JPH09100441A - Water-based coating material composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a composition, comprising a water-based polymer prepared by neutralizing an epoxy resin-modified polymer having a specific structure and carboxyl group with a base and an amino resin, excellent in water resistance and processability and useful for coating the metallic surface. SOLUTION: This water-based coating material composition comprises a water-based polymer prepared by neutralizing a modified polymer obtained by reacting (A) an epoxy resin having partially phosphoric esterified epoxy groups with (B) an acrylic or a methacrylic ester-based graft copolymer comprising preferably (i) a macromonomer, obtained by copolymerizing a hydroxyalkyl (meth)acrylate with an N-alkoxymethyl(meth)acrylamide and other α,β- ethylenically unsaturated monomers and having one radically polymerizable terminal, (ii) an α,β-ethylenically unsaturated carboxylic acid, (iii) a hydroxyalkyl (meth)acrylate, etc. and (iv) other α,β-ethylenically unsaturated monomers with a base and an amino resin. The epoxy groups in the component (A) in a smaller amount than the equiv. amount based on carboxyl groups in the component (B) are reacted therewith.

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 that gives a film having excellent water resistance. The water-based coating composition of the present invention is used for metal plates used in metal cans, home appliances, automobiles and the like. It is especially useful as a water-based paint.

[0002]

2. Description of the Related Art Paints for metal cans for packaging soft drinks or processed foods are required to have properties such as water resistance and processability under heating. Organic solvent-based paints such as epoxy / amino resins, acrylic / amino resins, and polyester / amino resins that form excellent coating films by heat curing have been used. However, in these solvent-based paints, a large amount of organic solvent evaporates into the atmosphere during coating, and thus has problems such as environmental pollution and waste of resources.

The use of water-based paints using water as a medium instead of the solvent-based paints has been studied. However, conventional water-based paints are inferior in water resistance and can withstand hot water treatment such as boiling water. At present, when subjected to a treatment with steam under pressure of 120 ° C. or higher (retort treatment), the physical properties of the coating film are significantly deteriorated. There have been many proposals for water-based paints that can withstand pressure steam treatment.
No. 577 discloses an aqueous acrylic resin containing a vinyl aromatic monomer and an alkyl (meth) acrylate as main components and neutralizing a copolymer having a carboxyl group and a hydroxyl group in a molecule with a base, a hydroxyl group-containing polyol and A water-based paint comprising an amino resin has been proposed. However, the physical properties of the resulting coating film have not yet reached a practically satisfactory level.

On the other hand, in JP-A-4-236279, a reaction product of an epoxy resin partially added with phosphoric acid and a carboxyl group-containing acrylic resin is dissolved in an aqueous medium in the presence of a base. A water-based paint composed of a water-based resin and an amino resin has been proposed, but it was still a step forward in terms of physical properties.

[0005]

SUMMARY OF THE INVENTION The present invention provides an aqueous coating composition capable of forming a coating film that maintains excellent water resistance and processability even when subjected to a treatment with pressurized steam at 120 ° C. or higher. That was the task.

[0006]

Means for Solving the Problems The present inventors have made intensive studies to solve the above-mentioned problems, and as a result, have completed the present invention. That is, the present invention comprises (a) an epoxy resin in which a part of the epoxy groups is phosphorylated and (b) a macromonomer method to synthesize a hydroxyl group or N-alkoxymethylamide in a branch polymer based on the macromonomer. (Meth) acrylic acid ester-based graft copolymer having a hydroxyl group and a carboxyl group in the trunk polymer, and the epoxy group in the epoxy resin is equivalent to the carboxyl group in the graft copolymer. A water-based coating composition comprising an amino resin and an aqueous polymer obtained by neutralizing a carboxyl group-containing epoxy resin-modified polymer obtained by reacting at a ratio of less than 1 with a base.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail. As described above, (a) in the present invention is an epoxy resin in which a part of the epoxy groups is phosphorylated (hereinafter referred to as phosphoric esterified epoxy resin),
The epoxy resin of the base resin is preferably a bisphenol A type epoxy resin obtained by condensation of bisphenol A and epichlorohydrin and having a polystyrene-reduced number average molecular weight of 300 to 6,000 by gel permeation chromatography. As a commercially available bisphenol A type epoxy resin, Epicot 100
1, 1002, 1004, 1009 (all manufactured by Shell Chemical Co., Ltd.) and the like. The bisphenol A type epoxy resin is usually composed of molecules having 1 to 2 epoxy groups per molecule. In the present invention, a part of the epoxy groups in the epoxy resin is converted into phosphoric acid ester. Phosphorylation of an epoxy resin is a known technical means for improving the storage stability of an epoxy resin, whereby an epoxy resin or an epoxy-modified resin obtained by reacting an epoxy resin with another resin is obtained. It is possible to suppress thickening with time.

Of the epoxy groups in the above epoxy resin,
The preferred ratio of the epoxy group to be phosphoric acid ester is 5
It is 0% or less, and more preferably 30 to 50%. In the epoxy resin in which more than 50% of the epoxy groups are phosphorylated, the epoxy resin that does not react when reacted with the (meth) acrylate graft copolymer of the component (b) in the next step Since the amount of resin increases and the epoxy resin is insoluble in water, it is difficult to obtain a homogeneous aqueous coating composition. Examples of preferable phosphoric acid esterifying agent to be reacted with an epoxy group include diethyl phosphate, isopropyl phosphate and n-butyl phosphate. The reaction is carried out in an organic solvent such as methyl ethyl ketone, toluene, butanol or butyl cellosolve at a temperature of 60 to 150.
It is preferably carried out at a temperature of ° C. The amount of epoxy groups contained in the phosphoric acid esterified epoxy resin obtained by the above reaction is usually about 0.2 to 2.4 mmol / g.

The (b) in the present invention is composed of units based on the following radically polymerizable components, and the ratio of each unit is (a) 3 to 30 weight units based on the macromonomer based on the total amount thereof. %, Unit 3 based on (b) 3
˜20 wt%, 5 to 40 wt% based on (c) and 10 to 89 wt% based on (d) (meta).
Acrylic ester-based graft copolymers are preferred. (A) Hydroxyalkyl (meth) acrylate or N
-A macromonomer having radical polymerizability at one end of a polymer obtained by copolymerizing an alkoxymethyl (meth) acrylamide with another α, β-ethylenically unsaturated monomer (b) α, β-ethylenic Unsaturated Carboxylic Acid (c) Addition of ε-caprolactone to hydroxyalkyl (meth) acrylate or hydroxyalkyl (meth) acrylate (d) Other α, β-ethylenically unsaturated monomer ) To (d) will be described in order.

The preferred number average molecular weight of the macromonomer (a) above is 1,00 in terms of polystyrene equivalent number average molecular weight by gel permeation chromatography.
0 to 30,000. Further, the radically polymerizable group in the macromonomer is preferably a (meth) acryloyl group or a styryl group. Specific examples of the hydroxyalkyl (meth) acrylate that forms the polymer portion of the macromonomer (hereinafter sometimes simply referred to as the skeleton) include hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, ( Examples thereof include 3-hydroxypropyl (meth) acrylate and hydroxybutyl (meth) acrylate, while specific examples of N-alkoxymethyl (meth) acrylamide include N-methoxymethyl (meth) acrylamide and N-butoxymethyl (meth). ) Acrylamide and N-isobutoxymethyl (meth) acrylamide. By using hydroxyalkyl (meth) acrylate or N-alkoxymethyl (meth) acrylamide, a hydroxyl group or N-alkoxymethylamide group which reacts with an amino resin to form a crosslinked structure is introduced into the backbone of the macromonomer. .

In addition to the above-mentioned hydroxyalkyl (meth) acrylate or N-alkoxymethyl (meth) acrylamide, other α, β-ethylenically unsaturated monomers can be used for constructing the skeleton of the macromonomer.
Other α, β-ethylenically unsaturated monomers include
Methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, (meth) acrylic acid 2
-Ethylhexyl, alkyl (meth) acrylates such as cyclohexyl (meth) acrylate, styrene,
Examples thereof include styrene derivatives such as α-methylstyrene and p-methylstyrene, nitrile group-containing vinyl monomers such as (meth) acrylonitrile, and (meth) acrylic acid alkylamino ester.

The preferred proportion of hydroxyalkyl (meth) acrylate or N-alkoxymethyl (meth) acrylamide (hereinafter collectively referred to as crosslinking group-containing monomer) monomer units in the skeleton of the macromonomer is the same as that of the skeleton. 3-40 based on the total amount of all the monomer units constituting
%, And more preferably 5 to 20% by weight.
When the amount of the crosslinking group-containing monomer unit is less than 3% by weight, the water-based coating composition obtained has poor water resistance, while 40% by weight.
If it exceeds, the processability of the coating film will be poor.

The proportion of units based on the above macromonomer in the (meth) acrylic acid ester-based graft copolymer (hereinafter simply referred to as a graft copolymer) obtained by polymerizing (a) to (d) is 3% by weight. When the amount is less than the above, among the physical properties of the obtained coating film, the physical properties such as water resistance, processability or hardness are poor, and when it exceeds 30% by weight, the processability is poor. A more preferable ratio of the units based on the macromonomer in the graft copolymer is 5 to 20% by weight.

(B); Examples of the α, β-ethylenically unsaturated carboxylic acid include acrylic acid, methacrylic acid, crotonic acid, maleic acid, maleic anhydride, fumaric acid and itaconic acid, and preferably acryl. Acid and methacrylic acid. If the proportion of α, β-ethylenically unsaturated carboxylic acid units in the graft copolymer obtained by polymerizing each component is less than 3% by weight, it is difficult to make the resulting graft copolymer water-soluble. If it exceeds 20% by weight, the water resistance of the coating film is poor.

(C): A hydroxyalkyl (meth) acrylate or an ε-caprolactone adduct to a hydroxyalkyl (meth) acrylate is reacted with an amino resin as a backbone polymer in a (meth) acrylic acid ester-based graft copolymer. It is used for the purpose of introducing a hydrophilic hydroxyl group. Ε to hydroxyalkyl (meth) acrylate
-The caprolactone adduct specifically has a (meth) acryloyl group at one terminal of the molecule obtained by ring-opening polycondensation of ε-caprolactone in the presence of hydroxyethyl (meth) acrylate. , A low-polymerization polyester having a hydroxyl group at the other molecular end, and commercially available products such as Praxel FM or FA series (manufactured by Daicel Chemical Industries, Ltd.). If the proportion of units (c) based on (c) in the graft copolymer is less than 5% by weight, curing will be insufficient and the hardness of the coating film will be poor, while if it exceeds 40% by weight, processability and water resistance will be poor. A more desirable ratio of units based on (C) is 10 to 30% by weight.

(D); Other α, β-ethylenically unsaturated monomers include methyl (meth) acrylate, ethyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, and (meth) acrylic. Butyl acid, alkyl (meth) acrylate such as cyclohexyl (meth) acrylate,
Aromatic vinyl monomers such as styrene and α-methylstyrene, (meth) acrylic acid alkylamino ester, N-
Methoxymethyl (meth) acrylamide and N- (n
-Butoxy) methyl (meth) acrylamide and the like can be mentioned, and these can be used alone or in combination of two or more kinds. The proportion of units based on (d) in the graft copolymer is 100% by weight minus the sum of the proportion of units based on (a) to (c) above, and is 10 to 89% by weight. In the present invention, one of the units based on (a) and the other α, β-ethylenically unsaturated monomer of (b) which constitutes the (meth) acrylic acid ester-based graft copolymer of (b). Part or all is preferably an alkyl (meth) acrylate monomer unit, and the ratio of the alkyl (meth) acrylate monomer unit in the graft copolymer is such that all the constituent units of the graft copolymer are More preferably, it is 30% by weight or more based on the total amount.

In the present invention, a more preferable graft copolymer is the above-mentioned (a) because the coating film has excellent low temperature curability.
It is a graft copolymer having an N-alkoxymethyl (meth) acrylamide monomer unit as an essential unit in addition to the units based on (c) to (c), and the content ratio of each constituent unit is the following graft copolymer. -(A) Units based on macromonomer 3 to 30% by weight-Units based on (b) 3 to 13% by weight-Units based on (c) 5 to 35% by weight-N-alkoxymethyl (meth) acrylamide monomer Unit 3 to 20% by weight Other α, β-ethylenically unsaturated monomer unit 2 to 8
6% by weight However, (A) to (C), N-alkoxymethyl (meth)
The total amount of acrylamide monomer units and other α, β-ethylenically unsaturated monomer units is 100% by weight.

The above polymerizable components are almost 100% by the radical polymerization method which will be outlined below.
Since the polymerization can be carried out at the above-mentioned polymerization rate, the macromonomer and each of the monomers can be subjected to the polymerization in a proportion corresponding to the constitution in order to obtain the copolymer having the above constitution. As a polymerization solvent, isopropyl alcohol, n-butanol, isobutyl alcohol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, or the like is used, and a radical generating compound such as azobisisobutyronitrile is used as a polymerization initiator, and the temperature is 60 to 150. It is preferable to carry out the solution polymerization at ° C. If necessary, the molecular weight of the resulting graft copolymer can be adjusted by using an appropriate amount of a chain transfer agent such as n-dodecyl mercaptan, mercaptoacetic acid, thiomalic acid, mercaptoethanol and mercaptopropionic acid. The preferred average molecular weight of the graft copolymer in the present invention is 2,000-in number average molecular weight.
20,000, more preferably 3,000 to 1
5,000.

In the reaction of the above graft copolymer with the epoxy resin (a), it is necessary to obtain an aqueous polymer by neutralizing the carboxyl group in the obtained polymer with a base after the reaction. Both of them are reacted in a molar ratio in which the amount of epoxy groups in the epoxy resin is small with respect to the amount of carboxyl groups in the graft copolymer.
As described in the section regarding (a), the amount of epoxy groups in the phosphoric acid esterified epoxy resin is usually 0.2 to
The amount of carboxyl groups in the graft copolymer is 0.4-2.
It is about 8 mmol / g. The reaction ratio between the graft copolymer and the phosphoric acid esterified epoxy resin may be set based on the concentrations of these functional groups. In the present invention, the amount of the phosphoric acid esterified epoxy resin used is preferably 1 to 45 parts by weight, more preferably 3 to 25 parts by weight, based on 100 parts by weight of the graft copolymer. When the proportion of the phosphoric acid esterified epoxy resin is less than 1 part by weight, the adhesion of the coating film with the aqueous coating composition to the metal substrate and the processability of the coated substrate are poor, while when it exceeds 45 parts by weight. The gloss of the coating film is reduced and it tends to turn yellow.

The reaction between the above graft copolymer and the phosphoric acid esterified epoxy resin is preferably carried out in an organic solvent. The reaction solvent is not particularly limited, and a polymerization solvent such as isopropanol, n-butanol or ethylene glycol monomethyl ether used when the graft copolymer is synthesized can be used as it is. In the reaction, it is preferable to add a tertiary amine such as trimethylamine, triethylamine or dimethylethanolamine as a catalyst. The reaction temperature is preferably 50 to 100 ° C., and the reaction time is, strictly speaking, the time until the epoxy group disappears, but it is about 1 to 5 hours. The progress of the reaction is
This can be confirmed by sampling the reaction solution at any time and measuring the acid value or epoxy value by a titration method.

Next, the epoxy resin-modified polymer having a carboxyl group (hereinafter simply referred to as epoxy resin-modified polymer) obtained by the above reaction is neutralized with a base. As the base, monoethanolamine, dimethylamine, diethylamine, triethylamine, triethanolamine,
Organic amines such as diethylethanolamine and dimethylethanolamine, and ammonia can be used. A specific neutralization operation is performed by stirring the organic solvent solution of the epoxy resin-modified polymer while adding the above base into the solution until the neutralization point is reached, and then reducing the organic solvent contained in the reaction solution under reduced pressure. After distilling off with water, water is added to obtain an aqueous polymer as an aqueous solution or an aqueous dispersion. The preferred solid content concentration in the aqueous solution or dispersion of the aqueous polymer is 20 to 70% by weight.

By mixing the aqueous solution or dispersion of the above aqueous polymer with the amino resin described below,
The aqueous coating composition of the present invention is obtained. Examples of the amino resin include alkyl etherified melamine such as methyl etherified melamine and butyl etherified melamine; alkyl etherified urea resin; alkyl etherified benzoguanamine such as methyl etherified benzoguanamine and ethyl etherified benzoguanamine. Alternatively, two or more kinds can be used in combination. Further, with respect to the alkyl etherified melamine, alkyl etherified urea resin, alkyl etherified benzoguanamine and the like, dimers, trimers and other multimers can be used in addition to those monomers, and the degree of alkyl etherification is Any of those in which all or part of the active hydrogen atom of the amino group is substituted with an alkyl ether group can be used. Amino resin is
It is preferable to select according to the application of the water-based coating composition, and for applications requiring high water resistance such as metal cans for food packaging, alkyl etherified benzoguanamine is suitable, and automobile-related products requiring weather resistance. Alkyl etherified melamine is suitable for use in. The preferred amount of the amino resin used is 10 to 80 parts by weight (amino resin solid content) per 100 parts by weight of the solid content of the aqueous polymer. The amino resin is usually handled as a solution using alcohol or water as a medium. The solid content concentration of the obtained aqueous coating composition is preferably from 30 to 70% by weight.

The water-based coating composition of the present invention may contain various paint additives in addition to the above-mentioned water-based polymer and amino resin. One example thereof is a silicone-based leveling agent or film-forming aid. Examples thereof include ethylene glycol monobutyl ether. Targets to which the aqueous coating composition is applied include aluminum, stainless steel, tinplate, zinc-treated steel sheets, and various other treated steel sheets.
Instead of directly applying to the metal surface, it may be applied to ink or a primer, and any of undercoating, intermediate coating and topcoating can be used.

[Examples and Comparative Examples]

Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples. Reference Example 1 (Synthesis of Graft Copolymer) The following monomers were mixed,
Polymerization was performed as one monomer solution. In this example, as the macromonomer, cyclohexyl methacrylate unit / 2-ethylhexyl methacrylate unit / 2-hydroxyethyl methacrylate unit / styrene unit =
A macromonomer M-1 having a structure of 5/55/25/15 (wt%) and having a methacryloyl group at one end of a polymer having a number average molecular weight of 3,300 was used. Macromonomer M-1 ───── 25.0 g Styrene (hereinafter referred to as St) ───── 24.4 g Ethyl acrylate (hereinafter referred to as EA) ───── 18.1 g n-Butyl acrylate (hereinafter referred to as BA) ────── 15.0 g Acrylic acid (hereinafter referred to as AA) ───── 6.9 g 2-Hydroxyethyl methacrylate (hereinafter referred to as HEMA) 10.6 g 1 of the above mixture liquid / 3, mercaptoethanol 0.
38 g, butyl cellosolve 18.0 g and isopropyl alcohol 42.0 g were charged into a glass flask equipped with a stirrer, a reflux condenser, two dropping funnels, a gas introduction tube and a thermometer, and the temperature was raised to 87 ° C.

Next, from the one dropping funnel, the remaining 2/3 of the mixed solution and 0.38 g of mercaptoethanol were added.
While dripping the mixed solution of 3 hours at the same time, from the other dropping funnel, 6.0 g of butyl cellosolve, 14.0 g of isopropyl alcohol and 0.2 g of 2,2′-azobis (2-methylbutyronitrile) were formed. The polymerization initiator solution was added dropwise over 3 hours. Then, butyl cellosolve 6.0 g and isopropyl alcohol 14.
0 g and ABN-E 0.46 g were added dropwise over 2 hours. Then, stirring was continued for 2 hours to synthesize a target polymer. The number average molecular weight of the copolymer was 8,600. The obtained polymer solution was heated to 40 ° C., and isopropyl alcohol was distilled off under reduced pressure to obtain a graft copolymer solution A having a solid content concentration of 70% by weight.

<Reference Examples 2 to 3 and Comparative Reference Example 1> Graft copolymer solutions B and C (Reference Examples 2 and 3) were prepared in the same manner as in Reference Example 1, except that the components shown in Table 1 were used. )
And a linear random copolymer solution D (Comparative Reference Example 1) were synthesized.

[0027]

[Table 1]

In Table 1, M-2, HA, NMMA and Praxel FM3 represent the following compounds, respectively. M-2: having a structure of ethyl acrylate unit / N-methoxymethyl acrylamide unit = 93/7 (wt%),
Macromonomer having methacryloyl group at one end of polymer having number average molecular weight of 4,100 HA: 2-ethylhexyl acrylate, NMMA: N-
Methoxymethyl acrylamide, Praxel FM3: polycaprolactone monomer having methacryloyl group

[0029]

Example 1 A phosphoric acid esterified epoxy resin was synthesized by the following method. In a flask, butyl cellosolve 91.
Epicoat 1001 [Bisphenol A type epoxy resin manufactured by Shell Chemical Co., Ltd., Mn = 1000] in 4 g; 2
00 g was dissolved, and then 13.2 g of dibutyl phosphate was reacted to obtain a phosphoric acid esterified epoxy resin solution having a solid content concentration of 70% by weight. The epoxy group content in the epoxy resin was 1.11 mmol / g. Butyl cellosolve solution 12 of graft copolymer A obtained in Reference Example 1
9 g (concentration of solid content: 70% by weight, solid content: 90 g) and 14.3 g of the phosphoric acid esterified epoxy resin solution
(10 g of solid content) was stirred and dissolved at 85 ° C., 3 g of dimethylethanolamine was added as a catalyst, and the mixture was reacted for 2 hours. Then, the mixture was cooled to room temperature, 3 g of dimethylethanolamine and 17 g of water were added to carry out neutralization and hydration to obtain an aqueous polymer solution having a solid content concentration of 60% by weight.

The resulting aqueous polymer solution (100 solids)
70 parts by weight of amino resin Mycoat 106 [dimethylimino-type benzoguanamine, manufactured by Mitsui Cyanamid Co., Ltd.] was added to 70 parts by weight of the resin composition to obtain an aqueous coating composition. A silicon-based leveling agent, butyl cellosolve and water are further added to the above aqueous coating composition to prepare an organic solvent; 2
The composition was 5% by weight, water; 40% by weight, and solid concentration: 35% by weight. This composition was applied onto an aluminum plate with a bar coater to a film thickness of 5 to 6 μm,
It was cured by heating at 0 ° C. for 10 minutes. Various physical properties were evaluated for the obtained cured coating film and the coating film after pressure steam treatment by a pressure cooker device (standing in steam at 130 ° C. for 30 minutes). The results are as shown in Table 2.

[0031]

Examples 2 to 3 Using the graft copolymer B (Example 2) or the graft copolymer C (Example 3) obtained in Reference Examples 2 and 3, the same procedure as in Example 1 was carried out. A water-based coating composition is synthesized, and then a coating film is formed from the composition,
Its performance was evaluated.

[0032]

[Table 2]

The physical properties of the coating films in Table 2 are all JI
It was measured by the measurement method specified in SK 5400. a. Impact resistance: DuPont impact test (having a 1/2 inch, 500 g load). b. Water resistance: A method based on the boiling water resistance test (sample immersion time is 60 minutes). c. Adhesion ──── A method according to the cross-cut tape method test method (evaluated by the coating film residual rate after tape peeling). d. Hardness ──── Test method for pencil scratch test.

Comparative Example 1 Using the random copolymer D obtained in Comparative Reference Example 1, a phosphoric acid esterified epoxy resin was reacted in the same manner as in Example 1 and further neutralized with an amine. Then, with respect to the water-based polymer and the water-based coating composition using the amino resin, the physical properties of the coating film were measured in the same manner as in the examples. As a result, the physical properties before the steam treatment are not particularly inferior to those of the water-based coating compositions of Examples, but the physical properties after the steam treatment are remarkably deteriorated, and specifically, shown in Table 3. It was as it was. <Comparative Example 2> The graft copolymer A obtained in Reference Example 1 was used to make it aqueous without reacting it with a phosphoric acid esterified epoxy resin.
The coating film physical properties were measured. The results are the same as those in Comparative Example 1 described above, and the physical properties after the steam treatment are remarkably lowered, and specifically, as shown in Table 3.

[0035]

[Table 3]

[0036]

EFFECT OF THE INVENTION According to the aqueous coating composition of the present invention, a coating film which is water-based and is excellent in retort treatment resistance due to the characteristics of the graft copolymer used as the main component and having a unique constitution, that is, Even after the same treatment, a coating film having excellent water resistance, workability, hardness and gloss can be formed on a substrate such as a metal. The aqueous coating composition of the present invention is particularly suitable for coating metal surfaces such as metal cans, home appliances and automobiles.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display area C09D 161/20 PHK C09D 161/20 PHK

Claims (3)

[Claims] 1. A hydroxyl group or an N-alkoxymethylamide group in a branch polymer based on a macromonomer, which is synthesized by (a) an epoxy resin in which a part of an epoxy group is phosphorylated and (b) a macromonomer method. And a (meth) acrylic acid ester-based graft copolymer having a hydroxyl group and a carboxyl group in the trunk polymer, the epoxy group in the epoxy resin is less than the equivalent to the carboxyl group in the graft copolymer. An aqueous coating composition comprising an amino resin and an aqueous polymer obtained by neutralizing with a base an epoxy resin-modified polymer having a carboxyl group obtained by reacting at a ratio of 2. The (meth) acrylic acid ester-based graft copolymer of (b) is a radical-polymerizable component (a) to
Units based on (d), based on the total amount thereof, units based on (a) 3 to 30% by weight, units based on (b) 3 to 20% by weight, units based on (c) 5 40
The aqueous coating composition according to claim 1, which has a composition of 10% to 89% by weight based on (%) and (d). (A) Hydroxyalkyl (meth) acrylate or N
-A macromonomer having radical polymerizability at one end of a polymer obtained by copolymerizing an alkoxymethyl (meth) acrylamide with another α, β-ethylenically unsaturated monomer (b) α, β-ethylenic Unsaturated Carboxylic Acid (c) Addition of ε-caprolactone to hydroxyalkyl (meth) acrylate or hydroxyalkyl (meth) acrylate (d) Other α, β-ethylenically unsaturated monomers 3. A part of a unit based on the other α, β-ethylenically unsaturated monomer of (a) and (d) which constitutes the (meth) acrylic acid ester-based graft copolymer of (b). The water-based coating composition according to claim 1 or 2, wherein all or all are alkyl (meth) acrylate monomer units.