Weight reduction made easy!

Saving Resources – Minimizing Costs

In the ongoing discussion about the commonly referred to "Great Pacific Garbage Patch" or "Pacific Trash Vortex", not only the topic of eliminating plastic waste, but also of reducing weight in plastic packaging, has come into focus of the plastic processing industry. Environmentally conscious end users attach great importance to saving natural resources in plastics packaging. W. MÜLLER GmbH in Troisdorf, Germany has acted based on this changing awareness and introduced its innovative foam blow molding technology using only physical blowing agents.

As one of the renowned market leaders in the area of extrusion blow molding systems, we have developed new extrusion heads for the production of containers with up to 20% weight reduction. Regardless, if bottles are used for packaging of personal care products, household chemicals or pharmaceuticals, a reduced use of plastic leads to potential cost savings and is of interest, particularly for low margin products.

An additional cost saving potential for our customers is transportation: Freight cost of containers shipped over long distances or internationally, can be lowered because of a reduced weight. The newly developed foam technology for blow molded containers makes it possible to produce ecologically friendly plastic packaging solutions that offer cost saving aspects and provide a lighter, yet more solid container at the same time. Another positive result is the prospect of making plastics packaging more acceptable in daily life.

The new foam blow molding technology developed by W. MÜLLER is innovative and highly economical.

Contrary to earlier attempts to successfully foam blow mold containers, our process is based on existing, well established trilayer technology with a foamed middle layer, embedded between a thin natural inner layer and a colored outer layer. With such trilayer structure, mechanical properties are adjustable. Two thin cover layers combined with a foamed core provide high rigidity and a light weight at the same time.

In our system, the middle layer is foamed with nitrogen, a purely physical process. The advantage is that no chemical blowing agent is required. This environmentally friendly, non-additive solution complies with the prevailing food packaging laws.

Nitrogen is introduced into the extrusion head via an injection module. In our process nitrogen gas is kept in solution in the plastic melt until the parison exits from the dies, where a fine cellular structure is formed – an ideal method to control cell size and foam quality.

Unlike in other foam extrusion processes, gas is not introduced and dispersed in the extruder and is, therefore, independent of the extruder speed. The gas injection and dispersion takes place in the extrusion head. The mixer has its own drive to control the generation of the cellular structure. To support the formation of the cellular structure, natural talc powder is added as a nucleating agent. Only a small amount is necessary to build a fine cellular structure.

The existing extruder and the screw delivering the middle layer require no modifications. In addition to foam blow molding, our equipment can be used to produce trilayer structures without a foamed core. This is an additional benefit providing economic justification for our equipment.

Field Test

Example: 1 Liter bottleWithout foamWith foam
Gross weight91 g73 g
Net weight70 g60 g
Density solid / foamed0.958 g/cm30.774 g/cm3
Outer layerHDPE + colorHDPE + color
Middle layerHDPE + RegrindHDPE + Talc + Regrind
Inner layerHDPEHDPE
Cycle time22.5 s [1]20.0 s [1]
Blow time17.0 s [1]13.5 s [1]
Blow pressure6.0 bar2.5 bar
Head / Die temperature195°C / 180°C160°C / 150°C
Die / Mandrel diameter33 / 32 mm27 / 26.5 mm

[1]: Parameters set on WMB 2-100 blow molding machine in W.MÜLLER laboratory

In summary, the bottle with a foamed middle layer has a 14 % lower weight than a bottle without foam. Foamed bottles require less blow time and less cycle time; also blow pressure is reduced to prevent the cellular structure from collapsing. Nevertheless, the results are clear: Considerable weight savings and a consistently high rigidity in containers.

It should be noted that due to the reduced blow pressure, certain details in the mold, such as engravings or small radii cannot be replicated and must therefore be altered. These modifications are required especially in the neck area. However, snap-on caps have been proven to be generally unproblematic. Since the new foam blow molding technology is primarily considered for new products and new molds, these restrictions are not an obstacle in 80% of all cases.

The chart below shows top load and deflection of a 65 gram trilayer bottle with a foamed middle layer in comparison with a solid 70 gram bottle without foam, proving that the yield load of the lighter foamed bottle is equal, if not higher, than the solid bottle, even though deflection is slightly higher.

Economic savings potentials:

Even though the economic justification for our foam blow molding system depends on factors, such as project specific equipment costs, the potential for cost savings is unquestionable. One of the main advantages of our system is the fact that the gas injection and dispersion unit can, under certain conditions, be added to an existing trilayer extrusion head and extruder. Furthermore, our foam blow molding technology is license-free and patent rights do not need to be taken into consideration.

Example calculations have shown, that the additional costs for compressor, gas injector, flow control valve and dynamic mixer are only 25% higher than for conventional trilayer equipment. Customers that use only monolayer extrusion blow molding equipment should consider upgrading to trilayer technology, which has become well established throughout the blow molding industry, even without foam.

While reduced resin usage saves considerable amounts of money, the main feature for many of our customers to use the foam blow molding technology is the environmental aspect of saving resources. Melt temperatures, as well as extrusion die temperatures, are lower compared to a conventional extrusion blow molding process and contribute to energy savings. Also, in comparison with conventional extrusion blow molding, molds need to be cooled more intensely, because the heat conductivity of the foam layer is reduced. Inexpensive solutions can be the use of a chiller, or of molds with cooling channels in close proximity to the cavity wall.

Future outlook

Already our new, environmentally friendly foam blow molding technology has shown to provide significant cost and resource savings. The success story of W. MÜLLER GmbH, lasting for more than 40 years, will be continued with further developments in the field of foam blow molding.

Our approach to not use chemical blowing agents and additives for foaming and to apply techniques that do not interfere with any existing blow molding equipment our customers operate, has proven to be the right direction. This is clearly evident from the positive feedback received after the first successful sampling projects were completed for our customers. 

We are continuing our research and development with focus on special resins with different flow characteristics that may open even more opportunities for achieving finer cell structures. Parallel to this, we will continue developing our sequential foam blow molding technologies to place foam in different positions of hollow shapes, for example for the production of tubular conduits with reinforced sections.

Foamed Components

Left without foam, right with foam

Intensive development strategies are applied in many areas to manufacture plastic components with reduced material consumption, while still achieving, or even optimizing the required product properties. For instance, it is possible to create a honeycomb-like structure by integrating an expanded layer in the wall of the container. The benefits of this are felt not only by packaging manufacturers, but also by users in the automotive industry.

The following examples illustrate this:

  • Reduction of the actual product weight
  • Reduction of ventilation system noise caused by air flow
  • Enhancement of the insulation effects of packaging and car ventilation systems
  • Reduction of turbocharger pipe noise