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FLEXO Magazine : September 2011
TesT TargeT FormulaTion The test target file was prepared using Adobe Illustrator CS5. Each object on the test print target was printed in two separate colors to observe consistency. Arrows were placed near each object to identify print direction when analyzing small sections of the sample either optically or with a pro- filometer. (See Figure 1.) Ink film thickness and surface uniformity. The test target for ink film thickness and surface uniformity was measured by a profilometer. The targets for these tests consisted of a solid 1-inch square surrounded by two squares with a 50-micron stroke, each with a 10-micron gap. These squares are further surrounded by a 50-micron stroked square with a 100-micron gap between it and the adjacent square. Registration. Registration was measured optically using various methods of magnification. Registration squares were located in nine places on the test target. Each square, consist- ing of 10-micron strokes, had a “grid” of 10-micron strokes at each corner. Each registration grid had eight lines parallel to each edge of the square. The square was printed in one color and the grid in another to determine the strength of precision achievable through typical flexographic printing. Edge definition. Edge definition was tested optically, although a profilometer was used to analyze the precision of the diagonal lines. The six lines crossing to make a star-like pattern helped to determine how accurate lines at different angels can be produced. Print direction versus crossprint direction is important to note for this characteristic. Minimum feature size. Minimum feature size was mea- sured optically through a series of lines of various stroke widths from 10 microns to 50 microns, in increments of 10 microns. Although testing 5-micron capabilities would be ideal for the application of printed electronics, Adobe CS5 ap- plications and Cal Poly ’s platemaking equipment (2,540 dots per inch) together were incapable of producing such feature sizes. In addition to determining the reproducibility of various strokes, each of the strokes is rotated in a series of 90-degree angles to test the affect of print direction. Moreover, gaps of 10 to 50 microns, in increments of 10, were also measured optically at a series of 90-degree angles. Press parameters. See sidebar, “Press Parameters,” at right. TesT TargeT PlaTe analysis Conventional analysis devices used for traditional graphic printing include densitometers, spectrophotometers and plate readers (such as betaflex), among others, for two-dimen- sional examination. For the initial analysis of the test target, a betaflex plate reader was used as well as various magnifica- tion methods for optical review. Line and dot reproduction capabilities. The platemaking technology used at Cal Poly can easily produce a 20-micron line because the laser has a spot size of about 15 to 18 mi- crons wide. However, the 10-micron line was an issue for the current laser, as it is smaller than the laser spot size. Addition- ally, although the experiment involved reproducing line work, some natural sharpening was expected, so a 15-micron line sent to the device came out just a little thinner because of the stain level of the material. TesT TargeT PrinT analysis Analyzing the functional layers of printed electronics re- quires three-dimensional examination by using profilometers. Profilometers can include scanning electron microscopes, atomic force microscopes, electron beams, laser triangula- tion and micrographs. The Cal Poly Material Engineering Department assisted in analyzing the test target by providing the profilometer equip- ment. Within the Materials Engineering Department, we used an Ambios XP-1 Stylis Profilen profilometer. The profilometer ran at a consistent speed of 0.05 nanometers per second and tested two samples. The first sample was taped to the slide at the edges and the second was adhered to the slide using the adhesive backing on the film. The profilometer analyzed the ink film thickness and surface uniformity of the test target. Figures 2 through 4 disclose the data from the profilometer analysis. Some of the results are inconclusive. In addition to analyzing the print with a profilometer, im- age analysis was conducted using ImageXpert and MacRail software. Also, a Beta Screen SKS 50XSD loop was used to deter- mine approximate line widths. inTerPreTaTions and ConClusions Flexography may not be fit as the sole method of printing for producing all printed electronics. However, flexography could be used with other printing methods to create a hybrid printing technology for the production of printed electronics. In-the- round plate mounting should be used to optimize flexography for the production of printed electronics. Without it, flexography would be nearly impossible to use in achieving the necessary Press ParameTers Press: Mark Andy 220-7 press, 100 fpm Substrate: Fasson 2.0 mil CL BOPP TC/S692N/1.2 mil PET Stickyback: 3M 1015, combination/medium com- pression tape Unit 3: Green ink Water Ink Technologies, Inc. Ultra Plus II Hexachrome Green Viscosity: 30 seconds on #2 Zahn pH: 9.5 Anilox Roll: 800 line count, 60 screen angle, 1 .99 actual volume Unit 4: Black Ink Performa G74CPC, Black. XGLO44635, Batch # H2297 Viscosity: 31 seconds on #2 Zahn pH: 9.3 Anilox Roll: 800 line count, 60 screen angle, 1 .95 actual volume Doctor Blade: Allison Systems Corporation, Bevel Blade CX: Bright Carbon Steel; SUP: superhoned 72 FLEXO september 2011 www.flexography.org