Introduction to the basic knowledge of water-based ecological synthetic leather manufacturing

There are many types of synthetic leather manufacturing processes, but the main ones can be classified into three categories: the first is the wet process type; The second category is dry process technology. Thirdly, for the direct coating surface treatment process type, due to the essential difference in the dispersion media between water-based resins and oil-based resins, there are also significant differences in mechanical requirements.

Regarding wet process equipment: The oil-based wet process involves the solidification of PU resin containing DMF in a water tank and the formation of a porous structure by water displacement of the DMF solvent. After drying, an elastic skin-like substance is formed. In contrast, in the water-based wet process, since the solvent is water, it is impossible to perform wet processing by water displacement. The porous structure can only be achieved through special aqueous solutions or partial dissolution of the substrate after curing and molding in water. Therefore, the process and equipment need to be adjusted completely differently.

Regarding dry process equipment: Water-based and oil-based resins share a very similar aspect in the dry process of synthetic leather. They are generally processed and manufactured through coating, drying, bonding, transfer, paper-leather separation, and winding. Therefore, with the existing dry process line, water-based ecological synthetic leather can be processed with almost no modification. However, due to the different natures of water and oil substances, The requirements for dry-process production lines will also vary. Xie Zhenming, the director of the Lishui Water-based Ecological Synthetic Leather Technology Innovation Service Platform in Zhejiang Province, said that strictly speaking, all existing dry-process production lines have the necessity and space for transformation. Specifically, there are several reasons and transformation plans as follows: One reason is that the heat absorption energy of water and oil during drying is different, and the requirements for the length of the drying oven are also different. Generally speaking, synthetic leather produced from water-based resins requires a longer drying oven. Secondly, the film-forming mechanisms of water-based resins and oil-based resins are different, and the requirements for equipment are also different. Xie Zhenming, the director of the Lishui Water-based Ecological Synthetic Leather Technology Innovation Service Platform in Zhejiang Province, also mentioned that during the film-forming process of oil-based resins, due to the evaporation of solvents, the surface film exposed to higher external temperatures can remain in a molten state until it is completely dry. Therefore, the surface temperature during film formation is always relatively low. However, when the interface temperature of water-based resin is relatively high, it will form a film first. Since water cannot dissolve the film of water-based resin, under conventional drying conditions, the interface temperature may be even higher. This can cause many problems during film formation due to the evaporation of moisture in the inner layer. To maintain a good temperature change from the inside to the outside for film formation, Water-based resins are suitable for mid-wave infrared equipment to achieve infrared penetration through the film and form a balance of temperature inside and outside, improving the film-forming performance. However, oil-based resins do not require such a device, but of course, they cannot be used either because there are a large number of flammable hazards when oil-based resins volatilize. Thirdly, due to the different film-forming mechanisms of water and oil, for water-based ones, it is advisable to use a thin coating and multiple scraping process as much as possible, which will impose higher requirements on the precision of the equipment.

Regarding the surface treatment process equipment for direct coating: If knife coating is adopted for direct coating, the equipment for water-based and oil-based coatings is almost the same. However, the length of the oven for water-based coatings can be longer as much as possible, mainly considering production efficiency. If roller coating is adopted, then it is necessary to select the appropriate roller coating machine and roller coating device to ensure the smoothness of the resin slurry during the transfer process as much as possible.