JP2007264178A - Plate making method for flexographic printing plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a plate making method for making a flexographic printing plate having a less dot gain quantity. <P>SOLUTION: The plate making method for the flexographic printing plate is characterized in performing (5) surface processing for carrying out irradiation with ultraviolet rays of 200 to 300 nm in wavelength by 3.6 J/cm<SP>2</SP>after (1) back exposure, (2) main exposure, (3) development, and (4) drying. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for making a flexographic printing plate.

  Flexographic printing plates are widely used for printing on various packaging materials using paper, film and the like. In general, a flexographic printing plate has a photopolymerizable layer sandwiched between a base material and a protective sheet. This photopolymerizable layer contains a photopolymerizable composition containing an elastomer binder, a monomer, and a photoinitiator. It is known that it is manufactured by a method in which it is supplied to a nip of a sheet and formed.

  In a flexographic printing plate, a photopolymerizable layer is insolubilized by photopolymerization by selectively exposing only an image portion using a mask such as a negative film. By immersing the plate in a developer with water, a solvent, a surfactant, or a mixture thereof, or by rubbing the unexposed area with a brush or the like while spraying the developer in a shower shape, the photopolymerizable layer Unexposed portions are removed, leaving convex portions used for printing.

  In this exposure process, a general method for bringing a mask such as a negative film into close contact with the photopolymerizable layer is to evacuate between the sheets after covering them with a vacuum sheet or the like. In recent years, development of a plate material in which a layer capable of forming a mask on the surface of the photopolymerizable layer without requiring a negative film has been developed and put into practical use.

  The developed plate material is dried with warm air or the like in order to remove the developer that has penetrated into the photopolymerizable layer. By performing exposure with ultraviolet rays as a surface treatment for finishing, the tackiness of the flexographic printing plate surface can be removed. It is known that ultraviolet light (UV-C) having a wavelength of 300 nm or less is used for exposure for eliminating the adhesiveness (see, for example, Patent Documents 1 and 2).

In recent years, there has been an increasing demand for printing quality, and the performance required for flexographic printing plates has been higher than before. That is, there is an increase in printed materials in which a halftone dot image representing a photographic image as a dot is arranged on the same printing plate together with a solid image and a character image. There is a need for printing plate performance that can achieve an appropriately controlled dot gain. Here, the dot gain amount means an amount by which the dot size on the printed material becomes larger than the dot size on the printing plate due to the printing pressure, and is expressed by an amount gained compared to the original size. Increasing the tone density of the solid image portion requires a large printing pressure during printing, but a larger printing pressure results in a larger dot gain in the halftone image portion. Therefore, it can be said that a small dot gain amount is one of important performances required for a printing plate.
Japanese Patent Laid-Open No. 55-135838 Japanese Unexamined Patent Publication No. 1-1121858

  An object of the present invention is to provide a plate making method for producing a flexographic printing plate showing a smaller dot gain amount in order to improve printing quality.

That is, in the present invention, after 1) back exposure, 2) main exposure, 3) development, 4) drying, 5) surface treatment of irradiating ultraviolet rays having a wavelength of 200 to 300 nm at 3.6 J / cm ² or more is performed. It is the plate making method of the flexographic printing plate characterized.

  According to the present invention, it is possible to control a printing ink transfer in a printing process and produce a flexographic printing plate showing a smaller dot gain amount.

  Embodiments of the present invention will be described below.

  A known printing plate can be used as the flexographic printing plate used in the present invention. Although the plate making process is different, a printed image for ink transfer is formed on the plate material by forming a relief image with a resin or rubber composition and utilizing its physical height difference and chemical resistance. It can be formed and printed.

  Next, although an example of the plate making method will be described, the present invention is not limited to this. In order to form a relief image for printing on a flexographic printing plate, first, ultraviolet rays having a wavelength of 300 to 400 nm are irradiated from the substrate side (generally referred to as back exposure), and then the protective sheet is peeled off. A negative or positive mask is placed on top and irradiated with ultraviolet rays (generally called main exposure), and insolubilization is performed by photopolymerization. In this exposure order, the back exposure need not always be performed first, and the main exposure may be performed first and the back exposure may be performed later. Depending on the exposure apparatus, it can be performed simultaneously. Examples of the light source include a high-pressure mercury lamp, an ultra-high pressure mercury lamp, a metal halide lamp, a xenon lamp, a carbon arc lamp, and a chemical lamp. Examples of standard light sources include the PHILIPS TL / 10 series and SYLVANIA 350 Blacklight. These light sources are usually arranged at a distance of about 3 to 200 cm from the flexographic printing plate, and are used by changing the exposure time from several seconds to several tens of minutes according to the sensitivity of the flexographic printing plate and the fineness of the mask.

  Next, a relief image can be formed on the substrate by eluting the photopolymerizable layer portion that has not been irradiated with ultraviolet rays with a spray developing device or a brush developing device. The developer depends on the chemical properties of the photopolymerizable layer to be developed and removed, and an organic solvent, an aqueous solution, tap water, or the like is used. Organic solvent developers include aromatic or aliphatic hydrocarbons and aliphatic or aromatic halogenated hydrocarbons such as n-hexane, petroleum ether, hydrated petroleum oil, limonene or other terpenes or toluene, isopropyl Benzene and the like, ketones such as methyl ethyl ketone, halogenated hydrocarbons such as chloroform, trichloroethane, or tetrachloroethylene, esters such as acetic acid or acetoacetic acid esters, or mixtures of these solvents with suitable alcohols. The aqueous solution developer usually contains water and an alkaline substance. For example, general-purpose soap components such as fatty acid sodium salt, fatty acid potassium and carbonate are preferably used. When the surfactant is contained, the content thereof is preferably 0.01% by weight to 10% by weight and more preferably 0.1% by weight to 3% by weight with respect to the total weight of the developer. The development time varies depending on the development model, the properties of the flexographic printing plate, and the relief depth, but is usually in the range of 1 to 30 minutes.

  After development, in order to remove the developer and photosensitive resin adhering to the plate surface, it is washed with a plate surface cleaning solution, and then subjected to a drying treatment with warm air or an infrared oven. An unused developer is generally used as the plate surface cleaning solution. The drying time varies depending on the drying temperature and the properties of the flexographic printing plate, but is usually at a temperature that does not cause distortion such as shrinkage of the base material of the flexographic printing plate, for example, at 60 ° C. for 5 to 240 minutes. .

After drying, a surface treatment is performed. An essential feature of the present invention is the surface treatment of a flexographic printing plate that is irradiated with ultraviolet rays having a wavelength of 200 to 300 nm of 3.6 J / cm ² or more. The ultraviolet irradiation amount is preferably 4.8 J / cm ² or more, more preferably 7.2 to 14.4 J / cm ² . Moreover, as an ultraviolet-ray to irradiate, a 254 nm ultraviolet-ray (UV-C) is used preferably. This surface treatment is generally carried out as the final step of the plate making as described above, but it is possible to modify the printing surface of the flexographic printing plate by giving a certain amount of energy, and as a result. As a result, it is possible to control the thickening amount (dot gain amount) of the halftone dot which will greatly affect the print quality. When the amount of ultraviolet irradiation irradiated by this surface treatment is less than 3.6 J / cm ² , the dot gain amount increases and print quality deteriorates.

  Furthermore, the surface treatment can remove the tackiness of the surface of the flexographic printing plate, and a flexographic printing plate that can withstand practical printing can be obtained. Various printing obstacles such as adhesion of dust and dust in the air during printing, adhesion of paper dust, and "paper mess" that peels off the surface of the paper that occurs when the flexographic printing plate surface is sticky Can be prevented. In addition, in order to improve the physical strength of the printing plate, ultraviolet rays having a wavelength of 300 to 400 nm may be further irradiated.

  Regarding the modification of the surface of the printing plate, it can be confirmed by its surface tension, and it can be modified to have a larger surface tension by giving more energy. In other words, being easily wetted with printing ink means that a uniform ink film can be formed on the printing plate surface, and as a result, the effect of reducing the amount of thickening of halftone dots is generated. Print quality can be controlled.

  Another advantage of the present invention is that it can be employed for various types of flexographic printing plates. Preferably, it is useful for flexographic printing plates that are water-developed. The present invention is useful for analog exposure, digital exposure, or direct engraving type flexographic printing plate.

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

Examples 1-5, Comparative Examples 1-3
"GPP500F" (manufactured by Toray Industries, Inc.) with 14 "TLK40W / 10R" (manufactured by Philips) lamps installed on A4 size "LT114SR3" (manufactured by Toray Industries, Inc.) The exposure work was performed using a water-developable flexographic printing plate making machine. First, after performing back exposure for 15 seconds from the plate substrate side, the plate cover film was peeled off, the negative film was vacuum-contacted, and then exposed from the negative film side for 5 minutes. The negative film was prepared for evaluation of the plate material and contained 150% 2%, 50% halftone dot chart, 40 μm wide thin line, and the like.

  After completion of the exposure, development work was performed using “GPP500F”. As a developer, a solution obtained by dissolving 0.2% by weight of Nissan high-density powder soap (manufactured by Nissan Soap Co., Ltd.) as a surfactant in 25 liters of neutral water at 50 ° C., development by manual batch processing for 5 minutes A printing plate was obtained by performing drying for 10 minutes and post-exposure for 5 minutes.

The operation was repeated in this way, and eight printing plates were produced under the same plate-making conditions, and surface treatment with different energy amounts was performed on each of them. The surface treatment was performed for 0 to 60 minutes using a surface treatment device (manufactured by JEOL Ltd.) in which 17 SANKYO electric germicidal lamps GL15 were arranged. That is, printing plates having eight different energies of 0, 0.2, 2.4, 4.8, 7.2, 9.6, 12, and 14.4 J / cm ² were produced. Printing was performed using the printing plate after the finishing treatment, and the dot gain amount at each halftone dot 50% portion was measured. UV500 indigo (manufactured by T & KTOKA) was used as the printing ink, and MA830 (manufactured by MarkAndy) was used as the printing machine. Table 1 shows the dot gain measurement results.

Examples 6-8, Comparative Examples 4-6
A4 size "LT114R2" (manufactured by Toray Industries, Ltd., water development type photosensitive flexographic printing plate material), "NS114" (manufactured by Toyobo Co., Ltd., water development type photosensitive flexographic printing plate material), AQS114 "(manufactured by DUPONT The development type photosensitive flexographic printing plate material) was exposed by “FTW350LII” manufactured by Fuji Photo Film Co., Ltd.) in which six “TLK40W / 10R” (Philips Chemical Lamp) were installed. After back exposure for 15 seconds from the material side, the plate cover film was peeled off, the negative film was vacuum-contacted, and then exposed for 10 minutes from the negative film side, which was prepared for evaluation of the plate material. The content included halftone dot charts of 2% and 50% lines and third grade Mincho characters.

  After completion of the exposure, development work was performed using “GPP500”. As a developing solution, a solution obtained by dissolving 1% by weight of Nissan powder soap (manufactured by Nissan Soap Co., Ltd.) in 25 liters of neutral water at 50 ° C. is used. A relief depth of 5 mm was obtained. Next, drying was performed with warm air of 60 ° C. for 10 minutes, and post-exposure was performed for 10 minutes to obtain a printing plate.

The operation was repeated in this manner, and two printing plates were produced under the same plate-making conditions, and surface treatments with different amounts of energy were performed on each. For the surface treatment, two types of treatments of 10 minutes and 30 minutes were performed using a surface treatment apparatus (manufactured by JEOL Seiki) in which 17 SANKYO electric germicidal lamps GL15 were arranged. That is, printing plates having two different energies of 2.4 and 7.2 J / cm ² were produced. Printing was performed using the printing plate after the finishing treatment, and the dot gain amount at each halftone dot 50% portion was measured. UV500 indigo (manufactured by T & KTOKA) was used as the printing ink, and MA830 (manufactured by MarkAndy) was used as the printing machine. Table 2 shows the results of dot gain measurement.

Claims (1)

1) Back exposure, 2) Main exposure, 3) Development, 4) After drying, 5) Surface treatment by irradiating ultraviolet rays having a wavelength of 200 to 300 nm at 3.6 J / cm ² or more is performed. Plate making method.