(This article is an original article from Bisheng. It is forbidden to reprint, and reprinting must be corrected)
Liquid crystal inks have added compounds with crystalline properties. 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. Packaging and decoration products printed with this ink can respond to changes in temperature. If it is used for printing calendars, it will show different colors with the change of temperature in four seasons. It is a new ink material with vitality and yet to be developed. Promoting its use in the field of packaging and decoration, its anti-counterfeiting effect is also inestimable.
Composition of liquid crystal ink
Liquid crystal ink is mainly composed of water-soluble resin, liquid crystal capsules, additives, linking materials, and defoaming agent.
The water solvent resin is mainly acrylic copolymer emulsion, etc. The capsule is mainly made of natural polymer gelatin or gum arabic, with a diameter of 5-30 μm, and the liquid crystal is mainly cholesteryl benzoate. The defoamer is glycerin.
Attachment: typical formula
Proportion of aqueous solution: 1 part gelatin, 12.1 parts distilled water
Cholesteryl Nonanolate: 70 servings
Cholesterol chloride: 25 servings
Cholesterol cinnamate: 5 servings
Gum Arabic: 1 serving
Distilled water: 95.6 servings
Pentylene glycol aqueous solution: 25 parts
Polyvinyl alcohol aqueous solution: 10 parts
Characteristics and main uses of liquid crystal ink
Liquid crystal inks do not use pigments, have a viscosity between 4000 and 6000 centipoise, and are characterized by low thixotropy and good leveling. 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 printing materials that require color changes such as advertisements, trademark labels, arts and crafts and other decorations.
With the development of the printing and packaging industry and the diversification of printing processes, liquid crystal ink printing is used in product packaging and printing crafts. Most of the liquid crystal ink printing uses screen printing. The screen printing process is as follows:
Screen printing plate
The general wire mesh can be nylon wire mesh or polyester wire mesh. If a large amount of ink is required on the printing plate, a stainless steel screen can be used for plate making. The screen mesh number is generally 100-175 mesh, which is selected according to the requirements of smuggling of fine ink capsules and the thickness of the ink layer. The diameter of the microcapsules is generally between 10-30 μm. A photosensitive emulsion with strong water resistance is used in plate making.
Screen printing liquid crystal ink
The key to liquid crystal printing is that the liquid crystals that display bright colors at different temperatures must be in a series of color gamut values, and the liquid crystal microcapsules must not be crushed during the printing process. The application range of liquid crystal printing is very wide. In terms of its function, it is mainly used for temperature display and color change.
a. The printing plate must be filled with sufficient ink at a time, and it is best not to refill the ink halfway to prevent blistering.
b. Because the microcapsule ink is easy to block the plate, if it is found that the network is blocked or blistered during printing, it should be immediately eliminated and washed thoroughly with alcoholic water.
c. When printing, you should pay attention to the uniform and sufficient ink supply. Insufficient ink on the printed substrate will affect the color development effect.
d. The printing pressure should not be too large to prevent the liquid crystal capsules from being broken, which will also reduce the color development effect.
e. It also makes the printing part have obvious color development, and the printing background color should be ink color or dark color. The base color can be used with water-soluble ink or organic solvent ink. The printing method can be screen printing, offset printing, gravure printing. When using organic solvent ink, it must be fully dried after printing, and the ink film must not leave organic solvent, otherwise it will react with the liquid crystal and affect the color development effect.
f. The printing ink layer should be smooth and clean, and the thickness of the ink layer should be controlled to 15-35μm. The uneven or too thin ink layer will reduce the color effect.
g. In the printing sequence, the background color can be printed with black (or dark color) ink first, and then the desired pattern can be printed with liquid crystal ink; the thin background can be printed with liquid crystal ink first, and then the negative image can be printed with water-based black (or dark color) ink Covering the pattern can improve the color development effect.
h. It is best to coat the surface of the printed matter with varnish or paste a protective film to protect the gloss of the ink layer and improve the wear resistance and temperature resistance.
Dry after printing
1. The drying method is preferably natural drying. It can also be dried with warm air at about 40 ℃.
2. Do not press hard when stacking printed materials, and do not apply pressure when cutting.
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