JP3051476B2 - Aqueous paint composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyol resin-based water-based coating composition, and more particularly to a water-based coating composition which forms an excellent coating film as a metal coating composition, particularly as a coating for inner surface coating of cans. .

[0002]

[Background Art and Problems] The use of organic solvents in solvent-based paints using organic solvents has been in the direction of restricting the use from the viewpoint of resource saving, energy saving and environmental protection. There is a need for a shift to paints that use.

[0003] In particular, in the case of paints for cans and anticorrosion paints for painting metal surfaces, the transition to paints using aqueous solvents has been studied mainly for epoxy resin paints. Has been proposed.

For example, JP-A-53-1228 and JP-A-53-1285 disclose an acrylic resin containing a carboxyl group-containing monomer using a radical initiator such as benzoyl peroxide in the presence of an epoxy resin. A method is disclosed in which a system monomer is polymerized and grafted from an aliphatic site of an epoxy resin, and the obtained polymer is dispersed in water using a basic compound such as ammonia or an amine.

However, according to the above method, it is necessary to increase the graft ratio to obtain a highly stable emulsion, during manufacture, a radical initiator such as dangerous high Ben zo peroxide expensive explosion, mass Had the disadvantage that it had to be used.

As a solution to this problem, Japanese Patent Application Laid-Open No. 55-3481
JP-A-55-3482 discloses that a carboxyl group-containing vinyl polymer is esterified with an epoxy group of an epoxy resin in the presence of an amine-based esterification catalyst to substantially contain an epoxy group. A method is disclosed in which a carboxyl group-containing vinyl polymer-modified epoxy resin is obtained, which is neutralized with a base and dispersed in water.

However, according to the above-mentioned method, the reaction is carried out until the epoxy group of the epoxy resin is substantially completely consumed, so that it is inevitable that the resin has a high molecular weight or a high cross-linking. In particular, paints for cans are required to have flexibility that can withstand processing together with the hardness of the coating film, but resin coatings with high molecular weight or high cross-linking have poor flexibility and have problems in the processability of coating films. is there.

Further, when these compositions are used for paints for inner surfaces of cans, low-molecular-weight compounds originating from epoxy resins and acrylic resins as main components are eluted into the contents of the cans, which has a problem in food hygiene. Was. Furthermore, in order to prevent the elution of such low-molecular-weight compounds, it is necessary to completely cure the coating film. Therefore, it is necessary to perform baking at a high temperature. The problem was that it was too late.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to provide an aqueous coating composition for a metal coating, which has excellent stability over time,
An object of the present invention is to provide an aqueous coating composition which can cure a coating film at a low temperature, has a low content of low molecular weight components, and provides a cured coating film having excellent adhesion to a metal substrate and excellent workability.

That is, the present invention relates to
The number average molecular weight and the average number of epoxy groups
Aromatic polyol resin having an average of 0.4 to 0.01 primary hydroxyl group (provided that 2,2-bis @ p-
(3-butoxy-2-glycidyloxypropyloxy)
C) phenyl｝ propane, if necessary,
Reacting glycidyl compound and polyhydric phenol
Molecular weight of 1500 to 29000
Advan with an epoxy value of 0.06 or more
( Excluding epoxy resin) (A) and an ammonium salt and / or an amine salt of a reaction product (C) of a carboxyl group-containing acrylic resin (B), wherein component (A) and component (B) are converted to solid content. (A) / (B) = 95 / by weight ratio
An aqueous coating composition characterized in that the ratio is 5 to 5/95.

Here, an aqueous coating composition wherein the carboxyl group-containing acrylic resin has a number average molecular weight of 300 to 60,000, a carboxylic acid unit of at least 25% by weight and an acid value of 25 to 450 is preferred.

Hereinafter, the present invention will be described in detail. The component (A) of the present invention is obtained by modifying an aromatic epoxy resin with a terminal blocking agent.

The aromatic epoxy resin used as a raw material is not particularly limited as long as it has an aromatic resin skeleton. Bisphenol A epoxy resin, bisphenol AD epoxy resin, bisphenol F epoxy resin and novolak epoxy resin Resins and the like are exemplified.

The aromatic epoxy resin used as the raw material usually has an average of 1.1 to 2.0 epoxy groups in one molecule, and has a number average molecular weight of 700 or more, preferably
1400 or more.

[0015] The terminal blocking agent used blocks the terminal epoxy group of the aromatic epoxy resin, and includes phenols, carboxylic acids, primary amines, secondary amines,
There are mercaptans, alcohols and water.

These terminal blocking agents are those having a reactive hydrogen atom, but are not limited thereto. For example, alkyl terminal halides, Grignard reagents, and alkyllithium reagents such as nucleophilic reagents may be used. Sealants without hydrogen atoms are also readily available.

For example, the phenols include bisphenol A, alkyl monophenol, resorcinol and the like.

The carboxylic acids, monocarboxylic acid compounds, benzoic acid, palmitic acid, lauric acid, myristic acid, stearic acid elevation Gerare, as polycarboxylic acid compound, glutaric acid, maleic acid, adipic acid, succinic Acids, trimellitic acid, pyromellitic acid and the like.

The primary and secondary amines include hydroxylamines such as ethanolamine and diethanolamine, and alkylamines such as propylamine, ethylamine, dipropylamine and diethylamine.

When it is necessary to increase the molecular weight of the aromatic epoxy resin, phenols, especially bisphenol A, are useful. By using an excess amount of bisphenol A with respect to the concentration of the epoxy group of the raw material epoxy resin, it is possible to increase the molecular weight and seal the epoxy resin terminal.

When it is not necessary to increase the molecular weight, monocarboxylic acid compounds and primary and secondary amines are useful because of their high reactivity with epoxy groups.

The terminal blocking agent used is not limited to one kind.
Two or more kinds may be used in combination.

The terminal blocking agent has a number average molecular weight of 350 to 40,000 in the modified component (A), an average of 0 to 0.4 epoxy groups in one molecule, and one primary hydroxyl group in one molecule. It is used in an amount of 0.01 to 1.0 on average. It is more preferable that the epoxy group in the modified component (A) be in this range, because the instability of the aqueous dispersion and the deterioration of the coating film due to the ring opening reaction of the epoxy group can be prevented. It is more preferable that the primary hydroxyl group in the component (A) be in this range, since the generation of a microgel having a network structure due to an excessive esterification reaction can be suppressed.

The carboxyl group-containing acrylic resin (B) used in the present invention comprises (i) a carboxyl group-containing vinyl monomer (ii) an aromatic vinyl monomer (iii) α, β
-At least one monomer selected from the group consisting of alkylesters, hydroxyalkylesters and N-hydroxyalkylamides of ethylenically unsaturated carboxylic acids, such monomers or mixtures thereof being used so that the polymer has a carboxyl group. It can be obtained by polymerization or copolymerization in a combination and an organic solvent at a temperature of 60 ° C. to 150 ° C. using a usual radical polymerization initiator such as azobisisobutyronitrile or benzoyl peroxide.

(I) Examples of the carboxyl group-containing vinyl monomer include acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid and fumaric acid.

(Ii) Examples of the aromatic vinyl monomer include styrene monomers such as styrene, vinyltoluene, 2-methylstyrene, t-butylstyrene and chlorostyrene.

(Iii) Examples of the alkyl ester of an α, β-ethylenically unsaturated carboxylic acid include methyl acrylate, ethyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate and n-amyl acrylate , Isoamyl acrylate, n-hexyl acrylate, 2-ethylhexyl acrylate, n acrylate
Acrylates such as octyl, decyl acurylate, dodecyl acrylate;

Methyl methacrylate, propyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-amyl methacrylate, isoamyl methacrylate, n-hexyl methacrylate, 2-ethylhexyl methacrylate, n-octyl methacrylate, methacryl And methacrylic esters such as decyl acid and dodecyl methacrylate.

Further, hydroxyalkyl esters of α, β-ethylenically unsaturated carboxylic acids include, for example,
Examples include hydroxylalkyl ester monomers such as hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate, and hydroxypropyl methacrylate.

Other N-hydroxyalkylamides of α, β-ethylenically unsaturated carboxylic acids include, for example, N-substituted (meth) acrylamides such as N-methylol (meth) acrylamide and N-butoxymethyl (meth) acrylamide. Acrylic monomers and the like can be mentioned.

In the carboxyl group-containing acrylic resin, the amount of the carboxyl group-containing vinyl monomer used is preferably 25 to 75% by weight based on the total amount of the monomers. Within this range, the dispersion stability in an aqueous medium, the solvent resistance of the coated film are excellent, and the flavor when used on the inner surface of the can is also good. Further, the viscosity at the time of production of the copolymer is appropriate, the production is easy, the water resistance is excellent, and especially when used on the inner surface of a can, no whitening appears in the coating film after retort treatment such as boiling.

The carboxyl group-containing acrylic resin has a number average molecular weight of 300 to 60,000, preferably 400 to 20,000. When the number average molecular weight is in this range, the crosslink density of the coating film is appropriate and the processability is good, and on the other hand, no gelation occurs during the reaction with the aromatic polyol resin (A). The acid value is suitably from 25 to 450, preferably from 200 to 350 in terms of solid content.

In the present invention, the reaction product (C) of the aromatic polyol resin (A) and the carboxyl group-containing acrylic resin (B) is preferably xylene, ethylbenzene, dibutyl cellosolve, diethyl carbitol,
Component (A) and component (B) are mixed in a high boiling point solvent having no hydroxyl group such as dibutyl carbitol in the presence or absence of an ammonia or amine catalyst.
It can be obtained by reacting in a temperature range of 0 ° C to 200 ° C, preferably 120 ° C to 170 ° C.

In the present invention, it is necessary to make the esterification reaction between the primary hydroxyl group of the aromatic polyol resin (A) and the carboxyl group of the carboxyl group-containing acrylic resin (B) the main reaction. Requires relatively high temperatures. When the reaction temperature is in the above range, the reaction time is within a practical range, and the reaction between the secondary hydroxyl group in the aromatic polyol resin (A) and the carboxyl group in the component (B) proceeds. It is less likely to gel.

The reaction between the components (A) and (B) can be controlled within a desired range by measuring the decrease in the acid value and measuring the molecular weight distribution by gel permeation chromatography.

The solid content ratio between the component (A) and the component (B) in the reaction product (C) is in the range of 95/5 to 5/95.
Preferably it is selected from the range of 90/10 to 50/50. Since the water-based coating composition of the present invention is mainly used for the inner surface of a can, a water-resistant coating film is obtained, the coating film does not whiten after retort treatment such as boiling, and the reaction product (C) It is important to properly select the amounts of the components (A) and (B) so that the compound is sufficiently self-emulsified in an aqueous medium and separation does not occur during storage.

The excess carboxyl group in the reaction product (C) is converted into an ammonium salt or an amine salt using ammonia or amines. Preferably, ammonia or amines are added in such an amount that the pH of the final composition is between 5 and 11.

The amines used include, for example, alkylamines such as trimethylamine, triethylamine and butylamine, alcohol amines such as 2-dimethylaminoethanol, diethanolamine, triethanolamine, aminomethylpropanol and dimethylaminomethylpropanol, and morpholine. Is done. Polyamines such as ethylenediamine and diethylenetriamine can also be used.

The composition of the present invention is added to an aqueous medium, dispersed and used as an aqueous coating. Here, the aqueous medium means water alone in which at least 10% by weight is water or a mixture of water and a hydrophilic organic solvent. Examples of the hydrophilic organic solvent include methanol, ethanol, n-propanol, isopropanol, and the like. Alkyl alcohols such as n-butanol, sec-butanol, tert-butanol, isobutanol, methyl cellosolve, ethyl solosolve, propyl cellosolve, butyl cellosolve, methyl carbitol, ether alcohols such as ethyl carbitol, methyl cellosolve acetate, ethyl Ether esters such as cellosolve acetate, dioxane, dimethylformamide, diacetone alcohol and the like are used. The ratio of the reaction product (C) to the aqueous medium is
5/95 to 50/50, preferably 10/90 to 40 /
60. This is to improve the stability of the aqueous dispersion.

The aqueous coating composition of the present invention is used as an aqueous coating by adding a pigment. Various known pigments are used as the pigment. If necessary, for example, an aqueous aminoplast resin such as hexamethoxymethyl melamine, a methylolated benzoguanamine resin, a methylolated urea resin, and a phenolic resin or a surfactant for improving paintability, a defoaming agent and the like are added. It can be used as a paint.

As the substrate to be coated, a metal plate such as an untreated steel plate, a treated steel plate, a zinc iron plate, a tin plate, etc. is suitable. As a coating method, a spray coating such as an air spray, an airless spray and an electrostatic spray is used. However, dip coating, roll coater coating, electrodeposition coating and the like are also possible. The baking conditions are preferably a temperature of 150 ° C. to 24 ° C.
It can be selected from the range of 0 ° C., time, and 2 to 30 minutes.

[0042]

The present invention will be described below with reference to examples and comparative examples. In the description, “parts” and “%” indicate “parts by weight” and “% by weight”, respectively. In each of the examples and comparative examples, the evaluation of the paint or the coated plate was performed in the following manner, unless otherwise specified. Table 1 shows the results.

(1) Preparation of Coated Plate Using a 30 bar coater, the composition was applied on a 0.3 mm thick tin plate (JIS.G.3303) and baked at 200 ° C. for 5 minutes to be cured. The thickness of the coating film was about 6 to 10 μm.

(2) Retort Resistance A part of the coated plate was boiled at 125 ° C. for 30 minutes to examine whether or not the coating film was whitened by the retort treatment.
Similarly, the adhesion of the coating film after the boiling treatment was also evaluated.

(3) Adhesion A 1 mm width and 1 mm width and 1 mm width, respectively, was applied to the coating surface with a knife.
Make one cut on the grid. The number of unpeeled portions of the cross section when the cellophane adhesive tape having a width of 24 mm is closely adhered to the painted surface and strongly peeled off is represented by a molecule. Separately, a coating film having no cross-cut was similarly evaluated.

(4) Workability The coated plate is folded in two by a mandrel tester, and one or two plates are sandwiched as necessary (denoted as 0T, 1T, 2T), and manually press-molded. The paper was further bent at a pressure of 15 kg / cm ^{2 with} a press, the bent portion was spread, and a cellophane adhesive tape was adhered to the film. 0 points: 0% remaining 1 point: 20% remaining 2 points: 40% remaining 3 points: 60% remaining 4 points: 80% remaining 5 points: 100% remaining

(5) Corrosion resistance A test piece having a cross mark on the coating film surface was immersed in a 1% saline solution at 125 ° C. for 1 hour using a knife.
Determine the degree of corrosion near the x mark. No abnormalities …………… ◎ Slightly corroded …… ○ Quite eroded ……… △ △ Corrosion altogether ……… ×

Example 1 Preparation of Aromatic Polyol Resin Solution In a four-necked flask purged with nitrogen gas, 1000 parts of bisphenol A type epoxy resin (number average molecular weight: about 3200, epoxy equivalent: about 2700) and 200 parts of xylene were added. The mixture was gradually heated to raise the internal temperature to 120 ° C, stirred for 1 hour to completely dissolve, and then gradually heated to 150 ° C. After reaching 150 ° C, di-n-propylamine 34.4
Was added dropwise over 1 hour, and after further reacting for 6 hours, the mixture was cooled to room temperature.
An aromatic polyol resin solution having a solid content of 81% or more of 00 or more was obtained. The number average molecular weight was 3,000, and the number of epoxy groups in one molecule was 0.1 or less on average, and the number of primary hydroxyl groups was about 0.5 on average.

-Preparation of Carboxyl Group-Containing Acrylic Resin- In a four-necked flask purged with nitrogen gas, 500 parts of n-butyl alcohol was charged, heated to 80 to 90 ° C., and while maintaining the temperature, 70 parts of styrene. , 40 parts of methyl methacrylate, 140 parts of methacrylic acid, and 500 parts of n-butyl alcohol were gradually added dropwise to the four-necked flask over 2 hours.
After stirring for an hour, the solvent, n-butyl alcohol, is distilled off under reduced pressure, and the remaining resin is further removed under reduced pressure.
After drying at 50 ° C. for 6 hours, a carboxyl group-containing acrylic resin having a number average molecular weight of about 1000, a carboxylic acid unit of 56%, and an acid value of 300 was obtained.

-Preparation of aqueous coating composition- In a four-necked flask purged with nitrogen gas, 123.5 parts of the previously prepared aromatic polyol resin solution was charged and heated to raise the internal temperature to 120 ° C. 25 parts of the carboxyl group-containing acrylic resin produced above was added. Furthermore, the internal temperature was raised gradually to 150 ° C. by heating gradually, and then reacted at that temperature for 1 hour. Then, 36.9 parts of ethylene glycol monobutyl ether and 35 parts of n-butyl alcohol were added, and the mixture was cooled to 100 ° C. did. Next, after adding 5 parts of 2-dimethylaminoethanol, the mixture was stirred at that temperature for 30 minutes. Further, when 275 parts of ion-exchanged water were gradually added using a disperser, the solid content was 25% and the viscosity was 4000.
A milky white dispersion of cps was obtained. The obtained dispersion was stored at room temperature for 3 months, but no abnormality was observed. The ratio of component (A) to component (B) in the solid content was 4: 1.

Comparative Example 1 The procedure was the same as in Example 1 except that the aromatic polyol resin solution obtained in Example 1 and the carboxyl group-containing acrylic resin solution were used and were not mixed but reacted. Then, ethylene glycol monobutyl ether, n-butyl alcohol, 2-dimethylaminoethanol and ion-exchanged water were added, but no aqueous dispersion was obtained.

(Example 2)-Preparation of acrylic resin containing carboxyl group-Acrylic acid 85.2 was placed in a four-necked flask purged with nitrogen gas.
Then, 60 parts of styrene, 30 parts of methyl methacrylate, 39.2 parts of methacrylic acid, 85.2 parts of acrylic acid, and 5 parts of benzoyl peroxide were mixed while maintaining the temperature. The obtained homogeneous solution was gradually added dropwise to the four-necked flask over 2 hours, and after completion of the addition, the mixture was further stirred at the same temperature for 2 hours, and then the solvent n-butyl alcohol was distilled off under reduced pressure. The remaining resin was dried under reduced pressure at 150 ° C. for 6 hours to obtain a carboxyl group-containing acrylic resin having a number average molecular weight of about 1,000, a carboxylic acid unit of 58%, and an acid value of 390.

-Preparation of aqueous coating composition- An aqueous coating composition was prepared in the same manner as in Example 1 except that the obtained carboxyl group-containing acrylic resin was used and the reaction temperature was changed to 135 ° C and the reaction time was set to 1 hour. The obtained aqueous coating composition had a solid content of 25% and a viscosity of 2,700 cps. The ratio of component (A) to component (B) in the solid content was 4: 1.

Comparative Example 2 Aromatic polyol resin solution,
The carboxyl group-containing acrylic resin was prepared in the same manner as in Example 2. The preparation of the aqueous coating composition is carried out at a reaction temperature of 1
The procedure was performed in the same manner as in Example 2 except that the temperature was changed to 50 ° C. No aqueous dispersion was obtained.

The aqueous coating compositions obtained in Examples 1 and 2 were mixed with Regitop PL4523 manufactured by Gunei Chemical Co., Ltd. at a weight ratio of 5: 1 to prepare an aqueous coating, and a coating film performance test was performed. Was. The results are shown in Table 1.

Example 3 Preparation of Aromatic Polyol Resin A four-necked flask purged with nitrogen gas had a number average molecular weight of about 37.
Then, 1000 parts of a bisphenol A type epoxy resin having an epoxy equivalent of about 2700, 36.9 parts of benzoic acid, and 200 parts of xylene were charged, gradually heated to an internal temperature of 120 ° C., stirred for 1 hour, and completely dissolved. Later, another 130
Heated slowly to ° C. After reaching 130 ° C., 3.0 g of pyridine were added. Further, at 130 ° C. to 140 ° C., 5
After reacting for an hour, xylene was distilled off to obtain an aromatic polyol resin having an epoxy equivalent of 30,000 or more. The number average molecular weight was about 3,800, and the number of epoxy groups in one molecule was 0.1 on average and the number of primary hydrogen groups was 0.6 on average.

Preparation of Carboxyl Group-Containing Acrylic Resin Dioxane 29 was placed in a four-necked flask purged with nitrogen gas.
2 parts were charged and heated to 70 to 80 ° C., and while maintaining the temperature, a uniform solution obtained by mixing 35 parts of styrene, 20 parts of methyl methacrylate, and 70 parts of methacrylic acid was added over 2 hours.
After gradually adding dropwise to the four-necked flask, stirring the mixture at the same temperature for 3 hours after the completion of the addition, and then cooling to room temperature,
A carboxyl group-containing acrylic resin having a solid content of 30% was obtained. The number average molecular weight was 200, and the carboxylic acid unit was 56% by weight, and the acid value was 360.

-Preparation of aqueous coating composition- In a four-necked flask purged with nitrogen gas, 100 parts of the previously prepared aromatic polyol resin and 83.3 parts of the previously prepared carboxyl group-containing acrylic resin solution were added. Preparation,
Heat to raise the internal temperature to 120 ° C, then at that temperature,
After reacting for 1 hour, 30 g of cyclohexanone was added, and the reaction was further performed for 3 hours. Next, the solvent was distilled off under reduced pressure, and 34.1 parts of ethylene glycol monobutyl ether and 56.8 parts of n-butyl alcohol were added thereto.
Cooled to 0 ° C. Next, 10 parts of 2-dimethylaminoethanol was added, and the mixture was stirred at that temperature for 30 minutes. Further, using a disperser, 288 parts of ion-exchanged water was gradually added, and the solid content was 24% and the viscosity was 350 cps.
To obtain a milky dispersion. The obtained dispersion was stored at room temperature for 3 months, but no abnormality was observed. The weight ratio of component (A) to component (B) in the solid content was 4: 1.

[0059] was prepared in the same manner (Comparative Example 3) aromatic polyol resin Contact and carboxyl group-containing acrylic resin solution in Example 3 a. Example 3 was repeated except that they were not mixed but reacted.
In the same manner as in the above, ethylene glycol, monobutyl ether, n-butyl alcohol, 1-dimethylaminoethanol and ion-exchanged water were added, but no aqueous dispersion was obtained.

[0060]

[Table 1]

[0061]

The aqueous coating composition of the present invention is water-soluble and can be applied without using an organic solvent. Further, it has excellent stability over time and can cure the coating film at a low temperature, and the resulting cured coating film has excellent retort resistance, adhesion to a metal substrate, and workability. The compositions of the present invention are widely used for painting metal surfaces.

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-3-179018 (JP, A) JP-A-56-112969 (JP, A) JP-A-1-230678 (JP, A) JP-A-56- 109243 (JP, A) JP-A-54-3900 (JP, A) JP-A-56-26961 (JP, A) JP-A-59-136357 (JP, A) (58) Fields investigated (Int. ⁷ , DB name) C08G 81/00-81/02 C09D 5/02 C09D 167/00-167/08 C09D 133/00-133/26 C09D 163/00-163/10 CA (STN) REGISTRY (STN)

Claims (2)

(57) [Claims] (1) a number average molecular weight of 350 to 40,000 and
And 0 to 0.4 epoxy groups on average per molecule
Aromatic polyol resin having an average of 0.01 to 1.0 acid groups (provided that 2,2-bis @ p- (3-butoxy-
2-glycidyloxypropyloxy) phenyl @ pro
Bread, if necessary, polyglycidyl compound other than this component
Product and a polyhydric phenol.
Having a molecular weight in the range of 1500 to 29000
Advanced epoxy resin with a xy value of 0.06 or more
Excluding) (A) an ammonium salt and / or an amine salt of the reaction product (C) of the carboxyl group-containing acrylic resin (B), wherein the component (A) and the component (B) are in a weight ratio in terms of solid content. (A) / (B) = 95/5 to 5/95. 2. The method according to claim 1, wherein the carboxyl group-containing acrylic resin (B) has a number average molecular weight of 300 to 60,000, a carboxylic acid unit of at least 25% by weight, and an acid value of 25 to 450. Aqueous coating composition.