Synthetic Leather

1. Coloring:
   The next step is selecting the color for the synthetic leather. Synthetic leather is available in a wide range of colors and is used as a versatile material for various applications. The coloring process involves adding pigments and dyes to the polymer layers. These pigments and dyes are mixed in the coating formula to achieve a uniform and vibrant color throughout the leather. Coloring can be done through different methods, such as directly adding pigments to the polymer mix or using digital printing techniques to create complex patterns on the synthetic leather surface.
2. Selecting Softeners:
   Softeners improve the flexibility and softness of the synthetic material, preventing it from becoming hard or stiff, and give it a more natural texture.
3. Coating Process:
   This process involves applying polymer layers onto a carrier surface, which is usually a type of release paper. These layers consist of polymers and additives, and their specific composition varies depending on the desired properties of the synthetic leather, such as flexibility, color, durability, or water resistance. Polymer layers are applied using methods such as blade coating, rollers, or spraying. After application, the polymer layers undergo curing via heat or chemical treatment to allow the coating to swell and reach the required thickness.
4. Bonding Polymer Foam to Fabric:
   To provide stability and additional properties, polymer foam is often adhered to a backing material, which is usually a polyester fabric. The foam and fabric are bonded together primarily through rollers using adhesives with the application of heat and pressure. This fabric layer not only increases the durability and stability of synthetic leather but also adds comfort, especially when used in furniture or apparel production.
5. Embossing Process:
   To achieve the precise texture and appearance of natural leather, synthetic leather is often subjected to embossing. This process creates grain patterns and textures on the leather surface, enhancing its visual appeal and tactile experience. During embossing, the coated fabric is pressed against a patterned roller or plate under heat and pressure. The roller or plate carries a pattern that transfers onto the synthetic leather. The embossing process can replicate various leather grain patterns such as smooth, pebbled, or reptile-like textures.

After synthetic leather materials go through these various production steps, the final stage involves finishing and ensuring the product’s quality. These steps include cutting, edge coloring, and performance testing.

After cutting, synthetic leather has raw or rough edges. To give the product a beautiful appearance, the edges are carefully colored. A skilled craftsman applies a specific edge paint using a brush or spray techniques that match the main color or coating. This step not only improves the appearance but also helps stabilize the edges of the leather and prevents wear or deterioration over time. Additionally, synthetic leather products may undergo performance tests for durability, strength, and usability. This process helps manufacturers identify weaknesses and take necessary actions to improve the quality and longevity of the product.

In general, synthetic leather is industrially produced using two types of polymer coatings: PU and PVC, through different methods.

PU Leather Production Process:

PU leather production is now well established and used worldwide across various industries. The production process of PU leather is divided into four main stages:

1. The first stage involves pouring the polymer solution onto a carrier substrate, which is often made of silicone-coated release paper. The mixture is passed between heated rollers to compress and even out the layer.
2. The second stage involves pouring a foaming agent onto the polymer coating, then passing the entire mixture into a heated oven, which causes the polymer layer to swell or foam.
3. The third stage involves bonding a fabric layer made of a cotton-polyester blend onto the polyurethane foam using an appropriate adhesive, which increases strength and durability. In this stage, the paper substrate that served as the carrier for the polymer coating is separated from the leather composite by heat.

Using the appropriate adhesive, leather pieces can be glued together to create strong and durable joints. These joints can withstand pressure, stretching, and other common stresses in various applications.

In the past, solvent-based adhesives made from polychloroprene or polyurethane were used in the production process of polyurethane synthetic leather. These adhesives often consisted of polymers dissolved in a solvent. When the adhesive was applied, the solvent would evaporate, leaving behind the sticky material that formed the bond between surfaces.

However, nowadays, to ensure the health and safety of both producers and consumers, and to reduce environmental impact, the use of water-based adhesives has been steadily increasing in the global market. Water-based adhesives are environmentally friendly and have low volatile organic compounds, making them a suitable alternative to solvent-based adhesives. These adhesives do not pose significant health risks and do not emit toxic or unpleasant vapors.

Water-based polyurethane adhesives are made by dispersing polyurethane prepolymers and additives in water. These adhesives are suitable for porous and non-porous surfaces and are activated by applying pressure and heat. Water-based polyurethane adhesives are environmentally compatible and maintain the health of both consumers and manufacturers. Additionally, their non-flammability during storage and transport, the absence of hazardous waste production, and the ease of cleaning production line equipment are other prominent features of these adhesives. Also, having a higher solid content than solvent-based adhesives and forming strong and durable bonds ensures reliable adhesion and long-lasting durability. Their ease of use, optimal consumption, and resistance to hardening or yellowing over time have made them a preferred choice in the synthetic leather industry. This product is available in different heat resistance grades depending on the application.

4. The fourth stage involves applying a polyurethane coating on the surface of the leather, then passing it under a press to create leather-like grooves and a glossy finish.