Analysis of the method of producing refractive effect on the surface of metal substrates
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The refraction effect is a surface finishing process that is processed on the surface of some metal-printed substrates to have a varying metallic luster at various viewing angles and a clear and distinct stereo image. It is widely used in book covers, tobacco and alcohol packaging, calendars, desk calendars and greeting cards. It shows the magical effect of infinite change and sparkling, which can greatly improve product quality and enhance the anti-counterfeiting effect of products.
The refractive effect is produced. The first condition is that the surface of the substrate has a metallic luster, and it is preferable that the gloss has a certain specular reflection effect. The second condition is that the surface of the substrate is printed with a refractive texture. A refractive texture is a series of texture patterns consisting of a series of regularly parallel, equally spaced, very thin solid lines with several different angles. The formation of the refractive effect is the result of the interaction of the light with the refractive texture. When light enters the surface of the substrate printed with the refractive texture from all directions, the reflected light is affected by the refractive texture, which produces more reflections. Some of the light even interferes with the reflection and strengthens the reflection effect, eventually forming a sparkling effect. Refraction effect.
The refraction process is classified into common types, which can be divided into three types: traditional mechanical refraction, laser refraction, and currently popular screen printing refraction. In fact, the essence of these three methods is the same, and the refraction texture pattern is copied by imprinting. To the surface of the substrate. Mechanical refraction is by laser engraving or etching, engraving the refraction texture pattern on the metal plate, and then using a large pressure to transfer the refraction texture pattern onto the surface of the substrate. The mechanical refraction can be rounded or flattened. The round flattening method is suitable for large-area and large-volume operations; the flat flattening method is suitable for local small-area and small-batch operations.
The laser embossing method is somewhat similar to mechanical refracting, except that the formation of the refracting plate texture is much more complicated: first, the laser records the picture information on the holographic recording material, and then uses the electroforming method to copy the refraction texture to the rigid On the metal stencil, a very dense, unrecognizable grating is formed. Mechanical refraction and laser refraction do not require ink. The rigid stencil is used to imprint the refraction texture onto the surface of the substrate by pressure, while the screen printing refraction uses ink, ie UV refraction ink. Screen printing is the printing of refraction texture onto the surface of the substrate by screen printing. The screen printing 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 refractive effect is also strong, and the average cost is low for small batch products. Therefore, the screen printing refraction has developed rapidly in recent years and is highly respected by many small and medium-sized enterprises.
Screen printing process: original design → production of electronic refractive texture → output of refractive texture film → stretch net and coated photosensitive adhesive → close contact of film and screen → development → revision → screen printing → UV curing.
Design and production of refractive texture
To make a refraction texture, some images are usually used as the basemap to be simulated by the refraction texture lines, such as company logo or Chinese and English names. These logos and names of the refraction texture lines can be represented by parallel lines. It is best to arrange the line angles 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 stand out. Marks and Names The perimeter of the refraction texture can be designed with some central radial lines, or regularly arranged, monotonously repeated geometric shapes. The angle of the refraction texture lines of these geometric figures should not be too much, generally 4 to 7. If the angle is too much, the reflection of the light will be dispersed, and the refractive effect will naturally not be strong. The thickness of the texture lines and the design of the line spacing also have a strict requirement. The general thickness is required to be between 0.10 and 0.15 mm, and the line spacing is generally equivalent to the line thickness. Fine lines, such as 0.08mm, are not only highly demanding on printing screen plates and inks, but also difficult to restore. Thick lines are not technically demanding and easy to print, but the refractive effect is worse. For products that need to be closely observed and appreciated, such as book covers, greeting cards, tobacco and alcohol packaging, etc., you can design fine lines, and for long-distance viewing works, such as calendars, you can design thicker lines.
The design of the refraction texture pattern has special software. The well-known domestic ones have the Founder Super Line 3.0 anti-counterfeiting design system and the Mongolian version 5.0. Through them, in fact, as long as some art skills, and mastered certain operational skills, you can easily design some refraction texture patterns. After designing the electronic texture pattern, you can output the PDF document, or you can directly output the film through the laser imagesetter for the drying screen.
Refraction screen production and related requirements
1. Screen selection and stretching
First of all, it is necessary to select a suitable screen, which requires the screen to have good elasticity, and is resistant to friction. The expansion ratio is very small, the mesh is large, and the photosensitive material layer is thick. In practice, we chose a nylon mesh with good performance and stretched mesh, with a mesh count of 450 mesh/inch.
2. Coating photoresist
The photosensitive glue should be slightly thicker. The coating photoresist should be evenly flat and have a considerable thickness, and it is generally required to apply a plurality of times to ensure that the printing ink layer has a sufficient thickness.
3. exposure
In order to ensure that the fine, dense folded light strips can be completely dried out, it must be printed on a plate printer with a vacuum suction device. When printing, the film should be closely attached to the surface of the screen film, and the exposure time should be accurately controlled when printing.
4. development
Place the sun-dried screen into the pool in the darkroom and soak for 1 minute. Then use a high-pressure water gun to flush the screen, and use water pressure to rinse off the photoresist of the line of the texture image. Of course, care should be taken to adjust the water pressure and the uniformity of the water mist during rinsing. The screen is dried after sufficient development.
5. Revision check
Check the layout for pinholes, air bubbles, etc., and repair them.
6. Double exposure
After the screen is dried, a double exposure is also carried out to completely cure the photosensitive film of the printing plate, thereby improving 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 smoothly transfer the ink to the substrate with other general UV inks. surface. According to the viscosity and transfer of the ink, a certain proportion of the diluent specified by the manufacturer of the UV refractive ink may be appropriately diluted for printing.
Screen printing
This article uses the semi-automatic screen printing machine as an example to introduce the points that need attention in the printing process.
(1) The same type of UV refractive ink produced by different manufacturers has certain differences in quality and performance. Generally, it must first pass the printing test to determine the quality is stable and reliable before mass production.
After printing, curing is carried out by UV equipment under standard conditions. Then, the refractive ink, adhesion, scratch resistance, folding endurance, and the like of the printing surface were tested. If the test results are not satisfactory, adjust the conditions including ink, light intensity and temperature and humidity until satisfactory results are obtained. A UV light meter is recommended during the test.
(2) The ink must be thoroughly stirred before use.
(3) Pay attention to the curing of the UV refractive ink during the printing process to avoid affecting the hardness and adhesion fastness of the ink layer due to incomplete curing.
(4) During production, pay attention to keep the temperature of the darkroom at around 23 degrees Celsius and the air humidity at around 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 darkroom ventilated to dissipate gases that are harmful to human health.
(5) UV ink is irritating to the skin. Be careful when taking it, avoid contact with the skin. If the skin is stuck with ink, rinse it immediately with soapy water.
(6) The ink storage period is generally 6 months, and should be sealed and stored at low temperature (2 to 18 degrees Celsius), avoiding light and avoiding heat, so as to avoid changes in ink performance.
The anti-counterfeiting effect of screen printing is slightly less than mechanical refraction or laser refraction, which is relatively easy to imitate, but its appearance is not inferior to the latter two, and it is simple and easy to design and manufacture, and the cost is low. Will be more and more widely used.