JP2005232279A - Manufacturing method of hydrophobized zinc oxide powder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of fine particle zinc oxide powders which exhibit remarkable effects that the oil absorption is low and the apparent specific volume is low, the effects that are useful as cosmetic powders. <P>SOLUTION: The manufacturing method of hydrophobization-treated zinc oxide powders comprises dispersing zinc oxide powders into a solvent and performing surface treatment with a phosphate of a specific structure which has a perfluoroalkyl and an ester of a specific structure which is led from a copolymer of 2-ethylhexyl acrylate with a mol. wt. of 30,000-300,000, methacrylic acid, methyl methacrylate and butyl methacrylate and a methylpolysiloxane whose methyl groups are partially substituted by hydroxypropyl groups. In the manufacturing method, fine particle zinc oxide powders having a primary particle diameter of ≤1 μm are used, and the solvent is used in an amount of 50-90 mass% based on the zinc oxide powders. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for producing a hydrophobized zinc oxide powder. More specifically, the present invention relates to a method for producing a fine particle zinc oxide powder having characteristics of low oil absorption and apparent specific volume.

  The finely divided zinc oxide powder obtained by the present invention has a remarkable effect of low oil absorption and low apparent specific volume. Therefore, it is extremely useful as a cosmetic blended powder and can be stably blended in cosmetics. .

  Among the ultraviolet rays of sunlight, a wavelength of 280 to 320 nm in the middle wavelength ultraviolet region causes erythema called sunburn on the skin, and in severe cases, causes water bubbles similar to burns. Further, it is known that the wavelength of 320 to 400 nm in the long-wavelength ultraviolet part causes skin darkening, and when any wavelength repeatedly acts for a long time, it promotes skin aging.

  In order to prevent the harmful effects of ultraviolet rays on the skin, sunscreen cosmetics containing ultraviolet absorbers and ultraviolet protective powders are used.

  Among these, fine zinc oxide powder is used as a material that effectively protects the long wavelength ultraviolet region and has high transparency in the visible region. In addition, it is known that the W / O type emulsion composition is good in terms of sweat resistance.

  When blending fine particle zinc oxide with the W / O emulsion composition, surface treatment is necessary from the viewpoint of the stability of the preparation. However, if the surface treatment is not uniform, zinc ions may elute and harm the stability of the system, and the finely divided zinc oxide is extremely difficult to stably blend into the surface treatment method and the W / O emulsion composition. It was a powder.

  On the other hand, in makeup cosmetics, a technique for imparting sebum resistance to pigments by treating the surface of the pigment with water or water / oil repellent treatment for the purpose of preventing breakup of makeup is known. For example, Patent Documents 1 to 4 describe techniques relating to surface treatment with a perfluoroalkyl phosphate compound. Patent Document 5 describes a cosmetic comprising a powder surface-coated with an acrylic-silicone graft copolymer, which improves the adhesion to the skin and the usability.

  As a further improvement of the above technique, Patent Document 6 discloses that a cosmetic pigment powder is surface-treated with the phosphoric acid ester of the general formula (1) and the ester of the general formula (2) used in the present invention. Thus, a technology for hydrophobizing has been developed.

  The hydrophobized pigment shown in Patent Document 6 can be easily dispersed in a cosmetic and has a problem to solve the effect of giving a moist use feeling. The paragraph “0019” exemplifies many inorganic pigments, organic pigments and resin powder pigments as various cosmetic pigments to be surface-coated. Discloses cosmetics in which pigment powders obtained by hydrophobizing pigments of titanium oxide, sericite, mica, talc, yellow iron oxide, red iron oxide, and black iron oxide are disclosed.

However, Patent Document 6 generally does not describe any method for surface treatment of fine zinc oxide powder, which is highly transparent unlike pigment powder, and is a scattering agent for long-wavelength ultraviolet rays. There is no suggestion of a new problem to reduce the oil absorption and the apparent specific volume of the fine zinc oxide powder achieved by the invention and its remarkable effect.
Japanese Patent No. 2724257 Japanese Patent No. 2672913 Japanese Patent Publication No. 5-86984 JP-A-3-246210 JP-A-5-339125 JP 2001-302455 A

  In view of the above-mentioned viewpoints, the inventors have focused on fine-particle zinc oxide powder useful as a highly transparent ultraviolet scattering agent, and are excellent in water repellency and oil repellency, and stable in W / O type emulsion sunscreen cosmetics. As a result of earnest research on a surface treatment method that can be easily blended, in the surface treatment method described in Patent Document 6 for simultaneous treatment with a specific phosphate ester and a copolymer ester, fine particle zinc oxide having a primary particle diameter of 1 μm or less When the powder is used and the amount of the solvent used is in the range of 50 to 90% by mass with respect to the zinc oxide powder, a fine zinc oxide powder that exhibits a remarkable effect of low oil absorption and low apparent specific volume is obtained. The inventors have found that it can be produced efficiently and have completed the present invention.

  The fine zinc oxide powder obtained by the present invention has excellent effects of low oil absorption and low apparent specific volume, and at the same time, is excellent in water repellency and oil repellency, and can be stably blended into a preparation, Hydrophobized powder with excellent scattering effect.

（式中、Rfは炭素数３〜21のパーフルオロアルキル基または、パーフルオロオキシアルキル基を示し、直鎖状あるいは分岐状であって、単一鎖長のものであっても複合鎖長のものであってもよい。ｎは１〜12の整数を示し、yは1〜3の数を示す。）

That is, the present invention disperses zinc oxide powder in a solvent,
A phosphoric acid ester having a perfluoroalkyl represented by the general formula (1);
A copolymer of 2-ethylhexyl acrylate, methacrylic acid, methyl methacrylate, butyl methacrylate having a molecular weight of 30,000 to 300,000 represented by the general formula (2) and a part of methyl group of methylpolysiloxane In a method for producing a hydrophobized zinc oxide powder by performing a surface treatment with an ester substituted with a hydroxypropyl group,
A method for producing a hydrophobized zinc oxide powder, characterized in that a fine particle zinc oxide powder having a primary particle diameter of 1 μm or less is used, and the amount of solvent used is in the range of 50 to 90% by mass with respect to the zinc oxide powder. Is to provide. More preferably, it is 60-80 mass%.

(In the formula, Rf represents a perfluoroalkyl group having 3 to 21 carbon atoms or a perfluorooxyalkyl group, which is linear or branched and has a single chain length or a complex chain length. (N represents an integer of 1 to 12, and y represents a number of 1 to 3).

In addition, in the present invention, when the specific surface area of the fine zinc oxide powder is X (m ² / g), the sum of the usage amounts of the phosphate ester of the general formula (1) and the ester of the general formula (2) is The present invention provides a method for producing the above hydrophobized zinc oxide powder, which is carried out in the range of X / 10 to X / 5 mass% with respect to the zinc oxide powder.

  Further, in the present invention, the mass ratio of the usage amount of the phosphoric acid ester of the general formula (1) and the ester of the general formula (2) is the phosphoric acid ester of the general formula (1) / the general formula (2) The present invention provides a method for producing the above hydrophobized zinc oxide powder, characterized in that the esterification is carried out with 1 to 5.

  In addition, the present invention is a hydrophobic fine particle having a primary particle diameter of 1 μm or less, characterized in that the hydrophobized zinc oxide powder produced by the above surface treatment method has an oil absorption of 15 to 40 mL / 100 g. The present invention provides a modified zinc oxide powder.

  According to the production method of the present invention, it is possible to produce a finely divided zinc oxide powder that exhibits a remarkable effect of low oil absorption and low apparent specific volume.

The finely divided zinc oxide powder obtained by the present invention is considered to be a gently agglomerated treated powder because it has a low specific oil area and a relatively high specific surface area. This makes it easy to obtain a low-viscosity formulation even when blended into a continuous phase of a general W / O type formulation, and since the specific surface area is maintained, the share when applied to the skin It is possible to effectively protect against long wavelength ultraviolet rays without loosening and whitening.
Further, the fine zinc oxide powder obtained by the present invention has a low apparent specific volume, so that it can be easily dispersed in oil, and is particularly suitable for the production of cosmetics and the like.
Of course, the effect of being excellent in water repellency and oil repellency and being able to be stably blended into the preparation is also exceptional.

  Hereinafter, the present invention will be described in detail.

  The present invention is produced by surface-treating fine zinc oxide powder having a primary particle diameter of 1 μm or less in place of the cosmetic pigment to be surface-treated in the method described in Patent Document 6. Preferably, a fine particle zinc oxide powder of 0.1 μm or less is used. The primary particle size is the average particle size of primary particles.

  Examples of the fine particle zinc oxide having a primary particle diameter of 1 μm or less include FINEX-50 manufactured by Sakai Chemical Co., Ltd., ZnO-350 manufactured by Sumitomo Osaka Cement Co., Ltd., and zinc oxide FZO-50 manufactured by Ishihara Sangyo Co., Ltd. Alternatively, fine zinc oxide MZ-500 manufactured by Teika Co., Ltd. can be used. In addition, fine zinc oxide powder (having a carnation petal-like appearance) described in WO99 / 25654 (Japanese Patent Application No. 11-525984) can be used.

  As the phosphoric acid ester having a perfluoroalkyl group represented by the general formula (1), for example, perfluoroalkyl phosphoric acid which is a solid content of an aqueous dispersion emulsion commercially available under the name AG-530 from Asahi Glass Co., Ltd. Ester diethanolamine salt or perfluoroalkyl phosphate sodium salt, perfluoroalkyl phosphate potassium salt, perfluoroalkyl phosphate ammonium salt, etc. having the same molecular structure but different salt form using amine What removed salt, ammonium salt, and alkali metal salt can be used.

  Examples of the ester represented by the general formula (2) (hereinafter sometimes referred to as “acrylic silicone copolymer”) include the names KP-541, KP-543 and KP-545 from Shin-Etsu Chemical Co., Ltd. Examples include commercially available isopropyl alcohol, butyl acetate, a copolymer dissolved in volatile silicone, or an acrylic silicone copolymer called KP-544 dissolved in another organic solvent.

The total coating amount of the perfluoroalkyl phosphate ester and acrylic silicone copolymer represented by the general formulas (1) and (2) is X / 5 to 5 when the specific surface area of the fine zinc oxide powder is Xm ² / g. By adjusting to X / 10% by weight, sufficient water repellency and oil repellency can be obtained. If the coating amount is outside this range, the phosphoric acid ester of the general formula (1) is deposited in a powder form other than the powder surface and coexists in the powder, and excessive aggregation of the powder can be ignored. There is a possibility that the defensive ability of the long-wavelength ultraviolet part may be reduced and the water repellency and oil repellency may be insufficient.
Therefore, in the present invention, when the specific surface area of the finely divided zinc oxide powder to be surface-treated is X (m ² / g), the amount used of the phosphate ester of the general formula (1) and the ester of the general formula (2) Is preferably performed in the range of X / 10 to X / 5% by mass with respect to the zinc oxide powder.

  Moreover, the mass ratio of the usage-amount of the phosphate ester of General formula (1) and the ester of the said General formula (2) is the ester of General formula (1) / ester of General formula (2) = 1-5. It is preferable to carry out with 2-4. If the content is outside this range, the resulting powder may have poor affinity with commonly used cosmetic oils, or water resistance (oil repellency) may be insufficient when applied to the skin as a formulation. There is.

  The present invention is characterized in that the amount of the solvent is in the range of 50 to 90% by mass with respect to the zinc oxide powder. Surprisingly, when the surface treatment is carried out according to a conventional method using the phosphoric acid ester of the general formula (1) and the ester of the general formula (2), the low oil absorption and the apparent specific volume are low. Hydrophobized finely divided zinc oxide powder with excellent water and oil repellency is produced. The amount of the solvent is the amount of all the solvents present in the system in which the powder is dispersed, and is all the solutions excluding the compounds of the general formulas (1) and (2). The powder need not be dispersed in a solvent in advance and added to the processing container. A method is preferred in which the powder is first added to the processing container, then the processing agent solutions (solutions) of the general formulas (1) and (2) are added, and finally the solvent is added and stirred.

  The solvent is a lower alcohol such as methyl alcohol, ethyl alcohol or isopropyl alcohol, an ester solvent such as ethyl acetate or butyl acetate, or an organic solvent such as volatile silicone or acetone. Isopropyl alcohol (hereinafter referred to as IPA) is preferably used. In addition, in this invention, the solvent used 50 to 90 mass% with respect to zinc oxide powder is the total amount of solvent containing the solvent used when dissolving a surface treating agent previously.

A flow sheet of the production method of the present invention is shown in FIG.
(1) First, a fine particle zinc oxide powder having a primary particle diameter of 1 μm or less, a phosphate ester of the general formula (1), an ester of the general formula (2), and a solvent are added to the processing container. The order of addition is not particularly limited, but it is preferable to add in the order of powder, treating agent (solution), and solvent.
The surface treatment agent may be added as it is, or may be added in a state dissolved in a solvent in advance, but it is preferably added in a state dissolved in a solvent in advance for production efficiency.
The solvent that dissolves the surface treatment agent is not limited. Usually, it is easy to handle by adding it in a state of about 30 to 70% dissolved in a solvent such as isopropyl alcohol.
Further, as the amount of the solvent to be added, the total amount with the solvent for dissolving the treating agent in advance is preferably 50 to 90% by mass, more preferably 60 to 80% by mass with respect to the amount of powder to be treated. If it is less than 50% by mass, the ratio of the powder that cannot be sufficiently dispersed in the solvent and is agglomerated and coated (incomplete surface treatment) becomes high. On the other hand, if the amount exceeds 90% by mass, the powder is sufficiently dispersed, but the apparent specific volume is unlikely to decrease, and the coating itself is performed at the timing when the solvent is almost removed. The time will be longer. That is, it is not preferable because the solvent is excessive and inefficient.
The method of mixing (dispersing) the powder is not particularly limited, but usually a suitable mixing (dispersing) machine, such as a rotating ball mill, vibratory ball mill, planetary ball mill, sand mill, attritor, bag mill, poni mixer, planetary mixer, rai It is carried out using a paddle machine, a Henschel mixer, a super mixer, a kneader, a medium stirring mill (bead mill) or the like.
The mixing time is not limited, but is usually 0.1 to 2 hours.
(2) Next, the solvent is removed. Solvent removal is carried out with stirring and optionally heating the dispersion. More efficiently, it can be carried out by maintaining a reduced pressure state with a vacuum pump provided with a trap.
(3) Next, pulverization is performed. The grinding method is not particularly limited, but a high-speed rotary grinding machine (hammer mill, cage mill, pin mill, disintegrator, screen mill, turbo mill, centrifugal classification mill, etc.), ball mill (rolling mill, vibrating ball mill, planetary mill), stirring Milling (tower mill, stirring tank mill, flow pipe mill, annular mill), lab mill, jet mill, shear mill, compression-type mill, colloid mill, etc.
(4) Finally, dry.
Drying is performed using an electric heating type heat dryer or a dryer which is supplied with heated gas.
Although drying time is not specifically limited, It is desirable to perform in 1-250h and drying temperature in the range of 50-150 degreeC. Otherwise, sufficient drying may not be performed or the processing agent may be deteriorated.

The finely divided zinc oxide powder obtained as described above has a remarkable effect of low oil absorption and low apparent specific volume.
The preferred oil absorption of the finely divided zinc oxide powder according to the present invention is 15 to 40 mL / 100 g.
This oil absorption is a numerical value measured using a method according to JISK5101 21. or using a commercially available oil absorption measuring instrument.
The preferred specific volume of the fine zinc oxide powder according to the present invention is 0.5 to 0.9 mL / g.
This apparent specific volume is a numerical value (mL / g) representing a volume (mL) per gram measured according to the tap method described in JISK5101 20.2.

  The fine zinc oxide powder obtained by the present invention has excellent effects of low oil absorption and low apparent specific volume, and at the same time, is excellent in water repellency and oil repellency, and can be stably blended into a preparation, Hydrophobized powder with excellent scattering effect. The blending amount when blended into the cosmetic is appropriately determined depending on the type and dosage form of the cosmetic. Usually, the amount according to the purpose can be blended at 0.1% by mass or more. Generally 0.1 to 60% by mass, preferably about 0.1 to 40% by mass is desirable.

  The cosmetic can be blended in any form such as powder, cake, pencil, stick, ointment, liquid, and emulsion. The types of cosmetics are facial cosmetics such as lotion, milky lotion and cream; makeup cosmetics such as foundation, lipstick, eye shadow, blusher, eyeliner, nail enamel and mascara; hair treatment, hair liquid, set lotion Hair cosmetics, sunscreen cosmetics, etc.

  The present invention will be described in detail with reference to examples. The technical scope of the present invention is not limited by these examples. In addition, unless otherwise indicated about a compounding quantity, it shows with the mass%.

"Example 1"
300 g of perfluoroalkyl phosphate ester of general formula (1) having 12 carbon atoms (Rf: carbon number 10, n = 2, 1 ≦ y ≦ 2) and ester of general formula (2) (acryl silicone copolymer) : Shin-Etsu Chemical Co., Ltd. KP-544: a copolymer of 2-ethylhexyl acrylate, methacrylic acid, methyl methacrylate, butyl methacrylate having a molecular weight of 30,000 to 300,000 represented by the general formula (2) 100 g of an ester obtained by substituting a part of methyl groups of methylpolysiloxane with a hydroxypropyl group) and 3.5 kg of IPA (solvent) were prepared. Using these, a 50 mass% solution of the phosphoric acid ester of the general formula (1) and a 60 mass% solution of the ester of the general formula (2) were prepared.
Fine particle zinc oxide powder described in WO 99/25654 (Japanese Patent Application No. 11-525984) (with carnation petal-like appearance, specific surface area (X) = 60 m ² / g) in a 20 L high-speed stirring mixer 5 kg was added, and a solution of the phosphoric acid ester of the general formula (1) and a solution of the ester of the general formula (2) were added. Further, the remaining IPA was added, and the total amount of IPA as the total amount of solvent was 3.5 kg. Then, after stirring at 60 ° C. for 1 hour, the mixture was heated to 120 ° C. and the inside of the high-speed stirring mixer was reduced in pressure and maintained for about 2 hours to completely remove IPA as a solvent.

  Next, after discharging from the inside of the mixer, the mixture was pulverized with a hammer mill equipped with a 2 mm screen and heated at 130 ° C. for 24 hours to obtain 6% perfluoroalkyl phosphate ester having 12 carbon atoms and an acrylic silicone copolymer. Particulate zinc oxide surface-coated with 2% was obtained.

The amount of oil absorption of the powder was 30.8 mL / 100 g as a result of measurement using silicone oil as the oil content according to the method of JISK5101. The apparent specific volume of the powder was 0.71 mL / g as a result of measurement according to the tap method described in JISK5101 20.2. The contact angle of the powder was 52 ° as a result of measuring the contact angle formed by preparing pellets of the powder using a tablet molding machine or the like and dropping liquid paraffin thereon.
The amount of the solvent used in the production method of Example 1 is 70% by mass with respect to the zinc oxide powder.
Moreover, the sum of the usage-amount of the phosphate ester of General formula (1) and the ester of General formula (2) is 8%, and the ester of General formula (1) / ester of General formula (2) = 3.

"Examples 2 to 10, Comparative Examples 1 to 3"
The same production as in Example 1 was carried out. That is, in accordance with “Table 1” of the production recipe described later, fine zinc oxide powder, perfluoroalkyl phosphate ester of general formula (1) having 12 carbon atoms (Rf: carbon number 10, n = 2, 1 ≦ y ≦ 2 ), And ester of general formula (2) (acrylic silicone copolymer: KP-544 manufactured by Shin-Etsu Chemical Co., Ltd .: 2-ethylhexyl acrylate having a molecular weight of 30,000 to 300,000 represented by general formula (2) , An ester of a copolymer of methacrylic acid, methyl methacrylate, butyl methacrylate and a methylpolysiloxane in which some of the methyl groups are substituted with hydroxypropyl groups), and IPA (solvent).
Into a 20 L high-speed stirring mixer, 5 kg of fine zinc oxide powder was added, and then a 50 mass% solution of the phosphoric acid ester of the above general formula (1) and 60 of the ester of the above general formula (2) dissolved in IPA in advance. A mass% solution was added. Furthermore, IPA was added in order to adjust the total amount of IPA to be the total amount of solvent. Then, after stirring at 60 ° C. for 1 hour, the mixture was heated to 120 ° C. and the inside of the high-speed stirring mixer was reduced in pressure and maintained for about 2 hours to completely remove IPA as a solvent to obtain surface-coated fine particle zinc oxide.
In the same manner as in Example 1, the oil absorption, apparent specific volume, and contact angle with liquid paraffin of the obtained powder were measured.

＊１）ＷＯ９９／２５６５４号公報（特願平１１−５２５９８４号）記載の微粒子酸化亜鉛粉末（カーネーションの花びら状の外観を有するもの，比表面積（Ｘ）＝６０m²/g）
＊２）微粒子酸化亜鉛ＦＩＮＥＸ−５０（堺化学社製、比表面積（Ｘ）＝５０m²/g）

Examples and comparative examples are summarized in “Table 1” as follows.

* 1) Fine zinc oxide powder described in WO99 / 25654 (Japanese Patent Application No. 11-525984) (having a carnation petal-like appearance, specific surface area (X) = 60 m ² / g)
* 2) Fine zinc oxide FINEX-50 (manufactured by Sakai Chemical Co., Ltd., specific surface area (X) = 50 m ² / g)

  Further, the above surface treatment conditions are graphs of the amount of oil absorption and the apparent specific volume with respect to the parameter of the amount of solvent used relative to the amount of powder and the ratio of phosphate ester of general formula (1) / ester of general formula (2). As shown in FIG. 2, “FIG. 2”, “FIG. 3” and “FIG. 4” are obtained.

  From these figures, by controlling the amount of solvent with respect to the amount of powder and appropriately controlling the apparent specific volume and oil absorption, it is extremely blended (dispersed) in cosmetics, especially in cosmetics characterized by being dispersed in oil. Can be made easier. In addition, since the ratio and amount of the treatment agent have an influence on the apparent specific volume and the amount of oil absorption, and are also related to the oil repellency that contributes to the improvement of the longevity of cosmetics, by selecting these conditions, It can be seen that this is a very useful surface treatment method because it can satisfy both the preparation width at the time of preparation (particularly, the improvement in the affinity between the powder coated with a fluorine compound and existing raw materials) and the function as a cosmetic.

  ADVANTAGE OF THE INVENTION According to this invention, the hydrophobic compound process fine particle zinc oxide powder which has the characteristic which is excellent in water repellency and oil repellency, and has a low oil absorption amount and apparent specific volume can be manufactured. The fine particle zinc oxide powder obtained by the present invention is extremely useful as, for example, a cosmetic blended powder.

It is explanatory drawing which showed the process drawing of the manufacturing method of this invention. It is a graph of the value of the oil absorption amount with respect to the solvent usage-amount with respect to the amount of powder, and the apparent specific volume. It is a graph of the amount of solvent use with respect to the amount of powder, and the value of the oil absorption amount and the apparent specific volume with respect to the parameter of the ratio of phosphate ester of general formula (1) / ester of general formula (2). It is a graph of the contact angle (vs. liquid paraffin) with respect to the parameter of the ratio of the ester of the general formula (1) / the ester of the general formula (2).

Claims (6)

Disperse zinc oxide powder in a solvent,
A phosphoric acid ester having a perfluoroalkyl represented by the general formula (1);
A copolymer of 2-ethylhexyl acrylate, methacrylic acid, methyl methacrylate, butyl methacrylate having a molecular weight of 30,000 to 300,000 represented by the general formula (2) and a part of methyl group of methylpolysiloxane In a method for producing a hydrophobized zinc oxide powder by performing a surface treatment with an ester substituted with a hydroxypropyl group,
A hydrophobized zinc oxide powder characterized by using a fine particle zinc oxide powder having a primary particle diameter of 1 μm or less and using a solvent in an amount of 50 to 90% by mass based on the zinc oxide powder. Production method.

(In the formula, Rf represents a perfluoroalkyl group having 3 to 21 carbon atoms or a perfluorooxyalkyl group, which is linear or branched and has a single chain length or a complex chain length. (N represents an integer of 1 to 12, and y represents a number of 1 to 3).

When the specific surface area of the fine zinc oxide powder is X (m ² / g), the sum of the amounts used of the phosphate ester of the general formula (1) and the ester of the general formula (2) is the zinc oxide powder. The method for producing a hydrophobized zinc oxide powder according to claim 1, wherein the method is carried out in a range of X / 10 to X / 5 mass%.   The mass ratio of the usage-amount of the phosphate ester of the said General formula (1) and the ester of the said General formula (2) is the ester of the general formula (1) / ester of the general formula (2) = 1-5. The method for producing a hydrophobized zinc oxide powder according to claim 1, wherein the method is performed.   Primary particles produced by the surface treatment method according to any one of claims 1 to 3, wherein the hydrophobicity-treated zinc oxide powder obtained has an oil repellency (against liquid paraffin) of 35 ° or more. Fine particle hydrophobized zinc oxide powder with a diameter of 1 μm or less.   The primary particle diameter of 1 μm or less, wherein the hydrophobicity-treated zinc oxide powder produced and obtained by the surface treatment method according to any one of claims 1 to 3 has an oil absorption of 15 to 40 mL / 100 g. Fine particle hydrophobized zinc oxide powder. The apparent specific volume of the hydrophobized zinc oxide powder produced and obtained by the surface treatment method according to any one of claims 1 to 3 is 0.5 to 0.9 mL / g. Fine particle hydrophobized zinc oxide powder having a primary particle diameter of 1 μm or less.

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