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
  • C14C3/04—Mineral tanning

Definitions

• composition suitable for use as a tanning agent in the preparation of leather and to a tanning process using the composition.
• chromium (III) The most commonly used and effective commercial tanning agents are salts of chromium (III).
• these suffer two serious drawbacks (i) that chromium imparts a substantial blue coloration to the tanned leather which causes problems with the preparation of pale-shade or undyed leathers and (ii) there are doubts about the toxicity of chromium (III) which make its presence undesirable in industrial effluents.
• a recently proposed alternative tanning agent comprising a composition of a mixed complex of aluminium (III) and titanium (IV) ions masked with a poly(hydroxy)monocarboxylic acid, is described in GB 2,165,859A.
• this tanning agent is non-toxic and does not colour the leather, its tanning performance is pH sensitive and a number of pH adjustments are required before and during tanning.
• the tanned leather requires aging for 24 hours or more before it is suitable for use. It has now been found that the performance of, and ease of tanning with, this masked Al/Ti complex can be improved by the presence of certain salts.
• a tanning agent comprising a composition of a mixed complex of aluminium (III) and titatium (IV) ions masked with a poly(hydroxy)monocarboxylic acid characterised in that the composition contains from 2.5% to 45% of a basic salt of an alkaline earth metal (expressed as weight of metal oxide) based upon the total weight of the composition.
• the preparation and masking of the mixed complex is described in GB 2,165,859A (see particularly page 1 line 63 to page 2 line 33 and Examples 1 to 3).
• the present invention allows the employment of a broader range of Al:Ti ratios than are disclosed in the aforementioned patent.
• the ratio of aluminium ions to titanium ions expressed as Al2O3 and TiO2 respectively, may conveniently vary from 0.8: 1 to 8: 1 and more preferably from 0.8: 1 to 4: 1; an especially preferred ratio is 2:1.
• the combined alumiunium and titanium content (expressed as Al2 O3 + TiO2) of the agent is preferably from 10% to 30% by weight.
• the aluminium and titanium ions are preferably present as salts with a strong acid, especially as sulphates.
• the poly(hydroxy)monocarboxylic acid which may be in the form of a water-soluble salt, especially with an alkali metal, is preferably of the type described in UK 2,165,859 A, especially an acid derivable from monosaccharides, such as a poly(hydroxy)hexanoic or poly(hydroxy)heptanoic acid, e.g. the heptonic acid and glucoheptanoic acid and the hexonic acids, gluconic acid, galactonic acid and mannonic acid.
• monosaccharides such as a poly(hydroxy)hexanoic or poly(hydroxy)heptanoic acid, e.g. the heptonic acid and glucoheptanoic acid and the hexonic acids, gluconic acid, galactonic acid and mannonic acid.
• Any basic salt of an alkaline earth metal i.e. one having a pH > 7 in aqueous solution
• preferred salts are those of calcium, magnesium and barium, such as carbonates, sulphites, thiosulphates etc., and especially the naturally occurring complex carbonates of magnesium and calcium, such as dolomite.
• a process for the tanning of animal hides or skins comprising treating the hides with a composition of a mixed complex of aluminium (III) and titatium (IV) ions masked with a poly(hydroxy)monocarboxylic acid characterised in that the composition contains from 2.5% to 45% of a basic salt of an alkaline earth metal (expressed as weight of metal oxide) based upon the total weight of the composition.
• the tanning process is conveniently performed in the pickling liquor with from 1% to 20%, more preferably from 3% to 10% by weight of the composition based on the total weight of hides, by gentle tumbling for periods of from 6 to 20 hours at or around ambient temperature and without any pH adjustment.
• Hides which have been tanned using the present composition can be subsequently re-tanned even after they have been dried which means that hides can be lightly tanned ("pre-tanned”) and dried for protection, immediately after they have been removed from the animal, and subsequently stored and/or transported to a new location, in a dry condition, at a reduced weight and with reduced risk of bacterial spoilage.
• the pre-tanned hides can then be re-wetted and re-tanned, to give full leathers, in accordance with local practice.
• the present tanning agent can also be used in conjunction with chrome tanning agents, such as chromium salts, for the tanning of hides in order to reduce the quantity of chromium salts, and thus to alleviate the effects of the aforementioned problems associated with the use of chromium salts alone in the tanning of hides.
• chrome tanning agents such as chromium salts
• the use of the present agent allows reductions in the usage of chromium salts of up to 70% compared with normal usage 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 and yet are only very faintly coloured. Furthermore, the liquor at the end of the tanning process is virtually exhausted of chromium salts and therefore poses a less serious problem for disposal.
• the amount of chromium can vary with in wide limits, up to 500%, with respect to the sum of the aluminium and titanium (expressed as Al2O3 and TiO2) but is preferably from 10% to 300% and more preferably from 35% to 250%, by weight.
• a leather having a shrinkage temperature in excess of 90°C by the use of less than 1% by weight of a chrome tanning agent (expressed as Cr2O3 with respect to the hides) in conjunction with about 0.5% by weight of the present tanning composition (expressed as Al2O3 + TiO2 with respect to the hides) and by increasing the proportion of the latter to from 1-2%, more preferably 1.5-2.0%, the shrinkage temperature can be raised to in excess of 95°C. Where a lower shrinkage temperature can be tolerated the proportion of chromium can be reduced further with proportional benefits in a reduced colour of the leather and reduced chromium content of the shavings and offcuts and the tanning liquor at the end of the process.
• the hides can be treated concurrently with the present composition and the chrome tanning agent or they can be used consecutively in either order.
• pre-tanned or fully tanned leathers resulting from the use of the present agent and process 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.
• 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.
• 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 > 95°C) the blue coloration associated with conventional chrome tanning of leather is reduced significantly. It has been found that this permits the more effective coloration of the leather with standard acid dyes.
• the new tanning agent 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 composition 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, on the animal or after skinning, are more effectively masked by conventional dyes when the leather is tanned with the present tanning agent and process, in place of conventional tanning processes. This means that the quality of hides can be upgraded by use of the present tanning agent and process.
• a complex tanning agent was prepared by mixing 800 parts of Agent A, 100 parts of calcium carbonate powder and 100 parts of magnesium carbonate powder.
• the leathers could be dried, for storage and/or transportation, and subsequently re-wetted ready for de-tanning and/or re-tanning with chrome or other tanning agents when rewetted in a pickling liquor.
• a complex tanning agent was prepared by mixing 600 parts of Agent A with 400 parts of powdered dolomite DRB 30 having the following chemical composition:
• Agent A A mixture was made of 800 parts of Agent A with 100 parts of magnesium carbonate, 50 parts of calcium carbonate and 50 parts of calcium formate.
• Chrome Tanning Agent 2 was a liquor or chromium sulphate obtained by reducing NaCr2O7 with glucose having a Cr2O3 content 0.123g/l and a basicity of 42°Sch (this is a relatively high basicity in solution such that it represents about half of its volume of commercial chromium sulphates in conventional powder form).
• the leather was then retanned without maturation. by adding 200 parts of water at 30°C and 2.4 parts of degreasing agent for each 100 parts of the original hides and rotating the drum for 30 minutes when the pH of the bath was 3.7-3.8. The liquors were then drained from the bath and replenished with 120 parts of water at 40°C and 6 parts of Agent D. Following rotation for 2 hours, the pH rose to 4.6 and the liquors were again drained. The leather was then stuffed by tumbling for 1 hour with 60 parts water at 60°C, 8 parts emulsifying fat liquor, 0.6 parts raw fat liquor and 0.005 parts of antiseptic when the pH was 4.9. After adding 2.2 parts of formic acid the drum was rotated for 30 minutes when the pH was 4.2. The resultant leather was white and very light, and could be buffed to provide Nubuck, or corrected grain, or used without further treatment as full-grain, white finish.
• a mixture is prepared of 700 parts of Agent A, 100 parts of calcium carbonate, 100 parts of magnesium carbonate and 100 parts of barium carbonate.
• a mixture was prepared of 800 parts of Agent A, 186 parts of dolomite DRB 30 and 14 parts of sodium sulphite.
• Chrome Tanning Agent 3 was an organo-metallic tannin, comprising a chrome salt complexed with aldolised beta-naphthol sulphonic acid (A-BNSA), neutralised with ammonia and re-acidified with acetic acid, of which a solution of 28% dry extract contains:
• A-BNSA aldolised beta-naphthol sulphonic acid
• a mixture was prepared of 900 parts of Agent A, 60 parts of Dolomite DRB 30 and 40 parts of calcium formate.
• Example 3 The procedure of Example 3 was repeated except that Chrome Tanning Agent 2 was replaced by 5 parts of Chrome Tanning Agent 6 (a commercial "self-basifying” chrome salt) and 5 parts water.
• Chrome Tanning Agent 6 a commercial "self-basifying” chrome salt

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Publications (2)

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• 1988
  • 1988-04-11 EP EP88303210A patent/EP0290143B1/en not_active Expired - Lifetime
  • 1988-04-11 GB GB888808435A patent/GB8808435D0/en active Pending
  • 1988-04-11 DE DE8888303210T patent/DE3866770D1/de not_active Expired - Fee Related
  • 1988-04-11 ES ES198888303210T patent/ES2028275T3/es not_active Expired - Lifetime
  • 1988-04-21 MA MA21495A patent/MA21254A1/fr unknown
  • 1988-04-22 DK DK221388A patent/DK221388A/da not_active Application Discontinuation
  • 1988-04-22 JP JP63098461A patent/JPS6438500A/ja active Pending
  • 1988-04-22 AU AU15082/88A patent/AU614514B2/en not_active Ceased
  • 1988-04-22 FI FI881893A patent/FI881893A/fi not_active Application Discontinuation
  • 1988-04-22 NZ NZ224348A patent/NZ224348A/xx unknown
  • 1988-04-22 ZA ZA882876A patent/ZA882876B/xx unknown
  • 1988-04-22 NO NO881763A patent/NO173745C/no unknown
  • 1988-04-23 KR KR1019880004624A patent/KR880012773A/ko not_active IP Right Cessation
  • 1988-04-25 MY MYPI88000431A patent/MY104304A/en unknown
• 1991
  • 1991-12-12 GR GR91401840T patent/GR3003330T3/el unknown

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