Letters (May 01, 2004)

Questions about CaCO3 use in blown film

Dear editor:

Regarding suggestions for use of calcium carbonate in blown film (6 Ways to Find More Profit, March 2004). I retired from NOVA/Union Carbide in film/tech service. While I was working, we studied the use of calcium carbonate as a filler and noticed the following problems:

1. Output greater because density of calcium carbonate greater than plastic;

2. Moisture absorption due to filler;

3. Die and screw wear very serious;

4. Printing problems, gels, etc.

Joe Luczak

Montreal, QC

Dear editor:

With regard to Mr. Luczak’s comments:

1. The output itself is not driven by the density difference between the polymer and the carbonate. Rather it is the result of improved cooling of the bubble. Calcium carbonate allows the heat to get into the melt inside the extruder faster (it doesn’t melt) and out of the finished film faster for essentially the same reason. This enhanced cooling effect as demonstrated at several of the major resin company’s labs increases lineal foot output thereby producing more lineal feet of film per hour.

2. In all of the field trials we’ve done, and in every instance where literally millions of pounds of carbonate are added to film, we have seen no instance of moisture absorption due to the presence of calcium carbonate. This is because the proper carbonate used in these applications is coated in such a way to prevent moisture absorption. If an untreated carbonate is used there may be some moisture absorption but I cannot verify this statement as we do not in any case suggest or recommend its use.

3. Our product, OM-FT, is a 1.4 micron nominal particle size treated product. There is absolutely no evidence we have been able to uncover that would suggest that excessive wear occurs with this product. Larger, less expensive carbonate products are available to the market but I would strongly suggest against their use. They might contain co-minerals such as silica or iron oxide which could cause wear.

4. We’ve seen no evidence of gels/printing problems. The ultimate proof of this is that calcium carbonate is being used in ever increasing amounts in extrusion coating where printability is paramount. In fact, the presence of carbonate in these applications enhances printability because it roughs up the surface of the film so that ink adherence is improved. With respect to gels, these are usually caused by different molecular weight materials within the melt.

Jim Cara

Polyolefins Sales Manager

Omya Inc.,

West Columbia, TX