DE2520927B2 - Aqueous coating composition for the interior painting of metal containers for beverages and process for their production - Google Patents

Description

characterized in that

(A) the copolymer consists of the following units obtained by vinyl polymerization:

(1) 5 to 25% acrylamide or methacrylamide units of the structure ^: "

R-C-C-NH-CH.-OR
C.

in which R 'is a methyl radical or hydrogen and R is hydrogen or a butyl radical and 50 to 100% of the radicals R are butyl radicals.

(2) 3 to 25% acrylic acid units,

(3) 5 to 75% styrene units and ³ ">

(4) 5 to 75% ethyl acrylate units,

(B) the copolymer in the presence of a catalyst and in the absence of a mercaptan has been made

Is (C) the copolymer by partial neutralization ^{4 (Sieren l} with such an amount of an amine solubilized that no more 0.764 milliequivalents of salt are to be present per gram of resin solids, and

(D) the coating composition of 5 to 60% by weight of the ⁴ 'partially neutralized copolymer and 40 to 95% by weight of a liquid medium of 60 to 100% by weight of water and 40 to 0% by weight of one in water soluble or water-miscible organic solvent.

?. Coating composition according to Claim 1, characterized in that that used for neutralizing Amine is dimethylethanolamine or mono- r> ethanolamine.

3. Coating composition according to claim 1 or 2, characterized in that the copolymer contains 10 to 15% acrylamide or methacrylamide in the form of the units of the specified structure, 5 to 15% _b n acrylic acid units and 40 to 60% styrene units and 20 to 50% ethyl acrylate units .

4. Coating composition according to claim 3, characterized in that the amide is N-butoxymethylacrylamide is. Hi

5. A method for producing a water-containing coating composition according to claim I, characterized through the following stages:

(A) Polymerize a monomer mixture that is an amide of the structure

R 'O
H ₂ C = C-C-NH-CH, -OR

where R 'is a methyl radical or hydrogen, R is hydrogen or a butyl radical and 50 to 100% of the residues R are butyl residues. Contains acrylic acid, styrene and ethyl acrylate in one Mixture of water-soluble or water-miscible organic solvents, wherein the solvent mixture consists of an ether alcohol from the group of Ethylene glycol monoethyl ether and ethylene glycol monobutyl ether and a lower alkanol from the group of ethanol, propanol, Isopropanol and butanol consists in the presence of a polymerization catalyst with formation of the copolymer in solution,

(B) removing part of the solvent by distillation,

(C) adding an amine to the copolymer solution,

(D) adding water with stirring to the copolymer solution, so that a dispersion of the copolymer is formed, and

(E) aging the dispersion by heating to 70 to 9O ⁰ C with stirring until the viscosity of the dispersion has become substantially constant.

6. The method according to claim 5, characterized in that the water added in step (D) is deionized water preheated ^{to a temperature of 50 to 99 0 C.}

7. The method according to claim 5, characterized in that the mixture of the with water Miscible solvent is a mixture of isopropanol and ethylene glycol monobutyl ether or Ethylene glycol mono is ethyl ether.

8. The method according to claim 5, characterized in that the amine added in stage (C) Is dimethylethanolamine or monoethanolamine.

Beverages, such as beer, carbonated and non-carbonated drinks, and fruit juices, are often used in Metal containers, for example made of aluminum, untinned Steel or tinned steel, packed. Many of these beverages are corrosive the metal off, so as to protect the container and avoid contaminating the packaged Material a hygienically perfect coating can be applied to the inner surface of the container got to. The use of such coatings is associated with some problems, with particular ones Difficulties in the cloudiness and in the change in taste of the beverage can be seen.

Since vinyl polymers based on vinyl chloride are relatively tasteless, they are on a large scale has been used for the interior painting of containers for beverages. The vinyl polymers have that Disadvantage that they are made from solutions in volatile organic compounds

Solvents with a relatively low solids content can be applied, causing either significant air pollution or a expensive facility for recovering the solvent vapors is required.

More recently, efforts have been increasing to keep the environment as free from pollution as possible. This results in the desire to also get on this area to use water-based coating compounds for the interior painting of beverage containers. Under "water-containing" or "on an aqueous basis" is meant here a solvent that predominantly consists of Water exists. This reduces the handling of the coating compositions and the emission of fumes from organic solvents significantly reduced. The known topping compositions are water-based but not satisfactory for this purpose. It turns out that they lead to cloudiness of the drinks and also change the taste of the drinks in an undesirable way.

The following combination is used for coating compounds for the interior painting of metal containers for beverages Desired for properties that have not previously been achieved by water-based coating compounds:

2 j (A) Properties of the cured paint

(1) Adhesion to the metal

It has excellent adhesion to metals including aluminum, untinned steel, and w tinned steel is desirable. This property enables the coating compound to be applied in one stroke or as a base line and / or as a back line in a two-line system.

(2) taste characteristics

The taste properties should be at least as good as the best "taste-free" Vinyl polymers that are applied from solutions in solvents and are used extensively for containers be used.

(3) Haze resistance

After packaging, pasteurization and storage, the drinks should not become cloudy or in otherwise adversely affect their appearance.

(4) Machining properties

Machining properties include a combination of flexibility, ductility and adhesion understood, which allows the shaping operations of the painted metal without cracks or other Damage to the continuous paint film occurs.

(5) Pasteurization resistance

Beer is generally pasteurized at a temperature of 60 ° C for 15 to 40 minutes. Occasionally higher temperatures of around 71 to 82 ° C are also reached during pasteurization. Among these no The paintwork should be resistant to conditions.

(6) Low curing temperature

The hardening temperature of the coating mass should not be very high, as some containers with imprints t> 5 that discolor and become unsightly at higher temperatures. Also be with some containers adhesives udei BiuuciViiüe! which are damaged by hardening at higher temperatures.

(7) Extractability

There should be no unwanted materials out of the paintwork during processing and storage extracted.

(8) Liability to other coatings

To enable use as a base line or, if necessary, to repair errors or additional To be able to apply strokes, the coating should be used with itself and with others, usually for The materials used for coatings adhere well.

(B) Properties of the uncured
composition

(1) Application properties

Application should be possible using standard methods and facilities. So it should be possible to apply the composition by dipping, roller coating, spraying, and the like.

(2) Shelf Life

The coating composition must be in a physical form that allows handling and storage made possible under changing conditions. Water-based compositions are in emulsion form for example usually not stable in storage unless additives are added, which in general are undesirable in coatings for beverages and other foodstuffs.

For exterior painting and, to a certain extent, interior painting of containers amide-containing copolymers have already been proposed, compare, for example, US Pat. No. 2,870,117 and 3117 693 and CA-PS 7 66 103. In none of these patent documents are coating compounds on water-based base for hygienically perfect paintwork.

In US-PS 30 07 887 copolymers of (meth) acrylic acid-N-methylol (meth) acrylamide, acrylic esters and methacrylic esters and aqueous solutions of such copolymers are described, and also it is mentioned that these copolymers are also used as coating compositions for containers for beverages can be. These copolymers do not contain any polymerized styrene or their methylol groups are in a free state.

CA-PS 7 66 103 relates to containers for beverages and food with an interior coating. These Interior painting should consist of a mercaptan-free coating compound essentially from a copolymer of an ethylenically unsaturated carboxamide. a vinyl aromatic monomer or an alkyl ester an ethylenically unsaturated carboxylic acid, optionally an ethylenically unsaturated carboxylic acid and optionally an ethylenically unsaturated nitrile. The amido groups of the copolymer should at least partially reacted with formaldehyde and alkoxy with a monohydric alcohol be lured. These copolymers are produced and used in organic solvents and the polymerized acidic monomer is in the form of the free acid.

These known coating compositions also do not meet the requirements

of beverage containers in terms of taste and hygiene with regard to the durability of the Coating compounds and the adhesion to the metal substrate are provided.

This invention is therefore based on the object to provide an improved water-containing coating composition for Interior painting of metal containers for beverages and a process for their production are available too place.

According to the invention, this object is achieved by an aqueous coating composition for interior painting of metal containers for beverages based on a copolymer partially neutralized by an amine the end

(1) an acrylamide or methacrylamide derivative.

(2) an ethylenically unsaturated carboxylic acid,

(3) a curing ethylenically unsaturated monomer and

(4) a plasticizing ethylenically unsaturated monomer,

this coating composition being characterized in that

(A) the copolymer consists of the following units bc obtained by vinyl polymerization:
(1) 5 to 25% acrylamide or methacrylamide units of the structure

O
R '- C - C - NH - CH ₂ --OR

in which R 'is a methyl radical or hydrogen and R is hydrogen or a butyl radical and 50 to 100% of the residues R are butyl residues.

(2) 3 to 25% acrylic acid units.

(3) 5 to 75% styrene units and j-,

(4) 5 to 75% ethyl acrylate units.

(B) the copolymer in the presence of a catalyst and has been produced in the absence of a mercaptan,

(C) the copolymer by partial neutralization -> o ren has been solubilized with such an amount of an amine. that no more than 0.764 Milliequivalents of salt are present per gram of rosin solids and

(D) the coating composition from 5 to 60% by weight of the partial neutralized copolymer and 40 to 95 wt .-% of a liquid medium from 60 to 100 % By weight of water and 40 to 0% by weight of a water-soluble or water-miscible one organic solvent. t> o

Such a coating mass meets all of the above requirements for a hygienic and interior coating of beverage containers with perfect taste, b)

The invention is also directed to a method for Production of such a water-containing coating mass, which is characterized by the following stages:

(A) Polymerize a monomer mixture that is an amide of the structure

R 'O

I il

H ₂ C = CC-NH-CH ₂ -OR

where R 'is a methyl radical or hydrogen, R is hydrogen or a butyl radical and 50 to 100% the radicals R are butyl radicals. Contains acrylic acid, styrene and ethyl acrylate in a mixture of in Water-soluble or water-miscible organic solvents, the solvent mixture from an ether alcohol from the group of ethylene glycol monoethyl ether and Ethylene glycol monobutyl ether and a lower alkanol from the group of ethanol, propanol. Isopropanol and butanol consists, in the presence of a Polymerisationskaiaiysators with formation of the copolymer in solution,

(B) removing part of the solvent by distillation,

(C) Adding an amine to the copolymer solution.

(D) adding water with stirring to the copolymer solution, so that a dispersion of the copolymer is formed and

(E) Aging the dispersion by heating to 70 to 90 ^° C. with stirring until the viscosity of the dispersion has become essentially constant.

The amide units from which the copolymers used in the invention are built up are conductive differs from acrylamide or methacrylamide. The preferred amide is N-butoxymethylacrylamide. It Mixtures of N- (butoxymethyl) acrylamide and N-methylolacrylamide can also be used. These substituted amides can be prepared by various methods. A preferred method consists in the reaction of an acrylamide with formaldehyde and butanol under acidic conditions and in the presence of a polymerization inhibitor. This procedure is detailed in U.S. Patent 3Q 79 434. The resulting N- (butoxymethyl) acrylamide is then mixed with the other monomers copolymerized.

In the method outlined above, the substituted amide units of the copolymer are first separately and prepared prior to interpolymerization with the other monomers. Alternatively you can the substituted amide units "in situ" or afterwards after the formation of the copolymer be generated. So you can first copolymerize the acrylamide with the other monomers and then react the product obtained with an aldehyde, for example formaldehyde and butanol. This method is described in detail in US Pat. No. 3,037,963. The method of operation has the disadvantage that excess Formaldehyde, which has an unpleasant odor, must be removed. In addition, the degree of etherification is the Methylol groups more difficult to control in this process. However, preference should be given in the specified Formula all of the nearly all R-residues be butylrecte.

It thus follows that the acrylamide or the methacrylamide in the copolymer with at least 50% butoxymethyl groups are present, the introduction of the Buiöxymcinylsubsüiuenicr

vcdcr

takes place as part of the amide starting material or by reacting the polymerized amide with formaldehyde and butanol. It is customary to indicate the proportion of the amide in these copolymers with reference to the unsubstituted amide, that is to say acrylamide or methacrylamide. This occurs because the butoxymethyl group can be present or absent in the monomer mixture used for the preparation of the copolymer. If present, it can also have a different molecular weight depending on the particular residue contained. In addition, these residues are split off when the copolymer coating cures and are essentially lost. It is therefore indicated in the description of this invention in the ₅ description and in the claims, the content of the amide in the manner described. For example, a copolymer which is stated to contain 10% acrylamide can be obtained from a monomer mixture which itself contains 10% acrylamide. The copolymer is later reacted with formaldehyde and an alkanol. The same copolymer can be formed by polymerizing a monomer mixture containing N- (butoxymethyl) acrylamide. This monomer is present in such an amount that the copolymer has an acrylamide molecule fraction of 10% without the butoxymethyl group. In the latter case, such a component is referred to as "acrylamide as NBMA" in the examples.

The copolymers in the coating compositions according to the invention preferably contain 10 to 15% Acrylamide or methacrylamide.

For similar reasons, the content of the partially neutralized copolymers is calculated on the basis of the copolymers with unsubstituted amide groups, that is, those without the butoxymethyl substituent. The calculated values largely correspond to the experimental values, based on the content of non-volatile solids of the copolymer, as obtained by allowing it heated two hours 15O ⁰ C. This simulates the loss that occurs when the butoxymethyl groups are split off during curing.

The units of the copolymer derived from ethylenically unsaturated carboxylic acids are retained best when using acrylic acid or methacrylic acid as acidic monomers. But it can also use itaconic acid, crotonic acid and maleic acid and half esters of maleic and fumaric acid. In the Half-ester is one of the carboxyl groups esterified with an alcohol, with the identity of the alcohol is not essential as long as this does not hinder the polymerization and the desired application does not disrupts Typical examples are butyl hydrogen maleate and ethyl hydrogen fumarate.

Contain the copolymers in the top coat 3 to 25% of such acidic units. The best results in terms of hardenability and Ease of solubilization is obtained with mixed eo polymers which contain 5 to 15% acidic units. In some cases the copolymers contain more acid than is normally used to solubilize the Product is required Often this is desirable in order to achieve satisfactory hardenability of the copolymer to reach.

The other units of the copolymer are derived from a combination of hardening and plasticizing monomers to obtain the desired combination of properties. That curing monomers is styrene. The copolymers contain 5 to 75 styrene units. with a salary of 40 to 60% of such units is preferred.

The copolymers contain ethyl acrylate in an amount of 5 as a plasticizing monomer up to about 75%, with 20 to 50% of such units being preferred.

Ih the coating composition according to the invention are 5 to about 60 wt .-%, preferably 15 to 40 wt .-%, Copolymer present and the remainder consists of the liquid medium.

The copolymer is made by polymerization in the presence of a catalyst for vinyl polymerization manufactured. Preferred catalysts are azo compounds, such as alpha, alpha'-azobis (isobutyric acid nitrile). Other suitable catalysts are tert-butyl perbenzoate, tert-butyl pivalate, isopropyl percarbonate and similar connections. In some cases, other free radical forming catalysts such as Benzoyl peroxide and cumene hydroperoxide can be used.

As already stated, the polymerization is carried out in the absence of a mercaptan. This is an important measure, since in practice usually small amounts, for example 1 to 3%, mercaptan as a chain transfer agent for the production of amide copolymers of the desired type were used. It was found, however, that the presence of this little one too Mercaptan quantities, the copolymers for use in paints for beer containers or Makes containers unsuitable for similar beverages. When a mercaptan is present in the paint is, the coating gives the drink, especially when stored for several weeks, a unwanted taste. Since packaged beverages can usually be stored for longer periods of time, will this ruled out the use of such copolymers for interior paints.

The coating compositions according to the invention are in the form of dispersions of the copolymers characterized above in a liquid medium. The liquid medium can in some cases consist entirely of water consist, but usually consists of a mixture of a larger proportion of water and one smaller proportion of a water-soluble or water-miscible organic solvent. Suitable organic solvents are ether alcohols, such as ethylene glycol monobutyl ether and ethylene glycol monoethyl ether, lower alkenols with 2 to 4 carbon atoms, such as ethanol, propanol, isopropanol, butanol and like that. Smaller amounts of hydrocarbon solvents can also be present in the liquid medium may be present such as xylene, toluene and the like. Mixtures of solvents of the type can also be used Use ether alcohols and lower alkanols. The preferred water-soluble or water-based Miscible organic solvents are mixtures of ethylene glycol monobutyl ether and isopropyl alcohol. The liquid medium of the paint composition according to the invention contains 60 to 100% by weight, preferably 80 Wt .-% water and 0 to 40 wt .-%, preferably 20 wt .-% of a water-soluble or with water miscible organic solvent. The water can be plain tap water, but is preferred Deionized or distilled water is used

Based on the total weight of the paint, the composition can contain 40 to 95% by weight, preferably contain 60 to 85 wt .-% of the liquid medium.

The copolymer used in the invention is made dispersible by adding an amine as a solubilizing agent. It is known per se that copolymers containing acid groups can be made soluble or dispersible in water by neutralization or partial neutralization with an amine. In general, the low molecular weight amines known for this purpose are used for this purpose, including ammonia, ethylamine, butylamine, dimethylamine, cyclohexylamine, morpholine, monoäinanoiamine. Diethanolamine, Diäihyiäihanoiamin \ i and the like. The preferred amines are monoethanolamine and dimethylethanolamine, with dimethylethanolamine being particularly preferred because it gives the best results. Although amines can be used in general, it is useful to consider certain considerations in neutralizing a particular system. For example, some amines are more effective in achieving stable compositions depending on the degree of neutralization of the interpolymer.

The term »degree of neutralization« refers on the proportion of the acid neutralized with the amine in the copolymer. For example, if 20% of the theoretical amount of acid of the copolymer have been neutralized by the amine, is the Degree of neutralization at 20% of the theoretical neutralization. When 30% of the theoretical amount of acid have been neutralized, the degree of neutralization is 30% of the theoretical neutralization. In all Cases, the degree of neutralization and the amount of amine used is sufficient to ensure a stable To give a composition, which is understood to mean a composition that is not in separates different phases. This stability of the composition is intended to be maintained during storage stay. If one aims to achieve this with a relatively low degree of neutralization, that is, below about 30%, should be the preferred amines, that is, dimethylethanolamine and monoethanolamine can be used. At higher degrees of neutralization, i.e. 30% or higher, are other amines effective. For example, diethylethanolamine can be used at 30% of the theoretical neutralization with good results and with 50% of the theoretical neutralization almost all of those mentioned Use amines with good results.

The amount of amine used in the coating compositions according to the invention has an influence on the Dispersibility of the copolymer. This amount is particularly important when the degree of neutralization is low Copolymer is essential for achieving a stable composition.

The amount of amine used can in some cases be so low that they are 0.180 milliequivalents of salt per Equivalent to grams of resin solids. Usually, however, the amount of amine is so large that it is at least 0.200 Corresponds to milliequivalents of salt per gram of resin solids. The expression "milliequivalents of salt per Grams of Resin Solids "refers to the number of acid milli-equivalents per gram of resin solids Copolymers which have been neutralized with a base, that is to say with an amine. The number of Milliequivalents of salt per gram of resin solids can be calculated using the following formula

Weight of acid content x 10
Equivalent weight of acid

XN = milliequivalents of salt per gram of Hafz solids

In this formula, N denotes the degree of neutralization. A degree of neutralization greater than 100% indicates that an excess of base has been used. In in such a case the value of 100% in the above formula is used. The compositions of the invention contain at least 0.200 milliequivalents of salt per gram of resin solids.

The upper limit for the amount of amine used is less important and depends largely on the mode of use. For example, if the composition is to be brush, roller, or dipping applied, the amine can be used in an amount such that there are amounts as large as 3.47 milliequivalents of salt per gram of resin solids. Even in these methods of application, however, it is preferred that the amine used do not exceed an amount which will give 1.910 milliequivalents of salt per gram of resin solids, however, if the composition is to be applied by spray, the amount of bo amine used should usually not exceed 0.764 milliequivalents of salt per gram Resin solids, although in some cases the amount of amine can make up to 1.40 milliequivalents of salt per gram of resin solids.

In the production of the coating compositions by the process according to the invention, the period of time depends on the aging under heating, that is, stage (E), of some factors such as the composition of the Copolymer, the solids content of the composition, the initial viscosity of the copolymer formed and the stirring speed. In general, this period varies between one Hour or even less up to about 11 hours.

In a preferred method, the monomers are used in an excess of a solvent mixture polymerized, which consists essentially of ethylene glycol monobutyl ether and isopropanol, wherein the excess solvent is essentially isopropanol. The polymerization takes place under Use of an azo catalyst. Then the excess solvent is from the resulting polymer solution, which consists essentially of isopropanol, by distillation at atmospheric or depressed pressure or both. The amine is then added to the copolymer solution Deionized water is then added to the solution at a temperature between 50 and 99 ° C Stirring is added, a dispersion of the copolymer being formed. Finally, the copolymer dispersion is added aged by heating

This preferred embodiment for the production of the water-containing coating compositions according to the invention has a number of advantages. First, it is advantageous that the two solvents so far boiling points that differ from one another (ethylene glycol

col monobutyl ether 171.2 ° C, isopropanol 82.4 ° C). This large difference in boiling points enables the isopropanol to be easily removed from the mixture, for example by distillation. For example, if, as in the present case, an excess of solvent is desirable in the polymerization process, this excess consists essentially of isopropanol, since the isopropanol can be easily removed afterwards so that the paint has the desired solvent content. In addition, the isopropanol in the solvent mixture acts as a chain transfer agent and thereby controls the molecular weight of the copolymer in this system. This eliminates the need to use an external or added rate transfer agent, η such as mercaptan, which is commonly used for this purpose . Finally, the addition of hot water to the solution of the mixed polymer is advantageous, since this facilitates the formation of the dispersion of the mixed polymer and enables the desired viscosity of the coating composition to be reached more quickly.

The processes outlined above are aimed at the production of preferred water-containing coating compositions in which part of the organic solvent which was originally used in the production of the copolymer remains in the finished coating composition. As has already been stated, however, water-containing coating compounds in which the liquid medium consists entirely of water can also be used in the invention. Such jo compositions can be prepared using the previously characterized method steps, by still adjoins the step (E), a further stage one can, for example, the organic solvent remaining J5 reduction after step (E) in the cooperation, by remove various working methods, such as by distillation or liquid chromatography.

The water-based or water-based coating compositions according to the invention can be applied by customary application methods, such as brushing, dipping, with a roller, spraying and the like, with special methods such as those previously used for painting containers were used. The exact formulation of the coating composition, for example total solids content and viscosity, depends in the individual case on the type of application and the determination of the individual factors presents no difficulties for the person skilled in the art.

After application , the coating compositions are dried and cured by heating to elevated temperatures, producing a hard, crosslinked film. The curing conditions depend on the nature of the particular composition, the nature of the substrate and the use. In general, the hydrous coating compositions of the invention can be cured using the conditions and equipment conventional in the container industry. Typical curing conditions use temperatures ranging from about 150 to about 215 ° C and times from 2 to about 15 minutes.

The invention is explained in more detail in the following examples. All data relating to parts and percentages are weight data, unless expressly stated something else is indicated. The solids contents in the examples were at 105 ° C as a test for the Quality control carried out

example 1

This example explains the production of a water-containing coating composition according to the invention.

In a reactor equipped with a reflux condenser. Heating devices, stirrer, thermometer and a device for introducing nitrogen were equipped, 159.0 grams of ethylene glycol monoethyl ether, 325.0 grams of isopropanol and 290 grams of a monomer mixture of 5.9% glacial acrylic acid, 28.2% of a 61.5% solution of N- (butoxymethyl) acrylamide (NBMA) in a 1: 3 solvent mixture of toluene and butanol, 32.1% styrene, 32.5% ethyl acrylate and 1.3% alpha, alpha'-azobis (isobutyronitrile). Based on monomer solids, the monomer formulation contained 10% acrylamide as NBMA, 41% styrene, 41.5% ethyl acrylate and 7.5% acrylic acid. The batch mixture was then heated under nitrogen to reflux temperature (about 90 to 93 ⁰ C) over the course of about 45 minutes. After reflux began, an additional 1081 grams of the above monomer mixture was added to the reactor over about 3 hours. Then 12.0 grams of p-butyl perbenzoate was added in three equal portions of 4 grams each over the course of about 6 hours, one portion being added every 2 hours. At the end of this 6 hour period, 337 grams of solvent (slightly more than the amount of isopropanol originally used) were driven off from the resulting solution of interpolymer by distillation at atmospheric pressure at a temperature of about 94 ° C over about 75 minutes. At this point, a sample of the reaction mixture was examined for its total solids content and it was found that the solids content found at 150 ° C. was 73% by weight. 49.8 grams (50% of the theoretical neutralization) of dimethylethanolamine were then added to the reaction mixture, the mixture having a temperature of 97.degree. After the addition of the dimethylethanoiamine was complete, 1939 grams of deionized water were preheated to 75 ° C. and then added to the reaction mixture with stirring. After this addition was complete, stirring was continued for an hour.

The aqueous-based paint obtained is an all-in-one dispersion of the copolymer liquid medium with the following characteristics:

Mixed polymer Mixed polymer
units
(%) Acrylamide as NBMA *)
Styrene
Ethyl acrylate
Ice acrylic acid 10.0
41.0
41.5
7.5 Liquid medium Weight percent Deionized water
Organic solvents **) 83.8
16.2

*) N-i-butoxymethyl / acrylamide.

*) A mixture of ethylene glycol monoethyl ether, isopropanol, Toluene and butanol.

Other properties of the paint were like

follows:

Polymer solids content:

Liquid medium:
Viscosity:

Acid number:

Milliequivalent salt per
Grams of resin solids:
Resistance:

33.4% by weight of the total mass

65.6% by weight of the total mass

14OmPa s, Brookfield viscosity at 25 ° C, spindle no. 4 at 20 rpm
16.1

0.521
Well

Liquid medium *):
Viscosity:

Acid number:

Milliequivalents of salt per
Grams of resin solids:
Resistance:

mixture added. After this addition, 5085 grams of deionized water was preheated to 75 ° C and the reaction mixture, as in Example 1, fed.

The aqueous-based coating composition obtained had the following formulation:

Mixed polymer

The composition was coated on a metal substrate and cured for two minutes at about 19O ⁰ C. A smooth, hard and durable film was obtained.

Example 2

In this example, Example 1 was repeated except that the one used for neutralization Amount of dimethylethanolamine was reduced by 40% (to 30% of the theoretical neutralization) and the Amount of isopropanol was increased by 10% to adjust the viscosity. The finished composition had the following properties:

Polymer solids:

35% by weight of the total mass

65% by weight of the total mass

100 mPa s, Brookfield viscosity at 25 ° C, No. 4 spindle at 20 rpm
17.43

0.314
Well

*) 85 wt .-% deionized water and
15% by weight of organic solvents

After mounting on a metal substrate and baking for 2 minutes at about 190 ^° C., a smooth, hard and permanent film was obtained.

Example 3

In this example the production of a preferred water-containing coating composition explained, in their production as ether alcohol ethylene glycol monobutyl ether is used.

In the reactor of Example 1 were 477 grams of ethylene glycol monobutyl ether, 975 grams of isopropanol and 870 grams of the monomer mixture of Example 1, but without the alpha, alpha'-azobis (isobutyronitrile). The mixture was heated to reflux temperature as in Example 1 under nitrogen The start of reflux was an additional 3189 grams of the monomer mixture from Example 1 and 54 grams aIpha, aIpha'-azobis (isobutyronitrile) was introduced into the reactor over 3 hours as in Example 1 Thereafter, 12.0 grams of t-butyl perbenzoate, as in Example 1 added. Then 981 grams of organic solvent were added by distillation atmospheric pressure and at temperatures between about 95 and about 120 ° C. Afterward were 89.4 grams (30% of the theoretical neutralization) of dimethylethanolamine to the reaction wt .-% Total residuals = 38.5

Mixed polymer units (%)

Acrylamide as NBMA
.. styrene

Ethyl acrylic
Ice acrylic acid

10.0

41.0

41.5

7.5

Liquid medium

Wt% total liquid = 61.5

Wt%

Deionized water 83.5

Organic solvents *) 16.5

*) Consists of ethylene glycol monobutyl ether, isopropanol, Toluene and butanol.

jo The composition had the following properties:

Total solids:

Acid number:

Viscosity:

Milliequivalents of salt per
Grams of resin solids:
Resistance:

38.5%
17.7

300 mPa s, Brookfield viscosity at 25 ° C, No. 4 spindle at 20 rpm

0.313
Well

One applied to a metal substrate in the same way as the previous examples cured film was smooth, hard, and durable.

Example 4

In this example a water-based coating composition was used prepared in the same way as in Example 3, with the exception that additional Ethylene glycol monobutyl ether was used to reduce the organic solvent content of the composition to increase. The mass had the following formulation:

total weight Copolymer of Example 3 37.5% Liquid medium 62.5% Weight percent Deionized water 79.5 Organic solvents 20.5 The crowd had the following Characteristics: Total solids: 37.5% Viscosity: 16.5 seconds, No. 4 Ford mug Acid number: 18.6 Milliequivalents of salt per Grams of resin solids 0.313 resistance Well

The topcoat produced after application to a metal substrate and after baking, as in the Examples 1 to 3, a flat, hard and durable one Movie.

Examples 5 to 8

These examples illustrate the influence of the degree of neutralization, i.e. the milliequivalents of salt per Grams of solids, on the stability of the water-hooked Coating compositions according to the invention.

The compositions were made in essentially the same manner and using the same Copolymer, as in Examples 3 and 4, prepared, with the exception that the amount of

Dimethylethanolamine used was such that the degree of neutralization of the copolymer 3O ¹ VO of the theoretical neutralization (in Example 5, 25% of the TN in Example 6.20% of the TN in Example 7 and 15% of the TN in Example 8). Since the low degrees of neutralization resulted in high viscosities of the compositions, Examples 6 to 8, the solids content of these compositions was reduced by adding additional solvent in the form of an 80/20 mixture of deionized water and ethylene glycol monobutyl ether. The compositions obtained had the following formulations and properties:

example 6th 7th 8th C. Mixed polymer % theoretical neutralization 25th 20th 15th Total solids (wt%) 30th 33.1 18.0 25th Total liquid medium (% by weight) 36.4 66.9 82.0 75 Viscosity, No. 4 Ford Cup, seconds at 63.6 31 25th - 25 C 26th Acid number 19.4 12.9 12.1 Milliequivalents of salt per gram 18.6 0.261 0.208 0.156 Resin solids 0.312 resistance Well moderate, bad. Well easy; separation Drop in two phases

As can be seen from these examples, the stability of the composition depends on the degree of neutralization and consequently on the amount of salt per gram of resin solids.

The preceding examples were made using monoethanolamine in place of dimethylethanolamine repeated with similar durability.

Example 9

This example illustrates a water-based coating composition according to the invention, which at low Hardens temperatures.

The coating composition was produced essentially in the same way as in Examples 1 to 8, with the exception that the Monomeran_satz 10% acrylamide as NBMA, 10% acrylic acid, 30% ethyl acrylate and contained 50% styrene. The solvent was driven off under reduced pressure and the degree of neutralization of the acid groups in the copolymer was 27% of the TN. The received Composition was the following formulation and properties:

Mixed polymer
(as stated):
Liquid medium *):
Viscosity:

35 wt%
65% by weight

340 mPa s, Brookfield viscosity at 25 ° C, No. 4 spindle at 20 rpm

*) 82.3% by weight of deionized water and 17.7% by weight organic solvents consisting of ethylene glycol monobuiyiüther, isopropanol, sutane! and xylene.

Acid number: 25.3
Milliequivalents of salt per

Grams of resin solids: 0.375

Persistence: good

A coating of this composition on a metal substrate gave after curing at 160 ° C for 4 Minutes a smooth, hard and lasting film.

As already indicated, the compositions according to the invention are particularly useful as coating compositions suitable for the hygienically perfect interior painting of liquid containers. Such containers are subjected to a series of tests. These checks are made both before and after after filling the containers with beverages, for example beer. When such a container is filled with beer and sealed, the beer is subjected to pasteurization and other normal processing operations. After storage, the containers are opened and both the beer and the paintwork examined. The more important tests for hygienically perfect coating compounds for beverage containers are listed below:

(a) Adhesion to the metal

(b) turbidity

(c) Extractability

(d) taste and

(e) Pasteurization Resistance

In the following Examples 10 to 13, samples of the water-containing coating compositions of Examples 1, 2, 4 and 9 were used for the interior coating of beer containers. These containers were then subjected to the above tests and the results are in · f «-tJrTf» nH ^ r) To Hi * Π Ρ βΠί

030 133/178

17th 25 20 927 18th 12th 13th Examples
10 11th Example 4 Example 9 Formulation of Example 1 Example 2 P.
P.
P.
P.
P. P.
P.
P.
P.
P. Test and result
Adhesion to the metal
Gloom
Extractability
taste
Pasteurization resistance P.
P.
P.
P.
P. P.
P.
P.
P.
P. ρ = positive result.

As can be seen from the table, all the tests from Example 1 passed, but 2.5% tested compositions all tests. Contained mercaptoethanol as a chain transfer agent,

A composition which failed that of Formulation 20 in the taste test

Claims (1)

Patent claims: 1. Aqueous coating compound for the interior painting of metal containers for beverages based on -, a copolymer partially neutralized by an amine (1) an acrylamide or methacrylamide derivative, (2) an ethylenically unsaturated carboxylic acid, (3) a curing ethylenically unsaturated * monomer and (4) a plasticizing ethylenically unsaturated monomer,