SKINS, KIPS, HIDES

Leather IndustryHistory Leather is known to be “the most historic

of useful materials” The original primitive method was simply

drying, either in air & in sunlight. In 1200 B.C., (age of the Homeric heroes)

Greeks were using leather garments and later spread throughout the Roman Empire (The protective armor of the Roman soldier was a heavy leather shirt.).

o By trial and error, man discovered methods of preserving and softening leather treating animal skins with smoke, grease and bark extracts.

o Hebrews originated the tanning effects of leaves/ barks of certain trees in water.

In the middle ages, “England” – center for leather making & for the export of leather.

o Chinese knew the art of making leather.o “Buckskin tan” – type of leather

made by the Indians developed great skills in

leather work before the coming of the white man.

knew nothing of the bark tanning methods used in Europe.

In 1632, Bark tanning methods were introduced by French in Canada & English in New England

In 18th century, Sir Humphry Davy – discovered other barks that could be used for tanning aside from oak & sumac.

In 19th century, Vegetable tanning, i.e., tanning using the extracts from the bark of certain kinds of trees, was supplemented by chrome tanning.

o “Chrome-tan leather” was introduced by Augustus Schultz & Robert Foerderer, with the improvement of machinery made it possible to produce leather cheaper.

Definition:

Leather –a material created through the tanning of hides and skins of animals that has been made pliable & resistant to decay thru the chemical treatment called tanning.

Types of Skins:

• Skin – used as a generic word to denote skin from all kinds & sizes of animals.

1. Hides – skins from larger animals (weighs 34 lbs. up)

2. Kips - skins from half-grown animals of larger varieties (weighs 5 lbs. in wet state)

3. Skin – skins from smaller animals4. Cattle hides – most important source of

leather raw materials • sources:US, Argentina, Australia, Brail &

Canada5. Calfskin – used for expensive shoes,

handbags and similar articles; finer grained & lighter in weight than cattle hides

• sources: US & Europe6. Kidskin – imported from countries where

goats are raised for milk & meat • sources: India, SA, & Central Africa7. Horse hides – used for shoes, jackets &

sports equipment • sources: France & Belgium8. Pigskin – sources: US, Central Europe &

South America9. Lizards & Snakes Skin – provide leather

with unusual textures and colors for shoes, handbags, & luggage

10. Deerskin & Buckskin – skins from the deer11. Water Buffalo, ostriches, seals, &

sharks – for unusual leather.

Layers of Animal Skin

a) Epidermis – outer layer constituting 1% of the total skin & chiefly consists of protein keratin.

b) Derma/corium – a thick layer of living tissue below the epidermis - is chemically resistant, allowing

the epidermis to be easily removed by chemical means.

c.) Flesh – is an extraneous layer of adipose tissue which must be removed to ensure tannin penetration on both side of the corium.

Infos: Addition of hot water causes slow

solubilization to collagen when producing gelatin

Hair has large keratin which grows thru both the derma & epidermis.

Comparison of Skins & Leather:

Skins/Hides Leather

PliabilitySoon lose pliability & become hard & brittle

Retains Pliability

Permanence Putresce very quickly

Extremely permanent, not attacked by bacteria

Water resistance

Absorb water & are permeated easily by it

Possesses great resistance to water

Boiling water

Are converted to gelatin by hydration

Attacked with great difficulty

Mechanical strength Fairly good Very good

Characteristics of Leather:

o Uneven chemical compositiono Tensile strength – determines to what

degree the leather may subjected to stretching.

o Permeability – determines to what extent the leather of a shoe garment will allow the removal of water of perspiration from the body/feet.

o Changeability of area – determines the degree of physical discomfort in a shoe resulting from the variability of relative humidity.

o Temper – measured by folding lightly in upper leather

o Leather resilience – for soles and heelso Susceptibility to acid o Resistance to wearo Resistance to heat & watero Ability to hold embossingo Ability to absorb heato Porous

Kinds of Leather

1.Heavy Leather – for sole and belting Sole leather – a vegetable tanned (good

thickness & firmness). Light Sole leather – a vegetable tanned

(pliability & suppleness). Insoling & Offal Leather – vegetable

tanned, no fillers are necessary. Belting Leather – made from high

quality hides Chrome belting leather – fat liquored,

greater resistance to moisture & acid vapors.

Chrome sole leather – for sport boots.2. Light & Dressing leather - for boot

uppers, harness & upholstery. Bark-tanned uppers – a.) russet leather,

if finish is on the grain side b.) wax leather, if finish is on the left side.

Chrome tanned uppers – one-bath or two-bath process tanned.

Combination tanned uppers – combination of chrome & vegetable tanned.

Harness leather - for clothing, leggings…

Bark-tanned pigskin – for bags & cases, leggings.

Vachette leather – for furniture, motorcars…

Japanese leather – similar to alum-tanned leather, for braces.

3. Fine leather – for gloves, lining, and bookbinding

Fancy leather – for handbags & other articles, made from crocodiles, snakes, lizards…

Glove leather – includes alum salt leather, nappa leather, & chamois leather

4. Technical leather – for hose, straps, drums & parchments. Belting leather Hose leather - for pumps Lace leather Strap leather Machine leather Gas mask leather Parchment & drum leather – made from

pigskin, calfskin, goat skin & sheep skin.

Raw Materials: Animal Hides/Skins – Batangas & Cebu

are the main sources of hides in the Phils.

Sodium Sulphide – a sharpening agent used in accelerating the dehairing process.

Lime water – unhairing agent Chrome (Cr 3+ ) – exhibits a slight

tanning effect; source: Masinloc, district of Zambales

Chromic sulphate – exhibits a stronger tanning effect.

Formic acid – swelling agent in the soak water.

Sulfuric acid – used in regulating the pH & in the tanning process; a pickling acid together with HCOOH.

Atlasol – degreasing & wetting agent Syntans (Synthetic tanning agents) –

condensation products of sulfonated phenols & formaldehyde, capable of converting animal skin to leather.o Classification acc. to use: a.)

Auxiliary tannins, b.) Complementary tannins, c.) Replacement tannins

Sodium Sulphate – prevents acid swelling. sources: Nueva Viscaya

Fat Liquors Dye Stuffs – either powder or liquid Sodium Dichromate – main raw

materials for tanning process

Manufacturing Process

Terms:o Tanning – the skin is turned into leathero Tannins – complex mixtures of

glucosides of various polyphenols, combining between the collagen fibers of the skin. liberates sugar during the tanning

processSKIN + TANNIN = LEATHER + SUGAR

acidity of pH is controlled by the used of sulfuric acid.

o Keratin – a protein containing crystine residue which is easily attacked by an alkali.

o Neutralization – adjustment of pH for different types of skin

o Liming – loosening & removing the epidermis & hair from the hide

10% lime, 2% Na2S (based on hide weight)

3 – 7 days/vatso Retanning – gives the required handles

to the leather & modify the dyeing characteristics

o Dehairing – usually placed in a vat of warm water which permits easier removal of hair.

o Fat liquoring – it restores the fatty oilso Preservation – usually by salts to avoid

decomposition of hideso Pickling – reduces the pH of the skin to

between 2.0 to 2.5.o Bating/deliming – uses ammonium

sulfate or chloride for the removal & alteration of certain proteins & for the improvement of the color of the grain Falling – (rxn. in bating), a reduction

in the degree of swelling of the protein constituents of the limed skin

Tannery Operations: a. Pretanning process – non-leather

making constituents of the skin are removed

b. Actual tanning process – skin is turned into leather

c. Post- tanning process – required color & appearance is imparted into the leather.

“geto” – graded, examined, trimmed, & open

flesh – removed by a spiral bladed cylinder

1% sodium terasulfide – hastens rehydration & produces more uniform hydration.

10% Ca(OH)2, 2% Na2S – sharpening

agent; sulphydrate, dimethylamine, cyanide salts.

or hand-scraped

tryptic enzymes

H20

Trimming Table

Soaking Pit3 – 24 hrs

Liming(3 -7 days)

Dehairing

Machine

Scudding bench

Bating, 90°F(20 – 30 mins)

Beaming

(Vegetable tanning)

(Chrome Tanning)

organic acids (A)pH 3.5

NaCl H2SO4

(B) (A) (B)

30% HCl

Na2Cr2O7.H2O

(60 days) Na2S2O3

Borax

oil

Embossing rolls

Preservation & Disinfection of Skins:

Curing - a method of short term preservationo Brine curing – immersing it in a

saturated brine solutiono Salt Curing - sprinkling it liberally on

both sides with common salt. requires 3 to 4 weeks @ 13°C

Dehydrates Salt Absorption

Methods of Tanning:

o Vegetable Tanning –used for heavy leathers, for soles & belting 2 Broad Groups:

Catechols Pyrogallols

usually done in 8x7 ft vats, 5 or 6 deep, containing tan liquors and hides.

from weakest tanning liquors thru liquors of increasing strength. to prevent complete plugging of

the surface pore Ratio (liquor/hide) = 4 to 6 lb

liquor/lb hide. Bleaching – is done by using dilute

solutions of oxalic acid or acidified solutions of sodium metabisulphite.

Stuffing – is done by adding several coats of compounds cont’g clay, mineral salts, corn ugar @ 60°C.

o Chrome Tanning – usually subdivided into 2 processes which penetrate the hide very rapidly One bath process – using chromium

sulfate Two-bath process – using sodium

dichromate requires 8 hrs. of continuous

process with the hides maintained between 2 to 4 pH.

o Oil tanning – an old method in which fish oil or other oil and fatty substances are stocked, or pounded, into dried hide until they have replaced the natural moisture of the original skin. used principally to make chamois

leather.

“Life is good when we’re having fun” - Bambini

Prepared by: Juphil LamanilaoRinsing Vat

Drenching

Vat

Pickling Drum

Tanning Vats(30 days)

1st bath 2nd bath

Lay-away Vat

Reduction Drum

Setting Drum

Rinsing Vat

FINISHING OPERATIONS

DyeingDrum

StuffingDrum

Splitting Machine

Jacking Bench

Drying Loft

MEASURING MACHINE