Coating-substrate adhesion

D.S. Rickerby, A Review of the Methods for the Measurement of Coating/Substrate Adhesion, Surface and Coatings Technology, Vol.36,1988, p.541. 

Introduction into polymer of both reinforcing fiber and filler produces considerable increase in the coating—substrate adhesive bond (Figs. 6.1 and 6.2, curves 2). 

Carpick et al [M] used AFM, with a Pt-coated tip on a mica substrate in ultraliigh vacuum, to show that if the defonnation of the substrate and the tip-substrate adhesion are taken into account (the so-called JKR model [175] of elastic adliesive contact), then the frictional force is indeed proportional to the contact area between tip and sample. Flowever, under these smgle-asperity conditions, Amontons law does not hold, since the statistical effect of more asperities coming into play no longer occurs, and the contact area is not simply proportional to the applied load. 

Hybrid Circuits. The use of parylenes as a hybrid circuit coating is based on much the same rationale as its use in circuit boards. A significant distinction Hes in obtaining adhesion to the ceramic substrate material, the success of which determines the eventual performance of the coated part. Adhesion to the ceramic must be achieved using adhesion promoters, such as the organosilanes. 

Itaconic acid is a specialty monomer that affords performance advantages to certain polymeric coatings (qv) (see Polyesters, unsaturated). Emulsion stabihty, flow properties of the formulated coating, and adhesion to substrates are improved by the acid. Acrylonitrile fibers with low levels of the acid comonomer exhibit improved dye receptivity which allows mote efficient dyeing to deeper shades (see Acrylonitrile polymers Fibers, acrylic) (10,11). Itaconic acid has also been incorporated in PAN precursors of carbon and graphite fibers (qv) and into ethylene ionomers (qv) (12). 

Fracture mechanics (qv) affect adhesion. Fractures can result from imperfections in a coating film which act to concentrate stresses. In some cases, stress concentration results in the propagation of a crack through the film, leading to cohesive failure with less total stress appHcation. Propagating cracks can proceed to the coating/substrate interface, then the coating may peel off the interface, which may require much less force than a normal force pull would require. 

Thin polymeric films have important industrial apphcations (e.g., as protective coatings, lubricants, adhesives, dielectric or nonlinear optic devices, etc.) and pose many fundamental problems of film stability [1,2,4]. An important question, therefore, is whether these films break up and spontaneously dewett the substrate, resulting in the formation of droplets. The... 

Adhesion the degree of attachment between a paint or varnish film and the underlying material with which it is in contact. The latter may be another film of paint (adhesion between one coat and another) or any other material such as wood, metal, plaster, etc. (adhesion between a coat of paint and its substrate). Adhesion should not be confused with cohesion (. v.). 

A method of evaluating the adhesive bond to a plastic coating substrate is a tape test. Pressure-sensitive adhesive tape is applied to an area of the adhesive coating, which is... 

With regards to the conversion coated substrate, Wittel (25) observed that at temperatures greater than 140°C, tetrahydrate zinc phosphates lose part of their water of hydration. It is likely that the water of hydration liberated in the phosphate recrystallization process has a negative effect on the adhesion of the polymer matrix to the B40 panel. 

Figure 9. SEM study of the conversion-coated substrate surface after adhesion failure of epoxy-ester coating in cathodic polarization testing. Reproduced from Ref. 29, copyright 1983, American Chemical Society.

Post-crosslinkable and substrate reactive polymers are widely used to Improve water and solvent resistance, strength, substrate adhesion and block resistance In binders, adhesives and coatings. The surprisingly rich chemistry of a new class of functional monomers (eg. 1 and 2) related to standard amide/aldehyde (amlnoplast) condensates, but which eliminate aldehyde emissions, was elucidated by monomeric model and mechanistic studies and discussed In the preceeding paper (1). Results with these monomers In copolymer systems are reported here. 

The fluorinated initiator is not only concentrated in the coating-air interface but also in the coating-substrate interface. At moderate concentrations the fluorinated compound acts as a wetting agent but if the concentration is too high the coating loses adhesion to the substrate. At the concentrations used in this study no loss of adhesion was observed. 

The most important use is in primers for zinc-coated substrates. The pH change occurring on hydrolysis of the calcium plumbate etches the zinc surface which improves adhesion of primers, especially on hot-dip galvanized steel [5.151],... 

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