Method for producing leather, and leather precursor

Abstract

Provided are: a method for producing leather with low environmental load; and a leather precursor. This method for producing leather involves: an immersion step for immersing a pelt in a treatment liquid including sugar and yeast of the genus Saccharomyces; and a first fermentation step for immersing the pelt in a treatment liquid and fermenting same.

Description

Leather manufacturing method and leather precursor

[0001] The present disclosure relates to a method for producing leather and to leather precursors.

[0002] Leather is produced by washing rawhide, removing fat and hair, and then tanning it. During the process of processing rawhide into leather, it may be transported from the place where it was harvested to a processing factory. During transport to the processing factory, the rawhide is subjected to preservative treatments, such as salting with salt, to prevent deterioration and spoilage, such as rotting. Furthermore, during the leather processing process, other processes are carried out, such as soaking, which removes salt from the preservative-treated rawhide (leather precursor), and liming, which removes hair and unnecessary protein from the rawhide. These processes produce large amounts of wastewater containing salt and lime, placing a significant burden on the environment.

[0003] Patent Document 1, which deals with a method for preserving rawhide using salt, points out the problems of the large amount of salt required for rawhide preservation and the fact that wastewater discharged from storage buildings and tanneries is significantly contaminated with soluble salt. It also points out that salt in wastewater is difficult to remove without incurring significant costs, and that in some countries used salt is designated as hazardous waste. It also points out that rawhide can be ruined by salt-resistant bacteria, and that the amount of salt required for short-term storage of rawhide is almost the same as the amount required for long-term storage.

[0004] Patent Document 2 points out the problem that, in a leather production method, skins are agitated with slaked lime and water to remove hair and loosen the skin fibers, but a large amount of sludge containing slaked lime as the main component, including hair detached from the skin, is generated, which must be disposed of as alkaline sludge. Regarding this problem, Patent Document 2 discloses a leather production method that can reduce the amount of sludge containing slaked lime as the main component, and the slaked lime used therein. This leather production method includes a step of treating animal rawhide with slaked lime, and when producing leather from the rawhide, the specific surface area of ​​the slaked lime is set within a predetermined range. Patent Document 2 discloses an example of the dehairing step in this leather production method, in which five salted pig hides are soaked and lined to completely remove salt, meat fragments, etc., before dehairing. In this unhairing process, the leather after lining (total weight 23.5 kg), water (200% of the leather after lining), and slaked lime (2% of the leather after lining, 0.47 kg) are put into a stainless steel drum and rotated and stirred, and while stirring, sodium sulfide (2%) and nonionic surfactant (0.3%) are added in order, and then stirred overnight.In addition, Patent Document 2 discloses an example of a re-liming process after unhairing process.In this re-liming process, the leather on the grain side (total weight 18.8 kg), water (200% of the leather), and slaked lime (1% of the leather, 0.188 kg) are put into the same drum as in unhairing, and stirred, and then nonionic surfactant (0.3%) is added, and then stirred for two days and nights.

[0005] Patent Document 3 discloses an antioxidant fermentation microbial agent used to reduce odors and volatile organic compounds emitted from processed leather products, leather containing the agent, and a method for producing the same. The antioxidant fermentation microbial agent contains salt, such as deep-sea natural salt. This leather production method uses raw hides preserved with salt, which must be removed during leather production. Furthermore, this leather production method uses a saturated aqueous solution of lime to dehair the hides.

[0006] Patent Document 4 discloses a method for preserving baked bakery products. The method includes a step of applying a solution containing a live leaven and / or live yeast onto the surface of the baked bakery product after baking the dough. An example of the yeast used in this method is a Saccharomyces cerevisiae strain.

[0007] Patent Document 1: JP 62-600 A Patent Document 2: JP 2000-45000 A Patent Document 3: WO 2007 / 12986 A Patent Document 4: JP 2023-504068 A

[0008] In the conventional leather manufacturing methods disclosed in Patent Documents 1 to 3, large amounts of salt (table salt, sodium chloride) are used to preserve rawhide, and waste liquid containing large amounts of salt is generated during the leather manufacturing process, which places a heavy burden on the environment. Furthermore, large amounts of lime are used during intermediate processes in processing rawhide into leather (e.g., hair removal and loosening of leather fibers), which generates waste liquid containing large amounts of lime, which places a heavy burden on the environment. Therefore, it is desirable to provide a leather manufacturing method and leather precursor that place a low burden on the environment.

[0009] The present disclosure has been made in view of the above circumstances, and its purpose is to provide a method for producing leather and a leather precursor that imposes a low environmental impact.

[0010] To achieve the above object, the method for producing leather according to the present disclosure includes a soaking step of soaking rawhide in a treatment solution containing sugar and yeast of the genus Saccharomyces, and a first fermentation step of soaking the rawhide in the treatment solution and fermenting it.

[0011] To achieve the above object, the leather precursor according to the present disclosure includes sugar, yeast of the genus Saccharomyces, and rawhide.

[0012] According to the present disclosure, it is possible to provide a method for producing leather and a leather precursor that have a low environmental impact.

[0013] Hereinafter, a method for producing leather and a leather precursor according to an embodiment of the present disclosure will be described. First, an overview of the method for producing leather and the leather precursor according to the present embodiment will be described.

[0014] The method for manufacturing leather according to this embodiment includes a soaking step in which rawhide is soaked in a treatment solution containing sugar and yeast of the genus Saccharomyces, and a first fermentation step in which the rawhide is soaked in this treatment solution and fermented.

[0015] The leather precursor according to this embodiment contains sugar, yeast of the genus Saccharomyces, and rawhide.

[0016] According to the method for producing leather according to this embodiment, it is possible to produce leather precursors and leather with a reduced environmental impact.

[0017] Specifically, the leather manufacturing method according to this embodiment has the following advantages. In the leather manufacturing method according to this embodiment, there is no need to use salt to preserve the rawhide during the manufacturing process. In other words, the leather manufacturing method according to this embodiment makes it possible to preserve the rawhide at the harvesting site and during transportation from the harvesting site to the processing plant without using salt. In this embodiment, preserving or preserving the rawhide means preventing the rawhide from spoiling or other changes or deterioration. Therefore, in the leather manufacturing method according to this embodiment, there is no need to use rawhide that has been preservatively treated by salting during the manufacturing process, and there is no need to remove salt from the rawhide. Therefore, the leather manufacturing method according to this embodiment does not generate waste liquid containing a large amount of salt during the leather manufacturing process, and therefore has a low environmental impact.

[0018] The leather manufacturing method according to this embodiment can also realize leather dehairing with reduced environmental impact (hereinafter referred to as the leather dehairing method according to this embodiment).

[0019] The method for dehairing skin according to this embodiment includes a soaking step in which rawhide is soaked in a treatment solution containing sugar and yeast of the genus Saccharomyces, and a first fermentation step in which rawhide is soaked in the treatment solution and fermented. The rawhide used is not salted.

[0020] Specifically, the leather hair removal method according to this embodiment has the following advantages: The leather hair removal method according to this embodiment allows hair removal without using large amounts of water or lime (slaked lime, calcium hydroxide). Therefore, the leather hair removal method according to this embodiment does not discharge large amounts of lime sludge as in conventional techniques, and has a low environmental impact.

[0021] In other words, the leather manufacturing method according to this embodiment includes the steps of realizing the leather dehairing method according to this embodiment. In the following explanation, the leather dehairing method according to this embodiment will be described as being included in the explanation of the leather manufacturing method according to this embodiment.

[0022] The leather manufacturing method and leather precursor according to this embodiment will be described in detail below.

[0023] In the leather manufacturing method according to this embodiment, the concept of leather includes rawhide that has been subjected to a preservation treatment (an example of a leather precursor), leather obtained by dehairing rawhide that has been subjected to a preservation treatment (another example of a leather precursor), leather obtained by tanning rawhide that has been subjected to a preservation treatment (another example of a leather precursor), leather, and leather products. The leather precursor according to this embodiment refers to rawhide that has been subjected to at least a preservation treatment and rawhide that has been processed (e.g., dehaired or tanned). In other words, the leather precursor according to this embodiment refers to leather that has been subjected to a preservation treatment and is an intermediate in the process of being processed into leather.

[0024] As an example, the method for producing leather according to this embodiment may further include, in addition to the soaking step and first fermentation step described above, a dehydration step in which a first precursor obtained by fermenting rawhide in the fermentation step is dehydrated, a sugaring step in which sugar is attached to the surface of the first precursor after the dehydration step, a second fermentation step in which the first precursor after the sugaring step is fermented, a dehairing step in which the second precursor obtained by fermenting the first precursor in the second fermentation step is dehaired, and a desulfurization step carried out after the dehairing step.

[0025] In addition, the first precursor and the second precursor before the dehairing step in each of the above steps are included in the leather precursor according to this embodiment.

[0026] In this embodiment, the rawhide may be skin collected from animals such as cows, buffalo, pigs, wild boars, goats, sheep, lizards, snakes, crocodiles, and fish. The rawhide may be collected, for example, as residue when the above animals are slaughtered for meat processing. A certain amount of meat is allowed to remain on the rawhide. Animal hair may remain on the front surface (body surface side, animal hair side) of the rawhide. It is not necessary to use rawhide collected from animals that has been salted. It is preferable that the rawhide is not salted. After initial washing, the rawhide is subjected to the soaking process described below.

[0027] In the initial cleaning, the rawhide is taken from the animal, and any dirt adhering to it is removed, and unnecessary parts such as the legs and tail are cut off, and then flesh and fat are removed using a fleshing machine or similar. In the initial cleaning, disinfectants (except salt) may be used to prevent early contamination or rapid spoilage. After cleaning, the rawhide is not salted.

[0028] The soaking step involves immersing the rawhide in a treatment solution containing sugar and yeast of the genus Saccharomyces. The dispersion medium or solvent of the treatment solution may be water.

[0029] An example of a yeast of the genus Saccharomyces is Saccharomyces cerevisiae, which may be included in so-called baker's yeast, glutinous rice yeast, or cassava yeast.

[0030] The yeast of the genus Saccharomyces used in the treatment solution may be a mixture of yeasts of multiple origins. For example, 100 parts by weight of baker's yeast containing Saccharomyces cerevisiae may be mixed with 10 to 50 parts by weight, preferably 30 parts by weight, of other yeasts containing Saccharomyces cerevisiae, such as glutinous rice yeast or cassava yeast, and this mixture may be used as the yeast of the genus Saccharomyces used in the treatment solution.

[0031] The yeast serves as a fermenting bacterium in the first fermentation step and the second fermentation step, which will be described later. The yeast metabolizes sugars, which will be described later, to cause alcoholic fermentation.

[0032] The sugar may be any sugar that can be alcoholically fermented by the yeast. Examples of suitable sugars in this embodiment include glucose, fructose, and sucrose. The sugar does not need to be pure, and may be molasses, java sugar, palm sugar, tapioca sugar, or granulated sugar containing at least one of glucose, fructose, and sucrose as its main component.

[0033] The treatment liquid may be prepared by mixing water containing sugar with a starter, which is prepared by adding yeast to a small amount of sugar and water and allowing it to pre-ferment.

[0034] The immersion of the rawhide in the treatment solution, i.e., the immersion step, may be carried out, for example, as follows.

[0035] First, the weight of the rawhide after the initial washing is measured. Note that the weight of the rawhide includes the weight of volatile substances (such as water) that the rawhide may naturally contain. Next, the rawhide is pre-treated by immersing it in a pre-treatment solution containing soap or antibacterial (a disinfectant, excluding salt) and soda ash (sodium carbonate) for 5 to 30 minutes, preferably 10 to 15 minutes. The hydrogen ion concentration index (pH) of the pre-treatment solution is weakly alkaline, with a pH of 7 to 9, preferably 8 to 9.

[0036] Apart from the above pretreatment, a starter is prepared by fermenting a predetermined amount of yeast and a predetermined amount of sugar in warm water.

[0037] The starter can be prepared by placing 3 g to 15 g, preferably 5 g to 10 g, of yeast and 3 g to 15 g, preferably 5 g to 10 g, of sugar into a container containing 20 ml to 100 ml of warm water (35°C to 65°C), and allowing the container to ferment for at least 10 minutes, preferably 15 minutes to 20 minutes, with the container sealed. The starter is preferably prepared by fermenting the liquid in the container until it foams.

[0038] The amount of hot water used to prepare the starter is preferably 30 ml to 70 ml, more preferably 40 ml to 60 ml. The temperature of the hot water used to prepare the starter is preferably 40°C to 60°C.

[0039] Then, water of a weight equivalent to that of the rawhide, specifically water of a weight of 50% to 200% of the weight of the rawhide (at room temperature, for example, 25°C), is measured out, and sugar of a weight of 1.5% to 30% of the weight of the rawhide is added to this water and dissolved to form a sugar solution.

[0040] The amount of water used to prepare the sugar solution is preferably 50% to 120% of the weight of the rawhide, more preferably 50% to 100%.

[0041] The temperature of water when preparing the sugar solution is suitably 20°C or higher and 35°C or lower, and preferably 20°C or higher and 30°C or lower.

[0042] The sugar used in preparing the sugar solution may be, for example, granulated sugar as described above. The amount of sugar used in preparing the sugar solution is preferably 3% to 30% of the weight of the rawhide, more preferably 5% to 30%.

[0043] After preparing the sugar solution, the entire amount of the starter is added to the sugar solution to prepare a treatment solution. The treatment solution is preferably stirred after the starter is added. The starter may be added to the sugar solution containing the pretreated rawhide, or to the sugar solution without the pretreated rawhide.

[0044] The treatment solution prepared as described above may contain water in an amount of 50% to 200% by weight of the rawhide, and sugar in an amount of 1.5% to 30% by weight of the rawhide. Having such a component ratio in the treatment solution may enhance the effect of preventing the rawhide from spoiling or deteriorating. Furthermore, having such a component ratio in the treatment solution may shorten the time required to prevent the rawhide from spoiling or deteriorating, i.e., the retention time (fermentation time) required in the first fermentation step.

[0045] The amount of water contained in the treatment solution is preferably 50% to 120% of the weight of the rawhide, more preferably 50% to 110%. The amount of water in the treatment solution is sufficient as long as the rawhide remains immersed in the treatment solution even after the treatment solution has permeated the rawhide.

[0046] The amount of sugar contained in the treatment solution is preferably 3% to 30% of the weight of the rawhide, and more preferably 5% to 30%. The amount of sugar contained in the treatment solution may be increased when the amount of water contained in the treatment solution is large, and may be decreased when the amount of water contained in the treatment solution is small. The ratio of water to sugar in the treatment solution is preferably 4.2% to 60% of the weight of water contained in the treatment solution.

[0047] It should be noted that a starter is not essential for preparing the treatment liquid. For example, yeast may be directly added to a sugar solution, and the sugar solution containing the yeast may be subjected to preliminary fermentation to prepare the treatment liquid.

[0048] The pretreated rawhide is immersed (soaked) in the treatment solution prepared as described above. In this embodiment, "immersing the rawhide in the treatment solution" means that the treatment solution is applied to at least the entire surface of the rawhide. The rawhide may be immersed in the treatment solution in a rotating drum. The drum may be, for example, a cylindrical drum with a horizontal rotation axis and a diameter of 2 m to 4 m. The drum rotation speed is, for example, 5 to 30 revolutions per minute, preferably 6 to 10 revolutions per minute.

[0049] Immersing the rawhide in the treatment solution in a rotating drum can sometimes help ensure that the treatment solution adheres to the entire surface of the rawhide. It also allows for thorough agitation of the treatment solution (starter and sugar solution). This can sometimes help ensure that fermentation in the first fermentation step, described below, progresses more efficiently throughout the rawhide.

[0050] The first fermentation step is the first step in which the rawhide immersed in the treatment solution is fermented. In the first fermentation step, the rawhide is kept immersed in the treatment solution. This allows the treatment solution to penetrate the rawhide, and yeast grows in the treatment solution and in the rawhide (within the skin tissue), causing fermentation to proceed. In other words, the first fermentation step is a step in which the rawhide is immersed in the treatment solution and kept fermented.

[0051] The concept of keeping the rawhide immersed in the treatment solution in the first fermentation step includes both cases where the treatment solution and the immersed rawhide are stationary, and cases where the treatment solution and the immersed rawhide are moving, for example, due to stirring. In the first fermentation step, fermentation will proceed as long as the rawhide is immersed in the treatment solution.

[0052] In the first fermentation step, ethanol is produced in the treatment solution and rawhide through the above-mentioned fermentation. That is, the first precursor is rawhide containing sugar and yeast of the genus Saccharomyces. The rawhide as the first precursor preferably does not contain salt added for preservation. Depending on the fermentation state, the first precursor may also contain ethanol. Note that in this embodiment, salt contained in the rawhide from the time of collection as biological tissue is not included in the concept of salt added for preservation.

[0053] In the first fermentation step, the rawhide is immersed in the treatment solution and kept therein for 2 hours to 72 hours, preferably 3 hours to 15 hours, more preferably 4 hours to 15 hours, and even more preferably 12 hours to 15 hours, to be fermented.

[0054] In this embodiment, the rawhide that has undergone the first fermentation process is referred to as the first precursor. That is, the first precursor is the rawhide that has been subjected to the first fermentation process and thereafter. More specifically, the rawhide that has undergone the first fermentation process (first precursor) is the rawhide that has been immersed in the treatment solution through the soaking process, and is the rawhide from the point in time when fermentation in the first fermentation process has started. Except for cases where the rawhide is handled in an atmosphere that inhibits the progress of fermentation (for example, when refrigerated to the extent that fermentation stops), the point in time when the rawhide is immersed in the treatment solution in the soaking process can be the start point of the first fermentation process.

[0055] In this way, by subjecting the rawhide to the first fermentation step, the effect of preservation treatment is exerted, which prevents the rawhide from changing or deteriorating, such as putrefaction. The first fermentation step is a step that prevents the rawhide (first precursor) from changing or deteriorating, such as putrefaction. The first fermentation step is also a step that exerts an effect of preventing the first precursor after the first fermentation step from changing or deteriorating, such as putrefaction.

[0056] By setting the retention time (fermentation time) in the first fermentation step to 2 hours or more, i.e., by immersing the rawhide in the treatment solution and allowing it to ferment for 2 hours or more, the fermented treatment solution (yeast) can fully penetrate the rawhide, and the preservation effect of preventing deterioration and spoilage of the rawhide (first precursor) can be more effectively achieved. Furthermore, conditions are created that make it easier for fermentation to proceed within the rawhide, enhancing the effectiveness of the preservation treatment. Furthermore, the preservation effect of the first precursor can be maintained even after the first fermentation step is completed.

[0057] If the retention time (fermentation time) in the first fermentation step is 4 hours or more, for example, if the rawhide is immersed in the treatment solution and left to ferment for 12 hours, fermentation will progress sufficiently in the rawhide.

[0058] The atmosphere in the room, warehouse, or other space where the first fermentation step is carried out may have a temperature of 15°C to 40°C and a relative humidity of 30% to 80%. The atmosphere preferably has a temperature of 15°C to 30°C and a relative humidity of 30% to 80%, and more preferably a temperature of 20°C to 30°C and a relative humidity of 60% or less. By carrying out the first fermentation step in such an atmosphere, fermentation in the treatment solution and the rawhide is promoted, thereby further enhancing the effectiveness of the preservation treatment that prevents deterioration and alteration, such as putrefaction, of the rawhide (first precursor).

[0059] In addition, if the rawhide has animal hair, the first fermentation step also has the effect of making the animal hair of the first precursor more likely to fall off. In other words, the hide dehairing method according to this embodiment may include the first fermentation step. Some of the animal hair falls off as fermentation progresses in the first fermentation step. This makes the dehairing step (finish dehairing step) described below easier.

[0060] The first precursor is in a state where the proliferation of ethanol purified by yeast through the metabolism of sugars and the proliferation of yeast or the proliferated yeast makes it difficult for bacteria (hereinafter simply referred to as "bacteria") that particularly promote spoilage to grow. That is, the first precursor is one in which the progression of spoilage is inhibited even without the use of salt. Hereinafter, the inhibition of the progression of spoilage may be referred to as "preserved," etc. Furthermore, the inhibition of the progression of spoilage may be referred to as "preserving," etc.

[0061] Since the first precursor is prevented from decaying as described above, it can be stored for a few days to a week, for example, when rawhide is transported between factories. As described above, salt is not required in the production of the first precursor. Therefore, wastewater containing a large amount of salt is not generated during the production process of the first precursor.

[0062] In this embodiment, the first precursor may be further subjected to a second fermentation step. The second fermentation step is a step in which the first precursor is further fermented.

[0063] In order to carry out the second fermentation step, it is preferable to additionally supply sugars that the yeast can metabolize. In this embodiment, the first precursor may be subjected to the second fermentation step after a sugar addition step in which sugars are attached to the surface of the first precursor.

[0064] In this embodiment, a dehydration step of dehydrating the first precursor may be performed prior to the sugar addition step and the second fermentation step. Note that dehydration in this embodiment refers to removing a portion of the liquid component from the first precursor. In this embodiment, the liquid component contained in the first precursor is primarily a fermented processed liquid (mainly water).

[0065] The dehydration of the first precursor in the dehydration step may be performed by squeezing the first precursor. The dehydration of the first precursor in the dehydration step may be performed, for example, using a thumbing machine, a press, or a centrifuge. By squeezing out a certain amount of liquid components (water) from the first precursor in the dehydration step, it becomes easier for sugar to adhere to the surface of the first precursor in the sugar addition step. Furthermore, the dehydration step can suppress the growth of unwanted bacteria. Furthermore, by dehydrating the first precursor and then adhering sugar to it, the free water in the first precursor can be reduced, thereby suppressing the growth of unwanted bacteria. In other words, the dehydration step can provide better preservation.

[0066] The dehydration rate (squeezing rate) in the dehydration step is preferably 40% or more and 60% or less. The dehydration rate (squeezing rate) is the percentage (%) of the weight of the dehydrated water when the weight of the first precursor immediately before dehydration is taken as 100%. That is, in the dehydration step, it is preferable to remove 40% or more and 60% or less of the liquid component based on the weight of the first precursor.

[0067] In the sugar addition step, the attachment of sugar to the surface of the first precursor may be achieved by sprinkling or applying sugar particles (powder or granules) to the surface of the first precursor. Alternatively, the attachment of sugar to the surface of the first precursor may be achieved by applying a sugar paste in which sugar is dissolved at a high concentration to the surface of the first precursor. When using a sugar paste, the sugar concentration in the sugar paste is preferably 10% by weight or more, more preferably 20% by weight or more.

[0068] The sugar attached to the surface of the first precursor in the sugar addition step is a sugar (second sugar) prepared separately from the sugar (first sugar) contained in the treatment solution. In other words, the concept of the sugar attached to the surface of the first precursor in the sugar addition step does not include the sugar in the treatment solution remaining on the surface of the first precursor.

[0069] The sugars that can be used in the second fermentation step are the same as those listed as examples of sugars that can be used in the treatment solution in the first fermentation step. The sugars contained in the treatment solution and the sugars attached to the surface of the first precursor do not need to be different components or types. The sugars contained in the treatment solution and the sugars attached to the surface of the first precursor may be the same components or types, or may be different components or types.

[0070] The attachment of sugar to the surface of the first precursor may be carried out on at least one of the front surface (epidermis, animal hair surface) or the back surface (dermis) of the hide. The attachment of sugar to the surface of the first precursor is preferably carried out on the back surface. The back surface of the first precursor has greater irregularities than the front surface, making it suitable for attachment of sugar.

[0071] In the sugar addition step, an antibacterial agent may be added together with the sugar. When an antibacterial agent is added, it is sufficient to add the antibacterial agent in an amount of 0.3% by weight to 1.0% by weight based on the weight of the sugar. An example of the antibacterial agent is p-cresol.

[0072] In the sugar-adding step, sugar is attached to the surface of the first precursor in an amount of 1% to 30% by weight, preferably 1% to 25% by weight of the rawhide. Adding sugar to the first precursor in this ratio facilitates attachment of the sugar to the surface of the first precursor, is effective in inhibiting the growth of bacteria, and promotes fermentation in the second fermentation step, thereby providing better preservation.

[0073] In the second fermentation step, the first precursor to which sugar has been attached as described above is fermented. Fermentation in the second fermentation step may be carried out in a dry or normal humidity space. The second fermentation step may be carried out, for example, in a fixed factory or warehouse, or in a warehouse that doubles as a transport container, such as a cargo container for trucks, trains, ships, or airplanes.

[0074] In the second fermentation step, fermentation in the rawhide, i.e., the growth of yeast in the rawhide and the production of ethanol through the metabolism of the yeast, progresses. In this embodiment, the rawhide after sugar is attached to the surface of the first precursor and fermentation in the second fermentation step is initiated (after being subjected to the second fermentation step) is referred to as the second precursor. In other words, the second precursor is rawhide that contains sugar and yeast of the genus Saccharomyces, just like the first precursor. As with the first precursor, the rawhide of the second precursor preferably does not contain salt added for preservation. Depending on the fermentation state, the second precursor may also contain ethanol.

[0075] The second precursor in the process of the second fermentation step and the second precursor after the second fermentation step are extremely well preserved without the use of salt due to at least one of the effects of reducing free water by adding sugar, the effect of yeast growth, and the effect of ethanol produced by fermentation. Therefore, by carrying out the second fermentation step, the preservation effect of preventing deterioration and changes in quality such as putrefaction of rawhide is further enhanced.

[0076] The atmosphere in the room, warehouse, or other space where the second fermentation step is carried out is preferably somewhat dry, specifically, the relative humidity is 30% or more and 70% or less. The humidity of the atmosphere is preferably 40% or more and 60% or less. The temperature of the space where the second fermentation step is carried out may be, for example, 20°C to 40°C. The temperature of the atmosphere is preferably 20°C or more and 30°C or less. By carrying out the second fermentation step in such an atmosphere, the effect of the preservation treatment in the second fermentation step is further enhanced.

[0077] The period for which the second fermentation process is carried out is preferably from 1 day to 50 days, more preferably from 3 days to 30 days. When the period for the second fermentation process is from 1 day to 1 day, preferably from 3 days to 30 days, the effects of the preservation process during and after the second fermentation process can be fully obtained. When the period for the second fermentation process is from 30 days to 50 days at the longest, the effects of the preservation process are sufficiently high. When the period for the second fermentation process is from 1 day to 50 days, the effects of the preservation process can be maintained for at least 4 to 5 weeks after the second fermentation process. In other words, the second fermentation process makes it possible to preserve the rawhide (second precursor) for at least 12 weeks, including the period during which the second fermentation process is carried out.

[0078] In the second fermentation step, the first precursor may be stored by folding the sugar-adhered surfaces together, with the surfaces facing each other. Specifically, for example, the first precursor may be folded in half with the surfaces facing each other, and then folded again into a quarter-fold state. The folded first precursor may be stored in a stacked state. By folding the first precursor with the surfaces facing each other, the sugar attached to the first precursor can be prevented from falling off from the surface of the first precursor, and a decrease in the preservative effect can be suppressed.

[0079] Since the second precursor is extremely well preserved as described above, the second precursor is suitable for long-term storage, for example, about 12 weeks, preferably 1 day to 50 days, long-term transportation between distant factories, and long-term transportation such as import / export from rawhide producing countries to user countries where rawhide is processed into leather. As described above, no salt is required in the production of the second precursor. Therefore, wastewater containing a large amount of salt is not generated during the production process of the second precursor.

[0080] The second fermentation step may be carried out during transportation. That is, the second fermentation step can also be used as a transportation method to prevent deterioration or spoilage of the rawhide.

[0081] In the second fermentation step, if the rawhide has animal hair, the second precursor will have the effect of making the animal hair more likely to fall off. Some of the animal hair will fall off as fermentation progresses in the second fermentation step. In other words, the hide dehairing method according to this embodiment may include the second fermentation step. These steps facilitate the dehairing step (finish dehairing step) described below.

[0082] The hair removal step (finishing hair removal step) is, for example, a step of removing hair from a second precursor. The hair removal step may be a step of removing hair from a first precursor. The following describes an example in which the hair removal step is a step of removing hair from a second precursor.

[0083] In the unhairing step, potassium hydroxide or sodium hydroxide in an amount of 0.3% to 1.0% by weight, relative to the weight of the rawhide, and sodium sulfide in an amount of 0.8% to 2.0% by weight or a mixture of sodium hydrogencarbonate and sodium bicarbonate in an amount of 0.8% to 2.0% by weight, are added to the second precursor and stirred. In the leather manufacturing method of this embodiment, unhairing is also promoted in the first fermentation step and the second fermentation step, so this unhairing step is a step in which finishing unhairing is performed in the leather manufacturing method of this embodiment, or in other words, a finishing unhairing step. Note that the leather unhairing method of this embodiment may include this finishing unhairing step.

[0084] The amount of potassium hydroxide or sodium hydroxide added in the dehairing step is preferably 0.6% to 0.9% by weight of the rawhide. Sodium hydroxide is preferably used in the dehairing step.

[0085] When sodium sulfide is added in the dehairing step, the amount added is preferably 0.8% or more and 1.50% or less based on the weight of the rawhide.

[0086] When a mixture of sodium bicarbonate and sodium bicarbonate is added during the hair removal process, the ratio of sodium bicarbonate to sodium bicarbonate is preferably set to approximately 50:50, more specifically, in the range of 40:60 to 60:40.

[0087] The agitation in the dehairing step may be carried out in a rotating drum, as in the immersion step. The drum rotation speed is 5 to 12 revolutions per minute, preferably 5 to 9 revolutions per minute, and more preferably 7 to 8 revolutions per minute. A stirring time of about 15 minutes is sufficient. The stirring time is usually 10 to 15 minutes. By such a dehairing step, the animal hair is completely separated from the hide (second precursor).

[0088] The hair removal process of this embodiment does not use large amounts of water or lime (slaked lime, calcium hydroxide) as in conventional techniques. The hair removal process of this embodiment does not require the use of lime, and does not require the so-called liming process of conventional techniques. In other words, the hair removal process of this embodiment does not discharge large amounts of lime sludge as in conventional techniques, and therefore has a low environmental impact. Furthermore, the hair removal process of this embodiment also uses a small amount of sodium sulfide.

[0089] The desulfurization process is a process for removing sulfur content (sulfur groups) from the first precursor or second precursor after the dehairing process. In the desulfurization process, an oxidizing agent is added to the first precursor or second precursor after the dehairing process in an amount of 0.8% to 2.0% by weight based on the weight of the rawhide, and the mixture is stirred. This removes sodium sulfide and other substances. As in the soaking process, stirring may be performed in a rotating drum. The drum rotation speed is, for example, 5 to 12 revolutions per minute.

[0090] An example of an oxidizing agent that can be used in the desulfurization process is H ２ S, Na ２ O ２ , Na ２ H ３ CO ６ or H ２ O ２ and other peroxides.

[0091] The desulfurization step is carried out for, for example, 30 to 60 minutes. Usually, about 45 minutes is sufficient for the desulfurization step. The desulfurization step does not need to be time-controlled; it can be carried out until the smell of hydrogen sulfide gas disappears from the first precursor or the second precursor after the dehairing step, or until the color of the liquid seeping out from the first precursor or the second precursor after the dehairing step becomes light brown.

[0092] After the desulfurization step, a so-called dealkalization step is carried out in which potassium hydroxide or sodium hydroxide is removed from the first precursor or second precursor after the unhairing step using a mixture of weak acids such as acetic acid, citric acid, and formic acid. In this step, a bleaching agent such as sodium hydrogen sulfate may be used in combination, if necessary. The dealkalization step may be carried out in a drum subsequent to the previous step.

[0093] After the dealkalization step, a tanning process can be carried out to finish the first precursor or second precursor into leather (tanned hide). If the rawhide does not have animal hair, the second precursor (second precursor that has not been subjected to the dehairing process) immediately after the second fermentation step can be tanned to finish into leather (tanned hide). The tanned hide may be further subjected to a dyeing process or the like.

[0094] As described above, it is possible to provide a method for producing leather and a leather precursor that have a low environmental impact and do not require the use of large amounts of salt for preserving rawhide or large amounts of lime or water for dehairing.

[0095] Example 1: Cowhide (unsalted) was prepared as rawhide. First, the rawhide was initially washed, weighed, and pretreated with soap and soda ash. Hereinafter, the weight of the rawhide simply refers to the weight of the rawhide measured after the initial washing. Then, water (25°C) and granulated sugar (5%, 10%, 15%, and 20% of the weight of the rawhide) were placed in a container in an amount equal to the weight of the rawhide.

[0096] In parallel with the above, a starter was prepared by adding 10 g of yeast (Saccharomyces cerevisiae), 5 g of sugar, and 50 ml of warm water (50°C) to a separate container and allowing it to ferment for 20 minutes in a sealed state.

[0097] The prepared starters were added to the containers containing the rawhide and other ingredients, stirred, and then the containers were covered and stored at room temperature to initiate fermentation of the four samples. The room temperature was approximately 25°C to 35°C, and the relative humidity was 40% to 70%. After that, the condition of the rawhide (corresponding to the first precursor) was checked at predetermined intervals.

[0098] After one day, no hair loss was visually observed, and no hair loss occurred even when the rawhide was pinched or rubbed with the fingertips.

[0099] After two days, the amount of hair loss was the same as on day 1. There was a change in odor compared to day 1. The same change was observed in all four samples containing different amounts of sugar.

[0100] After three days, hair loss (hereinafter referred to as hair loss) was observed in thin-haired areas such as the abdomen in the samples containing 5%, 10% and 15% sugar.

[0101] After four days, hair loss was observed evenly in thin hair areas for all four samples containing different amounts of sugar.

[0102] After 5 days, all four samples showed uniform hair loss in the thin hair areas.

[0103] After 6 days, about 80% of the hair in each of the four samples was easily removable.

[0104] After 4 weeks, the odor of hydrogen sulfide gas and ammonia began to be detected, as well as odors indicating the decomposition of keratin and globular proteins. The odor of alcohol also increased.

[0105] After seven weeks, complete hair loss was observed in all four samples, but there was also a decrease in the tear strength of the skin.

[0106] As described above, the rawhide fermented in the treatment solution, i.e., the first precursor, could be preserved and preserved for less than 7 weeks without adding salt. Furthermore, after fermentation for a predetermined number of days (e.g., 3 days), the effect of promoting dehairing was observed.

[0107] (Example 2) Fermentation of four samples was started in the same manner as in Example 1. After 12 hours, the rawhide (corresponding to the first precursor) was squeezed and dehydrated using a press. The squeezing rate was 40%. The squeezing rate is the percentage of the weight of the dehydrated water relative to the weight of the rawhide including water immediately before dehydration, which is taken as 100%.

[0108] After dehydration, the backside of each rawhide sample was uniformly sprinkled with sugar (sucrose) in an amount of 20% by weight relative to the weight of the rawhide. Each sugar-sprinkled sample was folded in half with the sugar-coated side facing each other, then folded in quarters and stacked, and stored in a dry room (warehouse). The room temperature was approximately 20°C to 30°C, and the relative humidity was 40% to 60%. Thereafter, the condition of the rawhide (corresponding to the second precursor) was checked at predetermined intervals.

[0109] After one day, no hair loss was visually observed, and no hair loss occurred even when the rawhide was pinched or rubbed with the fingertips.

[0110] After two days, the amount of hair loss was the same as on day 1. There was a change in odor compared to day 1. The same change was observed in all four samples containing different amounts of sugar.

[0111] After three days, hair loss (hereinafter referred to as hair loss) was observed in thin-haired areas such as the abdomen in the samples containing 5%, 10% and 15% sugar.

[0112] After four days, hair loss was observed evenly in thin hair areas for all four samples containing different amounts of sugar.

[0113] After 5 days, all four samples showed uniform hair loss in the thin hair areas.

[0114] After 6 days, for all four samples, about 80% of the hair had fallen out easily, and about 95% of the hair was in a state where it could be easily removed.

[0115] After 4 weeks, the odor of hydrogen sulfide gas and ammonia began to be detected, as well as odors indicating the decomposition of keratin and globular proteins. The odor of alcohol also increased.

[0116] After seven weeks, no deterioration of the hide was visually observed in any of the four samples. Since no decrease in tear strength was observed and no deterioration of the hide was visually observed, it was determined that the protein degradation of the rawhide had not progressed.

[0117] No difference was observed between the 12-week and 7-week periods.

[0118] As described above, fermentation continued even after the rawhide was removed from the treatment solution, and the effect of promoting hair removal was obtained. Furthermore, the rawhide coated with sugar, i.e., the second precursor, could be preserved and stored for at least 12 weeks.

[0119] In comparison with the samples of Example 1, the samples of Example 2 showed no decrease in the tear strength of the leather after 7 weeks.

[0120] When rawhide is stored in the treatment solution for a long period of time, as in the samples of Example 1, excessive fermentation occurs, producing acids such as acetic acid, which makes the treatment solution acidic. This is thought to be why the acid caused protein decomposition (hydrolysis) in the samples of Example 1, resulting in a decrease in tear strength. However, no such decrease in tear strength was observed in the samples of Example 2. Therefore, for longer-term storage of rawhide, it is more preferable to complete the first fermentation process within a specified period, transition to the second fermentation process, and store the rawhide in the second precursor state.

[0121] Thus, it was found that, particularly in the state of the second precursor, it can be well preserved at room temperature for at least 12 weeks without deterioration in appearance or physical properties (tear strength) and without the addition of salt.

[0122] As explained above in Examples 1 and 2, the leather manufacturing method according to this embodiment does not require salt to preserve the rawhide, and does not produce waste liquid containing large amounts of salt during the leather manufacturing process, resulting in a low environmental impact.

[0123] Furthermore, it was found that rawhide preserved in the above manner (treated in the first fermentation step or the first and second fermentation steps) has its dehairing accelerated during preservation. Therefore, the dehairing process after the first or second fermentation step does not require the liming step required in conventional techniques, which reduces the environmental impact. In other words, the dehairing method according to this embodiment does not discharge large amounts of lime sludge, which reduces the environmental impact.

[0124] When the leather manufacturing method according to this embodiment is not used for preserving rawhide but is used as the dehairing method according to this embodiment, the rawhide to be subjected to the first fermentation step and the second fermentation step may be salted. In this case, although waste liquid containing salt may be generated in the leather manufacturing process (the process of carrying out the dehairing method according to this embodiment), a large amount of lime sludge is not discharged, and the environmental load is still small.

[0125] As described above, a method for producing leather and a leather precursor that places less strain on the environment can be provided.

[0126] [Another embodiment] (1) In the above embodiment, the depilation step of depilating a second precursor was described as an example. However, the depilation step is not limited to the case of depilating a second precursor. The depilation step can also be performed in the case of a first precursor, as described above. That is, the depilation step may be, for example, a step of depilating a first precursor. In this case, the depilation step may include a step of adding potassium hydroxide or sodium hydroxide in an amount of 0.3% to 1.0% by weight and sodium sulfide in an amount of 0.8% to 2.0% by weight or a mixture of sodium bicarbonate and sodium bicarbonate in an amount of 0.8% to 2.0% by weight, relative to the weight of the rawhide, to the first precursor and stirring the mixture.

[0127] (2) In the above embodiment, the atmospheric conditions in the first fermentation step and the second fermentation step and the holding time (fermentation time) required for the first fermentation step were described, but these atmospheric conditions and holding times (fermentation times) are not essential requirements. The first fermentation step and the second fermentation step are yeast growth and metabolism, i.e., so-called microbial reactions, and therefore the requirements related to the atmospheric conditions and holding times (fermentation times) in the first fermentation step and the second fermentation step only affect the rate at which the microbial reaction progresses. In the leather manufacturing method according to this embodiment, the effects of the preservation treatment and the dehairing effects described in this embodiment are realized as long as the microbial reaction in the first fermentation step and the second fermentation step progresses.

[0128] It should be noted that the embodiments disclosed in this specification are merely examples, and the embodiments of the present disclosure are not limited to these, and can be modified as appropriate within the scope of the purpose of the present disclosure.

[0129] The present disclosure is applicable to methods for making leather and leather precursors.

Claims

A method for manufacturing leather, comprising: a soaking step of soaking rawhide in a treatment solution containing sugar and yeast of the genus Saccharomyces; and a first fermentation step of soaking the rawhide in the treatment solution and fermenting it. 　 The method for manufacturing leather according to claim 1 , wherein the treatment liquid contains water in an amount of 50% to 200% by weight of the rawhide, and sugar in an amount of 1.5% to 30% by weight of the rawhide.

3. The method for producing leather according to claim 2, wherein the first fermentation step is carried out in an atmosphere having a temperature of 15° C. or higher and a relative humidity of 30% or higher and 80% or lower.

4. The method for producing leather according to claim 3, wherein in the first fermentation step, the rawhide is fermented by immersing it in the treatment solution for a period of time ranging from 2 hours to 72 hours.

5. The method for producing leather according to claim 1, further comprising: a dehydration step of dehydrating a first precursor obtained by fermenting the rawhide in the first fermentation step; a sugar addition step of attaching sugar to a surface of the first precursor after the dehydration step; and a second fermentation step of fermenting the first precursor after the sugar addition step.

6. The method for producing leather according to claim 5, wherein in the sugar adding step, sugar is attached to the surface of the first precursor in an amount of 1% to 30% by weight of the rawhide. 　 The method for producing leather according to claim 6, wherein in the second fermentation step, the first precursor is fermented in an atmosphere having an air temperature of 20°C or higher and 40°C or lower and a relative humidity of 30% or higher and 70% or lower for a period of 1 day or higher and 50 days or lower.

8. The method for producing leather according to claim 5, further comprising a dehairing step of dehairing a second precursor obtained by fermenting the first precursor in the second fermentation step, wherein in the dehairing step, potassium hydroxide or sodium hydroxide in an amount of 0.3% to 1.0% by weight and sodium sulfide in an amount of 0.8% to 2.0% by weight, relative to the weight of the rawhide, are added to the second precursor and stirred. 　 The method for producing leather according to claim 8, further comprising a desulfurization step carried out after the unhairing step, wherein in the desulfurization step, an oxidizing agent is added to the second precursor in an amount of 0.8% to 2.0% by weight based on the weight of the rawhide and stirred.

5. The method for producing leather according to claim 1, further comprising a dehairing step of dehairing a first precursor obtained by fermenting the rawhide in the first fermentation step, wherein in the dehairing step, potassium hydroxide or sodium hydroxide in an amount of 0.3% to 1.0% by weight and sodium sulfide in an amount of 0.8% to 2.0% by weight, relative to the weight of the rawhide, are added to the first precursor and stirred. 　 The method for producing leather according to claim 10, further comprising a desulfurization step carried out after the unhairing step, wherein in the desulfurization step, an oxidizing agent is added to the first precursor in an amount of 0.8% to 2.0% by weight based on the weight of the rawhide, and the first precursor is stirred.

12. The method for producing leather according to claim 1, further comprising a step of preparing a starter containing the yeast, wherein in the step of preparing the starter, 5 g to 10 g of the yeast, 5 g to 10 g of sugar, and 30 ml to 70 ml of hot water having a temperature of 40° C. to 60° C. are fermented in a sealed state for 15 minutes to 20 minutes to prepare the starter. 　 A leather precursor comprising sugar, yeast of the genus Saccharomyces, and rawhide.

14. The leather precursor of claim 13, further comprising ethanol.