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Thermal management

Extrusion-molding resin for cooling line
in EV battery thermal management systems

The growing prevalence of water-cooled thermal-management systems in battery electric vehicles—and the essential role of cooling line

The BEVs that are rapidly becoming ubiquitous everywhere around the world typically rely on lithium-ion batteries, which require thermal-management systems to maintain operating temperatures in the range 0-45°C. In particular, in recent years the urgent need for higher battery capacities and shorter charging times has driven a steady increase in BEV voltages—and this, in turn, has spurred broader adoption of water-cooled thermal-management systems for their superior cooling efficiency. (Go here for details on “Materials for thermal management systems in battery electric vehicles"

The shift toward water-cooled thermal-management systems creates an increasingly crucial role for the cooling line responsible for delivering coolants to various cooling subsystems. 

Asahi Kasei is proud to offer two families of resin solutions for cooling line in EV water-cooled thermal-management systems: 
1.For multilayer pipes, a combination of XYRON™ modified PPE resins for inner layers and LEONA™ polyamide 612 resins for outer layers.
2. For monolayer pipes, LEONA™ polyamide 612 resins.

Suggestions for multilayer piping
Outer layer: Polyamide (PA) 612 resin | Inner layer: Modified PPE resin
LEONA™ XYRON™ combination of

For pipes of water-cooling systems in electric and fuel-cell vehicles (FCVs) operating below 135°C, we recommend a two-layer pipe structure consisting of an inner layer of XYRON™ modified PPE resin with an outer layer of LEONA™ PA612 resin. This combination, illustrated in the schematic diagram below, offers good bending properties, low elution, and long-life coolant (LLC) resistance.

Combination of inner layer modified PPE resin XYRON™ with excellent bending workability, low elution property, and LLC resistance / outer layer polyamide (PA) 612 resin LEONA™ Multilayer piping
Multilayer pipes: Inner layers of XYRON™ paired with outer layers of LEONA™

Combination of inner layer modified PPE resin XYRON™ / outer layer polyamide (PA) 612 resin LEONA™ Layer composition
Structure of multilayer pipes

Resin pipes with inner layers made from XYRON™ modified PPE resin offer the following advantages: 

  • Bending properties
    Minimal springback reduces processing time and cost. In addition, the reduced risk of interference with other components offers greater freedom in layout design. 
  • Low elution
    Low ion elution ensures minimal variation in the electrical conductivity of coolants. This reduces the risk of vehicle fires due to coolant leakage, and helps to reduce the frequency with which ion-exchange resins in FCVs must be replaced. 
  •  LLC resistance
    Inner layers offer the same superior LLC resistance provided by PP-based resin pipes.
  •  Pressure resistance
    Modified PPE resins offer excellent pressure resistance at high temperatures (80, 135°C), and enable pipes to be made with thinner walls to reduce weight. 

Also, pipes formed from an inner XYRON™ layer and an outer LEONA™ layer can be formed in a two-layer structure with no need for an adhesion layer, helping to reduce overall cost. 

The following table compares the performance of XYRON™/LEONA™ pipes (far left column) to pipes made from various other materials. 

Features of pipes made from various materials 
Features of pipes made from various materials 

Advantage 1: Bending properties

For components of vehicle cooling systems, whose layout must be carefully designed to satisfy stringent space requirements, good bending properties are essential. Here we compare the bending properties of multilayer pipes made from two pairs of materials: (1) an inner layer of XYRON™ modified PPE resin with an outer layer of LEONA™ PA612 resin, and (2) an inner layer of PP resin with an outer layer of PA612 resin. 

Whereas the PP/PA612 component exhibits significant deformation at high temperatures due to springback of the right-angle bend, the XYRON™/LEONA™ component exhibits a dramatic reduction in springback angle. This helps cut processing time and cost and minimizes risks of interference with other components, offering greater freedom in layout design. 

Comparison of bendability of XYRON™ / LEONA™ multilayer pipe
Comparison of bending properties of XYRON™/LEONA™ and PP/PA612 multilayer pipes. 

Advantage 2: Low elution

The electrically insulating or conducting properties of coolant liquids are a subject of growing concern in thermal-management systems for BEVs. Higher-conductivity coolants pose a greater risk of vehicle fires due to coolant leakage in BEVs, while in FCVs the voltage of the FC stack may lead to electrical breakdown of the entire cooling system. To preserve the insulating properties and electrical conductivity of coolants in BEVs and FCVs, the pipes conveying these coolants must be made from materials exhibiting low elution of various ionic species.

Here we compare the elution properties of the materials we recommend for resin pipes—XYRON™ modified PPE resins and LEONA™ PA612 resins—to those of commercially-available PA612, PA12, and PP resins. For each material, we immersed a material sample in purified water at 95°C and measured the total organic carbon (TOC) and conductivity due to eluted ions. As shown in the figure, the results of these tests confirmed that pipes with a XYRON™ inner layer exhibit dramatic reductions in both TOC and conductivity compared to PA612 and PA12. 
This promises reduced risk of vehicle fires due to coolant leakage and less frequent replacement of ion-exchange resins in FCVs. 

XYRON™ / LEONA™ multilayer pipe dissolution comparison
Comparison of elution properties of XYRON™/LEONA™ multilayer pipes and pipes made from conventional commercial resins. 

Further results of this comparison, and a discussion of the methods used to characterize pipe features, may be found in the following document. Please contact us to ask any questions or discuss any concerns regarding this material.

Asahi Kasei's recommendation for mono-layer pipesDevelopment grades of  Leona PA612 extrusion-molding resins 

For mono-layer pipes, Asahi Kasei recommends extrusion-molding grades of our LEONA™ PA612 resins.

PA612 offers multiple superior properties—including flexibility, hydrolysis resistance, thermal-aging resistance, and chemical resistance—that make it an excellent choice of material for coolant pipes. 
Asahi Kasei provides a full lineup of PA612 extrusion-molding resins with various elastic moduli, offering an excellent balance of cost and performance. 

PA612 resin LEONA™ Developed material for extrusion molding Single layer piping
Mono-layer pipes: Development grades of LEONA™ PA612 extrusion-molding resins 

Physical properties table of PA612 resin LEONA™ developed material for extrusion molding
Material properties of development grades of LEONA™ PA612 extrusion molding resins

Note: The values in this table are typical values obtained by established test methods, and are not guaranteed. This information is provided for reference to assist in identifying suitable material grades for specific applications. Values may change due to improvements in material properties. Physical properties of mass-produced products may differ from those of prototypes or product samples.

Further information, and a discussion of procedures and results for characterization of practical pipe performance, may be found in the following document. Please contact us to ask any questions or discuss any concerns regarding this material. 

Technical support

Asahi Kasei's testing and characterization capabilities

Asahi Kasei offers a range of capabilities—from material characterization to practical evaluation of component performance—to help meet the development needs of our customers.

In particular, the testing and characterization capabilities we can offer include the following: 

  • Extrusion molding of pipes (two-layer straight pipes or three-layer Colgate pipes) 
  • Tensile testing of pipe shapes 
  • Burst pressure testing 
  • Electrical conductivity measurement 
  • Ion elution testing 
  • Testing of durability under LLC (long-life coolant) immersion
  • Testing of thermal aging resistance
Characterization and testing image 

Other themes

Related information

LEONA™ polyamide resin

LEONA™ has excellent heat resistance, strength and toughness, insulation, and oil resistance. It is widely used in automotive parts, electrical and electronic parts.

XYRON™ m-PPE resin

XYRON™ has excellent flame retardancy, electrical properties, dimensional stability, and water resistance. It is used in photovoltaics (PV), batteries, and 5G communication components.