I. Project Background and Customer Requirements

Target product Robot vacuum cleaner track (long-term exposure to water, high temperatures, and friction environments)
Core pain points ：

1. Material failure The original TPU track is prone to hydrolysis-induced discoloration and strength degradation, with a service life of less than 6 months.
2. Performance defect The TV70D-0D material exhibits severe deformation and insufficient tensile strength (<5 MPa). The TV90B material, on the other hand, is excessively hard (>95 Shore A) and has poor slip resistance, causing the robot to slip and jam.
3. Process requirements : Requires adaptation for 200℃ injection molding, with a yield rate exceeding 90%.

 

II. Material Selection and Problem Analysis

In the early stages of the project, the team tested three materials to meet the sweeping robot’s requirements for high-temperature resistance, hydrolysis resistance, and deformation resistance in its tracks:

1. TV70D-0D (Low-Hardness TPE) ：

Problem manifestation The customer reported severe dynamic deformation of the material, with a set-elongation strength of only 4.5 MPa (the requirement is ≥8 MPa). Under conditions involving frequent bending of the track, permanent deformation is likely to occur.

Root cause analysis The material has insufficient crosslinking, resulting in weak molecular chain resistance to creep and an inability to withstand long-term dynamic loads.

2. TV90B (High-hardness TPV) ：

Problem manifestation With a hardness as high as 95 Shore A, the track experiences insufficient friction with the ground (friction coefficient < 0.6), causing the robot to slip frequently during operation.

Root cause analysis Excessive hardness disrupts the material’s elastic modulus, preventing the surface’s microscopic texture from effectively “gripping” the ground and rendering the anti-slip function ineffective.

3. Original TPU material ：

Historical issues After prolonged exposure to the pool environment, the ester bonds in the TPU molecular chains undergo hydrolysis, causing discoloration and a reduction in strength of the tracks, resulting in a service life of less than six months.

Conclusion ：

• The TV70D-0D lacks sufficient strength, and the TV90B has poor slip resistance—neither can meet the functional requirements.
• The traditional TPU chemical structure is not hydrolysis-resistant and needs to be developed. New Dynamic Vulcanized Rubber (TPV) System It boasts weather resistance, mechanical strength, and process compatibility.

III. Development Plan and Key Technological Breakthroughs

1. Materials System Design

• Substrate Selection : Adopted Dynamically Vulcanized EPDM/PP Blending System By leveraging the saturated main-chain structure of EPDM, the risk of hydrolysis of TPU ester bonds is avoided while retaining the high-temperature resistance characteristic of TPV.
• Reinforcement and optimization ：
  • Add 15% nano-silicate to enhance the set tensile strength (from 5 MPa to 8 MPa).
  • Introducing a 0.3% graphene modifier to enhance wear resistance (wear rate reduced by 35%).

2. Performance-balanced design

• Hardness regulation Adjust the EPDM/PP ratio to precisely control the hardness at 88 Shore A, striking a balance between elasticity and rigidity and avoiding the issue of excessive hardness seen in TV90B.
• Anti-slip design ：
  • The surface design features micron-scale irregularities to enhance mechanical interlocking with the ground.
  • Adding a 2% silicone-modified additive increases the coefficient of friction in wet and slippery conditions to 0.8 (compared to only 0.6 for the original TPU).

3. Injection Molding Process Optimization

• Temperature adaptation At an injection molding temperature of 200℃, the melt index is 9 g/10 min (5 kg, 190℃), ensuring complete filling of thin-walled tracks.
• Mold improvement ：
  • Increase the density of cooling channels, shorten the molding cycle, and reduce deformation caused by internal stresses (deformation rate < 0.5%).
  • Using high-gloss mirror molds enhances the smoothness of the track surface and reduces dirt adhesion.

IV. Test Verification and Mass Production Performance

1. Key Performance Comparison

• Tensile strength at a fixed elongation Increased from 4.5 MPa to 8.0 MPa for the TV70D-0D, meeting dynamic load requirements;
• Hydrolysis resistance After undergoing a 1000-hour damp-heat aging test at 85℃/95% RH, the tensile strength retention rate exceeds 90% (compared to only 50% for the original TPU).
• Anti-slip performance The friction coefficient on slippery surfaces reaches 0.8, boosting the robot’s climbing performance by 30% and reducing the slip rate from 15% to below 3%.

2. Mass Production Results

• Improved yield The injection molding yield has increased from 75% for TV70D-0D to 95%, and production efficiency has improved by 25%.
• Cost optimization The material cost is 25% lower than that of imported TPU, resulting in annual savings of approximately 100,000 yuan in production costs.

3. Customer validation feedback

“ TV85B-JQRLD Black The issues of track deformation, slippage, and hydrolysis-induced discoloration have been completely resolved. In continuous tests simulating a one-year usage cycle, no failures occurred, and the new solution has fully replaced the original TPU approach.

 

V. Summary of Experience and Industry Insights

1. Technological breakthrough ：

Hydrolysis-resistant design: Replacing TPU with an EPDM/PP dynamically vulcanized system to circumvent the chemical vulnerability of ester bonds.

Performance-balancing logic: 88 ShoreA hardness + 8 MPa tensile strength, precisely matching dynamic load requirements with anti-slip needs.

2. Process innovation ：

High-gloss mold + silicone additive: synergistically enhance surface performance and reduce maintenance costs;

Nano-reinforcement + graphene modification: Achieving a dual breakthrough in strength and wear resistance.

3. Market value ：

Provide long-lasting weather-resistant solutions for high-humidity and high-temperature environments (such as smart cleaning devices and outdoor equipment).

Promote the substitution of domestically produced TPV materials for imported TPU to reduce supply-chain costs.