GB2109383A - Anti-corrosion epoxy resin coating composition - Google Patents

Abstract

Crosslinking compositions suitable for formulation into a variety of primers including solvent and water-base primers that cure within conventional schedules to protect substrates against corrosion, even in the absence of inhibiting pigments such as chromates, comprise:- (A) a substantially gell-free reaction product, optionally at least partially neutralized, made by reacting in non-aqueous medium; 1. A non-carboxy-ester linked epoxy reactant that has an average of at least about two epoxy groups per molecule; 2. An amine reactant selected from the group consisting of secondary amines and primary and secondary amines having a total of up to about 20 carbon per amino nitrogen and comprising at least about 75 mole percent hydroxy amine containing one or more primary hydroxy groups removed at least one carbon from any amino nitrogen, in an equivalent amount such that the reaction product (A) comprises tertiary amino and primary and secondary hydroxy groups and is substantially free of unreacted epoxy groups: (B) Optionally, a di or polyhydroxy compound; (C) An amino resin crosslinking agent at about 5-35% by weight of the combined weight of (A) and (B), and (D) an acid catalyst, especially from 0.1 to 5% by weight, based on the total weight of (A) and (B), of one or more hydroxy organophosphate esters of the general formula:- <IMAGE> wherein n is 1 or 2 and R, or each of the groups R independently, represents a mono- or di hydroxy-substituted hydrocarbon group having up to 10 carbon atoms.

Description

1

SPECIFICATION

Anti-corrosion coating compositions This invention relates to coating compositions for protecting corrodable substrates such as ferrous metals from corrosion and includes, in particular, resins suitable for incorporation into such composi tions, and corrosion protection methods.

The corrosion of steel immersed in an aqueous 75 environment can often be slowed to an acceptable rate by the introduction of corrosion inhibitors solu ble in the aqueous medium. In the case of steel struc tures subjected intermittently to a corrosive envi- ronment, or under conditions which preclude effec- 80 tive incorporation of a corrosion inhibitor into the corrosive medium, protective organic coatings are often used. One of the major functions of these coat ings is to act as s reservoir for sparingly soluble inorganic corrosion inhibitors which act to slow the 85 rate of corrosion at coating defects and other inci pient anodic corrosion sites. Among the most effec tive inhibitors are inorganic chromates whose safety has been questioned by some. While the elimination of these pigments may therefore be desirable, it is found that in the absence of effecitve corrosion inhibiting pigments extensive adhesion failure adja cent to coating defects and flaws can take place, resulting ultimately in the uncontrolled spread of corrosion. The principal cause of corrosion-induced 95 adhesion failure is generally thought to be displace ment and/or degradation of the coating resin by cathodically produced hydroxide ion. Corrosion inhibitors suppress this effect by slowing the overall rate of corrosion, limiting the amount of alkali pro duced. In the absence of corrosion inhibitors it is therefore necessary that the coating resin be excep tionally resistant to displacement and/or degrada tion by corrosion-produced hydroxide.

According to the present invention, there is pro vided a crosslinking composition which comprises:

(A) a substantially gell-free reaction product, optionally at least partially neutralized, made by reacting in non-aqueous medium; 1. A non-carboxy-ester linked epoxy reactant that 110 has an average of at least about two epoxy groups per molecule; 2. An amine reactant comprising (a) a primary hydroxy amine or (b) a secondary amine and, optionally, a primary amine and comprising at least mole percent hydroxy amine; the reactants being reacted in an equivalent amount such that the reac tion product (A) comprises tertiary amino and prim ary and secondary hydroxy groups and is substan tiallyfree of unreacted epoxy groups; (B) Optionally, an additional di- or polyhydroxy compound; (C) An amino resin crosslinking agent at about 5-35% by weight of the combined weight of (A) and (B), and (D) one or more hydroxy organophosphate esters of the general formula:

0 GB 2 109 383 A 1 11 (R-0). - P - (OW3-n wherein n is 1 or 2 and the or each of the n groups R is separately selected from mono- or di hydroxysubstituted hydrocarbon groups having up to 10 carbon atoms.

Surprisingly such compositions may be cured within commercially acceptable curing schedules without volatilisation of the amine to provide coatings that are resistant to deg radati on/d isplacement under corrosive conditions and may advantageously be cu red at even lower temperatures in the presence of catalyst.

Preferably the amine reactant is a secondary amine or a mixture of primary and secondary amines, each having a total of up to about 20 carbons per amino nitrogen and comprising at least 75 mole percent hydroxy amine containing one or more primary hydroxy groups removed at least one carbon from any amino nitrogen.

The crosslinking compositions of the invention may be formulated into solvent-based coatings such as spray primers that exhibit corrosion resistance considerably in excess of certain conventional primers. Moreover, the crosslinking compositions may be formulated into waterbased primers that exhibit desirable properties.

The discovery that corrosion prevention maybe accomplished in the absence of inhibiting pigments provides an alternative means of preventing corrosion that is believed to utilize a mechanism different than when inhibiting pigments as chromates are included. More particularly, available evidence indicates that cured coatings, as described more fully herein, rather than slowing the overall rate of corrosion by retarding anodic dissolution of iron as a means to retard corrosion, provide an adherent cross-linked network which is exceptionally resistant to deg radation/displacement by cathodically produced hydroxide and thus limit the total area over which the corrosion reactions can occur.

The preferred components of the crosslinking compositions of this invention will now be described in more detail. The combination of the components in a fashion that forms crosslinking compositions useful in solvent-base and water-base primer coating compositions will then be described. Compositional Ingredients EPOXY-AMINEREACTIONPRODUCT The epoxy amine reaction product is formed in non-aqueous medium by reacting a di or polyepox- ide (that is free of carbody ester moieties lining the epoxide groups) with certain amines.

1. Epoxy Reactant -The epoxy reactant essentially should contain at least abouttwo, on the average, epoxy groups per molecule and may contain three or more with a molecular weight preferably above about 300 (number average) and up to about 10,000 or more, depending on factors such as desired viscosity and solids content.

One class of suitable epoxy compounds for the epoxy reactant include reaction products of di or polyhydric, mono, di or polycyclic compounds with epihalohydrins of the formula 0 X-CH2-CY -CH2 2 GB 2 109 383 A 2 wherein X is halogen, especially chloro, and Y is hydrogen or lower a Ikyl such as methyl or ethyl. The epihalohydrin reaction products are exemplified by such straight-chain epoxy-terminated compounds containing glycidyl ether groups as bis-phenol A-epichlorohydrin reaction products that are com mercially available as, for example, under the trade names Epon 828, 1001 or 1004 (marketed by Shell Chemical Company). Such products contain aroma tic groups such as benzene nuclei at a preferred average of at least about one, more preferably for this invention at least about two, on the average, for each terminal epoxy group. Especially suitable are bis-phenol A-epichlorohydrin reaction products comprising in major amounts up to 10 or more bis phenol moieties within the epichlorohydrin reaction product backbone, e.g. molecular weights in a range of up to about 8000, preferably 700-6000, on a number average basis.

Other examples of epoxy compounds for the 85 epoxy reactant include polyepoxy compounds (averaging more than about two epoxy groups per molecule) which are also commercially available. In this group of epoxy compounds are the "Novolac" epoxy resins, e.g. Epon 152 and 154 (marketed by Shell Chemical Company). These polyepoxy resins include epoxidized products of phenol formaldehyde resins that contain terminal glycidyl ether groups from aromatic moieties.

Aliphatic (including cycloaliphatic) epoxy com pounds having, on the average, at least about two epoxy groups per molecule may also be employed.

Such aliphatic epoxy compounds include epihalohydrin and aliphatic di- or polyols, such as glycols, reaction products, epoxidized polybut dienes, vinylcyclohexenedioxide and dipentene dioxide. Still further, hydrogenated bis-phenol A-epichlororhydrin products may also be employed.

Compatible mixtures of any of these epoxy com pounds are also suitable.

In one preferred embodiment, the epoxy reactant comprises relatively high molecular weight (e.g.

number average above about 7000) epoxy com pound that have hydrophobic groups (such as epihalohydrin reaction products of a diol, e.g. bis phenol-A) for these have been found to advantage ously further provide enhanced moisture resistance to the cured coatings as compared to lower molecu lar weight epoxy compounds made in this way.

Alternatively, as will be more fully described hereinafter, certain lower molecular weight epoxy compounds may be reacted with primary and sec ondary alkanol amines to provide epoxy amine reac tion products that similarly provide more desirable moisture resistance. Preferably, however, the epoxy reactant comprises higher molecular weight epoxy compounds such as those bis-phenol A-epichlorohydrin reaction products that have at least about 25 mole percent (more preferably at least about 75 mole percent) of compounds that have two or more, e.g. about 3-10 aromatic groups per epoxy group.

2. Amine Reactants -The amine reactant prefer ably comprises secondary or primary and secondary amine desirably having a total of up to about 20 car- bons per amino nitrogen and with at least one hydroxy amine having one or more (preferably two) primary hydroxy groups on carbon atoms that are not adjacent to any amino nitrogen. Secondary amines are typically suitable with higher molecular weight epoxy compounds whereas combinations or primary and secondary amines are advantageous with lower molecular weight epoxy compounds as the epoxy reactant so as to increase the molecular weight of the epoxy amine reaction product. Secondary monoamines are normally employed with polyepoxides having three or more epoxy groups per molecule.

The hydroxy group of the hydroxy amine serves as a moiety that is believed to chemically react with at least a portion of the amino resin crosslinking agent during curing so as to provide a cross-linking coating; it is preferred that the hydroxy amines have primary hydroxy attached to aliphatic carbon. Also, at least one amino nitrogen of the hydroxy amine is preferably substituted only by aliphatic carbon, although other substituents are possible, for example, substituents comprising a carbon chain which is interrupted, for example by non-interferring heteroatoms such as oxygen, or substituted by aromatic groups, such as aryl groups or by tertiary amine groups.

Hydroxy aliphatic secondary amines and, particularly hydroxy alkyl secondary monoamines are advantageous forthe amine reactant in many instances, and especially desirable are hydroxy alkyl amines wherein the alkyl group is preferably lower alkyl i.e. containing up to 10 (more preferably up to 7) carbon atoms. In one preferred embodiment, the amine reactant comprises all or nearly all (e.g. 90 mole percent or greater) secondary amine that is amino alcohol and especially amino alcohol bearing two hydroxy alkyl substituents as, for example, diethanol amine.

A class of preferred hydroxy amines are illustrated according to the following formula: H I R-1 4-R' wherein R and Ware independently hydrogen of straight or branched chain aliphatic groups of up to about 10 carbons each providing that (a) at least one of R and R'is not hydrogen and (b) at least one of R and R'is substituted by hydroxy on a primary carbon atom that is not adjacent to any amino nitrogen. R and R'can also form part of a ring compound as a six membered ring. More preferably, R and Ware independently selected from alkyl groups and desirably contain up to 7 carbons each and especially for water-base formulations hydroxy (primary) alkyl up to 4 carbons each.

A variety of amines, however, may be suitably employed together as, for example, primary and secondary amines which are mixtures of alkyl amines and hydroxy alkyl amines. The important criterion is that there be suff icient hydroxy functionality, especially primary hydroxy, in the reaction product of the amine reactant and epoxy reactant to insure adequate reaction with the amino resin 130 crosslinking agent.

41 ffi 3 GB 2 109 383 A 3 Preferably, however, about 90 or more mole percent of the amine reactant comprises amino alcohols with primary hydroxy groups and di (hydroxy alkyl) monoamines preferably bearing a prim- ary hydroxy on both alkyl groups are especially preferred.

3. Reaction Conditions for Product of Epoxy Reactant and Amine Reactant The epoxy and amine reactants are reacted at conditions that allow opening of the epoxy ring by amino nitrogen and provide a gell-free reaction product. With secondary amines, this generally results in tertiary amino groups whereas primary amines provide secondary amino groups which may undergo further reaction with an unreacted epoxy group of the same or more probably of another molecule epoxy reaaaactant resulting in chain extension.

The reaction medium preferably comprises a non-aqueous medium preferably of polar character which serves to maintain contact of reactants, control reaction speed, maintain desirable viscosity and other functions well known in the art. Thus, suitable solvents and diluents for the reaction medium include aromatic and aliphatic hydrocarbons, organic halides, ethers, alcohols and ketones such as methylamyl ketone, n-amyl ether, xylene, butanol, oxygenated solvents such as propylene glycol monopropyl ether, cellosolves such as 2-methoxy ethanol, 2-butoxy ethanol, carbitols as ethoxy butoxy ethanol, and the like including mixtures of these. Moreover, di- and polyhydroxy compounds, as hereinafter disclosed, may also serve as reaction medium or part thereof.

Elevated reaction temperatures may be employed to facilitate reaction between the epoxy reactant and amine reactant and the reaction may be conducted stepwise. The reaction is complete when the product is substantially free of unreacted epoxy groups.

Nearly equivalent amounts (e.g. about 0.9-1.0 amine equivalents per 1 to 1.1 epoxy equivalent wherein an amine equivalent is one for a mole of secondary monoamine and two for a mole of primary monoamine and mole of diepoxide compound, for example, has two eqsuuuivalents) are preferred. Thus, the reaction product of the epoxy reactant and amine reactant should contain iess than 20% of the original unreacted epoxy groups, more desirably lessthan 10% as 5% or less unreacted epoxy groups, based on the number originally present. AMINO RESIN CROSSLINKING AGENT The amino resin crosslinking agent may be admixed with the above reaction product (A) at levels of about 5-30 weight percent of the combined weight of (B) and optional ingredient (C) as hereinafter described. Preferred amino resin crosslinking agents are the well known and commercially available materials that are principally condensation products of amino or amido compounds with aldehydes which may be modified by monohydric alcohols of normally up to about four carbons.

Especially preferred amino resin crosslinking agents are partially alkylated melamines (melamine formaldehyde resins modied by alcohols) e.g. par- tially methylated melamines and butylated mela- mines. Another preferred crosslinking agent is urea formaldehyde condensate modified by an alcohol such as a butylated urea formaldehyde resin. Mixtures of crosslinkers such as mixtures of alkylated melamines and alkylated ureas are found especially suitable as, for instance, in solvent base primers using butylated types at weight ratios of (a) buty lated melamine resin to (b) butylated urea resin of a: b of between 1: 1 to 10: 1.

Other suitable crosslinkers that are amino resins include glycoluril resins and benzoguanimine resin.

ADDITIONAL D1- OR POLYHYDROXY COMPOUND Di- and polyhydroxy compounds of diverse char acter may be employed to modify film properites as well as solvents (including reactive solvent) for solubilizing the crosslinking compositions. These compounds can also impart increased flexibility as well as reducing cratering in spray primers formulated with (A) and (B) above.

A preferred class of hydroxy compounds include aliphatic di hydroxy compounds, especially glycols and glycol ethers of the formula HO(-CaH2a0x (CbH2bO)YH wherein a, b, and Y are independent integers and a and b are from 2 to 6 and x and Y are from 0-10withthesum of xandY being 10 orless. Examples include ethylene glycol, dipropylene glycol, and 1, 6 hexanediol. Another class of glycols include hydroxy terminated polybutadienes, hydrogenated bis-phenol-A, such hydroxy compounds being of generally hydrophobic character and having molecular weights of about preferably 100-5000, number average. Higher boiling solvents (e.g. boiling point above about 180'C such as 190-250') that are of polar charactertend to interact with the crosslinking composition and thereby allow higher solids content.

ORGANOPHOSPHATE ESTER The hydroxy organophosphate ester is included as a catalyst forthe crosslinking compositions. This material is employed preferably between about 01-5% by weight of the combined weight of (A) epoxy amine reaction product and (B) amino resin crosslinking agent and provides not only reduced cure temperature but also, as distinguished from other usual strong catalysts advantageously does not increase moisture sensitivity in certain formulations, particularly solvent based primers and can also lead to improved corrosion resistance in water base primers as spray primers. The hydroxy orga- nophosphate ester comprises a hydroxy functional organophosphate which is present in the composition as a monoor diester or as mixture of such mono-and diesters. The hydroxy functional organophosphate esters useful in the composition of the invention have the formula: 0 - 11 (R-0)-n P - (OH),- wherein n = 1 to 2 and R is hydroxy substituted hydrocarbon, preferably selected from the group consisting of mono- or hydroxy alkyl, cycloalkyl, or aryl radicals. Preferably the alkyl, cycloalkyl, or aryl radicals contain 3 to 10 carbon atoms, and especially desirable are aliphatic or cycloaliphatic radicals 4 GB 2 109 383 A 4 substituted by hydroxy. Heterocyclic radicals, prefer ably containing oxygen as the heteroatom may be present as substituent.

Among the numerous suitable mono- or dihyd roxy functional radicals are: 2 - ethyl - 3 - hydroxy hexyl; 4 - methylolcyclohexylmethyl; 2,2 diethyl - 3 - hydroxypropyl; 8 - hydroxyoctyl; 6 - hydroxyhexyl; 2,2 - climethyl - 3 hydroxy - propyl; 2 - ethyl - 2 - methyl - 3 - hydroxypropyl; 7 hydroxyheptyl; 5 - hydroxypentyl;4-methyfolbenzyl;3-hydroxy- phenyl; 2,3 d,hydroxypropyl; 5,6 clihydroxyhexyl; 2 - (3 - hydroxycyclohexyl) - 2 hydroxy ethyl; and 2 - (3 - hydroxypentyl) - 2 - hydroxyethyl.

The above radicals are intended to be only exem plary and numerous other radicals failing within the 80 defined scope of the organophosphate esters useful in the compositions of the invention will be apparent to those skilled in the art. Among the most preferred radicals are mono- or dihydroxy functional alkyl radicals containing 3 to 10 carbon atoms.

A preferred method for preparing the hydroxy functional organophosphate esters useful in the compositions of the invention is by an esterification reaction between an excess of an aliphatic, cyc loaliphatic or aromatic diol or triol or mixture thereof and phosphorous pentoxide. When a triol is used as a reactant, preferably at least one of the hydroxyl groups should be secondary. The reaction between the diol or triol and the phosphorous pentoxide is generally carried out by adding phosphorus pentox- 95 ide portionwise to an excess of diol or triol in a liquid state or in solution in a suitable solvent. A preferred temperature for carrying out the reaction is between about 500C and about 600C. Due to the multiple hydroxy functionality of the diol ortriol reactant, minor amounts of polymeric acid phosphates as well as certain cyclophosphates are also generated during the reaction. These polymeric and cyclic materials also serve as a reactive catalyst and, therefore, need not be separated from the hydroxy phosphate esters described above. It is advan tageous in preferred embodiments of the invention to employ all reaction products, i.e., the hydroxy functional organophosphate esters and the minor amount of polymeric acid phosphate cyclophos phates, as well as excess diol or triol in the crosslinking compositions. Excess diol or triol may serve in those compositions as all or a portion of the optional hydroxy functional additive. Reactive catalysts prepared by the above preferred method will generally include about a 1 to 1 ratio of the mono- and cliester organophosphate.

Still another preferred method of preparing the hydroxy functional organophosphate esters useful in compositions of the invention is by an esterifica tion reaction between phosphoric acid and an aliphatic, cycloaliphatic or aromatic mono epoxide compound. This reaction is carried out by adding between about 1 and about 2 moles, preferably between about 1 and about 1.5 moles, of the mono-epoxy material to 1 mole of phosphoric acid or its solution in a suitable solvent. During the esterification reaction which occurs, a hydroxyl group is formed. If a clihydroxy radical is desired in the organophosphate ester, a monoepoxicle-bea ring 130 hydroxy functionality may be used as a reactant. Preferred monoepoxide materials useful in this method are well known monoepoxides selected from monoepoxy ethers, monoepoxy esters and alkylenes oxides. Exemplary of preferred monoepoxides for use in this esterification reaction are: propylene oxide, butylene oxide, cyclohexene oxide, styrene oxide, n-buty[glycidyl ether and ethy[glycidyl ether. As will be understood by those skilled in the art, the proportion of monoester and diester formed by the reaction with vary with the selected molar ratio of the monoepoxide and the phosphoric acid. When 1 mole of monoepoxide is used, per mole of phosphoric acid primarily monoester is formed while a molar ratio of 2to 1 results in primarily diester. A molar ratio of 1.5 to 1 will result in an approximately 1 to 1 mixture of mono- and diesters. In all cases a minor amount of the triester will be formed. While this triester obviously will not serve as a reactive catalyst, it will crosslink with the amino crosslinking agent of the composition and, thus, may be safely included.

The hydroxy functional organophosphate ester component of the crosslinking composition of the invention is a reactive catalyst which allows the composition to cure rapidly at a low temperature. The acid functionality of the mono- or diester or mixture of such esters reacts with the hydroxy reactive functionality e.g., amino resin crosslinking agent so as to include the reactive phosphate in the crosslinked network thereby not deleteriously effecting moisture resistance and, in some cases, improving corrosion resistance.

OTHER OPTIONAL INGREDIENTS Pigments maybe used in the primer compositions of this invention in accordance with the usual technique except, if desired, chromate pigments need not be included to get good corrosion resistance. Exemplary pigments include titanium dioxide, silica, carbon black, and barytes and are employed at pigment; binder (i. e. sum of (A) and (B) above) weight ratios of about 40:60-60:40. Other ing redients such as solvents, diluents, surfactants, catalysts and the like may also be included for their respective functions.

Other catalysts and especially acid catalysts may be used to accelerate cure of the primer compositions herein as by lowering.cure temperatures required to effect crosslinking within a 15-30 minute bake cycle from about 1800C to 140'Cor even less. Acid catalyst include proti-tor Lewis acid materials preferably at about.05-5.0% by weight of the pri'mer composition and.typlcat. acids include strong acids such as phosphoric acid, paratoluene sulfonic acid, and substituted boron compounds as trialkoxy boron compounds, although, however, certain of these materials may result in films which exhibit less than desired moisture resistance.

PRIMER FORMULATION The crosslinking compositions comprising epoxy reactant and amine reactant reaction product, amino resin crosslinking agent, organophosphate ester and, optionally, di or polyhydroxy compound may be formulated into a variety of primer formulations including those based on non-aqueous medium and b GB 2 109 383 A 5 water base medium. Such primers may be used as coatings for bare and treated steels (conversion coated with phosphates) as well as guide coats over previously deposited primers applied as by elec trodeposition. Conventional modifying ingredients 70 may be used in the primer formulations including, for example, flow control agents, pigment disper sants, thixotropes, anti-cratering aids, photostabiliz ers and the like.

1. Solvent Base Primers Solvent base primers exhibit good thermal and shelf stability and may be applied to metal subs trates according to usual techniques as by spray, curtain, dip and other such coating methods.

2. Water Base Primers Water base primers may be formulated from the crosslinking compositions as hereinbefore and hereinafter described. These water-based primers are made with at least partially neutralized epoxy amine reaction products. The amino resin crosslink- 85 ing agent is selected from water soluble and dispers ible agents as also described and employed at simi lar levels. The water-based primers may be applied as spray primers and also can be electrodeposited.

Water-based spray primers are advantageously prepared in water compatible solvents and diluents as ethylene glycols and alkylated glycols, e.g.

oxygenated solvents as cellosolves and carbitols and thereafter at least partially neutralized by acid, particularly weak organic acid as formic, acetic or butyric acid. Coupling agents may be advantage ously employed.

Water-based spray primers can be formulated with high levels of water e.g. greater than 10% as about 30-50% by weight and yet cure within conventional conditions as 1800C for 20-30 minutes and even less with certain catalyst as reactive hydroxy phosphate catalyst as herebefore and hereinafter described.

It is found that particularly advantageous water base spray primers may be formulated as stable emulsions when epoxy and amine reactants are reacted in water miscible solvent and the amine reactant comprises one or more water soluble amino alcohols containing up to 20 carbons, especially water soluble hydroxy alkyl amines, particularly secondary amines containing at least two primary hydroxy groups such as diethanol amine and dip ropanolamine.

Especially suitable water miscible solvents (water miscible as used herein means the solvent forms at 25PC a continuous phase with water when at 20% by weight of water or more) include as examples monohydroxy ethers such as Cj-C6 etherified glycols, e.g. of the formula R-(O(CH)x)y-OH wherein R is an alkyl group of from 1-8 carbons and x is 2-4 and Y is 1-10 and particularly those which have boiling points below about 1800C, e.g. 2-methoxy ethanol, 2-ethoxy ethanol, and propylene glycol monopropyl ether.

Other suitable solvents include ethanol, propanol, isopropanol and the like. Higher boiling e.g. above about 1800C glycols may also be used as co-reactive solvents.

In a convenient method of manufacture, a con centrate is made from reacting the epoxy reactant and the amine reactant in a water miscible solvent and thereafter at least partially neutralizing with weak organic acid of up to 4 carbons such as formic, acetic or axalic acid in the presence of an amino resin crosslinking agent to form a concentrate that may be thereafter readily dispersed in waterfor spraying.

Moreover, partially methylated or butylated melamine resins are preferred. Conventional pigment dispersants and other additives including silanes and organotitanates may also be employed.

3. Alternative Embodiment- Multicomponent Coating Composition The epoxy and amine reactants along with the amino resin crosslinking agent and, preferably, di or polyhydroxy compound, all as above described, may alternatively be reacted together on the substrate to be coated. Thus, in this embodiment the epoxy and amine reactants and desirable di or polyhydroxy compound (preferably having boiling points in excess of about 2000C) are initmately admixed and applied to the substrate to be coated and cured thereon. In this embodiment, however, the amine reactant can also comprise solely primary amine that is a hydroxy amine. The primary amine, however, is normally employed with di-epoxides.

Preferred primary amines, forthis embodiment, that contain a primaryhydroxy group, are hydroxy lower alkyl amines such as ethanol amino, propanolamine, pentanol amine and the like. If secondary amines that are hydroxy amines are employed, then such amines preferably also lower hydroxy aliphatic arilines such as dialkyl amines containing up to 7 carbon atoms, e.g. diethanolamine or as lower alkyl hydroxy alkyl amines such as 2- (methylamino)-ethanol.

In this embodiment, it is important for corrosion resistance properties that primer formulations are admixed shortly, e.g. within less than a few hours of but desirably greater than one half hour before application and cure. Advantageously, uncatalyzed multi-component crosslinking compositions may be cured within conventional curing schedules and, if desired, be accelerated by a catalyst. On the other hand, it is important that the amino resin crosslink- ing agent and epoxy reactant not be permitted to stand for an undue length of time (e.g. several weeks) prior to formulation with the amine reactant comprising primary amine and application to the substrate. Preferably, the multicomponent system is applied to substrates between about 30-600 minutes after mixing.

As mentioned, this alternative multicomponent embodiment preferably also utilizes a di- or polyhydroxy compound such that, for example, the di- or polyhydroxy compound advantageously serves as reactive solvent which allows crosslinking compositions and ulitmate coating compositions as primers which have high solids content. Moreover. film properties as flexibility may be enhanced through incorporation of the di- or polyhydroxy compound. In this regard, glycols of the formula HO-(C,,H2aO-)-)C--(CbH2bO-)-,H wherein a and b are independently 2-6 and x and y are independently 2-10 wherein the sum of x and y is 2-10 are prefer- ably employed.

6 GB 2 109 383 A 6 The alternative multicomponent coating composition advantageously may be formulated into a solvent base primer which may be applied in a variety of ways to the substrate as, for example, through 5 dip, spray, curtain and like coatings.

Regardless of the method of application, the composition is preferably cured by heating at temperatures of up to 1800C for 20-30 minutes.

The following examples are intended as illustrat- ing some of the more preferred aspects and, accordingly, should not be considered as necessarily limiting the scope of invention. All degrees are in degrees Celsius and parts in parts by weight unless specified otherwise.

EXAMPLE1

A heat curable coating composition suitable for automotive application is prepared from a bis phenol - A - epichlorohydrin epoxy resin, alkanolamine, and an amino resin crosslinking agent in the manner hereinafter set forth: Part A Preparation of Epoxy- alkanolamine Resin Parts by Weight 625 625 200 Materials Epon 1004M 25 Diethanolamine Methylarnyl ketone Butanol Reactor Charge Diethanolamine 30 Methylarnyl ketone 625 (1) Product of Shell Chemical Company; the reac tion product of epichlororhydrin and bis phenol-A, described as being a solid with a melting point of 95-1 OSOC; Gardner-Holt viscosity at 250C of G-U (40% wt solution in butyl Dioxtol (Trade Mark); Epoxide equivalent 875-1000 (g. resin per g-equivalent of epoxide). Equivalent weight (g resin to esterify one mole acid) 175. Data sheet SC:69-58.

The reactor charge is heated to 70-80C in a reac tion vessel equipped with a stirrer, reflux condenser, 90 and thermometer. The Epon 1004 is added over a four hour period. The temperature is maintained at 70-80PC throughout the addition of the epoxy resin and forfour hours thereafter. The epoxy alkanolamine resin so formed is then cooled to 500C and diluted with butanol. The resin is then cooled to room temperature, filtered and formulated into a primer as hereinafter described.

Part B Formulation of Primer Materials Epoxy-alkanolamine resin from part A Butylated melamine resin (RN602) (2) Urea resin (RN512) (3) Titanium dioxide pigment C-Black pigment Silica pigment Barytes pigment Xylene Butanol Reaction product (4) of 2-ethyl-1,3-hexandiol with PQ, (1 %based on resin solids) An unpigmented primer is prepared by dissolving the epoxy-alkanolamine resin, the butylated melamine, the urea resin, and the reaction product of 2-ethy]-1, 3-hexamediol with PO,, in the butanol and xylene. A mill base is then prepared using one- third of the unpigmented primer and the pigments shown above. The remaining clear primer is then added and thoroughly dispersed with the mill base. The resulting fully formulated primer is filtered, applied to cold rolled, unphosphated steel panels by spraying and cured at 1400C for 20 min. The cured coating displays excellent corrosion resistance in salt spray, good xylene solvent resistance, flexibility and hardness.

(2) Products of Mobil Chemical Company described as a butylated melamine formaldehyde resin with a viscosity of V-X; 58% non volatiles; acid number 2 maximum; solvent; n butanol.

(3) Product of Mobil Chemical Company described as a butylated ureaformaldehyde resin with a viscosity of V-Y; non volatiles 50% - 2%; acid number 3.5-4.5; colour Gardner/max; solvent 80% n-butanol and 20% ethyl-benzene.

(4) Prepared as follows:

In a three-necked round bottom flask equipped with a stirrer dropping funnel and a thermometer are placed 2500 grams of dry (dried over molecular sieves) 2-ethy]-1,3-hexanediol. Phosphorus pentoxide (450 grams) is added portionwise with continuous stirring and an exothermic reaction occurs. The addition of phosphorus pentoxide is regulated to maintain the temperature at 500C. Afterthe addition is complete, the reaction mixture is stirred at 500C for one more hour and then filtered. The acid equivalent weight by titration with medium hydroxide solution isfoundtobe357.

EXAMPLE 11

A heat curable water-based coating composition suitable for automotive application is prepared from epoxyamine reaction product and amino resin crosslinking agent in the manner as hereinafter set forth: Part A Preparation of epoxy alkanolamine reaction product Parts by Weight 39.9 4.6 0.67 15 11 102 50 110 0.23 Materials 95 Epon 1004(1) Diethanol amine Propasol P(2) Reactor Charge Diethanol amine loo Propasol P(2) Parts by Weight 405.27 45.41 299.31 45.41 299.31 (1) See Example 1, a product of Shell Chemical Company. (2) A product of Union Carbide Corporationpropylene glycol mo nopropyl ether.

The reactor charge is heated to 80-85'C in a reaction vessel equipped with a stirrer, reflux condenser and thermometer. The Epon 1004 is added over a 2 hour period. The temperature is maintained at 80-13TC throughoutthe addition and for 16 hours thereafter. The epoxy alkanol amine reaction product so formed is then cooled to room temperature and formulated into a water-based primer as hereinafter described:

0 it Ub 2 'IUU;Jbj A 1 7 Part B Preparation of Millbase Materials Epoxy alkanol amine reaction 5 product from part A PropasolP Barytes pigment Titanium dioxide pigment Iron oxide 10 Silica Parts by Weight 160.00 41.04 115.64 15.84 15.84 11.08 To 160 parts of the epoxy alkanol amine reaction product is added, 4.04 parts of Propsaol P is added and then shaken for 30 minutes. A homogeneous solution is obtained. To this then the pigments as Fully Formulated Primer Millbase from Part B Melamine resin (RN602) (2) 70 Acetic acid Reaction product (3) of 2-ethyl, 1-3-hexanediol and P,O, Water Parts by Weight 87.2 4.80 1.39 0.24 94.40 Unphosphated steel panels coated with the fully pigmented primer display excellent corrosion resistance to salt spray, good xylene solvent resistance, flexibility and hardness. (1) See Example XXI, a product of Union Carbide Corporation. shown above are added and then shaken for 6 hours. 80 (2) See Example 11, a product of Mobil Oil Chemical A Hegmann gauge reading of 6 to 7 is obtained. This is then used for preparation of fully formulated pigmented primer. Fully Formulated Water-Based Primer Materials Mi Ilbase from Part B Butylated melamine resin (RN602) (1) 25 Acetic acid Reaction product (2) of 2-ethyl, 1-3-hexanediol and IR2Q, Water (distilled) Parts by Weight 79.6 4.8 104 0.40 69.30 The mill base is weighed into a stainless steel con- tainer. To this millbase is added the melamine resin and stirred well using a disperator. Then the reaction product of 2 ethyl- l, 3-hexanediol with P0, is added and mixed well. The acetic acid is weighed into 10 parts of water in a glass container and then added to the millbase, melamine resin and phosphate reaction product under stirring. The balance of water is then added in 10-15 minutes under vigorous stirring. The whole mixing is accomplished in 15-20 minutes. The resulting fully formulated primer is filtered.

applied to cold rolled, unphosphated steel panels by spraying and cured at 18TC for 20 minutes. The cured coating displays excellent corrosion resistance in salt spray, good solvent resistance to xylene and good flexibility and hardness.

(1) See Example I; a product of Mobil Oil Company. 110 (2) See Example [for method of preparation. EXAMPLE111 The procedures for Example 1 are repeated with the following differences: The millbase is prepared with 30.5 parts of Propasol P instead of 41.04 parts and the fully pigmented primer contained higher level of water. The ingredients remain the same in kind. Part B Preparation of Millbase materials Epoxy - alkenol amine reaction product from Part A, Example 1 Propasol P (1) Barytes Titanium dioxide Iron Oxide Silica It is mixed as in Part B, Example 1.

Parts by Weight 160.00 30.50 115.64 15.84 15.84 11.08 Company. (3) See Example I for method of preparation.

It will be appreciated from the above examples that the preferred embodiments of the invention provide resins which are suitable for use in organic coatings which are highly resistant to alkali degradation. Coating formulations incorporating the resins of the invention enable ferrous substrates to be protected against corrosion without the incorporation of possibly deleterious corrosion inhibitive pigments. The preferred coating compositions of the invention are suitable for primers for automotive steel substrates and have application and handling characteristics, including shelf stability, which are compat-

Claims (19)

ible with conventional commercial painting operations and practice. CLAIMS

1. Acrosslinking composition which comprises:

(A) a substantially gell-free reaction product, optionally at least partially neutralized, made by reacting in non- aqueous medium: 1. A non-carboxy-ester linked epoxy reactant that has an average of at least about two epoxy groups per molecule; 2. An amine reactant comprising (a) a primary hydroxy amine or (b) a secondary amine and, optionally, a primary amine and comprising at least 75 mole percent hydroxy amine; the reactants being reacted in an equivalent amount such thatthe reaction product (A) comprises tertiary amino and primary and secondary hydroxy groups and is substantially free of unreacted epoxy groups; (B) Optionally, an additional di-orpolyhydroxy compound; (C) An amino resin crosslinking agent at about 5-35% by weight of the combined weight of (A) and (B); and (D) One or more hydroxy organophosphate esters of the general formula: 0 11 (R-O)n - P - (OH)3-n wherein n is 1 or 2 and the or each of the n groups R is separately selected from mono- or di hydroxy- substituted hydrocarbon groups having up to 10 carbon atoms.

2. A composition according to claim 1 wherein the amine reactant comprises either a secondary amine or a mixture of primary and secondary amines, each such primary or secondary amine hav- 8 kib Z 'I UU JU4 A ts ing a total of up to 20 carbon atoms per amino nitrogen and comprising at least 75 mole percent hydroxyamine containing one or more primary hydroxy groups removed by at least one carbon atom from 5 any amino nitrogen atom.

I A composition in accordance with claim 1 or claim 2 wherein the epoxy reactant comprises at least 25 mole percent of an epoxy compound containing at least two aromatic groups for each epoxy group.

4. A composition in accordance with anyone of claims 1 to 3 wherein (13) is present and comprises a glycol.

5. A composition in accordance with anyone of clairris 1 to 4 wherein the amino resin crosslinking agent comprises a melamine-formaldehyde resin, or a urea-formaidehyde resin or both.

6. A coin position in accordance with anyone of claims 1 to 5 wherein the amine reactant comprises an hydroxy aliphatic amine.

7. A composition in accordance with Claim 6 wherein the amine reactant comprises an hydroxyalkyl secondary amine.

8. A composition in accordance with claim 7, wherein the hydroxy-alkyl secondary amine comprises a dialkanol-amine.

9. A composition in accordance with anyone of claims 1 to 8 wherein the epoxy reactant comprises a bis-phenol-epichlorohydrin reaction product having a number average molecular weight above 700.

10. A composition in accordance with anyone of claims 1 to 9 wherein the hydroxy organophosphate esters are present in an amount of from 0.1 to 5% by weight, based on the total weight of (A) and (B).

11. A composition in accordance with claim 10 wherein R, or each group R independently, is a mono- or di-hydroxy aliphatic group.

12. Acrosslinking composition substantially as described herein in any one of the examples.

13. A primer composition containing a solvent and a crosslinking composition according to any one of claims 1 to 12.

14. A method for protecting a corrosion- susceptible substrate which comprises applying to the substrate a composition according to any one of claims 1 to 13, and curing the composition.

15. A method according to claim 14 wherein the composition is cured at a temperature of up to 180'C for 20-30 minutes.

16. A method in accordance with claim 14or claim 15 wherein the coating is applied by spraying.

17. A method in accordance with claim 14 wherein the coating is applied by electrodeposition.

18. A method of retarding corrosion of a corrosion-susceptible substrate substantially as hereinbefore described in any one of the Examples.

19. A substrate having a coating applied thereto in accordance with any one of claims 14to 17.

Printed for Her Majesty's Stationery Office by The Tweeddale Press Ltd., Berwick-upon-Tweed, 1983. Published at the Patent Office, 25 Southampton Buildings, London, WC2A lAY, from which copies may be obtained.

T ir