Development history and characteristics of thermal printing paper
Development history of thermal printing paper
In the 1930s, wax-type thermal printing paper using thermal recording was first used in electrocardiography.
In the 1940s, the United States developed a thermal copy method that uses infrared rays as a heat source to turn the original image into a thermal image.
In the 1950s, the 3M Company of the United States invented the thermal printing paper of the metal compound system.
In the 1960s, NCR Company invented thermal printing paper using the reaction of leuco dyes and phenolic compounds, which is also the most widely used thermal recording method.
In the 1970s and 1980s, the application of thermal printing paper in communication and faxing developed rapidly, the annual output increased rapidly, and the technology also made great progress. The recording speed changed from the G1 machine to the current G4 machine.
After the 1990s, thermal fax paper was affected by the gradual popularization of plain paper fax machines, and the output of thermal fax paper declined. However, the application of thermal printing paper in other fields is still developing rapidly.
Characteristics of thermal printing paper
It is easy to use and suitable for various thermal recording devices; the thermal recorder itself is cheap, simple and compact, almost maintenance-free, and has low recording noise; the recording is fast, and the text pattern is clear; the recording pattern and text have a short storage period, usually only one time. Year; the price is higher than ordinary paper.
The basic structure of thermal paper
Characteristics and requirements of thermal printing paper base paper
Stable quality, less appearance paper defects; high smoothness; good evenness, moderate thickness; small porosity, no pinholes, moderate air permeability; high dry strength, with a certain wet strength; high sizing; high whiteness.
Composition and function of precoat
It is composed of pigments, adhesives and additives; its main functions are: improve the smoothness of the paper surface; make the heating element and the thermal coating on the paper surface contact more closely; it is beneficial to the color reaction; improve the clarity; play a certain heat insulation Function; make the heat-sensitive coating concentrated by heating, and the color will be more fully developed.
Composition and color development mechanism of heat-sensitive coatings
It consists of color-forming agent (leuco dye), color-developing agent (solid organic acid), sensitizer, lubricant, pigment, adhesive and other related auxiliaries. When the heating element applies a certain amount of heat energy to the heat-sensitive coating, the components of the coating will be melted and chemically reacted, thereby showing the color.
Heat-sensitive leuco dye, developer, sensitizer
The heat-sensitive leuco dye itself is a colorless or light-colored organic compound, which reacts with a color developer to develop color when heated. At present, fluoran compounds with lactone ring structure are the most widely used. When they come into contact with acidic substances (color-developing agents), their lactone rings are cracked to produce compounds with corresponding colors;
The color developer is generally a solid organic acid substance, usually a phenolic compound. The color developer acts as a proton donor to develop color by reacting with the leuco dye. At present, the most commonly used color developers are bisphenol A (BPA), carboxybenzoate (POB), bisphenol S (BPS), etc.;
The sensitizer is usually a neutral organic compound, and its function is to promote the reaction of the leuco dye and the developer, and to improve the sensitivity, depth and durability of the color. The sensitizer usually has a low melting point and no sublimation; the viscosity within the melting point range is low, and it has good compatibility with leuco dyes and color developers.
Quality Control Points for Thermal Printing Paper
Color rendering depth and clarity, color rendering sensitivity (sensitivity), color rendering durability (preservation), whiteness, smoothness, running suitability for thermal recording, thickness, surface strength (printing type), appearance paper defects.
The main factors affecting the color rendering effect of thermal paper
Raw materials and formulations of pre-coating coatings; raw materials and formulations of thermal-sensitive coatings; particle size of coatings; coating amount; smoothness; printing speed and output energy; printing pressure, etc.
Precautions for the use of thermal paper
The ideal storage environment for thermal paper is below 25°C and below 65% RH. Avoid storing in high temperature, high humidity and direct sunlight, otherwise it will affect the thermal performance.
After heat-sensitive color development, it should be stored in the dark under the temperature below 25℃ and the humidity below 65%RH.
Avoid contact with the following items, such as wet diazo carbon paper, soft polyvinyl chloride products, erasers, marker pens, adhesive tape, correction fluid, back-coated carbon and carbonless carbon paper, etc. Discoloration or fading of the hair color may occur.
When using glue, water-based glue such as starch, polyvinyl alcohol or CMC should be used.
Avoid touching the thermal paper with wet or sweaty hands, otherwise it will leave fingerprints and contaminate the colored part.
Avoid discoloration caused by friction and heat of thermal paper.