Estimating Ink The SPTF Way Change! People in the screen printing

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1 PRODUCTION All Screen Printers Estimating Ink The SPTF Way Change! People in the screen printing industry have embraced a lot of it in recent years, but they have resisted change as well. While not all change is good, the fact of the matter is, you can t improve without change. The first step to accepting change is adjusting attitude. The old adages, This is the way we have always done it, or if it ain t broke, don t fix it, have never brought improvement or promoted progress. In fact, these attitudes in today s rapidly advancing technology can turn out to be killers. So the question begs to be asked, why is it when new scientifically substantiated information becomes available, we don t readily accept and use it? Case in point: In the screen printing industry, we have used various marginally accurate ink estimation formulas for years without question. These formulas were the best the industry had until the Screen Printing Technical Foundation (SPTF) came up with a more accurate method more than six years ago. Since the SPTF ink estimation formula was introduced, it has been published in a mesh chart listing various specifications as a replacement for the theoretical ink volume typically listed by mesh manufacturers. Several companies are reporting that this estimate matches the actual ink deposit when tested in production. While the formula has gained some acceptance, there is also some resistance. One company that developed a small software program to estimate ink deposit is purposely using the old formula (Fabric Thickness x Percent Open Area) even though they are fully aware of SPTF s research and concede that the new method works better. Their reason? They believe that what people want is what they are accustomed to getting. Another company developed an expensive state-of-the-art ink mixing and dispensing system, but they used the outdated formula for the ink consumption calculation. Further proof of this resistance to change is seen in the mesh manufacturers specifications, which still do not list or promote the newer more accurate ink estimates. Are you satisfied with the status quo, knowing there is a better way? This article will show how ink estimates can affect your business, and describe the new practical method to estimate the ink for a job. Why Estimate Wet Ink Deposit? If you can accurately estimate the wet ink deposit that a given mesh will produce, you can then estimate the total quantity of ink required for a job. Estimating wet ink deposit allows you to mix the volume of ink adequate to finish the job (with a safety margin); no more and no less. With an accurate estimate, you would not have excessive left-over ink and it would not be necessary to mix up additional ink during the print run. You could also estimate ink costs for a job, and have this accurately represented in your by Dawn M. Hohl, SPTF R&D Engineer, Screen Printing New research can help you more accurately estimate the ink you need to complete a job and increase your bottom line. But you have to be open to change! Visit SGIA at SGIA Journal April

2 prices. Ink thickness estimates are also very useful for selecting a mesh to generate a specific ink deposit for a given application. Better Estimates Lead to Higher Profits Being able to estimate the amount of ink to run a job is an important element to pricing an order. If you overestimate, extra ink sits on a shelf until that particular color is run again costing you money. If you underestimate the amount of ink needed, money is lost quickly on press downtime while 22 SGIA Journal April 1998 ink is re-mixed, and the job ends up being priced lower than it should have been. To complicate matters more, if a custom color match is involved, you can have a difficult time precisely matching the first ink mix to complete the job. Ultimately, the best remedy for each of these situations is to avoid them by accurately estimating ink volume in the first place. Research Produces a Better Way to Estimate Ink For a Job SPTF has outlined a new way to estimate ink for a job that is based on the results of several research projects. For a detailed account of how SPTF developed the ink estimation method six years ago, see the article in March/April 1997 issue Screen Graphics magazine entitled, Research for the Real World. Further information regarding the formula can be found in SPTF s Practical Application Bulletin Estimating Ink Deposit in Screen Printing: Improving Your Accuracy. Included in this new method are updated ink deposit estimation factors for mesh with 27 micron thread diameters, and factors to use with the manufacturer s fabric thickness. These new factors increase the accuracy of estimates when using manufacturer specifications (as opposed to measured fabric thickness) and address mesh with thin threads. This effectively expands the number of previously established SPTF factors from three to eight. These additional factors were derived from information generated in an SPTF ink deposit study on 27 different mesh counts completed two years ago. Also unique to this method is an option to add the effect stencil thickness has on ink deposit when printing fine detail. In the past, many people in the industry have added the stencil thickness directly to the ink deposit thickness. Research has indicated, however, that the relationship is not direct. An initial experiment was completed, and a preliminary relationship defined based on several stencil thickness ranges. As a result, SPTF researchers have developed new factors to more accurately represent the additional ink generated by the stencil. These factors are included with the method outlined in this article. Calculating Ink the SPTF Way A detailed step-by-step description of SPTF s method of estimating ink is outlined on the following pages. Each color of ink printed in a job must be estimated individually and added together to find the total amount of ink needed for the job. The SPTF method is not accurate for clear coat inks and has yet to be tested for textile inks. When making these calculations on the Ink Estimating Worksheet provided at the end of this article, it is essential Visit SGIA at

3 that numbers used in the formulas have the same units. Failure to observe this will produce erroneous results. Take care to write down what units are used throughout the worksheet. As with any type of estimation system, final accuracy is heavily dependent on the accuracy of the information put into it. In other words, garbage in garbage out. It is also important to keep in mind that estimations are just that, estimations. Current industry methods only give a general estimate of deposit, and SPTF s model is no different in its purpose. Conditions shop to shop may influence whether the estimate from this system is consistently over or under. A Time for Change in a Changing Time Process-oriented research at SPTF has been going on for the last eight years. New conclusions in the areas of rapid tensioning, sample preparation, squeegee design, changes in mesh dimensions during tensioning, and measurement techniques for a number of parameters have not only provided practical tools, tips and practices to the industry, but have challenged old theories and promoted new thinking about the screen printing process. This is a real example of how changing what we do can bring direct cost and time savings. Change is necessary You can either handle change in a proactive way or a reactive way. The first will put you ahead of the pack, while the latter lets the pack run over you. Let s not settle for the status quo anymore. There are better ways to do things. It s time to work together to find those better ways. We all must do our part. Screen printing will only progress as people in the industry accept and proactively move toward change. Let s take on a new attitude as we usher in the twenty-first century. Editor s Note: The Screen Printing Technical Foundation assumes no responsibility for the use of information presented herein, or for the results obtained or not obtained, and hereby disclaims all liability in regard to such use and/or results. STEP 1 Calculate the Ink Deposit Estimate for the Mesh Using SPTF s formula, listed below, calculate the ink thickness from the mesh being used for the job. You must know the mesh count, thread diameter, weave type, and fabric thickness to make this calculation most effectively. Fabric thickness should be measured at tension with an electronic thickness gauge for the most accurate estimate. It is vital that you observe proper measurement techniques when using these instruments to measure fabric, or that you use a specially designed screen printing probe. SPTF s Practical Application Bulletin Using Electronic Thickness Gauges Effectively in the Screen Printing Process outlines these techniques. If fabric thickness measurement is not possible, the manufacturer s specified fabric thickness can be used to make the calculation. To estimate ink thickness from a mesh: 1. Identify the mesh count, thread diameter, and weave type of the mesh being used. Note: This estimator is not recommended for mesh counts below 110 threads/inch (43 threads/cm). 2. Measure the fabric thickness at printing tension using an electronic thickness gauge, or identify the manufacturer s specified fabric thickness. Convert to microns if necessary. 3. Identify the correct factor in the chart below based on the mesh count, thread diameter and weave type of the mesh used. Measured Fabric Thickness SPTF Factor Plain Weave mc/inch ( mc/cm) Plain Weave 355 and up mc/inch 0.35 (140 and up mc/cm) Twill Weave 0.31 Mesh with micron threads 0.45 Manufacturer Specification for SPTF Factor Fabric Thickness Plain Weave mc/inch ( mc/cm) Plain Weave 355 and up mc/inch 0.33 (140 and up mc/cm) Twill Weave Mesh with micron threads 0.39 Figure 1 Stencil Stencil Stencil Ink Deposit Profile Squeegee 4. Plug the fabric thickness (in microns) and correct factor in the following formula and multiply to find the ink thickness estimate in microns. Fabric Thickness x Appropriate SPTF Factor = Ink Deposit Estimate STEP 2 Estimate Ink Deposit from the Stencil This step should only be completed if you are printing primarily halftone or fine detail images. Skip this step if these conditions are not present. Stencil thickness will only add ink deposit thickness when the images being printed are small: 300 micron (0.012 inches) or below. Images larger than this permit the squeegee to force the mesh into direct contact with the substrate, thus eliminating the stencil thickness from increasing the resulting ink deposit (Figure 1). To determine stencil thickness above the mesh thickness, an electronic thickness gauge must be used to measure the exposed screen. For more information on this measurement, read SPTF s Practical Application Bulletin Using Electronic Thickness Gauges Effectively in the Screen Printing Process. Based on the results of SPTF research, the additional ink deposit will be a percentage of the Ink Deposit Profile Stencil Visit SGIA at SGIA Journal April

4 stencil thickness on the mesh. These percentages vary based on the thickness of the stencil, and the mesh. Research shows that adding the total thickness of the stencil to the ink deposit, which has been practiced, is not accurate. To estimate ink thickness from the stencil: 1. Measure the stencil thickness above the mesh as calculated by subtracting the fabric-only measurement from the mesh/stencil combination measurement. The stencil thickness must be entered in microns. 2. Identify the correct SPTF Stencil Factor in the chart below based on the stencil thickness. Stencil Thickness SPTF Stencil Factor Stencil Thickness is less than 3 No Additional Deposit Stencil Thickness is equal to 0.15 or greater than 3, but less than 5 Stencil Thickness is equal to 0.30 or greater than 5, but less than 7 Stencil Thickness is equal to 0.50 or greater than 7, but less than 9 Stencil Thickness is equal to 0.60 or greater than 9, but less than 17 Stencil Thickness is equal to 0.50 or greater than Based on the following formula, multiply the stencil thickness (in microns) by the correct stencil factor to find the ink thickness estimate for the stencil in microns. Add that product to the ink deposit estimate calculated in Step 1 to calculate the adjusted ink deposit estimate in microns. (Stencil Thickness x SPTF Stencil Factor) + Ink Deposit Estimate from Step 1 = Adjusted Ink Deposit Estimate STEP 3 Calculate Image Area Per Sheet In this crucial step, you must estimate the area that the image covers. If the art is computer generated, the software may provide the precise area of the image. More often than not, however, the estimator must guess. The accuracy of the guess will have a significant impact on the closeness of the estimate. An area calculator, which is a transparent grid pattern that is laid on the image, can be a helpful tool in determining image area. Estimate coverage for each square in the grid, and then add up each square s results. Another tool is an electronic area calculator that is used in printed circuit board manufacturing. This device analyzes an image based on a light and dark ratio, and will provide the correct area on halftone and line art images. To calculate image area per sheet: 1. Determine the substrate s length and width in inches or centimeters. 2. Determine the percentage that most accurately represents the image area coverage based on the entire substrate area. If in doubt between two percentages, use the higher one. 3. Based on the following formula, multiply the substrate length by the substrate width to find the total substrate area. Multiply that product by the percent image area coverage estimate that has been divided by 100. This calculation will give the total image area per sheet. (Substrate Length x Substrate Width) x (Percentage of Coverage Estimate Divided By 100) = Total Image Area Per Sheet STEP 4 Calculate Ink Volume Per Sheet To calculate volume per sheet: 1. Convert the ink deposit estimate calculated in Step 1 or 2 to match the units of the total image area per sheet calculated in Step 3. Convert to inches if image area is in square inches, or convert to centimeters if image area is in square centimeters. total image area per sheet by the ink deposit estimate to find the ink volume per sheet. Total Image Area per Sheet (Step 3) x Ink Deposit Estimate (from Step 1 or 2) = Ink Volume per Sheet STEP 5 Calculate Total Ink Volume Needed To calculate ink volume needed: 1. Determine the number of prints required and the allowed overage (set-up and reject allowance) and add them together for the total sheets to be printed. Number of Prints Required + Allowed Overage = Total Sheets to be Printed total sheets to be printed by the ink volume per sheet calculated in Step 4 to find the total volume of ink needed. Total Sheets to be Printed x Ink Volume per Sheet (Step 4) = Total Volume of Ink Needed STEP 6 Calculate Set-up Ink Volume Needed (Optional) This is an optional section that will add to the estimate the ink needed to print one sheet on the press. On large-format work, this can be a substantial amount of ink and should be considered as part of the estimate. If you do not wish to include set-up ink in the estimate simply skip this step. To calculate set-up ink: 1. Measure the squeegee length and squeegee stroke length being used. 2. Determine if the ink viscosity is thin, medium or thick. Ink Viscosity: Thin Viscosity Medium Viscosity Thick Viscosity SPTF Set-Up Factor: inches or cm inches or cm inches or cm 24 SGIA Journal April 1998 Visit SGIA at

5 3. Identify the correct SPTF Set-Up Ink Factor in the chart based on the viscosity selection. Figure 2 4. Use the following formula to calculate set-up ink volume. Multiply the squeegee length by the squeegee stroke length. Multiply that product by the set-up ink viscosity factor. It is essential that all three numbers have the same units. (Squeegee Length x Squeegee Stroke Length) x Set-Up Ink Viscosity Factor = Set-Up Ink Volume 5. Add set-up ink volume to the total volume of ink needed from Step 5 to determine the adjusted total volume of ink needed. Set-Up Ink Volume + Total Volume of Ink Needed (Step 5) = Adjusted Total Volume of Ink Needed STEP 7 Convert Ink Volume Convert the Total Ink Volume calculated in Step 5 or 6 to a usable unit of measure using the conversion table provided on the ink estimating worksheet. STEP 8 Convert Ink Volume to Ink Weight (Optional) For those wanting to mix their ink by weight rather than volume, a conversion can be made in the formula. This conversion is optional, and if not needed simply leave the area blank on the worksheet. To complete this step you must know the approximate weight of the ink in pounds per gallon or grams per liter. There are three ways to find this information: 1. Call the ink manufacturer and ask for the weight in either pounds per gallon, grams per liter, or specific gravity of an ink. Make sure the information they give you is specific to the ink line and color you are using. Keep a chart of all weights of your ink lines for future reference. 2. When a new gallon or quart of ink arrives, put it on the scale to get the pounds per gallon, or grams per liter. Convert as necessary. Add to the chart of all weights of your ink lines for future reference. 3. Measure the ink with a weight-per-gallon cup (Figure 2). When the ink weight is determined for the cup according to the instructions, convert it to pounds per gallon or grams per liter. Add to the chart of all weights of your ink lines for future reference. Weight-pergallon cups are available from Paul N. Gardner Co., Inc., , at a cost of around $150. To calculate ink weight: 1. Determine the ink unit weight in either pounds per gallon or grams per liter. ink unit weight by the total volume of ink in gallons or liters (using the same units as the ink unit weight) to get the required weight of ink. Ink Unit Weight x Total Volume of Ink (Converted in Step 7) = Required Weight of Ink STEP 9 Calculate Ink Cost (Optional) To calculate ink cost: 1. Determine the unit cost of ink per gallon, quart or liter. unit cost of ink by the converted total volume of ink from Step 7 (use the same units as the unit cost of ink) to get the estimated cost of ink. Unit Cost of Ink x Total Volume of Ink (converted to correct units) = Cost of Ink Visit SGIA at SGIA Journal April

6 SPTF Ink Estimating Worksheet Read the step by step instructions presented in the article and complete the following worksheet to estimate ink for each color in a job. Job Name Ink Color Ink Brand and Series STEP 1 Calculate Ink Deposit Estimate for the Mesh STEP 3 Calculate Image Area Per Sheet Mesh Count inch cm Thread Diameter microns Substrate Size length width inch cm Weave Type PW (Plain Weave) TW (Twill Weave) Fabric Thickness microns Measured Manf. Specification SPTF Factor (select factor below based on mesh information) Measured Fabric Thickness SPTF Factor Plain Weave mc/inch ( mc/cm) Plain Weave 355 and up mc/inch (140 and up mc/cm) 0.35 Twill Weave 0.31 Mesh with micron threads 0.45 Manufacturer Specification for Fabric Thickness SPTF Factor Plain Weave mc/inch ( mc/cm) Plain Weave 355 and up mc/inch (140 and up mc/cm) 0.33 Twill Weave Mesh with micron threads 0.39 Fabric Thickness in Ink Deposit Estimate Microns SPTF Factor in Microns X = Estimate of % Coverage of Image Area on Substrate 5 % 30% 55% 80% 10% 35% 60% 85% 15% 40% 65% 90% 20% 45% 70% 95% 25% 50% 75% 100% Total Image Area Substrate Substrate % Coverage Per Sheet Length Width Estimate (Square in. or cm) ( X ) X ( /100) = STEP 4 Calculate Ink Volume Per Sheet Units for both numbers must be the same. Convert Ink Deposit Estimate to inches or centimeters using conversion chart. Use the Ink Deposit Estimate from Step 1 if Step 2 was not needed, or use the Adjusted Ink Deposit Estimate from Step 2. Total Image Area Ink Deposit Estimate Per Sheet (From Step 1 or 2) Ink Volume Per Sheet (Square in. or cm) Converted to inches or cm* (Cubic inches or cm) STEP 2 Estimate Ink Deposit from the Stencil This step should ONLY be completed if you are printing primarily HALFTONE or FINE DETAIL IMAGES. Simply skip this step if these conditions are not present. *Microns x = Inches Microns x = Centimeters Measured Stencil Thickness microns SPTF Stencil Factor (select from table below) Stencil Thickness Stencil Thickness is less than 3 SPTF Stencil Factor No Additional Deposit Stencil Thickness is equal to or greater than 3, but less than Stencil Thickness is equal to or greater than 5, but less than Stencil Thickness is equal to or greater than 7, but less than Stencil Thickness is equal to or greater than 9, but less than Stencil Thickness is equal to or greater than Adjusted Ink Stencil Thickness SPTF Stencil Ink Deposit Estimate Deposit Estimate in Microns Factor from Step 1 in Microns ( X ) + = STEP 5 Calculate Total Ink Volume Needed Number of Prints Overage (Set up Total Required and Reject Allowance) Sheets + = Total Ink Volume per Sheet Total Volume of Sheets (Step 4) Ink Needed (Cubic in. or cm) 26 SGIA Journal April 1998 Visit SGIA at

7 STEP 6 Calculate Set-up Ink (OPTIONAL) This is an optional section that will add to the estimate the ink needed to print one sheet on the press. On large-format work, this can be a substantial amount of ink and should be considered as part of the estimate. If you do not wish to include set-up ink in the estimate simply use the ink volume calculated in Step 5. Squeegee Length inches cm STEP 8 Convert Ink Volume to Ink Weight (OPTIONAL) To complete this step the approximate weight of the ink in pounds per gallon or grams per liter must be known. There are three ways to find this information. (1) Call the ink manufacturer and have them provide either pounds per gallon, grams per liter, or specific gravity for the ink line and color you are using. (2) When a new gallon or quart of ink arrives, put it on the scale to get the pounds per gallon, or grams per liter. Convert as necessary. (3) Measure the ink with a weight per gallon cup and convert it to pounds per gallon or grams per liter. Squeegee Stroke Length inches cm Ink Unit Weight Lb. per Gallon Grams per Liter Ink Viscosity Thin: Factor = inches or cm Medium: Factor = inches or cm Thick: Factor = inches or cm Units for all numbers must be the same. Ink Viscosity Factor used must be in the same units as the squeegee length and stroke length. Squeegee Squeegee Stoke Ink Viscosity Set-up Ink Volume Length Length Factor (Cubic in. or cm) Ink Unit Total Volume of Ink Weight of Ink Weight In Gallons or Liters Needed (Step 7) ( X ) STEP 9 Calculate Ink Cost (OPTIONAL) Total Volume of Ink Adjusted Total Volume Set-up Ink Volume Needed (Step 5) of Ink Needed (Cubic in. or cm) (Cubic in. or cm) (Cubic in. or cm) Unit Cost of Ink $ Per Quart Per Gallon Per Liter Convert Total Volume of Ink (Step 7) to same Units as Cost of Ink is Expressed + = Unit Cost Converted Total Cost of of Ink Volume of Ink Estimated Ink STEP 7 Convert Ink Volume Converted Total Volume of Ink Units (Using Appropriate Formula Below) Ink Volume in Cubic inches x = US Pints Ink Volume in Cubic inches x = US Quarts Ink Volume in Cubic inches x = US Gallons Ink Volume in Cubic inches x = Liters Ink Volume in Cubic centimeters x = US Pints Ink Volume in Cubic centimeters x = US Quarts Ink Volume in Cubic centimeters x = US Gallons Ink Volume in Cubic centimeters x = Liters CONVERSION FACTORS Length Inch x 2.54 = Centimeters Inch x = Microns Mil x 25.4 = Microns Centimeter x = Inches Microns x = Inches Microns x = Centimeters Volume Cubic inch x = Cubic Centimeters Cubic Centimeter x = Cubic Inches Liter x 1000 = Milliliters Liter x = Gallons Gallon x = Liters Gallon x 4 = Quarts Gallon x 8 = Pints Weight Pound x 16 = Ounces Pound x = Grams Grams x.0022 = Pounds Grams x.0353 = Ounces Visit SGIA at SGIA Journal April