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Techniques
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Thermal printing (ordirect thermal printing) is adigital printing process which produces a printed image by passing paper with athermochromic coating, commonly known asthermal paper, over a print head consisting of tiny electrically heated elements. The coating turns black in the areas where it is heated, producing an image.[2]
Most thermal printers are monochrome (black and white) although some two-color designs exist.Grayscale is usually rasterized because it can only be adjusted by temperature control.[3]
Thermal-transfer printing is a different method, using plain paper with a heat-sensitive ribbon instead of heat-sensitive paper, but using similar print heads.Thermal transfer printer require the use of wax-based ribbons that adhere to the substrate during the printing process.[4][5] As a result, users must load both labels and ribbon, essentially using an alternative ink system.[6]
A thermal printer typically contains at least these components:
Thermal paper is impregnated with asolid-state mixture of a dye and a suitable matrix, for example, afluoranleuco dye and anoctadecylphosphonic acid. When the matrix is heated above its melting point, the dye reacts with the acid, shifts to its colored form, and the changed form is then conserved in metastable state when the matrix solidifies back quickly enough, a process known asthermochromism.
This process is usually monochrome, but some two-color designs exist, which can print both black and an additionalcolor (often red) by applyingheat at two different temperatures.[7]
In order to print, the thermal paper is inserted between the thermal head and the platen and pressed against the head. The printer sends anelectric current to theheating elements of the thermal head. The heat generated activates the paper's thermochromic layer, causing it to turn a certain color (for example, black).
Thermal print heads can have a resolution of up to 1,200dots per inch (dpi). The heating elements are usually arranged as a line of small closely spaced dots.[8]
Early formulations of the thermo-sensitive coating used in thermal paper were sensitive to incidental heat,abrasion,friction (which can cause heat, thus darkening the paper), light (which can fade printed images), andwater. Later thermal coating formulations are far more stable; in practice, thermally printed text should remain legible for at least 50 days.[citation needed]
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 | This article needs to beupdated. The reason given is: Printing and display technology progresses. There's been less need for hard copies, and better non-thermal printers as well, shifting the demand and application of thermal printers. The comparison with the largely obsolete (for about 20 years!) technology of dot-matrix impact printing is very emblematic for this issue. Please help update this article to reflect recent events or newly available information.(August 2024) |
Thermal printers print more quietly and usually faster than impactdot matrix printers. They are also smaller, lighter and consume less power, making them ideal for portable and retail applications.
Commercial applications of thermal printers includefilling station pumps, informationkiosks,point of sale systems, voucher printers inslot machines,print on demand labels for shipping and products, and for recording live rhythm strips on hospital cardiac monitors.
Many popular microcomputer systems from the late 1970s and early 1980s had first-party and aftermarket thermal printers available for them, such as theAtari 822 printer for theAtari 8-bit computers, theApple Silentype for theApple II, and theAlphacom 32 for theZX Spectrum andZX81. They often use unusually-sized supplies (10CM wide rolls for the Alphacom 32 for instance) and were often used for making permanent records of information in the computer (graphics, program listings etc.), rather than for correspondence.
Through the 1990s, manyfax machines used thermal printing technology. Toward the beginning of the 21st century, however,thermal wax transfer,laser, andinkjet printing technology largely supplanted thermal printing technology in fax machines, allowing printing on plain paper.
Thermal printers are commonly used in seafloor exploration andengineering geology due to their portability, speed, and ability to create continuous reels or sheets. Typically, thermal printers found in offshore applications are used to print realtime records ofside scan sonar andsub-seafloor seismic imagery. In data processing, thermal printers are sometimes used to quickly create hard copies of continuous seismic or hydrographic records stored in digitalSEG Y orXTF form.
Flight progress strips used inair traffic control (ACARS) typically use thermal printing technology.
In many hospitals in theUnited Kingdom, many commonultrasoundsonogram devices output the results of the scan onto thermal paper. This can cause problems if the parents wish to preserve the image by laminating it, as the heat of mostlaminators will darken the entire page—this can be tested beforehand on an unimportant thermal print. An option is to make and laminate a permanent ink duplicate of the image.
TheGame Boy Printer, released in 1998, was a small thermal printer used to print out certain elements from someGame Boy games.
Reports began surfacing of studies in the 2000s finding the oestrogen-related chemicalbisphenol A ("BPA") mixed in with thermal (and some other) papers. Whilethe health concerns are very uncertain[citation needed], various health and science oriented political pressure organizations, such as theEnvironmental Working Group, have pressed for these versions to be pulled from market.[9]
Thermal printing was first used in the 1930s in electrocardiograph recorders. In 1950, this technology was used by 3M in the Thermofax copy machine.[10] However, the first versions of this process were based on the destruction by temperature of a white dye layer, under which was placed a paper pre-colored in black or other contrasting color.[11][12] This process was unreliable and was later replaced by a better process based on leucopigments, first introduced by NCR for military communications in the 1960s.
Compared to other printing solutions, thermal printer printing is very cost-effective.[13][14][15] No ink or consumables required. The main advantages are:
Main disadvantages:
