Rotary printing method

Abstract

The present invention relates to a rotary printing process for the application of functional coatings to a print substrate, to a coated print substrate produced by the said process, and to the use thereof, in particular in the packaging sector.

Claims

1. A rotary printing process for the application of a coating to a print substrate (12), where cells (6) arranged on a rotating anilox roll (3) are filled with a printing ink (4) in a filling step and the printing ink (4) from the cells (6) of the anilox roll (3) subsequently wets front faces (13) of screen dots (10) in a wetting step, where the screen dots (10) have front faces (13) and lateral surfaces (14) adjacent thereto and are arranged on a flexible printing plate (9) attached to a rotating plate cylinder (8), and where, in a transfer step, the print sub-strate (12) is pressed radially against the printing plate (9) by a rotating impression cylinder (11) and the printing ink (4) is transferred to the print substrate (12), characterised in that the printing ink comprises a functional material and in that at least 50 percent of the screen dots (10) on the printing plate (9) dip into the cells (6) of the anilox roll (3) during the wetting step, where, besides the front faces (13), the lateral surfaces (14) of the screen dots (10) are also wetted with the printing ink (4).

2. A rotary printing process according to claim 1, wherein the lateral surfaces (14) of the screen dots (10) are partly or completely wetted with the printing ink (4).

3. A rotary printing ink according to claim 1, wherein at least 70 percent of the screen dots (10) dip into the cells (6).

4. A rotary printing process according to claim 1, wherein the screen dots (10) have a screen dot size G and the cells (6) have a width W and the ratio G/W represents a value in the range from 0.05 to 0.80.

5. A rotary printing process according to claim 4, characterised in that the ratio G/W represents a value in the range from 0.15 to 0.60.

6. A rotary printing process according to claim 1, wherein the printing plate and the anilox roll each have a line count in the range from 34 lines/cm to 60 lines/cm.

7. A rotary printing process according to claim 1, wherein the printing plate is provided with screen dots over its entire surface.

8. A rotary printing process according to claim 1, wherein the print substrate is a cellulose-containing material.

9. A rotary printing process according to claim 8, wherein the cellulose-containing material is selected from uncoated paper, coated paper, card, kraft paper or kraft liner.

10. A rotary printing process according to claim 1, characterised in that the printing ink comprises functional polymer materials.

11. A rotary printing process according to claim 10, wherein the functional polymer materials are liquid-crystalline materials or electrically conductive polymers.

12. A rotary printing process according to claim 1, wherein the printing ink comprises functional pigments and at least one binder.

13. A rotary printing process according to claim 12, wherein the functional pigments are selected from UV or IR light-absorbent or reflective pigments, electrically conductive pigments, electrically semiconducting pigments, magnetisable pigments and/or luminescent pigments.

14. A rotary printing process according to claim 12, wherein the functional pigments have an isotropic or anisotropic shape.

Description

BRIEF DESCRIPTION OF FIGS.

(1) FIG. 1 shows a diagrammatic structure of a flexographic printing machine

(2) FIG. 2 shows a diagrammatic view of part of a printing plate with a number of screen dots

(3) FIG. 3 shows a diagrammatic view of part of an anilox roll having a number of cells (6) (mechanically engraved) and lands (15)

(4) FIG. 4, 5 show a diagrammatic view of the wetting of a screen dot in accordance with the prior art

(5) FIG. 6, 7 show a diagrammatic view of the wetting of a screen dot in accordance with the invention

(6) FIG. 8, 9,10 show a diagrammatic view of the wetting and ink transfer in accordance with the invention

EXAMPLE 1

(7) The print substrate (12) used is the pale (WK1) or dark (WK2) side of corrugated cardboard for packaging purposes (in each case kraft liner which serves as surface covering for corrugated cardboard). The viscosity of a solvent-containing printing ink (4) comprising 30% by weight of an electrically conductive pigment based on flake-form mica substrates having a coating comprising (Sb,Sn)O.sub.2 having a particle size of 5-25 m (product of Merck KGaA, Germany), and 70% by weight of a solvent-containing, binder-containing varnish (Siegwerk NC-201 from Siegwerk Druckfarben AG, solids content about 35%), is adjusted to 33 sec (4 mm efflux cup, in accordance with DIN 53211) using a mixture of ethanol and ethyl acetate 2:1. This printing ink is introduced into the inking system (2) of a flexographic printing machine via a feed device (5). The cells (6) of a rotating anilox roll (3) are brought into contact with the inking system and filled with the printing ink (4) in the process. Excess printing ink is wiped off the surface of the anilox roll with the aid of a doctor blade (7).

(8) The anilox roll has a line count of 34 l/cm 60 (cell width W 265 m) or 60 l/cm 60 (cell width W 129 m).

(9) A flexographic printing plate (9) having a line count of 34 l/cm or 60 l/cm (DuPont DEC 2.84, Tesa 52121 adhesive tape) is attached to a plate cylinder and brought into contact with the rotating anilox roll. The screen dot size G of the screen dots (10) on the printing plate (9) varies in the range from 26 m to >275 m (34 l/cm, 5% to 95% area coverage AC) and 10 m to >170 m (60 l/cm, 5% to 95% area coverage AC). The transfer of the printing ink to the print substrate (printing operation) takes place at a speed of 30 m/min. The coated print substrate is left to dry.

(10) The electrical surface resistance of the printed cardboard is measured using a Milli TO3 ohmmeter from Fischer Elektronik. A two-point electrode with spring pressure having a contact rubber or electrode diameter of 4 mm, electrode separation 6.4 mm, spring force about 3.5 N, total pressure 7 N, is used. In the case of surface resistance values in the range <5*10.sup.5 ohm the measurement is carried out at a voltage of 4 V (low), in the case of surface resistance values in the range >5*10.sup.5 ohm the measurement is carried out at a voltage of 100 V (high).

(11) Table 1 shows the electrical resistance values achieved by the coating under the respective printing conditions.

(12) The electrical surface resistance of an unprinted corrugated cardboard is about xE+10 ohm (x*10.sup.10).

(13) TABLE-US-00001 TABLE 1 Line screen Line screen Electrical of printing of anilox Size of screen resistance plate roll dot [m] [ohm] G/W 34 l/cm 34 l/cm 60 >275 (95% AC) 2.0E+10 (WK1) >1.04 >275 (90% AC) 1.0E+10 (WK1) >1.04 275 (75% AC) 1.5E+10 (WK1) 1.04 201 (50% AC) 1.0E+10 (WK1) 0.76 126 (25% AC) 9.5E+05 (WK1) 0.47 90 (15% AC) 4.3E+05 (WK1) 0.34 66 (10% AC) 1.6E+05 (WK1) 0.25 40.5 (8% AC) 1.5E+05 (WK1) 0.15 26 (5% AC) 1.8E+05 (WK1) 0.10 60 l/cm 60 l/cm 60 >170 (95% AC) 1.3E+10 (WK2) >1.32 170 (90% AC) 9.4E+09 (WK2) 1.32 139 (75% AC) 8.6E+09 (WK2) 1.08 112 (50% AC) 5.5E+09 (WK2) 0.87 69 (25% AC) 3.5E+06 (WK2) 0.54 40.5 (15% AC) 2.3E+06 (WK2) 0.31 26 (10% AC) 1.8E+06 (WK2) 0.20 20 (8% AC) 3.5E+05 (WK2) 0.16 10 (5% AC) 8.0E+05 (WK2) 0.08

EXAMPLE 2

(14) Example 1 is repeated with the modification that an aqueous printing ink (varnish: Senolith 350 298 from Weilburger, solids content about 40%, viscosity adjustment to 33 sec. using water) is used with an anilox roll line count of 60 l/cm 60 and a printing plate line count of 60 l/cm. The other conditions correspond to those from Example 1.

(15) The results of the resistance measurement are shown in Table 2.

(16) TABLE-US-00002 TABLE 2 Electrical Electrical Size of screen resistance [ohm], resistance [ohm], dot [m] WK1 WK2 G/W >170 (95% AC) 1.7E+10 6.0E+09 >1.32 170 (90% AC) 1.5E+10 6.1E+09 1.32 139 (75% AC) 7.0E+09 6.8E+09 1.08 112 (50% AC) 7.0E+09 3.3E+07 0.87 69 (25% AC) 1.0E+06 4.0E+05 0.53 40.5 (15% AC) 9.5E+05 1.7E+05 0.31 26 (10% AC) 1.8E+06 1.0E+05 0.20 20 (8% AC) 4.3E+06 9.5E+04 0.16 10 (5% AC) 8.0E+06 6.8E+04 0.08

EXAMPLE 3

(17) On use of a coated cardboard as print substrate, it is even possible, on printing of a solvent-containing printing ink of the composition given in Example 1, to obtain electrical resistances having values of about 6E+04 with a line count of the anilox roll of 34 l/cm 60 and a line count of the printing plate of 34 l/cm at a ratio G/W of 0.34 to 0.76 (area coverage 15 to 50%), and electrical resistances having values of about 4.5E+04 with a line count of the anilox roll of 60 l/cm 60 and a line count of the printing plate of 60 l/cm at a ratio G/W of 0.08 to 0.20 (area coverage 5 to 10%).

LIST OF REFERENCE NUMERALS

(18) (1) Rotary printing machine (2) Inking system (3) Anilox roll (4) Printing ink (5) Feed device (6) Cells (7) Doctor blade (8) Plate cylinder (9) Printing plate (10) Screen dots (11) Impression cylinder (12) Print substrate (13) Front face of the screen dot (14) Lateral surface of the screen dot (15) Lands