Cyclic olefin copolymers, or COCs, are a new family of amorphous engineering thermoplastics with high clarity, moisture barrier, HDT, and chemical resistance.

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Injection-blow molded COCs are starting to appear in applications such as these pharmaceutical vials from Schott Glas AG in Germany and clinical bacteria culture tubes from Becton Dickinson Microbiology Systems in the U.S. Attractive features are high clarity, better breakage resistance than glass, good moisture barrier, and resistance to steam sterilization and chemicals.

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
374-446464-518500-554

 

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