The authoritative public forum
  for Metal Finishing since 1989
-----

White plastic stains over powder coating (looks like bleaching)

December 14, 2009

Hi:
I have a question. We have a product that we pack with UV plastic and then stretch film (we used at contact points bubble and cardboard).
But when the costumer received the product it looks like the paint is bleaching. But it looks like the plastic reacts with the paint and the catalyze is the moisturize.
it will be better change the plastic or use something between the product and the plastic.

  

Regards.

Victor Kuznetsov
Paint Process Eng. - H. Matamoros, Tamaulipas, Mexico

---

Hi Victor,
You do seem to be experiencing at lot of coating problems lately. Firstly, the two materials you do not use directly next to your coating film would beÆ flexible plastic sheet as it contains a plasticiser to create flexibility. Under certain atmospheric conditions this plasticiser will leach out of the plastic and deposit on the surface of the powder coating. The second material you should not use next to a coating is cardboard. Cardboard can be manufactured from waste products; old news paper, cardboard etc, however, top grade is made from virgin wood chip. It is a known fact that should the cardboard/coating interface become loose during transportation from one location to another, then the cardboard will act like sandpaper and scour the coating surface. Have you thought of using moulded rigid foam spaced at regular intervals along the poles length to transport the items? Shaped to the contours of the container with a half moon cut-out for the pole. The pole could then be wrapped in tissue paper to keep away dust and dirtÆ I feel that this is worthy of further investigation as I believe this method should meet with your requirements.
Sorry I have not offered any suggestions to your delaminating problems. I was reading an internet conversation that referred to the preparation of aluminium prior to PCÆ for what it's worth here are the main points raised.
a)Shot blast casting to a white or near white colour.
b)We purchase a fluoride free iron phosphate to which we add our own quantity of ammonium bi-fluoride. The fluoride etches the Al to provide a better key.
I could e-mail the whole item if required.

Terry Hickling
Birmingham, United Kingdom
December 16, 2009

---

December 17, 2009

Thanks Sir, yes send me the info.
About this paint problems we always have been working with this problem, but I work to eliminate them.
About the wrap issue, what about if we use tissue paper between the pole and the plastic?
We thought a few months ago use a foam type at the poles but we have too a lot of carrier damages..
That's the reason of this wrap type. (plastic sheet+bubble at contact points+cardboard)
This problems is more common at the bronze color...
Backing at the paint problems, I worked to change the pretreatment.. We are using iron phosphate to our aluminum pieces, but we don't have any other surface preparation.
Next month I will working with a new oven supplier and the paint booth supplier too.
I think that we never invest at the area, and with this is only to level to a normal process.

Victor Kuznetsov
- H. Matamoros, Tamaulipas, Mexico