DE2520927A1 - WATER BASED COATING COMPOUND FOR THE INTERIOR PAINTING OF METAL CONTAINERS FOR BEVERAGES - Google Patents

Description

Dr. Michael Hann F / W (789)

Patent attorney
63 casting
Ludwigstrasse 67

PPG Industries, Inc., Pittsburgh, Pa., USA

WATER-BASED COATING COMPOUNDS FOR THE INTERIOR PAINTING OF METAL CONTAINERS FOR BEVERAGES

Priorities: May 16, 1974 / USA / Ser. No. 470 Aug 5, 1974 / USA / Ser. No. 494

Beverages such as beer, non-carbonated and non-carbonated beverages, and fruit juices are often packaged in metal containers made from aluminum, untinned steel, or tin-plated steel, for example. Many of these beverages have a corrosive effect on the metal, so that a hygienically sound coating must be applied to the inner surface of the container in order to protect the container and to avoid contamination of the packaged material. The use of such coatings is associated with some problems, with particular difficulties being seen in the cloudiness and in the change in taste of the beverage.

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Because vinyl polymers based on vinyl chloride are relatively tasteless, they are by and large Scope has been used for the interior painting of containers for beverages. The vinyl polymers have but the disadvantage that it is made from solutions in volatile organic solvents with a relatively low solids can be applied, causing either significant air pollution occurs or a complex device for the recovery of the solvent vapors is required.

More recently, efforts have increased to keep the environment as free from pollution as possible. This results in the desire to use water-containing coating compounds for the interior painting of beverage containers in this area as well. “Water-containing” or “on an aqueous basis” is understood here to mean a solvent that predominantly consists of water. This significantly reduces the handling of the coating compounds and the emission of vapors from organic solvents. However, the known aqueous-based coating compositions are unsatisfactory for this purpose. It turns out that they lead to clouding of the drinks and also change the taste of the drinks in an undesirable way.

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The following combination of Desired properties that were previously not achieved by water-based coating compounds:

(A) Properties of the cured paint (1) Adhesion to the metal

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

(2) taste characteristics

The taste properties should be at least as good as the best "tasteless" vinyl polymers, which are excited from solutions in solvents and used extensively for containers will.

(3) Haze resistance

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

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(4) Machining properties

The processing properties are understood as a combination of flexibility, ductility and adhesion, which enables the shaping processes of the painted metal without causing cracks or other damage of the continuous paint film occur.

(5) Pasteurization resistance

Beer is generally pasteurized at a temperature of 60 C for 15 to 40 minutes. Occasionally be higher temperatures of around 71 to 82 ° C are also reached during pasteurization. Under these conditions the paint should be resistant.

(6) Low curing temperature

The curing temperature of the coating composition should not be very high, as some containers have prints that can be used at higher temperatures discolor and become unsightly. In addition, some containers use adhesives or binders which are damaged by hardening at higher temperatures.

(7) Extractability

No unwanted materials should be extracted from the paintwork during processing and storage.

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(8) Adhesion 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 work with itself and with others, usually materials used for coatings adhere well.

(B) Properties of the uncured composition (1) Application properties

Application should be possible using standard methods and facilities. Thus, the composition should be applied by dipping, with the roller, spraying and the like.

(2) Shelf Life

The coating composition must be in a physical form that enables handling and storage under changing conditions. Compositions on aqueous basis in emulsion form are not stable in storage, for example, in general, if not additives are added which are generally undesirable in coatings for beverage and other food products.

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For the exterior painting and to a certain extent also the interior painting of containers amide-containing copolymers have already been proposed, compare, for example, US-PSS 2,870,117 and US Pat 3 117 693 and CA-PS 766 103. In none of these patents, however, are coating compositions on aqueous The basis for hygienically perfect paintwork is described.

This invention is therefore based on the tasks an improved water-based coating compound for the interior painting of metal containers for beverages to provide.

According to the invention, this object is achieved by a Dissolved aqueous coating composition, which essentially consists of:

(A) about 5 to about 60 weight percent of an amine neutralized or partially neutralized Copolymer, which in the presence of a catalyst for vinyl polymerization and in the absence of a mercaptan was produced, this copolymer having the following components contains:

(1) about 5 to about 25% of acrylamide or methacrylamide units of the following structure:

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R '-CC-NH-CH ₉ -OR
C.

in which R ^{1 is} a methyl radical or hydrogen and R is hydrogen or a lower alkyl radical and at least 50 % of the radicals R are lower alkyl radicals,

(2) about 3 to about 25% of ethylenically unsaturated units obtained by vinyl polymerization Carboxylic acids from the group of acrylic acid, methacrylic acid, itaconic acid, crotonic acid and Maleic acid and the half-ester of maleic and fumaric acid,

(3) from about 5 to about 75 percent units obtained by vinyl polymerization of curable monomers from the group of styrene, vinyl toluene and alkyl methacrylates with 1 to 4 carbon atoms and

(4) from about 5 obtained to about 75% by vinyl polymerization units of plasticizing monomers selected from the group of alkyl acrylates with up to 13 carbon atoms in each alkyl group and Al kylmethacrylat having 5 to 16 carbon atoms in each alkyl radical, said copolymer

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by neutralizing or partially neutralizing with a sufficient amount of an amine is solubilized such that at least 0.200 ml! equivalent salt per gram of resin solids are present, and

(B) about 40 to about 95% by weight of a liquid medium, that from a mixture of a water-soluble or water-miscible organic solvent and water, this mixture containing at least 60% by weight of water.

Such a coating mass fulfills all of the above requirements for a hygienically perfect one Interior painting of beverage containers.

The invention is also directed to a method for producing such a water-containing coating composition, which is characterized by the following levels:

(A) Polymerizing a monomer mixture containing an amide from the group of N- (alkoxyalkyl) acrylamide and N- (alkoxyalkyl) methacrylamide, an ethylenically unsaturated carboxylic acid from the group of acrylic acid, methacrylic acid, itaconic acid, crotonic acid, maleic acid and the half-ester of maleic acid - And fumaric acid, a hardening monomer from the group of styrene, vinyl toluene and alky! methacrylate with

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1 to 4 carbon atoms and a plasticizing monomer from the group of alkyl acrylate with up to contains to 13 carbon atoms and alkyl methacrylates with 5 to 16 carbon atoms, in one Mixture of water-soluble or water-miscible organic solvents, the Solvent mixture consisting essentially of an ether alcohol from the group of ethylene glycol mono-ethyl ether (ethyl Cellosolve) and ethylene glycol monobutyl ether (butyl Cellosolve) and a lower alkanol from the group of ethanol, propanol, isopropanol and butanol, in the presence of a polymerization catalyst to form the Mixed polymer in solution,

(B) removing part of the solvent by distillation,

(C) adding an amine to the copolymer solution,

(D) Adding water to the mixed polymer solution with stirring, so that · a dispersion of the mixed polymer arises and

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

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- ίο -

The units from which the copolymers used in the invention are built up include Units derived from acrylamide or methacrylamide. These units can be substituted by Amides, such as N- (alkoxyalkyl) acrylamide or methacrylamide, are formed. N * (alkoxyalkyl) acrylamides or methacrylamides, in which the alkoxy group is a butoxy group, that is, the radical R in the formula given is a butyl radical, - are special preferred, since copolymers of such substituted amides provide the most balanced equilibrium in terms of stability and hardenability. Mixtures of N- (alkoxyalkyl) acrylamide and N-methylolamide can be used. These substituted amides can be by various Process are produced. A preferred method is to react an unsaturated one Amides, for example acrylamide, with formaldehyde and an alkanol, for example butanol, under acidic Conditions and in the presence of a polymerization inhibitor. This procedure is detailed in U.S. Patent 3,079,434. The N- (alkoxyalkyl) acrylamide obtained, for example N- (butoxymethyl) acrylamide, is then copolymerized with the other monomers.

In the method outlined above, the substituted amide units of the copolymer are added

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only prepared separately and before the interpolymerization with the other monomers. Alternatively you can the substituted amide units generated "in situ" or subsequently after the formation of the copolymer will. So you can first copolymerize the unsaturated amide with the other monomers and then the product obtained with an aldehyde, for example formaldehyde and an alkanol, for example Butanol. This process is described in detail in U.S. Patent 3,037,963. The way of working has the disadvantage that excess formaldehyde, which has an unpleasant odor, has to be removed. In addition, the degree of etherification of the methylol groups is more difficult to control in this process. It could therefore be the proportion of R radicals that are alkyl radicals instead of hydrogen in the formula given are not to be what is wanted. For a good resistance, however, at least 50% of this Be radicals alkyl radicals, preferably all or almost all of these radicals are alkyl radicals.

The result is that the acrylamide or methacrylamide is introduced into the copolymer with substituted alkoxymethyl groups, the alkoxymethyl substituent being introduced either as part of the amide starting material or by reacting the polymerized amide with it

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Formaldehyde and an alkanol. It is customary to increase 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 alkoxymethyl group can be present or absent in the monomer mixture used for the preparation of the copolymer. Furthermore, when present, it can 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. In describing this invention in the description and in the claims, the content of the amide is therefore given in the manner described. For example, a copolymer which is stated to contain 10% acrylamide can be obtained from a monomer mixture which contains 10 % acrylamide itself. The copolymer is later reacted with formaldehyde and an alkanol. The same copolymer can be formed by polymerizing a monomer mixture containing N- (alkoxymethyl) acrylamide. This monomer is present in such an amount that the copolymer has an acrylamide molecule fraction of 10% without the alkoxymethyl group . In the latter case, such a component is referred to as "acrylamide as NBMA" in the examples.

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The copolymers in the coating compositions according to the invention contain about 5 to about 25% acrylamide or methacrylamide, with the range from about 10 to about 15% being preferred.

For similar reasons, the content of the partially neutralized copolymers is calculated on the basis of the copolymers with unsubstituted amide groups, that is to say those without the alkoxymethyl substituent. The calculated values largely correspond to the experimental values, based on the content of non-volatile solids in the copolymer as obtained by heating it to 150 ^° C. for two hours. This simulates the loss that occurs when the alkoxymethyl groups are split off during hardening.

The units of the copolymer which are derived from ethylenically unsaturated carboxylic acids are best obtained when using acrylic acid or methacrylic acid as acidic monomers. Itaconic acid, crotonic acid and maleic acid and half esters of maleic and fumaric acid can also be used. In the monoesters one of the carboxyl groups is esterified with an alcohol, wherein the identity of the alcohol is not critical so long

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this does not hinder the polymerization and does not interfere with the desired application. Typical examples are butyl hydrogen maleate and ethyl hydrogen fumarate.

The copolymers in the coating composition can contain about 3 to about 25% of such acidic units. The best results in terms of curability and ease of solubilization obtained with copolymers containing 5 to 15% acidic units. Included in some cases the copolymers have more acid than is normally required to solubilize the product is. This is often desirable in order to achieve satisfactory hardenability of the copolymer .

The other units of the copolymer are derived from a combination of hardening and plasticizing monomers in order to obtain the desired combination of properties. The curing monomer is usually styrene, but vinyl toluene or alkyl methacrylates with 1 to 4 carbon atoms are also suitable. The copolymers contain about 5 to 75 units which are derived from hardening monomers, a content of 40 to 60% of such units being preferred.

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One or more substituted alkyl esters of acrylic acid or methacrylic acid can be used as plasticizing monomer are used, the alkyl radicals from 1 to 13 carbon atoms in the case of the acrylic esters and from 5 to 16 carbon atoms Contains carbon atoms in the case of the methacrylic ester. Typical "examples are ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, decyl methacrylate and lauryl methacrylate. The copolymers contain about 5 to about 75% of the plasticizing Monomer-derived units, with about 20 to about 50% of such units being preferred.

In the coating composition according to the invention there is about 5 to about 60% by weight, preferably 15 to 40% by weight, of the copolymer present and the rest consists of the liquid medium.

The copolymer is produced by polymerization in the presence of a catalyst for vinyl polymerization. Preferred catalysts are azo compounds, such as alpha, alpha ¹ -azobis (isobutyronitrile). Other suitable catalysts are tert-butyl perbenzoate, tert-butyl pivalate, isopropyl percarbonate and similar compounds. In some cases, other free radical forming catalysts such as benzoyl peroxide and cumene hydroperoxide can also be used.

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As already stated, the polymerization is carried out in the presence of a mercaptan. This is an important measure because in practice, as from the patent specifications mentioned usually small amounts, for example 1 * to 3%, of mercaptan as a chain transfer agent were used for the preparation of amide copolymers of the desired type. But it was found that the presence of even these small amounts of mercaptan, the copolymers for the Makes use in paints for beer containers or containers for similar drinks unsuitable. If a mercaptan is present in the paint, the paint gives the drink, in particular if stored for several weeks, an undesirable taste. Packaged drinks there Normally longer periods of time can be stored, this makes the use of such copolymers excluded for interior painting.

The paint 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, but usually consists of a mixture of a larger proportion of water and a smaller proportion of a water-soluble or water-soluble medium

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2520327

miscible organic solvents. Suitable organic solvents are ether alcohols such as ethylene glycol monobutyl ether, ethylene glycol monoethyl ether and the like, lower alkanols with 2 to 4 carbon atoms, such as ethanol, propanol, isopropanol, butanol * and the like. Smaller amounts of hydrocarbon solvents such as xylene, toluene and the like can also be present in the liquid medium. It is also possible to use mixtures of solvents of the ether alcohol type and the lower alkanol type. The preferred water-soluble or water-miscible organic solvents are mixtures of ethylene glycol monobutyl ether and isopropyl alcohol. The liquid medium of the paint composition according to the invention can contain about 60 to about 100% by weight, preferably 80% by weight of water and about 0 to about% by weight, preferably 20% by weight of a water-soluble or water-miscible organic solvent. In any case, the liquid medium contains at least 60% by weight of water. The water can be normal tap water, but deionized or distilled water is preferred. Based on the total weight of the paint, the composition can contain about 40 to about 95% by weight, preferably about 60 to 85 % by weight of the liquid medium.

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The copolymer used in the invention is made by adding an amine as a solubilizing agent Made dispersible. It is known per se that copolymers containing acid groups soluble or dispersible in water by neutralization or partial neutralization with an amine can make. In general, the low molecular weight amines known for this purpose are used for this purpose, including ammonia, ethylamine, butylamine, dimethylamine, cyclohexylamine, morpholine, Monoethanolamine, diethanolamine, diethylethanolamine and the same. The preferred amines are monoethanolamine and dimethylethanolamine, with dimethylethanolamine is particularly preferred as it gives the best results. Although amines can be used in general, it is advisable to take certain aspects into account when neutralizing a particular system. For example, some amines are more effective in achieving persistent compositions on the degree of neutralization of the copolymer.

The term "degree of neutralization ¹¹ relates to the proportion of the acid in the copolymer that has been neutralized with the amine. If, for example, 20% of the theoretical amount of the acid in the copolymer has been neutralized by the amine, this is

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Degree of neutralization at 20% of the theoretical neutralization. When 30% of the theoretical amount of acid has 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 give a stable composition, by which is meant a composition that does not separate into different phases. This stability of the composition should be maintained during storage. If one strives to achieve this at a relatively low degree of neutralization, that is, below about 30%, the preferred amines, that is, dimethylethanolamine and monoethanolamine, should be used. At higher degrees of neutralization, i.e. 30% or higher, other amines are effective. For example, at 30% of the theoretical neutralization, diethylethanolamine can be used with good results and at 50% of the theoretical neutralization, almost all of the amines mentioned can be used with good results.

The amount of amine used in the coating compositions according to the invention is an important feature of the invention. This amount is essential for achieving a stable composition, especially when the interpolymer has a low degree of neutralization.

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The amount of amine used can in some cases be so low that it is 0.180 milliequivalents of salt per gram of resin solids. Usually, however, the amount of amine is so large that it is at least Corresponds to 0.200 milliequivalents of salt per gram of resin solids. The term "milliequivalents Salt per gram of resin solids "refers to the number of acid milliequivalents per gram of resin solids of the copolymer, which have been neutralized with a base, that is, with an amine. The number of milliequivalents of salt per gram of resin solids can be calculated using the following formula will

Weight of acid content χ 10 milliequivalents

χ N = salt per gram

Acid equivalent weight resin solids

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

The upper limit for the amount of amine used is less important and depends largely on

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the way of application. If, for example, the composition is brushed on, with a roller or through When dipping is to be applied, the amine can be used in an amount as large as 3.47 milliequivalents of salt per gram of resin solids "But even in these application methods, it is preferred that the amine used does not contain an amount which gives 1.910 milliequivalents of salt per gram of resin solids. However, if the composition is to be applied by spraying, the amount of amine used usually should not result in greater than 0.764 milliequivalents of salt per gram of resin solids, although in some cases the amount of amine can also yield up to 1.40 ml / 11 equivalent salt per gram of resin solids.

In a preferred process for the production of the water-containing coating compositions according to the invention do the following:

(A) the mixture of substituted amide, ethylenically unsaturated acid, hardening and plasticizing monomers is polymerized in "an excess of a mixture of water-soluble or water-miscible organic solvents, the solvent mixture consisting essentially of an ether alcohol from the group of ethylene glycol monoethyl ether and ethylene glycol monobutyl ether and from a low alcohol

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get from the group of ethanol, propanol, isopropanol and butanol and wherein the excess solvent in the mixture is essentially which is the lower alkanol. The polymerization takes place in the presence of a catalyst with the formation of a solution polymer instead.

(B) The excess of solvent, which consists essentially of lower alkanol, is eliminated Distilling at atmospheric or reduced pressure, or both, stripped off.

(C) The amine is added to the solution of the copolymer.

(D) Water is added to the copolymer solution with stirring, a dispersion being formed.

(E) For aging the dispersion to a temperature is heated from about 70 to about 9O ⁰ C with stirring, has become constant until the viscosity of the dispersion substantially. *

The "excess" used herein in connection with the organic solvent mixture in step (A) means that the total amount of the organic solvent mixture which was used in the polymerization exceeds the total amount of the organic solvent which is desired in the final composition.

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increases. The period of time for aging under heating, i.e. stage (E), depends on a number of factors, such as the composition of the copolymer, the solids content of the composition, the initial viscosity of the copolymer formed, the stirring speed and the like. In general, this period varies between an hour and even less up to about 11 hours.

In a particularly preferred process, the monomers mentioned 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, consisting essentially of isopropanol, by distillation at atmospheric or reduced Pressure or both aborted. The amine is then added to the copolymer solution. Afterward deionized water is added to the solution at a temperature between 50 and 99 ° C while stirring, a dispersion of the copolymer is formed. Finally, the copolymer dispersion aged by heating.

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This preferred embodiment for producing the water-containing coating compositions according to the invention has a number of advantages. First of all, it is advantageous that the two solvents have boiling points that are so far apart (ethylene glycol monobutyl ether 171.2 ° C., isopropanol 82.4 ° C.). This large difference in the 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 the solvent is desirable in the polymerization process,
this excess consists essentially of isopropanol, since the isopropanol can easily be 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 chain transfer agent such as mercaptan, which is commonly used for this purpose. Finally, there is the addition of hot water
for the solution of the copolymer advantageous because
this facilitates the formation of the dispersion of the copolymer and a faster achievement of the
allows the desired viscosity of the coating composition.

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The processes outlined above are aimed at the production of preferred water-containing coating compositions, where part of the organic solvent originally used in the manufacture of the copolymer was used, remains in the finished coating mass. But as has already been stated, come in the invention also consider water-containing coating compositions in which the liquid medium is completely consists of water. Such compositions can be made using the process steps already characterized by adding another stage to stage (E). One can for example the organic solvent remaining in the composition after the step (E) by various means Remove procedures such as distillation, liquid chromatography, and the like.

The water-containing 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, in particular those methods are used as previously used for painting containers became. The exact formulation of the coating composition, for example total solids content, viscosity and the like, depends in the individual case on the type of application and the definition of the individual

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Factors are no problem for the person skilled in the art.

After application, the paints are dried and cured by heating to elevated temperatures, "resulting in 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 according to the invention using the conditions and facilities used in the container industry are common to be hardened. In typical curing conditions, temperatures in Range 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 parts and percentages are given by weight, unless expressly stated otherwise. The solids contents in the examples were carried out at 105 ^° C. as a test for quality control.

example 1

This example illustrates 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

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was equipped to introduce nitrogen, 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 ¹ -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 to reflux temperature (about 90 to 93 ° C) under nitrogen 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 removed from the resulting copolymer solution by distillation at atmospheric pressure at a temperature of about 94 ° C over about 75 minutes . To this

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At this point in time, a sample of the reaction mixture was examined for its total ^{solids content and it was found that the solids content determined at 150 °} C. was 73% by weight. 49.8 grams (50% of the theoretical neutralization) were then added to the reaction mixture, the temperature of the mixture being 97.degree. After the addition of the dimethylethanolamine 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 a dispersion of the copolymer in a liquid gen medium with the following characteristics:

Mixed polymer mixed polymer

Units ( % )

Acrylamide as NBMA * 10.0

Styrene 41.0

Ethyl acrylate "41.5

Ice acrylic acid 7.5

Liquid medium weight percent

deionized water 83.8

organic solvents ** 16.2

* N- (butoxymethyl) acrylamide

** a mixture of ethylene glycol monoethyl ether, isopropanol, toluene and butanol

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Other properties of the paint were as follows:

Polymer solids content: 33.4 wt% of Ge velvet mass liquid medium: 65.6% by weight of Ge • velvet mass Viscosity: 140 cp, Brookfield Viscosity at 25 ° C, - Spindle no. 4 at 20 rpm Acid number: 16.1 Milliequivalents of salt per gram Resin solids: 0.521 Reliability: Well

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 amount of dimethylethanolamine used for neutralization 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:

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Polymer Solids: "35% by weight of the total mass

liquid medium *: 65% by weight of the total mass

Viscosity: 100 cp, Brookfield viscosity

at 25 ⁰ C, No. 4 spindle at 20 rpm

Acid number: 17.43 Mi11! Equivalent salt per

Grams of resin solids: 0.314

Persistence: good

* 85 wt% deionized water and 15 wt% organic solvents

After drawing to a metal substrate and baking for 2 minutes at about 19O ⁰ C a smooth, hard and durable film was obtained.

Example 3

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

477 grams of ethylene glycol monobutyl ether, 975 grams of isopropanol and 870 grams of the monomer mixture from Example 1, but without the alpha, alpha ¹ - azobite (iaobutyronitrile), were added to the reactor of Example 1. The mixture was taking

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Nitrogen heated to reflux temperature as in Example 1. After the start of reflux, an additional 3189 grams of the monomer mixture of Example 1 and 54 grams of alpha, alpha ¹ -azobis (isobutyronitrile) were added to the reactor over 3 hours as "in Example 1. Thereafter, 12.0 grams of T Butyl perbenzoate was added as in Example 1. 981 grams of organic solvent were then driven off by distillation at atmospheric pressure and at temperatures between about 95 and about 120 ^° C. 89.4 grams (30% of theoretical neutralization) of dimethylethanolamine were then added After this addition, 5085 grams of deionized water was preheated to 75 ° C and added to the reaction mixture as in Example 1.

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

Copolymer wt% total

solids - 38.5

Mixed polymer units (%)

Acrylamide as NBMA 10.0

Styrene 41.0

Ethyl acrylate 41.5

Egg sacryic acid 7.5

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Liquid medium

Weight% total liquid * 61.5

Weight%

deionized water organic solvents *

83.5 16.5

* consisting of ethylene glycol monobutyl ether, isopropanol, Toluene and butanol

The composition had the following properties:

Total Solids: Acid Number:
Viscosity:

Milliequivalents of salt per gram of resin solids:

Resistance:

38.5% 17.7 300 Cp, Brookfield viscosity at 25 ⁰ C,

No. 4 spindle at 20 upir.

0.313 good

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

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Example 4

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

total weight

Copolymer from Example 3 37.5 liquid medium 62.5

Weight percent

deionized water 79.5

organic solvents 20.5

The mass had the following properties:

Total solids: 37.5 % Viscosity: 16.5 seconds, No. 4 Ford mug Acid number: 18.6 Mill! Equivalent salt per gram Resin solids: 0.313 Resistance: Well

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The paint, when applied to a metal substrate and after baking, gave as in FIG Examples 1 to 3, a smooth, hard and durable film.

Examples 5 to 8

These examples explain the critical influence of the degree of neutralization, i.e. the milliequivalents Salt per gram of solids, on the stability of the water-containing coating compositions, according to the invention.

The compositions were prepared essentially in the same way and using the same copolymer as in Examples 3 and 4, with the exception that the amount of dimethylethanolamine used was such that the degree of neutralization of the copolymer was 30 % of the theoretical neutralization (at 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 led to high viscosities of the compositions, Examples 6 to 8, the solids content of these compositions reduced by adding additional solvent in the form of an 80/20 mixture of deionized water and ethylene glycol monobutyl ether.

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was given. The compositions obtained had the following formulations and properties:

example

Mixed polymer

% theoretical neutralization

Total solids (wt%)

Total liquid medium (% by weight)

Viscosity, No.4 Ford cup, seconds at 25 ° C

Acid number

Milliequivalents of salt per gram of resin solids

resistance

as in example 4

36.4 63.6

26th
18.6

0.312 good

25th

33.1

66.9

31 19.4

0.261 good

20th

18.0

82.0

25 12.9

15 25 75

12.1

0.208 0.156

massive, bad, easy separation settling into 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 above examples were repeated using monoethanolamine instead of dimethyhanolamine and the durability was similar.

509847/1173

Example 9

This example illustrates a water-containing coating composition according to the invention, which can be used at low temperatures hardens.

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

Copolymer (as stated): 35% by weight

liquid medium *: 65% by weight

Viscosity: 340 cp, Brookfield

Viscosity at 25 ^° C., No. 4 spindle at 20 rpm

Acid number:. * 25.3

Milliequivalents of salt per gram

Resin solids: 0.375

Persistence: good

* 82.3% by weight of deionized water and 17.7 % by weight of organic solvents consisting of ethylene glycol monobutyl ether, isopropanol, butanol and xylene

509847/1173

A spread of this composition on a metal substrate gave a smooth, hard and permanent film ^{after curing at 160 ° C. for 4 minutes.}

As already indicated, the compositions according to the invention are particularly suitable as paints for suitable for the hygienically perfect interior painting of liquid containers. Such containers are subjected to a series of tests. These tests are done both before and after filling the container 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 are 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

509847/1173

In the following Examples 10 to 13, samples of the hydrous coating compositions of the Examples were used 1, 2, 4 and 9 used for the interior painting of beer containers. These containers were then subjected to the above tests and the results are given in the following table.

Examples 11 12th 13th - 10 Ex.
2 Ex.
4th Ex.
9 Formulation of Example,
1 Test and result: P. P. P. Adhesion to the metal P. P. P. P. Gloom P. P. P. P. Extractability P. P. P. P. taste P. P. P. P. Pasteurization
resistance P.

ρ - positive result

As can be seen from the table, all compositions tested passed all tests.

A composition which corresponded to that of the formulation of Example 1, but which contained 2.5% mercaptoethanol as a chain transfer agent, failed the taste test.

509847/1 173

Claims (22)

Patent claims: 1. Aqueous coating compound for the interior painting of metal containers for beverages, characterized in that it consists essentially of (A) about 5 to about 60 weight percent of an amine neutralized or partially neutralized copolymer which is in the presence of a catalyst for vinyl polymerization and in the absence of a mercaptan, this copolymer as follows Components contains: (1) from about 5 to about 25 percent acrylamide or methacrylamide units of the structure 0
R ¹ - C - C - NH - CH ₀ - OR in which R ^{1 is} a methyl radical or hydrogen and R is hydrogen or a lower alkyl radical and at least 50 % of the radicals R are lower alkyl radicals, 5 0 9 8 A 7/1 1 7 3 (2) about 3 to about 25 % units of ethylenically unsaturated carboxylic acids from the group of acrylic acid, methacrylic acid, itaconic acid, crotonic acid and maleic acid and half esters of maleic and fumaric acid, obtained by vinyl polymerization, (3) about 5 to about 75 % of units of curing monomers from the group of styrene, vinyl toluene and alkyl methacrylates having 1 to 4 carbon atoms and obtained by vinyl polymerization (4) from about 5 to about 75 percent by vinyl polymerization obtained units of plasticizing monomers from the group of alkyl acrylates with up to 13 carbon atoms in each alkyl radical and alkyl methacrylates with 5 to 16 carbon atoms in each alkyl radical, this copolymer being made soluble by neutralizing or partially neutralizing with a sufficient amount of an amine so that at least 0.200 milliequivalents of salt are present per gram of resin solids and (B) about 40 to about 95% by weight of a liquid medium consisting of a mixture of an in water-soluble or water-miscible organic solvent and water, said mixture containing at least 60 wt% water. 509847/117 3 2. Coating composition according to claim 1, characterized in that the lower alkyl radical R is a butyl radical. 3. Coating composition according to claim 1 or 2, characterized in that that the ethylenically unsaturated acid is acrylic acid. ' 4. Coating composition according to one of claims 1 to 3, characterized in that that the curing monomer is styrene. 5. Coating composition according to one of claims 1 to 4, characterized in that that the plasticizing monomer is ethyl acrylate. 6. Coating composition according to one of claims 1 to 5, characterized in that that the amine used for neutralization is dimethylethanolamine or monoethanolamine. 7. Coating composition according to one of claims 1 to 6, characterized in that the organic solvents in the liquid medium are ethylene glycol monobutyl ether, ethylene glycol monoethyl ether, isopropanol, butanol, xylene, toluene and mixtures thereof. 509847/1173 8. coating composition according to one of claims 1 to 7, characterized in that that they are about 15 to 40% by weight of the copolymer and about 60 to about 85% by weight of the liquid Contains medium. 9. Coating composition according to one of claims 1 to 8, characterized in that the copolymer contains about 10 to about 15 % acrylamide or methacrylamide in the form of the units of the specified structure, about 5 to about 15% of the specified acid units and about 40 to about 60% of the specified units of the curing monomer and about 20 to about 50% of the units of the specified plasticizing monomer. 10. Coating composition according to claim 9, characterized in that the substituted amide is N-butoxymethylacrylamide, the acid is acrylic acid, the hardening monomer is styrene and the plasticizing monomer is ethyl acrylate. 509847/1173 11. Coating composition according to claim 10, characterized in that that the amine used for neutralization is dimethylethanolamine or monoethanolamine. 12. Coating composition according to claim 1, characterized in that it consists essentially of (A) about 15 to about 40 weight percent of that neutralized or partially neutralized by an amine Mixed polymer containing the following components: (1) about 10 to about 15% of the acrylamide or methacrylamide units, (2) about 5 to about 15% of the ethylenically unsaturated Carboxylic acids, (3) about 40 to about 60% of the units of the curing monomers and (4) about 20 to about 50 % of the units of the plasticizing monomers, - and (B) about 60 to about 85% of the liquid medium. 13. Coating composition according to claim 12, characterized in that in the structure of the acrylamide or methacrylamide units R is a butyl radical, the acid is acrylic acid, the hardening monomer is styrene and the plasticizing monomer is methyl acrylate. 509847/117 3 14. Coating composition according to claim 13, characterized in that it is dimethylethanolamine as the neutralizing amine or contains monoethanolamine. 15. Process for producing a water-containing coating compound, characterized by the following levels: (A) Polymerization of a monomer mixture, which is an amide from the group of N- (alkoxyalkyl) acrylamide and N- (alkoxyalkyl) methacrylamide, an ethylenically unsaturated carboxylic acid from the group of acrylic acid, methacrylic acid, itaconic acid, crotonic acid, maleic acid and maleic half-esters - and fumaric acid, a hardening monomer from the group of styrene, vinyl toluene and alkyl methacrylates with 1 to 4 carbon atoms and a plasticizing monomer from the group of alkyl acrylates with up to 13 carbon atoms and alkyl methacrylates with 5 to 16 carbon atoms, in a mixture of in Water-soluble or water-miscible organic solvents, the solvent mixture consisting essentially of an ether alcohol from the group of ethylene glycol monoethyl ether and 509847/117 3 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 the formation of the mixed polymer 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 arises, and (E) Aging the dispersion by heating to 70 to 90 ^° C. with stirring until the viscosity of the dispersion has become essentially constant. 16. The method according to claim 15,
characterized in that the amount of amine added in step (C) is sufficient to produce at least 0.200 milliequivalents of salt per gram of resin solids. 17. The method according to claim 15,
characterized in that the water added in step (D) is deionized water preheated to a temperature of about 50 to about 99 ° C. 50934 7/1173 18. The method according to claim 15,
characterized in that the monomer mixture contains N- (butoxymethyl) acrylamide, acrylic acid, styrene and ethyl acrylate. 19. The method according to claim 15,
characterized geke η η marks, ■ that the mixture of the water-miscible solvents is a mixture of isopropanol and ethylene glycol monobutyl ether or ethylene glycol monoethyl ether. 20. The method according to claim 15,
characterized in that the amine added in stage (C) is dimethylethanolamine or monoethanolamine. 21. The method according to any one of claims 15 to 20, characterized in that that the polymerization in a mixture of isopropanol and ethylene glycol monoethyl ether or Ethylene glycol monobutyl ether is carried out. 509847/1173 22. Use of the coating composition according to any one of claims 1 to 14 for painting the interior of metal ! containers for beverages. 7/1173