Coloring of Plastics

In the coloring of plastics, a plastic must be opaque before color pigments are used for shading and white pigments are generally used for white coloring and color pigments are added for shading.

Titanium dioxide is generally used because of its excellent hiding power - the ability to hide (make plastic opaque).

In using white pigment to make plastic opaque results in a fairly large amount of pigments and this raises the price of the colored plastic. Colorists are careful to maintain a low pigment loading in order to offer better pricing.

And it is common to have requests asking for a specific color and translucency. In plastics coloring, these are the two major concerns:

- optimum pigment loading
- matching translucency

If the colorists or chemists are able to offer the above, there will be happy customers.

Computer Color Matching Alogrithm

Computer Color Matching (CCM) has become one of the standard methods in the paint, plastics and ink industry for fast and accurate recipe prediction. The advantages when compared to manual matching include better first shot accuracy, reduced number of corrections, exact prediction of metamerism and price and thus higher efficiency and productivity.

A color matching system consists of a spectrophotometer, a PC and the matching software itself. The major differences between systems are the spectrophotometer, the mathematical algorithm of the software, the software features and user-friendliness of the software and, last but not least, the ongoing service and support offered by the supplier.

The accuracy of a match is dependent not only on the software and its mathematics but also on the accuracy of the calibration samples, the reproducibility in production and between the laboratory and the production. The quality of production can only be influenced by the user of the matching system. However the reliability of the measurements directly depends on the instrument used.

In this context, the short- and long-term repeatability of a spectrophotometer is very important as is the inter-instrument and inter-model agreement.

A critical case in color matching, which cannot be solved by standard matching software is mat­ching of products which are neither opaque nor transparent, but translucent. In theses cases, not only the color but also the opacity has to be matched. This cannot be achieved with the commonly used Kubelka-Munk-Model or Lambert-Beer Law. Other physical models have to be found to de­scribe the complex effect of absorption and scattering of such layers.

A layer is translucent, if there is a difference between the measurements of the layer over white background compared to the one over black background. Therefore paints and inks are applied on contrast cards and plastic samples are measures over such cards or with help of the opacity holder of the instrument.

The bigger the color difference between the layer over white and over black, the more translucent it is. For translucent layers, there are 2 more variables to take into account: the thickness of the layer and the background. Both will change the color appearance if they are changed.

Latest CCM technology uses multi-flux algorithm and is able to handle translucent coatings.

Computer Color Matching

In textile, plastics, inks, paints and coatings industries, color formulation and development is critical. Computer color matching (CCM) is a key process at each step of the product development cycle.

A good CCM system helps save time, shorten color development and rationalize the workflow.

A CCM system consists of a spectrophotometer link to a computer color matching software. The CCM software helps to simplify and optimize your color matching processes by improving assessment of color feasability, reliability of coloration, pigments optimisation, recipe calculation and update and quality control.

The software performs hundreds of iterations in a short period of time to produce a recipe to match the intended color. It provides a recipe almost immediately for a colorist to work on. And is a valuable business tool as it provides options of a low cost match with the least metamerism and shade differences.

CCM technology is based on complex mathematical calculations and with the advent of personal computer, the price of a CCM system has decreased through the years.