Screen Printing, Quality Measurement, and Color Separation

Flashcards covering screen printing concepts, equipment, quality measurement, and color separation process control.

Which major printing process is compared to printing paperback books?

Offset lithography.

Which printing process is compared to printing a label on a bottle of Miracle Whip?

Flexography.

Which printing process is compared to printing National Geographic magazine?

Gravure.

Which printing process is famously associated with printing t-shirts?

Screen printing.

What is the technical definition of screen printing (serigraphy)?

Transferring an image by forcing ink through a stencil (opening).

Which civilization first developed screen printing around 1000 AD?

The Chinese, who adapted it as an art form from woodblock printing.

What material was originally used to construct the mesh in early Chinese screen printing?

Silk thread.

When did t-shirts become popular items of clothing?

During World War II (WWII) as an undergarment.

When did custom screen-printed t-shirts emerge as a major trend?

The late 1950s, continuing through the 1960s.

What are four key advantages of choosing screen printing?

1. Very versatile (can print on almost any substrate and uneven surfaces). 2. Can make a thick ink deposit (durable outdoors, varied ink surface effects). 3. Opaque ink covers well. 4. Can produce very brilliant colors.

Why is screen printing advantageous for short production runs?

Shorter press runs can be economically viable.

What are the main relative disadvantages of screen printing?

Slower production speed, longer prep time, shorter run lengths due to mesh/stencil wear, potential moiré or mesh patterns, and expensive image carrier (mesh).

How is ink rheology defined in screen printing?

The nature of ink flow.

What is monofilament mesh?

Screen mesh woven from threads consisting of a single strand per thread.

What are the primary advantages of monofilament mesh?

It is stronger, thin, cleans easily, and can be reused many times.

What is multifilament mesh?

Screen mesh woven from threads containing many strands twisted together.

What is a main disadvantage of multifilament mesh?

It cleans poorly due to having more surface area for ink to adhere to, so many shops discard it after one use.

What is the structural pattern of a plain mesh weave?

One thread woven over one thread (1 over 1).

What is the structural pattern of a twill mesh weave?

One weft thread crossing over two warp threads, then under one.

How do plain weave and twill weave compare regarding moiré formation?

Twill weave is more likely to cause moiré, whereas plain weave is less likely to produce moiré.

What are the characteristics and limitations of nylon screen mesh?

It flexes and stretches well for container printing, but absorbs water and liquids, which can cause size changes and make registration difficult.

What are the key advantages of polyester screen mesh?

It does not elongate much, is dimensionally stable, stronger, and takes tension better.

What are the unique physical properties of stainless steel screen mesh?

It is very strong and conducts electricity.

What are the three main functions of a stencil system?

1. Blocks ink in non-image areas. 2. Allows ink to pass through in image areas. 3. Provides edge definition.

What are three general categories of screen stencils?

Hand-cut stencils, Tusche stencils, and Photographic stencils.

What is the tusche stencil technique?

A stencil technique created by drawing directly on the screen using a greasy pencil or brush technique.

How is a direct photo stencil created?

Liquid emulsion is coated directly onto the screen, exposed through a film positive, and washed out with water.

Which photosensitive stencil method is the cheapest and most durable for long press runs?

Direct photo stencil.

What is capillary film emulsion?

Pre-manufactured light-sensitive emulsion on a plastic support sheet that provides uniform thickness, fast application, and a gasket seal for fine edge definition.

What are the characteristics of indirect photo stencils?

Emulsion on a plastic support sheet that is exposed, developed, and washed out before being adhered to the screen; it provides fine detail but is not durable for long runs or rough meshes.

What general rule of thumb relates mesh count to halftone lpi to minimize moiré?

The mesh count should be 3 to 4 times the line per inch (lpi) halftone frequency (e.g., $85\text{ lpi} \times 4 = 340$ threads per inch).

What happens if a photo stencil is under-exposed?

The stencil can break down or come off the mesh during washout or printing.

What happens if a photo stencil is over-exposed?

Fine details and halftone dots can be lost or filled in.

What are two methods used in digital direct-to-screen (CTS) imaging?

1. Inkjet printing a film positive image directly onto the emulsion-coated stencil. 2. UV Laser light exposing the stencil directly.

What does the acronym SGIA stand for?

Specialty Graphic Imaging Association.

How many industry segments are formally listed by SGIA?

20 segments.

How is industrial screen printing defined?

Screen printing performed as part of a broader manufacturing process by companies not traditionally classified as commercial printing businesses.

What are real-world examples of industrial screen printing?

Printing University soap dispensers, Airtherm fan speed control faceplates, and toaster oven temperature/timer panels.

What are the five major component parts of any screen printing press?

1. Flood bar. 2. Squeegee. 3. Mesh. 4. Flat bed or cylinder platen. 5. Register method.

What is the function of the flood bar on a screen press?

It moves ink across the screen to fill the mesh openings and prepare for the next print stroke.

What is the primary function of the squeegee?

It forces ink through the open stencil areas onto the substrate, or shears ink off the top of the mesh.

What are the four basic screen printing press systems?

1. Flatbed press. 2. Cylinder press. 3. Rotary press. 4. Carousel press.

What press designs belong to the flatbed screen printing family?

Clamshell, Gripper Clamshell, and 4-poster (available as hand-operated, semi-automatic, or fully automatic).

What is the typical production speed range of a cylinder screen press?

$4{,}000$ to $6{,}000$ impressions per hour.

What is the maximum printing speed of a rotary screen press?

Up to $200\text{ ft/min}$.

What products are primarily printed using a carousel screen press?

Garments (such as t-shirts and caps) and CDs/DVDs.

What is off-contact setup on a screen press?

A small gap between the stencil and substrate ensuring the screen snaps off immediately behind the squeegee, preventing smudging and image spread.

When is on-contact screen printing used?

When heavy ink deposits are needed and image sharpness/detail is not important.

What is the peel control adjustment on a press?

A press mechanism that progressively lifts the screen frame upward as the squeegee travels across to accentuate off-contact snap-off.

What five squeegee variables must be maintained for quality assurance?

Sharpness, squeegee pressure, profile shape, flexibility/hardness, and blade angle.

What is the consequence of applying excessive squeegee pressure?

It drags the screen fabric in the direction of the stroke, distorting image registration.

Which squeegee profile is most commonly used for flat surfaces and general design?

Square blade.

Which squeegee blade profile deposits the thickest layer of ink, making it ideal for fabrics?

Round edge blade.

Which squeegee blade profile is best suited for printing on uneven container surfaces?

Double-bevel blade.

How does squeegee durometer (hardness) affect the printed ink deposit?

Soft squeegees deposit a thick layer of ink; hard squeegees yield a thin, sharp ink layer.

What four materials are commonly used to manufacture screen printing frames?

Wood, steel, aluminum, and stainless steel.

How do wood, steel, aluminum, and stainless steel frames compare in durability?

Wood is the least durable, steel rusts, aluminum resists corrosion, and stainless steel is the longest lasting (and most expensive).

How do frame cross-sectional profiles rank in structural strength?

Combination profiles are best, rectangular profiles are good and easy to make, and round profiles are less effective.

What is optical density in graphic communications?

The measure of the light-blocking or light-absorbing property of a printed product.

What two press variables directly influence ink film optical density?

Ink Film Thickness (IFT) and Ink Pigment Loading (IPL).

What numerical range represents optical density measurements?

Numbers ranging from $0$ to $6.0$ (expressed as decimals, e.g., $0.05$, $2.64$).

Why are measurement instruments required to monitor printed production quality?

1. To provide objective control. 2. Because human vision is inconsistent and subject to physiological limitations.

What percentage of the male and female populations have color vision deficiencies?

Approximately $3\%$ of females and $7\%$ of males.

What diagnostic color vision test uses plates of colored dots to identify deficiencies?

The Ishihara color vision test.

What two mathematical methods compute dot area percentage from density readings?

1. Murray-Davies. 2. Yule-Nielsen (which incorporates an n-factor).

What is spectrodensitometry?

Measuring density using a spectrophotometer, which measures spectral reflectance curves to calculate density values with superior accuracy.

What factors justify the investment in a spectrophotometer ($2245$+)?

High Return on Investment (ROI), eliminating human vision subjectivity, meeting client ISO 9000 compliance, and ensuring process repeatability.

What is the function of an IT8 test target in graphic arts?

A standardized color target used for color profiling, scanner calibration, and characterization.

What is a P2P test target used for?

Proof-to-Print calibration (used in G7 process control).

What does the acronym GRACoL stand for?

General Requirements for Applications in Commercial Offset Lithography.

What unit of measurement expresses film and substrate thickness in the US?

Mils ($1\text{ mil} = 0.001\text{ inch}$).

What unit of measurement expresses screen mesh tension?

Newtons per centimeter ($N/cm$).

What scales are used to measure squeegee and rubber material hardness?

Shore A, Shore D, or Rockwell R scales.

What device measures UV curing lamp energy and intensity?

A UV Power Puck (or UV radiometer).

What four elements are required for human color perception?

1. Light source (white light). 2. Object/pigment (reflects/emits some light, absorbs others). 3. Eye (receives light energy). 4. Brain (perceives the color).

What is the wavelength range of visible light in the electromagnetic spectrum?

$400\text{ nm}$ to $700\text{ nm}$.

What visible color corresponds to the $400\text{ nm}$ wavelength region?

Violet / Blue light.

What visible color corresponds to the $550\text{ nm}$ wavelength region?

Green light.

What visible color corresponds to the $700\text{ nm}$ wavelength region?

Red light.

What three mechanisms deliver color light energy to the human eye?

Reflection, Transmission, and Emission.

What are the primary additive colors of light?

Red, Green, and Blue (RGB).

What color is created when all three additive primary light beams are combined at full intensity?

White light.

How do transparent ink layers interact on a substrate?

Light passes through transparent layers, enabling optical mixing of colors beneath or within the ink film.

How do opaque ink layers interact on a substrate?

Opaque inks block light from reaching lower layers, so no color mixing occurs and only the top ink layer reflects color.

What are the subtractive primary colors of inks and pigments?

Cyan, Magenta, and Yellow (CMY).

Which primary light color is absorbed (subtracted) by Yellow ink?

Blue light ($400\text{ nm}$).

Which primary light color is absorbed (subtracted) by Magenta ink?

Green light ($550\text{ nm}$).

Which primary light color is absorbed (subtracted) by Cyan ink?

Red light ($700\text{ nm}$).

What color is produced by combining Yellow and Magenta transparent inks?

Red.

What color is produced by combining Magenta and Cyan transparent inks?

Blue.

What color is produced by combining Cyan and Yellow transparent inks?

Green.

Why is Cyan ink added to Red ink in 4-color process printing?

Cyan acts as the graying component to darken the red and render image details.

What screen angle separation between major process colors is required to prevent moiré?

A $30^\circ$ angle difference.

What is a rosette pattern in halftone printing?

A symmetrical, circular pattern formed by properly angled halftone dot screens that minimizes objectionable moiré.

What is the standard 4-color process screen angle for Yellow?

$0^\circ$.

What is the standard 4-color process screen angle for Cyan?

$15^\circ$.

What is the standard 4-color process screen angle for Black?

$45^\circ$.

What is the standard 4-color process screen angle for Magenta?

$75^\circ$.

What are the four fundamental steps to control or adjust in color reproductions?

1. Gray balance. 2. Tone reproduction. 3. Color correction. 4. Image detail enhancement.

What is Gray Component Replacement (GCR)?

Replacing the chromatic graying component (the third CMY color) in shadow/dark areas with Black ink (K) to reduce overall ink film thickness while maintaining visual color appearance.