JP2007513808A - Printing on a moving substrate - Google Patents

Abstract

  An ink jet printing apparatus for printing on a moving substrate (16) is disclosed. The apparatus includes a plurality of inkjet print heads (4) for printing on the surface of the substrate, and a plurality of rollers configured to move the substrate (16) relative to the plurality of print heads 4. (12, 14) and a pressure source (22). The pressure source (22) is configured to apply a negative gauge pressure (32) to the substrate (16). By applying pressure, the substrate can be held flat and undesirable movement of the substrate relative to the rollers (12, 14) can be reduced. With this apparatus, a high-quality full-color image can be printed in a single pass on a substrate using an inkjet printer.

Description

  The present invention relates to printing. The present invention is particularly applicable to printing on a moving substrate, but is not limited thereto. The preferred examples to be described relate to ink jet printing, and in particular to a transport mechanism and transport method for moving a substrate in an ink jet printer.

  Examples are given below for single pass inkjet printing where the substrate is passed through the printhead device only once.

  Inkjet printing has certain advantages over other printing methods because images can be switched quickly. However, it may be difficult to form a high-quality image.

Conventional printing devices (eg, offset lithographic printing and flexographic printing) can print full-color images with high quality on continuous webs or multiple sheets, but this can be done using existing inkjet printing technology. There are some difficulties to achieve.
JP-A-10-315551

  In an inkjet printing process, for example, an array of ink droplets is formed on the surface of a substrate in a pattern to form the required image. Ink droplets are typically ejected from a plurality of arranged nozzles of an inkjet printhead. This usually requires relative movement between the inkjet printhead and the substrate during the printing process of the entire required image to be printed on the substrate. Depending on the configuration, this movement may occur while ink is being ejected from the nozzles of the printhead, and alternatively, or in addition, printing may be paused when the movement is taking place. If the relative movement between the print head and the substrate occurs during image printing, errors in alignment may occur, which can reduce image quality.

  This is particularly a problem when halftone images are printed. Very slight errors in registration between multiple colors can cause noticeable color errors in halftone printing due to moire effects. The Moire effect appears as a pattern that can occur when two or more geometric patterns, such as a lattice, are superimposed, for example a herringbone pattern. In inkjet printing, these may occur, for example, when two or more grids of printed droplets of different color images are not correctly aligned. This can be a problem even when printing monochrome images when several printheads are used at intervals in the printing direction.

  In traditional printing, this can be controlled by rotating multiple screens for the various colors to be printed, thereby forming small moiré rings that are not considered visually problematic. Is done. However, in an inkjet apparatus, particularly a single-pass configuration, this type of approach is not possible because an image is formed directly by a single movement of the substrate by a plurality of arranged nozzles.

  Therefore, in inkjet printing, particularly single-pass printing, it is considered necessary to control the relative movement of the substrate and the plurality of print heads in the lateral direction with high accuracy. Usually, lateral movement of 20% of the dot pitch may cause unacceptable banding during printing. Therefore, in an image with a resolution of 200 dpi, banding may occur due to an error of about 0.001 inch.

  A particular problem may arise when moving the substrate during the printing process, as unnecessary movement of the substrate may occur that degrades print quality as a result of alignment errors.

  Substrates to be printed, such as rigid sheets, are often conveyed on a conveyor belt. However, it is difficult to configure a conveyor belt device that performs the required precision movement, and the base may slide on the conveyor belt.

  Some existing inkjet printers use a vacuum in combination with a plurality of conveyor belts and rollers for transporting a substrate to be printed (see, for example, FIGS. 9a and 9b of Patent Document 1). Such a system is configured to index the substrate (feed by a predetermined amount) during printing of a plurality of print strip areas and hold the substrate while ink is ejected from the print head. In order to maintain a constant spacing between the print head and the surface of the substrate, a vacuum may be used to hold the substrate against the platen or belt. Since the indexing distance between the plurality of print belt regions is small and is usually 1 cm, the linear velocity of movement of the substrate is low and is usually 0.1 m / s. Such a system can only process flexible substrates such as paper. Other approaches are needed for single pass printing at speeds in excess of 1 m / s on rigid materials such as cardboard.

  Several aspects of the present invention seek to mitigate one or more of the problems discussed above.

  According to a first aspect of the present invention, there is provided an inkjet printing apparatus that performs printing on a moving substrate, such that the ink is ejected toward the surface of the substrate and is stationary during the ejection of the ink. A plurality of inkjet printheads configured; a plurality of rollers configured to move the substrate relative to the plurality of printheads; and a pressure source. An ink jet device is provided that is configured to exert a negative gauge pressure on the substrate and preferably hold the substrate against a plurality of rollers. Applying pressure preferably keeps the substrate flat and / or helps to reduce unwanted relative movement of the substrate relative to the roller.

  The negative gauge pressure preferably creates a “pressing” effect on the substrate that increases the static friction of the substrate with the roller, thereby reducing unwanted movement of the substrate.

  By applying a negative gauge pressure, the slippage of the substrate on the roller can be reduced or eliminated. Otherwise, such slipping may occur, for example, when the roller is driven by a stepping motor, for example when the movement of the roller suddenly changes. This reduction of slip is particularly effective for substrates having a low coefficient of friction, for example, substrates having a plastic material such as polypropylene.

  The substrate is preferably conveyed directly on the roller, for example so that the substrate is in direct contact with the roller.

  The action of flattening the substrate can also be obtained by applying a vacuum. In this way, a controlled spacing (eg about 2 mm) can be maintained between the print head and the surface of the substrate. If the substrate is not flattened, the substrate may collide with the print head, smudge ink, and damage the print head. In particular, when the substrate is susceptible to being moved by a nearby air stream, for example, when the mass of the substrate is small, the influence of undesirable external forces acting on the substrate can be reduced by the “pressing” effect.

  Producing a “pressing” effect by applying a negative gauge pressure is also advantageous in that this effect can be produced without special consideration of the outer shape of the edge of the substrate. Can be used for printing on substrates of various shapes and sizes with little or no modification.

  The substrate is preferably substantially flat.

  The roller is advantageous because, for example, it can be made with high precision and can be accurately attached to the bearing so that it hardly causes unnecessary lateral movement. It is also possible to ensure that the rollers rotate at the same speed, so that the static friction of the roller with the substrate is lost, and as a result, the substrate is twisted and therefore the risk of the substrate moving laterally can be reduced. is there.

  The roller is preferably configured to support the substrate on the upper surface of the roller. Conveniently, the roller is generally cylindrical. The outer surface of the roller may have the following shape. The plurality of rollers are preferably arranged substantially parallel to each other, and when rotated, the substrate is moved in a substantially linear direction. Support of the substrate (for example, the substrate can simply be placed on top of a plurality of rollers) and, for example, by rotating the rollers synchronously or otherwise rotating and moving the substrate by rotation A plurality of rollers is particularly suitable because it can be used both for moving the substrate in the desired direction.

  Alternatively or additionally, the substrate may be held in other orientations during printing. By applying a vacuum, various orientations can be possible, so that the substrate may be held from above, for example when the print head is directed upward on the underside of the substrate, May move vertically or horizontally, a vertical surface may be formed by a plurality of rollers.

  The plurality of printheads preferably include one or more rows of print nozzles. The plurality of print heads may be provided individually or may be combined in one or more print head devices.

  The apparatus is preferably configured to print on the surfaces of separate substrates. The apparatus is preferably configured to print on a plurality of material sheets. Such an apparatus is in contrast to, for example, a printer configured to print on a continuous material web.

  While the apparatus is preferably configured to print on a plurality of material sheets, it is understood that the substrate may be in other forms. In general, any shape of substrate can be transported in a printer using the methods described herein. This method is particularly applicable to substrates having at least one flat area on the surface that can be subjected to negative gauge pressure.

  The precise alignment of the individual material sheets is particularly difficult to hold, using conventional methods, in which case the “pressing” effect is particularly advantageous.

  The roller may be made of any suitable material and may further include a high friction outer surface that increases the friction between the roller and the substrate.

  The apparatus preferably includes at least three rollers configured to move the substrate relative to the print head. In many applications, it has been found that at least three rollers are required to provide adequate control of substrate movement. The number and size of the rollers used will depend on the size, shape and weight of the substrate moved by the rollers. It is envisaged to use at least 4, more preferably at least 5 rollers. In the preferred example, 10 rollers are used.

  The rollers are preferably arranged to have a rotation axis that is substantially perpendicular to the printing direction. The plurality of rollers are preferably arranged adjacent to each other, are preferably arranged immediately adjacent to each other, and are preferably arranged in the printing direction. The printing direction is preferably coincident with the moving direction of the substrate.

  By using a combination of "pressing" by vacuum and a roller that moves the substrate, the substrate can be precisely controlled, thereby improving the accuracy with which droplets can be deposited on the substrate, A high-quality image with reduced inconvenience due to banding can be obtained. The apparatus preferably further includes a controller for controlling the movement of the roller. The controller is preferably configured to control relative movement between the substrate and the print head.

  In this configuration, it is preferable that the relative displacement of the substrate in the direction perpendicular to the printing direction is within a predetermined tolerance.

  It will be appreciated that it is preferable to closely control the speed of the rollers. The two friction surfaces (motion surfaces) of the substrate may be moved at different linear velocities due to the difference in speed between the rollers in the plane of the substrate. This can cause the substrate to “twist” as it moves along the rollers. This is preferably reduced by controlling the rotation of the rollers so that the speed difference is zero or approaches zero.

  The rollers are preferably mounted substantially parallel to adjacent rollers, and the angle between adjacent rollers should not exceed 6 milliradians relative to parallel, and should not exceed 4 milliradians. Is more preferred and does not exceed 2 milliradians.

  The rollers are preferably rotatable, and the apparatus has a range in which both peripheral speeds of adjacent rollers (preferably the speed of the outer surface of the roller holding the substrate) are within 1% of each other, preferably 0. The rotation is preferably controlled so as to be within a range of 5%, preferably within 0.3% of each other.

  Control of the movement of the substrate in the direction perpendicular to the printing direction, that is, in the lateral direction, is particularly important because it is easily noticeable even if the alignment error in this direction is slight.

  The predetermined tolerance is preferably selected depending on the acceptable quality of the perceived image and the nozzle pitch of the print head in the relevant direction.

  The relative misalignment is preferably less than 30 percent of the dot pitch of the printed image, preferably less than 20 percent of the pitch, more preferably less than 15 percent of the pitch, and 10 percent of the pitch. Most preferably, it is less than.

  It is preferred to apply a negative gauge pressure to the substrate in the region between adjacent rollers. With such a configuration, the pressing of the substrate can be improved.

  It is preferred to apply a negative gauge pressure to the substrate only in the region between the rollers. The negative gauge pressure is preferably not allowed to act through the rollers themselves, for example by forming a plurality of holes in the rollers.

  The size of the vacuum applied to the substrate can be selected in consideration of the properties of the substrate and the required print quality. Large pressures can better hold the substrate, thus reducing the possibility of slipping, resulting in better print quality, but higher costs, and the risk of damage to the substrate, for example, as a result of bending the substrate. Increases nature.

  The apparatus preferably further includes a member disposed between the plurality of rollers adjacent to the substrate, and the member is preferably configured to limit the airflow between the plurality of rollers.

  By using the cover member, the airflow passing through the gaps between the plurality of rollers can be reduced, and thus the required size of the vacuum pump can be reduced. This also avoids excessive airflow adjacent to the substrate that disturbs the ejection of ink droplets ejected from the printhead. Further, the pressure can be applied to the substrate more quickly.

  In the case of a porous substrate, the covering member keeps the vacuum action away from the central portion of the substrate between the rollers, and in the areas of the substrate near the rollers where the vacuum action is required. The covering member is particularly preferred because it is concentrated.

  Alternatively or additionally, the member is arranged to reduce deformation of the substrate between the plurality of rollers. This member may have a member different from the covering member, or may be the same member that performs two or more functions.

  When the substrate is placed on a roller, there is an area between the rollers where there is no contact between the roller and the substrate. This region is preferably a region where a vacuum is applied. If the substrate is not very stiff, the substrate may be deformed in this region by applying a vacuum. The member may be configured to support the substrate as the substrate passes between the plurality of rollers. This is particularly advantageous when the substrate is porous. As will be appreciated, the support member may serve the additional function of restricting the airflow as described above.

  However, in other configurations, there is preferably a gap between the substrate and the member. This is particularly preferred when the substrate moves quickly through the device.

  The apparatus preferably further comprises a guide for guiding the leading edge of the substrate. This may be realized as one function of the aforementioned member. The guide is preferably disposed between the plurality of rollers. The above-mentioned member may form a guide surface that guides the base that moves forward. Such a guide can also help prevent material from wrapping around the roller by guiding the leading edge of the substrate.

  The member and / or guide preferably has a hard material with low surface friction.

  It is understood that a wide variety of substrates can be printed using the apparatus described herein. This device is particularly useful when the substrate is stiff, i.e. has a rigid material. Such materials are not easily deformed or damaged by the action of vacuum and / or passing over rollers. The substrate preferably has a substantially rigid material. In a preferred configuration, the substrate has a substantially flat and rigid sheet. The substrate may comprise one or more of paper, card, wood, metal, plastic, or ceramic material.

  When printing on a rigid substrate, the outer surface of the roller preferably has a deformable material, for example an elastomer.

  The substrate is preferably configured to be placed on a deformable surface during printing. In this way, the pressing of the substrate is improved because the deformable surface can be aligned with the surface of the substrate when a vacuum is applied. The outer surface of the roller may have an elastomer.

  When printing on substrates that are not very stiff, use rollers with a shaped outer surface, preferably with a corresponding guide, in order to reduce the risk of the substrate getting caught in the gap between the guide and the roller. Can do.

  The leading edge of the guide member is preferably not straight.

  It is also preferred that the arrangement is such that no roller is required to contact the surface of the substrate during printing. This configuration is feasible to apply a negative gauge pressure as described herein.

  The printer is preferably configured to print on the substrate in a single pass. The printer preferably prints the desired image with a single movement of the substrate through the printer.

  Single pass printing can dramatically reduce printing time compared to multipass printing. However, in such a printing technique, it is necessary to maintain the position of the substrate with particularly high accuracy when it is necessary to minimize printing defects.

  In multi-pass printing, the substrate is usually placed on a reciprocating table. The trajectory of this table is controlled very accurately. Such a configuration is not practical for single pass printing because it takes a long time to put on and take off the table.

  The print head is preferably stationary during printing. In a preferred configuration, the print head is stationary relative to the roller. This provides a reference point for controlling the movement of the substrate as it moves along the plurality of rollers. The use of a stationary printhead also requires that the substrate position be maintained with particularly high precision if printing defects need to be minimized. Any unintentional movement of the substrate when moving relative to a stationary printhead during the period between droplet ejections is intended for the next ejected droplet. It is likely to become a factor that becomes out of alignment with the target and results in inaccurate alignment of the next droplet. If the substrate alignment remains inaccurate, the pattern printed by the inkjet printhead will be inaccurately aligned.

  The print head is stationary during ink ejection. In some preferred examples, the print head does not move during substrate printing. In some examples, the printhead does not move at all in the plane of the plane to be printed, but height adjustments can be made.

  The substrate preferably moves during ink ejection. The moving speed of the substrate with respect to the print head is preferably faster than 0.5 m / s, preferably faster than 1 m / s, and preferably in the printing direction. The substrate is preferably moved at a speed exceeding 0.5 m / s, preferably at a speed exceeding 1 m / s.

  The system is preferably adapted to print a color image. The system may be adapted to print a halftone image. In such images, accurate alignment of the droplets on the substrate is more important to obtain acceptable print quality. In particular, for color, a color image is formed by sequentially depositing droplets of various colors on the area to be printed. Any unwanted movement of the substrate between different color prints can dramatically reduce the image quality. For example, the same effect may occur when using a plurality of print heads for monochrome printing in order to improve addressability.

  By using several printheads, a high quality printed image is obtained. However, it can be seen that if there is unnecessary movement of the substrate between printing by different print heads, the image quality can be drastically reduced.

  The apparatus preferably has a drop-on-demand printhead.

  The apparatus is preferably adapted to print an image having a resolution greater than 120 dpi. The resolution of an image to be printed preferably exceeds 120 dpi in a direction perpendicular to the moving direction (printing direction) for printing. The resolution preferably exceeds 120 dpi in the printing direction. The resolution is preferably over 150 dpi.

  Another aspect of the present invention is a transport device that moves a substrate through a plurality of print heads in an inkjet printer, the plurality of the plurality of substrate being configured to move relative to the print head. The apparatus includes a roller and a pressure source, the pressure source configured to apply a negative gauge pressure to hold the substrate against the roller.

  Another aspect of the present invention is a method for printing on a substrate in an inkjet printer having a plurality of print heads, a plurality of rollers, and a pressure source, the substrate moving on the rollers relative to the print head And a step of applying a negative gauge pressure to the substrate to hold the substrate against the roller, and the print head is stationary while ejecting ink toward the substrate. Provide a way. The substrate is preferably printed in a single pass.

  The present invention provides a substrate printed using a printer as described herein and / or using a method as described herein.

  Other aspects of the invention include an apparatus substantially as described herein with reference to the accompanying drawings and as shown in the accompanying drawings, and the accompanying drawings. To provide a method substantially as herein described.

  The configuration of one embodiment of the present invention may be provided in any appropriate combination with the configurations of other aspects.

  Several preferred configurations of the invention will now be described purely by way of example with reference to the accompanying drawings.

  FIG. 1 shows a drop of ink as a sheet is passed through a printer so that it passes through a printhead device 4 by a transport mechanism 10 on a plurality of successive rigid sheets of a substrate 16, 16 ′, 16 ″. Fig. 1 schematically shows an inkjet printer 2 having a stationary printhead device 4 applied thereto, the substrate being passed through the printer so that it passes through the printhead device 4 only once in single pass printing.

  The first transport device 6 moves the unprinted base body 16 ′ toward the transport mechanism 10. A second transport device 8 moves the printed substrate 16 "away from the transport system. Both transport devices 6, 8 have conveyor belts, but other configurations can be used. Conventional methods may be used to load and unload the printed material on both conveying devices 6 and 8.

  The transport mechanism 10 is configured to accurately move the base 16 through the print head device 4. The length of the transport mechanism 10 in the printing direction and the width of the transport mechanism in the direction perpendicular to the printing direction are preferably selected so that the entire substrate 16 is supported by the transport mechanism 10 during image printing.

  The printhead device 4 has four sets of printheads, and each set prints a different color selected from cyan, magenta, yellow, and black to form a full color image on the substrate. Do. The print head device 4 does not move during the printing operation. However, the print head may be moved up and down to accommodate various substrate thicknesses.

  In this example, the substrate 16 has a flat rectangular sheet of corrugated cardboard having a thickness of about 2 mm. However, the described apparatus can be used to print on various types of substrates, such as carton boards, plastic materials, such as sheets of PVC, and various shapes of substrates.

  2 and 3 are a schematic side view and a plan view of a part of the transport mechanism 10, respectively. The transport mechanism 10 of this example includes ten cylindrical rollers, and only two rollers 12 and 14 are shown in FIGS. 2 and 3 for the sake of clarity. Four rollers are shown in the perspective view of FIG. The rollers 12 and 14 are disposed adjacent to and parallel to each other, resulting in a uniform gap between the plurality of rollers forming a cavity 28 between a pair of adjacent rollers. The substrate 16 is supported on the roller contact surfaces 18 and 20.

  The transport mechanism 10 moves the substrate 16 in the printing direction 30 (shown from right to left in FIG. 3) by the rotation of the rollers 12 and 14 in the counterclockwise directions 38 and 40. A few, if not all, rollers may be driven and the other rollers may be free to rotate. Alternatively, all the rollers may be driven synchronously by a roller driving device. In this example, the device has a gear train and a single motor to drive all 10 rollers, but other configurations may be used, for example, individual direct drive motors for each roller. it can.

  The rollers 12 and 14 are rotated at a controlled angular velocity that is constant or variable in the counterclockwise directions 38 and 40. In this example, the roller rotates at 300 rpm and the linear speed of the substrate on the roller is slightly over 1 m / s. The rotation axes of the plurality of rollers are substantially parallel to each other. Since unbalanced forces acting on the substrate can cause undesired lateral movement of the substrate, the speed of movement of the plurality of rollers is minimized by the contact surface 18 to minimize such unbalanced forces. , 20 are substantially equal.

  The roller is cylindrical and is considerably longer than its diameter. The roller is made of steel. Other suitable rigid materials can also be used, such as plastics, polymer materials, or other metals.

  The transport mechanism 10 further includes a pressure mechanism 22 that acts to hold the substrate 16 in contact with the rollers 12 and 14 to keep the substrate flat and reduce slippage of the substrate. The pressure mechanism 22 is configured to cause a negative gauge pressure 32 to act on the cavity 28 and thus the substrate, and hold the substrate 16 in contact with the contact surfaces 18 and 20 of the roller.

  Therefore, unnecessary movement of the substrate 16, particularly movement in the lateral direction 36 (perpendicular to the printing direction 30 in the plane of the substrate 16) can be reduced. The lateral movement of the substrate can lead to printing alignment errors during printing and is therefore highly undesirable.

  In order to reduce the lateral movement of the roller, the roller is attached to one end of the roller using a deep groove ball bearing so as to minimize the axial movement of the roller. A roller bearing is used at the other end to avoid excessive restraint.

  As shown in FIG. 5, the pressure mechanism 22 includes a fan 24. The pressure mechanism 22 includes a housing 26 that surrounds a plurality of lower surfaces of the roller device. The fan 24 is attached to the bottom of the housing, and is configured to allow air to flow out of the housing 26 to create a vacuum at the lower surface of the roller device. In this example, a Vent-Axia duct fan ACH315-12A was used.

  The applied vacuum can be selected to provide a favorable pressing of the specific substrate to be printed onto the roller. In this example, where the substrate is 2 mm thick cardboard, the pressure used is equal to 50 mm water pressure.

  A covering member 100 is disposed between a pair of rollers 12 and 14 adjacent to each other. A vacuum suction port 26 is provided below the covering member 100. The covering member squeezes the airflow caused by the vacuum and through the gaps 102 between the covering member and the roller surfaces 18, 20, thereby reducing the required size of the vacuum pump 24, and The front edge of the base 16 is guided so as to prevent the rollers from being wound, and the base 16 is supported between a plurality of rollers to reduce the risk of bending the base. When the substrate is porous, the structure of the covering member 100 concentrates the pressure acting on the substrate around the upper end of the roller, thereby minimizing the bending of the substrate.

  In this example, the covering member 100 is made of stainless steel and has a T-shaped outer shape. A plurality of arms of this member form a guide surface of the base 16.

  In this example, the roller has a diameter D of 75 mm, and the rollers adjacent to each other are mounted with a distance A of 100 mm between the rotation axes. The gap 102 between the arm of the covering member 100 and the surface 20 of the roller is 1.5 mm.

  The flat upper surface 104 of the covering member 100 also forms a guide surface for the leading edge of the substrate as the substrate moves from roller to roller. In this example, the covering member 100 is mounted such that the flat upper surface 104 of the covering member 100 is located at a distance C of 1.5 mm below from the top of the roller. This reduces the risk that the substrate will be damaged on the leading edge of the covering member 100.

  FIG. 3 shows an image 109 printed by the printhead device 4. The print head device 4 shown in FIG. 6 includes 16 print heads 105 for each of cyan 110, magenta 112, yellow 114, and black 116, and a total of 64 print heads. Groups of four print heads of each color are arranged side by side so that they can be printed on the surface of the substrate substantially the full width during one pass of the substrate. Here, the printing width is 260 mm. In this example, the print head is a plurality of Spectra SE print heads with a print resolution of 50 dpi arranged at four depths per color to obtain 200 dpi print addressability.

  With this apparatus, a high-quality full-color image can be printed on a substrate in a single pass using an inkjet printer.

  It will be appreciated that the invention has been described above by way of example only and modifications of detail can be made within the scope of the invention.

  For example, if the substrate to be printed has a rigid lower surface, the outer surfaces of the rollers 18, 20 will deform to help hold the substrate against the roller when negative gauge pressure is applied to the substrate. It may have a deformable material, for example foam material or rubber.

  When printing on a thin flexible substrate using the above-mentioned apparatus, the substrate may be drawn around the roller and clogged into the gap between the roller and the cover member, or may enter straight into the vacuum space. is there. This may limit the thinness and flexibility of the substrate that can be handled by a specific device. Figures 7 and 8 show other examples that are particularly adapted for use with more flexible substrates.

  Referring to FIG. 7, the plurality of rollers 200 have non-uniform radii along the length direction, and an outer surface on which teeth are formed is formed. The cover / guide members 215 and 220 disposed adjacent to the roller are formed in a shape having a plurality of teeth 230 corresponding to a plurality of regions where the radius of the roller is reduced. Thus, the front edge of the cover / guide member is not straight, so that the risk of the base passing between the roller and the guide member is reduced.

  FIG. 8 shows another example in which a plurality of teeth on the leading edge of a guide / cover member are connected to adjacent guide / cover members to extend to form a guide / cover grid 350 on a plurality of rollers 300. Is shown. This further reduces the risk that the substrate will be damaged on the guide / cover member.

  It is conceivable to apply a negative gauge pressure to the substrate from a plurality of rollers having a vacuum cavity inside. In this case, it is possible to use a roller that is substantially hollow and has a perforated skin through which a vacuum is applied.

  Each feature shown in the description and (where appropriate) the claims and drawings may be provided alone or in any appropriate combination.

It is a figure which shows typically the inkjet printer containing a conveyance mechanism. It is a figure which shows a part of conveyance mechanism of FIG. It is a typical top view of a part of conveyance mechanism of FIG. FIG. 2 is a perspective view of a part of the transport mechanism in FIG. 1. It is a figure which shows typically the pressure mechanism of the conveyance mechanism of FIG. It is a figure which shows typically arrangement | positioning of a some print head. It is a figure which shows the alternative structure of a roller and a covering member. It is a figure which shows the other alternative structure of a roller and a covering member.

Claims (20)

An inkjet printing apparatus that performs printing on a substrate,
A plurality of ink jet print heads that eject ink toward the surface of the substrate and are adapted to remain stationary during ink ejection;
A plurality of rollers configured to move the substrate relative to the plurality of print heads;
A pressure source;
Have
The pressure source is configured to apply a negative gauge pressure to the base to hold the base against the roller.
Inkjet printing device.   The apparatus of claim 1, wherein the apparatus is configured to print on a surface of a plurality of separate substrates.   The apparatus according to claim 1 or 2, comprising at least three rollers configured to move the substrate relative to the plurality of print heads.   In any preceding claim, wherein the rollers are mounted substantially parallel to adjacent rollers such that the angle between the adjacent rollers does not exceed 6 milliradians relative to parallel. The device described.   An apparatus according to any preceding claim, wherein the rollers are rotatable and the rotation is controlled such that the circumferential speeds of the rollers adjacent to each other are within 1% of each other.   An apparatus according to any preceding claim, wherein the negative gauge pressure is applied to the substrate in the region between adjacent rollers.   An apparatus according to any preceding claim, further comprising a member disposed between a plurality of rollers adjacent to the substrate.   The apparatus of claim 7, wherein the member is configured to restrict airflow between the plurality of rollers.   9. An apparatus according to claim 7 or 8, wherein the member is configured to reduce deformation of the substrate between the plurality of rollers.   An apparatus according to any preceding claim, further comprising a guide for guiding a leading edge of the substrate.   An apparatus according to any preceding claim, wherein the substrate comprises a substantially rigid material.   An apparatus according to any preceding claim, wherein the substrate is configured to rest on a deformable surface during printing.   An apparatus according to any preceding claim, wherein the substrate is adapted to move at a speed in excess of 1 m / s.   An apparatus according to any preceding claim, adapted to print a color image.   An apparatus according to any preceding claim, wherein the apparatus is adapted to print an image with a resolution greater than 120 dpi. A transport device for moving a substrate through a plurality of print heads in an inkjet printer,
A plurality of rollers configured to move the substrate relative to the print head;
A pressure source;
Have
The pressure source is configured to apply a negative gauge pressure to the base to hold the base against the roller.
Conveying device. A method of printing on a substrate in an ink jet printer having a plurality of print heads, a plurality of rollers, and a pressure source,
Moving the substrate relative to the printhead on the roller;
Applying a negative gauge pressure to the substrate to hold the substrate against the roller;
Have
The print head is stationary while ejecting ink toward the substrate.
Method.   A substrate printed using the printer of any of claims 1 to 16 and / or using the method of claim 17.   An apparatus substantially as herein described with reference to the accompanying drawings and shown in the accompanying drawings.   A method substantially as herein described with reference to the accompanying drawings.

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