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
  • C14C3/04—Mineral 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

Definitions

• This invention relates to a process for tanning hides. More particularly, the invention relates to a process for tanning hides for vamps and peltry, by means of ammonium titanyl sulphate.
• ammonium titanyl sulphate can be utilized as a tanning agent for hides. It has been proposed to subject delimed hides to a pretreatment with an activating substance, for example phthalic anhydride; tanning follows, with the ammonium titanyl sulphate, and alkaline substances are then added to the bath, and tanning can be completed with synthetic organic tanning agents.
• an activating substance for example phthalic anhydride
• tanning causes in the hides an acid swelling, which is irreversible and renders the tanned hide brittle.
• the ammonium titanyl sulphate tends to precipitate in the form of titanium hydroxide, which adversely affects the qualitative constancy of the article and gives rise to losses of the tanning agent.
• the present invention aims to provide a process for tanning hides, particularly for vamps and peltry by using ammonium titanyl sulphate, which process avoids acid swelling of the hides, thus imparting to the tanned leather a higher tearing resistance.
• the invention also aims to provide a process in which the ammonium titanyl sulphate is practically fully absorbed by the hides, with consequent both economical and ecological advantages, as practically no titanium compounds are discharged along with the residual waters.
• a further aim of the invention is to provide a process capable of producing a tanned hide having a high compactness (hide of closed texture), with good stretch recovery (firm hide) and free from blowings (loose grain).
• the present invention provides a process for tanning hides, in particular a process for the tanning of hides for vamps and peltry by means of ammonium titanyl sulphate.
• This process comprises the consecutive steps that delimed hides are treated, in the presence of water, with ammonium sulphate and naphthalene sulphonic acid; ammonium titanyl sulphate is added to the bath, while maintaining the temperature at not more than 40°C; a complexing agent for tetravalent titanium ion is optionally added, maintaining the temperature at not more than 40°C; the bath is graudally made alkaline by repeatedly adding (adding batchwise) sodium sulphite and hexamethylenetetramine until there is obtained a pH value in the hide of from 4.0 to 5.0, while maintaining the temperature at not more than 40°C; the hides are removed from the bath and are allowed to rest; the hides are pressed, sheared (shaved) and washed with water; the
• the final titanium content of the bath is very low, and does not normally exceed about 0.3 g/liter (calculated as Ti0 2 ), so that tanning agent losses do not practically occur and the discharging of the bath does not practically give rise to ecological problems deriving from the presence of titanium.
• ammonium titanyl sulphate and a method of preparing the same are described in French patent No. 2,042,206. Another preparation method is described in Italian patent application No. 20571 A/83.
• the ammonium titanyl sulphate utilized in the present invention is not subjected to the stabilizing treatment described in French patent No. 2,042,206.
• the naphthalene sulphonic acid utilized in the first step of the process of the invention may be the alpha-naphthalene sulphonic acid or beta-naphthalene sulphonic acid, or mixtures thereof.
• the tanning drum is generally rotated until the reagents have passed through the hide section before adding the ammonium titanyl sulphate.
• ammonium titanyl sulphate calculated as TiO z , are preferably used, more preferably from 2% to 4% thereof. If no complexing agent is added, the tanning drum is rotated, after addition of ammonium titanyl sulphate, for a time generally ranging from 3 to 7 hours.
• the tetravalent titanium ion complexing agent is preferably an alkali metal citrate or tartrate, for example of sodium or of potassium. As already explained hereinbefore, it can be added either after the ammonium titanyl sulphate or during the deacidification step or in both steps.
• the total amount of alkali metal citrate utilized in one step or in both steps is preferably from 0.05 to 0.4 mole per mole of Ti0 2 contained in the ammonium titanyl sulphate; in the case of the alkali metal tartrate, such amount is preferably from 0.07 to 0.6 mole per mole of Ti0 2 .
• the complexing agent is used in both steps, about 50-80% of such amounts are preferably added after the ammonium titanyl sulphate, the remaining amount being added during the deacidification step.
• the complexing agent When the complexing agent is added during the tanning step with the ammonium titanyl sulphate, it is usually added when the tanning agent has substantially passed through the hide section, after about 2-4 hours. After addition of the complexing agent, the drum is usually rotated for 1 to 3 hours.
• the alkalinisation step follows. Sodium sulphite and hexamethylenetetramine are gradually added batchwise to the bath, until there is obtained a pH value in the hide of from 4.0 to 5.0. Preferably, such pH is from 4.0 to 4.5. Usually, the addition of sodium sulphite and of hexamethylenetetramine occurs in 3-4 batches, for example at constant time intervals totally lasting about 6 hours.
• the sodium sulphite:hexamethylenetetramine weight ratio is usually about 1: 1.
• the alkali metal substance used in the deacidification step is preferably sodium bicarbonate or sodium sulphite. Deacidification is continued until there is obtained, in the hide, a pH value of from 5.0 to 6.5, preferably from 5.0 to 6.0. When a tetravalent titanium ion complexing agent is used during the deacidification step, it is usually added together with the alkaline substance.
• the hides are then washed with water, after which there follows the step of completing the tanning with one or more synthetic tannins and/or a suitable polymeric material.
• the synthetic tannin is preferably selected from phenol and formaldehyde sulphonated condensates and from naphthalene and formaldehyde sulphonated condensates.
• the polymeric material for completing the tanning is preferably selected from polyurethane polymers, acrylic polymers and styrene-maleic polymers.
• the bath is then discharged and the hides are dyed and greased according to conventional techniques.
• the hides previously subjected to the usual liming, fleshing and delim- ing treatments, are introduced into a drum. All the amounts referred to below are indicated in per cent by weight with respect to the pelt weight of the hides, unless otherwise specified.
• the temperature generally ranges from 20 to 25°C.
• the drum is generally rotated until the reagents have passed through the hide section, which requires generally from 2 to 4 hours.
• the pH of the bath generally ranges from 4.0 to 4.5.
• ammonium titanyl sulphate calculated as Ti0 2
• the drum is usually rotated during 3 to 7 hours. If the complexing agent is added, the drum is generally rotated, before introducing said agent, until the tanning agent has passed through the hide section, which takes generally 2 to 4 hours; when the complexing agent is added, in the case of alkali metal citrate, from 0.05 to 0.3 mole of citrate for each mole of Ti0 2 is generally used at this stage. After the complexing agent has been added, the drum is generally rotated during 1 to 3 hours.
• the alkalinisation step terminates when the pH, in the whole section of the hide, is from 4.0 to 4.5. This generally takes 6 to 8 hours.
• the bath is practically free from tetravalent titanium: its maximum residual concentration does not exceed 0.3 g of Ti0 2 per liter.
• the temperature must not exceed 40°C.
• the hides are taken out from the bath and are allowed to rest during a period of time generally varying from 24 to 28 hours.
• the hides are then pressed, sheared and subsequently washed with about 300% of water at 30-35°C.
• the deacidification treatment is generally carried on until the hide, in its entire section, has reached a pH value of from 5.0 to 6.0; this generally takes from 1 to 3 hours.
• the drum is generally rotated until the reagent or the reagents has/have passed through the section of the hide; this generally takes from 2 to 3 hours.
• the bath is discharged and the hides are dyed and greased according to conventional techniques.
• the hides tanned by the process of the present invention exhibit a good tearing resistance. They are very compact, with good stretch recovery and free from blowings.
• the delimed hides of 3 calves were placed into a tanning vessel (rotative drum).
• the hides were treated with 120% of water' at 25°C, 3% of (NH 4 ) 2 S0 4 and 3% of commercial-grade naphthalene sulphonic acid. After a 3-hour rotation, the pH in the whole section of the hides was equal to 4.5.
• the drum was discharged and the hides were allowed to rest during 48 hours.
• the hides were pressed, sheared and washed with 300% of water at 30°C, whereafter deacidification was accomplished.
• the hides were introduced again into the drum (sheared weight: 12 kg), and 200% of water at 35°C, 2% of sodium citrate and 2% of sodium bicarbonate were added.
• the drum was rotated for 90 minutes; after which the pH value of the bath and of the whole section of the hide was equal to 6.0.
• the bath was discharged, and the hides were washed with 300% of water at 35°C.
• the complementary tanning step was then commenced. To this purpose, 150% of water at 30°C and 8% of a mixture of synthetic tannins, consisting of a naphthalene - formaldehyde sulphonated polycondensate and of a phenol - formaldehyde sulphonated polycondensate, was added. The drum was rotated during 2 hours. The hides were checked and a complete penetration was ascertained.
• the bath was discharged and the hides were dyed and greased.
• the resulting leathers were compact and relatively soft, not elastic, and did not give rise to blowings. They were suitable for vamps.
• the delimed hides of 3 calves (pelt weight: 25 kg) were placed into a tanning drum and were treated as in Example 1 until completion of the tanning step with the ammonium titanyl sulphate. 8 kg of sheared hides were then deacidified by addition of 200% of water at 30°C and of 1.8% of sodium sulphite. The drum was rotated for 2 hours. The bath and the whole section of the hides exhibited a pH value of 5.8.
• the complementary tanning step was carried out. To this purpose, 150% of water at 30°C, 5% of a synthetic tannin consisting of a sulphonated polycondensate of naphthalene and formaldehyde, and 4% of acrylic resin were added.
• the resulting leathers were compact and soft and did not give rise to blowings. They were suitable for vamps and soft bag articles.
• the delimed hides of 4 calves were placed into a tanning drum.
• the hides were treated with 120% of water at 25°C, 2.5% of (NH 4 ) 2 S0 4 and 2.5% of commercial-grade naphthalene sulphonic acid. After a 3-hour rotation the pH of the bath and of the entire section of the hides was equal to 4.3.
• the resulting leathers were compact, not elastic and did not give rise to blowings. They were suitable for the manufacture of suit-cases and bags.

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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)

Applications Claiming Priority (2)

Publications (2)

Family

ID=11210538

Family Applications (1)

Country Status (6)

Family Cites Families (2)

• 1984
  • 1984-12-03 IT IT23870/84A patent/IT1178688B/it active
• 1985
  • 1985-11-28 BR BR8505963A patent/BR8505963A/pt unknown
  • 1985-11-28 TR TR48212/85A patent/TR23452A/xx unknown
  • 1985-12-02 ES ES549493A patent/ES8704548A1/es not_active Expired
  • 1985-12-03 DE DE8585308779T patent/DE3568799D1/de not_active Expired
  • 1985-12-03 EP EP85308779A patent/EP0187473B1/en not_active Expired

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