Hydroxypropyl methylcellulose (HPMC), a commonly used functional additive in waterborne coating systems, combines thickening, water retention, stabilization, and improved workability, making it a key raw material for enhancing the overall performance of coatings. Proper selection and correct use of HPMC can not only improve the storage stability of coatings but also optimize film quality and brush feel.
1. Selecting the Appropriate Viscosity and Substitution Degree Based on the System
The viscosity grade of HPMC has a significant impact on coating application. High viscosity grades (e.g., above 100,000 mPa·s) can significantly improve the low to medium shear viscosity of the system, helping to improve anti-sagging and thixotropic properties during application; however, excessively high viscosity increases the difficulty of mixing and affects leveling. Medium viscosity grades (30,000–60,000 mPa·s) are more suitable for most latex paints, achieving a balance between thickening and leveling. For exterior wall coatings or high-filler systems, higher viscosity is recommended; while for interior matte wall systems, medium viscosity can be used to enhance application smoothness.
The degree of substitution of HPMC with methoxy and hydroxypropoxy groups affects its solubility and stability. A higher degree of substitution improves water solubility and salt tolerance, resulting in greater stability in formulations with high pigment and filler content or those experiencing significant pH fluctuations.
2. Mastering the Correct Dissolution and Dispersion Methods
HPMC requires proper dispersion to achieve stable thickening properties. Two common dissolution methods are:
Room Temperature Stirring Method:Evenly sprinkle HPMC into cold water under high-speed stirring, ensuring it is fully wetted without clumping, then continue stirring until completely dissolved. Avoid adding large amounts at once, as this may form clumps that are difficult to disperse.
Hot Water Dispersion Method:First disperse HPMC in hot water at 80–90°C, then add cold water to cool and dissolve it. This method is suitable for high-viscosity formulations and improves dissolution efficiency.To improve operability, slow-solving HPMC can be selected, significantly reducing clumping problems and improving production efficiency.
3. Techniques to Enhance Coating Stability
HPMC can improve the suspension of pigments and fillers and reduce sedimentation and stratification, but it requires synergy with other additives in the formulation:
In high PVC coatings, the amount of HPMC added can be appropriately increased to improve storage stability.
Unlike cellulose ether thickening systems, HPMC is sensitive to salts and calcium ions; therefore, salt-stabilized HPMC should be selected in systems with high hardness water or high CaCO₃ content.
If the coating exhibits pseudo-thickening, the pH can be appropriately increased or a rheology modifier can be used to improve shear recovery.
4. Optimizing Brush Application and Film Quality
HPMC has good thixotropic and wetting properties, which can improve brush feel and increase coating coverage. Application techniques include:
In high-frequency application systems (such as engineering coatings), the viscosity can be slightly reduced to improve roller coating smoothness.
To improve leveling, HPMC can be compounded with HEUR or ASE-type thickeners to create a more suitable rheological profile.
When applying paint in a dry environment, increasing the HPMC content helps improve water retention and prevents dry edges, brush marks, or film defects.
5. Properly Control the Addition Amount
Generally, the HPMC addition amount for interior wall latex paint is approximately 0.2–0.5%, while for exterior walls it can be increased to 0.3–0.6%. However, adjustments need to be made based on the type of PVC, pigments, fillers, and thickening system. Excessive addition may lead to poor leveling, prolonged drying time, and even a sticky feel.
6. Synergistic Use with Other Thickeners
Optimal paint rheology often relies on a combination of thickeners. HPMC handles medium-to-low shear thickening and water retention; HEUR handles high shear viscosity; and ASE provides a cost advantage. The combination of these three creates an ideal rheological profile, resulting in paint that is both non-sagging and easy to apply.
Post time: Dec-03-2025