PUR book binding hot melt adhesive

What is PUR

PUR is a polymer compound with an urethane bond (NH-CO-O), and the molecular chain end is an isocyanate group. The basic composition of PUR is a polyhydric alcohol (polyester, polyether, etc.) with active hydrogen at the end and an addition polymer of low molecular weight diol (chain extender) and isocyanate. Glycol and isocyanate react to form rigid molecular segments, while polyol and isocyanate react to form flexible molecular segments, so PUR is a hot melt adhesive with both rigidity and flexibility. In addition, the isocyanate groups encounter irreversible cross-linking reaction with moisture in the air, forming a strong adhesive layer, which is the characteristic of PUR hot melt adhesive.

The background of PUR

With the diversification of printing products, the printing industry uses a variety of different weights of printing paper, plastic films, varnishes, and inks. The latest PUR adhesives will not be difficult when applied to these materials. . PUR hot melt adhesive can firmly bond the coated paper, and its bonding strength is 40-60% higher than traditional adhesives. In ordinary wireless binding, the printing ink on the paper will migrate to the spine, and PUR hot melt adhesive will not have this problem at all.

What makes PUR unique is that it can bond a variety of materials, including varnish coatings, UV curing layers, plastic films, and coated paper.

The development process of PUR

Although the first-generation PUR hot melt adhesive can achieve linkage production, it takes 24 hours after book binding to reach the maximum bonding strength, at this time it can withstand the external forces in transportation.

The second generation of PUR hot-melt adhesive was launched in 1994, and realized linkage cutting. If there is a certain amount of moisture in the paper, the binding area maintains a high air humidity, and after 4 hours of glue application, sufficient adhesion strength can be obtained. Nevertheless, the second-generation PUR still has deficiencies: in the cold winter, the relative humidity of the air 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 one hour, and only requires the moisture in the paper to complete the moisture curing cross-linking reaction, and the books can be directly taken offline for plastic sealing. However, the improvement of the third-generation PUR hot-melt adhesive also brought negative effects. Because PUR can achieve initial bonding strength in a short time, some manufacturers found that PUR soon became sticky in the glue pot during use. , Especially in wet areas and those manufacturers that mainly bind thin booklets, because PUR stays in the glue applicator for a long time when binding thin booklets.

The fourth-generation PUR is already on the market. It has better fluidity than the third-generation PUR hot-melt adhesive and can achieve the expected initial tack strength, while prolonging the residence time of PUR in the glue pot. The fourth-generation PUR has replaced most of the second- and third-generation PUR products, and is particularly successful in new nozzle systems. At the same time, books bound by the fourth-generation PUR hot-melt adhesive can be shipped to all places on the same day. Due to the fast drying and fixing speed, the productivity of books and periodicals is improved, and at the same time, the production flexibility is also improved.