Photopolymerisable layered composite for producing flexo printing elements

Abstract

Laminate comprising a) a photopolymerizable relief-forming layer, at least containing an elastomeric binder, ethylenically unsaturated monomers and a photoinitiator and optionally further additives, b) an optionally photopolymerizable elastomeric substrate layer, at least containing an elastomeric binder, optionally ethylenically unsaturated monomers and a photoinitiator and optionally further additives,
the relief-forming layer a) having a hardness of 30 to 70 Shore A and the elastomeric substrate layer b) having a hardness of 75 Shore A to 70 Shore D in each case in the photopolymerized state, and the layer b) having a hardness of at least 5 Shore A greater than the layer a).

Claims

1. A laminate comprising a) a photopolymerizable relief-forming layer comprising an elastomeric binder, ethylenically unsaturated monomers, a photoinitiator, and optionally further additives; b) an elastomeric substrate layer which is optionally photopolymerizable comprising an elastomeric binder, optionally ethylenically unsaturated monomers, a photoinitiator, and optionally further additives; wherein said photopolymerizable relief-forming layer a) has a hardness of 30 to 70 Shore A and said elastomeric substrate layer b) has a hardness of from 75 Shore A to 70 Shore D in the photopolymerized state, and wherein said elastomeric substrate layer b) has a hardness of at least 5 Shore A greater than that of said photopolymerizable relief-forming layer a), and wherein the photopolymerizable relief-forming layer a) is present on the elastomeric substrate layer b).

2. The laminate of claim 1, wherein said laminate comprises the sequence of layers (1) to (6): (1) a substrate film; (2) optionally a release layer; (3) the elastomeric substrate layer b); (4) the photopolymerizable relief-forming layer a); (5) optionally a release layer; and (6) a cover sheet.

3. A hollow cylinder comprising the laminate of claim 1.

4. A process for producing a photopolymerizable, cylindrical, continuous, seamless, flexographic printing element from a laminate comprising a) a photopolymerizable relief-forming layer comprising an elastomeric binder, ethylenically unsaturated monomers, a photoinitiator, and optionally further additives; b) an elastomeric substrate layer which is optionally photopolymerizable comprising an elastomeric binder, optionally ethylenically unsaturated monomers, a photoinitiator, and optionally further additives; wherein said photopolymerizable relief-forming layer a) has a hardness of 30 to 70 Shore A and said elastomeric substrate layer b) has a hardness of from 75 Shore A to 70 Shore D in the photopolymerized state, and wherein said elastomeric substrate layer b) has a hardness of at least 50 Shore A greater than that of said photopolymerizable relief-forming layer a), said process comprising: (i) cutting the edges of the laminate to be joined to size by means of mitre cuts; (ii) pushing on and locking a hollow cylinder on a rotatably mounted support cylinder; (iii) applying an adhesion-promoting layer to the outer surface of the hollow cylinder; (iv) mounting the laminate cut to size, with the elastomeric substrate layer b), on the hollow cylinder provided with the adhesion-promoting layer, the ends provided with the mitre cut resting substantially one on top of the other but not overlapping; (v) optionally peeling off a cover sheet from said photopolymerizable relief-forming layer a); (vi) joining the cut edges by bringing the surface of the photopolymerizable layer on the hollow cylinder into contact with a rotating calender roll with heating until the cut edges are joined to one another; and (vii) removing the processed hollow cylinder from the support cylinder.

5. The process of claim 4, wherein the elastomeric substrate layer is photopolymerizable and preexposed to actinic light from the side facing away from the cover sheet, directly or through the substrate film, prior to (iii).

6. The process of claim 4, wherein said adhesion-promoting layer is a double-sided adhesive tape.

7. The laminate of claim 1, wherein the elastomeric substrate layer is photopolymerizable.

Description

EXAMPLES

General Method for the Production of the Substrate Layers Used

(1) The substrate layers used were produced by means of casting from solution in toluene onto a PET film as a substrate film, which was coated with a 5 m thick layer as the polyamide Makromelt 6900 as the release layer.

General Method for the Production of the Laminates Used

(2) The laminates used according to the invention are produced by extruding the photopolymerizable material, discharging it through a slot die and calendering it between the substrate layer and the cover sheet. The extrusion process is described in detail in EP-B 084 851. The substrate layers described below under A) are used as the substrate layer, and the cover sheet used is a PET film coated with 5 m Makromelt 6900. The laminate comprising substrate layer and photopolymeric layer has a total thickness of 1.14 mm.

General Method for the Production of a Seamless/Continuous Printing Plate

(3) For carrying out this process step, the core to be occupied by the laminate is first pushed onto the air cylinder of the mounting apparatus. The adhesive film is then cut to size on the mounting table, the air cylinder is caused to rotate and the film is slowly pushed into the gap between auxiliary roll and the air cylinder provided with the core. The adhesive film is carried along by the rotation, the auxiliary roll uniformly pressing the film onto the core so that the adhesive film adheres firmly to the core without bubbles. The protective film is then peeled off from the adhesive film. The core is now provided with an adhesion-promoting layer. In the next step, after removal of the substrate film (optionally including release layer), the photopolymerizable laminate cut to size is pushed into the gap, carried along and pressed firmly by the auxiliary roll. The substrata layer is directed towards the core. The calender roll and the air cylinder provided with core, adhesion-promoting layer, substrate layer and photopolymerizable layer are brought into contact with one another and caused to rotate, and the gap is closed by calendering with introduction of heat.

General Method for the Further Processing of the Seamless/Continuous Printing Plate

(4) By means of a ring coater, the seamless/continuous printing plates are provided with a digitally imageable layer. The coating is effected by means of a ring coater, and the coating solution used is a DSL II 80 solution (Flint Group Germany GmbH). After the application of the digitally imageable layer, the latter is imaged by means of the respective suitable technique and the sleeve is then exposed by means of actinic light through the resulting mask in a manner known in principle. Suitable actinic, i.e. chemically active, light is known to be in particular UVA or UV/VIS radiation. Cylindrical exposure units for the uniform exposure of sleeves are commercially available.

(5) The development of the imagewise exposed layer is effected in a conventional manner using the washout agent Nylosolv A (Flint Group Germany GmbH).

(6) Starting materials used:

(7) Styroflex 2G66: SBS block copolymer (BASF AG)

(8) Styrolux 3G55: SBS block copolymer (BASF AG)

(9) Kraton D-1102: SBS block copolymer (Kraton Polymers)

(10) Kraton D-4150: SBS block copolymer with 33% of mineral oil (Kraton Polymers)

(11) Polyl 130: Oligobutadiene, plasticizer (Degussa)

(12) Laromer HDDA: 1,6-Hexanediol diacrylate (BASF)

(13) HDDMA: 1,6-Hexanediol dimethacrylate (Rohm GmbH & Co. KG)

(14) Lucirin BDK: Benzil dimethyl ketal (BASF)

(15) Kerobit TBK: 2,6-Di-tert-butyl p-cresol (Raschig)

A) Production of the Substrate Layers

Example 1

Production of the Substrate Layer 1 (SL-1)

(16) The substrate layer 1 (SL-1) was produced as described in the general method, using the composition stated in Table 1. The thickness of the dry substrate layer was 75 m.

(17) TABLE-US-00001 TABLE 1 Composition of the substrate layer 1 Component Amount SBS block copolymer (Styroflex 94% 2G66) Hexanediol dimethacrylate monomer 5% Benzil dimethyl ketal (photoinitiator) 1% Total 100%

Example 2

Production of the Substrate Layer 2 (SL-2)

(18) The substrate layer 2 (SL-2) was produced as described in the general method. The composition of the substrate layer corresponded to that of the substrate layer 1 but the thickness of the dry substrate layer was 125 m.

Example 3

Production of the Substrate Layer 3 (SL-3)

(19) The substrate layer 3 (SL-3) was produced as described in the general method, using the composition stated in Table 2. The thickness of the dry substrate layer was 125 m.

(20) TABLE-US-00002 TABLE 2 Composition of the substrate layer 3 Component Amount SBS block copolymer (Styrolux 3G55) 94% Hexanediol dimethacrylate monomer 5% Photoinitiator 1% Total 100%

Comparative Example 1

Substrate Layer 4 (SL-4)

(21) A commercially available PET film having a thickness of 175 m was used as substrate layer 4.

Comparative Example 2

Substrate Layer 5 (SL-5)

(22) The substrate layer 5 was produced as described in the general method, using the composition stated in Table 3. The thickness of the dry substrate layer was 125 m.

(23) TABLE-US-00003 TABLE 3 Composition of the substrate layer 3 Component Amount Kraton D-4150 74% Polyl 130 plasticizer 20% Hexanediol dimethacrylate monomer 5% Photoinitiator 1% Total 100%

Example 6

Determination of Melt Flow Indices and Hardness of the Substrate Layers Produced

(24) For determining the melt flow indices and hardness of the substrate layers produced, the substrate layers 1, 2, 3 and 5 were peeled off from their substrate film. The substrate layer 4 was used in the form acquired. The melt flow index (MVR) was determined at a temperature of 80 C. and in an applied weight of 5 kg according to DIN ISO 1133.

(25) The measurement of the Shore A hardness was effected according to DIN 53 505. For this purpose, layers corresponding to the examples were produced in a thickness of 1 mm and crosslinked by uniform exposure for 15 minutes to UVA light (exposure unit F III, Flint Group Germany GmbH). In each case 6 1 mm thick layers of each layer type were stacked one on top of the other in order to achieve a total layer thickness of 6 mm. The hardness of the 6 mm thick layer stacks was determined using a hardness-measure apparatus (type U72/80E, Heinrich Bareiss Prfgertebau GmbH) according to DIN 53 505.

(26) The results are summarized in Table 4. For comparison, melt flow index and hardness of the photopolymeric layer are likewise stated.

(27) TABLE-US-00004 TABLE 4 Melt flow indices of the substrate layers produced. SL-1 SL-2 SL-3 SL-4 SL-5 FL Melt flow index MVR (5 kg/200 C.), cm.sup.3/10 min. 34 46 46 0 >150 >150 Hardness Hardness, Shore A 94 99 99 32 62 Tensile test: Stress in unexposed state, 17.3 18.3 14.4 125 0.3 0.2 Stress in exposed state, N/mm.sup.2 18.1 22.7 21.5 125 1.8 5.8 Elongation in unexposed state, N/mm.sup.2 547 410 500 69 1070 290 Elongation in exposed state, N/mm.sup.2 281 290 260 69 430 403 Modulus of elasticity (@ 125%) in unex- 5.3 10.2 8.7 n.d. 0.1 0.1 posed state, % Modulus of elasticity (@ 125%) in exposed 10.1 16.9 17.4 n.d. 0.5 2.2 state, % SL = substrate layer PL = photopolymeric layer

B) Production of the Laminates

Examples 7a-7f

(28) The laminates were produced as described in the general method. The photopolymeric layer was based on the formulation stated in Table 5.

(29) TABLE-US-00005 TABLE 5 Composition of the photopolymeric layer Component Amount SBS block copolymer (Kraton D 1102) 55% Plasticizer (polybutadiene oil) 32% Monomer (hexanediol diacrylate) 10% Benzil dimethyl ketal (photoinitiator) 2% Additives (heat stabilizer, dye) 1% Total 100%

(30) The photopolymeric layer was calendered between the substrate layers produced according to A) and in each case a cover sheet. In each case a PET film coated with 5 m Makromelt 6900 was used as cover sheets. The laminate comprising substrate layer and photopolymeric layer had a total thickness of 1.14 mm without cover sheet and without substrate film. Table 6 gives an overview of the finished laminates.

(31) TABLE-US-00006 TABLE 6 Finished laminates Substrate layer Photopolymeric layer Example 7a None PL-1 (1140 m) Example 7b SL 1 PL-1 (1065 m) Example 7c SL 2 (125 m Styroflex) PL-1 (1015 m) Example 7d SL 3 (125 m Styrolux) PL-1 (1015 m) Example 7e SL 4 (PET film) PL-1 (965 m) Example 7f SL 5 (125 m Kraton D- PL-1 (1015 m) 4150)

(32) Comparative examples are Examples 7a (no substrate layer), 7e (PET film as substrate layer) and 7f (soft photopolymeric layer). The adhesion of the laminates produced on the foam adhesive tape (Rogers SA2520) are compared in Table 7.

(33) TABLE-US-00007 TABLE 7 Properties of the laminates Ex. 7a Ex. 7e Ex. 7f Compar- Ex. Ex. Ex. Compar- Compar- ison 7b 7c 7d ison ison Adhesion to foam 0.1 >5 >5 >5 >5 0.3 adhesive tape [N]

(34) The results in Table 7 show that the mechanical properties of the laminates produced are substantially improved by the substrate layer. The substantially improved adhesion to foam adhesive tape should additionally be singled out.

(35) Production of the Seamless/Continuous Printing Plates:

(36) Seamless/continuous printing plates were produced from the laminates produced in Examples 7a-7f, as described in the general method. The support used was an Onyx core from Polywest, and a double-sided foam adhesive tape (Rogers SA 2520) was used for fixing the laminate to the core. These were provided with a digitally imageable layer, imaged, exposed to light, washed out, dried and aftertreated.

(37) Printing Experiments

(38) Proof printing with the printing plate was effected on a W&H printing press, a PE film was used as print substrate and the printing speed was 150 m/min. Table 8 shows the quality of the printing plates with regard to the appearance of tape and plate gap and occurrence of starting edges in the printed image.

(39) TABLE-US-00008 TABLE 8 Quality of the printing plates Laminates from Tape gap Plate gap Starting edge Example 7a (comparison) visible not visible visible Example 7b not visible not visible not visible Example 7c not visible not visible not visible Example 7d not visible not visible not visible Example 7e (comparison) not visible visible not visible Example 7f (comparison) not visible not visible not visible