Comparative Form of Potting Compounds for LED Strips

impact of temperature on cure time

Table of Contents

The LED industry is witnessing strong growth. As a crucial part of the industry, the production of LED strips is rising at an exponential rate. The surface potting materials developed by the Company for the light strip market will also face unprecedented opportunities and challenges. In order to better compare the differences between the main potting materials on the market, and to make it more intuitive for customers to understand, our laboratory hereby compares and analyzes the characteristics of each potting material in the form of data as follows:

(Name of material)
\ (Main technical parameters)
Epoxy potting compoundsPU potting compoundsPU potting compoundsRemarks
AppearanceColorless and transparentColorless or light yellow and transparentColorless or light yellow and transparent
ComponentSingle-componentTwo-componentTwo-component
Component ratio4:1, 5:1, 1:11:1There are multiple ratios in terms of epoxy potting compounds and PU potting compounds on the market. The ratio adopted for the product in the experiment is 1:1
Viscosity4500 – 5000LS3000 – 4000LS3000 – 3500LS
Density (g/cm3)0.681.051.18The amount of PU potting compounds and epoxy potting compounds used for the same volume of light strips is much more than that of silicone potting compounds, and the same weight of silicone potting compounds can encapsulate more strips
Operating time at room temperature (with 200g adhesive)20min150min40minThe more epoxy potting compounds, the shorter the operating time, while there is no obvious change in terms of silicone potting compounds
Service conditionsNo special requirementsNo special requirementsRelative humidity: below 70%The higher the relative humidity, the lower the adhesion of the PU potting compounds to the substrate, while the situation is opposite for silicone potting compounds. However, both potting compounds will accelerate the curing as the humidity increases. When the relative humidity is over 85%, the operating time of the silicone potting compounds produced by the Company is only about 50min.
Human body’s reaction to adhesiveNo adverse reactionNo adverse reactionMost people suffer from red and swollen eyes, sore throat, skin allergies, etc.The extremely volatile free (toxic) monomers in the PU potting compounds will lead to adverse reactions of most people except for those with good physical quality, while this will not happen to silicone potting compounds.
Full cure time at room temperature (25°C)4-8hr24-28hr14-18hrThe lower the temperature, the longer the cure time of the epoxy potting compounds. Although heat curing can accelerate the cure, the yellowing time will also be accelerated. The silicone potting compounds are not sensitive to temperature.
Surface characteristics of colloid after full cureFlat and smooth, without aftertackFlat and smooth, without aftertackFlat but not smooth, with aftertack (after applying silicone oil, the aftertack is alleviated)The low molecular gas released during the cure of the PU potting compound will stay on the surface of the colloid for a certain period of time, preventing the adhesive from further reacting, thereby leading to the aftertack on the colloid surface. After applying a layer of silicone oil on the surface of the PU potting compounds the phenomenon can be improved
Available aging test time48hr48hr48hrThe time is the aging experiment time for this experiment
Characteristics of colloid at -35 °CNo obvious change 72hr laterCracked with foggy surface 6hr laterBecame brittle obviously and broke easily 24hr later
Characteristics of colloid at 120°CNo obvious change 72hr laterTurned yellow obviously and became deformed and softened 2hr laterTurned yellow slightly 12hr later
Characteristics of colloid at 180°CNo obvious change 72hr laterTurned brown, and part of it melted 20min laterTurned yellow, and became deformed and softened 2hr laterAt temperatures over 150°C, the PU potting compounds are easy to hydrolyze, their adhesion will become poor and they will be easily peeled off
Characteristics of colloid after 72hr of continuous lighting in seawaterNo obvious changeSerious fogging on the surfaceFogging on the surfaceThe water-proof and dust-proof level of silicone potting compounds produced by the Company can reach IP68
Luminous transmittance97.6%82.1%91.7%The data are the real-time test data after 72hr of cure at room temperature
Refractive index1.421.381.40The data are the real-time test data after 72hr of cure at room temperature
thermal conductivity coefficient (w/m.k)0.6610.0570.051
Shore Hardness (A)254739
Elongation197%155%290%
Breakdown voltage > 10000V > 15000V >8000V
Dielectric strength>27>27 >18
Dielectric constant3.23.82.8
Volume resistivity>10000000000 >12000000000 >8000000000
Peel strength to PCB board (KN/m)15.26.511.3
Surface tensionPoorGoodGoodThe silicone potting compounds have excessively low surface tension. When using them on a surface without a groove, drip twice to achieve better results

In addition to the above data, the following data figures are made to reflect the characteristics of each colloid more intuitively:

impact of storage time at room temperature on refractive index

Figure I Impact of storage time at room temperature on refractive index

Figure I shows that after one year of storage, the refractive index of silicone materials does not decrease obviously (that is, there is no yellowing phenomenon), but that of the epoxy resin decreases dramatically, indicating that the yellowing phenomenon is serious, and the luminous transmittance is less than 50% in half a year. On this occasion, it is basically necessary to replace the light strips. It can be seen that the service life of the light strips encapsulated with silicone materials is much longer than that of the light strips encapsulated with epoxy resins.

impact of temperature on cure time

Figure II Impact of temperature on cure time

It can be seen from Figure II that the cure time of silicone materials is significantly shorter than that of epoxy materials when cured at room temperatures (25-30°C). The higher the temperature, the faster the cure of epoxy resins, while silicone materials are not sensitive to temperature changes, indicating that silicone materials are more suitable for room temperature operation.

Additionally attached: The water resistance and anti-aging comparison photos of epoxy potting compounds and silicone potting compounds are as follows:

service conditions of epoxy potting compounds 2
service conditions of epoxy potting compounds #2

Figure I Service conditions of epoxy potting compounds

service conditions of silicone potting compounds
service conditions of silicone potting compounds #2

Figure II Service conditions of silicone potting compounds

This report mainly compares two potting compounds from technical parameters. It can be seen from the above specific data that the silicone potting compounds are weaker than PU potting compounds and epoxy potting compounds in mechanical strength (elongation at break), hardness, and surface tension, but far superior to them in environmental protection (human body’s reaction to adhesive), operability (operating time), weatherability (high and low temperature test, heat dissipation), waterproof (light up in seawater), cohesion (peeling force), and optical properties (luminous transmittance, refractive index); and environmental factors have a serious impact on the overall effect of PU potting compounds after curing; silicone potting compounds are not sensitive to environmental impacts, and the colloid after curing is more stable. It can be thereby proved that silicone potting compounds are more suitable for LED flexible strips.

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