JPH064813B2 - Coating composition for cans - Google Patents

Description

TECHNICAL FIELD The present invention relates to a can coating composition excellent in workability, retort resistance, adhesion to a base metal and the like.

(Prior Art) Metal cans are made of tin, tin-free steel, aluminum, etc., and protective paints are usually used on the inner and outer surfaces of the cans to prevent corrosion of these metals and metal elution in the contents. ing. As the can lid for metal cans, the pull-tab type easy-open lid is now popular.
As the inner and outer surface paints, paints having excellent metal protection properties such as epoxy resin-phenol resin paints, epoxy resin-amino resin paints, epoxy resin-acrylic resin paints are usually used. However, although the coating film of these conventional paints is excellent in metal protection in the flat part of the coating, the processing is difficult in the processed part after molding the metal material, for example, in the pull tab type lid mounting part. Therefore, the coating film is often cracked and the base metal is exposed. Therefore, the exposed metal part is often repaired after processing. Since such repair complicates the process and is disadvantageous in terms of cost, there is a demand for the development of a paint with excellent workability characteristics that does not require repair. In response to this demand, a vinyl chloride-based organosol paint has been developed, but it has excellent lid processability, but it has poor retort resistance due to the large amount of thermoplastic resin components. In other words, whitening of the coating film by retort treatment Also, there are drawbacks such as deterioration of the enamel feathering property at the time of pull tab opening (a phenomenon that the coating film remains at the opening) due to deterioration of the adhesion between the coating film and the base metal, and corrosion of the base metal. Currently, it can only be used for can lids of unnecessary contents.

In addition, bisphenol A type epoxy resin has been conventionally used in the epoxy resin-phenolic resin type paint,
It was considered to blend a bisphenol A type phenoxy resin having an average molecular weight of 20.000 or more in order to improve processability, but the phenoxy resin has an average of 0 to 1.0 epoxy groups in one molecule. Since it does not exist, it has poor adhesion to metals and reactivity with the thermosetting resin compounded in the paint, and has the drawback of poor retort resistance.

As described above, the current can paint has excellent lid workability that does not require the application of repair paint after lid processing, and furthermore, the development of internal and external coatings that can be applied to all contents regardless of the presence or absence of retort treatment has not been developed. It was difficult.

(Problems to be Solved by the Invention) The present inventors have succeeded in satisfying all the required performances in an epoxy resin-phenolic resin-based coating material even if a large amount of bisphenol A-type phenoxy resin is blended.

In the present invention, an aluminum alcoholate or an aluminum complex compound contributes as a cross-linking reaction agent for the phenoxy resin and the other resin, and thus, the retort resistance is improved. However, if only the aluminum alcoholate or aluminum complex compound is blended, the adhesion to the base metal is rather deteriorated and the coating film floats in the processed part. The drawback is that the coexistence of an organic acid improves the adhesion to the base metal.

(Means for Solving Problems) That is, the present invention provides 40 to 80 parts by weight of a bisphenol A type phenoxy resin having an average of 0 to 1.0 epoxy groups in a molecule having an average molecular weight of 20,000 or more, and a bisphenol A type epoxy. Resin 40 to 100 parts by weight, phenolic resin 10 to 60 parts by weight, general formula Al (OR) _n (L) _3-n
(In the formula, R is an alkyl group, L is a keto-enol tautomeric compound, and n is an integer of 0 to 3.) An aluminum alcoholate or an aluminum complex compound 2.0
25 to 25 parts by weight and 0.2 to 10.0 parts by weight of organic matter.

The bisphenol A type epoxy resin according to the present invention is obtained by condensing epihalohydrin and bisphenol A to a high molecular weight in the presence of an alkali catalyst or by condensing epihalohydrin and bisphenol A into a low molecular weight epoxy resin in the presence of an alkali catalyst. It is produced by subjecting a resin and bisphenol A to a polyaddition reaction.

A bisphenol A type phenoxy resin having an average molecular weight of 20.000 or more is also produced by the same production method as that of the bisphenol A type epoxy resin. Examples of commercially available bisphenol A type phenoxy resin include phenoxy PKHH (manufactured by Union Carbide Co.), Phenototo YP-50, and Phenototo YP-40 (manufactured by Toto Kasei Co., Ltd.).

The phenolic resin in the present invention is obtained by a known method of addition-condensing formaldehyde to phenols under a catalyst, and includes those modified with a phenolic hydroxyl group or an alcoholic hydroxyl group. The phenols include phenol, o-cresol, m-cresol,
p-cresol, p-tert-butylphenol, p-nonylphenol, p-octylphenol, p-phenylphenol, methylphenol, ethylphenol,
Propylphenol, isopropylphenol, butylphenol, p-tert-amylphenol, 4,4'-
sec-butylidenephenol, p-cyclohexylphenol, 4,4'-isopropylidene-diphenol,
Xylenol, phenyl-o-cresol, etc. are used alone or as a mixture of two or more, and as catalysts, organic amines such as ammonia, ethylamine, butylamine, diethanolamine, sodium hydroxide, magnesium hydroxide, calcium hydroxide, barium hydroxide, etc. The basic compound is also 37% aqueous solution or 40% formaldehyde.
A butanol solution or the like is used.

The aluminum alcoholate or aluminum complex compound in the present invention is represented by the general formula Al (OR) _n (L) _3-n .

Examples of the aluminum alcoholate with n = 3 include aluminum triisopropoxide, aluminum tri-n-butoxide, aluminum triisobutoxide and the like. The aluminum complex compound with n = 0, 1, 2 is a keto-enol tautomeric compound such as bis- (β-diketone) represented by acetylacetone, acetoacetic acid ester, malonic acid ester, etc. as L. It is included, and can be easily obtained by mixing the above-mentioned keto-enol type tautomeric compound with aluminum alcoholate. In the present invention, either aluminum alcoholate or aluminum complex compound can be used. However, since aluminum alcoholate is easily hydrolyzed, it requires careful handling work and may impair the storage stability of the resulting composition. Therefore, some or all of the alkoxy groups are replaced with keto-enol tautomeric compounds. The aluminum complex compounds described above are preferable, and among them, aluminum tributoxide and diisopropoxyaluminum acetoacetic acid ester exhibit excellent advantageous effects for achieving the object of the present invention.

Organic acids in the present invention include benzoic acid, sebacic acid, maleic anhydride, phthalic anhydride, terephthalic acid, itaconic acid, fumaric acid, adipic acid, and other aliphatic, aromatic or saturated acids, unsaturated acids, and monobasic acids. , Polybasic acids can be used. It is preferable that these organic acids are chemically stable and do not separate from the coating film during baking, and therefore, organic acids having a boiling point of 150 ° C. or higher are preferable.

As a method for producing a coating material in the present invention, a bisphenol A type epoxy resin solution containing a bisphenol A type phenoxy resin dissolved in an organic solvent is mixed with a resol type phenol resin, and then aluminum alcoholate or an aluminum complex compound and Organic acids can be added at any time in any order. Also in this case,
Almost the same performance can be obtained by pre-condensing the ester resin solution and the resol-type phenol resin with organic acids and then adding an aluminum alcoholate or an aluminum complex compound. However, in these manufacturing methods, the contribution of aluminum alcoholate or aluminum complex compound to the cross-linking reaction is only during the baking process after the coating of the base metal, so that the retort resistance is superior to the conventional coating. In the strong retort condition, some whitening of the coating film occurs. Therefore, bisphenol A containing bisphenol A type phenoxy resin
The retort resistance is further improved by reacting the epoxy resin with an aluminum alcoholate or an aluminum complex compound at 80 ° C. to 150 ° C. for 0.5 hours to 5 hours and then adding a phenol resin and an organic acid. Further, in this case, by adding the phenol resin and the organic acid and then precondensing, it is possible to reduce the temperature or the time during the baking step.

In the present invention, the mixing ratio of each component of the coating composition is 40 to 100 parts by weight of phenoxy resin, 40 to 60 parts by weight of epoxy resin, 10 to 60 parts by weight of phenolic resin, aluminum alcoholate or aluminum complex compound of 2.0 to 25.
By weight, the organic acid is 0.2-10.0 parts by weight. If the amount of the epoxy resin in the total amount of the coating material is increased beyond the above range, the retort resistance tends to deteriorate, and similarly, if the amount of the phenol resin is increased, the workability of the coating film deteriorates. When the aluminum alcoholate or aluminum complex compound increases, the workability deteriorates due to the increase in the crosslink density, and conversely, when it decreases, the retort resistance deteriorates as described above. When the amount of organic acid is more or less than the optimum range, the processability deteriorates, but when it is more than the optimum range, it is due to lack of flexibility of the coating film due to the increase in crosslink density. This is because the adhesion of the metal to the coating film deteriorates, causing peeling of the coating film at the processed part.

The coating composition for a can of the present invention has 3 to 1 on the surface of the base metal for a can.
It is used by forming a 5μ cured coating film.
As a method for forming a coating film, a known method in which a composition dissolved in an organic solvent is roll-coated and applied, and baking is suitable. As the solvent, an organic solvent such as a ketone type, an ester ether type, an alcohol type, or a hydrocarbon type may be appropriately blended and used according to the solubility, viscosity and coating conditions of the resin.

The baking conditions are a temperature of 150 to 300 ° C. and a baking time of 0.
5 to 30 minutes.

(Example) Preparation of phenoxy resin solution (A) Phenoxy PKHH (manufactured by Union Carbide) 100
Parts were dissolved in a mixed solvent of 100 parts of cellosolve acetate and 100 parts of xylene.

Preparation of Epoxy Resin Solution (B) 100 parts of Epicoat 1009 (manufactured by Shell Chemical Co., Ltd.) was dissolved in a mixed solvent of 100 parts of cellosolve acetate and 100 parts of xylene.

Preparation of Epoxy Resin Solution (C) 100 parts of Epicoat 1007 (manufactured by Shell Chemical Co., Ltd.) was dissolved in a mixed solvent of 100 parts of cellosolve acetate and 100 parts of xylene.

Preparation of Epoxy Resin Solution (D) 100 parts of Epicoat 1001 (manufactured by Shell Chemical Co., Ltd.) was dissolved in a mixed solvent of 100 parts of cellosolve acetate and 100 parts of xylene.

Preparation of phenol resin (E) 228 parts of bisphenol A, 40% of formaldehyde
225 parts of n-butanol solution, 25% ammonia water 17
Parts were reacted at 100 ° C. for 5 hours, and then xylene, n-
Butanol and cyclohexanone were added to dilute and further dehydrated to prepare a 33.3% phenol resin solution.

Preparation of phenol resin (F) 108 parts of p-cresol, formaldehyde 40% n-
After reacting 75 parts of butanol solution and 0.56 parts of magnesium hydroxide for 1.5 hours at 100 ° C., neutralized with phosphoric acid, added xylene, n-butanol, cyclohexanone and a large amount of water for 5 hours. After standing, the aqueous layer containing the produced salt was separated and removed, and further azeotropically dehydrated to produce a phenol resin solution having a resin content of 33.3%.

Example 1 40 parts of phenoxy resin solution (A), 100 parts of epoxy resin solution (C), and 30 parts of phenol resin solution (E) were mixed and stirred, and after sufficiently mixing, ethyl acetoacetate aluminum diisopropyi was added thereto while stirring. Rate 3.
3 parts were mixed, 0.5 part of maleic anhydride was further mixed, and the coating material obtained by sufficient stirring was roll-coated on an aluminum plate having a thickness of 0.30 mm so that the coating thickness would be 8 μm.
A coated plate was obtained by baking at 0 ° C. for 40 seconds or 190 ° C. for 10 minutes.

Examples 2 to 5 Painted plates were prepared with the composition ratios shown in the following Table 1 by the same composition method and the same preparation method as in Example 1.

Example 6 After mixing 40 parts of a phenoxy resin solution (A) and 100 parts of an epoxy resin solution (C), 3.3 parts of ethyl acetate aluminum diisopropylate was added thereto, and 1
The reaction was carried out at 10 ° C for 3 hours. Thereafter, the mixture was cooled to 40 ° C. or lower, 30 parts of the phenol resin solution (E) was mixed, and 0.5 part of adipic acid was further mixed to obtain a coating material, and a coated plate was prepared in the same manner as in Example 1.

Example 7 A coating material was prepared from the composition of Example 4 by the same production method as in Example 6, and by the same coating plate production method.

Example 8 A paint was prepared by the same manufacturing method as in Example 6 and was coated with the same composition as in Example 7, except that aluminum tris (ethylacetoacetate) was used instead of ethyl acetoacetate aluminum diisopropylate. It was created by the board creation method.

Comparative Example 1 40 parts of phenoxy resin solution (A), 100 parts of epoxy resin solution (C), and 30 parts of phenol resin solution (E) were mixed and stirred, and after sufficiently mixing, ethyl acetoacetate aluminum diisopropyi was added thereto while stirring. Rate 3.
A coating material prepared by mixing 3 parts and sufficiently stirring was prepared by the same method as in Example 1.

Comparative Example 2 A coating material was produced without adding an organic acid in the composition of Example 4, and the coating plate was produced in the same manner as in Example 1.

Comparative Example 3 A coating material was prepared without adding an organic acid in the composition of Example 6, and the coating plate was prepared in the same manner as in Example 1.

Comparative Example 4 A coating material was produced without adding ethyl acetoacetate aluminum diisopropylate in the composition of Example 3, and the same method as in Example 1 was used to produce a coated plate.

A coating film performance test for cans was conducted on the coated plates obtained in each example, and the results are shown in Table 2 (baking conditions: 270 ° C.-40 seconds) and Table 1 (baking conditions: 90 ° C.-10 minutes). The conditions for each coating performance test are as follows.

Workability and bendability After the coated plate was bent at 180 ° C, the cracked state of the coating film when a load of 2 kg was dropped from a height of 50 cm on the bent portion was observed with a magnifying glass, and is very good (◎) The grade was evaluated as good (○), slightly changed (△), and markedly changed (×).

Workability and lid workability A coated plate was lid-processed with a press machine, and the cracked state of the coating film in the processed part and the floating of the coating film were observed with a magnifying glass, and evaluated using the same criteria as above.

Adhesion The coated plate was hit in the form of a cup with a diameter of 3 cm and a depth of 1.5 cm, and the coating film floating on the side surface and the film peeling state were observed and evaluated according to the same criteria as above.

Retort resistance, coating whitening The coating whitening state after retorting at 125 ° C for 40 minutes was visually observed and evaluated according to the same criteria as above.

Retort resistance and saltwater-whitening resistance After immersing the coated plate in a 3% aqueous sodium chloride solution, the retort treatment was carried out, and the whitening state of the coating film was visually observed and evaluated according to the same criteria as above.

Retort resistance and salt water corrosion resistance After the coated plate is capped with a press machine and immersed in a 3% sodium chloride aqueous solution, the retort treatment is performed and the corrosion state of the processed part and flat part is visually observed. It evaluated by the same standard as.

(Effect of the Invention) Since the can coating composition of the present invention contains the bisphenol A-type phenoxy resin having the property as a thermoplastic resin, the coating film has good processability. In addition, since the aluminum alcoholate or aluminum complex compound and organic acid are blended as essential curing catalyst components, the reactive groups in the coating resin react quickly and are excellent in rapid curing property and have good adhesion to the metal substrate. The resin has excellent heat resistance, and since it also has retort resistance, in this respect, the pull tab method of PVC organosol-based paints, to which retort treatment could not be applied in the past, was used. It is intended to expand the scope of application in place of the can lid.

Claims (2)

[Claims] 1. A bisphenol A phenoxy resin having an average of 0 to 1.0 epoxy groups in a molecule having an average molecular weight of 20,000 or more, 40 to 80 parts by weight, bisphenol A type epoxy resin, 40 to 100 parts by weight, and phenol resin 10.
˜60 parts by weight, general formula Al (OR) _n (L) _3-n (wherein R is an alkyl group, L is a keto-enol type tautomeric compound,
n shows the integer of 0-3. ) Aluminum alcoholate or aluminum complex compound represented by
A coating composition for a can, characterized in that it has 0.2 parts by weight and 0.2 to 10.0 parts by weight of organic acids. 2. The can coating composition according to claim 1, wherein the bisphenol A type epoxy resin containing the bisphenol A type phenoxy resin and the aluminum alcoholate or aluminum complex compound are preliminarily heated and reacted.