Starch pick-up, sizing solution

Note:  The sizing solution itself introduces some important variables with respect to size penetration, these include the surface tension of the solution, its wetting properties, viscosity, concentration (or solids content), and temperature.

1. Viscosity is of particular importance in determining size penetration.
— penetration varies inversely as the square root of the viscosity of the solution.
— viscosity must be regulated with considerable care.

2. Temperature and concentration are important practical considerations as these variables are not only of consequence by themselves, but also exercise a direct control over viscosity.
— normally the end use of the paper will dictate the starch concentration required.
— the use of a higher starch concentration than is required for sheet bonding or ink specifications may result in a reduction in brightness and opacity.

3. The surface tension of the sizing solution also plays a significant role in size penetration. Surface tension refers to the cohesive forces present at the surface of a liquid, which affects its ability to spread and wet the paper fibers evenly. A lower surface tension allows for better wetting and penetration of the sizing solution, resulting in improved bonding between the fibers and the starch.

4. Wetting properties of the sizing solution determine how well it spreads and adheres to the paper fibers. A good wetting property ensures uniform coverage and adhesion of the starch to the fibers, preventing uneven distribution and potential defects in the paper.

5. The concentration or solids content of the sizing solution is crucial in controlling the amount of starch pick-up during the size press process. Higher concentrations of starch can lead to excessive pick-up, resulting in increased stiffness and reduced flexibility of the paper. On the other hand, lower concentrations may result in insufficient bonding and reduced strength.

6. The temperature of the sizing solution affects its viscosity, which in turn influences size penetration. Higher temperatures decrease viscosity, allowing for better flow and penetration of the starch into the paper fibers. However, excessive temperatures can lead to rapid drying and uneven distribution of the sizing solution, compromising the quality of the final product.

In conclusion, the sizing solution used in the size press process has a significant impact on the pick-up of starch and ultimately the properties of the paper. Factors such as viscosity, temperature, surface tension, wetting properties, and concentration must be carefully controlled to achieve desired results in terms of size penetration, bonding strength, brightness, and opacity. Proper regulation of these variables ensures the production of high-quality paper with optimal sizing characteristics.