EP0432300B1 - Process for making split leather and its application - Google Patents

Abstract

To make split leather, a limed animal hide is split into a grain split and a flesh split, the flesh split is divided into a butt and a neck and flank part and the butt is relimed, bated, chrome-tanned, fat-liquored, dried and dressed. Here low-shrinkage split leather is obtained by first reducing the butt, between the chrome-tanning and the fat liquoring, to a thickness of 1.1 to 2.5 mm by shaving on the split and flesh side, retanning, and, after the dried butt has been dressed on the split side, producing from it a middle split 0.5 to 1.0 mm in thickness by shaving on the flesh side, and subsequently dressing the middle split also on the flesh side. This low-shrinkage split leather is particularly suitable for two-dimensionally adhered leather trim subjected to temperature and humidity changes, in particular in motor cars.

Description

The invention initially relates to a method for producing split leather, wherein a washed-out animal skin, in particular cowhide, is split into a grain split and a meat split, the meat split is broken down into a croupon and neck and flank parts, and the croupon is washed, stained, chrome-tanned, greased, is dried and prepared. The invention also relates to the use of the split leather thus produced.

According to the known method of the type mentioned (Ullman's Encyklopadie der Technischen Chemie, 4th edition, volume 16 "Lagerwerkstoffe bis Milch", Verlag Chemie GmbH Weinheim, 1978, pages 109 to 177), no split leather that is so low in shrinkage can be produced to date. that it is for flat glued leather panels that are exposed to high temperature and moisture cycling, such. B. on dashboards of automobiles or integral seats of convertibles.

The invention has for its object to produce a low-shrink split leather with the aforementioned method.

The solution to this problem according to the invention is that the croupon between the chrome tanning and fats is first brought to a thickness of 1.1 to 2.5 mm, preferably 1.2 to 1.5 mm and retanned by folding on the gap and flesh side, and that after dressing the dried croupon on the gap side, a 0.5 to 1.0 mm, preferably 0.7 to 0.9 mm thick central gap is produced therefrom by folding on the meat side, which is then also prepared on the meat side.

The invention is based on the knowledge that a split leather with a high degree of low shrinkage can be produced by deliberately folding, retanning and dressing a croupon middle gap.

There are several possibilities for the further configuration within the scope of the invention. Thus, according to a particularly preferred embodiment, the chrome-tanned croupon is first made on the gap side with a straight pressure roller to a thickness of 2.0 to 2.2 mm, then on the meat side with a curved pressure roller of a thickness of 1.5 to 1.7 mm and then again on the gap side convex pressure roller folded to a thickness of 1.2 to 1.5 mm; the use of the cambered pressure roller takes account of the fact that leather is a natural material, that is to say not a material with properties that remain the same over the surface, but rather has lower strength in the edge regions than in the back region. For the rest, it is advisable to dewater the greased croupon mechanically and to dry it over rods at 50 to 70 ° C for 3 to 5 hours. The gap-side dressing of the dried croupon and the meat-side dressing of the croupon middle gap are expediently carried out in each case by roller application and / or spraying on of aqueous polyurethane and / or polyacrylate dispersions and ironing of the layers. Of course, the meat-side dressing can also be carried out in the course of and / or by subsequent gluing. It is recommended for the reasons mentioned above also, to carry out the meat-side folding producing the middle gap again with a cambered pressure roller. Finally, the measure to pre-shrink the croupon middle gap, which was also prepared on the meat side, by means of heat treatment leads to particularly good results. In this context, it is advisable to shrink the Croupon middle gap by hanging it in a drying chamber at 80 to 140 ° C for 1 to 6 hours, preferably at 105 to 120 ° C for 1.5 to 2.5 hours.

In any case, the invention also relates to the use of the split leather produced in the manner described for temperature-sensitive and moisture-alternating, surface-glued leather claddings, in particular in automobiles. In this case, a support base can also be brought into its final shape during and / or after the split leather has been glued on.

The invention is explained in more detail below using an exemplary embodiment:
The starting material is a so-called meat crack, which is a waste product in the manufacture of upholstery leather when splitting after liming. For this purpose, the dehaired, ashed beef skin is split horizontally into two layers on a band knife splitting machine. The upper layer is the so-called scar gap and histologically represents the scar membrane (papillary layer) and part of the underlying reticular layer. The lower layer is the so-called meat gap and histologically represents part of the reticular layer and the subcutaneous connective tissue.

The meat crack is then crouponed. This means the breakdown of the entire skin into three skin parts, namely the croupon (middle part), the neck part and the side flank parts. Only the meat split croupon is processed. The meat cracking croupon is first of all after-washed by treating it in a saturated solution of calcium hydroxide at 25 ° C. for 24 hours while rotating slowly in the barrel. The lime contained is then neutralized by adding weak organic acids and / or acid salts. Then it is pickled; For this purpose the croupon is treated with enzymes of the pancreatic gland at a temperature of 38 ° C for 4 hours with intensive movement in the barrel.

The meat cracking croupon is now acidified across its entire cross-section by treatment with mixtures of inorganic / organic acids and then chrome-tanned by adding basic, III-valent chromium sulfates, for 12 hours at 40 ° C. a partial drainage by pressing with hydraulic pressure between two press rolls.

Now a thickness adjustment is made by folding: First the gap side is folded with a straight pressure roller towards the neck of the shield to a thickness of 2.0 to 2.2 mm. The flesh side is then folded with a 32/100 convex pressure roller in the direction from the neck to the middle of the shield to 1.5 mm, the back to 1.7 mm and the belly, as the veins require and allow. All other folding processes are also carried out with a cambered roller. The gaps are then left covered over night. Finally, the seam is finished on the gap side in the direction of the shield - neck, to the following final fold thicknesses: Back line (approx. 50 cm from the tail) 1.2 to 1.3 mm Belly (approx. 5 cm from the edge) 1.3 to 1.4 mm Edge (approx. 1 cm from the edge) 1.4 to 1.5 mm.

After folding, retanning is followed by intensive post-treatment with basic, III-valent chromium salts, such as those used in tanning, and then neutralization with weakly alkaline salts. For dyeing, the croupon is treated with aniline dyes. Greasing is carried out with aqueous emulsions of vegetable fats (coconut oil, rapeseed oil) or animal fats (fish oil). Then it is mechanically dewatered and dried over rods at 60 ° C for about 4 hours.

To prepare the dressing, the meat crack croupon is treated on both sides on rotating rollers covered with emery paper to level the fibers on the surface. The grinding dust is removed with the aid of a blown air dedusting machine. For dressing, aqueous and organic polyurethane and polyacrylate dispersions are applied in layers using roller application and spraying machines. The applied films are then ironed to produce a closed color film that seals the surface. Then the gap side is embossed using an embossing calender.

A central gap is then produced, namely by folding the meat side with a cambered pressure roller to a final thickness of 0.7 to 0.9 mm. After dedusting (as above), the back is treated by applying aqueous polyacrylate dispersion on roller application machines. Then iron under pressure and temperature.

Finally, the finished Croupon middle gap is hung in a drying chamber and shrunk there at 90 ° C for 5 hours.

The split leather produced in this way is very low in shrinkage and is excellently suited for surface-clad leather claddings that are exposed to temperature and moisture changes, particularly in automobiles.

Claims (13)

1. A process for manufacturing a split leather, wherein a limed animal hide, particularly cowhide, is split into a grain split and a flesh split, the flesh split is separated into a butt and a neck and flank portion, and the butt is subsequently limed, drenched, chrome tanned, lubricated, dried and dressed, characterised in that the butt is first brought to a thickness of 1.1 to 2.5 mm between chrome tanning and lubrication by shaving on the split and flesh sides and is subsequently tanned, and that after dressing the split side of the dried butt a central split 0.5 to 1.0 mm thick is produced from the latter by shaving on the flesh side, which central split is also subsequently dressed on the flesh side.
2. A process according to claim 1, characterised in that the chrome tanned butt is brought to a thickness of 1.2 to 1.5 mm by shaving on the split and flesh sides.
3. A process according to claim 2, characterised in that the chrome tanned butt is first shaved on the split side, using a straight pressure roll, to a thickness of 2.0 to 2.2 mm, is then shaved on the flesh side, using a cambered pressure roll, to a thickness of 1.5 to 1.7 mm, and is subsequently shaved again on the split side, using a cambered pressure roll, to a thickness of 1.2 to 1.5 mm.
4. A process according to any one of claims 1 to 3, characterised in that the tanned butt is mechanically de-watered and is dried hanging over bars at 50 to 70°C for 3 to 5 hours.
5. A process according to any one of claims 1 to 4, characterised in that the dressing of the dried butt on the split side and the dressing of the butt central split on the flesh side are effected by roll application in layers and/or by spraying on aqueous polyurethane- and/or polyacrylate dispersions and pressing the layers.
6. A process according to any one of claims 1 to 5, characterised in that a central split 0.7 to 0.9 mm thick is produced by shaving the butt, which is dressed on the split side, on the flesh side.
7. A process according to any one of claims 1 to 6, characterised in that the shaving operation which produces the central split is carried out using a cambered pressure roll.
8. A process according to any one of claims 1 to 7, characterised in that the butt central split, which is also dressed on the flesh side, is pre-shrunk by heat-treatment.
9. A process according to claim 8, characterised in that the butt central split is pre-shrunk by hanging it in a drying chamber at 80 to 140°C for 1 to 6 hours.
10. A process according to claim 9, characterised in that the butt central split is pre-shrunk at 105 to 120°C for 1.5 to 2.5 hours.
11. The use of the split leather manufactured according to any one of claims 1 to 10 for glued-together sheet leather soft trim subjected to changes of temperature and humidity, particularly in automobiles.
12. A use according to claim 11, wherein a supporting base is provided during and/or after sticking on the split leather in its final shape.
13. A process according to any one of claims 1 to 10 and a use according to claims 11 or 12, wherein the dressing on the flesh side is carried out in the course of and/or by means of gluing together.