Tuesday, April 28, 2015
Wednesday, June 4, 2014
Which Stacker to use for your POST PRESS- Log or a Compensating Stacker.
Why this comparison?
On every Post Press project we have
two challenging choices ahead of us:
1) What are the right machines for the
productions which will be run on the press
2) How do I layout these machines in
order to optimize
ƒ
the
available space and the plant logistic
ƒ
the
product flow through the system (including intelligent back-up
ƒ
the
ergonomics for the operators (easy access, free floor space, safe environment)
This
comparison wants to be a help for question 1) with a focus on small and medium
presses with limited need of automation where the Post Press mostly consists of
a conveying system and either a compensating stacker (optionally with a
trimming line) or a semi-automatic log stacker.
Unfortunately we still see plants
inefficiently running books, directories or magazine work through a
compensating stacker or retail work through a log stacker from where they pile
down loose bundles.
Here the two
main question which help to make the right choice:
ƒWhat
will the press print : books – directories – magazines & catalog –
inserts – newspapers
What
is the degree of automation (manual pocket feeding or stream feeders) in the
bindery
Here under a fast and simple guide to
what could be the best machine for your operation. It is not a “black or white”
choice since space; budget, future plans etc. will also influence the choice:
Compensating Stacker - best for..off the press products“
- For retail applications, with our without trimming (finished products)
- For Loose, compensated bundles, 100-250 mm
- Newspaper printing (direct print, at the end of inserters,..)
- Builds loose, counted & compensated bundles behind web presses
- As alternative solution in magazine / catalogue printing to handle WIP
Speed
|
pagination
|
sizes
|
application
|
<120 .000cph="" span="">
|
2-128p
|
magazine-tabloid
|
heat set + coldest
|
Semi-automatic Log Stackers – best for „work-in-process“
- For magazine / catalogue applications (unfinished work-in-process WIP)
- For book & directory Compressed, counted and secured logs, 450 – 800mm
- Printing (direct print, at the end of inserters,..)
- Builds compressed & strapped logs behind web presses
- Copies in the strapped & stable logs are secured between two end boards
Speed
|
pagination
|
sizes
|
application
|
<70 .000="" cph="" span="">
|
4-64p
|
magazine-tabloid
|
Heatset + coldest
|
COMPENSATING STACKER
|
LOG STACKER
|
Delivers loose, counted, compensated and unstrapped bundles
|
Delivers counted, compressed, uncompensated logs secured by two
end boards and safely strapped.
|
100-250 mm bundles height ( in average)
|
450-800 mm log length on semi automatic
log stacker.
|
No need of consumables for the loose
bundles. Possibly need of consumables ( strapping belt/film) to stabilize &
protect the pallets
|
End boards and strapping material needed
for each log. Normally no additional cosnumables needed to stabilize &
protect the pallets.
|
The stacks are only shortly compressed in
the stacker. After placing the products on the pallet the spine will tend to
build up again ( memory effect on the paper). The higher position of a bundle
on the pallet the more air will be in the bundle>no uniform bundles
|
The logs are compressed resulting in
completely flat sections with no risk of folded edges. No alternation will
happen to the products once they are placed onto the pallet> all products
are flat & uniform.
|
The loose bundles on the pallet are
unprotected. They tend to move, especially in the lower layers. Loose bundles
are exposed t dust, temperature and humidity. The level of compression also
varies with the position of the bundles on the pallet ( with high compression
on 1st layer, no compression on last layer).
|
All products in the log are equally
compressed. The products in the log are protected, they can not move (
neither in the log nor on the pallet). The products are not exposed to dust,
temperature or humidity.
|
Slip sheets & pallet film wrapping
will protect the loose bundles. This adds costs for labor & consumables.
The use of film can lead to folded edges of the sections which can increase
the risk of jams in the bindery. Optionally carton corners can be used before
film wrapping.
|
Slip sheets may be used but no film is
necessary. No costs for additional consumables. No folded edges of the
sections.
|
Work load of a compensating stacker is
higher-higher frequency of bundles which are mostly placed manually on a
pallet. Example 7 layers x 14 stacks = 98 movements per pallet.
|
Lower frequency of logs which can be
placed manually ( short logs) or by means of a semi-automatic clamp or a log
palletizer on a pallet. Example: 4 layers x 4(6/11) logs = 16 ( 24/44)
movements per pallet.
|
One man operation on compensating stacker
behind slower and smaller presses. Two men operation on compensating stacker
behind high volume and faster presses.
|
One man operation on semi-automatic log
stacker. One man operation on two fully automatic log stackers (
configuration allowing).
|
It is difficult to stack pallets with
loose bundles w/o damaging the product. Securing the pallets entails
additional costs.
|
Easy stacking of pallets.
|
Pallets will have to be shrink wrapped if
transported to a bindery which is not in house.
|
Printed products are secure whether to be
taken to a bindery in house or outside. Only end boards need to be returned.
|
Tuesday, September 4, 2012
Offset Printing: The Next Greatest Thing in Blanket Cleaning
Offset Printing: The Next Greatest Thing in Blanket Cleaning: I don't like to promote products, especially ones that are unproven. But there was a new product released at Drupa by Grafinkontrol for ...
Monday, November 7, 2011
Dot Gain....!!!!!
Dot gain
Dot gain is a phenomenon that causes printed material to look darker than intended. This happens because the diameter of halftone dots increases during the prepress and printing process. The optical and physical properties of the media and machines used both in preparing the job for print and the printing process itself cause this behavior. Below is an example of what happens when a nice flat tint (left) gets printed on newspaper stock: ignore the fact that the paper is grayish – look at how the dots get fuzzy and a lot bigger.
Simulation of dot gain in a newspaper
Prepress and press operators can try to minimize certain types of dot gain but cannot avoid that dot gain occurs. As such it is also the responsibility of the designer to be aware of dot gain and to anticipate its effect. You typically find dot gain controls in applications like Adobe Photoshop.
Dot gain controls in Photoshop
Dot gain basics
Dot gain is expressed as a numerical value which equals the difference between the wanted value and the resulting value. For instance: if a page has a 50% flat tint as a background but after measuring the printed result, this flat tint is now 65%, the dot gain equals 15%.
•Please note that the convention for specifying dot gain is slightly weird: it is expressed as a percentage at a certain tint. The percentage however is not a real percentage but an absolute value – 20% dot gain at 50% does not mean the end result are halftone dots that are 60% but that the resulting halftone dots measure 70%!
•If no target percentage is specified, it is assumed that dot gain is specified for a 50% tint.
Dot gain is not identical for all the colors used in color printing. There are slight differences in dot gain between cyan, magenta, yellow and black.
Total dot gain is the difference between the dot size on the source file and the corresponding dot size on the printed result.
Dot gain is sometimes refered to as TVI (tone value increase). TVI is a more generic description of the difference in tone value between a requested value and the final output. It is also a more suitable name for processes in which some devices may not actually deliver a dot in the final output.
Types of dot gain
There are different types of dot gain in the prepress and printing process.
Dot gain caused by imaging devices & media
The optical system in computer to plate systems or imagesetters is not always perfectly linear. In order to make sure that the media are exposed sufficiently, the laser beam is a bit wider than needed so that the lines that are exposed slightly overlap each other. Depending on the process (positive/negative), this may cause either a slight dot gain or a dot loss.
Media such as plates or film also can be non-linear: some are but polymer plates for instance can have a dot gain of 5 percent of so.
Mechanical dot gain on a printing press
On an offset printing press ink is transferred from the printing plate to the blanket and from the blanket to the paper. Each time the dots get squashed a little bit, increasing the physical diameter of the printed dot. The ink that is used, the fountain solution, the blanket, the pressure (over/underpacking) and the speed at which the press runs all influence this type of dot gain.
When ink is absorbed in paper, this occurs both vertically (into the paper) and sideways, which again increases the dot diameter. This effect is more pronounced 0n newsprint than it is on coated paper.
Optical dot gain
When light hits the printed surface, it becomes slightly diffused around the dots. The human eye (as well as measuring devices) perceive this as a darkening. Dots appear to be larger than they really are.
Compensating for dot gain
Applications like Adobe Photoshop will automatically compensate for dot gain when images are converted from RGB to CMYK. This is done based on the selected preferences, as shown in the above screen capture of Photoshop CS3′s color settings. Designers need to be aware of this and make sure that their software is configured properly for the printing process that will be used to print their jobs. They also need to be aware that vector based applications like Adobe Illustrator don’t compensate for dot gain. If you draw infographics for a newspaper, you need to make sure that flat tints don’t get too dark in print.
Prepress operators are expected to make sure that plates delivered to the press are linear, with a typical tolerance of around 2%. Workflows and RIPs come with calibration tools to achieve this. If a system has 5% dot gain, instructing the RIP to image a 50% tint as a 45% tint assures that the end result is once again 50%. This process is called linearisation.
Given the fact that so many people supply files that are optimised for sheetfed offset printing with a dot gain between 12 and 20%, operators may tweak other devices such as digital presses to mimic the dot gain behavior of offset presses.
In general higher screen rulings exhibit more dot gain. Vendors of workflow and computer to plate systems sometimes anticipate this: for the very fine dots that are used in screening algorithms such as stochastic screening, they create screen cells that aren’t linear – the 50% dots may for instance be 38% dots. By including a pre-compensation in the screen cells, printers achieve better results with the out-of-the-box set-up and only have to focus on fine-tuning the system to their particular needs.
Dot gain is a phenomenon that causes printed material to look darker than intended. This happens because the diameter of halftone dots increases during the prepress and printing process. The optical and physical properties of the media and machines used both in preparing the job for print and the printing process itself cause this behavior. Below is an example of what happens when a nice flat tint (left) gets printed on newspaper stock: ignore the fact that the paper is grayish – look at how the dots get fuzzy and a lot bigger.
Simulation of dot gain in a newspaper
Prepress and press operators can try to minimize certain types of dot gain but cannot avoid that dot gain occurs. As such it is also the responsibility of the designer to be aware of dot gain and to anticipate its effect. You typically find dot gain controls in applications like Adobe Photoshop.
Dot gain controls in Photoshop
Dot gain basics
Dot gain is expressed as a numerical value which equals the difference between the wanted value and the resulting value. For instance: if a page has a 50% flat tint as a background but after measuring the printed result, this flat tint is now 65%, the dot gain equals 15%.
•Please note that the convention for specifying dot gain is slightly weird: it is expressed as a percentage at a certain tint. The percentage however is not a real percentage but an absolute value – 20% dot gain at 50% does not mean the end result are halftone dots that are 60% but that the resulting halftone dots measure 70%!
•If no target percentage is specified, it is assumed that dot gain is specified for a 50% tint.
Dot gain is not identical for all the colors used in color printing. There are slight differences in dot gain between cyan, magenta, yellow and black.
Total dot gain is the difference between the dot size on the source file and the corresponding dot size on the printed result.
Dot gain is sometimes refered to as TVI (tone value increase). TVI is a more generic description of the difference in tone value between a requested value and the final output. It is also a more suitable name for processes in which some devices may not actually deliver a dot in the final output.
Types of dot gain
There are different types of dot gain in the prepress and printing process.
Dot gain caused by imaging devices & media
The optical system in computer to plate systems or imagesetters is not always perfectly linear. In order to make sure that the media are exposed sufficiently, the laser beam is a bit wider than needed so that the lines that are exposed slightly overlap each other. Depending on the process (positive/negative), this may cause either a slight dot gain or a dot loss.
Media such as plates or film also can be non-linear: some are but polymer plates for instance can have a dot gain of 5 percent of so.
Mechanical dot gain on a printing press
On an offset printing press ink is transferred from the printing plate to the blanket and from the blanket to the paper. Each time the dots get squashed a little bit, increasing the physical diameter of the printed dot. The ink that is used, the fountain solution, the blanket, the pressure (over/underpacking) and the speed at which the press runs all influence this type of dot gain.
When ink is absorbed in paper, this occurs both vertically (into the paper) and sideways, which again increases the dot diameter. This effect is more pronounced 0n newsprint than it is on coated paper.
Optical dot gain
When light hits the printed surface, it becomes slightly diffused around the dots. The human eye (as well as measuring devices) perceive this as a darkening. Dots appear to be larger than they really are.
Compensating for dot gain
Applications like Adobe Photoshop will automatically compensate for dot gain when images are converted from RGB to CMYK. This is done based on the selected preferences, as shown in the above screen capture of Photoshop CS3′s color settings. Designers need to be aware of this and make sure that their software is configured properly for the printing process that will be used to print their jobs. They also need to be aware that vector based applications like Adobe Illustrator don’t compensate for dot gain. If you draw infographics for a newspaper, you need to make sure that flat tints don’t get too dark in print.
Prepress operators are expected to make sure that plates delivered to the press are linear, with a typical tolerance of around 2%. Workflows and RIPs come with calibration tools to achieve this. If a system has 5% dot gain, instructing the RIP to image a 50% tint as a 45% tint assures that the end result is once again 50%. This process is called linearisation.
Given the fact that so many people supply files that are optimised for sheetfed offset printing with a dot gain between 12 and 20%, operators may tweak other devices such as digital presses to mimic the dot gain behavior of offset presses.
In general higher screen rulings exhibit more dot gain. Vendors of workflow and computer to plate systems sometimes anticipate this: for the very fine dots that are used in screening algorithms such as stochastic screening, they create screen cells that aren’t linear – the 50% dots may for instance be 38% dots. By including a pre-compensation in the screen cells, printers achieve better results with the out-of-the-box set-up and only have to focus on fine-tuning the system to their particular needs.
Wednesday, August 3, 2011
Saturday, June 4, 2011
Printing Blanket Problems and Trouble shooting...... PART 2
11. Problem - Pinholes In Blanket
Cause:
Blanket defect; particles coming out of blanket surface.
Corrective Action:
Make sure hole is in surface rubber rather than a hickey on blanket or plate surface.
Replace blanket and save for evaluation and replacement by manufacturer.
12. Problem - Plate Blinding
Cause:
Excess plate to blanket squeeze
Blanket surface too hard
Improper pH
Improper form roller settings
Bad or improperly made plate
Corrective Action:
Adjust plate to blanket squeeze to a measured .004" to .005".
If blanket old and hard to the touch, try a new blanket.
Compressible blankets will give more packing latitude.
Check pH and conductivity.
13. Problem - Plate Cracking
Cause:
Loose plate.
Poor plate bend.
Packing short or askew.
Incorrect plate gage.
Sharp cylinder edge.
Corrective Action:
Check cylinder clamps and adjust or repair as necessary.
Re-clamp plate.
Check bending jig.
Re-make plate.
14. Problem - Plate Cracking Con’t
Cause:
Plate gap not hitting inside blanket gap.
Corrective Action:
Check packing and replace if necessary.
Verify correct thickness and measure plate.
Smooth down edge.
Retime cylinders to correct settings.
15. Problem - Registration---Circumferential
Cause:
Loose blanket or improper packing from one unit to the next
Stock feed problem
Excessive moisture gain between printing units
Erratic infeed tension
Unstable stock
Corrective Action:
Insure blanket is properly torqued.
Check proper packing of plate and blanket between units where fit is an issue.
Reduce water feed or change stock if absorbing excess water is changing stock dimension.
Check infeed rolls set properly.
Verify plate installed and bent properly.
16. Problem - Registration---Lateral
Cause:
Often relates to excess water absorption by paper
Excess nip pressure causes paper to spread
Paper roll tensioned poorly by mill
Press infeed tension erratic
Corrective Action:
First check nip pressure by verifying blanket packing. Use less packing if overpacked.
Try reducing water to minimize absorption.
Adjust press infeed tension settings.
May require paper change. Discuss with paper supplier.
17. Problem - Scumming
Cause:
Incorrect ink/water balance.
Improper water form roll setting.
Contaminated fountain solution.
Plate sensitized in non-image area.
Incorrect fountain solution mix.
Incorrect printing pressure.
Out of round or hard form rolls.
Running abrasive paper.
Corrective Action:
Increase water or decrease ink.
Check stripe and adjust if necessary.
Clean system and replace solution.
Clean and desensitize plate.
Remake plate.
Check pH and conductivity and correct.
Check plate to blanket squeeze.
Check hardness and run out and replace rolls if necessary.
Change paper.
Add non-piling agent to fountain solution.
18. Problem - Slurred Print
Cause:
Excess nip pressure at plate & blanket or blanket & impression
Loose blanket
Improper form roller settings
Improper ink water balance
Corrective Action:
Check blanket packing and plate packing. On sheetfed or business forms web, check
squeeze to impression cylinder…adjust.
Check torque of blanket lock up.
Many times too much ink or improper ink water balance is the problem. Check ink train
settings.
19. Problem - Streaking
Cause:
Press condition known as gear streaks
Can be made worse by excess bearer pressure or plate to blanket squeeze
Ink form rolls set wrong or too hard
Corrective Action:
Older or worn press ears can cause streaking. Compressible blankets can help minimize this.
Other factors can include blanket or plate overpacked. Insure proper nip pressure between plate and blanket.
Check bearer pressures…adjust.
Adjust form rollers, replace if durometer too hard.
20. Problem - Tinting
Cause:
Ink too low in viscosity.
Too acid fountain solution.
Ink not resistant to alcohol or fountain solution.
Corrective Action:
Increase viscosity, contact ink supplier.
Increase pH to a minimum of 3.5.
Reformulate ink.
21. Problem - Trap/Poor
Cause:
Ink tack out of sequence.
Improperly balanced ink strength.
Poor ink/water balance.
Ink tack cross o ver.
Excessive heat generated.
Paper coating not ink receptive.
Corrective Action:
Revise ink tacks or laydown sequence.
Contact ink supplier.
Adjust as necessary, run as little water as possible.
Contact ink supplier.
Check vibrator temperature and reduce coolant temperature.
Contact paper supplier.
Cause:
Blanket defect; particles coming out of blanket surface.
Corrective Action:
Make sure hole is in surface rubber rather than a hickey on blanket or plate surface.
Replace blanket and save for evaluation and replacement by manufacturer.
12. Problem - Plate Blinding
Cause:
Excess plate to blanket squeeze
Blanket surface too hard
Improper pH
Improper form roller settings
Bad or improperly made plate
Corrective Action:
Adjust plate to blanket squeeze to a measured .004" to .005".
If blanket old and hard to the touch, try a new blanket.
Compressible blankets will give more packing latitude.
Check pH and conductivity.
13. Problem - Plate Cracking
Cause:
Loose plate.
Poor plate bend.
Packing short or askew.
Incorrect plate gage.
Sharp cylinder edge.
Corrective Action:
Check cylinder clamps and adjust or repair as necessary.
Re-clamp plate.
Check bending jig.
Re-make plate.
14. Problem - Plate Cracking Con’t
Cause:
Plate gap not hitting inside blanket gap.
Corrective Action:
Check packing and replace if necessary.
Verify correct thickness and measure plate.
Smooth down edge.
Retime cylinders to correct settings.
15. Problem - Registration---Circumferential
Cause:
Loose blanket or improper packing from one unit to the next
Stock feed problem
Excessive moisture gain between printing units
Erratic infeed tension
Unstable stock
Corrective Action:
Insure blanket is properly torqued.
Check proper packing of plate and blanket between units where fit is an issue.
Reduce water feed or change stock if absorbing excess water is changing stock dimension.
Check infeed rolls set properly.
Verify plate installed and bent properly.
16. Problem - Registration---Lateral
Cause:
Often relates to excess water absorption by paper
Excess nip pressure causes paper to spread
Paper roll tensioned poorly by mill
Press infeed tension erratic
Corrective Action:
First check nip pressure by verifying blanket packing. Use less packing if overpacked.
Try reducing water to minimize absorption.
Adjust press infeed tension settings.
May require paper change. Discuss with paper supplier.
17. Problem - Scumming
Cause:
Incorrect ink/water balance.
Improper water form roll setting.
Contaminated fountain solution.
Plate sensitized in non-image area.
Incorrect fountain solution mix.
Incorrect printing pressure.
Out of round or hard form rolls.
Running abrasive paper.
Corrective Action:
Increase water or decrease ink.
Check stripe and adjust if necessary.
Clean system and replace solution.
Clean and desensitize plate.
Remake plate.
Check pH and conductivity and correct.
Check plate to blanket squeeze.
Check hardness and run out and replace rolls if necessary.
Change paper.
Add non-piling agent to fountain solution.
18. Problem - Slurred Print
Cause:
Excess nip pressure at plate & blanket or blanket & impression
Loose blanket
Improper form roller settings
Improper ink water balance
Corrective Action:
Check blanket packing and plate packing. On sheetfed or business forms web, check
squeeze to impression cylinder…adjust.
Check torque of blanket lock up.
Many times too much ink or improper ink water balance is the problem. Check ink train
settings.
19. Problem - Streaking
Cause:
Press condition known as gear streaks
Can be made worse by excess bearer pressure or plate to blanket squeeze
Ink form rolls set wrong or too hard
Corrective Action:
Older or worn press ears can cause streaking. Compressible blankets can help minimize this.
Other factors can include blanket or plate overpacked. Insure proper nip pressure between plate and blanket.
Check bearer pressures…adjust.
Adjust form rollers, replace if durometer too hard.
20. Problem - Tinting
Cause:
Ink too low in viscosity.
Too acid fountain solution.
Ink not resistant to alcohol or fountain solution.
Corrective Action:
Increase viscosity, contact ink supplier.
Increase pH to a minimum of 3.5.
Reformulate ink.
21. Problem - Trap/Poor
Cause:
Ink tack out of sequence.
Improperly balanced ink strength.
Poor ink/water balance.
Ink tack cross o ver.
Excessive heat generated.
Paper coating not ink receptive.
Corrective Action:
Revise ink tacks or laydown sequence.
Contact ink supplier.
Adjust as necessary, run as little water as possible.
Contact ink supplier.
Check vibrator temperature and reduce coolant temperature.
Contact paper supplier.
Tuesday, May 3, 2011
Printing Blanket Problems and Trouble shooting...!
1.Problem - Area of Weak Print
Cause:
4. Problem- Dot Doubling
5. Problem-Dot Grain
Corrective Action:
To be continued....!
Cause:
Improper Bearer pressure. Packing Damaged.
Blanket Smash
Insufficient packing or back cylinder pressure
Low spot in cylinder
Plate Blinding
Corrective Action:
Check for smashed area and blanket and/or packing. Also try adjusting back cylinder setting.
Check blanket height, repack or replace.
Press condition…over pack or spot pack.
Check plate to blanket squeeze
Remake plate
2. Problem-Bar Pull Off/Out
Cause:
Over tensioned blanket.
Improperly applied bar.
Incorrect bar used.
Improperly installed into cylinder reel rod.
Out of square blanket.
Corrective Action:
Check means of tensioning and calibration of equipment.
Over/under specified mounted thickness.
Insufficient epoxy width or thickness.
Check press listing and bar dimensional specifications.
Check for bent blanket bar legs.
Check for unequal gap bend marks on back of blanket.
Check for contaminated cylinder reel rod and clean if necessary.
Check squareness of blanket.
3.Problem- Delamination
Cause:
Solvent attack.
Excess blanket squeeze.
Ink build up on edges.
Blanket edges not sealed.
Corrective Action:
Obtain samples of blanket wash and ink with MSDS and send to lab for evaluation.
Check back of blanket for excessive use of wash.
Check surface of blanket for face cuts that would allow solvent to attack cement.
Check packing pressure.
Use mourning bands.
Undercut packing.
Seal edges.
4. Problem- Dot Doubling
Cause:
Loose blanket.
Excessive squeeze.
Excessive ink feed to achieve density.
Film/plate movement during exposure.
Corrective Action:
Retension blanket, incorrect installation.
Reduce plate to blanket packing or blanket to impression cylinder setting.
Decrease ink/water amounts.
Change to more ink receptive blanket.
Check dots on plate.
5. Problem-Dot Grain
Cause:
Ink form rolls set too tight.
Ink form rolls too soft.
Low ink viscosity or tack.
Poor ink/water balance.
Ink has too much water pickup.
Excessive squeeze.
Fountain solution temperature too high.
Incorrect fountain solution pH.
Under/over exposed plate/film.
Improper blanket surface.
Corrective Action:
Replace with high viscosity ink or increase tack.
Adjust press speed.
Reduce amount of ink and water.
Have ink checked by ink supplier.
Reduce plate to blanket squeeze.
Reduce blanket to impression cylinder setting.
Reduce temperature to 55 to 60 degrees F.
Adjust solution pH to read between 3.5 to 5.0.
Check dot size on plate and re-make if necessary.
Change to more compatible blanket.
6.Problem- Embossed Blanket
Cause:
Blanket swollen due to excessive pressure, very high ink tack, or lack of cleaning with proper blanket wash.
Solvents in ink may affect blanket (UV inks for example)
Corrective Action:
Check blanket thickness and packing. Use quality blanket wash and clean blankets on a regular basis.If blanket is old, change to a new blanket, or one that works better with your inks.
UV inks and washes can often swell blankets. Try a UV compatible blanket.
7. Problem-Ghosting
Cause:
Ink form rollers starved for ink
Job layout causing problem
Ink/water balance issue
Corrective Action:
Not a blanket issue. Check roller settings, run a thicker ink film with minimum of water.
Job layout often contributes to the problem…change direction of run or general layout if possible.
8. Problem-Loss of Print at Gap
Cause:
Blanket over-torqued. Packing incorrect.
Packing slipped
Press out of phase (timing issue)
Corrective Action:
Insure proper packing of blanket and use torque wrench to tighten to press manufacturer specs. Check torque wrenches for accuracy.
Some print length problems are due to cylinders being out of phase. Check cylinder timing to print length.
9. Problem-Mottled Print
Cause:
Running too much water.
Blanket surface contamination.
Incompatible blanket style with fountain solution.
Excessive fountain solution temperature.
Excessive water absorption of paper.
Partially blind image on plate.
Using course grain plate.
Improper ink/water balance.
Not enough squeeze.
Corrective Action:
Reduce the amount of water.
Inspect surface of blanket for glaze, shiny steaks or spots, excessive talc, etc., clean with solvent and rinse with water.
Change type of blanket used or type of fountain solution.
Reduce temperature to 55 to 60 degrees F.
Contact paper supplier.
Remake plate
Change to finer grained plate.
Adjust balance.
Adjust packing.
10. Problem-Piling---Ink
Cause:
Most frequently an ink problem (ink too short and not water repellent), fountain solution PH or conductivity wrong, or rollers set wrong & heat building up.
Blanket underpacked
Corrective Action:
The blanket is least likely to be the cause of ink piling even though the ink piles on the blanket. If blanket-related, it is generally due to insufficient packing. Verify proper packing and nip pressures. Check ink feed, roller settings and set to minimum, check fountain solution PH & conductivity.
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