Paint Design

Formulation and Manufacture of Architectural Coatings

Introduced by Dr Tony Van Dyk BSc (Hons), PhD
Research and Development Manager Resene Limited

(See the left frame for list of all papers)

Extract:

Coatings are specified to address commercial, performance, HSNO, NZPASS, EC requirements. These requirements are balanced against materials performance, application and economic issues.

The theory of formulating alkyd primers and waterbased semigloss coatings is reviewed. Formulations are developed to meet specified requirements with available materials and manufacturing practices. Tint systems and pigment selections are designed to give colour performance. Compromises including colour range, durability, opacity, cost, number of bases are reviewed.

Formulations for commercial manufacture of 1,000 litre batches are developed. High speed disperser theory and practice is reviewed. Quality control and batch adjustment protocols are developed.

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Presentation:

Thank you all for making the effort to come along today. Its great to see such a good turnout. There's worries that SCANZ has lost touch with its basic aims. Seeing you all here today, I'm sure there's hope for us yet.

We all know the Surface Coatings industry in New Zealand, and Australia too, is retrenching. Increasingly, "High Technology" is the provenance of large multinationals, with R&D headquarters in Europe or America. These powerhouses have resources we can only dream about, and it doesn't take much effort to see that they have accumulated hundreds of patents for new chemistries, polymers and coatings. But these industrial leviathans are constrained by huge minimum batch sizes and the need for globally homogenised products.

Universities see some profit in research partnerships with industry, and I think there is scope for mutual benefit. But the pressures of time, and commercial reality, frequently demand answers faster and more economically than the academic system can manage.
Adapting coatings, to suit new requirements in the local market, is something many of us are involved in: Whether from sourcing, selling or developing new materials, or from developing and testing the coatings, or making and selling them. There are certainly challenges for the industry ahead of us. But I think our contacts, our practical expertise in the basics of coatings development, and our knowledge of the local market, give us an advantage. Our small size gives us flexibility, we can quickly adapt to the market, and take advantage of the small opportunities.

Our programme today follows the development of two paints, one alkyd and one acrylic.

Bas has given us an introduction to New Zealand's new HSNO bill and we'll hear tomorrow how New Zealand legislation and regulations affect manufacture of our paints.

Our programme today is the development of an alkyd wood primer and an acrylic semigloss, from manufacture and selection of materials, through to formulation and manufacture of the paints.

Greg and Jacqueline will describe to us how modern, commercial binders are developed and selected for our paints. Neal will describe some of the many additives available and how to use them. Kevin is going to discuss biocides. He'll explain how they work and discuss some legislative and toxicity issues which will affect our selection. Chris will explain to us the complexities of in plant, and point of sale, colourants and take us through the selection of particular colourants for our paints.

My part in this project, is the formulation and manufacture of our two demonstration paints. Over the next few minutes I'll itemise the product specifications, and design parameters, I've set for all of us to work to.

Starting with the solvent based alkyd primer, its to be a wood primer for timber. It's going to be used both inside, and outdoors. It will have a VOC under 300 g/L, to allow compliance with New Zealand Environmental Choice specifications. Its composition and performance will conform to both NZ PASS and NZ Environmental Choice. Odour and toxicity are to be kept low. The paint is to be produced as a white, and be tintable to a limited range of colours, off white.

Now that we've got some application and performance guidelines, the next thing to sketch out are some product features. Good performance and low cost are often uneasy companions. For the alkyd primer part of our project I've asked that we focus mainly on achieving performance, and pay less attention to cost.

First impressions are important. A customer is more likely to go back to the same brand of paint if the first tin opened looked good. Wood has fairly poor water resistance. Timber painted with a good primer has better dimensional stability and water resistance than unpainted timber. Drier systems can get pretty fancy and specific to particular binders. I've asked to keep ours simple. Touch dry in one to four hours is fairly standard for a wood primer. I've asked for a broad spectrum preservative package to keep mould and bacteria at bay.

There are still many ways to make an alkyd wood primer. To narrow down the options, I've set a series of Technical Specifications. The binder is to be mainly long oil alkyd. A Paint Volume Solids content over 61% will put additional constraints on the binder and our solvent selection.

Titanium dioxide at 250 g/L is commonly used for primers and gives us partial coverage at one coat. From decades of research, paint chemists have found that alkyd wood primers perform best with a pigment volume concentration between about 35 and 40%. Wood primers can be formulated in a range of gloss levels, so to narrow down our options I've asked for a gloss in the range of 5 to about 20%. Finally, I've set some specific pigmentation guide lines. And this gives us enough information to start working on developing our alkyd wood primer.

Our acrylic semigloss is to be used both over previously painted or primed surfaces and direct to timber. It must perform under both exterior and interior conditions. We want a VOC under 100 g/L, and lower if possible. It must conform to NZ Environmental Choice specifications. Additionally we will minimise Alkyl Phenol Ethoxylates and use lower hazard materials wherever we can. We want it to comform to NZPASS performance specifications for interior and exterior latex semigloss paints. The paint is to be made in white, plus a sufficient range of tint bases to produce a comprehensive colour range. We want to produce our full colour range with the least number of tint bases, so as to minimise the number of tins needed for retail stock.

Good performance is the first priority for our acrylic semigloss, but we also want to pay attention to costs. We want to use lower cost materials and formulating principles where we can, and where we use more expensive materials, we want to make sure we get something extra. The flagship of the range is to be a high opacity white which will give near complete coverage at 12 m2/L in one coat. As with our alkyd primer, we want the paint to look good in the can after storage. The paint is to be applied by brush or roller, and we don't want roller spatter. The paint, and the binder in particular, should suit New Zealand conditions. Our range of temperatures and humidities, and our UV levels, are important. Market and consumer preferences for colours, appearance, feel, and odour are also important factors. We want the paint to have good dirt, stain, mark and mar resistance. Adhesion to alkyds, including old chalky alkyds, is required.

I've set these technical specifications to narrow down the material selection and design process. Acrylic semigloss paints are usually formulated at volume solids ranging from lows around 30% up to highs approaching 50%. I've set a target here of 40% minimum volume solids. In order to work out our tint system, and the number and type of bases we need, I've set our tint limits at 8% by volume. This will require the tint bases to be underfilled 8%, and all our colours will have to be formulated to be topped up to 8%. The other factor needed to specify the tint system is coverage required for the colour range. We'll aim for coverage in one coat for many colours, and no more than 2 to 3 coats for most of the rest. I've set the equivalent TiO2 loading at 400 g/L and asked that opaque polymer is used in the high opacity white. The term semigloss has come to have a fuzzy meaning these days, so I've set the level at about 40%, which will also fit within the range specified by AS3730.2 and .9. Finally, I've asked for an open time of at least 6 minutes.