Following dyeing, later treatments may be performed on the fabric in order to achieve special characteristics for the end textile product.
The fabric’s characteristics may be changed by performing physical or mechanical treatments (dry finishing processes) or by applying chemicals (wet sizing processes).
In some cases, the results could be achieved in any of both ways, as is the case of lustre. In others, only one possible way exists, as is the case of impermeability or fire-retardant qualities.
All wet treatments are principally based on the coating or impregnation of the fabric with different substances, which may be applied indistinctly to bleached or dyed fabrics.
Normally, the wet finishing subprocesses follow the operations below:
• Application of the finishing products, by immersion in a bath containing the chemicals, and later squeezing in the foulard; application of finishes using minimal impregnation techniques; foam systems; scraper devices, etc.
• Fixation by the effect of temperature.
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4.2.6. Types of finishing sub processes
4.2.6.1. Mechanical finishing
The most common mechanical finishing processes are described below:
Heat setting
This is a “dry” subprocess aimed at stabilising and contributing suitable properties to synthetic fabrics, or to those that have a high proportion of synthetic material. When the thermoplastic fibres are thermostabilised, they keep their shape and width throughout the following finishing stages, in addition, acquiring physical properties of resistance and elasticity making the garment more suitable for its end use.
Brushing and raising
These are used to reduce the fabric’s shine due to rubbing against a surface, changing the appearance of the fabric, breaking some individual fibres by means of small hooks.
Softening or calendering
Calendering through the effect of the temperature and pressure gives rise to the softening of the surface of the fabric and lustre increases. In calendering, the fabric passes between two or more cylinders, one of which is made of steel, while the others are made of very soft material (normally the contact surface is cotton).
The steel cylinder may also be heated using gas or steam.
Embossing
This is an effect that may be achieved in a calender that has a cylinder with motifs in relief, which are transferred to the fabric.
Chintz effect
This is one of the effects that may be achieved by means of a calender with a microgrooved cylinder, which gives the characteristic lustre to the treated fabrics. Luminosity may be given to the fabric by compressing both surfaces of the fabric, which may be achieved by passing the fabric between the two calender cylinders. The lustre may be improved if the cylinders have grooves.
Shearing
Shearing levels the height of pile or fibre by passing the fabric through a shearer. When the aim is to eliminate all fibres that protrude, the operation is known as levelling.
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Sanforizing
Using the principle of compressive shrinkage, the tendency of the fabric to shrink during its end use is reduced, following a series of successive washes.
4.2.6.2. Chemical finishes
The most common chemical sizing processes have specific functions: softening, hydrophobing, waterproofing, flame-retardant treatment, bactericide, etc.
The main finishing subprocesses are as follows:
Chemical softening
Different types of softeners may be used:
• Cationic softeners such as: quaternary ammonium salts, amino esters and amino amides
• Non-ionic glycolic polyester or polyether glycol-type softeners
• Reactive softeners such as fatty acid amides and triazine derivatives
Anti-static treatment
The aim of this process is to reduce the static charge of synthetic fibres by means of treatment with an aqueous solution of anti-static agents (magnesium chloride, polyethylene glycol and polyalkylene oxide).
Flame-retardant treatmment.
The aim of this process is to increase the fire resistance of textiles materials with the application of flame-retardant products (normally organophosphates and halogenated compounds).
Shrink-resistant treatment
The aim is to avoid diminishing dimensions due to external causes, especially by washing with water. The operation consists of relaxing the fabric in an aqueous medium, or by applying chemicals, normally resins.
Waterproofing
This consists of the treatment of the fibres with hydrophobic agents, that is to say, water repellents (silicones, fluorocarbons, paraffin emulsions with aluminium salts and zirconium, resins).
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Crease resistant treatment
The aim of this process is to prevent fabrics from creasing easily with wear. This is achieved through cross-linking treatment - reactive products that are exempt of free formaldehyde, which may be applied by drying and heat condensation, or by polymerisation after the garment has been made, among others.
Coating
This consists in the application to the fibres, on one or both sides, of a plastic layer (PVC, PVA, PUR, copolymers of vinyl acetate/chloride). The coating is applied thermally, in a layer, in such a way that the coat fixes to the fabric through cooling.
Other textile coating operations are:
• Powder coating (thermoadhesive resins for interfacing) • Application of paste coating • Transfer coating
Rot proofing treatment, mothproofing and fungicide treatment
This consists of treating the fabric with an aqueous solution which contains between 0.1-0.25% of mildew-proofing, moth-proofing and fungicide agents, (chlorated aromatic hydrocarbons and copper organic compounds). The moth-proofing treatment for wool is carried out during th
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