LCD ink printing and its application
We are a big printing company in Shenzhen China . We offer all book publications, hardcover book printing, papercover book printing, hardcover notebook, sprial book printing, saddle stiching book printing, booklet printing,packaging box, calendars, all kinds of PVC, product brochures, notes, Children's book, stickers, all kinds of special paper color printing products, game cardand so on.
For more information please visit
http://www.joyful-printing.com. ENG only
http://www.joyful-printing.net
http://www.joyful-printing.org
email: info@joyful-printing.net
Liquid crystal ink is a new type of special ink originated in the United States in the 1970s, which means that a compound having crystallinity is added to the ink. Liquid crystal ink, in terms of production method, belongs to the type of microcapsule structure ink; from the application point of view, it belongs to the category of thermosensitive color-changing ink.
1 Composition of liquid crystal ink
The liquid crystal ink is mainly composed of a water-soluble resin, a liquid crystal capsule, an auxiliary agent, a binder, an antifoaming agent, etc., and is prepared by dispersing a liquid crystal and an auxiliary agent enclosed in a microcapsule in a binder. Its main components are as follows.
1) LCD
Liquid crystals are substances which have liquid fluidity and have the same chemical properties as crystals. Very sensitive to conditions such as electric field, magnetic field, temperature, chemical environment and stress.
2) Capsules
Since liquid crystal is an organic compound between liquid and crystal, it can be directly added to the binder like ordinary ink. In order to avoid the liquid crystal being contaminated by other substances, in order to ensure the coloring effect, the liquid crystal is wrapped in the microcapsules, and then mixed with the connecting material to form a microcapsule ink. The wall of the microcapsule is composed of gelatin, gum arabic, formaldehyde, acetic acid, sodium hydroxide and the like.
3) Other
The water-soluble resin is mainly an acrylic copolymer emulsion, which has good durability and mechanical strength; the binder is a water-based resin, commonly used is a water-soluble polyvinyl alcohol, a hydrosol resin; and the antifoaming agent is glycerin.
2 Preparation of liquid crystal ink
1 part of gelatin and 12.1 parts of distilled water were made into an aqueous solution, and when heated to 55 ° C, a liquid crystal melt of 70% cholesteric salt, 25% cholesteryl chloride, 5% cholesteryl cinnamate was added, and then it was stirred with a mixer. Dispersed into particles having a diameter of 15 to 30 μm. In a separate container, 1 part of gum arabic and 95.6 parts of distilled water were mass-adjusted, the temperature was controlled at 55 ° C, and a gelatin aqueous solution was slowly added to adjust the pH to 4.85. When the mixture was cooled to 15 ° C, a 25% aqueous solution of pentanediol was mixed, dehydrated by a dehydrator to obtain a concentrated capsule slurry, and a 10% aqueous solution of polyvinyl alcohol was further mixed to prepare a liquid crystal microcapsule ink.
3 color rendering mechanism of liquid crystal ink
The liquid crystal integrally forms a spiral structure, and when light is incident from a spiral axis direction parallel to the plane, it is divided into two kinds of circularly polarized light, left-handed light and right-handed light. Light of one of the components is transmitted, and light of the other component is totally reflected. This phenomenon is called circularly polarized light dichroism. In the wavelength region on both sides of the cholesteric liquid crystal selective light scattering band, it has strong rotatability, and the directions of rotation around the light scattering band are different. Since the pitch of most cholesteric liquid crystals is highly dependent on temperature, as long as the temperature changes slightly, the wavelength (color) of the selected scattered light changes greatly. In general, the color forming mechanism of liquid crystals is formed by selectively reflecting light of a specific wavelength. The liquid crystal ink utilizes the characteristics of the liquid crystal, so that under the influence of weak current and temperature, the crystal lattice changes to display a light and dark pattern and color, and the reaction temperature of the liquid crystal is -100 to 700 °C.
4 Technical requirements for LCD ink printing
The key to liquid crystal printing technology is to be able to display brightly colored liquid crystals at different temperatures, and to form a series in the color temperature domain. The liquid crystal microcapsules should be small and uniform, and the walls of the capsules are transparent and thin. After being mixed with ink, the solvent resistance is required to be stable, reliable, and long-lived; the liquid crystal microcapsules are not damaged during the printing process; the surface is covered with a protective film, etc. .
1) Selection of materials for liquid crystal ink printing
The printing material for printing is preferably water-absorbent paper, and synthetic paper is also suitable. The liquid crystal ink can be printed by screen or gravure, and screen printing is often used in order to reduce damage to the capsule during printing. For the choice of screen, nylon mesh or polyester mesh is generally available. If the amount of ink required on the plate is large, a stainless steel mesh plate can be used. The diameter of the microcapsules is generally between 10 and 30 μm, so the selection of the mesh size should be selected according to the requirements of the diameter of the ink microcapsules and the thickness of the ink layer. Usually, the mesh size is preferably from 100 to 175 mesh. Since the screen liquid crystal microcapsule ink is water-soluble, a photosensitive resin having high water resistance should be used for plate making.
2) Points to note when printing liquid crystal inks
◎ On the printing plate, it is necessary to load enough ink at a time, and the ink should be evenly distributed. It is best not to replenish the ink in the middle to prevent foaming. If the amount of ink on the printing substrate is insufficient, the coloring effect will be affected.
◎ Since the microcapsule ink is easy to block the screen, if there is a blockage or blistering phenomenon in the printing, it should be stopped immediately, and usually cleaned with alcohol water.
◎ Choose the right printing pressure. The pressure is small, the amount of ink on the printed substrate will be insufficient; if the pressure is too large, the liquid crystal capsule will be destroyed and the color development effect will be affected.
◎ In order to make the printed part bright, the printed background should be black or dark. Water-soluble inks can be used for the bottom layer, and organic solvent inks can also be used. When the organic solvent ink is selected, it must be sufficiently dried after printing, and the organic film may not remain in the ink film, otherwise it will react with the liquid crystal to affect the color development effect. The hardness of the squeegee is preferably 60-70 Shore hardness, the squeegee angle is 60°-70°, and the mesh distance is 4-5 mm.
◎ In order to improve the color development effect, it is necessary to ensure that the ink layer is smooth and smooth, and the thickness of the ink layer is generally controlled at 15 to 35 μm. The uneven or too thin ink layer may affect the color development effect.
◎ Printing color sequence arrangement. You can use black + or dark color, ink to print the background color, and then use liquid crystal ink to print the desired pattern. You can also use liquid crystal ink to fill the bottom, then use water-soluble black + or deep color, ink to print the desired negative pattern. cover.
3) Precautions for post-press processing
◎ The drying method is preferably natural drying. It can also be dried by hot air at around 40 °C. Do not use temperament, dry or high-temperature heating.
◎ Do not stress when the printed materials are stacked. After drying, try not to stack too much overlap. It is not advisable to add excessive partial pressure to cut off the liquid crystal microcapsules.
◎ When using liquid crystal ink, the color temperature range and liquid crystal durability should be determined according to the purpose of use. In order to improve the surface wear resistance, temperature resistance, gas barrier properties and maintain the gloss of the ink layer, the surface may be coated with a varnish or a protective film.
5 LCD ink applications and advantages
Liquid crystal ink printing has a wide range of applications, and its functions are mainly used for temperature display and color change. Its advantages are mainly manifested in the following points.
1) Easy to save for a long time
The liquid crystal capsule can protect the liquid crystal from external pollution, improve the printability, prolong the service life and facilitate long-term storage.
2) Detection function
It is mainly used on substrates with temperature display requirements such as thermometers, thermometers, automatic temperature recorders, testing machines and testing instruments. At present, there are hospital LCD printing papers as disposable body temperature testers. It can also be used as a relaxation card for measuring human looseness and for non-destructive inspection of materials.
3) Entertainment features
Mainly used for advertising, trademark labels, arts and crafts, medals, jewelry and other decorative and anti-counterfeiting printing products. If used to print a calendar picture, the picture will have different effects as the temperature of the four seasons changes; if printed in a children's book, the color of the picture can be changed with the child's finger touch, which improves the children's reading interest.
4) Prompt function
Mainly used for trademarks, wrapping paper, etc., attached to some products that are similar to frozen foods and other heat-sensitive products. According to the change of the color of the packaging pattern, you can understand the quality change of the contents of the interior. If the bright picture on the candy wrapping paper becomes gray, you should eat the candy as soon as possible, otherwise it will melt. A liquid crystal pattern is printed on the container to display the temperature of the contents of the container. On large items that are expensive, hot, and cold, LCD ink printing can be used as a reminder card to maintain temperature.
5) Temperature identification
It can be used for cold and warm appliances, indoor temperature signs, and accurately predicts the temperature range through the color change of liquid crystal prints. The technology can be used for temperature control in the greenhouse vegetable cultivation process, and farmers can properly adjust the temperature in the vegetable greenhouse through the color change of the liquid crystal print. This technology also has a certain guiding significance for the control of the temperature of the printing workshop and printing warehouse.
6) Anti-counterfeiting function
The liquid crystal print has anti-counterfeiting function by utilizing the characteristics of liquid crystal temperature and color change. Nowadays it has played a big role in the field of anti-counterfeiting packaging and decoration.