JP2015067783A - Method for producing fluorine-containing polymer solution and method for producing fluorine-containing coating material composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the discoloration of a fluorine-containing polymer solution including a fluorine-containing polymer containing a carboxyl group just after it is produced and to achieve good storage stability.SOLUTION: In a method for producing a fluorine-containing polymer solution including (A) a fluorine-containing polymer having a carboxyl group by reacting (X) a fluorine-containing polymer having a hydroxyl group and (Y) a polybasic acid anhydride produced from a polybasic acid having two or more carboxylic groups, the fluorine-containing polymer (X) and the polybasic acid anhydride (Y) are reacted in (B) an organic solvent containing (B1) a polycyclic aromatic hydrocarbon in a ratio of 0.1-50,000 mass ppm. A method for producing a fluorine-containing coating material composition comprises adding a specific curing agent (C) to the fluorine-containing polymer solution produced by the production method as mentioned above.

Description

  The present invention relates to a method for producing a fluorine-containing polymer solution and a method for producing a fluorine-containing coating composition.

  As a coating composition used for coating on substrates such as transportation equipment, civil engineering members, building members, and electronic parts, a curing agent, a pigment, and the like are blended in a fluoropolymer solution containing a fluoropolymer and an organic solvent. Fluorine-containing paint compositions are widely used. The fluorine-containing coating composition can form a coating film with excellent durability, can reduce the amount of VOC (volatile organic compound) generated, and is excellent in the environment, so that it is particularly useful as a coating for PCM (pre-coated metal). Demand is expanding.

As the fluorine-containing polymer used in the fluorine-containing coating composition, for example, a carboxyl group-containing fluorine-containing polymer having a carboxy group is known. As a method for producing a fluoropolymer solution (varnish) containing a carboxy group-containing fluoropolymer, for example, the following methods are known.
In an organic solvent such as xylene, a hydroxyl group-containing fluorine-containing polymer having a hydroxyl group and a polybasic acid anhydride obtained from a polybasic acid having two or more carboxy groups are reacted to form at least a structural unit having a hydroxyl group. A method of converting a part into a structural unit having a carboxy group (Patent Documents 1 to 4).

However, in the above production method, the reaction time of the hydroxyl group-containing fluoropolymer and the polybasic acid anhydride is slow, so that the reaction time is long and the thermal history of the fluoropolymer solution tends to be long. . Therefore, the fluoropolymer solution immediately after production is likely to be colored due to yellowing of the polymer, and as a result, the formed coating film is also likely to be colored.
Further, even during storage, the fluoropolymer solution tends to be colored, and the molecular weight of the carboxy group-containing fluoropolymer tends to increase. For this reason, it is difficult to obtain good storage stability. For example, when stored in a storage place where the temperature cannot be controlled with a drum can or the like in summer, the fluoropolymer solution may gel. Moreover, when the molecular weight of the carboxy group-containing fluoropolymer increases, the pigment dispersibility in the fluorine-containing coating composition is lowered, and it may be difficult to form a coating film having good gloss.

JP 58-136605 A JP-A-6-41223 Japanese Patent Laid-Open No. 7-2106020 Japanese Patent Laid-Open No. 10-95888

  The present invention includes a fluorinated polymer solution containing a carboxy group-containing fluoropolymer, in which coloring immediately after production is suppressed and having good storage stability, a method for producing the same, and the content obtained by the production method. Provided is a method for producing a fluorine-containing coating composition using a fluoropolymer solution and capable of forming a good coating film.

In order to achieve the above object, the present invention adopts the following configuration.
[1] A fluorine-containing polymer having a carboxy group by reacting a fluorine-containing polymer (X) having a hydroxyl group with a polybasic acid anhydride (Y) obtained from a polybasic acid having two or more carboxy groups A method for producing a fluoropolymer solution containing a coalescence (A),
In the organic solvent (B) containing the polycyclic aromatic hydrocarbon (B1) at a ratio of 0.1 to 50,000 mass ppm, the fluoropolymer (X) and the polybasic acid anhydride (Y) A process for producing a fluoropolymer solution, characterized in that
[2] The polycyclic aromatic hydrocarbon (B1) is naphthalene, acenaphthylene, acenaphthene, fluorene, phenanthrene, anthracene, fluoranthene, pyrene, chrysene, benzo (a) anthracene, benzo (b) fluoranthene, benzo (k) fluoranthene. Benzo (j) fluoranthene, benzo (a) pyrene, benzo (e) pyrene, indeno (1,2,3-cd) pyrene, dibenzo (a, h) anthracene and benzo (g, h, i) perylene The method for producing a fluoropolymer solution according to [1], which is at least one selected from the group consisting of:
[3] The fluoropolymer solution of the above [1] or [2], wherein the fluoropolymer (X) is a fluoropolymer (X1) having the following structural units (α1) to (α3): Production method.
Structural unit (α1): a structural unit based on a fluoroolefin.
Structural unit (α2): a structural unit based on a monomer having a hydroxyl group.
Structural unit (α3): a structural unit based on a monomer having no fluorine atom or hydroxyl group.
[4] The hydroxyl value of the fluoropolymer (A) is 0.1 to 200 mgKOH / g, the acid value is 0.05 to 30 mgKOH / g, and the number average molecular weight is 3,000 to 200,000. A method for producing a fluoropolymer solution according to any one of [1] to [3].
[5] The fluoropolymer solution was obtained by reacting the fluoropolymer (X) with the polybasic acid anhydride (Y) by the production method of any one of [1] to [4]. Fluorine-containing coating composition to which at least one curing agent (C) selected from the group consisting of isocyanate curing agent (C1), blocked isocyanate curing agent (C2) and amino resin (C3) is further added Manufacturing method.

According to the method for producing a fluorine-containing polymer solution of the present invention, a fluorine-containing polymer solution containing a carboxyl group-containing fluorine-containing polymer, suppressing coloration immediately after production and having good storage stability can be obtained.
According to the method for producing a fluorine-containing coating composition of the present invention, a fluorine-containing coating composition capable of forming a good coating film in which discoloration, gloss reduction, etc. are suppressed can be obtained.

In this specification, the term “repeating unit directly formed by polymerization of monomers” and the term “repeating unit obtained by chemical conversion of a part of the repeating units formed by polymerization of the monomer” are collectively used. This is called “structural unit”.
In the present specification, the monomer represents a compound having a polymerizable double bond.
In this specification, the description of (meth) acrylic acid represents at least one of acrylic acid and methacrylic acid.
In the present specification, a compound represented by the formula (1) is referred to as a compound (1). The same applies to compounds represented by other formulas.

<Method for producing fluoropolymer solution>
The method for producing a fluoropolymer solution of the present invention is a method for producing a fluoropolymer solution containing a fluoropolymer (A) having a carboxy group.
In the method for producing a fluoropolymer solution of the present invention, a fluoropolymer (X) having a hydroxyl group and a polybasic acid anhydride (Y) obtained from a polybasic acid having two or more carboxy groups, The reaction is carried out in an organic solvent (B) containing a polycyclic aromatic hydrocarbon (B1).

The reaction between the fluoropolymer (X) and the polybasic acid anhydride (Y) is an esterification reaction. A structural unit in which at least a part of the structural unit having a hydroxyl group in the fluoropolymer (X) has a carboxy group by an esterification reaction of the fluoropolymer (X) and the polybasic acid anhydride (Y). To obtain a fluoropolymer (A).
For the reaction between the fluoropolymer (X) and the polybasic acid anhydride (Y), it is preferable to use a catalyst (Z) that accelerates the reaction.

  In the method for producing a fluoropolymer solution of the present invention, a fluoropolymer (X) and a polybasic acid anhydride (B) are contained in an organic solvent (B) containing a polycyclic aromatic hydrocarbon (B1) at a specific ratio. Y) is reacted.

[Organic solvent (B)]
The organic solvent (B) includes a polycyclic aromatic hydrocarbon (B1) and another organic solvent (B2) other than the polycyclic aromatic hydrocarbon (B1).
The ratio of the polycyclic aromatic hydrocarbon (B1) in the organic solvent (B) used for the reaction is 0.1 to 50,000 mass ppm (0.00001 to 5 mass%). If the ratio of the polycyclic aromatic hydrocarbon (B1) is within the above range, the hydroxyl group of the fluoropolymer (X) and the polybasic acid anhydride ( The reaction with Y) proceeds rapidly. As a result, the reaction time is shortened and the thermal history of the fluoropolymer solution is reduced, so that coloring immediately after production is suppressed and a fluoropolymer solution having excellent storage stability is obtained.
Moreover, since polycyclic aromatic hydrocarbon (B1) is toxic, setting the ratio of polycyclic aromatic hydrocarbon (B1) within the above range is friendly to the environment and the human body.

  The ratio of the polycyclic aromatic hydrocarbon (B1) in the organic solvent (B) is preferably 0.5 to 45,000 mass ppm (0.00005 to 4.5 mass%), and preferably 1 to 40,000 mass ppm. (0.0001-4 mass%) is more preferable, and 1.5-35,000 mass ppm (0.00015-3.5 mass%) is further more preferable. When the ratio of the polycyclic aromatic hydrocarbon (B1) is at least the lower limit, the reaction between the hydroxyl group of the fluoropolymer and the polybasic acid anhydride proceeds promptly. If the ratio of the polycyclic aromatic hydrocarbon (B1) is not more than the upper limit, the coloring of the fluoropolymer solution derived from the polybasic acid anhydride and the amine adduct, and the molecular weight of the fluoropolymer (A) Is easily suppressed, and a fluoropolymer solution having excellent storage stability is easily obtained.

As the polycyclic aromatic hydrocarbon (B1), naphthalene, acenaphthylene, acenaphthene, fluorene, phenanthrene, anthracene, fluoranthene, pyrene, chrysene, benzo (a) anthracene, benzo ( b) fluoranthene, benzo (k) fluoranthene, benzo (j) fluoranthene, benzo (a) pyrene, benzo (e) pyrene, indeno (1,2,3-cd) pyrene, dibenzo (a, h) anthracene and benzo ( g, h, i) At least one selected from the group consisting of perylene is preferred.
Polycyclic aromatic hydrocarbon (B1) may be used individually by 1 type, and may use 2 or more types together.

Other organic solvents (B2) include, for example, alcohols such as methanol, ethanol, propanol and butanol; monocyclic aromatic hydrocarbons such as xylene and toluene; carbonyl compounds such as methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone; butyl acetate And acetic acid esters such as amyl acetate; and propylene glycol alkyl ethers such as propylene glycol monomethyl ether.
Other organic solvents (B2) are preferably alcohols such as methanol, ethanol, propanol and butanol.
Another organic solvent (B2) may be used individually by 1 type, and may use 2 or more types together.

[Fluoropolymer (X)]
The fluoropolymer (X) is a fluoropolymer having a hydroxyl group. That is, the fluoropolymer (X) is a fluoropolymer having a structural unit having a hydroxyl group.
As the fluoropolymer (X), the fluoropolymer (X1) having the following structural units (α1) to (α3) is preferable from the viewpoint of the weather resistance of the coating film and the adhesion to the substrate.
Structural unit (α1): a structural unit based on a fluoroolefin.
Structural unit (α2): a structural unit based on a monomer having a hydroxyl group.
Structural unit (α3): a structural unit based on a monomer having no fluorine atom or hydroxyl group.

(Structural unit (α1))
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.
2-8 are preferable and, as for carbon number of a fluoro olefin, 2-6 are more preferable.
The number of fluorine atoms in the fluoroolefin (hereinafter referred to as “fluorine addition number”) is preferably 2 or more, and more preferably 3-4. When the fluorine addition number is 2 or more, the weather resistance of the formed coating film is improved. In the fluoroolefin, one or more hydrogen atoms not substituted with fluorine atoms may be substituted with chlorine atoms.

Examples of the fluoroolefin include fluoroolefins having 2 or 3 carbon atoms such as tetrafluoroethylene, chlorotrifluoroethylene, trifluoroethylene, vinylidene fluoride, hexafluoropropylene, and pentafluoropropylene.
As the fluoroolefin, tetrafluoroethylene and chlorotrifluoroethylene are preferable and chlorotrifluoroethylene is more preferable from the viewpoint of the weather resistance of the coating film.

The structural unit (α1) possessed by the fluoropolymer (X1) may be one type or two or more types.
As the structural unit (α1), a structural unit directly formed by polymerizing a fluoroolefin is preferable.

(Structural unit (α2))
Specific examples of the monomer having a hydroxyl group include the following compounds.
2-hydroxyethyl vinyl ether, 3-hydroxypropyl vinyl ether, 2-hydroxypropyl vinyl ether, 2-hydroxy-2-methylpropyl vinyl ether, 4-hydroxybutyl vinyl ether, 4-hydroxy-2-methylbutyl vinyl ether, 5-hydroxypentyl vinyl ether, Hydroxyalkyl vinyl ethers such as 6-hydroxyhexyl vinyl ether;
Ethylene glycol monovinyl ethers such as diethylene glycol monovinyl ether, triethylene glycol monovinyl ether, tetraethylene glycol monovinyl ether;
Hydroxyalkyl allyl ethers such as 2-hydroxyethyl allyl ether, 4-hydroxybutyl allyl ether, glycerol monoallyl ether;
Hydroxyalkyl vinyl esters such as 2-hydroxyethyl vinyl ester and 4-hydroxybutyl vinyl ester;
Hydroxyalkyl allyl esters such as hydroxyethyl allyl ester and hydroxybutyl allyl ester;
(Meth) acrylic acid hydroxyalkyl esters such as hydroxyethyl (meth) acrylate.

  As the monomer having a hydroxyl group, hydroxyalkyl vinyl ethers are preferable from the viewpoint of easy availability, 2-hydroxyethyl vinyl ether, 3-hydroxypropyl vinyl ether, 4-hydroxybutyl vinyl ether are more preferable, 2-hydroxyethyl vinyl ether, 4-hydroxybutyl vinyl ether is more preferred.

The structural unit (α2) possessed by the fluoropolymer (X1) may be one type or two or more types.
As the structural unit (α2), a structural unit directly formed by polymerizing a monomer having a hydroxyl group is preferable.

(Structural unit (α3))
The structural unit (α3) is a structural unit based on a monomer having no fluorine atom and hydroxyl group (hereinafter also referred to as monomer (a)).
The monomer (a) preferably has no carboxy group, epoxy group, oxetane group or alkoxysilyl group in addition to the hydroxyl group. The monomer (a) is preferably one that enhances the solubility of the fluoropolymer (X1) in the organic solvent (B).

  Examples of the monomer (a) include vinyl ethers, allyl ethers, isopropenyl ethers, carboxylic acid vinyl esters, carboxylic acid allyl esters, carboxylic acid isopropenyl esters, methallyl ethers, and carboxylic acid methallyl esters. , Α-olefins, (meth) acrylic acid esters and the like.

Examples of vinyl ethers include alkyl vinyl ethers such as ethyl vinyl ether, butyl vinyl ether, cyclohexyl vinyl ether, fluoroalkyl vinyl ether, and perfluoro (alkyl vinyl ether).
Examples of allyl ethers include alkyl allyl ethers such as ethyl allyl ether and cyclohexyl allyl ether.
Examples of isopropenyl ethers include alkyl isopropenyl ethers such as methyl isopropenyl ether.
Examples of carboxylic acid vinyl esters include Veova 10 (trade name, manufactured by Shell Chemical Co., Ltd.), a fatty acid vinyl ester having a branched alkyl group, vinyl butyrate, vinyl acetate, vinyl pivalate, vinyl versatate, and the like. And fatty acid vinyl esters.
Examples of carboxylic acid allyl esters include fatty acid allyl esters such as allyl propionate and allyl acetate.
Examples of α-olefins include ethylene, propylene, isobutylene and the like.
Examples of the (meth) acrylic acid ester include (meth) acrylic acid methyl ester, (meth) acrylic acid ethyl ester, (meth) acrylic acid butyl ester, and the like.

As the monomer (a), vinyl ethers, carboxylic acid vinyl esters, allyl ethers, and carboxylic acid allyl esters are preferable from the viewpoint of excellent copolymerizability with a fluoroolefin, and a linear chain having 1 to 10 carbon atoms. Alkyl vinyl ethers and fatty acid vinyl esters having a linear, branched or alicyclic alkyl group are more preferred.
The structural unit (α3) possessed by the fluoropolymer (X1) may be one type or two or more types.

(Percentage of each structural unit)
20-80 mol% is preferable and, as for the ratio of the structural unit ((alpha) 1) with respect to all the structural units (100 mol%) in a fluoropolymer (X1), 30-70 mol% is more preferable. If the proportion of the structural unit (α1) is at least the lower limit value, excellent weather resistance can be easily obtained. When the proportion of the structural unit (α1) is not more than the upper limit value, adhesion to the substrate can be ensured.

  0.5-60 mol% is preferable and, as for the ratio of the structural unit ((alpha) 2) with respect to all the structural units (100 mol%) in a fluoropolymer (X1), 1-50 mol% is more preferable. When the proportion of the structural unit (α2) is at least the lower limit, it reacts with the curing agent, and a tough cured coating film is obtained. When the proportion of the structural unit (α2) is not more than the upper limit value, the water resistance of the coating film is unlikely to decrease.

  0.5-60 mol% is preferable and, as for the ratio of the structural unit ((alpha) 3) with respect to all the structural units (100 mol%) in a fluoropolymer (X1), 1-50 mol% is more preferable. When the proportion of the structural unit (α3) is equal to or higher than the lower limit, the flexibility of the coating film and the adhesion to the base material are good. If the proportion of the structural unit (α3) is not more than the upper limit value, the influence on the weather resistance of the coating film is small.

What is necessary is just to adjust suitably the hydroxyl value of fluoropolymer (X) according to the hydroxyl value and oxidation of the target fluoropolymer (A).
The hydroxyl value of the fluoropolymer (X) is preferably from 0.1 to 200 mgKOH / g, more preferably from 0.5 to 150 mgKOH / g. If the hydroxyl value of fluoropolymer (X) is more than a lower limit, it will react with a hardening | curing agent and a tough cured coating film will be obtained. If the hydroxyl value of the fluoropolymer (X) is not more than the upper limit, the flexibility of the coating film and the adhesion to the substrate will be good.
Fluoropolymer (X) may be used individually by 1 type, and may use 2 or more types together.

(Production method of fluorine-containing copolymer (X))
The method for producing the fluorinated copolymer (X) is not particularly limited, and a method of copolymerizing a monomer mixture containing a fluoroolefin, a monomer having a hydroxyl group, and the monomer (a) as essential components. Is preferred.

A known radical polymerization method can be adopted as the polymerization method. The polymerization form is not particularly limited, and solution polymerization, suspension polymerization, emulsion polymerization and the like can be employed.
Although the reaction temperature at the time of superposition | polymerization changes also with the radical polymerization initiator to be used, 0-130 degreeC is preferable. The reaction time is preferably 1 to 50 hours.

  Examples of the polymerization solvent include ion-exchanged water; alcohol solvents such as ethanol, butanol and propanol; saturated hydrocarbon solvents such as n-hexane and n-heptane; aromatic hydrocarbon solvents such as toluene and xylene; Examples thereof include ketone solvents such as methyl ethyl ketone and cyclohexanone; ester solvents such as ethyl acetate and butyl acetate.

Examples of the radical polymerization initiator include the following compounds.
Peroxydicarbonates such as diisopropyl peroxydicarbonate, di-n-propyl peroxydicarbonate;
peroxyesters such as t-hexylperoxypivalate and t-butylperoxypivalate;
Ketone peroxides such as cyclohexanone peroxide and methyl ethyl ketone peroxide;
Peroxyketals such as 1,1-bis (t-hexylperoxy) cyclohexane and 1,1-bis (t-butylperoxy) cyclohexane;
peroxycarbonate esters such as t-hexylperoxy-n-butyl carbonate and t-butylperoxy-n-propyl carbonate;
Diacyl peroxides such as isobutyryl peroxide and lauroyl peroxide;
Dialkyl peroxides such as dicumyl peroxide and di-t-butyl peroxide.

When employing emulsion polymerization, the polymerization can be carried out by using an initiator such as a water-soluble peroxide, a persulfate, or a water-soluble azo compound in water and in the presence of an anionic or nonionic emulsifier.
In addition, since a trace amount of hydrochloric acid or hydrofluoric acid may be generated during the polymerization reaction, it is preferable to add a buffer in advance during the polymerization.

[Polybasic acid anhydride (Y)]
The polybasic acid anhydride (Y) is a polybasic acid anhydride obtained from a polybasic acid having two or more carboxy groups. That is, it is an anhydride obtained by dehydration condensation in the molecule of two carboxy groups of a polybasic acid having two or more carboxy groups. The polybasic acid anhydride (Y) is preferably a dibasic acid anhydride obtained from a dibasic acid having two carboxy groups from the viewpoint of reactivity with a hydroxyl group.
The polybasic acid anhydride (Y) is preferably the following compound (1) from the viewpoint of solubility in the reaction solvent.

However, in Formula (1), R is a divalent organic group.
Examples of R in the compound (1) include an alkylene group, a cycloalkylene group, and an aromatic group.
R is preferably an alkylene group having 2 to 8 carbon atoms from the viewpoint of solubility in an organic solvent (B), reactivity with a hydroxyl group, and little varnish coloring.

As the compound (1), succinic anhydride, glutaric anhydride, itaconic anhydride, adipic anhydride, phthalic anhydride, 1,8-naphthalic anhydride, maleic anhydride, 1,2-cyclopentanedicarboxylic anhydride, anhydrous 1,2-cyclohexanedicarboxylic acid, 1,2-cycloheptanedicarboxylic anhydride, cis-4-cyclohexene-1,2-dicarboxylic anhydride, hexahydrophthalic anhydride, methylhexahydrophthalic anhydride, octahydronaphthal anhydride Examples include acid and methyl octahydronaphthalic anhydride.
As the compound (1), succinic anhydride and hexahydrophthalic anhydride are preferable from the viewpoints of solubility in an organic solvent (B), reactivity with a hydroxyl group, and little varnish coloring.
A polybasic acid anhydride (Y) may be used individually by 1 type, and may use 2 or more types together.

[Catalyst (Z)]
As the catalyst (Z), a known catalyst for accelerating the esterification reaction can be used, and an amine catalyst is preferable from the viewpoints of reaction acceleration and ease of catalyst removal. The amine catalyst has a property of easily coloring the fluoropolymer solution. However, in the present invention, the fluorine-containing polymer (X) and the polybasic acid anhydride (Y) can be sufficiently reacted in a short time even with a small amount of amine catalyst. Therefore, even when an amine catalyst is used as the catalyst (Z), a small amount of amine catalyst may be used, and coloring of the fluoropolymer solution can be sufficiently suppressed.
As the amine catalyst, tertiary amine compounds such as triethylamine and tributylamine are preferable.
A catalyst (Z) may be used individually by 1 type, and may use 2 or more types together.

[Reaction conditions]
The reaction conditions in the reaction between the fluoropolymer (X) and the polybasic acid anhydride (Y) are preferably the following conditions.
30-200 degreeC is preferable and, as for reaction temperature, 35-150 degreeC is more preferable. If reaction temperature is more than a lower limit, reaction of a fluoropolymer (X) and a polybasic acid anhydride (Y) will advance easily. If reaction temperature is below an upper limit, it will be easy to suppress coloring of a fluoropolymer solution.

  The reaction time is preferably 10 to 300 minutes, more preferably 30 to 180 minutes. When the reaction time is at least the lower limit, a fluoropolymer solution containing a fluoropolymer (A) having a high acid value can be easily obtained. If the reaction time is less than the upper limit, it is easy to suppress the coloring of the fluoropolymer solution and the increase in the molecular weight of the fluoropolymer (A), and it is easy to obtain a fluoropolymer solution excellent in storage stability. .

What is necessary is just to set the usage-amount of a polybasic acid anhydride (Y) suitably according to the hydroxyl value and acid value of the target fluoropolymer (A). Specifically, the amount of polybasic acid anhydride (Y) used is calculated on the assumption that 1 mol of polybasic acid anhydride (Y) reacts with 1 mol of hydroxyl group of the fluoropolymer (X).
The amount of the polybasic acid anhydride (Y) used is preferably a molar ratio of the fluoropolymer (X) to the hydroxyl group of 0.01 to 1.5, more preferably 0.05 to 1.2. If the usage-amount of the said polybasic acid anhydride (Y) is more than a lower limit, the pigment dispersibility with respect to an organic pigment or carbon black will improve. If the usage-amount of the said polybasic acid anhydride (Y) is below an upper limit, it will be hard to color a varnish under the influence of the remaining polybasic acid anhydride.

  What is necessary is just to adjust the usage-amount of an organic solvent (B) suitably so that the ratio of the organic solvent (B) in the below-mentioned fluoropolymer solution may be satisfy | filled.

  0.01-1000 mass ppm is preferable with respect to polybasic acid anhydride (Y), and, as for the usage-amount of a catalyst (Z), 0.1-500 mass ppm is more preferable. If the usage-amount of the said catalyst (Z) is more than a lower limit, reaction of a fluoropolymer (X) and a polybasic acid anhydride (Y) will advance easily. If the usage-amount of the said catalyst (Z) is below an upper limit, it will be easy to suppress coloring of a fluoropolymer solution.

[Fluoropolymer solution]
The fluoropolymer solution obtained by the production method of the present invention comprises a fluoropolymer (A) obtained by the reaction of a fluoropolymer (X) and a polybasic acid anhydride (Y), and an organic solvent (B ).

(Fluoropolymer (A))
The fluorine-containing polymer solution produced by the production method of the present invention has the following fluorine-containing polymer (A) as the fluorine-containing polymer (A) from the viewpoint of the weather resistance of the coating film and the workability of the coated substrate when coated. It is preferable to include at least one selected from the group consisting of the combination (A1) and the fluoropolymer (A2).
(A1) A fluorine-containing polymer comprising the structural units (α1) to (α4).
(A2) A fluorine-containing polymer comprising the structural unit (α1), the structural unit (α3), and the structural unit (α4).

The structural units (α1) to (α3) are as described above.
The structural unit (α4) is a structural unit having a carboxy group introduced by a reaction between the hydroxyl group of the fluoropolymer (X) and the polybasic acid anhydride (Y). That is, it is a structural unit converted from the structural unit (α2) by the reaction between the fluoropolymer (X) and the polybasic acid anhydride (Y).
The structural unit (α4) has a group containing an ester bond and a carboxy group. Specifically, for example, when the compound (1) is used as the polybasic acid anhydride (Y), the structural unit (α4) is represented by the formula: —O—C (═O) —R—COOH (where R is It is the same as R in the compound (1).

Fluoropolymer (A1):
The fluoropolymer (A1) has both a hydroxyl group and a carboxy group.
The fluorinated polymer (A1) is a fluorinated polymer obtained by reacting a part of the hydroxyl groups of the fluorinated polymer (X) with the polybasic acid anhydride (Y). That is, the fluoropolymer (A1) is a fluoropolymer obtained by converting a part of the structural unit (α2) of the fluoropolymer (X) into the structural unit (α4).

  20-80 mol% is preferable and, as for the ratio of the structural unit ((alpha) 1) with respect to all the structural units (100 mol%) in a fluoropolymer (A1), 30-70 mol% is more preferable. If the proportion of the structural unit (α1) is at least the lower limit value, excellent weather resistance can be easily obtained. When the proportion of the structural unit (α1) is not more than the upper limit value, adhesion to the substrate can be ensured.

  0.5-50 mol% is preferable and, as for the ratio of the structural unit ((alpha) 2) with respect to all the structural units (100 mol%) in a fluoropolymer (A1), 1-45 mol% is more preferable. When the proportion of the structural unit (α2) is at least the lower limit, it reacts with the curing agent, and a tough cured coating film is obtained. When the proportion of the structural unit (α2) is not more than the upper limit value, the water resistance of the coating film is unlikely to decrease.

  0.5-60 mol% is preferable and, as for the ratio of the structural unit ((alpha) 3) with respect to all the structural units (100 mol%) in a fluoropolymer (A1), 1-50 mol% is more preferable. When the proportion of the structural unit (α3) is equal to or higher than the lower limit, the flexibility of the coating film and the adhesion to the base material are good. If the proportion of the structural unit (α3) is not more than the upper limit value, the influence on the weather resistance of the coating film is small.

  0.1-30 mol% is preferable and, as for the ratio of the structural unit ((alpha) 4) with respect to all the structural units (100 mol%) in a fluoropolymer (A1), 0.3-20 mol% is more preferable. When the proportion of the structural unit (α4) is at least the lower limit, the pigment dispersibility with respect to the organic pigment or carbon black is improved. When the proportion of the structural unit (α4) is not more than the upper limit value, the storage stability of the varnish is unlikely to decrease.

  The hydroxyl value of the fluoropolymer (A1) is preferably from 0.1 to 200 mgKOH / g, more preferably from 0.5 to 150 mgKOH / g. When the hydroxyl value of the fluoropolymer (A1) is at least the lower limit, a tough coating film is likely to be formed by crosslinking with the curing agent. If the hydroxyl value of the fluoropolymer (A1) is not more than the upper limit, the flexibility of the coating film and the adhesion to the substrate will be good.

  The acid value of the fluoropolymer (A1) is preferably from 0.05 to 30 mgKOH / g, more preferably from 0.1 to 20 mgKOH / g. If the acid value of a fluoropolymer (A1) is more than a lower limit, the dispersibility with respect to an organic pigment or carbon black will improve. If the acid value of a fluoropolymer (A1) is below an upper limit, it will become easy to suppress that a coating film becomes weak, and it will become easy to form the coating film which has favorable water resistance.

The number average molecular weight of the fluoropolymer (A1) is preferably from 3,000 to 200,000, more preferably from 5,000 to 100,000. When the number average molecular weight of the fluoropolymer (A1) is at least the lower limit value, it is easy to form a coating film excellent in weather resistance. If the number average molecular weight of the fluorine-containing polymer (A1) is not more than the upper limit, it is easy to obtain a fluorine-containing coating composition having an appropriate viscosity.
A fluoropolymer (A1) may be used individually by 1 type, and may use 2 or more types together.

Fluoropolymer (A2):
The fluorine-containing polymer (A2) does not have a hydroxyl group but has a carboxy group.
The fluorine-containing polymer (A2) is a fluorine-containing polymer obtained by reacting all the hydroxyl groups of the fluorine-containing polymer (X) with the polybasic acid anhydride (Y). That is, the fluoropolymer (A2) is a fluoropolymer in which all of the structural units (α2) of the fluoropolymer (X) are converted into structural units (α4).

  20-80 mol% is preferable and, as for the ratio of the structural unit ((alpha) 1) with respect to all the structural units (100 mol%) in a fluoropolymer (A2), 30-70 mol% is more preferable. If the proportion of the structural unit (α1) is at least the lower limit value, excellent weather resistance can be easily obtained. When the proportion of the structural unit (α1) is not more than the upper limit value, adhesion to the substrate can be ensured.

  0.5-70 mol% is preferable and, as for the ratio of the structural unit ((alpha) 3) with respect to all the structural units (100 mol%) in a fluoropolymer (A2), 1-60 mol% is more preferable. When the proportion of the structural unit (α3) is equal to or higher than the lower limit, the flexibility of the coating film and the adhesion to the base material are good. If the proportion of the structural unit (α3) is not more than the upper limit value, the influence on the weather resistance of the coating film is small.

  0.1-30 mol% is preferable and, as for the ratio of the structural unit ((alpha) 4) with respect to all the structural units (100 mol%) in a fluoropolymer (A1), 0.3-20 mol% is more preferable. When the proportion of the structural unit (α4) is at least the lower limit value, the dispersibility for organic pigments and carbon black is improved. When the proportion of the structural unit (α4) is not more than the upper limit value, the storage stability of the varnish is unlikely to decrease.

  The acid value of the fluoropolymer (A2) is preferably 0.05 to 30 mgKOH / g, more preferably 0.1 to 20 mgKOH / g. If the acid value of a fluoropolymer (A1) is more than a lower limit, the dispersibility with respect to an organic pigment or carbon black will improve. If the acid value of a fluoropolymer (A1) is below an upper limit, it will become easy to suppress that a coating film becomes weak, and it will become easy to form the coating film which has favorable water resistance.

The number average molecular weight of the fluoropolymer (A2) is preferably from 3,000 to 200,000, more preferably from 5,000 to 100,000. If the number average molecular weight of the fluoropolymer (A2) is at least the lower limit value, it is easy to form a coating film excellent in weather resistance. When the number average molecular weight of the fluorinated polymer (A2) is not more than the upper limit, it is easy to obtain a fluorinated coating composition having an appropriate viscosity.
A fluoropolymer (A2) may be used individually by 1 type, and may use 2 or more types together.

As the fluoropolymer (A), the fluoropolymer (A1) is more preferable among the fluoropolymer (A1) and the fluoropolymer (A2) from the viewpoint of storage stability of varnish. Further, the fluoropolymer (A) has a hydroxyl value of 0.1 to 200 mgKOH / g, an acid value of 0.05 to 30 mgKOH / g, and a number average molecular weight of 3,000 to 200,000. It is preferable.
1 type may be sufficient as the fluoropolymer (A) contained in a fluoropolymer solution, and 2 or more types may be sufficient as it.

(Ratio of each component)
The proportion of the fluoropolymer (A) in the fluoropolymer solution (100 mass%) is preferably 10 to 70 mass%, more preferably 20 to 60 mass%. When the proportion of the fluoropolymer (A) is at least the lower limit, it is easy to design a viscosity that is optimal for coating when used in a paint. If the ratio of a fluoropolymer (A) is below an upper limit, a varnish will be hard to color and storage stability will not fall easily.

  30-90 mass% is preferable and, as for the ratio of the organic solvent (B) in a fluoropolymer solution (100 mass%), 40-80 mass% is more preferable. If the ratio of the organic solvent (B) is at least the lower limit value, the varnish is difficult to be colored and the storage stability is difficult to be lowered. If the ratio of the organic solvent (B) is less than or equal to the upper limit, it is easy to design a viscosity that is optimal for coating when used in a paint.

  The ratio of the polycyclic aromatic hydrocarbon (B1) in the fluoropolymer solution (100% by mass) is preferably from 0.01 to 100 ppm by mass, and more preferably from 0.03 to 50 ppm by mass. When the ratio of the polycyclic aromatic hydrocarbon (B1) is at least the lower limit, the solubility of the fluoropolymer is improved, and even when the varnish is stored in a low temperature environment, the varnish is less likely to be haze. If the ratio of the polycyclic aromatic hydrocarbon (B1) is not more than the upper limit, coloring of the fluoropolymer solution and increase in the molecular weight of the fluoropolymer (A) are easily suppressed, and the storage stability is excellent.

[Function and effect]
In the method for producing the fluoropolymer solution of the present invention described above, in the organic solvent (B) containing the polycyclic aromatic hydrocarbon (B1) at a specific ratio, the fluoropolymer (X) and Since the polybasic acid anhydride (Y) is reacted, the reaction time can be shortened. As a result, the heat history of the fluoropolymer solution is reduced, so that coloring of the fluoropolymer solution immediately after production is suppressed. Further, since the fluoropolymer (X) and the polybasic acid anhydride (Y) can be sufficiently reacted in a short time even if the amount of the catalyst (Z) used is small, the fluoropolymer solution can be colored. Is suppressed. Further, the fluoropolymer solution obtained by the production method of the present invention has excellent storage stability in which coloring of the fluoropolymer solution during storage and increase in the molecular weight of the fluoropolymer (A) are suppressed. It has sex.

<Method for producing fluorine-containing coating composition>
The manufacturing method of the fluorine-containing coating composition of this invention is a method of adding a hardening | curing agent (C) to the fluorine-containing polymer solution obtained by the manufacturing method of this invention.
Moreover, in the manufacturing method of the fluorine-containing coating composition of this invention, in addition to a hardening | curing agent (C), you may add a pigment component (D) and another component (E) as needed. In the fluorine-containing coating composition obtained by the production method of the present invention, the fluorine-containing copolymer (A) reacts with the curing agent (C) to form a crosslinked structure and form a coating film. .
In the manufacturing method of the fluorine-containing coating composition of this invention, it is preferable to add a pigment component (D).

In the method for producing a fluorine-containing coating composition of the present invention, the fluorine-containing polymer solution obtained by the production method of the present invention, a curing agent (C), a pigment component (D) and other components used as necessary. The order of mixing the component (E) is not particularly limited.
As a mixing method of each component, a method usually used for producing a coating composition can be used. For example, a method using a ball mill, a paint shaker, a sand mill, a jet mill, a rocking mill, an attritor, a three-roll, a kneader and the like can be mentioned.

[Curing agent (C)]
The curing agent (C) is at least one curing agent selected from the group consisting of an isocyanate curing agent (C1), a blocked isocyanate curing agent (C2), and an amino resin (C3).

(Isocyanate curing agent (C1))
As an isocyanate type hardening | curing agent (C1), a non-yellowing polyisocyanate and a non-yellowing polyisocyanate modified body are mentioned, for example. The isocyanate group of the isocyanate curing agent (C1) is not blocked.
Examples of the non-yellowing polyisocyanate include alicyclic polyisocyanates such as isophorone diisocyanate (IPDI) and dicyclohexylmethane diisocyanate (HMDI); and aliphatic polyisocyanates such as hexamethylene diisocyanate (HDI).

Examples of the non-yellowing polyisocyanate-modified product include the following modified products (c1) to (c4).
(C1) Isocyanurate of aliphatic diisocyanate or alicyclic diisocyanate.
(C2) A modified product having a structure represented by -C (= O) -NH-, wherein aliphatic diisocyanate or alicyclic diisocyanate is modified with a polyol or polyamine.
(C3) A modified product having a structure represented by -C (= O) -NH-, in which a part of the isocyanate group of an aliphatic diisocyanate or an alicyclic diisocyanate is modified with a polyol.
(C4) A modified product comprising a mixture of the modified product (c1) and the modified product (c2).

(Blocked isocyanate curing agent (C2))
The blocked isocyanate curing agent (C2) is obtained by blocking the isocyanate group of the isocyanate curing agent.
The isocyanate group can be blocked by epsilon caprolactam (E-CAP), methyl ethyl ketone oxime (MEK-OX), methyl isobutyl ketone oxime (MIBK-OX), pyrridine, triazine (TA), and the like.

(Amino resin (C3))
Examples of the amino resin (C3) include melamine resin, guanamine resin, sulfoamide resin, urea resin, aniline resin, and the like. Especially, a melamine resin is preferable from the point that a cure rate is quick.
Specific examples of the melamine resin include alkyl etherified melamine resins that are alkyl etherified. Especially, as a melamine resin, the melamine resin substituted by at least one of the methoxy group and the butoxy group is more preferable.

When the isocyanate curing agent (C1) or amino resin (C3) whose isocyanate group is not blocked is used as the curing agent (C), the curing agent (C) is blended into the fluorine-containing coating composition. It is performed immediately before applying the fluorine-containing coating composition.
A hardening | curing agent (C) may be used individually by 1 type, and may use 2 or more types together.

[Pigment component (D)]
The pigment component (D) is preferably at least one pigment selected from the group consisting of rust preventive pigments, colored pigments and extender pigments.
The rust preventive pigment is a pigment for preventing corrosion or alteration of the substrate on which the fluorine-containing coating composition is applied. Lead-free rust preventive pigments are preferred because of their low environmental impact. Examples of lead-free rust preventive pigments include cyanamide zinc, zinc oxide, zinc phosphate, calcium magnesium phosphate, zinc molybdate, barium borate, and calcium cyanamide zinc.

  The color pigment is a pigment for coloring the coating film. Examples of the color pigment include titanium oxide, carbon black, iron oxide, moazo yellow, phthalocyanine blue, phthalocyanine green, and quinacridone red. In the case of using a titanium oxide pigment, it is preferable that the pigment surface is treated for suppressing the photocatalytic action for the purpose of further improving the weather resistance of the coating film. D918 (trade name, manufactured by Sakai Chemical Co., Ltd.) and PFC105 (trade name, manufactured by Ishihara Sangyo Co., Ltd.) can be particularly recommended.

The extender pigment is a pigment for improving the hardness of the coating film and increasing the thickness. Examples of extender pigments include talc, barium sulfate, mica, and calcium carbonate.
As the pigment component (D), titanium oxide is particularly preferable in terms of excellent weather resistance.
A pigment component (D) may be used individually by 1 type, and may use 2 or more types together.

[Other ingredients (E)]
In the manufacturing method of the fluorine-containing coating composition of this invention, you may add other components other than each component mentioned above. For example, in addition to the organic solvent (B) contained in the fluoropolymer solution, an organic solvent (E1) may be further added. Moreover, you may add a curing catalyst (E2) in order to accelerate | stimulate a crosslinking reaction. In particular, when curing at a low temperature in a short time, it is preferable to add a curing catalyst (E2). The curing catalyst (E2) accelerates the curing reaction of the fluoropolymer (A) and improves the chemical performance and physical performance of the coating film.

(Organic solvent (E1))
The organic solvent (E1) is not particularly limited as long as it can dissolve or disperse the fluoropolymer (A) and the curing agent (C).
Examples of the organic solvent (E1) include aromatic compounds such as xylene and toluene; carbonyl compounds such as methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone; acetates such as butyl acetate and amyl acetate; propylene glycol such as propylene glycol monomethyl ether Examples thereof include alkyl ethers.
An organic solvent (E1) may be used individually by 1 type, and may use 2 or more types together.

(Curing catalyst (E2))
What is necessary is just to select suitably as a curing catalyst (E2) according to the kind etc. of hardening | curing agent (C).
For example, when the curing agent (C) is an isocyanate curing agent (C1) or a blocked isocyanate curing agent (C2), the curing catalyst (E2) is preferably a tin catalyst or a zirconium catalyst.
Examples of the tin catalyst include tin octylate, tributyltin dilaurate, and dibutyltin dilaurate.
As a zirconium catalyst, a zirconium chelate etc. are mentioned, for example. Examples of commercially available zirconium catalysts include “K-KAT XC-4205” (trade name, manufactured by Enomoto Kasei Co., Ltd.).

When the curing agent (C) is an amino resin (C3), a blocked acid catalyst is preferable as the curing catalyst (E2).
Examples of the blocked acid catalyst include amine salts of various acids such as carboxylic acid, sulfonic acid and phosphoric acid. Of these, higher alkyl-substituted sulfonic acid amine salts such as diethanolamine salt or triethylamine salt of p-toluenesulfonic acid, diethanolamine salt or triethylamine salt of dodecylbenzenesulfonic acid are preferable.
A curing catalyst (E2) may be used individually by 1 type, and may use 2 or more types together.

  Moreover, in the manufacturing method of the fluorine-containing coating composition of this invention, as another component (E), a light stabilizer, a ultraviolet absorber, surfactant, a silane coupling agent, a pigment dispersant, a fluorine-containing copolymer ( Other resins other than A) may be added.

Examples of the light stabilizer include hindered amine light stabilizers.
Examples of the ultraviolet absorber include benzophenone compounds, benzotriazole compounds, triazine compounds, cyanoacrylate compounds, and the like.

If a surfactant is added, the surface tension of the coating composition can be controlled, which is effective in adjusting the surface concentration of a specific component.
As the surfactant, any of a nonionic surfactant, a cationic surfactant, and an anionic surfactant may be used.

If a silane coupling agent is added, it is easy to form a coating film with good adhesion to the substrate.
Examples of the silane coupling agent include a silane coupling agent having at least one functional group selected from the group consisting of an epoxy group, a vinyl group, an amino group, a (meth) acryloyl group, a styryl group, a mercapto group, and an isocyanate group. Is mentioned. Of these, a silane coupling agent having an epoxy group is preferable.

  Examples of the pigment dispersant include an anionic compound, a cationic compound, a nonionic compound, and a polymer compound having a molecular weight of thousands to tens of thousands. Especially, the compound which has at least 1 sort (s) chosen from the group which consists of a sulfate group, a sulfonic acid group, a phosphate group, and a fatty acid amine base from the point of the color floating property and color separation nature of cyanine blue and carbon black is preferable.

Examples of other resins include non-fluorinated resins and fluorine resins other than the fluorine-containing copolymer (A).
Examples of non-fluorine resins include acrylic resins, polyester resins, acrylic polyol resins, polyester polyol resins, urethane resins, acrylic silicone resins, silicone resins, alkyd resins, epoxy resins, oxetane resins, and the like.
The other resin may be a resin that has a crosslinkable group and is cured by being crosslinked by the curing agent (C).

[Ratio of each component]
The addition amount of the curing agent (C), the pigment component (D) and the other component (E) to the fluoropolymer solution is adjusted so that a fluorine-containing coating composition satisfying the ratio of each component shown below is obtained. It is preferable.
10-80 mass% is preferable and, as for the ratio of the fluoropolymer (A) in a fluorine-containing coating composition (100 mass%), 20-70 mass% is more preferable. If the ratio of a fluoropolymer (A) is more than a lower limit, the weather resistance of a coating film will not fall easily. When the ratio of the fluoropolymer (A) is not more than the upper limit, it is easy to design a viscosity that is optimal for coating when used in a paint.

  1-40 mass parts is preferable with respect to 100 mass parts of a fluoropolymer (A), and, as for the ratio of the hardening | curing agent (C) in a fluorine-containing coating composition, 3-30 mass parts is more preferable. If the ratio of a hardening | curing agent (C) is more than a lower limit, a tough coating film will be easy to be obtained by sufficient bridge | crosslinking. If the ratio of a hardening | curing agent (C) is below an upper limit, it will be easy to suppress the foaming of the coating film by reaction with an isocyanate group and a water | moisture content favorably.

  5-55 mass% is preferable and, as for the ratio of the total amount of the organic solvent (B) and organic solvent (E1) in a fluorine-containing coating composition (100 mass%), 15-50 mass% is more preferable. If the ratio of the said total amount is more than a lower limit, the viscosity of a fluorine-containing coating composition will become lower and an application | coating operation | work will become easy. If the ratio of the said total amount is below an upper limit, it will become easy to remove an organic solvent (B) and an organic solvent (E2), and to form a coating film.

  When the pigment component (D) is added to the fluorine-containing coating composition, the proportion of the pigment component (D) is 50 to 500 with respect to 100 parts by mass of the solid content other than the pigment component (D) in the fluorine-containing coating composition. A mass part is preferable and 100-400 mass parts is more preferable. If the ratio of the pigment component (D) is at least the lower limit value, the function of the pigment component (D) is easily obtained. If the ratio of the pigment component (D) is less than or equal to the upper limit value, the coating film is difficult to be damaged due to raindrop collision or the like, and a coating film having excellent weather resistance is easily formed.

  When the curing catalyst (E2) is added to the fluorine-containing coating composition, the proportion of the curing catalyst (E2) is preferably 0.001 to 5.0 parts by mass with respect to 100 parts by mass of the curing agent (C). If the ratio of the curing catalyst is at least the lower limit value, the catalytic effect can be sufficiently obtained. If the ratio of a curing catalyst is below an upper limit, it will be easy to suppress that a curing catalyst remains and it affects a coating film and water resistance falls.

  In the fluorine-containing coating composition (100% by mass), the proportion of the component (E) other than the organic solvent (E1) and the curing catalyst (E2) is preferably 10% by mass or less, and more preferably 5% by mass or less.

[Coating method]
The fluorine-containing coating composition obtained by the production method of the present invention can form a coating film by, for example, curing the formed coating layer after coating on a substrate.
As a method for applying the fluorine-containing coating composition, a known coating method can be adopted, and examples thereof include a method using a brush, a roller, a spray, a flow coater, an applicator and the like. What is necessary is just to select the application quantity of a fluorine-containing coating composition suitably according to the target dry film thickness.

The curing temperature is preferably room temperature to 250 ° C, more preferably 50 to 200 ° C.
There is no restriction | limiting in particular as a heating method in the case of heating an application layer, For example, the sealing furnace which can be sealed, a tunnel furnace etc. which can be continuously hardened are mentioned. The heating source is not particularly limited, and hot air circulation, infrared heating, high frequency heating, or the like can be employed. Among these, from the viewpoint of continuous productivity, a hot air circulation and infrared heating are preferable from the viewpoint of a tunnel furnace and a uniform heat transfer method and a uniform cured coating film.

  The use of the fluorine-containing coating composition of the present invention is not particularly limited, and examples thereof include coating applications for substrates such as transportation equipment, civil engineering members, building members, and electronic parts, and in particular, it is used as a coating for PCM (pre-coated metal). It is preferable.

[Function and effect]
In the method for producing a fluorine-containing coating composition of the present invention, since the curing agent (C) is further added to the fluorine-containing polymer solution obtained by the method of the present invention, a good coating with suppressed discoloration is obtained. A fluorine-containing coating composition capable of forming a film is obtained. Moreover, since the increase in the molecular weight of the fluoropolymer (A) is suppressed, the dispersibility of the coating film can be suppressed because the pigment dispersibility is excellent, so that the decrease in gloss of the coating film can be suppressed.

EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited by the following description.
<Compound>
The compounds and abbreviations used in the examples are as follows.
[Monomer]
CTFE: chlorotrifluoroethylene,
HBVE: 4-hydroxybutyl vinyl ether,
EVE: ethyl vinyl ether.

[Radical polymerization initiator]
PBPV: t-butyl peroxypivalate.

[Organic solvent (B)]
SF01: Trade name “Cactus Fine SF-01” (ratio of aromatic hydrocarbon solvent, polycyclic aromatic hydrocarbon (B1) (naphthalene): 0.02 mass%, manufactured by JX Nippon Oil & Energy Corporation).
S150ND: Trade name “Solvesso150ND” (Aromatic hydrocarbon solvent, polycyclic aromatic hydrocarbon (B1) (naphthalene) ratio: 0.8 mass%, manufactured by ExxonMobil Corp.).

[Organic solvent (for comparison)]
S150: Trade name “Solvesso150” (Aromatic hydrocarbon solvent, polycyclic aromatic hydrocarbon (B1) (naphthalene) ratio: 7.3% by mass, manufactured by ExxonMobil Corp.)

[Measurement of solid content]
The solid content concentration of the solution was determined by measuring the heating residue in accordance with JIS K 5601-1-2 (established in 2009).

[Measurement of hydroxyl value]
The hydroxyl value of the fluoropolymer was measured by the following method.
5 mL of acetic anhydride was placed in a volumetric flask, and pyridine was added to make 100 mL, which was stirred well to obtain an acetylating reagent.
Next, 1 g of the measurement varnish obtained by removing the solvent from the xylene solution of the fluoropolymer was weighed into a 225 mL glass bottle, 5 mL of the acetylating reagent and 10 mL of pyridine were added, and then the glass bottle was covered. Heated in an 80 ° C. oven for 2 hours and cooled to room temperature. Thereafter, 1 g of ion-exchanged water was added, and further heated in an oven at 80 ° C. for 10 minutes, cooled to room temperature, and then 25 g of ethanol and 25 g of toluene were added to obtain a sample solution.
Next, 5 to 6 drops of 1% phenolphthalein was added to the obtained sample solution while stirring, titrated with a 0.1 mol / L potassium hydroxide-ethyl alcohol solution, and consumed by reaction with hydroxyl groups. The amount of acetic anhydride was calculated and used as the hydroxyl value.
In addition, the hydroxyl value (mgKOH / g) of the fluoropolymer is a hydroxyl value in a state where the nonvolatile content of the obtained fluoropolymer is 100% by mass.

[Measurement of acid value]
The acid value of the fluoropolymer was measured according to JIS K 5601-2-1.

[Measurement of number average molecular weight]
The number average molecular weight of the fluoropolymer was measured by GPC (manufactured by Tosoh Corporation, HLC-8220). Tetrahydrofuran was used as a developing solvent, and polystyrene was used as a standard substance.

[Measurement of reaction rate]
The reaction rate was calculated from the increase / decrease in the peak derived from the hydroxyl group and the increase / decrease in the peak derived from the acid anhydride group in the IR spectrum.

<Evaluation of fluoropolymer solution>
[Production Example 1]
A stainless steel pressure resistant reactor with an internal volume of 2500 mL equipped with a stirrer was charged with 11 g of calcium carbonate, 590 g of xylene, 170 g of ethanol, 131.7 g of HBVE, and 326.9 g of EVE, and degassed with nitrogen Thus, dissolved oxygen in the liquid was removed. Into this reactor, 660 g of CTFE was introduced and the temperature was gradually raised. When the temperature reached 65 ° C., a polymerization reaction was carried out by intermittently adding 12.14 g of PBPV as a radical polymerization initiator. It was.
After 10 hours, the reaction was stopped by cooling the reactor with water. After cooling the obtained reaction liquid to room temperature, the unreacted monomer was purged, and the reaction liquid was filtered through diatomaceous earth to remove solids.
Next, a part of xylene and ethanol were removed by distillation under reduced pressure to obtain a xylene solution (solid content concentration: 50% by mass) of a hydroxyl group-containing fluoropolymer (fluoropolymer (X1-1)).

[Example 1]
500 ml of the xylene solution (solid content concentration 50% by mass) of the fluoropolymer (X1-1) obtained in Production Example 1 was added to a 2 L four-necked flask equipped with a thermometer, reflux condenser and stirrer. 0.0 g and 325.0 g of SF01 were charged and heated to 60 ° C. with stirring. Thereafter, xylene was removed by distillation under reduced pressure under a condition of a vacuum degree of 1 mmHg (about 1.33 × 10 ² Pa) until the xylene content was less than 1% by mass.
Next, a mixed solution of 2.23 g of succinic anhydride which is a polybasic acid anhydride (Y) and 75.0 g of cyclohexanone is put into the flask, and it is visually confirmed that the solution in the flask is uniform. After confirmation, a mixed solution of 0.2 g of triethylamine and 1.0 g of cyclohexanone was added into the flask. Then, it heated up at 90 degreeC and reacted for 1 hour.
The ratio of the polycyclic aromatic hydrocarbon (B1) in the organic solvent (B) in the esterification reaction was 16 mass ppm.

When the progress of the reaction was confirmed by IR spectrum, the characteristic absorption (1850 cm ⁻¹ , 1780 cm ⁻¹ ) of the acid anhydride disappeared, and strong absorption of carboxylic acid (1710 cm ⁻¹ ) and ester (1735 cm ⁻¹ ) was confirmed. It was done. Moreover, when the reaction rate was measured by titration, it was 99.0%.
The obtained reaction solution was filtered through diatomaceous earth to obtain a fluoropolymer solution (I-1) (solid content concentration: 40.2% by mass) containing the fluoropolymer (A1-1).

[Example 2]
The reaction was performed in the same manner as in Example 1 except that S150ND (325.0 g) was used instead of SF01 (325.0 g). The ratio of the polycyclic aromatic hydrocarbon (B1) in the organic solvent (B) in the esterification reaction was 6,400 mass ppm.
When the progress of the reaction was confirmed by IR spectrum, characteristic absorption of the acid anhydride disappeared, and strong absorption of carboxylic acid and ester was confirmed. Moreover, when the reaction rate was measured by titration, it was 99.0%.
The obtained reaction solution was filtered through diatomaceous earth to obtain a fluoropolymer solution (I-2) (solid content concentration 40.1% by mass) containing the fluoropolymer (A1-2).

[Comparative Example 1]
The reaction was performed in the same manner as in Example 1 except that S150 (325.0 g) was used instead of SF01 (325.0 g). The ratio of the polycyclic aromatic hydrocarbon (B1) in the organic solvent (B) in the esterification reaction was 58,400 mass ppm.
When the progress of the reaction was confirmed by IR spectrum, characteristic absorption of the acid anhydride disappeared, and strong absorption of carboxylic acid and ester was confirmed. Moreover, it was 94.5% when the reaction rate was measured by titration.
The obtained reaction solution was filtered through diatomaceous earth to obtain a fluoropolymer solution (I-3) (solid content concentration: 40.0% by mass) containing the fluoropolymer (F-1).

[Comparative Example 2]
The reaction was conducted in the same manner as in Example 1 except that S150 (325.0 g) was used instead of SF01 (325.0 g) and the reaction time was 10 hours. The ratio of the polycyclic aromatic hydrocarbon (B1) in the organic solvent (B) in the esterification reaction was 57,500 ppm by mass.
When the progress of the reaction was confirmed by IR spectrum, characteristic absorption of the acid anhydride disappeared, and strong absorption of carboxylic acid and ester was confirmed. Moreover, when the reaction rate was measured by titration, it was 99.0%.
The obtained reaction solution was filtered through diatomaceous earth to obtain a fluoropolymer solution (I-4) (solid content concentration: 40.2% by mass) containing the fluoropolymer (F-2).

[Coloring evaluation immediately after production]
The degree of coloring of the fluorinated copolymer solution immediately after production in each example was evaluated according to the following criteria.
“◯”: Yellowing is not confirmed.
“Δ”: Slight yellowing is confirmed.
“×”: Remarkable yellowing is confirmed.

[Evaluation of storage stability]
The storage stability of the fluorinated copolymer solution in each example was evaluated as follows.
The initial weight average molecular weight Mw ¹ of the fluoropolymer in the fluoropolymer solution of each example was measured. In addition, 100 g of the fluoropolymer solution of each example was put in a heat-resistant container and stored in a thermostat bath at 70 ° C. and RH 50% for 14 days, and then the weight average molecular weight Mw ² of the fluoropolymer was measured. The weight average molecular weight of the fluoropolymer was measured by size exclusion chromatography (SEC) using tetrahydrofuran (THF) as a developing solvent and a polystyrene sample having a known molecular weight as a standard substance for molecular weight conversion.
Mw increase rate was calculated | required with the following formula | equation.
(Mw increase rate) = (Mw ² / Mw ¹ ) × 100
Moreover, the coloring degree of the fluoropolymer solution after 14-day storage at 70 degreeC was confirmed visually. Evaluation was performed according to the following criteria.
“1”: Mw increase rate is less than 150%, and no discoloration (yellowing or cloudiness) is confirmed in the fluoropolymer solution.
“2”: The Mw increase rate is less than 150%, but significant discoloration (yellowing or cloudiness) is confirmed in the fluoropolymer solution.
“3”: Although no significant discoloration (yellowing or cloudiness) is observed in the fluoropolymer solution, the Mw increase rate is 150% or more.
“4”: Mw increase rate is 150% or more, and significant discoloration (yellowing or cloudiness) is confirmed in the fluoropolymer solution.

Table 1 shows the measurement results and evaluation results for the fluoropolymer solutions and fluoropolymers of each example.
In addition, the ratio of the polycyclic aromatic hydrocarbon (B1) in Table 1 means the ratio of the polycyclic aromatic hydrocarbon (B1) to the total amount of the organic solvent during the esterification reaction.

As shown in Table 1, the fluoropolymer solutions (I-1) and (I-2) obtained in Examples 1 and 2 were not colored immediately after production and were stored at 70 ° C. for 14 days. Later, the increase in Mw was suppressed, the increase in the degree of coloring was not confirmed, and the storage stability was excellent.
On the other hand, in the fluoropolymer solutions (I-3) and (I-4) of Comparative Examples 1 and 2, coloring was observed immediately after production, and Mw greatly increased after being stored at 70 ° C. for 14 days, An increase in the degree of coloring was observed, and the storage stability was poor.

<Evaluation of fluorine-containing paint composition>
[Example 3]
To 35.3 g of the fluoropolymer solution (I-1) obtained in Example 1, 7.5 g of phthalocyanine blue (manufactured by Clariant Japan, trade name “PV Fast Blue A2R”), 64 of butyl acetate 1.1 g of a pigment dispersant (manufactured by BYK Chemie, trade name “BYK-106”) was added, and 108.8 g of glass beads having a diameter of 1 mm were further added, followed by stirring with a paint shaker for 2 hours. After stirring, filtration was performed to remove the glass beads to obtain a pigment composition.
Next, to 100 g of the pigment composition, 134.8 g of the fluoropolymer solution (I-1) and HDI (hexamethylene diisocyanate) nurate type polyisocyanate resin (Nippon Polyurethane Co., Ltd.) as the curing agent (C). 13.6 g of the product name “Coronate HX”) and dibutyltin dilaurate as a curing catalyst (E2) (diluted 4 to 10 times with xylene to 4 g), and mixed. A fluorine-containing coating composition (1) was obtained.

[Example 4]
A fluorinated coating composition (2) was obtained in the same manner as in Production Example 2, except that the fluorinated polymer solution (I-2) was used instead of the fluorinated polymer solution (I-1).

[Comparative Example 3]
A fluorine-containing coating composition (3) was obtained in the same manner as in Production Example 2, except that the fluorine-containing polymer solution (I-3) was used instead of the fluorine-containing polymer solution (I-1).

[Comparative Example 4]
A fluorinated coating composition (4) was obtained in the same manner as in Production Example 2, except that the fluorinated polymer solution (I-4) was used instead of the fluorinated polymer solution (I-1).

[Pigment dispersibility]
About the fluorine-containing coating composition obtained in each example, the presence or absence of the aggregate of a pigment was confirmed with the microscope, and the pigment dispersibility was evaluated on the following references | standards.
○ (Good): Aggregates of pigments are not confirmed in the fluorine-containing coating composition.
X (Poor): Many aggregates of pigments are confirmed in the fluorine-containing coating composition.

[Evaluation of film gloss]
Apply the fluorine-containing paint compositions (1) to (4) obtained in each example to one side of the chromate-treated aluminum plate so that the film thickness becomes 40 μm, and at room temperature (25 ° C.). The test piece with a coating film was obtained by leaving for one week (curing drying).
About the obtained test piece with a coating film, based on JISK5600, the 60 degree gloss value of the coating film was measured, and the following reference | standard evaluated.
○ (Good): The gloss value of the coating film is 80 or more, and no aggregates of pigments and resins are confirmed on the coating film surface.
X (defect): The gloss value of the coating film is less than 80, and aggregates of pigment and resin are confirmed on the coating film surface.

  The evaluation results of pigment dispersibility and coating film gloss in each example are shown in Table 2.

As shown in Table 2, in Examples 3 and 4, the pigment dispersibility in the fluorine-containing coating compositions (1) and (2) was good, and a highly glossy coating film was obtained.
On the other hand, in Comparative Examples 3 and 4, when confirmed by a microscope, a large number of pigment aggregates were confirmed in the fluorine-containing coating compositions (3) and (4), and the gloss of the obtained coating film was low. Aggregates of pigment and resin were also observed on the film surface.

Claims (5)

A fluorine-containing polymer (A) having a carboxy group is obtained by reacting a fluorine-containing polymer (X) having a hydroxyl group with a polybasic acid anhydride (Y) obtained from a polybasic acid having two or more carboxy groups. ) Containing a fluoropolymer solution comprising:
In the organic solvent (B) containing the polycyclic aromatic hydrocarbon (B1) at a ratio of 0.1 to 50,000 mass ppm, the fluoropolymer (X) and the polybasic acid anhydride (Y) A process for producing a fluoropolymer solution, characterized in that   The polycyclic aromatic hydrocarbon (B1) is naphthalene, acenaphthylene, acenaphthene, fluorene, phenanthrene, anthracene, fluoranthene, pyrene, chrysene, benzo (a) anthracene, benzo (b) fluoranthene, benzo (k) fluoranthene, benzo ( j) From the group consisting of fluoranthene, benzo (a) pyrene, benzo (e) pyrene, indeno (1,2,3-cd) pyrene, dibenzo (a, h) anthracene and benzo (g, h, i) perylene. The method for producing a fluoropolymer solution according to claim 1, which is at least one selected. The method for producing a fluoropolymer solution according to claim 1 or 2, wherein the fluoropolymer (X) is a fluoropolymer (X1) having the following structural units (α1) to (α3).
Structural unit (α1): a structural unit based on a fluoroolefin.
Structural unit (α2): a structural unit based on a monomer having a hydroxyl group.
Structural unit (α3): a structural unit based on a monomer having no fluorine atom or hydroxyl group.   The hydroxyl group value of the fluoropolymer (A) is 0.1 to 200 mgKOH / g, the acid value is 0.05 to 30 mgKOH / g, and the number average molecular weight is 3,000 to 200,000. The manufacturing method of the fluoropolymer solution as described in any one of claim | item 1 -3.   After producing the fluoropolymer solution by reacting the fluoropolymer (X) and the polybasic acid anhydride (Y) by the production method according to any one of claims 1 to 4, Further, production of a fluorine-containing coating composition, to which at least one curing agent (C) selected from the group consisting of an isocyanate curing agent (C1), a blocked isocyanate curing agent (C2) and an amino resin (C3) is added. Method.