Environment-friendly leather dyeing method based on combination of plant indigo and chrome tanning

Abstract

The invention discloses an environment-friendly leather dyeing method based on combination of plant indigo and chrome tanning, and belongs to the technical field of leather dyeing. The method comprises the following steps: by taking indigo mud prepared from round-leaf indigo plants as a natural dye, carrying out dip dyeing and oxidation on deacidified sheepskin for multiple times by virtue of a process of dyeing first and then tanning, and then carrying out after-finishing such as chrome tanning, neutralization and fat liquoring. By quantifying the key process links of indigo mud preparation, dye liquor preparation, dyeing times, tanning parameters and the like, the standardized and industrial application of the traditional plant dyeing technology is realized; the color fastness and the hand feeling softness of the leather are remarkably improved by utilizing the complexing effect of the chrome tanning agent and indigo molecules; meanwhile, synthetic dye is partially replaced by vegetable dye, the chrome tanning process is optimized, and environmental pollution is reduced. A reproducible, efficient and environment-friendly technical scheme is provided for large-scale production of plant-dyed leather, and the method is suitable for development of high-end ecological leather products and has multiple values of cultural inheritance, green manufacturing and industrial popularization.

Description

Technical Field

[0001] This invention relates to the field of leather dyeing technology, specifically to an environmentally friendly leather dyeing method based on the combination of plant indigo and chrome tanning. Background Technology

[0002] Traditional leather dyeing has long relied on synthetic dyes such as azo compounds and metal complexes, which easily generate toxic wastewater during production and use, causing water and soil pollution and posing a threat to the ecological environment and human health. In recent years, with the deepening of green manufacturing and sustainable development concepts, plant dyes have received widespread attention due to their natural sources, biodegradability, and environmental friendliness. However, the application of plant dyes in leather dyeing still faces technical bottlenecks such as the reliance on empirical process parameters, unstable dyeing effects, poor color fastness, and difficulty in coordinating with leather tanning processes, and has not yet achieved large-scale, standardized application.

[0003] Existing plant dyeing techniques are mostly concentrated in the textile field. For example, the indigo dyeing technique using round-leaved Polygonum hydropiper, passed down in Butuo County, Liangshan Prefecture, my country, although a non-material cultural heritage, suffers from problems in leather dyeing, such as inconsistent fermentation levels, difficulty in controlling dye concentration, and reliance on experience for oxidation time. This results in significant fluctuations in dyeing depth, uniformity, and color fastness, making it difficult to meet the consistency requirements of industrial production. Direct dyeing on already tanned leather often leads to uneven dyeing, low rubbing fastness, and a stiff leather feel due to weak dye-fiber bonding. Furthermore, the dyeing process conflicts with tanning, fatliquoring, and other leather-making processes, affecting the overall process coordination and finished product performance.

[0004] Therefore, there is an urgent need to develop a leather dyeing method based on plant indigo, which can both inherit the cultural connotation of traditional dyeing techniques and solve problems such as dyeing stability, color fastness and leather feel through process innovation and parameter standardization, so as to promote the practical application of plant dyeing technology in the leather industry and achieve an organic combination of environmental protection, cultural heritage and industrial development. Summary of the Invention

[0005] This invention aims to provide an environmentally friendly leather dyeing method based on the combination of plant indigo and chrome tanning. By using a pre-dyeing and post-tanning process and the complexation effect of chrome tanning agent with indigo molecules, it solves the problems of low color fastness, hard hand feel, and difficulty in standardizing the process of traditional plant-dyed leather.

[0006] To achieve the above objectives, the present invention provides the following technical solution: an environmentally friendly leather dyeing method based on the combination of plant indigo and chrome tanning, comprising the following steps:

[0007] S1. Raw material preparation: Prepare indigo mud, sheep's tannin bark, and dyes and chemicals including reducing agents and dyeing auxiliaries, which are extracted from Polygonum rotundum through fermentation.

[0008] S2. Deacidification treatment: The sheepskin is deacidified until the pH value is neutral to obtain deacidified sheepskin;

[0009] S3. Dye solution preparation: Based on the quality of the deacidified sheepskin, prepare either a cooling dye solution or a hot dye solution.

[0010] The preparation of the cold dyeing solution includes: weighing 1% to 10% of the weight of the deacidified sheepskin indigo mud, dissolving it in 20 times the weight of the indigo mud in water, adding 30% of the weight of the indigo mud in sodium carbonate as a dyeing aid and 10% of the weight of the indigo mud in sulfate as a reducing agent, and stirring at 20°C to 30°C until the dyeing solution turns yellow-green.

[0011] The preparation of the hot dyeing solution includes: weighing 1% to 10% of the weight of the deacidified sheepskin indigo mud, 75% of the weight of the indigo mud indigo mud as a dyeing aid, and 75% of the weight of the indigo mud indigo mud as a reducing agent, dissolving it in water at a temperature of 40°C to 60°C at 20 times the weight of the indigo mud, stirring evenly, boiling, and cooling to 40°C for later use;

[0012] S4. Immersion and Oxidation: Immerse the deacidified sheepskin in the dye solution prepared in step S3, and after taking it out, oxidize it in the air until the surface changes completely from yellow-green to blue.

[0013] S5. Repeat staining: Repeat the staining and oxidation process of step S4 at least once;

[0014] S6. Cleaning after dyeing: Wash the dyed leather with clean water until the water color remains unchanged;

[0015] S7. Chrome tanning: Chrome tanning is performed on the cleaned and dyed leather.

[0016] S8. Finishing: Neutralizing, fatliquoring, drying and finishing the tanned leather.

[0017] Preferably, in step S1, the indigo mud is prepared through the following steps:

[0018] Harvest the stems and leaves of Polygonum tinctorium, and ferment them in piles to make cakes;

[0019] The extract is obtained by soaking the cake or fresh round-leaved Polygonum indica in water;

[0020] Add 5% to 12% of quicklime by mass to the leachate, stir to oxidize, let stand to settle, and collect the precipitate to obtain indigo mud.

[0021] Preferably, in step S2, the pH value after deacidification is 6.5 to 7.5.

[0022] Preferably, in step S4, the immersion time is 5 to 15 minutes.

[0023] Preferably, in step S5, the number of times the dyeing and oxidation are repeated is 8 to 12.

[0024] Preferably, in step S7, the amount of chromium powder used in the chromium tanning treatment is 3.5% to 8% of the initial weight of sheepskin, and the pH value at the tanning endpoint is 3.8 to 4.2.

[0025] Preferably, step S7 is based on twice the initial mass of the sheepskin, and the specific process is as follows:

[0026] Pickling: In an aqueous solution containing 0.5% pickling oil GLH and 8% sodium chloride, first add diluted formic acid, then add diluted sulfuric acid, controlling the endpoint pH to be 2.6 to 3.0, and treat overnight;

[0027] Tanning: Add 6% to 8% of chromium powder with an alkalinity of 33% to the pickled system and rotate for 300 minutes; then add 1% sodium formate and rotate for 30 minutes; finally, add sodium bicarbonate solution in portions to control the final pH to 3.8 to 4.2, then add hot water at 40°C to 50°C equivalent to 100% of the initial mass of the sheepskin, and continue to rotate for 300 minutes;

[0028] They rode horses and spent the night.

[0029] Preferably, a sheepskin indigo dyeing system comprises:

[0030] The raw material processing unit is used to deacidify sheepskin;

[0031] The dye solution preparation unit is equipped with a cold dyeing preparation module and a hot dyeing preparation module;

[0032] The dyeing and oxidation unit is equipped with a dyeing tank and an oxidation platform;

[0033] The tanning and finishing unit is used for chrome tanning and subsequent finishing processes on dyed and cleaned leather.

[0034] The control unit, connected to each unit, is used to control process parameters.

[0035] Preferably, a sheepskin leather product is made from an environmentally friendly leather dyeing method based on a combination of plant indigo and chrome tanning.

[0036] The beneficial effects of this invention are as follows:

[0037] The present invention provides an environmentally friendly leather dyeing method based on the combination of plant indigo and chrome tanning, which has the following significant advantages compared with the prior art:

[0038] By systematically quantifying key aspects such as indigo mud preparation, dye liquor ratio, oxidation cycles, and tanning parameters, traditional experience-based techniques are transformed into standardized processes that are detectable, controllable, and replicable, laying a technological foundation for the large-scale production of plant-dyed leather.

[0039] The "dye-then-tan" process allows indigo molecules to fully penetrate the leather fibers. Then, through the complexation of chromium ions with indigo during chrome tanning, colorfastness (such as resistance to rubbing and light) is significantly improved. The resulting leather has a uniform color and a soft feel, overcoming the problems of traditional plant-dyed leathers such as hardening and color fading.

[0040] By clearly defining the connection between dyeing, tanning, and finishing processes, a systematic control of the entire process can be achieved, avoiding damage to the dyeing effect or decline in leather performance caused by process conflicts, and ensuring product consistency and production efficiency.

[0041] Replacing synthetic dyes with natural plant indigo reduces the use and emission of toxic chemicals; optimizing the chrome tanning process controls the amount of chrome powder used and improves chrome absorption rate, thereby reducing heavy metal residues and environmental pollution, which meets the requirements of green and sustainable development.

[0042] Using the local specialty plant, Polygonum tinctorium, as the core raw material, and combining it with traditional dyeing techniques, we have built an integrated industrial chain encompassing planting, extraction, dyeing, and leather making, thereby increasing the added value of agricultural products and promoting regional economic development and cultural heritage.

[0043] This invention not only provides a complete process route, but also can be equipped with an automated dyeing system to achieve precise control of key processes, providing a reliable and scalable system solution for enterprises to implement green dyeing technology. Attached Figure Description

[0044] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0045] Figure 1 This is a process flow diagram of the present invention;

[0046] Figure 2 This is a schematic diagram of the steps in the preparation process of indigo mud in an embodiment of the present invention;

[0047] Figure 3 This is a schematic diagram of the dye solution preparation and dyeing oxidation process in an embodiment of the present invention;

[0048] Figure 4 This is a flowchart of the chrome tanning and finishing process in an embodiment of the present invention;

[0049] Figure 5 This is a schematic diagram of the structure of the sheep leather indigo dyeing system provided in an embodiment of the present invention. Detailed Implementation

[0050] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0051] Example 1: An environmentally friendly leather dyeing method based on the combination of plant indigo and chrome tanning

[0052] according to Figure 1 , Figure 2 , Figure 3 , Figure 4 As shown, this embodiment provides an environmentally friendly leather dyeing method based on the combination of plant indigo and chrome tanning. The specific steps are as follows:

[0053] I. Preparation of Indigo Paste

[0054] 1. Raw material processing: In summer, the round-leaved indigo plant, unique to Butuo County in Liangshan, is harvested. Its stems and leaves are rich in blue sap. The harvested indigo is piled up and fermented for about 6 months to make honeycomb-shaped cakes for long-term preservation.

[0055] 2. Extraction and precipitation: Soak the cake of ginseng or fresh Polygonum tinctorium in water for 2 to 3 days until the extract turns greenish-blue. Let the extract stand to settle for 2 to 3 days.

[0056] 3. Blueing and Oxidation: Quicklime is added during the precipitation process, at a rate of 8% to 10% of the leachate mass, compared to the traditional ratio of about 5%. Thorough stirring allows the liquid to oxidize upon contact with air, causing the leachate to change from bluish-green to blue, forming a precipitate.

[0057] 4. Collection of Indigo Paste: Collect the sediment to obtain a paste-like or muddy indigo paste. Tests have shown that under optimized conditions, such as fermentation at 37℃, approximately 360.45 mg of refined indigo can be obtained from 100 grams of fresh Polygonum tinctorium leaves, with an extraction rate of approximately 0.36%. Traditional indigo paste contains impurities and moisture, resulting in a slightly lower actual indigo content.

[0058] II. Material Preparation

[0059] Leather material: sheep's tan leather, pH approximately 2.8 to 3.2.

[0060] Dyeing materials:

[0061] Cold dyeing reducing agent: sulfate, such as sodium sulfate.

[0062] Cold dyeing auxiliary agent: sodium carbonate.

[0063] Reducing agent for heat dyeing: glucose.

[0064] Thermal dyeing auxiliary agent: calcium hydroxide.

[0065] Tanning materials: chromium powder with an alkalinity of 33%, formic acid, sulfuric acid, sodium chloride, soda ash, sodium formate, baking soda, GLH tanning oil, etc.

[0066] III. Preparation of Deacidified Sheepskin

[0067] Based on the initial weight of sheepskin, recorded as 100%, deacidification treatment is performed:

[0068] After deacidification, the pH of the leather should be controlled between 6.5 and 7.5.

[0069] IV. Dye Solution Preparation

[0070] Before dyeing, the amount of indigo mud to be used needs to be calculated based on the weight of the leather. The amount used is 1%-10% of the weight of the deacidified sheepskin. The specific amount is adjusted according to the volume of the dye solution, that is, the amount of water required to immerse the leather.

[0071] 1. Preparation of cold dyeing solution:

[0072] Weigh out the indigo mud and add 20 times the amount of water at a temperature of about 25°C.

[0073] Add 0.3 times the amount of sodium carbonate as a dyeing aid and 0.1 times the amount of sulfate as a reducing agent.

[0074] Continue stirring until the dye solution turns yellow-green, which takes approximately 20 to 40 minutes. The dye solution should be used within 24 hours of preparation.

[0075] 2. Preparation of hot dyeing solution:

[0076] Weigh out indigo mud, 0.75 times the amount of calcium hydroxide as a dyeing aid, and 0.75 times the amount of glucose as a reducing agent.

[0077] Prepare 20 times the amount of water, heat it to 50℃, add the above ingredients, and stir well.

[0078] Continue heating until boiling, then turn off the heat and cool to approximately 40°C, removing any surface foam. The dye solution should be used within 24 hours of preparation.

[0079] V. Dyeing Process

[0080] 1. Immersion: After draining the deacidified sheepskin, immerse it in the dye solution, gently turning it over to ensure that the leather is completely submerged. The immersion time is 10 minutes.

[0081] 2. Oxidation: Remove the leather, gently squeeze out the dye, and lay it flat in the air to oxidize. Once the surface has completely changed from yellowish-green to blue, turn it over and continue oxidizing.

[0082] 3. Repeat staining: Repeat the above staining and oxidation steps a total of 10 times to obtain a uniform and deep blue color.

[0083] 4. Washing: After dyeing, rinse repeatedly with clean water until the color no longer changes.

[0084] VI. Chrome Tanning

[0085] The initial weight of sheepskin is used as the baseline, denoted as 100%.

[0086] VII. Post-processing

[0087] After chrome tanning, the following treatments are performed in sequence:

[0088] 1. Neutralization: Adjust the pH of the leather to 5.0 to 5.5 with a neutralizing agent.

[0089] 2. Fat Addition: Adding synthetic fat additives or natural oils improves the softness and feel of the leather.

[0090] 3. Drying: Allow to air dry naturally in a well-ventilated environment or dry at a low temperature.

[0091] 4. Finishing: Softening, polishing, ironing and other mechanical finishing processes are carried out to obtain the finished leather.

[0092] VIII. Technological Advantages

[0093] 1. The process is quantifiable and replicable: By clarifying key process parameters such as the preparation of indigo mud, the formulation of dye solution, the number of dyeing times, and tanning parameters, the intangible cultural heritage techniques have been standardized and industrialized.

[0094] 2. Balancing dyeing and performance: The "dye-then-tan" process avoids the problem of leather hardening after dyeing, while the chrome tanning agent forms a complex with indigo molecules, significantly improving color fastness.

[0095] 3. Green and environmentally friendly: It partially replaces synthetic dyes with plant-based indigo, reducing chemical pollution; it optimizes the chrome tanning process, reducing the amount of chrome used and emissions.

[0096] 4. Industrial chain collaboration: Establish an industrial chain for the planting, extraction, dyeing, and leather making of Polygonum tinctorium to promote the protection of local intangible cultural heritage and rural revitalization.

[0097] IX. System Implementation

[0098] according to Figure 5 As shown, the present invention can also be implemented through the following system:

[0099] Raw material processing unit: used for the deacidification of sheep's sauerkraut.

[0100] Dye liquor preparation unit: It is equipped with two configuration modules for cold dyeing and hot dyeing, and supports automatic metering and stirring.

[0101] Dyeing and oxidation unit: includes dyeing tank and oxidation platform, supports timed turning and oxidation monitoring.

[0102] Tanning and finishing unit: integrates functions such as chrome tanning, neutralization, fatliquoring, drying, and finishing.

[0103] Control unit: Based on PLC or industrial computer, it realizes real-time control and recording of process parameters.

[0104] 10. Product Examples

[0105] The sheep leather produced using the above method has a warm, natural indigo blue color, a soft feel, and high color fastness, namely, dry abrasion ≥4, wet abrasion ≥3, and lightfastness ≥4. It is suitable for high-end leather goods, clothing, home furnishings, and other fields, and has both ecological and cultural added value.

[0106] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. An environmentally friendly leather dyeing method based on the combination of plant indigo and chrome tanning, characterized in that, Includes the following steps: S1. Raw material preparation: Prepare indigo mud, sheep's tannin bark, and dyes and chemicals including reducing agents and dyeing auxiliaries, which are extracted from Polygonum rotundum through fermentation. S2. Deacidification treatment: The sheepskin is deacidified until the pH value is neutral to obtain deacidified sheepskin; S3. Dye solution preparation: Based on the quality of the deacidified sheepskin, prepare either a cooling dye solution or a hot dye solution. The preparation of the cold dyeing solution includes: weighing 1% to 10% of the weight of the deacidified sheepskin indigo mud, dissolving it in 20 times the weight of the indigo mud in water, adding 30% of the weight of the indigo mud in sodium carbonate as a dyeing aid and 10% of the weight of the indigo mud in sulfate as a reducing agent, and stirring at 20°C to 30°C until the dyeing solution turns yellow-green. The preparation of the hot dyeing solution includes: weighing 1% to 10% of the weight of the deacidified sheepskin indigo mud, 75% of the weight of the indigo mud indigo mud as a dyeing aid, and 75% of the weight of the indigo mud indigo mud as a reducing agent, dissolving it in water at a temperature of 40°C to 60°C at 20 times the weight of the indigo mud, stirring evenly, boiling, and cooling to 40°C for later use; S4. Immersion and Oxidation: Immerse the deacidified sheepskin in the dye solution prepared in step S3, and after taking it out, oxidize it in the air until the surface changes completely from yellow-green to blue. S5. Repeat staining: Repeat the staining and oxidation process of step S4 at least once; S6. Cleaning after dyeing: Wash the dyed leather with clean water until the water color remains unchanged; S7. Chrome tanning: Chrome tanning is performed on the cleaned and dyed leather. S8. Finishing: Neutralizing, fatliquoring, drying and finishing the tanned leather.

2. The method according to claim 1, characterized in that, In step S1, the indigo mud is prepared through the following steps: Harvest the stems and leaves of Polygonum tinctorium, and ferment them in piles to make cakes; The extract is obtained by soaking the cake or fresh round-leaved Polygonum indica in water; Add 5% to 12% of quicklime by mass to the leachate, stir to oxidize, let stand to settle, and collect the precipitate to obtain indigo mud.

3. The method according to claim 1, characterized in that, In step S2, the pH value after deacidification is 6.5 to 7.

5.

4. The method according to claim 1, characterized in that, In step S4, the immersion time is 5 to 15 minutes.

5. The method according to claim 1, characterized in that, In step S5, the immersion and oxidation are repeated 8 to 12 times.

6. The method according to claim 1, characterized in that, In step S7, the amount of chromium powder used in the chromium tanning process is 3.5% to 8% of the initial weight of sheepskin, and the pH value at the tanning endpoint is 3.8 to 4.

2.

7. The method according to claim 1, characterized in that, Step S7 is based on twice the initial mass of the lanolin, and the specific process is as follows: Pickling: In an aqueous solution containing 0.5% pickling oil GLH and 8% sodium chloride, first add diluted formic acid, then add diluted sulfuric acid, controlling the endpoint pH to be 2.6 to 3.0, and treat overnight; Tanning: Add 6% to 8% of chromium powder with an alkalinity of 33% to the pickled system and rotate for 300 minutes; then add 1% sodium formate and rotate for 30 minutes; finally, add sodium bicarbonate solution in portions to control the final pH to 3.8 to 4.2, then add hot water at 40°C to 50°C equivalent to 100% of the initial mass of the sheepskin, and continue to rotate for 300 minutes; They rode horses and spent the night.

8. A sheepskin indigo dyeing system for implementing the method of any one of claims 1-7, characterized in that, include: The raw material processing unit is used to deacidify sheepskin; The dye solution preparation unit is equipped with a cold dyeing preparation module and a hot dyeing preparation module; The dyeing and oxidation unit is equipped with a dyeing tank and an oxidation platform; The tanning and finishing unit is used for chrome tanning and subsequent finishing processes on dyed and cleaned leather. The control unit, connected to each unit, is used to control process parameters.

9. A sheepskin leather product, characterized in that, Made by the environmentally friendly leather dyeing method based on the combination of plant indigo and chrome tanning as described in any one of claims 1-7.

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