What is leather? The raw hides with roughly complete original structure are tanned into non-perishable materials; the hairs on the hides have generally been removed, but they may not be removed deliberately. Leather can also be made from raw hides or skins split into several layers. Splitting can be carried out before or after tanning (QB/T 2262-1996 Leather Industry Terminology). Note: If the tanned leather is crushed by a machine or chemically made into fibrous particles, small pieces or powder, and then it is made into flakes or other shapes regardless of the use of bonding without adhesives, such flakes or other shapes Nothing can be called leather. Raw material for tanning The raw material for tanning is animal skins, and most animal skins can be used for tanning. Although there are many types of raw skins for tanning, according to a series of laws and regulations such as the animal protection regulations issued by the international, the raw skins that can be used for production are subject to certain restrictions to some extent. Pigskin, cowhide, and sheepskin are of good quality. With large output, it has become the most common and commonly used leather raw material in our lives. The difference between raw hide and leather. Pig leather: The pores on the surface of pig leather are usually arranged in groups of three, arranged in a 'product' shape. Among the three pores in a group, the middle pore is the largest and the angle with the grain is the smallest. The pores of pig skin almost traverse the entire thickness of the skin, and are deep. Because the pores of pig skin are larger than the fat cone formed on the meat surface layer, the papillae on the nipple layer are higher, so the grain surface of the pig leather is rougher. The subcutaneous adipose tissue of pigskin is well developed, and subcutaneous fat cells grow into the dermis. After the skin has been degreased into leather, the fleshy surface of the skin shows a fat cavity. The whole piece of pig leather has a large difference in parts. The buttocks are thicker. The collagen fiber bundles are cross-woven, with very strong strength and low extensibility. The collagen fibers on the back and abdomen are woven obliquely, and the thickness and strength are not as good as hip leather. Scalp leather: The surface of the scalp leather board has small and dense pores, smooth papillae, and fine grain. The pores are oblate, compact and even, arranged irregularly, like a starry sky. Needle hair roots grow deeper into the skin, and villi roots grow shallower into the skin. The sweat glands are well-developed and grow at the junction of the papillary layer and the reticular layer. In the dermis, the papillary layer and the reticular layer are clearly demarcated. The papillary layer accounts for about 20% of the total skin thickness. The collagen fiber bundles are thinner, and the collagen fiber bundles in the reticular layer are thick and tightly woven. The yellow cowhide board has a large width, the thickness of each part is relatively uniform, and the difference between parts is small. Buffalo leather: The width of buffalo leather is larger, thicker and uneven than that of cattle, with thick pores and irregular dots. The papillae on the grain surface are tall, dense and have deep wrinkles. Therefore, the buffalo cowhide has a rough grain surface. There are many fiber bundles at the junction of the papillary layer and the reticular layer. The fiber bundles are small, tightly woven, and relatively thin, accounting for about 4% to 12% of the total thickness of the skin; the net-like layer is particularly thick, almost entirely composed of collagen fibers, the fiber bundles are thick and the weaving is loose, and the main direction of the fiber bundles is ' Head to tail'. Sheep leather: The pores of sheep leather are composed of needle pores and down pores. Several needle hairs and down pores form a group, arranged in a semi-crescent shape. There are many fat cells in the sheep leather skin board, and the fat content accounts for about 30% of the cortex. The grain layer accounts for 50% to 70% of the thickness of the dermis, and some even reach 80%. There are many fatty glands, sweat glands, hair follicles and other tissues, and the pores and papillae are small, so the sheep leather feels more comfortable and soft, smooth and delicate, and has great extensibility. Because the tissue structure is relatively loose, the fiber bundles of the reticular layer are relatively thin, mostly parallel to each other, and the strength of sheep leather is lower than that of goat leather. Goat leather: The pores of goat leather are small, flat, and evenly arranged in a corrugated shape. The pores are generally divided into inner and outer layers. The outer layer is needle pores, and the inner layer is fluff pores. The needle hairs are basically arranged in three layers. It is a group, arranged in the shape of '一' or '品' to form the unique structure of the pores of the goat grain. Goat leather board fiber weaves tightly, and its grain surface roughness, smoothness and hand feel are slightly worse than that of sheep, but its strength is higher than that of sheep and lower than that of cowhide. The grain layer occupies about 50% to 70% of the dermis. The papillary layer in the dermis is tightly organized with less fat, and the reticular layer of collagen fibers is also tightly woven. Deer leather: Deer leather has a thicker plate, with a thicker grain surface layer than a mesh layer. The grain surface is similar to goat skin. Because it contains a large number of glands such as fat glands, the finished leather is softer and has larger pores than sheepskin. Arranged in the shape of 'oneKangaroo leather: Kangaroo leather board has a unique fiber structure, and the whole piece is triangular.
