Viscoelastic foams are materials characterized by their low resilience and slow recovery, which can be defined as the property of some materials to return to their original shape after being subjected to deformation or stress.
Resilience can be measured using a resilience meter, an instrument that tests the rebound of a steel ball dropped from a specific height onto a test specimen, in this case, the foam. The foam’s deformation and its recovery to its original state (shape) can be measured with a dynamometer. Both tests have well-established norms and parameters.
For comparison, low-resilience foams have a rebound value of less than 20% on the resilience meter, while conventional foams exceed 40%. The recovery time to the original state for conventional foams is considered immediate, whereas for viscoelastic foams, it is gradual and takes a few seconds.
Learn About Viscoelastic Foam Cylinder Production
For foam to exhibit viscoelastic characteristics, its internal viscosity at room temperature can be increased by reducing the difference between the room temperature and the glass transition temperature (Tg) of the foam’s soft segment. This slows the recovery rate. The desired glass transition temperature is generally influenced by the equivalent weight of the polyols used in the foam. Conventional flexible foam, based on a triol polyether with a molecular weight of 3000, typically has a Tg of around -50°C. By shifting the Tg above 0°C using polyols with lower equivalent weights combined with those of 3000 molecular weight, the foam’s recovery slows, and its resilience decreases while maintaining flexibility. However, increasing the overall Tg of the soft segment also tends to increase the foam’s stiffness.
The physical properties of low-resilience foams are highly sensitive to index variations. A wide range of foam hardness levels can be achieved, with indices ranging from 55 to 85.
These foams have found many specialized applications, such as in clothing, hospital mattresses, and packaging due to their soft feel and pressure point reduction when used to support loads. They also exhibit excellent sound and vibration damping properties.
Challenges in Producing Viscoelastic Foam Cylinders
Producers using a batch process, commonly known as “box” production, face challenges when creating viscoelastic foam cylinders due to the height required for these blocks and the viscoelastic properties that hinder lamination. The slow recovery to their original shape often causes defects and undesired forms in laminated foam. Although rectangular box molds dominate viscoelastic foam production for comfort layers in mattresses, producing foam rolls for quilting presents difficulties. These include interruptions in continuous production, requiring frequent operator intervention, which slows production and increases the likelihood of defects in quilting.
Amino Química’s Viscoelastic Foam for Cylinders
AMINO has developed a viscoelastic foam system for cylinders with outstanding results. This innovation was designed to help mattress manufacturers increase productivity on quilting machines when producing quilts with this type of foam. The viscoelastic characteristics of the foam are maintained, but the block remains uniform during handling, enabling the lamination of cylindrical blocks without the typical issues associated with viscoelastic foam.
The system developed by AMINO consists of a polyol (AMIPOL BCVE 2036) with special silicones and amines with delayed catalytic effects to allow for the full growth of blocks up to 220 cm in height. The isocyanate used is a mixture of MDIs (AMISO BCVE 1009), which helps create foam with the viscoelastic properties and firmness needed to keep the block uniform during curing, storage, and lamination. Production is recommended for molds with a maximum diameter of 1.80 meters.
Key Parameters of AMINO’s Viscoelastic System
Key Parameters of AMINO’s Viscoelastic System
- Foam Density: 30–33 Kg/m³
- Cream Time: 16–22 seconds
- Rise Time: 130–170 seconds
- Isocyanate/Polyol Ratio: 59/100
Below is Table I, showcasing the properties of cylindrical viscoelastic foam produced using AMINO’s system.
Table I – Properties of Viscoelastic Foam (Isocyanate/Polyol Ratio: 59/100)
Ratio: 59/100)
For additional details, contact AMINO to learn more about our solutions tailored for viscoelastic foam production.
