Polyurethane casting resins - hydrophobic casting compounds
Polyurethanes, also abbreviated as PUR or PU, are classified as plastics or synthetic resins. 2K polyurethane casting resins, which consist of a resin and a hardener, are commonly used to protect electronic components. These resins can be formulated as solid materials or foams, which can be open- or closed-cell. In the electronics industry, compact, highly hydrophobic polyurethanes are primarily used to protect components from moisture.
We are experts in polyurethane casting resins based on virgin oils. This raw material base makes our potting compounds highly water-repellent. We can customize the following properties: hardness (ranging from soft to hard), behavior (ranging from tough to brittle), viscosity (ranging from low to high), and curing time (ranging from very fast to slow).
We can also incorporate additional properties, such as flame retardancy, thermal conductivity, thermal insulation, and compressibility, into the resin. For instance, we can formulate hydrophilic polyurethane casting resins to improve adhesion to certain surfaces.
Our customers receive a casting resin customized for their specific application or one of our certified standard systems that have been proven effective over many years. Our casting resins protect millions of electronic components in the automotive industry, electronics manufacturing, and electrical installations.
Polyurethane casting resins - properties & product selection
Explore our product range of polyurethane casting resins for electronics potting. The overview provides you with technical information such as mixing viscosity, Shore hardness and mixing ratio. Use the filter to find products that meet your specific requirements such as flame retardance, low viscosity or transparency.
Product features
Mixed viscositiy (25°C; rot.; 1 s-1)
Hardness
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resin : hardener
Mixed viscositiy (25°C; rot.; 1 s-1)
Hardness
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Flame retardancy with polyurethane casting resins
Flame retardant concepts are reaching their limits, particularly with low-viscosity casting resins. Solid additives must be used in high concentrations, which can reduce flowability and, consequently, casting quality. Although liquid flame retardant additives, such as phosphoric acid esters (TCPP or TPP), improve processability, they can migrate unless firmly integrated into the polymer network. Additionally, there is growing regulatory relevance. TCPP was recently classified as H351 in 2024, and TPP is now listed as a substance of Very High Concern (SVHC).
Therefore, ISO-ELEKTRA focuses on future-oriented solutions.
ISO-PUR® A785 and ISO-CAST® A765-MIUL are polyurethane casting resins that achieve high flame retardancy classes without the use of flame retardants that migrate from critical substance groups. These resins combine regulatory safety, reliable fire protection, and stable processing properties, even in demanding applications with low layer thicknesses.
The requirement of flame protection for casting resins is continuously increasing, especially in electronics. Compact construction and low casting heights place high demands on materials and safety. By the targeted use of solid and liquid flame retardant additives, polyurethane casting resins can be formulated to be flame resistant and self-extinguishing.
Self-extinguishing properties are usually assessed in accordance with UL94 or rather DIN EN 60695-11-10, whereby a distinction is made not only between horizontal (HB) and vertical (V) test positions, but also between different layer thicknesses of the test specimen.
Typical tests are performed at thicknesses of 13, 6, 3, and 1.5 mm. The thinner the test specimen’s layer thickness, the more difficult it is to pass the test. For this reason, a UL94 classification is only meaningful when the layer thickness being tested is explicitly stated.
A UL94 V-0 rating at 1.5 mm is particularly demanding and highlights the material’s performance – a criterion that ISO-PUR® A785 meets.
Different applications with polyurethane
Fig. 1 Structure of a non-crosslinked polyurethane
We all use products containing polyurethane on daily basis. A large number of chemical raw materials, additives, fillers and other aggregates make it possible to realize a wide range of application profiles. PU cast resins can be found in the furniture industry in the form of mattresses or upholstery, as well as in vehicle interiors. They are also indispensable in the shoe industry, especially in shoe soles. In the building materials sector, polyethane casting resins can be found in a wide variety of applications, either in floor coatings or in insulation and assembly foams. In all industries the use of polyurethane protective coatings represents a very broad and elementary field of application.
Chemically, polyurethanes are made up of polyols and isocyanates (Fig. 1), whereby polymers with varying degrees of cross-linking are generally sought. In contrast to hotmelt adhesives, these are not thermoplastic. A large number of industrial polyols (polyether, polyester, polybutadiene, etc.) and isocyanates are available for the production of polyurethanes, allowing a wide variety of products and properties to be customized, so to speak.
Another important chemical reaction of the isocyanate group is its reaction with water, which releases carbon dioxide and an amine. For this reason, when casting polyurethanes, especially for solid components, care must be taken to work under moisture free conditions as far as possible in order to achieve an optimum, bubble-free result. The addition of water-adsorbing fillers, so-called zeolites, can absorb residual moisture from the raw materials used, which makes application easier.
CO2 formation is used specifically in the formation of foams (insulation foams, mattresses, shoe soles) and pre-existing bubbles reinforce this effect further.
Through the formation of amines, NCO-terminated prepolymers can also cure with atmospheric moisture, making 1-component systems for sealants and adhesives possible.
Fig. 2: Water - isocyanate reaction