Dividing and Characteristics of Leather There are many types of raw hides used in tanning and fur, especially fur raw hides. The varieties of raw hides are more complex. The following is a brief introduction to the raw hides used in tanning. Looking at the world's tanning industry, the main raw materials for leather are cowhide, sheepskin and pigskin, in addition to some other leathers. 1. The number of cattle hides in the world was estimated at more than 1.435 billion cows in 1997. The annual slaughter rate is about 15%~25% (the differences vary greatly between countries and regions), totaling about 300 million cows. The annual output of cowhide is about 100,000 tons. It has grown in recent years. Cowhide includes cowhide, buffalohide and other types of cowhide. Cowhide accounts for about 2/3 (65%~70%) of the world's total leather production, 67% of which is used to make leather shoes, and 33% is used to process clothing, leather goods, furniture, etc. In recent years, cowhide is used to process automobile seat cushion leather. There is an increasing trend. Cowhide is the most important raw material resource for the world's leather industry. my country's annual output of cowhide is about 12 million pieces. (1) Types There are many types of cowhide, such as cowhide, beef cowhide, grazing cowhide, cowhide, bullhide, uncastrated bullhide and castrated bullhide. In our country, there are also yellow cowhide, buffalohide, yakhide and yakhide. Depending on the raw leather conditions and needs, they can be made into almost all kinds of leather products. The type, origin, age, gender, feeding conditions and methods of cowhide, climate, area size, thickness, weight grade, fat content, sweat glands and blood vessels, and hair density directly determine the tissue structure of cowhide and thus affect it. The application value of cowhide and the performance of the leather produced. The thickness of the skin skinned from slaughtered cattle varies with the breed of cattle, but is generally about 3~12mm. In the dermis used for tanning, the loose papillary layer accounts for 10% to 20% of the total thickness, the tighter fleshy layer accounts for about 70% to 80%, the epidermis accounts for about 0.5% to 1%, and the subcutaneous tissue accounts for about 70% to 80% of the total thickness. 5%~10%, the latter two are all removed during tannery processing. The area size varies between 2.0 and 5.5 square meters depending on the place of origin and age. The structure of calf leather is similar to that of ordinary cowhide, but it has a more detailed fiber weave and structure. The total thickness of rawhide is about 1.5~3.5mm, of which the papillary layer accounts for about 25%~30%, the reticular layer accounts for about 50%~60%, the surface layer accounts for about 1%, and the subcutaneous tissue layer accounts for 10%~20%. With the improvement of breeding, that is, enrichment of breeding, the fat content in cowhide is also gradually increasing. Because calfskin has very fine pores and a tight grain, it can be used to make very fine grain leather. The younger the calf, the finer the grain of the leather. However, the processing of calfskin is more difficult than that of cowhide. The main task is to open up the fat lines. Moreover, calfskin rawhide resources are limited. Calf leather is mainly used to make high-end shoe upper leather that is bright and fine-grained. Buffalo leather mainly originates from Indonesia and most areas in central and southern my country. Compared with cowhide, buffalo leather has thicker hair, sparse hair and rough grain. The surface is thicker, but the local collagen fibers are loosely woven. Generally, buffalo leather is processed into industrial leather (such as belt leather, etc.), shoe upper leather, etc. In recent years, it has been more used to make furniture leather (such as sofa leather, car seat cushion leather, mat leather, etc.). 2. Sheep skin sheep The world's total population is about 1.2 billion, with an annual slaughter rate of 25% to 45%. In 1996, the number of sheep and goats in my country was estimated to be 260 million. Sheep leather accounts for about 10% to 12% of total leather production. In addition to being used for tanning, a considerable part of sheep skin is also used to make fur (i.e. fur) and fur leather. (1) Types of sheep skin include native sheep, hybrid sheep and fine-wool sheep. Tannery generally uses native-bred sheep or hybrid sheep, commonly known as sheep leather. Native sheep skin is the best raw material for tanning. Sheep skin can be processed into clothing leather, writing and packaging leather, glove leather, and lining leather. Sheep skin with a compact structure, such as native sheep skin, can be made into shoe upper leather. Most of the sheep's lambskin and fine-wool sheepskins are used to make fur. (2) Tissue structure characteristics The purpose of raising sheep is mainly to obtain wool and meat. Generally speaking, the finer the wool of the sheep's coat and the looser the skin structure, the lower the tanning value of the skin.
The thickness of sheepskin is about 1~3mm. The rawhide contains many sweat glands and hair follicles that penetrate deep into the skin. The papillary layer accounts for 40%~60% of the dermis thickness, and the reticular layer accounts for about 25%~40%. Sheepskin contains more It has fat cells and relatively developed subcutaneous tissue. It is a fatty skin. The fat content of sheep skin accounts for about 30% or more of the skin weight. Because the structure of sheepskin is relatively loose, the leather made from it has a more comfortable feel, but its strength is relatively low. Lambskin has a similar structure, but with a finer, tighter structure. The average area of ??sheep skin is about 0.4~0.9 square meters, and that of lamb skin is about 0.3~0.7 square meters. 3. Goat leather The world's goat population is about 600 million, and the annual slaughter rate is about 20% to 40%, accounting for 8% to 10% of the total leather production. my country is rich in goat skin resources, with an annual output of about 30 million pieces, among which the goat skins from Sichuan Road and Hankou Road have the best quality. Goat skin can be used to make various leathers in tanning, including high-end leather such as polished shoe upper leather, and can also be processed into strong and durable clothing leather, writing leather, clothing leather and shoe lining leather. Glove leather with fine grain can also be made from suede. The quality of goatskin varies greatly depending on the breed, place of origin, age, and feeding conditions. It has higher fastness than sheepskin. In terms of goatskin thickness, the papillary layer accounts for about 30% to 40%, and the reticular layer accounts for about 40% to 50%. The soft sheepskin is more closely combined between these two layers. Since there are fewer oil glands and sweat glands in the skin, its sickle-shaped and orderly arranged pores form the unique and beautiful grain pattern of goat skin. Suede generally has a finer fiber weave and fine grain. The area of ??goatskin is about 0.5~0.9 square meters, and the area of ??suede is about 0.2~0.5 square meters. 4. Pigskin The world’s pig population is about 800 million, and the annual slaughter rate is nearly 100%. Pig leather accounts for about 3% to 5% of the total leather. Artificially raised pigskin is partly used to make shoe upper leather, clothing leather, bag leather, shoe lining leather and sole leather. my country is the country that produces the most pig skins in the world, and the quality of pig leather is also top-notch in the world. The proportion of pig skin suede products is also high. Pig leather and its products are mainly exported to Europe and the United States and other countries and regions. In addition to pig skins peeled from artificially raised pigs, there are also wild boar skins. The famous South American wild boar is also called PEKALI. This kind of wild boar skin has obvious pig skin pores and grain characteristics. Due to its special collagen fiber structure, it can be processed into very soft clothing leather or glove leather, which is of high value. Compared with other mammalian skins, pig skin does not have a mesh layer in terms of tissue structure characteristics. The papillary layer accounts for 80% to 90% of the total skin thickness, and the subcutaneous tissue accounts for about 10% to 20%, and is composed of fatty connective tissue and muscle. In addition, pig skin has a high fat content, accounting for about 20%-30% of the skin weight. The location difference is large, and the thickness difference ratio is as high as 1: (3~5). The pores are thick and arranged in a "pin" shape, which constitutes the unique grain characteristics of pig skin. Due to shortcomings such as thicker pig skin grains and larger area differences, pig breeds have been improved, such as lean pigs with smaller area discrepancies and finer grains. In addition, the quality of pig skins in different regions and different pig breeds in my country is not only large in output but also of good quality. In other areas, especially in the north, pig skin is large, with thick pores, obvious location differences, poor quality, and low peeling rate. The area of ??pig skin is generally 0.7~1.3 square meters. 5. Horse Hide There are about 66 million horses raised in the world. In terms of species, there are domesticated tame horses and wild horses. Compared with cowhide, horsehide has a looser nipple layer. The biggest feature of horsehide is that it has very dense and strong crotch skin. Strand leather is more difficult to process and is generally made into solid bottom leather or special industrial leather. Someone in our country has studied and solved the problem of leather tanning and applied for a patent. Other parts of horsehide can be used to make clothing leather, shoe upper leather, sofa leather, etc. 6. Reptile skins Reptiles are mainly distributed in the equatorial region of the earth, and the amount of artificial breeding is also large. The protection of wildlife should be considered during processing. Reptile leather accounts for less than 0.2% of leather production. Types include crocodile skin, short-nosed crocodile skin, lizard skin, snake skin, bullfrog skin, etc. The surface of crocodile skin is composed of a special cuticle that is not easily deformed. The longer the crocodile skin grows, the harder and more prominent the horny "scales" on its surface become. Crocodile leather only has two-dimensional fiber weaving, so it is less elastic and difficult to make leather with good feel.
But the advantage of this type of leather is that it has good formability and a special appearance. Therefore, crocodile leather is highly valuable. Crocodile skin belly leather is mostly used to be processed into leather bags, leather shoes, etc. A small number of crocodile skins with distinct horny "scales" are used for wall decoration. In short, crocodile skin is a rare and valuable leather. Lizard and snake skins have different grains and grain patterns due to the diversity of their species. Generally, "scales" are attached to make leather with a beautiful three-dimensional grain pattern. For lizard skin or snake skin with beautiful color and pattern, measures can be taken to retain its beautiful grain color during processing. Snake skin is thin and has low strength. It is generally used for the decoration of bags and shoes or as the veneer of high-end belts and watch straps. Bullfrog leather is unique due to its interesting raised dotted grain. Nowadays, more bullfrogs are raised in some areas of our country, which is also an available breeding resource. 7. Fish skin The amount of fish skin tanning worldwide is very small, accounting for less than 0.1% of the total. Seawater fish skins include shark skin, cod skin, anchovy skin, eel skin, etc.; freshwater fish skins include grass carp, carp skin and other scaly fish skins. Most fish skins have scales. The removal of scales during tanning processing leaves "scale nests" on the leather surface, giving fish leather a special three-dimensional appearance. Fish skin has the characteristics of a "layered" woven structure, and the connections between the layers are weak. Therefore, if the meat is removed excessively, the mesh layer of the fish skin will be easily thinned. Many fish skin species are sensitive to high temperatures and highly concentrated chemicals, which can easily lead to excessive protein hydrolysis. There are few marine fish skin resources in my country, but freshwater fish are cultured in large quantities and are widely distributed. Freshwater fish skin (such as grass carp, etc.) resources can be used for tanning to make novel leather with special appearance. Fish skin can be used for packaging, decoration and embellishment of leather shoes. 8. Other leather types account for less than 1% of the total leather, including deerskin, antelope skin, camel skin, kangaroo skin, ostrich skin, emu skin, etc. The structure of deerskin is similar to sheepskin and is used to make soft clothing leather, oil-tanned wipe leather, aviation kerosene filter leather, etc. Camel hide is used to make shoe upper leather. Kangaroo leather is mainly produced in Australia. It has fine grain and can be processed into packaging leather and shoe upper leather. Ostrich skins are mainly produced in Africa and other places. They are now artificially raised all over the world, and my country has a large number of them. It is estimated that 100,000 people are skinned every year, and the number of breeding and skinning is gradually increasing. Ostrich skin has a larger width (about 0.8~1.2 square meters). After the large feathers are removed, the prominent "pore cap" is left. This feature makes ostrich skin a rare and valuable species. Ostrich leather is mostly processed into high-end packaging or used for decorative embellishments on leather shoes. Ostrich claw leather has a very beautiful appearance and can be used to make high-end leather shoes or belts. Emu leather is similar to ostrich leather, but its width is smaller (about 0.3~0.5 square meters). Its pore characteristics are not as prominent as ostrich leather, and the effect is obvious. It can be processed into glove leather, clothing leather, etc. Other leather types include dog skin, rabbit skin, etc. In short, cow, sheep and pig skins are the three main types of raw materials for tanning. Other rare leather types occupy a certain share in the leather market because of their unique appearance. However, the quantity is generally smaller and the price is higher. . Color quality requirements Color and aesthetics of coat The natural color of coat plays an important role in identifying the quality of fur. The color of hair fibers is determined by the pigments present in the cortex and medulla. Melanin and brown pigment are common pigments in the animal kingdom, and many other colors are adjusted by the content and mixture of these two pigments. Pigment has two states, one is granular, which produces darker colors; the other is diffuse, which produces lighter colors. Hair fibers appear yellow, brown, or brown due to different proportions of brown pigment; melanin appears gray or black. When black and brown are mixed, different shades of brown or earthy yellow are produced depending on the content of one of the pigments. If pigment is missing, it appears white. The average length of the pigment particles of standard color mink is 0.68 microns, and the pigment weight accounts for 4.3% of the wool fiber; the size and shape of the dark brown pigment particles of silver-blue mink are not very regular, with a length of 0.19 to 0.28 microns, accounting for 1.3% of the fiber weight; The pigment weight of brown mink accounts for 2.3% of the wool fiber. The colors and tones of the coats on different parts of most animals are different, and even the colors at the upper and lower ends of the same hair fiber are different. The luster of hair is related to its surface shape and structure. The finer the hair, the greater its surface curvature, the smaller the total reflection of light, and the greater the diffusion formed by the internal and external reflections of the hair, so it makes the light particularly soft, similar to silver light. The luster of the hair is also related to the close arrangement of the scales on the hair surface.
Generally speaking, the thinner the scales, the closer they are to the hair shaft, the smoother the surface, the stronger the reflection, and the brighter the luster, so the reflection of coarse hair is relatively strong. If the hair is corroded by chemicals or bacteria and the scales are damaged, the luster of the hair will become darker and it will not be dyed in bright colors, and the appearance quality will be affected. The color and luster of the coat are related to the beauty of the fur. Different coats have unique coat tones. Therefore, the requirement for coat color lies in whether the coat color matches the animal shape and whether the coat color is correct. All animals with the same coat color must have the same pure and consistent coat color throughout their skins. No different-colored hairs are allowed. The color should be consistent throughout the body and should not be darker or lighter. The coat is composed of two or more colors of plush, which should be matched and coordinated to form a natural and beautiful tone; animals with markings and spots should have clear and obvious markings and spots; for animals with flower bends and patterns, Fur should have tight and tight curls, with many and obvious patterns; fur with a large distribution area and floral bends should have tight tufts, with many, even and obvious bends, and less fuzz. This kind of fur is mainly for appearance and supplemented by warmth. Because they have unique patterns and spots, their shape, quantity and distribution have become one of the important indicators that determine the quality of this type of fur. Since the color and beauty of the fur are related to the value of the fur, people often use low-grade fur to imitate high-grade fur, such as rabbit skin to imitate "mink" and sheep shearling to imitate striped "tiger skin" and "leopard skin". wait. If necessary, turn the raw hide over and turn it over into a tubular shape so that the sock-like leather panel faces outwards. The operation is as follows: Hold the neck of the hide with your left hand, put your right hand into the mouth hole, push it in, push it deep, and finally push out the buttocks to flip it over. . The operation of changing the cylindrical skin from the plate facing outward to the plate facing in: push the arm inward and push it until it comes out of the mouth hole and it will turn over. Note that pushing is necessary. Start from the arms and do not pull hard. Do not pull the fur through the mouth hole to pull the skin out. Push it out gradually. If the leather board is very dry and fragile or the leather board is thick and needs to be turned over, then rewet the leather board until it can be turned over. If the plate of the tube-shaped or sock-shaped skin is facing inward, put a wet cloth through the mouth hole to wet it, and then turn it over after a certain period of time. It is not advisable to turn over the dried skin as it will tear the skin. If flipped, proceed as above. Raw skin shaping: After the raw skin is peeled, degreased, fleshed, and cleaned, the fresh wet skin needs to be straightened and flattened immediately according to standards, without creases, evenly dried, and the length and width of the skin meet the specified requirements before it is sold. According to the characteristics of each raw material leather, the corresponding drying and forming dimensions are recommended to become the most effective leather shape. The instrument used to dry and shape the skin is a last board, which is composed of a whole wooden board or two half-drawn wooden boards. For fox, raccoon dog and other raw material skins, planting boards with small heads and large bottoms are commonly used. The length and width of the last board should be suitable for the size of the hide. For example, a large fox fur last board is 125cm long, 16-17cm wide at the lower end, and 13-14cm wide at the upper end. The edges and corners of the last board are rounded and smoothed to avoid damaging the skin. A swinging last board is made of round sticks with a wedge-shaped head; a movable last board made of laths has a metal plate clamp at the top. The opening angle of the plate clamp can be adjusted according to the type and size of the hide. Round sticks and laths The lower end of the last board is fixed with ropes and laths, and then the dried skin is adjusted. Preservation of raw leather: The method of preventing microorganisms from multiplying in the moist leather and damaging the hair when the moisture content of fresh leather reaches 60% is called anticorrosion. Bacteria that destroy raw material skins are generally called putrefactive bacteria. In a humid environment, putrefactive bacteria on the skin will multiply more quickly. During the period of reproduction and growth, a rancid smell is emitted from the skin. Fresh wet leather panels are most susceptible to rot and acne when they are in a warm and humid environment without oil removal. The fur has been damaged before the rancid smell is smelled. Therefore, anti-corrosion treatment is an indispensable process. Preservative methods include sweetened plate method, dry salt method, wet salt method, freezing method and acid salt method. The sweet drying method occupies a large proportion of the skins slaughtered and purchased separately because this method is simple and easy to implement, that is, it does not require the addition of salt and relies on warm air convection to dry the skins. The sweet drying method can be dried outdoors under a shade or in an indoor greenhouse at 25-35°C. The skin should be as close to the ceiling as possible because the temperature of the ceiling is relatively high. Putrefactive bacteria develop and multiply in the early stages of fur drying. When the moisture content drops to 10% to 15%, the leather board is still relatively soft, and the putrefactive bacteria can no longer develop and lose their destructive power to the leather board. The drying time depends on the thickness of the skin. Thin skin dries quickly and thick skin dries slowly. The skin is considered dry only when the thick areas are dry. Use the touch method to determine the degree of dryness, especially the thick parts and parts that are not easy to dry such as the head, nose, tail, etc. When the drying temperature exceeds 40°C, the leather is easy to gel, the leather board is easily brittle, and the wool quilt is not strong.
Therefore, drying is not allowed under the hot sun and within 0.5m from the fire. The salting method uses table salt or brine to treat the prepared fresh skin, causing the bacteria to lose water and shrink, thereby inhibiting bacterial activity. The advantage of this method is that it has little impact on the quality of the raw leather and can be stored for a longer period of time. Salting method is divided into salting method and brine soaking method. The salt-drying method is a combination of salting and natural drying, that is, salting the skin first and then drying it to reduce the moisture content of the skin to 18% to 20%. It is easier to soften than sweet dry leather, and the leather will not be stiff, broken or insect-eaten during storage. The freezing method inhibits the activities of bacteria and enzymes on the skin through freezing, thereby achieving the purpose of antisepsis. The freezing method is mainly used in northern areas, where the climate is cold in winter and the water in the fresh skin is not easy to evaporate. It is best to make full use of freezing to prevent corrosion. Some factories have built cold storages to store fresh skins at 5 to 0°C without using salt at all. Before putting the skins in, the temperature can be raised to thaw before use. The acid salt method is to sprinkle a mixture of table salt (85% to 90%), aluminum alum (5% to 8%) and ammonium chloride (5% to 8%) on the leather board and rub it into the skin. Then pile up at least 3 to 4do Aluminum alum is a large crystal, which should be crushed first, and then the components are carefully mixed (turn in a drum or turn over with a shovel on the floor several times) for application. The dosage of the mixture is 30% to 50% of the weight of the fresh skin. This method is suitable for the preservation of sheepskin, lambskin, rabbit skin, marmot skin, etc. Formaldehyde is a strong preservative that can kill a variety of microorganisms. Formaldehyde rule uses formaldehyde solution to treat raw hides. Due to the antiseptic and tanning effects of formaldehyde, the reactive properties of hide proteins are reduced and the hides are dehydrated, thereby preventing the hides from decaying. However, industrial formaldehyde contains formic acid, which has adverse effects on proteins, especially the epidermis. Sodium thiosulfate should be added to formaldehyde. In order to reduce the volatilization of formaldehyde, ammonium sulfate combined with formaldehyde can be added and processed in closed equipment.