PROCESS FOR THE PREPARATION OF CARBOXYLATED AMIDE BINDERS

Abstract: The invention provides a process for the preparation of water-reducible carboxylated amide binders comprising the consecutive steps: A. reacting: 1. a substantially epoxy-free compound of general formula wherein A is the organic residue of a ring opening reaction of a vicinal epoxy group of a polyepoxide with ammonia or an amine having at least two amino hdyrogens, R¹, R³ and R⁴ each is hydrogen or a C 1-6 alkyl group, with the proviso that at least one of R¹, R³ and R⁴ is hydrogen, R² is a C 2-12 alkylene group, x is 0 or 1 and y is a number from 0 to 4, with 2. a carboxyl group-containing mono- or polyester compound derived from a di- or polycarboxylic acid and a polyhydric alcohol having at least one glycol group per molecule, with the proviso that only one carboxyl group per molecule of di- or polycarboxylic acid has been esterified and the or each ester group is a β-hydroxyester group, at a temperature in the range of from 80 to 160 °C, and B. neutralizing the carboxylic groups or the residual amine groups in the product of step A.

Description: This invention relates to a process for the preparation of hydrolytically stable binders, more in particular to the preparation of hydrolytically stable carboxylated amide binders wherein the carboxyl groups are linked to the binder via an amide group, to coating compositions containing said hydrolytically stable binders and to their use for application via electro deposition or by conventional application techniques. Although water-soluble and/or water-reducible binders are being used on an ever increasing scale, one of the problems frequently encountered with the aqueous coating compositions based on said binders is their insufficient hydrolytic stability. This phenomenon may especially be observed with the anionic type of water-reducible binders, i.e. those binders which derive their ultimate water-reducibility from the presence of a sufficient number of built-in carboxyl groups. The insufficient hydrolytic stability of the anionic binders in aqueous media, is generally related to the presence of hydrolytically instable ester linkages which are frequently introduced simultaneously with the introduction of the carboxyl groups. One of the many methods which have been proposed to prepare ester linkage-free anionic binders, has been described in GB-A 2 037 291. With said method an essentially epoxy-free, amino group-containing binder is reacted with a cyclic anhydride of a dibasic carboxylic acid to provide after a ring opening reaction a carboxylated amide binder, which upon neutralization with a suitable base becomes water-reducible. Although said method claims the synthesis of a new class of ester linkage-free water-reducible binders, it is felt that there is room for further improvement. A problem related to the use of cyclic anhydrides is that these generally solid materials will not always dissolve completely in the reaction medium or only at relatively high temperatures. Furthermore such anhydrides may contain, depending on the degree of purity, a certain amount of free acid. Both unreacted anhydride and free acid are very difficult if not impossible to remove from the rather viscous reaction media. When such anhydrides are employed in the preparation of water-borne binders the presence of unconverted anhydride or free acid in the ultimate coating composition may well have a negative effect on the electrodeposition characteristics. It can thus be concluded that the preparation of the hereinbefore described carboxylated amide binders leaves room for further improvement. Therefore the problem underlying the present invention is to develop a method for the preparation of carboxylated amide binders which does not suffer from the hereinbefore described disadvantages. The invention provides therefore a process for the preparation of water-reducible carboxylated amide binders comprising the consecutive steps of: A) reacting: 1. an essentially epoxy-free amino group containing compound obtained via a ring opening reaction of a polyepoxide with ammonia or an amine having at least two amino hydrogens per molecule the amine being a compound of general formula per molecule, R¹, R³ and R⁴ each individually is hydrogen or a C₁₋₆ alkyl group with the proviso that at least one of R¹, R³ and R⁴ is hydrogen, R² is a C₂₋₁₂ alkylene group, x is 0 or 1 and y is 0 to 4, with 2. a carboxyl group-containing mono- or polyester compound derived frown a di- or polycarboxylic acid, which carboxylic acid has the ability to form a cyclic monoanhydride, and a polyhydric alcohol having at least one glycol group per molecule, with the proviso that only one carboxyl group per molecule of the di- or polycarboxylic acid has been esterified and the or each ester group is a β-hydroxyester group, at a temperature in the range of from 80 to 160 °C, and B) subsequently partially reacting, in the product as prepared under A: 1. the carboxyl groups with a basic compound, or 2. the residual amino groups with an acid. The epoxy compounds which may be employed in the preparation of the essentially epoxy-free amino group-containing compounds are polyepoxides, which do not contain hydrolyzable groups, e.g. epoxy compounds which do not contain ester linkages. Examples of such epoxy compounds include reaction products of epihalohydrins and e.g. polyhydric phenols. Said polyhydric phenols include both polyhydric mononuclear phenols such as catechol, resorcinol, hydroquinone, pyrogallol and the like, as well as polyhydric polynuclear phenols such as 1,1-bis(4-hydroxyphenyl)methane, 1,1-bis(4-hydroxyphenyl)ethane, 2,2-bis(4-hydroxyphenyl)propane and their isomers, as well as novolac resins of general formula wherein R represents an alkylene, e.g. CH₂ group, R¹ represents an alkyl group, e.g. a methyl, p -t-butyl, octyl or nonyl group, q and p are numbers having average values 0<q<6 and 0<p<2, or of general formula wherein R² represents an alkylene, e.g. CH₂ group, R³ represents an alkylene, e.g. CH₂ or C(CH₃)₂ group, a carbonyl group, an oxygen or sulphur atom and q′ is a number having an average value in the range of from 0 to 2. Another example of a suitable polyhydric polynuclear phenol is 1,1,2,2-tetra(4-hydroxyphenyl)ethane. Polyglycidyl ethers derived from polyhydric phenols of formulae II and III are known and are described, together with processes for their preparation, in, for example, US-A 2,844,533, NL-A 8100830, DE-A 2 656 867 and GB-A 2 001 991. Other suitable epoxy compounds include mono- and polyglycidyl ethers of respectively mono- and polyhydric alcohols. A class of polyglycidyl ethers which is preferred when the ultimate carboxylated amide group-containing binder prepared according to the process of the present invention, is used in can coating compositions are polyglycidyl ethers having an average n epoxy groups per molecule, where 1 < n < 2, which comprise the reaction product of a multifunctional polyglycidyl ether having an average x epoxy groups per molecule, where x > 2, with (x-n) mol of a mono-functional phenol per mol of the multi-functional polyglycidyl ether and which polyglycidyl ethers have been described in EP-A 0127915. These polyglycidyl ethers may be used in combination with "conventional" diglycidyl ethers. Diglycidyl ethers of 2,2-bis(4-hydroxyphenyl)propane having an epoxy group concentration (EGC) in the range of from 1000 to 5500 mmol/kg are preferred diglycidyl ethers. Epoxy compounds such as those described hereinbefore can be converted into essentially epoxy-free compounds of A1. according to the invention via a ring opening reaction with ammonia or an amine having at least two amino hydrogens per molecule. Examples of suitable amines include primary mono-amines such as n-propylamine, isopropylamine, n-butylamine, isobutylamine, sec-butylamine as well as primary amines having alkyl chains with more than 4 carbon atoms. Another class of suitable amines are polyamines such as ethylenediamine, 1,3-propylenediamine, 1,4-butylenediamine, 1,6-hexylenediamine, 1.4-diaminocyclohexane, methylamino-propylamine and hydrazine. When the compound of A1. according to the invention results from a ring opening reaction with ammonia, R¹ and R⁴ are hydrogen and y is 0; when a primary monoamine is used R¹ or R⁴ is an alkyl group and y is 0; when hydrazine is used for the ring opening reaction R¹, R³ and R⁴ are hydrogen, x is 0 and y is 1; and when a polyamine is used for the ring opening reaction R³ is hydrogen, x is 1 and y is 1 to 4. Which of the reactive amino hydrogen-containing compounds will be used will amongst others be determined by the ultimate application of the carboxylated amide binder. Should the ultimate field of application be e.g. in coatings for food and beverage cans, ammonia and amino group-containing compounds which have been approved e.g. by the Food and Drugs Administration, will preferably be used. A further criterium for selecting a suitable amino compound may be the functionality of the epoxy compound, in view of the risk of gelation when the functionality of both epoxy and amino compound are high. Methods for the preparation of the essentially epoxy-free amino group-containing compounds of A1. according to the invention are known and have been described e.g. GB-A 1221906, US-A 4,176,221 and EP-A 0017894. Di-or polycarboxylic acids on which the carboxyl group-containing mono- or polyester compounds as described under A-2 hereinbefore may be based, include dicarboxylic acids such as maleic acid, succinic acid, chlorosuccinic acid, nonenylsuccinic acid, dodecenylsuccinic acid, glutaric acid, o-phthalic acid, 1,2-cyclo hexenedicarboxylic acid and 1,2-cyclohexanedicarboxylic acid, and tricarboxylic acids such as trimellitic acid. Polyhydric alcohols containing at least one glycol group as described under A-2 include ethylene glycol, propylene glycol, 2,3-butanediol, glycerol, xylitol, D-sorbitol, L-sorbitol and hydrolysed mono- and polyepoxy compounds. Preferably the polyhydric alcohols have glycol groups comprising a primary and a secondary hydroxyl group. Preferably the carboxyl group-containing mono- or polyester compound is a mono-β-hydroxy ester compound. A mono-β-hydroxy ester compound based on trimellitic acid and propylene glycol is especially preferred. The carboxyl group-containing mono- or polyester compounds may be obtained in high yield and selectivity by reacting at least one mol of the cyclic anhydride of a di-or polycarboxylic acid and one mol of a polyhydric alcohol as described hereinbefore, at a temperature of up to approximately 150 °C. The preparation of the carboxylated amide binder may conveniently be effected by heating the amino group-containing compound, e.g. as a solution in a solvent, preferably a water-miscible solvent such as 2-n-butoxyethanol, together with a carboxyl group-containing compound described hereinbefore in the required ratio and at a temperature in the range of from 80 to 160 °C, preferably from 100 to 120 °C. The time required to complete the conversion of amino groups into carboxylated amide binders (hereinafter referred to as amidation) will depend both on the reaction temperature as well as on the degree of amidation. The degree of reaction can be established by determination of the residual amino group concentration. When only a relatively low percentage of the amino groups are to be converted the ultimate binder will be a carboxyl group-containing cationic binder, which will require neutralization with an acid, e.g. lactic acid to become water-reducible. An anionic binder may be obtained if a larger percentage of the amino groups are converted. Such a binder will require neutralization with a basic compound to become water-reducible. With the latter mode of binder preparation it may be beneficial to select a carboxyl group-containing ester compound, derived from an alcohol which is at least partly water-miscible. The process of the present invention also affords the possiblity to prepare carboxylated amide binders wherein both a sufficient number of amino groups are present to make the binder water-reducible after neutralization with an acid, as well as suffficient carboxyl groups to impart water-reducibility after neutralization with a base, i.e. "amphoteric" binders. The carboxylated amide binders may be employed to prepare water-reducible coating compositions and aqueous coatings based thereon. To this end the binders may be blended with a crosslinking agent before or after neutralization. The crosslinking agents which may be employed in the preparation include water-thinnable, as well as solvent borne and non-water thinnable crosslinking agents such as melamine-, urea- and phenolformaldehyde resins. Said crosslinking agents are preferably used in a ratio of carboxylated amide binder to crosslinking agent in the range of from 95:5 to 60:40 w/w. Pigments, fillers, dispersing agents, and other components known in the art of paint formulation may further be added. Addition of small amounts (up to 1 %w) of non-ionic surfactant may be useful for further stabilization of aqueous compositions or improvement of the wetting during application. Co-solvents, such as 2-n-butoxyethanol and, especially, 2-n-hexyloxyethanol, may advantageously be included. The water for use in the aqueous compositions is preferably purified, such as by destillation or demineralization. The water-dilutable compositions may be applied by a variety of methods known in the art such as spraying, dipping and electro-deposition, onto a variety of substrates, in particular metals such as bare steel, phosphated steel, chromate-treated steel, zinc, tin plate (for can coating), and aluminium (also e.g. for can coating), to produce cured coatings of desirable thickness from 2 micrometres upwards up to in general 40 micrometres. Curing of the coating compositions made according to the process of the present invention can be performed by stoving, for example, at temperatures of from 170 to 220 °C, with curing times varying from 3 to 20 minutes. The invention will be further understood from the following examples in which parts and percentages are by weight, unless otherwise indicated, and for which the following information is provided: Preparation of amino group-containing compound A 272 g of a 25 %w aqueous ammonia solution and 600 g of tetrahydrofuran (THF) were added to and blended with 3103 g of a 60 %w solution of EPIKOTE 1007 (trade mark) (a bisphenol A-epichlorohydrin copolymer having an epoxy group concentration (EGC) of 537 mmol/kg) in 2-n-butoxyethanol to arrive at a clear "solution". Thereupon the temperature of the reactor contents was gradually raised to about 60 °C in approximately 6 hours during which period virtually all the epoxy groups had reacted. Subsequently the temperature in the reactor was increased to 120 °C, in as short a time as possible, and maintained at that temperature to remove excess ammonia, water and THF by distillation using a nitrogen puree. The ammonia removal was checked with the aid of wet paper-pH-indicator. The reaction product was found to contain 0.39 meq/g solids of total amino nitrogen 0.27 meq/g solids of primary amino groups 0.10 meq/g solids of secondary amino groups 0.02 meq/g solids of tertiary amino groups Preparation of amino group-containing compound B 1) Polyglycidyl ether preparation 615 g of a multifunctional epoxy diphenylolpropane novolac resin, having an average molecular weight 615 and on average 3.1 epoxy groups per molecule was heated with 352 g nonylphenol under stirring to 140 °C, whereupon 0.48 g of a 50 %w aqueous tetramethylammonium chloride solution was added. The reactor contents were maintained at 140 °C until the reaction had been completed, i.e. the calculated EGC (1550 mmol/kg) had been obtained. After slight cooling 2-n-butoxyethanol was added to arrive at a solution containing 66.7 %w solids. 2) Preparation of amino group-containing compound 1450.5 g of the polyglycidyl ether solution prepared under 1), 708 g of EPIKOTE 1001 (trade mark) (a bisphenol A-epichlorohydrin copolymer having an EGC 2119 mmol/kg) and 634.5 g 2-n-butoxyethanol were homogenized by heating to 90 °C with stirring. After cooling to 25 °C 408 g of a 25 %w aqueous ammonia solution and 772.5 g of a 4/1 w/w THF/ethanol blend were blended in to arrive at a clear "solution". From here on the same procedure was followed as with the preparation of amino group-containing compound A. The reaction product was found to contain 0.98 meq/g solids of total amino nitrogen 0.82 meq/g solids of primary + secondary amino groups 0.16 meq/g solids of tertiary amino groups Preparation of 2-hydroxypropyl dihydrogen trimellitate (β-hydroxyester of trimellitic acid (TMA) and propylene glycol wherein propylene glycol has reacted with the anhydride moiety of TMA thus forming a composition carrying two carboxyl groups and one β-hydroxy group. 192 g of trimellitic acid (TMA) and 76 g of propylene glycol were heated to 140 °C in approximately 40 minutes under continuous stirring, and maintained at said temperature for 15 minutes in which period all the anhydride had reacted. Final acid content 7.4 mol/kg. Examples I-V Preparation of carboxylated amide binders and of the corresponding aqueous solutions a) Binder preparation Amino group-containing compound A or B (60 %w in 2-n-butoxyethanol) and 2-hydroxypropyl dihydrogen trimellitate were heated to 120 °C in amounts as indicated hereinafter and maintained at said temperature for a period of time as indicated in Table 1 hereinafter, which Table also gives the amounts of the individual reagents as well as additional process data and product charcteristics. b) Aqueous solution preparation The carboxylated amide binders were further tested for their water reducibility characteristics. To this end the cationic binder system was partially neutralized with an acid and the anionic binder systems were partially neutralized with a base. The neutralization was effected by mixing the neutralizing agent at approximately 20 °C with the relevant binder solution. Subsequently the neutralized binder solutions were gradually diluted with water under vigorous stirring to arrive at the required solids content. Details are given in Table 1 together with some characteristics of the aqueous systems. Example VI Anionic coating compositions and coatings prepared therewith The aqueous anionic binder composition as prepared in Example I was used to prepare a number of aqueous coating compositions in combination with different amounts of repectively an approximately 100 %w non-volatile liquid hexamethoxymethylmelamin crosslinking agent Cymel 301 (trade mark) or an approximately 100 % non-volatile phenolic resin Phenodur PR 217 (trade mark). The coating compositions were prepared by mixing the aqueous binder composition and the relevant crosslinking agent in the ratio (weight percent solids) as indicated in Table 2 hereinafter. The thus obtained coating compositions were applied by bar coater in a 5 µm dry film thickness onto 0.5 mm standard tin plate and stored according to the schedule indicated in Table 2, which Table also gives some film performance properties. For the latter the following information is provided: MEK res. = solvent resistance expressed as the number of double rubs with a methylethylketone-moistened cloth necessary to remove the coating. The sterilization resistance of the coatings was determined by exposure to water or lactic acid at 121 °C for 90 minutes and rated according to a numerical scale ranging from 5: no blushing to 0: very heavy blushing. Example VII Cationic coating compositions and coatings prepared therewith 36 g of the carboxylated amide binder solution (61 %w in 2-n-butoxyethanol) as prepared in Example II was blended consecutively with 7.3 g of Cymel 1156 (trade mark), being an approximately 100 % non-volatile highly viscous hexabutoxymethylmelamin resin, 2.2 g 2-hexyloxyethanol monohexylether of ethyleneglycol and 1.34 g of lactic acid (90 %w in water). Subsequently the homogeneous blend was gradually diluted with 148 g demineralized water under stirring. The thus obtained coating composition was filtered (through an E-D-schnellsieb 80 my filter) before use and was found to have the following characteristics: Solids content %w 15 Binder/crosslinking agent ratio 75/25 Acid value (on solids), mgKOH/g 6 Degree of neutralization 0.7 pH 4.8 Conductivity, µs/cm 560 This coating composition was used to coat 330 ml tin-plate cans (2-piece Drawn and Wall Ironed (DWI) cans) and 0.5 mm tin-plate panels (E₂ quality) by cathodic electrodeposition. The can or the panel formed the cathode of an electrodeposition cell, the anode being a stainless steel member inserted within the can at a substantially uniform separation of 2 millimetres from the cam, or in case of the panel a stainless steel panel was used as the anode and positioned at a distance of 2.5 cm from the tin-plate panel. The deposition conditions are given in Table 3 which also gives some performance properties of the coatings, which were obtained following the procedures described in Example VI.

Claims: A process for the preparation of water-reducible carboxylated amide binders comprising the consecutive steps: A. reacting: 1. a essentially epoxy-free, amino group containing compound, obtained via a ring opening reaction of a polyepoxide with ammonia or an amine having at least two amino hydrogens per molecule, the amine being a compound of general formula wherein R¹, R³ and R⁴ each individually is hydrogen or a C₁₋₆ alkyl group, with the proviso that at least one of R¹, R³ and R⁴ is hydrogen, R² is a C₂₋₁₂ alkylene group, x is 0 or 1 and y is a number from 0 to 4, with 2. a carboxyl group-containing mono- or polyester compound derived from a di- or polycarboxylic acid, which carboxylic acid has the ability to form a cyclic monoanhydride, and a polyhydric alcohol having at least one glycol group per molecule, with the proviso that only one carboxyl group per molecule of di- or polycarboxylic acid has been esterified and the or each ester group is a β-hydroxyester group, at a temperature in the range of from 80 to 160 °C, and B) subsequently partially reacting, the product as prepared under A: 1. the carboxyl groups with a basic compound, or 2. the residual amino groups with an acid. A process according to claim 1 wherein in general formula I R¹ and R⁴ are hydrogen and y is 0. A process according to claim 1, wherein in general formula I R¹ is an alkylgroup, R⁴ is hydrogen and y is 0. A process according to claim 1, wherein in general formula I R¹, R³ and R⁴ are hydrogen, x is 0 and y is 1. A process according to claim 1, wherein in general formula I R³ is hydrogen, x is 1 and y is 1 to 4. A process according to any of claims 1 to 5, wherein said polyepoxide is derived from a polyglycidyl ether of a polyhydric phenol. A process according to any of claims 1 to 5, wherein said polyepoxide is derived from a polyglycidyl ether having on average n epoxy groups per molecule, where 1 < n < 2, which comprises the reaction product of a multifunctional polyglycidyl ether having on average x epoxy groups per molecule, where x > 2, with (x-n) mol of a monofunctional phenol per mol of the multifunctional polyglycidyl ether. A process according to claim 7 wherein the polyglycidyl ether had been blended with a diglycidyl ether of 2,2-bis(4-hydroxyphenyl)propane having an epoxy group concentration in the range of from 1000 to 5500 mmol/kg. A process according to any of claims 1 to 8, wherein carboxyl group-containing ester compound is a mono β-hydroxy ester compound, optionally based on trimellitic acid and propylene glycol. Water-reducible coating compositions comprising as solids, 95-60 %w of a water-reducible carboxylated amide binder made by or process as claimed in any one of claims 1 to 9 5-40 %w of a crosslinking agent.

Inventors: KOOIJMANS, PETRUS GERARDUS, SIKKING, ARJAN, VAN IPEREN, ROELAND
Applicants: SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ B.V.
Application year: 1988
Main classification: C08G69
IPC codes: C09D163, C09D177, C08G69, C09D161