Polystyrene is one of the most widely used plastics. Expanded polystyrene, a thermoplastic, melts when heated and turns solid when cooled. It has excellent and lasting thermal insulation, unique cushioning and shock resistance, anti-aging and waterproofing, so it has been widely used in various fields such as construction, packaging, electrical and electronic products, ships, vehicles and aircraft manufacturing, decoration materials, and housing construction. widely used. More than 50% of them are electronic and electrical shock-absorbing packaging, fish boxes and agricultural products and other fresh-keeping packaging, which greatly facilitates our lives.
EPS steam forming – mainstream process in the industry
Usually the EPS molding process includes the following key steps: pre-foaming → curing → molding. Pre-flashing is to put the EPS beads into the barrel of the pre-flashing machine, and heat it with steam until it softens. The foaming agent (usually 4-7% pentane) stored in the EPS beads begins to boil and vaporize. The transformed pentane gas increases the pressure inside the EPS beads, causing them to expand in volume. Within the allowable foaming speed, the required foaming ratio or particle gram weight can be obtained by adjusting the pre-expansion temperature, steam pressure, feed amount, etc.
The newly formed foam particles are soft and inelastic due to the volatilization of the foaming agent and the condensation of the residual foaming agent, and the interior is in a vacuum state and is soft and inelastic. Therefore, there must be sufficient time for air to enter the micropores inside the foam particles to balance the internal and external pressures. At the same time, it allows the attached foam particles to dissipate the moisture and eliminate the static electricity naturally accumulated by the friction of the foam particles. This process is called curing, which generally takes about 4-6 hours. The pre-expanded and dried beads are transferred to the mold, and steam is added again to make the beads cohesive, and then cooled and demolded to obtain a foamed product.
It can be found from the above process that steam is an indispensable thermal energy source for EPS bead foam molding. But the heating of the steam and the cooling of the water tower are also the most important energy consumption and carbon emission links in the production process. Is there a more energy efficient alternative process for the fusion of particle foam without the use of steam?
Electromagnetic wave radio frequency melting, the Kurt Esa Group (hereinafter referred to as “Kurt”) from Germany gave their answer.
This revolutionary research and development technology differs from the traditional steam process, which uses radio waves for heating. Radio wave heating is a heating method that relies on the object to absorb radio wave energy and convert it into heat energy, so that the whole body heats up at the same time. The basis of its realization is the dielectric alternating field. Through the high-frequency reciprocating motion of the dipole molecules inside the heated body, “internal friction heat” is generated to increase the temperature of the heated material. Without any heat conduction process, the inside and outside of the material can be heated. Simultaneous heating and simultaneous heating, the heating speed is fast and uniform, and the heating purpose can be achieved only by a fraction or several tenths of the energy consumption of the traditional heating method. Therefore, this disruptive process is especially suitable for processing expanded beads with polar molecular structures. For the treatment of non-polar materials including EPS beads, it is only necessary to use appropriate additives.
Generally, polymers can be divided into polar polymers and non-polar polymers, but this classification method is relatively general and not easy to define. At present, polyolefins (polyethylene, polystyrene, etc.) are mainly called non-polar polymers, and polymers containing polar groups in the side chain are called polar polymers. In general, it can be judged according to the nature of the functional groups on the polymer, such as polymers with amide groups, nitrile groups, ester groups, halogens, etc. are polar, while polyethylene, polypropylene and polystyrene There are no polar groups on the equimolecular chain, so the polymer is also not polar.
That is to say, the forming process of electromagnetic wave radio frequency melting only needs electricity and air, and does not need to install a steam system or a water basin cooling tower device, which is simple and convenient, and saves energy and protects the environment. Compared with the production process using steam, it can save 90% of energy. By eliminating the need to use steam and water, using a Kurtz WAVE FOAMER can save 4 million liters of water per year, which is equivalent to the annual water consumption of a minimum of 6,000 people.
In addition to energy saving and environmental protection, electromagnetic wave radio frequency melting can also produce high-quality foam products. Only the use of electromagnetic waves in the frequency range can ensure the best melting and forming of foam particles. Usually, the stability requirements of the steam valve are very high using the traditional steam process, otherwise it will cause the product to shrink and be smaller than the predetermined size after cooling. Different from steam molding, the shrinkage rate of products produced by electromagnetic wave radio frequency melting molding is significantly reduced, the dimensional stability is significantly improved, and the steam absorption of the foam particles and the residual moisture and foaming agent in the mold caused by condensation are greatly reduced. A video, let’s experience it together!
In addition, the radio frequency melting technology greatly improves the recovery rate of foamed particle materials. Typically, the recycling of foam products is carried out either mechanically or chemically. Among them, the mechanical recycling method is to directly chop and melt the plastic, and then use it to prepare low-quality recycled materials, and the material properties are often inferior to the original polymer (Figure 1). The obtained small molecules are then used as raw materials to prepare new foam particles. Compared with the mechanical method, the stability of the new foam particles is improved, but the process has high energy consumption and low recovery rate.
Taking polyethylene plastic as an example, the decomposition temperature of this material needs to be above 600 °C, and the recovery rate of ethylene monomer is less than 10%. The EPS produced by the traditional steam process can recycle up to 20% of the material, while the EPS produced by the radio frequency fusion technology has a recycling rate of 70%, which perfectly fits the concept of “sustainable development”.
Currently Kurt’s project “Chemical-Free Recycling of EPS Materials by Radio Frequency Fusion Technology” has won the 2020 Bavarian Energy Prize. Every two years, Bavaria awards the award to outstanding achievers in the energy sector, and the Bavarian Energy Prize has become one of the highest awards in the energy sector. In this regard, Rainer Kurtz, CEO of Kurtz Ersa, said: “Since its establishment in 1971, Kurtz has continued to lead the development of the foam molding manufacturing industry, and has continued to develop sustainable processes to contribute to sustainable production in the world. Contribution. So far, Kurtz has developed a variety of industry-leading patented technologies. Among them, the Kurtz WAVE FOAMER – radio wave foam molding process technology, which is not only energy-saving and environmentally friendly, but also can produce high-quality foam, it has completely changed the Production of traditional foam products, creating a green future for sustainable foam processing”.
At present, Kurt’s radio wave foam molding technology has begun to mass-produce EPS foam products. In the future, Kurt plans to apply this technology to degradable materials and EPP materials. On the road of sustainable development, we will go further and further with our customers.
Post time: Jun-20-2022