JPH0959560A - Composition for water paint - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject composition having excellent adhesion to a substrate or an undercoating material to reduce the application cost by dispersing a fluorine-containing copolymer having a fluoroolefin unit and a specific (meth)acrylate copolymer in water. SOLUTION: This water paint composition is produced by dispersing (A) a fluorine-containing copolymer containing a polymer unit derived from a fluoroolefin as essential component preferably in an amount of 20-80mol% and (B) a (meth)acrylic copolymer having an alicyclic group as well as a light- stable group and free from fluorine atom in (C) water. The component A is preferably produced by the emulsion polymerization of a fluoroolefin and a hydrocarbon monomer in the presence of a monomer having hydrophilic part. The fluoroolefin is preferably a perhaloolefin. The component B is preferably produced by the copolymerization of an acrylic monomer such as (meth)acrylic acid ester, a (meth)acrylic monomer having alicyclic group such as cyclohexyl methacrylate and a methacrylic monomer having a light-stable group with a hindered amine structure.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a water-based coating composition which is excellent in weather resistance and gives a coating film showing good adhesion to various base materials and undercoat materials.

[0002]

2. Description of the Related Art Conventionally, a copolymer composed of a fluoroolefin, cyclohexyl vinyl ether and various other monomers is soluble in an organic solvent at room temperature, has a transparent and high gloss when used as a paint, Moreover, it is known to provide a coating film having excellent properties of a fluororesin such as high weather resistance, water / oil repellency, stain resistance, and non-adhesiveness (for example, Japanese Patent Laid-Open No. 55-44083). Its use in the field is increasing.

On the other hand, since the use of organic solvents is being regulated in recent years from the viewpoint of air pollution, there is a high demand for water-based paints and powder paints that use a small amount of organic solvents, and for fluororesins as well. It has been reported that those having no functional group can be produced by emulsion polymerization (JP-A-55-25411).

Further, a product obtained by emulsion-polymerizing a fluorine-containing copolymer having a functional group such as a hydroxyl group is disclosed in JP-A-57 / 57.
-34107 and JP-A-61-231044. Further, a fluorine-containing copolymer aqueous dispersion having improved mechanical stability and chemical stability is disclosed in JP-A-2-22555.
0, etc.

[0005]

A coating material using a conventional aqueous dispersion of a fluorine-containing copolymer gives a highly weather-resistant coating film, but has a problem of insufficient adhesion to various base materials and undercoat materials. there were. Further, since the fluorine-containing copolymer is expensive, there is a problem that the coating cost tends to increase.

The present invention has been made to solve these problems, and provides a composition for an aqueous coating composition which has excellent adhesion to various base materials and undercoating materials and which reduces the coating cost.

[0007]

The present invention provides (A) a fluorocopolymer having a fluoroolefin-based polymerized unit as an essential constituent, and (B) an alicyclic group and a photostable group in the molecule. And an acrylic or methacrylic copolymer which does not contain a fluorine atom and is dispersed in water.

As the fluorine-containing copolymer (A) having a polymerization unit based on a fluoroolefin as an essential constituent in the present invention, a copolymer of a fluoroolefin and a hydrocarbon-based monomer has weather resistance and pigment dispersibility. It is preferable because the physical properties of the coating film are excellent. Further, as the fluorine-containing copolymer, one produced by emulsion polymerization is preferable because it has excellent stability (chemical stability, mechanical stability) and a uniform dispersion can be obtained. Those obtained by emulsion polymerization in the presence of a monomer having a hydrophilic site are more excellent in stability and preferred.

The fluoroolefin is preferably a fluoroolefin having about 2 to 4 carbon atoms such as vinylidene fluoride, trifluoroethylene, chlorotrifluoroethylene, tetrafluoroethylene, hexafluoropropylene. Particularly, a perhaloolefin is preferable.

Further, the fluorine-containing copolymer obtained by emulsion polymerization preferably has a polymerized unit based on a monomer having a hydrophilic site. When this unit is contained as an essential constituent component of the fluorinated copolymer, the mechanical and chemical stability of the aqueous dispersion is improved, and the film-forming property and the water resistance of the coating film are also improved.

The monomer having the hydrophilic portion is preferably a macromonomer because the stability is further improved. The macromonomer refers to a low molecular weight polymer or oligomer having a radically polymerizable unsaturated group at one end. That is, it is a compound having a radically polymerizable unsaturated group at one end and having at least two repeating units. Usually, those having 100 or less repeating units are preferable from the viewpoint of polymerizability and water resistance.

Examples of the monomer having a hydrophilic moiety include the polyethers and polyesters having a radically polymerizable unsaturated group at one end as described below.

(1) CH ₂ = CHO (CH ₂ ) _p (OC
H ₂ CH ₂ ) _q (OCH ₂ CH (CH ₃ )) _r OX [p
Is an integer of 1 to 10, q is an integer of 2 to 20, r is 0 to 20
X is a hydrogen atom, a lower alkyl group or an acyl group, and the oxyethylene unit and the oxypropylene unit may be arranged in any of a block type and a random type].

(2) CH ₂ = CHCH ₂ O (CH ₂ ) _p
(OCH ₂ CH ₂ ) _q (OCH ₂ CH (CH ₃ )) _r O
X [p is an integer of 1 to 10, q is an integer of 2 to 20, r is 0
Is an integer of 20 to 20, X is a hydrogen atom, a lower alkyl group or an acyl group, and the oxyethylene unit and the oxypropylene unit may be arranged in any of a block type and a random type].

(3) CH ₂ = CHO (CH ₂ ) _s O (C
O (CH ₂ ) _t O) _u X [s is an integer of 1 to 10 and t is 1
Is an integer of 10 to 10, u is an integer of 1 to 30, and X is a hydrogen atom, a lower alkyl group or an acyl group].

Of these, ones having a vinyl ether type structure at one end are preferred because of their excellent copolymerizability with fluoroolefins. In particular, it is preferable that the polyether chain portion is composed of oxyethylene units, or oxyethylene units and oxypropylene units, and has oxyethylene units in such a proportion that it becomes hydrophilic.

Further, a monomer having two or more oxyethylene units in the monomer having a hydrophilic moiety is preferable from the viewpoint that various properties such as stability can be achieved. Further, if the total number of oxyalkylene units such as oxyethylene units and oxypropylene units is too large, the water resistance and weather resistance of the coating film deteriorate, which is not preferable.

The macromonomer having such a hydrophilic moiety can be produced by a method such as ring-opening polymerization of a compound having an alkylene oxide or a lactone ring.

The macromonomer having a hydrophilic portion has a chain in which a hydrophilic ethylenically unsaturated monomer is radically polymerized and has a radically polymerizable unsaturated group such as vinyl ether or allyl ether at the terminal. May be

Such a macromonomer is a Polymonomer
m. Bull. , 5.335 (1981). That is, an ethylenically unsaturated monomer having a hydrophilic group is radically polymerized in the presence of an initiator having a condensable functional group or a chain transfer agent having a condensable functional group to give a polymer having a condensable functional group. An example is a method of producing a polymer, and then reacting a functional group of this polymer with a compound such as glycidyl vinyl ether or glycidyl allyl ether to introduce a radically polymerizable unsaturated group at the terminal.

Examples of the ethylenically unsaturated monomer used in the production of this macromonomer include acrylamide, methacrylamide, N-methylolacrylamide and N-
Methylol methacrylamide, 2-methoxyethyl acrylate, 2-methoxyethyl methacrylate, diacetone acrylamide, hydroxyethyl acrylate,
Examples include hydroxypropyl acrylate, hydroxybutyl acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, hydroxybutyl methacrylate, acrylic acid esters of polyhydric alcohols, methacrylic acid esters of polyhydric alcohols and vinylpyrrolidone.

In addition to the above, as a copolymerizable monomer,
Acrylamide derivative, methacrylamide derivative, N-
Methylol acrylamide derivative, acrylic acid ester of diethylene glycol monoethyl ether, acrylic acid ester of triethylene glycol monomethyl ether, 2-hydroxyethyl acryloyl phosphate,
Butoxyethyl acrylate and the like.

As the initiator used for the production of this macromonomer, 4,4'-azobis-4-cyanovaleric acid, 2,2'-azobis-2-amidinopropane hydrochloride, potassium persulfate, ammonium persulfate, azo are used. Examples include bisisobutyronitrile and benzoyl peroxide.

The fluorinated copolymer in the present invention may further contain a polymerized unit containing a reactive group selected from a hydroxyl group, an epoxy group, a carboxyl group, a carbonyl group and a hydrazine residue.

The polymerized units based on the monomer containing a hydroxyl group can be introduced by a method of copolymerizing a monomer containing a hydroxyl group or a method of polymerizing a polymer to form a polymerized unit containing a hydroxyl group. .

Examples of the hydroxyl group-containing monomer include hydroxyalkyl vinyl ethers such as hydroxybutyl vinyl ether, hydroxyalkyl allyl ethers such as hydroxyethyl allyl ether, and acrylic acid or methacrylic acid such as hydroxyethyl acrylate and hydroxyethyl methacrylate. Examples thereof include hydroxyalkyl esters.

As a method of polymerizing a polymer to form a polymer unit containing a hydroxyl group, after the polymerization, a hydrolyzable vinyl ester is copolymerized and then hydrolyzed to form a hydroxyl group. This method is exemplified.

The polymer unit containing a carboxyl group can be introduced by a method of copolymerizing a monomer containing a carboxyl group, a method of reacting a dibasic acid anhydride with a polymer having a hydroxyl group to form a carboxyl group.

The carboxyl group-containing monomer is C
H ₂ = CHOR ¹ OCOR ² COOH, CH ₂ = CHC
H ₂ R ³ OCOR ⁴ COOH [R ¹ and R ³ have 2 carbon atoms
Is an alkylene group of 15 to 15 and R ² and R ⁴ are saturated or unsaturated linear or cyclic divalent hydrocarbon groups] and the like.

The polymer unit containing an epoxy group can be introduced by copolymerizing a monomer containing an epoxy group. Examples of the epoxy group-containing monomer include epoxy group-containing alkyl vinyl ethers such as glycidyl vinyl ether, epoxy group-containing alkyl allyl ethers such as glycidyl allyl ether, glycidyl acrylate, epoxy group-containing alkyl acrylates or methacrylates such as glycidyl methacrylate. It is illustrated.

The polymer unit containing a carbonyl group can be introduced by copolymerizing a carbonyl group-containing monomer such as diacetone acrylamide, acetoacetoxyethyl methacrylate, crotonaldehyde, acrolein.

Polymerized units containing a hydrazine residue include dicarboxylic acid dihydrazide (eg, isophthalic acid dihydrazide, adipic acid dihydrazide) or hydrazine hydrate in a carbonyl group-containing polymer in an amount of 0.02 to 1 It can be introduced by reacting in a molar amount.

The fluorine-containing copolymer in the present invention may contain, in addition to the above units, polymerized units based on a monomer copolymerizable with them. Examples of such monomers include olefins such as ethylene and propylene, aliphatic or alicyclic alkyl vinyl ethers such as ethyl vinyl ether, propyl vinyl ether, butyl vinyl ether and cyclohexyl vinyl ether, and carboxylic acids such as butanoic acid vinyl ester and octanoic acid vinyl ester. Examples thereof include vinyl esters, aromatic vinyl compounds such as styrene and vinyltoluene, allyl compounds such as ethyl allyl ether, acrylic acid or methacrylic acid esters such as butyl acrylate and ethyl methacrylate. In particular, olefins, vinyl ethers, vinyl esters, allyl ethers and allyl esters are preferable.

Here, the olefins have 2 to 1 carbon atoms.
Those having about 0 are preferable, and as vinyl ethers, vinyl esters, allyl ethers and allyl esters, those having a linear, branched or alicyclic alkyl group having about 2 to 15 carbon atoms are preferable. In such a monomer, at least a part of hydrogen bonded to carbon may be replaced with fluorine.

The fluorine-containing copolymer in the present invention preferably has 20 to 80 mol% of polymerized units based on fluoroolefin. If the amount of the polymerized units based on the fluoroolefin is too small, the weather resistance will not be sufficiently exhibited, and if it is too large, the water dispersibility will be extremely deteriorated, which is not preferable. It is particularly preferably 30 to 70 mol%.

In producing the fluorine-containing copolymer of the present invention, it is preferable to carry out emulsion polymerization in the presence of a nonionic emulsifier having an HLB of 12 to 18 and an anionic emulsifier. If the HLB of the nonionic emulsifier is out of this range, the stability during emulsion polymerization will be low, or the stability of the resulting dispersion will be low. Particularly preferred H
LB is 14-16. Further, the anionic emulsifier alone has a high stability during emulsion polymerization, but the obtained dispersion easily aggregates when an inorganic substance is added, and when it is formed into a coating film, its high hydrophilicity reduces water resistance. Cheap.

On the other hand, when the nonionic emulsifier is used alone, a very small amount of a viscous substance is easily generated during emulsion polymerization, and when the aqueous dispersion is stored for a long period of time or stored at high temperature, the viscous substance triggers. It may thicken and may change into purine in some cases.

When emulsion polymerization is carried out in the presence of a nonionic emulsifier having an HLB of 12 to 18 and an anionic emulsifier, the stability of the coating composition is high, the storage stability is high, and the weather resistance and water resistance are excellent. A fluorinated aqueous dispersion which gives a coating film is obtained.

As the lipophilic group of the nonionic emulsifier, those not containing a polyfluoroalkyl group are preferable from the viewpoint of forming a dense coating film. Specific examples thereof include alkylphenol ethylene oxide adducts, higher alcohol ethylene oxide adducts, and block copolymers of ethylene oxide and propylene oxide.
The amount of the emulsifier used can be appropriately changed according to the conditions, and is usually 0.1 to 100 parts by weight of the monomer to be emulsion polymerized.
About 5 parts by weight is preferable.

Similarly, the lipophilic group of the anionic emulsifier preferably does not contain a polyfluoroalkyl group. Specific examples thereof include alkylbenzene sulfonate, alkylnaphthalene sulfonate, higher fatty acid salt, alkyl sulfate ester salt, alkyl ether sulfate ester salt, and phosphate ester salt.

The initiation of the emulsion polymerization in the present invention is carried out by adding a polymerization initiator in the same manner as the usual initiation of the emulsion polymerization.
As the polymerization initiator, an ordinary radical initiator can be used, and a water-soluble initiator is preferable. Specifically, a persulfate such as ammonium persulfate, hydrogen peroxide or a redox initiator composed of hydrogen peroxide or a combination thereof with a reducing agent such as sodium bisulfite or sodium thiosulfate, and a small amount of iron or ferrous salt , Inorganic initiators in the presence of silver sulfate, or dibasic acid peroxides such as disuccinic acid peroxide and diglutaric acid peroxide, organic initiators such as azobisisobutylamidine hydrochloride and azobisisobutyronitrile An agent is illustrated.

The amount of the polymerization initiator used can be appropriately changed depending on the type, emulsion polymerization conditions and the like, and normally about 0.005 to 0.5 part by weight is preferable per 100 parts by weight of the monomer to be emulsion polymerized. These polymerization initiators may be added all at once, or may be added in portions if necessary.

For the purpose of raising the pH of the emulsion, p
An H modifier may be used. As such a pH adjusting agent,
Examples thereof include inorganic bases such as sodium carbonate, potassium carbonate, sodium hydrogen orthophosphate, sodium thiosulfate and sodium tetraborate, and organic bases such as triethylamine, triethanolamine, dimethylethanolamine and diethylethanolamine.

The amount of the pH adjusting agent added is usually about 0.05 to 2 parts by weight, preferably about 0.1 to 2 parts by weight, per 100 parts by weight of the emulsion polymerization medium. The higher the pH, the faster the polymerization rate.

The optimum value of the emulsion polymerization initiation temperature is selected depending on the type of the polymerization initiator. Usually 0-100
C., preferably about 10 to 90.degree. C., is preferably adopted. The reaction pressure can be appropriately selected and is usually 1 to 100 kg / cm.
^It is desirable to adopt ² G, especially about ^{2 to} 50 kg / cm ² G.

In such a production method, a monomer,
Additives such as water, emulsifier, and initiator may be charged all at once to polymerize, and for the purpose of reducing the particle size of the dispersed particles and improving various properties such as stability of the dispersion and gloss of the coating film. Alternatively, before adding the polymerization initiator, the mixture may be pre-emulsified by using a stirrer such as a homogenizer, and then the initiator may be added for polymerization. Further, the monomers may be added in portions or continuously, and in that case, the monomer compositions may be different.

The fluorinated copolymer used in the present invention may be a known aqueous dispersion. For example, JP-A-61-1
261367, JP-A-61-231044, JP-A-62
-243603, JP-A-63-314202, JP-A-2
-147601, JP-A-3-33148, JP-A3-1
81540, JP-A-3-199179, and JP-A-4-33.
941 and Japanese Patent Application Laid-Open No. 4-33942.

In the composition of the present invention, (B) an acrylic or methacrylic copolymer containing an alicyclic group and a photostable group in the molecule and containing no fluorine atom is dispersed in water. This (meth) acrylic copolymer is obtained by copolymerizing monomers containing an acrylic monomer such as (meth) acrylic acid ester as a main component. A copolymerizable monomer such as styrene may be used as the monomer component of these copolymers.

This (meth) acrylic copolymer must contain an alicyclic group and a photostable group in the molecule. The alicyclic group functions to reduce the water absorption of the copolymer coating film and consequently improve the weather resistance. The method of introducing the alicyclic group is not particularly limited, but it has an alicyclic group (meth)
The method of copolymerizing acrylic monomers is simple and reliable. Specific examples thereof include cyclohexyl methacrylate, isobornyl methacrylate, dicyclopentadienyl methacrylate and the like.

The light-stable group suppresses deterioration of the copolymer coating film by light and improves weather resistance. As the photostable group,
The group is not limited as long as it has a function of capturing an alkyl radical or a peroxide radical generated by photodegradation and stopping a chain reaction. Preferred light stable groups include groups having a hindered amine structure. The method for introducing this group is not particularly limited, and a methacrylic monomer having a hindered amine structure in its molecule (for example, ADEKA STAB LA-82 and ADEKA STAB LA-8 manufactured by ADEKA ARGUS CORPORATION) is used.
7) and the like are preferable because they are easy to carry out.

Further, this (meth) acrylic copolymer does not contain a fluorine atom. With a (meth) acrylic copolymer, even if it contains a fluorine atom, there is no significant change in weather resistance. Moreover, the introduction of a fluorine atom, for example, the copolymerization of a fluorine-containing (meth) acrylic monomer requires a large amount of raw material cost. Cause a rise.

The method of dispersing this (meth) acrylic copolymer in water is as follows: solution polymerization followed by substitution with a polar solvent,
A method of neutralizing and then dispersing in water, a method of using an aqueous dispersion obtained by an emulsion polymerization method as it is, or the like can be adopted. In order to easily obtain an aqueous dispersion having good dispersion stability, it is preferable to use the aqueous dispersion obtained by the emulsion polymerization method as it is. As the emulsifier and the polymerization initiator, those known as an acrylic copolymer aqueous dispersion may be used.

In the present invention, a fluorine-containing copolymer containing a polymerized unit based on a fluoroolefin as an essential constituent, an alicyclic group and a photostable group are contained in the molecule and a fluorine atom-free (meth) acryl is contained. It is important that the system copolymer is dispersed in water. The (meth) acrylic copolymer improves the adhesion to various base materials and undercoating materials without deteriorating the excellent weather resistance of the fluorocopolymer, and at the same time, makes it a coating material using the fluorocopolymer alone. In comparison, the price can be quite low.

The mixing ratio of these fluorine-containing copolymers and the (meth) acrylic copolymer is 100% by weight of the fluorine-containing copolymer.
(Meth) acrylic copolymer 5 to 100 parts by weight
0 parts by weight, particularly 25 to 150 parts by weight is preferred. When the ratio of the fluorinated copolymer is low, the weather resistance of the obtained coating film is low, and when the ratio of the (meth) acrylic copolymer is low, the adhesion to various base materials and undercoat materials is insufficient. Not improved.

The composition for aqueous paints of the present invention can be used as it is as an aqueous paint, and if necessary, a coloring agent, a film-forming aid, a plasticizer, an ultraviolet absorber, a leveling agent, an anti-cissing agent, and a skin burr prevention. Additives that are usually added to water-based paints such as agents, pigment dispersants, and thickeners may be mixed.

Examples of the colorant include dyes, organic pigments and inorganic pigments. The use of inorganic pigments is preferred when excellent weather resistance of the coating film is expected. Further, a metallic pigment such as aluminum paste may be used.

As the film-forming aid, dipropylene glycol-n-butyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether,
Examples thereof include polyhydric alcohol monoethers such as diethylene glycol monoethyl ether and diethylene glycol monobutyl ether, organic acid esters thereof, 3-ethoxypropionate and the like.

Examples of the plasticizer include conventionally known ones, for example, low molecular weight plasticizers such as dioctyl phthalate, high molecular weight plasticizers such as vinyl polymer plasticizers and polyester plasticizers.

[0059]

EXAMPLES The present invention will be specifically described below with reference to Synthesis Examples and Examples, but the present invention is not limited to these. In the following, "part" is "part by weight".

"Synthesis Example 1 (Synthesis of Fluorine-Containing Aqueous Dispersion 1)" 18.1 parts of ethyl vinyl ether, 18.5 parts of cyclohexyl vinyl ether, 1.9 parts of hydroxybutyl vinyl ether, hydrophilic in an autoclave made of stainless steel and equipped with a stirrer. Monomers with moieties (EOVE)
2.1 parts, deionized water 100 parts, emulsifier (Nippon Emulsifier: N-1110) 2 parts, emulsifier (Nikko Chemicals:
(SLS) 0.1 part, potassium carbonate 0.2 part, and ammonium persulfate 0.07 part were charged, the mixture was cooled with ice, and nitrogen gas was pressurized to 3.5 kg / cm ² G and degassed.

After repeating this pressure deaeration twice, 10 m
After reducing the pressure to mHg to remove the dissolved air, 59.4 parts of chlorotrifluoroethylene was charged and the reaction was carried out at 30 ° C. for 12 hours to obtain a milky white fluorocopolymer aqueous dispersion. This is called fluorinated aqueous dispersion 1. EOV
E is CH ₂ = CHO (CH ₂ ) ₄ O (CH ₂ CH
₂ O) _n H having a number average molecular weight of about 500.

[Synthesis Example 2 (Synthesis of Fluorine-Containing Aqueous Dispersion 2)] In an autoclave made of stainless steel and equipped with a stirrer,
Vinyl 6,6-dimethylheptanoate 42.6 parts, hydroxybutyl vinyl ether 3.2 parts, crotonic acid 1.1
Parts, ion-exchanged water 85.1 parts, emulsifier (manufactured by Nippon Emulsifier:
N-1110) 2.1 parts, emulsifier (manufactured by Nikko Chemicals:
2.1 parts of SLS) and 1.1 parts of sodium tetraborate were charged and cooled with ice, and nitrogen gas was degassed under pressure to 3.5 kg / cm ² G.

After repeating this pressure deaeration twice, 10 m
Dissolved air was removed by reducing the pressure to mHg, 53.2 parts of chlorotrifluoroethylene was charged, and ethylene was further added to 1
It was press-fitted so as to have a pressure of 5 kg / cm ² . While increasing the internal temperature to 80 ° C. and controlling the system internal pressure to 30 kg / cm ² , 20 parts of a 3% aqueous solution of potassium persulfate was added over 2 hours, and then the internal pressure became 30 kg / cm ^2. Stir for 12 hours while supplementing with ethylene,
A milky white fluorocopolymer aqueous dispersion was obtained. This is called fluorinated aqueous dispersion 2.

[Synthesis Example 3 (Synthesis of Acrylic Aqueous Dispersion 1)] 40 parts of cyclohexyl methacrylate, 20 parts of n-butyl methacrylate and 10 parts of 2-ethylhexyl methacrylate were placed in a glass three-necked flask equipped with a stirrer and a cooling tube. Part, acrylic acid 1 part, a monomer having a light-stable group (manufactured by ADEKA ARGUS: ADEKA STAB LA-87)
2 parts, deionized water 75 parts, emulsifier (manufactured by Nippon Emulsifier:
N-1120) 1 part, emulsifier (manufactured by Nikko Chemicals: SL
S) 1 part was charged, ammonium persulfate 0.1 part was added, and the gas layer in the system was replaced with nitrogen. Then, the temperature was raised to 65 ° C., and stirring was continued for 12 hours to obtain a milky white acrylic copolymer aqueous dispersion. This is called acrylic aqueous dispersion 1.

"Synthesis Example 4 (Synthesis of Acrylic Aqueous Dispersion 2)" The same procedure as in Synthesis Example 3 was carried out except that a monomer having a light-stable group was not used to obtain an acrylic copolymer aqueous dispersion. . This is called acrylic aqueous dispersion 2.

[Synthesis Example 5 (Synthesis of Acrylic Aqueous Dispersion 3)] The same procedure as in Synthesis Example 3 was conducted except that 40 parts of ethyl methacrylate was used in place of the cyclohexyl methacrylate of Synthesis Example 3, and the acrylic copolymer was used. An aqueous dispersion was obtained. This is called acrylic aqueous dispersion 3.

"Examples 1 to 3 (Examples) and Examples 4 to 6 (Comparative Examples)" Aqueous coating compositions were prepared according to the formulations shown in Table 1. These aqueous coating compositions were applied on a phosphoric acid-treated aluminum plate by an applicator so that the dry film thickness would be 40 μm, dried at 60 ° C. for 20 hours, and the following tests were conducted.

Adhesion test: A cross-cut tape peeling test of 1 mm square was performed, and 10 points were evaluated according to JIS. Weather resistance test: An accelerated weather resistance test was conducted for 5000 hours with a sunshine weatherometer, and the gloss retention rate after the test was 8
Those with 0% or more were marked with ◯, and those with less than 80% were marked with x.

[0069]

[Table 1]

[0070]

EFFECT OF THE INVENTION The composition of the present invention can provide a coating film having excellent weather resistance and exhibiting good adhesion to various base materials and undercoat materials.

Claims (2)

[Claims] 1. A fluoropolymer containing (A) a fluoroolefin-based polymerized unit as an essential constituent, and (B) an alicyclic group and a photostable group in the molecule and no fluorine atom. A water-based coating composition comprising an acrylic or methacrylic copolymer dispersed in water. 2. The composition for aqueous paints according to claim 1, wherein the ratio of (B) to 100 parts by weight of (A) is 5 to 1000 parts by weight.