The use of ink can have a drawback. It is often observed that a coating on a
ductile plastic results in a brittle fracture during impact loading, whereas
the uncoated part tested under the same conditions deforms in a ductile
manner. The ink layer can result in a 40-fold reduction of the fracture
energy, especially when a rigid ink is used. On loading of the part, the
brittle ink fractures first and the crack may propagate through the substrate.
Additionally, solvents in the ink
might lead to environmental stress cracking. High internal stresses in the
part near gates, weld lines and wall thickness transitions, but also stresses
due to external loads, in combination with aggressive solvents, may cause
cracks in the surface of the substrate.
