JPH08218032A - Water-based coating composition - Google Patents

Abstract

PURPOSE: To provide a coating composition containing alkanols, glycol ethers and glycols, having an aromatic epoxy resin, etc., as a resin skeleton and exhibiting excellent applicability, film-forming property, corrosion resistance, flavor resistance, retort resistance and processability. CONSTITUTION: This coating composition contains (A) 0.5-10wt.% of alkanols of formula, R1 -OH (R4 is a 2-8C alkyl), (B) 3-20wt.% of glycol ethers of formula (R2 is a 1-6C alkyl; R3 is H or methyl) and (C) 1-10wt.% of glycols of formula, HO-R4 -OH (R4 is a >=2C alkyl or ether group) and further contains (D) preferably (i) 30-90wt.% of an aromatic epoxy resin containing >=0.5 epoxy groups, (ii) 7-70wt.% of an acrylic polymer containing carboxyl group and (iii) 1-30wt.% of a resol-type phenolic resin as resin skeletons and, as necessary, (E) ammonia or an amine as a neutralizing agent.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an aqueous coating composition. More specifically, the present invention relates to an aqueous coating composition having excellent coating performance as an inner surface coating for metal cans, and having good corrosion resistance, flavor resistance, retort resistance, and processability.

[0002]

2. Description of the Related Art Conventionally, the inner surface of a metal can made of steel, aluminum, tin-free steel or the like has been coated to prevent corrosion due to molding and external impact and to retain the flavor of the contents. ing. Conventionally, solvent-based paints such as epoxy / phenol, epoxy / amino, vinyl organosol, etc. have been used for coating the inner surface of cans. However, in recent years, epoxy / acrylic water-based paints have been used for reasons such as resource saving, improvement of working environment, and low pollution. Conventionally, as a water-based paint for the inner surface of a can, a water-based paint containing an epoxy resin as a main component has been proposed. The epoxy resin is modified with a high acid value acrylic resin, neutralized with a base such as amine, and an aqueous dispersion is prepared. The method is mainly used.

For these water-based paints, an organic solvent of about 5 to 20% by weight is used for the purpose of ensuring the wettability to the base metal and the leveling property. For example, Japanese Patent Publication No. 62-4929
The publication No. 1 describes alcohols, glycol derivatives, ethers, ketones, etc. As an example of use, ethylene glycol monobutyl ether / butanol /
Octanol or ethylene glycol monobutyl ether / butanol / cyclohexanone combinations are disclosed. Further, in JP-A-2-107679, a polyhydric alcohol such as ethylene glycol or diethylene glycol is used for the purpose of improving the stability of a coating, and in JP-A-6-228496, a specific water-miscible organic compound is used. Excellent film-forming property due to the combination of solvent / specific non-water-miscible organic solvent / other organic solvent
It is disclosed to provide armpit resistance and paint stability.

[0004]

These water-based coating compositions certainly exhibit excellent coating properties and film-forming properties, and also have good corrosion resistance, flavor resistance, retort resistance, and processability. There is. However, the range and combination of the amount of each solvent used is somewhat unclear, and in the dry baking process with a rapid temperature rise, there is a problem of cracking when thick film is formed, and the stability of the coating is not sufficient. It is performance that cannot be said.

[0005]

Means for Solving the Problems As a result of intensive studies to solve the above problems, the present inventor has found that the following three kinds of organic solvents are used as essential components, an aromatic epoxy resin, and a carboxyl group-containing acrylic polymer. We have found a water-based coating composition containing a polymer and a resol-type phenol resin as a resin constituent. That is, as an organic solvent, alkanols R ₁ —OH 0.5 to 10% by weight Glycols HO-R ₄ -OH 1~10 wt% (wherein, R ₁ represents an alkyl group straight or branched having 2 to 8 carbon atoms, R ₂ is 1-6 linear carbon atoms A branched or branched alkyl group, R ₃ represents a hydrogen atom or a methyl group, R ₄ represents an alkyl group having 2 or more carbon atoms or an ether group, and n represents 1 or 3.)
Aromatic epoxy resin 30-90 containing three kinds of organic solvent (A) and containing 0.5 or more epoxy groups per molecule (A)
% By weight, (B) carboxyl group-containing acrylic polymer 7 to
70% by weight, (C) resol type phenolic resin 1 to 30
An aqueous coating composition obtained by neutralizing wt% with ammonium or amine, which is a resin constituent.

The organic solvent used in the present invention has the formula (I),
From the three types of structures represented by (II) and (III), one or more types, respectively, of a total of three or more types of solvents are used. Alkanols R ₁ -OH (I) ₄ -OH (III) (In the formula glycol HO-R, R ₁ is a straight-chain or branched alkyl group having 2 to 8 carbon atoms, R ₂ is 1-6 straight-chain or carbon atoms A branched alkyl group, R ₃ represents a hydrogen atom or a methyl group, R ₄ represents an alkyl group having 2 or more carbon atoms or an ether group, and n represents 1 or 3.)

Alkanols represented by the formula (I) include methanol, ethanol, n-propyl alcohol, isopropyl alcohol, n-butanol, isobutyl alcohol, n-hexanol, n-pentanol, n-amyl alcohol and isoamyl. Examples thereof include primary alcohols having a linear or branched alkyl group such as alcohol. The amount of alcohol solvent used is 0.5-
10% by weight is preferable, and if it is less than 0.5% by weight, there is no effect on cracking and sagging at the time of baking the coating, and if it exceeds 10% by weight, stability such as separation and sedimentation in the coating tends to decrease.

The glycol ethers represented by the formula (II) include ethylene glycol monobutyl ether, ethylene glycol monohexyl ether, isobutyl glycol, 2-ethylhexyl glycol, phenyl glycol, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether and diethylene glycol mono. Examples include propyl ether and diethylene glycol monohexyl ether. If it is less than 3%, the wettability is lowered, and if it exceeds 20%, the stability of the coating is lowered.

Examples of glycols represented by the formula (III) include ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol, dipropylene glycol, butylene glycol and hexylene glycol. Glycol is particularly preferred. Less than 1% has less effect on armpits, 10%
If it exceeds, wettability is affected.

Aromatic epoxy resin (A) used in the present invention
Examples thereof include bisphenol A type epoxy resin and bisphenol F type epoxy resin, and those having an epoxy group of 0.5 or more in one molecule and a number average molecular weight of 300 or more, preferably 900 or more are used. . As commercially available products, Epicoat 1004, Epicoat 1007, Epicoat 1009, Epicoat 101 manufactured by Yuka Shell Co., Ltd.
0, D.C. manufactured by Dow Chemical Company. E. FIG. R. 669E, D.E.
E. FIG. R. 668E, Araldite AER6 manufactured by Asahi Ciba
007, Araldite AER6019, Araldite A
ER6039 etc. are mentioned. The epoxy resin content in the component is preferably 30 to 90% by weight.
If it is less than 0% by weight, the workability, adhesion and corrosion resistance tend to deteriorate, and if it is more than 90% by weight, the dispersion stability tends to decrease. The number of epoxy groups per molecule in the epoxy resin is preferably 0.5 or more. If it is less than 0.5, the adhesion to the base metal and the corrosion resistance tend to be reduced.

The carboxyl group-containing acrylic polymer in the present invention can be synthesized by a known method in which solution polymerization is carried out in the presence of a radical-generating polymerization initiator, and is a kind of a carboxyl group-containing monomer and other vinyl monomers. The above can be selected and used. The following are acrylic monomers. Carboxyl group-containing monomer; examples thereof include acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid and fumaric acid. Alkyl ester monomer; methyl acrylate,
Ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, n-amyl acrylate, 2-ethylhexyl acrylate, n-hexyl acrylate, n-octyl acrylate, decyl acrylate,
Acrylic ester monomers such as dodecyl acrylate, and methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-amyl methacrylate, isoamyl methacrylate, n-hexyl methacrylate, 2-ethylhexyl methacrylate, n
-Methacrylic acid ester monomers such as octyl methacrylate, decyl methacrylate, dodecyl methacrylate, and lauryl methacrylate.

Hydroxyl group-containing monomer: Examples include monomers such as hydroxyethyl acrylate, hydroxypropyl acrylate, 2-hydroxyethyl methacrylate and hydroxypropyl methacrylate. Amide-based monomer; N-methoxy (meth) acrylamide, N-ethoxymethyl (meth) acrylamide, N
-Butoxymethyl (meth) acrylamide, N-isopropylmethyl (meth) acrylamide and the like can be mentioned. Aromatic vinyl monomers such as styrene and α-methylstyrene.

The monomer composition ratio in the acrylic polymer is not particularly limited, but the ratio of the carboxyl group-containing monomer content in the composition components is preferably 10% to 80% by weight. If it is less than 10% by weight, the stability of the dispersion tends to decrease, while if it exceeds 80% by weight, the adhesion and workability are deteriorated, resulting in poor corrosion resistance. The number average molecular weight of the acrylic polymer is 8000 to 800.
A range of 00 is preferred. When it is less than 8,000, the crosslink density is increased and the workability and adhesion are deteriorated.

The resol type phenol resin used in the present invention is a resin obtained by condensing an arbitrary phenol component and formaldehyde in the presence of a basic catalyst. Examples of the phenol component constituting the resol-type phenol resin include p-cresol, o-cresol and p-tert.
-Butylphenol, p-ethylphenol, 2,3-
Bifunctional phenols such as xylenol, p-nonylphenol, p-phenylphenol and p-cyclohexylphenol, trifunctional phenols such as carboxylic acid, m-cresol, m-ethylphenol, 3,5-xylenol and m-methoxyphenol. , Monofunctional phenols such as 2,4-xylenol and 2,6-xylenol,
One or two of tetrafunctional phenols such as bisphenol A, bisphenol B and bisphenol F
It is possible to combine more than one species.

As the basic catalyst, ammonia, amine, hydroxide of alkaline earth metal, hydroxide of alkali metal, oxide of alkaline earth metal, oxide of alkali metal or the like can be used. If the resol type phenol resin is less than 1% by weight, the crosslink density will be low and the adhesion and corrosion resistance will be poor, and if it exceeds 30% by weight, the crosslink density will be too high and the workability will tend to be lowered. Therefore 1-
30% by weight is preferred.

The mixture of (A) the aromatic epoxy resin, (B) the carboxyl group-containing acrylic polymer, and (C) the resol-type phenol resin used in the present invention contains (A) and (B) with or without a catalyst. The method of esterification under the conditions of (C) and blending with (C), and then using ammonia or amine to form an aqueous dispersion, (A) and (C) are precondensed with (B) mixed with a catalyst or A method in which an esterification reaction is carried out under a condition without a catalyst and then an aqueous dispersion is prepared using ammonia or amine, and (B) and (C)
There is a method in which (A) is mixed with the pre-condensed product, the esterification reaction is carried out under the condition with or without a catalyst, and then an aqueous dispersion is prepared by using ammonia or amine. The reaction is usually carried out at a temperature of 60 to 130 ° C. with some epoxy groups remaining.

The catalyst may be a tertiary amine, preferably dimethylaminoethanol. Examples of the amine used for neutralization include trimethylamine,
Alkylamines such as triethylamine and butylamine, dimethylaminoethanol, diethanolamine,
Examples include alcohol amines such as aminoethyl propanol and volatile amines such as morpholine.

The organic solvent used in the above esterification reaction dissolves both the aromatic epoxy resin and the carboxyl group-containing acrylic polymer, and is stable to the aqueous dispersion of the reaction product. One or more organic solvents that are optionally mixed with are used. The organic solvent is selected from the three types of structures described above.

The aqueous coating composition of the present invention may optionally contain a wax in order to prevent scratches on the coating film during processing and transportation after forming the coating film. Applicable substrates include aluminum plate, steel plate, zinc steel plate, tin plate, and other treated or untreated metal plates. Examples of the undercoat include a plate already coated with an epoxy-based or vinyl-based primer, and a plate laminated with a plastic film such as polyethylene terephthalate. As a coating method, various methods known in the art such as roll coater coating, spray coating, electrodeposition coating and dip coating can be used. The baking and drying conditions can be selected from the range of 150 ° C to 240 ° C for 1 minute to 30 minutes.

[0020]

EXAMPLES The present invention will be specifically described below with reference to examples. All parts and% are based on weight.

Production Example 1 Production of Epoxy Resin Solution (A1) A four-necked flask was charged with 480 parts of Epicoat 1009 (produced by Yuka Shell Epoxy Co., Ltd.) and 320 parts of ethylene glycol monobutyl ether, and the mixture was heated to 100 under a nitrogen stream. It was heated to ℃, stirred for 1 hour while maintaining this temperature, and then cooled to 60% solid content.
To obtain an epoxy resin solution (A1).

Production Example 2 Production of Epoxy Resin Solution (A2) Epicoat 1009 (produced by Yuka Shell Epoxy Co., Ltd.) 480 parts Diethylene glycol monobutyl ether 320 parts Epoxy resin solution having a solid content of 60% by the same method as Production Example 1 (A2) was obtained.

Production Example 3 Production of Acrylic Polymer Solution Containing Carboxyl Group (B) 400 parts of n-butanol was charged into a four-necked flask equipped with a stirrer, a reflux condenser, a thermometer, a dropping funnel and a nitrogen inlet. Next, 112 parts of styrene, 56 parts of ethyl acrylate, 112 parts of methacrylic acid and 7.5 parts of benzoyl peroxide (75% of active ingredient) were weighed in a beaker to prepare a premix. The temperature of n-butanol in the flask was heated to 105 ° C., at which temperature the preconditioned monomer mixture was added dropwise from the addition funnel over 2 hours. Further, the reaction mixture was kept at the same temperature for 2 hours to complete the reaction and then cooled. Weight average molecular weight about 3000
A carboxyl group-containing acrylic polymer solution having a solid content of 40% (hereinafter referred to as "acrylic polymer solution (B)") was obtained.

Production Example 4 Production of Phenolic Resin (C) Bisphenol A 228 parts (1 mol), 37% formalin 649 parts (8 mol), 35% sodium hydroxide 229
Parts (2.0 mol) were mixed and reacted at 50 ° C. for 2 hours and then n-
Butanol (250 parts) was added, and 20% hydrochloric acid (401 parts) (2.2 mol) was further added. After stirring at 60 ° C. for 10 minutes, the mixture was allowed to stand, and two layers were separated in a few minutes. The upper layer was a phenol resin-containing organic compound layer, and the yield was 430 parts. As a result of washing and neutralizing this organic compound layer with water and ammonia, 330 parts of a resin solution having a solid content of 30% was obtained as a pale purple transparent phenol resin (C). The content of tetramethylolated bisphenol A compound in this phenol resin solution was 63%, and the remaining 37% was a polymethylol compound of a bisphenol A dimer or more.

Example 1 250.0 parts of the above-mentioned epoxy resin solution (A1) 125.0 parts of the above-mentioned acrylic resin solution (B) Dimethylaminoethanol 10.0 parts The above-mentioned phenol resin solution (C) 33.3 parts Ion-exchanged water 581 .7 parts Ethylene glycol monobutyl ether 20.0 parts Propylene glycol monobutyl ether 30.0 parts Propylene glycol 50.0 parts Into a four-necked flask was charged with and added with stirring under nitrogen stream. The internal temperature was raised to 80 ° C., the mixture was stirred for 2 hours, and then cooled to room temperature. The reduction rate of oxirane was 70%. Add while stirring,
Further, was added little by little to obtain an aqueous dispersion. Next, the solvent was removed under reduced pressure at 55 ° C to obtain a solid content of 25% and ethylene glycol monobutyl ether 6.25%.
Furthermore, was added to finally obtain an aqueous dispersion having a solid content of 20%.

Examples 2 to 7 In the same manner as in Example 1, the epoxy resin (A1) or (A2) and the acrylic resin (B) having the composition shown in Table 1 were heated and stirred, and then cooled to cool the phenol resin. Solution (C) was added, and ion-exchanged water was added little by little to obtain an aqueous dispersion. Further, various organic solvents were added to prepare an aqueous dispersion having a solid content of 20%.

[0027]

[Table 1]

Comparative Example 1 250.0 parts of the above-mentioned epoxy resin solution (A1) 125.0 parts of the above-mentioned acrylic resin solution (B) Dimethylaminoethanol 10.0 parts The above-mentioned phenol resin solution (C) 33.3 parts Ion-exchanged water 581 0.7 parts Propylene glycol monobutyl ether 50.0 parts n-Butanol 50.0 parts were charged into a four-necked flask, and was added with stirring under nitrogen stream. The internal temperature was raised to 80 ° C., the mixture was stirred for 2 hours, and then cooled to room temperature. The reduction rate of oxirane was 70%. Add while stirring,
Further, was added little by little to obtain an aqueous dispersion. Then, the solvent was removed under reduced pressure at 55 ° C. to obtain a solid content of 25% and ethylene glycol monobutyl ether 6.25%. Furthermore, was added to finally obtain an aqueous dispersion having a solid content of 20%.

Comparative Examples 2 and 3 In the same manner as in Comparative Example 1, water dispersions were prepared with the formulations shown in Table 2.

[0030]

[Table 2]

Performance Test The following tests were carried out on the aqueous coating compositions obtained in Examples 1 to 7 and Comparative Examples 1 to 3 above. (1) Storage stability test: Store the paint in a 50 ° C incubator,
The appearance and properties after 5 days, 10 days, and 30 days were observed and evaluated. Good storage stability ・ ・ ・ ○ Gelation, sedimentation, separation, etc. occurred during storage ・ ・ ・ × (2) Armpit resistance: A film thickness of 20μ or more on a tin plate using a bar coater Paint, and put in an oven at 200 ℃ or higher to bake and dry. Bubbles generated in the coating film and on the surface of the coating film were visually evaluated.

No bubble generation ・ ・ ・ ○ Micro bubble generation ・ ・ ・ △ Bubble generation on the entire surface ・ ・ ・ × (3) Film forming property: Bar coater so that the film thickness was 10 μm on the tin plate. After applying the coating composition at 20 ° C., it was allowed to stand at 20 ° C., and the state of film formation was visually evaluated. Normal continuous film was formed ・ ・ ・ ○ Partially cracked ・ ・ ・ △ Cracked on the whole surface ・ ・ ・ × (4) Surface condition: Bar on tin plate to have a film thickness of 3μ The paint was applied with a coater, and the surface smoothness and the presence or absence of cissing and lumps were visually evaluated.

Normal surface condition: ○ Slightly lacking in smoothness, partial repelling occurred: △ Total repelling occurred: × (5) Adhesion: on tin plate A coating material was applied by a bar coater to a lower film thickness of 5 μm, and baked and dried at 200 ° C. for 5 minutes to prepare a test panel. Width 1.5mm vertically and horizontally using a cutter knife on the coating surface
The remaining amount of the coating film when the notches were made, and the cellophane tape having a width of 24 mm was adhered and strongly peeled off was displayed. (6) Water resistance: A coated plate prepared by the same method as the above adhesion test was treated in water at 125 ° C for 40 minutes, and the surface condition of the coating film was evaluated.

No change in bleaching / blister etc. occurred. ○ Partial bleaching occurred. △ △ Whitening / blister occurred on the entire surface ・ ・ ・ ×

[0035]

[Table 3]

[0036]

According to the present invention, a solvent having three kinds of structures, that is, alkanols, glycol ethers,
By using each solvent of glycols and glycols, the water resistance can be improved, and the water-based coating having excellent adhesion and water resistance can be obtained.

Claims (2)

[Claims] 1. An alkanol as an organic solvent R ₁ —OH 0.5 to 10% by weight Glycols HO-R ₄ -OH 1~10 wt% (wherein, R ₁ represents an alkyl group straight or branched having 2 to 8 carbon atoms, R ₂ is 1-6 linear carbon atoms A branched or branched alkyl group, R ₃ represents a hydrogen atom or a methyl group, R ₄ represents an alkyl group or an ether group having 2 or more carbon atoms, and n represents 1 or 3). An aqueous coating composition comprising an epoxy resin, a carboxyl group-containing acrylic polymer, and a resol-type phenol resin as a resin skeleton. 2. (A) Aromatic epoxy resin containing 0.5 or more epoxy groups per molecule 30 to 90% by weight (B) Carboxyl group-containing acrylic polymer 7 to 70% by weight (C) Resol type phenol resin 1 % To 30% by weight of (A) to (C) as constituents, and ammonia or amine is used as a neutralizing agent.