Frequently Asked Questions (Page 2)
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Q. Process Color Ink Tacks & Color Sequence?
Q. Correct Densitometer Readings
Q. Printing Solids and Screens on Envelopes
Q. Buying a Press Out-of-State
Q. Critical Color Match Went Bad
Q.: What is the story on process color ink tacks and color sequences?
A.: Tack has to do with the stickiness of an ink. As an example, there are sheetfed inks that are so stiff they nearly break your ink knife trying to get some out of the can. On the other hand there are other colors that are so runny they barely stay on the ink knife. Both of these inks could have the same "tack."
The difference is in the "body" of the ink and has little to do with the stickiness of the ink, although the two are somewhat related.
To insure proper "trapping" on a multi-color press, most sheetfed process inks are "step tacked." What this means is, that the first color printed must be the highest in tack so that successive colors of wet ink will stick to the colors already printed on the sheet. (An alternative to "step-tacked" process inks is the "unitack" system, more popular in some foreign countries, wherein all colors are the same tack).
Those of you who have overprinted colors on a T-51 color head or other presses using a common offset printing blanket, will better understand the concept of trapping, whereby the overprinting color often needs the addition of some tack reducer to print sharp and clean over the other color.
In this country, the majority of process printing is run in a dark-to-light color sequence, that is, black, cyan, magenta, yellow, so the inks are "step-tacked" for that color sequence. The exception might be for a job where for some reason black needs to go down last, and a special "4th down black" is used.
Other cases might have to do with low grade paper or presses that have mechanical problems where a different sequence is preferred. In these cases we mix and match inks from a different sheetfed process ink series to provide the necessary tack ranges. We might use a high definition process yellow with a tack rating of 16 along with a low tack red or magenta rated at 14, followed with a normal process black rated at 13 and a special low tack process blue or cyan rated at 11 to finish the set.
It is possible to run inks in the incorrect sequence, but you may experience poor trapping which will produce a lot of color variation as the run progresses and the temperature of the press changes, particularly in areas where two or more colors are combined to produce a third color.
Q.: What does the term "chalking" refer to, and what can we do to avoid problems?
A.: "Chalking" is a condition whereby sheetfed ink rubs off the sheet as though it is wet, but in reality the vehicle has drained down into the sheet and dried, leaving the pigment particles sitting on top without anything to bind them there. Chalked ink usually exhibits a dull, lifeless finish due to the fact that most of the varnish is underneath the pigment, deep in the fibers of the paper. Certain blues and reds often chalk when other colors do not.
Chalking is most prevalent on matte sheets, but may occur on nearly any coated paper including cast coateds. Since the problem is caused by the vehicle draining into the sheet before it can set, anything that thins the viscosity of the ink will make things worse. This might be any or all of the following list: tack reducers and solvents added to improve ink setting, using an ink that is too "soft" or flows too easily, using too much heat with hot air or infrared driers, and using too much spray powder.
Anything that might "stiffen" the body of an ink will tend to minimize chalking. Many years ago we added binding varnish to ink that would be run on matte or C1S cover. When cobalt drier was also added there was more of a tendency toward chalking due to the reduction of tack imparted by the oils in the drier. We sometimes used paste drier, with unpredictable results.
Today, the problem seems to be worsening, due to the papers becoming more porous and sheetfed printing inks being formulated for faster setting, thereby crowding the margins of successful printing.
As far as avoiding the problem, we have a four color process set of rub resistant inks manufactured by Superior Ink Co. that virtually eliminates most chalking problems, even on matte sheets. For standard colors we have an additive, Slip-Dri Compound that must be added to the ink at press side. It is comprised of several driers and some high tech wax that assures both drying and slip, thereby eliminating chalking and scuffing in most cases. Most sheetfed metallic inks are very problematic when it comes to chalking, so it is recommended to overprint with varnish to minimize the problem.
I recently collected a weeks’ stack of junk mail and checked many pieces by rubbing the sheet against itself and I was amazed that the vast majority of the pieces scuffed off very easily. Any sheets that appeared to have been varnished didn’t scuff appreciably. Many of the pieces exhibited the well known "carbon paper" setoff transferred by pressure of the cutter blade when sheets with bleeds were trimmed.
Some press sheets from jobs I printed in the early 1970’s rub off in a like manner, so drying is definitely not the problem.
If you get to a large trade show, notice how many of the new sheetfed presses are using single or double coating towers. The really big sheetfed printers coat everything. The first coater puts down a layer of some kind of "primer," as they call it, to seal in everything and prevent ingredients in the gloss coating from reacting with pigments in certain ink colors. An aqueous coating is then applied to provide the gloss and protect the printing.
I hope this answers your questions. Planning ahead still remains the number one way to avoid ending up with a chalked job.
Q.: What’s the story on soy inks, and where can I get them?
A.: In recent years, inks formulated with soy oils have been aggressively promoted by America’s soy bean farmers as the best solution for environmentally safe ink formulating.
While it is true that replacing petroleum distillates with soy oil can provide some tangible benefits, most notably the reduction of VOC’s and the use of a renewable resource material (soy beans) in place of petroleum product, it is also very important to realize that in sheetfed ink formulations, any vegetable oil can provide these same benefits.
Soy beans contain no inherent advantages over any other vegetable oil source. In fact, soy oils can actually compromise the setting and drying properties of a sheetfed ink formulation on coated stocks. Soy oil is a semi-drying oil, which dries much slower and produces a softer film than vegetable oils like linseed oil and tung (Chinawood) oil, which are full drying oils.
When the predominant vegetable oil used in a sheetfed ink is soy oil, many formulators often end up adding other materials to correct the setting and drying characteristics, which add VOC’s and negate the value of using the soy oil in the first place.
Superior Printing Ink has used soy oil plus other vegetable oils in most of their inks for many decades, even before the "environmental" movement came about. Different vegetable oils offer different characteristics, and it is this careful balance that enables them to produce an ink that is both low in VOC’s and high in performance when compared to an ink with only one type of oil.
If your intention is to operate a facility that uses the most environmentally responsible materials, then definitely specify low VOC inks, but there’s no legitimate reason to unnecessarily limit how your supplier formulates them. Also consider carrying the thought further into your pressroom to other more VOC-heavy pressroom materials like press washes, alcohol and fountain solutions, etc.
Q.: What are the correct densitometer readings we should use to make sure our printing matches the proof?
A.: In the sheetfed job work market there are only some guidelines that you might use as a starting point, but there are no actual numbers that will assure success.
Depending on who you ask, the following numbers will often be cited: Yellow, 85-95, or 90-115; Red, 125-135, or 135-145; Blue, 135-145, or 125-135, or 125-150; Black, 160 to 180, or so.
As you can see, there is enough variation to totally mess up most printed jobs, just judging by the percentage of range of the numbers.
The reality is that you must first get the job made ready, then make a decision about how you will be printing it, particularly the density of each color. Then you use the densitometer reading you took off of your own press sheet, and that becomes your target. I ran one job where I had to run the red and blue at a density over 200 to plug the screen enough to match what another printer had previously printed. It looked horrible, but they loved it. In fact, it was a rerun because when we first printed it to a more correct density it looked beautiful, but they didn’t want it that way, so they rejected it.
Another challenge is that presses often print different on different days. I once ran a press proof because our customer didn’t trust the proof the color separator furnished. It looked great, so the next day when I ran the job, using the same cans of ink, the same batch of paper, and the same densities, the job looked like it came off a totally different press! I went by the densities instead of judging the printed photos and matching them. In truth, my proofs were probably a few percent to the left of the furnished proof, and the finished job was probably a few percent to the right of the furnished proof, so either one by itself compared favorably to the furnished proof, just not to each other.
If you’re not running on a four color press, what I would recommend to get you started would be to get a set of color key proofs on your next four color job. By running your first one or two colors, you can then insert your sheet under the remaining colors of the color key to better help you judge what the finished job might look like. Then, get your colors where you decide to run them to come closest to the proof. At that point, you take a densitometer reading and maintain your colors throughout the run. Don’t forget to also stand back a bit occasionally throughout the run and compare your "okay" sheet to what you are running then, because as your press warms up it may begin to print slightly different, possibly necessitating density adjustments to maintain the correct appearance of the job.
Remember: Don’t become fixated on the color bar densities, they’re simply a tool, they trim off anyway. It’s the overall job that your customer will see.
Q.: We seem to be getting a lot of hickeys in solids lately. What can we do to solve this problem? Would a hickey-picker roller help?
A.: Hickey-picker rollers have been used successfully in certain presses for a number of years. The presses that seem to be the most successful are presses equipped with conventional dampeners, due to the fact that the roller is made from a special material that simply moves the offending particles around on the plate and captures some others as well. Because of the fact that these rollers must be thoroughly cleaned daily for best performance, they are normally put in the #1 form position. On a press equipped with an alcohol dampener, where the #1 form roller is also the water form roller, you will most likely experience severe dampening problems because of the specialized finish on a hickey-picker roller. If you install it in the #2 position, it will be buried in the inker and cleaning will be a real project.
Another concern is that a hickey-picker roller cannot act as an inking roller, so it is not unusual to end up with ghosts and patterns in both screens and solids, due also to the fact that you have actually "lost" one of your form rollers.
I have seen ink that contained large particles that caused problems on the press, but, in general, even ink that appears grainy will perform just fine. If you are concerned about your ink, have your ink supplier come to your shop and test the suspicious ink with a grind gauge. All ink will exhibit some particulate matter; it is only when the particles are over a certain size that hickeys begin to show up on the printed sheet.
The most reliable way to eliminate or minimize hickeys is to always keep your rollers squeaky clean. When offset printing rollers are new they have a smooth, velvety tacky surface. As they become glazed and worn this tack goes away or is simply buried under a layer of glaze. A cuff of dried ink grows on the ends of the rollers as well.
If you are running simple jobs, small particles of dried ink from the cuff break off and cruise around in your inker. You may see a hickey or two and not become too concerned. Many of these particles will wash off and end up in your ink tray. Some will cling to hard ink rollers where they will remain until removed forcibly with some sort of scraper that could damage the surface of the roller.
The other 99% of potential hickeys will remain as roller cuffs waiting for you to run a large solid on coated stock. The oscillators work on the roller cuffs and pieces continue to break off and move from the ends of the rollers inward where they show up in abundance near the outside edges of the plate.
All forms of deglazing will leave these cuffs right where they are, so it is recommended to remove all rollers from the press at least quarterly and clean the cuffs off and manually deglaze the roller surfaces. As you reinstall the rollers, check each pressure stripe and readjust as necessary.
With the cuffs gone and the velvety finish restored to the roller surface, any problem with hickeys will be dramatically improved. I remember going for months at a time without seeing even a single hickey after performing this thorough cleaning ritual. Don’t forget any bars or shafts in the inker area that might tend to accumulate dirt. A thorough cleaning followed by a light coating of grease will minimize problems in that area.
Q.: How can I find out how fast I can expect to run each of my presses?
A.: The speed you can expect to run any given press depends on many, many things. For instance, an old, worn-out press might not be capable of running at top speeds without damaging itself or ruining the job you’re printing. Certain presses over the years were rated at speeds much higher than they could ever actually run and produce salable work.
Most of the modern presses out there today will, in fact, produce top quality work at their highest speed, with an operator that is experienced at running fast.
In general, most presses have a certain speed where they perform the best, and this speed may vary on different kinds of work, depending on coverage, etc. Very few presses perform very well at their slowest speed, due in part to the fountain solution drying up on the surface of the plate and causing problems with proper balance and color control.
To determine the best speed for a particular job, start out running in the 6,000 - 7,000 iph range and adjust up or down from there. Obviously, a run of 250 doesn’t require a great deal of speed to finish, whereas, you can afford to invest a bit of time adjusting feeder, delivery, etc., to gain another notch or two of speed on a longer run. Common sense will normally dictate the best speed in the long run.
If you think you’re running too slow on everything, and your competitors are "eating your lunch" on larger jobs, ask your press service man for advice, or talk to other printers who own the same model of press about their experience. Manufacturers’ ratings are seldom to be relied on, they tend to be either overly cautious or overly optimistic in most cases.
Q.: We’re getting so much foam in the recirculating system for our fountain solution that the tank runs over if we don’t watch it and turn off the pump occasionally to let it settle down. What can we do to prevent this?
A.: The quickest fix is to buy a gallon of our Anti-Foam fountain solution additive and add some to your fountain solution.
The reason this is happening is because most modern pumps have a second pipe on the pump that is normally connected to the return line from the water tray in the press to suck the extra fountain solution back into the tank. Most pumps are set up for a maximum pumping effort as in the case of a large press where a lot of water is usually moved back and forth. A lot of air is sucked back into the tank along with the extra fountain solution. There are several different impellers available for most pumps to provide the correct volume for a particular press, or you can often install a valve into the return line to cut down on the flow of excess air. If your press is set up with a gravity flow back into the tank, be sure the vacuum port on the pump is capped off, because you won’t need it, and it will suck in a lot of air.
If you are not getting any excessive air flow and the foaming is still troublesome, try to find a smaller impeller for the pump, because the foam may be caused by cavitation, whereby the fountain solution is simply being swirled so fast that a mechanical foam is being generated.
When the hot weather comes, you will come to like your recirculating system even more. If you bought the one with a refrigerator, you can cool the water to minimize toning all year around, and you’ll really appreciate it during the summer months when the really hot days can cause some trouble. If you don’t have the refrigeration system, you can throw in baggies of ice to cool things down during the hottest days.
Q.: We have been getting a lot of ink slime floating on top of the fountain solution in our recirculating tanks. What’s going on?
A.: This is a natural occurrence as ink particles and droplets of oil or solvent find their way into the tank. We sell a product called Ink Grabber that is put into the tank to float on top where it can soak up any oily residues until it is dirty, at which time it is simply discarded.
Q.: We’re having a lot of trouble printing screens and solids on envelopes, and it also seems to be very difficult to control certain colors as well. We use the same press to run the letterheads and business cards, with no problems, what’s wrong?
A.: I suspect you’re using a different offset printing blanket for the envelopes. Perhaps one of those famous "envelope blankets" I see in some shops. The one that is so old and glazed that the rubber will actually crack if you bend it too far.
This might seem like a good way to save money, but I don’t believe it saves anything. Back when I was first in the trade, back in the 60’s, an old timer showed me a trick to keep from smashing the blanket, and giving you better quality at the same time. He backed off the impression pressure as though he was going to run cardboard, then he put 2 layers of masking tape on the impression cylinder, in the image area only. By bringing up the impression pressure until everything printed properly, he was able to print fine screens, halftones and delicate colors right over flaps with absolutely no telltale streak. And, since the masking tape is softer than the blanket, it smashes down to accommodate the varying layers of the envelope.
I remember one particularly problematic 6x9 catalogue I had to print; it had graduated screens in green and process blue, coming from opposite ends and covering most of the envelope. We had found a roll of 4" wide masking tape, so we just taped up the cylinder, stopping at about a quarter of an inch from the tail. After running a few envelopes we had a small slur near the tail, which was air trying to escape. By running the envelopes through blank we saw that the air was ironed out and the slur went away. So, we ran the black run first on another press then finished the two screens without any further events.
Another difficult job called for us to print a duotone over the flap on a deckle edge baronial envelope. This duotone was a bit tricky, too. The printer we were printing it for sent the film, with the brown being 150 line and the black being 300 line, to match an invitation and annual report they were printing. We finally put on 3 layers of masking tape and tweaked the pressure a bit and ran the job, and it virtually matched the sample of the invitation they had printed on their Miehle!
This is still how I print envelopes. Give it a try…what have you got to lose?
Q.: We found a good used 4-color press out of state. We are getting a really good deal on it, but I don’t know how to avoid problems if something goes wrong during the move.
This can be a very difficult situation. I personally bought and paid for several "handyman special" folders. When they arrived one of them wasn’t even the same machine, and was all apart in boxes. The other one was missing a lot of parts. Since I had paid up front, there was nothing I could do.
If it’s a small machine, I would recommend taking it with you in a rental truck or whatever, or otherwise, in the case of a larger machine, be on site when it is being taken out and loaded onto a truck that you have hired. If you see anything suspicious you can just walk away from the deal.
If there is a local dealer where the machine is located, see if he is reputable and whether or not he will take care of the logistics for a reasonable fee.
As far as paying for the machine, I believe funds can be set aside at either your bank or the seller’s bank, to be released upon delivery or acceptance of the machine.
I once bought a press from a large eastern equipment dealer. He shipped the machine with a 10% down payment, to a local warehouse, which was "bonded." This bond somehow assured the seller that the machine wouldn’t be released without payment, and the truck didn’t have to hang around waiting for me to drive to my bank and wait for somebody to get back from lunch to sign the cashier’s check. The down payment would have paid for the return trip if I didn’t come up with the money.
Another possibility would be to contact a dealer you do business with on a regular basis and have him contact the party who owns the machine. Often-times he can negotiate a better purchase price than you can, and any commission you might pay him could be thought of as "cheap insurance." Also, he may be able to find out something about the machine through another dealer he might know.
For those of you who are not very adventurous, the safest way to buy used machinery is to contact a dealer you trust and have done business with and tell him what you are looking for. Then it’s up to him to find a good unit, then sell it to you either "reconditioned," "rebuilt," "up and running on your floor," or whatever else you both agree on. And, if a lawsuit breaks out over something, local is better in most cases.
Another area of concern is insurance. Most truck lines will only pay you 10¢ per pound for proven damages. This probably wouldn’t even pay for an estimate of repairs. You should contact your own insurance agent and buy some insurance to cover the entire transportation portion of the affair until the machine is sitting level on your own floor.
A side note here is to be aware that some well known machines may have originally been manufactured for delivery to some foreign country where the electrical or safety requirements are quite different. Rewiring or replacing motors and controls or addition of safety guarding can add up rather quickly.
Q.: We’re looking at a new press and can’t decide what size to buy. Everybody we ask tells us something different. Any ideas?
A.: Yes, buy a 54 x 78" 12 color press and you’ll have the largest one available so the decision is really a no-brainer.
Seriously, though, no matter what press you end up buying you’ll sooner or later need it to be the next size up. When I had a shop we had a bunch of 10 x 15" Multis. The image size was 10 x 13¼", so we were always running into a problem with 8½ x 14" carbonless. When we bought an A. B. Dick 360 we ran lots of 11½ x 17½" through it, and luckily we had the new style that would take an 11¾" sheet so we could move a little sideways in case we needed to bleed off of one side. One job trimmed to 18½" so we managed to skip feed and get a 19" sheet through. I don’t know haw many of you realize this, but the A. B. Dick 375 was made two inches wider to accommodate the 11¾" sheet trim width common in Europe. Then the A. B. Dick 9800 was made longer to accommodate the 11 x 17" bleeds we like in this country.
Eventually we bought a Harris 23 x 29" press. Worked great until the time we needed to run 30½" index. We cut the sheets in half and it turned into 100,000 impressions. The Harris 22 always got into trouble with 23" paper, but by removing the opposite side guide we got it through. The Harris 36 took a 25½ x 36½" sheet, so we often ran full sheets of 25½ index and 25 x 38" parent sheets. We removed the pin that stopped the feeder from going back to 26", and tried to portrait feed some 26 x 20" sheets to get gripper room, but the electronic sheet detector got confused by the length of the sheet and kept shutting the feeder down.
Back when I was running a 42 x 58" Harris, they were going to run the New Mexico State maps on some 44 x 60" stock, because even though everybody had been calling the machine "A 2-color Sixty," it was in reality a 58" machine, so they wound up reducing the size slightly to run 4-up on a 37½ x 57½" sheet. That quarter inch of plate on each side was a constant problem with scumming because the water form probably needed to be a bit longer to provide some margin; 38 x 50" sheets ran very easily.
I was talking to a pressman who had worked in a large shop in the East and he said it was a constant problem with somebody wanting to run 80" sheets through their 78" 6-color.
So, you can see, the battle never stops. At one time their was talk of a 119" wide press, but then, why not 120"?
The actual answer to the very serious question is, buy the largest press you think you can afford, keeping in mind your present workflow and whatever growth you are currently interested in. If you’re simply interested in streamlining your present operation, then perhaps a true 2-color will replace or supplement that T-head machine, or a 4-color will assist that 2-color.
Don’t let the machine dealer push you farther than you feel comfortable; the auction notices over the years have been full of shops that tried to go too far all at once.
Q.: We recently printed a job in a dark brown ink with heavy coverage. We had the ink matched by our normal ink supplier and finally got it to match on the third try. Then the customer rejected the job because they claim the color doesn’t match the furnished sample. We had numerous people look at both the original sample and sheets we ran and everybody agrees that the color matches perfectly. Our ink supplier blamed the color, saying it was "meta-something." What is going on?
A.: Metamerism is probably what your ink supplier was referring to. Metamerism is the effect whereby a printing ink color that might match the sample exactly under the 5000 Kelvin lights at the ink company, or in a color viewing booth, will look considerably different under the ordinary fluorescent lights in your customer’s office.
This is why many printers insist that their customers approve jobs on the press, and sign a press sheet at the beginning of the run. Then when a sample ends up not matching under his office lights, you have the proof that it is, indeed, the effect of Metamerism.
Certain colors are more Metameric than others. If your office is lit with warm white bulbs, some of the yellow will appear to be missing. Likewise, a color matched under cool white bulbs will appear totally different under daylight bulbs.
To understand why colors are metameric, you must first realize that although many different brands of rubine red, for instance, all look basically the same, they might each be made from different pigments. This is because there are many, many sources for pigments used in sheetfed printing ink. Two different pigments might come from totally different sources, and both look like rubine red under correct lighting. But under other lighting, certain undertones may emerge to distort our color perception. This is an entire science better left to the experts.
Graphic Arts Technical Foundation produces what is known as a "GATF/RHEM Light Indicator." The copy I saw was a small sticky backed label printed with five color blocks. Under the standard 5000 Kelvin lighting it appears as a single solid color. Under other lights it appears as five different colored blocks. These won’t help you to match colors, but they will prove to your customer that light sources really do affect color perception. You can contact GATF at 412-621-6941, or try their website at http://www.gatf.lm.com. This is also the source for various color bars.
Another problem that crops up occasionally is known as "Bronzing," whereby the color looks great while the ink is still wet, but after it dries it has a yellowish cast that can normally only be seen from an angle. Rubbing the surface of the dried ink with a finger disturbs this coating and the color appears normal.
Jobs that have become bronzed can often be saved by overprinting with varnish or transparent white. This has the effect of burying the yellow cast and bringing back the true color. Some pressmen report that if you know a particular job will have a tendency to bronze, the addition of from five to ten percent of overprint varnish to the ink will prevent the bronze look.
Q.: How long should a blanket last? We have a Hamada 2-color, an A. B. Dick and 2-color Heidelberg.
A.: Blanket life span will vary dramatically, dependent on many, many variables. "Conventional" blankets, also called "non-compressible," are seldom used in this country, and are very easily destroyed by even the smallest of paper jams.
A cheap, "built-to-fit-a-price" style offset printing blanket won’t generally last very long. These printing blankets normally have a skimpy compressible layer that is easily smashed. (While there is actually no such thing as a "semi-compressible," this style blanket comes close).
The old cast-surface offset printing blankets are also somewhat susceptible to smashes and wouldn’t normally be expected to last very long.
Amongst the modern, ground-finish offset printing blankets, there are many different price ranges as well as many different qualities, so price might not reflect anything more than what a manufacturer expects you to pay for his product.
Compressible offset blankets are constructed with varying degrees of compressibility. For instance, our Day 9600 blanket is a very hard compressible blanket, intended for larger presses and coated papers, where the finest of screen dots are intended to be printed. A Day 3000 compressible blanket is somewhat softer and gives the best ink transfer on a large variety of papers and presses. The Day 9500 is a very soft compressible blanket, very forgiving of smashes and lasts and lasts, through smashes that would destroy most blankets. With a powerful microscope you might be able to see a difference in quality between the printing done with any two of the above named blankets.
Let me say here that I put a Day 9500 blanket on our old 360, around 4 years ago, and it still runs screens and solids with no sign of the many smashes it has endured. I realize that 4 years is absolutely ridiculous as a life span for an offset printing blanket in the real world, but I’ve left the thing on just to see what would happen. I would guess it has around 400,000 impressions on it by now, including 30,000 #10 envelopes, 5,000 9 x 12 envelopes, many thousands of sheets of 11 x 17 bond used for this newsletter, thousands of sheets of 8-1/2 x 11, and lots of sheets of 10 pt. coated cover used to test new sheetfed printing inks and fountain solutions.
Back to the original question, you will get the best offset printing blanket mileage by carefully setting and monitoring cylinder pressures. Don’t let offset printing blanket color influence your decision. I once used a green printing blanket that was just horrible, so I still have a suppressed stigma against green blankets, even though I know better. The Day 9500 printing blanket is a "pretty pink," so us "macho" guys shouldn’t let the color enter into our decisions when evaluating performance.
Q.: What actually causes toning and how do we get rid of it?
A.: There are many causes of toning, so we’ll just cover the most insidious one here. Don’t confuse toning with scumming, which is a shortfall of water on the surface of the plate, usually caused by improperly adjusted water rollers or simply running out of water.
Today’s most common toning is usually made up of bars that run across the cylinder, as opposed to a tint that occurs only on one side of the press.
For purposes of this discussion we’ll assume that your offset printing rollers are not so old to have turned to stone and that they are correctly adjusted both to the oscillators or distributors and to the plate.
When offset printing rollers are manufactured, the material is applied to the steel roller core then cooked in some sort of oven or autoclave to cure the rubber material. The roller at that point is not even close to being round, so it must be ground and polished to bring it to its final size. The grinding produces a somewhat rough finish consisting of hills and valleys, and the polishing slightly flattens the tops of the hills while the valleys remain as shown in Figure 1.
These valleys fill up with ink and help it to transfer from the ink fountain to the plate. It has been said that if a perfectly smooth printing press roller could be made, it wouldn’t transfer ink efficiently enough to print with because it would have an extreme tendency toward skidding and would build up a lot of heat.
As the roller is inked up and washed up, certain contaminants begin to build up in the valleys of the roller, as depicted in Figure 2. If proper cleaning procedures are followed, this condition may remain for a long period of time. With today’s papers, though, that is not likely to happen.
When the valleys fill up, the ink has nowhere to go, and nothing to hang on to, so you are forced to run too much ink to attain color density, and because the ink has nothing to grab hold of, the roller will have a tendency to skid. A skidding printing press roller acts like a squeegee, scraping ink and water across the plate. The effects of other rollers in the ink train often produce the "gear streaks" we often see on a press with contaminated rollers.
We use the word "contaminated," as opposed to "glazed," because problems often begin to show up long before true glaze is able to form. The old fashioned glaze a lot of us remember was actually shiny, and we had a lot of problems with it back in the old days, but we had simple ways to remove it. The rubber compounds were much different back then, back before MSDS requirements brought about changes that wouldn’t permit the harsh cleaners we used to use.
In summary, skidding offset printing press rollers are the normal culprit of common toning, so by keeping them "squeaky clean," and properly adjusted, most problems will be avoided.
Incidentally, one more cause of toning is often the oscillator that hangs under the bottom ink form roller on many small presses; it is normally friction-driven by the form roller, so if it is in need of lubrication or your ink is too thin, the ink form roller will skid and cause uncontrollable toning that some will have a difficulty diagnosing. Drop the oscillator away and the toning will go away if this is the cause.
Q.: We’re having a lot of trouble with the paper drill we recently bought. We keep breaking bits or burning the paper and the guy we bought it from says that’s normal.
A.: Maybe you bought it from the wrong dealer.
There are a few things to know about paper drill bits to avoid these problems. The very first things to know are that you can’t properly drill with a dull paper drill bit or one that isn’t properly adjusted for depth. The next thing to know is that you must provide some sort of lubrication both to the outside and inside of the hollow bit. This is easily accomplished by the application of a small amount of "Drill Ease" before starting, periodically during the drilling operation and when the job is completed.
Paper has a small amount of moisture in it, and when the bit warms up from friction against the paper, this moisture may actually boil and end up on the inside of the hollow paper drill bit and cause a slight film of rust to form. This rust then has a tendency to cause the paper chips to stick inside. If the chips don’t move freely through the drill bit, additional pressure is normally applied, causing the drill bit to heat up even more, with paper drill bit breakage being the end result.
A slight touch to the bottom of the drill bit with the Drill Ease stick will cause a bit of the lubricant to adhere to the chips already in the drill bit and lubricate the inside of the hollow bit as the next chips push their way through. A tiny amount of Drill Ease should also be applied to the outside of the paper drill bit to keep heat and burning down to a minimum. Some folks use paraffin wax, but binderies that do a lot of drilling tell me the Drill Ease does a far superior job, and their paper drill bits stay sharp longer, plus they virtually never have any burning.
Small diameter paper drill bits are also to be avoided if at all possible. Some of your customers may request 1/8" holes in cover stock. This can be done; however, I don’t remember ever doing it easily or without breaking drill bits. This size of paper drill bit is normally only intended to drill through less than a half inch of paper at a time, if you’re lucky.
The smallest size recommended is normally 5/32", and 3/16" is even better. The reason for this is that the paper chips must scrunch down small enough to pass through the hollow paper drill bit, and even with correct lubrication this is a real challenge, particularly with cover stock.
I hope this helps you out. We also sell Teflon coated paper drill bits for some of the more popular paper drills. Drill operators tell me that they also lubricate these, although not as often as the steel bits.
Drill blocks should also be changed when they become full of burned drill holes. We sell these by the dozen for most of the popular paper drills, and they go a long way toward producing clean holes through the bottom sheets of each lift of paper.
Q.: We are having a terrible time getting sheets to land in the press delivery and jog properly. The loads look like a haystack and we have to run the press slower than normal.
A.: I have been seeing a lot of this lately. I suspect that because of the wet weather followed by dry, hot spells, your paper doesn’t have much of a chance to acclimate to the environment in the pressroom. Presses hate paper that is different than the current humidity and temperature in the pressroom, and static is often generated during the printing process.
In some cases it is a simple matter of sheet curl often found in sheets that came from near the center of the mill roll, or waviness due to a higher humidity in the pressroom than the paper contains within the sheet.
Either way, the use of paper wedges will often minimize or at least lessen jogging problems in most presses. When I was first running the big presses, an old timer showed me how to place wedges under the 4 corners of the sheet in the press delivery, plus another, larger wedge in the center of the sheet in front of the back jogger. He pointed out that the use of wedges did several things. First, it kept sheets from sneaking under the joggers at the beginning of a load, while at the same time causing newly delivered sheets, which normally have a slight downcurl, to land corners first on the load, thereby allowing the sheet settle on a cushion of trapped air. This also has the effect of giving the sheet a little longer exposure to the air to assist in the initial setting of ink.
The main thing to remember is that it is much easier for the jogger wings to push a sheet downhill than uphill, so jogging is normally more consistent.
Believe it or not, I even use a couple of small wedges when running our old A. B. Dick 360 to print the red on the masthead for our newsletter, "Star Bulletin." It enables me to run about 20% faster than normal and the jogging, such as it is, is somewhat better. I seldom use any wedges on sheets smaller than 8½ x 11 because they’re too small to benefit.
In addition, a piece of a broomstick can be stuck at the bottom of your load, from front to back, off center a little, to break a tail curl that might be affecting accurate jogging on thin sheets.
Looking at the feeder end of stream-fed presses, I always put a wedge under both leading edge corners so the sheet doesn’t stumble and curl under. If the sheet has a down curl toward the tail of the load, I also put a couple of wedges under the rear corners as well to break that curl and assist in feeding.
I also use 4 wedges, one under each corner, in pile-fed folding machines. This also has the effect of preventing the front edge from stumbling on the feed board and causes a pocket of air to be trapped in the top 10 to 20 sheets to provide better separation and avoid doubles.
I used to make wedges out of wood, but splinters and a few close calls with my table saw helped me decide to just buy the plastic ones and avoid the problems.
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