Proper use of EVA hot melt adhesive, open the perfect binder and analyze common problems (one)
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Proper use of EVA hot melt adhesives and the opening of wireless perfect binding machines is a very important issue in the current post-press binding. It is related to the product quality and social impact of our books and magazines, and directly related to the benefits of factory enterprises. In order to assist each bookbinding processing unit to correctly understand, use EVA hot melt adhesive, open a perfect wireless binding machine, correctly handle the common quality problems of wireless binding, and ensure that the quality of processed products meets the standard requirements, and put forward the following views for peers. reference.
First, VA hot melt adhesive and its use
EVA hot melt adhesive is the most used type of bonding material in China, namely, the adhesive material of the perfect binding; the most used is because it has many advantages, and it is suitable for publishing books quickly, which can shorten the publishing period and adapt. The fast-paced needs of modern society. The following is a brief introduction to EVA hot melt adhesive and the correct use:
1. What is EVA hot melt adhesive
EVA hot melt adhesive is a kind of fusible polymer which does not require solvent and does not contain 100% solids of water. It is solid at normal temperature, and is heated and melted to a certain extent to become a flowable and viscous liquid, ie, a gel. . The molten EVA hot melt adhesive is a light brown translucent or white binder. The composition of EVA hot melt adhesive consists of basic resin (ethylene and vinyl acetate polymer), tackifier, viscosity modifier, antioxidant and cold resistance agent, heat resistance agent and the like.
2. Features of EVA hot melt adhesive
1 It is usually a solid at normal temperature. When heated to a certain extent, it melts into a liquid adhesive. Once cooled below the melting point, it quickly turns into a solid (solidified and solidified) and is easy to store and store.
2 Fast curing, low pollution, strong adhesion, the rubber layer has certain flexibility, and has a certain hardness, which is very suitable for the bonding of books and magazines.
3 has re-adhesiveness. When the glue is applied to the adherend, and the glue layer is cured or hardened, it can be heated and melted and softened to restore the adhesive shape and re-bond. Conducive to the recovery of defective products.
4 Easy to use. As long as the hot melt adhesive is placed in the reservoir and heat-melted into a liquid adhesive of the desired viscosity and applied to the adherend, after being properly pressed, the adhesive curing can be completed in a few seconds, about 3 minutes. It can achieve the degree of hardening, cooling and drying, and can be cut into a book immediately.
Due to the above characteristics of EVA hot melt adhesive, it is suitable for the needs of modern high-speed linkage production.
3. Use of EVA hot melt adhesive
EVA hot melt adhesives produced and used in China are generally suitable for binding and are generally divided into high speed and low speed glue; high speed glue cures slightly faster than low speed glue. According to the different substances to be bonded, it is divided into different glues for offset paper and coated paper; and there are adhesives (back cover glue) and side adhesive glue to meet the strength and needs of the adherend. Both good bonding and cost reduction.
Use hot melt adhesives to prepare for use to ensure smooth operation.
1 Storage glue. According to the correct choice of the type and type of the glue, the amount of glue should be determined according to the quantity used; if the storage of the glue is too much, the melting will cause waste, and too little will affect the normal operation.
2 Preheat. The solid block must be preheated before use so that it can be first melted into a liquid. There are two preheating methods: one is preheating with an oil bath, that is, preheating with a jacketed crucible; the other is preheating with a hot plate, that is, directly preheating in a preheating pot with a hot plate device. The preheating time is generally 2 hours. When the colloid reaches the required heating temperature and has a good fluidity, the glue is released into the working glue pot with 160-180 ° C through the constant temperature pipe for use in the application of the book. .
3 Temperature adjustment. Adjust the temperature of the glue according to the technical parameters of the adhesive. The temperature requirement of the glue is extremely strict, and it must be set according to the standard parameters. The glue temperature cannot be increased or lowered arbitrarily, and the normal fluid is destroyed. In special cases, the swimming amount is at most ±10 °C. Wait until everything is ready for normal operation.
4. Adhesion and suitability of EVA hot melt adhesive
The adhesion of EVA hot melt adhesive, in the actual production and use process, will vary with the temperature of the hot melt adhesive, the difference and the inferiority of the material to be bonded, the width and depth of the milling back, the height of the rubberized wheel and the glue. Different bonding speeds will result in different bonding effects.
1 The relationship between the temperature and the tensile force of EVA hot melt adhesive.
The softening point of EVA hot melt adhesive (when bonding books and magazines) should generally be above 80 °C, that is, it can soften and start to melt when heated to 80 °C. This temperature and effect is only the temperature at which the hot melt melts, so that it can be bonded to the book, and the heating temperature is raised to 130 ° C ~ 180 ° C before use. The gel reaching this temperature, whether it is viscosity or viscosity , liquidity, etc., are suitable for the bonding of books and magazines.
According to the measurement of foreign data, it can be sizing on ordinary book paper, the tensile test value of hot melt adhesive can reach 8.83±0.44N/cm when the glue temperature is 170°C; when the glue temperature rises to 180°C, the hot melt adhesive The tensile test value will drop to 7.33 ± 0.33 N / cm; otherwise, when the glue temperature drops to 155 ° C, the tensile test value is only 5.22 ± 0.25 N / cm. It can be seen that the melting temperature of the hot melt adhesive must be strictly controlled, and should not be too high or too low (except in special cases). The temperature of the glue is too high. Although the fluidity and permeability of the gel increase (thin), the viscosity and the bond strength decrease, which affects the pulling force of the colloid. The gel temperature rises and the viscosity of the colloid increases (thickness), but it affects the flow of the glue. Sexuality and wettability and permeability to the back of the book, but also reduce the tensile strength, consistency, toughness, etc. of the hot melt adhesive, and even the glue or the back of the book does not stick or stick tightly after the glue is applied. Therefore, the heating temperature of EVA hot melt adhesive must be strictly controlled within an optimal and appropriate range of technical parameters to achieve the desired glue temperature and reliability of bonding.
2 The relationship between the texture of the book paper and the temperature of the glue
There are many types of papers for making books and magazines, and the textures are different. This is directly related to the temperature at the time of gluing. The different sizing temperatures of the paper are different, which is not only the reason for the difference of the paper fibers, but more importantly, the difference in the thermal conductivity of the colloid and the change of the curing speed and the cooling rate due to the difference in the properties of the paper. To. For example, the thermal conductivity of coated paper, light coated paper (coated paper), and book paper (non-painted letterpress paper, etc.), the former cures the gel faster than the latter because it is contained in the coated paper. The inorganic matter is about ten times higher than the book paper (including letterpress, news, etc.), and the inorganic material has good thermal conductivity, which can accelerate the curing and cooling hardening speed of the hot melt adhesive.
If the gluing temperature is 170 ° C, the tensile test value of the hot melt adhesive can reach the above-mentioned tensile force value of 8.83 N/cm on the non-coated book paper; and the coated paper tensile test value of the paint can only reach 1.86 ± 0.11. N/cm (65 g/m2 paper) and 1.64 N/cm (100 g/m2 paper). The colloidal pull force value of the coated paper is so low that it obviously does not meet the bonding requirements. Therefore, to increase the tensile force value after the coated paper glue, it is necessary to increase the strength of the glue and the temperature of the glue. When the temperature of the sizing is 180 to 190 ° C (copper paper glue), the hot melt adhesive has a tensile force of 4.1 to 3.9 N/cm. It can be seen that the use temperature of the hot melt adhesive should also vary depending on the texture of the paper material in the book.
3 The relationship between the opening time of EVA hot melt adhesive and the running speed of the perfect binding machine.
There are many types of wireless nailing machines, including high speed, medium speed and low speed. High-speed 12000 copies/hour, 10000 copies/hour, 8000 copies/hour, etc., medium speed has 6000 copies/hour, 5000 copies/hour, 3000 copies/hour, etc., but all belong to the linkage production line. Low speed machines generally refer to single machines, such as disc binders, elliptical binders and long plastic nailers, and the speed is generally 200-2000 copies/hour.
In order to cooperate with different machine speeds, there are three times (also called three points) in addition to the melting point when using EVA hot melt adhesive to bond books. This must be strictly controlled and mastered.
A. Opening hours. Opening time refers to the time when the glue is applied to the adherend (back of the book or the adhesive mouth) to be stuck, usually 7 to 13 seconds. This time is from the glue coating machine to the cover and the back of the book after the binding machine transmits the milling back. The working process of sticking and clamping (including sticky cardboard), that is, the equipment must be completed in 13S during operation. If the equipment is not completed in the 13S during operation, the bonding effect is definitely not ideal, and there will be stickiness, empty back, lost pages, loose pages, and so on. Therefore, the opening time of the hot melt is selected, and it is necessary to determine which type is suitable according to the operation speed of the perfect binding machine.
B. Curing time. Curing time refers to the process of solidification of liquid adhesive. The curing time is generally 7 to 14 seconds, which is basically the same as the opening time. The user hopes that this time can be shortened and is more conducive to the setting and cooling of the book.
Hardening time. The hardening time refers to the time when the book is viscous and the shape is firmly fixed. In addition to a certain degree of opening and curing time, it is also required that the adhesive should be cooled and hardened (dried) as soon as possible so that the finished product can be cut smoothly. This time requirement is fast and accurate, especially for the processing glue of the wireless binding production line. Because this production line is a line of linkage production from the beginning of the collating machine to the cutting of the book, the working process of each part is according to the movement. The beats are coherent. Therefore, it is necessary to have a certain regularity and accuracy when the book is placed on the cover and sent to the cutting position to achieve the desired effect after the book is cut. That is to say, the delivery time of the book must be ensured that when the book reaches the part under the knife of the cutting machine, the back of the book (the adhesive mouth) has reached the degree of cooling hardening and drying, so that the quality of the finished product after cutting can be guaranteed. This time is generally applied in 3 minutes to complete, otherwise it will cause deformation of the back of the book, unstable size, sticky knife, dirty books and so on. Therefore, the length of the conveyor belt of the book-feeding conveyor of the linkage production line should be selected according to the running speed. Generally, the length of the conveyor belt is about 45m. If the conveyor belt is provided with a stacking device, it can be set at about 20m. In short, the book with the cover should be placed. Cool down for 3 minutes (min) during the transfer process and then reach the cutting machine.