JPH07316489A - Water-based coating composition and metallic sheet or plate coated therewith - Google Patents

Abstract

PURPOSE:To obtain the title composition which can form a coating film having water resistance high enough to withstand a high-temperature treatment, good processability and high coating film hardness. CONSTITUTION:This composition comprises 20-80 pts.wt. water-based acrylic resin prepared by copolymerizing an alpha,beta-ethylenically unsaturated carboxylic acid with a hydroxy mono(meth)acrylate monomer containing epsilon-caprolactone- modified monomer, an N-alkoxymethyl(meth)-acrylamide with a 4C or lower alkyl group and an aromatic vinyl monomer copolymerizable with the above monomers and/or alkyl (meth)acrylate and 10-60 pts.wt. water-based amino resin.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an aqueous coating composition having excellent water resistance and processability of a coating film by using an aqueous acrylic resin containing a hydroxyl group-containing acrylic monomer having a specific structure and a nitrogen-containing monomer. Regarding things.

[0002]

2. Description of the Related Art The outer surface of a beverage can containing soft drinks and a food can containing food prevents corrosion of the can material, enhances the aesthetic value of the product, and withstands the heat treatment process during food sterilization. The film is formed by the coating film.

Conventionally, acrylic /
An organic solvent type paint such as amino resin or polyester / amino resin resin is applied by a roll coater or spray painting. However, from the viewpoint of air pollution and resource saving due to the discharge of a large amount of organic solvents, the demand for water-based paints has increased, and various water-based paints have been proposed.

There are two types of known water-based paints, a water-dispersed type and a water-soluble type, and many of the water-dispersed types are usually synthesized by an emulsion polymerization method using a surfactant and the like. Even after the coating film is formed, it remains in the coating film, and there is a drawback that the water resistance is lowered. On the other hand, there is also a method of synthesizing a resin containing a carboxyl group in an organic solvent system without using a surfactant, and neutralizing it with a volatile base to make it a dispersion or water-soluble. The resin skeleton requires an acid component having an acid value of 20 or more, and there is a drawback that performance such as water resistance and alkali resistance is poor.

In order to improve these drawbacks, paints mainly composed of an aqueous film-forming resin such as an acrylic resin or a polyester resin and an aqueous amino resin have been proposed, but if the amount of the amino resin is increased, the processability of the coating film will be improved. On the contrary, when the amino resin is reduced, the coating film hardness tends to decrease,
It was difficult to balance water resistance, coating film hardness, and workability. To improve these drawbacks, Japanese Patent Publication No. 52-
1735, Japanese Patent Publication No. 54-85231 and the like have proposed water-based paints using a film-forming resin having a specific structure. However, although the water resistance of the paint film is improved, its performance is 130. It was not at a level that could withstand the heat sterilization treatment (retort treatment) up to -30 minutes.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and its object is to
It is an object of the present invention to provide an aqueous coating composition which forms a coating film having water resistance capable of withstanding a treatment at 130 ° C. for 30 minutes, processability and coating film hardness.

[0007]

The inventors of the present invention have found that a coating film having a workability, hardness, appearance, and physical properties of 130% can be obtained without impairing it.
As a result of earnest studies for the purpose of developing a water-based coating composition capable of withstanding water resistance at 30 ° C. for 30 minutes, an acrylic resin containing a monomer having a specific structure and an aqueous amino resin were obtained. The present inventors have found that the blended coating material has a coating film excellent in performance such as the above-mentioned water resistance, and arrived at the present invention.

The first invention is (a) an aqueous acrylic resin obtained by copolymerizing the following (I) to (IV): 20 to 80 parts (I) α, β-ethylenically unsaturated carboxylic acid (II) ε Hydroxyl group-containing mono (meth) acrylate monomer containing caprolactone modified monomer (III) Aroma copolymerizable with N-alkoxymethyl (meth) acrylamide (IV) (I) to (III) having an alkyl group having 4 or less carbon atoms Group vinyl monomer and / or alkyl (meth) acrylate (b) Aqueous amino resin
It is an aqueous coating composition containing 10 to 60 parts.

A second invention is a metal plate coated with the aqueous coating composition of the first invention.

The water-based acrylic resin used in the present invention is
It can be obtained by usual solution polymerization. That is, (I) α, β-ethylenically unsaturated carboxylic acid, (II) ε
A hydroxyl group-containing mono (meth) acrylate monomer containing a caprolactone-modified monomer, (III) an N-alkoxymethyl (meth) acrylamide having an alkyl group having 4 or less carbon atoms, and (IV) the above (I) to (III) A copolymer solution obtained by radically polymerizing a mixture of a polymerizable aromatic vinyl monomer and / or an alkyl (meth) acrylate in an organic solvent is added with water or a hydrophilic solvent and water in the presence of a volatile base. Can be made water-based or water-dispersed by the addition of a mixture thereof with, a mixture of water with an aqueous resin, and the like.

Examples of the α, β-ethylenically unsaturated carboxylic acid used for the aqueous acrylic resin include acrylic acid,
Methacrylic acid, maleic acid, fumaric acid, itaconic acid and the like can be mentioned, with acrylic acid and methacrylic acid being preferred. The amount of these used is preferably in the range of 1 to 20% by weight. If it is less than 1% by weight, it becomes difficult to make it aqueous, and if it is 20% by weight or more, the water resistance of the coating film decreases.

Hydroxyl group-containing mono (meth) acrylate monomers include hydroxymethyl acrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxypropyl acrylate and their corresponding methacrylates.

The ε-caprolactone modified monomer is represented by the following formula: CH ₂ = CR-COOCH ₂ O (COC ₅ H ₁₀ O) _n H [wherein R is H or CH ₃ and n is an integer]. Examples include monomers.

In the present invention, the above ε-caprolactone modified monomer can be used alone or in combination with a hydroxyl group-containing mono (meth) acrylate monomer. The amount of the hydroxyl group-containing monomer used is preferably 3 to 40% by weight based on all the monomers. If it is less than 3% by weight, the hardness of the coating film decreases, and if it is 40% by weight or more, the workability of the coating film decreases.

As the alkyl group-containing N-alkoxymethyl (meth) acrylamide having 4 or less carbon atoms, N-methoxy (meth) acrylamide, N-ethoxymethyl (meth) acrylamide, N-butoxymethyl (meth) acrylamide, N- Examples thereof include isopropylmethyl (meth) acrylamide, and N-methoxymethylacrylamide is preferable. The amount of these used is preferably 1 to 25% by weight in the aqueous acrylic resin. If it is less than 1% by weight, the water resistance of the coating film is insufficient due to insufficient curing, and if it is 25% by weight or more, the adhesiveness and processability are poor, and the coating film becomes markedly colored to lower the aesthetic commercial value.

Examples of the aromatic vinyl monomer copolymerizable with the above (I) to (III) include styrene, α-methylstyrene, vinyltoluene and the like. Examples of alkyl (meth) acrylates include alkyl acrylates such as methyl acrylate, ethyl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, methyl methacrylate, butyl methacrylate, stearyl methacrylate, cyclohexyl methacrylate, or methacrylic acid. . The amount of these monomers used is 15 in all monomers.
It is up to 90% by weight, and it is possible to select from two or more kinds in consideration of the balance of the workability and hardness of the coating film.

The polymerization initiator used in the aqueous acrylic resin is a peroxide such as benzoyl peroxide or 2,
Radical polymerization is carried out using an azo compound such as 2'azobisisobutylnitrile as a catalyst. Further, as the solvent used during the polymerization, alcohol solvents such as methanol, ethanol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, n-amyl alcohol, isoamyl alcohol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol mono are used. Ether solvents such as butyl ether, ethylene glycol monoisopropyl ether, propylene glycol methyl ether, propylene glycol ethyl ether, propylene glycol butyl ether, diethylene glycol monobutyl ether, 3-methyl-3-methoxybutanol, and 3-methoxybutanol are preferable.

The aqueous amino resin is an amino resin which can be dissolved or dispersed in an aqueous medium, and is a compound such as melamine, benzoguanamine, spiroguanamine, acetoguanamine, phthaloguanamine, etc., the functional group of which depends on an alcohol solvent or the like. Also included are those that are partially or fully etherified. The amount of these amino resins used is 10 to 60% by weight based on the total resin solid content. If it is less than 10% by weight, the water resistance and hardness of the coating film are insufficient, and if it exceeds 60% by weight, the processability of the coating film is deteriorated.

If necessary, the aqueous coating composition may contain an acid catalyst, or an amine blocking agent thereof, such as p-toluenesulfonic acid, dodecylbenzenesulfonic acid, dinonylnaphthalenesulfonic acid, or these amine blocking agents.
As a curing catalyst, 0.1 to 100 parts of resin solid content
It can be used by adding 4.0 parts. Similarly, a defoaming agent, a leveling agent, a lubricant and the like can be added.
Further, titanium oxide, an aluminum pigment, a pigment such as quinacridone is dispersed and kneaded with the above-mentioned aqueous acrylic resin or a mixture of the aqueous acrylic resin and another aqueous resin using a known disperser such as a sand mill and a disperser, and a pigment paste. Can be made into a paint by the same method as described above.

In the aqueous coating composition, water-soluble resins and water-dispersible resins which are generally used, such as polyester, polyether polyol, polyester polyol, polyurethane polyol, maleated fatty acid, ethylene oxide of bisphenol A or It is also possible to mix with a resin such as a propylene oxide adduct.

The aqueous coating composition of the present invention can be coated on a substrate by a known means such as roll coating, spraying or brush coating.

The metal plate is a drawn steel plate having a plate thickness of 0.01 to 2.0 mm, a stainless steel plate, an aluminum alloy plate, or the like. The surface of these alloy plates is sometimes chrome,
One or more alloys or composites of inorganic metals such as tin, zinc and nickel and organic substances such as acrylic resin are plated, vapor-deposited, coated and further treated with zirconium, alumite, phosphoric acid and the like. Further, a metal plate obtained by laminating a resin film such as polyethylene terephthalate or polybutylene terephthalate on these plates can be used.

[0023]

EXAMPLES The present invention will be described below with reference to examples. In the examples, “part” means “part by weight”, and “%” means “% by weight”.

Production Example 1 (Synthesis of Aqueous Acrylic Resin A-1) 100 parts of n-butanol was charged into a four-necked flask equipped with a thermometer, a stirrer, a reflux condenser, a dropping tank and a nitrogen gas blowing tube, and nitrogen gas was added. While introducing and stirring the temperature to 10
Keeping at 5 ° C, 20 parts of styrene, 45 parts of ethyl acrylate, 5 parts of 2-hydroxyethyl acrylate from the dropping tank.
Parts, ε-caprolactone-modified 2-hydroxyethyl acrylate (trade name “Placcel FA-3”, Daicel Chemical Industries, Ltd.) 10 parts, N-methyl acrylamide 10 parts,
A solution prepared by dissolving 5 parts of benzoyl peroxide in 100 parts of a mixture of 10 parts of methacrylic acid was added dropwise over 3 hours.
Thereafter, the mixture was kept at 105 ° C. and reacted for 1 hour, 0.5 part of benzoyl peroxide was added, and the reaction was carried out for 1 hour. N-Butanol was distilled off under reduced pressure at 80 ° C. until the nonvolatile content reached 80%, and then 11.8 parts of diethylethanolamine and water were added to the mixture to give a nonvolatile content of 50%, n-
Transparent and viscous water-based acrylic resin A- containing 10% butanol
Got 1.

Production Example 2 (Aqueous acrylic resin A-2 to A-
Synthesis of 8) A monomer composition shown in Table 1 was prepared according to Synthesis Example 1, and A
Aqueous acrylic resins of -2-A-8 were obtained.

Examples 1 to 6 and Comparative Examples 1 to 4 Table 2 using the water-based acrylic resin obtained in Production Examples 1 and 2
After mixing the components according to the composition shown in 3 (however,
In Example 6 and Comparative Example 4, the acrylic resin solution and the titanium oxide pigment were dispersed and kneaded in advance. ) And butyl cellosolve are added to adjust the amount of the organic solvent in the paint to 10%, and to this, p-toluenesulfonic acid amine salt is added to 0.3%.
Parts, and 0.3 parts of a silicone-based leveling agent were added, and the rest was adjusted by adding ion-exchanged water to obtain an aqueous coating composition. As an amino resin, Cymel 112
3 (trade name, manufactured by Mitsui Cyanamid Co., Ltd.), and CR-95 (trade name, manufactured by Ishihara Sangyo Co., Ltd.) was used as titanium oxide.

The test results of the paints prepared in the examples and comparative examples are shown in the test results of Table 4.

Each test method is as follows. [Paint test] ○ Paint stability test After the paint was stored at room temperature for two months, the state of gelation and separation of the resin in the paint was visually observed. ◯: No change Δ: Viscosity increased ×: Gelation

[Film property test] An electroplated tin plate having a plate thickness of 0.23 mm is coated by roll coating so that the film thickness after drying becomes 7 μ, and baked in a gas oven at an atmospheric temperature of 190 ° C. for 10 minutes. Created a panel.

○ Adhesion Test A cross-cut peeling test was performed, and the peeled area was visually evaluated. ○: 0% to 5% △: 5% to 39% ×: 40% or more

○ Water resistance test A coated panel was immersed in water and heat-treated at 130 ° C for 30 minutes, and then an adhesion test was conducted. ○: 0% to 5% △: 5% to 39% ×: 40% or more

○ Coating film hardness JIS standard "pencil scratch test" (JIS NO.K5
It was performed according to the method registered in 400).

Impact resistance test Using a DuPont impact tester, 1/2 inch diameter, 500
Tested under g-load.

Workability test According to the Erichsen test (JIS Z-2247), extrusion processing was performed to the point where the underlying metal started to crack, and then the state of the coating film was evaluated. ○: No change △: Some cracks ×: Cracks all over

○ Yellowing Test The coated panel was baked in a gas oven at an ambient temperature of 190 ° C. for 10 minutes, and the yellowing was visually evaluated. ○: No change △: Some yellowing ×: Dark yellowing

[0036]

[Table 1]

[0037]

[Table 2]

[0038]

[Table 3]

[0039]

[Table 4]

[0040]

The water-based coating composition of the present invention is excellent in water resistance, processability, hardness, etc. of a coating film by using ε-caprolactone modified monomer and N-alkoxymethyl (meth) acrylamide as acrylic monomers. Performance can be provided. Therefore, the aqueous coating composition of the present invention is effective as an external coating for beverage cans and food cans that require heat sterilization at high temperatures.

Claims (2)

[Claims] (A) Aqueous acrylic resin obtained by copolymerizing the following (I) to (IV): 20 to 80 parts (I) α, β-ethylenically unsaturated carboxylic acid (II) ε-caprolactone modified monomer A hydroxyl group-containing mono (meth) acrylate monomer containing (III) an aromatic vinyl monomer copolymerizable with N-alkoxymethyl (meth) acrylamide (IV) (I) to (III) having an alkyl group having 4 or less carbon atoms, And / or alkyl (meth) acrylate (b) aqueous amino resin
An aqueous coating composition comprising 10 to 60 parts. 2. A metal plate coated with the aqueous coating composition according to claim 1.