GRAFIMPEX

GRAFIMPEX
Equipment & Solutions for Newspaper and Commercial Printers

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.

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.

Tuesday, May 3, 2011

Printing Blanket Problems and Trouble shooting...!

1.Problem - Area of Weak Print

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.

To be continued....!

Thursday, February 24, 2011

Success in Business Relationships….!!!! Do we treat our business relations the same way we treat our personal relationships..!!

It is imperative for every businessman, whether a budding entrepreneur or a CEO of a large corporation to spend time and analyze the guiding values in his and his organizations business relationships.

Aren’t your business relationships an extension of how you interact in your personal relations..? Do you treat your business partners with same standards as you treat your personal relations?

It won’t take long for an intelligent person to understand that the four key elements that one needs to incorporate into any business transaction or relationship

The four key elements of any successful business relationships are:

TRUST – Business relationships are a two way street. Both parties should come out of the relationship having gained something. If only one party wins, then it's an unfair relationship.

One needs to be able to trust a business partner and vendor. If that a partner is not living up to their obligations in being trustworthy, then the relationship may be severed. I believe that the same expectation must be extended to us by our customers and business partners. If we are not honest with our customers and business partners then why would they continue to do business with us? They wouldn't.

RELIABILITY - I believe that it's our duty as a business person to offer reliable services to our customers. We do not gain by over committing our selves and taking on to deliver what we can not in terms of products, services or time to serve etc.

HONESTY- It's definitely in your best interest as a businessperson to conduct yourself in an honest manner. I believe that people need to present the truth as they see it and be honest with their customers and business partners. If your partners and customers see you as an honest person then they will be more likely to do more business with you.

INTEGRITY - Integrity is defined by dictionary.com as having a strong moral and ethical code. Each person has a different code of morals and ethics and I'm not saying that it has to come from a set of belief system.

I believe that every businessperson needs to form their own code of conduct. That code of conduct needs to have a set of morals and ethics. This set of morals and ethics is like a road map and must be consistently applied.

If you adhere to your set of morals and ethics you will conduct yourself with integrity.

Your business partners and customers will see you as a principled person who has a set of standards that can be trusted.

I believe that incorporating trust, reliability, honesty and integrity into your business relationships are vital to being a success in business…! Happy relating..!!!



Friday, February 18, 2011

Print Glossary- Helping You Make Sense of Web Offset Printing

You certainly don’t have to be an expert in web offset printing to make your projects look fantastic. But, having an understanding of the most common terms can be a real advantage!

Blanket: a piece of rubber that has fabric on it. In a web offset printing press, a blanket is used to transfer images and letter from the metal plate onto the paper.

Coldset Web Offset Printing: a printing process in which ink is left to dry manually through air exposure and evaporation. It is also called “non-heatset web offset printing”.

Color Proof: a representation of the final product made before the mass printing is done.

Final Trim Size: the finished size of a magazine, postcard, brochure, flyer, etc. In web offset printing, documents are printed on larger paper, then trimmed to the right size at the end.

Finishing: refers to any post-printing process, such as trimming or folding.

Heatset Offset Printing: a web offset printing process in which the ink is dried rapidly while passing through a special oven, instead of waiting for the ink to dry through air exposure. Heatset offset printing is used for glossier papers that are not particularly absorbent.

Offset Printing: a method of printing in which images or letters are put onto metal plates, then transferred to either a blanket or rubber rollers, then transferred onto paper. Since the rubber is flexible, it conforms to any surface – including wood, canvas, or cloth; It is also called “offset lithography”.

Perfecting Press: a printing press that is capable of printing on both sides of paper during a single pass through the machine. Offset printing is the only printing technique that is capable of using a perfecting press.

Sans Serif: a typeface that doesn’t have any serifs – or small strokes at the end of each letter. Arial is a sans serif font; Times New Roman is not.

Specifications Web Offset Publications: refers to guidelines for each printing project – including information on the font, color bars, and proofing stock. Also called “SWOP”, it ensures that each member of the printing team is on the same page when it comes to web offset printing projects, so that each image and document looks uniform.

Web Offset Printing: a form of offset printing in which paper is fed continuously through the printing press on a roll, rather than feeding each sheet into the printer individually. Web offset printing is used primarily for high-volume publications – like newspapers, magazines, and catalogs.

Wednesday, February 9, 2011

The best solution for combined newspaper / commercial printing in Post Press

It is not so easy to find the right post press solution for semi-commercial presses. Bulky newspaper stackers might give you the necessary speed for thick, large-format newspapers but often lack the finesse to give a proper stack quality which is necessary for commercial-/semi-commercial products. With more than 9000 stackers sold worldwide, RIMA-SYSTEM is an expert in stacking technology and has the perfect machine for the necessary capacity in newspaper printing AND giving great stack quality for the semi-commercial productions.

At El Comercia and El Universo in Ecuador the customers have equipped their presses with RS 36 indexing stackers from RIMA-SYSTEM. The stackers can run at speeds of more than 100.000cph per hour and at the same time guarantee perfect stable bundles thanks to the indexing forks in the upper bin and the servo-pusher with synchronized delivery-belt making it the ideal machine for modern hybrid-presses..

Sunday, January 9, 2011

Waste Management in Newspaper Printing

Newsprint is the highest cost component for a Newspaper Printer, and we can easily classify the total pape rwaste in a press by taking difference of Newsprint supplied to the press and total sellable copies printed, the difference is a thumb rule WASTE.

In order to effectively manage waste in a press, lets look at further classifications and then dwell on process and areas where we can monitor, control and manage waste..!

1. Tare waste (Wrapper waste)

2. Mat Waste (Tear sheet waste)
3. Reel end waste (Core waste)
4. Sweep Waste (Scrap waste)
5. Print Waste (Bad Copies waste)

Lets look at the costeliest yet controllable waste out of the aobe five categories which is the PRINT WASTE-

What are the factores that contribute most towards generating higher Print Waste?


Press Condition- A press which is ignored for prevantive and routine maintenance by the press crew will obviosly generate higher waste. Does the operators and maintenance staff understand the press well, have they been trained by the supplier? Normally the focus is on production and as long as the crew is able to deliver production the machine problems are ignored, deficiencies are patched up which subsequently result in break downs or excessive wear and tear of critical components directly effecting Print quality and generation of non sellable copies.
A good printer will understand that any deficiency in print quality may have originated from a dormant press problem which is being overlooked. Check for unhealthy signs in the printing operation before it suddenly surfaces and when it is too late...!

Normally the maintained scheduled times are considered as non productive , part of down time of the machines . this is a dangerous perspective . the management and print crew should recognize the print need for allocating adequate time for maintenance.

The machines maintenance. In short, is identifications and eliminations of each and every factor that limits quality, reduces speed lengthened make ready time and these factor are being the waste factors , there are simple strategies to be adopted , while attending the press.
  • Look for defect in printing like dot gain , slur trapping register errors etc (if you do not have facilities for measurements , visual information will suffice). For every symptom , analyze all possible contributory factors by the press . check, ascertain, attend and correct the defect .
  • Closely Monitor and look for abnormal sound . heat vibrations and machines load.
  • Look for defect in web running like loose web , web break, and margin and register shift etc. for every symptom analyses and correct the defect.
  • Closely monitor and look for abnormal sound , heat, vibration and machines load, all through the production run. Parameters indicate probable defects like lake of lubrication , wear un balanced alignment related problems. Analyses and attend.
  • In all the three situations given situations given above . do a deep study. Any wrong diagnosis will lead to waste of time . man hours and may lead to furder complications.
  • Do not attend to eliminate symptoms, but handle the root causes.
  • While disassembling and re-assembling , apply the mind . do not perform the act mechanically.
  • For repairing , use the right tools . wrong and in – appropriate tools will cause delay and damaged to the part handled.
  • Keep relevant drawing always for reference.
  • Try to understand the functional aspects of each and every machines element and their locations and positioning relevance.
  • Go through the daily weekly and monthly maintance schedules as recommended by the manufacturers.
  • Maintain a health card for every machines
  • The replacement parts and others consumables will be best if bought from the manufacturers themselves . any temptations for saving by going for cheaper items will prove to be costly in a long run.
  • Be pro-active and not re-active.
  • Engage the press crew for the basic maintenance and not a separate team.
  • Give the press the best. It is due to it.
Please have a raport with the press. Do not consider it as an inert machine, you can communicate with it and you will find that machine always respond positively to your loving gestures....!!!