Odisha CHSE +2 Vocational Printing Technology cheat sheet

Printing is the transfer of an image from a master (plate, screen, block, cylinder) to a substrate, repeated to produce multiple identical copies.

Five classical processes: relief (letterpress, flexography), planographic (offset lithography), intaglio (gravure), porous (screen), and non-impact (inkjet, electrophotography).

Reproduction steps in order: copy preparation, image carrier preparation, printing, and finishing/binding.

Image carriers differ by ink-transfer logic: raised areas ink in relief; ink-repellent/ink-accepting planes in lithography; recessed cells in gravure; open mesh in screen printing.

Typographic measures: 12 points = 1 pica, 72 points = 1 inch, 1 point = 0.3528 mm; 1 pica = 4.233 mm.

Process selection rule: long runs of high-quality colour favour offset or gravure; short runs and variable data favour digital; textiles and irregular shapes favour screen printing.

Halftone screening converts continuous tone into dots; dot area percentage governs apparent tone, and 100% dot area equals solid ink.

DPI describes device resolution, LPI describes screen ruling, and PPI describes image pixel density; they are not interchangeable.

Prepress workflow order: job receipt, copy preparation, image capture/scanning, typesetting/composition, imposition, proofing, plate-making, and press-ready output.

Colour separation converts RGB originals into CMYK process channels; GCR/UCR controls black generation and total ink coverage.

Common total area coverage limits: about 300-320% for coated sheetfed, 240-280% for newsprint and uncoated stocks.

Imposition arranges pages on a press sheet so that folding yields correct page order; a 16-page signature is standard on sheetfed presses.

Trapping (spread or choke, typically 0.05-0.2 mm) compensates for registration variation between adjacent colours.

Overprint, knockout, and rich black (for example 60C 40M 40Y 100K) decisions must be fixed at prepress, not on press.

CTP plate-making exposes and processes aluminium offset plates directly from digital data, eliminating film and contact frames.

Proof types: soft proof (calibrated monitor), digital contract proof (colour-managed inkjet), and press proof (actual press sheet).

Bitmap (raster) images are resolution-dependent pixel grids; vector images are resolution-independent mathematical paths suited to type and logos.

Required scan resolution = screen ruling (LPI) x quality factor (usually 1.5-2) x enlargement factor.

Image mode rules: CMYK for process-colour offset, RGB for screen and web, grayscale for single-colour work, bitmap/1-bit for line art.

File formats: TIFF for lossless print images, EPS/PDF for vector and page interchange, JPEG (lossy) only where compression artefacts are acceptable.

Type rules: body text 9-11 pt, leading about 120% of type size, line length 45-75 characters for comfortable reading.

Hierarchy is built from size, weight, contrast, spacing and position; alignment and consistent grids control order on a page.

Resolution arithmetic: a 300 ppi image printed at 600 ppi effective size halves its physical dimensions without loss of quality.

Trapping and bleed (typically 3 mm) must be built into page layout so trimming does not expose unprinted edges.

Offset lithography uses the immiscibility of ink and water: dampening solution wets non-image areas, ink wets image areas, and a blanket cylinder transfers ink to paper.

Offset press units: plate, blanket and impression cylinders, plus inking, dampening, feeder and delivery systems.

Flexography uses photopolymer relief plates and anilox rollers; anilox cell volume (cm3/m2) and line count set ink film thickness.

Gravure uses a copper-plated, chromium-faced cylinder with engraved cells; doctor blade wipes surplus ink and capillary action draws ink from cells.

Screen printing: mesh count (threads per cm), emulsion stencil, squeegee angle (about 60-75 degrees), off-contact distance and snap-off control deposit.

Key offset settings: ink-water balance (dampening pH about 4.5-5.5, conductivity controlled), squeeze pressure, and register with register marks.

Digital presses (electrophotographic or inkjet) require no plate; costs are largely fixed per page, so they win on short runs and versioning.

Press sheet defects map to causes: hickeys to paper dust, ghosting to ink distribution, set-off to insufficient drying or excess pile height.

Paper is measured by substance (gsm = grams per square metre); common text stocks 60-120 gsm, covers 200-350 gsm, newsprint about 45 gsm.

Bulk = thickness per unit substance; a bulky sheet feels thicker at the same gsm and affects spine width and mailer thickness.

Grain direction runs parallel to the machine direction of the paper machine; folds crack when made against the grain.

Paper properties that govern printability: smoothness, absorbency, opacity, brightness, whiteness, dimensional stability and surface strength (pick resistance).

Coated papers give higher gloss and finer screens (150-200 LPI); uncoated and newsprint suit coarser rulings (85-133 LPI) and higher ink absorption.

Ink components: pigment (colour), vehicle/varnish (carrier and gloss), solvent or water, and additives (driers, waxes, anti-set-off).

Ink drying routes: absorption, oxidation, evaporation, radiation curing (UV/EB) and penetration setting; the route must match the substrate.

Tack is ink stickiness; it must fall through the press sequence (first unit highest) to prevent picking and trapping failure.

Cutting: guillotine trims to trim size plus bleed; blade clearance and clamp pressure control cut quality and squareness.

Folding types: parallel, right-angle, gate, and accordion; fold direction must follow paper grain to avoid cracking.

Binding methods: saddle stitching (wire through spine, multiples of 4 pages), perfect binding (glued square spine, from about 40-48 pages up), spiral/wire-o (lay-flat), case binding (hard cover, sewn or glued blocks).

Lamination, varnish and UV coating protect and gloss; spot UV applies effect to selected areas only.

Die cutting uses a steel-rule die; creasing rules are used where folding thick board would otherwise crack the coating.

Embossing and debossing raise or recess an image using matched male/female dies; foil stamping transfers metallic foil by heat and pressure.

Pagination arithmetic for saddle stitching: total pages must be a multiple of 4, and each signature's pages must satisfy the imposition scheme.

Post-press quality checks: trim allowance, fold accuracy, spine squareness, stitching position, and absence of set-off or scuffing.

Daily machine checks: ink duct and rollers, dampening solution pH/conductivity, blanket and plate condition, gripper and feeder settings, delivery pile.

Roller maintenance: settings measured with a roller gauge or strip (typically 0.1-0.15 mm squeeze for inking rollers against the vibrator/distributor).

Lubrication schedules follow the manufacturer's manual; over-lubrication and missed points are both failure causes.

Guards, interlocks, two-hand controls and nip guards must never be bypassed; nip points between rollers are the main crush hazard.

Lockout/tagout (energy isolation) is mandatory before clearing jams, changing blankets or reaching into any powered unit.

Chemical safety: store solvents and fount solution away from ignition sources, keep SDS sheets accessible, use gloves and eye protection, and ventilate pressrooms.

Solvent-based wash-up liquids require earthing/bonding of containers to prevent static-ignited fire; waste ink and solvent are hazardous waste, not general refuse.

Preventive maintenance records (vibration, roller hardness, bearing temperature, belt tension) allow faults to be predicted rather than repaired after breakdown.

Additive colour (RGB) mixes light; subtractive colour (CMY plus K) mixes pigments and inks; RGB is device light, CMYK is print ink.

Colour attributes: hue (family), value/lightness, and chroma/saturation; metamerism occurs when a pair matches under one light but not another.

Densitometry measures ink film density (solid ink density, SID); typical offset SIDs are about 1.30-1.50 for K, 1.30-1.45 for C, 1.35-1.50 for M, 1.00-1.20 for Y, depending on stock.

Dot gain = printed dot area minus original dot area; TVI (tone value increase) is measured at 50% and is commonly 12-20% for sheetfed offset.

Print contrast = (D solid - D tint)/D solid x 100; higher contrast means cleaner highlight separation.

Colour management uses ICC profiles, a source/target profile pair, and rendering intents (perceptual, relative colorimetric, absolute colorimetric, saturation).

Control strips and test forms carry solids, tints, slur targets, register marks and grey balance patches; measurement at the start, middle and end of a run detects drift.

Tolerance-based acceptance: define SID, dot gain, register (typically within 0.1 mm) and Delta E limits (Delta E of about 2-3 is a common visual match threshold) before the run starts.

Job cost = material + labour + machine/overhead + outsourced post-press + wastage allowance + profit margin.

Paper cost is usually the largest single cost in a print job; calculate from sheet size, gsm, number of sheets including spoilage (often 3-10% for make-ready and running waste).

Break-even quantity = fixed costs / (selling price per unit - variable cost per unit).

Depreciation of presses (straight-line or reducing balance) is an overhead that must be recovered in the hourly machine rate.

Working capital cycle: pay for paper and labour before the customer pays; quote credit terms and track receivables to avoid cash starvation.

Small-business registrations in India: Udyam (MSME) registration, GST registration above the turnover threshold, current account, and shop and establishment licence.

Quotation must state specifications that drive cost: size, paper, colours, quantity, finishing, proof type, delivery date and payment terms.

Pricing methods: cost-plus, market/competitive, and value-based; record actuals against estimates to build reliable future quotations.