answer:
In order to solve this problem, it is necessary to clarify two things: one is why the thermal paper can be colored by heat, and the other is why the scratch paper can generate heat.
First, explain the principle of color rendering. Ordinary thermal paper is composed of a paper base layer as a substrate and a thermal color rendering layer that plays a major role. If you add a protective layer to the thermal coating, you get three heat-sensitive paper with better waterproof, oilproof and anti-friction properties. Thermal paper can be divided into two types according to the principle of color development, physical type and chemical type, the difference is whether the color development process contains chemical reactions.
Physical thermal paper is divided into melt transparent type, melt transfer and sublimation type, etc., mainly using the change of state of matter after heating of thermal materials. For example, the melt transparent type is coated with a non-transparent waxy layer on the black substrate paper, and the waxy material melts into transparency after local heating, showing the black color of the substrate.
Chemical thermal paper is mainly divided into two types: metal compound color thermal paper and colorless dye two-component thermal paper. The commonality is that the components that are reactants are fused as coatings, and after local heating, the solid material becomes a molten state and begins to undergo a chemical reaction, thereby developing color. For example, the reactants of metal compound color thermal paper are heavy metal salts and reducing agents based on fatty acids, while the reactants of colorless dye two-component thermal paper are colorless dyes and color developers containing inner lipid rings.
And "scratching paper can generate heat" uses the principle of friction heat generation. According to the formula:
It is not difficult to get the heat generated when paddling. Among them is the coefficient of friction between the nail and the thermal paper, which is the pressure and the relative displacement.
Resources:
Liu Yingyao, Chen Gang, Tang Aimin, et al. On the production and technology of thermal paper[C]// The 2010 Annual Conference of the Newsprint Professional Committee of the China Paper Society and the 2010 Annual Conference of the Guangdong Paper Society. Chinese Paper Society; Guangdong Paper Society, 2010.
How much do you know the secret behind the receipt paper?
The scientific principle of thermal paper
Frictional heat generation | friction heat generation formula
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