Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Patent
1995-08-15
1996-12-03
Hoke, Veronica P.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
523216, 523457, 523459, 523514, 523516, 523527, C08J 932
Patent
active
055809073
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates generally to organic solvent-based, water-borne and powder, coating compositions. Particularly, this invention relates to an improvement coating composition which provides enhanced resistance to environmental attack of metallic substrates and which can be applied by any conventional coating technique. More particularly, this invention relates to a coating composition comprising zinc-powder (as defined herein) and lightweight, hollow, glass microspheres dispersed uniformly throughout the thickness of the coating which satisfies the objects set forth herein. The coatings deposited by the composition of the invention are highly electrically conductive and highly cathodic when applied over a ferrous metal substrate, and can be recoated with any topcoat at any time.
BACKGROUND OF THE INVENTION
The outstanding corrosion resistance afforded by galvanizing has made it the most effective means for the long term protection of steel from oxidation (rusting) and subsequent corrosion. It is the conventional method of providing protection for guardrails, transmission towers, light poles, electrical equipment and dozens of other specific applications. Five mils or 125 microns of a galvanizing composition (applied to light poles and transmission towers) will protect exposed equipment for a period in excess of 20 years. Guardrails may be coated with an average deposition of 75 microns and provide approximately 10 years of corrosion protection in an average rainfall environment. Galvanizing compositions are applied both by hot dipping and electroplating, in applications where surface coatings do not provide adequate corrosion resistance.
Galvanizing compositions are made from zinc "ingots" and become oxidized only when exposed to the elements. The high conductivity of galvanizing compositions provides excellent cathodic protection to steel (which acts as the cathode, zinc being the anode), when exposed to a saline environment or other forms of oxidation caused primarily by water in its various forms, moisture, vapor and ice. Zinc-rich primers have been considered to be optimum anti-corrosion coatings on iron or steel substrates. However, certain problems have restricted their use as industrial type primers. The action of zinc in inhibiting rust is based on an electrochemical interaction between the zinc and the steel substrate. In order not to insulate the zinc particles from each other and from the substrate the prior art has considered it necessary to use very little binder, with satisfactory corrosion protection achieved only when the zinc to binder ratio is at least about 9:1. The high zinc level and the relatively high density of zinc often cause undesirable settling during short term storage, Hence, the zinc is often added just prior to application and mixed rapidly during application to prevent settling and clogging of spray equipment. This deters efficient field use.
A lower zinc content is disclosed in U.S. Pat. No. 3,998,771, issued December 1976 to T. J. Feneis, Jr. et al. Water-based coating compositions are disclosed for application on iron supports to obtain anti-corrosive coatings. Single phase compositions in this patent include about 2% to 10% by weight of a non-volatile liquid epoxy resin, with low viscosity, derived from bisphenol A and an epihalohydrin, e.g., epichlorohydrin; about 2% to 10% by weight of a modified polyamide, i.e., an addition product of a water soluble polyamide and a liquid epoxy resin; and about 55% to 70% by weight of a zinc pigment having an average particle size of about 2 to 15 microns.
U.S. Pat. No. 4,417,007, issued November 1983 to G. A. Salensky et al, discloses a one component composition containing from about 4% to 25% by weight epoxy or phenoxy resin binder and a polyamine hardener, about 43% to 90% by weight zinc dust, about 3% to 38% by weight Mn.sub.3 O.sub.4 fume pigment, up to 35% by weight additional pigments including pigment extenders and fillers (such as talc, clays, diatomaceous silica and silica), up to 5% by weig
REFERENCES:
patent: 3998771 (1976-12-01), Feneis, Jr. et al.
patent: 4417007 (1983-11-01), Salensky et al.
patent: 4621024 (1986-11-01), Wright
patent: 4748194 (1987-05-01), Geeck
patent: 4891394 (1990-01-01), Savin
patent: 5098938 (1992-03-01), Savin
patent: 5167701 (1992-12-01), Savin
patent: 5182318 (1993-01-01), Savin
patent: 5252632 (1993-10-01), Savin
patent: 5334631 (1994-08-01), Durand
patent: 5338348 (1994-08-01), Savin
patent: 5413628 (1995-05-01), Savin
Zinc Dust and Powder--International Lead Zinc Research Organization (pp. 7 to 17 (1982).
Hoke Veronica P.
Hunting Industrial Coatings
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