JPH0733842A - Fluorine-containing block copolymer and coating composition - Google Patents

Abstract

(57) [Summary] [Structure] Having at least two different block chains,
Further, each block chain is composed of a copolymer of fluoroolefin and another vinyl-based monomer, and the difference in glass transition temperature between the copolymers forming each block chain is 5 ° C. or more. Copolymer. [Effect] The fluorine-containing block copolymer of the present invention has a T
It has both bendability and hardness, and is useful when used as a precoat paint. Further, if the combination of block chains having different physical properties other than the glass transition temperature is selected, the application will be further expanded, and it is useful as a resin for a novel paint.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a fluorine-containing block copolymer and a coating composition.

[0002]

2. Description of the Prior Art The applicant of the present invention has found that fluoroolefin, cyclohexyl vinyl ether, alkyl vinyl ether,
Hydroxyalkyl vinyl ether copolymers can be cured by baking at room temperature and with a curing agent such as melamine and isocyanate, giving a weather-resistant coating film with excellent gloss, solvent resistance, chemical resistance, and water repellency. It has already been found (JP-A-57-34107 and JP-A-58-136).
662).

However, the above-mentioned copolymer is inferior in T-folding property to the conventional thermoplastic coating made of polyvinylidene fluoride / acrylic resin, and when used as a coating for pre-coated metal, it has an edge portion after bending. If the glass transition temperature of the coating film is lowered in order to easily cause microcracks, the hardness of the coating film becomes insufficient and the surface becomes tacky.

[0004]

DISCLOSURE OF THE INVENTION The present invention overcomes the drawbacks of the above-mentioned fluorine-containing copolymer, which has hitherto been difficult to achieve both T-bending property and hardness of a coating film as a coating material for precoat metal, and has mechanical properties. An object of the present invention is to provide a fluorine-containing block copolymer and a coating composition that give excellent coating properties.

[0005]

In the present invention, the production of the fluorine-containing block copolymer is carried out at least 2 per molecule.
It can be carried out by using a polymerization initiator having a certain type of polymerization initiation group or generating a new polymerization initiation group after the first stage polymerization. When the A block portion is polymerized using such a polymerization initiator, a polymeric initiator having a polymerization initiation group in the molecule is produced. Further changing the polymerization conditions B
If the block portion is polymerized, an AB block copolymer is produced.

As the initiator used here, there is a radical polymerization initiator having two or more kinds of polymerization initiation groups having sufficiently different decomposition temperatures in one molecule. For example, an asymmetric alkyl perester compound as shown in [Chemical formula 1], Examples thereof include an azo compound containing an alkyl perester group as shown in 2] and a peroxyketal compound as shown in [Chemical Formula 3].

[0007]

[Chemical 1]

[Chemical 2]

[Chemical 3]

Further, the polymerization mode may be different between the polymerization of the A block portion and the polymerization of the B block portion.
It is also possible to use the following initiators in which the block portion starts by heating. Examples of such compounds include alicyclic azoamidine compounds represented by [Chemical formula 4] and ketone peroxide compounds represented by [Chemical formula 5].

[0009]

[Chemical 4]

[Chemical 5]

The amount of the polymerization initiator used can be appropriately changed depending on the kind and the conditions of the copolymerization reaction, but usually 0.05 to 0.5% by weight based on the total amount of the monomers to be copolymerized. % Is used.

In the fluorine-containing block copolymer of the present invention, the fluorine-containing copolymer resin composition of the A block and the B block contains 40 to 60 mol% of the fluoroolefin polymer unit represented by [Chemical Formula 6], 0] to 55 mol% of the vinyl-based polymer units represented by [7] and 0-55 mol% of the polymer units having a curing reactive site represented by [Chemical Formula 8].

[Chemical formula 6], [Chemical formula 7] and [Chemical formula 8]
In the formula, X ¹ is fluorine, chlorine, a perfluoroalkyl group having 1 to 8 carbon atoms (provided that the perfluoroalkyl group may contain an ether bond) or 1 carbon atom.
Represents a perfluoroalkoxy group of ~ 8. R ¹ represents hydrogen or a methyl group. R ² is an alkyl group having 1 to 12 carbon atoms, a cycloalkyl group having 3 to 12 carbon atoms, or 2 carbon atoms.
It represents a fluoroalkyl group of 10 to 10. R ³ represents hydrogen or a methyl group. R ⁴ represents a divalent organic group. Z represents a curing reactive site. p, q and r are each independently 0 or 1
Represents

[0013]

[Chemical 6]

[Chemical 7]

[Chemical 8]

The fluorine-containing copolymer of the A block portion of the fluorine-containing block copolymer of the present invention is obtained by copolymerizing the monomers represented by the following [Chemical Formula 9], [Chemical Formula 10] and [Chemical Formula 11]. It can be obtained by

[0015]

Embedded image CF ₂ ═CFX ¹ (wherein X ¹ is fluorine, chlorine, or a perfluoroalkyl group having 1 to 8 carbon atoms (provided that
An ether bond may be contained in the perfluoroalkyl group. ) Or a perfluoroalkoxy group having 1 to 8 carbon atoms. )

[0016]

Embedded image CH ₂ ═CR ¹ (CH ₂ ) _p O (C═O) _q
R ² (wherein R ¹ represents hydrogen or a methyl group. R ² represents an alkyl group having 1 to 12 carbon atoms, a cycloalkyl group having 3 to 12 carbon atoms or a fluoroalkyl group having 2 to 10 carbon atoms. P Represents 0 or 1, and q represents 0 or 1.)

[0017]

Embedded image CH ₂ ═CR ³ (CH ₂ ) _r OR ⁴ Z (wherein R ³ represents hydrogen or a methyl group, R ⁴ represents a divalent organic group, r represents 0 or 1) Z Represents a curing reactive site.)

Here, if the amount of the fluoroolefin-based polymer represented by [Chemical Formula 6] is less than the above range, sufficient weather resistance cannot be obtained when used as a paint base, which is not preferable. On the other hand, if the amount is too large, the solubility in various solvents decreases, making it difficult to use as a paint base or paint additive.

Examples of the fluoroolefin-based monomer represented by [Chemical Formula 9] include tetrafluoroethylene, chlorotrifluoroethylene, trifluoroethylene, vinylidene fluoride, hexafluoropropylene, pentafluoropropylene and the like having 2 to 2 carbon atoms. Fluoroolefin of about 4 or perfluoropropyl vinyl ether, perfluoro-2-methyl-3-oxahexyl vinyl ether, X ¹ is a linear, branched or cyclic perfluorovinyl ether having about ¹ to 8 carbon atoms. Is mentioned.

If the vinyl-based polymer unit represented by the formula [Chem. 7] is less than the above range, the properties of the coating film will not be sufficient, and if it is too large, the weather resistance of the coating film will deteriorate. Is not preferable. A particularly suitable range of the vinyl polymer unit represented by [Chemical Formula 8] is 5 to 55 mol%.

Examples of vinyl monomers represented by [Chemical Formula 10] include the following.

Vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, propyl vinyl ether, butyl vinyl ether and cyclohexyl vinyl ether.

Isopropenyl ethers such as methyl isopropenyl ether, ethyl isopropenyl ether, propyl isopropenyl ether, butyl isopropenyl ether and cyclohexyl isopropenyl ether.

Linear vinyl carboxylates or carboxylic acids such as vinyl acetate, vinyl propionate, vinyl butyrate, vinyl caproate, vinyl caprylate, vinyl stearate, isopropenyl acetate, isopropenyl propionate, isopropenyl butyrate, etc. Isopenyls.

Allyl ethers such as ethyl allyl ether, propyl allyl ether, butyl allyl ether and isobutyl allyl ether.

Allyl carboxylates such as allyl acetate, allyl propionate, allyl butyrate and allyl isobutyrate.

Further, the polymerized unit having a curing reactive site represented by [Chemical Formula 8] affects the curability, solubility, compatibility of the resin and the adhesion to the substrate. A particularly preferable range of the polymerized unit having a curing reactive site represented by [Chemical Formula 8] is 5 to 20 mol%.

As the curing reactive site of the vinyl-based monomer having the curing reactive site represented by [Chemical Formula 11], a hydroxyl group, a carboxyl group, an acid amide group, an amino group, a mercapto group, a β-keto ester group can be used. , An active hydrogen group such as a silanol group, an active halogen group such as an epoxy group, bromine or iodine, and the like.

Of these, the active hydrogen-containing group is preferable in that it has excellent reactivity with isocyanate type curing agents and aminoplast type curing agents which are usually used as curing agents, and helps improve compatibility with other resins. Especially preferred are hydroxyl and carboxyl groups.

Further, R ⁴ of the vinyl monomer having a curing reactive site represented by [Chemical Formula 11] is an alkylene group, a cycloalkylene group, an arylene group, a (poly) oxyalkylene group, (poly ) Ester chains and (poly) siloxy groups are preferred. Also, if the chain length of R ⁴ is increased,
A flexible coating film can be obtained, but if it is too long, the weather resistance and coating film hardness may decrease, which is not preferable. Further, if it is too short, the reactivity of the curing-reactive site becomes low and it may be difficult to obtain a cured coating film. Suitably, the chain of R ⁴ is a bond of 1 to 20, especially 2 to 12, atoms.

Examples of the vinyl-based monomer having a curing reactive site include the following vinyl-based monomers having active hydrogen.

2-hydroxyethyl vinyl ether, 3
-Hydroxypropyl vinyl ethers such as hydroxypropyl vinyl ether, 4-hydroxybutyl vinyl ether, 9-hydroxynonyl vinyl ether, 1-hydroxymethyl-4-vinyloxymethyl cyclohexane and 3-chloro-2-hydroxypropyl vinyl ether.

2-hydroxyethyl isopropenyl ether, 3-hydroxypropyl isopropenyl ether, 4-hydroxybutyl isopropenyl ether, 9
-Hydroxyalkyl isopropenyl ethers such as hydroxynonyl isopropenyl ether, 1-hydroxymethyl-4-isopropenoxymethyl cyclohexane and 3-hydroxy-2-chloropropyl isopropenyl ether.

Hydroxyalkyl allyl ethers such as 2-hydroxyethyl allyl ether.

[Chemical formula 12], [Chemical formula 13], [Chemical formula 14],
Polyether macromonomers having a vinyloxy group, an isopropenoxy group, or an allyloxy group at one end and a hydroxyl group at the other end, such as [Chemical Formula 15].

Polyester macromonomers having a vinyloxy group or an isopropenoxy group at one end and a hydroxyl group at the other end, such as [Chemical Formula 16].

Polysiloxane macromonomers having a vinyloxy group or an isopropenoxy group at one end and a hydroxyl group at the other end, such as [Chemical Formula 17].

A monomer having a vinyloxy group or an isopropenoxy group at one end and a carboxyl group at the other end, such as [Chemical Formula 18].

A monomer having a vinyloxy group or an isopropenoxy group at one end and a β-ketoester group at the other end, such as [Chemical Formula 19].

[0040]

[Chemical 12]

[Chemical 13]

[0041]

[Chemical 14]

[Chemical 15]

[0042]

[Chemical 16]

[Chemical 17]

[0043]

[Chemical 18]

[Chemical 19]

As the vinyl-based monomer having a curing reactive site other than active hydrogen, a chain-like or alicyclic epoxy or glycidyl group such as [Chemical Formula 20], [Chemical Formula 21] or [Chemical Formula 22] is used. And a monomer having a vinyloxy group or an isopropenoxy group.

[0045]

[Chemical 20]

[Chemical 21]

[Chemical formula 22]

These monomers represented by [Chemical Formula 9] to [Chemical Formula 11] may be used alone,
Multiple types may be used in combination.

The difference in glass transition temperature between the A block chain and the B block chain of the fluorine-containing block copolymer of the present invention is preferably 5 ° C. or more. If the temperature difference is less than this, there is almost no difference between the thermodynamic and mechanical properties of the A and B chains, which is meaningless.

Further, the higher glass transition temperature is preferably in the range of 20 to 60 ° C. due to the restriction of the bending property of the coating film, and the lower glass transition temperature causes the tackiness of the coating film surface. It is desirable that the temperature is within the range of -20 ° C to 30 ° C so as not to occur.

When the fluorine-containing block copolymer of the present invention is used as a paint base, the intrinsic viscosity in tetrahydrofuran at 30 ° C. in the uncrosslinked state (hereinafter,
[Η]) is preferably 0.05 to 2.0 dl / g. When [η] is smaller than the above range, the strength of the coating film is difficult to obtain, and when it is large, it is not preferable because it is poor in paintability and coating workability. In particular, [η] is 0.1
Those of 1.5 dl / g are preferable.

In the copolymerization reaction of the A block portion of the block copolymer, the reaction mode is not particularly limited as long as the polymerization conditions of the A block portion and the B block portion are different, and bulk polymerization, Although suspension polymerization, emulsion polymerization, solution polymerization and the like can be adopted, emulsion polymerization, suspension polymerization, t-butanol, etc. in an aqueous medium are taken into consideration due to the stability of the polymerization operation and the ease of separation of the produced copolymer. Solution polymerization using alcohols, esters, hydrogen-containing saturated halogenated hydrocarbons containing one or more fluorine atoms and hydrogen atoms, aromatic hydrocarbons such as xylene, etc. as a solvent is preferably adopted.

When the copolymerization reaction is carried out in an aqueous medium, a basic buffer is added to adjust the pH of the liquid during the polymerization.
It is preferable that the value is 4 or more, preferably 6 or more.
The addition of the basic substance is also effective in the case of solution polymerization. Further, the polymerization reaction of the B block portion is not particularly limited, and all the above reaction modes can be adopted.

Further, these methods are batch type, semi-continuous type,
Of course, it can be performed by a continuous operation. In this copolymerization reaction, the copolymerization reaction temperature is -3.
Within the range of 0 ° C to + 150 ° C, the optimum value is appropriately selected depending on the type of the polymerization initiator, the polymerization medium and the like. When using a polymerization initiator in which both the A block portion polymerization and the B block portion polymerization are initiated by heating, the polymerization temperature difference between A and B is 20 ° C. or more in order to obtain a sufficiently high blocking efficiency. Is desirable. When the polymerization reaction is carried out in an aqueous medium, a temperature of 0 ° C. to + 100 ° C., preferably 10 ° C. to 80 ° C. can be adopted. In order to carry out the polymerization reaction in a solution medium, 0 ° C to 150 ° C,
Preferably, about 30 ° C to 120 ° C is adopted. Also,
The reaction pressure can be appropriately selected, but is usually 1 to 10
It is desirable to adopt 0 kg / cm ² , especially about ² to 50 kg / cm ² .

In order to suppress the [η] of the produced copolymer within the above range, a reaction medium having a relatively large chain transfer constant may be used, or the copolymerization reaction may be appropriately performed in the coexistence of a chain transfer agent. Is preferred.

When the fluorine-containing block copolymer of the present invention is used as a coating base, a coating composition can be prepared by adding a curing agent or the like. As the curing agent, one having a group capable of reacting with the curing reaction site of the fluorine-containing copolymer of the present invention and giving a good cured product is adopted. Examples of such a curing agent include polyisocyanates, aminoplasts, polybasic acid anhydrides, metal alkoxides, and the like.

Examples of the polyisocyanate system include polyisocyanate compounds such as hexamethylene diisocyanate and isophorone diisocyanate, silyl isocyanate compounds such as methylsilyl triisocyanate, partial condensates and polymers thereof, and isocyanate groups blocked with phenol and the like. Examples include blocked polyisocyanate compounds blocked with agents. Particularly, a non-yellowing type is preferably used.

As the aminoplast, melamine resin,
Guanamine resin, urea resin, etc. are adopted. Among them, methylol melamine at least partially etherified with one or more lower alcohols such as methanol, ethanol, propanol and butanol is used.

As the polybasic acid anhydride, phthalic anhydride,
Examples thereof include aromatic polyvalent carboxylic acid anhydrides such as trimellitic anhydride, and aliphatic polyvalent carboxylic acid anhydrides such as maleic anhydride and succinic anhydride.

In the present invention, when a curing agent is blended to prepare a coating composition, the blending amount of each component can be appropriately selected, but the fluorine-containing block copolymer of the present invention has weather resistance and the like. In order not to impair the excellent coating film performance, the curing agent should be 0.10 parts per 100 parts of the fluorine-containing block copolymer.
An amount of about 5 to 300 parts by weight is used. In particular, the curing agent is added in an amount of 5.0 to 100 per 100 parts of the fluorine-containing block copolymer.
It is preferably about 100 parts by weight.

The coating composition of the present invention may optionally contain various additives in addition to the above two components. Such additives include solvents, synthetic resins, curing catalysts, dryers, heat stabilizers, leveling agents, lubricants, pigments, dyes,
Viscosity modifiers, dispersion stabilizers, ultraviolet absorbers, gelation inhibitors and the like can be mentioned.

Particularly, when an ultraviolet absorber is added,
Even when a transparent coating film is formed, the effect of protecting the substrate is sufficiently exhibited, which is preferable. As such an ultraviolet absorber, it is possible to use all of the ultraviolet absorbers that can usually be blended in the paint,
For example, a phenyl salicylate-based, benzotriazole-based, benzophenone-based ultraviolet absorber or the like can be used. Further, by using a reactive ultraviolet absorber, it is possible to exert its effect for a long period of time. The ultraviolet absorber is about 0.01 to 50 parts by weight per 100 parts of the fluorine-containing block copolymer, and particularly,
It is preferably used in the range of about 0.1 to 30 parts by weight.

When the fluorine-containing block copolymer of the present invention is dissolved or dispersed in an organic solvent, the solvent includes aromatic hydrocarbons such as xylene and toluene, alcohols such as n-butanol, and butyl acetate. In addition to the esters, ketones such as methyl isobutyl ketone, and ethyl cellosolve glycol ethers, various commercially available thinners can be adopted, and these can be mixed and used at various ratios.

When preparing the coating composition of the present invention,
Various compounding machines such as a ball mill, a sand mill, a jet mill, a kneader, a triple roll, and a paint shaker which are usually used for compounding a resin composition can be used.

[0063]

EXAMPLES The present invention will be specifically described below with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples and Comparative Examples.

Example 1 80.1 g of cyclohexyl vinyl ether (hereinafter referred to as CHVE) and 4-hydroxybutyl vinyl ether (hereinafter referred to as HBVE) were placed in a 500 ml stainless steel autoclave equipped with a stirrer.
18.4 g, cupric chloride (anhydrous) 0.006 g,
2.2 g of 2,2'-azobis [2- (2-imidazolin-2-yl) propane] dihydrochloride (VA-061: manufactured by Wako Pure Chemical Industries, Ltd.) and polyvinyl alcohol (hydrolysis rate 70%) of 0.2 g were used. 3 g and 304 g of water were charged, and after cooling with ice, dissolved oxygen was removed by pressurizing nitrogen and degassing.

Thereafter, 92.5 g of chlorotrifluoroethylene (hereinafter referred to as CTFE) was introduced into the autoclave, and stirring was continued at 40 ° C. for 5 hours. Then, the reaction product was poured into a large amount of methanol to remove the supernatant liquid, and then dried at room temperature under a reduced pressure of 1 mmHg for 24 hours to obtain 154.4 g of prepolymer A. The glass transition temperature of this prepolymer was measured by differential scanning calorimetry (DS
It was 46 ° C. as measured by C). Next, in an autoclave made of stainless steel having an internal volume of 250 ml, 54.7 g of the prepolymer A, 21.0 g of n-butyl vinyl ether (hereinafter referred to as n-BVE), HBVE6.
1 g, xylene 94.4 g, ethanol 26.6 g, and potassium carbonate 0.8 g were charged, and dissolved oxygen was removed by solidification and deaeration with liquid nitrogen.

Thereafter, 30.5 g of CTFE was introduced into the autoclave, and the temperature was gradually raised. After the temperature in the autoclave reached 65 ° C., the reaction was continued under stirring for 24 hours, and then the autoclave was cooled with ice to stop the reaction.
After reaching room temperature, unreacted monomers were purged and the autoclave was opened.

The polymer obtained was treated with water / methanol (1:
1), and after removing the supernatant liquid, the mixture was heated to 120 ° C., dried under a reduced pressure of 1 mmHg for 4 hours, and then crushed with an impact hammer to obtain a homopolymer of a fluorine-containing block copolymer, and 109.4 g of a mixture of homopolymers of a fluorine-containing copolymer was obtained. The glass transition temperature of this mixture was measured by DSC, but no clear peak was observed. The value of [η] of the obtained fluorine-containing block copolymer was 0.10 dl / g. Further, it was confirmed from the IR spectrum that polymerized units such as CTFE and vinyl ether were copolymerized.

In order to know the glass transition temperature of the block chain polymerized in the second stage, a homopolymer having the same composition as this block chain was polymerized. N-BVE 23.0 g, HBV in a stainless steel autoclave with an internal volume of 250 ml
E6.8 g, xylene 104.9 g, ethanol 29.
6 g, t-butyl peroxy-2-ethyl hexanoate (Perbutyl O: manufactured by NOF CORPORATION) and 0.9 g of potassium carbonate were charged, and dissolved oxygen was removed by solidification and deaeration with liquid nitrogen.

After that, 33.9 g of CTFE was introduced into the autoclave, and the temperature was gradually raised. After the temperature in the autoclave reached 65 ° C., the reaction was continued under stirring for 24 hours, and then the autoclave was cooled with ice to stop the reaction.
After reaching room temperature, unreacted monomers were purged and the autoclave was opened.

The obtained polymer was mixed with water / methanol (1:
It was put into 1), and after removing the supernatant liquid, it was heated to 120 ° C., dried under a reduced pressure of 1 mmHg for 4 hours, and then pulverized with an impact hammer to obtain 58.8 g of a homopolymer. The glass transition temperature of this homopolymer was −5 ° C.

Example 2 CHVE 44.1 g and EVE 4 were placed in a stainless steel autoclave having an internal volume of 500 ml.
2.0 g, HBVE 27.1 g, xylene 142.8
g, ethanol 35.7 g, potassium carbonate 2.8 g, and di-t-butylperoxytrimethyl adipate (Kayaester TMA: manufactured by Kayaku Akzo Co., Ltd.) 1.65 g,
Dissolved oxygen was removed by solidification and degassing with liquid nitrogen.

After that, 135.8 g of CTFE was introduced into the autoclave and the temperature was gradually raised. After the temperature in the autoclave reached 65 ° C., the reaction was continued under stirring for 5 hours, and then the autoclave was cooled with ice to stop the reaction.
After reaching room temperature, unreacted monomers were purged and the autoclave was opened. Then, the reaction product was poured into water / methanol to remove the supernatant liquid, and then dried at room temperature under a reduced pressure of 1 mmHg for 24 hours to obtain 230.6 g of a prepolymer B. The glass transition temperature of this prepolymer was 36 ° C. as measured by DSC. When the amount of active oxygen in this prepolymer B was determined by iodometric titration, it was found that 0.44 active oxygen was contained per chain length of prepolymer B.

Next, 48.0 g of the above prepolymer B and CHVE1 were placed in a stainless steel autoclave having an internal volume of 250 ml.
1.6 g, n-BVE 9.2 g, HBVE 5.3 g, and xylene 73.0 g were charged, and dissolved oxygen was removed by solidification and deaeration with liquid nitrogen.

Thereafter, 27.0 g of CTFE was introduced into the autoclave and the temperature was gradually raised. After the temperature in the autoclave reached 120 ° C., the reaction was continued for 5 hours with stirring, and then the autoclave was cooled with ice to stop the reaction.
After reaching room temperature, unreacted monomers were purged and the autoclave was opened. Then, the reaction product was poured into water / methanol, and after removing the supernatant liquid, the mixture was heated to 120 ° C. for 1 m.
After drying under reduced pressure of mHg for 4 hours, the resulting mixture was crushed with an impact hammer to obtain a mixture of a homopolymer of a fluorine-containing block copolymer and a homopolymer of a fluorine-containing copolymer 6.
1.3 g was obtained. The glass transition temperature of this mixture is determined by DSC
However, no peak was observed. The value of [η] of the obtained fluorine-containing block copolymer was 0.1.
It was 0 dl / g.

In order to know the glass transition temperature of the block chain polymerized in the second stage, a homopolymer having the same composition as this block chain was polymerized. CHVE 18.0 g, n-BV in a stainless steel autoclave with an internal volume of 250 ml.
E14.4g, HBVE8.2g, xylene 114.3
g, perbutyl O 0.3 g and potassium carbonate 0.9 g
Then, dissolved oxygen was removed by solidifying and degassing with liquid nitrogen.

Thereafter, 42.3 g of CTFE was introduced into the autoclave and the temperature was gradually raised. After the temperature in the autoclave reached 65 ° C., the reaction was continued under stirring for 24 hours, and then the autoclave was cooled with ice to stop the reaction.
After reaching room temperature, unreacted monomers were purged and the autoclave was opened.

The obtained polymer was mixed with water / methanol (1:
1), and after removing the supernatant liquid, the mixture was heated to 120 ° C., dried under a reduced pressure of 1 mmHg for 4 hours, and then pulverized with an impact hammer to obtain 76.2 g of a homopolymer. The glass transition temperature of this homopolymer was 12 ° C.

Comparative Example CHVE 44.1 g and EVE 4 were placed in a stainless steel autoclave having an internal volume of 500 ml.
2.0 g, HBVE 27.1 g, xylene 142.8
g, ethanol 35.7 g, and potassium carbonate 2.8.
g, perbutyl O 0.65 g was charged, and dissolved oxygen was removed by solidification and degassing with liquid nitrogen.

After that, 135.8 g of CTFE was introduced into the autoclave, and the temperature was gradually raised. After the temperature in the autoclave reached 65 ° C., the reaction was continued under stirring for 5 hours, and then the autoclave was cooled with ice to stop the reaction. After reaching room temperature, unreacted monomers were purged and the autoclave was opened. Then, the reaction product was poured into water / methanol, the supernatant was removed, and the residue was dried at room temperature under reduced pressure of 1 mmHg for 24 hours to obtain 228.6 g of homopolymer C. When the glass transition temperature of this homopolymer was measured by DSC, a clear peak appeared at 42 ° C.

In a similar manner, CTFE 36.4 g, EV
E9.0 g, n-BVE12.6 g, HBVE7.2 g
The homopolymer D was polymerized at a ratio of. The glass transition temperature was 8 ° C.

[Test example of coating film] 1) Fluorine-containing block copolymer of Example 1, 2) Fluorine-containing block copolymer of Example 2, or 3) Mixing of homopolymers C and D of Comparative Example Of the epoxy primer (Toagarmet primer). : Manufactured by Tope Co., Ltd.) in a thickness of 3 μm on a zinc steel plate (Zincoat MO Shinnitz 20G / M: manufactured by Nippon Test Panel Co., Ltd.)
Bar coater No. so that the film thickness becomes 25 μm. Painted at 5. The results of various tests are shown in Table 2.

[0082]

[Table 1]

[0083]

[Table 2]

[0084]

EFFECT OF THE INVENTION The fluorine-containing block copolymer of the present invention can achieve both T-bending property and hardness of the coating film, and is useful when used as a precoating paint. Further, if the combination of block chains having different physical properties other than the glass transition temperature is selected, the application will be further expanded, and it will be useful as a resin for a novel paint.

Claims (6)

[Claims] 1. A copolymer having at least two types of different block chains, each block chain being composed of a copolymer of fluoroolefin and another vinyl-based monomer, and forming each block chain. A fluorine-containing block copolymer having a difference in glass transition temperature of 5 ° C. or more. 2. The polymerization initiator according to claim 1, which has at least two different polymerization initiation groups in the same molecule, or is obtained by using a polymerization initiator capable of generating a new polymerization initiation group after the first-stage polymerization. Fluorine-containing block copolymer. 3. The method according to claim 1, wherein the other vinyl-based monomer copolymerizable with the fluoroolefin contains at least one selected from alkyl vinyl ether, cyclovinyl ether, vinyl carboxylate and allyl ether as an essential component. Fluorine block copolymer. 4. It is soluble in an organic solvent in an uncrosslinked state, and has an intrinsic viscosity of 0.05 to 30 at 30 ° C. in tetrahydrofuran.
The fluorine-containing block copolymer according to claim 1, which has a content of 2.0 dl / g. 5. A coating composition containing the fluorine-containing copolymer according to claim 1. 6. A steel sheet for precoated metal, which is coated with the coating composition according to claim 5.