GB2189191A

GB2189191A - Leather finishing process

Info

Publication number: GB2189191A
Application number: GB08706865A
Authority: GB
Inventors: Elie Gras
Original assignee: Anver SA
Current assignee: Anver SA
Priority date: 1986-04-16
Filing date: 1987-03-23
Publication date: 1987-10-21
Also published as: CN1012824B; GB8706865D0; PL154236B1; DE3712579A1; CN87102611A; KR870010198A; AU7091787A; IT1215424B; SU1623568A3; FR2597505A1; MA20947A1; CS266187A2; JPS62243700A; ES2003259A6; TNSN87053A1; HUT45278A; ZA872146B; BR8701837A; IT8720097A0; PL265180A1

Description

SPECIFICATION Leather finishing process This invention relates to the finishing of leather and is especially concerned with the manufacture of finished pieces of leather, for example for making shoes, fancy leather goods or other leather articles, from pieces of raw leather. Finishing processes for leather, which give the raw material, for example the rough polished fleshed hide coming from a splitting machine, the sought after qualities of flexibility, texture and aesthetic appearance, are generally directly applied in a tannery. They comprise depositing on the rough hide, first of all, a dressing, intended to amalgamate the fibres, then, after drying, applying a finish compound to obtain the texture and colour desired. A third operation is then usually performed in order to give the leather its grain. This operation uses a high pressure hydraulic press with heating, using metal texturing moulds which are suitable for giving the grain appearance. According to an already known variant of the process, it has been suggested to make a previous deposit of dressing followed by finishing product on a transfer support, for example of type paper, and the coating thus obtained is then heat-transferred on to the raw leather (see, for example, French Patent No. 72.25120 published under No. 2 146 748; West German Patent No. 3 309 992 and European Patent No. 0002465). Such a transfer process has the advantage that it increases the possibilities of use and adaptation of leather pieces used in fancy leather work and the manufacture of shoes. However, this process brings into play thermal presses able to develop high pressures of at least 8 to 10 kg/cm . These are expensive pieces of equipment and are expensive in energy. Also the high temperatures obtained on the metallic plate of the thermal press, often 160 to 180[deg]C or more, induce sticking or adhesion of the coating existing on the transfer support and, above all, decomposition and deterioration of the coating and of the finishing product because these latter are usually constituted by plastics materials and polymerised products which are often heat sensitive. Now it has been found that these drawbacks may be avoided in the known process of transfer on to raw leather of finishing products from an intermediate support and this makes it possible to extend the range of use of the process in all fields where leather is finished. According to this invention, we provide a process for finishing a raw leather piece, ready for use, for example, in making shoes or fancy leather goods, in which a dressing and then a finishing composition are applied to an intermediate support, independent from the leather piece and then the coating consisting of layers of the dressing and finishing composition is transferred on to the raw leather piece in a moulding/pressing machine where the coating is heated by high frequency electromagnetic radiation. The intermediate support may be of any material which is suitable for constituting an insulation. for the high frequency radiation and for receiving, by uniform spreading, sufficiently adherent layers of dressing and thermoplastic finishing compound. A material which is particularly suitable for this purpose is silicone treated paper, which is known for other purposes. The composition of the dressing and finishing product used in the above mentioned transfer process do not constitute critical factors in the implementation of the invention. They can be chosen from among the products or blends of products which are known for the traditional treatment of leathers, such, for example, as acrylic resins, liquid rubber, vinyl polymers, and polyurethanes. The manner of the application to the transfer support of various layers of coatings mentioned above is not specifically part of the invention and, for this purpose known techniques of scraper coating, spray coating and calendaring may be used. Nevertheless, it is important that the dressing and/or finishing products for the leather shall be able to be reactivated when hot and that they have dielectric losses for the thermal transfer by the use of high frequency electromagnetic radiation heating. This is most often the case when the known compositions, set out above, based on plastics and/or synthetic latex are used. To implement the invention known moulding and/or pressing apparatus incorporating high frequency heating developed many years ago, particularly by the Applicant, may be used. For example, French Patent No. 75.27466 discloses a carousel type HF membrane press and French Patents Nos. 76.35532, 78.32827, 80,03658 disclose moulds which can be used in such HF presses, namely silicone moulds. Thanks to the use of HF heating the abovementioned disadvantages in the use of externally applied heat, and pressing in metallic moulds are avoided. The pressures used in the process are lower (in practice 3 to 5 Kg/cm ), the energy yields are better and, in addition, a stabilisation in pressure and temperature is obtained for the dressing and finishing products to be transferred, owing to the fact that the heating of these products is effected by internal dielectric losses and not by the external supply of heat as from a metallic heating plate. Among the other advantages of the process of the invention the following can be particu- larly noted:- Considerable operating and utilisation flexibility for the manufacturers of shoes or fancy leather goods who can thus have an inventory of coated paper supports and only perform the transfer onto raw leather according to his order schedule; The possibility also, for the above mentioned manufacturers or any other users, to hold a large quantity of fleshed or split hides, unfinished, and to use them as needed, with respect to the desired colour and grain; The elimiation of difficulties due to the technique of directly dressing the raw leather according to the traditional tannery method, which often leads to materials which are too stiff because of the considerable absorption of the dressing by the raw leather;Owing to the use of a transfer support, the application of uniform and thin layers of dressing and finishing compounds, which provide both a saving in the quantities of these products and the possibility of obtaining coatings of very limited thickness, for example a few tenths of a millimetre, thus providing microporous coverings which let the leather breathe, which is not possible with the traditional technique of dressing and finishing; The possibility of only depositing the transfer coat at certain specific points on the raw leather piece, by simply cutting out the paper support as desired. For example, on a shoe piece one may want to obtain a central portion in lizard grain while keeping the rest of the piece looking like non-treated raw fleshed hide; one has only then to cut a shape in the form of the portion desired, centre it on the leather piece and then perform the transfer. According to a variant of the process of the invention a back and front transfer can be effected, that is, provide graining on the two faces of the leather piece at the same time. For this purpose one has only to arrange, on each of the two faces of the raw leather piece the silicone treated paper and its finishing coating (for example, with different colours); then hot transfer the coating as described above, after which the substrate papers are removed and the treated leather sandwiched between the coatings is placed between the two plates or moulds of the HF heated press to execute the graining. Finally, it should be noted that, if the compounds used for the dressing and finishing are compatible with polyvinyl chloride (habitually used for HF moulding), an HF printing process can be combined to heat-bond motifs in relief and different colours directly on the leather while executing a graining on the flat parts of the leather piece.

Claims

1. A process for finishing a raw leather piece, ready for use, for example, in making shoes or fancy leather goods, in which a dressing and then a finishing composition are applied to an intermediate support, independent from the leather piece and then the coating consisting of layers of the dressing and finishing composition is transferred on to the raw leather pieces in a moulding/pressing machine where the coating is heated by high frequency electromagnetic radiation.

2. A process according to the Claim 1, wherein after the transfer operation, a final operation of graining the face or faces of the finished leather piece is carried out in the high frequency heated machine.

3. A process according to Claim 1 or Claim 2, wherein the intermediate support consists of silicone treated paper.

4. A process according to any one of Claims 1 to 3, wherein both the dressing and finishing compositions are suitable for being reactivated hot and both of which have dielectric losses.

5. A process according to any one of Claims 1 to 4, wherein the transfer operation and the graining operation when present and performed on all or part of both sides of the raw leather piece.

6. A process according to Claim 2 or any one of Claims 3 to 5 when dependent on Claim 2, in which the final graining operation in the machine is combined with high frequency heat-bonding of motifs in relief and in different colours to the leather piece.

7. A process according to Claim 1, substantially as described herein.

8. A leather piece finished by a process in accordance with any one of the preceding Claims.