NZ234138A - Freezing treatment of animal skin before separation of leather from surface coating - Google Patents

Description

* 23 4 138 ! Priority Date!;:': . .'p. i | Complete £pC"- : - . VK ; Cl~ss: i Publication Do:-.: ...?® AU? 1993 P.O. Journal.

NEW ZEALAND PATENTS ACT. 1953 No.' Date.

COMPLETE SPECIFICATION I PROCESS AND INSTALLATION OP TREATMENT OP AN ANIMAL SKIN -W We. L'AIR LIQUIDE, SOCIETE ANONYME POUR L'ETUDE ET L'EXPLOITATION DES PROCEDES GEORGES CLAUDE, a French company of 75, Quai d'Orsay, 75321 Paris Cedex 07, France hereby declare the invention for which"-*- 7* we pray thaT'a patent may be granted to j»a-/us, and the method by which it is to be performed, to be particularly described in and by the following statement:- (followed by page la) L J 4 PROCESS AMD INSTALLATION OF TREATMENT OF AM ANIMAL SKIN The present inver.t:cr. concerns the treatment o: urinal skins with a view of separating the leather fron its surface cover of wool 3 or hair.

In practice, this separation is carried out by chemical or biological means which leads to a pollution of water which must be treated afterwards. Besides, chemical separation of the wool lowers the quality of the wool ana partly that of the leather. In the same 10 way, biological removal of the wool partly reduces the quality of the leather. Furthermore, these treatments are particularly long C from 12 to 2j hours) from the start of the wool removal operation and the final cleaning of the leather (washing and neutralisation).

This is the reason why it has already been proposed to carry 15 out the separation of the leather of an animal skin from its surface coating by submitting it to the action of a very low temperature which produces a kind of freezing making it much easier to to remove the wool from sheep skins, but this process, which is still very rudimentary and in a stage of simple experimentation, has not yielded * the anticipated optimum results as the intense and brutal cold produced causes fissures, ruptures and/or deformation of the skins treated in this manner.

The present invention envisages a process of treatment of the skin of this last type which is particularly satisfying as it 25 avoids all crazing and/or fissures and/or deformations of the treated skins, while operating speedily with an efficienct final wool removal which is particularly satisfactory.

Hie objectives are achieved, in a process according to the invention, by producing the said stiffening by freezing in a final 30 stage of intense freezing with liquid nitrogen, applying it to the said skin simultaneously on the leather and on the wool or hair side, this stage being preceded by a progressive pre-cooling stage below 0°C carried out ensentiallv on the leather side with cold nitrogen gas which evaporates from the liquid nitrogen used for the final intense cooling stage.

According to one form of execution of the process according to the invention, the skin, being essentially arranged in a hori zogfrawaL^^ position, with the leather side at the bottom, the final inten cooling is carried out by an upwards spraying on the leather ^2 8 JUNI9907 1q <,*■ / 23 L\ 0 of liquid nitrogen atomised into fine droplets, and on the wool or hair side, by a spray of liquid nitrogen drops falling by gravity across a receiving screen for liquid air.

According to the process of the invention, the progressive 5 pre—cooling with cola nitrogen gas is effected by blowing the evaporated nicrogen into a confined area adjacent to the leather side of the animal skin.

This method of operation has been arrived at following many feasibility studies carried out on sheep skins, studies which have 10 shown that it is necessary to obtain a temperature of the skin of below -12Q°C in order to achieve an easy extraction of the wool. In fact, at this temperature it can be pulled out easily by hand.

According to the quality and the provenance of the skin wool removal temperature can vary from -120°C to -1S0°C.

However, the method of cooling is very delicate and in order to avoid internal contractions in the skin, it is best to proceed in a progressive and homogeneous fashion. The process according to the invention makes it possible to proceed in this progressive and homogeneous manner as from the initial temperature drop, and to carry 20 out this cooling action essentially on the leather side, which makes it possible to reduce the skin to a cold temperature below 0°C, for example a temperature of the order of -10°C after which the intense freezing of both sides of the skin can be achieved without the risk of producing any fissures.

A treatment installation for animal skins is equally an objective of the invention. This is of a type which comprises a tunnel with a thermal insulating partition, and incorporating a conveyor belt for the skins which is permeable to gases, characterised by devices for gas stirring in the upstream section which is adjacent to the inlet, and in the downstream section which is adjacent to the 30 outlet, bv means of atomising and spraying liquid nitrogen upwards, located below the conveyor belt, and by devices for producing a droplet spray of liquid nitrogen located above the conveyor belt.

The characteristics and advantages of the invention will.moreover become clear in the description which follows by way 35 of example, with reference to the attached drawing of which the soT&';~ - -figure is a schematic longitudinal cross section view of an E installation according to the invention. //*, \28jUM99oH 2 - i ; u With reference to the drawing a treatment installation for skins comprises a tunnel 1 with a thermal insulation partition 2 with a vault 3 and a floor 4, showing an inlet 5 and an outlet 6. In the interior of the tunnel 1 a conveyor belt 8 is installed which is permeable to gas and resistant to low temperatures, with two guide rollers 9 and 10, forming two belt sheets 8a and 8b_, the inlet 5 being equipped with a gas collector 12 with an exhaust 13.

An upstream section 15 of the tunnel 1 adjacent to the inlet has a low vault 3a while a downstream section 16 adjacent to the outlet 6 has a high vault 3b. Preferably, the downstream section 16 has the vault 3b at a distance from the conveyor belt 8 which is less than the distance of the floor 4 from the conveyor belt 8.

In the section 15 a low vault 3a_ is arranged, below the lower return sheet 3h^ of the conveyor belt 8, a horizontal array of stirrers 17 (four in the drawing) of which the vertically oriented axes are moved by the motors IS.

In the downstream section 16, there is on the one hand an array of ramps for spraying fine droplets of liquid nitrogen 21 throwing the droplets upwards in the direction of the belt 8 in a low position, while on the other hand and in a high position there are the screens 22 for the purpose of producing a rain of liquid nitrogen droplets.

On the floor 4 of the tunnel 1 there are recovery vessels 23 in the downstream section 16 and extending beyond this into the upstream section 15, approximately under half the stirring devices 17.

The installation operates as follows: On starting up it is convenient to first cool down, and for this purpose the liquid nitrogen is fed at the same time to the sprays 21 and the atomising screens 22, which causes a considerable lowering - • of the temperature in the downstream section and the cooling of the /• i conveyor belt 8. Simultaneously the cold nitrogen gas originating * from the evaporation of the liquid nitrogen is directed, thanks to the effect of the exhaust 13, upstream in counter current to the | movement of the conveyor belt S. This nitrogen gas, as well as the V.--nitrogen 'which is evaporating, deriving from the recovery of the liquiJkT^V S nitrogen in the vessels 23 is taken up by the stirring devices' 17 producing thereby turbulent movement.

Once the tunnel is cold the skins 30 are successively introduced on the top sheet 8a_ of the conveyor belt 8, the skin being positioned in such a manner that the leather side 31 faces sheet 8a of 3 r?4i3 the belt 8, and conversely the wool or hair surface 32 faces upwards.

In a first section 15a of the upstream section 15 the skins 30 start to be subjected to a pre-cooling bv taking up the sensible heat of the nitrogen gas which has previously been evaporated in the 5 downstream section 16 and has been partially reheated in the second section 15b_ of section 15 where the cryogenic action of the evaporated nitrogen is assisted by an additional evaporation of liquid nitrogen flowing from downstream to upstream in the recovery vessels 23. It should be noted that this first cooling essentially takes place on 10 the leather surface which gradually cools down to a temperature below 0°C where the cooling can be superficial or total depending on the thickness and the material (greater or lesser flexibility) of the leather of the skin.

In the second section 15b_ cooling is also produced by forced 15 convection from the stirring devices 17 but this occurs with help of the nitrogen gas originating from the downstream section 16 which has not yet been reheated, and above all by means of the effect of evaporation of the liquid nitrogen present at this level in the recovery vessels 23. At this level the temperature ctf the skins again 2i"' drops progressively.

A direct double cooling of the skins, therefore takes place in section 16 of the tunnel 1. - on the one hand by atomisation of liquid nitrogen below the skin on the leather side, the liquid nitrogen passing across the J" conveyor belt 8. - on the other hand by sprinkling liquid nitrogen, in the"-form of droplets of about 1 mm diameter, which penetrate directly into the thick pad of wool where evaporation takes place under good Sft. ; conditions because of the very large heat exchange surface presented/ in bv the wool. :i - q -i 3v adjusting the quantities of liquid nitrogen deposited ip--. the wool, .and atomised underneath the leather, the final temperature,. '; for achieving wool removal, is controlled. At the outlet of the tunnel wool removal can take sufficiently long so that the skins reheat (even slightly) and wool removal will no longer be possible. According to a preferred mode of execution of the invention an excess quantity of liquid nitrogen is poured into the wool which, by continuing to i ••• U 2 3 4 1 3 evaporate during the wool removal stage itself, ensures that a sufficiently low temperature is maintained.

Claims (10)

WHAT WE CLAIM IS:

1 . Process of treatment of an animal skin with a view of separating the leather from its surface coating of wool or hair, in which a stiffening of the skin by freezing is produced before proceeding to the separation, characterised by the fact that the stiffening by freezing is produced in a final intense freezing stage with liquid nitrogen which is brought into contact with the skin simultaneously on the leather side and the surface coating, preceded by a pre-cooling stage in which the skin is progressively cooled to below 0°C by applying to the leather side cold nitrogen gas obtained by evaporation of the liquid nitrogen applied in the final intense freezing stage.

2. Process of treatment of an animal skin according to claim 1, characterised by the fact that the skin is stretched out substantially in the horizontal plane, with the leather side facing downwards, the final intense freezing is brought about by spraying liquid nitrogen, atomised into fine droplets, upwards onto the leather side, and by a spray of large drops of liquid nitrogen flowing by gravity across a receiving screen for liquid nitrogen onto the surface coating.

3. Process according to claim 1 or 2, characterised by the fact that the quantity of liquid nitrogen poured as a spray onto the surface coating is sufficient so that the liquid nitrogen remains present in the coating substantially till the end of the operation of separation.

4. Process of treatment of an animal skin according to any one of claims 1 to 3, characterised by the fact that the progressive pre-cooling with cold nitrogen gas is obtained by stirring of evaporated nitrogen m the confined section adjacent to the leather side of the animal skin.

5. Installation for the treatment of animal skins, comprising a tunnel with a thermal insulation partition, incorporating a conveyor belt for skins, which is permeable to gas, characterised by gas stirring devices in an upstream section adjacent to the inlet, and, in a downstream section, adjacent to the outlet, atomising and upward spraying devices for liquid nitrogen located below the conveyor belt,/ and devices for generating a spray of liquid nitrogen droplets located above the conveyor belt.

6. Installation for the treatment of animal skins, according.to claim 5, characterised by the fact that the downstream section of the tunnel has a tunnel vault at a distance from the conveyor belt which is less than the distance of the tunnel floor from the conveyor belt. 234138

7. Installation fcr the treatment cf animal skins according to claim 5 or 6, characterised by recovery vessels for liquid nitrogen in the whole downstream section and the recovery vessels extend into the upstream section below the stirring devices.

8. A process according to claim 1 and substantially as herein described with reference to any embodiment disclosed.

9. An animal skin when treated by the process of any one of claims 1 to 4 and 8.

10. An installation for the treatment of animal skins substantially as herein described with reference to the accompanying drawing. / 7