Bleeding - the situation in which parts of the colouring constituents either stain an adjacent contact material or are released into a surrounding solvent.
Blooming - migration of pigment or additive particles in the component to the surface which results in the appearance of a ‘haze’ or bloom on the surface of the product. Generally confined to a few organic pigments and some UV stabilizers this effect can take some time to develop. It is more likely to be seen in masterbatches where the higher concentrations of colourants and additives may exceed their compatibility with the carrier polymer.
Blue Wool Scale - (ISO 105-B01-1988) is a means of measuring the colour fastness to natural daylight of a colour by comparing it to a blue wool standard. It was originally developed to compare the fastness properties of textile dyes. Expressed on a scale of 1-8, where 1 is the lowest value, the next digit corresponds to twice the fastness level of the previous digit. i.e. double the exposure time at the same exposure level.
Colour Index - a system of classifying colourants by their chemical type. For example titanium dioxide is C.I. Pigment White 6 and a fluorescent yellow dye is C.I. Solvent Yellow 98.
Dispersing aids - additives incorporated into the masterbatch formulation to promote dispersion and development of the active constituents. These can work in a number of ways, reducing friction, wetting and separating the pigment particles, helping to break down pigment aggregates, improving melt rheology, lubricating the particles to name a few.
Dispersion - defines the quality of the breakdown of pigment aggregates and separation of pigment particles to maximize colour development. Usually referred to in the general terms of good and bad. Poor dispersion results in pigment specks being present in the final part and low colour strength. Pigment specks can lead to low impact strength and process failures in blow moulding or film extrusion. In metallic and pearl colours poor dispersion can also be (erroneously) applied to the streaking caused by the pigment platelets being orientated in different directions.
Distribution – describes how well the masterbatch pellets are spread throughout the base polymer. Poor distribution can appear as variations in colour between successive mouldings.
Dyes - powdered colourants that are soluble in the molten polymer matrix (see pigment).
Fillers - solid additives, usually inert inorganic compounds (e.g. Chalk, Talc etc) added to plastics and masterbatches to increase polymer bulk or reduce costs. Some fillers are incorporated to produce specific physical properties, for example stiffness, temperature resistance or raised specific gravity in polymer compounds.
Granule – standard pellet size of 3.2mm
Grey Scale - (ISO105-A02-1993) is a scale from 1-5 (where 5 is no change) used to describe colour change due to weathering and other environmental exposure.
Heavy metal pigments -the coloured salts of heavy metals (lead and cadmium) that make good, economical pigments. Concerns about heavy metals in the waste/recycling chain and in toys and food containers have led to their control by legislation in some applications and their replacement with organic substitutes.
Homogenisation - the term to describe the evenness of mixing of the constituents in the compound. Poor homogenisation appears as colour streaks in the parts.
Lamination - occurs when there is stratification of the polymer due to poor homogenisation of the masterbatch. Usually a processing problem, it is often blamed on masterbatch incompatibility although it can be created by inappropriate use of universal masterbatches.
Let Down Ratio (LDR) - the level at which a master batch is incorporated into the base polymer. Hence an LDR of 3 (%) is 97 % polymer, 3% masterbatch.
Melt fracture - describes the alternation of adhesion/slip between the extrudate and the side of the extruder barrel or die on processing plant giving a ‘sharkskin’ effect on the products, especially film and profile or hose extrusions.
Metamerism - the term used to describe the phenomena in which two colours are a good match under one illumination but are not a good match when illuminated under a different light source. This is due to different pigment combinations in the composition of each colour and the different absorption and reflection characteristics of each pigment under the differing illuminations. To avoid metamerism it is important to specify the illumination conditions under which the final part will be used, especially if it will be alongside other materials (fabrics, painted items etc) that it is required to match in colour.
Micro-pellet – granules with a standard size of 0.8mm
Migration - a term applied to the mobility of colourants usually attributed to the partial solubility in the polymer of one of the components of the colour. It can appear as ‘bleeding’ or ‘blooming’
Mini-pellet – granules with a standard size of 1.1mm
Monopigment concentrates – special masterbatches featuring high pigment loadings up to 65% developed for in-house processors who want to minimize contamination and reduce cleaning costs, or those wishing to produce their own colours or masterbatches
Multi-functional masterbatches - composite masterbatches that combine colour with functional additives, for example UV stabilizers, anti-oxidants, anti-static additives.
Pigment - powdered colourants that are dispersed through the polymer matrix (see dyes).
Plate out - this is the separation during processing and deposition on the metal surfaces of the equipment of one or more components of a material. It appears as staining on processing equipment and is sometimes referred to as ‘mould staining’ although it can also affect extruder screws and dies. Usually it is attributed to a limited compatibility of part of the formulation
Polymer specific masterbatch - a masterbatch in which the carrier for the colourant(s) or active additives is the same polymeric type as the polymer it is to be used in (see universal).
Prill - spherical beads typically 1.2 to 1.5mm diameter – presents a high surface area that gives better distributive mixing of pigments and additives and hence significantly enhanced homogenization. Smaller spherical pellets present higher surface areas that give better distributive mixing of pigments and additives and hence significantly enhanced homogenization. For applications requiring only low levels of colour or additive the low LDRs involved can lead to poor distribution due to the small number of masterbatch pellets present in the mix. As the masterbatch pellet size decreases the number of pellets rises for any given LDR, greatly improving their distribution and the quality of the final product. The smallest pellets also are of great benefit when adding colour or additives to powdered base materials. Addition of conventionally sized masterbatch to powders such as PVC blends can lead to separation after mixing; Mini- or Micro-pellets are much closer in size to the powders and are much less likely to separate during conveying or feeding into the process equipment.
Slip - as the name implies this refers to the ‘slippery’ nature of a polymer surface (low co-efficient of friction). Also used to describe a family of additives that increase this property.
Universal masterbatch - a highly concentrated masterbatch in which the ‘carrier’ or ‘binder’ is formulated from ingredients selected for their compatibility with a range of polymers enabling it to be used in a number of different polymers. It should be recognized that use of a universal masterbatch to colour several different polymer types is unlikely to result in components that are all the same shade. This is due to the different base colours of polymers and the effects that some polymer types have on colourant chemistry.
Weld line - the meeting of two material flows in a moulding. This can be a source of potential failure of the part under stress if the two flow fronts do not retain sufficient energy to mix well when they meet. Weld lines can be particularly noticeable in mouldings containing metallic or pearlescent colours. In these cases the laminar nature of the pigments results in their being oriented in a particular direction by the flow of the polymer, leading to an unsightly boundary line where the flows meet. Visibility and strength of weld lines can be optimized by tool design and moulding conditions.