JPH0128365B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a novel photosensitive resin composition for letterpress printing plates, more specifically, a photosensitive resin composition that can be developed with water when removing uncured areas after exposure, and a photosensitive resin composition using the same. This invention relates to a method of manufacturing a resin plate. There are two known photosensitive resin compositions: a solvent-developed type in which the composition is developed with an organic solvent, and a so-called water-developable type in which water or a suitable washout agent or dispersant is used in combination with the water. . Among these, in the case of the solvent development type, since organic solvents are used for development, it is necessary to take appropriate measures for the development equipment, drying equipment, and exhaust equipment from the viewpoint of pollution control, work environment, and fire prevention. Problems have been pointed out, such as the need for protective equipment such as protective gloves and masks to protect the skin from harmful organic solvents. On the other hand, the water-developable type does not use particularly harmful, toxic or flammable substances during development, so there is no need for special consideration in terms of working environment or pollution control, and special protection for workers is required. It has the advantage that no utensils are required. Therefore, the development of water-developable photosensitive resins, regardless of whether they are liquid photosensitive resins or solid photosensitive resins, is actively underway, and in some cases, this type of photosensitive resin has already been put into practical use. ing. However, with this water-developable type photosensitive resin, the cleaning ability of the developing solution is often insufficient, so the number of plates that can be developed per batch (hereinafter referred to as the number of continuous plates) is small, and the developing solution must be replaced frequently. This may be uneconomical and cause the work to be interrupted, etc.
It was unsuitable for mass plate making. Furthermore, if a prepolymer with high hydrophilicity is used, the above-mentioned problems will not occur and it can be easily developed with water. However, the cured product absorbs moisture and swells over time, and in some cases, the absorbed moisture causes the cured product to undergo hydrolysis, resulting in a decrease in mechanical strength. Furthermore, in recent years, various properties required for resin plates, such as abrasion resistance, moisture resistance, and solvent resistance, have increased, and it has become necessary to design prepolymers that meet these requirements. Although the photosensitive resin composition used has an extremely small number of printing plates,
From the beginning, the water developability was poor, such as insufficient washing, and it was difficult to reach a practical technical level with the capabilities of known developers used for water development. The present inventor has completed the present invention as a result of intensive research aimed at developing a photosensitive resin composition with greatly improved water developability. That is, the present invention is a photosensitive resin composition whose main components are a combination of a specific prepolymer having a number average molecular weight of 500 or more, an ethylenically polymerizable unsaturated monomer, and a photopolymerization initiator,
The present invention provides a photosensitive resin composition for letterpress printing plates having excellent water developability, which contains at least one surfactant in the range of 0.01 to 20 parts by weight per 100 parts by weight of the composition. be. Surfactants are used in a variety of fields; for example, in the textile industry, they are used as a dispersion stabilizer for spinning oils, dyes and pigments in dyeing and printing, and in the synthetic resin industry, they are used as emulsifiers in emulsion polymerization. In the pharmaceutical, agrochemical, drug, cosmetic, and food industries, it is used as an emulsifier and dispersion stabilizer. In the construction industry, it is used as an asphalt emulsion. In the ink industry, it is used to stabilize the dispersion of pigments and resins in inks. There are various examples in which surfactants are used as agents and in developing solutions in the field of resin plates, but even in these examples, there is no known technique for adding surfactants to photosensitive resins. On the other hand, it is known to add various additives to photosensitive resin compositions, but the purpose of this is to improve and modify the surface properties and mechanical properties of photocured products.
It is not known that a surfactant is added for the purpose of improving water developability. The surfactant used in the present invention is a compound having a hydrophilic part and a hydrophobic part in one molecule, and generally
It is classified into (i) nonionic surfactants, (ii) anionic surfactants, (iii) cationic surfactants, and (iv) amphoteric surfactants, and at least one component from these may be used. (i) to (iv) may be used alone or in an appropriate combination; however, when added to photosensitive resins that are difficult to develop with water, two or more surfactant components of the same or different types are generally used as a mixture. The effect of the present invention becomes remarkable. In this case, when (iii) is used in combination, the formation of precipitates in the photosensitive resin can be prevented by selecting in advance a system that does not easily form precipitates.
When selecting the type of surfactant to be added, it is preferable to select one from among those that have excellent compatibility with the photosensitive resin to be added. If the compatibility is poor, depending on the amount added, the surfactant may separate during storage of the photosensitive resin or may bleed after curing. One method for selecting a surfactant to be added is to conduct a water development test on the photosensitive resin composition before adding the surfactant, and select a surfactant that is effective as a developer. As the surfactants corresponding to (i) to (iv) above, the following can be exemplified. (i) Nonionic surfactant (a) R ₁ -O- (CH ₂ CH ₂ O-) _o H: n = natural number from 2 to 30, R ₁ = linear or side chain consisting of C ₅ to _{C 20} an alkyl group, an alkenyl group having (b) n = natural number of 2 to 30, R ₂ = C ₅ to C ₂₀ linear or side chain alkyl group or alkenyl group. or R ₃ = C ₅ to C ₂₀ linear or side chain alkyl group or alkenyl group. X ₁ , X ₂ = H, C ₁ to C ₁₀ alkyl group or alkenyl group,

[Formula] (Z ₁ = C ₅ to C ₁₂ alkyl group or alkenyl group) Y ₁ , Y ₂ , Y ₃ =
H, C ₁ to C ₅ alkyl group,

[Formula] l, m, n are natural numbers from 2 to 40, and 10≦l
+m+n≦100. Among these, it is generally preferable that either X ₁ or X ₂ is H.

[Formula] or

[Formula] R ₄ = C ₅ to C ₂₀ alkyl group or alkenyl group having a linear or side chain.

[Formula] or R ₅ = C ₅ to C ₂₀ straight chain or side chain alkyl group or alkenyl group. or R ₆ = C ₅ to C ₂₀ linear or side chain alkyl group or alkenyl group. (ii) Anionic surfactant

[Formula] M ₁ = Na or K, R ₇ = C ₈ to C ₂₀ linear or side chain alkyl group or alkenyl group. (b) R ₈ OSO ₃ M ₂ ; M ₂ = Na or K, R ₈ ~ C ₂₀
an alkyl group or an alkenyl group having a straight or side chain.

[Formula] M ₃ = Na or K, R ₉ = C ₈ to C ₂₀ linear or side chain alkyl group or alkenyl group.

[Formula] M ₄ =Na or K, R ₁₀ = C ₈ to C ₂₀ linear or branched alkyl group or alkenyl group.

[Formula] M ₅ = Na or K, R ₁₁ = C ₈ to C ₂₀ linear or side chain alkyl group or alkenyl group, R ₁₂ =
Methyl, aryl group. R ₁₃ = C ₈ to C ₂₀ linear or side chain alkyl group or alkenyl group; M ₆ = divalent metal such as Ca or Mg. (iii) Cationic surfactant

[Formula] R ₁₄ = C ₈ to C ₂₀ straight chain or side chain alkyl group or alkenyl group. R ₁₅ = C ₈ to C ₂₀ straight chain or side chain alkyl group or alkenyl group. R ₁₆ = C ₈ to C ₂₀ straight chain or side chain alkyl group or alkenyl group. (iv) Ampholytic surfactant (a) R ₁₇ NHCH ₂ CH ₂ COONa; R ₁₇ = C ₈ to _{C 20} alkyl group or alkenyl group having a straight chain or side chain.

[Formula] R ₁₈ = C ₈ to _{C 20} alkyl group or alkenyl group having a linear or side chain; R ₁₉ = C ₁ to _{C 5} alkyl group.

[Formula] R ₂₀ = C ₅ to C ₂₀ alkyl group having a straight chain or side chain,
alkenyl group. Among these surfactants, nonionic surfactants and anionic surfactants generally have excellent cleaning performance, and it is desirable to add at least one of them. When these surfactants are added to a photosensitive resin composition, the amount added is 0.01% relative to the composition base.
If it is less than 20% by weight, it is not substantially effective in improving water developability, and if it is more than 20% by weight, the effect of improving developability is sufficiently exhibited, but on the contrary, the mechanical strength and physical properties of the cured product may deteriorate, which is not preferable. . Addition amount is 0.01~
20% by weight is appropriate, and a range of 0.1 to 5% by weight is particularly easy to balance in terms of cleaning effect and retention of mechanical strength properties of the cured product. Among active agents other than those mentioned above, a surfactant used as a penetrating agent may be used in combination. Examples include aerosol OT type surfactants, Necal BX type surfactants, butyl oleate sulfate, and the like. Furthermore, even surfactants for other uses can be used as long as they meet the purpose of the present invention, depending on the type of photosensitive resin composition. In addition, for the purpose of further improving water developability, a known organic builder may be used, but the amount added should be determined depending on the type of surfactant used, the concentration added, and the compatibility with the photosensitive resin. good. In the present invention, the photosensitive resin composition to which a detergent surfactant is added is one that is polymerized by actinic rays, and consists of a water-insoluble rubber prepolymer having an ethylenically polymerizable unsaturated group and an ethylenically unsaturated It is a composition consisting of a monomer, a photopolymerization sensitizer, and, if necessary, a thermal polymerization inhibitor. The above water-insoluble rubber prepolymer is
Examples include unsaturated polyesters having rubber segments, unsaturated polyurethanes, and various rubber compounds having carbon-carbon double bonds. The number average molecular weight of these prepolymers is essentially 500
It is necessary that it is above. Such unsaturated polyesters include, for example, unsaturated dibasic acids such as maleic acid, fumaric acid, and itaconic acid, or 1,4-polybutadiene having anhydrous acid and a terminal hydroxyl group, hydrogenated or non-hydrogenated 1,4-polybutadiene, etc. Polyhydric alcohols and polyesters such as 2-polybutadiene, butadiene-styrene copolymer, butadiene-acrylonitrile copolymer, or a part of the above acid components are combined with succinic acid, adipic acid, phthalic acid, isophthalic acid, phthalic anhydride, trimerizate, etc. Examples include polyesters substituted with saturated polybasic acids such as acids, and polyesters modified with drying oil fatty acids or semi-drying oil fatty acids. Examples of unsaturated polyurethanes include polyols having at least two terminal hydroxyl groups, such as 1,4-polybutadiene, hydrogenated or non-hydrogenated 1,4-polybutadiene,
Through urethane groups derived from 2-pributadiene, butadiene-styrene copolymer, butadiene-acrylonitrile copolymer and polyisocyanate, such as toluylene diisocyanate, diphenylmethane-4,4'-diisocyanate, hexamethylene diisocyanate. Examples include those in which an ethylenically unsaturated group is introduced by utilizing the terminal isocyanate group or the terminal hydroxyl group of the compound connected with the compound. Furthermore, various rubber compounds having carbon-carbon double bonds include ()1,4-polybutadiene,
1,2-polybutadiene, butadiene-styrene copolymer, butadiene-acrylonitrile copolymer, EPDM, water additives of () (), isobutylene-isoprene copolymer, ethylene-propylene copolymer and as shown in () Examples include unsaturated modified rubbers in which ethylenically unsaturated groups are introduced into various rubber compounds using known techniques.
Although the compound () can be used as it is, in order to introduce the unsaturated group, it is convenient to use various rubber compounds having a terminal functional group. Also, 1,
In the case of a rubber compound having a 2-polybutadiene segment, the unsaturated group can be easily introduced by adding maleic anhydride to the compound. Among these prepolymers, when a rubber-based unsaturated polyurethane having the above-mentioned rubber segment is used as a prepolymer, it is possible to use polyurethane for its excellent mechanical properties and for applications that use alcohol-based inks and solvents, such as flexographic printing. By imparting excellent solvent resistance to the cured product and adding a surfactant, water development can be made possible. Various known compounds can be used as the ethylenically unsaturated monomer, and examples of such compounds include unsaturated carboxylic acids such as acrylic acid and methacrylic acid, or esters thereof, such as alkyl-, cyclo-, Mono- or Acrylamides, methacrylamides or derivatives thereof, such as diacrylates and methacrylates, trimethylolpropane triacrylates and methacrylates, pentaerythritate tetraacrylates and methacrylates, such as alkyl, hydroxyalkyl N-substituted or N,N'-substituted acrylamides and methacrylamides. , diacetone acrylamide and methacrylamide, N,N'-alkylene bisacrylamide and methacrylamide, allyl compounds such as allyl alcohol, allyl isocyanate,
diallyl phthalate, triallyl cyanurate, etc., maleic acid, maleic anhydride, fumaric acid or their esters, such as mono- or dimaleates and fumarates of alkyl, alkyl halides, alkoxyalkyl, other unsaturated compounds such as styrene, vinyltoluene, Examples include divinylbenzene, N-vinylcarbazole, and N-vinylpyrrolidone. In addition, some of these monomers may be substituted with azide compounds such as 4,4'-diazidostilbene, p-phenylene-bisazide, 4,4'-diazidobenzophenone, 4,4'-
Diazidophenylmethane, 4,4'-diazidochalcone, 2,6-di(4'-azidobenzal)-cyclohexanone, 4,4'-diazidostilbene-α
-carboxylic acid, 4,4'-diazidodiphenyl,
It can also be replaced with sodium 4,4'-diazidostilbene-2,2'-disulfonate. These monomers may be added in an amount not exceeding 200 parts by weight per 100 parts by weight of the prepolymer. As the photopolymerization sensitizer, various known photosensitizers can be used. Examples of such substances include benzoin, benzoin alkyl ethers such as benzoin ethyl ether, benzoin-n-propyl ether, benzoin-isopropyl ether, and benzoin isobutyl ether, dimethoxyphenylacetophenone, benzophenone, benzyl, diacetyl, and Phenyl sulfide, eosin, thionin, etc., and for the composition
It can be used in a range of 0.001 to 10% by weight. Thermal polymerization inhibitors added as necessary include:
Hydroquinone, mono-tert-butylhydroquinone, benzoquinone, 2,5-diphenyl-p-benzoquinone, picrylic acid, di-p-fluorophenylamine, p-methoxyphenone, 2,6-di-tert-butyl-p-cresol etc. can be given. It is desirable that these thermal polymerization inhibitors prevent thermal polymerization reactions (dark reactions). Therefore, it is desirable that the amount of the thermal polymerization inhibitor added is in the range of 0.005 to 5.0% by weight based on the total amount of the prepolymer and the crosslinking agent. The photosensitive resin composition of the present invention having excellent water developability can be exposed and then developed by various known methods. For example, a method in which a plate that has been exposed to image formation is mounted on a drum or flat plate with the surface to be developed facing outward, and a developer is sprayed onto the plate surface to wash out uncured areas.
A method in which a brush is immersed in a developer solution and the uncured areas are removed using the brush;) A method in which a developer is supplied to the plate surface and the uncured areas are washed away with a brush. Examples include a method in which the uncured portion is removed by forced flow, a method in which the uncured portion is washed out manually with a brush or sponge, and a method in which the uncured portion is washed out by hand with a brush or sponge, and a method in which a combination of the above is used. When developing the photosensitive resin composition of the present invention after image forming exposure, various surfactants and inorganic salts can be used as developers, but in order to further improve water developability, various surfactants and inorganic salts can be used in the resin. It is preferred to use at least one component of the added surfactant. According to the present invention, by adding an appropriate surfactant to a photosensitive resin composition that has conventionally been water-developable to some extent, the water-development time can be shortened and the number of printing plates can be greatly increased. Of course, water developability can be achieved by the above methods while imparting a high degree of excellent properties as a printing plate, without the need for complex synthesis of prepolymers or synthesis using special raw materials to improve water developability. It is possible to provide a photosensitive resin composition that can be easily prepared. The details of the present invention will be explained below with reference to Examples and Comparative Examples, but these are not intended to limit the present invention in any way. The parts listed below are parts by weight unless otherwise indicated. Reference Example 1 300 parts of water-added 1,2-polybutadiene (average molecular weight = 3000, water addition rate 95%) with terminal hydroxyl groups having an average of 1.6 hydroxyl groups per molecule and toluidine diisocyanate (hereinafter abbreviated as TDI).
2,4 bodies/2,6 bodies = 3/2) 17.4 parts were mixed,
After reacting at 60℃ for 3 hours with stirring,
- 8.6 parts of hydroxypropyl methacrylate, 0.1 part of hydroquinone and dibutyltin dilaurate
Add 0.1 part of the mixture and place on an infrared chart at 80℃.
A prepolymer of 13000 was prepared by reacting in an atmosphere of dry air until the characteristic absorption of NCO (λ = around 2260 cm ^-1 ) was almost no longer observed.
To 100 parts of this prepolymer were added 40 parts of lauryl methacrylate, 10 parts of dimethacrylate of =400 polypropylene glycol, 3 parts of benzoin amyl ether, and 0.1 part of p-methoxyphenol to obtain a photosensitive resin composition (a). . Reference example 2 Carboxyl-terminated liquid NBR (AN content 18%,
Mn=1800), add 17 parts of dicrycidyl ether of bisphenol A and 0.5 part of trimethylbenzylammonium hydroxide, and
The mixture was allowed to react for hours, and then 15.6 parts of glycidyl methacrylate was added, and the reaction was carried out at 160°C for 4 hours to obtain a prepolymer (=4200). For 100 parts of this prepolymer, 20 parts of 2-hydroxypropyl methacrylate, 10 parts of styrene, 10 parts of stearyl methacrylate, 1.5 parts of benzoin, and hydroquinone.
0.2 part was added to obtain a photosensitive resin composition (b). Reference example 3 Molar ratio of liquid 1,4-polybutadiene (=1000) fumaric acid and adipic acid with hydroxyl group terminals
100 parts of unsaturated polyester resin (acid value 25) obtained by condensation in the ratio of 0.5/0.25/0.25, 20 parts of methacrylic acid, and diethylene glycol dimethacrylate.
20 parts, 1 part of benzoin methyl ether, and 0.1 part of hydroquinone were added to obtain a photosensitive resin composition (c). Reference example 4 1,2-polybutadiene (Mn=30000; 1,
2-Structure 90%; crystallinity 20%) 80 parts for 400 parts
of maleic anhydride was added by a conventional method to obtain a polymer in which 100% equivalent of the added maleic anhydride was converted into Li salt. A ratio of 10 parts of amyl methacrylate and 2 parts of benzoin ethyl ether to 100 parts of this polymer was stirred and dissolved in 5000 parts of a tetrahydrofuran-water mixed solvent to obtain a photosensitive resin solution (d'). Example 1 To 100 parts of the photosensitive resin composition (a) obtained in Reference Example 1, 0.8 parts of polyoxyethylene glycol octylphenyl monoether, which is a nonionic surfactant, and stearyl, which is an anionic surfactant. A photosensitive resin composition (A) was obtained by adding 0.2 part of sulfate ester sodium salt. Next, a polypropylene film with a thickness of 20 μm was closely adhered to the negative film as a cover film, the composition (A) was poured onto this, a polyester film with a thickness of 100 μm was laminated thereon as a support, and image-forming exposure was performed using a chemical lamp. I went. Next, the cover film was removed, the exposed plate was fixed on a drum, and a nonionic activator was added using the same surfactant that was added to the resin.
An aqueous solution (60) prepared at a concentration of 3.5% and an anionic activator of 0.5% was used as a developer, heated to 50°C, and the drum was rotated at a discharge pressure of 1.8 Kg/cm ² and a discharge rate of 100/min. Spray development for 2 minutes while circulating the developer, then press a brush that is placed parallel to the drum and rotates in the opposite direction to the drum against the plate (length of the brush in contact with the plate is approximately 1 mm), and spray develop onto the plate surface. Brush development was performed for 7 minutes while pouring a developing solution heated to 50°C with the same composition as the one used at a rate of 1/min. A plate with a depth of 1 mm (image area ratio of approximately 40%) was obtained.
In the same way, 30 plates of A-2 size plates that had been exposed were developed continuously without changing the developer.
I obtained a well-developed version that was no different from the first version.
(The image area ratio is a number expressed by (image area/total plate area) x 100.) Example 2 A nonionic surfactant was added to 100 parts of the photosensitive resin composition (b) obtained in Reference Example 2. A photosensitive resin composition (B) was obtained by adding 1 part of nonylphenol ether of polyethylene oxide (addition number of ethylene oxide = 12) as an agent. Next, a polypropylene film with a thickness of 20 μm was closely adhered to the negative film as a cover film, the composition (B) was poured onto this film, a polyester film with a thickness of 100 μm was covered as a support, and image-forming exposure was performed using a chemical lamp. I went. Next, the cover film was peeled off, the exposed plate was fixed on a flat plate, and 0.4% of the same surfactant used for addition, an anionic surfactant, α-
Aqueous solution consisting of olefin sulfonate 0.2% 70
was used as a developer, heated to 40℃, and the discharge pressure was 1.
When development was carried out by spraying for 5 minutes while circulating the developer at a discharge rate of 20 kg/cm ² and a discharge rate of 20/min, no uncured resin adhered to the relief surface.
A plate with a relief depth of 1.5 mm was obtained which was successfully developed.
Furthermore, when 35 A-3 size plates (image area ratio approximately 50%) were developed under the same conditions using the same developer, the development was comparable to that of the first plate. Example 3 To 100 parts of the photosensitive resin composition (c) obtained in Reference Example 3, a Pluronif surfactant (n=1≒10 in formulas (i) and (d)), which is a nonionic surfactant, was added. ,
0.5 part of m=15) was added to obtain a photosensitive resin composition (C). Next, image forming exposure was carried out in the same manner as in Example 2, and development was carried out for 2 minutes in the same manner as in Example 2 using an aqueous solution consisting of 0.5% sodium carbonate and 1% surfactant added to composition (C) as a developer. However, A-
Even after reaching the 50th plate of 3 sizes (image area ratio approximately 30%), uncured resin did not adhere to the relief surface.
A plate with a relief depth of 1.0 mm was obtained without any uncured resin remaining in the non-image area. Example 4 Photosensitive resin composition (d') obtained in Reference Example 4
Per 1000 parts, 2 parts of polyoxyethylene glycol-nonylphenyl monoether (number of ethylene oxide additions = 10), which is a nonionic surfactant,
Add 0.1 part of sodium oleyl sulfate, an anionic surfactant, stir uniformly, remove water and THF, and heat mold at 100°C to obtain a solid photosensitive resin composition in the form of a sheet with a thickness of 2 mm (D). I got it. Next, a negative film was closely attached to one side of the composition (D), and image-forming exposure was performed using a chemical lamp through the film. Next, the negative film was peeled off, fixed on a flat plate, and using only 40°C water as a developer, a flat brush was brought into contact with the plate surface, and the plate with the plate fixed was immersed in the developer, alternating forward and reverse directions. When the plate was developed for 5 minutes while rotating once, a well-developed plate with a relief depth of 1.0 mm (image area ratio of about 40%) was obtained, with no uncured resin adhering to the relief surface. Comparative Example 1 Using the photosensitive resin (a) obtained in Reference Example 1 to which no surfactant was added, image formation exposure and development were performed under the same conditions as in Example 1. Uncured resin adhered to some parts of the image, making it impossible to develop it properly. Furthermore, even after preparing a new developer and performing spray development for 5 minutes and brush development for 15 minutes, the relief surface, especially the crowded letters,
A portion of the uncured resin still adhered to the image, making it impossible to develop it sufficiently. Comparative Example 2 Using the photosensitive resin (b) obtained in Reference Example 2 without adding a surfactant, image forming exposure and development were performed under the same conditions as in Example 2. Up to the 6th plate, Example 2 Similar development was achieved, but after the 7th edition, some uncured resin was observed to adhere to the relief surface, and by the 10th edition, the extent of this adhesion increased, and uneven development occurred in some places in the non-image area. . Comparative Example 3 Using the photosensitive resin (c) obtained in Reference Example 3 without adding a surfactant, image formation exposure and development were carried out under exactly the same conditions as in Example 3. Only about 15 plates could be clearly developed. After that, even if the development time was set to 10 minutes, uneven development occurred over the entire plate, and uncured resin was observed to adhere to the relief surfaces of fine letters and detailed designs, in particular.

Claims (1)

[Scope of Claims] 1. The main component is a combination of a water-insoluble rubber prepolymer having an ethylenically unsaturated group having a number average molecular weight of 500 or more, an ethylenically polymerizable unsaturated monomer, and a photopolymerization initiator. A letterpress printing plate having improved water developability, which is a photosensitive resin composition, characterized in that it contains at least one surfactant in a range of 0.01 to 20 parts by weight per 100 parts by weight of the composition. Photosensitive resin composition for use. 2. The photosensitive resin composition according to claim 1, wherein the surfactant is a nonionic surfactant or an anionic surfactant. 3 The water-insoluble rubber prepolymer is 1,4-polybutadiene, 1,2-polybutadiene, butadiene-styrene copolymer, butadiene-acrylonitrile copolymer, EPDM and hydrogenated products thereof, isobutylene-isoprene copolymer The photosensitive resin composition according to claim 1, which is a compound having an ethylenically polymerizable unsaturated group derived from at least one of , an ethylene-propylene copolymer, and a modified product thereof. 4. The photosensitive resin composition according to claim 1, wherein the water-insoluble rubber-based prepolymer is a rubber-based unsaturated polyester. 5. A photosensitive resin composition whose main components are a water-insoluble rubber prepolymer having an ethylenically unsaturated group and a number average molecular weight of 500 or more, a combination of an ethylenically polymerizable unsaturated monomer and a photopolymerization initiator. 0.01 to 20 parts by weight of at least one surfactant is added and mixed to 100 parts by weight, and this is used to form a photosensitive layer on the support, and after image forming exposure, it is added to the composition. 1. A method for producing a photosensitive resin plate for letterpress printing, which comprises developing with an aqueous developer containing at least one of the same surfactants.