Thermal Insulation Coating for preventing energy loss in refrigerant pipes of EVs

An electric vehicle’s energy efficiency is important in terms of cruising range and sustainability, and this is the reason why overall thermal management is so crucial for EVs. The dissipation of heat to control the temperatures of heat sources such as motors, inverters, and batteries is a key issue for EVs; but equally important is thermal insulation of the entire vehicle, using generated heat effectively for air conditioning and other functions. It is well-known that the cruising range of EVs becomes shorter in the winter when the heater is used to warm a vehicle’s interior. Thermal insulation is therefore required even for refrigerant pipes that cool down heat sources to prevent the unintended release of heat leading to energy loss.

Insulation blankets were typically used to heat insulate pipes, but they were difficult to apply in small spaces and caused corrosion as they absorbed moisture. Existing heat insulation coatings with resin filled with hollow particles were also insufficient because of their high thermal conductivity, and because they did not form a thick-enough single-coat layer and had to be coated multiple times until sufficient thickness (thermal resistance) was achieved. This made existing coating materials inadequate as a replacement for conventional thermal insulation methods.

As a solution, Resonac proposes its Thermal Insulation Coating with excellent heat-insulating performance and increased single-coat dry film thickness. Resonac’s product achieves thermal conductivity of 0.03 W/(m･K) and a maximum single-coat dry film thickness of 2 mm. It requires only one coat to demonstrate superior thermal insulation performance compared with conventional materials, and the product is easy to use in small spaces and water-repellent and corrosion resistant as well.

Innovative Solution

Thermal Insulation Coating achieving superior thermal resistance with its nano-sized porous structure and high porosity

Thermal conductivity with conventional thermal insulation coatings was limited to the range of 0.05-0.10 W/(m･K), because the large pores in the insulation materials allowed convection to occur in the pores and contributed to heat transfer. Another issue was the low-density porous insulation compounds added to resin in high volumes and dispersed widely would cause the coating to crack easily. Also to prevent sagging the dry film thickness of a single coat could only be up to 0.5-1.0 mm. But Resonac’s Thermal Insulation Coating offers a porous structure with nanoscale pores (avg. 20 nm), smaller than the mean free path of air molecules (67 nm). With its high porosity (80-90%) and low solid density, the product achieves thermal conductivity of 0.03 W/(m･K). The product is also resistant to sagging with the components’ interactions displaying non-Newtonian behavior (viscosity lowers as the shear rate increases, and vice versa), and realizes a maximum dry film thickness of 2 mm when applied only once.

Thanks to these properties, Resonac’s product demonstrates higher single-coat thermal insulation performance than conventional materials. As the product also forms a thermal insulation film with a high concentration of hydrophobic elements, it offers high water repellency and corrosion resistance. As a hybrid material containing organic compounds, the coating is resistant to cracking even when force is applied and provides its flexibility.

Product Features

High thermal resistance (by a single coat) and excellent water repellency

Resonac’s product forms a thick coating with excellent thermal insulation performance and water repellency. A comparison was made with conventional commercially available thermal insulation coatings A and B and thermal insulation sheet C by calculating the single-coat thermal resistance (by applying the materials and the sheet only once) and measuring the contact angles of water on their surfaces.

As shown in the chart below, Resonac’s product displays greater single-coat thermal resistance and a larger contact angle than the conventional products. These results support the Resonac-developed coating’s excellent thermal insulation performance and water repellency.

Nearly double²⁾ the energy-saving effect compared with conventional materials

According to Resonac’s estimates, based on the conditions of a 100℃ heat source, 25℃ ambient temperature, and 2-mm-thick thermal insulation coating, the Resonac-developed product saves energy by 40% compared with the case with no thermal insulation, whereas conventional products showed a 21-28% energy-saving effect.

• 2) Comparison between commercial coating B and Resonac’s product.

• ※ The data shown are representative values that represent examples of the results of measurements, calculations, etc., and are not guaranteed values.

Update date: 9th August, 2023