Finishing is a series of steps that result in the ENNOBLING of a fabric, integrated into the production process depending on the type of item that you need to produce.
The various processes are carried out in sequence and range from scouring to a thorough final control and packing.
All the various stages, especially the last two, have to comply with the initial demands of the customer that ordered the batch of fabric.
Respecting the “order specifications” avoids the possibility or unwanted surprises during printing and production.
The series of processes carried out on the fabric starts with the cleaning of the raw/yarn that may be soiled, contaminated by protective or waste products.
Natural fabrics nearly always go through a machine that has lots of small flames that “burn off” the down on the yarn and make it smoother so it can absorb the next steps in the finishing process.
Scouring is generally done on synthetic fabrics when it is necessary to eliminate oil residue applied during spinning and warping in order to facilitate weaving, and stains or marks made during handling and transport.
The purpose of washing natural or delicate fibres is to eliminate the remains of bolls (shells) from cotton, stems from linen, hemp, and jute, traces of the animal in wool, or spinning processes, as well as pieces of packing materials used for transport.
Any remaining “sizing” has to be removed, i.e. the special glue applied to discontinuous yarns during warping to prevent the yarn breaking during weaving.
It is removed by winding the fabric onto large reels and continuously moving it for up to 24/36 hours, left in a bath containing enzymes that detach the glue naturally without weakening the fibre.
In this stage, synthetic fabrics that are sensitive to heat, go through an oven called a “stenter”, whose temperature and speed has been set for the specific properties of the yarn, in order to set the fibres and guarantee the fabric’s dimensional stability so that it does not shrink during subsequent processes.
Before it enters the oven, the fabric can be IMPREGNATED and certain products added, such as:
|Optical brightening agents||To achieve an optic white|
|Fire resistant agents||To obtain self-extinguishing, flame retardant products|
|Water repellent||So that drops of water slide off the surface|
|Wetting agents||To increase absorption during dye and /or printing processes|
|Anti U.V. agents||To increase resistance to U.V. light of products designed for use outdoors|
Cleaning and dimensional stability are fundamental requisites in order to obtain optimum results during subsequent stages of finishing, especially dying as the ability to absorb dye is linked directly to how clean the yarn is: a less contaminated yarn will absorb dye more readily.
After the raw material has been cleaned and stabilised, it can be sent for dyeing using various machines depending on the fabric and the final look you want to achieve.
There are three types of dyeing methods:
|used mainly for lightweight items.|
The fabric is wound onto perforated “beams” and the pressurised dye enters into the beam, passing through the holes so it dyes the fabric.
|used for items with a compact and/or heavy weave.|
The raw fabric is wound onto a reel and remains submerged in a tank full of dye that dyes the fabric before it is wound onto another reel. After the full amount of material has passed through, it repeats the process backwards and continue turning until it has absorbed sufficient dye to get the shade of colour required.
|used for knitted fabrics or fabrics that are not heat set but left free to resume their own technical properties.|
The fabric is gathered together as if it were a rope, and is inserted into the guide tube. It is moved continuously and remains submerged in the dye, transiting along a looped path until it takes on the shade of colour as required.
The main categories of dyes used are:
Acids to dye Nylon, Wool and Silk fabrics
Dispersing to dye Polyester fabrics
Reactive/Direct/Sulphur/Indanthrene for fabrics in Cotton, Viscose, and Acetate
Pigments for any fabric type
An industrial calendering roller is designed differently to a roller used for transfer printing. It has two cylinders where the fabric is passed through and so it is subjected to adjustable pressure.
If the cylinders are heated, the result is a shiny effect (chintzing); if they remain cold, they are used to simply squash the fibres and obtain as smooth a surface as possible, so the subsequent processing is able to adhere to the fabric better.
When specific technical properties offering a better performance – compared to fabrics treated simply with the Heat Setting process described earlier – are required, it is essential to use a machine with a “distributor” (bench) and a “blade” that spreads a layer of a chemical product (Resin or Coat) over one of the sides of the fabric, and a stenter oven to dry it so it gets the technical properties as required.
This all takes place with one or more passages in line (and so necessarily in sequence) for the application of products that, depending on the amount applied will make the fabric:
|Waterproof||Resistant to water passing through|
|Fireproof||Self-extinguishing, flame retardant|
|Run resistant||Resistant to traction and runs|
|Printable||E.g. Digital plotters|
|Other specifications||For industrial use|
Regardless of whether the fabric will remain raw, semi-finished or finished, it has to pass quality controls before it can be shipped.
Specially designed “fabric inspection” machines are used to take the fabric off the big reels coming out of production. It slides over a surface so that the inspectors can:
- roll it into smaller and more manageable pieces
- check it matches the set specifications
- report any faults found, checking whether the fabric is suitable for shipment or should be rejected and re-manufactured.
The main systems to assess any faults found comply with international standards, designed for every type and application of fabric, defining the final classification of the product (first quality, “sub prime”, seconds, other) are:
- Demerit point, assigning a set score to each fault
- Number defect, where the number of faults is simply counted.
In view of the countless variables in the potential use of fabrics, it is always wise to define the exact quality standards in order to avoid any discussion as the how standards should be read and above all in cases of special needs, analysing and agreeing a mixed system where both the number and types of fault are taken into account, writing all specifications for the supply.
In this stage, the fabric is packed as agreed, which could envisage:
- The use of specific tubes (diameter, thickness, length, composition)
- Roll length
- Possibility to leave cuts or full pieces only
- If and how faults are to be reported
- Fault mapping
- Filling out a packing list
- Where to attach labels and what information should be on the label (bar code, production batch data, item codes…)
- Type of packing (just nylon, pluriball, boxes…)
- Other systems for protection (caps).
As far as the finishing of the fabrics is concerned, the main steps in transfer printing to monitor are SCOURED in order to clean the fabric and HEAT SETTING used to achieve maximum dimensional stability and avoid shrinkage during printing.
It is very important to use chemicals designed to withstand high temperatures as they must not weaken, change, or become sticky in order to prevent damage to machinery. It is always wise to test all materials prior to production with due care.