UV pinning is the process of applying a dose of low intensity
ultraviolet
Ultraviolet radiation, also known as simply UV, is electromagnetic radiation of wavelengths of 10–400 nanometers, shorter than that of visible light, but longer than X-rays. UV radiation is present in sunlight and constitutes about 10% of ...
(UV) light to a
UV curable ink (UV ink). The light's
wavelength
In physics and mathematics, wavelength or spatial period of a wave or periodic function is the distance over which the wave's shape repeats.
In other words, it is the distance between consecutive corresponding points of the same ''phase (waves ...
s must be correctly matched to the ink's
photochemical
Photochemistry is the branch of chemistry concerned with the chemical effects of light. Generally, this term is used to describe a chemical reaction caused by absorption of ultraviolet (wavelength from 100 to 400 nm), visible (400–750&nb ...
properties. As a result, the ink droplets move to a higher
viscosity
Viscosity is a measure of a fluid's rate-dependent drag (physics), resistance to a change in shape or to movement of its neighboring portions relative to one another. For liquids, it corresponds to the informal concept of ''thickness''; for e ...
state, but stop short of full
cure
A cure is a substance or procedure that resolves a medical condition. This may include a medication, a surgery, surgical operation, a lifestyle change, or even a philosophical shift that alleviates a person's suffering or achieves a state of heali ...
. This is also referred to as the "
gelling" of the ink.
UV pinning is typically used in UV
ink jet
Inkjet printing is a type of computer printing that recreates a digital image by propelling droplets of ink onto paper or plastic substrates. Inkjet printers were the most commonly used type of printer in 2008, and range from small inexpensive ...
applications (e.g. the printing of
label
A label (as distinct from signage) is a piece of paper, plastic film, cloth, metal, or other material affixed to a container or product. Labels are most often affixed to packaging and containers using an adhesive, or sewing when affix ...
s, the printing of
electronics
Electronics is a scientific and engineering discipline that studies and applies the principles of physics to design, create, and operate devices that manipulate electrons and other Electric charge, electrically charged particles. It is a subfield ...
, and the fabrication of 3-D
microstructure
Microstructure is the very small scale structure of a material, defined as the structure of a prepared surface of material as revealed by an optical microscope above 25× magnification. The microstructure of a material (such as metals, polymer ...
s).
Purpose
UV pinning enhances the management of drop size and image integrity, minimizing the unwanted mixing of drops and providing the highest possible image quality and the sharpest colour rendering.
Challenge:
Overcome the wetting problems that were causing UV-Curable inks to spread and cause ink droplets to bleed into each other before full curing single-pass digital printing of narrow web labels.
Solution:
A UV pinning system that uses high power UV light emitting diodes (
LED
A light-emitting diode (LED) is a semiconductor device that emits light when current flows through it. Electrons in the semiconductor recombine with electron holes, releasing energy in the form of photons. The color of the light (corresp ...
s) installed next to the inkjet array (print head). The UV light from the pinning system, typically lower than that of the full cure UV system, causes the UV ink to thicken, also known as gelling, but not fully cure. This ink thickening stops dot gain and holds the ink droplet pattern in place until it reaches the full cure UV system.
References
* Enhancing label print quality with UV pinning, Sept 2007, Andrew Ridyard and Dr. Mark Bale
* Enhancing Label Print Quality with UV Pinning, August 2016, Senior Global Application Manager, Excelitas Canada Inc.
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Photochemistry
Ultraviolet radiation
Viscosity