GB2254616A

GB2254616A - Anticorrosive coating composition

Info

Publication number: GB2254616A
Application number: GB9112747A
Authority: GB
Inventors: Leonard Wisniewski
Original assignee: HANDS HARRY FREDERICK
Current assignee: HANDS HARRY FREDERICK
Priority date: 1991-04-11
Filing date: 1991-06-13
Publication date: 1992-10-14
Also published as: GB9112747D0

Abstract

A coating composition which is suitable for the cathodic protection of iron or steel against electrolytic corrosion includes N-type pyrolysed graphite and/or an organic semi-conductor such as pyrolysed polyacrylonitrile, phthalocyanine, or phenazine. The semi-conductor may be dispersed in a binder which may be selected from epoxy, acrylic, phenolic and vinyl resin solutions. The composition may further include tetrachloroquinone. Uses:- Coating steel hulls of ships and structural steel.

Description

The present invention relates to coating compositions and to a method of protecting a metal substrate against electrolytic corrosion.

More particularly, the invention relates to coating compositions which are suitable for the cathodic protection of iron or steel against electrolytic corrosion, for example the steel hull of a ship, structural steel, and so on.

According to one aspect of the invention, a coating composition includes pyrolysed graphite. The pyrolysed graphite may be an N-type pyrolysed graphite.

The composition may further include an organic semi-conductor.

According to another aspect of the invention, a coating composition includes an organic semiconductor.

The organic semi-conductor in either aspect of the invention may be selected from the group consisting of pyrolysed polyacrylonitrile, phthalocyanine, and phenazine.

The semi-conductor may be dispersed in a binder, which may be selected from the group consisting of epoxy, acrylic, phenolic, and vinyl resin solutions.

The composition may include tetrachloroquinone.

The invention extends to a method of protecting a metal substrate against electrolytic corrosion, which comprises coating the substrate with a layer of coating composition as defined above.

The invention will now be described in more detail with reference to the following examples. The value for the energy gap associated with electron activation within the conjugated structure is also indicated.

Example 1 A coating composition or paint containing, in approximate percentages by weight: Polyacrylonitrile 12% N-type pyrolysed graphite 18% Epoxy ester resin 35% Solvent 35% -0.6 ev to -1.4 ev Example 2 A coating composition or paint containing, in approximate percentages by weight: Phthalocyanine 13,5% Tetrachloroquinone 0,5% N-type pyrolysed graphite 15,0% Phenazine 1,0% Phenolic resin 35,0% Solvent 35,0% -0.4 ev to -0.8 ev Example 3 A coating composition or paint containing, in approximate percentages by weight: Polyacrylonitrile 12 N-type pyrolysed graphite 18% Acrylic resin 35% Solvent 35% -0.6 ev to -0.8 ev Example 4 A coating composition or paint containing, in approximate percentages by weight:: Phenolic resin 8% N-type pyrolysed graphite 22% Vinyl resin 30% Solvent 40% -0.6 ev to -1.2 ev It is believed that by applying a coating in accordance with the invention to a steel substrate there is created an electro potential difference between the substrate and the protective organo-anodic film compound. The coating compound utilises ionic electrical charges from water molecules. When in contact with water a change of polarity between the coating and the protected steel substrate is caused.

This results in the coating film becoming anodic to the steel substrate, which prevents oxidation (corrosion of the steel surface). Furthermore, the coating does not have any sacrificial elements which oxidise when the negativity towards the substrate arises. The semiconductive coating does not deteriorate when in contact with water molecules. The contact forms an electric field which protects the steel against electrolytic corrosion. The coating is an organic semi-conductive, water and gas proof coating for application to metal substrates. When in contact with water, the coating traps electrons from water molecules and transfers them to the metal substrate. Thereafter the metal electrical double layer remains in equilibrium, in which condition occurrence of corrosion is inhibited.

In other words, anti-corrosive protection is provided by the transfer of negative electrical charges from water molecules through the semi-conductive film coating to the metal substrate.

The coating provides double action protection, firstly by sealing off the substance from the environment and secondly, when contact with water arises, it protects the steel against corrosion electronically.

A further aspect is that materials are provided in a paint which is suitable for coating metal surfaces to protect them against corrosion, The coating has included in it a dispersion of elements and compounds capable of trapping and transferring electrons from water molecules to the metal surface.

The composition to be applied to the metal surface comprises a mixture of materials having a certain ohmic conductivity and value for energy gap associated with electron activation within the conjugated structure as follows: Pyrolysed polyacrylonitrile Phthalocyanine (metal free) (C6H4C2N)4 N4 N-type pyrolytic graphite Phenazine C6H4N2C6H4 Impurities at ratio of 1 : 10 000 may be iron carbonyl, amorphous carbon tetrachloroquinone (C6Cl4O2) and voids in the coating.

The semi-conductive materials may include impurities which are dispersed in binders such as poly esters, epoxy ester, epoxy, acrylics, vinyls, phenolics and chlorinated rubber, ground to a particle size of 5 microns. The binder may be thinned to a suitable consistency by the addition of aromatic solvents such as xylene, toluene or propylo carbinol and ketones.

After application to the metal surface by brush, roller or spray the coating composition forms a dry tri-dimensional film, which is relatively water and gas proof.

Recommended thickness of the film is about 25 micron. The coating may be over-coated if required by any decorative paint or enamel. The electrical properties functioning will then be dormant until establishing contact with water.

The applicant does not wish to be bound by any of the theoretical explanations of the manner in which the metal substrate is protected against corrosion by transfer of electrons from water molecules to the substrate by the semi-conductive coating film on the metal surface as et out herein. However, it is believed that the coating film consists of carbon of which solid crystrallites are flat, parallel and equidistant carbon layers of hexagonally arrayed atoms, well aligned with respect to each other to form well ordered carbon layers: The sign (polarity) depends on included impurities, which are substances which do not interact with the coating composition and are inert irrespective of its intrinsic energy gap. No interaction will take place between the components of the coating composition. Moreover magneto resistance proves high mobility in basal plane of the crystals contained in the coating.

Finally, the semi-conductance and the transfer of energy in the organic compound is due to electron and holes concentration and the transfer of energy is achieved through the overlapping molecular orbitals by neighbouring molecules.

A coating composition according to the invention is particularly suitable for anti-corrosive protection of iron and steel, bridge construction, ship hulls etc.

Claims

1. A coating composition which includes pyrolysed graphite.

2. A coating composition as claimed in claim 1, wherein the pyrolysed graphite is an N-type pyrolysed graphite.

3. A composition as claimed in claim 1 or claim 2, which further includes an organic semi-conductor.

4. A coating composition which includes an organic semi-conductor.

5. A composition as claimed in claim 3 or claim 4, in which the organic semi-conductor is selected from the group consisting of pyrolysed polyacrylonitrile, phthalocyanine, and phenazine.

6. A composition as claimed in any one of claims 3 to 5, which includes a binder and in which the semiconductor is dispersed in the binder.

7. A composition as claimed in claim 6, in which the binder is selected from the group consisting of Epoxy, acrylic, phenolic, and vinyl resin solutions.

8. A composition as claimed in any one of the preceding claims, which further includes tetrachloroquinone.

9. A coating composition which includes the following constituents, approximately in percentage by weight: Polyacrylonitrile 12% N-type pyrolysed graphite 18% Epoxy ester resin 35% Solvent 35%

10. A coating composition which includes the following constituents, approximately in percentage by weight: Phthalocyanine 13,5 Tetrachloroquinone 0,5% N-type pyrolysed graphite 15,0% Phenazine 1,0% Phenolic resin 35,0% Solvent 35,0%

11. A coating composition which includes the following constituents, approximately in percentage by weight: Polyacrylonitrile 12% N-type pyrolysed graphite 18% Acrylic resin 35% Solvent 35%

12. A coating composition which includes the following constituents, approximately in percentage by weight: Phenolic resin 8% N-type pyrolysed graphite 22% Vinyl resin 30% Solvent 40%

13. A method of protecting a metal substrate against electrolytic corrosion, which comprises coating the substrate with a layer of coating composition as claimed in any one of the preceding claims.

14. A coating composition substantially as herein described.

15. A method of protecting a metal substrate against electrolytic corrosion, substantially as herein described.