was C pulverized with a jet mill so that the D50 became 2.3 μm, thereby obtaining the silica powder of Comparative Example 4.

[0099] (Comparative Example 5) As the silica powder of Comparative Example 5, a commercially available wet silica pulverized product (manufactured by Tokuyama Corporation, Fine Seal E-50 with a specific surface area of 200 m 2 / g) was used as it was.

[0100] (Comparative Example 6) As the silica powder of Comparative Example 6, a commercially available gel method silica (manufactured by Beijing Aerospace Saide Co., Ltd., gel method silica SD-450) was used as it was.

[0101] (Comparative Example 7) Using raw material particles with a specific surface area of 297 m 2 / g, τ700 of 0.084, bulk density of 27 g / L, and particle density of 2.208 g / cm 3Fumed silica was used. 5 Kg of these raw material particles were put into a Henschel mixer with an internal volume of 300 L and stirred and mixed. Then, nitrogen gas was introduced into the mixer to replace the atmospheric gas in the mixer with nitrogen gas. Subsequently, while maintaining the temperature inside the mixer at room temperature (25°C), 750 ml of aqueous ammonia with a concentration of 10 ppm (pH = 10.2) was supplied into the mixer at a flow rate of 500 ml / hr using a single-fluid nozzle, thereby obtaining a wet mixture in which the raw material particles were wetted with aqueous ammonia. ェ (This seems to be an incorrect or incomplete Japanese term. It's hard to accurately translate without more context. Maybe it should be something like "work" or similar, but for now it remains as is.)

[0102] Subsequently, while continuously stirring the wet mixture, nitrogen was supplied into the mixer at 40 L / hr and the temperature was raised to 180°C at a rate of 100°C / hr. Then, by holding the inside of the mixer at 180°C for 1 hour, the silica powder of Comparative Example 7 that had been dried was obtained.

[0103] (Comparative Example 8) The silica powder of Comparative Example 7 was pulverized by a jet mill so that the D50 of the particle size became 2.6 μm, thereby obtaining the silica powder of Comparative Example 8. C

[0104] (Comparative Example 9) The silica powder of Comparative Example 7 was pulverized by a jet mill so that the D50 of the particle size became 1.1 μm, thereby obtaining the silica powder of Comparative Example 9. C

[0105] (Comparative Example 10) In the same manner as in Comparative Example 7, a basic aqueous solution addition step was carried out to obtain a wet mixture in which the raw material particles were wetted with aqueous ammonia. Subsequently, the wet mixture was pulverized using a single-track jet mill (manufactured by Seishin Enterprise Co., Ltd., FS4 type). Then, the obtained pulverized product was placed in a rack dryer of the rectifying type and dried at a temperature of 120°C until the moisture content in the pulverized product reached 3%, thereby obtaining the silica powder of Comparative Example 10.

[0106] (Comparative Example 11) ​​​By performing the basic aqueous solution addition step in the same manner as in Comparative Example 7, a wet mixture in which the raw material particles were wetted with aqueous ammonia was obtained. Subsequently, the wet mixture was pulverized using a pin-attached disk mill free grinder (Model M-3, manufactured by Nara Machinery Co., Ltd.). Thereafter, the obtained pulverized material was placed in a 1-L metal wide-mouth bottle and dried at a temperature of 55°C for 20 minutes, and then placed in a rack-type shelf dryer and dried at a temperature of 120°C until the moisture content in the pulverized material reached 3%, thereby obtaining the silica powder of Comparative Example 11.

[0107] (Comparative Example 12) The silica powder of Comparative Example 11 was pulverized again using a pin-attached disk mill free grinder (Model M-3, manufactured by Nara Machinery Co., Ltd.) to obtain the silica powder of Comparative Example 12.

[0108] (Comparative Example 13) Fumed silica with a specific surface area of 297 m 2 / g, τ700 of 0.084, a bulk density of 54 g / L, and a particle density of 2.208 g / cm 3 was used. 5 kg of this raw material particle was put into a Henschel type mixer with an internal volume of 300 L and stirred and mixed, and then the atmosphere gas in the mixer was replaced with nitrogen gas by introducing nitrogen gas into the mixer. Subsequently, while heating the temperature in the mixer to 70°C, 3000 ml of an aqueous sodium silicate solution (pH 10.8) obtained by diluting sodium silicate No. 3 specified in JIS K 1408 to a concentration of 1% by mass was supplied into the mixer to obtain a wet mixture in which the raw material particles were wetted with the aqueous sodium silicate solution. ェ (This seems to be an incorrect or incomplete Japanese term. It's hard to accurately translate without more context. Maybe it should be something like "work" or similar, but for now it remains as is.)

[0109] Subsequently, the wet mixture was pulverized using a single-track jet mill (Model FS4, manufactured by Seishin Enterprise Co., Ltd.). Then, the obtained pulverized material was placed in a rack-type shelf dryer and dried at a temperature of 127°C until the moisture content in the pulverized material reached 4.2%, thereby obtaining the silica powder of Comparative Example 13.

[0110] (Comparative Example 14) Fumed silica having the same specific surface area, particle density, and τ700 as those used in Example 1, except that the bulk density was 25 g / L, was used as the raw material particles. Except for the different raw material particles used, the basic aqueous solution addition step and the drying step were carried out in the same manner as in Example 1. Then, the silica after the drying treatment was C pulverized by a jet mill so that the D50 of the particle size became 1.1 μm, thereby obtaining the silica powder of Comparative Example 14.

[0111] (Comparative Example 15) Fumed silica having the same specific surface area, particle density, and τ700 as those used in Example 1, except that the bulk density was 120 g / L, was used as the raw material particles. By carrying out the same process as in Example 1 except for the different raw material particles used, the silica powder of Comparative Example 15 was obtained.

[0112] (Comparative Example 16) Except that the addition amount of aqueous ammonia to the raw material particles was 780 ml, the basic aqueous solution addition step and the drying step were carried out in the same manner as in Example 1 to obtain dried silica powder. Next, the silica after the drying treatment was pulverized by a jet mill and adjusted so that the D50 of the particle size became 1.4 μm, thereby obtaining the silica powder of Comparative Example 16. C

[0113] (Comparative Example 17) Except that the addition amount of aqueous ammonia to the raw material particles was 165 ml, the basic aqueous solution addition step and the drying step were carried out in the same manner as in Example 1 to obtain dried silica powder. Next, the silica after the drying treatment was pulverized by a jet mill and adjusted so that the D50 of the particle size became 1.4 μm, thereby obtaining the silica powder of Comparative Example 17. C

[0114] The production conditions of the silica powders of each example and comparative example are shown in Tables 1 and 2. Also, the physical property values of the paints prepared using the silica powders of each example and comparative example, and the evaluation results of the paint films formed using this paint are shown in Tables 3 and 4. ​​

[0115]

Table 1

[0116]

Table 2

[0117]

Table 3

[0118]

Table 4

[0119] <Evaluation of Dispersibility in the Resin Composition for Paint> Regarding the silica powders of Example 6 and Example 10 and the silica powder of Comparative Example 14, the dispersibility in the resin composition (a resin composition mainly composed of an aliphatic urethane resin) used for preparing the paint was evaluated by the following procedure.

[0120] First, 3.75 g of silica powder was added on top of 100 g of the resin composition (manufactured by Shenlan Technology Co., Ltd., BLLK - 2000 (aliphatic urethane paint; solid content: 15%, solvent content consisting of toluene / IPA (isopropyl alcohol) = 9 / 1 (mass ratio): 85%)) filled in a container. Next, it was stirred at 2500 rpm (peripheral speed 5.2 m / S) with a dispersing blade stirrer having an outer diameter of 40 mm. At this time, stirring was continued until the silica powder was uniformly dispersed throughout the resin composition. Whether the silica powder was uniformly dispersed throughout the resin composition was visually confirmed. And the time from the start of stirring to the end of stirring was measured. As a result, it was confirmed that the time until the silica powder was uniformly dispersed throughout the resin composition was 4 minutes for the silica powder of Example 6, 5.3 minutes for the silica powder of Example 10, and 8 minutes for the silica powder of Comparative Example 14.

Claims

1. having an aggregated structure in which primary particles are aggregated, wherein the particle size ratio R represented by the following formula (1) is 4.3 to 5.2, the absorbance of an aqueous dispersion with a concentration of 1.48% by mass with respect to light with a wavelength of 700 nm is 0.6 or less, and Silica characterized in that the particle density measured by a He pycnometer is 2.18 g / cm ３ or more. ・Formula (1) R = Ｌ D50 / Ｃ D50 〔In the above formula (1), Ｌ D50 represents the volume-based cumulative 50% particle diameter (μm) of the silica measured based on the laser diffraction scattering method, Ｃ D50 represents the volume-based cumulative 50% particle diameter (μm) of the silica measured based on the Coulter counter method.〕

2. The volume-based cumulative 50% particle size Ｌ The silica according to claim 1, characterized in that D50 is 1.7 μm or more.

3. Silica according to any one of Claims 1 or 2, characterized in that the bulk density is 35 g / L or more.

4. Silica according to any one of Claims 1 to 3, characterized in that it is used as a matting agent for paints.

5. Silica according to Claim 4, characterized in that the paint is any paint selected from the group consisting of clear paints and black-based paints.

6. comprising at least a matting agent and a resin, The matting agent has a structure in which primary particles are aggregated, the particle size ratio R shown in the following formula (1) is 4.3 to 5.2, the absorbance of a 1.48 mass% aqueous dispersion with respect to light with a wavelength of 700 nm is 0.6 or less, and the particle density measured by a He pycnometer is 2.18 g / cm ３ or more, and the paint is characterized by containing silica. ・Formula (1) R = Ｌ D50 / Ｃ D50 〔In the formula (1), Ｌ D50 represents the volume-based cumulative 50% particle diameter (μm) of the silica measured based on the laser diffraction scattering method, Ｃ D50 represents the volume-based cumulative 50% particle diameter (μm) of the silica measured based on the Coulter counter method.〕

7. Paint according to Claim 6, characterized in that it is any one selected from the group consisting of clear paints and black-based paints.

8. A basic aqueous solution addition step of preparing a wet mixture by adding a basic aqueous solution containing a basic substance in a concentration of 5 N or more in the range of 4 parts by mass to 13 parts by mass with respect to 100 parts by mass of fumed silica having an absorbance of 0.14 or less with respect to light with a wavelength of 700 nm in an aqueous dispersion with a concentration of 1.48% by mass and a bulk density of 40 g / L to 110 g / L; and A method for producing silica, characterized by passing through at least a drying step of heating and drying the wet mixture at a temperature equal to or higher than the boiling point of the basic substance.

9. The method for producing silica according to Claim 8, characterized in that the basic aqueous solution is aqueous ammonia having a concentration of 5 N or more.

10. further comprising a pulverizing step of pulverizing the silica obtained through the drying step using a pulverizing device selected from the group consisting of a jet mill and a pin mill, In the pulverization step, the volume-based cumulative 50% particle size measured based on the Coulter counter method of silica after the pulverization treatment Ｃ The method for producing silica according to claim 8 or 9, characterized in that the pulverization treatment is carried out until D50 is 3.5 μm or less.

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