Third, the gap between domestic EVA adhesive and foreign EVA adhesive
Practically speaking, domestic EVA hot melt adhesives still have a certain gap compared with foreign EVA hot melt adhesives, mainly in the following aspects:
1. The intrinsic quality is relatively poor, mainly because the content of domestic adhesive EVA resin is relatively low, and the content of auxiliary fillers such as rosin is high. Zhang Shuheng mentioned that they used the same machine (Wellenberg glue binding line) and paper to produce the EVA hot melt adhesive and the imported hot melt adhesive separately under the same basic environmental conditions. The result was bound with imported glue. Books and magazines need only 0.2-0.3mm thickness for coating, and the low temperature resistance is better. However, using domestic EVA glue binding requires slotting 0.5mm and then applying 0.6-0.8mm to achieve the application requirements.
2. Compared with foreign countries, domestic glue is not doing well in the combination of process and materials, so that there is no suitable material for the process; there is a corresponding process of the material can not keep up. In addition, the speciality of foreign hot melt adhesives is very strong, and it is very particular about which part is used in connection with it. Domestically, it is doing relatively poorly.
3. Domestic hot-melt adhesives have high melt index, poor resistance to aging, brittleness, poor flexibility, large coating thickness, low bond strength, and poor flatness after binding. Domestically produced hot melt adhesives have a low rate of innovation and innovation, and their synthetic process is backward (especially the EVA resin cannot be copolymerized in our country at present). The production equipment is simple and the process control is not strict.
Fourth, PUR adhesive characteristics and application prospects
Since hot melt adhesives still have such problems in use, foreign countries have introduced a new type of hot melt adhesive, PUR, in recent years. What characteristics does this new type of adhesive have? When will it be applied in our country? We have listened to the opinions and suggestions of experts on these issues.
1. Characteristics of PUR Adhesive
According to Cao Hua, PUR (Polyurethane Resins) is a polymer with a free cyanate group formed by reacting diisocyanate with an organic compound containing two or more active hydrogen atoms, mainly through its contained groups. They react with each other under the action of heat or a certain catalyst, or react with water, ethylene glycol, etc. to form a thermosetting material. PUR adhesive can be made into hot melt type, reactive type and moisture curing type. Hot-melt adhesives are made by melt blending, and their thermal rheology, thermal stability, moisture curing, aging resistance, low-temperature brittleness, etc. are all superior to EVA hot-melt adhesives currently used in China. The reaction type is “cold glue”, which is blended and cured at room temperature, and does not require heat melting during binding. The moisture-curing type can cure itself under high humidity conditions. There is no problem such as poor fluidity when the EVA hot melt adhesive is insufficient for heating, aging and aging due to too long heating time, and surface crusting and permeability deterioration caused by moisture evaporation.
Zhou Qiping and Zhang Shuheng also pointed out that PUR adhesive is a non-reusable, irreversible reactive polyurethane hot melt adhesive with strong adhesive strength, good weather resistance, and flexibility, requiring only a very thin coating adhesive layer ( For example, 0.1mm) can achieve high usage requirements, so some European and American countries now use this glue binding process in some hardcover books.
PUR glue binding book stall is very good
2. Factors affecting the application of PUR adhesive in China
Although PUR adhesive has many advantages and has been rapidly developed and applied abroad, experts say that in the short term, PUR adhesive will not be popularized and applied in China, and EVA hot melt adhesive will still be used in domestic bookbinding in the future. The main adhesive. The main reason is:
1) Currently, PUR adhesives produced in China are mostly single-component adhesives, rather than the two-component PUR adhesives produced abroad, so the required curing time is too long. Wang Huaizhu mentioned that this PUR adhesive takes approximately 30-40 minutes to cure and dry, and is not suitable for high-speed production. It does not match the rubber-binding linkage line currently used in China.
2) The two-component PUR adhesive produced abroad can be cured in more than 10 seconds when the relative humidity is more than 60%. The drying speed can meet the requirements of the existing rubber-bonded linkage line, but the price is too expensive, per ton. To more than 10 million. Judging from the current binding market in our country, books and periodicals publishers do not have this requirement, which will affect their application to a certain extent.
3) Existing glue-binding equipment in China cannot meet the requirements for the use of PUR glue. Zhou Qiping mentioned that at present, there is no automatic glue production line that meets the requirements for the use of the glue. Li Jiaxiang and Zhang Shuheng also pointed out that to use PUR adhesive, firstly, the glue application site of the glue-binding equipment needs to be sealed. In order to effectively infiltrate with the moisture in the air during the coating process, the glue will encounter the moisture in the air. It is solidified, and it is irreversible; secondly, the workshop must maintain a certain degree of humidity. At present, domestically produced disc machines and linkage lines, including imported Martini, Kolbus, Warrenberg, and other rubber-bonded linkage lines, are glued to open areas rather than sealed.
It seems that the key to the application of PUR glue in China lies in the fact that there is no market demand. Even if the publishers have this requirement, there are still problems such as the modification of glue-binding equipment and the price of plastics. To improve the quality of existing bookbinding, it is still necessary to solve the problem of production and use of EVA hot melt adhesives. In the next period, we will invite relevant experts to talk about the quality problems and solutions of bookbinding.
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