Flexible Open-Cell Foam
formulation is particularly designed to make flexible but firm
open-cell foam by either hand-mixing or machine casting. This
material may be suitable for products that require some load bearing
property but need to be flexible. The firmness of this material is
similar to that of microcellular foams, but it is lighter than
microcellular foams. This material may also be suitable for some
bumper or vibration dampening parts.
The components are
liquid at room temperature. It has relatively long pot life (40 –
45 seconds) for a flexible foam material, so it is easier to handle
by a manual hand-mixing method. This material can be open-cast into
a slab for farther fabrication or molded in a compression mold. The
free-rise density of the foam is 8 pounds per cubic foot, and the
cell structure is open-cell.
component for this formulation is MDI, which is generally considered
safer than TDI. This formulation does not use auxiliary blowing agent such as Freon,
HCFC, CFC, or flammable hydrocarbon materials. Only normal
handling for typical industrial chemicals is required. Relatively
safe and easy handling and the physical properties of this foam
satisfy the requirements for a variety of custom applications.
Physical Properties of the Cured
Foam Density (Free Rise)
Tear Resistance (Die-C)
Tear Resistance (Sprit Tear)
Surface Hardness (Shore
35 - 40A (Open Top Skin)
22% (Open Top Skin)
above data is typical properties of the free-risen foam tested in
our generic test method. Compression-molded foam will have
different deflection property.
(Part-A) Curing Agent (Part-B)
Number: MSA-018 PLE-016
Mixing Ratio (Part-A) (Part-B)
Mold/Substrate 100 - 110 ºF
* The ideal
temperature for the mold and substrate is 100 - 110 ºF. However, if
you are using plastic mold, this may not be necessary. For all
metal molds, the temperature needs to be between 100 to 110 ºF.
20 – 25 seconds (for manual hand-mix)
Pot life (pour
within) 40 seconds
time 30 - 40 minutes
Complete Cure Cycle:
24 hours at room temperature
We recommend testing
small amounts to see how the material behaves, then develop your
processing method accordingly. When you process/test, please be
sure to operate in a well-ventilated area or large open area, wear
rubber gloves, long sleeves, and protective eyeglasses to avoid
skin/eye contact. Read the Material Safety Data Sheets for details
on the safety and handling of the component materials.
Before you start your test, there is a chance the part-A material
being frozen during the transportation or storage in cold seasons.
Freezing may cause phase separation within the components.
Indication of frozen material includes cloudy color, high-viscosity,
gel-consistency, or complete solid. In such case, you need to heat
the part-A component to 140 – 160 °F to thaw and agitate the content
by rolling the container(s). Do not open the container for part-A
(MSA-018) until you are ready to use as it is a moisture
sensitive material. Use metal or plastic spatula to agitate. Do
not use a wooden paint stick as it contains moisture which
contaminates the material. After agitating the component, remove
from the heat and keep it at a room temperature between 70 and 90
ºF. Storing the components at a higher temperature accelerate
deterioration of the quality.
Pre-heat the mold and substrate to between 100 and 110 ºF if
Apply mold release into the mold. Do not use silicone-base mold
release as it destroys the foam surface.
Calculate the total inside volume inside the mold (or the finished
part volume) in cubic feet. Multiply it by the density (8 in this
case). This will give you the weight of the component mixture at the
free-rise density in pounds. Multiply by 1.1 for 10 % compression
rate. (See below for more detailed information on compression
molding). This will give you the total weight for the two
Take the correct ratio of part-A and part-B into a mixing cup. Mix
well with a steel or plastic stir stick for 20 to 25 seconds.
Agitate vigorously and thoroughly. Scrape the material off the
side and bottom of the cup as you mix.
The pot life is
short, thus there is a limit to the quantity you can mix well by
hands. Employing a meter mixing/casting machine may be best for
your production if your part is large or your production quantity is
Cast the mixture into the mold. The mold should be between 100 and
110 ºF. You may use ambient temperature if you are using plastic
mold/substrate that does not absorb heat very much. If your mold is
of metal or other heat-absorbing material, the foam may not cure
properly under the room temperature. Excess heating also affects
the foam quality, so do not over heat.
Cure the foam in the mold for at least 35 - 40 minutes before
demolding. Please check the strength of the foam surface before
demolding. The surface of the foam may be fragile at this point.
The open top surface may still be tacky, but this is normal.
The foam should be open cell if you are simply open casting the
foam. However, if you modify mixing ratio or molding it in a
compression mold, the cells in the foam may not be sufficiently
opened. If the cells in the foam are not opened, this will lead to
substantial shrinkage after the foam is cooled. Compress the foam
with hands to test to see if the foam has an open-cell structure.
If it bounces back strongly like when you push a balloon as you
press farther, the foam cells are not opened. In this case, you may
need to adjust or tighten the control of your mixing ratio,
compression rate, temperature, or other processing parameters.
Even with open-cell structure, this foam shrinks slightly. Design
your mold accordingly if tighter dimensions are required.
Store at room temperature for 24 hours to complete the cure cycle
Foam needs to fill
the mold space by putting a controlled amount of foam material into
the mold. The controlled expansion pressure of the foam sends the
foam material to fill the mold to the expected shape. The mold
therefore needs to be close mold and has to have a capacity to
retain the internal pressure. A simplest compression mold will be
an open-top box with a lid. The lid needs to be clamped to hold the
pressure. The air trapped in the mold could make large voids if it
is not released. For this purpose, you need to have very small vent
holes to let the trapped air escape from the mold.
The mold material can
be metal, plastic, or elastomeric polymers. Mold surface needs to
be slick as foam could stick to any porous surface. Metal molds
tend to absorb the heat. The mold may need to be heat to 100 to 110
ºF in case of metal molds. If your mold is made of a plastic or
elastomeric material, such as silicone rubber, epoxy, and urethane,
this may not be necessary.
Compression rate is
the rate in which how much more material you would put in to create
the internal pressure. Typically, about 10 % compression should
give enough pressure to distribute the foam within the mold. Using
higher rate makes the foam denser and stronger. However, it will
increase the chance of closed-cell/shrinkage problem described
- 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
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.
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
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
Applications that requires
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
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.
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.
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.
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.
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
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.
questions, please contact Northstar Polymers.
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