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102 Cards in this Set

  • Front
  • Back
Explain how resin and solvent comprise the vehicle.
Resins are solids that must be dissolved by a liquid solvent in order to flow through ink train.
Volatility
Speed of evaporation.
Five ways to dry/cure ink.
Evaporation, Absorption, Oxidation, Heatset and Energy Cured.
Evaporation
Volatile solvents evaporate and resin becomes solid (flexo, gravure, screen)
Absorption
Mineral oils penetrate the substance and leave the ink, so it stiffens - never truly dries (paperbacks, newsprint)
Oxidation
Vegetable oils, such as linseed or tung, react with oxygen to polymerize the oil to a solid. Driers like cobalt and manganese are additives that act as catalysts to speed up oxidation process (offset litho)
Heatset (a combination of evaporation and oxidat
Litho inks that allow the solvent to flash off quickly to set the ink, then use heat to speed up the oxidation throughout. Used for high-end publication.
Energy Cured
Radiation acts as catalyst to polymerize the ink.
UV ink
Contains photo-initiators that polymerize under intense UV energy. Do not always fully cure.
Electron Beam
Energy field starts polymerization without photo-initiators. Fully cures.
Mineral oils vs. vegetable oils
Vegetable oil (linseed, tung, soy) react w/oxygen to polymerize the oil to a solid. Mineral oils penetrate the substrate and leave the ink, so it stiffens - never truly dries.
Role of cobalt and manganese
Driers like cobalt and manganese are additives that act as catalysts to speed up oxidation process.
Cobalt
Sets the ink, top drier.
Manganese
Dries the ink, through drier.
Plasticizers
Impart flexibility to brittle resins; interfere with the alignment of the polymerized resin. Also impart gloss, adhesion, and protect against cold temperatures (brittleness)
Waxes
Improves rub resistance, improves slip, improves resistance to water. Excessive wax can crystallize ink (making ink trap difficult), reduce gloss, and increase drying time.
Paste ink (properties)
Pseudoplasticity, thixotropy, tack, long/short ink (how far it can be stretched before snapping).
Paste ink (printing processes)
Offset lithography (long ink train, 3 ink splits, delivers very thin ink film) and screen-printing (short transfer, paste ink, single split, thick ink film)
Liquid ink (properties)
Must flow in and out of cells easily - low viscosity. Must be rewet between impressions. Must dry quickly - high volatility (dry ink films mean no tack issues, dry ink films mean better ink trapping, dry ink films mean faster run speeds)
Liquid ink (printing processes)
Flexography (liquid ink, short ink transfer, two ink splits, thin to thick ink film, depending on anilox) and gravure (liquid ink, very simple ink system, one ink split, thin or thick ink film, depending on engraving)
Pseudoplasticity
As the ink is worked, the shearing forces reduce viscosity.
Thixotrophy
Whether the pseudoplasticity occurs quickly or slowly (high thixotrophy means the ink is slow to thin and slow to set. Ink must thin out in the ink train but stiffen up quickly once printed on the sheet. If too thick on the sheet, it can cause picking, effect mileage and coverage).
Ink tack
Tack is the resistance to the ink film splitting, too great of a tack leads to picking. Tack is stepped in print sequence, high to low, test with inkometer.
Ink length
Paste inks are formulated to be long or short, referring to how far it can be stretched before snapping. Litho inks tend to be long, screen-printing inks tend to be short.
Viscosity
Viscosity is resistance to flow, not exclusive to liquid ink, measure with Zahn or Dinn cup. Solvent controls viscosity, for water-based inks, pH has tremendous influence on viscosity.
pH
Measure of hydrogen ions in a solution. Range of 0-14, 7 being neutral, (0-7 is acid, 7-14 is base).
pH ranges
6-7 precipitate, ink and resin separate.
7-8 unstable, dirty, fuzzy print, high viscosity and build up on plate.
8-9.5 good flow characteristics, good print and adhesion.
9.5-11 pigment burnout, excess foam, corrosive to steel and iron, lack of water resistance. pH gets too low, ink will build up on plate and give a dirty print. pH too high will give poor water resistance, unstable ink and odor problems. ALWAYS adjust pH before adjusting viscosity**
Why is pH important?
Viscosity control, solubility of the ink, drying speed, trapping ability, color consistency and ink film thickness.
Extender
Ink without pigment. Allows adjustment of color strength.
Reducer
Adding solvents to the ink (change the viscosity), in offset, it would refer to changing the tack.
Retarder
Slow the drying (glycol).
Surfactants
Increase wetability by changing the surface tension of the ink.
End use properties tests
Abrasion resistance, coefficient of friction, lightfastness, gloss, drying, adhesion and grind.
Abrasion resistance test
Sutherland rub test
Coefficient of friction test
Static and dynamic
Lightfastness test
Fadeometer and weatherometer
Gloss test
Gloss meter
Drying test
Scratch test
Adhesion test
Tape test
Grind test
Grind gauge
Applied research
Attempt to solve a known problem, an exercise in practical problem solving.
Pure research
Knowledge for the sake of knowledge. What happens if...
Scientific method
Observation (define the problem), develop theory, make prediction (formulate hypothesis), test hypothesis (via experiment), and interpret the results.
Hypothesis statement
In proving your hypothesis, the assumption you must overcome is that there is no difference. This is the null hypothesis. Your experiment will either reject or accept the null hypothesis based on the probability that the results could not have happened by chance.
Statistical significance
If the probability of the result occurring by chance is small, reject the null. The test is statistically significant. If the result can be attributed to chance, accept the null.
Library resources
Database (PIRA and Compendex), reference librarian (Priscilla Munson).
Experimental design
Manipulate an independent variable (the independent variable is the experimental treatment), control all extraneous variables (match conditions or block effects), and observe/measure the predicted effect on the dependent variable.
Validity
The degree to which the result, instrument, or experimental design does what it is design to do.
Internal validity
The degree to which the experimental treatment made the difference as opposed to extraneous variables. History (stuff happens), maturation (learning), mortality (lose press sheets), pre-testing (clues), instrumentation, regression, differential selection, and expectancy (experimenter bias).
External validity
The degree to which the results can be generalized beyond the experimental conditions. Pre-testing, differential selection and experimental procedures.
Reliability
The degree to which the results are repeatable (are the results consistent).
Extraneous variables
Anything other than the experimental treatment that might effect the outcome. If not controlled, they represent threats to the validity.
Sample size selection
Not cost effective to measure everything; statistics allow inferences from sample of population.
Sampling size
If N is small, n must be small.
If variance is small, n can be small.
If bound is small, n must be large.
If probability of error is low, n must be large.
If cost is high, n is preferably small.
Randomization
Random selection reduces threats of regression, differential selection, and interaction factors.
What is density.
Density is the ability of an object to absorb light. Cyan absorbs red light, magenta absorbs green light, yellow absorbs blue light, and black absorbs all light.
Explain how ink film thickness impacts density.
Density is highly correlated to ink film thickness. Density is controlled through pigment load in the ink and the amount of ink on paper.
Explain how ink film thickness impacts TVI and ability to print.
The amount of ink is controlled by ink film and halftone dots. Ink film thickness and dot gain are directly proportional; as IFT goes up, dot gain goes up. Ink film thickness and lpi are inversely proportional; as IFT goes up, printable lpi goes down.
Dot area (Murray-Davies)
Meaure densities, convert to dot area, murray-davies formula includes optical gain.
Dot area (Yule-Nielsen)
Yule-Nielsen formula assigns a correction for surface light scatter with "n". Application of "n" factor provides mechanical dot gain. Tools like the betaflex use a camera to magnify and capture dot area. The magnification minimizes optical gain so that mechanical can be calculated.
Print contrast
For best tone reproduction, detail within the image depends on contrast. Thin ink film (weak density) means low dot gain, but low contrast as image is washed out. Thick ink film has greatest range but high dot gain means limited tones within the range; poor detail. Print contrast is a key evaluation metric to optimize for tone reproduction. It is a quantitative measure of the ability to hold shadow detail.
PC =
D solid - D tint * 100. The tint is the 3/4 tone - 75% dot for litho and 70% dot for flexo.
Using print contrast to determine IFT
Flexo (run banded anilox roll), litho (run densities high, cut off ink and monitor falling densities). Print contrast can be used to optimize other variables affecting tone reproduction: viscosity, tack, pH, stickyback, blankets, etc.
CIELAB L*
A measure of the lightness of an object and ranges from 0 (black) to 100 (white).
CIELAB *a
A measure of redness (positive a*), or greenness (negative a*).
CIELAB *b
A measure of yellowness (positive *b), or blueness (negative *b).
Polymers
A subset of the class of molecules known as macromolecules. Polymers are macromolecules that have a repeating structure (DNA, carbohydrates, synthetic polymers).
Macromolecules
Very large molecules held together by covalent bonds.
Plastics
A polymer that has the ability to be shaped and formed at relatively low temperatures (as compared to glass and metals).
Film extrusion
Exploiting the formability of plastics to make film.
Process of film extrusion
Transport plastic pellets, plasticate (melt) them, and pump them through a shaping system (die).
Main components of an extruder
Screw, barrel, breaker plate, screen pack, feed throat, feed hopper, barrel heating, barrel cooling, extrusion drive, gear reducer, gear pumps, and instrumentation and control.
After the resin exits the extruder
The molten polymer enters a die to shape the molten polymer. There are many types of dies, only a couple for films (cast film extrusion - flat, blown film extrusion - round).
Cast film
Channel resin into a flat shape. Width exiting die determines thickness. Commonly called a coat hanger die, shape prevents dead spots in die, and promotes even flow rate of polymer across die. After the die, plastic is quenched (cooled) using chill roll, three roll stack, or water quench. This removes heat of the molten polymer from the film and freezes the extrudate into a film shape.
Blow film
Channel molten polymer into a circular shape. Extrudes into a tube. Moving polymer into round shape requires a larger and more complicated die than flat profile die. After the die, inflate the tube we are extruding. tube expands with air pressure (the bubble). The more it expands the thinner the film becomes, the ratio of the tube diameter to the bubble diameter is known as the blow up ratio. In blown film we quench with air, air blows on the outside of the bubble from the "air ring". The air ring controls the bubble and cools it down.
How cast film maintains uniform thickness
Flatness control in flat profile dies, for printing we need flat films. Planar surface for ink transfer from cylinder or plates, distortion/wrinkle free. Flat profile dies can control flatness using flexible die lips. These are manually controlled using bolts or electronically controlled using heated bolts.
How blow film maintains uniform thickness
Rotating equipment may be used to randomize thick spots from the die. Rotating winder platforms, rotating extruders, and rotating collapsing frame.
How extruder plasticates (melts) resin pellets
Through a heated barrel with pressure.
Why do coextrusion and lamination
We need the benefit of more than one layer. LDPE may give us a good seal but not a great print surface or barrier. Aluminum may give us a good barrier but not a good seal or print surface. Oriented polyester may give us a good print surface but not a great seal or barrier. Therefore we combine layers.
Multilayer extrusion equipment
Multiple extruders, special dies or combining blocks.
Multilayer extrusion dies
Cast film, blown film, other common polymer processing systems, dies must have systems to route polymers, prevent mixing of layers, and promote even flow characteristics.
Multilayer extrusion layers
7 and lower are most common, 9 are available, and 11 coming on stream. Adhesion, barrier layers (protect other layers), outer temperature resistant layer, inner sealant layer. Layers may occur more than once for curl resistance. Not as stable as oriented films, may be thicker than non-coex sealant films.
Lamination
Begins with a coating step (coating an adhesive), add a second web material, combining nip is heated. Most laminators can also be used as laminators (except 100% solids).
Laminating equipment
Solution laminators (solvents/water must be dried via drying ovens), 100% solid laminators (coating applied as a liquid, all part of adhesive, no drying), and extrusion coating.
Oriented films
Thinner, more dimensionally stable, higher clarity, better barrier.
How do oriented films work
Consider stretching a plastic sample, at first it gives (yield), then it necks in and stretches (cold draw), then it gets harder to pull (strain hardens), then it breaks.
Result of oriented films
takes the "stretchiness" out of a polymer, makes it more stable for printing registration, arranges polymer chains into a more orderly fashion, improves clarity, and increases strength.
Biaxial
Tentered vs. Double Bubble
Tentered
Sequential vs. Simultaneous
Heat set
Dimensional stability, registration more consistent, can take enough heat to allow for drying of solvent based or water based inks, high quality print possible.
Shrink film
Printable but requires careful drying, dimensional stability ok below shrink temperature.
Flame
Gas and air mixed and combusted over surface of film. Controlled flame contained in very small area. Flame changes surface of film (vaporize low molecular weight molecules, oxidize the surface).
Corona
Uncontrolled plasma operating at atmospheric pressure, typically in air. Result is generally some form of oxidation of film surface. Usually corona affects surface only, bulk properties of film are unchanged.
Plasma
Air is not a conductor of electricity (no free electrons). If you apply a high voltage across an air gap, the atoms will move about and collide. The collisions of air molecules release electrons, thus creating free electrons. The air heats up, conducts electricity and glows (it is now a plasma). The excited electrons and ions will collide with the film surface, creating a different surface.
What plasma does
Oxidizes the surface, creating more polarity on non-polar molecules (improve wetting). Vaporizes short chain molecules off of the surface. Creates free radicals as adhesion sites. Break some polymer chains, cross link some polymer chains. Measure/verify treatment.
Priming
Different from flame and corona treatment. Apply a coating, known as primer. Darby's law (sticking). Chemically compatible with: film surface, ink, and other coatings you may need (eg adhesive).
Metallization
Applying aluminum to a web.
"Can't extrude it"
Melting point too high for polymeric web.
"Can't coat it"
No solvents will dissolve it.
Vacuum deposit
Provides a thin barrier (metals impede oxygen, water vapor, flavors, etc. from moving through package), provides aesthetically pleasing look, multifunctionality (same web can be sealable and barrier).
Process of metallized films
Load rolls at atmospheric pressure, pull vacuum, metallize, return to atmospheric pressure, remove rolls, load new rolls.
To maximize productivity
Wide, thin, large OD roll.