In the U.S., almost 80 percent of polyethylene, the type of plastic used to make plastic bags, is produced from natural gas. This includes feedstock, process and transportation energy.
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.
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
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.
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.
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.
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.
How much SAFOAM®/SAFTEC® should I use?
Tables on the PRODUCT SELECTION page give guidelines for use of SAFOAM®/SAFTEC®.
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.
What causes sinks and splay?
Please click here for the IM SUGGESTION GUIDE in Adobe PDF format.
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.
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.
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.
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.
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.
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.
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
What SAFOAM®/SAFTEC® grade should be used and at what additive level?
Follow the guidelines given on the PRODUCT SELECTION page.
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.
Are physical properties affected?
Yes. Impact strength is reduced by foaming, but stiffness normally is increased compared to the unfoamed part.
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.
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.
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.