FLEXOGRAPHIC PRINTING PLATE PRECURSOR

Abstract

The present invention provides a flexographic printing plate precursor which makes it possible to precisely reproduce the pattern of a microcell on the surface of a printing plate without requiring the use of any specialized device or any additional step, and thus to improve the ink laydown on a solid-printed part. A flexographic printing plate precursor comprising at least a support (A), a photosensitive resin layer (B), an oxygen barrier layer (C) and a heat-sensitive mask layer (D) which are laminated in this order, wherein a photosensitive resin composition constituting the photosensitive resin layer (B) comprises (a) a polymer prepared by polymerizing a conjugated diene, (b) an ethylenically unsaturated compound and (c) a photopolymerization initiator, and wherein the content of the photopolymerization initiator (c) in the photosensitive resin composition is 2 to 9% by mass.

Claims

1. A flexographic printing plate precursor comprising at least a support (A), a photosensitive resin layer (B), an oxygen barrier layer (C) and a heat-sensitive mask layer (D) which are laminated in this order, wherein a photosensitive resin composition constituting the photosensitive resin layer (B) comprises (a) a polymer prepared by polymerizing a conjugated diene, (b) an ethylenically unsaturated compound and (c) a photopolymerization initiator, and wherein the content of the photopolymerization initiator (c) in the photosensitive resin composition is 2 to 9% by mass.

2. The flexographic printing plate precursor according to claim 1, wherein the ethylenically unsaturated compound (b) includes a (meth)acrylate compound (i) having a number average molecular weight of 100 to 600, wherein the content of the (meth)acrylate compound (i) having a number average molecular weight of 100 to 600 in the photosensitive resin composition is 5 to 16% by mass, and wherein the ratio of the mass of the photopolymerization initiator (c) to the mass of the (meth)acrylate compound (i) having a number average molecular weight of 100 to 600 in the photosensitive resin composition is within the range of 0.20 to 0.55.

3. The flexographic printing plate precursor according to claim 2, wherein the ethylenically unsaturated compound (b) further includes a (meth)acrylate compound (ii) having a number average molecular weight of more than 600 and not more than 20,000, and wherein the content of the (meth)acrylate compound (ii) having a number average molecular weight of more than 600 and not more than 20,000 in the photosensitive resin composition is 5 to 25% by mass.

4. The flexographic printing plate precursor according to claim 1, wherein the development is performed by using a water-based developing solution.

5. A flexographic printing plate obtained by exposing and developing the flexographic printing plate precursor of claim 1, characterized in that a microcell is applied to a solid-printed part formed on the printing plate.

6. A flexographic printing method, characterized in that the method uses the flexographic printing plate according to claim 5.

Description

EXAMPLE 1

Preparation of Photosensitive Resin Composition

[0064] A butadiene latex (Nipol LX111NF, non-volatile content: 55%, manufactured by Zeon Corporation) (86 parts by mass) that served as the polymer prepared by polymerizing a conjugated diene, an acrylonitrile-butadiene latex (Nipol SX1503, non-volatile content: 42%, manufactured by Zeon Corporation) (24 parts by mass) that served as the polymer prepared by polymerizing a conjugated diene, a polybutadiene-terminal acrylate having a number average molecular weight of 10000 (BAC45, manufactured by Osaka Organic Chemical Industry Ltd.) (15 parts by mass) that served as an ethylenically unsaturated compound, trimethylolpropane trimethacrylate having a number average molecular weight of 338 (Light Ester TMP, manufactured by Kyoeisha Chemical Co., Ltd.) (10 parts by mass) that served as ethylenically unsaturated compound, benzyl dimethylketal (3 parts by mass) that served as a photopolymerization initiator, and a hydrophilic polymer (PFT-4, non-volatile content: 25%, manufactured by Kyoeisha Chemical Co., Ltd.) (20 parts by mass), a butadiene oligomer (B2000, manufactured by Nippon Soda Co., Ltd.) (9.9 parts by mass), a thermal stabilizer (4-methoxyphenol) (0.1 part by mass), and an ultraviolet ray absorber (Tinuvin 326) (0.01 part by mass) that served as auxiliary components were mixed together in a container so as to produce a dope. The dope was charged into a pressurized kneader, and then the solvent was removed under a reduced pressure at 80° C. so as to produce a photosensitive resin composition.

[0065] Preparation of Flexographic Printing Plate Precursor

[0066] Carbon black dispersion (AMBK-8 manufactured by ORIENT CHEMICAL INDUSTRIES CO., LTD.), copolymerized polyamide (PA223 manufactured by TOYOBO CO., LTD.), propylene glycol, and methanol were mixed at a mass proportion of 45/5/5/45 so as to obtain an heat-sensitive mask layer coating solution. After a releasing treatment was performed on both sides of a PET film (E5000 manufactured by TOYOBO CO., LTD., thickness: 100 μm), the heat-sensitive mask layer coating solution was applied onto the PET film using a bar coater so that a thickness of a coating film after being dried was 2 μm, and dried at 120° C. for 5 minutes so as to obtain a film laminate (I). An optical density thereof was 2.3. The optical density was measured using a black-and-white transmission densitometer DM-520 (SCREEN Holdings Co., Ltd.). Polyvinyl acetate (KH2O manufactured by NIHON GOSEI KAKO Co., Ltd.) having a saponification degree of 80% and a plasticizer (glycerin) were mixed at a mass proportion of 70/30 so as to obtain an oxygen barrier layer coating solution. The oxygen barrier layer coating solution was applied onto the film laminate (I) using a bar coater so that a thickness of a coating film after being dried was 2.0 μm, and dried at 120° C. for 5 minutes so as to obtain a film laminate (II). The photosensitive resin composition was disposed on a PET film support (E5000 manufactured by TOYOBO CO., LTD., thickness: 125 μm) coated with a copolymerized polyester-based adhesive, and the film laminate (II) was superposed on the photosensitive resin composition. These were laminated at 100° C. using a heat pressing machine so as to obtain a flexographic printing plate precursor including a PET support, an adhesive layer, a photosensitive resin layer, an oxygen barrier layer, a heat-sensitive mask layer, and a cover film. A total thickness of the plate was 1.14 mm.

[0067] Production of Printing Plate from Flexographic Printing Plate Precursor

[0068] The production of a printing plate from a flexographic printing plate precursor was performed in the following two patterns in which different images to be formed were used.

Pattern 1

[0069] The printing plate precursor was subjected to back exposure from the PET support side for 10 seconds. Subsequently, the cover film was peeled off. This printing plate was wound around CDI4530 manufactured by ESCO Graphics, and the imaging was performed at a resolution of 4000 dpi. As to the image, a test chart having a normal solid-printed part (without microcell) and solid-printed parts to which each of microcells MG45, MG34, MG25, WSI and MC16 was applied respectively was used. An imaged pattern was produced by arranging the test chart with 10 increments between boost values of 50 to 170. The main exposure was performed using an LED built in CDI4530 at a luminance of mW/cm.sup.2 for 480 seconds. After that, the plate was detached from CDI, and development was performed for 8 minutes using a developing machine (Stuck System, 1% aqueous washing soap solution, 40° C.) manufactured by A & V Co., Ltd., and water droplets on the plate surface were removed with a drain stick. Thereafter, the plate was dried in a dryer at 60° C. for 10 minutes, subjected to finishing exposure for 7 minutes, and finally irradiated with light from a germicidal lamp for 5 minutes, whereby a flexographic printing plate was thus obtained. The back exposure and finishing exposure were performed using TL-K 40W/10R lamp (peak wavelength: 370 nm, luminance at 350 nm: 10 mW/cm.sup.2) manufactured by Philips. As to the germicidal lamp, a germicidal lamp GL-40 (peak wavelength: 250 nm, luminance at 250 nm: 4.5 mW/cm.sup.2) manufactured by Panasonic Corporation was used. It was confirmed that the relief depth of the resultant printing plate was 0.6 mm.

Pattern 2

[0070] The printing plate precursor was subjected to back exposure from the PET support side for 10 seconds. Subsequently, the cover film was peeled off. This plate was wound around CDI4530 (manufactured by ESCO Graphics), and was then subjected to abrasion at a resolution of 4000dpi using a test image having dots (at 175 lpi, 0 to 10%, in 0.3% increment), isolated dots (between 0 to 300 μm, in 50 μm increment), and dot gradation parts (fade-out parts) where the dot gradation shifts to zero. After the ablation, the plate was taken out, returned to the plane shape, and subjected to main exposure for 7 minutes. Thereafter, development was performed for 8 minutes using a developing machine (Stuck System, 1% aqueous washing soap solution, 40° C.) manufactured by A & V Co., Ltd., and water droplets on the plate surface were removed with a drain stick. Thereafter, the plate was dried in a dryer at 60° C. for 10 minutes, subjected to finishing exposure for 7 minutes, and finally irradiated with light from a germicidal lamp for 5 minutes, whereby a flexographic printing plate was thus obtained. The back exposure, main exposure and finishing exposure were performed using TL-K 40W/10R lamp (peak wavelength: 370 nm, luminance at 350 nm: 10 mW/cm.sup.2) manufactured by Philips. As to the germicidal lamp, a germicidal lamp GL-40 (peak wavelength: 250 nm, luminance at 250 nm: 4.5 mW/cm.sup.2) manufactured by Panasonic Corporation was used. It was confirmed that the relief depth of the resultant printing plate was 0.6 mm and dots each having a diameter of 16 μm were reproduced on the printing plate.

EXAMPLES 2 TO 12 AND COMPARATIVE EXAMPLES 1 TO 5

[0071] Flexographic printing plate precursors were prepared in the same manner as in Example 1 except that the composition ratio of each component in the photosensitive resin composition constituting the photosensitive resin layer was changed as presented in Tables 1 and 2. The time of back exposure was adjusted so that the relief depth became 0.6 mm.

COMPARATIVE EXAMPLE 6

[0072] A flexographic printing plate precursor was produced in the same manner as in Example 1, except that an oxygen barrier layer was not formed in the production of the flexographic printing plate precursor. Subsequently, in the production of a printing plate from the flexographic printing plate precursor, Membrane100 was laminated as an oxygen barrier layer on the heat-sensitive mask layer that had been subjected to imaging, by using a dedicated laminator. After the main exposure, Membrane100 was removed. Then, a flexographic printing plate was produced in the same manner as in Example 1.

[0073] Evaluation results of Examples 1 to 12 and Comparative Examples 1 to 6 are shown in Tables 1 and 2.

TABLE-US-00001 TABLE 1 Examples 1 2 3 4 5 6 Components of polymer prepared by butadiene polymer (LX111NF) 47 43 43 47.5 44 50 photosensitive polymerizing NBR polymer (SX1503A) 10 10 7 10 10 10 resin layer conjugated diene (% by mass) ethylenically (meth)acrylate having low molecular weight 10 10 13 10 13 7 unsaturated (Light Ester TMP) compound (meth)acrylate having low molecular weight (Light Ester 1,6 HX) (meth)acrylate having low molecular weight (Light Ester 19ND) acrylate having high molecular weight (BAC45) 15 15 15 15 15 15 (meth)acrylate having high molecular weight (TE2000) photopolymerization benzyl dimethylketal 3 5 7 2.5 3 3 initiator hydrophilic polymer PFT4 5 5 5 5 5 5 plasticizer butadiene oligomer (B2000) 9.9 9.9 9.9 9.9 9.9 9.9 thermal 4-methoxyphenol 0.1 0.1 0.1 0.1 0.1 0.1 polymerization inhibitor ultraviolet ray Tinuvin 326 0.01 0.01 0.01 0.01 0.01 0.01 absorber Ratio of amount of photopolymerization initiator/(meth)acrylate having low molecular weight 0.30 0.50 0.54 0.25 0.23 0.43 Oxygen barrier layer present present present present present present Evaluation results reproducibility of microcell on printing plate ∘∘ ∘∘ ∘∘ ∘ ∘∘ ∘∘ ink laydown on hiding rate of normal solid- 90 89 88 90 89 91 solid-printed printed part (%) part hiding rate upon application 97 97 96 94 97 97 of microcell (%) improvement in hiding rate by 7 8 8 4 8 6 application of microcell (%) reproducibility of isolated dot ∘ ∘ ∘ ∘ ∘ ∘ (100) (100) (100) (100) (100) (100) durability of printing plate ∘ ∘ ∘ ∘ ∘ ∘ Examples 7 8 9 10 11 12 Components of polymer prepared by butadiene polymer (LX111NF) 44 50 47 47 47 59 photosensitive polymerizing NBR polymer (SX1503A) 8 12 10 10 10 13 resin layer conjugated diene (% by mass) ethylenically (meth)acrylate having low molecular weight 10 10 10 10 unsaturated (Light Ester TMP) compound (meth)acrylate having low molecular weight 10 (Light Ester 1,6 HX) (meth)acrylate having low molecular weight 10 (Light Ester 19ND) acrylate having high molecular weight (BAC45) 20 10 15 15 0 (meth)acrylate having high molecular weight (TE2000) 15 0 photopolymerization benzyl dimethylketal 3 3 3 3 3 3 initiator hydrophilic polymer PFT4 5 5 5 5 5 5 plasticizer butadiene oligomer (B2000) 9.9 9.9 9.9 9.9 9.9 9.9 thermal 4-methoxyphenol 0.1 0.1 0.1 0.1 0.1 0.1 polymerization inhibitor ultraviolet ray Tinuvin 326 0.01 0.01 0.01 0.01 0.01 0.01 absorber Ratio of amount of photopolymerization initiator/(meth)acrylate having low molecular weight 0.30 0.30 0.30 0.30 0.30 0.30 Oxygen barrier layer present present present present present present Evaluation results reproducibility of microcell on printing plate ∘∘ ∘∘ ∘∘ ∘ ∘∘ ∘ ink laydown on hiding rate of normal solid- 89 90 90 89 90 89 solid-printed printed part (%) part hiding rate upon application of 97 97 97 94 97 94 microcell (%) improvement in hiding rate by 8 7 7 5 7 5 application of microcell (%) reproducibility of isolated dot ∘∘ Δ ∘ ∘ ∘ Δ (50) (150) (100) (100) (100) (200) durability of printing plate ∘∘ Δ ∘ ∘ ∘ Δ

TABLE-US-00002 TABLE 2 Comparative Examples 1 2 3 4 5 6 Components of polymer prepared by butadiene polymer (LX111NF) 49 50.5 53.5 41 47 47 photosensitive polymerizing NBR polymer (SX1503A) 10 12 12 9 10 10 resin layer conjugated diene (% by mass) ethylenically (meth)acrylate having low molecular weight 10 6 3 10 10 10 unsaturated (Light Ester TMP) compound (meth)acrylate having low molecular weight (Light Ester 1,6 HX) (meth)acrylate having low molecular weight (Light Ester 19ND) acrylate having high molecular weight (BAC45) 15 15 15 15 15 15 (meth)acrylate having high molecular weight (TE2000) photopolymerization benzyl dimethylketal 1 1.5 1.5 10 3 3 initiator hydrophilic polymer PFT4 5 5 5 5 5 5 plasticizer butadiene oligomer (B2000) 9.9 9.9 9.9 9.9 9.9 9.9 thermal 4-methoxyphenol 0.1 0.1 0.1 0.1 0.1 0.1 polymerization inhibitor ultraviolet ray Tinuvin 326 0.01 0.01 0.01 0.01 0.01 0.01 absorber Ratio of amount of photopolymerization initiator/(meth)acrylate having low molecular weight 0.10 0.25 0.50 1.00 0.30 0.30 Oxygen barrier layer present present present present absent — Evaluation results reproducibility of microcell on printing plate x Δ x ∘ x ∘∘ ink laydown on hiding rate of normal solid- 90 90 91 84 88 90 solid-printed printed part (%) part hiding rate upon application 90 91 91 89 88 97 of microcell (%) improvement in hiding rate by 0 1 0 5 0 7 application of microcell (%) reproducibility of isolated dot ∘ ∘ ∘ x ∘ ∘ (100) (100) (100) (300) (100) (100) durability of printing plate ∘ ∘ ∘ x ∘ ∘

[0074] Details of the ethylenically unsaturated compound in the above Tables are as follows.

[0075] Light Ester TMP: Trimethylolpropane tri(meth)acrylate, number average molecular weight: 338, manufactured by Kyoeisha Chemical Co., Ltd.

[0076] Light Ester 1,6 HX: 1,6-hexanediol dimethacrylate, number average molecular weight: 254, manufactured by Kyoeisha Chemical Co., Ltd.

[0077] Light Ester 19ND: 1,9-nonanediol di(meth)acrylate, number average molecular weight: 298, manufactured by Kyoeisha Chemical Co., Ltd.

[0078] BAC45: Polybutadiene-terminal acrylate, number average molecular weight: 10000, manufactured by Osaka Organic Chemical Industry Ltd.

[0079] TE2000: Polybutadiene having a methacrylate group introduced at terminal thereof, urethane-bonded type, number average molecular weight: 3,000, manufactured by Nippon Soda Co., Ltd.

[0080] As apparent from the evaluation results shown in the table, in Examples 1 to 12 in each of which the amount of a photopolymerization initiator, the amount of a (meth)acrylate compound having a low molecular weight, and the blend ratio of the photopolymerization initiator to the (meth)acrylate compound having a low molecular weight are within the ranges defined in the present invention, the reproducibility of a microcell on a printing plate and the ink laydown performance in a solid-printed part were excellent. In addition, by further adding a (meth)acrylate compound having a high molecular weight, even when the photopolymerization initiator is added in a larger amount, the reproducibility of isolated dots and the durability of a printing plate are not deteriorated (see the comparison between Examples 1 to 6, and 9 to 11 with Examples 7, 8, and 12).

[0081] In contrast, in Comparative Example 1, because the amount of the photopolymerization initiator added was small which was the same amount level as that employed conventionally, the reproducibility of a microcell on a printing plate and the ink laydown performance in a solid-printed part were inferior. In Comparative Example 2, because the amount of the photopolymerization initiator added was small, even when the ratio of the amount of the photopolymerization initiator to the amount of the (meth)acrylate compound having a low molecular weight was proper, the reproducibility of a microcell on a printing plate and the ink laydown performance in a solid-printed part were inferior. In Comparative Example 3, because the amount of the photopolymerization initiator added was small and the amount of the (meth)acrylate compound having a low molecular weight added was small, the reproducibility of a microcell on a printing plate and the ink laydown performance in a solid-printed part were inferior. In Comparative Example 4, because the amount of the photopolymerization initiator added was too large, the plate hardness in the solid-printed part was too high, whereby the ink laydown on the solid-printed parts was deteriorated. In addition, reproducibility of isolated dots and durability during printing were inferior. In Comparative Example 5, any oxygen barrier layer was not provided. Therefore, even though the amount of the photopolymerization initiator added, the amount of the (meth)acrylate compound having a low molecular weight, and the ratio of the amount of the photopolymerization initiator to the amount of the (meth)acrylate compound having a low molecular weight were proper, the reproducibility of a microcell on a printing plate and the ink laydown performance in a solid-printed part were inferior. In Comparative Example 6, the reproducibility of a microcell on a printing plate and the ink laydown performance on a solid-printed part were excellent. However, in Comparative Example 6, an oxygen barrier layer was laminated onto a heat-sensitive mask layer after the imaging instead of being formed between a photosensitive resin layer and a heat-sensitive mask layer. Therefore, a dedicated laminate was required for the lamination of the oxygen barrier layer, and the printing plate production process was complicated.

INDUSTRIAL APPLICABILITY

[0082] In the flexographic printing plate precursor according to the present invention, an oxygen barrier layer is provided between a photosensitive resin layer and a heat-sensitive mask layer and the content of a photopolymerization initiator in the photosensitive resin composition is increased compared with the conventional flexographic printing plate precursor. Therefore, a microcell pattern can be reproduced precisely on the surface of a printing plate without requiring the use of any specialized device or any additional step and without being affected by the oxygen-induced polymerization inhibition during exposure, particularly main exposure. As a result, the ink laydown on a solid-printed part in the printing plate can be improved. Therefore, the flexographic printing plate precursor according to the present invention is very useful in the industrial field.