Finished Leather
Section through finished leather - Diagram by Advanced Leather Solutions
Research
Information regarding the care of
leather is scarce, often contradictory, misleading, or simply wrong.
Misinformation can lead to inadvertent damage to your vehicles leather
upholstery; my goal is to present clear, concise, accurate information.
There is a great deal of conflicting
information on leather care being put out by leather experts themselves who use
baffling pseudo scientific techno speak as another marketing ploy, which makes
it difficult to find a definitive, unbiased answer. It had always confounded me
that such a simple subject has been made into something so complicated.
After various meetings and discussions
with leather tanners, fat liquoring formulators, their chemists and many
leather care product manufacturers I’ve gained an understanding of this
versatile material on both a practical and scientific level.
I have always thought that the more
facts and information you have at hand the easier it is to judge what
information you are being given. After all, how can you fully understand and
properly use any product unless you have all the facts? In the final analysis;
it’s your vehicle, your hard earned money and your choice
Original
Equipment Manufacturers (OEM) Technology
Automotive
equipment technology is becoming more and more complex requiring educated and
skilled technicians to work on them. As the materials used are constantly
changing we must maintain our knowledge base and utilize the correct products
and application methodologies to keep up with emerging technologies. It is very
important to be able to recognise the various finishes and materials used as
they all require different methodologies and products for proper care and
maintenance.
A competent
detailer never stops learning; knowledge
of new technology and application methods also make detailer’s an asset to both
a company and its clients and increase the value of the services offered. A
detailer should know how to tell the difference between -
a) Single stage paint and a base coat clear coat paint
system and be able to match the correct products to each system
b) Coated and uncoated aluminium wheels and what products
to use for each finish
c) Finished and uncoated leather and the appropriate care
products to use
Product
choices
Diagnosis is the key, not
guess work. Before deciding on what products to use, you need to ascertain
the grade of leather and the type of leather finish applied.
There are a few different types of leather and several types of
finishes applied to the leather used for vehicles upholstery. There are also a
myriad of leather care products available, which need to be used in accordance
to the type of and finish used for your vehicles upholstery
Automotive leather is a rather difficult category to define as
OEM descriptions of leather finishes vary, often incorrectly from that of
leather industry manufacturer’s descriptions. Automobile manufacturers have
blurred the distinguishing lines on what exactly constitutes leather and the
ambiguity of the information provided by leather care vendors make the
selection of the correct products for the types of finished leather used in
automobiles very difficult.
History
Prior to 1939 leathers produced were solely vat dyed. Usually
these colors faded quickly and developed into strange shades of greens or
browns after exposure to the sun. Although the surfaces did not crack and chip
as badly, the leather still became dry and stiff.
After 1945 new technology
created new demands and brighter colors quickly became popular with the
availability of nitrocellulose resin emulsion lacquers. Leathers that were vat
dyed were now surface coated as well. In the early 1980’s nitrocellulose
lacquers gave way to the resin-base dyes in use today.
Before 1980 most automotive leather upholstery used was high
quality top grain full grain leather with a pigmented solvent-based
Nitrocellulose lacquer coating and their unstable plasticizers would easily
migrate in the heat from sun exposure and again create 'fogging' on the
internal surfaces of the windows. As a result of this plasticizer migration the
use of oil-based products that contained solvents to keep them from becoming
brittle and cracking, creams, waxes and oils were needed in aftercare products
to try and bring the suppleness back into the leather by applying an oil-based conditioner
This can be accomplished by covering the seats with a plastic
bag to help retain the heat and them leave overnight will ensure the oils
permeate the lacquer and reach the leather hide. This process can also be used
for equestrian tack; bridles, harnesses’, saddle and leather chaps and riding
boots.
This nitrocellulose resin conditioning methodology for some reason has been carried over
to modern finished
leather. Even though urethane’s only requirement is to be kept clean and
hydrated, it doesn’t require conditioning. Products such as leather (Saddle) soaps, oil-based
Conditioners, Neat-foot oil, Mink oil and Connolly Hide Food still prevail as
top sellers, albeit most are made for equestrian tack. These are very different
leathers with drastically differing care requirements. The exact reason for
this type of misapplication is unclear.
It’s possible that there
is an association with old world quality (i.e. European automobiles with unfinished
leather upholstery and real burl wood interiors) with these types of products,
despite the fact that the automotive industry has been using aqueous (water-
based) urethane covered pigmented leather since 1980.
Materials Technology
Automotive
OEM technology is becoming more and more complex requiring educated and skilled
technicians to work on them. As the materials used are constantly changing we
must maintain our knowledge base and utilize the correct products and application
methodologies to keep up with emerging technologies.
Automobile manufacturers have blurred the distinguishing lines
on what exactly leather is. There are many so-called ‘leathers’ that are
actually the bottom split (the fibrous part of the hide) which are covered with
a vinyl or urethane coating. Diagnosis is the key, not guess
work. Before deciding on what products to use, you need to
ascertain the grade of leather and the type of leather finish applied
The leather used for automotive upholstery has a finish applied
that comprises a polyurethane protective layer and an abrasion
resistant topcoat.
Polyurethane is a polymer composed of a
chain of organic units joined by Ethyl carbamate (urethane) links; the polyurethane
used is categorized as an elastomers; it has elastic properties while
maintaining some rigidity.Polyurethane is semi-permeable and has micro pores
that allow hydration (transpiration and evaporation of moisture); otherwise
it would become less supple and the finish will be subject to cracking.
Be cognizant that the leather and
finishes used for automotive upholstery varies from leather industry standard
descriptions and although the names are similar the type of leather,
pigmentation and finish are often very different. Si it is very important
to be able to recognise the various finishes and materials used by OEM’s as
they all require different methodologies and products for proper care and
maintenance.
Automotive model ranges use different materials for their
vehicles interiors; leather upholstery like Aniline Immersion Dyed, Aniline
Micro Pigmented, (Urethane) Finished, Artificial leather such as MB-Tex and
unfinished materials like Synthetics and Alcantara, and sometimes combinations
of products (Alcantara seat inserts on leather seating) as well as various
grades of leather hide, full-grain, top-grain and split –grain (which is
protected with urethane) all of which require different products and applications
methods.
After various meetings and discussions with leather tanners,
their research and development teams, chemists and fat liquoring formulators
and many leather care product manufacturers I've gained an understanding of
this versatile material on both a practical and scientific level.
It had always confounded me that such a simple subject has been
made into something so complicated. I have always thought that the more facts and
information you have at hand the easier it is to judge what information you are
being given. After all, how can you fully understand and properly use any
product unless you have all the facts? In the final analysis; it’s your
vehicle, your hard earned money and your choice
Be cognizant that you’re dealing
with the finished coating on the leather not with the leather hide itself
. Automotive Interior Environment
The interior environment of an automobile can be extremely
demanding on any material used. Temperatures range from hot dry summer days, to
freezing nights. Both high and low humidity, even air conditioning that cools,
but also dries. Leather's greatest enemies are; sun, heat, body oils,
perspiration (that contains urea as well as organic salts and acids) and body
heat, which causes acids to become more aggressive and alters the viscosity of
oils, allowing them to permeate the leathers finish, and ultra violet radiation
(UV), which dries the hide, fades the colour by bleaching, and can cause the
leather to fail by drying out the fibres causing the urethane and / or the hide
to crack.
Vehicle upholstery leather must allow hydration (transpiration
and evaporation of moisture); otherwise it will become less supple and the
finish will be subject to cracking. Hydration is simply the
replacement of moisture and can be introduced via any perforated areas or
places where the leather is joined together with stitching. These punctures in
the surface coating are natural release areas where the leather begins to lose
its moisture, especially in hot / dry environments.
Unfinished
vs. Finished leather
a)
Unfinished leather - the appeal of this
type of leather is its initial "natural" look and the soft, supple
texture. The downside is aesthetic vulnerability; due to the porous nature of
untreated leather, it stains easily and it is sensitive to ultra violet (UV)
light, which means that the colour is subject to photochemical degradation
(bleaching, (fading), discolouration chalking, brittleness and cracking) all
indications of UV deterioration. The porous nature of unfinished leather will
allow a water- or oil-based solution to permeate the leather.
b)
Finished or micro pigmented
leather - is commonly used for automobile as these resins create a film
that protects the leather. The water-based polyurethane pigmented (colour) coat
and the clear topcoat provides abrasion and stain resistance. This type of
leather finish is the most durable and easiest to care for but tends to be
stiffer than both unfinished and micro pigmented leather. When Ford first introduced
its King Ranch leather in their F-Series trucks it had unfinished leather,
later they adopted a micro pigment type finish
Using advanced micro pigments this finishing technique
makes the finish rigorous enough to stand up to the conditions it would be
subjected to in an automobile. Generally speaking micro pigment style
leathers come in very earthy natural colours, incorporating a small quantity of
pigment (a thin clear sealant that provides a uniform colour and affords some
protection) but not so much as to conceal the natural characteristics of the
hide so it will still retain the soft hand of Aniline leather. This type of
leather is also used for perforated leather finishes.
Now virtually 95% of leather in domestic (American) and Imported
(Asian) vehicles use finished (polyurethane coated) upholstery. Among European car makers aniline and recently
semi-aniline (micro pigmented) leather upholstery is still much more common
than with domestic models, but urethane finished leather is becoming more prevalent
Automobile model ranges use different materials for their
vehicles interiors; there are also various finishes applied -
·
Aniline
Leather (Immersion Dyed)
·
Semi-aniline (Micro pigment) leather
·
Finished leather
As well as various grades of leather hide, full-grain, top-grain
and split –grain, along with artificial leather such as MB-Tex and unfinished
materials like Synthetics and Alcantara, and sometimes combinations of products
(Alcantara seat inserts on leather seating) Using any product not specifically
designed for your leather finish can cause staining and permanent damage.
Cross section through leather hide
Leather
Hides
Raw hides have four main parts - an epidermis, grain, corium
and flesh
Two of these layers, the epidermis (which is a thin
protective layer of cells during the life of an animal) and the flesh
are
removed during tanning by a process called liming.
This leaves just the grain and
the corium, the parts that are used for automotive leather
upholstery .The grain layer is made of collagen and elastin protein fibres and its
structure varies quite a bit depending on the age, breed and lifestyle of the
animal. The grain carries many distinctive marks such as insect bites, growth
marks and wound scars giving the leather a unique appearance.
The corium [Latin term for the dermis] or skin
layer, is packed with collagen protein fibres, arranged in larger bundles and
interwoven to give the structure great strength, excellent elasticity and
durability. In the tanning process these fibres and impregnated with collagen's that are designed to hold them together and keep them supple after which they
are sealed, these polymers are neither volatile nor migratory, rendering the use oil-based
conditioner a mute point
Fat
liquoring
Leather, at the time of completion of the tannage does not
contain sufficient lubricants to prevent it from drying into a hard mass.
Almost all light leathers need a greater softness and flexibility than is
imparted by tannage. This is attained in the fat liquoring process by
introducing oil into the leather, so that the individual fibres are uniformly
coated. The percentage of oil on the weight of leather is quite small, from
3-10 %. The precise manner in which this small quantity of oil is distributed
throughout the leather materially affects the subsequent finishing operations
and the character of the leather.
Proper lubrication or fat
liquoring greatly affects the physical properties of break, stretch, stitch
tear, tensile strength, and comfort of leather. Over lubrication will result in
excessive softness and raggy leather in the bellies and flanks. Under
lubrication, or improper penetration, results in hard bony leather that may
crack in use.
To allow a small amount of oil to be spread uniformly over a
very large surface of the leather fibres it is necessary to dilute the oil.
Although this could be done with a true solvent such as benzene,
it is cheaper, safer and more convenient to use the method of emulsification.
In an emulsion with water, the oil is dispersed in microscopically small
droplets, giving it a white, milky appearance.
It is important that the oil drops in water should remain as an
emulsion until they penetrate the leather, and should not separate out as large
drops or as a layer of oil, which could not penetrate the leather fibre and
would only give a greasy surface layer.
Hydration
The other critical factor is moisture (re-hydration) any leather
is going to lose its moisture in hot ambient environments. Much of the suppleness of leather comes from
its moisture content, which is the reason maintain the moisture content of the grain
layer
is so important. When leather tanners talk about leather
conditioning they specifically mean replacing its moisture content
(re-hydration). After tanning the
skin is protected with pigmented (colour) polyurethane and then a clear
topcoat.
Applied
finish
The leather used for automotive upholstery is finished leather
comprising a polyurethane protective layer and an abrasion
resistant topcoat. Polyurethane is a polymer composed of a
chain of organic units joined by Ethyl carbamate (urethane) links
Pigmented Coating
Polyurethane (urethane) has micro-pores that allow evaporation and hydration (the
passage of water vapour through a membrane or pore) they are not sealed per se.
Oils are not compatible with water-based pigmented urethane coatings and their
molecules are too large to permeate, although some may enter via stitching, usually
it remains on the surface to be removed by clothing
Since the leather hide has a pigmented urethane layer and clear topcoat
finish, when treating the leather, so you are in fact dealing with a urethane
(to all intents and purposes, a ~150 µ (micron) thick plastic surface coating,
about the same thickness as automobile clear coat paint; that simply needs to
be kept clean and hydrated…it really is that simple.
Topcoat - extremely
hard wearing water-based clear polyurethane is used to improve abrasion
resistance and colour fastness, making the surface much easier to clean and
less prone to staining, while increasing resistance to perspiration, grease and
oil. It greatly increases surface durability and also improves surface texture
giving it a smooth, soft and silky feel.
It also has micro-pores that allow transpiration, i.e.
evaporation and hydration (the passage of water vapour through a membrane or
pore) they are not sealed per se. Urethane pigmented finished leather doesn't readily absorb liquids because of the
protective properties of the finish making for easier clean-up.
A
simple test – place a drop of moisture on the surface of the leather - if it
soaks into the leather you have unfinished leather (sometimes called aniline
style) If there is a very light color or clear coat on top of aniline-dyed
leather, it is often referred to as “semi-aniline.” Semi-aniline leather offers
modest protection while retaining much of the aesthetic beauty of unfinished
aniline-dyed leather but still remain absorbent to moisture. If the moisture
sits on the surface and does not soak in and darken the material you have
finished leather.
TOGWT® Autopia Detailing Wiki Articles
1. “Unfinished leather” - http://www.autopia.org/forum/autopia-detailing-wiki/145381-unfinished-eather.html#post1543547
2. “Proper Finished Leather Cleaning and Care” - http://www.autopia.org/forum/guide-detailing/136421-proper-finished-leather-cleaning-care.html
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