Ins and outs of above-ground pools

Years ago, a family down the street set up an above-ground swimming pool, and it instantly became the top destination resort for neighborhood children. A simple ladder provided access to the pool, but to climb back out you pretty much had to hoist yourself over the side.

Creative Plastics, a rotomolder based outside Baltimore, makes two products that address this problem. Called simply the Economy Step and the Deluxe Step, both are plastic stairs that rest on the bottom of the pool and attach to a ladder on the outside. Home & Rome and Leisure Source distribute them nationally.

The biggest challenge, says Creative Plastics' president Thomas Eckert, was coming up with a material that would provide the desired granite appearance and still rotomold well. "We used to make a granite-like material of a cross-linked polyethylene," he says, "which was very easy to do because the material catalyzes in the oven and becomes fixed, keeping the particles separated and giving a great granite look."

But a medium-density polyethylene didn't give them the stiffness they desired. Early on, engineers modified the design slightly by adding a gusset of material up the back of the steps to reduce flex.

A linear material would offer greater stiffness, but the different melt rate would cause the colors to bleed into one another. Wanting the best of both materials, Eckert turned to Dow Plastics (Midland, MI). "We went to them and talked about materials and melt indexes," he says, "and they came up with something stiffer that allows us to make the blue mottled color we wanted."

The material is a special version of Dow's AFFINITY polyolefin plastomer (POP) resin, called DSQ 1504. "We developed DSQ to address customers' desire for a stiffer material," says Alan Whetten, Dow Plastics North American technical leader for rotational molding.

"The DSQ material has a very high flexure modulus for a rotomolded polyethylene," Eckert explains. "Usually, using a high-density polyethylene in rotomolding will give you a higher incidence of warpage. But not with the DSQ."

Dow Plastics' literature describes AFFINITY POP as a new resin made with INSITE Technology, which produces a rotomolding material with high stiffness and rigidity and no loss of impact resistance. INSITE is a proprietary, single-site, constrained-geometry catalyst technology and optimized solution process. Though sometimes referred to generically as metallocene technology, the company says that INSITE is chemically different from metallocene and exclusive to Dow Plastics.

No matter the reason, to Creative Plastics the advantage of DSQ has been slightly lighter parts with excellent stiffness. "If we would have had a material like this early on," says Eckert, "we probably wouldn't have had to put in the additional stiffener."