Batch Test Instructions
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. Northstar Polymer prohibits duplication of the contents of this web site for the purposes of public display and/or using on another web site without a written authorization by Northstar Polymers, LLC.
Test Batch Instructions
For Most of Microcellular Foam, Based on High Performance Polyurethane with Elevated Temperature Process
This is generic information for testing typical polyurethane microcellular foam materials. This document does not contain the mixing ratio or other specifics of the particular materials you may be using. Please see the separate information provided by Northstar Polymers for details on the specific formulation.
Recommended Processing:
We recommend testing small amounts to see how the material behaves, and then develop your casting method accordingly. When you batch, please be sure to operate in a well-ventilated area or large open area with a good air circulation, wear rubber gloves, long sleeves, and protective eyeglasses to avoid skin/eye contact. Read the enclosed Material Safety Data Sheet for details on the safety and handling.
Before you start your test, there is a chance the materials being frozen during the transportation when the whether is cool. This may cause separation of the constituents within the components. If in such case, you need to agitate the components in the cans. If MNA-014 arrives with some gel-like material in the container, it is likely the material has been exposed to some low temperature. In this case, heat the content to 140 – 160 °F and lightly stir (or roll the container) to re-blend the material in the container. You may use a drum mixer at medium speed for 15 to 20 minutes to agitate the material in a drum. After re-blending, keep it at a room temperature above 72 ºF. MNA-014 will not freeze at room temperature.
For small samples: Do not open the can for part-A until you are ready to use as it is a moisture sensitive material. Lightly shake the unopened can to agitate the content.
A type of compression molding method is required for this material in order to prevent a major shrinkage of the foam. When the foam is rising, it is expanded with heated carbon dioxide gas created from the chemical reaction within the material. Since this foam has a closed-cell structure, the gas is trapped in the cells. When this gas cools as the foam cools down, the volume of the gas decreases; each cell then shrinks down together as this happens. In a severe case of shrinkage, the entire foam shrinks down to like a prune.
To prevent this severe shrinkage, the foam requires internal out-word pressure when it is created. By pouring a higher volume of foam material into smaller closed mold space, the gas is created with an out-word pressure in each cell and it can balance against shrinkage when it is properly controlled. If your foam part shrinks after cooling down, this indicates that the internal pressure has not been enough when the foam is molded. To alleviate this, you can increase the amount of foam to increase the internal out-word pressure. The mold needs to enclose the material in order to withhold the expanding pressure of the foam.
The suggested small quantity test procedure follows:
Pre-heat the mold and substrate to between 110 and 120 ºF if needed.
Apply mold release into the mold if needed. Do not use silicone-base mold release as it destroys the foam surface.
Calculate the total inside volume of the mold (or the finished part volume) in cubic feet. Divide it by the free rise density. This will give you the weight in pounds of the component mixture at the free-rise density. Multiply by 1.1 for 10 % compression rate. (See below for compression molding). This will give you the total weight for the two components. Use the specific gravity data above to calculate the volume ratio if needed.
Take the correct ratio of part-A and part-B into a mixing cup. Mix very well with a steel or plastic stir-stick for at least 20 seconds. Agitate vigorously and thoroughly. Scrape the material off the side and bottom of the cup as you mix.
Cast the mixture into the mold and close the mold. The mold should be between 110 and 120 ºF. The material may not cure properly if mold is too cold.
Cure in the mold for the recommended demolding time before demolding. Check the strength of the foam surface before demolding. Using higher mold temperature (up to 180 ºF) can allow a faster demolding. Experiment to find the optimum de-molding time.
The foam cures at room temperature gradually for about 24 to 48 hours to yield the final physical properties that are good to be used in the application. Post-curing at 180 ºF would complete cure faster.
Compression Molding
Foam needs to fill the mold space by put slightly larger amount of foam into the mold. The expansion pressure of the foam sends the foam material to fill the mold as well as to keep it from shrinking. The mold therefore needs to be a close mold and has to have some capacity to retain the expansion pressure. The simplest mold will be just an open-top box with a lid. The lid then needs to be clamped to hold the pressure. The air trapped on the top side of the mold could make a large void if it is not released. For this purpose, you need to have small vent holes to let the trapped air escape from the mold.
The mold material can be metal, plastic, or elastomeric material. Mold surface needs to be slick as foam could stick to any porous surface. Metal molds tend to absorb the heat. Heat created from the chemical reaction is required for foam to cure. If mold is cold, this heat is absorbed and the foam does not cure properly. The mold needs to be heat to 100 to 120 ºF in case of metal molds if metal mold. If your mold is plastic or elastomeric mold, this may not be necessary as those materials retain heat better than metal molds.
Compression rate indicates how much more of component material is put into the mold. The rate indicates the percentage of excess amount of material to the amount in which to fill the mold using the foam’s free-rise density. Typically, about 10 % compression should give enough pressure to distribute the foam within the mold. However, you may need to increase the compression rate if your foam part shrinks after cooling. Using higher rate also makes the foam denser and stronger.
Shrinking problem for closed-cell microcellular foams and semi-rigid foams:
Polyurethane foam uses a chemical reaction within the components to create carbon dioxide as a source of foaming. Because the gas is hot when it is created, it contracts when the foam is cooled to the room temperature. Closed cell foam with flexibility can shrink together with this contracting gas as it cools. The compression molding method gives outward pressure to the gas in foam cells to compensate this shrinking force. If your foam shrinkage is too much, try increasing the compression rate to compensate. (This does not apply to open-cell foams and rigid foams.)
Fire-retardant Applications
This foam is not fire-retardant grade 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 and it may be regulated by laws. It is the user's responsibility to conform to the applicable regulations. We also do not recommend this foam to be used in 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 a 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. Contact Northstar Polymers for source information for fire retardant additives.
Storage and Handling Information:
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 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. When part-A component material is reacted with a large amount of water, it may create a violent chain reaction, which could even start fire. This material must be stored indoor where there is no chance of contact with a large amount of water.
Sometimes when the containers are opened many times during the storage, small amount of moisture comes into the container and start to react with the component. This contaminated (reacted) byproduct is usually heavier than the rest of the material. So, old material may have a settlement of this bi-product at the bottom of the container. This bi-product settlement is often thicker and cloudier. Do not mix-in this settlement. Avoid using the settlement at the bottom of an old container.
The storage temperature for both part-A and part-B should be at a room temperature between 68 and 90 ºF.
Generally, all constituents of the part-B material are compatible and stay blended in homogeneously. However, if the material is stored for a long time, some constituent may start to separate. It is a good practice to agitate the container before dispensing if you have stored the material for a long time. Avoid moisture and enfolding excess air when agitating.
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 handles these materials needs 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.
When conducting a test or producing your parts using this material, 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.
Possible Freezing:
When part-A material is exposed to a low temperature; the constituent material may freeze and separate within. During the cold seasons, the material may arrive frozen after traveling in a cold truck. If you see gelling within the material after the material has arrived, it is likely the material has been frozen. If the material has had a chance to be frozen, you need to thaw re-blend. Heat the container so that the content is about 140 °F, then agitate content gently to re-blend before dispensing any from the container. Part-B material has less chance of freezing or separation.
For any questions, please contact Northstar Polymers.
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Northstar Polymers, LLC
3444 Dight Avenue South
Minneapolis, MN 55406
Tel: 612.721.2911
E-Mail: info@northstarpolymers.com