There are some defects of the finishing products

1. Defects of the finishing products
Name:Tanvir Siddike Moin
University: University of Dhaka
Department:Leather Engineering

2. Finishing defects
Defects of the finishing products
Sedimentation
Causes:
 Pigment finishes, lacquer emulsions and mixed finishing products are multicomponent
systems with different specific weights of the single components.
 During storage the components having a high specific weight sediment and stick firmly
together.
Remedy:
 Basically, the products should be thoroughly stirred in the containers before use.
 Failure to do so results in a greatly varying concentration.
 This leads to a variable content of solids in the finishing floats and to a more or less
significant difference in shade in pigment finishes.
 In the case of binders, film formation is impaired which reduces the fastness properties.

3. Separation of layers
Causes:
 Mixed products containing components with different charges and emulsified systems can
break and result in phase separation into two or more layers.
Remedy:
 The products should be stirred well in the containers before use.
 Absolute homogeneity of the product is important, otherwise it should not be used
Coagulation
Causes:
 Finishing products on an aqueous basis and especially thermoplastic binders are susceptible
to the cold.
 Irreversible coagulation is caused by frost.
 Damaged products cannot be used any more and should be disposed of.
Remedy:
 It is absolutely necessary to protect the products against cold during transportation and
storage.

4. Foul smell
Causes:
Finishing products containing casein are particularly affected by heat and
bacterial attack and are subject to decomposition.
The products become completely unusable, depending on how long they were
exposed.
With the beginning of decomposition a disagreeable odor develops and turns
into a strong foul smell.
In this case the product cannot be used any more.
Remedy:
The products should be stored in cool rooms or cooling chambers, especially in
hot climates. Short-term storage is recommended for these products.

5. Change of pH value
Causes:
When using nitrocellulose lacquer emulsions, acids may be eliminated by
saponification in the presence of ester-based solvents and water.
This reduces the pH value in the product and makes the emulsion instable.
This results in cracking or the formation of water-insoluble lacquer droplets
which produce annoying glossy dots in the film.
Remedy:
The fineness of emulsion can be restored by adding some drops of ammonia
and thorough mixing.
It is recommended that the product be passed through a fine-meshed sieve.

6. Varying content of solid substances
Causes:
 The finishing products are supplied in specified concentrations.
 In certain exceptional cases the products may contain less amounts of
solid substances than specified due to different raw materials or
fluctuations in production.
Remedy:
 If the finishing results vary, the content of solid substances should be
checked from time to time.

7. Defects of the finishing floats
Agglomeration
Causes:
 Inadequately ground pigment colours may agglomerate in the finishing float and thus
reduce the intensity of colour and result in dull shades.
 These agglomerates may also impair film formation and reduce the fastness properties of
the finish.
Remedy:
 Use well dispersed, well-ground pigments from specialized suppliers.
Flocculation
Causes:
 Flocculation may occur in finishing floats if using brightening colours with a high content of
extenders or in binder mixtures which have little resistance to electrolytes.
Remedy:
 Use liquid dyes which have a low content of neutral salts and binders which are stable to
electrolytes.

8. Pigment suspensions and separations
Causes:
 If diluted pigment preparations contain inorganic and organic pigments quick separation in the
float may occur.
 In particular very fine carbon-black pigments may rise, whereas heavy pigments separate
down to the bottom of the vessel.
 This results in a change of shade or uneven finishes.
Remedy:
 Frequent stirring of these floats is absolutely necessary.
Incrustation
Causes:
 If finishing floats are stored in open vessels for some time, solid incrustations may be
produced at the edges by drying.
 If some of these incrustations fall into the finishing float, they impair film formation and do
not provide a smooth finish surface.
Remedy:
 Avoid storing the floats in open vessels for a longer period, or cover the vessels. Soiled
finishing floats should be sieved.

9. Possible defects of application
Tearing of the finish curtain
Causes:
 Caused by insufficient or excessive viscosity of the finishing float, by the use of polymer
binders that are not resistant to electrolytes, by foaming and trapped air during recirculation.
Remedy:
 Adjust correct viscosity by means of stabilizing thickening agents, use binders which are
stable to electrolytes or reduce the recirculation speed of the finishing float by diminishing
the pump pressure.
Curtain shadow
Causes:
 Caused by tearing of the finish curtain or by placing the leathers unevenly on the conveyor
belt.
Remedy:
 Stabilize the finish curtain and smooth the leathers by preliminary ironing.
 Paste leathers, vacuum dried leathers or leathers stretched in the wet state respond well.

10. Formation of creases during printing
Causes:
Uneven feeding of very thin, soft leathers into the print roller results in the formation of
creases and thus misprints on the leather
Remedy:
Feed the leathers smoothly and without folds.
Crumbling
Causes:
Mostly caused by application methods with intensive rubbing or beating effect (plush or
brushing machines) by the presence of unstable polymer dispersions.
During rubbing, crumbles form on the coat surface which result in a rough film after drying.
Remedy:
 Use polymer dispersions which are stable to crumbling for the finishing floats.
 Preliminary testing of the polymer dispersions for stability to crumbling is possible by rubbing
the undiluted binder between the fingers.

11. Spraying coats too dry
Causes:
If spraying is too dry, the finish coats have no closed film.
Flow out, covering effect and fastness properties of the finish are impaired.
Remedy:
Apply an adequately thick spraying coat.
If necessary, reduce the spraying pressure.
Spray noses
Causes:
Caused mainly by manual wet spraying of leathers hung up vertically.
Especially if using liquors of low viscosity the wet coat begins to run and form raised dye or
film grooves, so-called "spraying noses", in these sections after drying.
Remedy:
Adjust correct spraying pressure and apply correct amounts of dye.
If applying large amounts of liquor the leathers should lie on a horizontal surface and not be
hung up vertically or sloping for drying.

12. Spray specks
Causes:
 If the spraying pressure is too high and the spraying distance too great, spray drops of higher
viscosity may form on the leather surface by quick evaporation of the spray mist.
 These drops dry on the surface as dots, result in a rough surface handle and reduce the
fastness properties of the finish.
Remedy:
 Avoid the causes.
Spray streaks
Causes:
Caused by irregular overlapping of the webs following each other.
This results in streaky shadows which are covered to a different extent.
Remedy:
Adjust each spray jet exactly to the following web.
 Adjust the through-feed speed of the leather exactly to the movement of the spray guns and
the width of the spray jet.

13. Formation of streaks during padding
Causes:
Cracking of finish coats occurs if they have not dried adequately before the next coat is applied.
Uneven padding of the finishing float or the use of worn out plush pads may also result in the
formation of streaks and thus in unlevelled coats.
Remedy:
Avoid the causes.
Deposition of dust and dirt
Causes:
Buffing dust on the leather, particles of dust and dirt in the finishing room or dried residues of
finishing float in feed-in lines, spray guns, spray booths and drying sections are deposited in the
finish coat and result in a rough surface.
Remedy:
Dedust the leathers thoroughly and keep the finishing rooms, drying devices and machines as
clean as possible.
In patent leather production, work with an overpressure in the spraying and drying room to
avoid inclusion of dust particles owing to the high thickness of coat and thus long drying time.

14. Intermediate fixation too strong
Causes:
Excessive intermediate fixation of casein finishes or polymer finishes with a
larger content of albumen binders may cause hardening of the grain, brittleness
or loss of elasticity and even cracking of the finish.
Remedy:
 Proportion the amounts of formaldehyde finishes with care.
On no account should acetic acid or chromium salts be additionally used for
intermediate fixation.

15. Finishing defects on the leather
Marking off
Causes:
Excessive quantities of brightening dyes or organic pigments, insufficient amounts of binders in
the pigment finishes or top coats which have been applied too thin may result in marking off of
the finish.
Remedy:
Avoid the causes
Cracking off
Causes:
• Use of polymer binders which are not cold-resistant, very hard pigment finishes or top coats,
inadequate content of plasticizers or impaired adhesion of the individual finish coats.
Remedy:
• Avoid the causes.

16. Stripping of the finish
Causes:
• Impaired adhesion of the individual finish layers caused by an insufficient
absorption capacity of the leather when applying the base coat and by
inadequate reswelling of the preceding finish.
Remedy:
• If the absorbing capacity is not adequate, use a penetrative pretreatment primer.
• Reduce the use of sealing, water-resistant binders.
• If using cross-linking binders continue processing without storing the leathers for
a longer period as otherwise the film becomes insoluble by subsequent reactions.

17. Powdering of surface layers
Causes:
• Occurs in very hard casein finishes which have been applied in a very thick coat.
• Boarding treatments in particular cause a fine powdering of the entire finish coat.
Remedy:
• Reduce the thickness of coat.
• It is recommended that several thin coats be applied with intermediate drying.
• Addition of small amounts of polyacrylate dissolved in alcohol to the base coating agent
prevents powdering of the finish coat.
Migration of plasticizers
Causes:
• Excessive drying temperatures, direct application of nitrocellulose floats to the leather without
previous base coating.
Remedy:
• Control the drying temperatures and if using nitrocellulose finishes apply a barrier layer on the
basis of polymer binders.

18. Chalking
Causes:
• Caused in finish coats by migration of white pigments based on titanium oxide on exposure to
light.
• Changes the shade of pastel colours.
• Contact with soft metals may also produce dark streaks.
Remedy:
• Replace the white titanium oxide pigments by pigments based on zinc white which have a
slightly reduced covering effect.
Fissures in the finish coat
Causes:
• Very high pliability of the leather and inadequate elasticity of the finish coats.
• Insufficient drying of polymer binders, especially if they contain organic solvents.
• These binders require a prolonged drying time as the finish films are solubilized and swelled.
Remedy:
• Use softer, more elastic finishing floats and dry each finish coat thoroughly.

19. Exudation of plasticizers
Causes:
• If excessive amounts of non-gelatinizing plasticizers are used such as castor oil or rape oil, they
may exude by storing the leathers in cool and warm places alternately or by ironing with
excessive temperatures.
• Visible as a fatty, oily film on the leather surface.
Remedy:
• Reduce the amounts of non-gelatinizing plasticizers or choose a combination with gelatinizing
plasticizers.
Leaden appearance
Causes:
• Foggy film on the finish surface occurring especially on dark shades.
• Appears mostly if using highly covering, inorganic pigment colours.
• This effect may also be produced on matting, colourless top coats of very coarse-pore grain
leathers by an unfavourable refraction of light.
Remedy:
• Use appropriate quantities of organic pigment colours or brightening colours in the pigment or
top coats.

20. Brittleness or breaking of the film
Causes:
• Very hard or thick pigment and top coats of glaze finishes.
• Inadequate addition of plasticizers also causes embrittlement and crackiness of the film.
• On furniture leathers upholstered with polyurethane foam and in nitrocellulose finishes
breaking of the finish coat is mostly caused by exudation of amines.
• Brittleness is also produced by excessive amounts of hardeners in reactive systems, or cross-
linking agents in cross-linking binders.
• Pigment colours on the basis of copper, cobalt or manganese cause heavy embrittlement by
cross-linking with butadien binders and breakup of the finish films.
Remedy:
• Avoid the causes.
• Be careful when using pigment colours in finishes containing butadiene binders.

21. Bronzing
Causes:
• Migration of basic dyes from the pigment coat into the top coat.
• Migration of organic pigments by the presence of excessive amounts of plasticizers and ironing
with excessive temperatures.
Remedy:
• Reduce or change the application quantities, apply polyamide lacquers as barrier layer_or do
not use finishing floats containing solvents.
Fish eyes
Causes:
• Circular stains in the finish films caused by hardly wettable surfaces of the leathers, base and
finish coats.
• The subsequent finishing float spreads unevenly and forms small, open craters in some
sections.
• With spray coats this effect may also be produced by oil droplets carried along by the
compressor, especially in aqueous finishes.
Remedy:
• Add penetrators or flow-control agents and check the air separator.

22. Inadequately settled surface appearance
Causes:
• Uneven and inadequate application of the finishing floats.
• Different wetting of the leather surface by over fatliquoring or very intensive
water-repellent treatment.
• Very great difference in colour between the aniline dye and the shade to be
reached in the finish.
• Insufficient quantities of pigment colours in the finishing floats.
• Use of highly penetrative, nonfilling binders.
• Immediate further processing on finish coats which have not dried completely.
Remedy:
• Avoid the causes.
• Add appropriate amounts of filling or matting substances to improve the settled
surface appearance of the leather

23. Greyness
Causes:
• Caused by uneven refraction of light in leathers with coarse hair pores, especially
in dark-coloured glaze finishes or in leathers with very thin finish coats.
• A very high content of matting agents or chromium salts in the fixation may also
cause greyness.
Remedy:
• Reduce the amount of matting agents or do not use them at all.
• Increase the filling effect of the finishing floats or apply a polishing ground first.
• Add brightening colours to colourless top coats.