Microcapsule technology is a micro-packaging technology that can wrap solid liquid or gaseous particulate matter in a natural or synthetic polymer film to protect unstable or susceptible functional substances. In tiny containers with a diameter of 1-1000um, it protects substances from environmental conditions, improves stability, controls the release of protected substances, shields taste, color and odor, reduces toxicity, and prolongs the storage time of volatile substances. Mixed compound isolation and other functions.
Carbonless copy paper consists of an upper sheet (CB paper), a middle sheet (CFB paper) and a lower sheet (CF paper), and a color developing agent layer is coated on the back of the CB paper and CFB paper.
The chromogenic agent layer is composed of a chromogenic agent, a buffer and a binder. The chromogenic agent is microcapsules, which play a role in color development. The buffer is made of cellulose powder or cellulose starch, which is finer than the microcapsules. Pressure buffer material, so that the carbonless copy paper does not develop color under slight pressure overlapping. Generally, starch slurry or styrene-butadiene copolymer emulsion is used as the adhesive to make the chromogen layer and the base paper firmly bonded.
Coat the developer layer on the front of CFB paper and CF paper. The developer layer is formed by dispersing active clay (acid clay or kaolin, etc.) in the aqueous solution of the binder, coating, drying.
The color development principle of carbonless copy paper is that the pressure of the pen tip breaks the microcapsule wall of the chromogenic agent during copying, and a color chemical reaction occurs as soon as the oil-soluble colorless dye contacts the acid clay in the chromogenic agent, and electrons are supplied during the chemical reaction. The given leuco dye loses electrons and turns into a colored dye with a quinone structure, and the electron-accepting acidic color-developing material clay absorbs electrons to complete the color reaction, and the copied document is obtained.
Microcapsule is the key material of carbonless copying paper, which directly affects the clarity of copying and the number of copies.
Generally, the diameter of microcapsules is about 3-8umI, and the particle size distribution is required to be uniform. If the particle size is too large, the wall is thin and easy to break, and it is easy to develop color during production and transportation. This will affect the quality of copying and the copy image. The number of carbonless copying paper structures. Therefore, the wall thickness of the microcapsules directly affects the quality of carbonless copying paper products, and controlling the appropriate wall thickness is the key.
Qualified microcapsule particles can be obtained by selecting appropriate capsule wall materials, adopting appropriate preparation methods, and controlling appropriate process conditions.
For example, when chitosan is selected as the wall material and the core-to-wall ratio of microcapsules for carbonless copy paper is controlled to be 4:1, the qualified rate of microcapsule particle size and the embedding rate of the core material (the actual embedding amount of the core material accounts for the original
Another example is the in-situ polymerization method using styrene maleic anhydride copolymer (SMA) as an emulsifier, which is oriented on the surface of the core material, so that the surface of the oil phase droplet of the core material (that is, the leuco dye CVL oil-soluble liquid) forms a strong Negative electric field, the negative electric field acts on the positively charged wall material in the liquid.
It is mainly the dimethylolurea produced by the addition reaction of urea and formaldehyde, which becomes a positively charged active prepolymer (NHCH2) in an acidic medium to generate adsorption, so that the wall material material is enriched and carried out on the surface of the core material droplet. The polycondensation reaction finally wraps the core material and solidifies to form the microcapsule wall.
The optimal preparation process conditions are 'the molar ratio of urea to formaldehyde is 1:2, pH=3-4, the temperature is 70°C and the temperature is kept for 6H, the particle size distribution of the obtained microcapsules is uniform, and the sealing property of the capsule wall is good.
