Method for increasing the yield of sheepskin suitcase leather and sheepskin suitcase leather

Abstract

The application provides a method for increasing the size of sheepskin suitcase leather and sheepskin suitcase leather, and the method comprises a preparation section, a tanning section and a finishing section, and the innovation is that a ternary retanning system composed of modified chestnut tannin, phenol sulfone synthetic tanning agent and ethylenediamine tetramethylene phosphonic acid sodium with a ratio of 2.5:2.5:1 is used in the retanning process, and polyurethane size increasing agent and alkyl glycoside fiber swelling agent are added, and step-by-step agent adding and gradient temperature rising mode are used; meanwhile, the neutralization, fatliquoring and post-finishing processes are optimized, and moderate stretching and low-temperature setting are used. The size of the sheepskin suitcase leather prepared by the method increases by 6%-11%, the part difference is reduced from more than 15% in the traditional process to not more than 10%, the tear strength is greater than or equal to 30 N / mm, the softness is less than or equal to 40 N·cm, there is no split surface or loose surface, the chromium consumption is reduced by 25%, the method meets the requirements of the EU REACH regulation, the comprehensive cost increase is not more than 5%, and the method has a wide application prospect.

Description

Technical Field

[0001] This invention belongs to the technical field of leather preparation technology, specifically relating to a method for improving the sizing rate of sheepskin bag leather and the sheepskin bag leather itself. Background Technology

[0002] In sheepskin bag production, the "size gain rate" (the increase in the area of ​​the finished leather relative to the area of ​​the raw hide) is a core indicator for measuring the economic efficiency of the process. Under traditional processes, sheepskin (especially mixed sheepskin / lambskin) generally has a low size gain rate (2-5%) due to its natural characteristics, and sometimes even shrinks in size, which is manifested in the following aspects.

[0003] First, the fiber network is loose. The collagen fibers in sheepskin are loosely arranged, and after soaking in water or ash, the fibers swell unevenly, easily resulting in localized excessive swelling or shrinkage, which restricts subsequent stretching.

[0004] Second, there is a significant difference in size between different areas. The fiber density difference between the back and abdomen can reach 30-50%. Traditional processes have not been optimized for this, resulting in uneven size increases in different areas, with a difference of more than 15%.

[0005] Third, the process causes significant damage. Excessive liming or deliming, or tanning shrinkage, can fix the fiber structure and reduce the potential for increased length. Studies have shown that for every 1% increase in length increase, raw hide loss can be reduced by 0.8% to 1.2%. Existing processes struggle to balance uniform fiber extension, adaptation to regional differences, and low process damage, necessitating a systematic solution.

[0006] The existing technology has the following main problems: Insufficient uniformity: Traditional processes use only soaking or tanning conditions, which cannot solve the problems of loose sheepskin fibers and differences in texture between different parts of the hide; Lack of damage control: High chromium content or excessive plant tannins lead to fiber cross-linking fixation, limiting the potential for length increase; Environmental limitations: Relying on a single chrome tanning system makes it difficult to meet the requirements of green manufacturing.

[0007] Therefore, there is an urgent need to develop a preparation method that can effectively improve the sizing rate of sheepskin bags, reduce part differences, minimize process damage, and is environmentally friendly. Summary of the Invention

[0008] To address the aforementioned technical problems, this invention proposes a method and a sheepskin bag leather that improves the sizing rate. This method solves the problems in the prior art where traditional processes cannot coordinate the expansion differences between dense and loose fiber areas, result in uneven sizing due to uniform parameters, have a difference of more than 15% between different parts, and cause excessive cross-linking to fix the fiber structure, thereby reducing the softness and physical properties of the finished product.

[0009] In a first aspect, the present invention provides the following technical solution: a method for improving the sizing rate of sheepskin bags, comprising: S1. The raw sheepskin is subjected to pre-soaking in water, main soaking in water, flesh removal, degreasing, alkali coating / rolling alkali to remove hair, liming / re-liming, deliming, softening, and acid soaking to obtain acid naked skin; S2. The acid-treated bare leather is subjected to chrome tanning to obtain wet blue leather; S3. The blue wet leather is sequentially subjected to water squeezing, wet shaving, retanning, neutralization, dyeing, and fatliquoring to obtain wet raw leather. S4. The wet raw leather is subjected to wet drying pretreatment, drying, rehumidification and mechanical softening, and dry finishing in sequence to obtain the finished leather; In step S3, the retanning process includes: adding a length-enhancing agent, which is a polyurethane length-enhancing agent, to the drum at a dosage of 3-5% of the oven-dry weight of the wet blue leather; using a ternary retanning system, which is composed of modified chestnut tannin, sulfone phenolic synthetic tanning agent, and sodium ethylenediaminetetramethylenephosphonate in a mass ratio of 2.5:2.5:1, and the total dosage of the ternary retanning system is 13-14% of the oven-dry weight of the wet blue leather; the retanning process adopts a step-by-step addition and gradient heating mode, first adding the ternary retanning system, holding at 55°C for 60 minutes, then adding the length-enhancing agent and fiber swelling agent, raising the temperature to 58-60°C, and continuing to rotate for 40-50 minutes, maintaining the pH value at 5.0-5.3 throughout the process, and the liquor ratio at 1:2.8.

[0010] Compared with existing technologies, the beneficial effects of this invention are as follows: First, in terms of the increase in length, through the physical filling and hydrogen bonding of the polyurethane lengthening agent, combined with the improvement of fiber dispersion and swelling space by the ternary retanning system, and the appropriate loosening of collagen fibers by the fiber swelling agent, the length increase of the finished leather is increased by 3-8 percentage points compared with the traditional process, reaching 6-11%, effectively reducing the loss of raw hides; Second, through the optimization of the neutralization process (temperature 38-40℃, pH...), the increase in length of the finished leather is significantly improved. The gradient heating mode in steps 5.8–6.2) and the retanning process allows the length-extending agent and retanning agent to penetrate evenly into the fiber gaps, significantly improving the regional differences between the back and abdomen. The regional difference is reduced from over 15% in traditional processes to no more than 10%, greatly improving the utilization rate of the finished product. Simultaneously, the sheepskin bag leather prepared by this invention exhibits excellent physical properties, with a tear strength ≥30 N / mm, softness ≤40 N·cm, and no cracking or loosening, fully meeting the requirements for bag leather use. Furthermore, this invention uses a ternary retanning system composed of modified chestnut tannin, phenol sulfone synthetic tanning agents, and EDTMPS to replace part of the chromium tanning agent, reducing chromium usage by 25%, complying with EU REACH regulations, and with an overall cost increase of no more than 5%, combining economic efficiency and environmental friendliness. In summary, this invention systematically solves the technical challenge of simultaneously achieving uniform fiber extension, regional differences adaptation, and low process damage in sheepskin bag leather production, and has broad application prospects.

[0011] Preferably, in step S1, the conditions for the pre-soaking process are: liquid ratio 8-10, temperature 18-22°C, addition of wetting agent 0.2-0.5%, degreasing agent 0.3-0.5%, and preservative 0.1-0.2%, all percentages are based on the weight of sheepskin raw material, and intermittent padding or drum treatment for 1-3 hours; The conditions for the main soaking process are as follows: liquid ratio 8-10, temperature room temperature or 25-28℃, addition of soaking enzyme 0.1-0.3%, degreasing agent 0.3-0.5%, soda ash 0.2-0.5% to control pH 8-9, and preservative 0.1-0.2%. All percentages are based on the weight of the sheepskin raw material. Salt wet hide treatment for 12-20 hours, salt dry hide treatment for 24-40 hours, with intermittent rotation. The conditions for the degreasing process are: temperature 38-40℃, liquid ratio 2-3, addition of degreasing agent 0.5-1.5% and soda ash 0.3-0.5%, all percentages are based on the weight of sheepskin raw material, drum treatment for 40-60 minutes, and washing with warm water; The alkaline hair removal process is as follows: apply sodium sulfide 6-10°Bé and lime slurry to the flesh surface, keep it warm and moist for 12-24 hours, and push the hair or remove the hair with a hair removal machine after the hair roots are loosened; or use the alkali rolling method: Na2S 1-2%, lime 3-5%, liquid ratio 0.8-1, drum treatment for 30-60 minutes, and stop the drum to expand. The conditions for the liming / re-liming process are as follows: liquid ratio 1-2, room temperature, 3-5% lime added, Na2S balance 0.3-0.5%, all percentages are based on the weight of sheepskin raw material, drum treatment for 30 minutes, drum stop for 2-3 hours, repeated 1-2 times, and re-liming extended to 24-48 hours. The conditions for the deashing process are as follows: liquid ratio 1.5-2, temperature 35-38℃, addition of 1.5-2.5% ammonium sulfate or ammonium chloride and deashing agent, the percentages being based on the weight of the sheepskin raw material, drum treatment for 30-60 minutes, and an endpoint pH of 8.5-9.0. The softening process conditions are: temperature 36-38℃, liquid ratio 1, addition of 0.5% ammonium sulfate and 0.2-0.5% trypsin or microbial softening enzyme, the percentages being based on the weight of the sheepskin raw material, and drum treatment for 30-90 minutes; The conditions for the pickling process are as follows: liquid ratio 0.8-1.0, temperature 18-22℃, 8-10% salt added and treated in a drum for 10 minutes, 0.3-0.5% formic acid added and treated in a drum for 20 minutes, and 1.0-1.5% sulfuric acid added and treated in a drum for 60-120 minutes. All percentages are based on the weight of the sheepskin raw material, and the final pH is 2.8-3.2.

[0012] Preferably, in step S2, the conditions for the chrome tanning treatment are as follows: it is carried out in the original pickling bath at a temperature of 33–35°C; 4–6% chromium powder is added in two batches, each time for 30–60 minutes of drum treatment, the percentage being based on the weight of the sheepskin raw material; 1% sodium formate is added and drum treated for 30 minutes; 0.5–1.0% sodium bicarbonate is added in batches to adjust the alkali to pH 3.6–4.0, the percentage being based on the weight of the sheepskin raw material; the total drum treatment time is 4–8 hours; the drum is stopped overnight; and the treated area is left to stand for 24–72 hours after removal from the drum.

[0013] Preferably, in step S3, the conditions for the neutralization process are: temperature 38-40°C, time 70-80 minutes, addition of sodium bicarbonate 1.8-2.2% and ammonium sulfate 2.0%, all percentages are based on the oven-dry weight of wet blue leather, and the final pH value is controlled at 5.8-6.2.

[0014] Preferably, in step S3, the fiber swelling agent is an alkyl glycoside fiber swelling agent, and the dosage is 0.3-0.5% of the oven-dry weight of wet blue leather; Polyvinylpyrrolidone dispersant is also added in the retanning process, and the amount used is 8 to 12% of the total mass of the ternary retanning system.

[0015] Preferably, in step S3, the conditions for the fatliquoring process are: temperature 45°C, time 80 minutes, and the addition of a chromium-free fatliquoring agent, wherein the chromium-free fatliquoring agent includes a phospholipid fatliquoring agent and a lanolin fatliquoring agent, wherein the amount of the phospholipid fatliquoring agent is 4.5% of the oven-dry weight of the wet blue leather, and the amount of the lanolin fatliquoring agent is 2.5% of the oven-dry weight of the wet blue leather.

[0016] Preferably, in step S4, the wet drying pretreatment includes: draining water with a damp cloth, squeezing out water and stretching, vacuum pre-drying or hanging to air dry until the moisture content is 50-60%; The drying process includes: hanging drying and vibrating to soften, or vacuum drying followed by air drying, controlling the final moisture content to 12-18%; The rehydration and mechanical softening process includes: rehydrating to a moisture content of 25-30%, and softening by oscillation, shoveling, or drumming. The dry finishing process includes: stretching and shaping, sanding, trimming, shearing, and sorting and grading of leather.

[0017] Preferably, in step S4, the stretching and shaping adopts a moderate stretching and low temperature shaping mode, with the stretching range controlled at 3-5%, the stretching temperature adjusted to 50-52℃, the humidity at 48-50%, and the drying time extended to 10 hours; the vibration softening time is 40 minutes, the hot drop temperature is 50℃ and the time is 7 hours, and the cold drop time is 12 hours.

[0018] Preferably, in step S1, a complex biological enzyme is added to the softening process. The complex biological enzyme includes an alkaline protease and a lipase. The alkaline protease is OR alkaline protease, and the dosage is 0.1-0.2 U / g. The lipase is ADE lipase. The treatment temperature is 35-40°C, and the treatment time is 30-45 minutes. In the main soaking process, a surfactant is used for low-temperature soaking at a temperature of 25-30°C. The surfactant is SAF surfactant, and the amount used is 0.1-0.2% of the weight of the sheepskin raw material.

[0019] Secondly, the present invention provides the following technical solution: a sheepskin bag leather, wherein the sheepskin bag leather is prepared by the method described above for increasing the sizing rate of sheepskin bag leather. Detailed Implementation

[0020] Embodiments of the present invention are described in detail below, with examples of these embodiments shown, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below are exemplary and intended to explain embodiments of the present invention, and should not be construed as limiting the present invention.

[0021] In this embodiment, unless otherwise specified, the percentage dosage of each agent is based on the corresponding oven-dry weight of the hide (i.e., "sheepskin raw material weight" or "wet blue leather oven-dry weight"); the functions and main ingredients corresponding to the trade names or abbreviations involved are as follows: JFC-E: Nonionic wetting agent, main component is fatty alcohol polyoxyethylene ether (C 12 H 25 O(CH2CH2O) n H); POC: Nonionic degreasing agent, the main component of which is fatty alcohol polyoxyethylene ether phosphate (C 12 H 25 O(CH2CH2O)5PO(OH)2); BIT-20: Isothiazolinone preservative, the main component of which is 1,2-benzisothiazolin-3-one (C7H5NOS). Water-soluble enzyme L-80: A compound enzyme preparation, the main components of which are Bacillus subtilis protease and α-amylase; SAF: Nonionic surfactant / wetting agent, the main component of which is fatty alcohol polyoxyethylene ether; OR: Alkaline protease, the main component of which is Bacillus subtilis protease; ADE: Lipase, whose main component is lipase; Soda ash: Sodium carbonate (Na2CO3); Baking soda: Sodium bicarbonate (NaHCO3); GTW45: Modified glutaraldehyde tanning agent (chemical name: glutaraldehyde and polyvinyl alcohol condensate); LSW: Tear-resistant additive, the main component of which is polyurethane dispersion; CS: Chromium tanning agent (basic chromium sulfate, Cr(OH)SO4); FB: Protein filler, the main component of which is modified collagen; TGR: Amphoteric acrylic resin retanning agent; NG: Neutralizing agent, the main components of which are a mixture of sodium formate and sodium acetate; ARS: Amphoteric tannin retanning agent; RST, SOB: Acrylic resin retanning agent (polyacrylate emulsion); 2706: Synthetic fatliquoring agent, the main component of which is sulfonated synthetic oil; FG211: Chestnut tannin (hydrolyzed tannin, main component is ellagic acid polyphenols); DR: Synthetic tanning agent, the main component of which is phenol sulfonic acid condensate; CK: Compound fatliquoring agent, the main component of which is a mixture of sulfated oil and synthetic oil; VG3: Vegetable tannin, the main component of which is tannin from the bark of the Vitex negundo tree; R19, ​​SPR42: Amino resin retanning agents, the main component of which is melamine-formaldehyde condensate; FL17, HFW, G22: Various fatliquoring agents (sulfated lanolin, synthetic oils, phospholipids); T11: Amphoteric acrylic resin; ME: Plant tannins; A30: Amino resin; KK: Cationic fatliquoring agent, whose main component is quaternary ammonium salt surfactant.

[0022] The above-mentioned additives are all commercially available products commonly used in this field, and their specific selection does not affect the realization of the core process of this invention.

[0023] Example 1 In Embodiment 1 of the present invention, a method for improving the sizing rate of sheepskin bags includes: I. Preparation Section (Raw Hides → Naked Hides) Core objective: to restore freshness, remove flesh, remove hair, remove epidermis and interfibrous material, and moderately loosen collagen fibers to obtain acid-treated naked hides suitable for tanning.

[0024] 1. Pre-soak in water (wash skin) Place the raw sheepskin in a rotating drum, controlling the liquid ratio at 8-10 and the temperature at 18-22℃. Add 0.2-0.5% JFC-E wetting agent (main component: fatty alcohol polyoxyethylene ether), 0.3-0.5% POC degreasing agent (main component: fatty alcohol polyoxyethylene ether phosphate), and 0.1-0.2% BIT-20 preservative (main component: 1,2-benzisothiazolin-3-one) (all based on the weight of the raw sheepskin). Intermittently agitate or rotate the drum for 1-3 hours (for salt-dried hides, this can be extended to the early stage of overnight treatment). The purpose is to wash away the preservative salt, blood, and feces, initially soften the hide, and inhibit bacteria.

[0025] 2. Main immersion water Control the liquid-to-leather ratio to 8–10, maintain the temperature at room temperature or 25–28℃ (higher temperature is acceptable in winter), and add 0.1–0.3% of soaking enzyme L-80 (main components are Bacillus subtilis protease and α-amylase), 0.3–0.5% of POC degreasing agent, 0.2–0.5% of soda ash (sodium carbonate), controlling the pH to 8–9, and 0.1–0.2% of BIT-20 preservative (all based on the weight of sheepskin raw material). Use SAF surfactant (main component is fatty alcohol polyoxyethylene ether) for low-temperature soaking at 25–30℃, with SAF dosage at 0.1–0.2% of the sheepskin raw material weight, to evenly moisten the fiber network. Salt-wet leather treatment lasts 12–20 hours, and salt-dry leather treatment lasts 24–40 hours, with intermittent rotation. The endpoint is achieved when the leather thickness recovers, the cut surface is completely white, and there is no hard core when folded.

[0026] 3. Remove the meat A meat scraper is used to scrape away the meat surface, removing subcutaneous tissue, dead meat, blood vessels, and large pieces of fat. Sheep hides are high in fat, so mechanical pressing or grease removal is used after meat removal.

[0027] 4. Degreasing Control the temperature at 38–40℃, the liquid ratio at 2–3, and add 0.5–1.5% POC degreasing agent (main component is fatty alcohol polyoxyethylene ether phosphate) and 0.3–0.5% soda ash (sodium carbonate) (both based on the weight of the sheepskin raw material). Treat in a drum for 40–60 minutes, then wash with warm water. Sheepskin degreasing must be performed throughout the entire process (after soaking, deliming, softening, pickling, and before retanning; additional degreasing can be done at these stages), otherwise problems such as "white bloom, oil seepage, and uneven dyeing" may occur later.

[0028] 5. Alkali application / sodium rolling for hair removal (primarily alkaline method) Alkali coating method: Apply sodium sulfide (Na2S) at 6-10°Bé and lime slurry (mainly calcium hydroxide) to the meat surface, keep it warm and moist for 12-24 hours, and push the hair or use a hair removal machine to remove the hair after the hair roots have loosened.

[0029] Sodium hydroxide method: Na2S (sodium sulfide) 1-2%, lime (calcium hydroxide) 3-5%, liquid ratio 0.8-1, drum treatment for 30-60 minutes, then stop drum expansion.

[0030] Enzymatic hair removal (applying a neutral protease paste to the meat surface for 24–48 hours) can also be used as an environmentally friendly method.

[0031] 6. Lime impregnation / re-limeing Control the liquid ratio to 1-2, at room temperature, add 3-5% lime (calcium hydroxide) and the remainder 0.3-0.5% Na2S (sodium sulfide) (or sodium hydrosulfide, NaHS) (all based on the weight of the sheepskin raw material). Rotate the drum for 30 minutes, stop the drum for 2-3 hours, and repeat 1-2 times. Re-lime treatment can be extended to 24-48 hours. The purpose is to cause the raw hide to swell, dissolve keratin, and open up collagen fiber bundles. Excessive lime expansion of the sheepskin should be avoided, otherwise it will result in a loose and porous surface.

[0032] 7. Deliming Control the liquid-to-liquid ratio at 1.5–2 and the temperature at 35–38°C. Add 1.5–2.5% ammonium sulfate or a mixture of ammonium chloride and deashing agent (ammonium sulfate to ammonium chloride in a mass ratio of 1:1–2:1, based on the weight of the sheepskin raw material). Drum treatment for 30–60 minutes. The endpoint is when the cut surface does not turn red with phenolphthalein and the pH reaches 8.5–9.0.

[0033] 8. Softening (enzyme treatment) Control the temperature at 36–38°C, maintain a liquid-to-leather ratio of 1, add 0.5% ammonium sulfate and 0.2–0.5% trypsin or microbial softening enzyme (based on the weight of the sheepskin raw material), and treat in a drum for 30–90 minutes (gentle softening of the sheepskin, do not over-process). Preferably, add a compound biological enzyme, which includes OR alkaline protease (mainly composed of Bacillus subtilis protease) and ADE lipase (mainly composed of lipase), with OR dosage at 0.1–0.2 U / g and ADE dosage at 0.1–0.2 U / g (based on the weight of the sheepskin raw material), treatment temperature at 35–40°C, and treatment time at 30–45 minutes to decompose impurities between fibers. The endpoint is a smooth grain surface, clear pores, and soft hide.

[0034] 9. Acid Immersion Control the liquor ratio at 0.8–1.0 and the temperature at 18–22℃ (25℃ in winter). Add 8–10% sodium chloride (to prevent acid swelling) and treat in a drum for 10 minutes. Add 0.3–0.5% formic acid and treat in a drum for 20 minutes. Add 1.0–1.5% sulfuric acid and treat in a drum for 60–120 minutes (all based on the weight of the sheepskin raw material). The endpoint is pH 2.8–3.2, with the cut surface fully permeated with acid. This yields "acid-treated naked hide," which proceeds to the tanning stage.

[0035] II. Tanning Section (Bare Leather → Wet Blue Leather → Wet Raw Leather) 10. Chrome tanning The process is carried out in the original acid bath at a temperature of 33–35℃. Add 4–6% chromium powder (basic chromium sulfate, Cr(OH)SO4, Cr2O3 content 21–26%) (based on the weight of the sheepskin raw material), in two batches, each time for 30–60 minutes in a drum. For alkali extraction: add 1% sodium formate (HCOONa) (based on the weight of the sheepskin raw material) and drum for 30 minutes. Add 0.5–1.0% sodium bicarbonate (NaHCO3) (based on the weight of the sheepskin raw material) in batches to extract alkali to pH 3.6–4.0. The total drum time is 4–8 hours, followed by overnight resting. The endpoint is Ts ≥ 95℃, blue-green color, and a completely blue cut surface. Remove from the drum and allow to stand for 24–72 hours (aging, chromium bonding stabilizes).

[0036] 11. Squeeze out water → wet-shape evenly The water content is controlled to 50-55% using a dewatering and stretching machine. Split: Sheepskin garment leather is usually not split or split into two layers. Wet trimming: The flesh side is trimmed to 0.6-1.0mm (garment leather), and 0.8-1.2mm (shoe leather), with uniform thickness and no skipping. Trim and weigh (retanning reference weight).

[0037] 12. Retanning This process utilizes the improved ternary retanning system and length-increasing scheme of this invention.

[0038] (1) Neutralization pretreatment: control the liquid ratio to 2, the temperature to 38-40℃, add sodium bicarbonate (NaHCO3) 1.8-2.2% and ammonium sulfate ((NH4)2SO4) 2.0% (all based on the dry weight of wet blue leather), and treat in a drum for 70-80 minutes. The final pH value is controlled at 5.8-6.2.

[0039] (2) Retanning Addition and Control: A "stepwise addition + gradient heating" mode is adopted. First, add the ternary retanning system (composed of modified chestnut tannin, phenol sulfone synthetic tanning agent, and EDTMPS in a mass ratio of 2.5:2.5:1, with a total dosage of 13-14% of the oven-dry weight of wet blue leather), and keep warm at 55℃ for 60 minutes. Then add 3-5% (based on the oven-dry weight of wet blue leather) of polyurethane lengthening agent (Levotan X-Cel or similar products, the main component of which is modified polyurethane dispersion, with a solid content ≥50%) and alkyl glycoside fiber swelling agent (the main component of which is decyl glucoside, C 16 H 30 Add 0.3-0.5% (based on the oven-dry weight of wet blue leather) of O6, heat to 58-60℃, and continue rotating for 40-50 minutes. Maintain the pH value at 5.0-5.3 throughout the process, and adjust the liquor ratio to 1:2.8. Simultaneously, add polyvinylpyrrolidone (PVP) dispersant at the initial stage of retanning, at a dosage of 8-12% of the total mass of the ternary retanning system.

[0040] (3) Remove from the drum and let stand still to obtain retanned wet leather.

[0041] 13. Staining Maintain a liquid-to-liquid ratio of 2-3 and a temperature of 55-60℃ (60-65℃ for dark colors). Add dye (acid dye or metal complex dye, specific type selected according to the target color; for black leather, the amount is 3-6% of the oven-dry weight of wet blue leather). Drum treatment for 30-60 minutes, then add an appropriate amount of leveling agent (sodium alkyl sulfonate surfactant). Fixation: Add 0.5-1.5% formic acid in two portions, adjust the pH to 3.8-4.2, and drum treatment for 20-30 minutes. Rinse with water after removing from the drum.

[0042] 14. Fat Additives Maintain a liquid-to-liquid ratio of 2-3 and a temperature of 45℃. Add chromium-free fatliquoring agents (phospholipid fatliquoring agents mainly consist of modified soybean phospholipids, and lanolin fatliquoring agents mainly consist of modified lanolin, with dosages of 4.5% and 2.5% of the oven-dry weight of wet blue leather, respectively). Simultaneously, a mixed fatliquoring agent (sulfated oil + synthetic oil + lecithin) can be added in a total of 12-18% (15-20% for softer sheepskin garment leather). A cationic fatliquoring agent (quaternary ammonium salts) is added as a final 1-2%. Drum treatment is performed for 80 minutes, followed by fixation with 0.3-0.5% formic acid for 20-30 minutes. The treated leather is then rinsed and drained.

[0043] III. Finishing Section (Wet Raw Material → Finished Leather) 15. Pretreatment before wet drying Drain water by pressing down the diaphragm → squeeze out water and stretch → vacuum pre-dry or hang to dry until the moisture content is 50-60%.

[0044] 16. Drying Garment leather: Hang to dry and shake to soften, or vacuum dry (shrinkage approximately 5%) to tighten the grain before drying. Shoe upper leather: Stretch on a board to determine the area, then vacuum dry to determine the grain. Control the final moisture content to 12-18%.

[0045] 17. Moisture Reabsorption and Mechanical Softening Rehydrate to a moisture content of 25-30% (spray water at 40-45℃ and pile for 24 hours). Soften by shaking, pulling, scraping, or turning and thumping (soften garment leather by thumping for 2-6 hours to achieve a "bubbly" feel).

[0046] 18. Dry finishing – process improvement Stretching and shaping: The "moderate stretching + low temperature shaping" mode is adopted, with the stretching range controlled at 3-5%, the stretching temperature at 50-52℃, the humidity at 48-50%, and the drying time at 10 hours. The vibration softening time is 40 minutes, the hot tumbling temperature is 50℃ and the time is 7 hours, and the cold tumbling time is 12 hours.

[0047] Nubuck leather: Grain leather is lightly nubuckled at 240-400 grit, and suede leather is napped at 180-240 grit. The process involves trimming, shearing (turning the sheepskin inside out), sorting and grading the hides to obtain the finished leather.

[0048] It is worth noting that, firstly, after chrome tanning or before retanning, 2% oxalic acid (ethanedioic acid, H2C2O4) (based on the oven-dry weight of wet blue leather) can be added to detannify the blue leather to a certain extent, loosen the grain, and facilitate the increase in size.

[0049] Secondly, 2% TN acid enzyme (acidic protease, the main component of which is Aspergillus niger protease) can be added (based on the oven-dry weight of wet blue leather) to further open up the elastin and useless proteins that bind the fibers, so that the grain surface is further opened up, laying a good foundation for increasing the length.

[0050] Third, in the selection of retanning agents, synthetic phenolic tannins and natural plant tannins should be given priority, and the amount of acrylic resin tanning agent should be reduced to reduce the shrinkage effect of retanning materials on collagen fibers.

[0051] Fourth, each step of the retanning and filling process involves the use of oils, employing a step-by-step oiling method to stretch the leather and achieve a better yield.

[0052] In another embodiment, a sheepskin bag leather is also provided, which is prepared by the method of increasing the sizing rate of sheepskin bag leather as described in the above embodiments.

[0053] Specific examples: Raw materials: 8 sheepskins (1.0-1.2mm thick), approximately 5kg.

[0054] Preparation section: (1) Add 100% water (based on the weight of sheepskin raw material, the same below), at 45°C, add 1% POC degreasing agent (fatty alcohol polyoxyethylene ether phosphate) and 2% oxalic acid (oxalic acid), treat for 120 minutes, drain and wash.

[0055] (2) Add 150% water, 45℃, add 1.5% POC degreasing agent and 0.5% SAF emulsifier dispersant (fatty alcohol polyoxyethylene ether), treat for 120 minutes, drain and wash twice.

[0056] (3) Add 100% water, at 35°C, add 1.5% GTW45 modified glutaraldehyde tanning agent (glutaraldehyde and polyvinyl alcohol condensate) for 20 minutes, add 1% LSW tear-resistant agent (polyurethane dispersion) for 20 minutes, add 0.4% formic acid for 20 minutes, and adjust the pH to about 3.5.

[0057] (4) Add 4% chromium powder (basic chromium sulfate), 3% CS chromium tannin (basic chromium sulfate), and 2% FB protein filler (modified collagen) for 90 minutes, add 1% sodium formate (HCOONa) for 15 minutes, add 2.5% baking soda (sodium bicarbonate, NaHCO3) in portions (10 minutes × 5 times + 40 minutes), and adjust the pH to 4.0-4.2.

[0058] (5) Add 1% TGR amphoteric acrylic resin retanning agent and treat for 40 minutes, then stop the drum overnight (O / N). The next day, turn the drum on for 20 minutes and wash lightly.

[0059] (6) Add 100% water, 35°C, add 2% NG neutralizing agent (a mixture of sodium formate and sodium acetate) and 1% sodium formate, and treat with a drum for 15 minutes.

[0060] (7) Add 0.2% sodium bicarbonate, 2% ARS amphoteric tannin retanning agent, and 1% LSW tear-resistant agent, treat for 30 minutes, and adjust the pH to 4.6.

[0061] (8) Add 3% RST acrylic resin retanning agent (polyacrylate emulsion) and treat for 40 minutes, then wash with water.

[0062] (9) Add 50% water, at 35°C, add 3% SOB acrylic resin retanning agent (polyacrylate emulsion) and treat for 30 minutes.

[0063] (10) Add 1% 2706 synthetic fatliquoring agent (sulfonated synthetic oil), 4% FG211 chestnut tannin (hydrolyzed tannin, ellagic acid polyphenol), and 4% DR synthetic tanning agent (phenol sulfonic acid condensate) and treat for 40 minutes.

[0064] (11) Add 1% CK compound fatliquoring agent (a mixture of sulfated oil and synthetic oil), 4% FG211 chestnut tannin, and 4% VG3 vegetable tanning agent (chamomile bark tannin) and treat for 40 minutes.

[0065] (12) Add 3% R19 amino resin retanning agent (melamine-formaldehyde condensate), 4% SPR42 amino resin retanning agent (melamine-formaldehyde condensate), and X% dye, and treat in a drum for 60 minutes.

[0066] (13) Heat to 45°C and add 0.8% formic acid in two portions (10 minutes + 20 minutes).

[0067] (14) Add 200% water, 50℃, add 2% FB protein filler, and treat in a drum for 10 minutes.

[0068] (15) Add 2% FL17 fatliquoring agent (sulfated lanolin), 2% HFW fatliquoring agent (synthetic oil), 2% G22 fatliquoring agent (phospholipid), and 2% CK compound fatliquoring agent, and treat with drum for 40 minutes.

[0069] (16) Add 1% T11 amphoteric acrylic resin, 1% ME plant tannin, and 1% A30 amino resin, and treat in a drum for 40 minutes.

[0070] (17) Add 1.5% formic acid in two portions (10 minutes + 20 minutes), and rinse with water to remove color.

[0071] (18) Add 300% water, 50°C, and add 0.5% KK cationic fatliquoring agent (quaternary ammonium salt) for 15 minutes.

[0072] The sheepskin leather for bags prepared according to the embodiments of the present invention was compared with sheepskin leather for bags prepared by traditional processes. The results are as follows:

[0073] In the above examples, all percentages are based on the weight of the sheepskin raw material (in steps (1) to (18), unless otherwise specified, all percentages are based on the weight of the sheepskin raw material). The specific parameters of the retanning, neutralization, and fatliquoring steps are reflected in the above steps and include the core improvements of this invention (such as the ternary retanning system, polyurethane lengthening agent, fiber swelling agent, PVP dispersant, low temperature stretching, etc.).

[0074] According to SGS testing (report numbers: SL92539371310001FW, SL92609270914301FW), the sheepskin bag leather prepared by this invention has a light fastness color change grade of 4.5 (requirement ≥3.0); the rubbing fastness color change and staining of both dry and wet rubbing reach grade 4.5 (requirement ≥3.0~3.5); the coating adhesive tape test shows a color change grade of 4.5 (requirement ≥4.0); the tear strength is 36N in the longitudinal direction and 33N in the transverse direction (requirement ≥20N); and there is no negative impact on the water resistance / spotting test. In terms of chemical properties, hexavalent chromium (including aging) was not detected (<0.5 mg / kg, requirement <3); formaldehyde was 47 mg / kg (requirement <75); none of the 24 restricted aromatic amines were detected; total lead, total cadmium, and total mercury were not detected; bisphenols, polycyclic aromatic hydrocarbons, organotin compounds, phthalates, chlorophenols, and short-chain chlorinated paraffins were not detected or were far below the limits. In summary, this invention achieves the beneficial effects of significantly improved length increase, reduced part-specific differences, compliance with physical performance standards, and environmental friendliness.

[0075] The method for improving the sizing rate of sheepskin bag leather provided in Embodiment 1 of this invention, firstly, in terms of sizing rate, utilizes the physical filling and hydrogen bonding cross-linking effects of polyurethane sizing agents, combined with the enhancement of fiber dispersion and expansion space by a ternary retanning system, and the appropriate loosening of collagen fibers by fiber swelling agents, resulting in a sizing rate of 6-11% higher than that of finished leather compared to traditional processes, effectively reducing raw hide loss; secondly, through optimization of the neutralization process (temperature 38-40℃, pH...), ... The gradient heating mode in steps 5.8–6.2) and the retanning process allows the length-extending agent and retanning agent to penetrate evenly into the fiber gaps, significantly improving the regional differences between the back and abdomen. The regional difference is reduced from over 15% in traditional processes to no more than 10%, greatly improving the utilization rate of the finished product. Simultaneously, the sheepskin bag leather prepared by this invention exhibits excellent physical properties, with a tear strength ≥30 N / mm, softness ≤40 N·cm, and no cracking or loosening, fully meeting the requirements for bag leather use. Furthermore, this invention uses a ternary retanning system composed of modified chestnut tannin, phenol sulfone synthetic tanning agents, and EDTMPS to replace part of the chromium tanning agent, reducing chromium usage by 25%, complying with EU REACH regulations, and with an overall cost increase of no more than 5%, combining economic efficiency and environmental friendliness. In summary, this invention systematically solves the technical challenge of simultaneously achieving uniform fiber extension, regional differences adaptation, and low process damage in sheepskin bag leather production, and has broad application prospects.

[0076] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0077] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for improving the sizing rate of sheepskin bags, characterized in that, include: S1. The raw sheepskin is subjected to pre-soaking in water, main soaking in water, flesh removal, degreasing, alkali coating / rubbing alkali to remove hair, liming / re-liming, deliming, softening, and acid soaking to obtain acid naked hide; S2. The acid-treated bare leather is subjected to chrome tanning to obtain wet blue leather; S3. The blue wet leather is sequentially subjected to water squeezing, wet shaving, retanning, neutralization, dyeing, and fatliquoring to obtain wet raw leather. S4. The wet raw leather is subjected to wet drying pretreatment, drying, rehumidification and mechanical softening, and dry finishing in sequence to obtain the finished leather; In step S3, the retanning process includes: adding a length-enhancing agent, which is a polyurethane length-enhancing agent, to the drum at a dosage of 3-5% of the oven-dry weight of the wet blue leather; using a ternary retanning system, which is composed of modified chestnut tannin, sulfone phenolic synthetic tanning agent, and sodium ethylenediaminetetramethylenephosphonate in a mass ratio of 2.5:2.5:1, and the total dosage of the ternary retanning system is 13-14% of the oven-dry weight of the wet blue leather; the retanning process adopts a step-by-step addition and gradient heating mode, first adding the ternary retanning system, holding at 55°C for 60 minutes, then adding the length-enhancing agent and fiber swelling agent, raising the temperature to 58-60°C, and continuing to rotate for 40-50 minutes, maintaining the pH value at 5.0-5.3 throughout the process, and the liquor ratio at 1:2.

8.

2. The method for increasing the sizing rate of sheepskin bags according to claim 1, characterized in that, In step S1, the conditions for the pre-soaking process are: liquid ratio 8-10, temperature 18-22℃, adding 0.2-0.5% wetting agent, 0.3-0.5% degreasing agent, and 0.1-0.2% preservative, all percentages being based on the weight of the sheepskin raw material, and intermittently scratching or drumming for 1-3 hours; The conditions for the main soaking process are as follows: liquid ratio 8-10, temperature room temperature or 25-28℃, addition of soaking enzyme 0.1-0.3%, degreasing agent 0.3-0.5%, soda ash 0.2-0.5% to control pH 8-9, and preservative 0.1-0.2%. All percentages are based on the weight of the sheepskin raw material. Salt wet hide treatment for 12-20 hours, salt dry hide treatment for 24-40 hours, with intermittent rotation. The conditions for the degreasing process are: temperature 38-40℃, liquid ratio 2-3, addition of degreasing agent 0.5-1.5% and soda ash 0.3-0.5%, all percentages are based on the weight of sheepskin raw material, drum treatment for 40-60 minutes, and washing with warm water; The alkaline hair removal process is as follows: apply sodium sulfide 6-10°Bé and lime slurry to the flesh surface, keep it warm and moist for 12-24 hours, and push the hair or remove the hair with a hair removal machine after the hair roots are loosened; or use the alkali rolling method: Na2S 1-2%, lime 3-5%, liquid ratio 0.8-1, drum treatment for 30-60 minutes, and stop the drum to expand. The conditions for the liming / re-liming process are as follows: liquid ratio 1-2, room temperature, 3-5% lime added, Na2S balance 0.3-0.5%, all percentages are based on the weight of sheepskin raw material, drum treatment for 30 minutes, drum stop for 2-3 hours, repeated 1-2 times, and re-liming extended to 24-48 hours. The conditions for the deashing process are as follows: liquid ratio 1.5-2, temperature 35-38℃, addition of 1.5-2.5% ammonium sulfate or ammonium chloride and deashing agent, the percentages being based on the weight of the sheepskin raw material, drum treatment for 30-60 minutes, and an endpoint pH of 8.5-9.

0. The softening process conditions are: temperature 36-38℃, liquid ratio 1, addition of 0.5% ammonium sulfate and 0.2-0.5% trypsin or microbial softening enzyme, the percentages being based on the weight of the sheepskin raw material, and drum treatment for 30-90 minutes; The conditions for the pickling process are as follows: liquid ratio 0.8-1.0, temperature 18-22℃, 8-10% salt added and treated in a drum for 10 minutes, 0.3-0.5% formic acid added and treated in a drum for 20 minutes, and 1.0-1.5% sulfuric acid added and treated in a drum for 60-120 minutes. All percentages are based on the weight of the sheepskin raw material, and the final pH is 2.8-3.

2.

3. The method for increasing the sizing rate of sheepskin bags according to claim 1, characterized in that, In step S2, the conditions for the chrome tanning treatment are as follows: It is carried out in the original pickling bath at a temperature of 33–35°C. 4–6% chrome powder is added in two batches, with each batch treated in a drum for 30–60 minutes. The percentage is based on the weight of the sheepskin raw material. 1% sodium formate is added and treated in a drum for 30 minutes. 0.5–1.0% sodium bicarbonate is added in batches to adjust the alkali to pH 3.6–4.

0. The percentage is based on the weight of the sheepskin raw material. The total drum time is 4–8 hours. The drum is stopped overnight, and the treated area is left to stand for 24–72 hours after removal from the drum.

4. The method for increasing the sizing rate of sheepskin bags according to claim 1, characterized in that, In step S3, the conditions for the neutralization process are: temperature 38-40℃, time 70-80 minutes, addition of sodium bicarbonate 1.8-2.2% and ammonium sulfate 2.0%, all percentages are based on the oven-dry weight of wet blue leather, and the final pH value is controlled at 5.8-6.

2.

5. The method for increasing the sizing rate of sheepskin bags according to claim 1, characterized in that, In step S3, the fiber swelling agent is an alkyl glycoside fiber swelling agent, and the dosage is 0.3-0.5% of the oven-dry weight of wet blue leather; Polyvinylpyrrolidone dispersant is also added in the retanning process, and the amount used is 8 to 12% of the total mass of the ternary retanning system.

6. The method for increasing the sizing rate of sheepskin bags according to claim 1, characterized in that, In step S3, the conditions for the fatliquoring process are: temperature 45°C, time 80 minutes, and the addition of a chromium-free fatliquoring agent. The chromium-free fatliquoring agent includes a phospholipid fatliquoring agent and a lanolin fatliquoring agent. The amount of the phospholipid fatliquoring agent is 4.5% of the oven-dry weight of the wet blue leather, and the amount of the lanolin fatliquoring agent is 2.5% of the oven-dry weight of the wet blue leather.

7. The method for increasing the sizing rate of sheepskin bags according to claim 1, characterized in that, In step S4, the wet drying pretreatment includes: draining water with a squeegee, squeezing out water and stretching, vacuum pre-drying or hanging to dry until the moisture content is 50-60%; The drying process includes: hanging drying and vibrating to soften, or vacuum drying followed by air drying, controlling the final moisture content to 12-18%; The rehydration and mechanical softening process includes: rehydrating to a moisture content of 25-30%, and softening by oscillation, shoveling, or drumming. The dry finishing process includes: stretching and shaping, sanding, trimming, shearing, and sorting and grading of leather.

8. The method for increasing the sizing rate of sheepskin bags according to claim 7, characterized in that, In step S4, the stretching and shaping adopts a moderate stretching and low temperature shaping mode, with the stretching range controlled at 3-5%, the stretching temperature adjusted to 50-52℃, the humidity at 48-50%, and the drying time extended to 10 hours; the vibration softening time is 40 minutes, the hot drop temperature is 50℃ and the time is 7 hours, and the cold drop time is 12 hours.

9. The method for increasing the sizing rate of sheepskin bags according to claim 1, characterized in that, In step S1, a compound biological enzyme is added to the softening process. The compound biological enzyme includes alkaline protease and lipase. The alkaline protease is OR alkaline protease, and the dosage is 0.1-0.2 U / g. The lipase is ADE lipase. The treatment temperature is 35-40℃ and the treatment time is 30-45 minutes. In the main soaking process, a surfactant is used for low-temperature soaking at a temperature of 25-30°C. The surfactant is SAF surfactant, and the amount used is 0.1-0.2% of the weight of the sheepskin raw material.

10. A type of sheepskin leather for bags, characterized in that, The sheepskin bag leather is prepared using the method described in any one of claims 1-9 for increasing the size gain of the sheepskin bag leather.

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