GMI Ink & Substrate Interaction 1 — Questions and Answers
Question 1: Which substrate property most directly affects the rate at which ink is absorbed after printing?
- Surface energy
- Porosity (Correct answer)
- Basis weight
- Caliper thickness
Correct answer: Porosity
Porosity determines how quickly and deeply ink penetrates a substrate's fiber structure, directly controlling absorption rate.
Question 2: In the context of offset lithography, what does 'ink tack' refer to?
- The viscosity of the ink at rest
- The resistance of ink to splitting between surfaces (Correct answer)
- The adhesion strength between ink and substrate after drying
- The pigment concentration in the ink formulation
Correct answer: The resistance of ink to splitting between surfaces
Ink tack is the resistance to splitting that occurs when the ink film is pulled apart between the plate, blanket, and substrate surfaces.
Question 3: What phenomenon occurs when ink laid down in a later printing unit fails to adhere properly to ink already printed by an earlier unit?
- Ink strike-through
- Poor ink trapping (Correct answer)
- Dot bridging
- Ink emulsification
Correct answer: Poor ink trapping
Poor ink trapping happens when a subsequent ink color does not properly adhere to a previously printed ink layer, causing color shifts and density loss.
Question 4: Coated papers generally produce smaller printed dot sizes compared to uncoated papers because:
- Coated papers have higher caliper, restricting dot spread
- The coating layer reduces ink absorption and lateral spread (Correct answer)
- Coated papers have lower surface energy repelling the ink
- The clay coating chemically reacts with ink pigments to fix them faster
Correct answer: The coating layer reduces ink absorption and lateral spread
The smooth, non-porous coating layer prevents ink from spreading laterally into the substrate, resulting in sharper, more controlled dot reproduction.
Question 5: Surface energy of a substrate is measured in which units?
- Newtons per meter squared (N/m²)
- Dynes per centimeter (dyn/cm) (Correct answer)
- Pascals (Pa)
- Grams per square meter (g/m²)
Correct answer: Dynes per centimeter (dyn/cm)
Surface energy is measured in dynes per centimeter (dyn/cm), indicating the substrate's ability to be wetted by inks and coatings.
Question 6: Which of the following best describes the term 'ink dry-back' in print production?
- The reversible softening of dried ink when rewetted
- The apparent density reduction that occurs as ink dries and loses gloss (Correct answer)
- The migration of ink pigment from substrate to substrate in a stack
- The curling of substrate caused by ink solvent evaporation
Correct answer: The apparent density reduction that occurs as ink dries and loses gloss
Ink dry-back refers to the decrease in apparent optical density and gloss that occurs after ink initially sets and fully dries, which must be compensated for during color management.
Question 7: In offset printing, 'picking' is a defect most directly caused by:
- Excessive ink viscosity combined with high ink tack pulling substrate fibers or coating off the surface (Correct answer)
- Too little dampening solution causing ink to deposit unevenly
- Substrate porosity exceeding the ink's penetration rate
- Ink pigment settling in the ink fountain over time
Correct answer: Excessive ink viscosity combined with high ink tack pulling substrate fibers or coating off the surface
Picking occurs when the ink film's tack force exceeds the surface strength of the substrate, tearing away fibers or coating particles from the paper surface.
GMI Ink & Substrate Interaction 1
Which substrate property most directly affects the rate at which ink is absorbed after printing?