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Accumulation of Ink on Blanket in a Non-Image Area
The information below outlines the possible causes and solutions for accumulation of ink on a blanket in a non-image area.
Dampening level too low
Ink too fast
Ink tack too high
Insufficient blanket/blanket nip squeeze
Blanket surface too smooth
Blanket surface too tacky
Blanket exposed to heat
Increase water supply to blanket surface
Change color sequence or use slower inks
Reduce ink tack
Use rougher surface blanket
Avoid the use of rejuvenators
Keep heat of dryer away from blankets in the last unit
Applying Gloss Coatings
Applying a gloss coating may trap solvents and oils in the ink films and slow down the drying process. Some oils may never fully dry, causing scuffing and rub-off problems days, or even weeks, later. Certain techniques and processes may minimize problems.
How They Work:
Aqueous and UV (ultraviolet) coatings, the two main types of gloss coatings, differ greatly in composition and how they work.
Aqueous coatings replace press varnish or serve as a primer before applying an UV coating.
Small amounts of spray are often used with aqueous coatings, but none is necessary after applying UV.
Drying and Curing:
Aqueous coatings dry, but UV coatings cure.
Suggestions for both coating processes:
Use low solvent inks to prevent ink-drying problems.
Although it is not always practical, off-line coating is recommended. This allows sheetfed inks to begin drying before being sealed.
Suggestions for UV coating:
When off-line applying UV coatings, the inks must be wax-free. If the ink contains any type of wax, the surface energy of the printed image will not allow the UV coating to "wet out," and it will puddle on the surface (i.e., cause "fish-eyes").
If there is any foreign material on the printed surface, such as clumps of offset spray powder, the UV coating will crack and break apart.
If the UV coating has been under-cured or over-cured, it may flake.
In an aqueous coating, water evaporates, and no curing occurs since the starting materials are completely polymerized prior to mixing. On press, air knives accelerate this evaporation, and all aqueous coating stations include infrared (IR) light sources that heat the surface of the paper or board to further speed evaporation. The heat, which varies between 90 and 100 degrees F, is retained in the printed pile and continues the drying process. The aqueous coatings are thoroughly dry within eight to ten hours.
In the UV coating process, the coated press sheet passes under UV light energy generated by special lamps, most commonly medium pressure mercury lamps, which emit visible light plus UV and IR heat energy. Several lamps may be required, depending on wattage, type of coating, ink coverage, and ink colors.
The UV coating is said to "cure" because, in a two-step chemical process, it changes from a wet to a dry film nearly instantaneously. First, the photoinitiator converts to free radicals and absorbs UV light energy, then these free radicals attack the acrylate chemical construction, causing the coating to polymerize.
For aqueous coating, keep sheetfed ink solvent levels to less than 15% to prevent drying problems. Oil-based sheetfed inks may have a wetting problem with aqueous coatings. Wax-free inks are recommended when applying UV coatings on web offset presses.
For off-line applications, wax-free inks provide the best adhesion and wetting action for both aqueous and UV coating applications; in the latter case, IR heat may melt the wax in the inks, affecting adhesion between the ink and the coating.
The information below outlines the possible causes and solutions for blanket delamination issues.
Dry ink accumulation
Ink accumulation on outside edges
Indentation too high
Swollen packing and blanket
Plate edge cutting in blankets
Unsealed blanket edges
Damaged blanket surface
Increase water supply to blanket surface
Reduce width of blanket underpacking to minimum possible
Change underpacking; avoid solvents that attack blanket surface or edges
Ensure edge sealing
Brightness: Measurements and Effect on Paper
Brightness is extremely important in the printed appearance of paper because it affects the contrast, and brilliance of the sheet. It also affects the cost.
Generally, the brighter the sheet, the more expensive it is to make, because a higher brightness requires more fillers and chemicals (such as titanium dioxide or calcium clay). However, a brighter sheet is more appropriate for applications that require high-contrast printed areas.
The brightness of papers is measured on a brightness meter. It is common in the industry to refer to the "GE" brightness; however, General Electric is no longer the manufacturer of the brightness meter. Technidyne Corporation is one such company that makes brightness testing equipment.
Calcium Carbonate Buildup in Fountain Solution
The following infomation outlines possible causes and detailed solutions for calcium carbonate buildup.
Rollers stripping - Lack of water pickup on dampening system
Fountain solution - Rise in conductivity (increased ions in fountain over 8-10 hrs)
Plates sensitive - Rise in conductivity will cause the plates to go blind. (They can't differentiate ink and water, thus producing no image)
The printing press should be purged. Clean the entire fountain system. Follow these steps in the order listed below for cleaning the fountain solution and press rollers.
Drain and clean with a solution of 1 part bleach mixed with 12 parts water (e.g., 1 quart of Clorox and 3 gallons of water)
Run this solution in the tanks for about 3/4 to 1 hour
Rinse with clean water
Wash the printing press
Use Lime-Away and water (1 to 1 ratio)
Rinse with pure solvent wash
Rinse press rollers once a week with water and vinegar (1 to 1 ratio) as a maintenance follow-up.
Definitions of Printing Dots
Some definitions that are helpful when discussing printing dots.
An increase in half-tone value during the printing process as compared to the dot on the film. This aspect is also called enlargement of halftone dots. The increase is due to several factors: processing, material, and machines. Thus, it can't be directly controlled by the pressman. To a certain degree, the pressman can counteract dot gain, especially by manipulating the inking. It is common practice for the prepress function to compensate for normal dot gain.
The reduction of non-printing areas, up to their complete disappearance. Filling-in may also be caused by slur or doubling.
A decrease in halftone value as compared to the dot on the film. In practice, the term sharpening is often used to describe the reduction in anticipated dot gain, though the print may still be fuller when compared to the film.
The form of the halftone dot is changed during the printing process due to relative motions between plate and blanket and/or blanket and printing sheet. That is, a circular point may become oval. Slur in the printing direction is called circumferential slur, and slur at right angles to the printing direction is called lateral slur. Diagonal slur results if both forms of slur occur at the same time.
In offset printing, a small, shadow-like, unintended ink dot appears besides the intended halftone dot. Doubling is caused by an incongruent retransfer of ink by the subsequent blanket.
The term offset is used to describe the transfer of ink from freshly printed matter on to another surface, often in the delivery pile of a sheetfed press.
Dot Gain Too High
The information below outlines possible causes, solutions and tips for dot gain being too high.
Impression settings too high
Untrue rolling conditions
Too much water in ink
Form roller setting to plate
Unsuitable ink tack
Unsuitable blanket surface
Ink temperature too high
Readjust to recommended value
Synchronize rolling conditions
Adjust ink water balance to lower level or use different ink
Adjust setting to recommendation
Change ink to higher tack
Reduce ink value to optimum level for contrast/density
Change blanket with very low dot gain value
Keep ink level in fountain low for frequent refreshing
Ink Sequence is B C M Y (Black, Cyan, Magenta, Yellow)
Biggest dot on black because it goes through three more units
Yellow will have the least dot gain
Doubling in Print--Gripper to Trailing Edge (Circumferentially)
The information below outlines the possible causes and solutions for doubling in print on the gripper to trailing edge (circumferentially).
Improper web tension (on webs)
Untrue rolling conditions
Different blanket types
Unsuitable subject lay down
Different packing thickness
Improper packing height
Over/under packed cylinders resulting in different speeds between cylinders causing slippage
Uneven, soft, loose blankets
Excessive play in gears and bearings of plate and blanket cylinders
Too much pressure between plate and blanket
Running excessive amount of ink—ink film too thick
Unitack or Monotack inks and tacks out of sequence
Check blanket tension
Synchronize cylinder speeds
Inspect mechanical conditions
Ensure that blankets in press are all of the same type
Try to modify your ink tack accordingly
Ensure same packing height
Change packing, reduce amount of solvent for blanket cleaning
Adjust packing to requirements
Adjust packing to equalize diameter of cylinder
Tighten blanket clamps, adjust packing or change blanket
Adjust according to manufactures specifications
Check and use "kiss impression"
Reduce the amount of ink
Make sure ink tacks are in proper order
Doubling in Print--Side to Side (Laterally)
The information below outlines the possible causes and solutions for doubling in print on side to side (laterally).
Incorrect paper quality
Improper packing height
Underpacking thickness variation
Incorrect blanket direction
Ensure paper quality
Adjust packing to requirement
Ensure that packing is 100% equal both sides
Ensure the cylinders are adjusted to 100% "spirit level"
Ensure correct blanket installation
Check blanket for uniformity
Check mechanical conditions on press
Fluting is a physical distortion of light and medium weight papers when printed by web offset. It is characterized by machine-direction ridges, running parallel to the paper machine (and press) web travel. It occurs primarily in heavily inked areas; preventive measures to minimize fluting are possible. Other names for fluting include corrugations and waffling.
What is Fluting
Fluting is periodic ridges, running parallel to the machine direction of the paper. Usually seen in printed areas, the ridges are approximately ½" - 1" apart. They are normally only seen on web offset printing, particularly regions where there is heavy ink coverage on both side of the paper.
More pronounced in the areas of heavy ink coverage
Aggravated by heavy back to back coverage
More prevalent in light-medium basis weights: 32# -100# text
Generally does not develop in coated paper over 100# text
Often relax with time in finished signatures but do not necessarily disappear completely
Totally absent in sheetfed presses, gravure presses and web UV printing
NewPage conducted a controlled study in cooperation with four large printers. The goal was to learn what caused flutes and how they might be prevented. Unfortunately, they could not be prevented or eliminated. Once fluting developed, it was reduced in severity only by time.
Conclusions of the Study
Fluting is initiated by tension but not affected by variations in tension.
Fluting is preserved in heavily inked areas due solidification of the ink when it is cooled.
It can be observed on all web offset presses.
It can be made to disappear by turning off press dryers (however, this is not practical).
Fluting is directly related to ink coverage. (This was true in all printing plants where documented, for all basis weights up to and including 80#, and for all dryer types).
A general relationship was found to exist between the width spacing of the flutes and the basis weight of paper. Spacing was narrow on low basis weights and wider on higher basis weights. To observers, wider spacing was more objectionable than narrow spacing.
No relationship was found between the mechanical condition of unprinted paper (ridges, ropes, etc.) and printed flutes. 95% of the paper that had some severe fluting was paper totally free of mechanical defects.
Summary of Causes:
Fluting is initiated by the differential shrinkage of the web in the CD direction as it proceeds through the dryer. Areas where there is no printing shrink faster than areas where there is heavy ink coverage; i.e., the ink acts as a barrier to moisture diffusion out of the paper. The flutes are preserved in the heavily inked sections as the ink cools and solidifies on the chill rolls. Ink that cures by exposure to UV radiation did not reveal fluting, as there is little heat applied to the web. Similarly, fluting is not seen in gravure printing for the same reason. The following items did not appear to influence any of the observations or data collected during this study and therefore are not believed to be major factors affecting fluting:
Press manufacture (5 different tried)
Press dryer type (3 different tried)
Press speed (severe fluting observed at speeds 140 FPM-1270 FPM)
Inks (7 different suppliers, all contained fluting)
Paper manufacturers (7 different supplies, all contained fluting)
Bulk Moisture after printing (varied from 1% - 5.4%) no relationship found)
Printers (5 different, all produced pronounced fluting in one job or another)
We do not believe that fluting is due to defective paper, and that a paper's contribution to the result is a function inherent in the total system.
Apply an overprint varnish to the non-image areas (or a flood varnish)
Optimize press ovens to a minimum
Optimize chill system to prevent "ink set" shock
Reduce ink coverage if possible
Change layout of form to eliminate back-to-back heavy ink coverage
Several factors play into an effective and safe fountain solution. The water condition, buffers, alcohol, and alcohol substitutes are all important considerations.
Fountain solution is also called the "dampening solution," "fountain etch," "dampening etch," or just "the water." It is water, buffered acid, gum, and probably wetting agents (alcohol or alcohol substitutes such as glycol ethers) used in the lithographic printing process to keep the non-image areas of the plate moist, and prevent them from accepting ink.
The dampening of the offset plate is one of the most critical factors in quality offset printing. Through combining a fountain concentrate with water, a solution is created that performs several essential functions on press.
The most important of these is the wetting and desensitizing of the nonimage area of the plate.
The fountain solution also lubricates the plate and blanket. This helps to reduce image wear and prolong life.
It also helps cool and maintain the working properties of the ink and aids in proper blanket reduction which reduces piling on the blanket.
Since approximately 98% of a working fountain solution is water, it is essential to be aware of your water conditions. Water can be hard or soft, alkaline or acid, and water can vary seasonally, monthly, or even daily.
Water Hardness Scale
Soft - 0-100
Medium - 100-200
Hard - 200+
For purity and consistency, you should use water that has been deionized, demineralized, or processed through reverse osmosis.
Maintaining the proper pH level is essential to plate performance and print quality. The correct level of acid in the solution is absolutely necessary to permit gum arabic to bond to the nonimage surface of the plate.
It is important to remember that the pH scale is logarithmic to the 10th power. Each full number represents a 10-fold increase or decrease in acid or alkaline concentration.
Conductivity is the measurement of the ability of a fountain solution to conduct electricity. This very important measuring device is essential when running a buffered fountain solution. Since pH is constant in these solutions, conductivity is the only measure available and is very effective in indicating the slightest variation in concentration.
The important fact to remember is that there is no conductivity standard. You must determine the individual standard for your plant. Establish a baseline.
Buffers are chemicals that are used in fountain concentrates to help stabilize the pH level of the mixed solution. The buffers reduce the tendency of pH to drift (become more acidic or alkaline) due to the introduction of contaminants such as paper coatings, inks, etc.
Alcohol and Alcohol Replacement:
Due to Federal, State and Local regulations do not encourage isopropyl alcohol use. As a result, alcohol substitutes play an increasingly prominent role.
What Alcohol Does and What Alcohol Substitutes Should Do:
Reduces surface tension of water
Increases the viscosity of water
The ability of a liquid to wet and spread over solid surfaces is inversely related to its surface tension. In other words, high surface tension equals low wettability.
The combined effect of reduced surface tension and increased viscosity, due to the presence of alcohol, improves press performance.
Less water is needed to keep the plate clean. Less water means less emulsification with the ink and less water to swell, curl or dissolve the paper.
Disadvantages of Alcohol:
Expensive, evaporates quickly
It's a VOC (Volatile Organic Compound), which means that alcohol vapor is photo chemically active and can be catalyzed by sunlight. This leads to the formation of ozone. In the lower atmosphere, ozone is a contributing factor to smog formation.
May effect density and gloss
Use of Alcohol Substitutes:
Must lower surface tension and increase viscosity comparable to alcohol.
Should not have excessive emulsification.
Should not create excessive foaming.
Fountain solutions usually come in soft, medium and hard versions to correspond to the type of water being used.
Test any new material on press before adopting it fully.
Durometer and nip relationships are primary considerations.
a.Normally, metering rollers are supplied with a durometer of 25 to 30 and sometimes will harden further after being run on press. We recommend that the durometer of the metering roller be reduced to between18 and 22 when running alcohol substitutes. The softer roller tends to be more water-receptive and will increase the nip between the metering roll and the chrome roller.
b. Another necessary deviation from normal conditions when running alcohol substitutes is the reduction in nip between the chrome roller and the dampening roller. If slippage between the chrome and the form roller is not sufficient there will be a tendency for the form roller to drive the chrome roller.
If the dampening system can be run at the same speed as when alcohol is used, the substitute is working
Problems Related To Alcohol Substitutes:
Metering roller sensitivity. Ink is picked up by the chrome roller and distributed to the metering roller.
Banding due to hard metering roller. Normal durometer 25-30 is too hard for substitutes, resulting in streaking around cylinders and on the print.
Overheating and circuit breaks of the dampening system motor. Potentiometer reading increases due to the form roller driving the chrome roller. This problem is noticed when the potentiometer readings increase as the press speeds increase.
Organic growth in recirculating system.
Ink and water emulsification. Excessive fountain solution may occur as the dampening roller speed increases.
Flooding during press trip-offs.
Plugging. Shadow tones begin to fill in due to emulsified ink.
White salty deposit on metering roller. These deposits will take on ink. Build-up usually occurs when the press is idle overnight.
Excessive water feed (when alcohol is added to a substitute). Or picking that results from low ink/water film thickness. Some substitutes require that ink and water be balanced at a lower point than normal in order to print cleaner. The lower film results in greater stress on the sheet which increases the tendency for picking.
Solutions for Alcohol Substitutes:
Etch the chrome roller. Clean with phosphoric acid then go over with gum arabic. Usually, this will restore water receptiveness. Or you may apply silicate coating.
Urethane metering rollers can be less sensitive to substitutes. Obtain softer metering rollers.
Not enough slippage. Establish metering roller setting so that the potentiometer reads as it would if alcohol were being run.
Clean system once a week and use fungicides.
Reduce the speed of the dampening rollers and check instability.
Shut the dampening system off when the press is to be idle more than a minute or two.
Use anti-foaming agents when necessary, especially if foam builds to a point that it starts splashing.
Add a small amount of alcohol--not more than 5%. This is usually only necessary in alcohol extenders, not true substitutes.
Back metering roller away form chrome roller, wipe it down with Naptha, and flush with alcohol.
Do not add alcohol beyond manufacturers recommended levels. If alcohol is not to be used with a substitute, don't use it.
a. By trial and error, optimum settings can be obtained prior to full-scale use of substitutes.
b. Increase ink film thickness.
c. Use a less tacky ink.
Gas Fuming or Gloss (Chemical) Ghosting
What causes gloss ghosting and how to prevent it.
Gas fuming, or gloss/chemical ghosting, is the chemical reaction that occurs when first-down ink does not dry sufficiently before the second side is printed. Solvent evaporating from the first side affects ink on the other side.
Sheets offering high ink holdout, and work-and-turn jobs are the most susceptible.
Fast-drying ink is not recommended by the Graphics Arts Technical Foundation (GATF) because cobalt-drying agents promote gas fuming
Inks should suit the job, not be changed, and have no extra drier added
The first side printed should be left 24 hours before backing up
Small stacks, and careful winding, dissipate heat
The side with heavy ink coverage should be printed first
Varnishing may eliminate gas fuming on a dried job; ink must be dry before applying varnish
Coarser spray powder is helpful, but it is hard on the press
Glazing Blanket Surface
The information below outlines the possible causes and solutions of a glazed blanket surface.
Remnants of paper coating
Additives in fountain solution
Untrue roller conditions
Ink drier additives
Use anti-glazing solvents daily
Contact your supplier
Avoid UV ray exposure
Synchronize cylinder speeds
Avoid use of additives
Use only recommended cleaning solvents
The information below outlines the possible causes and solutions of ink emulsification.
Extreme water pick-up of ink
pH too low (3.0 - 3.5)
Too much alcohol in fountain
Poor ink quality
Ink too thin
Form roller setting to plate
Poor ink transfer to stock
Low water pick-up
Fountain solution emulsifies ink
Ink is too soft
Reduce water quantity
Try ink with lower water pick-up
Adjust pH to 4.0 - 4.5
Adjust percentage to about 15%
Try higher quality ink
Try thicker ink or add varnish
Adjust proper pressure
Check nip pressure of plate/blanket/stock
Water pick-up should be 60%
Use ink with more body
Ink Emulsification and Fountain Solution pH
The behavior and quality of the fountain solution has a big impact on the printed results.
Ink emulsification is a condition in offset lithography that results from the mixing of excessive fountain solution (water based) and ink (oil based) on the press - generally a contamination of the ink by the fountain solution.
The pH of the fountain solution has many effects on the chemistry of the printing process.
If the pH is too acidic, there will be adverse effects on the ink, plates and paper performance.
If the ink's chemistry is attacked by the acidity of the fountain solution, it can cause emulsification and slow ink drying.
The plates will become desensitized, causing scumming, the halftone to plug, excessive dot gain and rapid plate wear.
The ideal fountain solution is around 4.0 to 5.5 pH.
Overall Slurred or Double Image
The information below outlines the possible causes and solutions to an overall slurred or double image.
Improper gripper settings
Unstable paper--paper is fanning out in successive units
Loose, uneven or soft blanket
Over or under packed cylinders resulting in different speeds between cylinders, causing slippage
Excessive play in gears and bearings of plate and blanket cylinders
Too much pressure between plate and blanket cylinders. Overpacked plates or blankets.
Running excessive amount of ink--ink film too thick
Unitack or Monotack inks and tacks out of sequence
Adjust and repad grippers if necessary
Check ink/water balance and adjust water to lowest amount possible
Check plate and tighten if necessary
Tighten blanket clamps, adjust blanket packing or replace blanket
Adjust packing to equalize diameters of cylinder
Adjust according to manufacturer's specifications
Check or use "kiss impression"
Reduce the amount of ink
Make sure ink tacks are in proper sequence
Overprint Varnishes for Sheetfed Offset Printing
How varnishes work, the best uses for them, and how to prevent problems when using them.
There are several coatings that improve gloss, ink adhesion or physical surface properties. For example, overprint varnishes (OPVs), water-based coatings, and ultraviolet (UV) coatings. This article will address overprint varnishes.
OPVs are cheaper than UV or water-based coatings. Unlike other coatings, no special equipment is needed to apply the varnish. There are two disadvantages to a varnish application: it is more likely to yellow, and it takes longer to dry than water-based and UV coatings.
Applied through the ink train (the same was as any other ink), OPVs provide:
A protective film or barrier overprinting inks and paper. This prevents finger smudges on areas with solid ink coverage.
Aesthetically pleasing effects, such as gloss or dullness, that enhance the graphics in the print job.
A receptive barrier over inks that may not be receptive to another process (such as imprinting or coating).
Resins, which provide strength, body and gloss, are the backbone of any good manufactured varnish, especially its chemical and physical characteristics.
The resins are dissolved in drying oils such as tung, linseed, or an alkyd. Resins that are dissolved primarily with tung and linseed oil provide the best gloss, but they have a tendency to yellow over time.
Certain resins made with select alkyds yield a non-yellowing varnish, but with less gloss and hardness. To ensure proper press performance of a varnish, it is important to check film clarity, tack (using an inkometer), color, grind, flow rates, rub resistance, and water pickup.
The varnish is applied through the ink train on a sheetfed press, either in-line or off-line, depending on the desired result or process.
In-line varnishing is the term used to describe the application of an OPV over wet ink. It is usually done on an offset press with five or more printing units, with the OPV being applied at the last unit.
During in-line varnishing, it is very important to monitor the varnish's film thickness on the stock, since some of the varnish migrates into the wet ink film (and may affecting the desired finish).
In-line varnishes require a low tack for good trap and are fast-setting to minimize absorption.
To optimize gloss on a particular job, you can choose to apply the varnish off-line, when the inks are dry and provide a solid surface on which the varnish can set.
Off-line varnishing (trapping over a dry ink film) produces higher gloss because a thicker film of varnish can be applied.
Spot varnishing is used to describe the application of OPVs to selected sections of a printed sheet to highlight that area. This process can be done with either a gloss or a dull varnish, depending on the effect you are trying to achieve. Spot varnishing can be done either in-line or off-line.
Improper varnish/water balance
Pay close attention to the varnish/water balance during printing.
Too much water in the varnish will slow drying process and may produce a poor print quality.
Insufficient varnish holdout
Some papers may have a poor surface holdout, which means the varnish may be absorbed into the sheet.
One cure is to apply a clear dextrin sizing solution to the stock prior to printing.
Improper film thickness
Printing a thick film of varnish may enhance the desired effect, but it can also cause misting of the varnish at high press speeds, blocked press sheets in the delivery pile.
If the fountain solution is too acidic, calcium can leach from an alkaline substrate and increase the pH. If a press operator compensates for the pH change by adding more fountain solution, the varnish can become over-emulsified, slowing the drying process of the OPV.
To avoid this, closely monitor and compensate for any changes as they occur.
Properly used, anti-offset spray powder prevents sheets from sticking together in the delivery pile.
Too much powder, however, reduces the printed gloss and can give the printed sheets a sandpaper-like feel.
Alcohol substitutes in dampening solutions
Many printers have converted to alcohol-free dampening solutions.
Many of these solutions contain surfactants and glycol ethers that can attack an OPV, causing it to pick up excess water. This increases OPV drying time and reduces print quality.
Using water-based coatings over OPVs
Although water-based coatings dry quickly over freshly printed inks and varnishes, some of the water-based coatings contain a high alkaline (ammonia) content that may alter the color of the ink and yellow the OPV.
It is imperative to pretest the varnish before going to press. The pH of the water-based coating should be 7.5-8.0.
Make sure you contact and discuss with your OPV manufacturer the right varnish for a particular job. A varnish that works well with one set of inks and grade of paper may not be suited for another set of inks and grade of paper.
OPV suppliers can formulate any tack value to make them compatible with the tack values of the ink being used. Don't hesitate to ask your supplier for technical assistance.
Low slip varnishes are used to reduce the tendency of printed materials to slide when stacked. Imprintable and nonimprintable, scuff resistance, non-yellowing, low odor, non-toxic are other types of formulated varnishes.
Store away from direct heat--at room temperature or slightly cooler. Try not to store the varnish for more than 30-60 days. Varnishes contain driers, and over a long period of time, they will become too viscous.
Tips to Remember:
It is extremely important for the printer to know if one or more areas of a gloss varnished piece will be imprinted at a later date. Or, in case of folders, if glue will be applied later to tabs.
Picking, reticulation, slow drying and other problems may occur, if the varnish and inks are not compatible. Work with both the ink and varnish suppliers.
Never change one variable without thinking what effect on other variables. Example would be when changing the dampening solution, consider the formulation of the varnish.
Reverse embossing is a printing defect caused by the stresses created during the separation of the paper from the blanket.
The paper stretches, raising the printed surface areas and creating a depression on the back. This distorts the sheet of paper and may prevent it from laying flat. Ink emulsification could cause reverse embossing. Water pick-up may have induced the embossing with an excessive amount of water absorbed into the sheet. Large amounts of water can break down the internal bond strength of paper.
Tight Edges and Paper Stability
Exposing paper to very low humidity levels can cause tight edges. Following some basic guidelines will help prevent this problem.
The problem appears as raised corner(s) on the sheets to be dished, and is not incurred during the paper manufacturing process. Tight edges are caused by exposing paper to humidity levels much lower than that of the stock itself, which causes it to release moisture.
The following precautions that should be taken in the pressroom to protect paper stability problems:
Printer's pressroom should be R.H. controlled--NewPage recommends 45 to 52 R.H.
Paper should be allowed to acclimate to the new condition before opening the stock to perform the printing.
Paper should not be stored around heating or cooling unit, or in an airstream of heated or cooled air.
Paper should remain in the wrapper until immediately prior to be processed.
Paper being held between processing steps should be protected by vapor proof wrappers while awaiting additional processing operations.
Varnish reticulation is a splotchy appearance caused by an incompatibility between the ink and varnish.
Our experience indicates that it generally occurs when varnish is applied off-line. We suggest that the printer work with their suppliers to ensure that the inks and varnishes being used are compatible for both wet and dry trapping.