GB1604733A - Method of inhibiting corrosion of metal surfaces - Google Patents

Description

(54) A METHOD OF INHIBITING CORROSION OF METAL SURFACES (71) We, PRODORITE LIMITED, Eagle Works, Leabrook Road, Wednesbury, West Midlands, WSl0 7LT, a British Company, 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 following statement: This invention relates to a method of inhibiting corrosion of metal surfaces and, in particular, mild steel surfaces.

According to the invention, a method of inhibiting corrosion of a metal surface comprises the step applying to the surface an adherent coating of a mixture including one or more film-forming aqueous copolymer latices and one or more reactive fillers, the temperature of the metal surface and the surroundings being higher than the minimum film-formation temperature of the latices during application of the coating and subsequent drying.

Preferably, the mixture contains between 10 and 1000 parts by weight of said one of more reactive fillers for every 100 parts by weight of the solid component or components in said one or more copolymer latices.

More preferably, the mixture contains between 200 and 500 parts by weight of said one or more reactive fillers for every 100 parts by weight of the solid component or components in said one or more copolymer latices.

It is to be appreciated that the term "reactive filler" is used throughout the present specification in its commonly accepted sense to mean a filler of the type which sets and hardens by hydration rather than by reaction with atmospheric carbon dioxide. Suitable reactive fillers are therefore Portland cement, aluminous cement and other types of hydraulically setting powders, such as pulverised fuel ash, pozzolani and gypsum plasters. The fillers should be in a finely ground condition when mixed with said one or more copolymer latices.

The copolymer latices employed in the method of the invention should exhibit an essentially non-ionic colloidal character such that the latices have sufficient chemical and mechanical stability to render them relative insensitive and stable to large changes in pH and to the presence of relatively large proportions of inorganic electrolytes and a wide variety of solid inorganic fillers, including said one or more reactive fillers. The aqueous copolymer latices should also be chosen so as to be filmforming at the ambient temperature at which the coating mixture is applied to the metal surface to be protected. Thus the temperature of the metal surface and of the surroundings should be higher than the minimum film-formation temperature of the latex at the time of applying the mixture and during drying.Moreover, it is desirable to ensure that the minimum filmformation temperature of the latex does not exceed about 20"C, when the latex is substantially free of hydrolysis-resistant filmforming additives such as plasticizers and coalescing solvents. Nevertheless, it is possible to employ such additives to reduce the minimum film-formation temperature of a particular latex or to promote the rate of film formation of thg latex under the prevailing ambient conditions. In this respect, it is to be understood that the minimum film-formation temperature of a copolymer latex to be employed in the method of the invention can be determined by any of the methods well known in the art, such methods being described, for example, by H.Warson in "The Application of Synthetic Resin Emulsions ", Emest Benn Limited, London, 1972, particularly at page 147. It is, however, to be appreciated that, in evaluating the suitability of a particular latex for use in the method of the invention under any given set of ambient conditions, the minimum film formation temperature should be determined in the absence of fillers.

Suitable copolymers for use as the disperse phases in the latices employed in the method of the invention include: (a) copolymers of butadiene, styrene and ethylenically unsaturated carboxylic acids containing between 15% and 60% by weight of copolymerized butadiene units, between 70% and 40% by weight of copolymerized styrene units, and between 0.25% and 7% (preferably between 0.5% and 2%) by weight of copolymerized units of one or more ethylenically unsaturated carboxylic acids;; (b) the copolymers indicated at (a) and containing units derived by copolymerisation of one or more monomers selected from alpha-methyl styrene, methyl methacrylate, acrylonitrile, methacrylonitrile, alkyl esters of acrylic acid containing 4 or more carbon atoms in the alkyl radical, acrylamide, methacrylamide, and methylolacrylamide, (c) copolymers of alkyl esters of acrylic acid containing 2 or ignore carbon atoms in the alkyl radical such as n-butylacrylate with ethylenically unsaturated carboxylic acids, wherein the copolymers contain between 20% and 90% by weight of units of copo iymerized alkyl acrylate, and between 0.25% and 5% tpreferably between 0.5% and 2%) by weight of copolymerized units of one or more ethylenically unsaturated carboxylic acids; and (d) the copolymers indicated at (c) and containing units derived by copolymerization of one or more monomers selected from styrene, methyl methacrylate, acrylonitrile, methacrylonitrile vinyl chloride, vinyl acetate, vinyl esters of aliphatic carboxylic acids containing from 3 to 17 carbon atoms such as vinyl propionate, vinyl stearate or a vinyl ester of Versalic (registered Trade Mark) acid (i.e. a branched aliphatic carboxylic acid having approxi- mately 10 carbon atoms), acrylamide, methacrylamide and methylacrylamide.

The preferred copolymer latices are derived from 30 to 50 parts by weight of butadiene copolymerized with 70 to 50 parts by weight of styrene and 1 to 2 parts by weight of acrylic acid or itamonic acid.

The required copolymer latices are prepared by emulsion polymerization according to conventional procedures, but it is important that the nature and proportion of the surfactants and stabilisers used in the preparation are selected so that the latices exhibit the required characteristics of good chemical and mechanical stability, of being relatively unaffected by large changes in pH and of being relatively insensitive to the addition of, and stable to the presence of, substantial proportions of inorganic electrolytes and a wide variety of solid inorganic fillers including the reactive fillers as hereinbefore defined. Moreover, since the latices are required to be essentially non-ionic in colloidal character, they contain major proportions of non-ionic colloids and only minor proportions of ionic surfactants and ionic stabilisers.A review of suitable proparative methods is to be found in the book by P. C. Bhckley entitled "Emulsion Polymerization" published by Applied Science Publshers Ltd., London, in 1975, pages 310319. Detailed descriptions of polymerization processes employing exclusively nonionic surfactants and stabilisers are also to be found in U.S. Patent Specification No.

2,795,564 in Belgian Patent Specification No. 615,682.

Those skilled in the art will readily appreciate how to adapt the known copolymerisation procedures to yield copolymer latices which have optimum colloidal properties and fall within the range of chemical compositions listed above.

For example, it will be understood that the copolymerisation of ethylenically unsaturated carboxylic acids is best carried out with the pH controlled at a relatively low value in order to ensure adequate total conversion rates of monomer to polymer and a high proportion and ideal distribution of the carboxylic acid units bound in the copolymer. These conditions require the presence of surfactants and stabilisers which remain soluble in water at these relatively low pH values. Certain non-ionic surfactants remain soluble virtually independent of pH value and may be added before, during or after the polymerization, to a total proportion of between 2 and 12 parts by weight per 100 parts by weight of all monomers. On the other hand, any anionic surfactants used should yield substituted sulfonate, sulfate or phosphate ions, carboxylic surfactants being insoluble at low pH values.It will, however, often be found desirable or necessary to employ minor proportions of such soluble anionic surfactants in order to achieve adequate polymerization rates and/or stability, in addition to the non-ionic surfactants and/or non-ionic stabilisers and/or non-ionic colloids, but the proportion of such anionic surfactants should not exceed 0.5 parts by weight per 100 parts by weight of all monomers and preferably should lie in the range 0-0.15 parts by weight. It is preferred that such anionic surfactants should belong to the class of substituted phosphates, especially the polyoxethylated alkyl phosphates.

After polymerization is complete, it is preferred that the pH value of the latex should be raised to between 8 and 10 by the addition of inorganic or organic bases or ammonia since raising the pH assists in further stabilising the latex. At this stage minor proportions of carboxylic surfactants and stabilisers may be added for the sake of enhanced stability.

As previously stated, it is important that the copolymer latices employed in the method of the invention are essentially of non-ionic colloidal character and a suitable test for this property is as follows: To 100 g. of the latex previously filtered on a 200 mesh screen at pH 5.5, 2.5 ml of 0.1 molar aluminium sulfate are added with stirring. The latex is then filtered on a 200 mesh screen and no coagulum should be formed. The test is then repeated using 2ml.

of 1 molar calcium formate and again no coagulum should be formed.

It is also important that the copolymer latices should be prepared so as to contain the absolute minimum of inorganic electrolytes. Thus to ensure that the coatings produced in accordance with the method of the invention have good corrosion resistance it is desirable that the latices should contain not more than i0.5 parts by weight of inorganic electrolytes per 100 parts by weight of the solids in the latices.

Other ingredients may be present in the mixtures employed in the method of the invention, such as non-reactive fillers, antifoaming agents, pigments, antifreeze agents, bactericides, antioxidants, sequestering and chelating agents for metal ions, as well as known substances for eccelerating or retarding the setting of hydraulic cements and the above-mentioned hydrolysisresistant plasticizers and coalescing solvents.

The mixtures described above are particularly intended for direct application to metal surfaces, especially mild steel surfaces, for the purposes of preventing corrosion. Thus it is preferable that these surfaces should not previously have been painted or coated with a continuous organic polymeric surface coating, although the surfaces may have been treated in other ways, such as, for example by phosphation or by application of other inorganic or organic but non-oily low molecular weight corrosion inhibitors, by anodisation or by plating with other metals such as by zinc plating on mild steel.Examples of metal surfaces which can be protected by the method of the invention are the outsides and insides of storage tanks, the sides and decks of ships, machinery, roofing metal, guttering, the exterior of any kind of pipe work, car under bodies, and any other type of exposed metal surfaces. The best results are obtained when the metal surface is to be protected from corrosion by the effects of atmospheric weather conditions.

It is to be understood that the mixtures employed in the method of the invention are essentially water-borne paints or surface coating materials so that the coatings deposited are relatively thin after drying and setting compared with cement and plaster renderings and screeds which are applied by such techniques as trowelling in the prior art. While multi-coat application of the mixtures employed in the invention is possible, it is usually found to be preferable to apply a single coating to a total thickness not greater than about 0.5 cm. in order to secure excellent corrosion prevention.

Typically the total coating thickness is about 0.1 cm.

It is to be appreciated that the ability to protect exposed metal surfaces from corrosion by the application of water-borne paints or surface coating materials, especially those based on polymer latices, rather than for example by the use of organic solventborne coating materials, is highly desirable since latex-based paints and surface coating materials possess the advantages of nonflammability, ease of use. absence of emission of odorous and toxic, noxious and/or flammable organic vapours, cheapness, high build properties, etc. Moreover, the deposited coatings exhibit good physical properties by reason of the high molecular weight of the polymers or copolymers comprising the disperse phase.The aqueous mixture employed in the method of the invention are particularly desirable in being relatively inexpensive with respect to raw material costs as well as being highly effective in practical use under 'a wide variety of conditions. In addition to possessing the aforesaid advantages of latex surface coating materials they are rapidly air-drying compositions, which dry and set to form coatings which exhibit excellent adhesion and a low porosity to air and which impart excellent corrosion resistance to the metal substrate, and which are ex ceptionally tough and durable.

A special advantage of the method of the invention is the fact that if a mild steel surface is already rusted, then provided that any loose deposits of scale are removed for example by wire-brushing, then the mixtures described above may be applied over the already corroded area to impart excellent adhesion and protection from further corrosion. Thus the method of the invention exhibits the advantage of applicability to areas too inaccessible for complete removal of deposits already formed as a result of corrosion, for example too inaccessible for removal by shot blasting. If the metal surface has already been finished with a continuous organic polymeric coating, then it will be necessary to expose sufficient of the metal surface by scoring, for example, in order to provide a key for application of the required adherent coating.If the metal surface carries an oily deposit, this should preferably be removed before application of the coating compositions in the interest of good adhesion.

The dried and set coatings deposited by the method of the invention are tough, hard, durable, adherent and exhibit good ageing properties. They may comprise the entire coating on the metal surface to be protected from corrosion, or they may be finished with one or more subsequent coats of suitable paint or paints already known in the prior art. The aqueous mixtures employed in the method of the invention can be applied by known methods for applying paints and surface coating compositions, such as brushing, trowelling, roller coating, spraying and curtain coating.

The invention will now be more particularly described with reference to the following Example.

EXAMPLE A copolymer exhibiting essentially nonionic colloidal properties was pepared from a mixture of monomers consisting of butadene, styrene and acrylic acid in the proportions by weight of 40. 59 and 1 respectively. To an amount of 100 parts by weight of this monomer mixture were added 0.8 parts by weight of t-dodecylmercaptan and 100 parts by weight of water containing in solution 8 parts by weight of a commercially available non-ionic surfactant in the form of a nonylphenol condensate with a 30-molar proportion of ethylene oxide, together with 0.15 parts by weight of a commercially-available synthetic anionic surfactant in the form of an acid alkyl phosphate condensate with ethylene oxide.

The mixture was heated to 60"C with agitation and a solution of 0.05 parts by weight of ammonium persulfate in water was injected into the mixture. Heating and agitation were continued until substantially 100% conversion into the required latex was obtained.

Portions of the latex were adjusted to a pH of about 5.5 and were subjected to a colloidal stability test by means of electrolyte additions. No coagulum was formed under the test conditions.

To the latex was added 5% sodium hydroxide to raise the pH to a value of 10-10.5, whereafter an antioxidant dispersion was introduced into the latex. The resultant latex was then filtered using a 200-mesh screen. The solids content of the latex was found to be about 48%.

One part by weight of the filtered latex was then mixed with two parts by weight of Portland cement (British Standard 12.

1971) to produce a lumpfree mixture having a paint-type consistency, the mixing being achieved without the formation of coagulum.

The mixture was then applied, by brushing, to a mild steel surface free of oil, grease and loose scale so as to produce a primer coat. The primer coat was then allowed to cure for 16-24 hours depending on the drying conditions and, after over-coating with a conventional maintenance paint. it was found that the rate of rusting of the mild steel surface was reduced as compared with conventional rust protection treatments.

It has been found that a mild steel surface provided with a protective primer coating in accordance with the method on the invention showed no corrosion creep after 1000 hours in a salt spray according to ASTM B117-73 or after 270 hours in a Moisture Corrosion Cabinet according to DIN 500 17.

WHAT WE CLAIM IS:- 1. A method of inhibiting corrosion of a metal surface comprising the step of applying to the surface an adherent coating of a mixture including one or more film-forming aqueous copolymer latices and one or more reactive fillers, the temperature of the metal surface and the surroundings being higher than the minimum film-formation temperature of the latices during application of said coating and subsequent drying.

2. A method as claimed in claim 1, wherein the mixture contains between 10 and 1000 parts by weight of said one or more reactive fillers for every 1()0 parts by weight of the solid component or components in said one or more copolymer latices.

3. A method as claimed in claim 1, wherein the mixture contains between 200 and 500 parts by weight of said one or more reactive fillers for every 100 parts by weight of the solid component or components in said one or more copolymer latices.

4. A method as claimed in any preceding claim wherein the or each reactive filler is Portland cement, aluminious cement, pulverised fuel, pozzlani or gypsum plaster.

5. A method as claimed in any preceding claim wherein the or each polymer latex exhibits an essentially non-ionic colloidal character.

6. A method as claimed in any preceding claim wherein the minimum film formation temperature of the or each latex is not greater than 20"C.

7. A method as claimed in any preceding claim wherein the copolymer of the or one latex is a copolymer of butadiene, styrene and one or more ethylenically unsaturated carboxylic acids containing between 15% and 60% by weight of copolymerized buta- diene units, between 70% and 40% by weight of copolymerized styrene units, and between 0.25% and 7% by weight of copolymerized units of one or more ethylenically unsaturated carboxylic acids.

8. A method as claimed in claim 7 wherein the copolymer of butadiene, styrene and one or more ethylenically unsaturated carboxylic acids contains between 0.5% and 2% by weight of copolymerized units of said one or more acids.

9. A method as claimed in claim 7 or claim 8 wherein the copolymer is derived from 30 to 50 parts by weight of butadiene

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Claims (17)

1. **WARNING** start of CLMS field may overlap end of DESC **.

   protected from corrosion, or they may be finished with one or more subsequent coats of suitable paint or paints already known in the prior art. The aqueous mixtures employed in the method of the invention can be applied by known methods for applying paints and surface coating compositions, such as brushing, trowelling, roller coating, spraying and curtain coating.

   The invention will now be more particularly described with reference to the following Example.

   EXAMPLE A copolymer exhibiting essentially nonionic colloidal properties was pepared from a mixture of monomers consisting of butadene, styrene and acrylic acid in the proportions by weight of 40. 59 and 1 respectively. To an amount of 100 parts by weight of this monomer mixture were added 0.8 parts by weight of t-dodecylmercaptan and 100 parts by weight of water containing in solution 8 parts by weight of a commercially available non-ionic surfactant in the form of a nonylphenol condensate with a 30-molar proportion of ethylene oxide, together with 0.15 parts by weight of a commercially-available synthetic anionic surfactant in the form of an acid alkyl phosphate condensate with ethylene oxide.

   The mixture was heated to 60"C with agitation and a solution of 0.05 parts by weight of ammonium persulfate in water was injected into the mixture. Heating and agitation were continued until substantially 100% conversion into the required latex was obtained.

   Portions of the latex were adjusted to a pH of about 5.5 and were subjected to a colloidal stability test by means of electrolyte additions. No coagulum was formed under the test conditions.

   To the latex was added 5% sodium hydroxide to raise the pH to a value of 10-10.5, whereafter an antioxidant dispersion was introduced into the latex. The resultant latex was then filtered using a 200-mesh screen. The solids content of the latex was found to be about 48%.

   One part by weight of the filtered latex was then mixed with two parts by weight of Portland cement (British Standard 12.

   1971) to produce a lumpfree mixture having a paint-type consistency, the mixing being achieved without the formation of coagulum.

   The mixture was then applied, by brushing, to a mild steel surface free of oil, grease and loose scale so as to produce a primer coat. The primer coat was then allowed to cure for 16-24 hours depending on the drying conditions and, after over-coating with a conventional maintenance paint. it was found that the rate of rusting of the mild steel surface was reduced as compared with conventional rust protection treatments.

   It has been found that a mild steel surface provided with a protective primer coating in accordance with the method on the invention showed no corrosion creep after 1000 hours in a salt spray according to ASTM B117-73 or after 270 hours in a Moisture Corrosion Cabinet according to DIN 500 17.

   WHAT WE CLAIM IS:- 1. A method of inhibiting corrosion of a metal surface comprising the step of applying to the surface an adherent coating of a mixture including one or more film-forming aqueous copolymer latices and one or more reactive fillers, the temperature of the metal surface and the surroundings being higher than the minimum film-formation temperature of the latices during application of said coating and subsequent drying.
2. 2. A method as claimed in claim 1, wherein the mixture contains between 10 and 1000 parts by weight of said one or more reactive fillers for every 1()0 parts by weight of the solid component or components in said one or more copolymer latices.
3. 3. A method as claimed in claim 1, wherein the mixture contains between 200 and 500 parts by weight of said one or more reactive fillers for every 100 parts by weight of the solid component or components in said one or more copolymer latices.
4. 4. A method as claimed in any preceding claim wherein the or each reactive filler is Portland cement, aluminious cement, pulverised fuel, pozzlani or gypsum plaster.
5. 5. A method as claimed in any preceding claim wherein the or each polymer latex exhibits an essentially non-ionic colloidal character.
6. 6. A method as claimed in any preceding claim wherein the minimum film formation temperature of the or each latex is not greater than 20"C.
7. 7. A method as claimed in any preceding claim wherein the copolymer of the or one latex is a copolymer of butadiene, styrene and one or more ethylenically unsaturated carboxylic acids containing between 15% and 60% by weight of copolymerized buta- diene units, between 70% and 40% by weight of copolymerized styrene units, and between 0.25% and 7% by weight of copolymerized units of one or more ethylenically unsaturated carboxylic acids.
8. 8. A method as claimed in claim 7 wherein the copolymer of butadiene, styrene and one or more ethylenically unsaturated carboxylic acids contains between 0.5% and 2% by weight of copolymerized units of said one or more acids.
9. 9. A method as claimed in claim 7 or claim 8 wherein the copolymer is derived from 30 to 50 parts by weight of butadiene

   copolymerized with 70 to 50 parts by weight of styrene and 1 to 2 parts by weight of acrylic acid or itaconic acid.
10. 10. A method as claimed in claim 7 or claim 8 wherein the copolymer further contains units derived by copolymerisation of one or more monomers selected from alpha-methyl styrene, methyl methacrylate, acrylonitrile, methacrylonitrilA, alkyl esters of acrylic acid containing 4 or more carbon atoms in the alkyl radical, acrylamide, methacrylamide and methylolacrylamide.
11. 11. A method as claimed in any one of claims 1 to 6 wherein the copolymer of the or one latex is a copolymer of alkyl esters of acrylic acid containing 2 or more carbon atoms in the alkyl radical with one or more ethylenically unsaturated carboxylic acids containing between 20% and 90% by weight of units of copolymerized alkyl acrylate, and between 0.25% and 5% by weight of copolymerized units of one or more ethylenically unsaturated carboxylic acids.
12. 12. A method as claimed in claim 11 wherein the copolymer also contains units derived by copolymerization of one or more monomers selected from styrene, methyl methacrylate; acrylonitrile, methacrylonitrile, vinyl chloride, vinyl acetate, vinyl esters of aliphatic carboxylic acids containing from 3 to 17 carbon atoms, acrylamide, methacrylamide, and methylalcrylamide.
13. 13. A method as claimed in any preceding claim wherein the or each latex contains not more than 0.5 parts by weight of inorganic electrolytes per 100 parts by weight of the solids in the latex.
14. 14. A method as claimed in any preceding claim wherein the thickness of said adherent coating does not exceed 0.5cm.
15. 15. A method as claimed in any preceding claim comprising the further step of applying a layer of a finishing paint to said adherent coating after drying and setting thereof.
16. 16. A method as claimed in claim 1 of inhibiting corrosion of a metal surface substantially as hereinbefore described.
17. 17. A metal surface provided with a corrosion inhibiting coating by a method as claimed in any preceding claim.