Thermal paper is also called thermal fax paper, thermal recording paper and duplicating paper. The surface of thermal paper is coated with a solid mixture of a dye and an appropriate substrate, such as a combination of Freon dyes. First, the substrate is heated to its melting point, and then the dye reacts with an acid, usually bisphenol A (BPA), which is the reactant acid in thermal paper, causing the dye to develop a color, and then the substrate solidifies rapidly, thus preserving the altered state. This is why such a convenient printing method is popular in industries such as facsimile machines, medical care, metrology systems, or the production of POS and logos. However, the service life of thermal paper varies depending on the substrate and coating material, and in harsh environments, thermal paper can fade.
Thermal paper in the material are ordinary thermal material and three anti-thermal material. Ordinary thermal paper is characterized by the price is cheap, but its preservation time is shorter, generally only about half a year. Can meet in the field of general retail, bar code printing. The three anti-thermal paper refers to: waterproof, oil-proof, scratch-resistant. Its surface has a layer of polyvinyl chloride chemicals, greatly increasing the protective effect, making the paper life up to 25 years.
Not only different materials will lead to different service life. Different storage environments will also lead to a shorter life of the thermal paper, such as being placed in the sun exposure and the temperature exceeding 30 degrees Celsius, it can only be saved for about ten days, but if in the shade, saving a year or so is not a problem. Environment, strong temperature, humidity, and light will accelerate the aging of thermal paper. Therefore, in use, we also need to correctly store thermal paper to ensure its service life.
The reason why the thermal paper can show the text, the principle is because the thermal paper in the drum driven forward movement, and in contact with the printhead, the print head heat generated by the melting of the thermal paper surface dyes and acids, so that the two chemical reaction after the production of color color. But this color reaction is reversible, which also means that when these newly formed colored structures again encounter the right conditions, they will be back to the colorless state.
Prolonged exposure to strong sunlight or ultraviolet rays will also accelerate the decomposition of chemicals in the thermal coating and the fading of colors. Thus, the normal service life of the thermal paper is not achieved.
Strong sunlight brings not only strong UV rays, but also high temperatures. Excessive temperatures can also accelerate chemical reactions and decomposition processes in the thermal layer, leading to image fading. Similarly excessively high humidity may cause the thermal paper to become damp, leading to the occurrence of color fading.
If the thermal paper is not damaged, we can place the thermal paper on a flat surface and photograph the surface of the paper with a digital camera, then adjust the contrast and brightness of the image in Photoshop or Corel draw to help restore the disappeared handwriting, or alternatively, create a negative image and use the color difference to enhance the revealed handwriting.
If you are not very proficient in these image editing software, the traditional heating method may also help, we just need to set the hair dryer to a medium temperature, place the thermal paper at arm's length, and then turn on the hair dryer until the text or image becomes visible, if you do not use the hair dryer, it is also possible to point the thermal paper to a light source with a certain temperature, here we need to pay attention to is that It is very important to keep the distance between the thermal paper and the heat source.
In the process of using, we should firstly pay attention to keep the thermal paper dry and clean. Secondly, we should also avoid storing in strong sunlight or humid places. Because humidity will accelerate the fading of thermal paper, strong light will make the thermal paper become yellow and brittle. At the same time, in the process of use, hard friction and smear, will also make the coating on the thermal paper damaged, resulting in color fading and unclear text. When storing, we should try to avoid contact with acidic, alkaline or greasy substances. The chemical reaction caused by this will also cause damage to the thermal paper.
For the use, we want to keep or more important thermal paper, we can through certain physical means to protect it. For example, the use of ziplock bags or plastic bags, the thermal paper wrapped up to avoid it coming into contact with dust or other pollutants to provide a certain degree of protection.
Lastly, the quality of the thermal paper is a direct influence on the print results and how long it can be kept; some poor quality thermal papers can only be kept for about six months, but good quality ones can be kept for 25 years. Not only that, higher quality thermal paper usually means that there will be higher whiteness, even paper quality and higher heat resistance. So in order to efficiently avoid some fading problems, we should have to choose higher quality thermal paper to use.
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