Unit 5: Printing
Introduction to Chemical Processing notes · PTU syllabus (BSTD 201-20)
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Unit summary
Printing applies colour in patterns. This unit covers methods and styles of printing, special prints and printing defects.
After this unit you can
- Describe methods of printing
- Distinguish direct, discharge and resist styles
- Describe special prints
- Identify printing defects
PTU syllabus topics
- Methods of printing
- styles of printing
- special prints
- printing defects
Direct
Colour printed onto the fabric
Most printed cotton
Discharge
Print removes dyed ground colour
White pattern on dark ground
Resist
Paste blocks dye from areas
Batik, Bagru dabu
Special prints
Effects added to fabric
Flock, foil, burn-out
Topic 1
Methods of printing
Block printing
Carved wooden blocks pressed by hand
Traditional crafts (Bagru, Sanganer); slow, artisanal
Screen printing (flat bed)
Paste forced through a mesh stencil with a squeegee
Versatile; one screen per colour
Rotary screen printing
Cylindrical nickel screens
High-speed continuous production
Roller (engraved copper)
Engraved rollers transfer paste
Fine detail; long runs (declining)
Transfer (sublimation) printing
Disperse dyes printed on paper, transferred by heat
Polyester; sportswear
Digital inkjet printing
Ink jetted directly from a digital file
Unlimited colours, short runs, low water use
- 1Thickener (gum, alginate, synthetic) + dye or pigment + auxiliaries
- 2Print
- 3Dry
- 4Fix (steaming for dyes; curing at 150–160 °C for pigments)
- 5Wash off (for dye prints)
Topic 2
Styles of printing
Direct style
Colour printed directly on white or light ground
Most prints
Discharge style
Fabric dyed, then printed with a discharging (reducing) agent that destroys ground colour — white discharge or coloured (illuminated) discharge
Dark grounds with fine white motifs
Resist style
Resist paste (wax, clay, chemicals) printed first prevents later dye uptake
Batik, dabu (mud resist), Ajrakh
Pigment style
Pigment with binder; cured
Economical; all fibres
Topic 3
Special prints
- Burn-out (devoré)
- Chemical dissolves one fibre of a blend leaving sheer areas
- Flock printing
- Adhesive printed; short fibres stuck on for a velvet effect
- Khadi and foil printing
- Metallic foil or puff effects with heat
- Puff (expandable) print
- Raised 3-D effect
- Glitter and pearl prints
- Special particles in binder
- Photographic and digital prints
- Images reproduced exactly
Topic 4
Printing defects
Misfit (out of register)
Screens or blocks not aligned
Accurate registration marks
Bleeding (colour spreading)
Thin paste, excess moisture
Correct paste viscosity; dry quickly
Smudging
Fabric moved before drying
Proper drying
Pinholes and specks
Blocked or damaged screen, undissolved dye
Clean and repair screens; filter paste
Uneven colour
Uneven squeegee pressure
Even pressure, correct mesh
Poor fastness
Inadequate fixation or wash-off
Correct steaming or curing; thorough washing
Scrimp and creases
Folded fabric under the screen
Smooth fabric feeding
Key terms
- Thickener
- Agent making print paste viscous
- Rotary screen printing
- Printing with cylindrical screens
- Discharge printing
- Removing ground colour in a pattern
- Resist printing
- Preventing dye in printed areas
- Devoré
- Burn-out print dissolving one fibre
Quick revision
- Block, flat screen, rotary, roller, transfer, digital printing.
- Print paste; steaming and curing.
- Direct, discharge, resist, pigment styles.
- Burn-out, flock, foil, puff, glitter prints.
- Misfit, bleeding, smudging, pinholes, uneven colour, poor fastness.
Important exam questions
Practice questions written to the PTU exam pattern for this unit's syllabus: short answers (Section A style) and long answers (Sections B and C style).
Short-answer questions
- Q1.What is the function of a thickener?
- Q2.Which printing method suits short runs best?
- Q3.Distinguish discharge and resist printing.
- Q4.Name a traditional resist print of India.
- Q5.What is flock printing?
- Q6.What causes misfit?
Long-answer questions
- Q1.Describe methods of printing.
- Q2.Explain the styles of printing with examples.
- Q3.Describe special prints and printing defects.
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