Chromium-free dyeing method for leather

Abstract

The invention relates to the technical field of leather dyeing, and discloses a chromium-free dyeing method for leather, which comprises the following steps: adding 30-35 DEG C deionized water and crust leather into a rotary drum, adding 1.5% of sodium formate, 0.6% of sodium bicarbonate and 0.2% of neutralizing aid, adjusting the pH value to 5.3-5.5, rolling for 60 minutes, and draining; intermittently washing the leather for 2-4 times by using deionized water at 60-65 DEG C; cooling to 30-33 DEG C, sequentially adding 0.3% of ammonia water, 1% of a permeation synergist, 6% of a main dye, 2% of a saturation improver, 2% of a disperse dye and 0.6% of a leveling agent, and carrying out roll dyeing; adding 0.3% formic acid in four times, rolling for 10-20 minutes each time, adjusting the pH value, and continuously rolling for 30 minutes; and finally, washing twice with deionized water, and discharging from the drum after 8-12 minutes. The method realizes deep and uniform penetration of the dye, has high color fastness, is chromium-free and environment-friendly, and significantly improves the leather dyeing quality and environmental protection performance.

Description

Technical Field

[0001] The present invention relates to the technical field of leather dyeing, and in particular, to a chromium-free dyeing method for leather. Background Art

[0002] As a key link in the leather preparation process, leather dyeing not only affects the appearance color, uniformity, and fastness of the finished leather, but also directly relates to the environmental protection performance and end applicability of the product. In traditional dyeing processes, chromium-containing compounds (especially chromium tanning agents) are widely used to improve dye adsorption and leather durability. However, chromium, especially trivalent chromium, is easily converted into highly toxic hexavalent chromium during production and wastewater treatment, posing a serious threat to the ecological environment and human health. With the increasingly strict environmental protection regulations and the promotion of the concept of green manufacturing, developing a chromium-free, low-pollution, and highly efficient and stable leather dyeing process has become one of the key research directions in the industry.

[0003] In terms of dye permeability in existing chromium-free dyeing technologies, conventional disperse dyes are difficult to break through the dense structure of leather fibers, resulting in a shallow dyeing layer and a faint color; in terms of the dye binding mechanism, the lack of the coordination effect of chromium ions makes the binding force between the dye and collagen fibers weak, prone to dye spots and color blooming; in terms of the auxiliary agent system, the compatibility of traditional neutralizing agents and penetrants is poor, resulting in a high pH sensitivity and a narrow process window during the dyeing process; in terms of dye synthesis, existing azo-type and anthraquinone-type dyes generally have problems such as complex synthesis routes, large amounts of organic solvents used, and difficult post-treatment.

[0004] These problems together make it difficult for existing chromium-free dyeing processes to simultaneously meet the industrial requirements of deep penetration, uniformity, color fastness, and environmental protection. Summary of the Invention

[0005] In view of this, the present invention proposes a chromium-free dyeing method for leather, aiming to solve the problem that existing chromium-free dyeing processes in the current technology are difficult to simultaneously meet the requirements of deep penetration, uniformity, color fastness, and environmental protection.

[0006] On the one hand, a chromium-free dyeing method for leather proposed by the present invention includes the following steps: S1: Inject deionized water at 30 - 35 °C into a rotary drum, and put in the leather embryo; Add a bath solution according to the percentage of the mass of the leather embryo; the bath solution is 1.5% sodium formate, 0.6% sodium bicarbonate, and 0.2% neutralizing agent; Adjust the pH value of the bath solution to 5.3 - 5.5, keep rolling at 30 - 35 °C and 10 - 15 rpm for 60 min, and drain the water; S2: Add deionized water at 60 - 65 °C to the rotary drum, intermittently roll to continuously rinse the leather, roll for 2 - 3 min each time, and repeat 2 - 4 times; S3: Lower the temperature to 30 - 33 °C and sequentially add, by percentage of the mass of the leather embryo: 0.3% ammonia water, 1% penetration synergist, 6% main dye, 2% saturation promoter, 2% disperse dye, and 0.6% leveling agent, then start tumbling dyeing. Check the cross-section of the leather every 30 min and stop when the penetration thickness of the dye ≥ 5 mm or the tumbling dyeing time > 180 min. S4: Sequentially add 0.30% formic acid four times, by percentage of the mass of the leather embryo. After each addition, tumble for 10 - 20 min, finally adjust the pH value to 3.6 - 3.7, and continue tumbling for 30 min. S5: Wash twice with deionized water at 25 - 30 °C, control the washing time within 8 - 12 min, and take out of the drum.

[0007] Further, in step S1, the mass ratio of the warm water to the leather embryo is 3 - 8:1.

[0008] Further, in step S1, the neutralization aid is prepared by mixing glycine, triethanolamine, and sodium cocoyl glutamate in a mass ratio of 2:1:1.

[0009] Further, in step S3, the main dye is an azo-β-ketone type dye, and the disperse dye is an anthraquinone-amino acid copolymer dye.

[0010] Further, the main dye is obtained through the following method: 1) Dissolve p-hydroxyaniline under acidic conditions, dropwise add a sodium nitrite solution, and carry out a diazotization reaction at 0 - 5 °C for 30 - 50 min to generate a diazonium salt solution A. 2) Dissolve 2-butanone and ethanolamine under alkaline conditions with stirring at room temperature, adjust the pH to 8.5 - 9.0 to form a nucleophilic conjugation liquid B. 3) Slowly drop the diazonium salt solution A into the nucleophilic conjugation liquid B, maintain the system temperature at 10 - 15 °C, and continue stirring and reacting for 2 h to obtain an intermediate C. 4) Add chlorosulfonic acid to the intermediate C for sulfonation modification, control the reaction temperature at 40 - 50 °C, react for 1 h, adjust the pH to neutral, then carry out ethanol precipitation and filtration to obtain a crude product D. 5) Redissolve the crude product D in deionized water, use membrane separation to remove small molecule impurities, and obtain the main dye through freeze-drying. Further, the molar ratio of p-hydroxyaniline: 2-butanone: ethanolamine: chlorosulfonic acid is 1:1:1:1.5.

[0011] Further, the disperse dye is obtained through the following method: 1) Take 1,4-diaminoanthraquinone and dissolve it in ethylene glycol monomethyl ether, add maleic anhydride, and reflux and react at 90 °C for 3 h to generate an intermediate A. 2) After cooling the intermediate A to room temperature, slowly add L-glutamic acid, add a mixed solvent of ethanol with a concentration of 50%, then add EDC and NHS, adjust the pH to 5.5 - 6.0, and stir for copolymerization reaction at room temperature for 6 h to form intermediate B; 3) Add chlorosulfonic acid to intermediate B and carry out sulfonation modification reaction at 45 °C for 1 h, adjust the pH to neutral, and cool to 5 °C; 4) Add absolute ethanol for precipitation, filter after standing for 1 h to obtain crude product C; 5) Redissolve the crude product C in water, use a 12 kDa cut-off membrane for membrane separation to remove unreacted amino acids and small molecule impurities, and obtain the said disperse dye after freeze-drying for 24 h; Furthermore, 1,4-diaminoanthraquinone and maleic anhydride are added in equimolar amounts; The molar ratio of intermediate A:L-glutamic acid:EDC:NHS is 1:2:2.5:1.5; The molar ratio of intermediate B:chlorosulfonic acid is 2:1.

[0012] Furthermore, in step S3, the penetration synergist is nonylphenol polyoxyethylene ether, the saturation promoter is an equimolar mixture of hydroxypropyl guar gum and polycarboxylate polymer, and the leveling agent is coconut oil dimethylamine oxide.

[0013] Furthermore, in step S4, color matching and washing are carried out immediately after the third addition; The washing liquid for color matching and washing is deionized water, a mixed liquid of 0.1% EDTA-2Na and 0.3% weak anionic surfactant based on the mass of the leather embryo.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: By reasonably regulating the pH value and buffer system of the dyeing bath solution, the present invention effectively stabilizes the acidity and alkalinity of the dyeing environment, avoids the aggregation and precipitation of dye molecules in leather fibers, and promotes the uniform diffusion and deep penetration of dyes. The neutralization assistant not only improves the buffer capacity of the bath solution, but also enhances the hydrophilicity and dye affinity on the surface of collagen fibers, thereby enhancing the binding strength between the dye and the fiber and reducing the phenomena of dye spots and color streaks.

[0015] The used azo-β-ketone type main dye and anthraquinone-amino acid copolymer disperse dye contain nucleophilic groups and hydrophobic copolymer units in their structures, endowing the dye molecules with strong multi-point binding ability and good water dispersibility. Its synthesis process enhances the water solubility and fiber affinity of the dye through sulfonation modification, thereby improving the penetration depth and binding stability of the dye, replacing the coordination binding provided by traditional chromium ions, and achieving the effect of high color fastness.

[0016] The penetration synergist can reduce the interfacial tension of dye molecules and improve the diffusion behavior of dyes between leather pores and fibers; the polymer network structure formed by the saturation booster helps to fix dye molecules, preventing the migration and aggregation of dyes on the fiber surface, thereby enhancing the dyeing uniformity and color fastness; the leveling agent promotes the uniform dispersion of dye molecules by improving the surface activity and emulsifying properties of the dye bath, reduces the local concentration gradient, and avoids uneven dyeing.

[0017] Formic acid is added step by step to gradually reduce the pH, enabling the dyes to be gradually fixed on the collagen fibers, preventing premature precipitation or loss of dye molecules during the dyeing process, and thus enhancing the dye fixation rate and dyeing fastness. In the color matching rinse water, EDTA-2Na and a weak anionic surfactant are added, which can chelate residual metal ions, reduce the concentration of polyvalent cations on the fiber surface, prevent uneven deposition of dyes and impurities, and further ensure dyeing uniformity and environmental protection emission standards. Specific embodiments

[0018] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention. Embodiment

[0019] Put the pretreated wet leather embryo into a rotating drum, inject deionized water at a temperature of 32 °C, and the mass ratio of water to leather embryo is 5:1. Add a bath solution, which contains 1.5% sodium formate, 0.6% sodium bicarbonate and 0.2% neutralizing aid based on the mass of the leather embryo. The neutralizing aid is prepared from glycine, triethanolamine and sodium cocoyl glutamate in a mass ratio of 2:1:1. Adjust the pH of the bath solution to 5.4, keep the rotating drum rolling at 12 revolutions per minute for 60 minutes, and then drain the water. Add deionized water at 62 °C to the rotating drum, intermittently roll and wash the leather 3 times, with each rolling for 2 minutes. Cool down to 31 °C, and sequentially add 0.3% ammonia water, 1% nonylphenol polyoxyethylene ether, 6% azo-β-ketone type main dye, 2% equimolar mixture of hydroxypropyl guar gum and polycarboxylate, 2% anthraquinone-amino acid copolymer dispersion dye and 0.6% coco dimethyl amine oxide, and start tumbling dyeing. Check the cross-section of the leather every 30 minutes, and stop tumbling dyeing when the dye penetration thickness reaches 5 mm, with a cumulative time of 170 minutes. Add formic acid in four portions, 0.3% each time, and roll for 15 minutes after each addition. Finally, adjust the pH to 3.7 and continue to roll for 30 minutes. Immediately after the third addition of formic acid, perform color matching rinse water, wash twice with deionized water at 25 °C for 8 minutes each time, and the washing solution contains 0.1% disodium EDTA and 0.3% weak anionic surfactant. After washing, take out the drum to complete the dyeing. Embodiment

[0020] Take deionized water at a temperature of 33 °C, with a mass ratio of water to leather embryo of 7:1, and immerse the leather embryo in it. Add a bath solution containing 1.5% sodium formate, 0.6% sodium bicarbonate, and 0.2% neutralizing assistant by the mass of the leather embryo. The neutralizing assistant is prepared by mixing glycine, triethanolamine, and sodium cocoyl glutamate in a mass ratio of 2:1:1. Adjust the pH value to 5.3, and roll the drum at 10 revolutions per minute for 60 minutes, then drain the water. Add deionized water at 64 °C to the drum for 4 rinses, with each roll lasting 3 minutes. When the temperature drops to 30 °C, add 0.3% ammonia water, 1% nonylphenol polyoxyethylene ether, 6% azo-β-ketone type main dye, 2% equimolar mixture of hydroxypropyl guar gum and polycarboxylate, 2% anthraquinone-amino acid copolymer dispersion dye, and 0.6% coconut oil-based dimethylamine oxide, and start the tumbling dyeing. When the dye penetration reaches 5 mm, stop after 180 minutes of tumbling dyeing. Add formic acid in four portions, each portion being 0.3%, and roll for 10 minutes after each addition, and finally adjust the pH to 3.6. Immediately after the third addition of formic acid, wash twice with color-matching wash water containing 0.1% disodium EDTA and 0.3% weak anionic surfactant, each wash lasting 10 minutes, and the water temperature being 28 °C. After washing, take out the drum to complete the dyeing. Example

[0021] Add deionized water to the drum, control the water temperature at 35 °C, and set the mass ratio of water to leather embryo to 6:1. Add a bath solution containing 1.5% sodium formate, 0.6% sodium bicarbonate, and 0.2% neutralizing assistant. The neutralizing assistant is prepared by mixing glycine, triethanolamine, and sodium cocoyl glutamate in a ratio of 2:1:1, and adjust the pH value to 5.5. Roll the drum at 15 revolutions per minute for 60 minutes, then drain the water. Subsequently, add deionized water with a set temperature of 60 °C and rinse the leather 3 times, with each roll lasting 2 minutes. When the temperature drops to 32 °C, add 0.3% ammonia water, 1% nonylphenol polyoxyethylene ether, 6% azo-β-ketone type main dye, 2% equimolar mixture of hydroxypropyl guar gum and polycarboxylate, 2% anthraquinone-amino acid copolymer dispersion dye, and 0.6% coconut oil-based dimethylamine oxide in sequence for tumbling dyeing. Check the cross-section of the leather every 30 minutes and stop when the dye penetration thickness reaches 5 mm or the tumbling dyeing time exceeds 150 minutes. Add formic acid in four portions, each portion being 0.3%, and roll for 20 minutes after each addition, and finally adjust the pH to 3.6. Immediately after the third addition of formic acid, wash twice with color-matching wash water containing 0.1% disodium EDTA and 0.3% weak anionic surfactant, with each washing time controlled at 12 minutes, and the washing water temperature being 30 °C. After washing, take out the drum to complete the dyeing process.

[0022] For the above 3 examples, the following tests were conducted, and the test results are shown in Table 1:

[0023] As can be seen from the table, through the test results of the chromium-free dyeing method proposed in the present invention in three embodiments, it can be seen that the penetration depth of the dye reaches or exceeds 5 mm, indicating that the dye can effectively and evenly penetrate into the leather interior, ensuring the deep penetration of dyeing. The low color standard deviation indicates uniform dyeing and avoids the phenomena of color streaks and dye spots. The color fastness test results show that it reaches above grade 4 in terms of wash fastness, perspiration fastness, dry and wet rubbing, etc., reflecting the firmness and stability of the combination of the dye and leather fibers.

[0024] The test results of the wastewater environmental protection indicators show that no harmful chromium ions are detected during the dyeing process, and the chemical oxygen demand (COD) remains at a low level, meeting the chromium-free environmental protection discharge standards, proving that this solution effectively avoids the environmental pollution caused by the traditional chromium tanning and dyeing process. The dye fixation rate is as high as 88%-90%, indicating that the dye is fully utilized and fixed on the leather fibers, reducing the waste and loss of the dye.

[0025] In summary, the present invention stabilizes the dyeing environment by reasonably designing the pH buffer system of the dyeing bath solution, effectively prevents the agglomeration and precipitation of the dye, promotes the uniform and deep penetration of the dye, thereby ensuring the deep penetration and uniformity of dyeing. The azo-β-ketone type main dye and anthraquinone-amino acid copolymer dispersion dye adopted, combined with the penetration synergist, saturation booster and leveling agent, realize the multi-point combination and high affinity of the dye and collagen fibers, greatly improving the dyeing fastness. Adjusting the pH step by step makes the dye gradually fixed, preventing loss and precipitation, and further improving the color fixation rate. In terms of wastewater treatment, by removing chromium ions and reducing COD, environmental protection discharge is ensured, responding to the requirements of green environmental protection.

[0026] While ensuring the deep penetration, uniformity and high color fastness of leather dyeing, this solution avoids the environmental pollution of traditional chromium dyeing, realizes the breakthrough of chromium-free high-efficiency environmental protection dyeing technology, and meets the dual demands of the leather industry for high quality and green production.

[0027] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: the specific implementation manners of the present invention can still be modified or equivalently replaced, and any modification or equivalent replacement without departing from the spirit and scope of the present invention shall be covered by the protection scope of the claims of the present invention.

Claims

1. A chrome-free dyeing method for leather, characterized in that, It includes the following steps: S1: Inject deionized water at 30 - 35°C into the rotating drum, and put in the leather embryo; Add the bath solution according to the percentage of the mass of the leather embryo; the bath solution is 1.5% sodium formate, 0.6% sodium bicarbonate and 0.2% neutralizing assistant; Adjust the pH value of the bath solution to 5.3 - 5.5, keep rolling at 30 - 35°C and 10 - 15 rpm for 60 min, and drain the water; S2: Add deionized water at 60 - 65°C to the rotating drum, intermittently roll and continuously rinse the leather, each rolling for 2 - 3 min, repeat 2 - 4 times; S3: Lower the temperature to 30 - 33°C, and sequentially add according to the percentage of the mass of the leather embryo: 0.3% ammonia water, 1% penetration synergist, 6% main dye, 2% saturation promoter, 2% disperse dye and 0.6% leveling agent, start drum dyeing, check the cross-section of the leather every 30 min, and stop until the dye penetration thickness ≥ 5 mm or the drum dyeing time > 180 min; S4: Sequentially add 0.30% formic acid four times according to the percentage of the mass of the leather embryo, roll for 10 - 20 min after each addition, finally adjust the pH value to 3.6 - 3.7, and continue to roll for 30 min; S5: Wash twice with deionized water at 25 - 30°C, control the washing time at 8 - 12 min, and take out of the drum.

2. The chrome-free dyeing method for leather according to claim 1, characterized in that, In step S1, the mass ratio of warm water to the leather embryo is 3 - 8:

1.

3. The chrome-free dyeing method for leather according to claim 1, characterized in that, In step S1, the neutralizing assistant is prepared by mixing glycine, triethanolamine and sodium cocoyl glutamate according to the mass ratio of 2:1:

1.

4. The chrome-free dyeing method for leather according to claim 1, characterized in that, In step S3, the main dye is an azo-β-ketone type dye, and the disperse dye is an anthraquinone-amino acid copolymer dye.

5. The chrome-free dyeing method for leather according to claim 4, characterized in that, The main dye is obtained through the following method: 1) Dissolve p-hydroxyaniline under acidic conditions, dropwise add sodium nitrite solution, carry out diazotization reaction at 0 - 5°C for 30 - 50 min to generate diazonium salt solution A; 2) Dissolve 2-butanone and ethanolamine under alkaline conditions and stir at room temperature, adjust the pH to 8.5 - 9.0 to form nucleophilic conjugation liquid B; 3) Slowly dropwise add diazonium salt solution A into nucleophilic conjugation liquid B, maintain the system temperature at 10 - 15°C, continue to stir and react for 2 h to obtain intermediate C; 4) Add chlorosulfonic acid to intermediate C for sulfonation modification, control the reaction temperature at 40 - 50°C, react for 1 h, adjust the pH to neutral and then carry out ethanol precipitation, filter to obtain crude product D; 5) Redissolve crude product D in deionized water, use membrane separation to remove small molecule impurities, and obtain the main dye by freeze-drying method.

6. The chrome-free dyeing method for leather according to claim 5, characterized in that, The molar ratio of p-hydroxyaniline: 2-butanone: ethanolamine: chlorosulfonic acid is 1:1:1:1.

5.

7. The chrome-free dyeing method for leather according to claim 4, characterized in that, The disperse dye is obtained through the following method: 1) Take 1,4-diaminoanthraquinone and dissolve it in ethylene glycol monomethyl ether, add maleic anhydride, and reflux and react at 90°C for 3 h to generate intermediate A; 2) After cooling intermediate A to room temperature, slowly add L-glutamic acid, add a mixed solvent of ethanol with a concentration of 50%, then add EDC and NHS, adjust the pH to 5.5 - 6.0, and stir and copolymerize at room temperature for 6 h to form intermediate B; 3) Add chlorosulfonic acid to intermediate B and carry out sulfonation modification reaction at 45 °C for 1 h, adjust the pH to neutral, and cool to 5 °C; 4) Add absolute ethanol for precipitation, filter after standing for 1 h to obtain crude product C; 5) Redissolve crude product C in water, use a 12 kDa cut-off membrane for membrane separation to remove unreacted amino acids and small molecule impurities, and obtain the said disperse dye after freeze-drying for 24 h.

8. The chrome-free dyeing method for leather according to claim 7, wherein 1,4-diaminoanthraquinone and maleic anhydride are added in equimolar amounts; The molar ratio of intermediate A: L-glutamic acid: EDC: NHS is 1:2:2.5:1.5; The molar ratio of intermediate B: chlorosulfonic acid is 2:

1.

9. The chrome-free dyeing method for leather according to claim 1, characterized in that, In step S3, the penetration synergist is nonylphenol polyoxyethylene ether, the saturation promoter is an equimolar mixture of hydroxypropyl guar gum and polycarboxylate polymer, and the leveling agent is coconut oil dimethylamine oxide.

10. The chrome-free dyeing method for leather according to claim 1, characterized in that, In step S4, color matching and washing are carried out immediately after the third addition; The washing liquid for the color matching and washing is deionized water, a mixed solution of 0.1% EDTA-2Na and 0.3% weak anionic surfactant based on the mass of the leather embryo.

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