Compositions: coating or plastic – Coating or plastic compositions – Corrosion inhibiting coating composition
Patent
1998-02-24
2000-07-04
Green, Anthony
Compositions: coating or plastic
Coating or plastic compositions
Corrosion inhibiting coating composition
106 1441, 106 1444, 106404, 106419, 106447, 106450, 106460, 106462, 106480, 106493, 106494, 106499, 106505, C09B 5710, C09C 100, C08K 542, C09K 312, C09D 534
Patent
active
060833084
DESCRIPTION:
BRIEF SUMMARY
The incorporation of traditional anti-corrosive pigments such as red lead, lead silicochromate, strontium chromate, zinc tetroxy chromate and zinc potassium chromate into coating systems for use over metallic substrates enables high levels of corrosion protection to be realised. This corrosion protection refers particularly to both retention of adhesion of the coating system to metallic substrates (under moist and/or corrosive conditions) and prevention of rusting of the substrate. These otherwise effective pigments are however toxic. Accordingly, they have either been replaced by available lower or non-toxic alternatives or their continued use is coming under increasing scrutiny and regulation.
Examples of existing commercial lower or non-toxic alternative pigments are metal salts of phosphates, phosphosilicates, borosiicates, borates, metaborates, molybdates, polyphosphates, triphosphates and phosphites using typically calcium, strontium, barium, zinc and aluminium as the metallic cations. Ion-exchanged silicas such as calcium-exchanged silica have also been introduced. Zinc phosphate is currently by far the most widely used low or non-toxic anti-corrosive pigment.
It has been found that these alternative pigments do not always achieve the same level of performance as the traditional pigments. In some applications, performance differentials are so great as to preclude use of the available non-toxic pigments.
While the above discussion applies to both non-aqueous solvent-borne and water-borne coating systems, in the developing field of water-borne technology, there is the additional problem of matching anti-corrosive performance levels otherwise achievable with non-aqueous solvent-borne counterparts. The traditional pigments enable quite good performance levels to be achieved in water-borne coating compositions, but there is little interest to develop new water-borne systems based on such pigments in view of the toxicity problems.
In many types of coatings, the non-toxic alternative pigments are sometimes used in combinations of two or more pigments in an effort to improve performance levels. This approach has met with varying degrees of success. The use of combinations of pigments naturally adds to the complexities involved in coating development and manufacture.
Currently, there is increasing emphasis on anti-corrosive pigments entirely free of heavy metals, including zinc. This is particularly true in water-borne systems as a result of waste water problems. Unfortunately, the non-toxic alternative pigments given above typically do not satisfy this zinc-free requirement. The zinc-free pigments that are available generally provide a lower level of corrosion protection than pigments which contain zinc and/or other heavy metals.
Organophosphonic acids and their water-soluble salts are known in the field of water treatment chemicals where they are used to help inhibit is scale formation and metal corrosion. These compounds are added to water systems such as cooling water and boiler water at very low concentrations, typically in the ppm range. The formulation of an effective water treatment chemical is very complex, but to exert adequate corrosion inhibition, such organophosphonic compounds are normally used in conjunction with ppm levels of polyvalent metal cations such as calcium and zinc.
Some attempts have been made at using specific organophosphonic species in the formation of anti-corrosion pigments, but the results obtained have not been very convincing. Such pigments are mostly useful only in combination with other anti-corrosive pigments. Thus, there remains a need for improved anti-corrosion pigments which provide excellent corrosion protection while avoiding the need to use zinc and/or other heavy metals.
SUMMARY OF THE INVENTION
Effective anti-corrosion pigments (suitable for incorporation into polymeric and protective materials such as coatings, adhesives, sealants and organic pretreatments) have now been found. The anti-corrosive pigments of the invention provide performance superior to conv
Cross Charles A.
Green Anthony
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