ES2702480T3 - Procedure for the improvement of leather - Google Patents

Abstract

Method for producing leather shrinkage, comprising the following steps: a) washing at least one skin tanned with chromium (Chromwetblue) in a wash solution containing approximately 200% (w / w) of water and approximately one 0.2% (w / w) of a nonionic surfactant; b) the neutralization of the treated skin in a neutralizing solution containing approximately 100% (w / w) of water, approximately 1.5% (w / w) of sodium formate and approximately 3% (w / w) ) of sodium bicarbonate; c) preliminary greasing, which comprises incubating the skin with approximately 0.5% (w / w) of a solution of a fatty acid ester, approximately 2% (w / w) of a polymeric tanning agent and about 20% (w / w) solution of a retanning agent; d) dyeing the skin in a dyeing solution comprising about 50% (w / w) of water, about 1.5% (w / w) ammonia and anionic dye; e) greasing by adding approximately 100% (w / w) of water and 4.5% (w / w) of greasing mixture, where this greasing mixture comprises 45% (w / w) of long chain paraffins and 55% (w / w) sulphited oils; f) fixation by the addition of approximately 3.5% (w / w) of formic acid; g) the adjustment of the final shade by transferring the skin to a toner solution of approximately 200% (w / w) of water with an anionic dye of the acid type that does not need mordant; h) fixation by the addition of approximately 0.5-1.0% (w / w) of formic acid; i) washing the skin in approximately 200% (w / w) of water; j) drying the skin; k) the application of a binder mixture solution comprising a mixture of binders and an inorganic pigment dispersion in a ratio of 4: 1, wherein the binder mixture solution comprises about 40% (w / w) of a finely divided polyurethane dispersion and about 30% (w / w) of a modified polyurethane / acrylate copolymer emulsion; l) the application of an aqueous emulsion varnish based on polyurethane having an active agent content of approximately 25% (w / w); m) ironing and softening of the skin; n) skin whitening with continuous supply of moisture; o) the dehumidification of the skin to a moisture content of approximately 25% (w / w) on the skin; p) conditioning the skin and reducing the moisture content to approximately 15% (w / w) or less; and q) the application of a fixing solution comprising approximately 30% (w / w) of polyurethane dispersion, wherein the urethane is crosslinked 2-isocyanate and the binder-water mixture ratio is 3 parts: 10 parts , with which the contracted grain leather is obtained.

Description

DESCRIPTION

Procedure for the improvement of leather

The invention relates to measures for the treatment and refinement of leather. In particular, it relates to a process for the production of leather contraction comprising the following steps: a) washing at least one skin tanned with chromium (Chromwetblue) in a washing solution, b) neutralizing the treated skin in a solution of neutralization, c) preliminarily greasing the skin, d) dyeing the skin in a dyeing solution, e) greasing by adding a mixture of greasing means, f) fixing by the addition of formic acid, g) adjusting the final shade, h) fix, i) wash the skin, j) dry the skin, k) apply a binder mixture solution, l) apply an aqueous emulsion varnish, m) iron and soften the skin, n) abate the skin with continuous supply of moisture, or) dehumidify the skin, p) condition the skin and further reduce the moisture content and q) apply a fixing solution.

Leather with artificially drawn scars, the so-called contracted leather, has been used in the footwear and handbag industry for many years. A general description of the production of various types of leather is described in "Handbuch of Gerbereichemie und Lederfabrikation", 2nd ed., 1955, Springer Verlag.

Commercially available leathers have surfaces with very varied patterns and can have a smoother or higher texture.

There are numerous patent specifications describing the conventional shrinkage process by means of the so-called contraction of the state of nudity with the corresponding pretreatments with synthetic tanning agents available on the market containing sulfonic acid, for example, in the publications for information of patent application and patent specifications DE1150488B, DE1257353B, EP0265657A1, DE617015A, DE2843233A1 and DE1053517B.

Particularly acidic phenols are used as contraction tanning agents, such as Tanigan CLS 50 or Irgatan LV fl.conc. or Mimosa and Sumach. These tanning agents can be added to further increase astringency with formic acid HCOOH to reinforce the effect of contraction. An exception is only glutaraldehyde, which does not become more astringent with acid, but in which the nudity must be alkaline to experience an intense contraction.

There is still a disadvantage of conventional methods hitherto in the unevenness of the contraction grain a) seen on the surface of a single skin and b) in the comparison of skins within a batch (batch). This is mainly due to the different structure within the skin, but also to the circumstance of the difficult adjustment of the thickness in the step of nudity.

In particular, there is a high demand for high quality calf contracted leather in the thickness range of 2.1 2.6 mm. Therefore, it would be desirable, by simultaneously achieving a high rate of mixing or performance for the processor by means of a huge homogenization in the contraction image (texture of the surface of the leather) at the same time as the faults are reduced the rejection rate in finished state of the leather.

The technical problem underlying the invention can be seen, therefore, in the provision of an effective process for the production of leather shrinkage, which avoids the aforementioned disadvantages of the prior art. Therefore, the invention relates to a process for the production of leather contraction comprising the following steps:

a) washing at least one skin tanned with chromium (Chromwetblue) in a wash solution containing about 200% (w / w) of water and about 0.2% (w / w) of a nonionic surfactant;

b) the neutralization of the treated skin in a neutralizing solution containing approximately 100% (w / w) of water, approximately 1.5% (w / w) of sodium formate and approximately 3% (w / w) ) of sodium bicarbonate;

c) preliminary greasing, comprising incubating the skin with about 0.5% (w / w) of a fatty acid ester solution, about 2% (w / w) of a tanning polymeric agent and about 20% (w / w) of a fatty acid ester; % (w / w) solution of a retanning agent;

d) dyeing the skin in a dyeing solution comprising about 50% (w / w) of water, about 1.5% (w / w) ammonia and anionic dye;

e) greasing by the addition of approximately 100% (w / w) of water and 4.5% (w / w) of greasing mixture, in which this greasing mixture comprises 45% (w / w) of long chain paraffins and 55% (w / w) sulphited oils;

f) fixation by the addition of about 3.5% (w / w) of formic acid;

g) the adjustment of the final shade by transferring the skin to a toner solution of approximately 200% (w / w) of water with an acidic anionic dye that does not need mordant;

h) fixation by the addition of about 0.5-1.0% (w / w) of formic acid;

i) washing the skin in approximately 200% (w / w) of water;

j) drying the skin;

k) the application of a binder mixture solution comprising a mixture of binders and an inorganic pigment dispersion in a ratio of 4: 1, in which the binder mixture solution comprises about 40% (w / w) of a dispersion of finely divided polyurethane and about 30% (w / w) of a modified polyurethane / acrylate copolymer emulsion;

l) the application of an aqueous emulsion varnish (polyurethane dispersion) with approximately 25% (w / w) content of active agents;

m) ironing and softening the skin;

n) the fulling of the skin with continuous supply of moisture;

o) the dehumidification of the skin to a moisture content of approximately 25% (w / w) in the skin;

p) the conditioning of the skin and reduction of the moisture content to approximately 15% (w / w) or less; Y

q) the application of a fixing solution comprising approximately 30% (w / w) of polyurethane dispersion, in which the urethane 2-isocyanate is crosslinked and the binder-water mixture ratio is 3 parts: 10 parts, to achieve leather contraction.

The data of concentrations in percentage by weight (w / w) are related to the weight of the depilated skin to be treated. The term "approximately" means that concentrations may deviate from the set value by / -15%, preferably / -10% or preferably / -5%. However, with particular preference, the concentrations correspond exactly to the established values. This interpretation is applied for quantities, times or temperatures.

It is understood that with the method according to the invention more than one skin can be treated simultaneously. Accordingly, it should be understood that with the method according to the invention, at least one chrome-tanned leather can be treated to a plurality of leathers, that is, two, three or more skins tanned with chrome.

The steps of the wet treatment, ie steps a) to i), are preferably carried out in mobile containers and preferably in rotating containers. Particularly preferred for this purpose are wooden barrels. The skins can be left in the same container to perform the steps of the individual process or transferred to a different container.

The drying steps used in the process can be carried out using vacuum drying techniques, drying in suspension or drying tunnels. The beating and stretching treatments are preferably carried out by rolling mills.

The application of the binder mixture solution in step k) and the fixing solution in step q) are preferably carried out by means of a rotary spraying machine.

In step k) the application is carried out 2 to 3 times, in which the binder mixture solution is applied in an amount of about 107.6-161.4 g per square meter. Subsequently, a treatment is carried out by means of a continuous drying tunnel at approximately 80 ° C. The steps are preferably repeated 3 times. In step q), an application of the fixing solution is preferably carried out in an amount of 107.6 mg per square meter.

The ironing steps are preferably carried out by means of a continuous ironing machine at approximately 80 ° C.

The softening is preferably carried out with a continuous softening machine.

The term "nonionic surfactant" refers to a surfactant that does not contain dissociable functional groups and does not separate into ions in aqueous solution. Nonionic surfactants generally consist of a non-polar part and a polar part. The non-polar part is generally a fatty alcohol (preferred chain length between C12 and C18) and usefull C ldi hid i ét tá t id example, in polyethylene glycol or monosaccharides. A particularly preferred "non-ionic surfactant" within the meaning of the invention is a polyalkylene glycol ether (fatty alcohol ethoxylates (FAEO), fatty alcohol propoxylates (FAPO), alkyl glycosides, alkyl polyglycosides (APG), octylphenol ethoxylates or ethoxylates. nonylphenol.

As "polymeric tanning agent" in the sense of the invention, reference is made to a tanning agent, which consists of macromolecules, called repetitive constituent units. As basic bodies for polymers that are effective in tanning, produced artificially, for example, acrylates and polyurethanes can be used. As the reactive groups, aldehydes, isocyanates, isothiocyanates and succinimide esters can be used. A polymeric tanning agent in the context of the invention preferably consists of a condensate of aliphatic aldehydes and one or more compounds selected from the group comprising urea, dicyanodiamide, melamine and guanidine, particularly preferably a condensation product of dicyanodiamide and formaldehyde.

Retanning means the after-treatment of pre-tanned leather, often tanned with chromium. Retanning is preferably used to emphasize the special characteristics of the skin type, for example, color optimization, grain fineness, grain firmness, softness, fullness, shape retention, skin weight. , the behavior against water (hydrophobicity) or the fixation of tannins. Suitable retanning agents can be synthetic or natural substances, for example, mineral tanning agents such as chromium, aluminum or zirconium, synthetic retanning agents such as naphthalene-phenol condensates, fats or aldehydes. A "retanning agent" within the meaning of the invention is preferably a synthetic retanning agent, for example a condensation product of naphthalene-phenol.

As anionic dyes, also called acidic dyes, reference is made to dyes, which have one or more acidic residues, generally sulfonic acid residues, and are transferred from an aqueous medium directly onto the fiber. Anionic dyes are preferably used to dye polyamide and wool fibers, which form electrovalent bonds with the amino group. Anionic dyes usually have an azo, nitro or anthraquinone chromophore. Representative anionic dyes are, for example, naphthol yellow S and patent blue dyes. An "anionic dye" within the meaning of the invention is preferably an anionic dye of the acid dye type which does not need mordant, more preferably Congo red or benzopurpurine.

A "finely divided polyurethane dispersion" is preferably a two-phase fluid system consisting of water and a polymer, ie, a dispersed plastic belonging to the class of polyurethanes, for example isocyanates, polyols and polyamines, and optionally other components . The polyurethane particles are normally present in a stable dispersion and are spherical entities that vary in size between about 30 nm and 1000 nm, thus providing a milky white appearance of the dispersion. The size distribution can have a maximum (monomodal) and two maximums (bimodal). Below the particle size of 50 nm, the dispersion appears increasingly transparent, above 1000 nm, the particles tend to settle. The weight ratio of the polyurethane solid in the dispersion is usually between 30% and 60%. As a measure of the fineness of a dispersion, the so-called LD value (light transmission value of the dispersion) can be used. The LD value is preferably measured by measuring the dispersion in an aqueous solution at 0.01% (w / w) in a cuvette of 2.5 cm edge length with light of wavelength of 546 nm, and comparing it with the dispersion of water under the conditions mentioned above. The water dispersion is 100%. The finer the dispersion, the higher the LD value measured by the procedure described above. A polyurethane dispersion with an LD value greater than or equal to 50%, 60%, 70%, 80%, 85%, 90% or 95% is preferred. Particularly preferred is a finely divided aqueous polyurethane dispersion of crosslinked 2-isocyanate with an active ingredient content of about 30%. Preferred finely divided dispersions are also described in the publications for German patent application information EP 0257412 A1, WO 2010/139654 A2.

A "modified polyurethane / acrylate copolymer emulsion" within the meaning of the invention is preferably an emulsion of a polyurethane-acrylate copolymer having chemical modifications. In this context, when referring to a copolymer as an acrylate copolymer, this should be understood as copolymers that have been copolymerized from acrylic acid or its derivatives. Included within the term acrylate within the meaning of the invention also include acrylamides, acrylic esters such as acrylic acetates, etc., but also copolymers in which the acrylate is the predominant polymer present. Particularly suitable copolymers according to the invention as copolymers are copolymers derived from acrylic acid or methacrylic acid and derivatives thereof, such as amides and esters, in particular acrylic acid, acrylamides and acrylic esters. Optionally, they may contain basic co-monomers, such as primary, secondary, tertiary or quaternary amino substituents, for example, quaternization products of dimethylaminoethyl methacrylate or diallyldimethylammonium acrylic acid; hydrophobic substituents, such as long chain alkyl groups having from 10 to 30, preferably from 12 to 24 carbon atoms, acid substituents, such as sulfonate, phosphate and carboxyl groups or hydroxyl group containing moieties, such as vinyl alcohol. Copolymers of vinylpyrrolidone / dialkylaminoalkyl acrylate or methacrylate are also suitable. The polyurethanes also include polyurethane polyvinyl pyrrolidones, polyester polyurethanes, polyether polyurethanes and polyureas. The polyurethane can be, for example, an aliphatic, cycloaliphatic or aromatic copolymer of polyurethane, polyurea / urethane or polyurea. The polyurethanes can also be made of linear or branched polyesters or alkyds having mobile hydrogen.

In the following, a preferred process is described in detail in the context of the invention.

Here preference is given to the use of so-called chrome-tanned leather, (intermediate tanning product with a chromium oxide content of at least 1.5%). In chromium tanning, the chromium (III) salts (chromium hydroxide) are normally used for the preparation of chromium tanned leather. The corresponding procedures are known in the art.

This initial step of so-called chrome-tanned leather allows a more precise control of thickness and moisture within the skin compared to the nudity procedure. The subsequent refinement requires a high degree of precision in the management of the process and is largely responsible for shaping the grain of contraction or desired grain image (leather surface).

For this purpose, rotary containers are fed at 12 revolutions per minute (rpm), preferably in wooden barrels, according to the weight of depilated skin, with 200% water at 40 ° C and 0.2% of a non-ionic surfactant for wash the leather tanned to the chrome supplied. The execution time is 30 minutes. The skins are then neutralized in a neutralization solution containing 100% (w / w) of water, 1.5% (w / w) of sodium formate and 3% (w / w) of sodium bicarbonate during a 150-minute period. The final pH value remains at a pH> 6. This is followed by a preliminary greasing with 0.5% of a fatty acid ester for 60 minutes, in combination with 2% of a polymeric tanning agent for 40 minutes and 20 minutes. % of a synthetic retanning agent (condensation product of naphthalene-phenol) for 60 minutes. The following steps start dyeing with anionic dyes and go directly to the greasing with long chain paraffins and hydrophobic emulsifiers.

The dyeing is achieved with 50% water at 20 ° C with 1.5% ammonia and anionic dyes, preferably substantive acid dyes, for 60 minutes at approximately 12 rpm, are greased in the same medium with the addition of 100 % water at 60 ° C and 4.5% fatliquoring mixture, with a content of 45% (w / w) of long-chain paraffins and a content of 55% (w / w) of sulphited oils in a 1: 1 ratio for 40 minutes and fixed by the addition of 3.5% formic acid, at 85% for 60 minutes.

The final shade adjustment of the color is carried out in a fresh bath with 200% water at 50 ° C and an addition of anionic dyes of the acid type that does not need mordant for 60 minutes and is fixed and completed by the addition of 0.5-1.0% 85% formic acid for 20 minutes. The final pH is between 3.5 and 3.6.

This is followed by a wash with 200% water at 20 ° C for 10 minutes.

After wet work, drying is initiated by intensive squeezing and stretching by commercially available roller machines. The preliminary drying is carried out using the vacuum technique at 60 ° C for 3 minutes and drying in the drying tunnel for 8 hours at 50 ° C. Through the intensive humidification of the leather matrix to a water content> 50%, a reconditioning of the fiber is achieved. The leather matrix is then re-dried to a water content of less than 15% by vacuum technology at 60 ° C for 1-2 minutes and dried for at least 8 hours at 40 ° C. The intensive softening of the fiber is carried out by means of a commercial machine of continuous softening with bolt tools and is a preparatory operation for the coating of the surface (finishing).

The finishing consists of a finely divided polymer blend of approximately 40% active agent content and finely divided polyurethane dispersions of approximately 30% active agent content (modified polyurethane emulsion / acrylate copolymer), which obtain their coloration by the addition of inorganic pigment dispersions. 400 parts of the binder mixture are mixed with 100 parts of inorganic pigments and 350-400 parts of water. The binder mixture is applied to the surface of leather 2 3 times (107.6-161.4 g / square meter of leather) by means of a commercially available rotary spraying machine and then subjected to treatment with an ironing machine continuous at 80 ° C. This operation is repeated 3 times. By means of a one-time intermediate coating with an aqueous emulsion varnish based on polyurethane with an active agent content of 25% of approximately 107.6 g / square meter of leather, the finishing film is adjusted with medium strength .

Then it is ironed at approximately 80 ° C with the continuous ironing machine. By means of a repetitive softening by means of a continuous softening machine an intensive loosening of the fiber is achieved, which represents a preliminary treatment for the beating in barrel. The work process of beat is decisive for the expression of the grain and the leather surface resulting from it (retraction optics).

The continuous introduction of humidity for 2 hours in the barrel (1.5 m wide, 2 m high, 40 liters of water / 70 pieces of leather) and, at the same time, the rotating mechanical work to at least 18 rpm guarantees the conditioning of the fiber. After a period of 3 hours, the systematic extraction of moisture to a water content of 25% of the leather begins, while maintaining mechanical machining for 6 to 8 hours, which determines the grain size of the image of contraction while determining the grip (the firmness and the so-called cracks of the finished leather).

The subsequent conditioning in the drying tunnel at 40 ° C for 2 hours and the reduction of the leather water content below 15% fixed the grain image

The final adjustment of the shrink grain is achieved by applying dispersions of finely divided polyurethanes, 2-isocyanate (approximately 30%) in a mixing ratio of 30 parts of binder in 100 parts of water with an application amount of at least 107.6. mg / square meter of leather with a rotary spraying machine commercially available.

Advantageously, in the process of the invention, there should not be a premature selection of assortment in an early stage of the production of leather (water workshop), nor should special shrink-tanning agents be used to achieve a reliable amount of surfaces qualitatively uniform. Achieving this uniform surface and the guaranteed assortment determination by pre-selection compared to the nudity classification allows maximum use of the surface for further leather processing. The approach in the present method in comparison with conventional methods in the art is a different one and is based on the use of a calf skin containing substances, which is traditionally tanned after the procedure with undissolved chromium.

The above explanations and interpretations are applied mutatis mutandis to the following preferred embodiments of the process according to the invention.

In a preferred embodiment of the method according to the invention, the contracted grain leather has a thickness of 2 to 3 mm, preferably of 2.3 to 2.5 mm.

An embodiment of the process according to the invention is preferred, wherein steps a) and d) are carried out in a rotary vessel at 12 rpm.

Furthermore, preference is given to an embodiment of the process according to the invention, wherein the washing in step a) is carried out at about 40 ° C for about 30 minutes.

Also preferred is an embodiment of the process according to the invention, wherein the neutralization in step b) is carried out at about 40 ° C for about 150 minutes and a final pH value greater than pH 6.0 is achieved. in the solution.

Also preferred is an embodiment of the process according to the invention, wherein the incubation time for the incubation of the skin in step c) with approximately 0.5% (w / w) solution of a fatty acid ester takes about 60 minutes, with solution of about 2% (w / w) of a polymeric tanning agent takes about 40 minutes and with the solution of about 20% (w / w) of a retanning agent takes 60 minutes.

An embodiment of the process according to the invention is preferred, in which the dyeing in step d) is carried out at about 20 ° C for about 60 min.

Also preferred is an embodiment of the process according to the invention, in which the greasing in step e) is carried out for about 40 minutes.

Preference is given to an embodiment of the process according to the invention, in which the fixation in step f) is carried out for approximately 60 minutes.

Also preferred is an embodiment of the process according to the invention, in which the final pitch adjustment in step g) is carried out at about 50 ° C for about 60 minutes.

Preference is given to an embodiment of the process according to the invention, in which the fixation in step h) is carried out for about 20 minutes and a final pH value between 3.5 and 3 is reached in the solution, 6 In addition, preference is given to an embodiment of the process according to the invention, in which step i) is carried out for about 10 minutes at about 20 ° C.

Also preferred is an embodiment of the process of the invention wherein the drying in step j) comprises a step of squeezing and stretching the coating, a preliminary drying is carried out for about 3 minutes using vacuum at about 60 ° C, and drying for about 8 hours (h) at about 50 ° C.

Also preferred is an embodiment of the process of the invention in which whipping in step n) is carried out for about 2 hours and the dehumidification in step o) is carried out for about 6 to 8 hours in a rotary container 18 rpm for about 10 minutes at about 20 ° C.

Finally, an embodiment of the process according to the invention is preferred in which the conditioning in step p) is carried out for about 2 hours at about 40 ° C.

Finally, the invention also relates to a leather shrinkage, which can be obtained by the method according to the invention described above and preferably has a coating thickness of 2 to 3 mm, preferably of 2.3 to 2.5 mm .

FIGURES

Figure 1 shows a schematic overview of the method according to the invention comprising washing steps of at least one skin tanned with chromium (Chromwetblue) in a washing solution containing 200% (w / w) of water and 0.2 % (w / w) of a nonionic surfactant, based on the weight of the depilated skin (101); the neutralization of the treated skin in a neutralization solution containing 100% (w / w) of water, 1.5% (w / w) of sodium formate and 3% (w / w) of sodium bicarbonate (102 ) based on the weight of the depilated skin; the preliminary greasing, which comprises incubating the skin with about 0.5% (w / w) of a solution of a fatty acid ester, about 2% (w / w) of a polymeric tanning agent and about 20% ( p / p) of solution a retanning agent (103); dyeing the skin in a dyeing solution comprising about 50% (w / w) of water, about 1.5% (w / w) ammonia and anionic dye (104); lubrication by the addition of approximately 100% (w / w) of water and 4.5% (w / w) of the lubrication mixture, in which this lubrication mixture comprises 45% (w / w) of long chain paraffins and 55% (w / w) sulphited oils (105); fixing by the addition of about 3.5% (w / w) of formic acid (106); adjusting the final shade of the color by transferring the skin to a toner solution of approximately 200% (w / w) of water with an acidic anionic dye that does not require mordant (107); fixation by the addition of 0.5-1.0% (w / w) of formic acid (108); washing the skin in approximately 200% (w / w) of water (109); drying the skin (110); the application of a binder mixture solution comprising a mixture of binders and an inorganic pigment dispersion in a ratio of 4: 1, in which the binder mixture solution comprises about 40% (w / w) of a polyurethane dispersion finely divided and about 30% (w / w) of a polyurethane / modified acrylate copolymer emulsion (111); the application of an aqueous emulsion varnish based on polyurethane having an active agent content of 25% (w / w) (112); ironing and softening the skin (113); the skinning of the skin with continuous supply of moisture (114); the skin is dehumidified to a moisture content of approximately 25% (w / w) on the skin (115); the conditioning of the skin and reduction of the moisture content to approximately 15% (w / w) or less (116); the application of a fixing solution comprising approximately 30% (w / w) of polyurethane dispersion, in which the urethane is crosslinked 2-isocyanate and the binder-water mixture ratio is 3 parts: 10 parts, for obtain the contracted grain leather (117).

Figure 2: Figure 2A shows the surface of a uniform contraction of calf leather, which was produced by the method according to the invention. For comparison, the surface of a non-uniform contraction of calf leather that was not produced by the method according to the invention is illustrated in FIG. 2B.

EXAMPLES

The following embodiments serve only to illustrate the invention and should not be used to limit the scope of protection.

Example: production of a calf leather with a skin thickness of 2.3 to 2.5 mm.

The so-called Chromwetblue (intermediate tanning product with a chromium oxide content of at least 1.5%) was used.

Rotating wooden barrels were fed, at 12 rpm, according to the weight of the depilated skin, with 200% water at 40 ° C and 0.2% of a non-ionic surfactant to wash the chrome-tanned leather. The execution time was 30 minutes. Then, the leathers were neutralized in a neutralization solution containing 100% (w / w) of water, 1.5% (w / w) of sodium formate and 3% (w / w) of sodium bicarbonate for a period of 150 minutes The final pH value remained at a pH> 6. This was followed by a preliminary greasing with 0.5% of a fatty acid ester for 60 minutes, in combination with 2% of a tanning polymeric agent for 40 minutes and 20 minutes. % of a synthetic retanning agent (condensation product of naphthalene-phenol) for 60 minutes. The following steps initiate dyeing with anionic dyes and go directly to greasing with long chain paraffins and hydrophobic emulsifiers.

The dyeing was achieved at 50% water at 20 ° C with 1.5% ammonia and a substantive acid dye for 60 minutes at approximately 12 rpm and greased in the same medium with the addition of 100% water to 60 ° C and 4.5% fatliquoring mixture, with a content of 45% (w / w) of long-chain paraffins and a content of 55% (w / w) of sulphited oils in a ratio of 1: 1 during 40 minutes and fixed by the addition of 3.5% formic acid, at 85% for 60 minutes.

The final color tone adjustment was carried out in a fresh bath with 200% water at 50 ° C and the addition of anionic dyes of the acid type that did not need mordant for 60 minutes and was fixed and completed by the addition of 0.5-1.0% 85% formic acid for 20 minutes. The final pH value was between 3.5 and 3.6.

This was followed by a wash with 200 % water at 20 ° C for 10 minutes.

After wet work, drying was initiated by intensive squeezing and stretching by commercially available roller machines. The preliminary drying was carried out using the vacuum technique at 60 ° C for 3 minutes and drying in the drying tunnel for 8 hours at 50 ° C. By intensive humidification of the leather matrix to a water content> 50%, a reconditioning of the fiber was achieved. The leather matrix was then re-dried to a water content of less than 15% by vacuum technology at 60 ° C for 1-2 minutes and dried for at least 8 hours at 40 ° C. The intensive softening of the fiber was carried out by means of a commercial continuous softening machine with bolt tools and is a preparatory operation for surface coating (finishing).

The finishing consisted of a finely divided polymer blend of approximately 40% active agent content and finely divided polyurethane dispersions of approximately 30% active agent content (modified polyurethane emulsion / acrylate copolymer), which obtained their coloration by the addition of inorganic pigment dispersions. 400 parts of the binder mixture were mixed with 100 parts of inorganic pigments and 350-400 parts of water. The binder mixture was applied on the surface of leather 2 3 times (107.6-161.4 g / square meter of leather) by means of a commercially available rotary spray machine and then subjected to treatment with an ironing machine continuous at 80 ° C. This operation was repeated 3 times. By means of a one-time intermediate coating with an aqueous emulsion varnish based on polyurethane with an active agent content of 25% of approximately 107.6 g / square meter of leather, the finishing film was adjusted with medium strength .

Subsequently, it was ironed with an ironing machine at approximately 80 ° C. By means of a repetitive softening by means of a continuous softening machine an intensive loosening of the fiber was achieved, which represents a preliminary treatment for the beating in barrel. The work process of beat is decisive for the expression of the grain and the leather surface resulting from it (retraction optics).

The continuous introduction of humidity for 2 hours in the barrel (1.5 m wide, 2 m high), (40 liters of water / 70 pieces of leather) and, at the same time, the rotating mechanical work to at least 18 rpm guaranteed the conditioning of the fiber. After a period of 3 hours, the systematic extraction of moisture to a water content of 25% of the leather was started, while mechanical machining is maintained for 6 to 8 hours, which determines the grain size of the image of contraction while determining the grip (the firmness and the so-called cracks of the finished leather).

A subsequent conditioning in the drying tunnel at 40 ° C for 2 hours and the decrease in the water content of the leather below 15% fixes the grain image.

The final fixing of the shrink grains was achieved by applying a finely divided aqueous (approximately 30%) polyurethane dispersion of cross-linked 2-isocyanate in a mixing ratio of 30 parts of binder in 100 parts of water with an application amount of at least 107.6 mg / square meter of leather by means of a commercially available rotary spray machine.

The contraction of the calf skin thus obtained predominantly shows a homogenously structured surface as shown in Figure 2A.

Claims (15)

1. Procedure for producing leather contraction, comprising the following steps: a) washing at least one skin tanned with chromium (Chromwetblue) in a wash solution containing approximately 200% (w / w) of water and approximately 0.2% (w / w) of a nonionic surfactant ; b) the neutralization of the treated skin in a neutralizing solution containing approximately 100% (w / w) of water, approximately 1.5% (w / w) of sodium formate and approximately 3% (w / w) ) of sodium bicarbonate; c) preliminary greasing, which comprises incubating the skin with approximately 0.5% (w / w) of a solution of a fatty acid ester, approximately 2% (w / w) of a polymeric tanning agent and about 20% (w / w) solution of a retanning agent; d) dyeing the skin in a dyeing solution comprising about 50% (w / w) of water, about 1.5% (w / w) ammonia and anionic dye; e) greasing by adding approximately 100% (w / w) of water and 4.5% (w / w) of greasing mixture, where this greasing mixture comprises 45% (w / w) of long chain paraffins and 55% (w / w) sulphited oils; f) fixation by the addition of approximately 3.5% (w / w) of formic acid; g) the adjustment of the final shade by transferring the skin to a toner solution of approximately 200% (w / w) of water with an anionic dye of the acid type that does not need mordant; h) fixation by the addition of approximately 0.5-1.0% (w / w) of formic acid; i) washing the skin in approximately 200% (w / w) of water; j) drying the skin; k) the application of a binder mixture solution comprising a mixture of binders and an inorganic pigment dispersion in a ratio of 4: 1, wherein the binder mixture solution comprises about 40% (w / w) of a finely divided polyurethane dispersion and about 30% (w / w) of a modified polyurethane / acrylate copolymer emulsion; l) the application of an aqueous emulsion varnish based on polyurethane having an active agent content of approximately 25% (w / w); m) ironing and softening of the skin; n) skin whitening with continuous supply of moisture; o) the dehumidification of the skin to a moisture content of approximately 25% (w / w) on the skin; p) conditioning the skin and reducing the moisture content to approximately 15% (w / w) or less; Y q) the application of a fixing solution comprising approximately 30% (w / w) of polyurethane dispersion, wherein the urethane is crosslinked 2-isocyanate and the ratio of binder-water mixture is 3 parts: 10 parts , with which the contracted grain leather is obtained Method according to claim 1, in which the contracted grain leather has a thickness of 2 to 3 mm, preferably of 2.3 to 2.5 mm. 3. Method according to claim 1 or 2, wherein steps a) and d) are carried out in a rotary vessel at approximately 12 rpm. 4. Process according to any of claims 1 to 3, wherein the washing in step a) is carried out at about 40 ° C for about 30 min. The process according to any of claims 1 to 4, wherein the neutralization in step b) is carried out at about 40 ° C for about 150 minutes and in the solution a final pH higher than pH 6.0 is reached . 6. Method according to any of claims 1 to 6, wherein the incubation time for incubating the skin in step c) is about 60 minutes with a solution with about 0.5% (w / w) of a fatty acid ester, approximately 40 minutes with a solution with approximately 2% (w / w) of a polymeric tanning agent and approximately 60 minutes with a solution with approximately 20% (w / w) of a retanning agent . Process according to any of claims 1 to 6, wherein the dyeing in step d) is applied at about 20 ° C for about 60 min. Method according to any of claims 1 to 7, wherein the greasing in step e) is carried out for about 40 minutes. 9. Process according to any of claims 1 to 8, wherein the one set in step f) is carried out for about 60 minutes. The method according to any of claims 1 to 9, wherein the final tone adjustment in step g) is carried out for about 60 minutes at about 50 ° C. The process according to any of claims 1 to 10, wherein the one fixed in step h) is carried out for about 20 minutes and in the solution a final pH value of between 3.5 and 3 is reached, 6 12. Process according to any one of claims 1 to 11 wherein step i) is carried out for about 10 minutes at about 20 ° C. Process according to any one of claims 1 to 12, wherein the drying in step j) comprises a step, in which the skin is squeezed and spread, a preliminary drying is carried out at about 60 ° C for about 3 min using vacuum, and finally drying at about 50 ° C for about 8 h. The method according to any of claims 1 to 13, wherein the smoothing in step n) is carried out for about 2 hours and the dehumidification in step o) is carried out for about 6 to 8 hours in a rotating vessel at about 18 rpm for about 10 minutes at about 20 ° C. 15. Process according to any of claims 1 to 14, wherein the conditioning in step p) is carried out for about 2 hours at about 40 ° C.