JP2002268228A - Photosensitive resin composition for flexographic plate with improved image formability - Google Patents

Abstract

(57) [Problem] To provide a photosensitive resin composition for flexographic printing which forms a relief image having a low halftone dot density, has a large shoulder angle, and has a deep recess. SOLUTION: At least (A) a photosensitive resin layer, (B)
On layer (A), at least 320 nm to 420 nm
Contains a compound having an ultraviolet absorption region in the range of
A photosensitive resin composition for flexographic printing plates comprising a slip layer comprising at least one polymer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photosensitive resin composition for flexographic printing, which is a plate material used for flexographic printing.

[0002]

2. Description of the Related Art A general resin composition for flexographic printing comprises a support layer such as a polyester film which is transparent to ultraviolet rays, and a photosensitive resin layer provided thereon. When preparing a plate for flexographic printing using this photosensitive resin composition, first, the photosensitive resin layer is partially cured by irradiating ultraviolet rays to the entire support layer side of the composition,
A uniform cured layer controlled to a predetermined thickness was provided from the support layer side interface inside the photosensitive resin layer, and then the photosensitive resin layer was exposed to ultraviolet light through a negative film covering the photosensitive resin upper part. Thereafter, the unexposed portion of the photosensitive resin layer is washed away with a developer to obtain a printing plate on which a target image, that is, a relief image is formed.

Here, the negative film is required to have uniform adhesion to the photosensitive resin layer. If this uniform adhesion is poor and an air layer is locally formed between the photosensitive resin layer and the negative film, the irradiation range of ultraviolet rays may be partially widened in the image exposure process, Since the reaction is inhibited by air interposed at the interface of the resin layer, the relief image of the exposed plate cannot accurately reproduce the image of the negative film.

On the other hand, in flexographic printing, it is common to form a plurality of printing plates with one negative film. Therefore, after exposing the image, the negative film is easily peeled off and reused. It is also required to have good releasability from the photosensitive resin layer interface. However, since the photosensitive resin layer generally has an adhesive property, when a negative film is directly placed thereon, it is not only difficult to uniformly adhere the negative film to the photosensitive resin surface, When the negative film is peeled from the photosensitive resin layer after the image exposure, the negative film stuck to the photosensitive resin layer is damaged and cannot be reused, which is not preferable in terms of cost.

In order to address these problems, a thin flexible layer called a slip layer has conventionally been provided between the photosensitive resin layer and the negative film. This slip layer has sufficient adhesion to the photosensitive resin layer,
It also has sufficient release properties for negative films. Therefore, a sheet of thin polyethylene or the like called a vacuum sheet is covered over the negative film placed on the slip layer, and air interposed between the negative film and the slip layer is evacuated to a vacuum provided in the exposure machine. By evacuating with a device, a uniform relief image can be obtained by bringing the negative film into uniform contact with the slip layer.
Further, after image exposure and after breaking the vacuum of the system, the negative film can be easily peeled off from the slip layer without damaging the negative film.

However, when a conventional slip layer is used, the irradiation range of the ultraviolet light that has passed through the negative film and then has passed through the slip layer and reached the photosensitive resin layer has an extent corresponding to the thickness of the slip layer. In addition, due to refraction and scattering at the interface between the negative film and the slip layer and between the slip layer and the photosensitive resin layer, the photosensitive resin is easily cured in a wider range than the original relief image. In addition, the cross section of the relief image of the convex portion has a trapezoidal shape with a large and wide tail (in such a case, the shoulder angle of the relief is small), and the concave portion has a substantially required engraving depth. Disappears.

When printing is performed using such a printing plate, the ink is transferred to a wider area than the original image, and the printing surface becomes thicker at the convex portions and the printing surface becomes narrower at the concave portions, so that optimum printing quality is obtained. The allowable width of printing pressure for
It becomes difficult to obtain good printed matter. Furthermore, in recent years, from the demand for high quality printed images, there has been a tendency to increase the irradiation amount of ultraviolet rays in order to obtain a fine relief image, and therefore, the shoulder angle of the relief plate tends to be further reduced. In the case of using a photosensitive resin composition having a relief printing plate including an image having a low halftone dot density, a relief image having a large shoulder angle of a convex portion and a large depth of a concave portion and exhibiting good print quality is formed. Is becoming more and more difficult.

[0008]

SUMMARY OF THE INVENTION The present invention provides a flexographic printing plate having an excellent relief shape in order to obtain a flexographic print having a good print quality even in a relief including an image having a wide printing tolerance and a low halftone dot density. It is an object of the present invention to provide a photosensitive resin structure provided with a slip layer capable of forming a resin.

[0009]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to achieve the above object, and as a result, the following problems can be solved by using the following photosensitive resin composition for flexographic printing plates. Was found. That is, the present invention includes at least (A) a photosensitive resin layer and (B) a layer (A);
An object of the present invention is to provide a photosensitive resin composition for flexographic printing plates containing a compound having an ultraviolet absorption region in at least a range of 320 nm to 420 nm and including a slip layer composed of one or more polymers.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
In the photosensitive resin composition for flexographic printing plates used in the present invention, at least (A) a photosensitive resin layer that can be selectively photopolymerized by ultraviolet irradiation through a negative film and can be developed with a developing solvent; B) It has a structure including two layers of a slip layer.

The slip layer (B) in the present invention usually has a thickness of 0.5 to 20 μm and completely covers the relief forming surface of the photosensitive resin layer with a uniform thickness. The slip layer (B) needs to contain a compound having an absorption wavelength in an ultraviolet region of at least 320 to 420 nm. When the absorption wavelength region of the ultraviolet absorbing compound contained in the layer (B) includes at least this range, the relief shape after exposure has a large shoulder angle and a deep concave portion. Preferably, at least 330-400
nm, more preferably 340-380n.
m.

Particularly, when the UV transmittance of the slip layer (B) containing the ultraviolet absorbing compound at a wavelength of 320 nm to 390 nm is 50 to 70%, the pattern including a fine image, which is a feature of the present invention, is obtained. In particular, the effect of forming a good relief image having a large shoulder angle and a sufficient depth of the concave portion in a practical image exposure ultraviolet irradiation time is remarkable. The ultraviolet transmittance of the entire slip layer (B) is, for example, 320 n
m-390 nm light meter (MO-2 manufactured by Oak Co.)
It can be easily known by a commonly known measuring method.

The above-mentioned ultraviolet absorbing compound is, for example, an azo-based oil-soluble dye, Va, manufactured by Orient Chemical Co., Ltd.
liosol Yellow MYE, Val made by the company
ifast Yellow 4120, 4126,
AizenSpiron Yellow manufactured by Hodogaya Chemical Co., Ltd.
w GRH, Diaresin Yel manufactured by Mitsubishi Chemical Corporation
low A and UV absorber (manufactured by Nippon Ciba Geigy)
Tinuvin 1130).

The content of these compounds depends on the ultraviolet absorbance of each compound and the polymer constituting the slip layer (B), the thickness of the slip layer (B), and the like. The layer (A) is appropriately adjusted within a range in which a sufficient amount of ultraviolet rays for exposure and curing can be irradiated to the layer (A). Generally, it is 0.1 to 50%, preferably 0.1 to 30%, based on the total weight of the slip layer (B). The polymer forming the slip layer (B) has a necessary property as a general slip layer for a flexographic photosensitive resin composition, and is, for example, polyamide, alkyl cellulose, hydroxyalkyl cellulose, nitrocellulose, cellulose. A single polymer or two kinds selected from the group consisting of ester, a copolymer of a monovinyl-substituted aromatic hydrocarbon and a conjugated diene, and a hydrogenated reaction product of a copolymer of a monovinyl-substituted aromatic hydrocarbon and a conjugated diene; Combinations of the above polymers can be mentioned.

As a method of forming the slip layer (B), a polymer as a slip layer raw material and a predetermined ultraviolet ray absorbing compound are dissolved or dispersed in a solvent or the like, and coated on a film as a protective layer of a plate material. It can be obtained by drying. At this time, in order to secure necessary characteristics of the slip layer (B),
A release agent, a plasticizer, an adhesion adjuster, and the like can be appropriately added. As a protective film, usually, dimensional stability,
A polyester film having a thickness of 50 to 200 μm is used from the viewpoint of heat resistance and mechanical strength.

The relief image obtained by selectively exposing the photosensitive resin layer (A) has a characteristic generally required as a flexographic printing plate, that is, a relief image formed on a paper or film to be printed. There is no particular limitation as long as it exhibits good printing performance. Examples of the binder polymer that forms the photosensitive resin layer (A) having such properties include a styrene-butadiene-styrene block copolymer and a monovinyl-substituted aromatic represented by a styrene-isoprene-styrene block copolymer. And a thermoplastic elastomer comprising a group hydrocarbon and a conjugated diene.
In order for the mechanical properties of the finally obtained flexographic printing plate to be at a practical level, these binder polymers are usually 40 to 90% by weight based on the entire photosensitive resin layer.
Occupy. In particular, liquid rubber as a plasticizer elastomer, such as LPB manufactured by Nippon Petrochemical Co., Ltd., NISS manufactured by Nippon Soda Co., Ltd.
Examples thereof include OPB, Polyoil manufactured by Huls, etc., and preferably have a molecular weight of 500 to 5,000 and contain 5 to 40% by weight based on the entire photosensitive resin layer.

The photosensitive resin layer (A) also contains an ethylenically unsaturated compound that can be polymerized by ultraviolet rays, such as an acrylate compound, a methacrylate compound, a maleimide derivative, and a fumaric acid ester. In particular, a compound containing one or more acrylate groups per 200 molecular weight of the compound and containing two or more acrylate groups in one molecule is more preferable. Such compounds include, for example, hexanediol diacrylate,
Examples thereof include nonanediol diacrylate and long-chain aliphatic diacrylate, and a mixture of two or more of these diacrylate compounds can also be used. Further, another ethylenically unsaturated compound can be used if necessary. By including these diacrylate compounds in the photosensitive resin, it is possible to form a relief image with a smaller amount of irradiation in the step of curing the photosensitive resin layer with ultraviolet rays, thereby improving productivity.

The photosensitive resin layer (A) may further contain a known radical polymerization initiator such as an aromatic ketone or benzoin ether in an amount of 3 to 20% by weight based on the total weight of the photosensitive resin layer. For example, benzophenone, Michler's ketone, benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, α-methylol benzoin methyl ether, α-
Examples thereof include methoxybenzoin methyl ether and 2,2 diethoxyphenyl acetophenone, and these compounds can be used alone or in combination of two or more.

Finally, additives such as a thermal polymerization inhibitor and a colorant can be contained according to the characteristics required for the photosensitive resin layer. The photosensitive resin layer (A) can be prepared by various methods. For example, the above-described components can be melt-kneaded by a kneader roll mill having a heating device or a screw extruder, and can be formed into a plate having a desired thickness by a T-die, a press forming machine, or the like. Alternatively, a solvent may be used, for example, dissolved and mixed in a solvent such as chloroform, tetrachloroethylene, methyl ethyl ketone, and toluene, cast into a mold, and evaporated to form a plate.

As the support layer located below the layer (A), a dimensionally stable polyester film having a thickness in the range of 75 to 300 μm can be used. In some cases, the photosensitive resin layer and the support layer are firmly connected. An adhesive layer may be provided on the support layer in order to adhere to the support. In order to form a multilayer photosensitive resin structure in which a support layer, an adhesive layer, a photosensitive resin layer, a slip layer, and a protective film are laminated in this order, a protective film coated with a slip layer, and an adhesive layer It can be obtained by laminating and contacting a photosensitive resin layer between the applied support layers.

Examples of the ultraviolet light source for exposing and curing the photosensitive resin layer include a high-pressure mercury lamp, an ultraviolet fluorescent lamp, a carbon arc lamp, a xenon lamp, and sunlight. A desired relief layer can be obtained by exposing the photosensitive resin layer to ultraviolet rays through a negative film. In order to adjust the height of the relief image, the entire surface is irradiated with ultraviolet rays from the support layer side. . Either the relief forming exposure or the exposure from the support layer side may be performed first, and may be performed simultaneously. However, it is preferable to perform the exposure from the support side first from the viewpoint of image reproducibility.

After exposure of the photosensitive resin layer, the developer used to wash out the unexposed portions includes, for example, a chlorine-based organic solvent such as tetrachloroethylene, a petroleum fraction, toluene,
Solvents such as hydrocarbons such as decalin and esters such as 3-methoxybutyl acetate and heptyl acetate and mixtures of alcohols such as propanol, butanol and pentanol can be used. Hereinafter, the present invention will be specifically described based on examples.

[0023]

Examples 1-4, Comparative Example 1 Macromelt 6900 (manufactured by Henkel) 90 as a polymer for forming a slip layer
Parts by weight and 10 parts by weight of Tuftec M1913 (manufactured by Asahi Kasei Corporation) were previously heated at 150 ° C. and 10
The mixture was kneaded at 0 rpm for 5 minutes to prepare a mixed polymer. Next, this polymer was dissolved in a mixed solvent of isopropyl alcohol / toluene = 1/1 to prepare a solution having a concentration of 15% by weight. [Example 1] Vali of a dye having absorption in the ultraviolet region
osol YellowMYE (Orient Chemical)
0.70 parts by weight based on 71 parts by weight of the polymer solution,
This was added to prepare a slip layer solution. Example 2 A slip layer solution was prepared using 0.88 parts by weight of the dye of Example 1. Example 3 A slip layer solution was prepared using 0.35 part by weight of the dye of Example 1. Example 4 A slip layer solution was prepared using 0.25 parts by weight of the dye of Example 1. [Comparative Example 1] Without adding a dye to the polymer solution,
The slip layer solution was used as it was.

Next, this solution was applied on a polyester film to be a cover sheet having a thickness of 100 μm using a blade coater so that the application amount after drying was 5 to 5.5 g / m ² , For 2 minutes to obtain a cover sheet coated with a slip layer. AFP-1500 exposure machine (Asahi Kasei Corporation lamp: Philips 60W-10R type) is used as a light source for the amount of absorption of these ultraviolet rays.
The transmittance of the slip layer from which the cover sheet was removed was measured using a light meter (MO-2 manufactured by Oak Co., Ltd.) having a detection wavelength of 320 to 390 nm. Table 1 shows the results.

Next, 70 parts of Clayton DKX-405 (styrene-butadiene-styrene block copolymer manufactured by Clayton Polymer), 23 parts of B-2000 (liquid polybutadiene manufactured by Nippon Petrochemical Co.), 1,9-nonanediol diacrylate 7 parts, 1.5 parts of 2,2-dimethoxy-2-phenylacetophenone and 0.3 part of 2,6-di-t-butyl-p-cresol were kneaded together in a heating kneader mill to prepare a photosensitive resin composition. did. This photosensitive resin composition was coated on a 125 μm polyester film support with a support layer coated with an adhesive layer, and a cover sheet coated with the slip layer prepared in Examples 1 to 4 and Comparative Example 1.
2. sandwich the coated surface on the photosensitive resin side;
Using a 0 mm spacer, a press machine was used at 130 ° C. under a hydraulic pressure of 200 kg / cm ² for 4 minutes to obtain a photosensitive resin composition for flexographic printing plates having different slip layers.

A printing plate was prepared from the photosensitive resin composition according to a normal plate making process. That is, each photosensitive resin composition was exposed on an exposure machine (AFP-1500 exposure machine manufactured by Asahi Kasei Corporation), the cover sheet was peeled off, and a line number of 133 lines / inch, a halftone dot of 1% density, 100 μm
A negative film for evaluation incorporating an image of a m-width convex line and a 500 μm-width concave line was placed, covered with a vacuum sheet, and brought into close contact with a vacuum device. UV lamp on the support layer side (60W-10R manufactured by Philips)
Ramp) to adjust the height of the relief body.
A back exposure of 0 mJ / cm ² was performed, and then a relief exposure on the image side (a lamp having the same specification as the back exposure) was performed at 8000.
Irradiation at mJ / cm ² was performed. When the intensity of the ultraviolet lamp at this time was measured with a light meter (MO-2 UV-35 filter manufactured by Oak Corporation), the lower ultraviolet lamp for back exposure was 4.0 mW / cm ² , and the upper ultraviolet lamp for relief exposure was It was 7.9 mW / cm ² .

Next, AFP-150 was prepared using tetrachloroethylene / n-butanol = 3/1 (volume ratio) as a developing solution.
A developing machine (manufactured by Asahi Kasei Corporation), affixing the support side of each photosensitive resin composition to the plate cylinder with double-sided tape, and heating at 25 ° C.
For 4 minutes. After the development, the film was dried with a dryer at 60 ° C. (AFP-1500 dryer manufactured by Asahi Kasei Corporation) for 2 hours to obtain a printing plate having a relief image for flexographic printing. The state of the formation of the halftone dots of the printing plate having different slip layers, the shoulder angle measured from the cross section of the convex line having a width of 100 μm, and the depth of the concave line having a width of 500 μm are measured with a depth microscope (Nissho Precision Optical KY-90) Then, the results shown in Table 1 were obtained. In order to obtain a relief plate having good print quality, a relief image having 133 Line / inch and a halftone dot density of 1% can be formed, and a convex shoulder angle of 100 μm width is 5 μm.
It is necessary that the depth is not less than 0 ° and the depth of the concave line of 500 μm width is not less than 100 μm.

When Valiosol YellowMYE having an absorption wavelength in the ultraviolet region is added to the slip layer, the required number of lines is 133 lines / inch, the formation of halftone dots having a concentration of 1% is ensured, and the shoulder angle of a convex line having a width of 100 μm is secured. Is large, and the depth of the concave line with a width of 500 μm is increased, forming a fine relief image necessary for printing, and having a large shoulder angle for obtaining a good printed matter and ensuring a sufficient depth of the concave portion. A printing plate compatible with the obtained relief image was obtained. Further, when printing was performed on a polypropylene film using the obtained flexographic printing plate, 133 lines / inch, 1% of halftone dots were printed, and a printed matter with a small thickness was obtained. Moreover, it has a wide allowable range of printing pressure.

[0029]

Example 5 As a polymer for forming a slip layer, 90 parts by weight of Macromelt 6900 (manufactured by Henkel) and 10 parts by weight of Tuftec M1913 (manufactured by Asahi Kasei Corporation) were previously heated in a kneader roll mill at 150 ° C. and 100 rpm. For 5 minutes, then 10 parts by weight of this polymer, Va
0.2 parts by weight of Lifest Yellow 4120 (manufactured by Orient Chemical Co., Ltd.) was dissolved in a mixed solvent of isopropyl alcohol / toluene = 1/1 to prepare a slip layer solution having a concentration of 15% by weight.

A slip layer was formed on the cover sheet in the same manner as in Example 1, and the transmittance at 320 to 390 nm of the slip layer from which the cover sheet had been removed was measured to be 63%. Further, a photosensitive resin composition for flexographic printing was formed on the photosensitive resin layer used in Example 1 by the same method, and a printing plate was prepared according to the plate making process described in Example 1. A halftone dot having a line number of 133 Line / inch and a density of 1% is formed, and the shoulder angle of a convex line having a width of 100 μm is 5
The depth of the concave line having a width of 4 ° and a width of 500 μm was 180 μm. As a result of printing on coated paper using this printing plate, as in Examples 1 to 4, a halftone dot of 133 Line / inch was printed, a printed matter with a small thickness was obtained, and a printing pressure allowable width was wide. Met.

[0031]

[Table 1]

[0032]

The resin composition for flexographic printing comprising a slip layer containing a compound having an ultraviolet absorbing region and a photosensitive resin layer has a large shoulder angle, a sufficient depth of recesses, and a fine relief image. Is formed, the obtained flexographic printing plate has a wide allowable printing pressure, and the printing quality is improved.

Claims (5)

[Claims] 1. At least (A) a photosensitive resin layer,
(B) on layer (A), at least 320 nm-42
A photosensitive resin composition for a flexographic plate, comprising: a compound having a UV absorption region in the range of 0 nm; and a slip layer comprising at least one polymer. 2. The slip layer (B) has a thickness of 320 to 390 nm.
The structure according to claim 1, wherein the transmittance at 50 is 50 to 70%. 3. The slip layer (B) is conjugated with polyamide, alkyl cellulose, hydroxyalkyl cellulose, nitrocellulose, cellulose ester, a copolymer of a monovinyl-substituted aromatic hydrocarbon and a conjugated diene, and a conjugate with a monovinyl-substituted aromatic hydrocarbon. The hydrogenation reaction product of a diene copolymer, a single polymer selected from the group consisting of, or a combination of two or more polymers.
~ 2. 4. A photosensitive resin layer (A) comprising 40 to 90 parts by weight of a thermoplastic elastomer obtained by polymerizing a monovinyl-substituted aromatic hydrocarbon and a conjugated diene, and having a molecular weight of 500 to
4. The composition according to claim 1, which is formed from a composition comprising 5 to 40 parts by weight of 5,000 liquid rubber, 3 to 20 parts by weight of an ethylenically unsaturated compound, and 0.1 to 3 parts by weight of a photopolymerization initiator. Construct. 5. The composition according to claim 4, wherein the ethylenically unsaturated compound has at least one acrylate group per 200 molecular weight, and has at least two acrylate groups in one molecule. .