Finishing refers to the processing process of improving the appearance and internal quality of textiles, improving the wearing performance or other application performance of textiles, or some special functions through physical, chemical, or physical and chemical methods, as well as biological methods.
It can be concluded as follows:
1. Standardize the fabric: the fabric door width is consistent and the size and shape are stable.
2. Improve fabric handle: soft, firm and plump.
3. Improve the appearance quality of the fabric: enhance luster, whiteness, fluff and fuzz.
4. Give the fabric new functions: carry out special finishing, such as waterproof, fireproof, antibacterial, UV resistant finishing, etc.
Finishing methods of knitted fabrics
I. according to the principle
1. Physical mechanical finishing: the purpose of finishing is achieved by using water, heat, pressure and their mechanical functions. It is characterized by chemical changes in the fibers.
2. Chemical finishing: chemical reaction between reactive chemical finishing agent and fabric fiber is used to change the physical and chemical properties of the fiber.
3. Comprehensive finishing: chemical finishing and mechanical physical finishing are combined. After finishing, there are both mechanical and chemical changes. Such as polyester cotton fabric durability finishing.
II. According to the sorting effect
1. Soft or firm handle.
2. Shape and finish, stretch, fluff or whiten.
3. Appearance finishing, fluffing, fluffing or whitening.
4. Special finishing, waterproof, fireproof, antibacterial and UV resistant finishing.
III. according to the durability of finishing effect
1. Temporary,
2. Semi durability,
3. Durability.
Finalizing and finishing method
After finishing, a certain form of stability (shape and size) is obtained, that is, to eliminate the accumulated stress and strain in the fabric, so that the fibers in the fabric are in a proper arrangement state, thus reducing the deformation factors of the fabric.
Method:
1. Adjust the fabric structure mechanically. Such as stretching and preshrinking.
2. Eliminate the internal strain of the fiber in the fabric with a strong expanding agent. Such as mercerizing, liquid ammonia treatment.
3. Covalent cross chain method was used to determine the fiber structure. Such as resin finishing. Theoretically speaking, the shrinkage deformation of the fabric can be improved by any of the methods mentioned above, but in fact, two or more methods are often combined to achieve the goal.
Example
Stenting (setting)
1. Principle: make use of the plasticity of cotton fiber in the wet and hot state, slowly widen the door width to the specified size (refer to the weft dimension) to meet the specification requirements of finished printing and dyeing products, eliminate the existing wrinkles on the fabric and improve the dimensional stability of the fabric.
2. Equipment: clip chain stenter and heat setting machine.
3. Main functional components of the equipment: humidification, stretching drying and cooling.
1) for humidification, the moisture content is generally 15-20%, and uniform humidification is required. Methods: wet ring heating (intermittent), brush drum splashing water, steam spray to wet, high pressure water spatter to wet, steam to wet, etc., you can also first dip the fabric, drying to half dry, and then stretching. The latter is mostly used, and often combined with various functions. Wet with finishing agent.
2) stretching: it is gradually stretched by binding the cloth edge with two strings of clip chains. An overfeed device is arranged at the cloth feeding position, which can overfeed - 10 ~ - 50%. By adjusting overfeeding, the weight of cloth can be controlled in a certain range. The length of clip chain is 15-34m, generally 27m. The fabric enters the drying room with the clip chain running. The width of the fabric increases with the distance between the clip chains on both sides. Later, the distance between the clip chains keeps a certain range, so that the fabric maintains the required width, and the final distance decreases gradually, so as to facilitate the fabric to leave the clip chain. Generally, the upper and lower limits of finished fabrics are within the required dimensional tolerance.
3) heating mode: hot air is the most popular way. Use a powerful blower to send air to the heater for heating, and spray it to the fabric through the hot air pipe. As the fabric with a certain amount of moisture into the drying room, so the front of the more humid air can be excluded from the outdoor, the latter part of the more dry can be used. Generally speaking, the distance before the surface of the fabric reaches the required setting temperature is called the preheating zone, and the distance from the preheating zone to the heating zone is called the setting zone. Generally, the temperature and humidity in the setting area are controlled according to the variety and requirements of the fabric and the conditions of the mechanical equipment, generally within 20-60 seconds.
4) cooling: after the fabric leaves the setting area, it is necessary to try to keep it in the state of setting for forced cooling. The cooling method is to blow cold air to the fabric or use the fabric to pass through the cooling roller. Generally, the cloth dropping temperature is required to be below 50 ℃. Otherwise, after the fabric is piled into the cloth box or rolled, it will not only shrink due to the effect of heat, but also may produce wrinkles that are difficult to eliminate.
Setting of polyester knitted fabric
Polyester is a kind of thermoplastic fiber. In a series of processing processes, such as dyeing, due to many times of mechanical action and many times of stretching, the original geometric shape of the door and coil of the fabric has changed, resulting in deformation and contraction, and even skewness of the horizontal silk, which seriously affects the quality of the product.
The purpose of heat setting is to heat the polyester knitted fabric under tension, and bake the fabric under the specified temperature, so as to intensify the heat movement of the secondary valence bond and the molecular segment between the fiber molecules, so that the molecules can be recombined and arranged, and the internal stress is relatively stable.
Heat setting of polyester and other synthetic fibers
1. Polyester and other synthetic fibers are thermoplastic fibers. In their macromolecular structure, the hydrophilic group, the fiber structure is tight, the moisture absorption is very low, the expansion degree of the fiber after wetting is small, and the shrinkage phenomenon is not significant under normal conditions. The stability of the size and shape of synthetic fiber fabric mainly refers to the shrinkage and deformation of the fabric when it is heated, especially under high temperature. This reduces the use value of the fiber, so it is necessary to carry out heat setting processing.
The processing principle is to use the thermoplastic property of synthetic fiber to keep the fabric in a certain size and shape, heat it to the required temperature, and then rapidly cool it to fix the microstructure changed after heating, so as to stabilize the size and shape of the fabric. In essence, it is due to the rearrangement of the macromolecular segments of the fiber, so as to eliminate the internal stress.
2. Spandex (stretcher) is also synthetic fiber, belonging to thermoplastic fiber, so elastic cotton fabric containing spandex, like other synthetic fibers, should be pre-set and post set to improve the stability of its size and shape in thermal processing, reduce the generation of wrinkle marks that are difficult to eliminate, and control the door width and weight.
There are two key points in the heat setting process of polyester knitted fabric: controlling the setting temperature and setting time.
If the heat setting temperature is too low and the time is too short, it can cause defects such as uneven surface, unsteadiness, shrinkage of the door width, etc., and lose the setting effect; if the setting temperature is too high or the time is too long, it will cause the fabric to become hard and brittle, reduce the strength, reduce the elasticity, sublimate some disperse dyes and produce color difference, and even melt the fiber seriously.
Practice has proved that:
The suitable setting temperature of polyester knitted fabric is 180-210 ℃, setting time is 20-90s, and cooling temperature is about 50 ℃.
It can be calculated according to the following formula (according to different shaping mechanisms):
Setting time (s) = setting length (m) / fabric linear speed (M / min) × 60
When the setting temperature is 185-190 ℃, the linear speed of all kinds of polyester knitted fabrics is: 10-15m / min for polyester warp knitted mosquito net fabric, 12-18m / min for polyester warp knitted shirt fabric, 12-20m / min for polyester warp, weft and outer knitted garment fabric, and 7-lom / min for polyester color woven jacquard fabric.
The tension and overfeeding of the fabric should not be neglected in setting.
If the width of the stretch exceeds the width of the door, the shrinkage will increase and the strength will decrease.
If the overfeeding is too large or the tension is not the same, it is easy to cause the latitudinal wave shape (commonly known as "ear edge"), otherwise, it will produce stripes in the meridional direction. In a word, the technological conditions such as width, tension and overfeeding should be strictly controlled during operation.
