SO WHAT’S BEST?
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So now you want to produce plastic parts in a number of colours and use masterbatch to achieve a good, cost effective result. This is easy to say, and with due consideration of a few material facts, is relatively easy to do.
First, what masterbatch should you use? A number of factors will influence your choice but the most important consideration is the base polymer of the masterbatch.
As mentioned earlier there are two types of masterbatch: universal and polymer specific. Universal types are convenient to use. They work in most polymers, can be used at low dosage levels, are readily available in a range of standard colours, and in small quantities.
However, they do have limitations. It is essential to check that the colourants in the masterbatch are suitable for the material you plan to mould. In addition, universal masterbatches generally have low melting points and this means that they cannot be pre-dried with polymers. Another consideration is overdosing, as this can lead to compatibility problems that manifest as reduced physical properties and poor appearance in moulded products – not to mention the additional cost of using more masterbatch than is required.
Another dilemma is that the perceived versatility of universal masterbatches encourages moulders to purchase them in the belief that any surplus can be used again on another job. In reality, colours are rarely re-used and bags of material simply pile up in the materials store. It does not help that with universals the final shade imparted will vary depending on the material to which it is introduced.
Conversely, compatibility is less likely to be a problem with polymer specific masterbatches. Further, this type of masterbatch can be pre-dried with suitable polymers and this is especially useful if you are processing engineering polymers. Some producers offer small lots of custom colour matched polymer-specific masterbatch in 24 hours so lead time is not an issue.
Another essential consideration that affects the choice of masterbatch type is mouldings with thin wall sections. If opacity is required, dosing levels can be high and this means that excessive amounts of the carrier resin are added to the moulding material and this may change its physical characteristics.
Having chosen the masterbatch type the next major decision is how to add it to the material you will be moulding. The choices are to manually-mix pre-weighed masterbatch and polymer prior to filling the machine hopper, or use in-line volumetric or gravimetric dosing equipment to add predetermined amounts of masterbatch to known quantities of polymer.
Either way, it is important to ensure that the machine on which the processing is to take place is presented with evenly distributed masterbatch. Smaller granules equal better distribution in the polymer being processed. However, while the particle size of the masterbatch should be similar in form to the host polymer it should not be so small as to fall to the bottom during mixing. In addition, the quantity of masterbatch (dose level) should be within the capacity of the dosing machine and should take into account shot weight. This can be critical because if your shot weight is, for example, two grams and you are adding masterbatch at 1 percent it amounts to a mere 0.02 grams of masterbatch. If you think of this as one granule per hundred granules of polymer, you can see that dosing has to be finely controlled.
How much masterbatch should be added?
The ideal dosing level is determined by a number of factors. As mentioned above small shot weights benefit from higher doses of weaker masterbatches because this helps to ensure even distribution from shot to shot. The age and efficiency of moulding plant can also be an important factor. Expecting homogenisation of a 1 percent masterbatch by a 20-year-old machine that has never been serviced is wishful thinking!
In reality, the amount of actual colourant required is governed by your customer’s requirements for wall thickness, opacity, colour and application. These considerations directly affect dosing levels and hence masterbatch type. For instance, a thin wall HIPS container may require 4% titanium dioxide to achieve the opacity required by the customer. Obviously this is not going to be achieved by using a universal masterbatch (typically 70 percent TiO2) at 1 percent!
Personal preferences are also important. Using small quantities of strong universal masterbatch is extremely cost effective, whereas, the level of control with a weaker (cheaper) masterbatch is greater and can be readily fine-tuned to achieve optimum processing.
What to ask for and what to expect in return from a masterbatch supplier.
All masterbatch suppliers offer a colour matching service. The speed at which they respond with a quotation or return a match will depend upon the complexity of the colour required and the information you give them. If you have a colour that you would like the supplier to match you will need to provide the following information with a sample if you have one.
Colour required – your colour reference
Company/department internal reference – this is an important as it helps to avoid confusion with any subsequent colour matches
Process - injection moulding / blow moulding /profile extrusion / film extrusion / sheet extrusion
Quantity of polymer you need to colour in kgs/tonnes
Preferred type of masterbatch:
Will it be used for toys, packaging?
Will it be in contact with potable water?
Does it need to be FDA approved?
Will the RoHS & WEEE directives need to be taken into account?
Does it need to be free of heavy metals?
Does the masterbatch need to include any performance enhancing additives such as antistatic, slip, UV stabilizer, or antioxidant?
Is it going to be used indoors or outside?
What form of supply is expected?
A colour plaque?
Material sample? (Check the minimum quantity offered by the supplier)
Time frame - how soon do you expect to see plaques/samples?
Polymer the masterbatch will be used in:
Provide as much detail as possible. Brand name, grade number as well as generic polymer type. This information is essential if you plan to colour an engineering polymer.
State the colour standard you wish to work to, for example: RAL/BS/ Pantone colour reference number or some other standard?
Lastly and most importantly, do not be tempted to over specify what you need. As this has an escalating effect on costs! Ensure you meet only the requirements of the application.
Once you have approved your colour the masterbatch should be produced within a few days.
ColourTone Masterbatch Limited
Pant Glas Farm Industrial Estate
Telephone: 01222 888910
Fax: 01222 868487
Telephone: 01428 723211
Fax: 01428 722371