+++Viscoelastic Foam
Viscoelastic Foam
Northstar Polymers, LLC
3444 Dight Avenue So.
Minneapolis, MN 55406
Tel: 612.721.2911
Fax: 612.721.1009
E-Mail: info@northstarpolymers.com
Northstar Polymers, LLC is a member of Polyurethane Manufacturers Association.
Copy right reserved by Northstar Polymers, LLC 2000 - 2007.
Viscoelastic Foam Formulation
Viscoelastic foam has a very unique recovery property and very low compression deflection property. When the foam is compressed bay a hand, it can leave imprint of the hand, and then it slowly comes back to the original shape. Viscoelastic foam has been used in a variety of applications such as toys, pillows, mattresses, and many other unique applications. This formulation is composed of low freezing point components, and the foam remains soft at lower temperature range than some other viscoelastic class foams.
VEF-10
(Viscoelastic Open-cell Flexible Foam)
Components:
Part-A: MSA-018
Part-B: PPF-019
Mixing Ratio:
A: B = 1.000 : 3.300 by weight
A: B = 1.000 : 3.783 by volume
Processing Conditions
Component Temperature: Ambient
Mold Temperature: 100 - 120 °F
Mold Release: Non-silicone
Typical Compression Rate: 10%
Curing Pattern:
Pot-life: 40 seconds (pour within 30 seconds)
Demolding: 9 - 12 minutes
(The foam may need physical crushing to induce open-cell foam structure at 20 minutes point.)
Typical Foam Density: 10 pounds per cubic foot
(The density may change depending on the size of the part.)
This material can be cast into frame to make foam buns, or into a mold to make molded product. A compression mold may be used to mold this foam. The material should be tested at a small amount for the processability.
Trouble Shooting
- Shrinking Problem from Closed-Cell Structure
This material uses a chemical reaction within the formulation to create CO2 (carbon dioxide) gas as a source of foaming. This reaction happens when the material is hot, so this gas is hot when foam is made. As the foam cools after curing, CO2 gas also cools; as it cools, the volume of gas contracts. If the cells in the foam are closed, this CO2 gas take the whole foam down and shrink the foam significantly. It would look like a prune.
To alleviate this, you need to make an open-cell foam structure. At the specified mixing ratio, the foam should have open-cell structure when it is free-risen. However, by compression-molding, it increases the wall strength of the foam cells, and this may prevent the cell from opening. This often happens when the compression rate is too high. When this happens, the foam quality becomes “balloon-like” when you push the foam by hands soon after cured (40 to 60 minutes after pouring). If possible, you can crush this foam soon after it is cured, but while the foam is still worm. You may hear popping sounds from the foam as you crush. You can keep crushing until you hear no more popping sound. This will open the cell inside of foam and will prevent the large shrinking. If your parts are too thick, this may be difficult. You may need to adjust your processing parameters such as mixing ratio, compression rate, or mold temperature.
- Prevent Air Voids by Vent Holes
When you compression-mold a foam, you would trap the air inside of the mold in corners and it makes large voids. Sometimes, this is erroneously thought that there is not enough material in the mold. If you try to compensate this with increasing the compression rate, you may have the closed-cell-structure problem mentioned above.
You need to develop parameters for where in the mold the material should be placed, and how the mold should be positioned while foam is forming in the mold. This will determine where the air in the mold is pushed when the foam expands.
When you find the pattern for the air void(s), you would need to put very small holes to where the voids form so you can release the in-mold air. The vent holes should be small enough so that they will be closed when the air is pushed out by the expanding foam material and then the material closes the vent holds, so you will still have the internal pressure. After the part is demolded, you may need to machine off the small amount of material squeezing out from the vent holes.
- Inconsistent/Large Foam Cells
If you see many small voids in the foam, this may be because the material is cast in while the mixture is creaming and loosing its flow. You may be enclosing more air into the foam while the mixed liquid has a high viscosity. You may need to finish agitating sooner to avoid enclosing too much air.
Another possible cause is that the material may be touching the side wall before it is dropped to the proper position for the material to be placed in the mold. The material on the side wall starts to foam before the expanding foam from the bottom reaches there. The foam material stuck on the side wall blocks the passage, which can cause voids. Place the mold in such position that you can pour the material to the bottom without touching the side wall of the mold.
If you see inconsistent foam cells near the mold surface, your mold release may be affecting the quality. Try using different mold release. Silicone and a few other mold release constituents can affect the surface tension of foam material, which may destroy the cell structure. Also, if the mold temperature is too high, it would affect the cell structure near the mold surface. Try at lower mold temperature.
Other Information
Applications that requires fire-retardant property:
This foam is not fire-retardant foam, and it is not recommended for applications, which require or should be using fire-retardant grade materials. The applications such as automotive interior, building material, and components for some electronic parts often require fire-retardant grade materials by law. It is the user's responsibility to conform to the applicable regulations. We also do not recommend this foam to be used to the applications in which the foam can be exposed to high temperature or being near an ignition source.
By adding fire retardant additives, this foam may be modified to fire-retardant grade foam. The user must test the foam modified with the fire retardant additives for the fire-retardant property and the conformance to the applicable regulations.
Storage:
Part-A component (prepolymer) contains isocyanate component, which is very much sensitive to moisture. If it is left in air, part-A will react with atmospheric moisture and will be ruined. This reaction is non-reversible. Soon after opening a can and dispensing the content, nitrogen gas or negative-40-degree-due-point dry air needs to be injected to the can to blanket the material. Silica gel or calcium chloride desiccant filter should be installed to 55 gallon drum-vent for your drum feeding system. The storage temperature should be at a room temperature between 65 and 90 ºF.
Part-B component may be hygroscopic. If the material is exposed to ambient air, it may absorb moisture. Moisture contaminated part-B material may become source of degradation or excessive bubbles in the product. Avoid exposure of the material to air. Purging the empty space in the container with nitrogen gas or negative-40-degree-due-point dry air is also recommended to prevent moisture contamination of part-B as well. The storage temperature should be at a room temperature between 65 and 90 ºF.
Safety:
The component materials are industrial-grade chemicals. Please keep them in a secure place and prevent access from any unauthorized individual. The personnel who handle these materials need to read the Material Safety Data Sheet (MSDS) for detail information on safety and handling of the material. The MSDS for each component is sent with the shipment of the material.
Whenever using this material, please be sure to operate in a wide-open area with good air movement or in a well-ventilated area. Wear rubber gloves, long sleeves, and protective eyeglasses to prevent skin/eye contact of the material. When your operation involves heating or spraying of the material, we recommend, in addition to the above, installation of a proper ventilation system and using a half-face respirator recommended for the use to prevent inhalation of the fume.
Direct contact of polyurethane raw materials to skin/eye, as well as ingestion may lead to health problems. No eating or smoking should be permitted at the working area. The operator should wash hands well with soap and water after handling the materials. Please refer to the MSDS for each component for the detailed health information.
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Northstar Polymers, LLC
3444 Dight Avenue South
Minneapolis, MN 55406
Tel: 612.721.2911
Fax: 612.721.1009
E-Mail: info@northstarpolymers.com
Notice: All of the statements, recommendations, suggestions, and data concerning the subject material are based on our laboratory results, and although we believe the same to be reliable, we expressly do not represent, warrant, or guarantee the accuracy, completeness, or reliability of same, or the material or the results to be obtained from the use thereof, neither do we warrant that any such use, either alone or in combination with other materials, shall be free of the rightful claim of any third party by way of INFRINGEMENT or the like, and NORTHSTAR POLYMERS DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, OF MERCHANTABILITY and FITNESS FOR A PARTICULAR PURPOSE.