JP2015199881A - Method of producing fluorine resin-containing aqueous dispersion liquid - Google Patents

Abstract

An object of the present invention is to provide a method for producing a fluororesin aqueous dispersion capable of forming a coating film having high hardness and excellent scratch resistance.
A fluorine-containing resin comprising a step (x) of producing a fluorine-containing resin aqueous dispersion containing a fluorine resin by emulsion polymerization, and a step (y) of bringing the fluorine-containing resin aqueous dispersion into contact with a synthetic adsorbent. A method for producing an aqueous dispersion.
[Selection figure] None

Description

  The present invention relates to a method for producing an aqueous fluororesin dispersion.

  Conventionally, concrete products for building materials, outer wall materials (metal siding materials, etc.), architectural glass, guard rails, civil engineering members such as bridges, tanks, plants, etc. are used by being exposed to the external environment. The surface is coated with a fluorine-containing resin paint excellent in weather resistance, chemical resistance (acid rain resistance), and warm water resistance.

As the fluorine-containing resin paint, for example, a paint based on a fluorine-containing resin aqueous dispersion containing a fluorine resin is known. Specifically, the following have been proposed.
(1) A paint containing, as a paint base, an aqueous fluorine-containing resin dispersion in which a fluorine-containing copolymer having a polymer unit based on a macromonomer having a hydrophilic site as an essential constituent is dispersed in water (Patent Document 1) .
(2) A paint-based fluororesin aqueous dispersion in which a fluorocopolymer containing polymer units based on fluoroolefin, polymer units based on propylene, polymer units based on ethylene, polymer units based on butylene is dispersed in water (Patent Document 2)
(3) A paint comprising an aqueous solution or dispersion of a fluororesin emulsion and an acrylic copolymer (Patent Document 3).

JP-A-2-225550 JP 2001-164173 A Japanese Patent Laid-Open No. 2004-250637

  However, in paints using fluororesin aqueous dispersions as in Patent Documents 1 to 3, low molecular weight substances are produced when the dispersions are produced by emulsion polymerization, so that the hardness of the formed coating film decreases. The scratch resistance may be lowered.

  An object of the present invention is to provide a method for producing an aqueous fluororesin dispersion capable of forming a coating film having high hardness and excellent scratch resistance.

The method for producing an aqueous fluororesin dispersion of the present invention is a method having the following step (x) and step (y).
(X) The process of manufacturing the fluororesin aqueous dispersion containing a fluororesin by emulsion polymerization.
(Y) A step of bringing the aqueous fluororesin dispersion into contact with a synthetic adsorbent.

  According to the method for producing an aqueous fluororesin dispersion of the present invention, an aqueous fluororesin dispersion capable of forming a coating film having high hardness and excellent scratch resistance can be obtained.

The following definitions of terms apply throughout this specification and the claims.
The “fluorinated resin aqueous dispersion” means a dispersion of a fluorine-containing resin in an aqueous medium.
“Structural unit” means a unit derived from a monomer formed by polymerization of the monomer. It may be a unit directly formed by a polymerization reaction, or may be a unit in which a part of the unit is converted into another structure by treating the polymer.
“Monomer” means a compound having a radically polymerizable unsaturated group.
The “crosslinkable group” means a group capable of forming a crosslinked structure by reacting with a curing agent, or a group capable of forming a crosslinked structure by reacting with each other.
The “macromonomer” means a low molecular weight polymer or oligomer having a radical polymerizable unsaturated group at one end.
The “hydrophilic part” means a part having a hydrophilic group, a part having a hydrophilic bond, or a part composed of a combination thereof.
The “synthetic adsorbent” means a molded body made of a spherical crosslinkable polymer having a porous structure.
The “low molecular weight body” means an oligomer having a molecular weight reduced by radicals generated during polymerization moving onto the main chain to break the main chain.
The “curing agent” means a compound having two or more groups capable of reacting with the “crosslinkable group” and capable of forming a crosslinked structure by reacting with the crosslinkable group.

<Method for producing fluororesin aqueous dispersion>
The method for producing an aqueous fluororesin dispersion of the present invention includes the following step (x) and step (y).
(X) The process of manufacturing the fluororesin aqueous dispersion containing a fluororesin by emulsion polymerization.
(Y) A step of bringing the aqueous fluororesin dispersion into contact with a synthetic adsorbent.

[Step (x)]
In the step (x), a fluororesin aqueous dispersion containing a fluororesin is obtained by performing emulsion polymerization. Specifically, a monomer for producing a fluororesin is emulsion polymerized in the presence of an aqueous medium and a polymerization initiator to obtain an aqueous fluororesin dispersion containing the fluororesin.

(Fluorine resin)
The fluororesin contained in the fluororesin aqueous dispersion produced in the step (x) is not particularly limited, but the fluorocopolymer (I) described later, a structural unit based on the fluoromonomer, and an olefin as necessary. A fluorine-containing polymer (provided that the fluorine-containing monomer is at least one selected from the group consisting of tetrafluoroethylene, vinylidene fluoride, hexafluoropropylene and perfluoroalkyl vinyl ether). And fluorine copolymer (I) are excluded.).
As the fluororesin, the structural unit (A) based on the following monomer (a) (hereinafter referred to as the structural unit (A) is used because it can form a coating film excellent in weather resistance, water resistance, chemical resistance, and heat resistance. And a structural unit (B) based on the following monomer (b) (hereinafter referred to as the structural unit (B)), and the following monomer (c) The fluorine-containing copolymer (I) having a structural unit (C) based on
Monomer (a): fluoroolefin.
Monomer (b): A monomer having a crosslinkable group and having no fluorine atom.
Monomer (c): Monomer other than monomer (a) and monomer (b).
That is, in the step (x), it is preferable to use a monomer mixture containing the monomer (a) and the monomer (b) and, if necessary, the monomer (c) for emulsion polymerization.

Monomer (a):
The monomer (a) is a fluoroolefin. A monomer (a) may be used individually by 1 type, and may use 2 or more types together.
A fluoroolefin is a compound in which one or more hydrogen atoms of an olefin hydrocarbon (general formula C _n H _2n ) are substituted with a fluorine atom. In the fluoroolefin, one or more hydrogen atoms not substituted with fluorine atoms may be substituted with chlorine atoms.
The number of fluorine atoms in the fluoroolefin is preferably 2 or more, more preferably 3 to 6, and even more preferably 3 or 4. When the number of fluorine atoms in the fluoroolefin is 2 or more, it is easy to form a coating film excellent in weather resistance.

  Examples of the fluoroolefin include fluoroolefins having 2 to 4 carbon atoms such as vinylidene fluoride, trifluoroethylene, chlorotrifluoroethylene, tetrafluoroethylene, pentafluoropropylene, and hexafluoropropylene. Of these, chlorotrifluoroethylene and tetrafluoroethylene are preferable from the viewpoint of weather resistance, and chlorotrifluoroethylene is more preferable.

Monomer (b):
The monomer (b) is a monomer having a crosslinkable group and not having a fluorine atom. A monomer (b) may be used individually by 1 type, and may use 2 or more types together.
The crosslinkable group is not particularly limited, and examples thereof include a hydroxyl group, an alkoxysilyl group, a carboxy group, an amino group, an isocyanate group, an epoxy group, a vinyl group, an allyl group, a propenyl group, an isopropenyl group, an acryloyl group, and a methacryloyl group. These radically polymerizable unsaturated groups are mentioned.
As the crosslinkable group, a hydroxyl group, a carboxy group, an amino group, and an epoxy group are preferable, and a hydroxyl group is particularly preferable because the mechanical stability and chemical stability of the fluororesin aqueous dispersion are improved and the crosslinkability is also excellent. .

As the monomer (b) having a hydroxyl group, the following monomer (b1) and monomer (b2) are preferable.
Monomer (b1): A hydroxyl group-containing monomer represented by the following formula (b1).
Monomer (b2): a macromonomer having a hydrophilic site.
XYZ (b1)
However, X is a radically polymerizable unsaturated group, Y is an n-nonylene group or a cyclohexane-1,4-dimethylene group, and Z is a hydroxyl group.

  X has a radically polymerizable unsaturated group and, if necessary, a linking group that links the radically polymerizable unsaturated group and Y. Examples of the radical polymerizable unsaturated group include a vinyl group, an allyl group, a propenyl group, an isopropenyl group, an acryloyl group, and a methacryloyl group. The linking group is preferably an ether bond.

Examples of the monomer (b1) include the following.
_{(1) CH 2 = CHOCH 2} -cycloC 6 H 10 -CH 2 OH
_{(2) CH 2 = CHCH 2} OCH 2 -cycloC 6 H 10 -CH 2 OH
(3) CH ₂ = CHOC ₉ H ₁₈ OH
(4) CH ₂ = CHCH ₂ OC ₉ H ₁₈ OH

  The monomer (b1) is excellent in alternating copolymerization with the monomer (a), and the weather resistance of the coating film formed from the fluororesin aqueous dispersion is improved. What has is preferable.

  Examples of the monomer (b2) include compounds having a radically polymerizable unsaturated group at one end and having at least two structural units such as oxyethylene units in the main chain. The number of structural units is preferably 100 or less from the viewpoint of polymerizability, water resistance and the like.

  The hydrophilic group constituting the hydrophilic portion may be any of ionic, nonionic, amphoteric and a combination thereof. From the viewpoint of chemical stability of the fluororesin aqueous dispersion, a portion having a nonionic or amphoteric hydrophilic group and a portion having an ionic hydrophilic group are combined, or a portion having a hydrophilic group It is preferable to combine with a site having a hydrophilic bond.

Examples of the monomer (b2) include the following macromonomer.
Monomer (b21): a macromonomer having a polyether chain or a polyester chain in the main chain and a radically polymerizable unsaturated group at one end.
Monomer (b22): a macromonomer having a chain obtained by radical polymerization of a hydrophilic ethylenically unsaturated monomer and having a radical polymerizable unsaturated group (vinyloxy group or allyloxy group) at one end.

Examples of the monomer (b21) include the following.
(1) CH ₂ = CHO (CH ₂ ) _a [O (CH ₂ ) _b ] _c OR ¹
However, a is an integer of from 1 to 10, b is an integer of 1 to 4, c is an integer from 2 to 20, ^{R 1} is a hydrogen atom or an alkyl group having 1 to 10 carbon atoms (hereinafter, lower This will be referred to as an alkyl group.).
_{(2) CH 2 = CHCH 2} O (CH 2) d [O (CH 2) e] f OR 2
However, d is an integer from 1 to 10, e is an integer from 1 to 4, f is an integer of 2 to 20, ^{R 2} is a hydrogen atom or a lower alkyl group.
(3) CH ₂ = CHO (CH ₂ ) _g (OCH ₂ CH ₂ ) _h (OCH ₂ CH (CH ₃ )) _k OR ³
However, g is an integer of from 1 to 10, h is an integer of 2 to 20, k is an integer of 0 to 20, ^{R 3} is a hydrogen atom or a lower alkyl group, oxyethylene units and oxypropylene The unit may be arranged in either block or random form.
_{(4) CH 2 = CHCH 2} O (CH 2) m (OCH 2 CH 2) n (OCH 2 CH (CH 3)) p OR 4
However, m represents an integer of 1 to 10, n is an integer of 2 to 20, p is an integer of 0 to 20, ^{R 4} is a hydrogen atom or a lower alkyl group, oxyethylene units and oxypropylene The unit may be arranged in either block or random form.
_{(5) CH 2 = CHO (} CH 2) q O (CO (CH 2) r O) s H
However, q is an integer of 1-10, r is an integer of 1-10, and s is an integer of 1-30.

As the monomer (b21), one having a vinyl ether type structure at one end is preferable from the viewpoint of excellent copolymerizability with the monomer (a), and from the viewpoint of excellent hydrophilicity, Particularly preferred are those in which the ether chain portion is composed of oxyethylene units, or composed of oxyethylene units and oxypropylene units.
The monomer (b21) is preferably one having two or more oxyethylene units from the viewpoint that various properties such as stability are improved. If the number of oxyalkylene units is too large, the water resistance, weather resistance, etc. of the coating film may be reduced.

  The monomer (b21) can be produced by a method of polymerizing formaldehyde or diol with a vinyl ether or allyl ether having a hydroxyl group, or a method of ring-opening polymerization of a compound having an alkylene oxide or a lactone ring.

A monomer (b22) can be manufactured by the following method, for example.
A polymer having a condensable functional group can be produced by radical polymerization of an ethylenically unsaturated monomer having a hydrophilic group in the presence of an initiator having a condensable functional group and a chain transfer agent. A method in which a functional group is reacted with glycidyl vinyl ether, glycidyl allyl ether or the like to introduce a radical polymerizable unsaturated group at the terminal (Yamashita et al., Polym. Bull., 5.335 (1981)).

  Examples of the ethylenically unsaturated monomer having a hydrophilic group include acrylamide, methacrylamide, N-methylol acrylamide, N-methylol methacrylamide, 2-methoxyethyl acrylate, 2-methoxyethyl methacrylate, diacetone acrylamide, hydroxyethyl acrylate, hydroxy Examples include propyl acrylate, hydroxybutyl acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, hydroxybutyl methacrylate, polyhydric alcohol acrylate, polyhydric alcohol methacrylate, and vinylpyrrolidone.

Monomer (c):
The monomer (c) is a monomer other than the monomer (a) and the monomer (b).
The monomer (c) is not particularly limited, and examples thereof include olefins (ethylene, propylene, etc.), vinyl ethers (ethyl vinyl ether, propyl vinyl ether, butyl vinyl ether, cyclohexyl vinyl ether, etc.), vinyl esters (butanoic acid vinyl ester). , Octanoic acid vinyl ester, etc.), allyl ethers (ethyl allyl ether, etc.), allyl esters (ethyl allyl ester, etc.), aromatic vinyl compounds (styrene, vinyl toluene, etc.), (meth) acrylic acid esters (acrylic) Acid butyl, ethyl methacrylate, etc.).

As the monomer (c), olefins, vinyl ethers, vinyl esters, allyl ethers, and allyl esters are preferable.
As olefins, olefins having 2 to 10 carbon atoms are preferable.
As vinyl ethers, vinyl esters, allyl ethers, and allyl esters, those having a linear, branched or alicyclic alkyl group having 2 to 15 carbon atoms are preferred.

Composition unit ratio:
The ratio (A / B) of the number of moles of the structural unit (A) to the number of moles of the structural unit (B) is preferably 0.5 to 800, more preferably 1.5 to 300. When A / B is not less than the lower limit, the weather resistance and water resistance of the coating film become better. If A / B is not more than the above upper limit value, the dispersibility becomes better.
The ratio (C / (A + B)) of the number of moles of the structural unit (C) to the total number of moles of the structural unit (A) and the structural unit (B) is preferably 0.01-1.

(Aqueous medium)
Examples of the aqueous medium include water, a mixture of water and a water-soluble organic solvent, and the like.
Examples of the water-soluble organic solvent include tert-butanol, propylene glycol, dipropylene glycol, dipropylene glycol monomethyl ether, and tripropylene glycol.

When a water-soluble organic solvent is contained in the aqueous medium, the dispersibility of the monomer and the dispersibility of the generated fluororesin are improved, and the productivity is increased.
When an aqueous medium contains a water-soluble organic solvent, 1-40 mass parts is preferable with respect to 100 mass parts of water, and, as for content of a water-soluble organic solvent, 3-30 mass parts is more preferable.

(Polymerization initiator)
Examples of the polymerization initiator include known radical polymerization initiators. Specifically, for example, persulfate (ammonium persulfate, etc.), redox initiator (a combination of hydrogen peroxide and sodium hydrogen sulfite, etc.), and inorganic initiators (ferrous salts, silver nitrate, etc.) , A dibasic acid peroxide (disuccinic acid peroxide, diglutaric acid peroxide, etc.), an organic initiator (azobisbutyronitrile, etc.) and the like.

  The usage-amount of a polymerization initiator is not specifically limited, 0.01-5 mass parts is preferable with respect to 100 mass parts of total amounts of the monomer to be used.

(Chain transfer agent)
In the emulsion polymerization in the step (x), a chain transfer agent may be used. By using a chain transfer agent, the degree of polymerization (molecular weight) of the fluororesin can be adjusted. Moreover, the sum total of the density | concentration of the monomer in an aqueous medium increases.
Examples of the chain transfer agent include alkyl mercaptans (tert-dodecyl mercaptan, n-dodecyl mercaptan, stearyl mercaptan, etc.), aminoethanethiol, mercaptoethanol, 3-mercaptopropionic acid, 2-mercaptopropionic acid, thiomalic acid, thioglycol. Acid, 3,3′-dithio-dipropionic acid, 2-ethylhexyl thioglycolate, n-butyl thioglycolate, methoxybutyl thioglycolate, ethyl thioglycolate, 2,4-diphenyl-4-methyl-1- Examples include pentene and carbon tetrachloride.

  The usage-amount of a chain transfer agent is not specifically limited, 0-2 mass parts is preferable with respect to 100 mass parts of total amounts of the monomer to be used.

(emulsifier)
In the emulsion polymerization in the step (x), an emulsifier may be used, and an emulsifier may not be used as long as emulsion polymerization is possible without using an emulsifier.
Examples of the emulsifier include an anionic emulsifier, a nonionic emulsifier, and a cationic emulsifier. As the emulsifier, a nonionic emulsifier and an anionic emulsifier are preferable.

Nonionic emulsifiers include alkylphenol ethylene oxide adducts, higher alcohol ethylene oxide adducts, block copolymers of ethylene oxide and propylene oxide, and the like.
Examples of the anionic emulsifier include alkyl benzene sulfonate, alkyl naphthalene sulfonate, higher fatty acid salt, alkyl sulfate ester salt, alkyl ether sulfate ester salt, and phosphate ester salt.

  When using an emulsifier, the usage-amount of an emulsifier is the quantity used as 0.01-10 mass% with respect to 100 mass% of total amounts of a fluororesin aqueous dispersion.

The method of emulsion polymerization is not particularly limited, and examples thereof include batch polymerization, monomer dropping polymerization, emulsion monomer dropping polymerization, and the like.
The conditions for emulsion polymerization are not particularly limited. For example, the polymerization start temperature is preferably 0 to 100 ° C, more preferably 10 to 90 ° C. Further, the reaction pressure is preferably 0.1 to 10 MPa, and more preferably 0.2 to 5 MPa.
Examples of the reactor used for emulsion polymerization include a stainless steel autoclave with a stirrer (manufactured by Pressure Glass Industrial Co., Ltd.).

[Step (y)]
In the step (y), the fluororesin aqueous dispersion obtained in the step (x) is brought into contact with the synthetic adsorbent. Synthetic adsorbents have the property of adsorbing various organic substances from the solution due to physical interaction between the pore surface of the crosslinkable polymer and the adsorbed substance, so the fluororesin aqueous dispersion is brought into contact with the synthetic adsorbent. By doing so, the low molecular weight substance produced in the fluororesin aqueous dispersion is adsorbed and removed. Thereby, by using the fluororesin aqueous dispersion after contact with the synthetic adsorbent, a decrease in hardness due to the low molecular weight body is suppressed, and a coating film having excellent scratch resistance can be formed.

Examples of the method for bringing the fluororesin aqueous dispersion into contact with the synthetic adsorbent include the following methods.
-A method in which a synthetic adsorbent is introduced into an aqueous fluororesin dispersion and stirred (batch method).
-A method of passing a fluororesin aqueous dispersion through a packed tower packed with a synthetic adsorbent (continuous method).

The contact time between the fluororesin aqueous dispersion and the synthetic adsorbent is preferably 10 to 420 minutes, more preferably 10 to 360 minutes, and even more preferably 30 to 360 minutes. When the contact time is equal to or greater than the lower limit, the low molecular weight substance is easily removed sufficiently, and a coating film having high hardness and good scratch resistance is easily formed. If the contact time is less than or equal to the above upper limit value, the treatment can be performed efficiently in a short time.
Further, since the synthetic adsorbent is excellent in durability against acid and alkali conditions, a wide range of adsorption and elution conditions can be applied.

  The ratio of the amount of the synthetic adsorbent to the fluororesin aqueous dispersion (the mass of the synthetic adsorbent / the mass of the fluororesin aqueous dispersion) is 1/50 from the viewpoint of the hardness and scratch resistance of the coating film to be formed. ~ 1/3000 is preferable, 1/50 to 1/2000 is more preferable, and 1/100 to 1/2000 is more preferable.

(Synthetic adsorbent)
The synthetic adsorbent is not particularly limited, and examples thereof include aromatic synthetic adsorbents and methacrylic ester synthetic adsorbents. Of these, aromatic synthetic adsorbents are preferable and styrene-divinylbenzene synthetic adsorbents are more preferable from the viewpoints of the hardness and scratch resistance of the coating film.
A synthetic adsorbent may be used alone or in combination of two or more.

The specific surface area of the synthetic adsorbent is preferably from ^{300~900m 2 / g, 400~800m 2 /} g is more preferable. If the specific surface area of the synthetic adsorbent is not less than the lower limit, the adsorbate can be adsorbed without liberation. If the specific surface area of the synthetic adsorbent is not more than the above upper limit value, small molecules can be adsorbed efficiently.
The specific surface area of the synthetic adsorbent is measured by the BET method using nitrogen adsorption.

The shape of the synthetic adsorbent is preferably spherical.
The average particle size of the synthetic adsorbent is preferably 100 to 1600 μm, and more preferably 300 to 1300 μm. If the average particle diameter of the synthetic adsorbent is not less than the lower limit, low molecular weight impurities can be efficiently adsorbed. If the average particle size of the synthetic adsorbent is not more than the above upper limit value, it can be adsorbed efficiently without being clogged even if it is brought into contact with the aqueous fluororesin dispersion.
In addition, the average particle diameter of a synthetic adsorbent is measured by sieving in which sieves are stacked.

  Examples of commercially available synthetic adsorbents include trade names “HP20”, “HP30”, “SP800”, “SP205” manufactured by Mitsubishi Chemical Corporation, and trade names “PAD600”, “PAD900” manufactured by Purolite. It is done. Among them, from the viewpoint of the hardness and scratch resistance of the coating film, trade names “HP20”, “HP30”, “SP800”, “SP205” manufactured by Mitsubishi Chemical Corporation are preferable, and stability of the fluororesin aqueous dispersion is improved. From the viewpoint, “HP20” is more preferable.

[Addition of optional components]
In the production method of the present invention, a polymer other than the fluororesin, a colorant, a curing agent, and other additives may be added to the resulting fluororesin aqueous dispersion. These optional components may be added before step (y) or after step (y).

(Other polymers)
The other polymer is not particularly limited, and examples thereof include an acrylic polymer and a polyester polymer.
The addition amount of another polymer is not specifically limited, 0-200 mass parts is preferable with respect to 100 mass parts of fluororesins.

(Coloring agent)
Examples of the colorant include dyes, organic pigments, and inorganic pigments.
The addition amount of the colorant is not particularly limited, and is preferably 0 to 100 parts by mass with respect to 100 parts by mass of the total amount of the fluororesin aqueous dispersion.

(Curing agent)
In order to further improve the weather resistance, water resistance, chemical resistance, heat resistance and the like, a curing agent may be added to the fluororesin aqueous dispersion. The fluororesin aqueous dispersion obtained by the production method of the present invention may be a one-component paint or a two-component paint, but when a curing agent is included, a two-component paint is used. It is preferable to mix both solutions immediately before.

Examples of the curing agent include block isocyanate (hexamethylene isocyanate trimer, etc.) or an emulsified dispersion thereof, melamine resin (methylated melamine, methylolated melamine, butyrolated melamine, etc.), urea resin (methylated urea, butylated) Urea) and the like.
The addition amount of a hardening | curing agent is not specifically limited, 0.1-20 mass parts is preferable with respect to 100 mass parts of fluororesins.

Examples of other additives include components derived from alkali compounds, plasticizers, UV absorbers, leveling agents, repellency inhibitors, anti-burr agents, pigment dispersants, antifoaming agents, and thickeners.
The component derived from an alkali compound means that, in addition to the alkali compound used for adjusting the pH, an ion derived from the alkali compound in the case where the alkali compound forms a salt with other components.

[Function and effect]
According to the above-described method for producing an aqueous fluororesin dispersion of the present invention, the low molecular weight produced in the aqueous fluororesin dispersion by emulsion polymerization is sufficiently removed by the synthetic adsorbent. A fluororesin aqueous dispersion capable of forming a coating film excellent in scratch resistance is obtained.
Further, in the present invention, by producing the fluorinated copolymer (I) having the structural unit (A) and the structural unit (B) as the fluororesin, the weather resistance, water resistance, chemical resistance, heat resistance, etc. are improved. An aqueous fluororesin dispersion capable of forming an excellent coating film is obtained.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited by the following description. In the examples, “part” means “part by mass”.

[Coating evaluation]
210 parts of titanium oxide (Tipure R-706 manufactured by Dupont), 21 parts of pigment dispersant Disperbyk190 (manufactured by Big Chemie, copolymer having affinity for pigment, acid value of 10 mgKOH / g), defoamer dehydrane 1620 ( 4.5 parts of Cognis), 64.5 parts of ion exchange water, and 300 parts of glass beads are mixed, dispersed using a disperser, and the glass beads are removed by filtration to prepare a pigment composition. did. To 55 g of the pigment composition, 193 g of the fluororesin aqueous dispersion obtained in each example, 0.5 part of the thickener Vermodol 2150 (manufactured by Akzo Nobel), 10 g of dipropylene glycol mono n-butyl ether, And 15 parts of a water-dispersed isocyanate curing agent, Bihijoule (registered trademark) 3100 (manufactured by Sumika Bayer) were added and mixed to obtain a coating composition.
The coating composition was applied on one side of a chromate-treated aluminum plate to a thickness of 20 μm and dried at 80 ° C. for 1 hour to form a coating film.
(Pendulum hardness)
The pendulum hardness of the coating film was measured according to ASTM D4366 using a pendulum hardness tester manufactured by Elcometer Instruments Ltd.

[Measurement of pH]
About the fluororesin aqueous dispersion obtained in each example, the pH immediately after stirring was measured. Further, the fluororesin aqueous dispersion was stored, and the pH was measured after 1 week and 2 weeks.

[material]
(Monomer (a))
CTFE: chlorotrifluoroethylene (Asahi Glass Co., Ltd.).
TFE: Tetrafluoroethylene (manufactured by Asahi Glass Co., Ltd.).
(Monomer (b))
_{EOVE: CH 2 = CHOCH 2 -cycloC} 6 H 10 -CH 2 O (CH 2 CH 2 O) n H, average molecular weight 830 (hydrophilic macromonomer) (manufactured by Nippon Emulsifier Co.).
_{HCVE: CH 2 = CHOCH 2 -cycloC} 6 H 10 -CH 2 OH ( hydroxyl group-containing monomer) (manufactured by BASF).
(Monomer (c))
CHVE: cyclohexyl vinyl ether (manufactured by BASF).
2-EHVE: 2-ethylhexyl vinyl ether (manufactured by BASF).
(Non-fluorine emulsifier)
SLS: Sodium lauryl sulfate (anionic non-fluorinated emulsifier) (manufactured by Nikko Chemicals Co., Ltd.).

[Example 1]
Step (x):
In an autoclave with a stainless steel stirrer with an internal volume of 2500 mL (manufactured by Pressure Glass Industrial Co., Ltd.), 330 g of CHVE, 183.5 g of 2-EHVE, 16.6 g of EOVE, 27.1 g of HCVE, ion-exchanged water 1020 g, 2.5 g of potassium carbonate (K ₂ CO ₃ ), 0.7 g of ammonium persulfate (APS), 51 g of nonionic emulsifier (Newcol-1110: manufactured by Nippon Emulsifier Co., Ltd.), 0.1 g of SLS are charged. The mixture was cooled with ice, pressurized with nitrogen gas to 0.7 MPa, and degassed. This pressure degassing was repeated twice, and after degassing to 0.01 MPa to remove dissolved air, 470 g of CTFE and TFE were charged, and a polymerization reaction was performed at 50 ° C. for 24 hours. After the polymerization reaction, unreacted monomers were removed to obtain a fluororesin aqueous dispersion-1.
Step (y):
In a 200 mL beaker, 1 g of a synthetic adsorbent (manufactured by Mitsubishi Chemical Corporation, trade name “HP20”), 100 g of the fluororesin aqueous dispersion-1 and a stirrer were placed, and stirred at 200 rpm for 1 hour.

[Example 2]
Step (x) was performed in the same manner as in Example 1 to obtain a fluororesin aqueous dispersion-1.
The step (y) was performed in the same manner as in Example 1 except that the synthetic adsorbent (trade name “HP20” manufactured by Mitsubishi Chemical Corporation) was not used.

The evaluation results of each example are shown in Table 1. In addition, the symbol in Table 1 shows the following meaning.
HP20: synthetic adsorbent (trade name “HP20” manufactured by Mitsubishi Chemical Corporation).

As shown in Table 1, the aqueous fluororesin dispersion of Example 1 brought into contact with the synthetic adsorbent has a higher hardness than the aqueous fluororesin dispersion of Example 2 not brought into contact with the synthetic adsorbent. A coating film could be formed.
Further, the aqueous fluororesin dispersion of Example 1 had a lower degree of pH decrease after storage than the aqueous fluororesin dispersion of Example 2, and the pH was kept above 6. If the pH of the fluororesin aqueous dispersion is maintained at more than 6, it is possible to prevent the curing rate from becoming too high when forming the coating film, and it is possible to form a coating film with high uniformity. Moreover, generation | occurrence | production of the rust of the base material by an acid component can also be suppressed.

Claims (1)

The manufacturing method of the fluororesin aqueous dispersion which has the following process (x) and process (y).
(X) The process of manufacturing the fluororesin aqueous dispersion containing a fluororesin by emulsion polymerization.
(Y) A step of bringing the aqueous fluororesin dispersion into contact with a synthetic adsorbent.