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2020 Technical Brochure

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Chamber Doctor Blade Systems

There are two different blade systems; single reverse-angle blade systems and the more commonly used, enclosed or chambered Doctor Blade systems. Angles on a chambered, system are pre-set, and the industry standard is 30 to 350 for doctoring and 20 to 350 for closing.

Flater angles create a greater contact area, requiring more doctor blade pressure to get a clean wipe. This increase in pressure creates excessive Anilox and blade wear.

30-350

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30-350

Single Reverse Angle Doctor Blade Systems

This set up provides excellent printing and wiping. To obtain best results, the blade holder must be cleaned carefully and in good condition. The MDC Doctor Blade must be mounted absolutely straight and without waves. To prevent waves, tighten bolts in the blade holder from the centre out. As always, minimal pressure is the key to successful printing. The optimal angle for a single blade set up is also 30 to 350.

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Proper System Alignment

For consistent ink metering, best print quality and optimised blade life, an enclosed chamber system requires perfect alignment (both horizontal and vertical) so that both blades have equal amounts of pressure. Incorrect alignment creates uneven blade pressure, blade wear and/or ink leakage. A common error that results from correcting alignment problems is excessive blade pressure. This excessive pressure will lead to a variety of problems, like score lines.

Correct Incorrect

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Bevel faces into the chamber

Which way around do the blades go?

CHAMBERED SYSTEM

SINGLEBLADE

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Minimum pressure ensures consistent blade wear and Anilox life. The thinner the tip, the less pressure required to achieve a clean and brilliant print result. It is recommended to use the same material on both sides of the chamber to eliminate uneven pressure, unless a different closing blade has been specifically paired or recommended.

Increased pressure leads to a deflection of the Doctor Blade, resulting in a reduced angle and therefore an increased contact area. The actual wiping is done by the back of the blade, leading to excessive Anilox and blade wear.

The result of high pressures

Excessive blade pressure creates free floating metal slivers that contaminate ink systems. When a hard particle becomes trapped between the deflected blade tip and the Anilox, this particle rides there, effectively destroying rows of cells. These rows of cells appear as thin bands running the circumference of an Anilox and are commonly called score lines.

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Bleeding

Causes: • Humidity is too high – water

is condensing in the sovent-based ink

• Amount of retarder used is excessive

• Ink viscosity is too low• Pick-up volume is too high• Print speed is too high

Solutions:• Mix fresh ink• Use an ink with a faster

solvent• Adjust the viscosity• Replace the anilox roller• Reduce the print speed –

increase the drying capacity

Suggested products:The doctor blade is not the decisive element; however, we recommend sharp doctoring.

• Use coated doctor blades• Use bevel or lamella

configuration – to scrape more sharply

Ink spitting

Causes:• The doctor blade has entered

the area of the cylinder rim• The surface of the anilox

roller is damaged or dirty• Wrong ink temperature

Solutions:• Replace the blade• Look for dried ink at the ends

of the cylinders• Check the cylinder radius• Adjust the ink temperature

Suggested products:• BLUESTAR• ONE STEP TIP

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Dot gain

Causes:• Excessive impression setting

between the plate cylinder and the substrate

• Doctor blade lamella contact zone is excessive

• Temperature of the central cylinder is incorrect

• Excessive pick-up volume

Solutions:• Reduce impression setting• Reduce the doctor blade

contact zone in relation to the anilox roller

• Check the temperature of the central cylinder

• Check the anilox roller with the manufacturer

Suggested products:Doctor blade lamella with the thinnest possible contact zone.

• BLUESTAR• STAINLESS• LONGLIFE

Ghosting effect

Causes:• The range of inks is too low

as the pick-up volume of the anilox roller is too low

• Ink is drying in the cells• The cells are inadequately

filled• Print speed is too low

Solutions:• Use an anilox roller with a

higher pick-up volume• Add retardant to the ink• Increase the pressure in the

chambered doctor blade system

• Increase speed or ink viscosity

Suggested products:Hard setup of the chambered doctor blade system.

• BLUESTAR• STAINLESS• LONGLIFE

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Halo effect

Causes: • The scooping volume of the

anilox roller is too high• The additional pressure

between anilox roller and printed material is too high

• The pressure in the blade chamber system is too low

• The additional pressure between anilox roller and plate cylinder is too high

Solutions:• Choose anilox roller with

smaller scooping volume• Reduce additional pressure• Increase pressure in the

blade chamber system

Suggested products:Lamella doctor blade with thinner contact zone.

• BLUESTAR• STAINLESS• LONGLIFE

Longitudinal streaks

Causes:• The blade is worn• There is dried ink in the

chambered doctor blade system

• The anilox roller is dirty or ink has dried on the anilox roller

• There are particles in the chambered doctor blade system

Solutions:• Replace the doctor blade• Clean the chamber• Install an ink filter

Suggested products:We recommend coated doctor blades to increase service life and to reduce the particles.

• BLUESTAR• STAINLESS• LONGLIFE

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Lateral streaking

Causes:• The pressure setting between

the plate cylinder and the printing substrate is too high

• The print speed is too high• The pressure setting between

the anilox roller and the pressure plate is wrong

• There is a mechanical fault

Solutions:• Reduce the pressure setting• Reduce the print speed• Adjust the pressure setting• Check the mechanical parts

of the printing machine

Troubled ink lay

Causes:• Ink viscosity is too low• Too high a proportion of

retardant in the ink• Substrate surface is uneven• Incorrect doctor blade

pressure

Solutions:• Add fresh ink/ new solvent• Reduce the retardant in the

ink• Use softer printing plates• Check the doctor blade

pressure

Suggested products:• BLUESTAR• STAINLESS• LONGLIFE

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Excessive ink film thickness

Causes:• Contact area of the Doctor

Blade is too large

• Blade pressure is too high causing the blade to bend and wipe with the back

• Anilox cell count and volume does not match Doctor Blade selection

• Anilox line count and volume is too large

• Doctor Blade is not set parallel to the Anilox

Solutions:• Match blade tip to Anilox

screen size

• Check set up is optimal to ensure low peressure can be used.

Suggested products:• BLUESTAR

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Anilox Wear

Cause:• Over pressuring doctor blade

Solution:• Look for the reasons for the

need of excessive pressure and correct

• Install stops to limit adjustment to insure that chamber does not contact the anilox roller

• Metal filings from blade tip in the form of slivers (excessive pressure causes wiping to be done with back of blade instead of tip. Blade tip becomes thin and wears through releasing slivers into the inking system. This can cause score lines)

Cause:• Contact area too large

Solution:• Reduce contact area• Use correct width doctor

blade (check with the

holder manufacturer for correct size)

• Use reduced thickness blade tip

• Reduce blade thickness if using straight steel

• Check blade angles (send worn blade samples to MDC for evaluation)

Cause:• Incorrect blade material

Solution:• Have steel analysed for purity• Check for excessive roughness

on blade tip (use fine polishing paper to correct)

• Try alternate blade materials (check with MDC to correctly match blade blade materials to application)

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Leaking Chamber

Cause:• Alignment of chamber

incorrectSolution:

• Check to make sure chamber is parralel to the anilox roller and both top and bottom blades are contacting anilox roller at the same time (check empty chamber with a machinist level and feeler gauge without end seals in place)

Cause:• Incorrect end seals or

incorrect settingSolution:

• Contact Daetwyler UK for free end seal samples.

• Check blade settings (make sure blade extension is correct to match the cut on the end seal

Cause:• Wavy blades

Solution:• Improper seating of blade in

holder allows ink to escape holder

• Bad holder condition• Missing or worn bolts

Cause:• Re-doctoring of ink from

containment bladeSolution:

• Reduce excessive blade pressure

• Correct ink viscosity• Incorrect containment blade

for press, holder or anilox (use a thinner alternative material such as mylar, polyester or plastic)

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Cylinder1219mm

1168mm51mm

1270mm

Doctor BladeBack Up BladeDoctor Blade holder

Fine adjustments are required for optimal printing results

The Gravure industry recommends a Doctor Blade contact angle of approximately 55 to 65 degrees. Flat angles create a greater contact area, thereby increasing hazing and drag outs. Angles too steep produce chattering.

A precise adjustment Doctor Blade angle is crucial for an optimal contact zone.

55-650

20-25mm

3mmMDC Doctor Blade

Back Up Blade

3:1

The correct installation of the doctor blade into the Doctor Blade holder

For best results, the blade holder and back up blade (if used), must be cleaned carefully and be in good condition. The MDC Doctor Blade must be mounted absolutely straight, without waves. To prevent waves, tighten bolts in the blade holder beginning in the centre and working your way out, alternating sides.

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Blade Pressure

Lower blade angle

Doctor blade angleContact Area

Doctor Blade pressure: Less is more

We strongly recommend using minimal Doctor Blade pressure. The thinner the tip, the less pressure required to achieve a clean and brilliant printing result. A certain amount of flexibility is needed to compensate for things such as deviation of the cylinder surface or changes in diameter.

Higher pressure

Blade angleContact Area

Excessive Doctor Blade pressure

Too much pressure will result in excessive deflection of the Doctor Blade. Increased deflection creates a lower contact angle and wider contact area, which leads to hazing and tonal value changes in the printed product.

Customise MDC Doctor Blades to fit your cylinder

To prevent excessive pressure at the ends of your cylinder, which could damage your Doctor Blade, we recommend that the back up blade be cut at an angle at both ends. The cut should end approximately 12.7 mm inside each end of the cylinder to include allowance for oscillation travel. Ideally, the ends of your cylinder should be equally rounded.

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Hazing/Scumming

Causes:• Blade angle is too shallow• Excessive blade contact

pressure• Ink is not drying quickly

enough• Incorrect roughness of the

printing cylinder

Solutions:• Increase the blade angle• Use thinner lamella• Check the blade pressure• Check ratio support blade to

lamella (max. 5 mm)• Add accelerator, check the

viscosity• Check the roughness of the

cylinder• Dechrome or rechrome the

cylinder if necessary

Suggested products: Use a coated doctor blade with a thin configuration.

• GAMUTSTAR• LONGLIFE

Drying

Causes:• Ink viscosity is high• Ink temperature is high• Solvents evaporating

prematurely• Incorrect cylinder

temperature• Ambient temperature

Solutions:• Check ink viscosity• Wash out the printing

cylinder• Check the cylinder

temperature and the ambient temperature

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Unsmooth gradations

Causes:• High ink viscosity• Incorrect screen or cell

geometry• High cylinder and ambient

temperature• No electrostatic assist

Solutions:• Check ink viscosity• Discuss screen or cell

geometry with cylinder manufacturer

• Check cylinder and ambient temperature

• Flat doctoring• Check electrostatic printing

assist (ESA)

Suggested products: Check blade configuration.

Chatter marks

Causes:• Ink is collecting under the blade• Blade angle is not set correctly• The main cylinder gearbox is

not running true• Inadequate contact pressure• The doctor blade is loose in the

blade holder causing vibrationSolutions:

• Reduce the printing speed• Set the doctor blade angle to

60° to 70°• Check the main cylinder

gearbox for concentricity• Reset oscillation• Tighten the blade adjusting

screws and their holder• Correct blade installation• Pay attention to cleanliness• Use blade supports

Suggested products:• Multiblade• Select thicker doctor blades

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Drag outs

Causes:• The upper side of the lamella

is contaminated (dust, etc.)• Ink viscosity is too low

Solutions:• Wipe off the doctor blade

with a pointed wooden stick (clean the doctor blade)

• Increase the ink viscosity• Use an ink filter

Suggested products: It is essential to use a hard coating.

• GAMUTSTAR• LONGLIFE

Ink streaks

Causes:• Ink contains colour particles• Ink filter not being used• Doctor blade contact zone is

faulty• Surface roughness and/or

grinding pattern is wrong

Solutions:• Wipe off the doctor blade

with a pointed wooden stick (clean the doctor blade)

• Fit an ink filter• Replace the doctor blade• Check the surface roughness

and/or grinding pattern• Check and adjust the ink

viscosity

Suggested products: • GAMUTSTAR• LONGLIFE

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Missing dots

Causes:• Cells are not emptying due to

the electrostatic charge• The surface of the substrate

cannot contact the ink/the cylinder

• Coarse paper surfaces and/or uncoated papers

Solutions:• Electrostatic printing assist

(ESA). Not with metal composite or with metallised inks!

• Reduce the screen width/resolution (offer more surface)

Suggested products: Since the choice of blade is not decisive, we recommend the following:

• Use a soft set-up• Shallower blade angle

Voids (spots)

Causes:• Due to holes in the

impression roller - no ink transfer onto the substrate

• Due to scoring in the impression roller - no ink tranfer onto the substrate

Solutions:• Keep the impression rollers

clean, check for cracks, holes and scratches before installation

• If necessary, change the impression rollers

Suggested products: • The choice of blade is not

directly decisive

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Cylinder wear

Causes:• Uncoated doctor blade in use• High blade pressure• Flat blade angle• Non-optimal surface

roughness of the cylinder

Solutions:• Use coated blades• Reduce the blade pressure• Increase the contact angle of

the blade - sharper doctoring• Adjust the roughness of the

cylinder or rechrom

Suggested products: Adjust the set-up to prevent the blade from being deflected.

• GAMUTSTAR• LONGLIFE

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MDC Max Daetwyler UK LtdUnit 10 Star WestWestmead Industrial EstateSwindon, WiltshireUK, SN5 7SW

01793 719202 info@daetwyler.co.uk

© 2020 MDC Max Daetwyler UK Ltd