Patent Publication Number: US-6910354-B2

Title: Process and an apparatus for processing animal hides

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to a process and an apparatus for treating animal hides. 
   In particular, the invention relates to an industrial process for transforming the fresh hide into wet white state. 
   DESCRIPTION OF THE PRIOR ART 
   As it is known, the term “wet white” indicates animal hide stripped of the hair, flesh and other surface impurities, integral or divided in leather grain and split leather, stabilized definitely, humid or dry and whitish. 
   The last mentioned characteristic makes the “wet white” hides different from the “wet blue” hides, which are obtained by tanning using chemical agents such as chromium giving the characteristic bluish or anyway, not natural, color. 
   For a very long time, the animal hides have been treated with substances which fix to the hides irreversibly. 
   Then, the tanning has become an industrial process, mainly after the chromium treatment had allowed to considerably reduce the process time. 
   Actually, the tanning process usually includes a series of steps, whose execution requires long times. 
   The very tanning is preceded by different preparing treatments, which remove still present impurities and fat and subsequently, hair. 
   The main problem of the animal hides treatment results from the fact that the hide, being of natural origin, is subject to rapid putrefaction, specially in those areas where the climate accelerates the bacterial action, which causes the decomposition thus ruining the hide commercial value. 
   The first treatment of animal hides usually takes place in the fresh hides collecting plant, and sometimes even in the slaughter houses, where the hides are treated with sodium chloride, i.e. common kitchen salt, so as to prevent the decomposition and putrefaction. 
   The treatment of the inner part of the hide, with sodium chloride causes pollution and moreover, it can damage the so-called grain of leather, thus causing a quality decay, if not rejection of the hide, which would result in further problem of disposal. 
   This salting and preserving phase affects a great part of the whole tanning process, which includes a long series of treatments by different systems and substances creating an unhealthy working environment and compromising the environment situation. 
   The salt is used also later, in the so-called “pickling” operation, which determines a better penetration of tanning salts, e.g. chromium salts. 
   The above treatments are usually performed in special drums, with appropriate liquid substances. 
   The drums are big, so as to allow high productivity, since the time of the treatment is long, anyway changing in relation to the characteristics of treated hides. 
   Therefore, a particular problem occurring in the examined field results from the necessity to reduce the environment pollution caused by tanning industry, in particular by industrial discharges. 
   Actually, the substances used for treatments are highly polluting and their remains can be dispersed in the environment only after an appropriate depuration. 
   SUMMARY OF THE INVENTION 
   The object of the present invention is to propose a process which allows to treat animal hides, reducing the environmental impact thereof, and in particular, eliminating the use of chemical substances, thus avoiding the necessity to use any depuration system. 
   Another object of the present invention is to propose a process which reduces working time and production costs, without affecting the product quality. 
   A further object of the present invention is to propose a process which reduces considerably the quantity of the substances used in various -treatments, in particular using a reduced quantity of easily available and widely available substances. 
   A still further object of the present invention is to propose an apparatus, which carries out the above described process, by a simple, practical, and compact structure occupying very limited space. 
   The above mentioned objects are obtained, in accordance with the claims, by a process for treating animal hides including:
         spreading hides to be treated astride respective support plates;   introducing said supporting plates with said hides to be treated into a container, which is them closed hermetically;   setting said container under vacuum;   introducing a liquid treating solution into said container kept under vacuum;   driving said container into vibration, so as to make said treating solution introduced therein move in a constant and uniform way.       

   According to a second embodiment, the process includes:
         spreading hides to be treated astride respective support plates;   introducing said supporting plates with said hides to be treated into a container, which is then closed hermetically;   setting said container under vacuum;   introducing a liquid treating solution into said container kept under vacuum.       

   The process is carried out by an apparatus for processing hides and the like, characterized in that it includes: 
   a series of plates supporting hides to be treated, spread astride said plates; 
   a container, which is closed hermetically, said supporting plates with hides to be treated being introduced into said container; 
   means for setting said hermetically closed container under vacuum; 
   at least one mixing reservoir, fed with water and suitable active principles, so as to obtain a liquid solution for treating said hides, said mixing container being set in communication with said hermetically closed container kept under vacuum, so as to introduce thereinto said liquid solution; 
   a vibrating element for driving said container into vibration, so as to make said liquid solution introduced into said hermetically closed container move in a constant and uniform way. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The characteristic features of the present invention will be pointed out in the following description with reference to the enclosed drawings, in which: 
       FIG. 1  is a schematic prospective view of a table, on which the hides to be treated are prepared; 
       FIG. 2  s a lateral view of a hide placed on a support plate; 
       FIG. 3  is a schematic lateral view of a device for transferring the hides to be treated to a treatment container; 
       FIG. 4  is a lateral view of an enlarged particular of the treatment container, which shows pliers means used in the proposed apparatus; 
       FIG. 5  is a corresponding front view of the above pliers means used in the proposed apparatus; 
       FIG. 6  is a schematic view of the above treatment container and the means connected thereto; 
       FIG. 7  is a schematic view of the whole apparatus for treating animal hides according to the present invention; 
       FIG. 8  is an analogous schematic view of the whole apparatus, according to a different embodiment of the proposed invention. 
   

   BEST MODES OF CARRYING OUT THE INVENTION 
   With reference to the above described figures, reference numeral  1  indicates hides to be treated in the proposed way. 
   The proposed process begins with fresh or refrigerated hides, as generally produced in slaughter houses, and not treated with salt, but specially selected in relation to quality and size types, and stripped of possible parts, which cannot be treated. 
   The hide  1  to be treated is first examined on a preparation table  5 , formed by two surfaces brought close to each other, classified, prepared and then spread astride a support plate  2 , with the grain part turned outward. The head—tail axis is located near the upper edge of the plate  2  (FIG.  1 ). 
   The plate  2 , made of a plastic material, has many holes, which are aimed at receiving hooks  4  for fastening the hide  1 . 
   Actually, the hide  1  is maintained stretched and adhering to the plate  2  by the hooks  4  applied manually to the hides edges (FIG.  2 ). 
   Different lots of hides are weighed and placed on suitably numbered metallic carriages, each of which is equipped with a card containing information about the load. 
   Afterwards, the carriages are moved to a magazine refrigerating chamber, from which they are taken when the treatment is to begin. 
   According to the proposed process, the hides  1  are treated in only one container, indicated with the reference numeral  10 , inside which the hides are folded over the relative plates  2 . 
   The hides are taken out from the container  10  when the cycle is finished and the hides have reached the wet white state. 
   More precisely, the container  10  includes a cylindrical pot  11 , made of metal and featuring a watertight cover, inside which a basin  12  is situated and fixed therein. 
   The basin  12  is made of stainless steel and does not have a cover (see FIG.  6 ). 
   The structure of the outer pot  11  is such that it resists to a negative pressure of −0.9÷−0.975 atmospheres. 
   The pot  11  is coated externally with a heat-insulator, so as to avoid heat dispersion and facilitate inner temperature stability. 
   In fact, the function of the pot  11  is to create a hollow space filled with water around the basin  12 . 
   The plates  2  with the hides  1  are placed inside the basin  12 . 
   A transferring device  3  including a pair of pliers means  30  introduces the plates  2  into seats defined by guiding means  20  fastened inside the basin  12  (FIG.  3 ). 
   As shown in detail in  FIGS. 4 and 5 , the pliers means  30  include respectively a fork  31  featuring a tapered introduction section into which the plate  2  is introduced, and a coupling element  32  operated by a pneumatic actuator  33 , so as to couple with a corresponding hole  22  made in the plate  2 . 
   The guides  20  are fastened to the opposite walls of the basin, so as to form grooves, which receive the plates  2  carrying the hides. 
   The guides  20  are made of stainless steel bars, and their upper ends are suitably tapered to facilitate the plates  2  introduction. 
   The pliers means  30  are moved vertically by a pneumatic piston  34 , carried by a first slide  35 , which is moved by suitable operating means along a second horizontal slide  36  (see again FIG.  3 ). 
   The pliers means  30  are carried by a third slide  37 , which is moved horizontally and perpendicularly to the second horizontal slide  36 , by a corresponding fourth slide  38  fastened to the stem of the piston  34 . 
   Consequently, the transferring device  3  allows to move the pliers means  30  in three orthogonal directions, so as to move them between a taking position  30   a , in which the plates  2  are taken from a carriage  6  and a release position  30   b , in which the plates  2  are released inside the basin  12 . 
   A heating member  21 , e.g. an electric resistor, a thermometer  23  for controlling the temperature and a manostat  24  are situated on the bottom of the pot  11 . 
   A proximity switch  25  for controlling the water level is situated in the upper part of the pot  11 . 
   The pot  11  is connected to a vacuum pump  13 , which creates an environment with a negative pressure aimed at enlarging the hides pores. 
   The environment created by the vacuum pump  13  is not subject to the atmospheric pressure, thus it facilitates the circulation and efficiency of substances which are introduced into the basin  12  during each treatment step. 
   The equipment includes also an electrically operated vibrating element  14 , positioned in such a way as to transmit the vibrating movement to the cylindrical pot  11  and consequently, to the inner basin  12 . 
   The vibration determines a continuous, constant and uniform movement of the solution introduced into the basin, assuring the complete treatment of the outer surface of the hide or its grain. 
   The inner parts of the hide are treated only slightly, as protected by the supporting plate  2 , to which the hide adheres. 
   The water is fed to the container  10  from a tank  7  by a pipe  8 , along which a pump  9  is situated. 
   The basin  12  has squared cross-section, which matches with the known shape of the half-piece of hide. The bottom of the basin is inclined. 
   The basin  12  is connected, by a unique stainless steel pipe  26  passing through the cylindrical pot  11 , to mixing reservoirs  40 ,  50  and to decantation reservoirs  60  and to liquid collection reservoirs  70 , in which the liquids are collected at the end of the cycle (FIG.  7 ). 
   It is to be pointed out that the above reservoirs can advantageously have same volume as the basin  12 . 
   An outlet connector is connected to the lower part of the sloping bottom of the basin  12  and is joined to a pipe, which sucks the liquid and solid remains, when the cycle is completed. The sucked remains are conveyed to the decantation reservoirs  60 , if the remaining water is to be reused, or to the collection reservoirs  70 , if the remaining water is to be treated by boiling. 
   More precisely, the mixing reservoir  40  mixes water, sodium hydroxide i.e. caustic soda, and hydrogen dioxide. 
   The hydrogen dioxide and the caustic soda are taken from respective tanks  41 ,  42  connected to the mixing reservoir  40  by a pipe  43  equipped with a liquid meter  44 . Also a water supply pipe  46  is connected to the pipe  43 . 
   The mixing reservoir  50  mixes the hydrochloric acid, taken from a related container  51  by a pipe  53 , which is a branch of the pipe  43 . 
   The apparatus includes also a reservoir  80  for collecting solid remains and connected to an additional suction pipe  81  or alternatively, to the main suction pipe  13 . 
   Moreover, the equipment includes an evaporator  90 , which basically includes a boiler made of copper enclosed in a insulated concrete container. 
   The decantation reservoir  60  and collection reservoir  70  for collecting liquids when the cycle is finished, are fed by the pipes  61 ,  71  which are branched from the pipe  26  going out of the basin  12 , and are connected to the evaporator  90  by further pipes  62 ,  72 . 
   The decantation reservoir  60  and liquids collecting reservoir  70  are connected also to the caustic soda container  42  by a pipe  47 . 
   All the movements of the liquids and remains, their dosing, mixing and relative paths, are controlled by relative motor-powered pumps  45 ,  55 ,  65 ,  75 ,  85  and  95 , operated according to predetermined time programs. 
   The motor-powered pumps, as well as the valves disposed along the above mentioned pipes and suction pipes are controlled electronically by a control unit  15 , which receives also signals given by the measuring instruments such as thermometers, manostats, pH-meters and the like, connected to different containers or reservoirs. 
   It is enough to introduce into the control unit  15  only the data concerning the weight and color of the hides to be treated, to define automatically all the variables, throughout the production cycle, such as the quantity of liquids, mixing times, pressure and temperature values and the like. 
   In practice, the proposed process includes a first step, during which the hides are cleaned, and which starts with heating to about 30° C., the water contained in the cylindrical pot  11 . The water fills the pot up to a level slightly lower than the edge of the basin  12 . 
   An aqueous solution is composed by adding 96% by volume of water, 2% by volume of caustic soda and 2% by volume of hydrogen dioxide, in the mixing reservoir  40 . The quantity of the aqueous solution is calculated in relation to the weight of the hides to be treated. The aqueous solution is heated at the same temperature. 
   When the above mentioned temperature is reached, the fresh hides to be treated, placed each one on a supporting plate  2 , are taken from the carriage  6  and introduced into the basin  12  by the transferring device  3 . 
   Afterwards, the cylindrical pot  11  is closed tightly and the suction pump  13  is started, until a negative pressure of about −0.5 atm is obtained inside the container  10 . 
   After about 15 minutes, the vibrating element  14  is operated, while the vacuum condition and the temperature of the liquid are maintained constant by the special manostat  24  and thermostat  23 . 
   Due to the pressure difference, by opening the connecting pipe, the solution contained in the mixing reservoir  40  is sucked completely into the basin  12 . 
   This solution, already quantified according to the above mentioned parameters, reaches a level which covers the whole mass of hides  1  placed in the basin  12 . 
   When the solution has been transferred to the basin  12 , a new mixture of water, caustic soda and hydrogen peroxide is prepared in the mixing reservoir  40 , in quantity necessary for the next cycle. 
   The vibration of the container  10 , maintained for a period of time necessary for the treatment, makes better the action of the solution introduced into the basin  12 , ensuring the complete treatment of the outer surface, or grain, of the hides, while the inner surface is treated only slightly, since protected by the plate  2 , to which it adheres. 
   Thermostat  23  and manostat  24  ensure the constancy of the temperature inside the basin  12  and of the negative pressure inside the container  10  during the whole operation. 
   It is to be noted that the solution, in which the fresh hides are immersed, stops the hides decomposition, due to the caustic soda contained in the solution. 
   The proposed process can be used also in areas with particularly hot climate, because it begins almost immediately after the fresh hides have been taken from the refrigerating chamber. 
   The hides are subject to the action of the above mentioned solution, with the temperature, pressure and vibration generally constant, for a predetermined period of time corresponding to seven hours in case of hides with black hair, four hours in case of white hide, and six hours if the hair is of different color or spotted. 
   The hair is decomposed due to the action of the hydrogen peroxide and caustic soda. 
   The oxidative and radicalic action of the hydrogen peroxide takes place on; the cuticle membrane and the alpha-keratins constituting the hair. 
   The cutting action takes place in the neck area, which is usually intracutaneous. 
   Due to the decompression, the neck comes out and thus can be attacked more rapidly, because its section is smaller with respect to the hair medium section. 
   The action of the hydrogen peroxide can be either radicalic or oxidative on the membrane and the glycocalyx, the glicoproteic structure present on the membrane surface which confers the adherence between the cells. 
   The change of the fatty acid structure determines a loss of the membrane stability with breaking the structure
 
ROH+HO*→RO*+H 2 O
 
2RO*→R—O—O—R
 
RO*+R—NH 2 →ROH+R—NH*
 
 R—NH*+R—OH→R—NH 2 +RO*
 
   The radicals attack the structure of the glucides and amino acids on the groups —OH and —NH 2 ; moreover, the action of the hydrogen peroxide oxidizes the groups R—CH 2 —OH and R—CO—H. 
   This way, all the structures stabilized by hydrogen links are changed due to breaking of the interactions. 
   The caustic soda acts on different levels on the membrane changing the structure due to phospholipidic hydrolysis 
                 
 
   This way, the structure is destroyed and the carbo-amidic link is hydrolyzed thus releasing the amino acids of the alpha-keratin protein. 
   After the first treatment has been finished, its duration being determined by a timer, the hides are devoid of hair and cleaned in a strongly basic environment, with the pH value of about 14. 
   When the hides cleaning step is finished, the basin  12  is brought back to the atmospheric pressure and all the liquid contained therein, including the organic debris of the cleaning process, is sent to the mixing reservoir  50 , to start hide stabilization step. 
   A quantity of hydrochloric acid sufficient to neutralize the caustic soda, e.g. equal to 0,5% of the initial water volume, is taken from the container  51 . 
   The hydrochloric acid is conveyed to the mixing reservoir  50 , into which a jet of air flows to facilitate complete liquids mixing. 
   Meanwhile, the basin  12  is brought back to decompression and after a negative pressure of −0.5 to −0.6 atmospheres has been reached, the whole contents of the reservoir  50  is sucked. 
   The task of the hydrochloric acid is to neutralize the quantity of soda present in the solution and absorbed by the hide. 
   This takes place by the combination of the hydrochloric acid with the soda dissolved in the basin  12 , which generate sodium chloride. 
   This operation is controlled by a special pH-meter, which, when the neutral value is reached, gives the end-of-cycle command by starting the pump, which sucks the whole solution or suspension contained in the basin. 
   The hydrochloric acid causes also narrowing of the hide pores, thus avoiding the damages to the hide grain by the tanning products during the wet white tanning or coloring. 
   The above described step of hide stabilizing does not have a fixed duration, because it depends on the initial pH value and on the time necessary to bring it to the value 7. 
   Then, the basin  12  is brought again to the atmospheric pressure, the hides are removed therefrom and placed in a special rack to dry. A remains treatment step follows. 
   The aqueous suspension resulting from the process can be conveyed to the collection reservoir  70 , if it is to be evaporated. If the solid debris are to be decanted and only the surface aqueous solution is to be collected, and conveyed to the evaporator  90 , for next use, then the aqueous suspension is sent to the decantation reservoir  60 . 
   In the first case, partially dried solid remains are obtained, which are sucked from the collecting reservoir  80 , while the water depurated by boiling in the evaporator  90  can be sent to the mixing reservoir  40  for the next cycle, or dispersed in the environment. 
   In the other case, after the separation of the surface liquid, the sediment is sucked by the collecting reservoir, as in the previous case. 
   It is to be noted that in both cases, before the resulting substance is sent to the evaporator  90  or the collecting reservoir  80 , it is treated by adding caustic soda until pH reaches value 7. 
   The soda is taken from the related container  41  and automatically sent to the decantation reservoir  60  or  70 . 
   Thus, the described process achieves the object of providing an animal hides treatment which reduces the negative effect on the environment, in particular eliminating the use chemical substances, and consequently avoids the necessity for a depuration system. 
   A first characteristic of the proposed process is the elimination of the initial salting, used in known tanning methods, since the process starts with fresh hides. 
   In this way, costs of salting, desalting and soaking are avoided, as well as the damages which such operations can cause not only to the hides, but also to the environment. 
   Actually, the described process can be intended as the continuation of the slaughtering operations, rather than tanning and pre-tanning, even if the results are the same, as to the nature and destination of the final product. 
   Another characteristic of the proposed process is to considerably limit substances used for different treatments. 
   In particular, the process requires only three substances easily available and of moderate cost (hydrogen dioxide, caustic soda and hydrochloric acid), yet obtaining best results in hides stabilizing as well as in semi-finished product properties. 
   Consequently, all the chemical substances used in known tanning art are eliminated and likewise, the relative disposal operations. 
   Actually, the proposed process does not need any depuration equipment, since the corresponding operation is reduced to a simple treatment of wastes, which can be re-cycled e.g. in agricultural field. 
   Another advantage of the proposed process results from the fact that sodium chloride is generated during the hides treatment, and the hides are prepared to receive it uniformly and deeply. 
   Another advantage of the invention derives from the compactness of the system using only one treating basin, thus eliminating hides transferring and the use of traditional drums, and reducing the occupied space. 
   The proposed solution is particularly suitable also for slaughter houses. 
   This is very advantageous in case of principal hide producing countries, where the law obstacles, or even forbids exporting of raw hides, while it allows to export semi-finished hides, i.e. “wet-white”. 
   The proposed process allows also to reduce considerably the working time and production costs. 
   A very important advantage of the proposed process lies in saving a very precious good, i.e. water, whose consumption is insignificant, especially considering the fact that the remaining solutions are collected and reused. 
   Moreover, traditional tanning processes reduce the hides surface, while the proposed process tends to extend it by 5÷7%. 
   It is to be particularly pointed out that the proposed process does not involve an environmental impact, in complete accordance with the regulations in force concerning the disposal of industrial wastes. 
   In fact, as it has been said, the working wastes produced by the treatment for transformation raw hides in the wet-white state is a suspension of an aqueous liquid and organic particles. 
   After having been subjected to boiling and evaporation, the treatment wastes suspension are divided into liquid wastes and solid wastes. 
   The analysis of the above wastes gives the following results. 
   The pH, COD and chlorides parameters of the liquid wastes have been checked and the obtained results remain within the emission limits for industrial waste water as required by the regulation in force. Therefore, it is possible to apply for a regular authorization to discharge wastewaters to the surface waters. 
   The quality characteristics of the waste waters make them suitable to be reused in a production cycle. 
   As far as the solid wastes are concerned, all the parameters remain within the fixed limit values requested by the regulation in force concerning “use of depuration mud in agriculture”. 
   Therefore, according to the provision of the related law, the wastes defined as “solids” deriving from the wet-white production process are classified as “special, not dangerous wastes, mud not containing chromium”. 
   Thus, according to the processes concerning the compostible wastes, they can be reused in agriculture or disposed in a controlled discharge for urban solid wastes and the like. 
   The proposed process not only ensures a deep and complete treatment of the hides, but also improves the product quality at lower costs, with respect to the quality obtained by known tanning process. 
   From the economic-ecological point of view, the advantages of the proposed process, are still more evident. It is enough to mention the elimination of the salting and numerous chemical additions, and in particular, the investments and the operation and maintenance costs of the present depuration systems, which are often of poor efficiency and do not resolve the serious problem of the disposal of toxic muddy wastes. 
   The modular structure of the system is to be pointed out, i.e. the system can have dimension selected in relation to the quantity flow of the available hides. 
   Apart from economic consideration, like the amortization one, it is possible to produce equipments able to treat fifty or a hundred or a thousand or even more hides per day. 
     FIG. 8  shows a different embodiment of the equipment designed for biological tanning treatment, without using chemical products. 
   In particular, the biological tanning uses a tanning agent deriving from the combination of biological tannin (obtained from the plants containing tannin, such as leaves of fig, eucalyptus, and the like) and animal hair. 
   The apparatus uses an additional container  52  for the tanning agent, connected to the mixing reservoir  40  by a pipe  43 . 
   In this case, the procedure includes first a hides cleaning step, as previously described. 
   Then, the aqueous solution composed of water, caustic soda and hydrogen dioxide is prepared in the mixing reservoir  40 . 
   The solution prepared in the mixing reservoir  40  is sucked into the basin  12  containing the hides to be treated and previously set in vacuum condition, and the vibrating system  14  is started to facilitate the solution action. 
   When the hides cleaning step is finished, the depilating liquid is withdrawn from the basin  12  and introduced into the collecting reservoir  70 . 
   Then, the mixing reservoir  50  is fed with water and then with a suitable quantity of hydrochloric acid taken from the container  51 . 
   It is to be noted that the quantity of hydrochloric acid is equal to the quantity of caustic soda used for hides cleaning. 
   The so obtained acid solution is introduced into the basin  12  containing the hides for pickling. 
   The hydrochloric acid combines with the sodium hydroxide, thus generating sodium chloride which causes the pH lowering. 
   When the pickling is completed, the pickling water is removed from the basin  12  and introduced into the decantation reservoir  60 . At the same time, a suitable quantity of the tanning agent is taken from the relative container  52  and introduced into the collecting reservoir  70 , already containing the depilation liquid. 
   The so obtained solution of the depilation liquid and the tanning agent is introduced into the basin  12  to perform a further treatment step, called with more precision re-tanning. 
   When the re-tanning has been completed, the liquid removed from the basin  12  is introduced again to the collecting reservoir  70 . 
   A suitable quantity of hydrochloric acid taken from the container  51  is added thereto, so as to bring the pH to about 7. 
   Therefore, the liquid, no more acid, can be introduced into the evaporator  90  and boiled. 
   As in the previous case, the depurated water can be discharged or reused, while the solid remains can be collected and used as fertilizers in agriculture. 
   It is understood that what above, has been described as a pure, not limitative example, therefore, possible variants of the invention remain within the protective scope of the present technical solution, as described above and claimed hereinafter.