RTP Company: The Global Leader in Specialty Compounding

Foaming Agent Masterbatches or Concentrates

RTP Company's foaming agent masterbatches provide several benefits to injection molded plastic articles:

• Reductions of plastic part weight by up to 20% for density critical applications such as fuel floats and energy saving transportation equipment.
• Elimination of sink marks on injection molded parts — sink marks are shallow depressions on a part surface and are the result excessive shrinkage in thicker areas of the part — they can be minimized by adding a small amount of foaming agent which creates just enough internal pressure within the molded part to offset excessive shrinkage and reduce sink marks.

Foaming agent masterbatches are available for most thermoplastics. Choosing the proper masterbatch grade is important:

• It should activate and foam at a temperature slightly below the normal processing temperature of the host polymer.
• Masterbatch carriers must also be compatible with the host polymer to avoid blistering and delamination during molding.

RTP Company has developed specific foaming agent masterbatches that have excellent activation and compatibility with intended polymer systems.

Foaming Agent Masterbatch (FCX) Products

Exothermic

Grade	Activation Temperature	Recommended Polymer Use(s)
FCX 27301	300-350 °F / 150-175 °C	PP, PE, POM, PA 11, & PA 12
FCX 27314	300-350 °F / 150-175 °C	PS, HIPS, SAN, & ABS

Endothermic

Grade	Carrier	Compatible w/
FCX 111263	PE	Polyolefins
FCX 111261	PE	Polyolefins

Usage Recommendations

Foam Molding with FCX Foaming Agent Masterbatches

1. Maximum foaming of a material should never exceed a 20% density reduction; 10-15% reductions are preferred. The recommended level of foaming agent is 2-5% FCX.
2. For a foamed part, a clamp requirement of approximately one ton/in² (14 N/mm²) is adequate.
3. Wall thickness for a foamed part should normally be 0.250 in (6 mm) thick with an absolute minimum of 0.187 in (5 mm).
4. The surface of a foamed part typically contains many swirls and flow lines compared to standard injection molding.
5. Injection speeds should be set as fast as possible so material entering the cavity is hot; running a hotter mold assists in the process. This way, the foaming agent expands and fills the cavity before solidification occurs. Such temperatures, plus internal pressure from the foaming agent, mean the part must cool long enough to form a rigid skin that is thick enough to resist deformation upon demolding. We recommend closed mold times of 2 to 3 times longer than standard molding.
6. Use low holding pressure and zero cushion.
7. A foamed part is generally more stress free and, therefore, less likely to distort or warp.
8. Shut-off nozzle is required.

Sink Control Molding with FCX Foaming Agent Masterbatches

1. Molding conditions and requirements are identical to normal injection molding parameters.
2. Shut-off nozzle is required.
3. To eliminate sinks, recommended using 0.5% FCX.
4. Press requirement is approximately 4 tons/in² (55 N/mm²).
5. Use low holding pressure and minimum cushion.

Mold Design Recommendations

1. Gate placement should be in a thin area.
2. Runner size should be 0.375 in x 0.250 in (10 mm x 6 mm) trapezoidal to allow as much flow as possible.

Troubleshooting

Troubleshooting procedures for foamable resins are much the same as for other thermoplastics. This table is presented as a quick reference guide. Only one solution to a given problem should be tried at any one time; never attempt to combine possible remedies.

Suggested Remedies Increase to improve Decrease to improve

MODIFICATION

P R O B L E M

Heavy Part

Post Blow

Elephant Skin

Short Shot

Flash

Warpage

Sinks

Voids

Slowing Speed

Poor Surface

Brittleness

Brown Streaks

Charred Areas

Part Sticking

Poor Weld Lines

Delamination

Increase to improve Decrease to improve Suggested Remedies

MODIFICATION

This information is intended to be used only as a guideline for designers and processors of modified thermoplastics for injection molding. Because injection mold design and processing is complex, a set solution will not solve all problems. Observation on a "trial and error" basis may be required to achieve desired results.