The finishing of ultrafine fiber fabrics has a significant impact on product quality, especially the sanding finish. The sanding finishing is closely related to the pre-treatment of textiles, especially in terms of fiber opening and pre molding, and dyeing processing also has a significant impact on sanding; On the contrary, sanding processing also has an impact on the color of the fabric. In addition, post finishing also includes deepening finishing, suede like finishing, anti-static finishing, etc.
4.1 Deepening and organizing
Deepening finishing can improve the color rendering of ultrafine fiber fabrics to a certain extent, and can be used as an auxiliary means to improve deep dyeing properties.
There are two ways to enhance the depth of finishing. One is to roughen the fiber surface by changing the fiber properties, grooving the fiber surface, anisotropy of the fiber cross-section, changing the yarn structure, alkali reduction treatment or plasma treatment, etc., thereby increasing the diffuse reflection of light and visually enhancing the color depth; Another type is to use low refractive index resin finishing methods in post finishing to reduce the reflectivity of the fabric surface to incident light and achieve a deepening effect.
4.2 Imitation suede finishing
Suede like finishing refers to the processing of textile fabrics by sanding them to give them a suede like appearance and feel. Suede suede is a brushed product made of fine denier synthetic fibers for woven or knitted fabrics, with a soft and plump feel, comfortable to wear, and a suede like style. The general process for suede like finishing of polyester ultrafine fabrics is:
Preparation of base fabric → relaxation → (alkali reduction) → fuzzing → pre molding → dyeing → drying → polyurethane resin finishing → sanding → stretching → baking (also heat setting) → finished product
Polyurethane resin has superior performance, low temperature resistance (below -30 ℃), friction resistance, and can form a soft, flexible, and strong porous film. The artificial suede treated with it not only has superior elasticity and a soft and plump feel, but also has good breathability and moisture permeability. There are three types of polyurethane resins: solvent based, water dispersed, and high solid content. Solvent based synthesis is convenient, with good quality and wide adaptability, but solvents are toxic, flammable, and explosive, requiring solvent recovery devices and corresponding environmental safety measures; Water dispersed polyurethane has low pollution and safe production, which is the future development direction; The appearance of the high solid type is granular or powdery, and it is first dissolved with solvent when applied. The advantages are high solid content and convenient transportation, but the difficulty in synthesis technology is higher.
If solvent based carbamate is used, it is dissolved in dimethylformamide (DMF) to make a working solution. The fabric is soaked and rolled with this solution [with a dosage of 4% (o.m.f) and a rolling rate of 70%]. The solution penetrates into the micropores of the fabric, which can improve the elasticity of the fabric. Then, when passing through the water bath, the surface layer of the fabric first comes into contact with water, and the DMF in it immediately diffuses towards the water phase. The concentration of DMF on the surface layer of the fabric decreases, forming a concentration difference with the DMF inside the fabric, which promotes the internal DMF to gradually diffuse towards the surface layer of the fabric and then towards the water bath; And the water in the coagulation bath gradually diffuses into the fabric. As this double diffusion process progresses, the solubility of polyurethane in DMF decreases, the concentration increases, and the cohesion increases. The original position occupied by DMF in polyurethane is replaced by water to form micropores, which quickly solidify into a continuous porous membrane with a sponge like structure containing micropores. This membrane is both water resistant and permeable