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We get a lot of questions when it comes to preventing board warp in the book binding and printing industry. Printing and binding are a lot like cooking, and external factors like excess heat and humidity can harm your final product. 

In this article, we break down some of the top questions we get about board warp and cover how you can prevent issues in your production process. Use these tips to improve your printing and binding results.

What materials are we talking about specifically?

While board warp can affect many materials, like wood, we are focusing on printing and graphics boards used to create books and signage. 

Spec Board, also known as High-Density board, is often used for library binding and school books. The high-density board is very rigid due to its construction. The high-density board and the thick book blocks they are adhered to are hefty, which means extra strong binding methods are required to make these books withstand long-term use.

Graphic Board is usually defined as a board to be used for graphical purposes, book binding, and rigid boxes. Graphic board has excellent surface properties for printing and ink distribution, but are not as smooth as more expensive boards made from virgin fibers. However, one of the leaders in the board industry, ESKA, produces true graphic boards that are suitable for all printing techniques.
Virgin Board is made from virgin fibers only. This means the cellulose fibers used to make the board contains no recycled content and is made directly from the pulp of trees. Virgin board is more expensive but offers a smoother surface for printing board games, puzzles, and graphics. 

Recycled Board is made from, you guessed it, recycled fibers. Most book binding boards are made from recycled products. In fact, the book binding materials provided by ESKA are made with 100% post-consumer recycled fibers. 

How much does the external environment affect board warp?

When paper and board are exposed to the surrounding environment, they absorb or evaporate moisture depending on the relative humidity. The absolute moisture content of the board will range from 5% to 8%, depending on the manufacturer. ESKA Board, for example, has an absolute moisture content of 7%. 

Suppose the relative humidity of the environment is below 50%. In that case, moisture will evaporate out of the unprotected pallets of the board, resulting in a concave warp of the top sheets on the pallet.

When the relative humidity is above 55%, the board will absorb moisture out of the environment, and in theory, should result in a convex warp of the top sheets. However, since expansion forces are much less than contraction forces, the convex warp will not be noticed.

Do temperature and humidity play a big role in causing board warp?

Yes, as answered above. The most important factor to know, however, is the moisture content of the board. 

Generally, end product warp of books, files, game boards, and puzzles is caused by liner weights, grain directions, and the type and amount of adhesives used. However, in winter and summer periods, when the pallets of the board come out of a warehouse and are converted without acclimatization, there is a high risk of warping and blister issues. 

To prevent this from happening, when the pallet of boards is more than 10°F (5°C) lower than the temperature on the working floor, acclimatization is necessary for at least 48 hours while the pallet is still wrapped in its original plastic packaging.

How can board warp be prevented?

  • Always let the board acclimatize to working floor condition, still wrapped in the original plastic packaging.
  • Use grain directions of all materials parallel to the spine of the book. Game boards, puzzles, wraps, and liners should be placed in parallel directions with the board.
  • Use cover or wrapper material with as little case making adhesive as possible, preferably 1 mill.
  • Make sure that case making adhesive is applied homogeneously over the width of the sheet.
  • Choose an end sheet with the same or higher fiber weight compared to the wrapper.
  • Use as much casing in adhesive as necessary to create a flat case, preferably 1.5 – 2 mil.
  • Ensure the casing coated in the adhesive is applied homogeneously and with equal amounts on the front and backside of the book block.

Does working in a temperature-controlled environment help?

Generally, working in cool areas with low humidity helps prevent warping issues, especially in dry winter months. We recommend working at a temperature of 75°F with a relative humidity of 50% when printing or binding. However, if you use the tips above, you should manufacture products with a problem regardless of your environment.

Get Help from the Experts

Thank you to ESKA, a leader in high-performance packaging solutions, for providing information for this blog. Located in the Netherlands, ESKA is a renowned partner with many brands worldwide.

If you’re still experiencing board warp or have questions about how to improve your bookbinding or printing process, our network of experts can help. We’re always here to answer questions.

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Topics: board warp, causes of board warp, printing, digital printing