NZ710857B2 - Method for producing leather - Google Patents

Abstract

method of producing leather comprising a plurality of steps, wherein methanesulfonic acid is used in at least one step selected from deliming, and wherein the pH in the deliming step is provided to be between pH 4 and 9. The methane sulfonic acid may be used in the form of a mixture with salts and/or other acids and/or acid derivatives such as e.g. ammonium sulfate. The leather product is preferably a chrome-tanned leather. The invention thereby aims to provide soft and attractive leathers and is efficient in practice. d/or other acids and/or acid derivatives such as e.g. ammonium sulfate. The leather product is preferably a chrome-tanned leather. The invention thereby aims to provide soft and attractive leathers and is efficient in practice.

Description

Method for producing r The present invention relates to a method of producing leather comprising a plurality of steps, wherein methanesulfonic acid is used in at least one step.

Leather is one of the oldest materials, yet in the current day and age is still expected to meet very high requirements with regard to durability and visual and haptic ties among others.

Processes for producing leather generally comprise a multiplicity of steps. Multiple steps of leather production are carried out in an aqueous medium at a specified pH. It is very important for this to be the optimum pH because of its influence on the leather obtained. ularly the choice of a suitable acid to neutralize the leather after a preceding operation in an alkaline medium has a distinct influence on the y of the leather obtained. This is the case in the deliming step, for e.

Usage of an excessively strong acid, for example, can have an adverse influence on the visual and physical properties of the leather, possibly because the untreated hides swell up excessively. The choice of an excessively weak acid can have the effect that the pH is slow to become established or that the acid or other substances needed to produce the leather do not completely penetrate the untreated hide. The pH aside, the properties of leather are all influenced by the chemicals used and the production process in a way which is not always predictable.

Conventional methods of producing leather employ, for example, approximately 1% lactic acid, dilute acetic acid, formic acid or other organic acids in the deliming step to dissolve out the adherent liming-step lime residues before the actual tanning. Suitable acids further include, for e, ammonium salts such as ammonium sulfate or ammonium chloride, boric acid, phosphoric acid or carbonic acid. Use of hydrochloric acid or ic acid is se possible. Usage of these acids in r production is well known to a person skilled in the art and is described, for example, in Römpp’s Chemie Lexikon under the headword ei [tannage]. ng brings the pelt to the correct acidity for a subsequent mineral tannage, usually with inorganic acids and brine, ally also with additions of organic acids.

EP 563 139 describes the use of methanesulfonic acid for pickling leather.

The problem addressed by the present invention was that of providing a method of producing leather without the disadvantages of the prior art in that it produces soft and 40 attractive leathers and is ent in practice.

The problem was solved by a method of ing leather comprising a plurality of steps, wherein methanesulfonic acid was used in at least one step. In a particular aspect of the invention, there is provided a method of producing leather comprising a plurality of steps, n methanesulfonic acid is used in the deliming step, wherein methanesulfonic acid is 45 used in the form of a from 0.05 to 0.5 wt% aqueous solution and wherein the pH in the deliming step is 4 to 9.

PF 74767 The method of the present invention proceeds in practice from animal hides or part-processed hides. Animal hides can come from any d dead animals, for example from cattie, calves, pigs, goats, sheep, kangaroos, fish, ostriches or wild animals. it is immaterial for the purposes of the present invention whether the animals whose hides are desired to be treated were slaughtered, hunted or died of natural causes.

Processes for producing leather generally comprise a multiplicity of steps. In the unhairing step, the hair is removed from the animal hide. This step is also known as the liming step. To unhair the animal hide, it is generally treated with alkaline nces such as lime. Frequently, sodium hydroxide, sodium carbonate, sulfides or organosulfur compounds are se added. in the fleshing step, flesh residues and subcutaneous adipose tissue are removed from the animal hide, mechanically for example. in the deiiming step, the alkaline components from the unhairing step are partially or tely neutralized. In hating, the animal hide is loosened up and readied for the absorption of the tanning agent and hence for the actual tanning step. When a mineral tannage is to be carried out uently, the pelt is brought to the correct acidity for tanning by pickling, usually with inorganic acids and brine, optionally also with additions of organic acids. Hair roots, hair ts, short-hair and fatty substances remaining in the epidermis are often impossible to remove by washing off or rinsing alone. Therefore, a scudding step is carried out, particularly in artisanal facilities, where, for e, a scudding knife is applied to the hides on a ’s beam.

The actual tanning steps take place in the presence of a tanning agent. le g processes comprise the use of mineral salts (chromium(l|i), aluminum, zirconium or iron , vegetable tanning with vegetable tanning agents ns in , bark, woods and fruit), oil tannage changeably also known as chamcis e) with fish and marine-animal oils (train oils) or with brain fats, synthetic tannage with synthetically produced tanning agents (syntans, resin type tanning agents, rtype tanning agents, polyphosphates, paraffin suifochioride), aldehyde tannage (formerly formaldehyde, now mainly glutaraldehyde). it is also le to combine s tanning processes.

After g, the leather is generally dewatered mechanically (by sammying) and shaved to a uniform thickness.

Especially in chrome tannage and in the production of chromium-free leathers by a combined pretannage with aldehydes and synthetic tanning agents, the final properties of the leather such as softness, color, fullness, e, extensibility, water absorbence, etc., are determined by the wet-on-wet finish.

Further operations frequently include retanning, deacidifying or neutralization, dyeing, fatliquoring and fixing the dye and uor materiais. Retanning can in principle be carried out with any of the groups of tanning materials which were described in connection with the 40 principal tannage. But particular significance in retanning is possessed by synthetic tanning materials, vegetable-type tanning materials and resin and polymer-type tanning materials, since these frequently have a particularly favorable effect on the fullness and texture of the leather.

PF 74767 The deacidifying step frequently comprises neutralizing the residues of strong acids, which generally results in better stability for the leather.

Dyeing is frequently carried out with dyes which form a chemical bond with the leather fiber.

Many dyes possess not only good dyeing properties (for example: affinity for leather, compatibility, wide color gamut) and fastnesses but also minimal impact on the environment.

The natural color of leather depends infera/ia on the tanning agent used. Chrome tannages frequently produce a light grayish green color, while vegetable-tanned leathers can be, for example, yellowish brown or reddish brown. Aluminum salts and synthetic tanning materials frequently produce white to pale beige leathers. Glutaraldehyde and oil type tanning agents generally dye the rs yellowish.

Fatliquoring imparts better softness and suppleness. Fatliquoring agents enclose the leather fibers with a thin film of fat. As a result, the fibers do not stick together as much during drying and can slide over each other more easily. uoring is generally preceded by a pH of4 to 6.5 being set, preferably a pH in the range from 4.5 to 6. A more acidic pH is set during the fatliquoring step, in particular at the end of the fatliquoring step, in order that uniform fixing of the fatliquoring agent may be achieved throughout the leather cross section. In general, the pH set at the end of the fatliquoring step is in the range from 2 to 6 ably 2.5 to 5, more ably in the range from 3 to 4 and even more preferably in the range from 3.2 to 3.5. hobicizing agents can be used to render leathers dirt and water repellent, or waterproof.

The abovementioned steps are frequently carried out in the stated order in the manufacturing ion. However, within limits it is also possible to carry them out in different orders or for steps to be carried out conjointly and combined.

The aforementioned steps do not all have to be carried out to produce leather. In addition, methods of producing leather may also include further steps in addition to the aforementioned steps.

The present ion is that methanesulfonic acid is used in at least one of the steps for 3O production of leather. The esulfonic acid serves primarily to set the pH. The methane— sulfonic acid is preferably added to the animal hide at the start of the actual operation. in the case of deliming, the operation consists essentially in neutralizing alkaline components with acids which, according to the present invention, comprise methanesulfonic acid. For the es of the present ion, the use of methanesulfonic acid in a ied operation is to be understood as also encompassing the on of methanesulfonic acid before the actual operation or after the preceding operation when the latter is preparatory for the actual operation.

Methanesulfonic acid is preferably used in one of the following steps: deliming, bating, pickling, scudding, tanning, retanning, dyeing, uoring.

Methanesulfonic acid is more preferably used at least in deliming and/or bating and/or pickling and/or fatliq uoring.

PF 74767 in a preferred ment, methanesulfonic acid is used in the deliming step at least.

In another preferred ment, methanesulfonic acid is used in the uoring step at least.

Methanesulfonic acid in the present invention is generally employed in the form of an aqueous solution. Methanesulfonic acid is generally used in the form of a 0.05 to 0.5 wt% aqueous solution, preferably in the form of a 0.07 to 0.2 wt% aqueous solution and more preferably in the form of a 0.08 to 0.15 wt% s solution. 1O in one embodiment, methanesulfonic acid is used er with salts and/or other acids and/or acid derivatives. Suitable acid tives include, for example, esters or acid anhydrides. in one embodiment, methanesulfonic acid is employed together with salts of methanesulfonic acid. Suitable salts of methanesulfonic acid include, for example, alkali or alkaline earth metal salts such as, for example, sodium, potassium, magnesium or calcium salts of methanesulfonic acid.

In another embodiment, methanesulfonic acid is employed together with inorganic salts.

Suitable inorganic salts include, for example, salts of sulfuric acid, halohydric acids, phosphoric acid, boric acid, carbonic acid, nitric acid. Examples of suitable inorganic salts include, for example, ammonium sulfate, sodium sulfate, sodium chloride, ammonium chloride. in another embodiment, methanesulfonic acid is employed er with salts of organic acids.

Suitable salts of organic acids include, for example, ammonium, alkali metal or alkaline earth metal salts of organic acids such as ammonium, sodium, potassium or magnesium salts of organic acids. Suitable salts of organic acids include, for example, salts of monocarboxylic acids or oxylic acids. Examples of suitable salts of organic acids are, for example, salts of formic acid, acetic acid, propionic acid, oxalic acid, c acid, succinic acid, glutaric acid, adipic acid, ic acid, lactic acid, phthalic acid, terephthalic acid, maleic acid, fumaric acid. in another embodiment, methanesulfonic acid is employed together with other acids. Suitable other acids can be c acids or inorganic acids. Suitable inorganic acids include, for example, sulfuric acid, hydrochloric acid, boric acid, carbonic acid, phosphoric acid. Suitable 3O organic acids include, for example, monocarboxylic acids or dicarboxylic acids. Examples of suitable organic acids are formic acid, acetic acid, lactic acid, formic acid, propionic acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, tartaric acid, lactic acid, phthalic acid, terephthalic acid, maleic acid, fumaric acid.

In one embodiment, esulfonic acid is employed in ation with ammonium sulfate.

In another embodiment, methanesulfonic acid is employed in combination with formic acid. in another embodiment, methanesulfonic acid is employed in ation with one or more ammonium salts of dicarboxylic acids.

In another embodiment, methanesulfonic acid is employed in combination with one or more 40 tic dicarboxylic acids. in r embodiment, methanesulfonic acid is employed in combination with one or more carbowlic esters.

PF 74767 The amount of salts, other acids or acid derivatives can vary within wide limits. in one embodiment, an aqueous solution sing from 0.05 to 0.2 wt% of esulfonic acid and 0.5 to 2 wt% of ammonium sulfate is employed.

A pH of4 to 9, preferably 6 to 8.5 and more preferably 7.5 to 8.5 is typically set in the deliming step of the method according to the present invention.

The deliming step generally takes from 30 minutes to 4 hours but may in exceptional cases also take longer or less time. The deliming step is preferably concluded within 45 to 90 s.

Methods of the t invention are simple to carry out and enable efficient and rapid pH setting in their individual steps.

Methods of the t invention further make possible the production of leathers having advantageous visual and haptic properties. They are more particularly notable inter a/ia for pleasant softness and do not swell up as much, do not bulge up as much as leathers obtained according to conventional methods.

The leathers obtained according to the present invention are notable for good softness and have a pleasant, attractive, fine and clean grain pattern. They are also notable for good dyeing properties such as high uniformity and color brightness.

The physical properties such as tensile strength, tear strength, elongation at break or grain extensibility of leathers ed according to the method of the t invention are comparable or or to those of leathers obtained according to the prior art. in particular, leather obtained according to the present invention by using esulfonic acid in the deliming step, in addition to the advantages described above, is notable in that calcium ions are very efficiently removable from the leather. This has an advantageous influence on leather tear strength and softness in particular.

Leather obtained according to the present invention by using esulfonic acid in the fatliquoring step, in addition to having the above~described advantages, is e in that, if it is chrome-tanned leather, only minimal amounts of chromium compounds are washed out of the leather.

The present invention further provides leather obtained according to the method of the present invenfion.

PF 74767 Examples The invention is r explicated by working examples.

Abbreviations used: DecaltallR) RN: acid-reacting mixture of ammonium salts of inorganic acids and of organic dicarboxylic acids Decaltal Example l.2: mixture A: aqueous solution comprising 0.1 wt% of sodium hydrogensulfite and 0.5 wt% of um sulfate. mixture B: aqueous solution comprising 0.1 wt% of sodium hydrogensulfite and 0.3 wt% of DecaltallR) Pic 8 and 1.5 wt% of ammonium sulfate. e L3: mixture A: aqueous solution comprising 0.1 wt% of sodium hydrogensulfite and 0.5 wt% of DecaltallR) RN. mixture B: aqueous solution comprising 0.1 wt% of sodium hydrogensulfite, 0.14 wt% of methanesulfonic acid (70 wt% in water) and 1.5 wt% of DecaltallR) RN.

Example l.4: mixture A: aqueous solution comprising 0.1 wt% of sodium hydrogensulfite and 0.5 wt% of al PF 74767 Example l.5: mixture A: aqueous solution comprising 0.1 wt% of sodium hydrogensulfite and 0.14 wt% of methanesulfonic acid (70 wt% in water). mixture B: aqueous solution comprising 0.1 wt% of sodium hydrogensulfite, 0.14 wt% of methanesulfonic acid (70 wt% in water) and 1.2 wt% of Decaltal ESN.

Example l.6. mixture A: aqueous on comprising 0.1 wt% of sodium hydrogensulfite and 0.25 wt% of DecaltaliR) Pic 8. mixture B: aqueous solution sing 0.1 wt% of sodium hydrogensulfite, 0.25 wt% of DecaitarR) Pic 8 and '1 .2 wt% of DecaltallR) ESN.

The use of methanesulfonic acid made it possible to establish the pH within a shorter period and yielded clean and flat rawhides which were not swollen up as much as hides delimed without methanesulfonic acid.

The leathers obtained by using methanesulfonic acid in the deliming step are softer than leathers obtained as per the prior art, and they have attractive, fine and clean grain patterns.

The physical properties are comparable or superior to those of leathers obtained as per the prior art.

Example ".1 Four pieces of a raw cattlehide were unhaired and fleshed. Unhairing was accomplished by addition of burnt lime and sodium sulfide. For deliming, the hides were lly washed at room temperature with water for 20 minutes and then d with a 1.2 wt% solution of ammonium sulfate initially and then with a 3.5 wt% solution of ammonium sulfate and left to soak for minutes to establish a pH of 8.3 to 8.5. e ".2 Two pieces of the rawhide from e ".1 were then admixed with an aqueous solution comprising 0.6 wt% of methanesulfonic acid to establish a pH of 8.3 The aqueous solutions of Examples ".1 and ".2 were ed for their pH and calcium ion content after 10, 20, 40, 80 and 140 minutes. The results are reported in Table 1. [t][min] i 10 l20 [40 lso 1140 ] pH e ll. 1 8.45 843 C],a2+]Example ".1 [9pm] iCa2+], Example "2 415 PF 74767 Table 1: pH and calcium ion concentration in ppm in the deliming solution of Examples ".1 and ".2, Ca2+ concentration determined via atomic emission spectroscopy The pH of the deliming solutions in Examples ".1 and ".2 was in both cases between 8.3 and 8.43, and was very r.

The content level of free calcium ions in the deliming solution of Examples ".1 and ".2 was distinctly higher with addition of methanesulfonic acid than without addition of methanesulfonic acid.

Example ".3: Determination of calcium content of leather The uent method was carried out on different pieces before ng the ng process and also after concluding the deliming process.

The leathers of Examples ".1 and ".2 were dried before starting and after concluding the deliming, respectively. 0.15 g of leather was placed in a 50 ml conical flask and 4 ml of a mixture of nitric acid and hydrochloric acid (mass ratio 1.3) were added. As soon as the mixture had cooled back down to room temperature, 1 ml of hydrogen peroxide (32 wt% in water) was added thereto. The mixture was heated to 120°C for 180 min. The mixture was cooled down to room temperature and made up to 50 ml with water. The content level of calcium ions in the 2O leather was determined by ining the concentration of m ions in the solution by atomic absorption spectroscopy.

It ired that the tion of calcium removed from the leather was 29% on using ammonium sulfate as neutralizing agent and 52% on using ammonium sulfate and methane- ic acid.

Example ".4 The leathers of Examples ".1 and ".2 were washed twice with water for 10 minutes. The hides were then subjected to tanning and retanning with identical chrome tannage formulations.

The leathers of Example ".2 (with addition of methanesulfonic acid) were less swollen and softer than the leathers of Example ".1 (without methanesulfonic acid).

Example lll Chrome-tanned wet-blue leather e) was cut into pieces 1 x 1 cm in size and 25 g at a time were uced into a 250 ml glass flask. In each case 5 g of fatliquoring agent as per Table 2 were added and also in each case sufficient completely ion-free (CIF) water for the amount of liquid in the flask including the fatliq uoring agent to be 75 ml. The flasks were heated to 40°C for three hours.

The mixtures thus obtained were adjusted in accordance with Table 2 to various pH values 40 using formic acid or methanesulfonic acid. The mixtures thus obtained were heated to 40°C for PF 74767 three hours. Of the mixtures thus obtained, a sample of the supernatant solution was taken and measured by atomic absorption spectroscopy for its content of chromium salts.

The results are ed in Table 2. hromium hromium ontent ontent PF 74767 sulfated castor oil no fat- liquoring agent Table 2: Chromium t of wastewater from various wet—blue leathers on addition of formic acid or MSA in the fatliquoring step; fatliquoring agents used: 88: sulfonated rapeseed oil, SIM: sulfite fish oil, OSL: sulfite fish oil, SXL/N: combined fatliquoring agent, sulfate/castor oil; amount particulars of acid in wt% ve to leather used.

At the same pH, distinctly less chromium is washed out of leather in the presence of MSA than in the presence of formic acid.

Claims (4)

We claim:-

1. A method of producing leather comprising a plurality of steps, wherein methanesulfonic acid is used in the deliming step, wherein methanesulfonic acid is 5 used in the form of a from 0.05 to 0.5 wt% aqueous solution and wherein the pH in the deliming step is 4 to 9.

2. The method according to claim 1, n methanesulfonic acid is used in the form of a e with salts and/or other acids and/or acid derivatives.

3. The method according to claim 1 or 2, wherein the leather is chrome-tanned leather.

4. The method of claim 1, substantially as herein described with reference to any one 15 of the Examples thereof.