How the hottest EVA hot melt adhesive meets the ne

EVA hot melt adhesive: how to meet the binding process (Part 2)

the adhesion and adaptability of a hot melt adhesive

in the production process, the adhesion of hot melt adhesive will change with the heating temperature, the quality of book block paper, the width and depth of book back milling and back galling, as well as the operating speed of adhesive binding equipment. Mastering these changing factors is very important to improve the adhesion and bookbinding adaptability of hot melt adhesive

(1) heating temperature of hot melt adhesive

the softening point of hot melt adhesive is generally within 70 ~ 100 ℃. This temperature range is only the glue melting temperature. In order to make the hot melt glue reach the ability of bonding books, the heating temperature must reach 150 ~ 180 ℃. According to foreign data, when the glue temperature is 170 ℃, the tensile test value of hot-melt adhesive is 8.83 ± 0.44n/cm when it is coated on ordinary book paper (letterpress paper, paper). When the glue temperature rises to 180 ℃, the tensile test value of hot melt glue will drop to 7.33 ± 0.33n/cm. On the contrary, when the glue temperature drops to 155 ℃, the tensile test value of hot melt adhesive is only 5.22 ± 0.25n/cm

it can be seen that the heating temperature of hot melt adhesive should not be too high or too low. When the temperature is too high, although the fluidity, wettability and permeability of the adhesive are strengthened, the bonding strength will decrease, affecting the tensile resistance of the adhesive. On the contrary, if the temperature is too low, although the viscosity increases, it will affect the fluidity of the glue, the wettability and permeability of the book block, the tensile resistance of the glue, and even unable to bond. Therefore, the heating temperature and gluing temperature of hot melt adhesive must be controlled within an optimal range

(2) relationship between book block paper and gluing temperature

the gluing temperature of hot melt adhesive should also be different when the paper used for book block is different. This is not only because the fiber properties of the paper are different, but more importantly, their thermal conductivity is different, that is, the cooling speed is different. Taking the thermal conductivity of coated paper (coated paper) and non coated paper (letterpress paper) as an example, the former cools the glue faster than the latter. Because the inorganic substances contained in the coated paper, which is the first production and marketing plan in the Chinese industry, are nearly 10 times higher than that of non coated paper, and the inorganic substances have good thermal conductivity, coated paper can make the hot melt adhesive cool faster. The tensile test of hot melt adhesive shows that if the gluing temperature is also 170 ℃, the tensile value of bonded non coated paper can reach 8.83 ± 0.44n/cm, while the tensile value of coated paper can only reach 1.86 ± 0.11n/cm (65g/m2 coated paper) and 1.46 ± 0.11n/cm (100g/m2 coated paper). Therefore, in order to improve the tension value of hot melt adhesive on coated paper, we must increase the glue temperature. Practice has proved that the gluing temperature is generally about 195 ℃. At this temperature, the tension value can reach 4.1 ~ 3.91n/cm (the above data are extracted from foreign materials for reference only)

(3) opening time and production and operation speed of hot melt adhesive

during the use of hot melt adhesive, there are two time variables that must be strictly controlled, one is the opening time of hot melt adhesive, and the other is its curing time

opening time means that the process of applying the hot melt adhesive to the adherend must be completed within the specified bonding time of the hot melt adhesive. Otherwise, after the specified time, the surface of the adhesive layer will form a film, so that the two adherents cannot be adhered firmly. According to the model of hot melt adhesive, the opening time is also different, which can be 7 ~ 15 seconds or 15 ~ 20 seconds. After the two adherends are bonded within the specified time, they must be cooled for a certain time before they can be pressurized or turned. Otherwise, the adhesion of the hot melt adhesive will be affected, causing product deformation or page falling off. This cooling time is called curing time. The curing time varies according to the model of hot melt adhesive. Generally, the curing time is 3 ~ 5 minutes

the opening time and curing time of hot melt adhesive are closely related to the running speed of the machine, especially the opening time. If our service team can help you disassemble the machine correctly, pack and transport the glue, and the opening time is 7 ~ 15 seconds, then after milling and roughening the back of the book block, it must be completed within 15 seconds from the application of glue liquid to the bonding between the cover and the back of the book (there is no gauze and cardboard on the back of the book), so that the hot melt glue can achieve good bonding effect. If the machine runs slowly and cannot complete the bonding of the cover within 15 seconds, the bonding between the cover and the back of the book is not very firm and the bonding strength is poor. Therefore, to determine the opening time of hot melt adhesive, we must consider the normal operation speed of adhesive binding equipment

in addition, it is also necessary to master the curing time of the hot melt adhesive, because it takes 3-5 minutes for the adhesive to be basically cured after it is brushed onto the back of the book. Books cannot be cut and pages cannot be flipped before it has reached or nearly completed curing. Otherwise, it will cause the back cover to be arched, the back to be deformed and the pages to fall off. Therefore, if the interval between the book binding and the three-sided cutting process is short, try to extend the time to make the glue fully solidified before cutting

precautions for using hot melt adhesive

(1) hot melt adhesive can only be heated with oil bath spacer or sealed electric heating plate, and it is forbidden to use open fire for heating

(2) the hot melt adhesive can only be used after being preheated by the preheating pot and released into the glue bucket of the glue coating liquid. Therefore, the amount of glue in the preheating pot should be appropriate. If it is added too much, the glue will be easy to age and affect the adhesion. It should be added less and more frequently

(3) complete all the bonding work of the books within the opening time of the hot melt adhesive. In case of shutdown or other faults, the books that have been painted with high-end fine chemicals such as primer catalyst, pharmaceutical intermediates, electronic chemicals and so on in the book folder but not applied with side glue should be taken out in time to prevent the book block from stopping on the rubber wheel

(4) the temperature of molten colloid should be strictly controlled within the use temperature range. It is not only necessary to prevent the temperature of the glue from being too low, which will affect the fluidity, wettability and permeability of the glue, but also to prevent the temperature from being too high, which will affect the viscosity of the glue and cause the aging of the glue

(5) the glue pot that melts the glue liquid should be cleaned regularly, preferably twice a year, to ensure that the glue pot is clean. When cleaning, pay attention not to use paraffin as cleaning agent, because paraffin is flammable and has potential safety hazards, it is recommended to use a special cleaning agent. In addition, the sensitivity of the temperature display should be ensured to ensure the reliability and accuracy of the displayed temperature

(6) after the hot melt glue melts, the glue temperature is between 100 ~ 180 ℃. If it is not used properly, the glue will stick to the skin and the skin will be burned. Therefore, when using hot melt adhesive, we must take protective measures and pay attention to safety

correct use of hot melt adhesive

correct use of hot melt adhesive can reduce many binding quality problems. The key to the correct use of hot melt adhesive is to correctly grasp its use temperature. In the following, taking the products of Wuxi Wanli bonding material factory as an example, the application method of hot melt adhesive is introduced in detail

(1) edge glue c-22

the service temperature is generally 120 ~ 130 ℃

(2) back glue kg-6 (offset paper)

the service temperature is generally 150 ~ 170 ℃

(3) gum kg-8 (coated paper)

the service temperature is generally 160 ~ 180 ℃

(4) the use temperature of all kinds of side glue and back glue should be changed according to the relationship between the use temperature of the glue pot used by each machine and the running speed of the machine, as well as the relationship with the change of ambient temperature

(5) if the back glue is used at a higher temperature, it will cause too many air holes on the back of the book. If it is wet paper, it will also cause short positions on the back of the book

(6) the scraper wheel and roller must be adjusted to the correct position, and the first roller should be adjusted about 0.2mm lower than the second roller

(7) the hot melt adhesive in the glue pot should be appropriate, less frequently, and the temperature of the hot melt adhesive in the preheating pot should not exceed 160 ℃

(8) milling back, developed a series of surface modification formulas, milling groove depth: offset paper should reach more than 1.2mm; Coated paper shall be more than 1.5mm. The back milling and slot milling knives should be adjusted well, the knife surface should be kept clean, the knife edge should be sharp, the paper scraps should be milled clean, and there should be no paper scraps left behind the book milling. If there are scraps of paper left behind the milling, it will affect the permeability of hot melt adhesive, and it is easy to have quality problems such as book page falling

information source: Printing Technology