GB1595324A - Copolymers suitable for cathodic electrodeposition of paints - Google Patents

Description

PATENT SPECIFICATION ( 11) 1595324

0 ( 21) Application No 11307/80 ( 22) Filed 30 Nov 1977 ?'t ( 62) Divided out of No 1 595 323 ( 19) ( 31) Convention Application No 746 298 i ( 32) Filed 1 Dec 1976 U ( 31) Convention Application No 845 891 _ ( 32) Filed 31 Oct 1977 in ( 33) United States of America (US) ( 44) Complete Specification published 12 Aug 1981 ( 51) INT CL 3 C 08 F 8/00 ( 52) Index at acceptance C 3 J CE C 3 B 1 D 2 C 1 N 11 1 N 18 X 1 Nl A 1 N 1 F 1 N 2 A 1 N 4 B 1 N 6 D 3 1 N 6 D 5 1 N 6 D 7 1 N 7 1 N 8 B F C 3 W 211 C 3 Y B 212 B 215 B 230 B 240 B 242 ( 72) Inventor ISIDOR HAZAN ( 54) MODIFIED COPOLYMERS SUITABLE FOR CATHODIC ELECTRODEPOSITION OF PAINTS ( 71) We, E I DU PONT DE NEMOURS AND COMPANY, a Corporation organised and existing under the laws of the State of Delaware, United States of America, located at Wilmington, State of Delaware, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the 5 following statement:-

The present invention relates to modified copolymers, suitable for use in cathodically depositing polymeric coatings and coating compositions including the modified copolymers More specifically, it relates to modified copolymers suitable for use in a method of depositing coatings of acrylic polymers containing amino functionality with 10 minimum retained water and acid in the coatings.

It is known that organic coatings can be electro-deposited either on an anodicallycharged conducting substrate or on a cathodically-charged substrate Although most of the earlier work in electrodeposition was done with anodic deposition, that type of is process has certain disadvantages Anodic electrodeposition is normally done in a 15 coating bath having a basic p H The p H decreases at the surface being coated, creating conditions which, when combined with the electrolytic action of the coating bath, can cause the dissolution of substrate metal ions and their subsequent deposition in the coatings being formed This can be a source of staining and diminished corrosion resistance Also, electrolysis tends to attack preformed phosphate coatings Further 20 more, oxygen formed at the anodic substrate being coated can cause a variety of difficulties such as degration of coatings by oxidation.

Electro-endoomosis tends to expel water from anodic coatings being formed, leading to low water retention with about 85 to 95 % solids in the coatings This is an advantage over cathodic coating in which this phenomenon would not be expected to 25 be helpful (Parts and percentages herein are by weight except where indicated otherwise, and the expression of a range as " X to Y " or as " X-Y ", wherein X and Y are numbers is meant to be inclusive of both X and Y) Cathodic electrodeposition has developed more slowly, due in part to the acidic p H needed for the bath Also, water tends to be drawn into the coatings and held 30 there, along with acid residues from the bath It is apparent that this can lead to difficulties in the coatings In contrast to the oxygen formed at anodes in anodic electrodeposition, hydrogen is formed at the cathode in cathodic electrodeposition Even though this hydrogen can cause pinholes in coatings, it, of course, does not cause oxidative film degradation 35 Prior to coating with protective organic coatings, metal surfaces, particularly iron and steel, are normally given a pretreatment such as phosphatizing U S Patent 870,937-Coslett ( 1907) describes a method of treating iron or steel surfaces with phosphoric acid solutions which may include iron powder or iron phosphates In the evolution of phosphatizing coatings for metals, particularly ferrons metals, several chemical modifications of the phosphate coating have been found desirable, including the incorporation of calcium and molybdenum into the coating and postrinsing with chromate solutions 5 Processes and compositions for the cathodic electrodeposition of paints are described in U S Patent 2,345,543-Wohnsiedler, et al, ( 1944), which uses a cationic melamine-formaldehyde resin, and in U S Patent 3,922,212-Gilchrist ( 1975) , among others Gilchrist is directed to a process for supplementing the bath composition with a make-up mixture of materials containing an ionizing acid that is not consumed at as 10 fast a rate as the resin The acid is present in the make-up at lower concentrations than are used in the bath, so as not to build up the concentration of the acid in the bath Gilchrist uses particular aminoalcohol esters of polycarboxylic acids and discloses that acrylic polymers can be codeposited with zinc phosphate from solution on a cathodic substrate at low p H's such as 2 7 with phosphoric acid as the ionizing acid 15 Two U S patents dealing with nitrogen-based copolymers and their cathodic electrodeposition are 3,455,806 and 3,458,420, both to Spoor, et al, ( 1969) Cathodic sulfonium systems are described by Wessling et al on pages 110-127 of "Electrodeposition of Coatings ", Ed E F Brewer, American Chemical Society ( 1973) .

Electrodeposition processes have been frequently described in the literature Two 20 useful reviews of the technology are: " Electro-painting Principles and Process Variables", Brewer, Metal Finishing, September, 1976, p 58; and " Coatings Update:

Electrocoating ", Americus, Pigment and Resin Technology, August, 1976, p 17 However, neither of these articles nor any of the patents mentioned above suggest means for obtaining cathodically electrodeposited resin coatings with optimally low levels of water 25 and acid retention and high corrosion resistance.

SUMMARY OF THE INVENTION.

Our copending Patent Application No 49861/77 (Serial No 1 595 323) provides a process for electrocoating with a coating composition a negatively-charged substrate immersed in a coating bath containing an aqueous dispersion of said coating 30 composition, said bath having a cathode zone containing said substrate and an anode zone containing a charged anode, said substrate and said anode constituting oppositelycharged electrodes, the charged electrodes being maintained in electrical contact with each other by means of said bath, wherein said bath comprises a cationic film-forming polymer, an acidic ionizing agent, and a crosslinking agent, which process corm 35 prises:

employing phosphoric acid as an acidic ionizing agent; employing as a cationic film-forming polymer a modified copolymer having a backbone portion containing secondary and/or tertiary amine functionality, said modified copolymer being stabilized in the aqueous dispersion by a phos 40 phate salt of the amine functionality said backbone portion being reacted with hydrophobic copolymer derived from epoxy esters, said hydrophobic copolymer having a high enough concentration in the modified copolymer that the coating deposited on the substrate has at least about 83 % solids content and so that the phosphoric acid concentration in the deposited coat 45 ing composition is no more than about 17 5 % of the phosphoric acid concentration in the bath; and employing as the crosslinking agent a composition which is nonreactive in the bath but reactive with said film-forming polymer at elevated temperatures.

The present invention comprises acrylic resins particularly suited for use in 50 coating compositions for such processes, and is especially directed towards a resin suitable for use in primer compositions Our copending Application No 8011308 (Serial No 1,595,325) is concerned with a resin suitable for top-coat compositions which can be used either as a single coat or applied cathodically over an electricallyconductive primer 55 The primer resin is a modified copolymer of an epoxide portion reacted with an acrylic backbone and comprises, by weight based on the modified copolymer, about:

1,595,324 a in the acrylic backbone portion: 15 to 25 % of a polvmer or copolymer of at least one unit selected from alkyl, aminoalkyl, and hydroxyalkyl acrylates and methacrylates, said polymer or copolymer containing 0 02 to 0 1 (preferably 0 02 to 0 06) equivalent of secondary and/or tertiary amine functionality and optionally 0 01 to 0 05 (preferably 0 01 to 0 02) equivalent 5 of quaterary ammonium functionality; and b in the epoxide portion: 75 to 85 % of a copolymer contributing:

3 to 7 % of a glycidyl ester of a tertiary carboxylic acid containing 9 to 11 carbon atoms, and 72 to 80 % of a blend of a 55 to 60 % condensation polymer of epichloro 10 hydrin and bisphenol-A with 15 to 20 % tall oil fatty acids.

(Equivalents herein means equivalents of functionality per 100 grams of modified copolymer) One preferred embodiment is a modified copolymer comprising by weight based on the modified copolymer, about: 15 a 17 to 21 %, preferably 19 %, of a copolymer contributing:

3 to 5 %, preferably 4 %, methyl methacrylate 4 to 6 %, preferably 5 %, butyl acrylate, 1 to 4 %, preferably 3 %, hydroxyethyl methacrylate, 1 to 3 %, preferably 2 %, dimethylamino ethyl methacrylate, and 4 to 6 %/, preferably 5 %, t-butylamino ethyl methacrylate, reacted with 20 b 83 to 79 %, preferably 81 %, of mixture of about 5 % of 01 O R 2-C C-O-CH 2-CH CH 2 I R 3 wherein the R, R 2 and R 3 groups are saturated aliphatic chains which contain a total of 7 to 9 carbon atoms, and at least one of R 1, R 2 and R 3 is a methyl group, and 25 74 to 78 %, preferably 76 %, of a blend of 57 to 60 %, preferably 58 5 %, of a condensation polymer of 27 to 31 %, preferably 29 5 %/, epichlorohydrin and 27 to 31 %, preferably 29.25 %, bisphenol-A with 16 to 19 %, preferably 17 5 %, tall oil fatty acids.

DETAILED DESCRIPTION OF THE INVENTION 30

The present invention provides modified copolymers suitable for providing a practical means for cathodically electrodepositing first a passivating phosphate salt coating, preferably as at least a monolayer, and then electrodepositing over the phosphate a protective resin coating having low water and acid retention and high resulting durability and corrosion resistance The process can be used either on pretreated metal 35 such as phosphatized steel or on bare metal such as steel which has been cleaned but not phosphatized It can also be used on other metal substrates containing zinc, such as galvanized steel, as well as on aluminum and various alloys Since the process deposits a phosphate coating underneath the polymer coating, it is less sensitive than other electrocoating processes to variations in the substrate and its pretreatment If 40 the process is applied to material which has already been phosphatized, this versatility of the invention would enhance the phosphate coating However, phosphate pretreatment is not necessary.

There is preferably provided in the bath a water-soluble dihydrogen phosphate salt, M(H 1,2 P 0)2 (M=Fe, Zn, Ca, Mg or A 1) With the cathodic electrodeposition 45 the p H rises at the cathode, creating a boundary layer perhaps 0 01 to 0 1 cm thick, in which the soluble phosphate salt converts to an insoluble phosphate salt, M(HPO 4) or M 3 (PO 4)2, which is deposited onto the substrate surface Thus, the driving force for the salt deposition is a p H change and precipitation at the substrate surface The same type of p H change phenomenon also causes deposition of dense polymer coating 50 with the present invention This leads to denser coatings than electrophoresis of quaternary ammonium salts wherein a concentration gradient is the main driving force.

1,595,324 In a specific embodiment, with the coating voltage applied while a ferrous metal substrate is being immersed into the coating bath, the phosphoric acid in the bath dissolves small amounts of ferrous ion from the substrate The Fe(H 1,0 j), salt so formed is soluble in the bath at p H levels of 3 0 or below However, a boundary layer of increased p H quickly develops at the substrate, leading to the formation and deposi 5 tion on the substrate of the insoluble salts Fe(HPO 4) and Fe,(P Od), These salts give effective corrosion protection which is enhanced by the fact that they generally form a continuous layer on the substrate, usually at least a monolayer, rather than being entirely dispersed up into the overlying subsequently-formed resin coating.

Preferably, water-soluble zinc salts are included in the bath, and they too deposit 10 as insoluble phosphates at the substrate The dihydrogen phosphate of zinc, Zn(HP 04)j, is stable in the bath at a p H of 2 5 to 3 5 The invention is useful at p H values in the range of 2 0 to 4 0, preferably 2 5 to 3 0 At a p H below about 3.0, free phosphoric acid in the bath will react with ferrous metal substrates to generate the soluble dihydrogen phosphate of iron, Fe(H 2 P 04), Since the solubility of the di 15 hydrogen metal phosphates decreases with increasing temperature, the process of the invention is best operated with a bath temperature of 20 to 250 C When zincsalts are dissolved in the bath, the phosphate coating formed on the steel may likely include two minerals as the principal constituents These are phosphophyllite, Zn Fe(P 0), 4 H 2 O, and hopeite, Zn,(PO,), 4 H 10 20 The lack of practical success of several previous cathodic electrodeposition painting processes is due at least in part to the amount of water that is held in the resin coating and the acids and salts that are dissolved in that water, not readily removable from the coating The water can lead to coating failure by various mechanisms, and the acid residues can encourage subsequent corrosion, either directly or by providing 25 a hygroscopic material in the coating which encourages penetration of water and other corrosive agents.

In contrast to the useful effect of electroendoosmosis at the anode in anodic electrodeposition of paint which tends to expel water from an anodic coating, water is not electrically expelled from a cathodic coating and may actually be drawn into the 30 coating by electrical forces However, water held in a cathodic coating can be particularly undesirable To minimize such effects, the present invention provides resins with a degree of hydrophobicity and hardness or denseness of the coating which combine to expel water from the coating as the coating is formed.

The desirable effects of the invention are achieved by using certain hydrophobic 35 modified copolymers containing in their backbone portions secondary and/or tertiary amine functionality Such functionality aids in adhesion of the resin coating to the substrate even after heating the deposited coatings to cause them to crosslink This is an advantage over cathodic sulfonium systems in which hydrophobicity is only developed after thermal decomposition of the sulfonium groups Thermal decomposition of sul 40 fonium groups during crosslinking of the film would make them unavailable for enhancing adhesion of the resin coating to the substrate Also, although quaternary ammonium salts can be present in film-forming polymers of the invention, they cannot replace the secondary or tertiary amine groups The quatemary ammonium salts would decompose to some extent when the film is heated to cause crosslinking, thereby 45 losing their effectiveness in promoting adhesion to the substrate The polymer compositions of the invention are discussed in more detail below.

In the process using the resins of the invention, although there are advantages in using live entry, in which the coating voltage is applied while the articles to be so coated are being immersed into the bath, it will be apparent that reduced voltage 50 can be applied upon entry if desired for certain special effects However, the additional electrical apparatus required for reduced voltage entry is not normally necessary or desirable It is desirable for the coated substrate to be removed from the bath with the coating voltage still applied or soon after it is turned off.

For operating electrocoating baths using resins of the invention, the tank can be 55 lined with an organic coating resistant to the acidic p H of the bath, and stainless steel or plastic piping and pump parts can be used to minimize corrosion However, carbon steel parts often can be used, and the ferrous ions added to the bath by gradual dissolution of the equipment could be helpful rather than harmful to the coating process Due to its autopassivating effects, phosphoric acid is less corrosive to steel 60 than some other mineral acids at the p H levels used, so that more expensive materials of construction often are not necessary.

It has been found that common bacteria do not grow in the aqueous coating compositions of the invention Therefore, ordinary ultrafiltration can be used in recir1,595,324 culating the bath components to rinse contaminants from the coated parts Furthermore, membranes and ordinary flushed anodes may be desirable but are unnecessary.

As an alternative to flushed anodes, excess phosphoric acid build-up in the bath can be consumed by additions of zinc, Zn O, Zn(OH)2, or other metals or compounds which form the dihydrogen metal phosphates in solution 5 Although an uncoated tank can be used as the anode, in commercial practice one would normally use stainless steel anodes having a surface area smaller than that of the cathodic substrate which is to be coated This gives a favorable current density distribution.

In the electrocoating process using resins of the invention, the metal article pro 10 viding the substrate to be coated is immersed in a bath of an electrocoating cell, The bath is an aqueous dispersion of about 2-35 % by weight of a cationic film-forming polymer at least partially neutralized with an acidic material Preferably phosphoric acid is used in an amount of from 60 % of that required for stoichiometric reaction of the first hydrogen of the trivalent acid with all of the available amine group bonds 15 in the polymer to an excess of 120 % of stoichiometric The use of less than about % of the stoichiometric amount of phosphoric acid can lead to instability in the bath More than 120 %, even as high as 270 % or higher, can sometimes be tolerated, even though a low p H limit of 2 2 to 2 5 is approached as more free phosphoric acid is present In the presence of the acid, the film-forming polymer forms cations in the 20 bath.

The metal article is connected to the negative side of a direct current (D C) power source to become the cathode of the cell A voltage of about 1 to 500 volts is passed through the cell for the full dwell time of the article in the bath, about 0 01 to 5 minutes, and a coating of the cationic polymer is deposited When the coating reaches 25 the desired thickness, the article is removed from the bath Preferably, the article is rinsed with water or with filtrate taken from the process to remove excess coating.

Then the article is dried at ambient temperatures or baked for about 5 to 40 minutes at about 1000 to 300 C to give a finshed coating about 0 1 to 5 mils thick Typical efficiencies of about 30 mg film solids deposited per coulomb of electricity are obtained 30 The current density used in the electrocoating cell generally does not exceed 1.85 amperes/cm 2 ( 0 3 amperes/in 2) of anode surface which is immersed in the bath, and it is preferable to use lower current densities In the deposition of the cationic film-forming polymer, voltages of 5 to 400 for 0 25 to 2 minutes are preferred to form a high quality finish 35 Coating compositions of the present invention can contain pigments The pigments are normally added to the composition in the usual manner by forming a mill base or pigment dispersion with the pigment and the aforementioned cationic filmforming polymer or another water-dispersible polymer or surfactant This mill base is then blended with additional film-forming constituents and the organic solvents When the 40 mill base is subsequently acidified and dispersed in water, the polymers tend to wrap themselves around the pigments This has the effect of preventing destabilization of the dispersion or other undesirable effects that could come from using a basic pigment such as Ti O, in an acidic dispersion Pigments stable in acidic media can be used, such as the surface-treated Ti O, pigments of U S Patent 3,941,603-Schmidt ( 1976) Other 45 pigments that could be used include metallic oxides such as zinc oxides, iron oxides, and the like, metal flakes such as aluminum flake, metal powders, mica flakes with and without surface treatment such as with titania and carbon black, chromates such as lead chromates, sulfates, carbon black, silica, talc, aluminum silicates including china clay and finely divided kaolin, organic pigments and soluble organic dyes 50 Aside from cathodic electrodeposition, the novel coating compositions of the present invention can also be applied by any conventional method such as spraying, electrostatic spraying, dipping, brushing, flowcoating and the like, Reaction of the amine groups of the polymer with phosphoric acid is generally not necessary when the coating composition is to be used for purposes other than electrodeposition Organic 55 thermally decomposable acids, such as formic acid, can be used to obtain water solubility for such purposes The coating would then be baked for about 5 to 40 minutes at about 175 to 2000 C to give coatings of about 0 1-5 mils thickness When applied by cathodic electrodeposition, coating compositions of the invention are preferably applied to give dried thicknesses of about 0 8-1 2 mils 60 A crosslinking agent which can be water dispersed along with the filmforming constituent is used in the novel composition Based on the proportions of solids in the bath, which are roughly equal to the proportions of solids in the film, about 60 to %, preferably about 70 %, of cationic film-forming polymer are used along with 1,595,324 about 5 to 40 %, preferably about 30 %, of crosslinking agent.

Typical crosslinking agents that can be used with the invention are melamine formaldehyde, alkylated melamine-formaldehyde resins such as hexakis(methoxymethyl) melamine and partially-methylated melamine formaldehyde resins, butylated melamine formaldehyde resins, methylated urea-formaldehyde resins, ureaform 5 aldehyde resins, phenolformaldehyde and the like One particularly useful cross-linking agent which forms a high quality product with the cationic polymers is a benzoguanamine-formaldehyde resin A preferred benzoguanamine formaldehyde resin is XM 1125 produced by American Cyanamid Co, an acidic self-catalyzed crosslinking agent with an acid number of 25 to 32 10 When the novel compositions of this invention are used as primers over metals including treated and untreated steel, aluminum and other metals, conventional acrylic enamels, acrylic dispersion enamels and other coating compositions can be applied directly as topcoats over such primers Acrylic lacquers, acrylic dispersion lacquers, and acrylic powder coatings can be applied over the novel compositions, but a 15 suitable intermediate coat such as a sealer can be used to improve adhesion of the lacquer or powder topcoat to the primer.

The glycidyl ester used in the primer compositions and the epoxy-fatty acid constituents used in the primer composition contribute sufficient hydrophobicity to the polymer so that the electrodeposited film contains at least about 83 % solids, and 20 preferably 85 to 95 % solids Although such high solids levels are not uncommon for anodically deposited coatings, they are not readily achieved in cathodic electrodeposition because of the amount of water usually entrapped The phosphoric acid concentration of the electrodeposited film is in the range of 10 to 15 % of the concentration of phosphoric acid in the bath This is on the order of about 0 05 % of the 25 electrodeposited film itself These figures apply to the film as electrodeposited, before drying and baking The amine functionality in the film causes some small phosphate concentration in the film, but retained water will deleteriously increase the phosphoric acid content Empirical tests have shown that 20 to 25 % of the concentration of phosphoric acid in the bath being present in the film is an undesirable level, causing 30 diminished corrosion resistance, blistering, and other undesirable effects.

In the process using the modified copolymers of the invention, the critical concentration of phosphoric acid in the dry film is specified in terms of a percentage of the concentration of phosphoric acid in the bath Equivalents of phosphoric acid, in the form of phosphates reacted with amine groups of the polymer and metal phosphate 35 salts, are included in the term "phosphoric acid" for these purposes Relative to the entire electrodeposited coating, the metal phosphate layer directly on the substrate will contribute negligible amounts of phosphate Most of the phosphoric acid equivalents will be present as free phosphoric acid or as amine salts along with the water entrapped in the film The amount of phosphate ionically bound in the polymer 40 will vary depending on the amount of amine in the polymer Larger amounts of amines will lead to larger amounts of bound phosphate reacted with them Most of the phosphate is released from the polymer as phosphate ion as a result of p H change and electrical phenomena when the polymer is deposited on the substrate, but a variable amount remains in the film The most reliable measurement of the concen 45 tration of phosphate to be deposited is as a proportion of the concentration in the bath This is a dynamic value which depends upon coating speed, dragout and flushing rates It is best averaged over a period of time as phosphoric acid is added to the bath and partially removed in the coatings.

Although the process uses phosphoric acid for several reasons, most importantly 50 to allow the production of a phosphate coating on the substrate in the same process that produces the paint coating, other acids could be used in addition to the phosphoric acid for similar results Acids which form water soluble salts of the desirable metals at low p H, especially such salts of zinc, iron, calcium, magnesium and aluminum, and which then convert to insoluble salts in the boundary layer at increased p H, can be 55 useful Oxolic, chromic, sulfamic, benzoic and boric acids can have such effects However, the deposited salts of such acids in the absence of phosphates may not have the passivating or corrosion-inhibiting effects of phosphates.

Compositions of the invention can include additional adjuvants that do not materially change the basic and novel characteristics of the invention Some such 60 adjuvants are thickeners, defoamers, pigments, microgels, pigments dispersants, polymeric powders, microbiocides, and coalescing solvents Typical coalescing solvents which might be used at a concentration of about 0 5 % of the total bath volume are ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, and cyclohexanol.

1,595,324 7 1,595,324 7 Secondary amines in the backbone portion of the modified copolymer can function similarly to tertiary amines Secondary amines can be provided, for instance, by reacting glycidyl methacrylate with ammonia to form a primary amine which is converted to a secondary amine on reacting with appropriate amounts of epoxides It should be kept in mind that reaction to produce compositions of the invention changes secondary 5 amines in the reactants to tertiary amines and likewise changes primary amines to secondary amines and tertiary amines to quaternary ammonium salts.

Quaternary ammonium salts would be coated onto the substrates mainly by concentration gradient effects rather than by p H changes in the narrow boundary zone io which cause the deposition of secondary and tertiary amines The concentration 10 gradient effect is more gradual than the boundary zone effect, leading to softer, less dense coatings in the absence of the secondary and tertiary amine groups Such softer coatings would be bulkier and more porous and, therefore, more conductive.

This means that they would continue to build up in thickness with further electrodeposition In contrast, the self-limiting effect of less conductive films gives coatings 15 of more uniform thickness In addition to increasing the adhesion of the film to the substrate after baking, secondary and tertiary amines in the backboneportion also enhance stability of the polymer in water dispersions.

For enhanced adhesion to substrates and dispersion stability in water, the filmforming polymer of the invention preferably contains 0 04-0 8 equivalent of tertiary 20 amine functionality The preferred primer contains about 0 04 equvalent of tertiary amine functionality The preferred secondary amine before grafting is tbutyl amino ethyl merhacrylate, and the preferred tertiary amine is dimethylaminoethyl methacrylate.

Tertiary amines in the acrylic backbone portion before reaction with the epoxide 25 portion which are converted to quaternary ammonium salts upon reaction with the epoxide portion serve the useful purpose of enhancing the reaction Therefore, modified copolymers of the invention preferably contain about 0 01 to 0 05 (more preferably about 0 01 to 0 02) equivalent of quaternary ammonium functionality However, the quaternary ammonium functionality need not be built into the backbone portion but 30 can be provided as an external catalyst to enhance the polymerization In such a case, the somewhat deleterious effects of quaternary ammonium functionality in the backbone portion of electrodeposited coatings are avoided.

Although it is difficult to meaningfully quantify the softness or hardness of the resin, it is known that certain resins of the invention have a degree of hardness which 35 is useful in combination with the hydrophobicity characteristics of the resins in forcing water out of films to obtain the indicated levels of retained water and acid.

The molecular weights of polymers of the invention are generally not critical.

However, typical average molecular weights determined by gel permeation chromatography are: for the backbone portion-12,000; and for the primer modified copolymer 40 -11,000 to 12,000 These figures show that typically 80 to 85 % of the epoxide is grafted onto the backbone portion.

Although thoughts are expressed herein on why and how the advantages of the invention are obtained, the invention is described by the claims and does not depend upon theories 45 Specific examples will now be given of the preparation of modified copolymers of the invention and their use in cathodic electrodeposition processes.

EXAMPLE I.

A black primer coating composition is prepared and used as follows:

Part I and Part II describe the two resin compounds that are reacted and used 50 with the pigment dispersions of Part III in the paint of Part IV.

Part I.

This part describes the preparation of an epoxy ester for reaction with the backbone portion.

The following ingredients are charged into a reaction vessel equipped with a stirrer, 55 thermometer, reflux condenser and a heating mantle to form an epoxy ester resin solution:

1,595,324 Portion 1.

Epoxy resin (Epon 1001) (Epon 1001 is an epoxy resin of the formula Parts by Weight 1677 00 0 CH 3 CH 2-CH-CH 2-0 o C-0 o O _ CH 3 C-G O-CH 2-CH-CH 2 CH O k.1 CH 3 where m is an integer sufficiently large to provide a Gardner-Holdt viscosity at C of D-G measured in a 40 % weight solids polymer solution using ethylene glycol monobutyl ether solvent, and the resin has an epoxide equivalent of 450550.

Portion 2.

Tall oil fatty acids Benzyl trimethylammonium hydroxide Portion 3.

Ethylene glycol monoethyl ether 503 10 1.70 419 30 Portion 1 is charged into the reaction vessel, blanketed with nitrogen and heated to about 128 to 140 C to melt the resin Portion 2 is then added, and the ingredients are heated to about 150 to 160 C for about 3 hours with constant agitation until the reaction mixture has an acid number of 0 01 Portion 3 is added, and the ingredients are cooled and filtered.

The resulting epoxy ester resin solution has a solids content of about 84 %, an acid number no higher than 0 01, an epoxide equivalent of 1300-1900, and a GardnerHoldt viscosity of D-F at 25 C in a 40 % solids polymer solution using ethylene glycol monoethyl ether solvent.

Part I 1.

This part describes the preparation of an acrylic resin epoxy ester described above with it.

Portion 1.

Isopropanol Portion 2.

Methyl methacrylate monomer Butyl acrylate Tertbutylaminoethyl methacrylate Dimethylaminoethyl methacrylate Hydroxyethyl methacrylate Portion 3.

Isopropanol Methylethyl ketone Azobisisobutyronitrile Portion 4.

Methylethyl ketone Azobisisobutyronitrile and the reaction of the Parts by Weight 400 00 Parts by Weight 00 00 00 40.00 75.00 00 25.00 10.00 8.00 1.00 0 O Portion 5.

Ethylene glycol monoethyl ether 350 00 Portion 6.

Epoxy ester prepared in Part I 2300 00 Ethylene glycol monoethyl ether 350 00 5 Cardura E-10 125 00 (glycidyl ester of epichlorohydrin reacted with versatic acid 911 produced by Shell Oil Co) Dionized water 50 00 Portion 1 is charged into a reaction vessel, equipped as described above, and is 10 heated to its reflux temperature The reaction mixture is held under nitrogen during the entire reaction Portions 2 and 3 are separately premixed and added slowly simultaneously over a 90-minute period while maintaining the reaction mixture at its reflux temperature The reaction is containued for an additional 60 minutes The Portion 4 is added, and the reaction mixture is held at its reflux temperature for an additional 15 minutes Stripping of the reaction solvent is conducted simultaneously with the addition of Portion 5 which is to replace the reaction solvent When 533 00 parts of solvent are stripped and all of Portion 5 is added to the reaction vessel, Portion 6 is added and the temperature is brought at 1150 C to 1170 C and maintained for 4 hours with continuous agitation At the end of that period the epoxy number is determined 20 When the epoxy equivalent is zero or less than 1 epoxy unit per 500,000 gm, the reaction is finished The solids content is 70 %, and the Gardner-Holdt viscosity at % reduction of solids with ethylene glycol monoethylether is U to X.

Part III.

A black pigment dispersion is prepared as follows: 25 Parts by Weight Solution polymer prepared in Part II 318 00 Ethylene glycol monoethylether 84 00 Carbon black pigment 31 80 The above ingredients are premixed and charged into a conventional sand mill 30 and ground at a rate of 30 gallons per minute while controlling the temperature of the mixture below 70 C The resulting carbon black dispersion has about 58 % solids content.

An extender pigment dispersion using Al-silicate as the extended pigment is prepared as follows: 35 Parts by Weight Solution polymer prepared in Part II 193 00 Ethylene glycol monoethylether 142 00 Aluminium silicate 206 00 The above ingredients are premixed and charged into a conventional sand mill 40 and ground at a rate of 30 gallons per minute while controlling the temperature of the mixture below 70 'C The resulting aluminum silicate dispersion has about 63 % solids.

A water soluble phosphate salt of zinc, zinc dihydrogen phosphate, that is added to the ccating composition of above polymer to improve its corrosion resistance when 45 cathedically electrodeposited, is prepared as follows:

Parts by Weight Zn O (zinc oxide) 4 00 Phosphoric acid ( 85 %) 14 00 Deionized Water 500 00 50 The above ingredients are mixed for 5 to 8 hours at room temperature until complete solubility of the zinc oxide takes place The p H of the solution is 2 6 to 3 0.

1,595,324 Part IV.

The electrocoating composition of a flated black paint is prepared as follows:

Portion 1 Parts by Weight Resin solution of Part II 320 00 Black pigment dispersion of Part III 97 00 5 Aluminum silicate pigment dispersion of Part III 440 00 Benzoguanamine formaldehyde solution (XM 1125 produced by American Cyanamid Co, 85 % in ethylene glycol monobutyl ether) 190 00 Portion 2 10 Deionized water 632 00 Phosphoric acid ( 85 %) 22 00 Portion 3.

Zinc dihydrogen phosphate 510 00 Portion 1 is added into a mixing vessel, heated to 150 'F and mixed for 3 hours, 15 applied to the cell for 2 minutes at an ambient temperature of 20-250 C, and a mixed for 10 minutes, and Portion 1 is added into Portion 2 with continuous agitation.

The pigmented water dispersion is mixed for 2 hours and diluted to about 15 % solids with deionized water and Portion 3 so that the concentration of zinc dihydrogen phosphate salt in the paint dispersion will be 450 ppm based on the total weight of 20 the electrocoating composition.

The electrocoating composition, having a p H of 2 7 and a conductivity of 1700 micrcmhos, is charged into a stainless steel tank for electrodeposition An untreated cold rolled steel panel or a phosphatized steel panel is positioned in the centre of the tank, electrically connected to the negative side of a DC power source, and forms the 25 cathode of the electrocoating cell The tank is connected to the positive side of a DC power source and forms the anode of the cell A direct current of 150 volts is applied to the cell for 2 minutes at an ambient temperature of 20-25 C, and a paint film of about 0 6 mils is deposited on the panel The coated metal panel is removed from the electrocoating cell, washed and baked at about 160 WC for 30 30 minutes The resulting primer film has excellent adhesion to the metal substrate, is hard and has very good corrosion and saponification resistance over bare cold rolled steel and phosphatized steel An acrylic enamel adheres to the primer film, and conventional acrylic lacquers can be applied with a conventional sealer coat over the primer to form a high quality finish 35 Typical deposited films contain 90 to 95 % solids and 10 to 12 % of the phosphoric acid present in the bath.

This coating composition is particularly useful for priming automobile and truck bodies by electrodeposition for maximum corrosion protection over all parts of the car including areas of poor phosphate pretreatment or no pretreatment at all 40 EXAMPLE I

A white pigment dispersion is prepared as follows:

Parts by Weight Solution polymer of Part II of Ex I 314 00 Ethyleneglycol monoethylether 137 00 45 Titanium Oxide 549 00 The above ingredients are premixed and charged into a conventional sand mill and ground at a rate of 30 gallons per minute while controlling the temperature of the mixture below 70 C The resulting titanium oxide dispersion has about 76 % solids content 50 A white coating composition is prepared as follows:

Portion 1 Parts by Weight Resin solution of Part II of Ex 1 560 00 Benzoguanamine formaldehyde resin solution ( 85 % in ethylene glycol monobutyl ether) 245 00 55 Titanium dioxide pigment dispersion 700 00 1,595,324 Portion 2.

Phosphoric acid ( 85 %) 30 00 Deionized water 1400 00 An electrocoating composition of 15 % solids and p H of 2 8 is prepared using Portions 1 and 2 and electroccated following the procedure described in Example I 5 This coating composition is useful either as a primer or as a single coat directly on metal for appliances or industrial equipment It has good corrosion resistance and detergent resistance over bare cold rolled steel or phosphatized steel.

Coatings prepared as in Example I give similar results.

Claims (1)

1. WHAT WE CLAIM IS: 10

   1 A modified copolymer comprising an epoxide portion reacted with 4 an acrylic backbone portion and comprising, by weight based on the modified copolymer, about:

   a In the acrylic backbone portion: 15 to 25 % of a polymer or copolymer of at least one unit selected from alkyl, aminoalkyl, and bydroxyalkyl acrylates and methacrylates, said polymer or copolymer containing 0 02 to 0 1 equi 15 valent of secondary and/or tertiary amine functionality; and b in the epoxide portion: 75 to 85 % of a copolymer contributing:

   3 to 7 % of a glycidyl ester of a tertiary carboxylic acid containing 7 to 9 carbon atoms, and 72 to 80 % of a blend of 55 to 60 % of a condensation polymer of epichlorohydrin and bisphenol-A with 15 to 20 % tall oil fatty 20 acids.

   2 A modified copolymer according to Claim 1 also containing in said acrylic backbone portion about 0 01 to 0 05 equivalent of quaternary ammonium functionality.

   3 A modified copolymer according to Claim 1 or 2 containing in said acrylic backbone portion about 0 02 to 0 06 equivalent of secondary and/or tertiary amine 25 and 0 01 to 0 02 equivalent of quaternary ammonium functionality.

   4 A modified copolymer according to Claim 1, 2 or 2 comprising by weight based on the modified copolymer, about:

   a 17 to 21 % of a copolymer contributing:

   3 to 5 % methyl methacrylate, 30 4 to 6 % butyl acrylate, 1 to 4 % hydroxyethyl methacrylate, 1 to 3 % dimethylamino ethyl methacrylate, and 4 to 6 % t-butylamino ethyl methacrylate, reacted with 35 b 83 to 79 % of mixture of about 5 % of R 1 0 0 R 2-C C-O-CH 2-CH CH 2 R 3 wherein the R,, R 2 and R 3 groups are saturated aliphatic chains which contain a total of 7 to 9 carbon atoms, and at least one of R 1, R 2 and R, is a methyl group, and 74 to 78 % of a blend of 57 to 60 % of a condensation 40 polymer of 27 to 31 % epichlorohydrin and 27 to 31 % bisphenol-A with 16 to 19 % tall oil fatty acids.

   1,595,324 A modified copolymer according to Claim 4 comprising, by weight based on the modified copolymer, about:

   a 19 % of a copolymer contributing:

   4 % methyl methacrylate, 5 % butyl acrylate, 5 3 % hydroxyethyl methacrylate, 2 % dimethylamino ethyl methacrylate, and % t-butylamino ethyl methacrylate, reacted with b 81 % of mixture of about 5 % of R 1 0 0 R 2-C-C-O-CH 2-CH CH 2 10 I R 3 wherein the R 1, R, and R, groups are saturated aliphatic chains which contain a total of 7 to 9 carbon atoms, and at least one of R,, R 2 and R, is a methyl group, and 76 % of a blend of 58 5 % of a condensation polymer of 15 29.25 % epichlorohydrin and 29 25 % bisphenol-A with 17 5 % tall oil fatty acids.

   6 An aqueous coating composition comprising a modified copolymer according to any one of the preceding claims which has been dissolved in organic solvents, phosphoric acid reacted with the amine groups of the modified copolymer, and a crosslinking 20 agent, said composition being dispersed in water.

   7 An aqueous coating composition according to Claim 6 containing about 2-35 % by weight of the modified copolymer.

   8 An aqueous coating composition according to Claim 6 or 7 which has been adjusted to a p H of 2 0-4 O by the addition of phosphoric acid 25 9 An aqueous coating composition according to Claim 6, 7 or 8 in which the cross-linking agent is a benzoguanamine formaldehyde resin.

   An aqueous coating composition according to any one of Claims 6 to 9 which also contains dissolved dihydrogen phosphate salts of one or more of zinc, iron, calcium, aluminum and magnesium 30 11 An aqueous ccating composition according to any one of Claims 6 to 10 which also contains titanic pigments which have been added to the modified copolymer before it is dispersed in water.

   12 A copolymer according to Claim 1 substantially as herein described and exemplified 35 13 A method of making a copolymer according to Claim 1 substantially as herein described.

   14 An aqueous coating composition according to Claim 6 substantially as herein described and exemplified.

   15 A method of making an aqueous coating composition according to Claim 6, 40 substantially as herein described.

   For the Applicants, CARPMAELS & RANSFORD, Chartered Patent Agents, 43 Bloomsbury Square, London, WC 1 A 2 RA.

   Printed for Her Majesty's Stationery Office by the Courier Press, Leamington Spa, 1981.

   Published by the Patent Office, 25 Southampton Buildings, London, WC 2 A l AY, from which copies may be obtained.

   1,595,324