FAQ

In practice, we are often faced with repeated questions on the use or features of our products. Some of these questions are answered here in this FAQ corner.

QUESTIONS AND ANSWERS

FAQ No. 1:
Why should we use a CONTI-AIR® printing blanket?

Optimum cost/benefit ratio

• minimum thickness tolerances (far better than ISO 12636)
• extremely good smash resistance
• less press downtime
• long service life
• high resistance to swelling
• uniformity of compressibility from batch to batch thanks to patented manufacturing
• process for compressible layer
• worldwide sales networ

Best print quality in screens and solids

• adapted, constant increase in tonal value
• smooth printing of solids
• good quick-release properties with paper
• excellent suppression of streaking
• minimum sinking

Compressibility (quasi-static/printing blanket tensioned)

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FAQ No. 2:
How should printing blankets be stored correctly?

• between 15°C and 30°C
• between 50% and 65% relative humidity
• avoid direct sunlight (danger of ozone cracks)
• away from electric motors (danger of ozone cracks)
• lying flat or suspended
• always rubber to rubber and fabric to fabric
• use "first in, first out" principle

Special drawer units are available which provide excellent storage for pressure plates, packings, foils and also printing blankets.

 

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FAQ No. 3:
Which cleaning solvents are best?

The most important feature for the user, of course, is that the solvents should clean the printing blankets as quickly and easily as possible. An extremely wide range of solvents of varying performance is commercially available.

It is important to note that we distinguish between printing blankets used for conventional inks and UV inks.

• Printing blankets used for conventional inks should be cleaned with a solvent which does not contain any polar substances, e.g. esters.
• In the case of printing blankets used with UV inks, the solvents should not contain any non-polar substances, e.g. benzene.
• Ink manufacturers also offer solvents which are suitable for their inks and which have been approved by FOGRA before they are launched.
• Press manufacturers also issue lists of recommended materials.

How can I determine whether my printing blanket solvent is aggressive towards the printing blanket?

• Take a special jar (available from appropriate trade outlets),
• cut the printing blanket to the size of the lid and measure the thickness (e.g. 1.95 mm),
• fill the glass approx. ¼ with the solvent,
• wedge the test piece into the lid (with the rubber cover towards the inside of the jar),
• screw the lid onto the jar, invert the jar and leave for 22 hours,
• after 22 hours turn the jar upright, remove the test piece and re-measure the thickness (e.g. 1.98 mm). In this example the difference in thickness is 0.03 mm,
• an increase in access of 0.06 mm is considered aggressive

In cases of doubt ContiTech is happy to carry out the appropriate tests! To do so, we require approx. 50 ml of the medium to be tested and the relevant safety data sheet in German or English.

These CONTI-AIR Distribution Partners manufacturing prerss room chemicals are at your disposal for any information you may require:

Frithjof Tutzschke GmbH (www.siegel-co.de)

Prisco (www.prisco.com)

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FAQ No. 4:
What torque is used to tension a printing blanket?

Torque in rotating wheels, shafts and screws/bolts is the product of the magnitude of the force and the perpendicular distance between the axis of rotation and the line of action of the force, expressed in Nm.

Depending on the printing blanket tension take-up system, printing blankets are tensioned at 1.5 to 130 Nm. This results in a printing blanket being elongated by 1% to 2%.

The low torque figures apply to tensioning bolts on bar systems - e.g.1.5 Nm - while the high figures apply to tensioning spindles in large-format offset presses - e.g. 130 Nm.

A torque wrench should be used to ensure compliance with the torque specified by the press manufacturer. Torque wrenches which cannot be adjusted but which measure only the specified torque value have proved ideal.

The purpose of using a torque wrench when tensioning the printing blanket is to ensure reproducible printing blanket tensions in all printing plants and with all press operators.

Calibrate torque wrenches regularly and keep tension take-ups clean.

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FAQ No. 5:
How often should I retension?

Tensioning of the printing blanket after "running-in" is regarded as part of the fitting process for the printing blanket. The next tensioning of the printing blanket after this counts as the first retensioning.

The retensioning frequency depends on:

• printing blanket size,
• printing blanket impression,
• radius of the gap edges,
• bend of the printing blanket at the gap edge,
• printing length between the gap edge and the printing blanket tensioning tool,
• and the take-up mechanism; there are take-up systems that tension the blankets on on side only or on two sides - tensioning on both ends can happen separately or simultanously.

Depending on the above conditions, retensioning one to three times may be appropriate.

The "normal" retensioning frequency should be specified in an in-house work instruction - e.g. "Tensioning printing blankets".

Divergences from these empirical values can indicate:

• errors in fitting the printing blanket,
• differing restricted elongation of the printing blanket,
• damage to the printing blanket,
• inadequate bar adhesion,
• stiff take-up system.

Divergences should be analysed immediately and the causes rectified. In the case of CONTI-AIR® products, the user can call on our company's technical service representatives .

Failure to retension or check the printing blanket tension results in:

• doubling
• greater temperature increase in the printing blanket
• reduced printing blanket service life
• greater plate wear
• creeping of the packings

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FAQ No. 6:
What is the service life of a printing blanket?

The service life refers to the operating period of a printing blanket during which it meets the user's requirements.

We recommend recording the service life in cylinder revolutions. Do not count in copies or operating hours!

The service life of a printing blanket depends on::

• impression in the printing blanket,
• operating conditions and the external influences which result in damage,
• washing system for the printing blanket,
• print quality.

Average service lives in cylinder revolutions are as follows:

• 1-3 million on sheet-fed offset presses
• 5-8 million on heatset presses
• >8 million on coldset presses

Recommendation:
Determine in-house service lives and check regularly that these are being met. This requires that the dates on which the printing blanket is fitted and removed must be recorded, together with the reason for removal.

Regular checks on the condition of the printing blankets must be carried out to ensure that minor faults do not turn into major problems. Accessibility to the printing blanket is often impeded by the printing blanket washing system on modern presses. In addition to automatic washing, therefore, we recommend carrying out regular visual inspections and checks on the adjustment of the printing blanket washing system.

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