JPH04180976A - Water-base coating composition - Google Patents

Abstract

PURPOSE:To obtain a water-base coating composition for a metal can, which gives a film excellent in the resistances to processing conditions, corrosion and retorting and flavor retentivity and having very low leachability by mixing an allylated resol phenolic resin and an epoxy resin modified with an acrylic resin. CONSTITUTION:A water-base coating composition composed mainly of an epoxy resin (A) modified with an acrylic resin, and an allylated resol phenolic resin (B). It is desirable that the amount of component B in terms of resin solids is 0.1-50wt.% based on component A. Examples of component A include a combination of an epoxide with carboxyl groups through partial reaction, one obtained by the ring opening of an epoxide by an amine and the formation of a quaternary salt between the amine and carboxylic groups, and a mere mixture of an acrylic resin and an epoxy resin substantially without any combination between them. Component B can be obtained by reacting a resol phenolic resin with an allyl halide in the presence of an alkaline catalyst.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a water-based coating composition, and more specifically, it is composed of an acrylic resin-modified epoxy resin and an allylated resol type phenolic resin, and has excellent processing resistance, corrosion resistance, The present invention relates to a water-based baking paint composition for metal cans that has excellent retort resistance and flavor retention and is particularly suitable for coating the inner surfaces of food and beverage cans.

(Prior art) Paints for metal cans must be able to sufficiently withstand the conditions imposed by the processing, distribution, and contents of metal cans, and in particular, paints for food and beverage cans must satisfy food hygiene requirements. It is necessary.

In this field, water-based paints that do not use organic solvents have been developed. For example, Japanese Patent Publication No. 63-63586 discloses that an α,β-olefinically unsaturated carboxylic acid and at least one other vinyl polymerizable monomer are polymerized in an amine resin solution, and then an epoxy resin is mixed. A method of heating and partially neutralizing with ammonia or amine to obtain an aqueous dispersion is disclosed. In addition, Japanese Patent Publication No. 1-25488 discloses that an acrylic resin, an epoxy resin partially bonded thereto, and both, or a phenol resin composition precondensed with the epoxy resin are heated to pH 4 with ammonia or amine.
-11 are described. Also,
Japanese Patent Publication No. 1-2548 describes a method of using a specific phenol resin condensed with an alkali catalyst as the phenol resin.
It is disclosed in Publication No. 9. Furthermore, JP-A-63-750
No. 75 discloses a self-emulsifying and self-crosslinking epoxy.
A water-based paint for cans is described which comprises an aqueous dispersion containing an acrylic resin and a resol-type phenol-aldehyde resin from oil-soluble phenols.

However, with conventional techniques, there were problems in that process resistance, corrosion resistance, retort resistance, flavor retention, etc. were insufficient due to elution of formalin or residual unreacted phenolic hydroxyl groups. .

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

(Means for Solving the Problems) As a result of intensive studies to solve the above problems, the present inventors have developed an aqueous dispersion in which a resol-type phenolic resin having a specific functional group is blended with an acrylic resin-modified epoxy resin. However, the inventors have discovered that the above object can be achieved, and have completed the present invention.

That is, the present invention is a water-based coating composition characterized by containing (A) an acrylic resin-modified epoxy resin and (B) an allylated resol type phenol resin as main components.

Hereinafter, the water-based coating composition of the present invention will be explained in detail.

The epoxy resin used as component (A) of the present invention is a resin having two or more epoxides in one molecule, and a resin that is made to react with a fatty acid, a tribasic acid, bisphenol A, F, or B to eliminate the epoxide. The epoxy resin obtained by condensing ebihalohydrin with bisphenol A, F, or B, etc. in the presence of an alkaline catalyst in a liquid containing partially or partially leftover materials is a material that improves the physical strength, adhesion, and chemical The average molecular weight is preferably 300 or more, preferably 1.000 or more since it has excellent chemical resistance. Examples of 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 tribasic acids include maleic acid and fumaric acid.

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

The acrylic resin used to modify the epoxy resin is a copolymer consisting of an unsaturated basic carboxylic acid such as acrylic acid or methacrylic acid and another copolymerizable monomer. It is usually 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 copolymerizable monomers include (meth)acrylic acid alkyl esters, styrene monomers, hydroxyl group-containing monomers, N-substituted (meth)acrylamides, oxirane group-containing monomers, maleic acid dialkyl esters, fumaric acid dialkyl esters, and acrylic acid. Examples include nitrile, and one or more of these can be used in combination.

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

The average molecular weight of acrylic resin is 3.000 to so, ooo
is preferred. If it is less than 3,000, the workability decreases and s
If it exceeds o, ooo, the solids content at a proper coating viscosity decreases.

Modification of epoxy resin with acrylic resin.

The solid content weight ratio of acrylic resin to epoxy resin is 1/1/
It is preferable to use it in the range of 10 to 1/1. If the amount of acrylic resin used is less than 1/10, the dispersion stability of the coating composition will decrease, and if it exceeds 1/1, the corrosion resistance will decrease.

In addition to the method described above, the acrylic resin-modified epoxy resin of component (A) can also be produced by preparing an epoxy resin mono(meth)acrylate in advance and then copolymerizing it with a copolymerizable polymer.

What is the modified epoxy resin using acrylic resin here?
It also includes a bond resulting from a partial reaction between an epoxide and a carboxyl, a compound in which an amine rings an epoxide to form a quaternary salt with the carboxyl, and a compound in which an acrylic resin and an epoxy resin are simply mixed without substantially bonding.

The resol type phenolic resin used as component (B) can be produced by a known method. i.e. phenol, alkylphenol or bisphenol A,
It is obtained by condensing F or B and formaldehyde in the presence of an alkaline catalyst at 100°C or less. The number average molecular weight is preferably 1.000 or less. When it exceeds 1.000, the dispersion stability of the coating composition decreases. Examples of the alkylphenol include p-cresol, 0-cresol, ethylphenol, 1)-tert-butylphenol, and 1-octylphenol.

Allylation of resol type phenolic resin is obtained by reacting allyl halide with resol type phenol resin in the presence of an alkaline catalyst. As the allyl halide, allyl chloride, allyl fluoride, allyl chloride, etc. are preferably used.

The blending ratio of the acrylic resin-modified epoxy resin (A) and the allylated resol type phenolic resin (B) is such that component (B) is preferably O1 to 50% by weight as resin solids,
More preferably, it is 1 to 10% by weight. If it is less than 0.1% by weight, corrosion resistance, retort resistance, and curing properties will deteriorate.

If it exceeds 50% by weight, processing resistance and flavor retention will decrease. Component (A) is preferably 999 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 it to ~11. The amines used include alkyl amines such as trimethylamine, triethylamine, and tributylamine; 2-dimethylamine ethanol, jetanolamine, triethanolamine;
Examples include aminoalcohols such as aminomethyl propatool, or morpholine.

The water-based coating composition of the present invention uses, as a base material, a steel plate, an aluminum plate, a plated steel plate in which the surface of the steel plate is plated with one or more metals such as zinc, tin, chromium, nickel, and aluminum, or the surface thereof. chromic acid,
It can be applied to materials that have been chemically or electrolytically treated with phosphoric acid or the like.

As the coating method, generally known methods can be used.

That is, air spray, airless spray, electrostatic spray, dip coating, roll coater, electrodeposition coating, etc.

The baking conditions include a temperature range of 150 to 300°C and
A time of 0 seconds to 30 minutes is preferred.

The aqueous coating composition of the present invention can be used as a rust-preventing primer, a rust-preventing paint, a printing ink, etc. by blending a rust preventive agent, pigment, filler, etc. suitable for the purpose within a range that does not impair the properties of the composition. can also be used.

(Function) The water-based coating composition of the present invention suppresses the amount of free phenolic hydroxyl groups by allylating the resol-type phenolic resin, so it has excellent processing resistance, retort resistance, hot water resistance, and flavor retention. Also, 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, improving the mechanical strength of the coating film and further improving the processing resistance.

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

Synthesis Example 1 94 parts of carbolic acid, 405 parts of 37% formalin and 211 parts of 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-bucnol=1/l to obtain a resol type phenol resin with a solid content of 80%.

Synthesis Example 2 After reacting in the same manner as in the same example with the same formulation as in Synthesis Example 1,
80 parts of allyl chloride was added and reacted at the same temperature for 1 hour, and treated in the same manner as in Synthesis Example 1 to obtain an allylated resol type phenol resin with a solid content of 80%.

Synthesis Example 3 108 parts of p-cresol, 162 parts of 37% formalin and 180 parts of 25% sodium hydroxide aqueous solution were mixed,
The reaction was carried out at 0°C for 2 hours. After neutralization with hydrochloric acid, extraction was carried out with a mixed solvent of n-butanol/kijirol=1/l to obtain a resol type phenol resin with a solid content of 70%.

Synthesis Example 4 Using the same formulation as Synthesis Example 3, after reacting in the same manner as in the same example,
80 parts of allyl chloride was added, the mixture was reacted at the same temperature for 1 hour, and treated in the same manner as in Synthesis Example 3 to obtain an allylated resol type phenol resin with a solid content of 70%.

Synthesis Example 5 Bisphenol A 228 parts, 37% formalin 243
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 to obtain a resol type phenol resin with a solid content of 60%.

Synthesis Example 6 Using the same formulation as Synthesis Example 5, after reacting in the same manner as in the same example,
360 parts of allyl iotide was added and reacted at the same temperature for 1 hour, and treated in the same manner as in Synthesis Example 5 to obtain an allylated resol type phenol resin with a solid content of 60%.

Synthesis Example 7 30 parts of the resol type phenolic resin obtained in Synthesis Example 1 was mixed with 50 parts of Ebiko 1-828 (trade name, manufactured by Nigel Chemical Co., Ltd., epoxy equivalent: 190), and reacted at 60°C for 2 hours to form a solid A resol type phenol resin with a content of 90% was obtained.

Synthesis Example 8 An allylated resol with a solid content of 90% was prepared in the same manner as in Synthesis Example 7, except that 30 parts of the allyl-modified resol-type phenolic resin of Synthesis Example 2 was used instead of the resol-type phenolic resin of Synthesis Example 1. type phenolic resin was obtained.

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

Synthesis Example 10 A flask was charged with 80 parts of Epicote 1009 (trade name, manufactured by Nigel Chemical Co., Ltd., epoxy equivalent: 3.000) and 53 parts of butyl cellosolve, and the mixture was stirred and dissolved 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, stirred to make it homogeneous, and then 66 parts of 2-dimethylaminoethanol was added, and the mixture was heated at 80°C.
After stirring for 30 minutes, the mixture was cooled to room temperature. Furthermore, 567 parts of deionized water was gradually added little by little to this.
The milky white dispersion was then distilled off under reduced pressure,
An acrylic resin-modified epoxy resin dispersion having a pH of 6.5 and a solid content of 20% was obtained.

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

This was applied to one side of a 0.25 mm thick aluminum plate in a dry coating amount of 70 mg/dm2. Dry coating amount 60-90 mg/d on both sides of 100 micron aluminum foil
m” and baked at 250°C and 280°C for 30 seconds each.
Corrosion resistance, retort resistance, and hot water resistance were evaluated on the double-sided coated board, and potassium permanganate consumption and flavor retention were evaluated according to the following test methods, and the results are shown in Table 1.

a) Place an aluminum plate of the same thickness between the workability test pieces and tighten in a vise. The degree of cracking of the coating film in the processed area was determined using a 50x magnifying glass.

○ No cracking △: Some cracking ×: Significant cracking b) Corrosion resistance A test piece whose back side was sealed with polyester tape was immersed in boiling 3% saline for 1 hour to determine the degree of corrosion on the coating surface. did.

○: No corrosion △ Slight corrosion ×: Significant corrosion C) Retort resistance The test piece was treated in a retort sterilizer at 125°C for 30 minutes, and the degree of whitening of the coating film was determined.

○: No whitening △: Slight whitening ×: Significant whitening d) Hot water resistance The test piece was immersed in ion-exchanged boiling water for 1 hour to determine the degree of whitening of the coating film.

○・No whitening △・Slight whitening ×・Significant whitening e) Consumption of potassium permanganate Place the double-sided coated test piece in a pressure-resistant glass bottle so that the contact ratio with the painted surface is 1 cm2/1-. After pouring in activated carbon-treated tap water and sealing it, sterilize it in a retort sterilizer for 12 hours.
After treatment at 5°C for 30 minutes, the treated solution was measured according to the test method described in the Food Sanitation Law.

○: ! 5 ppm or less △・5 to 10 ppm x: iopm or more f) Flavor retention A double-sided coated test piece was placed in a pressure-resistant glass bottle, and activated carbon-treated tap water was added so that the contact ratio with the coated surface was 1 cm"/11 nI. After putting it in and sealing it, use a retort sterilizer to
It was treated at 25°C for 30 minutes. After that, it was stored at 50°C for 3 months, and then a sensory test was conducted.

○: No change at all △: Slight change ×, Significant change Example 2 Coating was carried out in the same manner as in Example 1 except that 5.7 parts of the resin obtained in Synthesis Example 4 was used as the allylated resol type phenol resin. A membrane was created.

The evaluation results of the coating film are shown in Table 1.

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

The evaluation results of the coating film are shown in Table 1.

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

The evaluation results of the coating film are shown in Table 1.

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

The evaluation results of the coating film are shown in Table 1.

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

The evaluation results of the coating film are shown in Table 1.

Comparative Example 3 A coating film was prepared in the same manner as in Example 1, except that 33 parts of the resol type phenolic resin of Synthesis Example 5 was used instead of the allylated resol type phenolic resin of Synthesis Example 2.

The evaluation results of the coating film are shown in Table 1.

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

*Membrane evaluation results are shown in Table 1.

Examples 5 to 8 To 200 parts of the acrylic resin-modified epoxy resin dispersion obtained in Synthesis Example 10, 12.5 parts, 25 parts, and 37 parts of the allylated resol type phenolic resin obtained in Synthesis Example 2 were added, respectively.
．． 5 parts and 50 parts were added to Examples 5, 6, 7, and 8, respectively, and coating films were prepared in the same manner as in Example 1. The evaluation results of the coating films are shown in Table 2.

(Effects of the Invention) As shown in the Examples, the water-based paint composition of the present invention has a low viscosity, so the solid content of the paint can be increased, and the processability, corrosion resistance, and It is an excellent paint with extremely excellent retort resistance and flavor retention, and a very small amount of elution.

Claims (1)

[Claims] An aqueous coating composition characterized by containing (A) an acrylic resin-modified epoxy resin and (B) an allylated resol type phenolic resin as main components.