What is paper sizing?

Paper sizing refers to the treatment or coating applied to paper during the manufacturing process to improve its performance characteristics. The primary purpose of paper sizing is to control the absorption of ink or other liquids, preventing them from being absorbed too quickly into the paper fibers.

There are two types of paper sizing: internal sizing and surface sizing.

1. Internal sizing: It is the process of adding sizing agents directly into the pulp during papermaking. Common internal sizing agents include rosin and alkyl ketene dimer (AKD). Internal sizing agents make the paper more resistant to water absorption, improving its ability to handle ink and preventing smudging or bleeding.

2. Surface sizing: It is the application of sizing agents on the surface of the paper after it has been formed. The surface sizing solution is applied with a big roller called a size press. Surface sizing enhances the smoothness, ink holdout, and water resistance of the paper, making it more suitable for printing and writing. Common surface sizing agents include starch, modified starches, and synthetic polymers.

Paper sizing is crucial in various applications such as printing, publishing, and packaging, where ink needs to be controlled for sharpness and consistency. Sizing also helps prevent excessive feathering or spreading of ink, retains the ink on the surface for better color reproduction, and prevents show-through or excessive drying time for printed materials.

Different papers require different sizing treatments, depending on their intended purpose. For example, newsprint paper used for newspapers or inexpensive printing may have lower sizing levels, while high-quality coated papers used for magazines or advertising materials may have higher sizing levels for improved ink absorption control.

It is important to note that paper sizing can affect the recyclability of paper products. Some sizing agents, especially those derived from synthetic materials, can hinder the recycling process as they may not break down easily. However, advancements in environmentally friendly sizing agents and recycling technologies are aimed at reducing the negative impact on paper recyclability.

In summary, paper sizing is a crucial step in the papermaking process that improves the printability and performance of paper. It controls ink absorption, enhances surface smoothness, and influences the overall quality of printed materials.