JPH07188606A - Water-based coating composition - Google Patents

Abstract

PURPOSE:To obtain a water-based coating compsn. excellent in retorting resistance, processability, applicability and pigment-dispersing properties, and capable of decreasing the solvent content thereof, by blending an acrylic resin with a bisphenol A-ethylene oxide or -propylene oxide adduct and an amino resin. CONSTITUTION:A water-based coating compsn. comprises as the resin components (a) 20-80 pts.wt. acrylic resin having an acid value of 10 to 100 and a hydroxyl value of 1 to 20, (b) 1-20 pts.wt. bisphenol A-ethylene oxide or -propylene oxide adduct of the formula, and (c) 10-60 pts. wt. amino resin [provided that the total amt. of (a)+(b)+(c) is 100 pts.wt.]. In the formula, (m) and(n) are each 1 to 20. This water-based coating compsn. can be cured under a wide variety of baking conditions ranging from baking at 150 to 200 deg.C for about 10min to high-temp. short-time baking at 250 deg.C for about 10sec.

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, which is excellent in retort resistance, processing resistance and paintability, and further in pigment dispersibility at the time of adding a pigment to reduce the content of the solvent. It relates to the properties of an aqueous coating composition that can be used.

[0002]

2. Description of the Related Art The outer surfaces of beverage cans containing soft drinks and foods and food cans can prevent corrosion of can materials, enhance aesthetic commercial value, and withstand the heat treatment process during food sterilization. It is formed of a coating film. Conventionally, these coating materials are coated with an organic solvent solution of an epoxy / amino resin, an acrylic / amino resin, a polyester / amino resin or the like by a roll coater and baked and cured by a gas oven. However, these paints cause a large amount of solvent volatilization during baking, causing air pollution,
This is not good in terms of resource saving. Therefore, the advent of a water-based paint capable of solving these problems has been desired.

There are two types of known water-based paints, water-dispersible and water-soluble, and most water-dispersible resins are usually synthesized by an emulsion polymerization method using a surfactant. 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, the water-soluble type needs to have a polar group with strong hydrophilicity in the molecule, and a resin containing a carboxyl group and a hydroxyl group is synthesized to obtain an acid value of 20 or more,
Although those having a hydroxyl value of 20 or more are used, it is better that the resin used as the coating film has less hydrophilic groups from the viewpoint of water resistance.
There was a defect that the performance such as water resistance and alkali resistance was inferior. In order to improve these drawbacks, a method of mixing a large amount of an aqueous amino resin such as hexamethoxymethylmelamine and methylated benzoguanamine has been carried out, but the processability is largely decreased, while the processability is improved. When the amount of water-based amino resin is reduced to improve, the coating film hardness tends to decrease, and it is difficult to balance water resistance, coating film hardness, and processability, and a practically satisfactory aqueous coating material is provided. It wasn't something.

As another method, a method of mixing a phosphoric acid- or carboxylic acid-modified epoxy resin has been carried out. However, since it has poor compatibility with an acrylic resin, it is particularly useful for storage stability of coating materials and leveling in coating film formation. There was a problem, and this tendency was particularly remarkable when the pigment was dispersed. Further, the conventional water-soluble paint contains 10% or more of an organic solvent in order to improve the storage stability of the paint and the leveling in forming a coating film, and it is still unsatisfactory from the viewpoint of air pollution and resource saving due to volatilization of the solvent during baking. It was enough. Furthermore, conventional water-based paints have been obtained that have no abnormalities even when treated with boiling water as water resistance, but beverage cans, coffee, which is the most severe in the heat treatment process of sterilizing food cans, etc. When a milk beverage is treated with pressurized boiling water at 130 ° C for 30 minutes, the coating film becomes blistered or whitened, making it difficult to balance water resistance and processability that can be processed into various can forms. Met.

[0005]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above situation, and its purpose is to:
Water resistance that can withstand the heat treatment process of beverage cans and food cans, especially boiling water treatment at 130 ° C, coating film hardness in hot water, and excellent processability that can be processed into various can forms. The present invention provides a water-based coating composition for the outer surface of a can, which forms a coating film and has a low organic solvent content.

[0006]

The first invention is (a) an acrylic resin having an acid value of 10 to 100 and a hydroxyl value of 1 to 20.
20 to 80 parts by weight, (b) 1 to 20 parts by weight of bisphenol A ethylene oxide and propylene oxide adduct represented by the following general formula, general formula

[0007]

[Chemical 2]

(C) Amino resin 10 to 60 parts by weight, the above (a), (b) and (c) are added to the resin component (provided that
The total amount of (a) + (b) + (c) is 100 parts by weight. ) It is a water-based coating composition characterized by the following.

The bisphenol A ethylene oxide or propylene oxide adduct in the present invention is bisphenol A to which ethylene oxide or propylene oxide is added in an amount of about 1 to 20. The ethylene oxide or propylene oxide may be in any sequence. This oxide adduct is used in an amount of 1 to 20 parts by weight based on the resin solid content of the entire coating composition.
If it exceeds 0 parts by weight, the water resistance will decrease. Preferably 1 to
10 parts by weight.

The acrylic resin used in the present invention is a carboxyl group-containing vinyl monomer such as (meth) acrylic acid, fumaric acid or maleic acid, hydroxymethyl (meth) acrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, acrylic. Hydroxyl group-containing vinyl monomers such as acid hydroxyamyl acrylate, and monomers capable of covalently polymerizing with them, for example, acrylic acid acrylic esters such as ethyl acrylate and methyl acrylate, aromatic vinyl monomers such as styrene and vinyltoluene, N-
A wide range of compounds such as those obtained by appropriately selecting and copolymerizing with N-alkoxyalkyl-substituted amide group-containing vinyl monomers such as (methoxymethyl) acrylamide can be used, and have an acid value of 10 to 100 and a hydroxyl value of 1 to 20. is there. If the acid value is less than 10, it is difficult to make water-soluble, and if it exceeds 100, the water resistance is poor.
Water resistance capable of withstanding boiling water under pressure for 0 minutes and workability cannot be balanced, and a hydroxyl value is preferably 10 to 20.
The water-based acrylic resin is used in an amount of 20 to 80 parts by weight based on the resin solid content of the entire coating composition. If it is less than 20 parts by weight, the adhesion to the base material is lowered, the water dispersibility is poor, the storage stability of the coating is poor, and the pigment dispersibility is poor when the pigment is added. If it is 80 parts by weight or more, the hardness is lowered and the water resistance is poor.

The aqueous amino resin used in the present invention is an amino resin that can be dissolved or dispersed in an aqueous medium, and is a partially alkyl etherified melamine resin, a partially alkyl etherified benzoguanamine resin, or spiroguanamine alone or spiroguanamine. It is selected from spiroguanamine resins in which a mixture with melamine or benzoguanamine is methylolated and partially alkyl etherified with an alcohol having 1 to 3 carbon atoms. In particular, spiroguanamine resin is preferable in that it has less tar-like low molecular weight generated during baking of the paint as compared with melamine resin or benzoguanamine resin. The aqueous amino resin is used in an amount of 10 to 60 parts by weight based on the resin solid content of the entire coating composition. If it is less than 10 parts by weight, the hardness is not sufficient, and if it exceeds 60 parts by weight, the workability of the coating film is deteriorated.

In the coating composition of the present invention, if necessary, an acid catalyst or its amine blocking agent such as p-toluenesulfonic acid, dodicylbenzenesulfonic acid, dinolylnaphthalenesulfonic acid, etc., is used as a curing aid. Solid content 1
0.1 to 1 part can be added to 00 parts.
Similarly, conventionally known leveling agents, defoaming agents, lubricants, antioxidants and the like can be added. Further, pigments such as titanium oxide, aluminum pigments, quinacridone and the like are kneaded using the above acrylic resin, polyester resin and a known disperser such as a sand mill and a disper to prepare a pigment paste, and made into a paint by the same method as described above. it can.

Further, water-soluble resins and water-dispersible resins generally used as resins for water-based paints, such as water-soluble or water-dispersible epoxy resins modified with amines or acids, maleated fatty acids, polyester resins, etc. It is also possible to mix. The water-based paint of the present invention can be applied to a substrate by a known means such as roll coating, spraying or brush coating. As the base material, there are metal base materials such as electric tinned steel plate, tin-free steel and aluminum. The water-based paint of the present invention has a temperature of 150 to 200 ° C.
It can be cured under a wide range of baking conditions, from baking for about -10 minutes to baking at a high temperature for about 10 seconds at 250 ° C.

[0014]

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 (Production of Aqueous Acrylic Resin Solution A-1) A four-necked flask equipped with a temperature type, a stirrer, a reflux condenser, a dropping tank and a nitrogen gas blowing tube was charged with 100 parts of n-butanol, and nitrogen gas was added. Temperature while stirring while introducing
Keep at 5 ° C., and add 20% styrene, ethyl acrylate 47, 2-hydroxyethyl acrylate 3 from the dropping tank.
%, Methyl methacrylate 20%, acrylic acid 10%
What melt | dissolved benzoyl peroxide 5 parts in 100 parts of the mixture of was added dropwise over 3 hours. After that, the temperature was kept at 105 ° C., the reaction was carried out for 1 hour, 5 parts of benzoyl peroxide was added, and the reaction was further continued for 1 hour to complete the reaction. It is n
-Butanol was distilled off until the nonvolatile content became 83%, and then 14.6 parts of diethanolamine and water were added, and a solid viscous acid content of 50% and residual n-butanol of 10% and a viscous acid value of 80 and a hydroxyl value of 15 were used. Aqueous acrylic resin A-1 was obtained.

Production Example 1 (Production of Aqueous Acrylic Resin Solution A-2) 100 parts of n-butanol was charged into a four-necked flask equipped with a temperature type, a stirrer, a reflux condenser, a dropping tank, and a nitrogen gas blowing tube, and nitrogen gas was added. Temperature while stirring while introducing
Keeping at 5 ° C, styrene 20%, ethyl acrylate 47, 2-hydroxyethyl acrylate 10 from the dropping tank.
%, Methyl methacrylate 20%, acrylic acid 10%
What melt | dissolved benzoyl peroxide 5 parts in 100 parts of the mixture of was added dropwise over 3 hours. After that, the temperature was kept at 105 ° C., the reaction was carried out for 1 hour, 5 parts of benzoyl peroxide was added, and the reaction was further continued for 1 hour to complete the reaction. It is n
-Butanol was distilled off until the non-volatile content became 83%, and then 14.6 parts of diethanolamine and water were added to the mixture to give a solid viscous content of 50% and residual n-butanol of 10%, a transparent viscous acid value of 80 and a hydroxyl value of 50. Aqueous acrylic resin A-2 was obtained.

Examples 1 to 4 and Comparative Examples 1 to 3 Table 1 shows the ratio of the solid content of each component in percentage. After mixing each component according to this Table 1 (however,
In Example 3, the acrylic resin solution and the pigment were first kneaded. ) Butyl cellosolve and water were added to adjust the amount of organic solvent in the paint to 10% and the solid content to 35%. To this, 0.3% of amine salt of p-toluenesulfonic acid and 0.3% of silicone leveling agent were added to obtain an aqueous coating composition. Table 2 shows the results of examining the stability and coating film physical properties of the coatings prepared in Examples and Comparative Examples.

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 separation of the resin in the paint was observed. Coating film physical property test An electroplated tin plate having a plate thickness of 0.23 mm was coated by roll coating so that the coating film thickness was 7 μ after drying, and a baking coating panel was prepared in a gas oven at an atmospheric temperature of 190 ° C. for 10 minutes. The scratch resistance was evaluated by preparing a 3-piece can in which a coated plate was formed so that the coated surface was the outer surface of the can. ○ Water resistance test The coated panel was immersed in water, subjected to hot water treatment at 100 ° C for 30 minutes and pressurized boiling water treatment at 130 ° C for 30 minutes, and then the whitening state of the coating film was evaluated. Workability test According to the Erichsen test and JISZ-2247, the state of the coating film was evaluated after extrusion processing to the point where the underlying metal plate started to crack. ○ Adhesiveness A peeling test was performed. Similarly, the evaluation after the treatment with pressurized boiling water at 130 ° C. for 30 minutes was also performed. ○ Impact resistance Using a DuPont impact tester, 1/2 inch diameter, 500
Tested under g-load. ○ Pencil hardness test JIS standard “Pencil scratch test” (JIS No. K5
It was performed according to the method registered in 400). ○ Scratchability The contents were packed in a can, and the outer surface of the can was contacted in warm water at 80 ° C to evaluate the degree of scratching of the coating film. Paintability test ○ Immediately after coating with a flow roll coater, baking was performed in a gas oven to evaluate the leveling state.

[0019]

[Table 1]

[0020]

[Table 2]

[0021]

EFFECT OF THE INVENTION The water-based coating material of the present invention is water-resistant to withstand the heat treatment process for sterilizing beverage cans and food cans, and in particular, milk beverages such as coffee, which are the most severe in the heat treatment process, are boiled under pressure at 130 ° C. for 30 minutes. A coating film having water resistance that can withstand treatment with water, excellent processability capable of being processed into various can forms, and coating film hardness in hot water can be obtained. Even when the content of the organic solvent is 15% by weight in the aqueous medium, the coating stability is good and the coating suitability is excellent.

Claims (1)

[Claims] (A) An acid value of 10 to 100 and a hydroxyl value of 1 to
20 to 80 parts by weight of acrylic resin 20, (b) bisphenol A ethylene oxide represented by the following general formula,
And 1 to 20 parts by weight of a propylene oxide adduct, the general formula: (C) Amino resin 10 to 60 parts by weight, the above-mentioned (a), (b), and (c) are resin components (provided that the total amount of (a) + (b) + (c) is 100 parts by weight). .) A water-based coating composition.