Due to its strong process adaptability, screen printing can be used for light pressure, thick film, and coarse particle ink printing, so it is a decorative method often used in various types of packaging prints. This article introduces several new types of packaging screen printing decoration technology.
1. Luminous printing
The ink used for luminous printing is a luminous ink containing luminous materials. The light storage ink is made of luminescent pigments, organic resins, organic solvents and additives at a certain ratio through special processing techniques.
1. Luminous Pigment (Light Storage Pigment)
The light storage pigment is a long afterglow luminescent material, referred to as long afterglow material, also known as luminous material. This type of material only has structural defects and impurity defects in the crystal lattice of the crystal formed during the synthesis process. The luminescence caused by the material lattice defects is called self-excitation light, and the luminescence caused by impurity defects is called activated light emission. Most of the various types of luminescent materials actually used are the latter.
Luminous materials emit light according to the principle of photoluminescence. The excitation light source is generally sunlight and artificial light sources. It absorbs excitation light energy and stores it. After the light excitation stops, the stored energy is slowly released in the form of light. come out. Absorbing light → glowing → storage → relighting, this process can be repeated indefinitely many times, and it is similar to the repeated use process of mobile phone battery charging → discharging → recharging → recharging.
This luminescent material emits light in a dark environment without an external light source, and its luminescence time is called afterglow time. Long afterglow materials with better performance, such as silicate system long afterglow materials with various luminescent colors, the afterglow characteristics of rare earth activated alkaline earth aluminate are the most superior, which can achieve afterglow luminescence for more than 20 hours.
2. Application of long afterglow materials
Long afterglow materials involve a wide range of applications, and there are many types of products. Long afterglow materials are made into luminous paints, luminous inks, luminous plastics, luminous fibers, luminous paper, luminous glass, luminous ceramics, luminous marble, etc. Safety emergency, transportation, building decoration, etc. In the field of modern printing, it is suitable for packaging and printing of official documents, securities, certificates, and high-end commodities such as high-grade cigarettes, alcohol, medicines, and cosmetics.
3. Preparation of phosphorescent ink
Pay attention to the following points when preparing light storage ink:
(1) The particle size of the light storage pigment
The particle size of the light storage pigment should be controlled at 45-65um, so as to make a practical light storage ink.
(2) Selection of resin
Since the light storage material is an alkaline substance, the color of the resin has an influence on its luminous brightness, so the following two points should be noted when selecting the resin.
â‘ Colorless or light color resin with good transparency should be selected.
â‘¡Neutral or weak acid resin and varnish should be selected.
Resin varieties are epoxy resin (E440), polyurethane resin, amino varnish, polyester resin, acrylic resin, hydroxy acrylic resin, acrylic polyurethane varnish (two-component).
(3) Selection of ink adjustment oil
Different types of transparent inks are usually selected according to different substrates. If the substrates are metallic, metal inks should be used. The substrates are made of PVC, and PVC inks can be used.
(4) Preparation method
â‘ Glass or enamel containers should be used for the preparation of light storage ink.
â‘¡ In order to distribute the light storage material evenly, high-speed stirring method can be used, but grinding method is not allowed.
â‘¢ The relative density of the light storage material is between 3.6 and 4.1, and it is easy to sink when preparing the ink. You can increase the storage period of the light storage ink by adding a precipitation inhibitor to the resin. Domestic fumed silica is divided into No. 2 and No. 4, of which No. 4 is better.
4. Highlights of phosphorescent ink screen printing
(1) The viscosity of the prepared ink is about 300-500Pa · s. During printing, the viscosity of the ink should be adjusted with thinner according to the material and printing speed of the substrate.
(2) When printing patterns or logos with light-storage inks, polyester screens below 200 mesh / inch should generally be selected. Screen printing with 80-120 meshes / inch can achieve better luminous effect.
(3) Print light storage ink on the white substrate as much as possible, so as to improve the luminous effect and afterglow time of printed graphics.
(4) When the thickness of the printing ink coating is controlled at 130-150um, its luminous effect is the best, so it is printed twice with a screen of 80 mesh / inch (if a thick version is used, it can be printed once), this can be achieved thickness.
(5) When the substrate is a transparent object, the white ink should be printed before printing the phosphorescent ink, so as to improve the luminous effect.
5. Applications
(1) Ink formula (mass ratio) PVC ink (SS-777): Light storage material (PLO-7D) = 50: 50
(2) Printing method
â‘ Use 100 mesh / inch screen to make plate.
â‘¡ Print twice on the copperplate not on offset paper.
(3) Afterglow brightness value of the printing ink layer Afterglow brightness value of the printing ink layer. [next]
2. Crystal glue printing
The method of using crystal glue (the main component is a high-molecular transparent resin) to print a three-dimensional effect of crystal glue droplets on gold and silver cardboard is called crystal glue printing. The viscosity of the crystal glue is very high, the printing ink layer is very thick, and the printing pressure required is large.
There are two types of crystal glue for printing: thermosetting type and UV curing type. If thermosetting crystal glue is used, the screen should be properly heated during printing, and should be dried on the infrared thermal drying device immediately after printing. The new UV-curable crystal glue salty film on the market is fast, and the wear resistance and brightness are better. In addition, in order to enhance the stereoscopic impression of the crystal glue printing, the crystal glue is dried into a droplet-like crystal clear three-dimensional effect before leveling.
3. Crystal gloss printing
Crystal gloss printing refers to that the surface of the printed product produced is transparent, and the ink layer contains a crystalline flash material. When the daylight or light incident angle changes, it can produce a colorful and shiny special decorative effect, crystalline Most of the flashing materials are particles crushed after being colored by polyester spray coating or particles crushed with special flashing fibers.
When using the screen printing method for crystal gloss printing, the crystal flash particles are mixed into the connecting material to make a screen printing ink, which is directly printed on the parts of the printed matter that need to be decorated. It is worth noting that because the flash crystal is contained by the ink layer, and at the same time considering the ink transfer factor, it is not possible to choose a flash crystal with too coarse particles.
4. Mirror ink printing
The mirror ink is a metallic color screen printing ink, which is made of plastic resin mixed with special metallic toner. It is a solvent volatile ink. Print it on the back of a transparent plastic sheet to obtain a metallic color mirror printing effect, just like hot stamping. effect.
The main points of mirror ink printing are as follows:
(1) Due to the low viscosity of the mirror ink, a screen with a high mesh number should be used, usually a polyester screen with a mesh size of 270-300 mesh / inch, the tension of the stretched mesh should be slightly lower, and a solvent-resistant photosensitive adhesive should be applied .
(2) The network distance should be smaller.
(3) Choose a doctor blade with higher hardness, usually its hardness is HS80-85.
(4) Since the relative density of metal toner, plastic resin, additives and additives is different, each component in the ink will be layered during storage, so it must be thoroughly stirred before use.
(5) In order to prevent the occurrence of the phenomenon of blocking the network, care should be taken not to print in a place with air circulation.
(6) In order to prevent the decline of the gloss of the mirror surface due to the absorption of moisture by the ink, the humidity should be avoided during printing and storage, and it should be dried in a low temperature environment immediately after printing.
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