[avarseir]

Dear Chemical Experts,

We recently encounter a problem with the PVC we use to make leathery coating for some of our products. The problem is that the material becomes something like a sticky goo instead of the usual leathery material.

Some of the parameters that would be helpful:

1. Our curing parameters are 150-200 degrees C for around 3-4mins in a custom-made oven.
2. Our PVC resin has a K-value of 67.
3. We use DOP as our main plasticizer.

We never have problems with our coating before, but currently we seem to consistently get coatings which does not want to cure and its sticky (gooey).

We suspect either the PVC or the DOP is the culprit but we haven't changed vendor because this vendor is very reputable in terms of their quality.

So have any of you encountered PVC which doesn't want to cure properly and becomes sticky and gooey?

Need advice!

cheers all.

[marquis]

Here is a starting point. There are many possibilities.

One of the most likely is based on the DOP.  DOP is a plasticizer.  If the level is unusually high, the
PVC will seem sticky. There are several extraction techniques for determining the amount of DOP
present.  It sounds like a good first step would be to check the DOP level.

It sounds like the form of PVC you are using is a plastisol.  These are high molecular weight PVC chains.
The curing is caused by swelling of the PVC.  If something is wrong with the oven (not high enough
temperature, for example), you could get the sticking.  On a similar note, if the molecular weight of the
PVC is low, you will also see the sticking.  Checking the oven is a good first step.  The molecular weight
of the PVC is best checked with Gel Permeation Chromatography (GPC), although you can get an idea
with other tests (such as inherent viscosity).  You may have to send the samples to an outside lab for
this testing.

Good luck.