RUST INHIBITING OVERCOAT COMPOSITION Field of the invention
The present invention relates to a rust inhibiting overcoat composition. More particularly, the present invention relates to an rust inhibiting coating composition which is applicable across a host of surfaces, thereby enabling the inhibition or complete prevention of rust formation on ferro-metallic surfaces. The composition of the invention finds appRcation in several industries such as shipping, automobile, petroleum and petrochemical industries, cement and steel industries, construction, agro-based industries, pipelines, storage tanks, railways, dams and bridges, food and beverage industries, defence installations, water supply industries, and the like. Background of the invention
Corrosion and rusting and associated problems result in tremendous losses in several industries, particularly in the fields of plant, machinery, storage tanks, pipelines, construction, and the like. The losses take the form of actual corrosive damage and reduction in operational life of the equipment, thereby resulting in losses due to maintenance, shut down, repair time, and the like. Rust preventing compositions are a field where a large degree of research has been undertaken with a view to overcome some of the above mentioned problems. It is known in the art to use rust preventers, protectors, enamel and epoxy coatings to overcome or minimize such losses. However such methods are found to be economically not effective, since a multiplicity of coatings are required. It is also foimd that such coatings need to be applied at periodic intervals, thereby resulting in a recurrent cost. Another problem faced with some of prior art compositions is that they result in a reduction of the strength of the ferrometallic surface to which they are applied due to presence of phosphates therein, thereby reducing the life of the substrate.
US Patent 3,753,924 discloses a rust inhibitor containing tannins with a chelation catalyst and a cross-linking agent. The composition of this patent comprises essentially a rust inhibitor such as tannic acid, and a catalyst capable of initiating chelation of iron atoms such as aluminium sulfate, ferric chloride, stannic chloride, maleic acid, oxalic acid, and phthalic acid, and a and cross linking agent such as formaldehyde, glyoxal, hexamethylene diamine, and paraphenylene diamine.
Japanese Patent 11246311 teaches a rust control agent containing an active compound isolated from Zingiber officinale Rose, and mixing the active compound with a carrier, a surfactant, a dispersant, an auxiliary and the hke.
US Patents 4,363,889; 4,239,804; 6,464,763; 5,239,002 all disclose various water soluble compositions for surface coating to prevent atmospheric corrosion of substrates. However, none of the above patents teach the inhibition and prevention of corrosion.
Another disadvantage of prior art rust preventive or rust inhibiting compositions is that their action is physical — i.e. they prevent the formation of rust by forming a coating on the substrate. As a result of natural conditions, such coatings tend to degrade and erode over a period of time and therefore require repeated appHcation as indicated above. The physical functioning of such coatings also means that once rust sets in on the substrate, the rust layer itself tends to result in the peeling off of the coating, thereby exposing further portions of the substrate to oxidation and formation of rust.
In addition, another significant disadvantage of the prior art formulations is that they require not only several layers of the rust preventive composition but also several layers of an overcoat composition. Prior art overcoat compositions also undergo degradation due to ambient conditions and are a short term solution.
It is therefore imperative to provide compositions which enable the reforming of rust from ferrometallic surfaces and also do not degrade the surface, do not require repeated applications and at the same time are economically efficient. It is also important that such compositions function not just physically as a coating on the ferrometallic substrates but actually chemically remove or reform the rust thereon and also prevent the formation of rust thereon.
Our copending Indian Patent AppHcation No. 607/DEL/2003 filed on the same day discloses a rust reforming and inhibiting overcoat composition which comprises a synergistic mixture of latex, tannic acid, oxalic acid, anti-foaming agent, clay, zinc oxide, barium chloride, wetting agent, the mixture being dissolved in water. The latex used is preferably acid stabilized to a pH in the range of 2 to 5. The anti-foaming agents comprise conventional anti-foaming agents such as silicon based defoamers. The clay used is preferably a thixotropic flow modifier such as a
mineral colloid. Wetting agent is preferably selected from ethylene glycol and esters thereof.
The composition of the copending application when applied to any ferrometallic substrate reacts with the surface and sub-surface rust and changes it chemically to a non-corrosive organo-metallic complex. This results in the stabilization of the surface and also arrests the process of rusting. A significant advantage of this composition is that it does not contaia phosphoric acid or any phosphates and therefore does not result in a weakening of the ferrometallic substrate. The rust already formed on the surface or sub-surface of the ferrometallic substtate is converted into the form of an organo-metal matrix which is non-corrosive. This matrix is easily removable from the substrate. Additionally, the composition of our copending application forms a tenacious polymer coating on the substrate and thereby seals the surface of the substrate from the elements. The polymer coating so formed is strong and durable thereby ensuring that the surface is not subjected to further oxidation. The strength of the coating also ensures that repeated periodic applications are not required, thereby saving on the recurrent expenditure and shut down otherwise seen in the use of prior art formulations for rust prevention.
Our copending Indian Patent application No. 607/DEL/2003 discloses a composition comprising primarily latex in an amoimt of 55 — 65%, tannic acid in an amount of 3 — 6%, oxalic acid in an amount of 3 to 6%, antifoamitig agent in an amoimt of 3 to 6%, clay in an amount of 2 - 5%, zinc oxide in an amount of 0.5 to 1%, barium chloride in an amoimt of 0.5 to 1%, a wetting agent in an amount of 0.5 to 1%, all amounts being expressed in terms of weight of the total composition, the entire composition being dispersed in water.
In addition to rust reforming and rust inhibition, it is desirable also to provide at least one overcoat composition which enables the prevention of rust formation for a longer period than achieved in the prior art. It is also desirable to provide a overcoat composition which does not require repeated applications to be effective and also does not require to monitored firequentiy for degradation and consequent re-application. It is also desirable to provide a overcoat composition
which does not impact on the finish of the ferro-metallic surface or degrade the
surface.
Objects of the invention
The main object of the invention is to provide a rust inhibiting overcoat composition which enables the prevention of rust formation for a longer period than achieved in the prior art.
It is another object of the invention to provide a overcoat composition which does not require repeated appRcations to be effective and also does not require to monitored frequently for degradation and consequent re-appRcation.
It is another object of the invention to provide a overcoat composition which does not impact on the finish of the ferro-metalRc surface or degrade the surface Summary of the invention
It has now been founmd that in addition to reforming and inhibition of rust formation as achieved by the composition of our copending appRcation, appRcation of a further overcoat composition provides significandy advanced results in terms of finish, rust prevention and substantial rust inhibition on ferro-metalRc surfaces.
Accordingly the present invention provides a rust inhibiting overcoat composition comprising essentially of latex in an amount of 60 to 70%, an anti-foaming agent in an amount of 0.4 to 0.6 %, a clay in an amount of 0.5 to 1.0 %, TiO2 in an amoxmt of 2 to 4%.
In one embodiment of the invention, water is added to obtain the desired thickness for storage and/or final appRcation on the ferro-metalRc surface.
In another embodiment of the invention, the latex is preferably of a pH in the range of 2 to 5.
In another embodiment of the invention, the and-foaming agent is preferably a siRcone based defoaming agent.
In another embodiment of the invention, the clay used can be a thixotropic flow modifier or a mineral colloid.
In another embodiment of the invention, additional pigments such as carbon black paste, conventional grey, green, etc. can also be added in an amount of 2 to 4%.
The composition of the invention is a synergistic composition with unexpected properties over the aggregate properties of the individual ingredients. Detailed description of the invention
The present invention provides a rust inhibiting overcoat composition comprising essentially of latex in an amount of 60 to 70%, an anti-foaming agent in an amount of 0.4 to 0.6 %, a clay in an amount of 0.5 to 1.0 %, TiO2 in an amount of 2 to 4%. Water can be added to obtain the desired thickness for storage and/or final application on the ferro-metaliic surface, the latex is preferably of a pH in the range of 2 to 5, and the anti-foaming agent is preferably a sihcone based defoaming agent. The clay used can be a thixotropic flow modifier or a mineral colloid. Additional pigments such as carbon black paste, conventional grey, green, etc. can also be added in an amount of 2 to 4%.
The composition of the invention is a synergistic composition with unexpected properties over the aggregate properties of the individual ingredients.
The overcoat composition of the invention provides an additional high strength protective polymer coating to protect the original paint coat. The overcoat forms a polymeric barrier and therefore seals the metal surface from the environment.
The composition of the invention is prepared by admixing the various ingredients in the ranges of proportions mentioned above under conditions suitable for the formation of a complete mixture.
The present invention will now be described with reference to the following examples which are illustrative and should not be construed as limiting the scope of the invention in any manner.
Examples for copending application composition:
(Rust reforming composition of copending application No. 607/DEL/2003) Example 1:
Several batches of the composition of the invention were prepared comprising latex in an amount of 55 — 65%, tannic acid in an amount of 3 — 6%, oxalic acid in an amount of 3 to 6%, antifoaming agent in an amount of 3 to 6%, clay in an amount of 2 — 5%, zinc oxide in an amoimt of 0.5 to 1%, barium chloride in an amount of 0.5 to 1%, a wetting agent in an amoimt of 0.5 to 1%, aU amoimts
being expressed in terms of weight of the total composition. The batches were dispersed in water. Example 2
A mild steel rod was coated with one coating of the composition of the invention. After 26 hours of curing, the rod was immersed in 5 to 10% salt solution in water at normal ambient temperature. On contact with water, a bluish black colored dispersion was obtained. After about 30 minutes, the dispersion in water resulted in solid specks of dark colored particles. The coated mild steel rod was left overnight in water (for about 14 hours) and then dried for about another 14 hours. It was noted that no further rust formed even after prolonged immersion in water. Example 3
Another mild steel rod piece was first coated with the composition of the invention, cured for about 36 hours, and then immersed in boiling water with a saline content of 5 to 10%. After boiling for about 30 minutes, natural reduction in water level and increase in salt concentration did not result in any visible impact on the substrate. The rod piece was removed and dried for 18 to 20 hours. No physical or chemical change was seen thereon, establishing that the composition of the invention prevented rust formation. Example 4
A single coat of the composition of the invention was applied on several rusted pieces of icon sheets and mild steel rods. The coated substrates were then buried in moist mud and kept covered for 2 weeks. The substrates were then washed and dried. No further formation of rust was noted. Example 5
The composition of Example 1 was applied as a single coating on a metal sheet which had been completely rusted as well as on 2 pieces of steel pipes which were partly rusted and on pieces of mild steel rods which were fully rusted. The composition was applied in free flowing form similar to primer paint. The surface drying time was uniform on all surfaces - from 20-30 minutes. After drying, the separate pieces of metal were smooth to the touch showing that no granulated pieces which serve as an indication of presence of rust, were present. Example 6
A first coat of the composition of Example 1 was applied on three pieces of mild steel. After 30 minutes, a second coating was applied and it was observed that the viscosity was good and the spread of the coating on the surface was even. The reaction with the rusted portions was observed to start immediately and a blue-black colour was prevalent after 60 minutes of drying. The samples were shaken vigorously before the second coating and some frothing was observed. A defoaming agent was added to the composition and the experiment repeated. It was observed that the problem of frothing was overcome. Example 7
The experiment of Example 6 was repeated with the addition of an oxygen scavenger to the composition. Separate batches of the composition of example 1 were prepared with different oxygen scavengers selected from ascorbic acid, aminopolycarboxylic acid, sodium sulphate, diethylhydroxyl amines and pyrogallic acid. It was observed that the performance in terms of rust inhibition was improved significantly. Example 8
The first application was done simultaneously on a fully rusted metal sheet, scraped and cleaned before apphcation, on one side, and on the other surface, which was partially rusted.
a) It was observed after 4 hours of surface drying that the fully rusted sheet had turned completely black and on the partially rusted side, the rusted portions had turned black but the non-rusted portions were coated with a transparent film.
b) After 8 hours and 24 hours/48 hours, there was no further change in the color or texture of the appHcation and the observations made after 4 hours drying was maintained.
c) Water was not splashed on these metal sheets at any time during the drying periods.
Example 9
The composition of the invention was applied simultaneously on three small pieces of rusted MS rod, and the following was observed.
a) After 4 hrs. sxirface drying, the first piece was immersed in a beaker of water. Almost immediately the water was discolored as numierous black particles were
dispersed from the metal piece and this process continued slowly until the water was dark brown. The metal piece was taken out after 24 hrs. immersion and almost all the composition appHcation was removed.
b) After 8hrs. of surface drying, the results were almost identical to those observed after 4 hrs. surface drying. The only difference was that the dispersion was no so complete and the resultant water in the beaker was only slightly lighter than the earlier experiment. After 24 hrs. immersion, the metal piece was partially covered with the composition.
c) After 24 / 36 Hrs. of surface drying, the third piece was immersed in water. There was no immediate discoloration, but after 2 hrs. of immersion the water was discolored with small black particles. After 24 hrs. immersion, the dispersion remained almost the same, but on removing the metal piece from the water the application was observed to be coming off by touch and rubbing. However, the effect was only minimal though some rusted portions could be observed on the basis where the appHcation had been rubbed off
A fresh composition was prepared by adding further polymer. Example 10
The composition of the invention was kept in an open beaker for 36 hrs. There was some evaporation. Ordinary water was added to the beaker in the same proportion as that which had evaporated. The resultant mixture was applied on a rusted metal strip in comparison with the first application of the composition on the same strip - applied 36 hrs. earHer. The sample containing the evaporated solution and diluted by adding water, was applied side by side and after surface drying of 24 hrs. It was observed that though the original appHcation was completely black and covered the entire applied portion, the diluted appHcation was also quite effective. The applied portion was almost entirely black approx. 90-95% and in the portions where the black coloring did not take place, it was observed that the rusted portions underneath were cured and the appHcation had formed a transparent film over these portions. Example 11:
Batches of the overcoat composition of the invention were prepared comprising latex in an amount of 60 to 70%, an anti-foaming agent in an amoimt of
0.4 to 0.6 %, a clay in an amount of 0.5 to 1.0 %, TiO2in an amount of 2 to 4%. Pigment comprising carbon black paste in an amoimt of 2 to 4% was also mixed into the composition. AH percentages are expressed in terms of weight of the composition. The batches were dispersed in water. Example 12:
A metal sheet (completely rusted) and two pieces of steel pipes (partially rusted) were coated with one coating each of the paint composition of our copending application. The surface drying was uniform in all three cases and showed no blotches. After drytng (in about 20 to 30 minutes), the surfaces were smoodi to touch. After the paint composition had dried, a further coat of the overcoat composition of the invention was applied and was observed to be free flowing, non-blotching and free of granulation.
It was observed that the overcoat completely covered the surface and formed a paint-like to-coat cover. A further coat of the overcoat composition of the invention with a second pigment was applied to the metal surfaces. The user of a different pigment merely resulted in parts of the underlying first coat being visible. Example D:
The metal sheet of Example 3 was then sprinkled and washed with water and allowed to dry in sunlight. This was done after about 16 hours of drying time. No visible deterioration or discoloration was observed. After 24 hours, with more water being sprinkled, it was again noted that no discoloration or deterioration occurred. Example 14:
The metal surfaces of Example 4 were then buried underground in moist mud for a period of about a week. No rust was visible thereby establishing that the appUcation of the overcoat composition prevented the rusting process. Example 15:
3 pieces of metal were coated with the paint of the copending application, after curing and drying, a coating of the overcoat composition was applied. The metal surfaces were allowed to cure for 3 days and after this one piece was immersed in water, the second in saline solution (5% salt) and the third in water
exposed to UV radiation. It was observed after three days of such treatment, that the overcoat composition did not taint the water or disperse color into the water in the first case. The overcoat composition also bonded well with the surface. The second piece immersed in saline also did not show any degradation. Only in the third piece exposed to UV radiation was some fading in color seen. However no degradation of the coat layer itself was seen. Example 16
A set of specimens of the composition of copending application was prepared with pigmentation in three colors i.e. Bluish-Black, Grey and Green. a) These three pigmented samples were applied on a metal sheet, which was already coated with the first application of the composition.
After 4 hrs. of applying the composition of copending application, the topcoat of the present invention was applied in the three pigments given. It was observed that the bluish-black completely covered the first application and was smooth and looked effective. The Grey and Green, though they took on the coloring of the pigment, were not very smooth.
After 8 hrs. of applying the composition of copending application, the three topcoats of the present invention were applied and there were no noticeable differences from the 4 hr. application.
After 36 hrs. there was also no difference in the texture or in the drying as those observed in the 4 and 8 hrs. application. Example 17
The composition of copending application was applied on three sets of metal and dried for 40/45 minutes. A second coat of the overcoat composition of the invention was applied on the three sets of metal and it was observed to be free flowing like paint, did not blotch and was free from granulation. The second coat application dried in 20/ 30 minutes and was smooth to the touch. Due to the pigmentation used i.e. Carbon Black, the first coat and metal below was completely covered and there was no places where there was no original rusting, that could be seen as the second coat application gave a complete paint like top-coat cover. Example 18
A dark green pigmented overcoat was applied as in Example 17 above on the metal sheet and M. S. Rod pieces. The second application also surface dried within 20/25 minutes, but within a few hrs. of applying, the coloring became slightly darker and though the surface was smooth and even, at places the first coat application was visible — more so on the M. S. Rod. It was also applied on a partly rusted sheet, which was partially covered with the first appHcation, and in this case portions of the first coat and metal sheet were visible.
The metal sheet having two coat appHcation of both the Dark Grey and Dark Green of top coat composition of the invention were copiously sprinkled and splashed with water and allowed to dry in sunlight - this was done after 16 hrs. drying time of both appHcations. No visible deterioration or discoloration was noticeable in either appHcation. A further observation of this was done after another 24 hrs. with more water being sprinkled and exposure to normal weather conditions. No change or deterioration was observed. Example 19
A single appHcation of composition of copending appHcation and a topcoat appHcation of overcoat composition of the invention containing 46% PVDC Latex were applied on an iron sq. pipe as well as M.S. Rod pieces. These were buried umderground in moist and wet mud for over 2 weeks. While gloss and sheen of overcoat were lost and the metal was patchy, dull black color, but there is no rust visible. Example 20
A single appHcation of composition of copending appHcation and a topcoat appHcation of topcoat composition of the invention containing 75% PVDC Latex were applied on around icon pipe as well as M.S. Rod pieces. These were buried \mderground in moist and wet mud for over 2 weeks. The results are very encouraging as the topcoat has been fully retained with its gloss gloss and sheen and there appears to be no reaction on the metal pieces, which were cured. However, the untreated areas have rusted heavily. Example 21
The composition of the invention was applied on mild steel plates after 60 mins of applying composition of copending appHcation and then allowed to dry.
The flow and texture of the topcoat was even and the appHcation was similar to a paint application. On vigorous shaking the frothing was quite excessive but it did not interfere in the appHcation itself These 3 sets of plates were allowed to cure for 3 days and after this one plate was immersed in water, the 2nd in saHne water (5% salt) and the 3rd in water exposed to sunHght-UV.
It was observed after 3 days that the first piece in ordinary water did not disperse any color or taint the water in any way. The top coat appeared to be bonded very well.
The 2nd metal piece was also rust free after 3 days immersion in saline water and this was very encouraging.
However the third pc in saline water exposed to sunHght, showed some fading in color below the water line and some small particles of surface rust were visible.
In conclusion it is apparent that for normal topcoat application of RG-020 in all weather conditions it was found adequate.
The above examples are non-limiting and are illustrative of the composition of the invention. Modifications and variations therefrom are possible without departing from the spirit of the invention.

We claim
1. A rust inhibiting overcoat composition comprising essentially of latex in an amount of 60 to 70%, an anti-foaming agent in an amount of 0.4 to 0.6 %, a clay in an amount of 0.5 to 1.0 %, TiO2 in an amount of 2 to 4%.
2. A composition as claimed in claim 1 wherein water is added to obtain the desired thickness for storage and/or final application on the ferro-metallic surface.
3. A composition as claimed in claim 1 or 2 wherein the latex is preferably of a pH in the range of 2 to 5.
4. A composition as claimed in claim 1 to 3 wherein the anti-foaming agent is preferably a silicone based defoaming agent.
5. A composition as claimed in claim 1 to 4 wherein the clay used is a thisxotropic flow modifier or a mineral colloid.
6. A composition as claimed in claim 1 to 5 wherein additional optional pigments such as carbon black paste, conventional grey, green, are added in an amount of 2 to 4%.
7. A method for the manufacture of rust inhibiting overcoat composition comprising essentially of latex in an amoimt of 60 to 70%, an anti-foaming agent in an amount of 0.4 to 0.6 %, a clay in an amount of 0.5 to 1.0 %, TiO2 in an amount of 2 to 4%, all amounts being expressed in terms of weight of the total composition, the method comprising admixing the above ingredients in the ranges of proportions mentioned above under conditions suitable for the formation of a complete mixture.
8. A method as claimed in claim 7 wherein if desired water is added to obtain the desired thickness for storage and/or final application on the ferro-metaliic surface.
9. A method as claimed in claim 7 or 8 wherein the latex is preferably of a pH in the range of 2 to 5.
10. A method as claimed in claim 7 to 9 wherein the anti-foaming agent is preferably a siHcone based defoaming agent.
11. A method as claimed in claim 7 or 10 wherein the clay used is a thixotropic flow modifier or a mineral colloid.
12. A method as claimed in claim 7 to 11 wherein additional optional pigments such as carbon black paste, conventional grey, green, are added in an amount of 2 to 4%.
13. A rust inhibiting overcoat composition substantially as described hereinbefore and with reference to the foregoing examples.
14. A method for the manufacture of rust inhibiting overcoat composition substantially as described hereinbefore and with reference to the foregoing examples