**4. Conclusions**

 APC

This paper experimentally studied the improvement of stain resistance for exterior wall paints in a typical western city in China, Chongqing. Three different designs, named Design 1, Design 2 and Design 3, were studied in this paper. The results for Design 1 sugges<sup>t</sup> that the stain resistance of architectural paints with different paint structures was different. After comparing the water resistance, alkali resistance and stain resistance of silicone–acrylic paint, styrene–acrylic paint and pure acrylic paint, the results show that the stain resistance of the silicone–acrylic-paint-based exterior wall paints was the most suitable among the three. The results for Design 2 show that the exterior wall paints' PVC had a grea<sup>t</sup> influence on the stain resistance, and the film reflectivity decreased gradually with an increase in PVC. When the PVC increased to about 45%, the film reflectivity significantly decreased and then increased sharply with an increase in PVC, indicating that when PVC ≤ CPVC, the stain resistance of the paint increased with an increase in PVC. In Design 3, the effects of thickeners, cosolvents and wetting and dispersing agents were compared. When the content of a thickener (hydroxyethyl cellulose ether) increased, the reflectivity decline rate also decreased, and hence, the stain resistance of the paint was enhanced. When the ratio of the associated thickener to the non-associated thickener was 4:1, the reflectivity decline rate was the smallest, and the stain resistance of the paint was the most suitable. When the content of a cosolvent (propylene glycol) was 5%, the reflectivity decline rate, the contamination resistance, decreased significantly, suggesting that the stain resistance of the paints with 5% propylene glycol was the most suitable in the comparison group. The reflectivity decline rates for the two paints with different wetting and dispersing agents were basically the same, indicating that the contributions of the two wetting and dispersing

agents in the stain resistance of the paints in this group of experiments were basically the same.

**Author Contributions:** Data curation, D.Z.; formal analysis, X.H.; investigation, D.Z.; writing – original draft, C.W.; writing – review & editing, X.H. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Acknowledgments:** The authors gratefully acknowledge financial support from the Hong Kong Polytechnic University and Sichuan University.

**Conflicts of Interest:** The authors declare no conflict of interest.
