Room-Temp Processing Info
May room-temperature-curable polyurethane casting materials have lower viscosity and slower pot-life (open time) to release major bubbles from the liquid. However, with hand mixing, you cannot completely avoid bubbles. If it is necessary to eliminate bubbles, you can vacuum the blended material in a cup or the mold into a vacuum chamber to degas.
For your production, using an airless mixing/dispensing machine will allow you to produce bubble free products.
9. Cleaning agent
This is for cleaning the tools. You can use MEK, DBE, acetone, n-pyloridone, isopropanol, or other industrial solvents. Mineral spirit or paint thinner does not work well with this material. Please consult your supplier for the safety and handling of the solvent or cleaning agents.
10. Paper Towels
For cleaning. If you use cloth towel or rag, expect you cannot re-use. Cured polyurethane does not come off by washing. Follow your local rules when disposing.
11. Nitrogen gas
When you are done with mixing, the part-A material needs to be blanketed with nitrogen gas and the lid has to be closed tight for storage. Praxair 800-772-9247 can provide you information on how to obtain nitrogen gas supply.
The part-A has chemical called isocyanate, which is highly reactive to water/moisture. It is so reactive that it reacts to any form of water including the moisture in the air very quickly. If you leave this material out, it will react with the moisture in the air, which will spoil the material. When part-A is reacted with moisture in the air, it will loose isocyanate content and will not cure properly. In a worse case, it hardens itself and will be deposited at the bottom of the container or make a skin on top. Nitrogen gas will not react to isocyanate, so it will keep the quality for longer time.
Minus 40 ºF ( - 40 ºC) dewpoint dry air can also be used instead to blanket the components.
If you are using the entire content of part-A at a one time only or using it up in very short time, you may not have to use nitrogen gas.
All materials and tooling should be in room temperature (about 70-100 ºF), when you do not need to heat the material.
1. Heat the material (100 to 180 ºF), if needed. Consult Northstar Polymers for the appropriate temperature range.
2. Prepare the mold. Apply the mold release lightly. Be sure to dry the solvent (if needed).
3. Calculate the correct amounts of each part-A and part-B material.
4. Open the can of part-A or B, pour the necessary amount into the container as you weigh. It is a good idea to pour thicker (higher viscosity) material first. If the viscosity is the same, pour part-A or B whichever the smaller ratio component first. (The order of part-A and part-B to be poured into the mixing container is not critical. Pour whichever is more convenient first.)
5. Open the can of the other component, pour into the container as you weigh necessary amount.
6. Close the cans. When you close the can of part-A, be sure to blanket the material with nitrogen gas and close the lid tight.
This part-B material is not as much moisture sensitive as part-A, so no need to blanket with nitrogen gas. However, it is a good idea to close the lid tight to avoid moisture and other contamination, when you store.
7. *** omitted
When mixing by hands, use a stir-stick and agitate it vigorously, but try not to fold in air. Scrape the side and bottom of the mixing container as you agitate. If you do not heat thicker component, it may take a longer time to mix. Mix carefully so the components are mixed homogeneously.
If the material is less than a half gallon, mix at least one to two minutes. Even if the material appears to be mixed, they are often not enough. Thorough mixing is very important.
If you use a hand-held powered mixer, mix at a lower speed. High speed can fold the air into the material. Also, scrape the side and bottom of the container for thorough mixing even with a powered mixer.
9. Place the container in a vacuum chamber (Option)
Put 29" Hg of vacuum until you see most of the bubbles are gone. If your vacuum does not reach 29" Hg, it can take longer time to degas. Do not leave the material too long in the vacuum as it many start quick reaction.
10. Pour it in the mold
If the part is small, you can pour in one paddle. If you pour bigger parts, avoid pouring layers; pour straight from one end to the other and try not to come back. If you are pouring a flat part with different depth, pour the deeper end first and move to the shallower end.
For your information, the time between you mix the part-A and part-B and the time the material becomes too thick to pour is called "pot life". The typical pot life of this type material is about 8 to 25 minutes. Curing time pattern can be controlled by catalyst level. Consult us for your specific curing time requirements.
11. Clean up the tools with isopropanol and paper towels
Curing is the process that the components of polyurethane react to each other and harden. First they are both liquid. Then the mixture becomes thicker. It will be too hard to pour as liquid, it will be a gel that is do not move itself, and finally becomes solid.
Observe the change in hardness of the material. It will be useful later to know the shortest time you can demold without damaging the part. For testing, cure over night before de-mold.
The material hardens gradually and it becomes solid. De-molding time of parts differs depending on the formulation as well as the part sizes, curing pattern of the material, and complexity of the part. Heating (up to 180 ºF) will accelerate curing and ensure the part integrity when demolding.
When you are evaluating the mechanical properties of the material for your specific application, please conduct at least for 3 days as it gets the final hardness. This material continuously hardens for several days until it comes to the final hardness. If you need to conduct physical test sooner, you can post cure at 180 ºF for 12 to 16 hours and cool to room temperature.
Cold tooling (molds, frame, or model) could hinder the curing process of polyurethane. If you are using steel or other metal for mold or tooling, especially in wintertime, you may need to warm up the tooling at around 100 to 120 ºF. Do not heat it too hot (exceeding 180 ºF) as it could affect the quality of urethane. When you are using a natural stone for mold, the same situation may be.
Heating up the material would help curing; however, it also shortens the pot life.
At overnight de-molding, the material may be solid but still soft. Pull away from the mold slowly and carefully. It may be difficult to demold, if you have not put enough mold release.
The time between when you mix and the material becomes hard enough to demold is called "demolding Time". Demolding time can also be controlled by level of catalyst.
The curing pattern varies depending on the formulation, catalyst level, and temperature. Consult Northstar Polymers for information on curing pattern of the particular formulation.
Modification of the system
Curing Pattern (Catalyst Modification)
The cure pattern can be modified. We can change pot life, demolding time, and complete cure time; however they are all related. Shorter one element gets, also shorter the other elements to be. We can control it by modifying the formulation to accommodate your production requirement.
You can use polyurethane grade colorants/pigments to add colors to the material. Particulate dispersion type colorants are commonly used with this type of polyurethane casting materials. They are typically dispersed into polypropylene glycol ether. We recommend using colorant paste dispersed in polypropylene glycol ether of above 3000 molecular weigh. You can add this type of colorant at concentration of 0.1% to 2 % of the total weight without having major concern of the effect to the properties of polyurethane materials.
You can obtain those colorants from the distributors of the following manufacturer:
Plasticolors: http://www.plasticolors.com/ (440) 997-5137
Fillers can be added to obtain certain properties. However, addition of solid filler would deplete strength of the polyurethane material. Also, microscopic surfaces of the filler would introduce a large amount of air into the polyurethane, and will cause bubbles to form. If the bubbles are a concern, degassing by vacuum is needed. In general, fillers cannot contain moisture as polyurethane components react with moisture and will have adverse effects. High moisture filler materials such as wood powder, pulp, cannot be used. Commonly used fillers are dry clay, silica granule, wollastnite, milled glass, and microsphere glass bubbles. Low moisture calcium carbonate (lime stone powder) may be used at lower concentration with vacuum. Fumed silica is often used to develop thixotropic effect to the liquid material.
Other modifications including adding colorant, UV absorbing agent, anti-bacteria agent, and other additives as well as change in mixing ratio are also available. Northstar Polymers customizes the formulations for each customer.
Some materials are sensitive to cold weather. If the material has been in a cold temperature during the shipping etc., separation within the material could occur. If you see crystallization or gelatin of the component, use a drum heater, or put the container into an oven and heat it to 160-180 ºF, then agitate the material before use to ensure homogeneous re-mixing. Generally, part-A materials are more sensitive to cold weather.
In cold weather, cold toolings (molds, frame, or model) could hinder the curing process of polyurethane.
In hot weather, condensation of moisture could cause a problem. If you store the material in cooler place then bring it to hotter/humid place just before the operation, the material itself and the container could create dew on the surface, which causes bubbling problem. Be sure to leave the materials and toolings in the temperature that is what you are going to operate. If the work place is very humid, it could also cause a problem related to moisture contamination.
Handling Information for the Component Materials
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 80 ºF.
Part-B component is 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; however most of the cases, keeping in an airtight container will be sufficient. Store it in a dry indoor storage at a room temperature between 65 and 80 ºF. The moisture contamination of part-B material is reversible. By heating material to 160 - 180 ºF and vacuuming it at about 29" Hg negative pressure for several hours will reduce the moisture level.
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 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/or using an appropriate type of respirator 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 and follow the other procedures of the Standard Industrial Hygiene Practices. Please refer to the MSDS for each component for the detailed health information.
Person with isocyanate hypersensitivity
In normal operations, this material should have MDI in vapor under the threshold limit value of 0.02 ppm. However, an individual who has been sensitized by an isocyanate (TDI/MDI/IPDI etc.) may have hypersensitivity reactions such as irritation of the eyes and respiratory tract (similar to asthma-like responses) even under this threshold value. To minimize the risk due to the exposure to the materials containing an isocyanate, operate under well-ventilated condition (dynamic ventilation), wear protective cloths and gloves should be worn. A half-faced respirator can also be used for extra protection.
For any questions, please contact Northstar Polymers.
Northstar Polymers, LLC
3444 Dight Avenue South
Minneapolis, MN 55406
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.