EP3538373B1 - Method for printing a varying pattern of landing zones on a substrate by means of ink-jet printing - Google Patents

Description

The invention relates to a method for printing a substrate by means of ink-jet printing. In this case, landing zones, which correspond to a landing zone type, are specified on the substrate in a landing zone grid consisting of landing zone rows and landing zone rows aligned perpendicular thereto. The landing zone grid is aligned relative to the printhead in such a way that the rows of landing zones run essentially parallel to the printing direction, and the printhead is controlled such that one or more drops of one or more printhead nozzles generate a pattern of landing points within the landing zone. The printhead nozzles generate fictitious nozzle lines on the substrate surface with a lateral resolution representing the distance between the nozzle lines.

One method of printing on a substrate is shown in FIG US 2014/184683 A1 disclosed.

In particular, the invention relates to the printing of both rigid and flexible substrates, in which a predetermined amount of functional liquid (called ink here) is to be dosed into several landing zones such as sensor areas, pixels, reaction areas for medical applications, etc.

The prerequisite for the method is of course that the position of the landing zones on the substrate must be known at least approximately.

To determine the position of the landing zones, there is known to be the possibility of determining the orientation of the substrate relative to the print heads, for example by means of a camera which records the alignment mark on the substrate and the coordinate position of the substrate is determined with a subsequent pattern recognition process. The alignment markings were applied to the substrate in previous production steps and thus represent the geometry of the substrate in the pattern recognition process.

In principle, however, there is also the possibility of determining the orientation of the substrate and the position of individual landing zones directly, i.e. not from the alignment markings applied in previous production steps but, for example, by recognizing the landing zones as a result of their identification, for example through physical activation.

A substrate can have one or more types of landing zones. Different types of landing zones can, for example, have to be dosed with different inks or have different geometries. Furthermore, several substrates can be processed at the same time.

• Druckrichtung:
  Die Druckrichtung ist die Richtung in der der Druckkopf relativ zum Substrat unter Ausbringung von Tropfen mittels Druckkopfdüsen bewegt wird.
• Düsenline:
  Die Bewegung des Druckkopfes erfolgt in der Regel als eine Linearbewegung. Die Projektion auf die Oberfläche des Substrats einer dabei vollzogenen Bewegungslinie einer Druckkopfdüse wird als Düsenlinie bezeichnet. Dabei ist die Düsenlinie nicht physisch vorhanden; sie ist vielmehr fiktiv.
• Landezonen:
  Als Landezonen werden Bereiche auf dem Substrat bezeichnet, in denen eine vorgegebene Menge funktionaler Flüssigkeit (hier Tinte genannt) dosiert werden soll. Diese Landezonen können beispielsweise dem Aufbau von Sensorflächen, Pixel, Reaktionsflächen für Medizinanwendungen etc. dienen. Die Landezonen haben eine vor dem Drucken bereits definierte Sollposition.
• Landezonentyp:
  Ein Substrat kann einen oder mehrere Landezonentypen aufweisen. Unterschiedliche Landezonentypen können beispielsweise mit unterschiedlichen Tinten, Tintenmengen, Landepunkten oder dgl. zu dosieren sein oder unterschiedliche Geometrien aufweisen.
• Landezonenraster:
  Das auf dem Substrat zu erzeugende Muster wird aus einem Landezonenraster, das in Landezonenreihen und Landezonenzeilen geordnet ist, erzeugt. Wird das Landezonenraster relativ zur Bewegung des Druckkopfes ausgerichtet, so bilden die in Druckrichtung hintereinanderliegenden Landezonen die Landezonenreihen und die senkrecht zur Druckrichtung nebeneinanderliegenden Landezonen die Landezonenzeilen.
• Ansteuern einer Druckkopfdüse:
  Das Ansteuern einer Druckkopfdüse bewirkt das Ausbringen eines Tropfens aus der Druckkopfdüse. Durch das Ansteuern kann weiterhin das Tropfenvolumen und/oder die Tropfenzahl gesteuert werden.
• Landepunkt:
  Als Landepunkt wird der Flächenschwerpunkt einer Fläche auf dem Substrat bezeichnet, die durch das Auftreffen eines Tropfens Tinte aus einer Druckkopfdüse benetzt wird.
• Lateralauflösung:
  Unter der Lateralauflösung wird die Anzahl der Düsenlinien pro Längeneinheit verstanden, die zueinander einen kleinsten Abstand a zwischen den Düsenlinien aufweisen. Der kleinste Abstand a kann durch folgende Maßnahmen einzeln oder in Kombination verändert werden:
  1. a) durch eine Erhöhung der Anzahl von Druckdüsen pro Längeneinheit einer Druckkopfdüsenzeile und/oder
  2. b) durch Anordnung mindestens einer zu einer ersten Druckkopfdüsenzeile quer zur Druckrichtung versetzten zweiten Druckkopfdüsenzeile und /oder
  3. c) durch eine statische Verdrehung des Druckkopfes derart dass seine Druckkopfdüsenzeile(n) einen Winkel zwischen >0° und <90° zur Druckrichtung einschließen und/oder
  4. d) durch ein n-faches Überfahren des Druckkopfes relativ zum Substrat, wobei der Druckkopf bei jeder Überfahrt beispielsweise um einen Betrag $x=i\ast a+\frac{a}{n},$
     
     mit i = 0, 1, 2, 3... quer zur Druckrichtung verschoben wird. Eine Erhöhung der Lateralauflösung bedeutet dabei eine Verringerung des Abstandes a.
• Düsenansteuerschema:
  Es kann vorgesehen werden, dass der Vorgabe zur Ansteuerung der Düsen eine Ansteuerungsalgorithmus überlagert wird, der festlegt welche der Druckkopfdüsen, die eigentlich angesteuert werden könnten, da ihre Düsenlinie eine Landezone schneiden, nicht angesteuert werden.

The following terms are assumed here.

• Print direction:
  The print direction is the direction in which the print head is placed is moved relative to the substrate with the application of drops by means of print head nozzles.
• Nozzle line:
  The printhead is usually moved as a linear movement. The projection onto the surface of the substrate of a line of movement of a printhead nozzle that is completed is referred to as a nozzle line. The nozzle line is not physically present; rather, it is fictional.
• Landing zones:
  Landing zones are areas on the substrate in which a predetermined amount of functional liquid (called ink here) is to be dosed. These landing zones can be used, for example, to build sensor areas, pixels, reaction areas for medical applications, etc. The landing zones have a target position that has already been defined before printing.
• Landing zone type:
  A substrate can have one or more types of landing zones. Different types of landing zones can, for example, have to be dosed with different inks, amounts of ink, landing points or the like or have different geometries.
• Landing zone grid:
  The pattern to be produced on the substrate is generated from a landing zone grid which is arranged in landing zone rows and landing zone rows. It will Landing zone grid aligned relative to the movement of the print head, then the landing zones lying one behind the other in the printing direction form the landing zone rows and the landing zones lying next to one another perpendicular to the printing direction form the landing zone lines.
• Controlling a print head nozzle:
  The activation of a printhead nozzle causes a drop to be ejected from the printhead nozzle. The control can also control the drop volume and / or the number of drops.
• Landing point:
  Landing point is the center of gravity of an area on the substrate that is wetted by the impact of a drop of ink from a printhead nozzle.
• Lateral resolution:
  The lateral resolution is understood to mean the number of nozzle lines per unit of length which have the smallest distance a between the nozzle lines from one another. The smallest distance a can be changed individually or in combination with the following measures:
  1. a) by increasing the number of print nozzles per unit length of a print head nozzle line and / or
  2. b) by arranging at least one second line of printhead nozzles offset transversely to the printing direction relative to a first line of printhead nozzles and / or
  3. c) by static rotation of the print head such that its printhead nozzle line (s) enclose an angle between> 0 ° and <90 ° to the printing direction and / or
  4. d) by traversing the print head n times relative to the substrate, the print head, for example, by an amount with each pass $x=i\ast a+\frac{a}{n},$
     
     with i = 0, 1, 2, 3 ... is shifted across the printing direction. An increase in the lateral resolution means a decrease in the distance a.
• Nozzle control scheme:
  Provision can be made for a control algorithm to be superimposed on the specification for controlling the nozzles, which determines which of the printhead nozzles that could actually be controlled because their nozzle lines intersect a landing zone are not controlled.

The state of the art of the above-mentioned method for metering functional liquids on substrates is that such a metering task is carried out by means of dispensers, chemical vapor deposition, analog printing methods and inkjet printing. The invention relates to inkjet printing.

It is generally advantageous in many applications to limit the variation in the dosed amount per type of landing zone, for example in order to reproducibly dose active OLED material or color filters for displays, but also active sensor materials, so that the variation in the functional properties of the landing zones within the finished product given limits of a substrate exceeds. This is necessary in order to keep the luminosity variation within a display but also the variation in the sensitivity of a signal from sensor to sensor as part of a mother substrate within the tolerable limits.

When using inkjet printing for metering, it is the state of the art that exactly the same number of inkjet drops are placed on the landing points in the landing zones which are supposed to fulfill the same function.

It is also prior art that an attempt is made to advantageously adapt the lateral resolution to that of the landing zone grid by rotating the print heads and / or the substrate. This adjustment is carried out so that the largest possible number of nozzle lines intersect the landing zones.

There are situations in which the adaptation of the lateral resolution by rotation to the landing zone grid cannot be carried out, or the complex rotation of print heads and / or substrates should be avoided entirely or a print head should be used which does not continuously adjust the resolution Rotation allows, such as powerful modern print heads with more than one nozzle line.

1. a) Das Substrat weist einen produktionsbedingten Verzug des Landezonenrasters zur einem ideal orthogonalen Landezonenraster auf, der eine Ausrichtung der Düsenlinien an eine große Zahl von Landezonen des Substrats nicht erlaubt. Dies ist beispielsweise bei flexiblen Substraten der Fall.
2. b) Die Landezonen sind nicht hinreichend gleichmäßig auf einem Raster verteilt - entweder produktionsbedingt oder absichtlich - so dass keine praktikable Ausrichtung gefunden werden kann.

It is not practicable to rotate the print heads and / or the substrate, for example, in the following situations:

1. a) The substrate shows a production-related delay of the landing zone grid to an ideally orthogonal one Landing zone grid that does not allow alignment of the nozzle lines to a large number of landing zones of the substrate. This is the case, for example, with flexible substrates.
2. b) The landing zones are not sufficiently evenly distributed on a grid - either due to production or on purpose - so that no practicable alignment can be found.

The invention relates to the situations described above in which the adaptation of the lateral resolution to the landing zone raster by rotating the print head relative to the substrate or, more precisely, to the printing direction should not be carried out or cannot be carried out or is not advantageous.

It is therefore the object of the invention to provide a method for printing a substrate by means of ink-jet printing with which a precise printing of a landing point grid that is shifted, twisted or distorted, in particular non-linearly distorted, compared to an ideally orthogonal landing point grid can be made with little effort.

1. 1. die Lateralauflösung so groß gewählt wird, dass der kleinste Abstand der Düsenlinien kleiner ist als der minimale Abstand zwischen den Landezonenreihen und
2. 2. dass bei einer durch das Substrat vorgegebenen Variation des Abstandes benachbarter Landezonenreihen zwischen verschiedenen Landezonenzeilen (Verzerrung) die Lage der Landezonen einer Landezonenzeile relativ zu den Düsenlinien ermittelt wird und daraus nur die Druckkopfdüsen, deren Düsenlinie eine Landezone schneiden, entsprechend einem Düsenansteuerschema und dem entsprechenden Landezonentyp angesteuert werden.

This object is achieved according to the present invention in that in a method of the type mentioned at the beginning

1. 1. the lateral resolution is chosen so large that the smallest distance between the nozzle lines is smaller than the minimum distance between the rows of landing zones and
2. 2. that given a variation in the distance between adjacent rows of landing zones between different rows of landing zones (distortion) the position of the landing zones of a landing zone line is determined relative to the nozzle lines and from this only the print head nozzles whose nozzle line intersects a landing zone are controlled according to a nozzle control scheme and the corresponding landing zone type.

In one embodiment of the method, it is provided that the lateral resolution is increased by selecting a print head with a number of print nozzles in a print head nozzle line, the distance between which is less than the minimum distance between the rows of landing zones.

The method can be designed in that the lateral resolution is increased by selecting a print head in which at least one second print head nozzle line offset from a first print head nozzle line transversely to the printing direction is arranged.

It is also possible that the lateral resolution is increased by rotating the print head relative to the printing direction, such that its print head nozzle line (s) enclose an angle between> 0 ° and <90 ° to the printing direction.

Another possibility is that the lateral resolution is increased by traversing the print head n times relative to the substrate, the print head being displaced transversely to the printing direction with each pass.

A variant is characterized in that the print head is shifted by an amount x = i * a + a / n, with i = 0,1,2,3 ... with each pass.

To compensate for a moiré effect, it is provided that the Position of the landing points within their landing zones is randomized. Since the positions of the landing points are chosen randomly within the permissible limits, repetitive patterns that would be visible due to their repetitive structure are avoided. The landing points can then be positioned by adding or subtracting a randomly selected value in the position coordinates.

In a further embodiment of the method it is provided that a pattern of landing points in an individual landing zone is printed by more than one, advantageously several, nozzles. A repetitive structure can also be avoided in this way.

Another possibility for avoiding repetitive structures is that the pattern of the landing points is randomly shifted from landing zone to landing zone by one or more lateral resolution steps.

It is possible that the control of the nozzles for a respective landing zone is random or pseudo-random.

In a further embodiment of the method it is provided that the pattern of the landing points is selected by a combination of nozzles with different drop volumes in such a way that the amount of ink deposited in similar landing zones deviates by a maximum of 10%.

To adjust the amount of ink in a landing zone, it is possible that the dosage of drops in a landing zone takes place in such a way that those nozzles which the corresponding Sweep over the landing zone as a result of the relative movements, apply a defined number of drops to one or more landing points within the landing zone.

It is possible that the number of drops is specified in the nozzle control scheme or in the type of landing zone.

To determine the position and the distortion, it is provided that the position of the landing zones is determined by scanning alignment markings on the substrate, that their actual positions are compared with the target positions of an undistorted substrate, that distortions within the substrate beyond linear position deviations and angular deviations of the substrate are compared Substrate are determined and that the position of the landing zones are calculated according to the distortions of the substrate by means of a mathematical model.

It is possible for landing zones to be used as alignment marks.

Fig. 1

ein Beispiel eines RGB(W)-Pixels, bestehend aus vier Landezonen,

Fig. 2

ein Beispiel RGB-Pixels, bestehend aus drei Landezonen,

Fig. 3

ein Beispiel eines RGB-Pixels auf einem flexiblen EPD,

Fig. 4

eine Darstellung der Toleranzen für die Farbpixelposition im TFT-Pixelbereich mit vier Landezonen,

Fig. 5

eine longitudinale Druckauflösung in Druckrichtung gesteuert durch die Strahlfrequenz,

Fig. 6

eine Lateralauflösung (in y-Richtung), gesteuert vom Druckkopfwinkel,

Fig. 7

ein einfarbiges Tröpfchen auf einem Landeplatz innerhalb einer Landezone,

Fig. 8

eine Farbpixelmatrix mit 3x3 Landeplätzen innerhalb einer Landezone,

Fig. 9

eine typische nichtlineare Verzerrung von Pixelpositionen in flexiblen Displays nach dem Lösen vom starren Träger, blau = Designpositionen, rot = aktuelle Positionen,

Fig. 10

Designdaten von Ausrichtungsmarken und Pixelpositionen,

Fig. 11

eine Darstellung der Messung von Ausrichtungsmarken,

Fig. 12

eine Darstellung einer Rotationskorrektur,

Fig. 13

eine Darstellung einer Vergrößerungskorrektur,

Fig. 14

eine Darstellung einer Berechnung von Pixelpositionen (Landezonen) entlang Polynomen basierend auf der Ermittlung von Ausrichtungsmarkenpositionen,

Fig. 15

ein schematisches Beispiel der Verzerrungskompensation,

Fig. 16

eine schematische Darstellung der Wirkungsweise von gesteuerten Druckkopfdüsen während des linearen Druckbandes zur Korrektur der Verzerrung,

Fig. 17

eine Darstellung, dass eine größere Lücke zwischen den Pixeln eine systematische optische Kontraständerung erzeugt, und

Fig. 18

eine randomisierte Pixelverschiebung in y-Richtung.

The invention is to be explained in more detail below using an exemplary embodiment. In the accompanying drawings shows

Fig. 1

an example of an RGB (W) pixel consisting of four landing zones,

Fig. 2

an example of RGB pixels, consisting of three landing zones,

Fig. 3

an example of an RGB pixel on a flexible EPD,

Fig. 4

a representation of the tolerances for the color pixel position in the TFT pixel area with four Landing zones,

Fig. 5

a longitudinal print resolution in the print direction controlled by the beam frequency,

Fig. 6

a lateral resolution (in y-direction), controlled by the printhead angle,

Fig. 7

a single-colored droplet on a landing site within a landing zone,

Fig. 8

a color pixel matrix with 3x3 landing places within a landing zone,

Fig. 9

a typical non-linear distortion of pixel positions in flexible displays after detachment from the rigid support, blue = design positions, red = current positions,

Fig. 10

Design data of alignment marks and pixel positions,

Fig. 11

a representation of the measurement of alignment marks,

Fig. 12

a representation of a rotation correction,

Fig. 13

a representation of a magnification correction,

Fig. 14

a representation of a calculation of pixel positions (landing zones) along polynomials based on the determination of alignment mark positions,

Fig. 15

a schematic example of distortion compensation,

Fig. 16

a schematic representation of the mode of operation of controlled print head nozzles during the linear print band to correct the distortion,

Fig. 17

a representation that a larger gap between the pixels results in a systematic optical contrast change generated, and

Fig. 18

a randomized pixel shift in the y-direction.

The exemplary embodiment relates to a method for printing flexible substrates.

Printing color filters directly on the surface of an active matrix display is a well known technology. As in FIGS. 1 and 2 shown, three colors (RGB = red, green, blue) are usually printed on subpixels of a high-resolution pixel array, which leads to an RGB display. The subpixels represent landing zones in the sense of the invention. Consequently, the pixel arrays are generated by means of landing zone arrays.
Typical numbers of pixels in an active matrix display are between a few thousand and a few million pixels per display. Common screen resolutions are between 50ppi and over 300ppi.

Common color filter arrays are RGB or RGBW (RGBW = red, green, blue, white, where W is not printed). While in this exemplary embodiment each color has only one geometry of the landing zone and in particular the geometry of the landing zones R, G and B is chosen to be the same in the example, the geometry of the landing zones can generally also be different and more than one geometry, ie more than one type of landing zone per Color exist.

A flexible EPD (EPD = electronic paper display) will serve as an example of a flexible substrate. As in Fig. 3 shown, the original b / w resolution (b / w = black / white) is 150 ppi, each with 170 µm TFT pixel size (TFT = thin film transistor). To produce a color display, an RGB filter is printed on top of the b / w TFT pixel, with each color pixel usually being slightly smaller than the TFT pixel size (e.g. 150 µm). The resulting color display resolution here is 75 ppi.

An important criterion is the placement of color pixels, consisting of landing points of ink jet drops, in each TFT pixel, ie each landing zone, as shown in FIG Fig. 4 is shown. While other criteria could also apply, it is a condition that the color pixel within the TFT pixel must not overlap into neighboring TFT pixels, but rather must lie within the TFT pixel area for all pixels via an active matrix display.

1. 1. Eine Funktionserkennungskamera erkennt mehrere Ausrichtungsmarkierungen (normalerweise 4) innerhalb der aktiven Matrix oder außerhalb der aktiven Matrix (Ausrichtungsmarkierungen, die normalerweise während des Prozessablaufs des TFT-Arrays erzeugt werden). Alle TFT-Pixelpositionen der aktiven Matrixanzeige in Bezug auf die Ausrichtungsmarkierungen sind durch die Gestaltung der Anzeige bekannt.
2. 2. Abhängig von der Platzierung des Display-Substrats auf einem Haltetisch der Ink-Jet-Druckmaschine kann diese einen x- und y-Offset kompensieren, indem sie den Haltetisch oder den Druckkopf zur Korrektur der Startposition bewegt und die Drehung normalerweise durch Drehen des Haltetischs in die gewünschte Position ausgleicht.
3. 3. Die Ink-Jet-Druckmaschine beginnt mit dem Drucken mit linearen Druckkopfstreifen über das Substrat (normalerweise bewegt sich der Haltetisch in Druckrichtung (x-Richtung in Richtung der Druckstreifen) und die Druckköpfe bewegen sich quer zur Druckrichtung (y-Richtung).
4. 4. Die Steuerung der Landepunkte (Longitutinalauflösung) in x-Richtung (Druckrichtung) erfolgt durch Steuerung der Ausstoßfrequenz von Druckkopf und Haltetischgeschwindigkeit, wie dies in Fig. 5 dargestellt ist.
5. 5. Die Auflösung in y-Richtung wird durch die native Auflösung des Druckkopfes angegeben. Die Auflösung in y-Richtung kann erhöht werden, indem der Druckkopf entsprechend gedreht wird, wie dies in Fig. 6 dargestellt ist.
6. 6. Wie in Fig. 7 und 8 dargestellt, kann die Erzeugung von Farbpixeln in jedem TFT-Pixel durch ein einfarbiges Tintentröpfchen oder durch Ausstoßen einer Matrix von mehreren Farbtintentröpfchen innerhalb jedes TFT-(Sub-)Pixelbereichs (Landezone) erfolgen.

Typically, a printing color filter that is produced by means of an ink jet has the following process steps:

1. 1. A functional recognition camera detects multiple alignment marks (usually 4) inside the active matrix or outside the active matrix (alignment marks normally generated during the TFT array process). All of the TFT pixel positions of the active matrix display with respect to the alignment marks are known by the design of the display.
2. 2. Depending on the placement of the display substrate on a holding table of the ink jet printing machine, the latter can compensate for an x and y offset by moving the holding table or the print head to correct the starting position and the rotation normally by turning the holding table in the desired position.
3. 3. The ink-jet printing machine starts printing with linear printhead strips over the substrate (normally the holding table moves in the printing direction (x-direction in the direction of the printing strips) and the printheads move transversely to the printing direction (y-direction).
4. 4. The control of the landing points (longitudinal resolution) in the x-direction (pressure direction) is carried out by controlling the Print head output frequency and platen speed as shown in Fig. 5 is shown.
5. 5. The resolution in the y-direction is given by the native resolution of the print head. The resolution in y-direction can be increased by rotating the print head accordingly, as shown in Fig. 6 is shown.
6. 6. As in Figures 7 and 8 shown, the generation of color pixels in each TFT pixel can be done by a single color ink droplet or by ejecting a matrix of several color ink droplets within each TFT (sub) pixel area (landing zone).

Typical color ink jet printers for color filter printing on an active matrix display use print heads with a native resolution of up to 600 ppi and a single droplet size of> 30 µm.
Active matrix display arrays typically have an orthogonal (linear / rectangular) arrangement of TFT pixels across the display area. The color filter printing process described above is based on the exact position of each subpixel and external alignment marks, which allow only slight deviations (a few µm at most). This is not a problem as active display arrays are typically created on rigid glass substrates.

Also, the printing process of a flexible high resolution display is typically performed while the flexible substrate is bonded to a rigid glass support. As long as the substrate is or is bonded to glass, the arrangement remains rigid and the following color filter printing process can rely on known subpixel positions with respect to the alignment marks as dictated by the design.

For a manufacturing process of displays on flexible substrates The manufacturing flow may require color filter printing after the flexible substrate (with the completed TFT array process) is released from the rigid glass support. As each flexible substrate (e.g. PEN, PI, PET, ...) is detached from its rigid (glass) carrier, the flexible substrate experiences significant distortion. Both the alignment marks and the TFT pixel positions of the display panel will shift nonlinearly.

The amount of displacement as shown in Fig. 9 is shown increases as the display size increases. Any change in temperature also has a significant expansion / retraction effect on the flexible substrate. As a result, the alignment marks no longer match the design position, the TFT pixel position with respect to alignment marks no longer matches the design position, and all TFT pixel positions in the array will also deviate from the design positions. Offsets can range from 5 µm to a few hundred µm. The offset values (distortion) are different for each display. But color filter printing requires a precise pixel position; any deviation of> 5-10 µm would make the color filter process impossible, since color pixels can no longer be printed exactly in TFT pixels. This maximum permissible deviation is exceeded in that the flexible substrate is detached from the rigid carrier and the flexible substrate is distorted.

As a result, the ink jet printing machine would scan alignment marks with feature recognition (e.g., at the four corners of a display) and find non-rectangular positioning of those alignment marks. Non-linearly shifted TFT pixel positions cannot be determined, calculated and compensated. Only an average rectangular grid can be calculated and used for the print position calculation. The actual TFT pixel positions give way however, by more than 5-10 µm for most of the display area from which the print result will suffer.

The approach to overcoming the problem is to combine two concepts. First, a mathematical model is used to predict the pixel position on a warped display substrate (determination of landing zones). Second, a high-resolution ink-jet print head is used for color filter printing, which compensates for distortions while maintaining a high production throughput.

1. 1. Eine Erkennungs-Kamera scannt 4 Ausrichtungsmarkierungen. Abhängig von der Anzeigegröße, der erforderlichen Genauigkeit und der Verzerrung. Je nach Art und Größe der Verzerrung kann sich die Anzahl der abzutastenden Ausrichtungsmarkierungen erhöhen. Für eine typische ∼10" Displaygröße sind 8 Ausrichtungsmarkierungen ausreichend.
   Die Auswahl der Ausrichtungsmarkierungen sollte so erfolgen, dass die Anzeigeverzerrung gut genug erfasst werden kann. Dies wären typischerweise 4 Ausrichtungsmarkierungspositionen an der Ecke der Anzeige und 4 Ausrichtungsmarkierungen an der Seite der Anzeige. Je näher die Ausrichtungsmarkierungen an der aktiven Fläche liegen, desto besser ist das spätere Berechnungsergebnis. Auch Ausrichtungsmarkierungen innerhalb der aktiven Matrix können verwendet werden (Ausrichtung am obersten Pixel der TFT-Matrix; wenn EPD-Medien vorhanden sind, können Ausrichtungsmerkmale direkt in die Anzeige eingetrieben werden).
2. 2. Ein mathematisches Modell wird angewendet, um alle Pixelpositionen der Anzeige vorherzusagen, wobei alle 8 (oder mehr) Ausrichtungsmarkierungen berücksichtigt werden und die beste Anpassung berechnet wird. Die resultierende Matrix der x- und y-Position von Pixeln in der Anzeige ist kein lineares Gitter, sondern eine Matrix von Polynomlinien. Hierbei wird angenommen, dass die Verzerrung innerhalb der aktiven Matrix im Allgemeinen der Verzerrung folgt, die an den Ausrichtungsmarkierungen gemessen wird. In der Realität wird immer noch ein gewisser Versatz zwischen berechneter und tatsächlicher Pixelposition vorhanden sein. Dies ist akzeptabel, solange die Abweichung für alle Pixel klein genug ist.
3. 3. Die Ink-Jet-Druckmaschine erhält nun die berechneten Pixelmittelpositionen (Landezonen) und ein Druckbild für jedes zu druckende Farbpixel (Landezonentyp). Die Verwendung von hochauflösenden Druckköpfen mit einem kleinen Tropfenvolumen ermöglicht es, ein Farbpixel als eine Matrix aus vielen kleinen Farbpunkten (auf den Landepunkten) zusammenzusetzen. Für die hier besprochene Anwendung ist eine typische Tropfengröße 15-20µm. Um beispielsweise ein Farbpixel von 150x150 um zu erzeugen, kann eine Farbmatrix aus 12x12-Tröpfchen aufgetragen werden, während sich die Tröpfchen überlagern. Ein typisches zu druckendes Farbpixelbild ist quadriert. Aber mit hoher Auflösung und kleinen Tröpfchen können auch andere Formen gedruckt werden, um die optische Leistung des Farbfilters zu beeinflussen und Prozessbetrachtungen (wie Düsenausstoßabweichungen) zu kompensieren.
4. 4. Beim Ink-Jet-Drucken kann jeder Streifen nur einer linearen Bewegung folgen. Die Verzerrungskompensation wird jetzt angewendet, indem die hohe Auflösung des Druckkopfs und die Maschinengenauigkeit verwendet werden. Zum Beispiel wird hier ein nativer 1200 dpi-Druckkopf verwendet, der bei 2400 dpi betrieben wird. Dies ermöglicht eine Tröpfchenplatzierung aller ∼10 µm innerhalb von nur 2 Druckbändern. Eine solche Auflösung ist hoch genug, um jeden Farbbereich ausreichend zentriert auf jedem TFT-Pixel anzuordnen. Eine höhere Auflösung ist möglich, wenn mehr Farbbänder für den Farbpixeldruck ausgeführt werden. Dadurch wird allerdings der Durchsatz in der Produktionsumgebung beeinträchtigt.
   Wie in den Fig. 15 und 16 dargestellt, erfolgt die tatsächliche Kompensation während des linearen Druckbandes durch Steuern der einzelnen Strahldüsen, die während der linearen Bandbewegung ein- und ausschaltet werden. Ein gegebener Satz von Düsen wird die Farbpixel entlang des Bandes drucken, solange die Mittenposition innerhalb von ∼5µm der Farbpixelmatrix liegt. Wenn die Mittelposition die 5µm-Grenze überschreitet, wird eine Düse der Matrix ausgeschaltet und die nächste Düse auf der gegenüberliegenden Seite der Matrix wird eingeschaltet. Auf diese Weise bleibt die Farbpixelmatrix gleich, aber das Farbpixel springt um ∼10µm (Lateralauflösung). Das Farbpixel befindet sich immer noch innerhalb des erlaubten TFT-Pixelbereichs. Dies wird kontinuierlich entlang der Druckrichtung durchgeführt, wodurch alle Farbpixel genau genug entlang des berechneten Polynoms platziert werden können.
5. 5. Mit einem derartigen Verzerrungskompensationsansatzes wird die Ink-Jet-Maschine keine mechanische Drehung der Vakuumspannvorrichtung oder des Druckkopfs mehr benötigen. Die Drehung des Haltetisches wird normalerweise ausgeführt, um den Rotationsversatz während des Platzierens des Substrats zum Einspannen zu kompensieren. Mit dem hier besprochenen Ansatz wird auch eine leichte Rotation des Substrats mit der gleichen Methode kompensiert.
   Die Drehung des Druckkopfs ist normalerweise nicht erforderlich, um die native Auflösung des Druckkopfs an die erforderliche Druckauflösung anzupassen. Mit dem hier besprochenen Ansatz wird die erforderliche Druckauflösung erreicht.

The process sequence as described in the Figures 10 to 14 is shown is the following:

1. 1. A recognition camera scans 4 alignment marks. Depending on the display size, required accuracy and distortion. Depending on the type and size of the distortion, the number of alignment marks to be scanned may increase. For a typical ∼10 "display size, 8 alignment marks are sufficient.
   The alignment marks should be selected so that the display distortion can be captured well enough. This would typically be 4 alignment mark positions on the corner of the display and 4 alignment marks on the side of the display. The closer the alignment marks are to the active area, the better the subsequent calculation result. Alignment marks within the active matrix can also be used (alignment at the top pixel of the TFT matrix; if EPD media is present, alignment features can be driven directly into the display).
2. 2. A mathematical model is applied to predict all of the display's pixel positions, taking into account all 8 (or more) alignment marks and calculating the best fit. The resulting matrix of the x and y position of pixels in the display is not a linear grid, but a matrix of polynomial lines. This assumes that the distortion within the active matrix generally follows the distortion measured at the alignment marks. In reality there will still be a certain offset between the calculated and actual pixel position. This is acceptable as long as the deviation is small enough for all pixels.
3. 3. The ink-jet printing machine now receives the calculated pixel center positions (landing zones) and a print image for each color pixel to be printed (landing zone type). The use of high-resolution print heads with a small drop volume makes it possible to assemble a color pixel as a matrix from many small color points (on the landing points). For the application discussed here, a typical drop size is 15-20 µm. For example, in order to generate a color pixel of 150x150 µm, a color matrix of 12x12 droplets can be applied while the droplets are superimposed. A typical color pixel image to be printed is squared. But other shapes can also be printed with high resolution and small droplets in order to influence the optical performance of the color filter and to compensate for process considerations (such as nozzle output deviations).
4. 4. In ink-jet printing, each strip can only follow one linear movement. The distortion compensation is now applied by the high resolution of the print head and the Machine accuracy can be used. For example, a native 1200 dpi printhead is used here that operates at 2400 dpi. This enables droplet placement of all ∼10 µm within just 2 pressure bands. Such a resolution is high enough to place each color area sufficiently centered on each TFT pixel. A higher resolution is possible if more ribbons are used for color pixel printing. However, this affects the throughput in the production environment.
   As in the Fig. 15 and 16 shown, the actual compensation takes place during the linear pressure band by controlling the individual jet nozzles, which are switched on and off during the linear movement of the band. A given set of nozzles will print the color pixels along the belt as long as the center position is within ∼5µm of the color pixel matrix. If the center position exceeds the 5 µm limit, one nozzle of the matrix is switched off and the next nozzle on the opposite side of the matrix is switched on. In this way the color pixel matrix remains the same, but the color pixel jumps by ∼10µm (lateral resolution). The color pixel is still within the allowed TFT pixel range. This is done continuously along the printing direction, which means that all color pixels can be placed accurately enough along the calculated polynomial.
5. 5. With such a distortion compensation approach, the ink jet machine will no longer need mechanical rotation of the vacuum chuck or the print head. The rotation of the support table is normally carried out to compensate for the rotational offset during the placement of the Compensate substrate for clamping. With the approach discussed here, a slight rotation of the substrate is also compensated for using the same method.
   Rotation of the printhead is usually not required to match the native resolution of the printhead to the required print resolution. With the approach discussed here, the required print resolution is achieved.

Such an approach, as described above, can have another problem which is solved below and as in Fig. 17 is shown.

A lateral resolution is used with a high-resolution printhead for correcting pixel positions in the y-direction. The lateral resolution is, for example, 1200 dpi and when printing with 2400 dpi (in two passes) the distance a between the points is 10.58333333 μm. The TFT pixel design of the display has an exact size of 170 µm (pixel to pixel). The effect is that the lateral resolution of the printhead cannot be divided equally by the resolution of the pixel size.

For example, 16 points in the y-direction result in 16 x 10.58333333 µm = 169.33333333, which has a remainder of 0.6666666 µm. This is a small offset that is acceptable for a TFT pixel. But every 15 TFT pixels the remainder adds up to um10um. Therefore, after 15 TFT pixels, the sub-color pixel has to "jump" a nozzle distance (10.5 µm) to compensate.

Since the positions of nozzles are fixed (given by the lateral resolution), this "jump" will take place regularly along the y-direction and be evenly distributed over the display along the x (print) direction. The result is that every 15 TFT pixels in the y-direction the gap between two adjacent color sub-pixels is different compared to all other gaps (∼ 10 µm). This larger gap is located over the entire y-position along the printing direction and is repeated every 15 TFT pixels. This systematic offset is visible to the human eye as a local contrast difference that is strong enough to be seen as lighter and darker lines along the printing direction. The visual impression (similar to the moire effect) disturbs the visual uniformity of the brightness across the display and is not acceptable.

Depending on the substrate placement (rotation) on the vacuum chuck, these may be repeating lines in the angular direction across the display rather than straight lines along the printing direction. This is due to the rotation correction discussed above, which now superimposes the resolution compensation.

To reduce the effect, the print resolution can be increased to 4800 dpi (4swaths). The resulting "jump" will now happen every 8 TFT pixels and the "jump" is now only ∼ 5m. This reduces the visual effect, but does not eliminate it. It also increases process time by a factor of two, which is undesirable in the mass production environment.

The better one and here in Fig. 18 The solution shown is a random change in the "jump" positions in the y-direction along the printing direction. The result is an interruption of the systematic lines, whereby the offset for the resolution compensation cannot be detected by the human eye.

List of reference symbols

1

Landing zone

2

Landing site

3

Printhead

Claims (15)

1. Method for printing a substrate by means of ink-jet printing, wherein landing zones (1) which correspond to a landing zone type are predefined on the substrate in a landing zone pattern, consisting of landing zone lines and landing zone rows aligned at right angles thereto, the landing zone pattern is aligned relative to a print head (3) in such a way that the landing zone rows extend substantially parallel to the printing direction, and the print head is activated in such a way that one or more drops of one or more print head nozzles produce a pattern of landing points within the landing zone, wherein the print head nozzles produce imaginary nozzle lines on the substrate surface with a lateral resolution representing the spacing between the nozzle lines,
   characterized in that the lateral resolution is chosen to be large enough that the smallest spacing of the nozzle lines is smaller than the minimum spacing of the landing zone rows and in that, in the event of a variation in the spacing of adjacent landing zone rows between various landing zone lines, predefined by the substrate, the position of the landing zones of a landing zone line relative to the nozzle lines is determined and, from the latter, only the print head nozzles of which the nozzle line intersects a landing zone are activated in accordance with a nozzle activation scheme and the corresponding landing zone type.
2. Method according to Claim 1, characterized in that the lateral resolution is increased by the choice of a print head having a number of print nozzles in a print head nozzle line, the spacing of which is lower than the minimum spacing of the landing zone rows.
3. Method according to Claim 1 or 2, characterized in that the lateral resolution is increased by the choice of a print head in which at least one second print head nozzle line is arranged to be offset with respect to a first print head nozzle line transversely relative to the printing direction.
4. Method according to one of Claims 1 to 3,
   characterized in that the lateral resolution is increased by a rotation of the print head relative to the printing direction in such a way that its print head nozzle row(s) enclose(s) an angle between > 0° and < 90° to the printing direction.
5. Method according to one of Claims 1 to 4,
   characterized in that the lateral resolution is increased by means of an n-fold pass of the print head relative to the substrate, wherein the print head is displaced transversely with respect to the printing direction during each pass.
6. Method according to Claim 5, characterized in that the print head is displaced during each pass by an amount x = i*a + a/n, where i=0, 1, 2, 3....
7. Method according to one of the preceding claims,
   characterized in that the position of the landing points within their landing zones is randomized.
8. Method according to one of Claims 1 to 7,
   characterized in that a pattern of landing points in an individual landing zone is printed by more than one nozzle, advantageously multiple nozzles.
9. Method according to Claim 8, characterized in that the pattern of landing points is displaced randomly by one or more steps from landing zone to landing zone.
10. Method according to one of Claims 1 to 8,
    characterized in that nozzles for a respective landing zone are activated randomly or pseudo-randomly.
11. Method according to Claim 10, characterized in that the pattern of landing points is chosen by means of a combination of nozzles having different drop volumes such that the quantity of ink deposited in identical landing zones deviates by a maximum of 10%.
12. Method according to one of Claims 1 to 11,
    characterized in that the metering of drops into a landing zone is such that those nozzles which sweep over the corresponding landing zone as a result of the relative movements apply a defined number of drops to one or more landing points within the landing zone.
13. Method according to Claim 12, characterized in that the number of drops is defined in the nozzle activation scheme or in the landing zone type.
14. Method according to one of Claims 1 to 13,
    characterized in that the position of the landing zones is determined by alignment marks on the substrate being scanned, in that their actual positions are compared with target positions of a non-distorted substrate, in that distortions within the substrate exceeding linear position deviations and angular deviations of the substrate are determined therefrom, and in that the position of the landing zones is calculated by means of a mathematical model according to the distortions of the substrate.
15. Method according to Claim 14, characterized in that landing zones are used as alignment markings.

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