Little knowledge about hot melt adhesive in glue machine(1)

Hot melt adhesive is a kind of plastic adhesive. Its physical state changes with temperature within a certain temperature range, while its chemical properties remain unchanged. It is non-toxic and tasteless, and is an environmentally friendly chemical product. Because the product itself is solid, it is easy to package, transport, store, solvent-free, pollution-free, non-toxic; and the production process is simple, high value-added, high bonding strength, fast speed and other advantages.

Temperature has a great influence on the adhesiveness, fluidity, wettability, and permeability of hot melt adhesives, and the adhesive properties of different types of hot melt adhesives are different. For the same kind of hot melt adhesive, as the temperature increases, the fluidity and wettability of the glue become better, and the fastness of the glue binding becomes better. However, when the temperature is too high, the polymer, the main component of the hot melt adhesive, may undergo thermal depolymerization, thereby reducing the adhesion of the hot melt adhesive and causing the glue to become carbonized and brittle.

Hot melt adhesive has good viscosity and wettability at 130°C~180°C. The gluing temperature of the hot melt adhesive varies with the paper used for the book core. The reason is that different papers have different thermal conductivity. We divide paper into coated paper (such as coated paper) and non-coated paper (such as offset paper and letterpress paper). The thermal conductivity of the two is very different. The inorganic matter contained in coated paper Nearly 10 times higher than non-coated paper. Inorganic materials are excellent heat conductors, so coated paper makes hot melt adhesives cool and solidify faster.

The tensile test shows that when the temperature setting for non-coated paper is used, when used on coated paper, the adhesion tensile value will drop to less than 30%. Therefore, the application temperature of hot melt adhesive needs to be increased for coated paper during use, and it is recommended to increase 5~10℃ can make the binding of coated paper have good strength.

The curing time refers to the time required for the hot melt adhesive to be coated on the substrate after it has melted, and then solidified into a solid, and the next step can be performed. That is, after the cover and the book block are bonded, they are cooled and dried for a period of time before entering the next process. If the hot melt adhesive is not cooled and dried, the back of the book will easily be deformed, which will affect the appearance quality of the book. The wet glue is easy to stick to the cutting blade, resulting in dullness of the blade and unstable cutting size. The curing time of hot melt adhesive is generally 3~5 minutes.

The gluing thickness of the hot melt adhesive should be determined by the thickness of the book, the type of printing and cover paper, and the type and quality of the hot melt adhesive. Generally speaking, the fastness of perfect binding mainly depends on the thickness of the book block. The thinner the book block, the better the bonding fastness. The thickness of the book block is 10mm, and the thickness of the glue layer is 0.4mm; the thickness of the book block is 20mm, and the glue layer must be 0.8mm. Coated paper should be about 0.2mm thicker than non-coated paper.