Finishing of technical textiles Description of different techniques used in wet processing to develop Technical Textiles Dr Muhammad Mushtaq Mangat www.mushtaqmangat.org Dec 31, 2012

Finishing of technical textiles

  Textile Finishing:   A process to improve the performance and

appearance of textile   It may be mechanical or chemicals processes   It could be temporary or permanent   examples:

  Calendering   Peaching   Raising   Coating   Deposition of chemicals (fire retarding)

Mechanical finishes

  Calendering

  Modification of fabric surface by passing fabric through hot roller

  Rollers may be engraved or polished

Purposes of calendering smoothing the surface of the fabric,

  increasing the fabric lustre

  closing the threads of a woven fabric

  decreasing the air permeability

  increasing the fabric opacity

  improving the handle of a fabric, i.e. softening

  flattening slubs

  obtaining silk-like to high gloss finishes

  surface patterning by embossing

  consolidation of nonwovens. [1]

Flattening effect on fabric of calendering

Calender definition and process

  A mechanical process to impart certain temporary or permanent effects on web, fabric or batt

  Material is passed through a nip of rollers, normally hot

  Rollers may be plane, polished, covered with fabric, engraved, embossed

Calender parameters   Calender speed (dwell time in nips)

  Temperature of calender

  Pressure of rollers (pressure per linear inch)

  Surface of rollers (polished, covered)

  Speed variation between bottom and top rollers

  Number of passes

  Over Feeding or under feeding

Calendering and Application of finishes

  Dry Calendering without application of finishes

  Drying and Calendering together

Pad Mangle and Calendering

[1]

Calendering of fabrics made by natural and synthetic fibers

  Natural fibers

  Need high pressure to defeat the physical memory and get a new shape, temperature role is less important than pressure

  Strength of web depends upon the cohesion of fibers, need high pressure to achieve a certain homogeneity

  Synthetic fibers

  Synthetic fibers require the presence of heat to defeat the physical & thermal memory of the fiber

  High temperature and low pressure are commonly in practice

  Speed of rollers should be same to avoid any un-wanted luster [2]

Rolling Calender for synthetic fibers [2]

Rolling Calender   It provides:

  smooth or gloss fabric surface   Reshape fibers, make them flatten and increase

cohesion by more tightly stack around (nestle effect)   Composed of three rollers   100-150 meter per minute for normal fabric and 30-35

for nonwoven   Can be run at 3000 PSI   Four or five rolls   Alternative rolls (polished and filled)   The intermediate resilient roll is of wool felt paper,

cotton, khaki wool and resilient wool and cotton blends which affords the extension of the webs [2].

SILK FINISHING CALENDER

  It provides a smooth fabric surface, light

luster and improved hand

  Provides comparatively soft

  Combination of small and big roller, provides wide nip. It will break any stiffness on the surface due to auxiliaries or weaving or knitting

Silk Calender [2]

FRICTION CALENDER - NOT FOR MOST NONWOVENS

  To give highly polished surface

  Also creates water repellency

  Normally used for apparel fabric

  Friction calender can be operated at different speeds

  Set of three rollers,; one filled and two polished

Friction calender [2]

SCHREINER CALENDER

  Used to obtain a controlled opacity, a desired softness luster and translucency

  Light reflection is changed due to changes on surface

  Pattern is engraved on the heated steel roll

  Name derived from the pattern which is 260 lines per inch at a 26 ó degree angle and only .001” of an inch deep

  It can consolidate the fibers by as much as 4% to 16%

  Can be used for natural, synthetic and blended or coated fabrics that are both knit and woven or non woven [2]

SCHREINER CALENDER [2]

EMBOSSING CALENDER

  Rollers with embossed patterns

  Can be used for types of fabrics including woven, non-woven and knitted cloth

  Desired shapes can be achieved by having certain patterns on calender rollers

  Other properties are similar to normal calender

  Can be used for all sorts of fabrics

  There are forged steel top roll and a filled bottom roll with the filling of wool felt [2]

Embossed Calender [2]

CIRÉ CALENDER

  The Ciré calender is used for glazing and glossing fabric surfaces using both high temperatures >425 F and high pressures >1500 PLI

  Porosity reduction and compaction is done

  Various types of fabrics can be processed

CIRÉ CALENDER

HI-DWELL - HEAT TRANSFER PRINTING CALENDER

  Also called paper printing machines

  Purpose is to transfer print from paper to fabric

  Hot rollers are used for paper printing

  Mostly used for polyester fabric

  Disperse dyes are used

Paper printing rollers

RESILIENT ROLLS

  Also called calender bowls

  Made by using high tonnage of pressure; 120,000 tons of pressure the cotton rings to be able to use as calender

  Rollers are quite hard in nature

RESILIENT ROLLS

[2]

Raising (Brushing)

  Raising is a process in which fabric is brushed with the help of wired rolls to give a brushed (napped) look

  Fibers are pulled from the yarn to make a soft feel and increased thickness

  It gives a hairy surface

  More air is trapped and thermal resistance increased

  Rotating rolls fitted with wires are used

Fabric Brushing Machine

Raising Methods

  Hooked or bent steel wires are used for brushing

  Angle, speed and pressure are main factors

  Number of rotating rollers, width of rollers define the capacity of machine

  More than one pass is normally require for uniform surface

[1]

Shearing

  A process in which piles of fabric are cut to

have a uniform and smooth surface

  Lawn mover (grass cutter) machine principle is applied

Compressive Shrinkage

(Compaction)

  Shrinkage on washing is a common phenomenon

  It is due to residual stress or strain in fabric during process

  Very common use

  Makes fabric more stable and minimize the shrinkage

[2]

Sueding (Peaching)

Sueding Technique

Sueding

  To give a peach look

  Brush or zero sand paper is used

  Improve hand feel

  Better thermal resistance

  Currently much demanded and in practice

Heat setting

  To make a stable fabric

  Used to ensure that there will be no change in dimensions

  Only used for synthetic fibers

  Required temperature is above the softening temperature of fibers

  Certain temperature and time is required for heat setting

Heat-setting mechanisms

  1. chain stiffness

  2. strong dipole links

  3. hydrogen bonds

  4. crystallization [1]

Influencing factors   Temperature, Moisture, stress.

  PET fabric is passed through stenter at 180-190 C for 30-60 seconds

  Sudden cooling effect, called decatizing is done for better setting

  Little moisture helps for better heat setting

  In general heat setting temperature is with in 20-20–40 °C of the fiber melting point.

  Hold at this temperature under tension for approximately 20 s.

  Cool fabric before removing tension

  After heat setting shrinkage should be less than 1% [1]

Transition temperatures

  Glass transition temperature:

  Molecules tarts moving in amorphous region

  Substance starts changing from a glassy solid to a rubbery solid

  Loosening starts and dyeing is possible

  Melting point   Thermal energy increases than holding

energy

Pleated Fabric

Permanent Pleats

  To give better look

  Increase usability

  Some special purpose fabric is made

  Common for ladies clothing

  Bags are produced for more space

Pleat Making Machine

Chemical Treatment   Fire retarding

  Water repellant

  Stain proof

  Ant bacteria, moth proof

  Self cleaning

  Flavored

  Anti pilling

  Anti slippery

 

Stiffening and filling process

  Polymers are used to create stiffness

  Stiff effect is required for certain purpose e.g. collar lining, curtain lining etc.

  Most common are poly vinyl acetate and poly vinyl chloride

  Applied on padding

High Wicking

  Wetting agents are used to increase wicking power of fabric

  Towels, T shirts, shorts are treated with wetting agents

  Applied on exhaust and padding

Anti-static finish

  PE is much popular to reduce the static effect

  Improve comfort of clothing

  Much required for sensitive skin

Anti-pilling finish

  Mostly enzymes are used to remove protruding fibers

  Also called bio-polishing

  Cleans the surface

  Reduces the chances

Non-slip finishes

  To have better grip

  Rough surface is developed

  Silica gel is commonly used

  Gives a crispy hand feel

Fire Resistant or Flame Retardant

  Flame retardants are materials which can minimize the spread of fire

  For better safety, becoming popular in every area,

  Many laws are being formulated to have Fire-retardant items at work event at homes

  Two techniques:   Application of chemicals on fabric surface   Making changes in fiber to make them fire

retardant

Anti-microbial finish   Microbes are the tiniest creatures, Cannot seen by the

naked eye

  Bacteria, Fungi, Algae and viruses are part of this group

  Bacteria are uni-cellular organisms, it grows rapidly under wet and warm conditions [3]

  Ant-microbial finishes are required to improve safety and comfort

  Brominated phenols, quaternary ammonium compounds, organo-silver and tin compounds, are used

  Pad or exhaust methods are used

Conti…   It controls the odor due to bacteria reproducing

  Finishes will stop bacteria reproducing

  It will minimize the amount of odor

  Stops cross infection by pathogenic micro organisms and control the infestation by microbes

  Arrest arrest metabolism in microbes in order to reduce the formation odour

  Protects the textile products from staining, discoloration and quality deterioration.

  [3]

[3]

Self Cleaning Fabric   To make clothing cleaner – permanently

  Possible by a polymer film of polyglycicidyl methacrylate sprinkled with silver nanoparticle

  Not actually self-cleaning

  High resistance to dirt

  Concept is based on the lotus plant

  Lotus leaves are well-known for their ability to ‘self-clean due to repelling properties of water and dirt

  Some water to rinse away dirt and stains, but cleaning will be quicker [5]

Hybrid Polymer Nanolayers [5]

Lotus Leaf

References [1] Hall, M.E., Finishing of technical textiles, in Handbook of Technical Textiles A.R. Horrocks, Anand, S. C., Editor 2000, Woodhead Publishing Ltd Cambridge.

[2] Gunter, D.S., Perkins, B. F. . THE BASIC MECHANICS OF CALENDERING AND EMBOSSING NONWOVEN WEBS. 2012; Available from: http://www.idspackaging.com/common/paper/Paper_320/calendering_wp.pdf.

[3] Aravin, P. , and Myvizhirajeswari, G. SILVER BASED ANTI‐ ?MICROBIAL FINISHING ON COTTON

[4] Tanveer Malik, T. and Nogja, S., Goyal, P. Self cleaning textile - an overview http://www.fibre2fashion.com/industry-article/4/389/self-cleaning-textile-an-overview2.asp

[5] http://www.technovelgy.com/ct/Science-Fiction-News.asp?NewsNum=271