COMPOSITIONS FOR RUST TREATMENT

Abstract: A composition for rust treatment comprises an aqueous film-forming emulsion and an effective amount of pyrogallol as a chelating agent for iron oxides.

Description: - - Compositions for rust treatment The present invention relates to compositions for rust treatment for use on articles made of iron and steel, whether free from oxidation or not, of the kind comprising a dispersion or emulsion of a film-forming agent such as a polymer emulsion together with a chelating agent for chelating iron oxides. Compositions of this kind have already been proposed, for example in German Offenlegungsschrift No. 25 55 597 t Swiss Patent Specification 580 152 and British Patent Specification No. 1 212. In these prior disclosures gallic acid and tannin, among others, are disclosed as suitable chelating agents for chelating iron oxides. Pyrogallol (l, 2, 3-trihydroxybenzene) has also been proposed as a chelating agent for chelating iron oxides in such compositions. It is the aim of this invention to provide a water-based corrosion-inhibiting paint or varnish which, when applied to steel (whether rusted or not), will give a coating capable of substantially preventing further oxidation or corrosion and durable under severe conditions of damp and frost and durable against oil, acid or alkaline or other corrosive environments. To be effective in practice a corrosion-inhibiting paint or varnish should be compatible with surface coatings in general use. The adhesion and fastness of the varnish film when properly applied should not be less than those of surface coatings in general use and superior in providing a primed surface to allow good finishes to be obtained. The varnish must be of low toxicity and not in itself strongly acid or caustic, not inflammable and must not give off inflammable, explosive or toxic vapours. It must be applicable by painting, spraying or dipping and should cure and dry at ambient temperatures and humidities in a relatively short time. It has been found that particularly useful film- forming emulsions (or latices) for the purposes of the present invention are those described in the paper by A. J. Burgess, D.Caldwell and J.C. Padget in the Journal of the Oil and Colour Chemists- Association Volume 64, May 1 81 pages 175-185, and also in the British Patent Specification No. 1558 4l 1 and European Patent Application 0 030 080 A1 « These documents are incorporated herein by reference. Products of the kind there described are sold by Imperial Chemical Industries Ltd as Haloflex 202 and Haloflex 208 ("Haloflex" is a registered Trade Mark). The invention described and claimed in the aforesaid British patent is an aqueous latex comprising a copolymer derived from (i) vinylidenβ chloride, (ii) vinyl chloride, (iii) one or more alkyl acrylates having 1 to 12 carbon atoms in the alkyl group and/or one or more alkyl methacrylates having from 2 to 12 carbon atoms in the alkyl group and (iv) one or more aliphatic alpha-beta-unsaturated carboxylic acids, the proportion of vinylidenβ chloride being from 65 to 90 parts by weight the proportion of the said alkyl acrylates and/or methacrylates being from 2 to 15 parts by weight and the proportion of the said carboxylic acids being from 0.2 to 8 parts by weight, per hundred parts by weight of the total vinylidene chloride and vinyl chloride. The aforesaid European patent application describes and claims an aqueous latex comprising a copolymer of (i) vinylidene chloride, (ii) vinyl chloride and (iii) one or more alkyl acrylates or alkyl methacrylates having from 1 to 12 carbon atoms in the alkyl group, characterised in that:- (a) the proportion of vinylidene chloride is from 20 to 95 parts by weight per hundred parts by weight of total vinylidene chloride and vinyl chloride, ■ -c_ . " _ (b) the proportion of vinylidene chloride is not more than 75 parts by weight per hundred parts by weight of total vinylidene chloride, vinyl chloride and the said acrylate(s) and/or methacrylate(s) and (c) the proportion of the said acrylate(s) and/or methacrylate (s) is more than 15 but less than 4 parts by weight per hundred parts by weight of total vinylidene chloride and vinyl chloride. The present invention therefore in one embodiment provides a corrosion-inhibiting paint or varnish comprising a film-forming latex as defined in the preceding paragraphs together with an effective amount, as chelating agent, of pyrogallol. The permeability of water varnishes based on this latex was in the order of 1 of similar latices not 100 containing vinylidene. The addition of Pyrogallic acid introduced remarkable corrosion resisting qualities not otherwise easily obtained, for instance by the use of quarternary compounds or phosphoric acid. Butyl Glycol ethers and ester alcohols were used to produce lower setting temperature effects and greater salt resistance. Considerable difficulty was experienced with other chelating agents such as Taniiic acid in that the ' ejKEJ C H latex became unstable without other additives which reduced efficiency. One embodiment of the invention comprises the following composition: Haloflex 202 80 - 98$ Pyrogallol 2 - Water 0 - 10 The preferred composition is that in which the pyrogallol is present at 3 * 0 and the pH is less than 6, preferably less than 4 the optimum being 1.8 - 2.5. This product was subject to the testing procedures described below. Tests were carried out on mild steel plates 6 inches x 4 inches and on motor car body panels. 1« The compositions tested were in two main groups, (a) an acrylic/methacrylic copolymer emulsion containing 3° pyrogallol and (b) a vinylidene chloride/ vinyl/copolymer emulsion containing 3% pyrogallol (the preferred composition described above). 2. The plates used were from the same stock of bright mild steel, some of which had been exposed to 2% salt spray and extensive exposure out of doors to promote heavy rusting and pitting. 3. All plates were wire brushed and rubbed with coarse sandpaper prior to applying the protective coatings. •v-. • Both sides of the plates were treated. 4. The rusted motor car body panel was brushed and sandpapered then washed with clean water. A one inch wide bristle paint brush was used to apply the protective emulsion except when an air sprayer was used for the car panel and some of the topcoats. The first coat of the protective emulsion was allowed to dry thoroughly before any subsequent coats were applied. A dark blue-black colour developed on the treated plates indicating the complexing of the iron surface. Comparisons were made after treating the painted plates to 100 hours in a salt spray cabinet using a 2 sodium chloride solution at 20 - 30 C. Those plates treated with the acrylic polymer preparations- 1 coat showed rusting in 24 hours 2 coats " " " 36 hours Those plates treated with the vinylidene/chloride/ vinyl chloride copolymer 1 coat showed slight rusting in 0 hours 2 coats showed No rusting in more than 100 hours Those plates which were pre-rusted did not show significant differences from the bright metal plates. Where the second coat was allowed 24 hours to dry and then smoothed with wet sandpaper the surface was rust free fo_r more than 100 hours in the salt spray. The second part of these tests involved the assessment of compatability of (b) with various types of paint and was applied to both bright steel and rusted steel plates. In general all varieties of paints tried showed good adhesion. More speci ically; Aerosol paints both cellulose and synthetic varnish gave excellent results. Automotive finishes in cellulose and 2 part acryllic, applied by brush and by spraying were completely satisfactory. A rusted car panel was sprayed with 2 coats of the vinylidene copolymer preparation, the black surface was allowed 24 hours to harden before spraying with an epoxy type filler, this was built up to cover the rust pitting and rubbed down before applying a cellulose decorative paint - after 48 hours drying the section was immersed in a water tank for 7 days when no blistering or loosening of the filler was observed. In further tests, treated places with 2 coats of the vinylidene preparation were subjected to 2 hours stoving at 80 C and then painted with an acryllic resin paint and stoved for a further 2 hours. The resulting finish was found to be as durable as the paint makers* claims, in resisting damp, attrition and bending. There being no apparent difference between the bright metal and the rusted plates. The composition of the present invention, when applied to articles already rusted, showed superior adhesion to Haloflex alone. Another embodiment of the invention is as follows : preferred variation Haloflex 202 82.6% 75 - 85% Water 3.6% 0 - 4% Pyrogallic acid 1.8% 5 - 3% Butyl Ethoxol 4.0% 0 - 5% Isopropanol 8.0% 5 - 12% 100.0 Haloflex 208 may be used in place of Haloflex 202. TEST RESULTS 1. Plates of grit blasted steel painted with two coats of the preferred formula. a) were tested in a salt spray cabinet at 25 C after 1000 hrs a few very small blisters occurring near cut edges were observed. b) Similar plates coated with cellulose, acrylic and alkyd paints showed serious rusting. Plates coated with two coats of the inhibiting paint * T_p_ 1w ' - '- before painting with these finishing enamels showed no significant corrosion after 1000 hrs saltspray. c) Water permeability of the latex used has been assessed and found to be in the order of 1% of that of most other emulsion latices, and comparable to or better than chlorinated rubber paints. d) Grit blasted plates coated with 2 coats of the preferred formula were immersed in water for three months without showing signs of deterioration or rust creeping in from cut edges. The latex used has a very low toxicity and does not cause eye damage or respiratory hazard. The finished dried film is flame retardant. ^here rray be added to the composttions of the present invention other substances well known as additives to paints and varnishes such as fillers, extenders, wetting agents, surfactants and the like. Co:r-positions according * to the invention can be painted ever damp or wet rusted metal. The water is absorbed from the iron or steel surface but is prevented from ΓP urning as the composition dries. .- •■ J

Claims: CLAIMS 1. A composition for rust treatment comprising an aqueous film-forming emulsion and an effective amount of pyrogallol as a chelating agent for iron oxides. 2. A composition as claimed in Claim 1 wherein the aqueous film- orming emulsion is an aqueous latex comprising copolymers of vinylidene chloride. 3. A composition as claimed in Claim 2 wherein the emulsion is a copolymer of vinylidene chloride, vinyl chloride and one or more alkyl acrylates or methacrylates, 4. A composition as claimed in any of claims 1 to 3 wherein the proportion of pyrogallol lies between 0.5 to 5. A composition as claimed in any of the preceding claims and containing 0 to butyl ethoxol. 6. A composition as claimed in any of τhe preceding claims and containing from 5 to 123 isopropanol. 7. A composition substantially as herein described. 8. A composition substantially as herein described in Example 1. 9. A composition substantially as herein described with reference to Example 2. 10. A method of applying a protective coating to a substrate characterised in that there is employed an aqueous latex claimed in any of claims 1 to 8.

Inventors: ROBERTS DANIEL CLARKSON, ROBERTS, DANIEL, CLARKSON
Applicants: DOUBLE H INT LTD, DOUBLE H INTERNATIONAL LIMITED
Application year: 1983
Main classification: C09D5
IPC codes: C09D5, C09D127, C09D133