JP6368879B1 - Method for preparing aqueous clear coating composition containing silicone resin emulsion - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for preparing an aqueous clear coating composition containing a silicone resin emulsion. A method for preparing an aqueous clear coating composition containing a silicone resin emulsion comprising the following steps: a mixture of a silicone resin (A) and an organic solvent (B), and a mixture of an emulsifier (C) and an aqueous medium. An emulsification step of performing a mechanical emulsification treatment or mechanically emulsifying a mixture of the silicone resin (A), the organic solvent (B) and the emulsifier (C) with an aqueous medium to obtain an emulsified mixture; The organic solvent (B) is at least partially removed from the resulting emulsified mixture to obtain a silicone resin emulsion; and the resulting silicone resin emulsion and inorganic oxide fine particles (D) are mixed. And a step of preparing an aqueous clear coating composition, wherein the silicone resin (A) is a branched organopolysiloxane. A method comprising Sun (A1). [Selection figure] None

Description

  The present invention relates to a method for preparing an aqueous clear coating composition containing a silicone resin emulsion.

  Various exterior coating compositions are applied to the wall surfaces of buildings such as houses and buildings for the purpose of maintaining the quality and appearance of the wall surfaces under conditions of exposure to wind and rain and direct sunlight. Such a coating composition is required to have properties such as weather resistance against wind and rain, water resistance, light resistance, discoloration resistance, and adhesion to a substrate. In the field of paints, in recent years, water-based coating compositions have been promoted from the viewpoints of environmental impact, safety in painting work, and hygiene. As an aqueous coating composition for an exterior, a coating composition containing an acrylic resin emulsion is widely used.

  When long-term weather resistance and durability are required, a coating composition containing an acrylic silicone resin-based emulsion that has been silicone-modified with a modifier having a specific silicone structure is used. In recent years, there has been a demand for further improvement in performance, and there has been a demand for an aqueous coating composition that exhibits excellent weather resistance and durability that can maintain an appearance for a long period of time even in harsh outdoor environments. Yes. Further, for example, in an aqueous clear coating composition, in addition to the above weather resistance and durability, it is also required that the obtained coating film has high transparency, that is, transparency in the visible light range.

  As an example of means for improving the performance such as weather resistance, for example, a means for increasing the proportion of the silicone structural component contained in the acrylic silicone resin emulsion can be considered. For example, Japanese Patent Application Laid-Open No. 2001-172340 (Patent Document 1) discloses a polyalkoxypolysiloxane obtained by reacting a polyalkoxypolysiloxane (a1) with a polymer compound (a2) having a functional group capable of reacting with the siloxane. A resin composition comprising a siloxane compound (A), a polymer (B ′) of a radical polymerizable unsaturated monomer (B) and a silicate oligomer (C) is described. It is described that this resin composition can improve the weather resistance of the coating film.

  As another example of means for improving performance such as weather resistance, for example, means for preparing a silicone resin emulsion in which a silicone resin is dispersed in an aqueous medium can be considered. For example, in Japanese Unexamined Patent Application Publication No. 2014-031413 (Patent Document 2), (i) the solvent component of an organic solvent solution of a silicone resin (A) synthesized in an organic solvent is replaced with a nonionic emulsifier (B). A silicone resin containing no organic solvent, comprising: a nonionic emulsifier solution of silicone resin (A); (ii) adding water to the nonionic emulsifier solution of silicone resin (A); and (iii) emulsifying. A method of making the emulsion is described.

  In JP 2003-213005 (Patent Document 3), a dispersion liquid mainly composed of an organopolysiloxane, a surfactant, and water is branched into at least two passages, and then the dispersion liquids are jetted. In a method for producing an organopolysiloxane emulsion that is made fine by collision, a method for producing an organopolysiloxane emulsion is described, wherein the dispersion is jetted and collided at a flow rate of 400 m / s or more.

JP 2001-172340 A JP 2014-031413 A JP 2003-213005 A

  In the method described in Patent Document 1, since a radical polymerizable unsaturated monomer is used in addition to the silicone structural component, the range in which the ratio of the silicone structural component can be increased is naturally limited. On the other hand, since the method described in Patent Document 2 is a method of dispersing the silicone resin itself, an emulsion in which the content of the silicone resin is increased can be obtained, and in terms of coating film weather resistance and durability. There are advantages. However, as a result of studies by the present inventors, in the method described in Patent Document 2, depending on the structure of the silicone resin, the storage stability of the emulsion may be inferior, and there is a problem in the preparation of an aqueous clear coating composition. There was found.

  An object of the present invention is to solve the above-described problems of the prior art. More specifically, an object of the present invention is to provide a method for producing an aqueous clear coating composition having excellent weather resistance and durability, and having high transparency of the resulting coating film.

In order to solve the above problems, the present invention provides the following aspects.
[1]
A method for preparing an aqueous clear coating composition comprising a silicone resin emulsion comprising the following steps:
The mixture of the silicone resin (A) and the organic solvent (B) and the mixture of the emulsifier (C) and the aqueous medium are mechanically emulsified, or the silicone resin (A), the organic solvent (B) and the emulsifier ( An emulsification step of mechanically emulsifying the mixture of C) and an aqueous medium to obtain an emulsified mixture;
The organic solvent (B) is at least partially removed from the obtained emulsified mixture to obtain a silicone resin emulsion, and the obtained silicone resin emulsion and inorganic oxide fine particles (D) are mixed. Preparing a water-based clear coating composition,
Including
The silicone resin (A) includes a branched organopolysiloxane (A1) having a weight average molecular weight in the range of 5,000 to 100,000.
The organic solvent (B) is an organic solvent that is mixed with the silicone resin (A) at an arbitrary ratio and has a solubility in water of 1 g / 100 g H ₂ O or a mixture thereof, or a mixture thereof. One type is conditional on having an azeotropic point with water,
The mass ratio (A) :( B) of the silicone resin (A) and the organic solvent (B) in the mixture before the mechanical emulsification treatment containing the silicone resin (A) and the organic solvent (B) is (A): (B) = 1: 2 to 1: 0.2, and the mass ratio (A) :( B) of the silicone resin (A) and the organic solvent (B) contained in the emulsion mixture is: , (A) :( B) = 1: 2 to 1: 0.2
The inorganic oxide fine particles (D) have an average particle diameter in the range of 20 to 300 nm.
Method.
[2]
A method for preparing an aqueous clear coating composition comprising a silicone resin emulsion comprising the following steps:
The mixture of the silicone resin (A) and the organic solvent (B) and the mixture of the emulsifier (C) and the aqueous medium are mechanically emulsified, or the silicone resin (A), the organic solvent (B) and the emulsifier ( An emulsification step of mechanically emulsifying the mixture of C) and an aqueous medium to obtain an emulsified mixture;
The organic solvent (B) is at least partially removed from the resulting emulsified mixture to obtain a silicone resin emulsion, and the resulting silicone resin emulsion, inorganic oxide fine particles (D), and A step of preparing an aqueous clear coating composition by mixing a preliminarily prepared emulsion containing a linear organopolysiloxane (A2) having a weight average molecular weight in the range of 1,000 to 30,000,
Including
The silicone resin (A) includes a branched organopolysiloxane (A1) having a weight average molecular weight in the range of 5,000 to 100,000.
The mass ratio of the branched organopolysiloxane (A1) and the linear organopolysiloxane (A2) contained in the aqueous clear coating composition is (A1) :( A2) = 98: 2 to 40:60. Is in range,
The organic solvent (B) is an organic solvent that is mixed with the silicone resin (A) at an arbitrary ratio and has a solubility in water of 1 g / 100 g H ₂ O or a mixture thereof, or a mixture thereof. One type is conditional on having an azeotropic point with water,
The mass ratio (A) :( B) of the silicone resin (A) and the organic solvent (B) in the mixture before the mechanical emulsification treatment containing the silicone resin (A) and the organic solvent (B) is (A): (B) = 1: 2 to 1: 0.2, and the mass ratio (A) :( B) of the silicone resin (A) and the organic solvent (B) contained in the emulsion mixture is: , (A) :( B) = 1: 2 to 1: 0.2
The inorganic oxide fine particles (D) have an average particle diameter in the range of 20 to 300 nm.
Method.
[3]
The silicone resin (A) is further
Linear organopolysiloxane (A2) having a weight average molecular weight in the range of 1,000 to 30,000,
Including
The mass ratio of the branched organopolysiloxane (A1) and the linear organopolysiloxane (A2) contained in the coating composition is within the range of (A1) :( A2) = 98: 2 to 40:60. Is,
The method of [1] above.
[4]
The method as described above, wherein the organic solvent (B) includes at least one selected from the group consisting of benzene, toluene, xylene, hexane and cyclohexane.
[5]
The method as described above, wherein the emulsifier (C) contains an anionic surfactant.
[6]
The mechanical emulsification process in the emulsification step is one or more selected from the group consisting of a pressure shear stirring process, an opposing collision process, a collision stirring process, and a high-speed rotation stirring process.
The above method.
[7]
The said silicone resin emulsion is the said method whose average particle diameter exists in the range of 100-500 nm.
[8]
The amount of inorganic oxide fine particles (D) contained in the aqueous clear coating composition is based on 100 parts by mass of the total resin solid content of the branched organopolysiloxane (A1) and linear organopolysiloxane (A2). 3 to 30 parts by mass,
The above method.
[9]
The branched organopolysiloxane (A1) has the following structure [R ¹ SiO _3/2 ] _m [R ² ₂ SiO] _n.
Wherein R ¹ and R ² are each independently a hydroxyl group, a linear hydrocarbon group having 1 to 6 carbon atoms, or an aromatic hydrocarbon group having 5 to 7 carbon atoms. ,
m is in the range of 1 to 1,000, n is in the range of 1 to 100, and m + n is in the range of 1 to 1,000. )
A branched organopolysiloxane (A1) having
The linear organopolysiloxane (A2) has the following structure R ^3- [R ⁴ ₂ SiO] _x -R ^5.
(In the formula, R ³ is a hydroxyl group, a linear hydrocarbon group having 1 to 6 carbon atoms, or an aromatic hydrocarbon group having 5 to 7 carbon atoms,
R ⁴ is a linear hydrocarbon group having 1 to 6 carbon atoms, or an aromatic hydrocarbon group having 5 to 7 carbon atoms,
R ⁵ is hydrogen, a linear hydrocarbon group having 1 to 6 carbon atoms, or an aromatic hydrocarbon group having 5 to 7 carbon atoms,
x is in the range of 1 to 400. )
A linear organopolysiloxane (A2) having
The above method.
[10]
The viscosity of the mixture of the silicone resin (A) and the organic solvent (B) in the mixture before the mechanical emulsification treatment containing the silicone resin (A) and the organic solvent (B) is in the range of 10 to 1,500 mPa · s. The above method.
[11]
The inorganic oxide fine particles (D) include at least one selected from the group consisting of silicon oxide, titanium oxide, zinc oxide, tin oxide, cerium oxide, antimony oxide, and double oxides thereof.
The above method.
[12]
The inorganic oxide fine particles (D) are inorganic oxide fine particles obtained by a step of stirring using medium particles having an average particle diameter of 0.01 to 0.1 mm.
The above method.
[13]
An aqueous clear coating composition comprising a silicone resin emulsion and inorganic oxide fine particles (D),
The silicone resin emulsion has a branched organopolysiloxane (A1) having a weight average molecular weight in the range of 5,000 to 100,000, and
An emulsion of a silicone resin (A) containing a linear organopolysiloxane (A2) having a weight average molecular weight in the range of 1,000 to 30,000,
The mass ratio of the branched organopolysiloxane (A1) and the linear organopolysiloxane (A2) contained in the aqueous clear coating composition is (A1) :( A2) = 98: 2 to 40:60. Is in range,
The inorganic oxide fine particles (D) have an average particle diameter in the range of 20 to 300 nm.
Water-based clear coating composition.

  According to the production method of the present invention, it is possible to produce a silicone resin emulsion containing a branched organopolysiloxane (A1) that is fine and excellent in storage stability. By the production method of the present invention, an aqueous clear coating composition containing a silicone resin emulsion and inorganic oxide fine particles can be produced. The water-based clear coating composition has an advantage that it can maintain the ultraviolet blocking property and the visible light transparency for a long period of time.

  The background to the present invention will be described. As shown in Patent Documents 2 and 3 above, various studies have been made in the preparation of silicone resin emulsions. On the other hand, as a result of investigations by the present inventors, it has been found that these conventional techniques have the following problems.

In the manufacturing method described in Patent Document 2, a nonionic emulsifier solution is substituted for a solvent component of an organic solvent solution of a silicone resin synthesized in an organic solvent to form a nonionic emulsifier solution of a silicone resin, and water is added to this to emulsify It is a manufacturing method characterized by doing. However, in this method, it has been found by experiments of the present inventors that, depending on the type of silicone resin, the particle size of the emulsion becomes large and the storage stability is inferior.
The manufacturing method described in Patent Document 3 is a manufacturing method characterized in that a dispersion containing an organopolysiloxane, a surfactant, and water is jetted and collided with a jetting collision type emulsifying device to form fine particles. . Since this method includes the step of jetting collision, when the viscosity of the dispersion is high, that is, when the viscosity of the organopolysiloxane is high, it may be difficult to perform jetting collision.

  The present inventors have aimed to develop a method capable of preparing an emulsion having a sufficiently fine particle diameter and excellent storage stability even when, for example, a high viscosity silicone resin is used. It was. And by emulsifying in the state of a mixture containing a silicone resin and an organic solvent, and then removing the organic solvent, even when using a high viscosity silicone resin, it has a sufficiently fine particle size, It has been found that a silicone resin emulsion having good storage stability can be prepared. And by using the silicone resin emulsion thus prepared and the specific inorganic oxide fine particles, an aqueous clear coating composition capable of maintaining the ultraviolet blocking property and the visible light transparency for a long time has been completed. . Hereinafter, the preparation method of the present invention will be described.

One embodiment (hereinafter referred to as “first embodiment”) of a method for preparing an aqueous clear coating composition containing a silicone resin emulsion includes the following steps:
The mixture of the silicone resin (A) and the organic solvent (B) and the mixture of the emulsifier (C) and the aqueous medium are mechanically emulsified, or the silicone resin (A), the organic solvent (B) and the emulsifier ( An emulsification step of mechanically emulsifying the mixture of C) and an aqueous medium to obtain an emulsified mixture;
The organic solvent (B) is at least partially removed from the obtained emulsified mixture to obtain a silicone resin emulsion, and the obtained silicone resin emulsion and inorganic oxide fine particles (D) are mixed. And a step of preparing an aqueous clear coating composition.
In this first embodiment, the silicone resin (A) used for the preparation of the emulsified mixture has a weight average molecular weight in the range of 1,000 to 30,000 in addition to the branched organopolysiloxane (A1). It is preferable to contain the linear organopolysiloxane (A2) which is inside.

Another embodiment (hereinafter referred to as “second embodiment”) of a method for preparing an aqueous clear coating composition containing a silicone resin emulsion includes the following steps:
The mixture of the silicone resin (A) and the organic solvent (B) and the mixture of the emulsifier (C) and the aqueous medium are mechanically emulsified, or the silicone resin (A), the organic solvent (B) and the emulsifier ( An emulsification step of mechanically emulsifying the mixture of C) and an aqueous medium to obtain an emulsified mixture;
The organic solvent (B) is at least partially removed from the resulting emulsified mixture to obtain a silicone resin emulsion, and the resulting silicone resin emulsion, inorganic oxide fine particles (D), and A step of preparing an aqueous clear coating composition by mixing a previously prepared emulsion containing a linear organopolysiloxane (A2) having a weight average molecular weight in the range of 1,000 to 30,000.
In this embodiment, after preparing the silicone resin emulsion, an emulsion containing a linear organopolysiloxane (A2) prepared in advance and having a weight average molecular weight in the range of 1,000 to 30,000 is mixed.

Emulsification step The emulsification step involves mechanically emulsifying the mixture of the silicone resin (A) and the organic solvent (B) and the mixture of the emulsifier (C) and the aqueous medium, or the silicone resin (A), In this step, a mixture of an organic solvent (B) and an emulsifier (C) and an aqueous medium are mechanically emulsified to obtain an emulsified mixture. In the above production method, a mixture of the silicone resin (A) and the organic solvent (B) or a mixture of the silicone resin (A), the organic solvent (B) and the emulsifier (C) is used in the emulsification step, and The mass ratio (A) :( B) of the silicone resin (A) and the organic solvent (B) in the mixture before mechanical emulsification treatment containing the silicone resin (A) and the organic solvent (B) is (A ) :( B) = 1: 2 to 1: 0.2, and the mass ratio of the silicone resin (A) and the organic solvent (B) contained in the emulsion mixture (A) :( B) Satisfies the relationship of (A) :( B) = 1: 2 to 1: 0.2.

Silicone resin (A)
In the above method, the silicone resin (A) contains a branched organopolysiloxane (A1) having a weight average molecular weight in the range of 5,000 to 100,000. The branched organopolysiloxane (A1) preferably has a weight average molecular weight in the range of 5,000 to 80,000, and more preferably in the range of 5,000 to 50,000. When the weight average molecular weight is within the above range, it is possible to prepare a silicone resin emulsion having good storage stability. Furthermore, the coating film obtained from the aqueous clear coating composition prepared using the silicone resin emulsion has an advantage of having good weather resistance and the like.

  The aqueous clear coating composition containing the branched organopolysiloxane (A1) has an advantage of being able to form a coating film having good coating strength. On the other hand, the branched organopolysiloxane (A1) has a relatively high viscosity. For this reason, when a silicone resin containing a branched organopolysiloxane (A1) is emulsified to prepare an aqueous clear coating composition, preparation of the emulsion may be difficult due to its high viscosity. This is because when a silicone resin containing a branched organopolysiloxane (A1) having a high viscosity is emulsified, it is difficult to prepare a fine particle emulsion, and the storage stability of the obtained emulsion may be inferior.

  In the above method, in emulsification of the silicone resin (A), the emulsion before the mechanical emulsification treatment is emulsified in a state containing the silicone resin (A) and the organic solvent (B). This made it possible to prepare fine particle emulsions.

The branched organopolysiloxane (A1) is a compound having a structure represented by the following formula, for example.
[R ¹ SiO _3/2 ] _m [R ² ₂ SiO] _n
In the above formula, R ¹ and R ² are each independently a hydroxyl group or a monovalent organic group having 1 to 20 carbon atoms, which may have a substituent as necessary.
m is in the range of 1 to 1,000;
n is in the range of 0-100.
In the above formula, m + n is preferably in the range of 1 to 1,000.

Specific examples of R ¹ and R ^{2 in} the above formula include, for example, methyl group, ethyl group, propyl group, butyl group, pentyl group, hexyl group, heptyl group, octyl group, nonyl group, decyl group, dodecyl group, tetradecyl group. Group, hexadecyl group, octadecyl group, cyclopentyl group, cyclohexyl group, cycloheptyl group, etc., alkyl group having 1-20 carbon atoms; aryl having 6-20 carbon atoms, such as phenyl group, tolyl group, xylyl group, naphthyl group, etc. Group; an alkenyl group having 2 to 20 carbon atoms such as a vinyl group and an allyl group; a hydroxyl group; and the like. These groups may have a substituent as needed. Examples of the substituent include polar group-containing substituents such as halogen atoms, amino groups, acryloxyl groups, methacryloxyl groups, epoxy groups, mercapto groups, and carboxyl groups.
In the above formula, R ¹ and R ² are each independently a hydroxyl group, a linear hydrocarbon group having 1 to 6 carbon atoms, or an aromatic hydrocarbon group having 5 to 7 carbon atoms. Is preferred.

The branched organopolysiloxane (A1) is a compound having a structure represented by the above formula. In the above formula, R ¹ and R ² are each independently a hydroxyl group and a straight chain having 1 to 6 carbon atoms. A chain hydrocarbon group or an aromatic hydrocarbon group having 5 to 7 carbon atoms, m is in the range of 1 to 1,000, n is in the range of 1 to 100, and m + n is More preferably, it is in the range of 1 to 1,000.

In R ¹ and R ² in the above formula, 30 mol% or more is more preferably a methyl group, and 50 mol% or more is more preferably a methyl group.

In the above formula, m represents the number of [R ¹ SiO _3/2 ] units, and n represents the number of [R ² ₂ SiO] units. By containing [R ¹ SiO _3/2 ] units, a branched organopolysiloxane is obtained. Here, the molar ratio m: n of the above unit is preferably in the range of 2: 8 to 10: 0, more preferably in the range of 3: 7 to 10: 0, and 4: 6 to 10. : More preferably in the range of 0. In the said ratio, when the ratio of n is 8 or less, the hardness of the coating film obtained becomes a favorable range, and there exists an advantage which can obtain favorable durability.

  The branched organopolysiloxane (A1) can be prepared, for example, by hydrolyzing a silane compound such as chlorosilane or alkoxysilane and performing a condensation reaction. A commercially available product may be used as the branched organopolysiloxane (A1). Examples of commercially available products include 804RESIN, 805RESIN, 840RESIN, SR-2400 manufactured by Toray Dow Corning; KR-220L, KR-242A, KR-251, KR-225, KR-271, KR manufactured by Shin-Etsu Chemical Co., Ltd. -282, X40-2406; SILRES K, SILRES KX, SILRES HK46, SILRES REN50, SILRES REN60, SILRES H62C, SILRES MES100 manufactured by Asahi Kasei Wacker Silicone.

In the said 1st aspect, it is preferable that a silicone resin (A) contains linear organopolysiloxane (A2) in addition to the said branched organopolysiloxane (A1). Examples of the linear organopolysiloxane (A2) include compounds having a structure represented by the following formula.
R ³ — [R ⁴ ₂ SiO] _x —R ⁵
(In the formula, R ³ is a hydroxyl group, a linear hydrocarbon group having 1 to 6 carbon atoms, or an aromatic hydrocarbon group having 5 to 7 carbon atoms,
R ⁴ is a linear hydrocarbon group having 1 to 6 carbon atoms, or an aromatic hydrocarbon group having 5 to 7 carbon atoms,
R ⁵ is hydrogen, a linear hydrocarbon group having 1 to 6 carbon atoms, or an aromatic hydrocarbon group having 5 to 7 carbon atoms,
x is in the range of 1 to 400. )

  The said 2nd aspect is a preparation method which mixes the emulsion containing the linear organopolysiloxane (A2) prepared previously, after preparing the emulsification mixture and preparing a silicone resin emulsion. In this preparation method, the silicone resin (A) used for preparing the emulsified mixture contains a branched organopolysiloxane (A1). On the other hand, the linear organopolysiloxane (A2) may or may not be included.

  In both the first and second embodiments, the mass ratio of the branched organopolysiloxane (A1) and the linear organopolysiloxane (A2) contained in the aqueous clear coating composition is (A1) :( A2 ) = 98: 2 to 40:60. When the mass ratio (A1) :( A2) is within the above range, there is an advantage that the water resistance and chemical resistance of the resulting coating film are improved.

When the aqueous clear coating composition is prepared according to the first aspect, there is an advantage that it is easy to adjust the viscosity of the mixture of the silicone resin (A) and the organic solvent (B) to an appropriate range. Furthermore, when the silicone resin (A) contains a linear organopolysiloxane (A2) having a relatively small molecular weight, there is an advantage that it is easier to adjust the viscosity to an appropriate range.
Moreover, when preparing a water-based clear coating composition by the said 2nd aspect, the compounding quantity of the silicone resin emulsion containing branched organopolysiloxane (A1) and the silicone resin emulsion containing linear organopolysiloxane (A2) Since the ratio is appropriately determined when forming the paint, there is an advantage that the physical properties of the obtained coating film can be appropriately adjusted according to the performance required by the application.

Organic solvent (B)
The organic solvent (B) is an organic solvent that is mixed with the silicone resin (A) at an arbitrary ratio and has a solubility in water of 1 g / 100 gH ₂ O or less, or a mixture of such organic solvents. And it is on condition that at least 1 sort (s) of the said organic solvent has an azeotropic point with water. The mixing of the organic solvent (B) and the silicone resin (A) means mixing at an arbitrary ratio at 20 ° C. In the present specification, the “organic solvent having an azeotropic point with water” means an organic solvent that azeotropically shows a minimum azeotropic point when a mixture of water and the organic solvent is boiled by heating or the like. Further, "an organic solvent solubility in water is less than 1g / 100gH ₂ O" refers to solubility in 20 ° C..

  In the present specification, the “organic solvent having an azeotropic point with water” means an organic solvent that azeotropically shows a minimum azeotropic point when a mixture of water and the organic solvent is boiled by heating or the like. The organic solvent (B) preferably has an azeotropic point with water at 60 to 95 ° C. at normal pressure. When the azeotropic point of the organic solvent (B) is in the above range, there is an advantage that handling is easy in the emulsification step and the desolvation step.

Among the organic solvents (B), specific examples of organic solvents having a solubility in water of 1 g / 100 gH ₂ O or less and an azeotropic point with water include, for example, benzene, toluene, xylene, and hexane. Organic solvents containing one or more of hydrocarbon solvents such as cyclohexane. The organic solvent (B) is more preferably one or more selected from the group consisting of benzene, toluene, xylene, hexane and cyclohexane, and is selected from the group consisting of benzene, toluene, hexane and cyclohexane. More preferably, it is one or more.

  By using the organic solvent, in the desolvation step after obtaining the emulsified mixture, it can be easily distilled off by azeotropy with water. Thereby, the solvent odor is reduced, and there is an advantage that an aqueous silicone resin emulsion having no flash point can be obtained.

Among the organic solvents (B), the organic solvent having a water solubility of 1 g / 100 gH ₂ O or less and having no azeotropic point with water is, for example, an aromatic organic solvent having 10 to 20 carbon atoms. And an organic solvent that does not have an azeotropic point with water and an organic solvent that has 8 to 20 carbon atoms and does not have an azeotropic point with water.

Emulsifier (C)
The emulsifier (C) used in the emulsification step is not particularly limited. For example,
Anionic interfaces such as alkyl sulfate, polyoxyethylene alkyl ether sulfate, polyoxyalkylene alkenyl ether sulfate, alkyl diphenyl ether sulfate, polyoxyethylene alkyl ether acetate, alkylbenzene sulfonate, alkenyl succinate Active agent;
Cationic surfactants such as quaternary ammonium salts;
Glycerin fatty acid ester, propylene glycol fatty acid ester, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene sorbitol fatty acid ester, polyoxyethylene alkyl ether, polyoxyalkylene alkyl ether, polyoxyethylene polyoxypropylene glycol, polyoxyethylene Nonionic surfactants such as hydrogenated castor oil, polyethylene glycol fatty acid ester, alkyl glyceryl ether, alkyl alkanolamide, alkyl polyglucoside;
Amphoteric surfactants such as alkylbetaines, imidazoline-type betaines, alkylamine oxides, alkylamidopropylbetaines, alkylhydroxysulfobetaines;
Etc. can be used.
These emulsifiers (C) may use only 1 type and may use 2 or more types together.

The emulsifier (C) preferably contains an anionic surfactant. By using the emulsifier (C) containing an anionic surfactant, an emulsified mixture and a silicone resin emulsion having an average particle diameter in a suitable range can be obtained, and a silicone resin emulsion excellent in storage stability is obtained. There are advantages that can be made.
Preferred anionic surfactants include, for example, polyoxyethylene alkyl ether sulfate ester salts such as New Coal 707SN, New Coal 714SN, New Coal 780SF, New Coal 2308SF (all manufactured by Nippon Emulsifier Co., Ltd.), polyoxyalkylene alkenyl ether sulfuric acid. Latemul PD-104 (manufactured by Kao Corporation), Aqualon KH-1025 (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), Neogen S-20F (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), neoperex G-65, Neoperex G-25 (all manufactured by Kao Corporation), alkyl diphenyl ether sulfate ester salt, Perex SS-L, Perex SS-H (all manufactured by Kao Corporation), Latemul, an alkenyl succinate ASK, Lattemul SK (all manufactured by Kao Corporation), and the like.

  Moreover, the aspect containing an anionic surfactant and a nonionic surfactant is mentioned as an example of the said emulsifier (C).

  The amount of the emulsifier (C) is preferably 0.5 to 10 parts by mass, and 2.5 to 10 parts by mass with respect to 100 parts by mass of the resin solid content of the silicone resin (A). More preferably. When the amount of the emulsifier (C) is within the above range, the average particle size can be reduced, and when an aqueous clear coating composition is prepared using the obtained silicone resin emulsion, There is an advantage that water resistance can be secured.

  In this specification, an aqueous medium is a medium consisting essentially of water. In some cases, the aqueous medium may contain a water-compatible organic solvent such as alcohol in the range of several mass%.

  In one embodiment of the emulsification step, first, a mixture of the silicone resin (A) and the organic solvent (B), and a mixture of the emulsifier (C) and the aqueous medium are prepared. Subsequently, these mixtures are subjected to a mechanical emulsification treatment to obtain an emulsified mixture. In another embodiment of the emulsification step, by preparing a mixture of the silicone resin (A), the organic solvent (B) and the emulsifier (C), further mixing an aqueous medium and performing a mechanical emulsification treatment, An emulsified mixture is obtained. These mixtures can be prepared by mixing using a stirrer usually used in the paint field. A commercially available product may be used as the mixture of the silicone resin (A) and the organic solvent (B).

  The viscosity of the mixture of the silicone resin (A) and the organic solvent (B) in the mixture before the mechanical emulsification treatment containing the silicone resin (A) and the organic solvent (B) is in the range of 10 to 1,500 mPa · s. It is preferable that it is in the range of 10 to 700 mPa · s, more preferably in the range of 10 to 200 mPa · s. The viscosity of the branched organopolysiloxane (A1) having a weight average molecular weight in the range of 5,000 to 100,000 is, for example, a high viscosity exceeding 1,500 mPa · s. Therefore, the silicone resin (A) The viscosity of the also increases. Here, by setting the viscosity of the mixture of the silicone resin (A) and the organic solvent (B) in the mixture before mechanical emulsification used in the emulsification step within the above range, an average particle diameter in a favorable range is obtained. There exists an advantage which can prepare the silicone resin emulsion which has.

  In the above-described method, the mixture before the mechanical emulsification treatment including the silicone resin (A) and the organic solvent (B) in the emulsification step is performed by the mass ratio (A) :( B) Mass ratio (A) of the silicone resin (A) and the organic solvent (B) contained in the emulsion mixture (that is, after the emulsion) satisfying the relationship of 1: 2 to 1: 0.2 : (B) satisfies the relationship of (A) :( B) = 1: 2 to 1: 0.2. Before and after the emulsion, the mass ratio of the silicone resin (A) and the organic solvent (B) is within the above range, whereby the silicone resin (A) converts the branched organopolysiloxane (A1). Even if it is included, a good silicone resin emulsion can be prepared.

  In the above production method, the mass ratio (A) of the silicone resin (A) and the organic solvent (B) in the mixture before the mechanical emulsification treatment containing the silicone resin (A) and the organic solvent (B) (that is, before emulsification). : (B) satisfies the above range, and the mass ratio (A) :( B) of the silicone resin (A) and the organic solvent (B) contained in the emulsion mixture (that is, after the emulsion) is within the above range. Satisfaction means that a certain amount of organic solvent is present both before and after emulsification. Therefore, for example, the production method in which the content of the organic solvent is less than the above range by distilling off the organic solvent before emulsification is not included in the production method in the present invention.

  The mass ratio (A) :( B) of the silicone resin (A) and the organic solvent (B) in the mixture (before emulsification) containing the silicone resin (A) and the organic solvent (B) before mechanical emulsification treatment is: It is preferable that (A) :( B) = 1: 1.5 to 1: 0.2. The mass ratio (A) :( B) of the silicone resin (A) and the organic solvent (B) contained in the emulsified mixture (after emulsification) is (A) :( B) = 1: 1.5. It is preferably ˜1: 0.2.

More specifically, the method for obtaining the emulsified mixture can be performed, for example, by the following procedure.
Procedure 1: A procedure in which the total amount of the mixture of the silicone resin (A) and the organic solvent (B) is once mixed with the total amount of the mixture of the emulsifier (C) and the aqueous medium, and then mechanically emulsified.
Procedure 2: The total amount of the mixture of silicone resin (A) and organic solvent (B) is subjected to mechanical emulsification treatment by first adding a part of the mixture of emulsifier (C) and aqueous medium, and then the rest A procedure in which a mixture of an emulsifier (C) and an aqueous medium is added to perform a mechanical emulsification treatment.
Procedure 3: A procedure in which the emulsifier (C) is once mixed with the total amount of the mixture of the silicone resin (A) and the organic solvent (B), and then mechanical emulsification treatment is performed while adding an aqueous medium.
Procedure 4: A part of the mixture of the silicone resin (A) and the organic solvent (B) and a part of the mixture of the emulsifier (C) and the aqueous medium are added first to perform a mechanical emulsification treatment, Procedure for adding the remaining mixture and performing mechanical emulsification.
Procedure 5: A mechanical emulsification treatment is performed by first adding a part of the mixture of the silicone resin (A) and the organic solvent (B) and the total amount of the mixture of the emulsifier (C) and the aqueous medium, and then the remaining silicone. A procedure in which a mixture of the resin (A) and the organic solvent (B) is added to perform a mechanical emulsification treatment.
Procedure 6: A part of the mixture of the silicone resin (A) and the organic solvent (B) is added to and mixed with the total amount of the mixture of the emulsifier (C) and the aqueous medium, and then the remaining silicone resin (A) and A procedure in which a mixture of organic solvent (B) is added to perform mechanical emulsification.

  The said mechanical emulsification process in an emulsification process means the emulsification process performed using a physical convection. Specific examples of the mechanical emulsification process include, for example, a pressure shear stirring process, an opposing collision process, a collision stirring process, and a high-speed rotation stirring process.

The pressure shear stirring process is a process of performing shear stirring under pressure conditions. As a pressurization condition, the pressurization condition of 10-100 MPa is mentioned, for example.
The opposing collision process is a process for refining particles such as an emulsion by applying a high pressure to a liquid that is a mixture and causing the liquid to collide and pass in a processing container (for example, a homovalve). As a pressurization condition, the pressurization condition of 10-100 MPa is mentioned, for example. As a specific example of the opposing collision process, for example, a homogenizer process under a pressure of 10 to 100 MPa is given. As a specific example of the facing collision process, for example, a facing collision process using a high-pressure homogenizer can be cited.
The collision agitation process is a process in which the objects to be mixed are divided into two or more, and each is agitated by being injected and collided with a high pressure (for example, a pressure of 10 to 100 MPa). The opposing collision process and the collision agitation process can be suitably used as a method for processing a relatively large amount of raw materials because the injection collision can be continuously performed. Specific examples of the collision stirring process include a collision stirring process using a microfluidizer.
The high-speed rotation stirring process is a stirring process by rotating the stirring bar at a high speed. As a high-speed rotation condition, the aspect which stirs at 5,000-30,000 rpm is mentioned, for example. As a specific example of the high-speed rotation stirring process, for example, a high-speed rotation stirring process using Claremix, Claremix W Motion (M Technique Co., Ltd.) or the like can be mentioned.

  For example, an emulsion having an average particle diameter in the range of 100 to 500 nm can be prepared by subjecting the mixture before the mechanical emulsification treatment including the silicone resin (A) and the organic solvent (B) to mechanical emulsification treatment. .

Desolvation Step A silicone resin emulsion can be obtained by at least partially removing the organic solvent (B) from the emulsification mixture obtained in the emulsification step (desolvation step). As a method for removing the organic solvent (B), a general desolvation method known to those skilled in the art can be used. As an example of the solvent removal method, for example, a method of removing the organic solvent (B) at least partially by heating and / or reducing pressure in a general stirred solvent removal tank, a falling film method or a rotary evaporator, or the like can be mentioned.

  In the above production method, even a silicone resin containing a branched organopolysiloxane (A1) can be satisfactorily emulsified with a sufficiently fine particle size. And by the said manufacturing method, the silicone resin emulsion excellent in the storage stability suitable for water-based clear coating composition preparation can be obtained. The average particle size of the silicone resin emulsion obtained by the above method is preferably in the range of 100 to 500 nm, and more preferably in the range of 100 to 400 nm.

  The average particle size of the resin emulsion in the present specification is an average particle size determined by a dynamic light scattering method. Specifically, an electrophoretic light scattering photometer ELSZ series (manufactured by Otsuka Electronics Co., Ltd.) is used. Can be measured.

Preparation of aqueous clear coating composition An aqueous clear coating composition can be prepared using the silicone resin emulsion obtained by the above-mentioned method. For example, in the first embodiment, the obtained silicone resin emulsion is mixed with the inorganic oxide fine particles (D), and pigments and additives used as necessary, using a stirrer that is usually used by those skilled in the art. By doing so, an aqueous clear coating composition can be prepared.

  For example, in the second embodiment, the obtained silicone resin emulsion, the inorganic oxide fine particles (D), and a linear organopolyethylene having a weight average molecular weight within the range of 1,000 to 30,000 prepared in advance. An aqueous clear coating composition is prepared by mixing an emulsion containing siloxane (A2), and further mixing pigments, additives, and the like used as necessary using a stirrer usually used by those skilled in the art. be able to.

  In the second embodiment, an emulsion containing a linear organopolysiloxane (A2) having a weight average molecular weight in the range of 1,000 to 30,000 can be prepared by a method commonly used by those skilled in the art. A commercial product may be used as the emulsion containing the linear organopolysiloxane (A2) having a weight average molecular weight in the range of 1,000 to 30,000.

Inorganic oxide fine particles (D)
The aqueous clear coating composition contains inorganic oxide fine particles (D) having an average particle diameter in the range of 20 to 300 nm. By including the inorganic oxide fine particles (D) in the aqueous clear coating composition, it is possible to maintain the weather resistance of the resulting coating film for a long period of time while maintaining the visible light transparency required in the clear coating composition. it can. As a result, the content of the organic UV absorber generally used in the clear coating composition can be reduced, and further, it becomes possible to prepare the clear coating composition without using the organic UV absorber. .

  Organic UV absorbers generally used in clear coating compositions (for example, benzotriazole UV absorbers, triazine UV absorbers, etc.) have high visible light transmittance, but have excellent UV blocking properties. Therefore, by using the organic ultraviolet absorber, it is possible to impart ultraviolet blocking properties to the coating film while maintaining the visible light transparency required in the clear coating composition. However, it has been found that the organic ultraviolet absorber as described above is difficult to maintain the ultraviolet blocking property for a long period of time.

  By using the inorganic oxide fine particles (D) having an average particle diameter within the above range, it is possible to impart ultraviolet blocking performance while maintaining the visible light transparency required in the clear coating composition, and ultraviolet rays. It became possible to maintain the blocking property for a long time.

  The average particle size of the inorganic oxide fine particles (D) is more preferably in the range of 20 to 230 nm, and still more preferably in the range of 20 to 100 nm.

In this specification, the average particle diameter of the inorganic oxide fine particles (D) means 50% volume particle diameter (also referred to as D ₅₀ , volume cumulative particle diameter D ₅₀ ). Specifically, in the particle size distribution of the inorganic oxide fine particles (D), when the total volume of the particles accumulated from the small particle diameter side to a certain particle diameter is expressed as a percentage of the total particle volume, This is the particle diameter when the value is 50%. The 50% volume particle diameter (D ₅₀ ) can be measured using a laser diffraction / scattering method, for example, UPA-150 (particle size distribution measuring device manufactured by Microtrack Bell).

  Examples of the inorganic oxide constituting the inorganic oxide fine particles (D) include silicon oxide, titanium oxide, zinc oxide, tin oxide, cerium oxide, antimony oxide, and double oxides thereof. The inorganic oxide fine particles (D) preferably contain at least one selected from the group consisting of silicon oxide, titanium oxide and zinc oxide, and include at least one selected from the group consisting of titanium oxide and zinc oxide. Is more preferable from the viewpoints of ultraviolet absorption performance and visible light transparency of the coating film. These inorganic oxide fine particles (D) are also advantageous in that the storage stability of the aqueous clear coating composition can be ensured.

  The inorganic oxide fine particles may be surface-treated particles. As the surface treatment, for example, an organic surface coating with an organosilicon compound may be formed. Alternatively, the inorganic surface may be coated with a hydroxide and / or oxide of one or more elements selected from silicon, aluminum, zinc, iron, titanium and zirconium. Further, both the inorganic surface coating and the organic surface coating may be formed.

  Examples of the organic surface coating include a silicone compound having a hydrogen-silicon bond, such as a methyl hydrogen polysiloxane copolymer, or a compound having an alkoxy group-silicon bond as a reactive group (for example, triethoxysilylethyl polydimethylsiloxyethyl dimethicone). And surface coating treatment using an organosilicon compound such as triethoxysilylethyl polydimethylsiloxyethylhexyl dimethicone). The organic surface coating treatment method is not particularly limited, and a known method such as dry treatment or wet treatment can be used. The organic surface coating is preferably performed in a quantity that falls within the range of 0.1 to 20% by mass with respect to the mass of the inorganic oxide fine particles after the coating treatment.

  The inorganic surface coating uses a surface treatment agent that provides an inorganic surface coating comprising a hydroxide and / or oxide of one or more elements selected from silicon, aluminum, zinc, iron, titanium and zirconium. It can be carried out. Specific examples of such surface treatment agents include, for example, sodium silicate, tetramethyl silicate and its condensate, tetraethyl silicate and its condensate, sodium aluminate, sodium zirconate, aluminum sulfate, aluminum nitrate, aluminum chloride, and others. Examples thereof include sulfates, nitrates and chlorides of the above elements.

  The inorganic surface coating treatment method using the surface treatment agent is not particularly limited. For example, inorganic oxide fine particles are dispersed in water to form a water slurry, and the surface treatment agent is added to the water slurry, followed by drying, firing, and grinding. A method in which inorganic oxide fine particles are dispersed in water to form a water slurry, a surface treatment agent is added to the water slurry, and neutralization, water washing, drying, and pulverization are performed; a surface treatment agent is added to the inorganic oxide fine particles, And a method of thermally decomposing the surface treating agent by firing. The inorganic surface coating is preferably carried out in an amount that falls within the range of 0.1 to 30% by mass relative to the mass of the inorganic oxide fine particles after the coating treatment.

  In the surface treatment, an inorganic surface coating treatment is performed as the first surface treatment to form an inorganic surface coating layer, and then an organic surface coating treatment is performed as the second surface treatment to form an organic surface coating layer. preferable. As a more preferable embodiment, for example, an inorganic surface coating layer is formed using hydrous silica as the first surface treatment, and then an organic surface coating layer is formed using organopolysiloxane as the second surface treatment. The mode to do is mentioned. Examples of the inorganic oxide fine particles subjected to such a surface treatment include FINEX series manufactured by Sakai Chemical Industry.

  Examples of the silicon oxide inorganic oxide fine particles include silica fine particles having an average particle diameter in the above range. Specific examples of such silica fine particles include, for example, methanol silica sol, IPA-ST, IPA-ST-ZL, EG-ST, NPC-ST-30, DMAC-ST, which are organosilica sols manufactured by Nissan Chemical Industries, Ltd. MEK-ST, MIBK-ST, XBA-ST, PMA-ST, PGM-ST and the like can be mentioned.

  As inorganic oxide fine particles of titanium oxide, for example, 1120Z, 2120Z, 6320Z manufactured by JGC Catalysts & Chemicals, TECNADIS-TI-220 manufactured by TECNAN, STR series manufactured by Sakai Chemical Industry Co., Ltd., TTO series manufactured by Ishihara Sangyo Co., Ltd. Etc.

  Examples of the inorganic oxide fine particles of tin oxide include CX-S303IP, CX-S301H, CX-S501M, and CX-S505M manufactured by Nissan Chemical Industries.

  Examples of the inorganic oxide fine particles of cerium oxide include CE-20A manufactured by Nissan Chemical Industries, TECNADIS-CE-220 manufactured by TECNAN, and the like.

  As inorganic oxide fine particles of zinc oxide, for example, F-2 and F-1 manufactured by Hux Itec Corp., ZnO-310, ZnO-410, ZnO-510 manufactured by Sumitomo Osaka Cement Co., Ltd., and TECNADIS-ZN-220 manufactured by TECNAN Corp. And the FEX series manufactured by Ishihara Sangyo Co., Ltd. and the like.

  Examples of the inorganic oxide fine particles of antimony oxide include PATOX-U manufactured by Nippon Seiko Co., Ltd.

Examples of the metal oxide double oxide inorganic oxide fine particles include zinc oxide (ZnO) and antimony pentoxide (Sb ₂ O ₅ ) double oxide (ZnSb ₂ O ₆ ). Specific examples of such a double oxide include CX-Z210IP-F2, CX-Z330H, and CX-Z610M-F2 manufactured by Nissan Chemical Industries.

  The inorganic oxide fine particles (D) are preferably subjected to a wet dispersion treatment. By performing the wet dispersion treatment, there is an advantage that the average particle diameter of the inorganic oxide fine particles (D) can be suitably adjusted in the range of 20 to 300 nm. As the wet dispersion treatment, a dispersion treatment method usually used in this field (for example, disper dispersion, mill dispersion, etc.) can be used. The dispersion viscosity is preferably 300 mPa · s or less, and more preferably 100 mPa · s or less.

  The inorganic oxide fine particles (D) are preferably inorganic oxide fine particles obtained by a stirring treatment step of stirring using medium particles having an average particle diameter of 0.01 to 0.1 mm. By carrying out the stirring treatment of the inorganic oxide fine particles (D) using the medium particles, there is an advantage that the average particle diameter of the inorganic oxide fine particles (D) can be adjusted to a more suitable range. As the stirring using the medium particles, wet medium stirring is preferably used.

  The material of the medium particles is not particularly limited, and examples thereof include alumina, zirconia, silicon carbide, silicon nitride, glass, steel, stainless steel, and ceramics. The material of the medium particles is preferably zirconia from the viewpoint of adjusting the particle diameter of the inorganic oxide fine particles (D).

  Wet medium stirring is a stirring method in which inorganic oxide fine particles are subdivided in a liquid containing a dispersant and an aqueous medium in the presence of the medium particles. The particle diameter of the medium particles used in the wet medium agitation is preferably 0.015 mm or more and 0.1 mm or less, and more preferably 0.015 mm or more and 0.05 mm or less.

As the dispersant, a polymer dispersant which is a dispersant used in the coating material field can be preferably used. Examples of the polymer dispersant include a polyester-based, polyacryl-based, polyurethane-based, polyamine-based, and polycaptolactone-based main chain, such as an amino group, a carboxy group, a sulfo group, and a hydroxy group in the side chain. Examples thereof include a dispersant having a polar group.
As a specific example of the polymer dispersant, for example,
(Co) polymers of unsaturated carboxylic esters such as polyacrylic esters;
Copolymers of aromatic vinyl compounds such as styrene and α-methylstyrene and unsaturated carboxylic acid esters such as acrylic acid esters;
(Partial) amine salts, (partial) ammonium salts or (partial) alkylamine salts of (co) polymers of unsaturated carboxylic acids such as polyacrylic acid;
A (co) polymer of a hydroxyl group-containing unsaturated carboxylic acid ester such as a hydroxyl group-containing polyacrylate or a modified product thereof;
Polyurethanes; Unsaturated polyamides; Polysiloxanes; Long-chain polyaminoamide phosphates; Polyethyleneimine derivatives (amides or their bases obtained by reaction of poly (lower alkyleneimines) with free carboxyl group-containing polyesters); Poly Allylamine derivatives (obtained by reacting polyallylamine with one or more compounds selected from the three compounds of polyesters, polyamides or ester-amide co-condensates (polyesteramides) having a free carboxyl group Reaction product); and the like.

  A commercially available product may be used as the polymer dispersant. Examples of commercially available products include the DISPERBYK series (manufactured by BYK Chemie), the Solsperse series (manufactured by Lubrizol), the EFKAPOLYMER series (manufactured by BASF), and the SN dispersant series (manufactured by San Nopco).

  The aqueous medium includes water. The aqueous medium may further contain an organic solvent as required in addition to water. Examples of organic solvents that can be included in the aqueous medium include alcohol solvents such as methanol, ethanol, propanol, and butanol; ketone solvents such as methyl ethyl ketone, acetone, methyl isobutyl ketone, and cyclohexanone; diethyl ether, isopropyl ether, tetrahydrofuran, and dioxane. Ether solvents such as ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, propylene glycol monomethyl ether, anisole and phenetol; ester solvents such as ethyl acetate, butyl acetate, isopropyl acetate and ethylene glycol diacetate; Dimethylformamide, diethylformamide, N-methyl Amides such as pyrrolidone solvent; and the like; methyl cellosolve, ethyl cellosolve, cellosolve solvents such as butyl cellosolve. When the aqueous medium contains the organic solvent, there is an advantage that the inorganic oxide fine particles can be wet-dispersed better.

  The amount of the inorganic oxide fine particles (D) contained in the aqueous clear coating composition is a resin solid content of the branched organopolysiloxane (A1) and the linear organopolysiloxane (A2) used as necessary. The amount is preferably 7 to 30 parts by mass and more preferably 10 to 30 parts by mass with respect to 100 parts by mass in total. When the amount of the inorganic oxide fine particles (D) is within the above range, there is an advantage that the weather resistance of the obtained coating film can be improved while maintaining the visible light transparency required in the clear coating composition. .

  The aqueous clear coating composition may contain a pigment other than the inorganic oxide fine particles (D) as necessary. However, when other pigments are used, they must be of the kind and amount that do not greatly impair the transparency of the aqueous clear coating composition. Other pigments are not particularly limited as long as the above conditions are satisfied, and examples thereof include extender pigments, inorganic color pigments, and organic pigments.

  In the preparation of the aqueous clear coating composition, additives usually used, such as viscosity modifiers, fillers, dispersants, UV absorbers, light stabilizers, antioxidants, matting agents, antifreeze agents, and antialgae You may mix with an agent, an antifoamer, a film-forming aid, antiseptic | preservative, a fungicide, a reaction catalyst, etc.

  The aqueous clear coating composition preferably contains 0.01 to 20% by mass of a viscosity modifier based on the resin solid mass. The amount of the viscosity modifier is more preferably 0.05 to 10% by mass, and further preferably 0.5 to 5% by mass with respect to the resin solid mass.

  Viscosity adjusting agents such as, for example, polyamide viscosity adjusting agents, urethane viscosity adjusting agents, polycarboxylic acid viscosity adjusting agents, cellulose viscosity adjusting agents, inorganic layered compound viscosity adjusting agents and aminoplast viscosity adjusting agents A regulator is mentioned.

Examples of the polyamide-based viscosity modifier include fatty acid amide, polyamide, acrylic amide, long-chain polyaminoamide, aminoamide, and salts thereof (for example, phosphate).
Examples of urethane-based viscosity modifiers include polyether polyol-based urethane prepolymers and urethane-modified polyether-type viscosity modifiers.
Examples of the polycarboxylic acid viscosity modifier include high molecular weight polycarboxylic acid, high molecular weight unsaturated acid polycarboxylic acid, and partial amidated products thereof.
Examples of the cellulose-based viscosity modifier include cellulose-based viscosity modifiers such as hydroxyethyl cellulose and hydroxypropyl cellulose.
Examples of the inorganic layered compound-based viscosity modifier include layered compounds such as montmorillonite, bentonite, and clay.
Examples of aminoplast-based viscosity modifiers include hydrophobically modified ethoxylate aminoplast-based associative viscosity modifiers.

  Only 1 type may be used for the said viscosity modifier, and it may use 2 or more types together.

A commercially available product may be used as the viscosity modifier. Examples of commercially available viscosity modifiers include:
Dispalon AQ-600 (manufactured by Enomoto Kasei Co., Ltd.), Anti-Terra-U (manufactured by BYK Chemie), Disperbyk-101, Disperbyk-130 (manufactured by BYK Chemie), etc., which are polyamide-based viscosity modifiers;
Anti-Terra-203, 204 (BYK Chemie), Disperbyk-107 (BYK Chemie), BYK-P104, BYK-P105 (BYK Chemie), Primal ASE, which are polycarboxylic acid-based viscosity modifiers -60, Primal TT-615 (manufactured by Dow Chemical), Biscalex HV-30 (manufactured by BASF), SN thickener 617, SN thickener 618, SN thickener 630, SN thickener 634, SN thickener 636 (manufactured by San Nopco) Such;
Urethane viscosity modifiers, Adecanol UH-814N, UH-752, UH-750, UH-420, UH-462 (made by ADEKA), SN thickener 621N, SN thickener 623N (made by San Nopco), RHEOLATE 244, 278 (Made by Elementis) etc .;
HEC Daicel SP600N (manufactured by Daicel Finechem), which is a cellulose-based viscosity modifier;
BENTONE HD (manufactured by Elementis Co., Ltd.), which is a layered compound type viscosity modifier;
Optiflo H600VF (manufactured by BYK Chemie), which is an aminoplast viscosity modifier;
Is mentioned.

  The viscosity modifier preferably contains one or more of a polycarboxylic acid viscosity modifier and a urethane viscosity modifier. A viscosity modifier containing a polycarboxylic acid viscosity modifier is more preferred. When the viscosity modifier includes a polycarboxylic acid viscosity modifier, it is more preferable to use ammonia as the neutralizer. In the case where the viscosity modifier contains a polycarboxylic acid-based viscosity modifier, by using ammonia as a neutralizing agent, the gel fraction (extracted insoluble in the organic solvent of the dried coating film, measured according to JIS K 6696) There is an advantage that the mass fraction of the minute) can be maintained in a favorable range.

  The aqueous clear coating composition is excellent in coating properties such as toughness and weather resistance by including the branched organopolysiloxane (A1) having a weight average molecular weight in the range of 5,000 to 100,000. A coating film can be formed. Moreover, the silicone resin emulsion in which the silicone resin containing the branched organopolysiloxane (A1) prepared by the above method is dispersed has excellent storage stability. Therefore, the obtained aqueous clear coating composition also has an advantage of excellent storage stability. And the said water-based clear coating composition has the advantage that the clear coating film which has the further outstanding weather resistance can be formed by containing the said inorganic oxide microparticles | fine-particles (D). The water-based clear coating composition has a characteristic that it has visible light permeability and excellent clear performance, but also has good ultraviolet blocking properties. Therefore, there is also an advantage that UV degradation of the coating film and the substrate existing in the lower layer of the clear coating film can be prevented.

  Further, the aqueous clear coating composition contains a branched organopolysiloxane (A1) having a weight average molecular weight in the range of 5,000 to 100,000 and a weight average molecular weight in the range of 1,000 to 30,000. When both of the linear organopolysiloxane (A2) are included, there is an advantage that a coating film excellent in good water resistance and chemical resistance can be formed. This is considered because the curing reactivity at the time of coating film formation is improved by including both components (A1) and (A2) in a specific range amount.

  The following examples further illustrate the present invention, but the present invention is not limited thereto. In the examples, “parts” and “%” are based on mass unless otherwise specified.

Production Example 1-1
Production of Silicone Resin Emulsion (S-1) In a stainless steel container, 25 parts by mass of Latem PD-104 (manufactured by Kao Corporation, anionic emulsifier; component content: 20% by mass) as an emulsifier (C-1) and 152 ion-exchanged water SR-2400 (manufactured by Dow Corning Toray Co., Ltd., branched organopolysiloxane; weight average molecular weight: 20,000, viscosity: 15 mPa · s, solid content concentration while adding mass parts and stirring as a silicone resin (A1-1) : 50 mass%, organic solvent (B-1): 200 mass parts of toluene) was added, and it stirred for 15 minutes at 1,500 rpm using the disper (total amount 377 mass parts, solid content 105 mass parts).
Subsequently, SN7777 (manufactured by San Nopco, defoaming agent) 0.057 parts by mass was added, and then treated with a high pressure homogenizer H20-H2 (manufactured by Sanwa Engineering Co., Ltd.) at 35 MPa, and 377 masses of the emulsified mixture. Got a part.
Further, the emulsion was heated to 55 ° C., desolvated under reduced pressure, the organic solvent (B-1) was distilled off together with water, and 247 parts by mass of the silicone resin emulsion (S-1) (solid content concentration: 42 mass). %).
The average particle diameter of the obtained silicone resin emulsion (S-1) was 345 nm.

Production Example 1-2
Manufacture of silicone resin emulsion (S-2) In a stainless steel container, 180 parts by mass of silicone resin (A1-1) and XC96-723 (momentive performance materials, linear) as silicone resin (A2-1) 10 parts by mass of organopolysiloxane; weight average molecular weight: 2,200, viscosity of 30 mPa · s, solid content concentration: 100% by mass) were mixed. The viscosity of the obtained mixture was 17 mPa · s.
In a separate container, 25 parts by weight of anionic emulsifier (C-1) and 152 parts by weight of ion-exchanged water were added, 190 parts by weight of the above mixture was added while stirring, and the mixture was stirred at 1,500 rpm for 15 minutes using a disper ( (Total amount 367 parts by mass, solid content 105 parts by mass).
Then, after adding 0.057 mass part of SN-777 (the Sannopco company make, antifoamer), it processed with 35 Mpa using the high voltage | pressure homogenizer H20-H2 (made by Sanwa Engineering Co., Ltd.), and 367 mass of emulsion mixture Got a part.
Further, the emulsion was heated to 55 ° C., desolvated under reduced pressure, the organic solvent (B-1) was distilled off together with water, and 247 parts by mass of the silicone resin emulsion (S-2) (solid content concentration: 42 mass). %).
The average particle diameter of the obtained silicone resin emulsion (S-2) was 350 nm.

Production Example 1-3
Production of Silicone Resin Emulsion (S-3) 120 parts by mass of silicone resin (A1-1) and 40 parts by mass of silicone resin (A2-1) were mixed in a stainless steel container. The viscosity of the obtained mixture was 22 mPa · s.
In a separate container, 25 parts by mass of an anionic emulsifier (C-1) and 152 parts by mass of ion-exchanged water were added, 160 parts by mass of the mixture was added while stirring, and the mixture was stirred at 1,500 rpm for 15 minutes using a disper ( (Total amount 337 parts by mass, solid content 105 parts by mass).
Subsequently, SN777 (manufactured by San Nopco, defoaming agent) 0.057 parts by mass was added, and then treated with 35 MPa using a high-pressure homogenizer H20-H2 (manufactured by Sanwa Engineering Co., Ltd.), and 337 masses of the emulsified mixture. Got a part.
Further, the emulsion was heated to 55 ° C., desolvated under reduced pressure, the organic solvent (B-1) was distilled off together with water, and 247 parts by mass of the silicone resin emulsion (S-3) (solid content concentration: 42 mass). %).
The average particle diameter of the obtained silicone resin emulsion (S-3) was 360 nm.

Production Example 1-4
Production of Silicone Resin Emulsion (S-4) 80 parts by mass of silicone resin (A1-1) and 60 parts by mass of silicone resin (A2-1) were mixed in a stainless steel container. The viscosity of the obtained mixture was 26 mPa · s.
In a separate container, 25 parts by weight of anionic emulsifier (C-1) and 152 parts by weight of ion-exchanged water were added, 140 parts by weight of the above mixture was added while stirring, and the mixture was stirred at 1,500 rpm for 15 minutes using a disper ( (Total amount 317 parts by mass, solid content 105 parts by mass).
Subsequently, SN777 (manufactured by San Nopco, defoaming agent) 0.057 parts by mass was added, and then treated with 35 MPa using a high-pressure homogenizer H20-H2 (manufactured by Sanwa Engineering Co., Ltd.), and 317 masses of the emulsified mixture. Got a part.
Further, the emulsion was heated to 55 ° C., desolvated under reduced pressure, the organic solvent (B-1) was distilled off together with water, and 247 parts by mass of the silicone resin emulsion (S-4) (solid content concentration: 42 mass). %).
The average particle diameter of the obtained silicone resin emulsion (S-4) was 350 nm.

Production Example 1-5
Production of Silicone Resin Emulsion (S-5) 40 parts by mass of silicone resin (A1-1) and 80 parts by mass of silicone resin (A2-1) were mixed in a stainless steel container. The viscosity of the obtained mixture was 28 mPa · s.
In a separate container, 25 parts by mass of an anionic emulsifier (C-1) and 152 parts by mass of ion-exchanged water were added, 120 parts by mass of the above mixture was added while stirring, and the mixture was stirred at 1,500 rpm for 15 minutes using a disper ( 297 parts by mass in total, 105 parts by mass of solid content).
Then, after adding 0.057 mass part of SN-777 (the Sannopco company make, an antifoamer), it processed by 35 Mpa using the high pressure homogenizer H20-H2 (made by Sanwa Engineering Co., Ltd.), and 297 masses of the emulsion mixture. Got a part.
Further, the emulsion was heated to 55 ° C., desolvated under reduced pressure, the organic solvent (B-1) was distilled off together with water, and 247 parts by mass of the silicone resin emulsion (S-5) (solid content concentration: 42 amount) %).
The average particle diameter of the obtained silicone resin emulsion (S-5) was 355 nm.

Production Example 1-6
Production of Silicone Resin Emulsion (S-6) To a stainless steel container, 25 parts by mass of anionic emulsifier (C-1) and 122 parts by mass of ion-exchanged water are added, and 100 parts by mass of silicone resin (A2-1) is added with stirring. And stirred for 15 minutes at 1,500 rpm using a disper (total amount 247 parts by mass, solid content 105 parts by mass).
Next, after adding 0.057 parts by mass of SN-777 (manufactured by San Nopco, defoaming agent), it was treated at 35 MPa using a high-pressure homogenizer H20-H2 (manufactured by Sanwa Engineering Co., Ltd.), and a silicone resin emulsion (S -6) 247 parts by mass (solid content concentration: 42% by mass) was obtained.
The average particle diameter of the obtained silicone resin emulsion (S-6) was 360 nm.

Production Example 1-7
Production of Silicone Resin Emulsion (S-7) In a stainless steel container equipped with a desolvation device, 140 parts by mass of silicone resin (A1-1), 30 parts by mass of silicone resin (A2-1) and organic solvent (B-2) 15 parts by mass of Cactus solvent P-150 (manufactured by JXTG Energy) was mixed to obtain 185 parts by mass of a mixture. The obtained mixture was heated to 75 ° C., and the solvent was removed under reduced pressure to distill off 70 parts by mass of the organic solvent (B-1). The viscosity of the mixture was 1,800 mPa · s.
In another stainless steel container, 25 parts by mass of emulsifier (C-1) and 107 parts by mass of ion-exchanged water were added, 115 parts by mass of the above mixture was added with stirring, and the mixture was stirred at 1,500 rpm for 15 minutes using a disper ( Total amount 247 parts by mass, solid content 105 parts by mass).
Subsequently, after adding 0.057 mass part of SN-777, it processed by 35 Mpa using the high voltage | pressure homogenizer H20-H2 (made by Sanwa Engineering Co., Ltd.), and 247 mass parts (solid) of the silicone resin emulsion (S-7) Partial concentration: 42% by mass).
The average particle diameter of the obtained silicone resin emulsion (S-7) was 1,800 nm. Moreover, when this silicone resin emulsion (S-7) was allowed to stand for 1 day, separation and precipitation occurred.

Production Example 1-8
Production of Silicone Resin Emulsion (S-8) In a stainless steel container equipped with a desolvation device, 140 parts by mass of silicone resin (A1-1), 30 parts by mass of silicone resin (A2-1) and organic solvent (b-1) 70 parts by mass of butoxypropanol was mixed to obtain 240 parts by mass of a mixture. The obtained mixture was heated to 75 ° C., desolvated under reduced pressure, 70 parts by mass of the organic solvent (B-1) was distilled off, and 170 parts by mass of a resin mixture containing only (b-1) as the organic solvent. Got. The viscosity of the mixture was 20 mPa · s.
To another stainless steel container, 25 parts by mass of emulsifier (C-1) and 152 parts by mass of ion-exchanged water were added, 170 parts by mass of the mixture was added while stirring, and the mixture was stirred at 1,500 rpm for 15 minutes using a disper ( Total amount 347 parts by mass, solid content 105 parts by mass).
Subsequently, after adding 0.057 mass part of SN-777, it processed by 35 Mpa using the high voltage | pressure homogenizer H20-H2 (made by Sanwa Engineering Co., Ltd.), and 347 mass parts (solid content 105 mass parts) of silicone resin emulsions. Obtained.
Further, the emulsion was heated to 55 ° C., desolvated under reduced pressure, 100 parts by mass of water and the organic solvent (b-2) were distilled off, and 247 parts by mass of the silicone resin emulsion (S-8). (Solid content concentration: 42 mass%) was obtained.
Although the average particle diameter of the obtained silicone resin emulsion (S-8) was 320 nm, when it was allowed to stand for 30 days, separation and precipitation occurred.

Production Example 1-9
Manufacture of silicone resin emulsion (S-9) To a stainless steel container equipped with a disper, 25 parts by weight of emulsifier (C-1) and 93 parts by weight of ion exchange water are added and mixed in advance while stirring at 1,500 rpm. 170 parts by mass of a mixture of 140 parts by mass of silicone resin (A1-1) and 30 parts by mass of silicone resin (A2-1) were mixed and stirred for 15 minutes (total amount 288 parts by mass, solid content 105 parts by mass).
The average particle diameter of the obtained silicone resin emulsion (S-9) was 10,000 nm or more. Moreover, when this silicone resin emulsion (S-9) was allowed to stand for 1 day, separation and precipitation occurred.

In addition, R calculated | required from the weight average molecular weight measured by the gel permeation chromatograph HLC-8220GPC (made by Tosoh Corporation), and 29Si-NMR DPX400 (made by Bruker) for the m / n value of the said silicone resin (A1-1). ^When calculated from the composition ratio of ¹ SiO _3/2 and R ² ₂ SiO, m / n = 180/60.

  The viscosity of the mixture before the mechanical emulsification treatment containing the silicone resin (A) and the organic solvent (B) is as follows. : 60 rpm).

  The average particle size of the silicone resin emulsion was measured using an electrophoretic light scattering photometer ELSZ (manufactured by Otsuka Electronics Co., Ltd.) by diluting the aqueous dispersion with ion-exchanged water so that the signal level was appropriate.

  The residual amount of toluene (B-1) contained in the silicone resin obtained by the above production example was measured using a gas chromatograph GC-2014 (manufactured by Shimadzu Corporation).

Production Example 2-1
Production of dispersion (d-11) of inorganic oxide fine particles (D-1 ) 100 parts by mass of FINEX-52W-LP2 (manufactured by Sakai Chemical Industry Co., Ltd.), which is a surface-coated zinc oxide, DISPERBYK2012 (manufactured by BYK Chemie, Polymer type polymer dispersant (non-volatile content 40%) 50 parts by weight, 176 parts by weight of ion exchange water and 14 parts by weight of butyl cellosolve are placed in a wet medium stirrer, and zirconia medium particles (average particle diameter 0.05 mm) are present The mixture was stirred for 30 minutes under wet conditions to obtain a dispersion (d-11) of inorganic oxide fine particles (D-1).
The average particle diameter (50% volume particle diameter D ₅₀ ) of the dispersion (d-11) of the inorganic oxide fine particles (D-1) was 290 nm.

Production Examples 2-2 to 4
Production of dispersions (d-12) to (d-14) of inorganic oxide fine particles (D-1) In the same manner as in Production Example 2-1, except that the wet medium stirring time was changed as shown in the following table. Dispersions (d-12) to (d-14) of inorganic oxide fine particles (D-1) were obtained.

Production Example 2-5
Manufacture of dispersion (d-21) of inorganic oxide fine particles (D-2) Surface coating treatment Instead of zinc oxide, except that it was changed to STR-100A-LP (made by Sakai Chemical Industry Co., Ltd.), which is titanium oxide. In the same manner as in Production Example 2-2, a dispersion (d-21) of inorganic oxide fine particles (D-2) was obtained.
The average particle diameter (D ₅₀ ) of the dispersion (d-21) of the inorganic oxide fine particles (D-2) was 110 nm.

The average particle diameter of the inorganic oxide fine particles (D) is 50% volume particle diameter (D ₅₀ ). The average particle diameter (D ₅₀ ) was measured using UPA-150 (a particle size distribution measuring device manufactured by Microtrack Bell).

Example 1
Preparation of aqueous clear paint composition 0.15 parts by mass of aqueous ammonia is added to 100 parts by mass of the silicone resin emulsion (S-2) obtained from Production Example (1-2), and then an alkali swelling thickener. 2 parts by weight of Primal ASE-60 (manufactured by Dow Chemical Co.) was added and mixed. Next, 14.6 parts by mass of the dispersion (d-11) of inorganic oxide fine particles (D-1) and 78.6 parts by mass of tap water are mixed, and further DIBUTYL TIN OXIDE (manufactured by Nitto Kasei Co., Ltd.) as a curing catalyst. Was added and mixed to obtain an aqueous clear coating composition.

Examples 2-16, Comparative Examples 1, 4-9
An aqueous clear coating composition was obtained in the same manner as in Example 1 except that the types and amounts of the silicone resin emulsion and the inorganic oxide fine particle dispersion were changed as shown in the following table.

Example 17
90 parts by mass of the silicone resin emulsion (S-1) obtained from the production example and 10 parts by mass of the silicone resin emulsion (S-6) were mixed, and 0.15 part by mass of aqueous ammonia was added and mixed. Next, 2 parts by mass of Primal ASE60 was added and mixed. Next, 14.6 parts by mass of the dispersion (d-11) of inorganic oxide fine particles (D-1) and 78.6 parts by mass of tap water are mixed, and further 1.23 parts by mass of DIBUTYL TIN OXIDE as a curing catalyst. In addition, mixing was performed to obtain an aqueous clear coating composition.

Comparative Examples 2 and 3
Instead of the dispersion (d-11) of inorganic oxide fine particles (D-1), TINUVIN 928 (manufactured by BASF, 2- (2H-benzotriazol-2-yl) -6- (1- Except that methyl-1-phenylethyl) -4- (1,1,3,3-tetramethylbutyl) phenol; component content: 100% by mass) is used in an amount of 4.3 parts by mass and 2.2 parts by mass, respectively. In the same manner as in Example 1, an aqueous clear coating composition was obtained.

Comparative Example 5
Acrylic resin emulsion Acrylic EX-41 (manufactured by Nippon Shokubai Co., Ltd., solid concentration: 43% by mass) as an acrylic resin emulsion is mixed with 100 parts by mass of 0.15 parts by mass of 25% aqueous ammonia, and the mixture is mixed with primal ASE -60 2 parts by mass were added and mixed. Next, 14.6 parts by mass of the dispersion (d-11) of inorganic oxide fine particles (D-1) and 78.6 parts by mass of tap water are mixed, and further, CS-12 (manufactured by Chisso Corporation) is used as a film forming aid. ) 1 part by mass was added and mixed to obtain an aqueous clear coating composition.

Comparative Example 9
An aqueous clear coating composition was obtained in the same manner as in Example 1 except that the dispersion (d-11) of inorganic oxide fine particles (D-1) was not used.

The organic solvent (B) and the emulsifier (C) used in each example and comparative example are as follows.
Organic solvent (B-1): Toluene (azeotropic point with water: 85 ° C., solubility in water: 0.047 g / 100 g H ₂ O)
Organic solvent (B-2): Cactus solvent P-150 (manufactured by JXTG Energy, azeotropic point with water: none, solubility in water: 0.04 g / 100 g H ₂ O)
Organic solvent (b-1): butoxypropanol (azeotropic point with water: none, solubility in water: 5.5 g / 100 g H ₂ O)
Emulsifier (C-1): Latem PD-104 (manufactured by Kao Corporation, anionic, component content: 20% by mass)

  The following evaluation was performed using the aqueous clear coating compositions obtained from the above Examples and Comparative Examples. The evaluation results are shown in the following table.

Evaluation of Paint Stability The silicone resin emulsions obtained in the above Examples and Comparative Examples were filtered through a 200 mesh filter and allowed to stand at 40 ° C. for 3 months. The state of the silicone resin emulsion after standing was visually observed, and the coating stability was evaluated according to the following criteria.
○: Separation / sedimentation does not occur ×: Separation / sedimentation occurs

Paint film appearance (initial paint film appearance after painting)
Using a doctor blade (2 mil), the dry film thickness of the aqueous clear coating composition obtained in Examples and Comparative Examples is 10 μm on a quartz glass plate (a substrate that does not absorb in the ultraviolet region). And then dried at 160 ° C. for 10 minutes to obtain an evaluation test plate. The coating film appearance of the obtained evaluation test plate was visually evaluated according to the following criteria.
○: The coating film is transparent and no aggregates are observed Δ: Slight white turbidity due to inorganic oxide fine particles and / or slight aggregation of inorganic oxide fine particles are recognized in the coating film ×: Inorganic in coating film Overall cloudiness due to fine oxide particles and / or numerous aggregates of fine inorganic oxide particles are observed

Measurement of UV transmittance and visible light transmittance (before accelerated weathering test)
Using a doctor blade (2 mil), the dry film thickness of the aqueous clear coating composition obtained in Examples and Comparative Examples is 10 μm on a quartz glass plate (a substrate that does not absorb in the ultraviolet region). And then dried at 160 ° C. for 10 minutes to obtain an evaluation test plate.
The light transmittance at a wavelength of 280 nm to 780 nm of the evaluation test plate obtained above was measured using an ultraviolet-visible spectrophotometer (UV-3100, manufactured by Shimadzu Corporation).
The light transmittance (%) in the wavelength range of 280 to 380 nm was determined as the ultraviolet transmittance (%). Specifically, a transmission spectrum from a wavelength of 280 nm to 380 nm was measured, and an ultraviolet light transmittance was determined from the integrated value. More specifically, the light transmittance in the wavelength range of 280 to 380 nm was measured at 51 points every 2 nm, and the average value thereof was defined as the ultraviolet transmittance.
As the visible light transmittance (%), an average value of light transmittance (%) in a wavelength range of 380 to 780 nm was determined. Specifically, the transmission spectrum was measured every 2 nm in the wavelength range of 380 nm to 780 nm, and the visible light transmittance was determined from the integral value.

Weather resistance evaluation (UV transmittance after accelerated weather resistance test)
The evaluation test plate obtained above was subjected to an accelerated weather resistance test using a sunshine weatherometer (manufactured by Suga Test Instruments Co., Ltd.) (operating conditions: conforming to JIS K 5400, operating time: 10,000 hours).
The ultraviolet transmittance (%) of the evaluation test plate after the accelerated weather resistance test was measured by the same method as described above.

Weather resistance evaluation (appearance evaluation of paint film after accelerated weather resistance test)
The evaluation test plate obtained above was subjected to an accelerated weather resistance test using a sunshine weatherometer (manufactured by Suga Test Instruments Co., Ltd.) (operating conditions: conforming to JIS K 5400, operating time: 10,000 hours).
The appearance of the coating film on the evaluation test plate after the accelerated weather resistance test was visually evaluated according to the following criteria.
○: No change ○ △: Slight whitening is observed in the coating film △: Whitening is observed in a part of the coating film △: Whitening and / or cracking is observed in the coating film ×: Significant whitening and / Or peeling is observed

The aqueous clear coating compositions prepared in the examples are all excellent in coating stability, and the obtained coating film has high visible light transmittance and low ultraviolet transmittance, and further after the accelerated weathering test. It was confirmed that the ultraviolet transmittance was also sufficiently low. Furthermore, it was confirmed that a good coating film appearance was maintained even after the accelerated weathering test.
Comparative Example 1 is an example in which the average particle diameter of the inorganic oxide fine particles (D) exceeds 300 nm. It was confirmed that the aqueous clear coating composition prepared in this example was inferior in coating stability, initial coating film appearance and coating film appearance after the accelerated weathering test.
Comparative Examples 2 and 3 are examples in which the inorganic oxide fine particles (D) are not included, and an organic ultraviolet absorber is included instead. In these examples, it was confirmed that the ultraviolet transmittance before the accelerated weathering test was sufficiently low, while the ultraviolet transmittance after the accelerated weathering test was high, and the coating film appearance was also deteriorated.
Comparative Example 4 is an example in which the silicone resin (A) does not contain the branched organopolysiloxane (A1). In this example, it was confirmed that the coating film appearance after the accelerated weathering test was inferior.
Comparative Example 5 is an example using an acrylic resin emulsion instead of the silicone resin emulsion. In this example, it was confirmed that the coating film appearance after the accelerated weathering test was inferior.
Comparative Example 6 is an example in which the organic solvent was removed before the emulsification step in the preparation of the silicone resin emulsion. In this example, it was confirmed that the obtained silicone resin emulsion was inferior in stability and paint stability was also inferior.
Comparative Example 7 is an example in which the organic solvent contained in the preparation of the silicone resin emulsion is a solvent other than the organic solvent (B). In this example, it was confirmed that the obtained silicone resin emulsion was inferior in stability and paint stability was also inferior.
Comparative Example 8 is an example in which mechanical emulsification is not performed in the preparation of the silicone resin emulsion. In this example, it was confirmed that the average particle diameter of the resulting silicone resin emulsion was very large, the stability was poor, and the paint stability was also poor.
Comparative Example 9 is an example that does not contain inorganic oxide fine particles (D) and does not contain an organic ultraviolet absorber. In this example, it was confirmed that the ultraviolet transmittance before the accelerated weathering test and the ultraviolet transmittance after the accelerated weathering test were high, and the appearance of the coating film after the accelerated weathering test was deteriorated.

  According to the production method of the present invention, it is possible to produce a silicone resin emulsion containing a branched organopolysiloxane (A1) that is fine and excellent in storage stability. By the production method of the present invention, an aqueous clear coating composition containing a silicone resin emulsion and inorganic oxide fine particles can be produced. The water-based clear coating composition has an advantage that it can maintain the ultraviolet blocking property and the visible light transparency for a long period of time. Furthermore, there is an advantage that an aqueous clear coating composition can be prepared without using an organic ultraviolet absorber.

Claims (12)

A method for preparing an aqueous clear coating composition comprising a silicone resin emulsion comprising the following steps:
The mixture of the silicone resin (A) and the organic solvent (B) and the mixture of the emulsifier (C) and the aqueous medium are mechanically emulsified, or the silicone resin (A), the organic solvent (B) and the emulsifier ( An emulsification step of mechanically emulsifying the mixture of C) and an aqueous medium to obtain an emulsified mixture;
The organic solvent (B) is at least partially removed from the resulting emulsified mixture to obtain a silicone resin emulsion, and the resulting silicone resin emulsion and inorganic oxide fine particles (D) are mixed. Preparing a water-based clear coating composition,
Including
The silicone resin (A), a branched organopolysiloxane weight average molecular weight in the range of 5,000 to 100,000 (A1), and, within the weight average molecular weight of 1,000 to 30,000 A linear organopolysiloxane (A2),
The mass ratio of the branched organopolysiloxane (A1) and the linear organopolysiloxane (A2) contained in the coating composition is within the range of (A1) :( A2) = 98: 2 to 40:60. And
The organic solvent (B) is an organic solvent that is mixed with the silicone resin (A) at an arbitrary ratio and has a solubility in water of 1 g / 100 gH ₂ O or less, or a mixture thereof, and at least the organic solvent One type is conditional on having an azeotropic point with water,
The mass ratio (A) :( B) of the silicone resin (A) and the organic solvent (B) in the mixture before the mechanical emulsification treatment containing the silicone resin (A) and the organic solvent (B) is (A): (B) = 1: 2 to 1: 0.2, and the mass ratio (A) :( B) of the silicone resin (A) and the organic solvent (B) contained in the emulsion mixture is: , (A) :( B) = 1: 2 to 1: 0.2
The inorganic oxide fine particles (D) have an average particle diameter in the range of 20 to 300 nm.
Method. A method for preparing an aqueous clear coating composition comprising a silicone resin emulsion comprising the following steps:
The mixture of the silicone resin (A) and the organic solvent (B) and the mixture of the emulsifier (C) and the aqueous medium are mechanically emulsified, or the silicone resin (A), the organic solvent (B) and the emulsifier ( An emulsification step of mechanically emulsifying the mixture of C) and an aqueous medium to obtain an emulsified mixture;
The organic solvent (B) is at least partially removed from the obtained emulsified mixture to obtain a silicone resin emulsion, and the resulting silicone resin emulsion, inorganic oxide fine particles (D), and A step of preparing an aqueous clear coating composition by mixing a preliminarily prepared emulsion containing a linear organopolysiloxane (A2) having a weight average molecular weight in the range of 1,000 to 30,000,
Including
The silicone resin (A) includes a branched organopolysiloxane (A1) having a weight average molecular weight in the range of 5,000 to 100,000.
The mass ratio of the branched organopolysiloxane (A1) and the linear organopolysiloxane (A2) contained in the aqueous clear coating composition is (A1) :( A2) = 98: 2 to 40:60. Is in range,
The organic solvent (B) is an organic solvent that is mixed with the silicone resin (A) at an arbitrary ratio and has a solubility in water of 1 g / 100 gH ₂ O or less, or a mixture thereof, and at least the organic solvent One type is conditional on having an azeotropic point with water,
The mass ratio (A) :( B) of the silicone resin (A) and the organic solvent (B) in the mixture before the mechanical emulsification treatment containing the silicone resin (A) and the organic solvent (B) is (A): (B) = 1: 2 to 1: 0.2, and the mass ratio (A) :( B) of the silicone resin (A) and the organic solvent (B) contained in the emulsion mixture is: , (A) :( B) = 1: 2 to 1: 0.2
The inorganic oxide fine particles (D) have an average particle diameter in the range of 20 to 300 nm.
Method. The method according to claim 1 or 2 , wherein the organic solvent (B) includes at least one selected from the group consisting of benzene, toluene, xylene, hexane, and cyclohexane. Wherein the emulsifier (C) comprises an anionic surfactant, the method according to any one of claims 1-3. The mechanical emulsification process in the emulsification step is one or more selected from the group consisting of a pressure shear stirring process, an opposing collision process, a collision stirring process, and a high-speed rotation stirring process.
The method according to any one of claims 1-4. The silicone resin emulsion has an average particle diameter in the range of 100 to 500 nm, The method according to any one of claims 1-5. The amount of the inorganic oxide fine particles (D) contained in the aqueous clear coating composition is based on 100 parts by mass of the total resin solid content of the branched organopolysiloxane (A1) and the linear organopolysiloxane (A2). 3 to 30 parts by mass,
The method according to any one of claims 1-6. The branched organopolysiloxane (A1) has the following structure [R ¹ SiO _3/2 ] _m [R ² ₂ SiO] _n.
Wherein R ¹ and R ² are each independently a hydroxyl group, a linear hydrocarbon group having 1 to 6 carbon atoms, or an aromatic hydrocarbon group having 5 to 7 carbon atoms. ,
m is in the range of 1 to 1,000, n is in the range of 1 to 100, and m + n is in the range of 1 to 1,000. )
A branched organopolysiloxane (A1) having
The linear organopolysiloxane (A2) has the following structure R ^3- [R ⁴ ₂ SiO] _x -R ^5.
(In the formula, R ³ is a hydroxyl group, a linear hydrocarbon group having 1 to 6 carbon atoms, or an aromatic hydrocarbon group having 5 to 7 carbon atoms,
R ⁴ is a linear hydrocarbon group having 1 to 6 carbon atoms, or an aromatic hydrocarbon group having 5 to 7 carbon atoms,
R ⁵ is hydrogen, a linear hydrocarbon group having 1 to 6 carbon atoms, or an aromatic hydrocarbon group having 5 to 7 carbon atoms,
x is in the range of 1 to 400. )
A linear organopolysiloxane (A2) having
The method according to any one of claims 1-7. The viscosity of the mixture of the silicone resin (A) and the organic solvent (B) in the mixture before the mechanical emulsification treatment containing the silicone resin (A) and the organic solvent (B) is in the range of 10 to 1,500 mPa · s. in a method according to any one of claims 1-8. The inorganic oxide fine particles (D) include at least one selected from the group consisting of silicon oxide, titanium oxide, zinc oxide, tin oxide, cerium oxide, antimony oxide, and double oxides thereof.
The method according to any one of claims 1-9. The inorganic oxide fine particles (D) are inorganic oxide fine particles obtained by a step of stirring using medium particles having an average particle diameter of 0.01 to 0.1 mm.
The method according to any one of claims 1-10. An aqueous clear coating composition comprising a silicone resin emulsion and inorganic oxide fine particles (D),
The silicone resin emulsion has a branched organopolysiloxane (A1) having a weight average molecular weight in the range of 5,000 to 100,000, and
An emulsion of a silicone resin (A) containing a linear organopolysiloxane (A2) having a weight average molecular weight in the range of 1,000 to 30,000,
The mass ratio of the branched organopolysiloxane (A1) and the linear organopolysiloxane (A2) contained in the aqueous clear coating composition is (A1) :( A2) = 98: 2 to 40:60. Is in range,
The inorganic oxide fine particles (D) have an average particle diameter in the range of 20 to 300 nm.
Water-based clear coating composition.