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
  • C14C1/00—Chemical treatment prior to tanning
  • C14C1/06—Facilitating unhairing, e.g. by painting, by liming

Definitions

• This invention relates to a process for the depilation of a skin which comprises treating it in a bath containing at least 10 g. per litre of an alkali metal dichromate and a strong mineral acid and then if desired subjecting it to an alkaline treatment.
• the present invention relates to a process for the depilation of skins intended for the manufacture of leather.
• a process for the depilation of skins has recently been proposed in which chlorine dioxide in acid medium is used.
• the dissolution of the hair is in this case due to the rupture of the disulphide bridges and to the formation of sulphonic groups along the protein portions.
• the present invention relates to a new oxidising process of depilation which comprises treating the skins in baths containing at least 10 g. per litre of an alkali metal dichromate and at least one strong mineral acid, and then if desired subjecting them to an alkaline treatment.
• the process according to the invention is based on the oxidation of the hair by the H+/Cr O couple.
• the forms (1), (2) and (3) preponderate and the skin keeps its hair. Depilation can then be obtained by hydrolysis of the oxidised derivatives by means of an alkaline treatment, for example with a concentrated alkali:
• the strong mineral acid may be, for example hydrochloric acid, nitric acid, sulphuric acid, or perchloric acid. Either one acid alone or a mixture of acids may be used.
• the acid content of the oxidising bath is preferably greater than 6 g. per litre. It is advisable to dis- 3,482,924 Patented Dec. 9, 1969 ice solve the dichromate in water, then add the acid and finally the skins.
• the oxidising treatment may be carried out directly on the cleaned, softened and fleshed skins.
• the depilation can then be accomplished by following the dichromate treatment with an alkaline treatment.
• an alkaline treatment it is advantageous to protect the hair side before the alkaline hydrolysis by a treatment with quinone, formaldehyde or other tanning agent.
• quinone, formaldehyde or other tanning agent One may also resort to rinsing for this purpose.
• the depilation process according to the invention enables chrome tanning to be carried out in-particularly advantageous conditions.
• the conventional process of preparation of leathers for chrome tanning comprises depilation effected generally with a mixture of lime and sodium sulphide or hydrosulphide.
• the skins are then brought back to a pH near to neutrality by treatment with acids, sulphites, bisulphites or ammoniacal salts.
• the process known as the one bath process in which the delimed skins are acidified by treatment with solutions of mineral or organic acids in the presence of salt, then treated with salts of trivalent chromium, the basicity of which is progressively increased;
• the process known as the two-bath process in which the skins are first treated in a bath containing sodium dichromate, an acid and frequently a little salt.
• the chromic acid thus fixed on the skins is then reduced in a second bath consisting of a mixture of sodium thios-ulphite and hydrochloric acid.
• chromic acid is fixed on their fibres. This acid may be reduced in situ by the two-bath tanning technique.
• the depilated chrome-tanned skins then follow the course of the usual subsequent operations. Skins which have undergone the oxidising treatment, then the reducing treatment, but are not yet depilated, are subjected to alkaline hydrolysis under the conditions recommended above.
• the not yet depilated skins may also be subjected directly after rinsing to alkaline hydroylsis and, after depilation and pickling, undergo a tanning treatment by the one-bath process, the tanning liquor being prepared by reduction of the residual depilating bath, from which the sludge may have been removed.
• the depletion process according to the invention offers the advantage that the products which have served for the depletion process itself can be used for tan- 11mg.
• the hair forms a sludge dispersed in the bath.
• the skins are then placed in a fulling machine containing 500 litres of a 20% solution of sodium hyposulphite. They are fulled for a quarter of an hour, then left in the fulling machine for 24 hours with a quarter of an hours rotation in each hour.
• the shrinkage temperature of the leathers is 97 C. The leath is left to mature for 48 hours on a rack before it is neutralised, dyed and nourished as usual.
• the leather is left in the fulling machine to stand overnight, and the next day is rotated for an hour.
• the pH is 6.
• Half the bath remaining from the preceding operation is evacuated, and 2 0 kg. of 40% commercial caustic soda are added through the axle of the fulling machine, the addition being made in a quarter of an hour. Rotation is continued for three quarters of an hour.
• the latice-gate is then put in position, the cold-water inlet through the axis is opened and rotation is carried out for an hour.
• the gate is replaced by a solid gate and rotation is effected for an hour with the following bath:
• EXAMPLE 3 The skins are treated as in Example 2, but the retanning with quinone is replaced by retanning with 7% of 40% formaldehyde.
• fuiling is carried out for 10 minutes with 200 litres of a 40% caustic soda solution at 100 g. per litre.
• the hairs are completely dissolved, and are eliminated by simple rinsing for an hour, the solid gate being replaced by the lattice gate.
• the skins are then treated for an hour in a fresh bath containing the following ingredients:
• EXAMPLE 5 In a falling machine resistant to the nitrochromic mixture, 19 kg. of commercial sodium dichromate are dissolved in 150 litres of water with stirring, and 26 kg. of 62% nitric acid are added, with continuous stirring. The temperature of the bath is checked so that it is not above 25 C. Then 100 kg. of cleaned, softened and fleshed skins are put in the fulling machine and are fulled for 12 hours, and left to stand overnight. The next day they are rotated for an hour so as to complete the dispersion of the residual hairs in the bath, then the skins are put in a falling machine containing 500 litres of a 20% solution of sodium hyposulphite.
• the shrinking temperature of the leathers is about 97 C.
• the leathers are left to mature for 48 hours on a rack before they are neutralised, dyed and nourished as usual.
• Process for the depilation of a skin which comprises treating it at a temperature not above 25 C. in an aqueous bath containing at least 10 g. per litre of an alkali metal dichromate and at least 6 g. per litre of a strong mineral acid.

Landscapes

• 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)

Applications Claiming Priority (1)

Publications (1)

Family

ID=8610390

Family Applications (1)

Country Status (6)

Citations (1)

• 1966
  • 1966-06-08 FR FR64578A patent/FR1491348A/fr not_active Expired
• 1967
  • 1967-05-24 BE BE698926D patent/BE698926A/xx unknown
  • 1967-05-30 DE DE19671669359 patent/DE1669359A1/de not_active Withdrawn
  • 1967-06-07 US US644053A patent/US3482924A/en not_active Expired - Lifetime
  • 1967-06-08 GB GB26413/67A patent/GB1186897A/en not_active Expired
  • 1967-06-08 NL NL6708003A patent/NL6708003A/xx unknown

Patent Citations (1)

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