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Artificial leather is a plastic product that looks and feels like leather and can be used instead of leather. It is usually made of fabric as the base, coated with synthetic resin and various plastic additives. There are three main types: PVC artificial leather, PU artificial leather and PU synthetic leather.
In the 1980s, expensive leather clothing and leather materials were unaffordable for most people. In response to market demand, artificial leather that imitated leather became popular and was widely used in clothing and bag making. Such imitation leather clothing and bags once flooded the streets, satisfying people's desire to wear leather. Compared with leather, artificial leather is easy to age and wear, and it is harmful to human health because it contains a large amount of chemical raw materials. In addition, the clothing and bags made of it are gradually losing the market due to their lack of durability until they are replaced by other raw materials.
In China, people are used to calling artificial leather produced with PVC resin as raw material PVC artificial leather (referred to as artificial leather); artificial leather produced with PU resin as raw material is called PU artificial leather (referred to as PU leather); artificial leather produced with PU resin and non-woven fabric as raw materials is called PU synthetic leather (referred to as synthetic leather).
A plastic product similar to leather. Usually with fabric as the base, a layer of resin mixture is coated or pasted on it, and then heated to plasticize it, and rolled flat or embossed to obtain the product. It is similar to natural leather and has the characteristics of softness and wear resistance. According to the type of covering, there are artificial leather for shoes, artificial leather for bags, etc. according to the use.
Early 20th century
Nitrocellulose varnished cloth made by coating fabric with nitrocellulose sol is the pioneer of artificial leather.
1930s
The industrialized production of polyvinyl chloride opened up new raw material resources for artificial leather and promoted the development of artificial leather production. The paste made by adding plasticizers, stabilizers, etc. to polyvinyl chloride is easy to color. After the coating is gelled, it can be made into a variety of products with leather-like appearance by printing, embossing or embossing and printing. Although its air permeability and moisture permeability are not as good as natural leather, it has certain strength and wear resistance. In particular, it is easy to produce, has abundant raw materials, uniform product quality, is easy to cut and use, is light, water-resistant, and has low cost. Therefore, it is widely used in the production of clothing, shoes and hats, luggage, furniture, decorations and various industrial accessories. With the development of plastic varieties and processing technology, artificial leather has formed a variety of product series. In addition to polyvinyl chloride, the raw materials of the coating layer also use polyamide, polyurethane, polyolefin, etc. There are also many varieties of base fabrics, such as plain cloth, canvas, knitted cloth, raised cloth, non-woven fabrics, etc. The production of artificial leather of different varieties and colors also differs from the coating and gelation methods of the base fabric surface layer, as well as the finishing process, such as the order of embossing, printing, surface treatment, and the composition of the surface treatment agent.
The development and application fields of China's artificial leather industry
China's artificial leather and synthetic leather industry is a new industry after the founding of the People's Republic of China. It started to develop in the late 1950s and is one of the earlier developed industries in the plastics industry. After decades of construction, the artificial leather and synthetic leather industry has a considerable economic scale; with the development of high technology and the application of advanced process equipment in China and abroad, the industry management, technical level, and product grade have made a fundamental qualitative leap. Artificial leather and synthetic leather have developed into one of the important industries in the daily consumer products industry, and have entered the ranks of world powers at the same time as the entire processing industry. It is a major producer, consumer, and import and export trading country in the world.
1. Distribution characteristics and explanation of the artificial leather and synthetic leather industry
1.1 The regional distribution of enterprises is relatively concentrated in developed urban areas such as Jiangsu, Zhejiang, and Guangdong
China's artificial leather and synthetic leather production enterprises are mainly distributed in the Pearl River Delta, the Yangtze River Delta, Beijing, Tianjin, Hebei, and developed coastal provinces and cities such as Hunan and Shandong Peninsula. There are nearly 1,000 artificial leather and synthetic leather enterprises above designated size in the country. We analyzed the data of more than 400 enterprises: the total number of enterprises in East China and Central and South China accounts for more than 60%, more than 200 in Jiangsu and Zhejiang, and more than 30 in Hebei Province. According to incomplete statistical data, they are mainly concentrated in coastal areas and provincial capitals. There are more than 100 in the "Wenzhou Synthetic Leather Capital" area developed in the Wenzhou model, and there are 22 artificial leather production bases in Zhouzhuang Town in the form of Jiangnan model.
1.2 Huge increase in production capacity and leading modernization level of large enterprises
According to data, there are 1,000 domestic production equipment for artificial leather and synthetic leather in China, and the imported equipment mainly comes from Italy, Japan, South Korea, Hong Kong, Taiwan and other countries and regions. The production capacity and production technology of Chinese-foreign joint ventures and Chinese equipment have fully reached the advanced level of developed countries. In 2001, the output of artificial leather and synthetic leather was 510,000 tons. For example, the output of PVC artificial leather and synthetic leather in Jiangsu accounted for 35.7% in 2001; Guangdong accounted for 26.8%, and Zhejiang accounted for 17.6%; for example, the output of PU artificial leather and synthetic leather in 1999 was 131,000 tons; Zhejiang accounted for 35.1%, Guangdong accounted for 19.5%, and Jiangsu accounted for 20.6%. Among them, functional mid-to-high-end products accounted for one-third. Most of them are practical artificial leather and synthetic leather. According to our statistical analysis of enterprises across the country, there are 107,000 industrial workers, with annual sales of more than 15 billion yuan, total assets have reached more than 12 billion yuan, and economic benefits are growing continuously.
1.3 The formation of the composite manufacturing industry chain of artificial leather and synthetic leather
The artificial leather and synthetic leather industry chain has formed thousands of upstream raw materials and tens of thousands of downstream manufacturers, and artificial leather and synthetic leather not only belong to the plastic industry, but also are distributed in leather systems, textile systems, troops, transportation and other systems. In addition, the production and manufacturing of artificial leather and synthetic leather is a highly professional discipline, involving the application of dozens of plastic polymer materials, inorganic filling media, different types of textile cloth base theory, intelligent automation application, printing profession, coating industry, clothing industry, footwear industry and other humanities theories; the product pattern design should apply aesthetics, philology, plants, animals, nature, geometry and other related cultural knowledge. In the manufacturing process, the molecular weight and other values and characteristics of upstream raw materials such as PVC resin, PU resin, DOP plasticizer, etc. should be studied in depth, especially the research on ultra-fine fibers and breathable leather should also be based on the understanding of the structure of natural leather, in order to better design its microporous structure. The production process of artificial leather and synthetic leather is quite complicated, including calendering, scraping, casting, steel belt method and post-processing process such as art spraying, color matching, printing, flocking, grinding, embossing and dozens of other process routes. The physical properties, chemical properties, texture, feel and visual effects of artificial leather and synthetic leather have reached the performance of animal skin, which is the crystallization of human productivity and wisdom. There are more than 3,000 varieties of artificial leather and synthetic leather, and the application of downstream products is becoming more and more extensive, involving the aerospace field, diving industry, transportation, sports equipment, medical equipment, building materials, including luggage fabrics, shoe fabrics, clothing fabrics, sofa fabrics, etc. that are necessary for people's daily life. The developed nanomaterials are applied to artificial leather and synthetic leather. The advent of radiation-resistant synthetic leather and infrared-proof synthetic leather, as well as the functions of deodorization, mildew resistance, acid resistance, alkali resistance and aging resistance have changed the status quo of the singleness of traditional products, and opened a new page in the history of the development of artificial leather and synthetic leather industry.
Application field
According to the type of covering, there are polyvinyl chloride artificial leather (PVC), polyurethane artificial leather (PU), etc. It can replace leather in almost any occasion and be used to make daily necessities and industrial products. According to whether the covering layer is foamed or not, it is divided into foamed artificial leather and flexible artificial leather. According to the purpose, there are artificial leather for shoes, artificial leather for bags, etc.
China's artificial leather has achieved rapid development in the past few years, but from the perspective of the industry as a whole, there are still many problems, such as small-scale production enterprises with poor environmental protection level, heavy pollution, low product added value, and insufficient innovation ability. "Analysis and Prospects of Production, Sales, Demand and Investment Opportunities in China's Artificial Leather and Synthetic Leather Industry" points out that eco-functional polyurethane synthetic leather emphasizes both functionality and environmental protection, representing the future development direction of the synthetic leather industry. In the future development, enterprises should focus on improving their overall strength, attach importance to product quality and technological innovation, increase R&D investment, improve the existing product technology level and industry environment, provide the market with more and better eco-functional polyurethane synthetic leather, and enable China's artificial leather industry to continue to develop healthily.
Due to the different synthetic resins used in artificial leather, different types of base materials, different production processes, whether there is foaming and different uses, artificial leather can be divided into many categories. Artificial leather is now classified according to the synthetic resin used, production process and use.
Classification by synthetic resin used
1. Polyvinyl chloride artificial leather
It is a mixture of polyvinyl chloride resin, plasticizer and other compounding agents, coated or bonded to the fabric, and made into a wake-up product through a certain processing process. In addition, there is also double-sided polyvinyl chloride artificial leather with plastic layers on both sides of the base material.
2. Polyamide artificial leather
It is a plastic product with a continuous cellular structure made by slowly coating nylon 6 or nylon 66 solution on the fabric and filming.
3. Polyolefin artificial leather
Polyethylene artificial leather is a kind of foam artificial leather, which is made of low-density polyethylene resin as the main raw material, mixed with modified resin, cross-linking agent, lubricant, foaming agent and other components.
4. Polyurethane artificial leather
Polyurethane artificial leather is divided into dry polyurethane artificial leather and wet polyurethane artificial leather. The so-called dry polyurethane artificial leather refers to a multi-layer structure composed of a multi-layer film obtained by evaporating the solvent of the solvent-based polyurethane resin solution and adding a base fabric. The wet polyurethane artificial leather is a multi-layer structure with good air permeability and moisture permeability, and a continuous porous layer, obtained by using a solvent-based polyurethane resin in an underwater film-forming method.
Classification by base material
According to the base material, it is divided into cotton cloth-based, synthetic fiber-based and fiber-based. Among them, cotton cloth base includes plain cloth, bleached cloth, dyed plain cloth base leather, canvas base leather, knitted cloth base leather and raised cloth base leather; synthetic fiber base includes nylon spun polyurethane leather and wet single coated polyurethane leather; fiber base includes paper-based polyvinyl chloride leather and non-woven cloth base leather.
The base materials used in large quantities in China are various types of cotton cloth, such as plain cloth, bleached cloth, dyed plain cloth, canvas, knitted cloth (including synthetic fiber), raised cloth, recycled cloth, non-woven cloth, etc.; some use cotton/chemical fiber blended cloth, such as nylon knitted cloth, etc.; a small amount of chemical fiber cloth, such as nylon silk, polyester silk, etc., is used; and synthetic fiber non-woven fabrics are rare. With China's reform and opening up, technological progress and the rapid development of the petrochemical industry, chemical fiber cloth and synthetic fiber non-woven fabrics will be rapidly developed.
Classification by production method
1. Direct scraping method artificial leather
The glue is directly scraped on the pre-treated base fabric with a scraper, and then put into the plasticizing box for gelation and plasticization, and then embossed, cooled and other processes to obtain the finished product.
2. Transfer scraping method artificial leather
The transfer scraping method is also called the indirect scraping method. The carrier used is release paper or stainless steel belt, so it is divided into release paper method and steel belt method. It is to scrape the paste on the carrier with a reverse roller or a scraper, and after gelation, the base fabric is compounded on the gelled material layer without tension, and then plasticized, cooled, and peeled off from the carrier, and then processed to obtain the finished product.
3. Calendering and laminating artificial leather
According to the formula requirements, the resin, plasticizer and other compounding agents are measured and put into the kneading machine for uniform mixing, and then plasticized by the internal mixer or extruder, and then sent to the two-roller or four-roller calender to be calendered into a film of the required thickness and width, and laminated with the preheated base cloth, and then embossed and cooled to obtain the finished product.
4. Extrusion laminating artificial leather
The resin, plasticizer and other compounding agents are mixed evenly in the kneading machine, and then plasticized, and then extruded into a film of a certain thickness and width by the extruder, and then laminated with the preheated base cloth on the two-roller setting machine, and then preheated, laminated, embossed, and cooled to obtain the finished product.
5. Rotary screen coating artificial leather
The emulsion polyvinyl chloride paste resin prepared according to the formula is coated on the cloth base through a rotary screen with a scraper to produce artificial leather.
6. Wet-process artificial leather
This method is for the following methods. For its definition, please refer to polyamide artificial leather. This method is suitable for the production of wet-process polyurethane artificial leather, polyamide artificial leather, etc.
Classification by use
Artificial leather can be divided into two categories: civil and industrial. Civil leather includes: shoe mouth leather, clothing leather, box leather, bag leather, handbag leather, glove car, furniture leather, etc. Industrial leather includes: vehicle leather, floor leather, etc.
Although 5 classification principles will be adopted for the classification of artificial leather, it should be noted that they are both interrelated and inseparable.
Mainly polyvinyl chloride artificial leather, in addition to polyamide, polyurethane, and polyolefin artificial leather.
There are 3 types of products:
¢ÙOrdinary artificial leather, also known as non-foaming artificial leather. It is usually made of plain cloth, canvas, and recycled cloth as the base, and is made by direct coating. Because the coating is dense and the paste can penetrate into the pores of the base cloth, the finished product feels hard and wear-resistant. It is mainly used to make wear-resistant packaging bags, construction and industrial accessories, etc.
¢Ú Foamed artificial leather. Usually, it is mostly made of knitted cloth as the base, and the surface paste contains foaming agent and its additives. When it is gelled, it foams to form a microporous structure, so the finished product is light, plump and soft. It is produced by transfer coating. It is mostly used to make gloves, bags, bags, clothing and furniture.
¢Û Suede artificial leather. Commonly known as artificial suede. It has a wide variety of varieties and a variety of production methods. The microporous surface layer of the artificial leather after gelling can be made into a suede leather after grinding with a sand roller. The coating layer is raised and stretched by a raising roller to produce curly suede. It is suitable for use as a toe cap and edging material for sports shoes. Adding soluble salts (such as salt) to the coating paste, dissolving the salt with water after gelation, can make the surface layer microporous and suede-like. Using the electrostatic flocking method, 0.5-1mm long synthetic fiber short pile is planted on the polyvinyl chloride artificial leather coated with adhesive to obtain flocked leather, which is suitable for making packaging bags and decorations.
Its moisture permeability and moisture absorption are better than polyvinyl chloride artificial leather, and it has a better appearance and feel. It is often used to make boxes, bags, etc.
A variety developed in the early 1960s. It is made of raised cloth as the base and polyurethane solution as the coating. The microporous layer obtained by impregnating and coating the raised cloth with polyurethane solution and coagulating it in a water bath becomes polyurethane suede leather after grinding. This kind of artificial leather is light, soft, wear-resistant, breathable, warm, and the feel is not affected by changes in temperature. It is suitable for making clothing, higher-grade bags, bags and decorative items.
Using low-density polyethylene as the main raw material, it is made by calendering and laminating. This artificial leather is light, firm and smooth on the surface, and is used to make leather bags and handbags.
Includes base fabric treatment, rubber preparation, coating, lamination, gelation, surface treatment, embossing, cooling, and winding. There are four main production methods.
The rubber is directly coated on the pre-treated base fabric with a scraper, and then put into the plasticizing box for gelation and plasticization, and then embossed, cooled and other processes to obtain the finished product. This method can produce ordinary artificial leather, film-laminated artificial leather and foamed artificial leather with various cloth bases.
Also known as indirect coating method. The paste is coated on the carrier (release paper tape or stainless steel tape) with a reverse roller or a scraper. After gelation, the cloth base is compounded on the gelled material layer without tension, and then plasticized, cooled and peeled off from the carrier, and then post-processed to obtain the finished product. This method is suitable for the production of knitted fabric or non-woven fabric-based foam artificial leather and ordinary artificial leather.
According to the formula requirements, the resin, plasticizer and other compounding agents are measured and put into the kneading machine for uniform mixing, and then plasticized by the internal mixer and open mill or extruder, and then sent to the three-roll or four-roll calender (see Plastic Machinery) to calender into a film of the required thickness and width, and laminated with the pre-heated base cloth, and then embossed and cooled to obtain the finished product. This method can produce various artificial leathers with different cloth bases. In order to improve the lamination effect between the base fabric and the film, a layer of adhesive is often applied to the base fabric first.
Mix the resin, plasticizer and other compounding agents evenly in a kneading machine, and after plastic refining, extrude a film layer of a certain thickness and width by an extruder, and then laminate it with the preheated base fabric on a three-roller setting machine, and then preheat, laminator, emboss, and cool to obtain the finished product. This method is used to manufacture thicker products, such as floor leather, conveyor belts, etc.
With the development of social science and technology, artificial leather technology has become increasingly mature, and product quality has been greatly improved, especially in the field of simulated leather, which can be indistinguishable from the real thing. It is similar to natural leather in many aspects such as breathability, flexibility, feel and appearance, but the price is much lower than natural leather. Therefore, in order to improve our identification ability, some simple and direct methods are introduced for reference.
First, the leather should be distinguished from the patterns and pores. The surface of real leather has clearer pores and patterns, the yellow cowhide has more uniform fine pores, the yak skin has coarse and sparse pores, and the goat skin has fish scale-like pores. The pores of pig skin are round and thick, arranged in a triangular shape. The patterns and pores distributed on the surface of these natural leathers do exist, and are unevenly distributed. There are animal fibers on the reverse side. The side section has clearly distinguishable layers. There are animal fibers in the lower layer. Scraping with fingernails will cause the leather fibers to stand up, and there is a feeling of velvet. A small amount of fibers may also fall off. The fabric can be seen on the reverse side of artificial leather, and there are no animal fibers on the side. Generally, the epidermis has no pores, but some have imitation leather artificial pores, and there will be inconspicuous pores. Some patterns are not obvious, or there are more regular artificial patterns, and the pores are also quite consistent.
Touching the surface of genuine leather with your hands, it feels smooth, soft, plump and elastic; while the surface of artificial leather is astringent, rigid and has poor softness. If you bend the front of the genuine leather downward by about 90 degrees, natural wrinkles will appear. If you bend different parts separately, the thickness and number of folds produced are obviously uneven. It can basically be determined that this is genuine leather, because genuine leather has a natural uneven fiber structure, so the wrinkle lines formed are also obviously uneven. Artificial leather feels like plastic, has poor recovery, and the thickness of the folds are similar when bent.
Genuine leather has a strong smell of fur, and the smell is more obvious even after processing, while artificial leather products have a smell of plastic, without the smell of fur.
Distinguish by smelling the burnt smell and looking at the state of the ash. When the leather burns, it will emit a smell of burnt hair. The burnt ash is generally easy to break into powder. After the artificial leather burns, the flame is also strong, shrinks rapidly, and has a very unpleasant plastic smell. It becomes sticky after burning, and hardens into blocks after cooling.
It can even reach the level of "real". This requires more careful identification and selection. Generally speaking, imitation leather is made by applying chemical raw materials on cloth. The appearance and feel of imitation cowhide are similar to cowhide; the appearance and feel of imitation sheepskin are similar to sheepskin, and the leather surface is shiny. But if you look closely at the leather surface, there are no pores, the bottom plate is not animal skin, and the leather surface will not wrinkle if you squeeze it hard, so it can still be distinguished from animal skin. But there are also microporous film artificial leather. In this case, it can still be distinguished by looking at the back base material.
The difference between artificial leather and synthetic leather
Artificial leather: refers to a material that is formed by artificial synthesis on a base fabric (including no base fabric) such as woven fabric, non-woven fabric (non-woven fabric) and other materials, with a film layer of resin such as polyvinyl chloride or a leather-like structure, and looks like natural leather. Synthetic leather: refers to a material that is formed by artificial synthesis on a base fabric such as woven fabric, non-woven fabric (non-woven fabric), leather and other materials, with a film layer of polyurethane resin or a leather-like structure, and looks like natural leather.
In China, people are accustomed to calling artificial leather produced with polyvinyl chloride (PVC) resin PVC artificial leather (abbreviated as artificial leather); artificial leather produced with polyurethane (PU) resin and traditional fabrics is called PU artificial leather (abbreviated as PU leather); artificial leather produced with PU resin and non-woven fabrics is called PU synthetic leather (abbreviated as synthetic leather). This is an introduction to the classification of synthetic leather and artificial leather in some literature. The classification is mainly based on the coating material and the base material: synthetic leather is made of polyurethane resin as the coating material and non-woven fabric as the base fabric, while artificial leather is made of polyvinyl chloride or polyurethane resin as the coating material and traditional fabric as the base fabric.
Dissolution and infrared spectroscopy analysis
When a small piece of fabric is soaked in ethyl acetate for 20 minutes, three situations will occur: (1) PU synthetic leather swells; (2) PVC artificial leather dissolves; (3) The epidermis of semi-PU synthetic leather swells in ethyl acetate, but the next layer dissolves. Use stainless steel tweezers to tweeze out the swollen epidermis and spread it on filter paper, then dry it with an infrared lamp (or air dry), and then use infrared spectroscopy to analyze the epidermis. The rest of the part can be made into a film on a NaCl salt sheet with the solution, and then the NaCl salt sheet and the film are used for infrared spectroscopy.
Infrared spectroscopy ATR technology
That is, attenuated total reflection technology, uses Fourier transform infrared spectrometer to directly collect infrared spectra of PU synthetic leather and PVC artificial leather coatings. By comparing the characteristic absorption peaks of the infrared spectra of the two leathers, the two leathers are qualitatively identified.
Put a small piece of fabric in gasoline for half an hour and then take it out. If it is PVC artificial leather, it will become hard and brittle, if it is PU synthetic leather, it will not become hard and brittle.
When burning, PVC artificial leather will emit green smoke, while PU synthetic leather will only emit black smoke.
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