Interpretation of PUR bookbinding hot melt adhesive (below)

3. Spine formation

When ordinary hot melt adhesives are used to bind irregularly textured art paper book blocks, a large amount of wrinkles are generated at the grooves. Because PUR hot melt adhesives are cold glue adhesives, the working temperature is low, so the moisture of the paper at the spine is not lost. At the same time, the PUR adhesive layer has a certain degree of ductility during the drying process, allowing the paper fibers to recover.

In addition, due to the small amount of PUR hot melt adhesive used in the binding process, very little adhesive is squeezed out on the encapsulating table, and the two sides of the splint firmly wrap the cover on the book block to form a stiff spine.

4. The smoothness of the book block cut is trapezoidal

Since the PUR hot melt adhesive has only half the thickness of other hot melt adhesives, the incision is smooth without trapezoidal shape and the edge of the book cover is also very smooth.

5. Solvent resistance

Some bookbinding experts believe that PUR is the only binding material that is both solvent and grease resistant. The dry-fixed PUR adhesive layer is immersed in solvents and greases used in the printing industry, such as methyl ethyl ketone and alcohol, and these chemicals have no effect on the PUR layer. On the other hand, some of the solvents used in the printing industry will completely soften or even dissolve frequently used hot-melt adhesives, such as EVA.

6. For hardcover cost savings

For many years, the book block of the hard-back book has been used for sewing, and before brushing, a tough adhesive is applied to the book block. According to the use of some users, put the lock book line book block flat, and then brush the PUR hot melt adhesive, this binding method can save about 30-40% of the cost.

7. Good rounding performance and arc deformation

Many hardcover books use round spine backs to enhance the beauty and durability of the book. Brush the PUR adhesive on the book block, and then round and ridge to get a more beautiful round spine. Since the PUR coating and the book block are dried in a circular state, the durability of the round book back is maximized. In the case of ordinary hot melt adhesives, when the book block is bound, the glue is generally first brushed and then rounded, so the durability of the circle cannot reach the effect of PUR adhesion.

PUR usage notes

Some precautions must be taken when using the PUR to prevent the PUR from being cross-linked enough to cause the adhesive layer to come off easily. In order to meet the needs of PUR gluing, there are already open plastisol and closed pressure nozzle systems for PUR gluing.

The PUR binding device using roller coating requires a sealed pre-melter that is not affected by the humidity of the air. The coating device, which is easy to clean at the end of the job, must remove the PUR residue after the gluing is completed. The coating roller can be easily detached and adhered. The glue is removed.

Because the PUR hot melt will react and solidify when exposed to air, an inert gas (such as nitrogen) must be used to form a protective layer. In addition, the fumes generated by the hot melt adhesive nozzle and the upper space of the plastic tank must also be promptly discharged.

When PUR is overheated (above 140°C), isocyanate gas is released, causing an impact on the human body, such as irritating the mucous membranes of the eyes, nose, and throat, and causing headaches and other symptoms when large amounts of smoke are inhaled. According to the experiment, the usual operating temperature cannot exceed 120°C. From a safety point of view, it is advisable to set a temperature control device and a local exhaust device for the heating of the glue to promote gas diffusion. When binding a thick book, it is necessary to configure a conveyor belt that is long enough to prevent the spine from deforming and to prevent the adhesive from adhering to the cutting edge.

Looking to the future

Annual reports and business magazine binding are one of the main application markets for PUR because these businesses need to bind advanced coated paper and textured art paper. Future PUR will continue to exert its advantages in this market.

With the popularity of PUR, some publishers have already felt the advantages of PUR. They demand the use of PUR binding books to ensure the quality of binding and the durability of books. Books with PUR binding will be more and more.

Hardcover books are the next area of ​​PUR application. PUR adhesives are cheaper than lock stitches. Fourth-generation PUR hot melt adhesives can be interlocked and many hardcover bookbinding manufacturers have begun investing in PUR binding. Due to the cost advantages and high quality of PUR's hardcover, more and more hardcover manufacturers use PUR hot melt adhesives.

Source: "Graphic Arts" Author: Wang Shouhong