JPH10312051A - Gravure printing sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce roughness at a light part and to obtain good gradation and a color tone with higher saturation by transferring ink so that at least either the shape of a printing dot or the number of scanning lines can not be recognized in a low density area. SOLUTION: In the low density area which is <=20% out of the whole density area of an image, the ink is transferred so that at least either the shape of the printing dot or the number of scanning lines can not be recognized. In such a case, the gradation of the light part is constituted of a cell having large area and small depth, the cross section of the cell is in the middle of a conventional gravure cell and dot gravure cell, and ink transfer from a light cell is dispersed so that the shape of the dot and/or the number of lines are not distinguished, whereby the ink is excellently transferred to a body to be printed. Therefore, the light part having no roughness, expressed with beautiful gradation and having the plentiful gradation and the high saturation is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a beautiful gravure printing sheet which has no roughness in a light portion, has a rich gradation expression, and uses a normal scanning ruling.

[0002]

2. Description of the Related Art Conventional gravure printing employs any one of conventional gravure printing, halftone gravure printing (direct gravure printing), and engraving gravure printing. As shown in the basic shape diagram of the cell in the conventional gravure printing plate of FIG. 1, the volume of the cell decreases in the order of the shadow portion, the medium portion, and the light portion, and the transfer amount of the ink to the printing material is reduced. At the same time, the cell area formed by the transferred ink is also reduced. In the case of the conventional gravure, no reduction in the cell area is seen in FIG. 1, but it is slightly reduced in the actual plate. The conventional gravure printing method has the advantage of being excellent in gradation expression, but has many unstable elements in the plate making process and the process is long, so today, the size of the cells formed on the plate surface, that is, the printed dot It has shifted to another two-plate format that expresses light and shade with large and small. In the two-plate system, the gradation change of the continuous tone image reproduced on the printed matter is generally determined by any one of the size of a halftone dot, the number of halftone dots per unit print area, the size of a halftone dot density, and a combination thereof. Is expressed. Generally, the pitch of a halftone dot array in gravure printing is a scanning line number (also referred to as a screen line number but hereinafter simply referred to as a line number) of 150-2.
50 lines / inch, the most mainstream line number is 175
Line / inch. In addition, printing with finer halftone dots gives a higher resolution and a higher definition print image that enables delicate gradation expression. Therefore, in stamp printing and the like, high definition printing with a line number exceeding 300 lines / inch is possible. It has been done.

[0003]

In halftone gravure printing, the interval between adjacent halftone dots is larger in a light portion. Although the isolated halftone dots in the light portion are not easily visible to the naked eye, they have a problem of giving the light portion a rough and irregular feeling, which hinders beautiful gradation expression. This is largely attributable to the fact that the cell size in the light portion is generally as very small as 20 to 30 μm, and therefore, the contact between the ink inside the cell and the printing medium is extremely disadvantageous as compared with the conventional gravure printing plate. . That is, there is a large difference in ink transfer during printing. The difference between the two ink transfers is shown by the ink transfer explanatory diagram based on the cell shape in FIG. FIG. 2A shows a case of conventional gravure printing, in which a large, shallow cell 2 is formed on a gravure printing plate 1 and filled with ink, and then a printing medium 3 comes into contact with the gravure printing plate 1. Most of the ink is transferred to the printing substrate 3. However, in the case of screen gravure printing, FIG.
As shown in (b), since the width of the cells is narrow, the contact between the printing medium 3 and the ink is poor, and there are some cells that are not transferred to the printing medium. ). In order to reduce the graininess, high-definition printing exceeding 300 lines / inch may be performed so as to reduce the interval between isolated halftone dots. However, it is necessary to accurately control the printing plate and the variable elements of the printing process. For this reason, there is a problem that the manufacturing cost is too high. In addition, not only in dot gravure printing but also in offset printing, in the case of multi-color printing, in the light portion where the dots are isolated, if the dot groups having screen angles different by 30 ° overlap each other, FIG.
There is a fatal problem that a rosette pattern appears as shown in FIG. Furthermore, as a result of mixing of the reflected light from the paper surface without halftone dots printed, the same printing color can be reproduced only as a cloudy color with less saturation compared to a case where the same printing color is printed in a solid color. There is. The present invention has been made in view of the aforementioned problems,
A gravure printing sheet with a light part having a richer tone and a higher color tone with less roughness, using a commonly used screen gravure printing method of about 175 lines / inch. For the purpose of providing.

[0004]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to form an aggregate of cells having a scanning line number not exceeding 200 lines / inch on a printing plate by a halftone dot gravure printing system. A print sheet on which an image having a continuous tone is formed by printing using a gravure printing plate comprising at least 20% of the entire density area of the image.
In the following low-density area, a gravure printing sheet is provided that has undergone ink transfer so that at least one of the printing dot shape and the scanning ruling cannot be recognized.

[0005]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in more detail with reference to the drawings. FIG. 4 is an explanatory diagram of an ink-filled state in the light portion of the gravure printing sheet. First, FIG.
Shows an in-key inlaid state in a conventional net gravure printing sheet. As described above, although the depth of the cell is large, the diameter is small, complete ink transfer is difficult, and halftone dots are missing or missing. On the other hand, the cross section of the cell in the light portion of the gravure printing sheet according to the present invention is located between the conventional gravure printing cell and the halftone gravure printing cell shown in FIG. A wide and shallow cell is formed.
Therefore, the transfer of the ink to the printing medium is performed better than in the case of the conventional net gravure printing. Particularly, in the case of a paper or a plastic sheet having a smoothness and a good compressibility in which the printing surface enters into the inside of the cell by the printing pressure, as shown in FIG. As a result, the ink protrudes out of the cell, making it difficult to determine the cell shape, and the number of lines is printed in a state in which it cannot be determined. However, as shown in FIG. 4C, a white spot phenomenon is likely to occur in a print medium in which the smoothness of the print medium is low or the surface is hard and cannot sufficiently enter the cells. In actual gravure printing, the behavior of the ink transferred from the cells to the printing medium greatly changes depending on the ink viscosity, the type of the ink solvent, the printing speed, and the like.
(B) Shows more complex ink transfer than shown in (c). As shown in FIG. 4 (d), when the ink transfer portion is enlarged, when the transferred ink is paper, the ink vehicle penetrates between the paper fibers and dries, and the ink is dried. Since the coloring agent is individualized, the coloring region has an irregular dispersed pattern. Thus, according to the invention, as in conventional gravure printing,
In the light portion, the roughness and rough feeling due to the halftone dots are eliminated, and a printing sheet having a soft design property like a silver halide photograph is completed. Such an ink diffusion increases the light-colored area of the printing medium in the light area,
Saturation is increased, and a bright light portion is obtained. Generally, the printing of a wood grain decorative board is performed by a gravure printing sheet with a blurred plate using a light-colored ink, but in the case of the gravure printed sheet according to the present invention, depending on the grain pattern to be reproduced, the blurred plate is not used. However, in some cases, it is economical and efficient.

Next, a method for producing a gravure printing sheet according to the present invention will be described. In order to manufacture the gravure printing sheet according to the present invention, it is necessary to provide a cell having a large area and a shallow cell in the light portion by the dot gravure printing method. In order to print a picture having a shadow portion, it is necessary to have a large and deep cell as in the case of the conventional halftone gravure printing. Therefore, first, at the stage of the image data, the picture is divided into an A region belonging to the shadow portion and a B region belonging to the light portion. Alternatively, output may be performed twice using a tone curve that divides the A region and the B region into two. Then, the depth of the most shadow cell in the region A is, for example, 40 μm,
Plate making is performed twice each so that the depth of the shadow cell in the region B becomes, for example, 15 μm. In this case, the area B is protected by the resist while the area A is corroded, and the area A is protected by the resist while the area B is corroded. In this case, it is necessary to adjust the tone curve of the second corrosion in advance so that the gradation is naturally connected in the divided portions by the second corrosion.

[0007]

EXAMPLES A sample of a gravure printing sheet according to the present invention was prepared by the following method and compared with a conventional net gravure printing sheet. First, the grain of a cypress having a delicate continuous tone in the light portion was photographed using a digital camera. This digital camera is equipped with a solid-state imaging device (CCD) of 45 million pixels, and the signal from the CCD is
The digital image information was converted from digital to 8-bit gradation and recorded on a hard disk. The digital image downloaded to this hard disk is transferred to CEPS (Sci
(Tex Corporation, PRIMAX) and subjected to partial density gradation correction, endless processing, and the like. The wood grain pattern image data corrected in this way is
It was converted into a gravure halftone dot of 175 lines / inch using a laser stream plate making apparatus (manufactured by Synch Laboratories) in two times. For this purpose, a first output (exposure) is performed by using a tone curve as shown in FIG. 5A with a laser on a cylinder previously coated with a resist photosensitive liquid, forming a resist pattern, and developing and corroding. went. Next, the entire surface of the cylinder was coated with a resist photosensitive solution again, and a second output (exposure) was performed with a laser using a tone curve as shown in FIG. 5B. This grain image is divided at a halftone portion with an image density of 30%. The laser exposure outputs L1 and L2 at the 30% portion are different as shown in FIG.
This is because the cell size and the cell depth (approximately 15 μm) were set to be substantially the same after the end of the corrosion.
By doing so, the grain image having continuous tone divided at the 30% portion was naturally connected. After these two corrosions, halftone gravure printing is performed using a printing plate whose plate surface has been finished with chrome plating, and there is no graininess and rich gradation that cannot be obtained with conventional halftone gravure or mechanically engraved gravure printing sheets. It was possible to obtain a gravure printing sheet having a light portion with high saturation and a shadow density unchanged from the ordinary. Therefore, it was found that desirable gradation expression was possible without using a blurred plate used for grain printing. Printed object: Titanium decorative paper, 80 g / m ² (produced by Kojin Co., Ltd.) Printing speed: 100 m / min Ink viscosity: 12 to 15 seconds [Zahn cup # 4] Ink color: brown special color 3 colors Ink density (L value of D65 light source) Maximum shadow part: 30 Highlight part: 85

[0008]

According to the present invention, the gradation of the light portion is constituted by cells having a large area and a small depth,
By dispersing the ink transfer from the light cells so that the halftone dot shape and / or the number of lines are indistinguishable, beautiful gradation expression without roughness is achieved, rich in gradation and high in saturation. It is possible to obtain a gravure printing sheet having a light portion and a shadow density unchanged from the ordinary. In addition, it is possible to supply a product with little variation in quality that does not require unstable elements such as conventional gravure printing and that does not require endless (joint portion) correction of cells on a plate at an economic cost.

[Brief description of the drawings]

FIG. 1 is a diagram showing a basic shape of a cell in a conventional gravure printing plate.

FIG. 2 is an explanatory diagram of ink transfer depending on a cell shape.

FIG. 3 is an explanatory diagram of a rosette pattern.

FIG. 4 is an explanatory diagram of an ink-inlaid state in a light portion of the gravure printing sheet according to the present invention.

FIG. 5 is a tone curve in the case of divided output.

[Explanation of symbols]

 1 gravure plate 2 cell 3 substrate

Claims (1)

[Claims] 1. A gravure printing plate in which an aggregate of cells having a scanning line number not exceeding 200 lines / inch is formed on a printing plate by a halftone dot gravure plate-making method, whereby an image having continuous gradation is printed. In a printing sheet, in a low density area of at least 20% or less of the entire density area of the image, ink transfer is performed so that at least one of a printing halftone shape and a scanning ruling cannot be recognized. A gravure printing sheet characterized by the above-mentioned.