Relief precursor having low cupping and fluting

Abstract

A digitally imageable, photopolymerizable relief precursor at least comprising, arranged one above another in the order stated, (A) a dimensionally stable carrier; (AH) optionally, an adhesion-promoting layer; (B) a relief-forming layer, at least comprising a crosslinkable elastomeric binder, a first ethylenically unsaturated monomer, and a photoinitiator; (C) at least one interlayer, at least comprising a first, non-radically crosslinkable elastic polymer; (D) a laser-ablatable mask layer, at least comprising a second, non-radically crosslinkable elastic polymer, a UVA light-absorbing material, and an IR light-absorbing material; and optionally (E) a removable cover layer; characterized in that the layer (C) and optionally the layer (D) comprise at least one second ethylenically unsaturated monomer.

Claims

1. A digitally imageable, photopolymerizable relief precursor at least comprising, arranged one above another in the order stated, (A) a dimensionally stable carrier; (AH) optionally, an adhesion-promoting layer; (B) a relief-forming layer, at least comprising a crosslinkable elastomeric binder, a first ethylenically unsaturated monomer, and a photoinitiator; (C) at least one interlayer, at least comprising a first, non-radically crosslinkable elastic polymer; (D) a laser-ablatable mask layer, at least comprising a second, non-radically crosslinkable elastic polymer, a UVA light-absorbing material, and an IR light-absorbing material; and optionally (E) a removable cover layer; characterized in that the layer (C) and optionally the layer (D) comprise at least one second ethylenically unsaturated monomer, and in that the concentration of the first ethylenically unsaturated monomer in layer (B) and the concentration of the second ethylenically unsaturated monomer in interlayer (C) differ by not more than ±2 wt %, based in each case on all the components of the layers (B) and (C) respectively.

2. The relief precursor as claimed in claim 1, characterized in that the layer thickness S of the interlayer (C) is from 0.1 to 30 μm.

3. The relief precursor as claimed in claim 1, characterized in that the first and second ethylenically unsaturated monomers are the same ethylenically unsaturated monomer.

4. The relief precursor as claimed in claim 1, characterized in that the second ethylenically unsaturated monomer is present in the interlayer (C) in a concentration K which is the same as or lower than the concentration of the first ethylenically unsaturated monomer in the relief-forming layer (B).

5. The relief precursor as claimed in claim 1, characterized in that the second ethylenically unsaturated monomer is present in the interlayer (C) in a concentration K of 0.1 to 25 wt %, based on all the components of the interlayer (C).

6. The relief precursor as claimed in claim 1, characterized in that the ratio of the layer thickness S of the interlayer (C) in μm to the concentration K of the first ethylenically unsaturated monomer in wt % is from 30:0.1 to 0.1:25 μm/wt %.

7. The relief precursor as claimed in claim 1, characterized in that the first and second ethylenically unsaturated monomers have at least 2 ethylenically unsaturated groups and a molecular weight of less than 600 g/mol.

8. The relief precursor as claimed in claim 1, characterized in that the first elastic, non-radically crosslinkable polymer has a solubility parameter of 15 to 26 (MPa).sup.1/2.

9. The relief precursor as claimed in claim 1, characterized in that the first and second elastic, non-radically crosslinkable polymers have a solubility parameter of 15 to 26 (MPa).sup.1/2.

10. The relief precursor as claimed in claim 1, characterized in that the first elastomeric, non-radically crosslinkable polymer in interlayer (C) has an oxygen permeability of less than or equal to 1.5*10.sup.5 cm.sup.3*μm/(m.sup.2*d*bar).

11. The relief precursor as claimed in claim 1, characterized in that the first elastomeric, non-radically crosslinkable polymer in interlayer (C) has an oxygen permeability of greater than 1.5*10.sup.5 cm.sup.3*μm/(m.sup.2*d*bar).

12. The relief precursor as claimed in claim 1, characterized in that the interlayer (C) comprises the first elastomeric, non-radically crosslinkable polymer in a concentration of 60 to 99 wt %, based on all the components of the interlayer (C).

13. The relief precursor as claimed in claim 1, characterized in that the interlayer (C) comprises particles having a particle size of 0.2 to 30 μm.

14. The relief precursor as claimed in claim 1, characterized in that the interlayer (C) comprises particles in a concentration of 0.5 to 35 wt %, based on all the components of the interlayer (C).

15. The relief precursor as claimed in claim 13, characterized in that the particles comprise the second ethylenically unsaturated monomer.

16. The relief precursor as claimed in claim 1, characterized in that between the relief-forming layer (B) and the interlayer (C) or between the interlayer (C) and the mask layer (D) it comprises a further layer (F) which is impermeable to oxygen.

17. The relief precursor as claimed in claim 16, characterized in that the layer (F) comprises a second ethylenically unsaturated monomer.

18. The relief precursor as claimed in claim 1, characterized in that the mask layer (D) comprises a second ethylenically unsaturated monomer.

19. A digitally imageable, photopolymerizable relief precursor at least comprising, arranged one above another in the order stated, (A) a dimensionally stable carrier; (AH) optionally, an adhesion-promoting layer; (B) a relief-forming layer, at least comprising a crosslinkable elastomeric binder, a first ethylenically unsaturated monomer, and a photoinitiator; (C) at least one interlayer, at least comprising a first, non-radically crosslinkable elastic polymer; (D) a laser-ablatable mask layer, at least comprising a second, non-radically crosslinkable elastic polymer, a UVA light-absorbing material, and an IR light-absorbing material; and optionally (E) a removable cover layer; characterized in that the layer (C) comprises at least a second ethylenically unsaturated monomer, and in that the concentration of the first ethylenically unsaturated monomer in layer (B) and the concentration of the second ethylenically unsaturated monomer in interlayer (C) differ by not more than ±2 wt %, based in each case on all the components of the layers (B) and (C) respectively; and in that the first elastic, non-radically crosslinkable polymer has a solubility parameter of 15 to 27 (MPa).sup.1/2 to allow the second ethylenically unsaturated monomer to be dissolved in layer (C).

20. A digitally imageable, photopolymerizable relief precursor at least comprising, arranged one above another in the order stated, (A) a dimensionally stable carrier; (AH) optionally, an adhesion-promoting layer; (B) a relief-forming layer, at least comprising a crosslinkable elastomeric binder, a first ethylenically unsaturated monomer, and a photoinitiator; (C) at least one interlayer, at least comprising a first, non-radically crosslinkable elastic polymer; (D) a laser-ablatable mask layer, at least comprising a second, non-radically crosslinkable elastic polymer, a UVA light-absorbing material, and an IR light-absorbing material; and optionally (E) a removable cover layer; characterized in that the layer (C) comprises at least a second ethylenically unsaturated monomer, and in that the concentration of the first ethylenically unsaturated monomer in layer (B) and the concentration of the ethylenically unsaturated monomer in interlayer (C) differ by not more than ±2 wt %, based in each case on all the components of the layers (B) and (C) respectively; and in that the first, non-radically crosslinkable elastic polymer is chosen from hydrolyzed polyvinyl acetates having a degree of hydrolysis of 30 to 80 mol %, ethylene-vinyl acetate copolymers, ethylene-vinyl alcohol copolymers, ethylene-vinyl acetate-vinyl alcohol copolymers, cyclic acetals of polyvinyl alcohol, copolymers containing two or more different vinyl acetal units selected from vinyl formal, vinyl ethyral, vinyl propyral, and vinyl butyral units.

Description

EXAMPLES

(1) Determination of the Micro-Shore A Hardness

(2) The micro-Shore A hardness was measured on specimens having a thickness of 1.7 mm and after exposure, development, drying and re-exposure, using a digi test II-M Shore A instrument (Bareiss Prüfgerätebau GmbH), which was installed in the B509 test bed (Bareiss Prüfgerätebau GmbH) and was controlled by the DTAA control unit (Bareiss Prufgeratebau GmbH). The measuring head (penetration body with 35° angle) was applied to a solid area for the purpose of the measurement, and was pressed by the digi test II analysis instrument with a pressing force of 235 mN and the hardness value was read off after 3 s. Measurement was carried out twice, and the arithmetic mean was formed. The measurements were carried out on the basis of DIN ISO 7619.

(3) Perthometer Measurements for Determining the Roughness:

(4) The Perthometer measurements were carried out with a MarSurf M 300 mobile roughness instrument from Mahr with the “MarWin XR20” software (V 4.26). A contacting speed of 0.5 mm/s and a measuring force of 0.00075 N were used.

(5) Oxygen Permeation Measurements:

(6) The oxygen permeability is determined by the carrier gas technique in accordance with ASTM D3985 in instruments from Mocon Inc. with a coulometric sensor, at 23° C. and 0% relative humidity. The samples were measured free-standing, with the measurement area being 5 cm.sup.2 or 10 cm.sup.2 and the sample thickness being between 75 and 108 μm.

(7) UV-VIS Measurement:

(8) For transparency measurement, the layer constituents were dissolved in a suitable solvent mixture and the solution was drawn down onto a transparent PET film (125 μm thickness). The assembly was subsequently dried in a drying cabinet at 110° C. for 30 minutes. The transparency measurement was carried out using a UV-VIS spectrometer Varian Cary 50 Conc with the Cary Win UV software in version 2.00(25). This was done by subtracting the values of the uncoated PET film as reference/baseline. Measurement took place in the wavelength range from 500 to 350 nm.

(9) Determination of Cupping:

(10) To determine the cupping, the 50% halftones at 146 lpi were measured using a MarSurf M 300 mobile roughness instrument from Mahr with “MarWin XR20” software (V 4.26). A contacting speed of 0.5 mm/s and a measuring force of 0.00075 N were used. Subsequently the shape of the individual halftone dots was analyzed, and a difference between the height of the margin and the middle of the dots was determined, the value of this difference being denoted as cupping and reported in μm. In each case three dots were measured, and the arithmetic mean was formed.

(11) Analysis of Fluting:

(12) For analysis of the fluting, a selected motif with a resolution of 2540 dpi was printed using different print precursors of thickness type 394 on a Bobst FFG 1228 NTRS Rapidset at a speed of 110 m/min using an anilox roll with a transfer volume of 15 cm.sup.3/m.sup.2. The ink used was from Siegwerk (black) and had a viscosity of 21 s. The washboard effect was assessed on these motifs, and divided into different classes. Motifs with severe fluting received the classification “−”, those with moderate fluting the classification “0”, and those with relatively minor fluting the category “+”.

(13) Determination of Amount of Ethylenically Unsaturated Monomer in the Interlayer:

(14) To determine the amount of the ethylenically unsaturated monomer present, here by way of example the HDDA content, the interlayer, without laser-ablatable mask layer, was applied to the photopolymer by extrusion and left there for four weeks. The interlayer was subsequently peeled off together with the cover film. 318 cm.sup.2 of the film with the layer were placed in 100 g of ethanol, in order to dissolve the HDDA and the layer binder. Differential weighing of the cover film with the layer and the film without the layer gave the surface weight of the interlayer. Subsequently, by means of GC analysis, a calibration curve was produced, by measuring different concentrations of a standard solution with a defined HDDA content (1.009 g in 20 ml of ethanol), and the HDDA content of the solution was determined. With the HDDA content of the solution and the surface weight of the interlayer, the HDDA content in the layer was calculated in accordance with the following formula:

(15) $\frac{\begin{array}{c}\mathrm{fraction}\mathrm{of}\mathrm{HDDA}\mathrm{in}\mathrm{sample}\mathrm{solution}\left[\frac{g}{\mathrm{ml}}\right]*\\ \mathrm{size}\mathrm{of}\mathrm{the}\mathrm{sample}\mathrm{amount}\left[\mathrm{ml}\right]\end{array}}{\mathrm{surface}\mathrm{weight}\mathrm{found}\left[\frac{g}{m^2}\right]*\mathrm{area}\mathrm{used}\left[m^2\right]}$

(16) The GC analyses were performed on a Perkin Elmer Clarus 500 with a TurboMatrix 40 sample collector and the TotalChrom software (Version 6.3.2). For the sample measurement, 1 μl of the extraction solution prepared was injected at the normal rate. The temperatures of the detectors were 200° C. and 310° C. The measurement was carried out over 28.5 minutes at a data rate of 12.5 pts. The individual constituents were separated using a Perkin Elmer Elite Series column (Perkin Elmer; PE17-HT, N931-6264 with a length of 30 m and internal diameter of 0.25 mm and also with a 0.15 μm film). Carrier gases used were compressed air and hydrogen. The gas flow rate was 450 ml/min for compressed air and 45 ml/min for hydrogen.

Example 1

(17) Production of materials in plate form: A photopolymeric mixture containing 73.75 parts of an SIS block copolymer (SIS triblock, with a styrene content of 14 to 15% and a diblock fraction of around 26%, vinyl group portion around 7-8%) as binder, 9.3 parts of hexanediol diacrylate (HDDA), 3.3 parts of hexanediol dimethacrylate, 5 parts of diisononyl cyclohexane-1,2-dicarboxylate as plasticizer and 5 parts of vinyltoluene-methylstyryl copolymer as extrusion assistant and also 2.5 parts of benzil dimethyl ketal as photoinitiator, and 1.25 parts of further constituents such as inhibitors and dyes, was melted at elevated temperatures (120 to 180° C.) in an extruder and calendared via a slot die between a cover film with laser-ablatable mask layer and optionally an interlayer containing 71 parts of polyvinyl butyral (OH fraction 18-21%, 14-20 mPas as 10% ethanolic solution), 15 parts of an inorganic, silicatic filler and 5 parts of an adhesion-promoting component and also ethylenically unsaturated monomer (HDDA) with a thickness of 100 μm, and a carrier film having a thickness of 125 μm, thus giving the relief precursor (photopolymer+films) a thickness of 1855 μm. The oxygen permeability of the interlayer was 6*10.sup.4 cm.sup.3*μm/(m.sup.2*d*bar).

(18) Various tonal value fields with between 1 and 100% coverage and with a halftone width of 146 lpi were generated on the precursors by laser ablation. The ablation was performed using a ThermoFlexx laser (Xeikon) with Multiplate software (Version 5.0.0.309) and the following parameters: wavelength 1064 nm, 10.5 revolutions per second, 35 W laser power. UV exposure took place using a Combi Fill exposure unit (Flint group) with tube light of intensity 13 mW/cm.sup.2 (solvent development) for 15 min or 24 mW/cm.sup.2 for 10 min (thermal development). Developing then took place with solvent in an Fill washout unit (Flint group) at 35° C., using nylosolv A (Flint group) as developing solution. Drying was carried out over 2 hours at 60° C. and at the same time there was re-exposure with UVA for 10 minutes and UVC for 5 minutes in a Combi Fill exposure unit (Flint group). As an alternative, a portion of the samples were developed with a nyloflex Xpress FIV device (Flint group, thermal development at a temperature of 163° C. (325° F.) and 14 revolutions with a pressing pressure of 4.13 bar (60 psi) and a speed of 0.7″/s, with simultaneous re-exposure with UVA for 10 minutes and UVC for 6 minutes in a Combi Fill exposure unit (Flint group).

(19) Samples from the 50% halftone were taken from the completed relief structures and were measured for cupping (table 1a).

(20) TABLE-US-00001 Cupping Cupping Frac- depth, depth, Thick- tion of solvent thermal ness HDDA development development of in (standardized (standardized Micro- inter- Inter- inter- to to example a1 Shore layer Example layer layer example a1) thermal) A (μm) Example No 0% 1 1 65.4 1a Example Yes 7 ± 2 0.87 0.59 65.8 4 ± 1 1b Example Yes 9 ± 1% 0.82 0.43 65.1 4 ± 1 1c Example Yes 0 1 1 65.4 4 ± 1 1d

(21) As can be inferred from the table above, the monomer in the interlayer reduces the cupping. The best result is achieved with 9% HDDA in the interlayer and thermal development, although even relatively small concentrations already produce a significant reduction. Presumably the cupping is reduced since monomer is able to diffuse from the interlayer into the exposed regions from above as well and not just from the unexposed regions, from the side.

Example 2

(22) Production of materials in plate form: A photopolymeric mixture containing 65 parts of an SBS block copolymer (SBS triblock, having a styrene content of 31% and a diblock fraction of around 17%) as binder, 6.5 parts of hexanediol diacrylate, and 2.5 parts of benzil dimethyl ketal as photoinitiator, 1 part of further constituents such as inhibitors and dyes, and 25 parts of a polybutadiene oil (vinyl content 2%, M.sub.n=5000 g/mol) as plasticizer, was melted at elevated temperatures (120-180° C.) in an extruder and calendared via a slot die between a cover film with laser-ablatable mask layer and optionally an interlayer containing 90 parts of polyvinyl butyral (OH fraction 18 to 21%, 14 to 20 mPas measured as a 10% ethanolic solution), 4 parts of an adhesion promoter and optionally 6 parts of monomer (HDDA), with a thickness of 100 μm, and a carrier film having a thickness of 125 μm, thus giving the relief precursor (photopolymer+films) a thickness of 4100 μm. The oxygen permeability of the interlayer was 5.8*10.sup.4 cm.sup.3*μm/(m.sup.2*d*bar).

(23) Various tonal value fields between 1 and 100% coverage with a halftone width of 146 lpi, and also various images, were generated on the precursors by laser ablation. The ablation was performed using a ThermoFlexx laser (Xeikon) with Multiplate software (Version 5.0.0.309) and the following parameters: wavelength 1064 nm, 10.5 revolutions per second, 35 W laser power. Exposure was carried out with a Combi Fill exposure unit (Flint group), using tube light with an intensity of 24 mW/cm.sup.2 for 10 min. Development was carried out in an Fill washout unit (Flint group) at 35° C., using nylosolv A (Flint group) as developing solution. Drying took place over 2 hours at 60° C., with simultaneous re-exposure with UVA for 10 minutes and UVC for 4 minutes, in parallel, in a Combi Fill exposure unit (Flint group).

(24) TABLE-US-00002 Example Interlayer HDDA (wt %) Fluting assessment Example 2a Yes 0 − Example 2b Yes 7 ± 2 + Example 2c No − −

(25) The print results show that it is possible to achieve a significant reduction in fluting by using a monomer-containing interlayer. As a result of the HDDA in the interlayer, there is presumably a better and more uniform crosslinking at the plate surface, which is capable of compensating the fluctuations in the substrate in the case of the corrugated card.

Example 3

(26) The relief precursors were produced by the method described above (example 1) with an HDDA content of 7±2% and were developed by solvent washout. For the experiments in this example, different polymers were used as binders of the interlayer: PVA: OH fraction 71.5 mol % to 73.5%, 5.6-6.6 mPas, as 4% aqueous solution PVB: OH fraction 18 to 21 mol %, 14 to 20 mPas, as 10% ethanol solution PA: softening point 130 to 155° C., MFR at 175° C.: 5 to 15 g/10 min, low-temperature flexibility −40° C.

(27) TABLE-US-00003 Poly- Solubility O2 Thickness mer parameter permeability Particle of in the of of interlayer (type inter- inter- polymer (cm.sup.3*μm/ and layer Cup- layer ((MPa).sup.1/2) (m.sup.2 * d * bar)) size) (μm) ping Example PVA 21-26 8.5 * 10.sup.2 — 5 ± 1 0 3a Example PVB 23 8.5 * 10.sup.4 silica, 5 ± 1 + 3b 4-6 μm Example PA 19-27 2.0 * 10.sup.5 — 4 ± 1 + 3c Example PA 19-27 3.7 * 10.sup.5 silica, 5 ± 1 + 3d 4-6 μm

Example 4

(28) The relief precursors were produced by the method described above (example 2) with an HDDA content of 7±2%. For the experiments in this example, different polymers were used as binders of the interlayer: BUNA S, styrene fraction 30 mol % (comparative example, crosslinkable polymer) PU: aromatic polyisocyanate based on tolylene diisocyanate, NCO content 12 mol %, equivalent weight about 350 PVB: OH fraction 18 to 21 mol %, 14 to 20 mPas, as 10% ethanol solution PA: softening point 130 to 155° C., MFR at 175° C.: 5 to 15 g/10 min, low-temperature flexibility −40° C. Ethyl cellulose: ethoxy fraction 48 to 49.5 mol %, 90 to 110 mPas, as 5% solution in 80% toluene and 20% ethanol

(29) TABLE-US-00004 O2 Solubility permeability Thick- Polymer parameter or interlayer Particle ness in the of (cm.sup.3 * μm/ (type of inter- polymer (m.sup.2 * d * and interlayer Flut- layer ((MPa).sup.1/2) bar)) size) (μm) ing Example BUNA S 17 — 4 ± 1 − 4a Example PU 23 silica 5 ± 1 0 4b 4-6 μm Example PVB 23 8.5 * 10.sup.4 5 ± 1 + 4c Example PA 19-27 2.0 * 10.sup.5 — 4 ± 1 + 4d Example PA 19-27 3.7 * 10.sup.5 silica, 5 ± 1 + 4e 4-6 μm Example Ethyl 20-21 — 4 ± 1 + 4f cellulose