Microcapsule Screen Printing Process and Common Problems Analysis II

1.2.3 Physical Methods

(1) Air Suspension Method: A fluidized bed is used to suspend a solid powder of a core material in air, followed by spraying a film forming solution that can form a capsule wall on the surface of the core material onto a fluidized bed. This method has three forms: 1 Wurster method: for example, 1,2-hydroxystearyl microcapsules of acetaminophen. 2 chemical film forming method: such as fertilizer microcapsules. 3 Liquid core material film formation method: The Wurster method is modified to microencapsulate the liquid core material. For example, dye-containing polystyrene microcapsules. (2) Spray-drying method: For example, microcapsules containing an aqueous fragrance. (3) Vacuum evaporation deposition; aluminum capsules such as polystyrene beads. (4) Electrostatic bonding method: The oppositely charged core material particles and the film forming material are released into the air through a sprayer and are combined together by electrostatic attraction. For example, nylon microcapsules containing glycerin.

2. The function and release method of microcapsules

2.1 Functions of Microcapsules

The functions of microcapsules are generally divided into two categories: protection of stored substances and changing the shape and properties of substances. Specific can be divided: (1) to protect volatile substances: such as the fragrance of perfume or pesticides lasting; (2) so that the interaction of substances can be mixed, coexist, such as the reactive adhesive body can be mixed with curing agent Microcapsules are mixed to change the original two-component state; (3) moisture-proof and resistance to light and oxygen. Some drugs that are susceptible to moisture or deteriorating under the influence of light and oxygen can be made into microcapsules to protect them; (4) The control of the drug's continued effectiveness, such as microencapsulated drugs, can be stabilized in the stomach and taken to the intestinal tract after administration. Dissolve to obtain sufficient curative effect; Pesticides and chemical fertilizers can also use microcapsules to control their durability at will; (5) Adjust the specific gravity: If using phenolic resin to encapsulate nitrogen, make it float in the upper part of the crude oil storage to prevent fire (6) Solidify the liquid, which is the most commonly used function of microencapsulation. For example, in the case of carbonless paper, the colorless dye oil is converted into a solid by microencapsulation and is stabilized on the paper surface; (7) The color is concealed, and the dyeing substance plus the microcapsules is white in appearance; (8) Photosensitivity, heat sensitivity and force sensitivity, such as heat can make the microcapsules deform and rupture to release the fire extinguishing agent; (9) has semi-permeable properties, and can be made into artificial red blood cells by selecting proper microcapsule protective film.

2.2 Microcapsule release method

The release method of microcapsule products is carried out by adjusting the temperature and humidity, melting, dissolving, pressure, diffusion, esterification, photolysis, adjusting the PH value, ultrasonic wave, and adding a surfactant.

3. Application of Microcapsule Technology in Printing Industry

3.1 Making Pressure Sensitive Paper

Pressure sensitive copy paper is a patent invented by the National Cash Register Corporation (NCR) in 1954 using microencapsulation technology, and is also one of the earliest and most practical applications of microcapsule technology. At present, there are more than 2 million tons of (carbon-free) pressure-sensitive carbon paper produced each year in the world. The pressure-sensitive writing paper produced by the use of the microcapsule technology is a kind of carbon paper which is indicated as white, and is colored and reproduced only when subjected to the pressure of a pen or printing. Therefore, it is a clean and easy-to-use copy paper.

There are two types of pressure-sensitive copying paper, one is a multi-layer type, and there are three kinds of copy paper used in the upper paper, the middle paper, and the lower paper. The upper paper is coated on the backside with a pigmented, pressure-sensitive pigment microcapsule called CB paper; the upper surface of the middle paper is coated with a color developer, the upper surface of the paper is coated with a color developer, and the back is coated with the upper paper. The same pressure-sensitive pigment microcapsules; and only the upper surface coated with a coloring agent called CF paper. When the upper, middle and lower papers are stacked in order, the microcapsules on the back of the upper paper are broken under the pressure of the pen writing or printing, and the solution of the pressure sensitive pigment is brought into contact with the color developing agent on the next layer of paper to develop color. , The results in the second, three sheets of carbon paper to obtain the effect of copying records; the other is self-capacitive carbon paper, also known as overlapping coated paper, directly on the front of the paper coated with micro-capsules of pressure sensitive pigments and reagents. This type of pressure-sensitive copy paper is generally used in a single sheet and can develop color under the pressure of the pen. The advantage is that no ribbons are used when printing on a typewriter, and no ink is needed in the teleprinter.

3.2 Home decoration printing

Microcapsules are used as carriers to enable microencapsulation of various substances such as fragrances, pigments, pigments, pharmaceuticals, insecticides, rodenticides, insect repellents, insecticides, bactericides, etc. Ink is printed on metals, wood, buildings, paper, and textiles. This technology has been applied in the field of home decoration and daily-use printing, which has greatly improved the function and added value of prints.

For example, cloves, mints, sandalwood and other aromatic oils can be encapsulated to form microcapsules, which can be used in home decoration prints to give people a fresh and pleasant feeling when they enter the room. They also have antibacterial agents, insecticides, and anti-caries agents. Microcapsules are used on printed matter, such as micro-capsules containing antibacterial agents printed on wallpaper or wall calendars. The use of micro-capsules slow release function can greatly extend its bactericidal and anti-fouling functions, and play a role in purifying the environment; After the anti-mouse agent cycloimide is first formed into a microcapsule, pigments are added into the pigment to become a pigment capable of repelling mice. Microencapsulation not only protects the cyclic imide from external environmental factors, but also has sustained release. The function extends the effective time of the repellent effect; if the microcapsules containing insect repellent are printed on wallpapers or carpets and other textiles or furniture cloths, the insect repellent (such as insect repellent and drive) can be produced for a long time. . In general, all expulsion drugs are safer than humans.

Another example is the printing or coating of antifouling pigments containing micro-capsules such as organic tin compounds on wood or metal surfaces, which will play a role in anti-mold, anti-fouling and anti-rust. (to be continued)