Coil Coatings
The coil coatings industry can be divided into two distinct sections,
- Interior items – mainly white goods with high gloss
- Exterior pre-coated metal - frequently dark colors and subdued gloss.
Both parts are dominated by the search for opacity, at decreasing film builds and uniformity of color and, for the exterior finishes, maximum durability as minimum chalking (color change) is essential. Titanium Dioxide pigments have an important part to play in all of these properties. Thus, the selection of the correct pigment is essential to the successful formulation of the finished product. Most modern Titanium Dioxide pigments can be easily dispersed using the High Speed Disperser rather than beadmilling, achieving optimized optical and durability performance without the need for prolonged slow milling. This gives significant cost savings during the manufacturing stage of the coating.
Opacity
The main purpose of using Titanium Dioxide pigments is to obtain opacity. Therefore maximizing opacity allows you, the formulator, to use the potential benefits of the increased opacity from the pigment in any one of several ways.
- To reduce TiO2 content and hence lower raw material cost.
- To run at reduced film weights, giving better mileage.
- To obtain an overall improvement in product quality at no extra cost.
The performance of modern, high quality, superdurable or multipurpose TiONA pigments is tailor made for the coil coatings industry, offering improved opacity in the final coatings with the possibility of reduced cost and maximized opacity when required.
Color
The color of a paint film is influenced by the following properties of the pigment
The main requirement is consistency between batches so that repeated batches of the same product give the same color with a minimum of color matching.
Nowadays modern oven and heat controls should minimize or even eliminate overbake discoloration, nevertheless TiO2 may affect over-bake resistance.
Durability
Exterior durability is normally measured by two parameters
- Chalk resistance
- Gloss Retention
Exterior coil coatings are often formulated to a subdued gloss. Therefore chalking, and its influence on perceived color, becomes the most important measure of durability. Titanium Dioxide pigment has a significant effect on chalk resistance and a dense silica encapsulated superdurable pigment is the best choice to avoid the free radicals generated by TiO2 under UV radiation. These with time will cause the polymer to breakdown and chalking.
Gloss
Gloss consistency is the most important factor, particularly where the finished coating has a controlled gloss. For interior white goods, maximum gloss is often the requirement. Gloss is controlled by:
- Particle size control
- Dispersion
- Formulation stability
Of these only particle size control is within the ability of the pigment manufacturer to control, the others are under the control of the formulator. However, to ensure that the gloss potential of the pigment is as high and consistent as possible, very close limits are set on the particle size distribution of the pigment.
Acid Catalyst Adsorption onto TiO2 Surface.
This difficult area is nevertheless critical. A fast speed of the modern production line is an advantage, and a lower amount of catalyst is always a cost saving. It is therefore recommended that you test the catalyst combinations with respect to the pigment used to ensure that the best catalyst is chosen and the minimum amount added.
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