JP5108577B2 - Photosensitive resin composition for flexographic printing plate and method for producing flexographic printing plate - Google Patents

Description

  The present invention relates to a photosensitive resin composition for flexographic printing plates particularly suitable for corrugated board printing, a method for producing flexographic printing plates, and a flexographic printing plate.

  A photosensitive resin printing plate generally used as a flexographic printing plate is formed as follows. First, an actinic ray is irradiated to a solid photosensitive resin or a liquid photosensitive resin as a raw material, and only the photosensitive layer in the relief portion is cured by a radical polymerization reaction (exposure process). Next, the uncured resin other than the relief portion is dissolved and removed with a predetermined cleaning solution (developer) or swelled and dispersed and mechanically removed (developing step). A method of forming a photosensitive resin printing plate by an exposure step and a development step is a method in which only a cured portion appears as a relief on the plate surface, and is preferably used because a fine relief can be formed in a short time.

A printing plate made of a liquid photosensitive resin (liquid photosensitive resin printing plate) has a short time for manufacturing the printing plate and can cope with a short delivery time. In addition, the uncured resin can be recovered and reused. The production cost is low, and it is widely used as a printing plate for corrugated cardboard.
The corrugated cardboard sheet generally has a structure in which a liner (paperboard) is attached to a corrugated core or a structure in which they are laminated. For this reason, the printing surface has irregularities due to the influence of the corrugated core, and the sheet itself is flexible due to the hollow structure, so that high flexibility is required as the material of the printing plate.
Moreover, in recent years, there has been a tendency to use a base paper having a light weight per unit area in order to produce a corrugated cardboard sheet at a low price, and the base paper weight, which has been at least about 150 g / m ² until now, is about 120 g / m ² . Some are increasing, and further, it is supposed to decrease to about 90 g / m ² . At the same time, the mixing ratio of recycled raw materials such as newspaper and waste paper to the base paper used for corrugated cardboard tends to increase year by year, and corrugated cardboard sheets tend to become more flexible.

  In such a situation, in the printing field, even if a material that has been positioned as a flexible type in a conventional corrugated cardboard printing plate, for example, a flexographic printing plate having a Shore A hardness of 20 to 30 degrees is used, a solid material that places importance on ink adherence. In an image (image region mainly composed of a wide range of coloring), there is an increasing phenomenon of drowning in which the concealment rate by ink is insufficient. On the other hand, when printing is performed with excessive pressure to increase the concealment rate of a solid image, the fine characters cannot be read as the print quality, and the corrugated core of the corrugated cardboard sheet is crushed, resulting in insufficient strength of the cardboard box Furthermore, the relief of the printing plate itself could not withstand the printing pressure and was destroyed.

As a technique to suppress the thickening of the printed image by the flexible type flexographic printing plate, it is possible to improve with a multilayer plate (cap plate) in which a relatively hard resin is arranged in the upper region in contact with the substrate of the fine image relief. In general, it is generally used as a technique for achieving both the print quality required for solid images and fine images.
Therefore, even for recent softening of corrugated cardboard sheets, a material having superior flexibility as a photosensitive resin that forms a single layer or as a photosensitive resin that bears the lower layer portion of the cap plate configuration described above Is an effective means, and research on reducing the hardness of the cured photosensitive resin is being conducted.
In general, a flexographic printing plate made of a photosensitive resin is adjusted to have a low hardness by using a prepolymer having a relatively high molecular weight or reducing the amount of polyfunctional monomer in the composition.

  On the other hand, Patent Document 1 discloses a liquid photosensitive resin composition having improved printing durability of a flexographic printing plate and durability during plate operation. In addition, it is disclosed that notch crack resistance is important as well as breaking strength and breaking elongation in a tensile test, which is a measure of mechanical strength, as physical properties related to printing durability of a flexographic printing plate and durability during plate operation. In addition, a composition for realizing notch crack resistance of 20 seconds or more necessary for durability in a printing operation is disclosed.

  Patent Document 2 discloses a photosensitive resin composition that achieves a hardness range of 20 to 30 degrees suitable for corrugated cardboard printing. And, by using tolylene diisocyanate with a specific isomer blending ratio as a raw material for polyurethane prepolymer having ethylenically unsaturated groups, which is the main component of the resin composition, it is possible to produce photosensitive resin plates that have both printing quality and durability It is disclosed that.

  Patent Document 3 discloses a photosensitive resin composition that has a high tensile breaking strength and can provide a low hardness type flexographic printing plate without using a special isocyanate. The photosensitive resin composition is a photosensitive resin composition mainly composed of a polyurethane prepolymer having an ethylenically unsaturated group having an average molecular weight of 2,000 to 8,000, and both ends of the polyurethane prepolymer are ethylene. And a structure modified with an ethylenically unsaturated group and a structure modified with an ethylenically unsaturated group only at one end. Then, as a method for synthesizing the polyurethane prepolymer, a polyurethane prepolymer precursor having isocyanate groups at both ends is synthesized by polyol and polyisocyanate, and one molecule of hydroxyl group and ethylenic double bond is formed in a part of the terminal isocyanate group. A method is disclosed in which a monomer contained therein is reacted and the remaining terminal isocyanate group is reacted with a polyol.

Japanese Patent Laid-Open No. 4-95959 JP-A-8-220737 JP 58-76828 A

  However, as a method of preparing a low-hardness type photosensitive resin plate, when using a relatively high molecular weight prepolymer or a method of reducing the amount of polyfunctional monomer in the composition, the viscosity of the uncured resin is handled. It is difficult to design in a predetermined area required from the viewpoint of safety, the mechanical strength related to the durability of the relief tends to be reduced, and the adhesiveness to the support used at the time of producing the printing plate is reduced. There were problems and there were practical limits to the level of hardness that could be achieved.

Patent Document 1 discloses that the notch crack resistance is 20 seconds or more, but the notch crack resistance tends to increase as the hardness of the resin cured product decreases. Cracking 20 seconds is only a requirement at the hardness level that was common in cardboard applications.
The cured resin obtained as an example of Patent Document 1 also has a tensile breaking strength of 90 kg / cm ² and a tensile breaking elongation of about 300%, and further improvements are required in the durability of flexographic printing plates.

  And in the Example which implement | achieved the hardness of 20-30 degree | times of patent document 2, it turns out that tensile strength tends to be low generally with respect to a comparative example, and it turns out that mechanical physical property is falling by the low hardness clearly.

In the method disclosed in Patent Document 3, since the modification reaction of the terminal structure with respect to the urethane prepolymer precursor is performed in two stages, it is extremely difficult to control the molecular weight from the viewpoint that it can also react with the urethane bond formed with the isocyanate group. .
Moreover, in the Example of patent document 3, it calculates | requires from the raw material preparation ratio by calculating | requiring the molecular weight and content ratio of the 2 types prepolymer from which the terminal modification structure differs, and there is no description which actually analyzed and measured them. Even if the produced prepolymer is ideally assumed, Patent Document 3 discloses a prepolymer in which an ethylenic double bond is arranged at one end of the prepolymer with respect to the physical properties of the cured product. It is disclosed that although the hardness decreases as the number increases, the tensile strength also decreases at the same time. Therefore, Patent Document 3 does not suggest that the mechanical strength currently required by the low-hardness resin plate is realized.

  As described above, even with the techniques disclosed in Patent Documents 1 to 3, the mechanical strength that can withstand practical printing operations at a resin plate hardness of less than 25 degrees Shore A hardness required for recent softened corrugated cardboard sheets. It was impossible to realize.

  The problem to be solved by the present invention is to provide a photosensitive resin composition for flexographic printing plates that can realize mechanical strength that can withstand practical printing operations at a resin plate hardness of less than 25 degrees Shore A hardness.

As a result of intensive investigations to solve such problems, the present inventors have found that a photosensitive resin composition containing as a main component an unsaturated polyurethane prepolymer whose methacrylic group addition amount at the end of the main chain is controlled solves the above problems. As a result, the present invention has been completed.
That is, the present invention provides the following photosensitive resin composition for flexographic printing plates, a method for producing flexographic printing plates, and flexographic printing plates.
[1]
Unsaturated polyurethane prepolymer whose main chain terminal is modified with a methacryl group: 100 parts by mass,
Ethylenically unsaturated monomer: 10 to 150 parts by mass,
Photopolymerization initiator: 0.01 to 10 parts by mass,
Including
The photosensitive resin composition for flexographic printing plates whose range of the methacryl group index calculated | required by following formula (1) of the said unsaturated polyurethane prepolymer is 1.50-1.85.
Methacryl group index = X / (8500 / Y) Formula (1)
(In the formula, X represents the methacrylic group content (%) in the unsaturated polyurethane prepolymer, and Y represents the number average molecular weight of the unsaturated polyurethane prepolymer.)
[2]
The photosensitive resin composition for flexographic printing according to [1], wherein the unsaturated polyurethane prepolymer has a number average molecular weight in the range of 10,000 to 40,000.
[3]
The unsaturated polyurethane prepolymer is obtained by reacting a low molecular compound containing a methacryl group and a hydroxyl group in one molecule and having a molecular weight in the range of 100 to 500 after the urethanization reaction with a polyol and a polyisocyanate. The photosensitive resin composition for flexographic printing plates according to [1] or [2].
[4]
The photosensitive resin composition for flexographic printing plates according to [3], wherein the polyol is a mixture of a polyether polyol and a polyester polyol.
[5]
Any one of [1] to [4], wherein among the ethylenically unsaturated monomers, a polyfunctional monomer having 3 or more methacrylic groups and / or acrylic groups in one molecule is 0.5 to 15% by mass. The photosensitive resin composition for flexographic printing plates described in 1.
[6]
Each process of the following (A)-(C),
(A) Curing that exposes the surface of a molded body formed using the photosensitive resin composition for flexographic printing plates according to any one of [1] to [5] to form a cured site on the molded body. Site formation process,
(B) a development step of developing the cured portion with a cleaning liquid;
(C) an actinic ray irradiation step for irradiating the surface of the developed cured portion with an actinic ray,
A method for producing a flexographic printing plate comprising
[7]
A flexographic printing plate obtained by the production method according to [6] above.

  ADVANTAGE OF THE INVENTION According to this invention, the photosensitive composition for flexographic printing plates which can implement | achieve the mechanical strength which can endure practical printing operation in the resin plate hardness below 25 degrees of Shore A hardness can be provided.

  Hereinafter, the best mode for carrying out the present invention (hereinafter referred to as the present embodiment) will be described in detail. In addition, this invention is not limited to the following embodiment, It can implement by changing variously within the range of the summary.

The photosensitive resin composition for flexographic printing plates of the present embodiment (hereinafter sometimes abbreviated as “photosensitive resin composition”) includes the following components (a) to (c):
(A) Unsaturated polyurethane prepolymer whose main chain terminal is modified with a methacryl group: 100 parts by mass,
(B) ethylenically unsaturated monomer: 10 to 150 parts by mass,
(C) Photopolymerization initiator: 0.01 to 10 parts by mass,
including.
As an aspect of the photosensitive resin composition in the present embodiment, it is liquid (that is, the liquid photosensitive resin composition), the uncured resin can be recovered and reused, and development with an aqueous cleaning liquid is possible. It is suitable from the viewpoint of productivity and work environment.
When the photosensitive resin composition of the present embodiment is used in a method for producing a flexographic printing plate, which will be described later, the viscosity of the photosensitive resin composition at room temperature is 10 to 10 from the viewpoint of expressing excellent thickness accuracy of the flexographic printing plate. The range is preferably 500 Pa · s. More preferably, it is the range of 20-300 Pa.s.

The unsaturated polyurethane prepolymer (hereinafter sometimes abbreviated as “unsaturated polyurethane prepolymer”) in which the main chain terminal of the component (a) in this embodiment is modified with a methacrylic group is included in one molecule. It is a polyurethane having a plurality of urethane bonds, a compound having a methacrylic group and capable of being linked with other monomers by a polymerization reaction.
As a method for producing such component (a), for example,
(I) A polyol and a polyisocyanate are reacted to form a polyurethane having an isocyanate group at the terminal at an arbitrary molecular weight, and then the polyurethane and a compound containing an active hydrogen and a methacryl group in one molecule How to react,
(Ii) A polyol and a polyisocyanate are reacted to form a polyurethane having a hydroxyl group at the terminal at an arbitrary molecular weight, and then the polyurethane is reacted with a compound containing an isocyanate group and a methacryl group in one molecule. How to
Is mentioned.

  Examples of the polyol in the present embodiment include polyether polyol, polyester polyol, polyether polyester copolymer polyol, and the like. These can be used alone or in combination of two or more.

  Examples of the polyether polyol include polyoxyethylene glycol, polyoxypropylene glycol, polyoxytetramethylene glycol, polyoxy 1,2-butylene glycol, polyoxyethylene / polyoxypropylene random copolymer, polyoxyethylene / poly Examples thereof include an oxypropylene block copolymer, a polyoxyethylene / polyoxytetramethylene random copolymer, and a polyoxyethylene / polyoxytetramethylene block copolymer.

Examples of the polyester polyol include diols obtained by repeating segments obtained by a polycondensation reaction between a diol (glycol) compound and a dicarboxylic acid compound. Examples of such diols include poly (ethylene glycol adipate) diol, poly (diethylene glycol adipate) diol, poly (propylene glycol adipate) diol, poly (1,4-butane glycol adipate) diol, poly (ethylene glycol adipate) diol, (1,6-hexaneglycol adipate) diol, poly (2-methylpropaneglycol adipate) diol, poly (3-methyl-1,5-pentaneglycol adipate) diol, poly (neopentylglycol adipate) diol, poly ( 1,9-nonane glycol adipate) diol, poly (2-methyloctane glycol adipate) diol, polycaprolactone diol, poly (β-methyl-δ-valerolactone) diol, etc. Can be mentioned.
Examples of the dicarboxylic acid compound constituting the polyester segment include adipic acid, succinic acid, glutaric acid, azelaic acid, sebacic acid, maleic acid, terephthalic acid, isophthalic acid, 1,5-naphthalenedicarboxylic acid, and the like. .
The diol and dicarboxylic acid components constituting the polyester segment are generally synthesized by a polycondensation reaction between single components as illustrated, but a plurality of components can be mixed and used in an arbitrary ratio. is there.

  The polyether polyester copolymer polyol is a copolymer having a structure in which the above-described repeating unit that forms the molecular chain of the polyether polyol and the repeating unit that forms the molecular chain of the above-described polyester polyol are blocked or randomly linked. A polymer can be mentioned.

  Examples of the polyisocyanate in the present embodiment include diisocyanate compounds such as tolylene diisocyanate, xylylene diisocyanate, hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, isophorone diisocyanate, and diphenylmethane diisocyanate.

As the compound containing active hydrogen and a methacryl group in one molecule in the present embodiment, the active hydrogen is preferably an active hydrogen derived from a hydroxyl group, that is, a compound containing a hydroxyl group and a methacryl group. Examples thereof include hydroxypropyl methacrylate, hydroxyethyl methacrylate, polypropylene glycol monomethacrylate, polyethylene glycol monomethacrylate, glycerin monomethacrylate, and glycerin dimethacrylate.
The compound containing an isocyanate group and a methacryl group in one molecule in the present embodiment is preferably a low molecular compound, and examples thereof include methacryloyloxyethyl isocyanate.

  The compound containing an active hydrogen or isocyanate group and a methacryl group in one molecule at the main chain terminal of the unsaturated polyurethane prepolymer (hereinafter sometimes abbreviated as “methacrylating agent”) is as described above. It is preferable that the molecular weight is in the range of 100 to 500.

In the present embodiment, a polyurethane prepolymer having a polyol structure constituted by a polyether segment is referred to as “polyether-based polyurethane prepolymer”, and a polyurethane prepolymer constituted by a polyester segment is referred to as “polyester-based polyurethane prepolymer”, polyether. A polyurethane prepolymer constituted by a segment and a polyester segment may be abbreviated as “polyether polyester-based polyurethane prepolymer”.
Among these, from the viewpoint of developing flexibility and durability as a printing plate relief, it is preferable to use a polyether polyester-based polyurethane prepolymer.
The polyether polyester polyurethane prepolymer can be produced using the polyether polyester copolymer polyol, or can be produced using a polyol mixture containing the polyether polyol and the polyester polyol.
The polyether polyester-based polyurethane prepolymer can be obtained by reacting a reaction product of a polyol mixture containing polyether polyol and polyester polyol and a polyisocyanate with a methacrylating agent. It is preferable from the viewpoint of developability and also from the viewpoint of controlling the unsaturated polyurethane prepolymer to a predetermined molecular weight.

In the unsaturated polyurethane prepolymer in the present embodiment, the main chain terminal is modified with a compound containing a methacryl group. As for the modification rate, the methacryl group index determined by the following formula (2) is 1.50 to 1.85, more preferably 1.60 to 1.80.
Methacryl group index = X / (8500 / Y) Formula (1)
(In the formula, X represents the methacryl group content (%) in the unsaturated polyurethane prepolymer, and Y represents the number average molecular weight of the unsaturated polyurethane prepolymer.)
In the present embodiment, the “number average molecular weight” is a value calculated as a polystyrene equivalent value in GPC measurement according to a method as described in the following examples.
In the present embodiment, “methacrylic group content in unsaturated polyurethane prepolymer” means protons after GPC fractionation of the synthesized unsaturated polyurethane prepolymer according to the method described in the following examples. This is a value obtained by quantifying the content of methacryl groups by NMR (nuclear magnetic resonance spectrum) analysis.
In the present embodiment, the “methacrylic group index” is a value indicating the degree of modification of the main chain end with a compound containing a methacrylic group, and the value 1.00 is one for one molecule of unsaturated polyurethane prepolymer. It means that the methacryl group of is modified.
When the unsaturated polyurethane prepolymer in the present embodiment has a value of 1.50 or more, when the flexographic printing plate is used, it is possible to prevent a decrease in adhesion between the polymerized cured product and the support. On the other hand, setting the value to 1.85 or less gives good mechanical strength in the range where the photosensitive resin cured product is less than 25 degrees Shore A hardness, and the flexographic printing plate is repeatedly used or roughly handled. It is possible to achieve good durability against the above.

  The number average molecular weight of the unsaturated polyurethane prepolymer in the present embodiment is preferably 10,000 to 40,000, more preferably 15,000 to 35,000, and further preferably 20,000 to 30. , 000. Setting the value to 10,000 to 40,000 gives good mechanical strength in the range where the polymerized cured product is less than 25 degrees Shore A hardness, and is suitable for repeated use of the flexographic printing plate or rough handling. Good durability can be realized. In addition, when the value is 40,000 or less, the photosensitive resin composition is given good developability with an aqueous cleaning solution, and it is easy to cope with a general-purpose developing device.

The structure of the main chain terminal of the unsaturated polyurethane prepolymer that is not modified by the methacrylating agent is from the viewpoint of expressing excellent mechanical properties in the polymer having a relatively low hardness, which is the object of the present embodiment. Although not particularly limited, a hydroxyl group or a monovalent saturated aliphatic group is preferable, and a hydroxyl group is more preferable.
Further, it is preferable to modify the end of the main chain of the unsaturated polyurethane prepolymer with the monovalent saturated aliphatic group from the viewpoint of adjusting the hardness of the photosensitive resin cured product and the swelling property with respect to the ink. From the viewpoint, modification with a saturated aliphatic group having 8 or less carbon atoms is preferred.
When the main chain terminal of the unsaturated polyurethane prepolymer is modified with a monovalent saturated aliphatic group, specifically, a compound containing active hydrogen and methacryl group in one molecule is used as a methacrylating agent. In the production method to be used, it can be produced by reacting a saturated aliphatic alcohol having 8 or less carbon atoms simultaneously with a methacrylating agent.

In the present embodiment, a preferred method for producing an unsaturated polyurethane prepolymer is that, first, in the production of polyurethane, which is a pre-stage of modification with a methacrylic group, the target number average of unsaturated polyurethane prepolymers relative to the polyol. Based on the molecular weight and the target number of terminal methacrylic groups at the end of the main chain of the unsaturated polyurethane prepolymer, the amount of the polyisocyanate is calculated, and the urethanization reaction is performed by mixing the polyol and the polyisocyanate.
Quantitative determination of the residual isocyanate value in the course of the urethanization reaction when the main chain terminal methacrylic group modification reaction is carried out using a compound containing active hydrogen and methacrylic groups in the molecule as the methacrylating agent. Observe and add the methacrylating agent one step before reaching the target value. At this time, the methacrylating agent is added 2 to 30 times the number of moles necessary for the modification of the methacrylic group at the end of the main chain of the polyurethane, thereby suppressing the main chain extension due to the urethanization reaction and enabling the desired methacrylic group modification To. Regarding the timing of adding the methacrylating agent, in order to ensure the control of the molecular weight of the unsaturated polyurethane prepolymer to be produced and the control of the number of methacrylic groups at the end of the main chain, the increase in viscosity in the production of polyurethane is observed, and the target polyurethane A method that targets the viscosity taken into consideration from the relationship between the molecular weight of the precursor and the viscosity is more preferable.
On the other hand, when the main chain terminal methacrylic group modification reaction is carried out using a compound containing an isocyanate group and a methacrylic group in one molecule as a methacrylic agent, the target is to form a structure in which both ends of the main chain are hydroxyl groups as polyurethane. The polyol according to molecular weight and the polyisocyanate are mixed and subjected to a urethanization reaction, and then the methacrylating agent is added in the number of moles corresponding to the target number of terminal methacrylic groups as an unsaturated polyurethane prepolymer. Modification of the main chain end is possible.

  In the present embodiment, as a method for synthesizing the unsaturated polyurethane prepolymer, a method using a compound containing active hydrogen and a methacryl group in one molecule as a methacrylating agent is preferable, and a methacrylating agent containing a hydroxyl group is used. The method of doing is more preferable. It is preferable to use a methacrylating agent containing a hydroxyl group in excess of the theoretical number of moles because the reaction system is diluted and a uniform reaction is realized, so that the molecular weight and methacryl group modification can be controlled reliably. .

In addition, as the component (a), a plurality of types of prepolymers synthesized by any of the methods described above can be mixed and used.
For example, by mixing a prepolymer designed and synthesized with a methacrylic index of 2.00 and a prepolymer designed and synthesized with a value of 1.00, the resulting methacrylic group index is 1.50. It is also possible to produce unsaturated polyurethane prepolymers that are 1.85.
However, from the viewpoint of the uniformity of the molecular weight distribution and the number of terminal methacryl groups, especially the mixing of components having a methacryl group index of less than 1.00 tends to reduce the adhesion between the photosensitive resin relief and the support. Therefore, it is preferable that the methacryl group index is in the range of 1.50 to 1.85 by the prepolymer synthesized as a single component, regardless of the method of mixing plural kinds of prepolymers.
In the present embodiment, the prepolymer synthesized as a single component is not a prepolymer obtained by a method of mixing plural kinds of prepolymers as described above, but after a urethanization reaction using a polyol and a polyisocyanate. It means a prepolymer obtained by reacting a methacrylating agent.

  In the present embodiment, the unsaturated polyurethane prepolymer is preferably 5 to 25% by mass, more preferably 10% of the polyoxyethylene segment in the component (a) from the viewpoint of developing good developability with an aqueous cleaning solution. It is included at a ratio of ˜20 mass%. Setting the ratio of the polyoxyethylene segment to 5% by mass or more can contribute to ensuring dispersibility in the aqueous cleaning liquid. On the other hand, when the content is 25% by mass or less, the swelling property of the photosensitive resin relief with respect to the printing ink can be suppressed to a certain value or less, which can contribute to a reduction in the risk that the relief swells during printing and adversely affects print quality.

Various known catalysts can be used for the production of the unsaturated polyurethane prepolymer in the present embodiment.
Among them, it is preferable to use a relatively low molecular weight catalyst from the viewpoint of reaction efficiency, and dibutyltin dilaurate and triethylenediamine are preferable. The catalyst is preferably used at a concentration of about 10 to 500 ppm based on the polyol used for the production of polyurethane. Setting the value to 10 ppm or more is preferable from the viewpoint of controlling the reaction time, while setting the value to 500 ppm or less is preferable from the viewpoint of suppressing the influence on the sensitivity or storage stability of the photosensitive resin composition.

The production of the unsaturated polyurethane prepolymer in the present embodiment is performed from the viewpoint that the photosensitive resin composition can be easily obtained by mixing the component (b) and the component (c) described later after the synthesis of the unsaturated polyurethane prepolymer. Preference is given to bulk polymerization with polyols, polyisocyanates and methacrylating agents.
On the other hand, when the target unsaturated polyurethane prepolymer has a high viscosity, it may be preferable to use solution polymerization in order to control the urethanization reaction and to make the polymer molecular weight distribution monodisperse. Inactive compounds such as methyl ethyl ketone and toluene can be used after dehydration.
Further, by using a compound inert to the isocyanate group, for example, alkyl-, cycloalkyl-, alkyl halide-, benzyl-, phenoxy- (meth) acrylate, as a diluent, these compounds can be used as component (b) Therefore, it is preferable from the viewpoint of enabling continuous production to subsequent resin mixing.
In the present embodiment, the composition containing an unsaturated polyurethane prepolymer and before mixing the component (b) and the component (c) may be referred to as a urethane prepolymer.

Examples of the component (b) in the present embodiment include unsaturated carboxylic acids such as acrylic acid and methacrylic acid; ester compounds of unsaturated carboxylic acids; (meth) acrylamide or derivatives thereof; allyl compounds; maleic acid, anhydrous Mention may be made of maleic acid, fumaric acid or esters thereof; and other unsaturated compounds. These can be used alone or in combination of two or more.
Examples of the ester compound of the unsaturated carboxylic acid include alkyl-, cycloalkyl-, halogenated alkyl-, alkoxyalkyl-, hydroxyalkyl-, aminoalkyl-, tetrahydrofurfuryl-, allyl-, glycidyl-, benzyl- , Phenoxy- (meth) acrylate; mono- or di (meth) acrylate of alkylene glycol or polyoxyalkylene glycol; trimethylolpropane tri (meth) acrylate; glycerol mono-, di- or tri (meth) acrylate; pentaerythritol tetra (meth) Acrylate; ditrimethylolpropane tetra (meth) acrylate and the like.
Examples of the (meth) acrylamide or derivative thereof include (meth) acrylamide, diacetone (meth) acrylamide, N, N′-alkylenebis (N-substituted or N, N′-substituted with an alkyl group or a hydroxyalkyl group ( And (meth) acrylamide.
Examples of the allyl compound include allyl alcohol, allyl isocyanate, diallyl phthalate, triallyl cyanurate, and the like.
Examples of the maleic acid, maleic anhydride, fumaric acid or esters thereof include alkyl, alkyl halide, alkoxyalkyl mono- or dimaleate, and fumarate.
Examples of the other unsaturated compounds include styrene, vinyl toluene, divinyl benzene, N-vinyl carbazole, and N-vinyl pyrrolidone.

  The component (b) in the present embodiment includes acrylic acid and methacrylic acid from the viewpoint of controlling flexibility, elasticity characteristics, mechanical strength required for durability, swelling property with respect to ink, and the like required for flexographic printing plates. Examples of the ester compound include propylene glycol mono (meth) acrylate, polypropylene glycol mono (meth) acrylate, diethylene glycol monoethyl ether mono (meth) acrylate, diethylene glycol monobutyl ether mono (meth) acrylate, diethylene glycol mono-2-ethylhexyl ether mono (meta) ) Acrylate, triethylene glycol monohexyl ether mono (meth) acrylate, tetradecyl (meth) acrylate, pentadecyl (meth) acrylate, N, N-diethylaminoethyl (Meth) acrylate, polypropylene glycol di (meth) acrylate, phenoxy (meth) acrylate, benzyl (meth) acrylate, polyethylene glycol di (meth) acrylate, polypropylene glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, Glycerol mono-, di- or tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, ditrimethylolpropane tetra (meth) acrylate, dipentaerythritol hexaacrylate and the like are preferably used.

In this Embodiment, as a compounding quantity of (b) component, it is 10-150 mass parts with respect to 100 mass parts of said (a) component, Preferably it is 10-100 mass parts. Setting the blending amount of the component (b) within the above range is preferable from the viewpoint of realizing a viscosity of the photosensitive resin composition at room temperature of 10 to 500 Pa · s, which is desired for good plate-making properties.
Among the components (b), the polyfunctional monomer having 3 or more methacrylic groups and / or acrylic groups in one molecule is preferably 0.5 to 15% by mass, more preferably 0.5 to 10%. % By mass. Setting the blending amount of the polyfunctional monomer within the above range is preferable from the viewpoint of adjusting the photosensitive resin cured product to a range below 25 degrees Shore A hardness and realizing mechanical strength that can withstand printing work.

Examples of the component (c) in the present embodiment include benzoin alkyl ethers such as benzoin, benzoin ethyl ether, benzoin-n-propyl ether, benzoin isopropyl ether, benzoin isobutyl ether, and 2,2-dimethoxy-2-phenyl. Examples include acetophenone, benzophenone, benzyl, diacetyl, diphenyl sulfide, and 9,10-anthraquinone. These can be used alone or in combination of two or more.
Here, the component (c) is preferably used in combination with a sensitizer from the viewpoint of increasing its reactivity. Examples of such a sensitizer include amines such as triethanolamine, methyldiethanolamine, triisopropanolamine, Michler's ketone, 4,4′-diethylaminophenone, 4-diethylaminobenzoic acid ethyl ester; and dyes such as eosin and thiocin. Etc. In particular, when a hydrogen abstraction type initiator is used as the component (c), it is preferable to use such a sensitizer in combination.

In this Embodiment, as a compounding quantity of (c) component, it is 0.01-10 mass parts with respect to 100 mass parts of said (a) component, Preferably it is 0.1-5 mass parts. Setting the blending amount of the component (c) within the above range is preferable from the viewpoint of satisfactorily balancing the storage stability, desired photocuring speed, and cured product properties of the photosensitive resin composition.
If necessary, the photosensitive resin composition of the present embodiment may further contain a thermal polymerization inhibitor, an ultraviolet absorber, a light stabilizer, a dye, a pigment, a lubricant, an inorganic filler, a plasticizer, and the like. it can.

The manufacturing method of the flexographic printing plate of the present embodiment includes the following steps (A) to (C):
(A) A cured part forming step (hereinafter referred to as “molding / exposure step”) in which the surface of a molded body formed using the photosensitive resin composition of the present embodiment is exposed to form a cured part on the surface of the molded body. ”).),
(B) a development step of developing the cured portion with a cleaning liquid;
(C) an actinic ray irradiation step for irradiating the surface of the developed cured portion with an actinic ray (hereinafter sometimes abbreviated as “post-exposure step”);
including.
Moreover, you may include the (D) drying process after the said (C) process.

The step (A) in the present embodiment may include a molding step in which the photosensitive resin composition is molded on the base material to a constant thickness inside a dedicated apparatus (plate making machine).
The molding / exposure process in the present embodiment includes, for example, the following processes (1) to (3):
(1) A negative film is placed on an ultraviolet light transmissive glass plate and covered with a thin protective film, and then a photosensitive resin composition is poured thereon, and a support is interposed through a spacer so that the plate thickness is constant. When forming a printing layer (thickness of 4 mm or more) used for corrugated cardboard printing, a base film is laminated and pressed onto it with an ultraviolet transmissive glass plate to form a photosensitive layer. In order to supplement the relief strength against the printing pressure during printing, it is preferable to form a shelf layer as a base. In this case, a photosensitive layer is formed by sandwiching a dedicated negative film (masking film) between the support and the upper glass plate. Photosensitive layer molding process),
(2) After the photosensitive layer molding step, the plate is irradiated with actinic rays (for example, having a wavelength distribution of 300 nm or more) from an upper glass side through a base film using an ultraviolet fluorescent lamp or the like as an active light source. A back exposure process for depositing a uniform thin cured resin layer (that is, a floor forming layer (back deposition layer)) on the entire surface of the support (masking exposure process in which a shelf layer is formed by the same exposure in a method in which a masking film is attached) ),
(3) After the back exposure step or the masking exposure step, a relief forming exposure step of irradiating the photosensitive layer with the same actinic ray as above from the lower glass side through the negative film to form an image,
Is included.
In a printing plate in which a shelf layer is formed by masking exposure, it is also preferable to form a back deposition layer on the entire surface of the support by removing the masking film after the relief forming exposure step and performing the back exposure step. One.

In the step (B) in the present embodiment, a surfactant aqueous solution is preferably used as the cleaning liquid used.
Here, as for the type and composition of the surfactant, an optimum one is selected according to the properties of the photosensitive resin composition to be used. From the viewpoints of fine portion cleaning properties and cleaning liquid stamina properties, anionic surfactants are used. Is preferred.
In addition, as a developing method, a method of immersing the exposed photosensitive resin plate in the developer, a method of spraying the developer on the exposed photosensitive resin plate surface from the spray nozzle, or an uncured resin swollen by immersion / spraying is used. A method such as scraping with a brush is applicable.

In the step (C) in the present embodiment, after the development in the step (B), an active ray is applied to the cured portion of the photosensitive resin composition mainly for the purpose of promoting the mechanical strength of the flexographic printing plate and removing the surface adhesiveness. It is the process of irradiating. Examples of such an active light source (active light source) include an active light source having a distribution in a wavelength region of 300 nm or more used for relief exposure (for example, a high pressure mercury lamp, an ultrahigh pressure mercury lamp, an ultraviolet fluorescent lamp, a carbon arc lamp, a xenon lamp). Etc.), an active light source having a distribution in a wavelength region of 200 to 300 nm (for example, a low-pressure mercury lamp, a germicidal lamp, a deuterium lamp, or the like) or a light source combining these is preferably used.
The post-exposure process may employ an underwater exposure method for the purpose of preventing polymerization reaction inhibition by oxygen in the air or an air exposure method that does not take measures against air inhibition, that is, oxygen inhibition. Among these, the underwater exposure method is preferable from the viewpoint of suppressing the expression of tackiness on the flexographic printing plate surface.

  The step (D) in the present embodiment is a step of drying moisture adhering to the surface of the photosensitive resin plate in the development step and the post-exposure step. It is preferable that such a drying process is performed using a dedicated housed hot air dryer.

  The manufacturing method of the flexographic printing plate of the present embodiment may further include other steps. For example, a plate making method disclosed in Japanese Patent No. 3592336 in which a treatment step for allowing a hydrogen abstracting agent to permeate the plate surface after the development step and then a post-exposure step is performed can be suitably applied.

  The flexographic printing plate produced by the method as described above using the photosensitive resin composition of the present embodiment has good ink transfer to a soft printing medium, particularly in a flexographic printing plate for corrugated cardboard, and is handled From the viewpoint of suppressing the relief fracture due to, it is preferable to have the Shore A hardness and the strength at break and elongation measured by a tensile test described below.

The flexibility of the flexographic printing plate of the present embodiment is preferably in the range of less than 25 degrees as Shore A hardness measured at a temperature of 20 ° C. and a humidity of 70%, more preferably from 10 to 25 degrees. The range of 10 to 25 degrees is preferable from the viewpoint of satisfying a solid image ink transfer property to a cardboard sheet using a liner and a core that is less than a paper weight of 150 g / m ² , and is required at a printing work site. The mechanical strength of the photosensitive resin relief can be effectively expressed. The Shore A hardness of the flexographic printing plate of the present embodiment is most preferably 10 to 20 degrees.

The flexographic printing plate of the present embodiment preferably has a tensile breaking strength (MPa) and a tensile breaking elongation (%) of 4 MPa or more and 400% or more, respectively, more preferably 5 MPa or more and 450% or more. .
Tensile rupture elongation is important as the amount of relief deformation required to mitigate impact, and tensile rupture strength is important from the viewpoint of suppressing the occurrence of relief rupture against excessive deformation. When the tensile elongation at break is in the above range, the durability of the flexographic printing plate required for corrugated board printing can be satisfactorily realized.

Next, the present embodiment will be described more specifically with reference to examples and comparative examples. However, the present embodiment is not limited to the following examples unless it exceeds the gist.
Note that the evaluation method and measurement method used in this embodiment are as follows.

[Measurement method of residual amount of isocyanate group]
A polyol and a polyisocyanate are reacted to form a polyurethane having an isocyanate group at the terminal at an arbitrary molecular weight, and then the polyurethane is reacted with a methacrylating agent containing an active hydrogen and a methacryl group in one molecule. When an unsaturated polyurethane prepolymer is produced by the method, an isocyanate group at the end point of the polyurethane formation reaction, which is a primary reaction, is used to confirm the molecular weight of the unsaturated polyurethane prepolymer and the control of the terminal modification rate by the methacrylating agent. The remaining amount of was quantified.
First, the following solutions A and B were prepared, and 10 ml of solution A was neutralized and titrated with solution B in advance to obtain a control titer.
Liquid A: 2% dibutylamine / monochlorobenzene solution Liquid B: 0.1 N hydrochloric acid / ethanol solution A sample of several grams was collected from the product of the polyurethane reaction, which is the primary reaction for the production of unsaturated polyurethane prepolymer, and the liquid A 10 ml was added and dissolved, and the isocyanate group contained in the polyurethane and the dibutylamine in the liquid A were reacted.
Thereafter, neutralization titration with the solution B was carried out, and the residual amount (mol / kg) of isocyanate groups in the sample was calculated from the difference from the previously obtained control titer.

[GPC measurement method]
About the manufactured urethane prepolymer, GPC measurement was performed on condition of the following, and the number average molecular weight by polystyrene conversion was calculated | required. Moreover, the content of the high molecular weight substance derived from the unsaturated polyurethane prepolymer component excluding the unreacted product of the methacrylating agent added excessively during the production was determined by the peak area ratio (%) obtained by GPC measurement.
Equipment: HLC-8220GPC manufactured by Tosoh Corporation
Column: TSLgelGMHXL manufactured by Tosoh Corporation
Solvent: Tetrahydrofuran Flow rate: 1 ml / min Injection volume: 100 microliter Detector: RI detector Calibration curve standard: Polystyrene (molecular weight 500 to 1260000)
Sample: 0.3 mass% tetrahydrofuran solution

[Method of measuring methacryl group content (% by mass) in unsaturated polyurethane prepolymer]
About the manufactured urethane prepolymer, GPC fractionation was performed on the following conditions, and the high molecular weight body originating in an unsaturated polyurethane prepolymer was fractionated.
1) Conditions for GPC preparation Equipment: LC-908 type manufactured by Nippon Analytical Industries, Ltd. Column: JAIGEL 4H-3H-2H (in series) manufactured by Nippon Analytical Industries, Ltd.
Solvent: Chloroform Flow rate: 3.3 ml / min Injection volume: 3 ml Detector: RI detector Sample: 3% by mass chloroform solution The fractionated unsaturated polyurethane prepolymer is dissolved in deuterated chloroform, and dimethylformamide is contained inside. In addition to the standard substance, proton NMR measurement was performed under the following conditions.
2) Proton NMR measurement conditions Apparatus: Bruker BioSpin Corporation Avance 600
Observation frequency: 600 MHz
Integration count: 1024 times Repetitive pulse waiting time: 1.0 sec
From the NMR spectrum obtained, the methacrylic acid contained in the sample was determined from the integrated value of the 5.6 ppm peak attributed to the double bond proton of the methacryl group and the 3.0 ppm peak attributed to the methyl group proton of dimethylformamide. The number of moles of the group was quantified and multiplied by the molecular weight 85 of the methacryl group to calculate the mass of the methacryl group contained in the GPC preparative sample.
The methacryl group content (% by mass) in the unsaturated polyurethane prepolymer was calculated by multiplying the value obtained by dividing the mass of the methacryl group finally calculated by the total sample mass obtained by GPC fractionation by 100.

[Viscosity measurement method]
When the photosensitive resin composition for flexographic printing plates is in liquid form, after leaving it in a constant temperature and humidity room at a temperature of 20 ° C. and a humidity of 70% for one day, a B-type viscometer type B8H (manufactured by Tokyo Keiki Co., Ltd.) Viscosity measurements were performed using this.

[Shore A hardness measurement method]
(1) A 4 mm-thick flexographic printing plate having a solid image (printing relief with a smooth surface and no recesses) of 5 cm square or more is prepared and placed in a constant temperature and humidity chamber at a temperature of 20 ° C. and a humidity of 70%. I left it for a day.
(2) JIS constant pressure loader GS-710 installed in the same room (ASTM Co., Ltd. ASTM: D2240A, JIS: K6253A, ISO: 7619A) with a 1 kg load, the value 15 seconds after the start of measurement I read it.

[Tensile property evaluation method]
(1) Two glass plates adhered with a transparent film of polyethylene terephthalate were molded into a constant thickness using a 1 mm thick spacer, and then a light amount of 1400 mJ / cm ² from one side (the light source was a chemical) Lamp) was sequentially irradiated from each surface to prepare a cured sample having a thickness of about 1 mm.
(2) Tensile properties were measured by a method based on JIS: K6301.

[Notch crack resistance evaluation]
(1) A 7 mm flexographic printing plate having a solid image area of 15 cm square or more is cut out as three strip-shaped sample plates having a width of 1 cm and a length of 5 cm, and a depth of 0.8 to 1 with a cutter in the central portion of the length of 5 cm. A 2 mm incisor was inserted.
(2) Hold the sample plate slightly curved so that the cut line is on the outside and hold it with one hand, and hold the fingers of the other hand so that the support located on the back side of the sample plate bends directly under the cut line As a result, the sample plate was quickly bent and the sample plate was supported so that the supports were in close contact with each other.
(3) The time from the moment when the plate was bent until the crack generated from the cut line reached the support was measured in seconds.
(4) The same measurement was performed on three sample plates, and an integer of 5 seconds close to the average value of the measurement results was defined as notch crack resistance.

[Support adhesion]
The support adhesiveness of the photosensitive resin relief was evaluated by placing a nail on the interface between the photosensitive resin relief of the flexographic printing plate sample and the support and pulling the photosensitive resin relief in the direction of peeling off the support.
As a result of the evaluation, those having adhesive strength enough to break the photosensitive resin relief were accepted, and those where the photosensitive resin relief was peeled off from the support and the support surface was exposed were rejected.

[Production Example 1] Production of urethane prepolymer A 900 parts by mass of poly (propylene glycol adipate) diol (hydroxyl value: 44 KOHmg / g. Hereinafter abbreviated as “PA2500”) and 1100 parts by mass of polyoxyethylene (EO) ) -Oxypropylene (PO) block copolymerized diol (hydroxyl value: 44 KOH mg / g, EO content 30 wt%, hereinafter abbreviated as “PL2500”), 300 ppm of dibutyltin dilaurate (hereinafter referred to as BTL). And abbreviated to 40.degree. C. until uniform. Next, 155 parts by mass of tolylene diisocyanate (mass ratio of isomers is 2,4-isomer / 2,6-isomer = 80/20, hereinafter abbreviated as “TDI”) and further stirred, and uniform When it became, it heated up to 65 degreeC. Thereafter, the temperature in the reaction system was controlled while measuring the viscosity and temperature of the product in the reaction system. When the temperature reached 520 poise (80 ° C.), a sample was taken and 259 parts by mass of the methacrylating agent was obtained. Polypropylene glycol monomethacrylate (average molecular weight 380, hereinafter abbreviated as “PPMA”) and 136 parts by mass of propylene glycol monomethacrylate (hereinafter abbreviated as “HPMA”) were added.
As a result of titration measurement of the isocyanate group residual amount of the collected sample, it was 0.104 mol / kg.
After adding the methacrylating agent, the reaction was allowed to proceed for about 2 hours. A part of the sample was taken out and the disappearance of isocyanate groups was confirmed with an IR spectrometer, and urethane prepolymer A was obtained.
As a result of analyzing the urethane prepolymer A, the unsaturated polyurethane prepolymer content was 87% by mass, the number average molecular weight was 21,000, and the methacrylic group content was 0.80% by mass. Therefore, the methacrylic group index was 1.98. And calculated.

[Production Example 2] Production of urethane prepolymer B The same method as in Production Example 1 except that the amount of TDI mixed is 150.4 parts by mass, 251 parts by mass of PPMA and 134 parts by mass of HPMA are used as the methacrylating agent. To obtain urethane prepolymer B.
The residual amount of isocyanate groups in the sample collected before the addition of the methacrylating agent was 0.089 mol / kg.
As a result of analyzing the urethane prepolymer B, the unsaturated polyurethane prepolymer content was 87% by mass, the number average molecular weight was 21,300, and the methacrylic group content was 0.71% by mass. Therefore, the methacrylic group index was 1.78. And calculated.

[Production Example 3] Production of urethane prepolymer C The same method as in Production Example 1 except that the mixed amount of TDI is 146.7 parts by mass, 245 parts by mass of PPMA and 132 parts by mass of HPMA are used as the methacrylating agent. As a result, urethane prepolymer C was obtained.
The amount of isocyanate group remaining in the sample collected before the addition of the methacrylating agent was 0.076 mol / kg.
As a result of analyzing the urethane prepolymer C, the unsaturated polyurethane prepolymer content was 87% by mass, the number average molecular weight was 22000, and the methacrylic group content was 0.63% by mass. And calculated.

[Production Example 4] Production of urethane prepolymer D The same method as in Production Example 1 except that the mixing amount of TDI is 143.1 parts by mass, 239 parts by mass of PPMA and 130 parts by mass of HPMA are used as the methacrylating agent. As a result, urethane prepolymer D was obtained.
The residual amount of isocyanate group in the sample collected before the addition of the methacrylating agent was 0.064 mol / kg.
As a result of analyzing the urethane prepolymer D, the unsaturated polyurethane prepolymer content was 87% by mass, the number average molecular weight was 23000, and the methacrylic group content was 0.52% by mass. And calculated.

[Production Example 5] Production of urethane prepolymer E To 2000 parts by mass of PL2500, 300 ppm of BTL was added and stirred at 40 ° C until uniform. Next, 150 parts by mass of TDI was added and further stirred, and when it became uniform, the temperature was raised to 65 ° C. Thereafter, the temperature in the reaction system was controlled while measuring the viscosity and temperature of the product in the reaction system. When the temperature reached 360 poise (80 ° C.), a sample was collected, and 139 parts by mass of a methacrylating agent was obtained. PPMA and 70 parts by mass of HPMA were added, and urethane prepolymer E was obtained in the same manner as in Production Example 1 below.
The residual amount of isocyanate group in the sample collected before adding the methacrylating agent was 0.072 mol / kg.
As a result of analyzing the urethane prepolymer E, the unsaturated polyurethane prepolymer content was 93% by mass, the number average molecular weight was 30000, and the methacrylic group content was 0.56% by mass. Therefore, the methacrylic group index was 1.98. And calculated.

[Production Example 6] Production of urethane prepolymer F The same method as in Production Example 5 except that the mixing amount of TDI was 145.3 parts by mass, 132 parts by mass of PPMA and 68 parts by mass of HPMA were used as the methacrylating agent. As a result, urethane prepolymer F was obtained.
The residual amount of isocyanate groups in the sample collected before the addition of the methacrylating agent was 0.059 mol / kg.
As a result of analyzing the urethane prepolymer F, the unsaturated polyurethane prepolymer content was 93% by mass, the number average molecular weight was 30,500, and the methacrylic group content was 0.47% by mass. And calculated.
The characteristics of the urethane prepolymers of Production Examples 1 to 6 are shown in Table 1.

[Example 1]
Urethane prepolymer B: 115 parts by mass, lauryl methacrylate (hereinafter abbreviated as “LMA”): 7.7 parts by mass, PPMA: 13.8 parts by mass, diethylene glycol-2-ethylhexyl ether acrylate (hereinafter, “DEEHEA”) ): 13.8 parts by mass, trimethylolpropane trimethacrylate (hereinafter abbreviated as “TMP-3MA”): 0.8 parts by mass, 2,2-dimethoxy-2-phenylacetophenone (hereinafter referred to as “TMP-3MA”) (Abbreviated as “DMPAP”): 0.9 parts by mass, 2,6-di-t-butyl-p-cresol (hereinafter abbreviated as “BHT”): 0.9 parts by mass at 60 ° C. A photosensitive resin composition was prepared by stirring and mixing in a warm state.
Using the prepared liquid photosensitive resin composition, a flexographic printing plate sample having a plate thickness of 4 mm was prepared by sequentially performing the following molding / exposure step, development step, post-exposure step, and drying step.
Molding / exposure process: exposure of masking exposure amount: 150 mJ / cm ² and relief exposure amount: 650 mJ / cm ² using ALF-213E type plate making machine (Asahi Kasei Chemicals Co., Ltd.) Under the conditions, a molding / exposure process of a 4 mm plate having a 15 cm square printing relief was performed.
In this case, BF-4B4 (Asahi Kasei Chemicals Co., Ltd.) is a polyester sheet having an adhesive layer suitable for a photosensitive resin mainly composed of a polyether polyester-based unsaturated polyurethane prepolymer. Co., Ltd.) and a polyethylene film was used as the cover film.
Development step: APR (registered trademark) detergent type W-10 capable of emulsifying the photosensitive resin composition after recovering the uncured resin (main agent: using an anionic surfactant, manufactured by Asahi Kasei Chemicals Corporation): 2 An aqueous solution containing 0.3% by mass of an antifoaming agent SH-4 (silicone blend, manufactured by Asahi Kasei Chemicals Corporation) was developed as a developer. Developed using an AL-400W type developing machine (drum rotating spray type, manufactured by Asahi Kasei Chemicals Corporation, drum rotation speed: 20 rotations / minute, spray pressure: 0.15 Pa) at a liquid temperature of 40 ° C. and a development time of 10 minutes. Then, it was washed with tap water to such an extent that bubbles from the developer dropped.
Post-exposure process: AL-200UP type post-exposure machine (manufactured by Asahi Kasei Chemicals Co., Ltd.) equipped with both an ultraviolet fluorescent lamp and a germicidal lamp is used in an underwater post-exposure system, and the exposure amount irradiated from each light source is photosensitive. ultraviolet fluorescent lamp in the cured resin surface: 1500 mJ / cm ^2, sterilization lamp: was exposed at 3000 mJ / cm ² and comprising exposure time.
Drying step: ALF-DRYER (manufactured by Asahi Kasei Chemicals Corporation) was used for drying for about 30 minutes until the moisture on the plate surface disappeared.
In addition, among the above-mentioned plate thickness 4 mm flexographic printing plate sample preparation methods, a 7 mm flexographic printing plate sample was prepared in the same manner except that the 7 mm plate molding / exposure step was performed with a masking exposure amount of 500 mJ / cm ² . .

[Example 2]
A photosensitive resin composition was prepared in the same manner as in Example 1 except that urethane prepolymer C was used in place of urethane prepolymer B in Example 1, and a flexographic printing plate sample was prepared.

Example 3
A photosensitive resin composition is prepared in the same manner as in Example 2 except that 0.8 parts by mass of TMP-3MA in Example 2 is changed to 1.5 parts by mass, and a flexographic printing plate sample is prepared. did.

Example 4
A photosensitive resin composition was prepared in the same manner as in Example 2 except that TMP-3MA in Example 2 was changed to 0.8 parts by mass to be 3.1 parts by mass, and a flexographic printing plate sample was prepared. did.

Example 5
Urethane prepolymer F: 108 parts by mass, LMA: 21.5 parts by mass, PPMA: 21.5 parts by mass, TMP-3MA: 2.2 parts by mass, DMPAP: 0.9 parts by mass, BHT: 0.9 parts by mass Was stirred and mixed in a heated state at 60 ° C. to prepare a photosensitive resin composition.
BF which is a polyester sheet having an adhesive layer suitable for a photosensitive resin mainly composed of a polyether-based unsaturated polyurethane prepolymer instead of the support BF-4B4 (manufactured by Asahi Kasei Chemicals Corporation) of Example 1. A flexographic printing plate sample was prepared in the same manner as in Example 1 except that -304 (manufactured by Asahi Kasei Chemicals Corporation) was used.

[Comparative Example 1]
A photosensitive resin composition was prepared in the same manner as in Example 3 except that urethane prepolymer A was used in place of urethane prepolymer C in Example 3, and a flexographic printing plate sample was prepared.

[Comparative Example 2]
A photosensitive resin composition was prepared in the same manner as in Comparative Example 1 except that TMP-3MA of Comparative Example 1 was not mixed, and a flexographic printing plate sample was prepared.

[Comparative Example 3]
The same method as in Example 1 except that urethane prepolymer D is used instead of urethane prepolymer B of Example 1 and TMP-3MA is changed to 0.8 parts by mass to 2.3 parts by mass. A photosensitive resin composition was prepared with a flexographic printing plate sample.

[Comparative Example 4]
The same method as Example 5 except that urethane prepolymer E is used instead of urethane prepolymer F of Example 5 and TMP-3MA is changed to 3.1 parts by mass instead of 2.2 parts by mass. A photosensitive resin composition was prepared with a flexographic printing plate sample.

[Comparative Example 5]
A photosensitive resin composition was prepared in the same manner as in Comparative Example 4 except that TMP-3MA in Comparative Example 4 was changed to 3.1 parts by mass to 0.8 parts by mass, and a flexographic printing plate sample was prepared. did.

Evaluation of the viscosity of the photosensitive resin compositions prepared in Examples 1 to 5 and Comparative Examples 1 to 4, Shore A hardness, tensile physical properties, notch crack resistance, and support adhesion of flexographic printing plate samples was performed.
Table 2 shows the characteristics and evaluation results of the photosensitive resin compositions of Examples 1 to 5 and Comparative Examples 1 to 4.
The total amount of ethylenically unsaturated monomers in Table 2 represents the total amount of the methacrylating agent, LMA, PPMA, DEEHEA and TMP-3MA present as a diluent for the urethane prepolymer. Moreover, the ratio of the trifunctional or higher-functional unsaturated monomer is represented by mass% of TMP-3MA in the total amount of the ethylenically unsaturated monomer.

From the results in Table 2, the following contents can be read.
(1) A flexographic printing plate obtained from the photosensitive resin composition of Examples 1 to 5 using an unsaturated polyurethane prepolymer having a methacryl group index in the range of 1.5 to 1.8 is Shore A. The hardness is in a range of less than 25 degrees, and a tensile breaking strength of 4 MPa or more and a tensile breaking elongation of 400% or more are obtained as a measure of the mechanical strength of the corrugated board printing plate. Further, the high level of notch crack resistance of 50 seconds or more is realized.
(2) Compared to Example 3, except that an unsaturated polyurethane prepolymer having a methacryl group index of 1.98 is used, Comparative Example 1, which has the same resin composition, shows the tensile breaking strength and tensile breaking elongation. Although the level of mechanical properties to be obtained is determined to be substantially equivalent due to the difference in balance, the Shore A hardness exceeds 25 degrees and is 11 degrees higher than that of Example 3. Further, in Comparative Example 2 in which the same unsaturated polyurethane prepolymer as in Comparative Example 1 was used and the hardness was reduced to be less than 25 degrees Shore A hardness by reducing the amount of TMP-3MA, the equivalent Shore A hardness was exhibited. Although the tensile elongation at break is the same as in Example 1 or 2, the tensile strength at break is greatly reduced.
(3) Compared to Example 5 using an unsaturated polyurethane prepolymer having a methacryl group index of 1.69, in Comparative Example 4 using an unsaturated polyurethane prepolymer having a methacryl group index of 1.98 in the same polyol species, Although the Shore A hardness exceeds 25 degrees, and in Comparative Example 5, it is in the range below the Shore A hardness of 25 degrees, but the tensile breaking strength is 4 MPa or more, which is obtained as a measure of the mechanical strength of the corrugated printing plate, and the tensile breaking elongation is It has not achieved over 400%.
(4) Comparative Example 3 is an example using an unsaturated polyurethane prepolymer having a methacryl group index of 1.41, which is in a range of less than 25 degrees Shore A hardness and is obtained as a measure of the mechanical strength of the corrugated board printing plate. The tensile strength at break of 4 MPa or higher and the tensile elongation at break of 400% or higher are satisfied, but the support adhesion is unacceptable.
From the above results, using an unsaturated polyurethane prepolymer having a methacryl group index of 1.50 to 1.85, the flexographic printing plate having a Shore A hardness of less than 25 degrees can increase mechanical strength. it can.

Example 6
A flexographic printing plate was prepared using a negative film containing solid images, fine characters and halftone dots.
First, the photosensitive resin composition prepared in Comparative Example 1 was used as a cap resin, applied to a cover film in the region of fine characters and halftone dot image portions with a uniform thickness of 0.3 mm, and from there as a base resin A 4 mm flexographic printing plate as a cap plate was produced under the same conditions as in Example 1 except that the support was laminated after applying the photosensitive resin composition prepared in Example 1.
The obtained flexographic printing plate was subjected to printing on a B-stage sheet having a paper quality of 120 g / m ² for the front liner (using recycled paper), the core and the back liner. As a result, a sufficient ink concealment ratio was obtained in the solid image area. And a printed material having excellent reproducibility of fine characters and halftone dot image portions.
Assuming handling in printing work, when the relief was pressed against the floor and dragged repeatedly, no abnormal traces were left on the relief.

[Comparative Example 6]
About the manufacturing method of the 4 mm flexographic printing plate of Example 6, except that it is not a cap plate but a single-layer plate (a plate manufactured with one kind of resin) using the photosensitive resin composition prepared in Comparative Example 1 All prepared flexographic printing plates by the same method as in Example 6, and performed the same printing evaluation as in Example 6.
As a result, the ink concealment rate of the solid image was not sufficient under the same printing conditions as in Example 6. Further, when printing was performed while adjusting the printing pressure gradually, the effect of image weight became significant in the fine character and halftone dot image portions before the ink concealment rate of the solid image became sufficient. Eventually, the core of the corrugated board was crushed without reaching a level satisfying the ink concealment rate.

[Comparative Example 7]
Regarding the method for producing a 4 mm flexographic printing plate of Example 6, all examples except that the photosensitive resin composition prepared in Comparative Example 2 was used instead of the photosensitive resin composition prepared in Example 1 as the base resin. A flexographic printing plate was prepared by the same method as in Example 6, and the same printing test as in Example 6 was performed.
As a result, a printed matter having a sufficient ink concealment ratio in the solid image area and excellent reproducibility of fine character and halftone dot image portions was obtained as in Example 6.
However, assuming that the printing plate surface is handled in the printing operation, when the relief is pressed against the floor and dragged, cracks occur on the side of the relief, and the same operation is repeated several times to complete the fine relief completely. I dropped out.

[Example 7 and Comparative Example 7]
A flexographic printing plate produced by the same method as in Example 6 and a flexographic printing plate produced by the same method as in Comparative Example 6 were prepared by a design composed of a general solid image and relatively large letters on the cardboard case. .
The prepared flexographic printing plate was subjected to comparative evaluation by commercial printing using a B-stage sheet in which the paper quality of the front liner and the back liner was 150 g / m ² and the paper quality of the core was 90 g / m ² .
As a result, the flexographic printing plate prepared by the same method as in Comparative Example 6 had an optimum printing speed of 100 m / min from the viewpoint of ink bleed of the solid image, but the flexographic printing prepared by the same method as in Example 6 was used. In the plate, it was possible to increase the printing speed up to 160 m / min while maintaining the same print quality.

  The photosensitive resin composition of the present invention can be suitably used particularly in the field of flexographic printing plates for cardboard printing.

Claims (7)

Unsaturated polyurethane prepolymer whose main chain terminal is modified with a methacryl group: 100 parts by mass,
Ethylenically unsaturated monomer: 10 to 150 parts by mass,
Photopolymerization initiator: 0.01 to 10 parts by mass,
Including
The photosensitive resin composition for flexographic printing plates whose methacryl group index calculated | required by following formula (1) of the said unsaturated polyurethane prepolymer is the range of 1.50-1.85.
Methacryl group index = X / (8500 / Y) Formula (1)
(In the formula, X represents the methacrylic group content (%) in the unsaturated polyurethane prepolymer, and Y represents the number average molecular weight of the unsaturated polyurethane prepolymer.)   The photosensitive resin composition for flexographic printing according to claim 1, wherein the unsaturated polyurethane prepolymer has a number average molecular weight in the range of 10,000 to 40,000.   The unsaturated polyurethane prepolymer is obtained by reacting a low molecular compound containing a methacryl group and a hydroxyl group in one molecule and having a molecular weight in the range of 100 to 500 after the urethanization reaction with a polyol and a polyisocyanate. The photosensitive resin composition for flexographic printing plates of Claim 1 or 2.   The photosensitive resin composition for flexographic printing plates according to claim 3, wherein the polyol comprises a mixture of a polyether polyol and a polyester polyol.   The polyfunctional monomer which has 3 or more of methacryl groups and / or acryl groups in 1 molecule among the said ethylenically unsaturated monomers is any one of Claims 1-4 which is 0.5-15 mass%. The photosensitive resin composition for flexographic printing plates as described. Each process of the following (A)-(C),
(A) The cured part which exposes the surface of the molded object formed using the photosensitive resin composition for flexographic printing plates as described in any one of Claims 1-5, and forms a hardening part in the said molded object Forming process,
(B) a development step of developing the cured portion with a cleaning liquid;
(C) an actinic ray irradiation step for irradiating the surface of the developed cured portion with an actinic ray,
A method for producing a flexographic printing plate comprising   A flexographic printing plate obtained by the production method according to claim 6.