Thermal paper

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A receipt printed on thermal paper. A heat source near the paper will color the paper. Thermal paper.jpg
A receipt printed on thermal paper. A heat source near the paper will color the paper.
Paper roll for thermal fax machine. ThermalPaperG3-TMG.JPG
Paper roll for thermal fax machine.

Thermal paper (often supplied in roll form, and sometimes referred to as an audit roll) is a special fine paper that is coated with a material formulated to change color locally when exposed to heat. It is used in thermal printers, particularly in inexpensive devices such as adding machines, cash registers, and credit card terminals and small, lightweight portable printers.

Contents

The surface of the paper is coated with a substance which changes color when heated above a certain temperature. The printer essentially consists of a transport mechanism which drags the paper across a thermal dot matrix print head. The (very small) dots of the head heat up very quickly to imprint a dot, then cool equally quickly.

Most thermal papers' coatings turn black when heated, but coatings that turn blue or red, and multicolor coatings, are sometimes used. An unintended heat source, such as a coffee cup, can discolour the paper and obscure any printing. A fingernail rubbed quickly across the paper may generate enough heat from friction to produce a mark.

History

The earliest direct thermal papers were developed by NCR Corporation (using dye chemistry) and 3M (using metallic salts). The NCR technology became the market leader over time, although the image would fade rather rapidly compared with the much more expensive, but durable 3M technology.

Texas Instruments invented the thermal print head in 1965, and the Silent 700, a computer terminal with a thermal printer, was released in the market in 1969. The Silent 700 was the first thermal print system that printed on thermal paper. During the 1970s, Hewlett-Packard integrated thermal paper printers into the design of its HP 9800 series desktop computers, and integrated it into the top of the 2600-series CRT terminals as well as in plotters.

In the 1970s and early 1980s, Japanese producers including Ricoh, Jujo, and Kanzaki, using similar dye-based chemistry, formed partnerships with barcode printer manufacturers including TEC and Sato and entered the emerging global bar code industry, primarily for supermarket receipt printers. U.S. producers including Appleton (NCR's license), Nashua Corporation, and Graphic Controls fought for market share. Users of pressure-sensitive label such as those made by Avery Dennison became major consumers of direct thermal label stock.

In the late 1980s and early 1990s, thermal transfer (distinct from direct thermal, and stable), laser printing, electrophotography, and, to a lesser extent, inkjet printing began to take away industrial and warehouse barcode applications due to better stability and durability of prints. Direct thermal made a strong comeback with point-of-sale receipt printing.

During 1998, Nintendo used thermal paper technology for their Game Boy Printer.

Mechanism of action

The printer essentially consists of a transport mechanism which drags the paper across a thermal dot matrix print head. The (very small) dots of the head heat up very quickly to imprint a dot, then cool equally quickly.

Chemistry

Four different types of imaging chemicals are used in thermally sensitive papers: leuco dyes, developers, sensitizers and stabilizers. [1]

Leuco dyes
The leuco dyes used in direct thermal paper are usually triaryl methane phthalide dyes , such as Yamamoto Blue 4450, or fluoran dyes, such as Pergascript Black 2C. A third widely used leuco dye is Crystal violet lactone. Red or magenta color can be achieved with dyes such as Yamamoto Red 40. Yellow can be produced by the protonation of a triaryl pyridine, such as Copikem Yellow 37. These dyes have a colorless leuco form when crystalline or when in a pH neutral environment, but become colored when dissolved in a melt and exposed to an acidic environment.
Developers
Leuco dyes, in general, provide little color when melted unless they are melted in conjunction with one or more organic acids. Examples of organic acids suitable for thermochromic papers are phenols such as Bisphenol A (BPA) and Bisphenol S (BPS). Other suitable acidic materials are sulfonyl ureas such as BTUM and Pergafast 201. Zinc salts of substituted salicylic acids, such as zinc di-tert-butylsalicylate have also been commercially used as developers .
Sensitizers
A leuco dye and a developer, when melted together, are enough to produce color. However, the thermal threshold of the coated layer containing the colorizing components is determined by the lowest melting component of the layer. Furthermore, developers and leuco dyes often mix poorly upon melting. To optimize the colorization temperature and to facilitate mixing, a third chemical called a sensitizer is commonly added to the imaging layer. Sensitizers are commonly simple ether molecules such as 1,2-bis-(3-methylphenoxy)ethane or 2-benzyloxynapthalene. These two materials melt at approximately 100°C, which is a practical lower limit for thermal coloration. These low-cost ethers are excellent low viscosity solvents for leuco dyes and developers, and this facilitates color formation at a well-defined temperature and with minimum energy input.
Stabilizers
Dyes in thermally sensitive paper are often unstable and return to their original colorless, crystalline forms when stored in hot or humid conditions. [2] To stabilize the metastable glass formed by the leuco dye, developer and sensitizer, a fourth type of material called a stabilizer is often added to thermal papers. Stabilizers often share similarities with developers and are often complex multifunctional phenols that inhibit recrystallization of the dye and developer, thereby stabilizing the printed image.

Paper stock

Papers are supplied either as rolls or (particularly for wider letter-size printers) sheets. They may have a stick-and-peel adhesive backing, for use as labels and similar purposes. Paper may be white, other colors, or transparent.

In 2006, NCR Corporation's Systemedia division introduced two-sided thermal printing technology, called "2ST".

Protective coating

Most direct thermal papers require a protective top-coating to:

Multicolored papers

Multicolor thermal paper first became available in 1993 with the introduction of the Fuji Thermo-Autochrome (TA) system. [3]

This was followed in 2007 by Polaroid's development of the Zink ("zero-ink") system. [4] Both of these methods rely on multi-layer coatings with three separate colorizing layers, with different methods used for independent activation of each layer. [5] The paper is used in compact photo printers. It has several layers: a backing layer with optional pressure sensitive adhesive, heat-sensitive layers with cyan, magenta and yellow pigments in colorless form, and overcoat. Zink technology allows the printing of full-color images in a single pass without requiring ink cartridges. The color addressing is achieved by controlling the heat pulse length and intensity. [6] The color-forming layers contain colorless crystals of amorphochromic dyes. These dyes form microcrystals of their colorless tautomers, which convert to the colored form by melting and retain color after resolidification. [7] The yellow layer is the topmost one, sensitive to short heat pulses of high temperature. The magenta layer is in the middle, sensitive to longer pulses of moderate temperature. The cyan layer is at the bottom, sensitive to long pulses of low temperature. The layers are separated by thin interlayers, acting as heat insulation, moderating the heat throughput. [8]

Health and environmental concerns

Some thermal papers are coated with BPA, a chemical considered to be an endocrine disruptor. [9] [10] This material can contaminate recycled paper. [11] [12] BPA can transfer readily to the skin in small amounts:

When taking hold of a receipt consisting of thermal printing paper for five seconds, roughly 1 μg BPA (0.2–0.6 μg) was transferred to the forefinger and the middle finger if the skin was rather dry, and about ten times more than this if these fingers were wet or very greasy. Exposure to a person who repeatedly touches thermal printer paper for about ten hours per day, such as at a cash register, could reach 71 micrograms per day, which is 42 times less than the present tolerable daily intake (TDI). [13]

The chemical bisphenol A (BPA) is used for thermal paper coatings because of its stability and heat-resistance. This allows inkless printing for receipts from cash registers. People who often are in contact with BPA coated receipts do have a higher level of BPA in their bodies than people with average contact. Therefore, the New York Suffolk County signed a resolution to ban BPA in thermal receipt papers. Violation of this new law, the "Safer Sales Slip Act", involves a US$500 penalty. The law became effective beginning January 3, 2014. [14]

From about 2013 bisphenol S (BPS), an analog of BPA that has been shown to have similar in vitro estrogenic activity to BPA, [15] [16] has been used in thermal paper coatings. The recycling of thermal paper coated with BPS can introduce BPS into the cycle of paper production and cause BPS contamination of other types of paper products. [12] Newer formulations are available which use either urea-based compounds or vitamin C, and are "phenol free". [17] [18] They can have comparable or even improved print quality, but cost more.

Related Research Articles

<span class="mw-page-title-main">Printer (computing)</span> Computer peripheral that prints text or graphics

In the field of computing, a printer is considered a peripheral device that serves the purpose of creating a permanent representation of text or graphics, usually on paper. While the majority of outputs produced by printers are readable by humans, there are instances where barcode printers have found a utility beyond this traditional use. Different types of printers are available for use, including inkjet printers, thermal printers, laser printers, and 3D printers.

<span class="mw-page-title-main">Laser printing</span> Electrostatic digital printing process

Laser printing is an electrostatic digital printing process. It produces high-quality text and graphics by repeatedly passing a laser beam back and forth over a negatively charged cylinder called a "drum" to define a differentially charged image. The drum then selectively collects electrically charged powdered ink (toner), and transfers the image to paper, which is then heated to permanently fuse the text, imagery, or both, to the paper. As with digital photocopiers, laser printers employ a xerographic printing process. Laser printing differs from traditional xerography as implemented in analog photocopiers in that in the latter, the image is formed by reflecting light off an existing document onto the exposed drum.

<span class="mw-page-title-main">Dye-sublimation printing</span> Digital printing technology with wide color range

Dye-sublimation printing is a term that covers several distinct digital computer printing techniques that involve using heat to transfer dye onto a substrate.

<span class="mw-page-title-main">Photographic paper</span> Light-sensitive paper used to make photographic prints

Photographic paper is a paper coated with a light-sensitive chemical formula, like photographic film, used for making photographic prints. When photographic paper is exposed to light, it captures a latent image that is then developed to form a visible image; with most papers the image density from exposure can be sufficient to not require further development, aside from fixing and clearing, though latent exposure is also usually present. The light-sensitive layer of the paper is called the emulsion. The most common chemistry was based on silver halide but other alternatives have also been used.

<span class="mw-page-title-main">Game Boy Printer</span> Printing accessory for the Nintendo Game Boy series of handheld games consoles

The Game Boy Printer, known as the Pocket Printer in Japan, is a thermal printer accessory released by Nintendo in 1998 which ceased production in early 2003. The Game Boy Printer is compatible with all the Game Boy systems except the Game Boy Micro and is designed to be used in conjunction with the Game Boy Camera. It also prints images from compatible late-generation Game Boy and Game Boy Color games. It runs on six AA batteries and uses a proprietary 38mm wide thermal paper with adhesive backing, originally sold in white, red, yellow and blue colors. In Japan, a bright yellow Pokémon version of the Game Boy Printer was released, featuring a feed button in the style of a Poké Ball.

<span class="mw-page-title-main">Thermal-transfer printing</span> Digital printing method

Thermal-transfer printing is a digital printing method in which material is applied to paper by melting a coating of ribbon so that it stays glued to the material on which the print is applied. It contrasts with direct thermal printing, where no ribbon is present in the process.

<span class="mw-page-title-main">Gelatin silver process</span> Photographic process

The gelatin silver process is the most commonly used chemical process in black-and-white photography, and is the fundamental chemical process for modern analog color photography. As such, films and printing papers available for analog photography rarely rely on any other chemical process to record an image. A suspension of silver salts in gelatin is coated onto a support such as glass, flexible plastic or film, baryta paper, or resin-coated paper. These light-sensitive materials are stable under normal keeping conditions and are able to be exposed and processed even many years after their manufacture. The "dry plate" gelatin process was an improvement on the collodion wet-plate process dominant from the 1850s–1880s, which had to be exposed and developed immediately after coating.

Photographic printing is the process of producing a final image on paper for viewing, using chemically sensitized paper. The paper is exposed to a photographic negative, a positive transparency , or a digital image file projected using an enlarger or digital exposure unit such as a LightJet or Minilab printer. Alternatively, the negative or transparency may be placed atop the paper and directly exposed, creating a contact print. Digital photographs are commonly printed on plain paper, for example by a color printer, but this is not considered "photographic printing".

<span class="mw-page-title-main">Thermal printing</span> Method of digital printing

Thermal printing is a digital printing process which produces a printed image by passing paper with a thermochromic coating, commonly known as thermal 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.

C-41 is a chromogenic color print film developing process introduced by Kodak in 1972, superseding the C-22 process. C-41, also known as CN-16 by Fuji, CNK-4 by Konica, and AP-70 by AGFA, is the most popular film process in use, with most, if not all photofinishing labs devoting at least one machine to this development process.

<span class="mw-page-title-main">Carbonless copy paper</span> Coated paper used for copying

Carbonless copy paper (CCP), non-carbon copy paper, or NCR paper is a type of coated paper designed to transfer information written on the front onto sheets beneath. It was developed by chemists Lowell Schleicher and Barry Green, as an alternative to carbon paper and is sometimes misidentified as such.

<span class="mw-page-title-main">Sun printing</span>

Sun printing may refer to various printing techniques which use sunlight as a developing or fixative agent.

<span class="mw-page-title-main">Thermochromism</span> Property of substances to change colour due to a change in temperature

Thermochromism is the property of substances to change color due to a change in temperature. A mood ring is an excellent example of this phenomenon, but thermochromism also has more practical uses, such as baby bottles which change to a different color when cool enough to drink, or kettles which change color when water is at or near boiling point. Thermochromism is one of several types of chromism.

<span class="mw-page-title-main">Carbon print</span> Photographic printing process

A carbon print is a photographic print with an image consisting of pigmented gelatin, rather than of silver or other metallic particles suspended in a uniform layer of gelatin, as in typical black-and-white prints, or of chromogenic dyes, as in typical photographic color prints.

Coated paper is paper that has been coated by a mixture of materials or a polymer to impart certain qualities to the paper, including weight, surface gloss, smoothness, or reduced ink absorbency. Various materials, including kaolinite, calcium carbonate, bentonite, and talc, can be used to coat paper for high-quality printing used in the packaging industry and in magazines.

A chromogenic print, also known as a C-print or C-type print, a silver halide print, or a dye coupler print, is a photographic print made from a color negative, transparency or digital image, and developed using a chromogenic process. They are composed of three layers of gelatin, each containing an emulsion of silver halide, which is used as a light-sensitive material, and a different dye coupler of subtractive color which together, when developed, form a full-color image.

<span class="mw-page-title-main">Bisphenol S</span> Chemical compound

Bisphenol S (BPS) is an organic compound with the formula (HOC6H4)2SO2. It has two phenol functional groups on either side of a sulfonyl group. It is commonly used in curing fast-drying epoxy resin adhesives. It is classified as a bisphenol, and a close molecular analog of bisphenol A (BPA). BPS differentiates from BPA by possessing a sulfone group (SO2) as the central linker of the molecule instead of a dimethylmethylene group (C 2), which is the case of bisphenol A.

<span class="mw-page-title-main">Photographic film</span> Film used by film (analog) cameras

Photographic film is a strip or sheet of transparent film base coated on one side with a gelatin emulsion containing microscopically small light-sensitive silver halide crystals. The sizes and other characteristics of the crystals determine the sensitivity, contrast, and resolution of the film. Film is typically segmented in frames, that give rise to separate photographs.

A contact copier is a device used to copy an image by illuminating a film negative with the image in direct contact with a photosensitive surface. The more common processes are negative, where clear areas in the original produce an opaque or hardened photosensitive surface, but positive processes are available. The light source is usually an actinic bulb internal or external to the device

<span class="mw-page-title-main">Zink (printing)</span>

Zink is a full-color printing technology for digital devices that does not require ink cartridges and prints in a single pass.

References

  1. ↑ Chemistry and Applications of Leuco Dyes, ed. Ramaiah Muthyala, Plenum Press, New York, pp. 125-203 (1997)
  2. ↑ "How to properly store thermal paper". 30 January 2017.
  3. ↑ U. S. Patent 5,216,438, Direct color thermal printing method for optically and thermally recording a full-color image on a thermosensitive recording medium, by S. Nakao, N. Katsuma and A. Nagata, Fuji Photo Film Co. (1993) U.S. patent 5,216,438
  4. ↑ U. S. Patent 7,166,558, Thermal imaging system, Bhatt et al., (2007) U.S. patent 7,166,558
  5. ↑ U. S. Patent 7,166,558, Thermal imaging system, Bhatt et al., (2007).
  6. ↑ "How Ink-free Mobile Photo Printers Work". howstuffworks.com. 24 June 2008.
  7. ↑ Peter Bamfield; Michael G. Hutchings (2010). Chromic Phenomena: Technological Applications of Colour Chemistry. Royal Society of Chemistry. p. 114. ISBN   978-1-84755-868-8.
  8. ↑ "THERMAL IMAGING SYSTEM". freepatentsonline.com.
  9. ↑ Babu, S., Uppu, S. N., Martin, B., Agu, O. A., & Uppu, R. M. (2015). "Unusually high levels of bisphenol A (BPA) in thermal paper cash register receipts (CRs): development and application of a robust LC-UV method to quantify BPA in CRs". Toxicology Mechanisms and Methods. 25 (5): 410–6. doi:10.3109/15376516.2015.1045661. PMID   26024012. S2CID   20335285.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  10. ↑ Liao C, Kannan K (August 2011). "High levels of bisphenol A in paper currencies from several countries, and implications for dermal exposure". Environ. Sci. Technol. 45 (16): 6761–8. Bibcode:2011EnST...45.6761L. doi:10.1021/es200977t. PMID   21744851.
  11. ↑ Fukazawa h, H. K.; Hoshino, K.; Shiozawa, T.; Matsushita, H.; Terao, Y. (2001). "Identification and quantification of chlorinated bisphenol a in wastewater from wastepaper recycling plants". Chemosphere. 44 (5): 973–979. Bibcode:2001Chmsp..44..973F. doi:10.1016/S0045-6535(00)00507-5. PMID   11513431.
  12. 1 2 Pivnenko, Kostyantyn; Pedersen, G.A.; Eriksson, E.; Astrup, T.F. (2015). "Bisphenol A and its structural analogues in household waste paper" (PDF). Waste Management. 44: 39–47. doi:10.1016/j.wasman.2015.07.017. PMID   26194879. S2CID   217938141.
  13. ↑ Biedermann, Sandra; Tschudin, Patrik; Grob, Koni (September 2010). "Transfer of bisphenol A from thermal printer paper to the skin". Analytical and Bioanalytical Chemistry. 398 (1): 571–576. doi:10.1007/s00216-010-3936-9. PMID   20623271. S2CID   7412010.
  14. ↑ "BPA Cash Register Roll Ban Enforced In Suffolk County" . Retrieved 6 December 2015.
  15. ↑ Viñas, R.; Watson, C. S. (2013). "Bisphenol S Disrupts Estradiol-Induced Nongenomic Signaling in a Rat Pituitary Cell Line: Effects on Cell Functions". Environmental Health Perspectives. 121 (3): 352–8. doi:10.1289/ehp.1205826. PMC   3621186 . PMID   23458715.
  16. ↑ Ji, K.; Hong, S.; Kho, Y.; Choi, K. (2013). "Effects of Bisphenol S Exposure on Endocrine Functions and Reproduction of Zebrafish". Environmental Science & Technology. 47 (15): 8793–8800. Bibcode:2013EnST...47.8793J. doi:10.1021/es400329t. PMID   23806087.
  17. ↑ "Phenol Free Thermal Paper Rolls". thermalroll.com. 6 January 2022.
  18. ↑ "The Surprising Benefits and Pitfalls of BPA-Free Thermal Paper Rolls". paperrollproducts.com. 31 May 2017.
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