Screen printing process of the hottest microcapsul

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Microcapsule silk printing process and common problems analysis III

3.3 thermal printing

here is only a case study of liquid crystal microcapsule ink. Substances with both liquid and solid crystal optical properties within a certain temperature range are called liquid crystals. Liquid crystal is a kind of turbid liquid that can flow. At the same time, it has the unique optical anisotropy of crystal, such as birefringence and other properties. According to the characteristics of liquid crystal molecular structure, they are divided into nematic, smectic and cholesteric types. For example, the unique optical property of cholesteric liquid crystal is that when light is irradiated, it does not regularly absorb light of a certain wavelength like ordinary liquids, but selectively reflects, transmits and scatters light like crystals. When the spatial structure and small changes are caused by the change of ambient temperature, the composition of refracted and reflected light also changes correspondingly, that is, there is a sensitive and strictly fixed correspondence between temperature and the light color reflected by cholesteric liquid crystal, so the temperature can be recorded by using this feature. Different kinds of cholesteric liquid crystals have different ranges of temperature reflected light color correspondence. It can be changed in the range of - 20 ~ 250 ℃, and the sensitivity of some color changes can reach 0.1 ℃. Therefore, different cholesteric liquid crystals can be selected according to the needs of measuring the temperature range, or the combination of cholesteric liquid crystals can be tested after several teacher inspections

cholesteric liquid crystal microcapsules are usually prepared by the composite coagulation method with gelatin and Arabic gum as raw materials, and in practice, they are made into thermochromic liquid crystal microcapsule printing ink. When this kind of ink is printed on the panel with black back, the liquid crystal temperature display can be obtained, and its color indicates the temperature. Some people also print this kind of ink on a certain part of the hat to show the temperature of the person wearing the hat. This kind of hat is especially suitable for children in sports or games, so as to know whether children exercise too much from the color change of the "thermometer" on the hat in time; If this liquid crystal microcapsule ink is printed on a certain part of the frozen food packaging bag to indicate the temperature, it can directly judge whether the freezing temperature is normal from the appearance, which is conducive to ensuring the quality of frozen food and extending the shelf life of food storage; It can also be applied to the shell of the machine in long-term operation to prevent the machine from overheating; If it is added to the anti-counterfeiting sign, it will change color due to temperature change when touched by hand, which plays an anti-counterfeiting role; If printed on the surface of the baby bottle, it can be used to indicate the temperature of the milk in the bottle to ensure that the milk is sucked by the baby at a suitable temperature

thermosensitive color changing liquid crystal microcapsules can be used for many purposes besides the above applications. For example, it can be used for nondestructive inspection of thermosensitive conduction system. After coating, it is difficult to check the cracks and other defects of the material with the naked eye. Usually, ultrasonic detection, infrared photography and other methods are used to detect, but the characteristics of different temperature areas formed by the disorder of heat conduction of the defective part of the pipeline can also be used to check with thermal microcapsules. Another application is the thermosensitive liquid crystal microcapsule "thermometer". When this liquid crystal microcapsule is mixed in the adhesive to form liquid crystal printing ink, it is printed on the wooden board with black back to get the liquid crystal temperature display screen, and its color is used to indicate the temperature

in a word, the principle of liquid crystal thermochromism will be widely used in the printing field

3.4 pressure sensitive printing

in packaging and printing, if the printed matter is subjected to different forces, resulting in different color changes, it will be very intuitive to show the force of the product or the force of the same product in different parts

this kind of microcapsule print is composed of two layers. Several pigment microcapsules of different colors are bonded on the back of the first layer. The wall thickness and strength of pigment microcapsules of the same color are the same. When they are subjected to the same pressure, they will burst and release pigment color, while the wall thickness and strength of microcapsules of different pigments are different, and some of them will burst under higher pressure. The second layer is the base layer, which is made of paper or other materials. When the pigment microcapsules on the back of the first layer are crushed, they will be imprinted on the same position of the second layer of 20 ~ 100hrb. When some articles with different weights are placed on this kind of microcapsule print, due to the different pressure generated in different parts, the microcapsules with different colors on the surface making microcapsule layer are broken, leaving different colors of the standard sample on the second layer of backing paper. Microcapsules that are usually broken under high pressure contain darker pigments. For example, a package printed matter composed of microcapsules of three colors, the microcapsules broken under the lowest pressure contain white pigments, the microcapsules broken under higher pressure contain colored pigments, and the microcapsules broken under higher pressure contain black pigments. The weight of the article or the force application at different parts can be judged according to the color rendering of the surface of the printed matter as white, orange and black

3.5 printing resistant to environmental impact

the pigments used in printing are not only required to be rich in color, but also required to resist the influence of the external environment and keep the pigments colorfast for a long time

although some pigments have rich color, their sun resistance and light resistance are poor. If microencapsulated, they can protect the pigments and greatly improve their ability to resist environmental impacts, so as to improve the quality of the pigments. Because the walls used to coat the pigments are colorless and transparent, they have no adverse impact on the gloss of the pigments. The pigments can maintain good color after long-term exposure to sunlight (ultraviolet). Practice has proved that the dispersibility, heat resistance, light resistance, chemical stability and anti-proliferation properties of microcapsules of various colors are significantly improved compared with those of non microencapsulated pigments. For example, phthalocyanine pigment is a pigment with bright colors, but it is expected to be fully produced in the third quarter of 2017; The light and corrosion resistance of the 20000 ton lithium hydroxide project is poor, and its performance has been greatly improved after the formation of microcapsules. In addition, according to the U.S. patent report, the phthalocyanine pigment or Quine (c20h12n2) pigment containing dentin and copper ions is used as the wall material to form microcapsules. The microcapsule of this pigment and the pigment made of aluminum powder in the ratio of 9:1 are made into ink and printed on the metal surface, showing a wonderful two-tone effect, which is significantly better than that before it is encapsulated

3.6 printing with pearlescent and shading effect

many inorganic powders such as titanium dioxide, calcium carbonate, barium sulfate, alumina (Al2O3 · 3H2O), zinc oxide, clay, etc. are inorganic pigments or shading agents with good covering ability. If these inorganic pigments are made into particles smaller than 1 μ M air containing sunscreen microcapsules can get better sunscreen effect. The microcapsule shading agent can be printed on the surface of paper, plastic, metal and wood to play the role of pearlescent or shading. Because the microcapsule contains air, its density is reduced. When printed on the surface of the paper, it can penetrate into the gap of the fiber, which has the effect of shading without increasing the thickness of the paper

(to be continued)

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