Classifications

• • C—CHEMISTRY; METALLURGY
  • C14—SKINS; HIDES; PELTS; LEATHER
  • C14C—CHEMICAL TREATMENT OF HIDES, SKINS OR LEATHER, e.g. TANNING, IMPREGNATING, FINISHING; APPARATUS THEREFOR; COMPOSITIONS FOR TANNING
  • C14C3/00—Tanning; Compositions for tanning
  • C14C3/02—Chemical tanning
• • C—CHEMISTRY; METALLURGY
  • C14—SKINS; HIDES; PELTS; LEATHER
  • C14C—CHEMICAL TREATMENT OF HIDES, SKINS OR LEATHER, e.g. TANNING, IMPREGNATING, FINISHING; APPARATUS THEREFOR; COMPOSITIONS FOR TANNING
  • C14C3/00—Tanning; Compositions for tanning
  • C14C3/02—Chemical tanning
  • C14C3/28—Multi-step processes
• • C—CHEMISTRY; METALLURGY
  • C14—SKINS; HIDES; PELTS; LEATHER
  • C14C—CHEMICAL TREATMENT OF HIDES, SKINS OR LEATHER, e.g. TANNING, IMPREGNATING, FINISHING; APPARATUS THEREFOR; COMPOSITIONS FOR TANNING
  • C14C3/00—Tanning; Compositions for tanning
  • C14C3/02—Chemical tanning
  • C14C3/04—Mineral tanning

Definitions

• compositions suitable for use as a sole or co-tanning agents in the preparation of leather and to tanning processes using the compositions are described.
• Aluminium compounds are probably the oldest known tanning agents, having been used in the preparation of leathers, with such adjuvents as flour and egg yolk, in the ancient Arabic and Mediterranean civilisations.
• aluminium salts to hydrolysis and the susceptibility of leather tanned therewith to hydrolysis at temperatures below 100°C have led to its replacement by salts of more effectively coordinated metals, such as chromium, which provide more robust protection of the leather.
• a new composition of metal ions has now been found which can be used in a simple and robust process for the preparation of non-coloured leather and can also be used in combination with any of the other known tanning agents, especially chromium salts, to improve their performance, particularly in those features where the use of the known agents give rise to problems.
• a composition suitable for use as a tanning agent in the preparation of leather comprising aluminium sulphage and at least one magnesium salt in which the amount of magnesium salt, expressed as MgO, is from 15% to 110% by weight with respect to the aluminium sulphate, expressed as Al2O3.
• the composition may contain one or more other salts of aluminium, such as a polychloride or a salt with an organic acid, provided that the amount of aluminium sulphate, expressed as Al2O3, is at least 40% by weight with respect to the total amount of aluminium salts, expressed as Al2O3, in the composition.
• one or more other salts of aluminium such as a polychloride or a salt with an organic acid, provided that the amount of aluminium sulphate, expressed as Al2O3, is at least 40% by weight with respect to the total amount of aluminium salts, expressed as Al2O3, in the composition.
• the composition preferably contains from 35% to 90% by weight of the magnesium salt.
• the magnesium may be in the form of salt with any suitable mineral acid, such as sulphuric or hydrochloric acid, or an organic acid, such as acetic acid. It is however, preferably the salt of a strong acid and especially magnesium sulphate, which may be prepared by the reaction of a basic magnesium compound, such as MgCO3 or MgO, with sulphuric acid.
• the presence of the water-soluble magnesium salt is believed to hold the aluminium ions, and those of any auxiliary mineral tanning agent, in solution during the tanning process in manner that allows the smooth take up of the aluminium and other metal ions by hides to produce leather.
• the soluble salts of magnesium are believed to modify the behaviour of aluminium salts, whether basified or not, with regard to the acidity of the solutions, the astringency of the solutions in tanning, their flocculation indices, their properties of dispersion from hydrogels to hydrosols during agitation in the tanning barrel, the partial peptisation of the solutions of titanium or aluminium and titanium, and their resistance to hydrolysis.
• the present invention thus encompasses a second composition comprising the the above-defined composition of aluminium and magnesium salts and a titanium salt or a mixture of titanium and aluminium salts, especially water-soluble or stabilised salts of titanium and aluminium.
• Such salts may be stabilised with organic complexing agents containing hydroxy and/or carboxy groups, e.g polyols, hydroxycarboxylic acid, phenols and naphthols or their water-soluble salts, such as citric, tartaric, phthalic, gluco­heptanoic gluconic and aldolised naphtholsulphonic acids and/or their alkali metal salts.
• organic complexing agents containing hydroxy and/or carboxy groups, e.g polyols, hydroxycarboxylic acid, phenols and naphthols or their water-soluble salts, such as citric, tartaric, phthalic, gluco­heptanoic gluconic and aldolised naphtholsulphonic acids and/or their alkali metal salts.
• Masked complexes of titanium and aluminium and the masking agents therefor, suitable for incorporation into the present composition are described in GB 2,068,999 and GB 2,165,859.
• the second composition may contain up to two moles of complexing agent per mole of total metal oxides but preferably contains from 0.35-1.5 mole/mole.
• the composition conveniently contains from 30% to 125% by weight of one or more titanium salts, expressed as TiO2, with respect to the total amount of aluminium salts, expressed as Al2O3 (i.e. molar ratios of Al2O3:TiO2 from 0.8:1 to 8:1 and preferably from 0.8:1 to 4:1).
• TiO2 titanium salts
• Al2O3 i.e. molar ratios of Al2O3:TiO2 from 0.8:1 to 8:1 and preferably from 0.8:1 to 4:1.
• the second composition preferably comprises a mixture of aluminium and titanium sulphates in the weight ratio 2:1 (expressed as Al2O3 and TiO2), containing about one mole of sodium gluconate per mole of aluminium and titanium salts taken together (expressed as Al2O3 and TiO2).
• the first or the second composition may be mixed with one or more auxiliary tanning agents, which may be vegetable or mineral to form a third composition in accordance with the present invention.
• auxiliary tanning agents are chromium and zirconium salts and the third composition, containing a chromium salt, can be used in place of chromium salts alone for the tanning of leather.
• the third tanning composition may contain up to 500%, but more preferably contains from 10% to 300% by weight of the auxiliary tanning agent with respect to the weight of the aluminium salts or aluminium and titanium salts (expressed as oxides) in the first or second composition. It is further preferred that the third tanning composition a mixture of the second tanning composition with, as auxiliary tanning agent, from 10% to 300%, more especially from 35% to 250%, by weight of a chromium or zirconium salt (expressed as Cr2O3) or ZrO2) with respect to the weight of aluminium and titanium salts (expressed as Al2O3 + TiO2).
• the use of the first, and more especially the second, tanning composition in conjunction with a conventional chromium salt tanning agent allows a substantial reduction, up to 70% (expressed as Cr2O3) with respect to the amount of hides) in the amount of chromium used, with only a slight reduction in the protection of the leather against hydrolysis.
• a tannage containing 0.45% of the second tanning composition (as Al2O3 + TiO2) and 0.8% of a chromium salt (as Cr2O3) will give a fully tanned leather having a shrinkage temperature greater than 90°C which is adequate for most purposes.
• the shrinkage temperature can be raised to around 100°C by increasing the quantity of the second tanning composition, preferably to within the range 1% to 2%.
• chromium salts Expressed as Cr2O3
• the significant reduction in chromium usage achievable with the third composition has advantages in reduced coloration of the leather and reduced amounts of chromium salts in the solid effluents from tanning, such as splits and shavings, and in the liquors after tanning.
• Lower proportions of the chromium salts may be used where a lower shrinkage temperature can be tolerated.
• the use of the second tanning composition in conjunction with about 200% (by weight with respect to the second tanning agent, expressed as oxides) of a standard chromium salt tanning agent allows a substantial reduction, of up to 70% by weight (expressed as Cr2O3 with respect to the amount of hides), in the amount of chromium used in a tanning process, with only a slight reduction in the protection of the leather against hydrolysis.
• Increasing the proportion of the second tanning composition will raise the shrinkage temperature back to the level achievable by a full 3% chrome tannage.
• the third tanning agent has been presented herein as a prepared composition it is not necessary to make it up before introduction into the tanning bath. In fact it is preferable to prepare the composition in situ, i.e. in the tanning bath by separate addition of the first or second tanning agent (or its various components) and the auxiliary tanning agent. In fact the two tanning agents can be added at different times during the tanning process, with either the present first or second tanning agent being added before or after the auxiliary tanning agent so that partial tanning with either is performed before addition of the other.
• any of the above-defined tanning compositions conveniently contains one or more basic salts of alkaline earth metals, especially calcium, with a weak acid, to act as an internal pH control, while the tanning agent is acting on the hides, and to adjust the final pH of the tannage to the most efficient level, between 3.5 and 4.5.
• a composition containing a basic salt of an alkaline earth metal forms a fourth aspect of the present invention.
• the amount of the alkaline earth metal salt, hereinafter referred to as the "internal pH controller", expressed as oxide is preferably from 25% to 200%, especially from 35% to 180%, by weight with respect to the total weight of aluminium salts and other metal salts having a tanning action, expressed as oxides, in the composition.
• a preferred internal pH controller is a salt of an alkaline earth metal with a weak acid, especially one containing calcium, such as calcium carbonate or dolomites.
• a process for the preparation of leather which comprises treating skins or hides (hereinafter referred to collectively as “hides”) with the first, second, third or fourth composition (herein nonethelessafter referred to as the first, second third or fourth tanning agent).
• the tanning process is conveniently performed on the hides immediately after they have been pickled, preferably to a pH of from 2 to 4, and may be performed by addition of the composition to the pickling liquor or to a fresh liquor, such as 10% brine, added to the pickling bath containing the pickled hides after removal of the spent pickling liquor.
• the amount of the tanning agent used is conveniently from 0.5% to 30% and preferably from 0.5% to 5%, by weight of tanning components, i.e. aluminium salts, titanium salts and auxiliary tanning agents, expressed as oxides, based upon the weight of the hides.
• Tanning is conveniently performed by tumbling the hides in the liquor for a period of from 4 hours to 24 hours at or around ambient temperature.
• a significant advantage of the present tanning process is that it is not necessary to make any adjustment of the pH of the tanning liquor.
• exhaustion of the bath and tanning is optimised if the fourth tanning agent, including an internal pH controller, such as calcium carbonate, is employed, because this ensures that the pH at the end of the tanning process is in the region or 3.5 to 4.5.
• Hides which have been treated by means of the present process with the first or second tanning agent are generally only partially protected against hydrolysis and are susceptible to shrinkage in water at temperatures above 80-85°C and such partial tanning is referred to herein as "pre-tanning".
• pre-tanning partial tanning
• hides which have been pre-tanned in accordance with the present process can be subsequently retanned, even after drying and rewetting, which means that they can be pre-tanned and dried for protection, immediately after they have been removed from the animal, and subsequently stored and/or transported to another location, in a dry condition, at a reduced weight and with reduced risk of bacterial spoilage.
• Pre-tanned leather from the first process can be used directly, where pre-tanning is sufficient to produce a leather of the quality required for a particular application, e.g. the production of finished sheepskins which will not be subjected to high temperature cleaning processes and in which "whiteness" is important.
• Hides which have been pre-tanned in accordance with the present process and dried can be re-wetted, e.g. in a new pickling bath or in 10% brine, and re-tanned in accordance with local practice.
• the re-tanning can be carried out with the present tanning composition, with any other mineral or vegetable tanning agent or with the third tanning agent.
• the mechanical treatments such as splitting and shaving, to which tanned leathers are generally submitted before finishing treatments are applied, can be given to the pre-tanned hides before the re-tanning operation.
• This has the advantage that the more expensive re-tanning and finishing agents are only applied to material which has commercial utility after tanning and that the waste materials from the mechanical treatments are not contaminated with the salts of heavy metals, such as chromium, which are commonly employed in re-tanning.
• the hides can be treated with a pre-formed tanning composition, i.e. the third or fourth tanning agent, or they may be treated, simultaneously or consecutively, with the first, second or fourth tanning agent and the auxiliary tanning agent, such as a chromium salt, in either order.
• a pre-formed tanning composition i.e. the third or fourth tanning agent
• the auxiliary tanning agent such as a chromium salt
• the pre-tanned or fully tanned leathers resulting from the use of the present agents and processes, especially those using the second, third and fourth tanning agents, are plumper (and retain their plumpness during subsequent treatments) than conventionally tanned or pre-tanned leathers which means that splitting and shaving can be performed more accurately and with less waste of leather.
• This increased plumpness improves the quality of the leather, which has better "plastic metal elasticity” i.e. shape retaining characteristics.
• This means that hides can be converted into quality leathers having a better "feel" than they can by the use of conventional agents and processes.
• the tanner can have greater freedom and confidence in the selection of tanned and pre-tanned leathers for the later and expensive finishing stages which are so vital to the production of top quality leathers.
• a second process for the preparation of leather which comprises treating a hide which has been pre-tanned in accordance with the first process with the first, second, third or fourth tanning agent.
• the process conditions for the second process are substantially the same as those for the first process. It is preferred, however, that the starting material is a leather which has been pre-tanned with the first or second tanning agent and that the re-tanning is performed with the third tanning agent, containing an auxiliary tanning agent.
• the pre-tanned leather can be treated with a pre-formed tanning composition, i.e. the third or fourth tanning agent, or it can be treated, simultaneously or consecutively, with the first, second or fourth tanning agent and the auxiliary tanning agent, such as a chromium salt, in either order.
• a pre-formed tanning composition i.e. the third or fourth tanning agent
• the auxiliary tanning agent such as a chromium salt
• the auxiliary tanning agent may vegetable or mineral, and in the latter case is a conveniently a water-soluble salt of a metal such as chromium (III), zirconium or titanium.
• a metal such as chromium (III), zirconium or titanium.
• the use of the auxiliary tanning agent permits the achievement of any advantages associated with the auxiliary tanning agent (e.g. the use of chromium or zirconium allows the achievement of higher shrinkage temperature) without the complex processing conditions (e.g. temperature, pH and agitation variations) required when the auxiliary tanning agent is used alone. Furthermore, there is a significant reduction in the coloration and toxicity problems encountered when chromium is the main, or sole, tanning agent.
• the use of the present first and second tanning agents allows reductions in the usage of auxiliary agents, such as chromium salts, of up to 70% compared with normal usages, without any significant reduction in the resistance of the tanned leather to hydrolysis. In this way it is possible to obtain leathers which are resistant to shrinkage in boiling water yet have only a very faint blue colour.
• auxiliary agents such as chromium salts
• the tanning bath liquor can be virtually exhausted with respect to chromium, or other heavy metals, at the end of the tanning process.
• Such a liquor does not present the disposal problems associated with the liquors from normal mineral tanning processes which frequently contain large amounts of heavy metals.
• the accumulation of toxic waste materials such as shavings and tannage waste liquors containing significant proportions of chromium salts, can be largely avoided and the waste disposal problems associated with the use of chrome tanning agents and processes can be greatly reduced.
• the present invention allows a significant reduction (up to 70%) in the quantity of chromium required to achieve a fully tanned leather (with shrinkage temperature around 100°C) the blue coloration associated with conventional chrome tanning of leather is significantly reduced. It has been found that this permits the more effective coloration of the leather with standard acid dyes.
• the new tanning agents permit the achievement of brighter deep shades and truer pastel shades. It has also been found that the dyes exhaust more fully into leather tanned with the present compositions which, in turn, allows more efficient use of dyes with less waste in the dye bath.
• any defects in the leather such as scarring or other surface damage, arising from damage to the hides either on the animal or after skinning, are more effectively masked by conventional dyes when the leather is tanned with the present tanning agents and processes in place of conventional tanning processes. This means that the quality of hides can be upgraded by use of the present tanning agents and processes.
• compositions, C1 to C8, in Table 1 were prepared by mixing the indicated quantities of the named components and adding sufficient water to give, in each case, a final total metal oxide content (Al2O3 + TiO2) of 2.4%.
• compositions C1 to C8 were used to tan calf hide, pickled to pH 3.5, by the following procedure..
• This tanning process permits the preparation of pre-tanned hides which can be stored or transported in the wet form ("wet whites") and subjected to the standard mechanical operations of sawing, shaving and splitting, prior to re-tanning to a finished leather.
• wet whites wet form
• the pre-tanning operation was performed upon bulls hide having a thickness after pickling from 4.5-11mm, which is recognised as a difficult material to tan.
• the wet hides (100 parts) after dehairing, liming, deliming and pickling to pH 3.2-3.5 were placed in a tanning barrel with 20% of their weight of water and 8% of their weight of NaCl and rotated for 10 minutes. Then an amount of Composition C4 containing 2.5 parts of Al2O3 was added followed by 1.5 parts of CaCO3. Rotation was continued at 3-5 rpm for 6 hours when the temperature of the contents had risen to about 37°C after which intermittent rotation (1 hour stationary and 1 hour rotation) was continued for a further 4 hours. The final pH of the tanning liquor was about 3.5.
• the leather obtained had a fine grain and was perfectly white, i.e. the natural skin colour. It had a shrinkage temperature of 77°C.
• the process was performed on calf-skin having a thickness from 3.5-7mm after pickling to a pH of 3.2-3.5.
• the pickled hides were placed in a tanning barrel containing 80% of their weight of water and 10% of NaCl. After 15 minutes of rotation 1% as metal oxides (Al2O3 + TiO2) of Composition C2 and 1.5% of CaCO3 was added. After 4 hours rotation the pH of the liquor was 3.5 and the hides had a shrinkage temperature of 69°C. After a further 2 hours rotation the pH rose to 3.8 and the shrinkage temperature of the hides was 75°C.
• the dried pre-tanned hides had a fine grain with a normal fullness and a creamy white colour. They could be re-wetted without difficulty and subjected to a classical chrome tanning operation without any problem.
• Calf hides pickled to pH 3.5 in a liquor at 80% volume were treated in a pickling bath with with 3%, measured as Cr2O3, of a salt of chromium at 33°Sch and the bath was rotated for 4 hours.
• the pH was then 2.7 and the shrinkage temperature of a sample of the leather was 67°C.
• 2.05%, as oxide (Al2O3 + TiO2), of Composition C6, prebasified to pH 3.4 with Na2CO3 and 1.5% of CaCO3 were added to the same bath and rotation continued for 5 hours when the pH of the bath was about 3.8.
• the leather had a shrinkage temperature of 92°C, a pale blue colour and a fine grain. It was ready for the usual complementary mechanical and chemical treatments.
• the resulting leathers were very fine grained, smooth and a pale beige colour. They had a shrinkage temperature of 95°C.
• a dry tanning agent was made by mixing 90.4 parts of a dried form of Composition C3 and 9.6 parts of CaCO3.
• Calf-skins, pickled to pH 3.6 were placed in a fresh bath of 80% water, 20 NaCl and 0.1% formic acid and rotated for 20 minutes when the pH was 3.5.
• To the bath was added 3% of a commercial Cr2(SO4)3 (CHROMOSAL B from Bayer) and rotation continued for 4 hours when the pH of the bath was 2.7.
• CHROMOSAL B commercial Cr2(SO4)3
• the bath was then drained and the leather re-tanned with 6% of the dry tanning agent, followed by a classical nourishing operation with 7% of a commercial agent, TRUPON DX (from Trumpier).
• the resulting leather was fined grained, of a white or very light blue colour and a very even texture.
• the barrel was then drained and the leather washed by rotation with water for 10 minutes at 35°C followed by water (100%) containing 0.4% soda ash and 0.04% antiseptic (BUSAN) for 45 minutes.
• the resulting leather had a very pale blue coloration and could be converted into a high quality finished leather by treatment with conventional finishing agents.
• Composition C9 is a composition of 80 parts of the masked Al/Ti component (d) described in Table 1 and 20 parts of MgSO4.

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• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• General Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Treatment And Processing Of Natural Fur Or Leather (AREA)

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Citations (3)

• 1988
  • 1988-04-11 GB GB888808436A patent/GB8808436D0/en active Pending
  • 1988-04-11 EP EP88303209A patent/EP0291165A1/en not_active Withdrawn
  • 1988-04-21 MA MA21494A patent/MA21253A1/fr unknown
  • 1988-04-22 JP JP63098462A patent/JPS63304100A/ja active Pending
  • 1988-04-22 DK DK221488A patent/DK221488A/da not_active Application Discontinuation
  • 1988-04-22 ZA ZA882877A patent/ZA882877B/xx unknown
  • 1988-04-22 NO NO881764A patent/NO881764L/no unknown
  • 1988-04-22 FI FI881894A patent/FI881894A/fi not_active Application Discontinuation
  • 1988-04-22 AU AU15083/88A patent/AU1508388A/en not_active Abandoned
  • 1988-04-23 KR KR1019880004625A patent/KR880012774A/ko not_active Application Discontinuation

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