THEORY EXAMINATION (SEM–VI) 2016-17 COATING OF TEXTILES

COATING OF TEXTILES (EC602)

Time: 3 Hours  Max. Marks: 100

SECTION – A (Short Answer Questions)

(10 × 2 = 20 Marks)

(a) Polymeric material

Polymeric materials are substances made up of long-chain molecules (polymers) formed by repeating structural units. They are widely used in textile coating due to flexibility, durability, and chemical resistance.

(b) Acrylic polymer

Acrylic polymers are synthetic polymers derived from acrylic acid or its derivatives. They are commonly used in textile coatings for weather resistance, transparency, and softness.

(c) Coating

Coating is the process of applying a polymer layer on fabric surface to improve properties such as water resistance, durability, abrasion resistance, and appearance.

(d) Calendaring

Calendaring is a finishing process where fabric passes through heated rollers to improve smoothness, gloss, thickness control, and surface uniformity.

(e) Rheology

Rheology is the study of flow and deformation behavior of materials, especially polymer compounds during coating and processing.

(f) Fabric

Fabric is a flexible textile structure formed by interlacing yarns through weaving, knitting, or nonwoven processes, used as a base for coating.

(g) Clothing comfort

Clothing comfort refers to the thermal, moisture, and tactile comfort experienced by a wearer while using a textile product.

(h) Breathable fabric

Breathable fabrics allow air and moisture vapor to pass through while restricting water penetration, enhancing comfort.

(i) Abrasion resistance

Abrasion resistance is the ability of a coated fabric to withstand surface wear caused by friction.

(j) Low temperature impact test

This test evaluates the resistance of coated fabric to cracking or damage at low temperatures, indicating cold-weather performance.

SECTION – B (Long Answer Questions)

(Attempt any FIVE – 5 × 10 = 50 Marks)

2(a) Concept of curing and curing of rubber coating

Curing is the process of cross-linking polymer chains to improve strength, elasticity, and durability.
In rubber coating, curing is achieved by heat or chemical agents (sulphur), converting soft rubber into a stable elastic material with improved mechanical properties.

2(b) Screen printing method for coating

In screen printing coating, a polymer paste is forced through a patterned screen onto fabric.

Advantages:                              Controlled coating thickness

Design flexibility                         Suitable for functional and decorative coatings

Used for protective and specialty textile coatings.

2(c) Roller coating process

Roller coating involves transferring coating material from rotating rollers onto fabric.
Examples include:

Forward roller coating

Reverse roller coating

It provides uniform coating thickness and is widely used for large-scale production.

2(d) Knife as a coating head

Knife coating uses a metal blade (knife) to control the amount of coating applied.
The fabric passes under the knife, and excess coating is scraped off, giving precise thickness control.

2(e) Relation between coating thickness and knife gap

Coating thickness is directly proportional to the distance between fabric and knife.
As the gap increases, coating thickness increases; reducing gap gives thinner coatings.

2(f) Plastisols and apparent viscosity

Plastisols are dispersions of PVC resin in plasticizers.
They remain liquid at room temperature and solidify upon heating.
Apparent viscosity refers to viscosity measured under specific shear conditions during processing.

2(g) Resistance to water penetration and testing

Water penetration resistance measures a fabric’s ability to prevent water from passing through.
Testing is done using:

Hydrostatic pressure test

Spray test
Higher resistance indicates better waterproofing.

2(h) Thermochromic vs Temperature Adaptable Fabric

SECTION – C (Very Long Answer Questions)

(Attempt any TWO – 2 × 15 = 30 Marks)

3. Estimation of GSM of coating

GSM (grams per square meter) of coating is calculated by:

Measuring fabric area

Weighing fabric before coating

Weighing fabric after coating

Coating GSM=Coated fabric GSM−Uncoated fabric GSM\text{Coating GSM} = \text{Coated fabric GSM} - \text{Uncoated fabric GSM}Coating GSM=Coated fabric GSM−Uncoated fabric GSM

This helps control coating weight and quality.

4. Rheological behavior of coating compounds

Rheological behavior depends on:                          Polymer type

Filler content                                                            Temperature

Shear rate                                                                 Materials may show:

Newtonian behavior                                                 Pseudoplastic behavior

Thixotropic behavior

Proper rheology ensures uniform coating and defect-free surfaces.

5. Short notes

(a) Impermeable coating

Impermeable coatings completely block air and water penetration, used in rainwear and protective textiles.

(b) Camouflage nets

Camouflage nets are coated textiles used for concealment, providing visual and infrared masking.

(c) Radiation cured coating

Radiation curing uses UV or electron beam radiation to instantly cure coatings, offering fast processing and low energy consumption.