Since its invention, polyester has achieved rapid development with its absolute advantages. Its quantity has accounted for 1/3 of the world’s textile fibers and about half of my country’s textile fiber processing volume. It has become the leader in synthetic fibers and is today’s Ideal textile material. Its superiority mainly depends on its specific macromolecular structure; it not only has a rigid benzene ring, but also has aliphatic chain links, making it not only melt-processable and easy to process into fibers, but also its macromolecules are sufficiently rigid. , giving the fiber a high initial modulus. Polyester has good comprehensive properties, high strength, good elasticity, and good processing performance. The fabrics made of it are crisp and not easy to deform. They do not need to be ironed after washing. They can be spun pure or blended or interwoven with various natural fibers. They are widely used in Clothing, home textiles and technical textiles. In terms of clothing, polyester-cotton blended fabrics can be used in shirts and bedding, while polyester filaments can be used in outerwear and sportswear. They can also be used to produce imitation wool, imitation silk, imitation linen and other imitation natural fiber products. Because polyester can be produced in large quantities, processing technology continues to improve, and production costs are reduced, the future of polyester is bright.
The dyeing defects of polyester bring a lot of trouble to the production of polyester products, so we must have a certain understanding of the basic knowledge of polyester dyeing and defects, such as color patterns during polyester dyeing , color spots and color differences, etc., and analyze the causes of these polyester dyeing defects, thereby proposing preventive measures to control polyester dyeing defects, solve these polyester dyeing defects, and reduce the production trouble caused by polyester processing and products.
Polyester and disperse dyes
1. Polyester
1.1 Structure of polyester
Polyester is the trade name of polyethylene terephthalate fiber. Observed under a general optical microscope, the longitudinal direction of ordinary polyester is a smooth, uniform, streak-free cylinder, and the cross-section is circular. The polyester macromolecular chain does not contain hydrophilic groups and lacks functional groups to bind to dye molecules. Therefore, it has poor hygroscopicity and dyeability, and is a hydrophobic fiber. The basic links of polyester macromolecules contain benzene rings, which hinder the internal rotation of the macromolecules and increase the rigidity of the main chain. However, the basic links of polyester macromolecules also contain a certain number of methylene groups, so they have a certain degree of flexibility. The macromolecular structure of both rigidity and softness gives polyester excellent properties such as excellent elasticity, stiffness, and good dimensional stability. Polyester macromolecules are linear molecules without large side groups and branched chains. The molecular chains are easily arranged in parallel along the fiber stretching direction, so the molecules are easily packed together tightly to form crystals, which gives the fiber high mechanical strength. and shape stability. The existence of ester bonds gives polyester molecules a certain chemical reaction ability, but due to the better stability of benzene rings and methylene groups, polyester has better chemical stability.
1.2 Properties of polyester
①Thermal properties
Polyester is a thermoplastic fiber with a glass transition temperature of 68 to 81°C. Below the glass transition temperature, the mobility of macromolecule segments is small, and polyester is not easily deformed by external forces, which is conducive to normal use; The softening point temperature of polyester is 230-240°C. Above this temperature, the fibers begin to de-orient, the molecular chains move and deform, and the deformation cannot be restored. During dyeing and finishing, the temperature should be controlled above the glass transition temperature and below the softening point. The heat setting temperature in printing and dyeing factories is generally 180-220°C. The temperatures for dyeing, finishing and garment ironing are all lower than the heat setting temperature. Otherwise, the qualitative effect will be destroyed due to intensified molecular chain activity. It is also the best among several major synthetic fibers. After polyester is heated at 150°C for 168 hours, its strength loss does not exceed 3%, while nylon turns yellow when heated at 150°C for 5 hours, and the fiber strength drops significantly. Most carbon chain fibers will deform when heated above 80 to 90°C, and their strength loss is difficult to recover. Therefore, when thermal processing polyester-cotton blended fabrics, the heat resistance of the cotton fiber itself should be considered. Polyester has a large allowable temperature range and can be used between -70 and 170°C. The fiber will not become brittle at low temperatures.
②Mechanical properties
Strength and elongation at break of polyester It is not only related to its molecular structure, but also closely related to the drawing and heat treatment process during fiber spinning. After stretching, the polyester macromolecular chains are arranged in a certain direction, and the orientation degree is improved, so that it can evenly withstand external forces, so the strength is improved. Usually the breaking strength of polyester short fiber is about 0.27~0.66N/tex, and the breaking elongation is between 25% and 50%. Under appropriate heat treatment conditions, the higher the degree of stretching of polyester during spinning, the higher the orientation of the fiber, the higher the breaking strength of the fiber, but the lower the elongation at break; conversely, it is possible to obtain Low strength and high elongation fiber. That is, by changing the stretching and heat treatment conditions, different types of fibers can be made, such as high strength and low elongation or low strength and high elongation. Polyester has excellent elasticity and is not easily deformed under the action of small external forces. When deformed by large external forces, its ability to return to its original shape is also strong after the external force is removed. Its deformation recovery ability is similar to that of wool.
③Chemical properties
The chemical properties of polyester are related to its molecular structure . In polyester macromolecules, benzene rings and methylene groups have better stability, so polyester has better chemical stability, and the presence of ester bonds gives the molecule a certain chemical reaction ability. Polyester has good acid resistance and is resistant torc=”” data-preview-group=”1″ src=”http://pic.168tex.com/Upload/News/image/2021/11/15/20211115093402171001.jpg”>
↑ Schematic diagram of the temperature rising dyeing curve when dyeing polyester with disperse dyes (dyeing at 70℃, temperature rising 1℃/min)
↑ High temperature and high pressure rope dyeing machine
3. Carrier dyeing method
Method: Place the polyester fiber A dyeing method in which dyeing is performed under normal pressure and high temperature in a dye solution containing a carrier.
Principle: The carrier effect is used to improve the dyeing performance of polyester fiber and disperse dyes.
Commonly used carriers: methyl salicylate, o-phenylphenol, benzoic acid, monochlorobenzene, dichlorobenzene and other benzene derivatives.
Features: The equipment is simple and the dyeing conditions are low, but the dyeing procedure is cumbersome and costly. The carrier is harmful to the human body and can easily cause environmental pollution, so the carrier dyeing method is rarely used.
4. Hot melt dyeing method
Method: Polyester fabric is dyed in A dyeing method that uses dry heating (i.e. baking) on a hot-melt dyeing machine to apply dyes under high-temperature (170~220°C) dyeing conditions.
Principle: Use high temperature effect to improve the dyeing performance of polyester fiber and disperse dyes.
Features: It has continuous production and high efficiency, but the dye utilization rate is low, the equipment investment is large, the dyeing product feels rough, the color brightness is average, and the selection of dyes is limited (E type dyes are not suitable) and other characteristics.
↑ Hot melt dyeing combined machine
4. Normal pressure and high temperature dyeing method
Polyester normal pressure and high temperature dyeing uses a padding method to apply disperse dyes to polyester fabrics and then dry them. Dry, and then use high-temperature superheated steam above 180°C to steam the fabric under normal pressure conditions to diffuse the disperse dye into the interior of the fiber, thereby dyeing the fiber. </p
