JPH0629965B2 - How to connect flexographic printing plates - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The standard printing method for sheet materials (materials made up of individual panels or individual webs) is flexographic printing,
In this method, a flexographic printing plate having a flexographic printing relief surface adhered to a substrate is attached to a printing cylinder to make contact. The ink on the relief portion of the relief surface is imagewise transferred to the sheet material. The relief should be molded of a flexible material. Flexographic printing plates can be made by engraving on a sheet of flexible material or, more commonly, by exposing the photosensitive resin in contact with the substrate with an image to remove the material in the non-image areas. The photosensitive resin is a liquid and is cured by exposure. Alternatively, in the case of a solid, if exposed, an unexposed portion is differentially dissolved by an alkali or an organic solvent.

If the length of the pattern to be printed, the length of the plate and the circumference of the printing cylinder are short, such as 30 cm or less, fix the flexographic printing plate to the printing cylinder with an adhesive method such as double-sided tape, and use the product name "Super glue". It is common to butt seam adjacent edges of the plate using solution adhesives such as those sold by.

This butt splice method has the disadvantage that the solvent in the printing ink or in the solution used to clean the printing cylinder erodes the seam and separates the plate edges.
The plate can also come off the cylinder as the solvent erodes the adhesive. Obviously, this is not desirable. Possible problems with the adhesion of the plate edges include shrinkage during exposure and / or subsequent processing,
Especially bad when using a plate made of a solid photosensitive resin with curled edges. Inks used to print paper bags and foil films are usually based on solvents that are particularly corrosive to butt splices with adhesive.

To prepare a printing plate, it is known to image-expose a plate having a substantially continuous cylindrical surface layer to prepare a cylindrical flexographic printing plate. For example, according to British Patent 2,043,274, a liquid photocurable resin is cast between a cylinder and a transparent cylindrical rigid plate. Older methods for obtaining a cylindrical photosensitive plate are JP-A-53-143404 and JP-A-53-2980.
It is described in No. 4. According to Japanese Patent Laid-Open No. 53-29804, a photocurable photosensitive printing plate is wound around a cylindrical substrate, and a liquid photopolymerizable resin is poured into the gap between the butt joint edges of the plates. There is.

This amount of liquid resin is such that the height of the resin in the gap is at the same or higher level as the top surface of the printing plate.
The liquid resin in the gap is gradually solidified by exposure. After inserting the liquid resin into the gap, the cylindrical printing surface layer is subjected to image exposure. This is because the photopolymerizable resin used for the butt joint is part of the image printed surface layer.

A method of imagewise exposing the plate before butt splicing, or butt splicing at the image part is possible if the overall quality of the joint and printing allows, but a preferable butt splice at the indented part without the image The method of doing so is the main interest of the present invention. Therefore, the disclosure of JP-A-53-29804 has nothing to do with the problem to be solved by the present invention.

JP-A-53-29804 does not suggest the use of a particular liquid photopolymerizable resin in the butt joint or any special properties of the resin. The findings after the present invention revealed that the conventional liquid photopolymerizable resin for butt splicing by the method described in JP-A-53-29804 was also of interest in the present invention even if a conventional liquid photopolymerizable resin was tried. However, if the printing is prolonged, the adhesive between the abutting edges is removed and the plate is easily peeled off from the base.

In this way, even if the method of JP-A-53-29804 is used not as a method of forming a printing surface layer that can form an image in a cylinder shape but instead of the conventional butt joint method, the solution type adhesive is used with the double-sided tape. Thus, it is not an advantageous method as compared with the conventional established method of performing the butt joint. Whichever method is used for conventional printing, the butt joint is inferior and there is a terrible tendency that the plate rises from the cylindrical substrate.

In the present invention, in order to butt one edge of the printing plate formed by photo-curing to the other edge adjacent to it, a liquid photopolymerizable resin is injected between the edges, and the resin is then exposed to light. Cure. The flexographic printing plate (one or more) formed by photo-curing originally has a relief printing image on the flexographic printing plate, or else after injection of a liquid photopolymerizable resin, the plate (one or more) ) Make the flexographic printing image a relief pattern. This liquid photopolymerizable resin contains 1,000 to 30,00 and unsaturated ethylene terminal groups.
It comprises 100 parts by weight of a gen-based prepolymer having a number average molecular weight of 0, 5 to 100 parts by weight of a polymerizable ethylenically unsaturated monomer compound, and 0.001 to 10 parts by weight of a photopolymerization initiator.

Compared with a butt joint using the solution type adhesive or using a large amount of liquid photopolymerizable resin, a resin composition of the above-mentioned specific type capable of obtaining a butt joint having an effective effect on deterioration even when used for a long time. It's amazing to find something. The resin used in the present invention has a special curing property, and is a butt joint that can withstand a troublesome application such as printing in a water-based ink or an organic solvent-based ink for a long time. Thus, the cured resin withstands water-based inks and organic solvent-based inks.

The gen-based prepolymer is a prepolymer obtained from gen added with an ethylenically polymerizable unsaturated group, and has a molecular weight of 1,000 to 30,000, preferably 2,000 to 20,000. When the molecular weight is less than 1,000, the photocured product becomes too hard and the tensile strength becomes low, resulting in insufficient adhesive strength. On the other hand, when the molecular weight exceeds 30,000, the viscosity of the composition becomes too high, which makes it extremely difficult to inject the liquid photopolymerizable resin for connecting the plates.

The above polymer obtained from a diene as a starting material is a liquid polymer and has a carboxyl group as a terminal functional group,
It contains any of a hydroxyl group, a mercapto group, an amino group and an epoxy group. This polymer is for example 1,
4-polybutadiene, 1,2-polybutadiene, hydrogenated 1,2
-Polybutadiene, styrene-butadiene copolymer, acrylonitrile-butadiene copolymer, (meth) acrylic acid ester-butadiene copolymer, polyisoprene,
1,3-polypentadiene or the like, or a chain-extended polymer obtained by a urethane bond, an ester bond or an amide bond in the polymer by utilizing the above functional groups in a conventional manner to obtain the prepolymer, and (Meth) acrylic acid residue, fumaric acid residue, itaconic acid residue,
An allyl group or the like may be introduced. Alternatively, the polyene itself can be used as the prepolymer of the present invention. In this case, it is preferably used together with polythiol.

Among the above prepolymers, the following prepolymers have excellent solvent resistance and tear strength. A prepolymer having terminal ethylenically unsaturated groups and a number average molecular weight of about 6,000 to 30,000, the main segment of which is (i) an average of about 1.2 to 2.0 terminal hydroxyl groups per molecule and about 50 to 100% of 1,2. -Residues of hydrogenated 1,2-polybutadiene having a hydrogenation rate of pendant vinyl groups of addition units, (ii) 2-20 hydrogenated 1,2-polybutadiene (i) obtained by reaction of diisocyanate Residue of chain-extended hydrogenated 1,2-polybutadiene having urethane bond, (iii) hydrogenated 1,2-having terminal carboxyl group obtained by reaction of hydrogenated 1,2-polybutadiene (i) with dicarboxylic acid A residue of polybutadiene, or (iv) a terminal hydroxyl group obtained by the reaction of hydrogenated 1,2-polybutadiene (i) with diisocyanate and 2 to 20
It is a residue of a chain-extended hydrogenated 1,2-polybutadiene having a terminal carboxyl group obtained by the reaction of a chain-extended hydrogenated 1,2-polybutadiene having one urethane group and a dicarboxylic acid.

The following are preferable examples of the polymerizable ethylenically unsaturated monomer composition.

Chemical formula -[-(CH ₂ ) ₄ -O-] _p -H (3) (1) Compounds of Chemical Formulas 1 to 3 wherein R ¹ represents hydrogen or methyl.

R ⁵ means an alkyl group having 1 to 20 carbon atoms, cyclohexyl, an alkoxylalkyl group having up to 15 carbon atoms, a third having up to 8 carbon atoms
It is an aminoalkyl group, a hydrogen atom, or an oxyalkylene group represented by the chemical formula 2 or 3.

R ³ is a hydrogen atom, methyl, means monochloromethyl methyl or mono bromomethyl, p is an integer of 1 to 20, - (CH _{2) q} -OH group (q within this is an integer of 5-20) , -CH ₂ C (CH ₃ )
₂ CH ₂ OH group or —CH ₂ C (CH ₂ Br) ₂ CH ₂ OH group is meant.

(2) The compound R ¹ of Formula 4 means hydrogen or methyl.

R ⁶ and R ⁷ each represent a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, cyclohexyl or benzyl. Or R ⁶ is hydrogen and R ⁷ is —R ⁸ —OH, where R ⁸ is 1
Is an alkylene having 12 carbon atoms.

(3) The compound R ¹ of Formula 5 means hydrogen or methyl.

g is an integer of 2 or 4 and R ⁹ means the residue of a polyol having g terminal hydroxyl groups and a number average molecular weight of up to 1,000.

(4) The compounds R ¹ and R ¹¹ of Formula 6 represent hydrogen or methyl, respectively.

R ¹⁰ means an alkylene group having 1 to 6 carbon atoms.

(5) The compound R ¹ of Formula 7 means hydrogen or methyl.

R ¹² means hydrogen, methyl, monochloromethyl, or monobromomethyl.

(6) An aromatic compound having at least one CH ₂ ═C group and one benzene nucleus.

(7) A heterocyclic compound having one ethylenically unsaturated group.

(8) Other ethylenically unsaturated monomer compounds.

Examples of compound (1) are as follows. Methyl acrylate or methacrylate, ethyl acrylate or methacrylate, isopropyl acrylate or methacrylate, n-butyl acrylate or methacrylate, n-pentyl acrylate or methacrylate, neopentyl acrylate or methacrylate, dibromo neopentyl acrylate or methacrylate, n -Hexyl acrylate or methacrylate, n-octyl acrylate or methacrylate, n-decyl acrylate or methacrylate, isodecyl acrylate or methacrylate, lauryl acrylate or methacrylate, stearyl acrylate or methacrylate,
2-ethylhexyl acrylate or methacrylate, cyclohexyl acrylate or methacrylate, methoxymethyl acrylate or methacrylate, ethoxybutyl acrylate or methacrylate, 2-methoxypropyl acrylate or methacrylate, n-butoxymethyl acrylate or methacrylate, cyanomethyl acrylate or Methacrylate, cyanobutyl acrylate or methacrylate, (N, N-dimethylamino) -methyl acrylate or methacrylate, 2- (N, N-dimethylamino) -ethyl acrylate or methacrylate,
2- (N, N-diethylamino) -ethyl acrylate or methacrylate, 2- (N, N-dibenzylamino) -ethyl acrylate or methacrylate, 2
-(N, N-dimethylamino) -propyl acrylate or methacrylate, acrylic acid, methacrylic acid,
And the same compound (i) as above.

Examples of compound (2) are as follows. Acrylamide, methacrylamide, N, N-dimethylacrylamide or methacrylamide, N, N-diethylacrylamide or methacrylamide, N, N-diisopropylacrylamide or methacrylamide, N, N-
Dodecyl acrylamide or methacrylamide, N
-Isopropylacrylamide or methacrylamide, N-cyclohexylacrylamide or methacrylamide, N-benzylacrylamide or methacrylamide, N-methylolacrylamide or methacrylamide, 2-hydroxyethylacrylamide or methacrylamide, 2-hydroxypropylacrylamide or methacrylamide, 4 -Hydroxy-n-butyl acrylamide or methacrylamide, and the products obtained from the ester-amide exchange reaction of methyl acrylate or methacrylate with amino-alcohols having up to 12 carbon atoms.

Examples of compound (3) are as follows. Ethylene glycol di-acrylate or -methacrylate,
Diethylene glycol di-acrylate or -methacrylate, triethylene glycol di-acrylate or -methacrylate, tetraethylene glycol di-acrylate or -methacrylate, polyethylene glycol (number average molecular weight: 200 to 1,000) di-acrylate or -methacrylate, Propylene glycol di-acrylate or -methacrylate, dipropylene-glycol di-acrylate or -methacrylate, polypropylene glycol (number average molecular weight: 100 to 1,000) di-acrylate or -methacrylate, butylene glycol di-acrylate or-
Methacrylate, trimethylolethane tri-acrylate or -methacrylate, trimethylolpropane tri-acrylate or -methacrylate, pentaerythritol tetra-acrylate or -methacrylate, pentaerythritol tetra-acrylate or -methacrylate, neopentryl glycol di -Acrylate or -methacrylate, dibromoneopentyl glycol di-acrylate or-
Methacrylate, 1,8-octanediol di-acrylate or -methacrylate, 1,9-nonanediodi-acrylate or -methacrylate, 1,10-decanediol di-acrylate or -methacrylate, 1,12-dodecanedioldi -Acrylate or-
Methacrylate, and 1,18-octadecanediol di-acrylate or -methacrylate and the like.

Examples of compound (4) are as follows. N, N'-methylene-bisacrylamide, N, N'-methylenebismethacrylamide, N, N'-trimethylenebisacrylamide, N, N'-trimethylenebismethacrylamide,
N, N'-hexamethylenebisacrylamide and N, N '
-Hexamethylenebismethacrylamide.

Examples of compound (5) are as follows. 2-acid phosphoxyethyl acrylate or methacrylate, 3
-Chloro-2-acid phosphoxypropyl acrylate or methacrylate and 3-bromo-2-acid phosphoxypropyl acrylate or -methacrylate.

The following are examples of compound (6). Styrene, α
-Methylstyrene, α-chlorostyrene, p-tert-butylstyrene, p-sec-butylstyrene, aminostyrene, methoxystyrene, vinyltoluene, vinylbenzoic acid, vinylphenol, allylbenzene, allyltoluene, monoallylphthalate, diallyl Phthalates and divinylbenzene.

Examples of compound (7) are as follows. N-vinylcarbazole, N-vinylpyrrolidone, 2-vinylpyridine, 4-vinylpyridine, vinylquinoline, 2-vinylimidazole, 4-vinylimidazole, 5-vinylimidazole, 2-vinylbenzimidazole, N-vinyltetrazole, 2 -Vinylpyrazine, 2-vinylthiazole, N-vinyloxazolidone, 2-vinylbenzoxazole, 2-vinylfuran, 2-isopropenylfuran and 2-vinylthiophene.

Examples of compound (8) are as follows. Vinyl acetate, vinyl propionate, vinyl laurate, methyl vinyl benzoate, β-hydroxyethyl vinyl benzoate, vinyl succinate, vinyl adipate, divinyl phthalate, divinyl terephthalate, 2,
2'-bis- (4-methacryloxydiethoxyphenyl) -propane, 2,2'-bis- (4-methacryloxyethoxyphenyl) -propane and 2,2'-bis-
Diphenylpropane derivatives such as (4-methacryloxyethoxyphenyl) -propane, acrylonitrile, and ethylene glycol, propylene glycol, polyoxyethylene diol with a number average molecular weight of up to about 400,
Alternatively, a polyoxypropylene or a mixture thereof having a number average molecular weight of up to about 400 is reacted with a dicarboxylic acid or a mixture thereof as described in the preparation of the prepolymer (IV) above to obtain a number average molecular weight of up to about 1,000 and a terminal ethylene. With an oligoester having a functionally unsaturated group, the oligoester thus obtained is reacted with a carboxylic acid or a dicarboxylic acid as described for the preparation of prepolymer (I). And the same alcohol as above (ii). Among the above compounds, t is 8 to 20 in the case of the compound of the chemical formula 8 or 9.
Is particularly effective for improving the solvent resistance of the photopolymerization product.

The amount and type of the polymerizable ethylenically unsaturated monomer compound are
It is appropriately selected according to the application, depending on the characteristics of the photopolymer and the processability of the photopolymerizable resin containing the monomer compound. The amount thereof is in the range of about 5 to 100 parts by weight, preferably 20 to 70 parts by weight, based on 100 parts by weight of the prepolymer.

The reaction of the photosensitive resin is initiated only by the action of appropriate light, and it is necessary that the resin is stable to heat. Therefore, it is preferable that the polymerization initiator is inert to heat at less than 40 ° C. and photopolymerization is initiated by irradiation with actinic light. The light is preferably ultraviolet light.

Examples of the photopolymerization initiator include the following. Benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin n-propyl ether, benzoin isopropyl ether, benzoin butyl ether, benzoin isobutyl ether, benzoin sec-butyl ether, benzoin amyl ether, benzoin isoamyl ether, α-methylbenzoin, α-ethylbenzoin, α-methylbenzoin methyl ether, α-
Phenylbenzoin, benzoins such as α-allylbenzoin, anthraquinone, chloroanthraquinone, methylanthraquinone, ethylanthraquinone, chloroanthraquinone, anthraquinones such as methylanthraquinone, ethylanthraquinone, tert-butyl-anthraquinone, diketones such as benzyl and diacetyl, Phenones such as acetophenone, benzophenone, ω-bromoacetophenone, 2,2-dimethoxyphenylacetophenone, 2-naphthalenesulfonyl chloride,
Diphenyl disulfide, diethyl sulfide such as tetraethyl thiuram disulfide, Eosin G (CI4
5380) and thionine (CI52025) dyes and others.

The amount of the above photopolymerization initiator used is about 0.001 to 10% by weight,
About 0.01 to 5% by weight of the total weight of prepolymer and polymerizable ethylenically unsaturated monomer compound is preferred.

A known stabilizer (that is, a thermal polymerization inhibitor) is used to maintain the storage stability (shelf life) of the photopolymerizable resin. Such a stabilizer may be added when the components of the photopolymerizable resin are mixed, or may be added to each component before the components are mixed.

Examples of stabilizers are hydroquinone, mono-tert-butylhydroquinone, 2,5-di-tert-butylhydroquinone,
Catechol, tert-butyl catechol, 2,6-di-tert
-Butylcresol, benzoquinone, 2,5-diphenyl-p-benzoquinone, p-methoxyphenol, picric acid and di-p-fluorophenylamine.

The reason for adding such a stabilizer is only to prevent thermal polymerization that does not depend on the actinic radiation without suppressing the photopolymerization reaction. Therefore, the amount of the stabilizer is preferably about 0.001 to 2.0% by weight, and about 0.005 to 1.0% by weight based on the total weight of the prepolymer and the polymerizable ethylenically unsaturated monomer compound.

Furthermore, in order to adjust the viscosity of the photopolymerizable resin and the mechanical properties after the photopolymerization, various compounds in an amount of about 0.01 to 100 parts by weight with respect to 100 parts by weight of the photopolymerizable resin are added. May be added to. Examples of such compounds include dioctyl phthalate, butylphthalyl butylene glycol coat, polyester plasticizers, epoxy plasticizers, various phosphates, polypropylene glycol process oils of polyester and liquid paraffin, butyl rubber of liquid rubber, and butadiene rubber.

Particularly suitable liquid photopolymerizable resins are described and exemplified in British Patent 1,575,584 and JP-A-50-8910. A suitable composition for use in the present invention is that supplied by Asahi Kasei (UK) under the tradename APR Photopolymer K11.

It is not necessary that the upper surface of the cured butt seam and the upper surfaces of the resin plates on both sides of the butt seam are at the same height, because the butt seam is usually made on the non-image portion of the printing plate, that is, the recessed portion. However, butt splicing can also be performed on relief-shaped image portions, in which case it is usually preferable that the relevant image portion is a portion that is not important as an image, such as a fold. Then, it is not necessary to completely match the surface of the butt joint with the surfaces of the image portions on both sides thereof.

The printing plate used in the present invention is preferably formed by imagewise exposure of a liquid photocurable resin formed by curing the relief printing surface layer, and is held on a polyester or other sheet base material. Often, the entire plate, apart from the substrate, is molded with a single composition, but it is also possible to mold the plate with two or more different compositions as described in British Patent No. 2,012,977. . The patent also describes a preferred photocurable resin.

Instead of imagewise exposing a liquid material to form a plate, image formation can also be performed by imagewise exposing a solid photosensitive resin material. The exposure may be before or after being fixed to the cylinder, or before or after the butt joint. Plates made of hard photosensitive resin are usually exposed before being fixed in the printing cylinder, ie before the butt splice.

When a solid photosensitive resin plate is imagewise exposed, the image area and the non-image area are different in solubility in a solvent such as an alkali or an organic solvent.

The plate may be a solid plate, such as rubber, which may be hand engraved before or after fixing the plate to the cylinder. However, the present invention is most useful for the method of placing the photopolymer plate on the printing cylinder.

If the plate is made of a liquid photosensitive resin, the liquid photo-curable resin may promote adhesion between the polymer and the edge of the plate, and thus may be the same as or chemically similar to the resin that made the printing plate. .

As a photosensitive resin suitable for molding butt joint plates,
British Patents 1,577,706, 1,552,653, 2,033,598
And No. 1,366,769, French Patent No. 2,103,825,
German Patents (DE) Nos. 2,456,439 and 137,416, JP-A-55-143,557, JP-A-54-110,289 and JP-A-56-6
There are solid compositions such as those described in 5,004.

Liquid photosensitive resins suitable for molding the plate used in the present invention include U.S. Pat.Nos. 3,783,152 and 3,556,691.
No. 3,858,510, 3,960,572 and 4,266,007
And British Patent No. 1,575,584.

The present invention can be used for butt splicing of two different printing plates that are usually supported by a substrate, but the present invention is particularly applicable to the butt splicing of one printing plate wound on a cylinder. It is worth it. The butt joint is sufficient to permanently fix the plate to the cylinder, but if necessary, an adhesive such as a double-sided adhesive tape may be provided between the plate and the cylinder. Since the butt splices are resistant to the solvents used in the printing inks, the solvent sensitivity of the adhesive tape is of little or no concern.

The present invention will be described with reference to the accompanying drawings which are partial cross-sectional views of a printing cylinder during the process of the present invention.

Flexographic printing plate 1 with an image in advance (eg page 27)
(Any one of the liquid resins described in lines 10 to 13) is wound around a cylinder 2 and a liquid photocurable resin 4 of the above type is used, for example, using a high-pressure injection gas and an injection needle. Pour into the gap where both ends of the plate are adjacent. This method is preferable for completely filling the gap with the liquid resin. It also drives oxygen out of the gap.
It is preferred to cover the liquid resin with a sheet 3 of transparent material such as polyester to minimize contact between the resin and oxygen and to smooth the surface of the liquid resin.

In order to cure the injected liquid resin, UV rays are usually emitted from the light source 5 through the transparent protective sheet. Usually, the dose is in the range of ^{300mJ / cm 2 ~5000mJ / cm 2} .
This amount may be determined by the sensitivity of the liquid photosensitive resin to be injected. After curing, the protective sheet is removed from the plate and the resin is dried with warm air and / or treated with a conventional surface chemical treatment solution to remove stickiness.

By adhering the edges of the printing plate according to the method of the present invention, the plate on the cylinder becomes uniform and does not leave discontinuous flaws on the substrate to be printed, which can be ignored.

Normally, a double-sided adhesive tape is used between the cylinder and the plate to fix the plate to the cylinder.

The method of the present invention is particularly suitable for continuous printing cylinders where the image-to-image gap is very small, especially where it is necessary to use small printing cylinders or high solvent content inks. An example of a method in which the present invention is useful is the printing of eg crimping packets on a paper bag or foil film.

The cylinder used in the method of the present invention preferably has a diameter of 5 to 30 cm. The total thickness of the plate used in the method of the present invention is usually 0.75 to 10 mm, preferably 3 to 7 mm. The relief depth is usually 0.5 to 5 mm. The gap to be filled is usually 0.2 to 5 mm.

Example 34.8 parts of polyethylene adipate (diol, n = 2000), 34.8 parts of toluidine diisocyanate (“TDI”, 2,4 bodies / 2,6 bodies = 3/2), and dibutyltin dilaurate were added.
0.5 part was added and reacted at 50 ° C. for 4 hours to obtain a polyethylene adipate having isocyanate groups at both ends. To this, polypropylene glycol (diol, n = 20
00) 100 parts, polyester with an average molecular weight of 6500
A polyether block (terminal isocyanate) was obtained. To 300 parts of the terminal isocyanate block, 25 parts of 2-hydroxyethyl methacrylate and 0.1 part of hydroquinone were added and reacted at 70 ° C. for 2 hours to obtain a prepolymer. To 100 parts of this prepolymer, 20 parts of 2-hydroxypropyl methacrylate, 10 parts of styrene, 10 parts of stearyl methacrylate, 1.5 parts of benzoin and 0.2 part of hydroquinone were added to obtain a liquid photosensitive resin.

An image-formed flexographic printing plate was prepared using the above-mentioned photosensitive resin, and this was wrapped around a cylinder.

On the other hand, terminal hydroxyl group-type hydrogenated 1,2-polybutadiene having an average of 1.6 hydroxyl groups per molecule (average molecular weight n
= 3000, hydrogenation rate 95%) 300 parts and TDI 17.4 parts are mixed,
After stirring and reacting at 60 ° C for 3 hours, 8.6 parts of 2-hydroxypropyl methacrylate, hydroquinone
Add a mixed solution of 0.1 part and 0.1 part of dibutyltin dilaurate, and absorb the characteristic absorption of NCO (λ = 2260 cm) on an infrared chart at 80 ° C.
^{(About -1} ) was hardly detected, and the reaction was performed in an atmosphere of dry air to prepare a prepolymer with n = 13,000.
For 100 parts of this prepolymer, 40 parts of lauryl methacrylate, 10 parts of dimethacrylate of polypropylene glycol of n = 400, 3 parts of benzoin amyl ether, p
-Methoxyphenol 0.1 part was added to obtain a liquid photopolymerizable resin.

The photopolymerizable resin was injected into a gap in which both ends of the plate wound around the cylinder were adjacent to each other using a high pressure injection gas and an injection needle. The injected photopolymerizable resin was covered with a transparent polyester sheet.

Next, the injected photopolymerizable resin was irradiated with ultraviolet rays at 1200 mJ / cm ² through a sheet to be cured, and then the resin was dried with warm air.

When flexographic printing was performed on kraft paper using a water-based ink containing 10% by weight of isopropanol in a plate connected on a plate in this way, even after printing 300,000 m, the part where the plate was connected peeled off. Never happened. Further, after the completion of printing, even when the plate was removed with a plate washing oil containing 10% of isopropanol and the ink was washed off, the plate joint portion was not peeled off. On the other hand, the liquid photosensitive resin used for making the printing plate is used in place of the liquid photopolymerizable resin having a specific segment in the present invention, and plate joining is performed in the same manner as described above, under the above conditions. When flexographic printing was performed, 700
I started peeling off from the edge of the plate joint from within m printing, and the plate completely peeled off from the edge of the plate joint within 1000 m.

[Brief description of drawings]

 The drawings are illustrations of the method according to the invention.

Claims (9)

[Claims] 1. A plate connecting method in which a liquid photopolymerizable resin is injected between adjacent edges of a flexographic printing plate formed by photocuring and the resin is cured by exposure to butt joint the adjacent edges of the plates. In, the printing plate is first provided with a relief-shaped flexographic printing image, or after injecting a liquid photopolymerizable resin, the printing plate is provided with a relief-shaped flexographic printing image, and Liquid photopolymerizable resin 100 parts by weight of a gen-based prepolymer having an unsaturated group of terminal ethylene and a number average molecular weight of 1,000 to 30,000, 5 to 100 parts by weight of a polymerizable ethylenically unsaturated monomer compound, and a photopolymerization initiator 0.001 A plate connecting method for flexographic printing plates, characterized in that it comprises 10 to 10 parts by weight. 2. A method as claimed in claim 1, characterized in that the printing plate has a relief-shaped flexographic image from before the butt splice. 3. A method according to claim 2 wherein the printing plate is made from a liquid photopolymerizable resin by imagewise exposure of the resin. 4. A method as claimed in any one of the preceding claims, characterized in that a butt joint is applied to the non-image areas. 5. The method according to any one of claims 1 to 4, wherein the edges to be butt-joined are both ends of one printing plate wound around a cylinder. 6. The method according to claim 5, wherein a double-sided adhesive tape is additionally used for fixing the printing plate to the cylinder. 7. The liquid photopolymerizable resin according to claim 1, wherein the liquid photopolymerizable resin is injected into the gap under a pressure sufficient to expel air from the joint. The method described. 8. The liquid photopolymerizable resin used for butt splicing is covered with a transparent film before exposure, according to any one of claims 1 to 7. Method. 9. A gen-based prepolymer is a prepolymer having an unsaturated group of terminal ethylene and a number average molecular weight of 6,000 to 30,000, the main segment of which has an average of 1.2 to 2.0 terminal hydroxyl groups per molecule. 50-100% 1,2
-Hydrogenated 1,2 having hydrogenation rate of pendant vinyl group of addition unit, chain-extended hydrogenation having 2-20 urethane bonds obtained by reaction of diisocyanate with 1,2-polybutadiene 1,
The method according to any one of claims 1 to 8, which is a residue of 2-polybutadiene.