Finishing Techniques for Leather
| ✅ Paper Type: Free Essay | ✅ Subject: Chemistry |
| ✅ Wordcount: 2256 words | ✅ Published: 18th Jan 2018 |
Summery
These papers make a brief clarification of some of the finishing technique which is to applied to two finishing procedure and clarification for full grain aniline leather finish and a full grain pigmented leather finish the material to be used in it and whey to apply such material for such both finishing type . also an observation on the needs for the finish for the leather . also a describe for the difference between the pigment and the dyes from their origin and behavior and other points of study for them . and after that an investigation about the organic and the inorganic pigment and the difference between them . plus a brief explanation about the comparison between cationic and ionic dyestuffs. more a study about two formulation for shoe upper finish for aniline and pigmented full grain leather plus study for the material to be applied for them . then end with product understanding from stahl mentioning their use and needs in the finish formulation and monitoring their behavior.
Introduction
Finishing
The term finishing is applied in the leather industries to help enhance the properties and the appearance of the final piece of the leather its gives the leather more enhanced color and remove defaults that could be caused through the leather operation or a nature defect. The piece of leather is enhanced by treating it with dyestuff solutions, pigments, preparations, top coating then it enters he mechanical treatment in terms of plating.
The basic rule in the leather finishing is the fewer blemishes on the raw hide
The less finish has to be applied.
The more grain layers is damaged layer is damaged, the more coats the leather required to replace
The natural grain.
Also the purpose of finishing is to provide different types of leather with special characteristics satisfy the requirement markets,
The processes of finishing the leather give the leather upgrading of the following characteristics such as
Color , brightness , matting , feel , softness , print pattern , water resistance and more .
Part 1
Dyes and pigments
Both dyes and pigments are powerful colorants material used to color other substances
Pigments
Pigments are the special type of dyeing material for wet processing technology.
Pigment can also be define as a water insoluble coloring material and a coloring substance that makes the color of the product look different because of its absorption of certain wavelengths .
dyes
Dyes are substances found naturally and also made synthetically too .
Dyes have the ability to change the color of the leather and material which they are applied.
In earlier times, most of the dyes were obtained from plant sources , roots ,wood , stem bark and plants leaves . also in the 19th century synthetic dyes were produced and since then many of synthetic dyes have been produced .
Special needs for the dyes in the surface coating where a high level of transparency is required,
Dyes vs pigments
|
Point of difference Chemical Composition Solubility Application method and bonding Size Structure during the application process Attraction |
Dyes Usually the dyes are organic (i.e carbon based compound) and contain auxo chrome in their chemical structure They are soluble Its application method is very easy because of its electrostatic charges serve as a method of attaching the dye to the surface Dyes molecules are comparatively very small During the application process there is a temporary alteration in the structure of the dyes Dyes have attraction for fibers |
Pigments Pigments are normally inorganic compound and often involving heavy toxic metals and no auxo chrome contains in pigments . They are completely insoluble in water and most of the solvent Need binders for application for gluing Pigment particle are about 1 – 2 micron in size During application , pigments have the capacity to retain particulate or crystalline structure . Pigments have no attraction for fibers . |
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Point of difference Uses Longevity factor Light fastness Color fastness Product resistance Varity number prices |
dyes Its generally used for dying The dye based do not last as long as pigmented based Lights destroy colored objects by breaking open electronic bonding within the molecule Generally ranged from average to excellent Lower as compared to pigments Available in large variety number Dyes are expensive than pigments |
pigments Generally used for film coating and printing The pigmented based lasts longer the dye based Traditionally pigments have been found to be more lightfast than dyes Color fastness is range from average to good Very high Comparatively available in less number Pigments are generally inexpensive than dyes . |
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Organic and inorganic pigments .
The difference between organic pigments and inorganic pigment are based upon some principle factors.
Such as
Molecular structure of the pigments
Carbon chains or carbon rings are always presented in the molecules of the organic pigments.
But in the molecules of the inorganic pigments , the cations of metal are found in an array from the non-metalic anions . which with this arrangement does not allow these pigment to dissolve in the solvent .
Source of pigments
the main source of organic pigment are plants and plant products.
The inorganic pigment are manufactured from topical cosmetic and dirt .
Inorganic pigment are non-ferrous metal oxides , or some metal insoluble metal salts .
Main difference between inorganic pigment and organic pigment
|
Point of difference source color dyeing color strength opacity molecular structure |
Inorganic Minerals Often dull Low Opaque Contain metal chain |
Organic Chemically refined oil Bright High Transparent Contain carbon chain |
Cationic and ionic dyes .
Anionic dyes have a negative charge and attached to cationic surfaces,
Cationic dyes have a positive charge and attached to anionic surfaces,
The cationic dyes react with anionic sites on the surface of the substrate, the cationic produce a bright shades.
The solubility of these dyes is very good in water in the presence of glacial acetic acid .
Both anionic and cationic dyes have poor levelling properties .
Part 2
One can ask the question.
Why are there so many different types of leather ? simple answer is its all down to cost .
The tanner should have the experience to sort and select the leather after the chrome tanning to forward each type leather batch selected and sorted to its category end use type product .
The tanner forward the sorted chrome leather batches to the retanning and dying process.
Such sorting is done according to the hide size, grain condition, surface grades , extra…
When it comes to finish the leather. The tanner already sort the leather in previous states
So he knows what is he going to do with such sorted leather to apply the required finish to it .
Almost all types of hides and skins can be finished .
The final uses of the different leather leads to the type of the finishing to be applied .
Type of the finish the tanner choose depend on the appearance he want sell his leather with it .
Among of the types of finishing types of leather is.
a – Aniline finish ( full grain aniline leather finish )
Aniline leather is the most natural looking leather with the unique surface characteristics of the hide remaining visible .
To get such aniline leather you need to apply what’s called “ aniline finish “
Leather with an aniline finish is colored with dyestuffs only which means no opaque finish ie transparent finish so that the original grain surface can be seen through.
Another transparent top coat can be applied to give bright finish and water repellent surface .
Aniline finished leather has excellent tooling , polishing , and redyeing properties .
B – Pigment leather finish ( full grain pigmented leather finish )
Such pigmented finish contains no aniline dyestuffs . the dyestuffs are all replaced with an opaque inorganic pigment , such mixture is bound together using a small amount of casein and a use of a binder ( mostely is thermoplastics type ) to form a continuous film , resulting in a more level finish and better coverage of the finish skin .
The presence of such small amount of casein contained in the finish ensures the leather does not become sticky .
After the leather is finally coated with a matt or bright water based lacquer emulsion to enable sealing the finish to give certain amount of resistance to wet , dry rubbing .
Full grain aniline finish vs full grain pigmented finish
|
Point of study Results of the leather grain Colorant used Binder Mechanical properties of the film Coating Looks and uniformity Machining operation |
Full grain aniline leather finish Too many faults and uneven grain to be produce with a very thin film coat Usually we use dyestuff only Natural casein is used to give the natural feel of the leather Range from poor to good All coats are transparent Leather retains its natural look but at the same time achieves a less degree of uniformity in color Very less machining applied to get such finish |
Full grain pigmented leather finish Very less faults and good uniform grain to be produced with rather a high film coat Mainly inorganic pigment to be used Thermoplastic binder and a very less casein is used to give uniform coating Range from good to excellent All coatings are opaque Leather gain a feel of artificial syntactic leather looks and at the same time achieves a high uniform in color More machines are applied to gain such thick pigmented coat from sprying,coating,plating ,roll coating or bycast , else ,.. |
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Material used Dyes Pigment Protein binder Thermoplastic binder Cross linkers Matting agent Fillers Thickening agent Nitrocellulose lacquers and emulsions Fluoring derivatives silicon |
Full grain aniline leather finish Usually used as a colorant Not used Used mainly Not used Not used Can be applied Not used Not used Emulsions transparent can be used Can be used to provide water or oil repellent Can be applied to give feel touch to the leather |
Full grain pigmented leather finish Usually not used Usually used Used slightly Usually used Can be applied to achieve special characteristics Can be applied Can be applied Can be applied Both nitro cellulose and emulsions can be applied Can be used to provide water or oil repellent Can be applied to give a feel touch to the leather |
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