Dyeing Process Of Superfine Fiber Synthetic Leather

There are many kinds of dyes used for PA6 and polyurethane dyeing respectively, including acid dyes, neutral dyes, disperse dyes, reactive dyes and so on.

When the PA6 and polyurethane are individually dyed, the single dye may have a good effect, but the situation is much more complicated for island type microfiber synthetic leather containing two components. Especially when dyed dark, even two or even three dyes need to be considered for blending dyeing.

Disperse dyes dyeing

Disperse dyes are nonionic dyes with strong hydrophobicity and small water solubility. There are no water-soluble groups in the structure, but they contain many polar groups, such as -NO2, -NH2, -CN, -OG and so on.

The dyeing rate of disperse dyes is different from that of dyestuffs. When dyes are applied, dyes should be selected with similar or better compatibility, such as disperse dyes and weak or neutral dyes, so as to adjust the chromatic light and improve the levelness.

The dyeing rate of disperse dyes depends on temperature. Therefore, temperature control should be paid attention to in dyeing.

The increase of temperature will reduce the absorption of disperse dyes, and increase the chance of collision between dyes.

On the other hand, the increase of temperature and the solubility of small particles and the increase of large particles increase the degree of stability, which will reduce the stability of the dispersion.

Therefore, the temperature of the prepared dye solution should be low, so long time heating should be avoided before dyeing.

It is usually dyed at 40~50 C and heated to about 0.5 /min.

According to the leveling and exhaustion of dyes, wash them again.

Disperse dyes can also dye nylon and polyurethane at the same time.

The active groups in dye are dyed and fixed by a large number of amide groups and terminal amino groups in PA6 molecule by hydrogen bond, Fan Dehua force and dipole force.

In addition, the PA6 molecule contains a large number of non-polar hydrophobic chains, which is why the hydrophobic disperse dyes can dye the birch.

Disperse dyes have smaller molecular weight, better diffusion properties, simpler dyeing methods, better levelling properties, better sunlight fastness and better coverage. They can avoid uneven dyeing caused by different size and different degree of elongation when nylon is polymerized.

However, the saturation value of PA6 with disperse dyes is very low, so it is difficult to dye it dark.

Disperse dyes have a good coloring effect on polyurethane, which is related to the molecular structure of polyurethane and the relatively compact foaming structure.

Polyurethane forms an incoherent polymer membrane on the surface and interior of the synthetic leather substrate, and its structure is composed of soft segments and hard segments.

Loose part of soft segment is the main position of disperse dyes.

The absorption of disperse dyes by polyurethane is very large and the amount of dye residue in dyeing residue is less. This is very necessary for dyeing dark colored varieties with high strength disperse dyes.

Within a certain range, with the increase of dyeing temperature, the amount of coloring is larger.

In addition, the color fastness of disperse dyes on polyurethane is also good.

Disperse dyes are the main dyestuffs for dyeing polyurethane superfine leather synthetic leather.

In contrast, other types of dyestuffs have poor coloring of polyurethane, but instead of polyamide, some of them even have better coloring of polyurethane, but at the same time, they can dye polyamide, which is very unfavorable for dyeing uniform and non chromatic products.

Even disperse dyes should be carefully controlled, because the color of nylon will not only affect its color, but also affect the color fastness of nylon.

Acid dyeing

Acid dyeing is an important dye in nylon dyeing, and fiber and dye are mainly bonded by ionic bonds.

If the pH value is low (PH < 3), the imido group in the chain can also be positively ionized (-N+H2-) and bind to the dye anion.

In addition, hydrogen bonds and van Edward forces also play an important role in acid or neutral dyeing of acid dyes, and their saturation values usually exceed the saturation values calculated by amino acid content.

Because the amino terminal content of nylon end is lighter than that of light music, when dyeing with two or more dyes, there will be a competition problem. Therefore, we should pay attention to the selection of dyes with better compatibility when making coloring.

The molecules of nylon are linear molecules, and there are no branched chains and large side groups on the molecular chains, but there are many groups that can form hydrogen bonds.

Dye molecules are easily disturbed by fiber molecules and have greater Fan Dehua force. Hydrogen bonds are easily formed between dyes and fibers. Therefore, the affinity of acid dyes to nylon is generally higher than that of wool.

The saturation value of polyamide with strong acid dyes is 2.3% and weak acid dyes are 5%~5.2%.

Therefore, weak acid dyes are used to dye polyamide fibers, and dye uptake is improved by means of Vander Ed Ley and hydrogen bonds.

The dyeing of polyamide with strong acid dyes is generally not very deep, because the ratio of the amphoteric groups is different (polyamide synthesis usually uses acetic acid or benzoic acid to regulate molecular weight, the terminal amino groups of some macromolecules are acylated, acetyl is increased in the form of benzamide, the amino content is lower than that of carboxyl group, and the cyclic amide group is also found in PA6.

Therefore, dyeing with a typical levelling acid dye, that is, only by Coulomb force dyeing, is difficult to dye deep color.

Acid dyes can also be used to dye polyurethane, because the polyurethane molecules in the Lou end contain amide, urea and carbamate, which combine to form Fan Dehua force, hydrogen bond and ionic bond, but the dyeing effect is not ideal.

In particular, strong acid dyes, almost all of the dye fixed on the surface of the fiber, can rarely penetrate into the fiber, soaping fade, serious color fastness is poor.

The weak compatibility dyes are slightly higher than those of strong acid dyes, and the washing fastness is good. However, the fastness to soaping is still not ideal, and the dye can not penetrate into the fibers, and the light fastness is poor.

Neutral dye dyeing

Neutral dyes are 1:2 type acidic media dyes, and metal atoms combine with dye molecules in proportion to 1:2.

The dye molecules do not contain water soluble groups such as sulfonic groups, and only contain hydrophilic groups with low water solubility, such as sulfonamido (-SO2NHR), sulfoxide (-SO2CH3) and so on. They are usually dyed in neutral or weak acid medium. This is the origin of the name.

The molecules of nylon have a large number of amino carboxyl end groups, which can be dyed with neutral dyes and get a deeper color. They have better wet fastness and fastness to sunlight. The color matching properties of dyes are better, less competitive dyeing, high dye utilization rate, and relatively simple dyeing process.

However, neutral dye chromatography is not complete, and because the dye molecules contain metal ions, the color is not bright enough, so it is suitable for dyeing deep color products.

Neutral dyes combine with PA6's amino positive ions to form an ionic bond in anionic form. At the same time, the dye molecules can also bind to the fiber with ammonia bond and fan Edward force, so neutral dyeing has better affinity to nylon.

Because the number of dye molecules adsorbed greatly exceeds the number of amino groups at the end of fiber macromolecules, the dye uptake percentage is high and the dyeing saturation value is larger.

In order to control the dye uniformly and slowly, the pH value of the dye bath should be slightly higher, so as to reduce the number of amino positive ions and reduce the Coulomb force.

For a lower percentage of dye, after a period of boiling dyeing, appropriate amount of glacial acetic acid (usually about 1% of the base weight) can be added to further dye the dye.

Neutral dyes can also be used to dye polyurethanes, mainly through hydrogen bonding, van Edward force and Coulomb force.

A suitable neutral dye variety can be selected for polyurethane dyeing and sufficient saturation value can be obtained.

Dyeing should be carried out under low tension and heat setting is necessary.

The absorption of neutral dyes on polyurethane showed a two element adsorption characteristic, that is, Langmuir type and Nernst type exist simultaneously, and with the decrease of dye IOB value, that is, the hydrophobicity is large, the contribution of Nernst absorption increases, the affinity increases, and the dye uptake rate increases obviously.

Neutral dyes have better effect on dyeing polyurethane than ordinary acid dyes.

Reactive dyeing

Reactive dyes are a class of dyes that can react with macromolecules of fiber and covalently bind.

The mechanism of dyeing PA6 with reactive dyes is rather complicated.

Due to the presence of a certain amount of sulfonic group in the molecule, it can combine with the amino acid at the terminal of the PA6 molecule to form an ionic bond under acidic conditions. Therefore, the reactive dyes are usually used in weak acid bath when the reactive dyes are dyed. The dye uptake is similar to that of acid dyes at this time.

Under weak acid conditions, X and K reactive dyes can also form covalent bonds with PA6.

KN type reactive dyes can not generate vinyl sulfonyl groups in acid bath, so they can not form covalent bonds with PA6 under acidic conditions.

The dyeing of nylon by reactive dyes can be divided into three stages: dye absorption by nylon, diffusion of dye absorbed into the fiber and penetration and combination of dye and fiber.

The covalent bonding between the two is very firm. The reason why reactive dyes have high wet fastness is this.

The ionic bond, dipole interaction, van Edward force and hydrogen bonding between dyes and polyamide are of great importance in the absorption stage of dyeing.

For dyed products, this combination is harmful and useless. It will seriously affect the wet fastness of finished products.

Therefore, the removal of dye core with non covalent bond is usually carried out by ammonia treatment.

In the process of treatment, on the one hand, the dye with reactive capacity and no reaction continued to react with nylon under the higher PH condition. On the other hand, the non reactive, especially the ionic bond dyestuff was desorbed from nylon, so as to ensure the color fastness of the finished product.

Reactive dye PA6 has many advantages such as bright color, good washing and rubbing fastness, high sublimation fastness and easy dyeing.

However, because of the small number of amino groups in the PA6 molecule, low color yield and poor levelness, it is used only in medium and light color varieties.

Reactive dyes are not widely used in polyurethane dyeing, but the presence of terminal hydroxyl groups in the chain of polyamine macromolecules makes it possible to stain with reactive dyes.

Dyeing with mixed dyes

In the dyeing process of sea island superfine fiber synthetic leather, single species of dyes often fail to achieve satisfactory desired results, especially when dyeing dark colored varieties.

At this point, we should consider the mixed dyeing process, and use two or more than two dyes together to meet the requirements.

By adjusting the proportion of different components in mixed dyes, the indexes were investigated.

The compatibility of dyes must be taken into consideration in dyeing many kinds of dyes.

Through studying the dyeing performance curves of different indicators, the dye with similar dyeing properties can be selected for compatibility, and suitable dyeing auxiliaries (including leveling agents, penetrating agents, dispersing agents, dispersing agents, fixing agents, etc.) should be selected to enhance the similar compatibility between dyes.

In dyeing process, mixed dye dyeing is also different from single dye dyeing and needs to be adjusted properly.

For example, different types of dyes require different pH values for dyeing and cannot be added to different dyes.

At this time, the following two ways can be resolved: step by step dyeing, that is to say, adding different types of dyestuffs separately, each dye in its adaptive pH range; pH sliding method, that is, adding PH slip agent (PH regulator and PH control agent) into the dye bath, so that the pH value of the dye bath in the dyeing process will automatically slide, so as to adapt to different types of dyes.

The PH regulators are organic esters and amide compounds, organic compounds with halogen groups, volatile organic acids, and basic oxidants containing aldehydes, hydroxyl or carboxyl groups. These substances can release acid at elevated temperatures, reduce pH value of the solution, and make it slide toward acid.