Unveiling the production process of PU leather

PU is more complex in manufacturing process than PVC leather. Since the PU base fabric is canvas PU material with good tensile strength, it can be coated on top of the base fabric or included in the middle, making the base fabric invisible from outside. PU leather has better physical properties than PVC leather: it is more flexible and flexible, has greater tensile strength, and is breathable (PVC is absent). The pattern of PVC leather is formed by hot pressing with steel pattern rollers; PU leather patterns are made by heating a type of patterned paper that is first pressed onto the surface of the semi-finished leather, then after cooling down, the paper and leather are separated for surface treatment.

Dry PU

The dry process is the earliest developed industrial method, characterized by using a drying oven to evaporate solvents from solvent-based polyurethane resin, then forming a multilayer structure consisting of multiple films and a base fabric. The most common process is the release paper method: first, surface and bottom layers of mixing liquids with different properties are coated onto release paper using a scraper. After drying and cooling, the fabric is then coated with an adhesive base layer. The base fabric is sent to laminate the base material and base material, then after drying and cooling, the final product is prepared using a peeling device artificial leather Roll separately with release paper. This method produces the ‘He’ finished leather It has excellent strength and firm adhesion, but relatively poor breathability, mainly used in footwear, ball games, bags, furniture decorations, and similar fields.

a. Release paper

b. Colored polyurethane resin is applied to release paper, then dried, and then carried out on the same assembly line for the next step

c. After coating the release paper with colored polyurethane resin, apply adhesive to the surface

d. Finished preparation of patterned dry-process polyurethane resin film

e. Then, on the same production line, bond the patterned polyurethane resin film to the base fabric to be bonded

f. Peel off the release paper and polyurethane resin, recycle the release paper, roll the laminated dry-process PU semi-finished product, and roll the release paper simultaneously to recycle it, so it can be used for the next time the pattern is needed

The above is the production process for dry PU semi-finished products. The PU texture and tactile feel produced after these steps have not yet appeared. The final step will be explained after the wet process is introduced below.

Wet PU

The wet process is a new method developed after the dry process. Its feature is the use of a water-based film formation method to obtain a multilayer structure with continuous porous layers. The general process is: add DMF solvent and other fillers and additives to polyurethane resin to form a mixed liquid, deaerate by vacuum machine, impregnate or coat the base cloth, then displace the solvent (usually DMF) in water. The polyurethane resin gradually solidifies, forming a microporous polyurethane granular layer, which is then rolled, dried, shaped, and cooled to obtain a semi-finished leather base (BASS)。 Further dry veneer or surface printing, compression, and skin smoothing processes for bass is called polyurethane lamination finished leather Finished product. This method produces combination finished leather It has excellent moisture permeability and breathability, feels soft, full, and light, and is more like natural leather in style and appearance.

a. This step is the most important to distinguish from dry PU. Preparation of the semi-finished bass: DMF solvent and other fillers and additives are added to the polyurethane resin to form a mixed liquid. After deaeration by vacuum machine, the material is impregnated or coated onto the base fabric, then the solvent (usually DMF) is displaced in water. The polyurethane resin gradually solidifies, forming a microporous polyurethane granular layer, which is then rolled, dried, shaped, and cooled. This entire process is completed on the production line shown in the image below.

b. The steps for applying polyurethane resin film to release paper are basically the same as the dry method, except that the base fabric used for lamination is replaced with a semi-finished leather base with base cloth. Finally, the peeling and recycling of the release paper are the same as those for dry PU.

c. Both dry and wet methods require kneading and texture treatment. This step relies on the appearance of grain and improving the tactile feel. The entire machine alone can hold nearly 300-400 meters of PU. Generally, after kneading the texture, the texture becomes noticeable and the texture becomes especially soft. However, mirror-finish PU may develop irregular creases after this step, which is unavoidable.

After the above process, the PU is basically finished and ready for inspection and packaging.