Thermal paper
Thermal paper is a special type of paper for the thermal printing process. It is provided on the print side with a heat-sensitive layer which forms a dye by the action of heat.
Properties
The paper containing a thermo-sensitive layer are contained in the pigments, binder, a color former, a developer and auxiliary agents. It is available in different font colors, but black is most commonly used, followed by blue. Due to different levels of pressure temperatures can also be more of color levels in special printers to ensure appropriate thermal paper. Due to the higher technical effort, it does not come with the typical commercial and industrial applications, however, are used.
Thermal paper is usually supplied wound on a plastic or cardboard core. It is in basis weights of from 48 to about 240 g / m² obtainable. For the document and receipt printing thermal paper rolls have standard, a paper weight 48-55 g / m². For tickets, vouchers, lottery tickets and documents the stronger qualities of paper are used. By the thick paper having a higher tolerance for mechanical stress, and the printing quality is maintained longer.
Be certified paper for the food industry ( released in Germany by the Isega research and investigation mbH, Aschaffenburg ) and for the environmental (next to the Blue Angel is also known as the certificate Nordic Swan, the latter but as a collaboration of several paper manufacturers and therefore not independent ).
Technology
The thermal paper is selectively heated to the points to be described by small heating elements, which are arranged in a row in the width of the paper to be printed. This react on paper housed former and developer and give the print image.
Simple thermal printer for domestic print the paper with at least 90 ° C, as discolor -household paper from about 70 ° C or slightly higher. Paper for parking tickets, which is exposed in the summer high temperatures and high radiation intensity is printed with up to 120 ° C, as the reaction temperature of the paper here must be higher. It is determined by the "static sensitivity ". Cheap fax machines can usually print only slightly faster than the data rate for fax transmissions requires ( about 10-15 seconds per side), high-quality paper for barcode label printing can be printed at speeds of up to 400 mm per second. In pressure-free areas, the paper can be transported of course faster.
More detailed chemical compositions are kept secret in many cases as a trade secret.
Storage
Cheap thermal papers age very quickly, so that the font has faded after a few weeks. There are also thermal papers with 25-year durability guarantee, in Japan of paper are produced with " virtually unlimited archived ". However, the specified values refer to about 20 ° C and 50% relative humidity, without direct sun light exposure - ie situations that are not to be found in private homes and in most offices.
Thermal paper prints are therefore generally not as waterproof. For invoices and other documents that must be retained for several years, this is problematic. It should be temporarily made a copy on plain paper on which is partially drawn on the back of these prints - so it is up to the customer to make copies of storage -enabled when needed.
To get the typeface as long as possible, thermal paper should not be exposed to direct sunlight, excessive heat one. Plasticizers, as contained eg in plastic sheeting or tape, can remove the font. Also, tannins, as they occasionally occur in leather ( wallets ) can, let it fade the image. The term can also be unreadable by contact with disinfectants.
Many thermal papers contain the harmful substance bisphenol A and other unacceptable compounds, some of which led to the recommendation to dispose of thermal paper as waste.
Development
In recent years, the printers and thermal papers were quality greatly improved, in particular progress in the shelf life of printed thermal paper were obtained. The development is currently for there to be rewritable thermal films for special applications that repeatedly describe themselves and can be deleted.