JP2019109436A - Flexographic printing original plate and flexographic printing plate - Google Patents

Abstract

To provide a flexographic printing original plate that gives a flexographic printing plate that reduces printing unevenness on corrugated cardboard, has excellent durability in repeated bonding in printing (particularly, prevents cracking), and has reduced chipping during use.SOLUTION: A printing original plate for a flexographic printing plate has a support, and a photosensitive resin layer put on the support. The photosensitive resin layer has at least one elastomer binder (A), at least one ethylene unsaturated copolymerizable monomer (B), at least one hydrocarbon compound (C), and at least one photopolymerizable initiator (D). In corrugated cardboard printing using a flexographic printing plate produced from the flexographic printing original plate, an absolute value of a difference between a maximum value and a minimum value of an area percentage of a dot diameter ink-transferred onto the corrugated cardboard by a 30LPI10% dot formation part is less than 6.0%.SELECTED DRAWING: None

Description

  The present invention relates to a flexographic printing original plate, and a flexographic printing plate.

  A photosensitive resin composition for flexographic printing contains, as described in, for example, Patent Documents 1 and 2, a thermoplastic elastomer, a photopolymerizable unsaturated monomer, a plasticizer, and a photopolymerization initiator. It is common.

  As a composition for flexographic printing plate, a polyester film or the like is used as a support, and a layer (photosensitive resin layer) containing the above-mentioned photosensitive resin composition is laminated thereon, and, if necessary, with a negative film In order to smooth the contact, it is generally constructed by further laminating a slip layer or a protective layer or an ultraviolet shielding layer containing an infrared sensitive material that can be removed by an infrared laser on the above layer.

  In order to make a flexographic printing plate from such a photosensitive composition for flexographic printing plate, first, the entire surface is exposed to ultraviolet light (back exposure) through the support to provide a thin uniform cured layer, and then through the negative film or Image exposure (relief exposure) is performed on the surface of the photosensitive resin layer directly from above the ultraviolet shielding layer, and the unexposed area is washed away with a developing solvent or after heat melting and absorption removal by an absorption layer, post-processing exposure It is generally manufactured by

JP, 2000-155418, A JP 02-108632 A JP 11-249305 A

  The flexographic printing plate produced as described above is used for printing film, paper, cardboard and the like. Here, in the direct printing of corrugated cardboard, the pressure applied to the portion other than the bonding portion is relatively lower than the pressure applied at the time of printing between the liner of the corrugated cardboard sheet and the bonded portion of the core base sheet As a result, a phenomenon (a phenomenon called step effect, washing plate effect or the like) in which density unevenness of printed matter (cardboard) occurs is generated. For example, Patent Document 3 describes a step, but a clear description of a method for improving such density unevenness can not be found. In addition, when the printing pressure as a whole at the time of printing becomes high, the density unevenness becomes larger. Therefore, the printing pressure changes depending on the setting of the printing conditions, and the quality of the printed matter may vary. Furthermore, the photosensitive resin composition used for the production of a flexographic printing plate for corrugated board often contains a plasticizer having no crosslinkable group, so that the flexographic printing plate is used repeatedly. Chipping occurs.

  According to the present invention, it is possible to obtain a flexographic printing plate which has reduced printing unevenness on a cardboard, is excellent in durability at repeated application during printing (in particular, suppresses the occurrence of cracks) and has reduced chipping in use. It aims at providing a flexographic printing original plate.

  As a result of intensive studies to solve the above problems, the present inventors use a flexographic printing original plate having a support as shown below and a specific photosensitive resin layer laminated on the support. Thus, the present inventors have found that it is possible to obtain a flexographic printing plate which is excellent in durability at the time of repeated application at the time of printing and in which the haze in use is reduced.

  That is, the factor which can obtain the flexographic printing plate (Hereafter, it is also only mentioned a "printing plate".) Excellent in the durability at the time of the pasting at the time of printing thinks as follows. However, the factor is not limited to this. The elastomeric binder (A) contained in the photosensitive resin layer is bonded to the ethylenically unsaturated copolymerizable monomer (B) by cleavage of the photopolymerizable initiator (D) at the time of exposure to generate radicals. A crosslinking reaction occurs and becomes insoluble in the developer. This crosslinking reaction is most likely to progress on the surface of the printing plate to which light is irradiated, and the inside of the printing plate tends to be difficult to progress because the light to be irradiated is reduced as compared to the surface of the printing plate There is. Therefore, the degree of crosslinking of the photosensitive resin differs between the surface of the printing plate and the inside of the printing plate, and a hardness gradient is formed in the photosensitive resin layer.

  At the time of corrugated board printing, the ink is transferred to the corrugated board by transferring the ink from the anilox roll to the surface of the printing plate and pressing the corrugated board against the surface of the printing plate, but the pressure applied to the surface of the printing plate at the time of printing The printing plate is deformed so that the contact surface with the cardboard becomes larger, and the ink transfer area becomes larger. On the other hand, if the hardness of the surface of the printing plate is high, the amount of deformation due to pressure applied to the surface of the printing plate will be small, and the transfer area of the ink will be small. On the other hand, when the hardness of the surface of the printing plate is too high, the shape of the surface of the corrugated board is deformed and crushed, and the transfer area of the ink is varied. However, even if the hardness of the surface of the printing plate is too high, if the hardness inside the printing plate is sufficiently low, the pressure applied to the surface of the printing plate during printing is transmitted to the inside of the printing plate, and the printing plate It has been found that the pressure can be absorbed inside and the shape of the surface of the cardboard can be prevented from being deformed and crushed.

  Thus, as a result of intensive studies, the inventors of the present invention have found that the microhardness of the printing surface side of the flexographic printing plate and the microhardness of a portion at a distance of 1.5 mm from the printing surface with respect to the cross section of the flexographic printing plate. When the difference with the hardness is 6 ° or more, in corrugated board printing using a flexographic printing plate, the maximum value and the minimum value of the area ratio of the dot diameter of ink transferred onto the corrugated board by the 30 LPI 10% dot forming portion It was found that the absolute value of the difference of was less than 6.0%.

  In addition, it has been found that the printed matter printed by the printing plate specified such that the absolute value of the difference between the maximum value and the minimum value is less than 6.0% has a significantly reduced difference in density unevenness visually. The As described above, the density unevenness due to the step during printing depends on the density dispersion of the ink transfer portion of the dot, and by controlling the absolute value of the difference between the maximum value and the minimum value of the area ratio of the dot diameter, It is surprising that the variation in ink density can be suppressed.

That is, the present invention is as follows.
[1]
A printing original plate for flexographic printing plate, comprising a support and a photosensitive resin layer laminated on the support,
The photosensitive resin layer is
At least one elastomeric binder (A),
At least one or more ethylenically unsaturated copolymerizable monomers (B),
At least one or more hydrocarbon compounds (C),
Containing at least one photopolymerization initiator (D),
In cardboard printing using a flexographic printing plate manufactured from the flexographic printing original plate, the absolute value of the difference between the maximum value and the minimum value of the area ratio of the dot diameter transferred onto the cardboard by the 30 LPI 10% dot forming portion Less than 6.0%,
Flexographic printing original plate.
[2]
The difference between the microhardness on the printing surface side of the flexographic printing plate and the microhardness of a portion at a distance of 2.0 mm from the printing surface with respect to the cross section of the flexographic printing plate is 6 ° or more.
The flexographic printing original plate as described in [1].
[3]
The styrene content of the elastomeric binder (A) is 30 to 40 parts by mass with respect to 100 parts by mass of the elastomeric binder (A),
The flexographic printing original plate as described in [1] or [2].
[4]
The ethylenically unsaturated covalent monomer (B) contains 3 to 10 parts by mass of a diacrylate monomer containing 7 or more carbon atoms with respect to 100 parts by mass of the photosensitive resin layer, [1] to [3] The flexographic original version as described in any of the above.
[5]
The flexographic original plate according to any one of [1] to [4], wherein the photosensitive resin composition layer contains at least two or more kinds of the photopolymerizable initiators (D).
[6]
Prepared from the flexographic printing plate precursor according to any one of [1] to [5],
Flexographic printing plate.

  According to the flexographic printing original plate concerning the present invention, it is possible to reduce the excellent durability at the time of repeated application at the time of printing and the chipping in use.

It is a schematic diagram which shows the evaluation method used in order to evaluate the scuff resistance in the Example.

  Hereinafter, modes for carrying out the present invention (hereinafter, simply referred to as "the present embodiment") will be described in detail. The following present embodiment is an example for describing the present invention, and is not intended to limit the present invention to the following contents. The present invention can be appropriately modified and implemented within the scope of the gist of the present invention.

[Flexographic printing original plate]
The flexographic printing plate precursor of the present embodiment has a support and a photosensitive resin layer laminated on the backing plate. A printing plate for flexographic printing plate (hereinafter also referred to as “flexo printing plate construction”). It is. In addition, the photosensitive resin layer of the present embodiment includes at least one or more types of elastomeric binders (A) (hereinafter, also simply referred to as “(A)”) and at least one or more types of ethylenically unsaturated copolymerizable monomers (B) (hereinafter also referred to simply as "(B)"), at least one or more hydrocarbon compounds (C) (hereinafter referred to simply as "(C)"), and at least one or more types of light And a polymerizable initiator (D) (hereinafter, also simply referred to as "(D)"). Furthermore, in the corrugated board printing using the flexographic printing plate manufactured from the flexographic printing original plate of the present embodiment, the maximum value and the minimum value of the area ratio of the dot diameter ink transferred onto the corrugated board by the 30 LPI 10% dot forming portion The absolute value of the difference is less than 6.0%.

(Support)
The support of the present embodiment is not particularly limited as long as it can support the photosensitive resin layer. As the support, for example, a polyester film is suitably used, and particularly preferably polyethylene terephthalate is mentioned.

(Photosensitive resin layer)
The photosensitive resin layer of the present embodiment is laminated on a support. The photosensitive resin layer can be obtained, for example, by sheet-forming the photosensitive resin composition constituting the photosensitive resin layer, bringing it into close contact with a support by roll lamination, and performing heat pressing after lamination. Moreover, according to such a method, the photosensitive resin layer further excellent in thickness accuracy can be obtained.

  The flexographic printing plate construction of the present embodiment can be prepared by various methods using a support, a photosensitive resin composition which is a raw material of a photosensitive resin layer, and the like. For example, the raw material of the photosensitive resin composition is dissolved in a suitable solvent such as chloroform, tetrachloroethylene, methyl ethyl ketone, toluene or the like and mixed, and cast into a mold to evaporate the solvent, and the plate is used as it is It can be Moreover, although it can knead | mix with a calender roll, a press, etc. after kneading | mixing with a kneader, a roll mill, or a screw extruder without using a solvent, it can be shape | molded to a desired thickness. It is not limited to what is obtained by the preparation method.

  Since the composition for flexographic printing plate usually has tackiness, it is a photosensitive resin in order to improve the contact with a negative film to be overlaid thereon during platemaking, or to enable reuse of the negative film. A solvent-soluble thin flexible protective layer (see, for example, Japanese Patent Publication No. 5-13305) may be further provided on the surface of the layer. Further, instead of the flexible protective layer, an ultraviolet shielding layer containing an infrared sensitive material may be provided, and the ultraviolet shielding layer itself may be used as a negative by direct drawing with an infrared laser. In either case, when the unexposed area of the photosensitive resin layer is washed out after the exposure is completed, the thin flexible protective layer or the ultraviolet shielding layer is also removed simultaneously.

  As a solvent-soluble thin flexible protective layer, for example, a layer of polyamide, partially saponified polyvinyl acetate, cellulose ester or the like which is soluble in the washing solution is to be provided on the surface of the photosensitive resin layer, This may be dissolved in an appropriate solvent and the solution coated directly on the photosensitive resin layer. Alternatively, the film may be coated (protective film) on a film of polyester, polypropylene or the like, and then this protective film may be laminated or pressed onto the photosensitive resin layer to transfer the protective film.

  The protective layer is obtained by sheet-forming the photosensitive resin composition constituting the photosensitive resin layer, bringing the photosensitive resin composition into close contact with the protective film by roll lamination, and heat pressing after lamination, as in the case of the support.

<Elastomer binder (A)>
The elastomeric binder (A) of the present embodiment means a polymer which can be plasticized at high temperature to be molded, and exhibits a property as a rubber elastic body at normal temperature. Among the elastomeric binders (A), thermoplastic block copolymers having aromaticity are preferable from the viewpoint of shortening of plate making time and image reproducibility of a printing plate.

  The thermoplastic block copolymer having aromaticity means a copolymer having at least a polymer block mainly composed of a vinyl aromatic hydrocarbon and a polymer block mainly composed of a conjugated diene. In the present specification, the term "main body" means that the content is 70% by mass or more.

  The vinyl aromatic hydrocarbon is not particularly limited, and examples thereof include styrene, P-methylstyrene, tertiary butylstyrene, α-methylstyrene, 1,1-diphenylethylene and the like, among them from the viewpoint of availability And styrene are preferred. One of these may be used alone, or two or more of these may be used in combination.

  The content of the vinyl aromatic hydrocarbon is preferably 10 parts by mass or more from the viewpoint of the cold flow resistance of the uncured resin structure with respect to 100 parts by mass of the elastomeric binder (A), and is solvent resistant From the viewpoint, it is preferably 60 parts by mass or less, more preferably 20 parts by mass to 50 parts by mass, and still more preferably 30 parts by mass to 40 parts by mass.

  The conjugated diene is not particularly limited, and examples thereof include butadiene and isoprene and / or a hydrogenated product thereof. One of these may be used alone, or two or more of these may be used in combination. The hydrogenation of the conjugated diene may be carried out after forming a thermoplastic block copolymer having aromaticity.

  Among them, butadiene and / or a hydrogenated product thereof is preferable from the viewpoints of reducing the tackiness of the surface, the abrasion resistance of the printing plate, and the haze resistance.

  The vinyl content in the conjugated diene block is preferably 5.0 parts by mass to 40 parts by mass from the viewpoint of the scuff resistance with respect to 100 parts by mass of the elastomeric binder (A).

  The structure of the thermoplastic block copolymer having aromaticity may be linear or radial of 3 to 6 branches from the viewpoint of easiness of production.

  The thermoplastic block copolymer having an aromatic group contains 10% by mass or more of a diblock having a vinyl aromatic hydrocarbon block and a conjugated diene block from the viewpoint of the flexibility of the printing plate and the scuff resistance. It is preferable to do.

  The elastomeric binder (A) may further contain a block mainly composed of ethylene or propylene, if necessary.

  The weight average molecular weight of the elastomeric binder (A) is not particularly limited, but it is preferable that the balance between molding processability and solid retention of the photosensitive resin to be obtained be excellent, and polystyrene conversion using gel permeation chromatography (GPC) The standard polystyrene equivalent is preferably 8 to 400,000.

  The content of the elastomeric binder (A) is preferably 20 parts by mass or more from the viewpoint of the cold flow resistance and the scuff resistance of the uncured resin structure with respect to 100 parts by mass of the photosensitive resin layer. From the viewpoint of the property, it is preferably 90 parts by mass or less, more preferably 30 parts by mass or more, more preferably 75 parts by mass or less, still more preferably 40 parts by mass or more, still more preferably 60 parts by mass Less than.

  If necessary, the photosensitive resin layer can contain 20 parts by mass or less of an elastomer (other elastomer) other than the elastomeric binder (A). As another elastomer, polyolefin, polyester, polyurethane etc. are mentioned, for example.

<Ethylene unsaturated copolymerizable monomer (B)>
The ethylenically unsaturated covalent monomer (B) of the present embodiment preferably contains a diacrylate monomer (for example, 1,9-nonanediol acrylate) containing 7 or more carbon atoms. The diacrylate monomer containing 7 or more carbon atoms can be further appropriately selected from the following specific compounds.

  The ethylenically unsaturated copolymerizable monomer (B) is not particularly limited, and, for example, esters such as acrylic acid, methacrylic acid, fumaric acid and maleic acid; derivatives of acrylamide and methacrylamide; allyl esters, styrene and derivatives thereof And N-substituted maleimide compounds.

  Specific examples of the ethylenically unsaturated copolymerizable monomer (B) include diacrylates and dimethacrylates of alkanediols such as hexanediol and nonanediol; ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, polyethylene glycol, butylene Diacrylates and dimethacrylates of glycols; trimethylolpropane tri (meth) acrylate, dimethylol tricyclodecane di (meth) acrylate, isoboronyl (meth) acrylate, phenoxy polyethylene glycol (meth) acrylate, pentaerythritol tetra (meth) acrylate N, N'-hexamethylene bisacrylamide and methacrylamide, styrene, vinyl toluene, divinyl benzene, dia Lil phthalate, triallyl cyanurate, fumaric acid diethyl ester, fumaric acid dibutyl ester, fumaric acid dioctyl ester, fumaric acid distearyl ester, fumaric acid butyl octyl ester, fumaric acid diphenyl ester, fumaric acid dibenzyl ester, maleic acid dibutyl ester And maleic acid dioctyl ester, fumaric acid bis (3-phenylpropyl) ester, fumaric acid dilauryl ester, fumaric acid dibehenyl ester, N-lauryl maleimide and the like. One of these may be used alone, or two or more of these may be used in combination.

  The ethylenically unsaturated covalent monomer (B) preferably contains 1 to 20 parts by mass of a diacrylate monomer containing 7 or more carbon atoms, and 3 to 10 parts by mass with respect to 100 parts by mass of the photosensitive resin layer. And more preferred.

  The content of the ethylenically unsaturated copolymerizable monomer (B) is at least a predetermined lower limit value with respect to 100 parts by mass of the photosensitive resin layer, thereby suppressing a decrease in the formation of fine points and characters, In order to suppress the fall of the cold flow resistance when the photosensitive resin layer before exposure is laminated | stacked, and the fall of the softness of a printing plate by being below the upper limit of this, 1.0-20 mass is preferable. %.

<Hydrocarbon compound (C)>
Although it does not specifically limit as a hydrocarbon compound (C) of this embodiment, For example, it is resin which consists of substance and carbon and hydrogen, and a paraffin hydrocarbon, an olefin hydrocarbon, a naphthene hydrocarbon etc. are mentioned, for example. One of these may be used alone, or two or more of these may be used in combination.

Paraffinic hydrocarbons are saturated chain compounds of the molecular formula C _n H _{2n + 2} , and include unbranched normal paraffins and branched isoparaffins.

The olefinic hydrocarbon is a chain hydrocarbon having a double bond, and when there is one double bond, it is represented by a general formula of C _n H _{2 n} .

A naphthenic hydrocarbon is a hydrocarbon containing at least one saturated ring (naphthenic ring) in one molecule, and is represented by the general formula of C _n H _{2 n} . Naphthenic hydrocarbons present in crude oil and petroleum products are those in which two or three naphthene rings are connected, those condensed with an aromatic ring, and further, various paraffin side chains are attached to the naphthenic ring and the condensed ring. There are things etc.

<Photoinitiator (D)>
The photopolymerization initiator (D) of the present embodiment means a compound that absorbs light energy and generates a radical. Moreover, although various well-known things can be used for a photoinitiator (D), It is suitable to use various organic carbonyl compounds, especially an aromatic carbonyl compound.

  Specific examples of the photopolymerization initiator (D) include, for example, benzophenone, 4,4-bis (diethylamino) benzophenone, t-butylanthraquinone, 2-ethylanthraquinone, 2,4-diethylthioxanthone, isopropylthioxanthone, 2,4 Thioxanthones such as dichlorothioxanthone; diethoxyacetophenone, 2,2-dimethoxy-1,2-diphenylethan-1-one, 2-hydroxy-2-methyl-1-phenylpropan-1-one, benzyl dimethyl ketal, Acetophenones such as 1-hydroxycyclohexyl-phenyl ketone, 2-methyl-2-morpholino (4-thiomethylphenyl) propan-1-one, 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butanone Benzoin methine Benzoin ethers such as ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin isobutyl ether; 2,4,6-trimethylbenzoyl diphenyl phosphine oxide, bis (2,6-dimethoxybenzoyl) -2,4,4-trimethylpentyl phosphine Oxides, acyl phosphine oxides such as bis (2,4,6-trimethyl benzoyl) -phenyl phosphine oxide; methyl benzoyl formate; 1,7-bisacridinyl heptane; 9-phenyl acridine and the like. One of these may be used alone, or two or more of these may be used in combination. However, the photosensitive resin layer preferably contains at least two or more photopolymerization initiators (D), and specifically, 2,2-dimethoxy-1,2-diphenylethane-1-one, A combination with 2-benzyl-2-dimethylamino-4′-morpholinobutyrophenone may be mentioned.

  The content of the photopolymerization initiator (D) is equal to or more than a predetermined lower limit value with respect to 100 parts by mass of the photosensitive resin layer, thereby suppressing a decrease in formation of fine points and characters, and a predetermined upper limit value The amount is preferably 1.0 part by mass to 5.0 parts by mass, and more preferably 1.5 parts by mass to 4.0 parts by mass in order to suppress a decrease in the transmittance of active light such as ultraviolet light by being as follows. It is.

<Conjugated diene rubber>
The photosensitive resin layer of the present embodiment can further contain a conjugated diene rubber.

  Conjugated diene rubbers are obtained from dienes. As the diene, isoprene and / or butadiene are preferable in terms of availability, and butadiene is more preferable from the viewpoint of cake resistance.

  Specific examples of conjugated diene rubbers include polybutadiene and polyisoprene. Moreover, B-2000 (brand name by Nippon Soda Co., Ltd.) is mentioned as a commercial item. One of these may be used alone, or two or more of these may be used in combination.

  The vinyl content in the conjugated diene rubber is preferably as high as possible from the viewpoint of the formation of minute images and resistance to scuffing, preferably 50 mol% or more, more preferably 70 mol% or more, and still more preferably 75 mol% It is above. The vinyl content in the conjugated diene rubber can be determined from proton NMR (nuclear magnetic resonance spectrum).

  The weight average molecular weight (Mw) of the conjugated diene rubber is preferably lower from the viewpoint of handleability and compatibility of the photosensitive resin composition, and higher from the viewpoint of scuff resistance, preferably 1000 to 50000, More preferably, it is 2000-30000, More preferably, it is 3000-20000. The weight average molecular weight of the conjugated diene rubber can be measured by gel permeation chromatography (GPC) as in the measurement of the weight average molecular weight of the component (C).

  The content of the conjugated diene rubber is preferably 3.0% by mass or more from the viewpoint of the image reproducibility, the scuff resistance, and the flexibility with respect to the total amount (100% by mass) of the photosensitive resin layer, and the printing plate From the viewpoint of the solid maintenance property of the photosensitive composition for use, the content is preferably 40% by mass or less, more preferably 5.0 to 30% by mass, and still more preferably 7.0 to 20% by mass

  The photosensitive resin layer of the present embodiment may further contain various auxiliary additive components, for example, a plasticizer, a thermal polymerization inhibitor, an ultraviolet light absorber, an antihalation agent, a light stabilizer, an antioxidant and the like, as desired. Can.

[Flexographic printing plate]
The flexographic printing plate of the present embodiment is prepared from the flexographic printing plate (photosensitive composition for flexographic printing plate) described above. As a general method of making a flexographic printing plate from a photosensitive composition for flexographic printing plate, first, the entire surface is exposed to ultraviolet light through the support (back exposure), a thin uniform cured layer is provided, and then through a negative film, Alternatively, image exposure (relief exposure) is performed on the surface of the photosensitive resin layer directly from above the ultraviolet shielding layer, and the unexposed area is washed away with a developing solvent, or after heat melting and absorption and removal by an absorption layer, post-processing exposure Manufactured by doing. Here, a "hardened layer" means the layer hardened | cured, for example by receiving the irradiation of an ultraviolet-ray among photosensitive resin layers.

(30LPI 10% area ratio of dot diameter)
In the corrugated board printing using the flexographic printing plate of the present embodiment, the absolute value of the difference between the maximum value and the minimum value of the area ratio of the dot diameter transferred onto the corrugated board by the 30 LPI 10% dot forming portion is 6.0. %, Preferably less than 5.6%, more preferably less than 5.3. The absolute value of the said difference is measured by the method as described in the Example mentioned later.

(Micro hardness)
The difference between the microhardness on the printing surface side of the flexographic printing plate of this embodiment and the microhardness of a portion at a distance of 2.0 mm from the printing surface with respect to the cross section of the flexographic printing plate is preferably 6 ° or more. More preferably, it is 7 degrees or more, Preferably it is 8 degrees or more. The said difference is measured by the method as described in the Example mentioned later.

〔cardboard〕
The corrugated paperboard of the present embodiment is not particularly limited as long as the paper is bonded to one side or both sides of the paper formed into a wave shape. The type of corrugated cardboard is a single-sided corrugated cardboard with core base paper pasted in a corrugated form into a single liner, a double-sided corrugated cardboard with a liner laminated to the top of the single-sided corrugated cardboard, and a single-sided corrugated cardboard on one side of a double-sided corrugated cardboard. Double-sided corrugated cardboard with tops laminated, double-sided corrugated cardboard with double-sided corrugated cardboard with double-sided corrugated cardboard with single-sided corrugated cardboard laminated on one side, A flute, B flute, C flute, E It is classified into flute, F flute, G flute and so on. The weight of the core (flute) is specified from the viewpoint of strength as a corrugated cardboard for exterior use, and a core of 80 to 160 g is used, but it is preferably 160 g from the viewpoint of strength.

  The Shore A hardness of the printing plate (thickness: 3.94 mm) of the present embodiment is preferably 50 ° or less, more preferably 45 ° or less from the viewpoint of suppressing transfer unevenness of the ink generated at the time of corrugated board printing. And more preferably 40 ° or less. After leaving a 3.94 mm thick flexographic printing plate in a constant temperature and humidity chamber at a temperature of 23 ° C. and a relative humidity of 50% for 1 day, a JIS constant pressure load device GS-710 (a durometer manufactured by Techlock Co., Ltd., durometer GS-719G ASTM) It can measure using: D2240A, JIS: K6253A, ISO: 7619A). The value after 15 seconds of load (mass 1 kg) on a solid surface is taken as Shore-A hardness.

  As image exposure for changing the surface tension of the surface of a printing plate, after exposing the ultraviolet-ray of a 200-300 nm wavelength range, you may expose with the ultraviolet ray of a 310-400 nm wavelength range.

  Either of the exposure from the negative film side (relief exposure) and the exposure from the support side (back exposure) may be performed first, or both may be performed simultaneously.

  Examples of the exposure light source include high pressure mercury lamps, ultraviolet fluorescent lamps, carbon arc lamps, xenon lamps, and diode lamps.

  Cleaning out of the unexposed area by the developing solvent is performed by jet from a nozzle or by brushing with a brush.

  As the post-treatment exposure, a method of irradiating the surface with light having a wavelength of 300 nm or less is generally used. If necessary, light larger than 300 nm may be used in combination.

<Hydrocarbon-containing cleaning solvent>
The hydrocarbon-containing cleaning solvent (developing solvent) of the present embodiment is used as a cleaning solvent for the photosensitive resin layer. Moreover, it is used also as a developing solvent used for developing an unexposed part. Examples of the hydrocarbon-containing cleaning solvent (E) include esters such as heptyl acetate and 3-methoxybutyl acetate; petroleum fractions, hydrocarbons such as toluene and decalin; chlorinated organic solvents such as tetrachlorethylene; propanol And alcohols such as butanol and pentanol, and mixtures of two or more thereof. In particular, a mixed solvent of decalin, tetrachlorethylene and propanol is preferable.

  Hereinafter, the present embodiment will be described in more detail based on examples, but the present embodiments are not limited to the following examples.

(Preparation of photosensitive resin composition)
Each material was mixed according to the composition shown in the following Table 1 and sufficiently stirred to obtain each photosensitive resin composition.

(Styrene content)
Analysis of Thermoplastic Elastomer
1) Total styrene content of block copolymer It calculated from the absorption intensity of 262 nm using the ultraviolet spectrophotometer (Hitachi UV200).
2) Number average molecular weight of block copolymer The number average molecular weight of the block copolymer is determined by gel permeation chromatography (GPC, measuring apparatus; manufactured by Waters, column; three combinations of MINIMIX manufactured by Polymer Laboratory, Solvent: tetrahydrofuran, measurement conditions; temperature 35 ° C., flow rate 0.4 mL / min, sample concentration 0.1% by mass, injection amount 40 μL) to obtain a chromatogram. The number average molecular weight herein is the following standard polystyrene (manufactured by Waters, 1.54 × 10 ⁶ , 4.1 × 10 ⁵ , 1.10 × 10 ⁵ , 3.5 × 10 ⁴ , 8.5 × 10 It is a conversion value from the calibration curve obtained by measuring at ³ , 1.8 × 10 ³ ).

The details of the materials in Table 1 are as follows.
[Elastomer binder (A)]
SBS-A (Styrene-Butadiene Copolymer)
SBS-B (Styrene-Butadiene Copolymer)
SBS-C (Styrene-Butadiene Copolymer)
SBS-D (Styrene-Butadiene Copolymer)
SBS-E (styrene-butadiene copolymer [ethylenically unsaturated copolymerizable monomer (B)]
1,9-nonanediol acrylate [hydrocarbon compound (C)]
Dodecane [photopolymerization initiator (D)]
2,2-Dimethoxy-1,2-diphenylethaneethane-1-one [conjugated diene compound]
B-2000 (product name of Nippon Soda Co., Ltd.)
[Washing solution]
3-methoxybutyl acetate

(Synthesis of elastomeric binder (A))
After thoroughly replacing the 10 L stainless steel reactor equipped with a jacket and a stirrer with nitrogen, 6,500 g of cyclohexane, 1.2 g of tetrahydrofuran and 300 g of styrene were charged, and the contents were set to about 55 ° C. by passing warm water through the jacket. After this, n-butyllithium cyclohexane solution (pure 0.96 g) was added to initiate polymerization of styrene. Three minutes after almost complete polymerization of styrene, 700 g of butadiene (1,3-butadiene) is added to continue polymerization, and butadiene is almost completely polymerized to reach a maximum temperature of about 90 ° C., and 4 minutes after Then, 1.25 g of dibromoethane as a coupling agent was added to cause a coupling reaction. Immediately after charging the styrene, the system was continuously stirred by a stirrer during this period. The solution of the obtained block copolymer is withdrawn, 10 g of water is added, and after stirring, 3.0 g of n-octadecyl-3- (3 ', 5'-di-tert-butyl-4'-hydroxyphenyl) propionate, The solvent was removed by steam-stripping the solution obtained by adding 1.5 g of 2,4-bis (n-octylthiomethyl) -O-cresol, to obtain a water-containing crumb. Subsequently, it was dehydrated and dried by a heat roll to obtain a sample of a thermoplastic elastomer (A) having an analysis value of SBS-A.

  Also, SBS-B, SBS-C, SBS-A, and SBS-A were the same as SBS-A except that the amount of styrene, n-butyllithium, butadiene and dibromoethane were changed as shown in Table 2. Samples of elastomeric binder (A) with analytical values of D and SBS-E were obtained.

(Production of flexographic printing original plate)
The photosensitive resin composition was kneadable by putting the raw material shown below into a kneader (Powrex Inc., FM-MW-3 type | mold), and mixing the composition of Table 1 at 180 degreeC for 60 minutes. The resulting photosensitive resin composition is sandwiched between a 125 μm thick polyester film support coated with an adhesive containing a thermoplastic elastomer and a 100 μm polyester cover sheet having a 4 μm thick polyamide layer. A photosensitive structure for a flexographic printing plate was molded by using a 4 mm spacer and a pressure of 200 kg / cm ² for 4 minutes at 130 ° C. in a press.

(Manufacture of flexographic printing plate)
In the photosensitive composition for flexographic printing plate as described above, the cover sheet is peeled off, a negative film is adhered on the photosensitive resin layer, and the lower part on an "AFP-1216E" exposure machine (trade name of Asahi Kasei Co., Ltd.). First, using the side ultraviolet lamp (UV lamp TL80W / 10R manufactured by PHILIPS, trade name), the entire surface was exposed at 600 mJ / cm ² from the support side so that the relief depth of the printing plate was 1.6 mm.

Subsequently, ultraviolet light of 8000 mJ / cm ² was irradiated from the black layer side with an upper lamp (UV lamp TL80W / 10R manufactured by PHILIPS, trade name). In addition, the exposure intensity | strength at this time was measured by UV luminometer MO-2 type | mold machine (Oak Manufacturing Co., Ltd. make, brand name, UV-35 filter) made by Oak Works.

  Next, development is carried out at a liquid temperature of 30 ° C. at a speed of 80 mm / min using an “AFP-1321P” developing machine (trade name of Asahi Kasei Co., Ltd.) using the washing solvent (E) as a developer, and 2 hours at 60 ° C. It was allowed to dry.

Thereafter, as post-exposure processing, using AFP-1216LF (trade name, manufactured by Asahi Kasei Co., Ltd.) and using a germicidal lamp having a central wavelength of 254 nm (trade name, manufactured by Toshiba Corporation, GL-30, trade name) It was exposed to 1000 mJ / cm ² to the entire rESIN plate surface. The post-exposure amount by the germicidal lamp here is calculated from the illuminance measured using the UV-25 filter of the "UV-MO2" machine.

(Micro hardness difference)
The hardened layer of each flexographic printing plate obtained is vertically cut at a width of 5 mm, and the microhardness is measured in 0.1 mm steps in the range of 0.1 to 1.5 mm from the plate surface side of the cut surface, and the maximum value The microhardness difference [°] was determined from the difference of the minimum value. The results are shown in Table 3.

(30 LPI 10% printing area rate difference)
A printing test was performed on a flexographic printing machine using the obtained 3.94 mm-thick printing plate. The negative film pattern used for printing plate preparation had a line number of 30 lpi and was printed with 10% (size: 10 cm × 75 cm) dots and was totally cured (size: 10 cm × 75 cm) It is a thing. Using Wasser Super Z Plus 3L (Osaka Printing Ink Mfg. Co., Ltd., trade name) as ink, using A-stage sheet (160 g core), 250 lpi anilox roll as printing material, at printing speed of 60 sheets / minute Ten sheets were printed, and the halftone dots of the final sheet print were evaluated. The ink transfer area ratio of halftone dots is calculated using LUZEX with nine halftone dots of the printed matter as one group, and measurement of 20 clusters is performed in the direction perpendicular to the bonding portion of the corrugated sheet, and the maximum value of the area ratio is The difference between the minimum values was taken as the printing area ratio difference, and the 30 LPI 10% grade was evaluated according to the following evaluation criteria. Further, in the entire surface cured portion, the printing portion curl was evaluated according to the following evaluation criteria. The results are shown in Table 3.
(Step evaluation criteria)
:: printing area ratio difference is less than 5% ○: printing area ratio difference is 5% to less than 6% Δ: printing area ratio difference is 6% to less than 8% ×: printing area ratio difference is 8% or more Evaluation criteria)
○: Ink transfer area is 99% or more Δ: Ink transfer area is 95% or more and less than 99% ×: Ink transfer area is less than 95%

(Aging resistance)
When a 1.5 cm long and 1 cm wide rhombus relief pattern is formed, a double-sided tape is attached to the slope of the blade shown in Figure 1 and the blade is dropped while sliding vertically with a guide from the height of 60 cm. The percentage of the plate missing area was visually confirmed, and the plate resistance was evaluated according to the following evaluation criteria. The results are shown in Table 3.
(Evaluation criteria)
○: The plate area is less than 10% ×: The plate area is 10% or more

Claims (6)

A printing original plate for flexographic printing plate, comprising a support and a photosensitive resin layer laminated on the support,
The photosensitive resin layer is
At least one elastomeric binder (A),
At least one or more ethylenically unsaturated copolymerizable monomers (B),
At least one or more hydrocarbon compounds (C),
Containing at least one photopolymerization initiator (D),
In cardboard printing using a flexographic printing plate manufactured from the flexographic printing original plate, the absolute value of the difference between the maximum value and the minimum value of the area ratio of the dot diameter transferred onto the cardboard by the 30 LPI 10% dot forming portion Less than 6.0%,
Flexographic printing original plate. The difference between the microhardness on the printing surface side of the flexographic printing plate and the microhardness of a portion at a distance of 2.0 mm from the printing surface with respect to the cross section of the flexographic printing plate is 6 ° or more.
The flexographic printing original plate of Claim 1. The vinyl aromatic hydrocarbon content of the elastomeric binder (A) is 30 to 40 parts by mass with respect to 100 parts by mass of the elastomeric binder (A),
The flexographic printing original plate of Claim 1 or 2.   The ethylenic unsaturated covalent monomer (B) contains 3 to 10 parts by mass of a diacrylate monomer containing 7 or more carbon atoms with respect to 100 parts by mass of the photosensitive resin layer. The flexographic original edition as described in or.   The flexographic original plate according to any one of claims 1 to 4, wherein the photosensitive resin composition layer contains at least two or more kinds of the photopolymerizable initiators (D). A plate made from the flexographic printing plate precursor according to any one of claims 1 to 5,
Flexographic printing plate.