Apparatus and method for manufacturing leather-imitating sheet structures from waste leather or raw hide

Abstract

The present invention provides an apparatus for manufacturing regenerated leather of an asymmetric layered structure similar to real leather from waste leather or raw leather. The apparatus includes a plurality of functional sub-units located at a leather-imitated sheet forming platform, which can be modularized and sized to meet different needs or requirements. The invention also provides a method for manufacturing regenerated leather from waste leather by using the equipment.

Description

Technical Field

[0001] The present invention relates to an apparatus and method for manufacturing regenerated leather, and more particularly to an apparatus and method for manufacturing a leather-like sheet structure from waste leather or raw hides without requiring cumbersome conditions and environmentally unfriendly reagents. Background Art

[0002] Waste leather comes from different stages of the leather manufacturing process, such as the preparation of wet blues, which are wet chrome-tanned raw hides. Such waste leather is usually irregular in shape and non-uniform in thickness, much like logs that must be sawn into planks or stakes before being put on the market. The raw wet blues must be prepared for the next manufacturing process, such as shaving to a uniform thickness and trimming off the irregular edges. The goal is to transform a pile of irregular raw tanned hides into a pile of tanned leather with a smooth surface, uniform thickness, and dimensions / shapes that meet the requirements for further processing. During this shaping (e.g., scraping / trimming) process, approximately 50% or more of the raw material will be trimmed off and become leather scraps. In the past, this waste leather was mainly disposed of by burying or burning, as it was generally considered to have limited value. However, the currently known general disposal methods have imposed a huge environmental burden. Therefore, efforts have been made to explore the possibility of recycling wet blues into some more useful and valuable materials such as regenerated leather. This can be achieved by re-bonding the waste leather, but other problems arise during the waste leather re-bonding process. Compared with metal or plastic scraps, leather scraps seem to be more environmentally friendly waste. However, the cold scientific fact is that waste leather is almost as bad as waste rubber tires, and they are both difficult to complete the recycling process. To operate an industrial-scale recycling process and meet strict waste emission standards, many technical challenges need to be overcome.

[0003] Leather can generally be classified into four types according to which layer of the animal skin is retained and which layer is removed: full grain leather, top grain leather, buffed leather, and suede leather. The manufacturing methods of full grain leather, top grain leather, and buffed leather are different, but they all have an outer layer (the grain layer), except for suede leather, which only has the bottom layer (the dermis layer) and the flesh layer of the animal skin. Among these three, the strongest and most valuable type is top grain leather, which includes the grain, the dermis layer, and some flesh layer. Generally, top grain leather is thicker and stronger than full grain leather, but still has sufficient water resistance. Therefore, top grain leather is considered the most valuable type among these three and is more widely used for different items, including but not limited to shoes, boots, and belts. It has both water-proofing function and breathability, so it is an ideal alternative material for making rain shoes. The flesh layer in top grain leather provides sufficient channels for air to flow through the products made from it.

[0004] Since both the grain surface and the flesh side of leather are composed of the same collagen fibers but arranged in different patterns / densities, the grain surface is generally more resistant to environmental erosion than the flesh side. On the other hand, the flesh side of leather usually provides a softer texture and is more flexible and heat-insulating than the grain surface because of its relatively loose collagen fiber structure.

[0005] To reconstruct such an asymmetric and inhomogeneous leather sheet structure, a specially designed machine is needed to produce a leather-like sheet from a modified slurry of collagen fibers derived from waste leather such as wet-blue shavings. Summary of the Invention

[0006] Accordingly, a first aspect of the present invention provides an apparatus for manufacturing a leather-like sheet structure from waste leather slurry.

[0007] Exemplarily, the apparatus of the present invention includes a platform on which a continuous regenerated leather sheet is formed from a modified slurry prepared from waste leather including wet-blue shavings. Other possible sources for preparing the modified slurry include raw hides, especially alkali-soaked raw hides. The platform according to various embodiments includes a number of modules, each module including a plurality of subunits and being for different functions.

[0008] In one embodiment, a vacuum suction module is provided on the platform and is configured to at least partially remove water from the modified slurry to form a leather-like sheet. To achieve the suction effect across the entire module, the vacuum suction module includes a plurality of vacuum suction subunits that are longitudinally adjacent to each other along the forming direction of the leather-like sheet or are alternately arranged with one or more other types of functional subunits. The one or more types of functional subunits that are alternately arranged with the vacuum suction subunits in the longitudinal direction along the forming direction of the leather-like sheet include, but are not limited to: a transport subunit, a heating subunit, and / or a vacuum enhanced embossing subunit. Other functional subunits not described herein may also be arranged adjacent to the vacuum suction subunits according to the needs or requirements of the apparatus in different applications.

[0009] In certain embodiments, the platform is formed by a continuous mesh that at least partially wraps around a plurality of motion drive subunits, and the functional subunits include vacuum suction subunits and other subunits, so as to be able to provide a movable belt that moves in the direction of leather-like sheet formation when the corresponding motion drive subunits are activated to drive the movement of the movable belt.

[0010] Preferably, the continuous mesh is selected from a perforated mesh to remove water through the mesh holes of the perforated mesh in a vacuum environment.

[0011] In some embodiments, the motion drive subunit includes a plurality of rollers around which the punching mesh is partially wound to form a movable belt.

[0012] In some embodiments, the plurality of rollers includes a center roller and a couch roll, and the punching mesh is partially wound around the center roller and the couch roll at two opposite ends to form a movable belt.

[0013] Preferably, the punching mesh is selected from stainless steel sheets with a mesh size of at least 150 or greater, for example, in the range of 150 to 200, and the movable belt also serves as a fine mesh filter for separating collagen fibers from the aqueous sample portion of the slurry.

[0014] In some embodiments, the transport subunits are evenly distributed along the movable belt to more smoothly drive the slurry on the belt in the direction of artificial leather sheet formation and avoid stress concentration on only one or more of the rollers.

[0015] In other embodiments, after the vacuum suction module but before reaching the pick-up roller, a plurality of vacuum enhanced embossing subunits are provided in a subsequent vacuum enhanced embossing module to apply an embossing effect on at least one side of the partially dried artificial leather sheet. The heating subunit and the transport subunit can be alternately arranged relative to the vacuum enhanced embossing subunit to evenly distribute the driving force and temperature throughout the module.

[0016] According to some embodiments, the device further includes a mixing chamber for mixing the collagen slurry and a doctor blade for evenly distributing the mixed collagen slurry in the transverse direction on the artificial leather sheet forming platform (i.e., the movable belt).

[0017] At the distal end of the movable belt, the device may further include a collecting device for collecting the artificial leather sheet after peeling it off the movable belt.

[0018] In some embodiments, the collecting device located at the distal end of the movable belt is selected from pick-up rollers.

[0019] A second aspect of the present invention provides an improved collagen slurry prepared from waste leather. Exemplarily, the improved collagen slurry contains neither hydrophobic contaminants nor hydrophilic contaminants.

[0020] To provide the collagen slurry, the waste leather is first crushed and then thoroughly washed to remove all kinds of unwanted contaminants, which includes but is not limited to washing off grease with a detergent and removing adhesives and surface coatings with a solvent.

[0021] In some embodiments, the waste leather is crushed into fragments of about 2 to 5 mm under dry conditions. The waste leather can be crushed under dry conditions by using any feasible method, including but not limited to a shredder.

[0022] In certain embodiments, the waste leather is degreased in an organic solvent.

[0023] In certain embodiments, the waste leather is degreased multiple times in an organic solvent such as acetone until all hydrophobic contaminants are eliminated.

[0024] In certain embodiments, the collagen fibers extracted from the waste leather are directly mixed with a detergent solution.

[0025] In certain embodiments, the collagen fibers are washed multiple times in the detergent solution until all hydrophilic contaminants are eliminated.

[0026] In certain embodiments, the average size of the collagen fibers is larger than the mesh size of the filter used to separate the collagen fibers from the aqueous portion of the slurry.

[0027] In certain embodiments, the separated collagen fibers have an average length of about 0.1 to 2.0 mm.

[0028] Preferably, the mesh size of the filter used to separate the collagen fibers from the aqueous portion of the slurry is about 150 mesh; the filter is selected from stainless steel sheets having a corresponding mesh size.

[0029] In certain embodiments, the filtration is carried out under a mild vacuum.

[0030] In certain embodiments, the collagen fibers need to be washed multiple times until a sufficiently pure collagen slurry is obtained.

[0031] In certain embodiments, the obtained collagen slurry is mixed with water at a weight percentage of about 90.0 - 99.5% before being fed to the movable belt of the device.

[0032] Optionally, a small amount of suspension stabilizer can be added to the collagen fiber slurry before or after mixing the collagen fiber slurry with water. Such suspension stabilizers can be water-soluble, biodegradable materials, including but not limited to: modified starch, alkoxy celluloses (AOC) such as carboxymethyl cellulose (CMC), methyl cellulose (MC), ethyl cellulose (EC), and hydroxypropyl methyl cellulose (HPMC). Other less preferred components that can be added to the collagen fiber slurry include latex, water-based polyurethane, water-based acrylic, and water-based epoxy resin.

[0033] The third aspect of the present invention provides a method for manufacturing a leather-like sheet using the device of the first aspect and the slurry of the second aspect.

[0034] Exemplarily, the method includes:

[0035] Provide the collagen slurry according to the second aspect into water;

[0036] Distribute the collagen slurry in water uniformly onto one side of a movable belt in the transverse direction, the movable belt being selected from fine mesh filters;

[0037] Initiate the circumferential movement of at least the center roll and the couch roll so as to drive the movable belt in the direction of artificial leather sheet formation;

[0038] Activate a vacuum suction sub-unit and a transport sub-unit arranged adjacent to the opposite side of the movable belt to at least partially remove water from the improved collagen slurry and facilitate the formation of a flat sheet;

[0039] After substantially removing most of the water, form a filter cake of collagen fibers along the movable belt in the longitudinal direction by self-aggregation; and

[0040] When subjected to the imprinting force applied by the periodically arranged vacuum suction sub-units along the movable belt, an asymmetric layered structure is gradually formed in the filter cake.

[0041] In certain embodiments, the improved collagen slurry has a desirable concentration range in water from 0.5 to 10.0% by weight.

[0042] In certain embodiments, the improved collagen slurry in water is uniformly distributed onto one side of the movable belt in the transverse direction with a depth (or height) of about 4 to 8 mm.

[0043] In one embodiment, the method further includes embossing at least one side of the artificial leather sheet.

[0044] Preferably, embossing at least one side of the artificial leather sheet is performed with an imprinting force applied only to one side of the artificial leather sheet and is further enhanced by vacuum suction.

[0045] In certain embodiments, after substantially removing all of the water, forming the artificial leather sheet on the side of the movable belt by self-aggregation of the remaining collagen fibers is a binder-free process.

[0046] In certain embodiments, after substantially removing all of the water from the artificial leather sheet, peel the artificial leather sheet from the movable belt.

[0047] In certain embodiments, the movable belt is made of a stainless steel sheet having a mesh size of at least 150 or greater, for example in the range of 150 to 200, and the movable belt also serves as a fine mesh filter for vacuum filtration.

[0048] In some embodiments, the leather-like sheet is also freeze-dried (lyophilized after freezing) to remove water from the frozen leather-like sheet and create voids.

[0049] In some embodiments, the resulting leather-like sheet can be as thin as 0.5 mm or thinner.

[0050] Other aspects of the present invention include bonded leather made from leather-like sheets manufactured according to various aspects of the present invention, wherein the leather-like sheet after lyophilization (the freeze-drying) is post-treated until it is cured or no longer water-dispersible.

[0051] In some embodiments, the post-treatment of the lyophilized leather-like sheet is treatment with one or more cross-linking agents including but not limited to dialdehydes, diepoxides, or diisocyanates such as succinaldehyde, glutaraldehyde, adipaldehyde, epoxidized soybean oil, epoxidized vegetable oil, diepoxybutane, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, 1,4-butanediol diglycidyl ether, 1,5-pentanediol diglycidyl ether, 1,6-hexanediol diglycidyl ether, diphenylmethane diisocyanate (MDI), toluene diisocyanate (TDI), hexamethylene diisocyanate (HDI), and isophorone diisocyanate (IPDI).

[0052] Compared with traditional methods / platforms, the present invention provides at least the following advantages / differences:

[0053] (1) The formation of the leather-like sheet in the present invention is a non-melting process carried out at room temperature and most humid conditions to avoid the formation of baking paper.

[0054] (2) The present invention uses a very mild washing process to remove both hydrophobic and hydrophilic substances from waste leather, rather than relying on conventional washing processes that rely on strong chemicals, high-speed centrifugation, enzymatic digestion, or cumbersome dialysis.

[0055] (3) The vacuum filtration used to dry the collagen slurry is a process from no heating to low heating, making the drying process more controllable, especially for materials that are more susceptible to temperature changes or more sensitive to temperature changes;

[0056] (4) The negative pressure applied during the vacuum filtration process is low and is preferably carried out at a temperature from room temperature to near zero degrees;

[0057] (5) The formation of the filter cake is achieved by self-aggregation of collagen fibers after substantially removing most of the water, rather than using a high-pressure hydroentangling process;

[0058] (6) The asymmetric layered structure in the imitation leather sheet is gradually formed over the longitudinal distance (length) of the movable belt by means of a vacuum and pressure gradient difference (rather than by means of the center of gravity); in the present invention, neither a rolling process for forming a dense / tightly packed layer structure in the imitation leather sheet nor a thermal foaming process for forming a loosely packed layer structure is used;

[0059] (7) Embossing is carried out by applying an imprinting force only on one side of the imitation leather sheet without any high compressive force;

[0060] (8) Since the shredding of waste leather is a dry process, any unused, shredded waste leather can be retained or sent back to the recycling process to produce collagen slurry at a later time;

[0061] (9) A freeze-drying process with a high vacuum of -80 °C to -60 °C is employed, which produces most of the voids by ice sublimation instead of using the conventional thermal foaming process;

[0062] (10) Except for the shredding and freeze-drying processes carried out under dry conditions, the remaining processes in this method are carried out under wet conditions;

[0063] (11) The finished imitation leather sheet with an asymmetric layered structure imitating real leather can be further processed into bonded leather and other leather products / sheets;

[0064] (12) The finished recycled leather can be thinner than 0.5 mm, while the average thickness of conventional recycled leather ranges from 2.0 to 4.0 mm.

[0065] This section "Summary of the Invention" is used to briefly introduce some concepts that will be further described in the following section "Detailed Description". This section "Summary of the Invention" is not intended to identify the key features or essential features of the subject matter to be protected, nor is it intended to be used as an aid in determining the scope of the subject matter to be protected. Other aspects of the present invention are disclosed in the embodiments described below. Brief Description of the Drawings

[0066] Like reference numerals in the drawings represent the same elements or elements that are functionally similar. The drawings include diagrams of certain embodiments to further illustrate and clarify the above and other aspects, advantages, and features of the present invention. It should be understood that these drawings only depict some embodiments of the present invention and are not intended to limit the scope of the present invention. The present invention will be described and explained with more features and details using the drawings, in which:

[0067] Figure 1 shows the structure of a conventional device for paper manufacturing;

[0068] Figure 2One embodiment of the apparatus for manufacturing smooth regenerated leather from an improved slurry of waste leather according to the present invention is schematically depicted in a side view, where V represents a vacuum suction sub-unit; T represents a transport sub-unit; H represents a heating sub-unit; the solid grey arrow indicates the forming direction of the leather-like sheet;

[0069] Figure 3 Another embodiment of the apparatus for manufacturing embossed regenerated leather from an improved slurry of waste leather according to the present invention is schematically depicted in a side view, where V represents a vacuum suction sub-unit; T represents a transport sub-unit; H represents a heating sub-unit; E represents a vacuum enhanced embossing sub-unit; the solid grey arrow indicates the forming direction of the leather-like sheet;

[0070] Figure 4A describes in words the arrangement of the sub-units of a conventional Fourdrinier table for paper manufacturing in a top view; D represents a drainage sub-unit; S represents a support; the grey arrow indicates the paper forming direction;

[0071] Figure 4B The arrangement of the sub-units of the platform of an apparatus for producing leather-like sheets according to one embodiment is described in words in a top view; D represents a drainage sub-unit; T represents a transport sub-unit; G represents a grain embossing sub-unit; the grey arrow indicates the forming direction of the leather-like sheet;

[0072] Figure 5 Another embodiment of the apparatus according to the present invention is schematically depicted in a top view of the platform for forming a leather-like sheet; the grey arrow indicates the forming direction of the leather-like sheet.

[0073] Those skilled in the art should understand that the elements in the drawings are shown only for simplicity and clarity purposes and are not necessarily drawn to scale. Detailed Description of the Invention

[0074] References to "one embodiment", "an embodiment", "exemplary embodiments", etc. in this specification mean that the described embodiments may include specific features, structures, or characteristics, but not necessarily every embodiment includes that specific feature, structure, or characteristic. Moreover, such phrases do not necessarily refer to the same embodiment. Additionally, when combining embodiments to describe specific features, structures, or characteristics, it should be recognized that within the knowledge of those skilled in the art, such features, structures, or characteristics can be implemented in combination with other embodiments, whether or not these embodiments are explicitly described herein.

[0075] The terms "a" or "an" are used to include one or more than one, and the term "or" is used to mean non-exclusive "or", unless otherwise specified. In addition, it should be understood that the words or terms used herein are for illustrative purposes only and do not constitute any limitation, unless otherwise specified. Moreover, all the disclosures, patents and patent documents referred to herein are incorporated herein by reference in their entirety as if each were incorporated separately by reference. If there are differences in the usage between this text and the documents incorporated by reference, the usage in the incorporated reference documents shall be considered as a supplement to the usage herein; for any contradictions or inconsistencies, the usage herein shall prevail.

[0076] Values in range format should be interpreted in a flexible manner to include not only the explicitly recited values that are the limits of the range, but also all individual values or sub-ranges subsumed within that range as if each value and sub-range were explicitly recited. For example, a concentration range of "about 0.1% to about 5%" should be interpreted to include not only the explicitly recited concentrations of about 0.1% to about 5% by weight, but also the individual concentrations (e.g., 1%, 2%, 3% and 4%) and sub-ranges (e.g., 0.1% to 0.5%, 1.1% to 2.2% and 3.3% to 4.4%) within the indicated range.

[0077] It will be apparent to those skilled in the art that various modifications can be made to the present invention, including additions and / or substitutions, without departing from the scope and spirit of the present invention. Specific details may be omitted so as not to obscure the present invention; however, the purpose of writing this disclosure is to enable those skilled in the art to practice the teachings herein without undue experimentation.

[0078] FIG. 1 schematically shows the structure of a conventional Fourdrinier paper machine for papermaking, which comprises: (a) a paper former: causing suspended cellulose fibers to aggregate with each other by gravity and vacuum filtration to form a continuous paper web; (b) a press: removing excess water in the wet paper by squeezing the wet paper between two felt rollers; (c) a dryer: drying to remove the remaining water by heating; (d) a sizing press: spraying a thin layer of cooked starch solution with a pair of rollers; (e) a calender: making the paper smoother by passing the paper between several pairs of rollers under high pressure; and (f) a reel (not shown in FIG. 1): winding the paper onto a reel for transportation.

[0079] In a conventional papermaking process using a Fourdrinier paper machine, the Fourdrinier table is equivalent to (a) a sheet former. The paper produced from wood pulp by a conventional Fourdrinier paper machine is baking paper (hard and dry), while the leather-like sheet produced by a significantly improved Fourdrinier table according to some embodiments of the present invention is different from the hard and dry baking paper, but has a leather-like sheet structure, which is stretchable and still wet. In Figure 2 One of these embodiments is depicted.

[0080] In Figure 2 an embodiment of the apparatus 10 of the present invention is provided, which is based on a conventional Fourdrinier table originally used for papermaking and has been significantly improved. It includes a perforated mesh 16 partially wound around a center roll 13 and a couch roll 14, wherein the perforated mesh 16 is arranged on a plurality of functional sub-units (V, T, H) between the center roll 13 and the couch roll 14 to form a fine mesh filter belt. As Figure 2 shown, by sufficiently mixing in a headbox 11, the improved collagen slurry is suspended in water at a weight percentage of 0.5 to 10%, and then the improved collagen slurry is evenly spread onto the fine mesh filter belt 16 along a transverse direction relative to the leather-like sheet forming direction (represented by the gray arrow) by a doctor blade 12. Thus, a uniformly distributed layer of the improved collagen slurry 17 is formed in a row. At the same time, the center roll 13 arranged at one end close to the headbox 11 and the doctor blade 12 and the couch roll 14 arranged at the opposite end of the center roll 13 are started to provide a circumferential movement in the same direction, so as to drive the fine mesh filter belt 16 to move in the leather-like sheet forming direction. That is, as Figure 2 shown, the fine mesh filter belt 16 is driven by the center roll 13 and the couch roll 14 to move clockwise, so that the uniformly distributed collagen slurry 17 moves away from the headbox 11 and the doctor blade 12 together with the fine mesh filter belt 16. A pick-up roll 15 is provided at the distal end of the fine mesh filter belt 16 for collecting the leather-like sheet peeled from the side of the fine mesh filter belt on which collagen fiber self-aggregates are formed.

[0081] In some embodiments, a vacuum suction sub-unit (V) and a transport (or friction traction) sub-unit (T) are alternately arranged on opposite sides of the fine mesh filter belt to promote the uniform distribution of the collagen slurry on the other side of the fine mesh filter belt.

[0082] Compared with a conventional Fourdrinier paper machine for papermaking as shown in, for example, FIG. 1, the apparatus of the present invention according to various embodiments provides more flexibility for users to assemble different sub-units as needed and change the size of the fine mesh filter belt. Figure 3 shows an example of one of the various embodiments of adding more functions to the Figure 2 improved Fourdrinier table.

[0083] InFigure 3 In this case, the apparatus 10 mainly provides two modules, namely, a vacuum filtration module 10a and a vacuum enhanced embossing module 10b. Figure 3 The vacuum filtration module 10a of the apparatus 10 in Figure 2 is similar to the apparatus shown, except that the distal end of the fine mesh filter belt 16 is no longer connected to the pick-up roll 15, but is connected to the vacuum enhanced embossing module 10b. This embodiment is particularly useful when embossing artificial leather sheets. The vacuum enhanced embossing module 10b includes a plurality of functional sub-units, such as a transport sub-unit (T), a heating sub-unit (H), and a vacuum enhanced embossing sub-unit (E), which provides a substantially seamless active area after the vacuum suction module through a continuous belt of a movable belt connected to the vacuum suction module, and the continuous belt is, for example, a continuous fabric connected to or extending from the movable belt. In the vacuum enhanced embossing module 10b, each type of functional sub-unit is alternately arranged with the other two types of functional sub-units along the longitudinal direction of the artificial leather sheet structure. However, the arrangement of different types of functional sub-units in the vacuum enhanced embossing module is flexible, which means that the user can freely assemble the functional sub-units in different orders in any one or both of the transverse and longitudinal directions of the improved fourdrinier table to a certain extent according to needs. The improved fourdrinier table described herein allows its user to easily add, remove, or replace any existing functional sub-unit according to needs. It also allows adjusting the size of the fourdrinier table in the transverse and / or longitudinal directions relative to the artificial leather sheet forming direction.

[0084] Figures 4A and 4B respectively depict in plan view a conventional arrangement of a fourdrinier table for papermaking (from U.S. Patent No. 4321108) and an arrangement of an improved fourdrinier table for vacuum filtration according to an embodiment of the present invention, where the text designation D represents a drainage sub-unit; S represents a support sub-unit; H represents a heating sub-unit; T represents a transport or friction traction sub-unit; G represents a grain embossing sub-unit. In the longitudinal direction, that is, along the same direction as the paper forming direction, the fourdrinier table in Figure 4A is provided with alternately arranged drainage and support sub-units, and only the drainage sub-unit is a functional sub-unit in this patent. Only a single function, namely, drainage, is provided on the conventional fourdrinier table for papermaking. In contrast, Figure 4B the improved fourdrinier table shown has different functional sub-units alternately arranged in the transverse and longitudinal directions, including drainage, transport, and heating sub-units. In addition to the drainage sub-unit (or described as a vacuum suction sub-unit herein), in Figure 4B the improved fourdrinier table shown, the alternately arranged transport sub-units reduce the stress concentration on the two main rollers, namely, the center roll and the couch roll, such as the stress concentration in the conventional fourdrinier table shown in Figure 4A. In Figure 4BAn improved Fourdrinier table is added with a heating subunit, which enhances the vacuum suction effect exerted on it during the formation of artificial leather sheets. By applying vacuum suction to the movable belt via the vacuum suction subunit, when forming the artificial leather sheet, the bottom surface of the artificial leather sheet closer to the vacuum suction subunit will form a more densely packed collagen layer, which is similar to the smooth and waterproof structure of the grain layer of animal leather. On the other hand, the upper surface of the artificial leather sheet farther from the vacuum suction subunit will simultaneously form a more loosely packed collagen layer, which is similar to the rough and breathable structure of the flesh layer of animal leather. There is an intermediate layer between the upper and bottom surfaces of the artificial leather sheet, and this intermediate layer has a collagen packing density that gradually changes from high to low along a virtual vertical axis that is substantially perpendicular to the average horizontal plane of the vacuum suction subunit (or perpendicular to the horizontal plane of the movable belt of the improved Fourdrinier table), which is similar to the dermis layer of animal leather. Therefore, the structure of the improved Fourdrinier table according to some embodiments of the present invention is configured to help form such an asymmetric and non-uniform layered structure in artificial leather or recycled leather sheets.

[0085] Figure 5 One embodiment of the vacuum enhanced embossing module of the device of the present invention is schematically depicted in a top view, wherein the vacuum suction subunit 501, the transport subunit 502, and the vacuum enhanced embossing subunit 503 are arranged alternately with each other along the transverse direction, and after the vacuum suction subunit 501, there are two transport subunits 502 and vacuum enhanced embossing subunits 503 arranged successively along the longitudinal direction. The grey arrow indicates the artificial leather sheet forming direction. In this embodiment, in the vacuum enhanced embossing module, the arrangement of the same set of functional subunits can be different between the transverse direction and the longitudinal direction. This embodiment again shows that the users of the device can freely assemble and rearrange according to their needs in any order and / or combination of different functional subunits.

[0086] According to some embodiments of the present invention, the vacuum enhanced embossing module is introduced at the wet end of the sheet forming process, so that when the sheet passes through the vacuum enhanced embossing subunit, the sheet is still wet, to avoid engraving on a baking paper-like, highly compressed hard material. After passing through the vacuum enhanced embossing module, the engraved pattern can be reversely transferred to the bottom surface of the artificial leather sheet without applying a high compression force to both surfaces of the sheet, which is different from the conventional papermaking process carried out by a traditional Fourdrinier table. Only the bottom surface of the artificial leather sheet is subjected to the imprinting force, while the opposite surface, which is the non-engraved surface, is only subjected to limited compression, which is similar to intaglio printing.

[0087] Those of ordinary skill in the art should understand that the alternating arrangement of different types of functional subunits can be carried out along the longitudinal axis, along the transverse axis, or along both the longitudinal axis and the transverse axis with respect to the artificial leather forming direction.

[0088] The following examples are provided herein to facilitate understanding of certain embodiments of the present invention. The scope of the present invention should be defined by the appended claims.

[0089] Example 1 - Production of thin and smooth baking paper-like regenerated leather

[0090] Use a shredder to dry-crush 100 g of wet blue leather into small pieces of 2 - 5 mm. Soak the crushed wet blue leather three times in 200 ml of acetone to remove most of the greasy substances. Put the degreased wet blue leather into a blender containing an appropriate amount of detergent solution to wash, remove minerals, and further reduce the size of the collagen pieces, thereby forming a subdivided and uniform slurry; then vacuum filter the slurry through a 150-mesh filter under a light vacuum to recover insoluble collagen fibers. Repeat the washing - mixing - filtering cycle at least three times to prepare as clean and fine collagen fibers as possible.

[0091] At the last washing, vacuum filter the collagen slurry for 30 minutes until it is roughly dry. Mix the dry collagen filter cake with 900 g of tap water to form a 10% by weight collagen slurry. Take 100 ml of this collagen slurry and pour it in one continuous pour under a light vacuum, along the transverse direction, on a 150-mesh stainless steel filter on a movable belt made of a stainless steel mesh filter, thereby forming a uniform collagen filter cake.

[0092] Once most of the water is removed, leave the filter cake in the vacuum for an additional 15 - 30 minutes to further dry. Finally, turn off the vacuum, carefully remove the still wet and brittle filter cake from the stainless steel filter, then sandwich it between a sufficient amount of dry newspapers, and place this combination in a press with sufficient air circulation for several days. Once the outer newspapers feel dry, take out this combination. The collagen filter cake sandwiched in the middle becomes a smooth and tough baking paper-like leather.

[0093] Example 2 - Production of thick and rough regenerated leather

[0094] Use a shredder to dry-crush 500 g of waste leather into small pieces of 2 - 3 mm. Soak the crushed waste leather three times separately in 1000 ml of acetone to wash away most of the hydrophobic substances. Put the degreased waste leather into a blender containing an appropriate amount of detergent solution to wash and further reduce the size of the collagen blocks, thereby forming a uniform slurry. Then vacuum filter such a uniform slurry through a 150-mesh filter under a light vacuum to recover insoluble collagen fibers. Repeat the washing - mixing - filtering cycle at least three times to prepare the cleanest possible final collagen slurry.

[0095] At the last washing, the collagen slurry is vacuum filtered for at least 30 minutes until it is substantially dry. The dry collagen filter cake is mixed with 9500 g of tap water to form a collagen slurry with a weight percentage of 5%. Take 1000 ml of such collagen slurry and pour it into a headbox above a modified fourdrinier table (minimum traveling speed is 5 - 20 cm / minute). Under a mild vacuum, the collagen slurry is uniformly applied in a single continuous pour in the transverse direction of a filter belt with a mesh size of 150 made of stainless steel sheets, thereby forming a collagen sheet.

[0096] Once the collagen sheet becomes non - flowing, the still - wet and fragile collagen sheet is carefully removed from the stainless - steel filter belt and then sandwiched between two thin and smooth nylon cloths. The sandwiched collagen sheet is rolled up and placed in a - 40 °C refrigerator and frozen overnight. On the next day, the fully - frozen collagen sheet roll is transferred to the drying chamber of a freeze - dryer. The frozen collagen sheet roll is kept in the freeze - dryer for about 3 to 5 days until most of the ice sublimes. Once the collagen sheet is completely dry, it is taken out and kept under ambient conditions for several days until it absorbs an appropriate amount of moisture from the surrounding atmosphere and becomes soft again. The soft collagen sheet is unrolled and stretched to a flat state (without applying compressive force). Then, conventional leather post - treatment steps are performed on the flat collagen sheet, such as fatliquoring, dyeing, and spraying. The final product is a regenerated leather that has an asymmetric texture, that is, one side is tough and "cold", while the other side is soft and "warm". "Cold" and "warm" are used herein to describe the touch feeling, rather than a quantitative assessment by measuring the surface temperature.

[0097] Although the present invention is described in certain embodiments, other embodiments that are obvious to those of ordinary skill in the art are also within the scope of the present invention. Therefore, the scope of the present invention should be defined only by the appended claims.

[0098] Industrial Applicability

[0099] Compared with the conventional methods of manufacturing paper or leather sheets, the device of the present invention is a continuous vacuum forming device that converts collagen slurry into regenerated leather without any cumbersome conditions such as elevated temperatures and substances harmful to our health and the environment. The method of the present invention is essentially a process for forming a non-adhesive artificial leather sheet structure. By using an improved collagen slurry substantially free of heavy metals, PU (polyurethane), and latex, the present invention is significantly different from the known traditional processes. In addition, after almost all the water is removed from the slurry by vacuum filtration, an artificial leather sheet structure can be directly formed on the movable belt of the device of the present invention. The movable belt employed on the basis of the improved long wire table provides a flexible and scalable active area for the formation of artificial leather sheets, allowing for easy maintenance and modification to meet different production specifications. The modular design of the improved long wire table in the present invention also makes it easier to emboss and size-adjust the artificial leather sheets compared to traditional long wire paper machines. Therefore, the present invention is more suitable for industrial-scale waste leather recycling.

Claims

1. An apparatus for manufacturing a leather-like sheet structure from a collagen slurry derived from waste leather or raw hides, said apparatus comprising at least: A leather-like sheet structure forming platform; A mixing chamber for mixing said collagen slurry; A doctor blade for uniformly distributing the mixed collagen slurry onto said leather-like sheet structure forming platform; Said leather-like sheet structure forming platform comprises a vacuum suction module, said vacuum suction module comprising: A plurality of functional subunits; A plurality of motion driving subunits; A movable belt that partially winds around some of said motion driving subunits in said motion driving subunits and covers said plurality of functional subunits to form said leather-like sheet structure forming platform, said movable belt is further configured to separate collagen fibers from the aqueous portion of said collagen slurry under the application of vacuum.

2. The apparatus according to claim 1, wherein said plurality of functional subunits comprises one or more of a vacuum suction subunit, a transport subunit, a heating subunit, and a vacuum enhanced embossing subunit.

3. The apparatus according to claim 1, wherein said plurality of motion driving subunits comprises at least a center roll, a couch roll, and a pick-up roll.

4. The apparatus according to claim 2, wherein said vacuum suction subunit and said transport subunit are alternately arranged along a longitudinal direction towards a distal end of said movable belt, at which end said leather-like sheet structure is formed.

5. The apparatus according to claim 3, wherein said center roll and said couch roll are each partially wound by said movable belt at two opposite ends relative to said mixing chamber and said doctor blade, such that when said center roll and said couch roll start a circular motion in the same direction, said movable belt is driven to move around said center roll and said couch roll in the same direction.

6. The apparatus according to claim 3, wherein said pick-up roll is arranged at an end of said movable belt remote from said mixing chamber and said doctor blade for collecting said leather-like sheet structure peeled off from said movable belt after substantially all of the water has been removed.

7. The apparatus according to any one of the preceding claims, wherein said movable belt is selected from stainless steel sheets with a mesh size of at least 150.

8. The apparatus according to claim 1, further comprising a vacuum enhanced embossing module, said vacuum enhanced embossing module being arranged after said vacuum suction module so as to form a continuous platform leading to said movable belt.

9. The apparatus according to claim 8, wherein said vacuum enhanced embossing module comprises a plurality of functional subunits and a continuous belt, said plurality of functional subunits comprises one or more of a heating subunit, a transport subunit, and a vacuum enhanced embossing subunit, said continuous belt is connected to said movable belt of said vacuum suction module and covers said plurality of functional subunits.

10. The apparatus according to claim 9, wherein said heating subunit, said transport subunit, and said vacuum enhanced embossing subunit are alternately or periodically arranged in any one or both of a transverse direction and a longitudinal direction of said continuous belt with respect to the direction of formation of said leather-like sheet structure.

11. The device according to claim 9 or claim 10, wherein the vacuum enhanced embossing sub-unit is configured to reversely transfer the engraved pattern onto the bottom surface of the artificial leather sheet structure, the bottom surface being close to the surface of the continuous belt on which the artificial leather sheet structure is transported.

12. The device according to claim 1, wherein the waste leather for preparing the collagen slurry comprises wet blue leather, and the waste leather is crushed, degreased, dechromed and filtered to obtain a soft and viscous slurry containing insoluble collagen fibers.

13. The device according to claim 12, wherein the soft and viscous slurry containing insoluble collagen fibers is mixed with water in a mixing chamber to obtain a collagen slurry in water with a weight percentage of 0.5 to 10.0%, and then it is evenly distributed onto the artificial leather sheet structure forming platform by a doctor blade.

14. The device according to claim 12, wherein the waste leather is degreased multiple times in an organic solvent until there are no residual hydrophobic contaminants.

15. The device according to claim 14, wherein the crushed and degreased waste leather is treated multiple times with a detergent solution until there are no residual hydrophilic contaminants.

16. A method for manufacturing a regenerated leather with an asymmetric layered structure similar to genuine leather from waste leather or raw hides soaked in lye, the method comprising: evenly distributing a collagen slurry in water onto an artificial leather sheet structure forming platform of the device according to any one of claims 1 to 15; starting a plurality of motion driving sub-units of the device to drive the movable belt of the vacuum suction module to move towards the artificial leather sheet structure forming direction; activating the vacuum suction sub-unit and the transport sub-unit of the vacuum suction module to separate insoluble collagen fibers from the aqueous portion of the collagen slurry to form a filter cake; forming an asymmetric layered structure in the filter cake when the filter cake is periodically exposed to the vacuum suction sub-unit along the movable belt; and peeling off the artificial leather sheet structure from the movable belt at the distal end of the movable belt and collecting the artificial leather sheet structure by a collecting device.

17. The method according to claim 16, further comprising: Before the peeling and collection of the artificial leather sheet structure, an engraved pattern is reversely transferred onto the bottom surface of the artificial leather sheet structure by a vacuum enhanced embossing module, the vacuum enhanced embossing module being arranged after the vacuum suction module to form a continuous platform leading to the movable belt.

18. The method according to claim 16 or claim 17, wherein the waste leather or raw hides soaked in lye are crushed, followed by a plurality of washing processes to remove both hydrophobic and hydrophilic contaminants to obtain a wet collagen slurry; then the wet collagen slurry is filtered and further crushed to produce a subdivided, homogeneous aqueous suspension of collagen fibers; then, the filtration and washing processes are repeated for the aqueous suspension of collagen fibers until the filter cake becomes soft and viscous.

19. The method according to claim 16, wherein a collagen slurry in water with a weight percentage of 0.5 to 10.0% is provided before the collagen slurry is uniformly distributed onto the artificial leather sheet structure forming platform of the device.

20. The method according to claim 16, further comprising: After being peeled off from the movable belt and collected by the collecting device, the artificial leather sheet structure is freeze-dried to remove voids in the artificial leather sheet structure.

21. The method according to claim 20, further comprising treating the artificial leather sheet structure with one or more cross-linking agents to form a waterproof and thermally stable leather.

22. The method according to claim 21, wherein the one or more cross-linking agents include dialdehydes, diepoxides, or diisocyanates such as succinaldehyde, glutaraldehyde, adipaldehyde, epoxidized soybean oil, epoxidized vegetable oil, diepoxybutane, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, 1,4-butanediol diglycidyl ether, 1,5-pentanediol diglycidyl ether, 1,6-hexanediol diglycidyl ether, diphenylmethane diisocyanate (MDI), toluene diisocyanate (TDI), hexamethylene diisocyanate (HDI), and isophorone diisocyanate (IPDI).

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