Method for manufacturing ultra-thick microfiber leather by combining surface alkali treatment with steam box splitting

Abstract

The invention discloses a method for manufacturing ultra-thick microfiber leather by combining surface alkali treatment with steam box splitting, and belongs to the technical field of manufacturing of superfine fiber synthetic leather. The method aims to solve the problems of non-uniform splitting, stiff hand feeling, poor air permeability and high production cost of a traditional immersion tank type alkali deweighting splitting process. According to the key points of the technical scheme, the method comprises the following steps: firstly, preparing polyurethane impregnation slurry with specific viscosity, and carrying out impregnation and solidification treatment on microfiber grey cloth; then applying alkali liquor with specific concentration to the surface of the impregnated base cloth in a roller coating manner, then entering a steam box for splitting reaction, and finally washing and kneading to obtain a finished product. According to the method, surface alkali treatment and steam box splitting are combined, the splitting degree and uniformity are effectively controlled, and the obtained microfiber leather has the advantages of being large in thickness, soft and plump in hand feeling, free of void feeling and excellent in air and moisture permeability and wear resistance. The method is particularly suitable for manufacturing high-end bags, shoes, clothes, automotive interiors and other products with high requirements for thickness and touch feeling.

Description

Technical Field

[0001] This invention relates to the field of microfiber synthetic leather (microfiber leather) manufacturing technology, specifically to a method for preparing ultra-thick microfiber leather through surface alkali treatment combined with steam oven fiber opening. This method, by optimizing the alkali-reducing fiber opening process, significantly improves the thickness, feel, breathability, and mechanical properties of microfiber leather while reducing production costs, making it suitable for high-end bags, footwear, automotive interiors, and other fields. Background Technology

[0002] Microfiber synthetic leather uses island-island fiber nonwoven fabric as the base material, impregnated with polyurethane slurry, and wet-coagulated to form a composite material. Then, through fiber-opening processes (such as dissolution and alkali reduction methods), the island-island fibers are separated into microfibers. Finally, after finishing, a polymer material with a three-dimensional network structure is obtained. Its mechanical properties (such as tensile strength and tear strength) can reach three times that of natural leather, and it possesses characteristics such as abrasion resistance, cold resistance, and breathability. However, it suffers from problems such as poor dyeability, insufficient formability, stiff feel, and limited breathability and moisture permeability.

[0003] Currently, the fiber opening process for microfiber leather is mainly divided into two categories: Solvent-based fiber opening (e.g., toluene reduction): This method achieves fiber opening by dissolving the "sea" component (such as low-density polyethylene) in the sea-island fiber using an organic solvent. While this method can form a dense fiber structure, toluene is flammable and explosive, posing safety hazards, and is also a non-biodegradable substance that easily causes environmental pollution.

[0004] Liquid alkali fiber opening method: The base fabric is immersed in a concentrated alkali solution for overall fiber opening. However, this method is energy-intensive and produces a large amount of carbon emissions. Furthermore, excessive corrosion of the fibers by the alkali solution can easily lead to problems such as reduced strength of the base fabric, a hollow feel, and a rough suede texture. Especially for microfiber leather with a thickness greater than 1.5mm, traditional dip-soaking fiber opening method is difficult to control the reaction depth evenly, and it is easy to have excessive fiber opening on the surface layer and insufficient fiber opening in the inner layer, resulting in uneven base fabric structure and deterioration of physical properties.

[0005] To address these issues, existing technologies have explored various optimization solutions. For example, a combination of needle punching and spunlace technology can be used to improve the surface smoothness of the base fabric, or a novel coloring melt-spinning technology can be used to directly prepare colored fibers, reducing the need for post-dyeing processes. However, these methods still struggle to balance fiber opening efficiency with product feel: insufficient fiber opening results in incomplete fiber separation and a stiff base fabric; excessive fiber opening leads to significant polyurethane loss, creating a hollow feel and affecting abrasion resistance and breathability. Furthermore, the production of ultra-thick microfiber leather (e.g., thickness ≥ 2 mm) demands extremely high fiber opening uniformity, and existing processes cannot simultaneously meet the requirements of low cost, high efficiency, and product performance.

[0006] Therefore, there is an urgent need to develop a new green, low-consumption process that can precisely control the fiber opening depth in order to break through the technical bottlenecks in the feel, breathability and mechanical properties of ultra-thick microfiber leather. Summary of the Invention

[0007] In traditional microfiber leather manufacturing, alkali reduction fiber opening is mostly achieved through an immersion bath process, which has the following drawbacks: Poor fiber opening uniformity: Especially for ultra-thick base fabrics with a thickness of ≥1.5mm, alkali solution has difficulty penetrating into the interior, which can easily lead to excessive fiber opening in the surface layer and insufficient fiber opening in the inner layer, resulting in uneven base fabric structure and stiff hand feel. Performance degradation: Prolonged immersion in strong alkali can corrode fibers, leading to polyurethane loss, reducing the tear strength and abrasion resistance of the base fabric, and at the same time, uneven fiber opening can reduce air permeability and moisture permeability. Energy consumption and environmental protection issues: The immersion process requires a large amount of alkali solution and has a long reaction time, which increases the cost of wastewater treatment and does not meet the requirements of green manufacturing.

[0008] This invention solves the above problems by combining surface alkali treatment with steam oven fiber opening process, achieving efficient and uniform fiber opening of ultra-thick microfiber leather, while improving hand softness, mechanical strength and breathability.

[0009] In a first aspect, the present invention provides a method for manufacturing ultra-thick microfiber leather through surface alkali treatment combined with steam oven fiber splitting, characterized by comprising the following steps: (1) Preparation of impregnation slurry: Mix 54-58 parts by weight of ultra-soft polyurethane resin, 38-40 parts by weight of N,N-dimethylformamide, 0.5-1 parts by weight of water-based color paste and 5-8 parts by weight of wet-process protein leather additives, stir and filter to obtain an impregnation slurry with a viscosity of 5000-7000 cps; (2) Impregnation treatment: After drying the microfiber fabric, it is immersed in the impregnation slurry obtained in step (1) for pre-impregnation, then enters the coagulation tank for coagulation, and then is washed and dried to obtain the impregnated base fabric; (3) Alkali reduction fiber opening: Apply 40-50% alkali solution to the surface of the impregnated base fabric obtained in step (2) by roller coating, then place it in a steam oven at 85-95 ℃ for 20-40 minutes, and then wash, knead and cool to obtain the ultra-thick microfiber leather.

[0010] Based on the above technical solution, the present invention can be further improved as follows: Furthermore, in step (1), the ultra-soft polyurethane resin is a polyester-type polyurethane, and the wet-process protein leather additives include penetrants and leveling agents; the impregnating slurry is filtered through a 60-mesh filter.

[0011] Furthermore, in step (2), the thickness of the microfiber fabric is 1.5-2.0 mm, the basis weight is 400-500 g / m², the pre-impregnation time is 15-20 minutes, the linear velocity is 5-10 m / min, and the concentration of the DMF aqueous solution in the coagulation tank is 15%-16% and the temperature is 45-48 ℃.

[0012] Furthermore, in step (3), the alkaline solution is an aqueous solution of sodium hydroxide, which is prepared by mixing caustic soda flakes and water at a mass ratio of (15-18):(2-3); the coating amount of the alkaline solution on one side during roller coating is 20-30 g / m².

[0013] Furthermore, in step (3), the linear velocity during steaming is 7-10 m / min, and the processing time is 25-35 minutes.

[0014] Furthermore, in step (3), the water washing is carried out using a vibrating water washing machine with a water pressure of 0.3-0.5 MPa; the texturing finishing is carried out at 60-80 ℃ for 30-45 minutes.

[0015] Furthermore, in step (3), after the alkali reduction fiber opening treatment, the fiber separation degree of the microfiber leather reaches more than 90%, the thickness is not less than 1.9 mm, the air permeability is 3.5-4.0 L / dm²·min, and the moisture permeability is not less than 3000 g / m²·24h.

[0016] Secondly, the present invention also provides an ultra-thick microfiber leather made by the above-mentioned manufacturing method, characterized in that the thickness of the microfiber leather is not less than 1.9 mm, the tear strength is not less than 80 N, the compression elastic recovery rate is not less than 85%, and it has a soft feel and no hollowness.

[0017] Furthermore, the microfiber leather is suitable for high-end footwear, apparel, bags, or automotive interiors. Beneficial effects

[0018] Compared with the prior art, the present invention has the following outstanding advantages: 1. Significantly improved fiber opening uniformity: The surface is coated with alkaline solution and combined with the hot and humid environment of the steam oven, so that the fiber opening reaction gradually penetrates from the surface to the inside, avoiding insufficient fiber opening inside or excessive fiber opening on the surface. The SEM of the base fabric cross section shows that the single fiber separation degree reaches more than 90%, and a uniform microporous structure is formed between the fiber bundles.

[0019] 2. Optimization of mechanical properties and feel: The tear strength is 15%-20% higher than that of the traditional impregnation method (due to the enhanced cohesion and friction between fiber bundles). Compression elastic recovery rate ≥85%, giving the material superior resilience and fullness; After the textured treatment, the hardness (according to ISO7619 standard) is ≤50 ShoreC, achieving a soft texture for ultra-thick base fabric (≥1.9mm).

[0020] 3. Improved breathability and moisture permeability: The three-dimensional mesh structure formed by the open fiber increases the air permeability to 3.5-4.0L / dm²·min (test standard: ISO9237) and the moisture permeability to ≥3000g / m²·24h (test standard: JISL1099).

[0021] 4. Environmental and energy consumption advantages: The amount of alkali solution used is reduced by 30% (due to surface coating rather than overall immersion), and the reaction time in the steam oven is shortened to within 30 minutes, reducing energy consumption and wastewater treatment load.

[0022] The correspondence between technical solutions and their effects is shown in the table below:

[0023] This invention achieves a synergistic improvement in fiber opening uniformity, mechanical properties, and comfort of ultra-thick microfiber leather through the combination of the above technologies, and is especially suitable for high-end footwear and apparel, automotive interiors, and other fields with strict requirements for thickness and feel. Attached Figure Description

[0024] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0025] To make the technical means, creative features, objectives, and effects of this invention easier to understand, the invention is further described below with reference to specific embodiments. However, the following embodiments are merely preferred embodiments of this invention and not all of them. Other embodiments obtained by those skilled in the art based on the embodiments described herein without creative effort are all within the protection scope of this invention.

[0026] Example 1 A method for manufacturing ultra-thick, soft microfiber leather, such as Figure 1 As shown.

[0027] 1. Preparation of polyurethane slurry Weigh 54 parts by weight of ultra-soft polyurethane resin (Impranil DLN-SD manufactured by Bayer, solid content 35%), 38 parts by weight of N,N-dimethylformamide (DMF, industrial grade, purity ≥99.5%), 0.5 parts by weight of water-based black pigment (Flexobrite 500 from Degussa), and 5 parts by weight of wet-process protein leather auxiliaries (containing penetrant Triton X-100 and leveling agent BYK-331, mass ratio 3:2). Add the above components to a reaction vessel and stir at 300 rpm for 40 minutes. Then filter impurities through a 60-mesh filter to obtain an impregnating slurry with a viscosity of 6000±200 cps (measured using a Brookfield DV2T viscometer, rotor model LV-3, rotation speed 12 rpm, 25℃), and place it in a sealed container for later use.

[0028] 2. Impregnation and solidification of base fabric A 1.9 mm thick, 450 g / m² island-island fiber nonwoven fabric (island-island ratio 60:40, fiber fineness 0.15 dtex) was pre-dried at 100°C for 2 minutes using a heatsink to remove surface moisture. It was then introduced into an impregnation tank at a linear speed of 7 m / min, with the sizing agent temperature maintained at 25±2°C for a pre-impregnation time of 17 minutes. The impregnated fabric was immediately transferred to a coagulation tank with a DMF aqueous solution concentration of 15.5% (calibrated using a saccharimeter), a temperature of 46±1°C, and a coagulation time of 3 minutes. Afterward, it was rinsed with 40°C warm water for 5 minutes to remove residual DMF, and finally dried in a 110°C hot air oven for 10 minutes. After cooling to room temperature, the impregnated base fabric was obtained.

[0029] 3. Surface alkaline treatment and fiber opening in the steamer A solution of caustic soda (sodium hydroxide, purity ≥96%) and water was prepared at a mass ratio of 17:3 (mass concentration approximately 45%). The solution was then uniformly coated onto both sides of the impregnated base fabric using a metering roller coating device, with a coating weight of 25 g / m² on each side. Immediately after treatment, the base fabric was placed in a steam oven and treated for 30 minutes at 90±2℃ under saturated steam (linear speed 9 m / min) to fully hydrolyze the "sea" component (polyethylene) of the island fiber. After fiber opening, the base fabric was rinsed for 5 minutes in a high-frequency vibrating washing machine (frequency 50 Hz, water pressure 0.4 MPa) to remove the caustic soda and hydrolysis products.

[0030] 4. Post-treatment and performance characterization After washing, the base fabric is fed into a texturer and tumbled and softened at 70°C for 40 minutes. Then, it is shaped at 120°C for 2 minutes and cooled to obtain microfiber leather with a thickness of 2.05mm.

[0031] The product has been tested and found to have the following characteristics: Breathability: 3.8L / dm²·min (Test standard: ISO9237); Moisture permeability: 3200g / m²·24h (Test standard: JIS L1099B-1 method); Tear strength: 85N (Test standard: ISO4674); Tactile evaluation: The tactile evaluation by a panel of 5 experts confirmed that there was no hollowness and the fineness of the velvet was rated as 4.5 out of 5.

[0032] 5. Effect Comparison This embodiment avoids the problem of uneven fiber opening inside and outside the base fabric caused by the traditional impregnation method by combining surface alkali treatment with steam oven fiber opening. Scanning electron microscopy (SEM) shows that the fiber separation degree reaches 92%, and the polyurethane loss is reduced by 18% compared with the impregnation method, which significantly improves the mechanical properties and hand feel of the product.

[0033] Example 2 This embodiment provides a method for manufacturing ultra-thick and soft microfiber leather. The process steps are basically the same as those in Embodiment 1, but some adjustments are made to the specific parameters of polyurethane slurry preparation, impregnation, and alkali reduction fiber opening, in order to further illustrate the technical breadth and effect stability of the present invention.

[0034] 1. Preparation of polyurethane slurry Weigh 58 parts by weight of ultra-soft polyurethane resin (same type as in Example 1), 40 parts by weight of N,N-dimethylformamide (DMF, industrial grade, purity ≥99.5%), 1.0 part by weight of water-based black pigment (same type as in Example 1), and 8 parts by weight of wet-process protein leather additive (composition same as in Example 1). Add the above components to a reaction vessel and stir at 350 rpm for 45 minutes. Then filter impurities through a 60-mesh filter to obtain an impregnating slurry with a viscosity of 6200±200 cps (test conditions same as in Example 1), and place it in a sealed container for later use.

[0035] 2. Impregnation and solidification of base fabric The same sea-island fiber nonwoven fabric substrate as in Example 1 (thickness 1.9 mm, weight 450 g / m²) was used. After pre-drying the substrate at 105°C for 2.5 minutes using an ironing wheel, it was introduced into the impregnation tank at a low linear speed of 5 m / min (the slurry temperature in the tank was maintained at 25 ± 2°C). The pre-impregnation time was controlled to be 20 minutes to ensure sufficient slurry penetration. The subsequent coagulation process was carried out at a DMF aqueous solution concentration of 16% and a temperature of 48°C, with a coagulation time of 3.5 minutes. Afterward, it was rinsed with 40°C warm water for 5 minutes and dried in a 115°C hot air oven for 12 minutes. After cooling to room temperature, the impregnated substrate was obtained.

[0036] 3. Surface alkaline treatment and fiber opening in the steamer A sodium hydroxide solution (purity ≥96%) was prepared by mixing caustic soda flakes and water at a mass ratio of 15:3 (mass concentration approximately 42%). The solution was then uniformly coated onto both sides of the impregnated base fabric using a metering roller coating device, with a coating weight of 28 g / m² on each side. After treatment, the base fabric was placed in a steam oven and treated at a slightly lower temperature of 85±2℃ for 40 minutes (linear speed 7 m / min) to achieve gentle yet thorough fiber opening. Following fiber opening, the base fabric was rinsed for 6 minutes in a high-frequency vibrating water washing machine (frequency 50 Hz, water pressure 0.4 MPa) to thoroughly remove residual alkali and hydrolysis products.

[0037] 4. Post-treatment and performance characterization After washing, the base fabric is fed into a texturer and tumbled and softened at 80°C for 35 minutes. Then, it is shaped at 125°C for 1.5 minutes and cooled to obtain microfiber leather with a thickness of 2.10mm.

[0038] The product has been tested and found to have the following characteristics: Breathability: 3.6L / dm²·min (Test standard: ISO9237); Moisture permeability: 3100g / m²·24h (Test standard: JIS L1099B-1 method); Tear strength: 88N (Test standard: ISO4674); Tactile evaluation: Through the expert panel's tactile assessment, it was confirmed that the fabric is soft and without any hollow feeling, and the fineness of the velvet surface is rated as 4.5 out of 5.

[0039] 5. Effect Description This embodiment successfully produced ultra-thick, highly breathable and moisture-permeable microfiber leather with an excellent hand feel by adjusting the slurry ratio (increasing resin content), reducing the impregnation line speed (extending impregnation time), and using a slightly lower alkali treatment temperature and a longer treatment time. This demonstrates that the manufacturing method of this invention has a certain degree of tolerance for process parameters, and different combinations of parameters for the key process steps (surface alkali treatment combined with steam oven fiber opening) can achieve the core beneficial effects of this invention, further proving the reliability and industrial application potential of this invention.

[0040] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples and are not intended to limit the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A manufacturing method of an ultra-thick and ultra-real microfiber leather by surface alkali treatment in combination with an opening of a steaming box, characterized by, Includes the following steps: (1) Preparation of impregnation slurry: Mix 54-58 parts by weight of ultra-soft polyurethane resin, 38-40 parts by weight of N,N-dimethylformamide, 0.5-1 parts by weight of water-based color paste and 5-8 parts by weight of wet-process protein leather additives, stir and filter to obtain an impregnation slurry with a viscosity of 5000-7000 cps; (2) Impregnation treatment: After drying the microfiber fabric, it is immersed in the impregnation slurry obtained in step (1) for pre-impregnation, then enters the coagulation tank for coagulation, and then is washed and dried to obtain the impregnated base fabric; (3) Alkali reduction fiber opening: Apply 40-50% alkali solution to the surface of the impregnated base fabric obtained in step (2) by roller coating, then place it in a steam oven at 85-95 ℃ for 20-40 minutes, and then wash, knead and cool to obtain the ultra-thick microfiber leather.

2. The manufacturing method according to claim 1, characterized in that, In step (1), the ultra-soft polyurethane resin is polyester polyurethane, and the wet-process protein leather additives include penetrants and leveling agents; the impregnating slurry is filtered through a 60-mesh filter.

3. The manufacturing method according to claim 1, characterized in that, In step (2), the thickness of the microfiber fabric is 1.5-2.0 mm and the basis weight is 400-500 g / m²; the pre-impregnation time is 15-20 minutes and the linear velocity is 5-10 m / min; the concentration of the DMF aqueous solution in the coagulation tank is 15%-16% and the temperature is 45-48 ℃.

4. The manufacturing method according to claim 1, characterized in that, In step (3), the alkaline solution is an aqueous solution of sodium hydroxide, which is prepared by mixing caustic soda flakes and water at a mass ratio of (15-18):(2-3); the coating amount of the alkaline solution on one side during roller coating is 20-30 g / m².

5. The manufacturing method according to claim 1, characterized in that, In step (3), the linear velocity during steaming is 7-10 m / min and the processing time is 25-35 minutes.

6. The manufacturing method according to claim 1, characterized in that, In step (3), the water washing is carried out using a vibrating water washing machine with a water pressure of 0.3-0.5 MPa; the texturing finishing is carried out at 60-80 ℃ for 30-45 minutes.

7. The manufacturing method according to claim 1, characterized in that, In step (3), after the alkali reduction fiber opening treatment, the fiber separation degree of the microfiber leather reaches more than 90%, the thickness is not less than 1.9 mm, the air permeability is 3.5-4.0 L / dm²·min, and the moisture permeability is not less than 3000 g / m²·24h.

8. An ultra-thick microfiber leather produced by the manufacturing method according to any one of claims 1-7, characterized in that, The microfiber leather has a thickness of not less than 1.9 mm, a tear strength of not less than 80 N, a compression elastic recovery rate of not less than 85%, and a soft feel without any hollowness.

9. The ultra-thick microfiber leather according to claim 8, characterized in that, The microfiber leather is suitable for high-end footwear, apparel, bags, or automotive interiors.

Images