KR20220103692A - Surface Treatment Precipitated Silica for Waterborne Paints - Google Patents

Abstract

The present invention is a surface-treated precipitated silica for an aqueous coating material having 0.5 to 5.0% of an etheric nonionic surfactant on the surface of the precipitated silica, wherein the surface-treated precipitated silica has an aluminum content of 0.30 to 0.30 in terms of Al ₂ O ₃ 1.00 mass %, the volume average particle diameter D50 measured by laser diffraction method is in the range of 3.0 to 10.0 μm, and the ratio D90/D50 is 2.0 or less, provided that D90 is in the particle size distribution measured by laser diffraction method It relates to the above-mentioned surface-treated precipitated silica, wherein the cumulative value of volume accumulation from the bottom in the above-mentioned surface-treated precipitated silica is the particle diameter at 90%. Advantageous Effects of Invention According to the present invention, it is possible to provide a surface-treated silica that can be wetted in a short time without causing agglomeration even when added directly to an aqueous coating material as a powder, and has good redispersibility even when it is precipitated with time.

Description

Surface Treatment Precipitated Silica for Waterborne Paints

The present invention relates to surface-treated precipitated silica used as a matting agent in water-based paints. More specifically, the present invention relates to a surface-treated silica that can be wetted in a short time without causing agglomeration even when added directly to a water-based paint, and has good redispersibility even when it is precipitated with time.

Cross-referencing of related applications

This application claims the priority of Japanese Patent Application No. 2019-209954 for which it applied on November 20, 2019, and the full description is used here especially as an indication.

Precipitated silica is one kind of amorphous synthetic silica that is roughly classified into wet silica along with gel silica. It is known that precipitated silica is used as a matting agent for paints, and in particular, precipitated silica whose size is controlled to microns by processing such as pulverization or classification is widely used as a matting agent for paints for metals and paints for plastics. On the other hand, surface-treated silica for coating materials in which a specific function is imparted by subjecting such silica to a surface treatment is also known. For example, Patent Document 1 discloses a surface-treated silica having good redispersibility even if it is precipitated in a coating material by surface-treating the wet silica with a multi-chain nonionic surfactant. Patent Document 2 discloses a matting agent in which a certain amount of polyethylene wax is coated on amorphous silica having a specific pore volume.

JP H9-25440 A JP H11-512124 A The entire description of Patent Documents 1 and 2 is particularly incorporated herein by reference.

In recent years, the regulation of VOCs emitted into the atmosphere has become more stringent because it has a harmful effect on the human respiratory system. Moreover, also from consideration to the environment, it is changing from the paint using the solvent harmful to a human body to the solvent-free paint which does not use a water-based paint or a solvent. Accordingly, the silica used as the matting agent is also required to be suitable for water-based properties.

The surface-treated silica of Patent Document 1 has good redispersibility for solvent-based paints, but when used for water-based paints, silica coagulates and precipitates to form a hard cake, and redispersibility is not possible. .

The matting agent of Patent Document 2 has good matting performance for a solvent-free or low-solvent UV-curable coating material. However, since this matting agent is surface-treated with wax, it is not sufficiently dispersed in the water-based paint, and there is a problem that the matting effect cannot be exhibited.

When precipitated silica is added directly to an aqueous paint as a matting agent, the precipitated silica causes agglomeration and is not dispersed in the paint, so-called bumps, or precipitates over time to form a hard cake. Therefore, in general, a silica dispersion liquid having a concentration of about 10 to 20% is prepared beforehand, and if necessary, it is added to an aqueous coating material containing a resin, a pigment, or the like, and used.

However, when a silica dispersion is added to a water-based coating material, the entire coating material is diluted, resulting in a low-concentration coating material. As a result, there existed problems, such as a change after a coating film, and the time and energy required for drying increase compared with a solvent type coating material. Also, from the viewpoint of reducing the number of steps, it is preferable that there is no step of preparing the silica dispersion.

Therefore, it is an object of the present invention to develop a surface-treated silica that can be wetted in a short time without causing agglomeration even when directly added as a powder to a water-based paint, and has good redispersibility even when it is precipitated with time.

In order to solve the above problems, the present inventors have intensively studied the development of surface-treated silica that can be wetted in a short time without causing agglomeration even when added directly to a water-based paint, and has good redispersibility even when it is precipitated with time. As a result, the present inventors have completed the present invention by discovering that silica obtained by treating the surface of a predetermined precipitated silica containing a certain amount of aluminum with an ether-based nonionic surfactant is effective. In particular, treatment with a polyoxyalkylenealkylether nonionic surfactant can provide a surface-treated precipitated silica having particularly good redispersibility even if it is precipitated with time.

The present invention is as follows.

[1] A surface-treated precipitated silica for an aqueous coating material having 0.5 to 5.0% of an ether-based nonionic surfactant on the surface of the precipitated silica, wherein the surface-treated precipitated silica has an aluminum content of 0.30 to 1.00 in terms of Al ₂ O ₃ in the range of mass %, the volume average particle diameter D50 measured by laser diffraction method is in the range of 3.0 to 10.0 μm, and the ratio D90/D50 is 2.0 or less, provided that D90 is the particle size distribution measured by laser diffraction method The surface-treated precipitated silica, wherein the cumulative volume accumulation value from the lower part of is a particle diameter at 90%.

[2] The surface-treated precipitated silica according to [1], wherein the surface-treated precipitated silica has a BET specific surface area in the range of 60 to 280 m 2 /g.

[3] The surface-treated precipitated silica according to [1] or [2], wherein the ether-based nonionic surfactant is a polyoxyalkylenealkylether nonionic surfactant.

[4] The surface-treated precipitated silica according to any one of [1] to [3], wherein the ether-based nonionic surfactant has an HLB in the range of 10.0 to 15.0.

[5] The surface-treated precipitated silica according to any one of [1] to [4], wherein the surface-treated precipitated silica has a heating loss of 9.0% or less.

[6] The surface-treated precipitated silica according to any one of [1] to [5], wherein the apparent specific gravity is in the range of 0.05 to 0.30 g/ml.

[7] The surface-treated precipitated silica according to any one of [1] to [6], wherein the surface-treated precipitated silica has an aluminum content in the range of 0.45 to 0.85 mass% in terms of Al ₂ O ₃ .

[8] The surface-treated precipitated silica according to any one of [1] to [7], wherein the volume average particle diameter D50 measured by the laser diffraction method is in the range of 3.5 to 9.0 µm.

[9] The surface-treated precipitated silica according to any one of [1] to [8], wherein the ratio D90/D50 is 1.4 to 1.9.

According to the present invention, it is possible to provide a surface-treated precipitated silica that can be wetted in a short time without causing agglomeration even when added directly to a water-based paint, and has good redispersibility even if it is precipitated with time. This surface-treated precipitated silica is useful as a matting agent for water-based paints.

The surface-treated precipitated silica of the present invention is a surface-treated precipitated silica for an aqueous coating material having 0.5 to 5.0% of an etheric nonionic surfactant on the surface of the precipitated silica. The surface-treated precipitated silica has an aluminum content in the range of 0.30 to 1.00 mass% in terms of Al ₂ O ₃ , and a volume average particle diameter D50 measured by laser diffraction method in the range of 3.0 to 10.0 μm, and a ratio D90/ D50 is 2.0 or less, with the proviso that D90 is the particle diameter in which the cumulative volume accumulation value from the lower part in the particle size distribution measured by the laser diffraction method is 90%. The surface-treated precipitated silica of the present invention is for water-based paints and is useful as a matting agent for water-based paints. The water-based paint in the present invention refers to a water-soluble resin paint, a dispersion paint, and an emulsion paint.

The surface-treated precipitated silica of the present invention has an aluminum content in the range of 0.30 to 1.00 mass% in terms of Al ₂ O ₃ . Precipitated silica with a low aluminum content of less than 0.30 mass% in terms of Al ₂ O ₃ in terms of Al 2 O 3 is difficult to be familiar with water, especially water containing minerals such as industrial water. It thickens and becomes easy to precipitate. On the other hand, since a large amount of aluminum is added to precipitated silica having an aluminum content of more than 1.00 mass% in terms of Al ₂ O ₃ in wet synthesis, silica aggregation during synthesis becomes strong. Therefore, the precipitated silica particle obtained becomes too hard, and even if it grind|pulverizes, a coarse particle will remain. Therefore, even if it surface _- treats precipitated silica whose aluminum content is more than 1.00 mass % in conversion _of Al2O3 with an ether type nonionic surfactant, aggregation becomes easy to precipitate with time.

The aluminum content (in terms of Al ₂ O ₃ ) is preferably in the range of 0.40 to 0.90 mass%, more preferably in the range of 0.45 to 0.85 mass%.

Precipitation of the precipitated silica in which the aluminum content of the surface-treated precipitated silica falls within the above range can be performed by a conventional method, and the method for adding aluminum in the conventional method is not particularly limited. However, from the viewpoint that the surface-treated precipitated silica does not cause interaction with other additives in the water-based paint, the addition of aluminum to the precipitated silica is not an addition by surface treatment, but is added to synthetic raw materials during the synthesis of precipitated silica or Or it is preferable to add it during synthesis.

The surface-treated precipitated silica of the present invention has a volume average particle diameter D50 measured by laser diffraction in the range of 3.0 to 10.0 µm, and a ratio D90/D50 of 2.0 or less. However, D90 is the particle diameter in 90% of the volume integration cumulative value from the lower part in the particle size distribution measured by the laser diffraction method. When the D50 is in the range of 3.0 to 10.0 µm and the ratio D90/D50 is 2.0 or less, the surface-treated precipitated silica can sufficiently exhibit a desired function as a matting agent. When D50 is less than 3.0 micrometers, since a particle diameter is too small, a silica particle is buried in a coating film, and sufficient matting effect cannot be acquired. When D50 is larger than 10.0 µm, the coating film surface is rough and the design is damaged, so it is not suitable for matting applications. When the ratio D90/D50 is greater than 2.0, when the surface-treated precipitated silica of the present invention is directly added to a water-based coating material, agglomerated precipitation occurs, which causes so-called bump generation in the coating material. D50 becomes like this. Preferably it is the range of 3.5-9.0 micrometers. Although the lower limit of ratio D90/D50 is not specifically limited, For example, it is 0.5, Preferably it is 1.0. The ratio D90/D50 is preferably in the range of 1.2 to 2.0, more preferably 1.4 to 1.9.

The surface-treated precipitated silica of the present invention has 0.5 to 5.0% of an etheric nonionic surfactant on the surface of the precipitated silica. If the amount of the ether-based nonionic surfactant is small, the penetrating effect (hereinafter, wettability) is small, and if it is large, it is eluted and adversely affects the paint, so it is set in the above range. The amount of the ether-based nonionic surfactant is preferably in the range of 1.0 to 4.0%, more preferably 2.0 to 3.0%.

In the present invention, the ether-based nonionic surfactant has good water wettability and does not substantially affect the resin component in the coating material or other pigments or additives to be added. In particular, as a result of the present inventors investigating many ether type nonionic surfactants, favorable results were obtained with polyoxyalkylene alkyl ethers. Although the reason for this is not certain and there is no intention to be limited by this reason, it is presumed that good results were obtained because the polyoxyalkylene addition was suitably compatible with the silica surface. More specific examples of polyoxyalkylene alkyl ethers are given below. All the following examples are available as a commercial item. Polyoxyalkylene branched decyl ether (NOIGEN XL, NOIGEN LF: The polyoxyalkylene part consists of a polymer of polyoxy short-chain alkylene and polyoxyethylene. Daiichi Kogyo Seiyaku (DKS Co., Ltd.) products, etc. ), polyoxyethylene isodecyl ether (NOIGEN SD: Daiichi Kogyo Seiyaku, etc.), polyoxyethylene lauryl ether (DKSNL: Daiichi Kogyo Seiyaku, etc.), polyoxyethylene tridecyl ether (NOIGEN) TDS: Daiichi Kogyo Seiyaku, etc.), polyoxyalkylene tridecyl ether (NOIGEN TDX: The polyoxyalkylene part is made of a polymer of polyoxypropylene and polyoxyethylene; Daiichi Kogyo Seiyaku, etc.); Polyoxyethylene polyoxypropylene alkyl ether (EMALGEN LS: manufactured by Kao Co., Pepole AS: manufactured by Toho Chemical Industry Co., Ltd., etc.), polyoxyethylene alkyl ether (NAROACTY CL, manufactured by Sanyo Chemical Industries, Ltd., etc.), polyoxyethylene 2-ethylhexyl ether (Newcol 1000 series: Nippon Nyukazai Co., Ltd., etc.) , polyoxyethylene cetyl ether (Newcol 1600 series: manufactured by Nippon New Chemicals, etc.), polyoxyethylene oleyl ether (EMALGEN 408: manufactured by Kaos, Newcol 1200 series: manufactured by Nippon New Chemicals, etc.) have.

Among these, it is preferable in the present invention to use NOIGEN XL-61 (polyoxyethylene tridecyl ether. HLB: 13), EMALGEN LS-106 (polyoxyethylene polyoxypropylene alkyl ether, HLB: 13), etc. .

The surface-treated precipitated silica of the present invention can be prepared by a method of providing an etheric nonionic surfactant on the surface of the precipitated silica. Examples of the preparation method (treatment method) include a dry treatment method in which precipitated silica and a surfactant are mixed with a high-speed flow mixer or the like, or a wet treatment method in which a silica slurry is mixed with a surfactant solution and dried. However, there is no limitation on the processing method. As the mixing method in the dry treatment method, an FM mixer, an axial mixer, or the like can be used. Although there exist a spin flash dryer (SFD), a spray dryer (SD), etc. as a drying method in a wet processing method, SD which can dry instantly is preferable.

If the HLB of the etheric nonionic surfactant is low, the wetting effect of the surface-treated precipitated silica is lowered because the surfactant is difficult to mix with water. When the HLB of the ether-based nonionic surfactant is high, the hydrophilicity becomes high, and the surfactant tends to detach from the solution side or the paint side from the silica surface. From such a viewpoint, the etheric nonionic surfactant has an HLB of preferably 10.0 to 15.0, more preferably 11.0 to 14.0, still more preferably 11.0 to 13.0.

The BET specific surface area of the surface-treated precipitated silica of the present invention is preferably in the range of 60 to 280 m 2 /g. The BET specific surface area here refers to the BET specific surface area of the silica (surface-treated precipitated silica) after surface treatment, and when it is 60 m 2 /g or more, the quenching effect of the silica becomes larger. When it is 280 m 2 /g or less, it is easy to produce precipitated silica, and the cohesive force between the primary silica particles is not too strong, and surface-treated precipitated silica that is difficult to precipitate even when added to an aqueous coating material is obtained.

The heat loss of the surface-treated precipitated silica of the present invention is preferably 9.0% or less. The smaller the loss on heating, the higher the silica content effective for quenching is, so it is preferable. The surface-treated precipitated silica of the present invention preferably has an apparent specific gravity in the range of 0.05 to 0.30 g/ml. When the apparent specific gravity is within this range, there are advantages in that handling is good because the specific gravity is to some extent large, and it is difficult to form a hard cake when it is settling because the specific specific gravity is not too large.

The surface-treated precipitated silica of the present invention can be suitably used for commercially available water-based paints. As for the water-based paint, a pigment for coloring, an additive, etc. are mix|blended with the water-soluble resin paint or dispersant paint or emulsion paint used as a base as needed. In general, the solid content concentration of the water-based paint is adjusted to 10 to 50%, and the viscosity is adjusted to several tens to several thousand centipoise. However, it is not intended to limit to the solid content concentration and viscosity of this range. The surface-treated precipitated silica of the present invention is most suitable for water-based paints used for painting plastic products, wood products, metal products, concrete products, mortar products, paper products, and leather products (leather products and synthetic leather products).

[Example]

Hereinafter, the present invention will be described in more detail based on Examples. However, the Examples are illustrative of the present invention, and the present invention is not intended to be limited to the Examples.

<Evaluation of surface-treated precipitated silica>

1) Measurement of aluminum content in surface-treated precipitated silica

The aluminum (Al) content in the surface-treated precipitated silica was quantified using a scanning fluorescence X-ray analyzer (model: ZSX PrimusII, manufactured by Rigaku Co.). The fluorescence X-ray intensity of a standard sample whose Al mass% concentration is known was measured, the relationship between the fluorescence X-ray intensity of Al element and the concentration was determined, and the content of Al element ( Quantitative analysis of the Al mass% concentration was performed using a calibration curve method for calculating the mass% concentration). The quantified aluminum content was converted into oxide with the analysis software attached to the apparatus, and the Al ₂ O ₃ mass% concentration was calculated. The measurement sample was produced by the pressure molding method in which the surface-treated precipitated silica was put into a ring-shaped mold and pressed.

2) Average particle diameter of surface treated precipitated silica (D50, D90, D90/D50)

The particle size distribution is measured using a laser diffraction type particle size distribution measuring device (Model: Microtrack MT-3000, manufactured by Microtrack Bell Co.), and the volume accumulation and accumulation from the lower part of the particle size distribution A value of 50% of the value (D50), a value of 90% (D90), and a ratio of D90 and D50 (D90/D50) were respectively obtained.

3) Heat loss of surface treated precipitated silica

Based on JIS K-5101, it calculated|required from the weight loss value after drying at 105 degreeC and 2 hours.

4) Apparent specific gravity of surface treated precipitated silica

It measured according to the apparent specific gravity measurement method by JISK-6220. 1.0 g of silica was poured into a cylinder (inner diameter 22.00 mm, depth 100 mm) and hit to level the silica surface. Next, the piston (outer diameter 21.80 mm, length 115 mm, mass 190 g) was dropped gently from the top, the piston height protruding from the upper part of the cylinder was measured, and the apparent specific gravity was computed by the following calculation.

G = S/{(H ₂ -H ₁ ) ×0.7854D ² }

G: Apparent specific gravity (g/cm3)

S: Weight of sample (g)

H ₂ : The difference between the height of the piston and the cylinder when the sample is present (cm)

H ₁ : The difference between the height of the piston and the cylinder when the sample is not present (cm)

D: diameter of cylinder (cm)

5) BET specific surface area of surface treated precipitated silica

The BET specific surface area of the surface-treated precipitated silica was measured by a one-point method using a fully automatic specific surface area measuring device (model: Macsorb(R) HM model-1200, Mountech Co.).

<Evaluation of wettability and paint of surface treated precipitated silica>

6) wettability; Assessment of wetting rate

Fill a 200 ml graduated disposable cup with 50 ml of water (pH 7.0, electrical conductivity 100 μS/cm), add 1 g of surface-treated precipitated silica from the top at once, and measure the time until the entire amount is completely familiar with water. It was measured as the wetting rate. Evaluation made A, 60-180 second B, 180 second or more C for the case where a wet rate is less than 60 second, and made A only A pass.

7) Water-based paint evaluation

A high-speed mixer (Type: Labolution; It was dispersed at 750 rpm for 5 minutes with Primix Co.) to obtain a paint.

7-a) dispersibility

Paint No. Precipitated silica aggregates of 200 μm or more that are applied to a commercially available ABS plate (100 mm × 200 mm, black, manufactured by Coating Testa Co.) with a 20 bar coater and exist in an arbitrary 8.9 mm × 6.7 mm range. The number of (so-called bumps) was counted with a videomicroscope. The number of bumps was measured at 5 places by moving the place, and the dispersibility was evaluated by the accumulated number of bumps.

Evaluation was judged on the following three levels of A to C, and only A was set as the pass.

A: Total number of bumps 0

B: cumulative number of bumps 1 to 4

C: Cumulative number of bumps 5 or more

7-b) redistribution evaluation

30 g of the paint was placed in a container with a cover of 50 ml, allowed to stand for 2 weeks, and then shaken for 1 minute with a shaker (model: V-SX, manufactured by Iwaki) to obtain a sedimentation observation sample. The sedimentation state was confirmed by the ratio of the silica remaining at the bottom of the container when the container was inverted so that the cover became the bottom. Evaluation of the sedimentation state was performed in three steps of the following A to C, and only A was set as the pass.

A: The state in which precipitation of silica cannot be confirmed on the bottom of a container after shaking and inversion.

B: A state in which a small amount of silica is precipitated on the bottom of the container after shaking and inversion.

C: A state in which a large amount of silica is confirmed at the bottom of the container after shaking and inversion.

Example 1

93.5 kg of hot water and No. 3 sodium silicate (SiO ₂ concentration 10.0 wt%, SiO ₂ /Na ₂ O molar ratio 3.2) were added to a jacketed 240 L stainless steel container equipped with a stirrer and a circulation pump until the pH reached 10.5, and stirred The temperature was raised to 86.0° C. while performing over-circulation (thereafter, stirring, circulation, and temperature conditions were performed under the same conditions until the reaction was stopped). Next, 66.5 kg of sodium silicate No. 3, 98.0 wt% concentrated sulfuric acid, and 0.674 kg of 30.0 wt% aluminum sulfate aqueous solution were simultaneously added dropwise over 200 minutes while stirring and circulation to maintain a pH of 10.0 to 11.0 to carry out a neutralization reaction, , After the completion of the neutralization reaction, sulfuric acid was added until the pH reached 3 to completely stop the reaction. Thereafter, the obtained reaction product was filtered and washed with a filter press to obtain a silica cake.

The obtained silica cake was slurried using a reciprocating rotary stirrer (model: Ajiter AP04 type: manufactured by Shimazaki Engineering Co.), and a commercially available polyoxyalkylene alkyl ether nonionic surfactant (trade name: NOIGEN) XL-61; Daiichi Kogyo Seiyaku Co., Ltd. (DKS Co.), HLB: 13) added 2.0% to silica, re-stirred, followed by a disk spray dryer (type: spray dryer AN-40R type, Niro Ashizawa) After spray-drying at an outlet temperature of 110° C. in an atomizer (Ashizawa NiroAtomizer Co.), pulverization was performed with a jet mill (type: PJM-100NP; manufactured by Nippon Pneumatic Kogyo Co.) , and a wind classifier (type: Classiel N-5 type, Seishin Enterprise Co.) to remove coarse particles, and surface-treated precipitated silica (Al ₂ O ₃ concentration: 0.80 mass%) was obtained.

Example 2

Surface-treated precipitated silica was obtained in the same manner as in Example 1, except that 0.5% of the polyoxyalkylenealkylether nonionic surfactant was added with respect to the precipitated silica.

Example 3

Surface-treated precipitated silica was obtained in the same manner as in Example 1 except that the amount of the polyoxyalkylenealkyl ether nonionic surfactant was added in an amount of 4.5% based on the precipitated silica.

Example 4

The same container and raw material as in Example 1, except that the internal temperature of the container was changed to 84.0°C, hot water to 74.0 kg, sodium silicate No. 3 to 86.5 kg, and aluminum sulfate aqueous solution to 0.933 kg, as in Example 1 Method to obtain surface-treated precipitated silica. This surface-treated precipitated silica had a low BET specific surface area and a slightly larger particle diameter compared to Example 1.

Example 5

In Example 1, surface-treated precipitated silica (Al ₂ O ₃ concentration: 0.40 mass%) was obtained in the same manner as in Example 1, except that the aluminum sulfate aqueous solution was changed to 0.337 kg.

Example 6

A commercially available precipitated silica, Nipsil E-150J (manufactured by Toso Silica) was used as raw powder, and this was slurried. Thereafter, in the same manner as in Example 1, 2.0% of polyoxyalkylenealkylether nonionic surfactant was added to the precipitated silica, followed by drying, pulverization and classification to obtain surface-treated precipitated silica.

Comparative Example 1

In Example 1, surface untreated precipitated silica was obtained in the same manner as in Example 1 except that no surfactant was added.

Comparative Example 2

Surface treatment sedimentation in the same manner as in Example 4, except that the polyoxyalkylenealkyl ether nonionic surfactant of Example 1 was changed to an anionic surfactant (trade name: NEOCOL YSK; Daiichi Kogyo Seiyaku Co., Ltd., HLB: 11). silica was obtained.

Comparative Example 3

In Example 1, surface-treated precipitated silica (Al ₂ O ₃ concentration: 0.20 mass%) was obtained in the same manner as in Example 1 except that the aluminum sulfate aqueous solution was changed to 0.169 kg.

Comparative Example 4

In the same manner as in Example 4 of Japanese Patent Application Laid-Open No. 9-25440 (Patent Document 1), a surface-treated precipitated silica obtained by adding 2.0% of a multi-chain nonionic surfactant to silica was obtained. That is, 1,000 g of commercially available precipitated silica, Nipsil E-200A (manufactured by Toso Silica), is injected into a Henschel mixer, and Discol 206 (Daichi Kogyo Seiyaku Co., Ltd.), a multi-chain nonionic surfactant having a molecular weight of 90,000 , HLB: 6.0) A solution of 20 g of 40 ml of ethanol was added by spraying under stirring and mixing so as to be uniform throughout the silica. After a further 10 minutes of mixing treatment, it was taken out and dried until the alcohol was completely dispersed to obtain precipitated silica surface-treated with a multi-chain nonionic surfactant.

Comparative Example 5

Surface-treated precipitated silica (Al ₂ O ₃ concentration: 1.2 mass%) was obtained in the same manner as in Example 1 except that the aqueous aluminum sulfate aqueous solution was changed to 1.01 kg in Example 1.

Comparative Example 6

Surface-treated precipitated silica was obtained in the same manner as in Example 1, except that in Example 1, the pulverization conditions in the jet mill were changed so that the average particle diameter (D50) after pulverization was 11.5 µm.

The present invention is useful in the field of matting agents for water-based paints.

Claims (9)

A surface-treated precipitated silica for water-based paints having 0.5 to 5.0% of an etheric nonionic surfactant on the surface of the precipitated silica, comprising:
The surface-treated precipitated silica has an aluminum content in the range of 0.30 to 1.00 mass% in terms of Al ₂ O ₃ , and a volume average particle diameter D50 measured by laser diffraction method in the range of 3.0 to 10.0 μm, and a ratio D90/ D50 is 2.0 or less, with the proviso that D90 is a particle diameter at 90% of the cumulative volume cumulative value from the bottom in the particle size distribution measured by laser diffraction method. The surface-treated precipitated silica according to claim 1, wherein the surface-treated precipitated silica has a BET specific surface area in the range of 60 to 280 m 2 /g. The surface-treated precipitated silica according to claim 1 or 2, wherein the ether-based nonionic surfactant is a polyoxyalkylenealkylether nonionic surfactant. The surface-treated precipitated silica according to any one of claims 1 to 3, wherein the ether-based nonionic surfactant has an HLB in the range of 10.0 to 15.0. The surface-treated precipitated silica according to any one of claims 1 to 4, wherein the surface-treated precipitated silica has a heat loss of 9.0% or less. The surface-treated precipitated silica according to any one of claims 1 to 5, wherein the apparent specific gravity is in the range of 0.05 to 0.30 g/ml. The surface-treated precipitated silica according to any one of claims 1 to 6, wherein the surface-treated precipitated silica has an aluminum content in the range of 0.45 to 0.85 mass% in terms of Al ₂ O ₃ . The surface-treated precipitated silica according to any one of claims 1 to 7, wherein the volume average particle diameter D50 measured by the laser diffraction method is in the range of 3.5 to 9.0 µm. The surface-treated precipitated silica according to any one of claims 1 to 8, wherein the ratio D90/D50 is 1.4 to 1.9.