FR2706494A1 - Process for graded dyeing of leathers - Google Patents

Abstract

Process for dyeing with uniform grading of the surface of leather articles, characterised in that, first of all, a batch of dyes is prepared from two dyes of extreme shades, this batch of dyes including a dark first dye (1), a light second dye (2), a third dye (3) obtained by mixing equal parts of the dark first dye (1) and the light second dye (2), a fourth dye (4) obtained by mixing the dark first dye (1) with the dye (3) obtained by mixing the first dye and second dye, a fifth dye (5) obtained by mixing equal parts of the second dye and of the third dye (3) and so on in order to obtain dyes of steadily decreasing shades, and in that the dyes obtained are deposited in successive segments onto the surface of a leather article (12) starting with the deposition of the darkest dye.

Description

 The present invention relates to the dyeing of leathers and it applies to leathers which have just been tanned but not yet dyed, as well as leathers already used for covering objects and previously dyed.

 Leather dyeing has been known for a long time; for this, pigments are used, usually organiclqui which are dissolved in suitable solvents. Aqueous solvents are used very frequently which have great advantages for organic pigments such as carbon black, and the like.

 The above pigments are then fixed using suitable products, for example based on butyl ketone.

 The present invention aims to allow the dyeing of new or already used leathers so as to obtain an absolutely regular color gradient, which makes it possible to adapt the color of various coatings to give them a particular visual appearance adapted to a style of decoration.

 The invention makes it possible, for example, to dye a piece of furniture such as a sofa so that the base of the piece of furniture is adapted to the color of the floor while the upper part is adapted to the color of a drapery.

 Other decorative effects can also be obtained, in particular for drapes of vehicle cabins whose color can change from that of a carpet to that of a ceiling.

 In accordance with the invention, the process for dyeing the surface of leather parts in a regular gradient is characterized in that a batch of dyes is first prepared from two dyes of extreme tones, this batch of dyes comprising a first dark dye, a second light dye, a third dye obtained by mixing equal parts of the first dark dye and second light dye, a fourth dye obtained by mixing the first dark dye with the dye obtained by mixing the first dye and the second dye, a fifth dye obtained by mixing equal parts of the second dye and the third dye and so on to obtain dyes of regularly decreasing tones, in that the dyes obtained are deposited in successive segments on the surface d 'a piece of leather starting with the deposit of the darkest dye and in that finally we apply a fixative s on the dyes successively deposited.

 Various other characteristics of the invention will also emerge from the detailed description which follows.

 Embodiments of the subject of the invention are shown, by way of nonlimiting examples, in the accompanying drawings.

 Fig. 1 is a diagram illustrating a mode of preparation of dyes used in the process of the invention.

 Fig. 2 is a schematic plan illustrating a sheet of leather being treated to ensure its degraded coloring in accordance with the invention.

 Fig. 3 is a diagram illustrating an installation for the degraded dyeing of a sheet of leather.

 Fig. 4 is a diagram similar to FIG. 3 but suitable for industrial processing.

 In what follows, the process is first described in its implementation on tanned leathers but which have not yet undergone a dyeing operation, that is to say on leathers often referred to in the art. "skin on stain".

 The dyes used are normally chosen to be included in the same range of tones.

 In what follows, for simplicity, it will be considered that the dyes extend over a range of gray from a light gray to a dark gray, without there being a solution of continuity in any place whatsoever. tinted leather surface.

 Different dyes can be used; preferably the process uses organic pigments miscible in water or in an aqueous solution containing a solvent to achieve a gradient in the gray scale from white to black.

 It is thus possible to use, as dye, carbon black and titanium dioxide as well as many other dyes known in the art.

 All the dyes forming a batch to be used are prepared in advance as described below.

 Referring to fig. 1, the darkest dye shown schematically by segment 1 is first prepared, then the lightest dye shown schematically by segment 2.

 Both of the two dyes 1 and 2 consist of solutions which are miscible.

 An intermediate dye which must correspond to the middle segment 3 is prepared by mixing 50% of the dyes from segments 1 and 2.

 50% of the dye of segment 3 is then mixed with 50% of the dye of segment 1 to obtain the shade of the intermediate segment 4. Similarly, 50% of the dye of segment 3 is mixed with 50% of the dye of segment 2 to obtain the dye of the second intermediate segment 5.

 The above is repeated for the other segments, that is to say that 50% of the dye of segment 1 is mixed with 50% of the intermediate segment 4 to obtain the dye solution corresponding to segment 6. Similarly, 50% of the dye solution from segment 4 is mixed with 50% of the dye from segment 3 to obtain the shade of segment 7 and so on.

 The following shows that we thus have coloring solutions a, b ... n whose value decreases in the gray scale.

The dye or dye solutions obtained are respectively stored in containers A,
B ... N as illustrated in fig. 3 containers which are connected by conduits 8av 8b ... 8n to a common collector 9 leading to a distributor 10 advantageously constituted by a downward spray gun.

 The conduits 8aS 8b - 8n are each provided with valves lla, 11b ... 11n which can be actuated selectively to allow the choice of the projected coloring solution.

 After possible degreasing and drying, the leather sheet 12 to be dyed is moved relative to the gun 10 so that a first segment 13 receives the darkest coloring solution a, which is obtained by opening the valve 11a while the valves llb ... 11n are closed.

 The coloring solution of container B is then used to be sprayed onto the second segment 14 immediately following segment 13.

 The solution contained in the container B is, at the start of the spraying, mixed with a residue of the previous solution still contained downstream of the valve 11a which is closed. This ensures an intermediate coloring, the gradient of which is further improved by ensuring that the color solution a contained in the container B is partially sprayed onto a covering strip 15 existing between the segments 13 and 14.

 The degradation is further facilitated by the porosity imparted to the leather used which is in the "skin on stain" state and which is degreased to have a permeability suitable for the penetration of the projected coloring solutions.

 The coloring solutions contained in the other containers are sprayed successively in the same manner as described above, using respectively the solutions a, b ... n obtained as described with reference to FIG. 1.

 In the case of "skin on stain", the application of successive dyes is carried out while said skin is stretched in a frame 16 or the like.

 Fig. 4 illustrates an industrial type application device in which a large number of containers A1, B1 ... Bn are used containing coloring solutions with very small difference in tone, the circuit of the containers being controlled by a device for servo 18 also ensuring the control of a table 17 for driving the skin 12 to be colored.

 Whatever the mode of application of the dyes, they are finally fixed using a fixative appropriate to the nature of the dye.

 When the dyes consist of organic materials in an aqueous support, it is advantageous to use a fixative based on butyl ketone or nitrocellulose.

 The movement of the sheet 12 is thus ensured in synchronism with the projection of the successive dyes which are deposited, preferably ensuring at least a slight overlap of each of them.

 As in the previous case, it is the projection of the darkest dye that takes place first.

 The invention can also be implemented on leathers already used for coating various objects, for example furniture. In this case, first protect the parts of the furniture that should not receive dye, then treat the leather to possibly discolour it, which can be achieved using mixtures of alcohol and aci salts - acetic acid, aromatic hydrocarbons such as toluene, ketones, trichlorethylene, etc. Next, the leather is subjected to degreasing compounds, for example saponifying products such as ethylene glycol monostearate. The coloring solutions prepared as set out in the foregoing are then preferably deposited with a spray gun in parallel strips or segments or in other combinations to obtain either a regular gradient or a degraded graphics whose shape can be adapted to that of the object being processed.

The invention is not limited to the exemplary embodiments, shown and described in detail, since various modifications can be made thereto without departing from its scope. In particular, the containers A1,
B1 .. Bn and spray guns to which each of them is connected, can be arranged in a battery so that each gun corresponds to a particular segment of the skin to be dyed so that the successive segments of degraded coloring a, b. .. n are produced simultaneously all the pistols then operating at the same time.

Claims (11)

 1 - Process for dyeing the surface of leather parts in a regular gradient, characterized in that a batch of dyes is first prepared from two dyes of extreme tones, this batch of dyes comprising a first dye (1 ) dark, a second light dye (2), a third dye (3) obtained by mixing equal parts of the first dark dye (1) and second light dye (2), a fourth dye (4) obtained by mixing the first dye dark (1) with the dye (3) obtained by mixing the first dye and the second dye, a fifth dye (5) obtained by mixing in equal parts the second dye and the third dye (3) and so on for the obtaining dyes of regularly decreasing tones, in that the dyes obtained are deposited in successive segments on the surface of a piece of leather (12) starting with the deposition of the darkest dye and in that finally we apply a fixer on the dyes successively deposited.  2 - Method according to claim 1, characterized in that intermediate dyes are solutions from mixtures of 50% of dark and light coloring solutions.  3 - Method according to one of claims 1 or 2, characterized in that the dyes are deposited by ensuring a covering of the less dark dye on the edge of the darkest dye.  4 - Method according to one of claims 1 to 3, characterized in that the deposition of successive dyes is ensured with a spray gun.  5 - Method according to one of claims 1 to 4, characterized in that the successive coloring solutions are contained in containers (A, B ... N) re linked to a spray gun (10) by conduits (8as 8b ... 8n) and a manifold (9), in that valves (lla, llb ... lln) are placed on said conduits (8as 8b ... 8n) and in that the valves are operated to ensure the successive projection of the different coloring solutions by ensuring that the dye residue remaining in the conduits (8aw 8b ... 8n) following the closing of the valves (lia, llb ... lln) is projected onto the end of a first colored segment to perfect the gradient.  6 - Method according to one of claims 1 to 5, characterized in that organic dyes are used in an aqueous support.  7 - Method according to one of claims 1 to 6, characterized in that one proceeds to a degreasing of the leather before the application of the coloring solutions to improve the porosity.  8 - Method according to one of claims 1 to 7, characterized in that, in the application to the treatment of just tanned leather, the leather sheet is kept stretched on a frame (16) during the projection of the coloring solutions successive.  9 - Method according to one of claims 1 to 7, characterized in that, in the application to stretched leathers on already existing objects, one proceeds to the recovery of the parts not to be dyed, then one proceeds to a stripping before applying the prepared coloring solutions.  10 - Method according to one of claims 1 to 9, characterized in that one provides a set of containers (A1, B1 ... Bn) each of a spray gun and valves controlled by a servo device (16) also ensuring the control of the movement of a table (17) carrying the leather sheet (12).  11 - Method according to one of claims to 9, characterized by a battery of containers (A1, B1) and pistols, arranged so that the projection of each pistol corresponds to a segment specific to one of the coloring solutions to be applied to the surface of the leather.