Performance of hot melt adhesive for bookbinding

High-performance adhesives exhibit significant changes in melt viscosity with temperature. Specifically, when the application temperature rises above 150 degrees Celsius, the adhesive's melt viscosity decreases rapidly to facilitate application and maintain appropriate penetration; conversely, as the temperature decreases, the viscosity increases rapidly, leading to quick curing and ensuring effective fast binding. Hot melt adhesives require a suitable melt viscosity to maintain good penetration, which is crucial for perfect binding. However, excessively low melt viscosity will result in insufficient adhesive on the spine. A melt viscosity of 4000-5000 centipoise is ideal for hot melt adhesives at 66 degrees Celsius. Good adhesion and penetration mean that the adhesive should quickly wet the spine when the equipment is running at high speed, possessing excellent cohesive strength to prevent stringing and cracking or page unraveling upon cooling.

To achieve this goal, changing the composition of the adhesive is one aspect, but the key is to improve the cohesiveness and toughness of the base resin, and to introduce resins with strong adhesion, hardness, low melt viscosity, and the ability to dissolve or solidify rapidly when the temperature changes. A good adhesive must also have good tensile strength. The loose pages, falling pages, and breakage that occur during the use of perfect-bound books are directly related to the tensile strength of the hot melt adhesive. Tensile strength is typically 20-30 kg/cm². The hot melt adhesive must also have good elongation at break. A high elongation at break means good toughness; only with good toughness can the book be prevented from breaking easily. Elongation should be greater than 300%.

The curing speed of the adhesive must be synchronized with the binding speed of the perfect binding equipment. The curing speed directly affects the forming quality and cutting quality of the perfect binding, especially for high-speed binding lines. If the curing speed is too slow, the spine of the book will deform during transport; a thick adhesive layer will cause the spine to be uneven, easily stick to the cutting blade, and the spine to tear and deform easily. The curing speed of hot melt adhesive is directly related to its softening point. Hot melt adhesives with high softening points should be selected. The softening point of a good quality adhesive should be greater than 850°C.