Term
| What is the principle of lithography? |
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Definition
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Term
| Lithography-- image and non-image areas? |
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Definition
The printing and non-printing areas of the plate are practically at the same level (chemical process)
printing area is "oil-like"-- oleophilic/hydrophobic
non-printing area is "water-like'-- oleophobic/hydropholic |
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Term
| What are the three cylinders on a sheetfed press? |
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Definition
| Plate, Blanket, Impression |
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Term
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Definition
Primary Colors = RGB
Secondary Colors = CMYK
Complementary Colors = Y and B, G and M, C and R
TV, computer monitor, projector (screen color) |
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Term
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Definition
Primary Colors = CMYK
Secondary Colors = RGB |
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Term
| What are the advantages and disadvantages of a rough grained litho plate? |
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Definition
advantages: traps water easily, better ink and water balance, durable plates
disadvantages: big holes and small dots = won't work/bad resolution
graining- rough plate surface to accept water easily
methods-
-mechanical: stone to grind, simple
-chemical: adjetate surface
-electrical: sparks to create pours
anodite: after graining harden surface |
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Term
| What is a negative plate? |
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Definition
contact plate
plates are exposed through negative film
commonly used in the US
Hardening of the light-sensitive layer by light
It becomes insoluble for the developer in the exposed areas (dots slightly bigger) |
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Term
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Definition
contact plate
plates are exposed through positive film
commonly used in Europe
Decomposition of the light-sensitive layer by light
It becomes soluble for the developer int he exposed area (dots slightly smaller)
**plate before exposure accepts ink everywhere! |
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Term
| Why is gum coated on the plate after it is developed? |
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Definition
gum arabic or synthetic gum- protects non-image area, very thin coating
developer bath: chemicals that removes areas you don't need (alwaysss remove non-image area!) |
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Term
| Image and non-image areas of a multi-metal plate? |
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Definition
copper = image area (likes oil)
aluminum = non-image (likes water)
chromium = non-image |
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Term
| Image and non-image area of a waterless offset plate? |
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Definition
silicon = non-image area
polymer = image area |
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Term
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Definition
| when the image areas do no accept inks |
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Term
| What causes plate blinding? |
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Definition
plate wear = pressure between plate-to-blanket, plate-to-ink rollers...plate wears out!! (most common)
ink contains large particles (scratches plate)
antisetoff spray (powder, starch gets on surface)
poor adhesion of photosensitive coating to plate base
fountain solution attacks image area |
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Term
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Definition
| when non-image areas accept ink |
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Term
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Definition
not enough fountain solution to cover non-image areas = 99% why!!!
non-image areas oxidized
fountain solution attacks aluminum base |
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Term
| L*A*B values of a neutral color? |
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Definition
L= lightness
A= red-green
B= yellow-blue
neutral color = A and B are very small and close to zero! |
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Term
| Color tolerance of human vision in terms of identifying color difference? |
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Definition
Human do not detect hue, chroma, and lightness equally
-detect hue difference first
-observe low chroma colors more accurately than high chroma colors
-more tolerant in green than orange colors (green is harder to notice differences, orange is easier) |
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Term
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Definition
describes a color
more sensitive with low saturated color if muddy |
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Term
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Definition
| describes the luminous intensity of a color |
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Term
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Definition
| (Saturation) describes the degree of intensity of colorfulness |
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Term
| Why is black added in color reproduction? |
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Definition
helps achieve a good gray balance
enhances shadow detailes
replaces color = saves money!
due to limited max density achieved by CMY |
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Term
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Definition
under color removal
adding black to get desired color by taking out percentage of each CMY |
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Term
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Definition
gray component replacement
not as good/clear |
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Term
| Which is better, UCR or GCR? |
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Definition
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Term
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Definition
aptitude module
halftone screening
same frequency
different size
dark areas = bigger dots
light areas = smaller dots
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Term
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Definition
frequency module
halftone screening
same size
different frequency
dark area = more dots
light area = less dots |
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Term
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Definition
SID: main way to adjust overall result during production
variation caused by the amount of ink fed to the plate |
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Term
| How do solid ink density, screen ruling, and substrates affect dot gain? |
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Definition
solid ink density
-smaller dots at high solid ink density = gloss coated paper
larger dots at lower solid ink density = newspaper
-higher dot gain requires lower density to match
screen ruling
-finer screen ruling = finer detail = higher dot gain
substrates
-newspaper = higher dot gain (lower SID) |
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Term
| From highlight, midtone, to shadow, which has the largest dot gain? |
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Definition
square dots: largest dot gain at midtone
elliptical dots: largest dot gain at highlight
round dots: largest dot gain at shadow |
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Term
| Why do you measure paper density before you measure solid ink density? |
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Definition
| you need to calibrate the densitometer with barium sulfate / pure white |
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Term
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Definition
increases tone value (dot percentage)
the main dot gain is in the midtone: 40-60% |
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Term
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Definition
deformation of dot due to surface speed difference of two cylinders, cause dot to elongate
slur only happens in printing direction! |
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Term
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Definition
occurs during printing
-ink feed: ^ink, ^density= ^dot gain
-slurring, doubling
-characteristics of plate, blanket and impression pressure
-water feed, press speed
zero dot gain = almost impossible
more ink = more problem = higher dot gain
higher density = higher dot gain
higher printing speed = lower dot gain
too much water = ink softens |
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Term
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Definition
not a real dot gain...confusion with vision
optical effect of light being trapped around the edge of the dot |
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Term
| Direction of slurring appearance? |
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Definition
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Term
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Definition
basically is a registration problem on multi-color presses
ink from blanket to paper in press...50% ink goes onto the paper and the blanket keeps the other 50%. Then you adjust registration = move plate to print again...but blanket has ink from last time before the plate was moved = double image |
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Term
| Direction of doubling appearance? |
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Definition
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Term
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Definition
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Term
| What can a start target tell? |
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Definition
determines dot gain, slur, and doubling
Good printing condition = still has a little white opening in the center
closed dot = excess dot gain
oval shape = slur
"8" filled in = doubling
if slur, horizontal lines get much thicker and vertical lines get longer |
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Term
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Definition
only a problem for offset printing
overprinting ink acceptability on printed areas vs. on unprinted areas
PB&J sandwich! |
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Term
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Definition
-dry trapping: dry between colors (best)
-wet trapping: print on top of wet ink
-Have tackier ink first (increases tack sequence)
-improve drying of first color by a) letting the paper dry completely (overnight) or b) slow down the press |
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Term
| What are the overprint colors? |
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Definition
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Term
| What color traps the beset and why? |
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Definition
| Green traps best because M is in between C and Y on the printing press! |
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Term
| Can the same amount of cyan, magenta and yellow mixture reproduce an ideal neutral color? Why? |
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Definition
Ideally you want the same about of CMY to make a neutral gray
realistically, need more C and less M & Y |
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Term
| What is print contrast? What will it indicate? |
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Definition
the ability of holding open the shadow areas while still maintaining high solid ink density
Print contrast is how much shadow you can print
how much shadow you can print!
Why measure print contrast? to see shadow detail! |
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Term
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Definition
General Requirements and Applications for Commercial Offset Lithogaphic
similar to SWOP
very popular! more detail with it!
Standards
smaller # = brighter paper |
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Term
| What is the roller in fountain solution pan called? |
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Definition
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Term
| What is a continuous dampening system? |
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Definition
better than conventional...constant supply
works without a ductor roller
rapid response to changes in fountain settings
Two Categories
1)integrated: inker feed system; uses ink form roller
2)segrated: plate feed system; has separate dampening form rollers
combining inker feed and plate feed features = has a bridge roller! |
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Term
| Components of a continuous dampening system? |
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Definition
-fountain pan
-water pan roller
-metering roller
-transfer roller
-form roller |
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Term
| What is a conventional dampening system? |
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Definition
old style ; intermittently (stop&go) supply
meter dampening
-control the rotation of fountain pan roller (faster or slower)
-adjust the length of time the ductor dwells against the fountain roller
-disadvantage: very slow reaction |
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Term
| metering dampening-- continuous |
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Definition
metering nip- between metering roller and chromium roller
The thickness of dampening film at nip depends on:
**the hardness of pan roller
**the pressure between rollers (less pressure = more solution)
**the viscosity of fountain solution (higher viscosity = transfer more fountain solution) |
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Term
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Definition
transfers ink onto plate
main ink flow fed to plate via first two form rollers
any roller on a press that contacts the plate directly
it is difficult to ink large solid areas on a plate with only one form roller
soft roller- synthetic rubber |
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Term
| What is the bridge roller in a continuous dampening system for (inker feed or plate feed)? |
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Definition
when you combine inker feed and plate feed features it has a bridge roller
usually rotates slower than the other rollers |
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Term
| What are two ways of controlling dampening level (the amount of dampening solution on plate)? |
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Definition
1)continuous dampening system
2)conventional dampening system
or......
1) IPA (isopropyl alcohol)
2) alcohol substitutes
??? |
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Term
| What are two ways of controlling the inking level (amount of ink or ink film thickness on plate)? |
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Definition
1) adjust ink key to vary the ink feed across the plate...opening between blade and fountain roller
screw ink key = old design, has side effects
ink zone system = new design, free from side effects
2) control the overall ink applied by controlling the contract between fountain roller and ductor roller-- ink strip width
more ink = longer contact
less ink = shorter contact |
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Term
| What is front-heavy inking system? |
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Definition
| the main ink flow is fed to the plate via the first two form rollers |
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Term
| Benefits of a front heavy inking system? |
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Definition
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Term
| What kind of roller is hard roller in inking system? |
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Definition
oscillator roller = hard plastic
evens out ink film by rotating/moving side to side |
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Term
| what is the ductor roller in an inking system? |
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Definition
soft roller made of synthetic rubber that's in the back of the press
goes back and forth...not contact all the time |
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Term
| How will fountain solution affect ink tack and ink viscosity? |
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Definition
it reduces ink tack
higher viscosity = transfer more fountain solution |
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Term
| What is the best pH of fountain solutions used in sheetfed offset printing? |
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Definition
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Term
| How to benchmark fountain solution? |
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Definition
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Term
| When to benchmark fountain solution? |
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Definition
| whenever you change water treatment, or change to a different brand of concentrate |
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Term
| What kind of water is best for mixing fountain solution? |
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Definition
Deionizing (DI)
removes dissolved ions |
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Term
| What are the sources of calcium in fountain solution? |
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Definition
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