Antistatic Finish

ANTI-STATIC FINISHES

Static electricity?

It is the ability of fibers to draw and retain electrical charges from the air resulting in a build up on the fabric’s surface. The electricity is generated by friction of a fabric against itself or against another fabric or object. Some fabrics are inherently static.

Fabrics with static electricity:• produce shocks• cause garments to cling together or to the wearer• attract dirt or lint• allow dirt to adhere to the fabric muting colors or fabric Warning for Static electricity

Antistatic Finish

Definition

Antistatic finishes involve chemical substances applied as wet finishes for the purpose of reducing or eliminating static. These chemicals absorb small amount of moisture from the atmosphere, thus reducing the dryness of the fabric that reduces the static conduct.

Purpose

Antistatic finishes tend to:

• improve the surface conductivity, and thereby helps the electrons to move either to the ground or to the atmosphere

• attract molecules of water to the surface, which increase the conductance and carry away the static charges

• develop an electric charge opposite that of the fiber, which neutralizes the electrostatic charge.

The most effective finish combines all the three effects.

Antistatic Finish

Fibers treated with Antistatic Finish:

• Hydrophobic fibers (synthetic fibers except acetate & rayon).

• Antistatic finish is also required for natural fibers, but only if they are very dry (wool, cotton ) in which case they act as if they are hydrophobic.

•Glass is an exception because of its composition.

Antistatic Finish

Other solutions to Static Problems

Some variants used are:

• Anti-static sprays applied to fabrics during the cutting & sewing

• Anti-static products used during the care or laundering of garments

• Anti-static rods are used in the manufacturing processes of fabrics

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Other solutions to Static Problems

•High voltage ionisers used in loom or other sheds

•Radio active eliminators are also used for the same purpose using radio isotope Thallium 204

•Anti-static agents can be applied to filaments, yarns or fabrics.

Mechanism

Antistatic agents increases the conductivity of the fiber surface and reduces the frictional forces through lubrication.

Forms an intermediate hygroscopic layer on the surface.

The effectiveness of hygroscopic layer depends greatly on the humidity of the surrounding air during actual use; lower humidity leads to lower conductivity and greater problems.

In non-polymeric antistatic finishes, the hydrophobic structure parts of the molecule act as lubricants to reduce charge buildup.

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Cationic antistatic agents align with hydrophobic group away from the fiber surface.

Antistatic effect from anionic and non-ionic increases conductivity from mobile ions and the hydration layer that surrounds the hydrophilic portion of the molecule.

Mechanism

Chemistry of Antistatic Finishes

There are two effects possible with antistatic finishes:

Non-Durable finishes

Durable finishes

Non-Durable Finishes

Preferred for fibers and yarn processing finishes. Since ease of removal is important.

General requirements of non-durable anti-stats are:

• low volatility

• low flammability

• non-yellowing (heat stable)

• non-corrosive

• low foaming properties Continued….

1. Esters of phosphoric acid

• Forms the largest group of non-durable anti-stats.

• Durability of phosphoric acid ester increases with molecular size.


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2. Quaternary ammonium:

•Forms the second largest group of non-durable antistats.

•Most widely used are

- di tallowdimethylammonium chloride

- di hydrogenated tallow di methylammonium chloride

•Common ingredients in laundry and dryer.


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3. Non-ionic compounds

•It includes

- ethoxylated esters

- alcohols

- alkylamines

•The non-ionic materials provide increased moisture absorption and cationic products provides the mobile counter ions.


Difficult to achieve

Principle involved

• to form a cross linked polymer network containing hydrophilic groups

Steps involved in application

• Polyamines are reacted with poly glycols to make cross linked structures

• Polymers are formed prior to application to fabric or in situ on the fiber surface

Durable Finishes

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• Variety of cross linking can be used based on poly epoxides

• Larger the hydrophilic portion, the more moisture is absorbed and greater the antistatic effect obtained

Durable Finishes

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Difficulties in cross linking

• Higher degrees of cross linking reduce the moisture absorption and subsequent swelling, thus decreasing the antistatic effectiveness

• Interferences with soil release and soil re-deposition properties.

Durable Finishes

Process

On the basis of their application, antistatic finishes can be classified as:

Chemical Process

Mechanical Process

Antistatic Finish as a Chemical ProcessInvolve chemical substances applied as wet finishes for the purpose of reducing or eliminating static buildup.

Chemical substances develops an electric charge opposite to that of the fiber and neutralizes the static charge buildup on the fiber by attracting molecules of water to the surface of the fabric.Some chemicals used:

• Quaternary ammonium compounds• Cationic organic compounds• Blend of cationic surface-acting agents

Applied by conventional wet-processing operations utilizing padding, spraying or exhaustion methods.

Antistatic Finish as Mechanical Process

Utilizes an antistatic mechanical eliminator, which ionizes the air around it producing enough ionization to neutralize the static buildup.

Antistatic mechanical eliminators include:•Shock less static bars•Enclosed static bars•Metal-encased static bars•Explosive-proof static bars•Circular static bars•One-point static bars•Introduction static bars •Environ stat static bars

Evaluation of Antistatic Finishes

It should be done in an environment where the temperature and relative humidity are thoroughly controlled.

Different tests done are:• Ash test• AATCC Test Method 115: Electrostatic clinging of fabrics• AATCC Test Method 76: Electrical resistivity of fabrics.• Charge Dissipation Test• AATCC Test Method 134:Electrostatic properties of carpets

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ASH TEST

This test is mainly used as a qualitative tool to distinguish between antistatic- treated and untreated fabrics.

•Fabric to be evaluated is rubbed briskly on a piece of plastic or rubber.

•Then fabric is placed over ashtray containing cigarette ash.

•The amount of ash transferred to the fabric indicates the amount of static charge imparted to the fabric.


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AATCC TEST METHOD 115: Electrostatic clinging of fabrics

Fabric to metal test also known as the CLING TEST

•A electrically charged fabric is placed next to a grounded inclined metal plate.

•Any residual electrical charges causes the fabric to cling to the plate.

•Time required for the fabric to be released from the plant is measured.

•The shorter the cling time better the antistatic properties.


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AATCC TEST METHOD 76: Electrical Resistivity Of Fabrics

Used to measure the surface resistivity of fabrics.

•The voltage drop across a ring electrode system is used to determine the fabric’s resistivity

•A resistivity value of 1011ohm/ square or lower is considered to be indicative of a fabric with negligible static propensity.

•The national fire protection Association (NFPA) has specified a resistivity of 1011ohm/ square for textiles intended for use in operating rooms with flammable anesthetic gases.


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Surface resistivity range(Ώ) Assessment

1x106 – 1x108 Very good

1x108 – 1x109 Good

1x109 – 1x1010 Satisfactory

1x1010 – 5x1010 Limit of sufficient

>5x1010 insufficient

Table showing values at normal climate with 65% relative humidity

•This method is easy and relatively reproducible to determine with the ring electrode.

•But it is based on a static test with no information about the important charging and discharging behavior of the textiles.

•Therefore, combination with a charge dissipation test is favoured.


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CHARGE DISSIPATION TEST

•This test is done with the Static Voltmeter

•Fabric sample is fixed vertically and charged with direct voltage or by rubbing with glass rod.

•The static Voltmeter measures the maximum charge generated as well as the charge decay.

•The time necessary for the charge to fall to one half its maximum value is recorded.

•Shorter this half-life, the better the antistatic properties.


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Table having values at normal climate with 65% relative air humidity:

Field intensity half-life time (s) Assessment

0-0.3 Very good

0.3-1 Good

1-2 Satisfactory

2-3 Sufficient

>3 insufficient


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AATCC TEST METHOD 134: Electrostatic properties of carpets

•A charge generated test for carpets

•The body voltage of a person wearing shoes with standard neoprene or leather soles is measured as they walk across a carpet.

•Maximum voltage after 30-60s is recorded.

•The lower the voltage, the better the antistatic properties.


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Points to be considered:

•Uniform fabric penetration is important for optimal performance.

•The use of wetting agents in the finish formulation is recommended.

•Pad, spray and Foam application are favoured.


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Side Effects of Antistatic Finishes:

•Decrease Wear comfort •Decrease Soil release properties•Increased soiling with dry soil•Yellowing after exposed to heat and•Impaired crock fastness of textiles dyed or printed with disperse dyes. •The permanence of antistatic finishing effects to repeat washings, even at 400C,is limited


Carpets for computer room.Upholstery fabrics Airbags for automobilesConveyor beltsFiltration fabricsAirmail bagsParachutes.Fabrics for hospital operating rooms.And protective clothing for work with flammable gases, liquids and powdered solids.

Uses

Research & Development

Antistatic Fibers

•Contains a section of carbon

•Some examples:

• Mosanto Chemical Company’s Ultron ® Nylon (used primarily for antistatic floor coverings )• Du Pont’s Negastat ® Polyster ( used primarily for clean room apparel as required in the aerospace and computer chip industries) •BHSF’s Resistant ® Nylon (Its uses include the antistatic conveyor belts, gloves and conductive brushes)

Conductive fibers

• Excellent durable control of static electricity is achieved by incorporating these fibers into fabric during spinning, knitting or weaving.

• These conductive fibers are always black or metallic in appearance and can be easily seen in most textiles, even at low levels of use thus limiting its use in very specialized apparel and carpeting.


MegatopiaInto

• Invented by TORAY Deutschland GmbH

•The perfect fusion of two great strengths, anti-static fiber and conductive fiber.

• High performance anti-static uniform material project made possible by a duct of new anti-static technologies.

• Blazing the frontier of the new age of anti-static uniforms.


Bibliography

Textile science – B.P.G. Gohl

Textile fiber to fabric – B.P. Corbman

Fabric finishing – J.J. Pizzuto

Understanding fabrics – Debbie Ann Gioello

Textile finishing - R.S. Pragya

Antistatic Finish

Documents

Transcript of Antistatic Finish