Thermal printer

Monday, 22 January 2007

Printers are commonly used for current computer users to print out data, like text data and colorful drawings. Computer technology is continually advancing, expanding the need for computers in the personal, business, and academic fields. As the need for computers has grown, so too has the need for various peripheral devices for use with computers, such as printers. Printers continue to become more and more sophisticated, in response to commerce demanding increasingly more functionality from printers. Printers used as information output apparatuses are broken down into impact printers, such as wire dot printers, and non-impact printers. Non-impact printers include laser printers and thermal printers. Since impact printers make a high amount of noise and are inferior in print quality, non-impact printers have been more popularly used recently. Among non-impact printers, thermal printers are suited for miniaturization, and thus, they have been used in a wide range of fields. Thermal imaging or thermography is a recording process wherein images are generated by the use of imagewise modulated thermal energy. Due to the fast development of the market for thermal label printers for label printing, especially barcode labeling, to improve capital asset management, inventory control or time and attendance reporting. The use of electronically controlled thermal printers has increased very rapidly over the last few years. Thermal printers are used, for example to print variable information including lot codes, bar codes, time and date, and other information on products and packaging, known as a web or substrate, in coding and marking operations. These printers comprise generally a thermal print head that transfers ink from a carrier, also known as a ribbon, disposed between the web and print head, which may be movable away from the ribbon when not printing. In a thermal printer, a thermal head having a heat generating element is brought into press contact with a platen roller, with printing performed on a heat-sensitive recording sheet sandwiched between the two members. Thermal printers can print on thermal paper which darkens or changes color when heated above a threshold temperature by the thermal print mechanism or printer head. The thermal transfer printing head is typically used in conjunction with a roller platen assembly and ink transfer printing film or ribbon, which carries a thermally transferable printing ink. By selectively activating discrete thermal elements in the printer head array as the thermal paper passes by, the desired information can be reproduced on the thermal paper.

A thermal printer is provided with a thermal head in which plural heating elements are arranged in rows in a main scanning direction. An image is printed on a recording paper by heating the heating elements that are contacted with a surface of the recording paper while feeding the recording paper in a sub-scanning direction. Platen rollers are commonly used in linear or serial printing to provide a firm foundation for various forms of print heads. In thermal printers, platen rollers are used for squeezing print media against a thermal print head to provide proper thermal conduction between the print head and media. Platen rollers also allow accurate movement of print media due to minimal friction characteristics. The thermal head includes an array of heating elements as resistors, which are arranged to record pixels arranged in one line. Modern thermal print heads have achieved levels of resolution based upon integrated circuit construction techniques which can locate a great number of individual heating elements in close proximity to each other. A color thermal printer is used with color thermosensitive recording material, which includes a support and at least three thermosensitive coloring layers overlaid thereon. The coloring layers are yellow, magenta and cyan coloring layers. Among the three, the yellow coloring layer is positioned the farthest from the support, and has the highest heat sensitivity. The cyan coloring layer is positioned the nearest to the support, and has the lowest heat sensitivity. In a typical color thermal printer, the dye ribbon in the form of a web dye-carrier may contain one or more series of spaced frames of colored heat transferable dyes mounted on a supply core. A dye ribbon comprises dye regions or frames of colors that can be printed in proportions to approximate true color, and a transparent overcoating region that can be disposed over printed dye to protect the printed dye from moisture degradation. A thermal head is used to record an image with pressure and heat to the continuous recording sheet being transported. Images of three primary colors are recorded in a frame-sequential recording, to obtain a full-color print. This type of thermal printer is commonly used to print digital photographs via direct connection to a personal computer or digital camera. In the case of thermal inkjet printers, a print head structure comprises a single or plurality of ink cartridges each having a nozzle plate that includes a plurality of nozzles. Each nozzle is in communication with a corresponding ink ejection chamber formed in the print head cartridge. Each ink ejection chamber in the cartridge receives ink from an ink supply reservoir containing, for example, yellow, magenta, cyan or black ink. In a color thermal printer, a full-color image is printed on a color thermosensitive recording sheet having at least three thermosensitive coloring layers. Thereby a thermal head heats the thermosensitive recording sheet to make coloring while the color thermosensitive recording sheet is shifted relatively to the thermal head. As the thermal printer, one head-three pass type and three heads-one pass type are well known. In the one-head three-pass type it is used a single thermal head that moves the color thermo-sensitive recording paper back and forth three times, to record a color image by three color frame sequential recording. In the three heads-one pass type, a yellow thermal head, a mazenta thermal head and a cyan thermal head are arranged along a feed path of the thermosensitive recording sheet. A yellow ultraviolet rays lamp is disposed between the yellow thermal head and the magenta thermal head. And a magenta ultraviolet rays lamp is disposed between the magenta thermal head and the cyan thermal head.

There are two types of thermal printers, including the direct thermal printing type and the thermal transfer type printers. In the direct thermal recording, a thermosensitive type of the recording material is used and heated by the thermal head to develop color. The color thermal printer of the direct printing uses a color thermosensitive recording material or recording sheet, in which thermosensitive coloring layers of magenta, yellow and cyan are formed on a support. The first coloring layer has the highest heat sensitivity, and develops its color in response to application of relatively low heat energy. The third coloring layer has the lowest heat sensitivity, and develops its color in response to application of relatively high heat energy. The coloring ability of the first and second coloring layers is destroyed upon application of visible or ultraviolet rays with particular wavelengths. Most of the direct thermographic recording materials are of the chemical type. On heating to a certain conversion temperature, an irreversible chemical reaction takes place and a coloured image is produced. When the recording material is transported, a thermal head is operated to heat and pressurize the recording material, the thermal head extending in a direction crosswise to the transport. So colors are developed in the coloring layers by the thermal recording. After this, a photo fixer is operated to apply violet or ultraviolet rays to the recording material. In direct thermal printing, the heating of the thermographic recording material may be originating from image signals which are converted to electric pulses and then through a driver circuit selectively transferred to a thermal print head. The thermal print head consists of microscopic heat resistor elements, which convert the electrical energy into heat via the Joule effect. The thermal transfer printers use an ink film and transfers ink from the ink film onto a paper by heating the ink film. In these printers, a nonsensitized web is customarily used and a transfer ribbon is interposed between the print head and the web having a coating of wax or resin which is selectively melted and thereby transferred to or chemically reacted with the web. This allows nonsensitized webs to be imaged and provides for a wide range of materials that can be used to form the image. In thermal transfer printing, a color ink sheet of great length is used, in which yellow, magenta and cyan ink areas are formed in cyclic fashion. The ink is thermally transferred to a recording sheet, to produce a full-color image. There are two types of thermal transfer printers, including a wax-transfer type and a sublimation type. The wax-transfer printer melts or softens ink of ink film, and transfers it to the recording sheet. The sublimation printer sublimates or disperses dye of ink film on to the recording sheet. Thermal transfer printers such as these are often used to print adhesive labels wherein the adhesive labels are serially mounted on a continuous web.

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