Screen-Printing Troubleshooting Glossary
Review this glossary of frequently misused terms concerning image integrity, and use it to develop a common language for your production floor.
Communication is seldom considered a critical basic skill in production. But whenever you are training employees, troubleshooting problems, collecting data, or documenting processes, your first stumbling block will be communication. The ideas and problems that you want to describe may not be as clear to your audience as they are to you, and the words that you choose to explain them can have a different meaning for a screenmaker than they do for an ink technician or press operator.
Words like "smear," "pinhole," "off-register," and "muddy color," for ex-ample, can also mean "bleeding," "dirt," "substrate shrinkage," and "insufficient ink deposit," depending on the listener's experience and background. At first, you may be tempted to dismiss this problem as mere semantics, but ignoring it won't make it disappear. In order to troubleshoot and solve a problem, you have to be able to describe it. In order to analyze problems, you have to be able to collect data about the various manifestations. And to train people in these skills, they must have the proper tools, including tools for communication.
Any action, object, process, or problem can be communicated with lengthy descriptions, but in the workplace we have no time for long dissertations. Our descriptions must be shortened to a few choice words, and these words must have an accepted meaning for all of us to communicate. This is why most industries rely on technical glossaries that make it possible to communicate not only within one's own company, but across the entire industry. In Germany, technical words are collected not only in glossaries, but are also codified in DIN specifications (Deutsche Industrie Norm) that provide standards for word usage between industries.
Screen printing certainly requires a set of agreed-upon words, and there are several technical glossaries available in the US through organizations such as the Screenprinting and Graphic Imaging Association Int'l (www.sgia.org). In addition to these glossaries, we are presenting 59 definitions that relate strictly to problems with screen-printed images. These definitions are based on the most frequently occurring problems and are organized under four subheads, including image definition, registration, color appearance, and ink performance.
Bleeding: 1. An enlargement of the image due to ink flowing beyond the boundaries of the stencil; 2. migration of colors into one another. Blocked edge: The printed edge is interrupted by unprinted voids.
Edge bubbles: Printed edges with irregularities caused by poor ink flow over previously printed edges or over edges that are parallel to the squeegee's length; also known as "skips and voids."
Double image: An overlapping light and dark double-edge resulting primarily from under-tensioned screens.
Edge dirt marks: Random imperfections along the image edges caused by dirt.
Edge mesh marks: A visible dot pattern along the image edge due to poorly cleaned screens.
Ink strings: Irregular, blurred edge caused by formation of tacky ink strings as the screen separates from the substrate.
Loss of detail: The space separating fine image elements is filled with ink.
Missing edge: The image edge is interrupted by "extensions" caused by missing stencil edges; opposite of "blocked edge."
Sawtooth: A raster or staircase appearance of the printed edge, usually caused by poorly prepared stencils.
Smear: Excessive ink deposit beyond the stencil edge that is caused by too much squeegee pressure or unwanted screen or substrate movement during printing.
Static strings: Forked hair-like extensions and dots of ink beyond the image edge due to static electricity buildup on the substrate and/or screen.
Area dirt marks: Small unprinted openings in the image area caused by dirt on the substrate or in the screen. Not to be confused with "pinholes."
Area mesh marks: A texture in the printed ink surface that corresponds to the thread pattern of the mesh.
Enlarged image area: See stretched image under "Registration errors."
Fisheye: A small round or oval imperfection with a dark center. This problem is usually caused by ink/substrate incompatibility.
Ghost image: A faint image visible in the newly printed image, primarily caused by remnants of a previous stencil that was not completely cleaned from the screen.
Incomplete image: A portion of the image is missing due to artwork or stencil problems. An image can also be incomplete as a result of a poorly tensioned screen set at a high off- contact distance.
Moiré pattern: See various moiré problems under "Ink-color problems."
Mottling: A faint, irregular pattern in the image area that is caused by either differing rates of ink absorption into the substrate or minor differences in substrate thickness.
Orange peel: A small round or oval imperfection similar to a "fisheye" but with a light center. Like fisheye, this problem is usually caused by ink/substrate incompatibility.
Pinholes: Small printed dots in the non-image areas caused by a poorly processed stencil. Not to be confused by dirt marks in the image areas.
Reduced image area: See screen shrinkage under "Registration errors."
Streaks: Faint lines in the printed image area that are usually the result of poorly sharpened squeegees or damaged flood bars.
Uneven ink deposit: A visible color difference in the image caused by nonparallel press components and/or uneven squeegee pressure. See also dichroism under "Ink-color problems."
Image movement: Misregistration caused by lateral movement of the screen.
Misaligned artwork: Color-separated artwork that cannot be registered properly using the existing registration targets.
Misaligned setup: Misregistration caused by the initial, uncorrected misalignment of separated images (or images to substrate) during job setup.
Screen growth: An enlargement of the image area on the screen when compared to the film-positive image used to produce the stencil.
Screen shrinkage: A reduction in the size of the image area on screen when compared to the film-positive image used to produce the stencil.
Stretched image: A distorted enlargement of the printed image area in the direction of squeegee stroke when compared to the film-positive image used to produce the stencil.
Substrate growth: An enlargement of the substrate due to temperature and humidity changes between curing and subsequent processing. The substrate enlargement usually involves a corresponding enlargement of the image area.
Substrate movement: Unwanted movement of the substrate during printing due to mechanical problems or poorly set up registration guides.
Substrate shrinkage: A reduction in the size of the substrate noticeable right after curing. The substrate shrinkage usually involves corresponding shrinkage in the image areas.
Background mismatch: Undesired color change resulting from the combination of substrate background color and printed color. The background can affect the perceived color even if the printed ink layer is fully opaque.
Chroma mismatch: A poorly matched color that is brighter (or duller) than the color required.
Dichroism: A change in color due to thinner or thicker ink deposit than is required.
Hue mismatch: A poorly matched color that is visibly and measurably different from the required color.Tamas S. Frecska
Ink opacity: The ability of a given ink-layer thickness to hide the visual difference between a black-and-white background.
Ink transparency: The ability of a given thickness of ink to transmit a major portion of light without distorting or "clouding" the underlying images.
Low opacity: A change in opacity due to thinner-than-required ink deposit.
Value mismatch: A poorly matched color that is lighter or darker than the required color.
Color order: The printing sequence of the four colors used in process-color printing that can affect the color appearance of the final printed product.
Dot gain: The enlargement of the printed dots due to low screen tension, underexposed screens, and poor printing-press setup (excessive off-contact distance and squeegee pressure). The net result is lighter-than-expected colors.
Film-to-film moiré: A moiré pattern that is inherent in the color-separated film positives, normally due to mistakes in the selection of halftone angles.
Film-to-mesh moiré: A moiré pattern that is caused by the interaction of halftone lines and mesh threads.
Ink density: The numerical value (as measured with a densitometer) of a solid block of any process-color ink after it is printed on a substrate.
Ink-to-ink moiré: A moiré pattern that develops as the third and fourth colors are printed, usually as a result of excessive ink-film thickness (most often seen as stacking of printed dots with UV inks).
Non-spec separation: Any color separation that does not meet the customer's or printer's specifications relative to halftone line count, screen angles, and color-density ranges.
Screen-to-substrate moiré: A moiré pattern that appears on a textured substrate (e.g., canvas); results from the interaction of the substrate texture, mesh, and halftone image.
Slur: A loss of dot and image definition due to smearing, bleeding, or substrate movement during printing.
Ink performance (curing related)
Abrasion resistance: The ability of the cured ink film to withstand rubbing and scratching action without visible degradation.
Adhesion: The force holding the cured ink on the surface of the substrate.
Blocking: The sticking action of undercured ink film that causes it to adhere to surfaces other than the one on which it was printed.
Chemical resistance: The ability of the cured ink film to withstand the chemical action of certain substances without experiencing physical (or visible) degradation.
Flexibility: The ability of the cured ink film to withstand repetitive bending without breaking, cracking, or delaminating from the substrate surface.
Weatherability: The ability of the cured ink film to withstand environmental and weather-related abuse (e.g., sun, wind, snow, water, etc.)
Ink performance (printing related)
Ink-film thickness: The vertical height of the ink deposit after curing.
Ink-film uniformity: The evenness of the printed surface and consistency of the overall ink-deposit thickness.