High Speed Inline Coatingfor Sheet Fed Printing Presses

High Speed Inline Coating for Sheet Fed Printing Presses

Preconditions

- up to 12,000 prints/h the usual processing instructions are to be observed

- for High Speed Inline Coating with a printing speed of up to 18,000 sheets/h the processing range must be adapted regarding

- substrate- ink layer thickness- coating viscosity- coating selection- performance of the dryer- distance under the dryer

High Speed Inline Coating for Sheet Fed Printing Presses

Substrate - Ink

- the combination of substrate and ink should be selected in a way to assure a good bond between ink and substrate

- poor ink drying cannot be improved by coating

- the result is bad rub resistance and insufficient scotch tape resistance

High Speed Inline Coating for Sheet Fed Printing Presses

Adhesion Substrate - Ink

Paper

Ink C oating

High Speed Inline Coating for Sheet Fed Printing Presses

Ink Layer Thickness

- Overinking of the ink layer thickness with parallel inline coating will reduce the performance of the printing press

- as by reducing the printing speed the drying time is adjusted

High Speed Inline Coating for Sheet Fed Printing Presses

Paper Paper

Ink C oating Ink C oating

Normal Inking Overinking

Ink Layer Thickness

High Speed Inline Coating for Sheet Fed Printing Presses

Cell Volume of the Screen Rollers

- the cell volume of a screen roller is indicated with the scoop amount of water in ml/m²

- the coating application amount corresponds to about 1/3 of the indicated cell volume of the screen roller

Example:

A cell volume of the screen roller

of 15 g/m² corresponds to approx 5 g/m² coating application

High Speed Inline Coating for Sheet Fed Printing Presses

Gloss Diagram after 24h Drying

30

35

40

45

50

55

0 5 10 15 20

Glo

ss i

n %

Drying Time in h

3 g/m²2 g/m²

1 g/m²

Wet-on- Wet Printing

High Speed Inline Coating for Sheet Fed Printing Presses

Coating Viscosity

- the coating viscosity depends on the temperature and is determined with a 4 mm DIN cup at 20°C

- when the temperature in the coating rises the viscosity will decrease

- in case of a viscosity decrease, e.g. below 25 sec., an even coating application cannot be assured any more

High Speed Inline Coating for Sheet Fed Printing Presses

Viscosity depending on the Temperature

Vis

cosi

ty i

n s

20

40

60

80

100

15 25 35 45

Temperature in °C

High Speed Inline Coating for Sheet Fed Printing Presses

Variable Coating Viscosities

Cooling Units for Coatings by EASYLAC keep the coating stable in viscosity

High Speed Inline Coating for Sheet Fed Printing Presses

Too high Coating Viscosity

- a too high coating viscosity, e.g. above 65 sec. can be adjusted by dilution with water to the required viscosity

- a too high coating viscosity in connection with High Speed Inline Coating will lead to splashing

High Speed Inline Coating for Sheet Fed Printing Presses

Dilution of the Coatings with Water

20

30

40

50

60

70

80

0 4 8 12 16 20

Vis

cosi

ty in

sec

.D

IN 4

mm

Cu

p a

t 20

°C

approximate Water Amount in %

High Speed Inline Coating for Sheet Fed Printing Presses

Coating Selection

- the drying behaviour of coatings depend on the coating type

- if for example the following coating types are used:

- matt- semi matt- protection- gloss- high gloss- UV coatings

their drying behaviour will be considerably different

High Speed Inline Coating for Sheet Fed Printing Presses

Coating Selection

For dispersion coatings:

The higher the gloss, the slower the thorough drying

Rule of thumb:

0

10

20

30

40

50

60

70

80

90

CartonGD2-

printed

DL 1176 DL 1351 DL VP385

DL 1200 DL 1300DL 1650

DL 1150 DL VP9756

Gloss in % Drying time in s

High Speed Inline Coating for Sheet Fed Printing Presses

Gloss Diagram: different coatings on the same substrate

High Speed Inline Coating for Sheet Fed Printing Presses

Influence of the Surface Structure of the Substrate

30

40

50

60

70

80

0 2 4 6 8 10 12

Carton 1

Carton 2

Application Amount g/m² wet

Glo

ss i

n %

High Speed Inline Coating for Sheet Fed Printing Presses

UV Coatings

- UV coatings dry immediately by photo-polymerisation using short wave light

- the acetone test shows whether the coatings have dried thoroughly

High Speed Inline Coating for Sheet Fed Printing Presses

Performance of the Dryers

- the drying behaviour of the coatings is determined by the performance of the dryer

- the thorough drying of dispersion coatings is primarily determined by the available amount of air

The more air, the better for the thorough drying- beginning at a pile temperature of approx. 35 °C problems may occur in the pile

High Speed Inline Coating for Sheet Fed Printing Presses

Drying of UV Coatings

- for UV coating processes the condition of the UV lamps and a sufficient performance are responsible for a good coating result

- the temperature in the pile is also decisive for UV coatings and may be responsible for subsequent problems in print finishing

- too high temperatures may result in breaking of the printed matter during the grooving and folding process

High Speed Inline Coating for Sheet Fed Printing Presses

Drying Distance

An extended delivery between coating tower and delivery is advantageous for the printing speed.

A short delivery is a disadvantage for High Speed Inline Coating.

High Speed Inline Coating for Sheet Fed Printing Presses

Printing Press with Double Extended Delivery

High Speed Inline Coating for Sheet Fed Printing Presses

Special Coating Applications

- for special coating applications, as e.g. application of blister coating, a coating amount of 6 – 8 g/m² has to be applied in order to assure good bonding with the plastic foil

High Speed Inline Coating for Sheet Fed Printing Presses

Result

High Speed Inline Coating with 18.000 prints/h will not present any problems if the appropriate coatings are used and the printing press is well adjusted.