Wood coatings progress

Citation

Bean, J. (2000), "Wood coatings progress", Pigment & Resin Technology, Vol. 29 No. 6. https://doi.org/10.1108/prt.2000.12929faa.001

Wood coatings progress

Wood coatings progress

Keywords Coatings, Wood

The 2nd Woodcoatings Congress, held in The Hague, The Netherlands, 23-25 October, revealed several new developments in this technology. The Congress Steering Committee consisted of delegates from 12 European organisations, including the principal organisers PRA. Copies of the papers presented can be purchased from the PRA at: 8 Waldegrave Road, Teddington, Middlesex TW11 8LD. Tel: +44 (0)20 8614 4811. Fax: +44 (0)20 8614 4812.

A paper by Trevor Jones, Roy Miller, Gerald Hamblin, Peter Kirkham, and David Sykes, independent UK wood finishing and joinery experts, dealt with "Maintenance-free paint for softwood windows". They said that it is generally recognised that a major cause of the decline in demand for wood windows is their relatively high maintenance requirements. This has prompted considerable effort in the coatings and joinery industries aimed at developing coating systems that provide maintenance intervals beyond the four to five years traditionally regarded as normal. This requirement was first recognised in the UK in the late 1960s in relation to industrialised building of schools and hospitals. Collaboration at that time between a coating manufacturer and a Local Authority consortium led to the first significant UK application of water-borne acrylic technology in the painting of softwood joinery. During the intervening 30 years experience has accumulated to show that the paint system used is capable of a remarkable order of performance. Examples exist of paint that has retained its integrity and protective capabilities for over 28 years of exposure without any maintenance. The paper then reviewed the development of the industrialised finishing process, and available information on the performance of the joinery and its paint system obtained from field experience and testing. The contributions to the long-term performance of the coated joinery from component design and construction, paint formulation, and paint film thickness were considered.

Dr Makoto Kiguchi of Japan's Forest Products Research Institute, Philip D. Evans, Australian National University, Jan Eksted, Trätek, Sweden and R. Sam Williams, Forest Products Laboratory, USA, prepared an interesting paper on "Improvement of clear coating durability by grafting of UV absorbers to wood surfaces".

Grafted photostablisers were used to improve the photostability of wood and clear coatings on wood surfaces. Reactive UV absorbers (UVAs), e.g. 2-hydroxy-4-(2,3-epoxypropoxy) benzophenone (HEPBP), were synthesised and the reaction conditions required to graft UVAs to wood were examined. Grafted reactive UVA was more effective than general UVAs or chromium trioxide in restricting losses in veneer weight and tensile strength during weathering. Grafting of UVA reduced photochemical changes at exposed wood surfaces, and thin wood veneers grafted with UVA provided greatly improved performance of clear coatings.

There were three papers on powder coatings for wood. One of these was "UV curable powder coatings for the finishing of wood composites", by Dr Kris Buysens of UCB Chemicals, Belgium. The powder coating systems he described were for the finishing of wood composites, e.g. medium density fibreboard (MDF). A UV powder primer can replace several layers of liquid primer-surfacer, and the surface preparation steps for each layer. He said that excellent finishes are achievable using a liquid or powder topcoat on the sanded UV powder primer. Textured finishes are obtainable in a one-coat process using special resins. The technology of the new process and the properties of the coatings were discussed.

There were eight papers in the session on waterborne systems. Developments in resin types for these systems were given in papers on alkyd emulsions, self-emulsifying aliphatic polyisocyanates, modified silicone polymers, and also acrylics and hybrid paints.

Acrylate powder coatings

A new generation of acrylate powder coatings from DuPont Performance Coatings (DPC) is said to have a great potential in the automotive parts sector. Conventional powder coatings based on polyesters or epoxy resins have limitations when high resistance to weathering is required in addition to a quality surface finish such as required in the automotive industry. With the availability of acrylate resins in 1997, excellent appearance was achieved, with high gloss and high resistance to weathering of the coated surfaces. Now DPC says that its new acrylates, which are combined with other, undisclosed, raw materials contained in the powder coating, enable the acrylates to exhibit their full potential, particularly with better weather-resistance properties. DPC adds that significantly lower film thicknesses are sufficient for the new powder coating system to produce the same visual properties as a conventional polyester powder clearcoat, thus reducing the consumption of material.

The new acrylate powders can be used to coat anything from wheels to trim strips and plastic components. The furniture market is said to be another promising sector in which the coatings could be used, such as on bathroom and laboratory furniture where high resistance to chemicals and scratching is vital.

Acrylate powder coatings are already used in the automotive industry. BMW, for example, is the world's first car maker to have made successful use of acrylate powder clearcoats since 1997. The resistance of these coatings to weathering (as determined by the Florida test method) meets the automotive industry's standards after a five-year test period.

Smooth powder coating for wood

Another powder coating development is the smooth finish powder coating for wooden furniture now commercially available from Sonneborn & Rieck of the UK. This is also believed to be based on acrylate resins. Until recently, only textured powder coating finishes for wood have been really successful. The introduction of a smooth finish is a major step forward. Sonneborn & Rieck says that in particular it will attract manufacturers of built-in bedroom furniture, office furniture, shopfitting, and shelving, who generally prefer smooth surfaces for their production. It could also have a major impact on the rapidly developing contract panels supply sector.

The pound is not strong – it is the Euro that is weak

In our news pages of this issue we carry a report that Millennium Inorganic Chemicals (headquartered in Maryland, USA) is making its second price increase for titanium dioxide sold in Europe this year. The increase now totals E310 per tonne. Gary Cianfichi, Sales Director, Europe, said: "Low prices in Europe and the weakness of the Euro make this increase necessary".

This is further proof that those who opposed the UK joining the Euro appear to have been right. It is not so much that the pound sterling is strong, but the Euro is weak. This does not amount to the same thing, as some would suggest, if it is borne in mind that against the US dollar the pound has fallen some 15 per cent over the past year.

John Bean