Dyeing method for leather fabric

Abstract

The invention relates to the technical field of leather dyeing, and discloses a dyeing method for a leather fabric, which comprises the following steps: firstly, performing degreasing, impurity removal and enzymatic enhancement hydrophilic treatment on a to-be-dyed leather fabric; then preparing dye liquor containing natural dye, a buffering agent and a leveling agent in deionized water; the pretreated leather fabric is dip-dyed in the dye liquor for dyeing; after dyeing, washing with deionized water for multiple times until the color does not fade; then soaking the fabric in a color fixing solution compounded by tannic acid and gelatin for color fixing treatment; and finally, the treated leather fabric is subjected to drying and heat setting. According to the invention, the problems of large color difference and poor fastness in traditional dyeing are effectively improved.

Description

Technical Field

[0001] The invention relates to the technical field of leather dyeing, in particular to a dyeing method for leather fabric. Background Art

[0002] With the widespread use of leather fabrics in clothing, footwear, and home furnishings, the demand for dyeing performance is becoming increasingly demanding. Dyeing must not only ensure vibrant and aesthetically pleasing color, but also ensure color uniformity and fastness. However, existing leather fabric dyeing methods commonly suffer from uneven dyeing and significant color variations, significantly compromising the visual quality and quality of the final product. Traditional dyeing methods often rely on physical immersion dyeing, which makes it difficult for the dye to evenly penetrate all parts of the leather fabric, leading to the formation of localized color spots and color variations.

[0003] Inadequate color fastness is also a common problem. Many dyeing processes using natural dyes suffer from a weak bond between the dye and the leather fabric, leading to fading after repeated washing or use, impacting the product's durability and lifespan. To improve dyeing efficiency, higher temperatures or strong acid and alkaline environments are often used during the dyeing process. This not only increases energy consumption but also easily damages the leather fabric's fiber structure, making it hard and brittle, reducing the fabric's feel and mechanical properties.

[0004] How to design a dyeing method for leather fabric to solve or improve the above problems is particularly important. Summary of the Invention

[0005] In view of this, the present invention proposes a dyeing method for leather fabrics, aiming to solve the problems of large color difference and poor fastness of dyeing in the current technology.

[0006] In one aspect, the present invention provides a method for dyeing leather fabric, comprising the following steps: S1) Pretreatment: The leather fabric to be dyed is subjected to degreasing, impurity removal and hydrophilicity increasing treatment in sequence, wherein the hydrophilicity increasing treatment is performed by enzymatic treatment with neutral protease and xylanase at a treatment temperature of 30-45° C. and a treatment time of 20-40 min.

[0007] S2) preparing a dye liquor: adding a natural dye, a buffer and a leveling agent composition to deionized water in sequence; the dye liquor comprises the following components: 0.5-2.5wt% natural dyes; Citric acid-sodium citrate buffer, pH controlled at 5.0-5.5; 1.4-1.9 wt% leveling agent composition; and the balance deionized water; S3) dyeing: placing the pre-treated leather fabric into a dyeing machine, adding the dye solution from step S2, and dyeing at a temperature of 45-60° C. for 40-90 min; S4) Washing: After dyeing, rinse with deionized water 2-3 times until the color does not fade; S5) color fixing treatment: soaking the leather fabric in a color fixing solution of tannic acid and gelatin, with a concentration of 0.5 wt % and a temperature of 60-80° C. for 10-30 min; S6) Drying and heat setting: The treated leather fabric is placed in an environment of 50-70°C to dry for 10-20 minutes, and then heat-set at a temperature of 70-85°C.

[0008] Preferably, the natural dye in the dye solution is a combination of one or more of gardenia yellow, indigo, hematoxylin and lac red.

[0009] Preferably, in step S2, an electric field-assisted dyeing method is adopted, and a DC voltage of 6-12 V is applied during the dyeing process, and the continuous action time is 15-40 minutes.

[0010] Preferably, the surfactant Tween-80 is added to the enzymatic treatment solution at a concentration of 0.05-0.2 wt %.

[0011] Preferably, the leveling agent composition comprises the following components: 1.0% sodium polyglutamate, 0.3-0.6% β-cyclodextrin, 0.1-0.3% γ-aminopropyltriethoxysilane and the balance water; Described sodium polyglutamate is prepared by the following method: Bacillus natto is inoculated into an activation medium for activation, and the activated Bacillus natto is inoculated into a main fermentation medium at an inoculum rate of 5-10%. The pH is adjusted to 6.8-7.2, the temperature is controlled at 35-37°C, and the fermentation is carried out in an aerated stirred reactor at 250 rpm for 48-72 hours. The fermentation broth is filtered through a plate and frame filter to remove bacterial cells. A 95% by volume ethanol solution is added to the fermentation broth to a final concentration of 70%, and the broth is allowed to stand for 12 hours to precipitate polyglutamic acid. The precipitate is collected by centrifugation or membrane filtration, redissolved in water, the pH is adjusted to neutral, and a 5-10% by mass sodium hydroxide solution is added dropwise to a pH of 7.0-7.5 to obtain sodium polyglutamate. The activation culture medium comprises: 20 g / L glucose, 1 g / L dipotassium hydrogen phosphate, 0.5 g / L magnesium sulfate and 10 g / L yeast extract; The main fermentation medium comprises: 40-80 g / L of sodium glutamate, 10-30 g / L of glucose, 2 g / L of dipotassium hydrogen phosphate and 1-3 g / L of ammonium sulfate.

[0012] Preferably, the dye liquor bath ratio is 1:10-15, and the dye liquor is swirled and circulated at a frequency of 5-10 times per minute.

[0013] Preferably, a finishing agent is added after the color fixing treatment, and the finishing agent includes: 0.3 wt% chitosan, 0.5 wt% amino silicone oil emulsion and 0.2 wt% eugenol.

[0014] Preferably, the leather fabric is polyester or nylon-based artificial leather, a microfiber non-woven fabric composite material or a sandwich structure leather material.

[0015] On the other hand, the present invention also protects a leather fabric obtained by the above dyeing method.

[0016] Compared with the prior art, the present invention has the following beneficial effects: This method effectively improves the hydrophilicity of the leather fabric surface and dye penetration by subjecting it to an enzymatic pretreatment to increase its hydrophilicity. This allows the natural dye to be more evenly and deeply distributed within the fabric fibers, significantly reducing the color differences and localized color spots commonly encountered during the dyeing process. The enzymatic treatment, which uses neutral proteases and xylanases, gently removes grease and impurities from the fabric surface while partially disrupting the fiber surface structure, increasing the number of binding sites for dye molecules and fundamentally improving dyeing uniformity and adhesion.

[0017] Buffers are used in the formulated dye liquor to precisely control pH, ensuring that natural dyes perform optimally in the most suitable environment. Leveling agent compositions synergistically inhibit dye aggregation, enhancing the stability and permeability of the dye liquor, further improving dyeing uniformity and vividness. Electric field-assisted dyeing technology utilizes electric field forces to promote faster and more uniform penetration of dye molecules into leather fabric fibers, shortening dyeing time while enhancing dyeing results.

[0018] The color-fixing treatment uses a composite solution of tannic acid and gelatin. This solution leverages the multi-point binding properties of tannic acid and protein, along with the film-forming properties of gelatin, to strengthen the bond between the dye and the fabric, significantly improving color fastness and minimizing fading due to washing or wear. Furthermore, the addition of a post-fixing agent further enhances the protective layer on the fabric surface, improving its abrasion resistance and feel.

[0019] The overall process of this invention is gentle, avoiding the damage to the fabric fiber structure caused by traditional high-temperature, strong acid and alkaline conditions, maintaining the softness and mechanical properties of leather fabrics and extending the service life of the fabric. By organically combining multiple technical means, this invention not only solves the problems of uniformity and fastness of natural dyes, but also reduces energy consumption, achieving a green and environmentally friendly dyeing process. DETAILED DESCRIPTION

[0020] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention. Example

[0021] First, the polyester-based artificial leather to be dyed was pre-treated with an enzymatic solution containing 0.1wt% neutral protease and 0.15wt% xylanase, with 0.1wt% Tween-80 added as a surfactant. The treatment temperature was controlled at 40°C for 30 minutes. Next, a dye solution was prepared, using gardenia yellow as a natural dye at a concentration of 1.5wt%, a citric acid-sodium citrate buffer adjusted to a pH of 5.2, and a leveling agent composition of 1.5wt%, including 1.0wt% sodium polyglutamate, 0.4wt% β-cyclodextrin, 0.1wt% γ-aminopropyltriethoxysilane, and the remainder deionized water. The dyeing process was carried out at 55°C for 60 minutes. An 8V DC voltage was applied for electric field-assisted dyeing for 25 minutes. The dye liquor ratio was 1:12, and the dye liquor was agitated 7 times per minute. After dyeing, the leather was rinsed three times with deionized water until no noticeable fading occurred. For the fixation treatment, the leather was immersed in a compound fixative containing 0.5wt% tannic acid and 0.5wt% gelatin at 70°C for 20 minutes. The leather was then dried and heat-set at 60°C for 15 minutes, followed by heat-setting at 80°C. Finally, a finishing agent consisting of 0.3wt% chitosan, 0.5wt% aminosilicone oil emulsion, and 0.2wt% eugenol was applied. Example

[0022] The microfiber nonwoven fabric composite to be dyed was pretreated with a neutral protease concentration of 0.08wt%, xylanase 0.12wt%, and Tween-80 0.15wt%, at a temperature of 35°C for 25 minutes. The dye liquor contained indigo at a concentration of 2.0wt%, and the buffer pH was adjusted to 5.5. The leveling agent composition comprised 1.7wt% of sodium polyglutamate 1.0wt%, β-cyclodextrin 0.6wt%, γ-aminopropyltriethoxysilane 0.1wt%, and the remainder was deionized water. The dyeing temperature was set at 50°C for 75 minutes, and an electric field-assisted dyeing process was performed with a DC voltage of 10V for 30 minutes. The dye liquor ratio was 1:15, and the dye liquor was agitated 10 times per minute. After dyeing, the fabric was rinsed twice with deionized water until it did not fade. During the fixation treatment, the concentrations of tannic acid and gelatin were both 0.5wt%, at a temperature of 75°C, and for 15 minutes. The drying stage temperature was 50°C for 10 minutes, and the heat setting temperature was 75°C. The final finishing agent used was chitosan 0.3wt%, amino silicone oil emulsion 0.5wt% and eugenol 0.2wt%. Example

[0023] First, the sandwich leather material to be dyed was pretreated with a neutral protease concentration of 0.12wt%, a xylanase concentration of 0.18wt%, and a low Tween-80 concentration of 0.05wt%. The treatment temperature was controlled at 38°C for 35 minutes. The dye solution contained a mixture of hematoxylin and lac red, with a total dye concentration of 2.2wt%, and the buffer pH was adjusted to 5.3. The leveling agent composition contained a total content of 1.6wt%, including 1.0wt% sodium polyglutamate, 0.5wt% β-cyclodextrin, and 0.1wt% γ-aminopropyltriethoxysilane. Dyeing was performed at 60°C for 80 minutes, with an electric field-assisted dyeing voltage of 12V for 35 minutes. The dye liquor ratio was 1:10, and the dye liquor was stirred at a frequency of 5 times per minute. After dyeing, the material was washed three times with deionized water. The fixing solution contained 0.5wt% each of tannic acid and gelatin, and the treatment temperature was 80°C for 25 minutes. The drying stage temperature was 65°C for 20 minutes and the heat setting temperature was 85°C.

[0024] The products obtained in Examples 1-3 were subjected to experimental testing. The test contents and test results are shown in Table 1.

[0025] 1. Physical performance testing 1.1 Color fastness test Test content: color fastness to washing, color fastness to rubbing (dry rubbing, wet rubbing), color fastness to light Test method: Color fastness to washing: in accordance with GB / T 3921-2008 "Textiles—Tests for Color Fastness—Determination of Color Fastness to Washing"; Color fastness to rubbing: According to GB / T 3920-2008 “Textiles—Tests for Color Fastness—Determination of Color Fastness to Rubbing”, test in both dry and wet conditions; Light color fastness: Using ISO 105-B02 standard, xenon lamp irradiation test; 1.2 Moisture absorption and breathability Test content: moisture permeability, moisture absorption rate Testing method: Water vapor transmission rate: using ASTM E96 vapor transmission rate test method; Moisture absorption rate: measured according to GB / T 21655-2008; 1.3 Tensile strength and elongation at break Test method: According to GB / T 228.1-2010 "Metal Tensile Test Methods Part 1: Room Temperature Test Method", or special standards for artificial leather (such as ISO 3376 Leather Tensile Strength Test) 2. Chemical performance testing 2.1 Dye adsorption rate and dyeing uniformity Detection method: Use ultraviolet-visible spectrophotometer (UV-Vis) to measure the change in dye concentration in the dye solution and calculate the dye adsorption rate; The uniformity of the stained samples was assessed using image analysis software; 2.2 Dye fixation rate Testing method: Calculate based on the dye concentration before and after dyeing, combined with the color fastness test results after dyeing 2.3 pH value and residual enzyme activity detection; Detection method: pH meter; Enzyme activity detection: enzyme-linked immunosorbent assay (ELISA) or colorimetric method to detect residual protease activity; 3. Environmental friendliness and safety testing 3.1 Detection of harmful substances in dye liquor and wastewater discharge; Test items: chemical oxygen demand (COD), total nitrogen (TN), heavy metal content; Detection method: COD according to HJ / T 399-2007 method; total nitrogen according to HJ 636-2012 method; heavy metals according to GB / T23170-2008 standard; 3.2 Safety of finishing agent ingredients Test items: harmful volatile organic compound (VOC) emission test; Detection method: Gas chromatography-mass spectrometry (GC-MS) analysis; Table 1 Test items Testing standards / methods Example 1 Example 2 Example 3 Washing color fastness GB / T 3921-2008 Level 4-5 Level 4-5 Level 5 Dry rubbing color fastness GB / T 3920-2008 Level 4 Level 4 Level 4-5 Wet rubbing color fastness GB / T 3920-2008 Level 3-4 Level 4 Level 4 Light fastness ISO 105-B02 Level 4 Level 4 Level 4-5 Dye adsorption rate UV-Vis photometry 78.50% 82.30% 85.70% Dye fixation rate Calculation and color fastness evaluation 74.20% 78.80% 81.50% Tensile strength (MPa) ISO 3376 15.8 16.5 17.2 Elongation at break (%) ISO 3376 45.2 47.8 49 Moisture absorption rate (%) GB / T 21655-2008 12.4 13.1 13.7 Moisture permeability (g / m²·24h) ASTM E96 340 365 380 Antibacterial rate (%) ISO 20743-2013 87.5 90.2 92.8 COD emissions (mg / L) HJ / T 399-2007 35 28 25 Total nitrogen (mg / L) HJ 636-2012 5.6 4.8 4.3 Heavy metal content (mg / kg) GB / T 23170-2008 <0.5 <0.5 <0.5 VOC emission (mg / m³) GC-MS 0.15 0.12 0.1 As can be seen from the table: the products obtained in Examples 1-3 were systematically tested in experiments, covering multiple aspects such as color fastness, mechanical properties, moisture absorption and air permeability, antibacterial effect, and environmental protection indicators. The results show: In terms of color fastness, all three examples showed good washing color fastness, all reaching level 4-5, indicating excellent color fastness, and Example 3 was slightly better than the other two examples in color fastness, especially in dry and wet friction color fastness and light color fastness, indicating that the natural dyes and electric field assisted dyeing technology used in the present invention can effectively improve dyeing stability and durability.

[0026] The dye adsorption rate and fixation rate are both high. The adsorption rate of Example 3 reaches 85.7% and the fixation rate is 81.5%, indicating that the dye can be more evenly and firmly bound to the surface of the substrate, ensuring the bright color and durability of the product.

[0027] In terms of mechanical properties, the tensile strength and elongation at break of the three products all meet the application requirements, and Example 3 has the highest mechanical properties, with a tensile strength of 17.2 MPa and an elongation at break of 49.0%. This shows that the pretreatment and dyeing processes used help maintain the structural integrity and flexibility of the material.

[0028] The moisture absorption rate and moisture permeability indicators show that the product has good moisture absorption and breathability. Example 3 performs best, with a moisture absorption rate of 13.7% and a moisture permeability of 380 g / m²·24h, which improves the wearing comfort.

[0029] The antibacterial performance test shows that all examples have a high antibacterial rate, with Example 3 reaching the highest rate of 92.8%. Thanks to the synergistic effect of chitosan and eugenol, the growth of bacteria is effectively inhibited, thereby improving the hygienic safety of the product.

[0030] In terms of environmental performance, COD and total nitrogen emissions are both lower than the industry standard, and decrease as the example number increases. In Example 3, the COD is 25 mg / L, the total nitrogen is 4.3 mg / L, and the VOC emission is also low, reflecting the green and environmental advantages of the dyeing and finishing process.

[0031] The surface morphology was observed by scanning electron microscopy (SEM), and the coating was uniform and dense, and the coating of Example 3 was fine and uniform, indicating that the composite leveling agent and electric field assisted dyeing technology used significantly optimized the distribution and adhesion effect of the dye.

[0032] In summary, the present invention effectively improves the dyeing uniformity and fastness of polyester-based artificial leather, microfiber nonwoven composite materials, and sandwich leather materials by combining enzymatic pretreatment with electric field-assisted dyeing technology. The synergistic effect of natural dyes and an innovative leveling agent system not only significantly improves color fastness and mechanical properties, but also enhances moisture absorption, breathability, and antibacterial effects. Environmental indicators show that the dyeing process is low-emission and low-pollution, meeting green production requirements. The surface coating is dense and uniform, improving the product's appearance, texture, and durability.

[0033] 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 it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered by the scope of protection of the claims of the present invention.

Claims

1. A dyeing method for leather fabric, characterized in that, The following steps are involved: S1) Pretreatment: Degreasing, removing impurities and increasing hydrophilicity of the leather fabric to be dyed are sequentially performed, wherein the hydrophilicity increasing treatment is performed by enzymatic treatment with neutral protease and xylanase at a temperature of 30-45° C. for 20-40 min; S2) preparing a dye liquor: adding a natural dye, a buffer and a leveling agent composition to deionized water in sequence; the dye liquor comprises the following components: 0.5-2.5wt% natural dyes; Citric acid-sodium citrate buffer, pH controlled at 5.0-5.5; 1.4-1.9 wt% leveling agent composition; and the balance deionized water; S3) dyeing: placing the pre-treated leather fabric into a dyeing machine, adding the dye solution from step S2, and dyeing at a temperature of 45-60° C. for 40-90 min; S4) Washing: After dyeing, rinse with deionized water 2-3 times until the color does not fade; S5) color fixing treatment: soaking the leather fabric in a color fixing solution of tannic acid and gelatin, with a concentration of 0.5 wt % and a temperature of 60-80° C. for 10-30 min; S6) Drying and heat setting: The treated leather fabric is placed in an environment of 50-70°C to dry for 10-20 minutes, and then heat-set at a temperature of 70-85°C.

2. The dyeing method for leather fabric according to claim 1, characterized in that The natural dye in the dye solution is a combination of one or more of gardenia yellow, indigo, hematoxylin and lac red.

3. The dyeing method for leather fabric according to claim 1, characterized in that In step S2, an electric field-assisted dyeing method is used, and a DC voltage of 6-12 V is applied during the dyeing process for a continuous action time of 15-40 minutes.

4. The dyeing method for leather fabric according to claim 1, characterized in that The surfactant Tween-80 is added to the enzymatic treatment solution at a concentration of 0.05-0.2 wt%.

5. The dyeing method for leather fabric according to claim 1, characterized in that The leveling agent composition comprises the following components: 1.0% sodium polyglutamate, 0.3-0.6% beta-cyclodextrin, 0.1-0.3% gamma-aminopropyltriethoxysilane and the balance water; Described sodium polyglutamate is prepared by the following method: Bacillus natto is inoculated into an activation medium for activation, and the activated Bacillus natto is inoculated into a main fermentation medium at an inoculum rate of 5-10%. The pH is adjusted to 6.8-7.2, the temperature is controlled at 35-37°C, and the fermentation is carried out in an aerated stirred reactor at 250 rpm for 48-72 hours. The fermentation broth is filtered through a plate and frame filter to remove bacterial cells. A 95% by volume ethanol solution is added to the fermentation broth to a final concentration of 70%, and the broth is allowed to stand for 12 hours to precipitate polyglutamic acid. The precipitate is collected by centrifugation or membrane filtration, redissolved in water, the pH is adjusted to neutral, and a 5-10% by mass sodium hydroxide solution is added dropwise to a pH of 7.0-7.5 to obtain sodium polyglutamate. The activation culture medium comprises: 20 g / L glucose, 1 g / L dipotassium hydrogen phosphate, 0.5 g / L magnesium sulfate and 10 g / L yeast extract; The main fermentation medium comprises: 40-80 g / L of sodium glutamate, 10-30 g / L of glucose, 2 g / L of dipotassium hydrogen phosphate and 1-3 g / L of ammonium sulfate.

6. The dyeing method for leather fabric according to claim 1, characterized in that The dye liquor bath ratio is 1:10-15, and the dye liquor is swirled and circulated at a frequency of 5-10 times per minute.

7. The dyeing method for leather fabric according to claim 1, characterized in that After the color fixing treatment, a finishing agent is added, wherein the finishing agent comprises: 0.3 wt% chitosan, 0.5 wt% amino silicone oil emulsion and 0.2 wt% eugenol.

8. The dyeing method for leather fabric according to claim 1, characterized in that The leather fabric is polyester or nylon-based artificial leather, a microfiber non-woven fabric composite material or a sandwich structure leather material.

9. A dyed leather fabric, characterized in that: The leather fabric is prepared by the dyeing method according to any one of claims 1 to 8.