Types, properties and applications of surface sizing agents commonly used in papermaking

4) CMC

CMC is a white powder, granular or fibrous substance, odorless, tasteless, non-toxic, is a good surface sizing agent. CMC generally has a viscosity below 300mPa.S and a degree of substitution between 0.6 and 0.75, and is more suitable for use as a surface sizing agent.

Compared with PVA, carboxymethyl cellulose (CMC) has higher advantages as a surface sizing agent:

(1) It has excellent film formation and whole film transfer performance, and can form a good closure and oil resistance on the surface of paper or cardboard.

(2) Due to the poor film formation of modified starch, it is impossible to form a continuous and complete film on the surface of the paper, and will form a "accumulation" on the surface of the paper and block the pores, resulting in spots when printing, therefore, starch with CMC, can largely overcome this shortcoming.

(3) CMC has good dispersion, it can fully disperse other rubber particles to form a single and stable system, and can effectively coagulate and precipitate in a certain period of time.

(4) If the appropriate amount of CMC glue into the surface sizing, you can form a continuous and complete and flexible film on the surface of the paper, this film has a moisture control function, can prevent paper or cardboard in the printing process warping deformation and eliminate the size error when overprinting.

(5) Due to the excellent bonding ability of CMC, it strengthens the combination between the fiber and the fiber on the surface of the paper or board, and between the fiber and the filler, thus effectively improving the surface strength of the paper. And make the surface of the paper (board) to obtain a good ink acceptance, improve the gloss of the paper, so that the printed text image is shiny and beautiful, but also reduce ink consumption. CMC film strength is large, oil resistance, but high viscosity, so the use of medium relative molecular weight, substitution degree of 0.5~0.7mol/g CMC, coated paper rupture strength and printing gloss is good.

5) Modified AKD

Modified AKD is mainly used in combination with starch on cardboard, which can improve the water resistance of cardboard and greatly reduce the cost of paper under the condition of relatively small dosage. The AKD curing problem that was previously worried has basically been solved, like ordinary high-strength corrugated or cow leather box board, the full curing period can also be completed within 2 hours. This modified AKD plus surface sizing starch method is also applied to ordinary cultural paper to completely replace in-pulp sizing. Add to the surface of the paper, so that not only can reduce the amount of AKD, but also shorten the aging time of AKD.

6) Copolymers

(1) Styrene-Maleic anhydride Polymer (SMA)

SMA is an alternate copolymer of styrene and maleic anhydride, a light amber colored mucus with a solid content of 25% to 40%, which can be infinitely diluted in water. Mainly used for coating, securities paper, greaseproof paper, carbon paper, copy paper, etc., can improve the wear resistance of paper, strength, oil absorption.

(2) Styrene-Acrylate Copolymer (SAE)

The copolymer (SAE) of styrene and acrylate prepared by emulsion polymer is usually used in latex form. At present, most of the SAE surface sizing agents used are aqueous anionic polymers, which will cause emulsion precipitation and have adverse effects on sizing because of AB+ and Ca2+ in the water during use. In order to improve the water resistance of the emulsion after film formation, it is generally necessary to add a small amount of surfactant, such as oxidized starch with better effect. Or directly add a small amount of aluminum sulfate to improve its sizing performance.

(3) Styrene-Acrylate-Maleic anhydride monoester copolymer (SAM)

Styrene-acrylate-maleic anhydride monoester copolymer (SAM) is a medium molecular weight product with random copolymerization of styrene, acrylic acid and maleic anhydride, and the effect is better than SMA. This will be the technical development direction of sheet paper surface sizing.

(4) Polyurethane aqueous dispersion (PU)

Polyurethane (PU) water dispersion is a new type of surface sizing agent, which can produce higher sizing degree with less dosage and improve paper performance. Mainly used for coated paper and offset paper, the application cost is high.

7) Animal glue

Animal glue is a protein extracted from the bones, skin or tendons of animals. High-grade skin glue and bone glue light and transparent, also known as gelatin. Both skin glue and bone glue can be used for surface sizing, but the most suitable for high-grade paper is skin glue, compared with bone glue, skin glue viscosity, covering ability and film formation are better than bone glue, can produce a stronger film, and therefore can give greater strength to the paper. Due to the high price of animal glue, it is mostly limited to the surface sizing of high-grade paper. When using animal glue, it is first fully swollen in cold water, and then dissolved in hot water of about 50 to 60 degrees, and a glue with a concentration of 4% to l0% is made in stirring. If necessary, a small amount of organic acids or bases can be added to improve solubility. In order to reduce its viscosity, an appropriate amount of aluminum sulfate can be added. Adding 2% ~ 3% soap to animal glue (the amount of animal glue) can improve the color, opacity and gloss of paper; Adding a small amount of sodium chloride, glycerin, non-drying oil, sodium acetate, etc., can also improve the kneading resistance of paper. When animal glue and starch are mixed, 0.25% ~ l.0% soap (for the amount of animal glue) can be added to prevent the dispersion of animal glue starch.