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Title:
ANTI-CORROSIVE COATINGS BASED ON ACID-BASE REACTIONS
Document Type and Number:
WIPO Patent Application WO/2020/178754
Kind Code:
A1
Abstract:
The present invention discloses an anti-corrosive coating with a first powder mixture of alkali metal oxide, and/or a sparingly soluble alkali metal phosphate, and/or a water reducer, a retarder, and/or a wetting agent and/or a filler; and; a second aqueous based mixture of alkali metal sulfate, and/or phosphoric acid, and/or alkanolamine and water. The present invention provides a coating composition inhibits corrosion of metals having increased working time based on acid-base reaction that works in extreme environment.

Inventors:
RAMKUMAR NATARAJAN (IN)
VARADHARAJAN NATARAJAN (IN)
PARIHAR DEEPAK KUMAR (IN)
SINHA ABHISHEK (IN)
Application Number:
PCT/IB2020/051833
Publication Date:
September 10, 2020
Filing Date:
March 04, 2020
Export Citation:
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Assignee:
NAVODAY SCIENCES PRIVATE LTD (IN)
International Classes:
C08G18/48
Domestic Patent References:
WO2015195670A12015-12-23
Foreign References:
US20020009622A12002-01-24
US5466280A1995-11-14
CA2746600A12010-07-01
Attorney, Agent or Firm:
RANA, Vikrant (IN)
Download PDF:
Claims:
CLAIMS:

1. An anti-corrosive coating composition comprising a mixture of:

• a solid or powder component comprising:

- an alkali metal oxide;

- a pigment;

- a retarder; and/or

- a filler; and/or

- a wetting agent; and/or

- a water reducing agent; and/or

- a sparingly soluble alkali metal phosphate

• an aqueous based component comprising:

- a mixture of alkali metal sulfate and/or phosphoric acid;

- water; and/or

- a source of alkanolamine.

2. The solid or powder component of anticorrosive coating composition as claimed in Claiml , comprising:

5-75% of alkali metal oxide;

0.1 -50% of sparsely soluble alkali metal phosphate;

0.5-20% of retarder;

0.1-20% of pigment;

0.1-5% of water reducing agent;

0.1-2% of wetting agent;

01 -20% of filler.

3. The aqueous based component of anti-corrosive coating composition as claimed in Claim 1, comprising:

5-50% of alkali metal sulfate;

Water (1-90%); and/ or

0.1-10% of acid phosphate/phosphoric acid; and/or

4. The solid or powder component as claimed in Claim 1 , wherein the alkali metal oxide is selected from but not limited to dead burnt magnesium oxide, lightly calcined magnesium oxide, Lightly Calcined Magnesite, Dead Burnt Magnesite calcium oxide, magnesium silicate, magnesium aluminate or mixtures thereof.

5. The solid or powder component as claimed in Claim 1 , wherein the sparingly soluble alkali metal phosphate includes but not limited to alkali earth dihydrogen phosphate MH2P04, alkali earth dihydrogen phosphate M(H2P04)2 or its hydrate, transition metal trihydrogen phosphate MH3(H2P04) or its hydrate, or mixtures thereof.

6. The solid or powder component as claimed in claim 1 , wherein the water reducing agent includes but not limited to polycarboxylate ether or lignosulfonates.

7. The solid or powder component as claimed in claim 1, wherein the retarders includes but not limited to alkali metal citrates, tartarates, borates, stannates, sulfates, alkanol amines or mixture thereof.

8. The solid or powder component as claimed in claim 1, wherein the filler is selected from but is not limited toan inorganic mineral silicate, talc, amorphous magnesium silicate, amorphous calcium silicate, diatomaceous earth, aluminosilicate, olivine, calcined kaolin, mullite, colloidal silica, silicon dioxide, and amorphous silicon dioxide, preferably Metakaolin or any kind of clay.

9. The aqueous based component as claimed in claim 1, wherein the alkali metal sulfate includes but not limited to magnesium sulphate.

10. A method of application of an anticorrosive coating composition as claimed in claim 1, the method comprising the steps:

12 - mixing of the blended powder and aqueous component for 3-5 minutes in the ratio of 1:0.3 to 1: 1.2 to form lump free consistency;

- processing of the slurry for a period of 10- 20 minutes;

- painting on the top of sand blasted carbon steel with the resulting solution;

- drying the coating for about 60-90 minutes;

- recoating of the carbon steel with freshly prepared solution after 2-4 hours;

- curing of the steel plate for 24-36 hours;

- incubating the coated steel sample inside the salt fog chamber at a temperature of 35-40 °C and in an atmosphere of 4% Sodium chloride solution used for creating a salty fog inside the chamber.

AMENDED CLAIMS

received by the International Bureau on 03 August 2020 (03.08.20)|

1. An anti-corrosive coating composition comprising a mixture of:

— a solid or powder component comprising:

5 to 75 % of an alkali metal oxide;

0.1 to 20 % of a pigment;

0.5 to 20 % of a retarder; and/or

0.1 to 20 % of a filler; and/or

0.1 to 2 % of a wetting agent; and/or

0.1 to 5 % of a water reducing agent; and/or

0.1 to 50 % of a sparingly soluble alkali metal phosphate

AND

— an aqueous based component comprising:

5 to 50 % of alkali metal sulfate and/or

0.1 to 10 % of acid phosphate/phosphoric acid;

1 to 90 % of water; and/or

a source of alkanolamine containing 1 to 20 % of alkanol amine.

2. The solid or powder component as claimed in claim 1 , wherein the alkali metal oxide is selected from but not limited to dead burnt magnesium oxide, Lightly Calcined Magnesite, Dead Burnt Magnesite calcium oxide, magnesium silicate, magnesium aluminate or mixtures thereof.

3. The solid or powder component as claimed in claim 1, wherein the sparingly soluble alkali metal phosphate includes but not limited to alkali earth dihydrogen phosphate MH2P04, alkali earth dihydrogen phosphate M(H2P04)2 or its hydrate, transition metal trihydrogen phosphate MH3(H2P04) or its hydrate, or mixtures thereof.

4. The solid or powder component as claimed in claim 1 , wherein the water reducing agent includes but not limited to polycarboxylate ether or lignosulfonates.

5. The solid or powder component as claimed in claim 1, wherein the retarders includes but not limited to alkali metal citrates, tartarates, borates, stannates, sulfates, alkanol amines or mixture thereof. 6. The solid or powder component as claimed in claim 1 , wherein the filler is selected from but is not limited to an inorganic mineral silicate, talc, amorphous magnesium silicate, amorphous calcium silicate, diatomaceous earth, aluminosilicate, olivine, calcined kaolin, mullite, colloidal silica, silicon dioxide, and amorphous silicon dioxide, more preferably Metakaolin.

7. The aqueous based component as claimed in claim 1, wherein the alkali metal sulfate includes but not limited to magnesium sulphate.

8. A method of application of an anticorrosive coating composition as claimed in claim 1, the method comprising the steps:

- mixing of the blended powder and aqueous component for 3-5 minutes in the ratio of 1:0.3 to 1: 1.2 to form lump free consistency;

- processing of the slurry for a period of 10- 20 minutes;

- painting on the top of sand blasted carbon steel with the resulting solution;

- drying the coating for 60-90 minutes;

- recoating of the carbon steel with freshly prepared solution after 2-4 hours;

- curing of the steel plate for 24-36 hours;

- incubating the coated steel sample inside the salt fog chamber at a temperature of 35-40 °C and in an atmosphere of 4% Sodium chloride solution used for creating a salty fog inside the chamber.

Description:
ANTI-CORROSIVE COATINGS BASED ON ACID-BASE REACTIONS

FIELD OF THE INVENTION

[001] The present invention relates to anti-corrosive coatings. Particularly, the present invention relates to anti-corrosive coatings based on acid base reactions. More particularly, the present invention provides coating composition comprising a mixture of a powder/solid component and an aqueous component for inhibiting corrosion of metals, wherein the coating prepared has increased working time based on acid-base reaction.

BACKGROUND OF THE INVENTION

[002] Corrosion of structural steel is a serious problem in construction and utility industry. Exposure to humid and saline environments causes rusting of metals due to reaction of metals with air and/or water. At elevated temperatures the rate of corrosion increases drastically causing the structure to collapse prematurely. To minimize or reduce the corrosion, various methods such as, painting, surface treatment, surface plating, alloys of steel, such as galvanized (zinc coated) compositions, or chrome plated compositions are used. While these approaches may solve the problem in the short run, however, the problem persists when the steel is exposed to extreme environments over longer time period.

[003] Earlier attempts to produce anticorrosive coatings based on acid-base reactions involved the use of phosphate solutions having a pH in the range of 1 -3 and mixing it with metal hydroxide solutions before spraying to form the coating. However, one of the drawbacks of these coatings is that it cannot be applied with a brush because of instantaneous setting since the reaction time between the acid and alkaline liquid is typically less than 2 minutes.

[004] The patent application WO2015195670A1 discloses the coating comprising of two aqueous mixtures. It consist of a low temperature setting aluminum-divalent metal phosphate ceramic coating composition comprising a first aqueous based mixture comprising a solution of monoaluminum phosphate; polyphosphate, pyrophosphate, or salts thereof; and a second aqueous based mixture comprising a divalent metal oxide or hydroxide; a hydrocarboxylic acid in an amount sufficient to retard the reaction of the monoaluminum phosphate and the divalent metal oxide or hydroxide is provided. The invention provides a fire and corrosion resistant quick drying coating system.

[005] The US patent application US5466280A discloses an inorganic coating composition having a curable powder which contains a hydraulic calcium aluminate compound, a metallic oxide reinforcing agent and a pigment, and a binder solution which contains an alkali-metal silicate solution and a soluble phosphate. This invention does not include the two different mixtures of solid/powder component and aqueous component. The disadvantage of this prior art composition is that it is quick setting in nature and cannot be applied manually.

[006] Therefore, there is a need to provide an anti-corrosive coating that will have a longer working time and protects the structures in extreme environments. The present invention provides one such coating comprising of acidic phosphate, alkaline metal sulfate and alkaline metal oxide components for inhibiting corrosion of metals having increased working time based on acid-base reaction.

OBJECT OF THE INVENTION

[007] The main object of the present invention is to provide an anti- corrosive coating for inhibiting corrosion of metals such as steel having increased working time based on acid-base reaction.

[008] Another object of the present invention is to provide an anti- corrosive coating for inhibiting corrosion of carbon steel having increased working time based on acid-base reaction.

[009] Yet another object of the present invention is to provide an anti- corrosive coating comprising a first powder blend of alkali metal oxide, and/or a sparingly soluble alkali metal phosphate, and/or a water reducer, a retarder, and/or a wetting agent, and/or a filler; and a second aqueous based mixture of alkali metal sulfate, and/or phosphoric acid, and/or alkanolamine and water. [0010] Still other object of the invention is to provide a method of preparation and application of the anti- corrosive coating on a substrate.

[0011] Other objects and advantages of the present invention will become apparent from the following description taken in connection with the accompanying drawings, wherein, by way of illustration and example, the aspects of the present invention are disclosed.

SUMMARY OF THE INVENTION

[0012] The present invention discloses composition and method of preparing an anti-corrosive coating comprising of a first powder mixture of alkali metal oxide, and/or a sparingly soluble alkali metal phosphate, and/or a water reducer, a retarder, and/or a wetting agent and and/or filler; and a second aqueous based mixture of alkali metal sulfate, and/or phosphoric acid, and/or alkanolamine and water.

DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 shows the carbon steel with coating (1) of the present invention and conventional anticorrosion primer (2) after being exposed in corrosion chamber for 500 hours. As shown in the figure, the carbon steel with the coating of the present invention shows no signs of rust formation or blistering.

DESCRIPTION OF THE INVENTION

[0014] The following presents a simplified description of the invention in order to provide a basic understanding of some aspects of the invention. This description is not an extensive overview of the present invention. It is not intended to identify the key /critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concept of the invention in a simplified form. [0015] Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope of the invention. In addition, descriptions of well-known functions and constructions are omitted for clarity and conciseness.

[0016] Features that are described and/or illustrated with respect to one embodiment may be used in the same way or in a similar way in one or more other embodiments and/or in combination with or instead of the features of the other embodiments.

[0017] The terms and words used in the following description are not limited to the bibliographical meanings, but, are merely used to enable a clear and consistent understanding of the invention. Accordingly, it should be apparent to those skilled in the art that the following description of exemplary embodiments of the present invention are provided for illustration purpose only and not for the purpose of limiting the invention.

[0018] It is to be understood that the singular forms“a,”“an,” and“the” include plural referents unless the context clearly dictates otherwise.

[0019] It should be emphasized that the term “comprises/comprising” when used in this specification is taken to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

[0020] Accordingly, the present invention discloses composition and method of preparing an anti corrosive coating comprising a mixture of a powder and an aqueous component.

[0021] The solid/powder component essentially comprises:

- an alkali metal oxide;

- a retarder;

- a pigment; and and may optionally comprise:

- a wetting agent; and/or

- a water reducing agent; and/or

- a sparingly soluble alkali metal phosphate; and/or

- a filler.

The aqueous phase/ liquid component essentially comprises:

- an alkali metal sulfate;

- water;

and may optionally comprise:

- acid phosphate/ phosphoric acid;

- a source of alkanol amine.

[0022] In an embodiment, the composition of the present invention comprises of a first powder mixture of alkali metal oxide, and/or a sparingly soluble alkali metal phosphate, and/or a water reducer, and a retarder, and/or a wetting agent and/or a filler; and a second aqueous based mixture of alkali metal sulfate, and/or phosphoric acid, and/or alkanolamine and water.

[0023] In an embodiment of the present invention, the invention discloses an anticorrosive coating comprising a mixture of an aqueous component and a solid or powder component. The aqueous composition with a pH range of 6- 10 comprises of (i) a mixture of phosphoric acid and/or magnesium sulfate and/or (ii) a source of alkanolamine and water, an oxidizer and/or unreactive filler. The powder component comprises of (i) an alkali metal oxide; and/or (ii) a sparingly soluble alkali metal phosphate (iii) a retarder; and/or (iv) a water reducer; and/or (v) a wetting agent and/or (vi) a filler; and (vii) a color pigment.

[0024] In an embodiment of the present invention, the alkali metal oxide is selected from dead burnt magnesium oxide, lightly calcined magnesium oxide, magnesium carbonate, Lightly Calcined Magnesite, Dead Burnt Magnesite, calcium oxide, magnesium silicate, magnesium aluminate or mixtures of thereof. The concentration of the metal oxide may be taken in the range of 5 to 75% of the total composition. [0025] The retarder reduces the oxidation of metal surface by acting as an anti- catalyst. It exerts a protective effect upon metals against attack of moisture. The retarder in the present invention is selected from alkali metal citrates, tartarates, borates, stannates. alkanolamines or mixtures thereof, The retarders may also be selected from the acids such as hydrocarboxylic acid, for instance, Citric acid, Tartaric acid etc. The corrosion retarders are used in amount of range 0.5-20% of the total composition. Preferably, the acid-base reaction retarder is an alkali metal borate. Preferably, the borate is borax.

[0026] The anti-corrosive component of present invention contains pigments to provide color to the coating. The pigment may be selected from titanium dioxide, or the like. The pigment is incorporated in the coating composition in amount of 0.1 to 20% of the total composition.

[0027] The first class of water reducing agent was the lignosulfonates derived from wood and paper industry, which are now substantially replaced by synthetic sulfonates and carboxylates. In the present invention of anti-corrosive composition, the powder component optionally comprises water reducer selected from polycarboxylate ether or lignosulfonates, or mixtures thereof. The concentration of the water reducer is preferably taken in the range of 0.1 to 5% of the total composition.

[0028] The powder component may optionally comprise sparingly soluble alkali metal phosphate. The sparingly soluble alkali metal phosphate is selected from alkali earth dihydrogen phosphate MH2P04, alkali earth dihydrogen phosphate M(H2P04)2 or its hydrate, transition metal trihydrogen phosphate MH3(H2P04)2 or its hydrate, or mixtures thereof. The concentration of the sparingly soluble alkali metal phosphate may be taken in the range of 0.1 to 50% of the total composition. The metal phosphate may also be selected from mono-aluminium phosphate and mono-potassium phosphate.

[0029] The wetting agent used herein are selected from Polycarboxylate ether, lignosulfonates in a concentration range of 0.1 to 2 % of the total composition. The advantages of using them is it increases the fluidity of the slurry so that it can be applied easily. [0030] The aqueous composition of the mixture has a pH range of 6-.10

[0031] The alkali metal sulfate may be taken in the range of 5 to 50%. The alkali metal sulfate is preferably Magnesium Sulfate.

[0032] The acid phosphate is mono aluminum phosphate. The mono aluminum phosphate may be in a concentration range of 0.1 to 10%.

[0033] The aqueous mixture may optionally comprise phosphoric acid in a concentration of 0.1 to 10%.

[0034] The aqueous mixture may optionally comprise alkanoamine in a concentration range of 0.1 to 20%. The alkanoamine may be selected from the group of Triethanol amine, Di ethanol amine, Di ethanol isopropyl amine and Tri iso propanol amine. Alternatively, any other source of alkanol amine may also be used.

[0035] The first powder further optionally comprises one or more of fillers selected from an inorganic mineral silicate, talc, amorphous magnesium silicate, amorphous calcium silicate, diatomaceous earth, aluminosilicate, olivine, calcined kaolin, mullite, colloidal silica, silicon dioxide, and amorphous silicon dioxide. Preferably. The filler is a Metakaolin or any kind of clay. The mono fillers may be in a concentration range of 0.1 to 20%. Further, the aqueous-based mixtures may also optionally comprise a filler as mentioned hereinabove.

[0036] Water used to prepare the aqueous solution is taken in the range of 1-90%.

[0037] In an embodiment of the present invention, the aqueous based mixture excludes wollastonite.

[0038] The present invention also provides a process of preparation and application of the coating composition on a metal/steel substrate as follows: - mixing of the blended powder and aqueous component for 3-5 minutes in the ratio of 1:0.3 to 1 : 1.2 to form lump free consistency.

- Mixing of the slurry for a period of 10-20 minutes.

- painting on the top of sand blasted carbon steel with the resulting solution.

- drying the coating at room temperature for about 60-90 minutes.

- recoating of the carbon steel with freshly prepared solution after 2-4 hours.

- curing of the steel plate for 24-36 hours.

- incubating the coated steel sample inside the salt fog chamber at a temperature of 35-40°C and in an atmosphere of 4% Sodium chloride solution used for creating a salty fog inside the chamber.

- measuring of the corrosion resistance property of the coating by observing the plates visually for the occurrence of any corrosion spots or products for every 48 hours. (This is as per the procedure mentioned in ASTM B 117).

[0039] The present invention may be better understood with the following examples without restricting the invention to the examples:

[0040] Example 1

Powder part:

Dead Burnt Magnesium Oxide (Purity less than 90%)- 39%

Mono Potasium Phosphate - 44.2%

Borax- 13.3%

Pigment - 1.8% (Titanium di oxide)

Polycarboxylate Ether - 0.9%

Liquid part:

• Water - 78.9%

• Magnesium Sulfate - 5.6%

• Triethanol amine - 12.7%

• Phosphoric acid - 2.8% [0041] Now, 1000 grams of the blended powder is mixed with 315 ml of the solution for about 3 minutes before it forms a lump free consistency. After mixing the powder and the liquid component, the resulting slurry has a working time of close to 20 minutes. The resulting solution is painted on top of sand blasted carbon steel of size and 4 X 6 inches. The coating is dried into solid in about 60 minutes and after two hour the panel is again recoated using the solution prepared freshly. A total of three coats are applied onto the steel plate and is cured for 24 hours. After 24 hours, the coated steel sample is placed inside the salt fog chamber to measure the corrosion resistance property of the coating. After 500 hours of continuous exposure to salt water, the specimens show no signs of rust formation or blistering indicating a strong corrosion protection property of the coating developed.

[0042] Example 2

Powder part:

• Lightly Calcined Magnesite - 47.8%

• Dead Burnt Magnesite - 23.9%

• Metakaolin - 12%

• Pigment - 15.8%

• Citric acid- 0.5%

Liquid part:

• Magnesium Sulfate - 43.8%

• Water - 56.2%

[0043] 1000 grams of the blended powder is mixed with 1000 ml of the solution for about 3 minutes before it forms a lump free consistency. After mixing the powder and the liquid component, the resulting slurry has a working time of close to 20 minutes. The resulting solution is painted on top of sand blasted carbon steel of size and 4 X 6 inches. The applied coating dried into solid in about 90 minutes and after three hours, the panel is again recoated using the solution prepared freshly. A total of three coats are applied onto the steel plate and is cured for 24 hours. After 24 hours, the coated steel sample is placed inside the salt fog chamber to measure the corrosion resistance property of the coating. After 500 hours of continuous exposure to salt water, the specimens show no signs of rust formation or blistering indicating a strong corrosion protection property of the coating developed. [0044] Figure 1 shows the carbon steel with coating (1) of the present invention and conventional anticorrosion primer (2) after being exposed in corrosion chamber for 500 hours. As shown in the figure, the carbon steel with the coating of the present invention shows no signs of rust formation or blistering.

[0045] Although the embodiments herein are described with various specific embodiments, it will be obvious for a person skilled in the art to practice the invention with modifications. However, all such modifications are deemed to be within the scope of the invention.