THIN THREAD MESH FOR TEXTILE PRINTING
Monofilament polyester yarn used to weave screen printing mesh has been steadily improved over the years, with new versions being introduced that display much higher modulus (high tensile strength with low elongation) than standard yarns. These advancements in yarn technology allowed the development & introduction of a new generation of high tensile strength screen mesh, woven with thinner threads, that confers multiple practical benefits & advantages to the discerning textile screen printer. A typical analysis of stress/strain curves, illustrated here for 55.48 (140/in) in Figure 1 to the right, shows the balanced elongation of both warp & weft directions of the weave, and low elongation of the fabric that’s required to reach & maintain a high tension level. This balance means that at increased tension levels the mesh openings remain square and consistent throughout the screen. This is most critical for halftone printing since we are putting Figure 2 a regular pattern of dots onto a fabric. If the fabric is not consistent in weave it can lead to moiré (this is only one of many causes of moiré). Mesh Mesh % Thread The excellent mechanical properties of these Mesh Type Count Count Open Diameter yarns has allowed the introduction of a range (c/m) (in) Area of fabrics with much higher % of open area compared to standard fabrics typically used thin 32 81 70 61 by garment decorators. The difference in both open area and thread diameter is illustrated normal 34 86 100 41 to the right in Figure 2 that compares 120/cm mesh (305/in) and shows the thin 43 110 64 53 difference between same mesh count woven with either 31 micron, or 40 micron yarn. normal 43 110 80 43 We can illustrate these differences in the Table 1 to the right that compares an equivalent range of thin 48 122 55 55 mesh counts typically used for textile printing. normal 49 125 70 40 The major printing benefits conferred by this new type of mesh result from a combination of thin 55 140 48 50 the high percentage of open area, that enables better ink coverage, and also from the thinner normal 55 140 64 41 threads, that allow finer detail to be printed. Now let’s look at both of these aspects thin 64 158 48 56 in more detail on the next page. normal 62 158 64 32
44 thin 78 198 40 44 42 40 38 36 normal 77 196 55 28 34 32 30 28 thin 90 230 40 38
m 26 c
N / 24 22 normal 90 230 48 27
Tension 20 18 16 14 thin 120 305 31 40 12 Weft 10 Warp 8 normal 120 305 34 29 6 4 2 0 normal 120 305 40 20 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Elongation % Figure 1 Table 1
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COVERAGE Mesh Mesh Measured Figure 3 below shows a comparison of printed Mesh Thread Count Count Ink Deposit results from standard 77.48 (196.48) mesh Type Diameter (c/m) (in) per m2 (left) with thin thread 78.40 (198.40) mesh (right) and clearly shows the superior coverage thin 43 110 64 29.7 when printing white ink on a dark garment. What is surprising here is that better coverage normal 43 110 80 35.5 can be achieved with a lower ink film weight. Table 2 on the right compares printed ink film thin 48 122 55 28.7 weight for a standardized image, using different selected mesh specifications, and in each case normal 49 125 70 44.3 you will see that printing with thin thread mesh consumes less ink than it’s ‘standard’ counterpart. thin 78 198 40 13.1
normal 77 196 48 15.9
Table 2
Because ink is easier to transfer through the This superior coverage, but with lower ink thin thread mesh by virtue of the thinner consumption, is the result of a smoother screen, and with high % of open area, & more continuous ink film. There are less much less squeegee pressure is required. voids, and less fibrillation, because garment This allows the ink film to be better managed fibers are less able to penetrate the ink film. and deposited on top of the substrate where The improved performance offers additional we need it, instead of being driven into it. benefits beyond just better looking prints with So, in addition to better visual quality of light inks on dark garments. Improved coverage the image, the printed garment also has with anti-bleed base also results in better softer hand, by virtue of less ink used, inhibition of dye migration when printing on but also including the smoother surface. poly/cotton blends, as shown in Figure 4 below.
110PW64 110PW80 110PW64 110PW80 Thin Thread Standard Thin Thread Standard Figure 3 Figure 4 - Comparison of dye migration of prints made with thin thread versus standard mesh
Figure 5 – mesh blockage obscures highlight dots
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The second big advantage of thin thread mesh is much easier ink transfer when printing fine for highlight areas of halftone prints. Figure 10% halftone dot on 55 lpi image with the details, including halftones. In addition to 5 to the right shows the interaction between mesh. In the case of the thin thread 78.40 providing screen tension, that lifts the stencil out 10% halftone dot on 55 lpi image with the (198/in) mesh the stencil openings are much of the wet printed ink film after the squeegee mesh. In the case of the thin thread 78.40 more open and free from obstruction. passes, the mesh is also a scaffold that provides (198/in) mesh the stencil openings are much For the equivalent standard mesh 77.48 support for the detail in stencil image. more open and free from obstruction. For (196/in) there is considerable blockage. Thinner threads provide a less intrusive scaffold, the equivalent standard mesh 77.48 (196/ During printing, this mesh interference restricts and result in less blockage & interference of in) there is considerable blockage. the highlight tonal range, with a loss of both fine details, and this is particularly relevant Figure 5 shows the interaction between detail and density as illustrated in Figure 6.
Figure 6 – better print results with thin thread mesh on the right
OTHER BENEFITS CONCLUSION Of course it’s possible to create, calibrate, and Although this type of mesh offers substantial Thin thread mesh offers textile & garment use compensation curves. These are applied to benefits to textile printers using any type of ink, decorators an additional tool that further extends the separated artwork and attempt to counteract the original concept was to develop a range the versatility and scope of the screen printing this dot loss, and ‘linearize’ the tone range of mesh specially designed for printers using process. Practical applications could include for the printed result. The process requires water-based inks. The higher % open area retards using thin thread 78.40 (198/in), instead of 62.64 a ‘compression’ of the tonal range, that is premature drying, or at least makes rewetting (158/in), to maintain ink coverage but with the transferred into the stencil during exposure, by easier after short print stoppage, and enables ability to reproduce finer details. Or, single artificially enlarging the effective size of highlight Plastisol printers to make an easier transition stroke printing with 48.55 (122/in), instead of dots in the region of tone range that needs help. to water based printing. It’s true that many top print, flash, print with 49.70 (125/in), to get the The greater the extent of mesh interference, the brands of water-based inks today have been same result but saving two open print heads. more extreme compression must be employed, improved in performance, so that premature Consumers of printed garments & sportswear are in attempt to maintain a linear printed tone range drying in the screen is much less of an issue than becoming more discerning and demanding. with full highlight detail. When this compromise in the past. However, the use of thin thread mesh, The advances in printing capability offered with requires excessive use of compression, it makes in addition to it’s previously mentioned benefits, these new mesh types will allow manufacturers to the stencil exposure and printing process also offers the advantage of wider process latitude continue to be creative in meeting their demands. more difficult to control within strict limits, when printing water-based inks under adverse and requires careful management of all press environmental conditions, or when trying to limit variables to master successful multicolor halftone the use of any added retarder. Surface treated printing. This is especially so for process color versions of thin thread mesh are also available, printing, where control of ‘gray balance’ is critical and these use a plasma based process to modify for fidelity when overlaying the transparent the mesh surface in order to promote extra stencil process color inks to create additional colors. adhesion. The plasma treatment uses an ionized Thin thread mesh requires less aggressive gas to raise the dyne level of the fabric. This compression of tones to linearize the printed promotes better wetting and encapsulation of the result, and thus allows a greater degree of threads with wet emulsion during screen coating, control and latitude in all steps that follow as well as raising the adhesion level of the in order to achieve acceptable prints. stencil itself, resulting in more durable screens. SAATI TECH TIP HANDOBOOK | To Place An Order, or For More Information | Call 1-800-431-2200 | Visit our website at www.saati.com | e-mail: [email protected] 13