The refraction effect is to process the surface of some substrates with metallic texture, so that it has a changing metal luster at various viewing angles and a surface finishing processing effect of a clear and distinct three-dimensional image. It is widely used in book covers, tobacco and alcohol packaging, wall calendars, desk calendars and greeting cards. It shows the magical effect of endless changes and sparkling, which can greatly improve the product grade and enhance the anti-counterfeiting effect of products.
To produce a refractive effect, the first condition is that the surface of the substrate has a metallic luster, preferably the luster achieves a certain specular reflection effect. The second condition is that the surface of the substrate is printed with a refractive texture. The refraction texture is a texture pattern composed of a series of regularly parallel, equally spaced, ultra-fine solid lines with several different angles. The formation of the refractive effect is the result of the interaction of light and refractive texture. After the light enters the surface of the printed substrate with the refractive texture from all directions, the reflected light will be reflected in more directions due to the influence of the refractive texture, and some of the light will even interfere to strengthen the reflection effect and eventually form a sparkling Refractive effect.
The refraction process is classified according to common types, which can be divided into three types: traditional mechanical refraction, laser refraction, and the currently popular screen-printed refraction. In fact, the essence of the three methods is the same, and the refraction texture pattern is copied by imprint To the substrate surface. Mechanical refraction is to engrave the refraction texture pattern on the metal plate by laser electronic engraving or etching, and then use a lot of pressure to transfer the refraction texture pattern to the surface of the substrate. The mechanical refraction can be round flattened or flat flattened. The round flattening method is suitable for large area and large batch operations; the flat flattening method is suitable for local small area and small batch operations.
The embossing method of laser refraction is somewhat similar to mechanical refraction, except that the formation of its refraction plate texture is much more complicated: first, the laser records the picture information on the holographic recording material, and then uses electroforming to copy the refraction texture to rigidity On the metal stencil, a very dense grating that cannot be recognized by the human eye is formed. Mechanical refracting and laser refracting do not require ink, just use a rigid stencil to use pressure to emboss the refracting texture to the surface of the substrate, and screen printing refracting uses ink, that is, UV refracting ink. Screen printing refracting is to copy the refracting texture printing to the surface of the substrate by screen printing. Screen printing refraction method is simple, and the technical requirements are not high. Although the production efficiency is relatively low, the anti-counterfeiting effect is slightly inferior to mechanical refraction and laser refraction, but the refraction effect is also very strong, and the average cost is low for small batches of products. Therefore, screen-printed refraction has developed rapidly in recent years and is highly respected by many SMEs.
The process of screen printing and refraction processing: manuscript design → production of electronic refraction texture → output of refraction texture film → stretch screen and coated with photosensitive adhesive → close exposure of film and screen → development → revision → screen printing → UV curing.
Design and production of refraction texture
When making a refraction texture, some pictures are generally used as the base map to be simulated by the refraction texture lines, such as company logos or Chinese and English names. The refractive texture lines of these signs and names can be expressed by parallel lines, and it is best to arrange the line angle at 45 degrees to 60 degrees or 120 degrees to 135 degrees. In this way, when the work is laid flat, the refractive effect of the logo or name will be very prominent. The center of the logo and the refraction texture can be designed with some radial lines at the center, or monotonously repeated geometric figures arranged regularly. The angles of the refractive texture lines of these geometric figures should not be too much, generally 4-7. If the angle is too much, the reflection of light will be scattered, and the refractive effect will naturally not be very strong. The design of the thickness of the texture lines and the spacing between the lines also has a strict requirement. The general thickness requirements are between 0.10 and 0.15 mm. The line spacing is generally equivalent to the line thickness. Very thin lines, such as 0.08mm, not only have high requirements for printing screens and inks, but also difficult to restore printing; thick lines are not technically demanding and easy to print, but the refractive effect is worse. For products that require close observation and appreciation, such as book covers, greeting cards, and tobacco and alcohol packaging, you can design thinner lines, while for remote viewing works, such as calendars, you can design thicker lines.
There are special software for the design and manufacture of the refraction texture pattern. The domestic well-known ones are Founder Hyperline 3.0 anti-counterfeiting design system and Mengtai pattern 5.0. Through them, in fact, as long as you have some art skills and mastered certain operation skills, you can easily design some refractive texture patterns. After designing the electronic texture pattern, you can output PDF documents, or you can directly output the film through the laser imagesetter to prepare the screen for printing.
Refractive screen production and related requirements
1. Selection of wire mesh and stretch net
First of all, we must choose a suitable wire mesh. The wire mesh must have good elasticity and be resistant to friction. The rate of expansion and contraction should be very small, the mesh opening should be large, and the photosensitive material layer should be thick. In actual operation, we choose a nylon screen with good ink passing properties and a stretched mesh, with a mesh number of 450 meshes / inch.
2. Coating photosensitive glue
The photosensitive glue is slightly thicker. The coating of photoresist should be uniform and flat, and it must have a considerable thickness. Generally, multiple coatings are required to ensure that the printing ink layer has a sufficient thickness.
3. exposure
In order to ensure that the fine and dense refracted light strip can be completely exposed, it must be exposed to the plate with a vacuum adsorption device. When printing, the film should be closely attached to the surface of the photosensitive film of the screen, and the exposure time should be accurately controlled when printing.
4. development
Place the sieved screen in the darkroom sink and soak for 1 minute. Then use a high-pressure water gun to flush the screen, and use the water pressure to wash away the photosensitive glue on the line part of the refraction texture image. Of course, pay attention to adjust the water pressure and the uniformity of the water mist when rinsing. After sufficient development, the screen is dried.
5. Revision check
Check the layout for pinholes, air bubbles and other defects, and make repairs.
6. Double exposure
After the screen is dried, a second exposure is required to completely cure the photosensitive film on the screen surface and improve the printing durability of the screen.
Ink selection
Since the surface tension of the mirror printing material (such as gold and silver cardboard) is smaller than that of ordinary paper, the printing ink must select the UV refractive ink for gold and silver cardboard, otherwise it is difficult to transfer the ink to the substrate smoothly with other general UV inks. surface. When printing, according to the viscosity and transfer of the ink, a certain proportion of the diluent specified by the UV refractive ink manufacturer can be added for dilution.
screen printing
This article uses the semi-automatic screen printing machine as an example to introduce some points to be noted during the printing process.
(1) The same type of UV refractive inks produced by different manufacturers have certain differences in quality and performance. Generally, they must be printed and tested first to ensure that the quality is stable and reliable before mass production.
After printing, it is cured by a UV device under standard conditions. Then, the printed surface was tested for refractive ink, adhesion, scratch resistance, folding resistance, etc. If the test results are not satisfactory, various conditions including ink, light intensity, temperature and humidity should be adjusted until satisfactory results can be obtained. During the test, it is recommended to use a UV light meter.
(2) The ink must be fully stirred before use.
(3) During the printing process, pay attention to the random inspection of the curing of the UV refractive ink to avoid affecting the hardness and adhesion fastness of the ink layer due to incomplete curing.
(4) During production, pay attention to keeping the temperature of the darkroom at about 23 degrees Celsius and the air humidity at about 60% to prevent the fluidity and transfer performance of the ink from being affected by fluctuations in environmental conditions. At the same time, pay attention to keeping the dark room ventilated to dissipate harmful gases.
(5) UV ink is irritating to the skin. Be careful when taking it to avoid contact with the skin. If the skin is stuck with ink, it should be washed with soapy water immediately.
(6) The storage period of ink is generally 6 months, it should be sealed and stored at low temperature (2 ~ 18 degrees Celsius), protected from light and heat to avoid changes in ink performance.
The anti-counterfeiting effect of screen printing refraction is slightly less than that of mechanical refraction or laser refraction, and it is relatively easy to imitate the production, but its appearance is not inferior to the latter two, and it is easy to design and produce, and the cost is low. Will be more and more widely used.
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