Method for dyeing cashmere fabric by using tannic acid

Abstract

The invention relates to a method for dyeing cashmere fabric by using tannic acid, which comprises the following steps: S1, a pretreatment step: putting cashmere loose fibers into a dyeing container, adding soft water for wetting, then adding a prepared mordant, heating and preserving heat, and then discharging pretreatment liquid; s2, a cleaning step: soft water is introduced into the dyeing container, and cleaning liquid is discharged after washing; s3, dyeing: adding soft water into a dyeing container, adjusting the pH value according to the obtained color, then adding a prepared tannic acid dyeing solution, heating and carrying out heat preservation treatment, and then discharging the dyeing solution; and S4, post-treatment: washing the dyed cashmere loose fibers with clear water at room temperature, and drying the washed cashmere loose fibers. According to the method for dyeing the cashmere fabric with the tannic acid, different colors are obtained by changing the pH value of dyeing according to the characteristic that the tannic acid dyeing liquid is sensitive to acid and alkali, and the tannic acid dyeing liquid belongs to microbial dye and further has the advantages of being short in production period, environmentally friendly, renewable and biodegradable.

Description

Technical Field

[0001] The present disclosure relates to the technical field of cashmere fabric dyeing, and more specifically, to a method for dyeing cashmere fabric by using tannic acid. Background Art

[0002] In the dye industry, traditional chemical synthetic dyes are derived from petroleum or coal tar and are known for their bright colors, good wash and light fastness, and easy mass production, but they cause significant pollution to the environment. With the improvement of environmental awareness, companies have begun to explore more environmentally friendly alternatives, and plant dyes have attracted attention as a natural source option. However, plant dyes have problems such as unstable raw material supply, complex production process, high cost, and insufficient color consistency, which limit their widespread application.

[0003] As an emerging solution, microbial dyes are naturally produced through the metabolic activities of specific microorganisms such as bacteria, fungi and algae, showing many advantages: short production cycle, low environmental impact, strong renewability and complete biodegradability. Using fermentation technology, high-quality microbial dyes can be produced quickly under a controlled environment to ensure color consistency and stability. In addition, with the help of genetic engineering and metabolic engineering technologies, microorganisms can be optimized to increase dye production and broaden the color range to meet the needs of the modern dyeing industry and promote the goals of green chemistry and sustainable development. Summary of the invention

[0004] In order to solve the problems existing in the prior art, the present invention provides a method for dyeing cashmere fabric using tannic acid.

[0005] The present invention provides a method for dyeing cashmere fabric using tannic acid, comprising: S1, pre-treatment step: place the cashmere loose fiber in a dyeing container, add soft water with a bath ratio of 1:10-1:30 to moisten it, then add the mordant, start the pump to circulate for 10-20 minutes, after the mordant is evenly mixed, raise the temperature to 80℃-100℃, keep warm for 30-40 minutes, and then discharge the pre-treatment liquid; S2, cleaning step: once again, add soft water to the dyeing container of S1, start the pump to circulate for 10-20 minutes, and then discharge the cleaning liquid; S3, dyeing step: add soft water with a bath ratio of 1:10-1:30 to the dyeing container of S2, start the pump to keep circulating, adjust the pH value according to the color to be obtained, then add tannic acid dye solution, raise the temperature to 80℃-100℃, keep warm for 40min-60min and then discharge the dye solution; S4, post-processing step: washing and drying the cashmere loose fibers obtained after dyeing in S2 at room temperature.

[0006] In one embodiment of the present disclosure, the S1 pre-treatment step further includes weighing 1% owf-3% owf ferrous sulfate and dissolving it with 60-80° C. soft water to obtain a mordant.

[0007] In one embodiment of the present disclosure, the S3 dyeing step further includes weighing 1% owf-3% owf tannic acid, dissolving it with 60-80° C. soft water to obtain a tannic acid dye solution.

[0008] In one embodiment of the present disclosure, the tannic acid is produced by a fermentation method.

[0009] In one embodiment of the present disclosure, the pH value is adjusted by adding glacial acetic acid or soda ash to the dyeing container.

[0010] In one embodiment of the present disclosure, when black dyeing is required, glacial acetic acid is added to the dyeing container to adjust the pH value to 5.5.

[0011] In one embodiment of the present disclosure, when gray dyeing is required, glacial acetic acid is added to the dyeing container to adjust the pH value to 4.

[0012] In one embodiment of the present disclosure, when brown dyeing is required, soda ash is added to the dyeing container to adjust the pH value to 7.

[0013] In one embodiment of the present disclosure, in the S3 dyeing step, after adjusting the pH value, it is necessary to start the pump circulation for 10-20 minutes, and then add the tannic acid dye solution after the pH value stabilizes.

[0014] In one embodiment of the present disclosure, the cashmere bulk fibers obtained after drying in the S4 post-treatment step are tested for color fastness.

[0015] The present disclosure provides a method for dyeing cashmere fabric using tannic acid, which utilizes the acid-base sensitivity of tannic acid dyeing solution to obtain different colors by changing the pH value of dyeing. The tannic acid dyeing solution is a microbial dye, which also has the advantages of short production cycle, environmental protection, renewable and biodegradable.

[0016] Other features and advantages of the present disclosure will become apparent from the following detailed description of exemplary embodiments of the present disclosure with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

[0018] Figure 1 The present invention provides a process flow chart of a method for dyeing cashmere fabric using tannic acid according to an embodiment of the present invention. DETAILED DESCRIPTION

[0019] In order to make the invention purpose, technical solution and beneficial technical effect of the present application clearer, the present application is described in detail below in conjunction with specific embodiments. It should be understood that the embodiments described in this specification are only for explaining the present application, not for limiting the present application.

[0020] For simplicity, only some numerical ranges are explicitly disclosed herein. However, any lower limit can be combined with any upper limit to form an unambiguous range; and any lower limit can be combined with other lower limits to form an unambiguous range, and any upper limit can be combined with any other upper limit to form an unambiguous range. In addition, although not explicitly stated, each point or single value between the range endpoints is included in the range. Thus, each point or single value can be combined as its own lower limit or upper limit with any other point or single value or with other lower limits or upper limits to form an unambiguous range.

[0021] In the description of this article, it should be noted that, unless otherwise specified, "above" and "below" are inclusive of the number itself, and "several" in "one or several" means two or more.

[0022] The above-mentioned summary of the invention of the present application is not intended to describe each disclosed embodiment or each implementation in the present application. The following description more specifically illustrates exemplary embodiments. In many places throughout the application, guidance is provided by a series of examples, which can be used in various combinations. In each example, enumeration is only used as a representative group and should not be interpreted as exhaustive.

[0023] The present disclosure provides a method for dyeing cashmere fabric by using tannic acid, comprising: S1, a pre-treatment step: placing cashmere loose fibers in a dyeing container, adding soft water to moisten the fabric, adding a prepared mordant, heating and heat preservation, and then discharging the pre-treatment liquid; S2, a cleaning step: passing soft water into the dyeing container, and discharging the cleaning liquid after washing; S3, a dyeing step: adding soft water to the dyeing container, adjusting the pH value according to the color to be obtained, and then adding a prepared tannic acid dye solution, heating and heat preservation treatment, and then discharging the dye solution; S4, a post-treatment step: washing the cashmere loose fibers obtained after dyeing with clean water at room temperature and drying them.

[0024] The present disclosure provides a method for dyeing cashmere fabric with tannic acid. The method utilizes the acid-base sensitivity of tannic acid dyeing solution to obtain different colors by changing the pH value of dyeing. The tannic acid dyeing solution is a microbial dye. Compared with traditional plant dyes, the production cycle of tannic acid dyes is greatly shortened. High-quality tannic acid dyes can usually be efficiently produced in just a few days. The entire production process has little impact on the environment, greatly reducing the use of chemical reagents and the discharge of wastewater. The dyeing solution and by-products can be naturally degraded and will not cause long-term pollution to the ecosystem.

[0025] like Figure 1 As shown, the present disclosure provides a method for dyeing cashmere fabric using tannic acid, comprising the following steps: S1, pre-treatment step: place the cashmere loose fiber in a dyeing container, add soft water with a bath ratio of 1:10-1:30 to moisten it, then add the mordant, start the pump to circulate for 10-20 minutes, after the mordant is evenly mixed, raise the temperature to 80℃-100℃, keep warm for 30-40 minutes, and then discharge the pre-treatment liquid; S2, cleaning step: once again, add soft water to the dyeing container of S1, start the pump to circulate for 10-20 minutes, and then discharge the cleaning liquid; S3, dyeing step: add soft water with a bath ratio of 1:10-1:30 to the dyeing container of S2, start the pump to keep circulating, adjust the pH value according to the color to be obtained, then add tannic acid dye solution, raise the temperature to 80℃-100℃, keep warm for 40min-60min and then discharge the dye solution; S4, post-processing step: washing and drying the cashmere loose fibers obtained after dyeing in S2 at room temperature.

[0026] Specifically, S1, pre-treatment step: Place the cashmere loose fiber in a dyeing container, add soft water with a bath ratio of 1:10-1:30, and the reason for choosing soft water is that the calcium and magnesium ions contained in hard water will react with the mordant, resulting in uneven dyeing and affecting the dyeing effect. Turn on the circulation pump at the bottom of the dyeing container to circulate the water in the dyeing container for 10-20 minutes to ensure that the fiber is completely wetted by water. During this process, the air on the fiber surface is discharged, and the water can fully penetrate into the fiber, thereby preparing for subsequent mordanting and dyeing.

[0027] After the fiber is fully wetted, add an appropriate amount of mordant to the dyeing container. The amount of mordant should be adjusted according to the specific dyeing requirements and the weight of the fiber, usually 1%-3% of the fiber weight. Turn on the circulation pump and continue stirring for 10-20 minutes to ensure that the mordant is evenly distributed on the fiber surface. The mordant combines with the active groups on the fiber surface to form a stable chemical bond, providing a good basis for the subsequent adsorption of dyes.

[0028] After the mordant is evenly distributed, the temperature in the dyeing container begins to be gradually increased until it reaches 80℃ to 100℃. The heating speed should be moderate. Too fast may cause uneven heating of the fiber and affect the dyeing quality, while too slow will prolong the process time and increase energy consumption. Once the temperature reaches the set value, it enters the insulation stage, which lasts for 30 minutes to 40 minutes. During this period, high temperature helps the mordant to better penetrate into the cashmere fiber and promote the chemical reaction between the dye molecules and the fiber, so as to obtain the ideal dyeing effect. Since cashmere fiber is relatively fragile, a temperature higher than 100℃ may damage the fiber structure, destroy the protein chain in the fiber, cause the fiber to become brittle, lose elasticity, and even break, which seriously affects the quality and feel of the final product. In addition, too high a temperature will increase the risk of equipment failure and may cause safety accidents. However, a temperature below 80℃ will significantly reduce the rate of chemical reaction, slow down the reaction between the mordant and the protein or other components in the fiber, and ultimately make the dye molecules and the fiber not tightly bound, resulting in poor dyeing effect, the color may appear light or uneven, and easy to fade. Then keep the heat for 30-40 minutes to ensure that the mordant fully forms a strong chemical bond with the cashmere loose fiber. Although too long a heat preservation time can ensure that the mordant and dye have enough time to react with the fiber, it will also bring a series of adverse effects. For example, the protein in the cashmere fiber may denature or degrade, making the fiber fragile, losing elasticity, or even breaking, seriously affecting the quality and feel of the final product. Too short a heat preservation time will result in incomplete chemical reaction and uneven dyeing, so the temperature and heat preservation time need to be strictly controlled.

[0029] Furthermore, the purpose of the S2 cleaning step is to remove the mordant and other impurities remaining on the surface of the cashmere loose fibers to prevent these substances from interfering with the subsequent dyeing process. At the same time, cleaning can also reduce color spots or unevenness that may occur during the dyeing process.

[0030] Based on this, the treated cashmere bulk fiber is dyed, and soft water with a bath ratio of 1:10 to 1:30 is added to the dyeing container of S2 to ensure that the water temperature is moderate (about 40℃-50℃). According to the required dyeing effect, glacial acetic acid or soda reagent is used to adjust the pH value of the dyeing solution. The pH value of the dyeing solution is monitored in real time using a pH meter to ensure that it is stable within the set range. According to the required dyeing depth, an appropriate amount of tannic acid dye solution is calculated and added. The amount of tannic acid is usually 1%owf-3%owf (owf represents the mass percentage based on the weight of wool or cashmere). Excessive addition of tannic acid is likely to cause waste, and adding too little will cause the problem of lighter color after dyeing. Therefore, adding an appropriate amount of tannic acid has an important influence on the dyeing results, and the specific amount should be adjusted according to the dyeing requirements. After adding the tannic acid dye solution, start the circulation pump to evenly distribute the dye solution in the dyeing container, ensure that each fiber can fully contact the dye solution and react with the mordant layer on the fiber surface to form a stable chemical bond, and gradually increase the temperature in the dyeing container to 80℃-100℃. The specific temperature can be adjusted according to the dyeing requirements. Under high temperature conditions, the combination reaction of tannic acid and fiber is faster and more stable. Keep the temperature for 40-60 minutes to ensure that the tannic acid dye fully forms a strong chemical bond with the fiber. The longer heat preservation time can ensure the color yield of the fiber and avoid the occurrence of color spots or unevenness.

[0031] Furthermore, the cashmere loose fibers dyed in the S3 dyeing step are washed multiple times with clean water at room temperature, each washing time is 5-10 minutes, and the washing process can ensure that the residues on the fiber surface are thoroughly rinsed off. After washing with clean water, a centrifuge or drying equipment is used to remove excess water from the fiber to ensure that the fiber is dried evenly.

[0032] In one embodiment of the present disclosure, the S1 pre-treatment step further includes weighing 1% owf-3% owf ferrous sulfate and dissolving it with 60-80° C. soft water to obtain a mordant.

[0033] Specifically, according to the weight of the cashmere loose fiber, 1% owf to 3% owf of ferrous sulfate is accurately weighed as a mordant. Too much mordant may make the fabric stiff, affecting its softness and comfort. At the same time, if the mordant concentration is too high, it may cause uneven dyeing, spots or stripes. If the mordant concentration is insufficient, it will not fully enhance the combination of dye and fiber, which may result in poor dyeing effect, light color, and reduce the color fastness of the dyed fabric, which is easy to fade or discolor. Ferrous sulfate can enhance the bonding force between dye and fiber and improve the fastness of dyeing. Too much or too little mordant will lead to uneven dyeing in the end, so the quality of ferrous sulfate needs to be precisely controlled. Use soft water with a temperature between 60°C and 80°C to dissolve ferrous sulfate. Within this temperature range, ferrous sulfate can be dissolved more fully. This process requires slight stirring to accelerate dissolution and ensure that the mordant forms a uniform solution. When the mordant is completely dissolved, carefully add it to the dyeing container containing cashmere loose fiber and turn on the circulation pump to allow the mordant to fully contact the cashmere fiber, while also preventing the fiber from being entangled or damaged.

[0034] In one embodiment of the present disclosure, the S3 dyeing step further includes weighing 1% owf-3% owf tannic acid, dissolving it with 60-80° C. soft water to obtain a tannic acid dye solution.

[0035] Specifically, according to the weight of the cashmere bulk fiber to be dyed, accurately weigh 1% owf to 3% owf of tannic acid. Adding too much tannic acid can easily cause waste, while adding too little will cause the color to be lighter after dyeing. Therefore, adding an appropriate amount of tannic acid has an important influence on the dyeing result. Add the weighed tannic acid into soft water at a temperature of 60°C to 80°C and stir it thoroughly until it is completely dissolved. This temperature range helps to accelerate the dissolution process of tannic acid while avoiding the damage to the tannic acid structure caused by excessively high temperatures. Ensuring that the tannic acid is completely dissolved is crucial to obtaining uniform dyeing results.

[0036] In one embodiment of the present disclosure, the tannic acid is produced by a fermentation method.

[0037] Specifically, compared with the method of extracting tannic acid from plants, the preparation of tannic acid by fermentation is not only environmentally friendly, but also can produce high-quality and high-purity tannic acid products, which is particularly suitable for textile dyeing processes that have high requirements for naturalness and sustainability. For example, the characteristic of Bacillus subtilis to produce tannic acid (gallic acid) under specific conditions can be utilized, and starch, corn syrup powder, inorganic salts, etc. can be selected as fermentation raw materials, and tannic acid (gallic acid) can be obtained by aerobic fermentation under suitable temperature, pH value and aerobic conditions. Among them, starch, as the main carbon source, can provide energy for bacteria and build the carbon skeleton required for cell substances; corn syrup powder is rich in nitrogen sources, providing necessary amino acids and other nitrogen-containing compounds for bacterial growth; inorganic salts such as phosphates and magnesium sulfate maintain the ion balance in cells and promote enzyme activity. During the fermentation process, samples are taken regularly to analyze the tannic acid (gallic acid) content in the fermentation broth, as well as other key parameters such as glucose concentration, pH value, etc., in order to evaluate the fermentation effect and adjust the fermentation conditions in time. When the tannic acid (gallic acid) production reaches its peak, the fermentation is stopped and the fermentation broth is centrifuged or filtered to remove the bacteria and insoluble impurities to obtain a clarified fermentation broth containing tannic acid (gallic acid).

[0038] In one embodiment of the present disclosure, the pH value is adjusted by adding glacial acetic acid or soda ash to the dyeing container.

[0039] Specifically, in view of the acid-base sensitivity of the tannic acid (gallic acid) dye system, different color effects can be achieved by adding glacial acetic acid or soda ash to the dyeing container to adjust the pH value. During the entire dyeing process, a high-precision pH meter is used to monitor the changes in pH value in real time to ensure that each adjustment is within the expected range.

[0040] In one embodiment of the present disclosure, when black dyeing is required, glacial acetic acid is added to the dyeing container to adjust the pH value to 5.5.

[0041] Specifically, when black dyeing is required, glacial acetic acid is added to the dyeing container and the pH value is adjusted to 5.5. At this time, when the pH value is close to neutral or slightly acidic, the tannic acid molecules begin to form more complex polymers and react with ferrous ions to generate dark-colored complexes. This complex has a high light absorption capacity and therefore appears rich black.

[0042] In one embodiment of the present disclosure, when gray dyeing is required, glacial acetic acid is added to the dyeing container to adjust the pH value to 4.

[0043] Specifically, when gray dyeing is required, glacial acetic acid is added to the dyeing container and the pH value is adjusted to 4. At a lower pH value, the degree of protonation of the phenolic hydroxyl groups in the tannic acid molecules is higher, resulting in a weakened binding force with cellulose or other protein fibers, and less aggregation between the dye molecules, thus presenting a lighter gray color.

[0044] In one embodiment of the present disclosure, when brown dyeing is required, soda ash is added to the dyeing container to adjust the pH value to 7.

[0045] Specifically, when brown dyeing is required, soda ash is added to the dyeing container and the pH value is adjusted to 7. Under neutral conditions, the binding of tannic acid molecules to fibers is more stably, and the structure of the complex formed with ferrous ions is also changed, causing the color to change to brown. As the pH value increases, the protonation degree of tannic acid molecules decreases, and more phenolic hydroxyl groups are exposed, which enhances the binding force with ferrous ions. In addition, hydration under neutral conditions may also affect the structure of the complex, making it appear rich brown.

[0046] In one embodiment of the present disclosure, in the S3 dyeing step, after adjusting the pH value, it is necessary to turn on the pump for circulation for 10-20 minutes, and then add the tannic acid dye solution after the pH value stabilizes.

[0047] Specifically, after the pH value adjustment is completed, the pump needs to be turned on for a certain period of time to allow the dye solution to flow fully in the entire container. The circulation time is set to 10 to 20 minutes. The specific time depends on the size of the dyeing container and the amount of dye solution. This circulation time can effectively avoid the local pH value difference from affecting the dyeing effect.

[0048] In one embodiment of the present disclosure, the cashmere bulk fibers obtained after drying in the S4 post-treatment step are tested for color fastness.

[0049] Specifically, color fastness refers to the fastness of dyes on fiber materials, and is usually rated on a scale of 1 to 5, where level 1 indicates very poor color fastness, and the dyes are easy to fade or bleed; level 2 indicates poor color fastness, and the dyes fade slightly under conditions such as friction, washing or sweat; level 3 indicates general color fastness, and the dyes are not easy to fade under normal use conditions; level 4 indicates better color fastness, and the dyes basically do not fade under normal use and washing conditions; level 5 is the best color fastness, and the dyes do not fade under any conditions.

[0050] Based on this, the present application conducted a total of five color fastness tests, namely, color fastness to rubbing, color fastness to washing, color fastness to water, color fastness to light and color fastness to alkali sweat. Among them, color fastness to rubbing is an important indicator to measure the color retention ability of textiles under friction, which is usually divided into dry rubbing color fastness and wet rubbing color fastness; color fastness to washing is an important indicator to measure the color retention ability of textiles when washed in solutions such as soap; color fastness to water is an important indicator to measure the color retention ability of textiles after being soaked in clean water for a period of time and the color staining of adjacent fabrics; color fastness to light is an important indicator to measure the ability of textiles to maintain their original color under sunlight; color fastness to alkali sweat is an important indicator to measure the color retention ability of textiles and the color staining of adjacent fabrics after a certain period of time, temperature and pressure in alkaline sweat containing histidine.

[0051] The above five color fastness tests were carried out on the cashmere bulk fibers dyed by the present application, and the test results were all recorded in Table 1. It can be clearly seen that the five color fastnesses of the cashmere bulk fibers dyed by the present application can all reach the results of level 3 (the dye is not easy to fade under normal use conditions) or above, among which, except for a few indicators at level 3, most indicators can reach level 4 (the dye basically does not fade under normal use and washing conditions) or above. Obviously, after dyeing with tannic acid dye, the color fastness of the cashmere bulk fibers is better.

[0052] Table 1

[0053] The present disclosure provides a method for dyeing cashmere fabric with tannic acid. The method utilizes the acid-base sensitivity of tannic acid dyeing solution to obtain different colors by changing the pH value of dyeing. The tannic acid dyeing solution is a microbial dye. Compared with traditional plant dyes, the production cycle of tannic acid dyes is greatly shortened. High-quality tannic acid dyes can usually be efficiently produced in just a few days. The entire production process has little impact on the environment, greatly reducing the use of chemical reagents and the discharge of wastewater. The dyeing solution and by-products can be naturally degraded and will not cause long-term pollution to the ecosystem.

[0054] Embodiments of the present invention have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The selection of terms used herein is intended to best explain the principles of the embodiments, practical applications, or technical improvements in the marketplace, or to enable other persons of ordinary skill in the art to understand the embodiments disclosed herein. The scope of the present invention is defined by the appended claims.

Claims

1. A method for dyeing cashmere fabric using tannic acid, characterized in that: The following steps are involved: S1, pre-treatment step: place the cashmere loose fiber in a dyeing container, add soft water with a bath ratio of 1:10-1:30 to moisten it, then add the mordant, start the pump to circulate for 10-20 minutes, after the mordant is evenly mixed, raise the temperature to 80℃-100℃, keep warm for 30-40 minutes, and then discharge the pre-treatment liquid; S2, cleaning step: once again, add soft water to the dyeing container of S1, start the pump to circulate for 10-20 minutes, and then discharge the cleaning liquid; S3, dyeing step: add soft water with a bath ratio of 1:10-1:30 to the dyeing container of S2, start the pump to keep circulating, adjust the pH value according to the color to be obtained, then add tannic acid dye solution, raise the temperature to 80℃-100℃, keep warm for 40min-60min and then discharge the dye solution; S4, post-processing step: washing and drying the cashmere loose fibers obtained after dyeing in S2 at room temperature.

2. The method for dyeing cashmere fabric using tannic acid according to claim 1, characterized in that: The S1 pre-treatment step also includes weighing 1% owf-3% owf ferrous sulfate and dissolving it with 60-80° C. soft water to obtain a mordant.

3. The method for dyeing cashmere fabric using tannic acid according to claim 1, characterized in that: The S3 dyeing step also includes weighing 1% owf-3% owf tannic acid, dissolving it with 60-80° C. soft water to obtain a tannic acid dye solution.

4. The method for dyeing cashmere fabric using tannic acid according to claim 3, characterized in that: The tannic acid is produced by a fermentation method.

5. The method for dyeing cashmere fabric using tannic acid according to claim 1, characterized in that: Adjust the pH by adding glacial acetic acid or soda ash to the dye container.

6. The method for dyeing cashmere fabric using tannic acid according to claim 5, characterized in that: When black dyeing is required, add glacial acetic acid to the dyeing container and adjust the pH value to 5.

5.

7. The method for dyeing cashmere fabric using tannic acid according to claim 6, characterized in that: When gray dyeing is desired, add glacial acetic acid to the dyeing container to adjust the pH to 4.

8. The method for dyeing cashmere fabric using tannic acid according to claim 7, characterized in that: When brown dyeing is desired, add soda ash to the dyeing container and adjust the pH to 7.

9. The method for dyeing cashmere fabric using tannic acid according to claim 1, characterized in that: In the S3 dyeing step, after adjusting the pH value, it is necessary to start the pump circulation for 10-20 minutes, and then add the tannic acid dye solution after the pH value stabilizes.

10. The method for dyeing cashmere fabric using tannic acid according to claim 1, characterized in that: The color fastness of the cashmere bulk fibers obtained after drying in the S4 post-treatment step was tested.

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