Abstract: This paper mainly introduces the production process of PVC PU leather, natural leather, PU synthetic leather and microfiber leather for car seats, analyzes the odor source in the leather production process, and explains aspects of raw materials. process replacement and improvement The way and method of leather to achieve low odor, and a practical guide for the production of green and environmentally friendly leather and the development of low odor leather for OEMs.
Key words: genuine leather; PVC leather; PU leather; microfiber leather; faint smell1 Seat leather overview
With the improvement of people's living standards and the development of the automobile industry, there are more and more leather car decorations. While people are chasing the shape and power of cars, they are also paying more and more attention to function. and the aesthetics of automotive interiors, as well as the breathability of interior materials, environmental protection and green automotive leather products, therefore, have become the focus of automotive interior leather manufacturers.
In China, artificial leather products based on textile or knitted materials and coated with PVC resin are called PVC artificial leather. Leather made from polyurethane (PU) resin is called PU synthetic leather. Synthetic microfiber leather (abbreviated microfiber leather) based on non-woven microfiber fabric and PU. Genuine leather is a natural animal fur product, cowhide is generally used, the pores are round, the pores are fine, the air permeability is good, the hand feels firm and elastic.
This document outlines the production process of PVC PU leather, PU synthetic leather, microfiber leather and genuine leather, and the causes and methods of eliminating odor, which is an important guiding for the development of green, environmental protection and low-odor seat leather.2 Introduction to the leather production process 2.1 Introduction to PVC imitation leather production process
PVC imitation leather is mainly composed of PVC resin, plasticizer, stabilizer, pigment and filler. The electron microscope image of PVC artificial leather is shown in Figure 1. There are two production methods for PVC artificial leather: coating method and calendering method.
Coating Method Prepare the mask layer, foam layer and glue layer according to the formula, apply the mask layer paste on the release paper with the required texture, dry it, apply the foam layer, and then apply the glue layer, and then paste the knitted fabric to it was plasticized and foamed. The block diagram of the production process is shown in Figure 2.
The calendering method first uses PVC resin emulsion plus plasticizer to make a paste, and then uses the roll coating method to stick on the base fabric. After the base fabric is dried and gelled, it is thermally laminated with calendered PVC film one or more times, further plasticized in a plasticizing oven, foamed and embossed, and finally made by leather surface treatment and other processes. The block diagram of the production process is presented in Figure 3.2.2 Introduction to the production process of genuine leather
Real leather is usually a finished cowhide product after processing. The production process of natural leather is as follows: raw hide → liming and depulping → tanning → peeling → loosening → oscillation → embossing → dyeing → hand cutting. The production process is shown in Figure 4.
Liming and deflashing are mainly intended for hair removal, deflashing and corrosion protection of other parts. Tanning is the removal of fibers and preparation for re-tanning Leather tanning is the chemical and physical treatment of leather proteins with tannins. It uses a number of processes and uses some chemicals to make a number of changes to the protein in the animal's skin and to denature the collagen. After tanning, the leather is soft and not easily damaged. Split leather is designed to cut cow leather into whole grain (top layer leather) and second layer leather depending on the thickness. effect. Oscillators soften the skin, dissolving dry fibers. Embossing applies a certain grainy pattern to the surface of the skin. Finishing puts the final color on the skin, increases elasticity and wear resistance, protects natural leather from ultraviolet radiation, is not comfortable to wear. Finally, the leather is cut by hand depending on the quality and standard of the car part or the scope of the project.2.3 Introduction to the production process of PU synthetic leather
PU synthetic leather is made from woven fabric as a baseand a mixed slurry of polyurethane resin (PU) and additives is applied to the surface. In terms of production process, there are basically two processes: wet process and dry process.
In the production process of dry polyurethane synthetic leather, release paper is usually used as a carrier. The PU resin slurry is applied to the release paper and peeled, and then enters the oven to be heated piecemeal to evaporate the solvent in the slurry to form a dense layer of PU polyurethane. After drying and cooling, the adhesive is applied, and the base fabric is bonded to the dense layer with base fabric laminating devices. After drying and cooling, the synthetic leather and release paper are separated, resin, DMF solvent, filler and dye are converted into a mixed solution after degassing by a vacuum machine, impregnated or applied to the base fabric using the principle of mutual solubility and mutual diffusion of water and dimethylformamide (DMF), and then the DMF solvent is replaced in a coagulation bath (usually a mixture of DMF and water), and then washed with water and dried to coagulate and cure the resin attached to the base fabric into a semi-finished product with a continuous microporous structure. structure, namely bass. Bass also manufactures PU synthetic leather products through surface printing, embossing, buffing and other processes. Figure 5 is an electron micrograph of PU synthetic leather.2.4 Introduction to microfiber leather production process
Microfiber leather is a substance surrounded by another substance in a thin and separated state, as if there are many islands in the sea. Its island and marine components are continuous, dense, and evenly distributed along the fiber axis. By removing the marine component, a bundle of ultrathin fiber bundles can be obtained.
Currently, microfiber leather is divided into fixed island superfiber and indeterminate island superfiber. base fabric, and then extract the alkaline polyester with sodium hydroxide to open the fibers. Among them are microfiber with a fixed island, nylon - "island", and soluble polyester - "sea". The short fibers in indefinite island ultrafine fibers are typically mixed with nylon and polyethylene in a 50:50 ratio to form a base nonwoven, and then toluene is used to draw the polyethylene to open the fibers. In an undefined island, microfiber, nylon is the "island" and polyethylene is the "sea." Figure 6 is an electron micrograph of microfiber leather.
Microfiber leather production process can be roughly divided into: sea island fiber → needle punched nonwovens → PU resin wet impregnation → recovery extraction → PU dry lining → microfiber leather. The specific process looks like this:
The short fibers of the sea island are opened and combed into a web, and then the fibers are weaved with each other using needle punching to create a base fabric with a three-dimensional structure. The above three-dimensional structure base fabric is impregnated with a polyurethane resin with excellent performance and high strength microporous structure to form a bass (semi-finished product) similar to natural leather, and the processed bass is immersed in toluene or sodium. hydroxide solution at a given temperature. Re-immersion, the purpose of which is to extract the "marine" component in the "sea-island" fiber and obtain a bonded ultra-fine fiber formed by the "island". Then apply the slurry prepared with polyurethane resin to the release paper by scraping, and form a polyurethane film after the solvent has evaporated; then transfer the PU film to the microfiber leather surface to form a superfiber with a specific skin color and pattern.3 Analysis and improvement of leather odor sources 3.1 Analyzing and improving the smell source of PVC artificial leather
A common type of PVC faux leather odor is ink odor, which comes from plasticizers. Plasticizers are added to polymers to shape and improve processability. The plasticizer is a phthalate, because the phthalate plasticizer evaporates easily, and then the PVC imitation leather will give off the smell of ink.
The odor improvement solution is to replace phthalate plasticizers with epoxy vegetable oil. Epoxidized vegetable oil contains macromolecular plasticizers, which are non-toxic, non-polluting, difficult to migrate, and a green and environmentally friendly product.3.2 Analyzing and improving the source of skin odor
The usual type of leather odor is sour, which comes from tannins. Tanning is the process of converting perishable hides into durable ones. The chemicals used in the tanning process are called tannins. The tannins currently used by manufacturers are usually chromium tanning (usually chromium sulfate), which gives the leather a sour taste.
The solution to improve the smell is to replace chromium sulfate with vegetable tannins. Vegetable tannins are a class of polyphenol derivatives widely present in plant cells that can tan raw hides into leather. Tannins extracted from plants contain many hydroxyl groups. The vegetable tanned leather surface smells like fur, and the non-acid smell is more comfortable.3.3 Analyzing and improving the smell source of polyurethane synthetic leather
A common type of PU synthetic leather odor is solvent odor. The solvent smell comes from the polyurethane resin. Whether it is dry-processed or wet-processed PU leather, solvent-based PU resin must be used in the manufacturing process. because the solvent type PU resin contains many chemical solvents such as dimethylformamide (DMF), toluene, etc., which give the PU synthetic leather a solvent smell.
The odor enhancement solution is a water-based polyurethane resin instead of a solvent-based polyurethane resin. The water-based polyurethane resin uses water as the dispersion medium and contains no solvents, evaporates as water vapor, and does not cause physical harm to consumers. It is a safe and environmentally friendly synthetic leather resin, harmless to the human body and the environment.3.4 Analysis and improvement of microfiber leather odor source
A common type of microfiber leather odor is solvent odor. The solvent smell comes from the surface coating. The coating is transferred through release paper. The coating consists of polyurethane resin, colortnoy paste, solvent and additives. Mix and stir if necessary evenly, and then perform defoaming treatment, the resulting mixture is a coating suspension, the solvent contains toluene, xylene and other organic substances, so it produces solvent smell.
The solution to improve odor is to use a water-based coating instead of a solvent-based coating in the topcoat. The water based coating uses water as the dispersion system and has no overt identifiable odour.4 Conclusion
As consumers pay more and more attention to the environmental issues in the car, the smell in the car has also attracted a lot of attention from OEMs and parts manufacturers in recent years. Environmental protection requirements for car interior materials are getting higher and higher. As a component of the seat, leather has a decisive influence on the smell of the car. New environmentally friendly processes are vigorously developed and applied, new materials and new technologies for environmental and green leather will also become key areas research for leather manufacturers in the future.