Tanning process for obtaining leather

Abstract

The invention concerns a process for tanning hide to obtain leather. The general process for obtaining the intermediary wet blue stage comprises the following steps: a) a picking step with acid and salt, followed by b) a tanning step with chromium salt, followed by c) a basification step. The invention is characterized in that the bath of the pickling step comprises organic acids selected from 2-Methyl glutaric acid (MGA), ethyl succinic acid (ESA) and mixture thereof instead of the traditional strong acid, generally sulfuric acid This process requires less basification agent and enables an increase of the up-taking of the re-tanning products. This invention provides leather with improved mechanical properties.

Claims

1. A process for tanning hides, comprising: a) immerging the hides in a bath with acid, salt, and an organic acid mixture, followed by b) immerging the hides in a bath with chromium salt, and subsequently c) immerging the hides in a bath with a basifying agent, wherein the organic acid mixture comprises: at least 70 weight % of 2-methyl glutaric acid; greater than 0 and at most 30 weight % of ethyl succinic acid; and between 0 and 15 weight % of adipic acid.

2. The process according to claim 1, wherein the amount of organic acids in the bath of step a) of the process is between 0.25 to 10% based on the weight of the hides.

3. The process according to claim 1, wherein the organic acid further comprises adipic acid.

4. The process according to claim 1, wherein the organic acid is a mixture comprising: between 80 and 95 weight % of 2-methyl glutaric acid; greater than 0 and at most 10 weight % of ethyl succinic acid; between 5 and 10 weight % of adipic acid.

5. The process according to claim 1, wherein the bath of step a) of the process further comprises, based on the weight of the hides, between 2.5 and 10 weight % of the salt.

6. The process according to claim 1, wherein the bath of step a) of the process further comprises based on the weight of the hides, between 0.4 and 2 weight % of formic acid.

7. The process according to claim 1, wherein the bath of step a) of the process further comprises a bleaching agent.

8. The process according to claim 1, wherein the pH of the bath of step a) of the process is between 3.0 and 5.0.

9. The process according to claim 1, wherein the pH of the bath of step a) of the process is between 3.4 and 4.0.

10. The process according to claim 1, wherein the amount of basifying agent used in step c) of the process is between 0.20 and 0.45%, based on the weight of the hides.

11. The process according to claim 2, wherein the amount of organic acids in the bath of step a) of the process is from 0.5 to 5%, based on the weight of the hides.

12. The process according to claim 5, wherein the bath of step a) of the process further comprises between 2.5 and 10 weight % of sodium chloride, based on the weight of the hides.

13. The process according to claim 1, wherein the amount of basifying agent used in step c) of the process is between 0.3 and 0.4%, based on the weight of the hides.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) In the process according to the invention, the amount of organic acids in the bath of the pickling step is advantageously comprised between 0.25 to 10%, preferably from 0.5 to 5% of the weight of the hides.

(2) In one particular embodiment of the invention, the organic acids further comprise Adipic Acid (AA).

(3) In the process according to the invention, the organic acids preferably comprise: between 70 and 100 weight % of MGA; between 0 and 30 weight % of ESA; between 0 and 15 weight % of AA.

(4) More particularly, the organic acids can comprise: between 80 and 95 weight % of MGA; between 0 and 10 weight % of ESA; between 5 and 10 weight % of AA.

(5) According to the invention, the bath of the pickling step can further comprise, with relation to the hide weight, between 2.5 and 10 weight % of a salt, in particular sodium chloride.

(6) It can also be preferred that the bath of the pickling step further comprises with relation to the hide weight, between 0.4 and 2 weight % of formic acid.

(7) In some embodiments, the bath of the pickling step further comprises a bleaching agent.

(8) According to the process of the invention, the pH of the bath of the pickling step is advantageously comprised between 3.0 and 5.0, and more preferably between 3.4 and 4.0.

(9) The process according to the invention can also be characterized in that the amount of basifying agent used in the basification step is comprised between 0.20 and 0.45%, preferably between 0.3 and 0.4% with relation to the weight hide.

EXAMPLES

Examples 1 to 3

Production of the Wet Blue Intermediary Stage

Example 1

(10) 200 kg of hide for which liming, unhairing and fleshing process are completed is washed in the tanning drum with the same weight of water for 10 minutes.

(11) For all examples, all ingredients added thereafter are weight percentage of the initial hide weight.

(12) After the washing the water bath is discharged and the hides are submitted to deliming and bating with the use of 1.8% of ammonium sulfate and 1% of a commercial deliming agent based on di-carboxylic acids (Ex: Rhodiaeco Descal SD commercialized by Rhodia Poliamida e Especialidades Ltda.). After all, bating process takes place, adding 0.08% of a standard commercial proteolytic enzyme (run 60 minutes), (pH=8.0). At the end of these operations the cross-section of the hide does not show a pink color with phenolphthalein indicator.

(13) The hides are washed twice with 100% of water, based on pelt weight, and the washings are discharged.

(14) Pickling Step:

(15) With relation to the hide weight, 40% of water is added followed by 5% of sodium chloride (B (Baum scale) 6 to 7) (run 15 minutes), 0.4% of a commercial bleaching (run for 15 minutes). After this time, 0.8% of 85% formic acid diluted in water (1 to 10) is added into the drum (run 30 minutes) followed by the addition of 0.75% of a mixture of 2-Methyl glutaric acid (MGA), ethyl succinic acid (ESA) and adipic acid (AA) diluted in water (1 to 3) and the drum is run for an additional 15 minutes. After this time the pH of the bath is around 3.5.

(16) Tanning Step:

(17) At this point, 3% of commercial chromium sulphate salt (ex: basic chromium sulphate, which presents 33% alkalinity and 25 to 26% chrome HI oxide) is added (run for 60 minutes). A second addition of 3% of chromium sulphate salt is added and the drum is run for additional 6 hours after which time the chromium has completely crossed the hide cross-section.

(18) Basifyinq Step:

(19) After this time, 20% of water is added followed by 0.35% of a commercial basifying agent (ex: magnesium oxide) (run 90 minutes). The water bath is heated from 35 C. to 50 C. during 5 hours, the drum is drained, the wet blue is washed with 100% of water (based on pelt weight), drained and washed again with 80% of water.

(20) The obtained Wet Blue is submitted to the analysis of the total chromium content, chromium in layers and evaluation by Scanning Electron Microscope (EDS) (Table 1 and FIG. 1a).

Example 2

(21) 1000 kg of hide for which liming, unhairing and fleshing process are completed is washed in the tanning drum with 100% of water (based on pelt weight) for 10 minutes. After that, the hides are submitted to deliming and batting according to example 1.

(22) With relation to the hide weight, 40% of water and 5% of sodium chloride (B 6 to 7) are added into the drum (run for 15 minutes), followed by 0.4% of a commercial bleaching (run 15 minutes). After this time, 0.8% of 85% formic acid diluted in water (1 to 10) is added (run 30 minutes) followed by the addition of 2.5% of an aqueous solution of a mixture of 2-Methyl glutaric acid (MGA), ethyl succinic acid (ESA) and adipic acid (AA) and the drum is run for an additional 15 minutes. After this time the pH of the bath is around 3.5.

(23) At this point a 3% of commercial chromium sulphate salt (ex: basic chromium sulphate, which presents 33% alkalinity and 25 to 26% chrome III oxide) is added (run 60 minutes). A second addition of 3% of chromium sulphate salt is added and the drum is run for an additional 6 hours, after which time the chromium has completely crossed the hide cross-section.

(24) After this time, 20% of water is added and 0.35% of a commercial basifying agent (ex: magnesium oxide) is added into the drum (run 90 minutes). The water bath is heated from 35 C. to 50 C. during 5 hours, the drum is drained, the wet blue is washed with 100% of water (based on pelt weight), drained and washed again with 80% of water.

Example 3

Comparative Example; Traditional Process with Strong Acidification

(25) 200 kg of hide for which liming, unhairing and fleshing process are completed is washed in the tanning drum with 100% of water (based on pelt weight) for 10 minutes. After that, the hides are submitted to deliming and batting according to example 1.

(26) With relation to the hide weight, 40% of water, 6% of sodium chloride (B 6 to 7) (run 15 minutes), 0.4% of a commercial bleaching are added into the drum (run 15 minutes). 0.6% of 85% formic acid diluted in water (1 to 10) is added into the drum (run 30 minutes) followed by the addition of 0.3% of sulfuric acid diluted in water (1 to 15)(run 15 minutes), 0.3% of sulfuric acid diluted in water (1 to 15)(run 15 minutes) and 0.4% of sulfuric acid diluted in water (1 to 15) (run 3 hours). After this time the pH of the bath is around 2.5 to 3.

(27) At this point 3% of commercial chromium sulphate salt (ex: basic chromium sulphate, which presents 33% alkalinity and 25 to 26% chrome III oxide) is added into the drum (run for 60 minutes). A second addition of 3% of chromium sulphate salt is added and the drum is run for additional 3 hours after which time the chromium has completely crossed the hide cross-section.

(28) After this time, 20% of water is added followed by 0.35% of a commercial basifying agent (ex: magnesium oxide) (run 90 minutes). A second portion of 0.15% magnesium oxide is added and the drum is run for an additional 90 minutes. The water bath is heated from 35 C. to 50 C. during 5 hours, the drum is drained, the wet blue is washed with 100% of water (based on pelt weight), drained and washed again with 80% of water.

(29) The obtained Wet Blue was submitted to the analysis of the total chromium content, chromium in layers and evaluation by Scanning Electron Microscope (EDS) (Table 1 and FIG. 1b).

Example 4

Production of the Retanned Hides (Crust Step) of Examples 1 to 3

(30) The Wet Blue obtained in the examples 1 and 3 are identified by different marks, combined and submitted to a standard re-tanning process. The marked Wet Blue hides are placed in the drum, and washed with 200% of water at 30 C. (based on Wet Blue weight) for 30 minutes and the washing is drained.

(31) 150% of water, 2% of sodium formiate and 0.3% of sodium bicarbonate are added into the drum and run for 60 minutes after which time the water bath showed a pH=4.4.

(32) The water bath is drained and 60% of water at 30 C., 2% of a commercial polyacrylate (powder) (run 60 minutes) and the water bath is drained.

(33) 150% of water at 60 C., 2% of commercial sulfited synthetic oil, 2% of commercial sulfated emulsified vegetal oil are added, the drum is run for 45 minutes and the water bath is drained.

(34) 0.3% of 85% formic acid diluted in water (1 to 5) is added (run 20 minutes), the water bath is drained and the re-tanned hides are washed.

(35) The re-tanned hides are left standing for 12 hours, stretched, naturally dried and softened.

(36) The properties of the re-tanned hides are evaluated and compared concerning tensile strength, breaking strength, tear strength, progressive tensile strength, up-taking of re-tanning products based on a square foot weight of crust, light fastness, color appearance and comparative evaluation by Scanning Electron Microscope (EDS). (Tables 2 to 4 and FIGS. 2a and 2b).

Examples 5 and 6

Production of the Wet Blue Intermediary Stage

Example 5

Comparative Example According to WO 2004/015148

(37) 500 kg of hide for which liming, unhairing and fleshing process are completed is washed in the tanning drum with 100% of water (based on pelt weight) for 10 minutes. After that, the hides are submitted to deliming and batting according to example 1.

(38) With relation to the hide weight, 40% of water, 5% of sodium chloride (B 6 to 7) (run 15 minutes) followed by the addition of 0.4% of a commercial bleaching (run for 15 minutes). 0.8% of 85% formic acid diluted in water (1 to 10) is added (run 30 minutes) followed by the addition of 0.75% of Dioro (commercial product from Rhodia Poliamida e Especialidades Ltda based on a mixture of di-carboxylic acids) and the drum is run for 15 minutes. After this time the pH of the bath is around 3.4 to 3.6.

(39) At this point a 3% of commercial chromium sulphate salt (ex: basic chromium sulphate, which presents 33% alkalinity and 25 to 26% chrome III oxide) is added (run 60 minutes). A second addition of 3% of chromium sulphate salt is added and the drum is run for an additional 6 hours after which time the chromium has completely crossed the hide cross-section.

(40) After this time, 20% of water is added and 0.35% of a commercial basifying agent (ex: magnesium oxide) and the drum is run for 90 minutes. The water bath is heated from 35 C. to 50 C. during 5 hours, the drum is drained, the wet blue is washed with 100% of water (based on pelt weight), drained and washed again with 80% of water.

(41) The obtained Wet Blue was submitted to the analysis of the total chromium content and chromium in layers (Table 1).

Example 6

Comparative Example; Traditional Process with Strong Acidification

(42) 500 kg of hide for which liming, unhairing and fleshing process are completed is washed in the tanning drum with 100% of water (based on pelt weight) for 10 minutes. After that, the hides are submitted to deliming and batting according to example 1.

(43) With relation to the hide weight, 40% of water, 5% of sodium chloride (B 6 to 7) are added and the drum is run for 15 minutes, followed by the addition of 0.4% of a commercial bleaching (run 15 minutes). 0.6% of 85% formic acid diluted in water (1 to 10) is added (run 30 minutes) followed by the addition of 0.3% of sulfuric acid diluted in water (1 to 15) (run for 15 minutes), 0.3% of sulfuric acid diluted in water (1 to 15) (run for 15 minutes) and 0.4% of sulfuric acid diluted in water (1 to 15) and the drum is run for an additional 2 hours. After this time the pH of the bath is around 2.6 to 3.

(44) At this point a 3% of commercial chromium sulphate salt (ex: basic chromium sulphate, which presents 33% alkalinity and 25 to 26% chrome III oxide) is added (run 60 minutes). A second addition of 3% of chromium sulphate salt is added and the drum is run for an additional 3 hours after which time the chromium has completely crossed the hide cross-section.

(45) After this time, 20% of water is added and 0.35% of a commercial basifying agent (ex: magnesium oxide) (run 90 minutes). A second portion of 0.15% magnesium oxide is added and the drum is run for an additional 90 minutes. The water bath is heated from 35 C. to 50 C. during 5 hours, the drum is drained, the wet blue is washed with 100% of water (based on pelt weight), drained and washed again with 80% of water.

Example 7

Production of the Retanned Hides (Crust Step) of Examples 5 and 6

(46) The Wet Blue obtained in the examples 5 and 6 are identified by different marks and submitted to a standard re-tanning process according to example 4.

(47) Results

(48) The properties of the re-tanned hides are evaluated and compared concerning tensile strength, breaking strength, tear strength, progressive tensile strength, up-taking of re-tanning products based on a square foot weight of crust, light fastness and color (Table 2 to 4).

(49) TABLE-US-00001 TABLE 1 Analysis of chromium in the final Wet Blue 3.5% minimum Reference Value Example 3 Example 1 Example 5 Dermis 5.0 5.0 5.2 Middle 3.5 4.0 3.6 Epidermis 4.2 4.5 4.5 Layers Average 4.2 4.5 4.5

(50) FIG. 1 represent Scanning Electron Microscope (EDS) of Wet Blue samples.

(51) FIG. 1.a is a wet blue according to example 1 of the invention

(52) FIG. 1.b. is a wet blue according to comparative example 3

(53) TABLE-US-00002 TABLE 2 Comparative weight of crust leather Example 1 compared Example 5 compared to Example 3 to Example 6 after re-tanning after re-tanning Crust mass variation +2.1 g 0.54 g (up taking of re-tanning products) Percentage Variation 5% 1.3%

(54) TABLE-US-00003 TABLE 3 Comparative physical-mechanical properties of crust leather Mini- Exam- Exam- Exam- Mea- mum ple 3 ple 1 ple 5 sure- Val- after re- after re- after re- ments ues tanning tanning tanning Tensile Direc- Breaking 150 156.8 133.1 149 Strength tion A Strength IULTCS (N) IUP6/ISO Tension 15 to 12.8 10.2 12.1 3376:2011 Strength 18 (N/mm2) Direc- Breaking 150.4 214.4 125.5 tion B Strength (N) Tension 14.5 17.1 10.5 Strength (N/mm2) Progressive Tensile Tear 50 63.2 74.7 50.6 Strength IULTCS 8/ISO Strength 3372-2:2002 (N) Specific 49.1 54.8 60.2 42.3 strength (N/mm)

(55) TABLE-US-00004 TABLE 4 Comparative light fastness Example 3 after Example 1 after Example 5 after re-tanning re-tanning re-tanning Light Fastness 4 >4 >4 NOTES: Xenon Lamp (Method EN ISO 105-B02:2002) Total exposure time: 24 hours, Filter Ultraviolet Irradiance: 445 W/m.sup.2 in 300 to 800 nm After the test the specimens are kept at least 1 hour in the dark in a conditioned environment at 23 +/ 2 C. and air relative humidity of 50 +/ 5%.

(56) FIG. 2 represent Scanning Electron Microscope (EDS) of Crust samples

(57) FIG. 2.a is a crust from wet blue according to example 1 of the invention

(58) FIG. 2.b is a crust from wet blue according to comparative example 3

CONCLUSIONS

(59) The use of the organic acids (in particular the mixture of 2-Methyl glutaric acid (MGA), ethyl succinic acid (ESA) and adipic acid (AA)) allows the complete elimination of the sulfuric acid during pickling step. The invention therefore provides a safer process and less risk for the employees.

(60) The invention requires less basifying agent (in particular MgO) in the basification step with regards to the standard process. The impact is economical (less chemicals) and also reduces the process time (economical, save energy).

(61) The wet blue obtained with the invention show a more homogeneous distribution of chromium with regards to the standard process and also with regards to the former process of the inventor. The physical-mechanical properties of crust and final leather are improved as regards the standard process and as regards the previous process of the inventor.