Antistatic finishes

Antistatic coatings Antistatic finishes Antistatic yarns Antistatin D Antisterility vitamin Antistick agents Antistick applications Anti-Stokes lines... 

Finish antistats Finish distressing Finishers Finishes... 

Electrical Behavior. The resistivity of acetate varies significantly with humidity with typical values ranging from 10 ohm-cm at 45% rh to 10 ohm-cm at 95% rh (16). Because of the high resistivity both acetate and triacetate yams readily develop static charges and an antistatic finish is usually apphed to aid in fiber processing. Both yams have also been used for electrical insulation after lubricants and other finishing agents are removed. 

Quantitative Relationship of Conductivity and Antistatic Action. Assuming that an antistatic finish forms a continuous layer, the conductance it contributes to the fiber is proportional to the volume or weight and specific conductance of the finish. As long as the assumption of continuity is fulfilled it does not matter whether the finish surrounds fine or coarse fibers. Assuming a cylindrical filament of length 1 cm and radius r, denoting the thickness of the finish layer as Ar and the specific conductance of the finish k, the conductance R of the finish layer is given by the equation (84) ... 

The required extent of durabiUty depends on the use of the treated article. For example, an antistatic finish that is removed after several launderings would be termed nondurable for blankets to be used in hospitals and motels where static protection through over fifty launderings is desirable. However, the same finish appHed to blankets for household use which would be laundered once or twice per year could be termed durable. Antistatic finishes have been widely reviewed (73—75,77,86,90—95). 

Durable Antistatic Finishes. The difficulty with nondurable finishes, as far as the consumer is concerned, is that they are water-soluble and thus easily removed by washing. An effective antistatic finish must be durable and capable of withstanding repeated laundering and dry-cleaning cycles. 

Only a small number of durable antistatic agents are available for textiles. Semidurable antistatic finishes for textile materials based on compounds of limited solubiUty and moderate resistance to wet treatments were known in the eady 1950s. 

Some commercial durable antistatic finishes have been Hsted in Table 3 (98). Early patents suggest that amino resins (qv) can impart both antisHp and antistatic properties to nylon, acryUc, and polyester fabrics. CycHc polyurethanes, water-soluble amine salts cross-linked with styrene, and water-soluble amine salts of sulfonated polystyrene have been claimed to confer durable antistatic protection. Later patents included dibydroxyethyl sulfone [2580-77-0] hydroxyalkylated cellulose or starch, poly(vinyl alcohol) [9002-86-2] cross-linked with dimethylolethylene urea, chlorotria2ine derivatives, and epoxy-based products. Other patents claim the use of various acryUc polymers and copolymers. Essentially, durable antistats are polyelectrolytes, and the majority of usehil products involve variations of cross-linked polyamines containing polyethoxy segments (92,99—101). 

Cross-linked finishes are not permanent in the tme sense of the word however, under optimum conditions the finish can last for the usehil life of the material. Wet abrasion during laundering is probably the principal cause of gradual removal of the finish. In order to retain antistatic protection for extended use, an excess of finish is often appHed The extent of chemical interaction between the durable antistatic agents and the fiber substrates to which they are appHed is not perfectiy understood. Certain oxidizing agents such as hypochlorite bleaches tend to depolymerize and remove some durable antistatic finishes. Some of the durable finishes have also produced undesirable side effects on textile materials, ie, harsh hand, discoloration, and loss of tensile properties. 

Application of Antistatic Finishes. Antistatic finishes are commonly appHed to textile materials by padding (dipping and squeezing off excess finish), exhausting (absorption from solution due to affinity of the antistat for the textile material), spraying, and coating (see Textiles, finishing). 

Eor instance, exhaust appHcation is possible with cationic finishes which have an affinity for the anionic groups in polymeric materials. After appHcation, the textile is dried. Durable antistatic finishes require cross-linking of the resin. Cross-linking is usually achieved by subjecting the treated, dried material to heat curing. A catalyst is often incorporated to accelerate insolubilization. 

Soiling of Antistatic Finishes. Soiling of fabrics having a tendency for accumulation of charges has been assumed to be an electrostatic phenomenon, and therefore it follows that if static is eliininated, soiling will be reduced. However, most antistatic agents have been developed and used for reasons other than the reduction of soiling. 

Some effects are similar or assist each other, for example silicone elastomers cause water repellency, softeners bring about antistatic effects and antistatic finishes can be softening. 

Some effects are obviously contradictory, for example hydrophobic finishes and hydrophilic antistatic finishes, or stiffening and elastomeric finishes, or stiffening and softening finishes. 

The combination of EC and antistatic finishes, achieved with selected products is important for synthetic microfibre textiles. Other common finish combinations include hand builders, flame retardant and antimicrobial agents, which generate valuable and useful multifunctional finishes. 

Effects of other finishes Compatible with antistatic finishes, easy-care finishes and other finishes not harmed by a hydrophilic surface. Not compatible with conventional repellent finishes and other finishes where hydrophilicity is detrimental to finish performance... 

Most non-polymeric antistatic finishes are also surfactants that can orient themselves in specific ways at fibre surfaces. The hydrophobic structure parts of the molecule act as lubricants to reduce charge buildup. This is particularly true with cationic antistatic surfactants that align with the hydrophobic group away from the fibre surface, similar to cationic softeners (see Chapter 3, Fig. 3.1). The main antistatic effect from anionic and non-ionic surfactants is increased conductivity from mobile ions and the hydration layer that surrounds the hydrophilic portion of the molecule since the surface orientation for these materials places the hydrated layer at the air interface. 

Perhaps the simplest test method for the evaluation of antistatic finishes is the ash test. A piece of the fabric to be evalnated is mbbed briskly on a piece of plastic or rubber (the vinyl covered arms of a chair, for example). The fabric is then placed over an ashtray containing cigarette ash. The amount of ash transferred to the fabric is an indication of the amount of static charge imparted to the fabric. Owing to the difficulty in quantifying the results, this test is mainly nsed as a qualitative tool to distinguish between antistatic-treated and untreated fabrics. 

Table 10.2 Surface resistivity and practical use of antistatic finished textiles ...

The performance of most antistatic finishes depends on the kind of fibre and sometimes also on the kind of fabric (anisotropic behaviour, for example, different... 

Permanent antistatic fmishes, based on crosshnked polyamines and polyglycols, need an alkaline catalyst. Therefore the one-bath combination with finishes, which need acid catalysis, is difficult but not impossible. Examples of acid-catalysed fmishes are the easy-care and durable press fmishes, durable hydrophylic silicone softeners and elastomeric finishes, also fluorocarbon-based repellency and some flame-retardant finishes. High finish effects result from a two-bath application with of the easy-care finish first followed by the surface-related antistatic finish. 

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