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Thread: Rubber Matt has Hazy Areas

  1. #1
    Join Date
    Dec 2016
    Posts
    105

    Rubber Matt has Hazy Areas

    Help,

    I have had a few of these rubber matts, and I always fight appearance issues... this one in no different.... Front of parts show ghosting or hazy areas in same spots every time. See picture of worst case.

    Matl is TPV.... (very similar to TPE in my opinion and I am not sure the difference to be honest.)

    This is an automotive rubber mat to be placed at the bottom of a console/ coin compartment, the longest dimension is about 5 inches.

    4 cavity family mold, all have same appearance issue
    Tunnel gated.
    Fast fill improves the appearance, but does not eliminate.

    Anybody know a way to make them look perfect, like our customer wants?

    thx,
    Joel
    Attached Thumbnails Attached Thumbnails mattbetter.jpg  

  2. #2
    Join Date
    Aug 2014
    Location
    Saint Paul, MN
    Posts
    147

    Re: Rubber Matt has Hazy Areas

    I'm not familiar with TPV but my first thought would be to treat it like any other filled material: raise the mold temp (& possibly melt temp) to try to get a resin-rich surface. Alternatively, if the parts start off looking good and get progressively worse during the run, you may have some additive plating out on the mold surface, which is a lot harder to deal with.

  3. #3
    Join Date
    Dec 2016
    Posts
    105

    Re: Rubber Matt has Hazy Areas

    Thanks JayDub,

    I actually had tried the other direction and it helped..... my thinking was the hazy areas were trapped gas on the surface, so I lowered all the barrel heats as low as possible to reduce material gas....... it helped somewhat.... also to note the start up parts look the exactly the same....... but after it ran an hour, the parts then actually looked slightly better.. also as stated filling fast makes them look better, and I like to think of it as "dispersing the gas", but this material is always so difficult to process and understand, I can't be sure.... so, now the parts look much improved from tool shop parts (I like them!), but still not perfect, so I am sure the customer will not like them

    Thanks again,
    Joel

  4. #4
    Join Date
    Oct 2018
    Posts
    12

    Re: Rubber Matt has Hazy Areas

    Can you stage clamp pressure during injection? Start out low and ramp it up?
    If not, maybe try reducing clamp pressure.
    You might also try slow inj speed at beginning and speed it up near end of fill.

  5. #5
    Join Date
    Aug 2011
    Location
    Upstate of South Carolina
    Posts
    615

    Re: Rubber Matt has Hazy Areas

    I see that your losing melt pressure on the resin and getting back filling in that area. Warm mold up, lower clamp and increase vents on the entire part; then shot as fast as possible ! TPV means there’s some cross linking or vulcanizing happening with the resin. A resin change to a resin made for such parts would make your life easier. I imagine it’s Santoprene resin. A Pibiflex or Kraiburg resin would run/look much better.
    Rick

  6. #6
    Join Date
    Dec 2016
    Posts
    105

    Re: Rubber Matt has Hazy Areas

    Thanks Rick and Doug!

    Will take these ideas into my next battle.

    Joel

  7. #7
    Join Date
    Dec 2012
    Location
    Serbia
    Posts
    81

    Re: Rubber Matt has Hazy Areas

    Im working few years now with TPE and TPV, and your problem can be also caused by not dry or over dried material. So you can do tests with different drying parameters. Beside that adding venting to tool (if possible) is never bad idea.
    Check also is any layer of dirt stays on tool.
    And is it always on same spot or is "moving" from shot to shot? And can you show me location of injection point?

    Regards,

  8. #8
    Join Date
    Feb 2016
    Location
    San Francisco Bay Area, CA
    Posts
    171

    Re: Rubber Matt has Hazy Areas

    Where is part gated?

    That thing?Click image for larger version. 

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    Definitely drying this material properly is critical - really any exposure to air for just a few minutes will absorb moisture and any cracks or air gaps in your dryer/feed system can be problematic.
    (learned this the hard way).

    Also working with this material I've experience better results filling on first stage - almost around 99.99999% full on first stage.
    Reason is because once the material starts to slow down - it STOPS

    Looking at your part I'm just imagining where the gate is, and how the flow-front would behave along part featues.
    If you filled with one injection speed your flow-front would be Fast in areas with small cross section and Slow in areas with large cross section, which is bad for a material that wants to STOP when it slows down. This could cause the hazyness, maybe.

    I'd recommend a shot size study and run fill-only parts at various transfer positions so you can visually see your flow-front at various stages and note any swirling/whirling that's going on. (10% full 20% full 30% full etc. etc.)
    With this information you can do your best to 'profile' the injection to try to maintain the same flow-front rate across part features.

    Steel surface finish also comes to mind..

  9. #9
    Join Date
    Dec 2016
    Posts
    105

    Re: Rubber Matt has Hazy Areas

    Thanks Chris, and Nemanja,

    Yes, Chris, you got the gate location correct!, tunnel gated, and looks ample in size, (if not too big. )

    We did dry the material, and I thought that was unnecessary, only because we usually don't dry TPE. but I am NOT the expert on this stuff! I might try different drying levels as you guys suggested.

    I didn't see anything much in the mold, I would clean the mold, and next shot looked the same. Playing with fill speed, I could move the hazy spots around a bit, and diminish a bit, but always in the same basic location.

    I ended up going Sloooow thru gate, then FAST the rest , or the gate would also look crappy. I can't remember doing parts at 50% full, I probably did(?), but I like that idea, and will look again.

    FYI - I also cut off the ribs on the back of the part, stuck them in the mold, and shot again, thinking I had at least the problem (Turbulence flowing over the ribs) clarified, but those next parts looked the same too!....

    Thanks for the feedback!
    Joel

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