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Roll Coating System Design

Roll Coating System Design

(OP)
Hi All,

I've been working on a design for an application where a film (LDPE) is to be coated with a acrylic polymer adhesive with a viscosity of roughly 5,000 cps. The initial concept is to coat the LDPE film with a layer of the adhesive between 10-50 microns at a max rate of 5 in/sec.

From what I've found in my initial research is that a roll coating application using a reverse roll coating configuration with a metering roller, application roller, and backing roller would be appropriate. The problem I'm running into is what type of roll to use for the metering roll, application roll, and backing roll.

Here's a picture of the reverse roll coating configuration I'm referring to:



My questions:

  • Does the reverse roll coating setup seem reasonable for my application?
  • Any suggestions or resources I could look into to find information on the type of rolls to use?
  • Where could I look for overall roll coater system design information?
Thanks for the insight.

RE: Roll Coating System Design

Reverse roll coating is not good for drawing the film thickness down from the metered thickness applied by the metering roller. You will generally get skip coating where the film will pull a strip of coating off the applicator roll then have a dry streak followed by another strip of coating. Reverse roll is usually run with the applicator roll going faster than the backing roll to get a smooth coating. Adjusting the applicator roller to backing roller speed ratio allows for very fine adjustment of average coating weight (side to side adjustments must be made with the metering roller gap).

To achieve a 10-50 micron coating thickness you definitely want to draw down the coating thickness. Forward roll coating is used for very thin coatings. It is often called kiss-roll coating. It works just like your drawing shows except that the backing roller and film move in the opposite direction. With forward roll coating it is possible to use and applicator roller speed ratio of 1 to 10 or greater.

The metering roller is usually rotated slowly to feed any grit particles through the gap so they do not cause continuous streaks by getting caught in the gap. The best coating smoothness is obtained when reverse rotating the metering roll so it sweeps grit particles back away from the metering gap. It also stops any ribbing in the coating, which occurs when you separate two wetted surfaces, which is what happens in the metering gap. However, reverse rotating the metering roll requires the added complexity of a doctor blade to scrape the metering roller clean before it makes a full revolution.

Precision roll coaters are very expensive. Depending on your requirements and coating width they cost $100,000 up to several million. Some coater manufacturers are Independent Machine in New Jersey, and Century design in Calif. Paper Film and Foil converter magazine has a good buyer's guide that will list many suppliers.

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