Soft, hydrolysis and low-temperature resistant Polyurethane formulation with a low compression set. Polyurethane (PU) is a high-performance plastic which is suitable for various applications around the globe.
To suit those requirements on this resource, a PU-processor needs to know exactly, which system of PU works best with a certain application.
By varying the basic building blocks isocyanate, polyol and chain extenders or by including different additives, one can obtain a multitude of properties:
- Hard or soft plastic
- Mechanical strength (tearproof, abrasion-proof, cut resistance)
- Flexible or dampening
- Resistance to hydrolysis and resistance to solvents
- Dirt-repellent, antistatic and many more.
This is by far the most important strength of ASMA GmbH. We develop formulations of polyurethanes which are tailored to our customers needs in machine manufacturing and plant engineering and therefore deliver the best performance possible.
A special challenge was presented to us by a customer in the apparatus engineering business. He was looking for a 55 Shore A polyurethane formulation for ejector rollers that can be used around the world. These should be able to be installed in vending machines in tropical and subtropical climates (such as India) as well as in the alpine region. The compression set of the ejector rollers must be very low at both -25°C and +45°C. Furthermore, the swelling (increase in diameter due to moisture absorption) must be kept as low as possible. Both to ensure the function of the vending machine in all circumstances. However, the same ejector roller should always be able to be used for all devices.
It was precisely these extreme environmental influences that made it so difficult to find a suitable formulation.
Polyester-based formulations are generally excluded, as they tend to hydrolysis in tropical and subtropical climates (splitting back into the starting materials). Furthermore, they are only partially suitable for low-temperature use.
Polyether-based formulations, on the other hand, have a worse compression set and a higher moisture absorption.
In order to master this balancing act, various formulations have been developed and tested by us. For this purpose, test plates were manufactured, stored in the climate chamber at different temperatures and relative humidity Then the mechanical strength values, compression set, moisture absorption, etc. were determined. At the same time, the ejector rollers were tested in devices in close cooperation with the customer in his laboratory. After hard development work, this challenge was also mastered with a special polyether-based formulation with a special crosslinker. The developed system is hydrolysis-stable and has an excellent compression set over the temperature range from -25°C to +60°C and thus meets all customer requirements.
Polyurethane (PU) is a high-performance plastic which is suitable for various applications around the globe. To suit those requirements on this resource, a PU-processor needs to know exactly, which system of PU works best with a certain application.
Dipl.-Ing. (FH) Rainer Baumgartner
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AT WHAT TEMPERATURES CAN PUR BE USED?
Depending on the type, polyurethanes can be used in temperature ranges down to approx. minus 20°C. Below 0°C the elasticity modulus (E-modulus) increases (and seems to be harder). However, despite this heightened stiffness the material will not break. Bending tests have shown that even at low temperatures the deformability remains very high.
At low temperatures, the damping capacities of polyurethanes remain very high, as the material will warm up under the dynamic load and will therefore quickly leave the critical (low) temperature range.
The upper temperature limit for polyurethane products in long-term usage is around 80°C. Short term exposure (a few hours) to up to 130°C is tolerable. Special types (as for instance our „Asmaprene D“) are designed to withstand temperatures of up to 150°C depending on the application. In choosing the appropriate material, it is also important to consider the mechanical stress (which leads to additional heat generation within the material).
The above indications regarding temperature apply to dry conditions only; any other chemical influence (humidity, grease, acids, etc.) may substantially reduce the material’s resistance to temperature changes.