Internal Sizing and its Need

Internal sizing is the process of adding some materials or sizing agents to improve the resistance of paper for the penetration or spreading of water and other liquids through the paper. Internal sizing does not make the paper waterproof but makes it worth to stand with repeated exposure to the press water dumping system.

The degree of paper’s internal sizing is determined by a number of tests such as Dry Indicator Method, Ink Flotation Method, Contact Angle Method, Curl Test Method, Feathering Test, and Water Immersion Method. Various top-rated internal sizing chemical suppliers use to provide high-quality internal sizing agents for using at the wet end of the paper pulp for decreasing the penetration and spreading of an aqueous solution through or across the paper.

There are three major product categories of internal sizing agents

  • Alkenyl Succinic Anhydride (ASA)

Alkenyl Succinic anhydrides or ASA sizing chemicals are widely used in the surface sizing of paper and paperboard in the neutral/alkaline papermaking process. They are oily monomer and colorless viscous liquids and added to the paper pulp stocks at room temperature in the form of an aqueous emulsion. Instead of cationic starch ASA emulsions use fine particles to resist liquid penetration through the paper surface.

  • Alkyl Ketene Dimers (AKD)

Alkyl Ketene Dimers or AKD sizing chemicals have lower reactivity than ASA sizing agents. Hence AKD is more feasible. These organic compounds are synthesized from fatty acids and usually found in the form of waxy solid material. It is used as an alkaline hydrophobic sizing agent by manufacturers of paper and paperboard.

  • Rosin

Rosin sizing agents are isolated from tall oil and are available in different sizings like paste, dry, and extended sizes. They are easily dissolvable in water. Rosin Soap Sizing is generally used for lower pH values. Alum is added to help the rosin by imparting a degree of acidity to paper. As a resinous material rosin is also used in printing inks and varnishes.

Applications of Using Sizing Agents

  • Printing & copier paper
  • Liner board and corrugated
  • Food packaging
  • Liquid packaging

Benefits of Using Internal Sizing Agents in Paper Industry

  • Improved printability
  • Water resistance
  • Oil and grease resistance
  • Coating and adhesive holdout
  • Dusting and picking can be reduced by this process
  • Holdout of liquid
  • Best toner adhesion
  • Improved size degree

Key Factors Affecting the Sizing Efficiency of the Sizing Chemicals

  • Dispersion of the sizing agent: Before adding to the system, it is imperative to get the sizing formation in a well-dispersed form.
  • Create a smooth mixture: The formulation of an internal sizing agent with the fiber furnish should be perfectly mixed for the uniform distribution of the material on the solid surface.
  • Retention efficiency: In the case of ASA sizing, at the forming section of the paper, the mixture of sizing agent with the fines they are attached must have higher retention efficiency.
  • Proper distribution of molecules of sizing agents: The individual molecules of the sizing agents should be perfectly distributed over the solid surface of the paper.
  • Good anchor and orientation ability: It is essential that on the surface of the fiber, the sizing agent molecules must be effectively anchored and oriented for their permanent effects.

The portfolio of surface sizing agent is inclusive of a variety of products that helps in improving the water resistance and oil resistance of food contact papers. For getting the best result a right quantity of the sizing agent should be added to the paper pulp.