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Types of Leather used in Automobiles

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Posted 04 December 2011 - 07:23 AM

Automobile manufacturers have blurred the distinguishing lines on what exactly leather is. Premium leather is the top split of the hide, there are many so called ‘leathers’ that are actually the bottom split (the fibrous part of the hide). Some of these ‘leathers’ are covered with a vinyl or urethane coating.

In accordance with US government standards theses should be labelled as split leather, instead they being sold by automobile manufacturers as ‘premium leather’ Leather is the most delicate and difficult to maintain of any vehicle surface. It ages and wears faster than surrounding materials which depreciates re-sale value, hence the need for protective covering to guard against abrasion, ultra violet degradation (fading) and to provide an even colour to the surfaces.

Automotive Leather Definitions

Leather upholstery used in automobiles is almost exclusively pigmented and has some kind of covering to protect it from years of heavy use, automobile leather varies from leather industry standard descriptions and although the names are similar the type of leather, pigmentation and finish are often very different.

Leather is a collective term for all hides and skins which have been tanned. These can come from any type of animal, but the majority of leather products are made from cow-hide, especially in the upholstery trade as these provide the skin area needed to cut the largest panels.

Leather Hides –are the skin of large animals, usually cattle. Leather is a natural product and because of this there will be some shade variation

Finished Leather - a generic term for all hides and skins which have been tanned and finished

Aniline leather – (this is a misnomer; aniline is a transparent dye not a type of leather) its absorbent and is dyed with an immersion type process rather than having a pigmentation added, the dye provides an even overall colour and, so that the original grain surface can be seen completely unhindered. It is then protected with a very thin layer of completely transparent, abrasion resistant urethane, hence there is very little, if any shade variation (unprotected Aniline is rarely use for automobile upholstery) a bit like staining wood rather than painting it.

Semi-aniline leather - is more often used for automotive upholstery as it is more durable than aniline whilst still retaining a natural appearance. Aniline leather which has received a surface coating containing a small amount of pigment in the base coat, this surface coating helps impart greater stain resistance. The increased durability is provided by the application of a light surface coating which contains both pigment (colour) and an anti-abrasion additive, This ensures consistent colour, imparts some stain resistance and helps with the abrasion of entering and exiting the vehicle

Coated Leather - the surface coating applied to the leather substrate does not exceed one-third of the total thickness of the product. A high tech water-based (waterborne) coating usually derived from OEM tannery specifications based on the use of hybrid polymers and urethanes to provide a very durable final coating..

Nappa Leather – is the tanned skin of a sheep and generally denoted as high quality, soft, full grain leather

Unfinished Leather - is left in its natural state without the application of a clear coat, unfinished leather is very rarely found in modern automobiles and must be maintained on a regular basis with products utilizing natural oils

Dyeing- more correctly the application of a pigment (colour) either by spraying, hand rubbing or immersion.

Pigmented - leather that has been applied with a surface colour in addition or instead of the dye process and is analogous to the "staining" of wood

Different leather finishes are available for use in automobile upholstery, but be cognizant that an automobile interior is a very harsh environment for leather, which is reflected in the finishes used. Pigmented and semi aniline leathers will have better fastness properties than anilines (or Alcantara ®). However, pigmented leathers are more likely to have a less natural appearance. Aniline leathers have a tendency to soil easily and are more difficult to clean.

Leather Surfaces

Upholstery -there are essentially two zones: contact areas i.e. seats, arm rests, vertical seat backs and rolls, and non-contact areas i.e. outside arms and back.

Most upholstery leather comes from a cowhide that is shaped irregularly and not all of it is suitable for use. The hide is approximately 7 feet x 7 feet. Shoulder - the shoulder is thick and strong but tends to crease easily as this part of the hide is affected by movements of the head. Butt - the fibres in this part of the hide are tightly packed and hence the strongest part of the hide. Belly - this part of the hide is quite thin and has a much looser fibre structure than the back, and often stretches under stress. Axillae - these are like the human armpits - they move a lot - so the fibre structure is quite loose, making it even more prone to loosening than the belly areas.

Science: for a material that is so versatile, stylish and practical you could be fooled into thinking it is an extremely complicated material; far from it! There are basically just three main materials from which hides and skins are made:-

• Water 60-65%
• Protein 25-30% (mainly collagen, which is transformed into leather by the tanning process)
• Fats 5-10%

Hides have four main parts - an epidermis (skin) 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 fleshy remains - are removed during tanning by a process called liming. This leaves just the grain and the corium, the interesting parts.

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 is packed with collagen protein fibres, arranged in larger bundles and interwoven to give the structure great strength, excellent elasticity and durability.

IICRC Course Description

The leather cleaning technician course addresses leather identification and cleaning techniques (Chemical, heat, agitation, time (CHAT) process) which covers any leather cleaning for professional on-location cleaners, restoration and inspection service providers, as well as other related industries. Emphasis shall be placed on theory, practical application, the correct identification of leather types, soiling conditions and proper professional solutions to the cleaning challenges faced by the individuals performing the work in the field - Welcome to the Institute of Inspection, Cleaning and Restoration Certification! The Certifying Body for the Inspection, Cleaning and Restoration Industry, Representing Certified Firms and Technicians World-Wide - International

Leather Upholstery Abrasion (Rub) Resistance Testing

The abrasion resistance of finished leathers thin urethane covering is designed to contend with clothing abrasion from exiting and entering the vehicle. Wear from abrasion is a complex phenomenon and the information Taber Industries provides at Abrasion Testing: Taber Industries-Material Test & Measurement is meant to give you an introductory understanding of the common wear processes and their underlying causes. Having this practical knowledge will help to address the cost of failures caused by wear and abrasion.

Dirt is the real enemy of leather, acts as an abrasive every time you sit down or change your position while driving. Abrasion wear is due to hard particles or hard protuberances forced against and moving along a solid surface. These hard particles might be commercial abrasives like silicon carbide and aluminium oxide, or naturally occurring contaminates like dust particles and sand [crystalline silica (quartz)]. If the abrasive particles are allowed to roll, rolling abrasion or three-body abrasion occurs.

This can lead to catastrophic wear, which is a rapidly occurring or accelerating surface damage, deterioration, or change of shape caused by wear to such a degree that the service life of a part is appreciably shortened or its function is destroyed.

ASTM D7255 Standard Test Method for Abrasion Resistance of Leather (Rotary Platform, Double-Head Method) this test method covers the determination of the abrasion resistance of leather using the rotary platform, double-head tester (RPDH).

[EDIT: Leather surfaces para added 12/25/2011]

Edited by TOGWT, 25 December 2011 - 09:04 AM.

Detailing Art; where applicable Chemistry meets Aesthetics See Autopia Detailing Wiki

#2 judyb


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Posted 04 December 2011 - 10:58 AM

Dyeing- more correctly the application of a pigment (colour) either by spraying, hand rubbing or immersion.

Pigmented - leather that has been applied with a surface colour in addition or instead of the dye process and is analogous to the "staining" of wood

Bit of confusion here I think.

Dyeing is the use of dyes that soak into the leather rather than a pigment that sits on the surface.

Dyeing is analogous to "staining" of wood
Pigmented is analogous to "painted" wood.

The wood analogy is a very useful one in terms of leather as it mirrors the leather colouring process closely.
Hope this helps
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Posted 04 December 2011 - 03:59 PM

Difference between a Dye and a Pigment

A distinction is usually made between a pigment (in the US the terms pigment and a dye are interchangeable, which is incorrect as they are applied differently) a pigment (colour) is insoluble resulting in a suspension, and a dye, which either is itself a liquid or is soluble, resulting in a solution that permeates the leather.

A dye is soluble in water and is used to colour porous materials. It’s a molecule or chemical which absorbs light more at some visible wavelengths than at others, added to a clear medium, it gives clear colours.

Detailing Art; where applicable Chemistry meets Aesthetics See Autopia Detailing Wiki

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