I. Introduction
Hot melt adhesive coating is a green environmental protection 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 machine is still in the immature stage in China. Many printing and packaging machinery manufacturers produce hot-melt adhesive coating Machine, its main quality problems have not been solved well.
Hot-melt adhesive, as the name implies, is a glue that becomes molten after being heated and is used to bond various materials together after coating. Compared with other adhesives, hot melt adhesives have the following characteristics: 100% solid composition, free of solvents and water; thermoplastic, that is, they can be repeatedly melted by heating and solidified by cooling, this process is reversible, and the chemical and physical properties of hot melt adhesives The properties will not change because of this; the hot-melt adhesive must be heated to become molten before it can be applied; the hot-melt adhesive will solidify upon cooling to produce adhesion.
Since its advent, hot-melt adhesives have been widely used in food packaging, book binding, disposable hygiene products industry, furniture industry, label industry and other fields due to their advantages such as high bonding strength and fast curing speed.
2. New technologies and development trends in the hot melt adhesive industry
1. Low temperature hot melt adhesive
Low-temperature hot-melt adhesive breaks through the use limit of general traditional hot-melt adhesive. Its normal operating temperature is only 110 ℃ ~ 130 ℃, the use temperature of low-temperature hot-melt adhesive is 30 ℃ lower than that of traditional hot-melt adhesive. Compared with traditional hot-melt adhesives, low-temperature hot-melt adhesives have significantly lower viscosity values ​​to ensure that they meet various coating process requirements under low-temperature operating conditions.
The direct benefit of low-temperature hot-melt adhesive is to save electricity costs and machine maintenance costs. A large number of practical applications show that the same hot-melt adhesive machine, using low-temperature hot-melt adhesive can save customers about 15% of electricity costs. And because the low-temperature hot-melt adhesive has almost no aging phenomena such as skinning and carbon deposition at its normal operating temperature of 110 ℃ to 130 ℃, the maintenance cost of the machine is greatly reduced. More importantly, the low temperature hot melt adhesive will not scald the PE film
2. Hydrophilic hot melt adhesive
Traditional hot-melt adhesives are generally hydrophobic. Hydrophilic hot-melt adhesives are made hydrophilic by a special formula. Each application of hydrophilic hot-melt adhesives can give products a higher added value and enable product production. In the current highly competitive market, manufacturers effectively differentiate their products and ultimately win consumers.
3. Other new technologies of hot melt adhesive
In addition to the above aspects, new technologies for hot melt adhesives include: oil-resistant hot melt adhesives; hot melt adhesives suitable for high-frequency spraying; high wet strength hot melt adhesives; degradable hot melt adhesives and so on.
3. Classification of melt coating technology
1. Squeegee system
In the coating process, the glue is often uneven, which requires a certain glue scraping mechanism to evenly scrape the glue. The glue scraping mechanism mainly includes stainless steel blade, comma scraper, scraper rod, wire scraper, air flow scraper, etc.
2. Textured coating
This type of coating equipment mainly uses anilox coating rollers for sizing coating. The coating is uniform, and the coating amount is relatively accurate. But once the types of coated anilox roller and glue are fixed, it is difficult to adjust the coating amount, which is the main reason why the application of the anilox coating roller is limited.
3. Calender coating
In this method, a calender is used to coat the rubber or the like on the surface of the paper or fabric substrate, which is divided into film calendering and powder calendering. The former is to make the coating plastic into a film, and then it is heated and melted on the surface of the substrate by the calender roller; the latter is sprayed with powdered resin on the surface of the substrate, and then heated and melted and bonded together by the calender roller.
4. Spraying system
This kind of coating equipment mainly melts the solid type glue by heating, and sprays the glue directly on the substrate through the coating die by the hydraulic device.
4. Scratch-free coating technology
In 2007, in response to market demand, it began to invest in the research and development of hot melt adhesive coating equipment technology for film materials. A new scratch-free hot melt adhesive coating head is introduced. The device has the following characteristics:
"Scratch-free" effect, especially suitable for the coating and compounding of PET, PVC, OPP and other materials; minimum gram weight up to 15g / ?, running speed up to 180m / min; high degree of automation, PLC control mode, multiple functions and The operation is integrated in the man-machine interface to ensure that the operator can easily control the device.
The successful research and development of this equipment fills the gap in China's technology in this regard, and is the first in China. It solves the situation that PET, PVC, OPP and other materials are dependent on imported equipment for hot melt adhesive coating and UV curing hot melt adhesive coating, saving a lot of capital investment for the replacement of products in the industry.
In recent years, foreign countries have developed a new generation of green and environmentally friendly new products such as biodegradable and water-dispersible hot melt adhesives. Because this improved adhesive is different from traditional thermosetting and solvent adhesives, it does not contain any solvents and will not pollute the environment due to solvent evaporation. Therefore, new environmentally friendly hot melt adhesives are increasingly attracting industry insiders. Attention and favored by the market.
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