Glass Interleaving Paper Quality Control Considerations


There are five major factors that influence how often defects occur and how severe defects are when they do occur in glass interleaving paper. Luckily, the last two factors are controllable and can eliminate the risk associated with the first three factors, which are uncontrollable.


  1. Humidity – humidity increases the risk and severity of defects
  2. Heat – the warmer it is (either b/c of ambient temperature or because you are interleaving warm glass), the greater the chance of of chemical reactions which lead to defects
  3. Time the glass is interleaved – the longer you leave the paper in the glass, the greater chance of a defect

Controllable – Can Eliminate Risk from #’s 1,2,3

  1. Thickness of the paper relative to its pH – thin papers need a very low pH to avoid problems, thicker papers can have a higher pH
  2. Resin content of the paper and pulp cleanliness – limiting resin levels and other pulp cleanliness characteristics can combine with the pH to eliminate your risk

The first three issues are uncontrollable. While some clients have added equipment to extend cooling sections and/or added extra climate control equipment which also comes with higher utility bills; this is not required if you use the proper paper.

The heat and humidity can vary by time of the year or even from week to week or day to day. It is prudent to investigate if your defects coincided with unusually humid days at your facility or high humidity at your customers’ facilities.

We have proven time and time again that controlling the pH and resin levels can eliminate these defects completely, Whether you buy from Flexlink or not, please be sure that the pH and resin content are measured multiple times while each order of your paper is being manufactured. Also know that if you do not use a paper produced specifically for glass interleaving, the paper mill can add chemicals to your paper any time they want. MG paper is used for bags for muffins, donuts etc. With this in mind, paper mills will often incorporate chemicals to decrease cost and increase efficiency assuming that the paper they are producing will go into bag applications.

In paper manufacturing silicone based defoamer agents can decrease cost and are therefore gaining in popularity. Unless the paper mill producing your paper is custom manufacturing a glass interleaving paper specifically for this application, they are likely to maximize efficiency without regard for how chemical changes can impact your products. In fact one of our current customers first came to us with a defect that was happening for months. Our laboratory analyzed the defect and determined that there was a thin coating of silicone on every window. As it turned out, the paper mill had switched to a silicone defoamer with the goal of decreasing their cost. The glass defect was costing hundreds of thousands of dollars annually. This customer switched to Flexsheen® and has not had an interleaving related defect since that time.

Whether you buy from Flexlink or not, please give the issues above some thought. Our Flexsheen® line of products is not the least expensive paper on the market. However, the cost of random QC problems, you will find that the Flexsheen® has the least total cost of ownership of any paper that you can use for glass interleaving.

Please contact us to discuss how Flexsheen® Glass interleaving paper may help resolve your QC problems.

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