CMC for paper coating

Sodium Carboxymethyl Cellulose (CMC) is an important water-soluble polymer compound, which is widely used in papermaking, textile, food, medicine, daily chemical and other fields. In the papermaking industry, especially in paper coating (coating), CMC has become one of the important coating additives due to its good film-forming property, adhesion, dispersibility and rheological properties.

1. Basic properties of CMC

CMC is an anionic cellulose ether made by introducing carboxymethyl groups into cellulose molecules based on natural cellulose by chemical methods. It is a white or slightly yellow powder, easily soluble in cold water, and forms a transparent viscous liquid. The main performance parameters of CMC include degree of substitution (DS), viscosity, purity, etc., among which the degree of substitution is usually between 0.4 and 1.4. The higher the degree of substitution, the better the water solubility of CMC; the viscosity determines the rheological properties and application occasions of its solution.

2. The role of CMC in paper coating

Paper coating refers to applying a layer of coating composed of pigments and binders on the surface of paper to improve the printing performance, gloss, smoothness and hiding power of the paper. As a functional additive in the coating formula, CMC has the following main functions:

Dispersant: CMC has good dispersibility and can effectively disperse inorganic pigments such as kaolin, calcium carbonate, talcum powder, etc. in the coating to prevent pigment flocculation and precipitation, thereby improving the stability of the coating.

Binder: CMC can enhance the binding force between pigment particles in the coating and between pigments and paper fibers, and improve the structural strength and wear resistance of the coating.

Thickener: CMC aqueous solution has a high viscosity and can adjust the rheological properties of the coating, so that it has good fluidity, spreading and suspension during the coating process.

Film-forming property: CMC can form a uniform film after drying on the surface of paper, improve the smoothness and glossiness of the coating, and improve the clarity of the printed image.

Lubricity and dust resistance: CMC can improve the lubricity of the coating, reduce mechanical wear, inhibit dust generation, and improve the quality of the production environment.

3. Usage and precautions

In paper coating applications, there are mainly the following methods for using CMC:

Direct addition as a coating component: Dissolve CMC dry powder in water to prepare a certain concentration of aqueous solution (generally 1%-5%), then add it to the coating and stir evenly.

Use in combination with other binders: To optimize the performance of the coating, CMC is often used in combination with latex (such as styrene-butadiene latex, ethylene-vinyl acetate emulsion, etc.) to play a synergistic role.

Adjust viscosity control: Different paper types and coating equipment have different requirements for coating viscosity. The required performance can be achieved by selecting CMC of different viscosity grades or adjusting the addition amount.

Precautions include:

Avoid agglomeration when dissolving CMC. Warm water can be used to slowly add and stir;

Avoid long-term contact with strong acids and alkalis to avoid degradation;

Keep the storage environment dry to prevent moisture absorption and agglomeration.

4. Application effect of CMC in coated paper

After applying CMC, all performance indicators of paper coating are significantly improved:

Surface smoothness and glossiness are improved;

Coating uniformity is enhanced;

Printing image clarity is better and printability is improved;

Paper stiffness, tensile strength and folding resistance are improved;

Coating sedimentation rate is reduced and storage stability is improved.

CMC is a green and environmentally friendly material that meets the requirements of modern papermaking industry for sustainable development.

5. Development trend

With the continuous improvement of quality requirements for high-end coated paper such as coated paper, cardboard, label paper, etc., the performance modification and efficient application of CMC have become a research hotspot. In the future, through compounding with new functional materials such as nanomaterials and biopolymers, it is expected to further improve the application level of CMC in the field of paper coating.