JP2008046447A - Method for manufacturing printing plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a printing plate achieving both of quality and manufacture efficiency, by which a high-quality relief can be formed in a short time. <P>SOLUTION: The method for manufacturing a printing plate includes at least steps of: (a) irradiating a photosensitive layer of a photosensitive printing plate original having the photosensitive layer and a support with active rays through an image mask; (b) removing a portion not irradiated with the active rays in the photosensitive layer by development to form a relief; and (c) correcting at least a part of the formed relief by laser engraving. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a printing plate manufacturing method. More particularly, the present invention relates to a printing plate manufacturing method in which a relief is formed by engraving with a laser after forming a relief by so-called analog plate making.

  As a method of forming a relief printing plate by forming irregularities on the surface, a photosensitive layer made of a photosensitive composition is exposed to ultraviolet light through an original film (image mask) to selectively cure an image portion. A method of removing uncured portions with a developer after so-called “analog plate making” is well known. In analog plate making, in many cases, vacuum contact is performed by covering a sheet made of vinyl chloride in order to make the photosensitive layer and the image mask adhere to each other. Therefore, by the time when ultraviolet light, which is an actinic ray, reaches the photosensitive layer from the light source, the interface between the air and the vinyl chloride sheet, the interface between the vinyl chloride sheet and the polyester film as the support for the image mask, and the polyester film and the photosensitive layer Light scattering occurs at the interface of the layers and the straightness of the light is impaired, so that there is a drawback that it is difficult to obtain a sharp relief.

  As a means for solving such problems associated with analog plate making, a relief printing plate precursor has been proposed in which a laser-sensitive mask layer element capable of forming an in situ image mask is provided on a photosensitive layer. (For example, refer to Patent Documents 1 and 2). In the plate making method using these original plates, laser irradiation is performed on the basis of image data controlled by a digital device, and an image mask is formed on the spot from the mask layer element. Thereafter, as in analog plate making, the image mask is formed. This is a plate making method in which the photosensitive layer and the image mask are developed and removed by exposure to ultraviolet light, and is called “digital CTP” in the industry of relief printing plates, ie flexographic plates and resin plates (letter press plates). Unlike analog plate making, digital CTP does not require the image mask to be in vacuum contact, and the ultraviolet light scattering interface is only the interface between air and the photosensitive layer, so it has the advantage of high light straightness and easy to obtain a sharp relief. There is. On the other hand, since exposure is performed in the air, polymerization is inhibited by oxygen on the surface of the photosensitive layer, so that there is a problem that a so-called relief is likely to occur, in which the intended relief cannot be obtained.

  As a plate making method for solving the problems of analog plate making and digital CTP, many direct engraving plate making using a laser, so-called “direct engraving CTP method” has been proposed (for example, see Patent Documents 3 to 4). Direct engraving CTP is a method of literally engraving with a laser to form irregularities that directly become relief. Unlike analog plate making using an original image film and digital CTP that uses an image mask that also functions as an original image film, there is an advantage that the relief shape can be controlled freely. For example, it is possible to sculpt deeply the part where the extracted character part is reproduced on the printed matter, or sculpture with a shoulder so that the halftone dot does not fall down due to the printing pressure at the part where the fine halftone dot is reproduced. The problem of direct engraving CTP is that laser engraving is slow. This is because the thickness of the mask layer element to be ablated in digital CTP is about 0.01 to 10 μm, whereas in direct engraving CTP, it is necessary to engrave at least 100 μm or more in order to directly form a relief. Because there is.

That is, analog plate making and digital CTP can form a relief in a short time, but there is a problem that it is difficult to control the relief shape and a phenomenon such as a relief jump tends to occur. On the other hand, the direct engraving CTP is easy to control the relief shape and is superior in terms of quality, but the engraving speed is slow and the production efficiency of the printing plate is a problem.
Japanese Patent No. 2773847 (pages 3-9) JP-A-9-171247 (pages 3-7) Japanese Patent No. 2846954 (pages 1-7) JP-A-11-338139 (page 2-6)

  In view of the above problems, an object of the present invention is to provide a method for producing a printing plate capable of forming a high-quality relief in a short time and having both quality and production efficiency.

In order to solve the above problems, the present invention mainly has the following configuration. That is,
“(A) a step of irradiating a photosensitive layer of a photosensitive printing plate precursor having at least a support and a photosensitive layer with an actinic ray through an image mask;
(B) a step of removing the actinic ray non-irradiated portion of the photosensitive layer by development to form a relief;
(C) correcting at least a portion of the formed relief by laser engraving;
Is a method for producing a printing plate containing at least

  According to the present invention, when producing a printing plate (hereinafter referred to as plate making), both quality and production efficiency can be achieved. After the relief is formed by analog plate making or digital CTP, an arbitrary relief shape can be produced in a short time by correcting the relief shape by laser engraving. The printing plate manufacturing method of the present invention can be applied not only to letterpress plates having a convex relief, flexographic plates and stamps, but also to intaglio plates having a concave relief, but the application range is not limited to these. Absent.

  Embodiments of the present invention will be described below.

The method for producing a printing plate in the present invention comprises at least the following steps. That is,
(A) a step of irradiating a photosensitive layer of a photosensitive printing plate precursor having at least a support and a photosensitive layer with actinic rays through an image mask;
(B) a step of removing the actinic ray non-irradiated portion of the photosensitive layer by development to form a relief;
(C) A step of correcting at least a part of the formed relief by laser engraving.

The relief formation by laser engraving has the advantage that the relief shape can be controlled arbitrarily. For example, it is possible to engrave deeply a part that reproduces the extracted character part on a printed matter, or to engrave a part that reproduces a fine halftone dot with a shoulder so that the halftone dot does not fall over due to the printing pressure. However, compared with the time required for removing the printing area, the development in analog plate making and digital CTP is at most about 15 minutes at most, whereas in laser engraving, in most cases, it exceeds 1 hour per 1 m ^2. There was a problem with efficiency.

  As a result of intensive studies, the present inventors have found that a high-quality relief can be efficiently obtained in a short time by engraving only a portion to be corrected with a laser after forming a certain level of relief by analog plate making. It was.

  In the present invention, as the photosensitive printing plate precursor having at least a support and a photosensitive layer, for example, a commercially available photosensitive flexographic plate for analog plate making or a photosensitive resin plate (letter press plate) can be used. These commercially available plate materials usually have a structure in which a support, a photosensitive layer and a cover film are sequentially laminated. In some cases, one or more adhesive layers are provided between the support and the photosensitive layer, and one or more slip coat layers are provided between the photosensitive layer and the cover film.

  The support serves as a foundation for the relief and has a function of maintaining the dimensional accuracy of the printing plate. A material that is dimensionally stable is preferably used. For example, metals such as steel, stainless steel, and aluminum, plastic resins such as polyester (for example, PET, PBT, PAN) and polyvinyl chloride, synthetic rubbers such as styrene-butadiene rubber, and plastic resins reinforced with glass fibers (such as epoxy resin and Phenol resin and the like), but is not limited thereto. Among these, a PET (polyethylene terephthalate) film and a steel substrate are preferably used. What is necessary is just to select the form of a support body according to whether a printing plate is a sheet form or a sleeve form. Although the thickness of a support body does not have limitation in particular, 0.05 mm-0.5 mm are preferable from the surface of handleability and cost.

  The photosensitive layer has a function of photocuring by irradiation with actinic rays and forming a relief. Such a photosensitive layer contains an ethylenically unsaturated monomer and a photopolymerization initiator. The ethylenically unsaturated monomer is a substance that can be cross-linked by radical polymerization, and is a known general one. The photopolymerization initiator is not particularly limited as long as it can polymerize a polymerizable ethylenically unsaturated group by light. Especially, what has the function to produce | generate a radical by self-decomposition or hydrogen abstraction by absorbing light is used preferably. For example, benzoin alkyl ethers, benzophenones, anthraquinones, benzyls, acetophenones, diacetyls and the like.

  The photosensitive layer may contain a carrier resin for the purpose of maintaining the form. As such a carrier resin, it is common to use properly depending on the printing ink used. For example, in order to obtain a flexographic plate using water-based ink, general-purpose rubbers and elastomers such as butadiene rubber, nitrile rubber, urethane rubber, isoprene rubber, and styrene rubber are used as the carrier resin. In order to obtain a letterpress plate in which oil-based ink is used, hydrophilic resins such as polyamide resin and partially saponified polyvinyl acetate are used.

  The cover film has a function of preventing scratches and dents on the relief by laminating on the photosensitive layer forming the relief. The thickness of the cover film is preferably 25 μm or more, more preferably 50 μm or more from the viewpoint of preventing scratches and dents. Moreover, 500 micrometers or less are preferable from a viewpoint of handleability.

  The adhesive force between the support and the photosensitive layer is such that when the photosensitive layer is peeled 90 ° from the support at a rate of 100 mm / min. It is preferably 0 N / cm or more or non-peelable, and more preferably 3.0 N / cm or more or non-peelable. When the adhesive force between the support and the photosensitive layer is insufficient, an adhesive layer may be provided between the two layers for the purpose of strengthening the adhesive force between the two layers. The adhesive force between the support / adhesive layer is the peel force per 1 cm width of the sample when the adhesive layer and the photosensitive layer are peeled 90 ° at a rate of 100 mm / min from the laminate comprising the support / adhesive layer / photosensitive layer. Is preferably 1.0 N / cm or more or non-peelable, and more preferably 3.0 N / cm or more or non-peelable. The adhesive force between the adhesive layer / photosensitive layer is such that when the adhesive layer is peeled 90 ° from the photosensitive layer at a rate of 100 mm / min, the peel force per 1 cm width of the sample is 1.0 N / cm or more or cannot be peeled off. Preferably, it is more preferably 3.0 N / cm or more or non-peeling.

  When the cover film is peeled 180 ° from the photosensitive layer at a rate of 200 mm / min, the peel force per 1 cm width of the sample is preferably 5 to 200 mN / cm, more preferably 10 to 150 mN / cm. If it is 5 mN / cm or more, the work can be performed without peeling the cover film during the work, and if it is 200 mN / cm or less, the cover film can be peeled without difficulty. A slip coat layer may be provided between the photosensitive layer and the cover film for the purpose of optimizing the peeling force of the cover film.

  The photosensitive printing plate precursor referred to in the present invention is not limited to the above-mentioned plate material for analog plate making, and may be a photosensitive flexographic plate for digital CTP or a photosensitive resin plate (letter press plate). The plate material for digital CTP usually has a structure in which a support, a photosensitive layer and a mask layer are sequentially laminated, and a commercially available product is available. In some cases, at least one adhesive layer is provided between the support and the photosensitive layer, at least one intermediate layer is provided between the photosensitive layer and the mask layer, and a cover film is provided on the outermost layer side of the mask layer. As the support, the adhesive layer, the photosensitive layer, and the cover film, the same materials as those described above in the section of the plate material for analog plate making can be used.

  The mask layer is ablated, decolored or colored by irradiating a laser to form an image mask. As a mask drawing laser, a near infrared laser having an oscillation wavelength in the near infrared is mainly used, and the mask layer needs to have a function of absorbing the near infrared laser. In addition, since a function as a mask for blocking actinic rays (mainly ultraviolet light) is required, black pigments and dyes such as carbon black that absorb light with a wide range of wavelengths are often used for the mask layer. In addition, a binder resin that disperses or dissolves these black pigments and dyes may be used.

  (A) The step of irradiating (exposing) actinic rays to the photosensitive layer of the photosensitive printing plate precursor having at least a support and a photosensitive layer through an image mask is a method in which the photosensitive printing plate precursor is a plate material for analog plate making. The process is different depending on whether it is a plate material for digital CTP or not.

  When using a plate material for analog plate-making, if a cover film is present, after peeling it off, an image mask (in many cases, a silver salt negative film) is placed on the exposed photosensitive layer surface, from the image mask side. Irradiate with actinic rays. Actinic rays having a wavelength of 300 nm to 500 nm are generally used. At this time, in order to bring the photosensitive layer and the image mask into close contact with each other, the whole is covered with a vinyl chloride sheet and is evacuated. In this case, as described above, since the actinic ray has a plurality of interfaces before reaching the photosensitive layer from the light source, light scattering occurs due to a difference in refractive index at the interface, and the straightness of light is lost. Therefore, the relief formed after development in the following step (b) is often not sharp. If printing is performed with a non-sharp relief, the printed image becomes thick and a high-definition printed matter cannot be obtained.

  When using a plate material for digital CTP, if a cover film is present, the cover film is peeled off, and then the exposed mask layer is irradiated with a laser corresponding to the image data to form an image mask directly on the surface of the photosensitive layer. . Next, actinic rays are irradiated through the formed image mask as in the case of analog plate making. Unlike analog plate making, exposure through a vinyl chloride sheet is not performed, so the straightness of light is not significantly impaired. Furthermore, since the exposure is performed in the air, the surface of the photosensitive layer is liable to cause curing failure due to polymerization inhibition by oxygen. Therefore, although the relief formed after the development in the following step (b) is sharp, there is a drawback that it is difficult to form high-definition independent points and halftone dots, that is, the necessary relief is likely to stop.

  In the case of a plate material having a photosensitive layer thickness exceeding 1 mm, such as a flexographic plate, so-called back exposure in which actinic rays are irradiated from the support side may be performed for the purpose of raising the floor on which the base is formed. The back exposure may be performed before the step (a) or after the step (a).

  (B) In the step of removing the actinic ray non-irradiated part (uncured part) of the photosensitive layer by development to form a relief, any of water development, chemical development or thermal development may be performed as a development means. . When the photosensitive layer and the mask layer can be developed with water, it is preferable to perform water development from the viewpoint of environmental hygiene. In the chemical development, a solvent that dissolves the photosensitive layer as a developer, for example, a flexographic plate mainly composed of rubber, a solvent such as trichlorethylene is used.

  Water development or chemical development is usually performed by brushing in a developer. On the other hand, heat development is solventless development and is performed by adsorbing a photosensitive layer softened or melted by heat onto a nonwoven fabric or the like. Although there is an advantage that development waste liquid is not generated, in order to reproduce a high-definition image, there is a problem that the developing ability is inferior.

  You may perform the drying process which volatilizes a developing solution after a process (b). In the case of water development, since drying is relatively quick, generally a drying time of about 10 minutes is sufficient. In the case of chemical development, since the chemical solution has a relatively high boiling point and the drying efficiency is poor and the chemical solution needs to be completely volatilized in consideration of the working environment of the printing operator, a drying time of several hours is often required.

  Next, in step (c), the relief shape is corrected by laser engraving. For example, in the relief formed in the step (b), it is possible to deeply sculpt the portion where the extracted character portion is reproduced on the printed matter, or to add a fine halftone dot shoulder. At this time, if a satisfactory relief is formed by analog plate making as much as possible, correction by laser engraving can be reduced. However, in many printing plates, 70% or more of the total area is a non-image portion, that is, a portion where no relief remains, so that only the portion where the relief is to be formed is solid-cured, that is, cured entirely and developed. After removing the photosensitive layer in the image area, the relief may be formed by laser engraving the remaining solid cured portion.

  Correction by laser engraving can be performed only in the direction of cutting the relief, that is, sharpening. Therefore, when reinforcing the relief, that is, when correcting the shape in a direction that is not sharp, between step (b) and step (c), apply a photosensitive resin to at least a part of the formed relief. A step of irradiating actinic rays can be added. That is, a photosensitive resin is applied to the periphery of the portion of the relief to be reinforced, and is photocured by irradiating with actinic rays. First, rough relief is corrected. In this rough relief correction, a relief larger than the intended relief is formed. Next, the intended relief can be obtained by correcting the larger relief in step (c) with a laser.

  The photosensitive resin used in the step (d) is not particularly limited as long as it can be applied, and may have the same composition as the photosensitive layer forming the relief, or may have a different composition. However, if the physical properties after curing (elasticity and strength) are significantly different from those of the photosensitive layer, or if the composition is insufficiently adhered to the photosensitive layer, printing defects may occur. Those having a similar composition are preferably used. In consideration of applicability, the photosensitive resin is preferably liquid, molten or solution, but can be used as it is when the photosensitive layer is flexible and rich in workability.

  In the step (c), the laser used for relief correction is preferably a carbon dioxide laser or a YAG laser that can achieve high output. In particular, since most of carbon dioxide laser has absorption at its oscillation wavelength, it is not necessary to include a laser absorber in the photosensitive layer. In addition, the laser cost per output is low, so it is preferably used.

  In the step of correcting these reliefs, the step (c) may be performed once, or the steps (d) and (c) may be performed once, but may be repeated a plurality of times.

  After the step (c), when the laser engraving residue adheres to the relief surface, a step of rinsing the engraving surface with a liquid such as water to wash away the engraving residue may be provided. As a means of rinsing, a method of spraying high-pressure water, a batch type or conveying type brush type washing machine known as a developing machine for photosensitive flexographic plates and letterpress plates, and brushing the engraving surface mainly in the presence of water The method of rubbing is mentioned. If the engraving residue cannot be removed, rinsing water to which soap or a surfactant is added may be used.

  When the process of rinsing the engraving surface is performed, it is preferable to dry the relief in order to volatilize the rinse liquid from the relief obtained by engraving.

  In addition, a process of irradiating UV light in the UVC region may be provided for the purpose of removing the adhesiveness of the plate surface, or a post-exposure process for irradiating the entire relief with actinic rays for the purpose of completely curing the relief. May be.

  The relief obtained in the present invention can be used for relief printing plates such as flexographic printing plates and letterpress printing plates, stamps, intaglio printing plates, stencil printing plates and the like.

  Hereinafter, the present invention will be described in detail with reference to examples.

<Comparative Example 1>
As a photosensitive printing plate precursor, “Cosmolite” NS114 (manufactured by Toyobo Co., Ltd., photosensitive flexographic printing plate) was prepared.

The following exposure and development were all performed by a batch type plate making machine “GPP500” (manufactured by Toray Industries, Inc.). The exposure unit was equipped with a high-intensity chemical lamp “TLK-40W 10R” (manufactured by Phillips), and the integrated light amount was 6,000 to 7,000 mJ / cm ² after 5 minutes exposure. The developing unit was equipped with a PBT (polybutylene terephthalate) brush, and the temperature of the developing bath was adjusted to 50 ° C. For image reproducibility evaluation, a negative film capable of evaluating 150 lines, 2% halftone dots, 3% halftone dots, 5% halftone dots, and white lines having a width of 300 μm was used. The halftone dot reproducibility evaluated whether each relief was formed on the printing plate. About the white line, the depth (white depth) of the formed groove was evaluated. Generally, as the white depth is deeper, white characters can be printed more clearly.

  First, “Cosmolite” NS114 was back exposed from the support side with a high-intensity chemical lamp for 20 seconds. Thereafter, the cover film was peeled off, and a negative film was placed on the exposed photosensitive layer, covered with a vinyl chloride sheet and adhered in a vacuum, and exposed from a negative film side with a high-intensity chemical lamp for 5 minutes.

  Subsequently, when it developed for 6 minutes in presence of the developing water of 50 degreeC, the relief image with a relief depth of 0.55 mm was formed. Thereafter, drying was performed in a perfect oven at 60 ° C. for 10 minutes to remove moisture from the relief. Thereafter, post-exposure was performed with a high-intensity chemical lamp for 10 minutes to obtain a flexographic printing plate. The total plate making time required from the back exposure to the post exposure was 35 minutes for the plate size A3.

  As a result of evaluating the image of the obtained flexographic printing plate, the white depth of 300 μm width was 50 μm, but the relief was not able to reproduce 2% halftone dots and 3% halftone dots, and as a flexographic printing plate The quality was not satisfactory.

<Comparative example 2>
In Comparative Example 1, plate making and evaluation were carried out in the same manner except that the exposure time with a high-intensity chemical lamp through a negative film was changed from 5 minutes to 10 minutes.

  The total plate making time was 40 minutes for the plate size A3. As a result of evaluating the image of the obtained flexographic printing plate, the relief was able to reproduce 2% halftone dots and 3% halftone dots. It was not quality.

<Comparative Example 3>
From the support side of “Cosmolite” NS114, exposure was performed for 20 seconds with a high-intensity chemical lamp, and then exposure was performed for 10 minutes with a high-intensity chemical lamp from the cover film side. After removing the cover film, it is mounted on a carbon dioxide laser engraving machine “ZED mini 1000” (Luescher Flexo), and the negative film image for evaluation of image reproducibility used in Comparative Examples 1 and 2 is converted into digital data. Laser engraving was performed based on this data. The laser engraving conditions are Pitch: 20 μm, Top Power: 10%, Bottom Power: 100%, Shoulder Width: 0.3mm, and the depth of relief to be engraved is 0.5 to 0.6mm. Adjusted Speed. As a result, it took 50 minutes to engrave the A3 size. Next, the laser engraving residue was washed by exposing the laser engraving plate surface to running tap water, and then the rinse solution was dried in an oven at 60 ° C. It took a total of 15 minutes to clean the laser engraving residue and dry the rinse solution. That is, the total plate making time required from exposure to drying was 80 minutes, which was considerably longer than those of Comparative Examples 1 and 2.

  As a result of evaluating the image of the obtained flexographic printing plate, it was possible to reproduce 2% halftone dots and 3% halftone dots, and the white depth of 300 μm was as deep as 80 μm, which was satisfactory as a flexographic printing plate. .

<Example 1>
The flexographic printing plate obtained in Comparative Example 2 was mounted on a carbon dioxide laser engraving machine “ZED mini 1000”, and only the shallow white portions were engraved to correct the relief. Thereafter, in the same manner as in Comparative Example 3, the laser engraving residue was washed and the rinse solution was dried. The time required for these corrections was 25 minutes, and the total plate making time was 65 minutes. The obtained flexographic printing plate had a white depth of 300 μm and a deep depth of 75 μm. The quality of the flexographic printing plate was satisfactory, and both the quality and the production efficiency were easily achieved.

<Example 2>
The halftone dot portion of the flexographic printing plate obtained in Comparative Example 1 was filled with an uncured photosensitive layer of “Cosmolite” NS114, and then exposed to a high-intensity chemical lamp for 10 minutes. Next, it was mounted on a carbon dioxide laser engraving machine “ZED mini 1000” and only the halftone dots were engraved to correct the relief. Since the white depth of 300 μm width was 50 μm, the white portion was not corrected by laser engraving. Thereafter, in the same manner as in Comparative Example 3, the laser engraving residue was washed and the rinse solution was dried. The time required for these corrections was 35 minutes from the filling operation with the photosensitive layer to the engraving, the cleaning of the engraving residue and the drying of the rinse solution, and the total plate making time was 70 minutes. As a result of evaluating the image of the obtained flexographic plate, 2% halftone dot and 3% halftone dot were reproduced, and the quality of the flexographic plate was satisfactory, and both the quality and the production efficiency were easily achieved.

Claims (2)

(A) a step of irradiating a photosensitive layer of a photosensitive printing plate precursor having at least a support and a photosensitive layer with actinic rays through an image mask;
(B) a step of removing the actinic ray non-irradiated portion of the photosensitive layer by development to form a relief;
(C) correcting at least a portion of the formed relief by laser engraving;
A method for producing a printing plate comprising at least Between the step (b) and the step (c),
(D) applying a photosensitive resin to at least a part of the formed relief and irradiating with actinic rays;
The method for producing a printing plate according to claim 1, further comprising: