How to use hot melt adhesive correctly, have you got it?

发布时间：2021-04-28 0

Factors Affecting the Use of Hot Melt Adhesive for Book Binding

Operating temperature



Temperature has a great influence on the adhesiveness, fluidity, wettability and permeability of hot melt adhesives. The adhesive properties of different types of hot melt adhesives are different. For the same hot melt adhesive, as the temperature increases, the adhesive The better the fluidity and wettability of the liquid, the better the binding fastness, but 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 is carbonized and becomes brittle. Senlai hot melt adhesive has good viscosity and wettability at 140℃~160℃. The gluing temperature of the hot melt adhesive varies depending on 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 It is nearly 10 times higher than non-coated paper, and inorganic matter is an excellent heat conductor, so coated paper makes the hot melt adhesive cool and solidify more quickly. The tensile test shows that when the temperature setting for non-coated paper is used, when used on coated paper, the bond tensile value will drop to less than 30%. Therefore, the application temperature of the hot melt adhesive needs to be increased for the coated paper during use, and it is recommended to increase it. 5~10℃ can make the binding of coated paper have good strength.

Opening hours



The open time refers to the liquid retention time of the hot melt adhesive coated on the substrate after the hot melt is melted, that is, the time that it is applied to the back of the book to be bonded and set. If this time is exceeded, the surface of the adhesive layer will conjunctiva, and the adhesion will decrease, causing page drop and uneven quality of the back of the book. When hot melt glue is used, there are three types of glue: low speed, medium speed and high speed glue according to the different glue machine. Low-speed perfect binding is about 2000 books/hour, and the opening time is 15-20 seconds; medium-speed perfect binding is about 2000-4000 books/hour, and the opening time is 5-10 seconds; high-speed perfect binding is about 4000 books/hour, and the opening time is 2-7 seconds.



Curing time



The curing time refers to the time required for the hot melt adhesive to be applied to the substrate after being melted and then solidified into a solid for the next step. 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 step. The time of the process. If the hot melt adhesive is not cooled and dried, the back of the book is likely to be deformed, which will affect the appearance of the book and periodicals. The wet glue is likely to stick to the cutting blade, causing the blade to become dull and the cutting size to be unstable. The curing time of hot melt adhesive is generally 3~5 minutes.



Adhesive layer thickness

The gluing thickness of the hot melt adhesive should be determined according to 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.



Production environment and equipment configuration



Hot melt adhesive is a kind of thermoplastic material. After application, it is greatly affected by the environmental temperature and humidity. For example, when the temperature is high in summer, the glue is not easy to solidify and cool down, causing sticky tape, sticking knives, dirty books, deformation, etc.; when the temperature is low in winter, the glue After the liquid is applied, it solidifies in advance, which shortens the opening time, and causes weak bonding, uneven book backs, peaks and pits formed by glue, etc.; in some areas, the humidity is too high, and the booklet is not shaped after the cover is wrapped, and the back of the book is twisted and deformed. When the book is cut, the back of the book will wrinkle and break too much due to slight pressure. In order to maintain the stability of the hot melt adhesive, the ambient temperature should be kept between 15°C and 26°C, and the humidity should be kept at about 50%. Generally speaking, the temperature of the environment is low in winter, and the temperature of the glue can be adjusted higher; otherwise, it should be lowered in summer. In addition, the equipment configuration of glue binding will also have an impact on quality. In contrast, the quality stability and production efficiency accuracy of imported glue binding machines are better than those of domestic models.