DYEING CRUST LEATHER BY EGEMEN

              1-OBJECTIVE

Practice 2:  We compare the leathers  with see the difference between a dye on wet-blue and crust. Compare two dye systems: crossed and  no crossed and see how they influence different load changers on intensity, hue,equalization, the affinity to the skin, the power of penetration and degree of fixation of the dye.

             2- TECHNICAL PART

              DYEING CRUST

•          Crust leaathers means  dried leathers. İt could  be chrome tanned or vegetable tanned or combined , fatliqoured adn treated mechanically witout finish operations. There is not fungi and yeasts attack  such as  wet blue storages.because dry conditions in strorage areas. İn crust leathers we have to know source of the rawstocks and the operations they have been subjected to since chrome oxide content, type and amount of vegetable extract, fat percentage and pH may vary considerably from one source to another. Commonly , crust is delivered by sorted amounts and thicknesses. However, it is necessary to do a visual check of their general state, and especially of the conditions of surface absorption.

•          Before the start  the process  curst leathers must be soaked a period time that   it depends on hard fibrils or  not too much hard structure. We have to give naturel humidity on leathers with  this way. The results of the dyeing will highly depend on how the leathers have been previously treated:

–        Type of tannage : it is possible  wet blue , vegetal or combined . these tannage variations effect to crust leathers.

–        Neutralisation :   we have to work suitable and optimal ph. Chemicals and leather ph must be equal.

–        Type of retannage : It depends on  what kind of leathers we want.

                     Type of fatliquor applied: we can use  sulphone , sulphate or sulphite oils or combined  among of them. It depends on softy or firmed.

Sulphate :  this  fatliquor  is  usually attacked on grain side. 

Sulphone : this  fatliquor  is  usually attacked on middle side.

Sulphate:  this  fatliquor  is  usually attacked on flesh side

3- MATARIAL AND PRODUCTS

It is very important when dyeing crust leather that the leathers are properly soaked, as they are dry and should recover their natural moist state.

And we use these products during the crust dyeing:

–        formic acid: Formic acid is a organic acid so that we usually use with 1/10 -  1/5 dilution rate  . this is formic acid formula   we use formic acid  a lot of processes. Fixation  to Dyestuffs , decrease ph in pickle .

This product reduces the pH below the pI value of the leather , so that the overall charge is cationic and has a greater capacity of reacting with the anionic products subsequently added. The density of reactive points increase since at acids pH, the carboxylic groups of the protein are not in dissociated form. A greater superficial performance is obtained.

–        Aluminium sulphate : resistant to water and with adequate hydrothermal stability aluminium gives strength for leathers and  relevant with  shrinkage  temperature and  developing appearance of dyeing on surface shortly, gives homogeneity dyeing on surface with slow penetration. we have bright tones.

This product is a strong cationic product.it is decrease in pH saused owing to the hydrolysis of basic sulphate and sulphuric acid, with resulting increase in total positive charge in the leather

In addition, complex between the collagen andaluminium sulphate can be formed.Although these are not as stable as basic chrome salts, they confer a quantitative leap in cationic  reactive points.

The basic aliminium sulphate used in a dyeing is usually an intermediate complex between:

İf a small amount of formic acid is added with aluminium sulphate  in order to decrease a little the basicity of the aluminium salt so that its reactionability with the leather surface is a little slower to improve the levelling out  of the intensity.

–        aluminium sulphate with different combinations with formic acid

–        cationic oil:  cationic lubricant are more resistant to change in pH . Also they attacking and fixation grain quickly.They can’t penetration very well.  

They consist of non-natural oxyethylated organic compounds and with anionic reactive groups.

The radicals of such products also have a certain fatliquoring effect, which will result in a surface which is less dry and coarge than when an inorganic or mineral charge changer is employed.

–        chrome salt with 33 % basicity  : most common using  basicity  chrome.  There are  only one OH  group İn its structure.so that  it occurred slowly  and deeply penetration. First , the salt is anionic; after dissolving ,its charge changes to zero , and finally it becomes cationic.

Once dissolved, the trivalent chrome salts present an acid  hydrolysis :

–        mimosa:  vegetable tanning substances ,gives tightness . they are connecting OH with amino groups.

–        Anionic polymer : this is retanning substance. Like as tanning material,gives plump structure.

–        Synthetic –phenolic  retanning substances:  gives plump structure well attitude.

–        aluminium chloride:

Common name AlCl3H2O compound with aluminum hydrochloride in the skin pores of thecompression feature. Shortly , it gives firmed leathers  gives light fastness and rubber effect

Commercially, the aluminium chloride employed  has a basicity of 60-65%  approximately.Thus, the basic complex will be most formed by

And  to lesser degree by

The basicity and hence reactionability of the complex can be reduced by adding  small amount of formic acid when dissolving the salt prior to adding it to the drum.

–        Humactante: it is nonionic  cleaning substance.They gives soft handle before  start to process because  crust leather very dry so that we must be carefully  to broken fibrillers .

–        Amoniac : it is help to penetration of colorante, give optimum pH rate for colorante and increase leather isoelectric point. This is main situation if  leather ph  equal with colorante ph , penetration is maximum.

Práctica 1: Tintura no atravesada

Pieles: crust de procedencia desconocida

% sobre peso seco

Remojo:          500%   Agua a 35ºC

                        0,5%    Humectante    (1:10)

                                    Rodar 30 minutos. Reposo 12 h, rodando 15 min/hora.

                                    Escurrir baño.

Tintura:            400%   Agua a 60ºC

                        1,5%    Colorante (1:20)

                                    Rodar 20 minutos.

                        1,5%    Ácido fórmico

                                    Rodar 20 minutos.

                        1,5%    Colorante (1:20)

                                    Rodar 20 minutos.

                        1,5%    Ácido fórmico (1:10).

                                    Rodar 20 minutos.

                                    Mirar pH.        

                                    Escurrir baño.

Práctica 2: Tintura atravesada

Pieles: crust de procedencia desconocida

% sobre peso seco

Remojo:          500%   Agua a 40ºC

                        0,5%    Humectante    (1:10)

                                    Rodar 30 minutos. Reposo 12 h, rodando 15 min/hora.

                                    Escurrir baño.

Tintura:            100%   Agua fría

                        1%       Amoníaco

                                    Rodar 15 minutos.

                        3%       Colorante

                                    Rodar 1 hora.

                        300%   Agua a 60ºC

                        0,5%    Ácido fórmico

                                    Rodar 15 minutos.

                        1%       Aceite catiónico

                                    Rodar

                        1,5%    Colorante (1:20)

                                    Rodar 30 minutos.

                        1,5%    Ácido fórmico (1:10)

Rodar 30 minutos.

                                    Mirar pH.        

                                    Escurrir baño.

Práctica 3: Tintura atravesada

Pieles: crust de procedencia desconocida

% sobre peso seco

Remojo:          500%   Agua a 40ºC

                        0,5%    Humectante    (1:10)

                                    Rodar 30 minutos. Reposo 12 h, rodando 15 min/hora.

                                    Escurrir baño.

Tintura:            100%   Agua fría

                        1%       Amoníaco

                                    Rodar 15 minutos.

                        3%       Colorante

                                    Rodar 1 hora.

                        300%   Agua a 60ºC

                        0,5%    Ácido fórmico

                                    Rodar 15 minutos.

                        1,5%    Sal de cromo del 33% de basicidad

                                    Rodar 45 minutos.

                        1,5%    Colorante (1:20)

                                    Rodar 30 minutos.

                        1,5%    Ácido fórmico (1:10).

                                    Rodar 30 minutos.

                                    Mirar pH.        

                                    Escurrir baño.

Práctica 4: Tintura atravesada

Pieles: crust de procedencia desconocida

% sobre peso seco

Remojo:          500%   Agua a 40ºC

                        0,5%    Humectante    (1:10)

                                    Rodar 30 minutos. Reposo 12 h, rodando 15 min/hora.

                                    Escurrir baño.

Tintura:            100%   Agua fría

                        1%       Amoníaco

                                    Rodar 15 minutos.

                        3%       Colorante

                                    Rodar 1 hora.

                        300%   Agua a 60ºC

                        0,5%    Ácido fórmico

                                    Rodar 15 minutos.

                        1%       Sulfato de aluminio

                                    Rodar 45 minutos.

                        1,5%    Colorante (1:20)

                                    Rodar 30 minutos.

                        1,5%    Ácido fórmico (1:10)

                                    Rodar 30 minutos.

                                    Mirar pH.        

                                    Escurrir baño.

Práctica 5: Tintura atravesada

Pieles: crust de procedencia desconocida

% sobre peso seco

Remojo:          500%   Agua a 40ºC

                        0,5%    Humectante    (1:10)

                                    Rodar 30 minutos. Reposo 12 h, rodando 15 min/hora.

                                    Escurrir baño.

Tintura:            100%   Agua fría

                        1%       Amoníaco

                                    Rodar 15 minutos.

                        3%       Colorante

                                    Rodar 1 hora.

                        300%   Agua a 60ºC

                        0,5%    Ácido fórmico

                                    Rodar 15 minutos.

                        1%       Cloruro de aluminio

                                    Rodar 45 minutos.

                        1,5%    Colorante (1:20)

                                    Rodar 30 minutos.

                        1,5%    Ácido fórmico (1:10)

                                    Rodar 30 minutos.

                                    Mirar pH.        

                                    Escurrir baño.

4 -  DISCUSSION AND CONCLUSION

 Vegetable dyeing has penetration on  crossline section with  direct dyestuff. When we  cut the crossline the leathers , observe homogenous areas  with dyeing.In addition we use humectante  for softy fıbres  before the process. This is different from wet blue dyeing. And we can make a sort for colour darkness  among the vegetal dyeing leathers: 2>3>4>1