Architects memo no.
51: April 1988
waterborne enamels an oxymoron surely
All is well - the paint industry continues its long tradition
of obfuscatory nomenclature.
True enamels are coatings made of ground coloured glasses, fused by
heat onto metal substrates. In coating terms, they are indeed the epitome;
hard, beautiful, enduring, and resistant to some of the most aggressive
environments. If they had some flexibility and were able to be applied
at room temperature they would indeed be perfect. It is not to be wondered
at that paint manufacturers would use such a material as an image for
their own products and when, in the early days, linseed oil based paints
were hardened by the addition of such materials as Kauri gum, the manufacturers
referred to them as being enamellised. The advent, in the 30s, of alkyd
resins and the hard thermosetting films they produced became universally
referred to as alkyd enamels, or simply enamels.
Acrylic polymers turn up in many guises - Perspex glazing sheets;
automotive lacquers and clears; the tough super-durable Uracryl coatings
- but their most ubiquitous form is as latex binders for the decorative
paint market. The original binders were designed to match existing soft,
rubber-latex binders and at this they were very successful. New Zealand
pioneered the use of high gloss acrylic house paints and ran foul of
the inherent soft nature of the polymers available. Dirt pick-up problems
were pandemic as were blocking problems. Blocking is the phenomena of
two soft, slightly tacky surfaces adhering firmly together under the
influence of pressure and/or heat and there are many windows around
that have never been opened since the sixties!
Although the polymer manufacturers responded and produced materials
more suited for gloss paints, their inherent thermoplastic nature precluded
their use on working joinery shelving and areas where they would come
in contact with fatty or oily materials such as kitchens or indeed anywhere
that may be handled a lot such as on cupboard doors.
An attempt was made in the mid 80's to produce super-hard acrylics
to enter this market. Fundamental flaws in the system lead to their
early demise.
It has taken a major technological development in the engineering
of acrylic polymers to be able to produce films which compete with the
market standard alkyd enamels. The technology involves fundamental changes
in how the polymer is assembled sub-microscopically to allow films that
form easily yet develop very fast block resistance. Further technology
allows subsequent curing to occur, changing the thermoplastic nature
of the coating and allowing the development of grease, solvent and sebum
resistance. These new materials, having matched alkyds at their traditional
strong points, bring additional benefits along. The absence of strong
solvent and curing odours is obvious as is the rapid dry time. Less
obvious is that fact that the products do not yellow over time, and
their exterior weather resistance is far superior to alkyds. This excellent
durability now allows a semi-gloss enamel to be used on exterior trim.
Acrylic enamels have arrived to stay. Oxymorons they are not; Resene
Enamacryl and Resene Lustacryl they are!
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