Patent Application
20250074087
This application claims priority to German Patent Application No. 10 2023 123 942.2 filed Sep. 6, 2023, the disclosure of which is hereby incorporated by reference in its entirety.
Given a device and a method for exerting a stretching on a on recording media, the recording medium can be transported in a transport direction along a transport path. In some printing devices, immobile printing units are used that are as wide as a page and stationary. In other printing devices, print heads that are movable transverse to the transport direction are used so that the image information is applied in a scanning manner to the recording medium. This is independent of whether the recording medium is present as roll material or as individual sheets. The recording medium can also be moved beneath the application unit. Alternatively, or in combination with this, it is not the recording medium that is moved but rather the application unit. Here an application unit can be a printing unit and/or coating unit.
In inkjet printing, the liquid ink is applied non-uniformly onto the recording medium depending on the print image to be generated. Both paper sheets or paper webs, as well as cardboard, can serve as a recording medium. However, other recording media, such as films, can also be used.
Given printing to paper with liquid link, moisture enters into the paper, whereby ripples arise in the paper that, without taking further measures, remain even after fixing the print image onto the paper. The moisture is affected by, for example, the water fraction, glycerol fraction, or similar fluids. The recording medium swells at different rates depending on the type of fluid. Moreover, the quantity of fluid/ink is distributed non-uniformly due to regions being printed to with different intensity. The ripples in the paper are particularly pronounced in regions of the paper that are printed to over their entire area. Although ripples in the paper also occur given other printing methods, such as in offset printing, this is not as strongly as in inkjet printing.
Similarly, the moisture is strongly influenced differently in local terms. In regions that have been printed to with a high quantity of ink, among other things the evaporation is often less, due to the film formation, than in regions that have not been printed to.
Depending on the manufacturing process, the paper has a machine direction (MD), i.e. the transport direction of the paper in the paper manufacturing, and a cross direction (CD) transverse to the machine direction, and thus transverse to the transport direction of the paper in the paper manufacturing. The paper properties in CD and MD differ significantly with regard to rigidity, moisture expansion, and rupture resistance. Paper swelling always avoids the primary fiber direction. Fibers swell 20× less in the fiber direction than transverse to it. Given paper (network of fibers) with a partial alignment, the relation is only 1:3 (MD:CD).
In high-capacity printing with printing speeds of greater than 1 m/s, up to the present speeds of 3 m/s, the paper in the form of a web that is to be printed to is often unwound taken off a paper roll. The machine direction is then in the take-off [unwinding, unrolling] direction or in the transport direction of the paper through the printing device. In printing to individual sheets, the machine direction is not set uniformly and can vary from charge to charge.
In addition to inkjet, the cited printing process encompasses all additional digital and analog printing methods, such as electrophotography, offset printing, flexography, and rotogravure. In addition to this, the application of coatings with or without colorant is likewise included.
The rippling due to the entry of fluid into the paper (or the different moisture distribution due to drying in the fixing process) that took place via the ink arises primarily in the cross direction. Given web printing, the recording medium is preferably unrolled along the MD direction and moved through the printer so that, upon printing to paper webs, the rippling arises transverse to the transport direction of the paper web.
It is an object of the invention to specify a device and a method for exerting a force on a recording medium to be printed to on its front side. With this force, the recording medium should be actively stretched in order to prevent ripple formation.
This object is achieved via a device having the features as described herein, and via a method having the features as described herein. Advantageous developments are described herein.
The invention is based on the realization that the ripples in the recording medium after being printed to with the aid of an inkjet printing device, even after the fixing of the print image on the recording medium, are reduced if a force in the cross direction is exerted on the recording medium upon printing to said recording medium, and/or between printing to said recording medium, and/or upon fixing the print image on said recording medium. The cross direction thereby relates to the direction in the paper manufacturing, and is also always transverse to the direction of running travel of the web given web printing. It has proven to be particularly advantageous if the force is exerted on the medium material during the fixing of the print image, in particular in the second half of the fixing unit, in which the print image is completely fixed or completely dried. This force should have at least one force vector in an optimally wide range in the CD between the lateral edges of the recording medium.
However, the front side of the recording medium, on which is located the print image that as of yet has not been fully fixed, should not be contacted upon exerting the force, in order to not negatively affect the print image and/or not prevent the fixing process, or in order to make an unprinted edge unnecessary.
Via the device as described herein, it is achieved that at least a portion of the bearing element regions are deformed such that they exert a force on the recording medium, said force being directed in the direction of the respective lateral edge. The respective lateral edge is thereby the lateral edge with the shorter distance from the contact region of the bearing element region. The contact regions contacting the back side of the recording medium preferably exert on the recording medium a tensile force transverse to the transport direction of the recording medium, i.e. a force in the direction of the lateral edge. The recording medium is preferably a recording medium in form of a web, in particular is a paper web. The material of at least the contact region of the bearing element region is matched to the material of the recording medium so that a static friction is present between the contact region and the back side of the recording medium, via which static friction a force can be transmitted from the contact region to the recording medium, which force generates at least one tensile force along the recording medium that reduces, or prevents to the greatest possible extent, the formation of ripples due to the moisture introduced into the recording medium by the ink. The quality of the printed recording medium can hereby be significantly increased.
It is also advantageous if a first end of each bearing element region is connected with the base body, and if the contact region is arranged at the second end of the bearing element region, said second end being distal from the base body. The bearing element region can hereby stand out from the base body, and the contact region can be arranged at a distance from the base body so that the recording medium can rest on the contact regions.
It is also advantageous if the lateral edges of the moving recording medium run parallel to the transport direction. A simple handling of the recording medium upon exerting the force to reduce and/or prevent ripples in the recording medium is hereby possible.
It is also advantageous if, in the transport direction, a first portion of the bearing element regions is arranged to the left and a second portion of the bearing element regions is arranged to the right of a center plane running orthogonal to the transport path and/or to the recording medium in the transport direction. The contact regions of the bearing element regions can hereby exert a tensile force in two opposite directions, i.e. tensile force and counterforce, on the recording medium. The recording medium is thus not laterally displaced upon transport of the recording medium.
The transport unit can transport the recording medium in a transport plane, wherein a center plane of the transport route runs orthogonal to the transport plane.
It is also advantageous if the end of at least one part of the bearing element regions that is connected with the base body has a smaller distance from a center plane, said center plane running orthogonal to the transport path/recording medium in the transport direction, than the contact region of the same bearing element. These bearing element regions hereby extend away from the center plane or, respectively, toward the lateral edges. The bearing element regions arranged at the outer edges of the recording medium are preferably arranged angled and/or curved and/or inclined, starting from the end connected with the base body, toward the respective lateral edge. Alternatively, or in combination, the bearing element might also have been produced from a solid material from which angled slits have been milled, or slightly pre-tensioned bearings that permit a twisting “outward” if a negative pressure is present. Upon applying the negative pressure, the recording medium is then drawn in the direction of the base body and exerts a force on the contact regions in the direction of the base body. Due to the inclined, angled, and/or curved arrangement of the bearing element regions, these are moved outward in the direction of the lateral edge and exert a force transverse to the transport direction on the recording medium, via which the force is exerted on the recording medium to reduce and/or prevent ripples in said recording medium.
It is also advantageous if the contact region of the first end of the bearing element region forms an angle vertex, wherein the route between angle vertex and contact region forms a first angle leg, and wherein the base body forms a second angle leg, wherein the angle of inclination that is so defined is arranged in a plane orthogonal to the transport direction and preferably has a value in a range of from 45° to 85°, preferably in a range of from 65° to 75°.
It is particularly advantageous if the contact region has the form of a lip, and/or if the bearing element region and/or the contact region extends parallel to the transport direction.
A simple arrangement of the device relative to the recording medium is hereby possible via which ripples in the recording medium can be reduced or avoided.
It is also advantageous if the device is arranged below the fixing unit for fixing an inkjet print image and below the printed recording medium. The device is hereby arranged on the back side of the recording medium, or opposite the back side of the recording medium. It is particularly advantageous if the device is arranged below the second half of the fixing unit in the transport direction.
An arrangement is also disclosed with a device as described herein, and a recording medium, wherein the recording medium is in particular a paper web and/or individual sheets.
The method having the features described herein has the same advantages as the device described herein.
Exemplary embodiments of the invention are explained in detail in the following using Figures. Shown therein are:
The terms Fig., Figs., Figure, and Figures are used interchangeably in the specification to refer to the corresponding figures in the drawings.
The printing unit 12 serves to print to the front side of the recording medium 18 in the form of a web, executed as a paper web. The recording medium 18 is supplied to the printer 10 in that, for example, it is taken off from a roll with the aid of a take-off [unwinder]30. The transport direction of the recording medium 18 through the printer 10 is specified by the arrow P1.
In the present exemplary embodiment, the printing unit 12 comprises four print bars 20, 22, 24, 26 to generate a respective color separation in the colors Y, M, C, K, and a unit for applying a primer onto the recording medium 18 supplied to the printing unit 12. The unit can comprise a further print bar 28 for applying a primer. This print bar 28 is then arranged upstream of the print bar 20 through 26 for application of the ink.
A print bar 20 through 28 of the printing unit 12 is preferably a unit that comprises at least one print head in order to print a line onto the recording medium 18. Upon printing the color separations, neither the print bars 20 through 28 nor the print heads of the print bars 20 through 28 are moved. The recording medium 18 is printed to across the width of the page with the aid of the print bars 20 through 28. In particular, each print bar 20 through 28 can comprise a plurality of print heads arranged one after another in two rows. The print head, or the print heads, of the print bars 20 through 28 can be driven based on print image data to print color separations printed atop one another. The color separations printed atop one another then yield a print image.
The fixing unit 14 serves to generate a robust surface by drying and fixing, onto the recording medium 18, the print image generated by the printing unit 12 on said recording medium 18, said print image being made up of ink. The recording medium 18 is taken up again onto a roll with the aid of a take-up 32 after being printed to with the fixed print images. The roll with the printed recording medium 18 can then be processed further at a later point in time.
Given alternative embodiments, the printing unit 12 can have more or fewer print bars 20 through 28 and/or not apply any primer. The printed recording medium 18 can also be directly supplied to a finishing unit, such as a cutting unit to cut the recording medium into single sheets, without being taken up again beforehand. Instead of the take-up 32, a further printer can also be arranged with the aid of which the back side of the recording medium is printed to. The further printer can have a design identical to that of the printer 10, wherein a turning unit known per se is then arranged between the two printers.
Given inkjet printing, in the printing state the liquid ink is applied non-uniformly onto the recording medium 18 depending on the print image to be generated. This is required to achieve different colors, for example locally different colors in images. However, it is also conceivable that the print heads also applies the ink from the side, which ink is liquid in the printing state. Moisture arrives into the recording medium 18 due to the application of liquid ink, whereby ripples arise in the recording medium 18, which ripples—without further measures—remain on the recording medium 18 even after the fixing of the print image with the aid of the fixing unit 14. Moreover, the quantity of fluid/ink is distributed non-uniformly on the front side of the recording medium 18 due to regions being printed to with different intensity. The ripples in the recording medium 18 are especially pronounced in regions of the recording medium 18 that have been printed to over their entire area.
Depending on the manufacturing process, the paper serving as a recording medium has a machine direction (MD), i.e. the transport direction of the paper in the paper manufacturing, and a cross direction (CD) transverse to the machine direction, and thus transverse to the transport direction of the paper in the paper manufacturing. Upon printing to paper webs 18, the paper to be printed to can be taken off a paper roll. The machine direction is then in the take-off direction or in the transport direction P1 of the paper web 18 through the printer 10.
The rippling due to the fluid entry into the paper of the recording medium 18, which took place via the ink, arises primarily in the cross direction, i.e. transverse to the transport direction of the paper web 18 upon printing to paper webs 18.
Ripples in the transport direction P1 can be reduced in particular in that a tensile force in the transport direction P1 is exerted on the recording medium 18. For this purpose, the recording medium 18 can be pulled by transport elements, in particular by a corresponding drive of the take-off 30 and of the take-up 32, and/or further transport elements of a transport unit for transporting the recording medium 18 through the printer 10.
In order to avoid, or at least to reduce, ripples transverse to the transport direction P1 in the recording medium 18, the printer 10 has a device 16 for exerting a force on the recording medium 18 that is printed to on its front side with the aid of the printing unit 12. Via this device 14, a tensile force is exerted on the recording medium 18 transverse to its transport direction P1, wherein the recording medium 18 is stretched by the tensile force upon fixing the print image on the front side of said recording medium 18. The position of the recording medium 18 transverse to the transport direction P1 thereby remains unchanged.
The device 16 has a belt 38 guided around two deflection rollers 34, 36, of which preferably at least one deflection roller 34, 36 is driven, said belt 38 having segments that respectively have a plurality of bearing element regions. One of these segments is designated with the reference character 40. The recording medium 18 rests with its unprinted back side, or with a back side having an already fixed print image, on the bearing element regions. The belt 38 is driven in the direction of the arrow P2 with the same velocity as the recording medium 18 is moved in the transport direction OP1.
The device 16 furthermore comprises a unit 42 for applying a negative pressure between at least two bearing element regions arranged side by side, in order to move the recording medium 18 via the negative pressure in the direction of a base body of the segment 40, and to deform at least a portion of the bearing element regions. The unit 42 comprises a negative pressure pump 44 and at least one negative pressure distribution chamber 46 that is covered by a belt segment. The bearing element regions stand out from the base body of the segment 40 in the direction of the recording medium.
The design and the function of the device 16 is explained in further detail in the following in connection with
Openings 120a, 120b, 122a, 122b, 124a, 124b, 126a, 126b 128a, 128b, 130a, 130b are present in the base body 140, through which the negative pressure generated by the negative pressure pump 44 arrives in the regions between two respective adjacent The bearing element regions 100a, 100b, 102a, 102b, 104a, 104b, 106a, 106b, 108a, 108b, 110a, 110b, 112 and there generates a negative pressure via which the recording medium 18 is drawn in the direction of the base body 140. The ends of the bearing element regions 100a, 100b, 102a, 102b, 104a, 104b, 106a, 106b, 108a, 108b, 110a, 110b that are distal from the recording base body are hereby pressed downward. Due to their materials, such a static friction exists, between the contact regions of the bearing element regions 100a, 100b, 102a, 102b, 104a, 104b, 106a, 106b, 108a, 108b, 110a, 110b, 112 and the recording medium, that said bearing element regions 100a, 100b, 102a, 102b, 104a, 104b, 106a, 106b, 108a, 108b, 110a, 110b, 112 exert a force on the recording medium further outward toward the lateral edges of the recording medium 18 in the form of a web if said recording medium 18 is moved toward the base body 140 due to the negative pressure between the bearing element regions 100a, 100b, 102a, 102b, 104a, 104b, 106a, 106b, 108a, 108b, 110a, 110b, 112. This force F is represented by force vectors in
Via this force F, the recording medium 18 is stretched laterally upon fixing the print image on said recording medium's front side, whereby the ripples created by the ink of the print image in the recording medium 18 are reduced or, at least upon viewing of the print product generated in this manner, entirely corrected upon fixing. The device 16 is arranged below the fixing unit 14, wherein the recording medium 18 is guided through between fixing unit 14 and device 16 for fixing. For this, the printer 10 may comprise transport elements (not shown) of a transport unit. The bearing element regions 100a, 100b, 102a, 102b, 104a, 104b, 106a, 106b, 108a, 108b, 110a, 110b, 112 extend at least in a region parallel to the lateral edge of the recording medium 18, or parallel to the center plane M.
The transport direction P1 of the recording medium 18 travels orthogonal to the plane of the page of
The devices according to
All receiving element regions are made of an elastically deformable material, in particular of an elastically deformable plastic such as an elastomer or rubber.
Upon printing to individual sheets, the machine direction is not uniformly established and can vary from charge to charge. This is to be taken into account in particular given application of the negative pressure by the device 16, in all embodiments.
The described bearing element regions are components of bearing elements, or respectively form a bearing element.
It is generally noted that a transport unit is not mandatory, since the recording medium can also be essentially immobile while the printing unit are moved over the recording medium. In particular for individual sheets, the present invention has the advantage that, after the application of fluid in the form of ink, finishing fluid such as varnish etc., the device according to the invention can stretch the recording medium along the primary plane of said recording medium, independently of the alignment of fibers, so that the ripples are smoothed or disappear entirely.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2023 123 942.2 | Sep 2023 | DE | national |
