JPH0228860B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a net gravure plate, and more particularly, to a method for manufacturing a net gravure plate with simple steps and improved stability.

In photolithographic and letterpress printing, the tone of the original is reproduced by changing the size of the halftone dot area, whereas in general gravure, the halftone dot area is the same and each halftone dot is a rectangular point. By making the depth of each halftone dot different, the density of each halftone dot transferred to the printing medium is made different, thereby reproducing the tone of the original.

The general gravure method mentioned above is called conventional gravure and is widely known, but in addition to this method, there is also a method called net gravure, which is characterized by the depth and shallowness of the halftone dots as well as the size of the halftone dot area. This method combines the effects of

The general plate manufacturing method for halftone gravure, that is, the plate-making method, is called Darziyan's method, which uses continuous tone positive and halftone positive. First, a half-tone positive is attached and printed, and then a continuous-tone positive is attached and printed to expose the unexposed areas corresponding to the halftone dots when the half-tone positive is attached and printed, as described above. The baked carbon tissue is transferred to the surface of a cylinder prepared in advance, and then developed and etched.

Although the Darziyan method is improved in terms of plate-making stability compared to conventional gravure, it is unavoidable to make corrections to color tone and gradation during plate-making, but such corrections are made in continuous tone positives. Normally, in order to completely reflect the correction results in continuous tone positives in printing, it is complicated to create halftone positives based on the corrected continuous tone positives, and the difference between continuous tone positives and halftones is complicated. Because two types of positives are required, it cannot be applied when only halftone positives are available for use in lithographic or letterpress printing, or when they are to be used for other purposes.In the end, continuous tone positives and halftone positives are newly created from the original. It needs to be fixed and is extremely inconvenient.

Another method of net gravure is to first attach a gravure white line screen to the sensitized carbon tissue and bake it, then attach a net positive to it and bake it, and then attach the net positive via a diffusion sheet and bake it. There is a three-step baking method, but the carbon tissue, which has a gelatin layer and is used by sensitizing the gelatin layer with an aqueous solution of dichromate, is inherently unstable and must be handled with great care. Therefore, when performing three-step printing on such carbon tissue, there is a problem of poor registration due to expansion and contraction of the carbon tissue, and there is also a problem of misregistration due to the expansion and contraction of the carbon tissue. When using color separation net positives, it is difficult to determine the screen angle, and interference between these color separation net positives and the gravure screen can easily cause moiré. It is extremely difficult to match the screen angle of the net positive and the angle of the gravure screen each time, and the work efficiency is poor, and the above-mentioned screen angle problems also occur when reprinting. .

In addition, as yet another method for net gravure, first a gravure net positive with a white line screen is attached and baked on the sensitized carbon tissue, and then a net gravure net positive with a white line screen is attached through a diffusion sheet. There is also a method of pre-printing, but when the white line screen for gravure is attached and printed through a diffusion sheet, the light incident from the part corresponding to the white line screen is diffused by the diffusion sheet, so it is not possible to The light also reaches shadow areas that should not be cured (hereinafter, shadow areas refer to areas with high density in a manuscript or printed matter), which promotes unnecessary hardening of the carbon tissue in the shadow areas and suppresses the progress of corrosion. It has the disadvantage that the required plate depth (depth of the gravure plate) cannot be obtained from this method.

The present invention has succeeded in overcoming all of the above-mentioned conventional drawbacks by adopting the configuration described in the claims.

The present invention will be explained in detail below.

First, in the present invention, a gravure screened net positive is closely attached to a sensitized carbon tissue and baked. The gravure screened net positive used here is used for the purpose of forming an ink cell bank to prevent ink from flowing out in the intermediate or shadow areas during gravure printing. In order to produce such a net positive with a gravure screen, for example, a net positive for planography or letterpress is adhered to a suitable photosensitive material, baked and developed to produce a net negative, and then the obtained net negative is used for gravure printing. After overlapping the negative screen, it is again brought into close contact with an appropriate sensitive material, printed, and developed. In addition to the silver salt film, photosensitive materials such as photochromic films can also be used as the sensitive material in the above. Further, as the negative screen for gravure used in the above, a black line screen used in the plate making of compensatory gravure, a negative of a contact screen for gravure (commonly known as a blur screen), etc. can be used. The number of lines of these screens is not particularly limited, but preferably 100 to 350 lines/inch, ie, about 4 to 14 lines/mm. In addition, the special contact screen for gravure mentioned above has a low density in the center, a high density towards the periphery, and the highest density in the periphery, making it look like a square with a blurred outline or a square with rounded corners. It consists of repetitions as a unit.

The carbon tissue that is the object of adhesion and baking of the gravure screened net positive formed as described above may be one that is normally used in conventional gravure, and the carbon tissue is immersed in an aqueous solution of potassium dichromate. After that, sensitize it by drying it in a dark room and use it.

For sensitized carbon fiber,
A so-called vacuum printing frame is used to adhere and print the gravure screened net positive, and a well-known light source used for printing, such as an ultra-high pressure mercury lamp, carbon arc, or xenon arc, is used to achieve the required exposure. It is preferable to monitor the amount using an integrating light meter or the like.

By closely contacting and baking the above gravure screened net positive, a thick hardened gelatin layer of carbon tissue is formed from the middle part to the shadow part, corresponding to the shape of the cell bank required for the gravure plate. A thick hardened gelatin layer is formed over the light area to determine the size of the halftone dots of the gravure plate.

To explain the process of printing a net positive without a gravure screen in close contact via a diffusion sheet, the net positive can basically be used as is for lithography or letterpress printing. Substantially, the net positive used in producing the gravure screened net positive can be used as is, and the baking method can be the same as the process of adhering and baking the gravure screened net positive. Can be done.

In addition, the diffusion sheet has a light transmittance of 60 to 90% and a thickness of about 50 to 100 μm, depending on the density range of the halftone positive used, the condition of the manuscript, the developing method, and the etching method. It can be selected and used as appropriate, and specific examples include matte film and diffusion glass. By printing through such a diffusion sheet, the light that passes through the net positive is diffused while passing through the diffusion sheet, and as a result, the amount of light that reaches the carbon film in the shadow area is small. The opposite effect occurs in the highlighted area, and this effect converts the halftone positive halftone dot image into a continuous tone image.

The above two baking steps in the present invention can be performed in any order, and the carbon tissue that has been baked in either order can be transferred to a printing plate such as a cylinder, further developed, and then etched. A gravure version can be obtained by This operation can be performed in substantially the same manner as in conventional gravure.
The baked carbon tissue is quickly transferred to a predetermined position on the printing plate. As the plate material, in addition to cylinders for ordinary rotogravure printing machines, copper plates and sleeve-shaped plates can also be used. The baked carbon tissue was transferred using a wet or dry method. After transfer, the insoluble parts remained on the printing plate, so the unsensitized parts were dissolved and removed with hot water to completely remove them. Afterwards, wash with water and dry.

Next, corrosion is carried out with an aqueous ferric chloride solution, and the corrosion is carried out by a method using several to seven types of ferric chloride aqueous solutions with different specific gravities, or by a one-liquid corrosion method using one type of ferric chloride aqueous solution. You can do it by holding it.

After corrosion, the surface of the plate material can be further plated with chromium or nickel to increase printing durability.

Since the present invention has the above configuration, it has the following various effects.

(b) Gravure plates can be manufactured using only net positives for planography or letterpress, and therefore net positives for planography or letterpress can be reused;
In addition, unlike in the Darziyan method, when only halftone positives for planography or letterpress printing are available, there is no need to newly produce continuous tone positives and halftone positives.

(b) Since the printing process only needs to be carried out twice, there are no problems such as poor registration due to expansion and contraction of the carbon tissue during printing, or variations in quality due to poor screen angles during printing or reprinting.

(c) Because the net positive is printed through a diffusion sheet, compared to the method of printing a net positive with a white line screen for gravure through a diffusion sheet, there is no need for carbon chips in the shadow area. There is no hardening and therefore the required depth of the shadow area can be maintained.

(d) Problems related to the screen angle in the three-step method, ie, moiré, do not occur.

In addition to the above-mentioned effects, the advantage of net gravure is that the volume (high density) of gravure is combined with the high reproducibility of the middle and highlights of planographic offset, and proof printing can be replaced with complicated gravure proofing. On the other hand, the present invention does not hinder the ability to perform offset calibration, and each step of the method of the present invention can be performed using known equipment and materials, and is stable and stable. Easy to implement.

Claims (1)

[Claims] 1. To the sensitized carbon tissue, a process of closely attaching a net positive with a gravure screen and baking it, and a process of attaching a net positive without a gravure screen via a diffusion sheet and baking it. A method for producing a net gravure plate characterized by: