The need for dyestuffs arose because people benefit from their environment and want to give objects and themselves a special appearance. Therefore, many dyes and dyestuffs were first obtained from nature. It is possible to see this even in very ancient times such as stone age times. Paintings and objects on the walls of caves in France and Spain dating back hundreds of years before Christ are proof of the existence of dyes and dyes in ancient times. The first dyes used were a mixture of metal oxides, clay soil and some plant sap.. It is thought that these are dissolved with water and applied to the surface to be painted. Ancient Egyptians mixed gum to give paint strength and shine. These have been found in mummies. In order to protect the paints from the effects of air, they are covered with wax. While dyes are inorganic, the dyestuffs used in textiles are organic. Examples of inorganic dyes are Fe2O3, Cr2O3, Pb3O4, HgS, graphite, etc. Dyes, on the other hand, are mostly synthetic as well as those of natural origin. The examples given above and the historical remains show that the paint has been used since ancient times. Most of the dyestuffs used today are obtained as a result of chemical synthesis.
Paints are substances used to protect the surface of objects from external influences or to make the object colorful in order to provide a beautiful appearance. The surface of the painted object is covered with a thick layer. This process is not painting, but actually covering. Paints do not make any changes on the surface on which they are applied, other than the appearance. They are separated from the surface by scraping.
On the other hand, dyestuffs are coloring substances that have affinity for a material either by themselves or with suitable reagents. Dyes are chemical compounds and they impart color to the object with which they are treated.. All dyestuffs are organic compounds. The object and the dyestuff combine in a continuous and durable way and change the surface of the object in terms of structure. Generally, the dyestuff combines with the surface of the object through a chemical and physicochemical relationship. When any physical effect of the paint is applied on the surface, the surface cannot take its initial state.
As explained above, dye and dyestuff are not the same concepts, but the only similarity between them is that they are both coloring agents. While the paint covers the surface with a layer, the bonding of the dyestuff with the surface distinguishes these two concepts from this aspect.
To the substances applied to make the objects (fabric, fiber, etc.) themselves colored. DYES It called.
What are impacted teeth?
When one or more teeth fails to grow in the correct position and is therefore held below the normal gum line, it is called an impaction. This can be complete, such as completely unerrupted (buried) third molars (wisdom teeth) or partial when just part of the tooth is visible in the mouth.
Why are impactions important?
For best function and appearance the teeth should grow in a healthy alignment. When one or more teeth is impacted, this can affect the function of that tooth but also the function and appearance of other teeth.
Whether all impactions should be treated is still controversial and your dentist and oral and maxillofacial team can explain the advantages and disadvantages or treatment for you, which is usually surgical.
However, not every color-giving or colored substance is a dyestuff. Coloring with dyestuffs is not like coloring with dyes. They are applied by various dyeing methods, usually as solutions or suspensions. All dyes are organic compounds. Objects to be painted change the surface of the object in terms of structure by combining with the dyestuff in a continuous and durable way. Generally, the dyestuff is combined with the surface of the object through a chemical or physicochemical relationship. The painted surface cannot take its original colorless state by physical processes such as scraping, wiping, washing.
Dyes that dye natural fibers
Dyestuffs that dye cellulose-based products
- Direct dyestuffs
- Reactive dyes
- Sulfur dyes
- Cube dyestuffs
- Pigment dyestuffs
- Soluble cube dyestuffs
- Oxidation dyes:
This dyestuff group is one of the oldest synthetic dyes. They are intermediate products that can dye the natural textile product well during oxidation. There are two groups:
1-Aniline black
2-Diphenyl black
The basis of dyeing with oxidation dyestuffs is to treat the material to be dyed with a suitable aromatic amine and then to form the dyestuff by oxidizing the amine on the material.
Aniline black is a black dye obtained on cotton by the oxidation of aniline. The aniline black is an example of this group as one of the fiercest, best blacks.
- Washing and light fastness is good.
- In some cases, chlorine fastness is good.
- Color intensity cannot be imitated.
- It is suitable for continuous operation.
Although Diphenyl Black is more expensive than Aniline black, it is advantageous in that the color tone does not turn green over time and there is less risk of damaging the fibers.
Dyestuffs that dye protein-based products
- Acid dyes
- Reactive dyes
- Chromium dyestuffs
- Metal complex dyestuffs
Dyestuffs that dye synthetic fibers
Dyestuffs that dye polyamide products
- Acid dyes
- Disperse dyes
- Chromium dyestuffs
- Metal complex dyestuffs
Dyestuffs that dye polyester products
- Disperse dyes
- Dyestuffs that dye polyacrylonitrile products
- Cationic dyes
- Disperse dyes
Classification of dyestuffs according to their solubility
Water-soluble dyestuffs
The dyestuff molecule carries at least one salt-forming group. If the starting materials used during the synthesis of the dyestuff do not contain a water-soluble group, solubility can be achieved by adding this group to the dyestuff molecule afterwards. These dyestuffs can be salt-forming according to the character of the group;
- 1-Anionic Water-Soluble Dyes: In Water They contain mostly sodium salts of sulfonic (-SO3¯) and partially carboxylic (-COO¯) acids as soluble groups. Acid and direct dyes are examples of this type.
- 2) Cationic Water-Soluble Dyes: A basic group (for example –NH2) as a solubilizing group in the molecule exists as a salt with acids. Organic acids [HCl or (COOH)2] are used as acids.
- 3) Dyestuffs with Zwitter ion character: Molecules contain both acidic and basic groups in their structures, and internal salt formation takes place. During dyeing, they show basic or neutral anionic dyestuff behavior according to their environment.
Water-insoluble dyestuffs
It is possible to divide the dyestuffs that are used in certain areas of the industry, especially in textiles and insoluble in water, into various groups.
- Substrate Soluble Dyes: Dyestuffs applied on synthetic fibers by dispersion method are in this class and their solubility in water is very low.
- Dyestuffs Soluble in Organic Solvents: Dyestuffs in this group have high solubility in organic solvents. These dyestuffs are called solvent dyestuffs that can be applied to the surface in spray or lacquer form and are used for coloring ink, wax and petroleum products.
- Dyestuffs with temporary solubility: They can be used after making them soluble with various reducing agents on the fiber. It is then oxidized together with fiber, making it insoluble in water. Sulfur dyestuffs can be given as examples of these dyestuffs.
- Polycondensation Dyestuff: It is a new method developed and they are known as dyestuffs that form large molecules by condensing with each other or with other molecules after they are applied on the fiber.
- Dyestuffs Created in Fibers
- pigments
Classification of dyestuffs according to dyeing properties
Generally, dyeing practitioners do not look at the chemical structure of the dyestuff, but by what method it can dye the fiber.
According to these methods, dyestuffs are classified as follows.
a) Basic (cationic) dyestuffs
They are in the form of hydrochlorides of organic bases and carry the cationic group in the colored part. They contain N or S atoms as positive charge carriers. Due to their structure, they are bound by fibers containing anionic groups because they act as proton fields. It is mainly used for dyeing polyacrylonitrile, partly wool and cotton fiber. The fiber-dyestuff relationship is ionic; The dyestuff cation forms salts with the anionic groups of the fiber.
Cationic dyestuffs are the most important dyestuff in the dyeing of polyacrylonitrile. Polyacrylonitrile fiber has anionic structure in the bath due to the comonomer added to its structure during production. Cationic dyestuff can be attached to the anionic ends of the polyacrylonitrile fiber. Light and wet fastnesses of cationic dyestuffs on acrylic fiber are excellent. Good wet fastness results from the durable bonds between the dyestuff and the fiber. The perfect light fastness is due to the ionic bond between the dyestuff and the fiber, and the hydrophobic character of acrylic fiber does not contain moisture and oxygen that cause fading. Color intensity is good even at low concentrations in dyeing with cationic dyestuffs. Accordingly, the color obtained is bright and the cost is low. Polyacrylonitrile fiber does not absorb the dyestuff up to 75 ºC, after this temperature there is a sudden shrinkage. Since cationic dyestuffs do not have migration capabilities, uneven dyeing occurs due to abrupt attraction. For this, it is necessary to keep the aspiration of the dyestuff to the fiber under control in order to eliminate the dyeing unevenness caused by the sudden withdrawal of the dyestuff after a certain temperature. Acrylic fibers are dyed with cationic dyes by retarder method or temperature setting between 80-90 ºC for proper dyeing.
b) Acid dyes
Acid dyestuffs, whose general formulas can be written as Bm- SO3¯ Na+ (Bm: Colored part of dyestuff), contain one or more –SO3H sulfonic acid groups or –COOH carboxylic acid groups in the molecule. These dyestuffs are primarily used for dyeing wool, silk, polyamide, cationic modified acrylonitrile fiber and paper, leather and food materials. The reason why these dyestuffs are named acid dyestuffs is that the application is made in acidic baths and almost all of them are salts of organic acids.
Acid dyes are anionic dyestuffs with a special luster, characterized by their affinity for protein fibers.
Acid dyestuffs are the most commonly used dyestuffs for dyeing wool, polyamide and natural silk fibers.
Advantages aspects
- It is cheap
- Easy and smooth paint
- Light fastness is good
- Vivid and bright color is obtained
Disadvantages
- Washing fastness is not good in some types.
- Dry cleaning fastness is mediocre
- Sweat fastness is low
Acid dyes are mostly azo dyes. Acid dyes contain one or more sulfonic or carboxylic acid salt functional groups. These provide solubility in water.
Acid dyestuffs can be grouped into three classes according to their dyeing methods and liquor conditions. These:
- Acid dyes that dye (well level) in a strongly acidic medium
- Acid dyes that dye (medium leveling) in moderately acidic medium
- Acid dyestuffs that dye weak acid/neutral medium (difficult quenching)
Acid Dyes That Dye (Good Leveling) in Strong Acidic Environment
In a strongly acidic environment, the number of ammonium (- NH3 +) groups in wool fibers is the highest and dyestuff anions are also bound to ammonium groups. In this case, a very fast dye uptake is achieved depending on the number of ammonium groups. Since the main force providing bonding is electrostatic attraction forces, the affinity of such dyestuffs against fibers is not high. Therefore, their post-smoothing ability is very good, especially at boiling temperature. It is not objectionable that the dyestuff is removed quickly and unevenly by the wool fibers. Since the migration capabilities are good, migration will start from the places where the dyestuff is high to the places where it is less at boiling temperature. Uniform dyeing is easy due to its high migration ability (small molecular structures and weak ionic bonds with the fiber).. For this reason, they are also called “leveling dyestuffs”. It has high light fastness. However, their wet fastness is bad. This situation is the same for all dyestuffs with post-smoothing ability. Because, in general, their molecular structures are small. Sulfuric acid is used for pH 2–3,5 adjustment. In addition, sodium sulfate salt is used to slow down the absorption of the dyestuff into the fiber. It is preferred for products that are difficult to dye properly (felted products) and do not require much washing.
Acid Dyestuffs Dyeing in Medium Strong Acidic Environment
These stain with formic or acetic acid at pH 4-5,5. It gives fastness properties in values between the other two groups of acid dyestuffs. At the end of the dyeing, the drawing is completed with the addition of formic acid. Life is connected by H-bridges and van der Waals forces, as well as electrostatic forces of attraction. Since the later smoothing abilities are low, the dyestuff must be taken properly from the beginning. For this purpose, it is studied at pH 4 – 5,5, where the number of ammonium groups is less. As it is known, around pH 5 – 7 (isoionic region), wool shows a neutral feature. That is, positively charged ammonium groups and negatively charged carboxyl groups are equal. Therefore, the addition of sodium sulfate to the liquor does not increase or delay the uptake. However, sodium sulfate is added to prevent uneven dyeing due to affinity differences in the material. 1–3% acetic acid (60%). After the product is treated for a while, dyestuff is added in a liquor with pH (4–5,5) at 5–10 40C containing 50-0% calcined sodium sulfate (Glauber's salt). It is reached to 30-45C in 80-850 minutes and dyeing is continued for 45-90 minutes. The wet fastnesses obtained with this acid dyestuff group are better than the leveled type. Nuanced can be done at the same temperature.
Acid Dyes that Dye in Weakly Acidic / Neutral Environment
They are acid dyestuffs with high fastness to wet finishing of wool (especially to resting). It is normally applied to protein fibers in weakly acidic or neutral dyebaths. Because of good listening fastness These are called resting dyes. Wet fastness is excellent, light fastness is good. However, the danger of dyeing unevenness is high. The migration ability of the dyestuff is low, so dyeing is quite difficult. It is not recommended for fabric dyeing as it is difficult to dye properly. It is used for dyeing fleece, scanning tape and yarns. These types of dyestuffs, which are of the disazo class in terms of their structure, are bound to wool fibers by various bonds (electrostatic attraction forces, H bridges, van der Waals forces) due to their high affinity. Therefore, the uptake of this type of dye by the fibers must be very slow. A smooth dyeing can be achieved with a smooth removal. In a weakly acidic or neutral environment (pH 5,5–6,5), wool fibers are neutral or anion-loaded. The dye anion and the fiber anion repel each other. Therefore, it is not possible to bond dyestuffs by electrostatic attraction. Salt is added to the medium to ensure that the dyestuff is absorbed by the fiber. Salt reduces repulsion and accelerates uptake by increasing the aggregation degree of the dyestuff. Depending on the increase in color tone, the amount of salt is also increased.
c) Direct dyestuffs
These are usually sodium salts of sulfonic, sometimes carboxylic acids. There is no definite boundary between direct and acid dyestuffs in terms of their structures. They differ in the method of dyeing. Direct dyestuffs are drawn directly from the dyestuff solution to the cellulose or wool without any prior treatment. They are stored in the inner micelles of the fiber without forming any chemical bonds. Direct dyestuffs containing basic groups in the colored part exist in aqueous solution as both anionic and cationic ions.
Direct dyestuffs are dyestuffs that can be dyed directly without requiring any pretreatment in dyeing cellulosic fiber.. They are also called substantive dyes. It differs from basic and acid dyestuffs by its high substantivity towards cellulosic fiber. Congo red was the first direct dye. They are drawn directly from the liquor. With these dyestuffs, which can be well leveled, dyes that penetrate into the material are obtained. They are soluble in water. Due to ionization, these dyes are anionic dyes. The wet fastness of these dyestuffs is not good. However, wet fastnesses can be improved with the help of suitable materials. Some of the direct dyestuffs have excellent light fastness and these are copper complexes. However, boiling and chlorine fastness of these dyestuffs is low.
Advantageous aspects:
- It is cheap
- water soluble
- Painting operations are very simple
- Does not require strong pH values during dyeing
- Gives good dyeing results in dark colors
Disadvantages of direct dyestuffs:
- Direct dyestuffs have low wet fastnesses.
- Age fastness is low.
- A significant part of these dyestuffs have a carcinogenic effect.
Most of the direct dyestuffs are azo dyes containing disazo-, polyazo groups. Thiazole, phthalocyanine and anthraquinone also contain direct dyestuffs. In this respect, the chemical structures of direct dyestuffs are similar to acid dyestuffs. In the structure of direct dyestuffs, there is an anionic group that can dissolve the dye molecule in water.
Since each of the dyestuffs behaves differently, direct dyestuffs analyzed in three groups.
Class A (Self-levelling dyestuffs):
Dyestuffs belonging to this group have good migration properties. Smooth dyeing is achieved without special precautions. Age fastness is low.
Class B (Dyestuffs that can be controlled with salt):
The migration capabilities of these dyestuffs are low. Therefore, they do not show proper dyeing properties. Addition of salt is required to adjust the drafting and leveling steps. If they are not taken regularly by the fiber at the beginning, it is very difficult to smooth them afterwards.
Class C (Dyes that can be controlled by temperature):
They are dyestuffs that are highly sensitive to salt and cannot be self-leveled and have low migration possibilities. Their attraction cannot be adequately controlled by the addition of salt. In addition, uniform dyeing is ensured by controlling the temperature.
d) Reactive dyestuffs
Structure of reactive dyestuffs Ç-Kr-KR
Here;
- C – The group that provides the resolution
- Kr – Chromophore (color giving) group
- K – Bridge group
- R – Reactive group
Means.
Since reactive dyestuffs are covalently attached to the fiber, their migration capabilities are not good. For this reason, it is essential to take it properly in dyeing. Binding of reactive dyestuffs to wool; It is provided by covalent bonds over -SH (thioalcohol) groups in a strongly acidic medium and - NH3 + (ammonium) groups in a weakly acidic medium.
They are dyestuffs containing reactive groups that can form true covalent bonds with functional groups in the fiber structure. These dyestuffs, which are used in dyeing and printing of cellulosic fiber and developed in recent years, are also used in dyeing wool, silk and polyamide. Due to the covalent bond, they are strongly attached to the fiber. The reactive group is attached to the colored part of the molecule. The common feature of all reactive dyestuffs is that they all contain a reactive group that provides solubility to the molecule, as well as a colored group carrying chromophore.
Reactive dyes form an important part of azo dyes. Azo dyes are used in very wide areas of industry. Reactive dyes usually contain one or two functional groups and these groups are capable of covalent bonding with a specific substrate.
They are dyestuffs containing reactive groups that can form real covalent bonds with the functional groups in the fiber structure to be dyed. They are strongly attached to the fiber due to the true covalent bond. The reactive group is attached to the colored part of the molecule.
Common feature in all reactive dyestuffs;
- All of them carry a reactive group and a group that gives solubility to the molecule, in addition to the chromophore group that gives the colored structure.
Reactive dyestuffs are the most consumed dyestuffs in our country. According to the reactivity of the reactive groups, they are grouped into two classes: dyes with high reactivity and dyes with low reactivity. Dyes with high reactivity are those containing reactive groups such as vinylsulfone, dichlorotriazine, difluoropyrimidine. Dyes with high reactivity provide faster dyeing compared to dyes with low reactivity, and at the same time, the consumption of chemicals and energy is less. In dyeing process with low reactivity dyestuffs, the loss of dyestuff is less due to the less risk of hydrolysis.
Unlike all other dyestuffs, reactive dyestuffs are dyestuffs that can react with fiber macromolecules and bind to fibers with real covalent bonds. They are highly water-soluble anionic dyes like direct dyes. It is the most widely used dyestuff with sufficient fastness in dyeing cotton products.
Advantages of reactive dyestuffs:
- Wide color palette with bright colors
- dark colors
- Excellent wet fastnesses
- Simplified staining method applicable to normal staining devices
Disadvantages of reactive dyestuffs:
- Chlorine fastness is low.
- There is a danger of hydrolysis of the reactive group in basic media.
- Water, energy consumption and time spent in washing processes after dyeing are high.
There are four groups in a reactive dyestuff.
- 1-Solubilizing group (S): This group allows the dyestuff to dissolve in water.
- 2-Chromophore group (Colorant) (C): It is the group that gives color to the dyestuff molecule.
- 3-Bridge group (part carrying the reactive group) (B): These are groups such as –NH, -CO, -SO2 that connect the colored group and the reactive group in the molecule.
- 4-Reactive group (R): It is the group that makes covalent bonds with the functional group in the fiber. It interacts with the fiber and creates a covalent bond between the fiber and the dyestuff.
Reactive dyestuffs are classified according to their reaction rates. It is examined in three groups according to the reactivity of the reagent group:
- 1-Dyestuffs that dye in the cold (with high reactivity)
- 2-Dyestuffs that dye in the warm (with moderate reactivity)
- 3-Dyestuffs that dye in hot (with little reactivity)
1-Cold Dyes (High Reactivity-IK) Dyestuffs
Since these dyestuffs have high reactivity, they can be dyed at cold (20–40 °C).
Advantages of dyeing with these dyestuffs:
- It is possible to paint faster.
- Less chemicals and energy are consumed.
- High dyestuff yield is provided.
- Repeatability is good.
- They are easy to wash after dyeing due to their low substantivity.
This type of reactive dyestuffs; Examples include Cibacron F, Procion MX, Remazol, Drimaren R/K, Lavafix E/EA/EN-H, HE, HX.
2-Dyestuffs that Dye in the Warm (Medium Reactive-IW) Dyes
This group is no longer common. It is generally evaluated in the cold group.
3-Dyestuffs that Dye at Hot (Low Reactivity-IN)
The reactivity of this class of dyestuffs is quite weak. Therefore, it is necessary to increase the dyeing temperature (60–80 °C) and increase the amount of alkali. This provides activity. Very smooth dyeing results are obtained due to the high dyeing temperature. Penetration abilities of this class of dyestuffs are excellent. The biggest advantage of these dyestuffs is the low risk of hydrolysis and better results. Reactive dyes with low reactivity; Procion H-EKL, Cibacron E, Drimaren X/XN, Basilen E/P are examples.
e) Dispersion dyestuffs
They are dyestuffs that are slightly soluble in water and therefore can be applied as dispersions in water. The dyestuff is drawn from the dispersion medium onto the hydrophobic fiber by diffusion during the dyeing process. Dyeing occurs as the dyestuff dissolves in the fiber. Dispersion dyestuffs are mainly used for dyeing polyester fiber. They also dye polyamide and acrylic fibers.
The most commonly used dyestuff in dyeing polyester fibers is disperse dyestuffs. Disperse dyestuffs have suitable fastness values and sufficient color palette on polyester fibers. It is commercially available in liquid or powder form. Dissolution of disperse dyestuffs in water is not in the usual sense like the dissolution of other water-soluble dyestuffs. Disperse dyestuff is suspended in the bath during dyeing of polyester. That is, the dye molecules remain suspended in the bath without dissolving. It is not completely insoluble in water like pigment dyes. When disperse dyestuffs started to be produced, there were small molecule ones before and their fastness was low. With the development of technology, disperse dyestuffs with larger molecules with high fastnesses were produced.
There are three main types of disperse dyes on the market;
- Small molecule disperse dyes: Dyeing is done by extrusion method with these dyestuffs.
- Medium molecular disperse dyestuffs: Dyeing is done by shrinking, sometimes by thermosol method.
- Large molecule disperse dyestuffs: Generally, the thermosol method is used. Sometimes it is also used in the puller method.
The adhesion rate (adsorption rate) of disperse dyestuffs on the fiber is very low below 80 ºC -below the vitrification point. The adsorption rate starts to increase from 85 ºC and it rises continuously above 100 ºC. The choice of disperse dyestuff is one of the factors that directly affect the quality of the dyeing. For this, the dyestuffs used in combination dyeing must be compatible with each other. Dyestuffs that have the same factors that directly affect the dyeing quality, such as dye attraction curves and fastness values in the manufacturer's catalogs of the dyestuffs to be used while creating the recipe, are selected.
f) Pigment dyestuffs
Organic ones are preferred. Pigments have no fiber affinity. They do not make chemical bonds and absorption. They are attached to the fiber surface with synthetic resins called binders.
It is used in organic and inorganic pigments in the coloring of textile materials. Since these are insoluble in water, there is no affinity between them and the fiber. They can neither chemical bond nor colloidal adsorption. Therefore, they cannot produce a dyeing in the classical sense. Pigments are attached to the fabric with the help of synthetic resins called binders (high molecular natural substances such as albumin, casein).. Since they are insoluble in water, they are applied either in oil-in-water or in water-in-oil emulsions as finely dispersed. In both cases, the pigment is present in the oil phase. After the emulsion is impregnated into the fabric, it breaks down and the pigment remains dispersed on the fiber. After that, the fabric is squeezed and dried. It is thermofixed at 140-170 oC. Polycondensation of the resin at this temperature results in a thin film layer that adheres the pigment to the fabric. Washing is usually not required after dyeing, as this layer also acts as a finishing. However, in some cases, for example, if the resin decomposes over time and has an odor, it is appropriate to wash it away. Water-insoluble azoic dyes, earring dyes, aniline black, phthalocyanines are used as pigment dyestuffs. Most of the azoic pigments are the same as formed on the fiber. However, although the choice of components (especially naphthol components) is limited in those formed on fibers, there is no such limit. Pigment dyestuffs are also used in the coloring of varnish, lacquer, printing ink and plastic materials besides textile fibers. The clamping components to be selected in azoic pigments are different from those in Naftol AS dyestuffs, and cheaper ones are preferred. For example, β-naphthol replaces Naftol AS. In the production of yellow pigments, mxilidide, 2,4-dihydroxy quinoline, which is not used in Naftol AS dyestuffs, is used.
Since there is no fiber affinity in pigment dyestuffs, it is easy to level them and obtain the same color tones on fiber mixtures. The interesting aspect of dyeing with pigment dyestuffs is that it is possible to select pigments with maximum light fastness. If a suitable binder is used, the washing fastness reaches a high standard. Light and washing fastness is good in light colors. The dyeing process can be combined with anti-crease and hardening finishes. Because both in dyeing and finishing, the order of operations is padding-drying-thermofix. Thus, since the application is simple and high production is possible with a small labor force, interest in this class of dyestuffs is increasing. Particle size is also very important in pigment dyestuffs, as the dyestuff must be finely dispersed in the binder liquid system. However, fine dispersion is possible not by grinding the synthesis product, but by careful control of the chelation, filtration and drying processes during production.
Disadvantages of pigment dyeing;
- Lack of high rubbing fastness
- Inability to obtain dark colors
- Weathering of the binder film layer
- The binder has a negative effect on the handle (touch) of the fabric, that is, it hardens the fabric.
In recent years, studies have been intensified and many progresses have been made to eliminate these defects.
Points to consider when choosing a connector are:
- In order for dyeing to have high wet fastness, it must be able to permanently bind the pigment to the fibers.
- The fabric should be soft and flexible enough to have a minimum of negative impact on the touch.
- Its viscosity should be in the form of liquid, which can be adjusted to the appropriate value of the padding.
- Its monomers must be able to transform into an insoluble form by polymerizing or polycondensing on the fiber.
It is not easy to find a binder system that fulfills all the conditions listed above. The connectors used or offered are::
- natural polymers: Casein, glue and gelatin are made insoluble with formaldehyde and then plasticized by the addition of glycerine or glycol. Their washing fastness is generally low. They are not used as the main binder in modern systems.
- Modified natural polymers: Although cellulose esters such as cellulose acetate and cellulose nitrate are also used as binders, they have disadvantages such as hardening the material, igniting quickly, not penetrating the fiber well and being expensive.
Therefore, alkali-soluble hydroxy ethers and cellulose ethers have been proposed. When the fabric is treated with acid after being padded with an alkali solution of ether with added pigment, the cellulose ether precipitates and covers the fabric with the pigment, then it is rinsed, soaped and dried. Cellulose xanthate (viscous solution) has been offered as binder. If the fabric is acid-treated after being padded with a pigment-added cellulose xanthate solution, the cellulose is separated on the fabric. This also has disadvantages such as changing the touch and not penetrating well.
- 3) Synthetic resins and polymers: The number of synthetic resins used as binders is very high. Of these, phenolic resins are not sufficient because they decompose under the influence of light. Urea and melamine formaldehyde resins (especially when modified or mixed with an alkyd or ethylenic polymer such as polyvinyl acetate, polyvinyl alcohol and synthetic rubber) give better results. Polyacrylic esters, which are soluble in water but rendered insoluble by treatment with alkali, and containing amino or imino groups, have also been patented. Published information on the chemical structures of all these products is very scarce.
The binder, the pigment, the fine dispersant of the pigment, the suitable catalyst and the stabilizer are combined in an oil-in-water or water-in-oil emulsion. For the preparation of water-in-oil emulsions, the aqueous phase is slowly added to the oil phase mixed with a high-speed mixer. Since the water thickens the emulsion, the viscosity of the emulsion is controlled by the amount of water added. Various variations have been proposed for the oil phase. All solvent-soluble resin types are suitable. For example, alkyd resins in xylene, solvent-soluble ethyl cellulose, butadiene-styrene, butadiene-acrylonitrile copolymers etc.
Classification of Pigment Dyes
a) Classification According to Fastness:
- Those with weak and medium resistance.
- Basic dyestuff lacquers.
- Those with close resistance to phthalocyanine pigments.
- Phthalocyanine pigments
b) Classification according to Color Index Numbers:
This classification is a classification used especially in commerce and is made according to the code numbers specified by the Color Index (CI) system.
c) Chemical Classification:
Conventional classifications of dyestuffs on the basis of chromophore groups can be made within pigments. Pigments can be classified as follows, considering different chromophore groups, different colors and fastnesses.
- Acetoacetaryl azo pigments
- Beta-Naphthol azo pigments
- 2-Hydroxy-3-naphthoarylide azo pigments
- 2-Hydroxy-3-naphthoic acid azo pigments
- naphthol sulfanic acid azo pigments
- Triphenylmethane azo pigments
- Phthalocyanine azo pigments
- Anthraquinone and indigoid azo pigments
- Quinacridone pigments
- Dioxyazine pigments
- Azomethine pigments
- Fluorubin pigments
- Naftindolizindione pigments
g) Mordant dyes
The word mordant means a substance or composition that fixes the dyestuff to the fiber. Many natural and synthetic dyestuffs fall into this class. They contain acidic or basic functional groups and form labile compounds with plant and animal fiber. Therefore, a substance (mordant) with the same chemical affinity for both the fiber and the dyestuff is placed on the fiber first; The fiber and dye are then reacted to give a water-insoluble compound. Like this It is ensured that the dyestuff adheres to the fiber. Al, Sn, Fe, Cr salts, which form water-insoluble hydroxides, are used as mordant.
h) Metal-complex dyestuffs:
Metal complex dyestuffs are water-soluble dyestuffs that enable polyamide fibers to be dyed easily with higher fastnesses than acid dyestuffs.
However, the colors of acid dyes are brighter and more vivid than these dyestuffs. Metal complex dyes are a kind of acid dyes. They are large-molecule dyestuffs that contain one or more atoms of chromium, nickel or cobalt metals in their structure, as well as the main colorant.
Metal complex dyestuffs are preferred for dyeing dark colors due to their high fastness. Despite its high affinity for polyamide fiber, due to its low migration capabilities, the dyestuff must be carefully used from the outset for uniform dyeing. must be pulled. For this, it is necessary to pay attention to factors such as pH, temperature, auxiliary chemicals and time.
Benefits
- It is cheap
- Light fastness is good
- Age fastness is good
Drawbacks
- It is not alive and bright
- Migration abilities are not good
During the production of metal complex dyestuffs, which are highly preferred for dyeing polyamide fibers, a complex is formed between the main colorant and metal ions. These dyestuffs are divided into two classes according to the complex of metal ions and dyestuff molecules as follows.
- 1:1 metal complex dyes
- 1:2 metal complex dyes
1:1 Metal Complex Dyes
Dyestuffs that form a complex with a metal ion and a dye molecule are called 1:1 metal complex dyes. The wet fastnesses of this dyestuff class are lower than 1:2 metal complex dyestuffs. It is necessary to increase the fastness in dark color dyeing. Since there is a risk of striped dyeing, auxiliary substances should be used. Since its migration capabilities are not good, it is necessary to use a leveling agent. Since 1:1 metal complex dyestuffs have a high affinity for polyamide fiber and bind with strong bonds such as van der walls, attraction forces and hydrogen bridges, dyeing is difficult to smooth out afterwards. For this reason, the dyestuff must be taken properly from the beginning. Proper removal should be done in a strongly acidic environment where the affinity of the dyestuff to polyamide fibers is the least. Since amino groups are converted into positively charged ammonium groups in a strongly acidic environment, bonding is achieved only by electrostatic attraction forces. Since the coordinate bonds do not form in a strongly acidic environment, it is possible to smooth them later. 1:1 metal complex dyestuffs act as a leveling acid dyestuff in a strongly acidic environment. The pH of the medium is adjusted in the range of 3-4 with formic acid. Sulfuric acid is not used since the strong acidic environment will degrade the polyamide.
1:2 Metal Complex Dyes
Dyestuffs that form a complex with a metal ion and two dye molecules are called 1:2 metal complex dyes. The fastness of these dyestuffs is quite good compared to 1:1 metal complex dyestuffs and acid dyestuffs. It has high light and washing fastnesses even in dark tone dyeing. Due to these properties, it is used for excellent fastness in medium and dark colors. However, their colors are not as bright as acid dyes. The affinity of 1:2 metal complex dyestuffs against polyamide fibers is quite high. Since the dyestuff molecule is very large, dyeing unevenness is high. For this, the dyeing pH must be adjusted well. The pH value should be increased in light tone dyeing and the pH value should be decreased in dark tone dyeing. As the pH value decreases, the rate of removal increases, especially in light-tone dyeing, since the concentration of dyestuff in the bath is low, it will be difficult to remove a small amount of dyestuff properly due to rapid absorption. Dyeing with 1:2 metal complex dyestuffs is started at pH 6,5-7. By reducing the pH value according to the darkness of the color, the remaining dyestuff in the bath is absorbed.
i) Cube dyestuffs
Cube dyestuffs are used in both dyeing and printing of cellulosic fiber. Cube dyestuffs of natural origin have been known since ancient times. An example of this is indigo dyestuff. Cube dyestuffs are indigo and anthraquinone derivatives that are insoluble in water and rendered soluble for dyeing. As it is the most important dyestuff class in which anthraquinoid dyestuffs are found, all indigoid dyestuffs are also in this dyestuff class. Cube dyestuffs are the most important class of carbonic dyestuffs. The first feature of cube dyestuffs is that they are insoluble in water. Therefore, the first step in dyeing is to make the vat dyestuff soluble in water (cubeing or tagging). Solubility is carried out in a basic medium (eg lye), with the aid of a reducing agent (eg hydrosulfite). The fiber is dyed with the soluble dyestuff and then, as a result of the oxidation (oxidation), it becomes water-insoluble dyestuffs in the fibers. Cube dyestuffs are easy to reduce and oxidize. But these steps need to be taken care of. The wet fastness of these dyeings is very good, since the dyestuff regenerated in the fiber as a result of oxidation does not dissolve at all in the aqueous medium. It has a high affinity for cellulose because its shrinkage degree and speed are good. In addition, although the color range of cube dyestuffs is wide, the colors are duller than reactive dyes.
Cube dyestuffs are insoluble pigments. Cube dyestuffs are made water-soluble by using a reducing agent. The fabric is then passed through the dyestuff solution. With its water-soluble nature, the dyestuff is attached to the fiber by hydrogen bridges and van der Waals forces. In the next step, the dyestuff is rendered insoluble again by contacting with open air or immersing it in oxidation baths such as bichromate, thus dyeing is done.
There is a close link between the molecular structures of vat dyes and the conditions required for dyeing. In solution, dyestuff molecules exist as aggregates. As with direct and sulfur dyestuffs, cube dyestuffs are not found alone in the bath, but are in the form of aggregates formed as a result of the combination of several molecules.
As the dyestuff molecule size increases, the ability to form aggregates also increases. In aggregates, molecules are connected to each other by hydrogen bridges. As the degree of aggregation (collection of dyestuff molecules) increases, the rate of adsorption also increases. A high degree of aggregation slows down the diffusion rate. Because in order for large aggregates to enter the fiber, they must be broken down into monomers. This takes a long time during dyeing. Since the diffusion step determines the speed of dyeing, it is necessary to decrease the degree of association in order to increase the dyeing speed. For this, the dyeing temperature can be increased. At the same time, the base concentration can be increased. Although not as important as temperature and base, the concentration of dyestuff in the liquor also affects the degree of association to some extent. Cube dyestuffs; It is available in powder, paste and dispersion form. Powder dye pigments are larger than other dispersed dyes. The cubing time is also longer.
Cube dyestuffs;
- in the cold
- in the warm
- in the heat
It is examined in three classes as dyeing cube dyestuffs. The temperatures of each class, the dyeing method and the ratios of chemicals used are also different.
- Colorants that dye in the cold (IK) (20–25°C)
- Warm dyestuffs (IW) (45–50°C)
- Hot dyeing dyes (IN) (55–60°C)
Dyeing methods, textile auxiliaries that should be added to the bath (caustic lye, hydrosulphite and salt amounts) are specified in the cube dyestuff catalogues. In dyestuffs that dye according to IK and IW methods, salt must be added to the bath. Generally, calcined sodium sulfate and table salt are used. IW dyestuffs are among the IK and IN dyeing methods in terms of their molecular size, dyeing properties and therefore dyeing conditions.
The amount of hydrosulfite required in IN dyestuffs is higher than the amount required in the IK method. The reason is the increased oxidative decomposition of hydrosulfite at high temperatures. The difference of vat dyestuffs from other dyestuffs is that the color of the reduced, that is, cubed dyestuff, can be very different from the desired real color. For example, while the color to be obtained is yellow, the earring color can be in very different colors such as brown and purple. The actual color emerges at the end of oxidation and the color change can be observed visually.
Batch, semi-batch and continuous dyeing methods have been developed for vat dyestuffs.
Batch (pulling) methods
- Temperature steps method
- Pigment-temperature steps method
- Pre-pigmentation method
Half-batch methods
- Pad-jig method
- Pad-fabric beam method
Continuous dyeing methods
- pad-steam method
- One-bath pad-steam method
- wet steam method
- Modified wet steam method
- Williams unit method
j) Developmental dyestuffs
They are dyestuffs formed by the complex formation of some azo dyestuffs with certain groups and metal ions. The azo group plays a role in the formation of the complex. Co, Cr, Cu, and Ni ions are used as metal cations. Chromium complexes are mostly used in wool, polyamide, and copper complexes are used in cotton and leather dyeing.
Classification of dyestuffs according to their chemical structures
While structurally classifying the dyestuffs, the basic structure of the molecule can be taken as basis, as well as the chromogen and coloring properties of the molecule.
a) Azo dyes
The number of azo dyestuffs, which constitute the most important class of organic dyestuffs, is equal to the sum of all other classes. They are characterized by the azo (N=N-) group, which is the chromophore group in their structure. Nitrogen atoms in this group are bonded to carbon atoms by sp2 hybridization. One of the carbon atoms attached to the azo group may be an aromatic (benzene, naphthalene and derivatives) or heterocyclic ring, and the other an enolizable aliphatic chain-linked group. Therefore, there is at least one aryl group in the molecule. Azo dyes can generally be formulated as: Ar-N=NR. where R is aryl, heteroaryl or enolizable alkyl. They are defined as mono, bis, tris, tetrakis..... azo dyes according to the azo group in the molecule. Those containing three or more azo groups Also called polyazo dyestuff.
- Monoazo dyes
- Diazo dyes
- Trisazo dyes
- Tetrakisazo dyes
It has 4 types.
b) Nitro and Nitroso dyestuffs
This class of dyestuffs contains an electron donor group along with a nitro or nitroso group in their chemical structure. Phenol or naphthols are nitrosated if treated with HNO2.
c) Polymethyne dyestuffs:
d) Arylmethane dyes and Aza analogues
e) Azo Annulen dyes
f) Carbonyl dyestuffs: It is the general name of compounds with conjugated double bonds in their structure containing at least two carbonyl groups.
g) Sulfur dyestuffs: They are called water-insoluble macro-structured colored organic compounds that are formed as a result of the reaction of phenols with sulfur, sodium polysulfide and sodium sulfide with aromatic amines. Its general formula is expressed as BM-SS-BM, if it is boiled with Na2S in basic medium, disulfide groups (...-SS-...) are converted to mercapto groups (...-S'Na4) and become soluble with water to form leuco compounds. .
They are water-insoluble dyestuffs. Sulfur dyestuff is made soluble in water with sodium sulfide (Na2S). After dyeing, it is oxidized with oxidizing agents containing high oxygen such as potassium bichromate (K2Cr2O7) or hydrogen peroxide (H2O2), making the dyestuff insoluble in water in the fiber.
Sulfur dyes are bonded to cellulosic fiber by hydrogen bonds and van der Waals forces.
It is a class of dyestuffs that contain sulfur atoms in their structure and normally dye in sodium sulfide solution. Sulfur dyestuffs were first made in 1879 and were used for cotton linen. It can be symbolized as dyestuff-sulphur-sulfur-colourant. It is mostly used in dark and matte colors such as khaki, navy blue, brown and black.
- Age, sweat and light fastness are good.
- Heat and chemical resistance is generally moderate.
- Being cheap is also an important advantage.
- Chlorine fastness is generally poor.
- It reduces the strength of the fabric in long-term storage, the color nuances may change.
- They do not have bright colors.
Sulfur dyes are examined in three groups:
- 1-water-insoluble sulfur dyestuffs
- 2-Water-soluble sulfur dyestuffs
- 3-Cube sulfur dyestuffs
1- Normal Sulfur Dyestuffs in Water Insoluble Structure
It is slightly soluble in water and has no affinity for cellulose. It is made soluble by reduction. The reduction is done in a basic medium, mostly using sodium sulfide (Na2S). It is also known as zirnik among the people. The reduced sulfur dyestuff has a high affinity for cellulose fibers, and care must be taken to obtain proper dyeing. Painting; It is made at high temperature, in alkaline environment, in an environment with excess salt content. Sulfur dyestuffs in this group are more suitable for overflow dyeing. The bath must be kept warm in order to keep the sulfur dyestuff soluble. However, as the temperature increases, the dye uptake will also increase. For this reason, there is a tonal difference between the beginning and the end of the fabric, especially in light colors, in the impregnation method.
2-Sulfur Dyestuffs Made Soluble in Water
They are sulfur dyestuffs that are soluble in water and not oxidized under normal conditions, by subjecting the reduced sulfur dyestuffs to the thiosulfation process. As such, the dye has no affinity, but is soluble in water. Due to these properties, sulfur dyestuffs in this group are more suitable for discontinuous and continuous dyeing methods.
3-Sulfur-Cube Dyes
It is a dyestuff class between sulfur and cube dyestuffs. It is cheaper than cube dyestuffs. Despite good light and washing fastnesses, their chlorine fastness is poor and can be easily reduced. In dyeing with these, starch finishing is avoided. The dyestuffs in this group are suitable for continuous and discontinuous dyeing methods.
Application methods of dyestuffs
1-The method of application of acid dyestuffs
It is mainly used for dyeing wool, silk, polyamide fiber and cationic modified polyacrylonitrile fiber. The dyeing process must be carried out in an acidic (pH= 2-6 bath. It is the sodium salt of sulfonic acids with molecular weights between 300-500. The temperature of the environment is increased up to 60 °C while these dyestuffs are applied.
2-Application method of direct dyestuffs
There is no need for mordanting in order to apply direct dyestuffs that can dye natural regenerated cellulosic fibers. In other words, it is possible to paint directly without the need for a pre-processing. The reason why there is no need for mordanting is the high substantivity of these dyestuffs against the fiber (the ability of the dyestuff to be absorbed by the fiber). For this reason, this group is also called substantive dyes.. While applying these dyestuffs, the temperature of the environment is increased up to 80 C°.
3-Application method of reactive dyestuffs
They are dyestuffs that react to form a covalent bond with textile fiber. Since the reactive group in their structure can react with fiber types such as cellulose, wool, silk, polyamide, it is used in these fiber classes. While applying these dyestuffs, the temperature of the environment is increased up to 80 °C.
4-Application method of dispersion dyestuffs
Dispersion dyestuffs capable of dyeing all synthetic fibers and acetate silk are insoluble in water in the conventional sense. The dyeing of the fiber is done in aqueous suspensions of the dyestuff. It is present in trace amounts dissolved in the bath during dyeing. When the dyestuff is absorbed by the fiber, the same amount of dyestuff re-disperses into solution. While applying these dyestuffs, the temperature of the environment is increased up to 130 °C.
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