JPH0259184B2 - - Google Patents

Description

[Detailed description of the invention]

This invention relates to water-dispersible coating compositions based on epoxy resins. Epoxy resins are capable of forming tough coatings that are highly resistant to hydrolysis and chemical attack. Coatings exhibiting a particularly high degree of resistance to hydrolysis are required, for example, as internal coatings for food and beverage cans that must withstand heating in contact with acidic aqueous solutions such as fruit juice or beer. be. The coating must not be subject to hydrolysis and elute certain substances that impair the flavor of the food or beverage, and must not be subject to conditions that cannot be avoided during sterilization of the food or beverage. It must be durable and adhere well to the can, usually made of tin or aluminum. However, it is difficult to produce water-dispersible coating compositions containing epoxy resins. Coatings based on volatile organic solvents are gradually being phased out because the evaporated solvents cause environmental pollution and the cost of organic solvents is rapidly increasing. The invention can be applied to a substrate from a water-based diluent solution or stable dispersion.
The purpose is to produce a coating composition based on epoxy resin. Patent Publication Nos. 6334 and 6336 disclose a solvent-soluble carboxyl-functional polymer; an aromatic polyether having oxirane functionality;
at least 5% of the aromatic polyether is made up of diepoxide, and the mixture of aromatic polyethers makes up at least 40% of the total resin solids;
and esterifying with an epoxy resin that provides a stoichiometric deficit of oxirane functionality of 1:2 to 1:20 with respect to the carboxyl functionality in the carboxyl-functional polymer; reacting the oxirane functionality with the carboxyl functionality in an organic solvent medium in the presence of an amine esterification catalyst in an amount greater than 2% by weight of the reactants to substantially completely eliminate the oxirane functionality. and reacting at least a portion of the carboxyl functionality in the resulting polymer-epoxy resin hydroxyester reaction product with a base, and converting the reaction product to water. A method for preparing a self-emulsifying epoxy ester copolymer mixture is described, which is characterized in that it is self-emulsifying.
In Pangzhou Patent Publication No. 6334, 4 to 10% by weight of the reactants is added to avoid gelation of the reaction mixture.
It has been shown that it is necessary to use a high ratio of amine esterification catalyst. British Patent Publication No.
In No. 2059968, in a mixture of water and an organic solvent,
Other methods of making water-dispersible coating compositions have been described in which an epoxy resin is reacted with a solution of a carboxyl-functional acrylic polymer and an amine. In this method too, a high proportion of amine is present in the reaction of the epoxy resin and the carboxyl-functional polymer. Another method for producing a water-dispersible coating composition based on an epoxy resin and an addition polymer containing carboxylic acid groups is disclosed in the US Patent No.
Described in No. 4212781. In this process, an epoxy resin is reacted with an addition polymerizable material having at least a partial carboxylic acid functionality in the presence of 6-7% by weight of a benzoyl peroxide catalyst. In this invention, water-dispersible coating compositions are prepared from epoxy resins without requiring the use of such high levels of catalysts. According to the present invention, at elevated temperature in the presence of an amine, (a) 40 to 90% by weight of an epoxy resin composition having an average epoxy functionality of 1.0 to 2.0 epoxide groups per molecule; 10-60% by weight of a copolymer, which is an addition copolymer of 10-85% by weight of an unsaturated carboxylic acid and 90-15% by weight of at least one olefinic unsaturated comonomer, is added to the carboxylic acid groups in (b) and ( Ratio to epoxide groups in a)
1.5:1 to 20:1 to produce a water-dispersible ester-grafted epoxy/acrylic polymer coating composition.
in the presence of 0.5 to 3.0 wt.% amine, but less than 1 equivalent of amine per equivalent of epoxy group, in a water-miscible organic solvent mixture containing 30 wt.% water, where the percentages of water and amine are (based on the total weight of the epoxy resin (a) and the copolymer (b)) is provided. In accordance with the invention, it is further provided that in a water-miscible organic solvent mixture containing from 5 to 30% by weight of water in the presence of from 0.5 to 3.0% by weight of an amine, (a)
40-90% by weight of an epoxy resin composition having an average epoxy functionality of 2.0 epoxide groups and (b) 10% by weight of an olefinically unsaturated carboxylic acid containing carboxylic acid groups;
10-60% by weight of a copolymer which is an addition copolymer of ~85% by weight and 90-15% by weight of at least one olefinic unsaturated comonomer with the carboxylic acid groups in (b).
Water-dispersible ester-grafted epoxy/acrylic polymers are reacted together at elevated temperature with the epoxide groups in (a) in a ratio of 1.5:1 to 20:1 (but in the presence of less than 1 equivalent of amine per equivalent of epoxy). producing a coating composition (the percentages of amine and water are based on the combined weight of epoxy resin (a) and copolymer (b));
There is also provided a method for producing a stably dispersible coating composition, which comprises mixing the water-dispersible coating composition with a base, primarily water in an amount sufficient to form a continuous aqueous phase. The epoxy resin preferably has an aromatic group bonded through an ether bond, and
Those having an average molecular weight of 1500 or more are preferable,
Particularly preferred are those having an average molecular weight of 2,000 to 12,000. Examples of useful epoxy resins include 2,2-bis(4-
Examples include condensed glycidyl ethers of bisphenols such as hydroxyphenyl)propane.
Such epoxy resins include "Epikote 1007" (epoxy functionality approximately 1.4), "Epikote 1009" (epoxy functionality approximately 1.2).
"Dow DER 668", "Dow DER 667"
and sold under the trade name "Dowdell 669". Alternatively, a suitable epoxy resin, such as Epicote 1001, has a relatively low molecular weight of about 2.0
can be prepared by reacting an epoxy resin having a functionality of 1 with a bisphenol, such as bisphenol A. Mixtures of epoxy resins can also be used, for example Epicote
Resins such as 1001 can be used in combination with higher molecular weight resins. High functionality epoxy resins, such as epoxy novolac resins, can be mixed with low functionality epoxy resins such as Epicote 1009 to provide epoxy resin mixtures having an average functionality of 1.0 to 2.0 epoxide groups per molecule. Examples of polymers having carboxylic acid groups include olefinic unsaturated carboxylic acids such as acrylic acid,
Addition polymers of methacrylic acid, maleic acid, itaconic acid or citraconic acid are preferred. Olefinic unsaturated acids are olefinic unsaturated comonomers, such as methyl methacrylate, butyl acrylate, ethyl acrylate, propyl acrylate, propyl methacrylate, butyl methacrylate, hexyl methacrylate, methacrylic acid. At least one of acrylic acid esters such as 2-hydroxypropyl, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, or 2-hydroxypropyl methacrylate; acrylamine methacrylate; styrene; or α-methylstyrene; It is preferable to copolymerize with. Preferably, the copolymer contains 10 to 85% by weight of unsaturated carboxylic acid units;
Particularly preferred are those containing ~60% by weight of unsaturated carboxylic acid units. The ratio of carboxylic acid groups in the polymer having carboxylic acid groups to epoxide groups in the epoxy resin is preferably 2:1 to 10:1. Polymers having carboxylic acid groups can be prepared using organic solvents that are fully or partially miscible with water, such as ether alcohols such as 2-ethoxyethanol, 2-methoxyethanol or 2-butoxyethanol;
Preferably, they are prepared by radical polymerization in alcohols such as ethanol or butanol, and/or esters such as ethyl acetate, butyl acetate or 2-ethoxyethyl acetate. A small amount of an aromatic hydrocarbon such as xylene or toluene could be mixed into the water-miscible organic solvent, which would avoid gelation in the subsequent esterification reaction. The reaction between the epoxy resin and the polymer having carboxylic acid groups is performed using an amine, preferably dimethylaminoethanol, diethylaminoethanol, triethylamine, triethanolamine, dimethylbenzylamine, N-ethylmorpholine or 2-ethylmorpholine.
Preferably it is catalyzed by a tertiary amine such as (N,N-dimethylamino)-2-methylpropanol. The amount of amine present is based on the total weight of the epoxy resin and the polymer with carboxylic acid groups.
It is preferably 0.5 to 3.0%, most preferably 1.0 to 2.0%. Although it is possible to use amines in higher proportions, we have determined that the amines may be used in proportions between 5 and 30%, preferably between 5 and 20%, based on the total weight of the epoxy resin and the polymer with carboxylic acid groups.
Alternatively, it has been found that when the reaction is carried out in the presence of 25% water, it is not necessary to use such a large amount of amine. If the amount of water present is less than 5% by weight, it is necessary to use a high proportion of amine to avoid gelation of the reaction mixture, while if more than 30% by weight water is present, Higher amounts of amine and organic solvent are required to achieve economically desirable reaction rates. The reaction between a polymer having carboxylic acid groups and an epoxy resin involves mixing the epoxy resin with the polymer having carboxylic acid groups, optionally with additional organic solvent, in a water-miscible organic solvent such as those mentioned above. It is preferable to carry out this by mixing with a solution of an acrylic polymer produced by solution polymerization. Preferably, the amine catalyst and water are premixed and added to the dissolved resin. Alternatively, the amine and water can be added to the solution of the carboxyl polymer before mixing the carboxyl polymer with the epoxy resin. The reaction is preferably carried out at a temperature in the range of 80 to 120°C, usually at a temperature of about 95 to 100°C, under reflux. Sufficient reaction time should be ensured for substantially all of the epoxy groups to react, this time being for example 2 to 8 hours. The acid value of the reaction product is preferably in the range of 30 to 100. Since the desired polymer having carboxylic acid groups and the desired epoxy resin will not form a compatible solution, the reaction mixture will be heterogeneous at the beginning of the reaction and will have a cloudy, dispersion appearance. In some cases, the reaction mixture tends to become a homogeneous mixture and clear toward the end of the reaction. After the reaction between the epoxy resin and the polymer having carboxylic acid groups is complete, a base is generally added to the reaction product to at least partially neutralize the excess free carboxylic acid groups. As the base, for example,
Ammonia or amines can be used and are generally added to the reaction mixture in the form of an aqueous solution. Preference is given to using tertiary amines such as, for example, triethylamine, triethanolamine or dimethylaminoethanol. In a preferred procedure, the base is sufficient to convert the coating composition into a stable dispersion with a water-based continuous phase such that it can be further diluted with water without loss of dispersion stability. Add as a dilute solution in a suitable amount of water. Preferably, the base is used in an amount sufficient to neutralize 40-120% or 130% of the free carboxylic acid groups in the reaction product. The smooth white dispersion that forms after addition of base and water can be used directly as a coating composition or further diluted with water to the desired viscosity. If desired, the organic solvent used in the preparation of the coating composition can be completely or partially removed from the composition and recovered.
For example, butanol, ethyl acetate and/or xylene can be removed from the coating composition by azeotropic distillation. The coating composition of this invention is particularly suitable for coating the internal surfaces of food and beverage cans, including fruit juice and beer cans. The coating has excellent adhesion to metals such as tinplate, steel and aluminum, as well as to polymers used in food and beverage can base coatings, and furthermore, the coating composition of the present invention has superior adhesion properties to metals such as tinplate, steel and aluminum. adhere well to each other. The coating composition may contain an aminoplast resin or a phenolic resin, if desired, although generally not required, to provide additional crosslinking to the coating for curing. The aminopsut resin can be added to the coating composition before or after the neutralization and dilution steps. Examples of suitable aminoplast resins include melamine formaldehyde resins, especially those consisting primarily of hexamethoxymethyl melamine. The coating composition is preferably applied to the substrate by spraying, but it can also be applied by dip coating, anionic electrocoating, direct roller coating or reverse roller coating, flow coating or rinse coating. The coating film is heated at 100 to 240℃ to cure it.
It is desirable to heat for 10 seconds to 20 minutes, and the temperature is particularly preferably 150 to 210°C. Next, the present invention will be explained with reference to examples. Example 1 An acrylic prepolymer solution was prepared as follows.

[Table] Compounds (1) and (2) were charged into a reactor equipped with a stirrer, reflux condenser, monomer tank, flow regulator, thermometer and addition funnel. This solvent mixture
Heat to 120° C. and add premixed monomers (compounds 3-5), solvent (7) and peroxide (6) over a period of 2 hours. The temperature of the batch was increased to 120°C during and for 2 hours after the monomer addition.
The batch was then cooled to room temperature. The acrylic solution polymer thus produced contained 36% solids and had an acid value (based on solids) of 254 mg KOH/g. An epoxy/acrylate polymer dispersion was prepared as follows.

[Table] Acrylic prepolymer solution (1) was charged to a reactor equipped with a stirrer, reflux condenser, thermometer and addition funnel. Heat the solution to 110°C, and
An epoxy resin was dissolved in this solution. When all the epoxy resin has dissolved, heat the reaction mixture to 90°C.
and the premixed water and amine (compounds 3 and 4) were added. This mixture is then stirred until the reaction is complete (generally about 4 hours).
It refluxed. The acid value of the polymer was 63 mgKOH/g. The remaining dimethylaminoethanol and deionized water (components 5 and 6) were premixed and heated to 70°C in a stainless steel vessel suitable for dispersing ester grafted epoxy/acrylic polymers. After completing the esterification step, the polymer was discharged into a mixture of water and amine. The dispersion was cooled to room temperature and filtered ready for use. The dispersion has a solids content of 25%, a viscosity of 25-35 seconds by Ford Cup No. 4 method at 25°C, and
The ratio of water to solvent was 80/20. Example 2 An acrylic prepolymer solution was prepared as follows.

【table】

Table: Butanol (compound 1) was charged to a reactor equipped with a stirrer, reflux condenser, monomer tank, flow regulator, thermometer and addition funnel and heated to reflux. Monomers and peroxides (compounds 2-
5) are pre-mixed in a monomer tank, and
Added to reactor over 2 hours. The temperature of the batch was maintained at reflux during the monomer addition and for an additional 2 hours, after which time the batch was cooled and the solids content was adjusted to 20% by addition of butanol (compound 6). The acid value of this acrylic polymer was 469.5 mgKOH/g. An epoxy/acrylate polymer dispersion was prepared as follows.

[Table] Acrylic prepolymer, butanol and ethylene glycol monobutyl ether (components 1 to 3)
was charged to a reactor equipped with a stirrer, reflux condenser, thermometer and addition funnel. Add this mixture to 110
℃ and the epoxy resin was dissolved in the mixture. When all the epoxy resin was dissolved, the mixture was cooled to 90°C and the premixed water and amine (components 5 and 6) were added. The reaction mixture is then heated to reflux until the reaction is complete (generally about 4 hours), thereby
A polymer with an acid value of 70 mg KOH/g was produced. When the acid number reached the above value, the remaining dimethylaminoethanol (7) and a portion of deionized water (8) were added to the polymer solution, followed immediately by the remaining deionized water. This allows the water to solvent ratio to
66/34 to form a dispersion containing 18% solids.
The dispersion can be adjusted to the desired solids content and water/solvent ratio by removing excess solvent by distillation. Comparative Example 1 An acrylic copolymer was produced by the method described in Example 2 from a 20% solids n-butanol solution containing methacrylic acid, styrene, and ethyl acrylate in a weight ratio of 47.6:27.9:24.5. The acid value of the copolymer was 300. An epoxy/acrylic polymer dispersion was prepared as follows.

[Table] Acrylic polymer solution (1) and solvents (2) and (3) were charged into a reactor equipped with a stirrer, reflux condenser and thermometer, then solid epoxy resin (4) was added and dissolved. . Amine catalyst (5) was added and the solution was heated to 115°C. The amount of amine catalyst (5) used is the resin solid content (1)
and (4) corresponded to 1.8%. Gelation of the reaction mixture was observed after 50 minutes, and within a short time thereafter the reaction mixture gelled into a solid mass. This gelled product could not be dissolved in solvents or dispersed in water and therefore could not be used as a coating.

Claims (1)

[Claims] 1. (a) 1.0 to 1.0 per molecule at high temperature in the presence of an amine;
40-90% by weight of an epoxy resin composition having an average epoxy functionality of 2.0 epoxide groups; and (b) an olefinically unsaturated carboxylic acid containing carboxylic acid groups.
10 to 60% by weight of a copolymer which is an addition copolymer of 10 to 85% by weight and 90 to 15% by weight of at least one olefinically unsaturated comonomer with carboxylic acid groups in (b) and epoxides in (a). Ratio with base 1.5:1~20:1
in a water-miscible organic solvent mixture containing 5 to 30 wt. of amine (but less than 1 equivalent of amine per equivalent of epoxy groups) (the percentages of water and amine are based on the combined weight of epoxy resin (a) and copolymer (b)). A method for producing a characteristic water-dispersible paint composition. 2. The method according to claim 1, wherein the reaction is carried out in a water-miscible organic solvent mixture containing 5 to 20% by weight of water based on the total weight of the epoxy resin (a) and the copolymer (b). . 3 The amount of amine present during the reaction
The method according to claim 1 or 2, wherein the amount is 1.0 to 2.0% by weight based on the total weight of (a) and copolymer (b). 4. The method according to any one of claims 1 to 3, wherein the amine is a tertiary amine. 5. A method according to any one of claims 1 to 4, wherein the epoxy resin contains aromatics bonded together by ether bonds and has an average molecular weight of 2000 to 12000. 6 Claim 1 in which the ratio of the carboxylic acid group in (b) to the epoxide group in (a) is from 2:1 to 10:1.
6. The method according to any one of Items 6 to 6. 7 In the presence of 0.5 to 3.0% by weight of amine, 5 to 30
(a) an epoxy resin composition having an average epoxy functionality of from 1.0 to 2.0 epoxide groups per molecule in a water-miscible organic solvent mixture containing % by weight of water;
90% by weight and (b) Copolymers 10 to 10 containing carboxylic acid groups and being addition copolymers of 10 to 85% by weight of olefinically unsaturated carboxylic acids and 90 to 15% by weight of at least one olefinically unsaturated comonomer. 60% by weight
The ratio of the carboxylic acid group in (b) to the epoxide group in (a) is 1.5:1 to 20:1 (however, 1.5:1 to 20:1 per equivalent of epoxy group)
(in the presence of less than an equivalent amount of amine) together at elevated temperature to produce a water-dispersible ester-grafted epoxy/acrylic polymer coating composition (wherein the percentages of amine and water are equal to or less than the epoxy resin (a) and the copolymer). (b)) and the water-dispersible coating composition is mixed with a base, primarily water in an amount sufficient to form a continuous aqueous phase. Production method. 8 Claim 7 in which the base is a tertiary amine
The method described in section. 9. A patent claim in which the amount of base used is sufficient to neutralize 40 to 130% of the free carboxylic acid groups in the reaction product of the epoxy resin composition and the carboxylic acid group-containing copolymer. The method according to item 7 or 8. 10. The method according to any one of claims 7 to 9, wherein the organic solvent used in forming the coating composition is completely or partially removed from the composition. 11. The method of claim 10, wherein the organic solvent is removed from the coating composition by azeotropic distillation.