the role of fillers in thermal paper

filler is one of the main components of coated paper. Its functions usually include: filling the unevenness of the paper surface, improving the flatness of the paper, thereby improving the printing effect; improving the whiteness, opacity and gloss of the paper; and improving the appearance of the paper. These effects are mainly achieved by adding natural pigments such as clay and talc, as well as synthetic pigments such as precipitated calcium carbonate, titanium dioxide, satin white powder and aluminum hydroxide.

In thermal paper, the filler not only needs to meet the requirements of the above-mentioned coated paper, but also must be adapted to the specific properties required for thermal recording.

In order to improve the color development sensitivity and recording speed of the thermal recording paper, it is necessary to add a low melting point substance to the thermal coating formulation to reduce the thermal melting point of the dye and the developer. These low-melting substances are usually hot-melt materials, such as fatty acid amides or various waxes, also known as sensitizers. The addition of these low-melting-point materials causes various adverse effects when the color-developing layer is brought into contact with the thermal head during recording.

In order to explain this problem, let's first look at the thermal head and the recording process: the thermal recording head is a component composed of heating elements, usually divided into thick film type and thin film type. They are made of coated on heat-resistant materials (e. g. TaCO₂NorRuO) on the wear-resistant film. During the recording process, the electric pulse corresponding to the signal will generate Joule heat, and transfer the heat to the corresponding area of the thermal paper that is in close contact with the recording head, thereby forming an image. Temperature up300°C, the surface temperature is80-100°C. In order to ensure good thermal conductivity from the recording head to the sheet, a pressure roller must be used to apply a considerable pressure between the sheet and the recording head. The recording head undergoes instantaneous heating and cooling during the continuous application of pressure to feed the sheet forward for recording. If the performance of the heat-sensitive material is not good, the following situations may occur:

(1)heat-sensitive layer is transferred to the heat-sensitive head. These molten substances will adhere to the thermal head, causing contamination of the thermal head, which is called "thermal head adhesion" or "residue accumulation". This affects the thermal conductivity of the recording head, resulting in insufficient temperature, which in turn affects the color development sensitivity and lowers the color density of the recording layer.

(2)of these hot-melt substances forms an adhesive layer on the thermal head. The build-up of this adhesive layer also leads to a reduction in print sharpness and a reduction in image quality.

(3)molten matter deposited on the thermal head may cause adhesion between the thermal head and the surface of the recording layer during subsequent thermosensitive recording. This hinders the smooth feeding of recording paper during continuous recording, causing operational obstacles such as pitch misalignment, character shortening and even image distortion.

(4)thermal paper will cause different degrees of physical or electrochemical wear to the print head during the recording process.

Therefore, thermal paper experts around the world have been trying various methods to change the above situation, that is, to overcome the problem of thermal print heads. According to various reports and our own research experience, fillers play an important role in overcoming the above problems. Therefore, it can be said that the filler in the thermal paper can not only improve the whiteness, opacity and smoothness of the paper, but more importantly, it can also ensure a good fit between the paper and the thermal print head, and overcome the above-mentioned adhesion And blocking problems.