DK3216916T3

DK3216916T3 - PROCEDURE FOR REFINING LEATHER

Info

Publication number: DK3216916T3
Application number: DK16159622.6T
Authority: DK
Inventors: Uwe Holubeck
Original assignee: Holupelli Consult Gmbh
Priority date: 2016-03-10
Filing date: 2016-03-10
Publication date: 2019-01-21
Also published as: WO2017153505A1; EP3216916B1; PL3216916T3; EP3216916A1; ES2702480T3; CN109072546A

Description

Method for refining leather

The invention has to do with measures to handle and refine leather. It relates in particular to a process to produce shrunken-grain leather including the following steps a) Washing at least one chrome-tanned skin (chrome wet blue) in a washing solution, b) Neutralizing the treated skin in a neutralisation solution, c) Preliminary fatliquoring the skin, d) Dyeing the skin in a dyeing solution, e) Fatliquoring by addition of a fatliquoring mixture, f) Fixing by adding formic acid, g) Final shade adjusting, h) Fixing, i) Washing the skin, j) Drying the skin, k) Applying a binder mixture solution, 1) Applying an aqueous emulsion varnish, m) Ironing and staking the skin, n) Drumming the skin with continuous moisturising, o) Demoistening the skin, p) Conditioning the skin and further reduction of moisture content and q) Applying a fixing solution.

Leather with artificially applied scars, so-called shrunken-grain leather, has been used for years in the shoe and purse industry. An overview of the manufacture of various types of leather is described in the “Manual of Tanning Chemistry and Leather Manufacturing.’^ Publisher, 1955,

Springer Verlag.

Commercially available leather has surfaces with widely varying patterns and can be smoother or have a more raised structure.

There are many patent documents which describe the classical shrinking process using so-called shrinking on the moulding state with corresponding pretreatments, customarily using sulphonic acid-containing synthetic tanning agents, for example, in the published patent specifications in DE1150488B, DE1257353B, EP0265657A1, DE617015A, DE2843233A1 and DE1053517B.

Phenols are especially employed as shrink tanning agents, such as Tanigan CLS 50 or Irgantan LV cone. fl. or mimosa or sumac. These tanning agents can be pasted in order to further increase astringency with HCOOH formic acid in order to strengthen the shrinking effect. A sole exception is glutardialdehyde, which is not made more astringent with acids, but where the raw skin must be set to an alkaline level in order to create intensive shrinking.

There continues to be a disadvantage in the usual procedures in their irregularity of the shrinkage a) seen in the area of the individual skins and b) in comparison to skins within a lot (batch). This is mostly due to the varied structure in the skins, and also the circumstance of difficult setting of thickness of the raw skins.

There is in particular a high demand for high-quality shrunken-grain calf leather with a thickness range of 2.1-2.6 mm. It would therefore be desirable, with a concomitant goal of a high use ratio and area yield for the processor, to have homogeneous shrinking behaviour (surface structure of the leather) and at the same time to reduce the reject rate of finished leather.

The underlying technical problem addressed by the invention is therefore seen in providing an effective method to produce shrunken-grain leather that avoids the aforementioned disadvantages of the prior art.

The invention is therefore a process to produce shrunken-grain leather, including the following steps: a) Washing at least one chrome-tanned skin (chrome wet blue) in a washing solution containing about 200% (w/w) water and about 0.2% (w/w) of a non-ionic surfactant; b) Neutralizing the treated skin in a neutralisation solution containing about 100% (w/w) water, about 1.5% (w/w) sodium formate and about 3% (w/w) sodium bicarbonate; c) Preliminary fatliquoring, including incubation of the skin with about 0.5% (w/w) solution of a fatty acid ester, about 2% (w/w) solution of a polymer tanning material and about 20% (w/w) solution of a retaining material; d) Dyeing the skin in a dyeing solution containing about 50% (w/w) water, about 1.5% (w/w) ammonia and an anionic dye; e) Fatliquoring by adding about 100% (w/w) water and about 4.5% fatliquoring material mixture, whereby this fatliquoring mixture contains about 45% (w/w) long-chain paraffins and about 55% (w/w) sulphated oils; f) Fixing by adding about 3.5% (w/w) formic acid; g) Final shade adjusting by putting the skin into a toner solution including about 200% (w/w) water with anionic acid substantive dye. h) Fixing by adding about 0.5-1.0 % (w/w) formic acid; i) Washing the skin in about 200% (w/w) water; j) Drying the skin; k) Applying a binder mixture solution including a binder mixture and an inorganic pigment dispersion with a 4:1 ratio, whereby the binder mixture solution consists of about 40% (w/w) of fine-particle polyurethane dispersion and about 30% (w/w) modified polyurethane/acrylate copolymer emulsion; l) Applying an aqueous emulsion varnish (polyurethane dispersion) with about 25% (w/w) active ingredient contents; m) Ironing and staking the skin; n) Drumming the skin with continuous addition of moisture; o) Demoistening the skin until it has a moisture content of about 25% (w/w) in the skin; p) Conditioning the skin and reduce the moisture content to about 15% (w/w) or less; and q) Applying a fixing solution of about 30% (w/w) polyurethane dispersion, whereby the polyurethane 2-indocyanine is wetted, and there is a binder to water mixture ratio of 3:1, whereby the shrunken- grain leather is preserved.

The information for concentration in weight percent (w/w) is related to the shaved weight of the treated skin. The term “about” means that the concentration varies from the nominal value by +/- 15%, and preferred is +/-10% or +/- 5%. Especially preferred, however are the concentrations which are exactly those of the nominal values. This interpretation applies to volume, time and temperature information accordingly.

It is understood that the invention procedure also applies to treating more than one skin at a time. Accordingly, there is with at least one chrome wet blue a variety of skins, i.e. two, three or more chrome wet blues, which are treated according to the invention.

The steps for moist treatment, or steps a) to i) are preferably conducted in moving vessels and preferably in rotatable vessels. Wood barrels are especially preferred for this. The skins can be left in them for conducting the individual procedural steps, or be transferred to another vessel.

The drying steps used in the process can be performed using vacuum drying techniques, hang drying or in drying tunnels. Tumbling and stretching handling can be performed preferably with rolling machines.

Applying a biner mixture solution in step k) and fixing solution in step q) is preferably performed using a rotating spraying machine.

In step k), the application is performed two to three times, whereby the binder mixture solution is applied at a volume of about 10-15 g per square foot. Then, it is preferred that a film is applied in a conveyor drying tunnel at about 80°. The steps are preferably performed three times.

In step q), there is a preferable application of the fixing solution with a volume of 10 mg per square foot.

Ironing steps are preferred using a conveyor ironing machine at about 80°C.

Staking is preferably performed with a conveyor staking machine.

The term “non-ionic surfactant” means a surfactant which contains no dissociable functional groups and does not split into ions in aqueous solution. 20 Non-ionic surfactants generally consist of one non-polar and one polar section. A non-polar part is usually a fatty alcohol (preferably with chain lengths between C12 and C18) or octyl or nonylphenol. Polar groups can be a hydroxyl group or an ether group, which are contained, for example, in polyethylene glycol or monosaccharide. A “non-ionic surfactant” in the sense of the invention is especially preferred 25 one polyalkylene glycol ether (fatty alcohol ethyl oxalate (FAEO), fatty alcohol propoxylate (FAPO), alkyl glucoside, alkyl polyglucoside (APG), octyl phenol ethyl oxalate or nonyl phenol ethyl oxalate. A “polymer tanning agent” in the sense of the invention is identified as a tanning agent which consists of 30 macro-molecules, so-called constitutional repeating units or repeated units. Acrylate or polyurethane can serve as the body for tanning, artificially produced polymers. Reactive groups can be aldehyde, isocyanate, isothiocyanate and succinimide ester. Preferably, a polymer tanning agent in the sense of the invention can consist of a condensate of aliphatic aldehyde 35 and one or more compounds from the urea group, dicyandiamide, melamine and guanidine, especially preferred from a condensation product made of dicyandiamide and formaldehyde. Post-tanning means post-treatment with pre-tanned, often chrome-tanned leather. Post-tanning is preferably used to add special colour characteristics to leather, for example to optimise colour, grain details, grain resistance, softness, feel, form retention, leather weight, water-repellent behaviour (hydrophobia) or tanning fixation. Post-tanning materials can be synthetic or natural materials, for example, mineral tanning agents such as chrome, aluminium or zirconium, synthetic post-tanning agents such as naphthalene-phenol-condensate, fat or aldehyde. “Post-tanning agent” in the sense of the invention is preferably a synthetic post-tanning agent, for example a naphthalene-phenol-condensate product.

Anionic dyes, also called acid dyes, are identified as dyes which have one or more acid residues, mostly sulphonic acid residues, and also apply aqueous medium directly onto the fibre. Anionic dyes are preferably used to dye polyamide fibres and wool, on which they form electrovalent compounds with amino groups. Anionic dyes typically possess an azo-, nitro- or anthraquinone chromophore. Representatives of anionic dyes are, for example, naphthol yellow S and patent blue dyes. “Anionic dye” in the sense of the invention is preferably an acid substantive anionic dye, especially preferred is Congo red or benzopurpurine. A “fine-particle polyurethane dispersion” is preferably a flowable two-phase system consisting of water and a polymer, i.e. a dispersed plastic which belongs to the polyurethane class, such as isocyanate, polyol or polyamine, as well as other optional components. The polyurethane particles typically are present in a stable dispersion and show sphere-shaped images in a size range between about 30 nm and 1000 nm, which gives the dispersion a milky-white appearance. Size distribution can be a maximum (monomodal) or two maximums (bimodal). Below 50 nm particle size, the dispersion looks increasingly transparent; above 1000 nm, the particles tend to precipitate. The weight portion of polyurethane solids in the dispersion is usually between 30 and 60%. The so-called LD value (light transparency value for the dispersion) can be used to measure the fine particle size in a dispersion. The LD value is preferably measured by measuring a dispersion in a 0.01% (w/w) aqueous solution in a cuvette with an edge length of 2.5 cm with 546 nm light, comparing the transparency of water under the aforementioned conditions. The transparency of water is therefore defined to be 100%. The smaller the particles in the dispersion, the higher the LD value, which is measured as described above. Preferred is a polyurethane dispersion with an LD value greater than or equal to 50%, 60%, 70%, 80%, 85%, 90% or 95%. Especially preferred is a 2-isocyanate wetted, aqueous, fine-particle polyurethane dispersion with about 30% material content. Preferred fine-particle dispersions are also revealed in the following publications: EP 0 257 412 Al, WO 2010/139654 A2. A “modified polyurethane/acrylate copolymer emulsion” in the sense of the invention is preferably an emulsion made of a polyurethane acrylate copolymer which has chemical modifications. If in this connection a copolymer is indicated as an acrylate copolymer, one should understand this to be copolymers which are copolymerised by acrylic acid or its derivatives. Included in the term “acrylate” in the sense of this invention are also acrylamide, acryl esters such as acryl acetate, etc., but also copolymers in which acrylate is the predominant polymer present. In the invention, modified copolymers considered above all are those which are derived from acrylic acids or methacrylic acids and their derivatives, such as amides and esters, especially acrylic acid, acryl amides and acrylic esters. They can, if applicable, be basic comonomers, such as primary, secondary, tertiary or quaternary amino substitutes, such as quaternary products of dimethyl aminoethylene methacrylates - or dialkyldimetyleammoniumacrylic acid components; hydrophobic substitutes, such as long-chain alkyl groups with 10 to 30, preferably 12 to 24 C atoms, acid substitutes, such as sulphonate, phosphate and carboxyl groups or hydroxyl group-containing moieties, such as vinyl alcohol. Also, copolymers of vinylpyrrolidone/acrylates and dialkylaminoalkylmethacrylate are suitable. Among polyurethanes, polyurethane polyvinylpyrrolidone, polyester polyurethane, polyether polyurethane as well as polyureas are included. Polyurethane can, for example, be an aliphatic, cycloaliphatic or aromatic polyurethane, polyurea/urethane or polyurea copolymer. Polyurethanes can furthermore be made of polyesters which are straight-chained or branched, or alkyd compounds which have mobile hydrogen.

Below, a preferred process in the sense of the invention is described.

Preferred here is the use of a so-called chrome wet blue (tanned intermediate product containing at least 1.5% chromium oxide). Typically, chrome (III) salts (chromium hydroxide) are used in chrome tanning to product chrome wet blue. Corresponding methods are known in the art.

This starting stage’s so-called wet blue enables more precise thickness and moisture settings in the skin in comparison to the raw methods. The subsequent refining requires high procession in process management, and is significantly responsible for shaping the desired shrinkage grain or grain pattern (leather surface).

To this, a 0.2% non-ionic surfactant and 200% water at 40°C related to shaved weight, are added to wash the chrome wet blue in a rotating container at 12 RPM, preferably a wooden vessel. The run time is 30 minutes. After this, the leather is neutralised for 150 minutes in a new liquid of 100% water at 40°C with 1.5% sodium formate and 3% sodium bicarbonate. The final pH is 6. Then preliminary fatliquoring is performed with 0.5% of a fatty acid ester for 60 minutes in combination with 2% of a polymer tanning agent for 40 minutes and 20% of a synthetic post-tanning agent (naphthalene phenol condensation product) for 60 minutes. The next steps create colouration with anionic dyes and go directly into the fatliquoring with long-chain paraffins and hydrophobic emulsifiers.

In this, thorough dyeing is achieved with 50% water at 20°C with 1.0% ammonia and anionic dyes, preferably acid-containing dyes, over 60 minutes at about 12 RPM and, in the same medium, 100% water at 60°C and 4.5% fatliquoring mixture with long-chain paraffins with about 45% substance contents and sulphated oils with about 55% substance contents are added at a 1:1 ratio, and fatliquored for 40 minutes, and fixed by the addition of 3.5% 85% formic acid over 60 minutes.

The final colour setting is performed in a fresh bath with 200% water at 50°C and an addition of acid substantive anionic dyes for 60 minutes and is fixed and finished with the addition of 0.5-1.0% of 85% formic acid over 20 minutes. The final pH is between 3.5 and 3.6.

Then a wash process is performed with 200% water at 20°C for 10 minutes.

To complete the wet work, drying is introduced with intensive dewatering and stretching using commercial roller machines Then drying is performed using a vacuum technique at 60°C for 3 minutes, and dried in a drying tunnel for 8 hours at 50°C. Intensive remoisturising of the leather matrix to >50% water contents achieves fibre reconditioning. Following this, the leather matrix is re-dried to less than 15% water contents using a vacuum technique for 1-2 minutes at 60°C and hanging drying for at least 8 hours at 40°C. The intense fibre softening is achieved using a commercial conveyor staking machine with rod tools’ this is a preparation work step for surface coating (finishing).

The finish consists of a mix of fine-particle polymers with approx. 40% material contents and fine-particle polyurethane dispersions with about 30% material contents (modified polyurethane/acrylate copolymer emulsion) which achieves its colouration by the addition of inorganic pigment dispersions. 400 parts binder mixture is mixed with 100 parts inorganic pigments and 350 to 400 parts water. The binder mixture is applied to the leather surface 2-3 times (10 to 15 g/square foot of leather) using a commercial rotating spray machine and then filmed with a conveyor ironing machine at 80°C. This work process is repeated three times. The finishing film is set to a medium-hard state with one-time intermediate painting with an aqueous polyurethane-based emulsion varnish with about 25% (w/w) material at about 10 g/square foot of leather.

Then it is ironed with the conveyor ironing machine at about 80°C.

Repeated staking using the conveyor staking machine achieves intensive fibre loosening, which is the pre-processing for subsequent tumbling in a tumbler. The tumbling work step is essential for the expression of the tumbling result and the resulting leather surface (shrink appearance).

Continuous addition of moisture over 2 hours in the tumbler (1.5m wide, 2m high; water: 40 litres/70 pieces of leather) and concomitant rotating mechanical processing at a speed of at least 18 RPM conditions the fibres. After running for three hours, a systematic removal of moisture down to 25% water contents in the leather with rotating mechanical processing is performed over 6-8 hours; the particle size of the shrink appearance with simultaneous feel (solidity and so-called “spring” in the finished leather) are set.

Subsequent climate conditioning in a drying tunnel at 40°C for two hours, and reducing the leather’s water content to below 15% fixates the grain.

Final fixation of the shrink grain is performed by coating with 2-isocyanate wetted, aqueous, fine-particle polyurethane dispersions (about 30%) in a mix ratio of 30 parts binder in 100 part water with an application volume of at least 10 mg/square foot leather using a commercial rotating spray machine.

Advantageously, in the process in this invention, neither premature assortment selection in an early stage of leather production (water workshop) need be made, nor must special shrink tanning agents be used in order to achieve a reliable quantity of assortment with uniform qualitative surfaces. By achieving this uniform surface and the assortment provided by pre-sorting in comparison to raw sorting, maximum surface use is made possible for the subsequent processing of the leather. The approach in the invention's process is different in comparison to the usual state of the art procedure and is based on the use of substance-containing calf skin, which is classically chrome-tanned using the undissolved chromium method.

The explanations given above and interpretations apply mutatis mutandis to the following preferred embodiments of the method according to the invention.

In a preferred embodiment of the method according to the invention, the shrunken-grain leather has a skin thickness of 2 to 3 mm, preferably 2. To 2.5 mm. A method according to the invention is preferred in which steps a) and d) are performed in a rotating vessel at 12 RPM.

Further preferred is an embodiment of the method according to the invention in which the washing in step a) is performed at about 40°C for about 30 minutes.

Also preferred is an embodiment of the method according to the invention whereby neutralisation in step b) is achieved at about 40°C for about 150 minutes and a final solution pH is reached that is higher than 6.0.

Also preferred is an embodiment of the method according to the invention whereby the incubation time for the skin incubation in step c) is performed with about 0.5% (w/w) solution of a fatty acid ester for about 60 minutes, with about 2% (w/w) solution of a polymer tanning agent for about 40 minutes and about 20% (w/w) solution of a post-tanning agent for 60 minutes.

Preferred is an embodiment of the method according to the invention in which the dyeing in step d) is performed at about 20°C for about 60 minutes.

An additional preferred embodiment of the method according to the invention in which the fatliquoring in step e) is performed for about 40 minutes.

Preferred is an embodiment of the method according to the invention in which the fixation in step f) is performed for about 60 minutes.

Also preferred is an embodiment of the method according to the invention in which the final colour setting in in step g) is performed for about 60 minutes at about 50°C.

Preferred is an embodiment of the method according to the invention whereby fixation in step h) is performed for about 20 minutes, and a final solution pH is reached that is between 3.5 and 3.6.

Further preferred is an embodiment of the method according to the invention in which step i) is performed at about 20°C for about 10 minutes.

Additionally preferred is an embodiment of the method according to the invention whereby drying in step j) includes a step in which the skin is dewatered and stretched, then pre-dried using a vacuum at about 60°C for about three minutes and dried for about 8 hours (h) at about 50°C.

Also preferred is an embodiment of the method according to the invention in which dewatering is performed in step n) for about 2 hours, and demoistening in step o) is performed for about 6 to 8 hours in a rotating vessel at 18 RPM for about 10 minutes at about 20°C.

Finally preferred is an embodiment of the method according to the invention in which the climate conditioning in step p) is performed for about 2 hours at about 40°C.

Finally, the invention also relates to shrunken-grain leather, which is obtained by the method according to the invention described above, and prefers a skin thickness of 2 to 3 mm, preferably 2.3 to 2.5 mm.

Figures

Figure 1 shows a schematic overview of the method according to the invention including a washing step with at least a chrome-tanned skin (chrome wet blue) in a washing solution containing, related to the shaved weight, the skin 200% (w/w) water and 0.2% (w/w) of a non-ionic surfactant (101); neutralise the treated skin in a neutralisation solution containing, related to the shaved weight of the skin, 100% w/w) water, 1.5% (w/w) sodium formate and 3% (w/w) sodium bicarbonate (102); pre-fatliquoring includes incubation of the skin with 0.5% (w/w) solution of a fatty acid ester, 2% (w/w) solution of a polymer tanning agent and 20% (w/w) solution of a post-tanning agent (103); dyeing of the skin in a dye solution including 50% (w/w) water, 1.5% (w/w) ammonia and an anionic dye (104); fatliquoring by the addition of 100% (w/w) water and 4.5% fatliquoring material mixture, whereby this fatliquoring material mixture contains 45% (w/w) long-chain paraffins and 55% (w/w) sulphated oils (105); fixation by the addition of 3.5% (w/w) formic acid (106); final colour setting by moving the skin into a toner solution including 200% (w/w) water with anionic acid substantive dye (107); fixation by adding 0.5-1.0% (w/w) formic acid (108); washing the skin in 200% (w/w) water (109); drying the skin (HO); applying a minding mixture solution including a binder mixture and an inorganic pigment dispersion at a 4:1 ratio, whereby the binder mixture solution contains 40% (w/w) fin-particle polyurethane dispersion and 30% (w/w) modified polyurethane/acrylate copolymer emulsion (111); apply an aqueous polyurethane-based emulsion varnish with about 25% (w/w) material contents (112); iron and stake the skin (113); dewater the skin with continuous moisture addition (114); remove moisture from the skin to a moisture contents of 25% (w/w) in the skin (115); climate condition the skin and reduce the moisture contents to 15% (w/w) or less (116); and apply a fixation solution including a 30% (w/w) polyurethane dispersion, whereby the polyurethane is wetted with 2-isocyanate and there is a mixing ratio of binder to water of 3 parts: 10, through which the shrunken-grain leather will be obtained (117).

Figure 2: Figure 2A shows the surface of even shrunken-grain calf skin which is produced with the method according to the invention. For comparison, Figure 2B shows the surface of uneven shrunken-grain calf leather which was not produced with the method according to the invention.

EXAMPLES

The following embodiment examples serve to illustrate the invention, and should not be interpreted in a way that restricts the protected area of the invention.

Example: Producing shrunken-grain calf leather with a skin thickness of 2.3 to 2.5 mm

So-called chrome wet blue was used (tanned intermediate product containing at least 1.5% chromium oxide). A 0.2% non-ionic surfactant and 200% water are added at 40°C related to shaved weight, are added to wash the chrome wet blue in a rotating container at 12 RPM in a wooden vessel. The run time was 30 minutes. After this, the leather was neutralised for 150 minutes in a new liquid of 100% water at 40°C with 1.5% sodium formate and 3% sodium bicarbonate. The end pH is >6. Then preliminary fatliquoring was performed with 0.5% of a fatty acid ester for 60 minutes in combination with 2% of a polymer tanning agent for 40 minutes and 20% of a synthetic post-tanning agent (naphthalene phenol condensation product) for 60 minutes. The next steps initiate dyeing with anionic dyes and go directly into the fatliquoring with long-chain paraffins and hydrophobic emulsifiers.

At this stage thorough dyeing was achieved with 50% water at 20°C with 1.5% ammonia and anionic dyes, preferably acid-containing dyes, over 60 minutes at about 12 RPM and, in the same medium, 100% water at 60°C and 4.5% fatliquoring mixture with long-chain paraffins with about 45% substance contents and sulphated oils with about 55% substance contents are added at a 1:1 ratio, and fatliquored for 40 minutes, and fixed by the addition of 3.5% 85% formic acid over 60 minutes.

The final shade adjusting is performed in a fresh bath with 200% water at 50°C and an addition of acid substantive anionic dyes for 60 minutes and is fixed and finished with the addition of 0.5-1.0% of 85% formic acid over 20 minutes. The final pH is between 3.5 and 3.6.

Then a wash process is performed with 200% water at 20°C for 10 minutes.

After the wet operations, drying was initiated by intensive dewatering and stretching using commercial roller machines. Then pre-drying was performed using the vacuum technique at 60°C for 3 minutes, and drying in a drying tunnel for 8 hours at 50°C. By intensive remoisturing of the leather matrix to >50% water contents a reconditioning of the fibre was achieved. Following this, the leather matrix was re-dried to less than 15% water contents using a vacuum technique for 1-2 minutes at 60°C and hanging drying for at least 8 hours at 40°C. The intense fibre softening was achieved using a commercial conveyor staking machine with rod tools’ this was a preparation work step for surface coating (finishing).

The finish consisted of a mix of fine-particle polymers with about 40% material contents and fine-particle polyurethane dispersions with about 30% material contents (modified polyurethane/acrylate copolymer emulsion) which achieves its colouration by the addition of inorganic pigment dispersions. 400 parts binder mixture was mixed with 100 parts inorganic pigments and 350 to 400 parts water. The binder mixture was applied to the leather surface 2-3 times (10 to 15 g/square foot of leather) using a commercial rotating spray machine and then filmed with a conveyor ironing machine at 80°C. This work process was repeated three times. The finishing film was set to a medium-hard state with one-time intermediate painting with an aqueous polyurethane-based emulsion varnish with about 25% (w/w) material at about 10 g/square foot of leather.

Then it is ironed with the conveyor ironing machine at about 80°C.

Continuous addition of moisture over 2 hours in the tumbler (1.5m wide, 2m high; water: 40 litres/70 pieces of leather) and concomitant rotating mechanical processing at a speed of at least 18 RPM conditions the fibres.

After running for three hours, a systematic removal of moisture down to 25% water contents in the leather with rotating mechanical processing is performed over 6-8 hours; the particle size of the shrink appearance with simultaneous feel (solidity and so-called “spring” in the finished leather) are set.

Final fixation of the shrink grain was performed by coating with 2-isocyanate wetted, aqueous, fin-particle polyurethane dispersions (about 30%) in a mix ratio of 30 parts binder in 100 parts water with an application volume of at least 10 mg/square foot leather using a commercial rotating spray machine.

The produced shrunken-grain calf leather predominantly shows a homogeneously-structured surface as shown in Figure 2A.

Claims

A method of making shrink leather, comprising the steps of: a) washing at least one chromium-tanned skin (chromium-wet blue) in a wash solution containing about 200% (w / w) water and approx. 0.2% (w / w) of a nonionic surfactant; b) neutralizing the treated skin in a neutralization solution containing ca. 100% (w / w) water, approx. 1.5% (w / w) sodium formate and approx. 3% (w / w) sodium bicarbonate; c) initial grease comprising incubating the skin with approx. 0.5% (w / w) solution of a fatty acid ester, approx. 2% (w / w) solution of a polymer tanning agent and approx. 20% (w / w) solution of a post-tanning agent; d) coloring the skin in a color solution comprising approx. 50% (w / w) water, approx. 1.5% (w / w) ammonia and anionic dye; e) greasing by adding approx. 100% (w / w) water and approx. 4.5% grease mixture, the grease mixture comprising approx. 45% (w / w) long-chain paraffins and approx. 55% (w / w) sulfated oils; f) fixation by adding approx. 3.5% (w / w) formic acid; g) final tone setting by transferring the skin to a toner solution comprising approx. 200% (w / w) water with anionic dye of the acidic substantive type; h) fixation by adding approx. 0.5-1.0% (w / w) formic acid; i) washing the skin for approx. 200% (w / w) water; j) drying the skin; k) applying a binder blend solution comprising binder blend and an inorganic pigment dispersion in a ratio of 4: 1, wherein the binder blend solution comprises approx. 40% (w / w) fine polyurethane dispersion and approx. 30% (w / w) modified polyurethane / acrylate copolymer emulsion; l) applying a polyurethane aqueous emulsion lacquer with approx. 25% (w / w) content of active ingredients; m) ironing and polishing the skin; n) rolling the skin with continuous moisture supply; o) dehumidifying the skin down to a moisture content of approx. 25% (w / w) in the skin; p) conditioning the skin and reducing the moisture content to approx. 15% (w / w) or less; and q) applying a fixation solution comprising a ca. 30% (w / w) polyurethane dispersion, wherein the polyurethane is 2-isocyanate cross-linked and the binder-water mixing ratio is 3 parts to 10 parts, thereby obtaining the shrink leather.

The method of claim 1, wherein the shrink leather has a skin thickness of 2 to 3 mm, preferably 2.3 to 2.5 mm.

The method of claim 1 or 2, wherein steps a) and d) are carried out in a rotating container at approx. 12 p.m.

The method according to any one of claims 1 to 3, wherein the washing in step a) is carried out at approx. 40 ° C for approx. 30 min.

The method according to any one of claims 1 to 4, wherein the neutralization in step b) is carried out at approx. 40 ° C for approx. 150 min, and a final pH value in the solution of more than pH 6.0 is obtained.

The method according to any one of claims 1 to 6, wherein the incubation time for the incubation of the skin in step c) is approx. 60 min. with approx. 0.5% (w / w) solution of a fatty acid ester, approx. 40 min. with approx. 2% (w / w) solution of a polymer tanning agent and approx. 60 min. with approx. 20% (w / w) solution of a post-tanning agent.

The method according to any one of claims 1 to 6, wherein the staining in step d) is carried out at ca. 20 ° C for approx. 60 min.

A method according to any one of claims 1 to 7, wherein the grease in step e) is carried out for approx. 40 min.

The method according to any one of claims 1 to 8, wherein the fixation in step f) is carried out for approx. 60 min.

The method according to any one of claims 1 to 9, wherein the final pitch setting in step g) is performed for about 10 minutes. 60 min. at about. 50 ° C.

A method according to any one of claims 1 to 10, wherein the fixation in step h) is carried out for approx. 20 min, and a final pH of the solution of between pH 3.5 and 3.6 is obtained.

A method according to any one of claims 1 to 11, wherein step i) is carried out for approx. 10 min. at about. 20 ° C.

The process according to any one of claims 1 to 12, wherein the drying in step j) comprises a step in which the skin is dewatered and cleaned, is dried at approx. 60 ° C for approx. 3 min. using vacuum and finally dried at ca. 50 ° C for approx. 8 hours.

A method according to any one of claims 1 to 13, wherein the rolling in step n) is carried out for approx. 2 hours and the dehumidification in step o) is carried out for approx. 6 to 8 hours in a rotating container at approx. 18pm for approx. 10 min. at about. 20 ° C.

A method according to any one of claims 1 to 14, wherein the conditioning in step p) is carried out for approx. 2 hours at approx. 40 ° C.