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Dairy coop decides on dual bag

California Dairies Inc. reportedly will be the first commercial user of a dual film bag system. CDI plans to offer the plastic bag as an alternative to multiwall paper bags for milk powders sold to confectioners, bakeries and cheese manufacturers.
FILED IN:  Machinery  > Filling/sealing  > Dry filling

When asked why California Dairies Inc. invested in new machinery and flexible materials to package its milk powders Dave Bush replied “We see this all-plastic Stratapac™ bag as extremely resistant to damage.”

Bush is vice president of manufacturing operations for CDI a recently formed dairy cooperative based in Artesia CA. CDI markets milk powder as a food ingredient to confectioners bakeries cheese manufacturers and other food processing firms.

Later this year Bush says CDI will begin to sell to domestic and export customers its nonfat dry milk powder in 25-kg (55-lb) Stratapac™ bags manufactured and developed by converter Holmes Packaging (Rotorua New Zealand). The total Stratapac “system” includes the bag plus an Avapac™ packer/filler and a Stratapac sealer. Both machines are made by Avalon Engineering (Hamilton New Zealand).

Bush tells Packaging World that CDI anticipates operating four of these systems. Flat prefabricated bags will be placed in the magazine of the Avapac then opened and filled at speeds of 8/min according to Bush.

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Holmes earned a DuPont (Wilmington DE) Award for the Stratapac system (see PW Feb. ’00 p. 26 or

In exclusive interviews with both CDI and Holmes PW learned that the equipment won’t be installed at CDI until this summer. The bags will be made by Holmes Packaging on equipment from Windmoeller & Hoelscher (Lincoln RI). The bag measures roughly 20”Wx35”H.

CDI will market the flexible Stratapac plastic bag within a block-bottom plastic bag as an alternative to the traditional multiwall kraft paper bag. The bag is especially suitable for hygienic food and pharmaceutical applications. Stratapac can be opened without releasing fiber particles common to multiwall paper bags. The exterior plastic bag resists moisture and also permits printing of attractive graphics.

Stratapac was test-marketed by the New Zealand Dairy Board in 1998. The pack was used to package 150 tons of milk powder for customers in Sri Lanka Saudi Arabia Germany the U.S. Taiwan and Venezuela. Commercial trials continued last year in South and North America as well as in Europe.

Unique sealing

The Stratapac sealer is unique in that it simultaneously seals the inner and outer bags using parallel sealing bars. A mechanical device then perforates the package between the two seal areas which are roughly 1” to 3” apart. The perforation allows the customer to easily open the outer bag. The intact inner bag can then be opened with a knife.

According to Kevin Piccione general manager at Holmes CDI will use two different structures one a “complex coextrusion high-barrier structure using nylon ethylene vinyl alcohol and DuPont’s Bynel® resin in an adhesive layer. The other will be a seven- or nine-layer linear low-density polyethylene-based material.” Final material decisions must still be made. The inner bag will be about 70 microns (2 ? mils) thick; the “robust” outer bag will be 140 microns (5 ? mils).


“We’ve taken the bag on a forklift and raised it 30 feet in the air and dropped the bags on our floor” says CDI’s Bush. “The outer bag absorbed the shock so well that the pouch inside was untouched. For multiwall paper bags we do the test from about four feet.”

Bush says CDI hasn’t made a final determination on whether the Stratapac will completely replace multiwall paper bags. But the new sealing equipment he says will handle both the Stratapac all-plastic bag combination as well as paper.

“A big benefit we see to the bag is that it is extremely resistant to damage” says Bush. “And the pricing of it is very competitive with the multiwall paper bags. In fact it appears that there will be a savings from the bag from Holmes. Whether that has to do with the value of the dollar or the highly automated technology that Holmes is using I don’t know.” But he’ll gladly take the economic advantage as well as the other benefits delivered by the Stratapac.

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