Sizing operations and additives in the paper industries
Introduction
In the paper industry, the fibers used have a high tendency to react with water, which is due to the hydrophilic nature of cellulose fibers.
The process that makes fibers resistant to water penetration is called “sizing”.
This process Sizing operations and additives in the paper industries the surface of fibers impermeable to water due to the addition of chemicals.
This is very important when the paper is used for printing purposes.
Because this process prevents the ink from spreading on the surface of the paper or leaking to the back of the paper.
If sizing process is not done on the paper, liquids will spread on the surface of the paper, which is called feathering.
There are various sizing materials such as rosin, paraffin waxes, and other wax-based solutions, as well as synthetic materials such as AKD and ASA, which make the paper hydrophobic according to the user’s needs.
:Internal sizing requirements include the following
The sizing agent should be easily available and have a stable chemical composition
Sizing materials should be able to spread well in cellulose fibers.
These materials should have a good storage capacity in the terminal
The molecules of these materials should be able to orient themselves well in the suspension solution so that their hydrophobic heads are not placed on the side of the fibers.
These materials should have an optimal water repellency capacity so that the sizing operation can be done at a lower cost
These materials should not cause negative effects and side problems in the paper production process.
:Paper sizing can be done in different ways
internal sizing, surface sizing , or external sizing.
In general, three types of external sizing are used, which include acidic sizing (alum-rosin), neutral sizing and alkaline sizing.
In internal sizing materials are added to the dough and mixed with it while in external sizing materials are used on the surface of the paper.
Acidic sizing (alum-rosin) has always been the most popular sizing process in papermaking due to its cheaper and reliability.
Of course, neutral processes (use of certain compounds of rosin) and alkaline processes (use of ASA or AKD) have been expanding strongly in the last few years.
The most important factor behind the transition from acidic sizing to neutral or alkaline sizing is the need for papers with special characteristics and environmental issues.
Among the weaknesses of the acid sizing process the negative impact on the durability and longevity of the paper the limitation of the use of calcium carbonate.
which has been increasing in the use of this material in the paper industry in the last few decades the phenomenon of corrosion in machines and equipment and the reduction of paper clarity.
Some of the benefits of AKD include the following
Increasing the life of equipment for less corrosion
Increasing color brightness and optical properties of paper
Increase paper durability
Positive effect on machinery speed due to better drainage
Improving the surface smoothness of paper
:Note
Keep in mind that the consumption of AKD has an optimal point and if the amount of consumption is higher than this point no change may occur in the paper or even cause a reverse effect on the quality of the paper.
