Spin Finish in Textile: Properties, Components and Problems
Spin Finish in Textile:
In the field of textiles, the specialist term “spin finish” has a wide
range of meanings today. Actually, a spin finish is a liquid or solid
composition that is applied to the surfaces of man made fibers
in order to improve the processing of such fibers in short staple or
long-staple spinning. The following terms are all used to define the
same thing: spin finish, spinning finish, waxing, size, dressing,
coating, fiber finish, spinning lubricant, agent, textile treating
composition, textile treating agent and condition agent.
During mechanical processing of fibers and fabric production, a lot of tension and friction is applied to the material. As a result of the high friction and abrasive stress, a number of negative effects appear, which are as follows:
- Undesired temperature increase of fibers and yarn
- Yarn breakage and machine stops, leading to lower product quality
- Uncontrolled yarn tension during fabric formation, leading to crease formation and shrinkage
- Electrostatic charge that leads to ballooning of multifilament yarns and adhesion to machine parts
- Development of fiber dust leading to machine failure.
Thus, it is important to prevent such effects and to control fiber friction and yarn tension during processing and to maintain well-controlled yarn tension during fabric production. Besides accurate control of climate (temperature and relative humidity) to stabilize the respective fiber properties, specific auxiliaries are also added on the fibers and yarn.
During production of synthetic fibers, for example polyester, polyamide, polyolefin or elastomer fibers, spin finishes are added as the last stage of the fiber production. Such spin finishes may include lubricants, emulsifiers, antistatic agents, bactericides and antioxidants. The effect of these chemicals is mainly based on the formation of a thin but uniform layer, which covers the fiber surface and thus reduces surface friction and flexural rigidity of the textile material.
Fibers need to be treated with surface finishes or lubricants to allow high-speed processing. The various processing steps such as drawing, bulking, and textile processing would be impossible without these spin finishes because so many of them rely on specific frictional properties of the fiber.
The primary function of a spin finish is to eliminate the build-up of static electric charges on fibers during processing. This is achieved in two ways. First, the finish makes the fiber hydrophilic in order to facilitate charge dissipation (leakage). Second, it reduces the static and dynamic friction of the fibers, and subsequently the yarns, while they are moving in contact with machine parts, diminishing the generation and build-up of charge.
Spin finishes can also control the amount of friction during processing. As an example, yarns experience drag as they pass over a ceramic guide or pass through the traveller during ring spinning. If the drag is too great, due to the degree of friction between fibers and machinery, fibers can be damaged. A spin finish can reduce the amount of friction to a level which avoids problems such as end-breaks in fibers. Friction can also cause local fusion of fibers, especially at points where the fibers rub guides and other machine parts during high-speed winding.
Properties of Spin Finishes:
Basic functions of a spin finish are to provide surface
lubrication to the fiber/filament, antistatic action and good
fiber-to-fiber cohesion. In order to perform these functions, a spin
finish should have the following desirable properties:
- It should provide good lubricity to reduce the fiber-to-metal (F/M) friction in order to prevent fiber abrasion and maintain low, uniform tension during processing.
- It should reduce the static charge build-up during processing.
- A balanced degree of cohesion is necessary, as too much lubricity may cause fiber slippage resulting in package distortion in winding and other operations.
- It should have a controlled viscosity range; too Iowa viscosity causes difficulties in slinging and low yam frictional values, while too high a viscosity causes excessive add-on coupled with high frictional values.
- For consistent viscosity, the spin finish must be resistant to bacterial growth; it also should not form insoluble resinous compounds in the presence of oxygen.
- Scourability (ease of removal): poor scourability would cause dyeing problems and potential soiling spots.
- It must be corrosion resistant and should not cause damage to rollers, guides or needles.
- It should be non-allergenic, non-toxic and ecologically acceptable.
- Spin finishes are generally applied in emulsion, hence they should be easily emulsifiable.
Components of Spin Finishes:
Today spin finishes consist of various components which are intended to create a system with various properties.
Spin finishes consist of several components, including:
- Lubricants
- Emulsifiers
- Antistatic (antistat) agents
- Cohering agents
- Antioxidants
- Pigments
- Antifoam agents
- Other additives (such as bactericides, corrosion inhibitors and wetting agents).
Whereby gliding agents, antistatic agents and emulsifiers make up approximately 90% of the system.
Key Requirements for Spin Finishes:
Spin finishes must meet a range of requirements if they are to be effective and to add value to the final product.
Requirements placed on a staple fiber spin finish:
- Optimum sliding and friction properties (fiber/fiber, fiber/metal, fiber/ceramics), static and dynamic
- Optimum antistatic properties
- Positive effect on the crimping behavior
- High stability of the spin finish film
- Good wetting behavior
- No aerosol formation
- No yellowing
- No foaming
- No tendency to conglutinate
- No waste gases
- Sufficient thermostability
- Long storage life
It is essential that the application of spin finishes should not affect fiber morphology and quality. A spin finish must be readily adsorbed and have good adherence to the fiber surface. It must have the ability to wet the fiber surface and spread evenly over it to avoid dry friction. On the other hand, it must be easily removed before dyeing. It must also have no effects on dyeing absorption, i.e. the dye affinity of fibers, or on dye fastness. Some spin finishes have been used to block certain dyes where this is required. It is important to ensure that the finish does not affect the shelf-life of the final yarn. Some finishes use titanium dioxide to enhance colors in fabric but the additive is abrasive and can weaken the yarn.
Spin finishes must not cause damage to metallic and non-metallic surfaces of machine parts (e.g. aprons, cots of top rollers of the drafting system, rotors in spinning machines). In particular, they must show low migration into polymer (e.g. rubber) components which could cause swelling and fracture. They must not exhibit any gluing effects which might cause fibers to adhere to machinery. They must be easy to clean from both fibers and machinery.
More generally, spin finishes must be toxicologically and physiologically safe. As an example, they must not cause workers inside a spinning mill to get dermatitis. They must also be environmentally friendly, i.e. compatible with environmental regulations and producing no toxic effects, especially when the spin finish is washed from the fiber during finishing. They should ideally be biodegradable and comply with environmental assurance programmes (EAP).
Environmental requirements placed on spin finishes:
- Biodegradability
- Low emissions – thermostability
- Skin tolerance
- No oral toxicity
- No fish toxicity
- No alga toxicity
- No bacterial toxicity
- No heavy metal or halogen content
Spin finishes must be capable of being stored for long periods, i.e. have high resistance to ageing, bacterial attacks and oxidation. The autoxidation of spin finish components, from being exposed to air and heat during the processing period, can be observed by yellowing and a change in solubility and viscosity. Finally, spin finishes should be reasonably priced.
Role of Spin Finish:
Although the spin finish is only a minor, transient part
of the total fiber production system, it plays a very important role in
the processing, performance and quality of the final product. The spin
finish coat is the true interface between the fiber and any other
contact surface, for example a guide roll, hot plate, knitting needle,
etc. In order to understand the specific role of the spin finish, it is
necessary first to consider the basic mechanisms involved in the three
primary functions of a spin finish, namely lubrication of the fiber
surface, antistatic action and cohesion of filament in a fiber assembly.
Cohesion becomes important in zero twist continuous filament yarns and
staple fiber processing.
Problems of Spin Finish in Short Staple Spinning:
Potential spin finish problems in short-staple plants include:
- Swelling of the rubber aprons and cots of the top rollers of the roller drafting system
- Flaking of fibers and an increase in static charge accumulation, caused by an uneven distribution of spin finish spraying
- The formation of hard coatings on different machine parts such as the teeth of the licker-in, opening roller pins (teeth) of the rotor spinning machines, trumpets on the card, or on the drawframe and the speed frames (flyers) and the pressing arm eyelet; this can lead to an increase in production costs due to the need for more cleaning and more downtime
- A decrease in wear in machine parts such as the sliding wall of the rotor spinning machine’s rotors, the traveller of the ring spinning machines, and the toothed cylinders of the feeding section of the rotor spinning machines, due to the fact that the spin finish recipes contain corrosion inhibitors. Whilst, overall, this is beneficial, it is well known that a degree of wear in machine parts enhances the quality of yarn spinning.