Method for generative production of relief printing plates by monomer diffusion through an integral mask layer

Abstract

The invention relates to a method for generative production of relief printing plates, wherein a support with a polymeric substrate layer and a laser-ablatable mask layer is provided, the polymeric substrate layer containing a first binder. A mask with openings corresponding to pixels is produced by imagewise laser ablation of the mask layer. A liquid containing a reactive monomer is then applied over the surface of the mask-covered polymeric substrate layer, and the liquid or the reactive monomer diffuses through the openings of the mask into the polymeric substrate layer for a defined exposure time so as to form a relief. The excess liquid or the excess monomer and optionally the mask are removed from the surface, and the resulting relief is fixed by crosslinking.

Claims

1. A method for the production of relief printing plates comprising the following steps: a) providing a support with a polymeric substrate layer and a laser-ablatable mask layer, wherein the polymeric substrate layer contains a first polymeric binder, b) producing a mask with openings corresponding to pixels by imagewise laser ablation of the mask layer, c) applying a liquid containing a reactive monomer over the surface of the mask, d) diffusion of the reactive monomer through the openings of the mask into the polymeric substrate layer for a predetermined exposure time, wherein a relief is formed, e) removing non-diffused monomer from the surface, and f) fixing of the resulting relief by cross-linking.

2. The method according to claim 1, wherein the polymeric substrate layer contains a photoinitiator.

3. The method according to claim 1, wherein the substrate layer is free of reactive monomer or contains less than 10 wt. % of reactive monomer.

4. The method according to claim 1, wherein the laser-ablatable mask layer contains a second polymeric binder and a light-absorbing component, wherein the diffusion rate of the reactive monomer in the second polymeric binder at room temperature is less than in the first polymeric binder.

5. The method according to claim 4, wherein the second binder is polyvinyl alcohol, partially or highly saponified polyvinyl acetate, polyvinyl butyral, cellulose, nitrocellulose, polyethylene oxide-polyvinyl alcohol copolymers, polycyanoacrylate or polyamide.

6. The method according to claim 1, wherein the application of the liquid to the mask in step c) takes place by immersion, roller application, spraying or doctoring.

7. The method according to claim 4, wherein the light-absorbing component is carbon black, graphite, nanosized carbon black particles or carbon nanotubes.

8. The method according to claim 1, wherein the first binder is styrene-butadiene-styrene (SBS), styrene-isoprene-styrene (SIS), styrene-butadiene/styrene-styrene, styrene-isoprene-butadiene-styrene (SIBS), styrene-butadiene (SB) block copolymers, or ethylene propylene diene monomer (EPDM) rubber.

9. The method according to claim 1, wherein the reactive monomer is ethylhexyl acrylate, hexanediol diacrylate, dodecanediol diacrylate, cyclohexyl acrylate, isobornyl acrylate, or the corresponding methacrylates.

10. The method according to claim 1, wherein the liquid is free of photoinitiators.

11. The method according to claim 1, wherein crosslinking of the relief according to step f) takes place by exposure to UV light.

12. The method according to claim 1, wherein the diffusion rate of the reactive monomer in the first polymeric binder at room temperature is at least 0.5 m/minute and at most 10 m/minute.

13. The method according to claim 1, wherein the exposure time in step c) is 1 minute to 60 minutes.

14. The method according to claim 1, wherein the relief formed has a height of 5 m to 500 m.

15. The method according to claim 1, wherein in producing the mask according to step b), the dimensions of the openings are greater than the relief elements to be produced.

16. The method according to claim 1, wherein in producing the mask according to step b), in an area around the openings, the permeability of the mask for the liquid is increased by writing in of a dot matrix, wherein further openings are produced at the dots of the dot matrix.

17. The method according to claim 16, wherein the dot matrix has a resolution of at least 5,000 dpi.

18. The method according to claim 5, wherein the non-diffused monomer and the mask layer are rinsed off with a mixture of an alcohol and water in step e).

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1 shows Perthometer measurement of a relief with two lines, and

(2) FIG. 2 shows an electron micrograph of a formed relief.

(3) The following input materials were used (all figures in % indicate wt. %):

(4) Quintac 3621C, radial styrene-isoprene-styrene block copolymer with 15% styrene from Nippon Zeon.

(5) BDK, benzildimethyl ketal from BASF.

(6) White oil Winog 70, paraffinic white oil from Shell.

(7) HDDA, hexanediol diacrylate, HDMA2, hexanediol dimethacrylate, EHA, 2-ethylhexyl acrylate, monomers from BASF.

(8) Levanyl Schwarz A-SF, aqueous carbon black dispersion from Lanxess.

(9) Zonyl FSN, flow promoter from DuPont.

Examples

(10) Test 1

(11) Production of the Polymeric Support Layer

(12) A polymer mixture composed of 85% Quintac 3621C, 5% BDK, and 10% white oil Winog 70 was melted in a model ZSK53 twin-screw extruder, homogenized, and discharged through a wide-slit nozzle and then calendered between two PET films. A 100 m thick siliconized Mylar PET film was used as a cover sheet. A Melinex D 740 film 125 m in thickness than had been pre-coated with a layer of adhesive varnish 5 m in thickness was used as a support film. The total thickness of the composite of support film, polymeric substrate layer, and cover sheet was 1.8 mm. The composite was peeled off on a vacuum suction band, and after cooling, cut into individual plates.

(13) Production of the Laser-Ablatable Mask Layer

(14) A coating solution of 70% Alcotex 72.5, 29.8% Levanyl Schwarz A-SF, and 0.02% Zonyl FSN was produced in a solvent mixture (water/n-propanol 3:1) with a solid content of 5%. The coating solution was blade-coated onto a 100-m-thick Mylar film and dried. The mask layer produced had a dry layer thickness of 3 m.

(15) Production of the Polymeric Support Layer with the Laser-Ablatable Mask Layer

(16) The siliconized mylar film was peeled off the polymeric support layer, and the Mylar film coated with the laser-ablatable mask layer was laminated onto the polymeric substrate layer at a laminating temperature of 120 C. After cooling of the composite, the Mylar film was peeled off, leaving the laser-ablatable mask layer remaining on the polymeric substrate layer.

(17) Determination of the Diffusion Rate of the Monomers

(18) In order to determine the diffusion rate of the various monomers in the polymeric substrate layer, the laser-ablatable mask layer was peeled off the polymeric support layer. An aluminum template 0.5 mm in thickness was placed on the surface of the polymeric substrate layer and fixed in place with weights. The template contained punched holes having diameters of 1 mm, 3 mm and 10 mm. The respective monomer was poured into the holes of the template at room temperature (22 C.) and left on the polymeric substrate layer for a defined exposure time. After this, excess monomer was removed by rinsing with n-propanol, and the resulting relief was fixed by irradiation with UVA light (10 minutes, tube exposure, nyloflex FIII exposure unit from Flint Group). After this, the surface was exposed to UVC light for a further 3 minutes (nyloflex F III exposure unit) in order to detackify the surface. The relief plateau was then measured using a Perthometer.

(19) If the experiment is carried out with different exposure times (1 minute, 10 minutes, 20 minutes, 60 minutes), one finds that the height of the relief plateau formed increases linearly with exposure time in a first approximation. Based on the slope of the lines, one can determine a diffusion rate in m per unit time for a given monomer/substrate pair. For the substrate material described, the defusion rates of HDDA, HDMA and EHA were determined (cf. Table 1). It is to be noted that the diffusion rates determined in this manner do not correspond precisely to the diffusion rates ordinarily defined in the scientific field. Rather, these are empirically determined diffusion rates that can be used to predict the structure of a relief according to the method of the invention.

(20) In order to determine the barrier action of the laser-ablatable mask layer, the tests were repeated with the three selected monomers, this time placing the aluminum template on the composite of support film, polymeric substrate layer, and laser-ablatable mask layer. Within the range of measurement accuracy, no relief formation was observed, even with the maximum exposure time (60 minutes).

(21) TABLE-US-00001 TABLE 1 Diffusion rate Diffusion rate in m/min (polymeric in m/min (laser ablatable Monomer substrate layer) mask layer) HDDA 0.7 <0.1 HDMA 1.3 <0.1 EHA 4.4 <0.1
IR Laser Imaging

(22) The composite of support film, polymeric substrate layer, and laser-ablatable mask layer was fixed on the drum of an IR laser (Thermoflex 20, Xeikon) and imaged with power of 30 W at a resolution of 5,080 dpi. Individual lines of different widths (20 m, 40 m, 60 m, 80 m, 100 m and 500 m) and 3-point lettering were written in as image data.

(23) Relief Generation by Diffusion

(24) The plate imaged in this manner was then mixed in a tank at room temperature with a reactive monomer mixture. A solution of equal parts of HDDA and HDMA was used as the monomer mixture. After an exposure time of 1 hour, the plate was removed from the tank and rinsed off with a 1:1 mixture of water and n-propanol. In this case, excess monomer was removed from the substrate surface, and the laser-ablatable mask layer was washed away at the same time. The wet plate was then carefully blown dry with compressed air and then immediately irradiated with UVA light for 10 minutes on a tube exposure unit (nyloflex F III, Flint Group), thus fixing the resulting relief. For detackification, the relief printing plate was then irradiated for 3 more minutes with UVC light, thus detackifying the surface.

(25) Evaluation of the Relief Printing Plate

(26) The relief printing plate was then evaluated by means of Perthometer measurements and electron micrographs. FIG. 1 shows an example of Perthometer measurement of the sharply formed 80 m and 60 m lines. FIG. 2 shows an electron micrograph of the writing relief formed. The relief heights of the respective relief lines were determined from the Perthometer diagrams. The results are summarized in Table 2. While the line element 500 m in width shows an expected relief height of 60 m, the finer line elements do not reach the required relief height due to lateral diffusion of the monomers. The 20 m line could no longer be measured by the Perthometer.

(27) Test 2

(28) The test was then repeated with modification of the area surrounding the line elements on both sides with a 50% matrix 0.5 mm in width. The plate was again lasered with a resolution of 5080 dpi. The individual ablated holes in the area surrounding the line element had a diameter of 5 m. The subsequent procedure was as in test 1. The resulting line profiles were again measured using the Perthometer. As expected, the lines were now formed on a planar base 1 mm in width that was 30 m height in accordance with the rastered tone value of 50%. The absolute line height (total of base height and line height) now reached the predetermined height of 60 m10 m for all of the line widths.

(29) TABLE-US-00002 TABLE 2 Relief height without Relief height with base/without surrounding base/with surrounding Width of line element matrix matrix 500 m 60 m 60 m 100 m 55 m 55 m 80 m 50 m 60 m 60 m 40 m 60 m 40 m 10 m 55 mm 20 m <10 m 50 m

(30) The relief printing plate produced in this manner was then glued to the cylinder of a flexographic printing machine using a compressible adhesive tape and printed with a low-viscosity flexographic ink. The printing parameters are summarized in Table 3.

(31) TABLE-US-00003 TABLE 3 Printing machine F&K FP 6S/8 Substrate PE film Printing ink Siegwerk NC4012 Cyan Viscosity of printing ink 22 sec Anilox roller 460 L/cm, 3.5 g/cm.sup.3 Adhesive tape Lohmann 5.3 Printing rate 50 m/min

(32) Because of the low relief height, the plate was printed without overprinting, i.e. by means of so-called kiss printing. All of the line elements were reproduced in printing with sharp edges. The tests show that flexographic relief printing plates can be produced by means of the method according to the invention that allow the production of high-resolution relief structures with low relief height.