DE1935784A1 - Contrast raster for direct or indirect offset printing - Google Patents

Description

No sign: 521 pg 69,101

Applicant:

Dr. Walter Gordaro, 1-00100 R ο πι / Italy

Designation: Contact grid for direct or indirect

Offset printing

Addition to German patent application P 17 72 372.7

The present invention relates to a contact grid for openset printing systems. In particular, the invention relates to a Contact grid for applying negatives or positives to plates, around printing matrices for printing on paper or other Carriers using the direct or indirect offset printing system to obtain.

The above contact grid and its application in direct rotary printing or with collotype are described in the German patent application P 17 72 372.7 of May 4, 1968. The constructive and geometrical characteristics of such a contact grid and the advantages of its use in rotary printing systems are described in detail in the description and claims of this patent application. It also shows the aforementioned Patent application accompanying drawing a preferred embodiment of the grid with rectangular border fields.

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According to the invention it has now been found that by using this grid in the direct or indirect lithographic offset printing system in black and white or in color results in terms of image clarity and color quality compared to conventional offset printing systems achievable results are significantly improved.

In offset printing, it is known to use various types of contact screens to produce screened transparencies; among other things, the chessboard grid, the elliptical dot grid, the respiraster or the colon grid are used most often.

Using these grids one can get good gridded positives. It should be noted, however, that this grid in End result does not provide a satisfactory result, as in different Cases deviations from the original (low fidelity) can be determined and in particular the outlines or The shape of the blackening is lost, the last passages are unclean, a flattening of the hard tones is noticeable etc.

In offset printing, these disadvantages therefore result in considerable disadvantages Trouble. In order to use offset printing in halftones Obtain a printed image in one or more colors, taking into account the sheen or luminosity of natural images Viewing with the naked eye is preserved to a sufficient degree, the rasterized slide must be as large as possible from shades from the deepest black to the most delicate Have tint. It is also essential that every gradation or passage be clear, especially with the harder tones is scanned.

The grid previously used, those in the above-mentioned patent application mentioned, this scanning of the gradations or not ensure passages in harsh tones.

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Although a size difference between the point maximum Blackening and the subsequent passes' is present, this difference does not appear in the print. In fact, the slight swelling of the point as a result of the Water bath and the crushing by the pressure to a merging of the points in the first stages of the hard Tones so that any difference between the colored surfaces is eliminated for maximum blackening. From this follows the well-known Disadvantage that the black masses are "cloudy" (kneading).

Note also that, generally speaking, the conventional offset contact rasters have a 1/1 ratio. On the grid therefore the surface that prints and covers is the same as that of the transparent, white part. To therefore a greater opacity of the black masses of the screened positive to obtain one must use high contrast negatives; the mass of the light then entering the higher tones is able to enlarge the point to almost complete closure. Even if this result is easily achieved note that the size of the dot is changed in semitones, causing excessive darkening the semitones themselves are the result. Otherwise one must note that it is practically impossible to use a screened positive good fidelity to the. To produce the original, assuming a negative that is too high in contrast.

In order to achieve a usable end result, the operator must process the rasterized positive by hand, making a Used a brush or red blood lye (potassium ferricyanide), or he must use other means until the proportions and size of the spots are restored to the naked eye. The result achieved here is of course not precise enough, as it is solely based on the visual evaluation of the operation smanne s rested.

The present invention aims to use one

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Contact grids in a direct or indirect offset printing system from, whereby most of the disadvantages are eliminated, which otherwise, i.e. when using the currently usual contact grid, are inevitable.

The main advantage of the screen according to the present invention is that it can produce prints with a number of gradations can produce in halftones that are greater than the prints that can be achieved with conventional means; twelve levels in the G-tone based on the standard Kodak scale.

Another advantage of the screen according to the invention is that you get better contrast or better softness achieved; thanks to its use, it is possible to obtain the double tone, what with the traditional direct or indirect ones Offset printing systems were never achievable. Indeed one has so far to achieve high-contrast images in the hard tones and in the bright lights and to achieve softer, more detailed Midtones in direct or indirect offset printing the image was printed once on top of each other in two print runs printed with an extremely soft positive and then subsequently with a positive that encompasses skeletal zones which the black masses were reinforced and detailed. With the grid according to the present invention, however, one can the double tone when printing by means of a single screened positive, a single transition and therefore a single one Establish pressure passage.

Another very important advantage of the grid according to the present invention Invention consists in doing the same, rasterized Positive with equal success in either direct or with the indirect offset printing system or with the rotary printing system can apply, a result that was previously never achievable with a single screened positive.

Another advantage of the grid according to the present invention consists in the fact that with a grid with right

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angular grid the so-called "moire effect" almost entirely Indeed, prints made with defective slopes have been found to be optimal Results were obtained.

The subject of the present invention is a contact grid for both negative and positive direct or indirect Offset printing in any size, shape or color with rectangular Rasterization, which is characterized in that each rectangular element is determined by two lines of different spacing where the ratio values between the opaque and transparent part (line / point ratio) given and are different on the short and on the long side of the rectangular element and. being the photographic Degree of contrast (color tint) of the internal shades in each individual rectangle on the short side strong and on the long side is weak.

It was found in accordance with the present invention that one by the rectangular grid in the direct or indirect Offset printing can produce excellent results could not be achieved with conventional grids, where the grid was square.

However, if you use a rectangular grid, then you have one over a long side that allows a subdivision into sufficiently distant ropes, while, the short side where the lines are closer together, supplies the denser grid, so that the grid is no longer visible to the naked eye.

It follows from this that with the aforementioned technical solution (rectangular grid) the merging of the transitions in the intermediate tones is avoided, since the soft tint, which is arranged on the longer side, is easily distinguishable is.

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In addition, the strong contrast of the tint on the . short side a clear separation of the high contrasts black-halftones-white, what in connection with the softness of the The transitions of the semitones on the long side emphasize the latter and prevent them from merging.

Thanks to the water bath and the pressure, the differences allow the ratio of the lines a larger line spacing on the long side.

When using the grid according to the invention, an etch with a parallelepiped shape is obtained in the plate different surface structure. In both cases (rotary printing and offset printing) these cause differences strong coloring of the first strong tints on printing; the rectangle is complete and the lines are very thin. In the immediately following pass, the rectangle experiences a considerably greater dimensional reduction on the long side and a significantly weaker reduction on the short side, which corresponds to a significantly smaller volume than that of the first notes.

The transitions are heavily graded in the middle tint with numerous variations on both the long and the short side: the differences on the short side prevent the fusion and the endpoints are very fine with large distances from each other. In the last rounds is the pressure effect is delicate, almost white, whereby the transition to perfect white takes place gradually without discontinuities.

The present invention will now be made with particular reference to FIG the drawing described, which is attached to the main application P 17 72 372.7, this drawing is only one of the inventive concept shows non-delimiting, preferred embodiment of the invention.

The description of the main application mentioned and that of the

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Drawing attached to the main application shows that the line / point ratio (ratio of the opaque to the translucent Part) is different on the two sides and is 1/3> 5 on the short side and 1 / 2.5 "on the long side, so that the lines or stripes are spaced sufficiently to withstand the aforementioned swelling phenomenon.

The present invention has been described with reference to a specific embodiment, but it will be understood that that this embodiment can be modified practically in many ways without departing from the concept of the invention.

Briefly summarized, the present invention relates to a contact screen for both negative and positive direct or indirect offset printing of any size, shape, or color by one or more of the following: is marked:

a) a different light transmission ratio (degree of photographic contrast; line / point ratio) within each grid element;

b) two adjacent sides of each grid field have a different line / dot ratio;

c) the number of lines per cm to produce a different one Line / point relationships are different.

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Claims (6)

A Ή SPRUG -HE 1 . Contact grid for both negative and positive direct or indirect offset printing in any size, shape or color, characterized by a different Light transmission ratio (photographic contrast ratio; Line / point ratio) within each grid element. 2. Grid according to claim 1, characterized in that two adjacent sides of each grid field have different line / point ratios. 3. Grid according to claim 1 or 2, characterized in that the number of lines per cm for generation of a different line / dot ratio are different. 4- · grid according to one of claims 1 to 3> characterized by rectangular grid fields with sides of unequal length. 5. Grid according to claim 4, characterized by a line / point ratio of 1/2, b on the long and 1/3 fb on the short side of the rectangle. 6. grid according to claim 4 or 5, characterized characterized in that the degree of photographic contrast of the inner shading in each individual rectangular grid field on the is strong on the short side and weak on the long side. 7 · grid according to one of claims 2 to b, characterized in that the line density of the long side 009838/1303 each of the individual fields is 60 per cm, while that of the short side is 90 per cm. - 009838/1303