Tanning extract based on metal complex modification as well as preparation method and application of tanning extract

Abstract

The invention relates to the technical field of leather chemical industry and leather manufacturing, in particular to a tannin extract based on metal complex modification and a preparation method and application of the tannin extract based on metal complex modification. 15 to 25 parts of aluminum sulfate; 5-10 parts of lanthanum sulfate / cerium sulfate; 0.5-2 parts of sulfuric acid; 0.5 to 2 parts of citric acid; and 500 to 600 parts of water. The modified tannin extract which is light in color, good in dispersity and excellent in tanning property is prepared through the steps of oxidative degradation, chelating masking, metal synergistic complexing and the like. The method is simple in process, environmentally friendly, efficient and suitable for industrial production, and the problems that a traditional vegetable tanning agent is low in whiteness and poor in light resistance stability when applied to white leather, and traditional metal tanning leather is hard in hand feeling, insufficient in light resistance and the like are effectively solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of leather chemical and leather manufacturing technology, in particular to a tannin based on metal complex modification and its preparation method and application. BACKGROUND

[0002] White leather is widely used in high-end clothing, shoes, bags, furniture and automotive interiors due to its white color, simple and elegant style. However, it is a technical challenge to achieve and maintain the whiteness, excellent hand feeling and physical properties of leather.

[0003] Traditional white leather processing relies on inorganic tanning agents such as aluminum salt, zirconium salt or aldehyde tanning agent for main tanning or retanning. These methods can achieve certain whiteness, but have the following inherent defects: 1) The leather is often hard, lacking the fullness and elasticity brought by vegetable tanning agents; 2) Poor water washing performance, generally low shrinkage temperature (usually below 80℃), limiting its application range; 3) Poor light resistance, prone to yellowing or discoloration under long-term exposure to ultraviolet light, affecting product life and appearance.

[0004] Vegetable tanning agent (tannin) is a natural polyphenol extracted from plants. As a traditional tanning agent and retanning filler, it can combine with collagen fibers to give leather excellent fullness, tightness and good filling performance. However, natural tannin has some outstanding problems such as dark color (usually red-brown to dark green), poor cold water solubility and dispersion stability, slow penetration, and easy oxidation and darkening due to its molecular structure containing a large number of phenolic hydroxyl groups and conjugated systems. These shortcomings seriously limit the application of tannin in light-colored leather, especially white leather with high whiteness and light resistance requirements.

[0005] In order to overcome the defects of natural tannin, some modification attempts have been made in the prior art. For example, sulfite treatment is a common method to improve the water solubility of tannin by introducing sulfonic groups to increase hydrophilicity, but the modification degree is limited and the color of the product is still dark, which cannot meet the high standard whiteness requirement of white leather. Simple sulfite treatment can significantly improve the dispersibility, but it will cause the color to deepen; the combined modification process of sulfite and oxalic acid decolorization achieves a good balance between dispersibility, color and tannability, but it mainly focuses on the modification of tannin itself and does not deeply explore how to structure the modified tannin with specific metal salt and systematically apply it to the multi-stage tanning process of white leather to achieve performance synergistic multiplication. SUMMARY

[0006] In view of the deficiencies of the prior art, the present application provides a tannin extract modified based on a metal complex as well as a preparation method and application thereof, which can maximize the inherent excellent filling property and fullness of vegetable tanning agents, fundamentally solve the problems of deep color and poor dispersion, and endow white leather with high and persistent whiteness, excellent soft hand feeling, high shrinkage temperature and excellent light resistance through synergistic effect with specific metal tanning agents.

[0007] The present application is realized by the following technical solutions: The present application provides a tannin extract modified based on a metal complex, which is prepared from raw materials including the following components by mass: Oak tannin extract 100 parts; aluminum sulfate 15-25 parts; lanthanum sulfate / cerium sulfate 5-10 parts; sulfuric acid 0.5-2 parts; citric acid 0.5-2 parts; hydrogen peroxide 1-2 parts; water 500-600 parts.

[0008] Further, the modified tannin extract is a light yellow to off-white powder, the whiteness L value of a 10% aqueous solution thereof is greater than or equal to 80, and the precipitation rate after standing for 24 hours under the condition of pH 4-5 is less than 5%.

[0009] Through the unique modification process of oxidative degradation, chelation masking and metal synergistic complexation, the dark chromophores (such as conjugated system and quinone structure) in the tannin extract molecules are successfully destroyed, and a significant lightening or even bleaching effect is achieved, which is the basis for applying the modified tannin extract to high-performance white leather. The low precipitation rate indicates that a ternary complex synergistic crosslinking network of “aluminum-rare earth-tannin” is formed through “stepwise coordination and bridge connection”, and this structure synergistically greatly enhances the stability of the modified tannin extract molecules, so that a highly stable colloidal dispersion system can be formed under weakly acidic conditions. High dispersion stability means that the modified tannin extract can uniformly penetrate into the leather fibers during leather tanning, avoiding local over-tanning or insufficient penetration caused by precipitation, thereby ensuring that the finished leather has a full and uniform hand feeling.

[0010] A preparation method of a tannin extract modified based on a metal complex, comprising the following steps: S1, dissolving and pretreating: mixing oak tannin extract with water, heating to complete dissolution to obtain a tannin extract solution, and then sequentially adding citric acid and hydrogen peroxide; S2, aluminum salt preliminary complexation: adding aluminum sulfate to the tannin extract solution obtained in step S1 to perform complexation reaction under acidic conditions; S3, lanthanum sulfate / cerium sulfate complexation: slowly adding lanthanum sulfate / cerium sulfate to the reaction system obtained in step S2 to generate a ternary complex of “aluminum-rare earth-tannin”, and the solution is light cream white without precipitation; S4, stabilization treatment: adding citric acid to the reaction system obtained in step S3 to adjust the pH of the system to 3.0-4.0; S5, post-processing: cooling, filtering and drying the reaction product obtained in step S4 to obtain the metal bate complex modified bate.

[0011] In step S1, solid bate (mainly composed of tannin and other polyphenols) that may have intermolecular aggregation is fully dispersed and dissolved in hot water to form a uniform and reactive bate molecular solution. The temperature is controlled at 60-70°C to accelerate dissolution and avoid self-oxidation or degradation of the bate caused by excessively high temperature. 0.3-0.5 parts of citric acid is added to remove Fe³⁺ / Mn²⁺ impurities in the reaction system and avoid the formation of a colored complex to stabilize the whiteness of the light-colored bate. 0.8-1.2 parts of 30% hydrogen peroxide is slowly added to control the pH at 4.0-4.5 and gently degrade the tannin macromolecules, ensuring the complexing ability of the bate with metal ions and avoiding color deepening caused by polymerization.

[0012] In step S2, aluminum sulfate is hydrolyzed to generate polynuclear hydroxy aluminum ions (such as [Al6(OH) 12 ] 6 ⁺), and Al³⁺ forms a "single aluminum-bate" complex with the phenolic hydroxyl and carboxyl groups of tannin. At this time, the electron cloud distribution of the tannin molecule is changed, and the conjugated system is destroyed, further lightening the color.

[0013] In step S3, La³⁺ / Ce³⁺ is inserted into the remaining coordination vacancies of the "aluminum-bate" complex and forms a stronger coordination bond with the phenolic hydroxyl groups of tannin, while serving as a "bridge" to connect adjacent "aluminum-bate" complexes, forming a three-dimensional crosslinked network.

[0014] A processing method of high-performance white leather, using white wet skin as raw material, sequentially including pretreatment, retanning filling, fatliquoring, dyeing, drying and finishing processes, the retanning filling process includes using 6-10% of the uniform leather mass of metal bate complex modified bate as a retanning filler.

[0015] By using a new type of modified bate that is essentially compatible with white leather, the obstacles to the application of plant tannins to white leather are fundamentally overcome; by utilizing the multiple reactivity of the modified bate, a multi-level and stable crosslinked network is constructed with collagen fibers, thereby simultaneously achieving fullness, high heat resistance and high strength.

[0016] As preferred, the white wet skin has a thickness of 1.2-1.6 mm, and is neutralized to pH 5.0-5.5 after pretreatment.

[0017] A thickness of 1.2~1.6mm is considered medium-thick raw leather. This thickness range ensures that the finished leather has a certain body and strength, while also allowing sufficient time for the modified tannin, other retanning agents, and fatliquoring agents mentioned in claim 4 to penetrate evenly throughout the entire cross-section of the leather. By neutralizing to pH 5.0-5.5, the collagen fibers become positively charged, generating a strong electrostatic attraction between them and the negatively charged retanning agents. This greatly promotes the rapid and uniform penetration and bonding of modified tannin and other materials into the leather fibers, avoiding problems such as surface over-tanning (excessive surface bonding, insufficient internal filling) and uneven penetration caused by charge repulsion. This is key to achieving deep filling and high absorption rate.

[0018] Furthermore, the retanning and filling process is a multi-stage retanning process, which includes the following steps in sequence: First stage: Add metal tannin complex modified tannin to the pretreated leather blank and rotate for 60 minutes; Second stage: Add 3-5% aluminum tanning agent by weight of the evenly shaved leather, and rotate for 40 minutes; Third stage: Add 4-8% acrylic resin tanning agent by weight of the shaved leather, and rotate for 30 minutes; Fourth stage: Add 2-4% of the weight of the leveled leather to a white synthetic tanning agent and rotate for 20 minutes; The pH of the system was then adjusted to 4.0-4.2, the temperature was raised to 45°C and rotated for 30 minutes to fix the system, and finally it was washed with water.

[0019] In the first stage, modified tannin binds to collagen fibers through hydrogen bonds and preliminary coordination bonds, establishing a three-dimensional network framework between the fibers, providing the leather with fundamental fullness, elasticity, and body. In the second stage, aluminum tanning agent binds to unsaturated coordination sites in the modified tannin molecules already bound to the fibers in the first stage, and to carboxyl groups on the collagen fibers, forming a more complex and stable collagen fiber-modified tannin-aluminum ion multi-component complex cross-linked network. This cross-linking greatly enhances the stability of the collagen fiber structure, directly resulting in a significant increase in the leather's shrinkage temperature. In the third stage, acrylic resin tanning agent forms a continuous, soft, elastic film on and between the fiber surfaces. The resin tanning agent effectively neutralizes the stiffness often found in pure metal tanned leather, giving the leather excellent softness and toughness. In the fourth stage, the white synthetic tanning agent has a relatively small molecular weight, exhibiting good dispersion and bleaching effects, further optimizing the grain smoothness, compensating for any minor defects, and through its own whitening effect and optical properties, giving the leather a brighter visual whiteness.

[0020] Furthermore, during the fatliquoring process, 8-12% of fish oil fatliquoring agent by weight of the shaved leather is added.

[0021] Fish oil fatliquoring agents can give leather a full, moist, soft and oily feel. This dosage range ensures that the leather obtains sufficient and uniform softness, which, together with the fullness provided by modified tannin and the elasticity provided by resin tanning agents, creates a high-quality "soft and full" feel.

[0022] White leather with a whiteness L value ≥85, shrinkage temperature ≥80℃, tear strength ≥40 N / mm, and lightfastness ≥4.

[0023] Compared with the prior art, the present invention has the following significant advantages: I. Modified tannin exhibits excellent performance: Light color: Through the synergistic effects of oxidative degradation, chelation masking, and metal complexation, the original dark chromophores of tannin are effectively destroyed, and the product color changes from the reddish-brown of natural tannin to light yellow or even off-white, laying the foundation for the preparation of white leather. The whiteness L value of a 10% aqueous solution is not less than 80, fundamentally solving the core problem that plant tannin cannot be used for white leather due to its excessively dark color.

[0024] Excellent dispersion stability: The "aluminum-rare earth-tannin" ternary complex synergistic cross-linking network formed by "stepwise coordination and bridging" enables the modified tannin to dissolve rapidly in water and form a stable colloidal dispersion system that is not prone to precipitation, thus ensuring the uniformity of the tanning process and the whiteness stability during use.

[0025] Enhanced tanning performance: The formed Al / rare earth / tannin multi-component complex retains the multi-point hydrogen bonding ability of plant tannins and collagen fibers, providing excellent filling and fullness; it also introduces the coordination crosslinking of metal ions, with Al³⁺ and rare earth forming coordination bonds with fibers, significantly enhancing the tanning effect and heat resistance. The sulfonic acid groups bring excellent dispersibility, resulting in a significant tanning synergistic effect, good filling properties, and full leather.

[0026] II. The white leather has excellent overall quality: Long-lasting white color: Modified tannin itself is light in color, and when combined with aluminum tanning agents and white synthetic tanning agents, it gives the leather a high degree of whiteness. The metal complex structure is stable and not easily oxidized, with a light resistance of 4-5, and it does not easily yellow with long-term use.

[0027] Soft and full-bodied feel: Modified tannin provides basic fullness, while acrylic resin tanning agent imparts excellent softness and elasticity, overcoming the shortcomings of traditional metal tanned leather being stiff and resulting in a comfortable feel.

[0028] Improved physical and mechanical properties: Multi-component complex cross-linking enhances the strength of the collagen fiber network, giving the finished leather higher tear strength (up to 45 N / mm and above) and shrinkage temperature (up to 84℃ and above).

[0029] Improved environmental friendliness and economic efficiency: Tannin modification has enabled partial replacement of chromium tanning agents, reducing the total amount of chromium salts used and lowering the environmental pollution load. Furthermore, utilizing tannin, a renewable resource, aligns with the trend of green chemistry development.

[0030] The processing method of this invention has a clear flow and well-defined parameters, making it easy to implement on existing leather production lines. It can be widely applied to the manufacturing of various white leather products such as clothing leather, shoe upper leather, and bag leather. It successfully solves the long-standing industry technical bottlenecks that have restricted the application of plant tannin in high-end white leather, such as its dark color, poor dispersion, and the hard feel and insufficient light resistance of traditional white leather. Ultimately, it produces high-quality white leather that exhibits excellent visual, tactile, and physical properties, resulting in significant overall benefits. Attached Figure Description

[0031] Figure 1 This is a color comparison diagram of the solutions of the original tannin sample (left) and the metal complex modified tannin sample (right) in Example 1 of the present invention.

[0032] Figure 2 This is the backscattered spectrum of the tannin sample in Example 1 of the present invention.

[0033] Figure 3 This is the backscattered spectrum of the metal complex modified tannin in Example 1 of the present invention.

[0034] Figure 4 The color comparison diagram shows the white leather sample (4, 6, and 8 are three equilibrium samples tanned with metal complex modified tannin) prepared in Example 2 of this invention, and the samples tanned with rubber tannin (1), rubber tannin / white synthetic tanning agent (2), rubber tannin / acrylic resin tanning agent (3), conventional aluminum tanning agent (5), and rubber tannin / aluminum tanning agent / acrylic resin tanning agent.

[0035] Figure 5 The white leather sample obtained in Example 2 of this invention is compared with white leather processed by conventional aluminum tanning process. Detailed Implementation

[0036] To clearly illustrate the technical features of this solution, the following detailed implementation method will be used to describe the solution.

[0037] Example 1: A method for preparing tannin based on metal complex modification includes the following steps: S1. Dissolution and Pretreatment: In a reactor equipped with a stirrer and a heater, add 500 kg of deionized water and 100 kg of tannin, stir, heat to 65°C, and maintain until the tannin is completely dissolved; add 0.3 kg of citric acid and stir for 20 minutes; slowly add 1.0 kg of 30% hydrogen peroxide, control the pH at 4.0~4.5, and react at 55°C for 60 minutes. S2, Preliminary complexation of aluminum salt: Add 25 kg of aluminum sulfate to the tannin solution obtained in step S1 in two portions, with an interval of 40 minutes between each addition, and react at 65°C for 90 minutes. S3, Lanthanum sulfate / Cerium sulfate complexation: Slowly add 5 kg of lanthanum sulfate / cerium sulfate (La³⁺:Ce³⁺=1:1) to the reaction system obtained in step S2, and react at 55℃ for 120 minutes to generate an “aluminum-rare earth-tannin” ternary complex. The solution is light milky white and there is no precipitate. S4. Stabilization treatment: Add 0.5 kg of sulfuric acid to the reaction system obtained in step S3 to adjust the pH of the system to 3.5, and then add 0.3 kg of citric acid to improve the stability of storage and application. S5. Post-treatment: Dry the reaction mixture at a low temperature of 60~65℃ for 4~6 hours, controlling the moisture content to ≤8%, to obtain approximately 115 kg of light milky white powdered modified tannin product.

[0038] A color comparison diagram of the solutions of tannin (left) and metal complex modified tannin (right) in Example 1 of this invention is shown below. Figure 1 The backscattered spectra of tannin (original sample) and tannin modified with metal complex are shown in the figures below. Figure 2 and Figure 3 .

[0039] Figure 2 The mid-spectral density exhibits a broad peak shape and strong scattering intensity, indicating significant particle aggregation or phase separation in the original sample. This suggests that natural tannin has strong intermolecular forces and readily forms large molecular aggregates, consistent with its description of "dark color and poor dispersibility" in the product manual.

[0040] Figure 3The narrower peak shape, weaker scattering intensity, and more uniform distribution in the mid-spectral spectrum indicate that the modified particles have a smaller size, significantly improved dispersibility, and enhanced system uniformity. This change stems from the stepwise metal complexation process during modification: aluminum ions initially complex and break intermolecular hydrogen bonds, while rare earth ions (lanthanum / cerium) further bridge to form an "aluminum-rare earth-tannin" ternary complex, inhibiting particle aggregation. The nanoscale dispersion system enhances light scattering and improves visual whiteness; simultaneously, the small-sized particles are less prone to sedimentation, explaining the low precipitation rate. Furthermore, the absence of abnormal peaks in the spectrum indicates complete metal complexation and no free metal salt precipitation, consistent with the description in Example 1 that "the solution is light milky white with no precipitation."

[0041] Comparative analysis shows that the color and stability of tannin modified with metal complexes are significantly improved compared to the original tannin. The modified tannin exhibits a more uniform molecular distribution, supporting the formation of ternary complexes. The modification process successfully broke the aggregated structure of tannin, achieving uniform complexation at the molecular level. Figures 2 to 3 The evolution of tannin directly reflects the transformation process from "aggregated state to uniform complexed state," highlighting the creativity of metal synergistic complexation. After modification, tannin changes from a multi-aggregated state to a uniformly dispersed state, and the changes in microstructure are highly consistent with the improvement in macroscopic properties (whiteness, dispersibility, tanning properties).

[0042] Example 2: Processing of high-performance white leather: Raw materials and chemicals (based on 100kg of evenly shaved, wet blue cowhide, 1.4mm thick): Modified tannin (prepared in Example 1): 8 kg; Aluminum tanning agent (commercial product, Al2O3 content ≥10%): 4 kg; Acrylic tanning agent (commercial product): 6 kg; White synthetic tanning agent (sulfones, commercial product): 3 kg; Commercially available fish oil fattening agent (sulfonated vegetable oil): 10 kg; Nonionic emulsifier: 0.8 kg; A method for processing high-performance white leather, comprising: X1. Pretreatment: Place the wet blue cowhide in a drum and wash it with 200% (based on the weight of the evenly shaved leather) room temperature water for 10 minutes, then drain. Add 150% water (30℃), add 1.5% neutralizing tannin (or baking soda), rotate for 60 minutes, adjust the pH of the system to 5.2, and wash with water.

[0043] X2. Retanning: liquor ratio 1.8, temperature 38℃.

[0044] The retanning and filling process is a multi-stage retanning process, which includes the following steps in sequence: Add 8 kg of modified tannin and rotate for 60 minutes.

[0045] Add 4 kg of aluminum tanning agent and rotate for 40 minutes.

[0046] Add 6 kg of acrylic resin tanning agent and rotate for 30 minutes.

[0047] Add 3 kg of white synthetic tanning agent and rotate for 20 minutes.

[0048] Adjust the pH to 4.1 using 1% sodium formate in two separate applications, slowly raise the temperature to 45°C, and rotate for 30 minutes.

[0049] Drain and wash with 200% water (35℃) for 10 minutes.

[0050] X3. Fat addition: liquid ratio 2.0, temperature 52℃.

[0051] Add 10 kg of commercially available fish oil fattening agent and 0.8 kg of nonionic emulsifier. Stir for 40 minutes.

[0052] X4. Drying and finishing: Remove from the drum and let stand overnight; vacuum dry at 70℃ for 2 minutes, then hang to dry until completely dry. Then, perform vibration softening (vibration frequency 800 times / minute, time 3 minutes) and pass-through ironing (temperature 80℃, pressure 100 bar).

[0053] Finally, measurements and grading were performed to obtain the finished white leather product.

[0054] The physicochemical properties of the white leather product obtained in Example 2 were tested and compared with those of conventional samples processed using conventional methods (without using the modified tannin of this invention). Figure 4 As shown, the white leather samples (3 balanced samples 4, 6, and 8) prepared in Example 2 of this invention exhibit a uniform and bright white color; the comparative samples tanned with rubber tannin (1), rubber tannin / white synthetic tanning agent (2), rubber tannin / acrylic resin tanning agent (3), conventional aluminum tanning agent (5), and rubber tannin / aluminum tanning agent / acrylic resin tanning agent show relatively dull colors and insufficient whiteness.

[0055] The white leather sample obtained in Example 2 of this invention was compared with white leather processed by conventional aluminum tanning process. The specific comparison results are as follows: Figure 5 As shown.

[0056] The comparative results show that the test data fully demonstrates that the white leather prepared by the modified tannin and processing method provided by this invention is significantly superior to traditional aluminum-tanned white leather in terms of whiteness, thermal stability, mechanical strength, light resistance, and subjective feel, exhibiting excellent overall performance.

[0057] Example 3: A method for preparing tannin based on metal complex modification includes the following steps: S1. Dissolution and Pretreatment: In a reactor equipped with a stirrer and a heater, add 600 kg of deionized water and 100 kg of tannin, stir, raise the temperature to 65°C, and maintain until the tannin is completely dissolved; add 1.0 kg of citric acid and stir for 20 minutes; slowly add 2.0 kg of 30% hydrogen peroxide, control the pH to 4.0~4.5 with sulfuric acid, and react at 55°C for 60 minutes. S2, Preliminary complexation of aluminum salt: Add 15 kg of aluminum sulfate to the tannin solution obtained in step S1 in two portions, with an interval of 40 minutes between each addition, and react at 65°C for 90 minutes. S3, Lanthanum sulfate / Cerium sulfate complexation: Slowly add 10 kg of lanthanum sulfate / cerium sulfate (La³⁺:Ce³⁺=1:1) to the reaction system obtained in step S2, and react at 55℃ for 120 minutes to generate an “aluminum-rare earth-tannin” ternary complex. The solution is light milky white and there is no precipitate. S4. Stabilization treatment: Add 2 kg of sulfuric acid to the reaction system obtained in step S3 to adjust the pH of the system to 3.5, and then add 1.0 kg of citric acid to improve the stability of storage and application. S5. Post-treatment: Dry the reaction mixture at a low temperature of 60~65℃ for 4~6 hours, controlling the moisture content to ≤8%, to obtain approximately 120 kg of light milky white powdered modified tannin product.

[0058] Example 4: A method for preparing tannin based on metal complex modification includes the following steps: S1. Dissolution and Pretreatment: In a reactor equipped with a stirrer and a heater, add 550 kg of deionized water and 100 kg of tannin, stir, raise the temperature to 65°C, and maintain until the tannin is completely dissolved; add 0.6 kg of citric acid and stir for 20 minutes; slowly add 1.5 kg of 30% hydrogen peroxide, control the pH to 4.0~4.5 with sulfuric acid, and react at 55°C for 60 minutes. S2, Preliminary complexation of aluminum salt: Add 20 kg of aluminum sulfate to the tannin solution obtained in step S1 in two portions, with an interval of 40 minutes between each addition, and react at 65°C for 90 minutes. S3, Lanthanum sulfate / Cerium sulfate complexation: Slowly add 8 kg of lanthanum sulfate / cerium sulfate (La³⁺:Ce³⁺=1:1) to the reaction system obtained in step S2, and react at 55℃ for 120 minutes to generate an “aluminum-rare earth-tannin” ternary complex. The solution is light milky white and there is no precipitate. S4. Stabilization treatment: Add 1.5 kg of sulfuric acid to the reaction system obtained in step S3 to adjust the pH of the system to 3.5, and then add 0.6 kg of citric acid to improve the stability of storage and application. S5. Post-treatment: Dry the reaction mixture at a low temperature of 60~65℃ for 4~6 hours, controlling the moisture content to ≤8%, to obtain approximately 118 kg of light milky white powdered modified tannin product.

[0059] The above description is not limited to the examples given above. Technical features not described in this invention can be implemented by or using existing technologies, and will not be elaborated here. The above embodiments and accompanying drawings are only used to illustrate the technical solutions of this invention and are not intended to limit this invention. This invention has been described in detail with reference to preferred embodiments. Those skilled in the art should understand that any changes, modifications, additions or substitutions made by those skilled in the art within the scope of this invention do not depart from the spirit of this invention and should also fall within the scope of protection of the claims of this invention.

Claims

1. A tannin modified based on a metal complex, characterized in that: It is prepared by reacting raw materials comprising the following parts by weight: 100 parts of tannin; 15-25 parts of aluminum sulfate; 5-10 parts of lanthanum sulfate / cerium sulfate; 0.5-2 parts of sulfuric acid; 0.5-2 parts of citric acid; 1-2 parts of hydrogen peroxide; 500-600 parts of water.

2. The tannin modified based on a metal complex according to claim 1, characterized in that: The modified tannin is a pale yellow to off-white powder. Its 10% aqueous solution has a whiteness L value ≥80, and the precipitation rate is less than 5% after standing for 24 hours under pH 4~5 conditions.

3. A method for preparing tannin based on metal complex modification as described in any one of claims 1 to 2, characterized in that: Includes the following steps: S1. Dissolution and pretreatment: Mix tannin with water and heat until completely dissolved to obtain a tannin solution; then add citric acid and hydrogen peroxide in sequence to control the pH of the system to 4.0~4.

5. S2, Preliminary complexation of aluminum salts: Add aluminum sulfate to the tannin solution obtained in step S1 and carry out a complexation reaction under acidic conditions; S3, Lanthanum sulfate / Cerium sulfate complexation: Lanthanum sulfate / Cerium sulfate is slowly added to the reaction system obtained in step S2 to form an "aluminum-rare earth-tannin" ternary complex. The solution is light milky white and there is no precipitate. S4. Stabilization treatment: Add citric acid to the reaction system obtained in step S3 to adjust the pH of the system to 3.0~4.0; S5. Post-processing: Cool, filter and dry the reaction product obtained in step S4 to obtain metal tannin complex modified tannin.

4. The method for preparing tannin based on metal complex modification according to claim 3, characterized in that: In step S2, the temperature of the complexation reaction is maintained at 60~70℃ and the pH is maintained at 3.5~4.

5.

5. The method for preparing tannin based on metal complex modification according to claim 3, characterized in that: In step S3, the temperature of the complexation reaction is maintained at 50~55℃ and the pH is maintained at 3.5~4.

5.

6. A method for processing high-performance white leather, using wet white leather as raw material, comprising the following steps in sequence: pretreatment, retanning and filling, fatliquoring, dyeing, drying and finishing, characterized in that: The retanning and filling process includes using 6-10% by weight of the shaving leather, of the metal tannin complex modified tannin as described in claim 1 or 2, as a retanning filler.

7. The processing method for high-performance white leather according to claim 6, characterized in that: The retanning and filling process is a multi-stage retanning process, which includes the following steps in sequence: First stage: Add metal tannin complex modified tannin to the pretreated leather blank and rotate for 60 minutes; Second stage: Add 3-5% aluminum tanning agent by weight of the evenly shaved leather, and rotate for 40 minutes; Third stage: Add 4-8% acrylic resin tanning agent by weight of the shaved leather, and rotate for 30 minutes; Fourth stage: Add 2-4% of the weight of the leveled leather to a white synthetic tanning agent and rotate for 20 minutes; The pH of the system was then adjusted to 4.0-4.2, the temperature was raised to 45°C and rotated for 30 minutes to fix the system, and finally it was washed with water.

8. The processing method for high-performance white leather according to claim 7, characterized in that: During the fatliquoring process, 8-12% of fish oil fatliquoring agent by weight of the shaved leather is added.

9. A high-performance white leather processed by the processing method of any one of claims 7 to 9.

10. The high-performance white leather according to claim 9, characterized in that: White leather with a whiteness L value ≥85, shrinkage temperature ≥80℃, tear strength ≥40 N / mm, and lightfastness ≥4.

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