Brittle PBT Parts

[brentb]

Resin: PBT 30% GF precolored white, UV stabilized from leading resin maker

Problem: Brittle parts

Job has run 15+ years

Last lot is brittle. Resin lot is new and now we are being told that this resin will be discontinued.

Analysis shows high aluminum concentration (pigment or pigment switch)?

Any ideas on cause and remedy?

Replacement resin suggested by resin company also failed.

Black PBT of similar grade does not and has never failed on these products.

Thanks for any input!

KOM!

brent

[Suhas]

Hi Brent,
Are the processing conditions on the two datasheets the same?
Are you using the same process sheet from the previous?
Can you run natural and see if you are getting the brittleness?
Regards,
Suhas

[brentb]

Yes,yes, and resin is pre-colored. Same grade of resin in black (also precolored) isn't brittle. Same resins and processes for 15 years.
White is being discontinued. Resin maker is best known for PBT.

KOM

brent

[rickbatey]

Got to be something they're putting in the white colorant. Maybe the OEM changed the color supplier? Maybe different pigment in the new colorant?
Rick.

[brentb]

Got to be something they're putting in the white colorant. Maybe the OEM changed the color supplier? Maybe different pigment in the new colorant?
Rick.

Rick,

Thanks, that was what I was thinking too!

KOM

brent

[Suhas]

Hi Brent,
I think I know this supplier very well :)
It could be that the carrier that they are using for the colorant is not compatible. What you can do is to run the black, mold parts. Then introduce the white, mold parts and show them the breaking. I am sure they will look into this.
Also ask them for a property datasheet for both the pre-blended colors. They should have it. Look at the impact strength values. Keep us posted.
Suhas

[JayDub]

Brent:

Have you compared MFI –
White resin to black resin
White before molding to white after molding
Also, if you have access to analytical equipment such as a DSC you might want to check there are no other resins lurking in there. I once had problems when a compounder used a masterbatch with a different base resin.

[brentb]

DSC found abnormally high amounts of aluminum. I don't know where that could come from!

"Before and after" MFI doesn't indicate degradation; thermal or hydro.

After all these years, resin is being discontinued, at least in white

Resin maker is the major player in PBT

Again, resins are precolored by resin maker.

All resins are in MFI range.


thanks,

KOM

brent

[rickbatey]

That aluminum must be some flakes or some other shape used in the white colorant. Maybe to brighten the white?
Brent, is there enough of a process window to try dropping the barrel heats? Maybe you need more heat to make the flakes disperse in the melt?!
Rick.

[Brisli]

are the parts brittle everywhere or just brittle in certain areas or feature related? high stress areas?

Brian