why different Masterbatch give different shrinkage during injection moulding process ?
Submitted by Faizan Anwer on Thu, 08/13/2009 - 5:39am
Hello every one,
I have just a quirry that why we get different shrinkage by using different masterbatches. Could any one give me an Answer
my email address is : faizananwar@gmail.com
Comments
differences between batches inherent
Materials have a "range" of acceptable characteristics so one batch will inherently be different than another batch. There are always variables between batches.
Degree of Crystallinity
I have experienced the same issue when moulding container lids - particularly in semi-crystalline materials. We had issues when changing colors on PP and PE products - reds and blues tended to shrink more than whites and yellows. There were also variations in differential shrinkage' We also noted a difference between organic and inorganic colorants.
We believed that this was due to the pigments acting as 'nucleation agents'. Masterbatches can have different particle size and shapes and electronegativity. These characteristics can all influence crystallinity and therefore shrinkage. Hopefully someone else can add to or confirm this.
semi-crystalline materials
We had similar problems using PA. We had different shrinkage with or without a black color. To compensate this we had to make two different tools for the colored and the not colored material.
Greeting Ralf