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NEW APPROACHES TO WOOD COATINGS

In probably the most significant regulatory change to hit paint products since the banning of lead, the EU is introducing legislation to limit the volatile organic compound (VOC) content in decorative paint, varnishes and wax. This group of fast-evaporating solvents not only gives you sore eyes and a headache, but is also a major contributor to ground-level ozone. Talk to any coatings supplier and the message is consistent: 'Customers will see very little difference in their favourite products.'

The EU product directive 2004/42/EC covers coatings applied to buildings, their trim and fittings, and associated structures when applied for decorative, functional and protective purposes. The legislation classifies these products into 12 categories (see page 34) and defines separate VOC limits within them for solvent- and waterborne products. These will be implemented in two phases: the first reduction will apply from January 2007, with tighter limits applying in January 2010.

Coatings manufacturers have put a great deal of work into product development and a wide range of reformulated low-solvent versions are already on the shelf. Sweden-based wood-finishes specialist Becker Acroma says that in the UK nearly half its business is in waterborne paints, and expects this to grow. Marketing co-ordinator Frances Armstrong says early waterborne lacquers weren't as good as traditional solvent-borne products for toughness, clarity or drying time, but that has changed in the last few years to the extent that durability is on a par with solvent-borne products, clarity is 'excellent' and drying times are 'very fast'. She cites Becker's Parquet Pro, developed about four years ago, as an example of a waterborne floor lacquer that copes with heavy traffic in a range of gloss levels.

However, technical consultant Jon Graystone, of the Paint Research Association, says that reformulation is not straightforward. 'Components of a formulation cannot be varied independently of each other. There will be conflicting measures of product quality and compromises must always be made.' Graystone adds: 'Water is arguably the best solvent on the planet, but it so happens that it doesn't dissolve many highmolecular-weight polymers.

This means waterborne binders are typically dispersions rather than solutions, resulting in inherent differences when compared with traditional solvent-based products. For example, dispersions don't penetrate the wood surface so well, or flow as well as solutions.' This can affect the aesthetic quality of a product applied to wood.

Graystone continues:

'Another difference is that waterborne dispersions are typically based on thermoplastic acrylic resins, while solvent-borne solutions are oil/alkyd-based and undergo oxygen-driven crosslinking after the solvent is lost, and this leads to different performance characteristics in terms of weathering and maintenance. Oil/alkyds can embrittle, leading to cracking and flaking, whereas acrylics are softer but more prone to pick up dirt and mould growth.

Alkyds are prone to yellow, especially indoors.' New technical approaches are attempting to find compromises.

For example, oil/alkyd solution resins can be emulsified into water, and blended with acrylic waterborne dispersions to give hybrid binders with some of the characteristics of each.

Ruth Robinson, technical services manager at Akzo Nobel Specialist Coatings, says high-gloss and ow are the toughest technical challenges, so traditional solvent-based trim paint and woodstains for doors, windows and architraves will be harder to reformulate.

The 2010 reduction targets are huge, she says, but 'three years is a long time in a lab. There will be solutions'.

ICI's director of marketing for paint brands, Steve Snaith, says next year will see little difference other than a higher viscosity in low-build woodstain. For the tougher 2010 limits, he says, 'some significant changes are needed that could mean some products are different. We are pursuing two or three different routes, and these will give different characteristics to their look, feel and application. But our objective is to match what we have at the moment.'

Hugh Williams, technical manager at the British Coating Federation, says: 'Things that will become difficult to obtain or will change are interior trim and cladding paints. . . you may only get waterborne trim paints because the technology to obtain a solvent-borne trim paint or varnish with the lower 2010 figures is evolving. It may be that you don't get such high-gloss trim paints. It may be that tastes will have to change in the UK.'

One option would be to stick to small markets for traditional finishes. Bill Martin, head of building, conservation and research at English Heritage, says it is seeking exemption for Grade I and II*listed buildings: '20th-century buildings would have had paint containing a high percentage of VOC. I'm hoping we will be able to maintain a limited use.'

Some requirements, he says, are more specific than others: 'For repairing areas on panelling, you're going to need a compatible material.' But for ooring where there is a lot of traffic, an exact match of original surface finishes may not be paramount: 'You might look at an alternative material and balance it against the practicalities of continual retreatment.' Ultimately, he says, waterborne finishes are not going to be a complete solution: 'It's great they try, but it's impossible to get exactly the same effect.'

By 2010, Farrow and Ball's classic oil-based finishes will only be available for specialist restoration. Frances Armstrong says: 'In recent years we have seen sales of satin and matt ooring lacquers increase dramatically - satin now outsells gloss by five to one.

High-gloss is still popular in gyms and sports halls where slip resistance is also wanted.'

Dr Glenda Thisdell is editor of the Paint Research Association's monthly business magazine, Coatings COMET This article was produced with the support of wood. forgood

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