During the production of color masterbatches used for plastics, compounders face two main processing challenges: pigment agglomeration and excessive equipment torque/die pressure. If not properly addressed these challenges can lead to poor quality masterbatch, low efficiency, and damage to expensive processing equipment.
In the manufacture of color masterbatches, pigment dispersion is a primary concern. Color masterbatches are highly filled with pigment particles, minerals, and other additives that have tendency to agglomerate if not properly dispersed. Poor pigment dispersion leads to reduced color yield and less efficient masterbatch.
Torque & Die Pressure
The high melt viscosity of a color masterbatch is the primary cause of excessive torque and die pressure during manufacturing. This torque and pressure can lead to off quality masterbatch and extended downtimes to fix manufacturing equipment. In addition to machinery wear-and-tear, excessive torque and pressure increase energy consumption and thus the cost of manufacturing operations.
The challenges to color masterbatch manufacturing outlined above need to be considered when formulating and optimizing a masterbatch. Improving the dispersion of pigments, fillers, and additives in a masterbatch formulation increases yield and makes for a more efficient end product. Likewise, reducing torque and die pressure can improve output and reduce the cost of manufacturing. Historically, achieving these two tasks often require tinkering with resin selection and extrusion parameters while also maintaining the desired physical properties of the end product. This can prove to be a daunting task. Luckily, there are dispersing agent additives that can improve both pigment dispersion and extrusion conditions without altering the tensile properties of the end product.
Epolene® Dispersants & Processing Aids
EPOLENE® is a line of polyethylene and polypropylene wax polymers that are outstanding dispersion agents for pigments and other additives used in masterbatch compounding. When added in small amounts (typically 1-4%) to masterbatch, Epolene® dispersants prevent the agglomeration of pigment particles help to produce a homogeneous dispersion. In addition, the Epolene® acts to reduce the amount of torque and die pressure required to pelletize the pigment masterbatch.
To demonstrate the usefulness of Epolene® as a polymeric pigment dispersant in color masterbatches, an independent lab study was performed in cooperation with Westlake Chemical that compared pigment particle size and distribution of a linear low density polyethylene / pigment blue 15:3 masterbatch compounded with and without Epolene®. The microscopy images from the study are below:
The images above show that the addition of EPOLENE® C-15 to the color masterbatch promotes a more homogeneous dispersion with far fewer pigment agglomerations. Quantitatively, EPOLENE® C-15 reduced particle size up to 80%. This improvement in dispersion also results in an increase in color yield that allows for less pigment to be used to achieve the desired color. The data below shows the effect EPOLENE® has on increasing color strength.
Another way to quantify this improvement in pigment dispersion is to monitor filter pressure values. The data below shows that as the level of EPOLENE® is increased in masterbatches the filter pressure value is reduced. This is evidence of the ability of EPOLENE® to prevent particle agglomerations that increase filter pressure.
EPOLENE® has also proved to be extremely useful as a processing aid for highly filled masterbatches. In a separate study, a 50% LLDPE/50% mineral filled masterbatch was compounded with and without EPOLENE®. The torque, die pressure, and mechanical properties of the masterbatch were measured. There was a 4% reduction in die pressure was observed at a 5% loading of EPOLENE® C-15 versus the control, and a 28% reduction in torque was observed at 5% loading of EPOLENE® C-15 versus the control.
Other studies including masterbatches containing organic pigments, with and without filler, were also carried out and also demonstrated a marked reduction in both average torque and die pressure, as seen below.
EPOLENE®'s ability to reduce torque and die pressure during compounding results in energy savings and an increase in production rate. Masterbatches are able to be compounded faster with a reduction in power consumption resulting in a more efficient and economical process. It is also important to highlight that while compounding pressure and torque were significantly reduced, the tensile properties of the control compared to the EPOLENE® modified plastic remained virtually unchanged.
Selecting an EPOLENE® Dispersant for Compounding
There are various commercially available grades of Epolene® that vary in polymer type, molecular weight, drop point, density, and melt viscosity. Additionally, certain grades of Epolene® are modified with maleic anhydride. These maleated grades are often used as compatibilizers in compounding composites.
*Solid at this temperature. Brookfield viscosity at 190°C = 300 cP
As with any formulation, selection of the proper materials is critical to success. If you would like assitance in selecting the appropriate grade of EPOLENE® for your application, contact us today to speak with our highly trained team of product experts.