Classifications

• • C—CHEMISTRY; METALLURGY
  • C14—SKINS; HIDES; PELTS; LEATHER
  • C14B—MECHANICAL TREATMENT OR PROCESSING OF SKINS, HIDES OR LEATHER IN GENERAL; PELT-SHEARING MACHINES; INTESTINE-SPLITTING MACHINES
  • C14B1/00—Manufacture of leather; Machines or devices therefor
  • C14B1/44—Mechanical treatment of leather surfaces
  • C14B1/56—Ornamenting, producing designs, embossing

Definitions

• the present invention relates to a process for producing patterns in relief on leather or any other material of a similar nature, such as imitation leather, plastic, etc.
• the most commonly used method for producing such patterns is an old press stamping method.
• This process uses a plate having an embossed surface, the recessed parts of which correspond to the raised parts of the pattern to be produced on the leather.
• a sheet of leather is pressed between this plate and the associated counter-plate, the side of the leather on which the relief is to be produced being pressed against the engraved surface.
• the leather sheet In this device, resulting from the very old method of pushing leather by hammering, the leather sheet must be of sufficient thickness so that a significant relief is obtained. In practice, this thickness varies between 1.5 and 2mm, which corresponds to relatively expensive leathers.
• the compression force applied by the press to the leather sheet must be high enough to plastically deform the leather sheet and avoid elastic return of the latter.
• Document FR-A-2,236,658 also discloses a process for producing relief patterns on leather or the like, consisting in heating and compressing in a press a multilayer assembly comprising a sheet of leather, a thermoformable material. and possibly a protective sheet, the leather sheet being placed against a plate of the press, the surface of which has recessed parts inside which the leather is repelled by the thermoformable material when the multilayer assembly is hot compressed.
• the sheet of leather which is placed against the engraved surface is softened by heat, then pushed back into the hollow parts of the engraved surface by the thermoformable material which "flows" in a plane parallel to the press plate between the parts in relief and the hollow parts thereof.
• the process illustrated in the aforementioned document makes it possible, on the one hand, to use sheets of leather which are thinner than those used in the old press stamping process and, on the other hand, to reduce the compression force exerted by press, which reduces raw material and tool costs.
• the pressure exerted by the thermoformable material on the leather sheet is never perfectly regular and is found to be appreciably weaker in the contour areas of the relief patterns produced, which results in relative inaccuracy in the formation of these contours.
• This imprecision in highlighting the leather sheet can prove to be extremely penalizing, in particular in the case where one wishes to print a design on the leather monochrome or polychrome in correspondence with the relief motif produced.
• the object of the present invention is to remedy these drawbacks by proposing a method for producing very fine relief patterns on leather or the like, even if the sheet of leather concerned is very thin.
• a method for producing relief patterns 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 heat-forming adhesive associated with a heat-expanding agent; 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, the temperature and the pressure being chosen so that the intermediate layer deforms plastically while swelling to repel the leather sheet in the hollow parts of the engraved surface; d) the relief assembly thus obtained is released from the press.
• the sheet of leather which is placed against the engraved surface is softened by heat, then pushed back into the hollow parts of the surface engraved by the intermediate layer which, placed between the sheet of leather and the protective sheet, swells under the effect of heat thanks to its thermo-expansive agent to uniformly repel the leather sheet inside the recessed parts.
• the distribution of the pressure exerted by the intermediate layer on the leather sheet is perfectly regular, so that the leather sheet faithfully follows the hollow and raised parts of the engraved surface, especially in the angular contour areas thereof.
• thermoformable adhesive is an adhesive based on polyurethane or acrylic polymer in aqueous phase or in solvent.
• the heat-expanding agent comprises micro-balls of explosive gases, for example micro-air balls.
• the heating temperature during step C) is at least equal to 140 "C, and preferably of the order of 150" C.
• the engraved surface against which the leather sheet is applied is advantageously produced on a copper plate attached to one of the press plates.
• a copper plate makes it possible to produce an engraving of good precision and therefore to obtain a relief pattern of optimum finesse.
• a sheet of silicone paper bearing a design intended to be transferred onto the leather sheet is placed between the leather sheet and the engraved surface.
• FIG. 1 is a schematic perspective view partially exploded of the press ready to receive a multilayer assembly according to the invention (the representation exploded trays were chosen for clarity, although in general presses of this type are hinged trays at a hinge);
• FIG. 2 is a schematic view in partially exploded cross section of the press ready to receive the multilayer assembly
• FIG. 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 method for producing patterns in relief on leather or the like according to the invention comprises different steps described below with reference to the figures.
• a first step consists in producing a multi-layer assembly 1 comprising a leather sheet 3, a protective sheet 5 and an intermediate layer 6 disposed between the sheets 3 and 5 and comprising a heat-forming adhesive associated with a heat-expanding agent. .
• the leather used for sheet 3 is a fine leather, with a thickness of between 0.6 and 1 mm, preferably having undergone tanning and retanning with chromium, followed by filling with oil and, optionally, d 'a tincture.
• the protective sheet 5 can be constituted by a strong canvas of the linen, cotton, acetate or triacetate type, or can also be constituted by a leather sheet. Linen in particular is a noble support in line with leather and very resistant to heat and aging. For optimum flexibility, especially in the field of clothing, a mesh fabric is preferred.
• thermoformable glue forming part of the intermediate layer 6 provides a bond between sheets 3 and 5 and can be hot molded.
• This adhesive can be constituted by a thermo-adhesive printed cold on the fabric 5 such as an adhesive based on polyurethane or acrylic polymer in aqueous phase or in solvent. Solvent products such as polyamide plastisoles, commonly used in the textile industry, can also be used. It is mixed with a thermo-expanding agent such as micro-balls of explosive gases. In a second step, the multilayer assembly
• the multilayer assembly 1 is arranged so that the leather sheet 3 is applied against the etched surface 11 of the plate 10.
• the etching of this surface is carried out beforehand so that the hollow parts 13 of this surface correspond to the raised parts of the pattern that we wish to obtain on the leather sheet.
• the plate 10 is preferably made of copper, the material best suited for producing engravings and allowing obtaining a pattern of optimal finesse.
• This plate can be produced 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 photo-engraving), the plate then being dug by immersion in an attacking agent, such than iron perchloride or nitric acid.
• an attacking agent such than iron perchloride or nitric acid.
• the depth of the hollows is made according to that of the desired reliefs on the leather.
• the press used within the framework of the invention can be a simple transfer press of the type of those used in screen printing, adjustable in temperature, time of heating and pressure. Such a press is directly available commercially and at low cost.
• a third step consists in hot compressing the multilayer assembly 1 in the press, as illustrated in FIG. 4.
• the leather sheet 3, which is placed against the engraved surface 11, is softened by heat and water vapor after mixing, and is pushed back into the hollow parts 13 of the etched surface 11, under the dynamic effect of the swelling of the thermo-expanding agent.
• the pressure force exerted by the press is very low compared to that necessary for conventional stamping and even compared to that necessary for the implementation of the known method using a thermo-formable material without thermo-expanding agent.
• thermo-expanding agent used in the process of the invention exerts by itself and in a uniform manner a pressure which pushes the leather sheet against the engraved surface.
• a sheet of leather is thus obtained with very fine relief patterns, the raised parts having a very clearly defined contour.
• the heating temperature can theoretically vary between 100 ° C and 200 "C, but will most often be at least 140" C, a minimum heating time being necessary to allow complete transmission of heat to the multilayer assembly 1
• the heating time and temperature are a function of the types of thermoformable adhesive and of thermo-expansive agent used, of the leather and of the nature of the plate 10.
• the heating temperature is of the order of 150 ° C. with maintenance for a minute.
• a final step is to identify press and allow the relief assembly thus obtained to cool.
• the fabric 5 gives the multilayer assembly 1 a capacity for resistance to stretching, making it possible to avoid elongation of this assembly which would cause a reduction in the reliefs.
• the final product obtained although having been produced from a sheet of thin leather, that is to say of low cost, has the appearance of thick leather , both from a tactile point of view and in terms of its mechanical behavior.

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• Engineering & Computer Science (AREA)
• Manufacturing & Machinery (AREA)
• Mechanical Engineering (AREA)
• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Treatment And Processing Of Natural Fur Or Leather (AREA)
• Laminated Bodies (AREA)
• Synthetic Leather, Interior Materials Or Flexible Sheet Materials (AREA)

Applications Claiming Priority (3)

Publications (2)

Family

ID=9462572

Family Applications (1)

Country Status (5)

Cited By (2)

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Family Cites Families (3)

• 1994
  • 1994-04-27 FR FR9405099A patent/FR2719317B1/fr not_active Expired - Fee Related
• 1995
  • 1995-04-25 ES ES95918640T patent/ES2116085T3/es not_active Expired - Lifetime
  • 1995-04-25 DE DE69502018T patent/DE69502018T2/de not_active Expired - Fee Related
  • 1995-04-25 WO PCT/FR1995/000541 patent/WO1995029262A1/fr not_active Ceased
  • 1995-04-25 EP EP95918640A patent/EP0757724B1/de not_active Expired - Lifetime

Non-Patent Citations (1)

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