JP2868611B2 - Aqueous paint composition - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a water-based coating composition, and more particularly, to an aqueous coating composition comprising an acrylic resin-modified epoxy resin and an allylated resole-type phenol resin, and having processing resistance, corrosion resistance, The present invention relates to a baked water-based paint composition for metal cans which has excellent retort resistance and flavor retention properties, and is particularly suitable for coating the inner surfaces of food and beverage cans.

(Prior Art) Metallic can paints need to withstand various conditions of processing, distribution or contents of metal cans, but food and beverage cans in particular satisfy food hygiene requirements. It is necessary.

In this field, water-based paints that do not use organic solvents have been developed. For example, in Japanese Patent Publication No. 63-63586,
In an amino resin solution, an α, β-olefinically unsaturated carboxylic acid is polymerized with at least one other vinyl polymerizable monomer, and then the epoxy resin is mixed and heated, and partially neutralized with ammonia or an amine. A method for obtaining an aqueous dispersion is disclosed. Further, Japanese Patent Publication No. 25488/1990 discloses that an acrylic resin, an epoxy resin partially bonded thereto, and a phenol resin composition precondensed with both or an epoxy resin are adjusted to pH 4 to 11 with ammonia or amine to form an aqueous solution. A resin dispersion is described. Japanese Patent Publication No. 1-25489 discloses a method of using a specific phenol resin condensed with an alkali catalyst as the phenol resin. Further, JP-A-63-75075 discloses an aqueous coating composition for cans comprising an aqueous dispersion containing a self-emulsifying and self-crosslinking epoxy-acrylic resin and a resole-type phenol-aldehyde resin from oil-soluble phenols. Is described.

However, in the conventional technology, there is a problem that the elution of formalin, or the remaining unreacted phenolic hydroxyl group, results in insufficient processing resistance, corrosion resistance, retort resistance or flavor retention. .

(Problems to be Solved by the Invention) The present invention solves the above-mentioned problems, and is excellent in processing resistance, corrosion resistance, retort resistance, and flavor retention of a coating film, and has extremely low elution property, and is a water-based paint for metal cans. It is intended to provide a composition.

(Means for Solving the Problems) The inventors of the present invention have conducted intensive studies to solve the above problems, and as a result, an aqueous dispersion obtained by blending a resole type phenol resin having a specific functional group with an acrylic resin-modified epoxy resin. However, they have found that the above object can be achieved, and have completed the present invention.

That is, the present invention is an aqueous coating composition comprising (A) an acrylic resin-modified epoxy resin and (B) an allylated resole type phenol resin as main components.

Hereinafter, the aqueous coating composition of the present invention will be described in detail.

The epoxy resin used in the component (A) of the present invention has two or more epoxides in one molecule and the epoxide is eliminated by reacting the resin with a fatty acid, a dibasic acid, bisphenol A, F or B. Included or partially left out. Among them, an epoxy resin obtained by condensing epihalohydrin with bisphenol A, F or B in the presence of an alkaline catalyst is preferable because the coating film has excellent physical strength, adhesion, chemical resistance and the like.
The average molecular weight is 300 or more, preferably 1,000 or more. Examples of the fatty acids include vegetable oil fatty acids such as dehydrated castor oil, soybean oil, cottonseed oil, safflower oil, tall oil, castor oil, coconut oil, and palm oil. Examples of the dibasic acid include maleic acid and fumaric acid.

These fatty acids can be used alone or as a mixture and / or as a mixture with a dibasic acid.

The acrylic resin used for modifying the epoxy resin is a copolymer composed of an unsaturated monobasic carboxylic acid such as acrylic acid or methacrylic acid and another copolymerizable monomer. Usually, it is obtained by copolymerizing both monomers in an organic solvent at a temperature of 80 to 150 ° C. using a free radical generator such as benzoyl peroxide or azobisisobutyronitrile as a polymerization initiator. Examples of the copolymerizable monomer include (meth) acrylic acid alkyl ester, styrene monomer, hydroxyl group-containing monomer, N-substituted (meth) acrylamide, oxysilane group-containing monomer, maleic acid dialkyl ester, fumaric acid dialkyl ester, acrylic Nitriles and the like can be mentioned, and one or more of these can be used in combination.

The content of unsaturated monobasic carboxylic acid in the acrylic resin is 12 to 70% by weight, preferably 25 to 60% by weight. 12
When the amount is less than% by weight, the dispersion stability in an aqueous medium, the adhesion of the coating film to the substrate, and the flavor retention depending on the application are all reduced. If it exceeds 70% by weight, the hot water resistance and the retort resistance of the coating film decrease.

The average molecular weight of the acrylic resin is preferably from 3,000 to 80,000. If it is less than 3,000, the processing resistance decreases, and if it exceeds 80,000, the solid content at an appropriate coating viscosity decreases.

The modification of the epoxy resin with the acrylic resin is preferably performed using the acrylic resin in a range of 1/10 to 1/1 in terms of the weight ratio of the solid content with respect to the epoxy resin. If the amount of the acrylic resin is less than 1/10, the dispersion stability of the coating composition is reduced,
If it exceeds 1, the corrosion resistance decreases.

The acrylic resin-modified epoxy resin as the component (A) can be produced by preparing an epoxy resin mono (meth) acrylate in advance and then copolymerizing a copolymerizable monomer, in addition to the above method.

The epoxy resin modified by the acrylic resin referred to here is a bond formed by a partial reaction between the epoxide and carboxyl, the amine opens the epoxide, the carboxyl and quaternary chloride, and there is substantially no bond between the acrylic resin and the epoxy resin. , Including those that are just mixed.

The resol type phenol resin used for the component (B) is
It can be manufactured in a known manner. That is,
It is obtained by a condensation reaction of phenol, alkylphenol or bisphenol A, F or B with formaldehyde at 100 ° C. or lower in the presence of an alkaline catalyst. The number average molecular weight is preferably 1,000 or less. If it exceeds 1,000, the dispersion stability of the coating composition decreases. Examples of the alkylphenol include p-cresol, o-cresol, ethylphenol, p-tert-butylphenol, 1-octylphenol and the like.

Allylation of the resole type phenol resin is obtained by reacting the resole type phenol resin with allyl halide in the presence of an alkaline catalyst. As allyl halide,
Allyl chloride, allyl fluoride, allyl iodide and the like are preferably used.

The compounding ratio of the acrylic resin-modified epoxy resin (A) and the allylated resole type phenol resin (B) is preferably the component (B) as the resin solid component, preferably 0.1 to 50% by weight.
More preferably, it is 1 to 10% by weight. If it is less than 0.1% by weight, the corrosion resistance, retort resistance and curing properties are reduced. If it exceeds 50% by weight, the processing resistance and the flavor retention deteriorate. Component (A) is preferably from 99.9 to 50% by weight.

The aqueous coating composition of the present invention has a pH of 4 by adding an amine.
It is preferable to adjust to ~ 11. Examples of the amine to be used include alkylamines such as trimethylamine, triethylamine and tributylamine; aminoalcohols such as 2-dimethylaminoethanol, diethanolamine, triethanolamine and aminomethylpropanol; and morpholine.

The water-based coating composition of the present invention, as a substrate, a steel sheet, aluminum plate and zinc, tin, chromium on the surface of the steel sheet,
The present invention can be applied to a plated steel sheet obtained by plating a single metal or a plurality of metals such as nickel and aluminum, or a steel sheet having its surface chemically or electrolytically treated with chromic acid, phosphoric acid, or the like.

As a coating method, a generally known method can be used. That is, air spray, airless spray, electrostatic spray, dip coating, roll coater, electrodeposition coating and the like.

The baking conditions include a temperature range of 150 to 300 ° C and 10 seconds to
A time of 30 minutes is preferred.

The aqueous coating composition of the present invention is a rust-preventive primer, a rust-preventive paint or a printing ink, etc., in which the properties of the composition are not impaired, by blending a rust inhibitor, a pigment or a filler suitable for the use. Can also be used.

(Action) The water-based coating composition of the present invention has excellent processing resistance, retort resistance, hot water resistance and flavor retention because the amount of free phenolic hydroxyl groups is suppressed by allylating the resole type phenol resin. In addition, since the allyl group is bonded to the phenolic hydroxyl group, the resin viscosity decreases. The double bond of the allyl group is thermally polymerized by baking or the like, thereby improving the mechanical strength of the coating film and further improving the processing resistance.

(Examples) Hereinafter, the present invention will be described in detail with reference to examples, but the scope of the present invention is not particularly limited by the examples.
Hereinafter, parts and% indicate parts by weight and% by weight, respectively.

Synthesis Example 1 94 parts of nitrocarbonate, 405 parts of 37% formalin and 211 parts of a 25% aqueous sodium hydroxide solution were mixed and reacted at 50 ° C. for 2 hours.

After neutralization with hydrochloric acid, the mixture was extracted with a mixed solvent of ethyl acetate / n-butanol = 1/1 to obtain a resol type phenol resin having a solid content of 80%.

Synthesis Example 2 After reacting in the same manner as in Synthesis Example 1 and in the same manner as in Synthesis Example 1, 80 parts of allyl chloride was added and reacted at the same temperature for 1 hour. An 80% allylated resole phenolic resin was obtained.

Synthesis Example 3 p-Cresol 108 parts, 37% formalin 162 parts and 25%
180 parts of an aqueous sodium hydroxide solution were mixed and reacted at 50 ° C. for 2 hours. After neutralization with hydrochloric acid, the mixture was extracted with a mixed solvent of n-butanol / xylol = 1/1 to obtain a resol-type phenol resin having a solid content of 70%.

Synthesis Example 4 The same formulation as in Synthesis Example 3 was reacted in the same manner as in Example 3, then 80 parts of allyl chloride was added, and the mixture was reacted at the same temperature for 1 hour. An allylated resole type phenol resin having a content of 70% was obtained.

Synthesis Example 5 228 parts of bisphenol A, 243 parts of 37% formalin and 100 parts of sodium hydroxide were mixed and reacted at 65 ° C. for 3 hours. After neutralization with hydrochloric acid, the mixture was extracted with n-butanol, and the solid fraction was extracted.
A 60% resol type phenol resin was obtained.

Synthesis Example 6 After reacting in the same manner as in Synthesis Example 5 and in the same manner as in Synthesis Example 5, 360 parts of allyl iodide was added, reacted at the same temperature for 1 hour, and treated in the same manner as in Synthesis Example 5. An allylated resole type phenol resin having a solid content of 60% was obtained.

Synthesis Example 7 To 30 parts of the resole-type phenol resin obtained in Synthesis Example 1, 50 parts of Epicoat 828 (trade name: manufactured by Shell Chemical Co., epoxy equivalent: 190) were mixed, and reacted at 60 ° C. for 2 hours to obtain a solid matter 90%. % Of a resol type phenol resin was obtained.

Synthesis Example 8 The same procedure as in Synthesis Example 7 was carried out except that 30 parts of the allyl-modified resole type phenol resin of Synthesis Example 2 was used instead of the resole type phenol resin of Synthesis Example 1, and allyl resole having a solid content of 90% was used. A phenolic resin was obtained.

Synthesis Example 9 210 parts of styrene, 210 parts of ethyl acrylate, 180 parts of methacrylic acid, 388 parts of butyl cellosolve and benzoyl peroxide
One-fourth of the 12 parts of the mixture was charged into a flask purged with nitrogen, heated to 80 to 90 ° C., and the remaining 3/4 was gradually dropped at that temperature over 2 hours. After completion of the dropwise addition, the mixture was further stirred at the same temperature for 2 hours to obtain a carboxyl group-containing acrylic copolymer resin.

Synthesis Example 10 80 parts of Epicoat 1009 (trade name: manufactured by Shell Chemical Company, epoxy equivalent: 3,000) and butyl cellosolve 5 in a flask
3 parts were charged and dissolved by stirring at 100 ° C. After cooling to room temperature, 33 parts of the carboxyl group-containing acrylic copolymer resin obtained in Synthesis Example 9 was charged, and the mixture was stirred to make it uniform. Then, 6.6 parts of 2-dimethylaminoethanol was added, and the mixture was heated to 80 ° C and stirred for 30 minutes. Then, it was cooled to room temperature. In addition, deionized water 567
Was gradually added little by little to obtain a milky white dispersion. Then, the solvent was distilled off under reduced pressure to obtain an acrylic resin-modified epoxy resin dispersion having a pH of 6.5 and a solid content of 20%.

Example 1 Acrylic resin-modified epoxy resin dispersion obtained in Synthesis Example 10
200 parts and 2.5 parts of the allylated resole type phenol resin obtained in Synthesis Example 2 were uniformly stirred and mixed to obtain a coating composition.

On one surface of an aluminum plate having a thickness of 0.25mm so, it applied as both sides of an aluminum foil having a dry coating amount of 70 mg / dm ^2, 100 microns a dry coating weight 60~90mg / dm ^2, 250 ℃ and 280 ° C. For 30 seconds each. For single-side coated boards, processing resistance, corrosion resistance, retort resistance and hot water resistance,
The potassium permanganate consumption and flavor retention of the double-sided coated plate were evaluated according to the following test methods, and the results are shown in Table 1.

a) Processing resistance One aluminum plate having the same thickness is sandwiched between test pieces, and is clamped with a vise. The degree of cracking of the coating film in the processed portion was determined using a 50-fold loupe.

：: No cracks △: Slight cracks ×: Significant cracks b) Corrosion resistance A test piece whose back surface was sealed with polyester tape was immersed in boiling 3% saline for 1 hour to determine the degree of corrosion of the coating film surface. Judged.

：: no corrosion Δ: slight corrosion x: considerable corrosion c) retort resistance The test piece was treated with a retort sterilizer at 125 ° C for 30 minutes to determine the degree of whitening of the coating film.

：: no whitening △: slight whitening ×: considerable whitening d) hot water resistance The test specimen was immersed in ion-exchanged boiling water for 1 hour.
The degree of whitening of the coating was determined.

○: No whitening △: There slight whitening ×: considerable whitening Yes e) putting specimens consumption sided coated potassium permanganate in a pressure glass bottle, the activated carbon so that the contact ratio of the coating film surface is 1 cm ^2/1 ml After the treated tap water was filled and sealed, it was treated with a retort sterilizer at 125 ° C. for 30 minutes, and the treated liquid was measured according to the test method described in the Food Sanitation Law.

○: 5 ppm or less △: 5~10ppm ×: 10ppm or f) putting a test piece of flavor retention sided coating in a pressure glass bottle, so that the contact ratio of the coating film surface is 1 cm ^2/1 ml, water was treated with activated carbon After adding water and sealing, use a retort sterilizer at 125 ° C for 30 minutes.
Minutes. After storage at 50 ° C. for 3 months, a sensory test was performed.

：: no change Δ: slight change ×: considerable change Example 2 Synthesis example 4 as an allylated resole type phenol resin
A coating film was prepared in the same manner as in Example 1 except that 5.7 parts of the resin obtained in the above was used.

 Table 1 shows the evaluation results of the coating films.

Example 3 Synthesis Example 6 as an allylated resole type phenol resin
A coating film was prepared in the same manner as in Example 1 except that 3.3 parts of the resin obtained in was used.

 Table 1 shows the evaluation results of the coating films.

Example 4 Synthesis Example 8 as an allylated resole type phenol resin
A coating film was prepared in the same manner as in Example 1 except that 20 parts of the resin obtained in the above was used.

 Table 1 shows the evaluation results of the coating films.

Comparative Example 1 A coating film was prepared in the same manner as in Example 1 except that 2.5 parts of the resole phenol resin of Synthesis Example 1 was used instead of the allylated resole phenol resin of Synthesis Example 2.

 Table 1 shows the evaluation results of the coating films.

Comparative Example 2 A coating film was prepared in the same manner as in Example 1 except that 5.7 parts of the resole phenol resin of Synthesis Example 3 was used instead of the allylated resole phenol resin of Synthesis Example 2.

 Table 1 shows the evaluation results of the coating films.

Comparative Example 3 A coating film was prepared in the same manner as in Example 1, except that 3.3 parts of the resole phenol resin of Synthesis Example 5 was used instead of the allylated resole phenol resin of Synthesis Example 2.

 Table 1 shows the evaluation results of the coating films.

Comparative Example 4 A coating film was prepared in the same manner as in Example 1 except that 20 parts of the resole phenol resin of Synthesis Example 7 was used instead of the allylated resole phenol resin of Synthesis Example 2.

 Table 1 shows the evaluation results of the coating films.

Examples 5 to 8 Acrylic resin-modified epoxy resin dispersion obtained in Synthesis Example 10
For 200 parts, 12.5 parts, 25 parts, 37.5 parts, 50 parts of the allylated resole-type phenol resin obtained in Synthesis Example 2 were added, respectively.
Parts, and in addition, Examples 5, 6, 7, and 8 were used, and coating films were formed in the same manner as in Example 1.

 Table 2 shows the evaluation results of the coating films.

(Effect of the Invention) As shown in the examples, the aqueous coating composition of the present invention
Due to its low viscosity, the solid content of the coating can be increased, and the coating is excellent in processing resistance, corrosion resistance, retort resistance and flavor retention, and has very little elution. is there.

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-60-215015 (JP, A) JP-A-60-215016 (JP, A) JP-A-63-43966 (JP, A) JP-A-63-43966 75075 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C09D 163/00-163/10 C09D 161/06-161/14 C08G 59/62 C09D 5/00 C09D 5/02

Claims (1)

(57) [Claims] 1. An aqueous coating composition comprising (A) an acrylic resin-modified epoxy resin and (B) an allylated resole type phenol resin as main components.