Note: Descriptions are shown in the official language in which they were submitted.
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Process for finishing animal hides or pelts
The invention relates to a process for finishing animal hides
or pelts. Animal hides and pelts are required in many areas of
daily life and also for industrial applications. Examples are
the clothing industry, medical articles, furniture industry,
automotive accessories, cleaning materials. The processing of
pelts and hides is a significant economic factor in
industrialized countries and in agrarian countries.
The hides or pelts have to be finished in accordance with the
various end uses. The principal aims of finishing are to
establish durability and to generate the desired morphological
(e.g. handle, tear strength, suppleness, water resistance) and
color properties.
The text below describes by way of example the customary
processing and finishing of pelts or skins, which corresponds
in large areas with the processing and finishing of leathers
and hides. The main function of the various pelt or hide
treatment steps is to reach a state of swelling of the skin
pores and of the hairs, in which state penetration of tanning
chemicals and thus the crosslinking and strengthening of the
collagen chains is possible. Unlike the preparation of leather,
where an unhairing step is required, pelt processing requires
unconditionally that the coat of hair is maintained. To aid
comprehension, the individual steps of conventional pelt or
skin finishing, which are detailed below, are reproduced at the
end of the description in the form of a flow diagram.
The pelts removed are usually not processed fresh but are
preserved by drying, salting or deep-freezing. The first
processing step in the finishing of skins, therefore, is a
soak, by means of which the pelts are prepared for subsequent
treatment. The soak is usually conducted with cold water to
which a certain amount of surfactants have been added. The
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soaking period is from 8 to 24 hours. The mass ratio between
the solution, in this case the soak solution, and the pelts,
which is referred to below as the liquor ratio, is between 6
and 12:1. After the end of the soak, the liquid discharged from
the soak tub together with the pelts is removed by centrifuging
and obtained together with the remaining soak solution as waste
water. The pelts are sorted and subjected to various mechanical
processing steps (turning, cutting, drawing).
In the next process step the pelts are washed. This usually
takes place with a warmed (25 - 35 C) water/surfactant solution
to which small amounts of salt have been added. The added salt
and the elevated temperature produces slight swelling of the
pores and of the keratin structure of the hair. The soaking
period and the liquor ratio are identical to those for the
soak. After the end of the wash, the pelts are again
centrifuged and mechanically processed. The wash solution is
obtained as waste water.
In a further bath, the pelts are "opened up". For this purpose
the pelts are treated in an aqueous solution the pH of which
has been set to 3.8 to 4. For this purpose, in most cases
organic acids are employed. To avoid hairslip the so-called
"pickling solution" used for opening up must have relatively
large amounts of salt added to it in order to attenuate the
effect of the acid. The aim of opening up is to widen the pores
- and the hair structure for subsequent tanning in order to
enable the tanning solution to penetrate. Here too, the liquor
ratios are from 6 to 12:1. The soaking periods are usually
substantially longer than in the case of the preceding baths
and are in the range from 12 to 48 hours. In the case of the
preparation of leather, the hides are unhaired at this point,
which is achieved by altering the pH and the salt concentration
in contrast to the dressing of skins. The opening-up solution
or, respectively, the unhairing solution is obtained as waste
water and must if appropriate be filtered and neutralized
before being introduced into the waste-water system.
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In the next processing step, tanning, the pelts are treated
with a buffered solution of tanning chemicals in water. As a
result of tanning, the peptide chains of the collagen are
crosslinked, strengthened and isolated from one another. In
this context, a very wide variety of tanning agents can be
employed. Plant-based tanning agents, synthetic organic tanning
agents and inorganic tanning agents are known. In the pelt
industry use is frequently made, owing to their comparatively
weak tanning action, of aluminum salts (e.g. potassium aluminum
alum * 10H20) as tanning agents, whereas in the preparation of
leather it is common to use chromium(III) salts, aromatic
syntans, enzymes or vegetable tanning agents or tanning-agent
extracts, alone or in mixtures. In the case of pelt processing
the tanning solutions are set to a pH of from 3.8 to 4. In
order to avoid acid swelling of the hides and hairslip, salt is
added to the tanning solutions. Tanning usually takes place in
tanning drums which rotate about the longitudinal axis.
However, dip-tanning or brush-tanning is also carried out. The
tanning periods are from 24 to 48 hours, while the liquor
ratios are from 6 to 12:1.
In addition to the actual aims of tanning, namely to prepare
for dyeing and to obtain water resistance and durability,
attempts are also made in the tanning process to obtain
additional properties of leather or skins. Thus, certain color
effects can be obtained even in the course of tanning.
Furthermore, the processed pelts are often fatliquored in the
tanning bath in order to obtain a particularly supple pelt with
a good handle. For this purpose, so-called leather oils or fats
are added to the tanning solution. These substances are usually
obtained from fats of land or marine animals or else from
vegetable sources. Since these fats and oils are usually
insoluble in water, emulsifiers are added to the tanning
solutions. However, problems frequently occur because the fat
uptake cannot be regulated with any great precision and because
not all fats (e.g. drumming fats, see below) can be emulsified
in sufficient quantity in the tanning solution.
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In a similar way as with the preceding baths, a considerable
amount of waste water is obtained in the case of tanning as
well. Especially when chromium salts, synthetic organic tanning
agents and tanning agents of plant origin are used, the waste
water is polluted with ecologically objectionable and/or poorly
degradable substances.
Where leathers rather than pelts are being dressed, the
finishing process is over at this point except for any dyeing
and relatively small post-processing steps which may be carried
out. The individual steps which are now described, therefore,
essentially apply only to the finishing of pelts or skins.
Tanning is followed by mechanical and thermal processing steps
(centrifuging, drying, cutting, drawing). Pelts in particular
are subsequently cleaned by means of sawdusting, by treating
them with sawdust in so-called clearing drums. In the course of
sawdusting, excess fatliquor is adsorbed and the hairs are
raised in order to give the pelt more volume.
In the processing of pelts, owing to the above-mentioned
problems with the fatliquors or leather oils, a subsequent
fatliquoring operation, so-called drum greasing is required. In
this operation, drumming grease is drummed or milled into the
pelts in wooden drums with the aid of wooden hammer mechanisms.
Relative to the weight of pelt introduced, about 20% drumming
grease is added which is incorporated over the course of 30 to
120 minutes. Greasing is followed first by a further cleaning
step with sawdust. Here, a small amount of the excess fat is
adsorbed. The majority of the excess drumming grease is removed
in a subsequent degreasing bath. Here, the pelts are removed in
a washing machine either with chlorinated hydrocarbons
(nonflammable) or, in the case of appropriate statutory
provisions, with substitutes. In this context there has been
use in recent times in particular of petroleum fractions, e.g.
high-boiling distillates (Tb.p. = 180 - 190 C, flammable). The
wash liquids are distilled and cleaned atmospherically (CHC) or
under vacuum (high boilers). The bottom residue (hide residues,
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hair, long-chain fats, sometimes water, albumen etc.) must be
disposed of as special waste.
After degreasing, the pelts are spun and dried and may be
subjected to mechanical post-processing. After a further
sawdusting process to deodorize the pelts and to produce a more
bulky appearance, a final check is carried out in the course of
which the pelts are mechanically processed once more and
possibly ground (buffed).
With the process described above, furs or leathers are obtained
which can be used without further aftertreatment. In many
cases, however, colored products are desired. The process steps
required for dyeing are not dealt with here since they are not
relevant in connection with the present invention.
As is readily evident from the above description of the
conventional dressing of skins, the process is highly labor
intensive, and even nowadays is still carried out largely by
hand. Including the intermediate steps, some of which have not
been described in detail, complete skin finishing requires up
to 70 operations, in which the hides or pelts are treated with
in some cases considerable amounts of chemicals. Since these
chemicals are almost always used in dilute aqueous solutions,
considerable amounts of waste water are obtained in the
finishing of leather or skins. It is nowadays common to have
, from about 20 to 40 t of waste water per tonne of finished
pelt. About 4 of this amount is waste water with a
comparatively low level of pollution, which comprises
essentially salt, surfactants and, in small amounts, organic
biodegradable acids or inorganic acids. About 1/4 of the amount
of the waste water, however, includes metal cations and/or
organic tanning agents. At best the cations involved here are
aluminum or iron cations. Chromium salts are frequently used,
especially in the preparation of leather. The organic tanning
agents usually are compounds which contain a large number of
fused aromatic rings and are therefore of poor
biodegradability.
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In addition, from 200 to 300 kg of degreasing agent are
required per tonne of pelt. These agents are halogenated
hydrocarbons or petroleum fractions. The degreasing agents can
be recovered by means of distillation. In this case the bottom
product obtained is a sludge which has to be disposed of as
special waste and which comprises, in addition to residues of
the degreasing agent, also fats, albumens and solid particles.
From about 100 to 300 kg of the sludge for disposal are
obtained per tonne of pelt.
Further consumables are sawdust or cornflour, which are
employed in the various cleaning steps. From about 1500 to 2000
kg of sawdust or flour are obtained per tonne of pelt, about
75% of which has to be disposed of as special waste owing to
pollution with tanning agents, solvent residues and salts in
the case of corresponding statutory regulations.
The situation depicted (manual labor-intensive and thus
expensive production, considerable environmental pollution,
expensive disposal) has led to a sharp drop in the processing
of leather and skins in the industrialized countries for some
years.
WO 94/08054 discloses a process for treating tanned or untanned
leather in which the leather is brought into contact with a
dense pressurized fluid, preferably supercritical or liquid
C02, in order to remove fat from the leather or to impregnate
the leather with certain substances. The process employs
exclusively the dense fluid as solvent, and the pressure
established during the treatment is always above the critical
pressure of the fluid that is used.
US 5 326 377 discloses a process for treating hides in which
the hides are first of all delimed, then soaked and
subsequently washed one or more times in a washing drum with a
slightly acidic washing solution which comprises carbon
dioxide. The carbon dioxide is fed into the washing drum, which
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is not under pressure, either by adding it directly to the
liquid in the washing drum or supplying it above the level of
the liquid, the carbon dioxide flowing continually through the
washing drum in a certain quantity during the treatment of
hides. After the washing operation described, the hides are
tanned.
EP 0 624 654 A2 discloses a process for preparing leather from
animal hides, in which the leather is delimed in an aqueous
solution with the aid of C02 under gentle pressure.
EP 0 439 108 Al discloses a leather treatment process which
employs C02 as deliming agent. In order to shorten the
treatment period required for deliming, this document proposes
that the stream of carbon dioxide which is passed through the
treatment vessel is raised at least once during the period of
treatment.
The object of the invention is to indicate a process for
finishing animal hides or pelts which is less labor-intensive
and which permits considerably more rapid dressing of hides or
pelts together with a significantly reduced use of chemicals,
thereby reducing at the same time the environmental pollution.
This object is achieved in accordance with the invention by a
process for finishing animal hides or pelts in which the animal
hides or pelts, following a conventionally conducted soak, are
treated with a conventional tanning solution in which carbon
dioxide has been dissolved under pressure. In this way, by
means of the process according to the invention, various of the
conventional baths and/or treatment steps can be combined into
a single treatment step, thereby significantly reducing the
overall processing time required for preparing the pelt or
leather.
The above-mentioned drastic reduction in treatment times is
attributed to the fact that the penetration and the resorption
or the reaction of the bath chemicals (surfactants, salts,
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fats, tanning chemicals) in the skin structure is considerably
accelerated by the presence of carbon dioxide. However, this
accelerating effect is only achieved if the hides or pelts to
be treated are at least wet. In accordance with the invention,
therefore, it is sufficient if the pelts or hides to be treated
are just dipped into the corresponding treatment solution and
then subsequently placed in a pressure vessel in which they are
subjected to carbon dioxide pressure. Alternatively, it is
possible for the pelts or hides that are to be treated to be
left immersed in the corresponding treatment solution and to
subject the vessel containing the hides or pelts and the
treatment solution to carbon dioxide pressure. In this case,
the vessel can be filled completely with the treatment solution
or there may be a carbon dioxide atmosphere over the aqueous
treatment solution. All that is essential for the process
according to the invention is that carbon dioxide has been
dissolved under pressure in the respective aqueous treatment
solution. This treatment solution can be a conventional soak
solution, tanning solution or a combination of the above-
mentioned solutions. Conventional soak solutions comprise a
mixture of anionic, cationic or nonionic surfactants and salt,
especially rock salt or common salt. Conventional tanning
solutions comprise a mixture of vegetable tanning agents or
tanning extracts (wattle), organic tanning agents, inorganic
tanning agents, anionic, cationic or nonionic surfactants,
leather oils and fatliquors based on plant or animal
substances, organic or inorganic acids and salt, especially
rock salt or common salt.
According to one embodiment of the process according to the
invention, soaked pelts are placed in the autoclave. Washing
and opening up are unnecessary. Tanning solution is introduced
until the pelts are covered. Then carbon dioxide is introduced
up to a pressure of between 5 and 300 bar, preferably from 10
to 200 bar and, with particular preference, from 15 to 50 bar.
At a temperature between 20 and 50 C, preferably from 25 to
C, the pelts or hides are tanned for from 30 to 300 minutes,
preferably from 45 to 180 minutes. After the autoclave has been
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let down the pelts or hides are removed and are processed
further in conventional manner or as described below. The
qualities obtained with this procedure correspond to those of
conventional processing.
A modification of the above-described exemplary embodiment is
to treat soaked and washed pelts or hides in tanning solution
under a carbon dioxide atmosphere. For this purpose the pelts
are soaked with soak solution (cold water, surfactants, a
little salt) and after the customary mechanical intermediate
steps are washed (warm water, surfactants, higher salt
concentration). The pelts thus pretreated are placed in an
autoclave. They can be introduced in a disordered form. In this
case, a roller autoclave must be employed for complete tanning.
Alternatively, they can be introduced on appropriate suspension
devices. In this case, fixed autoclaves can be employed. The
autoclaves are charged with sufficient tanning solution to just
cover the pelts or hides. After the introduction of carbon
dioxide with a pressure of between 5 and 300 bar, preferably
from 10 to 200 bar and, in particular, from 15 to 50 bar, the
pelts or hides are treated at a temperature between 20 and
50 C, preferably from 25 to 45 C, for from 30 to 300 minutes,
preferably from 45 to 180 minutes. Use is made of customary
tanning solutions whose principal ingredients, depending on the
intended application, are metal salts, tanning agents, tanning
extracts, enzymes, acids, buffers, salt, leather oil/fatliquor/
fat, surfactants/emulsifiers. Intensive contact between the
tanning solution and the material to be tanned can be brought
about by revolving the gas phase and/or liquid phase by means
of installed stirring elements or by means of external
circulation-promoting elements. After the end of the treatment
period, the contents of the autoclave are let down and the
carbon dioxide may, if appropriate, be recovered in whole or in
part. The pelts or hides are subsequently subjected to further
conventional processing (mechanical processing, drum greasing,
degreasing, cleaning [sawdusting]).
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To supplement this, in accordance with a further exemplary
embodiment of the process according to the invention, the
greasing of the pelts can be integrated into the tanning
process. This is done by using a special fat formulation which
is emulsified in aqueous phase with appropriate surfactants and
whose penetration into the hide structure is accelerated by
carbon dioxide. In this case it is necessary to increase the
treatment times to about 3 to 20 hours, preferably from 4 to 12
hours. The pressures and temperatures are within the above-
mentioned range (see previous paragraph). In this exemplary
embodiment, only a milling or drumming process (without the
addition of fat) and also cleaning steps and mechanical
operations are required for the subsequent further treatment of
the pelts or hides. Degreasing and the associated use of
hydrocarbons, halogenated hydrocarbons or other fat-dissolving
agents can be omitted.
Another possibility for the integrated greasing of the pelts or
hides is, following the tanning carried out under the action of
carbon dioxide, first to dry the pelts or hides and then to
grease them with the aid of carbon dioxide. In this case the
preferred apparatus is a vertical autoclave into which the
pelts or hides are introduced on an appropriate suspension
device. After the end of tanning the pelts/hides are either
dried thermally in the autoclave or else the suspension device
is removed together with the pelts or hides and drying is
- carried out in a separate drying cabinet. Post-greasing takes
place subsequently. For this purpose, the fatliquor formulation
is charged to an initial-charge autoclave. Carbon dioxide is
passed through the initial-charge autoclave. The pressure and
temperature are set such that the fat is dissolved in the
carbon dioxide. Typical conditions are from 100 bar to 350 bar
and from 40 to 80 C. The fat-laden carbon dioxide is introduced
into the autoclave, which has been charged with pelts. In this
autoc.lave the pressure and temperature are set such that the
solubility of the fats in carbon dioxide is reduced. Typical
pressures and temperatures are from 40 to 200 bar and from 25
to 50 C. The fat then precipitates preferentially on the pelts
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or hides which are present in the autoclave and in the hide
pores which have been penetrated by carbon dioxide. After the
end of greasing, the pelts or hides are removed. The excess fat
on the surface and on the hairs (in the case of pelts) is
worked in during the subsequent drumming process or removed in
cleaning processes. Degreasing by means of CHC, HC or other
fat-dissolving agents is not necessary.
Yet another exemplary embodiment of the process according to
the invention is characterized by the leading of the pelts and
of the tanning solution in countercurrent. The principle of the
process is explained with reference to a unit consisting of two
autoclaves. However, the process can also be employed in a unit
having only one autoclave and corresponding storage vessels, or
else in a multi-autoclave unit. Fresh, soaked pelts are placed
in an autoclave 1. In an autoclave 2, partially tanned pelts
are treated with fresh tanning solution. During this treatment,
the concentration of active substance in the tanning solution
is reduced, the partially tanned pelts or hides are tanned
completely, and are removed after the autoclave 2 has been let
down. The partially spent tanning solution withdrawn from the
autoclave 2 is added to the fresh pelts or hides in the
autoclave 1, where these pelts or hides are part-tanned, while
at the same time the concentration of active substance in the
tanning solution is reduced further. The resulting exhausted
tanning solution is obtained as waste water. For complete
- tanning of the pelts or hides, fresh tanning solution is then
added to the autoclave 1. In the intervening period, the
autoclave 2 is charged with fresh pelts or hides which are then
part-tanned using the partially spent tanning solution from the
autoclave 1. The advantage of this procedure is that the
concentration of tanning chemicals in the waste water is very
greatly reduced. This is particularly important since the
tanning chemicals are the most difficult waste substances to
degrade in the processing of pelts and hides.
The text below indicates a number of experimental examples of
the process according to the invention.
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Example 1:
A mink pelt treated in a soak bath (7 g/1 surfactants, 50 g/1
salt, 25 C, 12 h) and spun was placed in a high-pressure
autoclave (V = 200 ml, PmaX = 1000 bar, Tmax = 500 C) and
treated for 1 hour with liquid carbon dioxide at 200 bar and
25 C with the aim of opening up the skin and thus preparing it
for tanning. The autoclave was let down (10 minutes) and opened
and the pelt was removed. The pelt was then washed (10 g/1
surfactants, 40 g/1 salt, 30 C, 2 h) and opened up (10 g/1
organic acid, 60 g/l salt, pH 3.8 to 4, 30 C, 24 h). The pelt
(female mink) was then dipped briefly (2 minutes) in tanning
solution (40 g/l aluminum salt, Na acetate, pH 3.8 to 4.5, 3
g/1 synthetic surfactants, 15 g/l fatliquors). The ratio
between liquid absorbed and pelt weight (which corresponds to
the liquor ratio) was determined by weighing. The ratio was in
this case 1.3:1. The pelt prepared in this way was placed in an
autoclave having a volume of 600 ml and was treated for 3 hours
with carbon dioxide at 200 bar and 40 C. After letting down the
autoclave, the pelt was removed and subjected to conventional
further processing (see Example 1 [sic]). The pelt was
classified as very good in terms of the customary quality
criteria (see Example 1 [sic]). The tanning process, which
usually lasts from 12 to 14 hours and requires liquor ratios
from 6 to 12:1, was therefore replaced by a three-hour
treatment under a carbon dioxide atmosphere. In addition to the
considerable time saving, the treatment with carbon dioxide,
when the dipping technique is employed, reduces the amount of
tanning solution required by from 78 to 92%.
Example 2:
3 fox pelts, 5 mink pelts (male) and 1 muskrat pelt were placed
in an unordered pile in an 8 liter autoclave. The total volume
of the pelts was 5.9 liters. Above the pelts there was an empty
space of 10 cm. The pelts had been soaked (see Example 1) and
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pretreated for just a few minutes in an acid opening-up bath
(see Example 1). Installed at the bottom end of the autoclave
was a sinter plate (d = 139.8 mm, H = 3 mm, 200 m) in order to
prevent the entrainment of hairs. Tanning solution (4 liters,
composition see Example 1) was introduced until the pelts were
completely covered. The autoclave was closed and C02 was pumped
in up to 200 bar. After the first pressure buildup the tanning
solution was circulated using a liquid pump having a capacity
of about 6 liters/h and was sprinkled by way of a distributor
at the head of the autoclave. During the runup process (about
30 minutes) carbon dioxide dissolved in the liquid. In order to
compensate the pressure loss which this entailed, it was
necessary to pump in further C02 at intervals of 10 minutes.
Subsequently, tanning was carried out under constant pressure
for 2.5 h. The total contact time of the pelts with tanning
solution was 3 h. After the end of tanning, the tanning
solution was drained off at the bottom.
An initial test of the pelts showed that some pelts were tanned
completely while others had a few relatively small untanned
areas. This is attributed to inadequate distribution of liquid
and to piling problems (e.g. twisted pelts). The pelts were
subjected to conventional further processing. The quality of
the fully tanned pelts was classified as very good, whereas the-
pelts having obviously untanned areas were discarded.
Example 3:
The experiment described in Example 2 was repeated under
identical conditions. However, the pelts were introduced into
the autoclave in a form in which they were fixed on a
suspension device, in such a way that the head and tail end
hung on a ring attached to the autoclave lid and the pelts
therefore had a U shape. Above the ring there remained a gas
space of 10 cm in height. The autoclave was filled with tanning
solution to a point such that the pelts were completely
covered. The total tanning time was likewise 3 hours.
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Afterwards, the pelts were completely tanned. Following
conventional further treatment their quality was classified as
very good.
Example 4:
The experiment described in Example 3 was repeated in a roller
autoclave. The autoclave was placed on a motorized roller
device and during the experiment was moved at a rate of
circulation of 2 revolutions per minute. As a result of this,
the 9 pelts (see Example 2) introduced into the autoclave were
brought into intensive contact with the tanning solution. In
analogy to Example 3, the pelt quality obtained was classified
as very good.
Example 5:
A multistage tanning was conducted in two autoclaves connected
in series. The experiment shows that this procedure achieves a
considerable reduction in the concentration of tanning
chemicals in the waste water. The pelts employed had been
soaked (see Example 1) and washed (see Example 1). No opening
up was carried out.
, In the autoclave 1, 9 mink pelts (7 female, 2 male), 9 muskrat
pelts and 2 bassarisks were treated with fresh tanning solution
(composition see Example 2). The pelts were introduced on the
suspension device described in Example 3. The carbon dioxide
pressure was 50 bar. The tanning solution was sprinkled over
the pelts for 3 hours using a circulating pump having a
capacity of about 6 liters/h. The temperature was 40 C. The
tanning solution was subsequently transferred to the autoclave
2, into which a total of 18 muskrat pelts had been introduced.
The tanned pelts from autoclave 1 were removed and subjected to
conventional further processing. The pelt quality was
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classified as very good. 1 mink pelt (male) was analyzed. The
analytical values were as follows:
pH : 4.2
Difference number : 0.4
A1203 content : 1.3%
Dichloromethane extractables : 6.7% (= fat content)
Puncture resistance without hair : 29.2 N/mm
Tearing propagation resistance
without hair : 7.4 N/mm
Tensile strength without hair : 33.1 N/mm2
Shrinkage temperature in
distilled water : 54 C
Shrinkage temperature in
salt solution : 78 C
In autoclave 2, the partially spent tanning solution was
sprinkled over the pelts under a carbon dioxide pressure of 50
bar and at a temperature of 40 C for 3 hours. After the end of
the experiment the tanning solution was drained off. The
tanning solution was virtually water-clear. The residual
aluminum content was about 50 mg/l, i.e. the tanning solution
was almost completely exhausted.
Then fresh tanning solution was pumped into the autoclave 2 and
was sprinkled over the partially tanned pelts under a carbon
dioxide pressure of 50 bar and at a temperature of 40 C for 1.5
hours. After the end of the experiment the partially spent
tanning solution was drained off and was available for a
further tanning step in autoclave 1. The pelts remaining in the
autoclave 2, which were now fully tanned, were removed and
subjected to conventional (see Example 1) further processing.
The quality was classified as being good to very good.
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Example 6:
Two soaked (soak bath see Example 1) mink pelts (male) were
treated in a roller autoclave at 100 bar C02 pressure for 2
hours with addition of an increased amount of fatliquor and an
emulsifier (fatliquor + emulsifier: 200 g/1). The roller
autoclave was filled with enough solution to just cover the
pelts. The temperature was 35 C. After the end of the
experiment the pelts were removed and first of all were freed
mechanically from excess fat. The pelts were subsequently
dried, cleared with sawdust and drummed. After drumming, the
pelts were cut thin and finally drummed in cornflour. The
quality of the pelts was classified in accordance with the
customary criteria as being good to very good. With this
embodiment of the process, therefore, it is possible to save as
well on process steps required after tanning. Solvent wastes
from degreasing can in this way be avoided or reduced.
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Individual steps in skin processing
Hide stripping
Preservation
Drying/salting/
deep-freezing
Soaking
Water/surfactants, 15 - 25 C
8 - 24 h, LR = 6 - 12:1
Centrifuging
Mechanical processing
turning, cutting, drawing
Sorting
Washing
Water/surfactants (1 - 5 g/l)/salt
25 - 35 C, 2 h, LR = 6 12:1
Centrifuging
Mechanical processing
Cutting, drawing
Skin opening (pickling)
Water/acid (1 - 10 g/l,pH 3.8 - 4)/salt (40 - 80 g/1)
20 - 30 C, 12 - 48 h, LR =
Centrifuging
Mechanical processing
cutting, drawing
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Tanning
Water/aluminum salts (20 - 50 g/l)/salt/Na acetate (3,8-4)
Fatliquors
30 - 40 C, 24 h, LR - 6 - 12:1 or
dip or brush tanning
Centrifuging
Drying, mechanical
processing
cut-ting, drawing
Sawdusting
Beech sawdust (moist)
Fatliquoring or drum greasing
20% fat based on pelt weight
30 - 35 C, 0.5 - 2 h
Sawdusting
Deciduous wood sawdust
(moist/dry)
Degreasing
Trichloroethylene, per, benzine
SC ~ .
Drying, mechanical
post-processing
1 - 2-fold sawdusting, agitation
Deciduous wood sawdust (moist/dry)/organic solvent (tetra)
Mechanical post-processing
Buffing
