JP4703381B2 - Photosensitive resin composition for flexographic printing - Google Patents

Description

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

As described in Patent Documents 1 to 3, a photosensitive resin composition for flexographic printing generally contains a thermoplastic elastomer, a photopolymerizable unsaturated monomer, and a photopolymerization initiator.
As a photosensitive constituent for a flexographic printing plate, a polyester film or the like is used as a support, and on the photosensitive resin composition, a negative film is formed on the photosensitive resin composition as necessary. For the purpose of smoothing the contact, it is common to provide a slip layer or a 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 In general, it is produced by directly exposing the surface of the photosensitive resin layer to the surface of the photosensitive resin layer (relief exposure), washing away an unexposed portion with a developing solution, and performing post-processing exposure.

If a photosensitive resin composition with a large amount of relief exposure or high photoreactivity is used during plate making, fine lines and dots are formed, but the depth of white lines becomes shallow, ink is accumulated, and non-image The problem arises that the part is printed. Conversely, when a photosensitive resin composition with little relief exposure or low photoreactivity is used, white lines are deep and a sharp relief shape can be maintained, but there is a problem that fine dots are not formed. Thus, a problem arises when the exposure latitude for the image reproducibility is narrow.
When performing printing, an ink containing an ester solvent, an aqueous medium, a reactive monomer, etc. is supplied to the surface of the convex part of the uneven resin plate of the obtained flexographic printing plate with an ink supply roll, etc. In general, flexographic printing is performed by a printing machine having a mechanism for bringing a plate into contact with a printing medium and transferring ink on the surface of the convex portion to the printing medium.

  At that time, if the printing plate has low resistance to solvent ink or UV ink, printing for a long time will increase the thickness of the printing plate or decrease the hardness, resulting in the image becoming thicker or the white lines being buried. Can cause serious defects in print quality. Moreover, when a to-be-printed body is a film, in order to improve the ink receptivity of a film as patent document 7 shows, generally a corona discharge process is performed to a film. At this time, when ozone is generated and the ozone resistance of the printing plate is low, there is a problem that cracks occur on the surface of the printing plate after printing for a long time.

In order to solve these problems, the following methods have been proposed.
For example, Patent Document 4 describes a styrene-butadiene block copolymer having a vinyl content in butadiene of 20 mol% to 40 mol% in order to improve high exposure sensitivity during plate making and chipping resistance during development of a printing plate. Polymers are illustrated.
Patent Document 5 contains 45 wt% or less of a block copolymer including at least a block having isoprene and a block having a vinyl aromatic hydrocarbon having a vinyl content of 70 mol% or less in order to improve ink resistance. A photosensitive resin composition has been proposed.
Furthermore, for example, Patent Document 6 proposes to add a known ozone-resistant wax agent or a chloroalkane-based plasticizer in order to solve cracks due to ozone resistance. It is easily removed by the components, and the long-term sustainability is not sufficient, and since it has a chlorine component, health concerns arise.

As described above, in the conventional technique, a block copolymer having a block mainly composed of at least isoprene and a block mainly composed of vinyl aromatic hydrocarbon having a side chain group content including a vinyl group and the like of 40 mol% or more, A photosensitive resin composition containing at least wt% is not known.
JP 2000-155418 A Japanese Patent No. 2772055 Japanese Patent No. 2635461 Japanese Patent No. 3144870 Japanese Patent Laid-Open No. 10-104833 Japanese Patent No. 2068900 Japanese Patent Laid-Open No. 10-73921

  The technical problems in the present invention are wide exposure latitude for image reproducibility during plate making, high resistance to flexographic printing plate solvent ink and UV ink (ink resistance), and high plate surface cracking suppression effect against ozone (ozone resistance). It aims at providing the photosensitive resin composition for flexographic printing which satisfy | fills these simultaneously.

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. A photosensitive resin composition for flexographic printing comprising at least a thermoplastic elastomer (a), a photopolymerizable unsaturated monomer (b), and a photopolymerization initiator (c), wherein the thermoplastic elastomer (a ) Comprises at least one polymer block mainly composed of vinyl aromatic hydrocarbon and at least one block copolymer mainly composed of isoprene, and the side chain group content of the polymer block mainly composed of isoprene. (V) 40 mol% or more and 80 mol% or less, and the photosensitive resin composition for flexographic printing containing 50 weight% or more of thermoplastic elastomers (a).
2. The photosensitive resin composition for flexographic printing according to 1, wherein the side chain group content (V) of the polymer block mainly composed of isoprene is 45 mol% or more and 70 mol% or less.
3. The photosensitive resin composition for flexographic printing according to 1 or 2, wherein the vinyl aromatic hydrocarbon content (A) is 10% by weight or more and 35% by weight or less.

4. In the vinyl aromatic hydrocarbon content (A) and the side chain group content (V) of the polymer block mainly composed of isoprene, the value of (A) + (V) is 55 or more and 85 or less. The photosensitive resin composition for flexographic printing according to any one of 1 to 3, wherein:
5. The photosensitive resin composition for flexographic printing according to any one of 1 to 4, wherein the thermoplastic elastomer (a) in the photosensitive resin composition is 60% by weight or more.
6. The photosensitive resin composition for flexographic printing according to any one of 1 to 5, wherein the photosensitive resin composition is dissolved in a developing solvent.
7. A photosensitive composition for a flexographic printing plate having a laminated structure comprising a support and a layer of the photosensitive resin composition according to claim 1 formed on the surface thereof.

  The photosensitive resin composition of the present invention simultaneously satisfies a wide exposure latitude with respect to image reproducibility during plate making, high ink resistance and high ozone resistance of a printing plate.

Hereinafter, the present invention will be specifically described.
The thermoplastic elastomer (a) essential for the present invention comprises at least one polymer block mainly composed of vinyl aromatic hydrocarbon and at least one polymer block mainly composed of isoprene. It is a thermoplastic block copolymer having a side chain group content (V) in the combined block of 40 mol% or more and 80 mol% or less.
The polymer block mainly composed of isoprene in the thermoplastic elastomer (a) refers to a polymer block containing isoprene in an amount of 50% by weight or more and substantially comprising isoprene as a main component.
If necessary, in order to further improve the solvent resistance, the double bond in isoprene may be hydrogenated. However, if it is too high, the image reproducibility and chipping resistance of the printing plate will be reduced. The following is preferable, and 15 mol% or less is more preferable.

The side chain group content (V) in the polymer block mainly composed of isoprene of the present application is the isoprene having a 1,2-, 3,4-structure with respect to the total amount of isoprene and its hydrogenated compound, and those Of hydrogenated product.
When the side chain group content (V) is 40 mol% or more, a wide exposure latitude for image reproducibility at the time of plate making, all of ink resistance and ozone resistance of the printing plate can be achieved. Sufficient solids retention, good chipping resistance of the printing plate, and reduction in manufacturing cost can be achieved. More preferably, they are 45 mol% or more and 70 mol% or less, More preferably, they are 45 mol% or more and 65 mol% or less.

The hydrogenation rate and side chain group content (V) can be measured using a nuclear magnetic resonance apparatus ( ¹ H-NMR). JNM-LA400 (manufactured by JEOL, trade name) was used as a measuring device, and deuterated chloroform was used as a solvent to adjust the thermoplastic elastomer (a) concentration to 50 mg / ml. The observation frequency was 400 MHz, TMS (tetramethylsilane) was used as a chemical shift reference, pulse delay 2.904 seconds, scan count 64 times, pulse width 45 °, measurement temperature 26 ° C. Measurement is performed using a non-hydrogenated thermoplastic elastomer or a pre-hydrogenated thermoplastic elastomer, and a signal area of about 4.7 ppm derived from a 1,2-, 3,4-structure vinyl bond ( (α) When the signal area around 5.1 ppm derived from the 1,4-structure is (β), the side chain group content (V) (%) is determined according to the formula of α / (α + 2β) × 100. . In the case of a hydrogenated thermoplastic elastomer, since a signal derived from the hydrogenated structure appears, the hydrogenation rate can be calculated by comparison with a spectrum before hydrogenation.

The polymer block mainly composed of vinyl aromatic hydrocarbon in the thermoplastic elastomer (a) is substantially vinyl containing a vinyl aromatic hydrocarbon homopolymer block or vinyl aromatic hydrocarbon in an amount of 50% by weight or more. The polymer block which has an aromatic hydrocarbon as a main component is shown.
The vinyl aromatic hydrocarbon in the thermoplastic elastomer (a) may be distributed uniformly or non-uniformly (for example, tapered). A plurality of uniformly distributed portions and / or non-uniformly distributed portions may coexist in each block.
Examples of the vinyl aromatic hydrocarbon include monomers such as styrene, P-methylstyrene, tertiary butylstyrene, α-methylstyrene, 1,1-diphenylethylene, vinyltoluene, and among them, styrene is preferable. These monomers may be used alone or in combination of two or more.

If the content (A) of the vinyl aromatic hydrocarbon in the thermoplastic elastomer (a) is too high, the printing plate becomes too hard or the solvent ink resistance is lowered. Since solid maintenance property of a thing falls, 10 to 35 weight% is preferable. More preferably, it is 10 to 25% by weight. The content (A) of the vinyl aromatic hydrocarbon in the thermoplastic elastomer (a) can be calculated from the absorption intensity of 262 nm using an ultraviolet spectrophotometer (Hitachi UV200).
Further, the value of (A) + (V) is preferably 55 or more and 85 or less from the viewpoint of the balance between solid maintenance of the uncured resin composition and high photosensitive speed.

  The content of the thermoplastic elastomer (a) in the photosensitive resin composition is 50% by weight or more, and the ink resistance and ozone resistance of the printing plate can be achieved for the first time. Moreover, 85% by weight or less is preferable because of the flexibility of the printing plate. The content is preferably in the range of 60% by weight to 85% by weight, and more preferably in the range of 65% by weight to 85% by weight. In addition, although content of the thermoplastic elastomer (a) in the photosensitive resin composition is prescribed | regulated by the raw material composition ratio before photosensitive resin composition manufacture, also in the photosensitive resin composition after manufacture, It can be calculated by fractionating by gel permeation chromatography (GPC). The apparatus is LC-10 (manufactured by Shimadzu Corp., trade name), the column uses two TSKgel GMHXL (4.6 mm ID × 30 cm), the oven temperature is 40 ° C., and the eluent is tetrahydrofuran (1.0 ml / 1.0 ml). min). A specific molecular weight portion in the photosensitive resin composition can be fractionated by preparing a calibration curve using a polystyrene sample having a known molecular weight. Tetrahydrofuran was used as the solvent for the polystyrene sample / photosensitive resin composition. As for the content of the thermoplastic elastomer (a) in the photosensitive resin composition after production, the portion having a number average molecular weight of 80,000 or more is fractionated and purified, and the weight of the obtained purified product is used for the exposure of the sample. It can be calculated by dividing by the total weight of the functional resin composition.

Examples of the block copolymer of the thermoplastic elastomer (a) include those of the following general formula (I).
(A-B) _n, A- (BA) _n , A- (BA) _n- B (I)
B- (AB) _n
A linear block copolymer represented by the general formula (II)
[(AB) _k ] _m -X, [(AB) _k -A] _m -X
[(BA) _k ] _m- X [(BA) _k- B] _m- X (II)
A linear block copolymer or a radial block copolymer represented by the formula (In the above formula, A represents a polymer block mainly composed of vinyl aromatic hydrocarbons. B represents a conjugated diene polymer mainly composed of isoprene. X represents, for example, silicon tetrachloride, tin tetrachloride, epoxidized soybean oil, polyhalogenated hydrocarbon compound, carboxylic acid ester compound, polyvinyl compound, bisphenol type epoxy compound, alkoxysilane compound, halogenated silane compound, ester And a residue of a coupling agent such as a compound or a residue of an initiator such as a polyfunctional organolithium compound, where n, k and m are integers of 1 or more, generally 1 to 5. is there.

Moreover, the structures represented by the above general formula may be arbitrarily combined. In the present invention, the linear block copolymer represented by the formula (I) or the formula (II) is used from the viewpoint of the performance balance of the composition obtained, the productivity and the shape stability of the obtained plate. Of the structures, a block copolymer in which m is 4 or less is preferred.
These thermoplastic elastomers (a) may be used alone or in combination of two or more.

  In the thermoplastic elastomer (a), the weight (ii) of the linear block copolymer or radial block copolymer represented by the general formula (II) and the linear chain represented by the general formula (I) In the weight (i) of the combination of block copolymers, the weight ratio of (i), that is, (i) / ((i) + (ii)) is the productivity of the thermoplastic elastomer and the shape stability of the resulting printing plate In order to maintain the properties, it is preferably in the range of 0.13 to 0.40. More preferably, it is the range of 0.15-0.30. Even more preferred is a block copolymer in which, in general formulas (I) and (II), m is 4 or less and n is 1.

If necessary, a styrene butadiene block copolymer or a styrene isoprene block copolymer other than the thermoplastic elastomer (a) may be used in combination if the amount is small.
The molecular weight of the thermoplastic elastomer (a) is not particularly limited, but a thermoplastic elastomer (a) having a good balance between moldability and the solid maintenance property of the resulting photosensitive resin composition is preferable. The range of a preferable number average molecular weight is 80,000 to 500,000.
The number average molecular weight of the present invention is measured using gel permeation chromatography (GPC) and is converted from a polystyrene preparation having a known molecular weight.

Examples of the photopolymerizable unsaturated monomer (b) include esters such as acrylic acid, methacrylic acid, fumaric acid and maleic acid, acrylamide and methacrylamide derivatives, allyl esters, styrene and derivatives thereof, and N-substituted maleimide compounds. can give.
Specific examples include diacrylates and dimethacrylates of alkanediols such as hexanediol and nonanediol, or diacrylates and dimethacrylates of ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, polyethylene glycol, butylene glycol, Methylolpropane tri (meth) acrylate, dimethyloltricyclodecane di (meth) acrylate, isobornyl (meth) acrylate, phenoxypolyethylene glycol (meth) acrylate, pentaerythritol tetra (meth) acrylate, N, N'-hexamethylenebis Acrylamide and methacrylamide, styrene, vinyl toluene, divinyl benzene, diacryl phthalate, triallyl Anurate, diethyl fumarate, dibutyl fumarate, dioctyl fumarate, distearyl fumarate, butyl octyl fumarate, diphenyl ester fumarate, dibenzyl ester fumarate, dibutyl maleate, dioctyl maleate, Examples thereof include bis (3-phenylpropyl) fumarate, dilauryl fumarate, dibehenyl fumarate, N-lauryl maleimide, and the like. These may be used alone or in combination of two or more.

If the content of the photopolymerizable unsaturated monomer (b) in the photosensitive resin composition is too low, the formation of fine dots and characters is reduced, and if it is too high, the photosensitive resin composition before exposure. Since the cold flow resistance when the is laminated is lowered and the flexibility of the printing plate is lowered, the range of 0.5 wt% to 30 wt% in the photosensitive resin composition is preferable. The range of 1 wt% to 15 wt% is more preferable.
The photopolymerization initiator (c) 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-phenylpropan-1-one, benzyldimethyl ketal, 1-hydroxycyclohexyl-phenylketone, 2-methyl-2-morpholino (4-thiomethylphenyl) propane-1- Acetophenones such as ON, 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butanone; benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin iso 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 (c) in the photosensitive resin composition is too low, the formation of fine points and characters is reduced, and if it is too high, the transmittance of active light such as ultraviolet rays is reduced. The range of 0.1 to 10% by weight in the photosensitive resin composition is preferred. A range of 0.5 wt% to 5 wt% is more preferable.
Further, various auxiliary additive components such as a plasticizer, a thermal polymerization inhibitor, an ultraviolet absorber, an antihalation agent, a light stabilizer, and an ozone degrading agent can be added as desired.
The plasticizer is a liquid that is fluid at room temperature, hydrocarbon oils such as naphthenic oil and paraffin oil, liquid polybutadiene, liquid polyisoprene, modified liquid polybutadiene, liquid acrylonitrile-butadiene copolymer, liquid Examples thereof include styrene-butadiene copolymers, polystyrene having a number average molecular weight of 2,000 or less, sebacic acid esters, phthalic acid esters, and the like. A photopolymerizable reactive group may be added to these compositions.

The flexographic printing plate comes into contact with the substrate on the printing machine, but if the printing plate is too soft, a fine printed material cannot be obtained due to deformation due to compression, and if it is too hard, a printed material having a uniform solid surface cannot be obtained. Therefore, the Shore A hardness of the printing plate having a thickness of 2.54 mm is preferably in the range of 50 ° to 68 °.
The photosensitive composition for flexographic printing plates of the present invention can be produced 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 press after kneading with a kneader, roll mill or screw extruder without using a solvent, but the present invention is not limited to these production 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 thin flexible protective layer (see, for example, 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 removed after the exposure is completed, the thin flexible protective layer is also removed at the same time.

Moreover, you may contain matting agents, such as a silica, in a flexible protective layer.
When a thin flexible protective layer is to be provided on the surface of the photosensitive resin layer, a layer such as polyamide, partially saponified polyvinyl acetate or cellulose ester is dissolved in an appropriate solvent, and the solution is directly applied to the photosensitive resin layer. The layer may be coated. 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. Image exposure (relief exposure) is performed directly on the surface of the photosensitive resin layer from above, and the unexposed part is washed away with an organic solvent for development, or it is heated at 40 ° C. to 200 ° C. and absorbed in the absorption layer. It is generally produced by removing by shearing force and performing post-processing exposure.
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.

  As the support, a known support can be used. For example, a polyester film, a polyamide sheet, a metal plate, or the like can be used. Preferably, a dimensionally stable polyester film having a thickness in the range of 75 to 300 μm is used, and examples thereof include all aromatic polyester films such as polyethylene terephthalate film, polybutylene terephthalate film, and polyethylene naphthalate film. . Further, in order to ensure the adhesive force between the support and the photosensitive resin composition, for example, a known adhesive described in JP-A Nos. 2000-155410 and 2001-264959 is used. Can be applied.

Examples of the exposure light source include a high-pressure mercury lamp, an ultraviolet fluorescent lamp, a carbon arc lamp, a xenon lamp, a zirconium lamp, and sunlight.
Development organic 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 organics such as tetrachloroethylene. What mixed alcohols, such as propanol, butanol, and pentanol, with a solvent can be mentioned.
Unexposed areas are washed out by spraying from a nozzle or brushing with a brush.
However, from the viewpoint of physical properties and abrasion resistance of the plate, it is preferable that the photosensitive resin composition is dissolved in the developing organic solvent.
After development, the plate is generally dried in an oven at about 60 ° C. for 15 to 120 minutes. 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, although an example and a comparative example explain the present invention more concretely, the present invention is not limited to these examples.

[Examples 1 and 2, Comparative Examples 1 to 4]
(Preparation of photosensitive resin composition, photosensitive composition and flexographic printing plate)
As the photosensitive resin composition, the compositions shown in Examples 1 and 2 and Comparative Examples 1 to 4 in Table 1 were mixed with a kneader at 140 ° C. for 60 minutes to obtain a photosensitive resin composition.
The obtained photosensitive resin composition was coated with a polyester film support having a thickness of 125 μm and an ultraviolet transmittance of 30% coated with an adhesive containing a thermoplastic elastomer, and a polyamide having a thickness of 4 μm and an ultraviolet transmittance of 60%. A photosensitive composition for a flexographic printing plate, sandwiched between 100 μm thick polyester cover sheets having a layer and lacking pressure of 200 kg / cm 2 for 4 minutes at 130 ° C. with a press using a 2.5 mm spacer. Was molded. The ultraviolet transmittance was measured with a UV illuminance meter MO-2 manufactured by Oak Seisakusho using a UV-35 filter.

Next, the cover sheet of the photosensitive composition for flexographic printing plates is peeled off, and a negative film is adhered onto the polyamide protective film layer on the photosensitive resin layer, and an AFP-1500 exposure machine (trade name, manufactured by Asahi Kasei Chemicals). ) Using an ultraviolet fluorescent lamp having a center wavelength of 370 nm above, the entire surface was exposed from the support side so that the thickness of the cured layer was about 1.8 mm, and subsequently, 4000, 6000, 8000, 10000, Image (relief) exposure was performed at each exposure amount of 12000, 14000, and 16000 mJ / cm ² .
The exposure intensity at this time was measured using a UV-35 filter with a UV illuminance meter MO-2 manufactured by Oak Manufacturing Co., Ltd., and the intensity measured on the glass plate for ultraviolet rays from the lower lamp, which is the back exposure side, was 10 .3 mW / cm ² , the intensity of ultraviolet rays measured 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, a sterilization lamp having a central wavelength at 254 nm was used to expose the entire plate surface to 2000 mJ / cm ² , and then an ultraviolet fluorescent lamp was used to expose 1000 mJ / cm ² 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.

(Evaluation methods)
The performance was evaluated by the following method, and the results are shown in Table 1.
(A) Exposure latitude for image reproducibility during plate making Using a negative film having a halftone dot of 133 lpi and a white line of 500 microns, a flexographic printing plate having a thickness of 2.5 mm was formed by the plate making method described above. The exposure amount that is completely formed with no halftone dot of 133 lpi 2% is defined as “formation exposure amount”, and the exposure amount 4000 mJ / cm ² higher than the formation exposure amount is “formation exposure amount + 4000 mJ”. The depth of a 500 micron white line was measured with a micron depth height measuring machine KY-90 (manufactured by Nissho Precision Optical Co., Ltd., trade name). At these exposure amounts, the exposure latitude is wider when the deep white depth is maintained.

(B) Ink resistance of printing plate The solid surface of the obtained 2.5 mm flexographic printing plate is cut into a size of 5 cm × 3 cm and left in a temperature and humidity chamber at a temperature of 23 ° C. and a humidity of 50% for one day. The initial thickness and hardness were measured.
Hardness (Shore A hardness) is measured using a JIS constant pressure loader GS-710 (manufactured by Teclock Co., Ltd., Durometer GS-719G ASTM: D2240A, JIS: K6253A, ISO: 7619A), 1 kg load for 15 seconds. Later values were measured. In order to evaluate the solvent ink resistance, a mixed solvent of 30% by weight of ethyl acetate / 70% by weight of isopropyl alcohol was used as a model composition. As a model composition of UV ink, 1,9-nonanediol diacrylate monomer was used. The film was immersed for 4 hours under conditions of a temperature of 23 ° C. and a humidity of 50%, and the subsequent thickness and hardness were measured. The difference from the initial thickness and hardness was calculated as thickness increase (mm) / hardness decrease (°).
The smaller the change, the higher the ink resistance.

(C) Ozone resistance of printing plate In order to simulate the resistance of cracks generated in the printing plate by ozone generated by corona discharge treatment during film printing, the resin plate excluding the support is pulled from the printing plate. In this state, an ozone exposure test was performed to measure and evaluate the crack generation time.
Using a polyester film that is not coated with an adhesive as the support, a photosensitive resin composition for flexographic printing having a thickness of 2.5 mm was prepared in the same manner. After making the plate and removing the support, 2 cm × 15 cm The sample was cut using an ozone weathermeter OMS-HVCR (manufactured by Suga Test Instruments Co., Ltd., product name) at a measurement temperature of 40 ° C., an ozone concentration of 75 pphm, and a sample rotation speed of 2 rpm. % (Effective stretch size 2 cm × 10 cm), and the degree of cracking due to ozone was visually observed every 30 minutes. The time when the crack was visually confirmed was determined as the crack occurrence time.

  A photosensitive resin composition for flexographic printing comprising at least a thermoplastic elastomer (a), a photopolymerizable unsaturated monomer (b), and a photopolymerization initiator (c), wherein the thermoplastic elastomer (a) is A side chain of a polymer block mainly composed of isoprene, comprising at least one polymer block mainly composed of vinyl aromatic hydrocarbon and at least one block copolymer composed of a polymer block mainly composed of isoprene. By using a photosensitive resin composition having a group content (V) of 40 mol% or more and 80 mol% or less and further containing 50% by weight or more of the thermoplastic elastomer (a), white at the time of halftone dot formation in a flexographic printing plate The depth of the cut line is deep, and even if the exposure amount is increased by 4000 mJ, the deep depth is maintained, the ink resistance is high, and the crack resistance in ozone is also high. Door can be seen.

  The present invention is suitably used in the field of flexographic printing.

Claims (7)

A photosensitive resin composition for flexographic printing comprising at least a thermoplastic elastomer (a), a photopolymerizable unsaturated monomer (b), and a photopolymerization initiator (c), wherein the thermoplastic elastomer (a) is and at least one polymer block containing a vinyl aromatic hydrocarbon at least 50% by weight, isoprene consists at least one block copolymer containing at least 50 wt%, polymers containing isoprene least 50 wt% A photosensitive resin composition for flexographic printing, wherein the side chain group content (V) of the block is 40 mol% or more and 80 mol% or less, and the thermoplastic elastomer (a) is 50 wt% or more.
However, the side chain group content (V) refers to the content of isoprene having 1, 2, and 3, 4-structures and their hydrogenated products relative to the total amount of isoprene and its hydrogenated compounds.   The photosensitive resin composition for flexographic printing according to claim 1, wherein the double bond in isoprene is not hydrogenated. 3. The photosensitive resin composition for flexographic printing according to claim 1, wherein the side chain group content (V) of the polymer block containing 50% by weight or more of isoprene is 45 mol% or more and 70 mol% or less. .
However, the side chain group content (V) refers to the content of isoprene having 1, 2, and 3, 4-structures and their hydrogenated products relative to the total amount of isoprene and its hydrogenated compounds.   The photosensitive resin composition for flexographic printing according to any one of claims 1 to 3, wherein the content (A) of the vinyl aromatic hydrocarbon is 10 wt% or more and 35 wt% or less. In the vinyl aromatic hydrocarbon content (A) and the side chain group content (V) of the polymer block containing 50% by weight or more of isoprene, the value of (A) + (V) is 55 or more and 85 or less. The photosensitive resin composition for flexographic printing according to any one of claims 1 to 4.
However, the side chain group content (V) refers to the content of isoprene having 1, 2, and 3, 4-structures and their hydrogenated products relative to the total amount of isoprene and its hydrogenated compounds.   The photosensitive resin composition for flexographic printing according to any one of claims 1 to 5, wherein the thermoplastic elastomer (a) in the photosensitive resin composition is 60% by weight or more. 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 1-6 formed on the surface.