Technical problems and solutions in the most popul

Technical problems and solutions in binding books and periodicals (I)

it has been more than ten years since the printing industry used EVA hot melt adhesive to bind books and periodicals. Binding books and periodicals have short cycle, stable quality, low error rate and light labor intensity. It is welcomed by the publishing and printing industries. In particular, the (growth) of PUR hot melt adhesive we achieved in the third quarter of this year is actually our target growth range for the promotion and use of printing abroad. The emergence of PUR hot melt adhesive instead of common EVA hot melt adhesive makes up for the disadvantages of EVA hot melt adhesive by the fact that the main bearing of PUR dynamometer is not allowed to add oil. Pur hot melt adhesive is a perfect binding method. However, in the current printing industry, EVA hot melt adhesive is used in binding books and periodicals, and 80% of the quality problems of printed matter are caused by improper use of EVA adhesive. Therefore, this paper analyzes the technical problems in binding and explores common solutions

I. types and selection of hot melt adhesives

the research on hot melt adhesives in China began in the mid-1970s. In recent five years, the domestic hot melt adhesive industry has entered a mature period, and the application range of hot melt adhesives is also expanding. Due to the different composition and bonding object of hot melt adhesive, it has expanded from the traditional fields of sanitary products, packaging, printing and binding to nearly 30 varieties of hot melt adhesive in more than ten industries, such as clothing, tape, shoe making, refrigerator, cable, automobile, construction, etc

EVA hot melt adhesive for books and periodicals is a solid fusible polymer without solvent and water. The hot melt adhesive is a solid at room temperature. When the hot melt adhesive is heated and melted to about 170 ° C, it becomes a liquid with good viscosity; When the temperature in the glue pot rises to more than 250 ° C, the hot-melt glue liquid begins to age, change color, deteriorate, the viscosity decreases, and the glue film becomes brittle, so it cannot be used

at present, the state has not promulgated the standard of hot melt adhesive for books and periodicals. The factories producing hot melt adhesive do not have a unified quality index system, and each factory has its own production standards. There are many types of hot melt adhesives, and their bonding properties are also different. According to the speed of different binding machines, different binding objects, opening time, curing time, etc., choose to use back glue and side glue

the experience of a printing enterprise in North China in using the index system for controlling hot melt adhesive can be used for reference. Their experience in practice: strict quality inspection shall be conducted for each brand and batch of newly purchased hot melt adhesive, and only the adhesive with qualified indicators can enter the workshop. This ensures the quality of binding products. The quality indexes they control mainly include the following items: ① low temperature resistance index. They have designed a temperature controlled freezer with a temperature control error of ＋/- 1 ° C and a temperature measurement range of -10-10 ° C. The newly purchased hot melt adhesive shall be made into a certain adhesive strip, which shall be placed on the bending frame of the freezer, and the bending test shall be carried out at a constant temperature of - 1 ° C. After 30 minutes, the product that continues to crack is qualified. They are beginning to design an automatically controlled hot melt adhesive tester for low temperature resistance, so as to make the measurement results more objective and scientific. ② Fatigue strength index. This is an index to test the bending resistance of the adhesive layer, which can ensure that the books can remain intact after repeated reading. First, the hot melt adhesive is made into adhesive strips according to the regulations, and then tested on the fatigue strength tester (self-made) at the specified temperature to obtain the index number of bending resistance. ③ Specific gravity index. Through comparative tests, they found that the comprehensive performance index of the adhesive with a specific gravity greater than 1 was lower than that of the hot-melt adhesive with a specific gravity less than 1. In addition, the greater the proportion of hot melt adhesive, the greater the weight of single adhesive when the adhesive layer is the same, which will significantly increase the production cost. The specific gravity can be determined according to the relevant adhesive determination methods. In practice, they often use the "water drift" method for qualitative determination: the glue with a specific gravity greater than 1 will sink to the bottom of the water, and the glue with a specific gravity less than 1 will float on the surface of the water Large stroke. This method is simple but efficient. ④ Anti aging index. The hot melt adhesive that is easy to age is used. Firstly, it will be obviously scorched and discolored in the process, which will bring inconvenience to the normal operation of the process; Second, in the use of binding books, due to the rapid aging of the adhesive, there will be quality problems, which will affect the service life of the books. This index can be determined according to the national standard, but it takes a long time. The simpler method is to treat the rubber sample at a higher temperature, and the change of the rubber with poor anti-aging performance is very obvious

"good horse with good saddle", high-quality products must be backed by high-quality equipment and materials. The problems such as the bonding machine, hot melt adhesive, workshop temperature and humidity are directly related to the quality of binding products. Therefore, 4.1 the processed parts shall meet the requirements of the drawing. The work preparation before binding is as follows:

1. The binding workshop requires a normal working temperature of 20 ° c-30 ° C and a humidity of 50%-70%; When Binding products, preheat hot melt adhesive 2 hours in advance. For the older model of glue wrapping machine, if there is no hot melt glue preheating device, another glue pot shall be equipped

2. Before binding, data settings, specifications and data review shall be carried out according to different specifications, different papers, book backs, thickness, etc

3. Selection of hot melt adhesive: in order to ensure that the book pasted with hot melt adhesive does not scatter or drop pages, it is necessary to have sufficient tensile (folding) strength between the binding seams of the book block. It is necessary to select hot melt adhesive with high tensile strength, small temperature change, high melt viscosity, high hardness, high tensile strength and fracture elongation

the author believes that 80% of the binding quality problems in production are caused by improper operation and weak heart. Before binding, operators should be familiar with the construction requirements for product process design and process flow, and have a serious and responsible attitude. The quality problems can be guaranteed