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Thermal printers use heat to create an image.
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| All three techniques use much the same mechanism. The printhead is ceramic with "thick film resistors" on it. The resistors are something like 0.1 mm or less across giving a pixel size that is just visible to the naked eye. The contact with the medium and perhaps a metal backing bar gives rapid cooling after each use. There is usually a control circuit nearby to switch the resistors on and off. |  |
Printheads can be a ceramic chip with just 9 pixels to be scanned across the page like a dot matrix printhead. Once a production line is set up, however, there is no great difficulty in making a head with hundreds or thousands of elements. One of the most common kinds of thermal head is the type used in fax machines - a full 8 inch bar with about 1600 print elements in a row.
Thermal printing is generally rather overshadowed by
| Inkjet printers - aimed predominantly at home use. Inkjets might generally be characterised as cheap to buy but expensive to run. Thermal mechanisms are simpler and usually cheaper to un. |
| Laser printers - mainly used for office print jobs. Laser printers use more complex mechanisms but the main consumable is relatively innexpensive toner powder and the mechanism is possibly more reliable than an inkjet. Thermal printers are very simple and reliable. |
| Thermal printers are much more common than people generally realise. Lots of point of sale (POS), auto-teller (ATM) and ticketing machines use thermal mechanisms. Product labelling is a major field - almost anything that is tracked by product code or serial number is very likely to be labelled using some kind of thermal printer. The slightly higher operating costs of buying thermal printer paper are more than offset by the simple reliable mechanism. |  |
Thermal printing is also very commonly used to make commercial products - badges, signs and logos, banners and even decorations for ceramics. Again the costs are quite high but the thermal mechanism gives a simple manufacturing oute - and in manufacture time is money.
Photography is an area with considerable potential for thermal printers. This might be surprising - people commonly think of inkjets and particularly the piezo-head variety as the definitive printers for photographic material. Picture printing requires very dense paper cover, and once again the thermal printer can do a surprisingly good job. Several of the little photo-printers now available are thermal devices - dye sub and thermal autochrome. For printing on demand in the field the thermal mechanism is much more portable and reliable than an inkjet because there is no carriage movement and no nozzles to clog.
Basics. 
Thermal printing simply makes lasting patterns using heat. There are lots of ways to do this including laser-engravers but most thermal printers ely on very localised chemical reactions or melting of material.
Thermal printers used in industrial printing for bar-codes, point of sale, fax and tachograph charts are superficially simple devices - at least to look at. The printer has just one active part - a thin printhead of ceramic usually mounted on a metal bar. The head has no moving parts and at first glance there is no visible mechanism at all. Only a very close look shows that it contains tiny resistors- almost invisible to the naked eye. These resistors heat a material locally to the point where it changes colour - usually permanently. Typically a wax melts and
- transfers from a ribbon to the paper, or
- a chemical included with the wax reacts and changes colour.
Thermal printing has some similarities to photography but the materials are thermo -sensitive rather than photo-sensitive. Photosensitive materials are difficult to handle because we live bathed in light - we can’t see without it. Thermal printers operate in the infra-red spectrum where there is an ambient temperature but rather less interference. Since it is easier for an electronic device to make heat than light the thermal printer can also deliver more energy to the paper.
There are several kinds of thermal printing:
| Direct print on thermo-sensitive paper is the most common process. A coating on the paper incorporates a thin layer of leuco dye and acid wax. The dye is normally clear but changes colour to blue-black when the wax melts and releases a mild acid. This is the mechanism favoured by glossy-paper fax machines and in things like cash registers. |
| Thermal transfer uses a heat sensitive ribbon of wax or resin. The coloured wax on the ribbon adheres to paper when it is exposed to a short pulse of heat. Thermal transfer is used to print barcodes and for things like buttons and badges. It is also used in some photographic printers. |
| Dye sublimation printers use material from a ribbon or ink-stick to move material to paper or plastic through a gas phase - embedding the colour in the surface and giving a hard wearing finish. The main use is photographic print. |
The same printer can usually deal with either direct or thermal transfer printing just by changing material and a software setting. Specialist thermal printers can cope with a variety of materials - irregular paper like labels, cloth, vinyl and even ceramics.
Improvements in the process might
| make the printhead pixels smaller improving the image quality. |
| make the colourant more specific to a wavelength of infrared. |
| use a series of two or three reactions to form yellow, cyan and magenta colours |
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Thermo-sensitive or thermochromic materials turn black immediately on exposure to heat. Secret writing illustrates the basic idea - using something like lemon juice to write a note that will be invisible until the paper is heated. Thermochromic papers build an "ink" component into a material like paper or plastic cards then heat it locally to darken the ink.
Ideally the ink should be sensitive to very brief heating, preferably by a specific wavelength of infra-red. For fax, label and tachograph records the changes should be unlikely to occur accidentally and irreversible once they are made. Until quite recently thermal papers tended to go brown with age and placing them on a hot surface would fade the writing or turn the whole page black.
Chromisms.
Rather similar thermochromic and photochromic materials are the basis of recordable CDs and DVDs. A reversible reaction might be used to make rewriteable DVDs - although at present these tend to rely on crystallisation patterns in low melting point metal alloys. A reaction that fades can be used to make one-time rentable DVDs - the disk becomes unplayable after a few days. The various "chromisms" thermo, photo, electro, magneto and baryo have all become of considerable interest because they can be used in sensors and for data recording - as well as printers. Electro and magneto chromic materials form the basis of some of the new electronic papers.
Thermochromic papers may just be coated or "sized" with a low cost non toxic material that doesn't need protection. Higher value or less friendly materials might be incorporated in microcapsules.
Leuco Dyes.
Thermochromic papers are usually sized with a mixture of leuco dye ("white dye") such as flouran mixed with an acid that will trigger a reaction such as octadecylphosphonic acid. The dye is not strictly thermochromic but changes colour in response to a localised change in pH. The effect is the same
Leuco dyes are chemicals with two stable states, one colourless and the other highly coloured.
The octadecylphosphonic acid is a stable wax at low temperature but localised melting lets it mix with the flouran.
The flouran in thermochromic paper is transparent (yellowish) until the acid is melted. The dye then undergoes a chemical reaction and assumes its protonated form which is coloured. The state of the dye remains when the temperature falls. Actually the leuco form is more stable so the marks may gradually fade but a strong dose of acid improves permanence.
Two & Three Colour Print.
There are a wide range of substances that show this type of reaction. It is possible to make a two-colour print by having one reaction that occurs at a relatively low temperature and creates a red ink, then another at a higher temperature that turns the print black. This kind of thing might be useful in bank teller machines. Fuji Photo have patented a process where heat sensitive layers develop cyan, magenta and yellow colours - giving a direct print process with photographic potential.
Thermo Autochrome processes use three pigments. The yellow pigment is usually most sensitive, then magenta, then cyan. To prevent all cyan pigments also triggering yellow and magenta the printer incorporates an ultraviolet lamp which "fixes" the colours after the first two passes so that, for instance, the yellow reaction no longer occurs.
At least one version of the thermochromic process is eraseable - on one pass the paper takes up print, on another pass at a different temperature it is restored to a blank state. People worry about the waste of fax paper but with eraseable sheets this might seem much less of a problem, just drop the boring material back into the paper-in tray. Given that most computer printing is for "temporary" use eraseable paper might find a market.
The problem with erasable paper is that people tend to like neat, fresh sheets.
The nice feature of the basic thermochromic process is that print is direct. All that is needed to get a record on a till roll or label is a printhead bar in contact with the paper - usually supported by a rubber oller platen. The mechanism is simple to use so it has remained very popular in commercial and industrial processes.
Improvements.
Thermochromic papers get their waxy feel because that is the nature of the chemical coating involved.
This process was first used on any scale in the 1970s and became very popular as the basis for fax printing. Until the mid '90s the thermochromic process was often inconvenient, expensive and unstable. Faxes usually printed to inconvenient lengths that were difficult to file. The paper would turn brown and the printing would fade - especially exposed to the light. To cap it all the paper was rather expensive.
In the mid 90's most of these problems were eliminated. Thermochromic paper became quite cheap, not very prone to fading and fax machines were fitted with guillotines that cut the paper to A4.
Non of this was enough to save the thermal printer based fax because fashion turned against them. Office machine buyers had made their minds up that so called "plain paper" faxes based on inkjet printers were more convenient.
Development.
As suggested above the various "chromisms" inspire some interest for things like DVD recording. There are a range of industrial uses applying patterns and textures to things.
Wavelength sensitive materials don't rely on chemical reaction but on changes in crystal state. The crystals normal state transmits photons, but when energy of a particular wavelength hits it changes state permanently and absorbs instead. These materials are similar to photographic emulsions but usually sensitive to only a narrow wavelength.
There are also reversible thermochromisms, usually based on light interference patterns within liquid crystals. These aren't much use for permanent records - although papers that fade after an hour or so could be very useful. T-shirts that change colour in contact with the wearers body use this type of dye.
An interesting sideline on thermochromic papers is Touch-it color change paper. The paper has a reversible thermochromic paper that changes colour wherever the user handles it.
A thermal print-head contains small infra-red emitters which produce a dot-pattern on the paper. Thermal print-head elements have no moving parts, the emitters are usually resistor heaters coated onto or embedded in the ceramic - essentially the device is a group of "thick film resistors". Ceramics are normally insulators but by incorporating metals or carbon they can be conductive, so the printhead may effectively be a solid block with conductive and resistive paths. Ceramic printheads might themselves be micromanufactured using thermal transfer or inkjet printing. Printhead manufacture is a specialised field - it doesn't seem to be something the average workshop can do. Nevertheless printheads can be less costly to manufacture than mechanical devices with the same number of print-elements. Mechanically this object may be no more impressive than a pencil-thin ceramic bar with metal brackets and some relatively simple control and drive electronics.
One great advantage of thermal printing is that it is possible to make a thermal print-head to match the required paper width - every dot position across the page has a corresponding element in the head. All that needs to be added to make the printer is a motor to drive the paper across the print-head. Thermal printing has been widely used, particularly in fax machines. Point of sale, weighing and labelling machines also often have a thermal printer. Using several wide heads it is possible to make a fairly fast printer capable of enormous page-widths. Ten years ago it was quite common to find large plotters using multiple thermal heads on thermochromic paper.
Thermal printing is silent – the only noise is that of the feed motor and the creaking of the rubber traction wheels on the paper.
Problems.
Because they have few moving parts thermal printers can be very reliable and cheap to make. However
- Print quality is usually quite good compared with a pen-plotter, but poor compared to a laser or inkjet. Thermal heads typically provide a resolution of 203 dots per inch.
- The part which inevitably goes wrong is the print-head, and when it fails it can cost nearly as much to make a one-off replacement as it is to buy a new printer.
- The paper has to incorporate or be coated with a material that is sensitive to heat. Thermochromic material is more expensive than ordinary sizings and adds to the cost of the paper. The difference in appearance might not be liked by users.
- The print process is fairly fast - up to 100mm per second, but even with an element in the head to correspond with every dot across the paper it merely competes with a fast inkjet - not with the faster laser printers.
Paper Stability.
Thermo-sensitive paper has improved in the last decade but is not completely stable in a standard office environment. Over time, the images tend to fade and the paper yellows badly in sunlight, in the worst case putting a cup of hot coffee down on thermal paper will print black rings on its surface and blot out the writing.
Printhead Wear.
The print-head is in direct contact with the paper. Over time the paper polishes and erodes the ceramic, so parts of the head do not make good contact with the page. Print-heads eventually wear away, usually one pixel doesn't print. If the printhead is used for barcodes and a pixel goes down in the vertical bar then lots of codes will mis-read. The only possibility of repair is head replacement. Thermal head manufacture is a complex process so if the part is obsolete repair is not possible and the printer's life is over. Unfortunately for users there are few standards in thermal printheads, most models seem to be built for the printer and if they are not the manufacturer won't let on for fear of spoiling a nice sideline in spares.
A helpful hint for barcodes is to print them oriented so that a one-pixel fault will leave a horizontal streak on the code rather than interfering with its vertical bars.
A problem with thermal heads is that whilst they are ordinarily quite obust they are easily damaged by metal objects. If a label or anything else gets stuck to them it tends to bake on. Remove stray material using a damp cloth, meths or isopropyl alcohol - never use a knife. Printheads may not be expensive to manufacturers, but as spares they are often an incedible price!
Environment & Health. 
The paper used in thermal printing clearly does involve some exotic compounds. Octadecylphoshonic acid is a potential skin, eye and espiratory irritant but is generally regarded as non-hazardous. There do not seem to be any allegations that fax paper is a health or environmental hazard. The waxes used in thermal transfer are not thought hazardous - they could probably be made edible so people could dispose of documents by eating them. There seems to be some secrecy about precisely what the ingredients of more complex thermochromic paper are.
The standard complaint about thermal printing is the cost of the paper. "Plain paper" faxes using inkjet or laser output gained a foothold in the fax market because of the cost of the paper. In the last few years the price of thermal paper has fallen – and is often quite comparable with laser printing and cheaper than using an inkjet. Beware of low-cost plain-paper faxes that use inkjet technology and cost more to run than a thermal-paper model would have done. Inkjet printers tend to be a lot more fuss to use.
Some thermal labels are truly horrific prices - low cost label printers sold as address printers are a particular example. The problem is that these printers take no standard materials and the printer maker has copyright on the media - so there is no second source of supply.
Thermal printing will continue to be used for applications where simple eliable printing is the only demand - retail product weighing and labelling, portable printing and instrumentation logs. The fax market may disappear because of the growing use of computers for document-imaging and E-mail as a way to move information.
Thermal wax transfer uses a print-head similar to that in the direct thermal process. Many printers can do both. The transfer print method involves melting a very thin layer of a wax and / or resin substance which transfers to the paper. The wax is carried on a plastic backing ribbon or "foil", usually a very thin transparent polyester film. Foil can normally be used only once because it loses all colour in the area printed. Since the foil now has gaps it cannot be re-used, the material is normally taken up on a spool and discarded.
Thermal transfer is used for two fairly distinct purposes:
- Barcode labels
- Decorative labelling.
There is some overlap between thermal transfer and dye sublimation. True dye-sub uses a similar printhead but higher temperatures. Dye sub is capable of gradated colour for photography.
Thermal transfer is often used instead of direct thermal processes in printers intended for barcode label printing. The high density long lasting black image gives the maximum chance that the codes will read easily.
Thermal transfer barcodes can often be made on the same printers that are used for direct thermal labels with just a change in software setting. Some printers need an extra kit to wind the "foil" or ribbon alongside with the paper. Thermal transfer label printers generally run at about the same speed as direct thermal.
The foil can be wax, resin or both.
Wax gives a strong print on paper labels - but is degraded by damp and may be intolerant of chemicals so that slight contamination may destroy the image.
Resins are normally intended to print onto plastic labels - polyester, vinyl and polypropylene which are intended to be very long lasting. Resins often dissolve into the substance of the plastic label, making it esistant to chemical attack and scuffing.
Printers need to be told what grade of material they are using otherwise transfer may be poor or the foil may warp. Since printer manufacturers don't necessarily want users to buy consumeables from others the temperature control settings may not be user -accessible or self evident if they are. Caution is suggested in experimenting - pushing things too far can wreck printheads.
Colour.
Wax and resin ribbons are usually black. Certainly if the purpose of labelling is barcode scanning black ribbon on white label is best because it gives the maximum contrast.
Coloured waxes in blue or green might work slightly less well than black, but probably quite acceptably. Red or yellow might pose a problem for barcodes because the laser itself will be red and there may not be enough contrast. It's the contrast as seen by the laser scanner at red wavelength that matters, not the contrast seen by the human eye, so cyan which is often perceived as a light colour but absorbs all red should work well.
Thermal transfer printers are used for several decorative purposes such as vinyl signwriting, product labelling and badge making. The print process generally uses a "CMYK" process. One layer each of cyan, magenta, yellow and black are transfered between the head and the page. The term "page" can be used losely. A thermal transfer process can aim at anything from T-shirts to teacups.
Pagewidth Transfer.
Thermal printheads can be page-width, faster printers intended for barcode labelling usually take advantage of this. No thermal colour printer is particularly fast because making 4 passes across the page takes time.
The pagewidth colour print process uses a foil with three or four successive panes of coloured wax sufficient to cover a page - so typically A4 length. The printer lays down the first colour, then stops moving the foil and winds the paper back. Next colour, stop and rewind and so forth.
Ordinary label printers cannot do this because they cannot accurately ewind the paper. Rewind has to be accurate to below pixel resolution or the colour registration will be off and the resulting haloes will be immediately visible.
Colour wax transfer and dye sub printers tend to be fairly expensive to make because of the need for accurate paper and foil movement. Whether this is reflected in the purchase price is another matter. The printer manufacturer can use proprietary paper and foil registration methods so users may be a captive market and the manufacturer can recoup money in consumeable costs.
The problem with page width printing is that large areas of foil material can be wasted if a page is largely white - which pages of text often are.
Raster Scanning.
Thermal printheads can also be the size of a fingernail and raster scanned across the page in the manner of a dot-matrix or inkjet printer. Since the scanning is mechanical this process is innevitably much slower than handling a full pagewidth in one go. A big advantage of raster scanning is that in combination with thin selectable ribbons it can markedly reduce waste of ribbon.
Little portable printers from manufacturers like Alps have used this process. A typical printer is to all intents a dot matrix device but uses a 4-colour wax ribbon and a thermal printhead.
Roland are one of the makers of plotter /vinyl cutter machines using this technique. The plotter has grit-rollers to push the paper or vinyl and a fairly conventional carriage. The carriage holds a small printhead with perhaps a hundred elements in it and can also select from a row of six ribbons - Usually CMYK Gold and Silver.
Most older and industrial purpose thermal heads had a resolution of 203 pixels per inch. Heads intended to produce a higher resolution image are typically made for 300 or 600dpi.
Colour.
Thermal transfer is commonly said to be incapable of a grey-scale so most printers achieve colour using a dither pattern. Obviously a printhead with 203dpi resolution isn't going to give a very credible dither pattern. The basic CMYK process with no dither pattern or other control would give a gamut of just 8 colours at best (assuming the waxes mix rather than overlay). It is probably true that colour transfer isn't easy to control.
It is possible to vary pixel intensity or size to some extent. Even if dither is used pages produced by thermal transfer with a 600dpi resolution generally look excellent - the wax finish makes them look like pages of a glossy magazine. Thermal transfer can be used in photographic printers. Dye sublimation may do a better job - if it counts as a distinct process.
Thermal Transfer & Envrionment.
Thermal transfer printing uses material on a foil backing. Perhaps the most typical job for a thermal transfer printer is to produce a barcode label. Something like a quarter to a third of the wax or resin from the foil transfers to the label, the rest and the foil itself is wasted. This may not be an environmental disaster because neither the polyester of the foil nor the wax (which is presumably largely carbon black) seem to be precious and the actual quantity of material used is quite small. However given that the foil potentially represents a data protection problem recycling of some kind might be a good idea.
The main bulk of the waste produced with labelling is usually the wax backing paper for the labels themselves. In a busy warehouse there can be overflowing bins of this stuff.
True dye sublimation takes things a stage beyond thermal transfer. The difference is that a true dye sub devices vapourises its ink and the gasses are absorbed and diffused into the surface to be printed.
There are "true" sublimation printers but most if not all of those with a ceramic printhead are actually transfer and diffusion printers. The colourant doesn't gassify - it just gets very runny which gives something like the same effect.
The temperature s used by a dye-sub printer are significantly higher, which means the colourant will transfer a bit at a low temperature and a lot at a high termperature. Varying the temperature and duration of heating controls the amount of transfer. Dye sub printers can often take an 8 bit 256 level control range for each colour - not sufficient to give a visually acceptable grey-scale but sufficient to give very good looking colour reproduction even without any dither effect.
By nature the sublimation process tends to produce rather difuse pixels and this helps produce continuous tones of colour where pixels blend somewhat.
There seem to be two or three methods:
Film transfer looks just like wax transfer - a hotter process gives sublimation rather than melting.
Inkjet dye-sub looks similar to any other inkjet cartridge and can work in the same printer chassis.
Laser dye-sub can genuinely vapourise the colourant film.
The resolution of dye sublimation printers is typically 600 dpi and some inkjets claim resolution to 5000 dpi. Superficially it looks as though the inkjet has much better performance. The problem is that an inkjet has no greyscale. The dye-sub process has an advantage in producing some measure of grey scale and in the blending of pixels.
Printer makers describe the process as "sublimation". Sublimation is eally changing from solid to gas phase, then condensing and printers don't actually do this - they just transfer material without a gas phase.
One benefit of the multi-colour multi-pass foil process is that a final, fifth layer can be used to transfer a clear gloss finish that is ultaviolet resistant. This gives material both the look and resilience of traditional photographs.
Printer makers often make up retail packs of paper together with a transfer film.
The economics of film transfer look poor. In practice because photography uses so much solid colour it may be no more wasteful than using up inkjet cartridges.
A problem with thermal transfer from film is the price. The materials used are basically a wax mixed with coloured toners, thinly coated onto a plastic ribbon. A low speed printer will use a small cartridge of ribbon and scan this across the page in the same way as a dot-matrix might. The only real difference is that the print-head is a small infra-red emitter and has no moving parts.
The materials used - plastic film and wax - aren't particularly expensive. Clearly covering a thin plastic ribbon with a fine layer of coloured wax is not particularly cheap, so ribbons tend to be quite expensive. Because the ribbon can only be used for one pass if a page of text is printed most of the colour is not used.
Price -Fast & Photographic Printers
Faster printers have page-width heads and page-width ribbons. To print a CMYK colour image on a piece of A4 paper the printer will use 33 inches of backing material. A page of thermal printing can cost £1 per sheet.
Photographic reproduction changes the cost benefit calculation for thermal printers. A page of text has 5% cover and 95% of the wax is wasted. A photograph has 100% cover and quite a large proportion of the wax is used. £1 per sheet may seem expensive for text, but for photographic material the esults often look better than inkjets.
Thermal wax printers can produce some interesting effects- one is that an image can be placed onto a backing sheet and then transferred by hot ironing onto a tee-shirt or a banner (inkjets can do something similar with special paper). The wax can also carry silver or gold particles - so one nice feature of these printers is their ability to produce material that would be impossible with other computer print processes.
One point to note about thermal transfer is that the foil contains a ecord of its use - so if it contains names and addresses or other confidential material disposing of it carelessly would not only be a breach of security it would be illegal under data protection acts. Foils may shred (although that is difficult and messy). Foils will burn (but that will produce toxic smoke). Ideally the material might be recycled, but since it stretches and distorts in the printer and confidential information has to have a controlled route that may not be possible. Direct thermal material doesn't create this extra disposal problem.
Both wax transfer and dye-sub produce great looking pages and unusual print effects so it has a lot of potential. Large quantities of plastic backing may be an environmental and cost issue.
Wax could be jetted in droplets onto the page as with an inkjet, but this requires the entire head to be heated. The Xerox "Phaser" works this way.
Some inkjet printers are starting to use dye sub techniques. There are also the Xerox (formerly Tektronix) printers that use solid inks.
The idea of using wax sticks as a print medium has been tried several times. Where the transfer printer has to waste a lot of foil and wax a mechanism that could directly apply the material would waste very little. The printhead might be something like an inkjet cartridge but the material would be pre-heated to melting at or near the point of use.
Tektronix designed a line of printers that use wax sticks that are partly melted near to their point of use, transfered through a page-width printhead then onto an intermediate drum and finally onto to the paper. Xerox aquired Tektronix's printer division and technology in 2000.
Print quality would probably be judged between that of thermal transfer and dye sublimation. Resolution figures aren't usually fantastic - the basic mechanism is at about 300dpi but recent printers are capable of 850 x 450 dpi. The wax ink adheres but doesn't sink far into the page so colours are very bright.
In principle there is no waste so operating costs are comparable with colour laser printers. Generally the printers are cheaper to buy than colour lasers and the results look very similar to glossy magazine pages.
The Xerox / Tektronix machines have relatively low running costs for a colour printer capable of full page cover. The printers can also handle a wide range of media - including colour transparencies The wax blocks used are an inch on a side.
One problem users report with the phaser design is startup cost. The printer seems to use a lot of wax sticks at startup as it drains spent solid ink from printheads that had cooled and replaces it. Xerox have aimed to prevent this happening by keeping the printhead just above ink freezing point in standby - rather than completely shutting down.
Solid ink has been succesful for Xerox. This and other transfer / inkjet /dye sub seems to be insipring wider interest among manufacturers.
The problem with direct thermal operation is that the paper will decay on exposure to light or heat.
The most common direct thermal printer is the fax machine, mass manufacture has made thermal paper faxes and their paper low-cost.
Label printers can also use direct thermal processes. If the label is to be used for something transient like a couriers shipment barcode or manufacturing batch number then fading of the image may be acceptable.
Thermal transfer requires both a "ribbon" and paper stock, so it tends to be more expensive than direct thermal printing. Thermal transfer is mainly used for label printers - ranging from little battery powered strip printers costing less than £100 to big 6" label printers costing £3,000 upwards. The price of a label printer is broadly proportional to how wide the maxiumum print width is, and how fast it can place an image on paper.
There are a variety of special purpose printers using thermal transfer or dye sublimation processes. Credit and security cards can be overprinted with a photographic image, company logo and other information, whilst a magnetic strip on the back can be programmed with a digital ID.
Colour thermal transfer can achieve very good looking images comparable with laser printing. Printer costs are very varied. Some printers intended for the mass market are chaep - the head is a fax machine part). Printers intended for the industrial market tend to have unusual designs and specialist natures so they are expensive. Operating costs always tend to be rather high - reflecting the special materials.
Thermal Printers - Envronmental Impact.
Thermal direct and thermal transfer printers both suffer from a potential design defect. Given that only about 5 - 10% of a typical printed page is inked they both use enough "ink" to fully cover a page, whether it is needed or not.
The direct process does this because the whole paper surface is impregnated with material. It doesn't seem to be an expensive material. What the impact on recycling, landfill and incineration are needs some research.
The transfer process does this because the backing foil and any wax or resin not used are wasted. The volume of waste isn't usually impressive - the foils are very thin. It doesn't usually look as though the foils could be recycled even though they do usually get taken up on a spool in the printer. Unfortunately foils do quite frequently get snapped and mistreated so it wouldn't be an easy job to re-coat them.
The main use for thermal printers tends to be in labelling. The main volume of waste usually seems to be the wax-paper backing for the labels. Sometimes it might be practical to re-spool the paper - if it is being used on a production line for instance. What use could then be made of it is more questionable. Presumably it would be very difficult to re-load the material with labels, as they are made by cutting down big webs of the stuff.
Printers themselves are a contrasts to the consumables. The print mechanism is simple - just a ceramic printhead against a platen roller. Presumably making ceramic printheads is comparable with other thick-film resistor devices, perhaps not entirely benign but the heads do last a long time.
Printers have long lives. They could have still longer lives if new pritheads were more readilly available. There are all the usual logistics issues that apply to spare in the way of making this possible.
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© Graham Huskinson 2010