FR2651794A1 - PROCESS FOR PREPARING SYNTHETIC TANNING AGENT AND TANNING THE LEATHER - Google Patents

Abstract

The invention relates to a process for preparing a synthetic tanning agent comprising reacting a mixture of at least 30 mol% phenol and / or sulfonated cresols and at most 70 mol% phenol and / or of cresols in a neutral or alkaline medium, with at least 60 mol% of formaldehyde, calculated as a function of the ortho and para free positions of the aromatic rings, between 60 ° C and the boiling point of the mixture for 1 to 8 hours. The process can be combined with known tanning processes and used to prepare light colored leathers.

Description

The present invention relates to a method

  to prepare a synthetic tanning agent and for its use

  to make a chrome-free leather.

  Tanning is undoubtedly the most important of leather manufacturing operations during which

  skins and animal remains are transformed into

  which reasonably withstand the effects of the envi-

  ronment. Several different tanning methods have been developed since the beginning of mankind. In so-called inorganic tannages, the main component of the

  tanning composition is a salt of chromium (III), aluminum

  minium, zirconium (IV), titanium (IV) or iron (III).

  Some plant extracts are also suitable for

  swimming. Other agents such as certain aldehydes (eg formaldehyde and glutaraldehyde), sulfochlorides

  of alkyl and synthetic tanning agents (syn-

  tans) are mainly used as partners of

  combination for the two previous types.

  Syntans are syntactic organic materials

  thesis having a tanning effect. They are most often made by condensation of mono- or polynuclear mono- or polyphenols, partially sulphonated naphthalene with formaldehyde. Condensation is always done

  in an acidic medium providing only methyl bridges

  binds between adjacent benzene rings (see Knop, A., Scheib, W .; "Chemistry and Application of Phenolic Resins", Springer, 1979). The molecules of the syntans are large and polar enough to form bridges between the collagen chains via a hydrogen bond. Due

  the great distance between the phenolic hydroxy groups

  and the absence of other groups forming comple-

  In the molecules, they can not form stable chelate complexes and their reaction with inorganic tanning salts is therefore generally of minor importance in tanning. The catechol and pyrogallol derivatives are exceptions because they can form chelated rings with their phenolic hydroxy groups

  in ortho position and can lead to a tanning reason-

  nably stable in combination with aluminum. The incon-

  The common cause of these materials is their strong tendency to change color by oxidation (Sykes, R.L. et al., J. Soc., Leahter Tech Chem., 64, 29 (1980), 64, 32).

(1980)).

  Phenolic hydroxy groups can also be found

  adjacent plants in plant extracts capable of tanning. These high molecular weight colloidal materials can be strongly bound to the collagen chains by secondary valence forces and then cross-linked by aluminum via the chelate-forming groups, thereby increasing the stability of tanning (Slabbert, NP, J. Am. Leather Chem Assoc 76, 231 (1981)). The large size, slow diffusion and strong adsorption of plant tannin molecules make it difficult to obtain a uniform distribution across the fiber structure unless large amounts are used. The combination

  of vegetable agent-aluminum is practically limited to

  aluminum tanning of pretanned leather with a substance

plant, for the same reason.

  Evans, N.A. and Montgomery, K.C. (Proc.

  Congress of the International Union of Leather Technolo-

  Gists and Chemists, Melbourne, 1987, p. 292) were tanned by combination with a polydentate material

  chelating agent, obtained by the catalyzed condensation with

  salicylic acid with formaldehyde. With aluminum

  minium, they reached a withdrawal temperature of 88 C.

  The most commonly applied method is the tan-

  swimming with chromium (III) salts and this is exceptionally

  quickly, simply and economically. He gives

  products with extreme stability and phy-

  sico-mechanical advantages. Despite these advantages, efforts have been made to develop for some time other

  less harmful procedures and tanning materials, in

  its the polluting and toxic nature of chromium compounds. Aluminum may be a favorable choice for many reasons, including the pale color of most of its compounds. Unfortunately, the stability of the aluminum-collagen bond is low and when used in combination with chromium salts (to reduce the amount thereof), a hollow leather is obtained

relatively hard.

  The Applicant has now found that the tanning effect of the aluminum salts can be advantageously improved by combining them with a tanning agent.

  having phenolic hydroxy groups and

  thylol (oxymethyl) in the ortho position and containing

  lecule more than one aromatic ring carrying these substituents,

  at least 30% of these cycles also have sulpho groups

  nates. The presence of methylol groups in the ortho position is obtained by the reaction catalysed by alkali, phenol (and / or cresols) or sulfonated phenol (and / or

  sulphonated cresols) with not less than 60 mol% formaldehyde

  dehyde, calculated according to the ortho and para positions free in the phenol nuclei. By heating the reaction mixture above 60 ° C. for a few hours, a certain condensation of the methylol-substituted rings is obtained which forms methylene ether bridges,

  the oxygen atom of the ether function being still

  to enter chelated nuclei.

  From the foregoing, the invention provides a process for preparing a synthetic tanning agent, comprising reacting a mixture of at least 30 mol% phenol and / or sulphonated cresols and at most in moles of phenol and / or cresols in a medium

  neutral or alkaline, with at least 60 mol% of formaldehyde

  dehyde, calculated according to the ortho and para positions

  aromatic cycles, between 60 C and the point of

  boiling the mixture for 1 to 8 hours.

  The presence of non-complexing sulfo groups

  dissociated, preferably in the para position to

  the free ortho sites for the methylol substituents,

  is very important to increase the solubility and vi-

  diffusion rate and control the reactivity towards collagen and the charge of the metal complex. Due to its ability to form polynuclear chelated complexes with aluminum and its good diffusibility through the collagen fiber network, the synthetic tanning agent is suitable for providing reasonably stable tanning ie temperatures. much better withdrawal

  at 90 C. When using any of the syntans dis-

  industrially available in combination with aluminum, a much lower tanning stability is obtained due to the lack of chelate-forming groups, as reflected by the fact that the withdrawal temperature of tanned leather remains below 85 C (Bay, H . et al.,

  Leder u. High Markt, 37, (N 14) 28 (1985)).

  The invention also relates to a process for making a chromium-free leather, comprising the treatment of green skins prepared and / or pretanned in a known manner,

  with a water soluble aluminum salt and the tan agent

  synthetic substance forming a chelate, simultaneously or suc-

  terminally in any order. The quantity of the

  tan varies between 2 and 20% by weight expressed in dry solids, calculated on the weight of the green skin, or

  between 3 and 30% by weight of the weight weight.

  The process can be combined with any

  known process and tanning agent, these being applied

  as pre-or retannage. It is possible to obtain a leather which is acceptable from the point of view of the environment and hygiene and which at the same time has good stability.

  avoiding the use of chromium.

  The process can be combined with known tanning processes and used to prepare hides for

light color.

  The invention is further illustrated by the examples

  following non-limiting levels, in which the percentages

  are by weight unless otherwise indicated.

EXAMPLE 1

  A mixture of 8.2 moles of para-phenol sulphonic acid

  fonic, 1.2 moles of phenol and 300 g of water are

  added to a 30% solution of 8.5 moles of hydro-

  sodium hydroxide in a reactor equipped with heating means

  and refrigeration and a reflux condenser,

  a suitable speed for the heat of neutralization

  can be removed by the condenser. Then, 20 moles of formaldehyde are added in 37% solution to the hot mixture and the temperature is set at 80 ° C.

  the solution becomes clear, 1.5 mole of sodium hydroxide

  dium in 40% solution is added, the temperature is

  raised to reflux in one hour. The reflux is now

  held for two hours, the mixture is then cooled below 50 C and the pH lowered to a value between

  and 6 by addition of acetic acid. The product is a li-

  brownish quid of low viscosity, not containing

free phenol.

EXAMPLE 2

  4.7 moles of sodium hydroxide in% solution are added little by little to a mixture of 4.5 moles of para-phenol sulphonic acid, 1.5 moles of phenol, 4 moles of para- cresol and 500 g of water at such a rate that the heat of neutralization can be evacuated

  by the reflux condenser of the reactor described in Example

  1. Twenty moles of formaldehyde in 37% solution are added, the temperature is set between 75 and 80 ° C and 1.5 mole of sodium hydroxide is added in 40% solution. The temperature is then maintained at about 80, and 90 C for one hour each time. The last

  value is maintained until the sample

  lifted remains clear after cooling and acidification

  at pH 3 with diluted formic acid. This test helps to

  the condensation increasing the molecular weight

  That is, virtually every molecule contains sulfonate groups, which is necessary for good solubility. The product is then cooled

  below 50 C and the pH is lowered by addition of a-

  acetic acid to a value between 5 and 6. The viscosity of the liquid is a little higher than that of the prepared product

according to Example 1.

EXAMPLE 3

  300 kg of green skin of pelagic cattle with lime, chopped and washed are put in a drum with 6% of the mass of skin in 100% of floating mass at

  room temperature for 10 minutes, then 1% of oil

  electrolyte-stable sulfite, 1% formic acid

  and small portions of dilute sulfuric acid are added

  to a stable pH between 3.5 and 3.8.

  Then 1% glutaraldehyde and 8% sulphate are added.

  crystalline aluminum fate. After 2 hours in the drum

  bour, the pH is gradually increased by the addition of 1% of

  sodium formate, then 0.5 and 0.2% of

  sium until a value of 3.8 to 4.1 is obtained. The wet white obtained had a shrinkage temperature between 75 and 82 C. After removal of water, slitting and / or dying, the material is washed with 400% (from now on, the% refers to the doled mass) of water containing 0.5% acetic acid. The wet white is then placed in a drum with 80% water containing 3% of sodium chloride and 1% of sodium formate. Ten minutes later,

  2% of alkyl sulfochloride and 3% of stoichiometric sulphite

  electrolytes are added in the pre-emulated form.

  sified in 20% water. After 30 minutes in 4 drums, the pH is brought to 5 by addition of sodium hydrogen carbonate. A quantity of synthetic tanning agent according to Example 1 containing 8% of active substance is then

  added and after an additional hour the pH is

  reduced to 4.2 by successive additions of dilute hydrochloric acid. At the end, the withdrawal temperature

tanned leather reaches 95 C.

EXAMPLE 4

  The green skin of cattle peeled with lime, carefully dechlorinated and washed, is put in a drum with 50% water containing 0.4% of formaldehyde compared to the mass of green skin. A quantity of synthetic tanning agent prepared according to Example 2 containing% of active material is then added and after an additional 2 hours of drum, 1% of formic acid is added and treatment is continued for one hour.

  additional. The skin is then cleared of water,

  weighed and from then on, the quantities are counted in relation to the mass dolée. After washing, 1% formic acid and 0.3% sulfuric acid are added

  in 100% floating mass. When the condition of

  equilibrium is reached, a mixture of a synthetic tanning agent prepared according to Example 1 containing

  % active ingredient and a solution prepared separately

  4% of AlC13. 6H 2 O, 2% Na acetate, 3H 2 O and

  1.2% NaHCO3 in 20% water. After 2 hours of

  The pH is increased to 4.5 by addition of small amounts of NaHCO 3. Thus, the withdrawal temperature of the

tanned leather is 96 C.

Claims (2)

  1. A process for preparing a synthetic tanning agent, characterized in that it comprises the reaction of a mixture of at least 30 mol% of pie. and / or of sulphonated cresols and not more than 70 mol% of phenol and / or cresols in a neutral or alkaline medium, with at least 60 mol% of formaldehyde, calculated as a function of the ortho and para-free positions of the aromatic nuclei, between 60 and the boiling point of the mixture for 1 at 8 o'clock.   2. Tanning green skins pretreated in a known manner, characterized in that the synthetic tanning agent according to claim 1 containing 2 to 20% of active substance relative to the weight of green skin, or 3 to 30% is used. calculated by weight in relation to the weight   combination with aluminum salts.