JP2944164B2 - Liquid photosensitive resin composition for flexographic printing plates - Google Patents

Description

The present invention relates to a photosensitive resin composition for flexographic printing, which is in a liquid state before light irradiation. The composition of the present invention is used in a flexographic printing plate suitable for a printing plate having a large plate thickness and a large relief depth, particularly for printing on a corrugated cardboard sheet or a heavy bag.

[Conventional technology]

In flexographic printing such as cardboard printing and film printing, photosensitive resin plates have been used for a long time instead of rubber plates. And in applications where a plate with a deep relief is used, such as cardboard printing,
Excellent work environment because the uncured photosensitive resin in the non-image area that does not become relief can be reused, which has great economical advantages, sharp relief shape, and can be washed out with an aqueous cleaning solution. For this reason, liquid photosensitive resins are frequently used before photocuring.

Prior art relating to these liquid photosensitive resin compositions is disclosed, for example, in JP-B-54-41202, JP-B-55-13017, and JP-B-55-13017.
No. 55-13018, No. 55-48293, No. 52-7761, No. 52-36444, No. 55-34413, No. 53-35
Nos. 481, 59-50971 and 60-28291.

However, for a printing plate made from a liquid photosensitive resin conventionally used for the above applications, the relief is missing during printing or wiping the plate, or when cutting with a knife or the like to trim the plate, There was a problem that the plate was cracked, and improvement was desired. Incidentally, it is pointed out that in the above-mentioned known technology, the problem can be solved by improving the tensile strength and elongation and the tear strength of the cured product. It turns out that alone does not always solve the problem. That is, it has been found that even plate materials exhibiting the same level of tensile strength and elongation and tear strength physical properties may have significantly different degrees of plate chipping.

[Problems to be solved by the invention]

Under such circumstances, the present invention solves the above-mentioned problems of the prior art and demonstrates the features of the liquid photosensitive resin,
It is an object of the present invention to provide a liquid photosensitive resin composition having a practical balance of physical properties that has solved the above problems. For this purpose, as a result of diligent research, certain mechanical properties that have not been targeted so far, namely the notch crack resistance when cured, are important in addition to the tensile properties that have been conventionally taken up. I found it. And, by intensively studying a liquid photosensitive resin composition for bringing the mechanical properties to the required level revealed by the present invention, the specific composition of the present invention is required to satisfy the physical property level. Thus, the present invention has been completed.

[Means for solving the problem]

That is, the present invention has a weight average molecular weight, and segments, respectively 1.0 × 10 ³ 3 or more polyether diols and polyester diols, the molar ratio of the both diol is in the range of 1 / 2-2 / 1, and the two Prepolymer 100 whose terminal is (meth) acrylated and has a weight average molecular weight of 2.3 × 10 ^{4 to} 5.0 × 10 ⁴
Parts by weight; 20 to 60 parts by weight of an ethylene addition polymerizable monomer containing 45 to 95% by weight of a monofunctional monomer represented by the following general formula I and 5 to 15% by weight of a polyfunctional monomer represented by the following general formula II; formula _{I ... H 2 C = C (} R 1) -COO-R 2 formula _{II ... (H 2 C = C} (R 1) -COO n X [R ₁ in both formulas are H or CH _3, R ₂ Is the molecular weight of 2.0 × 10 ^{2 to} 1.0 ×
Alcohol residue of 10 ^3, X represents a polyol residue having a molecular weight 60 to 5.0 × 10 ^2. n = 2-6. However, the molecular weight is the molecular weight in the case of a compound having no molecular weight distribution,
In the case of a compound having a molecular weight distribution, it means a number average molecular weight. 0.1 to 5.0% by weight of the photopolymerization initiator with respect to the total amount of +, and 0.01 to 1.0% by weight of the thermal polymerization inhibitor with respect to the total amount of +.
% By weight of a photosensitive resin composition for flexographic printing plates, wherein the cured product of the composition has notch crack resistance of 20 seconds or more. To provide.

The weight average molecular weight or number average molecular weight in the present invention is an average molecular weight in terms of polystyrene using a GPC method, and is measured under the conditions described later.

The weight average molecular weight of the prepolymer used in the present invention is 2.
It is 3 × 10 ^{4 to} 5.0 × 10 ⁴ . If the weight-average molecular weight is less than 2.3 × 10 ⁴ , it is difficult to obtain a soft, high tensile strength and elongation plate with a shore A hardness required for corrugated cardboard printing of around 40 degrees, and a plate with excellent notch crack resistance is obtained. I can't get it. Also, if the notch cracking resistance is to be kept at a favorable level, the range of the obtained range viscosity is as low as about 100 poise because there is a limitation on the blending ratio of the ethylene addition polymerizable monomer, which is the main use of the present invention. There is also a problem that molding of a thick plate having a plate thickness of 4 to 8 mm cannot be controlled on the apparatus. On the other hand, if the weight average molecular weight exceeds 5.0 × 10 ⁴ , there is a limitation on the blending ratio of the ethylene addition polymerizable monomer, so that the range viscosity becomes too high, and it becomes difficult to handle the range during range production and plate making, and special Since humidification and handling means are required, a practical liquid photosensitive resin cannot be prepared.

In addition, from the standpoint of easy balance of various physical properties of the range, it is more preferable that the range be 2.5 × 10 ^{4 to} 4.0 × 10 ⁴ .

Known polyether diols and polyester diols used as segments of the prepolymer used in the present invention can be used. As these diols, those having a main chain composed of saturated bonds are preferable in order to obtain a flexible and tough plate.

That is, examples of such polyether diols include polyoxyethylene glycol (PEG), polyoxypropylene glycol (PPG), and polyoxyethylene glycol.
Propylene glycol random or block copolymer,
Examples thereof include polyoxytetraethylene glycol (PTMG), polyoxyethylene-tetraethylene glycol random or block copolymer, and polyoxypropylene-tetraethylene glycol random or block copolymer.

On the other hand, as the polyester diol, a polyester diol obtained by condensing a saturated dicarboxylic acid and an alkylene glycol or an oxyalkylene glycol, for example, polyethylene adipate diol, polydiethylene glycol adipate diol, polybutylene adipate diol, poly-1,6-hexane glycol adipate diol, Polyneopentyl glycol adipate diol,
And polypropylene adipate diol.
Further, for example, β-propiolactone and its substituted product, δ
-Valerolactone and a substituted product thereof, a lactone-based polyester diol obtained by ring-opening polymerization of a 5-membered ring, a 6-membered ring, a 7-membered ring or a more lactone such as ε-caprolactone and a substituted product thereof can also be used. Among lactone-based polyester diols, ε is preferred from the viewpoint of availability.
-Caprolactone polyesterdiol obtained from caprolactone is preferred.

The molecular weight of the diol used in the present invention is preferably not less than 1.0 × 10 ³ in weight average molecular weight, and is preferably 1.
5 × 10 ³ or more. When it is less than 1.0 × 10 ³ , the urethane bond concentration becomes high, and it becomes difficult to obtain a flexible plate. The upper limit is
It suffices if it is 1/2 or less of the prepolymer molecular weight.

It is important that the molecular weight is not in the number average molecular weight but in the above range defined by the weight average molecular weight. Although the reason has not been confirmed, it is considered that the notch cracking resistance is affected by the distribution of high molecular weight substances in the polymer.

The molar ratio between the polyether diol and the polyester diol is in the range of 1/2 to 2/1. When this ratio is less than 1/2, when the composition is made into a composition, the rubbery rebound resilience of the cured product is reduced, which makes the composition unsuitable especially for high-speed flexographic printing. If the ratio is more than 2/1, the notch cracking resistance, which is the object of the present invention, may be reduced, which may cause a practical problem.

Next, known diisocyanates used as chain extenders for diols are used. Specifically, the following compounds can be used, but when it is desired to avoid yellowing of the plate, it is preferable to use a non-aromatic diisocyanate.

That is, as the diisocyanate used in the present invention, for example, tolylene diisocyanate (2,4-TDI, 2,6
-TDI, 2,4-TDI / 2,6-TDI mixture), methylenebisdiisocyanate (MDI), 1,5-naphthalenediisocyanate (NDI), tolidine diisocyanate (TODI) and hydrogens thereof Addition type, hexamylene diisocyanate (HMDI), isophorone diisocyanate (IPDI), p
-Phenylene diisocyanate, transcyclohexane diisocyanate, xylene diisocyanate, trimethylhexamethylene diisocyanate (TMDI) and the like. Among these diisocyanates, TDI, MDI, HMDI and IPDI are usually preferably used from the viewpoint of availability and cost. In addition, when discoloration of the formed relief body is disliked, for example, HMDI, IPDI, hydrogenated TDI, hydrogenated
It is preferable to use MDI or the like.

Introduction of (meth) acrylic groups at both ends of the prepolymer can be easily performed by a known method. For example, a method of adding a (meth) acrylate compound having a hydroxyl group to a urethane compound at an isocyanate terminal, or a (meth) acrylate having a urethane compound at a hydroxyl group and a carboxylic acid or an acid anhydride or an acid chloride thereof or ( Examples thereof include a method of reacting (meth) acrylic acid and a method of reacting with a (meth) acrylic group-containing isocyanate compound as disclosed in JP-B-55-13017. In addition, what is necessary is just to use a well-known thing also as a (meth) acrylate compound used for these reactions.

That is, examples of (meth) acrylate compounds containing a functional group having active hydrogen such as a hydroxyl group and having an ethylene-type addition-polymerizable unsaturated group include 2-hydroxyethyl (meth) acrylate and 2-hydroxypropyl ( (Meth) acrylate, polyoxypropylene glycol mono (meth) acrylate (n300 to 1000), polyoxyethylene glycol mono (meth) acrylate (n300 to 1000) and the like.

Among the ethylene addition polymerizable monomers used in the present invention, the monomers specified by the following general formulas I and II are:
In the present invention, it is an essential component for satisfying both the improvement of notch crack resistance and the soft property.

General formula _{I ... H 2 C = C (} R 1) -COO-R 2 formula _{II ... (H 2 C = C} (R 1) -COO n X [R ₁ in both formulas are H or CH _3, R ₂ is a molecular weight of 2.0 × 10 ^{2 to} 1.0 ×
Alcohol residue of 10 ^3, X represents a polyol residue having a molecular weight 60 to 5.0 × 10 ^2. n = 2-6. However, the molecular weight is the molecular weight in the case of a compound having no molecular weight distribution,
In the case of a compound having a molecular weight distribution, it means a number average molecular weight. Specific examples of R _{2 represented by} the general formula I include PEG, PPG, PTMG
Monooxy (residues having 10 carbon atoms), such as polyoxyalkylene glycols, in which the hydroxyl groups at one end have been removed.
) Or monoallyl (within 10 carbon atoms) ether and a residue obtained by removing a hydroxyl group from a long-chain alcohol such as stearyl.
Among these, it is preferable that the former two monomers having R ₂ are mixed in at least 1/2 of the total amount of the monomers of the general formula I from the viewpoint of improving notch cracking resistance. When the molecular weight of R ₂ is lower than the lower limit, it is difficult to impart flexibility to the plate, which is preferable.
On the other hand, if it exceeds the above upper limit, the viscosity of the composition becomes undesirably high.

Specific examples of X of the polyfunctional monomer represented by the general formula II include a residue obtained by removing two or more hydroxyl groups from the following polyol. 1,3-butylene glycol, 1,4-
Butylene glycol, 1,6-hexanediol, neopentyl glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyoxyethylene glycol having a number average molecular weight of 5.0 × 10 ² or less, polyoxypropylene glycol, 2,2-bis [4 -(Hydroxyethoxy) phenyl] propane, 2,2-bis [4
-(Hydroxydiethoxy) phenyl] propane, 2,2-bis [4- (hydroxypolyethoxy) phenyl] propane having a number average molecular weight of 5.0 × 10 ² or less, trimethylolpropane, tetramethylol, pentaerythritol, bisphenol A With ethylene glycol or propylene glycol (number average molecular weight 5.0 × 10 ² or less), tris (hydroxyethyl) isocyanurate,
And neopentyl glycol-modified trimethylolpropane. If the molecular weight of X is less than the above lower limit, the notch crack resistance tends to decrease rather, which is not preferable. If the upper limit is exceeded, the notch cracking resistance starts to decrease, and it is difficult to maintain a high tensile strength of the plate, which is not preferable. Among them, it is more preferable to use a polyfunctional monomer having n of about 3 to 4 alone or in combination with a monomer having n of 2 from the viewpoint of improving notch cracking resistance.

As the other ethylene addition polymerizable monomer used together with the general formulas I and II, various known monomers can be used. Examples of these are known literature described in the section of the prior art, for example, Shinzo Yamashita et al., "Crosslinking Agent Handbook" Taiseisha (1981), Minoru Imoto et al., "UV / EB curing technology"
It is described in such books as the General Technology Center (1982) and Kiyomi Shimogami's "Ultraviolet Curing System" General Technology Center (1989).

For example, unsaturated carboxylic acids such as acrylic acid and methacrylic acid or esters thereof, in other words, alkyl-, cycloalkyl-, halogenated alkyl-, alkoxyalkyl-, hydroxyalkyl-, dialkylaminoalkyl-, tetrahydrofurfuryl-, allyl Acrylamide, methacrylic acid, such as-, glycidyl-, benzyl-, phenoxy-acrylate and methacrylate, alkylene glycol, polyoxyalkylene glycol mono- or diacrylate and methacrylate, trimethylolpropane triacrylate and methacrylate, pentaerythritol tetraacrylate and methacrylate Amides or derivatives thereof, for example, acrylamide and methacrylyl N-substituted or N, N'-substituted with an alkyl group or a hydroxyalkyl group , Diacetone acrylamide and methacrylamide, N, N'-alkylenebisacrylamide and methacrylamide, allyl compounds such as allyl alcohol, allyl isocyanate, diallyl phthalate, triallyl cyanurate and the like, maleic acid, maleic anhydride, fumaric acid Alternatively, other unsaturated compounds such as mono- or dimalate and fumarate of alkyl, alkyl halide, alkoxyalkyl and the like, for example, styrene, vinyltoluene, divinylbenzene, N-vinylcarbazole, N-vinylpyrrolidone and the like are used.

In addition, when curing shrinkage of the relief body is a problem,
As the ethylene type addition polymerizable monomer, for example, isobornyl acrylate or methacrylate, norbornyl acrylate or methacrylate, dicyclopentenoxyethyl acrylate or methacrylate, dicyclopentenoxypropyl acrylate or methacrylate,
Dicyclopentenyl cinnamate, dicyclopentenyloxycinnamate, such as acrylate or methacrylate of diethylene glycol dicyclopentenyl monoether, acrylate or methacrylate of polyoxyethylene or polypropylene glycol dicyclopentenyl monoether Etc. can be exemplified.

For 100 parts by weight of prepolymer, these ethylene addition polymerizable monomers must be used in the range of 20 to 60 parts by weight. If the amount is less than 20 parts by weight, the viscosity of the composition becomes extremely high, and it becomes difficult to obtain the strength physical properties. On the other hand, if it exceeds 60 parts by weight, the rubber elasticity becomes poor, and the notch cracking resistance may be further reduced.

In selecting the ethylene addition-polymerizable monomer, it is necessary that the cured product be substantially transparent at a temperature of 10 ° C. or higher when photocured. This is because if the cured product becomes cloudy, the notch crack resistance may rapidly decrease. The degree of transparency is 1 m in the wavelength region where the cured product does not have visible light absorption due to additives such as colorants and sensitizers.
It suffices that the transmittance of the sample piece of m is 80% or more.

From the viewpoint of the flexibility, rubber elasticity and notch cracking resistance of the cured product, the former is 45 to 95% by weight, and the latter is 5 to 15% by weight. If any of them is off, the object of the present invention cannot be satisfied. In particular, the polyfunctional monomer of the general formula II must not exceed the upper limit. Incidentally, a particularly preferred use range of the monomer is,
5 to 10% by weight.

As the photopolymerization initiator used in the present invention, any one of conventionally known compounds can be selected and used. Examples of such a photopolymerization initiator include benzoin, benzoin ethyl ether, benzoin-n-propyl ether, benzoin-isopropyl ether,
Benzoin alkyl ethers such as benzoin isobutyl-ether, 2,2-dimethoxy-2-phenylacetophenone, benzophenone, benzyl, diacetyl,
Examples include diphenyl sulfide, eosin, thionine, 9,10-anthraquinone, and 2-ethyl-9,10-anthraquinone.

These photopolymerization initiators may be used alone or in combination of two or more. Its content is 0.1 to the total amount of the prepolymer and the monomer.
It is in the range of 5% by weight.

Next, the thermal polymerization inhibitor used in the present invention is not particularly limited, and may be arbitrarily selected from those conventionally used in liquid photosensitive resin compositions.
Such include, for example, hydroquinone, mono-tert-butylhydroquinone, benzoquinone, 2,5-diphenyl-p-benzoquinone, picric acid, di-p-fluorophenylamine, di-p-methoxyphenol, 2,6-
Ditertiary butyl-p-cresol and the like can be mentioned. These thermal polymerization inhibitors are for preventing a thermal polymerization reaction (dark reaction), and therefore, the content of the thermal polymerization inhibitor is 0.01 to 1.1 with respect to the total amount of the prepolymer and the monomer.
It is selected in the range of 0% by weight.

The conditions for measuring the average molecular weight in terms of polystyrene by the GPC method used for defining the molecular weight in the present invention are as follows.

Column: The following polyethylene gel column was used. Two TSK GEL GMHXL (7.8mm x 300mm). Solvent: TH
F (no small addition of water). Flow rate: 1.0ml / min
(Perform correction). Sample concentration: 0.5% or less. Calibration curve preparation: The concentration is about 1/2 of the sample concentration. Significant digits: Displayed in two digits. GPC device: High-speed GPC HLC-8020 (manufactured by Tosoh Corporation). Detector: RI, UV (254 nm). Standard polystyrene: The molecular weight range is 5.00 × 10 ^{2 to} 1.26 × 10 ⁶ .

The method for measuring notch crack resistance, which is an essential requirement for achieving the object of the present invention, is as follows.

A photosensitive resin to be subjected to a test is extended on a polyester base support having a thickness of 0.1 mm in the configuration shown in FIG. 1 and the thickness including the support is set to 7 mm.

Irradiation is sequentially performed from both sides through a glass upper and lower glass to a predetermined exposure amount by a chemical lamp. From the support side, the light source intensity through the glass was irradiated 350 mJ / cm ² to about 1 mW / cm ^2, from the other surface, the light source intensity through the glass of about 1.5 mW / cm
² at 250 mJ / cm ² irradiation. Next, the cover film is removed, and further irradiated from the relief side with a chemical lamp of about 1200 mJ / cm ² . Light source intensity is manufactured by Oak Works, UV meter: UV-M01
(The intensity of the chemical lamp is measured by the sensor UV
−35, and a sterilization line lamp using a sensor UV-25).

The solid plate having a thickness of 7 mm thus obtained is cut into the size shown in FIG.

Knife depth 1+ along the line of dimensions shown in FIG.
/ Insert a 0.3 mm cut streak.

The scissors are held outward and bent quickly as shown in FIG. 3, and the time until the resulting crack reaches the support is measured in seconds. The measurement is repeated three times, and the average value is obtained (rounded off to the nearest whole number and displayed as an integer).

The time required for crack growth thus determined is expressed as the notch crack resistance of the sample.

〔Example〕

Hereinafter, the present invention will be specifically described with reference to Synthesis Examples, Examples, and Comparative Examples.

Synthesis Example-1 As a polyether diol, a block ether diol of PEG-PPG-PEG type (Mw <indicating a weight average molecular weight,
The same applies hereinafter> = 3.3 × 10 ³ , 1 mol of PPG / PEG molar ratio = 8/2), 1 mol of poly (propylene adipate) ester diol (Mw = 7.2 × 10 ³ ) as polyester diol and 0.5 gr of BTL as catalyst Mix well in a container. There is tolylene diisocyanate (hereinafter abbreviated as TDI,
2,4-form / 2,6-form molar ratio = 4/1) 2.4 mol was added, and the mixture was stirred well and the external temperature was raised from 40 ° C to 80 ° C. On the other hand, when it exceeds a little over 100%, 2-hydroxypropyl methacrylate and poly (oxypropylene) glycol monomethacrylate (Mn <representing the number average molecular weight; the same applies hereinafter) = 4.8 × 10 ² )
And 1 mol of each were added and stirred well. Cooling was started when the characteristic absorption of the isocyanate was no longer observed on the infrared spectrum, and when the temperature reached about 40 ° C., stirring was stopped and the contents were taken out. The polymer content from which the excess vinylating agent was removed was designated as prepolymer A.

When the polymer component was separated and its Mw was measured, it was 3.2 × 1
0 was ⁴ . When the polymer component was chemically decomposed, it was found that polyester and polyether were included in one molecule as a polymer segment at a predetermined ratio.

Synthesis Example-2 1 mol of poly (oxypropylene) glycol (Mw = 4.0 × 10 ³ ) as polyether diol, 1 mol of poly (propylene adipate) ester diol (Mw = 4.2 × 10 ³ ) as polyester diol, and BTL 0.5 as catalyst g
was placed in a reaction vessel and mixed well. There TDI (2,4-
(Formula / 2,6-form molar ratio = 4/1) 2.3 mol was added and stirred well, then the external temperature was raised from 40 ° C to 80 ° C, and the conversion of the isocyanate group was 100% of the calculated value. A little beyond
Two moles of 2-hydroxypropyl methacrylate were added and stirred well. Cooling was started when the characteristic absorption of isocyanate was no longer observed on the infrared spectrum,
When the temperature reached about 40 degrees, the stirring was stopped and the contents were taken out. The polymer content from which the excess vinylating agent was removed was designated as prepolymer B1. The polymer component was separated and its Mw was measured to be 3.7 × 10 ⁴ .

Synthesis Example-3 0.7 mol of poly (oxypropylene) glycol (Mw = 4.0 × 10 ³ ) as polyether diol, 1.3 mol of poly (propylene adipate) ester diol (Mw = 4.2 × 10 ³ ) as polyester diol, and BTL as catalyst
0.5 gr was put into a reaction vessel and mixed well. There TDI (2,
4-mol / 2,6-mol ratio = 4/1) 2.3 mol was added, and the mixture was stirred well and the external temperature was raised from 40 ° to 80 °, and the reaction rate of the isocyanate group was calculated with respect to the calculated value. At a little over 100%, 2 mol of 2-hydroxypropyl methacrylate was added and stirred well. When the characteristic absorption of isocyanate is no longer recognized on the infrared spectrum, cooling IC is performed,
When the temperature reached about 40 degrees, the stirring was stopped and the contents were taken out. The polymer content excluding the other excess vinylating agent was designated as prepolymer B2. The polymer component was separated and its Mw was measured to be 3.6 × 10 ⁴ .

Synthesis Example-4 A prepolymer B3 was synthesized in the same manner as in Synthesis Example-3 except that the charged moles of the polyether diol and the polyester diol were changed to 1.3 mol and 0.7 mol.
I got When the polymer component was collected and its Mw was determined, Mw was obtained.
= 3.9 × 10 ⁴ .

Comparative Synthesis Example-1 Prepolymer C was obtained in the same manner as in Synthesis Example-3 except that 0.4 mol of the polyether diol and 1.6 mol of the polyester diol were used. Mw of the polymer component was 3.8 × 10 ⁴ .

Comparative Synthesis Example-2 A prepolymer D was obtained in the same manner as in Synthesis Example-3 except that 1.6 mol of the polyether diol and 0.4 mol of the polyester diol were used. Mw of the polymer component was 3.7 × 10 ⁴ .

Synthesis Example-5 Poly (oxyethylene) glycol (Mw = 3.0 × 10 ³ )
1 mol and 1 mol of the polyester diol used in Synthesis Example 1 were charged, and 0.4 g of BTL was added dropwise, followed by thorough mixing and stirring. Then, hexamethylene diisocyanate (HMDI
2.2 mol) were charged all at once with stirring.
The temperature of the heating medium was raised from 50 degrees to 80 degrees, and the reaction was performed for 7 hours.
Then, 0.5 mol of poly (oxypropylene) glycol monomethacrylate (Mn = 6.0 × 10 ² ) was charged into the reaction vessel, and reacted until absorption of λ _NCO was not recognized on the infrared spectrum to obtain prepolymer E. Was. Mw of the polymer component was 4.7 × 10 ⁴ .

Comparative Synthesis Example-3 To 2 mol of the polyether diol used in Synthesis Example-1, 4 mol of TDI was added to synthesize an adduct having both ends isocyanate. Next, 1 mol of the polyester diol used in Synthesis Example 1 was charged therein and reacted for 4 hours to synthesize an ester / ether block polyurethane. Next, poly (oxypropylene) glycol monomethacrylate (Mn = 6.0 × 10 ² ) and BTL 0.3 gr were added, and the temperature of the heating medium was increased from 70 ° C. to 80 ° C., and the characteristics of the isocyanate group on the infrared spectrum were measured. React until no absorption is seen,
Prepolymer F was obtained. The _Mw of this polymer was 1.7 × 10 ⁴ .

Examples and Comparative Examples Using the prepolymers synthesized in the above Synthesis Examples and Comparative Synthesis Examples, photosensitive compositions shown in Table 1 were prepared.

The obtained composition was evaluated as follows. In addition, the measurement was performed at 20 degrees unless otherwise noted.

 Viscosity measurement: B type rotational viscometer used.

Hardness, hard ball drop type rebound resilience measurement: A solid plate with a thickness of 6 mm was prepared by irradiating ultraviolet rays from both sides (irradiation:
1400 mJ / cm ² was applied from both sides. The light source intensity meter used the measuring device described above. ) A Shore A type hardness meter was used. For rebound resilience measurement, place the sample on a metal surface plate so that it does not float, and measure the height from 30 cm above the sample to 10.5 mm in diameter.
The steel ball was dropped naturally and the height at which it rebounded was measured.

Tensile properties: Based on JIS K6301. The sample was prepared as follows. Using a 1 mm thick spacer, a light amount of 1400 mJ / cm ² (light source was a chemical lamp) was sequentially irradiated from each side from one side to prepare a cured sample having a thickness of about 1 mm.

 Notch crack resistance: Implemented with the dimensions described above The results measured by the above method are summarized in Table-2.

Application Examples Using the photosensitive resin compositions obtained in Examples and Comparative Examples,
Using Asahi Kasei Kogyo's APR plate making machine `` AJF '' type,
A printing plate having a total thickness of about 7 mm, a back deposition thickness (including the support) of about 1 mm, and a mask thickness (including the support) of about 4.5 mm was prepared. These plates were mounted on a cardboard printing machine via a carrier sheet, and cardboard printing was performed. The results are shown in Table-3. As shown in Table 3, the conventional plate having poor notch cracking resistance is detracted in terms of printing durability and scratch running during operation of a quadrant even if the tensile properties are the same, and the plate of the present invention has these points. It is clear that it is excellent.

[Effects of the Invention] As is clear from the above description, the present invention has greatly improved the printing plate durability and durability during plate operation of a flexographic printing plate such as a cardboard printing plate as compared with the prior art. As a result, the effect that the life as a plate was prolonged and the printing workability and the plate handling property were improved was obtained.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing the preparation of a sample used for measuring notch crack resistance, FIG. 2 is a perspective view of a sample for measurement, and FIG. FIG.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-49-133104 (JP, A) JP-A-49-109105 (JP, A) JP-A-50-19504 (JP, A) JP-A 50-108 108388 (JP, A) JP-A-1-100535 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G03F 7/027

Claims (1)

(57) [Claims] The weight average molecular weight is 1.0 × 10 ³ each.
The above polyether diol and polyester diol are used as segments, the molar ratio of both diols is in the range of 1/2 to 2/1, and both ends are (meth) acrylated, and the weight average molecular weight is 2.3 It contains 100 parts by weight of a prepolymer of × 10 ^{4 to} 5.0 × 10 ⁴ , 45 to 95% by weight of a monofunctional monomer represented by the following general formula I, and 5 to 15% by weight of a polyfunctional monomer represented by a general formula II. ethylene addition polymerizable monomer 20 to 60 parts by weight, the general formula _{I ... H 2 C = C (} R 1) -COO-R 2 formula _{II ... (H 2 C = C} (R 1) -COO n x [both In the formula, R ₁ is H or CH ₃ , and R ₂ has a molecular weight of 2.0 × 10 ^{2 to} 1.0 ×
Alcohol residue of 10 ^3, X represents a polyol residue having a molecular weight 60 to 5.0 × 10 ^2. n = 2-6. However, the molecular weight is the molecular weight in the case of a compound having no molecular weight distribution,
In the case of a compound having a molecular weight distribution, it means a number average molecular weight. 0.1 to 5.0% by weight of the photopolymerization initiator with respect to the total amount of +, and 0.01 to 1.0% by weight of the thermal polymerization inhibitor with respect to the total amount of +.
% By weight of a photosensitive resin composition for a flexographic printing plate, wherein a cured product of the composition has notch crack resistance of 20 seconds or more.