JPH02255773A - Aqueous coating composition - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention [Objective of the Invention] (Industrial Field of Application) The present invention relates to an aqueous coating composition with an extremely low organic solvent content, and more specifically, to an aqueous coating composition with an extremely low organic solvent content. The present invention relates to an aqueous coating composition that has excellent performance in terms of roll coating suitability and film forming properties.

(Conventional technology) Traditionally, when manufacturing canned goods in the can manufacturing industry.

Metal materials are coated on the inner surface of cans with various paints for the purpose of preventing the metal from leaching into the contents and preventing corrosion of the metal. In this process, the inner surfaces of the can bodies and can lids of three-piece cans are coated with various inner surface paints on metal materials using a natural roll coater.

A commonly used method is to bake the formed coating film to form an inner coating film. These interior paints are conventional.

It is in the form of an organic solvent solution, and therefore is subject to many regulations such as the Organic Solvent Poisoning Prevention Regulations and the Fire Service Act.

It is subject to air pollution and other pollution regulations. Therefore.

There has been a wide demand for a water-based coating for the inner surface of these cans. However, the inner surface of the can is painted with (1) a rust preventive oil such as cottonseed oil or dioctyl sebacate applied to the surface of the metal material for the purpose of rust prevention.

(2) After painting the inner and outer surfaces, it is baked in an oven, where there is a high possibility that lubricating oil or low molecular weight resin components contained in other paints will adhere to the coating base. The following working methods have been used in the past. If a water-based paint is used as the inner surface paint without changing these working methods, the "leakability" to the paint base will be insufficient and a repellent-like paint film defect will occur. As described above, if a coating film defect occurs, it may cause elution of the base metal into the contents or corrosion of the base metal. Therefore, in order to solve these problems, the water-based paints for the inside of cans that have been developed to date use a large amount of organic solvents (usually 15 to 40% in the paint) in addition to water, which makes it difficult to comply with the various regulations mentioned above. It was just an insufficient countermeasure.

(Problem to be solved by the invention) The above problems would naturally be solved by reducing the amount of organic solvent in water-based paints, but the proportion of organic solvents used in songs was reduced by conventionally known methods. In the case of low-solvent water-based paints produced by this process, repellent-like coating defects occur during roll coating, and striped ribs characteristic of roll coating occur, resulting in so-called flow defects. Furthermore, the formed coating film has the disadvantage of poor film-forming properties, such as being in the form of white powder or scales and easily peeling off.

[Structure of the invention]

(Means for Solving the Problems) As a result of intensive studies to solve the above problems, the inventors have discovered that one or more water-miscible organic solvents having a specific chemical structure and one or more hydrophobic By combining a mixed solvent with an organic solvent, the total organic abrasion in the paint can be reduced to 10% by weight.
It has been found that coating suitability equivalent to that of solvent-based paints can be obtained even when the coating composition is reduced to below.

That is, the present invention provides water-dispersible resin (A), organic solvent (B)
), water (C), and optionally additives (D), the organic solvent (B) has the following general formula % (wherein R is H or CHa group, R' is an alkyl group having 5 to 9 carbon atoms, n represents 1 or 2,
) and a water-miscible organic solvent (b,).

A hydrophobic organic solvent whose solubility in water and solubility in water at 25°C are both 2% by weight or less (
b,)/(b,)=9515 to 50150, the total amount of (b)) and (byo) is 4% by weight or more based on the total coating composition, and the organic solvent (B) The purpose of the present invention is to provide an aqueous coating composition with excellent roll coating suitability, characterized in that the amount thereof is 10% by weight or less based on the total coating composition.

The feature of the present invention is that the organic solvent component (B) in the water-based paint composition
It consists of a mixed solvent of a water-miscible organic solvent (bt) with a specific chemical structure and a hydrophobic organic solvent (bt).

A water-miscible organic solvent (bl) having a specific chemical structure is defined by the following general formula % formula % (wherein R is a H or CHz group, R' is an alkyl group having 5 to 9 carbon atoms, and n is 1 Or it represents 2.

), and examples of such solvents include ethylene glycol monoisoamyl ether, ethylene glycol monohexyl ether, ethylene glycol monophenyl ether, ethylene glycol monobenzyl ether, ethylene glycol monooctyl ether, diethylene glycol monoisoamyl ether, and diethylene glycol monohexyl ether. , propylene glycol monohexyl ether.

Dipropylene glycol monohexyl ether and the like can be mentioned.

Hydrophobic organic solvents (bz) are solvents whose solubility in water and solubility in water at 25°C are both 2% by weight or less. Examples of such solvents include toluene, xylene, ethylbenzene, isopropylbenzene, butyl Aromatic hydrocarbon solvents such as benzene and n-amylbenzene (both insoluble in water), methyl isobutyl ketone (solubility in water 1.7% by weight).

Water solubility 1.9% by weight, hereinafter shown in this order) Methylpentyl ketone (0.4% by weight, 1.4% by weight), dipropyl ketone (0.43% by weight, 0.871!1%) .

Diisobutylketone (0,043% by weight, 0.4% by weight
), ketone solvents such as holon (insoluble), isophorone (insoluble), 5ec-hexyl acetate (0.13% by weight.

2-ethylbutyl acetate, 2-ethylhexyl acetate (insoluble), cyclohexyl acetate (insoluble), and benzyl acetate (insoluble).

Organic solvents other than the above-mentioned specific water-miscible organic solvents (bl) and the hydrophobic organic solvent Cbt are not particularly limited, but examples include methyl alcohol, ethyl alcohol,
n-propyl alcohol, isopropyl alcohol, n
-Butyl alcohol, isobutyl alcohol 1 Alcohol organic solvents such as n-amyl alcohol and hexyl alcohol, cellosolve solvents such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, and ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether , carpitol-based solvents such as diethylene glycol monobutyl ether, etc. can be used.

Water-miscible organic solvent (bi) and hydrophobic organic solvent (b2)
It is currently not clear why the mixed solvent (B) with a water-miscible organic solvent (B) has excellent roll coating suitability despite having a low solvent content. 2.Although it is hydrophilic, it also has good solubility in coating film-forming resins, especially epoxy resins, which will be described later, so that a coating film with excellent wettability to the underlying metal and no repellency can be obtained.

In addition, since the water-miscible organic solvent (b) has a high boiling point of 180°C or higher, evaporation of the solvent from the surface of the coating film after painting is suppressed, and the solvent is retained in the coating film, forming a film. A coating film with good properties can be obtained. Also, hydrophobic organic solvents (
bt) adjusts the fluidity of water-based paint through interaction with the hydrophilic water-miscible organic solvent (bi), and improves flow by losing fluidity before ribs form and expand during roll coating. It is thought that it is possible to obtain a coating film with a high quality. For this reason.

bi /bg must be between -9515 and 50150; if this value is greater than 9575, roll coating suitability, especially flow, will be poor; conversely, if the above value is 50150
When it becomes smaller, repellency will occur. In addition, the total amount of the water-miscible organic solvent (bi) and the hydrophobic organic solvent (b) must be at least 4% by weight based on the total coating composition, including other organic solvents. All organic solvents are incorporated in an amount of 10% by weight or less based on the total coating composition.

The water-dispersible resin (A) used in the present invention includes, for example, an aromatic epoxy resin made dispersible in an aqueous medium by chemically or physically treating it. Chemical treatment is a method of potentially making it self-emulsifying by introducing a carboxyl group into one molecule.

There is a method of making a carboxyl group-containing acrylic resin self-emulsifying by reacting it in the presence of an esterification catalyst, and the two physical treatments are a method of reacting a carboxyl group-containing acrylic resin in the presence of an esterification catalyst to make it self-emulsifying. There is a method of mixing the acrylic resin with an organic solvent solution, neutralizing the carboxyl groups in the acrylic resin with ammonia water or amine water, and mechanically emulsifying and dispersing the resin component in the solution.

Aromatic epoxy resins used in the present invention include bisphenol A and bisphenol B.

There are epoxy resins obtained by polycondensation of bisphenols such as bisphenol F and epichlorohydrin, and a commercially available product is Epikoat 8 manufactured by Shell Chemical Co., Ltd.
28. Epicote 1001. Epicote 1007.
Epicote 1009. Examples include Epicote 1010.

The acrylic resin used in the present invention is acrylic acid.

With monobasic carboxylic acid monomers such as methacrylic acid.

Copolymerized by appropriately selecting acrylic acid alkyl esters such as methyl acrylate and ethyl acrylate, styrene monomers such as styrene and vinyltoluene, and hydroxyl group-containing monomers such as hydroxyethyl acrylate and hydroxypropyl acrylate. be.

In the present invention, the aqueous resin dispersion is prepared by adding ammonia or amine to the composite resin composition in an amount such that the final composition has a pH of 4 to 11, and then dispersing the mixture in an aqueous medium.

Examples of the amines include alkylamines such as trimethylamine, triethylamine, and butylamine, 2-dimethylaminoethanol, and jetanolamine.

Alcohol amines such as triethanolamine, morpholine, etc. are used.

An aqueous paint can be obtained by removing the organic solvent from the aqueous dispersion thus obtained by azeotropic distillation under reduced pressure, adjusting the amount of organic solvent to a predetermined amount, and, if necessary, adding the organic solvent later. Furthermore, if necessary, a surfactant, an antifoaming agent, etc. can be added to improve the coating properties and the composition can be used as a paint.

As a coating method for the aqueous coating composition of the present invention, coating with a natural roll coater is preferred, but coating with various coaters such as a reverse coater or curtain flow coater, spray coating, etc. are also possible.

Baking is performed at 150°C to 230°C for about 2 to 30 minutes. The applicable material metals include tin plated steel plates, chromium-treated steel plates, nickel-plated steel plates, and aluminum plates. These metal plates are coated with anti-rust oil such as cottonseed oil or dioctyl sebacate.

There is usually no degreasing process before painting.

The present invention will be explained below with reference to examples. In the examples, "part", "
%" indicates "parts by weight" and "% by weight," respectively.

Example 1 ■ Epicote 1009 37
5 parts ■ Butyl acetate 250 parts ■ Xylene 60 parts ■ Ethylene glycol monohexyl ether 80 parts ■ Acrylic resin solution Note 1) 223 parts ■ Phenol resin solution Note 2) 313 parts ■ 2-Dimethylaminoethanol 0.005 parts ■ 25% ammonia water 60 parts Ion-exchanged water 1834 parts 30% n-butanol solution of acrylic resin (weight average molecular weight 5000) whose monomer components are styrene/ethyl acrylate/methacrylic acid-4/115 Bisphenol A/p - Phenol resin containing cresol = 4/1 as the phenol component (weight average molecular weight 1000
) A 56% solution of n-butanol/xylene mixed solvent (1) to (2) in the above composition were charged into a 4-tube flask purged with nitrogen gas and dissolved. Next, add ■ and ■ and heat until reflux. While maintaining the reflux state, ① was added and the mixture was reacted for 3 hours. After the reaction is completed, the mixture is cooled, and when the temperature reaches 55°C, ① is added dropwise over 10 minutes. Further, (1) was added dropwise over 30 minutes or more to obtain an aqueous dispersion with a solid content of 20%. The above dispersion was mixed at a liquid temperature of 50°C.
, vacuum distillation was carried out under a reduced pressure of IOcmHg, and the solid content was reduced to 3.
8%, viscosity 360cps, organic solvent content in paint M5%
(Ethylene glycol-Note 1) Note 2) 4% monohexyl ether, 1% xylene; (bl
)/(b,”)=80/20) was obtained.

The obtained water-based paint was stored at 50°C for one month, but no abnormalities were observed.

Examples 2 and 3 Water-based paints were obtained in the same manner as in Example 1, except that xylene and ethylene glycol monohexyl ether in Example 1 were each replaced with the organic solvents shown in Table 1.

Examples 4 to 9 The organic solvents shown in Table 1 were added to the water-based paints obtained by replacing the xylene and ethylene glycol monohexyl ether of Example 1 with the organic solvents shown in Table 1 while stirring.

Comparative Example 1 A water-based paint was obtained in the same manner as in Example 1, except that 40 parts of the 80 parts of ethylene glycol monohexyl ether in Example 1 was replaced with ion-exchanged water.

Comparative Example 2 A water-based paint was obtained in the same manner as in Example 1, except that ethylene glycol monohexyl ether and xylene in Example 1 were replaced with the organic solvents shown in Table 1, respectively.

Comparative Example 3 This was prepared by replacing ethylene glycol monohexyl ether and xylene in Example 1 with the organic solvents shown in Table 1, and adding the obtained organic solvents with stirring.

Table 1 shows Examples 1 to 9. The organic solvent content in each water-based paint of Comparative Examples 1 to 3 and the ratio of (bl)/(bz) are shown.

(Painting, baking) Examples 1 to 9. The water-based paints obtained in Comparative Examples 1 to 3 were applied to a #25 tin plate with a thickness of 0.24 mm using a natural roll coater at a speed of 120 m/win to obtain a dry coating amount of 40 cm/100 cd. Got the board.

One side of the coated plate was air-dried at room temperature until it became tack-free, and the other side was baked at 185°C for 10 minutes in an open gas environment.

(Evaluation) (11. Roll coating suitability (a) The coated board after repelling and baking was evaluated by visual observation.

O: No cissing was observed at all.

△: Repellency is observed on a part of the painted board.

×: Repellency is observed on the entire surface of the painted board.

fb) Flow O: Good △: Ribs are noticeable, but within the practical range.

×: Not in practical range.

(2) Film-forming property (a) Transparency of coating film The coated plate was air-dried at room temperature, and the transparency of the coating film when it became tack-free was visually evaluated.

(bl Shape of Paint Film The shape of the air-dried paint film was visually observed and a peel test using cellophane tape was conducted.

O: There are no defects and the film peels off as a continuous film.

ΔD Some scales are observed.

×: The entire surface is scaly and the peeled film does not become a continuous film.

The results are shown in Table 2.

〔Effect of the invention〕

In the water-based paint of the present invention, even if the amount of organic solvent in the total paint composition is 10% by weight or less, repellency occurs during roll coating, and striped ribs peculiar to roll coating occur, resulting in poor flow. It has the same coating suitability as conventional solvent-based paints. Therefore, the water-based paint of the present invention can be applied to metal substrates without any special treatment in the same way as solvent-based paints, and can fully utilize the advantages of water-based paints.

Claims (1)

[Claims] 1. In an aqueous coating composition comprising a water-dispersible resin (A), an organic solvent (B), water (C), and optionally an additive (D), the organic solvent (B) is The following general formula HO-(CH_
A water-miscible organic solvent (b_1 ) and its solubility in water at 25°C and water solubility are both 2.
(b_
1)/(b_2) = 95/5 to 50/50, the total amount of (b_1) and (b_2) is 4% by weight or more based on the total coating composition, and the organic solvent (B) is 10% by weight or less based on the total coating composition.