FR2660246A1 - Films or recordings for reproduction and supports - cliches, plates, cylinders - for printing - Google Patents

Abstract

The subject of the present invention is: - films or recordings for reproduction, - supports for printing. On the said films, recordings or supports, are introduced characters which, according to the invention, allow one and the same document to be printed using different lines to the inch numbers.

Description

Films or recordings for reproduction and supports -cLiches, plates, cylinders- for printing.

 The present invention relates to films or recordings for reproduction. It also relates to supports - plates, plates, cylinders - for printing.

 The former are used to prepare the latter according to techniques familiar to those skilled in the art. Thus found on said films, recordings and media the essential characteristics of the present invention, developed below.

 Said invention is more particularly described in the context of printing. Its implementation facilitates and improves printing.

 However, it is not limited to this framework and can advantageously be used in other reproduction techniques, reprography for example.

 We know that printing consists in reproducing, in particular texts or images, by depositing ink on a material such as paper.

 Surfaces prepared for this purpose take the ink and deposit it on said material, directly or indirectly.

 The reproduction is made by decomposing the colors between two values, which are that of the material (for example white for white paper) and that of ink, printed in solid color (in solid black for example).

 Between these two extreme values, respectively called shade at O% for the color of the material (white of the paper for example) and shade at 100% for the solid color, there are all the intermediate shades. Those skilled in the art will say that they print a 50% shade at a specific location, if at this location the printed surface has 50% ink and 50% without ink. It is thus commonly used shades ranging from 0.5% to 99.5% and mainly ranging from 1% to 95%.

 To reproduce the different shades, we use a frame. This optically transforms said colors into a multitude of small dots whose centers are always equidistant from each other.

 Said small dots, the diameter of which varies, occupy a more or less large area. Thus, dark shades have an opaque surface with a small (transparent) dot in the middle that will not take ink, while light shades have a transparent surface with a small opaque dot in the middle that will take ink.

 Wefts are defined by the number of lines in linear inches or centimeters. The less line there is in an inch or a centimeter, the larger the weft - the details not reproduced and the points visible to the naked eye; the more line there is in inches or centimeters, the finer the weft - the details reproduced and the dots not visible to the naked eye -.

 The number of lines is between 20 and 600 but generally the newspapers which are printed on very ordinary paper use 65 or 80 wefts per linear inch. Wefts 120 and 133 are commonly used for ordinary jobs and wefts 150 and 175 for quality jobs on fine paper.

 The printing surfaces, that is to say those which take up ink, are in relief on the plates and plates used in letterpress and flexography. They are practically at the level of non-printing surfaces in wet offset and dry offset. In wet offset, the plate has encrophilic surfaces generally consisting of a varnish and hydrophilic surfaces consisting of the support advantageously treated, for example matt and anodized aluminum, matt chrome steel.

 In dry offset, the ink does not set on non-printing surfaces, because they are covered with a silicone-based coating.

 The printing surfaces are hollowed in gravure printing.

A copper cylinder is engraved at the places intended to collect the ink. A chemical etching is carried out with an acid such as iron perchloride which attacks only the surfaces not protected by a photosensitive lacquer of the Photo-Resist type or by a bichromated layer of the charcoal paper type, or a physical etching. The latter is carried out with a device of the type
HELIOKLISCHOGRAPH, machine having an engraving head provided with a diamond.

 The engraved cylinder is mounted on the printing machine. It bathes for a third in a tank filled with liquid ink and is wiped by a doctor blade, a kind of flexible and fine blade which leaves the ink only in the engraved parts of said cylinder. The paper passes between a rubberized pressure roller and said engraved copper cylinder and is thus covered by the ink remaining in the hollows of the engraved parts.

 Each printing process has its advantages and disadvantages.

 Thus, in letterpress, flexography, wet offset and dry offset, one encounters great difficulties in printing the details in the dark parts, which, especially with fine wefts, are generally blocked. The use of firmer inks does not solve these difficulties.

 In gravure printing, it is very difficult to reproduce light shades. Indeed, the engraved surface (intended to collect the ink) is very small in the clear parts and, when it is obtained by physical engraving, it is understood that the diamond does not penetrate as deeply into the copper in said clear parts as in the dark parts. There is therefore necessarily less ink than desired on the printed material. This lack of ink is further accentuated because the intervening doctor tends to wipe, that is to say to remove said ink from small surfaces engraved with light shades. In addition, when the support to be printed is not very flexible on the surface and / or poorly absorbent, as is the case with the synthetic or metallic materials used in the packaging industry, the ink in the small hollows of light shades tends to remain there and therefore transfers very poorly onto said support.

 Whatever the printing process used, the printing parts are created from information deposited on a photographic film or on a recording, for example a disc.

 To date, a film has been produced from a document to be reproduced, either by photographing and screening said document directly with conventional equipment, or by using scanners. According to this second variant, the document is read at high speed, by a head provided with a sort of densitometer. The densities of hues read are converted, for example into a binary system and recorded on a medium, such as a disc. The information thus recorded can be used by another electronic machine which, after having screened it, projects it on a "film" film. This latter machine is capable of rendering the information received as it is or after having modified it. We thus obtain a screened film with the desired number of lineations. The electronics can thus provide a film with little linearity, that is to say a large frame - weft 40 for example - or a film with a lot of linearity, that is to say a fine frame -frame 400 for example-.

 The above remarks show that to date, the reproduction of a document always involves the preparation of a screened film, whether obtained directly photographically or indirectly using the scanner. It is understood that future techniques will make it possible to directly use the information received - recording - for the production of the printing parts on a support - plate, plate, cylinder - for printing.

 However, to date, whatever the technique or the material used, a single and single line is used, per document to be reproduced.

 It has been found, and this is the object of the present invention, that it is possible to facilitate and improve printing by using for the same document different Lineatures.

 Thus, according to one of its objects, the present invention relates to a film or recording for reproduction, characterized in that the parts of said film or of said recording which are intended to generate inked surfaces, have at least two different numbers of frame line size.

 According to an advantageous variant of the invention, the parts of said film or of said recording which are intended to generate inked surfaces have numbers of weft linearity depending on their surface.

 Said films or recordings which have the characteristics set out above allow the preparation of supports for printing which have characteristics, deriving directly from those of said films or recordings.

 Thus, according to another of its objects, the present invention relates to a support - plate, plate, cylinder - for printing, comprising surfaces retaining ink and surfaces not retaining ink, characterized in that said surfaces The ink has at least two different weft line number.

 According to an advantageous variant of the invention, said surfaces retaining the ink have numbers of weft linearity depending on their surface.

 According to this variant, the number of screen weights (the size of the screen) is modulated according to the invention as a function of the colors to be reproduced, so as to obtain a gradual fade, without breaking on the printed material.

 Thus, according to the invention, for printing processes which have difficulty printing dark colors (typography, flexography, wet offset and dry offset) a lower number of lineations, that is to say a larger screen in the dark areas and for printing processes that have difficulty printing light shades (gravure), a lower number of lines, that is, a larger screen in the light areas.

 The ink-absorbing surfaces of the supports of the invention, useful in dry offset, wet offset, typography or flexography (plates or plates) therefore advantageously have, in the dark shades, a number of weft linearity than that in the light shades.

Thus, various variants of the invention developed within the framework of the techniques of dry offset, wet offset, typography or flexography, have as their object:
- plates or clichés, on which the number of screen weights in the ink-absorbing surfaces greater than 30% is less than the number of weft lines in the ink-absorbing surfaces less than 30%;
- plates or clichés, on which the ink-absorbing surfaces greater than 50% have a number of screen weights equal to 120 per linear inch while the ink-absorbing surfaces less than 50% have a number of screen weights equal to 175 per linear inch ;
- plates or plates, on which the weft lineage numbers are distributed as follows: - weft 175 in the parts from 0.1 to 20% (light shades) - weft 175 in the parts from 20 to 40% - weft 125 in parts from 40 to 60% - weft 100 in parts from 60 to 80% - weft 80 in parts from 80 to 99% (dark shades).

 In the same way, the surfaces retaining the ink of the supports of the invention, useful in rotogravure (cylinders) advantageously have in light shades a number of weft linearity less than that in dark shades.

Thus, other variants of the invention developed in the context of photogravure technique, relate to
- cylinders on which the number of screen weights in the surfaces retaining the ink less than 30% is less than the number of screen weights in the surfaces retaining the ink greater than 30%;
- cylinders, on which the number of weft lines in the dark parts from 30 to 95% is 200 while the number of wefts in the light parts from 30 to 1% is 100;
- cylinders, on which the weft lineage numbers are thus distributed - weft 240 in the parts from 99 to 60% (dark shades) - weft 120 in the parts from 60 to 20% - weft 60 in the parts from 20 to 0.5%.

 The above figures are given in Linear inch.

 The implementation of the present invention improves the quality of printing.

 In typography, flexography and offset, dry or wet, it clogs less, because in dark shades, there are fewer but larger non-ink-absorbing surfaces.

 In rotogravure, the light colors are printed better because there are fewer but larger ink dots there.

 The implementation of said invention also facilitates the work of the printer. It hardly brings any additional constraints.

 Indeed, the supports of the invention can be obtained by conventional techniques from the films or recording of said invention.

 The production of the films, with different numbers of screen weights, does not pose any problem according to the variant mentioned above, which involves the scanner. The document to be reproduced is saved, stored and possibly modified. It is returned after treatment according to the different frames desired. During these manipulations, the recordings of the invention intervene. From these, it is possible in particular to prepare the differently screened films and in a manner known per se, the plates or plates obtained, useful in typography, flexography, dry offset or wet offset, are obtained.

The preparation of the cylinders is more delicate, since the engraving head of the device of the type
HELIOKLISCHOGRAPH -with a diamond- uses an engraving speed which, in a known way, depends on the number of lines chosen for a document.

 According to the invention, it is proposed to modify said number of lines on the same document. It is therefore necessary, for the preparation of the cylinder intended to print said document, to adjust said HELIOKLISCHOGRAPH to use the slowest speed of the range of frames used for said document.

 It is also possible, for the preparation of a cylinder of the invention, to engrave it, partly physically and partly chemically. Such a method of preparation is illustrated in a nonlimiting manner, in Example 2 below.

 In conclusion, it will be emphasized that the development of the presently claimed invention is closely linked to that of scanners and more generally to that of printing techniques.

 However, the invention already has a certain interest in the context of the techniques commonly used.

 It is illustrated in the examples below.

Example 1
We want to print in wet offset on a beautiful coated paper a document representing on a surface of 30 cm x 17 cm on the one hand, a light shade (about 5%) and, on the other hand, a dark shade (about 92% ), the surface of each shade being 15 cm x 17 cm.

 To obtain a very uniform light shade, we used a 150 weft (that is to say having 150 lineations per linear inch) and to obtain a dark shade, which is not blocked and transformed into a solid color on printing, we used a frame 80 (that is to say having 80 lineations per linear inch).

 We use a Kodak film and a Crosfield scanner, using an elliptical screen. The scanner has been programmed to expose the first shade (light) with the lines of the frame 150 and then, the exposure of said first shade finished, the scanner insulates the second shade (dark) with the lines of the frame 80.

 The film thus obtained, after having been developed and fixed, was copied onto a positive offset plate of the company Innolith, based on a matt chrome steel. This plate, placed on the offset machine, made it possible to obtain a very uniform printing of high quality.

Example 1a
The same document was reproduced on the same paper using the same film, the same scanner and the same printing machine, but using a single screen 80.

 The impression was uniform. The large dots in the light shade are very visible to the naked eye and give the impression a coarse character.

Example 1b
The procedure was as in Example 1a, but using a single frame 150.

 The printer encountered great difficulties. First, the dark shade turned to a solid color. With firmer ink, the layer of paper peeled off and settled on the blanket. Finally, the light shade was not always well printed.

Example 2
We would like to print the same document in rotogravure, on beautiful coated paper. The screened film of Example 1 is used.

Using a HELIOKLISCHO type engraving machine
GRAPH, we engrave on a copper cylinder of dark shade, using a 150 weft. We then remove the partially engraved cylinder and cover it evenly with a layer
Photo-Resist sold by Promotec Graphic (France). The screened film representing the document is carefully placed so that the part of the film representing the light shade is perfectly placed on said copper-plated cylinder (next to the engraved part). We proceed to sunstroke and development. Dry, then protect with a varnish the parts of the cylinder not to be engraved. We then proceed, in a conventional manner, to chemical etching (in the part of the cylinder corresponding to the light shade), then remove the protective varnish and the Photo layer.
Resist.

 The two parts of the cylinder are thus engraved; that corresponding to the dark shade, physically; the one corresponding to the light shade, chemically.

 Put on the printing machine, the document printing is uniform, regular and of high quality.

Example 2a
Using another copper cylinder, the two shades are engraved with a single weft line (150). Put on the machine, the printing is very good for the dark shade but irregular for the light shade.

Example 2b
The procedure is as in Example 2a, but the number of lines in the frame used is 80.

 The print is good for the light shade but coarse for the dark shade.

Example 3
We want to print the same document in gravure printing. To this end, a copper-plated cylinder is physically etched according to a frame 80 for the light part and according to a frame 160 for the dark part.

 The engraving machine is set to the slowest speed. The diamond, in the clear part, engraves copper only one time out of two. In fact, in said clear part, we create, in weft 80, points with an area equal to that of two points in weft 160.

 The engraved plate provides a high quality impression.

Claims (10)

1. Film or recording for reproduction, characterized in that the parts of said film or of said recording which are intended to generate inked surfaces have at least two different numbers of screen line-out. 2. Film or recording according to claim 1, characterized in that said parts, intended to generate inked surfaces, have numbers of weft linearity dependent on their surface. 3. Support - plate, plate or cylinder - for printing, comprising surfaces retaining the ink and surfaces not retaining the ink, characterized in that said surfaces retaining the ink have at least two numbers of linearity of different frame. 4. Support - plate, plate or cylinder according to claim 3, characterized in that said ink-retaining surfaces have weft line number depending on their surface. 5. Support - plate or plate - according to one of claims 3 or 4, for Printing in dry offset, wet offset, letterpress or flexography, comprising ink-absorbing surfaces and non-ink-absorbing surfaces, characterized in that said ink-absorbing surfaces have a lower screen number in dark shades than in light shades. 6. Support - plate or plate - according to claim 5, characterized in that the number of weft lines in the ink-absorbing surfaces greater than 30% is less than the number of wefts line in the ink-absorbing surfaces less than 30%. 7. Support - plate or plate - according to claim 5, characterized in that the ink-absorbing surfaces greater than 50% have a number of weft linearity equal to 120 per linear inch while the ink-absorbing surfaces less than 50% have a number of weft line size equal to 175 per linear inch.  8. Support-cylinder according to one of claims 3 or 4, for rotogravure printing, comprising engraved surfaces retaining the ink and scraped surfaces not retaining the ink, characterized in that said surfaces retaining the 'ink present in light shades, a lower screen line number than in dark shades. 9. Support-cylinder according to claim 8, characterized in that the number of screen weights in the ink-holding areas of less than 30% is less than the number of weft lines in the ink-holding areas of more than 30 %. 10. Support-plate, plate or cylinder according to any one of claims 3 to 9, characterized in that it is obtained by implementing conventional techniques, from films or recordings according to one of claims 1 or 2.