Hot melt adhesive coating is a green and environmentally friendly coating and packaging technology. At present, although the development history of domestic hot-melt adhesive coating process has been more than ten years, the manufacturing technology of hot-melt adhesive coating machines is still in the immature stage in China, and many hot-melt adhesives produced by printing and packaging machinery manufacturers Machines, whose main quality issues have not been well resolved.
Hot melt adhesives, as the name suggests, are glues that, when heated, become in a molten state and are coated with various materials. Compared with other adhesives, hot melt adhesives have the following features: 100% solids composition, no solvent and water components; with thermal plasticity, that can be repeatedly heated to melt and cooling solidification, this process is reversible, the chemical physics of hot melt adhesives The nature will not change as a result; the hot melt adhesive must be heated to be in a molten state to be coated; the hot melt adhesive is cooled and solidified to produce adhesive force.
Since its inception, hot-melt adhesives have been widely used in food packaging, bookbinding, disposable hygiene products, furniture industry, label industry and other fields because of its advantages such as high bonding strength and fast curing speed.
Second, the hot melt adhesive industry new technologies and development trends
Low temperature hot melt adhesive
Low-temperature hot melt adhesives break through the limits of the use of traditional hot melt adhesives. Its normal operating temperature is only 110 °C ~ 130 °C, the use of low-temperature hot-melt adhesives than the traditional hot-melt adhesive temperature is lower than 30 °C. Low-temperature hot-melt adhesives have significantly lower viscosity values ​​than conventional hot-melt adhesives, ensuring that all coating process requirements are met at low-temperature operating conditions.
The direct benefits of low temperature hot melt adhesives are savings in electricity bills and machine maintenance costs. A large number of practical applications show that the same hot-melt adhesives machine can use low-temperature hot-melt adhesives to save customers about 15% of the electricity bill. Because the low-temperature hot-melt adhesive at the normal operating temperature of 110°C~130°C is almost completely free of aging phenomena such as skinning and carbon deposition, the maintenance cost of the machine is greatly reduced. More importantly, the low temperature hot melt adhesive does not scald the PE film.
2. Hydrophilic hot melt adhesive
Conventional hot-melt adhesives are generally hydrophobic. Hydrophilic hot-melt adhesives are made hydrophilic through special formulas. Each type of hydrophilic hot-melt adhesive application can give the product a higher added value and enable product production. Manufacturers in the current highly competitive market, effective product differentiation, and ultimately win consumers.
3. Other new technologies for hot melt adhesives
In addition to the above several aspects, the new hot melt adhesive technology also includes: oil-repellent hot melt adhesives; hot melt adhesives for high-frequency spraying; high-moisture strength hot-melt adhesives; degradable hot-melt adhesives and so on.
Third, the classification of melt adhesive coating technology
1. Squeegee system
In the coating process, the sizing is often uneven, which requires a certain squeegee mechanism to evenly squeegee the squeegee. Squeegee mechanisms include stainless steel scrapers, comma scrapers, scrapers, wire scrapers, and air scrapers.
2. Texture coating
This type of coating apparatus is mainly applied with a gravure coating roll for sizing. Its uniform coating, and the coating amount is more accurate. However, once the type of the anilox roller and the adhesive are fixed, it is difficult to adjust the coating amount, which is also the main reason that the application of the roller is limited.
3. Calender coating
This method uses a calender to apply a rubber compound or the like to the surface of a paper or fabric substrate, and has a film calender coating and a powder calender coating. In the former, the film is formed into a film by a coating plastic, and the film is heated and fused onto the surface of the substrate by a calender roll; the latter is a powdered resin that is sprayed on the surface of the substrate and heated and melted together by a calender roll.
4. Spraying system
The coating equipment mainly applies solid-state glue after being heated and melted, and the glue is directly sprayed on the substrate by the hydraulic device through the coating die.
Fourth, no scratch coating technology
In 2007, in response to market demand, it began to invest in the research and development of hot melt adhesive coating equipment for film materials. The new scratch-free hot melt adhesive coating head comes out. The device has the following features:
"Scratch-free" effect, especially suitable for coating compounding of PET, PVC, OPP and other materials; minimum weight up to 15g/m2, operating speed up to 180m/min; high degree of automation, PLC control, multiple functions and The operations are brought together on the human-machine interface to ensure that the operator can easily control the device.
The successful R&D of this equipment has filled China's technological gap in this area and is the first in China. Solved the hot melt adhesive coating of PET, PVC, OPP and other materials and the dependence of UV curing hot melt adhesive coating on imported equipment, saving a lot of capital investment for the upgrading of products in the industry.
In recent years, foreign countries have successively developed a new generation of green environmental protection products such as biodegradable, water-dispersible, and other hot melt adhesives. Because this kind of modified rubber is different from traditional thermosetting and solvent-based adhesives, it does not contain any solvent and will not pollute the environment due to solvent evaporation. Therefore, new environmentally friendly hot melt adhesives are increasingly attracting people in the industry. Attention and favored by the market