COLOUR CHANGE: FROM YELLOW PP TO NATURAL PP
In this case study Michael Knabe, our Distributor for Germany tells us how he achieved a colour change from a masterbatch of egg yolk yellow PP to natural PP and removed Carbon on a 280T Engel machine using Barrel Blitz Universal (BBU).
He knew this trial could reveal some interesting results as the machine’s screw hadn’t been pulled for about a year.
The customer’s biggest issue was staining from coloured material. Pigmented plate-out on the screw had degraded to carbon and had cracked allowing coloured material to get stuck between these cracks. Over time both Carbon and coloured material had become engrained onto parts of the machine.
In the image below you can see how the ‘egg yolk’ yellow PP (top left, at 9-12 o’clock) and the dirty yellow material (on the brown cardboard, 1 o’clock).
The latter is a combination of yellow PP and Carbon which has been removed from the machine.
This shows us that the BBU is effectively purging carbon material from the screw and barrel – unheard of in normal purging compounds.
GETTING A DEEP PURGE FROM BBU
At ’3 o’clock’ (in the image below) you can see a rust-coloured material.
Now this is interesting because it shows the depth of the BBU purge as it also removed red material which had been used in the run before the yellow PP.
Michael explains: “The purging technique previously used by this customer had skimmed over the engrained Carbon and the coloured material that had attached itself to the Carbon. Our customer thought they only needed to remove the yellow PP, so they were really surprised when the red colour started to appear!
And they were impressed because we used just a third of the screw volume to remove the Yellow PP, dirty red brown then to brown to light grey. We removed Yellow PP with 500g of BBU and finally 2.5kg to remove the red material from the earlier run.
COMBINING BBU & POLYCLEAR
Previously the manufacturer had been getting rejects even after 3 to 4 hours of purging. But when we used BBU for purging it only took 35 minutes to remove Carbon, yellow PP and the red brown material.”
After this initial purge the manufacturer only needed to use 1kg of BBU and 3kg of PolyClear. That’s because BBU is an effective screw cleaner, whereas PolyClear is better for cleaning the hot runner.
This approach will ensure the residual buildup of Carbon on the screw is regularly removed which would take just 20 minutes of purging every 3 months and will ensure Carbon does not appear in any future runs.
As BBU cleans with a scrubbing action, no added chemicals are required, so it can be used in food and drink products.
The hot runner splits material from one channel into multi-channels where they are injected into the moulds through complicated valve gate systems which is where the colours remain for the longest period.
Michael raised the temperature of the tips in the tool by 20 degrees and selected the Poly Clear with the most appropriate Melt Flow Index (MFI).
Michael explains: “It’s much quicker to raise the temperature at the tips than that of the entire hot runner as it doesn’t affect the change and the tip can heat up and cool down can be achieved quickly. This saves a considerable amount of time.
It’s necessary to do this because a residue of coloured materials forms at the tool tips which can result in a line of colour emanating from the tip area on subsequent runs. This residue can be very difficult to remove if you do not raise the temperature at the tip.”
POLYCLEAR: VERSATILE WITH VISCOSITY
Aquapurge offers 9 different PolyClear products which means we can purge materials of different viscosities, from the stiffest, heavy duty material to the easiest flowing PP. All you need is the optimal PolyClear product and the correct amount of pressure to purge material.
Choosing the right product is essential for ensuring you get the full part every time, particularly when you purge multi-cavity machines operating on short cycles. If you don’t purge with the correct product with a similar MFI you can’t run the machine in automatic mode or a short cycle because there’s a real danger of parts getting stuck in the machine. Hard plastic stuck in a cavity could damage the tool.
All we need to know is the MFI of the PE or PP material and we can advise you which PolyClear product will purge effectively. In complex or high multi-cavity moulds a customer’s sample can be evaluated in our lab to guarantee the correct Poly Clear grade is prescribed.
In the images below you can see white HR20 and clear PP products that are going to be used as lids and tops for shampoo bottles, initially some of the lids are yellow but after purging all products are pristine with no Carbon specs.
WOULD YOU LIKE TO TRY OUT BBU?
If you would like to find out how Aquapurge products, including Barrel Blitz Universal could optimise your manufacturing processes please get in touch.
BBU can be used in any type of injection moulding machinery. In this case study it was a 280T Engel machine and Aquapurge products enabled the manufacturer to switch easily between different colour material and produce black spec-free products saving time, money and material.
If you are not sure about the benefits we’re only a phone call or an email away.