Sodium Carboxymethyl Cellulose (Sodium CMC) is a versatile cellulose derivative widely used as a key functional additive in the production of coated paper, particularly high-quality grades like art paper (coated paper). In this application, CMC primarily functions as a rheology modifier and water retention agent within the coating color (the mixture applied to the paper surface).
Key Functions of Sodium CMC in Paper Coating
Rheology Modification (Thickening): CMC controls the flow behavior (rheology) of the coating color. It gives the coating the correct viscosity needed for application, ensuring an even and smooth layer deposited onto the paper substrate, whether using blade, roll, or air-knife coating methods.
Water Retention: This is perhaps the most critical function. CMC excels at holding water within the coating color. When the wet coating is applied to the absorbent raw paper, CMC prevents the water (and dissolved binders/additives) from migrating too quickly into the paper fibers.
Benefits: This ensures uniform binding strength, prevents defects like ‘misting’ or ‘streaking’, and maintains the smoothness of the final coated surface.
Binder Migration Control: By controlling water movement, CMC helps stabilize the distribution of optical brighteners and cobinders (like latex) within the coating layer, preventing them from migrating unevenly to the surface.
Improved Surface Properties: CMC helps create a strong, continuous film upon drying, which improves the surface strength (pick resistance), smoothness, gloss, and ink receptivity of the final coated paper, crucial for high-quality printing.
Specifications for Paper Coating Grade CMC
In paper coating, ultra low to medium-low viscosity CMC grades are typically preferred. This allows manufacturers to achieve high solids content in the coating color (reducing drying energy) while maintaining excellent rheology and water retention.
Typical Technical Parameters:
| Property | Typical Range(Paper Grade) |
| Viscosity Range | 10-200 |
| Degree of Substitution(D.S) | 0.6-0.95 |
| Purity, % | 90%-99% |
Comparison: Performance with and without CMC
The following visualizations illustrate the critical role CMC plays in stabilizing the coating process.
Visualizing the Effect of CMC on Coating Stability
In Image 1, the coating color without Sodium CMC is thin and runny. As it’s applied, the water quickly drains into the raw paper, causing the coating to become unstable. This results in significant streaking, poor coverage, and excess fluid splashing (misting) at the point of application. The final surface is rough and uneven.
In Image 2, Sodium CMC (likely low viscosity, D.S. 0.7-0.9) has been added. The coating color is now stable and holds water perfectly. Its optimized rheology allows it to flow evenly under the coater blade. It deposits as a flawless, continuous, and highly uniform film across the entire paper surface, completely eliminating streaks and misting. The resulting coated paper is smooth and consistent, ready for high-quality printing.
For more technical support, please inform us your coating speed, coating method, coating color solid, preparation temperature and operating temperature, so that we can suggest you the most suitable production formulation.
If you have any question about paper making grade Sodium CMC, please contact SINOCMC freely.
SINOCMC Team