materials | High density compounds
increasing awareness and regulatory pressure against the use and disposal of lead will continue to increase the demand for lead alternative materials. We have seen this transition in the nuclear and medical indus- tries, but we will continue to see this in other industries such as consumer and electronics,” he says. Dailey highlights a number of key points to consider
when formulating and selecting the appropriate high density compound for an application. “Firstly, the final compound density is obviously key. Ecomass can compound anything between 1-11 g/cm3
. Choice of base
Above: The radiation
shielding in the Niton XL2 XRF hand-held analyser relies on high density plastics
ments of the end-use application. US-based Ecomass Technologies is a specialist
compounder of high density thermoplastics. The company’s marketing director Ryan Dailey argues that high density compounds deserve a closer look by the plastics industry. “Awareness and relevant case or success stories for a given industry are the main drivers in high density at present. Despite the fact that high gravity compounds have been around for more than 20 years, they are still considered very niche in the plastics industry. We have grown accustomed to thinking of plastics as cheap and light. High density compounds might be the perfect solution, but the OEM or processor is unaware or inexperienced with these materials and does not consider them as a possible solution,” he says. “In addition, they might not be aware of some of the ways these materials are being used in the industry or by competitors. As companies see how others in their specific industries are using heavy plastics to deliver material solutions, they can make that connection to their own company and products. As a result, you see a snowball effect as these materials are introduced and take off in various industries and applications,” Dailey explains.
Perception of mass Dailey believes there is a growing demand for the value perception delivered through mass. “Many customers are looking for developments of standard products like plumbing fixtures, razor handles, bottle closures or cosmetic packaging, and wanting a densified material for their existing products as a way to add mass and portray luxury or quality through weight,” he says. “Ironically, many of these products such as plumbing fixtures are being produced in high density compounds to take advantage of the much more efficient and cost effective injection moulding process of plastic parts. They are then plated to give the look and feel of metal.” Lead replacement will also continue to drive the market for high density compounds in some areas. “The
64 COMPOUNDING WORLD | March 2016
resin involves exposure to chemicals and the required operating temperature, as well as physical properties such as rigidity, impact strength, tensile strength and flexural modulus. Other factors will obviously include the colour and whether it needs to be food contact approved, UV stabilised and thermal conductive,” he says. “A further consideration is if the finished part
requires painting, coating or plating, or if the part is going to be overmoulded or bonded with another. In most cases we start with an application and a material density and determine the cheapest formulation with a given resin. We would then look at the additional requirements,” Dailey explains.
Selection guidelines Selecting a filler is usually pre-determined as the cheapest option that will meet the density target while not exceeding the maximum volumetric loading level. “Barium sulphate is our cheapest available filler. However, it is also the lowest density of any filler we use at only 4.4 g/cm3
density of 2.7 g/cm3 pounds. At 19.2 g/cm3
. As such, we can only achieve a final for barium sulphate filled com- , tungsten is our highest density
filler available, which allows a final compound density of 11.0 g/cm3
,” he says.
“The other main consideration when it comes to particular filler choices is physical properties. The rule of thumb with high density compounds or filled materials in general is that the more you fill, the worse the physical properties,” Dailey says. “All the physical properties of the resulting high
density compound are derived from the base resin. As you fill the compound more you are decreasing the percentage of resin in the formulation, and are in essence substituting density for physical properties in the process. For less demanding applications, that may not be an issue, in which case density and price will dictate the filler choice. However, in some more demanding or tight-tolerance applications, we may be forced to move to a higher density and higher cost filler in order to deliver a resulting compound at the same material density but with a lower loading level and
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