Patent Publication Number: US-4321305-A

Title: Beta-diketone-epoxy resin reaction products useful for providing corrosion resistance

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to treating metallic substrates, particularly ferrous metal substrates, so as to impart corrosion resistance thereto. 
     2. Brief Description of the Prior Art 
     It is well known in the art that chromic acid and phosphating pretreatments can be used to impart corrosion resistance to substrates. Examples of these pretreatments are the phosphating treatments which include iron phosphating, mixed iron and calcium phosphating and zinc phosphating. Such pretreatments may optionally be followed by a chromic acid rinse. The pretreatment operations, although employed on many industrial electrodeposition lines, are undesirable for a number of reasons. First of all, pretreatments are expensive. Besides the cost of the chemicals themselves, a considerable capital investment is required for equipment. In addition, pretreatments cause pollution problems, the solutions of which add to their expense. Also known in the art are onium salts of monomers and polymers which can be used to pretreat metallic substrates to impart corrosion resistance. 
     The present invention relates to the reaction products of a beta-diketone and an epoxy material; presently said products can be used for the preparation of compositions which impart excellent corrosion resistance properties to substrates treated therewith. 
     Reference is hereby made to commonly assigned Ser. No. 193,047, filed even date herewith, entitled &#34;Beta-Diketone-Epoxy Resin Reaction Products Blended With Monomeric or Polymeric Phosphonium Salts Useful for Providing Corrosion Resistance.&#34; 
     SUMMARY OF THE INVENTION 
     In accordance with the foregoing, the present invention encompasses a novel composition of matter comprising the reaction product of: 
     (A) an epoxy material, and 
     (B) a beta-diketone of the formula: ##STR1##  wherein R 1 , R 2  and R 3 , each independently, is a hydrogen or a hydrocarbyl group preferably containing from about 1 to about 18 carbon atoms, selected from the group consisting of alkyl or aryl. 
     It is recognized that when R 1  or R 2 , each independently, is a hydrogen, the compound according to the afore-described structure would be a ketoaldehyde or a dialdehyde which could be as useful as the beta-diketone in preparing the instant novel compositions of matter. The carboxyl hydrogen of the aldehyde, particularly the dialdehyde, is, however, highly reactive and may, for that matter, be less desirable. Should that reactivity be made manageable, the aldehydes would be well suited for the present invention. 
     The term &#34;hydrocarbyl group&#34; as used herein denotes both unsubstituted and substituted hydrocarbons, provided that the substituent does not adversely affect the reactions of the beta-diketones or the use of their reaction products. 
     The term &#34;beta-diketone&#34; as used herein is, therefore, intended generically to classify the reacting compounds of the present invention in accordance with the afore-described structural formula. Severally, these compounds are also referred to herein as aldehydes and ketones. Consonant therewith, the beta-diketones that are useful herein are those which enolize in amounts that render them sufficiently acidic and reactable with the epoxy materials to provide the instant reaction products in sufficient amounts. 
     The present invention also encompasses water-dispersible compositions comprising the reaction product and a water-solubilizing group. Preferably, the water-solubilizing group is a precursor of an onium salt. Accordingly, the water-dispersible compositions of the present invention comprise an onium salt; said compositions contain the reaction product of: 
     (A) an epoxy material; 
     (B) a beta-diketone of the formula: ##STR2##  wherein R 1 , R 2  and R 3 , each independently, is a hydrogen or a hydrocarbyl group preferably containing from about 1 to about 18 carbon atoms, selected from the group consisting of alkyl or aryl; and 
     (C) an onium salt precursor which is an acid salt of a tertiary amine, a tertiary phosphine-acid mixture, or a sulfide-acid mixture. 
     The methods of preparing the novel compositions of matter, and the water-dispersible compositions thereof, particularly those comprising the onium salt, are encompassed by this invention. The methods of using the products of this invention to provide improved corrosion resistance to ferrous metal substrates are also encompassed by the present invention; particularly preferred is the method of electrodeposition. 
     The method of providing improved corrosion resistance to a metal, particularly a ferrous metal substrate, comprises the steps of: 
     (1) applying to the surface of the substrate an aqueous dispersion containing the reaction product of: 
     (A) an epoxy material; 
     (B) a beta-diketone of the formula: ##STR3##  wherein R 1 , R 2  and R 3 , each independently, is a hydrogen or a hydrocarbyl group preferably containing from about 1 to about 18 carbon atoms, selected from the group consisting of alkyl or aryl; and 
     (C) an onium salt precursor which is an acid salt of a tertiary amine, a tertiary phosphine-acid mixture, or a sulfide-acid mixture; followed by 
     (2) directly coating the surface with a coating material. 
     It has been found that the novel compositions can be formulated optionally with curing agents to provide compositions with improved properties. Films obtained therefrom are corrosion and solvent resistant; they are hard, and possess good appearance and substrate adhesion. 
     The metal substrates obtained by methods of this invention are also hereby encompassed. 
     DETAILED DESCRIPTION 
     The novel compositions of this invention can be prepared by reacting an epoxy material and a beta-diketone in a manner which is set forth more fully hereinafter. 
     The epoxy material may be of a resin class containing at least one 1,2-epoxy group. The resin may be, for example, among the general classes commonly referred to as polyethers, polyesters, acrylic, urethane, and the like. Although monoepoxides such as phenyl glycidyl ether, n-butyl glycidyl ether and the like can be utilized, it is preferred that the epoxy material contain more than one 1,2-epoxy group per molecule, i.e., polyepoxide. Examples of suitable polyepoxides are described in U.S. Pat. Nos. 2,467,171; 2,615,007; 2,716,123; 3,030,336; 3,053,855 and 3,075,999. 
     Particularly preferred polyepoxides are polyglycidyl ethers of cyclic polyols, particularly polyphenols such as bisphenol A. These may be produced by etherification of a cyclic polyol with epichlorohydrin or dichlorohydrin in the presence of alkali. Examples of cyclic polyols are bis(4-hydroxyphenyl)-2,2-propane, 4,4&#39;-dihydroxybenzophenone, bis(4-hydroxyphenyl)-1,1-isobutane, bis(4-hydroxytertiarybutylphenyl)-2,2-propane, bis(2-hydroxynaphthyl)methane, 1,5-hydroxynaphthalene or the like. Also, polyepoxides similarly produced from epichlorohydrin and novolak-type phenol resins may be employed. 
     Also preferred are the acrylic polymers containing epoxy groups. Preferably, these acrylic polymers are polymers formed by copolymerizing an alpha,beta-ethylenically unsaturated epoxy-containing monomer, such as, for example, glycidyl acrylate or methacrylate with other copolymerizable alpha,beta-ethylenically unsaturated monomers. 
     Any polymerizable monomeric compound containing at least one ##STR4## preferably in terminal position, may be polymerized with the unsaturated glycidyl compounds. Examples of such monomers include: 
     1. monoolefinic and diolefinic hydrocarbons; 
     2. halogenated monoolefinic and diolefinic hydrocarbons; 
     3. esters of organic and inorganic acids; 
     4. organic nitriles. 
     The acrylic polymers, their method of preparation and the copolymerizable monomers are known in the art. Examples thereof are disclosed by U.S. Pat. No. 3,928,156, column 4, line 40, through column 6, line 68, which is herein incorporated by reference. 
     As set forth hereinbefore, the beta-diketones that are useful in this invention are those which enolize in amounts that are sufficient to render them acidic and reactable with the epoxy material. The preferred beta-diketones have a percent of enolization of about 40 percent or higher. In accordance with the afore-described formula, the following are specific but non-limiting examples of the beta-diketones which are useful herein. 
     When either R 1  or R 2  is hydrogen, the beta-diketones useful herein are preferably 3-keto-1-butanol, 3-keto-1-hexanol and 3-keto-1-pentanol; and when both R 1  and R 2  are hydrogen, the beta-diketone useful herein is propane dialdehyde. 
     When R 1  and R 2 , each independently, is alkyl such as methyl, ethyl, propyl, butyl, pentyl and higher alkyl groups such as decyl, hexadecyl or the like, the beta-diketones useful herein are preferably 2,4-pentanedione; 2,4-hexanedione; 2,4-heptanedione; 5-methyl-2,4-hexanedione; 1-cyclohexyl-1,3-butanedione; and 5,5-dimethyl-1,3-cyclohexanedione. 
     When R 1  and R 2 , each independently, is an aryl group such as phenyl, naphthyl, anthracyl, diphenyl or the like, the beta-diketones useful herein are preferably 1-phenyl-1,3-butanedione; 1-(4-biphenyl)-1,3-butanedione; and 1-phenyl-5,5-dimethyl-2,4-hexanedione. 
     R 1  and R 2  each may be a member of a heterocycle, provided that the hetero-atom is not directly attached to the carbonyl carbon. Beta-diketones such as 1-(2-furyl)-1,3-butanedione and 1-(tetrahydro-2-furyl)-1,3-butanedione are illustrative of this group of beta-diketones. 
     R 3  is more preferably a hydrogen or a lower alkyl such as methyl, ethyl, and the like; hydrogen is particularly preferred. 
     Typically, the beta-diketones having a percent of enolization of about 40 to about 99 are particularly preferred. Accordingly, 1-phenyl-1,3-butanedione is very highly preferred. Others such as 2,4-pentanedione, 3-keto butyraldehyde and propane dialdehyde possess a high degree of enolization and would, therefore, be preferred. 
     In preparing the novel reaction product, the afore-described beta-diketones and the epoxy material are reacted, preferably in an equivalent ratio of about 0.1 to about 0.6, more preferably in an equivalent ratio of about 0.35 to about 0.45 of the beta-diketone to an equivalent of the epoxy material, in the presence of a catalyst. 
     Catalysts such as phosphonium salts, for example, ethyl triphenyl phosphonium acetate, ethyl triphenyl phosphonium iodide and tetrabutyl phosphonium acetate are present in the preparation of the novel composition of the present invention. The amount of catalyst ranges from about 0.1 to about 2 percent based on total weight of the reactants. A solvent is not necessary in this reaction even though one is often used in order to afford better control of the reaction. Solvents which are used in this reaction should be such as would not interfere with the enolization of the beta-diketone. The reaction is carried out over a time and temperature range which will not adversely affect the enolization of the beta-diketones. Preferably, the reaction is conducted over the temperature range of 100° to 160° C. for about 1 to 4 hours; the time and temperature, of course, depend on one another and on the specific reactants, catalysts and other reaction conditions. 
     Water-solubilizing groups are used to make the novel reaction product water-dispersible. The preferred water-solubilizing groups are precursors of cationic groups. Preferably, the cationic groups useful herein are onium groups such as a quaternary ammonium, phosphonium, and ternary sulfonium salt. An onium salt can be prepared by reacting the novel composition of this invention with an onium salt precursor. By the term &#34;onium salt precursor&#34; herein is meant a tertiary amine-acid salt, a tertiary phosphine-acid mixture or sulfide-acid mixture. U.S. Pat. Nos. 3,962,165; 3,894,922; 3,959,106 and 3,937,679 which are herein incorporated by reference, more fully describe the onium salt precursors useful in the present invention. Also, quaternary ammonium hydroxide-containing reaction products can be used. Formation of quaternary ammonium hydroxides is described in U.S. Pat. No. 4,081,341. 
     In preparing the onium salt, the epoxy-beta-diketone reaction product is prepared with residual epoxy groups in amounts which are reactable with the onium salt precursor to form the onium salts in amounts sufficient to form a stable aqueous dispersion. By &#34;stable&#34; is meant the dispersion will not sediment at room temperature after standing for 24 hours. However, if some sediment does form which can be redispersed with low shear mixing, this also is considered to be a stable aqueous dispersion. The reaction of the onium salt precursor with the reacting novel composition of matter is essentially the same as the onium salt formation reactions described in the aforementioned U.S. patents which have been incorporated by reference. 
     The amount of onium salt precursor which is reacted with the novel composition can be reckoned from the amount of the starting beta-diketone and the epoxy material. Accordingly, the equivalent ratio of the epoxy material to the beta-diketone to that of the onium salt precursor is, preferably, 1.0/0.1-0.6/0.4-0.9; more preferably, the equivalent ratio is 1.0/0.35-0.45/0.55-0.65. 
     Even though the above-described reaction scheme for the formation of the onium salt of the novel compositions is preferred, it is, however, believed that alternate schemes could be effectively adopted. 
     In other embodiments, the water-solubilizing groups are amine salts such as secondary or tertiary amine salts. They can be prepared by reacting the novel compositions of matter with primary or secondary amine followed by at least partially acid neutralizing the reaction product. Examples of amines are mono- or dialkylamines such as ethylamine or diethylamine, as well as hydroxyalkylamines such as diethanolamine. Examples of the acids are organic and inorganic acids such as lactic acid, acetic acid and phosphoric acid. 
     In the practice of the present invention, aqueous compositions of the novel reaction product can be employed to impart corrosion resistance properties to metals, particularly ferrous metals. Preferably, the aqueous compositions are in the form of dispersions or solutions. The concentration of the novel reaction product in the aqueous dispersion can be critical. The concentration will probably vary depending on application. If the concentration is too low, insufficient protection may be obtained. If the concentration is too high, corrosion resistance may again suffer. At a lower concentration limit, the dispersion should contain at least about 1 percent by weight of the novel reaction product; the percentage by weight being based on total weight of the aqueous dispersion. In general, an upper limit of 20 percent can be recommended. Preferably, water constitutes at least 25, preferably at least 50 percent of the aqueous medium with the remainder, if any, being organic cosolvents. 
     The dispersions of the novel composition can be applied to the surface of the substrate in any convenient manner such as by immersion, spraying, or wiping the surface either at room temperature or at elevated temperature. When desirable, the aqueous dispersions can be cathodically electrodeposited on substrates, under the general conditions of electrodeposition, without compromising the corrosion resistance properties or the properties of latter applied coatings (whether electrocoated or not). It should be appreciated that when the latter applied coating is by electrodeposition, the treated substrate (by electrodeposition) is not completely insulating. 
     After the application, the metal article is dried. Ferrous metal articles treated with compositions of this invention have been found to display good corrosion resistance properties. They can be exposed to the atmosphere without danger of atmospheric oxidation on the surface. After drying, the metal substrates can then be coated with a decorative or protective coating. 
     As set forth herein, the novel compositions can be formulated, in a combination, with curing agents to provide compositions with additional properties. When formulated with curing agents, it is preferred that the novel compositions also contain active hydrogens which are reactive at elevated temperatures with a curing agent. Examples of active hydrogens are hydroxyl, thiol, primary amine, secondary amine (including imine) and carboxyl, with hydroxyl being preferred. 
     The curing agents are those which are capable of reacting with the active hydrogens to form a crosslinked product. Examples of suitable curing agents are phenolic resins, aminoplasts, and blocked polyisocyanates which are preferred. 
     Suitable aminoplasts for use in the invention are described in U.S. Pat. No. 3,937,679 to Bosso et al in column 16, line 3, continuing to column 17, line 47, the portions of which are hereby incorporated by reference. As disclosed in the afore-mentioned portions of the &#39;679 patent, the aminoplast can be used in combination with methylol phenol ethers. The aminoplast curing agent usually constitutes about 1-60 and preferably 5-40 percent by weight of the resinous composition based on total weight of the acid-solubilized resinous vehicle and the aminoplast. 
     With regard to the capped or blocked polyisocyanate curing agents, these are described in U.S. Pat. No. 4,104,147, column 7, line 36, continuing to column 8, line 37, the portions of which are hereby incorporated by reference. Sufficient capped or blocked polyisocyanate is present in the coating system such that the equivalent ratio of latent isocyanate groups to active hydrogens is at least 0.1:1 and preferably about 0.3 to 1:1. 
     Aqueous compositions of the novel reaction product and a curing agent can be applied to the surface of the substrate in any convenient manner such as by immersion, spraying, or wiping the surface either at room temperature or at elevated temperature. When desirable, the aqueous compositions of the combination can be electrodeposited on a variety of substrates. After the application, the substrate can be baked at temperatures such as 90° to 210° C. for about 1 to 30 minutes. 
     The aqueous compositions of the combination are suited for use on a variety of substrates. Films of appreciable build having excellent appearance and substrate adhesion are obtained when the instant aqueous compositions are applied. It is noteworthy that the obtained films are corrosion resistant, particularly on ferrous metal substrates. 
    
    
     This and other aspects of the invention are further illustrated by the following examples. It is to be understood that the following examples and other aspects of the invention described herein are not intended to be limiting; rather, other equivalents of the invention are intended to be covered, as well. It is to be further understood that all percentage compositions expressed herein are parts by weight unless otherwise stated. 
     EXAMPLE I 
     This example illustrates the preparation of the novel composition of the present invention, and the quaternary ammonium salt derivative thereof. The following charge was used in the preparation: 
     
         ______________________________________                                    
Ingredients         Parts by Weight (Grams)                               
______________________________________                                    
EPON 1001*          500.0                                                 
1,3-diphenyl-1,3-propanedione                                             
                    70.8                                                  
2-ethylhexanol      70.0                                                  
Ethyl triphenyl phosphonium acetate                                       
                    1.3                                                   
Dimethylethanolamine lactate                                              
                    69.2                                                  
Deionized water     23.4                                                  
Deionized water     156.7                                                 
______________________________________                                    
 *EPON 1001 is a polyglycidyl ether of bisphenol A having an epoxy        
 equivalent of about 500 and a molecular weight of about 1000, commerciall
 available from Shell Chemical Company.                                   
 
    
     The EPON 1001, the diphenyl propanedione and the 2-ethylhexanol were charged to a properly equipped reaction vessel and heated under a nitrogen sparge for about an hour and twenty-five minutes, to a temperature of 92° C. The reaction mixture was allowed to cool, and at 32° C. the ethyl triphenyl phosphonium acetate (catalyst) was added. Thereafter, the reaction mixture was heated to 135° C.; there was an exotherm and a resulting temperature rise to 155° C. After a slight temperature drop to 151° C., the reaction mixture was heated to about 175° C. The temperature was maintained over the range of 170° to 175° C. for an hour to a Gardner-Holdt viscosity of E, measured as a 44 percent resin solids solution in 2-butoxyethanol at 25° C. 
     At 90° C., a solution of the dimethylethanolamine lactate in the first portion of water was introduced into the reaction vessel and the temperature was maintained over the range of 80°-90° C. for two hours. A clear brown solution was obtained which was thinned with the second portion of water. The resulting reaction product had a solids content of 72.5 percent. 
     The following illustrates the preparation of an electrodeposition bath using the quaternary ammonium salt group-containing polymer prepared as described above, use of the bath for electrodeposition of ferrous metal substrates, and the evaluation of the corrosion resistance of the coated substrates. 
     The electrodeposition bath was prepared by mixing at room temperature the following mixture of ingredients: 
     
         ______________________________________                                    
                       Parts by Weight                                    
Ingredients            (Grams)                                            
______________________________________                                    
The quaternary ammonium salt group-                                       
containing polymer     310.3                                              
Deionized water        1190.0                                             
______________________________________                                    
 
    
     The electrodeposition bath (15 percent resin solids) was then used to electrocoat iron phosphate pretreated steel substrates, zinc phosphate pretreated steel substrates, and untreated steel substrates. The substrates were electrocoated at standard electrocoating conditions. The coatings were baked and scribed with an &#34;X&#34; and then placed in a salt spray chamber at 38° C. (100° F.) at 100 percent relative humidity atmosphere of 5 percent by weight aqueous sodium chloride, for a period of 14 days. The coating and baking schedules, and the evaluation of the substrates in terms of the measurement of scribe creepage due to corrosion are reported in the examples of Table 1. 
     
                                           TABLE 1                                 
__________________________________________________________________________
             Voltage at Which                                             
                      Appearance of Film                                  
             Electrocoated                                                
                      After Baking at                                     
             for 90 seconds                                               
                      350° F. (177° C.)                     
                                Film Thickness                            
                                        Scribe                            
Substrate    at 80° F. (27° C.)                             
                      for 30 minutes                                      
                                in mils Creepage (in mm.)                 
__________________________________________________________________________
zinc phosphate pretreated                                                 
             200      clear and glossy                                    
                                0.06-0.08                                 
                                        0.0                               
steel                                                                     
zinc phosphate pretreated                                                 
             250      &#34;         0.10-0.15                                 
                                        --                                
steel                                                                     
iron phosphate pretreated                                                 
             250      glossy    0.3-0.5 --                                
steel                                                                     
iron phosphate pretreated                                                 
             200      &#34;         0.35    0.0                               
steel                                                                     
untreated steel                                                           
             200      glossy    1.2     0.0-0.6                           
untreated steel                                                           
             150      &#34;         0.6     --                                
zinc phosphate pretreated                                                 
             250      &#34;         0.55    --                                
steel                                                                     
untreated steel                                                           
             150      &#34;         0.6     --                                
__________________________________________________________________________
 
    
     EXAMPLE II 
     The following illustrates the preparation of coating compositions comprising quaternary ammonium group-containing polymers formulated with crosslinkers, and the electrodeposition thereof. 
     
         ______________________________________                                    
Ingredients         Parts by Weight (Grams)                               
______________________________________                                    
Quaternary ammonium salt group-                                           
containing polymer of Example I                                           
                    310.3                                                 
Crosslinker.sup.1   65.0                                                  
Catalyst paste.sup.2                                                      
                    8.8                                                   
Deionized water     1390.0                                                
______________________________________                                    
 .sup.1 The crosslinker is a fully blocked 2,4toluene diisocyanate which  
 was prepared as follows: 2548.4 grams of 2butoxyethanol was added to the 
 toluene diisocyanate over a period of three hours and over a temperature 
 range of about 21-29° C. Thereafter, the reaction mixture was     
 maintained at a temperature range of 30 and 35° C. for 1 hour. The
 reaction mixture was then heated up to 65-76° C. and 965.5 grams o
 trimethylolpropane was added; there was an exotherm and a resulting      
 temperature rise to 142° C. The reaction mixture was allowed to   
 cool to about 130° C. within an hour, and then held at 90° 
 C. for another hour. The reaction mixture was thinned with 3116.9 grams o
 butoxyethanol.                                                           
 .sup.2 The catalyst paste was a dibutyltin oxide with a quaternized epoxy
 resin grinding vehicle.                                                  
 
    
     The resinous composition, the crosslinker and the catalyst paste were blended under agitation followed by the addition of the deionized water. The resulting dispersion had a 15 percent resin solids content. 
     This dispersion was used to electrocoat various substrates at standard electrocoating conditions as reported in Table 2 below. The coatings were baked and the baked coatings were scribed with an &#34;X&#34; and subjected to salt spray corrosion testing as described in Example I. The coating and baking schedules and the evaluation of substrates in terms of the measurement of scribe creepage due to corrosion are reported in the examples of Tables 2 and 3. 
     
                       TABLE 2                                                     
______________________________________                                    
                       Appearance of                                      
          Voltage at Which                                                
                       Film After Bak-                                    
          Electrocoated                                                   
                       ing at 350° F.                              
                                   Film                                   
          for 90 seconds                                                  
                       (177° C.) for                               
                                   Thickness                              
Substrate at 80° F. (27° C.)                                
                       30 minutes  in mils                                
______________________________________                                    
zinc phosphate                                                            
          200          glossy      0.3 to 0.4                             
pretreated steel                                                          
iron phosphate                                                            
          200          glossy      0.45 to 0.5                            
pretreated steel                                                          
untreated steel                                                           
          150          glossy      0.9 to 1.0                             
______________________________________                                    
 
    
     
                       TABLE 3                                                     
______________________________________                                    
                       Appearance of                                      
          Voltage at Which                                                
                       Film After Bak-                                    
          Electrocoated                                                   
                       ing at 400° F.                              
                                   Film                                   
          for 90 seconds                                                  
                       (204° C.) for                               
                                   Thickness                              
Substrate at 80° F. (27° C.)                                
                       20 minutes  in mils                                
______________________________________                                    
zinc phosphate                                                            
          200          clear and glossy                                   
                                   0.15 to 0.3                            
pretreated steel                                                          
untreated steel                                                           
          150          clear and glossy                                   
                                    1.2 to 1.5                            
______________________________________                                    
 
    
     EXAMPLE III 
     This example further illustrates the use of the quaternary ammonium salt group-containing polymers of the present invention as pretreatment agents for steel substrates. 
     The quaternary ammonium salt group-containing polymer was prepared in essentially the same manner as described in Example I and dispersed in deionized water to form a 10 percent resin solids dispersion. 
     Ferrous metal articles were dipped in the dispersion at room temperature for 2 minutes, blown dry with air, baked at 300° and 400° F. (149° and 204° C.) for 5 minutes and then coated with a thermosetting acrylic coating composition sold commercially by PPG Industries, Inc. under the trademark DURACRON 200. Coating was accomplished by drawing down to approximately 1 mil thickness with a draw bar. The coated sample was then baked for 10 minutes at 400° F. (204° C.), scribed with an &#34;X&#34; and placed in a salt spray chamber for salt spray corrosion testing as described in Example I. 
     For the purposes of comparison, there were evaluated control panels in the form of substrates which were dipped in an art-known pretreatment agent which is an onium salt comprising the reaction product of EPON 1001 and an acid salt of a tertiary amine (no beta-diketone moiety), and then coated with DURACRON 200 as described above. 
     
                       TABLE 4                                                     
______________________________________                                    
                                Scribe                                    
Composition         Substrate   Creepage                                  
______________________________________                                    
                    Test Panels                                           
Quaternary ammonium salt of novel                                         
                    Untreated steel                                       
                                2.0 mm                                    
composition (10% resin solids)                                            
Quaternary ammonium salt of novel                                         
                    Untreated steel                                       
                                2.5 mm                                    
composition (20% resin solids)                                            
                    Control Panels                                        
Quaternary ammonium salt of EPON                                          
                    Untreated steel                                       
                                3.0 mm                                    
1001 (10% resin solids)                                                   
Quaternary ammonium salt of EPON                                          
                    Untreated steel                                       
                                3.5 mm                                    
1001 (20% resin solids)                                                   
______________________________________                                    
 
    
     While the illustrative embodiments of the invention have been described hereinabove with particularity, it will be understood that various modifications will be apparent to and can be readily made by those skilled in the art without departing from the scope or spirit of the invention. Accordingly, it is intended that claims directed to the invention be construed as encompassing all aspects of the invention which would be treated as equivalents by those skilled in the art to which the invention pertains.