Process and composition for obtaining a rubbery tissue

Abstract

The present invention refers to a process and a composition, containing latex, for the manufacturing of rubbery tissue sheets. The process of the present invention consists of the following steps: formulation of the composition, consecutive impregnation and smoking cycles; and maturation. Also, it is part of the scope of the present invention, a impregnation composition which is essentially an aqueous solution comprising latex, a sulfur source and a vulcanization accelerator. The rubbery tissue sheets obtained by the present invention can be submitted to the manufacturing of: suitcases, bags, purses, travelling bags, clothes, diaries, wallets, shoes and other objects usually made of leather.

Description

BACKGROUND OF THE INVENTION

[0001] 1. Field of Invention

[0002] The present invention refers to a process and a composition, containing latex, for the manufacturing of rubbery tissue sheets. The process of the present invention consists of the following steps: formulation of the composition, consecutive impregnation and smoking cycles; and maturation.

[0003] Also, it is part of the scope of the present invention, a impregnation composition which is essentially an aqueous solution comprising latex, a sulfur source and a vulcanization accelerator.

[0004] The rubbery tissue sheets obtained by the present invention can be submitted to the manufacturing of: suitcases, bags, purses, travelling bags, clothes, diaries, wallets, shoes and other objects usually made of leather.

[0005] 2. Prior Art Description

[0006] The conditioning of the latex extracted from the rubber trees started on the beginning of the last century in Brazil. On 1935, Brazilian Patent Document BR 23.282 described a device and a process for the manufacturing of artificial leather by impregnation of a nucleus of fiber material with liquids containing latex. The nucleus was compressed and decompressed alternatively and constantly during the impregnation, in order to guarantee that the impregnation would be complete on both sides of the fiber material. The device described was able to impregnate the fiber material in its both sides, making an effort of pressure, for the maximum absorption of the latex containing composition by the fiber material.

[0007] The physicochemical properties of rubbery tissue obtained by the above mentioned process were not acceptable, and there were no prior concern regarding the formulation used on the impregnation. The specification only mentions the use of a chemical composition containing latex, coloring agents, coagulation salts, vulcanization accelerators and solid substances, including sulfur. Also, no proportions or concentration ranges were defined. The proportions and amounts of the mentioned components influences on the quality properties of the rubbery tissue, therefore being fundamental for the process.

[0008] The Patent Application U.S. Pat. No. 3,524,792 of Apr. 1, 1963, describes a material similar to leather, with plastic and elastic properties, and the process of manufacturing the same. The material has a practical application on the shoemaking field, for example, where a section inserted on the top of the shoe, with a porosity that makes it permeable to air and humidity, obtaining an appearance similar to leather. The method consists on the impregnation of an interlaced raw rubber tissue with latex from a thermoplastic synthetic resin selected from the acrylic an vinyl polymers, immerging the tissue at room temperature and pressure during 5 to 6 seconds. Therefore, the tissue absorbs the impregnation solution.

[0009] The above mentioned invention is an advance towards the proper formulation of the impregnation composition, although the tissue is still impregnated on both sides and there are no concern regarding the quality of the finished product.

[0010] The Patent Application GB 1,251,829 of Dec. 19, 1968, describes a tissue adequate for use as a substitute for leather comprised by a fiber cloth, wherein most of the fibers are made of synthetic organic polymeric material. Collagen particles, linked to the cloth by synthetic polymeric linking agents or non-interlaced natural rubber, are uniformly spread. The leather is obtained by the impregnation of the cloth containing collagen with a polymeric linking agent, followed by heating of the impregnated cloth until coagulation and vulcanization or cure, if necessary.

[0011] The main concern on the patents filed on the 70s was the formulation used in the rubbery process. The Patent Application GB 1320547 of Jul. 13, 1970 describes a substitute for leather and method for manufacturing thereof. The method comprises the formation of a sheet from a slurry made of cellulose fibers and water. The sheet was saturated with aqueous polyurethane latex, containing anionic groups capable of forming salts and an urea aqueous solution.

[0012] The Patent Application U.S. Pat. No. 3,985,929 of Nov. 1, 1974, describes a tissue for the shoemaking industry. The non interlaced tissue is impregnated with a polymer prepared by the polymerization of acrylic or metacrylic acid with polyethylene oxide to improve the absorption.

[0013] The Patent Application BR 8903532-1 of Jul. 18, 1989 was an advance in the state of the art in that period, teaching a process for the fabrication of rubbery tissue with elastic properties and the resulting product thereof. This process consists of the fabrication of a rubbery tissue characterized by the use of pure natural rubber (latex), mixed with accelerators and chemical products, forming a paste. The paste is left for “rest” and is passed through a mixer, heated and taken to a calender, where it is laminated. The resulting blanket is applied by calendering over a tissue net, which is taken to an autoclave for vulcanization.

[0014] The Patent Application CN 93104820.6 of Apr. 4, 1993 describes a rubbery tissue material used on shoemaking. The process is comprised by 7 steps: (a) injection of raw material; (b) compensation; (c) pressurization; (d) flooding and filter pressing; (e) sulfured drying; (f) rolling, planning and labeling; and (g) rounding. The flooding fluid is a mixture of adhesives and coloring agents on the following proportions: 25% natural latex at 60%, 15% of styrol at 30%, 15% of coloring agent and 55% emollient. One of the steps of the manufacturing is flooding, where the tissue is immersed in a “V” shaped conductor and is submitted to pressure.

[0015] In the same year, The Patent Application BR 9304882-3 of Nov. 30, 1993 had improved the process of manufacturing a rubbery tissue. The tissue was successively impregnated with ammonia or caustic soda treated latex, and mixed with a solution containing a sulfur emulsion, an acrylic linker, a silicon based softener, a carbopol based thickening agent, an emulsifier, antioxidant agent, an anti ultraviolet agent and an anti ozonizating agent; all diluted in 1 L of water. Following the impregnation phase, the tissue is immediately exposed to smoke. These operations are done alternatively and repeatedly 5-10 times. After that, the tissue is exposed to solar light and is left to “rest” in the shadow or in a dry oven for drying, with all the superficial impurities and dirty being removed by the application of colorless liquid wax followed by the application of liquid silicon for polishing the material. After this last step, the material is ready for manufacturing the desired articles. This particular process presented a substantial advance compared to the others mentioned above, specially the BR 8903532-1, as the coagulation of the latex on the tissue happened during the and lamination phases.

[0016] The Patent Application BR 9400148-0 presents a smoking step very similar to the described on the Patent Application BR 9304882-3. This process is comprised of the extensive exposition of rubbery tissue with smoked latex to heat and smoke; conditioning for 24 hours in the oven, followed by heat exposure for 3-24 hours on the oven.

[0017] The Patent Application BR 9402908-3 of Jul. 22, 2001 was an improvement of the Patent Application PI9304882-3, describing a process comprising the following steps: addition of the latex extracted from rubber trees, 10%potassium hydroxide solution, at a proportion of 0.4% solid by the rubber dry weight on latex and a vulcanization solution; homogenization; sieving; heating of the mixture for using in consecutive impregnation applied to the tissue; curing; exposition to oven; and drying of the final product.

[0018] Despite the impregnation formulations had suffered improvements throughout the years, the majority of the above mentioned patent applications did not have a prior concern related to the quality of the rubbery tissue produced, especially regarding esthetic and superficial properties of the material. The rubbery tissue technology was applied for the manufacturing shoes or plastic bags.

[0019] The people skilled in the art knows that the properties of the mentioned rubbery tissue are direct influenced by the process of manufacturing, especially the tissue impregnation with the latex solution or polymeric mixture and, as a consequence, the impregnation solution used.

[0020] As far as, the rubbery tissue is obtained by a specific process, which can be differentiated of the “in natura” known latex bag waterproofing procedure, practiced by the Amazon rubber tree tapers, only by the addition of caustic soda to the latex, after collecting it, followed by addition of a chemical formulation, generally composed by sulfur emulsion in water, acrylic linker, silicon based softener, Carbopol based thickening agent and antioxidant.

[0021] The rubbery tissue obtained presents a variable thickness of the latex sheath, tending to be thinner on the top of the bag and thicker at the opposite edge. The color varies from dark yellow to dark brown. A strong mold odor remains on the polished product, due to the favorable conditions for mold development on the manufacturing process. In addition to that, the rubbery tissue presents several superficial imperfections such as: clot particles, blisters, holes, sheath separation, drippings, etc. Regarding the results on environmental conditions and accelerated artificial aging process such as: heat, light, oxygen and ozone, the product presents: sticking, parching, splitting, etc.

[0022] Due to the negative aspects related to the performance of the rubbery tissue obtained using the prior art, specially for using on the manufacturing of shoes, bags, purses and clothes, caused by the inadequate process of production, the applicant of the present invention has developed a new and surprising improvement on the process, comprising a process as a whole since (a) collecting and preservation of latex or, alternatively the use of synthetic latex or other vulcanization compound; (b) preparation of the impregnation solution with all the necessary elements for curing and protection against rubber degradation; (c) impregnation technique and latex application and coagulation from the curing; (d) previous drying and curing; (e) seepage and final drying; (f) finishing and packaging.

[0023] The present invention provides a solution to the technical problem by means of a process and composition for obtaining a rubbery tissue presenting a constant thickness, homogeneous coloring, and improved chemical and physical properties, providing a superior quality of the final product. The rubbery tissue obtained by the aforesaid process does not present neither superficial imperfections nor instability related to adverse environmental conditions.

[0024] Therefore, the material obtained by the present invention presents superior quality compared to rubbery tissues manufactured by the prior art processes and can be used in broad manufacturing applications, such as: bags, suitcases, diaries, notebooks, clothing, etc.

BRIEF DESCRIPTION OF THE INVENTION

[0025] The present invention is comprised by a process for obtaining a rubbery tissue comprising the following steps:

[0026] (a) fixation of the impregnable material in a support;

[0027] (b) treatment of the external surface of the impregnable material;

[0028] (c) formulation, pH adjustment, homogenization under heating and filtration of the impregnation composition;

[0029] (d) impregnation, using the impregnation composition, of the external surfaces of the impregnable material, assuring that the said material absorbs the said composition;

[0030] (e) smoking of the impregnable material;

[0031] (f) submitting the external surface of the material thereof to successive cycles of impregnation and smoking; and

[0032] (g) maturating the material thereof under temperature range of 50-100° C.

[0033] The extraction and collection of the natural latex from the rubber trees as well as the stabilization, can be done before the above mentioned steps. Alternatively, latex from chemical compound, for example, polymeric or synthetic vulcanization latex can be used, conferring the desirable properties for the final product.

[0034] Also, other steps can be added the present invention, after the maturation, such as: washing, drying and final conditioning of the rubbery tissue sheets.

[0035] It is also part of the scope of the present invention the composition used in the impregnation, which is comprised by a mixture of latex with the chemical compounds for the cure and protection of the obtained rubbery tissue, as well as the preservation and assurance of the high quality of the properties. The impregnation solution, according to the present invention, comprises essentially an aqueous solution containing latex, sulfur source, curing accelerator and optionally, stabilizing agent or agents, one or more dispersing agents, one or more thickening agents, one or more coloring agents, buffers, as needed.

BRIEF DESCRIPTION OF THE DRAWINGS AND PICTURES

[0036] The following drawings and pictures illustrate, in a schematic form, the preferred embodiment of the invention.

[0037] FIG. 1 shows the extraction and the collection of the natural latex from the rubber trees.

[0038] FIGS. 2 and 3 shows the latex stabilization using stabilizing agents.

[0039] FIG. 4 depicts the formulation, pH adjustment and homogenization under heating of the impregnation composition.

[0040] FIG. 5 shows the filtration of the impregnation composition.

[0041] FIG. 6 shows the fixation of the impregnable material on a support, such as a mat, for example.

[0042] FIG. 7 shows the treatment of the external surface of the impregnable material (scraping and brushing).

[0043] FIG. 8 shows the impregnation of the impregnation composition on the impregnable material.

[0044] FIG. 9 shows the smoking.

[0045] FIG. 10 shows the maturation on the oven.

[0046] FIG. 11 shows the washing

[0047] FIG. 12 shows the addition of the anti adherent agent on the rubbery tissue sheets.

[0048] FIG. 13 shows the packaging and distribution of the sheets;

[0049] FIG. 14 shows some products made from the processing of the rubbery tissue sheets obtained according to the process.

DETAILED DESCRIPTION OF THE INVENTION

[0050] According to the knowledge from the prior art, certain sorts of plants produce a milky substance when their surface is cut or wounded, for instance the Hevea, Manibot glaziiovii, Castilloa elastica, Ficus elastica, Landolphia specimens and others. This milky substance, called latex, presents physicochemical properties that, once processed, gives an industrial application of this natural resource, by a variety of industrial products.

[0051] Depending on the nature of the source and incision done on the plant the rubbery tissue produced from the collected latex will be different in terms of purity, molecular weight related to the amount of hydrocarbons, among other chemical and physical properties. Generally the amount of solids on fresh latex as it flows from an average aged rubber tree is about 32 to 35%. The amount of solids on latex of young rubber trees is sometimes less than 20% and for old trees, or for the ones which had been not cut for a long period, the amount of solids on the latex can reach 45%.

[0052] As mentioned above, there are several rubber trees species, each one produces different types of latex with different properties, such as, elasticity. In addition, the origin of cultivation also interferes on latex properties. Generally the native trees produce more latex than the cultivated ones, e.g., the rubber tree seeds that were grafted. Despite the chosen specimen, the rubber tree should be cut properly, in order to maximize latex extraction and the life of the tree.

[0053] Taking into account these two factors, the assignee identified the best way of making the tree incision and latex assessment. According to the present invention, first it is necessary to mark the area which will be submitted to the incision, which is generally referred to the “flag” of the rubber tree. The flag is fixed in a way that corresponds to a half or a third of the total perimeter of the rubber tree. These procedure is taken, mainly because a rubber tree that has 100% of the perimeter used, tend to have a very limited life cycle, in comparison with the ones that produce latex at one half or one third of the total perimeter per flag.

[0054] Once the flag is fixed, the incision is done in a inclined pattern, so that the latex flows between the channel determined by the incision. The depth of the channel is another important parameter of the incision. A rubber tree presents several superposed layers. The latex is generally located on the first layer, called “crust”. Therefore, the incision should not reach the other tree layers (“skin” and “wood”), otherwise the tissues of the rubber tree will be damaged, compromising the latex production and/or life cycle. The thickness of the crust depends on the type of trees, the trees with thicker crust produces more latex.

[0055] After the incision, a collector is quickly attached to the lower part of the incision on the rubber tree, for collecting and storing the latex during all the flow. Generally, the latex flows during 2-12 hours. After the end of the flowing the collector is taken and a stabilizing agent is added, to avoid coagulation.

[0056] While flowing from the tree, the latex is almost neutral, but due to the bacterial and enzymatic reactions, it becomes acid, tending to coagulation. In order to inhibit the coagulation and maintain the latex in a stable colloidal condition, preservatives and bactericides must be added as soon as the latex is collected from the rubber tree. Possible preservatives are: ammonia, formaldehyde, sodium hydroxide, soap and other chemical bactericides, such as pentachlorophenol salts are used to inhibit the coagulation.

[0057] The usual practice is to use a small amount of ammonia. However, the use of ammonia has some disadvantages such as the high cost, the unpleasant odor, the loss due to volatilization and the ability of some bacteria to develop resistance to this chemical compound. In the preferred embodiment of the present invention, potassium hydroxide is used for latex stabilization, which present some advantages compared with ammonia such as: the use of smaller amounts and the easiness in concentrate solids.

[0058] However, any other sorts of stabilizers or mixtures thereof, can be readily used for the purpose of this invention. Exemption is made for the stabilizers that reacts with the material to be impregnated or with one or more impregnation solution compounds, producing undesirable products.

[0059] The addition of the stabilizing agent is dependant on the climate of the region. In a warm and dry climate, the latex is more susceptible to coagulation. It is necessary to add the stabilizer simultaneously to the collection.

[0060] The extracted latex should be preserved for a short term with a stabilizing agent which, preferably must be added to the latex collection recipient, before the beginning of the process of collection. Generally, 10-100 mL of 10% potassium hydroxide for 1-16 L of latex, preferably 40-60 mL of 10% potassium hydroxide for 6-10 L of latex. On a preferred embodiment of the present invention, 10% of caustic soda solution is added in a proportion of 12 g of solution per Kg of latex containing 30% of total solids.

[0061] The latex solution is essential for the quality and the desired properties of the rubbery tissue, such as, heat, ozone, solar and ultra violet radiation resistance; curing compliance; mold and exudation absence; color and aspect.

[0062] The impregnation composition comprises a mixture of one or more sulfur sources, one or more curing accelerators, forming an aqueous solution containing latex. If desired, other compounds can be added such as protection and stabilization agents, dispersants, thickening agents, solvents, coloring agents, scents, buffers, etc., or mixtures thereof. Exemption is made for the above mentioned compounds and/or mixtures that undesirably reacts resulting a rubbery tissue with inferior properties.

[0063] The latex used in the formulation of the impregnation composition can be natural, e.g., extracted and collected from the rubber trees and stabilized. Alternatively, latex from chemical compounds can be used, such as polymeric or synthetic latex, or any compound that can be vulcanized to achieve the desired properties of the final product.

[0064] Any sulfur source known in the art can be used, pure sulfur or sulfur compounds, salts and solutions containing sulfur. It is still in the scope of the invention the addition of compounds or mixtures thereof that can potentially react, mix or interact, forming potential sulfur sources.

[0065] The same applies to the curing accelerator. Any accelerator or mixtures thereof known in the art can be used. Exemption is made to the particular ones that undesirably reacts interfering on the quality of the final product. The preferred accelerators are the ones suitable for curing at low temperatures.

[0066] The impregnation solution presents a 1:1-1:3 rate between the sulfur source and vulcanization accelerator; preferably the rate is 1:1,5. The impregnation solution is completed with water.

[0067] In the preferred embodiment of the present invention, the impregnation composition comprises: 4-12% of sulfur; 2-8% of zinc oxide; 6-21% of vulcanization accelerator (preferably ZDEC-Akzo NL); 6-21% of protecting and stabilizing agent (preferably Wingstay L-Goodyear EUA); 8-24% of dispersing agent (preferably Faxan 11P 10%-Montanoir F); 2-6% of thickening agent (preferably AlGum HV 3%-Mathon F); and 10-80% of water (all percentages in weight).

[0068] It can be necessary to add compounds in order to adjust the pH of the impregnation composition to a desirable range. The compounds must be added in order to result in a dispersion containing active chemical compounds enough to cure a certain amount of latex with a predetermined rubber amount. The rate between the active chemical compounds and the rubber in the latex is about 1:0.5 to 1:2, preferably 1:1.

[0069] Compared with the patent application BR 9402908-3 of Jul. 22, 1994, the impregnation composition herein described is superior to the composition described in the above mentioned patent application, mainly because of the low amount of sulfur (approximately 0.6%), avoiding the blooming effect (e.g., milky appearance); the use of a accelerator more active than the ZDBC and a protective material that avoids bleaching.

[0070] The finishing of the impregnation solution must be done carefully, by adding the vulcanization and protection elements previously dispersed, separately or in a single mixture to the latex with the amount of solids previously determined, with proper quantities related to the effective concentration of latex. After the addition of all the components, forming an aqueous solution with pH adjusted between 6 and 10, preferably between 7 and 10 and more preferable between 8 and 9, the mixture should be homogenized and filtered.

[0071] After all the components are added, the solution is mixed under moderated heat, between 30-80° C., preferably between 40-70° C., more preferably between 55-60° C. The previously heated composition is better applicable during the impregnation phase, consuming less energy and time for the process during the smoking time. It is important not to let the solution boil, otherwise it will compromise the elasticity of the final product.

[0072] The warm impregnation composition is filtrated, in order to separate the solids and eliminate insoluble impurities, and in case the composition not used immediately, it should be stored in a recipient, standing by for the impregnation of the composition on the impregnable material.

[0073] The material to be impregnated with the impregnation composition containing latex is fixed on supports, which can be made from any material that withstands the temperatures of the process described herein, without causing any impact on the quality and the properties of the rubbery tissue, as well as not reacting in a detrimental manner with the impregnation solution, forming undesirable side products.

[0074] In one of the preferred embodiments, the said impregnable material is cut in appropriate dimensions to be fixed on a vertical rectangular grid, with or without the manipulation rod fixed on the median part of the inferior side of the support. Preferably a 1.2 m×0.8 m grid is used, due to the better usage of the material during the manufacturing of the final product. The 1.2 m measurement was based on the average height of trousers, used by clothes stylists.

[0075] Alternatively, a mat or a mobile or rolling device can be used to sustain the impregnable material in order to have a continues process.

[0076] Regarding the type of impregnable material, any type of fabric can be used in the present invention, except the fabric that undesirably reacts with the impregnation solution, producing side products. Generally, any material, fabric, cloth made of wool, silk, cotton, linen, white cotton cloth, natural fiber artificial or synthetic, among others, can be used. However some synthetic fabrics present low absorption capacity and adherence to the impregnation solution. The preferred embodiment of the invention is to use a 100% cotton fabric.

[0077] After the cutting, the fabric is extended and fixed on the grid. The fixed fabric is then scraped and brushed, to eliminate lumps and wrinkles, softening the fabric and preparing it for a better absorption of the impregnation composition.

[0078] The fixation of the material on a grid or a mat, in case of a continues process, has a fundamental objective in the process claimed herein. Contrary to the processes mentioned on the state of the art, the material is not introduced or submerged in a recipient containing the impregnation solution. The applicant surprisingly found out that, by the direct impregnation in just one of the faces of the material supported on the grid, the rubbery tissue obtained has improved properties, as well as the aspects of quality and processing of the material for the production of manufactured goods with best finishing, such as: coats, wallets, suitcases, etc. So, the internal surface of the material is not directly impregnated with the impregnation solution.

[0079] In a non-theoretical way of thinking, the optimum properties of the rubbery tissue are obtained when the material absorbs partially the impregnation solution. Therefore, the impregnation should be done in a particular way to provide a leather appearance to the material, but not in excess, avoiding the accumulation of the material in the interstices, chemical compound molecules such as oxidants and vulcanization agents, capable of severely compromise the quality of the rubbery tissue in a long term. In a simple way, the impregnation composition must be applied to the external face of the material (between the grids of the fabric, for example), but the composition should not reach its interior face therefrom. Once it happens, the impregnation composition starts to drip on the internal face of the grid, influencing negatively the external face properties, by forming spots or clumps, which interferes on the appearance and on the final quality of the rubbery tissue obtained.

[0080] However, it must be assured that the impregnable material absorbs a sufficient amount of impregnation composition, in order to the latex will be vulcanized on the material, determining the desired leather appearance. For achieving this objective, the impregnation is done on multiple applications, for a gradual absorption of the impregnation composition by the impregnable material.

[0081] The first application is the most important, due to the fact that it is more difficult to apply the impregnation composition avoiding the surpassing of the impregnable material which is still in its natural state, e.g., raw. The subsequent steps present advantages when compared to the first one, because the impregnation is done on a already impregnated material, which means that the material is already coated meanwhile the impregnation composition is applied repeatedly. The vulcanized latex from the repeated applications will provide a protection layer to the material, avoiding the surpassing of the impregnation material.

[0082] In the first application, named “priming”, the impregnation composition should be carefully applied. The simplest form is to manually rub the impregnable material with the impregnation composition, in order to facilitate its adherence to the material, followed by the first longitudinal bath, from top to bottom, on the external face. The impregnation composition has to be spread, and cover the whole external face of the material. Non-manual applications can be also used, such as, by using a hose, spraying, etc., the limitation being that the pressure or flow rate of the impregnation should be optimized in order to avoid that the solution passes to the internal face of the material. Also, the impregnation should assure that the material absorbs the impregnation composition, providing a good adherence between the material and the rubber formed by the vulcanization of the latex on the material surface.

[0083] Therefore, the first application determines the initial absorption of the material in relation to the impregnation composition, specially on the porous and holes closer to the external surface of the material, which is put directly in contact with the solution.

[0084] The applications of the impregnation composition must be done with the grid slightly sloped and from top to bottom, consequently, the said impregnation composition flows on the external surface of the material, in all its extent, avoiding spots and regions with different concentrations as a result of composition reflux.

[0085] After the application of the impregnation composition and subsequent flow of the excess of the said impregnation composition, the impregnated material should be smoked, e.g., the impregnated surfaces of the said material should be exposed to the dense fumes of an oven, preferably a conic oven.

[0086] Generally, the said smoking can be done by the contact of heated vapors, promoting the vulcanization of the latex on the surface of the impregnated material. In a preferred embodiment of the invention, the smoking is done, by the smoke produced by a complete combustion reaction, e.g., composed by oxygen and carbon dioxide. However, any other heating method which promotes, in a satisfactory way, the vulcanization of the latex on the material can be used.

[0087] During the smoking, it is important to maintain, at least initially, the impregnable material slightly sloped in order to avoid the reflux of the composition on the surface. This avoids heterogeneous regions regarding the concentration and absorbed amount of impregnation composition. Generally, the material must be exposed to heat during smoking from 1 to 10 minutes, preferably from 2 to 7 minutes and mostly preferable from 3 to 5 minutes. The necessary exposure time will depend on the smoking method used.

[0088] The level of exposure can be evaluated by the color of material being smoked. When the material pass from a white to a yellowish color, it is a positive indication that the smoking has achieved the desired level. Excessive smoking should be avoided, otherwise ashes will be formed, interfering on the rubbery tissue properties. On the other hand, incomplete smoking can compromise the rubbery tissue properties, once the latex will not be completely vulcanized.

[0089] Another way of verifying the vulcanization of a rubbery tissue sheet, is a quick analysis based on the fact that any type of rubber absorbs test liquids (organic solvents, for example, or any other liquids or mixtures thereof known on the art) in a higher or lower grade. This particular method do not measure the level of vulcanization, only if any vulcanization thereof is present on the rubbery tissue sheets. Therefore, according to the method, the liquid absorption causes a increase on the rubber volume (“swelling”). As a consequence, the physical properties can be determined. The first sheets, of pure latex, are completely soluble in certain liquids, but the vulcanized sheets, as in the form Vulcatex 22.15, are virtually insoluble. Strong chemical bonds, such as the sulfur with the rubber chains, prevents the complete evolvement of the rubber chains by the liquid and restrict the rubber deformation.

[0090] In a practical way, a small sample of the sheet is cut to be analyzed. This sample is put in recipient containing liquid, for example, gasoline, for the test. After 90 minutes of immersion, the sample is removed from the recipient. If the sample is dissolved, this is a proof of the non-vulcanization of the material. For the partially vulcanized sample, it is observed that the rubber separates from the fabric, without dissolution. The totally vulcanized samples swell and twist, without dissolving.

[0091] Once smoked, the rubbery tissue is evaluated. In case of irregularities, such as the presence of granules, blisters or pits on the material surface, it is submitted to pressing only on the deformed areas, saving the properties of the material as a whole.

[0092] Following the above mentioned step, the material is once again submitted to a impregnation solution application, as described above. It is advisable to filtrate and mix the impregnation solution for each step of application.

[0093] From the second step on, the impregnation can be done by any non-manual means known on the art, such as the application of the impregnation composition by using hoses, sprays, etc., the said composition being pumped to be spread on the material surface uniformly.

[0094] The flow rate of the impregnation solution jet should be carefully adjusted, despite of the mechanism of application adopted, to avoid foam generation. The foam generates bubbles that, due to the wind action, can collapse forming “holes” on the external surface of the material and, therefore compromising the properties of the rubbery tissue obtained, specially its superficial and finishing properties. The optimal adjustment can be obtained by the proper dimensioning of the hose diameter or other method adopted.

[0095] In the preferred embodiment of the present invention, a hose application system for the impregnation solution was adopted. For an adequate application, considering the grid dimensions cited above, such device should present a 0.00254-0.0762 m (0.1-3 in) diameter, preferably 0.00762-0.0254 m (0.3-1 in) diameter, most preferably 0.010-0.016 m (0.4-0.6 in) diameter.

[0096] Impregnation and smoking cycles are repeated, according to the industrial process demands and quality standards. In order to reach adequate physicochemical properties, as well as a good leather appearance, and high superficial and finishing qualities for the manufactured products from the rubbery tissue, it is advisable to submit the impregnable material to 1-20 cycles, preferably 4-15 cycles, most preferably 6-12 cycles. The adequate impregnation of the material, as well as the number of cycles necessary to obtain a rubbery tissue with the desirable properties will strongly depend on the specific weight of the material used.

[0097] After various cycles of impregnation and smoking, the rubbery tissue sheets are placed in a oven and let for curing for 1-4 days, preferably 2-3 days. The smoking temperature for the leather sheets is 50-90° C., preferably 60-80° C., most preferably 70° C. It is possible, at the beginning of the maturation process, to establish a relatively high temperature, between 80-100° C., preferably 90-95° C., stabilizing afterwards the temperature to 70° C., during tanning.

[0098] It is also important to take into account the fact that the material, before being tanned, is very sensitive to humidity and other environmental agents. The sheets must not get exposure to hostile environments and weather conditions.

[0099] The tanned vegetal leather sheets can be washed thoroughly with water and/or other types of cleaning agents that do not undesirably reacts with the rubbery tissue, such as powder soap. After cleaning, the sheets are dried at room temperature or in the oven.

[0100] Alternatively, the rubbery tissue sheets can be removed from the oven and placed on a seepage tank, remaining on it for the desired period of time. After being taken out of the water, the sheets must be rubbed with a sponge and water. After washing and/or leaching, the rubbery tissue sheets must be put on the oven again, for final drying.

[0101] Finally, the rubbery tissue sheets submitted to the final drying must be removed, from the oven. The washed and/or leached and dried must be removed from the grid, examined and classified according to the quality standards before packaging.

[0102] The finishing of the rubbery tissue sheets, giving them a smooth touch, must be obtained by the application of the adequate product after the manufacturing of the product, not compromising the assembly with neoprene glue, for instance.

[0103] If desirable, it is possible to coat the rubbery tissue sheets with protecting agents, anti-adherents and mixtures thereof known in the art, however the agents applied cannot react undesirably with the obtained rubber tissue. This procedure is desired when the sheets are boxed in non foldable stacks, in order to avoid sticking among the sheets. An example of anti-adherent used on the preferred embodiment of the present invention is zinc stearate.

[0104] Before the packaging of the sheets, quality tests can be done to evaluate the physicochemical properties presented by the material, as well as the surface and esthetical properties. Therefore, toughness and color measurements, resistance and elasticity tests, degree of vulcanization, surface tests, among others, can be applied to the rubbery tissue sheets obtained by the present invention, according to the convenience of the industrial process used.

[0105] There are protection agents that can be applied to the sheets in other to prevent surface imperfections. By surface imperfections it is understood any irregularities caused by the use of inadequate material, bad latex distribution, scratches, dirty and other visible marks that tend to reduce the area of the sheet suitable for manufacturing. In addition to that, no color variation is allowed on the sheets.

[0106] Irregularities, like pits on the surface of the sheets and trapped on the blisters are from mineral sources (sulfur and silicon) and organic sources (accelerator). The pit formation is mainly due to a bad dispersion when mixing the impregnation solution.

[0107] Also, white lines can appear on the surface of the rubbery tissue sheets, as a result of scratches. Some of them can be more visible, due to the abrasive effect on the surface, for which the silicon oil is insufficient. In order to obtain a more accurate mechanical protection, it is advisable to cover the surface of the sheet with polyurethane resin, which provides a certain mechanical resistance, maintaining the “flexibility”. If the addition of these agents are undesirable for the subsequent manufacturing of the rubbery tissue sheets, the application of these agents should not be done. However, the application of the above mentioned agents on the products manufactured with the rubbery tissue sheet as a stating material is possible.

[0108] Once described the present invention on a general manner, it is important to mention that the examples referred above, specially on the preferred embodiments of the present invention are herein described only for illustrative means and do not have intention to limit the scope of the invention. Technicians specialized on the art will recognize several variants that take part of the scope of the invention and claims herein described.

Claims

1. Process for obtaining a rubbery tissue comprising the following steps:

(a) fixation of the impregnable material in a support;

(b) treatment of the external surface of the impregnable material;

(c) formulation, pH adjustment, homogenization under heating and filtration of the impregnation composition;

(d) impregnation, using the impregnation composition, of the external surfaces of the impregnable material, assuring that the said material absorbs the said composition;

(e) smoking of the impregnable material;

(f) submitting the external surface of the material thereof to successive cycles of impregnation and smoking; and

(g) maturating the material thereof under temperature range of 50-100° C.

2. Process for obtaining a rubbery tissue, according to claim 1, comprising the previous step of extraction and assessment of the natural latex from the determination of the flag; tree incision; and fixation of a collector recipient on the inferior part of the incision.

3. Process for obtaining a rubbery tissue, according to claim 2, wherein the flag corresponds to a half or a third of the total perimeter of the rubber tree and the incision is made in a inclined manner, allowing the latex flow.

4. Process for obtaining a rubbery tissue, according to any one of the preceding claims, comprising the step of latex stabilization by adding one or more stabilizing agents or mixtures thereof to the said latex.

5. Process for obtaining a rubbery tissue, according to claim 4, wherein a stabilizing agent is selected from the group comprised by, 10-100 mL 10% potassium hydroxide for 1-16 of latex, preferably 40-60 mL of 10% potassium hydroxide for 6-10 of latex, or 10% of potassium hydroxide solution, in a amount of 12 g of solution per Kg of latex containing 30% of total solids

6. Process for obtaining a rubbery tissue, according to any one of the preceding claims, comprising the step of treatment of the external surfaces of the impregnable material by scraping and brushing the said external surfaces.

7. Process for obtaining a rubbery tissue, according to claim 6, wherein the impregnable material is made of 100% cotton.

8. Process for obtaining a rubbery tissue, according to claim 6, wherein a support for the said treatment of external surfaces is a rectangular vertical grid of 1.2×0.8 m.

9. Process for obtaining a rubbery tissue, according to any one of the preceding claims, comprising a step of pH adjustment to a 6-10 range, preferably 7-9, most preferably 8; and homogenization under heating without boiling, in a 30-80° C. range, preferably 40-70° C., most preferably 55-60° C.

10. Process for obtaining a rubbery tissue, according to any one of the preceding claims, in which the impregnation process comprises the longitudinal application of an impregnation composition from the top to the bottom of the external surface of said impregnable material which is fixed on the said support; and spreading homogeneously on the said impregnable material.

11. Process for obtaining a rubbery tissue, according to any one of the preceding claims, comprising a first application of the impregnation composition by manually rubbing the said impregnation composition, in order to avoid the passage of the said composition to the internal surface of the said impregnable material.

12. Process for obtaining a rubbery tissue, according to any one of the preceding claims, comprising the application of the impregnation composition by using a hose.

13. Process for obtaining a rubbery tissue, according to any one of the preceding claims, comprising the application of the impregnation composition by using a hose with diameter of 0.00254-0.0762 m (0.1-3 in), preferably 0.00762-0.0254 m (0.3-1 in), most preferably 0.010-0.016 m (0.4-0.6 in).

14. Process for obtaining a rubbery tissue, according to any one of the preceding claims, comprising a smoking step, wherein the external surface of the impregnable material is exposed to the dense fumes of a conic oven.

15. Process for obtaining a rubbery tissue according to claim 14, wherein the external surfaces of the impregnable material on the smoking step are exposed during 1-10 minutes, preferably 2-7 minutes, most preferably 3-5 minutes.

16. Process for obtaining a rubbery tissue, according to any one of the preceding claims, wherein the impregnable material is slightly sloped during the impregnation and smoking steps.

17. Process for obtaining a rubbery tissue, according to any one of the preceding claim, wherein the smoked material is pressed previously to the subsequent impregnation step.

18. Process for obtaining a rubbery tissue, according to any one of the preceding claim, wherein the cycles of impregnation and smoking are repeated 1-20 times, preferably 4-15 times, most preferably 6-12 times.

19. Process for obtaining a rubbery tissue, according any one of the preceding claims, comprising a maturation step wherein the impregnated and smoked material is placed on a oven for 1-4 days, preferably 2-3 days at temperatures of 50-90° C., preferably 60-80° C., most preferably 70° C.

20. Process for obtaining a rubbery tissue, according to any one of the preceding claims, wherein at the beginning of the maturation step, a higher temperature is established, between 80-100° C., most preferably 90-95° C., followed by stabilization preferably at 70° C. during the maturation and curing steps.

21. Process for obtaining a rubbery tissue, according to any one of the preceding claims, comprising the additional steps of washing and drying of the impregnated, smoked and maturated material.

22. Process for obtaining a rubbery tissue, according to any one of the preceding claims, wherein the resulting rubbery tissue sheets are coated with protection and/or anti-adherent agents.

23. Impregnation composition, comprising an aqueous solution containing latex, sulfur source and a curing accelerator.

24. Impregnation composition, according to claim 23, wherein the proportion between the sulfur source and the vulcanization accelerator is 1:1-1:3, most preferably 1:1.5.

25. Impregnation composition, according to claim 23, comprising 4-12% sulfur; 2-8% zinc oxide; 6-21% vulcanization accelerator (preferably ZDEC-Akzo NL); 6-21% protecting and stabilizing agent (preferably Wingstay L-Goodyear EUA); 8-24% dispersing agent (preferably Faxan 11P at 10%-Montanoir F); 2-6% thickening agent (preferably AlGum HV at 3%-Mathon F); and 10-80% water (all percentages in weight), establishing a relationship among active chemicals and rubber amount of 1:0.5-1:2, preferably 1:1.

26. Impregnation composition, according to claim 25, comprising a lower level of sulfur, around 0.6%, in order to avoid the blooming effect; a more active accelerator than the ZDBC and a protective material that avoids bleaching.