Glass interleaving defects can be broken into uncontrollable and controllable factors. The uncontrollable factors are outside the control of the glass manufacturer and include humidity, heat and the length of time the glass is interleaved.

Fortunately, glass manufacturers can still control the quality of their glass by controlling the characteristics of their interleaving paper. The paper’s thickness, pH and chemical content all work to inhibit the effects of heat, humidity and time. Additionally, it is important to exclude silicone derivatives from all pulp and paper manufacturing processes.

Resin Level is a Controllable Factor

Moderate to high resin levels can cause pitting and corrosion in glass interleaving paper. High resin levels often appear as tiny specs in the sheet that can dent glass. Moreover, studies show that chemical impurities such as sulfates, agglomerate around these tiny specs. Thus, the areas around the tiny specs of resin have higher concentrations of harmful chemicals than other areas in the paper.

The removal of resin has two benefits:

• • It makes the paper stronger.
  • It makes the paper less water resistant. Absorbing water is important so the paper can act as a buffer against hydroxide ions and the alkalinity of the moisture that collects between the layers of glass.

Resin, often called “organic extractives”, can be largely removed from virgin paper. Resin is the chemical leftover from the lignin (often called “pitch”) that holds the cellulose fibers together in wood. Hardwood contains higher resin levels than softwood.

Age the Wood and Wash the Pulp

Properly aging the wood and thoroughly washing the pulp both reduce resin levels. Pulp mills that want to reduce resin levels age their wood for a year or more and send the pulp through significantly more washing.

Unfortunately, higher softwood percentages, extended aging of the logs and increased pulp washing are all expensive. As pulp mills are unable to process and segregate different types of pulp, very few pulp mills are willing and able to make pulp that is suitable for making glass interleaving paper.

Learn More by Downloading Our White Paper

The range of glass interleaving papers available is as varied as the level of knowledge regarding their use. With this in mind, our free white paper discusses the factors that allow a paper to effectively interleave glass:

• Uncontrollable and controllable factors in glass interleaving
  • Moisture
  • pH
  • Resin
  • Ambient heat
• Added chemicals like silicone-based defoamer agents

Download our free white paper to learn more about the factors to consider when selecting glass interleaving paper for your application!