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CMC in Coated Paper

CMC is widely used in paper coating, eg. blade coating, air-brush coating, roller coating. CMC plays a very important role as regards its rheological property, water retention, workability and other characteristics.

1. Properties:

1. High stability
2. Good water retention
3. Good viscosity
4. High binding strength
5. Good dispersibility
6. Brightening agent carrier
7. Auto-lubricating

Stability

CMC can improve the chemical and mechanical stability of coatings, facilitating high-speed blade coating.

Water retention

A good water retention capability is essential to the quality of coating. Paper is a porous water-absorbing material, capable of depriving water from the coating layer which leads to migration of adhesives. Low water retention may cause coating flaws, adhesive migration, rheological property loss, etc.

Rheoligical property

CMC-containing coating shows thixotropic effect, a property desirable for high-speed blade coating. The rheological property can be controlled by variation of types and quantity of CMC.

2. Performance test of CMC-IL10-50
(Evaluated by the Society of Paper Jiangsu Province and China Paper Institute)

1. Comparison test:

CMC	Total solid %	pH	Viscosity CPS% @ 25°C 60rpm	Thixotropic index	Water retention value
					25°C	30°C	40°C
IL10 Cellogen-7A IL20 IL50 FF5G FF10G	64.26 64.07 64.16 64.39 64.30 64.68	8.84 8.86 8.86 8.86 8.86 8.84	2765 2710 2870 3160 2380 2490	1.69 1.73 1.83 1.78 1.88 1.87	26 32 35 29 27 27	17 19 26 19 21 20	9 10 12 9 11 11

Note: IL10, IL20, IL50: Weiyi products.
Cellogen-7A: Japanese product.
FF5G. FF10G: Finnish Product.

Conclusion:

(1) IL50 shows the highest viscosity in 4% aqueous solution; IL10 is approximate to IL20, lower than FF10G and slightly higher than Cellogen-7A; FF5G is the lowest.

(2)FF5G, FF10G and IL20 perform better than the other three in respect of rheological property.

(3)IL20 has the best water retention capability, at room temperature (25°C) or elevated temperature (40°C). FF5G and FF10G are similar, both showing moderate WRV at room temperature. But at elevated temperature, they show better WRV than the other four saving IL20. Cellogen-7A, IL50 and IL10 perform not as well.

2. Viscosity-concentration curve of IL10 and Cellogen-7A.

3. Characteristics of CMC

1. Increases strength and abrasion resistance of paper
2. Enhances distribution of sizing agent
3. Good adhesion to fiber and fillings
4. Improves air permeability
5. Increase whiteness and gloss
6. Improves affinity to printing ink.

4. Application examples (only for reference)

1. Art paper

For high solid (55-60%),high speed (400-1000M/min), we recommend use of IL10 or IL20,in the rate of 0.35-1.0%.
For low solid (35-50%),low speed (100-400M/min),we recommend use of IL30, in the rate of 0.35-1.0%.

2. Board paper

Board paper varies in ingredients and water absorbing capability. User can choose different types of CMC for board paper according to solid content and speed. Rate of use is generally 0.35-1.5%.