PLATE/PRINT ANALYSIS
“The TSG Difference”
All Printing Resources' TSG (Technical Solutions Group) is excited to offer what is the most advanced print analysis available in our industry today, and no doubt will show another example and level of differentiation of TeamFlexo.
Obviously samples sent to us for evaluation can be labeled in whatever form you want to identify them, example: A, B, C, D.
TYPICAL ANALYSIS
When performing a one color press optimization, in this case with the focus being on ink and printing plates, the industry standard for evaluation is solid ink density and tonal range. Sometimes the file will include a slur target to indicate proper impression, ink to anilox, and any speed match issue between rolls (print cylinder/anilox/impression drum). Analysis of this simple test can be accomplished with a simple densitometer; results are reported in (2) two areas of interest – dot% and S.I.D.
COMPLETE QUANTITIVE ANALYSIS
Our Technical Solutions Group (TSG) has a significantly more analytical approach to what is arguably one of the biggest decisions you will make based on this press optimization trial and certainly affect the path you travel down for some time to come. Using the latest (calibrated) densitometers and image analysis systems we break down simple solid ink density (S.I.D.) and dot quality into the following areas of interest.
THE DIFFERENTIATOR - (Solid Ink Density, or S.I.D.)
Solid Ink Density, or reflective density to be more accurate, is a measure of the percentage of reflected light. In printing processes, this usually means the percentage of light that is reflected from the substrate and the ink. The relationship is explained by the following formula: Density = log10 1/Reflectance factor; Reflectance is calculated by the function: R= Ir/Io. This simple measurement is performed with a reflectance densitometer. But while we do obtain information about the ink film thickness and strength there is very few indicators of the smoothness and complete coverage of the ink delivered to the substrate. After the initial density measurements TSG takes a series of measurements to measure two additional characteristics of S.I.D.; graininess and mottle.
Graininess is another word for pinholing. The amount of pinholing is measured in terms of percentage of reflectance. When identifying this print characteristic, if a sample has 5% reflectance when measured then 95% of the area is covered with ink and 5% is left void or with pinholes. If put on a simple PASS or FAIL methodology 2% or less would be a pass or an indicator of exceptional level of coverage. Above 2% graininess/pinholing can be detected by the naked eye upon close examination. Note: this is only a measurement of coverage, not of the uniformity of the ink film thickness delivered to the substrate.
Smoothness is often a word to describe the uniformity of the ink laydown. The opposite of smooth would be mottle, or an orange peel effect. The amount of mottle is also measured in terms of percentage of reflectance. When identifying this print characteristic, if a sample has 5% reflectance when measuring for mottle then 95% of the sample appears to be smooth whereas 5% of the area experiences darker or lighter areas than the uniform area. Because mottle doesn’t necessarily mean you have a void in the ink (just a variation in thickness) it is more difficult to pick up with the naked eye. That being said, because you have dark/light areas of variations our eye perceives the combined optical difference of 5% being more like a 10% total variation. Therefore, we stick to the PASS - FAIL methodology of 2% or less would be a pass or an indicator of exceptional level of smoothness.
THE DIFFERENTIATOR - (Dot Quality – Tonal Range)
Dot Quality is often simplified to one of the most basic characteristics – gain. But a much better measurement is the ability to provide the widest tonal range while producing a dot that prints uniformly, predictable, and is stable and able to last the test of time. The problem with most methods of analysis is that they only take into consideration the gain or size of the dot and leave out all of the other important characteristic of the dot that make it perform at the highest level on long or short runs each time, every time. After all dot gain can be addressed with a simple curve, but an optimal high quality tonal range is executed by measuring the often unmeasured qualities of the screen.
Consistency or uniformity in size within a tonal patch is one of the most overlooked screen characteristics. It is an indicator of a properly exposed plate by indicating that dots are all formed uniformly, not broken or fragmented, and delivering ink evenly. Its also a strong indicator of the cleanliness of the screen. In order to measure consistency or uniformity TSG measures the dot Diameter Mean in microns (mm)- Diameter = the sq. root of 4A(area) divided by p. This is the average dot size diameter within a tonal patch. By dividing the mean by the standard deviation we come up with a percentage that indicates dot uniformity. If the dot diameter measurements are within 10% of one another it is deemed as a PASS. Over a 10% deviation indicates the start of dirty or inconsistent ink delivery.
Dot Stability is often referred to as Slur. TSG uses a method of measurement for slur referred to as Box Ratio. This is the ratio of the vertical dimension to the horizontal dimension of the minimum rectangle-bounding box that can be fit around the dot. In other words, this is the maximum vertical height of the dot divided by the maximum horizontal width of the dot. This is the measurement used to determine if the dot is elongated in the web or across web direction (slur). Measurements outside an acceptable range (.90 – 1.10) may indicate a speed match problem between the roller, such as the print cylinder and anilox roll, or even too much relief on the printing plate resulting in an unsupported dot. This measurement can be affected by plate selection to substrate, plate exposure, and impression settings on press.
Circularity of the dot is simply the smoothness of the radius around the dot. Arguably plate materials with flat top dot technology or some water wash technologies that claim to achieve a near 1:1 ratio could expect to have a more pixelated circumference than a conventional plate material. However, after ink it applied to the plate surface and impression to the substrate has been executed, we still see a rather smooth radius on the printed substrate. The formula for circularity we use is C= p2/(4pA), where p= the perimeter length and A= area. Note that for a perfectly circular dot, circularity = 1. For dots of any other shape, circularity > 1. For very small dots the circularity measurement accuracy may be compromised therefore have a value of < 1. Useful to analyze the smooth contour of the perimeter of the dot. One again our PASS range is .9 – 1.10.
Ink Transfer is possibly one of the most overlooked areas of analysis. The likely reason for this is that often the measuring equipment is not available to the user to compare mechanical dot gain to optical dot gain. Mechanical dot gain takes nothing more into consideration than the outmost edge of the dot; it takes no consideration for the fact that the center of the dot could be void of ink coverage. Optical gain takes into consideration how our eye sees gain and accounts for the amount of ink transferred across the face of the dot. The optimal level of ink coverage is when mechanical and optical dot% agree with one another; it indicates that the inner portion of the dot carries ink uniformly to the outer edge of the dot. We execute this comparison through the use of our densitometer and compare the result to the image analysis system that measures the mechanical dot value.