The emergence and development of hot melt adhesive for bookbinding

The emergence and development of hot melt adhesive for bookbinding

In 1989, PUR binding adhesive was first tested in North America, when PUR was only used for general paperback binding. Now, print bookbinders that originally used PUR hotmelts found PUR to be of high value in applications such as hardcover books, annual reports, catalogs, yellow pages and magazines.

Today, PUR has been rapidly promoted and applied in North America. In 1995, it was reported that only 28 manufacturers were using PUR in North America. By the end of 2002, this number had increased to 50. Compared with commonly used hot melt adhesives (EVA hot melt adhesive, PVA latex), PUR has many advantages. The most important point is that PUR has a high bonding strength, and the appearance of the book is smooth after opening, which is easy to read.

What is PUR

PUR is a polymer compound with a urethane bond (NH-CO-O), and the end of its molecular chain is an isocyanate group. The basic composition of PUR is an addition polymer of polyols (polyesters, polyethers, etc.) with active hydrogen at the end, and low molecular weight diols (stretchers) and isocyanates. Diols and isocyanates react to form rigid molecular refining segments, while polyols and isocyanates react to form flexible molecular refining segments, so PUR is a hot melt adhesive with both rigidity and flexibility. In addition, the isocyanate group will produce an irreversible cross-linking reaction when it encounters moisture in the air, forming a firm adhesive layer, which is the characteristic of PUR hot melt adhesive.

The background of the emergence of PUR

With the diversification of printing products, the printing industry uses a variety of printing papers, plastic films, varnishes and inks with different weights. The latest PUR adhesives are used in the bonding of these materials without great difficulties. . PUR hot melt adhesive can firmly bond the coated paper, and its bonding strength is 40-60% higher than that of traditional adhesives. In ordinary perfect binding, the printing ink on the paper will migrate to the spine, and PUR hotmelt does not have this problem at all.

PUR is unique in its ability to bond a wide variety of materials, including varnish coatings, UV cured layers, plastic films and coated papers.

The development process of PUR

Although the first generation of PUR hot-melt adhesives can achieve linkage production, it takes 24 hours after books and periodicals are bound to reach the maximum bonding strength, and then can withstand the external forces during transportation.

The second generation of PUR hot-melt adhesive was launched in 1994 and realized linkage cutting. If the paper has a certain amount of moisture, the binding area maintains a high air humidity, and sufficient adhesive strength can be obtained after 4 hours of gluing. Nevertheless, the second-generation PUR still has its shortcomings: in the cold winter, the relative air humidity drops to 20%, and the cross-linking and fixing of the PUR glue is a problem.

The third-generation PUR can be completely dried and fixed in only 1 hour, and only the moisture in the paper can complete the moisture-curing cross-linking reaction, and the books can be directly plastic-sealed offline. However, the improvement of the third-generation PUR hot melt adhesive has also brought negative effects. Since PUR can achieve initial bonding strength in a relatively short period of time, some manufacturers find that PUR quickly becomes sticky in the glue pot during use. , especially in wet areas and those manufacturers that mainly bind thin books, because PUR needs to stay in the gluer for a long time when binding thin books.

The fourth-generation PUR has been launched. It has better fluidity than the third-generation PUR hot melt adhesive, can achieve the expected initial tack strength, and at the same time prolong the residence time of PUR in the glue pot. Fourth-generation PURs have replaced most second- and third-generation PURs, and are used more successfully in new nozzle systems. At the same time, the fourth-generation PUR hot-melt adhesive-bound booklets can be shipped to various places on the same day. Due to the fast drying and fixing speed, the productivity of the book is increased, and the production flexibility is also increased.