JP2007279423A - Photosensitive resin composition for flexographic printing - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a photosensitive resin composition which satisfies minute image forming property and chipping resistance of a letter portion at the same time. <P>SOLUTION: The photosensitive resin composition for flexographic printing contains at least a thermoplastic elastomer (a) having one or more butadiene-based polymer blocks, liquid conjugated diene rubber (b), a photopolymerizable monomer (c) and a photopolymerization initiator (d), wherein the photopolymerizable monomer (c) contains at least an alkane diol dimethacrylate (c1) and an alkane diol diacrylate (c2), the amount of the c2 in the photosensitive resin composition is ≥3.1 wt.%, and the ratio between the c1 and c2 (c1/c2) is ≥0.61. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a photosensitive resin composition used for flexographic printing plates.

As described in Patent Documents 1 to 3, a general photosensitive resin composition for flexographic printing generally contains a thermoplastic elastomer, a photopolymerizable unsaturated monomer, and a photopolymerization initiator. It is.
As a structural body for flexographic printing plates, a polyester film or the like is used as a support, and on the photosensitive resin composition, a negative film is contacted on the photosensitive resin composition as necessary. For smoothing purposes, it is common to provide a slip layer or protective layer, or an ultraviolet shielding layer containing an infrared sensitive material that can be excised with an infrared laser.
In order to make a flexographic printing plate from such a photosensitive composition for a flexographic printing plate, first, the entire surface is exposed to ultraviolet rays (back exposure), a thin uniform cured layer is provided, and then through a negative film, or Image exposure (relief exposure) is performed directly on the surface of the photosensitive resin layer from above the UV shielding layer, and unexposed areas are washed away with a developing solvent, or absorbed and removed by an absorption layer after heat melting and post-process exposure. It is common to manufacture by doing.

In general printing using a flexographic printing plate, ink is supplied to the surface of a convex portion of an uneven resin plate with an ink supply roll or the like, and then the resin plate is brought into contact with the printing medium to produce a convex portion. This is done by transferring the ink on the surface of the part to the substrate.
In flexographic printing, which requires a high-definition design, it is possible to form minute images on the printing plate, and to prevent the character portion from being scratched during the wiping operation of ink adhered to the printing plate surface during printing or at the end of printing. Sex is required.
To date, various thermoplastic elastomers, plasticizers, and photopolymerizable monomers have been proposed for the photosensitive resin composition in order to improve various performances.

Examples 1 to 9 of Reference 3 include a styrene isoprene block copolymer as a thermoplastic elastomer, a hydrocarbon resin as a plasticizer, 3.7 wt% alkanediol dimethacrylate and 5.2 wt% as a photopolymerizable monomer. Alkanediol diacrylates have been proposed. In Examples 10 and 11, the thermoplastic elastomer is a styrene butadiene block copolymer, the plasticizer is a liquid polybutadiene, the photopolymerizable monomer does not contain alkanediol dimethacrylate, and 6.5 wt% alkanediol. Diacrylate has been proposed.
In Example 2 of Document 4, a thermoplastic elastomer is a styrene butadiene block copolymer, a plasticizer is a liquid polybutadiene, a photopolymerizable monomer is 3.0 wt% alkanediol dimethacrylate, and 5.0 wt% alkanediol diester. Acrylates have been proposed. The ratio (c1 / c2) of the alkanediol dimethacrylate (c1) to the alkanediol diacrylate (c2) is 0.60.

In Examples of Reference 5, a styrene butadiene block copolymer is used as a thermoplastic elastomer, a liquid polybutadiene is used as a plasticizer, and 5.0 wt% alkanediol dimethacrylate and 3.0 wt% alkanediol diacrylate are used as a photopolymerizable monomer. Has been proposed. The ratio (c1 / c2) of the alkanediol dimethacrylate (c1) to the alkanediol diacrylate (c2) is 1.67.
JP 2000-155418 A Japanese Patent Laid-Open No. 02-108632 Japanese Patent Laid-Open No. 04-342258 Japanese Patent Application No. 2005-138108 Japanese Patent Application No. 2004-327359

  The technical problem in the present invention is to provide a photosensitive resin composition that simultaneously satisfies (1) high formability of a micro image on a printing plate and (2) high anti-fogging property of a character portion of a printing plate. Objective.

As described above, the conventional technique contains a thermoplastic elastomer having at least one polymer block mainly composed of butadiene, a liquid conjugated diene rubber, 3.1 wt% or more of alkanediol diacrylate and alkanediol dimethacrylate. There is no document describing the ratio of alkanediol dimethacrylate to alkanediol diacrylate in the photosensitive resin composition for flexographic printing.
As a result of intensive studies to solve the above-mentioned problems, the present inventor has found that the problems can be solved by using the following novel photosensitive resin composition, and has reached the present invention.

That is, the present invention is as follows.
1. Contains at least a thermoplastic elastomer (a) having at least one polymer block mainly composed of butadiene, a liquid conjugated diene rubber (b), a photopolymerizable monomer (c), and a photopolymerization initiator (d). A photosensitive resin composition for flexographic printing, wherein the photopolymerizable monomer (c) contains at least alkanediol dimethacrylate (c1) and alkanediol diacrylate (c2), and c2 in the photosensitive resin composition A resin composition characterized in that the amount is 3.1 wt% or more and the ratio of c1 and c2 (c1 / c2) is 0.61 or more.
2. The amount of vinyl aromatic hydrocarbon in the thermoplastic elastomer (a) is 25 wt% or less. The resin composition as described.
3. The vinyl content in at least one kind of diene of the liquid conjugated diene rubber (b) contained in the photosensitive resin composition is 40 mol% or more. Or 2. The resin composition as described.
4. The ratio (c1 / c2) of alkanediol dimethacrylate (c1) to alkanediol diacrylate (c2) is in the range of 0.73 to 2.50. ~ 3. The resin composition in any one of.

5. The vinyl content in the diene in the total amount of the liquid conjugated diene rubber (b) contained in the photosensitive resin composition is 60 mol% or more. ~ 4. The resin composition in any one of.
6. The sum (c1 + c2) of alkanediol dimethacrylate (c1) and alkanediol diacrylate (c2) in the photosensitive resin composition is 9.0 wt% or more. ~ 5. The resin composition in any one of.
7. The Shore A hardness of a printing plate having a thickness of 2.54 mm is 50 ° or more. ~ 6. The resin composition in any one of.
8. The amount of the thermoplastic elastomer (a) in the photosensitive resin composition is 58 wt% or more. ~ 7. The resin composition in any one of.
9. The number average molecular weight of the thermoplastic elastomer (a) is 160,000 or more. ~ 8. The resin composition in any one of.

10. The vinyl content in the total amount of butadiene of the thermoplastic elastomer (a) is in the range of 5 mol% to 50 mol%. ~ 9. The resin composition in any one of.
11. The thermoplastic elastomer (a) is composed of a polymer block mainly composed of vinyl aromatic hydrocarbon and a block copolymer mainly composed of butadiene and containing alkylene. The resin composition described in 1.
12. The alkanediol dimethacrylate (c1) is 1,6-hexanediol dimethacrylate. ~ 11. The resin composition in any one of.
13. Support and formed on its surface -12. A photosensitive composition for flexographic printing plates having a laminated structure comprising a layer of the photosensitive resin composition according to any one of the above.
14. On the photosensitive resin composition layer, an ultraviolet shielding layer containing an infrared sensitive substance that can be excised with an infrared laser is provided. The photosensitive composition for flexographic printing described in 1.

  The photosensitive resin composition of the present invention simultaneously satisfies the high formability of a fine image on a printing plate and the high anti-fogging property of a character part.

Hereinafter, the present invention will be specifically described.
The flexographic printing composition is generally composed of a support layer, at least one photosensitive resin layer, a slip layer, or an ultraviolet shielding layer that can be removed with an infrared laser. The present invention relates to this photosensitive resin composition.
The thermoplastic elastomer (a) containing at least one polymer block mainly composed of butadiene, which is essential for the photosensitive resin composition of the present invention, is that at least 60 wt% of at least one polymer block contains butadiene. It is a thermoplastic elastomer.
Among these, in view of moldability and handling, a thermoplastic elastomer containing a polymer block mainly composed of butadiene and a polymer block mainly composed of vinyl aromatic hydrocarbon is preferable.

The term “mainly” in the present invention refers to 60 wt% or more in a block.
The butadiene content in the essential at least one polymer block in the thermoplastic elastomer (a) is more preferably 75 wt% or more because of the high abrasion resistance of the printing plate and the anti-fogging property of the character part. . More preferably, it is 85 wt% or more.
The amount of 1,2-butadiene (vinyl) in the total amount of butadiene in the thermoplastic elastomer containing a polymer block mainly composed of butadiene is not particularly limited. However, the fine formability of the printing plate and the character portion of the printing plate are not limited. From the viewpoint of high scratch resistance, 5 to 50 mol% is preferable. The range of 8 mol% to 50 mol% is more preferable, and 10 mol% to 40 mol% is more preferable.

For high solvent ink resistance, it is preferable to contain an alkylene unit in the polymer block mainly composed of butadiene. The content of the alkylene unit is preferably 3 wt% or more and less than 40 wt% in the polymer block mainly composed of butadiene. The range of 5 wt% to 35 wt% is more preferable, and 10 wt% to 30 wt% is more preferable.
The introduction of the alkylene unit is not particularly limited, and examples thereof include a method of polymerizing a monoolefin such as ethylene and butylene, or a method of hydrogenating a diene polymer block. From the economical point of view, hydrogenation of the butadiene block copolymer is preferred.
1,4-butadiene unit, 1,2-butadiene (diene) unit and butylene are contained in a polymer block mainly composed of butadiene because of high scratch resistance of the printing plate, high fine image formation and high ink resistance. It is preferred to contain all of the units.
The number average molecular weight of the polymer block mainly composed of butadiene in the thermoplastic elastomer (a) is 2 based on the shape maintenance property (cold flow resistance) of the photosensitive resin component and the anti-caking property of the character part of the printing plate. 10,000 to 250,000 is preferable. 30,000 to 200,000 are more preferable, and 40,000 to 150,000 are more preferable.

Examples of the vinyl aromatic hydrocarbon include monomers such as styrene, P-methylstyrene, tertiary butylstyrene, α-methylstyrene, 1,1-diphenylethylene, and among them, styrene is preferable. These monomers may be used alone or in combination of two or more.
The content of the vinyl aromatic hydrocarbon in the thermoplastic elastomer (a) containing the polymer block mainly composed of butadiene is high moldability of the photosensitive resin composition, high anti-caking property of the character part of the printing plate, and It is preferably 25 wt% or less from the viewpoint that high maintainability of the printing plate hardness can be obtained when the flexographic ink component adheres. On the other hand, 13 wt% or more is preferable from the viewpoint of the high cold flow property of the photosensitive resin component. The range of 15 wt% to 24 wt% is more preferable, and the range of 15 wt% to 23 wt% is more preferable.

The number average molecular weight of the polymer block mainly composed of vinyl aromatic hydrocarbon is preferably 100,000 or less from the viewpoint of high formability of a fine image on the printing plate, and high cold flow resistance of the photosensitive resin composition. Therefore, it is preferably at least 30,000. The range of 50,000 to 80,000 is more preferable, and the range of 50,000 to 60,000 is more preferable.
If necessary, a third component block may be contained.
The number average molecular weight of the thermoplastic elastomer (a) is preferably 160,000 or more from the viewpoint of the high scratch resistance of the character part of the printing plate. 200,000 or more is more preferable, and 230,000 or more is more preferable.

The amount of the thermoplastic elastomer (a) in the photosensitive resin composition may be 58 wt% or more from the viewpoint of the high cold flow resistance of the photosensitive resin component and the high anti-caking property of the character part of the printing plate. preferable. 63 wt% or more is more preferable, and 66 wt% or more is more preferable.
The content and ratio of butadiene, 1,2-butadiene (vinyl) and vinyl aromatic hydrocarbon can be measured using a nuclear magnetic resonance apparatus (1H-NMR). As an example of conditions, 1H-NMR measuring equipment is JNM-LA400 (manufactured by JEOL, trade name), solvent is deuterated chloroform, sample concentration is 50 mg / ml, observation frequency is 400 MHz, chemical shift standard is TMS (Tetra) Methyl silane), pulse delay 2.904 seconds, 64 scans, pulse width 45 °, and measurement temperature 26 ° C.
The molecular structure of the thermoplastic elastomer containing a polymer block mainly composed of butadiene is not particularly limited, and examples thereof include a linear structure and a branched structure.

Examples of the linear structure include those having the following general formula.
(AB) _n , A- (BA) _n , A- (BA) _n- B, B- (AB) _n
Examples of the branched structure include those having the following general formula.
[(AB) _k ] _m -X, [(AB) _k -A] _m -X
[(BA) _k ] _m -X, [(BA) _k -B] _m -X
(In the above formula, A represents a polymer block mainly composed of vinyl aromatic hydrocarbons. B represents a polymer block mainly composed of butadiene. X represents, for example, silicon tetrachloride, tin tetrachloride, epoxidized soybean oil. Residues of coupling agents such as polyhalogenated hydrocarbon compounds, carboxylic acid ester compounds, polyvinyl compounds, bisphenol type epoxy compounds, alkoxysilane compounds, halogenated silane compounds, ester compounds, or polyfunctional organolithium compounds N and k are 1 or more and m is an integer of 3 to 6. The coupling agent compound may be used alone or in a mixture of two or more. May be)

These structures may be used alone or in combination of two or more.
As a synthesis example of a thermoplastic elastomer containing a polymer block mainly composed of butadiene and a polymer block mainly composed of styrene as a vinyl aromatic hydrocarbon, polymerization of an organolithium compound is started in an inert hydrocarbon solvent. Styrene is polymerized as an agent, then butadiene is polymerized, and the block copolymer (a) is polymerized by a method in which these operations are repeated, and then a predetermined amount of a polyfunctional coupling agent is added to the polymerization system. And a coupling reaction to obtain a block copolymer composition of the block copolymer (a) and the branched block copolymer (b).

  Also, for example, in an inert hydrocarbon solvent, styrene is polymerized using an organolithium compound as a polymerization initiator, and then butadiene is polymerized to obtain a block copolymer (I), which is separately separated in an inert hydrocarbon solvent. Then, styrene is polymerized using an organolithium compound as a polymerization initiator, then butadiene is polymerized, and after adding a predetermined amount of a polyfunctional coupling agent to obtain a block copolymer (b), (a), (b) The method of mixing these two types of block copolymers is also mentioned. In this case, mixing is performed after completion of the polymerization reaction, and water, alcohol, acid, etc. are added to deactivate the active species, or after completion of the polymerization reaction (a), (b) the solution is deactivated separately. Then, after mixing, a method of obtaining the mixed solution by, for example, performing steam stripping or the like to separate the polymerization solvent, followed by drying may be mentioned. In addition, (a) and (b) a method in which a polymer obtained by individually separating and drying a polymerization solvent is blended with a roll or the like is also included.

  An antioxidant can be added to the thermoplastic elastomer containing a polymer block mainly composed of butadiene, if necessary. The antioxidant may be added by any method. For example, the antioxidant may be added to the solution after completion of the polymerization, or may be added and kneaded with, for example, a roll after drying.

  Examples of the antioxidant include 2,4-bis (n-octylthiomethyl) -O-cresol, 2,4-bis (n-dodecylthiomethyl) -O-cresol, and 2,4-bis (phenyl). Thiomethyl) -3-methyl-6-tert-butylphenol, n-octadecyl-3- (3 ′, 5′di-tert-butyl-4′-hydroxyphenyl) propionate, 2,2′-methylenebis (4-ethyl) -6-tert-butylphenol), tetrakis- [methylene-3- (3 ', 5'-di-tert-butyl-4'-hydroxyphenyl) propionate] -methane, 1,3,5-trimethyl-2,4 , 6-tris (3,5-di-tert-butyl-4-hydroxybenzyl) benzene, 2,6-di-tert-butyl-4-methylphenol, , 6-Di-tert-butyl-4-ethylphenol, 2-tert-butyl-6- (3-tert-butyl-2-hydroxy-5-methylbenzyl) -4-methylphenyl acrylate, 2,4-di -Tert-amyl-6- [1- (3,5-di-tert-amyl-2-hydroxyphenyl) ethyl] phenyl acrylate, 2- [1- (2-hydroxy-3,5-di-tert-pentyl) Phenyl) -ethyl] -4,6-di-tert-pentylphenyl acrylate, 3,9-bis [2- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) -propionyloxy]- Hindered phenol compounds such as 1,1-dimethylethyl] -2,4,8,10-tetraoxaspiro [5,5] undecane, pentaerythris -Tetrakis- (β-lauryl-thio-propionate), dilauryl-3,3′-thiodipropionate, dimyristyl-3,3′-thiodipropionate, distearyl-3,3′-thiodipropioate Sulfur compounds such as nates, phosphorus compounds such as tris (nonylphenyl) phosphite, cyclic neopentanetetraylbis (octadecyl phosphite), tris (2,4-di-tert-butylphenyl) phosphite Can be mentioned. These can be used alone or in combination of two or more.

The liquid conjugated diene rubber (b) essential for the present invention is a polymer mainly composed of diene, and has a viscosity of 2000 (Pa · s) or less at 30 ° C.
The viscosity can be measured according to JIS-K-7117.
The diene is preferably isoprene and / or butadiene from the viewpoint of availability, and butadiene is more preferable from the viewpoint of anti-caking property.
Two or more kinds of liquid conjugated diene rubbers may be used in combination. The vinyl content in the total amount of diene contained in at least one liquid conjugated diene rubber is preferably 40 mol% or more from the viewpoints of high formability of minute images and high anti-caking property. 70 mol% or more is more preferable, and 80 mol% or more is more preferable. The vinyl content in the conjugated diene rubber can be determined from the aforementioned proton NMR (nuclear magnetic resonance spectrum).

In the total amount of liquid conjugated diene rubber (b) contained in the photosensitive resin composition, the vinyl content relative to the amount of diene is the ability to form minute images, high scratch resistance of the character portion of the printing plate, or high ink resistance. Therefore, 40 mol% or more is preferable. 60 mol% or more is more preferable, and 70 mol% or more is further more preferable.
The number average molecular weight (Mn) in the conjugated diene rubber (b) is preferably low in terms of handleability and the compatibility of the photosensitive resin composition, while it is preferably high in terms of anti-scratch property. A range of 50000 is good. The range of 2000-30000 is more preferable, and the range of 3000-20000 is more preferable.
The content of the liquid conjugated diene rubber (b) is preferably 3 wt% or more in the photosensitive resin composition from the viewpoint of image reproducibility, anti-bake resistance and flexibility, and the solid state maintenance of the photosensitive constituent for printing plate In view of the properties, 40 wt% or less is preferable, a range of 5 wt% to 30 wt% is more preferable, and a range of 7 wt% to 18 wt% is more preferable.

  The essential alkanediol dimethacrylate (c1) of the present invention refers to the structure shown in Chemical Formula 1, for example, n = 6 1,6-hexanediol dimethacrylate of Chemical Formula 1, nonanediol dimethacrylate of n = 9, Examples include 2-butyl-2-ethyl-1,3-propanediol dimethacrylate. From the viewpoint of low volatility, n is preferably large, and from the viewpoint of high reactivity and flexibility, n is preferably low, and 1,6-hexanediol dimethacrylate of n = 6 is preferable.

  The essential alkanediol diacrylate (c2) of the present invention refers to the structure shown in Chemical Formula 2. Specific examples include 1,6-hexanediol acrylate with n = 6 in Chemical Formula 1, nonanediol acrylate with n = 9, 2-butyl-2-ethyl-1,3-propanediol acrylate, and the like.

In terms of odor and economy, both c1 and c2 are preferably n = 6 or 9.
The printing plate has a high anti-caking property and a high micro-image forming property because the alkanediol diacrylate (c2) is 3.1 wt% or more, and the alkanediol dimethacrylate (c1) and the alkanediol dimethacrylate (c2). This can be achieved for the first time when the ratio (c1 / c2) is 0.61 or more. c2 is more preferably 3.5 wt% or more, and further preferably 4.0 wt% or more. The ratio of c1 / c2 is more preferably in the range of 0.73 to 2.50.

The sum of the alkanediol dimethacrylate (c1) and the alkanediol diacrylate (c2) (c1 + c2) in the photosensitive resin composition is high in the formation of a micro image on the printing plate and in high scratch resistance of the character portion. On the other hand, it is preferably 20 wt% or less from the viewpoint of high flexibility of the printing plate. The range of 8.5 wt% to 15 wt% is more preferable, and the range of 9.0 wt% to 15 wt% is more preferable.
If necessary, photopolymerizable monomers other than alkanediol dimethacrylate (c1) and alkanediol diacrylate (c2) may be used in combination.

The qualitative analysis and quantitative analysis of alkanediol dimethacrylate (c1) and alkanediol diacrylate (c2) can be determined by gas chromatograph (GC) method and mass spectrometry (MS) method.
As a measurement example of the gas chromatograph (GC) method, the GC device has 6890 (manufactured by Agilent, product name), the column has DB-1 (manufactured by J & W, product name), and the column temperature is from 40 ° C to 320 ° C (increase). The temperature rate is 10 ° C./min), and the injection temperature is 320 ° C.
As an example of measurement of mass spectrometry (MS) method, MS instrument is AutomassSUN (manufactured by JEOL, trade name), ion source temperature is 240 ° C, interface temperature is 320 ° C, ionization method is electron impact ionization (EI) As a reaction gas in the chemical ionization (CI) method, isobutane is exemplified.

The photopolymerization initiator (d) in the present invention is a compound that absorbs light energy and generates radicals, and various known compounds can be used, but various organic carbonyl compounds, particularly aromatic compounds. Carbonyl compounds are preferred.
Specific examples include benzoxanthones such as benzophenone, 4,4-bis (diethylamino) benzophenone, t-butylanthraquinone, 2-ethylanthraquinone, 2,4-diethylthioxanthone, isopropylthioxanthone, and 2,4-dichlorothioxanthone; Ethoxyacetophenone, 2-hydroxy-2-methyl-1-phenylpropane-1-one, benzyldimethyl ketal, 1-hydroxycyclohexyl-phenylketone, 2-methyl-2-morpholino (4-thiomethylphenyl) propane-1 Acetophenones such as -one, 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butanone; benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin Benzoin ethers such as butyl ether; 2,4,6-trimethylbenzoyldiphenylphosphine oxide, bis (2,6-dimethoxybenzoyl) -2,4,4-trimethylpentylphosphine oxide, bis (2,4,6-trimethylbenzoyl) ) -Acylphosphine oxides such as phenylphosphine oxide; methylbenzoylformate; 1,7-bisacridinylheptane; 9-phenylacridine; These may be used alone or in combination of two or more.

If the content of the photopolymerization initiator (d) is too low, the formation of fine spots and characters will be reduced, and if it is too high, the transmittance of active light such as ultraviolet rays will be reduced, so in the photosensitive resin composition A range of 0.1 wt% to 10 wt% is preferable. The range of 0.5 wt% to 5 wt% is more preferable.
In addition to the essential components described above, various auxiliary additive components such as plasticizers, thermal polymerization inhibitors, ultraviolet absorbers, antihalation agents, light stabilizers and the like may be added to the photosensitive resin composition of the present invention. it can.
The plasticizer is a liquid that is fluid at room temperature, hydrocarbon oils such as naphthenic oil and paraffin oil, liquid acrylonitrile-butadiene copolymer, liquid styrene-butadiene copolymer, number average molecular weight 2,000. The following polystyrene, sebacic acid ester, phthalic acid ester and the like can be mentioned. A photopolymerizable reactive group may be added to these compositions.

A flexographic printing plate comes into contact with a printing medium on a printing machine during printing, but if the printing plate is too soft, a fine printed matter cannot be obtained due to deformation due to compression, and if it is too hard, a printed matter having a uniform solid surface is obtained. Since it cannot be obtained, the Shore A hardness of the printing plate having a thickness of 2.5 mm is preferably in the range of 50 ° to 68 °.
The number average molecular weight (Mn) and the weight average molecular weight (Mw) in the present application are molecular weights in terms of polystyrene measured by gel permeation chromatography (GPC).
LC-10 (manufactured by Shimadzu Corporation, trade name) is used for the apparatus, two TSKgelGMHXL (4.6 mm ID × 30 cm) are used for the column, the oven temperature is 40 ° C., and the solvent is tetrahydrofuran (1.0 ml / min). Went.

The flexographic printing plate structure of the present invention can be prepared by various methods.
For example, the raw material of the photosensitive resin composition is dissolved and mixed in a suitable solvent such as chloroform, tetrachloroethylene, methyl ethyl ketone, toluene, etc., and cast into a mold to evaporate the solvent. Can be made. Further, it can be molded to a desired thickness by a calender roll or a press after kneading with a kneader, roll mill or screw extruder without using a solvent, but the present invention is not limited to these adjustment methods. .

  Since the photosensitive resin composition usually has adhesiveness, a solvent is applied to the surface of the resin layer in order to improve the contact property with the negative film superimposed on it during plate making or to enable reuse of the negative film. A soluble thin flexible protective layer (for example, see Japanese Patent Publication No. 5-13305) may be provided. In addition, the flexible protective layer may be an ultraviolet shielding layer containing an infrared sensitive substance, and the flexible layer itself may be used as a negative by direct drawing with an infrared laser. In any case, when the unexposed portion is washed out after the exposure is completed, the thin flexible protective layer is removed at the same time.

If a solvent-soluble thin flexible protective layer such as polyamide, partially saponified polyvinyl acetate, or cellulose ester that is soluble in the washing solution is to be provided on the surface of the photosensitive resin layer, this is appropriate. The photosensitive resin layer may be directly coated by dissolving in a suitable solvent. Alternatively, a film (polyester, polypropylene, etc.) may be coated (protective film), and then the protective film may be laminated or press-bonded to the photosensitive layer to transfer the protective film.
The protective film and the support are usually adhered to the photosensitive resin composition by roll lamination after forming the sheet of the photosensitive resin composition, and a photosensitive resin layer with higher thickness accuracy can be obtained by heating and pressing after lamination.

To make a flexographic printing plate from a photosensitive composition for a flexographic printing plate, first, UV exposure is performed on the entire surface through a support (back exposure), a thin uniform cured layer is provided, and then a negative film or UV shielding layer is provided. Manufactured by performing image exposure (relief exposure) on the surface of the photosensitive resin layer directly from the top, washing away unexposed areas with a developing solvent, or after absorbing and removing with an absorbing layer after heat melting and post-processing exposure. It is common to be done.
Either the exposure from the negative film side (relief exposure) or the exposure from the support side (back exposure) may be performed first, or both may be performed simultaneously.
Examples of the exposure light source include a high-pressure mercury lamp, an ultraviolet fluorescent lamp, a carbon arc lamp, and a xenon lamp.

Developer solvents used to develop unexposed areas include esters such as heptyl acetate and 3-methoxybutyl acetate, hydrocarbons such as petroleum fractions, toluene and decalin, and chlorinated organic solvents such as tetrachloroethylene. And a mixture of alcohols such as propanol, butanol and pentanol.
The unexposed portion is washed out by spraying from a nozzle or brushing with a brush.
As post-processing exposure, a method of irradiating the surface with light having a wavelength of 300 nm or less is common. If necessary, light larger than 300 nm may be used in combination.

  Hereinafter, the present invention will be described more specifically with reference examples, examples, and comparative examples, but the present invention is not limited to these examples.

[Reference example]
(1) Thermoplastic elastomer (1-1) Synthesis of thermoplastic elastomer A 10 L stainless steel reactor equipped with a jacket and a stirrer was sufficiently purged with nitrogen, and then 7000 cc of cyclohexane, 1 g of tetrahydrofuran, N, N, N ′, N ′ -Tetramethylethylenediamine (3.5 g) and styrene (170 g) were charged, and warm water was passed through the jacket to set the contents at about 70 ° C. Thereafter, an n-butyllithium cyclohexane solution (1.15 g in pure content) was added to initiate styrene polymerization. After styrene is completely polymerized, 830 g of butadiene (1,3-butadiene) is added and polymerization is continued. After 4 minutes of complete polymerization of butadiene, 0.83 g of tetramethoxysilane is added and coupled. Reacted. A part of the obtained block copolymer solution was sampled, and then the solvent was removed by heating. The polymer had a styrene content of 17% by weight and a 1,2-vinyl bond content of the polyptadiene part of 55% by weight.
The styrene content was measured using ultraviolet spectroscopy (UV). The vinyl bond amount was measured using infrared analysis (IR) and calculated by the Hampton method.

Next, using the remaining block copolymer solution, hydrogenation was performed at a temperature of 70 ° C. using biscyclopentagenyl titanium chloride and n-butyl lithium as a hydrogenation catalyst. The hydrogenation rate was controlled by measuring the amount of hydrogen gas supplied with a flow meter and stopping the gas supply when the target hydrogenation rate was achieved. Thereafter, 10 g of water was added, and after stirring, 3.0 g of n-octadecyl-3- (3 ′, 5′di-tert-butyl-4′-hydroxyphenyl) propionate, 2,4-bis (n-octyl) 1.5 g of (thiomethyl) -O-cresol was added, and the resulting solution was subjected to steam stripping to remove the solvent and obtain a hydrous crumb. Subsequently, the sample was dehydrated and dried by a hot roll to obtain a hydrogenated thermoplastic elastomer A sample having a hydrogenation rate of 20%. The hydrogenation rate was confirmed using a nuclear magnetic resonance apparatus (NMR).
(1-2) Thermoplastic elastomer B
Styrene isoprene block copolymer D-1107 (manufactured by KRATON, trade name) was used.

(2) Preparation of photosensitive resin composition and photosensitive structure As the photosensitive resin composition, the composition shown in Table 1 was mixed at 140 ° C. for 40 minutes with a kneader to obtain a photosensitive resin composition.
The obtained photosensitive resin composition was coated with a 125 μm thick polyester film support coated with an adhesive containing a thermoplastic elastomer and UV transmittance of an ultraviolet fluorescent lamp 60W / 10R (trade name, manufactured by Philips). Is sandwiched between 100μ polyester cover sheets with a thickness of 4μ and a thickness of 4μ, and a pressure of 200 kg / cm 2 is applied for 4 minutes at 130 ° C. with a press using a 3 mm spacer. Thus, a photosensitive composition for flexographic printing plate was formed.
The UV transmittance of the polyamide layer was measured using a UV illuminometer MO-2 type machine (manufactured by Oak Seisakusho, trade name, UV-35 filter).

(3) Preparation of flexographic printing plate The cover sheet of the photosensitive composition for flexographic printing plate of Reference Example 2 is peeled off, and a negative film is adhered onto the polyamide protective film layer on the photosensitive resin layer. First, an entire surface exposure of 300 mJ / cm 2 was performed from the support side using an ultraviolet fluorescent lamp 60W / 10R (product name) manufactured by Asahi Kasei Chemicals Co., Ltd. having a central wavelength of 370 nm. Subsequently, an image (relief) exposure of 7000 mJ / cm 2 was performed through a negative film.
The exposure intensity at this time was measured on a glass plate by using a UV-35 filter with a UV illuminance meter MO-2 manufactured by Oak Seisakusho on the glass plate. The intensity was 10.3 mW / cm 2, and the intensity measured by ultraviolet rays from the upper lamp on the relief exposure side was 12.5 mW / cm 2.

  Next, using 3-methoxybutyl acetate as the developer, attach the plate to the rotating cylinder of the AFP-1500 developing machine (trade name, manufactured by Asahi Kasei Chemicals) with double-sided tape, and develop for 5 minutes at a liquid temperature of 25 ° C. And dried at 60 ° C. for 2 hours. Thereafter, as a post-processing exposure, the entire plate surface was exposed to 2000 mJ / cm 2 using a germicidal lamp having a central wavelength at 254 nm, and then exposed to 1000 mJ / cm 2 using an ultraviolet fluorescent lamp to obtain a flexographic printing plate. Here, the post-exposure amount with the germicidal lamp is calculated from the illuminance measured using the UV-25 filter of the MO-2 type machine.

(4) Evaluation Method (4-1) Formability of Micro Image (1) The 1% highlight portion of 59 lines (1 / cm) of the relief image obtained in (3) was evaluated using a microscope. If it was formed, it was good, and if it was not formed, it was a problem.
(4-2) Scratch resistance As shown in FIG. 1, a printing plate having characters with a size of 2 to 8 points is created in a pseudo manner as shown in FIG. Using a tester (made by Shinmura Printing Co., Ltd., trade name, contact body: cloth, load 1 kg), the degree of destruction of the characters when rubbed left and right 50 times was observed with a microscope. If the 4-point character was not destroyed, it was best rated as “◎”, if the 6-point character was not destroyed, it was rated as “good” next, and if the 6-point character was destroyed, it was rated as “X”.

[Examples 1 to 5 and Comparative Examples 1 to 4]
The evaluation test results of Examples 1 to 5 and Comparative Examples 1 to 4 are shown in Table 1.
In a photosensitive resin composition for flexographic printing, comprising a thermoplastic elastomer having at least one polymer block mainly composed of butadiene, a liquid conjugated diene rubber, 3.1 wt% or more of alkanediol diacrylate and alkanediol dimethacrylate It can be seen that, for the first time, when the ratio of alkanediol dimethacrylate to alkanediol diacrylate is 0.61 or more, it is possible for the first time to simultaneously achieve high formability of a fine image on a printing plate and high anti-fogging property of a character part.

It is a conceptual diagram of an anti-choke test.

Claims (14)

  Flexographic printing containing at least a thermoplastic elastomer (a) having at least one polymer block mainly composed of butadiene, a liquid conjugated diene rubber (b), a photopolymerizable monomer (c) and a photopolymerization initiator (d). Photosensitive resin composition, wherein the photopolymerizable monomer (c) contains at least alkanediol dimethacrylate (c1) and alkanediol diacrylate (c2), and the amount of c2 in the photosensitive resin composition is A resin composition characterized by being 3.1 wt% or more and a ratio of c1 and c2 (c1 / c2) of 0.61 or more. 2. The resin composition according to claim 1, wherein the amount of vinyl aromatic hydrocarbon in the thermoplastic elastomer (a) is 25 wt% or less.   3. The resin composition according to claim 1, wherein the vinyl content in at least one kind of diene of the liquid conjugated diene rubber (b) contained in the photosensitive resin composition is 40 mol% or more.   The ratio (c1 / c2) of alkanediol dimethacrylate (c1) to alkanediol diacrylate (c2) is in the range of 0.73 to 2.50. Resin composition.   5. The resin composition according to claim 1, wherein the vinyl content in the diene in the total amount of the liquid conjugated diene rubber (b) contained in the photosensitive resin composition is 40 mol% or more. object. 6. The sum (c1 + c2) of alkanediol dimethacrylate (c1) and alkanediol diacrylate (c2) in the photosensitive resin composition is 9.0 wt% or more. The resin composition as described. The resin composition according to any one of claims 1 to 6, wherein the Shore A hardness of a printing plate having a thickness of 2.54 mm is 50 ° or more.   The resin composition according to any one of claims 1 to 7, wherein the amount of the thermoplastic elastomer (a) in the photosensitive resin composition is 58 wt% or more. The resin composition according to any one of claims 1 to 8, wherein the thermoplastic elastomer (a) has a number average molecular weight of 160,000 or more.   The resin composition according to any one of claims 1 to 9, wherein the vinyl content in the total amount of butadiene in the thermoplastic elastomer (a) is in the range of 5 mol% to 50 mol%. 11. The resin composition according to claim 10, wherein the polymer block mainly comprising butadiene of the thermoplastic elastomer (a) contains an alkylene unit. The resin composition according to any one of claims 1 to 11, wherein the alkanediol dimethacrylate (c1) is 1,6-hexanediol dimethacrylate.   The photosensitive structure for flexographic printing plates which has a laminated structure which consists of a support body and the layer of the photosensitive resin composition in any one of Claims 1-12 formed on the surface.   The photosensitive composition for flexographic printing according to claim 13, further comprising an ultraviolet shielding layer that can be excised with an infrared laser and contains an infrared sensitive substance on the photosensitive resin composition layer.