Bleaching and dyeing; fluid treatment and chemical modification – Treatment of hides – skins – feathers and animal tissues – Tanning
Patent
1997-11-12
1999-11-09
Diamond, Alan
Bleaching and dyeing; fluid treatment and chemical modification
Treatment of hides, skins, feathers and animal tissues
Tanning
8 942, 8 9422, 8 9433, 8 9414, 8 9423, 427323, 427389, 4273934, 252 857, C14C 900
Patent
active
059805781
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
Field of the Invention
A process for waterproofing leather at low pH-values and leathers manufactured thereby
The present invention relates to a process for waterproofing leathers, furs, and other fibrous materials wherein the use of dispersing or stabilizing auxiliary agents with the water repellent renders the previously usual, but undesirable high pH-values no longer necessary to achieve a good water repellent action.
Description of the Background
Except for some special cases where water repellents are subsequently applied on the ready-made leather, hydrophobing is carried out from the aqueous float today. The water repellent effect can either be achieved by coating the fibrils and fibers of the leathers with hydrophobic compounds or it may be based on an incorporation of special emulsifiers capable of forming stable water-in-oil emulsions. As soon as water or moisture reaches or penetrates the leather, a water-in-oil emulsion is formed within the fiber interstices. The resultant swelling seals the leather. The structure and action of different kinds of auxiliary agents used for waterproofing is described by R. Nowak in "Leder- und Hautemarkt", 29 (1977), number 24.
Most of the water repellents used today are those responding to both of the above-mentioned mechanisms. Inversion makes it possible to convert products belonging to the class of substances forming water-in-oil emulsions into those forming oil-in-water emulsions. This may be effected by adding certain emulsifiers, changing the pH, by fixation with metallic salts, and other measures. Oil-in-water emulsions may be used in fatliquoring because of their optional dilutability with water. The water repellents used in practice belong to this type.
To achieve a good waterproofing effect, the water repellent must completely penetrate the leather cross section (Hodder, J. J., "Waterproof Leather Technologies and Processes", Waterproof Symposium on the occasion of the ALCA meeting, Pocono Manors, USA, 1994, publication in JALCA in preparation). A great handicap of the water repellents used so far lies in the fact that their oil-in-water emulsions tend to break at acid pH-values starting at about 5. Greasying on the grain and flesh side results, increasing in complete, mayonnaise-like precipitation of the product. The broken emulsion has an absolutely different emulsion or solution behavior which is likely to become apparent in the described precipitation, for example. The mayonnaise-like fatty substance can no longer penetrate the leather in fine or superfine dispersion to penetrate it uniformly. As a consequence the waterproofing effect becomes worse.
For this reason it has become common practice to set a pH-value preventing early emulsion breakdown, both in the float from which the water repellent or its oil-in-water emulsion is applied on the leather and in the leather. In this connection, neutralization has been of particular importance. Leather highly neutralized throughout the cross section, with a pH-value avoiding emulsion breakdown in all areas has been necessary to ensure penetration; in practice requiring a pH of 5 and above.
According to Friese et al. (Friese, H.-H., H. Constabel, W. Prinz, "Oberleder mit verbessertem Verhalten gegenuber Wasser", Leder-/Haute-Markt 35 , number 20, 1-3, 1983) neutralization to a pH-value of 5.5 in the leather cross section and 6.1 in the float was effected to make impregnated leathers of wet blue and a shaved substance of 2.2 mm. Uniform neutralization throughout the cross section is important in this context. Fatliquoring (here, the water repellent treatment carried out in the process step of fatliquoring) should be carried out at a minimum pH of 6.5 and at a highest possible temperature in order to achieve thorough "fatliquoring". If the leather had an insufficiently high pH-value across the whole cross section, but was more acidic in the middle, early breaking of the emulsion with reduced water equivalents could occur. The more acid central layer resulted in a kind of ca
REFERENCES:
patent: 5124181 (1992-06-01), Schaffer et al.
patent: 5433753 (1995-07-01), Dahmen et al.
Ullmann's Encylopedia of Industrial Chemistry, fifth edition, vol. A 15, pp. 274-277 (month unknown), 1990.
Kaussen Manfred
Stoelcker Helmut
Diamond Alan
Stockhausen GmbH & Co. KG
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