JPH02283774A - Water-based paint composition for cans - Google Patents

Abstract

PURPOSE:To prepare a water-based can coating compsn. giving a coating film excellent in the water resistance, hardness, and flexibility by compounding a water-based polyester resin with an alkyl-etherified amino resin obtd. from an amino compd. comprising a spiroguanamine. CONSTITUTION:A water-based can coating compsn. is prepd. by compounding, as the resin components, 5-60 pts.wt. alkyl-etherified amino resin which is obtd. by the polycondensation of a spiroguanamine of the formula or a mixture thereof with melamine with formaldehyde in such a way that at least three on an average formaldehyde molecules are bonded to one molecule of the spiroguanamine or mixture and by the etherification of the resulting polycondensate with methanol, ethanol, etc.; and 40-95 pts.wt. water-based polyester resin which is soluble or dispersible in an aq. medium in the presence of a volatile base and has an acid value of 10-100, a hydroxyl value of 10-300, a benzene ring content of 5-45wt.%, and a wt. average MW of pref. 1000-20000.

Description

Detailed Description of the Invention [Objective of the Invention] (Industrial Application Field) The present invention relates to alkyl etherified amino IJIM carboxyl group, hydroxyl group derived from spiroguanamine alone or an amino compound composed of melamine and spiroguanamine. The present invention also relates to a water-based paint composition for cans containing a water-based polyester resin containing a phenyl nucleus, and particularly to a water-based paint composition for cans that has excellent coating film water resistance, hardness, and flexibility.

(Prior art) The outer surface of beverage cans for storing soft drinks, etc. and food cans for packaging food products prevents corrosion of the can material, increases aesthetic and commercial value, and can withstand the heat treatment process during food sterilization. It is covered with a coating film. Conventionally, these paints are epoxy/
A method is used in which an organic solvent solution of amino resin, acrylic/amino resin, polyester/amino resin, etc. is applied using a roll coater, and then baked and hardened in a gas oven. However, these paints cause a large amount of solvent to volatilize during baking, causing air pollution, and are also unfavorable from the point of view of resource conservation. Therefore, the emergence of a water-based paint that can solve these problems is desired.

There are two types of known water-based paints: water-dispersible and water-soluble.
Water-dispersible resins are usually synthesized by emulsion polymerization using a surfactant, which has the disadvantage that the surfactant used remains in the coating after it is formed, reducing water resistance. Ta. On the other hand, there is a method of synthesizing a resin containing an acid content (carboxyl group) without using a surfactant in an organic solvent, and then neutralizing it with a volatile base to make it a dispersion or water-soluble.
These water-based paints have an acid value of 20 in the basic resin structure.
This method requires a higher acid content and has the drawback of poor performance such as water resistance and alkali resistance. In order to improve these drawbacks, a method of mixing a large amount of aqueous amino resin such as hexamethoxymethylmelamine or methylated benzoguanamine has been used, but the flexibility of the coating film is greatly reduced.

When the water-based amino resin is reduced in order to improve flexibility, the hardness of the coating film tends to decrease, making it difficult to balance the water resistance, hardness, and flexibility of the coating film.

In addition, conventional water-soluble paints contain 10% organic solvent to improve storage stability and leveling of paint film formation.
This was still insufficient in terms of air pollution due to solvent volatilization during baking and resource conservation.

(Problem B that the invention attempts to solve) The present invention has been made in view of the above-mentioned current situation.

The goal is to create a product that is water resistant enough to withstand the heat treatment process used to sterilize 3-meal beverage cans, hard enough to resist damage during transportation of single cans, and flexible enough to be processed into various can shapes. The present invention provides an aqueous paint composition for the external surface of a can, which forms a coating film with a low organic solvent content.

[Structure of the invention]

(Means for solving problems) In other words, one aspect of the present invention is.

(A) Addition or addition condensation of formaldehyde to spiroguanamine alone or a mixture of spiroguanamine and melamine so that each molecule of spiroguanamine or melamine has an average of 3 or more formaldehyde bonds, and then methanol or ethanol alone or 5 to 60% by weight of an alkyl etherified amino resin alkyl etherified with a mixture and.

(B) Acid value 10-100. The hydroxyl value is 10 to 3 oo, and the phenyl nucleus in the resin component is 5 to 45% by weight. This is an aqueous coating composition for cans, which contains as a resin component 40 to 95% by weight of an aqueous polyester resin that is soluble or dispersible in an aqueous medium in the presence of a volatile base.

The method for producing the alkyl etherified amino resin, component (A) of the present invention, is the same as that for conventionally known melamine resins.

It can be easily synthesized by appropriately selecting reaction conditions.

For example, add formaldehyde to spiroguanamine alone or to a mixture of spiroguanamine and melamine at 50 to 80°C.
It can be synthesized by carrying out an addition reaction at a temperature of 2 to 10 hours, and then heating a single or mixed alcohol of methanol or ethanol under acidic conditions (preferably pH 2 to 5) to form an alkyl ether.

In particular, in the alkyl etherification reaction under acidic conditions, the degree of condensation can be controlled and a desired molecular weight can be obtained by controlling the reaction time. The average number of formaldehyde bonds per molecule of spiroguanamine or melamine is preferably 3 or more. If the above number is less than 3, the alkyl etherified amino resin tends to become cloudy, and when used as a paint, it becomes a water-based resin. The compatibility with the paint is also poor, N separation and gelation occur, and the stability of the paint decreases.

In the case of a mixed system of spiroguanamine and melamine, it is preferable that spiroguanamine accounts for 20% by weight or more of the mixture.

When the alkyl etherified amine resin of the present invention is alkyl etherified with methanol, it has excellent water dilutability, and when used as a paint, the stability of the paint improves and it is possible to increase the solid content. Furthermore, when an alcohol having 3 or more carbon atoms is used, water dilutability is poor and paint stability is reduced. The alkyl etherification preferably has an average of 2 or more based on the molecular weight of spiroguanamine or melamine; if it is less than 2, the coating stability and water resistance decrease.

In addition, spiroguanamine is 2,4,8.10-tetraoxaspiro(5,5)undecane-3,9-bis(
2-ethylguanamine), and its structure is shown by the following formula. This product can be prepared by hand, for example, under the trade name CTU Guanamine manufactured by Ajinomoto.

The aqueous polyester resin of the component (B) of the present invention is as follows.

It is obtained by condensation polymerization of a polyhydric alcohol component and a polyhydric carboxylic acid, and the resin contains 5 to 45% by weight of phenyl nuclei introduced by using an alcohol component or a carboxylic acid component having a phenyl nucleus. . As an alcohol component containing a phenyl nucleus, bisphenol A
, bisphenol dihydroxypropyl ether, and ethylene oxide-added bisphenol A. Polyhydric alcohols other than the above include hydrogenated bisphenol A
, ethylene glycol, propylene glycol, 1.3
- Dihydric fluorols such as butylene glycol, 1,6-hexanediol, diethylene glycol, dipropylene glycol, neopentyl glycol, triethylene glycol, trimethylolethane, trimethylolpropane, trishydroxymethylaminomethane.

There are trihydric or higher alcohols such as pentaerythritol, dipentaerythritol, and diglycerin. Also.

Carboxylic acid components having a phenyl nucleus include (anhydrous) phthalic acid, isophthalic acid, terephthalic acid, hexahydro (anhydrous) phthalic acid, (anhydrous) trimellitic acid, (
(anhydrous) pyromellitic acid, etc. Other carboxylic acid components include tetrahydrophthalic anhydride, methylene diclohexene tricarboxylic anhydride), hymic acid (anhydride), adipic acid, azelaic acid, succinic acid (anhydride), maleic acid (anhydride), and fumaric acid (anhydride). Acids, polyhydric carboxylic acids such as sepatic acid and itaconic acid, or their anhydrides. In addition, monobasic acids such as benzoic acid and t-butylbenzoic acid may be used as the carboxylic acid component, and in addition to the alcohol component and the carboxylic acid component, if necessary.

Add oil ingredients such as castor oil, dehydrated castor oil, tung oil, safflower oil, soybean oil, linseed oil, tall oil, coconut oil, etc.
It may also be an alkyd resin obtained by reacting as a component. Alternatively, a graft-modified polyester resin obtained by grafting an acrylic resin onto the polyester resin obtained above may be used. If the content of phenyl nuclei in the aqueous polyester resin is less than 5% by weight, the hardness of the coating film will be poor, while if it exceeds 45% by weight, the flexibility of the coating film will be poor.

The water-based polyester resin has an acid value of 10-100. It is necessary that the hydroxyl value is in the range of 10 to 300.

If the acid value is less than 10, it will be difficult to make it water-based, and if it exceeds 100, the water resistance of the coating film will be poor. Furthermore, if the hydroxyl value is less than 10, the crosslinking density will be low, resulting in poor water resistance.

If it exceeds 300, the flexibility of the coating film will be poor. The molecular weight is preferably one weight average molecular weight of too much to 20,000.

The blending ratio of the alkyl etherified amino resin (component A) and the aqueous polyester resin (component B) in the coating composition of the present invention is such that the alkyl etherified amino resin accounts for 5 to 60% by weight, preferably 10 to 40% by weight. It is. If the content of the alkyl etherified amino resin is less than 5% by weight, the crosslinking density of the coating film will be low, resulting in poor water resistance, and if it exceeds 60% by weight, the flexibility of the coating film will be poor.

Volatile bases for dissolving or dispersing the aqueous polyester resin in an aqueous medium include monoethanolamine, dimethylamine, and diethylamine.

Triethylamine, triethanolamine, diethylethanolamine, dimethylethanolamine.

Organic amines such as morpholine. The amount of volatile base used may be any amount that at least partially neutralizes the carboxylic acid in the aqueous resin.

The aqueous medium is water or a mixed solvent containing water as a main component and a hydrophilic organic solvent. Examples include alcohol solvents such as isoamyl alcohol, ester solvents such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, and diethylene glycol monobutyl ether.

The coating composition of the present invention optionally contains an amine-blocked acid catalyst 2 as a curing aid, such as p-toluenebenzenesulfonic acid, dodecylbenzenesulfonic acid, dinonylnaphthalenedisulfonic acid, etc., at a resin solid content of 100 parts. 0.1 to 1 part is added to form a paint. Water-soluble resins and water-dispersible resins commonly used as resins for water-based paints include, for example, methylated melamine, methylated benzoguanamine, water-soluble or water-dispersible acrylic resins, and maleated fatty acids.

It is also possible to mix water-soluble polyether polyol resins, water-soluble polyester polyol resins, water-soluble or water-dispersible epoxy resins, and the like. Also.

Similarly, leveling agents, antifoaming agents, and lubricants can also be added. Alternatively, the pigment can be mixed with a polyester resin solution or a water-based resin such as a water-soluble acrylic resin to create a pigment paste, which can then be made into a paint in the same manner as described above.

The aqueous coating composition of the present invention can be applied by conventional means such as roll coating and spray brushing. Can materials include metal plates such as tin plated steel plates, tin-free steel plates, and aluminum plates.

Further, the water-based paint of the present invention can be cured under a wide range of baking conditions, from baking at 150 to 200°C for about 10 minutes to baking at a high temperature for about 10 seconds at 250°C.

Hereinafter, the present invention will be explained with reference to examples.In 0 examples, 1 part means part by weight, and 1% means % by weight, respectively.

Production 4M1 (Alkyl etherified amino resin solution A
-1) 27.8 parts of spiroguanamine was placed in a four-eye flask equipped with a thermometer, stirrer, reflux condenser, and nitrogen blowing tube.

40% methanol solution containing formaldehyde? f1. <Formin l-MH; manufactured by Koei Kagaku; the same applies to the following examples) 72
2 parts of the solution were added, the pH was adjusted to 10 with sodium methylate, and the mixture was heated at 60°C for 3 hours. Next, 0.1 part of phthalic anhydride was charged and the reaction was continued at 70° C. for 8 hours, after which methanol and water were removed under reduced pressure and filtered out using filter paper. The solid content was adjusted to 75% with butyl cellosolve.

Production example 2 (alkyl etherified amino resin solution A-2)
Using the same equipment as in Production Example 1, 22.9 parts of the spiroguanamine used in Production Example 1 and 77.1 parts of a 40% methanol solution containing formaldehyde were charged, and after adding 0.16 parts of 25% sodium hydroxide, the mixture was heated at 60°C. It was heated for 3 hours. Next, 0.15 part of 62% nitric acid (pH 3.5) was added, followed by reaction at 70°C for 8 hours. After the reaction was completed, the mixture was neutralized with 25% sodium hydroxide, methanol water was removed under reduced pressure at 70° C. or lower, the solid content was adjusted to 75% with butyl cellosolve, and the mixture was filtered out using a filter paper.

Production example 3 (alkyl etherified amino resin solution A-3)
Using the same equipment as in Production Example 1, 18.9 parts of spiroguanamine used in Production Example 2, 79.7 parts of a 40% methanol solution containing formaldehyde, and 1.4 parts of melamine were charged, and 25% hydroxylated l-IJ was prepared. After adding 0.2 part of um6
Heated at 0°C for 3 hours. Next, 0.13 parts of 62% nitric acid (p
H3,5) was added and then reacted at 70'C for 8 hours. After the reaction was completed, the mixture was neutralized with 25% sodium hydroxide, methanol and water were removed under reduced pressure at 70° C. or lower, the solid content was adjusted to 75% with butyl cellosolve, and the mixture was filtered out using a filter paper.

Production Example 4 (Alkyl etherified amino resin solution A-4
Using the same equipment as in Production Example 1, 14.7 parts of spiroguanamine used in Production Example 2, 82.5 parts of a 40% methanol solution containing formaldehyde, and 2.8 parts of melamine were charged, and 0.16 parts of 25% sodium hydroxide was added. After adding 60 parts
Heated at ℃ for 4 hours. Next, 0.015 parts of 62% nitric acid (pH
3, 5) were added and then reacted at 70°C for 8 hours.

After the reaction was completed and neutralized with 25% sodium hydroxide,
Methanol and water were removed under reduced pressure at 0°C or lower, the solid content was adjusted to 75% with butyl cellosolve, and the mixture was filtered out using a filter paper.

Table 1 shows the analysis results of the average number of bound formaldehyde per spiroguanamine or melamine molecule and the average bound alkyl ether group of the alkyl etherified amino resins A-1 to A-4 obtained as described above.

Production example 5 (aqueous polyester resin solution B-1) thermometer,
14.7 parts of ethylene glycol and 24.7 parts of neopentyl glycol were placed in a four-eye flask equipped with a stirrer, a reflux condenser with two separate seeds, and a nitrogen gas blowing tube. S part.

25.6 parts of adipic acid and 29.1 parts of terephthalic acid were charged, heated to 230°C while stirring while introducing nitrogen gas, and reacted until the acid value became 5 or less. 2.6 parts, trimellinotic anhydride 3.4 parts
The reaction was continued until the acid value reached 60. Cool to below 80'C and add 8.6 parts of ethylene glycol monobutyl ether.

8.1 parts of dimethylethanolamine and 69.1 parts of water were added to produce a transparent, neutralized acid value of 60.5% with a solid content of 50% and an organic solvent of 10%. Hydroxyl value 105. An aqueous polyester resin solution (B-1) having a phenyl nucleus content of 15.9% was obtained.

Production Example 6 (Aqueous polyester resin solution B-2) In a four-eye flask similar to Production Example 5, ethylene glycol 14
．． 2 parts, 23.9 parts of neopentyl glycol, and 56.4 parts of isophthalic acid were heated to 230°C while stirring while introducing nitrogen gas, and reacted until the acid value became 5 or less, and then heated to 70°C in the first stage. Cool, trimellitic anhydride 5.5
The reaction was continued and the reaction was terminated when the acid value reached 60. Cool to below 80°C, add 8.6 parts of ethylene glycol monobutyl ether, 8.2 parts of dimethylethanolamine, and 69.4 parts of water to obtain a solid content of 50%.
, 10% organic solvent, transparent and tone acid value 60 before neutralization. An aqueous polyester resin solution (B-2) containing 33% hydroxylated 103° phenyl base was obtained.

Production Example 7 (Aqueous polyester resin solution B-3) In a four-eye flask similar to Production Example 5, ethylene glycol 15
．． 7 parts, neopentyl glycol 26.3 parts, isophthalic acid 48.5 parts, and maleic anhydride 9.5 parts, and heated to 2°C while stirring while introducing nitrogen gas until the acid value was 5 or less. After reacting until
Add 87 parts of n-butanol and add 6 parts of acrylic acid to a drop tank.
A mixture of 9 parts of 2-hydroxyethyl acrylate, 15 parts of styrene, and 2.4 parts of benzoyl peroxide was added dropwise over 3 hours.

Thereafter, the mixture was kept at 105°C and reacted for 1 hour, and 0.2 parts of benzoyl peroxide was added, and the reaction was completed for 1 hour.

Cool to below 60°C and dimethylethanolamine 7°4
1 part, 200 parts of water were added, and the mixture was heated under reduced pressure at 80°C.
- Water is distilled out along with butanol, the solid content is 50%, the organic solvent is 10%, and the acid value before neutralization is 40.5. Hydroxylation 152. An aqueous polyester resin solution (B-3) with a phenyl nucleus content of 32.6% was obtained.

Example 1 3 parts of alkyl etherified amino resin solution A-121°,
Aqueous polyester resin solution B-148 parts.

0.1 part of amine-blocked paratoluenesulfonic acid.

30.7 parts of water and 0.1 part of a silicone leveling agent were mixed to form a paint.

Examples 2 to 7 Alkyl etherified amino resin solution A-1-A-4 and aqueous polyester resin solution B-1 were prepared in the same manner as in Example 1.
~B-3 were combined into paints as shown in Table 2.

Comparative Example 1.2 In the same manner as in Example 1, hexamethoxymelamine (Imel 303, manufactured by Mitsui Toatsu Chemical Co., Ltd.) and aqueous polyester resin solution B-1 were combined as shown in Table 2 to form a paint.

The coatings obtained in Examples 1 to 7 and Comparative Example 1.2 were subjected to coating stability tests and coating film physical property tests according to the following methods, and the results are shown in Table 2.

Each test method is as follows.

○Paint stability test After each paint was stored at room temperature for two months, the state of gelation and separation of the resin was observed.

○Coating film physical property test Roll coating was applied to electroplated tinplate to a film thickness of 7μ, and the temperature was 180℃ with the gas open.
Baked for 0 minutes to create a painted panel.

・Solvent resistance test A rubbing test was conducted using methyl ethyl ketone to determine the number of times the coating was rubbed back and forth until it peeled off.

・Water resistance test The painted panel was immersed in water and heated at 100℃ for 30 minutes for 12 minutes.
After heat treatment at 5° C. for 30 minutes, the whitening state of the coating film was evaluated.

・Pencil hardness test law evaluated.

・Adhesion test A cross-cut peeling test was conducted.

・Workability test An Erichsen test was performed.

・Impact resistance test DuPont method, 1 part 2 inches, 500g load.

〔Effect of the invention〕

The alkyl etherified amino resin blended into the coating composition of the present invention is a spiroguanamine containing a spiro ring in its constituent components, so it has excellent dilution with water, and when combined with an aqueous polyester resin, it improves the flexibility and water resistance of the coating film. It is possible to obtain a paint that has all the properties necessary for a paint for cans, such as hardness and hardness.

In addition, since the molecular weight of spiroguanamine is more than twice that of melamine, fumes generated during high temperature baking are reduced, so it has desirable properties as a coating material for can stock that requires high temperature and short time baking.

Contents of correction 1. Display of incidents Heisei 1 Year Patent Application No. 103380 1. The "Detailed Description of the Invention" column is amended as follows.

(1) Change “Hydroxyl value 105” on page 15, line 6 of the specification to “
Corrected to ``Hydroxyl value 165.''

(2) Change “Hydroxyl value 103” to “Hydroxyl value 103” on page 15, line 20 of the specification.
Corrected to ``Hydroxyl value 163.''

Name of the invention: Water-based paint composition for cans 3. Relationship with the case of the person making the amendment. Patent applicant address: 2-3-13 Kyobashi, Chuo-ku, Tokyo. Contents of the amendment in the "Detailed Description of the Invention" section of the specification. As per attached sheet

Claims (1)

[Claims] 1. (A) Addition or addition condensation of formaldehyde to spiroguanamine alone or a mixture of spiroguanamine and melamine so that each molecule of spiroguanamine or melamine has an average of 3 or more formaldehyde bonds; Then, 5 to 60% by weight of an alkyl etherified amino resin which has been alkyl etherified with methanol or ethanol alone or in a mixture; 45% by weight of an aqueous polyester resin soluble or dispersible in an aqueous medium in the presence of a volatile base, as a resin component.