Injection Blow Molding COC Arrives: Here's How to Do It

Cyclic olefin copolymers, or COCs, are a new family of amorphous engineering thermoplastics with high clarity, moisture barrier, HDT, and chemical resistance. Their first commercial injection-blow molded applications are just now beginning to appear on the market. Topas COCs from Ticona are being used to make drug and medical bottles that can withstand all the usual sterilization methods—steam, ethylene oxide, and electron and gamma radiation. Bottle sizes generally range from 20 to 40 cc, with typical wall thicknesses of 0.05 to 0.06 in. Topas COC has also been stretch-blow molded, resulting in moderately improved mechanical properties.

 

Molding tips

Since most processors are unfamiliar with these materials, Ticona’s technical experts provided PLASTICS TECHNOLOGY with basic recommendations for injection-blow molding a range of Topas grades. The injection molding portion of this process involves conditions similar to those recommended for plain injection molding of COCs (see accompanying tables and PT, Nov. ’02, p. 62 for more on injection molding COC). In the blow molding step, temperatures should be 54° F above the resin’s glass-transition point, and air pressure should be between 75 and 150 psi. Cycle time is usually 10 sec from injection to strip. 

INJECTION-BLOW MOLDING COCs (TYPICAL START-UP CONDITIONS)
Topas Grade MFR, g/10 min HDT, F @ 66 psi	8007-D61 30 167	6013-D61 13 266	6015-D61 4 302
Cylinder Temp., F Feed Barrel Zone Barrel Zone Barrel Zone Barrel Zone Nozzle	<140 374-428 392-446 392-446 392-446 392-500	<230 446-500 464-518 464-518 464-518 464-572	<230 464-518 482-554 482-554 482-590 446-590
Mold Temp., F Preform Neck Body Bottom Blowing Stretching*	122-158 122-150 122-158 130-158 122-158 212-248	212-230 194-212 212-266 212-230 194-212 212-248	212-266 212-230 266-302 284-320 212-230 356-392
Melt Temp., F *Stretch-blowing only	374-446	464-518	500-554

 

Undercuts at the neck should be as small as possible, Ticona advises, though minimizing undercuts involves balancing the need to keep the bottle on the machine during the process against the need to remove the finished bottle without cracking it. Bottles should be handled carefully while warm to prevent marring their surfaces.

If halos and rings show up on bottoms of bottles, they can be eliminated by cleaning the core rods and reducing the bottom temperature. If bubbles appear, reduce screw speed and increase backpressure. If voids occur, decrease cure time. Black specks can be eliminated by cleaning the manifold and lowering nozzle temperature. If neck cracking occurs, reduce the size of the undercut on the stripper plate

Injection-blow molding recommendations were provided by Ticona’s Ron Lamonte, development associate; Doug Hammond, business development engineer; Donal McNally, product marketing manager; and Ken Music, technical service engineer. Mr. Music passed away quite recently. In addition to being a Ticona engineer, he was an emergency medical technician and spent weeks at Ground Zero in N.Y.C. helping others after the 9/11/01 attacks.

Machine Settings
Injection Pressure, psi Hold Pressure, psi Backpressure, psi Injection Speed, mm/sec Screw Speed, rpm Screw Suck-Back Cushion Small  Screw Type PVC type  Nozzle Type Nozzle ID, mm  Draw Ratio Gate Diam., mm	7255-14,510 4353-7255 10-30 50-150 (0.5 to 2 sec) 100-150 None or minimal (4 mm typical) PVC type (long L/D) Free-flow 0.9-2.2 1:2 to 1:3 (stretch-blow) 1.8-2.2