Abstract:
An aqueous composition for the protection of metal surfaces against corrosion includes, as an emulsion in water at least one overbased compound which is a water-insoluble salt. The overbased compound has a basic neutralization number of more than 40. In addition to the overbased compound, the aqueous composition also includes at least one surfactant constituted by an ammonium salt of an organic acid.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention concerns an aqueous composition for the protection of a metal surface against corrosion, in particular a coating composition which can be applied directly to the surface or used as an additive in a paint for application to the surface. 
     2. Description of the Prior Art 
     A number of coating compositions have been proposed for the protection of ferrous and non-ferrous metals and alloys thereof against corrosion. Anticorrosion coatings are obtained by applying the compositions to the surfaces. The coatings obtained may be permanent for (example paint) or temporary (for example protective oils or waxes which can be eliminated by detergents or solvents). The compositions contain active elements and film-forming agents in solution or dispersed in organic solvents or water. Organic solvents, however, have a number of known disadvantages: evaporation after application of the coating causes pollution problems and in some cases toxicity problems; further, they are generally only slightly biodegradable, and so have an additional negative environmental effect; they are relatively expensive; they are flammable, etc. 
     Currently, then, aqueous emulsions are preferred and usually comprise water, a corrosion inhibitor, a temporary or permanent surfactant or emulsifier, a co-solvent and a wax and/or polymeric film generator. Within the context of the present description, the term &#34;temporary&#34; denotes a compound which acts as a surfactant in the emulsion from which the protective coating or film is to be prepared, then loses its surfactant properties after application of the coating to the surface to be treated, for example by means of a chemical reaction as the coating dries. In contrast, the term &#34;permanent&#34; denotes a compound which retains its surfactant properties after application of the coating to the surface to be treated and drying. 
     Aqueous emulsions have been disclosed in U.S. Pat. No. 4,479,981 from Ashland Oil, Inc., which uses an overbased organic sulfonate as the corrosion inhibitor and a sulfonate or an amide alkanol or an amine salt of a carboxylic acid as the surfactant. The same types of surfactant are used in the coating composition disclosed in U.S. Pat. No. 4,647,309 from Ashland Oil, Inc., which composition also contains carbon black. U.S. Pat. No. 4,395,286 from Cincinnati-Vulcan Company uses an amine salt (ammonium salts are excluded) or a monovalent metal salt of a sulfonic acid as the surfactant. 
     The disadvantage of these above-noted emulsions is that they use permanent surfactants which render the film formed from them sensitive to water. The performance of the corrosion-protective coating in corrosion tests such as the salt spray test is thus only mediocre. 
     The aim of the present invention is thus to overcome the disadvantages of the prior art by providing a novel composition in the form of an aqueous emulsion comprising a temporary surfactant, the composition being for the protection of a metal surface against corrosion, in particular for use as a coating composition which is directly applicable to the surface and as an additive in a paint for application to the surface. It should, however, be obvious that these applications of the composition of the invention are not limiting and that it can be used, for example, as an additive in an anticorrosive primer. 
     SUMMARY OF THE INVENTION 
     The composition of the invention comprises, as an emulsion in water: 
     a) at least one overbased compound which is a water-insoluble salt, wherein the overbased compound has a neutralization number of more than 40; and 
     b) at least one surfactant constituted by an ammonium salt of an organic acid. 
     Optionally, the composition can also contain a co-solvent. 
     The aqueous composition of the invention generally contains 40% to 95% water, preferably about 70% water. 
     Within the context of the present invention, the adjective &#34;overbased&#34; denotes substances which are also known to the skilled person as &#34;complexes&#34;, &#34;metal complexes&#34;, &#34;metal-rich salts&#34;, etc. Overbased substances are formed from a metal and an organic compound and contain an excess of metal with respect to the stoichiometry of the reaction between the metal and the organic compound under consideration. Examples of overbased compounds which can be used in the present invention include water-insoluble salts of alkaline-earth metals, such as sulfonates, phenates and alkylphenates, salicylates and alkylsalicylates, phosphonates, thiophosphonates, naphthenates, carboxylates, etc, and mixtures thereof. The aqueous composition usually contains about 10% to about 25% by weight of overbased compound. It preferably contains about 20% of overbased compound. 
     The surfactant is a &#34;temporary&#34; surfactant in that it acts as an emulsifier when it is present in the emulsion in the form of an ammonium salt and in that during drying it decomposes to ammonia which evaporates off and to an acid which reacts with the overbased compound to form a salt which is only slightly water-soluble. The temporary surfactant can, for example, be an ammonium salt of a carboxylic acid prepared by bringing a carboxylic acid into the presence of ammonia. Suitable carboxylic acids include linear or branched-chain saturated or unsaturated mono- or polycarboxylic acids containing 6 to 30 carbon atoms, and mixtures thereof. The temporary surfactant can also be an ammonium salt of a sulfonic acid obtained by reacting a sulfonic acid with ammonia. Suitable sulfonic acids include alkylsulfonic acids, linear or branched mono-, di- or trialkyl benzenesulfonic acids containing 8 to 60 carbon atoms, mono- or polyalkyl naphthalenesulfonic acids, compounds known as &#34;linear alkyl bottoms&#34; obtained by sulfonation of the bottom products from the distillation of alkylbenzenes, natural sulfonic acids, and mixtures thereof. Preferred sulfonic acids include monoalkyl- and dialkylbenzenesulfonic acids where the alkyl group is linear or branched and contains 8 to 60 carbon atoms, in particular monoalkylbenzenesulfonic acids in which the alkyl group contains an average of 24 carbon atoms. The temporary surfactant used in the present invention can also be an ammonium salt of one of the following acids: alkylphosphoric or alkylarylphosphoric acids, alkylphosphonic or alkylarylphosphonic acids, rosin acids and naphthenic acids. Finally, the surfactant of the invention may be a mixture of several of the compounds described above. The surfactant constitutes about 5% to about 15% of the total weight of the aqueous composition, preferably about 10% of the total composition weight. 
     The co-solvent, which stabilizes and liquefies the emulsion, prevents the inclusion of water in the film during drying by forming an azeotrope with water and facilitates the formation of a regular coating film, is generally selected from the following compounds: alkylethers of mono- or dialkyleneglycols or esters thereof, ether-alcohol esters and alcohols containing 3 to 12 carbon atoms. The co-solvent is preferably an alkylether of a dialkyleneglycol. The co-solvent constitutes 0% to 20% of the total weight of the aqueous composition, preferably 5% to 10% of the total composition weight. 
     The aqueous composition of the invention, in particular when it is used as a coating composition, can also contain at least one of the following compounds: 
     an anti-foaming agent to facilitate formation and application of a bubble-free film; 
     a biocidal preservative to prevent micro-organisms from attacking the emulsion constituents; 
     a filler to increase the strength of the film; 
     an anticorrosion pigment or a conventional pigment; 
     a specific anticorrosion agent to prevent the appearance of rust while the film is drying after its application to the surface to be treated; 
     an emulsified polymer or wax to increase film hardness, etc. 
     When it is used as a coating composition, the composition described above can be applied using any means known to the skilled person. As an example, the coating can be applied by dipping, brushing, spraying, die coating, roller coating, etc. The metal surfaces to be coated can, for example, be constituted by iron, aluminum, copper, zinc, etc, and alloys thereof. 
     When used as an anticorrosion additive in a paint, for example an acrylic type paint or a &#34;polyester&#34; type paint, the composition of the invention is advantageously added in a quantity of about 0.5% to about 25%, preferably in the order of 1%. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following example illustrates a preferred method of preparing one example of a composition according to the invention, which was tested as a coating composition and as an anticorrosion additive for paint. 
     EXAMPLE 
     Preparation of the emulsion 
     350 g of deionized water and 60 g of the butyl ether of ethyleneglycol were introduced into a 1 liter beaker. 42 g of a benzenesulfonic acid with a substituent containing 24 carbon atoms was dispersed at ambient temperature with agitation, using apparatus such as an Ultra Turrax available from JANKE &amp; KUNKEL, Staufen, Germany. About 7 g of 25% ammonia was then added. The solution obtained was clear and had a pH on the order of 8.5. 
     The solution was heated to about 60° C., avoiding loss of ammonia. 141 g of ARCOT 785 (formerly known as ARCOT 800) which had been melted at about 90° C. was slowly poured into the solution with vigorous shearing agitation. ARCOT 785 is a complexed compound derived from an overbased calcium carboxylate with a basic neutralization number on the order of 130 mg of KOH/g, available from P.C.A.S., Longjumeau, France. The resulting solution was cooled with agitation and stored at a temperature of about 30° C. 
     The composition was a fluid, homogeneous liquid which was brown in color and of low odor, with no perceptible odor of ammonia. The composition had a pH of 7.8. The composition (emulsion) was homogeneous at the end of its manufacture, after 24 hours and after one month. No drop-out, i.e. separation of the constituents, was observed. The Brookfield viscosity of the composition was measured at 23° C. The Brookfield viscosity was 4.250, 2.750, 1.700 and 1.200 cPs at rates of 2, 4, 10 and 20 respectively: the composition was thus fluid. The theoretical dry extract was 30%, measured after being in an oven at 105° C. for 18 hours. The dry extract was tacky and its fat edge formation temperature was over 100° C. 
     All the compositions shown in Tables 1, 2 and 3 were prepared in similar fashion to the above composition which is identified by the reference number 18. 
     A. Use of the emulsion as a coating composition 
     A film of the above composition (emulsion) was applied manually to a steel test piece edged with wax. Flash rusting on the film was evaluated visually by observing the surface and the density of any spots of corrosion after 24 hours of drying: no rust spots were visible on the film. A 180° bending test was also carried out on a test piece coated with a 100 micron film of the above composition, after cooling the test piece for one hour at -30° C. This test produced satisfactory results. Finally, the film was salt spray tested in accordance with standard NFX 41002. The number of hours of resistance in this test without significant formation of rust was measured, along with the film thickness after 72 hours of drying, to determine the resistance/thickness ratio. The results are given in Table 4. 
     Table 5 compares the results obtained in the salt spray test using composition 18 above and prior art anticorrosion compositions. 
     The composition tested thus had a much better salt spray resistance than the prior art compositions. 
     Identical tests were carried out on compositions 1 to 18 of Tables 1, 2 and 3. The results of these tests are shown in the tables. 
     COMPARATIVE EXAMPLES 
     Various coating compositions obtained using the teaching of the present invention were tested and compared. 
     Comparative example 1: Temporary surfactant 
     Six compositions of the present invention were tested, each comprising 20% by weight of ARCOT 645, an overbased sulfonic acid with a basic neutralization number of 170 mg KOH/g available from P.C.A.S., Longjumeau, France, 10% by weight of a temporary surfactant, 5% by weight of the (mono)butyl ether of diethyleneglycol and about 65% by weight of deionized water. 
     The surfactants used were respectively the ammonium salts of the following compounds: 
     Composition No 1: a benzenesulfonic acid with an alkyl substituent containing 24 carbon atoms. 
     Composition No 2: a carboxylic acid containing 8 carbon atoms. 
     Composition No 3: a carboxylic acid containing 18 carbon atoms. 
     Composition No 4: a benzenesulfonic acid with a substituent containing 19 carbon atoms. 
     Composition No 5: a benzenesulfonic acid with two substituents each containing 11 carbon atoms. 
     Composition No 6: a benzenesulfonic acid with a substituent containing 12 carbon atoms. 
     The results are shown in Table 1. 
     Comparative example 2: Temporary surfactant 
     The above tests were repeated, replacing ARCOT 645 with ARCOT 785. 
     Resulting compositions 7, 8, 9, 10 and 11 corresponded to compositions 1, 2, 3, 4, 5 and 6 respectively. 
     The results are shown in Table 2. 
     The principal parameters of the tested coating compositions were extracted from Tables 1 and 2, namely: emulsifier quality, flash rusting on drying, salt spray resistance. Each parameter was then classified into one of the following categories: very good, good, medium, poor, very poor. The quality of the emulsifier was then determined by visual evaluation of the homogeneity of the emulsions prepared over a period of time of up to one month. The emulsifier was deemed to be very good when the emulsions were homogeneous, medium when they became heterogeneous, poor when the observed drop-out was about 5%, and very poor at higher degrees of drop-out. 
     The results are shown in Table 6. 
     Comparative example 3: Filler and co-solvent 
     In Table 3, composition 15 contained 25% of talc. Compositions 16, 17 and 18 contained different proportions of co-solvent. 
     B. Use of the emulsion as an anticorrosion additive for paint 
     Table 7 illustrates a comparative test in which different characteristics of two acrylic paint compositions were evaluated, in particular the salt spray resistance. Composition 1 contained components conventionally used in such paints, The only difference between composition 1 and composition 2 was that composition 2 also contained 5.5% of an additive of the invention, corresponding to composition No 18 of Table 3. 
     Table 7 shows that the additive of the invention conferred excellent anticorrosion properties on the tested paint. 
     A further test was carried out using a &#34;polyester&#34; type paint to which 1% of a composition of the invention had been added. This composition was identical to composition No 18 of Table 3 except that the oil was removed from the ARCOT 785. 
     This test showed that after curing, the paint composition obtained had a salt spray resistance, determined in accordance with the standard cited above, of more than 500 hours. 
     
                                           TABLE 1__________________________________________________________________________Composition No         1      2      3      4      5      6__________________________________________________________________________ARCOT 645     20     20     20     20     20     20Sulfonic acid C24/NH.sub.4.sup.+         10Carboxylic acid C8/NH.sub.4.sup.+                10Carboxylic acid C18/NH.sub.4.sup.+                       10Sulfonic acid C19/NH.sub.4.sup.+   10Sulfonic acid 2 × C11/NH.sub.4.sup.+                                     10Sulfonic acid C12/NH.sub.4.sup.+                 10Deionized water         65     65     65     65     65     65Diethyleneglycol butylether         5      5      5      5      5      5TOTAL         100    100    100    100    100    100Appearance, end of manufacture         homogeneous                homogeneous                       homogeneous                              homogeneous                                     homogeneous                                            homogeneousAppearance, 24 h         homogeneous                homogeneous                       homogeneous                              homogeneous                                     heterogeneous                                            10% dropoutColor         beige  white  white beige                              brown beuge                                     beige  white beigeViscosity, 24 h         thick  liquid solid  very thick                                     thick  liquidAppearance, emulsion, 1 month         ˜homogeneous                ˜homogeneous                       5% droupout                              ˜homogeneous                                     eliminated                                            50% dropout% theoretical dry extract         approx. 30%                approx. 30%                       approx. 30%                              approx. 30%                                     approx. 30%                                            approx. 30%Tackiness     oily   oily+  greasy oily   oily   oilyFlash rusting (24 h)         medium 1 spot 0%     slight high   not testedTest No 1, salt sprayThickness (μm)         17.5   23.5   30     28     not tested                                            25.5Resistance (h)         170    140    10     150    not tested                                            8Resistance/thickness ratio (h/μm)         10     6      0      5      not tested                                            0Test No 2, salt sprayThickness (μm)         14     13     not tested                              26     not tested                                            31Resistance (h)         140    100    not tested                              140    nit tested                                            8Resistance/thickness ratio (h/μm)         10     8      not tested                              5      not tested                                            0__________________________________________________________________________ 
    
     
                                           TABLE 2__________________________________________________________________________Composition No         7      8      9      10     11__________________________________________________________________________ARCOT 785     20     20     20     20     20Sulfonic acid C24/NH.sub.4 +         10Carboxylic acid C8/NH.sub.4 +                10Carboxylic acid C18/NH.sub.4 +Sulfonic acid C19/NH.sub.4 +                       10Sulfonic acid 2 × C11/NH.sub.4 +                              10Sulfonic acid C12/NH.sub.4 +              10Deionized water         65     65     65     65     65Diethyleneglycol butylether         5      5      5      5      5TOTAL         100    100    100    100    100Appearance, end of manufacture         homogeneous                heterogeneous                       homogeneous                              heterogeneous                                     homogeneousAppearance, 24 h         homogeneous                heterogeneous                       homogeneous                              heterogeneous                                     homogeneousColor         brown beige                eliminated                       dark brown                              eliminated                                     light brownViscosity, 24 h         medium eliminated                       medium eliminated                                     mediumAppearance, emulsion, 1 month         homogeneous                eliminated                       homogeneous                              eliminated                                     5% dropout% theoretical dry extract         approx. 30%                approx. 30%                       approx. 30%                              approx. 30%                                     approx. 30%Tackiness     tacky  greasy greasy -                              oily   greasyFlash rusting (24 h)         0%     not tested                       medium not tested                                     0%Test No, salt sprayThickness (μm)         13.5   not tested                       27.5   not tested                                     18Resistance (h)         250    not tested                       900    not tested                                     8Resistanc/thickness ratio (h/μm)         19     not tested                       33     not tested                                     0Test No 2, salt sprayThickness (μm)         33     not tested                       30     not tested                                     32.5Resistance (h)         800    not tested                       850    not tested                                     8Resistance/thickness ratio (h/μm)         24     not tested                       28     not tested                                     0__________________________________________________________________________ 
    
     
                                           TABLE 3__________________________________________________________________________Composition No         13     14     15     16     17     18__________________________________________________________________________ARCOT 785     20     16     10.5   23.5   23.5   23.5Sulfonic acid C24/NH.sub.4.sup.+                15     10     7.5    7.5    7.5Sodium sulfonate         10Talc                        25Deionized water         65     62     47.5   64     62     59Diethyleneglycol butylether         5      7      7      5      7      10TOTAL         100    100    100    100    100    100Appearance, end of manufacture         homogeneous                homogeneous                       homogeneous                              homogeneous                                     homogeneous                                            homogeneousAppearance, 24 h         homogeneous                homogeneous                       homogeneous                              homogeneous                                     homogeneous                                            homogeneousColor         brown  dark brown                       beige brown                              brown  brown  brownViscosity, 24 h         liquid liquid liquid solid  thick  liquidAppearance, emulsion, 1 month         ˜heterogeneous                homogeneous                       10% dropout                              eliminated                                     ˜homogeneous                                            homogeneous% theoretical dry extract         approx. 30%                approx. 30%                       approx. 45%                              eliminated                                     approx. 30%                                            approx. 30%Tackiness     oily   tacky  ˜dry                              eliminated                                     eliminated                                            tackyFlash rusting (24 h)         1%     0%     0%     eliminated                                     0%     0%Test No 1, salt sprayThickness (μm)         43.5   54     32.5   eliminated                                     not tested                                            9Resistance (h)         250    &gt;1000  1000   eliminated                                     not tested                                            240Resistance/thickness ratio (h/μm)         6      &gt;20    31     eliminated                                     not tested                                            27Test No 2, salt sprayThickness (μm)         22     not tested                       not tested                              eliminated                                     not tested                                            20Resistance (h)         200    not tested                       not tested                              eliminated                                     not tested                                            1000Resistance/thickness ratio (h/μm)         9      not tested                       not tested                              eliminated                                     not tested                                            50__________________________________________________________________________ 
    
     
                       TABLE 4______________________________________Salt spray              Resistance/resistance     Thickness                   thickness ratio______________________________________approx. 240 hours           9 μm approx. 27 h/μmapprox. 1 000 hours          20 μm approx. 50 h/μmapprox. 1 500 hours          30 μm approx. 50 h/μm______________________________________ 
    
     
                       TABLE 5______________________________________       Salt spray          Resistance/Composition resistance Thickness                           thickness ratio______________________________________18 (Table 3)       1 500 h    30 μm 50 h/μmUS-A-4 851 043         360 h    --       --US-A-4 479 981       1 000 h    76 μm 13 h/μmUS-A-4 444 802         400 h    48 μm  8 h/μm13 (Table 3)         200 h    22 μm  9 h/μm______________________________________ 
    
     
                       TABLE 6______________________________________                 Rust prevention                            Salt sprayCompositions      Emulsifier on drying  resistance______________________________________1 and 7    Good       Good       Very good2 and 8    Medium     Good       Good3          Poor       Good       Very poor4 and 9    Very good  Poor       Good5 and 10   Poor       Poor       Not tested6 and 11   Poor       Good       Very poor______________________________________ 
    
     
                       TABLE 7______________________________________           1      2______________________________________CompositionAcrylic emulsion A             12.7%    12.7%Titanium oxide    4.4%     4.4%Talc              4.6%     4.6%Anticorrosion pigment             7.3%     7.3%Antifoaming agent 0.2%     0.2%Acrylic emulsion B             49.5%    49.5%Co-solvent A      1.7%     1.7%Co-solvent B      4.5%     4.5%Antirust agent    0.15%    0.15%Spreading agent   0.5%     0.5%Example 18        0        5.5%20.5 wt % NH.sub.4 OH             0.6%     0.6%Water             13.85%   8.35%CharacteristicsDry extract       41.0 wt %                      41.0 wt %pH                8.2      8.2Viscosity         250 cps  250 cpsPencil hardness   H        HB(ASTM D 3363).sup.1Adhesion, % eliminated             0%       0%(ASTM D 3359)Konig pendulum    69 s/cycle                      69 s/cycle(ASTM D 4366)Salt spray(ASTM B 117)75 hblistering.sup.2  2 F      0penetration       &gt;5 mm    0 mm250 hblistering        6 MD     0penetration       &gt;10 mm   &gt;5 mm______________________________________ .sup.1 B = rather soft HB = rather hard .sup.2 Grading in ASTM D 714 Blister diameter: 2 = approx. 6 mm; 4 = approx. 3 mm; 6 = approx. 2 mm; 8 = approx. 1 mm Blister density: F = low; M = medium; MD = high; D = very high