Knit Suede Process Control

- May 31, 2018-

Warp suede

 The warp suede suede is mainly composed of an extension line of the front comb, and the extension line forms short, dense, uniform, and homogeneous fuzz through processes such as raising, dyeing, shearing, and grinding. If the extension line is too long, although it is easy to fluff, but the fluffing is too long, the cost of the product is affected, and the body bone of the finished product is not ideal. Therefore, in the design, it should not be mandatory for easy fluffing. Instead, it should start from the requirements that are conducive to the production of short, dense fluff, and select the appropriate pile needle organization. The length of fluff is preferably 0.1 to 1 mm. When it is shorter than 0.1 mm, it is easy to expose the bottom, and the appearance of the suede is impaired, and when it is longer than 1 mm, it is easy to get tangled.

The warp knitted suede needs to have a tightly organized structure. The ground structure can be a comb or two combs, which is actually determined according to the product's areal density and cost requirements. If there is only one comb, the selection of the ground yarn needs to take into account the shrinkage effect. After pretreatment, the fabric webs have to shrink about 35 to 45%. After the fabric is subjected to post-treatments such as drawing, shearing, and grinding, the surface warp yarns are pulled off, and the ground yarn still needs to maintain a certain strength so that the product meets the dress code requirements. The warp-knitted and warped flat tissues often used in suede suede are shown in Figure 1. In addition, if the two combs are reversed, it is beneficial to weaving, but the hemming property is serious, which is not conducive to napping processing; the two combs adopt the same direction of the mat, which solves the curling and is conducive to raising. At the same time, in order to make the edge more smooth, an extra spandex is added to the edge during processing.

The control of tension on the warp knitted suede fabric is very important. The control of the tension of the pile yarn and the ground yarn and the choice of the finishing equipment will affect the suede effect. For suede fabrics, the tension of the front comb should be small, and the tension of the back comb should be larger, but it should be selected properly. If the tension is too large, the warp phenomenon will appear in the weaving of the grey cloth; if the tension between the pile yarn and the ground yarn is close, and the shrinkage of the warp yarn and the ground warp, the raised warp yarn will form an arc on the suede surface. It is difficult to pull and polish the fabric.

Warp suede production process

The general technological process of warp suede finishing is: white blank→initial shaping→fluffing→shearing→opening fiber→staining→heat setting→smoothing→finished product inspection→scrolling.

Due to the unevenness of the grey cloth, the width of the door is not uniform, so it is necessary to perform a predetermined shape treatment before raising the hair. When the heat setting, the temperature can not be too high, just remove the various wrinkles on the surface of the cloth, so that the cloth surface is flat, the width It can be consistent. Otherwise, due to the influence of high temperature on the ultra-fine fibers, the structure changes and it is difficult to raise the nap. Generally, the temperature is preferably between 155 and 165°C, and the setting temperature after fluffing may be appropriately higher, usually 185 to 195°C. The speed is over 30m/min. The grey fabric can be straightened and finished, and the effect of fluffing is better and uniform. After the dyeing, the color is bright and the shade is good.

Several important finishing processes are discussed below.

 Fiber opening process

Sea-island microfibers dissolve the sea components after they are made into fabrics, leaving island components to form continuous microfiber fabrics. Therefore, the solubility of the sea component is critical to the effectiveness of warp knitted suede. The dissolution of COPET in water conforms to the law of dissolution before swelling. The composition, structure, molecular weight, and external conditions of COPET all have a certain influence on the dissolution. The effect of external conditions on the dissolution of COPET is shown in FIG. 2 . Curve 1 is the dissolution of the water-soluble polyester in hot water at 95°C. It is based on dissolution; curve 2 is the dissolution of water-soluble polyester in a 0.5% NaOH aqueous solution at 95°C. It also has a swelling and dissolution process, but it swells slowly, and finally there is residue after dissolution. This may be Due to the presence of Na+ and OH- ions, the dissolution balance of the polymer was destroyed, the dissolution rate became slower, and NaOH reacted with some of the components in the polymer to form a precipitate. Curve 3 was water-soluble poly. The ester dissolves in an aqueous solution containing 0.5% NaOH and 1g/L 1227 accelerator at 95°C. Due to the addition of 1227 surfactant to the water, the surface of the water-soluble polyester is also hydrolyzed as it swells. Small molecules promote the progress of hydrolysis and accelerate dissolution. And according to different conditions to adjust the percentage of NaOH to control the dissolution rate.

The fibrillation process is carried out in an alkaline solution, which is advantageous for the complete dissolution of the sea component, but it also has a hydrolysis effect on the conventional PET island fibers. Therefore, the sea-island fiber has to reach the complete dissolution of the sea component, and its weight loss rate The ratio of the sea component is slightly larger. If the proportion of sea component is 20%, the weight loss rate of sea-island fiber is generally controlled to be about 22-26%, and the sea component can be completely dissolved. General open fiber technology curve shown in Figure 3.

Dyeing process

After the fabric is opened, the fabric must be washed thoroughly before dyeing. The amount of water must be large. In order to fully neutralize the lye on the grey fabric, wash it in a solution containing acetic acid (1g/L) at 70°C for 10 minutes, then use clean water. Rinse to a pH of 6.5-7. If the washing is insufficient, residual alkali and fiber impurities remain on the cloth, which can easily cause coloration. Dyeing process in addition to dyeing color, the fabric shrinkage has a great influence on the fabric density and subsequent processes.

Among the influencing factors of the dyeing process, the first is the effect of dyeing temperature on suede. General polyester fibers are affected by heat, and the shrinkage varies with temperature, and a significant effect can be obtained between 80 and 100°C. The dyeing temperature is 120-130°C. This is advantageous for increasing the shrinkage of the fabric and increasing the density and fluffiness.

The second is the effect of tension on the imitation of suede in the dyeing process. The ideal state of the fabric in the dyeing process is uniform longitudinal and lateral forces, but in fact, due to the longitudinal movement of the fabric in the dyeing machine, the longitudinal tension is greater than the transverse direction.

Sometimes, in order to make the fabric have a good sense of leather for polyurethane finishing, in solvent-based polyurethane finishing, the solvent has a certain degree of stripping effect on the disperse dyes, that is, the color becomes light, and the general color difference is about 0.5 to 1.5 grades. Therefore, in determining the color and dyeing process, can be increased on the basis of the normal amount of 5-10%, in addition to strictly control the heating rate (60 ~ 130 °C), the holding time not less than 45min, the best is 60min. Water-soluble polyurethane resins can now be used for finishing.

 Grinding process

The brushing and finishing process is to form a suede warp-knitted grey cloth under the control of a certain tension, pressure, and feeding speed into the ground area. Under the action of the high-speed rotating sand roller or belt, the fabric picking surface coil breaks and forms. Has a directional layer of fluff. Roughing is an important processing procedure for the production of suede-like suede, which has a great influence on the simulation of fabric suede. The length and coverage density of the fluff are mainly affected by the following six factors: the length of the front backing yarn, the speed of feeding, the speed of the sanding roller, the contact between the fabric and the sand roll, and the shape and specification of the sandpaper sand The distance between the pressure roller and the sand roller.

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