Analysis of Heat-developed Dry Non-silver Imaging Products and Technologies (4)

2 Dye-type thermal recording material coloration sensitivity and high sensitivity:

This thermosensitive recording material dynamic color profile shows the relationship between the power and color density of the thermal print head. This figure is ideal for achieving high-density recording (high sensitivity) with as little energy as possible. Most of the technical development of thermal paper is focused on this high sensitivity. The easiest method of high-efficiency is to lower the melting point of the color forming material used, but this causes deterioration of the pre-recording preservation and therefore has its limitations. Here are some of the more highly influenced methods.

Heat is transferred from the thermal print head to the surface of the color layer. The contact rate of the two affects the color sensitivity. When applied to different supports, the surface smoothness of the recording layer also changes. The lower graph shows the relationship between the smoothness of the surface of the recording layer and the coloration density when recorded at the same energy. The smoothness is represented by the Rp value, and the smaller the value, the higher the color concentration.

One of the means to increase the smoothness of the color-forming layer is to use a support having a high degree of smoothness, and after the color-forming layer is coated, a surface is treated with a calender. Due to the unevenness caused by the pulp, the smoothness of the paper is low. Therefore, the high-sensitivity heat-sensitive recording paper is coated on the paper base to fill in the unevenness. The application of calendering after coating is the most effective means of improving the smoothness of the colored layer. However, to increase the smoothness, it is necessary to increase the pressure of the calender. This will cause the contact between the color former and the color developer to generate fog, which requires The use of a low-pressure and high-smooth processing device and processing method. The gloss calender equipped with a metal roller and an elastic roller is more suitable for a heat-sensitive recording material than a calender equipped with a metal roller.

Thermal print heads have a thermal conductivity of only about 30% for thermal papers that improve smoothness and contact with thermal print heads. Excess thermal energy is directly discharged from the thermal print heads. Therefore, it is necessary to develop thermal print heads with better thermal efficiency. And its driving method.

In addition, the thermal insulation of the support helps to improve the color sensitivity. The undercoating has a thermal insulation effect, and the bottom layer is filled with hollow microcapsules, which greatly improves the insulation effect and improves the sensitivity. The foamed film called Synthetic Paper has a voidage of 20-40%, a large heat insulating effect, and a very good smoothness, but it is expensive. It is the most excellent type of high sensitive thermal recording material. Support. The dissolved color forming material diffuses and reacts with each other. The dissolution and mutual dissolution rate depend on the particle diameter of the color forming material. The smaller the diameter, the faster the speed and the higher the sensitivity. The following figure shows the effect of the particle diameter of the coupler on the thermal sensitivity of the thermal paper.

The most laborious research process for high-efficiency technologies is the addition of sensitizers. The sensitizer must be dissolved and diffused prior to the coupler and the developer. Therefore, a sensitizer having a suitably low melting point, good compatibility with the color forming material, and easy diffusion when dissolved therein should be used. There are many such compounds. The following table lists representative sensitizers. Sensitizer (a) was first used, has low compatibility with the coupler, and has a small effect, and was replaced by (b)-(e) developed later. Industrially, a sensitizer, a color former, and a color developer are finely ground at the same time, and they are more likely to dissolve in each other, which is advantageous for high sensitivity.