Archive for the ‘Corrugating’ Category

Is There a Repository of Corrugator Defect Documentation?

April 24, 2018

Daniel asks,

Ralph, you once mentioned digging up a 20 year old article on corrugator defect. Is there a repository of technical articles around boxmaking you can direct me to?

The document I was referencing is actually a book published by TAPPI. It’s called Corrugated Defect/Remedy Manual, Sixth Edition. TAPPI also has a number of other publications on corrugator and corrugating that may be helpful.

The trade magazine are another good source of information and often have technical article specific to corrugators. AICC’s BoxScore, Corrugated Today and International Paperboard Industries are the once we are most familiar with here. Unfortunately, there is not central repository for the articles in competing publications, but you may locate a list of article on their website, or by contacting them directly.


How Much Washboarding is Acceptable

April 24, 2018

Paul asks,

I would like to know about washboarding in corrugated – how much variation in surface flatness (in microns) is typically seen for the types of corrugated board used in applications like shelf ready packaging?

I don’t know that there is a published standard on how smooth the surface of a corrugated sheet should be for the type of printing used for display or shelf ready packaging, but I think we are safe to say pretty darned smooth.

One of the key elements of printing the type of quality high-graphics usually found in display work and shelf ready packaging is minimizing the impression (pressure) between the plate and the substrate. The greater the impression pressure the more the printing plates distort and that distortion results in growth and distortion of the dots that create your image. Typically in high-graphics printing we are looking for a kiss impression, just enough that the printing plate just touches or “kisses” the surface of the board and transfers the ink. For the best print results we want .0015” to .003” (~38 to 76 microns) impression when printing. Oh course the lightest impression we can get away with.

Now, if the high and low points of the board surface exceed this kiss impression depth then additional pressure will be necessary in order to obtain coverage in the low points caused by fluting. Then, as stated above, as we add more impression our printing starts to suffer. With large block print you might think you can get away with over impression and perhaps you can a tad more than you can with process or fine lines and text, but excess impression on solid coverage will result in color variation through striping of the print.

We should also note that typically washboarding is less prevalent on small flute (such as a E, F or N) because there are more support points and they are closer together than a C or B flute.

Digital printing may be a little more forgiving than offset, but we still have to remember that the smoothness of the surface contributes to the overall aesthetics of the packaging and not just the print quality.


Global Percent of Medium

March 6, 2018

Mike asks,

I have a question on what the % medium should be globally. I’m trying to get a handle on it algebraically so to speak.

Classic corrugated sheet, in my mind, is one 26# medium sheet and two 42# liner sheets.  The medium has a wiggle factor of ~1.3 so,

Medium % = 26*1.3/(26*1.3+42*2) = ~ 29%.

Does this sound reasonable?  As BWs tend downward, my gut tells me there is more % medium overall but I am thinking still less than a third.

Twenty five years ago, here, it was indeed 42/26/42 with C flute having a take up factor of 1.43.  Then the sheet feeders began to request 23# medium and corrugating rolls started to have lower profiles which reduced the take-up factor.  Then we moved to 35# and today that probably is 33/23/33.  Globally the World Containerboard Organization tracks total containerboard production.  Additional information may be available through them.

— Ralph

Decoding Customer’s Specs

January 3, 2018

Richard asks,

I was a given a spec for an RSC with the paper spec’d as:

K7K 230g + 140g + 230g Kraft C/F.

I don’t know how to interpret this. I’ve reached out to our board suppliers, but I thought you may be able to shed some light. I’m assuming this is a standard way to spec board in some other part of the world.

The paperweight is the easiest to decode. To convert the paper weights from grams to #/MSF simply divide the values by 4.88 and round accordingly to match the closest available weight.


  • 230g = 47.13
  • 140g = 28.68

The other parts of the specification may be a code that is specific to the customers operation. The K7K probably denotes Kraft over Kraft liners and not test liner. The 7 is the caliper, 7mm or .177”. The ‘Kraft C/F’ probably denotes Kraft Corrugated Fluting.

However, that’s a lot of ‘probablies’. To be on the safe side I would try to get the customer to confirm the K7K and the C/F.

– Ralph