CN110453509B

CN110453509B - Dyeing method for pad dyeing of leuco body

Info

Publication number: CN110453509B
Application number: CN201910246329.9A
Authority: CN
Inventors: 李瑞卿; 周长文; 王伟
Original assignee: Individual
Current assignee: Individual
Priority date: 2019-03-28
Filing date: 2019-03-28
Publication date: 2020-11-17
Anticipated expiration: 2039-03-28
Also published as: CN110453509A

Abstract

The invention discloses a dyeing method for pad dyeing of leuco, which comprises the following steps: padding and oxidizing, wherein the padding process comprises padding in a dye vat containing a penetrant and padding in a dye vat containing a leuco sodium salt dye liquor, the leuco sodium salt dye liquor is prepared from a composite reducing agent and a dye, and the composite reducing agent comprises: thiourea dioxide, reducing sugars and chemical potential control agents; wherein the chemical potential control agent is at least one of sodium nitrite, acrylamide, furfural, cyclohexanone and trichloroacetic acid. The invention adopts the composite reducing agent to apply the leuco body reduction method in pad dyeing, and the obtained dyed product has deep color and high fastness.

Description

Dyeing method for pad dyeing of leuco body

Technical Field

The invention relates to the field of dyeing, in particular to a dyeing method for pad dyeing of a leuco body.

Background

Dyeing methods are generally classified into dyeing methods such as disperse dye dyeing, acid dye dyeing, reactive dye dyeing and the like according to the difference of dyes. The above dyeing method has the following problems: (1) the polyester is dyed by adopting disperse dyes, so that the light fastness is poor; reduction cleaning is needed after dyeing, the color fastness of deep color is poor, and the color fades and becomes grey after cleaning; most of disperse dyes need to adopt a high-temperature process during dyeing, so that the energy consumption cost is high; the disperse dye is also easy to generate thermal coagulation, and easily causes defects such as color spots, color spots and the like; (2) when the acid dye is used for dyeing nylon, the light fastness and the soaping fastness of a finished product have the problem that the requirements of consumers cannot be met; the level-dyeing property of reactive dye dyed nylon is poor, the hand feeling of the fabric is hard and even the tearing strength is reduced easily due to high-temperature dyeing, and particularly the strength damage of 10D-30D light and thin nylon is large; (3) when the reactive dye is dyed with dark color, the soaping fastness of a dyed finished product is generally poor, and the dyed finished product is easy to fade, lighten, age and the like after being washed for many times; the fabric dyed by the reactive dye is not resistant to rinsing, and if 84 disinfectant is added during washing, local decolorization is caused, so that the wearing attractiveness is affected; (4) the dyeing process of the acid or reactive dye is longer, and the operation control difficulty is increased.

While the vat dye dyed products have excellent color fastness and stability against chemical treatment. In terms of color fastness, the light fastness is very excellent, and especially the fastness to (chlorine) bleaching and the fastness to chlorine water are not accessible to other dyes; in addition, the performance of strong alkali, strong acid and oxidation reducing agent resistance is also excellent; these advantages determine that vat dyes can be used in large quantities for dyeing various uniforms and textile work, especially garments for professional staff, medical staff and the like, which are required to work in outdoor harsh environments for a long time. With the increasing improvement of the material and cultural living standard of people, the richness requirements on the colors and patterns of the textiles are also continuously improved, and the dyeing (such as yarn, silk and loose fiber dyeing) before weaving of the textiles is also adopted more and more; the dyeing method before weaving has higher requirements on the selection of dyes and processes, and needs to meet the requirement that the color cannot be destructively influenced during subsequent dyeing and finishing (such as strong alkali mercerization and the like).

The vat dyes are dyed by methods such as leuco acids, suspensions, leuco bodies and the like. The processing and treatment of the leuco acid are difficult and less; suspension dyeing is common, but the dye suspension is insoluble in water, dye molecules in dye liquor are large in particle size, cannot enter the fiber fully, and the bonding force with the fiber is weak, so that the optimal fastness level which is reasonably reached cannot be ensured; the leuco dyeing method is to convert vat dye into sodium salt of leuco, which is adsorbed by fiber in dye bath and oxidized to form water insoluble dye lake fixed on fiber.

However, the existing leuco body staining still has the following defects: the initial dyeing is faster and the dyeing is easy; the dosage of the caustic soda and the reducing agent is still high, and the fiber damage is easy to cause. At present, most of factories adopt sodium hydrosulfite, and the sodium hydrosulfite is decomposed too fast, so that the decomposition rate is not easy to control, the factors influencing the decomposition are more, the change range of the reduction potential value is large, and the color is difficult to control. In actual operation, sodium hydrosulfite needs to be added for many times, so that the consumption of sodium hydrosulfite is large, waste is caused, and the environment is polluted. In recent years, thiourea dioxide has been used to replace sodium hydrosulfite for the reduction of vat dyes.

In the prior art, a combination of thiourea dioxide and glucose is studied, and in a paper of 'application of a novel redox system for dyeing sulfur dyes', a binary system of thiourea dioxide and glucose is studied, the concentration of a reducing agent in the study is low, and dyeing can be performed only on cloth which is pretreated. Although studies have been made on reducing sugars as dye reducing agents, there have been few fundamental studies on reducing systems of reducing sugars, such as information on the reduction potential of the reducing system. How to control the chemical potential of the reducing sugar is also a technical problem. The problem of controlling the over-reduction of thiourea dioxide is still a problem.

Dyeing methods are classified into exhaust dyeing and pad dyeing according to the manner of applying a dye to a dyed object and fixing the dye to a fiber.

The dyeing of vat dyes is generally carried out by a suspension pad dyeing method, mainly because the reducing agent is decomposed too fast in a leuco body state and is not stable enough, and the fabric is easy to be dyed. Leading to the impossibility of popularizing the leuco dyeing method in pad dyeing process.

Disclosure of Invention

The invention aims to provide a dyeing method for pad dyeing of leuco, which enables a leuco reduction method to be applied in a pad dyeing process, and the dyed product has uniform dyeing and good washing fastness.

In order to achieve the purpose, the main technical scheme of the invention is as follows: a dyeing method of leuco pad dyeing comprises the following steps: the method comprises the following steps of pre-configuring, padding and oxidizing a leuco sodium salt dye solution, wherein the padding process comprises padding in a dye vat for containing a penetrant and padding in the dye vat for containing the leuco sodium salt dye solution, the leuco sodium salt dye solution is prepared from a composite reducing agent and a dye, and the composite reducing agent comprises: thiourea dioxide, reducing sugars and chemical potential control agents; wherein the chemical potential control agent is at least one of sodium nitrite, acrylamide, furfural, cyclohexanone and trichloroacetic acid. The sodium nitrite plays a role in replenishing alkalinity at low temperature due to the characteristics of strong base and weak acid salt; because of weak oxidizability, the urea can be used as a reduction potential control agent in cooperation with a decomposition product of thiourea dioxide, namely urea, at high temperature; acrylamide, furfural, cyclohexanone and trichloroacetic acid are unsaturated aldehydes and ketones and are easy to generate nucleophilic reaction. Thiourea dioxide decomposes nascent hydrogen at high temperature to generate urea, sulfenic acid, sodium bisulfite, sodium sulfate and other substances in turn, the sodium bisulfite has strong nucleophilicity and reacts with acrylamide, furfural, cyclohexanone and trichloroacetic acid to generate an addition product, and the addition product decomposes into substances before the addition reaction under alkaline conditions, thereby slowing down the decomposition of a reducing agent. The synergistic effect of thiourea dioxide, reducing sugar and chemical potential control agent makes the chemical potential of the composite reducing agent stable and decompose slowly, and reduces the over-reduction phenomenon with dye. Therefore, the leuco sodium salt dye liquor is stable, does not dye flowers in pad dyeing, and is uniformly colored.

In the composite reducing agent, 30-75 wt% of thiourea dioxide is used.

In the composite reducing agent, the reducing sugar accounts for 60-20 wt%. The reducing sugar is at least one of glucose and sucrose.

In the composite reducing agent, the chemical potential control agent is 10-5 wt%: at least one of sodium nitrite, acrylamide, furfural, cyclohexanone and trichloroacetic acid.

The penetrant is an anionic/nonionic penetrant.

The preparation method of the leuco sodium salt dye solution comprises the following steps: (1) firstly, adding 50 wt% of water in a container, starting a stirrer to stir, heating to 30-60 ℃, and then pouring a certain amount of alkali; (2) adding dye while heating and stirring, and stirring for 20-30 min; (3) adding water, cooling to 50 ℃, adding a certain amount of the composite reducing agent, stirring for 45min, and adding cold water to 100 wt% of the liquid for later use. The dye liquor prepared by the preparation method is in a colloidal state, is still in a micro-colloidal state after being diluted by 10 times and 20 times, and has good binding force with fibers. The concentration of the composite reducing agent in the prepared leuco body sodium salt dye solution is 2-100g/L, and the concentration of the alkali is 2-120 g/L.

The penetrating agent padding adopts 1-4 dye baths at the temperature of 20-85 ℃.

The pad padding of the leuco sodium salt dye liquor adopts 1-6 dye baths at the temperature of 30-95 ℃.

The invention has the beneficial effects that: the composite reducing agent adopted by the invention has stable reduction potential and slow decomposition rate, reduces the occurrence of over-reduction reaction with dye, and the leuco sodium salt dye liquor prepared from the composite reducing agent and the dye is in a microcolloid state, still is in the microcolloid state after being diluted and kept still for a period of time, and has strong binding capacity with fiber, so that the leuco reduction method is applied to pad dyeing, compared with the product pad dyed by a vat dye suspension, the product has deeper color, the dye consumption is reduced, the cost is reduced, and the production efficiency is improved.

The following examples are only for clearly illustrating the technical solutions of the present invention and should not be taken as limiting the scope of the present invention, according to the following detailed description of the specific embodiments of the present invention with reference to the accompanying drawings.

Drawings

In the drawings:

FIG. 1 is a comparison of cotton bulk fibers dyed by the reduction dyeing method (A) and the reactive dyeing method (B) of the present invention after being soaked in 95 deg.C hot water for 30 minutes;

FIG. 2 is a diagram of a finished product dyed with vat dye using sodium hydrosulfite as a reducing agent;

FIG. 3 is a comparison of a finished product dyed by leuco pad dyeing according to the present invention (A in the figure) with a finished product dyed by a suspension pad dyeing method (B in the figure);

FIG. 4 is a graph showing the comparison between the high concentration leuco sodium salt dye diluted 20 times (A in the figure) and the low concentration normal leuco dye (B in the figure);

FIG. 5 is a comparison chart of the dyeing products of pad dyeing process by leuco body reduction method respectively using sodium hydrosulfite and the composite reducing agent of the invention with the same concentration;

Detailed Description

Example 1

This example is a comparative experiment of the composite reducing agent and sodium hydrosulfite under the same alkaline environment.

The higher the concentration of the mother liquor, the stronger the reducibility thereof. Preparing high-concentration mother liquor of the composite reducing agent and the sodium hydrosulfite with the same concentration, preparing 40g/L of alkali, 50g/L of mother liquor 1 of the composite reducing agent, and preparing 40g/L of alkali and 50g/L of mother liquor 2 of the sodium hydrosulfite.

The two mother liquors were diluted 5-fold and 10-fold respectively, and the variation of the reduction potential values of the mother liquor and the diluted solution was measured and observed. And (3) measuring the reduction potential value of the prepared mother solution, measuring the reduction potential value of the mother solution after the mother solution is diluted by 5 times for 15 minutes, diluting the mother solution by 10 times after the mother solution is diluted for 5 hours, and measuring the potential value of the mother solution after the mother solution is diluted for 30 minutes. The specific components and the measurement results are shown in table 1.

TABLE 1

	Mother liquor 1	Mother liquor diluted by 5 times	Mother liquor 1 diluted 10 times
				Combined base (g/L)	40	8	4
Compound reducing agent (g/L)	50	10	5
				Electric potential (mv)	-975	-914	-821
PH	13.38	13.40	13.19
					Mother liquor 2	Mother liquor 2 diluted 5 times	Mother liquor 2 diluted 10 times
Combined base (g/L)	40	8	4
				Sodium hydrosulfite (g/L)	50	10	5
Potential value	-1003	-666	-213
				PH	13.45	13.01	12.82

Through the reducibility comparison experiment of the composite reducing agent and the sodium hydrosulfite with the same concentration, the reduction potential value of the diluted high-concentration mother liquor of the composite reducing agent is not obviously attenuated, the reduction stability is strong, and the dye can be dyed favorably. The sodium hydrosulfite is decomposed too fast, and the reduction potential value is attenuated too fast, so that the dyeing requirement cannot be met.

Example 2

20g/L, 25g/L, 30g/L, 40g/L and 50g/L of composite reducing agent are respectively prepared, and the change of the reducibility of the prepared liquid is respectively measured at room temperature after the prepared liquid is placed for 1 hour and 20 hours under different alkalis. The details are shown in Table 2.

TABLE 2 determination of the values of the prepared solutions after standing for 1 hour

TABLE 3 measured values of the prepared liquid after 20 hours

According to data, the composite reducing agent is stable in a high-concentration region and has small potential fluctuation. The combined alkali concentration is more than 30g/L, and the composite reducing agent is more than 20g/L, so that the state of the leuco sodium salt can be stably generated. The composite reducing agent with the same concentration has the advantages of small change of the reductive potential value and strong stability after standing for 1 hour and 20 hours under the same alkaline environment. According to different dye performances, different combinations can be provided, and the requirements of pre-reduction are met.

Example 3

In this example, the dyeing of the dip dyeing process was carried out using the cotton loose fiber for the colored spun yarn and the composite reducing agent of the present invention. The specific process comprises the following steps:

preparing a leuco sodium salt dye solution with high concentration, which comprises the following steps: firstly, adding 50 wt% of water in a container, starting a stirrer, heating to 30-60 ℃, and then pouring caustic soda; adding dye while heating and stirring, and stirring for 20-30 min; adding water, cooling to 50 ℃, adding the composite reducing agent, stirring for 45min, and adding cold water to 100 wt% of the solution for later use. The leuco sodium salt dye liquor is in a microcolloid state. The specific ingredients are shown in tables 4 and 5:

TABLE 4 ingredient table

	3GL yellow	FB Red	Caustic soda	Composite reducing agent
					Concentration (g/L)	5	60	50	40

TABLE 5 proportion of composite reducing agent

And after unpacking the raw cotton, hoisting the loose fibers into a dyeing device, wherein the dyeing device can adopt a hanging frame type loose fiber dyeing machine. Adding cold water into the dyeing machine, circulating for 10-20 minutes from the inside to the outside of the central column, and ensuring uniform permeation at normal temperature.

Diluting the prepared leuco body sodium salt dye liquor mother liquor by 20 times, adding the diluted leuco body sodium salt dye liquor mother liquor into a dyeing machine, and keeping the leuco body sodium salt dye liquor which is diluted by 20 times in a microcolloidal state.

Refining and dyeing are divided into two steps, wherein in the first step, the temperature is increased to 60 ℃ at the speed of 0.3 ℃/min, and the temperature is kept for 20-30 minutes; and secondly, heating to 80 ℃ at the speed of 1 ℃/min, adding 5g/L of accelerating agent sodium chloride and 5g/L of chemical potential control agent furfural, and keeping the temperature for 10-40 minutes.

Washing with water for 30min or oxidizing with oxidant, soaping at 85 deg.C for 20 min, washing with cold water, and taking out.

The conventional dyeing of the loose cotton fiber can be carried out only by desizing and refining the pretreatment, draining the pretreatment solution in a cylinder body and then washing the cylinder body with water for many times. The embodiment adopts the composite reducing agent of the invention to realize the optimization of the dip dyeing process of the cotton loose fibers. The novel process combines the pretreatment and dyeing procedures, obviously shortens the process flow, reduces the treatment time and improves the production efficiency.

Because the pretreatment boiling-off and bleaching of the cotton loose fibers are carried out at a high temperature of more than 95 ℃ for a long time, the caustic soda and hydrogen peroxide treatment is too violent, the washing times are more, and the grease and the wax on the cotton fibers are removed too cleanly, so that the hand feel of the dyed cotton fibers becomes hard; meanwhile, the elasticity of the fiber is poor, the length is shortened, and the spinning and weaving process is easy to cause more neps and high end breakage rate. Although the softening agent and the antistatic agent can be added for improvement, the subsequent dyeing and finishing processing difficulty of the fabric is increased. In the process of the embodiment, the pretreatment and the dyeing are combined into one, so that the working procedure time is shortened, the refining and dyeing temperature is controlled below 80 ℃, the damage to the cotton fiber is reduced, and the strength and the hand feeling of the cotton fiber are improved; the fiber strength is protected, the wastewater discharge and the water and electricity consumption are reduced, and the energy-saving and consumption-reducing effects are obvious.

As shown in fig. 1, a in fig. 1 is a diagram illustrating the effect of the finished product of the cotton loose fiber of the present embodiment after being soaked in 95 degree hot water for 30 minutes. The cotton loose fibers of the embodiment are uniformly colored without a white core phenomenon. The dyed finished product has no decolorization phenomenon after being soaked in hot water at 95 ℃ for 30 minutes. In FIG. 1, B is the dyed product of cotton fiber dyed by the reactive dyeing method with the same depth of reactive dyeing, and the dyed product still has a decolorization phenomenon after being soaked in hot water at 95 ℃ for 30 minutes.

Example 4

The embodiment is a dyeing process of nylon fabrics, and the composite reducing agent is adopted to carry out a dip dyeing process. The present embodiment adopts rope dyeing equipment, and may adopt normal pressure overflow dyeing machine, and the bath ratio is 1: 10-1: 50. The specific process comprises the following steps:

preparing a leuco sodium salt dye solution with high concentration, which comprises the following steps: firstly, adding 50 wt% of water into a container, starting a stirrer, heating to 30-60 ℃, and then pouring combined alkali (10-60 wt% of caustic soda and 40-90 wt% of soda ash); adding dye while heating and stirring, and stirring for 20-30 min; adding water, cooling to 50 ℃, adding the composite reducing agent in the table 7, stirring for 45min, and adding cold water to 100 wt% of the solution for later use. The specific ingredients are shown in tables 6 and 7:

TABLE 6 ingredient tables

	Vane dye RSN blue	Combined alkali	Composite reducing agent
				Concentration (g/L)	100	60	40

TABLE 7 proportion of composite reducing agent

The method comprises the following specific steps:

putting the rope-shaped fabric into a normal-pressure overflow dyeing machine;

cold water is injected into the machine, and the rope-shaped fabric circulates in the machine for 5-15 minutes, namely the rope-shaped fabric circulates in the machine under the action of a cloth supporting roller and a nozzle of a normal-pressure overflow dyeing machine;

diluting the prepared high-concentration leuco body sodium salt dye solution by 20 times, adding the diluted leuco body sodium salt dye solution into a dyeing machine, and keeping the diluted leuco body sodium salt dye solution in a microcolloidal state;

refining and dyeing: heating to 60 ℃ at the speed of 0.5 ℃/min, preserving the heat for 20 minutes, and refining the impurities such as oil stains, dust and the like on the chemical fibers in the treatment process from cold water to 60 ℃ by combining alkali and a composite reducing agent. The combined alkali is consumed while oil stains and other companion substances are gradually removed, the dye liquor gradually diffuses from the surface layer to the core layer, the slow dyeing effect is achieved, and the phenomenon that dyeing is caused by too fast dyeing (nylon is dyed too fast initially, the dyeing saturation value is very low, and the color fastness is poor) is reduced.

Continuously refining and dyeing, heating to 75 ℃ at the speed of 1 ℃/min, adding 5g/L of accelerating agent sodium sulfate and 3-10g/L of chemical potential control agent trichloroacetic acid, and keeping the temperature for 30 minutes. In the treatment process of 60-75 ℃, the composite reducing agent produces refining effect on the nylon fiber under the alkaline condition. The full adsorption and dye-uptake of the leuco sodium salt are simultaneously completed in the refining process.

And discharging liquid after dyeing is finished, washing for two times by cold water for 20 minutes, washing for one time by hot water at 80 ℃, soaping for 15 minutes at 85 ℃, fully washing, and taking out of the vat.

In this embodiment, the rope dyeing machine puts the pretreatment desizing, refining and dyeing processes of nylon into the dyeing solution for synchronous treatment; in the existing dip dyeing process, after the fabric is pretreated in a machine, the machine pours out the pretreatment solution, the pretreated reactant is fully washed, after drainage and cleaning, the dyeing solution is added for dyeing, namely, the pretreatment and dyeing processes are divided, and the pretreatment and the dyeing processes cannot be carried out simultaneously.

The method realizes the combination of the original pretreatment and dyeing procedures into one procedure, completes the adsorption of dyeing while performing the pretreatment, slows down the completion of the dyeing process after the initial dyeing, obviously shortens the process flow, reduces the treatment time and the use of chemical auxiliaries, improves the production efficiency and saves the cost; reduce the friction on the surface of the fiber and improve the cloth cover effect. The temperature of dyeing and pretreatment is reduced from the high temperature of more than 98 ℃ in the prior art to the temperature of less than 80 ℃, and the fiber strength is protected and simultaneously the effects of energy conservation and consumption reduction are obvious.

The dyed product of this example: the dark blue nylon has uniform color, 4-grade dry rubbing fastness and 4-5-grade wet rubbing fastness according to the GB/T3920-2008 standard, and excellent dyeing performance.

Example 5

On the basis of the embodiment 4, the composite reducing agent in the embodiment 4 is changed into the sodium hydrosulfite reducing agent with the same concentration, the process steps in the embodiment 4 are adopted, firstly, the leuco sodium salt dye solution is prepared, the combined alkali in the embodiment 4 is added in the process of heating the leuco sodium salt dye solution by cold water, the dye is added under the stirring state at the temperature of below 80 ℃, the sodium hydrosulfite is added after 15 minutes, and at the moment, the dye solution is changed into a very viscous state. In order to improve the contrast effect, the all-cotton semi-finished product which is easier to dye is selected and is thrown into a dye vat to be heated according to the example 4, after the all-cotton semi-finished product is taken out of the dye vat, the all-cotton fabric is only stained, the dye loses the dyeing ability, as shown in figure 2, sodium hydrosulfite is used as a reducing agent, the process of the example 4 is adopted, the dyed product is lightly dyed, and the effect that the original pretreatment and dyeing processes are combined into one process cannot be realized.

Because the conventional reduction dyeing process is limited by the sodium hydrosulfite, the conventional reduction dyeing process cannot normally dye terylene, nylon and raw cotton loose fibers. The advantage of excellent light fastness and rinse fastness of the vat dye cannot be exerted.

Example 6

This example is an example of the application of the leuco reduction process to the pad dyeing process.

In the embodiment, cotton and linen and artificial tatting fabrics are taken as examples, and the pad dyeing process is carried out by using the composite reducing agent. A pad dyeing machine is adopted.

The specific process comprises the following steps:

preparing a leuco sodium salt dye solution with high concentration, which comprises the following steps: firstly, adding 50 wt% of water in a container, starting a stirrer, heating to 30-60 ℃, and then pouring alkali; adding dye while heating and stirring, and stirring for 20-30 min; adding water, cooling to 50 ℃, adding the composite reducing agent in the table 11, stirring for 45min, and adding cold water to 100 wt% of the solution for later use. The specific ingredients are as shown in tables 10 and 11:

TABLE 10 ingredient tables

TABLE 11 proportion of composite reducing agent

The method comprises the following specific steps: feeding cloth; padding in a tank added with a penetrating agent; padding in a tank added with high-concentration leuco sodium salt dye liquor diluted by 20 times; ventilating and oxidizing; washing with water; neutralizing with acid; soap boiling; washing with water; drying; and (6) discharging the cloth.

The number of the dyeing tanks added with the penetrant can be set to be 1-4, and the temperature is set to be 20-85 ℃. The dyeing tank for adding the leuco sodium salt dye solution can be set to be 1-6, and the temperature can be set to be 30-95 ℃. 1-4 dyeing tanks can be respectively selected for water washing, acid neutralization and soap boiling, and the temperature can be set at 20-95 ℃.

In the embodiment, the composite reducing agent disclosed by the invention is adopted, so that the vat dye leuco dyeing method is applied to pad dyeing. As shown in FIG. 3, A in FIG. 3 is an effect chart of the dyed product of the present example, and B in FIG. 3 is an effect chart of the dyed product dyed in suspension with the same concentration of the dyeing liquid. As can be seen from the figure, the finished product dyed by the leuco pad dyeing method of the embodiment is more deeply dyed, so that the cost of the dye for dyeing can be reduced by adopting the leuco pad dyeing method of the embodiment under the condition of dyeing the same depth; aiming at the frock and the medical fabric, better fastness to rinsing can be obtained, and the wearability is improved. The dyeing process is short, the process temperature is reduced, and energy conservation and consumption reduction are realized.

According to GB/T3920-2008, the fastness detection parameters of the dyed product obtained by pad dyeing of the leuco dye and the dyed product obtained by pad dyeing of the suspension are as follows:

TABLE 12 dyeing fastness parameters

	Leuco pad dyeing (FIG. 3A)	Pad dyeing of suspension (fig. 3B)
			Colour fastness to dry rubbing	4 stage	4 stage
Color fastness to wet rubbing	Grade 3-4	4 stage

The fastness of the dyed finished product adopting the leuco pad dyeing is adopted in the embodiment, wherein the dry rubbing fastness reaches 4 grades, the wet rubbing fastness reaches 3-4 grades, the color fastness is high, and the dyeing performance is excellent.

Example 7

FIG. 4 is a graph showing the effect of pad dyeing by leuco reduction. Wherein, B is an effect picture of low-concentration 3g/l normal leuco dye liquor after pad dyeing; and (B) an effect picture of the prepared high-concentration leuco sodium salt diluted into 3g/l dye liquor after padding. The composite reducing agent and other technological conditions are all carried out in the same state.

The low-concentration 3g/l normal leuco dye liquor is prepared by adopting the following formula:

TABLE 13 Normal leuco dye liquor composition

	Dye indigo	Caustic soda	Composite reducing agent
				Concentration (g/L)	3	3	3

The high-concentration leuco sodium salt is prepared by adopting the following formula:

TABLE 14 ingredients of high concentration leuco sodium salt

	Dye indigo	Caustic soda	Composite reducing agent
				Concentration (g/L)	60	60	60

The preparation method of the high-concentration leuco sodium salt comprises the following steps: firstly, adding 50 wt% of water into a container, starting a stirrer, heating to 30-60 ℃, and then pouring combined alkali (10-60 wt% of caustic soda and 40-90 wt% of soda ash); adding dye while heating and stirring, and stirring for 20-30 min; adding water, cooling to 50 ℃, adding the composite reducing agent, stirring for 45min, and adding cold water to 100 wt% of the solution. After the preparation of the high-concentration leuco sodium salt is finished, diluting by 20 times, wherein the concentration of the diluted leuco sodium salt is the same as that of the normally prepared low-concentration leuco dye solution.

From fig. 4, it can be seen that the dyeing product dyed by the method for preparing high-concentration leuco sodium salt, which is prepared by diluting the leuco sodium salt dye solution, has a color depth significantly deeper than the color depth of the dyeing product dyed by the leuco sodium salt dye solution with the same concentration prepared by the normal method. Because the high-concentration leuco sodium salt dye liquor still forms a microcolloid state after being diluted by 20 times and has negative ion property, the vat dye is combined with fibers by Van der Waals force, the binding force is strong, the dyeing property is strong, and the coloring firmness is high.

As can be seen from Table 15, the preparation method of high concentration leuco sodium salt is used for preparing a leuco sodium salt dye solution which is diluted and then dyed to obtain a dyed product with high fastness and excellent dyeing performance.

TABLE 15 fastness parameters of the dyed products

Example 8

FIG. 5 is a comparison chart of dyeing products of pad dyeing process by leuco body reduction method respectively using sodium hydrosulfite and the composite reducing agent of the invention. Leuco body mother liquor prepared from sodium hydrosulfite and a composite reducing agent with the same concentration is respectively subjected to pad dyeing after standing for 0.5 hour, 1 hour, 2 hours and 3 hours. As can be seen from FIG. 5, the leuco dye liquor prepared by the composite reducing agent of the present invention still maintains good coloring effect for a long time, and the leuco dye liquor prepared by the composite reducing agent and the dye of the present embodiment has good stability and excellent dyeing fastness through the pad dyeing process.

Thus, it should be appreciated by those skilled in the art that while a number of exemplary embodiments of the invention have been illustrated and described in detail herein, many other variations or modifications consistent with the principles of the invention may be directly determined or derived from the disclosure of the present invention without departing from the spirit and scope of the invention. Accordingly, the scope of the invention should be understood and interpreted to cover all such other variations or modifications.

Claims

1. A dyeing method of leuco pad dyeing comprises the following steps: padding and oxidizing, wherein the padding process comprises padding in a dye vat containing a penetrant and padding in a dye vat containing a leuco sodium salt dye liquor, the leuco sodium salt dye liquor is prepared from a composite reducing agent and a dye, and the composite reducing agent comprises: thiourea dioxide, reducing sugars and chemical potential control agents; wherein the chemical potential control agent is at least one of sodium nitrite, acrylamide, furfural, cyclohexanone and trichloroacetic acid; in the composite reducing agent, 30-75 wt% of thiourea dioxide, 60-20 wt% of reducing sugar and 10-5 wt% of chemical potential control agent.

2. The dyeing method of leuco pad dyeing according to claim 1, wherein the reducing sugar is at least one of glucose and sucrose.

3. The process for leuco pad dyeing according to claim 1, characterized in that the penetrant is an anionic/nonionic penetrant.

4. The dyeing method of leuco pad dyeing according to claim 1, characterized in that the preparation of said leuco sodium salt dye liquor comprises the following steps: (1) firstly, adding 50 wt% of water in a container, starting a stirrer for stirring, heating to 30-60 ℃, and pouring alkali; (2) adding dye while heating and stirring, and stirring for 20-30 min; (3) adding water, cooling to 50 ℃, adding the composite reducing agent, stirring for 45min, and adding cold water to 100 wt% of the solution.

5. The dyeing process of leuco pad dyeing according to claim 1, characterized in that the penetrant padding employs 1-4 dye baths at a temperature of 20-85 ℃.

6. The dyeing method of leuco pad dyeing according to claim 1, characterized in that the leuco sodium salt dye liquor padding employs 1-6 dye baths at a temperature of 30-95 ℃.

7. The dyeing method of leuco pad dyeing according to claim 4, characterized in that the concentration of said complex reducing agent in said leuco sodium salt is 2-100g/L, and the concentration of said alkali is 2-120 g/L.