EP1657355B1 - Method for the pictorial coloring of leather - Google Patents

Abstract

Imagewise dyeing of leather comprises applying an acrylate- or polyacrylate-containing mordant to the leather, drying and curing the mordant, applying a water-soluble dye to a transfer sheet by digital printing, and transferring the dye to the leather. An independent claim is also included for leather dyed as above.

Description

The invention relates to a process for the image-wise dyeing of leather, that is to the production of colored motif structures on leather.

A process for dyeing and printing leather is known, for example from DE 38 25 755 A1 known. In this case, metal complexes of metallizable monoazo and / or monoazomethine dyes are used as anionic metal complex dyes. Next, the leather is treated by the known method with a polymer which is obtainable, for example, by reacting a monofunctional or polyfunctional amine, inter alia, with cyanamide, dicyandiamide, guanidine or biguanidine. A further reaction is possible, for example, with formaldehyde or a formaldehyde-releasing compound.

Another important aspect of the dyeing of leather is the structure of the colored surface in addition to the nature of the used, in many cases environmentally hazardous substances. Frequently, a layer is applied to the surface of the leather, which is typically textured in the undyed state, which levelens the natural unevenness of the leather and thus gives the impression of a smooth plastic surface. The leather is thus coated more than dyed. The coating has the further disadvantage that it ruptures very easily, in particular under bending stress, and is therefore hardly suitable for a continuous load, for example in the case of shoes. For the reasons mentioned is usually dispensed with a pictorial coloration of heavily used leather and instead used uniformly colored leather.

The invention has for its object to provide a method for dyeing leather, which has a good environmental compatibility with a high resistance the coloring combines with largely preserving the typical surface structure of the leather. This object is achieved by a method according to claim 1 and by a leather according to claim 25.

According to the method of the invention, a stain containing acrylates and / or polyacrylates is applied to a leather in a first step. After a drying and curing time, a water-soluble dye is applied by means of an intermediate carrier to the leather in a further step. The motif structure in which the leather is to be dyed is first printed on the intermediate carrier, that is to say a paper, a foil or another flat object. From the intermediate carrier, the transfer of the image or the other motif structure takes place on the leather. The printing of the subcarrier is done in a digital printing process, similar to the usual printing on paper, and is thus particularly efficient with high achievable resolution. The dye transferred from the intermediate carrier to the leather reacts reactively with the leather as well as with the stain that has penetrated into it. In this way, the leather is dyed pictorially while largely preserving its surface structure, at the same time good durability, in particular color fastness and abrasion resistance, is given.

Leathers which can be dyed by the method are grain leather, for example nappa made of sheep, goat or cowhide and boxcalf or cowhide leather, for example suede, split suede, suede and nubuck leather. The process for imagewise dyeing can be used with any leather tanned, for example mineral, synthetic or combined tanned leathers. Likewise, the method for leathers of various thicknesses, such as bookbinding leather, glove leather, shoe leather, leather for handbags, shoe soled leather, upholstery leather, case leather, belt leather or leather for sporting goods is suitable. The specified method is particularly suitable for dyeing already colored leathers.

The stain to be used in the first step of the process may be painted, painted, doctored, rolled, sprayed or otherwise applied to the leather, for example by dipping. In the subsequent drying time, the stain spreads in the leather and combines with the leather surface, but without destroying their surface structure, for example by forming a closed, even layer. In addition to drying, hardening of the stain in the leather also takes place, in particular by polymerization reactions.

The liquid used as a pickling with acrylates or polyacralates allows by their chemical composition, a reaction with the leather and the applied dye and thus in a particularly environmentally friendly process, a constant coloration of the leather.

As dyes, so-called mordant dyes are preferably used, which have surprisingly been found to be particularly suitable for the imagewise coloring of leather. Bees dyestuffs are understood to mean a group of dyestuffs which has been widely used since the Middle Ages but is today rarely used because of the technically necessary effort. Dyestuff dyes belong to various classes of substances and have hitherto been used almost exclusively in the text industry, predominantly for dyeing wool, silk, cellulose fibers and other protein fibers. Not to be confused with the mordant dyes used herein are the so-called Farbstoffbeizen, which have long been known in particular as a colorant for wood.

Further advantageous embodiments of the invention will become apparent from the dependent claims. Advantageously, the dye reacts with the leather in a reactive manner by coupling dye groups to OH groups present in the leather. Leather of animal origin carries these OH groups as protein components. The dyes couple to the OH groups to form a permanent compound that is stabilized by the simultaneous presence of the acrylates or polyacrylates. The dyes are durable and resistant to the leather and not to an intermediate layer applied to the leather connected, whereby the natural surface texture of the leather is maintained.

Claims 3 to 8 relate to particularly preferred embodiments of the invention, in which the use of a selected stain contributes to the fact that the inventive method is particularly environmentally friendly. The stain used is preferably oil-free and has no inorganic constituents, such as chromium, nickel or silicon, in concentrations relevant to the effect of the stain, with the exception of water. The use of toxic solvents is therefore not required. The solids content in the pickle preferably ranges between 30% and 70%. A solids content of about 60 to 65% has proved to be particularly advantageous. However, even with a low solids content of about 30%, depending on the application, still achieve qualitatively sufficient results. By using a water-based stain, the method according to the invention can also be used in critical fields of application, for example in the food sector. The stain in the form of an aqueous dispersion is preferably non-toxic (for example, butyl acrylate is classified as irritant, danger symbol "Xi") and biodegradable, so that in particular the disposal of leftover stocks is easily possible. The use of a water-based stain, in combination with the water-soluble dye, leads in particular to the preference of the reactive compound of the dye with the OH groups of the leather. This is further favored by the relatively low solids content in the stain.

In a preferred embodiment of the invention, the finished pickle is recovered from a pickle concentrate, which is diluted with water. The pickling concentrate preferably consists of 60 to 90 wt .-% ethyl acrylate and 10 to 40 wt .-% butyl acrylate, which is mixed with water. This concentrate is then diluted with water at a ratio of 1: 3 to 1: 5 before use. Due to polymerization reactions, it is not always possible to calculate the solids content of the finished pickle arithmetically from the composition of To determine starting materials. In the pickling used in the process, a solids content of about 63% is established.

The solvent-free stain (in this context, water is not understood as a solvent) is preferably transparent or at least so slightly colored that the possibilities of subsequent coloring of the leather, even with high resolution, are not limited by the use of stain. The stain can also be mixed with chemical or physical additives (claims 9 and 10). For example, the stain can thickened with thickeners and thus adjusted for the brush or doctor job. In any case, all substances used in the process according to the invention are harmless under environmental, occupational safety and health aspects.

In an advantageous embodiment of the invention, the dye and / or the stain is applied in such a way that the dyed leather obtains a neutral pH of about 7. Extensive research has shown that the pH of the dyed leather is important for the stability of the reactive compound with the leather and the stain. If the color is applied without taking into account the pH value, the leather becomes more acidic in its pH. This is due to the fact that commercially available leather per se has an acidic pH in the range between 3 and 4. However, an acidic pH may adversely affect the stability of the reactive compound, especially the stability of the bond with the OH groups of the leather. When the paint and / or stain is applied in an alkaline region having a pH of about 7.5 to 9, the colored leather has an approximately neutral pH. As a result, the durability of the reactive compound of the dye is increased.

The total proportion of acrylates and polyacrylates in the stain is preferably less than 40% (claim 12). Preferred parameters for the treatment of the leather after the application of the stain, prior to the application of the dye, are mentioned in claims 13 to 14. Accordingly, that dries Leather at 100 ° C to 150 ° C, especially at about 130 ° C. These temperatures keep energy consumption relatively low. Alternatively, it is also possible to carry out the drying at room temperature. If the drying takes place at room temperatures above room temperature, drying takes about 10 minutes to 60 minutes, in particular about 30 minutes. After this drying, the pieces of leather treated with the stain can already be stacked.

The curing of the acrylates and polyacrylates of the stain, wherein a polymer self-crosslinking takes place at temperatures of 130 ° C to 170 ° C for half to two minutes, in particular about 1 min. The drying and curing times can be smoothly blended, with the temperature during cure time not being necessarily higher than during the previous drying time. The special features of the material leather, in particular its limited temperature resistance, must always be ensured by a suitable choice of parameters.

The dye used preferably has a weight-based solids content of less than 15% and is thus particularly suitable for the digital printing process. It is a water-soluble dye without using organic solvents (claims 16 and 17). The use of quinoline, which is generally suitable for the production of Sparbeizen, for the treatment of the leather is possible (claim 18).

Chemical and / or physical additives, such as, for example, defoamers and fillers, may be added to the dye in order to modify the leather surface or, for example, to promote the formation of a protective layer on the leather surface (claim 19). The dye applied to the leather, if no drying takes place at room temperature, preferably at 100 ° C to 150 ° C, in particular about 130 ° C for half to two minutes, especially about 1 minute, dried (claim 20 ).

Of particular advantage is a transfer of the dye from the intermediate carrier to the leather by vapor deposition. By evaporation or sublimation of the dye can be converted into the gaseous state and thus the intermediate carrier can be used as sublimation. The transfer of the dye to the leather can in this case be effected with the aid of a heatable press, for example a veneer press, as used in the same or similar manner by carpenters. Under the influence of the required pressure and temperature values, a sublimation of the dye takes place. In this context, sublimation is understood to mean not only a transition from the solid to the gaseous phase in the strictly physical sense, but also the entrainment of dye particles in a steam stream produced by the heating, whereby the dye particles do not necessarily undergo a phase change (claims 21 to 23) ).

The dye particles are released from the sublimation element, which was previously placed on the leather to be dyed, and applied to the leather. The sublimation element serves as a carrier material for the dye. At the same time still existing water evaporates from the stain previously applied to the leather. Pickle, dye and leather combine reactively such that after the completion of the pressing process, the dye is solid and irretrievable in the leather. Following application of the dye, a thin protective layer or varnish such as PUR may be applied to the leather to further protect the surface from environmental and wear. Preferably, a coating of an aqueous dispersion of self-crosslinking polymers is applied (claim 24). Even with this additional coating, the natural, textured surface of the leather remains substantially unchanged.

By the present method, a particularly environmentally friendly and thus contemporary dyeing of leather is possible. At the same time, the process is completely harmless to health. In contrast to previously known methods, the leather on which a print is to be applied, with a smooth coating provided no cover or seal the leather surface by a color print. Rather, the dyeing is done by an intrusion of the substances used in the leather, whereby a high quality coloration can be produced. A special feature of the dyeing results is that the surface character and the feel of the leather are fully preserved and the color and light fastness of the motive structure thus produced is given.

With the present dyeing method, it is in principle also possible to provide products made of leather over a large area with a uniform color or with coarse color structures. However, the advantages of the method are particularly evident in the application of image motifs with very fine motif structures in the order of a few millimeters, with no interpenetration of the colors. The process is particularly easy to carry out with low dye consumption and thus cost. It can be carried out using already existing machines and devices, whereby an introduction of the method or a conversion from previous methods to the inventive method without major investment costs is possible. The visually appealing results are retained even with prolonged use of the dyed leather product.

Fig. 1

ein vereinfachtes Ablaufdiagramm des erfindungsgemäßen Verfahrens und

Fig. 2

eine schematische ausschnittsweise Darstellung eines mit dem erfindungsgemäßen Verfahren gefärbten Leders.

In the following the invention will be described with reference to an embodiment which is explained in more detail with reference to the figures. Hereby shows:

Fig. 1

a simplified flow diagram of the method according to the invention and

Fig. 2

a schematic partial view of a dyed with the inventive process leather.

Fig. 1 shows a schematically greatly simplified flow diagram of the method according to the invention. In a first step 10, an oil-free stain in the form of an aqueous dispersion having a solids content of 63% is added to a treating piece of leather, which is provided for example for the production of sports shoes, applied. Apart from water, the stain is virtually free of inorganic constituents and is obtained from a staining concentrate diluted with water at a ratio of 1: 4, which consists of 70% by weight of ethyl acrylate and 30% by weight of butyl acrylate. After applying the stain to the leather, the stain that has penetrated into the substrate surface is dried. The drying can be done at room temperature, so that there are no energy costs. The drying process may alternatively take place at elevated temperatures, for example in the range of 100 ° C to 150 ° C. Depending on the drying temperature, the drying time is between a few minutes and a few hours. In addition to drying, hardening of the pickling takes place in the first step 10, with the substances contained therein at least partially polymerizing. To harden the stain, the leather is preferably brought to an elevated compared to the drying temperature of up to 170 ° C, the curing process takes only about one minute.

In a parallel to the application and drying of the stain on the leather feasible preparation step 11, the ultimately to be transferred to the leather motif structure on an intermediate carrier, preferably paper, printed. The printing is done in a digital printing process, as is common in principle, for example, in commercial inkjet printers and plotters. In this case, a digital printing method is not exclusively understood to mean a printing method in which a picture decomposed in pixels is processed by data technology, but also, for example, a vector graphic. Under a digital printing method, any printing method is subsumed in which a print template is stored digitally and the control of the printing press is done by means of a computer. If the representation is present as a pixel graphic, the dye is preferably applied line by line to the intermediate carrier. The same applies in cases in which there is a lettering or a combination of writing and graphic representation as the motif structure. The dye used is preferably a water-soluble, solvent-free ink suitable for digital printing without anthraquinones and alizarines, the solids content of which is less than 15%.

After completion of the first step 10 of the process, that is, the treatment of the leather with the stain in the form of an aqueous dispersion of acrylates and polyacrylates, as well as the preparation step 11, that is the digital printing of the intermediate carrier, in a further step 12, the motif structure transferred from the intermediate carrier to the pretreated leather.

The dye present on the intermediate carrier is applied to the leather in a sublimation process by placing the printed paper, the film or the like serving as an intermediate carrier, on the leather and heating it under pressure. Finally, the intermediate carrier is removed so that only the color remains on the leather. This ensures optimum durability and color fastness without significantly affecting the surface structure of the leather. In particular, the formation of a smooth, plastic-like layer on the leather surface is avoided.

For the described process of vapor deposition or sublimation of the dye on the leather in step 12, for example, a conventional heatable press is suitable. Typical press parameters are a press pressure of 5 to 15 bar and a temperature of for example 180 ° C, which can be achieved by electrical heating. Instead of an electrically heatable press, of course, other suitable devices can be used which allow evaporation of the dye and an introduction of the dye into the leather and a reactive connection between the stain, the dye and the leather. As far as the stain in the first step 10 is not fully polymerized, there is a further polymer self-crosslinking in step 12, which additionally contributes to the binding of the dye in the leather.

In a final step, not shown, a protective layer may be applied to the dyed surface of the leather which, like the layer of self-crosslinking polymers formed by the stain, is also colorless.

Finally, FIG. 2 shows a cross-section of a highly schematic illustration of a leather 1, which is dyed pictorially with the method described above. The stain applied to the leather 1 in step 10 has made a connection with it and is therefore not shown as a separate layer. The dye, which was transferred to the leather 1 in step 12, forms with this and the stain a color layer 2, which is shown in simplified form as a separate layer on the surface 3 of the leather 1. The leather 1 has an uneven surface 3 clearly visible in the cross-sectional representation. As can be further seen, the color layer 2 follows the unevenness of the surface 3 of the leather 1, wherein the color layer 2 is actually so thin, as far as this is predominantly a layer that is geometrically separate from the leather 1, that it is barely perceptible to the touch. Thus even a high-resolution pictorial coloring, for example a photographic representation, is possible without complete leveling of the surface 3 of the leather 1.

LIST OF REFERENCE NUMBERS

1.

leather

Second

coat of paint

Third

surface

10th

first step

11th

preparation step

12th

another step

Claims (25)

1. A process for imagewise dyeing of leather, the process comprising a first step (10) of applying to a leather (1) a mordant comprising acrylates or polyacrylates and, after a drying and curing time, a further step (12) of applying a water-soluble dye to the leather (1) by means of a transfer, the dye being initially applied to the transfer by a digital printing process and in the course of being transferred from the transfer to the leather (1) binding reactively with the latter and with the mordant penetrated thereinto.
2. A process according to claim 1,
   characterized in that
   the dye binds reactively with the OH groups in the leather.
3. A process according to claim 1 or 2,
   characterized in that
   the mordant is oil free.
4. A process according to any one of claims 1 to 3,
   characterized in that
   the mordant is free of inorganic constituents.
5. A process according to any one of claims 1 to 4,
   characterized in that
   the mordant has a solids content of less than 70%.
6. A process according to any one of claims 1 to 5,
   characterized in that
   the mordant has a solids content of at least 30%.
7. A process according to any one of claims 1 to 6,
   characterized in that
   the mordant is an aqueous dispersion.
8. A process according to any one of claims 1 to 7,
   characterized in that
   the mordant is solvent free.
9. A process according to any one of claims 1 to 8,
   characterized in that
   the coating of the leather (1) with the mordant is transparent.
10. A process according to any one of claims 1 to 9,
    characterized in that
    the mordant has been admixed with chemical or physical additives.
11. A process according to any one of claims 1 to 10,
    characterized in that
    the dye and/or the mordant is applied such that the dyed leather acquires a neutral pH of about 7.
12. A process according to any one of claims 1 to 11,
    characterized in that
    the total fraction of the mordant that is accounted for by the acrylates and polyacrylates is less than 40%.
13. A process according to any one of claims 1 to 12,
    characterized in that
    the mordant-treated leather (1) is dried at 100°C to 150°C and in particular at about 130°C.
14. A process according to any one of claims 1 to 13,
    characterized in that
    the drying of the mordant applied to the leather (1) takes 10 min to 60 min and in particular about 30 min.
15. A process according to any one of claims 1 to 14,
    characterized in that
    the mordant applied to the leather (1) is cured at 130°C to 170°C for half a minute to 2 minutes and in particular for about 1 minute in the form of a polymer's self-crosslinking reaction.
16. A process according to any one of claims 1 to 15,
    characterized in that
    the solids content of the dye is less than 15%.
17. A process according to any one of claims 1 to 16,
    characterized in that
    the dye is free of organic solvents.
18. A process according to any one of claims 1 to 17,
    characterized by
    the use of quinoline for treating the leather (1).
19. A process according to any one of claims 1 to 18,
    characterized in that
    the dye is admixed with chemical and/or physical additives such as for example defoamers, fillers, etc.
20. A process according to any one of claims 1 to 19,
    characterized in that
    the dye applied to the leather (1) is dried at 100°C to 150°C and in particular at about 130°C for half a minute to 2 min and in particular for about 1 min.
21. A process according to any one of claims 1 to 20,
    characterized by
    the dye present on the transfer being vapor deposited onto the leather (1).
22. A process according to any one of claims 1 to 21,
    characterized in that
    the transfer provided with the dye is used as a sublimation element.
23. A process according to any one of claims 1 to 22,
    characterized by
    the use of a heatable press to transfer the dye from the transfer to the leather (1).
24. A process according to any one of claims 1 to 23,
    characterized in that,
    after the dye has been applied, an additional coating of an aqueous dispersion of self-crosslinking polymers is applied to the leather (1).
25. Imagewise dyed leather (1)
    produced by
    a process according to any one of claims 1 to 24.

Images