JP2022143750A - fluorine-containing copolymer - Google Patents

Abstract

To provide a fluorine-containing copolymer that has a high Tg and can form a coating layer of high hardness when used in a fluorine-containing coating.SOLUTION: A fluorine-containing copolymer comprises a fluoroolefin-based unit (a), a vinyl lactam-based unit (b), and a unit represented by the following formula (c) (where L is an alkylene group having two or more carbon atoms).SELECTED DRAWING: None

Description

The present invention relates to a fluorine-containing copolymer.

A fluorine-containing copolymer is suitably used as a raw material for a fluorine-containing paint. A fluorine-containing copolymer usually contains structural units based on a fluoroolefin and structural units based on other monomers in many cases.
For example, the fluorine-containing copolymer described in Patent Document 1 contains units based on cyclohexyl vinyl ether (CHVE), which has a high homopolymer Tg, in addition to units based on fluoroolefin, in order to increase the glass transition temperature (Tg).

Republished Patent No. 2002-100956

However, in order to increase the Tg of the fluorine-containing copolymer, it is necessary to increase the proportion of units derived from the monomer having a high homopolymer Tg in the fluorine-containing copolymer. Therefore, a fluorine-containing paint produced using a fluorine-containing copolymer may not achieve desired properties. For example, when formation of a coating film with high hardness is required, even if the proportion of units based on CHVE is increased, it is difficult to obtain a coating film with sufficient hardness.

An object of the present invention is to provide a fluorine-containing copolymer that has a high Tg and that can form a coating film with high hardness when used in a fluorine-containing paint.

（式中、Ｌは炭素数２以上のアルキレン基である。）
［２］ さらに、ビニルエーテルまたはビニルエステルに基づく単位（ｄ）を含む、［１］に記載の含フッ素共重合体。
［３］ ガラス転移温度が２０℃以上である、［１］または［２］に記載の含フッ素共重合体。
［４］ 上記単位（ｂ）がＮ－ビニル－ε－カプロラクタムに基づく単位である、［１］～［３］のいずれかに記載の含フッ素共重合体。
［５］ 酸価が１ｍｇＫＯＨ／ｇ以上である、［１］～［４］のいずれかに記載の含フッ素共重合体。
［６］ 数平均分子量が１，０００以上である、［１］～［５］のいずれかに記載の含フッ素共重合体。 As a result of intensive studies, the inventors of the present invention have found that the above problems can be solved by the following configuration.
[1] a unit (a) based on a fluoroolefin;
units (b) based on vinyl lactams;
A fluorine-containing copolymer characterized by comprising a unit (c) represented by the following formula.

(In the formula, L is an alkylene group having 2 or more carbon atoms.)
[2] The fluorine-containing copolymer according to [1], further comprising units (d) based on vinyl ether or vinyl ester.
[3] The fluorine-containing copolymer according to [1] or [2], which has a glass transition temperature of 20°C or higher.
[4] The fluorine-containing copolymer according to any one of [1] to [3], wherein the unit (b) is based on N-vinyl-ε-caprolactam.
[5] The fluorine-containing copolymer according to any one of [1] to [4], which has an acid value of 1 mgKOH/g or more.
[6] The fluorine-containing copolymer according to any one of [1] to [5], which has a number average molecular weight of 1,000 or more.

The fluorine-containing copolymer of the present invention has a high Tg and can form a coating film with high hardness when used in a fluorine-containing paint.

Terms used in the present invention are explained below.
A unit is a general term for an atomic group based on one molecule of the above-mentioned monomer directly formed by polymerization of the monomer, and an atomic group obtained by chemically converting a part of the above-mentioned atomic group. The content (mol %) of each unit with respect to the total units contained in the polymer is determined by analyzing the polymer by nuclear magnetic resonance spectroscopy (NMR).
Acid value is a value measured according to the method of JIS K 0070-3 (1992).
The number average molecular weight (Mn) and weight average molecular weight (Mw) are values measured by gel permeation chromatography using polystyrene as a standard substance.
The glass transition temperature (Tg) is the value of the midpoint glass transition temperature measured by the differential scanning calorimetry (DSC) method.

上記式中、Ｌは炭素数２以上のアルキレン基である。 The fluorine-containing copolymer of the present invention (hereinafter also referred to as the present copolymer) comprises units (a) based on fluoroolefin, units (b) based on vinyl lactam, and units (c ) and including.

In the above formula, L is an alkylene group having 2 or more carbon atoms.

unit (a)
The fluoroolefins of unit (a) are olefins in which one or more of the hydrogen atoms have been replaced with fluorine atoms. In the fluoroolefin, one or more hydrogen atoms not substituted with fluorine atoms may be substituted with chlorine atoms. The number of carbon atoms in the fluoroolefin is preferably 2-8, particularly preferably 2-4.
Examples of fluoroolefins include CF2=CF2, CF2=CFCl, CF2=CHF, _{CH2 =} CF2, CF2 _{= CFCF3} , CF2 _{= CHCF3 , CF3 -} CH ₌ CHF _{, CF3} -CF= _CH2 . As the fluoroolefin, a coating film formed using a fluorine-containing paint using the present copolymer (hereinafter also referred to as a paint made from the present copolymer) (hereinafter also referred to as a coating film made from the present copolymer) From the viewpoint of weather resistance, CF ₂ =CF ₂ or CF ₂ =CFCl is preferred. Two or more fluoroolefins may be used in combination.

The content of the unit (a) based on fluoroolefin is, from the viewpoint of the dispersion stability in the paint of the present copolymer and the weather resistance of the coating film of the present copolymer, the content of the unit (a) based on the total units contained in the present copolymer. , preferably 20 to 80 mol %, more preferably 30 to 70 mol %, particularly preferably 45 to 55 mol %.

unit (b)
Unit (b) contributes to improving Tg and hydrophilicity of the present copolymer.
Vinyllactams are organic cyclic compounds containing the --C(.dbd.O)--N(-- _{CH.dbd.CH.sub.2} )-- group in the ring. Specifically, N-vinyl-β-propiolactam, N-vinyl-2-pyrrolidone, N-vinyl-γ-valerolactam, N-vinyl-2-piperidone, N-vinyl-ε-caprolactam, N- Examples include vinyl-heptolactam, 5-methyl-3-vinyloxazolidin-2-one, and the like. When the number of ring members increases, it becomes difficult to contribute to the improvement of the hydrophilicity of the present copolymer. Therefore, vinyl-lactams with a 7-membered ring or less are preferred. N-vinyl-ε-caprolactam is preferred from the viewpoint of improving Tg and hardness of the coating film. N-vinyl-ε-caprolactam is a compound represented by the following formula.

unit (c)
In unit (c), L is an alkylene group having 2 or more carbon atoms.
Although the number of carbon atoms in the alkylene group is not particularly limited, it is preferably 2 to 10, more preferably 4 to 6, and particularly preferably 5.
Specific examples of alkylene groups having 2 or more carbon atoms include ethyl, propyl, butyl, pentyl, hexyl and heptyl groups. The alkylene group may be linear or cyclic.
The unit (c) may be a unit formed by opening the lactam ring of the unit (b) during or after copolymerization.

The total content of units (b) and units (c) is preferably 20 to 80 mol%, more preferably 30 to 70 mol%, more preferably 45 to 55 mol%, based on the total units contained in the present copolymer. Especially preferred.

The content of units (c) is preferably 1 to 99 mol%, more preferably 10 to 50 mol%, and particularly preferably 16 to 20 mol%, based on the total of units (b) and (c).

The copolymer may contain units (d) other than units (a) to (c). As the unit (d), any unit other than the units (a) to (c) can be used without particular limitation.

unit (d)
Unit (d) may have a reactive group. Examples of reactive groups include hydroxyl groups, carboxy groups (excluding unit (c)), amino groups, epoxy groups, hydrolyzable silyl groups, and the like. The hydrolyzable silyl group is a group that becomes a silanol group by hydrolysis.
As the reactive group, a hydroxyl group is preferable from the viewpoint of the hardness of the coating film of the present copolymer.

Unit (d) may contain units based on any one selected from the group consisting of vinyl ether, vinyl ester, allyl ether, allyl ester, acrylate and methacrylate, and may contain units based on vinyl ether or vinyl ester. preferable.

Unit (d) is preferably a unit based on monomer (D) represented by the formula: X ² -Z ² .
X2 is _CH2 =CHO-, _CH2 =CHC(O)O-, ^CH2 = _CHCH2O- , _{CH2 =} CHCH2OC(O)-, _{CH2 =} CHOC(O)-, or CH ₂ =C(CH ₃ )C(O)O—.

Z ² is a monovalent hydrocarbon group having 1 to 24 carbon atoms. The monovalent hydrocarbon group may be linear or branched. Moreover, the monovalent hydrocarbon group may consist of a ring structure or may contain a ring structure. Moreover, the monovalent hydrocarbon group may be a monovalent saturated hydrocarbon group or a monovalent unsaturated hydrocarbon group.
The monovalent hydrocarbon group is preferably an alkyl group, a cycloalkyl group, an aryl group or an aralkyl group, and is an alkyl group having 2 to 12 carbon atoms, a cycloalkyl group having 6 to 10 carbon atoms, or an aryl group having 6 to 10 carbon atoms. Alternatively, an aralkyl group having 7 to 12 carbon atoms is particularly preferred.
Specific examples of alkyl groups include methyl, ethyl, tert-butyl, hexyl, nonyl, decyl and dodecyl groups.
A specific example of the cycloalkyl group is a cyclohexyl group.
A specific example of the aralkyl group is a benzyl group.
Specific examples of aryl groups include phenyl and naphthyl groups.

Two or more kinds of the monomer (D) may be used in combination.
Specific examples of the monomer (D) include ethyl vinyl ether, isobutyl vinyl ether, tert-butyl vinyl ether, 2-ethylhexyl vinyl ether, cyclohexyl vinyl ether, vinyl acetate, vinyl pivalate, and vinyl neononanoate (trade name "Veova 9" by HEXION). etc.), vinyl neodecanoate ("Veova 10", trade name of HEXION Co., etc.), and vinyl benzoate.
When the copolymer contains the unit (d), the content of the unit (d) is preferably 5 to 50 mol%, particularly preferably 10 to 30 mol%, based on the total units contained in the copolymer. .

The Tg of the present copolymer is preferably 20° C. or higher, more preferably 35° C. or higher, still more preferably 50° C. or higher, and particularly preferably 60° C. or higher, from the viewpoint of weather resistance of the coating film of the present copolymer. Although the upper limit of Tg is not particularly limited, it is preferably 150° C. or lower, more preferably 120° C. or lower, and particularly preferably 100° C. or lower from the viewpoint of liquid viscosity.

Mn of the present copolymer is preferably 1,000 or more, more preferably 5,000 or more, still more preferably 8,000 or more, and 10,000 or more, from the viewpoint of the impact resistance of the coating film of the present copolymer. is particularly preferred.
From the viewpoint of liquid viscosity, the Mn of the present copolymer is preferably 50,000 or less, more preferably 30,000 or less, and particularly preferably 20,000 or less.

The Mw of the present copolymer is preferably 10,000 or more, more preferably 20,000 or more, and particularly preferably 30,000 or more, from the viewpoint of the impact resistance of the coating film of the present copolymer.
From the viewpoint of liquid viscosity, the Mw of the present copolymer is preferably 100,000 or less, more preferably 80,000 or less, and particularly preferably 60,000 or less.

The acid value of the present copolymer is preferably 1 mgKOH/g or more, more preferably 5 mgKOH/g or more, still more preferably 10 mgKOH/g or more, and 20 mgKOH/g or more, from the viewpoint of the hardness of the coating film of the present copolymer. Especially preferred, 30 mgKOH/g or more is most preferred.
The acid value of the copolymer is preferably 100 mgKOH/g or less, more preferably 80 mgKOH/g or less, still more preferably 60 mgKOH/g or less, and particularly preferably 40 mgKOH/g or less, from the viewpoint of the stability of the copolymer. .

Method for producing a fluorine-containing copolymer As a specific example of the method for producing the present copolymer, a fluoroolefin and a vinyl lactam are copolymerized in the presence of a solvent and a radical polymerization initiator, and a ring in the vinyl lactam is A method of ring-opening the structure can be mentioned. In addition, you may add a monomer (D) further.
The vinyl lactam ring can be partially opened by, for example, heating a copolymer containing the units (a) and (b) at a high temperature of 60° C. or higher for a predetermined period of time.
The vinyl lactam ring can also be opened by using a basic catalyst. For example, by reacting a polymer with potassium t-butoxide as a basic catalyst, a partially ring-opened polymer can be obtained.

Specific examples of the polymerization method in the production method of the present copolymer include solution polymerization method, suspension polymerization method and emulsion polymerization method. Among these, the solution polymerization method is preferable because it is easy to control the content of Mn and each unit in the fluorine-containing copolymer within a predetermined range.

The solvent is preferably alcohol, and specific examples thereof include ethanol, butyl alcohol, propanol and butanol. Alcohol is superior to non-polar solvents such as xylene in dissolving fluoroolefins. Therefore, if alcohol is used as the polymerization solvent, it is easy to introduce the unit (a) into the present copolymer in an appropriate amount.

Specific examples of radical polymerization initiators include peroxydicarbonates, peroxyesters, ketone peroxides, peroxyketals, peroxycarbonate esters, diacyl peroxides and dialkyl peroxides.

The reaction temperature in polymerization is usually 0 to 130° C., the reaction pressure is usually 0 to 1.0 MPa, and the reaction time is usually 1 to 50 hours.

When preparing a fluorine-containing paint (hereinafter sometimes simply referred to as paint) using this copolymer, the copolymer is dispersed or dissolved in a solvent (water, organic solvent, etc.). It may be a powder coating composed of solid particles containing the present copolymer.
If the copolymer is dispersed or dissolved in a solvent (water, organic solvent, etc.), solvent-based paint in which the copolymer is dissolved in an organic solvent, or the copolymer is dispersed in water It is preferably a water-based paint that has

The content of the organic solvent in the solvent-based coating is preferably more than 90% by mass of the total mass of solvents contained in the solvent-based coating.
Specific examples of organic solvents include alcohols, ketones, esters and hydrocarbons. As the organic solvent, a weak solvent may be used from the viewpoint of environmental protection and excellent solubility of the present copolymer. Specific examples of weak solvents include organic solvents classified as class 3 organic solvents in the classification of organic solvents according to the Industrial Safety and Health Act, and mineral spirits are preferred. Two or more organic solvents may be used in combination.

The content of water in the water-based paint is preferably more than 90% of the total mass of the solvent contained in the water-based paint. The water-based paint may contain a water-soluble organic solvent as a solvent other than water.
Specific examples of water-soluble organic solvents include methanol, ethanol, butanol, acetone, and methyl ethyl ketone. Two or more kinds of water-soluble organic solvents may be used in combination.

In the case of a solvent-based paint or a water-based paint, the solid content concentration of the paint is preferably 25 to 80% by mass, particularly preferably 35 to 75% by mass. In the case of a solvent-based paint or a water-based paint, it may be a two-component paint that is used by mixing with a curing agent or the like immediately before coating, or a one-component paint that is used by coating the paint as it is. good.
If the paint is a solvent-based paint or a water-based paint, it may be a general liquid paint (paint applied by brush, roller, etc.) or an aerosol paint (paint applied by spraying). good.

When the paint is a powder paint, the powder paint may consist of the powder of the present copolymer alone, or may consist of a powder containing a component other than the fluorine-containing copolymer. The solid content concentration of the powder coating is preferably 95% by mass or more, particularly preferably 99% by mass or more.

The paint may contain additives. Specific examples of additives include pigments, curing agents, curing catalysts, film-forming aids, antifoaming agents, plasticizers, matting agents, UV absorbers, light stabilizers, leveling agents, degassing agents, fillers, Heat stabilizers, thickeners, dispersants, antistatic agents, rust preventives, silane coupling agents, and anti-pollution agents can be used.

The paint may contain pigments. Specific examples of pigments include antirust pigments, extender pigments, and color pigments.
Specific examples of antirust pigments include cyanamide zinc, zinc oxide, zinc phosphate, calcium magnesium phosphate, zinc molybdate, barium borate, and zinc calcium cyanamide.
Specific examples of extender pigments include talc, barium sulfate, mica, and calcium carbonate.
Specific examples of color pigments include quinacridone, diketopyrrolopyrrole, isoindolinone, indanthrone, perylene, perinone, anthraquinone, dioxazine, benzimidazolone, triphenylmethanequinophthalone, anthrapyrimidine, chrome, phthalocyanine, halogenated Phthalocyanine, azo pigment (azomethine metal complex, condensed azo, etc.), titanium oxide, carbon black, iron oxide, copper phthalocyanine, condensed polycyclic pigment.

Among the coloring pigments, the paint preferably contains a luster pigment.
Effect pigments consist of single metallic or inorganic particles or metallic or inorganic particles coated with a coating substance.
Specific examples of metal particles include particles containing metals (metals such as aluminum, zinc, copper, gold, silver, bronze, nickel, titanium, stainless steel, and alloys thereof), and particles containing oxides of these metals. (aluminum oxide particles, iron oxide particles).
Specific examples of inorganic particles include mica particles (mica powder), pearl particles, graphite particles, and glass flakes. Among them, metal particles are preferred, and particles containing aluminum are particularly preferred.

Two or more pigments may be used in combination.
When the paint contains a pigment, the content is preferably more than 0% by mass and 50% by mass or less with respect to the total mass of the paint.

The paint preferably contains a curing agent. The curing agent may be any compound that reacts with the present copolymer to form a crosslinked structure. A specific example of the curing agent is a compound that forms a crosslinked structure by reacting with the carboxyl group of the unit (c). Specifically, compounds having two or more epoxy groups, carbodiimide groups, oxazoline groups, or β-hydroxyalkylamide groups in one molecule are preferred.

Specific examples of compounds having two or more epoxy groups in one molecule include bisphenol-type epoxy compounds (A-type, F-type, S-type, etc.), diphenyl ether-type epoxy compounds, hydroquinone-type epoxy compounds, naphthalene-type epoxy compounds, and biphenyl-type epoxy compounds. Epoxy compounds, fluorene type epoxy compounds, hydrogenated bisphenol A type epoxy compounds, bisphenol A nucleated polyol type epoxy compounds, polypropylene glycol type epoxy compounds, glycidyl ester type epoxy compounds, glycidylamine type epoxy compounds, glyoxal type epoxy compounds, alicyclic compounds type epoxy compounds, alicyclic polyfunctional epoxy compounds, and heterocyclic epoxy compounds (triglycidyl isocyanurate, etc.).
Other specific examples of compounds having two or more epoxy groups in one molecule include "TM239" (manufactured by Nissan Chemical Industries, Ltd.) in which a methylene group is introduced into the glycidyl group portion of triglycidyl isocyanurate, and an epoxy compound having a triazine skeleton. "TEPIC-SP" (manufactured by Nissan Chemical Industries, Ltd.), and "PT-910" (manufactured by HUNTSMAN), which is a mixture of trimellitic acid glycidyl ester and terephthalic acid glycidyl ester.

Specific examples of compounds having two or more carbodiimide groups in one molecule include alicyclic carbodiimides, aliphatic carbodiimides, aromatic carbodiimides, polymers and modified products thereof.

Specific examples of compounds having two or more oxazoline groups in one molecule include addition-polymerizable oxazolines having 2-oxazoline groups and polymers of these addition-polymerizable oxazolines.
Other specific examples of compounds having two or more oxazoline groups in one molecule include Epocross WS-500, WS-700, K-2010, K-2020, and K-2030 manufactured by Nippon Shokubai Co., Ltd. (all trade names are ).

A specific example of the compound having two or more β-hydroxyalkylamide groups in one molecule is N,N,N',N'-tetrakis-(2-hydroxyethyl)-adipamide (PrimidXL-552, manufactured by EMS). , N,N,N',N'-tetrakis-(2-hydroxypropyl)-adipamide (Primid QM 1260, manufactured by EMS).

Two or more curing agents may be used in combination. For example, when the present copolymer contains a unit (d) having a reactive group in addition to the unit (c), an isocyanate curing agent or the like can be used in addition to the specific examples described above.
When the coating contains a curing agent, the content of the curing agent is preferably 2 to 50% by mass, particularly preferably 5 to 40% by mass, based on the solid content of the coating.

The paint may contain resins other than the present copolymer (fluorine-containing copolymers other than the present copolymer, non-fluorine resins, etc.). Non-fluororesins include alkyd resins, polyester resins, epoxy resins, urethane resins, vinyl acetate resins, (meth)acrylic resins, vinyl chloride resins, phenolic resins, silicone resins (including acrylic silicone resins, etc.), and the like.
When the paint contains the resin, it is preferably 1 to 200% by mass, more preferably 5 to 100% by mass, even more preferably 10 to 50% by mass, and 10 to 40% by mass, based on the copolymer in the paint. is particularly preferred.

Paints can be made using the copolymers.
When the paint is a solvent-based paint or water-based paint, the paint may be obtained by dissolving or dispersing the present copolymer in a solvent. At this time, components (additives, non-fluororesin, etc.) that may be contained in the paint described above may be added.
When the paint is a paint in which the present copolymer is dispersed in a solvent, the present copolymer is preferably present in the solvent in the form of particles. In this case, the average particle size of the particles of the present copolymer is preferably 10 to 200 nm.

When the paint is a powder paint, specific examples of the method for producing the paint include the following methods.
First, the present copolymer is melt-kneaded at 80 to 130° C. to obtain a melt-kneaded product. Next, the resulting melt-kneaded product is cooled to obtain a solidified melt-kneaded product. Then, the solidified melt-kneaded material is pulverized and classified to obtain a powder coating material having a desired particle size.
In the above method, the components (additives, non-fluororesin, etc.) that may be contained in the above paint can be added as appropriate. For example, the above components may be melt-kneaded together with the present copolymer, or may be dry-blended after pulverizing and classifying the present copolymer.
The average particle size of the powder coating is preferably 1-100 μm.

A paint is suitably used for producing a coated substrate having a substrate and a coating film formed on the substrate by the paint.
Specific examples of materials for the substrate include inorganic substances, organic substances, and organic-inorganic composite materials.
Specific examples of inorganic materials include concrete, natural stone, glass, and metals (iron, stainless steel, aluminum, copper, brass, titanium, etc.).
Specific examples of organic substances include plastics, rubbers, adhesives, and wood.
Specific examples of organic-inorganic composite materials include fiber-reinforced plastics, resin-reinforced concrete, and fiber-reinforced concrete.
Also, the base material may be one subjected to a known surface treatment (for example, chemical conversion treatment, etc.). Moreover, a resin layer (polyester resin, acrylic resin, etc.) may be formed on the surface of the substrate.

Among the above, the substrate is preferably metal, and particularly preferably aluminum. Base materials made of aluminum are excellent in anticorrosion properties, lightweight, and suitable for use as building materials such as exterior members.
The shape, size, etc. of the substrate are not particularly limited.
Specific examples of the base material include composite panels, curtain wall panels, curtain wall frames, window frames and other construction exterior members, tire wheels and other automobile members, construction machinery, and motorcycle frames.

The film thickness of the coating film is preferably 20 to 1,000 μm, particularly preferably 20 to 500 μm. For applications such as members for high-rise buildings such as aluminum curtain walls, the thickness is preferably 20 to 90 μm. The thickness is preferably 100 to 200 μm for applications requiring high weather resistance, such as outdoor units of air conditioners installed along the coast, traffic signal poles, and signs.

When the paint is a solvent-based paint or a water-based paint, a specific example of the method of forming the coating film is a method of coating the present paint on a base material to form a coating layer, and drying the coating layer to obtain a coating film. is mentioned.
When the paint is a solvent-based paint or a water-based paint, specific examples of the coating method include methods using a spray, applicator, die coater, bar coater, roll coater, comma coater, roller brush, brush, and spatula. .
When the coating contains a curing agent, the coating is preferably heat-treated. The heating temperature is preferably 50 to 120° C., and the heating time is preferably 1 to 60 minutes. It is preferable to cool after heating.

When the paint is a powder paint, as a specific example of the method of forming the coating film, the paint is applied onto the base material to form a coating layer, and the coating layer is heated to form a melt of the powder coating. A method of obtaining a molten film and cooling the obtained molten film to obtain a coating film may be used. The formation of the coating film may be performed simultaneously with the formation of the coating layer on the substrate, or may be performed separately after the coating layer is formed.
The heating temperature (hereinafter also referred to as "baking temperature") and the heating maintenance time (hereinafter also referred to as "baking time") for heating and melting the paint and maintaining the molten state for a predetermined time are determined by the paint. It is appropriately set according to the type and composition of the raw material components, the desired film thickness of the coating film, and the like.

The baking temperature is usually 120-250°C. Baking time is usually 1 to 60 minutes. The cooling temperature for cooling the molten film is preferably 20 to 25°C. Cooling may be rapid cooling or slow cooling, and slow cooling is preferable from the viewpoint of better adhesion of the coating film to the substrate.

When the paint is a powder paint, specific examples of the coating method include electrostatic coating, electrostatic spraying, electrostatic dipping, fluidization dipping, and spraying. Application of the powder coating is preferably carried out using an electrostatic coating gun such as a corona charge type coating gun or a friction charge type coating gun.

The present invention will be described in detail below with reference to examples. However, the present invention is not limited to these examples. Examples 1-5 are working examples, and example 6 is a comparative example.

(Meaning of abbreviations of ingredients used)
CTFE: chlorotrifluoroethylene NVC: N-vinyl-ε-caprolactam NVP: N-vinyl-2-pyrrolidone EVE: ethyl vinyl ether CHVE: cyclohexyl vinyl ether 2-EHVE: 2-ethylhexyl vinyl ether HBVE: 4-hydroxybutyl vinyl ether

上記式中、Ｌは炭素数５のアルキレン基である。
重合後の含フッ素共重合体をＮＭＲおよびＩＲで測定して得られた、含フッ素共重合体が含む全単位に対する、各単量体に基づく単位の含有割合を表１に示す。なお、表中、ＮＶＣに基づく単位のカプロラクタム環が開環して形成される単位をＮＶＣ開環体、ＮＶＰに基づく単位のカプロラクタム環が開環して形成される単位をＮＶＰ開環体と記載した。また、表中、ＮＶＣまたはＮＶＰに基づく単位と、ＮＶＣ開環体またはＮＶＰ開環体に基づく単位との合計モル数に対する、ＮＶＣまたはＮＶＰに基づく単位の含有割合を、ＮＶＣ／ＮＶＰ開環率と記載した。 [Example 1]
In the autoclave, 1,021 g of xylene, 2.75 g of Tinuvin292 (BASF product), 2.75 g of KW500SH (Kyowa Chemical Industry Co., Ltd. product), 255 g of CTFE, 244 g of NVC, and 51 g of HBVE were charged, and vacuum was applied. Degassed.
Next, a 10 mass % xylene solution (32 mL) of tert-butyl peroxypivalate was added as a polymerization initiator to carry out polymerization. During the polymerization, the above polymerization initiator (32 mL) was continuously added. Polymerization was continued with stirring, and after 8 hours, the autoclave was water-cooled to terminate the polymerization, and the solution in the autoclave was filtered to obtain a solution containing a fluorine-containing copolymer.
The obtained solution was vacuum-dried at 65° C. for 24 hours to remove the solvent, and further vacuum-dried at 130° C. for 20 minutes to obtain a sheet-like fluorine-containing copolymer.
When the IR spectrum of the obtained fluorine-containing copolymer was measured, the absorption of the tertiary amide (1650 cm ⁻¹ ) in the caprolactam ring of NVC and the carboxyl group of the unit formed by opening the caprolactam ring of NVC ( 1710 cm ^-1 ) was observed. Therefore, the fluorine-containing copolymer contains a unit (formula below) formed by opening the caprolactam ring of the NVC-based unit.

In the above formula, L is an alkylene group having 5 carbon atoms.
Table 1 shows the content ratio of units based on each monomer with respect to the total units contained in the fluorine-containing copolymer obtained by measuring the fluorine-containing copolymer after polymerization by NMR and IR. In the table, the unit formed by opening the caprolactam ring of the unit based on NVC is described as the NVC ring-opened product, and the unit formed by ring-opening the caprolactam ring of the unit based on NVP is described as the NVP ring-opened product. did. In addition, in the table, the content ratio of units based on NVC or NVP with respect to the total number of moles of units based on NVC or NVP and units based on the NVC ring-opened form or NVP ring-opened form is referred to as the NVC/NVP ring-opening ratio. Described.

The resulting fluorine-containing copolymer (67.3 g), and a curing agent (Cymel 303 (product of Nippon Cytec Co., Ltd., methylated melamine resin curing agent)) (28.9 g), (dibutyltin dilaurate (Tokyo Chemical Industry Co., Ltd.) and curing catalyst) (0.0002 g) were mixed using a disper to obtain a paint.
The resulting paint was applied by spraying to an alodine-treated aluminum substrate (thickness: 0.8 mm) of 150 mm × 70 mm, and cured by heating at 140°C for 30 minutes to form a coating film (thickness: 50 µm). ) to obtain a substrate with a coating film.
The obtained base material with a coating film was subjected to evaluation described later. Table 2 shows the results.

[Examples 2 to 6]
A fluorine-containing copolymer of each example was obtained in the same manner as in Example 1, except that the type and amount of the monomers used were changed. Furthermore, substrates with coating films of Examples and Comparative Examples were produced in the same manner as in Example 1 except that the type of fluorine-containing copolymer used was changed, and subjected to the evaluations described below. Results are shown in Tables 1 and 2.

上記式中、Ｌは炭素数３のアルキレン基である。 All of the fluorine-containing copolymers obtained in Examples 1 to 3 contained units (formula above) formed by opening the caprolactam ring of the NVC-based unit. Further, the IR spectra of the fluorine ^- containing copolymers obtained in Examples 4 and 5 were measured. Absorption of the carboxyl group (1710 cm ^-1 ) of the unit formed by opening the five-membered lactam ring of was observed. Therefore, the fluorine-containing copolymer contains a unit (formula below) formed by opening the five-membered lactam ring of the NVP-based unit.

In the above formula, L is an alkylene group having 3 carbon atoms.

[Adhesion]
The adhesion of the coating film to the substrate was measured by the cross-cut method according to JIS K 5600-5-6. The coating film of the test piece was cut in a grid pattern of 100 squares with 1 mm intervals, an adhesive tape was attached on it, and then the adhesive tape was peeled off. Adhesion was evaluated according to the following criteria from the number of squares (number of squares/100).
A: More than 90 squares.
B: The number of squares is less than 90.

〔hardness〕
The pencil hardness of the coating film was measured according to JIS K 5600-5-4.
There are 14 types of pencil hardness from 6B to B, HB, F, H to 6H, with 6B being the softest and 6H being the hardest.

含フッ素共重合体がＣＴＦＥに基づく単位、ＮＶＣに基づく単位またはＮＶＰに基づく単位、および、ＮＶＣまたはＮＶＰに基づく単位のカプロラクタム環が開環して形成される単位を有する例１～５は、含フッ素重合体のＴｇが高く、かつ含フッ素塗料に用いた場合に硬度が高い塗膜を形成できる。

Examples 1 to 5 in which the fluorine-containing copolymer has CTFE-based units, NVC-based units or NVP-based units, and units formed by opening the caprolactam ring of NVC- or NVP-based units include The Tg of the fluoropolymer is high, and when used in a fluorine-containing paint, a coating film with high hardness can be formed.

Claims (6)

fluoroolefin-based units (a);
units (b) based on vinyl lactams;
A fluorine-containing copolymer characterized by comprising a unit (c) represented by the following formula.

(In the formula, L is an alkylene group having 2 or more carbon atoms.) 2. The fluorine-containing copolymer according to claim 1, further comprising units (d) based on vinyl ether or vinyl ester. 3. The fluorine-containing copolymer according to claim 1, which has a glass transition temperature of 20° C. or higher. 4. The fluorocopolymer according to any one of claims 1 to 3, wherein the unit (b) is a unit based on N-vinyl-ε-caprolactam. The fluorine-containing copolymer according to any one of claims 1 to 4, which has an acid value of 1 mgKOH/g or more. The fluorine-containing copolymer according to any one of claims 1 to 5, which has a number average molecular weight of 1,000 or more.