A softening method for preventing leather damage

Abstract

The present invention belongs to the technical field of leather processing and manufacturing, and discloses a softening method for preventing leather damage. After the liming process in leather making is completed, first adjust the pH of the limed pelt to the optimum pH range of the softening enzyme, and keep the calcium content in the pelt not less than 65% of the calcium content of the limed pelt; then use the softening enzyme for softening operation; after softening is completed, remove the calcium in the softened pelt. The present invention can solve the technical problems of easy surface damage or loose surface in the existing leather softening technology, and at the same time can ensure the pickling and tanning effects and improve the quality of the finished leather.

Description

Technical Field

[0001] The present invention belongs to the technical field of leather processing and manufacturing, and particularly relates to a softening method for preventing leather damage. Background Art

[0002] Softening is a process that uses protease to catalyze hydrolysis and remove non-collagen proteins such as albumin, globulin, and elastin in the hide, and moderately disperse collagen fibers. As an indispensable biological treatment process in leather making, softening can improve the softness and water vapor permeability of the finished leather, and make the grain surface smoother. In addition, the smooth progress of the softening process can also create suitable conditions for the penetration and combination of materials in subsequent processes such as pickling, tanning, retanning, dyeing, and fatliquoring.

[0003] However, there are some technical problems that are difficult to solve in the existing softening methods. One of the main problems is that after the deliming process, the delimed raw hide processed in the softening process has no hair and epidermis protection and has been subjected to the action of strong alkali. If the softening operation is not careful, it is easy for the softening enzyme to damage the raw hide, resulting in leather quality defects such as damaged surface, loose surface, and hollow looseness. In order to obtain high-quality leather, it is necessary to minimize the damage to the leather collagen fibers as much as possible during the softening process and ensure the basic integrity of the structure of the leather collagen fibers. This is exactly the technical problem that the current leather softening process urgently needs to solve.

[0004] In view of this, the present invention is specifically proposed. Summary of the Invention

[0005] The purpose of the present invention is to overcome the deficiencies or drawbacks existing in the prior art and provide a softening method that can prevent leather damage.

[0006] An embodiment of the present invention provides a softening method for preventing leather damage. After the liming process in leather making is completed, first adjust the pH of the limed raw hide to the optimal pH range of the softening enzyme, and keep the calcium content in the raw hide not less than 65% of the calcium content of the limed raw hide; then use the softening enzyme for softening operation; after softening is completed, remove the calcium in the softened raw hide.

[0007] Preferably, the raw hide of the limed raw hide is any one of animal hides.

[0008] Preferably, the animal hide includes cowhide, sheepskin, pigskin, horsehide, deerhide, ostrich skin, etc.

[0009] Preferably, a pH regulator is used to adjust the pH of the limed raw hide, and the pH regulator is selected from any one or more of inorganic acids and their salts, organic acids and their salts.

[0010] Preferably, the softening enzyme includes any one or more of microbial protease, animal protease, and plant protease.

[0011] Preferably, a deliming agent or a decalcifying agent is used to delime or decalcify the softened hide to remove calcium in the softened hide.

[0012] Preferably, the deliming agent is selected from any one or more of ammonium salt deliming agents, low-ammonium salt deliming agents, and ammonia-free deliming agents.

[0013] Preferably, the decalcifying agent is selected from any one or more of calcium chelating agents such as sodium hexametaphosphate, sodium gluconate, and disodium ethylenediaminetetraacetate.

[0014] The present invention also discloses leather obtained by using any of the above-mentioned softening methods for preventing leather damage.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] 1. The softening method provided by the present invention adopts the method of softening first and then deliming, and controls the calcium content of the hide during the softening process to be not less than 65% of the calcium content of the limed hide. The operation sequence of the leather-making deliming and softening process steps in the prior art is changed, and the technical problem that the existing leather-making softening technology is easy to damage the leather is solved.

[0017] 2. The softening method provided by the present invention can also appropriately extend the softening time to make the softening enzyme more evenly distributed in the inner and outer layers of the hide, and improve the dispersion uniformity of leather collagen fibers.

[0018] 3. The softening method provided by the present invention does not need to additionally add special auxiliaries such as protease inhibitors and grain surface protectants, and has low cost and convenient operation.

[0019] 4. The softening method provided by the present invention can effectively remove calcium in the hide after softening, and the calcium content of the obtained hide (i.e., the calcium content of the hide before pickling) is even lower than that of the conventional softened hide (i.e., the calcium content of the conventional hide before pickling), which is more conducive to subsequent tanning and dyeing and finishing processes, and can improve the quality of the finished leather. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 are scanning electron micrographs of the grain surfaces of the softened hides obtained in Example 1, Comparative Example 1, and Comparative Example 2;

[0021] Figure 2 are stereomicrographs of the grain surfaces of the finished leathers obtained in Example 1, Comparative Example 1, and Comparative Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0022] To make the objectives, technical solutions, and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below in conjunction with specific embodiments. It should be understood that these descriptions are merely exemplary and are not intended to limit the scope of the present invention. In addition, in the following descriptions, the descriptions of well-known structures and technologies are omitted to avoid unnecessarily confusing the concepts of the present invention. For those not specified in the embodiments, they are carried out under conventional conditions or conditions recommended by the manufacturer. For reagents or instruments not specified for the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0023] During the implementation of the present invention, the applicant found that the lime introduced in the liming process not only has the effect of loosening collagen fibers but also can improve the structural stability of collagen fibers and help collagen fibers resist the hydrolysis of softening enzymes. In the existing leather-making process, the liming process is always followed by the deliming process to remove calcium from the limed raw hide, and then the softening operation is carried out. Such "liming-deliming-softening" operation obviously cannot fully utilize the natural protective effect of the lime / calcium salt introduced in the liming process on collagen fibers in the raw hide.

[0024] Based on this, the embodiment of the present invention provides a softening technical solution of "liming - pH adjustment - softening - deliming / demineralization", that is, a softening method for preventing leather damage. The method includes, after the leather-making liming process is completed, first adjusting the pH of the limed raw hide to the optimum pH range of the softening enzyme and keeping the calcium content in the raw hide not less than 65% of the calcium content of the limed raw hide; then using the softening enzyme for the softening operation; after the softening is completed, removing the calcium in the softened raw hide.

[0025] The key point of the embodiment of the present invention is that the calcium content of the raw hide is relatively high during softening (not less than 65% of the calcium content of the limed raw hide), and the deliming or demineralization operation is carried out only after the softening is completed to obtain a low calcium content (not higher than 20% of the calcium content of the limed raw hide) required for pickling or tanning the raw hide. After the raw hide is limed, its pH is generally 12 - 13, and the optimum pH of the softening enzyme is 8 - 10. Therefore, the pH range of the limed raw hide is not suitable for the action of the softening enzyme, and the pH of the limed raw hide needs to be adjusted. During the pH adjustment process, some calcium will inevitably be dissolved. To achieve the effects of this patent, it is necessary to ensure the calcium content in the limed raw hide while adjusting its pH. On this basis, softening is carried out first and then deliming, so as to not only solve the technical problem that the existing leather-making softening technology is easy to damage the leather, but also ensure the pickling and tanning effects, and finally improve the quality of the finished leather.

[0026] The limed raw hide is a limed raw hide prepared from common animal skins in the leather-making field, such as cowhide, sheepskin, pigskin, horsehide, deerhide, ostrich skin, etc., all within the protection scope of the present invention.

[0027] Adjusting the pH of the limed hide to the optimal pH range of the softening enzyme is carried out using a pH regulator, which is a commonly used pH regulator in the leather-making process. The adjusted pH is determined according to the softening enzyme used, and all the softening enzymes used are commonly used in the leather-making field. Therefore, those skilled in the art can select a suitable pH regulator according to the actual situation to adjust the pH of the limed hide to an appropriate range.

[0028] In some preferred embodiments, the pH regulator can be selected from any one or more of inorganic acids and their salts, organic acids and their salts.

[0029] In some preferred embodiments, the softening enzyme comprises any one or more of microbial protease, animal protease and plant protease.

[0030] Removing calcium from the softened hide means using a deliming agent or a decalcifying agent to carry out deliming or decalcifying treatment on the softened hide. The deliming or decalcifying treatment is a commonly used method in the leather-making field, and those skilled in the art can select the deliming agent or decalcifying agent used according to actual needs.

[0031] In some preferred embodiments, the deliming agent is selected from any one or more of ammonium salt deliming agents, low-ammonium salt deliming agents, and ammonia-free deliming agents.

[0032] In some preferred embodiments, the decalcifying agent is selected from any one or more of calcium chelating agents such as sodium hexametaphosphate, sodium gluconate, and disodium ethylenediaminetetraacetate.

[0033] The softening and deliming / decalcifying processes adopted in the embodiments of the present invention do not need to be particularly limited and are commonly used softening and deliming / decalcifying processes in the leather-making field, and their specific processes do not affect the effect of this patent.

[0034] For example, the specific process of the softening and deliming / decalcifying can be: calculated by the mass percentage of the limed hide, load the limed hide into a rotating drum, add 50 - 300% of water, adjust the temperature to 20 - 40°C, add a pH regulator to adjust the pH of the system to the optimal pH range of the corresponding softening enzyme, rotate for 5 - 20 min, and control the calcium content in the hide to be not less than 65% of the calcium content of the limed hide; then change the liquid, add 50 - 300% of water, adjust the temperature to 20 - 40°C, add 0.1 - 2.0% of the softening enzyme, rotate for 30 min, then adjust to intermittent rotation or continuous rotation, and the total time is 30 - 600 min; then change the liquid, add 50 - 300% of water, adjust the temperature to 20 - 40°C, add 0.5 - 6.0% of the deliming agent or decalcifying agent, rotate for 30 - 180 min, to obtain a hide that can be used for pickling or tanning.

[0035] The softening and deliming / demineralization process can also be as follows: Based on the mass percentage of the limed hide, load the limed hide into a rotating drum, add 50 - 300% water, adjust the temperature to 20 - 40°C, add a pH regulator to adjust the pH of the system to the optimal pH range of the corresponding softening enzyme, rotate for 5 - 20 min, and control the calcium content in the hide to be not less than 65% of the calcium content of the limed hide; then without changing the liquid, add 0.1 - 2.0% softening enzyme, after rotating for 30 min, switch to intermittent rotation or continuous rotation, with a total time of 30 - 600 min; then change the liquid, add 50 - 300% water, adjust the temperature to 20 - 40°C, add 0.5 - 6.0% deliming agent or demineralizing agent, rotate for 30 - 180 min to obtain a hide that can be used for pickling or tanning.

[0036] To make the present invention clearer, the softening method and effect for preventing leather damage are described in detail below through multiple specific examples.

[0037] Example 1

[0038] The following material dosages are all based on the mass percentage (wt%) of the limed hide.

[0039] Load the limed cowhide into a rotating drum, add 100% water, adjust the temperature to 32°C, add the pH regulator glycine to adjust the pH to about 8.5, rotate for 10 min, and control the calcium content in the hide to be 72.3% of the calcium content of the limed hide; then change the liquid, add 100% water, adjust the temperature to 32°C, add 1.0% softening enzyme (containing 2000 U / g of trypsin), rotate for 150 min; then change the liquid, add 100% water, adjust the temperature to 32°C, add 1.0% ammonium sulfate, rotate for 50 min to obtain a hide that can be used for pickling or tanning, and the calcium content in the hide is 16.7% of the calcium content of the limed hide.

[0040] Comparative Example 1

[0041] The following material dosages are all based on the mass percentage (wt%) of the limed hide.

[0042] Load the limed cowhide into a rotating drum, add 100% water, adjust the temperature to 32°C, add 3.0% ammonium sulfate, adjust the pH to about 8.5, rotate for 60 min for deliming, and control the calcium content in the hide to be 33.1% of the calcium content of the limed hide; then change the liquid, add 100% water, adjust the temperature to 32°C, add 1.0% softening enzyme (containing 2000 U / g of trypsin), rotate for 150 min; obtain a hide that can be used for pickling or tanning, and the calcium content in the hide is 22.3% of the calcium content of the limed hide.

[0043] Comparative Example 2

[0044] The following material dosages are all calculated as mass percentages (wt%) of the limed pelt.

[0045] Load the limed cowhide into a rotating drum, add 100% water, adjust the temperature to 32°C, add 2.0% ammonium sulfate, adjust the pH to about 8.5, rotate for 60 min for deliming, and control the calcium content in the pelt to be 49.7% of the calcium content of the limed pelt; then change the liquid, add 100% water, adjust the temperature to 32°C, add 1.0% softening enzyme (containing 2000 U / g of trypsin), and rotate for 150 min; obtain a pelt that can be used for pickling or tanning, and the calcium content in the pelt is 28.4% of the calcium content of the limed pelt.

[0046] Carry out corresponding softening effect tests on Example 1, Comparative Example 1, and Comparative Example 2; at the same time, carry out the same conventional pickling, tanning, dyeing and finishing treatments on the pelts obtained in Example 1, Comparative Example 1, and Comparative Example 2 to obtain leather, and conduct leather morphology and performance tests. The test results are as Figure 1 and shown in Table 1. According to Figure 1 the results, it can be seen that compared with the pelts and leather obtained in Comparative Example 1, the grain surface of the pelts and leather obtained in Example 1 is more complete and clear, indicating that Example 1 can protect the leather grain surface from being damaged by the softening enzyme. From the data in Table 1, it can be known that in the leather softening process of Example 1, it is ensured that the pelt used for softening has a relatively high calcium residue rate (72.3%). After the softening is completed, a deliming agent is used to remove the calcium in the softened pelt to obtain the low calcium content required for pickling or tanning the pelt (calcium residue rate 16.7%, even lower than 22.3% in Comparative Example 1 and 28.4% in Comparative Example 2, which is more conducive to the smooth progress of the subsequent pickling and tanning processes); the hydroxyproline concentration in the softening waste liquid of Example 1 is significantly lower than that in Comparative Example 1 and Comparative Example 2, which indicates that through the method provided by the present invention, the damage of the softening enzyme to the skin collagen fibers can be effectively reduced; the mechanical strength of the leather in Example 1 is higher than that in Comparative Example 1 and Comparative Example 2, which indicates that the method provided by the present invention can ensure the pickling and tanning effects and ultimately improve the quality of the finished leather. In summary, the softening method for preventing leather damage provided by the present invention can effectively solve the technical problems of easy surface damage or loose surface in the existing softening technology.

[0047] Table 1 Comparison table of softening effects

[0048]

[0049] Note: a. Calcium residue rate = calcium content of the pelt / calcium content of the limed pelt × 100%.

[0050] b. The higher the concentration of hydroxyproline (a characteristic amino acid of collagen) in the softening waste liquid, the greater the degree of damage to the skin collagen fibers.

[0051] Example 2

[0052] The dosages of the following materials are all calculated based on the mass percentage (wt%) of the limed hide.

[0053] Load the limed cowhide into a rotating drum, add 200% water, adjust the temperature to 35°C, add the pH regulator boric acid to adjust the pH to about 8, rotate for 20 min, and control the calcium content in the hide to be 66.3% of the calcium content in the limed hide; then change the liquid, add 50% water, adjust the temperature to 35°C, add 0.5% softening enzyme (containing 2000 U / g of papain), after rotating for 30 min, adjust to intermittent rotation or continuous rotation, and the total time is 210 min; then change the liquid, add 50% water, adjust the temperature to 30°C, add 2.0% ammonia-free deliming agent, rotate for 180 min to obtain a hide that can be used for pickling or tanning, and the calcium content in the hide is 12.5% of the calcium content in the limed hide.

[0054] Example 3

[0055] The dosages of the following materials are all calculated based on the mass percentage (wt%) of the limed hide.

[0056] Load the limed cowhide into a rotating drum, add 50% water, adjust the temperature to 20°C, add the pH regulator formic acid to adjust the pH to about 8.5, rotate for 10 min, and control the calcium content in the hide to be 71.5% of the calcium content in the limed hide; then change the liquid, add 200% water, adjust the temperature to 20°C, add 0.1% softening enzyme (containing 5000 U / g of subtilisin), after rotating for 30 min, adjust to intermittent rotation or continuous rotation, and the total time is 600 min; then change the liquid, add 200% water, adjust the temperature to 20°C, add 4.0% low-ammonium salt deliming agent, rotate for 100 min to obtain a hide that can be used for pickling or tanning, and the calcium content in the hide is 15.6% of the calcium content in the limed hide.

[0057] Example 4

[0058] The dosages of the following materials are all calculated based on the mass percentage (wt%) of the limed hide.

[0059] Load the limed sheepskin into a rotating drum, add 300% water, adjust the temperature to 35°C, add formic acid and sodium formate as pH regulators to adjust the pH to about 8, rotate for 20 min, and control the calcium content in the raw hide to be 67.4% of the calcium content in the limed raw hide; then change the liquid, add 300% water, adjust the temperature to 35°C, add 1.0% softening enzyme (containing 2000 U / g of Bacillus protease), after rotating for 30 min, adjust to intermittent or continuous rotation, with a total time of 120 min; then change the liquid, add 300% water, adjust the temperature to 35°C, add 6.0% sodium hexametaphosphate, rotate for 60 min to obtain a raw hide that can be used for pickling or tanning, and the calcium content in the raw hide is 11.4% of the calcium content in the limed raw hide.

[0060] Example 5

[0061] The following material dosages are all based on the mass percentage (wt%) of the limed raw hide.

[0062] Load the limed sheepskin into a rotating drum, add 100% water, adjust the temperature to 30°C, add sodium formate as a pH regulator to adjust the pH to about 10, rotate for 5 min, and control the calcium content in the raw hide to be 76.4% of the calcium content in the limed raw hide; then change the liquid, add 100% water, adjust the temperature to 28°C, add 1.0% softening enzyme (containing 3000 U / g of Bacillus licheniformis protease), after rotating for 30 min, adjust to intermittent or continuous rotation, with a total time of 180 min; then change the liquid, add 100% water, adjust the temperature to 30°C, add 2.0% ammonium-free dehairing agent and 1.0% sodium hexametaphosphate, rotate for 90 min to obtain a raw hide that can be used for pickling or tanning, and the calcium content in the raw hide is 17.3% of the calcium content in the limed raw hide.

[0063] Example 6

[0064] The following material dosages are all based on the mass percentage (wt%) of the limed raw hide.

[0065] Load the limed sheepskin into a rotating drum, add 50% water, adjust the temperature to 25°C, add acetic acid as a pH regulator to adjust the pH to about 8, rotate for 10 min, and control the calcium content in the raw hide to be 65.6% of the calcium content in the limed raw hide; then without changing the liquid, add 0.5% softening enzyme (containing 5000 U / g of trypsin), rotate for 30 min; then change the liquid, add 50% water, adjust the temperature to 25°C, add 0.5% disodium ethylenediaminetetraacetate, rotate for 60 min to obtain a raw hide that can be used for pickling or tanning, and the calcium content in the raw hide is 10.4% of the calcium content in the limed raw hide.

[0066] Example 7

[0067] The following material dosages are all based on the mass percentage (wt%) of the limed raw hide.

[0068] Load the limed pigskin into a rotating drum, add 300% water, adjust the temperature to 40°C, add the pH regulator sodium bicarbonate to adjust the pH to about 9.5, rotate for 20 min, and control the calcium content in the raw hide to be 70.6% of the calcium content in the limed raw hide; then change the liquid, add 300% water, adjust the temperature to 40°C, add 2.0% softening enzyme (containing 3000 U / g of bacillus licheniformis protease), after rotating for 30 min, adjust to intermittent rotation or continuous rotation, with a total time of 90 min; then change the liquid, add 300% water, adjust the temperature to 40°C, add 1.0% sodium gluconate and 1.0% ammonium chloride, rotate for 120 min to obtain a raw hide that can be used for pickling or tanning, and the calcium content in the raw hide is 14.7% of the calcium content in the limed raw hide.

[0069] Example 8

[0070] The following material dosages are all calculated as mass percentages (wt%) of the limed raw hide.

[0071] Load the limed horsehide into a rotating drum, add 200% water, adjust the temperature to 32°C, add the pH regulator acetic acid to adjust the pH to about 8.5, rotate for 10 min, and control the calcium content in the raw hide to be 70.9% of the calcium content in the limed raw hide; then change the liquid, add 200% water, adjust the temperature to 32°C, add 2.0% softening enzyme (containing 5000 U / g of trypsin), after rotating for 30 min, adjust to intermittent rotation or continuous rotation, with a total time of 300 min; then change the liquid, add 200% water, adjust the temperature to 32°C, add 3.0% ammonium sulfate, rotate for 90 min to obtain a raw hide that can be used for pickling or tanning, and the calcium content in the raw hide is 16.2% of the calcium content in the limed raw hide.

[0072] Example 9

[0073] The following material dosages are all calculated as mass percentages (wt%) of the limed raw hide.

[0074] Load the limed deer hide into a rotating drum, add 100% water, adjust the temperature to 32°C, add the pH regulator lactic acid to adjust the pH to about 9.5, rotate for 10 min, and control the calcium content in the raw hide to be 65.8% of the calcium content in the limed raw hide; then without changing the liquid, add 0.3% softening enzyme (containing 3000 U / g of bacillus licheniformis protease), after rotating for 30 min, adjust to intermittent rotation or continuous rotation, with a total time of 120 min; then change the liquid, add 50% water, adjust the temperature to 32°C, add 1.0% less ammonium salt dehairing agent and 2.0% sodium gluconate, rotate for 90 min to obtain a raw hide that can be used for pickling or tanning, and the calcium content in the raw hide is 8.6% of the calcium content in the limed raw hide.

[0075] Example 10

[0076] The following material dosages are all calculated based on the mass percentage (wt%) of the limed pelt.

[0077] Load the limed ostrich skin into a rotating drum, add 200% water, adjust the temperature to 40 °C, add adipic acid as the pH regulator to adjust the pH to about 8.0, rotate for 5 min, and control the calcium content in the pelt to be 66.7% of the calcium content in the limed pelt; then without changing the liquid, add 0.1% softening enzyme (containing 5000 U / g of papain), rotate for 30 min, then adjust to intermittent rotation or continuous rotation, with a total time of 90 min; then change the liquid, add 200% water, adjust the temperature to 40 °C, add 2.0% sodium gluconate, rotate for 30 min to obtain a pelt that can be used for pickling or tanning, and the calcium content in the pelt is 9.6% of the calcium content in the limed pelt.

[0078] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A softening method for preventing leather damage, characterized in that, After the liming process of leather making is completed, first adjust the pH of the limed hide to the optimum pH range of the softening enzyme, and keep the calcium content in the hide not less than 65% of the calcium content of the limed hide; then use the softening enzyme for softening operation; after softening is completed, remove the calcium in the softened hide.

2. The softening method for preventing leather damage according to claim 1, characterized in that, The raw hide for the limed hide is any one of animal hides.

3. The softening method for preventing leather damage according to claim 2, wherein The animal hide includes cowhide, sheepskin, pigskin, horsehide, deerhide, ostrich skin.

4. The softening method for preventing leather damage according to claim 1, characterized in that, Use a pH regulator to adjust the pH of the limed hide, and the pH regulator is selected from any one or more of inorganic acids and their salts, organic acids and their salts.

5. The softening method for preventing leather damage according to claim 1, characterized in that, The softening enzyme includes any one or more of microbial protease, animal protease and plant protease.

6. The softening method for preventing leather damage according to claim 1, characterized in that, Use a deliming agent or a decalcifying agent to carry out deliming or decalcifying treatment on the softened hide to remove the calcium in the softened hide.

7. The softening method for preventing leather damage according to claim 6, characterized in that, The deliming agent is selected from any one or more of ammonium salt deliming agents, low-ammonium salt deliming agents, ammonia-free deliming agents.

8. The softening method for preventing leather damage according to claim 6, characterized in that, The decalcifying agent is selected from any one or more of sodium hexametaphosphate, sodium gluconate, disodium ethylenediaminetetraacetate.

9. A leather obtained by using the softening method for preventing leather damage as described in any one of claims 1-8.

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