Method for dyeing and / or retanning leather

Abstract

The invention relates to a method for dyeing and / or retanning a leather article, said method comprising the following steps: providing (2) a leather article treated at least by a tanning process; introducing (4) the leather product into a processing chamber; subjecting (6) the leather article in the processing chamber to the action of a pressurized fluid; controlling (10) the pressure of the pressurized fluid to reach a supercritical state; subjecting the leather article to the action of a colouring agent and / or a retanning agent, said colouring agent or retanning agent being dissolved and / or transported in the pressurized fluid at least for a predetermined period of time when the pressurized fluid is in the supercritical state; reducing (12) the pressure in the processing chamber; removing (14) the leather article from the processing chamber; wherein the step of reducing the pressure in the processing chamber comprises controlling the pressure to be reduced over time.

Description

[0001] This application is a divisional application of the invention patent application with an international filing date of April 29, 2020, an invention name of “Method for leather dyeing and / or retanning”, and an application number of 202080032222.5. Technical Field

[0002] The invention relates to a method for dyeing leather products. Background Art

[0003] It is well known that dyeing is one of the more important steps in the field of leather manufacturing, as it is often the first characteristic of leather that consumers evaluate. Dyeing of leather is currently mainly carried out under wet conditions with acid dyes, sulphur dyes, direct dyes, premetallized dyes, reactive dyes or basic dyes, but acceptable high colour depth and high moisture fastness are difficult, so improved solutions are needed. It is also well known that water and processing aids such as dyes, retanning agents and fatliquors are used in large quantities in the leather dyeing process and can be energy intensive.

[0004] Therefore, the object of the present invention is to provide an advantageous and more environmentally sustainable dyeing process with high dyeing efficiency and high moisture fastness. Another object is to ensure that the leather quality meets all common physical and chemical test standards, including high color fastness. Summary of the invention

[0005] The present invention relates to a method for dyeing and / or retanning leather products, the method comprising the following steps:

[0006] - providing a leather product, said leather product being subjected to at least a tanning process,

[0007] - introducing said leather product into a treatment chamber,

[0008] - subjecting said leather article in said treatment chamber to the action of a pressurized fluid,

[0009] - controlling the pressure of the pressurized fluid to achieve a supercritical state,

[0010] - subjecting the leather product to the action of a dye and / or a retanning agent, which is dissolved and / or transported in the pressurized fluid at least for a predetermined period of time when the pressurized fluid is in the supercritical state,

[0011] - reducing the pressure in the process chamber,

[0012] - removing the leather article from the treatment chamber,

[0013] The step of reducing the pressure in the process chamber includes controlling the pressure to decrease over time.

[0014] Thus, using the method according to the invention it is possible to achieve a dyeing / coloring of leather products which, compared to conventional dyeing methods, is peculiar in that relatively large amounts of water are avoided in the dyeing process and, due to the reduced process time, less energy can also be used. This is achieved by using a dye which is soluble in the pressurized fluid at least in the supercritical state, whereby the dissolved dye in combination with the pressurized fluid in the supercritical state can penetrate into the leather structure including at least part of the inner structure and perform dyeing not only on the surface of the leather structure but also on the underlying structure, such as collagen fibers in the leather structure.

[0015] According to the invention, the step of reducing the pressure in the treatment chamber, for example at the end of the dyeing step in the supercritical state, comprises controlling the pressure reduction over time in such a way that the leather product retains the desired properties that are essential for the long-term use of the leather, for example, the color and surface properties are maintained, any tendency of the leather to delaminate is minimized or even completely avoided, and the requirements for the prevention of leather delamination are met. This may involve setting a minimum time period for reducing the pressure, setting a maximum number of pressure reduction gradients, setting a maximum number of average pressure reduction gradients, etc., which will ensure that the leather structure, in particular the leather structure that has been dyed with a dye and penetrated by a pressurized fluid in the supercritical state, is not adversely affected during the pressure reduction.

[0016] The step of reducing the pressure in the treatment chamber includes controlling the pressure reduction over time to meet leather delamination prevention requirements, for example meaning that the leather structure, particularly a leather structure that has been dyed with a dye and infiltrated by a pressurized fluid in a supercritical state, will not be affected by leather delamination during or after the dyeing process.

[0017] It is worth noting that the method according to claim 1 states that "leather products" are treated, but it is clear that two or more leather products may be treated simultaneously.

[0018] Furthermore, it should be noted that the dye may be introduced into the treatment chamber at any convenient stage and in any convenient manner, for example before the leather product is introduced, simultaneously with the introduction of the leather product, before or together with the introduction of the pressurized fluid, when the pressurized fluid reaches a supercritical state, etc.

[0019] According to one embodiment of the present invention, tanning is generally understood as the conversion of putrescible organic materials into stable materials that are resistant to biochemical attack.

[0020] In one embodiment of the invention, the step of reducing the pressure in the process chamber comprises removing the pressurized fluid from the process chamber.

[0021] Thus, the pressure reduction can be combined with the process of removing the pressurized fluid from the processing chamber, for example as a measure related to and in advance of removing the leather article from the processing chamber. In some embodiments, it is necessary to reduce the pressure of the processing chamber substantially to ambient pressure, for example, in order to be able to open the processing chamber and remove the leather article.

[0022] In one embodiment of the present invention, the method further comprises the step of removing residual dyeing and / or retanning agent from the pressurized fluid during or after the pressurized fluid is removed from the treatment chamber.

[0023] Thus, any dye that may not be absorbed or attached to the leather product can preferably be removed from the pressurized fluid, for example by distillation, precipitation processes, etc. (e.g. directly associated with pressure reduction). Excess dye can advantageously be reused and, more importantly, the purity of the pressurized fluid can be maintained and reused.

[0024] In one embodiment of the invention, the pressurized fluid removed from the process chamber is directed to a storage container at a storage pressure.

[0025] Thus, the pressurized fluid can be stored and prevented from leaking, for example, into the environment.

[0026] In one embodiment of the invention, the step of subjecting said leather article in said treatment chamber to said pressurized fluid comprises utilizing pressurized fluid from said storage container.

[0027] Thus, the pressurized fluid can be stored and reused later, for example for a subsequent dyeing cycle, for increasing the amount of the pressurized fluid, etc.

[0028] In one embodiment of the invention, the step of controlling the pressure in said processing chamber of said pressurized fluid to reach a supercritical state comprises increasing the pressure by maintaining it within predetermined limits over time.

[0029] Thus, the pressure is increased over time in such a way that the leather article retains the desired properties essential for its long-term use, for example, maintaining color and surface properties, minimizing or even completely avoiding any tendency of the leather to delaminate, and satisfying the requirements for preventing leather delaminate. This may involve setting a minimum time period for increasing the pressure, setting a maximum value for the gradient of the pressure increase, setting a maximum value for the average gradient of the pressure increase, etc., which will ensure that the leather structure, in particular the leather structure being dyed by the dye and about to be penetrated by the pressurized fluid in the supercritical state, is not adversely affected during the pressure increase.

[0030] The step of increasing the pressure of the treatment chamber comprises controlling the pressure increase over time to meet leather delamination prevention requirements, for example meaning that the leather structure is not affected by leather delamination during or after the dyeing process.

[0031] In one embodiment of the present invention, the step of subjecting the leather product to a dyeing agent comprises one of the following:

[0032] - introducing said dye directly into said treatment chamber,

[0033] - introducing the dye into the pressurized fluid before the pressurized fluid is introduced into the treatment chamber,

[0034] - introducing the dye into the treatment chamber together with the leather product, and

[0035] - introducing said coloring agent into said pressurized fluid when said pressurized fluid is controlled to reach or has reached said supercritical state.

[0036] In one embodiment of the present invention, the step of subjecting the leather product to a retanning agent comprises one of the following:

[0037] - introducing the retanning agent directly into the treatment chamber,

[0038] - introducing the retanning agent into the pressurized fluid before the pressurized fluid is introduced into the treatment chamber,

[0039] - introducing the retanning agent into the treatment chamber together with the leather product, and

[0040] - introducing said retanning agent into said pressurized fluid when said pressurized fluid is controlled to reach or has reached said supercritical state.

[0041] In one embodiment of the present invention, the dye is any dye related to leather and textile dyeing, and at least one type of dye selected from acid dyes, basic dyes, direct dyes, reactive dyes, chrome dyes, grinding dyes, metal complex dyes, mordant dyes and sulfur dyes, disperse dyes, reactive disperse dyes and natural dyes.

[0042] An example of a natural dye may be, for example, rose extract.

[0043] In one embodiment of the present invention, the stain is a collagen activity stain.

[0044] Thus, the dyeing process can be performed in a particularly advantageous manner, since, for example, priming of the leather, which may be mandatory in connection with conventional leather dyes, can be avoided. Thus, a simplified process can be achieved. Avoiding priming of the leather is achieved by using a dye that has an affinity for the non-primed collagen fibers in the leather, and a great advantage is that there is an intense color in the leather cross section, since the dye is fixed to all available collagen active sites.

[0045] Examples of reactive dyes may be Levafix Brilliant Blue E-BRA (CI Reactive Blue 114 of Dystar Japan Ltd.), Levafix Brill. Red CA (Dystar Japan Ltd.), Levafix Golden Yellow EG (CI Reactive Yellow 27 of Dystar Japan Ltd.), Eriofast Red B (Huntsman), Novacron Red P-BN GRAN (Huntsman), Lanasol Red 6G (CI Reactive Red 84 of Huntsman).

[0046] In one embodiment of the present invention, the processing aid is a retanning agent.

[0047] Thus, retanning agents can give fullness to leather by selectively filling the structure and provide a tight and even grain for leather finishing.

[0048] It should be noted that the present invention can be applied with particular advantage in connection with dyes, but the apparatus and method described herein can also be applied to leather processing in general using retanning agents. Retanning or a part of the retanning process can therefore be performed by the application of supplementary tanning agents such as inorganic or organic substances. Inorganic retanning agents that can be used in place of the above-mentioned dyes include chromium, aluminum, zirconium salts. Organic retanning agents include vegetable tanning agents, synthetic tanning agents, resins and aldehydes.

[0049] In one embodiment of the present invention, the amount of the dyeing agent and / or the retanning agent is dosed according to the weight, thickness and / or surface area of ​​the leather product.

[0050] Thus, the amount of dye, e.g. weight, volume etc., can be added to match the leather product, e.g. so that at least the necessary amount and possibly the exact amount is added to achieve the desired dyeing effect, and thereby, a minimum amount of dye will remain in the pressurized fluid after the dyeing process.

[0051] In one embodiment of the present invention, the amount of the dyeing agent and / or the retanning agent is dosed according to the type of the leather product.

[0052] Thus, the dosage of the dyeing agent, which can be automatic, can take into account such parameters as the type of leather, for example full grain leather or top grain leather, embossed grain leather, suede leather and nubuck leather, and the origin of the leather. Thus, the amount of residual dyeing agent can be reduced and the dyeing result can be optimized in this way.

[0053] In one embodiment of the present invention, the leather article is primed with a primer before being subjected to the pressurized fluid.

[0054] The primer may consist of a receptor polymer. The receptor polymer then forms the desired dyeing basis, since such leather itself is not suitable for dyeing. The finishing bottom layer may be part of a tanning, retanning and / or finishing process. Dyeing can in principle be performed at any time after the finishing bottom layer, as long as the applied dye matches the polymer of the finishing bottom layer.

[0055] Thus, it is achieved that a wide range of dyes can be used. Furthermore, additional effects can be achieved, for example, dyeing only certain parts of the leather product, which have already been coated with a base layer, the corresponding dye affecting the coloring. Thus, even two-tone dyeings and the like can be performed in the same dyeing process according to the invention. Even dyeing with two or more types of dyes, one requiring a base layer to be coated and one not requiring a base layer to be coated, such as collagen active dyes, can be performed. Other options are also possible.

[0056] In one embodiment of the invention, said pressurized fluid comprises CO2 having a purity of at least 99.0%, preferably at least 99.9%.

[0057] The pressurized fluid comprising CO2 may have a purity of up to 99.99%.

[0058] In one embodiment of the present invention, the method further comprises the step of adding a dye in an automatic manner based on the characteristics of the leather product.

[0059] Because dyeing process is relevant with one or more leather products that are cut and have predetermined size for a specific purpose, therefore can be equipped with basic accurate amount for dyeing process.Therefore, the coloring agent of specific amount can be for example automatically introduced into pressurized fluid, treatment chamber or (one or more) leather products relevant with technology.Thereby just realized that the waste of coloring agent is minimized, even avoids fully.In addition, the workload of removing unnecessary coloring agent and / or the subsequent cleaning of treatment chamber after a dyeing cycle from pressurized fluid can be minimized.

[0060] The characteristics of the leather product may be the weight and / or surface area of ​​the leather product, the type of leather (e.g., full grain leather or top grain leather, embossed grain leather, suede leather, and nubuck leather), and the origin of the leather. Other characteristics may also be relevant, or alternative.

[0061] In one embodiment of the present invention, the step of subjecting the leather product to the action of a dye and / or a retanning agent, wherein when the pressurized fluid is in the supercritical state, the dye or retanning agent is dissolved and / or transported in the pressurized fluid for at least a predetermined time period, also includes mixing, stirring or circulating the pressurized fluid in the supercritical state.

[0062] Other retanning agents and / or coloring agents also can be carried or transported by the pressurized fluid. In other words, retanning agent and / or coloring agent do not necessarily have to be dissolved in the pressurized fluid, as long as final dyeing and / or retanning can be obtained. For example, due to the flow velocity of the pressurized fluid under supercritical state, retanning agent and / or coloring agent can be carried and / or transported by the pressurized fluid.

[0063] In one embodiment of the present invention, the dyeing step includes using a fixing agent.

[0064] In one embodiment of the invention, the method comprises fatliquoring.

[0065] The fatliquoring process can be carried out simultaneously with dyeing, but can also be a separate process. Vegetable, animal or synthetic oils, fats and waxes can be used.

[0066] Examples of fatting agents that can be used include anionic fatting agents such as sulfonated fatting agents and sulfited oils, soap fatting agents, and cationic fatting agents. Nonionic fatting agents can also be used, including alkyl ethylene oxide condensates and protein emulsifiers. Expensive fatting agents as preparations of nonionic, anionic and cationic fatting agents can also be used in the fatting process.

[0067] In one embodiment of the invention, the method comprises a retanning agent.

[0068] Tanning as a primary tan may not be sufficient to maintain the desired properties and the leather may therefore be retanned.

[0069] Retanning agents can be inorganic minerals (chromium, aluminium, zirconium, titanium, iron salts or combinations thereof) or organic substances (aldehydes, vegetable and synthetic tanning agents, resins, oils).

[0070] Retanning can be carried out simultaneously with dyeing and / or fatliquoring, but can also be a separate process.

[0071] In an embodiment of the invention, the pressure of the pressurized fluid in the supercritical state is at least 70 bar, such as between 70 and 260 bar, such as 90 to 150 bar, such as 130 to 250 bar, or such as 180 to 240 bar.

[0072] In one embodiment of the present invention, the temperature of the pressurized fluid in the supercritical state is between 30 and 120 degrees Celsius, such as between 30 and 100 degrees Celsius, such as between 30 and 60 degrees Celsius, such as between 30 and 50 degrees Celsius, such as between 30 and 40 degrees Celsius.

[0073] In one embodiment of the present invention, the predetermined time, i.e., the leather product is exposed to the dyeing agent and / or retanning agent in the pressurized fluid in the supercritical state, is at least 1 minute, such as at least 15 minutes, such as between 15 minutes and 4 hours, such as between 25 minutes and 2 hours, such as more than 35 minutes.

[0074] In one embodiment of the present invention, the predetermined time for which the leather product is subjected to the action of the dye and / or retanning agent in the pressurized fluid under the supercritical state is at least 1 minute, such as at least 15 minutes, such as 1 minute to 40 minutes, such as 1 minute to 4 hours, such as 5 minutes to 2 hours, such as more than 15 minutes and such as less than 1 hour.

[0075] The predetermined time for which the leather product is subjected to the action of the dye and / or retanning agent in the pressurized fluid in the supercritical state may also be between 40 minutes and 4 hours, such as between 45 minutes and 2 hours, such as between 55 minutes and 2 hours, such as between 1 hour and 2 hours, such as more than 40 minutes.

[0076] In one embodiment of the invention, the method further comprises the step of providing a leather material, wherein the leather material is subjected to at least a tanning process, whereby at least one leather product is cut from the leather material before being provided and introduced into the treatment chamber.

[0077] The leather material that has been treated with at least a tanning process can be, for example, a hide or skin from a whole animal, wherein the hide or skin has been subjected to the effects of the usual initial hide or skin treatment including a tanning process and is ready for a dyeing process. According to this embodiment, the hide or skin is now cut by cutting one or more leather parts from the hide or skin. These leather products may have different uses, such as different parts of a shoe, and may, for example, also be expected to be dyed differently. Through this embodiment, one or more leather products can now be introduced into a treatment chamber so as to be dyed according to the present invention. Therefore, it is avoided that, for example, a whole hide or skin is dyed according to the long-known technology used in the art, because according to the prior art, this may result in a part of the whole dyed hide or skin being discarded. Therefore, through the embodiment, the waste of leather material can be reduced, and a higher degree of cost-effectiveness caused by, for example, the consumption of dyeing agents can be reduced, as well as reducing the impact on the environment. Furthermore, individual leather products may be specifically processed taking into account their specific properties, e.g., portions from the upper hide may be dyed with precise amounts of dyes to achieve the desired coloring taking into account, for example, the leather properties and intended use, while leather products from other parts of the hide (e.g., the belly) may be treated and dyed accordingly with precise amounts of dyes to match their specific origin and intended use.

[0078] In one embodiment of the present invention, the pressure of the pressurized fluid in the supercritical state and / or the temperature of the pressurized fluid in the supercritical state are controlled to provide a density of the pressurized fluid in the supercritical state within a predetermined range.

[0079] In one embodiment of the present invention, the pressure reduction is controlled over time so that the reduction period exceeds 5 minutes, such as a time interval of 5 minutes to 2 hours, such as 15 minutes to 45 minutes, such as 15 minutes to 30 minutes, such as 30 minutes to 2 hours, such as 30 minutes to 65 minutes.

[0080] In one embodiment of the invention, the pressure reduction is controlled over time such that the pressure reduction does not exceed a predetermined leather pressure reduction gradient, such as 10 bar / min, such as 8 bar / min, such as 6 bar / min or such as 4 bar / min.

[0081] In one embodiment of the present invention, the pressure of the pressurized fluid is controlled to reach a supercritical state so that the time period exceeds a predetermined 5 minute increase period, such as an interval between 5 minutes and 1 hour, such as between 15 minutes and 45 minutes, such as between 15 minutes and 30 minutes.

[0082] In one embodiment of the present invention, pressurizing the pressurized fluid in the treatment chamber to reach a supercritical state includes a pressure increase not exceeding a predetermined leather pressure increase gradient, such as 20 bar / min, such as 15 bar / min, such as 10 bar / min, such as 8 bar / min, such as 6 bar / min, such as 5 bar / min or such as 4 bar / min.

[0083] The present invention also relates to a device for dyeing leather products according to the method according to any one of claims 1 to 27, the device comprising:

[0084] - Processing chamber,

[0085] - the source of the pressurized fluid,

[0086] - the origin of the dyeing and / or retanning agents,

[0087] - a pump, such as a controllable compressor, for increasing the pressure of said pressurized fluid to achieve a supercritical state,

[0088] a pressure reducer, such as a pressure reducing component for reducing the pressure in the process chamber, and

[0089] - Controller,

[0090] Wherein, the controller is configured to control the pressure reducer to reduce the pressure of the treatment chamber over time after the leather product has been subjected to the dye dissolved in the pressurized fluid in the supercritical state for at least a predetermined time.

[0091] Thus, using the device according to the invention it is possible to achieve dyeing of leather products which, compared to conventional dyeing methods, is peculiar in that the use of relatively large amounts of water is avoided. This is achieved by the use of a dye which is soluble in the pressurized fluid at least in the supercritical state, whereby the dissolved dye, in combination with the pressurized fluid in the supercritical state, can penetrate into the leather structure including at least part of the internal structure and dye not only the surface of the leather structure but also the underlying structure, such as collagen fibers in the leather structure.

[0092] According to the invention, the controller is configured to reduce the pressure in the treatment chamber, for example at the end of a dyeing process in a supercritical state, so that the pressure is reduced over time in such a way that the leather product retains the desired properties that are essential for its long-term use, such as maintaining the color and surface properties, so that any tendency of the leather to delaminate is minimized or even completely avoided, and so that the requirements for the prevention of leather delamination are met. This may involve setting a minimum time period for decompression, setting a maximum number of pressure reduction gradients, setting a maximum number of average pressure reduction gradients, etc., which will ensure that the leather structure, in particular the leather structure that has been dyed with a dye and penetrated by a pressurized fluid in a supercritical state, is not adversely affected during the pressure reduction.

[0093] The controller is configured to reduce the pressure in the treatment chamber by controlling the pressure to decrease over time to meet leather delamination prevention requirements, for example meaning that a leather structure, particularly a leather structure that has been dyed with a dye and infiltrated by a pressurized fluid in a supercritical state, will not be affected by leather delamination during or after dyeing.

[0094] In one embodiment of the invention, the controller is further configured to control the pressure in said processing chamber of said pressurized fluid to achieve a supercritical state by increasing the pressure over time within predetermined limits.

[0095] It should be noted that a controller refers to a control device of one or more interactive circuits that may be pre-configured or configured to, for example, perform a desired method in the disclosed apparatus, such as the method claimed and described herein. The controller may thus include RAM or ROM memory.

[0096] Thus, the method of dyeing and / or retanning leather may be automated to varying degrees, including in a substantially fully automated manner, for example including one or more steps that are partially or fully automated, i.e.

[0097] - providing a leather product, said leather product being subjected to at least a tanning process,

[0098] - introducing said leather product into a treatment chamber,

[0099] - subjecting said leather article in said treatment chamber to the action of a pressurized fluid,

[0100] - controlling the pressure of the pressurized fluid to achieve a supercritical state,

[0101] - subjecting the leather product to a dye, which is dissolved in or carried / transported by the pressurized fluid at least for a predetermined time while the pressurized fluid is in the supercritical state,

[0102] and / or subjecting the leather product to a retanning agent while the leather product is in a pressurized fluid in a supercritical state

[0103] - reducing the pressure in the process chamber,

[0104] - removing the leather article from the treatment chamber,

[0105] The step of reducing the pressure in the process chamber includes controlling the pressure to decrease over time.

[0106] According to a further embodiment, the method may be applied in an at least partially automated manner by automation in combination with the steps and / or features as illustrated in the dependent claims.

[0107] Thus, the pressure is increased over time in such a way that the leather article retains the desired properties essential for its long-term use, for example, the color and surface properties are maintained, any tendency of the leather to delaminate is minimized or even avoided entirely, and the requirements for the prevention of leather delamination are met. This may involve setting a minimum time period for increasing the pressure, setting a maximum value for the gradient of the pressure increase, setting a maximum value for the average gradient of the pressure increase, etc., which will ensure that the leather structure, in particular the leather structure that has been dyed by the dye and penetrated by the pressurized fluid in the supercritical state, is not adversely affected during the pressure increase.

[0108] The increase in pressure in the treatment chamber comprises controlling the pressure increase over time to meet leather delamination prevention requirements, for example meaning that the leather structure is not affected by leather delamination during or after dyeing. BRIEF DESCRIPTION OF THE DRAWINGS

[0109] The present invention will be described below with reference to the accompanying drawings, in which

[0110] Figure 1-4 An example of processing leather products by dyeing and / or retanning according to an embodiment of the present invention is shown.

[0111] Figure 5a and 5b An example of an apparatus for dyeing and / or retanning according to an embodiment of the present invention is shown,

[0112] Figure 6a and 6b An example of an apparatus for dyeing and / or retanning according to an embodiment of the present invention is shown,

[0113] Figure 7 shows the phase diagram for carbon dioxide, and

[0114] Figure 8a and 8b A graph of pressure over time is shown. DETAILED DESCRIPTION

[0115] Figure 1 The composition of the entire process flow is shown.

[0116] First, a leather product is provided 2, either as a piece of leather that has not been previously cut or trimmed, or as at least one piece of pre-cut leather. The leather product is placed in a treatment chamber 4 and subjected to the action of a pressurized fluid 6. A dye is introduced 8 and brought to a supercritical state 10, for example by pumping, further compressing the fluid, etc. Finally, after the dyeing process has been carried out, the pressure is reduced 12 and the leather product is removed 14.

[0117] Figure 2 The components of the overall process are also shown. First, a leather product 2 is provided, either as a piece of leather that has not been previously cut or trimmed, or the leather product is at least one piece of pre-cut leather. The leather product is placed in a treatment chamber 4 and subjected to the action of a pressurized fluid 6. A dye is introduced 8, and a supercritical state is reached 10. Finally, the pressure is reduced 12, for example by a process such as distillation, precipitation, etc. associated with the pressure reduction, the dye residues are removed 16, and the leather product is removed 14.

[0118] Figure 3 The components of the overall process flow are further shown. First, a leather product 2 is provided, either as a piece of leather that has not been previously cut or trimmed, or as at least one piece of pre-cut leather. The leather product is placed in a treatment chamber 4 and subjected to the action of a pressurized fluid 6. A dye is introduced 8, and a supercritical state is reached 10. Finally, the pressure is reduced 12, the fluid is recirculated 18, for example into a container, from which it can be provided for subsequent use, as shown in the flow diagram, and the leather product is removed 14.

[0119] Figure 4 The components of the entire process are shown. First, leather material 22 is provided and cut into products 24. At least one leather product is placed in a treatment chamber 4 and subjected to the action of a pressurized fluid 6. A dye is introduced 8 and a supercritical state is reached 10. Finally, the pressure is reduced 12 and the leather product is removed 14.

[0120] Reference now Figures 1 to 4 , shows a process flow according to an embodiment of the present invention, wherein the treatment chamber in which one or more leather articles are placed is exemplified here as a box. However, it should be noted that the treatment chamber can have any form related to regulating optimal conditions to maintain supercritical conditions for a period of time. In one embodiment of the present invention, depending on a given application, the treatment chamber and equipment may appear on a small scale in some relationships and on a large scale in other relationships.

[0121] The pressurized fluid may be in liquid form, but may also be in gaseous form.

[0122] It is worth noting that retanning agents can be introduced to replace Figure 1-4 The stains in the examples shown.

[0123] Figure 5a and 5b An example of an apparatus in one embodiment of the present invention is shown, for example using a method according to one embodiment of the present invention.

[0124] Figure 5a The processing of the leather material 30 is shown. The leather material 30 may be a whole piece of leather without any pre-cutting, or may be a piece of leather, such as a leather product that has undergone a cutting or trimming step.

[0125] Figure 5b The processing of a leather material 30 is shown, wherein the leather piece has been through at least one process of cutting the leather into at least one small piece (eg, leather product 32) before entering a processing chamber.

[0126] exist Figure 5a and 5b In the process, the leather product, either as a piece of leather without pre-cutting 30 or as a piece of pre-cut leather 32, is subjected to the action of a treatment chamber 34. The treatment chamber can be configured in the form of a pressure chamber.

[0127] The pressure chamber can be connected to at least one controllable compressor 36 for pressurizing the fluid, which is provided by a high-pressure storage container 38. The pressure provided by the controllable compressor 36 is introduced into the pressure chamber 34 by an introduction component 42, such as a controllable valve or similar component. At the output end, the pressure can be reduced by a decompression component 44 (for example, in the form of a controllable valve, etc.). According to one embodiment of the present invention, the device can also include a separator 46, which receives the pressurized fluid that escapes, and wherein, for example, residual coloring agents can be separated from the pressurized fluid. The pressurized fluid can leave the separator 46 via an outlet 48, and the separated residual coloring agents can be collected via a residue outlet 50. The outlet 48 can lead to further processing for storage in places such as storage containers. A processing aid 56 is introduced into the treatment chamber from the source of the processing aid 52 through a controllable inlet 54, and in a preferred embodiment of the present invention, the processing aid is a dye.

[0128] The dye can be introduced into the treatment chamber simultaneously with the leather product, but can also be introduced already in the treatment chamber or after the leather product has been introduced into the treatment chamber.

[0129] Introduce pressure in the mode of reaching supercritical condition, and realize optimal dyeing condition in the mode that dyestuff dissolves and is best combined on leather.Release pressure in such a way, promptly keep the desired characteristic that is vital to leather long-term use, for example, keep color and surface characteristics, make any tendency of leather stratification minimize or even avoid completely, and make the prevention requirement of leather stratification be satisfied.Introduce and release of pressure and the introduction of dyestuff are controlled by controller 40, wherein controller 40 as shown in the figure can be connected with controllable compressor 36, introduction part 42, controllable inlet 54 and decompression part 44, to control these according to parameters such as characteristics of time, pressure, temperature, leather products.

[0130] The pressurized fluid may be in liquid form, but may also be in gaseous form.

[0131] Figure 6a and 6b An example of an apparatus in one embodiment of the present invention is further shown. Figure 6a and Figure 6b shown in and with Figure 5a and Figure 5b The features corresponding to the features shown in FIG. 3 are indicated by the same reference numerals. The leather product 30 is placed in a treatment chamber 34, wherein the treatment chamber can be configured in the form of a pressure chamber. The leather product can be a whole piece of leather that is not pre-cut or trimmed before processing, but can also be at least one pre-cut leather. Figure 6b The device shown is basically the same as Figure 6a The example shown corresponds to the example shown, but the modifications explained below can be implemented in any other embodiment described herein. After the dyeing process, the supercritical fluid with the dye can be circulated via the recirculation connection 80, and the pressurized fluid can leave the processing chamber via the separator 46. However, if Figure 6b As shown, the separator is omitted, and the separation of the residual dye can be performed in the treatment chamber 34, for example by reducing the pressure of the fluid, so that any residual or residual dye is separated from the fluid and finally falls to the bottom of the treatment chamber. After the residual dye is separated, the fluid such as carbon dioxide can be pumped from the treatment chamber 34, via the pressure reduction component 44, via the recirculation connection 70 and the recirculation compressor 82, whereby the fluid will be directed back to the storage container 38. With respect to the residual dye in the treatment chamber 34, it can be collected and / or a rinse cycle with, for example, carbon dioxide can be performed to clean the treatment chamber and its connections.

[0132] The pressurized fluid may be circulated from the pressurization chamber and reused back to the pressurization chamber, as shown by recirculation connection 80. The pressurized fluid may also be circulated and reused after leaving the separator 46 and returning to the high pressure storage vessel 38 via a recirculation compressor 82, or as a single process step.

[0133] Figure 7A proportional phase diagram for carbon dioxide is shown (schematically and not to scale). Carbon dioxide behaves as a gas G in air at standard temperature and pressure, or as a solid S when frozen. When both temperature and pressure are increased above the critical point CP of carbon dioxide, it has properties intermediate between gas and liquid L. Here, it behaves as a supercritical fluid SCF above the critical temperature (31.1°C) and critical pressure (73.9 bar).

[0134] Figure 8a The exemplary timeline of pressure P variation over time T is illustrated, for example, the condition of treatment chamber 34 in leather dyeing cycle is illustrated. Pressure can start from the pressure t1 of environment, and leather can be introduced into treatment chamber at this moment. After given time, pressure increases t2, and increases until critical point t3 of pressure CP, for example, by introducing and further pressurizing the pressurized fluid such as CO2. The gradient of pressure increase over time can be a sharp increase, wherein pressure increases in a shorter time period, or increase can also be slow, wherein pressure increases slowly in a given time. Between t3 and t5, supercritical state is maintained in a given time. In this example, the illustrated curve shows the flat top of constant pressure over time, however, the top can also have pressure increase over time, directly extend to reduction, and do not have a constant pressure over time. After given time period t4, pressure drops and drops over time until reaching environmental conditions. The gradient of pressure drop over time can be a sharp drop, wherein pressure drops in a shorter time period, or can also be a slow drop, wherein pressure drops slowly in a given time.

[0135] The dye may be added to the process chamber at the beginning of the process, for example at t1 or t2, but may also be added later, perhaps during supercritical conditions. When the pressure is reduced or conditions reach ambient conditions, any excess dye may be released and removed from the process chamber (or separated from the pressurized fluid leaving the process chamber).

[0136] Figure 8b A corresponding exemplary timeline of pressure P versus time T is shown, wherein Figure 8a The same pressure curve and the same time point in Figure 8b As an example, at time t7, i.e. after the liquid reaches the supercritical state, the dye is added to the treatment chamber. Therefore, as shown below the time axis (T axis), the leather product in the treatment chamber will be subjected to the action of the dye dissolved or diluted in the supercritical liquid during the period Td corresponding to t5-t7.

[0137] In addition, Figure 8bAs shown in the figure, the pressure reaches a maximum value at t8, after which the pressure remains substantially constant until t4. Therefore, as shown below the time axis (T axis), the leather product in the fluid will be subjected to the effect of pressure increase in the period Tinc corresponding to t8-t2. In addition, it can be seen that the pressure gradient can be determined and monitored, represented here as a numerical value |Pgrad-i|. The device can be configured to control the pressure increase by monitoring the period Tinc, which must exceed a predetermined increase period, such as 15 minutes, such as 25 minutes, such as 5 minutes to 1 hour, such as 15 minutes to 45 minutes, such as 15 minutes to 30 minutes, or the device can be configured to control the pressure increase by monitoring the pressure gradient, such as the numerical value |Pgrad-i|, which must not exceed a predetermined leather pressure increase gradient, such as 20 bar / min, such as 15 bar / min, such as 10 bar / min, such as 8 bar / min, such as 6 bar / min, such as 5 bar / min or such as 4 bar / min.

[0138] Furthermore, in Figure 8b The time axis (T axis) is shown below, and the leather product in the fluid will be subjected to the effect of pressure reduction in the time period Tred corresponding to t6-t4. In addition, it is shown that the pressure gradient can be determined and monitored, which is represented as a digital value |Pgrad-r|. The device can be configured to control the pressure reduction by monitoring the time period Tred, which must exceed a predetermined reduction period, such as 15 minutes, such as 25 minutes, such as 30 minutes, such as between 5 minutes and 2 hours, such as 15 minutes to 45 minutes, such as 15 minutes to 30 minutes, such as 30 minutes to 2 hours, such as 30 minutes to 65 minutes, or the device can be configured to control the pressure reduction by monitoring the pressure gradient, such as the value |Pgrad-r|, which must not exceed a predetermined leather pressure reduction gradient, such as 10 bar / min, such as 8 bar / min, such as 6 bar / min or such as 4 bar / min.

[0139] The diagram is schematic, the time intervals for pressurization and depressurization may differ from each other, even considerably, and the pressurization may be much faster than the depressurization, thus meaning that the curve for pressurization may be relatively steeper.

[0140] In this context, pressurized fluid and fluid refer to compounds that adopt properties intermediate between gas and liquid and behave as supercritical fluids.

[0141] Any substance has the characteristic of a critical point that it obtains under specific conditions of pressure and temperature. When the pressure and temperature to which a compound is subjected is higher than its critical point, the fluid is called "supercritical".

[0142] Carbon dioxide is the most widely used supercritical fluid because it is a naturally occurring gas and is readily available for industrial consumption.

[0143] Carbon dioxide usually behaves as a gas in the air at standard temperature and pressure, or as a solid (dry ice) when frozen. When both temperature and pressure are increased above the critical point CP of carbon dioxide, it has properties between gas and liquid. Here, it behaves as a supercritical fluid above the critical temperature (31.1°C) and critical pressure (73.9bar). In this way, supercritical carbon dioxide has a liquid-like density, which is beneficial for dissolving dyes, while having gas-like low viscosity and diffusion properties, which can lead to shorter dyeing times compared to water and dye penetration into the material.

[0144] The critical point of the pressurized fluid may vary depending on various conditions, such as the density and / or purity of the fluid. Therefore, the method for dyeing leather products may be performed not only in a supercritical state, but also in a near supercritical state. Supercritical state and near supercritical state may be used interchangeably herein. Therefore, it should be understood that when "supercritical pressurized fluid" or similar terms are mentioned in the claims and specification of the present application, such terms will include pressurized fluids that are in a near supercritical state.

[0145] The terms "supercritical carbon dioxide" or "SC-CO2" are used interchangeably herein. In addition, carbon dioxide and CO2 are used interchangeably herein.

[0146] The term "dye" or the term "dyeing" in this context refers to dyeing substances other than chromium-based compounds commonly used as tanning agents in the art, although it should be noted that in conventional tanning processes, for example, chromium-based substances usually result in a blue tint to the tanned leather. Thus, in this context, dye or dyeing refers to substances added for the purpose of obtaining the desired color. In other words, such dyeing within the scope of the present invention is preferably carried out under supercritical carbon dioxide conditions.

[0147] The dyeing process of the present invention may be carried out in a treatment chamber, but in general, it should be noted that the dyeing process may be applied using any suitable dyeing equipment that is designed for dyeing according to the provisions of the present invention.

[0148] The term leather or leather material means animal hide prepared for use by tanning or a similar process designed to protect it from decay and to render it pliable or soft when dried.

[0149] The type of leather used within the scope of the present invention may be any type of bovine derivative, such as cow or calf. Examples of the type of leather used within the scope of the present invention may be types such as full grain leather or top grain leather, embossed grain leather, suede leather and nubuck leather.

[0150] In principle, the leather may be from any source, including horsehide, goathide, sheephide, kangaroohide, etc. Even so, preferably the leather is mammalian or marsupial leather (i.e. rawhide derived from a mammal such as a cow or horse, or a marsupial such as a kangaroo). Cowhide hides are most commonly used.

[0151] The term "leather product" refers to any piece of leather available as a whole piece or in pre-cut leather pieces. Leather in this context is broadly understood as a product containing leather parts. In other words, leather products must include animal skin parts that have been prepared for use by tanning or similar processes aimed at protecting them from decay.

[0152] Leather products may also include, for example, yarns or filaments.

[0153] The leather product may be pre-cut parts, such as a shoe, wherein the parts may be, for example, an upper, a vamp, a toe cap, a quarter or a heel cap.

[0154] Leather products can of course also refer to other types of leather, including clothing, clothing parts, leather accessories such as bags, leather parts of bags, wristbands, mobile phone cases, etc. Leather products can also include automotive-related leather parts, such as leather products for seats, leather products for steering wheel covers, shift lever handle covers, etc.

[0155] Leather products may also refer to products comprising leather parts, such as filaments or yarns reconstructed from leather, for example as disclosed in PCT / EP2018 / 053849, PCT / EP2018 / 053848, which are hereby incorporated by reference. Such yarns or filaments are therefore to be understood as leather products within the scope of the present invention, as long as the small leather parts (also referred to as fibers in the above applications) originate from tanned leather, even if in this case the leather product also includes additives that promote the aggregation of such small leather parts.

[0156] It should be noted that "leather products" processed within the scope of the present invention may mean that one, two or more leather products may be processed at the same time.

[0157] Preferably, the leather type is carefully selected based on the characteristics of the leather and the chemicals used to pre-treat the leather, for example, during the tanning process.

[0158] In principle, the method can be carried out with any type of leather. Typically, however, the leather is already tanned.

[0159] Tanning is used as a conventional method for treating leather and can be applied to the present invention. Depending on the compounds, the color and texture of the fabric may change. The technical definition of tanning is well known in the art, but in short, according to Anthony D. Covington, Tanning Chemistry, Chapter 10, the only strict definition of tanning is the conversion of decomposable organic materials into a stable material that can resist biochemical attack. Tanning involves several steps and reactions, depending on the starting materials and the final product.

[0160] In the case of collagen, the side chains largely determine its reactivity and ability to be altered by the stabilizing reactions of tanning when making leather. In addition, the chemical composition of the backbone defined by the peptide chains provides different reactive sites that can be exploited in some tanning processes. During the tanning process, the modification of collagen by the chemical reactions of the tanning agents affects different characteristics of the material properties; the hydrophilic-hydrophobic balance of the leather may be significantly affected by the chemical reactions of the tanning agents by changing the relationship between the leather and the solvent, which in turn affects the balance of any reagent between the solvent and the substrate. In addition, the reactive sites between the reagent and the collagen may affect the isoelectric point of the collagen, and therefore, there may be different relationships between pH and the charge on the leather. The lower the isoelectric point, the charge on the material may be more anionic or less cationic at any pH: the higher the isoelectric point, the charge on the leather will be more cationic or less anionic at any pH. In addition, the relative reactivity at the side chains and the backbone of the protein may determine the type of reaction and thus the degree of stabilization of the tanning: the fastness of the reagent may be affected by the interaction between the reagent and the substrate.

[0161] Any type of tanned leather may be used, including metal tanned (e.g. using chrome, aluminum, zirconium, titanium, iron or combinations thereof), vegetable tanned (e.g. using tannins from tree bark or other sources), aldehyde tanned (e.g. using aldehydes) or natural tanned, such as oil tanned.

[0162] Typically, leather is either chrome tanned or vegetable tanned, with chrome tanned leather being the most commonly used.

[0163] Tanning as a primary tanning may not be sufficient to maintain the desired characteristics and therefore retanning may be used. The tannin used in this process may be different from that used in the primary tanning stage.

[0164] Fatliquor refers to the process of fixing fats / oils and waxes to the leather fibers. The main function of fatliquor is to prevent the fiber structure from re-adhering during drying by providing an oil surface to the fiber structure. Any fatliquor can be used, including anionic fatliquors such as sulfonated fatliquors and sulfited oils, soap fatliquors, and cationic fatliquors. Non-ionic fatliquors can also be used, including alkyl ethylene oxide condensates and protein emulsifiers. High-priced fatliquors, which are preparations of non-ionic, anionic and cationic fatliquors, can also be used in the fatliquor process.

[0165] The raw materials of fatliquor can be marine animal oils, such as fish oil; terrestrial animal oils and fats, such as claw oil, beef tallow, lard and bone fat; vegetable oils and fats, such as palm oil, sunflower oil, rapeseed oil, soybean oil, coconut fat, palm kernel fat and turkey red oil; waxes, such as bar palm wax, montan wax and lanolin. Grease; synthetic fats, such as paraffin oil, mineral oil, fatty alcohol and fatty acid esters.

[0166] As used herein, "at least one" means one or more, ie, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, etc.

[0167] The word "comprising" can be used as an open term, but it also includes the closed term "consisting of."

[0168] It should be noted that the application of the present invention in dyestuff has special advantages, but the apparatus and method described herein can also be applied to the leather processing of general use retanning agent. The part of retanning or retanning process can be carried out by for example using a supplementary retanning agent such as inorganic or organic substances. The inorganic retanning agent that can replace the above-mentioned determined dyestuff application therefore comprises chromium, aluminium, zirconium salts. Organic retanning agent comprises vegetable tanning agent, synthetic tanning agent, resin and aldehyde.

[0169] Reference numerals

[0170] 2. Provide leather products

[0171] 4. Leather products enter the processing room

[0172] 6. Subjected to pressurized fluid

[0173] 8. Introducing dye

[0174] 10. Pressurized fluid in supercritical state

[0175] 12. Reduce stress

[0176] 14. Remove leather products

[0177] 16. Remove stain residue

[0178] 18. Recirculating fluid

[0179] 22. Provide leather materials

[0180] 24. Cutting materials into products

[0181] 30. Leather products

[0182] 32. Pre-cut leather products

[0183] 34. Processing room

[0184] 36. Controllable compressor

[0185] 38. High pressure storage container

[0186] 40. Controller

[0187] 42. Introducing components

[0188] 44. Pressure relief components

[0189] 46. ​​Separator

[0190] 48. Export

[0191] 50. Residue export

[0192] 52. Sources of processing aids

[0193] 54. Controlled Entrance

[0194] 56. Processing aids

[0195] 70. Recirculation connection

[0196] 80. Recirculation connection

[0197] 82. Recirculation compressor

[0198] A. Environment

[0199] CP. Critical Point

[0200] G. Gas

[0201] L. Liquid

[0202] P. Pressure

[0203] S. Solid

[0204] SCF. Supercritical Fluid

[0205] T. Time

[0206] Tinc. Time of increased pressure

[0207] Tred. Time when pressure is reduced

[0208] IPgrad-iI. Pressure increase gradient

[0209] IPgrad-rI. Pressure reduction gradient

[0210] Td. Time of exposure to dye

Claims

1. A method for dyeing and / or retanning leather products, the method comprising the following steps: - providing (2) a leather product, wherein the leather product has been subjected to at least a tanning process, - introducing the leather product into (4) a treatment chamber, - subjecting the leather article in the treatment chamber to (6) a pressurized fluid, - controlling (10) the pressure of the pressurized fluid to achieve a supercritical state, - subjecting the leather product to the action of a dye and / or a retanning agent, said dye or retanning agent being dissolved and / or transported in said pressurized fluid at least for a predetermined period of time when said pressurized fluid is in a supercritical state, - reducing (12) the pressure in the process chamber, - removing (14) the leather article from the treatment chamber, Wherein, the step of reducing the pressure in the processing chamber comprises controlling the pressure to decrease over time, Therein, the pressure reduction is controlled over time so that the pressure reduction does not exceed a predetermined leather pressure reduction gradient of 10 bar / min.

2. The method according to claim 1, wherein: The step of reducing (12) the pressure in the process chamber includes removing the pressurized fluid from the process chamber.

3. The method according to claims 1 and 2, further comprising: The step of removing (16) residual dyeing and / or retanning agent from the pressurized fluid during or after the pressurized fluid is removed from the treatment chamber.

4. The method according to any one of claims 1 to 2, wherein: The pressurized fluid removed from the process chamber is directed to a storage vessel at a storage pressure.

5. The method according to claim 4, wherein: The step of subjecting the leather article in the treatment chamber to the pressurized fluid includes utilizing the pressurized fluid from the storage container.

6. The method according to any one of claims 1 to 2, wherein: The step of controlling the pressure in the processing chamber of the pressurized fluid to reach a supercritical state comprises increasing the pressure by maintaining it within predetermined limits over time.

7. The method according to any one of claims 1 to 2, wherein: The step of subjecting the leather product to a dyeing agent comprises one of the following: - introducing said dye directly into said treatment chamber, - introducing the dye into the pressurized fluid before the pressurized fluid is introduced into the treatment chamber, - introducing the dye into the treatment chamber together with the leather product, and - introducing said coloring agent into said pressurized fluid when said pressurized fluid is controlled to reach or has reached said supercritical state.

8. The method according to any one of claims 1 to 2, wherein: The step of subjecting the leather product to a retanning agent comprises one of the following: - introducing the retanning agent directly into the treatment chamber, - introducing the retanning agent into the pressurized fluid before the pressurized fluid is introduced into the treatment chamber, - introducing the retanning agent into the treatment chamber together with the leather product, and - introducing said retanning agent into said pressurized fluid when said pressurized fluid is controlled to reach or has reached said supercritical state.

9. The method according to any one of claims 1 to 2, wherein: The dye is any dye associated with dyeing leather and textiles, and at least one type of dye selected from acid dyes, basic dyes, direct dyes, reactive dyes, chrome dyes, milling dyes, metal complex dyes, mordant dyes and sulfur dyes, disperse dyes, reactive disperse dyes and natural dyes.

10. The method according to any one of claims 1 to 2, wherein: The stain is a collagen activity stain.

11. The method according to any one of claims 1 to 2, wherein: The amount of the dyeing agent and / or retanning agent is dosed according to the weight, thickness and / or surface area of ​​the leather product.

12. The method according to any one of claims 1 to 2, wherein: The amount of the dyeing agent and / or retanning agent is dosed according to the type of leather product.

13. The method according to any one of claims 1 to 2, wherein: The leather article is primed with a primer before being subjected to the pressurized fluid.

14. The method according to any one of claims 1 to 2, wherein: The pressurized fluid includes CO2 having a purity of at least 99.0%.

15. The method according to any one of claims 1-2, further comprising: The step of adding dye in an automated way based on the characteristics of the leather product.

16. The method according to any one of claims 1 to 2, wherein: The step of subjecting the leather product to the action of a dye and / or a retanning agent, wherein when the pressurized fluid is in the supercritical state, the dye or retanning agent is dissolved and / or transported in the pressurized fluid for at least a predetermined time period, and also includes mixing, stirring or circulating the pressurized fluid in the supercritical state.

17. The method according to any one of claims 1 to 2, wherein: The dyeing step includes the use of a fixing agent.

18. The method according to any one of claims 1 to 2, wherein: The method comprises fatliquoring.

19. The method according to any one of claims 1 to 2, wherein: The pressure of the pressurized fluid in the supercritical state is at least 70 bar.

20. The method according to any one of claims 1 to 2, wherein: The temperature of the pressurized fluid in the supercritical state is between 30 and 120 degrees Celsius.

21. The method according to any one of claims 1 to 2, wherein: The leather product is subjected to the dyeing and / or retanning agent in the pressurized fluid in the supercritical state for a predetermined time, the predetermined time being at least 1 minute.

22. The method according to any one of claims 1-2, further comprising: A step of providing (22) a leather material, wherein the leather material has been subjected to at least a tanning process, whereby at least one leather product is cut (24) from the leather material before being provided (2) and introduced (4) into the treatment chamber.

23. The method according to any one of claims 1 to 2, wherein: The pressure of the pressurized fluid in the supercritical state and / or the temperature of the pressurized fluid in the supercritical state are controlled to provide a density of the pressurized fluid in the supercritical state within a predetermined range.

24. The method according to any one of claims 1 to 2, wherein: The pressure reduction is controlled over time such that the reduction period exceeds 5 minutes.

25. The method according to any one of claims 1 to 2, wherein: The predetermined leather pressure reduction gradient is 8 bar / min.

26. The method according to any one of claims 1-2, wherein: The pressure of the pressurized fluid is controlled to reach a supercritical state such that the time period exceeds a predetermined 5 minute ramp-up period.

27. The method according to any one of claims 1 to 2, wherein: Pressurizing the pressurized fluid in the treatment chamber to reach a supercritical state includes increasing the pressure by no more than a predetermined leather pressure increase gradient of 20 bar / min.

28. An apparatus for dyeing and / or retanning leather products according to the method of any one of claims 1 to 27, the apparatus comprising: - Processing chamber, - the source of the pressurized fluid, - the origin of the dyeing and / or retanning agents, - a pump for increasing the pressure of the pressurized fluid to reach a supercritical state, - a pressure reducer for reducing the pressure in the process chamber; as well as - Controller, Wherein, the controller is configured to control the pressure reducer to reduce the pressure of the treatment chamber over time after the leather product has been subjected to the action of the dye dissolved in the pressurized fluid under the supercritical state for at least a predetermined time, and the controller is also configured to control the pressure reduction over time so that the pressure reduction does not exceed a predetermined leather pressure reduction gradient of 10 bar / min.

29. The apparatus for dyeing leather products according to claim 28, wherein: The controller is further configured to control the pressure in the processing chamber of the pressurized fluid to achieve a supercritical state by increasing the pressure over time within predetermined limits.

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