HPMC (Hydroxypropyl Methylcellulose) is a water-soluble polymer compound obtained by chemical modification of natural cellulose. It is widely used in the field of paints and coatings due to its good thickening, stabilization, and water retention properties. HPMC can significantly improve the rheology, stability, and construction performance of the coating, ensuring that the coating has stable performance during storage, transportation, and construction, and obtaining a uniform coating film.
(1) Basic properties of HPMC
HPMC is a non-ionic cellulose ether with the following characteristics:
Thickening effect: HPMC can form a viscous solution in both water and organic solvents, which can effectively increase the viscosity of the coating, thereby increasing the coating’s covering performance and coating thickness.
Water retention effect: HPMC has excellent water retention capacity and can prevent the rapid evaporation of water in the coating. It is especially suitable for water-based coatings that need to be applied in a dry environment.
Film-forming property: HPMC, as a film-forming aid, can help the coating form a smooth and uniform coating film during the drying process, improving the appearance and flatness of the coating film.
Compatibility: HPMC has good chemical stability and compatibility with a variety of formulation ingredients, and is suitable for various types of coating formulations.
(2) The main functions of HPMC in paints and coatings
1. Thickener
In paint and coating formulations, HPMC, as one of the main thickeners, helps adjust the rheology (i.e., fluidity and deformability) of the coating by changing its viscosity. Good rheological properties can prevent the coating from settling during storage and maintain appropriate fluidity and coating performance during construction.
The thickening effect has different effects on different types of coatings. In water-based coatings, HPMC increases the viscosity of the coating, making it easier to apply and evenly distribute on the surface, avoiding sagging. In solvent-based coatings, HPMC also helps adjust the viscosity and provide appropriate thixotropy (the coating thickens when it is left standing and thins when it is stirred or applied).
2. Water-retaining agent
The water-retaining effect of HPMC is particularly important, especially in water-based paints. It can effectively prevent the water in the paint from evaporating too quickly during the construction process, thereby ensuring that the coating has enough time to level and form a smooth and uniform coating film. Under dry or high temperature conditions, the evaporation of water in the paint too quickly may cause cracking of the coating film or uneven surface. HPMC can significantly slow down this process.
HPMC can also help the pigments and fillers in the paint to remain evenly dispersed during the construction process, preventing local drying or particle agglomeration, thereby ensuring the beauty and uniformity of the coating film.
3. Leveling agent and anti-sagging effect
As a leveling agent, HPMC can prevent the paint from sagging or sag during the drying process of the paint. Due to its special rheological properties, HPMC can provide good fluidity during the coating construction, allowing the paint to be evenly spread on the surface of the substrate. After stopping the operation, the viscosity of the paint gradually recovers to prevent excessive flow and the formation of sagging marks.
This feature is particularly critical in facade painting or other occasions where vertical application is required. The addition of HPMC ensures that the paint quickly acquires proper cohesion after application, so that it stays on the surface to which it is applied, and does not flow downward due to gravity.
4. Dispersant effect
HPMC, as a dispersant, can improve the dispersibility of pigments and fillers in paint. By improving the dispersibility of pigments and fillers, HPMC can ensure that the solid particles in the paint remain well dispersed, avoid agglomeration and sedimentation, and thus improve the uniformity and stability of the coating. This is important for color consistency and the mechanical properties of the coating.
5. Film-forming aid
During the film-forming process of the paint, HPMC can also be used as a film-forming aid to help form a uniform coating. This feature is crucial to improving the surface quality of the coating. During the drying process, HPMC ensures that the paint can dry evenly on the surface and inside by adjusting the evaporation rate of water, forming a flat and smooth coating. Especially in high-gloss paints and decorative paints, the role of HPMC makes the coating have a better appearance.
(3) Advantages of using HPMC
1. Improve the construction performance of the coating
The rheological regulation effect of HPMC makes the coating easy to operate during application, and the construction performance is significantly improved. The coating will not flow excessively or produce brush marks, the coating is more uniform, and the coating film formed after construction is smoother and flatter.
2. Improve the storage stability of the coating
HPMC can prevent the stratification and sedimentation of the coating during storage, and maintain the uniformity and stability of the coating. Its thickening and dispersing effects can effectively keep the pigments and fillers in the coating in a uniformly dispersed state, extending the storage life of the coating.
3. Improve the anti-cracking performance of the coating film
The water retention effect of HPMC ensures that the water in the coating can be gradually evaporated during the drying process, and the coating film will not crack due to rapid drying when it is formed, thereby improving the overall quality and durability of the coating film.
4. Adaptability to different environmental conditions
Since HPMC has a strong adaptability to changes in temperature and humidity, it is suitable for coating construction under various environmental conditions, especially in high temperature and low humidity environments. HPMC can effectively improve the water retention of the coating and prevent the coating from drying too quickly.
(4) Application of HPMC in different types of coatings
Water-based coatings: HPMC is mainly used for thickening, water retention and leveling adjustment in water-based coatings. It can improve the construction performance of water-based coatings, especially when used in a fast-drying environment, it can significantly improve the water retention capacity of the coating.
Architectural coatings: In architectural coatings, HPMC ensures long-term protection of wall or building surfaces by enhancing the crack resistance and durability of the coating. Architectural coatings usually require higher construction performance and weather resistance, and HPMC can help improve these properties.
High-gloss coatings: High-gloss coatings have higher requirements for surface flatness and smoothness. The leveling effect and film-forming property of HPMC can significantly improve the appearance quality of the coating, making it brighter and smoother.
HPMC plays many roles in paints and coatings, including thickening, water retention, leveling, dispersion and film formation. It can not only improve the construction performance of the coating, but also improve the quality and durability of the coating film. Therefore, HPMC is widely used in modern coating formulations and is an important additive to ensure the performance and quality of coatings.