CS237460B1 - Process for leaching of tanner raw-materials - Google Patents

Description

The invention relates to a method for leaching a tanning raw material.

As is well known, two processes take place during the leaching of the skin, namely the peeling and swelling of the clearing associated with its loosening. In the conventional leaching process, both of these operations are carried out simultaneously, although their effects contradict each other. It happens that the hair, before the sulphide effect is sufficiently agitated to remove it from the cheek, is closed by the swelling stick in the hair pouch, and is practically not removed during leaching. This proportion of hair is then usually found in the finished leather, where its hardness acts as a destructive element when straining the leather.

Also, the mechanical movement required to remove the hair adversely affects the fibrous structure of the skin, which is increasingly stressed, causing it to disrupt, which is manifested by uneven swelling, often accompanied by a contraction of the cheek, deteriorating the appearance of the finished leather. Because the presence of degraded hair by its presence undermines the standardization of the ongoing process, some of it varies depending on the type of raw material and the time of the year in which the cattle were slaughtered. again in uneven swelling. This changes the physical properties that characterize the clearing very well in terms of leaching and, moreover, show its readiness for subsequent operations; these changes can often negatively affect the physical properties of the finished leather.

In particular, in order to overcome these drawbacks, a method for leaching a tanning raw material has been developed, the subject matter of which is to treat the skins after an elbow in two separate baths, namely a peeling bath containing 1 to 3 weight percent sodium sulfide or 5% by weight of sodium sulfide, together with 0.01 to 1.8% by weight of calcium hydroxide, and a calcium bath containing 1.5 to 5% by weight of calcium hydroxide, optionally in combination with 0.01 to 1% by weight of sodium hydroxide, after which the skins are always washed separately and all waste water, ie liming. peeling, peeling and liming washes are collected separately into containers.

The technical effect of the process according to the invention is that the split baths are more peeling and the lime gives a more uniform alkaline swelling, which results in a cleared soil with improved properties. This in turn affects the more favorable course of further leather manufacturing operations and improves the physical and subjectively evaluated properties of the leather.

A further, very important factor is that the waste water from both operations as well as the wash water after these operations can be used as effective baths for further cycles of the leaching process and partly also for raw skin infiltration after accumulation. This is a significant environmental benefit, not only reducing the overall consumption of fresh water, but. also significant progress in waste water purity.

The process according to the invention is carried out in such a way that the operation is divided into separate peeling and separate liming. In the first operation with optimally selected concentrations of sulfides in the range of 1 to 3 weight percent of sodium sulfide or 1 to 5 weight percent of sodium sulfide and an alkali of 0.01 to 1.8 weight percent of calcium hydroxide removes hair, leaving the skin swollen so easier. In addition, the peeling can be accelerated by a strong mechanical effect, which at this stage has a positive effect not only on the peeling speed and perfection, but also as a continuation of the shoulder, and thus as a preparation for a more uniform alkaline swelling.

In the second operation, where the scrubbed and washed scrubs are treated with a swelling alkali solution of 1.5 to 5 weight percent calcium hydroxide, optionally in combination with 0.01 to 1 weight percent sodium hydroxide, the desired swelling and loosening occurs. structure. The composition of the solutions is precisely defined within the specified ranges and, moreover, it acts on pure clearwood without disturbing effects of degraded keratin residues from hair. The mechanical movement required for peeling can practically be eliminated at this stage; the bath volume is only mixed several times to homogenize the added chemicals. The consequence of this swelling is then a clearing with much more standard properties. .

In order to illustrate the beneficial properties of the tanning raw material leached by the method according to the invention, a graphical representation of some physical properties of the ground is shown in the attached drawing; Fig. 1 shows the compressibility of the wedge E, the relaxation after compression R and the disintegration coefficient K, while Fig. 2 shows the curves p.roAE and AR in mm. Points from individual measurements (1 to 7) are marked with triangles for K, for R crosses and for E rings, analogously for AE and ZiR; the curves for the method of the invention are shown in bold line and, for comparison, the curves for classical leaching are shown in weak line.

Commentary on the drawing: after leaching, the soil can be characterized by the degree of swelling, which can be measured, for example, by the thickness increase, but especially by its degree of disintegration, which can also be assessed as elasticity, or relaxation and compressibility of the soil. Prb numerical evaluation of these properties is used by measuring the thickness of the meter and the weight / 15 + 285 / g. The wrist E shall be measured by the contact thickness of the wrist (dl) and the thickness after 120 seconds of application of the weight (d 120) according to the formula:

л * dl / mm / - d 120 / mm /

E /% / = ------------------------ 100 dl / mm /

The elasticity of the groundwood R _1, measured as relaxation after compression, is then determined after removal of part of the weight,

285 g, after which the thickness (d 30) is read after 30 seconds. Calculation according to the formula:

d 30 / mm / - d 20 / mm / y /% / = ------------------------- · 100 dl / mm / - d 20 / mm /

The decay coefficient, K, is then calculated from the ratio of the values for R and E, ie

R

K = --E

From the technological point of view, it is possible to evaluate as optimum · a clearing, where the value of compressibility,

E, is about 15%, the R-value is at most 20% and the K-value is about 2. '

In addition, the method according to the invention is explained in more detail by two exemplary embodiments.

He did

The tanner mixer is filled with 5,000 kg of beef / Swedish beef weight class

24-33 kg / pc. And wash and soak operations are performed. After decanting waste námokové bath mixer 'contents ^and 7000 ^{1 dy} in ²⁴ ° C te r ^{e p} and ^added with ^{130 kg and} RN ^Cart with sodium ^p olečn ^{of 15 kg p.o. šk} b ^s caliber it calcium hydroxide. The mixer is allowed to rotate at 5 rpm for 180 minutes while peeling is performed. After completion dehaired waste bath drawn off the pump to Z ^and in Multiples ^{Cart kd Othe} í used ^{to live} and Hohn is ^p ro ^p ERE ^{7000 1 dy} in warm ²⁴ ° C ^{at 4} rpm / ndn. Washing takes 30 minutes. Waste bath of washing after unhairing are also withdrawn by a pump to supply ^to u. Odchlu ^p en ^s and you ^p early sheetings with ^P and ^AP n ^s in a ^bath-conn Raven ^E from · ^{7000 1} in ^d s, 22 ° C warm and 175 kg of powdered calcium hydroxide at 2 rpm for 240 minutes. The mixer is then stopped and left to rest for 10 hours until the next day. In the morning, the waste lime bath is withdrawn into a container for reuse and the soil is washed without bath at 6 rpm for 30 to ⁴⁰ days. At the conclusion ^of r Hohn in ^YP ere about ⁷⁰⁰⁰ liters ^{frictional h} of water te ^p ture of 20 ° ^{C, PR} and 8 rev / ^min at about 30 minutes, wherein the waste bath of washing after liming is drained to the reservoir for re-use . Further, the clearing is processed according to common practice.

AND

Example 2

The tanner mixer is filled with 4,500 kg of weight class domestic beef to 45 kg / pc and washing and draining operations are performed. After pouring the drip bath, the mixer was charged with 6,750 L of water at 24 ° C and added 90 kg of sodium sulfide # 25 kg of calcium hydroxide powder and 6 # 75 kg of pre-dissolved sodium hydroxide. The mixer is allowed to rotate at 4 rpm for 210 minutes while peeling is performed. After the combined peeling, the waste bath is withdrawn for reuse and washed with 7200 liters of water at 24 ° C at 4 rpm for 30 minutes. The washing bath after peeling is withdrawn and reused later. The peeled and washed scrubs are lime in a bath # prepared from 7,200 L of water at 24 ° C warm # of 117 kg of calcium hydroxide powder and 4.5 kg of pre-dissolved sodium hydroxide. The mixer is allowed to rotate for 120 minutes at 2 rpm # and then every hour, 5 minutes after 55 minutes of standing; 12 hours in total. After the liming is complete, the waste bath is withdrawn for further use. The following operations # are the same as Example 1.

Claims (1)

SUBJECT OF THE INVENTION A method of leaching a tanning raw material ########################################################################### with up to 1.8% by weight of calcium hydroxide # and a calcium bath containing 1.5 to 5% by weight of calcium hydroxide, optionally in combination with 0.01 to 1% by weight of sodium hydroxide, after which the skin is always washed separately and all waste water , i.e., liming, scaling, scrubbing, and scouring #, are separately collected in the containers.