26 May Characteristics of Squeegee Hardness
The physical characteristics of squeegee hardness and edge definition have been the subject of many technical articles and a favorite topic for screenprinters and manufacturers. The selection of hardness, which is the measure of the Shore A hardness of the polyurethane squeegee blade expressed in terms of 1 to 100. This article shows the results of different Shore A of squeegees.
I was engaged recently as a print consultant on a research project for Fimor. The project consisted of producing a series of 6 textile prints using white plastisol ink on a black jersey knit textile material. Each of the 6 prints would be printed with a different Shore of squeegee without any changes otherwise. They wanted to show the actual results of using each of the various blades they produced, through a controlled ink transfer process.
In order to most accurately show the results, it was necessary to print through a mesh count that would allow the detail without flooding the print with excess ink. Knowing that the 55-90-55 Shore A squeegee would produce the best opacity, we choose a mesh count that would allow us to just print a single pass to achieve opacity and let the other squeegee of different degrees of hardness fall where they would in order to show the differences as the print grew less opaque from the squeegee hardness.
Obviously, if one were attempting to print white ink on a black T-shirt, they would perhaps choose to print with a coarser mesh count, with a smaller thread diameter and/or with a higher emulsion over mesh ratio that was used in the test prints to achieve maximum opacity. Achieving opacity was not our goal, as we wanted to illustrate the differences in squeegee hardness.
The art (all six final prints are shown at the bottom of this article) was created with a good combination of open areas, solid areas, straight and round edges, and 50 lines per inch halftone areas, that were output with an elliptical dot pattern.
The shop, CGTex, where the testing was done in is an International award-winning shop known for its high-end printing for the most discriminating of contract clients.
The press was a 10-color M&R Gauntlet II, that was fairly new and had been well maintained. The parallel and geometric plane of the platens were checked, even though all prints were made on platen number 1 and on head number 1, and brought into the same plane ±0.010″. Next, we checked and adjusted all screens for plane, parallel and height about the platens to ±0.010″. The off-contact was set at 0.080″.
We used 23-inch x 31-inch O.D. the M3-UL Newman Roller Frames to print the 8-inch x 10-inch image, which was within the sweet spot of the frame size and allowed for ample free mesh area.
We chose 160 threads per inch mesh count with a 62-micron thread diameter. The mesh was tensioned to 30N/cm2 and work-hardened then retensioned back to 30N/cm2 until it was able to maintain its tension through the necessary press run.
The screens were coated with a dual-cure direct liquid emulsion of 40% solids and had an emulsion over mesh ratio of 9-percent, measured with an electronic thickness gauge on a nine-point pattern, and averaged.
The fill blade was set to just fill the mesh opening, leaving only the wetness of ink on the surface of the mesh to allow the squeegee to easily glide across the surface without creating drag. The speed was set at 75-percent of maximum speed through research for the need to just fill the mesh openings.
The squeegee blades were inserted into the holders and then sharpened to eliminate any deviations in the edge. The free height was checked to assure conformity.
The ink was Rutland Quick White, a non-phthalate plastisol ink. It was brought to an operating temperature of approximately 95 degrees and stirred well, prior to inserting it into the screen.
The squeegee blades were all set at approximately 4-degrees, each with a pressure of 30 lbs. and with a maximum stroke speed.
For the initial test, a dozen test prints were made with the press set at 400 prints per hour to bring the various components to production mode. At that point we began the test by inserting the blades into the press at print station number 1, bringing them into specifications and then making 10 prints all on platen 1.
After each ten prints, the squeegee was replaced with a different blade type/Shore and the test repeated.
I would encourage anyone interested in understanding more about squeegee hardness, to attend one of the trade shows where Fimor is exhibiting and see the printed samples for themselves.
The photos below were taken with a Nikon D50 in RAW mode, transferred to Photoshop and enlarged to 300-percent before capturing the screenshots below. No manipulation was made in Photoshop to the images. Each photo is labeled with the squeegee used to produce the print.
While most viewers will look at the opacity first, it is suggested that the viewer also consider edge definition and the amount of detail held or lost, as well. There are some subtle differences caused by the manner in which the dots fell onto or off of threads of the material.
Shown below are all six images, but at 72 dpi. It is more practical to view them at 300 dpi, which you can download by filling out the following form: