阅读说明：本技术 铬鞣剂 (Chrome tanning agent ) 是由 福尔克尔·拉贝 苏珊妮·杜佩特 于尔根·赖纳斯 于 2019-01-11 设计创作，主要内容包括：本发明涉及特定的铬鞣剂、还有其用于鞣制原料皮和毛皮的用途、以及可由此获得的皮革和裸皮。本发明进一步涉及一种新颖方法,其中从含有铬和胶原的材料、特别地例如从皮革生产废料诸如皮革削匀物刨花来获得本发明的蛋白质掩蔽的铬鞣剂。这使得能够再循环来自皮革生产的含铬废料,从而允许显著减少此类废料的量,这将产生相当大的经济、生态和物流优势。(The invention relates to a specific chrome tanning agent, also to the use thereof for tanning hides and skins, and to the leathers and pelts obtainable therefrom. The invention further relates to a novel process wherein the protein masked chrome tanning agent of the invention is obtained from materials containing chromium and collagen, in particular, for example, from leather production waste such as leather shavings. This enables recycling of chromium-containing waste from leather production, allowing a significant reduction in the amount of such waste, which would yield considerable economic, ecological and logistic advantages.)

1. A protein masked chrome tanning agent comprising chromium in the oxidation state 3 and protein obtained from alkaline hydrolysis of collagen, wherein the chrome tanning agent has a flocculation point in the range of from 66% to 150% alkalinity and the flocculation point is determined as follows: preparation of a catalyst containing Cr₂O₃An aqueous solution of chrome tanning agent, calculated as 2.6% by weight of chromium oxide, was stirred continuously at room temperature for 8h and titrated with 1.5 molar aqueous sodium carbonate solution until permanent flocculation was evident.

2. Protein masked chrome tanning agent according to claim 1, wherein the chromium oxide content is in terms of Cr₂O₃Calculated to be more than 5 wt%, preferably more than 8 wt% and more preferably from 10 to 26 wt%.

3. Protein masked chrome tanning agent according to claim 1 or 2, wherein the amount of protein obtained from hydrolysis of collagen is from 2 to 50 wt%, preferably from 4 to 25 wt% and more preferably from 5 to 12 wt%.

4. Protein masked chrome tanning agent according to one or more of claims 1 to 3, having a basicity of 0% to 65%, preferably 4% to 55%, more preferably 9% to 40%.

5. Protein-masked chrome tanning agent according to one or more of claims 1 to 4, present in the form of a powder, granules or an aqueous solution.

6. A process for the preparation of a protein masked chrome tanning agent, the process comprising the following process steps:

alkaline hydrolysis of at least part of the collagen component of the material containing chromium and collagen,

removing the insoluble components of the material obtained in the hydrolysis,

dissolving the insoluble fraction removed in the previous step by lowering the pH to a value of 1 to 6, preferably 1 to 3 and more preferably 2.5,

adding a chromium (III) compound to the solution obtained in the preceding step until said solution has a flocculation point in the range from 66% to 150% alkalinity.

7. A process according to claim 6, wherein the added chrome tanning agent is one or more chromium (III) compounds, preferably selected from chromium (III) oxide, chromium (III) hydroxide, chromium (III) halide and chromium (III) sulfate and mixtures thereof, more preferably basic chromium (III) sulfate.

8. A method according to claim 6 or 7, wherein the chromium and collagen containing material comprises chromium containing leather, preferably chromium containing leather shavings.

9. The method according to one or more of claims 6 to 8, wherein the lowering of the pH is done by adding an acid, preferably a mineral acid, more preferably sulfuric acid and/or hydrochloric acid, more preferably sulfuric acid.

10. The process according to one or more of claims 6 to 9, wherein the alkaline hydrolysis is carried out using an oxide or hydroxide of an alkali metal and/or alkaline earth metal, preferably an oxide or hydroxide of sodium, potassium and/or magnesium, more preferably potassium hydroxide.

11. Method according to one or more of claims 6 to 10, wherein the masked chrome tanning agent has a basicity of 0% to 65%.

12. Method according to one or more of claims 6 to 11, wherein after the addition of the chrome tanning agent, drying, preferably by spray drying, is carried out and the protein-masked chrome tanning agent is obtained in the form of a powder or granules.

13. The method according to one or more of claims 6 to 12, wherein the treatment step comprising lowering the pH and the treatment step comprising adding a chromium (III) compound are combined in a treatment step comprising lowering the pH by adding an acidic chromium (III) compound.

14. Use of a protein masked chrome tanning agent according to one or more of claims 1 to 5 for tanning or retanning leather.

15. A process for tanning and/or retanning leather or pelts by treating the hides or skins with a protein-masked chrome tanning agent according to one or more of claims 1 to 5.

Technical Field

The present invention relates to specific chrome tanning agents, to the production thereof, and also to the use thereof for tanning hides and skins, and to the leathers and pelts obtainable therefrom.

Background

In leather production, small leather shavings consisting mainly of collagen material are obtained at a thickness adjustment called shaving. Although leather has been previously tanned using a chromium tanning agent, tanned leather still in the wet state (also known as wet blue) contains not only collagen but usually also about 2 to 6 wt% of chromium in the oxidation state (III).

However, from a health point of view, the chromium (III) compounds present in professionally tanned leather are considered to be unthinkable, and incorrect tanning or insufficient post-treatment of the leather or shaving may lead to the formation of toxic or carcinogenic chromium (VI) compounds.

Since chrome tanning represents the most common tanning process, large waste volumes of chrome-containing leather trimmings are produced (approximately 17000 tons per year in germany alone). The separation into protein and chromium components and in particular the reuse of the chromium component, which is only possible at high cost and high complexity, means that complete recycling of large waste quantities is generally uneconomical, with the result that the leather shaving is disposed of and landfilled in its entirety as special waste, pressed to form a bonded leather material, or burnt under controlled conditions, albeit environmentally hazardous. In addition, a large amount of collagen is lost in the process, which collagen is inherently-i.e. not contaminated with chromium-useful for cosmetics, medicine, and human and animal nutrition.

Common methods for separating protein and chromium include decomposition of leather shavings using acids or bases and/or decomposition using microorganisms or enzymes with heating, which are often combined with each other in complex, multistage operations.

Overall, alkaline hydrolysis of leather shaves (possibly in combination with enzymatic hydrolysis) has the following advantages: as disclosed in DE4238979 a1, the protein component (as a component of greater economic interest) can be recovered in a first step in a chromium-free form, for example wherein the protein component obtained as gelatin has a chromium content of <0.1 ppm.

In the case of acidic treatment, in contrast, chromium is first separated off in order to obtain a protein fraction which is as free as possible of chromium. The problem here is that a relatively high proportion of chromium remains in the collagen after a single treatment of the chromium shaving with acid. Thus, Ferreira (Waste Management, 2010, 30, pages 1091-1100) describes how 55% -60% of the chromium can be recovered in a single, very long sulfuric acid treatment time of 3-5 days. The remaining protein residues still have such a high proportion of chromium (40-45%) and are produced by the inability to go through landfill disposal to toxic cr (vi) compounds. In order to achieve chromium removal from the leather, some acid treatment step is required in order to be able to reasonably reuse the protein components, as in the case of alkaline hydrolysis; however, in the acid solution formed, the fraction of broken proteins in solution is increasing and the concentration of chromium steadily decreases, so that reuse is more difficult. However, the large number of acidic extraction steps required to reduce the chromium content of the protein component to a level that allows its use in cosmetics, medicine or human and animal nutrition makes the overall operation uneconomical.

In US 2005/0069472 a, the chromium shaving is completely acid hydrolyzed and the obtained chromium hydrolyzate is used as tanning agent. In the described example, however, less than half of the chromium used is incorporated during tanning. Since the homogenate is completely hydrolyzed, it is impossible to obtain a protein fraction.

At present, the method mainly used for separating proteins and chromium is the decomposition of leather trimmings using alkali (optionally in combination with microbial and/or enzymatic decomposition with heating) (as described, for example, in Cabeza, l.f., JALCA [ journal of american society of leather chemists ], 1998, 93, pages 83-97). In the described process, the leather shavings are first decomposed with magnesium oxide to give not only gelatin but also chromium-containing residues (known as chromium cakes). The cake is further hydrolyzed by enzymes to give collagen hydrolysate and chromium containing solids. The problem here is that the chromium cake can no longer be used directly as a tanning agent, since it still contains a significant amount of protein which prevents the tanning effect. To remove the broken protein content, the chromium cake is dissolved in sulfuric acid in the prior art, and then the pH is raised in two further steps using sodium hydroxide to release chromium containing residues from the protein component. Each of these steps requires a filtration step, which not only produces large amounts of protein-like waste products that cannot be recycled, but ultimately produces purified chromium (III) sulfate that can then be reused as a chrome tanning agent. The multiplicity of treatment steps and the not insignificant fraction of the protein-like waste products which cannot be recycled are all comparable to the economic efficiency of the process.

Another method for treating chromium cakes is disclosed in CN 103014191 a. In this method, as in the example above, after alkaline hydrolysis of the homogenate and removal of the protein, the chromium cake is dissolved in a strong acid, after which a toxic and mutagenic cr (vi) compound is added in order to remove, by oxidation, the proteinaceous components still present. A reducing agent is subsequently added to remove excess cr (vi). This step must be carefully monitored because if the chromium (VI) residue is not completely removed, it is not possible to recover the chrome tanning agent again in this way. Thus, the recovered chrome tanning agent containing almost no protein can be subsequently used as a chrome tanning agent. However, the use of cr (vi) compounds imposes strict safety requirements on the production facilities and personnel in respect of the implementation of the process and is therefore not practically satisfactory.

Disclosure of Invention

It is therefore an object of the present invention to provide a method for recycling chromium and collagen containing materials, and more particularly leather shaving, which avoids the above disadvantages of the prior art.

The chrome tanning agent may be used directly, for example in the form of a chromium salt or a solution thereof, although for many applications it is advantageous to mask the tanning agent with an organic acid (examples are aliphatic or aromatic carboxylic acids such as acetic acid, for example or a salt thereof). Examples of such chrome tanning agents are described in DE 1230170B. Masked chrome tanning agents are known to be suitable for the mild and less risky tanning of leather, and also for the retanning of leather, and are known to have a relatively high alkali stability. Thus, the risk of chrome spotting during the neutralization stage of tanning is reduced. The obtained leather has better fullness and softer hand feeling. The grain appearance is particularly fine and smooth and increased without wrinkling. In addition, the coloration of leather is more concentrated and homogeneous, as disclosed, for example, in Bibliothek des Leders [ leather Bank ], volume 3, "Gerbmitel, Gerbung, Nachgerbang" [ tanning, retanning ], KurtFaber, 2 nd edition, 1990, pages 79-80. Because of the masking, the utilization of such tanning agents in tanning is indeed slightly lower than that of unmasked chrome tanning agents at the same final pH value; however, due to the higher alkali stability to masked tanning agents, higher final pH levels can also be employed during tanning and the losses thus achieved are comparable to unmasked chrome tanning agents but are accompanied by higher leather quality.

By determining the flocculation point, greater stability to alkali metals, expressed as percent alkalinity, can be measured.

The basicity of a chrome tanning agent is a measure of the number of hydroxyl groups per chromium ion and is likewise known to the skilled person. The interpretation of the terms and the methods used to determine the basicity are specified, for example, in Bibliothek des Leders [ leather Bank ], Vol.3, "Gerbmitel, Gerbung, Nachgerburg" [ tanning, retanning ], Kurt Faber, 2 nd edition, 1990, pages 73-75 and page 283- "285.

In determining the flocculation point of the masked chrome tanning agent, the amount of alkali up to the flocculation point is determined and the molar amount of hydroxide ions generated by the alkali is divided by three times the molar amount of chromium ions and added to the value of the alkalinity of the chrome tanning agent used. In this case, formally, at the flocculation point, there is one hydroxide ion per chromium ion at 33.3% alkalinity, two hydroxide ions per chromium ion at 66.6% alkalinity, and three hydroxide ions per chromium ion at 100% alkalinity. Due to the masking, in some cases, a larger amount of base is required for the precipitation to occur, and therefore the alkalinity value is likely to exceed 100%.

The amount of alkali required to change the basicity by 1% is known to the skilled worker and corresponds, for example, to Cr₂O₃Calculated 20.9mg of Na per 1000mg of chromium oxide₂CO₃(see Bibliothek des Leders [ leather Bank of America)]Vol.3, "Gerbmitel, Gerbung, Nachgerbang" [ tanning, retanning]Kurt Faber, 2 nd edition, 1990, page 75).

The flocculation point was determined by: preparation of a catalyst containing Cr₂O₃Calculated as 2.6 wt% chromiumAqueous solution of oxide chrome tanning agent (100ml), the solution was stirred continuously at room temperature for 8h and titrated with 1.5 molar aqueous sodium carbonate solution (dropping rate of 10 ml/min) until permanent flocculation was evident.

Since the flocculation point in the measurement depends not only on the initial concentration of chromium oxide in the solution but also on the stirring time after the chromium oxide content is established, the flocculation point in the case of the present invention is measured accurately for 8 hours after the chromium oxide content of the solution (which is continuously stirred at room temperature) is established to be 2.6%.

The above-mentioned advantageous effect of masking is particularly apparent in the flocculation point range of 66% to 150% alkalinity. Above 150%, it is believed by the skilled person that over-masking occurs and that the chrome tanning agent binds only very little to the collagen, or not at all, meaning that the tanning effect is greatly reduced or no longer present. At flocculation points of 65% alkalinity or less, masking is no longer effective.

It is therefore a further object of the present invention to provide a masked chrome tanning agent which is at least partially obtainable in an efficient and economical manner from recycled chrome and collagen containing materials.

It has now surprisingly been found that, in order to achieve the object of the present invention, it is not particularly necessary to release the protein component to the greatest possible extent from the insoluble residue obtainable in the alkaline hydrolysis of chromium-and collagen-containing materials, but instead the protein component can be successfully used for masking chrome tanning agents, provided that the flocculation point is established within a value in the range from 66% to 150% alkalinity.

The flocculation point can be established here by: a chrome tanning agent, especially a chromium (III) compound, preferably one or more compounds selected from the group consisting of chromium (III) oxide, chromium (III) hydroxide, chromium (III) halide and chromium (III) sulfate, and more preferably chromium (III) sulfate, is added.

The subject of the present invention is therefore a process for preparing a protein-masked chrome tanning agent, comprising the following process steps:

alkaline hydrolysis of at least part of the collagen component (fraction) of the material containing chromium and collagen,

removing the insoluble components of the material obtained in the hydrolysis,

dissolving the insoluble fraction removed in the previous step by lowering the pH to a value of 1 to 6, preferably 1 to 3 and more preferably 2.5,

adding a chromium (III) compound to the solution obtained in the preceding step until said solution has a flocculation point in the range from 66% to 150% alkalinity.

In a preferred embodiment, the last two treatment steps are combined by lowering the pH via addition of a chromium (III) acid compound. Suitable acidic chromium (III) compounds exhibit a pH of less than 6.0, preferably less than 4.0 and more preferably less than 2.0 at room temperature when mixed with water in a 1:9 ratio. Preferably, a chromium compound selected from chromium (III) oxide, chromium (III) hydroxide, chromium (III) halide and chromium (III) sulfate is used, and most preferably a basic chromium (III) sulfate is used. Incidentally, the latter name is derived from the alkalinity of the chrome tanning agent rather than the pH of its aqueous solution (pH < 7). Other acidic chromium (III) compounds which can be employed in the present invention are obtained from the chromium residue remaining in the tanning liquor after the tanning process, these acidic chromium (III) compounds being isolated by precipitation at elevated pH and subsequent dissolution at lower pH.

Protein-masked chrome tanning agent is understood here to be a mixture of chrome tanning agents, in particular chromium (III) compounds such as chromium (III) oxide, chromium (III) hydroxide, chromium (III) halide and/or chromium (III) sulfate, and also protein components obtainable by alkaline hydrolysis of collagen.

The chromium (III) compound added is preferably chromium (III) oxide, chromium (III) hydroxide, chromium (III) halide and/or chromium (III) sulfate or a mixture of these substances, more preferably basic chromium (III) sulfate.

The term "chromium and collagen-containing material" in its broadest definition encompasses all chromium-containing and collagen-containing materials; chromium-containing leather is preferred, and chromium-containing leather shavings are particularly preferred.

Lowering the pH is accomplished by adding an acid, preferably a mineral acid, more preferably sulfuric acid and/or hydrochloric acid, very preferably sulfuric acid.

Chrome-containing leather is understood to include hides and raw skins tanned via chrome tanning agents, and for this reason the shrinkage temperature of the tanned hide material is sufficiently high to achieve at least the hydrothermal stability of the hide material, such as to allow subsequent processing by mechanical manipulation and to prevent damage caused by mechanical and thermal exposure (e.g., frictional heat during shaving).

The chromium oxide content in the chromium and collagen containing material used is typically less than 10 wt%, more preferably less than 7 wt%, very preferably less than 5 wt%, based on the total mass of the chromium and collagen containing dry material at a residual moisture content of 10 wt%.

Alkaline hydrolysis refers to the reduction in the molecular weight of collagen under alkaline conditions. The alkaline hydrolysis is typically accomplished using an oxide or hydroxide of an alkali metal and/or alkaline earth metal, preferably an oxide or hydroxide of sodium, potassium and/or magnesium, more preferably magnesium oxide. The material obtained in this case comprises proteins, which typically have a weight average molecular weight Mw of less than 310 dalton, preferably less than 280 dalton and more preferably less than 250 dalton. In contrast, the protein obtained in the acidic hydrolysis of a material containing chromium and collagen has a weight-average molecular weight M of 320 daltons or more_w。

Attempts to use in the present invention proteins obtained from the acidic hydrolysis of chromium shaving instead of proteins obtainable from the alkaline hydrolysis of materials containing chromium and collagen have not resulted in satisfactory tanning results. It is postulated that the lower molecular weight of the proteins obtained by alkaline hydrolysis of the collagen enables the chrome tanning agent produced with it to have a higher penetration capacity and therefore to achieve a better tanning effect on the section of the hide.

In a preferred embodiment, the protein masked chrome tanning agent obtainable by the process of the invention is obtained in the form of an aqueous solution. In a further embodiment, the solution is converted into a powder or granules by drying, preferably spray drying.

Therefore, another subject of the present invention is a protein masked chrome tanning agent comprising chromium in the oxidation state 3 and proteins obtained from the alkaline hydrolysis of collagen, wherein the chrome tanning agent has a flocculation point in the range of from 66 to 150% alkalinity.

Preferably, not only the protein but also a part of the chromium in the +3 oxidation state originates from insoluble or poorly soluble residues obtained in the alkaline hydrolysis of materials containing chromium and collagen. In this case, another part of the chromium in the +3 oxidation state originates from a chromium tanning agent added to the residue in the form of a chromium (III) compound, preferably a chromium (III) oxide, a chromium (III) hydroxide, a chromium (III) halide and/or a chromium (III) sulfate or a mixture of these substances, more particularly an alkaline chromium (III) sulfate.

According to Cr₂O₃The calculated chromium oxide content of the protein masked chrome tanning agent is typically more than 5 wt%, preferably more than 8 wt% and more preferably from 10 to 26 wt%. The chromium oxide content is based on the total weight of the dried, protein-masked chrome tanning agent with a residual moisture content of 10 wt.% or less, preferably 5 wt.%.

The amount of protein obtained from alkaline hydrolysis of collagen in the protein masked chrome tanning agent is typically from 2 to 50 wt%, preferably from 4 to 25 wt% and more preferably from 5 to 12 wt%. The protein content is based on the total weight of the dried, protein-masked chrome tanning agent with a residual moisture content of 10 wt.% or less, preferably 5 wt.%.

The protein masked chrome tanning agent obtainable according to the process of the present invention typically has a basicity of from 0% to 65%, preferably from 4% to 55%, more preferably from 9% to 40%.

The protein masked chrome tanning agent may be present in the form of a powder, granules or an aqueous solution.

A further subject of the invention is the use of a protein-masked chrome tanning agent for tanning and/or retanning leather or pelts.

Another subject-matter is a process for tanning and/or retanning leather or pelts by treating the hides or skins with the protein-masked chrome tanning agent according to the invention.

In addition, the present invention also comprises the leather or pelt obtainable by the process for tanning and/or retanning leather or pelt according to the invention.

The present invention is therefore outstandingly suitable for recycling chromium and collagen-containing materials, more particularly leather production wastes such as, for example, leather trimmings, which can be converted into advantageous protein-masked chromium tanning agents and can be returned to the tanning operation, thus allowing a significant reduction in the amount of chromium-containing wastes in the leather production process, which would result in considerable economic, environmental and logistic advantages.

Detailed Description

Examples of the invention

The following examples illustrate the invention in more detail, but are in no way intended to limit the invention.

Preparation of chrome tanning agent

The chromium-containing solution a used in the following examples was from a commercial operating plant for alkali-processing chrome-tanned cattle hide trimmings, which produced a residue containing chromium and collagen (chrome cake). The residue was dissolved using sulfuric acid, and then the pH was adjusted to 2.3. The solution has a basicity of 9.1% and is expressed as Cr₂O₃The calculated chromium oxide content was 3.6%. The solids content was 35%. The flocculation point measured (for a solution diluted into 2.6% chromium oxide) is 520% alkalinity.

The chrome tanning agent added in the examples is a pulverulent alkaline chromium sulfate (from LanxessDeutschland GmbH)

B) Having a basicity of 33% and expressed as Cr₂O₃Calculated as a chromium oxide content of about 26%. The flocculation point measured for the solution diluted into 2.6% chromium oxide is 62% alkalinity.

M1) mixture of chromium solution A and alkaline chromium sulfate

In a stirred flask, 103g of water and 247g of basic chromium sulfate were added to 650g of chromium-containing solution A. The solution was then heated to 80 ℃ and stirred at this temperature for 1 h.

The mixture has a basicity of 24% and comprises Cr₂O₃Calculated as 8.8% chromium oxide. The flocculation point of the solution diluted to 2.6% chromium oxide is 89% alkalinity.

M2) mixture of chromium solution A and alkaline chromium sulfate

In a stirred flask, 505g of water and 295g of basic chromium sulfate were added to 200g of chromium-containing solution A. The solution was then heated to 80 ℃ and stirred at this temperature for 1 h.

The mixture has a basicity of 30% and comprises Cr₂O₃Calculated as 8.4% chromium oxide. The flocculation point of the solution diluted to 2.6% chromium oxide is 72% alkalinity.

M3) mixture of chromium solution A and alkaline chromium sulfate

In a stirred flask 288g of water and 412g of basic chromium sulphate were added to 300g of chromium containing solution A. The solution was then heated to 80 ℃ and stirred at this temperature for 1 h.

The mixture has a basicity of 30% and comprises Cr₂O₃Calculated as 11.8% chromium oxide. The flocculation point of the solution diluted to 2.6% chromium oxide is 76% alkalinity.

M4) mixture of chromium solution A and alkaline chromium sulfate

In a stirred flask, 155g of water and 545g of basic chromium sulfate were added to 300g of chromium-containing solution A. The solution was then heated to 80 ℃ and stirred at this temperature for 1 h.

The mixture has an alkalinity of 31% and contains Cr₂O₃Calculated as 15.2% chromium oxide. The flocculation point of the solution diluted to 2.6% chromium oxide is 69% alkalinity.

Examples of Properties Using chrome tanning agent

Application example 1: tanning

The starting material used comprised (bovine) pelts which were separated and weighed after liming and had a thickness of about 1.8-2.0 mm. All chemical amounts below are based on this reference weight (pelt weight).

After customary preparation operations familiar to the skilled worker, 18% of the chrome tanning agent prepared in solution in example M1 was added to the pickled pelts and the treatment was carried out for 60 min. This is followed by the addition of magnesium oxide as a slow acting alkalization product. The pH of the solution increased from 2.6 after addition of chrome tanning agent to a final pH of 3.8 within 8 h. The temperature likewise increases from the initial 20 ℃ to 40 ℃. Table 1 shows the processing steps according to the invention for producing semifinished leather products (wt% based on the pelt weight).

Table 1:

after the method according to the invention, the leather semi-finished product is stored on a rack, moistened and shaved.

These wet blue skins have>Shrinkage temperature of 100 ℃ and 4.1% Cr₂O₃And (4) content. Cr of residual bath₂O₃The content was 4.2 g/l.

The wet blue skins produced in this way are notable in particular for good fullness and a soft hand. The grain appearance is particularly fine and smooth, and the absence of wrinkles is increased.

Application example 2: tanning

As application example 1, but the final pH was 4.2.

These wet blue skins have>Shrinkage temperature of 100 ℃ and 4.4% Cr₂O₃And (4) content. Cr of residual bath₂O₃The content was 2.1 g/l.

Despite the increase in the final pH, the wet blue skin thus produced is completely free of chromium precipitates and has an attractive blue color. The fullness, feel, grain appearance and no wrinkling were comparable to those of application example 1.

Application example 3: tanning

As application example 1, only 14.5% of chrome tanning agent prepared according to example 3 was used. The final pH was 3.8.

These wet blue skins have>Shrinkage temperature of 100 ℃ and 4.3% Cr₂O₃And (4) content. Cr of residual bath₂O₃The content was 2.7 g/l.

The wet blue skins produced in this way are notable in particular for good fullness and a soft hand. The grain appearance is particularly fine and smooth, and the absence of wrinkles increases.

Application example 4: tanning

As application example 3, but the final pH was 4.1.

These wet blue skins have>Shrinkage temperature of 100 ℃ and 4.6% Cr₂O₃And (4) content. Cr of residual bath₂O₃The content was 1.9 g/l.

Despite the increase in the final pH, the wet blue skin thus produced is completely free of chromium precipitates and has an attractive blue color. They likewise have good fullness and a soft hand. The grain appearance is particularly fine and smooth, and the absence of wrinkles increases.

Comparative example 1: tanning

As application example 1, only 6.5% of basic chromium sulfate (

B)。

The final pH was 3.8.

These wet blue skins have>Shrinkage temperature of 100 ℃ and 4.5% Cr₂O₃And (4) content. Cr of residual bath₂O₃The content was 2.0 g/l.

The wet blue skins thus produced have a greener color than the wet blue skins produced using the chrome tanning agent of the present invention. In addition, they have a low fullness and a hard feel. The grain surface was rough in appearance and the lack of wrinkling was reduced.

Application example 5: retanning

The semifinished leather product shaved to a thickness of 1.1mm is treated by customary preparatory operations familiar to the skilled worker, such as washing, is then mixed with 12% chrome tanning agent prepared in solution in example M1, and the treatment is carried out 6And 0 min. Then slowly neutralized Syntan (from langson germany ltd) was added

PAK) and products with alkalinizing activity, and the pH was raised to 5.1.

This is followed by the application of typical retanning formulations for the production of furniture crust leather.

Table 2 shows the processing steps of the invention for producing crust leather (wt% based on shaved weight).

Table 2:

the crust leathers produced in this way are notable in particular for good fullness and a soft hand. The grain appearance is particularly fine and smooth, and the absence of wrinkles increases. The coloration of the crust leather is particularly concentrated and uniform.