How to classify leather grades?

Before we start talking about cowhide, let's talk about "skin" and "skin". Many people are vague about this concept. Nowadays, many people often refer to leather as leather for short and artificial leather as leather for short. This statement is incorrect and inaccurate. Skin refers to the state that collagen fibers of skin are still in animals (referring to chemical structure, without any treatment); Leather refers to the physical and chemical treatment of animal skin to remove useless components in the skin and change the chemical structure of skin collagen fibers, making them different from those in animals. Leather is soft and elastic in dry state and not easy to rot in wet state. Leather is the raw material of tanning, and leather is made of leather. Now "leather" is a fixed noun, which refers to the chemically treated "leather". Now some people call natural leather "leather" and unnatural leather "leather" in order to distinguish natural leather from synthetic leather. Cowhide is the most commonly used natural raw material, accounting for 2/3 of the total leather production in the world, of which 2/3 is used to make leather shoes, and the rest is used to process clothes, bags and furniture. The variety, origin, age, sex, feeding conditions and methods, climate, area size, thickness, weight grade, fat content, sweat glands, blood vessels and hair density of cowhide directly affect the price and product performance. According to texture: cowhide can be divided into multiple layers (up to 8 layers). The outermost layer is the first layer with the best quality, followed by the second layer, which is not as good as the first layer in strength, elasticity and air permeability. The first layer of kraft paper is the leather with textured surface of cattle, sheep and pigs. There are natural scars, traces of blood tendons and other primitive skin features on the skin surface, and occasionally there are knife wounds during processing and extremely low utilization of stomach parts. The first layer of kraft paper is composed of dense and thin fiber layer and slightly loose transition layer closely connected with it, which has good strength, elasticity and process plasticity.

The second layer of skin is sliced by a peeler, which is the loose second layer of fibrous tissue, that is, the lower layer of dermis. It is made by spraying chemical materials or coating films. The second layer of leather has only a loose fibrous tissue layer, which can only be used to make leather products after spraying chemical materials or polishing. It maintains some characteristics of natural elasticity and processing plasticity, but its strength is poor. Recycled leather is made by grinding waste skins and leather scraps from various animals and mixing them with chemical raw materials. Its surface processing technology is the same as leather trimming and embossed leather, which is characterized by neat edges, high utilization rate and low price. However, the leather body is generally thick (not thick) and its strength is poor.

The above kinds of leather are often used to make bags and car leather seats. But the top layer of cowhide used in the car must be a very high-end car. For example, the BMW 5 Series is only high-end, and almost all domestic cars are recycled leather (not black-hearted, but can't use good materials if they can't afford to sell). General furniture and sofas are made of recycled leather or double-layer leather. There is less recycled leather for leather shoes (because of poor strength), unless it is extremely cheap or used for local collage. Surface quality: According to the surface quality, cowhide can be divided into full grain upper leather, half grain upper leather and trimmed leather. Full grain leather is divided into soft leather, wrinkled leather and front leather. It is characterized by completely retaining the natural grain surface of leather, clear, fine and dense pores, irregular arrangement, plump and meticulous surface, elasticity and good air permeability, and it is a high-grade leather. Leather products made of this kind of cowhide are comfortable, durable and beautiful. Semi-grain cowhide is called semi-grain cowhide because the surface is slightly damaged, so it is polished into a light grain surface. It still maintains some styles of natural leather, with flat oval pores, irregular arrangement and hard feel. Generally, rawhide with poor grade is selected, so it belongs to mid-range leather. Due to the particularity of the process, its surface has no damage and scar, high utilization rate, and the finished product is not easy to deform, which is generally used for products with large area.

Leather trimming is characterized by a flat and smooth surface, without pores and dermatoglyphics. In the production process, the surface grain surface is slightly polished, and then a layer of colored resin is sprayed on the leather to cover the leather surface lines, and then a water-based light-transmitting resin is sprayed. In fact, disabled or rough natural leather is "cosmetic surgery". This kind of leather has almost lost its original surface state, and the pattern has been processed and unnatural. Smooth cowhide belongs to the category of shaved cowhide. Because of the different surface brightness, there are two kinds of matte cowhide and smooth cowhide. Matte cowhide has no luster. Bright cowhide uses a colorless resin with high brightness and good light transmittance in the bright layer, through which the following colors appear. Its leather surface is bright and dazzling, showing a gorgeous style, and it is a popular leather of fashionable leather goods. Cattle of different sizes: fetal cowhide, calf skin that died in the fetus or died after birth, with tender and smooth leather, moderate thickness, clear tread, good hand feeling and good elasticity. Fetal cowhide belongs to full grain leather in natural leather. Small pores, uniform and tight distribution, fine grain surface, plump and bright skin surface, thin skin, tight tissue fibers, uniform thickness and soft skin plate; It feels firm, elastic and breathable. Now some merchants generalize the concept of fetal cowhide for their own interests and needs. They are actually talking about calf leather that is tender than calf leather. Fetal cowhide is very fragile and easily damaged. Generally, it is not used to make leather shoes, but it can be used to make wallets. Calfskin/calfskin, calfskin under two years old, has smaller pores than Daniel, strong pulling force but higher price. Calfskin is a high-grade variety of cowhide, because its pore surface is small or clear. The so-called calf leather was slaughtered when the cow was still young. The size of each calf leather shall not exceed 15 square feet, and the leather shall be soft and smooth. Calfskin is one of the best raw materials for making leather upper leather, but it is more difficult to process than adult cattle. This is of course the reason why the price of this kind of leather after processing is higher than usual. The calf skin is tender and smooth, with moderate thickness, clear lines, good hand feeling and good elasticity. Then there is cowhide, which is not as delicate as calf leather in color and feel.

Regarding the identification of cowhide, what kind of cowhide is calfskin? Take a new cowhide product and curl it slightly. The finer and more uniform the wrinkles, the smoother the leather and the younger the cow. For the problem of making shoes with leather, cowhide is the best in the posterior cortex, followed by the abdomen and the shoulder and neck position is the worst. A good shoe factory only takes the best parts, and a slightly worse shoe factory will use them. The local cortex of the upper (such as the head before the three customs) is the best, and other parts are not as good as the upper. If it is a high-end brand, you generally don't have to worry too much about materials, let alone customization. In terms of materials, they will pay attention to one principle, that is, the same pair of shoes use the same leather, the parts are similar, the leather faces are symmetrical, the thickness is uniform, there is no obvious difference, the fiber thickness and fiber density are equal, and the rejection rate of good shoe factories will be higher. Variety and origin of cattle: cowhide, cowhide and calf leather are often said to belong to cattle. Due to the subtle differences in various parts of the body, the utilization rate of cowhide is very high. Some leather companies, such as Dooney &; Bourke, their most famous fabric is waterproof cowhide with special treatment and natural shrinkage, which ensures the durability of handbags; Among cowhide, buffalo hide ranks the lowest, because the whole area is large and the skin is thick and heavy, so it is often used to make sofas, mattresses and the like, and some shoes are made of buffalo hide. Cattle will leave some defects in the process of growing up, such as scars left by skin damage and stinging eyes left by mosquito bites. Will affect the quality of cowhide. Some obvious scars cannot be completely eliminated in the production process, and the first-class cowhide pays great attention to the surface appearance. For example, in Africa, due to climatic reasons, cows will inevitably leave scars and eyes, and most of the cowhide produced is low-grade cowhide. But good quality cattle will pay attention to this problem during their growth. The United States is the largest producer and exporter of cowhide in the world. Most cattle in the United States are kept in captivity, commercialized, suitable for the environment and advanced in slaughtering methods (mostly mechanical peeling), so the supply of raw cowhide in the United States is stable, the price is high and the quality is good. Brazil is the second largest producer of cowhide in the world. Argentina, Uruguay, Venezuela, Mexico and so on. It is also an important producing area of middle and low-grade cowhide. Europe is the most important exporter of raw cowhide in the world. The main exporting countries are Britain, Ireland, Belgium, Russia, France, Germany and Portugal. Generally speaking, the climate in Europe is suitable for grazing and the feeding methods are advanced, so the German cowhide, British cowhide and French cowhide in this area are all good raw materials for tanning. The good quality of Italian cowhide is due to the high development of Italian animal husbandry, suitable temperature, gnats, gnats and so on. And insects bite cattle and sheep less, so that the skin of cattle and sheep has no scar and high quality. Moreover, the cowhide raised indoors in Italy is characterized by natural disability, less scratches and cleaner skin. Powerful processing technology claims that a piece of cowhide can be divided into 1 1 layers. High level of raw material processing technology. After slaughter, it is refrigerated with ice cubes and immediately sent to the processing site. There is no need to preserve hides with chemical materials. Good processing technology, artificial curing or salting machine, compared with drum curing and salt bath dipping, has less mechanical action and operation of fur, less grain surface damage, and the grain surface and meat surface look cleaner, so the grade rate of blue wet leather and finished leather is higher.

Tanning technology: Tanning is an important technology for tanning and fur making. The physical and chemical process of changing rawhide into leather with tanning agent is called tanning. This is a process, in which the combination of hide and tanning agent degenerates the hide into non-perishable leather. The main tanning methods are vegetable tanning, chrome tanning, aluminum tanning and oil tanning.

Vegetable tanning is the processing of leather with vegetable tanning agent. The processing process is relatively environmentally friendly, but the color is limited, and many bright colors cannot be dyed. General vegetable tanning is the best choice for primary color leather goods and leather carving. Tanning refers to plant tissues, such as wood, bark, fruit, leaves and roots. It is rich in vegetable tannin (tannin content is 8%) and has industrial development value. After vegetable tanning treatment, it has good formability, full and elastic board surface and no greasy feeling; The grain surface and suede surface of leather are shiny, easy to soften when absorbing water, and have strong plasticity and easy to shape. The color ranges from light pink to light brown, which is most suitable for leather carving.

Vegetable tanned leather is tanned with natural vegetable tanning agent, which is very environmentally friendly. Vegetable tanned leather is easy to deform when it meets water, and it will be shaped if it is not treated in time. Because of the water absorption characteristics of vegetable tanned leather, the leather shoes made of vegetable tanned leather have the best hygroscopicity. Although the color of vegetable tanned leather is limited, it can be made into various bright colors by brush coating technology because of its good color adhesion. For example, Berluti, France's top leather shoes brand, has exquisite colored craft leather shoes.

Chrome tanning is the tanning of leather with chrome salt, which is trivalent basic chrome salt, the common chrome tanning agent is commercial chrome salt essence, and the effective component is basic chrome sulfate.

When chrome tanned leather is deformed by heat, it is not as waterproof and hygroscopic as vegetable tanned leather. Leather tanned with it is washable, storable and stable. Aluminum tanning, aluminum salts mainly include aluminum alum, aluminum sulfate and aluminum chloride (aluminum tanning agent). Alum is called alum for short, and there are three categories: potassium alum, sodium alum and ammonium alum. Ammonium alum is commonly used because of its good solubility. Vegetable aluminum combined tanning (aluminum retanning) with aluminum salt and vegetable tanning agent can increase the shrinkage temperature of leather, improve sweat resistance and flexibility, and save tannin extract.

Aluminum tanned leather is characterized by white color, softness, good ductility, moderate temperature resistance and water resistance. Tanning agent will be washed off when it meets water or is washed in water, resulting in drying and hardening after tanning.

Leather tanned by oil tanning method or oil tanning method is called oil tanning leather. The commonly used oil is marine animal oil, because it is rich in unsaturated fatty acids, contains at least two double bonds, and has high iodine value and low acid value. Skin treated with this oil will slowly oxidize under certain temperature and humidity conditions, and its oxidized polymer will wrap the collagen fiber, making the collagen fiber active and hydrophobic. The generated aldehydes and other oxides are crosslinked with skin collagen for tanning. Work boots made by this tanning process are more resistant to dirt.

Surface treatment technology of cowhide: In addition to primary colors, there are many unique colors of cowhide products on the market, which requires surface treatment of cowhide. Here are some surface treatment techniques.

Embossed leather and cowhide embryos are pressed with steel patterns under gravity embossing machine to make various patterns of leather products. Litchi pattern embossing is a very common style, which is mostly used for packaging products. Full grain (top layer) cowhide is often not used to make embossed products, because full grain itself is a symbol of quality.

Polished leather is a traditional leather treatment method. Casein is used as the surface coating, and then the leather surface is polished repeatedly with a machine glass roller to produce elegant transparent luster. This leather is called polished leather. At present, it is still used in high-grade calf leather, lambskin and snakeskin, and is suitable for high-grade leather shoes. This kind of leather shoes is favored in Europe because of its poor water resistance and bright colors.

Patent leather, the traditional patent leather finishing is a very labor-intensive method, which uses hot linseed oil for finishing, also called hot patent leather finishing. At present, the cold paint coating method is used to produce paint skin, that is, a thick layer of polyurethane brightener is coated on the bottom of pigment paste resin to obtain a high-gloss surface layer. The patent leather should be genuine leather, and the patent leather of artificial leather is airtight to wear.

Polishing effect The bottom of leather is painted with light color and the surface is sprayed with dark color. According to special needs, it can produce beautiful color gradient effect after wiping off or rubbing with cloth wheel, and then it can be used as cover and decorative surface.

Mucosal skin, commonly known as "flocking skin", is characterized by long fluff and good appearance, but it is easy to wear.

Waxing leather and polishing leather on cloth wheel with some synthetic wax can produce the effect of discoloration and carbonization. Waxed leather requires fine pores and no scars on the surface. The pores and skin lines of the finished product are very clear, and the surface luster is natural. After waxing, the skin is easy to absorb moisture and is easy to change color after being contacted by sweat and water. Special attention should be paid to prevent oil, coffee, milk and other liquids from dripping on the leather surface, so it is not allowed to wear it in rainy days.

Sanded leather: the surface of the rawhide is sanded into a sand surface with a sander, and then dyed with water. Frosted leather shoes have excellent comfort, small fluff and good feel, just like the surface of flannel, which is an important material mainly used for shoes that pay attention to warmth.

Scraping the oil skin with nails or applying it by hand will lighten the color, but it will return to normal after being smoothed by hand. It is characterized by sticky oil feeling, and the raw materials for coating coloring are color-changing grease and metal complex dyes. This skin has both aniline effect and cortical discoloration effect. Strong moisture resistance, weak leather brightness and good hand feel, so we should pay attention to professional nursing. Most of the shoes made of this kind of oil leather are casual shoes, and the common colors are black, dark brown and brown.

There are two kinds of skin falls: natural falls and crushing falls. Cowhide is soft, feels more comfortable and delicate, and looks more beautiful. It is widely used in bags and clothing. Generally, broken skin does not need grain surface, so some defective and imperfect skin can be well utilized through treatment.

Turning hair, also known as anti-hair, is divided into two layers: forward turning hair and reverse turning hair (commonly known as "first turning hair"). The second layer of inverted fur is to remove the epidermis of leather, expose the fibers in the dermis, and then process it by machine. Excellent air permeability, no crease when wearing, but the cortex is thin and weak. The second inversion is to turn the original leather upside down, with the dermis facing up and the epidermis facing down. It only carries out surface treatment on the exposed dermis, and the cortex itself is not destroyed, which is relatively firm compared with the other way around. Some military boots are made of this material and are very durable.

NAPPA has also been widely used in recent years. Napa mainly refers to a style and a representative craft. Now Napa is usually called the first layer of good quality cowhide. Napapie is soft to the touch. Because of its high cost, only luxury models will use Napapi as leather seats and interiors.

These are just some of the processing techniques. Some brands will have their own exclusive leather processing techniques, which also meet the various needs of consumers for leather patterns and colors. The above is just sitting in the well and watching the sky, throwing a brick to attract jade, and experts are welcome to criticize and correct me.