JPS5848089B2 - gravure seihanhou - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention uses a continuous tone positive in the gravure plate making method using carbon tissue, and by combining it with an arbitrary plain screen, it is possible to improve both the depth and depth of the plate and the size of halftone dots. It is related to the gravure plate-making method that reproduces gradation.

Conventional gravure plate making methods can be roughly divided into two: the conventional method, where the area of the gravure plate cells is constant and gradation is expressed only by changing the depth and depth of the cells; and the conventional method, where the cell depth is constant and the gradation is expressed only by changing the size of the halftone dots. It can be divided into single mesh gravure methods that express gradation.

In the conventional method, the difference in resist film thickness caused by photo-curing of the gelatin layer of sensitized carbon tissue is replaced by etching into the depth and depth of the plate. Because carbon tissue is used, there are no problems with baking, development, and corrosion. Each process has many unstable elements.

In particular, the depth of the plate needs to be about 1 μm for the highlighted part of the image, but it is difficult to stably obtain the desired depth.

On the other hand, in the single-dot gravure method, a photosensitive liquid is applied to the plate material, a halftone positive is printed in close contact with the plate material, and then developed and etched. When printing, the ink transfer is unstable, resulting in many dots and a rough-looking printed matter, which becomes especially noticeable when the printing material is paper, combined with the roughness of the paper surface. .

Additionally, in order to compensate for the drawbacks of the conventional method and the single-dot gravure method, a method has been considered in which gradation is expressed by both the depth and depth of the plate and the size of the halftone dots.

The most typical method is the two-plate positive method, in which a continuous tone positive method is used to incorporate the deep and shallow elements of the plate, and a halftone positive method is used to incorporate the large and small elements of the halftone dots. This method uses two positive plates and exposes each positive plate separately to a sensitized carbon tissue, but there are problems in the plate-making process due to the use of two types of positive plates with the same size. There are many.

For example, this method requires two continuous tone positives and halftone positives for each color, and for four-color printing, a total of eight positives are required and must be in register with each other.

For this reason, the effort of pasting in positives and making corrections becomes extremely complicated.

Further, if there is a change in specifications after the plate making is completed, not only does it take time and effort to make adjustments, but it also increases the amount of photosensitive material used, which poses many problems in terms of cost.

As mentioned above, both the conventional method and the single mesh gravure method have many problems in reproducing the tone of the light area, and the causes of this problem are as follows.

Figure 1 is an enlarged sectional view of the contact area between the gravure plate and the doctor blade in the conventional method, showing the cell cross section of the highlighted part, where 1 is the gravure plate cylinder, 2 is the cell, and 3
is a doctor. Blade 4 indicates the dowel part that supports the doctor.

From Figure 1, the contact width of the doctor blade is very wide relative to the width of one cell, and the depth is extremely shallow relative to the width of the cell, so when ink is scraped off on the plate with the doctor blade, it remains on the cell. It can be seen that the amount of ink tends to become unstable, and that even a slight change in the depth of the plate causes large fluctuations in cell volume.

In this way, the unstable highlight area moves to the middle area and becomes stable as the plate depth increases.

On the other hand, the light area of the single-dot gravure method is completely opposite to that of the conventional method; the depth is extremely deep compared to the area of the cell, and the width of the 5% halftone area with a line count of 17517 inches is is about 30μ, and the depth is about 30μ.

When a cell in this state is used to scrape off ink on the plate with a doctor blade during printing, the ink in the center of the cell becomes depressed, and the light area of the cell is deposited in the minute depressions in the paper that is the printing material. If they match, metastasis will be significantly worse.

Also, when the paper and plate are separated, some of the ink is transferred to the paper at a certain rate depending on the conditions at the time, and the rest remains on the plate.
At this time, if the plate is deep compared to the halftone dot area, the ink at the bottom will not be involved in the transfer, and if the printing conditions change even slightly, the ink transfer rate to the paper will fluctuate, and the density and gradation of the printed matter will become unstable. become.

As a method to solve these problems, a method can be considered to increase the size of the highlight halftone dot to the minimum size that allows stable ink transfer in accordance with the surface smoothness of the printing medium.

The present invention makes full use of the advantages of both the conventional method and the single gravure method, eliminates the instability of gradation reproduction in light areas, and provides a simple method.

Next, each process will be explained according to the drawings.

FIG. 2 shows the first step, in which 5 is a sensitized carbon tissue, and 6 and 7 are the constituent elements of the carbon tissue, which are a baryta paper and a gelatin layer, respectively.

Reference numeral 8 indicates a white line gravure screen, 14 indicates a photocured portion of the gelatin layer, and 9 indicates the direction of light during printing.

A commercially available carbon tissue may be used, and a gravure photoresist may be used instead of the carbon tissue.

The white line gravure screen used for printing may be the screen used in the conventional method, and if necessary,
0,175,200,250,300t/in
Use something like ch.

In this step, the white line gravure screen and the sensitized carbon tissue are brought into close contact with each other as shown in the figure and baked, and the portions of the gelatin layer corresponding to the dots are photocured.

FIG. 3 shows the second step, where 10 is a continuous tone positive, 1
1 is a highlight part, 12 is a shadow part, 13 is a plain mesh film, 13a is an opaque part that does not transmit light, 13b is a transparent part, and 15 is a gelatin part hardened by exposure in the second step.

As shown in the figure, this process involves sequentially superimposing plain mesh and continuous tone positive on the carbon chisosh obtained in the previous process and baking them in close contact. It's about putting it in.

The number of lines and the shape of the halftone dots of the plain screen used here are arbitrarily selected depending on the surface smoothness of the printing material and the expected tone, and this plain screen can be easily used from offset and gravure contact screens. You can make anything you want.

Note that the shape of the plain mesh may be any well-known shape and is not particularly limited, and circular, triangular, quadrangular, hexagonal, and other appropriate shapes may be adopted.

However, in general, when a plain net is made using the contact screen as described above, a circular net is likely to be obtained.

It is preferable to use a plain mesh having circular halftone dots because it is known that circular cells transfer the ink from the gravure plate to the paper better.

The number of lines of the plain mesh is not particularly limited as long as it is the same as the number of lines of an ordinary gravure screen commonly used in gravure printing.

As mentioned above, since the gravure screen is generally used with 150, 175, 200, 250, or 300 lines per inch, it is preferable to use 150 lines/inch or more in terms of print quality.

The relationship between the size of halftone dots required to stabilize the reproduction of light areas and the depth of the plate depends on the paper quality, ink viscosity and surface tension,
The shape and angle of the doctor blade will vary depending on the C printing conditions, but when selecting a plain screen, the most important issue is the condition of the surface of the printing material, and the minimum number of halftone dots in the highlighted area Decide on the size and depth and choose the plain netting you need.

When plain mesh and continuous tone positive are layered and baked in close contact,
In the light area, light passes through the positive and hardens the gelatin in areas other than the opaque area of the plain screen, and since the opaque area is not exposed to light, the gelatin underneath remains unhardened.

On the other hand, in the shadow part of the pattern, the concentration of positive is high, so almost no light passes through it, and no photocuring reaction occurs regardless of the presence or absence of a plain screen.

In the middle tone areas, the amount of light that is inversely proportional to the positive density reaches the gelatin layer, and the areas that correspond to the transparent areas of the plain screen are photocured in proportion to the amount of light, and the areas that correspond to the opaque areas are not cured. remain as is.

In the gelatin layer, hardened gelatin parts proportional to the amount of light transmitted are sequentially formed from the light to the shadow part.

FIG. 4 shows the third step, and 16 shows the gelatin hardening section.

The purpose of this process is to replace the continuous tone positive tone with the deep and shallow elements of the cell.

When continuous tone positive is printed in close contact with the carbon tissue obtained in the previous process, the light areas of the pattern that were blocked by the opaque areas of the plain screen in the second process are exposed to light and the gelatin hardens. .

In a part of the shadow, the dotted area remains hardened by the white line gravure screen, and even in this third baking step, since the positive density is high, only slight fog hardening occurs.

In other half-tone areas, the area covered by the opaque area of the plain screen is exposed to light for the first time in the second process, and the gelatin layer hardens in proportion to the amount of light, and in the transparent area of the plain screen, the second process In addition to the thin layer hardened by exposure to light, the third baking step causes further hardening of the gelatin layer.

Thus, a hardened relief of gelatin is formed which is inversely proportional to the overall positive concentration.

The fourth step is generally the same as the plate-making process of the conventional method, but as mentioned above, the size of the halftone dots is included in the highlighted area, so the relief of the gelatin layer will be thinner than that of the conventional method. Therefore, the corrosion of the highlighted portion starts relatively quickly, and the corrosion time of the entire tag is shortened, and the factors that vary the cell depth during the corrosion process are reduced.

In the shadow part of the picture, only the white line of the screen is burned in regardless of the plain net pattern, so the shape of the cell obtained by corrosion is exactly the same as that of the conventional method cell.

In the highlight area, the thickness of the hardened gelatin layer corresponding to the transparent area of the plain mesh is thicker than that in the shadow area, so the etching time is within the required time to obtain the required cell depth in the shadow area. However, the corrosion in the highlighted areas never ends.

Furthermore, the element of depth can be taken into account by reducing the cell area to a desired size.

For example, if a plain mesh is selected so that the highlight cell area is 17/3 of the normal size, the depth can be set to three times the normal size, that is, about 3 to 5 μm.

Accordingly, a plate having a very stable form due to the ink transfer mechanism can be obtained.

Furthermore, during the corrosion process in the halftone area, corrosion first progresses to the portion corresponding to the opaque portion of the plain screen, and then corrosion progresses to the cell portion of the transparent portion of the plain screen.

Therefore, a plate containing a slightly deeper portion and a shallower portion within one cell is obtained.

A cross-sectional view of the plate obtained as described above is shown in FIG. 5, and a plan view of the halftone area and highlight area is shown in FIGS. 6A and 6H.

In addition, in FIGS. 3 to 5, the position of the opaque part of the gravure screen and the position of the opaque part of the plain screen are shown to be the same, but this does not affect the effect of the exposure process of the present invention. It is shown this way for easy understanding.

In practice, it is not always easy to make the position of the opaque part of the gravure screen the same as the position of the opaque part of the plain screen, and it is well known that moiré patterns are likely to occur between two types of regular halftone dot patterns. Therefore, in order to prevent the occurrence of this moiré pattern, it is preferable that the halftone dot arrangement angle of the gravure screen and the halftone dot arrangement angle of the plain screen be different.

Also, in Figure 6, the positional relationship between the opaque area of the plain mesh and the opaque area of the gravure screen is different from that of Figures 3 to 5, but this is done by taking the above points into account. Figure 6 is designed to help you understand the angular relationship between the figure and the plain net, and Figure 6 shows the figure closer to the actual figure.

17 is a cross section of a cell in a highlight portion, and 18 is a cross section of a cell in a halftone portion, which is divided into a shallow portion 20 and a deep portion 21.

Reference numeral 19 shows a cross section of a portion of the shadow, and reference numeral 22 shows dots between cells.

Because the present invention has the above-mentioned configuration, it is possible to solve the problems of complexity and high cost of the photolithography process, such as the conventional two-sheet positive method and methods using special photoresists, and to prevent moiré in halftone dot reproduction. On the other hand, by making the plain screen slightly larger, it is possible to reproduce halftone dots without causing moire without changing the screen angle, and furthermore, when partially correcting the plate after plate making, the plate obtained by the present invention can be used. The depth of the highlighted area is several times as deep using the conventional method, so if you apply an etchant to the corrected area to make the plate deeper, or plate it to raise it up and make the cells shallower, use the conventional method. It is much easier than correcting highlight areas, and by appropriately selecting the plain mesh, it is possible to change the gradation reproduction without changing the photolithography process. Effects can be obtained.

[Brief explanation of drawings]

Fig. 1 is an enlarged sectional view of a conventional gravure plate and a doctor blade, Fig. 2 is a first process drawing showing the plate making process of the present invention, Fig. 3 is a second process drawing, and Fig. 4 is a third process drawing. The process diagram, FIGS. 5 and 6 are a sectional view and a plan view of a plate obtained by the present invention.

Claims (1)

[Claims] 1. A step of closely printing a white line gravure screen with a desired number of lines onto a sensitized carbon tissue in a gravure plate making method using continuous tone positive, and a plain color having a halftone dot area smaller than the cell area of the white line gravure screen. The carbon tissue obtained by the step of closely baking the mesh and the continuous tone positive onto the carbon tissue, and the step of closely baking the continuous tone positive onto the carbon tissue, is transferred to a gravure cylinder, developed, and etched. The gravure plate-making method consists of a process of