Among the adhesive options, PUR adhesives are highly resistant to extreme temperatures, oils, and solvents, and only a small amount of PUR is needed in the binding process. Therefore, PUR adhesive binding, which enables books to lie flat on a table when open, is not only a good option for paperback binding but also increasingly adopted in hardcover binding. Have you ever experienced the situation in which an adhesive-bound book turned loose leaves or adhesive failure occurred because of poor weather? Now, these problems can be solved by using PUR.

PUR, first used in bookbinding in 1989, is gaining in popularity as an adhesive that shows great potential and good value for high-quality bookbinding. It is mainly because PUR-bound materials tend to be better secured and lie flatter when open than those bound by other adhesives.

First-generation PUR-bound books: They had to sit for 24 hours to gather enough strength to withstand the rigors of trimming and delivery.

Second-generation PUR (developed in 1994)-bound books: They could be trimmed and delivered after they had been bound for four hours, providing that enough moisture was retained in the paper and in the binding area.

Third-generation PUR-bound books: They required only one hour before getting ready for trimming and delivery, and they could be shrink-wrapped directly offline.

Fourth-generation PUR: It allows for use of a smaller amount of PUR in the binding process than the third-generation PUR.

As PUR adhesive binding requires a small amount of PUR, provides strong adhesion, and allows for hands-free reading, it shall become a cost-saving and high-quality binding option in the future.

Advantages of PUR Adhesive Binding
Lower melting point:
The melting point of PUR adhesives is between 120℃ and 130℃, which saves energy and reduces wear on machine parts.

Stronger adhesion:
Due to its polar molecular structures, PUR can grab and hold films or sheets of paper together tenaciously. Page pulls average up to 40% to 60% better with PUR than with traditional adhesives.

Books can lie flatter when open:
When applied at its recommended thickness, which is 0.01 inch, PUR enables books to lie flatter when open than those that are bound through use of other adhesives, and, therefore, allows for hands-free reading.

Cold and heat resistance:
Temperature is a crucial factor in the quality of adhesive-bound materials that are to be shipped abroad. As PUR remains stable at extreme temperatures from - 40℃ to 93.3℃, materials bound by PUR will not fail even when shipped to the south pole or the north pole regions by air or by sea. You may carry out an experiment by placing a hot-melt adhesive-bound book and a PUR-bound book in a freezer overnight and see which one becomes loose the next day. With PUR’s resistance to extreme temperatures and humidity, PUR-bound books are suitable for being shipped over a long distance by sea.

Less wrinkling of spines:
Cross-grained paper bound with standard hot-melt adhesives sees considerable wrinkling of book spines. However, binding paper with PUR adhesives is operated at a lower temperature that will not remove too much moisture from paper. PUR remains somewhat malleable as it cures, which allows paper fibers to return to their original orientation and causes less wrinkling of spines.

Less wear on trimmers:
As PUR adhesives are applied at half the standard thickness of hot-melt adhesives, PUR adhesive binding causes less wear on trimmers.

Square spines:
Only a small amount of PUR is needed for binding, which allows for square spines of PUR-bound materials.

Solvent resistance:
While hot-melt adhesives dissolve in oils and solvents, cured PUR is fully resistant to oils and solvents.

Three reasons for using PUR:
1. It is designed specifically for binding coated paper.
2. PUR-bound pages are most unlikely to loosen from binding (PUR ensures good page-turning effects and
　 longevity of PUR-bound materials).
3. PUR is harmless to the environment; PUR-bound materials can be easily recycled.

Another reason: paper
More and more binders use PUR adhesives because of the changes in the ingredients of paper.

Nowadays, paper consists of more filling materials than before. High-fiber paper used to be common in the past, but now some types of paper that contains more clay, kaolinite, and other materials are increasingly used.

The percentage of filling materials for paper used to be 20% of the paper ingredients on average; nowadays, it is no more unusual that up to 54% of the paper ingredients are filling materials. This has caused many problems with perfect binding, as fewer fibers result in poorer adhesion. Fortunately, PUR can help solve the problems, and the key to the success lies in fiber sueding and spine making.

The future of PUR:
PUR adhesives have been widely used for the binding of catalogues, directories, travel guides, and books. Now, the use of PUR for hardcover binding is also on the increase, as the features of PUR can not only save the cost of sewing but also maintain high binding quality. Since the features of PUR ensure customer satisfaction, PUR will surely increase its market share in the binding sector.