Textile dyeing process and methods

The dyeing process is affected by three factors, namely dye, fiber and dye solution. All three factors are controlled by independent factors that affect the dyeing method itself. The dye must be soluble in water so that the textiles can be dyed with it. The nature of pigments is such that they can be solved by chemical interactions.

The process of dyeing textiles

Textile dyeing is done in the following three steps

Binding of dye molecules to the surface of the fibers

Dye penetration into intermolecular spaces and its diffusion between fibers

Orientation (and stabilization) of the dye along long chain molecules.

The dye solution used is called a “paint bath”. It may have a direct “mixed affinity” color with the fibers, or vice versa. For this reason, as soon as the fibers are immersed in the dye bath, the fibers physically (adsorbent) or chemically (chemically) retain the dye. Accumulation of pigments within fibers may be a gradual process; The rapidity of this accumulation is called the “dyeing rate”.

Dyeing rate is controlled by dye bath conditions, ie dye concentration, temperature and presence of electrolytes; Each of these factors corresponds to one or all three primary factors.

Dyeing speed is affected by the “substance to solution” ratio, which is expressed as a fraction; For example, the expression fraction 1:20 indicates that 1 part of the dye (in terms of weight) is in the dye bath, which is dissolved 20 times its own weight.

Dyeing speed decreases with increasing ratio of products to solution. In principle, pigments are dispersed in solution by a special dye to produce a specific “color shade”; The difference in color shades is due to the difference in “tones”. For example, a shade of blue may have a greenish or reddish undertone. The color required to form a certain saturation of the color shade is expressed as a percentage of the fabric load. For example, dyeing one-tenth shows a color shade that is dyed to produce 100 pounds of fabric with one pound of dye (commercial) under well-defined conditions. Dyeing conditions must be defined because of the effect it has on the “saliva” of the paint bath. Exhaustion determines the amount of dye that affects the fibers, or in other words, the amount of dye that occurs after the “balance” between the dye and the fibers is established (ie when dyeing is no longer done). The color remains in the bath.

“The process of applying dye to a mass of fibers, yarn or fabric is called dyeing.” In this process, the dye may penetrate completely or partially into the fibers or yarns.

Dyes that are often used to dye animal, plant, or synthetic fibers must have a combined affinity for them. Textile dyes include acid dyes that are mainly used directly or alone to dye wool, silk and nylon; In addition, these pigments have a high affinity for cellulosic fibers. Tooth dyes must be combined with chemicals such as salt to find a composite for the fabric to be dyed. After being treated with metal salts, they are applied to cellulosic fibers such as wool or silk. Sulfur dyes or conventional cellulose dyes are relatively cheaper, but produce dyes without radiance. Azoic pigments are insoluble pigments that fill the fibers when they are impregnated with them; This is done first with a combined solution of di-nitrogen. Curved pigments do not dissolve in water and are converted to soluble colorless compounds using alkaline sodium hydrosulfite. These colorless compounds are absorbed by celluloses and subsequently oxidized to an insoluble pigment. These pigments have high color fastness. Disperse dyes are suspensions that are divided into insoluble organic pigments of conventional dyes and are used for dyeing hydrophobic fibers such as polyester, nylon and cellulose acetate.

Reactive dyes combine directly with the fibers and show high color fastness. The first range of reactive dyes for cellulose fibers was introduced in the mid-1950s. Today, these types of pigments are very diverse in the market.

Textile dyeing methods

Beam Dyeing

In this method, the yarn is dyed before weaving. The manufacturers wrap the yarn around a mesh and pass the dye through the holes, so the yarn becomes saturated with dye.

Spot dyeing or dyeing of plant particles left in the fabric
This is generally done on woolen fabrics or yarns. In this method of dyeing, stains and wrinkles are covered using special color bonds that are present in many colors and shades of colors. This dyeing method is a completely manual method.

Jig Dyeing

In this method, dilution is performed on the products by means of a jig, pot, paint bath or open tank. The material is transferred from one roller to another through a dark-colored bath to obtain the required color shade.

Cross Dyeing

Cross-dyeing is a very popular dyeing method in which a variety of color effects are achieved in a dye bath for a fabric consisting of fibers with a different affinity for the dye used. For example, a blue pigment may give nylon 6 a shade of blue and nylon 6.6 a light blue, and have no desire to paint a healthy area of polyester or white.

Solution Dyeing

This method is also called polymer dyeing or spinning dyeing; In this method, colored pigments are bonded inside the solution and because the filaments are formed inside the solution, they quickly penetrate inside them. Cellulose and non-cellulose fibers are dyed in exactly the same way. Cellulose and non-cellulose fibers are dyed in exactly the same way.

Bale Dyeing

This is a special and cost-effective method for dyeing fabrics. In this method, the fabric is spread without cleaning or gumming in a cold water bath in which the threaded yarns have a mixed desire to dye. Imitation chit fabrics are often dyed this way.

Batik Dyeing

This method is one of the oldest known forms for humans. The origin of this dyeing method goes back to the Indonesian island of Java. In this method, parts of the material are covered with wax so that only the wax-free areas deal with the paint. This operation is repeated several times and several other colors may be used to create extraordinary effects. In this method of dyeing, colorful patterns, waves or meshes are created that are imitated in machine printing.

Continuous dyeing (Chain Dyeing)

This method is used when the dye and fabric have low resistance. Several cuts or pieces of material are sewn together head-on and temporarily, and passed through the paint as a continuous chain. This method can be used for mass production.

Piece Dyeing

Dyeing fabric through cuts, dents or balls of fabric is called dye dyeing. In this method, the dye follows the texture of the textiles and thus the fabric is dyed. Blue or green organza fabrics are dyed this way.

Random Dyeing

In this method, only certain parts of the yarn are dyed. There are three ways to do this type of dyeing: In one method, the threads that are completely compressed are dyed in two or more parts so that one side is dyed with one color and the other side with another color. Alternatively, the threads are threaded open onto the felt part of the printing press and printed in color.
In the third method, the spindles or bundles of yarn wrapped around the hollow spools are arranged in such a way that the yarn moves through the air through a punch; In addition, colored materials are sucked through these holes. The yarn absorbs the dye in the area near the punch, thus creating random color effects on the yarn.

Raw Stock Dyeing

The process of dyeing raw fibers takes place before spinning the fibers into yarn. Dyeing of fibers is done after degreasing of wool fibers and drying of the fiber bundle.

Yarn dyed

In this method, the yarns are dyed before weaving or after spinning. In this case, in order to dilute the yarn, it must be completely or partially immersed in the paint bath.

Dyeing process

In order for the fibers to be dyed, they must first be placed in a solution, often aqueous, called a dye solution or dye bath. The dyeability of the fabric and the amount of dye absorption by the fabric are the most important factors affecting the dyeing process.

Coloration

Dyeing should be relatively permanent: The paint should not be easily removed by washing in water or washing clothes by conventional methods. In addition, the color of the textiles should not fade quickly after exposure to light.

Absorption

The process of attaching dye molecules to fibers is the same throughout the adsorption process: In either case, the dye molecules must reach the surface of the fibers. There are four types of forces that dye molecules support fibers:

1) Ionic forces
2) Hydrogen bonding
3) van der Waals forces
4) Covalent chemical bonds

Wool dyeing

Because wool contains complex proteins containing 20 different amino acids; Therefore, in the wool dyeing process, vitro oil added to the dye bath causes ionic bonds with amino acid groups of wool proteins. During the dyeing process, the sulfate anion (negative ion) replaces the dyed anion. In the process of dyeing wool, silk, and synthetic fibers, hydrogen bonds are likely to be established between azo, amino, alkyl amino, and other Co-NH groups and amino groups. Covalent chemical bonds in the dye bath are formed by the reaction between fibers and reactive dye molecules that contain chemical reaction centers and a hydroxy group of cotton fibers in the presence of alkalis.

Chemical dyeing process

In the dilution process in any dyeing process, regardless of the chemical class of the dye used, the heat must be supplied from inside the dye bath; When transferring dye molecules in response to the fibers, energy is used, as well as energy causes the fibers to swell more and prepares them to accept more dye. This process is technically called salivation. The uniformity of dyeing quality is called smoothness or evenness, which is a very important quality feature and plays a vital role in the dyeing quality of natural and synthetic fibers. Smoothness or color equality is achieved by controlling the dyeing conditions.
Dyeing conditions can be controlled by stimulation to ensure proper contact between the dye solution and the textiles, and by using inhibitory agents to control the dyeing rate or dye removal rate by the textiles in the dye bath. In the solution dyeing process, serious attention has been paid to in-water dyeing methods, as the aqueous medium can replace soluble media such as chlorine hydrocarbons used in the cleaning process.

The advantages of the technologies used in soluble dyeing are:

Rapid wetting of textiles

Less swelling of the fibers

Increase dyeing speed in any volume of fabric

Energy saving; Because less heat is needed to heat or evaporate chloroethylene.

Reduction of problems related to effluent (pollution) which is part of the traditional methods of dyeing and polishing.

equipment and machinery

Modern dyeing machines are made of stainless steel. Steels containing 4% molybdenum should be exposed to the common acidic conditions of dyeing processes.
A dyeing machine essentially consists of a container in which a dye solution is placed; In addition, a dyeing device includes heating, cooling and cycling equipment that is used to circulate solutions around dyed textiles or to transfer dyed textiles from dyed solution. The type of device used depends on the characteristics of the products to be painted. Labor and energy costs associated with the total costs of the dyeing process are relatively high: The purpose of the dye is to reduce the dyeing time in order to save the steam energy and power required, and to prevent the textiles from rotting.
The conical pan of the mass fiber dyeing machine can be a widely used machine. If this device is used, the fibers are kept inside a conical container with wide edges and the dye solutions are pumped mechanically on them. The fibrous mass located in the narrow half above the cone tends to condense, which helps the effective circulation of the dye solution inside the fibers. In this case, the problems of color smoothness are greatly reduced, because by combining the dyed fibers before the spinning process, the color uniformity is largely guaranteed.
The Hussong dyeing machine is a common tool in the dyeing process. This device has a stretched tank with a square end and it is used as a paint bath; The frame of the handles that hold the fibers down comes down and moves the fibers into the bath. In this device, the dye solution is circulated by a propeller and moves through a false lattice floor in which the soldier’s steam line (the job of this line is to generate heat) is located. In modern machines, the circulation of the dye solution at the points of contact between the tank and the handles is improved. This leads to more color smoothness and elimination of color roughness due to non-uniform cooling of the fibers on them. In spinning machines, the paint is pumped in several directions and the pumping of the paint is not limited to only two directions.

The dye is pumped outwards through the mesh spindle and through the yarn bundles, and the dye enters the outer layers of the packages through an inverted path and exits the spindle.

In any case, the smoothness and uniformity of the color is very important. Some spinning machines are also capable of operating at temperatures above 130 ° C.
The winch, the oldest part of the dyeing machine, named after a board roller, moves a continuous string or strap of fabric in full width into the dye solution. Pressure winch machines are manufactured in the United States.
In a completely new idea, the Gaston County jet car spins the fabric in a string through a tube using a high-pressure paint fountain. The jet machine is mostly used in the dyeing process (with high temperature) of synthetic fibers, especially polyester fabrics. Another machine used in this field is another dyeing machine. The machine has a V-shaped opening that holds the dye and guide rollers to hold the fabric in full width between the two outer rollers; The fabric is alternately wrapped around each roller, meaning that the fabric is first moved forward, then moved back through the paint, and this process continues until the dyeing is complete. Modern machines that are automatically controlled and programmed may be enclosed

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