Chemical Foaming Agents Benefits for Plastics Molding and Extruding
Bergen International’s Foamazol™ Chemical Foaming Agents (CFAs) can provide plastic processors with many cost saving and processing benefits. Just look for your process to find some of the benefits Foamazol™ chemical foaming agents can provide.
Injection Molding with CFAs
Conventional injection molding is a process whereby a molten polymer is injected into a mold to shape it into a final product. This process allows manufacturers to create the intricate molded parts we see today.
Foamazol™ chemical foaming agents (CFAs) are generally used to reduce weight and prevent the formation of sink marks, and are added to the traditional injection molding process like any other additive master batch.
By reducing the shot size and adding Foamazol™, these CFAs help fill the mold resulting in part weight reduction. Common weight reductions for foam molded parts are around 10%. However, it is not unheard of for part weight reductions of 20-25% to be obtained with proper design.
Foamazol™ CFAs allow for molders to increase shot speeds, reduce pack and hold pressures and times, as well as reduce clamp tonnage. These benefits combined result in reduced cycle times, which have been demonstrated as high as 30% with Bergen’s foaming agents.
Sink mark removal is another benefit provided by Foamazol™. One grade in particular, Foamazol™ 62, has been proven in certain cases to eliminate sink with a Class A surface.
Structural Foam Molding with CFAs
Structural foam molding is an injection molding process that uses low pressure plastic injection to form large parts.
A gas is introduced into the melt by Direct Injection or by a Chemical Foaming Agent. The gas remains dissolved in the melt while the melt is under pressure. As the melt is injected into the mold the pressure is reduced allowing the gas to expand the polymer.
Foamazol™ chemical foaming agents control the size and distribution of the cells or bubbles in the expanding melt.
Bergen has developed a special line of CFAs for nucleation of physical blowing agent gases, such as Nitrogen, used in structural foam molding.
One product in particular, Foamazol™ 61, is used to control the size, shape, and distribution of gas bubbles or cells in structural foam parts made from olefins like HDPE and PP.
Gas Counter Pressure and Co-Injection Molding with CFAs
Co-Injection injection molding, also known as sandwich molding, allows for the injection of two dissimilar plastics. One injection unit shoots a solid plastic, the other a plastic containing a chemical foaming agent. The solid plastic injection stage begins a split second before the foamed plastic stage causing the foamed plastic to move to the inside of the solid material. The end product displays a solid skin with a foamed core.
Gas counter-pressure molding is an injection molding process where the mold is pressurized with an inert gas. This pressure pushes the injected foam melt against the mold walls forming a hard, solid skin. The inert gas is then released from the mold allowing the foam to expand within the part.
Foamazol™ chemical foaming agents yield a good density reduction while maintaining a good surface appearance. Bergen International also offers products for both Gas Counter Pressure and Co-Injection Molding, when surface appearance is critical in molded part applications, but significant part weight reductions is also required.
These two processes allow for the gasses released by Foamazol™ to form cellular structures in the core of the part which is encapsulated by smooth skins. Products such as Foamazol™ 95, XO-230, and XO-330 are great choices when looking to foam ABS, Polycarbonate, and PPO respectively in gas counter pressure molding.
Rotational Molding with CFAs
Rotational molding usually consists of 4 main steps (Filling the Mold, Heating or Curing, Cooling Part, Removal). Generally, the plastic raw material is in the form of powder or fine granules. After being filled with the raw materials, the molds are moved inside an oven and either spun on two different axis or spun on one axis and rocked back and forth on the other.
As the mold rotates in the oven, the plastic material continues to tumble against the mold walls until it begins to flux or melt. As the plastic melts it sticks to the mold walls coating them to form the part. After the heating cycle, the mold is moved to a cooling station, and once sufficiently cooled the mold is opened and the part removed.
Whether the rotational molding process is a one step shot, or it employs drop box technology, Bergen International has a chemical foaming agent product that can provide many benefits including finer more uniform cells, smoother skins, lighter more buoyant parts, better insulating properties, and other benefits.
Bergen rotational molding products include:
XOP-341 chemical foaming agent powder that is used in both types of rotational molding processes yielding fine cellular structures, excellent foam expansion, and even smooth skins in single stage applications.
Foamazol™ 14 exothermic chemical foaming agent compound designed specifically for foamed rotational molding applications, and is used to create a middle or inside foamed layer for rotational molded multilayer parts. Once the skin layer has been established, Foamazol™ 14 is added (neat) via drop box or through the vent tube in a delayed or secondary charge to the mold. The micro beads will give the part a smooth and even foam layer due in part to this micro bead pellet form. This controlled decomposition helps uniformity of cell size and foam dispersion thus minimizing voids.
XO-491 endothermic chemical foaming agent compound designed specifically for foamed rotational molding applications. Supplied as white pellets, XO-491 is for use in conjunction with LDPE powder resin to produce a two layer part in one step.
Chemical Foam Extrusion with CFAs
During the chemical foam extrusion process plastic resin and chemical foaming agents are mixed and melted. Foamazol™ CFAs can be added to any extrusion process the same way that other additive master batches are.
When the foaming agent decomposes either CO2 and/or Nitrogen gasses are liberated resulting in an extrusion with a fine, uniform cellular structure. This yields reduced densities, often times upwards of 50%, of the extruded sheet or profile. The gasses that are generated also cause the polymer to expand as it exits the die, and often times the line speed will be increased to compensate. Increases of 25-30% in line speed are not unheard of with Foamazol™ compared to non-foamed extrusions.
Direct Gas Extrusion with CFAs
In direct gas extrusion gases such as nitrogen, carbon dioxide, pentane, butane, etc. are injected under high pressure directly into the polymer melt. Chemical foaming agents are used in this process to nucleate the foam, yielding a finer and more uniform cell structure from the expansion of the injected gas.
Whether your direct gas extrusion process uses tandem extrusion or a twin screw extruder, Bergen International’s line of nucleating agents provide excellent nucleation for gasses such as CO2, Nitrogen, Z2, Hydrocarbons, and others.
Products such as XO-256 and XO-423 provide fine, uniform cell structures in direct gas extrusion of olefins, while Foamazol™ 73S is used in direct gas extrusions involving styrene.
And if VOC’s are a concern, the gases evolved by Foamazol™ allow for reduced usage of the physical blowing agent gas. Hydrocarbon gas usage has been reduced by as much as 17% in some instances with Foamazol nucleating agents.
Cellular PVC and Wood-Plastics Composites Extrusion with CFAs
Today there is a tremendous amount of activity in wood plastics composites. Some processors are using wood and plastic while others are using wood, plastic, and foaming agents. This is a typical profile extrusion process; however, the high moisture content of wood flour must be addressed, and specific polymer/wood blends usually require specific foaming agent formulations.
Bergen International offers several different endo/exo blends, which have been proven to outperform in profile extrusions of cellular PVC and wood plastic composites.
The combination of the two provides the benefit of the high gas pressure and volume from the exothermic portion, while also eliminating profile distortion due to the controlled gas yields of the endothermic portion.
Foamed Wire and Cable Extrusion with CFAs
Typically, foaming agents are used in the manufacture of co-axial cable. These cables usually have a foamed polymer layer that is used for insulation. The foamed insulation layers must have a uniform cell structure.
Bergen products such as XO-163 and XO-107 are designed with fluoropolymer and olefin wire and cable applications in mind. These CFAs produce fine uniform cell structures in both foamed jacket and insulation applications.