Pressure & Heat Sensitive Recording Materials

The pressure sensitive recording material is a material that forms an image record due to chemical or physical changes caused by pressure. The pressure-sensitive recording material itself is colorless, but it can display a clear color under pressure. In the preparation of pressure-sensitive recording materials, dye leuco (mainly colorless compounds that can display clear colors after contact with acidic substances) are mainly used. During the preparation process, the dye leucosome solution is wrapped in microcapsules with a diameter of only a few microns, and then the microcapsules are coated on the back of the upper paper, and the front of the lower paper is coated with an acid substance. The two layers of paper are stacked together, and the microcapsules rupture where the upper layer of paper is under pressure. The solution of the dye leuco encapsulated in the microcapsules flows out, and when it contacts the acidic substance, it immediately shows color on the corresponding position of the lower paper.

The heat recording material is a material that forms an image recording by chemical or physical changes caused by thermal energy. Generally speaking, the components of the heat recording material include coating structure, developer, coupler, sensitizer, stabilizer, surfactant and so on. Heat recording materials include thermal paper, transparent thermal materials, thermal CTP printing plates and many other varieties. There are many types of thermal paper, which occupies a dominant position in heat recording materials.

Applications:

With the rapid development of social economy and science and technology, pressure sensitive recording materials and heat recording materials have increasingly shown their important market positions, and are widely used in fax, cash register, labels, tickets, medicine, industry, digital imaging and other fields. Especially for heat sensitive recording materials, since more and more substances are used to make thermosensitive recording materials, the development is becoming faster and faster. For example, aromatic imine compounds, isoisocyanate compounds, phthalone compounds, panthione compounds, and diazonium salt compounds can be used to make thermal recording materials.

• Carbonless copy paper: Carbonless copy paper is a kind of invisible copy paper, which has the functions of direct copy and direct color development. The working principle of carbonless copy paper is that under the action of external force, the force sensitive pigment and oil solution in the microcapsules will overflow and come into contact with the developer to cause a dyeing reaction, thereby playing the role of copying. Carbonless copy paper is mainly used for multi-part forms, bills, continuous financial receipts, general business receipts, etc. Pressure sensitive recording materials have very important applications in the preparation of carbonless copy paper. The carbonless copy paper prepared from the pressure-sensitive recording material has the advantages of no pad during copying, no pollution, and clear writing.

Figure 1. Carbonless copy paper

• Medicine: Heat recording materials have a wide range of applications in medicine. Medical film refers to a medium used to carry medical image information, and is used as an auxiliary tool for medical staff to diagnose the condition. Using heat-responsive microcapsule technology, the leuco dye diazonium salt can be coated in the microcapsules, the color developer and the like are placed outside the microcapsules, and the hair coloring components are separated by the microcapsule wall at normal temperature. When the temperature of the microcapsule wall material is higher than the Tg temperature, the permeability of the material forming the microcapsule wall is significantly increased, so that the color developing agent penetrates into the capsule, and the color is developed due to the instant contact of the color developing component. Thus, a stable light-fixing thermosensitive recording material using a diazonium salt is obtained. This kind of heat sensitive recording material is commonly used in the manufacture of heat sensitive recording films in medicine.

Figure 2. Heat sensitive recording film

• Printing: Heat recording materials are most widely used in printing. The photo images printed by the sublimation printing system are clear and stable, with continuous tones and high resolution. Because of its excellent output effect and environmental protection effect, it is widely used in the output printing of digital photo ID photos, studio portraits, and artistic photography. The sublimation printing material is composed of an imaging dye band and an image receiving sheet. The heat-sensitive layer of the imaging dye tape is prepared by applying a coating solution containing imaging dye and adhesive to the polyester base. Due to the heat energy, the imaging dye on the imaging dye belt is sublimated and transferred to the receiving film or photo paper to form a visible image.

Figure 3. Thermal printing paper

References:

1. James A. (2018). "Nanoscale thermal transport aspects of heat-assisted magnetic recording devices and materials." Mount Royal University 37, 112-118.
2. Liu Zhuofu. (2011), "Studying thermal characteristics of seating materials by recording temperature from 3 positions at the seat-subject interface." Journal of tissue viability 20, 73-80.
3. Naoto Yanagihara. (2001), "Functional Materials for Direct Thermal Full Color Recording Paper." Journal of Synthetic Organic Chemistry 59(8), 800-808.