Fabric Science ll

End Term Assignment

Submitted By: Lakshita Saini

Q1. Write brief note on Importance of testing and classify different types of fabric
properties with examples.
Ans. Textile testing
The quality of a product is checked before it is put into large-scale usage. The quality of the product,
its performance, and its reliability are the key factors while testing is performed. Testing can be
defined as the methods or protocols adopted to verify the properties of a product. It can be divided
primarily into two types: regular process testing and quality assurance testing. Routine testing helps
to streamline the daily process. Quality assurance testing helps the product in the long run to
establish credibility.
The primary purpose of textile testing and analysis is to assess textile product performance and to
use test results to make predictions about product performance.
Examples of testing for end-use performance include testing draperies for light fastness or tire cords
for strength.

The main objective of testing and analysis are:

 Research and Development:

This helps textiles scientists determine how to proceed at the each stage of product
development. This category also includes testing in order to study theories of fabric or fabric or
fibre behavior.

 Quality Control
Manufacturers may use quality-control testing as a marketing tool, in that trade names imply to the
consumer that certain levels of quality are assumed to be standard for products produced by the
manufacturer. Quality-control testing aids the manufacturer in assuring that the expected level of
quality is maintained.

 Comparative Testing
Comparative testing compares two or more products being considered by a company. For example,
a jeans manufacturer may perform a series of tests on denim fabrics from different suppliers prior to
deciding which supplier to use for its product. In selecting between competitive products, a fabric
manufacturer also may test fibres or yarns from different suppliers.
 Analyzing Product Failure
Testing is done in this case to pinpoint defects in processing or design. The example of the trouser
pockets falls into this category. Results from this type of test can be used to improve products, and
are also used to determine liability in litigation.

 Government Regulations
Textile product testing is performed in order to meet government regulations. Such regulations
may require mandatory testing of products before they can be legally sold. An example of this is
the flammability testing of textiles.

 Selection of Raw Materials

‘Raw Materials’ is a relative term; the raw material of the spinner is the fibre, the raw material of the
weaver is yarn, and that of the finisher is cloth. Since prevention is better than cure it is sound policy
to test the available raw materials to ensure the smooth running of production processes. The
standards by which raw materials are accepted or rejected must be realistic, otherwise much will be
rejected which in fact is good enough, or else a large amounts of inferior material will find its way
into the flow of production and cause trouble..

 Process Control
Higher end-breakages in spinning and winding departments and excessive looms stops due to warp
or weft breaks affect the operatives as well as production. In a spinning mill the most common
characteristic measured is the weight per unit length of the lap, sliver, roving, or yarn. The nominal
hank or count is decided upon and control limits are calculated from test results. For maximum
effectiveness the ‘process control’ test should be close to the processing machinery. Quick answers
are required to prevent excessive amounts of faulty material from getting through before detection.

 Process Development
In each case investigations into better, cheaper, and quicker methods of manipulating fibres and
yarns are made. The success achieved is often measured by the improvement in one or more
characteristics of the material delivered after change in machine design or setting.

 Product Testing
The testing of the product helps in the continual search for new knowledge. Sometimes a forecast
of the probable performance in a subsequent process is required. The performance of a finished
article in actual service could be the object of a product test. One problem is the assessment of the
resistance of a fabric to the ‘wear and tear’ of everyday use. We could try to imitate the kind of
treatment meted out to the fabric, rubbing it against abrasives, wetting it and drying it, bending it,
stretching it, creasing it, and so on. We might subject the material to a series of laboratory tests, each
of which tests only one property at a time.

 Monitoring Production

Production monitoring, which involves testing samples taken from the production line, is known as
quality control. Its aim is to maintain, within known tolerances, certain specified properties of the
product at the level at which they have been set. A quality product for these purposes is defined as
one whose properties meets or exceeds the set specifications.

 Assessing the Final Product

In this process the bulk production is examined before delivery to the customer to see if it meets the
specifications. By its nature this takes place after the material has been produced. It is therefore too
late to alter the production conditions. In some cases selected samples are tested and in other cases
all the material is checked and steps taken to rectify faults.

 Investigation of Faulty Material

If faulty material is discovered either at final inspection or through a customer complaint it is

important that the cause is isolated. This enables steps to be taken to eliminate faulty production in
future and so provide a better quality product.

Fabric Properties

Physical properties of Fabrics

 Fiber or filament: type, size, length

 Yarn: diameter, twist, weight or size, count, fiber content for mixed yarns, ply.
 Weight: ounces per squared or yards per pound.
 Thickness: vertical depth.
 Fabric structure
 Woven fabrics: weave type, warp and filling yarn count per linear inch<li>
 Knitted fabric: knit type, wale and course count per inch
 Finishes: chemicals such as resins, starches, waxes and mechanical effects such as Calendaring
and napping applied to the woven fabric to yield or enhance style, durability, and utility values.
 Fabric width: The length of the filling or course
 Colour: Hue, value, and intensity (degree of brilliance)
 Fabric density: weight per unit of volume.
 Surface contour: the geometric dimension of the surface plane.

Physical characteristics of fabrics

 Style characteristics
 Utility characteristics
 Durability characteristics
 Product production characteristics

Style characteristics of a fabric

This is exemplified when a consumer handles a fabric and refers to the fabric with adjectives such as
stiff, soft, hand, etc. The three basic categories for style characteristics are:

 Hand characteristic – are the changes of the fabric plane with hand manipulations, which exert
tensile compression, molding, or supporting forces on the fabric. The hand characteristics
include some of the utility characteristics, such as elongation, elasticity, flexibility, etc.
 Tactile characteristics – refer to the changes in surface contour that result from a mechanical
force exerted on or against the surface structure. These changes apply to the surface contour
aspects of the fabric surface and not the fabric plane. Pile, napped, and any fabric whose surface
contour can be varied by tactile pressure, have obvious tactile characteristics. Designers specify
tactile characteristics with terms such as soft, coarse, rough, hard, smooth sticky, oily and greasy.
 Visual characteristics – are the changes in the color values when either the fabric or light is
moved. End – to – end shading, side – to – side shading and mark – off are three color
quality problems in addition to metamorphic fabrics.

 End – to – end shading – refers to changes in shade throughout the length; the shade of one
end of the bolt differs from the shade of another end.
 Side – to – side shading – refers to changes in shade from selvage to selvage; the shade of
the fabric along one selvage differs from the shade of the fabric along the other selvage.
 Mark – off – in the fabric is the phenomena of changing the shade and/or the intensity of the
fabric surface by rubbing it.
 Metamorphic – fabrics exhibit color difference with the change in the spectral
distribution(characteristics) of the illuminant
Utility Characteristics

Utility characteristics are changes in the fit, comfort, and wearing functions of the garment when the
fabric engages a mechanical thermal, electrical, or chemical force during the utilization of the
garment. The two major types of utility characteristics are transmission and transformation.
Transmission characteristics include:

 Air permeability ( includes all gases and vapor)

 Heat transmission ( thermal conductivity)
 Light permeability
 Moisture transmission
 Radioactivity transmission (the degree with which radioactive energy such as x-ray and gamma
rays can penetrate fabrics)

Transformation characteristics include:

 Colorfastness
 Crease resistance
 Crock resistance
 Dimensional stability
 Pilling
 Shrinkage
 Static electricity etc

Durability characteristics

Durability characteristics are the capacities of fabric to maintain the style and utility characteristics
during wear. It is the measure of stress which destroys the fabric or the fabrics ability to repeat a
desired style or utility characteristic. The durability characteristics are:

 Abrasive strength (the measure of rubbing action)

 Bursting strength (the measure of vertical pressure)
 Launder-ability (the measure of washing)
 Tearing strength
 Moth resistance
 Tensile strength
 Radiation absorption strength (the rate at which radiation energy either disintegrate a fabric or
destroys utility characteristics).
 Fire resistance
 Corrosive strength ( the measure of chemical action, acid or alkaline)
 Dry cleaning durability ( the measure of dry cleaning performance)

Product Production working characteristics

Product production working characteristics are those characteristics which affect the quality of
production with respect to quality values and the cost of production method. The working
characteristics of a fabric include:

 The coefficient of friction ( cutting, sewing, pressing and packing)

 Sewed seam strength
 Sewed seam slippage (yarn slippage)
 Sewing distortions
 Yarn severage
 Bondability strength (fused, cemented, and heat – sealed seams
 Pressing moldability (to what degree a flat piece of fabric may be skewed during pressing with
hand and /press buck).
 Die moldability – how well a flat seamless piece of fabric may be molded with dies into a given
from such as a bra cup or a hat.

Q2. Explain pre treatment process used in textile industry

Ans. Pre-treatment is a heart of processing of textile. In pretreatment, all these impurities are
removed and fabric is brought to a stage where it is more absorbent and white and can be easily
processed further for printing and dyeing. Uneven desizing, scouring, and bleaching in the
pretreatment processes might cause drastic deterioration in the qualities of processsed products,
such as uneven dyeing and decrease in fastness.

Objective of Pretreatment:

 To Convert fabric from hydrophobic to hydrophilic state (High and even Hydrophilicity /
Rewettability).

 To remove dust, dirt, foreign substances and seed husks from the fabric.
 To achieve the degree of desire whiteness.

 Good desizing effect

 Lowest possible fiber damage

 Good Physical/Technological ratings

 High color yield

Pretreatment Process of Textile Materials:

Inspection of grey fabric
(Assessment of different types of faults)
↓
Stitching
(Adding two or more than two fabric together)
↓
Searing and cropping
(Removal of excess thread from the fabric)
↓
Singeing
(Removal of short fiber ends from fabric surface by burning)
↓
De-sizing
(Removal of sizes, which was applied as weaving aid)
↓
Scouring
(Removal of natural or adventitious impurities)
↓
Bleaching
(Destruction of natural coloring and improving whiteness)
↓

Souring

(Neutralize the alkali with an acid)

 ↓
Mercerizing
(Treatment of cotton with strong alkali under tension)

↓
Washing

(Wash the fabric with hot and cold water)

↓

Rinsing

(Washing with clean water to remove soap, detergent, dirt or impurities from fabric)

↓
Drying
(Removal of excess water from fabric)

All the processes of this stream are carried out in an aqueous state or aqueous medium.
The main processes of this section include :
• Singeing • Desizing • Scouring • Bleaching • Mercerizing

Singeing
This is the burning off of protruding fiber ends from the surface of the fabric. If not done properly,
unclear print patterns, mottled fabric surfaces, and pilling results.
Necessity:

 Smooth appearance

 The protruding fibers obstruct the subsequent dyeing and printing process.

 Goods which are to be mercerized are signed to maximize the luster

 In fabrics of polyester and cellulosic fiber blends singeing is the best method to control pilling,
sometimes double singeing is done to minimize the pilling.

Singeing Process:

 Fabric surfaces are brushed lightly to raise the unwanted fiber ends.

 Then the fabric is singed with or passed over heated copper plates or open gas flames. The fiber
ends burn off.
 As soon as the fabric leaves the singeing area, it enters a water bath or desizing bath. This stops
any singeing afterglow or sparks that might damage the cloth.

Precautions:

 The fabric to be singed should be dry as wet fabric tend to scorch more readily than dry.

 Uneven singeing may cause streaks on fabric or bubbles when the fabric is finished.

 Improper singeing may lead to loss of 75 % loss in tensile strength loss in warp direction.

 The fabric should not contain any acid releasing salt, which may release acid on heating and
tender the fabric.

 Stopping the machines may cause bars on the fabrics.

 Possibility of thermal damage to temperature sensitive fabrics.

Desizing
Desizing eliminates sizing products to ensure the success of scour boiling and bleaching and the
production of faultless dyeing. Before starting this process, it is better to determine the type of the
sizes, to facilitate their removal.

Natural sizing agents:

 Starch and starch derivatives: native starch, degradation starch, chemically modified
starch products

 Cellulosic derivatives: carboxymethylcellulose (CMC), methylcellulose, oxyethylcellulose

 Protein-based starches: glue, gelatin, albumen

Synthetic sizing agents:

 Polyacrylates
 Modified polyesters
 Polyvinyl alcohols (PVA)
 Styrene/maleic acid copolymers

Desizing process:

Desizing, irrespective of what the desizing agent is, involves impregnation of the fabric with the
desizing agent, allowing the desizing agent to degrade or solubilise the size material, and finally to
wash out the degradation products. The major desizing processes are:

 Enzymatic desizing of starches on cotton fabrics

 Oxidative desizing
 Acid desizing
 Removal of water-soluble sizes
 Fermentative desizing
Necessity:

 To remove the starch material from the fabric.

 To increase the absorbency power of the fabric.

 To increase the affinity of the fabric to the dry chemicals.

 To make the fabric suitable for the next process.

 To increase the luster of the fabric increase of dyeing and printing.

Factors of Size Removal Efficiency:

 Type and amount of size applied

 Viscosity of the size in solution

 Ease of dissolution of the size film on the yarn

 Nature and the amount of the plasticizers

 Fabric construction

 Method of desizing, and

 Method of washing-off

Scouring
It is the process of removing natural impurities present in fibre. If those impurities present are not
removed, then it will be difficult to dye or print the fabric uniformly. Normally caustic soda ash is
used as main reagent fro scouring of cotton fabric.

Necessity:

 To remove natural as well as added impurities of essentially hydrophobic character as

completely as possible

 To increase absorbency of textile material

 To leave the fabric in a highly hydrophilic condition without undergoing chemical or physical
damage significantly.
Scouring process depends on:

 The type of cotton

 The color of cotton

 The cleanliness of cotton

 The twist and count of the yarn

 The construction of the fabric

Scouring Process:
1. Conventional scouring process:

 Kier boiling (discontinuous) scouring.

 Scouring in J or L box (continuous).

 Exhaust method

2. Special scouring process:

 Solvent scouring process.

 Vapor lock scouring process.

Precautions:

 Kier boiler should be cleaned.

 Material should be packed evenly.

 Complete immersion of the fabric need.

 After boiling the liquor should be removed in absence of water.

 Before starting all the joining parts should be checked.

 Fabric should always keep under scouring solution.

Bleaching
Bleaching is chemical treatment employed for the removal of natural coloring matter from the
substrate. The discoloration takes place by the breaking the chromophore. The material appears
whiter after the bleaching.
Necessity:

 Removal of coloured impurities.

 Removal of the seed coats.

 Minimum tendering of fibre.

 Technically reliable & simple mode of operation.

 Low chemical & energy consumption.

 Increasing the degree of whiteness.

Bleaching Agent:
A bleaching agent is a substance that can whiten or decolorize other substances. Bleaching agents
essentially destroy chromophores (thereby removing the color), via the oxidation or reduction of
these absorbing groups.
Type of Bleaching Agents

1. Oxidative Bleaching Agents

2. Reductive Bleaching Agents

3. Enzymatic Bleaching Agents

Mercerizing:
The material is immersed under tension in a cold sodium hydroxide (caustic soda) solution in warp
or skein form or in the piece, and is later neutralized in acid. The process causes a permanent
swelling of the fiber and thus increases its luster. It is the process of treatment of cellulosic material
with cold or hot caustic conditions under specific conditions to improve its appearance and physical
as well as chemical properties.
Necessity:
 To improve the lusture
 To improve the strength
 To improve the dye uptake and moisture regain.

Mercerizing process:
a. Impregnation of the material in in relaxed state,cold caustic solution of required strength and
wettability..
b. Stretching while the material is still impregnated in the caustic solution.
c. Washing off the caustic soda from the material while keeping the material still in the stretch state.
The effects of mercerization:

 Improved luster

 Increased ability to absorb dye

 Improved reactions with a variety of chemicals

 Improved stability of form

 Improved strength/elongation

 Improved smoothness

Process Requirements in litres/ kg of product

Process Water requirement (litres/kg)
Sizing 0.5-8.2
De-sizing 2.5-21
Scouring 20-45
Bleaching 2.5-45
Mercerizing 17-32
Dyeing 100-300
Printing 8-16

Q3 .Classify dyes and explain different stages and methods of dyeing with
parameters.
Ans. Textile dyes are substances used to color fabrics. The dyes soak into the fabric and change it
chemically, resulting in color that stays permanently through repeated use.

 Acid Dyes- Acid dyes are water-soluble anionic dyes, containing one or more sulfonic acid
substituents or other acidic groups. An example of the class is Acid Yellow 36. Acid dyes are
water-soluble anionic dyes that are applied to fibers using neutral to acid dye baths. Acid dyes
are not substantive to cellulosic fibers. Most synthetic food colors fall in this category. The dyeing
process is reversible and may be described as follows:

 Direct Dyes- These are the dyes which can be applied directly to the fabrics from an aqueous
solution. These are most useful for fabrics which can form hydrogen bonds with the Dyeing of
Fabrics. The colors are not as brilliant as those in the basic dyes but they have better fastness to
light and washing. They are water soluble because of sulfonic acid groups.
E.g Direct orange 26 is a typical direct dye.
 Azoic Dyes - Azo dyes contain at least one azo group (-N=N-) attached to one or often two
aromatic rings. These dyes are used primarily for bright red shades in dyeing and printing since
most other classes of fast dyes are lacking in good red dyes. Unless they are carefully applied
and well washed, they have poor fastness to rubbing or crocking. The production of bluish red
azoic dye from the following two components is an example.

 Disperse Dyes- Disperse dyes were originally developed for dyeing secondary cellulose acetate
fibers. These dyes are relatively insoluble in water and are prepared for dyeing by being ground
into relatively fine powder in the presence of dispersing agents. Disperse yellow 3, Disperse Red
4, and Disperse Blue 27 are good examples of disperse dyes.

 Sulphur Dyes- The sulphur dyes provide very deep shades, which have excellent resistance to
washing but poor resistance to sunlight. A problem with sulphur dyes especially the black colors
is that they make the fabric tender, or weaken its structure, so that it breaks easily. Sulfur dyes
are applied to cotton from an alkaline reducing bath with sodium sulfide as the reducing agent.
They are low cost and have good fastness to light, washings and acids.
 Reactive Dyes-These dyes react with the cellulosic fiber to form a covalent bond. This produces
dyed fiber with extremely high wash fastness properties. These are the dyeing of fabrics which
contain a reactive group which combines directly with the hydroxyl or the amino group of the
fibre. Because of the chemical reaction the colour is fast and has a very long life. Example:
Reactive Blue 5 dye
 Basic Dyes- Basic dyes were originally used to color wool, silk, linen, hemp, etc., without the use
of a mordant, or using agent. With a mordant like tannic acid they were used on cotton and
rayon. Basic dyes give brilliant colors with exceptional fastness to acrylic fibers. Basic Brown 1 is
an example of a cationic dye that is readily protonated under the pH 2 to 5 conditions of dyeing.
 Mordant Dyes (Chrome Dyes)- These Dyeing of Fabrics do not dye the fabric directly but
require a binding agent known as mordant. The mordant acts as a binding agent between the
fibre and the dye.The metallic precipitate is formed in the fiber producing very fast colors highly
resistant to both light and washing.
Example: Mordant Red 11
 Vat Dyes- Vat dyes are made from indigo, anthraquinone and carbazole. Vat dyes are also
used in the continuous piece of dyeing process sometimes called the pigment application
process. The dyeings produced in this way have high wash and light fastness. An example of a
vat dye is Vat Blue 4 (Indanthrene).
 Solvent Dyes- These dyes are water-insoluble but soluble in alcohols, chlorinated hydrocarbons,
or liquid ammonia. These colours are applied by dissolving in the target, which is invariably a
lipid or non-polar solvent. The Colour Index uses this as a classification and naming system. Each
dye is named according to the pattern: – solvent + base colour + number They are used for
coloring synthetics, plastics, gasoline, oils and waxes. Example: solvent yellow 32
 Naphthol dyes-
• They are soluble in water and have a limited color range.

• They are used mostly for brilliant reds, and also for maroon, brown and black.

• Washing fastness is equal to vat dyeing, but light fastness is less, while crocking fastness varies
with the color.

Some dye application:

Name of Dyes Application

Acid dye Man made fiber (Nylon),
Natural fiber (Silk, Wool)
Direct Dye Man made fiber (Viscose),
Natural fiber (Cotton)
Vat dye Man made fiber (Viscose),
Natural fiber (Cotton, Silk, Wool)
Disperse dye Nylon, Polyester, Acrylic,
Tri-acetate, Di-acetate
Basic dye Jute, Acrylic
Reactive dye Cotton, Wool, Silk, Viscose,
Nylon
Sulfur dye Cotton, Viscose
Mordant dye Cotton, Wool, Silk
Pigment Cotton, Man made fiber
Mineral Cotton, Wool, Silk
Azoic dye Cotton, Viscose
Aniline Black Cotton
Rapid and Rapidson Cotton
dye
Onium dye Cotton, Jute
There are various methods of textile dyeing which are as follows:

1. Fiber Stage Dyeing Method

2. Yarn Stage Dyeing Method

3. Fabric Stage Dyeing Method

4. Garment Stage Dyeing Method

Fiber Stage Dyeing Method

In this method, the dyeing is done at the fiber stage. Either the dyestuff is mixed in the chemical
solution to manufacture man-made fibers or the fibers are dyed in the dyebath.

Yarn Stage Dyeing Method

In this method, the yarns that are spun using fibers are immersed in the dyebath, partially and
completely. This is done before the yarns are used for the construction of fabrics. This is specially
used to create various designs in the fabric, such as:

 Stripes

 Checks

 Plaid

 Tweed

Fabric Stage Dyeing Method

In this method, color is applied to the fabric after its construction. The fabric is submerged into the
dyebath to get the desired color.

Garment Stage Dyeing Method

In this method, the finished garment is dyed in the dyebath in order to get the desired color.

These are the different ways in which textiles can be dyed. The various ways of dyeing textiles
are:

 Solution Dyeing

 Stock Dyeing

 Hank/Skein Dyeing

 Package Dyeing
 Beam Dyeing (Yarns)

 Winch/Beck Dyeing

 Jet Dyeing

 Jig Dyeing

 Pad Dyeing

 Beam Dyeing (Fabric)

 Paddle Dyeing

At the Fiber Stage

 Solution Dyeing

As the name suggests, the dyestuff is added to the chemical solution of the man-made fiber. When
the fiber filament appears from the spinnerette, the filament appears colored. The advantage of this
technique is that the colorfastness property of the textile will be excellent.

 Stock Dyeing

This technique also involves dyeing at the fiber stage. The loose fibers are immersed in the dyebath
before the processes of blending, combing, carding, and spinning take place. The advantages of this
technique are as follows:

 Excellent colorfastness property to the textile

 This allows creating a yarn of multiple colors to give a melange look in the fabric

 Uniform distribution of the dyestuff

This is the costliest method of dyeing. The reason is that the dyeing is done prior to manufacturing
of the yarn, which will incur some wastage of the fibers, depending on the quality of the yarn
required for further processing.

At the Yarn Stage

 Hank/Skein Dyeing

This technique involves dyeing at the yarn stage. The yarns are loosely arranged in a hank or skein
form over a ring in a large container. This is then immersed in the dyebath to get the desired colors
on the yarn. This is suitable for yarns which cannot be too stretched or compressed like wool.

 Package Dyeing

In this, the yarn is wound on yarn carriers in packages in the spinning stage. The packages could be
in the form of cones, cheeses, tubes etc. They are then arranged on perforated frames. The dye
solution is then penetrated through the packages in a continuous movement to get the desired
color.

 Beam Dyeing (Yarns)

This technique involves dyeing at the yarn stage. In bean dyeing, the warp yarns are wound on
cylindrical beams which are placed in a machine. The dyebath is run in a center-to-outside and then
in an outside-to-center motion to get the desired depth of the color.
At the Fabric Stage

 Winch/Beck Dyeing

The fabric ends are stitched together to make a continuous piece. The fabric is then immersed in the
dye liquor in a slack condition and is rotated by a roller in the dye liquor. The dye, in this case, is
stationary whereas the fabric moves.

 Jet Dyeing

This technique involves dyeing at the fabric stage. The fabric is placed in a rope-form in a tube-like
containment. There are pressure jets in the container and the dye liquor is penetrated through the
fabric through these jets.

 Jig Dyeing

This technique involves dyeing at the fabric stage. In this technique, the fabric in an open-width form
is held up on two rollers in a machine called a jig dyeing machine or a jigger. The fabric is unwound
from one side, immersed into the dyebath and then wound onto the other side. The action is
repeated until the desired color is obtained on the fabric.
 Pad Dyeing

This technique involves dyeing at the fabric stage. The fabric is wound on rollers in a pad dyeing
machine in an open-width form. The fabric in its long length is then made to pass through a trough
which contains the dye liquor, and moved along the roller. It is a continuous process and the excess
dye is squeezed out of the fabric.

 Beam Dyeing (Fabric)

This technique involves dyeing at the fabric stage. Just like in the yarn stage dyeing method, the
fabric is wound on large cylindrical beams. The dye liquor is then pushed through the beams to
impart color to the fabric.

At the Garment Stage

 Paddle Dyeing

This technique involves dyeing at the garment stage after the construction of the garment. The
garments are immersed in a dye solution placed in a large container in the paddle dyeing machine.
The garments are loosely packed and a motor driven paddle circulates the dye solution in the
container to impart color to the garments.
Q4. Explain styles and techniques of printing in detail.
Ans. A process for producing a pattern on yarns, warp, fabric, or carpet by any of a large number
of printing methods. The color or other treating material, usually in the form of a paste, is deposited
onto the fabric which is then usually treated with steam, heat, or chemicals for fixation.

There are three different printing 'styles' used to produce patterned effects on textiles, these being
termed as:

1. Direct Printing Style

2. Discharge Printing Style

3. Resist Printing Style

 Direct Printing Style

This method involves the direct application of the colour design to the fabric and is the most
common method of textile printing. The dyes used for direct printing are those which would
normally be used for a conventional dyeing of the fabric type concerned.

 Discharge Printing Style

In this method the fabric is pre-dyed to a solid shade by a traditional dyeing process and the
colour is then destroyed locally, by chemicals incorporated in the print paste especially for that
purpose. The result is a white patterned discharge on a coloured ground. In “white” discharge
printing, the fabric is piece dyed, then printed with a paste containing a chemical that reduces
the dye and hence removes the color where the white designs are desired.

 Resist Printing Style

In this method of printing the fabric is first printed with a substance called a 'resist' which will
prevent the dye from being taken up in a subsequent dyeing process. The resist functions by
either mechanically preventing the dye from reaching local areas of the fabric or by chemically
reacting with the dye or the fibre, to prevent adsorption.
The following methods can be applied for textile printing operation:.

 Block Printing:
The blocks are usually made of wood and the design is hand carved, so that it stands out in relief
against the background surface. The print paste is applied to the design surface on the block and
the block then pressed against the fabric. The process is repeated with different designs and
colours until the pattern is complete.

 Roller Printing:
It is also a versatile technique since up to a dozen different colours can be printed
simultaneously. The basic roller printing equipment consists of a number of copper faced rollers
in which the design is etched. There is a separate printing roller for each colour being printed.
Each of the rollers rotates over the fabric under pressure against an iron pressure roller. A colour
doctor blade removes paste or fibres adhering to the roller after contact with the fabric. After the
impression stage the fabric passes to the drying and steaming stages.

 Screen Printing :
This type of printing has increased enormously because of its versatility and the development of
rotary screen printing machines which are capable of very high rates of production. An additional
significant advantage is that heavy depths of shade can be produced by screen printing, a
feature which has always been a limitation of roller printing because of the restriction to the
amount of print paste which can be held in the shallow depth of the engraving on the print roller.
There are two basic types of screen printing process, the flat screen printing and the rotary
screen printing methods.

 Rotary screen printing:

Rotary screen printing uses seamless cylindrical screens made of metal foil. The machine uses a
rotary screen for each colour. As the fabric is fed under uniform tension into the printer section of
the machine, its back is usually coated with an adhesive which causes it to adhere to a conveyor
printing blanket. The fabric passes under the rotating screen through which the printing paste is
automatically pumped from pressure tanks. A squeegee in each rotary screen forces the paste
through the screen onto the fabric as it moves along. The fabric then passes to a drying oven.
 Heat Transfer Printing :
Transfer printing techniques involve the transfer of a design from one medium to another. The
 most common form used is heat transfer printing in which the design is printed initially on to a
special paper, using conventional printing machinery. The paper is then placed in close contact
with the fabric and heated, when the dyes sublime and transfer to the fabric through the vapor
phase.

 Ink-Jet Printing :
The types of machines developed fall into two classes, drop-on-demand (DOD) and continuous
stream (CS).

 Carpet Printing :
The printing of carpets only really achieved importance after the introduction of tufted carpets
in the late 1950s. Much of this carpet production was printed because the range of patterns
possible to produce using tufting machines was limited and there was a desire to produce a
greater flexibility of design for these types of carpet.

 Warp Printing:
The printing of a design on the sheet of warp yarns before weaving. The filling is either white or
a neutral color, and a grayed effect is produced in the areas of the design.

 Resist Printing:
A printing method in which the design can be produced: (1) by applying a resist agent in the
desired design, then dyeing the fabric, in which case, the design remains white although the rest
of the fabric is dyed; or (2) by including a resist agent and a dye in the paste which is applied for
the design, in which case, the color of the design is not affected by subsequent dyeing of the
fabric background.

 Photographic Printing:
A method of printing from photoengraved rollers. The resultant design looks like a photograph.
The designs may also be photographed on a silk screen which is used in screen printing.

 Pigment Printing:
Printing by the use of pigments instead of dyes. The pigments do not penetrate the fiber but are
affixed to the surface of the fabric by means of synthetic resins which are cured after application
to make them insoluble. The pigments are insoluble, and application is in the form of water-in-oil
or oil-in-water emulsions of pigment pastes and resins. The colors produced are bright and
generally fat except to crocking.
 Blotch Printing:
A process wherein the background color of a design is printed rather than dyed.

 Burn-Out Printing:
A method of printing to obtain a raised design on a sheer ground. The design is applied with a
special chemical onto a fabric woven of pairs of threads of different fibers. One of the fibers is
then destroyed locally by chemical action. Burn-out printing is often used on velvet. The product
of this operation is known as a burnt-out print.

 Direct Printing:
A process wherein the colors for the desired designs are applied directly to the white or dyed
cloth, as distinguished from discharge printing and resist printing.

 Discharge Printing:
In “white” discharge printing, the fabric is piece dyed, then printed with a paste containing a
chemical that reduces the dye and hence removes the color where the white designs are desired.
In “colored” discharge printing, a color is added to the discharge paste in order to replace the
discharged color with another shade.

 Duplex Printing:
A method of printing a pattern on the face and the back of a fabric with equal clarity.

 Engaved Roller Printing:

Engraved roller printing is an industrial method for large print runs; metal rollers are engraved with
a pattern and dye reservoirs apply the color as needed. As in screen printing, a roller is needed for
each color; the method is therefore too expensive for short runs of fabric, but it can be very
cost-effective for large print runs as hundreds of metres can be printed per minute.
 Transfer Printing:
Transfer dyes are applied to paper and then heat transferred to the fabric. You can do this with
transfer paints and an iron. These chemical transfer dyes are beter suited to synthetic fabrics, on
which they give a better depth of colour.

 Digital Printing:

A design can be made on the computer using computer-aided design (CAD) packages and then
either transferred on to paper (sublimation paper), which can be transferred to the fabric with heat,
or it can be directly printed on to the fabric using a textile printer and then steam heated to fix the
design.