Zinc-rich primers

C. W. Ho esch, A Methodfor Predicting Service Efie of Zinc Rich Primers on Carbon Steel, NASA technical memorandum 93101, Keimedy Space Center, Fla., 1986. 

Most pigments can be used in any type of binder therefore, paints cannot be identified by pigment type alone. For example, micaceous iron oxide pigment is traditionally in an oil-based binder but is being increasingly used in epoxies, etc. In the paint coating film, the pigment content may vary from 15 to 60 per cent. In the special case of zinc rich primers, it is over 90 per cent. 

Suitable paints for use underwater include vinyl resin systems, coal tar paints over inorganic zinc-rich primers, and some coal-tar epoxy primers have also proved themselves Special paints are available for application under water, e.g. epoxy modifications with polyamides. 

To avoid peeling of oleoresinous top coats from zinc-rich primers, a sufficient interval should be allowed between coats to permit the zinc-rich primer to weather first in sheltered conditions soluble products should be removed before recoating. 

Zinc-Rich Primer an anticorrosive primer for iron and steel incorporating zinc dust in a concentration sufficient to give electrical conductivity in the dried films, thus enabling the zinc metal to corrode preferentially to the substrate, i.e. to give cathodic protection. 

The primary function of a coating is to act as a barrier which isolates the underlying metal from the environment, and in certain circumstances such as an impervious continuous vitreous enamel on steel, this could be regarded as thermodynamic control. However, whereas a thick bituminous coating will act in the same way as n vitreous enamel, paint coatings are normally permeable to oxygen and water and in the case of an inhibitive primer (red lead, zinc chromate) anodic control will be significant, whilst the converse applies to a zinc-rich primer that will provide cathodic control to the substrate. 

Metallic Pigments, The leading metallic pigment is zinc dnst, which is used mostly in zinc-rich primers, where it acts as a passivating agent. Aluminum flake is used for the silvery metallic appearance that it imparts. 

Sacrificial coatings consist of (i) organic zinc-rich primers (ii) inorganic zinc-rich primers. Corrosion control mechanism by zinc-rich primers may be visualized to occur as shown in Figure 1.65. 

Organic zinc-rich primers are based on epoxy/polyamides, high-molecular-weight linear epoxies, moisture-cured urethanes, high-styrene resins, chlorinated rubbers and epoxy esters. In this type of primer zinc is covered with a monomolecular layer of the binder which facilitates the adhesion of the film to the substrate. 

Inorganic zinc-rich primers consist of zinc and a reactive binder such as an alkali metal silicate (sodium, potassium, lithium or quaternary ammonium silicate) or hydrolyzed ethyl silicate as binder. On mixing hard and cohesive films of silicate are formed. The structure of the inorganic zinc-rich silicate may appear as shown in Figure 1.66. 

The zinc silicate film is porous and readily absorbs corrosive electrolyte. The film is harder, stronger than organic zinc-rich films. These films have better resistance to solvent and heat than the organic zinc-rich primers and may be used for tank linings and other applications up to 400°C. 

In both organic zinc-rich and inorganic zinc-rich primers the duration of cathodic protection is finite and the effects of polarization of zinc and the production of zinc corrosion product on the surface results in a change of protection mechanism from... 

Part 5 gives, in the primer area, information about the type of primer to be used for the different corrodibility categories (classification of environment according to Part 2) and indicates whether the primer is zinc-rich or based on other anticorrosive pigments. For example, ISO 12944-5 requests for a zinc-rich primer a zinc dust content of 80% by mass (m/m) related to the non-volatile content of the primer [5.108]. 

Chemtec [ uthera Coatings] Zinc-rich primer. 

Ferrophos. [OxyChem] Enhancer ftx zinc-rich primers for weldable, conductive, or corrosion-resistant coatings. 

Anti-corrosion coating based on epoxy rein and zinc-rich primer ... 

The analytical examination of the test media after the end of the galvanic corrosion experiments involved determining the concentrations of iron, copper and zinc. The concentration of zinc was measured because some of the specimens tested had been coated with a zinc-rich primer. 

The effect of changes in materials in automobiles that contained body panels made from carbon steel, steel pre-painted with zinc-rich primer, or steel coated with zinc/zinc alloy. The data in Table 4.38 were obtained from 5- to 6-year-old vehicles in 1985 and 1993. 

As indicated in Table 10.18, a zinc-rich primer is often recommended. It can be an organic zinc-epoxy or an inorganic zinc-ethyl-silicate primer. Zinc-rich primers are also used as so-called shop primers, or prefabrication primers, for temporary protection of semi-manufactured steel goods. After fabrication, e.g. of welded steel structures, the shop primer surface must be cleaned (degreased), and possible shop primer defects and weld joints have to be blast cleaned and coated with a primer before the whole structure is painted. Iron oxide is also used as a pigment in some shop primers. These must not be overpainted with a zinc-rich paint. 

C3 Interiors with high relative humidity, some air pollution. Exteriors in urban and industrial Sa2 /2 Zinc-rich primer. Finishing coats vinyl, chlorinated rubber or epoxy 3-4 175-240... 

C5-M Interiors with almost Sa2 /2 Zinc-rich primer. 4-5 325-400... 

Chem. Descrip. Polyamidoamine (70%) in xylene Uses Crosslinking agent for epoxy resins in soiv.-based primers and coatings for min. and metallic substrates, anticorrosion primers, zinc-rich primers, coatings for lock gates, concrete, and underground conduits (in combination with tar)... 

Uses Epoxy curing agent for two-pkg. air-dry coatings, e.g., industrial maintenance primers, midcoats, and topcoats, anticorrosive marine primers, zinc-rich primers, methanol-resist, tank coatings, concrete floor coatings... 

Uses Epoxy for high-performance, two-package systems tor coatings (structural steel primers, concrete sealers and surfaces, tank linings, topcoats for zinc rich primers)... 

Uses Thixotrope for high polarity and oxygenated solv. systems such as nail lacquers, paints/coatings (nitrocellulose lacquers, sol n. vinyls, epoxies, acrylics, wash primers, inorg. zinc-rich primers, chlorinated mb-ber, unsat. polyesters)... 

Chem. Descrip. Org. paste in mineral spirits Uses Antisettling agent, antisagging agent in primers (especially zinc-rich primers), traffic paints and finishes where min. spirits are compat. Features Does not increase apparent vise. 

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