In the textile industry, achieving the perfect finish for fabrics is crucial. This often involves employing various specialized finishing techniques to enhance the quality of fabrics. One such critical process is Decatising.
It is a Stress-relaxation process, also known as crabbing, blowing, or decorating, which is the process of permanently setting a textile finish on a cloth to prevent shrinkage during garment making. The term is derived from the French word “décatir,” which means to remove the finish or “cati” from wool. It is mainly used for wool or wool blends like tweed, flannel, and cashmere, as they have a tendency to shrink and warp when exposed to heat and moisture. This process relaxes the wool fibers and arranges them in a smooth, even position, improving the fabric’s finish and stability.
However, this process can be applied to a variety of natural or synthetic fabrics, including cotton, linen, silk, polyester, and nylon. The specific requirements and results of the process may vary depending on the type and quality of the fabric. For instance, cotton fabrics may require more steam and pressure compared to wool fabrics, while synthetic fabrics may require minimal or no steam and pressure at all.
Why do we need Decatising ?
Decatising is a crucial step in textile finishing, particularly for high-quality garments, as it provides numerous benefits.
- Shrinking Prevention: Decatising pre-shrinks of the fabric helps prevent unexpected shrinkage during garment construction or after washing. This ensures that the final product maintains a consistent size and fit.
- Improved appearance: It enhances the fabric’s appearance by removing wrinkles, setting the fabric’s drape, and enhancing its luster.
- Enhanced Hand feel: It enhances the fabric’s hand feel, making it softer and more comfortable to wear.
- Setting pile: It helps set the fibers in raised pile fabrics like velvet, preventing matting or loss of definition.
- Pre-stabilization for Dyeing: Prepare wool fabrics for dyeing by stabilizing their structure and reducing the risk of uneven color absorption with pre-stabilization.
Types of Decatising :
- Wet decatising: This method involves steaming the fabric directly while it’s wet. The fabric is wrapped around a perforated roller, and steam is applied to penetrate the layers and set the fibers in place.
- Dry decatising: This technique uses dry steam instead of wet steam. The fabric remains dry, and the steam treatment is less intense than with wet decatising.
- Continuous decatising: This modern method passes the fabric continuously through a decatising machine. It’s suitable for large-scale production and ensures consistent results.
Controlling Parameters :
The effectiveness of decatising depends on
• Type of fibre
• Time of contact
• Amount of steam
• Tension
• Type of finish desired
Decatising Process:
Throughout the process, the fabric usually undergoes a decatising machine containing a sequence of steam-heated rollers or cylinders. Steam is passed through the cylinder for a few minutes and then reversed to pass through the fabric from the outside. The cylinder is rotated during this process. The steam causes the fibers to become softer, allowing them to relax, while the pressure from the rollers aids in smoothing out any wrinkles or creases in the fabric. Consequently, the fabric attains a more consistent and polished appearance.
Perforated metal blowing cylinders are covered with a special cotton or cotton/synthetic canvas wrapper. Which helps to:
– Ensure that the various layers of fabric are separated from each other during decatising.
– Prevent the fabrics from sticking together and leaving impressions on each other.
– Allow for the smooth and even flow of steam and moisture between the layers of the fabric to be decatised and the undercloth.
– Modify the fabric’s sheen or opacity as needed during the process.
Modern decatising machines come in the form of continuous decatisers and machines that can operate under vacuum or pressure. These machines are equipped with controls for regulating temperature and fabric tension and safety features. Due to the brief exposure of the fabric to steam, continuous decatisers are capable of providing wool fabrics with a light finish, which is suitable for acrylics, polyamides, viscose, and blends of these materials with polyester and wool.
How to Decatise Different Types of Fabrics:
- Wool and Wool Blends: Wool and wool blends can benefit greatly from decatising as it improves their softness, sheen, and drape. Wet decatising is often preferred for wool to ensure thorough penetration of steam.
- Silk: Silk fabrics should be handled with care. Dry decatising is commonly employed to avoid excessive moisture, which can harm the fragile fibers.
- Cotton: Cotton fabrics undergo either wet or dry decatising processes, depending on the desired finish. Wet decatising is frequently used for heavier cotton fabrics.
- Synthetic fibers: Synthetic fabrics such as polyester and nylon can be treated with dry decatising to set the fibers without using too much moisture.