Mobile phone shell stereo printing based on UV inkjet technology
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With the development of technology and the advancement of the times, high-performance smart phones have become a necessity for people's daily life, and the mobile phone case has gradually been valued by users because of its anti-drop, shockproof, waterproof and beautiful appearance. Along with the variety of beautiful and creative mobile phone cases, the mobile phone peripheral accessories market is hot. At present, the design and production of mobile phone shells on the market are mostly limited to two-dimensional planes. Here, the author will introduce a three-dimensional printing technology for mobile phone shells based on UV inkjet technology. Based on digital files, 3D printing ideas and UV spraying will be introduced. The combination of ink printing technology enables the pattern printed on the phone case to exhibit a three-dimensional effect of relief-like embossing by means of layered superposition.
Mobile phone shell stereo printing steps
Equipment and materials: Mimaki UJF 3042-HG UV inkjet printer, Mimaki LF-140 CMYKW five-color UV ink, PVC mobile phone case, Adobe Illustrator CC graphics software, Labthink CHY-C2 thickness gauge, 3M 610 ink adhesion test tape , SHEEN Ref-705 scratch resistance tester.
1. Select the substrate
A random questionnaire survey in densely populated areas found that about 92% of mobile phone users indicated that they would choose to use mobile phone cases, and people do not recognize the common mobile phone shell materials (such as silicone, leather, metal, plastic, etc.) on the market. In the same way, 80% of users have chosen a plastic case. Therefore, this experiment selects a plastic mobile phone case with a wide audience and high universality as a substrate to realize the embossed three-dimensional printing effect.
2. Acquisition and stratification of the original
When obtaining the original design of the surface of the mobile phone shell, the relevant pattern can be obtained by scanning or directly using the software design method, and then the layered processing is performed on each pattern element, so as to perform multi-layer printing to form a stereoscopic effect.
When layering, the visual distance between different stereo elements should be fully considered. Set according to the principle that "the farther the visual distance is, the smaller the number of printed layers is, the closer the visual distance is to the number of printed layers". If you use the design draft, you should try to use the vector file drawn by Illustrator software, in order to facilitate the adjustment of the design draft, but also can be applied to the production of a variety of models of mobile phone cases.
3. Positioning of the phone case
The quality of the three-dimensional printing effect of the mobile phone case depends largely on whether the center of the design graphic at the time of positioning and the center position of the mobile phone case can be highly coincident, which is a difficult point in the entire printing process.
The position of the Mimaki UJF 3042-HG UV inkjet printer printhead is adjusted to allow accurate positioning before printing begins. At the same time, in order to solve the problem that the mobile phone case is not easily fixed on the printing platform, the two sides of the mobile phone case can be fixed on the printing platform by using paper tape or a special mold. This can not only solve the problem of difficult positioning of the mobile phone case, but also prevent the ink from spreading to the sides of the mobile phone case.
4. Print effect test
(1) Effect of different print layers
Unlike substrates such as paper, inks cannot penetrate down on plastic to achieve greater adhesion. Therefore, before the start of printing, I designed the C, M, Y, K four-color printing layer test version shown in Figure 1 using Adobe Illustrator CC software (including lines and color blocks that need to print 1 to 12 layers of UV ink layers). Element), and the C, M, Y, K four-color line width test version shown in Figure 2 (including the same number of layers, different line width elements). The above two test plates were printed to determine the influence of the extreme value and line width of the printable three-dimensional layer on the surface of the mobile phone case on the adhesion of the ink.
(2) The effect of the minimum print layer difference
In order to highlight the three-dimensional element, it is necessary to determine the minimum difference in the number of printed layers between the two elements, that is, the difference in the thickness of the ink layer. Observing the printing effect of the above test version, the following conclusions are drawn: 1 When the difference in the number of printed layers is 1 layer, no stereoscopic effect is perceived by observation and touch; 2 when the difference of the number of printed layers is 2 layers, The stereoscopic effect can be perceived by observation and touch, but is not obvious; 3 when the difference in the number of printed layers is 3 layers, a stereoscopic effect can be perceived by observation and touch. Therefore, when the stereoscopic effect is exhibited, the minimum print layer difference should be 3 layers.
5. Measure the thickness of the ink layer
In this experiment, the thickness of the ink layer of CMYKW five color UV inks was measured in the printed product of the test version shown in Figure 1 using the Labthink CHY-C2 thickness gauge, so that when using Mimaki LF-140 in the future, we can understand the ink of each color. The relationship between the thickness of the ink layer and the number of printed layers.
Among them, since the Mimaki UJF 3042-HG UV inkjet printer used sets the white color as "feature", it is necessary to select "special version synthesis" in the "print mode" before measuring the W color, which will be 100% K (or C, M, and Y) can be replaced with 100% of W for printing, and then the data can be measured.
6. Print the finished product
According to the characteristics of the original and the stratification, the files to be printed are sequentially imported into the Mimaki RasterLinkPro 5 workstation queue matched with the printing machine, and the finished mobile phone case shown in Fig. 3 is printed.
Firstly, two bottom elements are printed: 2 layers of white ink and 1 layer of gradient background. On the basis of these two elements, the following elements are printed: 3 layers of ground pattern, 6 layers of skirt and upper body part. The top coat pattern and the flying hair are 9 layers. The mobile phone case shown in Figure 3 has a print layer of up to 12 layers.
Key issues discussion
1. Printed product performance test
(1) UV ink adhesion test
In order to test the UV ink adhesion of the printed mobile phone case, the author measured the international standard GB/T 5210-1985 "Measurement method of coating adhesion" in the actual production process, using 3M 610 tape. Print samples with a printed test version as shown in Figures 1 and 2. The results show that when the number of printed layers is 12 layers, it can fully meet the practical requirements of realizing the three-dimensional printing effect on the surface of the mobile phone case, and the width of the lines does not have any influence on the adhesion of the ink.
In order to verify whether the adhesion of the printed product meets the requirements, the author performed the same test on the printed product shown in FIG. In the actual test, the ink was not peeled off from the surface of the mobile phone case by the 3M 610 tape. This indicates that the UV ink on the printed product is firmly adhered to meet the user's needs, which is the same as the above test result.
It is worth mentioning that if the number of printed layers on the surface of the mobile phone case is too high, the adhesion of the UV ink on the surface of the plastic material can be enhanced by surface coating.
(2) Scratch resistance test
In real life, sharp objects such as keys often scratch the surface of the phone case, so scratch resistance is particularly important. In this experiment, the SHEEN Ref-705 scratch resistance tester was used to detect the critical value of the ink layer rupture of the UV ink on the mobile phone case by adding a weight. The test results are shown in Table 1.
When the test value is above 1000g, the ink layer is not broken, so that it can meet the use requirements in daily life. It can be seen from Table 1 that as the number of printed layers increases, the critical value of the ink layer rupture gradually decreases. When the number of printed layers is 12 layers, the critical value of the ink layer rupture is 1200 g, which indicates that the mobile phone case can meet the daily use requirements of the user.
2. How to avoid color cast
Since the Mimaki UJF 3042-HG UV inkjet printer used in this experiment sets white as the “feature”, if you do not select “Special Edition Synthesis”, white will not be printed when printing. However, if only the ink of the solid layer is superimposed according to the increase in the number of layers, serious color cast is generated, which is particularly prominent when printing gradients. Therefore, when printing an image that is affected by color superposition, in order to restore the color, it is necessary to print two layers of white ink as a bottom to solve the color cast problem caused by the increase in the number of printed layers.
3. Cost analysis
The cost of a single mobile phone case with a three-dimensional printing effect is mainly composed of the price of the mobile phone case and the ink consumed during printing, and the labor cost and equipment loss are not counted. Taking this experiment as an example, the cost is as follows.
(1) The purchase price of ordinary plastic mobile phone cases commonly found on the market is about 1.2 yuan/piece.
(2) The price calculation method of ink consumption is as follows. The LF-140 UV ink cartridge manufactured by Mimaki was used in this experiment. The capacity is 200 mL and the price is 850 yuan/box. Using this ink to print a single layer of 1 m2 consumes about 15 mL of ink, and the average price of ink consumed per 1 m2 of printing is 63.75 yuan. Take the best-selling iPhone in the market as an example. The full-page printing cost is 0.59 yuan/layer for iphone 6/6s and 0.78 yuan/layer for iphone 6/6s Plus.
However, in mass production, not only the cost of the mobile phone case substrate can be reduced, but also because the ink of the three-dimensional element portion decreases as the number of printed layers increases, so when the number of printed layers is 12 layers, each mobile phone is used. It is still relatively easy to control the total cost of the shell below 10 yuan or 10 yuan (slightly different depending on the design draft).
This paper makes up for the shortcomings of the traditional flat printing on the relief effect through the 3D printing method, and provides a new idea for the reproduction of the mobile phone shell with the stereo effect. This method has the characteristics of individualization, no plate making, high speed, high quality, low price, etc., but also fully utilizes UV inkjet curing speed, solvent-free volatilization, low energy consumption, good printing stability, etc. Advantages, with a certain universality, can also be promoted for printing on the surface pattern of substrates such as glass, ceramics and metal.