(ii) Raised cloth impregnated with polyurethane bass

　　1. Production process

　　The raised cloth is unrolled, and the stored cloth is heated by the ironing roller to remove moisture and then ironed into the impregnation tank to be impregnated with polyurethane compound slurry. After passing through the support roller and the gap roller, the excess slurry is scraped off and enters the coagulation tank to form a film. Most of the DMF aqueous solution is squeezed out by the squeezing roller, and then washed, dried, and rolled into bass.

　　2. Main raw materials

　　A. Polyurethane resin: same as the single coating method.

　　B. Wood powder: In the formula of impregnated bass, the amount of wood powder is small, generally not exceeding 10%, and the fineness is above 400 mesh.

　　C. Additives: In the formula of impregnated bass, in addition to C-70 and S-80 additives, there are also the following special additives.

　　① Defoamer: The main component is liquid silicone, and its main function is to eliminate air in the slurry and reduce pinholes on the surface of the leather. General silicone oil has poor compatibility with DMF and is not suitable for use. When designing the formula, special additives with certain compatibility with DMF and strong defoaming ability should be selected. The dosage is generally 0.5-1 part. Too little dosage will not work. When the dosage is too large, it will cause depressions on the surface of the leather due to poor compatibility with DMF.

　　② Leveling agent: Leveling agent is also a modified silicone additive. Its main function is to improve the flatness of the base surface and increase the affinity between the resin and the base fabric. The dosage is generally 0.1% of the resin mass.

　　③ Water: Water can also be used as an additive in the formulation of impregnated bass to adjust the pore structure and accelerate the solidification speed.

　　D. Solvent DMF: In the formulation of impregnated BES, the amount of DMF can reach 1.5 to 2 times the mass of the resin.

　　E. Raised fabric: Raised fabric used for impregnated bass leather is mostly double-sided raised fabric, with thickness ranging from 0.4-1.2MM, selected according to product thickness. The impregnation process requires that the raised fabric must have good degreasing and hydrophilicity, short and uniform nap, and a tight structure.

　　3. Key points of production process operation

　　(1) Preparation of polyurethane slurry: Add a certain amount of DMF into a mixing tank, then add wood powder and stir to disperse the wood powder in the DMF. Stop stirring and add C-70, S-80, water, defoamer, leveling agent, etc. in sequence. Continue stirring for 5 minutes, then add polyurethane resin and colorant. Stir at high speed for about 20 minutes. At the same time, vacuum degassing is performed and samples are taken to test the viscosity of the mixed liquid. If it does not meet the process requirements, it needs to be adjusted.

　　(2) Impregnation and solidification process: The prepared slurry is pumped into the impregnation tank with an air pump, and the base fabric is unrolled. Before entering the impregnation tank for impregnation, the base fabric is heated by an ironing roller to remove moisture from the base fabric, otherwise it is easy to produce a double-layer skin phenomenon on the surface of the leather. The base fabric enters the impregnation tank and the polyurethane slurry penetrates into the base fabric. As the base fabric moves continuously, air will be brought into the slurry in the impregnation tank, thereby generating bubbles. The air in the slurry will generate pinholes on the surface of the leather. In order to eliminate these bubbles in time, in addition to adding defoaming agent to the slurry formula, recycling the material in the impregnation tank is also a very effective method, that is, continuously pumping non-bubble material into the impregnation tank, while the material with more bubbles overflows from the impregnation tank. The overflowed slurry is stored in a special barrel, allowed to stand for a period of time to defoam, and then re-injected into the impregnation tank for use. After the base fabric comes out of the impregnation tank, use a scraper to scrape off the excess slurry. The scraper gap is also an important factor affecting the surface quality of the leather. If the gap between the scrapers is too small, it is easy to leak the fabric hair, resulting in an uneven surface; if the gap is too large, it is easy to have a double-layer skin phenomenon on the surface. The size of the gap should be adjusted appropriately according to the length of the raised fabric hair, and then put into water for solidification. The angle of the bass entering the water should be vertical for solidification. After entering the water, the horizontal distance should not be too long, preferably 6-8 meters. The quality of the raised fabric is the key factor in the quality of the bass. Raised fabrics with poor degreasing and poor hydrophilicity will cause a large number of pinholes on the surface of the bass, and even cause surface delamination. Therefore, the base fabric for wet method has strict requirements on degreasing and hydrophilicity. A simple method to test the hydrophilicity of the raised fabric is the climbing test, that is, a strip of cloth with a width of about 30MM and a length of 200MM is immersed in water at its lower end, and after a certain period of time (for example, 30 minutes), the height of the water climbing up along the cloth is measured. The higher it climbs, the better the water immersion of the cloth. The above method is actually a method to check the capillary effect of the cloth base. When there is a problem with the intrinsic quality of the base fabric, no matter how the formula is modified, it will be of no avail.

　　(3) Washing, drying and winding: The thickness of the impregnated bass is generally thicker, so the washing and drying time is correspondingly longer.