New products (formulations) are borne because someone requested a specific product for a new application. This becomes a new product available to others but, since no two applications are identical, the new formula may not suit another application the way it worked in the original project. Thus the possible trade-offs.
We always "fine tune" our formulations to limit the number of trade offs that a customer has to live with while using a product. In most cases it is rather easy to modify an existing formulation (i.e. reduce the viscosity, lengthen or shorten the handling time etc.) to make a product much more suitable for the use at hand. The end result is more profit for the customer.
It is your choice, you can use an off the shelf product with many or a "fine tuned product" with few or no trade-offs.
Wax melts with the application of heat and can be poured into moulds and allowed to harden into various shapes. To change the shape of the wax, all one has to do is re-melt it and pour it into a mould with a different shape. Thermoplastic materials function in this manner inasmuch as they consist of independent molecules of various lengths, shapes and sizes. The size and shape of the molecules determine the melt temperature and the pressure required to shape the material. Thermoplastic materials can be formulated yield a wide variety of properties including impact resistance, chemical resistance and adhesive strengths. They are widely used in sealing cartons and a variety of highly sophisticated applications.
Once an egg is cooked, no amount of heat can re-melt it back to a liquid. The same applies to thermoset plastics. When thermoset plastics harden, they form cross linked bonds that make the plastic dimensionally stable. The process begins with a mixture of independent molecules consisting of a variety of shapes and sizes; however, unlike thermoplastics, the independent molecules react with each other to form an interconnected polymer network. Although the application of heat will generally cause the product to become softer, once cured, the system can not be re-melted or re-shaped. Because of this cross linking, thermoset plastics, like most epoxy and urethane compounds, have better dimensional stability, high temperature and chemical resistance, and in most cases better adhesive properties.
Both Thermoset and Thermoplastic materials have unique properties and are useful in a variety of applications. Which is best to use will be determined by the processing and performance requirements of the application at hand.
With the exception of a few specific types of hardeners, epoxy systems are relatively impervious to moisture. As a rule epoxy system are better for outdoor use and are more widely acceptable in electrical and high voltage electronic applications.
Because each application is unique, the type of chemistry recommended will be dependent on the properties required by the end use. In some cases either a urethane or an epoxy might be suitable.
Please contact us for specific recommendations.
PROPERTY |
EPOXY |
URETHANE |
Adhesion |
Excellent |
Very Good |
Abrasion Resistance |
Good |
Excellent |
Chemical Resistance |
Excellent |
Average |
Component Stress |
Poor |
Good |
Cost |
Variable |
Variable |
CTE (Coefficient of thermal expansion) |
Low |
Medium |
Elongation |
Low |
High |
Exotherm (heat generated during cure) |
Higher |
Medium |
Handling |
Good |
Good |
High Temperature Operation |
Good |
Poor |
Impact Resistance |
Good |
Excellent |
Low Temperature Operation |
Average |
Good |
Moisture Sensitivity (Prior to cure) |
Low |
High |
Thin Film Cure |
Slow |
Variable |
Tensile Strength |
High |
Medium |
Tear Strength |
N/A |
Good |
Thermal Cycling ability |
Very Good |
Very Good |
The above general comparisons are based on materials with similar filler contents. As always, material selection must be based on the requirements of the application under consideration. For example; a roller used in the printing industry would probably be better cast with polyurethane and a component required to operate under high temperature/humidity conditions would fare better cast in epoxy.
The following are some of the more important details to speed material selection:
Item |
Note |
Desired material type |
Epoxy or Polyurethane - Single Component or 2 Component. |
Processing conditions |
Manual or Automated (i.e. dispense equipment). |
Processing temperature |
The maximum temperature available or allowed. |
Amount of material used at a time |
The desired amount of product to be mixed or used at a time. |
Desired working time |
How long the mixed material has to stay pourable. |
Desired cure conditions |
Cure time and maximum cure temperature available. |
Performance requirements |
The desired performance requirements for the final part. |
Final test parameters |
The testing to determine the part suitability (i.e. thermal cycling etc.) |
Embedded components if any |
The type of components embedded in the casting, if any. |
Special requirements if known |
Hardness, flammability, electrical properties etc. |
Part operating conditions |
i.e. indoor, outdoor, temperature, humidity, solvent resistance etc.) |
Potential volume |
Total volume or volume per part and the number of planned parts. |
|
Influences the type of product, reaction speed and cost factors. |
Our aim is to recommend the correct material in the very first instance. Based on our experience, we will also provide suggestions and recommendations toward improving the planned process and how to avoid possible complications that could arise.
The following are the most common published properties where care must be exercised when comparing different materials:
Property |
Should also indicate |
Mixed Viscosity |
Temperature |
Pot Life |
Temperature |
Elongation % |
Temperature or ASTM D 638 |
Hardness |
Temperature or ASTM D 2240 |
Linear Shrinkage % |
in/in or ASTM D 2566 |
Flammability |
Specimen Thickness |
Dielectric Strength |
Specimen Thickness or ASTM D 149 |
Dielectric Constant |
Frequency, Temperature, Test method ( ASTM D 150) |
Dissipation Factor |
Frequency, Temperature, Test method ( ASTM D 150) |
Volume Resistivity |
Test Specimen, Temperature, Test Method ( ASTM D 257) |
The above properties will be different under alternate test conditions. It is best to contact the material supplier and obtain test data under the desired conditions to compare different products.
Products are approved under certain specific categories and the details can be viewed by clicking the following links: Crosslink UL Listed Plastic Components / Crosslink UL Listed Insulation Systems In addition to the formally recognized products, Crosslink Technology Inc. has a number of formulations that meet specific UL® and CSA® requirements but to date have not been formally approved. Depending on the application at hand, these products are likely to pass if formal approval is necessary.
Please contact us for details.
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The key material properties are:
- Mixed viscosity
- Reactivity
- Exotherm
- Shrinkage
- Thermal stability
- Thermal conductivity
- Thermal shock capabilities
- Thermal expansion properties
The above properties are especially important when casting electrical and electronic components.
The batch to batch shade consistency can be problematic with certain light colours such as light blue. This is especially true with products that contain fillers. The reason for this is that the minor amount of impurities, inherent in the ingredients of a given formulation, will have a major impact on the pigments.
A slight shade difference in the colour of the fillers will necessitate an adjustment to the pigment in order to achieve the required colour. This is not the case with most primary colours.
Elevated post cure temperatures will have less impact on solid primary colours. All systems that require post cure at elevated temperatures will develop a yellow tinge due to the applied heat. This slight yellow tinge is not as visible with primary pigments.
Polyurethanes also posses "elastomeric memory" which means that they can withstand considerable deflection (in tension or compression) without permanent deformation. The abrasion resistance of Urethanes is far superior to Epoxies.
In epoxy and polyurethane formulations Cycloaliphatic resins are considered most suited to continuous outdoor operation.
These products depend on one of the following to cure:
- The evaporation of a volatile component within the formulation.
- The application on Ultra Violet energy (UV cure).
- The presence of moisture in the surrounding air (Relative Humidity).
These materials are usually limited to a maximum thickness in their application.
Having said all this, if you still want to proceed, you have to have access to the following information in order to do the calculation:
- The type of system you are using (TDI or MDI)
- The Equivalent Weight of your Curative
- The NCO content of your pre-polymer
- The % Stoichiometry to yield the desired cured properties
Once you have all the above information, view the attached document which will provide the formula along with an example on how to calculate the ratio and optimize for the properties most important in your application.
Remember that fillers do not enter into the reaction and must not be included in any ratio calculation.
See Formula and Example