US MASTERBATCH delivers consistently brilliant color masterbatch with exceptional
reliability and quality
The coloration of plastics is an area of technology in which everyone has an opinion, everyone else can do it better and cheaper and where the mistakes are highly visible and usually expensive . This Blog sets out to provide the reader with a practical insight in polymers, processes and applications applying to the plastics industry and the coloring solutions available from the US MASTERBATCH ranges of organic colorants.
US MASTERBATCH delivers consistently brilliant color masterbatch with exceptional reliability and quality. The low usage ratio (100:1), low minimum order quantities, and pelletized form for easy handling and storage make it a versatile and cost-effective choice. Using US MASTERBATCH can help reduce net working capital by cutting inventory costs.
Color masterbatch can be divided up into roughly the following types:
↗ Mono batches or “Single Pigment Color masterbatch” (SPC): Masterbatch from a certain pigment and a supporting base; wax and/or dispersing agents are often added
↗ Customized masterbatch: bespoke formulations, mixtures of various powder pigments
↗ Custom Coloring: mixture of different SPC granules to produce precisely the color the customer wants The main benefit for manufacturers by using co-rotating twin screw extruders is the very good quality of dispersion. This is the basis for a high quality masterbatch. The two co-rotating screws that engage with each other produce a self-cleaning effect. This allows fast cleaning and consequently a more rapid change of product. Another advantage of co-rotating twin screw extruders is the modular design of the screws and barrels, which, depending on the process, enables a fast set-up and conversion of the processing unit.
Color masterbatch largely consist of individual color pigments that are combined to produce a specific target color. Other components may include effect pigments, dispersing agents and additives. Their production places great demands on the dispersion process because raw materials with different properties have to be optimally incorporated in only one process step. What is crucial here is a knowledge of the properties of the pigments used (coloristics) and great expertise with respect to the extruder’s process parameters
In paste and liquid dispersions the particle size and hence the specific surface area of a pigment influence the rheology of the system. The larger the particle size, the lower the specific surface area of a pigment and consequently the viscosity is also lower. A pigment with a high specific surface area will require additional »wetting out« in order to obtain an optimum
dispersion. In many instances, pigments manufactured from the same chemistry are offered in differing milled forms. A coarser milling produces larger particles; this in turn leads to a higher opacity and lower color strength in comparison with a finer milled product. Particle size distribution is also an important factor in obtaining an optimum dispersion in plastics applications. A narrow band distribution with a minimum of over- and undersized particles will more readily disperse in to a thermoplastic system, particularly when physical dispersion forces and pigment wetting are at a premium.
Many organic pigments have been shown to influence the crystalline behaviour of polyolefins by inducing a nucleating effect. The effect that the shrinkage in the direction of flow is no longer equal to that across the direction of flow is known as warpage or dimensional misbehavior, particular prevalent in the processing of HDPE.
In critical applications such as thin films, transparent packaging, fibers, monofilaments, thin wall articles and components with integral hinges, the optimum pigment dispersion is essential to provide the functionality in use. For these applications organic colorants that have been specifically manufactured for use in plastics e. g. controlled in the synthesis for crystallite growth and subsequently for particle size and distribution should be selected. These, having then been tested for ease of dispersion in a plastic medium according to industry standard tests such as European Standard EN 13900-5» The determination of a filter pressure value in PP«, LDPE thin-film testing or dispersion hardness in PVC provide the assurance of suitability for the given application.
Of a colorant is primarily determined by its chemistry. Particle size and distribution can also be influencing factors. The light fastness values are obtained by exposing a colorant dispersed in a polymer matrix to a UV light source together with a Blue wool scale. The results are assessed against the Blue wool scale whereby fastness to step 8 indicates very high light fastness and to step 1 indicates very low light fastness. A high level of dispersion is critical to obtaining the values quoted for a particular colorant.
Feature of molecular structure and particle size. Many factors, most importantly polymer stabilization, pigment concentration and the strength of UV radiation can influence the result. Accelerated weathering in a weathero-meter can provide a good indication of the performance of a given formulation however, a pre-test under the applied conditions of use is always recommended. In plasticized polymers certain organic pigments can bleed out onto a contact substrate. This is a form of migration referred to as »bleeding«. Fastness to bleeding is tested for in plasticized PVC and is measured against the ISO Grey scale whereby step 5 = no bleeding and 1 = excessive. In the presence of additives with a migratory nature i. e.; Antistatic agents, a pigment can migrate with the additive from the polymer matrix onto the surface.
Refer to the total cost of coloring an end article and take into consideration the relative color strengths of the colorants as well as the kilo price of a given product. The formulation to calculate the coloration costs is given as;
|Colorant price €/kg x SD ¹⁄³ in g/kg = Coloring Cost in €/kg|
Strength is the means of comparing the tinting strengths of two or more colorants. The
DIN 53235 standard determines the test method for the assessment of colorants in reduced shade to International
Standard Depth ¹⁄³ (SD ¹⁄³) against a standard reference. The SD ¹⁄³ value obtained for a colorant is given in grams
of colorant per kilogram of polymer assuming the addition of either 1 % or 5 % titanium dioxide. The lower the given
value of a colorant the higher it’s relative color strength.