EP0757724B1 - Method for providing raised patterns on leather and the like - Google Patents

Description

The present invention relates to a method of production of relief patterns on leather or any other material of a similar nature, such as imitation leather, plastic, etc ...

In areas such as furniture interior, leather goods, upholstery, binding, or clothing, we sometimes wish carry out, for essentially aesthetic reasons, embossed patterns on leather or other similar materials such as plastics, cartons, etc.

Currently, the most common process used for the realization of such patterns is a process old press stamping. This process implements a plate with a surface engraved in relief, the recessed parts correspond to the raised parts of the pattern to be made on leather. A sheet of leather is pressed between this plate and the associated counter plate, the side of the leather on which the relief must be produced plated on the engraved surface. In this device, from very old process of pushing leather by hammering, the leather sheet should be thick enough to that a significant relief is obtained. In practice, this thickness varies between 1.5 and 2mm, which corresponds relatively expensive leathers. In addition, the effort to compression applied by the press on the leather sheet must be high enough to plastically distort the sheet of leather and avoid an elastic return thereof. The latter requirement at high compressive force requires on the one hand the acquisition of a powerful press and, on the other hand, the realization of an engraved surface presenting high mechanical characteristics. This surface engraved must therefore be made on a stamping plate made of a hard material such as steel and not copper, this which leads to a difficulty in manufacturing and obtaining an engraving of mediocre finesse. Consequently, the current stamping process has a manufacturing cost high, is ill-suited to small series manufacturing, usual in the areas mentioned above, and do not does not allow obtaining patterns of satisfactory fineness.

We also know from document FR-A-2,236,658, a process for producing relief patterns on leather or the like comprising the steps defined in preamble of claim 1. More specifically, this process consists of heating and compressing in a press a multi-layer assembly comprising a leather sheet, a thermoformable material and possibly a sheet of protection, the leather sheet being placed against a press plate whose surface has parts in hollow inside which the leather is repelled by the thermoformable material when the multilayer assembly is hot compressed. The leather sheet that is placed against the etched surface is softened by heat, then pushed back into the recessed parts of the engraved surface by the thermoformable material which "flows" in a plane parallel to the press plate between the parties in relief and the hollow parts thereof.

The process illustrated in the aforementioned document allows on the one hand to use additional sheets of leather thinner than those used in the process old press stamping and secondly reduce the compression force exerted by the press, which allows reduce raw material and tool costs. However, the pressure exerted by the thermoformable material on the leather sheet is never perfectly regular and is found to be significantly lower in contour zones of the relief patterns produced, which leads to a relative imprecision in the formation of these contours. This imprecision in highlighting the sheet of leather can be extremely penalizing, in particular if you want to print a design on the leather monochrome or polychrome in correspondence with the motif in relief made.

The object of the present invention is to remedy to these drawbacks by proposing a method of making very fine relief patterns on leather or similar, even if the leather sheet concerned is very slim.

a) on réalise un ensemble multicouches comprenant une feuille de cuir ou analogue, une feuille de protection et une couche intermédiaire disposée entre ces feuilles et comportant une colle thermo-formable ;

b) l'ensemble multicouches ainsi réalisé est placé dans une presse dont un plateau présente une surface gravée contre laquelle est appliquée la feuille de cuir dudit ensemble, la gravure de cette surface ayant été préalablement réalisée en fonction du motif désiré de façon que les parties en creux de la surface gravée correspondent aux parties en relief du motif à réaliser sur la feuille de cuir ;

c) l'ensemble multicouches est chauffé et comprimé dans la presse ;

d) l'ensemble à reliefs ainsi obtenu est dégagé de la presse ;

With a view to achieving this goal, a method is provided according to the invention for producing patterns in relief on leather or the like, comprising the following steps:

a) a multilayer assembly is produced comprising a sheet of leather or the like, a protective sheet and an intermediate layer disposed between these sheets and comprising a thermoformable adhesive;

b) the multilayer assembly thus produced is placed in a press, a plate of which has an engraved surface against which the leather sheet of said assembly is applied, the engraving of this surface having been previously carried out according to the desired pattern so that the parts in the hollow of the engraved surface correspond to the raised parts of the pattern to be produced on the leather sheet;

c) the multilayer assembly is heated and compressed in the press;

d) the relief assembly thus obtained is released from the press;

the process being characterized in that the glue thermoformable provided for in step a) is associated with an agent thermo-expansive and that, in step c), the temperature and the pressure are chosen so that the intermediate layer deforms plastically by swelling through the action of the heat-expanding agent to repel the sheet of leather in the recessed parts of the engraved surface.

So the sheet of leather that is placed against the etched surface is softened by heat, then pushed back into the recessed parts of the engraved surface by the intermediate layer which, placed between the sheet of leather and protective sheet, swells under the effect of heat thanks to its thermo-expansive agent to repel evenly the leather sheet inside the parts hollow. With such a process using a thermo-expanding agent, the distribution of the pressure exerted by the middle layer on the leather sheet is perfectly regular, so that the leather sheet hugs faithfully the recessed and raised parts of the surface engraved, especially in the angular contour areas of this one.

Advantageously, the thermoformable adhesive is a glue based on polyurethane or acrylic polymer in phase aqueous or solvent. The heat-expanding agent includes explosive gas micro-balls, for example micro-balls of air.

Preferably, the heating temperature during step C) is at least equal to 140 ° C., and preferably of around 150 ° C.

The engraved surface against which is applied the leather sheet is advantageously made on a copper plate attached to one of the trays of the hurry. Thus, the use of a copper plate allows achieve good precision etching and therefore obtain an embossed pattern of optimum finesse.

Optionally, a sheet of silicone paper bearing a drawing intended to be transferred to the sheet between the leather sheet and the surface engraved.

• la figure 1 est une vue schématique en perspective partiellement éclatée de la presse prête à recevoir un ensemble multicouches selon l'invention (la représentation éclatée des plateaux a été choisie pour plus de clarté, bien qu'en général les presses de ce type soient à plateaux articulés au niveau d'une charnière) ;
• la figure 2 est une vue schématique en coupe transversale partiellement éclatée de la presse prête à recevoir l'ensemble multicouches ;
• la figure 3 est une vue schématique en coupe transversale de l'ensemble multicouches avant déformation, disposé entre les plateaux de la presse selon l'invention
• la figure 4 est une vue analogue à la figure 3, lors de l'étape de chauffe et de compression.

Other characteristics and advantages of the invention will appear on reading the following description of a particular and non-limiting embodiment, in conjunction with the figures of the appended drawings where:

• Figure 1 is a schematic partially exploded perspective view of the press ready to receive a multilayer assembly according to the invention (the exploded representation of the plates has been chosen for clarity, although in general presses of this type are hinged trays at a hinge);
• Figure 2 is a schematic view in partially exploded cross section of the press ready to receive the multilayer assembly;
• Figure 3 is a schematic cross-sectional view of the multilayer assembly before deformation, disposed between the plates of the press according to the invention
• Figure 4 is a view similar to Figure 3, during the heating and compression step.

The process for producing relief patterns on leather or the like according to the invention comprises different steps described below with reference to the figures.

A first step is to make a set 1 multilayer comprising a sheet of leather 3, a protective sheet 5 and an intermediate layer 6 arranged between sheets 3 and 5 and comprising an adhesive thermo-formable associated with a thermo-expanding agent.

The leather used for sheet 3 is leather thin, between 0.6 and 1mm thick, having undergone preferably chrome tanning and retanning, followed by filling with oil and, optionally, a dyeing.

The protective sheet 5 can be formed by a strong linen type canvas, cotton, acetate or triacetate, or be made up of a sheet of leather. Linen in particular constitutes a noble support suitable for leather and very resistant to heat and aging. For optimum flexibility, especially in the area of clothing, we prefer a mesh fabric.

The thermoformable glue used in the constitution of the intermediate layer 6 provides a connection between sheets 3 and 5 and can be hot molded. This glue can be constituted by a thermo-glue cold printed on the canvas 5 such as a base adhesive polyurethane or acrylic polymer in aqueous phase or solvent. You can also use solvent such as polyamide plastisoles, commonly used in the field of textiles. She is mingled with a heat-expanding agent such as gas micro-beads explosives.

In a second step, the multilayer assembly thus produced is placed in a press having a tray upper 7 heated against which the canvas is applied 5 and a lower plate 8 covered with a thickness of silicone foam 9 forming a support for a plate 10 with an engraved upper surface 11. The assembly multilayer 1 is arranged so that the sheet of leather 3 is applied against the engraved surface 11 of the plate 10. The etching of this surface is previously made so that the recessed portions 13 of this surface correspond to the raised parts of the pattern that we want to get on the leather sheet.

The plate 10 is preferably made of copper, the material best suited for making engravings and allowing the obtaining of a motif of a optimal finesse. This plate can be made by a traditional print system in which a drawing is made by the artist directly on the plate with a protective varnish (or possibly by photoengraving), the plate then being hollowed out by immersion in an agent attacking agent, such as iron perchloride or acid nitric. The depth of the hollows is made according to that of the desired reliefs on the leather.

The press used in the context of the invention can be a simple transfer press of the type of those used in screen printing, adjustable in temperature, heating and pressure. Such a press is directly commercially available and low cost.

A third step is to compress hot the multilayer assembly 1 in the press, as illustrated by Figure 4. The leather sheet 3, which is placed against the etched surface 11, is softened by the heat and water vapor from the mixture, and is pushed back into the recessed parts 13 of the etched surface 11, under the effect dynamics of the swelling of the thermo-expanding agent. The press force exerted by the press is very low next to that required for conventional stamping and even compared to that necessary for the implementation of the known process using a thermoformable material without thermo-expanding agent. Indeed, the thermo-expanding agent used in the process of the invention exercises by itself and uniformly a pressure which repels the leaf of leather against the engraved surface. We thus obtain a leather sheet with very fine relief patterns, the raised parts having a drawn outline of very clearly.

The heating temperature can theoretically vary between 100 ° C and 200 ° C, but will most often be at less than 140 ° C, a minimum heating time being necessary to allow complete transmission of the heat to the multilayer assembly 1. Time and heating temperature depends on the type of glue thermo-formable and thermo-expanding agent used, leather and the nature of the plate 10. In practice, for a 1mm thick leather sheet placed between a copper plate, a material that conducts well heat, and a polyurethane adhesive containing an agent thermo-expansive of the micro-ball type of explosive gases, the heating temperature is around 150 ° C with a hold for one minute.

A final step is to identify press and allow the relief assembly to cool as well got. Intermediate layer 6, shaped and expanded during from the previous step, hardens on cooling and keeps the leather in its final shape.

In addition to its aforementioned protective function, the fabric 5 gives the multilayer assembly 1 a capacity of resistance to stretching to avoid elongation of this set which would cause a mitigation of landforms. In addition, the final product obtained, although having was made from a sheet of weak leather thickness, i.e. low cost, has the appearance thick leather, both tactile than at the level of its mechanical behavior.

Furthermore, during the compression operation when hot, it is possible to interpose between the sheet of leather 3 and the engraved surface 11 a sheet of paper silicone bearing a possibly polychrome design corresponding to the relief motif to be produced and intended for be transferred, in known manner, onto the sheet of leather 3 under the effect of the high temperature. We thus obtain in a single operation a product with polychrome reliefs of very fine. Such a transfer could not be envisioned with known methods due to imprecision of the contour of the reliefs produced.

The process which has been described for make embossed patterns on leather can be used with any other material having characteristics analogs, such as imitation leather and other plastics analogues.

Claims (9)

1. A method of making patterns in relief on leather or the like, and comprising the following steps:

   a) a multilayer sandwich (1) is made up comprising a sheet of leather (3) or the like, a protective sheet (5), and an intermediate sheet (6) disposed between said sheets and including a thermoformable adhesive;

   b) the multilayer sandwich (1) made up in this way is placed in a press having a plate that represents an etched surface (11) against which the sheet of leather (3) of said sandwich is applied, the etching of said surface having previously been implemented as a function of the desired pattern so that the setback portions (13) of the etched surface (11) correspond to the portions in relief of the pattern to be made on the sheet of leather (3);

   c) the multilayer sandwich (1) is heated and compressed in the press ; and

   d) the relief-bearing sandwich obtained in this way is released from the press;

      the method being characterized in that the thermoformable adhesive provided at step a) is associated with a thermo-expansive agent, and in that, at step c) the temperature and the pressure are selected so that the intermediate layer (6) deforms plastically, swelling under the action of the thermo-expansive agent to force the sheet of leather (3) into the setback portions (13) of the etched surface (11).
2. A method according to claim 1, characterized in that the thermoformable adhesive (6) is adhesive based on acrylic or polyurethane polymer in aqueous phase or requiring a solvent.
3. A method according to claim 1 or 2, characterized in that the thermo-expansive agent includes explosive microspheres of gas.
4. A method according to any preceding claim, characterized in that the heating temperature during step c) is at least 140°C, and is preferably about 150°C.
5. A method according to claim 1 or claim 2, characterized in that the etched surface (11) against which the sheet of leather (3) is pressed is made on a copper plate (10) applied to one of the plates of the press.
6. A method according to any preceding claim, characterized in that a sheet of silicone-impregnated paper carrying a design for transferring to the sheet of leather (3) is disposed between the sheet of leather (3) and the etched surface (11).
7. A method according to any preceding claim, characterized in that the press is a transfer press as used in silkscreen printing.
8. A method according to any preceding claim, characterized in that the protective sheet (5) is constituted by a linen cloth.
9. A method according to any one of claims 1 to 7, characterized in that the protective sheet (5) is constituted by a sheet of leather.

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