Publicaciones

August 2010

White is the most common colour for plastics. It is most often achieved by using titanium dioxide pigment, which tends to have a yellow undertone. This unwanted yellowness can be exaggerated by extending the white pigment with less pure fillers, or by a colour shift in the resin during processing.

Colour correction is a term frequently used to describe the effect observed when low concentrations of Ultramarine Blue and Violet or Manganese Violet pigments are added to media which possess an inherent yellowish tint. The improvement in apparent whiteness that can be achieved in this way is dramatic. “Whiter than white” shades can be produced and, with transparent materials, the apparent clarity can be greatly enhanced.

Correction of white and clear plastic

Ultramarine and Manganese Violet pigments are ideal for colour correction. Both pigment types strongly absorb yellow light.

It is the yellowish tinge which is often responsible for giving an unattractive appearance to many white or clear plastics. The effect of adding an appropriate amount of a colour correcting pigment is to give a more neutral shade. Although the overall brightness may be slightly reduced, this pigment addition produces a shade which is more aesthetically pleasing.

Ultramarine pigments can be used very successfully in combination with optical brighteners to achieve a synergistic effect. Ultramarines exhibit low absorption of ultra-violet light

Technical Support Manager
dave.masterman@holliday-pigments.com

and, therefore, do not interfere with the mechanism by which optical brighteners operate. As a consequence, the two products together give optimum results.

Both Ultramarine and Manganese Violet are transparent, so can be used to absorb unwanted yellowness in white articles and also in clear polymers such as PVC.

Colour correction is a subjective effect based on the aesthetic preference of the observer. Ultramarine Blue is used to produce what may be called a ‘cold’ white, whereas the violet pigments produce ‘warm’ whites. Very often, combinations of the blue and violet pigments are used to produce the desired effect. Where the initial degree of yellowness is high, an increase in the ratio of violet to blue can significantly improve the final result.

Addition Levels

The precise pigment concentration needed to produce the desired level of colour correction depends on the initial degree of yellowness. Generally it is not necessary to use concentrations higher than 0.05% and often addition levels are much lower.

The moderate colour strength of Ultramarines and Manganese Violet is a further advantage of these pigments. This enables accurate metering or weighing at the low pigment concentrations used for colour correction.

Recommended Grades

Recommendations for the correct grade of pigment to use in colour correction are dependent on the end application. However, the following general guidelines can be given:

• Ultramarine Blue Premier RM is suitable for the production of ‘cold’ whites and in instances where the initial degree of yellowness is very small.
• Ultramarine Blue Premier AR gives a similar result to Premier RM. However, it is acid resistant and is recommended for use in applications where acid attack of the pigment may be a threat.
• Ultramarine Violet Premier VU and Manganese Violet Premier VM. Both are suitable for the production of ‘warm’ whites and where a more pronounced degree of yellowness requires correction. When acid resistance is required, Manganese Violet is recommended whereas Ultramarine Violet produces better results where alkali resistance is necessary.

Colour Correction of Black and Grey Plastics

After titanium dioxide, Carbon Black is the most commonly used pigment for colouring plastics. When used as the sole pigment it gives a black colour, while combinations with titanium dioxide results in grey shades in a range of depths. It may seem strange to think of black and grey as “colours” but that is exactly what they are. Like any other colour they will have subtle tones and undertones that add range to the shade.

Higher strength Carbon Black pigments are invariably brown in undertone. In many situations this is undesirable. There are many instances where fashion or compatibility with related objects requires a bluer undertone grey than is possible with a high strength Carbon Black alone. For example, car and aircraft interiors, computer housings, office equipment etc. A blue undertone grey is effectively achieved by the addition of Ultramarine Blue.

As in the correction of whites, Ultramarine strongly absorbs the yellowness responsible for the brown undertone of these Carbon Blacks. Because black is such a strong colour it requires a higher addition rate of Ultramarine to have a noticeable effect. The addition level required can be minimised by using a high strength Ultramarine such as Holliday Pigments’ Premier RX.

In adjusting the shade of carbon black pigments, Ultramarine offers the following benefits:-

• Blue undertone grey
• Crisp, attractive shade
• Range of subtle tints
• Precise shade control
• Excellent lightfastness

Holliday Pigments is a world leading supplier of Ultramarine pigments, which are used in a variety of applications including plastics, coatings, cosmetics, artists’ colours and printing inks. Exporting to over 80 countries, Holliday Pigments has dedicated customer and technical service teams at its factory in France and its commercial office in Singapore.

Holliday Pigments has a proud 125-year history in the manufacture of technical quality Ultramarine and is the only Ultramarine manufacturer in the world to have invested in Flue Gas Desulphurisation technology, reducing sulphur dioxide emissions inherent in the manufacturing process by more than 99.5%

In August 2008, Holliday Pigments joined Rockwood Holdings Inc., becoming an important addition to the Color Pigments and Services Division

Rockwood’s Color Pigments & Services Division is one of the largest worldwide suppliers of colored pigments for construction, coatings, plastics and specialty applications. The Division’s manufacturing sites and customer service centers are located in the United States, United Kingdom, France, Italy, Germany, Australia and China with additional sales offices located in Singapore and Hong Kong. For more information on Rockwood, please visit www.rockwoodpigments.com

The Rockwood Color Pigments & Services Division is a business unit of Rockwood Holdings Inc., Princeton, N.J., U.S.A. Rockwood Holdings, Inc. is a leading global specialty chemicals and advanced materials company. Rockwood has a worldwide employee base of more than 9,500 people and annual net sales of approximately $3 billion. The company focuses on global niche segments of the specialty chemicals, pigments and additives and advanced materials markets.

For more information on Rockwood, please visit www.rocksp.com.

Further information on all Holliday Pigments’ products is available from:

© HPSA 2010
The information included in this literature is based on data determined by Holliday Pigments SA under standard laboratory conditions. Such information may be affected by different working or processing conditions beyond the control of Holliday Pigments SA and should always be verified by the end user.