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Production genuine leather

For a skin of really high quality, the stages of the technological cycle of its processing to the finished product should be less, the better. The "face" of the hide (the top layer of the skin) should be completely preserved, if not emphasized. This means that the wrinkles and pores present on the skin that is being processed must be preserved.

LEATHER PRODUCTION TECHNOLOGY

Leather production technology (processing of skins to finished leather) consists of three stages: skin preparation, leather tanning, leather finishing.

Preservation of hides

The procedure for preserving skins is done so that the skins are impregnated with salts. Why do they do this? When an animal is slaughtered, both its meat and skin immediately begin to deteriorate. When canning a hide, half of its moisture is lost; the hide is dried for three to six days. And only then the raw materials are sent to tanneries for further processing.

1. SKIN PREPARATION

Leather preparation means washing away the dirt and removing hair from the hides - the initial stage of processing raw materials for leather production, after which the leather enters the tanning shop. The purpose of these procedures is to remove animal matter from the skin. remove wool and subcutaneous tissue, and also prepare the skin for the second stage - tanning. At this stage, the skin with hair, which is called the dermis, turns into an untanned semi-finished product - golyo. At a hide processing plant, the animal's hide is treated with salts (sodium chloride and sodium carbonate), and then the preserved hide is dried. The leather is then processed using leather processing equipment.

Here, too, the following stages can be distinguished:

Soak

Soaking the skins: the skin should be soaked, washed with chemical solutions and water. The skins are cleaned of blood, dirt, preservative salts, fats, etc. This process lasts from eight to twenty hours (it all depends on how thick the skin is).

Gilding of hides

Ash in the process
Skinning involves removing hair and epidermis from the produced hide. Liding is the process of treating animal skins with a lime slurry. Ashing of the skin is necessary so that during the subsequent, further process of processing the skin, the hair can easily come away from the skin and achieve the necessary swelling of the hide fibers themselves.

Wool cutting (hair removal)

Wool cutting (hair removal) is done on machines whose name speaks for itself - hair cutting machines.

Semi-finished leather, after the wool has been removed from it, becomes Let's go.

Flesh

Skinning - this is the removal of the subcutaneous fat layer, excess flesh and muscles (mesh) using fleshing machines. The first fleshing is usually done on the skin after it has been partially soaked, and the second fleshing is done after the wool has been removed. When fleshing is performed poorly, bad defects such as snatches appear on the skin.

Cleaning the skin's face (skin cleaning)

Cleaning the face of the skin is the removal of remaining short hair from the skin.

Deliming

Deliming occurs to remove calcium compounds (salts) from the treated hide. If this is not done, the skin turns out to be tough, which subsequently creates defects such as facial breakage and swelling.

Skin washing

The skin is washed with water. This procedure is carried out in order to completely remove calcium salts and protein breakdown products. After washing, the raw material (nailed) is sent for tanning.

But for a few specific types of leather, additional preparatory procedures are used:

Double skin

Split leather is produced in splitting machines. Splitting of the skin is usually done when the skin has a fairly high
thickness. The need for double leather appears when producing relatively thin leather intended for the upper of shoe products.

Saddle cloth

Saddle dressing is the division of the produced hide into so-called topographic sections. Large skins are subjected to saddle cloth.

Skin softening

Skin softening is the treatment of the skin with various enzymes (as a rule, these are pancreatic enzymes), under the influence of which the skin becomes softer, more viscous and smoother. Softening is used, as a rule, when producing leather for clothes, haberdashery leather and soft shoe leather.

Pickling

Pickling of skins implies the treatment of the hide with an acid-salt solution - a pickle. In the process of pickling the skins, the skin is additionally loosened, which leads to an increase in its softness. Picking is inherently skin preservation, so skins can be stored for a long time without spoiling.

2. LEATHER TANNING

Tanning is a process when the obtained skins are processed in special tanning drums, resulting in a semi-finished product.

The purpose of tanning is to stabilize the shank, i.e. The skin must acquire elasticity, plasticity, and wear resistance. After tanning, the skin is used without any particular fear of damaging it.

3. LEATHER FINISH

Leather finishing means:

Skin coloring.

Skin coloring occurs with various dyes, which are obtained from oil.

Oily skin treatment.

After dyeing, the leather is treated with fat to make it softer.

After that, the skin is dried by stretching on special frames, which are later placed in a drying oven.

Kneading the skin makes it soft.

Rolling skin.

Skin ironing.

Skin pressing.

Leather embossing.

Applying lacquer to leather.

Grinding the front surface.

Not often the front surface of the skin has a surface without scars, cuts, abrasions and other defects. In order to hide these defects, the skin is polished.

Applying wax to the skin.

Giving leather properties such as gloss, water resistance, dirt repellency, fire resistance, etc.

How to make skin video

Leather production process

British Standard BS 2780 Definition of leather:

“A general term for a material that comes from the hide of an animal and retains the fiber structure of that hide more or less unchanged, tanned to stop the processes of decay. Fur and hair can be removed or left on the surface of the skin. No product can be called “leather” if, during its production, the original structure of the fibers of the animal skin is destroyed and processed into individual loose fibers and/or powder and/or other fragments by any chemical and/or mechanical method, followed by the reconstruction of these fragments into flat materials and/or other forms. If the leather has an outer covering, its thickness should not exceed 0.15mm"

The process of turning raw hide into leather is not a simple task, and in fact consists of a chain of sequential actions. These actions can be divided into four related groups, namely:

• Preparatory work in the tannery
• Tanning
• Retanning
• Finishing

Preparatory work in the tannery

The main goal of the preparatory work is to completely clean the hide of various undesirable components, such as wool or hair, unstructured proteins and residual flesh.

Soaking (soaking). During soaking, dirt and blood residues are removed from the surface of the skin. To avoid shrinkage of the skin during soaking, the water temperature is maintained at 20°C. Sometimes, for better purification, they add to the water detergents containing alkali; among other things, alkali allows the skin to absorb moisture more intensively. Moisturizing the hide is an important part of the soaking process.

Dehairing and ashing. At this stage, the skins are again soaked in an alkaline environment. This allows you to get rid of hairs, soften collagen fibers and destroy unstructured proteins (if they are not removed in time, the skin will turn out to be too hard).

Fleshment. In the process of skinning, pre-washed skins are passed through a special apparatus that removes unnecessary remnants of flesh, connective tissue and fat.

Double vision. Now the skin can be divided into two parts (more precisely, layers). The top (outer) layer of leather resulting from doubling is widely used in the leather industry and as frontal upholstery, as it contains a layer of grain, the pattern of which can then be preserved, corrected or embossed. The bottom layer (the so-called split) is used for the production of suede, as well as protected and pigmented leather. Split leather is often used when upholstering the back or side of a product.

Deliming. The task of the next stage is to reduce the amount of swollen and hard fibers. To do this, the existing alkaline environment is neutralized with substances containing acid, such as ammonium chloride or sulfate.

Softening. This process makes the hide smoother and flatter, highlighting its texture. In addition, it is thanks to it that the skin becomes softer and more elastic.

Pickling. The last stage of preparation for tanning. To reduce the pH (hydrogen value) of the material, it is again treated with acid (sometimes along with salt to prevent the hide from swelling excessively).

Tanning

Almost everyone knows about this procedure. And this is not surprising, because tanning leather is one of the most important stages in the process of its processing. Have you forgotten the strict scientific definition yet? According to him, a skin that has not been tanned cannot yet be considered leather as such. As a result of tanning, the collagen proteins contained in the hide become a durable material that is difficult to decompose and resistant to heat and moisture.

Humanity has invented many ways of tanning leather. The most popular in tanning and, perhaps, the only one that will be useful for you to hear about is the so-called wet blue (from the English wet blue: wet and blue) or “chrome tanning”. This term is applied to leather that has been tanned using chromium salts. But why "wet and blue"? The answer is indecently simple - the resulting material is really wet and has a bluish tint.

The processing of the skins takes place in large barrels (usually such a barrel holds up to three hundred skins at a time). Chromium reacts with the collagens contained in the skin and turns them blue. The tanning process is considered complete when the hide is resistant to high temperatures and does not shrink at 100°C. The advantages of this method include the high strength of the resulting material, as well as its resistance to heat and light. That is why chrome tanning is the most common and popular method of tanning leather today.

The final stage of tanning is to remove excess moisture from the skin. To do this, the skin is passed through a special apparatus equipped with felt pads, which squeeze out all the excess liquid.

Retanning

Neutralization. To prepare the skin for a chain of further chemical processes, it is treated with a weak solution of alkali.

Coloring. This stage probably does not need additional explanation. Leather is also dyed in barrels, most often using anionic dyes - they are negatively charged and therefore bind well to the previously “chromed” leather.

Fatliquoring. Special fats and oils are used to lubricate the leather fibers and make them softer. They penetrate the skin, filling all its pores. By the way, it is at this moment that the skin acquires its unique smell!

Drying. The skin is hung on poles, or laid out on special boards, and then dried with a stream of warm air. The latter method is especially popular, because it only takes a few minutes to dry one skin!

Breakdown. At this stage, the skin becomes softer. It is passed through a series of special blunt pins, which beat and crush the skin, thereby softening it.

Finishing

Finishing is a process that involves processing finished leather and applying various coatings to its surface. The benefits of coated (or “protected”) leather include:

• Greater durability
• Easy to care and maintain
• Improved water repellency
• Masking of natural defects
• Attractive color and appearance

There are three processes directly involved in finishing leather: sanding, coating and embossing. Depending on your skin type, some (or even all) of these steps may be excluded.

Grinding. If the upper porous surface of the leather is in good condition, then the leather is not processed at all - the so-called full grain leather is obtained. It is highly prized in the upholstery industry, and in fact only a very small percentage of hides are good enough to be used in the production of full grain leather.

Most often, the skin (for example, cow) bears traces of scratches, bites or cuts received by the animal during its lifetime. All these defects, of course, negatively affect the texture and need to be corrected. A special liquid filler (“skin restoration composition”) is applied to the damaged areas. Then the leather is dried and its porous part is processed with a special grinding machine with abrasive material to completely hide the existing imperfections. This type of leather is known as corrected grain or "faceted leather."

Grinding also serves another additional purpose - it prepares the skin for subsequent pigmentation, ensuring better penetration and fixation of the pigment.

Coating. Corrected leather pigmentation is applied to give the material the correct, uniform color. The concentrated pigment itself does not adhere to the skin; it requires a base, which is most often used as acrylic or some solvent containing substances that provide adhesion.

To fix the color, varnishing is done after applying the pigment. Varnish protects the leather and makes it more durable, but not only that - it is with the help of varnish that the required degree of shine of leather products is achieved.

There are three ways to apply pigment to the skin.

1. Manual spraying using an airbrush
2. Automatic spraying on conveyor belt
3. Pressing paint using rollers. Very often the second and third methods are used together.

Varnishes are applied by airbrush, manually or on a conveyor belt.

Embossing. After coating, the grain pattern can be changed artificially. To do this, a special metal mold with a pattern applied to it is applied to the top layer of leather. At a sufficiently high temperature, it is forcefully pressed into the surface of the skin, giving it the desired relief. And sometimes the skin is passed through rollers on which an artificial relief pattern is applied.

This, in the most general terms, is the path that leather takes from raw, unprocessed skin to the finished product familiar to us all.

For production leather bags Mainly used leather is obtained from the skins of cattle (cattle) as well as leather obtained from sheep skins. To give leathers a modern appearance Manufacturers use various technologies for finishing the outer layer of leather, which allows them to achieve a wide variety of leather products.

patent leather
chrome tanned leather with varnish coating (duplicated with varnish film)

Cattle leather
(cattle) with acrylic coating. Finishing leather with acrylic emulsions to form a transparent, shiny film.

Nappa
thin leather of increased elasticity, made from cattle skins.

Napplak
lacquered nappa.

Velours
chrome-tanned leather with the front surface processed by grinding or bakhtarma. A tanned semi-finished product with deep facial defects, unsuitable for the production of leather with a natural facial surface, is selected and processed into velor.

Leather with refined facial surface
leather from which the facial layer has been mechanically removed and an artificial layer of polymer has been applied.

Chevrette
chrome-tanned leather made from sheepskin.

Split
part of the hide (skin) obtained after splitting. There are front and melon splits.

Face split
the part of the skin after double vision in which the facial layer (upper part of the skin) is preserved.

Split melon
the part of the skin after double vision in which the bakhtarma (lower part of the skin) is preserved.

Bakhtarma
the undersurface of the tanned animal skin.

Double skin
leveling the skin in thickness and dividing it into several layers.

Mereya
natural pattern on the skin. On the skin of different species of animals, a measure is distinguished that is characteristic only of a given species of animal.

Face slicing (slicing skin)
applying patterns to the front surface of the skin, sometimes imitating various animals. Done with a hot stove. For example: the production of leather with a pattern like a deer, an ostrich, a crocodile, etc.

Nubuck
fleecy chrome-tanned leather with the front surface sanded with fine-grained abrasive material.

Leather painted with imitation painting
exclusive finishing of the outer layer of leather, which involves painting the leather with paints or printing a design, either manually or using special equipment.

Leather furniture - types of leather

Furniture made of leather is stylish and practical. There are 4 categories of skin:

Category A. Semi-aniline, fully adjusted. It has many defects and therefore undergoes the most thorough processing: the irregularities are puttied with a special compound, the skin is dried and sanded. Then it is pigmented and sanded again. After this, the skin is covered with a polymer that protects it from the adhesion of dirt and dust, and a relief is applied to it with rollers. This is the easiest to care for and most durable type of leather.

Category B. Partially corrected aniline and semi-aniline leather. The processing method is similar to the above for leather category A. This category is more expensive than the first, since the properties are close to category C.

Category C. Aniline, with a completely natural face. Such leathers, which have a natural top layer, are especially comfortable to use, as they are able to adapt to any temperature, “breathe” and support heat exchange between human skin and the environment.

Category S. Unlike C, leather category S has an artificial top layer and a high-quality sheep or calf inner layer. The properties of this leather allow you to give it any color and apply any design to it.

Leather is a natural material made from the skins of various animals. Just as no two animals are identical, no two pieces of leather are identical. These natural features are not defects, but only add to the uniqueness of each finished product. This especially applies to exotic leather.

Leather processing is perhaps one of the oldest crafts on earth. Primitive people began processing animal skins many thousands of years ago. This process can be called the very first manufacturing industry. According to archaeologists, in ancient Egypt the remains of leather clothes were found, which were made as early as the 13th century BC. Almost everything was made from leather. Ancient people used primitive shoes to protect their feet: they wrapped their feet with pieces of animal skins and secured them with leather strips or sinews. The very first shoes of man were sandals, which instead of a sole had a plank tied to the foot with leather straps.

Animals were hunted for their meat and fat, but the animal had to be skinned before food was used. For this, sharp pieces of flint were used, and later flint knives. Further, the skins were used to warm the bodies of people and wrapped around the legs, representing the first type of boots. But untreated skins soon began to decompose and rot. Drying the hides in the sun was observed to conserve them, but the result was a very hard, inflexible material, of little use for clothing. The skins had to be softened. This was done by rubbing the hide to be prepared with various fats.

The fat also helped prevent the hides from getting wet. This type of processing made animal skins soft and elastic. In addition, water was used to process the skins, to which various types of bark and berries were added. It was found that after such treatment, the skins became significantly softer and could resist decay. The active substances contained in extracts from certain plants and which produce such an effect on animal skins are called tannins. This was one of the first methods of tanning leather. Gradually, the technique of making things from leather improved, household items turned into real works of art.

Probably all the peoples of the Earth were engaged in leatherworking, because in ancient times leather was the most accessible material. Humanity learned to spin and weave much later. The Ugrians (a group of Finnish peoples - the Finno-Ugric language group) sewed boots from the skin of birds with plumage; many tribes decorated leather clothes and shoes with silk and gold embroidery, precious stones, painted, pearls. The Indians covered the seams on leather clothing with strips of colored prickly fish scales to prevent moisture from passing through the seams.

For the Slavs, leatherworking was also the oldest craft. Already in the 6th-7th centuries in Rus' they were known various ways tanning and processing of leather. The artistic processing of leather has especially developed in the North and Central Russia. For example, in the city of Torzhok, multi-colored morocco was made, and pillows, belts, wallets, pouches, and shoes were made from it embroidered with silver, gold, and silk. Before the First World War, these items were exported from Russia, as well as some types of leather that were superior in quality to their European counterparts.

It is also worth noting the widespread use of leather in book printing. For a long time, books were written on parchment - calfskin dried on a frame. In addition, book bindings themselves were made of leather.

The processes used to produce leather today were invented by our ancestors many thousands of years ago. Since ancient times, leather production has used a tanning process using animal brains as a source of emulsified oils. This process is known as "Indian tanning" and the practice is still used by some people on a small scale. This tanning process is most often used for tanning deerskin. This practice gave rise to the saying that "an animal has mental capacity, which are only enough to preserve his own skin, dead or alive.

Leather has not lost its relevance in the modern world. With all the development of technology and the emergence of new synthetic materials, leather continues to attract more and more new supporters and admirers. Nowadays, genuine leather products are in great demand, despite their high price.

PRODUCTION OF GENUINE LEATHER

Processing of raw hides

It is believed that the highest quality leather is made from the skins of cows (bull, calf). It is used for shoes, clothing, furniture upholstery, etc. Leather from sheep or goat skins (sheepskin, goat) is mainly used with hair (like fur). Leather made from pig skins is elastic, but has a persistent characteristic odor, therefore it is valued lower than others. Leather from crocodile, python, stingray, ostrich and other exotic animals is used for the production of leather goods, clothing, shoes and other business areas.

There is a rule: the higher the quality of the hide, the fewer stages in the technological cycle of its processing until the finished leather. The goal when processing skins with good face quality (face refers to the top layer of the hide) is usually to ensure that the face is preserved and even emphasized. The finished product retains the natural pattern of the face - wrinkles and pores that are present on the raw skin. By placing your palm on the surface of the leather with a natural face (fool grain), you get the feeling of a natural elastic product.

The skins of dairy calves (calfs), being thinner than the skins of adult animals, can compete with them in strength and wear resistance. This is explained by the thicker and denser fiber structure of the skins of dairy calves. The process of processing hides into finished leather can be simplified as a combination of three main stages:

Leather dressing.

Dressing is one of the most simple ways leather processing, at the same time the most ancient of them.

The production of finished leather is a rather labor-intensive and lengthy process, which consists of three main stages leather production:

soaking-ash processes;

preparatory processes and tanning;

chemical finishing and dyeing and greasing processes.

1. Soot-ash processes

Raw skins: skins of cattle, mainly skins of bulls and cows, taking into account their origin and weight category. Raw skins are supplied from the south of Germany and Switzerland, as well as from other regions: skins of wild animals - from the USA, South America, Australia, New Zealand, etc., in some cases water buffalo skins are used (India and Indonesia), less often - veal and pork skins.

Canning: If delivery of leather does not take much time and immediate processing is provided, then the leather is simply frozen. In all cases, the supply of salted skins is considered normal.

Soaking: First stage of processing. The skins are soaked to remove dirt. They gain moisture again. Biological moisturizers are used to soften the skin. First, preliminary softness is achieved, then the main one. Once the skin is softened, any remaining meat can be removed.

Gilding: Removal of the upper stratum corneum of the skin and hair. At this stage, the type of leather is determined, which serves as the basis for its further intended purpose. Chemicals used substances: lime and sodium sulfide, which are then neutralized with acid.

In this case, the following 4 goals are mainly set:

1) weaken the connections of the hair and epidermis with the dermis;

2) carry out partial saponification of fatty substances;

3) achieve sufficient swelling of the hide fibers;

4) bring the hide to the chemical state necessary for tanning.

In addition, the conditions of liming and ashling also affect such properties of the finished leather as tensile strength and moisture holding capacity. The strength of leather that has been subjected to intense action from the ash pit is always less. This is due to the destruction of bonds in the main chain (intramolecular bonds) during such processing.

Water resistance of leather decreases with intensive treatment with an ash solution, which is associated with an increase in their porosity.

2. Preparatory process With.

Wool cutting. Produced on special hair cutting machines. This operation is carried out after liming, when the connection between the hair and the dermis is weakened. The semi-finished product after wool removal is usually called golyem.

Flesh: Removal of meat cuts, tendons and subcutaneous fat layer (mendra). Mezdra is used for the production of technical gelatin. The treated leathers are ready for tanning and are called "golyo".

Face cleaning. This operation follows after fleshing. Cleaning consists of removing short hair (sagging), as well as partially the breakdown products of proteins and fats.

Deliming and pickling: The skin is cleaned of liming products through neutralization, and defermentation is carried out - pickling. The skin is thoroughly treated and becomes smoother. Ash shank is in a state of high swelling - strong swelling and contains a large amount of calcium compounds, both associated with collagen and deposited in the form of lime and calcareous salts.

Boiling: Serves as a preparation for the mineral tanning process. Golier is immersed in drums of brine and then treated with weakly concentrated acid. The tanning substances added during this process cannot yet act actively, but they evenly impregnate the fish.

Flushing. Washing is carried out with water to remove calcium salts and protein breakdown products. After washing, the raw material enters the tanning apparatus for tanning.

GhostingWetBlue: Legs obtained from large raw materials (bull, cow, bull, etc.) are subjected to doubling. When doubling, after liming, the skin is sawn on splitting machines into two layers: the upper face layer and the lower melon layer.

The golyo is cut into layers along its entire surface thickness. The layer with traces of skin defects is cut off evenly throughout its entire thickness. The remaining layers retain their natural uneven thickness. The top layer is the future natural leather. The bottom layers after tanning are called split leather. The top layer of leather used for the production of leather furniture is subjected to additional liming.

When sawing, the thickness of the face split is specified, so it is obtained with the same thickness over the entire area. Upper split leather is usually used for the manufacture of more important parts of shoes, melon leather for less important parts of shoes and haberdashery leathers.

It is necessary to take into account that the overall strength of the splits is low compared to the original bare metal.

In addition to the above preparatory operations, for some types of leather, additional doubling, saddle scraping, softening, and pickling are used.

2. 2. Tanning

Tanning shop.

The resulting raw materials are processed in special tanning drums, after which a wet blue chrome semi-finished product is obtained, which is ready for use.

The resulting bare is unsuitable for making shoes and other products. When watered, the fish swells greatly, absorbing large quantities of moisture and greatly increasing in volume.

Drying of the fish is accompanied by a sharp decrease in its volume, gluing of its structural elements and a change in mechanical properties. Dried fish become hard, horn-like and brittle. Golye is not resistant to heat when wet, the action of bacteria and enzymes. Thus, the shape and stability of the material are lost. To get rid of these phenomena, the naked is tanned, that is, treated with tannins.

According to modern concepts, tanning is the process of fastening collagen molecules with tanning agent particles (cross-linking of molecules)

The leather obtained as a result of tanning differs from bare leather in a number of properties:

♦moisture capacity decreases, since the ability to swell in water is lost;

♦stiffness increases, since during tanning, due to the formation of additional cross-links in the dermis, the mobility of skin collagen macromolecules is lost;

♦the strength of the structural elements of the track increases. But it should be remembered that excessive woodworking, on the contrary, reduces strength. This is explained by the fact that when tanning above a certain optimum, the strength decreases due to an increase in rigidity and a decrease in the ability to orient the structural elements of the skin;

♦increases elasticity and associated wear resistance;

♦heat resistance increases. This is due to an increase in the number of chemical cross-links and the welding temperature during tanning (Tcg);

♦porosity increases. This is explained by the fact that tanning agents, penetrating (wedging) into the structure of the dermis, separate the elements of the structure and this is subsequently fixed due to the formation of chemical cross-links;

♦ dimensional stability increases. This is due to the fact that tanning agents, forming cross-links between collagen macromolecules, do not allow the dermis to swell and, in addition, do not allow them to come closer together and stick together;

♦chemical resistance increases. This is due to the fact that the functional groups of dermal collagen are blocked by tanning agents;

♦improves appearance;

♦in the dermis after tanning, the thickness, area and angle of inclination of collagen fiber bundles increase. This already speaks of the economic efficiency of tanning and an increase, in particular, in the wear resistance of sole leather.

The modern theory of tanning considers tanning as a process consisting of a number of physical and chemical phenomena and occurring in two stages. The first stage is the diffusion of the tanning agent into the thickness of the skin, the second is the interaction of the tanning agent with collagen molecules. In this case, both processes occur simultaneously.

Tanning substances are classified into two groups:

1.Organic (tannides, aldehydes, fats).

2. Mineral (titanium, chrome, zirconium and aluminum compounds).

Basic tanning:

Chrome tanning is carried out with aqueous solutions of basic salts of trivalent chromium, which is not toxic. Tannins penetrate deeply into the leather, which helps strengthen it and will not cause damage if used normally. Hexavalent chromium is not used for tanning, as it is poisonous. After chromium penetrates into the treated leather, the remaining acid is partially drawn out, and the chromium is fixed in the leather fibers and thereby neutralized. Zirconium, aluminum and titanium tanning is carried out similarly.

Layering and wilting:

To set the tannins, the leather is laid out in layers and dried.

Folding (rolling):

Serves to even out skin thickness.

Neutralization: acids remaining in the skin are carefully neutralized with slaked lime. At subsequent stages of processing, skin groups are established.

Final tanning: modification and development of leather properties using stronger tannins in combination with primary tanning. Combination with vegetable and/or synthetic tannins, chromium and other minerals is possible.

3. Chemical finishing and dyeing and greasing processes

At the final stage of chemical finishing, the following operations are performed:

retanning (using chromium compounds, syntans, and other special agents); Dyeing: Leathers are dyed in dye baths with permanent dyes that penetrate deeply into the leather fibers. Only natural, non-toxic and environmentally friendly dyes are used. The paint penetrates deeply into the structure of the skin, fattening (fats, oils, emulsifiers, ammonia are used)

The final product of tanning production is leather, i.e. the entire technological production process is nothing more than the transformation of hide into finished leather.

Vegetable (aldehyde) tanned leather is leather whose tanning process uses tanning bark (hence the name “tanning”) and other ingredients obtained from plants, tree bark and similar sources. The result is an elastic material Brown. The right shade achieved by varying the quantity and quality of the ingredients used and selecting the color of the raw materials. Vegetable tanned leather is not water resistant. When exposed to moisture, it changes color, and if it absorbs liquid and then dries, it will decrease in size (“shrink”) and harden, becoming less elastic. In hot water, this type of leather shrinks greatly and becomes a hard, brittle material, which limits the possibility of its use.

Alum-tanned leather, the tanning process of which uses aluminum salts mixed with various binders and protein substances, for example, egg powder, etc. Purists argue that alum-tanned leather is technically "rawhide" rather than tanned because the resulting material will rot in water. This process produces leathers with desaturated tones, but the resulting material is not as flexible as vegetable tanned leather.

Rawhide is made by scraping the hide, soaking it in lime, and then stretching it to dry. Like alum-tanned leather, rawhide is not technically a "leather" but is commonly referred to in conjunction with other forms of leather. Rawhide is tougher and more brittle than other forms of leather and is used to make drums as well as cords used for lacing or stitching.

Boiled leather - leather products (vegetable tanned leather) that are immersed in hot water or boiling wax or similar substances to increase strength. Historically, such leather was used as armor due to its hardness and light weight, and was also used for book bindings.

Chrome tanned leather, invented in 1858, uses chromium sulfate and other chromium salts. This form of leather is softer and more flexible than vegetable tanned leather. In addition, it does not change color or lose shape when exposed to water, like vegetable tanned leather.

Leather (usually vegetable tanned leather) can be lubricated with certain oily substances to improve its water resistance. This increases the amount of natural fats found directly in the leather, which are washed out during use of leather products, which may be exposed to intense moisture. Frequently lubricating leather products with mink fat, refined oil or similar substances will maintain the softness of the leather and increase the life of the product.

Production of finished leather.

The production of finished leather is a rather labor-intensive and lengthy process that takes place in several stages.

Leather painting.

The sorted leather is transferred to the dyeing shop, where the so-called semi-finished product Crust is produced.

The semi-finished product is sorted and transferred for further coloring, which is carried out according to the latest technologies in special dyeing drums, which allows for economical use of chemicals and delicate treatment of leather.

Before dyeing, the color of the leather depends on the tanning method (fat tanning - mustard yellow color; chrome tanning - light green color; iron tanning - canary color, etc.).

Skins that do not have any defects, without spots and without masks, can be painted in various cysts; skin with spots turns black. To dye leather black, after tanning and washing, it is dyed, then fattened and dried. For color dyeing, leather is only dyed without being greased, as fat can leave stains.

For dyeing black, vegetable dyes and aniline dyes are used; for colored leathers - currently almost exclusively aniline dyes.

Aniline dyes are divided into basic and acidic.

At this stage, ideally smooth elite leather is ready to enter the packaging workshop.

Leather that is not smooth for one reason or another is embossed.

Experts determine the quality of the leather and the type of embossing that will help hide minor imperfections in the surface of the leather.

A variety of types of embossing are used: from very small (the so-called dust plate) to very large (the so-called Tigina), as well as shagreen embossing, used for sewing special-purpose shoes.

fine embossing

shagreen embossing

very fine embossing

very large embossing

large embossing

medium embossing

Before packaging and sending to the finished product warehouse, all leather undergoes final sorting and measurement.

When the hides arrive at the tannery after the preservation process, they are examined for damage or poorly treated and preserved hides. At this stage, the entire batch of leather may be rejected and returned to the manufacturer.

In turn, leather is classified according to the method of coloring:

1. Dip painting. Fold two leathers with the inner side and immerse them manually in a 40-50° dye bath; in this case, the inner side is painted only very lightly. This method is used when dyeing small leathers (goats, sheep, calves, etc.), with a small number of them.

2. Painting in a vat with wide rotating blades. When the blades rotate together with the dye bath, they also rotate the skin. With this method, especially suitable for large quantities of leather, both sides of the leather are dyed.

3. Painting in a washing drum, closed rotating vessel with hollow axes for adding coloring solution. This method requires a very "short" dye bath, so that the dyes can be used very well; This method is mainly used for chrome leather.

4. Applying paint with brushes produced for the most part for large skins. The leather is spread on the table, the top side is well wetted, and then paint is applied.

5. Dyes. To color leather tanned with vegetable oak substances, basic and acidic dyes are used, less often substantive ones. When using basic dyes, add 1 - 2 g of acetic acid per 1 liter of dye mixture. For acidic dyes, add 1-3 g of formic acid per 1 liter of water. Nothing is added to the substantive coloring matter. In all cases, painting is carried out at 45-50°.

6. Chrome leather coloring. For chrome leather, acidic dyes with the addition of acetic or sulfuric acid are used first. Before adding the dye, the skin should be treated with quebracho extract to better fix the dye. Basic dyes are also suitable for coloring chrome leather; the quebracho bath is accordingly enhanced. Acetic acid should be added to substantive colorants. The temperature of the dye baths can reach 50-60°.

7. Kid leather coloring. Kid leather is dyed like chrome leather, but the temperature of the dye baths should be lower (40-45°).

(They mainly use acidic and basic dyes.)

8. Suede leather coloring. When dyeing suede, use basic dyes (with Glauber's salt and acetic acid) and dye at a temperature of 30°. Acidic dyes are used with the addition of Glauber's salt, at a dye bath temperature of 40-45°.

9. Patent leather coloring. a) Black. The skin that they want to varnish is fixed in a frame, placed on a smooth board and sanded on the front side with a piece of pumice until the skin is no longer rough. Next, they take a good oil varnish, mix it with Dutch soot and make a liquid paint from this, with which they smear the skin; then the latter is exposed to the sun to dry, and carefully protected from dust.

Having done this, proceed as before, dry it again, take pumice and polish it; when the skin becomes smooth, it is dried for an hour, after which the paint that was applied is mixed with Dutch soot and smeared with liquid 2-3 more times.

When it is dry again, take felt and finely ground pumice stone and polish it until the leather is completely smooth.

Skin configuration

In production, leather is cut and has various configurations.

Scraping is the division of the skin into topographic sections. Scraping is subjected to large raw materials, the topographic sections of which are most differentiated in thickness and microstructure.

According to the configuration of the skin there are: whole skin, semi-skin, kulat, semi-kulat, collar, saddle.

Types of leather by finishing method

Smooth skin

The natural pattern is preserved as much as possible - at least, they are not embossed at all, or very fine “dust-like” embossing is applied to the front surface. Leathers of this group are made from the highest quality raw materials using the most modern chemical materials.

Sanded leather

Sanding the mesh side and additional splitting makes it possible to obtain “Velour”, which is used for the production of sports, indoor and dress shoes. However, there are leathers whose polishing is predetermined by the technology of their manufacture - this is Nubuck, which is indispensable for the manufacture of both men's and women's shoes. Colored nubuck inserts are widely used in the production of children's shoes.

Embossed leather

Leathers of medium and low price ranges are indispensable for inexpensive work or uniform shoes. They differ in pattern and depth of embossing. The finer the pattern and depth of the embossing, the less ability this embossing has to hide defects. All drawings can be divided into several categories:

patent leather

Depending on the properties and color of the coating, leather can acquire a wide variety of color and organoleptic properties. Such leather is very widely used in the production of both women's and men's dress shoes. Patent leathers are represented by the articles "Orion", "Naplak". Patent leather can be embossed to obtain the desired pattern. Patent leather shoes look great and always attract attention.

Splits

An artificial polymer “face” is applied to the split leather, imitating the natural front surface. Split leather manufacturing technology allows you to use inexpensive raw materials and obtain an excellent solution for the production of inexpensive shoes with a quality close to that of genuine leather with a grain surface. The assortment of split leather with an artificial face surface is represented by the article "Legend" with various embossing options. All options for embossing split leather are identical to the embossing of leather with a grain covering, which allows you to combine them in the production of shoes (vamp - grain leather, ankle boots, tops - split leather). Split leather without applying an artificial “face” is used for making shoe lining material and sewing workwear.

Krasty

Semi-finished leather obtained after drum dyeing (no surface finishing). Has a natural pattern on the front surface. The absence of surface finishing allows one to avoid most of the defects associated with the peeling of the “face” - marking and odor. Modern processing makes it possible to impart the property of hydrophobicity to the paint, and special dyeing provides through-coloring. Well-made crust is difficult to distinguish from leather with a smooth surface. Crusts are widely used by shoemakers to produce shoes for a wide variety of purposes.

Leatherettes.

We distinguish 4 main types of products we represent (3 types of artificial leather and PVC film):

Artificial leather (faux leather) MF. This modern leather based on microfibers (Micro Fiber)

Artificial leather (imitation leather) PU. This is a modern type of artificial polyurethane leather

Artificial leather (imitation leather) PVC. Classic PVC leather

PVC film. PVC film

Today, faux leather(faux leather), is a high-quality and environmentally friendly material that is superior to natural leather in some respects. If the customer wishes, the aesthetic appearance of artificial leather is no different from natural leather on both the front and back sides. At the same time, it is possible to produce artificial leather with a texture and color that is not characteristic of natural leather, which is skillfully implemented by designers in their fashionable modern projects.

Nowadays, most types of leather are made from cow hides, but the skins of other animals are also used. Lamb and deer skins are used to produce soft leather, which is used to make the most expensive clothing. Kangaroo hide is used as a raw material for the production of products that need to be strong but flexible, such as leggings. Leather made from the skins of more exotic animals, particularly certain types of reptiles, was very popular in its day. Products made from it were considered the most beautiful and sophisticated. For this reason, hunting for some species of snakes and crocodiles has become so widespread that it has brought the above-mentioned species of reptiles and cold-blooded animals to the brink of extinction.