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A compound having crystallinity is added to the crystal ink. Under the influence of weak current and temperature, the liquid crystal displays light and dark patterns and colors due to changes in the crystal lattice. Packages printed with this ink can react with changes in temperature. If it is used to print calendars, it will show different colors as the temperature of the four seasons changes. It is a new type of ink material that is very vital and needs to be developed. It is promoted and used in the field of packaging and decoration, and its anti-counterfeiting effect is immeasurable.
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, and an antifoaming agent.
The aqueous solvent resin is mainly an acrylic copolymer emulsion, and the capsule is mainly made of natural polymer gelatin or gum arabic, and has a diameter of 5 to 30 μm, and the liquid crystal is mainly cholesteric benzoate. The antifoaming agent is glycerol.
Attachment: Typical formula
Aqueous solution ratio: one part of gelatin, 12.1 parts of distilled water
Cholesterol salt: 70 parts
Cholesterol chloride: 25 parts
Cholesterol cinnamate: 5 parts
Gum arabic: 1 serving
Distilled water: 95.6 parts
Aqueous solution of pentanediol: 25 parts
Aqueous polyvinyl alcohol solution: 10 parts
The characteristics and main uses of liquid crystal inks
The liquid crystal ink does not use pigments and has a viscosity of between 4,000 and 6,000 centipoise, and has the characteristics of small thixotropy and good leveling property. It is mainly used for the printing of substrates with temperature display requirements such as thermometers, automatic temperature recorders, and detectors. It is also widely used in substrates such as advertisements, trademark labels, arts and crafts, and the like that require color change.
With the development of the printing and packaging industry, the printing process is diversified, and liquid crystal ink printing is applied to product packaging and printing crafts. Most of the liquid crystal ink printing is screen printing, and the screen printing process is as follows:
Screen printing plate
Generally, the mesh can be made of nylon mesh or polyester mesh. If the amount of ink required on the plate is large, a stainless steel mesh plate can be used. The mesh size is generally 100-175 mesh, which is selected according to the requirements of ink microcapsule smuggling and ink layer thickness. The diameter of the microcapsules is generally between 10 and 30 μm. The plate is made of a water-resistant emulsion.
Screen printing liquid crystal ink
The key to liquid crystal printing is that liquid crystals that display vivid colors at different temperatures must be series in the gamut value, and the liquid crystal microcapsules are not crushed during the printing process. The application range of liquid crystal printing is very wide. As far as its function is concerned, it is mainly used for two aspects of temperature display and color change.
a. It is necessary to have enough ink at one time on the plate, and it is best not to refill the ink in the middle to prevent foaming.
b. Since the microcapsule ink is easy to block the plate, when the net is found to be blocked or foamed in the printing, the removal should be stopped immediately, and thoroughly washed with alcohol water.
c. When printing, it should be noted that the ink is even and sufficient, and the amount of ink on the printed substrate is insufficient, which will affect the color development effect.
d. The printing pressure should not be too large to prevent the liquid crystal capsule from breaking, which will also reduce the color development effect.
e. It also makes the printed part brightly colored, and the printed background color should be ink or dark. The base color may be a water-soluble ink or an organic solvent ink. The printing method can be screen printing, offset printing or gravure printing. When using an organic solvent ink, it must be sufficiently dried after printing, and the ink film must not remain organic solvent, otherwise it will react with the liquid crystal to affect the color development effect.
f. The printing ink layer should be smooth and smooth, and the thickness of the ink layer should be controlled to 15-35 μm. If the ink layer is not flat or too thin, the color effect will be reduced.
g. The printing sequence can first print the ground color with black (or dark color) ink, and then print the desired pattern with liquid crystal ink. It can also print the thin base with liquid crystal ink and then print the desired negative image with water black (or deep color) ink. The pattern is covered to improve the color development.
h. The surface of the printed matter is preferably coated with a varnish or a protective film to protect the gloss of the ink layer and improve wear resistance and temperature resistance.
Post-press drying
1. The drying method is preferably natural drying, and it can also be dried by a warm air of about 40 ° C.
2. Do not stress when the printed materials are stacked, and it is not advisable to add pressure when cutting.