Neutral papermaking, the main improvement for paper is the strength properties and aging problems. Acid-made paper is degraded after about 100-150 years, while neutral paper is more than 500 years.
For the North American paper industry, the trend from acid papermaking to neutral papermaking began in the early 1980s, and this transformation process in China was later.
Neutral sizing is a new type of sizing for the development of neutral paper, and is mainly suitable for papers that require good durability.
Neutral papermaking is a method in which the pH value is maintained above 7.0 in the papermaking process. In principle, aluminum sulfate is not used. Because the pH is higher than 7.0, it is also called alkaline papermaking.
Neutral sizing usually has two forms: one is to use a reinforced rosin as a sizing agent, with or without alum, and a cationic resin as an additive.
Such as PAM, PAE, PAC and other cationic retention agents to replace alum, improve the retention rate of rosin, usually pH value is controlled at 5.5-7.0, the sizing agent and fiber can be firmly combined to obtain a satisfactory sizing effect, this kind Sizing is also known as "near-neutral sizing", as in the case of dispersed rosin gum;
Another form is the use of synthetic sizing agents in the absence of alum and neutral sizing, such as the current widely used AKD, ASA series of neutral sizing, and the amount of AKD is larger. .
Advantages of neutral copying:
(1) Excellent physical strength properties
In alkaline systems, an increase in the degree of fiber swelling provides more hydroxyl groups resulting in better strength characteristics.
Improvements in strength characteristics can be exploited in two ways:
a, can be used to produce better quality paper products to adapt to high speed printing.
b. The same strength properties can be maintained by reducing the degree of freeness by up to 30% or by replacing up to 4% of the fibers by filler.
(2) Use high whiteness calcium carbonate
Calcium carbonate has a high whiteness characteristic, which can save the amount of brightener in production, and the use of waste paper or broke containing calcium carbonate, especially coated broke.
(3) Lower inorganic salt load
In the acid papermaking process, there is a high load of inorganic salts in the paper machine system. Increasingly high environmental regulations are forcing the water circulation of paper machines to be more closed.
The increase in the degree of closure of the paper machine will inevitably lead to corrosion of the equipment. The alkaline salt system has a much lower inorganic salt loading.
(4) Excellent paper characteristics
Alkaline papermaking can obtain better product quality, mainly showing high whiteness, good printing adaptability, ability to resist alkaline liquids, potential improvement of paper strength and stiffness, and improvement of interlayer bonding strength. The increase in the shelf life, etc.