Lab / FAQ
The SAFOAM®/SAFTEC® family of endothermic chemical foaming agents are
designed to produce superior parts.
They are easy to use and provide the plastic
processor with new opportunities and applications. The answers to the most
commonly asked questions about SAFOAM®/SAFTEC® are given below. They are
based on our experience in the commercial use of SAFOAM®/SAFTEC® with
various customers.
General Information
1
What is the difference between endothermic and exothermic Chemical Foaming Agents (CFAs)?
Exothermic CFAs such as Azodicarbonamide (or 1,1-azobisformamide), 4,4- Oxybis (benzenesulfonyl hydrazide (OBSH), or 5-Phenyltetrazole (5-PT) release heat during decomposition and require care during handling and processing to avoid problems caused by overheating. Endothermic CFAs, such as SAFOAM®/SAFTEC®, need energy (i.e. they absorb heat) during decomposition resulting in improved processing properties such as:
• Extrusion speed
• Wider operating temperature
2
What makes SAFOAM®/SAFTEC® different from other endothermic CFAs?
Unlike the other endothermic CFAs, which are commonly a mixture of an acid
and sodium bicarbonate, SAFOAM®/SAFTEC® contains modified citric acid salts,
which are very tightly controlled on particle size and purity. This gives a predictable,
controlled gas release. SAFOAM®/SAFTEC® foaming agents are buffered, which
helps prevent corrosion due to acid or base reaction.
3
How does a controlled gas release help?
A controlled decomposition means that most of the gas is contained in the
polymer melt and does not escape at a rapid rate.
4
What are the effects of using a CFA at a high dosing level?
Using more CFAs than necessary for the desire effect is not only costly, but can
cause other problems (i.e. excessive surface splay, extended cycle time or post-blow
in injection molding). In extrusion, excessive CFA levels can cause sag or
dimensional control problems.
5
Which SAFOAM®/SAFTEC® should I use?
SAFOAM®/SAFTEC® are available as powders or concentrates. Most processors
prefer to use a concentrate for convenience. Refer to the PRODUCT SELECTION page
on this site for guidance in selecting a SAFOAM®/SAFTEC® product compatible
with your application or call Reedy International Corporation at (732-264-1777) for
recommendations.
6
How much SAFOAM®/SAFTEC® should I use?
Tables on the PRODUCT SELECTION page give guidelines for use of
SAFOAM®/SAFTEC®.
7
How do I get samples of SAFOAM®/SAFTEC® and technical assistance?
Contact Reedy International Corporation at (732) 264-1777. If you have a new or
challenging application, technical assistance can be provided on-site, if necessary.
Injection Molding
8
What causes sinks and splay?
Please click here for the IM SUGGESTION GUIDE in Adobe PDF format.
9
We have a warping problem caused by molded-in stress. Will SAFOAM®/SAFTEC® help relieve this?
Yes. The same technique used for sink marks can eliminate warp or molded-in
stress, and still allow good physical and appearance properties.
Structural Foam Molding (SFM)
10
We want to use SAFOAM®/SAFTEC® to produce SFM on our conventional
injection molding machines. What modifications are needed?
Several modifications are recommended if good, consistent quality parts are to be
produced:
1. A positive nozzle shut-off valve capable of providing a positive closure at cylinder
pressures in the range of 1,500-2,000 psi minimum. It can be hydraulic, pneumatic,
or spring actuated. Its purpose is to maintain pressure on the melt to prevent gas
escape, to stop 'drooling' of resin between shots, and to eliminate nozzle freeze-up.
2. A suck back is sometimes used to prevent 'drooling'.
3. Boosters to increase injection speed and an accumulator to increase capacity are
desirable modifications.
11
What clamp capacity is needed?
Clamp capacity is determined by the molding parameters since molded filling and
pressure profiles depend upon the molding process used. There is no need for the
high post-injection pressures used during cooling in solid parts. The mold needs
only to resist the relatively low pressure of the expanding gas as the part fills out. As
a guide, only about 10-20% of the clamp required for solid molding is needed for
SFM.
12
What other factors are important?
If the mold is not designed for SFM, then adequate venting must be provided.
Vents in the 0.005-0.010 inch (.127-.254 mm) range are used in SFM. Sprues,
runners and gates are usually generous in size in SFM.
13
We use the gas counter-pressure SFM process. Is SAFOAM®/SAFTEC® suitable for this?
Yes. Lower gas counter-pressures (40-60 psi) can be used. This is a positive
advantage over the high gas counter-pressures required by most other CFAs or
nitrogen.
14
We use the direct-gassed nitrogen low pressure SFM process. Should we use SAFOAM®/SAFTEC® ?
Yes. Low levels of SAFOAM®/SAFTEC® (.1 - .5% activity as a nucleant) will have
beneficial effects. These include better surface quality, fewer voids, and additional
weight reductions of up to 10%. SAFOAM®/SAFTEC® gas makes the nitrogen more
melt-soluble and smaller, more uniform cells are produced. This usually leads to
improved physical properties and shorter cycle times.
15
We currently use an exothermic CFA to produce SFM. Why should we change to SAFOAM®/SAFTEC® ?
Reduced cycle times (15 - 20%) mean higher output. Mold plate-out deposits are
eliminated. Faster de-gassing means faster post-finishing. The SAFOAM®/SAFTEC®
brochure lists several other advantages
Blow Molding
16
SAFOAM®/SAFTEC® be used in blow-molding?
Yes. Weight reductions of 5 - 15% have been achieved.
17
What SAFOAM®/SAFTEC® grade should be used and at what additive level?
Follow the guidelines given on the PRODUCT SELECTION page.
18
What blow-pressure is recommended?
Blow-pressure should be the minimum needed for part fill-out. It should not be
set so high as to compress the foam structure completely.
19
Are physical properties affected?
Yes. Impact strength is reduced by foaming, but stiffness normally is increased
compared to the unfoamed part.
20
What effect has SAFOAM®/SAFTEC® on fillers and pigments?
Any fillers or pigments present will produce extra nucleation which results in
finer cell structures. Because SAFOAM®/SAFTEC® has an opacifying effect, it may
be possible to use lower levels of pigments and opacifiers.
Rotational Molding
21
Can SAFOAM®/SAFTEC® be used to foam roto-molded parts?
Yes. SAFOAM®/SAFTEC® powders work well in roto-molding. The best results
are achieved by using SAFOAM®/SAFTEC® in combination with exothermic
foaming agents.
22
What special techniques are used to foam roto-molded parts?
The mold vent is plugged (or equipped with a pressure valve) to prevent escape
of the foaming gas during heating of the mold. The mold is filled with just enough
polymer and SAFOAM®/SAFTEC® to fill the mold (i.e., it is "short-shotted") and the
mold is heated.
After the mold is removed from the heat and prior to cooling, the vent plug is
removed or the pressure valve is opened. The gas now expands the melt to fill the
mold. The advantage of the pressure valve is that the mold can be pressurized prior
to heating and pressure is released in a controlled manner. This retards gas escape
and generally results in appearance improvements.