According to China's book printing quality standards and in order to adapt to international requirements, China has made new revisions to the paper and drafting standards for primary and secondary school textbooks. This new situation has accelerated the development of wireless glue binding. Booking has been gradually phase out iron wire.
According to statistics from related departments, China produces about 7 billion books each year, and its linked form uses about 4.2 billion copies in the form of wireless glue binding. This huge market has greatly stimulated the manufacturers of adhesives, and the number of manufacturers joining EVA hot melt adhesives with various investment methods has increased. Due to the short production time of EVA hot melt adhesives in China, the production process and raw materials of many manufacturers are not strictly controlled, the technical content of products is low, and the quality of hot melt adhesives produced is uneven; moreover, due to a considerable part of the printing manufacturers The lack of understanding of the properties of the glue and the improper use of the glue have resulted in an endless stream of binding quality accidents. According to the statistics of the quality inspection department, more than 60% of the print quality accidents are due to binding problems, such as book pages falling, shorts, and poor adhesion. Therefore, analyzing and studying the performance and characteristics of EVA hot-melt adhesives and using EVA hot-melt adhesives reasonably are issues that should be attached great importance in the current post-press processing industry.
EVA hot melt adhesive is a solid, fusible polymer that requires no solvent and no moisture. The EVA hot melt adhesive is a solid at room temperature, and when heated and melted to a certain extent, it becomes a viscous liquid with a certain viscosity. The molten colloid is a light brown translucent liquid.
The main components of EVA hot melt adhesive consist of 6 parts, namely basic resin, tackifier, plasticizer, filler, antioxidant and viscosity modifier:
1. The basic resin is the main component of making EVA hot melt adhesives, accounting for more than 50% of the glue ingredients, strong bonding strength, good curing, and the mechanical properties at the low temperature basically unchanged.
2. The function of the tackifier is to make the EVA hot melt adhesive more suitable for the penetration and adhesion of the paper. Adding the tackifier can improve the fluidity of the adhesive and the wettability to the adherend, increase the adhesive strength, and achieve the bonding requirements. Tackifiers generally use rosin, which has good compatibility with the resin.
3. Viscosity modifiers play a role in the hot melt adhesive to reduce the melt viscosity, increase fluidity, wettability; adjust the solidification rate, fast bonding firmly. Viscosity modifiers generally use waxes, and they must be properly proportioned with other additives.
4. The antioxidant is added to prevent premature aging and deterioration of the hot melt adhesive and ensure that the adhesive performance of the EVA hot melt adhesive is stable and does not change. Antioxidants are generally selected di-tert-butyl p-methylphenol, the best effect, the amount of control in the 0.1% to 1%.
EVA hot melt adhesive characteristics
1. The hot melt adhesive is 100% solid at room temperature and becomes a liquid when heated to a certain temperature, and quickly becomes a solid once it cools below the melting point. It has a melting point of 80° C., an opening point of 7 to 13 seconds, a solidification point of 7 to 14 seconds, and a cooling point of 2 to 3 minutes.
2. Has the characteristics of fast curing, low pollution, and strong adhesion. The adhesive layer has both a certain flexibility and a certain hardness.
3. There is re-stickiness. After it has been painted and solidified on the adherend, it can be re-heated and used again.
4. Easy to use. As long as the EVA hot melt adhesive is heated and melted into a liquid, it can be coated on the adhered object, and the full curing needs to be achieved after a few seconds of pressing and cooling.
How to use EVA hot melt adhesive
When using EVA hot-melt adhesive, glue can be added at any time according to the usage amount, and how much is added is needed, and the amount of glue should be properly grasped.
Use EVA hot melt adhesive to preheat for 2 hours, non-preheated adhesive cannot be used. The reason is as follows:
1. Because the hot melt adhesive is in a solid state at room temperature, if no preheating or no preheating device is used to place the glue block directly into the glue pot, the homogeneity of the colloid will be directly damaged, resulting in uneven coating and affecting the books. Appearance Quality.
2. Putting the dry glue block into the pot will destroy the temperature of the colloid and affect the opening time and curing time of the colloid, especially the adhesive force of the back glue. The dry glue sticks cannot be melted immediately when they are put into the glue pot, and the surface seems to be melted. In fact, the temperature is not evenly distributed among the molecules. This kind of melting is not suitable for reconciling non-uniform glue, and the fluidity and permeability are relatively poor. It directly affects the binding strength of the book and the firmness of the book.
3. Avoid direct heating with open flames. There are two heating methods for EVA hot melt adhesives: one is to use a spacer oil bath to heat; the other is to use a sealed hot plate for heating. Heating with an open flame is extremely difficult to control and the colloid will age and deteriorate rapidly.
4. Plastic pots should be cleaned regularly. The glue storage capacity of the general glue pot is about 5kg, and it is used once for 4 hours. However, due to the distance between the rubberizing wheel and the bottom of the glue tank, the glue at the bottom of the glue tank can not be used within 4 hours, and it has been heated. This part of the bottom glue has repeatedly heated itself and contains paper scraps. The separated impurities, which act as catalysts, will accelerate the aging effect of the newly added glue. Therefore, the plastic pot should be cleaned regularly, and it is usually cleaned half a year.
Adhesion and adaptability of EVA hot melt adhesive
1. The heating temperature must meet the requirements of the process flow, the softening point of the hot melt adhesive is too low, and the temperature of the wireless glue-stitching shop is too high, and the page-breaking phenomenon is likely to occur. When the regular paper book is glued, it is required that the temperature of the hot melt adhesive is controlled at about 170-180°C, and the adhesive force is best. The heating temperature of the hot-melt adhesive should not be too high or too low, and the adhesive strength of the excessively high temperature will decrease. If the temperature is too low, it will solidify again. In short, the temperature of the hot melt adhesive must be controlled within a suitable range.
2. The relationship between the paper quality and the gluing temperature also has a big difference. This is not only the difference in the properties of the paper fiber, but more importantly, its thermal conductivity is also different. The better the paper quality, the faster the cooling rate; on the contrary, the paper quality is somewhat slower than the cooling rate. Therefore, the gumming temperature should be changed depending on the material of the book block paper.
3. The open point of the hot melt adhesive also has a direct relationship with the speed of the machine operation. In the use of hot-melt adhesives, there are two points that must be mastered: one is the open point of the hot melt adhesive and the other is the solidification point. According to the process requirements, the EVA hot melt adhesive on the book back to the cover, must be completed in the hot melt adhesive bonding time, more than this time, the back of the book on the film, the book cover and the book back can not be bonded, This is why the open point and solidification point of the EVA hot melt adhesive must be controlled at about 7 to 13 seconds. The cooling and hardening point of the hot melt adhesive should be controlled at 2 minutes. When it does not reach the cooling hardening point, the book cannot be pressurized, turned, or cut, otherwise it will cause book back deformation or book off.
4. Use EVA hot melt adhesive environment and conditions. The factory building using EVA hot melt adhesive should maintain normal temperature and humidity. Under normal circumstances, the workshop should be kept at a constant temperature, and the temperature should be controlled at 15-27°C. The storage temperature of books produced with EVA hot-melt adhesives is between 1°C and 40°C, and the deformation of the paper caused by heat-induced deformation of the adhesive layer should be avoided.
According to the different models and different technical performances of hot melt adhesives, different types of hot melt adhesives are used in different seasons, and strict distinctions must be made. Different temperatures, opening hours and curing time will also change. Therefore, the glue temperature in summer should be lower than the ambient temperature by about 10°C to ensure the normal operation of the open point and solidification point.
Nowadays, a new type of polyurethane (PUR) adhesive has emerged abroad. It has better performance than EVA hot melt adhesives, and its adhesive force is stronger. It is the development direction of binding processing in the future.
