Web Growth: A Book Printing Phenomenon

Sometimes customers get their soft cover books and feel that something is amiss.  The pages are sticking out past the cover of the book.  It is natural to think that perhaps there was some mistake in the measurement of the paper or cover during the trimming process however this is not the case.  This phenomenon is known in our industry as web growth.

Digital vs Offset Printing

Paper travels into the furnace on a high-speed offset printing press.

Web growth refers to the expansion of paper after it is printed on a heat set printing press.  Paper can lose and subsequently absorb moisture depending on the environment that it is in.  Fibers that make up paper expand and contract in diameter depending on moisture levels in the environment.  When paper is printed on a heat set press, it runs through a dryer at one end of the press so that solvents can be flashed away before the paper is cut and folded to create signatures or groupings of pages.  Temperatures in these dryers can cause the paper to reach between 250 to 300 degrees Fahrenheit in a matter of seconds.  This process dramatically decreases the amount of moisture that the web (paper) had before it passed through the dryer.  Chill rolls typically follow the furnace to help set ink on paper.

Offset Printing Process

Paper in an offset printing press travels over a chill roller before being cut and folded.

In many high speed web presses, a silicon roller is used to reduce marking on coated paper stocks.  This part of the process helps reintroduce some moisture that the paper lost when passing through the furnace.  After paper exits the press, it is bundled and compressed into logs.  These logs are not unwrapped until signatures are fed into a binder leaving the paper little time to re-acclimate to the environment.  Only after signatures have been released from being bundled is when they start their re-acclimation process.  This is where web growth is most evident.  Pages in a book that were printed on an heat-set press can grow larger than their original trim size.  Covers typically do not experience this growth because they are made on sheet fed presses that do not utilize dryers.  The expansion of paper happens on all heat set presses but is generally only noticeable in softcover books.

Ann Arbor Book Printer

One of many humidifiers hanging from the ceiling in the Jackson Road Facility

At right, a book where pages have gained moisture and extended past the cover of the book.

This phenomenon makes it appear like the cover is shorter than the pages or that the book was not trimmed correctly.  In fact the pages of the book have grown slightly past the edges of the cover after the trimming process.  Web growth happens with all papers however it is much more noticeable with ground wood stocks.  Edwards Brothers Malloy takes many steps to ensure that web growth is minimized on all jobs.  Furnace temperatures are closely monitored to ensure they are high enough to be effective without altering the final look of the paper.  Silicon applied before the paper leaves the offset printing press helps speed up the acclimation process.  Humidifiers have been installed throughout our Jackson Road facility.  While they are not intended to reduce web growth, they help to control humidity in the environment.

Have you ever experienced web growth in books made by us?  How about books made by other manufacturers?  Where did you find information to help you understand why it was happening? If you have further questions about why web growth occurs or any other questions about the final look of your book, contact your sales or customer service representative.

Below is a a short video that we have produced explaining why web growth occurs.

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