JP2003098652A - Photosensitive structure for flexographic printing plate having improved infrared-ablative layer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve enhanced work efficiency and stable image reproducibility in plate making by improving the peelability of a cover sheet as well as by smoothening the fine creases of a non-infrared radiation shielding layer ablative with IR in a photosensitive structure for a flexographic printing plate for a plate making process in which an image converted to digital information is directly formed using an infrared laser. SOLUTION: In a photosensitive structure for a flexographic printing plate comprising (a) a support layer, (b) a non-infrared radiation sensitive resin layer present on the layer (a) and comprising a thermoplastic elastomer, an ethylenically unsaturated compound and a radiation sensitive initiator, (c) a non-infrared radiation shielding layer present on the layer (b) and ablative with IR and (d) a cover sheet on the layer (c), the non-infrared radiation shielding layer (c) comprises a polymer having a polyester backbone and a number average molecular weight of 300-10,000.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improved flexographic printing plate corresponding to a plate making process for directly drawing an image of digital information by using an infrared laser without using a photographic negative (hereinafter referred to as a negative film). It relates to a photosensitive construction for a printing plate.

[0002]

A conventional photosensitive composition for flexographic printing plates has a polyester film as a support, on which a thermoplastic elastomer, at least one ethylenically unsaturated compound, and at least one initiator sensitive to radiation are added. It is generally composed of a photosensitive resin layer containing. As a procedure for making a flexographic printing plate from such a photosensitive constituent for flexographic printing plate, first, the entire surface is exposed to ultraviolet light through the support (back exposure) to provide a thin uniform cured layer. Image exposure (relief exposure) is then performed on the surface of the photosensitive resin layer through a negative film, and the unexposed portion is washed away with a developing solvent to obtain a desired image, that is, a relief image, to obtain a printing plate. Here, a thin film often called a slip layer or a protective layer is provided on the photosensitive layer for the purpose of smoothing the contact with the negative film.

On the other hand, there is also known a technique concerning a photosensitive composition for a flexographic plate which can directly draw digitized image information without using a negative film and a plate making method thereof. The technique is to selectively ablate a non-infrared radiation-shielding thin layer provided on a non-infrared radiation-sensitive photosensitive resin layer with an infrared laser based on digital information processed by a computer. , To obtain the desired image. After drawing an image on the photosensitive resin layer, the conventional plate making process can be applied as it is. That is, back exposure is performed from the support side using an existing exposure apparatus, relief exposure is performed from the image side drawn with an infrared laser, and then a flexographic printing plate is obtained through a developing process. Compared with the method using a conventional negative film, this plate making method does not need to make a new negative film when an image correction occurs, and it can be handled by correcting the digitized image data on a computer, It has the advantage of saving time and effort. Further, it is also advantageous in dimensional stability as compared with the conventional negative film, which leads to improvement of reproducibility of relief image and eventually print quality.

For example, in Japanese Patent Laid-Open No. 8-305030, a non-infrared radiation shielding layer that can be ablated by infrared rays is disclosed.
It is described that the binder polymer used with the infrared absorber or the non-infrared radiation shielding substance is substantially incompatible with at least one low molecular weight substance of the photosensitive resin layer. Examples of the binder polymer used for the purpose of realizing such properties include polyamide, polyvinyl alcohol, polyvinyl alcohol / polyethylene glycol graft copolymer, amphoteric interpolymer, alkyl cellulose, hydroxyalkyl cellulose, nitrocellulose, and ethylene. Copolymers with vinyl acetate, cellulose acetate butyrate, polybutyral, cyclic rubber, copolymers of styrene and acrylic acid, polyvinylpyrrolidone, copolymers of vinylpyrrolidone and vinyl acetate, and combinations with these polymers. And so on.

However, the non-infrared radiation shielding layer prepared from these polymers may have a problem due to poor compatibility with the low molecular weight substance of the photosensitive resin layer. For example, because the combination of the non-infrared radiation shielding layer and the photosensitive resin layer has a small affinity,
The adhesiveness is small, and when the cover sheet is peeled off before laser drawing, the non-infrared radiation shielding layer is partially peeled off from the photosensitive resin layer and is peeled off while being attached to the cover sheet. Often happens.

In Japanese Patent Laid-Open No. 11-153865, at least one of the thermoplastic elastomers in the photosensitive resin layer is a polymer of a monovinyl-substituted aromatic hydrocarbon and a conjugated diene, and is a layer cleavable by infrared rays ( The binder polymer used in the non-infrared radiation shielding layer (hereinafter the same)) is a copolymer composed of a monovinyl-substituted aromatic hydrocarbon and a conjugated diene, or a copolymer composed of a monovinyl-substituted aromatic hydrocarbon and a conjugated diene. When the polymer is hydrogenated, the adhesion to the photosensitive resin layer is good, peeling off of the non-infrared radiation shielding layer that may occur when the cover sheet is peeled off, etc. It is described that it is possible to select a developing solvent.

However, depending on the compositional ratio of the monovinyl-substituted aromatic hydrocarbon / conjugated diene copolymer of the binder polymer and the weight fraction of the binder polymer in the layer, the elasticity of the layer cleavable by infrared ray may be reduced. Not enough,
Fine wrinkles may occur on the surface of the layer, which may adversely affect image formation. Further, the adhesiveness to the cover sheet becomes high, and it becomes difficult to peel off the cover sheet particularly in the case of a large size plate, which hinders the plate making work.
Furthermore, the cover sheet must be peeled off intermittently little by little, leaving peeling marks on the surface of the layer that can be cut off by infrared rays or accidentally lifting the photosensitive resin layer and scratching the photosensitive resin layer. It is also possible that you put on.

On the other hand, in Japanese Patent Laid-Open No. 2001-80225, by using a photosensitive printing element characterized by containing an aliphatic diester in an infrared ray cleavable layer, the flexibility of the infrared ray cleavable layer is improved. And high sensitivity has been realized. However, there is no description of means for facilitating the peeling between the cover sheet and the infrared-cuttable layer. There are various combinations of compositions that can be used in the layer that can be ablated by infrared rays, but the adhesiveness, mechanical properties, handleability required for this layer, and good laser drawing and developing properties It has been extremely difficult to select a composition having characteristics.

[0009]

SUMMARY OF THE INVENTION The present invention provides a photosensitive construction for a flexographic printing plate corresponding to a plate making process for directly drawing an image of digital information by using an infrared laser without using a negative film. In order to eliminate fine wrinkles on the surface of the layer that can be cut off by infrared rays and to improve the peelability of the cover sheet, it is possible to realize improved workability during plate making and stable image reproducibility.

[0010]

The present inventors have completed the present invention as a result of extensive studies on the above problems. That is, the present application provides the following inventions. (A) a support layer; and (b) a non-infrared radiation-sensitive photosensitive resin layer which is on the (a) layer and contains a thermoplastic elastomer, an ethylenically unsaturated compound and a radiation-sensitive initiator. (C) In a structure composed of a non-infrared radiation shielding layer that can be ablated by infrared rays on the layer (b) and a cover sheet on the layers (d) and (c), the infrared ray can be ablated by the infrared ray (c) A non-infrared radiation shielding layer contains a polymer having a polyester skeleton and having a number average molecular weight of 300 or more and 10000 or less.

For the support layer used in the present invention, a dimensionally stable film having a thickness of 75 μ to 300 μ such as a polyester film can be used, and an adhesive may be used between the support layer and the photosensitive resin layer, if necessary. The relief body obtained by imagewise exposing the photosensitive resin layer must have the characteristics required for a flexographic printing plate. That is, it must exhibit good printing performance even on a printing medium such as thick paper or a soft plastic film. Various examples of such a photosensitive resin layer are known, and examples thereof include those described in JP-A-55-48744, JP-A-47-32179, and JP-A-56-65004. Used. The photosensitive resin layer in the present invention is a thermoplastic elastomer as a binder polymer,
It is composed of at least one ethylenically unsaturated monomer capable of radical polymerization and a radiation-sensitive initiator.

As the binder polymer used in the photosensitive resin layer, a thermoplastic elastomer composed of a monovinyl-substituted aromatic hydrocarbon monomer and a conjugated diene monomer is used. A typical example is styrene-butadiene-polymer. Examples thereof include a styrene block copolymer and a styrene-isoprene-styrene block copolymer. At least one ethylenically unsaturated monomer is compatible with the binder polymer, and examples thereof include esters of t-butyl alcohol, lauryl alcohol, and other alcohols with acrylic acid and methacrylic acid. Maleimide derivatives such as lauryl maleimide, cyclohexyl maleimide and benzyl maleimide, or esters of alcohol and fumaric acid such as dioctyl fumarate, and further hexanedioldi (meth) acryle.
It is possible to use esters of polyhydric alcohols such as bisphenol, nonanediol di (meth) acrylate, trimethylolpropane tri (meth) acrylate with acrylic acid and methacrylic acid.

As the radiation-sensitive initiator, aromatic ketones such as benzophenone, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, α-methylol benzoin methyl ether, α-methoxybenzoin methyl ether, 2,
Selected from known photopolymerization initiators such as benzoin ethers such as 2-diethoxyphenylacetophenone,
Also, they can be used in combination. Further, in the photosensitive resin layer used in the present invention, additives such as a sensitizer, a thermal polymerization inhibitor, a plasticizer and a coloring agent can be used depending on the required characteristics. The photosensitive resin layer can be prepared by various methods. For example, if the composition is as described above, the raw materials to be blended are dissolved in a suitable solvent, for example, a solvent such as chloroform, tetrachloroethylene, methyl ethyl ketone, toluene, and mixed, and the mixture is cast in a mold to form the solvent. It can be evaporated to form a plate as it is. Also, without using a solvent, kneading with a kneader or a roll mill,
A plate having a desired thickness can be formed by an extruder, an injection molding machine, a press, or the like.

The infrared laser ablation layer for non-infrared radiation comprises a polymer having a binder polymer and a polyester skeleton, an infrared absorbing material and a non-infrared radiation shielding material. Although various polymers can be used as the binder polymer, a copolymer of a monovinyl-substituted aromatic hydrocarbon such as styrene, α-methylstyrene and vinyltoluene and a conjugated diene such as butadiene and isoprene is preferable. When a non-infrared radiation shielding layer is formed using these binder polymers, it has high affinity with the photosensitive resin layer and good adhesion.

The polymer having a number average molecular weight of 300 or more and 10000 or less and having a polyester skeleton contained in the layer which can be cut off by infrared rays is effective for improving the flexibility of the layer, and has mechanical properties and laser drawing. Although it can be selected and added within a range that does not impair the properties, it is used in an amount of 1 to 20% by weight, preferably 1 to 15% by weight, more preferably 5 to 12% by weight based on the components in the layer. A polymer having a polyester skeleton is a polymer having a repeating unit of a condensation product of diol and carboxylic acid in the main chain,
Diester and triester compounds having an ester bond only at the terminal are not included.

Examples of particularly preferable polyester skeletons are those synthesized from alkanediol and adipic acid, those synthesized from alkanediol and phthalic acid, polycaprolactone, or a combination of two or more of these polyesters. Can be mentioned. By using these polymers having a polyester skeleton, it is possible to eliminate the generation of fine wrinkles on the surface of the layer that can be cut off by infrared rays, and improve the peelability of the cover sheet. As a result, the range of selection of the film that can be used as the cover sheet is widened, and the plate making operation can be easily performed using various general-purpose films such as a polyester film. A polyester polyol having a hydroxyl group at its molecular end is particularly effective for improving the releasability of the cover sheet. Furthermore, these compounds having a polyester skeleton are amino groups, nitro groups, sulfonic acid groups, as long as the compatibility with the binder polymer is not impaired.
It may contain various functional groups such as halogen.

The infrared absorbing material is usually 750 to 2000
A simple substance or a compound having a strong absorption in the nm range is used. Examples of such materials include carbon black, graphite, copper chromite, inorganic pigments such as chromium oxide, polyphthalocyanine compounds, cyanine dyes,
Examples thereof include dyes such as metal thiolate dyes. These infrared absorbing substances are added within the range of giving a sensitivity that can be ablated by the laser beam used. Generally 10
Addition of ~ 80% by weight is effective. As the non-infrared radiation shielding material, a material that reflects or absorbs radiation such as ultraviolet rays can be used. Radiation absorbers such as ultraviolet rays, carbon black, graphite, etc. are good examples,
The addition amount is set so that the required optical density can be achieved.
Generally, it is necessary to add it so that the optical density is 2.0 or more, preferably 3.0 or more.

As an example of the adjustment method when carbon black is used as both a non-infrared radiation absorbing substance and a shielding substance, a binder polymer is prepared by using an appropriate solvent.
A solution is prepared, carbon black is dispersed therein, and then coated on a cover sheet such as a polyester film, and then this cover sheet is laminated or pressed on a photosensitive resin layer. A method of pressing and transferring a non-infrared radiation shielding layer that can be removed by an infrared laser is effective. As a method of dispersing carbon black in the binder-polymer solution, a method of using both forced stirring with a stirring blade and stirring using ultrasonic waves is effective. Alternatively, a method in which the binder polymer and the carbon black are pre-kneaded using an extruder or a kneader and then dissolved in a solvent is also effective for good dispersion of the carbon black. The thickness of the non-infrared radiation shielding layer should be determined in consideration of the sensitivity of ablation by an infrared laser and the non-infrared radiation shielding effect, but it is usually 0.1 to 20 g / m ^2. It is set in the range of.

As the cover sheet, a polyester film, polyethylene film, polypropylene film or the like having a thickness of 50 to 200 μm is used. These are present for the purpose of protecting the non-infrared radiation shielding layer, and are removed before being drawn by an infrared laser.
From the viewpoint of film strength and dimensional stability, it is preferable to use a polyester film. The infrared laser used in the plate making process has a wavelength of 750-2000n.
m can be used. This type of infrared ray
As a laser, a semiconductor laser of 750-880 nm or 1
A 060 nm Nd-YAG laser is common. The generation unit of these lasers is controlled by a computer together with the drive system unit, and digitized by selectively cutting off the non-infrared radiation shielding layer on the photosensitive resin layer. The image information is provided to the photosensitive composition for flexographic printing plate.

After the image drawing by the laser is completed, the non-infrared radiation used for photocuring the photosensitive resin layer of the photosensitive composition for flexographic printing plate includes visible light, ultraviolet light, X-ray, Although there are gamma rays and the like, ultraviolet rays are preferable.
Ultraviolet light sources include high-pressure mercury lamps, ultraviolet fluorescent lamps, and
There are Bon-ark lights, xenon lamps, and sunlight. A desired relief image can be obtained by exposing the image surface to radiation such as ultraviolet rays, but in order to make the relief image more stable against the stress during washing out of the uncured portion, a support is used. It is effective to perform the whole surface exposure from the side.

As a developing solvent used for washing the non-infrared radiation shielding layer and the unexposed portion of the photosensitive resin layer after irradiating the photosensitive resin layer with radiation such as ultraviolet rays to form an image, For example, chlorine-based organic solvents such as 1,1,1-trichloroethane and tetrachloroethylene, and esters such as heptyl acetate and 3-methoxybutyl acetate,
Hydrocarbons such as petroleum fraction, toluene and decalin are used. In addition, propanol, butanol,
It is also possible to use a mixture of alcohols such as pentanole. The non-infrared radiation shielding layer and the unexposed portion are washed out by jetting from a nozzle or brushing with a brush. The obtained printing plate is rinsed, dried and post-exposed to finish.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be specifically described below based on Examples.

[Examples 1 to 7],

[Comparative Examples 1 to 4] Asaflex 810 (manufactured by Asahi Kasei Corporation), which is a block copolymer of styrene and butadiene.
65 wt% and 35 wt% of carbon black were kneaded with a kneader and cut into pellets. 90 parts of the pellets and 10 parts of the compounds shown in Table 1 were used, and ultrasonic waves were used in a mixed solvent adjusted with a weight ratio of ethyl acetate / butyl acetate / propylene glycol monomethyl ether acetate = 50/30/20. A uniform solution having a solid content of 12 wt% was prepared by dissolving. Next, a knife coater was coated with this solution on a polyester film serving as a cover sheet having a thickness of 100 μm so that the coating amount after drying was 4-5 g / m ^2.
Was applied and dried at 80 ° C. for 1 minute to prepare a non-infrared radiation shielding layer that can be ablated by infrared rays. When these optical densities were measured by DM-500 (manufactured by Dainippon Screen Co., Ltd.), they were 3.0 to 4.0.

Next, Toughprene A (styrene-butadiene-styrene block copolymer manufactured by Asahi Kasei Corporation) 60
Parts, B-2000 (Nippon Petrochemical, liquid polybutadiene) 30 parts, 1,9-nonanediol diacrylate 7 parts, 2,2-dimethoxy-2-phenylacetophenone 2 parts, 2,6-di-t- Butyl-p-cresol.
Three parts were kneaded with a kneader and extruded to prepare a plate of the photosensitive resin composition. A plate of this photosensitive resin composition was sandwiched between a support of a 125 μm polyester film and a non-infrared radiation shielding layer on the cover sheet prepared above, and a press of 130 ° C. using a 3 mm spacer. Under the conditions of 4 minutes,
A pressure of 200 kg / cm ² was applied to mold the photosensitive construction for flexographic printing plates.

[0024]

[Table 1]

When the cover sheet of this photosensitive construction for flexographic printing plate was peeled off, when the polyester shown in Examples 1 to 7 was contained, the cover sheet could be peeled off smoothly and the entire photosensitive construction was lifted. The plate was not damaged and the surface of the layer capable of infrared ablation was smooth.
Attach this structure to the drum of the laser writing device,
Selectively ablating the non-infrared radiation shielding layer using an Nd-YAG laser with an energy density of 10 MW / cm ² .
After drawing a 3% -120 line / inch halftone dot pattern, using an ultraviolet fluorescent lamp having a center wavelength of 370 nm on an AFP-1500 exposure machine (manufactured by Asahi Kasei Corporation),
After performing the back exposure of 300mJ / cm ² first from the support side, we continue Lelie of 8000mJ / cm ² - was subjected to full exposure. Next, using tetrachloroethylene / n-butanol (volume ratio: 3/1) as a developing solution, AFP-
The composition was attached to a rotating cylinder of a 1500 developing machine (manufactured by Asahi Kasei Corporation) with a double-sided tape, and development was carried out at a liquid temperature of 25 ° C. for 5 minutes. As a result, a halftone dot pattern was faithfully reproduced.

On the other hand, in Comparative Example 1, peeling of the cover sheet was heavy, and the photosensitive component was lifted up when the cover sheet was peeled, and the peeling operation of the cover sheet was extremely difficult. When the cover sheet was strongly peeled off, the entire plate was bent and a scratch remained on the photosensitive layer. In addition, the flexibility of the infrared severable layer was poor, and many fine wrinkles were observed on the surface of the infrared severable layer during the work of mounting on the drum of the laser writing device. In Comparative Example 2-4 as well, the cover sheet was peeled off heavily, and it had to be peeled off intermittently little by little. Therefore, peeling marks remained in places on the surface of the layer that could be cut by infrared rays. After the cover sheet was peeled off from the photosensitive construction of Comparative Example 1-4, the flexographic printing plate obtained by plate-making in the same procedure as in Example 1-7 was observed.
Poor relief formation due to fine wrinkles and peeling marks was observed.

[0027]

INDUSTRIAL APPLICABILITY The photosensitive composition for a flexographic printing plate corresponding to the plate making process of directly drawing an image of digital information by using an infrared laser without using a negative film, has a polyester skeleton. By using a novel infrared ray ablatable non-infrared radiation shielding layer containing a polymer having an average molecular weight of 300 or more and 10000 or less,
By eliminating fine wrinkles in the layer that can be cut off by infrared rays and improving the peelability of the cover sheet, it is possible to improve workability during plate making and stable image reproducibility.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Akio Tanizaki             Asahi Kasei Co., Ltd. 1 No. 2 Samejima, Fuji City, Shizuoka Prefecture             In the company (72) Inventor Katsuhiro Takahashi             Asahi Kasei Co., Ltd. 1 No. 2 Samejima, Fuji City, Shizuoka Prefecture             In the company F-term (reference) 2H025 AA15 AB02 AC08 AD01 BC13                       BC42 CA00 CA02 CB11 CB16                       DA02 DA03 FA10                 2H096 AA02 AA03 BA05 CA20 EA04                       LA30

Claims (6)

[Claims] 1. A non-infrared radiation-sensitive sensitizer comprising (a) a support layer and (b) (a) layer, which comprises a thermoplastic elastomer, an ethylenically unsaturated compound and a radiation-sensitive initiator. A resin layer, a non-infrared radiation shielding layer on the layers (c) and (b) that can be ablated by infrared rays, and a cover sheet on the layers (d) and (c), The infrared-absorptive non-infrared radiation shielding layer contains a polymer having a polyester skeleton and having a number average molecular weight of 300 or more and 10000 or less. 2. (b) At least one of the thermoplastic elastomers in the photosensitive resin layer is a polymer of a monovinyl-substituted aromatic hydrocarbon and a conjugated diene, and (c) a non-infrared ray cleavable by infrared rays. The radiation shielding layer contains a copolymer of a monovinyl-substituted aromatic hydrocarbon and a conjugated diene as a binder polymer.
A photosensitive construction for flexographic printing plates as described in 1. 3. The weight fraction of the polymer having a polyester skeleton contained in the infrared ray ablation layer for non-infrared radiation which can be ablated by infrared rays is 1 to 20% by weight of the components in the layer. The photosensitive construction for a flexographic printing plate according to claim 1 or 2. 4. The (c) polymer having a polyester skeleton contained in the infrared ray eliminable non-infrared radiation shielding layer is a polyester polyol having a hydroxyl group at its molecular end. 4. The photosensitive construction for flexographic printing plate according to any one of 3 to 3. 5. (c) A polymer having a polyester skeleton, which is contained in a non-infrared radiation shielding layer that can be ablated by infrared rays, is synthesized from alkanediol and adipic acid, or is synthesized from alkanediol and phthalic acid. The photosensitive composition for flexographic printing plate according to any one of claims 1 to 4, wherein the photosensitive composition is a polycaprolactone or a combination of two or more of these polyesters. 6. The photosensitive composition for a flexographic printing plate according to claim 1, wherein the cover sheet (d) is a polyester film.