Question

What is the Inkjet Printing - What is inkjet printing??

Accepted Answer

A method of printing  this process creates an image by propelling droplets of ink onto a substrate  The image being printed is sent to the printer  where it is stored in the buffer memory of the printer  rollers draw the substrate through the printer and a stepper motor pulls the printhead back and forth across the substrate  Ink is drawn from a reservoir or cartridge and expelled through a nozzle or nozzles in the printhead before landing on the substrate where it dries in place  There are two main types of inkjet printing  which are categorised based on the method used to deposit ink onto a substrate         Continuous inkjet printing uses a printhead with a single nozzle to produce a constant stream of liquid ink  This stream is broken up into droplets by a piezoelectric crystal  piezoelectric materials generate an electric charge in response to an applied mechanical force  pressure  and generate a mechanical strain in response to an applied electrical field   Some of these droplets are given a charge by a charging electrode and are then deflected by electrostatic deflection plates to land in a particular place on the substrate  Some droplets are left uncharged  these    guard droplets    prevent electrostatic repulsion between neighbouring droplets and are not deflected by the plates  Instead  they fall into a collection gutter and are sent back to the ink reservoir to be reused  Continuous inkjet printing is commonly used for the marking and coding of products and packaging         Drop On Demand  DOD  inkjet printing creates and deposits droplets of ink only when and where they are needed  There are two methods of DOD inkjet printing  known as thermal and piezoelectric inkjet printing  Thermal DOD printing  sometimes known as    bubblejet     uses a thermal printhead and creates droplets of ink using heat  It requires ink cartridges that are made of a series of tiny chambers  each containing a heating element  usually a resistor   A pulse of current is sent to the resistor  which causes the liquid ink to vaporise and form a bubble  As the bubble expands  a droplet of ink is expelled out of that chamber  and either into the next chamber or out of a nozzle in the printhead   The bubble then cools and pops  which creates a vacuum and draws ink into the chamber to replace the ink that has been used  either from the next chamber or from an ink reservoir   This method of DOD printing uses a cheaper printhead but requires more expensive printing inks  they have a volatile component that allows them to vaporise and form a bubble          Piezoelectric DOD printing uses a printhead that has a piezoelectric material at the back of the ink chamber for each nozzle  An electric current is passed through the piezoelectric material  which causes the material to deform  As the material changes shape  the space in the ink reservoir is reduced and ink is forced out of the nozzle  When the pulse of current passes  the piezoelectric material returns to its original shape  creating a vacuum and pulling ink from the ink reservoir to replace the ink that has been expelled from the chamber  This method of DOD printing uses cheaper printing inks but a more expensive printhead  which contains piezoelectric material          Inkjet printing is a form of digital printing  the image or document being printed must be in a digital file format before the printing process can begin  A Raster Image Processor converts the document or image being printed into a raster image or  bitmap   so that the document or image is represented by a grid of pixels  points of colour   This bitmap is then sent to the printer for output and droplets of ink are directed  continuous  or deposited  DOD  in place to recreate the grid  and therefore the image  on the substrate         Multiple droplets of ink are required to recreate the correct colour of a single pixel  and dots may need to be layered and combined to create an accurate colour depth for photo quality images  This means that the resolution of the printer must be higher than the resolution of the image being printed  for example  you may need a printer with a resolution of 1200 dpi  printing dots per inch  to print an image with a resolution of 250 ppi  pixels per inch   The resolution that an inkjet printer is capable of producing is influenced by the number of nozzles in the printhead  DOD  and by the size of the dots that are produced  inkjet printers are capable of printing dots as small as 50-60 microns         Most desktop inkjet printers use aqueous  or water-based  liquid inks that include water  glycol  and a colourant  Inkjet inks can be made with either pigments or dyes as the colourant  pigment inks tend to hold their colour better but are more expensive  while dye inks are cheaper and offer a wider range of strong and consistent colours but fade much more quickly  Desktop printers tend to use cartridges with the CMYK process colours  the black is usually a separate cartridge  while the CMY colours can be separate or  more commonly  are combined into one cartridge  Cartridges can also be produced with specific spot colours or special purpose inks  such as white or metallic inks          As the inks as water-based  they are not waterproof  meaning inkjet printers cannot be used to make waterproof print unless special inks are used  Aqueous inks are also subject to a number of issues that result from these inks spreading or drying incorrectly  including bleed  strike-through  feathering  pinholing  blocking  blistering  skips  and set-off  Larger scale inkjet printers  such as wide format printers used in the printing industry  may use solvent inks  pigment inks that are waterproof and dry through the evaporation of the solvent   UV inks  dries through exposure to UV light   or sublimation dyes  traditionally used for printing on fabrics that contain polyester  to overcome some of the more common issues caused by using aqueous inks         Inkjet printers are low cost and capable of high quality output  including vivid colour and fine details  However  they can be costly in terms of the consumables that need to be replaced  including cartridges and printheads   are subject to problems with ink drying within the printhead or reservoir  often requiring a cleaning cycle during the printing process   and print issues resulting from the use of aqueous liquid inks

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