Polyethylene (PE) and polypropylene (PP) foams are incredibly versatile materials that are used in different capacities throughout various industries. In construction the foams can be used for soundproofing, thermal insulation, and reflective thermal insulation. In the automotive industry they can be used to soundproof a vehicle's interior. In the food industry they are used in single use tableware. And one of the more widely popular applications for PE and PP foam is packaging. But no matter the application, foam manufacturers must always strive for quality, efficiency, and transparency, especially when supplying all-important foam products in regulated industries.
This article will provide insight into two of the most common quality issues in PE and PP Foam Manufacturing. These topics can significantly affect the quality of products, lead to the formation of defects and reduce the efficiency of your foam production.
Overheating During Mixing
As an example, during the production of a packaging profile excessive expansion leads to changes in profile geometry and poor fit with the issues getting worse in complex foamed profiles which demand highly accurate geometric dimensions with minimal tolerance for deviations. Market demand for precision in foam manufacturing is growing quickly and many manufacturers are confronted with fundamental limitations inherent in equipment design which limit their ability to compete for growth in complex profile designs. This same issue impacts pipe insulation manufacturers who suffer from products with changing internal diameter due to variation in wall expansion and ovality resulting in a failure to meet market requirements.
Two major issues contribute to these issues - first and most serious error is the failure to properly melt and homogenize leading to excessive expansion of gas. Secondly, overheating of the polymer/gas mixtures increases the migration of GMS to the foam surface, leading to additional diffusion of gas during the maturation of the foamed product. PE and PP foam requires time to degas excess isobutane and replace it with air. While there are many factors which can contribute to the rate of gas exchange including the thickness of the product, the density of the foam, the number of meters in a roll, the temperature and humidity of the environment and the air exchange in the storage facility - the greatest impact on the rate of gas exchange is the dosage of GMS. You can read more below about the advantages of FAP twin-screw counter-rotating extrusion to address these serious issues.
Enhanced Mixing of Process Additives
Twin screw extrusion is by far the most optimal process for foam production. The mechanical sheer and mixing capabilities of a twin-screw extruder far surpass those of a single screw extruder. FAP twin-screw counter-rotating extrusion machines achieve superior uniformity and consistency of the melt by grinding the material at the screw contact point, thereby avoiding melt backpressure as is common with single-screw extruders. These advantages have various positive effects throughout the mixing/melting process including:
Twin screw extrusion is by far the most optimal process for foam production. The mechanical sheer and mixing capabilities of a twin-screw extruder far surpass those of a single screw extruder. FAP twin-screw counter-rotating extrusion machines achieve superior uniformity and consistency of the melt by grinding the material at the screw contact point, thereby avoiding melt backpressure as is common with single-screw extruders. These advantages have various positive effects throughout the mixing/melting process including:
- Reduced friction during the melting stage, which leads to decreased surface tension of the melt. All of which has an enhanced effect on the characteristics of the foam material including optimal cell wall thickness and density, reduced % residual deformation in compression, and increased dynamic modulus of the elasticity of the polyethylene and polypropylene foams when under load.
- Significant improvements in the mixing of additives and other agents in the melt; anything from dye concentrates, nucleators, and sliding agents to flame retardants and others. Optimal mixing of these various additives and agents leads to reduced time spent in adjusting the recipe during foam production and decreases in technological waste.
- Improved cooling and stability of the foamed polymer’s behavior during degassing. This is achieved thanks to FAP’s counter-rotating technology, which ensures that the melt is kept in constant rotation in the barrel. These factors help avoid negative effects such as localized points of overheated polymer and the overexpansion or collapse of the finished foam material.
Improved Dispersion of Gas in the Melt
The mixing of the melt with gas is a key process in the manufacturing of non-crossed linked physically foamed polyethylene and polypropylene. The use of Inadequate extrusion machinery can lead to significant limitations in the production process and limitations in the thickness of the foam that can be produced. These issues primarily stem from inadequate pressure in the gas injection zone, which leads to back pressure in the extruder barrel and filter screen and results in the mentioned limitations.
FAP foam extrusion lines employ a twin-screw design with counter rotating action that allow for various advantages in gas dispersion. Such advantages include:
The mixing of the melt with gas is a key process in the manufacturing of non-crossed linked physically foamed polyethylene and polypropylene. The use of Inadequate extrusion machinery can lead to significant limitations in the production process and limitations in the thickness of the foam that can be produced. These issues primarily stem from inadequate pressure in the gas injection zone, which leads to back pressure in the extruder barrel and filter screen and results in the mentioned limitations.
FAP foam extrusion lines employ a twin-screw design with counter rotating action that allow for various advantages in gas dispersion. Such advantages include:
- Sufficient pressure to the gas inlet zone of the extruder, all while maintaining adequately low pressure at the die outlet of the extrusion head.
- Additionally, the unique design of the screws at the inlet zone create a stronger mixing effect and allow for changes in the flow direction of the melt, all of which enables the gas to be dispersed with greater uniformity, resulting in a more homogeneous fine cellular structure (Microcell Technology).
- All of these factors allow for the production of foamed polyethylene (PE) and polypropylene (PP) at critically high and sufficiently low pressures, with greater range of product thickness from 0.5mm to 25mm, and with a smooth low density foamed polyethylene and polypropylene without waves on the same extrusion line.
Advantages of FAP Twin Screw Counter-Rotating Foam Extruder
Advantages of FAP Twin Screw Counter-Rotating Foam Extruder
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