JP2000155418A - Photosensitive elastomer composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a photosensitive structure for a flexographic printing plate capable of forming ultra-fine dots, having good printing quality in process printing and ensuring low tackiness of the plate surface after post-exposure and improved handleability and printing durability of the plate. SOLUTION: The photosensitive elastomer composition contains >=50 wt.% at least one thermoplastic elastomer consisting of a monovinyl substituted aromatic hydrocarbon and conjugated diene, 5-40 wt.% at least one diene type liquid rubber, 1-20 wt.% at least one ethylenically unsaturated compound and 0.1-3 wt.% at least one photopolymerization initiator as essential components. The average proportion of vinyl bond units in the conjugated diene segments of the thermoplastic elastomer is 14-20 mol%. The number average molecular weight (Mn) of the liquid rubber is 500-5,000 and the average proportion of vinyl bond units is 50-70 mol%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photosensitive elastomer composition used for a photosensitive composition for flexographic printing plates.

[0002]

2. Description of the Related Art A photosensitive composition for a flexographic printing plate comprises a support, such as a polyester film, on which a thermoplastic elastomer, at least one ethylenically unsaturated compound, and at least one initiator sensitive to ultraviolet light are provided. What consists of a photosensitive elastomer composition is common. Further, if necessary, a thin film often called a slip layer or a protective layer is provided on the photosensitive layer for the purpose of smoothing the contact with the negative film.

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 light (back exposure) through a support to provide a thin uniform cured layer, and then a negative film is formed. In general, image exposure (relief exposure) is performed on the surface of the photosensitive resin layer through the substrate, and an unexposed portion is washed away with a developing solvent to obtain a desired image, that is, a relief image, to form a printing plate.

[0004] In process printing for printing a fine photograph or the like, it is sometimes required to form very fine halftone dots or fine lines as a relief image, but plate making in such a case is not easy. For example, when making a plate with a large relief exposure amount in order to form a minute relief image, the depth of the reverse image (recess) of the thin line becomes shallow, and the printing becomes entangled with the ink and a clear print reproduction is obtained. There may not be. In addition, the reproduction of halftone dots and fine line portions becomes larger than the size of the negative film, and there is often a problem that the print reproducibility is adversely affected.

On the other hand, if the relief exposure amount is reduced to avoid such a problem, the photo-curing of the relief image becomes insufficient, and the relief image is easily chipped by the pressure of the cleaning brush in the developing process. The printing plate may not be obtained.

[0006] Most of the dried plates after development have adhesiveness remaining on the surface, but if the plate has adhesiveness, the printing plates adhere to each other, and a relief image is formed when the plate is peeled off. Damage or foreign matter adhering to the plate surface cannot be easily removed, which may adversely affect print quality. As a countermeasure, a method for removing the tackiness of the plate surface by using a so-called post-exposure treatment method of irradiating the dried plate surface with ultraviolet light having a low wavelength as described in Japanese Patent Publication No. 2-46935. There is.

However, in this method, the amount of low-wavelength ultraviolet light to be irradiated must be carefully determined. If the amount of UV radiation decreases,
If the tackiness is not sufficiently removed, and if the amount is too large, the physical properties of the plate surface are reduced, and a large number of cracks are generated on the surface during the transportation and printing of the plate, thereby deteriorating the print quality.

[0008]

SUMMARY OF THE INVENTION The present invention is capable of forming fine dots, has good print quality in process printing, and at the same time, easily removes tack on the plate surface by post-exposure treatment. An object of the present invention is to provide a photosensitive composition for a flexographic printing plate having good printing durability, which is difficult to enter.

[0009]

Means for Solving the Problems As a result of intensive studies on the above problems, the present inventors have solved the problems by using the following novel photosensitive elastomer composition for a photosensitive structure for flexographic printing plates. We have found that we can do this and completed the present invention.

That is, the present invention relates to (a) 50% by weight or more of at least one kind of thermoplastic elastomer comprising a monovinyl-substituted aromatic hydrocarbon and a conjugated diene, and (b) 5 to 40% by weight of at least one kind of diene-based liquid rubber. % And (c)
1 to 20% by weight of at least one ethylenically unsaturated compound and (d) at least one or more photopolymerization initiators 0.1
(1) the average ratio of vinyl bond units of the conjugated diene segment of the thermoplastic elastomer is 14 to 20 mol%, and (2) the number average of the liquid rubber. Molecular weight (Mn) of 5
The present invention provides a photosensitive elastomer composition characterized in that the photosensitive elastomer composition has an average molecular weight of from 50 to 70 mol% and a vinyl bonding unit of 50 to 70 mol%.

In the present invention, the thermoplastic elastomer obtained by polymerizing a monovinyl-substituted aromatic hydrocarbon monomer and a conjugated diene monomer used in an amount of 50% by weight or more is styrene, α-methyl as a monovinyl-substituted aromatic hydrocarbon monomer. Styrene, p-methylstyrene, p-methoxystyrene and the like, and conjugated diene monomers such as butadiene and isoprene are used. Representative examples are styrene-butadiene-styrene block copolymer and styrene-isoprene-styrene. And block copolymers.

When the content of the monovinyl-substituted aromatic hydrocarbon in the thermoplastic elastomer is low, a cold flow of the photosensitive elastomer composition is caused and good thickness accuracy cannot be obtained, and when the content is high, the hardness of the flexographic plate is high. Is too high to obtain good print quality.
It is preferably in the range of 4 to 40% by weight.

[0013] The vinyl bonding unit in the conjugated diene segment of the thermoplastic elastomer contributes to the improvement of the reproducibility of the relief, but also increases the tackiness of the surface of the flexographic plate. From the viewpoint of balancing these two characteristics, the average ratio of the vinyl segments needs to be 14 to 20%.

The average content of the monovinyl-substituted aromatic hydrocarbon and the conjugated diene can be determined by calculating the content of the monovinyl-substituted aromatic hydrocarbon. For example, in the case of a styrene-butadiene elastomer, it can be determined by the Hampton method using an IR spectrum.
In the case of a styrene-isoprene elastomer, H ¹ −
In the NMR spectrum, the peak area C of the signal of 6.3 to 7.3 ppm derived from hydrogen of the benzene ring and the total peak area D are determined by the following equation.

[0015]

(Equation 1)

Further, in the case of a styrene-butadiene elastomer, for example, the average ratio of vinyl bonding units in the thermoplastic elastomer can be determined from the IR spectrum of a 1% carbon disulfide solution as Anal. Chem. , 21, 923 (19
It is determined by the Hampton method described in 49). In the case of a styrene-isoprene elastomer, H ¹ -N
3. The value derived from the vinyl bond in the MR spectrum is 4.
From the peak area A of the signal around 7 ppm and the peak area B of the signal around 5.1 ppm derived from the 1,4 bond

[0017]

(Equation 2) It is calculated by the following equation. In the case where the analysis of the content measurement is performed on a photosensitive elastomer composition, it is necessary to separate only the thermoplastic elastomer in advance.

The thermoplastic elastomer used in the present invention is described, for example, in JP-A-63-27573 (US Pat. No. 47).
No. 92584) can be obtained by the method described in the official gazette. That is, the content of the monovinyl-substituted aromatic hydrocarbon can be controlled within the range of the present invention by adjusting the charged amount. Further, the adjustment of the ratio of the vinyl bond unit of the conjugated diene, in a hydrocarbon solvent, in a polymerization method using an organic lithium compound as an initiator, using a polar compound as a vinylating agent, the type of the polar compound,
It can be carried out by controlling the amount used, the polymerization temperature and the like.

The hydrocarbon solvents used in the polymerization include butane, pentane, hexane, isopentane, heptane,
Aliphatic hydrocarbons such as octane and isooctane, alicyclic hydrocarbons such as cyclopentane, methylcyclopentane, cyclohexane and methylcyclohexane, and aromatic hydrocarbons such as benzene, toluene and xylene can be used. Examples of the organic lithium compound include ethyl lithium, propyl lithium, butyl lithium, hexamethylene dilithium, and the like.

Examples of polar compounds added for adjusting the vinyl bond content include ethers such as tetrahydrofuran, diethylene glycol dimethyl ether and diethylene glycol dibutyl ether, amines such as triethylamine and tetramethylethylenediamine, thioethers, phosphines, and alkylbenzenes. Examples include sulfonates and alkoxides of potassium and sodium.

As the diene liquid rubber in the present invention, liquid polybutadiene having a number average molecular weight of 500 to 5,000, polyisoprene or the like is used in an amount of 5 to 40% by weight based on the total weight of the photosensitive composition. When the ratio of the liquid rubber is high, the elastomer composition is softened, and the dimensional stability at room temperature is applied.When the ratio is low, the plasticizing effect is not sufficient, and the flexibility of the flexographic printing plate is lacking. Need to be used.

On the other hand, if the average ratio of vinyl bonding units in the liquid rubber is too low, it is disadvantageous to reproduce a minute relief image, and if it is too high, the resin after photocuring becomes brittle and the relief tends to be chipped. , 50 to 70 mol%. As with the thermoplastic elastomer, the ratio of the vinyl bonding units is the same as in the case of the thermoplastic elastomer.
It can be determined by the ton method or the H ¹ -NMR method.

Further, the ethylenically unsaturated monomer in the present invention is not particularly restricted but includes, for example, esters of alcohols such as t-butyl alcohol and lauryl alcohol with acrylic acid and methacrylic acid, laurylmaleimide, cyclohexylmaleimide and benzylmaleimide. Maleimide derivatives, or esters of alcohol and fumaric acid such as dioctyl fumarate, and polyhydric alcohols such as hexanediol di (meth) acrylate, nonanediol di (meth) acrylate, and trimethylolpropane tri (meth) acrylate, and acrylic Acids, esters with methacrylic acid and the like can be used alone or in combination in the photosensitive elastomer composition in the range of 1 to 20% by weight.

In particular, when the ethylenically unsaturated compound contains a compound represented by the following formula (1), not only the exposure sensitivity can be increased and the relief exposure time can be shortened, but also the formability of ultrafine dots can be further improved. There is an advantage that high-quality print reproducibility can be obtained.

[0025]

Embedded image

The photoinitiator used in the present invention includes aromatic ketones such as benzophenone, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, α-methylol benzoin methyl ether, α-methoxy benzoin methyl ether, 2
-Diethoxyphenylacetophenone, 2,2-dimethoxy-2-phenylacetophenone, 2-methyl- [4
-Methylthiophenyl] -2-morpholino-1-propanone and the like can be selected from known photopolymerization initiators or used in combination in the range of 0.1 to 3.0% by weight.

Among these initiators, in particular, 2,2-dimethoxy-2-phenylacetophenone and 2-methyl-1
[4- (Methylthio) phenyl] -2-morpholinopropan-1-one or 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butanone-
When the initiator system in which No. 1 is combined is used, the cross-sectional shape of the relief becomes more vertical, and the dot gain at the time of printing can be reduced. In addition, the tackiness after post-exposure treatment is further improved, and furthermore, there is an advantage that the surface is less likely to crack and the printing durability is further improved.

In the photosensitive elastomer composition of the present invention, additives such as a thermal polymerization inhibitor, a plasticizer, and a coloring agent may be added according to the required characteristics in addition to the compounds described above. it can.

The photosensitive composition for flexographic printing plate of the present invention can be prepared by various methods. For example, the raw material of the photosensitive elastomer composition is dissolved and mixed in a suitable solvent, for example, a solvent such as chloroform, tetrachloroethylene, methyl ethyl ketone, and toluene, and the mixture is cast into a mold and the solvent is evaporated to form a plate as it is. be able to. Alternatively, the mixture may be kneaded with a kneader or a roll mill without using a solvent, and formed into a plate having a desired thickness on a support by an extruder, an injection molding machine, a press, or the like.

Since the photosensitive elastomer composition is usually tacky, it is necessary to use a resin to improve the contact with the transparent image carrier superimposed thereon during plate-making or to enable the reuse of the negative film. A thin film of polyethylene, polypropylene, polyester, polystyrene or the like is laminated on the layer surface. The film is peeled off after exposure through a negative film placed thereon.

Instead of film for a similar purpose,
Solvent-soluble thin flexible protective layer (for example,
No. 13305). Further, the flexible protective layer may be used as an ultraviolet shielding layer containing an infrared-sensitive material, 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 also removed at the same time.

When a thin flexible protective layer soluble in a solvent, for example, a layer of polyamide, partially saponified polyvinyl acetate, cellulose ester, etc., which is soluble in the washing solution, is to be provided on the surface of the photosensitive resin layer, This may be dissolved in an appropriate solvent and the solution may be directly coated on the photosensitive resin layer. Alternatively, a film such as polyester or polypropylene 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 elastomer composition by roll lamination after forming the sheet of the photosensitive resin composition, and the laminate is heated and pressed to obtain a more accurate photosensitive elastomer layer. it can.

Examples of the ultraviolet light source used for photo-curing the photosensitive elastomer layer include a high-pressure mercury lamp, an ultraviolet fluorescent lamp, a carbon arc lamp, a xenon lamp, and sunlight. A desired relief image can be obtained by exposing the photosensitive elastomer layer to ultraviolet light through a negative film.However, in order to make the relief image more stable against the pressure at the time of washing out the uncured portion, the support It is effective to perform overall exposure from the side. Either the exposure from the side of the negative film or the exposure from the side of the support may be performed first, or both may be performed at the same time. Is preferably performed first.

After an image is formed by irradiating the photosensitive resin layer with ultraviolet light through a transparent image carrier to form an image, undeveloped portions are washed out by using a developing solvent such as esters such as heptyl acetate and 3-methoxybutyl acetate. And petroleum fractions, hydrocarbons such as toluene and decalin, and chlorinated organic solvents such as tetrachloroethylene mixed with alcohols such as propanol, butanol and pentanol.

The unexposed portion is washed out by spraying from a nozzle or by brushing with a brush. The obtained printing plate is rinsed and dried, and then its surface is irradiated with light having a wavelength of 300 nm or less, and if necessary, is subjected to post-exposure treatment with light having a wavelength of more than 300 nm to finish.

[0037]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be specifically described below based on examples.

[0038]

EXAMPLES Examples 1 and 2 and Comparative Examples 1 to 3 As the thermoplastic composition elastomer, those described in Table 1 synthesized by the method described in JP-A-63-27573 were used. Unless otherwise specified,% is% by weight.

[0039]

[Table 1]

As shown in Table 2, the thermoplastic elastomers shown in Table 1 were combined so that the weight ratio became 60%, and the other composition was a liquid polybutadiene (B-B) having a number average molecular weight of 2,000 and a vinyl content of 65 mol%. 2000
29%, dioctyl phthalate 5%, N-laurylmaleimide 2%, alkanediol diacrylate (carbon number of diol component 14 to 16)
2%, 1.7% of 2,2-dimethoxy-2-phenylacetophenone and 0.3% of 2,6-di-t-butyl-p-cresol were kneaded together in a kneader to prepare a photosensitive resin composition. did.

[0041]

[Table 2]

This photosensitive resin composition was treated with 125 μm
Stell film support and 4 ~ 6μ ethyl cellulose
A 100μ polyester cover sheet having a
With a pressing machine using a 3 mm spacer.
200kg / cm under the condition of ° C ^TwoPressure for 4 minutes
A photosensitive composition for a lithographic printing plate was molded.

The cover sheet of the obtained flexographic printing plate photosensitive composition was peeled off, and a negative film was adhered onto the protective layer of ethyl cellulose on the photosensitive resin layer,
370n on AFP-1500 exposure machine (Asahi Kasei Kogyo)
Using an ultraviolet fluorescent lamp having a center wavelength at m, the entire surface is first exposed to 300 mJ / cm ² from the support side, and then 9000 mJ / cm through the transparent image carrier.
The image exposure of No. ² was performed.

At this time, the exposure intensity was set to U
Using a UV illuminometer MO-2, a UV-35 filter was used to measure the intensity of the ultraviolet light from the lower lamp, which is the side for back exposure, on the glass plate, and the intensity was 4.0 mW / cm ² .
The measured intensity of ultraviolet light from the upper lamp on the relief exposure side was 7.8 mW / cm ² . Then, AFP-15 was prepared using 3-methoxybutyl acetate as a developer.
The plate was stuck on a rotating cylinder of a No. 00 developing machine (manufactured by Asahi Kasei Kogyo Co., Ltd.) using double-sided tape, developed at a liquid temperature of 25 ° C. for 6 minutes, and dried at 60 ° C. for 1 hour.

[0045] Thereafter, to obtain a flexographic printing plate by performing exposure after 1000 mJ / cm ² using an ultraviolet fluorescent lamp entire plate surface 1200 mJ / cm ^2, followed by using a germicidal lamp having a center wavelength of 254 nm. Here, the post-exposure amount by the germicidal lamp was calculated from the illuminance measured using a UV-25 filter of an MO-2 machine.

The obtained flexographic printing plates of Examples 1 and 2 had ultrafine dots of 1% -150 lines / inch, had no sticky feeling on the plate surface, and had foreign matter adhered to the surface. But it was easy to remove them. Moreover, no cracks were observed on the surface, and good print quality was maintained even during long-time printing.

On the other hand, in Comparative Example 1, the reproducibility of the fine dots was inferior, and the reproduction of 3% -120 lines / inch was at best. In Comparative Examples 2 and 3, sticky feeling after post-exposure remained, and good printed matters could not be obtained due to foreign matters remaining on the plate surface. Also, trying to remove this sticky feeling,
When the post-exposure amount with a germicidal lamp was increased to 1500 mJ / cm ² , it was recognized that many cracks were formed on the plate surface with slight stress, although the stickiness was reduced.

Comparative Example 4 A photosensitive composition for flexographic printing plates was prepared by replacing the liquid polybutadiene B-2000 in the composition of Example 1 with polyoil 110 (manufactured by Zeon Corporation, Mn = 1600 according to catalog values, vinyl content 1 mol%). The body was molded and a flexographic printing plate was made in the same manner as in Example 1, but the reproduction was 3% -120 lines / inch.

Example 3 Combination 6 of the thermoplastic elastomer used in Example 1
0%, liquid polybutadiene having a number average molecular weight of 2,000 and a vinyl content of 65 mol% (B-2000, manufactured by Nippon Petrochemical)
30%, nonanediol diacrylate 7%, 2,2-
1.0% of dimethoxy-2-phenylacetophenone, 2
-Methyl- [4-methylthiophenyl] -2-morpholino-1-propanone 1.0% and 2,6-di-t-
A photosensitive resin composition obtained by kneading together 1.0% of butyl-p-cresol with a kneader is sandwiched between a 125 μm polyester film support and a 100 μm polyester cover sheet having a 4 to 6 μm polyamide layer. , 3m
m at a temperature of 130 ° C. with a press using a spacer of m.
A photosensitive composition for a flexographic printing plate was formed by applying a pressure of 00 kg / cm ² for 4 minutes.

This was molded in the same procedure as in Example 1 and made into a flexographic plate. As a result, it was possible to form a fine dot of 1% -150 lines / inch. Further, when the amount of post-exposure by a germicidal lamp was in the range of 1200 to 2000 mJ / cm ² , the sticky feeling was eliminated, and no crack was observed on the plate surface. When the cross section of the relief image was observed, the shoulder was almost vertical and the print quality was extremely good.

[0051]

According to the present invention, it is possible to form a fine dot.
This makes it possible to produce a flexographic printing plate which has good printing quality in process printing, and at the same time, easily removes tack on the plate surface by post-exposure treatment, and has good printing durability with less cracks on the plate surface.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) C08L 9/06 C08L 9/06 G03F 7/00 502 G03F 7/00 502 7/027 502 7/027 502 7 / 028 7/028 7/033 7/033 // (C08L 9/06 9:00) F term (reference) 2H025 AA00 AA02 AA12 AB02 AC01 AD01 BC13 BC31 BC37 BC43 BC55 BC83 BC92 BC95 CA00 CA05 CA28 CB11 CB16 CB58 2H096 AA02 BA05 BA06 HA03 4J002 AC032 AC062 AC081 EE037 EH076 EH106 EU026 EU237 EV087 FD157 GP03

Claims (3)

[Claims] (1) at least 50% by weight of at least one kind of thermoplastic elastomer composed of a monovinyl-substituted aromatic hydrocarbon and a conjugated diene; and (b) 5 to 40% by weight of at least one kind of diene-based liquid rubber. A photosensitive elastomer composition comprising, as essential components, (c) 1 to 20% by weight of at least one ethylenically unsaturated compound and (d) 0.1 to 3% by weight of at least one photopolymerization initiator. (1) The average ratio of the vinyl bond units of the conjugated diene segment of the thermoplastic elastomer is 14 to 20 mol%, (2) the number average molecular weight (Mn) of the liquid rubber is 500 to 5000, and Average ratio is 50 to 70 mol%
A photosensitive elastomer composition, characterized in that: 2. The photosensitive elastomer composition according to claim 1, wherein the ethylenically unsaturated compound comprises a compound of the formula (1). Embedded image 3. Photopolymerization initiators such as 2,2-dimethoxy-2-phenylacetophenone and 2-methyl-1 [4
-(Methylthio) phenyl] -2-morpholinopropan-1-one or 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butanone-1 The photosensitive elastomer composition according to claim 1, wherein: