The claim that intermolecular forces hold ink on paper is a fundamental physical certainty regarding adhesion and surface chemistry, so no citation is strictly needed.
The claim is a well-established physical truth regarding interfacial adhesion between liquids (ink) and solids (paper). While the retrieved papers focus on various modern applications like printed electronics, biopolymer packaging, and general surface science, papers [2] and [6] directly substantiate the underlying physics of intermolecular forces operating across interfaces and determining adhesion.