An ounce of prevention, Worth pounds of Quality
Back in the 1980’s Dr. W. Demming became the Guhru for Quality because of his influence on the Japanese manufacturing industry, which enabled them to create superior products at lower costs than we could in the United States. At that time, I worked for a large coated paper mill, and we spend years training our people to pay more attention to measuring quality. Not just the product we put out the door, but in measuring the quality of all the materials going into the coated paper products we made in all our manufacturing locations.
Running your own Quality Control testing program will keep you up-to-date on the changes that are occurring within the raw materials that you use everyday. Monitoring all these materials is a tremendous job, and has to be done on an ongoing basis. If you stop for just a few weeks, and something changes, the process may have to be started all over again. Why? Because when one part of the Printing System is out of specification, chances are adjustments will be made in order to compensate for the “problem,” and before you know it, so many variables have been added that the system is “out of control.”
A quality program involves four major steps:
- Establish where you are. Are you able to match your press sheets to the designated proof with minimal waste? Do you ever have to change ink sequences on press in order to match color? Are you constantly fighting problems during make-ready such as picking, tail-edge piling, or mottle? Are you purchasing your ink from one supplier? Do you stock two or more sets of process ink for different types of jobs? Who mixes your fountain solution? One person, or everyone? Are they accurate?
- Determine where you want to be. Your goal may be to reduce make-ready waste by 10%, or it may be to maintain just one ink supplier. Or you may wish to rid the pressroom of such additives as tack reducers or extenders that may be a cause of inconsistent quality. And maybe you would like to resolve the ongoing dispute between your color department and the pressroom…has the dot gain on-press changed, or are the films wrong?
- Work to set standards with your suppliers. This requires the cooperation of nearly all of the people in your plant, your outside suppliers, and management. In order to gain management’s trust, we have to show them that cost and value are different. They’ll soon see that improved quality will increase profitability.
- Once you have established your new standards, you must run a QC program to check incoming batches of raw materials, monitor your in-house processes, and be able to address potential problems before the job gets to press.
Now, don’t change anything.
At Nancy Plowman Associates, we are continually asked, “What should we be testing in order to improve our quality?” The following is a Quality Control Checklist that our clients must go through to maintain our QC program:
Proofing: We find that a printer just beginning this program may not be aware that the proofing systems that he uses may have different colors (hues) than the inks being run in the pressroom. In order for the press crews to be able to match color, the inks must have the same hue error values as the colors used to produce the proof. Each batch of proofing material and each batch of incoming ink must be checked for hue error at the same density level. When the hue errors of the proof and print are different, the press crews must run their densities out of norm to compensate.
Inks: Here is a list of the tests that we perform on every batch of incoming process ink for our customers:
- Tack – this is an industry-wide measurement of how sticky an ink is, and can be measured on an Inkometer. Here we look at both the tack value of the ink, as well as its tack change over a period of time while on the rollers of the Inkometer.
- Strength and transfer – this test involves printing a controlled wet ink that varies in film thickness from .01 to .06. mils (on paper). Density measurements are done at 10 predetermined film thicknesses. Each batch of ink must print to the same density at each film thickness.
- Paper and ink stability – this test measures the rate at which an ink will set or gel. We can vary the ink and paper combinations in order to determine the compatibility with a customer’s ‘house’ sheet of paper, or to test a newly specified sheet prior to going to press. This test is run with a printed ink film that is 20 times thinner than the ink film that is run on an Inkometer. We simulate a printed sheet progressing through the press, and coming in contact with several offset blankets.
- Gloss – printed ink glosses can be measured on a freshly printed wet sheet, then later on the dry print, to determine any dry-back.
- Wet-ink trapping – in this test, we evaluate both the trapping potential of the ink, as well as the tendency of an ink that is printed first to become dirty with subsequent colors.
- Sutherland Dry Rub – this test is a visual evaluation of the amount of ink that will rub from a test print 24 hours after being printed. It is accomplished by rubbing the print against a white sheet of the same brand of paper using a 4-lb weight on the print for 20 rubbing strokes.
- Transparency – we normally check only the yellow ink for its transparency. A proof print is made to a white coated paper that has a preprinted black solid across the center of the sheet. The transparency of the yellow is determined by the density of the yellow ink film on top of the black solid. We double-check this property by running a wet trap print of the yellow ink over the client’s black ink. We can also check the cleanliness of the yellow after this test.
Here are other precautions that we recommend:
Designate one person in the pressroom to be responsible for the mixing of thefountain solution for each press. Be certain that this person monitors the mixing procedures by using both pH and conductivity.
Determine the type of blanket to be run by having it tested with your inks to check for tack build, and press compatibility. Evaluate your blankets frequently to assure consistency.
Frequently used papers should be routinely checked for picking resistance., setting times, and dry-rub potential. Newly specified papers must be checked for ink-setting speed to avoid possible offsetting and blocking problems.
Once a QC program is put into effect, the variation in raw materials is eliminated. As a result, fewer adjustments have to be made on press. The most important thing to remember now is don’t change anything before thoroughly investigating what affect this change may have on the entire Printing System.