FR2867103A1 - Plate, useful for printing in humid offset, comprises an encrophilic surfaces on its surface corresponding to printing patterns - Google Patents

Abstract

Plate (A) useful for printing in humid offset, comprises a encrophilic surfaces on its surface corresponding to patterns to print, where at least one part of the encrophilic surfaces is lightened that is (A) containing small non encrophilic surface (I) of lightening in which a part of the lightened encrophilic surfaces is distributed in at least two groups. Plate (A) useful for printing in humid offset, comprises a encrophilic surfaces on its surface corresponding to patterns to print, where at least one part of the encrophilic surfaces is lightened that is (A) containing small non encrophilic surface (I) of lightening in which a part of the lightened encrophilic surfaces is distributed in at least two groups in which a first group of (I) has a sufficient area for its effectiveness and sufficient quantity to reduce at least 4% of the encrophilic surface concerned to lightening; and a second group of (I), which is inefficient by their too small area and the average area of (I) of the second group is generally lesser than 2/3 of the average area of (I) of the first group. Independent claims are also included for: (1) the preparation of (A); and (2) procedure of printing in humid condition comprising generating a copy of the coating to the encrophilic surfaces (which corresponds to patterns to print comprising small non-encrophilic surfaces of lightening), fixing the copied coating to a cylindrical coating-holder, moisturizing and inking the fixed copied coating or directly inking the fixed copied coating with an ink which is mixed with a base (ink/water), successively transferring the held ink on the lightening encrophilic surfaces and straining the material to be printed.

Description

2867103 1

  The present invention is in the context of wet offset and more specifically relates to: - plates, useful for wet offset printing, having at their surface inkjet surfaces corresponding to the patterns to be printed; at least a portion of said inkjet surfaces being lightened (i.e. containing small non-inkjet lightening surfaces) in an original manner; the preparation of such plates; io - their use in the context of wet offset printing.

  The use of the plates of the invention is particularly interesting because it ensures, on the surface of said plates, the homogeneity of the ink-water mixture (basis of the wet offset process), and this regardless of the exact context of this use that is: the nature of the printing material, the ink, the printing machine, the weft used, the size and distribution of the inkjet surfaces on the plate. Said plates thus provide excellent print quality. Their use also leads to better productivity, a decrease in the consumption of materials in general (ink, printing material, plate ...) and facilitates the drying of the deposited ink.

  It is known that the method of printing the wet offset uses supports (plates) on the surface of which (s) were generated inkjet and aquaphobe surfaces, which correspond to the patterns to be printed, to take the ink and the transfer and non-encrophobic and encrophobic surfaces to refuse the ink.

  The inkjet surfaces are obtained from an encrophilic light-sensitive layer, generally between 0.8 and 3.2 μm thick. They are generally obtained by insolation techniques, involving films or directly rays, U.V.

  or I.R., driven by software.

  The encrophobic surfaces are hydrophilic surfaces (generally exposed portions of the treated surface of the plate) wetted by a film of water, having a thickness of about 4.5 μm. Said water film is generated from the water deposited by the wet rollers 2867103 2 the printing machine or from the water contained in the ink (see below).

  On the printing machine, the plate is first wetted by wet rollers (unless a "fluid ink" type ink, consisting of an ink / water mixture) is used and then inked by rollers -encreurs. The inking rollers deposit the ink on the inkjet surfaces. It is always mixed with water, previously deposited by the roll-dampers or by its constitution ("fluid ink"). A blanket, cloth or metal covered with a rubbery material then takes the ink from said inkjet surfaces and deposits it on the printing material, for example paper, cardboard or metal.

  The printing is carried out in one or more colors (most often with yellow, magenta, cyan and / or black inks) on printing machines: - machine-leaf type: the material is printed on the sheet side by leaf side at speeds of up to 9,000 sheets per hour. Sheet machines print less quickly than presses (see below), usually on one side only. They use tongs to hold the material throughout the print. But the drawing of the ink on the blanket has a tendency to slide the material into said clamps, resulting in a distorted impression and / or to cause tearing of said material (thin paper and / or fragile), hence stops of the machine. The ink deposited must dry quickly to prevent smearing successively printed sheets and stacked. For this same purpose, it is generally involved, between each printed sheet, an extremely fine powder called anti-smudging. We aim to isolate each sheet of the next. The control of the intervention of the anti-misting powder is somewhat delicate; - or rotary type: the reel material, paper most often, is printed on one side or simultaneously on both sides, at print speeds of up to 600 m per minute. The deposited ink is generally dried by passing the inked material in a tunnel (oven) drying, whose length may exceed 12 m, brought to high temperature (between 150 C and 300 C).

  2867103 3 Whatever the printing technique involved, the use of the ink and more particularly its drying remains to be optimized. This optimization must obviously take into account the exact nature of the ink in question and the drying technique in question.

  Inks mainly consist of pigments, oils and adjuvants. Three types of ink are known, with reference to their consistency, with which it is intended to generate, on printing, homogeneous and balanced ink-water mixtures on the ink-forming surfaces of the plate (such mixtures are qualified homogeneous or balanced, if they retain within them the same quantity of water on all the inkjet surfaces of the plate, whatever the size and distribution of said surfaces) and therefore to ensure, without particular difficulties , quality prints. We know: - inks firm, concentrated and often bright, and / or high resistance (HT), usable in thin thickness. Used on smooth materials (papers) of good quality, they allow an accurate printing. But, they are pulling ("tack") and tend to remove each print a little of the surface of the material (paper), if it is not very adherent; This leads to frequent washing of the blankets and / or breaks the web of material at the start of the press. On the other hand, they generally mix with only a small amount of water, which can be critical, in large inkjet areas; - The so-called "soft" inks, more fluid and less concentrated in pigments than said firm inks, generally used in greater thickness on cardboard type materials, matte papers for books, newspapers. They allow in fact to print on materials of a lower price and / or more adapted to the reasons to print. These so-called "soft" inks mix more easily with the wetting water, sometimes mix too easily and can then become emulsified (which results in a loss of print quality, problems drying and generally a stop of the machine for cleaning ink rolls, plates and blankets).

  2867103 4 A special type of so-called "soft" ink is proposed, fluid inks. This is, as previously indicated, ink / water mixtures, pre-formed. They generally contain about 80% of ink and 20% of water. They are directly deposited, without prior wetting, on the inkjet surfaces of the plates. Their use is interesting. Exempt from the previous wetting step, printing is simplified, the duration of start-up and paper consumption are reduced. Fluid inks are generally used on matte papers, for small format prints, especially text. Their use is generally limited to these contexts because it is alleged that said inks are also deposited, inevitably, on the hydrophilic surfaces of the plate; - conventional inks, which are a compromise between firm inks and so-called "soft" inks.

  The thickness of the ink to be deposited, generally between 0.5 and 5 μm, depends mainly on the nature of the material on which it is deposited and the type of patterns to be printed.

  The ink / water mixtures to be produced on the surface of the plates during printing generally contain from 4 to 30% by weight of water, most often from 15 to 20% by weight of water. They must be as balanced as possible, whatever the size and distribution of the inkjet surfaces of said plates. With firm, conventional inks that more or less deny water, the inkjet surfaces refuse the water that accumulates on the other surfaces of the plates; with so-called "soft" inks which tend to mix with too much water, the emulsification of said inks is observed ... The control of the ink / water mixture on the surface of the plates being printed is a real problem technical and is often one of the main causes of printers' concerns.

  As regards the drying of said inks, its implementation is a delicate and expensive operation.

  The drying techniques developed to date are mainly four in number. They are familiar to the skilled person. They are adapted to the nature of the inks in question 2867103 5 - drying, by penetration into the inked support, for the so-called "coldset" inks: The supports in question are papers, type newsprint. The deposited inks dry by penetrating through the top layer of these absorbent media. These inks, reserved for this type of support can intervene as well on rotary machines as on machine-leaves ... The drying of said inks is not often complete and when one handles the inked support, it is carried out a transfer of non-dry ink on the manipulator's hands (the newspaper reader); drying, by evaporation, for so-called "heatset" inks: The use of these inks is reserved for presses. They are dried in the drying tunnels mentioned above; drying, by UV irradiation, for so-called U.V. inks: These inks dry almost immediately, by polymerization, under the action of U.V. rays (200 to 400 nm). They have a very important "tack". Their price is however very high and their use is therefore reserved for special media (type smooth and adherent surfaces of paper, metal, cardboard gloss ...), on which drying is known to be difficult; - Drying, by oxidation polymerization, for so-called "sheetfed" inks: The use of these inks is almost reserved for machine-sheets. The inks dry in the open air but not instantly. They use the oxygen of the air to generate within them peroxides (R00), precursors of free radicals (RO.). These free radicals allow the polymerization ...

  The reproduction is also made between two values, which are, on the one hand, the value "zero", that is to say the color of the material to be printed, blank and, on the other hand, the "maximum" value. ", that is to say the flattened with the ink used. To make the intermediate hues, we use frames: - mainly conventional frames, amplitude modulation: which allow to obtain more or less solid surfaces, depending on whether the intermediate hues are closer to the flat or color of the material. According to the printing method used, the nature of the material to be printed and the documents to be printed, more or less fine screens, such as frames 300, 200, 175, 150, 133, 120, 100, 80 are used. , 65 (this number indicates the number of lineaments per linear inch); - More rarely, stochastic frames or frequency modulation frames: these frames consist of small dots, of the same area, distributed more or less randomly. The different values are represented by a different density of points. The area of the points of a frame is chosen according to the quality of the material to be printed, the printing process and the ink used. Points of 225 pm 2 to more than 1200 pm 2 are recommended for mat and / or cheap papers (eg newsprint). Agglomerates are often produced by the coalescence of such points.

  Hybrid frames are now also proposed, consisting of a stochastic frame for light shades and a conventional frame for dark shades.

  In general, the points of the frames are square or more or less round and / or square, resulting from an assembly of pixels.

  Regarding the printing of texts, it is generally based on the standard P.P.I. (dots per inch, dots per inch) It ranges from 300 for ordinary texts (which equals conventional 80 and 100 frames) to 1200 for delicate texts, with, for example, small italicized characters, chemistry or mathematics formulas (equivalent to frames 133 and 150 classics). The choice of the standard also depends on the quality of the material to be printed (especially paper).

  The applicant, in the context referred to above, has shown the interest of lightening the impression, ie of creating small non-ink-free surfaces in the inkjet surfaces (small non-ink-free surfaces which become clogged and open during printing, so that they are effective and improve said printing). He described this principle of the relief in the patent application FR-A-2,660,245, he described an improvement in the patent application EP-A-770 228. According to said improvement, the small non-inking surfaces of lightening are randomly distributed according to one or more stochastic weft (s). It is recommended to use said small lightening surfaces in a proportion of 2 to 26%, preferably 8 to 14%, inkjet surfaces (thus lightened) and with an area of about 400 pm2. However, such small non-ink-bearing surfaces are provided of much smaller area (196 pm 2, for very beautiful paper for example) or much larger area (1600 pm 2, for coarse paper like newsprint, for example).

  The intervention of these small, non-inking lightening surfaces provides numerous advantages, which are listed in the text of said EP-A-770 228 application, and in particular a better homogeneity of the ink / water mixture. However, the said intervention has proved to be able to be developed only within certain limits: the surface area of the small surfaces must not be too small because then the said small surfaces are blocked and remain blocked by the ink throughout the printing and thus reveal totally ineffective. It must not be too big because then said small surfaces are visible on the printed support ...

  the number of said small surfaces must not be too small for the expected improvements to be manifested, nor too great not to interfere with the reproduction of the patterns, so as not to weaken the inkjet surfaces too much, so as not to make the adjustment too delicate anchorage ...

  Tests have confirmed that the area of ink removed can not be increased, in order to take advantage of the relief even more without affecting printing, by using a very large number of small non-inkling areas of less than area. small surfaces usually used, having shown their effectiveness. The results are disappointing, said small surfaces, whatever the paper, the frame, the ink, the machine used and the size and distribution of the inkjet surfaces on the plate, remain more or less blocked during the entire printing.

  In the context of the present invention, it proposes an original lightening that allows to lighten more without disadvantage and on the contrary, with certain advantages both in terms of the quality of printing and the implementation of said printing (homogeneity 2867103 8 of the ink / water mixture, amount of ink used, drying of the ink ...). In the context of the present invention, two types of small, non-inkless surfaces are made more light by two types of small non-inkjet surfaces being collaborated: small, non-encrophilic surfaces that are effective per se, and smaller, non-encrophilic, effective areas of by the presence of said small effective non-incrophile Persian surfaces.

  According to its first object, the present invention relates to plates, useful for wet offset printing, having at their surfaces πrophilic surfaces corresponding to the patterns to be printed; at least a portion of said inkjet surfaces being lightened; that is to say containing small non-inkling surfaces of lightening. They are plates, lightened in the sense of the documents of the prior art: FR-A-2,660,245 and EP-A-770,228; positive or negative plates, ready to use, of which at least a part of the inkjet surfaces is screened with thousands of small non-inkling lightening surfaces. We can thus have all the lightened encrophilic surfaces or only a part of them ...

  Characteristically, on the plates of this type, according to the invention, in at least a portion of the light inked surfaces, and advantageously in all said light inked surfaces, at least two groups of small non-inkjet lightening areas are found: a first group of randomly distributed small non-inked surfaces of sufficient area (s) to be effective and in an amount sufficient to lighten the surface (s) by at least 4%; the author (s) concerned by the relief; and a second group of small, non-inrophilic surfaces randomly distributed or not, advantageously in a random manner, which are not effective per se because of their (their) too small area (s); the average surface area of said small non-ink-forming surfaces of said second group generally being less than 2/3 of the average surface area of said small non-ink-free areas of said first group.

  The lightened encrophilic surfaces of the plates of the invention can be partly in an original manner according to the invention and partly in a conventional manner according to FR-A-2,660,245 and / or EP-A-770,228. are advantageously in total according to the invention: they contain small non-inking surfaces of the first group and small non-inking surfaces of the second group, whose effect (lightening) is cumulative.

  The small non-encrophile surfaces of the first group are lightening surfaces in the sense of EP-A-770 228. They are distributed randomly. They are effective in themselves by their size. They are also effective in that they make effective the small non-inkfilm surfaces of said second group, smaller, by their minimal amount of intervention and this, presumably by influencing the ink / water mixture, when printing .

  With regard to the area of said small non-ink-free surfaces of said first group, it should first be noted that it is not necessarily the same for all said small non-ink-free areas of said first group. According to an advantageous variant, all said small surfaces have the same area, but it is only a variant. It is quite possible to find on a plate of the invention small, non-incrophilic areas that are effective per se, of different surface areas. In any event, the area (s) in question is (are) sufficient to really lighten the impression (without systematic clogging of said small surfaces, when using the plate) but obviously remain reasonable area to not affect the impression too much.

  The person skilled in the art perfectly masters this notion of efficient, non-excessive lightening, which depends on many parameters of the process in question. In the context of the present invention, it is recommended, in no way limiting, that: for printing patterns with an amplitude modulated frame, the area (s) of said small non-inking areas of said first group remains (nt) less than the white point of the value 95%, and advantageously of the value 97%, of said frame; or - for printing the patterns with a stochastic frame, the area (s) of said small non-ink-free areas of said first group remain (s) less than 3 times the area of the point of said frame, is (are ) generally between 0.5 times and twice that area.

  For pattern printing with an amplitude-modulated frame, the area (s) of said small non-ink-free areas of said first group are (are) advantageously smaller than the area of the white dot weights between 95 and 99%, advantageously between 97 and 98%, of the frame used. Thus, for a weft often used as the weft 150, such small, non-ink-free surfaces having an area of between 286 μm (99%) and 14333.88 μm (95%), preferably 573.47 μm 2, are recommended ( 98%). Assuming that all the white dots of the 98% of said small non-inkling areas are on inkjet dots of 20% of the units, said 2% value would be reduced by x%, where x represents the lightening rate used. for example 10% (for a lightening rate of 10%, said value of 2% would become 2 0.2 = 1.98%, which would be practically not visible on the printed material). The skilled person also knows that the fattening phenomenon is able to make not visible on the printed material the white points of any reasonable relief.

  Frequency modulation stochastic frames are still not widely used today. The skilled person knows the advantages (very rare moiré between the colors, excellent reproduction of clear values) and disadvantages (poor reproduction of dark values, difficult adjustments of dampening and inking). In order to avoid, in a general way and particularly in the context of the invention, a too great reduction in the clear values at printing, it can be provided to compensate or to involve small non-encrophilic lightening surfaces only in the values dark. It is with reference to this selective lightening that in particular may be provided relief points larger than the points of the frame used.

  In any event, the skilled person is able to optimize the area (s) of the small non-encrophilic lightening areas of the first group.

  These small areas, present in the lightened acrylonitrile (s) surface (s), provide a lightening rate of at least 4%.

  It has been understood that the rate of relief, in this case 4%, represents the ratio between the area removed (the sum of the areas of all said small non-inkling areas) and the surface area of the (s) encrophilic surface (s) from where she is removed. This rate of relief by small areas of the first group is generally between 4 and 20%, preferably between 6 and 12%. It must be sufficient (> 4%) to make small non-encrophile surfaces of the second group effective.

  These small non-encrophilic surfaces of the second group are only likely to develop their lightening action in the presence of the small non-encrophilic areas of the first group; this, with reference to their area. Per se, they are too small. They can only be clogged and remain clogged under normal conditions of use. On the other hand, when used with the small non-encrophilic surfaces of the first group, they become active and their action (of lightening) is cumulative with that (lightening) of said small non-encrophilic surfaces of said first group.

  These small non-encrophilic surfaces of the second group are distributed randomly or not. They are advantageously distributed randomly.

  With regard to the area of said small non-ink-forming surfaces of the second group, it should be noted first of all that it is not necessarily the same for all said small non-inking areas of said second group. According to an advantageous variant, all said small non-inking surfaces of said second group have the same area, but it is only a variant. It is quite possible to find, on a plate of the invention, small non-encrophile surfaces that are not effective per se, of different surface areas. In any case, the area (s) in question is (are) lower than that (s) small non-inking areas of the first group. It is obviously difficult to indicate absolute values, or even relative values, in view of all the parameters involved. There are, however, on the surface of the plates of the invention, within the encrophilic surfaces, two types of nonencrophilic lightening surfaces: small ones, in the conventional sense of the term according to the teaching of FR-A-2 660 245 and EP-A-770 228 and smaller ones. It can be stated that, in general, the average surface area of the small non-inking areas of the second group is less than 2/3 of the average area of the small non-inking areas of the first group. According to an advantageous variant, the average surface area of said small non-ink-forming surfaces of said second group is between 1/4 and 2/3, advantageously between 1/4 and half, of the average surface area of said small non-ink-free surfaces of said first group. group.

  Said small non-inking areas of the second group can not be too small, since they may be ineffective, in which case the area (s) of the small areas of the first group and any the context of use. In principle, they have a diameter greater than 10 μm. In addition, there is the problem of their generation on the surface of the plate.

  Said small non-encrophilic areas of said second group advantageously intervene in an amount sufficient to lighten from 4 to 35%, advantageously from 8 to 20%, the surface (s) inks (s) concerned (s) concerned (s) by lightening.

  The lightening rates resulting from the small non-encrophilic areas of said first and second groups are cumulative. It has thus been found possible, quite surprisingly, to lighten according to the invention, in an interesting manner, at rates which according to the prior art (with a larger number of small areas of the first group and / or or with small areas of said first group of larger area) are very damaging to printing ...

  Incidentally, it is recalled here that the lightening rate of the inkjet surfaces of the plates of the invention is not necessarily constant; the rate of relief due to the small non-inking areas of the first group and / or the rate of relief due to small non-inking surfaces of the second group is not necessarily constant. We know the interest in lightening darker values.

  Characteristically, therefore, on the surface of the plates of the invention, more precisely in the lightened encrophilic surfaces of said surface (in only a part of them, and advantageously in all said lightened encrophilic surfaces), small surfaces non-encrophiles of the first group and small non-encrophilic areas of the second group. If no precaution is taken, there are also, ineluctably, small areas resulting from the partial superposition of a small non-inking area of the first group and a small non-inking area of the second group, or even the perfect fit (tangential) of two such small areas. Since it is difficult to print, by generating too large lightening surfaces, which can be visible on the printed medium, it can be ensured that none of the said small non-inkling surfaces of the second group are in contact (tangential and / or with superposition) of a small non-inked area of the first group. Precautions are to be taken in the preparation of the plate. It is thus possible to use software, generating all said small surfaces of the second group separated by at least one pixel of said small areas of the first group. According to an advantageous variant, in the lightened encrophilic surfaces of the plates of the invention, none of said small non-ink-forming surfaces of said second group is therefore in contact with a small non-ink-free surface of said first group.

  According to another advantageous variant, none of said small non-encrophilic surfaces of said first group is in contact with the edge of the encrophile surface in which it intervenes. It can thus be ensured that all said small non-inking surfaces of said first group are at least one pixel of said edges.

  It has previously been indicated that all said small non-ink-free areas of said first group advantageously have the same area (noted, for example: S) and that independently all said small non-ink-forming areas of said second group advantageously have the same area (for example, noted : s). Very advantageously, the plates of the invention have two main groups of small non-ink-forming surfaces: a first group, of area S and a second group, of area s; (with, incidentally, small non-encrophilic areas whose area is greater than s and is at most S + s).

  The plates of the invention as described above can be obtained by various types of processes, known per se. These methods are known for generating small lightening surfaces; it is recommended, according to the invention, to use them to generate at least two types of small surfaces of this type.

  It is possible, in a conventional manner (see applications FR-A-2,660,245 and EP-A-770,228), to insulate the plate through at least one film.

  As taught in WO-A-97 35233, it is possible to proceed by insolation of a positive presensitized band, insolation through the opaque surface and pierced with a tube; said strip being then cut into plates.

  It is still possible to proceed by direct exposure with software-driven rays. The same software can make it possible to obtain the inkjet surfaces corresponding to the patterns to be printed and the different groups of small nonencrophile lightening surfaces. You can also use several software ... All variants are possible.

  Successful software exists today.

  One can also proceed by any other technique, a projection technique. With nozzles, either the inkjet lacquer solution is sprayed onto the plate, or a solution capable of removing surfaces and small areas of the encrophile lacquer previously deposited on the plate. This last variant of the projection technique is described in application FR-A-2 843 558.

  It must be admitted that the processes for preparing the plates of the invention are methods by analogy, an implementation increasingly easy in view of advances in computing.

  The key to the invention the joint use of groups of different non-inkjet surfaces to lighten inkjet surfaces is totally innovative and has unexpected interesting results. We return to these later in this text.

  According to its last object, the present invention relates to a wet offset printing method. Said method is a conventional method, in that it comprises the successive steps of: - copying a plate, generating on the surface of said plate inkjet surfaces, corresponding to the patterns to be printed and containing small non-inking surfaces of relief; fixing said copied plate to a plate cylinder; - Wetting and then inking said fixed copied plate or directly inking with an ink based on an ink / water mixture; and - transfer of the ink retained on said inkjet surfaces on, successively, the blanket and the material to be printed.

  This is a process according to the applications FR-A-2,660,245 and EP-A-770,228 in that the copy of the plate comprises the introduction of small non-inkjet lightening surfaces in the inkjet surfaces.

  This is an original process according to the invention in that the lightened plate is a plate as described above. Typically, the copying step includes creating the two groups of small, non-ink-like surfaces in the inkjet surfaces.

  The interest of the present invention is recalled below.

  Improved lightening within the meaning of the invention has been effective on virtually all papers, with all machines, frames, inks and regardless of the size and distribution of inkjet surfaces on the plate.

  Said improved lightening provides the benefits of lightening (as in particular listed in EP-A-770 228) improved. Particular emphasis is placed on excellent print quality, best productivity, material and energy savings.

  In particular, ink consumption is reduced.

  The drying of the deposited ink is improved (in particular because of the better homogeneity of the ink / water mixture).

  The quality of printing is improved and this especially as it is implemented in medium conditions, or even bad.

  In addition, the specific relief of the invention does not "really weaken" the plates. Indeed, it can be estimated that by making the ink-water mixture more equilibrated on the surface of said plates and thus by decreasing the drawing of the ink in parallel, the longevity of said plates is increased by more than 60%. Said plates no longer have to be subjected to constraints as severe as those of the prior art (the deposits on blankets largely responsible for the wear of the plates have also been greatly reduced) ...

  Finally, the plates of the invention make it possible to use fluid inks ("fluid ink") more industrially.

  The invention is illustrated, in no way limiting, by the examples below.

  The plates used are Agfa Thermostar 830 nm thermal positive plates: - 785 x 1030 x 30/100 for a Roland sheet machine; - 708 x 1020 x 30/100, then cut in the middle (ie 708 x 510 x 30), for a Heidelberg Web 8 press.

  The plates are insolated with an Xcalibur G.L.V. , Print Drive, Double Burn, from Agfa, developed, rinsed, gummed and then dried. The stochastic frames are from Esko-Graphics, inks from Sun Chemical.

Example 1

  An offset plate is copied using three software packages.

  The first creates small, non-inkling lightening areas of about 150 pm 2 in area (which is about the area of a 98% white dot in frame 80). Said small surfaces intervene, according to a stochastic frame, in a number such that their total area represents 10% of the inkjet surface of the plate (of the surface of said plate).

  The second creates smaller lightening areas of about 1008 pm2 in area (about half the area of the smaller areas above). Said smaller lightening surfaces intervene, according to a stochastic frame, in a number such that their total area represents 12% of the inkjet surface of the plate (of the surface of said plate).

  Said encrophile surface is thus lightened by 10 + 12 = 22%.

  Said surface has small lightening areas of 2016 pm2, smaller lightening areas of 1008 pm2 and smaller enlarged lightening areas, whose area is greater than 2016 pm2 and is at most 2016 + 1008 = 3024 pm2 (depending on the relative layout of small areas and smaller areas).

  A third software transports texts in 600 P.P.I. and a reproduction with a frame 80.

  The plate is attached to the Roland sheet machine and is printed on matte paper with Sun Chemical's Washington Post Single Fluid Black ink. On said plate, there is a balanced ink / water mixture with about 20% by weight of water. The print quality is good. 3000 sheets are printed without any particular difficulties, with starting a quantity of paper limited to a few sheets. i0

Example 2

  The procedure is as in Example 1 but using a wetting step. The ink used is then a so-called "soft" ink (Sun Chemical Solar). The printing is done without difficulty. The print quality is good.

Example 2bis

  The procedure is as in Example 2 but with a relief of 22% of the acrobatic surface obtained only with small areas of 2016 pm2 area. The wetting settings are more delicate. We tend to have too much water. The print quality is not as good.

Example 3

  A plate is copied with software to generate on its surface small, non-inkling lightening areas of about 573 pm 2 in area (which is approximately the area of a 98% white dot in 150 grid), distributed random way, whose number represents 8% of the acrobat surface; and smaller non-inkjet lightening areas of about 191 pm 2 area (about one-third of the area of the small areas), randomly distributed, the number of which represents 12% of the acrobat surface area.

  Said encrophile surface is thus lightened by 8 + 12 = 20%.

  Another software copies on the plate patterns in a frame 150.

  The plate thus copied front and back is cut in the middle and two plates (one for the front, the other for the back) are attached to the press. The ink used is a firm ink (Maury LWC from Sun Chemical).

  The printing of the raster patterns is of a high quality. The flow rate of the inkwells could be adjusted to a flow less than the usual one.

Example 3bis

  The procedure is as in Example 3 but with a lightening of 20% obtained with only the small areas of 573 pm 2. When printed, the reproduction of the raster patterns is of insufficient quality. We observe the loss of several values and details.

Example 4

  Software generates small non-inkling lightening areas of about 573.4 μm 2 (which is about the area of a 98 h white dot in frame 150), randomly distributed, the number of which is 8% the inkjet surface of the plate; and smaller non-inkjet lightening areas of about 143 pm 2 area (about a quarter of the area of the small areas above), randomly distributed, the number of which represents 12% of said inkjet area.

  Said encrophile surface is thus lightened by 8 + 12 = 20%.

  Said encrophile surface consists of texts and screen reproductions (frame 150).

  The ink used is a firm ink (Maury LWC from Sun Chemical).

  On the press, the printing is of a high quality. The few small non-encrophilous areas with enlarged areas (greater than 573.4 pm2 and a maximum value of 573.4 + 143 = 716.4 pm2), representing areas of white dots, comprised between 98% and 97.51% of frame 50, are not visible on the printed paper.

Example Obis

  The procedure is as in Example 4 but with a reduction of 20% of the inkcrystallized surface obtained only with "more" small non-inkling surfaces of 143 pm 2 of area. The impression is irregular, with lightened places, which do not remain (the "more" small non-ink-filled surfaces are clogged and remain clogged with ink). There are more drawbacks than advantages of this "pseudoallocation".

Example 5

  Software generates raster print patterns in a frame 133.

  Another software generates small non-inkjet lightening areas of about 729.44 pm 2 (which is about the area of a 98% white dot in frame 133), randomly distributed, whose number represents 10 % of the acrobatics area.

  A third software generates very small non-inkling lightening surfaces of about 243 pm 2 (which is about one third of the area of the small areas above), randomly distributed, the number of which represents 12% of the surface area. ink-accepting.

  Said encrophile surface is thus lightened by 10 + 12 = 22%.

  The ink used is a conventional ink from Sun Chemical.

  Printing is done on medium-quality paper on the press. The print quality is good. The washings of blankets are spaced apart, the adjustment of the flow rate of the ink cups reduces by 6%.

Example 6

  The reasons to print are the texts of a paperback book, to print on a matte paper of standard quality. Software is used for said texts and other software for small non-inkling lightening surfaces: small areas of about 729 pm 2 representing 6% of the inkjet area; and smaller areas of about 243 pm 2 representing 4 hours of said inkjet surface.

  The ink used is a so-called "soft" ink (Sun Chemical Solar).

  The printing is very good and the flow of the ink is reduced by 3%.

Claims (2)

21 CLAIMS,   1. Plate, useful for wet offset printing, having on its surface inkjet surfaces corresponding to the patterns to be printed; s at least a part of said inkjet surfaces being lightened; The. comprising small non-ink-lightening lightening surfaces, characterized in that said small, non-ink-lightening lightening surfaces, in at least a portion of said lightened inkjet surfaces, are divided into at least two groups: a first group of small non-lightening surfaces; randomly-distributed adrenophiles, of sufficient surface area (s) to be effective perse and in an amount sufficient to lighten by at least 4% the relevant encrophilic surface (s) (s) ) by the relief; and a second group of small non-inrophilic areas, randomly distributed or not, advantageously in a random manner, not effective per se because of their (s) surface area (s) which are too small; the average surface area of said small non-ink-forming surfaces of said second group generally being less than 2/3 of the average surface area of said small non-ink-free areas of said first group.   2. Plate according to claim 1, characterized in that the average surface area of said small non-ink-forming areas of said second group is between 1/4 and 2/3, advantageously between 1/4 and half, of the average area. said small non-encrophilic surfaces of said first group.   3. Plate according to claim 1 or 2, characterized in that: - for printing patterns with an amplitude modulation frame, the (s) surface (s) of said small non-inking surfaces of said first group remains (s) less than the white point of the value 95%, and advantageously of the value 97%, of said frame; or - for printing the patterns with a stochastic frame, the area (s) of said small non-ink-free areas of said first group remain (s) less than 3 times the area of the point of said frame, is (are ) generally between 0.5 times and twice that area.   4. A plate according to any one of claims 1 to 3, characterized in that said small non-ink-free surfaces of said first group are involved in an amount sufficient to lighten from 4 to 20%, advantageously from 6 to 12%, the) encrophile surface (s) concerned by the relief.   5. Plate according to any one of claims 1 to 4, characterized in that said small non-encrophilic surfaces of said second group are involved in an amount sufficient to lighten 4 to 35%, preferably 8 to 20%, the (the) surface (s) in which the lightening is concerned.   6. Plate according to any one of claims 1 to 5, characterized in that the lightening rate of its inkjet surfaces is not constant.   7. Plate according to any one of claims 1 to 6, characterized in that none of said small non-inking surfaces of said second group is in contact with a small non-inkjet surface of said first group.   8. Plate according to any one of claims 1 to 7, characterized in that none of said small non-inking surfaces of said first group is in contact with the edge of the encrophile surface within which it intervenes.   9. Plate according to any one of claims 1 to 8, characterized in that said small non-ink-free surfaces of said first group have the same area and / or, advantageously, and said small non-inking surfaces of said second group have the same area.   A method for preparing a plate according to any one of claims 1 to 9, comprising copying said plate to generate on the surface of said plate the ink-like surfaces corresponding to the patterns to be printed as well as said non-ink lightening within said inkjet surfaces, characterized in that said non-inkjet lightening surfaces are copied - by a technique of insolation of said plate through at least one film and / or an insolation technique of a precursor strip of 2867103 23 positive presensitized plates through the opaque wall of a tube, and / or - by a technique of direct exposure of said plate with software-driven rays; and / or - by a projection technique.   11. Wet offset printing method, comprising: - copying a plate, generating on the surface of said plate inkjet surfaces, corresponding to the patterns to be printed and containing small non-inkjet lightening surfaces; io - fixing said copied plate to a plate cylinder; - Wetting and then inking said fixed copied plate or directly inking with an ink based on an ink / water mixture; the transfer of the ink retained on said light inked surfaces onto, successively, the blanket and then the material to be printed; characterized in that copying said plate generates a plate according to any one of claims 1 to 9.