REACTING WHEN IT COUNTS FOR IMMEDIATE IMPACT!
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Contact usBlinding : Part or all of image on plate does not take ink.
| MECHANICAL | |
| Causes | Remedies |
|---|---|
| Excessive amount of lint being deposited on plate. | Refer to LINTING section in this guide |
| Excessive plate-to-blanket pressure causing platewear | Re-set to specifications. Use packing gauge to check pressure. |
| Improperly set ink and dampening form rollers. | Rollers could be too hard – check durometer. Also check setting and re-set if too much pressure exists. |
| Abrasive particles destroying image. | Check ink grind, fountain solution, solvents, etc. Replace all contaminated material. |
| CHEMICAL | |
| Causes | Remedies |
|---|---|
| Too much acid in the fountain solution. | Check pH/conductivity and reduce acid to proper amount |
| Too much gum in fountain solution. | Re-etch plate and rub-up image areas with press ink. Drain fountain solution and refill with tap water. If image returns, replace tap water with fountain solution containing less gum |
| Plate cleaners and/or scratch removers have dried on plate image. | Always rinse plate thoroughly and immediately after using such items. |
| Detergent or solvent remains on rollers or has entered the dampening solution. | Wash inking unit thoroughly with good water-miscible wash, with water as the last step. Uni OD Deglazer should also be used as directed as part of your regular roller maintenance. Drain and thoroughly clean and flush dampening system with Uni Power Flush as directed and re-charge system with fresh dampening solution. |
| Ink will not adhere to image area due to excess amount of fountain solution being accepted by the ink. | Reduce dampening setting to minimum. If problem persists, consult ink manufacturer |
| Plate not completely developed. | Plate was improperly developed with gum remaining on image areas – wash plate. If problem persists, have plate re-made. |
| Calcium build-up on the plate. | Clean the plate with Uni Scratch Remover as directed on the label. Decalcify the rollers with Uni OD Deglazer and assure that you are using an ink formulated to combat this. Talk to your supplier. |
Chalking/Powdering : Ink is dry but rubs off easily under a little pressure.
| Causes | Remedies |
|---|---|
| Insufficient binder in ink. | Add good drying, high-viscosity binder. |
| Vehicle is too low in viscosity. | Add good drying, high-viscosity binder. |
| Stock is too porous for ink. | Add good drying, high-viscosity binder. |
Ink dries too slowly
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| Ink not formulated properly for substrate being printed on. | Consult your ink manufacturer. Addition of driers to ink or fountain solution may help. |
| Causes | Remedies |
|---|---|
| Contamination from paper. | Run with more dampening on the plate to avoid feedback. Drain and re-charge circulation system with fresh solution when conductivity gets out of workable range (most common with offset stocks). |
| Contamination from ink train – solvent left in rollers or ink breaking down | Wash rollers thoroughly, using water as final step, and allow press to idle for a couple of minutes. Assure good ink/water balance and proper roller settings to avoid ink breakdown. |
Dot gain : The halftone dots increase in size, causing the printed signature to lack sharpness
| Causes | Remedies |
|---|---|
| Blankets packed incorrectly. | Check with a packing gauge. Compressible blankets require about .006” (.15mm) between plate/blanket and blanket/paper to obtain optimal print. Assure that back pressure is set properly. |
| Plate imaging incorrect. | Check exposure element on the plate to assure imaging is correct. |
| Improperly set rollers and pressures. | Reset rollers and pressures. |
| Rollers or blankets too soft. | Condition or replace rollers or blankets. |
| Ink is too long in body or too low in tack. | Reformulate ink following recommended guidelines |
| Ink is too receptive to water. | Reformulate ink following recommended guidelines. |
| Piling. | Consult PILING section. |
| Poor plate exposure or processing. | Desensitize or re-make plate. |
| Dirty dampening system. | Drain tank and re-fill with fresh fountain solution. |
Drying too slow : Ink remains tacky during press delivery and bindery operations, resulting in set-off, marking or blocking.
| Causes | Remedies |
|---|---|
| pH/conductivity of fountain solution incorrect. | Drain circulation tank and make a fresh mix with correct amounts of etch and alcohol/ alcohol substitutes. |
| Stock has too high of a moisture content. | Substitute stock with one that has a correct moisture content. Allow stock to acclimatize. |
| Too much ink needed on sheet to obtain colour. | Use a higher pigmented ink or consider a UCR separation. |
| Wrong ink being used for substrate being printed on. | Check with manufacturer for correct ink. Inks with high vegetable oil content never dry hard. |
| Dryer temperature too low for speed of web. Insufficient solvent being released from ink film. | Increase dryer temperature to specification level. |
| Ink film thickness excessive. | Run less ink or consult ink manufacturer to increase strengths for this purpose. |
| Inadequate evacuation of solvent vapours clinging to web as it leaves dryer. | Increase velocity of air in air-knife scavenger at dryer exit. |
| Chill system not working properly – ink resins are not setting hard enough. | Lower chill-roll temperature. (Caution: Watch for chill-roll condensation.) |
| Ink takes on too much water. | Consult ink manufacturer for proper adjustment. |
| Plate dampening is uneven. | Keep dampeners clean and free from accumulated dirt. Prevent drafts, check windows, vents and forced-air systems. |
| Ink film is only surface-dried in oven and still wet underneath. After chilling, ink solvent will work its way towards surface causing set-off. Most likely to occur with heavier-than-normal ink film thickness or very non-absorbent stocks. | Reduce speed of press. Adjust oven temperature. |
| Ink films do not dry at normal dryer temperatures | Consult ink manufacturer for inks that dry at lower temperatures. |
Emulsification : The process by which one material becomes suspended in another – water emulsifies into ink, and ink emulsifies into water.
| Causes | Remedies |
|---|---|
| Poor ink/water balance. | Start with minimum amounts of ink and water to obtain desired colour. Check front edge of the plate for even scum line |
| Poor compatibility between ink and fountain solution. | Ink too soft or too tacky, not allowing controlled emulsion. Consult your ink manufacturer |
| Causes | Remedies |
|---|---|
| This is caused by many different things including ink residue left in the rollers, gum and residue chemistry picked up from the plates, calcium, etc. picked up from the surface of stock, by-products from the fountain solution, and so on. | The best way to combat this is with regular treatment (recommended weekly) of the rollers with a good deglazer such as Uni OD Deglazer. Assure that the form rollers are shimmed or locked properly to prevent sideways movement. |
Gloss and chemical ghosting : The printed image from the first side of a printed sheet can be seen in reverse on the second side printed.
| Causes | Remedies |
|---|---|
| Oxidizing ink. | Run heavier ink coverage side first. This avoids lighter coverage burning into facing, unprinted surface. |
| Ink drying too quickly. | Avoid the addition of drying accelerants to inks and fountain solution. |
Hickeys : Doughnut-shaped or irregularly-shaped white spots surrounding a small spot of ink.
| Causes | Remedies |
|---|---|
| Dried ink particles. | Keep ink rollers free of dried ink. Assure that impression and transfer cylinders are kept clean. Replace transfer cylinder coverings when needed. Avoid dried ink skin when removing ink from cans or kits. Protect ink remaining in a can or kit from oxidation drying and formation of ink skin by applying a sheet of paper or plastic on top of it. Clean the press thoroughly and remove all dried ink in the fountain or on the rollers before inking up the press. Prevent the ink in the ink fountain from mixing with dried ink around the ink fountain edges. Prevent ink from caking on the ends of rollers by lubrication and manual washing. Use a hickey-picker roller. This will pick up hickeys that are passed on to the plate. Remove the hickey-picker rollers and clean them thoroughly as needed. |
| Flakes on inking rollers. | Recondition the rollers and drums. Replace if necessary |
| Glazed rollers. | Use Uni OD Deglazer as directed. Or, remove the form rollers and alternately scrub the form rollers and the drums with pumice powder and ink solvent to remove the glaze. This is a temporary measure only. (See ROLLER CARE AND MAINTENANCE Section in latest Unigraph Maintenance Program booklet.) |
| Disintegration of dampener roller sleeves or rollers due to wear. | Replace suspect roller sleeves or rollers with new ones. |
| Foreign particles (i.e. dirt) from ceiling have fallen into press. | Vacuum the ceiling and everything overhead where dirt can accumulate. Paint the ceiling if necessary, or hang plastic sheeting over the press to catch the falling particles. Use a hickey-picker roller. This will pick up hickeys that are passed on to the plate. Remove the leather-covered rollers and clean them thoroughly as needed. |
| Loose paper dust on web or sheet. | Install vacuum sheet cleaner. Consult paper manufacturer. |
| Stock dirty due to paper dust from slitter or cutter. | Install sheet cleaner. Use impression on extra printing unit, if available, to dust the stock. Use Vario or Delta dampening, if available, to prevent hickeys. Treat edges of pile or roll with glycerine to prevent hickeys. |
Inconsistent color reproduction : Proof and printed sheet do not match. (Tonal variations when proof and printed sheet are compared).
| Causes | Remedies |
|---|---|
| Dot gains too high/low. | Check DOT GAIN section of this guide. |
| Colour on proof too strong (saturation). | Ink weight profile to be applied to proofer. |
| Proofing paper different from stock being printed on. | Change to qualified proofing paper. Apply paper white compensation to proofer output. |
| Print characteristic curve of the proof different from the press. Wrong ICC profile being applied. | Fingerprint the press to desired dot gain curve and determine the colour space it is able to print within. Create an ICC profile from the IT8 or ECI chart of the test form and apply it to the proof. Talk to Unigraph International for more information and assistance. |
| Insufficient ink film being run | Assure that you are using an ink that will allow you to run a normal ink film thickness on your rollers at realistic density standards. |
Ink/Water balance : Frequent adjustments required on press to maintain print quality.
| Causes | Remedies |
|---|---|
| Excessive or insufficient dampening solution being run. | Reduce or increase dampener settings. |
| Fountain solution too weak or improperly mixed. | Check pH/conductivity and adjust accordingly |
| Improper ink fountain settings. | Adjust the amount of ink at fountain. Allow adequate time for adjustment to take full effect. |
| Weak ink – i.e. low colour strength. | Consult ink manufacturer for proper adjustment. |
| Ink taking up too much water. | Consult ink manufacturer. |
| Poor inking and/or dampening roller settings. | Check and reset rollers to manufacturer’s specs. |
| Small window to work in – either running dry or washing out. This is caused by contamination in the ink train or fountain solution or both. | Wash rollers and treat with Uni OD Deglazer as directed. Clean and flush dampening system with Uni Power Flush. |
Linting : Pulling of fibres on uncoated stocks (See also the PICKING section of this guide).
| Causes | Remedies |
|---|---|
| Ink too tacky for stock being run. | Reduce tack of ink. |
| Dirty stock with poor pick resistance. | Install sheet cleaner. Use impression on extra printing unit, if available, to dust the stock. Change to different stock. |
| Impression set too high for ink/stock combination. | Reduce impression. |
| Running improper ink/water balance. | Adjust ink/water balance. |
| Blanket too tacky. | Treat blanket surface to reduce tack. Change to less tacky quick-release blanket. Also, check blanket wash solvent. |
| Blanket packed incorrectly, pulling at the surface of the stock. | Check manufacturer’s specs for correct cylinder rolling. Over-packing or underpacking will change surface speeds. |
| Too little water reaching paper. | Increase dampener setting for better performance. |
| Insufficient ink on rollers. | Reduce ink strength and increase ink flow across rollers to maintain ink density. |
Mechanical ghosting : Repeat of image patterns in solids.
| Causes | Remedies |
|---|---|
| Too much water on the plate. | Cut dampening to minimum possible. |
| Glazed or hard ink form rollers. | Check durometer of rollers – should be under 35 (25 to 30 is optimum). Deglaze rollers with Uni OD Deglazer. |
| Ink not being transferred properly through ink train to the plate. | Check roller settings and adjust to manufacturer’s specs. |
| Ink too transparent | Add small amount of silver or opaque white to ink. Ask ink manufacturer for more opaque ink. |
| Poor layout of form | Change layout to allow for better ink recovery to the rollers in the area of ghosting. |
| Poor distribution of ink. | Assure that ink train distributor rollers are set to full oscillation. Allow ink form rollers #2 and #3 to oscillate to help break up ghost. Do not let #4 oscillate, as this will likely cause more problems. |
Multicolor ink trapping (wet, multicolor printing) : Cannot achieve good colour balance or overall appearance.
| Causes | Remedies |
|---|---|
| Too much tack in relation to preceding ink. | Consult ink manufacturer. Reduce tack of the ink that is not trapping properly. |
| Unequal press stability of inks. Ink tacks up quicker than preceding ink. | Consult ink manufacturer to adjust stability to be in line with previous colour or colours. |
| Ink strength not balanced properly. | Consult ink manufacturer. |
| Poor ink-water balance. | Too much water and/or ink will create poor trapping. Establish good ink/water balance. Tack-graded inks may also be considered for better trapping. |
| Poor ink release from blanket. | Use quicker-release blanket. Consult blanket and/or ink manufacturer. |
| Colour sequence incorrect. | Lighter ink coverage should be printed first. Switching cyan-magenta sequence is sometimes necessary. |
Picking : Lifting of the coating from coated stocks onto blankets, plates or rollers.
| Causes | Remedies |
|---|---|
| Paper surface trash, coating dust, slitter or trimmer dust. | Make tape pulls from blankets. Consult paper manufacturer. |
| Base stock picks. | If serious, reject paper. Change to more lint-resistant or pick-resistant stock. |
| Pressure set too high for ink/stock combination being used. | Reduce impression pressure. Re-pack to manufacturer’s specs. |
| Blanket too tacky | Use blanket hardener. Change to less tacky, quicker-release blanket. |
| Ink too tacky. | Reduce tack of ink. Consult ink manufacturer. |
Picture framing : Ink accumulates on the blanket outside the dimensions of the sheet often to the point where it begins to spit onto other parts of the press.
| Causes | Remedies |
|---|---|
| Plate exposure or processing incorrect. | Use deletion fluid or hone small area of the plate where picture framing is occurring. If this area then stays clean, plate exposure or processing needs to be altered. Consult your plate supplier. |
| Poor form roller settings. | Check rollers and re-set to manufacturer’s specs |
| Form rollers oscillating on the plate. | Lock or shim rollers so that they do not move sideways. |
| Fountain solution not keeping background of the plate clean. | Check the pH and conductivity, flush and clean the circulation system and mix new fountain solution. Assure that proper amount of alcohol or alcohol substitute is being used. |
| Hickey removal system (Vario or Delta) being used. | This always runs a little dirtier due to the speed reduction of the dampening form roller on the plate. Turn the system off if not needed for the job that is being printed. |
| Deep or uneven grain plate being used. | Use a plate with a different grain. |
PILING : Ink builds up on areas of the rollers, blankets and/or plate, creating a dry accumulation known as “caking” or “piling.”
| Causes | Remedies |
|---|---|
| Pressure between plate and blanket incorrect. | Blanket and/or plate under-packed causing poor transfer and piling. A .004” to .006” (0.10mm to 0.15mm) pressure is required for proper transfer |
| Rollers of wrong durometer, improperly set. | Use proper rollers, check roller settings. |
| Ink is poorly ground. | Check grind of ink, re-grind if necessary. |
| Running improper ink/water balance. | Adjust ink/water balance. |
| Ink train too cool. | Adjust ink train temperature (25º to 27ºC, 77º to 81º F) to recommended level. |
| Ink tack too high. | Reduce tack only enough to eliminate piling – excessively low tacks will cause other problems. |
| Running too thin an ink film. | Weaken ink to increase ink film thickness. |
| Ink pigment piling. Ink lacks sufficient lubrication to transfer properly, or there is heavy, opaque pigment in the ink. | Small amount of boiled linseed oil added to the ink may help this. Contact ink supplier if problem persists. |
Plate wearing metal : Excessive plate wear. Fine lines and dots tend to disappear. Work loses clarity, printing becomes weak and streaked.
| Causes | Remedies |
|---|---|
| Tack of ink too high. | Reduce tack. |
| Fountain solution too acidic. | Check pH and adjust if necessary. |
| Incorrect packing of plate and/or blanket. Incorrect surface speeds of the cylinders in relation to each other will cause premature plate wear. | Check manufacturer’s packing specs. Use packing gauge to confirm correct packing in relation to the bearers. |
| Poor roller settings. | Assure that the rollers are not being driven by the plate. Normally, the setting to the distributor is slightly heavier than to the plate. Set to manufacturer’s specs. |
| Poorly ground ink wears plate. | Regrind ink. |
Print density control : Colour variation from sheet to sheet
| Causes | Remedies |
|---|---|
| Poor rollers or roller settings. | Check rollers for distortion and replace if necessary. Assure that all rollers are set to manufacturer’s specs. |
| Poor ink/water balance. | See INK/WATER BALANCE section in this guide. |
| Low ink level in the fountain. | Keep ink fountain full to maintain equal pressure |
| Ink emulsification. | Decrease water or add heavy body varnish. |
| Ink backing away from “fountain” roller. | Agitate ink in fountain or increase the ink flow. |
| Rollers stripping. | See ROLLERS STRIPPING section in this guide. |
| Contaminated ink fountain – dust, grit, etc. at the ink blade/roller nip. | Remove ink, clean fountain, replace with fresh ink. |
Roller stripping : Rollers do not accept ink in areas, starving the plate of ink in those places.
| Causes | Remedies |
|---|---|
| Fountain solution incorrect. | Test pH and conductivity of solution. Adjust to manufacturer’s recommendation. |
| Rollers too hard or glazed (hardness should be between 25 and 35 durometer). | Remove from press and deglaze with Uni OD Deglazer as per instructions on label. Replace rollers if durometer too high. |
| Too much water being run | Cut back water. |
| Copper rollers repelling ink/oxidized. | Wash rollers and treat with copper activator as directed on label. |
| Too much Gum Arabic in fountain solution | Replace fountain solution with one containing less gum. |
| Excessive alcohol in the fountain solution | Alcohol is a contributor to both hardening and glazing of rollers. Increase frequency of deglazing and replacing the rollers. |
| Ink film on rollers is too thin. | Run heavier ink film. |
| Detergents in dampeners. | Rinse them thoroughly. |
| Press wash absorbed by rubber rollers. | Wash with Unigraph Water-Miscible Wash and use water as the last wash-up step. |
| Hard water being used for dampening solution. | Change to deionized, reverse-osmosis (RO) or distilled water for dampening solution. Wash rollers with Uni OD Deglazer to remove contaminants. |
| Ink takes up too much water. | Consult ink manufacturer |
Scumming : The non-image area is not being kept clean and image may be plugging in.
| Causes | Remedies |
|---|---|
| Insufficient amount of water being applied to the plate. | Increase water feed to the plate. Check setting and condition of rollers. |
| Ink rollers of wrong durometer (too soft or too hard). | Check durometer, setting and condition of rollers. |
| Ink or water form rollers set improperly. | Check and reset rollers to manufacturer’s specs. |
| Wash-up solution left in the rollers. | Wash rollers with water-miscible wash and finish with water as the final wash-up step. |
| Plate not properly desensitized. | Desensitize or remake plate |
| Fountain solution out of balance. | Drain tank, flush thoroughly with Uni Power Flush, and re-fill with fresh fountain solution. |
| Roller train temperature too hot. | Maintain less than 90ºF (32ºC) in roller train. If press has ink-train cooling, set it at approximately 77ºF to 82ºF (25ºC to 27ºC). |
| Wear of plate due to abrasive material from the paper on the blanket. | Change to a better paper. Reduce plate-toblanket pressure to minimum. |
| Air movement across the plate. | Check for open doors or air vents directed at the press. Close doors, redirect air vents. |
Streaks : …across the plate cylinder. Streaks lighter than the colour being printed are normally related to the dampening system. Pulling dry solids makes it easier to measure and identify the source of the problem. Roller streaks can be identified by determining the circumference of the roller and measuring this amount from the gripper edge of the sheet minus the gripper margin.
| Causes | Remedies |
|---|---|
| Roller settings incorrect. | Check manufacturer’s specs. Assure that the setting to the distributor is heavier than the setting to the plate. |
| Rollers too hard or glazed | Check shore hardness of rollers. If over 35, they may not be able to lay down the ink properly and should be replaced.
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| Blankets packed incorrectly. | Pack blankets to press manufacturer’s specs. Over-packing changes cylinder surface speeds and creates streaks. |
| Old and worn blankets. | Mount new blanket and packing. Old, worn blankets may have marks right in them. |
| Settings incorrect in dampening system. | Check all the settings in the dampening system and assure they are to manufacturer’s specs. Too light of a setting between form roller and distributor will allow roller to slip. Running with the dampening system integrated with the ink train often gives an improved result. |
| Poor ink trapping. | Change colour sequence or modify ink to achieve a better trap. |
| Cylinder bearer pressure. | Many streaks close together may be a sign of incorrect bearer pressure. Contact press manufacturer to check and adjust, if necessary. |
| Calendaring of the stock. | Exchange paper for some without calendaring marks in it. |
Tinting : A light tint of the colour being printed is seen in the non-image background areas.
| Causes | Remedies |
|---|---|
| Plate not exposed or processed properly. | Check exposure element on the plate. Check processor chemistry. Clean and replace if necessary. |
| Solvent left in the rollers after wash-up. | Leave wash-up blade on until all solvent is removed from the rollers. Use water as the last step of the wash-up. Leave press run for a couple of minutes after the wash-up to allow solvent vapours to dissipate |
| Dampening solution contaminated. | Flush dampening circulation system and mix fresh dampening solution. Check pH and conductivity. |
| Form rollers oscillating on the plate. | Assure that form rollers are locked or shimmed properly to prevent sideways movement. The last form roller especially, will cause tinting part way up the plate. |
| Incorrect roller settings. | Check and reset to manufacturer’s specs. |
| Ink breaking down. | Check pH and conductivity of fountain solution. Check amount of alcohol or alcohol substitute in the solution. Check for contamination in the ink train. |
Wash marks : Streaks of light or uneven density at the leading edge of the image, increasing in density toward the trailing edge. Wash marks appear around the plate and blanket and in the print.
| Causes | Remedies |
|---|---|
| Weak dampening solution must be run in an excessive amount to clean non-image areas of the plate. The ink cannot absorb the extra dampening solution. |
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| Lighter line across the print. | The dampening form roller is slipping at the cylinder gap. Check setting and condition of dampening form roller. Run dampening in the “integrated mode.” |
| Lighter area from gripper to tail (washed out) caused by a bad dampening roller | Look for a low area in the rubber pan or metering roller. Replace roller if necessary |
Taking proper care of your inking and dampening rollers is extremely important as they are responsible for laying the ink down evenly and smoothly to the plate to give you the highest quality print. Unigraph has a full selection of high quality products to assist you in keeping your rollers in top condition.
Following are some guidelines for the care and maintenance of rollers.
A good roller should have a soft, velvety feel to it with a durometer between 25 and 32 (especially form rollers).
Once a roller has a durometer over 35, it no longer has the ability to lay the ink down smoothly and evenly and should be replaced.
Regular use of Uni O.D Deglazer will help keep the durometer of the rubber in the desirable range and increase the life of your rollers.
One of Unigraph’s water-miscible washes should be used for your regular wash-ups with water always being used toward the end to assure that the surfactants and other water-miscible particles are removed from the rollers.
Roller settings should be checked on a regular basis. A quick check each month would be advisable as it is normal for rollers to shrink somewhat during their usable life.
A good quality roller will shrink a little early in its lifespan, then very gradually change over the longer term.
Good quality, well maintained rollers can be expected to last two years or more.
Check press manufacturer’s recommendations for roller settings and in all cases keep the settings as light as possible as there is no positive side to a heavier setting.
Heavier settings will create more heat in the ink train and cause rollers to deteriorate quickly.
They can also cause deflection in the rollers which will give you an uneven stripe on the distributor roller and have the roller touching the plate in some areas and not others.
Colour inconsistency may also be experienced as the heavier settings may not allow the ink to flow evenly and consistently through the nip of the rollers.
Form rollers should be checked for side play as any sideways movement in the rollers can cause premature glazing as well as negative effects on print quality, some slurring of the dots and tinting or toning on the printed sheet.
Make sure that new form rollers are shimmed and fitted properly to prevent any sideways movement.
If form rollers are purposely allowed to move sideways from time to time to combat a ghosting problem, never allow the last form roller (usually #4) to oscillate as this is a clean-up roller. Also assure that the rollers are locked up properly again after the ghosting form is completed to prevent wear in the journals and glazing of the rollers.
Poorly maintained rollers are a major cause of poor print quality. Assure that this is not the case in your shop and make Unigraph products a part of your regular roller care.
In the form of precipitated calcium carbonate or ground calcium carbonate, it is used as a filler in papers. The paper you print on is changing. Twenty years ago, almost all of the mills in North America produced paper using an acid process. By 1992, 20-30% of these mills were producing alkaline paper. In Europe, this figure is 50-60%. Alkaline paper making in North America is expected to grow during the next five years until 90% of these mills will be producing alkaline paper.
The move from acid paper toward alkaline paper is not an arbitrary one. Alkaline paper offers several advantages over acid paper:
For all the benefits, alkaline paper now creates a whole new set of printing parameters that printers must now face and learn to troubleshoot in order to produce quality results.
From the blanket, calcium carbonate is transferred to the plate and now causes hickeys, toning and water is less receptive to the non-image area of the plate, which in turn, you start to scum. The ink and water forms pick up the calcium carbonate from the plate which causes rollers to glaze and harden.
As the run lengthens, calcium carbonate will find its way into the dampening system and contaminate the water, which will increase pH and conductivity.
Some calcium carbonate may leach out of the paper during the printing process. When this happens, the transparent calcium carbonate flakes, which have sizing particles attached to them, migrate to the upper form roller. Once there, they are milled into the ink and dispersed throughout the moisture system and the ink train.
The discovery of special alkaline-compatible sizing systems made the production of alkaline paper a reality. But once again, this key ingredient in alkaline paper causes some problems in the print process. As mentioned previously, when these calcium carbonate particles leach out of the paper, they have sizing bonded to them. Eventually, these calcium carbonate/sizing particles come into contact with the ink. These sizing compounds sometimes activate the ink driers prematurely, resulting in both ink feedback on metal-surfaced dampening rollers and a calcium glaze build-up on the blanket.
Conventional blanket and roller washes will not remove the build-up that results from the leaching of calcium carbonate/sizing particles. You must use water-miscible wash to remove this type of glaze. Leaving this glaze untreated is not an option – you will experience a noticeable decrease in print quality.
Unigraph fountain solution product is designed to break these calcium carbonate/sizing bonds and keep them “tied up” (sequestered is the technical term) until they are removed during roller wash-up.
These products are high quality emulsions containing silicone and other chemicals emulsified with water which enable a variety of printing operations.
These silicone emulsions assist and benefit a number of printing operations.
Solutions with different solid concentrations are helpful when applied on different surfaces, finishing processors, and when presses are running at different speeds.
All Unigraph silicone products contain high levels of anti-static additives. However, if required, some extra Unigraph anti-stat can be added, approx. 1 to 3 ounces per gallon of mixed solution.
Accurate dosage is important for performance and economy. Excessive amounts of anti-stat or silicone product can be detrimental to the final performance. Unigraph recommends Dosatron Graphic D14MZ10 doser which offers the following benefits: Extremely accurate dosage between 1 – 10%, economical use of emulsion, non-electrical application, trouble and services free, easy installation.
Soft water is preferred because it produces a stable solution, free from fluctuation of town water. Hard water can produce a surface scum which interferes with even film on applicator roller.
One definition of piling is a build-up of ink (or ink components) and paper linters, generally on the blanket. This is a major concern for web printers because of the waste generated each time that the blankets must be cleaned. As these materials build and the blanket thickness increases in local areas, print quality will deteriorate. You will generally see this build-up in the non-image area of the blanket, and it tends to be worse at the trailing edge of solids.
When piling becomes thicker, the trailing edge of the image will begin to lift off the blanket and stop printing. Piling is a very good indicator of fountain solution, ink, and paper compatibility. On good stock, the blankets may only require cleaning every 200,000 impressions. The image does not usually pile, because fresh ink is constantly being transferred from plate to blanket to paper. This constant transfer tends to prevent any significant accumulation of foreign material on the blanket.
There are several contributing factors that influence the rate of piling:
Linting is caused by stock with loose surface fibers or by excessive tack of the ink or blanket. Paper fibers are pulled off the sheet and then build-up on the blanket. “Release Agents” are often included in fountain solutions or alcohol substitutes to decrease the “tackiness” of the blanket surface and reduce the tendency to pull the fibers off the sheet. Typical non-piling additives are made from glycols that will tend to keep the blanket moist. Some printers will run paper that has loose surface fibers through a dummy unit before laying down the first color. Some of the loose surface fibers will be pulled off and stick on the dummy blanket reducing linting in subsequent units.
Are you using the right deglazer to effectively remove calcium from your press? This may seem like an odd question to ask a pressman. A good brand-name deglazer should do the job, right? Not necessarily. With all the changes that have been made to the paper in the last 10 years, it is crucial to understand exactly what is happening on press and what a deglazer should be doing for you. Let’s breakdown what glaze is. Glaze can form and accumulate from 4 primary sources:
A good deglazer should be able to clean what is water-soluble (sources 1, 3 and 4) and what is solvent soluble (source 2).
One of the biggest changes in our industry has been the introduction of alkaline-based paper to replace acid-based paper. There have been many reasons for the change (environmental issues in making the paper and brightness of the sheet) and there have been many issues printers have had to address because of it.
One of the most notorious problems has been the effect of calcium coming off the sheet and being introduced into the printing process. Here are some of the most common problems caused by calcium contamination.
There is really no way of stopping calcium from coming off the paper. Let’s go through what actually happens as you start your press and paper passes through it.
What’s the end result of all this? You now have a glaze that is literally locked into the pores of your rubber rollers due to the crystallization of the calcium. How do you remove the contamination from your press and control it? Use O.D. Deglazer!
Unigraph offers you a short and practical guide in helping circumvent one of the most common printing problems: scumming (greasing). Scumming occurs when non-image areas of the plate begin to accept ink. Do not confuse scumming with tinting, which is generally characterized by a light uniform ink film over the entire plate. There also exists simple procedures to distinguish between both problems. Increase the flow of fountain solution or hone the plate with a desensitizing stick while the press is stopped. At restart, if the problem diminishes or disappears, it’s most likely scumming. If your diagnosis leans toward scumming, we suggest a series of probable causes and associated remedies.
Scumming may arise due to inadequate dosage of fountain concentrate, alcohol or alcohol substitute:
| Cause | Remedy |
|---|---|
| Not enough concentrate. | Check dosage, keep at recommended pH and conductivity. |
| Too much concentrate. | Check dosage, keep at recommended pH and conductivity. |
| Low alcohol or alcohol substitute. | Contact your fountain solution manufacturer. |
Scumming may be ink related:
| Cause | Remedy |
|---|---|
| Too much ink being carried and squashed over non-image areas. | Reduce ink feed or use a denser ink pigment. |
| Ink is too soft and spreads over non-image areas. | Add heavy bonded varnish to ink. |
Scumming may appear if insufficient dampening solution is transferred to the plate:
| Cause | Remedy |
|---|---|
| Too little fountain solution. | Increase flow of fountain solution. |
| High dampening temperature (low viscosity). | Ideally, should range between 10-15º C (50-60º F). |
| Dirty, worn dampener sleeve or metering roller. | Clean or change devices. |
| Improper dampening settings. | Reset dampeners to appropriate settings. |
| Improper form roller settings. | Check and adjust stripe on plate. |
| Improper roller durometer. | Measure and change to specifications. |
| Improper plate/blanket packing. | Set according to instruction manual. |
| Glazed blanket. | Clean all gum, ink and particulates. |
Too quick evaporation of the thin water film on the plate may cause scumming:
| Cause | Remedy |
|---|---|
| High dampening temperature. | Ideally, should range between 10-15º C (50-60º F). |
| Air drafts blowing on the plate. | Prevent or shield from air drafts. |
Scumming may also come from a faulty plate:
| Cause | Remedy |
|---|---|
| Improper gumming. | Clean plate with water and/or cleaner conditioner. |
| Plate not opening or not desensitized. | Gum plate on press. |
| Sensitive or light-struck plate. | Desensitize plate, apply scratch remover or plate cleaner. |
| Prepress problems: exposure or development. | Make new plate. |
Going through this troubleshooting procedure may help you to identify the problem and the cause, thus leading to the appropriate action to take. Keep in mind that tinting, bleeding and plugging may leave an image similar to scumming, however, the causes could be essentially different.
Lithography is really a very simple process. With great precision and at high speed, water and ink are metered to the plate simultaneously. They mix with each other in a meticulously-controlled way on the form rollers and are deposited separately, each to its own designated area on the plate.
Experienced press people know that the lithographic process relies on the equilibrium of the ink-water mixture. One of the most difficult variables to control is the ever-changing relationship between ink and water on the plate surface. To ensure minimal use of ink and water and to achieve the best possible ink-water balance during a press run, a fountain solution with a surface tension between 32 and 45 dynes/cm, according to the type of press used, is essential.
Besides the minimum ink-water balance, there’s a second important factor that contributes to the success of a good impression – the cleanliness of the non-image area of the plate.
A fountain solution containing a natural Arabic gum (14ºBe) ensures a continuous formation of a protective film that desensitizes the plate’s non-image. Maintaining precise control over the protective film will ensure minimal use of water and result in an optimal ink-water balance.
Experienced press professionals understand this. They realize that a fountain solution’s surface tension always affects the printing process since it acts directly on the quality of the water that’s transported as well as the ink-water mixture. It facilitates the formation of a thin, uniform and reproduceable water film before each application of ink. These two key requirements (fast plate wetting and the ability to form a thin water film) are critical for lithographic dampening systems. And they are largely determined by the surface tension of the fountain solution.
Pure water has a surface tension of 72 dynes/cm. In dampening solutions containing an alcohol concentration of 10% – 25%, the surface tension will be reduced to 35 – 45 dynes/cm. This enables the solution to spread over the plate rapidly in a thin, continuous film.
In general, a fountain solution will consist of water, acid and gum (see above), corrosion inhibitors to prevent the solution from reacting with the plate, fungicide, anti-foaming agent to prevent build-up. Last but not least, we find wetting agents such as isoproponol or alcohol substitutes, which decrease the surface tension of water and water-based solutions.
When alcohol or these substitutes are mixed with a fountain solution on a press using a dampening system employing alcohol, the surface tension is reduced. The result: alcohol or its substitutes help the water to wet the dampener form roller evenly, requiring less dampening solution.
A thinner film of solution will help keep the non-image area of the plate clean. It will also help to spread water properly over the ink on the rubber bareback form rollers that apply both the ink train – therefore less dampening solution is applied to the paper. Thinner film also aids in preventing water spotting because the fountain has finer drops dispersed in the ink. It also suppresses foaming.
The addition of alcohol in the fountain solution increases the viscosity of the water, which in turn allows a thicker layer of dampening solution to be applied to the ink and non-image area and improves the performance of the ink, paper and printing plates.
When using substitutes, the fountain solution is metered by the squeezed rolls used in the majority of continuous contact-type dampeners. The immediate effect is that the dampener speed must be turned up, which leads many press operators to conclude, erroneously, that they must use more water to print with a substitute.
To partially offset the loss in the viscosity produced by eliminating alcohol, the dampening solution can be cooled to 50 – 55ºF. Substitutes differ from alcohol in several key properties – how they affect viscosity, surface tension, pH and conductivity.
In alcohol-free dampening solutions, surface tension is reduced by additives called surfactants. These are organic chemicals that concentrate at interfaces because of their polar molecular structures. They travel to the interfaces between the dampening solutions, and both air and the ink on the image areas of the plate. At higher press speeds, interfaces are used and reformed rapidly. Surfacants may diffuse rapidly to replenish new interfaces. An excess of surfactants can contribute to excessive ink emulsification.
Alcohol substitutes also offer an excellent opportunity to dramatically cut the amount of VOC emissions from a press. Because alcohol substitutes do not have a diluting effect on ink when used in proper concentrations, less ink and water are needed for good colour reproduction. Sharper dots are produced and there is less of a tendency for dot gain.
VOCs (Volatile Organic Compounds) are unhealthy for many reasons - they can also harm the environment by helping form smog, which damages crops and forests in addition to being harmful to lungs. Some blanket washes also contain chemicals called Hazardous Air Pollutants (HAP’s), which may also harm human health and the environment.
By using blanket washes containing fewer VOC’s, you can significantly reduce the impact that your printing operations have on employee health and the environment. You may also be able to reduce your regulatory requirements. To find out the VOC content and other components of your current blanket wash, ask your supplier and check the product’s Material Safety Data Sheets ( MSDS ). Suppliers can recommend substitutes containing less VOC’s.
PRESS WASHES?: SOLVING THE DILEMMA
History tells us that the best press washes are those that break down and remove ink quickly, evaporate fast and are easy to use. History also tells us that these traditional washes typically contain 90 % to 100 % petroleum distillates ( VOC’s ).
Today’s environmental climate and the issuing of increasingly stringent regulations are creating a situation where these traditional, high-VOC washes are no longer acceptable. The current target for low-VOC washes is that they contain less than 30 % VOC’s ( by weight ) which equates to approximately 2.5 lbs. per gallon.
The obvious question is how do we move from efficient, high-VOC traditional washes to the more Environmentally acceptable low-VOC products ?
Unfortunately, none of the alternatives are perfect. The surfactants typically used to formulate emulsion-based washes, if not properly removed, can build up on rollers and blankets, causing poor ink transfer, stripping and emulsification. The vegetable oil washes often require a rinse step, leave a greasy residue, and are also slow to evaporate. With wash-ups sometimes taking place up to 15 times a day, this can have a substantial impact on production costs. Include periodic deep cleanings using a wash such as Unigraph’s Color Change Wash Step1 and 2 to eliminate surfactant build up.
Washes containing exempt solvents are efficient and sacrifice little in productivity, but they present problems and frustrations for the press operator. If you attempt to go from a solvent-based wash to a low-VOC alternative overnight, the most practical and cost-effective approach is to do the changeover in several steps. While reducing VOC’s is critical, cost of restarts, paper and quality of printing must all be considered.
Making the transition to a low-VOC wash doesn’t have to cause undue sacrifice or frustration. The following steps can eliminate some of the problem areas and make the changeover successful. While this procedure doesn’t completely eliminate VOCs, it significantly reduces them without sacrificing cost effectiveness and print quality.
Choose a good quality, low-VOC wash from a reputable manufacturer.
Begin using on rollers. Periodically deep clean them with a traditional two-step color change wash to eliminate surfactant build-up.
After a period of successful use on rollers, begin using as a blanket wash, always following the manufacturer’s recommended procedures. In cases of unusually difficult cleaning, a traditional wash should be used.
To help avoid problems, continually monitor rollers and blankets. Look for signs of surfactant build-up, such as greasy residue, ink emulsification, poor ink transfer or slow cleanup.
While this procedure does not completely eliminate all VOC’s, it significantly reduces them.
To date there are no perfect low-VOC washes. But with a strong commitment and understanding that these washes perform differently and require more attention, a pressroom can effectively eliminate a substantial percentage of VOC’s from its press washes without sacrificing efficiency and print quality.
The development of higher-performance, more effective low-VOC washes is always continuing - find out which one is right for your shop.