JP3812723B2 - Letterpress printing method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a relief printing method in which ink is attached to the projections of a plate having depressions and projections on the surface, and the ink is transferred to a printed material for printing.
[0002]
[Prior art]
In general, letterpress printing is a process in which ink is attached to the convex portions of a plate having concave and convex portions formed on the surface, and the ink is transferred to a printed material for printing.
[0003]
FIG. 6 is an external plan view showing the configuration of a relief printing apparatus used for conventional relief printing.
[0004]
As shown in FIG. 1, a conventional relief printing apparatus 10 comprises a plate cylinder 4, an ink roller 5, and an impression cylinder 6 on which a plate 3 having convex portions 3a and concave portions 3b on the surface is attached. The cylinder 4 and the ink roller 5 are arranged to face each other, and the plate cylinder 4 and the impression cylinder 6 are arranged to face each other.
[0005]
The ink 7 supplied to the outer peripheral surface of the ink roller 5 adheres to the surface of the convex portion 3a of the plate 3, and the printing paper 8 conveyed between the plate cylinder 4 and the impression cylinder 6 By being pressed by 6, the ink 7 adhered to the convex portion 3 a of the plate 3 is directly transferred to the printing paper 8 and printing is performed.
[0006]
In such a relief printing method, as shown in FIG. 7A, the thickness of the ink 7 attached to the projection 3 a of the plate 3 is substantially uniform, and the projection 3 a and the recess formed on the plate 3. A high pressure is applied by the impression cylinder 6 to the printing paper 8 supplied between the plate cylinder 4 and the impression cylinder 6 so that the image composed of 3b is transferred to the printing paper 8 without blur. Then, a part of the ink 7 attached to the surface of the convex portion 3a of the plate 3 is transferred in a state of being pushed out to the outer peripheral side of the convex portion 3a.
[0007]
Then, the ink 7 transferred to the printing paper 8 is dark along the halftone dot outline 7a and the halftone dot center portion 7b becomes thin as shown in FIG. .
[0008]
This marginal phenomenon is one of the features of letterpress printing. When halftone printing is performed, particularly at the start and end of the halftone dot composition, and both side edges, that is, the outer edge portion of the dot pattern. There is a tendency that marginal generation is observed, the outer edge of the printed image is darker than the central portion, and the printed matter has a poor appearance with a difference in shading.
[0009]
[Problems to be solved by the invention]
The present invention has been made in view of the above-described problems, and the object of the present invention is, in particular, a printed image that is transferred to a printed matter even when a marginal phenomenon peculiar to halftone relief printing occurs. It is an object of the present invention to provide a relief printing method that can suppress the difference in printing density of the print and enables a beautiful finish of the entire printed matter.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, a relief printing method according to the present invention comprises a plate having concave and convex portions formed on the surface, a plate cylinder on which the plate is attached to the outer peripheral surface, and a plate cylinder facing the plate cylinder. An impression cylinder that presses the plate against the printed matter, and deposits ink on the convex portion of the plate and transfers the ink to the printed matter, the convex portion of the plate The surface is constituted by halftone dots composed of aggregates of minute convex portions , and the halftone dot area ratio at the outer edge portion of the halftone dot constituting portion of the plate is determined from the halftone dot area ratio at the center portion of the halftone dot constituting portion of the plate. Is also set to be small.
[0011]
According to the present invention, even if a part of the ink adhered to the surface of the convex portion of the plate by the pressing of the impression cylinder is transferred to the printed material in a state of being extruded to the outer peripheral side of the convex portion, Since the halftone dot area ratio at the outer edge of the plate is set in advance smaller than the target halftone dot area ratio at the center of the halftone dot composition portion of the plate, the halftone dot composition portion transferred to the printed matter, that is, the printed image The difference in printing density between the center portion and the outer edge portion of the paper can be suppressed, and a beautiful finish of the entire printed matter becomes possible.
[0012]
The halftone dot area ratio at the center of the halftone dot composition part of the plate is set to the target halftone dot area ratio, and the halftone dot area ratio is gradually increased toward the outer edge of the halftone dot constitution part of the plate. The difference between the halftone dot area ratio at the outer edge of the halftone dot composition portion of the plate and the halftone dot area ratio at the center portion of the halftone dot constitution portion of the plate may be set to be reduced. It should be changed as appropriate depending on the printing speed and the like.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, a preferred embodiment of a relief printing method according to the invention will be described in detail with reference to the accompanying drawings.
[0014]
FIG. 1 is an external plan view showing the configuration of a relief printing apparatus used in the method of the present invention, FIG. 2 is a plan view schematically showing an example of a plate production method shown in FIG. 1, and FIG. 3 is shown in FIG. 4 is an enlarged plan view showing the structure of the negative film, FIG. 4 is an enlarged plan view showing the structure of the plate shown in FIG. 2, and FIG. 5 is a view for explaining the operation of letterpress printing according to the method of the present invention.
[0015]
As shown in FIG. 1, a known printing apparatus can be used as the relief printing apparatus used in the method of the present invention, and this printing apparatus 20 is a plate having convex portions 13a and concave portions 13b formed on the surface. 13 includes a plate cylinder 14 attached to the outer periphery thereof, an ink roller 15, and an impression cylinder 16. The plate cylinder 14 and the ink roller 15 face each other, and the plate cylinder 14 and the impression cylinder 16 face each other. Are arranged to be.
[0016]
The ink 17 supplied to the outer peripheral surface of the ink roller 15 is attached to the surface of the convex portion 13 a of the plate 13, and the printed material 18 conveyed between the plate cylinder 14 and the impression cylinder 16 is transferred to the impression cylinder 16. By applying a predetermined pressure, the ink 17 attached to the convex portion 13a of the plate 13 is directly transferred to the printed matter 18 and printing is performed.
[0017]
The method of the present invention is characterized in that the surface of the convex portion of the plate 13 set on the plate cylinder 14 of the printing apparatus 20 is set to a specification different from the conventional one. An example of a method for producing this plate is shown in FIG. explain.
[0018]
As the plate material, a known photosensitive resin 11 can be used. This photosensitive resin 11 is made of a resin material such as polyester, styrene, acrylamide or the like as a photosensitive agent (photocrosslinking agent), alcohol-soluble nylon as a main component, or the like. And further contains a photopolymerization initiator, a thermal polymerization inhibitor, and the like.
[0019]
The content of the photopolymerization initiator only needs to be within a range in which the photopolymerization of the resin material is effective, and the content of the thermal polymerization inhibitor can obtain the necessary thermal stability depending on the composition of the photosensitive resin. As long as it is within the range, the content is not particularly limited.
[0020]
Then, the surface of the photosensitive resin 11 is exposed to ultraviolet light from the negative screen 12 of the halftone screen on which the image to be printed is mirror-imaged, and the exposed area to be the image area 12a is cured to form the non-image area 12b. Dissolve the exposed area.
[0021]
At this time, in the image portion 12a of the negative film 12, the halftone dot area ratio at the outer edge portion 12a1 is set to be smaller than the halftone dot area ratio at the central portion 12a2.
[0022]
That is, in the present embodiment, as shown in FIG. 3, the halftone dot area ratio in the central portion 12a2 of the image portion 12a of the negative film 12 is set to 10% of the target halftone dot area ratio. The halftone dot area ratio at the outer edge portion 12a1 of the twelve image portions 12a is set to a halftone dot area ratio that is smaller than the halftone dot area ratio at the central portion 12a2 of the image portion 12a.
[0023]
The negative film 12 of this halftone screen is placed on and closely adhered to the photosensitive resin 11 and exposed to ultraviolet rays from the negative film 12 so that the halftone dot area ratio of the outer edge portion 12a1 is increased on the photosensitive resin 11. An image set smaller than the target halftone dot area ratio is cured. Thereafter, the negative film 12 is removed, and the surface of the photosensitive resin 11 is washed with, for example, water, alcohol, an aqueous alkali solution, an aqueous surfactant solution, or the like, and an unexposed area that becomes the non-image area 12b is dissolved.
[0024]
Thus, the exposure area | region which the photosensitive resin 11 hardened | cured is formed as the convex part 13a, and the halftone dot structure part which comprises this convex part 13a is the outer edge part 13a1 by which the halftone dot area rate was set to 5%. The unexposed area in which the photosensitive resin 11 is dissolved is formed as a concave portion 13b, and the plate 13 is manufactured (see FIG. 4).
[0025]
Although not shown, in the halftone dot constituting portion constituting the convex portion 13a of the plate 13, the halftone dot area ratio in the central portion 13a2 is set to the target halftone dot area ratio, and gradually toward the outer edge portion 13a1. Alternatively, the halftone dot area ratio may be set to decrease.
[0026]
Next, the operation of letterpress printing according to the method of the present invention will be described with reference to FIG.
[0027]
As already described with reference to FIG. 1, the ink 17 supplied to the ink roller adheres to the convex portion 13a of the plate 13 attached to the outer peripheral surface of the plate cylinder 14 with a uniform thickness. The surface of the convex portion 13a is composed of halftone dots composed of an assembly of minute convex portions 130, 130,..., And the halftone dot constituent portion has a halftone dot area ratio at the outer edge portion 13a1. It is set smaller than the halftone dot area ratio in 13a2. For this reason, as shown in FIG. 5, the adhesion amount of the ink 17 on the surface of the outer edge portion 13a1 of the halftone dot constituting portion constituting the convex portion 13a of the plate 13 is smaller than the adhesion amount of the ink on the surface of the central portion 13a2. I understand that
[0028]
On the other hand, the printed matter 18 supplied between the plate cylinder 14 and the impression cylinder 16 comes into contact with the convex portion 13 a of the plate 13 and is pressed from the back side by a predetermined pressing of the impression cylinder 16. By the pressing of the impression cylinder 16, the ink 17 between the surface of the printed material 18 and the halftone dot constituent portion surface of the plate 13 is crushed and pushed toward the outer edge portion 13 a 1 of the halftone dot constituent portion of the plate 13. Thus, the ink 17 is thickened at the outer edge portion 13a1.
[0029]
However, even if the ink 17 is thickened at the outer edge portion 13a1, that is, marginal occurs, the dot area ratio on the surface of the outer edge portion 13a1 is larger than the dot area ratio on the surface of the center portion 13a2 that is the target dot area ratio. Since the amount of ink 17 deposited is smaller than the amount of ink deposited on the surface of the central portion 13a2, the outer edge portion 13a1 has a halftone dot area ratio of the central portion 13a2 due to the thickening of the ink 17. It can be seen that the ink 17 transferred to the surface of the printed material 18 eliminates the difference in adhesion amount between the central portion 13a2 and the outer edge portion 13a1 of the halftone dot component, that is, the difference in the density of the printed image.
[0030]
Therefore, in the image of the plate 13 transferred to the surface of the printed material 18, the difference in density of the printed image can be suppressed, so that a printed material with a beautiful finish as a whole can be provided.
[0031]
In the present embodiment, an example in which the halftone dot area ratio at the outer edge portion 13a1 of the halftone dot constituent portion of the plate 13 is set smaller than the halftone dot area ratio at the central portion 13a2 of the halftone dot constituent portion of the plate 13 will be described. However, the halftone dot area ratio in the central portion 13a2 of the halftone dot constituent portion of the plate 13 is set to the target halftone dot area ratio, and the halftone dot gradually increases toward the outer edge portion 13a1 of the halftone dot constituent portion of the plate 13. The dot area ratio may be set so as to decrease. Thus, if the dot area ratio in the halftone dot forming portion is set so as to gradually shift from the central portion 13a2 to the outer edge portion 13a1, as described above. Ink adhesion unevenness can be further reduced, and the difference in printing density in printed matter can be further suppressed.
[0032]
【The invention's effect】
As described above in detail, according to the present invention, a part of the ink adhered to the surface of the convex portion of the plate by the pressing of the impression cylinder is transferred to the printed matter in a state of being pushed out to the outer peripheral side of the convex portion. In the halftone dot composing portion constituting the convex portion of the plate, the halftone dot area ratio at the outer edge portion is set in advance smaller than the target halftone dot area ratio at the center portion, so that the image transferred to the printed matter The difference in ink density between the central portion and the outer edge portion of the ink can be eliminated, and a printed matter with a beautiful finished print image can be provided.
[0033]
Also, the halftone dot area ratio at the center of the halftone dot composition part of the plate is set to the target halftone dot area ratio, and the halftone dot area ratio is gradually increased toward the outer edge part of the halftone dot constitution part of the plate. If it is set so as to decrease, it is possible to further reduce the unevenness of ink adhesion and to further suppress the difference in printing shade in the printed matter.
[Brief description of the drawings]
FIG. 1 is an external plan view showing a configuration of a relief printing apparatus used in a method of the present invention.
FIG. 2 is a plan view schematically showing an example of a manufacturing process of the plate shown in FIG.
FIG. 3 is an enlarged plan view showing the configuration of the negative film shown in FIG.
4 is an enlarged plan view showing a configuration of a plate shown in FIG. 2. FIG.
FIG. 5 is a diagram for explaining the operation of letterpress printing according to the method of the present invention.
FIG. 6 is an external plan view showing a configuration of a relief printing apparatus used for conventional relief printing.
7A and 7B are diagrams for explaining problems in conventional relief printing, in which FIG. 7A is an enlarged cross-sectional view of printing paper supplied between a plate cylinder and an impression cylinder, and FIG. 7B is a diagram illustrating the surface of the printing paper. It is an enlarged plan view shown.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 11 Photosensitive resin 12 Negative film 12a Image part 12b Non-image part 13 Plate 13a Convex part 13a1 Outer edge part 13a2 Center part 13b Concave part 14 Plate cylinder 15 Ink roller 16 Pressure cylinder 17 Ink 18 Printed matter 20 Letterpress printing apparatus

Claims (2)

A plate having a concave portion and a convex portion formed on the surface; a plate cylinder on which the plate is attached to an outer peripheral surface; and an impression cylinder arranged to face the plate cylinder and press the plate against a printed matter. And a relief printing method in which ink is attached to the convex portions of the plate and the ink is transferred to the printed matter,
The convex portion surface of the plate is constituted by halftone dots composed of a collection of minute convex portions , and the halftone dot area ratio at the outer edge portion of the halftone dot constituting portion of the plate is determined at the central portion of the halftone dot constituting portion of the plate. A letterpress printing method, wherein the halftone dot area ratio is set smaller than the halftone dot area ratio.   Set the halftone dot area ratio at the center of the halftone dot composition part of the plate to the target halftone dot area ratio, and gradually increase the halftone dot area ratio toward the outer edge of the halftone dot structure part of the plate. 2. The relief printing method according to claim 1, wherein the relief printing is set so as to decrease.

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