Chromium tanning agents

Abstract

The invention relates to specific chrome tanning agents and also to their use for the tanning of hides and skins, and to the leather and pelts obtainable as a result. It further provides a new process wherein the protein-masked chrome tanning agents of the invention are obtained from materials containing chromium and collagen, more particularly from leather production wastes such as leather shavings, for example. This enables recycling of chromium-containing leather production wastes, thereby permitting a significant reduction in the amount of such wastes, a fact which leads to considerable economic, environmental and logistical advantages.

Claims

1. Protein-masked chrome tanning agents comprising chromium in the oxidation state 3 and proteins obtained by basic hydrolysis of collagen, wherein the chrome tanning agents have a flocculation point in the range from 66 to 150% basicity, and the flocculation point is determined by preparing an aqueous solution of the chrome tanning agent containing 2.6 wt % of chromium oxide, calculated as Cr.sub.2O.sub.3, stirring the solution continuously at room temperature for 8 h and titrating it with 1.5 molar aqueous sodium carbonate solution until permanent flocculation is apparent.

2. Protein-masked chrome tanning agents according to claim 1, wherein the chromium oxide content, calculated as Cr.sub.2O.sub.3, is more than 5 wt %.

3. Protein-masked chrome tanning agents according to claim 1, wherein the amount of proteins obtained by basic and/or enzymatic hydrolysis of collagen is from 2 to 50 wt %.

4. Protein-masked chrome tanning agents according to claim 1, which have a basicity of 0 to 65%.

5. Protein-masked chrome tanning agents according to claim 1, present in the form of a powder, granules or an aqueous solution.

6. Protein-masked chrome tanning agents according to claim 2, wherein the chromium oxide content, calculated as Cr.sub.2O.sub.3, is more than 8 wt %.

7. Protein-masked chrome tanning agents according to claim 3, wherein the amount of proteins obtained by basic and/or enzymatic hydrolysis of collagen is from 4 to 25 wt %.

8. Protein-masked chrome tanning agents according to claim 4, which have a basicity of 4 to 55%.

9. Process for preparing protein-masked chrome tanning agents, comprising the following process steps: (i) hydrolyzing at least part of the collagen fraction of a material containing chromium and collagen by basic hydrolysis, (ii) removing the insoluble constituents of the material obtained in the basic hydrolysis, (iii) dissolving the insoluble constituents removed in step (ii), by lowering of the pH to a value of 1 to 6, (iv) adding chromium(III) compounds to the solution obtained in step (iii) until said solution has a flocculation point in the range from 66 to 150% basicity.

10. Process according to claim 9, wherein the chrome tanning agents added are one or more chromium(III) compounds.

11. Process according to claim 9, wherein the material containing chromium and collagen comprises chromium-containing leather.

12. Process according to claim 9, wherein the lowering of the pH is accomplished by addition of an acid.

13. Process according to claim 9, wherein the basic hydrolysis is accomplished using oxides or hydroxides of the alkali and/or alkaline earth metals.

14. Process according to claim 9, wherein the masked chrome tanning agents possess a basicity of 0 to 65%.

15. Process according to claim 9, wherein after adding chromium(III) compounds in step (iv), drying takes place.

16. Process according to claim 9, wherein the process step comprising lowering the pH and the process step comprising adding chromium(III) compounds are combined in a process step comprising the lowering of the pH by adding acidic chromium(III) compounds.

17. Process for the tanning and/or retanning of leather or pelts by treatment of hides or skins with protein-masked chrome tanning agents according to claim 1.

18. Process according to claim 10, wherein the chrome tanning agents added are chromium(III) compounds selected from chromium(III) oxides, chromium(III) hydroxides, chromium(III) halides and chromium(III) sulfates and mixtures of these substances.

19. Process according to claim 12, wherein the lowering of the pH is accomplished by addition of a mineral acid.

20. Process according to claim 13, wherein the basic hydrolysis is accomplished using oxides or hydroxides of sodium, potassium and/or magnesium.

Description

EXAMPLES

(1) The examples which follow elucidate the invention in more detail, without any intention that they should limit the invention.

(2) Preparation of the Chrome Tanning Agents

(3) The chromium-containing solution A used in the examples below comes from a commercially operated plant for the basic processing of the shavings of chrome-tanned cattle hide, which produces a residue containing chromium and collagen (chrome cake). This residue is dissolved using sulfuric acid and then the pH is adjusted to 2.3. The solution possesses a basicity of 9.1% and the chromium oxide content of the solution, calculated as Cr.sub.2O.sub.3, is 3.6%. The solids content is 35%. The flocculation point measured (for the solution diluted to 2.6% chromium oxide) is at 520% basicity.

(4) The chrome tanning agent added in the examples is a pulverulent basic chromium sulfate (ChromosalB from Lanxess Deutschland GmbH), which possesses a basicity of 33% and a chromium oxide content of around 26%, calculated as Cr.sub.2O.sub.3. The flocculation point measured for the solution diluted to 2.6% chromium oxide is at 62% basicity.

(5) M1) Mixture of Chromium Solution A and Basic Chromium Sulfate

(6) In a stirred flask, 103 g of water and 247 g of basic chromium sulfate are added to 650 g of the chromium-containing solution A. The solution is then heated to 80 C. and stirred at this temperature for 1 h.

(7) The mixture possesses a basicity of 24% and contains 8.8% of chromium oxide, calculated as Cr.sub.2O.sub.3. The flocculation point for the solution diluted to 2.6% chromium oxide is at 89% basicity.

(8) M2) Mixture of Chromium Solution A and Basic Chromium Sulfate

(9) In a stirred flask, 505 g of water and 295 g of basic chromium sulfate are added to 200 g of the chromium-containing solution A. The solution is then heated to 80 C. and stirred at this temperature for 1 h.

(10) The mixture possesses a basicity of 30% and contains 8.4% of chromium oxide, calculated as Cr.sub.2O.sub.3. The flocculation point for the solution diluted to 2.6% chromium oxide is at 72% basicity.

(11) M3) Mixture of Chromium Solution A and Basic Chromium Sulfate

(12) In a stirred flask, 288 g of water and 412 g of basic chromium sulfate are added to 300 g of the chromium-containing solution A. The solution is then heated to 80 C. and stirred at this temperature for 1 h.

(13) The mixture possesses a basicity of 30% and contains 11.8% of chromium oxide, calculated as Cr.sub.2O.sub.3. The flocculation point for the solution diluted to 2.6% chromium oxide is at 76% basicity.

(14) M4) Mixture of Chromium Solution A and Basic Chromium Sulfate

(15) In a stirred flask, 155 g of water and 545 g of basic chromium sulfate are added to 300 g of the chromium-containing solution A. The solution is then heated to 80 C. and stirred at this temperature for 1 h.

(16) The mixture possesses a basicity of 31% and contains 15.2% of chromium oxide, calculated as Cr.sub.2O.sub.3. The flocculation point for the solution diluted to 2.6% chromium oxide is at 69% basicity.

(17) Performance Examples Using the Chrome Tanning Agents

Use Example 1: Tanning

(18) The starting material used comprises (cattle) pelts which have been split and weighed after liming and whose thickness is approximately 1.8-2.0 mm. All of the following amounts for use of chemicals are based on this reference weight (pelt weight).

(19) After customary preparatory operations with which the skilled person is familiar, 18% of the chrome tanning agent prepared in example M1, in the form of a solution, is added to the pickled pelts, and treatment is carried out for 60 min. This is followed by addition of magnesium oxide, as a slow-acting, alkalizing product. The pH of the solution climbs as a result from 2.6 after addition of the chrome tanning agent to a final pH of 3.8 within 8 h. The temperature is likewise increased, from 20 C. initially to 40 C. Table 1 sets out the steps in the process of the invention for producing semi-finished leather products (the wt % are based on the pelt weight).

(20) TABLE-US-00001 TABLE 1 Run time Process wt % Chemicals [min] Remarks 200 Water 32 C. 10 Drain float 50 Water 32 C. 1.5 Ammonium chloride 0.2 Na bisulfite 45 Cut with phenolphthalein: colourless, pH 8.6 Drain float 50.0 Water 35 C. 5 0.20 PELTEC ADN 1:5 0.15 LEVAZYM AF 60 Drain float 100 Water 20 C. 6.0 Sodium chloride 5 0.4 Formic acid 1:10 10 0.8 Sulfuric acid 1:10 90 pH 3.4 18 Mixture M1 60 + 0.4 BLANCOROL 480 BA-I pH 3.8 Automatic 40 C. Drain float

(21) After the process of the invention, the semi-finished leather products are stored on a trestle, sammied and shaved.

(22) The wet blues have a shrinkage temperature of >100 C. and a Cr.sub.2O.sub.3 content of 4.1%. The Cr.sub.2O.sub.3 content of the residual float is 4.2 g/l.

(23) The wet blues thus produced are notable in particular for good fullness and a soft feel. The grain appearance is particularly fine and smooth and there is increased absence of puckering.

Use Example 2: Tanning

(24) As use example 1, but with final pH of 4.2.

(25) The wet blues have a shrinkage temperature of >100 C. and a Cr.sub.2O.sub.3 content of 4.4%. The Cr.sub.2O.sub.3 content of the residual float is 2.1 g/l.

(26) The wet blues thus produced, in spite of the increased final pH, show no chromium precipitation at all and possess an attractive blue colour. The fullness, the feel, the grain appearance and the absence of puckering are comparable with use example 1.

Use Example 3: Tanning

(27) As use example 1, only with 14.5% of the chrome tanning agent prepared according to example 3. Final pH 3.8.

(28) The wet blues have a shrinkage temperature of >100 C. and a Cr.sub.2O.sub.3 content of 4.3%. The Cr.sub.2O.sub.3 content of the residual float is 2.7 g/l.

(29) The wet blues thus produced are notable in particular for good fullness and a soft feel. The grain appearance is particularly fine and smooth and the absence of puckering is increased.

Use Example 4: Tanning

(30) As use example 3, but with final pH of 4.1.

(31) The wet blues have a shrinkage temperature of >100 C. and a Cr.sub.2O.sub.3 content of 4.6%. The Cr.sub.2O.sub.3 content of the residual float is 1.9 g/l.

(32) The wet blues thus produced, in spite of the increased final pH, show no chromium precipitation at all and possess an attractive blue colour. They likewise possess good fullness and a soft feel. The grain appearance is particularly fine and smooth and the absence of puckering is increased.

Comparative Example 1: Tanning

(33) As use example 1, only with 6.5% basic chromium sulfate (Chromosal B).

(34) Final pH 3.8.

(35) The wet blues have a shrinkage temperature of >100 C. and a Cr.sub.2O.sub.3 content of 4.5%. The Cr.sub.2O.sub.3 content of the residual float is 2.0 g/l.

(36) The wet blues thus produced, compared to the wet blues produced using the chrome tanning agents of the invention, have a greener colour. Moreover, they possess less fullness and a harder feel. The grain appearance is coarser and the lack of puckering is lower.

Use Example 5: Retanning

(37) Semi-finished leather products shaved to a thickness of 1.1 mm are treated by customary preparatory operations with which the skilled person is familiar, such as washing, then admixed with 12% of the chrome tanning agent prepared in example M1, in the form of a solution, and treatment is carried out for 60 min. Then a slowly neutralizing Syntan (Tanigan PAK from LANXESS Deutschland GmbH) and product with an alkalizing activity are added, and the pH is raised to 5.1.

(38) This was followed by application of a typical retanning formula for the production of furniture crust leather.

(39) Table 2 sets out the steps of the process of the invention for producing crust leather (the wt % are based on the shaved weight).

(40) TABLE-US-00002 TABLE 2 Material: wet blue mm: 1.0-1.1 Process % Chemicals min Remarks 300 Water 40 C. 0.4 BLANCOROL CGA 15 0.3 Peltec SW pH 4.1 Drain float 200 Water 45 C. 12.0 Mixture M1 60 pH 3.4 2.0 TANIGAN PAK 1.0 Sodium formate 10 + 1.0 Sodium bicarbonate 60 pH 5.1 Drain float 50 Water 35 C. 4.0 X-Biomer P 1:4 4.0 TANIGAN BN 1:4 20' 5.0 TANIGAN VR + 3.0 Chestnut tanning agent 2.0 TANIGAN PR 10 2.0 BAYKANOL TF 2N 2.0 BAYGENAL Red GT 30 + 8.0 LEVOTAN XB 6.0 LEVOTAN W 1:4 60 + Heating to 50 C. 3.0 Formic acid 85% 1:5 30 pH 3.3 Drain float + 300 Water 50 C. 10 Drain float 300 Water 20 C. 10 Drain float Vacuum drying, milling

(41) The crust leathers produced in this way are notable particularly for good fullness and a soft feel. The grain appearance is particularly fine and smooth and the absence of puckering is increased. The colouring of the crust leathers is notably intense and uniform.