EP2697067B1 - Printing test method on a substrate and device for the implementation thereof - Google Patents

Description

The invention relates to a graphical printing test method on a substrate and to a device for implementing the method.

The invention will be more particularly described with regard to a printing on paper, without being limited thereto. The invention applies in fact to printing on any type of substrate, paper, plastic, glass, fabric, flat or embossed (three-dimensional volumes) etc ...

In addition, the invention relates to all types of contact printing processes such as offset, screen printing, flexography, rotogravure, digital printing, whose printing results are listed in ISO 12647 of 23/11/2004, and more particularly ISO 12647-2 for offset, ISO 12647-6 for flexography, ISO 12647-5 for screen printing, and ISO 12647-4 for gravure printing.

The invention also relates to contactless printing, however specific to digital printing considered in ISO 12647-7.

On the other hand, the invention does not concern non-contact printing by photocopier and projection machine (laser or ink jet) such as an office printer, which are covered by the ISO 12647-8 standard. It is known to appreciate the print quality of a graphic on paper, by comparing this graphic with reference elements, such as colorimetric control strips.

For example, the European patent application EP2008818 discloses a method for densitometrically and spectrally measuring color elements to regulate the amount of ink provided by inking zones on a print. The control system implemented is a closed-loop system opening and closing ink segments with respect to setpoint values. The measuring method is operated by technical means without intervention of the eye of an observer who can be the operator of the machine.

However, the method described in this document relates exclusively to offset printing which provides ink delivery by zones, but does not cover applications by a different ink supply such as from a screen, a cylindrical cylinder in flexography or rotogravure, or according to digital printing.

Moreover, in a printing machine, in addition to the density and the ink spectral measurement delivered, other criteria must be verified in order to agree on satisfactory printing and its reproducibility, for example, the image length, the printing pressure, the possible mechanical distortion due to the printing medium substrate and / or the process of printing, the parallelism of the printing cylinders, the surface coverage of the weft dot expressed in inked percentage.

• les tolérances acceptées pour les valeurs spectrales des couleurs cyan, magenta, jaune et noir dans le système L*, a*, b*; en fonction des substrats et des procédés d'impression
• les valeurs normatives de l'augmentation de la valeur tonale pour chaque couleur accompagnées des tolérances. en fonction des substrats et des procédés d'impression

In addition, the ISO 12647 standard of 23/11/2004 specified the set of criteria, also referred to as "target values", to which a printing machine must respond on a substrate of a given material, in particular:

• Accepted tolerances for the spectral values of the cyan, magenta, yellow and black colors in the L *, a *, b * system; depending on substrates and printing processes
• the normative values of the increase of the tonal value for each color accompanied by the tolerances. depending on substrates and printing processes

However, this standard gives no indication of the means for obtaining the target values and whether they are reached when using a printing machine.

Today, no test protocol exists to control and measure in a simple way, in particular visually by the human eye, the possible defects of a printing machine and / or to optimize the settings of a machine. in order to launch production cycles during which the stability of the printing process is guaranteed so as to reach the target values required by the ISO 12647 standard of 23/11/2004.

The object of the invention is therefore to propose a printing test method for a printing machine so that this machine meets the ISO 12647 standard, while providing a reproducibility of the printing result at any time of the one or more production cycles of the machine to define the technical capabilities (limits and possibilities). This process applies to the contact or non-contact machine outside the ISO 12647-8 part of the standard.

In addition, the method of the invention must make it possible to define the limits and the possibilities of reproduction capacity of a given printing technique in relation to the substrate on which the printing is performed. It makes it possible to conduct comparative studies to choose materials and raw materials, in particular for printing media, inks, consumables (offset blanket blanks).

The document US-A-6,128,090 discloses a printing test method.

• il comprend une pluralité d'éléments graphiques d'évaluation imprimés sur le substrat de test, les éléments étant distincts dans leurs formes et leurs couleurs et comprenant pour certains des tramés,
• l'analyse est visuelle,
• l'un des éléments graphiques à analyser consiste en une pluralité de formes géométriques identiques, du type carré ou autre, dont la couleur de chaque forme est un noir tramé avec une trame différente selon une incrémentation, chaque forme comportant un graphisme, tel qu'un nombre, qui est visualisable sur le substrat de test en cas de défaut.

According to the invention, the method of printing tests with or without contact on a substrate using a printing machine, the printing being of the offset type, screen printing, flexography, gravure printing, and the printing being performed on a test substrate constituting the type of substrate on which the machine is intended to print, the method comprising a step printing on the substrate using the printing machine according to initial machine setting conditions, a step of analyzing the printing with respect to a reference test protocol, is characterized in that than

• it comprises a plurality of graphic evaluation elements printed on the test substrate, the elements being distinct in their shapes and their colors and including for some of the screenings,
• the analysis is visual,
• one of the graphical elements to be analyzed consists of a plurality of identical geometrical shapes, of the square or other type, the color of each form of which is a raster black with a different frame according to an incrementation, each shape comprising a graphic, such as a number, which is viewable on the test substrate in the event of a fault.

The term "visual" concerning the test protocol means an appreciation of the graphic elements by the human eye.

The term "viewable" in the sense that the graphic appears visually according to a colored gray in the form with background halftone incremented 5% in 5% for example. In particular, this graphic is colored because its appearance corresponds to a defect relating to the setting of the color combination to elaborate the black raster and in particular a lack of adjustment on the color of the graphics appearing on the black background raster.

Thus, these colors are composed of cyan, magenta and yellow, printed "trapped" (term of trade) in a reserve (the full graphic form) of the black screen.

The percentage of the raster obtained by the colors black, cyan magenta and yellow comes from the target values of the standard. The graphic design (a number) represents an image for which a percentage of points (corresponding to a surface coverage) is attributed, this percentage being representative of the tones of each color. It is for this reason that the invention makes it possible to visually identify the distortions of a tonal value when the image takes on a colored tendency. It can be deduced, for example, that there is too much cyan in the target values such as 15% to 35% because, in each of the raster forms corresponding to these raster percentage values, an image appears (FIG. percentage of raster: respectively 15, 20, 25, 30, 35) which is colored in cyan. The surface covers will then be corrected electronically during the preparation of the printing matrix via the computer tool called "Raster Image Processor" (RIP).

The process is indeed of interest only for the four-color process, the color printing.

The geometric shape can be a square, a round, an ellipse or any other shape. This shape must be full of black raster color.

Of course, the print was programmed to develop this graphic element: a background of black raster with a graphic drawing in stoned.

This process, which presents specific graphic elements and which must be analyzed according to a predefined chronology of observation and intervention, with, first of all, the analysis of the forms in black raster and figures in gray colored (which appear in case of default), can be used to derive deviations in various print parameters from ISO 12647 for each type of contact printing.

According to the invention, for a non-contact printing, the method of printing tests said without contact on a substrate using a printing machine, is the same, the method corresponding to the printing results of the ISO 12647-7 standard outside the ISO 12647-8 part of that standard.

Therefore, the method allows a simple "glance" on the graphical element shapes raster black and numbers in gray color, to validate or not the test print. This graphic element makes it possible to know whether the printing meets the standard or not. If a graphic appears in the raster black background, then a fault is detected, the print does not meet the standard.

If no defect is found on the graphical element of the forms in black raster, we validate the production cycle in print. If a fault is detected, the process of analyzing the adjacent graphical elements is started.

This process is very advantageous because it makes it possible to have an anticipatory approach, well before the production phase, in particular during so-called calibration operations, in order to avoid potential risks that could be encountered in production. Of course, the corrective step in case of malfunction in production can be provided by the method of the invention.

According to the method of the invention, the sequence of geometric shapes with black halftone and colored gray numbers is the translation of a curve of the spectral and densitometric measurement in comparison with target ISO values, the sequence of the forms corresponds to a percentage incrementation of the screen, for example from 5% to 5%, in particular with the 40% screen value.

Preferably, in case of appearance of the graphic in a geometric form of raster black and numbers in colored gray, the graphic is a number and corresponds to the number of the percentage of the raster.

Advantageously, are printed by being distributed on the test substrate in different areas, several of said graphic element consisting of a plurality of forms of black raster.

In addition, the method is carried out using measuring tools, in particular using a densitometer and spectrocolorimeter, for certain graphic elements if a defect has been visually identified on the graphic element of the raster black forms.

According to the invention, the analysis of at least some of the graphic elements, after the analysis of the graphical element of the raster black forms and the colored gray numerals, is carried out sequentially in a determined order.

According to one characteristic, each graphic element of the graphical printing test method with or without contact corresponds to at least one adjustment parameter of the machine and if one of the graphic elements taken in the sequential order defined by the protocol does not respond not to the reference criteria established by the protocol, the method comprises a step of deducing the setting parameter to be modified on the machine.

According to the method of the invention, steps of printing on the test substrate, and analysis of the graphic elements are repeated until no defect is detected in the analysis of each of the graphic elements or that the impact of the defect is quantified, the aim being to define the technical capabilities, limitations and possibilities of the printing process.

Advantageously, one of the graphic elements to be analyzed, called the scale, consists of a scale composed of a multitude of lines, each line being obtained by the superposition of all the printing colors of the machine, and arranged near at least one of the edges of the substrate in the vertical direction. The observation of this scale makes it possible in particular to validate the identification (color overlay) of the colors when it presents a colorimetric neutrality, to detect a deformation of the substrate during printing, give an absolute value of the measurement, especially in the case of anamorphosis techniques.

The notion of "vertical" refers to the reading direction of the substrate by an observer who reads in a vertical direction from top to bottom or from bottom to top the substrate when the substrate is positioned opposite the observer.

The terms "upper", "lower", "horizontal" are defined in relation to the meaning given above to the term "vertical".

Preferably, at different levels of the scale, one of the lines extends so that this extension corresponds to the succession of each of the printing colors adjacent.

According to another characteristic, one of the graphic elements to be analyzed consists of at least four black ink strips respectively and primary printing colors of the machine, the strips being printed in the vertical direction of the substrate, and said element comprises vertically several halftone areas of these color bands, each halftone area being compared with each other. This graphic element corresponds in particular to the criterion of distribution of the inking between the beginning of printing and the end of printing.

According to yet another characteristic, one of the graphical elements to be analyzed consists of a graphical form of the square type composed of vertical, horizontal and oblique adjacent lines, and in that several of said graphic element are printed on the test substrate, in particular in part upper and lower, to the different colors of the printing machine (primary color and black).

Advantageously, one of the other graphic elements to be analyzed consists of at least one diagram of each printing color, the diagram consisting of circular sectors that are rasterized, each of the sectors having a raster different from the others, in particular according to a coverage incrementation of 2 or 5% relative to a given screen, preferably diagrams are printed in the upper part and in the lower part of the test substrate. This allows in particular to define the technical capacity of printing a frame with a given screen.

The invention also relates to a printing test device for the implementation of the method. This device comprises computerized support means on which the evaluation graphic elements to be printed are stored, as well as means for supporting a database of analysis data comprising for each graphic element the manner of analyzing said element once printed in order to deduce the eventual defects and to indicate the parameters of the machine on which a setting action is to be performed.

Advantageously, the database constitutes a written explanatory note, preferably whose support means is in the form of a computer file accessible by computer and accessible on any type of suitable medium of the CD-ROM type, USB key, site Internet.

Thus, the method and its implementation device make it possible to detect the adjustment defects of the printing machine, whatever the type of printing and the nature of the substrate, and to provide repeatability in the printing process. , to define its technical capacity for restitution by indicating the limits and possibilities.

• Les figures 1 à 5b illustrent les éléments graphiques pris indépendamment et constituant les moyens d'évaluation du protocole de tests de l'invention;
• La figure 6 illustre l'impression graphique de test de l'invention regroupant la totalité des éléments graphiques d'évaluation.

The present invention is now described with the aid of examples which are only illustrative and in no way limit the scope of the invention, and from the attached illustrations, in which:

• The Figures 1 to 5b illustrate the graphical elements taken independently and constituting the evaluation means of the test protocol of the invention;
• The figure 6 illustrates the graphical test printing of the invention comprising all the graphical evaluation elements.

The printing test method of a printing machine according to the invention consists in printing graphic test elements on a test substrate from an implementation device developed according to the invention.

In known manner, the printing machine incorporates a matrix which will be of distinct type according to the printing technique, for example offset plate, rotogravure cylinder, screen printing, flexographic printing.

The test substrate is the type of substrate on which the machine is intended to print. This is for example paper, fabric, glass, etc ...

The method of the invention consists in printing a test form on the test substrate in order to analyze by visual estimation and measurements using appropriate tools of the densitometer and spectrocolorimeter type, specific graphic elements according to the invention for to deduce deviations in various print parameters from ISO 12647.

The printing step is carried out on the basis of initial machine setting conditions to be tested, that is to say to check whether the machine meets the ISO 12647 standard and / or to know its capabilities.

According to the invention, it is printed on the test substrate 70, opposite the figure 6 , a specific illustration 7, called test illustration. This illustration includes various graphical elements 1 to 6 which are detailed below.

According to the invention, an observer who is preferably the operator of the machine or a person skilled in the art, visually analyzes first and then, if necessary, using standard measuring instruments, the test illustration printed on the basis of an analysis protocol.

The illustration of the invention with the specific graphic elements very advantageously leads to bringing together on the single substrate all the elements useful for the analysis.

In addition, the configuration of certain graphic elements makes it possible, by a simple visual inspection, to detect any printing defects and to act accordingly on the adjustment of the machine and to conduct the investigations directed by the implementation device.

The analysis protocol includes several evaluations, each in relation to a specific graphic element. In addition, the evaluations are made for certain graphic elements in a sequential order determined.

• les paramètres de la machine d'impression qui engendrent les défauts d'impression lorsqu'ils ne sont pas correctement réglés potentiellement,
• la manière d'agir sur ces paramètres pour rectifier la qualité d'impression.

Advantageously, the analysis protocol includes for each evaluation, explanations on:

• Print machine settings that cause print defects when not properly adjusted,
• how to act on these parameters to correct the print quality.

As soon as an evaluation on a graphic element causes the detection of a defect, the operator after understanding the parameter on which it is necessary to intervene, acts on the machine. Once set, a new test print is started. These steps are repeated until the graphical test element corresponding to said parameter has no defect.

The interest of the process is to be able to visualize very quickly several graphical elements to deduce the defects, the observer having a panoramic view of the substrate and able to analyze with intellectual vivacity.

• soit gérer les défauts un par un en agissant sur un paramètre de la machine à la fois et procéder aux tests d'impression jusqu'à ce que chacun des paramètres soient correctement réglés ;
• soit gérer certains défauts en même temps en intervenant sur plusieurs paramètres de la machine avant de lancer un ou plusieurs tests d'impression jusqu'aux réglages convenables. Le dispositif de mise en oeuvre du procédé l'aide dans cette démarche.

It is possible to detect several faults almost concomitantly. In this respect, the operator will have the choice of

• either manage the faults one by one by acting on one parameter of the machine at a time and carry out the printing tests until each parameter is correctly set;
• either manage certain faults at the same time by intervening on several parameters of the machine before launching one or more tests of impression until the suitable settings. The device for implementing the method helps it in this process.

• Les valeurs de couverture de surface du point de trame avant linéarisation et après compensation destinées à réaliser la matrice d'impression
• - Les valeurs de longueurs d'impression dans l'absolu
• - Les écarts de longueurs d'impression entre les couleurs
• - Les déformations mécaniques des substrats dues aux pressions
• - Les déformations mécaniques du substrat dues aux caractéristiques intrinsèques du substrat
• - Les déformations dues aux défauts mécaniques inhérents à la machine
• - Les écarts de répartition d'encrage circonférentiel et l'influence sur la couverture de surface. Le terme « circonférentiel » s'entend par la direction d'avancement du substrat dans la machine d'impression depuis le début d'impression jusqu'à sa fin. Ce terme se traduit également par la notion de direction verticale sur le substrat imprimé.
• - Les glissements de surface en circonférentiel, en latéral, en oblique
• - L'évaluation qualitative optique qui sera examinée à partir de segments de trames juxtaposés et progressifs
• - Les caractéristiques de reproductibilité du procédé d'impression exprimées par exemple par le pourcentage de couverture de surface en relation avec la linéature. On rappelle que la linéature s'exprime en nombre de lignes par inch ou cm (par exemple 150 lignes par inch ou 60 lignes par cm)
• - La répétabilité du résultat d'impression en fonction des vitesses et des configurations
• - L'épaisseur du film d'encre déposée et mesurée en valeurs densitométriques à partir du contraste optimal de l'encrage
• - Les valeurs spectrales des couleurs à partir d'une épaisseur d'encre, dite également charge d'encre, optimisée
• - La couverture de surface en regard de valeurs cibles selon la technique d'impression et le substrat utilisé
• - L'équilibre de la balance des gris colorés sur l'ensemble de la courbe dite de balance des gris.

The defects detected by the analysis protocol of the invention relate to the following information, without being exhaustive:

• The surface coverage values of the pre-linearization and compensated weft dot for making the print matrix
• - Print length values in absolute terms
• - The differences in print lengths between colors
• - The mechanical deformations of the substrates due to the pressures
• - The mechanical deformations of the substrate due to the intrinsic characteristics of the substrate
• - Deformations due to mechanical defects inherent to the machine
• - Differences in circumferential inking distribution and influence on surface coverage. The term "circumferential" refers to the direction of advancement of the substrate in the printing machine from the beginning of printing to its end. This term is also translated by the notion of vertical direction on the printed substrate.
• - Circumferential surface slippage, lateral, oblique
• - The optical qualitative assessment which will be examined from juxtaposed and progressive frame segments
• - The reproducibility characteristics of the printing process expressed for example by the percentage of surface coverage in relation to the screen. It is recalled that the line is expressed in number of lines per inch or cm (for example 150 lines per inch or 60 lines per cm)
• - The repeatability of the print result according to the speeds and configurations
• - The thickness of the ink film deposited and measured in densitometric values from the optimal contrast of the inking
• - The spectral values of the colors from an ink thickness, also called ink charge, optimized
• - The surface coverage next to target values according to the printing technique and the substrate used
• - The equilibrium of the colored gray balance on the whole of the so-called balance of gray curve.

The six evaluation graphic elements 1 to 6, useful for the implementation of the method and arranged on the printed test illustration of the figure 6 , are now described with respect to Figures 1 to 6 .

The dimensional values for the graphic elements are given hereinafter by way of example for an illustration printed on a test substrate with dimensions 800 mm x 1100 mm.

These dimensional values will of course be adapted according to the size of each test substrate.

Graphical element 1:

Graph 1, illustrated in detail on the figure 1 consists of at least four ink strips respectively of black color 10 and primary colors, cyan 11, magenta 12, and yellow 13, the strips being printed parallel and contiguous, in the vertical direction of the substrate, or so-called usual "circumferential" meaning, meaning corresponding to the delivery of the ink on the substrate during the printing process.

The number of strips corresponds to the total number of colors used by the printing machine, here four. In practice, there would be as many bands as colors able to be delivered by the machine.

The printed strips preferably extend over the entire height of the substrate.

Preferably, the colors of the substrate edge side towards the interior of the substrate are set in the following order: black, cyan, magenta, yellow.

Each vertical color band is contiguous to the other and has a given width equal for example to 6 mm. The width of the strip is adapted to be measurable using a densitometry apparatus or spectrocolorimetry.

In addition, several raster zones, arranged transversely to the strips 10 to 13, such as four zones 14, 15 and 16 and arranged respectively in the upper part of the substrate, in the middle part, and in the lower part extend according to the width of the four strips. The halftone areas extend across the width of the four strips to have a halftone surface by color. The height of the screened area is adapted for its analysis with a measuring device. It is for example of the order 5 mm.

Preferably, the zones are 80% screened.

The halftone zones are intended to circumferentially measure the surface coverage as a function of the ink charges (or density) of each color, that is to say to ensure the homogeneity of the ink deposit as as you go through the printing process. The measurement is made in a known manner using the Murray Davis formula which is integrated into the measuring apparatus.

Several measurement points are located, for example, here on the four distinct halftone areas 14A, 15A, 16A, 17A, adjacent to four zones 14 to 17 which are not framed. Depending on the densitometric measurement of each halftone area, the surface coverage is measured. If a measurement deviation of the surface coverage is found, for example between the zone 14A and the zone 15A, the operator will intervene on a mechanical adjustment of the machine as for the distribution of ink.

The graphic element 1, by its first band, is arranged at a precise distance from the edge of the substrate so that the strips are not deformed at the edge of the substrate during printing, not distorting the observations to the using the measuring device.

Based on the results provided by the meter and the location of the defect (lower, middle or upper), the observer will be able to detect a defect in the ink distribution by evaluating the criticality of the surface coverage and will act on the machine to rebalance the ink charge circumferentially.

Graphical element 2

The graphic element 2 to print, next to the figure 2a , is in the form of a square by color, which will be called optical amplifier.

On the printed substrate ( figure 6 ), advantageously four squares 2A to 2D are illustrated to correspond to the four colors and are arranged both in the upper part and the lower part.

Each square is made of a combination of at least vertical and horizontal lines 21, and also oblique lines 22.

More specifically, the square comprises a frame having two opposite horizontal sides 23 and 24 consisting of vertical lines 20, and two opposite vertical sides 25 and 26 consisting of horizontal lines 21. The center 27 of the square, inside the frame, is formed oblique lines 22.

The square has dimensions sufficient to visually translate defects. The square is of the order of 3 or 4 cm.

The thickness of the lines and the pitch between the lines have dimensions adapted to the type of printing substrate, in order to observe the defects on said substrate.

For example, for a paper substrate, the pitch is 0.105 mm.

This graphic element makes it possible to detect certain defects on the printing machine and / or the substrate which are listed below without being exhaustive.

The machine and / or the substrate do not exhibit the defects mentioned below when the square is of neutral color ( figure 2b ), that is, when no vertical, horizontal or oblique line is visualized.

• les déformations de matériau du substrat par pression excessive,
• les déformations de matériau du substrat liées aux conditions climatiques environnantes, par exemple un stockage du matériau dans un environnement défavorable tel qu'un environnement trop humide
• un blanchet insuffisamment tendu,
• des longueurs d'impression différentes,
• des défauts mécaniques relatifs à de mauvais réglages de synchronisation,
• des défauts mécaniques relatifs à une usure mécanique de la presse,
• des défauts de diamètre des cylindres entraînant des vitesses angulaires et circonférentielles différentes ou des défauts de glissements de surface lors de la phase d'impression,
• un excès d'encre.

The appearance of lines makes it possible to detect:

• material deformations of the substrate by excessive pressure,
• the material deformations of the substrate related to the surrounding climatic conditions, for example a storage of the material in an unfavorable environment such as a too humid environment
• a blanket insufficiently stretched,
• different print lengths,
• mechanical defects related to incorrect synchronization settings,
• mechanical defects relating to mechanical wear of the press,
• cylinder diameter defects resulting in different angular and circumferential speeds or surface slip defects during the printing phase,
• an excess of ink.

The graphic element 2 which is visually evaluated is analyzed only after the graphic element 1 has been examined.

Graphical element 3

The graphic element 3 visible on the figure 6 and opposite the partial figure 3a and the detail view of the figure 3b , is a scale composed of a multitude of lines 30 spaced with a constant pitch.

The scale 3 is positioned vertically (circumferentially) on the printed substrate ( figure 6 ) and arranged on both vertical sides of the substrate.

The scale 3 is close to the edge of the substrate without being too close, for example at least 8 mm from the edge, to promote the ability to disengage or the separation of the inked surface vis-à-vis the matrix.

The scale or the graphic element 3 is located near the edge of the substrate, being systematically arranged before the graphic element 1 from the edge of the substrate in the horizontal direction toward the center of the substrate.

The scale is formed of a multitude of horizontal lines spaced at a constant pitch along the vertical.

The width of the scale, that is to say the length of a line according to the horizontal, is for example of the order of 2 to 3 cm. The size must be sufficient to appreciate each trait.

The lines of the scale are at least four-color, that is to say, according to a superposition of the four colors cyan, yellow, magenta and black. When the printing machine has a larger color palette, each stroke will consist of the combination of all these colors.

This scale makes it possible to appreciate the offset in the superposition of the colors. A misregistration results in the coloration of the scale, visible to the naked eye. An additional observation with the son count will allow a more accurate diagnosis in this case a misregistration or different printing lengths.

We can better visualize with a magnifying glass the offset in its detail, one or more colors at the level of one or more lines. The figure 3c shows such a defect at a line, while the figure 3d presents a perfect superposition of colors.

The scale 3 extends over the entire height of the substrate in order to identify any circumferential printing defects with regard to the entire vertical extension of the substrate.

The scale has a vertical height so that it can be measured by a length measuring tool, such as a ruler using the metric system. Indeed, in case of detected fault, the length of the scale will be different from that expected without defect. Thus, if the scale is configured so that its printing corresponds for example to 10 cm while once printed, the measurement is 10.08 cm, a defect will be detected with a length variation of 0.08 cm.

Measuring the length of the scale makes it possible to check the anamorphosis during bending of clichés (matrices) in flexography for example.

Next to the detail view of the figure 3b , the scale 3 has references numbered 31 according to integers from 1, here the number 9, and in numerical order. Each reference is arranged at a line of the scale which extends on the side of said scale. This extended feature is later named "referenced trait".

The referenced line thus has an extension whose magnitude relative to the width of the scale is for example of the order of one third of the width of the scale.

The spacing between each referenced line is constant, each spacing step incorporating a constant plurality of lines. The reference 1 starts at the first line at the upper end of the substrate.

The referenced line corresponds to a superposition of the printing colors except at its end 32 opposite to the scale for which each of the printing colors succeeds one another in an adjacent manner, for example in a width of 1 mm for each of the colors. colors. These aligned segments of the different colors not superimposed will facilitate the appreciation of the differences in printing lengths and the quality of superposition of colors called registration in terms of trade. These aligned segments are observable with a magnifying thread count or magnifying glass.

Thus, the observation of this scale makes it possible to validate the identification (superposition of colors) of the colors when it presents a colorimetric neutrality. On the contrary, when a coloration is detected, this reflects a deformation of the substrate during its passage through the printing machine by an excess of pressure exerted on it or a different print length on one or more colors.

In addition, this scale also makes it possible to give an absolute value of the measurement, in particular in the case of anamorphosis techniques.

Graphical element 4

Graph 4, next to the figure 4 is in the form of a circular sector diagram 40. The diagram corresponds to a zone of inking of the machine.

Diagram 4 is of a given color.

Advantageously, a graphic element 4 is printed on the test substrate per printing color. In the example shown here, next to the figure 6 , are arranged four graphic elements 4A to 4D for respectively each of the three primary colors and for black.

The diagram 4 consists of a plurality of sectors 40 of a specific screen, each of the sectors having a screen different from the others.

The sectors are presented adjacent to each other following each other in a coverage incrementation of, for example, 2 or 5%.

The sectors are large enough to be measured with a densitometer or spectrocolorimeter.

The observation of the graphic element 4 is done first visually, then in a second time with a densitometer if nothing abnormal has been detected with the naked eye.

It also allows the use of a child-son to observe on the one hand the smallest point reproduced according to the line and on the other hand in the largest halftone area, the closure of the point. This makes it possible to define the technical printing capacity of a frame with a given screen.

This technical capacity information is only analyzed last, after having analyzed all the potential defect parameters and that these have been neutralized. The operator will return to the analysis of this graphical element 4 after analysis of all the other elements.

The visual test is conclusive, a priori therefore without defects, when the gradient of color by a gradual framing of said graphical element appears regular, therefore without missing apparent points and when the outline of the points forming the screen is well defined and not fringed, the outline being visible with a son-account.

This graphic element allows the measurement of the surface coverage with a densitometer but above all a visual appreciation of the balance between the water / ink mixture in the application of the offset, it is also used to evaluate the printing pressure.

Advantageously, the 80% screened area allows the calculation of the optimum contrast of the inking.

Graphical element 5

Graphical element 5, illustrated on the Figures 5a and 5b , provides a simulation of colored gray scales. It can only be used for four-color process.

The graphic element 5 is composed of a plurality of identical geometric shapes, of the square type, the color of each of which is a screened black, with a different frame for each in order to form a gradient of gray, thus going from black to light gray. , even white. The incrementation of the frame is for example 2%.

In addition, each geometric (square) shape is designed so that it is visualized in the square, when a defect in the printing machine exists as for the gray balance, a number. The number corresponds to the percentage of the screen. The appearance of the number indicates the detection of a defect in the gray balance and the number itself allows to locate the corresponding place on the curve of the gray scales.

For example, are illustrated on the figure 5a four squares 50 to 54 of gray scales for which a number appears, while the figure 5b shows squares of distinct halftone backgrounds devoid of numbers.

The number is large enough to be visible to the naked eye and measured spectrally.

When the balance of gray is balanced in the printing machine, the raster black is confused with the number which is then not perceptible on the printed substrate ( figure 5b ).

When a number appears ( figure 5a ), the gray balance is not balanced. It will be necessary to intervene on the machine or on the curve of the gray scales during the realization of the matrix of impression.

The dominant color of the number appearing in the square reflects a defect related to the other colors or to the dominant color Thus, if the number has a yellow dominance, the defect can be located at the level of the yellow itself which is too strong in intensity ( the intensity corresponding to the component L in the color model L * a * b), or at the level of the other colors, such as cyan and magenta which are too weak in intensity. The device for implementing the method allows analysis.

Advantageously, at least two graphical elements 5 will be printed on the one hand in the vertical direction of the substrate and on the other hand in the horizontal direction. Indeed, they will thus be perpendicular to the grippers of the machine to not suffer the inking areas and translate circumferential ink input gaps.

The figure 6 shows six graphical elements formed of a plurality of grayscale squares, including two elements 5A and 5B arranged side by side along the vertical side of one of the edges of the substrate, two other elements 5E and 5F also vertical and side side by side towards the opposite edge, and two elements 5C and 5D arranged according to the horizontal, respectively in the upper part and in the lower part.

The elements 5A and 5B on the one hand, and 5E and 5F on the other hand, are adjacent by being arranged head to tail by their screen. Thus, the first square 55 of the screen of element 5A or 5E in the upper part corresponds to a 2% screen, while the adjacent square 56 of element 5B or 5F corresponds to a 100% screen, each graphic element being composed of a number of squares decomposing according to a framing of 2 to 100%.

Graphical element 6

Graphical element 6, next to the figure 6 , includes several images of the type photographs according to categories of images with different style presenting or not technical difficulties of realization.

The images are preferably printed in the central zone of the substrate, the other graphic elements 1 to 5 being arranged around.

These images are intended to be appreciated by their color rendering intent, but no measurement with a device is made on them. For example a snow landscape is white, if the snow is red we will immediately identify the distortion

• le clair-obscur (contraste élevé entre le clair et le foncé) : cette illustration est sensible à la perte des détails lorsque les conditions d'impression ne sont pas optimisées ;
• les tons chair clair et chair foncé : cette catégorie est très sensible à la perception de casssures dans les demi-tons à cause du processus de tramage ;
• les gris colorés homogènes : notre acuité visuelle très performante permettra d'identifier des dominantes colorées ;
• les forts contrastes colorés : ce type d'image est purement illustrative de notre limite de perception visuelle quant à des écarts de couleur ;
• les images dites à forts risques techniques potentiels : l'image imprimée comporte des charges d'encres dans les tons sombres pouvant provoquer des risques pendant la phase d'impression et en post impression. Elles servent d'alerte si des traces de maculage (traces d'encre au verso du substrat) apparaissent.
• Image connue très détaillée, par exemple image d'un monument : à l'observation de ce type d'image, l'oeil sera discriminant pour percevoir des écarts colorimétriques en raison de l'environnement connu de l'image par l'observateur

There are for example the following categories of images:

• chiaroscuro (high contrast between light and dark): this illustration is sensitive to the loss of detail when printing conditions are not optimized;
• light skin tones and dark flesh: this category is very sensitive to the perception of semitone breaks because of the screening process;
• the homogeneous colored gray: our very powerful visual acuity will make it possible to identify dominant colors;
• the strong colored contrasts: this type of image is purely illustrative of our limit of visual perception as to color deviations;
• images said to have high potential technical risks: the printed image includes ink charges in dark tones that can cause risks during the printing phase and post-printing. They serve as an alert if traces of smearing (traces of ink on the back of the substrate) appear.
• Known very detailed image, for example image of a monument: at the observation of this type of image, the eye will be discriminating to perceive color differences because of the known environment of the image by the observer

According to the invention, the method provides a sequential order of analysis of the different graphic elements. When defects are detected at each analysis step of an element, they are corrected as and when analyzing the graphical element again until no fault is revealed by said element. The operator can then proceed to the analysis of another element.

1. 1) élément graphique 5 : la balance des gris
2. 2) élément graphique 3 : l'échelle
3. 3) élément graphique 1 : les bandes d'encre
4. 4) élément graphique 2 : l'amplificateur optique
5. 5) élément graphique 4 : les diagrammes à secteurs circulaires
6. 6) élément graphique 6 : les images photographiques.

Advantageously, the sequential order of analysis is as follows:

1. 1) Graphical element 5: The gray balance
2. 2) graphic element 3: the scale
3. 3) graphic element 1: the ink strips
4. 4) graphic element 2: the optical amplifier
5. 5) graphic element 4: circular sector diagrams
6. 6) graphic element 6: photographic images.

The first analysis of the graphical element 5 shapes in black raster and numbers in gray colored with visualization of a graphic on it in case of default, allows to know immediately whether the printing meets or not the ISO 12647 standard.

If no defect is detected on this graphical "greyscale" element, the printing machine meets the standard. The other adjacent graphical elements can be checked for any other pre-cited defects.

If a fault is detected on this graphical element "greyscale", the machine does not meet the standard, it is absolutely necessary to start a process of correction and adjustment on the machine from the analysis of the adjacent elements and according to a chronological intervention on the machine. If after all the checks on the machine, the operator understands that the machine settings are in fact correct but that defects persist on the test print, he will then intervene on the print matrix to adjust the target values to one. operation called compensation on the halftone values expressed as a percentage. The operator will decrease or increase the surface coverage electronically via the RIP.

Moreover, until then, the operators could not visually detect the adequacy of the target values with the standard. They used a densitometer to evaluate the percentage of color tone. If they detected a defect, not knowing the initial causes of the defect, they were content to intervene, not on the machine, but on the printing matrix by electronically correcting the target values by the compensation of the surface covers. However, if the malfunction was actually on the machine, no intervention having been made on it and its mechanical organs continuing to be requested abnormally, it could inadvertently cause other incidents in cascades. The invention now makes it possible to remedy this problem.

Thus, the test method of the invention proposes a set of different graphic elements described above which should be analyzed one by one to detect possible adjustment faults on the machine, each graphic element being linked to a identifiable parameter on the machine.

Therefore, the method of the invention makes it possible to qualify, optimize, validate or invalidate a printing method in relation to a specific printing substrate, and to check its repeatability, in order to to provide a homogeneous production of the first substrate printed last in a production cycle.

Finally, according to the invention, the test protocol comprises on the one hand the graphic evaluation elements to be printed by the machine on a test substrate, and on the other hand explanations on the manner of analyzing the graphic elements. and to identify the parameters to be set on the printing machine, is preferably implemented by the following device.

• des moyens de support informatisés sur lesquels sont stockés les éléments graphiques d'évaluation à imprimer sur le substrat de test,
• des moyens de support d'une base de données d'analyse comprenant pour chaque élément graphique la manière d'analyser ledit élément une fois imprimé pour en déduire le ou les éventuels défauts et pour indiquer les paramètres de la machine sur lesquels une action de réglage est à opérer avec une chronologie d'intervention stricte permettant de neutraliser certains paramètres.

Preferably, the device comprises:

• computerized support means on which the graphic evaluation elements to be printed on the test substrate are stored,
• means for supporting an analysis database comprising, for each graphic element, the manner of analyzing said element once printed in order to deduce therefrom any defects and to indicate the parameters of the machine on which a setting action is to operate with a strict intervention chronology allowing to neutralize certain parameters.

The support means of the evaluation graphic elements are loaded into the control system of the printing machine so that the machine can print the illustration 7 of the figure 6 . The support means are computerized in the sense that they are in the form of an electronic file stored on any type of support that can be deciphered by reading means of the computer type. The support may for example be a CD-ROM, a USB key, a website, etc.

The support means of the analysis database may be in the form of a paper document of the book type, or of an electronic file that can be consulted by computer and accessible on any type of suitable medium of the CD-Rom type. , USB key, website.

As a preferred example, the graphic evaluation elements to be printed on the test substrate and the analysis database will be downloadable on the Internet.

A plurality of defects can be demonstrated by the method of the invention that should be corrected in a specific order to achieve the fastest to neutralize and obtain the desired optimal impression.

By way of example, some potential defects of the offset process are hereinafter given when the test substrate is visualized according to the method and these defects are clearly assigned to an adjustment parameter of the machine thanks to the implementation device. of the method, in particular via the support means of the analysis database. Example 1 corresponds to the first analysis to be performed for the graphical element 5 of the gray scales. Examples 2 to 4 relate to other graphic elements of the process of the invention.

Example 1

A number appears in the gray balance (graphic element 5), for example 50 with a magenta colored trend.

It follows that ISO 12647 is not achieved.

A spectrocolorimeter is then used and it is deduced whether the intensity is greater on the component L of the magenta or insufficient on the cyan and yellow. If a deviation is found, the compensation curves used to make the print matrix are corrected.

Example 2

• on relève les mesures de diamètres des cylindres de la machine d'impression par rapport aux valeurs constructeurs ;
• si une différence est constatée, on corrige les diamètres à l'aide d'éléments de compensation tels que des feuilles calibrées de différentes épaisseurs ;
• on vérifie également les valeurs de consignes relatives à la pression d'impression si celle-ci est en dehors des tolérances et provoque une surpression, cette surpression provoquant une déformation du matériau en éventail par lamination, et identifiée par une coloration de l'échelle en fin d'impression.

It is noted that the scale 3 is not neutral colorimetrically. Using a thread count, the registration deviation is evaluated and the color with a length defect is identified. From the analysis database, we proceed as follows:

• the diameters of the cylinders of the printing machine are measured in relation to the manufacturer values;
• if a difference is found, the diameters are corrected by means of compensation elements such as calibrated sheets of different thicknesses;
• the values of the instructions relating to the printing pressure are also checked if it is outside the tolerances and causes an overpressure, this overpressure causing a deformation of the material in fan by lamination, and identified by a coloration of the scale in end of printing.

Example 3

• on vérifie la charge d'encre à l'aide du contraste optimal de l'encrage ;
• si une différence existe, on effectue une correction ;
• si le défaut persiste, on vérifie la tension des blanchets et on contrôle le diamètre des cylindres à l'aide d'un comparateur d'habillage et ou en faisant des tests en aplat.

It can be seen that the optical amplifier 2 translates thicker lines horizontally. The following steps are then implemented:

• the ink charge is checked using the optimum contrast of the ink;
• if a difference exists, a correction is made;
• if the fault persists, the blanket tension is checked and the diameter of the rolls is checked by means of a dressing comparator and / or by flat tests.

Example 4

It can be seen that the circular sectors of the diagram 4 corresponding to an inking zone have irregularities due to a lack of screen dots. Then, one checks or changes the set values of the printing pressures.

Claims (15)

1. A method for testing contact type or contactless four-color or color printing on a substrate using a printing machine, wherein the printing is of the offset, screen printing, flexography or gravure printing type, and is applied on a test substrate of the type of substrate on which the machine is intended to print, wherein the method comprises a step of printing on the substrate with the printing machine in the initial conditions of machine adjustment, a step of analyzing the printing against a reference test protocol, characterized in that

   - it comprises a plurality of assessment graphics elements printed on the test substrate, wherein the elements are distinct in their shapes and colors, and some of them include halftones,

   - the analysis is visual,

   - one of the graphics elements (5) to analyze consists in a plurality of identical geometrical shapes, particularly a square, where the color of each shape is halftone black with different incremented screens, wherein each shape comprises graphics, such as a number, that can be seen on the test substrate in the event of a defect.
2. A method for testing printing according to claim 1, characterized in that it meets the print result requirements of the standard ISO 12647, particularly ISO 12647-7, not including the ISO 12647-8 part of said standard.
3. A method for testing graphics printing according to claim 1 or 2, characterized in that the sequence of the geometric shapes with halftone black is the translation of a curve of spectrum and densitometry measurement compared with target ISO values, where the sequence of shapes corresponds to halftone percentage incrementing, for example in steps of 5%, particularly with a 40% halftone value.
4. A method for testing graphics printing according to the preceding claim, characterized in that if the graphics element appears in a geometric halftone black shape, the element is a number and is the halftone percentage number.
5. A method for testing graphics printing according to any of the preceding claims, characterized in that several (5A, 5B, 5C, 5D) of said graphics element made of a plurality of halftone black shapes are printed and distributed over the test substrate.
6. A method for testing graphics printing according to any of the preceding claims, characterized in that it additionally uses measurement tools, particularly densitometer and spectrocolorimeter, for some graphics elements if a defect is identified visually on the graphics element of halftone black shapes.
7. A method for testing graphics printing according to any of the preceding claims, characterized in that the analysis of at least some of the graphics elements, after an analysis of the graphics element of halftone black shapes, is carried out sequentially in a given order.
8. A method for testing graphics printing according to the preceding claim, characterized in that each graphics element corresponds to at least one machine adjustment parameter and if one of the graphics elements taken in the sequential order defined by the protocol does not meet the reference criteria established by the protocol, the method comprises a step for deducing the adjustment parameter to be modified on the machine.
9. A method for testing graphics printing according to any of the preceding claims, characterized in that the steps of printing on the test substrate and analysis of the graphics elements are reiterated till no defect is detected during the analysis of each of the graphics elements or till the impact of the defect is quantified.
10. A method for testing graphics printing according to any of the preceding claims, characterized in that one of the graphics elements (3) to analyze, known as the scale, consists in a scale made up of a multitude of lines (30), wherein each line is obtained by superimposing all the printing colors of the machine and arranged near at least one of the edges of the substrate in the vertical direction, and in that at different steps of the scale, one of the lines is extended so that the extension corresponds to the adjacent succession of each of the printing colors.
11. A method for testing graphics printing according to any of the preceding claims, characterized in that one of the graphics elements (1) to analyze consists in at least four bands of ink, black (10) and the primary printing colors of the machine (11, 12, 13) respectively, wherein the bands are printed in the vertical direction of the substrate, and in that said element comprises along the vertical several halftone zones (14A, 15A, 16A, 17A) of those color bands, wherein each halftone zone is compared with the others.
12. A method for testing graphics printing according to any of the preceding claims, characterized in that one of the graphics elements (2) to analyze consists in a graphics shape of the square type made up of adjacent vertical lines (20), horizontal lines (21) and oblique lines (22) and in that several of said graphics element (2A, 2B, 2C, 2D) are printed on the test substrate, particularly at the top and bottom, in the different colors of the printing machine.
13. A method for testing graphics printing according to any of the preceding claims, characterized in that one of the graphics elements (4) to analyze consists in at least one diagram of each print color, wherein the diagram is made up of halftone circular sectors (40), wherein each sector has a halftone screen different from the others, particularly with coverage incremented by 2 to 5% in relation to a given ruling, where diagrams (4A, 4B, 4C, 4D) are preferably printed at the top and the bottom of the test substrate.
14. A device for testing printing to implement the method according to any of the preceding claims, characterized in that it comprises computerized storage means on which the assessment graphics elements to print are stored, wherein one of the graphics elements consists in a plurality of identical geometrical shapes, particularly a square, where the color of each shape is halftone black with different incrementing halftone screens, wherein each shape comprises graphics, such as a number, which can be seen on the test substrate in the event of a defect, and storage means for an analysis database comprising for each graphics element the manner of analyzing said element after it is printed in order to deduce any defect or defects and indicate the parameters of the machine on which adjustment action is to be applied.
15. A device according to the preceding claim, characterized in that the database constitutes written explanations, preferably where the storage means take the form of a computer-readable electronic file accessible on all types of adapted medium of the CD-ROM, USB stick or website type.

Images