METHOD FOR THE ADDITIVE PRODUCTION OF RELIEF PRINTING PLATES

Abstract

The invention relates to a process for the production of relief printing plates, where a carrier with a polymeric substrate layer is provided and a relief is formed layer-by-layer on a surface of the substrate layer, where the relief is formed by means of a) single or multiple application of a liquid comprising at least one reactive monomer to the surface of the substrate layer, b) diffusion of the reactive monomer into the polymeric substrate layer for a prescribed exposure time and c) hardening of the relief, where in step a) the liquid is applied in accordance with an image to the surface and where, after the prescribed exposure time of step b), any liquid that remains on the surface, having not diffused into the material, is removed from the surface, and in step c) the relief that is hardened comprises the polymer of the substrate layer and reactive monomer that has diffused into the material.

Claims

1.-18. (canceled)

19. A process for the production of relief printing plates, where a carrier with a polymeric substrate layer is provided and a relief is formed layer-by-layer on a surface of the substrate layer, where the relief is formed by means of a) single or multiple application of a liquid comprising at least one reactive monomer to the surface of the substrate layer, b) diffusion of the reactive monomer into the polymeric substrate layer for a prescribed exposure time and c) hardening of the relief, where in step a) the liquid is applied in accordance with an image to the surface and where, after the prescribed exposure time of step b), any liquid that remains on the surface, having not diffused into the material, is removed from the surface, and in step c) the relief that is hardened comprises the polymer of the substrate layer and reactive monomer that has diffused into the material.

20. The process as claimed in claim 19, characterized in that the steps a) to c) are implemented only once with, in step a), only single application of the liquid.

21. The process as claimed in claim 19, characterized in that the steps a) and b) are implemented from 2 to 100 times and hardening in step c) takes place after the final implementation of the step b).

22. The process as claimed in claim 21, characterized in that the step c) is also executed after every nth implementation of the steps a) and b), following the step b), where n is from 2 to 10.

23. The process as claimed in claim 19, characterized in that the liquid is applied via application of a mask to the surface and application of the liquid through the mask, where the liquid reaches the unmasked portions of the surface, and where the design of the mask is such that a prescribed replicated image is produced.

24. The process as claimed in claim 19, characterized in that the liquid comprises at least 50% by weight of reactive monomer.

25. The process as claimed in claim 19, characterized in that the liquid comprises further components selected from the group consisting of photoinitiators, plasticizers, emulsifiers, diffusion aids, solvents and surface-active substances.

26. The process as claimed in claim 19, where the reactive monomer is an ester or an amide of acrylic acid or methacrylic acid with mono- or polyfunctional alcohols, amines, aminoalcohols or hydroxyethers or -esters, an ester of fumaric or maleic acid, or an allyl compound.

27. The process as claimed in claim 19, characterized in that selection of the reactive monomer of the liquid and selection of the polymeric substrate layer are such that the diffusion velocity of the reactive monomer in the polymeric substrate layer is in the range from 0.5 m/min to 100 m/min.

28. The process as claimed in claim 19, characterized in that the polymer of the polymeric substrate layer is selected from the group consisting of styrene-butadiene-styrene (SBS), styrene-isoprene-styrene (SIS), styrene-butadiene/styrene-styrene, styrene-isoprene-butadiene-styrene (SIBS) and styrene-butadiene (SB) block copolymers and ethylene-propylene-diene rubber (EPDM).

29. The process as claimed in claim 19, characterized in that the polymer of the polymeric substrate layer is selected from polyvinyl alcohol, partially or highly hydrolyzed polyvinyl acetates and polyamide.

30. The process as claimed in claim 19, characterized in that the substrate layer is free from reactive monomer or comprises less than 10% by weight of reactive monomer.

31. The process as claimed in claim 19, characterized in that the substrate layer comprises a plasticizer selected from white oil, butadiene oil, liquid polyisoprene, high-boiling-point esters and paraffin oil.

32. The process as claimed in claim 19, characterized in that the substrate layer comprises one or more photoinitiators.

33. The process as claimed in claim 32, characterized in that the liquid is free from photoinitiators.

34. The process as claimed in claim 19, characterized in that the carrier is composite material comprising at least one dimensionally stable carrier sheet and the substrate layer.

35. The process as claimed in claim 19, characterized in that the hardening in step c) takes place via exposure to UV radiation.

36. The process as claimed in claim 19, characterized in that the carrier provided takes the form of a cylinder sleeve.

37. A relief printing plate obtained according to the method of claim 19.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0076] FIG. 1 shows a plateau formed by the diffusion of a droplet into the material,

[0077] FIG. 2 shows a measured relief built up from two relief layers without immobilization,

[0078] FIG. 3 shows a measured relief built up from two relief layers with immobilization,

[0079] FIG. 4 shows a measured relief, experiment 1, diffusion through 1 mm perforated template,

[0080] FIG. 5 shows a measured relief, experiment 1, diffusion through 3 mm perforated template and

[0081] FIG. 6 shows a measured relief, experiment 1, diffusion through 10 mm perforated template.

[0082] The following starting materials were used (all % data in % by weight): Quintac 3621C, radial styrene-isoprene-styrene block copolymer having 15% of styrene from Nippon Zeon.

[0083] Kraton KX405, linear styrene-butadiene-styrene block copolymer having 24% styrene content from Kraton.

[0084] Styroflex 2G66, a styrene-butadiene/styrene-styrene block copolymer having 65% styrene content from Styrolution.

[0085] Nordel IP4725P, an EPDM rubber having 70% of ethylene, 25% of propylene and 5% of ethylidenenorbornene from Dow.

[0086] BDK, benzil dimethyl ketal from BASF.

[0087] Winog 70 white oil, paraffinic white oil from Shell.

[0088] Nisso PB1000, polybutadiene oil having >85% 1,2-vinyl content from Nippon Soda.

[0089] Hexamoll DINCH, diisononyl 1,2-cyclohexanedicarboxylate from BASF.

[0090] Syloid ED50, amorphous silicon dioxide, average particle size about 8 m, from Grace.

[0091] HDDA, hexanediol diacrylate, HDMA2, hexanediol dimethacrylate, EHA, 2-ethylhexyl acrylate, monomers from BASF.

EXAMPLES

[0092] Experimental Determination of Diffusion Velocities of Selected Monomers in Selected Polymeric Substrate Materials

[0093] The polymeric substrate layers described in table 1 (all data in table 1 being in % by weight) were produced as follows. The respective binders, with the stated plasticizers and in each case 5% by weight of photoinitiator, were melted and homogenized in a ZSK 53 twin-screw extruder, and discharged through a slot die, and then calendered between two PET sheets. A siliconized Mylar PET sheet, thickness 100 m, was used as top sheet. A Melinex D 740 carrier sheet, thickness 125 m, which had previously been coated with an isocyanate-based adhesive lacquer layer of thickness about 5 m, was used as carrier sheet. The total thickness of the composite made of carrier sheet, polymeric substrate layer and top sheet was 1.8 mm. The composite was drawn off on a vacuum suction belt and, after cooling, cut to size to give individual sheets.

TABLE-US-00001 TABLE 1 S-I-S block S-B-S block EPDM S-B/S-S block copolymer copolymer rubber copolymer Quintac 3621C 85% Kraton KX405 75% Nordel IP 4725P 75% Styroflex 2G66 75% BDK 5% 5% 5% 5% Winog 70 10% 20% white oil Nisso PB 1000 20% Hexamoll DINCH 20%

[0094] Diffusion velocities were determined by, in each case, applying a macroscopic droplet of a monomer by means of a metering syringe (volume 50 l) to a selected carrier material. The droplet was allowed to remain on the polymeric substrate layer for a defined exposure time. Excess monomer was then removed by rinsing with isopropanol, and the resultant relief was fixed by irradiation with UVA light (10 minutes of exposure to light from tubular, nyloflex FIII lamps from Flint Group). The surface was then irradiated with UVC light (nyloflex F III lamps) for a further 3 minutes in order to render the surface non-sticky, and a Perthometer was used to measure the resultant relief.

[0095] FIG. 1 shows an example of measurement at a temperature of 30 C., based on a droplet, using HDDA as monomer and, as carrier material, the SIS-based carrier material from table 1. Diffusion time was 20 minutes. A resultant height of the relief of 20 m can be determined from the plot.

[0096] If the experiment is carried out for various exposure times, it is then surprisingly found that the height of the resultant relief increases in proportion with the diffusion time. Diffusion of the monomer into the polymeric carrier layer is therefore not adversely affected by any saturation concentration. From the gradient of the straight lines it is possible to determine a diffusion velocity in m per unit of time for a given monomer/substrate pairing. Table 2 shows the diffusion velocities determined for selected monomers and the polymeric substrates from table 1 at room temperature (22 C.). It should be noted that the diffusion velocities thus determined are not precisely scientifically defined, but rather represent an empirically determined diffusion velocity which can be used for calculations relating to the build-up of a relief by the process of the invention.

TABLE-US-00002 TABLE 2 Diffusion velocity Polymer carrier layer Monomer in m/min S-I-S HDDA 0.7 S-I-S HDMA 1.3 S-I-S EHA 4.4 S-B-S HDDA 2.2 S-B-S HDMA 3.2 S-B-S EHA 3.9 S-S/B-S HDDA 1.7 S-S/B-S HDMA S-S/B-S EHA 3.9 EPDM HDDA EPDM HDMA EPDM EHA 2.0

[0097] Within the limits imposed by accuracy of measurement, it was not possible to determine diffusion velocities for all monomer/substrate pairings. In the case of the very nonpolar carrier layer based on EPDM rubber, measurable diffusion was determinable only for the comparatively nonpolar material EHA.

[0098] Build-Up of a Plurality of Relief Layers

[0099] The following experiments were carried out in order to simulate the application of a plurality of mutually superposed relief layers in accordance with an image. 20 l of a 1:1 mixture of HDA2 and HDMA2 were applied in droplet form at 30 C. to a carrier layer based on S-I-S rubber (see table 1 for composition) into which 2% by weight of amorphous silicon dioxide (Syloid ED 50) had also been incorporated as filler, and the droplets were allowed to remain on the carrier layer for precisely 2 minutes. The carrier layer was then immersed in isopropanol in order to remove excess monomer, and blow-dried by means of compressed air. A 2 l droplet of the same monomer mixture was then applied to the center of the resultant circular relief plateau, and again allowed to remain on the plate for precisely 2 minutes at 30 C. The plate was then again immersed in isopropanol and blow-dried. The plate was then irradiated for 10 minutes with UVA light and then for 3 minutes with UVC light (nyloflex F III lamps), and the resultant relief was fixed, and the surface was detackified.

[0100] FIG. 2 shows the profile of the resultant relief, measured by a Perthometer. Two plateaus are discernible. The relief height of the first plateau is about 7 m, and the relief height of the second plateau is higher, being about 10 m. Diffusion of the monomer mixture into the substrate material into which monomer has already diffused therefore takes place more rapidly than into a substrate material comprising no monomer.

[0101] The experiment was repeated with the difference that, before application of the second droplet, a brief intermediate irradiation (30 seconds of UVA irradiation, nyloflex FIII lamps) was carried out in order to immobilize the monomers that had diffused into the material and to fix the first relief stage. FIG. 3 shows the corresponding Perthometer-measurement profile. The relief height of the first plateau is about 8 m. The relief height of the second plateau is now smaller, being about 5 m. The relief edges are significantly sharper. The monomers that have diffused into the material in the first stage are immobilized by the intermediate irradiation, and can no longer diffuse laterally; a steeper relief edge is thus formed. The monomers that have diffused into the material in the first stage crosslink with the polymeric binder of the carrier layer and form a three-dimensional network; subsequent diffusion is thus retarded.

[0102] The experiments show that a relief can be built up layer-by-layer via repeated diffusion of the monomers. In order to calculate the relief height in advance, it is necessary to determine the diffusion velocities of the monomer(s) into the respective polymeric carrier layer individually for each relief layer that is to be applied.

[0103] Mask Experiments

[0104] Experiment 1

[0105] Holes measuring 1 mm, 3 mm and 10 mm were punched into an aluminum sheet of thickness about 0.5 mm to produce a template. This template was placed onto the SIS-based carrier layer (table 1) and loaded with weights at the edges in order to ensure intimate contact between mask and surface of the polymeric carrier layer.

[0106] The holes in the template were filled with HDA2 at room temperature (22 C.). After a diffusion time of 60 minutes, the template was removed from the carrier layer. Excess monomer was removed by washing with isopropanol, and the relief plate was blow-dried with compressed air. The relief was then fixed by irradiation with UVA light (10 minutes, nyloflex F III lamp), and the surface was detackified by means of UVC irradiation (3 minutes, nyloflex F III lamp). A Perthometer was used to measure the resultant relief (see FIGS. 4, 5 and 6).

[0107] The built-up spots had steep sides. The spot surfaces were level and uniform. The relief heights determined were 42 m (10 mm spot), 42 m (3 mm spot) and 40 m (1 mm spot).

[0108] Experiment 2

[0109] Experiment 1 was repeated, except that the temperature for diffusion of the monomer into the material was set to 40 C.

[0110] Again, the built-up spots had steep sides and a level, uniform surface. Relief height was greater because of the higher diffusion velocity. The relief heights were 108 m (10 mm spot), 106 m (3 mm spot) and 108 m (1 mm spot).

[0111] A compressible adhesive tape was then used to bond the relief printing plate to the cylinder of a flexographic printing machine, and alcohol-based ink was used for printing. Table 3 collates the printing parameters.

TABLE-US-00003 TABLE 3 Printing machine F&K FP 6S/8 Substrate PE sheet Printing ink Siegwerk NC4012 cyan Viscosity of printing ink 22 sec Anilox roll 460 l/cm, 3.5 g/cm.sup.3 Adhesive tape Lohmann 5.3 Print velocity 80 m/min Print setting +30 m in relation to kiss print

[0112] Printout of all of the relief spots was uniform with the print setting selected. Each printed spot exhibited full coverage and no excessive squeeze edge. The diameters of the surface of the spots on the printing plate and in the printed image were determined microscopically at the start of printing and after 500 prints. Micro-Shore-A hardness was moreover measured on the surface of the spots (see Table 4).

TABLE-US-00004 TABLE 4 Template hole diameter 1 mm 3 mm 10 mm Upper spot diameter on printing 0.74 mm 2.55 mm 9.40 mm plate Printed spot diameter 0.82 mm 2.73 mm 9.62 mm (start of printing) Printed spot diameter 0.80 mm 2.75 mm 9.58 mm (end of printing) Micro-Shore-A hardness Not measurable 68 67

[0113] The diameters of the relief spots at the surface are in all cases smaller than the respective template hole diameter. In contrast, the diameters of the printed spots are larger, by from 0.1 mm to 0.2 mm, than the spot diameters on the relief printing plate. This increase is typical of flexographic printing and can be attributed to squeeze effects relating to the low-viscosity flexographic printing ink. Within the limits imposed by accuracy of measurement, it was not possible to discern any swelling of the printing plate via the printing ink, i.e. the size of printed spots did not change during the printing process. Micro-Shore-A hardness was determined on the larger relief spots. Again, these values were in the range typical for flexographic printing: 67 and 68 Shore A. The Micro-Shore-A hardness of the surface of a flexographic printing plate (nyloflex ACE 1.7 mm from Flint Group) subjected to standard prior art irradiation and leach-out procedures is 64.

[0114] The experiment confirms that the diffusion process of the invention can achieve additive build-up of relief printing plates typically used in flexographic printing and that the process of the invention provides flexographic printing plates with the necessary softness and resilience and resistance to swelling.