In most cases, the short answer is YES. Unfortunately, in most cases, since no two applications are alike, it is not often that a "standard" off the shelf product will be best suited for a specific project. Although standard Epoxy or Urethane products will work, chances are that there will be a significant number of trade-offs involved in the use and implementation.
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.
To describe the difference, one can use the simple analogy of reshaping wax and cooking an egg.
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.
It depends on the application. Epoxies excel in certain applications while Urethanes are better in others. Epoxies tend to be better performers outdoors while urethanes have much better abrasion resistance and elongation properties. In terms of processing and safety precautions there are some slight differences. The general hygiene recommendations are basically the same for both product types but urethanes are significantly more moisture sensitive and therefore require extra precautions in storage and dispensing, especially in high humidity environments. All containers, components to be embedded and substrates to be adhered to must be free of moisture for best performance.
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.
Although in many applications Epoxy and Urethane compounds can be used interchangeably, they each have specific unique characteristics which make each type of product more suitable in certain applications.
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.
|
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 more thorough and complete the information provided the more likely it is that the correct material will be recommended for the process at hand. First and foremost, it is important to provide a general description of what is to be done, how it is to be done and the desired end result sought. Beyond this, it is wise to provide as many known details as possible in order to assist in narrowing the search.
The following are some of the more important details to speed material selection:
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.
|
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. |
It is extremely important to carefully consider the test conditions under which the data was generated. Due to the lack of uniform standards in the formulating industry, there is no guarantee that the materials being compared were tested under identical conditions to obtain the published properties. Furthermore, some test results are totally meaningless unless the test conditions are also stated. For example; the dielectric strength is expressed in volts/mil over a specified specimen thickness. This figure is meaningless unless the thickness of the specimen is known because various thicknesses will yield different figures for the same product.
The following are the most common published properties where care must be exercised when comparing different materials:
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.
|
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) |
Crosslink Technology Inc. has several products that are recognized by the Underwriters Laboratories Inc. as well as the Canadian Standards Association (CSA). A summary of these products are found at UL Rated Products on this web site.
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.
Significant amounts of time can be saved by prior preparation, not to mention the possible incomplete or erroneous test results that can cause having to repeat the whole process over again to assure product suitability. The object of the exercise is to approve the product in the current or planned processing environment. This will ensure that the final transition will be smooth and trouble free.
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There are a number of considerations for selecting the best material to provide a solid, bubble free, crack free, functional and cosmetically pleasing casting.
The key material properties are:
- Mixed viscosity
- Reactivity
- Exotherm
- Shrinkage
- Thermal stability
- Thermal conductivity
- Thermal shock capabilities
- Thermal expansion properties
Most primary colours are available as well as most standard or traditional pigments. Specialty colours or requests for colour matching would have to be considered on an individual basis.
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 have a much wider hardness range from 5 Shore A up to 85 Shore D, whereas the useful hardness range for epoxies would be from 40D to 90D. Urethanes tend to be less brittle and have higher tensile elongation than other materials with similar hardness.
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.
Epoxy advantages are physical strength, high temperature resistance and excellent adhesion to most substrates. Urethane advantages are low temperature performance, low exotherm and faster cure speeds.
All Epoxy and Polyurethane compounds are good general purpose adhesives. Since the overall bond strength is dependent on the type of substrates to be bonded, the surface preparation and the thickness of the bond line, it is best to use products that have been formulated specifically for adhesive applications.
A component that is partially or totally exposed to the elements during its service life must contain epoxy or urethane products that are suitable for outdoor use. On the other hand, components that operate outdoors but are covered from direct exposure to the elements need not be manufactured using outdoor materials.
In epoxy and polyurethane formulations Cycloaliphatic resins are considered most suited to continuous outdoor operation.
There are certain single component epoxy and urethane products that can be cured at room temperature.
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).
The short answer is yes, but you should not deviate from the mix ratio specified by your supplier. Changing the mix ratio will have a major impact on the cured properties of your system and, if taken to extremes, your product may not cure at all.
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
