Transparent water-based polyurethane dispersions (PUDs) have evolved in automotive interiors from traditional protective coatings into multifunctional material solutions combining environmental performance, appearance, tactile comfort and intelligent interaction. RELANET Automotive Material has developed a transparent water-based PUD platform to offer automakers another option. The following sections describe the characteristics of R-5610.
1. Product performance characteristics
- 1. Outstanding transparency and optical clarity
Transparency is one of the most important advantages of R-5610 in automotive interiors. The source manuscript reports light transmission above 90% (Figure 1). Aliphatic water-based polyurethane synthesized from aliphatic isocyanates such as HDI or IPDI can provide yellowing resistance, weatherability and high transparency. Whereas an aromatic polyurethane may show clear yellowing after three to six months of outdoor exposure, an aliphatic PUD can retain color for one to three years under the stated comparison. The resulting transparent layer preserves the natural texture and color of the substrate and provides an optical basis for further functional integration-for example, allowing the dynamic colors of an electronic-paper display beneath the layer to remain visible.
Figure 1. Light transmission of RELANET R-5610 water-based PUD
- 2. Environmental and health-related attributes
As a water-based system, R-5610 has low VOC content and low odor and is intended to improve cabin air quality. RELANET's transparent PUD can be produced in advanced facilities without the use of solvent, substantially reducing VOC emissions. Some development products also use renewable raw materials to reduce the carbon footprint of a coating or adhesive formulation. For example, in the bio-based waterborne polyurethane dispersion cited by the source manuscript, 38% of the carbon content in the raw materials came from plant-derived feedstock. This bio-based figure describes that development material and does not automatically apply to every R-5610 batch. The odor test is shown in Figure 2.
Figure 2. Odor test
- 3. Weathering and yellowing resistance
Automotive interiors face prolonged sunlight and high temperatures, placing severe demands on weathering resistance. Through an aliphatic molecular structure, a transparent PUD can resist ultraviolet-driven yellowing, chalking and cracking. Automotive interior coatings may need to withstand 70-85°C heat, tens of thousands of abrasion cycles, perspiration, migration and contamination; weakness in any one area can prevent OEM approval. Aliphatic water-based polyurethane is suited to applications requiring one or more of the following: resistance to yellowing, long-term exposure, transparent appearance, flexibility and lower-emission processing. In the R-5610 test reported by RELANET, the change in b after oven aging at 85°C was less than 1, indicating strong yellowing resistance. The data are shown in Table 1.
Figure 3. Test specimens
Figure 4. Colorimeter
Table 1. Yellowing-index test data for the specimens
| Condition | L | a | b | ΔYI |
|---|---|---|---|---|
| Reference | 99.95 | 0.03 | -0.01 | 0.01 |
| 500 hours | 104.36 | 0.01 | -0.13 | -0.22 |
| 750 hours | 104.72 | -0.01 | -0.18 | -0.31 |
| 1,000 hours | 104.51 | 0.00 | -0.17 | -0.29 |
| 1,600 hours | 104.17 | -0.03 | -0.09 | -0.17 |
- 4. Mechanical performance and durability
The transparent water-based PUD shows strong mechanical and bonding performance in the source test. The data are shown in Figure 5.
| Maximum peel force (N) | Minimum peel force (N) | Average peel force (N) | Peel strength (N/mm) |
|---|---|---|---|
| 80.555 | 39.741 | 60.935 | 6.093 |
Figure 5. R-5610 bond-strength test
- 5. Configurable tactile and visual effects
Molecular-structure design can give transparent water-based PUD a range of tactile effects:
- Self-matting effect: some PUDs create a matte surface through the chemical and physical structure of the resin itself, without added matting powder. This avoids settling and particle defects while producing a uniform, durable low-gloss appearance. A self-matting PUD can give automotive interiors very low gloss and a soft, substantial skin-like feel, reducing the inexpensive visual impression of molded plastic.
- Dark-substrate clarity: a self-matting PUD designed for dark substrates can enhance color depth while maintaining a refined skin-like feel and strong leveling.
