MEMBERS QUESTION:

I do have a technical question for you however that I would welcome the benefit of your experience on. And that concerns Cobb test values on containerboard. Duration of test aside, most producers specs only show the maximum absorption allowed but clearly to get a good bond you need a minimum water absorption value in order for starch solids to penetrate. Do you know if there is a generally recognized minimum Cobb test value on either a 1 or 2 minute Cobb test? I am only familiar with maximum Cobb values being agreed specifications. But maybe you know differently. Your advice would be appreciated. Thanks in advance

 

Ask Ralph Responds:

To give a direct and concise answer to you question, specifications and not competitive evaluations generally deliver a “targeted” two minute Cobb on the wire side of the sheet between 40 and 55 gsm. I am not aware of a MINIMUM value. However reading more into your question, I also offer the following information to you.

 

Corrugated adhesion is dependent on many variables such as the character of the medium and its conditioning; the viscosity, rheology, application, and pH of the adhesive itself; the smoothness/roughness profile of the wire side; the single facer and the positive contact dwell time at the nip; and temperatures.  One should look to the combined and converted vales of Edge Crush, Flat Crush, caliper, Pin Adhesion, and Fibre Pull to determine the best operating conditions for combining containerboards.

 

Thank you for the question.