EP0145560B1 - Treating process for leather, particularly for leather shoe-uppers, shoe-uppers and shoes manufactured according to this process - Google Patents

Description

The invention relates to the shaping of leather, more particularly for the manufacture of shoe uppers.

In the "Journal of the American Leather Chemists Association", vol. 73, no 3, March 1978, p. 131 is described a leather surface treatment method in which three successive layers adhering to the leather are applied. The top coat contains crosslinked polyurethane while the other coats contain methane polyester.

In DE-A-2 336 957 a chasing rod and a method for manufacturing it are described. The upper comprises a leather support material covered with a layer of poromeric polyurethane.

FR-A-2 507 444 describes a hunting rod made of a material other than leather welded to a sole by a high-frequency current and a method for obtaining this set.

Many shoes are made by assembling a shoe upper with a sole; for this assembly, the upper is placed on a shape, one face of which adjacent to the edge of the upper acts as a wall of a molding cavity into which the plastic material intended to constitute the sole is injected, thus secured to the upper by its edge during the very molding; or else the rod having been placed on the form and coated with an adhesive on its edge, the sole is applied to it, in leather or in plastic, thus assembled with the rod by gluing or welding.

For the manufacture of shoes with leather uppers, the shoe manufacturer receives hides from the tanner from which he cuts the uppers. Before delivery, however, the tanner treats the leather by applying the finishing layer desired by the manufacturer to give the upper the desired end look for the shoe upper, from the point of view of color and / or view of the surface finish.

After having found that, all too often, the sole adhered insufficiently to the upper coming from a leather thus treated and determined that this defect came from a bad bond between the finishing layer and the leather, the shoe manufacturer has become accustomed, before assembly, to rid the finishing layer of the marginal area of the upper intended to come into contact with the sole. This treatment is usually done by glassing or carding.

But, very often, it happens that the carded or glassed area does not coincide with the part of the upper which, subsequently, comes into contact with the sole. If the glassed or carded area is too wide, then the shoe, after the sole has been secured, shows a more or less regular selvedge devoid of topcoat. This shortcoming requires costly manual touch-ups. If, on the other hand, the locked or carded part is too narrow, the sole will have insufficient adhesion with the edge not locked or carded and the shoe will have to be discarded too often. In all cases, the grip of the sole on the upper is limited to the part of the surface that has been locked or carded.

The invention relates in particular to a process which, taking the opposite of what has been proposed hitherto, namely to eliminate, before joining with the sole, the product received by the skin, provides to bring on the latter a deposit chosen to obtain the desired final effect, namely a bonding of the leather thus treated with the sole at least as good as with a leather stripped of all products by glassing or carding.

The process is particularly advantageous for the production of sports shoes, such as jogging or training shoes, in which the leather constituting the upper must be light in color, even white, the irregularities in the glassing or carding then being unacceptable, especially when the sole includes a peripheral projection intended to partially cover the upper.

According to the invention, a deposit adhering to the leather is formed on the surface of the leather, by adding material, allowing, without carding or locking the leather, the attachment of a leather shoe upper thus treated with a sole, either by direct injection of the material of the sole, either by welding or gluing on a prefabricated sole.

The shoe manufacturer thus has no prior operation to perform on the leather delivered to him by the tanner, after having undergone the surface treatment according to the invention. Furthermore, the latter does not imply an increase in cost for the tanner, since this treatment replaces the finishing operations which were previously necessary to obtain the surface appearance and the mechanical properties of the leather which are desired by the shoe manufacturer. .

We eliminate, for the establishment of soles, the carding or glassing operation, manufacturing waste and also the need for touch-ups while retaining the same versatility as for the models of shoes manufactured.

According to the invention, the deposit is formed on the surface of the leather by a multiplicity of superimposed layers, each of which is chosen to be adherent to the underlying layer.

In a prayer phase of the process, the leather receives a prefond, constituted by a polyurethane emulsion containing pigments and a crosslinking agent, in a sufficiently diluted form, as presented by the acrylic prefonds usually used to ensure its good impregnation in the dermis.

The process provides, before the introduction of the prefond, a synthetic retanning of the skin using chemicals usually used by the tanner, such as condensed phenolic sulfonated and anionic derivatives, phosphoric esters and polyglycol esters, etc. , excluding all products of plant or animal origin. The bond between the prefond and the fibers of the leather is then not only mechanical, but the adhesion is considerably increased by the chemical bonds of the hydrogen type occurring between the polyurethane binder of the prefond and certain functional groups of the retanning product.

The method also provides that it will very advantageously be possible to sand the skin flower before the introduction of the prelude.

According to a second phase of the process, the skin receives an "inter" which has a composition similar to that of the foreground, but which is of a greater concentration both in emulsion and in pigments, the emulsion also being added with crosslinking agent.

The skin thus treated is subjected to a first hot plating to ensure complete chemical crosslinking of the two layers thus provided and also perfect adhesion and cohesion of the leather assembly, in and out, while preparing the desired surface appearance. for the upper of the shoe.

A surface finish layer is then applied, which consists of a dissolution in the solvent phase of a polyurethane resin, of pigment and of a crosslinking agent. The appearance of this finish can be glossy or satin. It adheres well to leather due to the prior treatment of the latter.

Finally, we proceed to a second hot plating followed by graining giving the leather its final surface appearance.

The leather is ready for delivery by the tanner to the shoe manufacturer.

In what follows, we give a few examples of the treatment of a leather allowing the manufacture of the shoe by joining a sole to it without any other prior treatment of the leather.

Preliminary example

extrait sec # 21,5 %The composition is as follows (by weight):

dry extract # 21.5%

Apply 4 to 6 g of dry product per square foot of leather. Example of "Inter"

extrait sec # 54,7 %The composition is as follows (by weight):

dry extract # 54.7%

9 to 12 g of dry product are applied per square foot of leather which has received the prefond.

Example of surface finish

extrait sec * 13,5 %The composition is as follows (by weight):

dry extract * 13.5%

2 to 3 g of dry product are applied per square foot of leather having received the prefond and the inter.

Hot plating: It is carried out on conventional tanning equipment (heating presses) at 100 ° C for 2 to 4 seconds.

The above examples are in no way limiting.

Furthermore, it is known that, for economic reasons, synthetic materials or composite materials are used frequently in the manufacture of shoe uppers, instead of natural leather, at least the part facing outwards. is synthetic, which we seek to give the appearance of natural leather.

In particular, by the so-called "high frequency" process, shoe uppers with the external appearance of leather are produced from sheet materials of which at least the face facing outwards is not of leather, such as fabrics coated with polyvinyl chloride or plastisols lined with a fabric or split leather previously glued.

To this end, for example, by means of a crosslinkable silicone elastomer, the imprint of a model obtained by flattening a leather shoe stem from the disassembly of a shoe is taken. A sheet of the type mentioned above is placed on which it is desired to give the appearance of natural leather in the mold thus produced and the sheet is passed through by a high-frequency electric current, which causes the sheet to soften or melt. , the surface of which then follows the irregularities of the mold wall and thus acquires the surface configuration of the natural leather upper which has been imprinted.

The use of a high frequency current also allows the heat sealing, on the face of the sheet facing outwards, of appliques or reinforcements made of a material having suitable dielectric properties.

These sconces or reinforcements are usually placed in corresponding housings of the mold, these housings having been advantageously provided by the imprints of sconces or reinforcements present on the natural leather upper used as a model.

Usually, the modification of the surface configuration of the sheet and the heat sealing are carried out in the same operation.

For the implementation of this process, the mold containing the sheet to be treated and, if necessary, the appliques or reinforcements to be placed, are placed between two electrically conductive plates and a high frequency current is passed through. between the two plates through the mold and its contents.

This process, very inexpensive, makes it possible to manufacture shoe uppers having the appearance of leather and possibly provided with appliques and / or reinforcements under particularly economical conditions.

Despite the efforts made in this area, it has not been possible until now, using a high frequency current, to modify the surface configuration of the leather, this term designating here exclusively natural leather as opposed to synthetic products.

As for the joining of discontinuous surface reinforcements and / or reinforcements on leather shoe uppers by implementing a high frequency current, it is currently physically impossible to achieve.

The word "upper" is used here to denote both a part of the finished shoe and a cut sheet intended to constitute, after shaping, this part of the shoe.

Another object of the invention is then to allow the application, to the uppers of leather shoes, of the high frequency process, and this with the same economic advantages as those which it presents in its known application to uppers of synthetic materials .

However, it has now been found that, surprisingly, it is possible, thanks to a deposit formed on the surface of the leather, as defined above, not only to obtain a connection between the leather and a sole also good than that obtained by partially eliminating the flower (epidermis) from the leather, but also to obtain, by the high frequency process, a modification of the surface configuration of such a deposit on the one hand, and its direct adhesion, without mechanical treatment or intervention of adhesives, to appliques or reinforcements on the other hand.

The appliques and / or reinforcements can be made of synthetic materials having a suitable dielectric permeability, for example plastisols, polyvinyl chloride and vinyl copolymers, as in the prior art.

The invention further provides for putting in place leather appliques and / or reinforcements, after their face turned towards what will constitute the shoe upper, whether the latter is made of a sheet material other than leather, or in treated leather, has also been subjected to the surface treatment defined above.

It is also possible to produce a relief decoration on the face intended to be turned towards the outside of the appliques and / or reinforcements, that is to say their face opposite to that in contact with the rod, by providing for irregularities. surface in the mold recesses.

When the appliques and / or reinforcements are made of leather, the face to be decorated should also have undergone the surface treatment described above. Such a decoration is for example an imitation of seams, obtained by taking the imprint of a model comprising appliques and / or reinforcements fixed by seams.

The invention provides, in the implementation of the high-frequency process to take into account the fact that the resistivity of the leather is a function of the tanning conditions and the humidity level, and can be very high, to compensate for the resistivity of the leather by reducing that of the mold, for example by incorporating into the constituent material of the latter conductive particles such as metal powder particles.

It is also important to keep the mold under pressure during current flow and during cooling.

A shoe upper having undergone the surface treatment according to the invention (and, where appropriate, a high-frequency shaping treatment) can be directly secured to a sole, either that it is mounted on a form forming part of 'A mold which receives the sole in PU, TR, PVC, etc., by injection, as usual, either that, on a form, a previously manufactured sole is attached to it by bonding or welding. In either case, no treatment of the leather by the shoe manufacturer is necessary and, in particular, no glazing or carding, and the adhesion of the sole takes place over the entire surface in contact with the leather, in the case of an injected sole, or over the entire surface of the leather which will have received the glue, in the case of a glued or welded sole.

Experience shows that the adhesion of the sole to such a leather constituting a simply cut upper, not locked or carded, is at least as good as that obtained after carding or locking.

The manufacture of the shoe is simplified. Rejects are avoided as well as rework.

The cost price of the set is reduced.

The invention contemplates modifications with respect to the surface treatment described in the examples.

It is in particular possible, and even advantageous in the case where the leather must then be shaped by means of a high-frequency current, to eliminate the hot plating operations and / or to increase the quantity of the product intended to form at least one of the successive layers, for example the second layer called inter, so as to obtain a more accentuated relief on the shoe upper.

The invention also provides that the treatment of the face of the leather intended to be turned towards the exterior comprises the application not of three layers, as described above, but of only two layers, the prelude or the inter being omitted. Such treatment is provided, whether or not the leather thus treated is intended to be subjected subsequently to the high-frequency shaping treatment.

The invention also provides a surface treatment of the leather which comprises the application to the leather of a single layer, then relatively large, in the foreground to allow shaping of the leather analogous to that of the leather to which three successive layers have been applied. as described above.

The invention also relates to a shoe upper, the manufacture of which uses the shaping process which has just been defined, and a shoe comprising such a upper.

The invention applies to the different kinds of leather used in the shoe industry, both those called "skin" and those called "crust". It finds a particularly interesting application for the manufacture of sports shoes.

The invention also applies in fields other than that of shoe uppers, in particular for the use of leather in clothing, furniture, luggage, saddlery. It also generally provides for the application of high frequency treatment for the assembly of leather elements after they have undergone an appropriate surface treatment or for their welding to themselves after folding.

Claims (28)

1. Process for the surface treatment of leather, characterised in that:

a) an undercoat in the form of a dilute aqueous polyurethane emulsion is applied to the leather to which it adheres;

b) an intermediate coating is applied to the leather treated according to step a) to which it adheres, the coating being in the form of an aqueous polyurethane emulsion having a polyurethane concentration greater than that of the emulsion mentioned in step a); and

c) a finishing coat of a polyurethane solution is applied to the leather treated according to step b) which adheres to the intermediate coating,

the undercoat, the intermediate coating and the finishing coat containing pigments and a crosslinking agent.

2. Process according to claim 1, characterised in that, prior to step a), the leather is retanned by means of synthetic chemical products.

3. Process according to claim 2, characterised in that the synthetic chemical products are selected from the group comprising sulphonated and anionic condensed phenolic derivatives, phosphonic esters and esters of polyglycol.

4. Process according to one of claims 2 and 3, characterised in that hydrogen chemical bonds are formed between the polyurethane of the undercoat and the functional groups of the retanning products, thus increasing the adhesion of the undercoat to the retanned leather.

5. Process according to one of the preceding claims, characterised in that application of the intermediate coating is followed by glazing.

6. Process according to any of the preceding claims, characterised in that the application of the finishing coat is followed by glazing and graining.

7. Process according to one of claims 5 and 6, characterised in that the glazing is carried out with heat.

8. Process for working leather, characterised in that the leather is first subjected to a surface treatment according to one of the preceding claims, and then a working treatment is applied to the so-treated leather by means of a high frequency current.

9. Process according to claim 8, characterised in that the working comprises forming hollows or reliefs.

10. Process according to claim 9, characterised in that the surface configuration of the leather is modified by superficial softening or melting by means of the high frequency current.

11. Process according to one of claims 8 to 10, characterised in that the working comprises the addition, by bonding, of ornaments and/or reinforcements.

12. Process according to claim 11, characterised in that the ornaments and/or reinforcements are made of synthetic materials.

13. Process according to claim 11, characterised in that the ornaments and/or reinforcements are made of materials selected from the group comprising plastisols, polyvinyl chloride and vinyl copolymers.

14. Process according to claim 11, characterised in that the ornaments and/or reinforcements are of leather which has previously been subjected to surface treatment according to one of claims 1 to 7.

15. Process according to one of the preceding claims, characterised in that the leather is prepared for use as a footwear upper.

16. Process according to one of claims 8 to 10, characterised in that the working comprises applying the leather as ornaments and/or reinforcements to another material by bonding.

17. Process according to claim 16, characterised in that the other material comes from a sheet of the said material and is prepared for use as a footwear upper.

18. Process according to one of claims 9 to 17, characterised in that the high frequency current is applied in a mould whose wall exhibits irregularities complementary to the configuration of the surface to be obtained and/or carries ornaments and/or reinforcements to be bonded.

19. Process according to claim 18 characterised in that the mould is made by taking an impression of a leather footwear upper model to be reproduced, previously laid out flat.

20. Process according to one of Claims 18 and 19, characterised in that the mould is made of silicone elastomer.

21. Process according to one of claims 18 to 20, characterised in that particles which conduct electricity are incorporated in the mould material.

22. Process according to one of claims 18 to 21, characterised in that the wall of the mould exhibits irregularities facing the ornaments and/or reinforcements so as to produce a relief pattern on their external faces.

23. Process according to any of Claims 14, 16 and 17 in combination with claim 22, characterised in that the said external faces of the applied leather ornaments and/or reinforcements have been subjected to surface treatment according to one of claims 1 to 7.

24. Process according to one of claims 18 to 23, characterised in that the mould is maintained under pressure during passage of the current and during cooling.

25. Leather footwear upper coated with a multiplicity of superposed layers, namely.

- an undercoat of a dilute aqueous polyurethane emulsion and adhering to the leather,

- an intermediate coating applied in the form of a more concentrated aqueous polyurethane emulsion than the undercoat, and adhering to the latter; and

- a finishing coat applied in the form of a polyurethane solution and adhering to the intermediate coating, the undercoat, the intermediate coating and the finishing coat containing pigments,

such that it may be obtained by the process according to claim 15.

26. A footwear upper of a material other than leather onto which leather ornaments and/or reinforcements are welded by a high frequency current, such that it may be obtained by the process according to one of claims 17 to 24.

27. Footwear containing an upper according to one of claims 25 and 26.

28. Process for the manufacture of footwear, characterised in that a sole is fixed on an upper according to claim 25.