Glass interleaving paper is used when interleaving powder does not work. In most cases, this occurs because the glass surface is not perfectly flat or when specific environments cause dust and beads from interleaving powder to be problematic. Interleaving powder is largely used by the flat glass manufacturing industry.

Glass interleaving paper was the standard in flat glass packaging, but then many manufacturers started switching to powder as a more economical solution. This may be the case for flat glass packaging, but glass interleaving paper remains the most effective solution for non-flat glass.

Issues with using glass interleaving powder:

• Curved or bent surfaces prohibit interleaving powder from remaining in place.
• The dirt and dust associated with interleaving powders can cause problems in a multitude of situations.
• Powder may only provide spot contact and neutralization of alkali, leaving a mottled stain pattern in the case of heavy condensation.

As a result, many glass manufacturers and fabricators turn to glass interleaving paper as an alternative. However, the range of papers available are as varied as the level of knowledge regarding their use.

Preventing Glass Corrosion

In his article “How to Prevent Glass Corrosion”, Paul Duffer of PPG Industries discusses the chemical reactions that occur which create staining and corrosion in soda-lime-silica glass compositions. He explains that Stage One Corrosion can take place in minutes if the glass comes in contact with water while packaged. Duffer describes the chemistry of the interaction in detail, but put simply, the water takes sodium ions from the silica glass thereby increasing the hydroxide ions and the alkalinity (pH) of the moisture on the glass’s surface.

Duffer goes on to explain “As long as the solution pH levels remain well below 9.0, Stage 1 corrosion proceeds as the predominant reaction at the glass surface. During this period, optical quality and surface integrity remain essentially unaffected…However, unrestrained Stage 1 corrosion can lead, as previously mentioned, to highly alkaline conditions.”

Stage Two Corrosion

Finally, Duffer makes it clear that a whole new reaction takes place when the pH of the silica glass reaches 9.0 or greater. Glass industry experts call this “Stage Two Corrosion”. It occurs when the hydroxide ions attack the actual silica network in the glass. The defects are displayed as “microscopic pitting of the surface” and evolve into a “widespread iridescence” or a “dense, translucent haze”. Duffer also mentions reactions that occur with the moisture from carbon dioxide in the atmosphere that also creates residues.

While the overall strength of the glass is not impacted from the pitting, fogging and hazing; the optical quality of the glass is destroyed to a point that only substantial grinding and polishing can remove the defects. In many cases, scrapping the defective glass is more economical than re-conditioning it.

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!