As a supplier of weft knitting spandex yarn, I am often asked about the production process of this essential textile material. In this blog post, I will take you through the step-by-step journey of how weft knitting spandex yarn is made, from the raw materials to the finished product.
Raw Materials
The primary raw material for spandex yarn is a polymer called polyurethane. Polyurethane is a synthetic material known for its excellent elasticity and durability. It is made by reacting diisocyanates with polyols, which are long-chain molecules with multiple hydroxyl groups. The specific formulation of the polyurethane can vary depending on the desired properties of the spandex yarn, such as its stretchability, strength, and resistance to heat and chemicals.
In addition to polyurethane, other raw materials may be used in the production of weft knitting spandex yarn. These can include additives such as antioxidants, UV stabilizers, and lubricants, which help to improve the performance and stability of the yarn. The choice of additives depends on the intended application of the yarn and the environmental conditions it will be exposed to.
Polymerization
The first step in the production of weft knitting spandex yarn is the polymerization of the polyurethane. This process involves mixing the diisocyanates and polyols in a reaction vessel under controlled conditions of temperature and pressure. The reaction between the diisocyanates and polyols forms a long-chain polymer with elastic properties.
There are two main methods of polymerization used in the production of spandex yarn: solution polymerization and melt polymerization. Solution polymerization involves dissolving the diisocyanates and polyols in a solvent, such as dimethylformamide (DMF), and then heating the mixture to initiate the reaction. This method is commonly used for the production of high-quality spandex yarns with precise control over the polymer structure and properties.
Melt polymerization, on the other hand, involves heating the diisocyanates and polyols directly without the use of a solvent. This method is more energy-efficient and environmentally friendly, but it can be more challenging to control the reaction and achieve the desired polymer properties. Melt polymerization is often used for the production of lower-cost spandex yarns with less demanding performance requirements.
Spinning
Once the polymerization process is complete, the resulting polyurethane polymer is ready to be spun into yarn. Spinning is the process of converting the polymer solution or melt into continuous filaments of yarn. There are several different spinning methods that can be used for the production of weft knitting spandex yarn, including dry spinning, wet spinning, and melt spinning.
Dry spinning is the most common method used for the production of spandex yarn. In this process, the polymer solution is extruded through a spinneret, which is a small device with multiple holes. As the solution emerges from the spinneret, it is exposed to a stream of hot air, which evaporates the solvent and solidifies the polymer into filaments. The filaments are then wound onto bobbins or packages for further processing.
Wet spinning is similar to dry spinning, but instead of using hot air to evaporate the solvent, the polymer solution is extruded into a coagulation bath containing a liquid that causes the polymer to solidify. This method is often used for the production of spandex yarns with special properties, such as high strength or low shrinkage.
Melt spinning is a process in which the polymer melt is extruded through a spinneret and then cooled to solidify the polymer into filaments. This method is commonly used for the production of other types of synthetic fibers, such as polyester and nylon, but it can also be used for the production of spandex yarn. Melt spinning is a faster and more efficient method than dry or wet spinning, but it can be more challenging to achieve the same level of control over the yarn properties.
Drawing and Heat Setting
After the spinning process, the spandex yarn is typically subjected to a drawing and heat setting treatment to improve its strength, elasticity, and dimensional stability. Drawing is the process of stretching the yarn to align the polymer molecules and increase its orientation. This helps to improve the yarn's strength and elasticity by making it more resistant to deformation.
Heat setting is the process of heating the yarn to a specific temperature and holding it there for a certain period of time. This helps to relax the polymer molecules and set the yarn in its stretched state, improving its dimensional stability and reducing its tendency to shrink or stretch during use. Heat setting is typically carried out using a hot air oven or a steam chamber.
Twisting and Plying
Once the drawing and heat setting treatments are complete, the spandex yarn may be twisted and plied to improve its performance and appearance. Twisting is the process of rotating the yarn around its axis to give it a helical structure. This helps to improve the yarn's strength, abrasion resistance, and handling properties.
Plying is the process of combining two or more single yarns together to form a multi-ply yarn. Plying can be used to increase the yarn's strength, thickness, and durability, as well as to create different textures and effects. The number of plies and the twist direction can be varied depending on the desired properties of the final yarn.
Finishing
The final step in the production of weft knitting spandex yarn is the finishing process. Finishing involves applying various treatments and coatings to the yarn to improve its performance, appearance, and functionality. Some common finishing treatments for spandex yarn include:
- Lubrication: Applying a lubricant to the yarn to reduce friction and improve its handling properties during knitting or weaving.
- Antistatic Treatment: Treating the yarn with an antistatic agent to reduce static electricity and prevent the yarn from sticking together or attracting dust.
- Dyeing and Printing: Dyeing or printing the yarn to add color and patterns. Spandex yarn can be dyed using a variety of dyes, including acid dyes, disperse dyes, and reactive dyes.
- Coating: Applying a coating to the yarn to improve its water repellency, stain resistance, or other properties. Coatings can be applied using a variety of methods, including dip coating, spray coating, and roll coating.
Quality Control
Throughout the production process, strict quality control measures are in place to ensure that the weft knitting spandex yarn meets the highest standards of quality and performance. Quality control begins with the selection of the raw materials and continues through every stage of the production process, from polymerization to finishing.
Some of the key quality control parameters that are monitored during the production of weft knitting spandex yarn include:
- Yarn Count: The yarn count is a measure of the thickness or fineness of the yarn. It is typically expressed in denier (D), which is the weight in grams of 9,000 meters of yarn. The yarn count can have a significant impact on the performance and appearance of the final fabric, so it is important to ensure that the yarn count is consistent and within the specified range.
- Tensile Strength: The tensile strength is a measure of the maximum amount of force that the yarn can withstand before breaking. It is an important property for weft knitting spandex yarn, as it determines the yarn's ability to withstand the stresses and strains of knitting and use.
- Elongation: The elongation is a measure of the amount of stretch that the yarn can undergo before breaking. It is an important property for weft knitting spandex yarn, as it determines the yarn's ability to provide elasticity and comfort in the final fabric.
- Shrinkage: The shrinkage is a measure of the amount of shrinkage that the yarn undergoes when exposed to heat or moisture. It is an important property for weft knitting spandex yarn, as it determines the yarn's dimensional stability and the ability of the final fabric to maintain its shape and size.
- Color Fastness: The color fastness is a measure of the ability of the yarn to retain its color when exposed to various environmental conditions, such as washing, light, and perspiration. It is an important property for weft knitting spandex yarn, as it determines the durability and appearance of the final fabric.
Conclusion
In conclusion, the production process of weft knitting spandex yarn is a complex and highly technical process that involves multiple steps and stages. From the selection of the raw materials to the finishing and quality control, every aspect of the production process is carefully controlled to ensure that the final product meets the highest standards of quality and performance.
As a supplier of weft knitting spandex yarn, we are committed to providing our customers with the highest quality products and services. We offer a wide range of spandex yarns in different deniers, colors, and finishes to meet the diverse needs of our customers. Some of our popular products include 20D (20505) Spandex Yarn AA Grade, 15D (15501) Spandex Yarn AA Grade, and 30D (30501) Spandex Yarn AA Grade.
If you are interested in learning more about our weft knitting spandex yarn products or would like to discuss your specific requirements, please do not hesitate to contact us. We look forward to working with you and providing you with the best possible solutions for your knitting needs.
References
- Morton, W. E., & Hearle, J. W. S. (2008). Physical Properties of Textile Fibres. Woodhead Publishing.
- Zeronian, S. H., & Collins, P. J. (1989). Wool and Keratin Fibres. Woodhead Publishing.
- Postle, R. (1995). Synthetic Fibres: Nylon, Polyester, Acrylic, Polyolefin. Woodhead Publishing.