ES2361033T3 - METHOD FOR PRINTING A SUBSTRATE USING AN ANILOX ROLLER, ANILOX ROLLER FOR A PRINTING METHOD AND A PRINTING DEVICE. - Google Patents

Abstract

Anilox roller (5) for a printing apparatus for transferring fluid, such as ink, comprising a cylinder having a surface (100), where the surface comprises a distribution structure for receiving the fluid, distributing the fluid through a cylinder, and transferring the fluid, wherein said fluid distribution structure is arranged to transfer in a first operational mode to print heavy layers of ink with a relatively large drop of fluid and in a second operational mode to print details with a relatively small drop of fluid by a combination of restrictions on the fluid distribution structure, characterized by the fact that the fluid distribution structure has a channel (24) formed on the surface to distribute the fluid over the fluid distribution structure, said channel (24 ) meanders on the surface, the channel having a waveform, more specifically a sine wave, and the channel it would have a width of between 10 and 150 µm, preferably between 20 and 100 µm, and even more preferably between 30 and 80 µm.

Description

[0001] The invention relates to an anilox roller. The invention also relates to the printing of substrates where an anilox roller is used. The invention also relates to a printing apparatus, comprising an anilox roller. The invention also relates to the use and formation of an anilox roller.

[0002] Anilox rollers have been used in flexographic methods in the graphic industry. This printing method was generally used for different printing substrates such as papers, labels, bands, bags and boxes (plastic). Anilox rollers can be used in printing methods other than flexographic methods. I also print "Offset" and "intaglio". An anilox roller is used in these other methods to transfer ink in precise and constant amounts.

[0003] An anilox roller comprises a generally hard cylinder, with a steel or aluminum core. A thin layer of ceramic has been provided above the core. In the thin layer, small cells of ink, referred to as now, are usually etched. In a known embodiment, the cells are created with a hexagonal or panel-shaped design or the surface of the anilox roller. Cells have a volume to receive ink based on cell size and cell depth. The size of the cells on the surface of the anilox roller will determine the density of the cells. The density of cells is expressed in lines per linear centimeters. The cell volume will determine the operating mode of the anilox roller. The designs and cells of the surface of the anilox roller can be formed using a laser using a laser engraving method. The method may comprise a continuous or pulsing laser. The laser is directed on the surface of the anilox roller forming a laser point, said point will engrave a design on the surface. The intensity of the laser is sufficient to vaporize locally the material of the outer layer of the anilox roller, for example chromium oxide. This will form a cell. A cell comprises a local gap in the surface of the roller surrounded by cell walls. A single cell wall can be a wall for two adjacent cells, thus separating the cells.

[0004] The anilox roller is installed by bearings in a printing apparatus such as a flexographic apparatus. The anilox roller comprises the longitudinal ends of the cylinder that can be mounted on a frame of the printing apparatus. The anilox roller is mounted so that it can be disassembled to allow it to be cleaned or replaced quickly. The anilox roller can rotate on its longitudinal axis in a circumferential direction.

[0005] The rotating anilox roller can be partially emerged in an ink fountain or a fountain roller is partially emerged in an ink source, said fountain roller being in contact with the anilox roller to transfer the ink to an anilox roller already The cells When the printing apparatus comprising the anilox roller is operating, it will operate to transfer ink onto the surface of the anilox roller and the surface structure is arranged to retain ink on and within the surface. The ink is viscous. A flap is used to scratch the excess ink from the anilox roller or the ink roller. The ink will remain in the cells formed on the surface of the anilox roller.

[0006] When operating, the anilox roller will rotate and the surface of the anilox roller will contact a rotating printing cylinder. The printing cylinder will receive in an operating mode of the anilox roller a part of the ink collected on / within the surface of the anilox roller. The amount of ink transferred will depend on the image to be printed. The printing cylinder will transfer the ink in the next step to the substrate. A problem with transferring the ink from the anilox roller onto the printing roller is that ink remains may remain in these cells formed on the surface of the anilox roller. The viscosity of the ink as well as the speed of the printing process can result in the remaining ink in the anilox roller. This will effect printing on the substrate. More ink residue will remain in the cells.

[0007] After a partial transfer of the ink from the surface of the anilox roller, this part of the surface will rotate again and reach the ink roller or ink fountain again. The cells can function as an air pump by carrying air into the ink making the ink expand, and said air in the cells will limit the remains of ink in the cell. The air in the cells should be replaced by ink and a certain amount of time is needed to carry out such a replacement, limiting the speed of rotation and finally the printing speed.

[0008] The desired color intensity of the substrate to be printed will directly influence the volume of the cells. If the volume of the cells increases, more ink will be printed on the substrate, thus adding intensity to the resulting color. Heavy layers of ink are formed on the substrate having cells with a relatively large volume, transferring relatively large amounts of ink droplets, while details in the printing are obtained using cells with a relatively small volume.

[0009] Cell density is expressed in lines per centimeter. The known line patterns for prior art cell surface structures are for example 100-180 lines per centimeter. Different line frames have specific objectives. An anilox roller with 100 lines per centimeter would be suitable for printing heavy layers of ink on a substrate. A relatively large volume of ink will be transferred in an anilox roller operating mode. Anilox rollers that have 180 lines per centimeter will have a high resolution, being more suitable for printing details on a substrate. Rollers that have an upper line weft will transfer ink droplets with a relatively smaller volume which will result in less total ink transfer in this

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Anilox roller operating mode. An anilox roller with a high line weft is less suitable for heavy layers of ink printing.

[0010] In the printing methods of the prior art, a balance between a high resolution and color intensity was sought. A higher line frame can be provided with cells that contain greater depth. Which would increase the volume of the cell. However, in practice the use of cells with increased depth will result in an increase of ink residue remaining in the cell. Not all ink in the cell will be transferred to the print roller. Therefore the printed substrate would not yet show the desired color intensity.

[0011] One of the problems of the prior art of anilox rollers is the fact that an anilox roller can only have a line pattern. Known anilox rollers do not allow printing an image on a substrate whose image comprises both heavy layers of ink and details. Replacing an anilox roller is a considerable expense of time and an expensive process, since printing would be temporarily disabled and different anilox rollers with different line patterns should be provided.

[0012] Another problem in relation to known anilox rollers is the need to repeatedly clean the anilox roller due to the amount of ink remaining in the cells of the anilox rollers. This is due to the fact of the nature of the cells of the anilox rollers. It will also result in a waste of ink. Ink from subsequent printing processes will accumulate in the cells. The properties of the anilox roller will deteriorate. The anilox roller will have to be cleaned regularly. What is a time-consuming process that is difficult.

[0013] It is therefore an object of the invention to alleviate or reduce at least one of the known problems of anilox rollers. Another objective may be to provide improved methods to form an anilox roller.

[0014] The invention provides an improved anilox roller. The anilox roller comprises a cylinder with a roller surface. On the surface a fluid distribution structure is arranged to receive, distribute and transfer a fluid such as ink. The fluid can be a liquid or a dough. The fluid distribution structure comprises a channel formed in the cylinder for distributing fluid over the fluid distribution structure. A channel improves the transfer properties of the fluid in relation to the cells. The fluid is more easily received in a channel, and a channel is cleaned more easily. A channel comprises a gap formed in the surface of the anilox roller surrounded by channel walls. The channel has a course that is generally parallel to the direction of the channel walls on both sides of the channel part. Channel walls can locally converge or diverge.

[0015] In one embodiment the fluid distribution structure is arranged to transfer in a first operational mode to print thick layers of ink with a suitable drop of relatively large fluid and in a second operational mode to print details with a drop of relatively small suitable liquid. This is allowed according to the invention by a suitable combination of the restrictions provided in the fluid distribution structure, wherein a restriction is formed by at least a local change in the depth of the channel and / or the width of the channel and / or shape of the channel and / or the wall of the channel. In a structure and in the same distribution structure both functions, details and heavy layers are arranged on the same surface depending on the operating mode.

[0016] An operating mode of the anilox roller is a functional behavior during the transfer of the fluid to the printing substrate. When printing details, relatively small amounts of ink would be required and to print heavy layers of ink relatively large amounts of ink would be required. An anilox roller according to this embodiment combines both properties by providing restrictions formed on the surface of the anilox roller.

[0017] In one embodiment, the relatively small droplets suitable for printing details are provided by open cells formed in the fluid distribution structure only partially surrounded by channel walls. The open cells are at least partially interconnected, allowing the formation of a droplet size in the first operating mode that is convenient for heavy layers of ink printing by combining the ink volume of different cells.

[0018] A restriction according to one embodiment comprises a change in the course of a channel or in particular in a part of the channel. This allows to form a meandering channel. Ink can be distributed to the surface of the anilox roller in the channel. But the distribution is hindered by the meandering channel.

[0019] The anilox roller comprises, in an embodiment for the first operating mode, a fluid distribution structure comprising a meandering channel on the surface of the roller. The meandering channel forms a restriction. A relatively large volume of ink is received in the channel. The meandering channel forms a device for printing a heavy layer of ink. The device for printing a heavy layer of ink is part of the fluid distribution structure. The restrictions cooperate to form a structure of relatively small volumes in the channel, however these volumes can be combined to form a relatively large drop of ink depending on the operating mode. The operating mode is determined by the transfer of fluid from the anilox roller onto the printing roller. The printing roller comprises the image to be printed. The image may comprise details or a heavy layer of ink or another image of ink volume and determines the amount of ink to be transferred.

[0020] In one embodiment, the anilox roller comprises, for the second operating mode, channel parts formed in the channel, preferably winding, said channel parts with a drop volume suitable for

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Print details. The channel parts form a device for printing details that is formed in the fluid distribution structure. Every part of the channel is arranged to transfer a drop of fluid of relatively small size to allow printing of details. The channel part, on at least two opposite sides surrounded by channel walls, forms a restriction that allows a particular operational mode.

[0021] In an advantageous embodiment the device for printing a heavy layer of ink and the device for printing details overlap, allowing one and the same part of the channel to operate according to the operating mode as determined by the ink transfer properties of the print roller

[0022] In one embodiment, the adjacent channel parts are positioned at an angle to each other to prevent a linear distribution of fluid received in said channel in a direction of course of this channel. As the channel parts are connected and the course of the channel parts is positioned at an angle, the formed channel allows a meandering distribution of the fluid received in the channel.

[0023] In one embodiment, the connection formed is relatively large with respect to the size of the drop, and allows a drop to move between the parts of the adjacent channel, although the angle and the meandering shape of the channel prevent a linear distribution of the ink.

[0024] In an embodiment of an anilox roller, one skilled in the art can indicate / recognize different parts of the channel. Even so, a channel can be a relatively continuous, preferably meandering combination of channel parts that collectively form the fluid structure. The side walls of the channel allow a meandering distribution of the fluid received in the channel. The side walls of the channel are arranged to wind a flow of ink throughout the fluid distribution structure, but also restrict the linear flow. The ink can be received in the channels, but it can also be transferred to print the substrate.

[0025] It is noted that on page 72 of the book "The Anilox Roll" by Joseph P. Trungale (ISBN 1-885067-03-8, published in 1997) an anilox roller with a cell structure is described, the cells that are surround by plots or walls with varying heights. According to the book, the structure was designed to allow both the process and the printing of lines. As such, the book does not reveal an anilox roller with a meandering channel.

[0026] It is noted that US 4,819,558 on behalf of van C. J. Counard discloses an anilox roller. The anilox roller described comprises a diamond-shaped cell structure with a pyramid-shaped depth. On the surface of the anilox roller two cells are connected by a straight channel of limited depth. In US 4,819, 558 the channel is not arranged to allow two operational paths to be combined and to be coated on a single surface, and particularly US 4,819,558 does not reveal a channel with channel parts that combine to form a channel where the course of the channel is angled. The structure described will only allow an operating mode depending on the size of the cells. The side walls of the channels are not arranged to allow a meandering flow of fluid over the fluid distribution structure. The surface structure of the anilox roller according to US 4,819,559 is only a cell structure.

[0027] It is noted that US 4,301, 583 discloses an anilox roller. The known anilox roller comprises a honeycomb cell structure. Two adjacent cells connect through a straight channel. The cells and channels form a single row in a circumferential direction of the anilox roller. The course address of the channels in a row is located on a single line. The center point of the connected cells are positioned in a single row. The linear distribution of the fluid is allowed in a circumferential direction of the anilox roller in the known embodiment. The side walls of the channel are not arranged to allow the meandering of a fluid through a fluid distribution structure. The described structure does not combine a device for printing heavy layers of ink and a device for printing details, but they can only work according to an operating mode.

[0028] Thanks to WO 96/40443, an engraved roller with a structure for distributing a fluid on the surface of the roller is known. The known structure comprises diamond-shaped cells, the cells are located in the circumferential direction of the roller in a single line. The cells are interconnected through small channels. The course of the channels extends in the circumferential direction of the roller. The side walls of the structure as described in WO 96/40443 are symmetrically located around the longitudinal axis of the

[0029] channel, that is, the course of the channel. The known channel allows a linear distribution of the fluid in a circumferential direction of the roller. According to the invention the restrictions will prevent such linear distribution.

[0030] A restriction to be used in combination with the fluid distribution structure may be the channel depth. By reducing the channel depth, a local change of the fluid distribution structure is obtained, which allows reducing the size of the ink drop to be received in the part of the channel with reduced channel depth. Such local change can form a weak connection between cells formed in both ends of the channel with reduced depth. The depth of the channel can for example be reduced by at most 50%, but preferably at most by 30%. Since varying the channel depth will locally influence the size of the ink drop to be received in the part of the channel, such restriction is not preferred. In experiments by the applicant it is shown that a local change of the cooperating constraints to allow a constant local droplet size in the structure results in improved printing properties.

[0031] The channel preferably has a single level or generally flat bottom. This allows the channel to receive relatively large amounts of ink along its entire length or at least much of its entire length. A

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Flat bottom improves the capabilities to print in the first operating mode to print heavy layers of ink.

[0032] A channel comprises channel parts that are connected to each other. The channel parts are arranged to receive ink droplets of relatively small size suitable for printing details. The connection between the channel parts preferably comprises a connection of the same channel depth as the channel parts. This allows a physical interaction between the volumes of fluid received in the adjacent channel parts.

[0033] In one embodiment the channel parts have a generally constant width. This allows fluid to be transported between the channel parts in a relatively simple way. The fluid flow between the channel parts is decreased by changing the course of the channel. In such an embodiment the channel lacks local congestion and / or rising pressure points. The rising pressure points have a negative impact on the printing properties since the ink will be removed from the channel. This will prevent the distribution structure, which reduces the function of the device for printing heavy layers of ink, from being completely filled with fluid. In particular, the upward pressure may be the result of a blade that scrapes the roller. US 4,819,558 discloses such an upward pressure point formed by converging walls, which converge in a direction parallel to the circumferential / rotational direction.

[0034] In one embodiment the restrictions are formed by side walls of the channel. The restrictions preferably comprise at least 90%, in an embodiment at least 95%, and in an embodiment at least 98% restrictions in the form of wall parts. A wall part extends over the fluid level when the fluid is received in the structure, between the parts of the wall.

[0035] It is possible that the wall portions that form side walls of a channel extend perpendicularly from the bottom of the channel. By applying perpendicular side walls that restrict the bottom of the channel, a channel can receive a relatively large amount of ink. The channel preferably has a cross section in the form of

U. The channels may have limited depth with respect to the pyramid-shaped cells, which reduces the chances of ink remaining in the channel after transferring ink into the printing roller. A generally flat bottom will prevent the formation of stagnation or rising pressure points / regions in the channel.

[0036] The anilox roller with a surface according to the invention allows combining the properties of an anilox roller with a cell structure of 100 lines per centimeter (first operating mode) and an anilox roller with a cell structure of 180 lines per centimeter ( second operating mode). The invention allows a resolution of up to 300-500 lines per centimeter, and such an anilox roller according to the invention is even capable of printing heavy layers of ink with the desired color intensity properties. An anilox roller will have a surface that will allow the ink to be distributed more evenly. The tension is reduced in the ink. The ink spreads calmly on the surface of the anilox roller, which will allow a subsequent transfer.

[0037] Ink is received in the channel parts more easily compared to a cell structure. Ink can be transferred from the surface of the anilox roller more easily. The tensions in the ink will be reduced during the transfer. Rotation of the anilox roller during the printing process will result in less scraping of the ink from the anilox roller compared to a cell structure. The ink is pressed in front of the blade and is received in the open structure of the channels. The internal tension of the ink is reduced. An advantage is that it is possible to print a heavy layer of ink, while having a grid of fine lines that allows printing details on a substrate.

[0038] The distribution of the fluid is allowed according to one aspect of the invention in a limited manner. By limiting the distribution of the fluid in the fluid distribution structure, a known problem of the prior art anilox rollers is avoided. Anilox rollers with known straight parallel channels allow too much fluid to be distributed, which causes it to not be able to dose the ink in a suitable amount, in particular to print details. The restrictions according to the invention allow such dosage in relatively small amounts of ink.

[0039] In one embodiment the parts of the walls of a channel part are positioned in a radial position of a position in the fluid distribution structure at a distance of less than 120 µm, in an embodiment of less than 100 µm, preferably less than 80 µm. Every location of the fluid distribution structure is surrounded by a restriction in a relatively short distance.

[0040] This will prevent a linear distribution of the fluid efficiently. It is advantageous to prevent the distribution of fluid in the radial direction using wall parts. Only a limited distribution is allowed. The channel comprising parts of the channel does not extend linearly, but is adequately curved.

[0041] The curvature in one embodiment is at least such that straight connections in the lines between locations in different parts of the channel are avoided. A suitable curvature may be an angle of at least 30 degrees, in an embodiment at least 45 degrees and in an embodiment at least 90 degrees.

[0042] In one embodiment, foaming is avoided by the extension of channel parts, and preferably a channel having channel parts that generally extend in a circumferential direction of the anilox roll. Such channels can be conveniently formed as will be explained in more detail below or using known techniques to form said channels, where said channels extend adjacent to each other in a circumferential direction of the anilox roll.

[0043] Preferably in a longitudinal direction adjacent to a first channel, a second channel is formed. The second channel is parallel to the first channel. A fluid distribution structure may comprise channels

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undulating or oscillating parallel. Such oscillating channels can be formed parallel to each other. The channels can be separated from each other by a separation or side wall. A meandering fluid flow is allowed in a channel, preferably in a circumferential direction of the anilox roller. The ink can be distributed to the anilox roller. The free path in the channel structure is limited by restrictions according to the invention that allow the printing of details on a substrate due to relatively small volumes of ink formed in the fluid distribution structure.

[0044] A wall between the first channel and the second channel may have a width of less than 4 µm, preferably in a range of 1 to 3 µm. The relatively small wall arrangements result in a relatively large amount of anilox roller surface usable to receive fluid. The amount of ink received and transferred in combination with the high resolution of the details is substantially improved with respect to the prior art arrangements and allows its operation in both operational modes. In combination with the perpendicular side walls that extend from the bottom of the channel, the channel will have a relatively larger volume for receiving ink, said ink volume being easily transferable, leaving a reduced amount of ink residue, for printing details. The channels include restrictions that allow printing details on the image printed on the substrate. The restrictions are formed by the channel wall parts. The amount of ink that can be transferred is, when the ink is combined from different parts of the channel, sufficient to allow the printing of heavy layers of ink on the substrate.

[0045] To allow a meandering flow of fluid in the channel, the side walls of the channel may be anti-symmetrical in relation to the course of the channel. This would allow a wavy or oscillating channel design to be formed. The channels have a course that follows one breast. The course of the channel changes in each position and this change forms a restriction according to the invention, which allows the anilox roller to operate according to both operational modes. The channel wall portions, in this embodiment of oscillating wall portions, allow a connection between the volumes of ink received in the channel along the channel, but also allows the connection between the volumes of ink to be disconnected as a result of the curvatures in the course of the channel, allowing to obtain relatively small volumes of ink to print details.

[0046] The oscillating channels may have an amplitude that is generally equal to or preferably greater than the width of the channel. This will prevent the linear distribution of fluid in the oscillating channel. A flow of fluid in the channel will force the ink to follow the winding channel, already curved at a distance from the side walls of the channel.

[0047] In one embodiment, the channels have a width in the range of 10 -200 µm, in an embodiment 10 -100 µm, preferably 15 -80 µm.

[0048] In one embodiment, a part of the channel is in the form of a cell. The cell shape should be interpreted as having no closed cell. It is possible that the fluid distribution structure comprises a number of separate wall parts surrounding the cell-shaped channel parts. Separated wall parts are fluid conduit walls that allow fluid to flow in a desired direction. A meandering distribution of the fluid in the channel formed between the cell-shaped channel parts is allowed. A linear fluid distribution is prevented. The fluid can be distributed over a large area of the fluid distribution structure, but the distribution is diverted by restrictions that allow only a meandering distribution.

[0049] The cell-shaped channel parts have at least three open connections with the adjacent cell-shaped channel parts. This allows a distribution of the received fluid in the parts of the channel and allows a meandering distribution. The parts of the cell-shaped channel are unlike the prior art cells, part of a channel that receives ink drops suitable for printing details. The connection between the channel parts is arranged to allow a relatively substantial amount of the volume of droplets to move freely between the adjacent channel parts, but does not allow a linear distribution. The surface structure of the anilox roller according to the invention formed by the restrictions is not a cell structure that allows to receive fluids in the respective cells and the structure according to the invention does not allow an unlimited linear distribution of the fluid on the surface.

[0050] The parts of the cell-shaped channel are in an embodiment characterized by the parts of the channel wall that converge towards a connection part that forms the connection between the first cell-shaped channel and another channel part shaped like a cell. In one embodiment, a part of the channel according to the invention is provided only if the connection part is at least 10% of the channel width. 10% of the width guarantees a sufficient distribution.

[0051] In one embodiment, a cell-shaped channel part has at least two connections in adjacent cell-shaped channel parts. This allows the combination of the volume of fluid received in the parts of the channel in a first operational mode, because the connections allow the two volumes of ink to be combined, and in a second operational mode, since the connection between the connected cells can be separated into a second operational mode, allowing a transfer of small volumes of ink. If multiple connection parts are present between two adjacent cell-shaped parts, the connection parts may be smaller. In one embodiment such connection parts may be less than 5% of the channel width. The smaller connection parts preferably do not have a reduced channel depth.

[0052] In addition, a width of an open connection between channel parts is preferable by at least 40%, and more preferable by at least 60% of a width of a cell-shaped channel part.

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[0053] In one embodiment, a cell-shaped channel part has at least three adjacent cell-shaped channel parts. This will allow you to obtain ink volumes to print heavy layers of ink straight ahead. In a preferred embodiment, the cell-shaped channel part has at least two connections to which each cell-shaped channel part is adjacent. This will allow to easily transfer ink and a combination of ink volumes during transfer in a first operational mode.

[0054] In one embodiment the lower part of the connection between parts of the channel is at the same level as the lower parts of the channel parts. A restriction on the flow between the channels is reduced and only limited by the position of the channel walls. The channel depth is not a point of congestion for the ink, which would imply a non-optimal application of the properties of the fluid distribution structure.

[0055] The open channel structure allows a high frame of lines of preferably about 120 lines per centimeter and in an embodiment at least 150 lines per centimeter. This allows printing in high resolution. The open structure allows the transfer of high volumes of ink which in the prior art arrangement would only be possible if the cell structures were used with relatively low line wefts. The invention allows a high line pattern and the printing of heavy layers of ink with a desired intensity.

[0056] The channel formed on the surface of the anilox roller extends over a relatively large surface area through connections. This relatively large surface area allows a large amount of ink to be collected during transfer. The connected channel parts may have a surface area at least four or six or even ten times larger than the cell surface of the anilox rollers according to the prior art total.

[0057] According to one embodiment, the fluid distribution structure has a grid. The grid is repeated along the surface of the roller. The grid is formed by channel wall parts and the channel parts formed between the wall parts. The grid forms the fluid distribution structure that allows a limited fluid distribution of preferably at most four times the size of the grid. In one embodiment, a linear connection between two points in the fluid distribution structure is limited to a length of at most four times the size of the grid. The person skilled in the art will be able to determine a grid size. A grid size can be determined similarly for prior art arrangement, for example lines per centimeter.

[0058] In one embodiment the free travel, which is the straight line length of a point in the fluid distribution structure that is located between two walls in a first direction, is more than four times the free travel in the second address perpendicular to the first address. The second direction is preferably a connection line between two generally parallel walls or the direction of the course of the channel part. The distribution as a result of a free floating path is in this embodiment in the form of an ellipse. The limited distribution is preferably correlated with the grid size and therefore with the length of the connection line between at least two side walls parallel to two different open cells. The limited distribution according to one embodiment is subsequently limited to at most three times the grid size.

[0059] Preferably an anilox roller is provided with a channel part that is in the form of a cell with a combined surface area of at least 20,000 and more particularly at least 40,000 µm2. In one embodiment, the combined surface area extends along the entire cylinder. The combined surface area is the accumulation of each connected cell open in the channel. Such surface area may be substantially larger than the surface of the comparable anilox roller cell structure according to the prior art. Such surface areas are similar to at least four connected cells of known grid design (100 lines per centimeter) for anilox rollers with cells.

[0060] In one embodiment, channel parts generally extend in a circumferential direction of the anilox roller. This allows an open connection between parts of the channel in a circumferential direction. This is advantageous for filling the channel parts with the fluid. Because the channels are connected to other channel parts in a circumferential direction, the ink is more easily received in the channel with respect to the anilox rollers having cells according to prior art arrangements, while the channel parts, which preferably having a width reduction of at least 40% in a connection between parts of the channel, it allows the air trapped in the channel receiving the fluid to escape. This reduces the amount of ink expansion during the printing procedure.

[0061] In an advantageous embodiment a restriction structure formed by walls is provided with a model of wall parts and wall parts located perpendicularly to the first wall part, where said wall parts are at least twice the size of the channel width of the channel formed between the wall parts. This is a particularly simple embodiment of an open structure with a limited free travel. In advantages of one embodiment, the free travel is four times greater than the width of the channel.

[0062] The invention also relates to a printing apparatus. The printing apparatus comprises a printing device with a supply for a substrate for printing and an ink supply, where the printing device comprises an anilox roller mounted on a support, said anilox roller comprises at least one of the characteristics mentioned above.

[0063] The invention also relates to a method of forming an anilox roller. The method comprises supplying a cylinder for an anilox roller that has an external surface to be worked. The preferable method comprises supplying at least one laser source and a laser that etches the external surface of the anilox roller. It will be clear that a

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One skilled in the art will be able to use future techniques that work similarly to a laser, for carrying out the method according to the invention.

[0064] The method according to the invention comprises a laser that engraves the external surface of the anilox roller with a laser point that is formed with the laser source. The laser and its laser point are able to focus the intensity of the beam in a small position on the anilox roller. This allows to thread the anilox roller. The anilox roller can be used in the printing industry.

[0065] The method according to an embodiment of the invention comprises applying an optical guide in the laser light path to allow the laser point to execute a reciprocal movement on the external surface to be worked. The reciprocal movement leads to repetitive movement in the position of the laser point. The reciprocal movement preferably causes a deflection of the laser point on the anilox roller in a direction that is mainly parallel to a longitudinal axis of the anilox roller. This creates the ability to execute a repetitive movement of the laser point on the surface to be worked, in a surprisingly simple way.

[0066] In one embodiment, the laser point will primarily move at a constant speed on the surface of the roller. An even general evaporation of the surface material of the surface of the anilox roller is obtained. This allows to form a generally uniform channel. The depth of the channel will generally be at a similar level throughout the formed channel. In addition, the channel will have a generally U-shaped cross section.

[0067] In one embodiment the optical guide is a crystal. Reciprocal movement is caused by supplying a variable current to the crystal. With this, deflection in the path of the laser beam can be caused, resulting in the movement of the laser point. The variable current may be a sinusoidal current, such as a well known alternating current (AC). With this, a reciprocal sine-like movement is generated.

[0068] Preferably, the method comprises a deviation in the reciprocal movement of the laser point that is at least larger than the width of the laser point in the same direction. In this way, it is possible to laser engrave an external surface with a width of two or more times the width of the laser point. The surface can be etched in a single operation of the method to form an anilox roller. The result is that laser engraving is done faster.

[0069] It is also advantageous to laser engrave the anilox roller, while rotating the anilox roller around a longitudinal axis of the anilox roller. In addition, the laser can be moved in a direction primarily parallel to the longitudinal axis of the anilox roller. Therefore, the entire surface of the anilox roller can be worked. This technique is known by the state of the art. By applying the reciprocal motion guide, the prior art methods can be accelerated.

[0070] It is exceptionally advantageous to apply the method using a continuous laser. This allows the possibility of moving it continuously while moving the laser point on the surface. In combination with the rotating anilox roller, which can rotate around its longitudinal axis, a tilting track can be burned. This track is comparable to a track on a CD or DVD. The method of forming an external surface comprising such a tilting groove, surrounded by walls that remain unburned, can advantageously be applied in the graphic industry. Laser engraving is used here to form a channel that extends in a rotational direction of the anilox roller.

[0071] Another object of the invention is obtained by an apparatus for forming an anilox roller for use in a printing process, comprising a support unit for supporting the cylindrical shaped anilox roller and for rotating the anilox roller around a longitudinal axis According to one aspect of the invention, the apparatus comprises an engraving unit that is arranged for parallel movement with respect to a cylinder axis of the anilox roller to engrave a structure on the external surface of the anilox roller, especially in combination with a rotating anilox roller . The apparatus also comprises a transmitter unit that transmits engraving settings for the engraving unit. Engraving settings are the transmission parameters for engraving, with which engraving can be influenced. The person skilled in the art will understand how to adjust the engraving.

[0072] Advantageously, the engraving unit comprises at least one laser for laser engraving the outer surface of the anilox roller with a laser point. At least one objective is obtained when the engraving unit also comprises an optical guide for adjusting the laser light path, and more specifically for moving the laser point reciprocally or repetitively. With this, an additional deflection of the laser point is possible. The position that must be worked can also be chosen in this way. Using an optical guide, it is possible to make an additional deviation of the point, which allows small and fast deviations. More specifically, these detours can be repetitive.

[0073] In another advantageous embodiment, the optical guide is a deflector. A deflector, such as a crystal can be used, with which the laser path, and thus the position of the laser point can be adjusted, more specifically deflected. The baffle can be controlled quickly and accurately. The person skilled in the art will be familiar with the different baffles to create a repetitive transition of the laser spot. In an advantageous embodiment, the crystal can be connected to a power supply, more specifically a controllable or actionable supply, where the voltage supplied is in proportion to a certain deflection and more specifically to a laser point offset.

[0074] In one embodiment, the crystal can be arranged to deflect the incoming laser beam in a manner that depends on the voltage.

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[0075] In another advantageous embodiment, the engraving unit comprises an optical guide that is located in the laser light path, where the guide is movably connected to the engraving unit. This allows the movement of the laser point on the surface of the anilox roller, in addition to the movement of the incision unit assembly. The extra movement is superimposed.

[0076] It is especially advantageous to connect the optical guide to the engraving unit by means of a movement unit, where the movement unit is arranged to allow the laser point to execute a reciprocal movement. In this way, a repetitive and reciprocal movement of the laser spot can be used to form a regular structure on the anilox roller. This regular structure can be obtained by engraving a rotating anilox roller, and additionally by moving the laser in a longitudinal direction along the roller. The structure thus formed is different from the structure of lines formed in a usual way.

[0077] The preferable reciprocal movement causes a movement of the laser point in a direction primarily parallel to the cylindrical axis. With this, a larger surface can be worked in a single work step. Preferably, the offset is at least larger than the width of the laser point in the same direction. This allows to work an area with a width of at least twice the size of the point. Also, with this, a wave-like movement can be obtained when the reciprocal movement is combined with a rotation of the anilox roller around its longitudinal axis.

[0078] According to the invention, the laser can be a continuous laser. Especially in combination with a rotating anilox roller and a reciprocating guide, a track or a channel is formed in the anilox roller. The track has a swing. The transmission unit is preferably connected to the support unit and the movement unit. The transmission unit may be arranged for rotation of the anilox roller during laser engraving with a reciprocal laser point of motion. This enables the manufacture of a new anilox roller, having advantageous properties to transfer the ink. Ink can be easily absorbed temporarily in the oscillating channels.

[0079] It is advantageous to provide engraving with an objective lens. The lens is able to focus the laser. The lens can be the optical guide that performs a reciprocal movement.

[0080] It is possible to provide the engraving unit with two lasers or more lasers and / or with one or more beam separators. In this way multiple channels can be provided on the anilox roller simultaneously.

[0081] In a preferred embodiment, the reciprocal movement leads to a deflection of the laser point of at least 20 µm. This small deflection may be sufficient to create an oscillation in the channel on the worked surface of the anilox roller.

[0082] Although the invention is described and will be described with respect to the preferred embodiments, it will be clear that within the scope of the invention, different and multiple embodiments are possible. It is an objective of this application to protect the described embodiments, the embodiments indicated by the claims, as well as equivalents thereof. The person skilled in the art will be able - now that the advantages of the invention are experimentally known - to construct different embodiments. It is also an intention of the inventor to protect these embodiments with this application.

[0083] More specifically, the person skilled in the art is capable of forming restrictions on the surface of an anilox roller according to the description in this application that allows one or more advantages to be obtained. Functional protection should therefore be allowed.

[0084] Previously, as in the following description, aspects of the invention and advantages of the measures are described. The inventor tries to protect all the mentioned and non-mentioned advantages that the invention has with respect to the state of the art, using this application and / or divisional applications.

[0085] The invention will be described in reference to the following description taken in conjunction with the accompanying drawings in which:

Figure 1 is a schematic side view of a printing apparatus for a flexographic process;

Figures 2a and b are detailed views of a surface of an anilox roller engraved according to the state of the art.

Figures 3a-h are detailed views of embodiments of an external surface of an anilox roller according to the present invention.

Figure 4 is a detail of a part of the channel section of an anilox roller according to the embodiment of Figure 3b, and

Figure 5 is a schematic view of an embodiment of an engraving device according to the invention.

[0086] Figure 1 shows a schematic side view of a part of a printing apparatus 1 used for example in a flexographic process. The printing apparatus 1 can be part of a series of printing apparatus for printing with different inks or with various techniques. The person skilled in the art will be familiar with the different embodiments of a printing apparatus 1. The printing apparatus 1 is convenient and arranged to apply ink to a substrate in a desired model.

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[0087] In the embodiment shown, the printing apparatus 1 comprises a fountain roller 2 that is partially emerged in an ink fountain 4 comprising a certain amount of ink 3. The fountain roller is rotatable, and the outer surface of the source roller can be a rubber coating.

[0088] Next to the source roller 2 a rotating measuring roller or anilox roller 5 is located, where the longitudinal axis of the anilox roller 5 is located parallel to the longitudinal axis of the source roller. This allows to form a point of contact

or contact line 6. Rollers 2 and 5 are in contact, or almost in contact with each other. Adjacent to a circumferential side of the measuring roller, a blade 7 is located at least a part of the length of the measuring roller. According to the longitudinal axis of the measuring roller 5, a rotating printing cylinder 9 is placed. The printing cylinder comprises elevations and recesses, the elevations form a negative of the image to be printed.

[0089] Elevations and recesses determine the operating mode for the anilox roller 5. When the image contains details, ink in the form of relatively small droplet sizes should be transferred from the anilox roller onto the substrate, while for printing heavy layers of Ink should be transferred relatively large drop sizes:

[0090] The substrate 13 or the product for printing may be located next to a circumferential side of the printing cylinder. The substrate moves in a longitudinal direction. A rotating printing roller 11 is located next to one side of the printing roller 9, where the printing roller 9 and the printing roller 11 are positioned on both sides of the substrate.

[0091] The figure shows an example of a substrate 13. It is obvious that different types of substrates can be printed 13. The person skilled in the art will be able to adapt the printing apparatus to the substrate to be printed.

[0092] An operative method of the apparatus shown will be described below. When the apparatus is driven, the source roller 2 will be activated, resulting in a rotation of the source roller 2 so that the external surface of the roller will move through the ink 3 of the ink source 4. The external surface of the source roller may comprise a layer of rubber, the ink will be absorbed and transported in the direction of the anilox roller 5, which is rotating in the opposite direction compared to the source roller. Near the contact point 6, the ink will be transferred from the source roller 2 to the anilox roller 5. The surface of the anilox has a structure for absorbing ink. The structure will be described in more detail in Figure 2.

[0093] The anilox roller 5 will absorb a certain amount of ink from the source roller 2. The blade 7 ensures that there is not an excess of ink, so that the anilox roller 5 absorbs and retains an adequate amount of ink. Then, the ink will be transferred onto the printing roller 9. A thin layer of ink is transferred over the elevations of the printing roller 9. In comparison with the anilox roller 5, the printing roller 9 is rotating in the opposite direction. The printing roller 5 will continue rotating and will apply the image to the substrate 13. The printing roller 11 supports the substrate during the printing process.

[0094] Other configurations are also possible. The apparatus may be provided with a closed ink source 4 comprising an ink supply and an ink drain. It is also possible to provide multiple blades 7. The configuration description only serves as an example. Multiple configurations of the anilox 5 roller are possible, without deviating from the invention, which may be obvious.

[0095] Figure 2a shows a detailed view of a surface of an anilox roller 5. The surface structure shown is known from the prior art. The anilox roller 5 has a structure 14, which can be formed by a plurality of regularly positioned cells 15. Cells 15 are formed by recesses in the anilox roller 5. Cells 15 are separated from each other by side walls 17 with a width w1. According to the state of the art, the width w1 can be 10-80 µm. The side walls ensure that the ink cannot move from one cell to another. If ink is provided on the surface of the anilox roller with the surface structure 14, the side walls 17 will extend over the ink level. The ink will be inserted into cells 15. Blade 7 will eliminate excess ink.

[0096] The cells have an overall size h of between 10-80 µm. Each cell has a depth (not shown). Each cell has a certain volume. The ink volume corresponds to the ink drop to be transferred onto the printing roller and the substrate.

[0097] In the embodiment shown, the cells are hexagonal in shape, and the cells are positioned in a honeycomb structure. The distance c between the center point of two neighboring cells, where the distance is measured perpendicular to the rotating direction of the roller, determines the line pattern of the anilox roller. Known line frames of the prior art cell surface structures are 100, 120, 140, 180 lines per cm.

[0098] Figure 2b shows another embodiment of an external surface of an anilox roller according to the state of the art. In these embodiments the channels 18 are applied along an external surface of the measuring roller. The channels have a width h (of 15 80 µm) and are separated from each other by a wall 19 with a thickness t. The longitudinal direction of the channels is positioned at an angle a with respect to the direction of rotation R of the measuring roller. Such an embodiment is convenient for applying ink to the substrate in a homogeneous manner. It is clear that the channels are straight lines and therefore there is no restriction on the extent of the ink in the channel.

[0099] The currently known anilox rollers do not individually match the criteria set in the printing industry. Therefore it is necessary in many applications the use of different anilox rollers, which is something that

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It slows down the printing procedure and that makes the work of the printing procedure intensive long-term and expensive.

[0100] Figure 3a shows a first embodiment of an anilox roller. Figure 3a shows a view of the rolling surface 100 of an anilox roller where a fluid distribution structure is applied. The fluid distribution structure is shown more specifically by wall portions of the channels that are formed in the structure. The wall parts are repeatedly indicated with lines. The "empty" parts of Figure 3a are recesses in the lamination surface, which can for example be formed by laser and laser engraving and / or evaporation.

[0101] The part of the rolling surface 100 shown in Figure 3a is provided with a model, formed by two wall parts 21, 22 that are positioned at an angle to each other. The wall parts form dams or restrictions and have a thickness t. The wall portions 21, 22 are surrounded by a channel 20 that extends over the outer surface of the anilox roller. The channel is arranged to absorb mass, more specifically ink. The ink can be resumed in the formed channel 20 and can be spread on the outer surface, where restrictions ensure that the ability to flow is limited.

[0102] In one embodiment the first restrictions 22 are placed at an angle of approximately 90 degrees with respect to the second restrictions 21. The first restrictions 21 are also located at an angle γ with respect to the direction of rotation R of the roller anilox. Preferably γ is equal to 0 degrees. The second restrictions are positioned longitudinally from the first restriction, and the restrictions are positioned at an angle of 90 degrees to each other. Other angles are of course imaginable. In this embodiment, a normal model can be obtained. In one embodiment, the model can form a fishbone model.

[0103] Preferably the anilox roller model is formed such that a volume of ink has only a limited free travel or path distance, measured from an arbitrary point on the absorption surface 20. The path distance is defined as a distance in which a part of ink can be moved in a radial random direction starting from a random point in a channel until a wall is reached. Preferably the free path is less than 150 µm, and in the embodiment shown less than 100 µm. Preferably the free path is less than 50 µm. The free path ensures that the ink can freely flow along a certain, but restricted length. Due to the fact that the free path is limited, a resistance force is applied to the ink so that the ink cannot flow freely over a too large part of the roller. Due to the fact that the restrictions are positioned at a relatively short distance from each other, a large distribution of ink is impossible. Surprisingly, in this way an anilox roller is obtained which on the one hand has an open structure, but where on the other hand the cells, in this case open cells can be recognized. Printing tests with such an anilox roller have shown that such a structure allows the printing of heavy layers with sufficient color intensity as well as the printing of small detailed structures. According to the state of the art, this result was only obtainable by two-step printing, more specifically using first an anilox roller with a small line weft, and then using an anilox roller with a large line weft, or vice versa.

[0104] In one embodiment the restrictions have a width t that is less than 8 µm. Preferably the restrictions have a width of less than 5 µm. Even more preferably the restrictions have a width t between 2 and 3 µm. In this way, the walls are only part of the total surface area of the very small anilox roller circumference. It is clear to the person skilled in the art that the wall parts according to the present invention function primarily as restrictions against the free distribution of ink, when there is ink between the walls.

[0105] The location of the restrictions makes it possible to form open connections in the structure on the external surface of the anilox rollers. The ink can be distributed well on the anilox roller, especially when the ink is absorbed into the channel. The restrictions are placed in a certain way to ensure that the ink cannot flow freely, especially when the ink is being released. The wall parts form restrictions on the anilox roller and ensure that the ink is properly maintained on the anilox roller. The presence of the large absorption surface 20 ensures that the anilox roller according to the present invention is capable of absorbing a large volume of ink. In addition, restrictions allow ink to be absorbed well from the source roller. The position of the restrictions is such that the ink received in the fluid distribution structure can freely, but limitedly, be distributed over the anilox roller, so that generally a small layer of ink film is provided in the anilox roller.

[0106] Additionally, an unlimited distribution of ink by the restrictions is avoided, since the restrictions form natural barriers against the flow of ink. Additionally, the structure of the anilox roller ensures that the transfer of ink onto the printing roller is possible in several operational models. The negative parts of the printing roller are supplied with a metered amount of ink, where also the detailed parts of the negative are provided with the appropriate amount of ink.

[0107] It is therefore possible with an anilox roller according to the present invention to obtain a good intensity of color and heavy layers, as well as fine structures in the line art. Therefore it is no longer necessary to change the anilox roller in specific cases where both the intensity of the color and the details are important. Only one anilox is needed to print both heavy layers and fine details.

[0108] Another advantage of the anilox roller according to the present invention is that it does not need to be cleaned as often. The

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Anilox rollers according to the state of the art have large amounts of walls 17, 19. In addition, walls 17, 19 require a large amount of space with respect to the total available ink surface. According to the present invention the wall parts require less than 10%, in an embodiment less than 5% or 3%, preferably less than 2%, of the total surface area of the anilox roller.

[0109] To transfer an adequate amount of ink, cells 15 and channels 18 according to the prior art have a relatively large depth. Frequently, the depth of the cell or channel is greater than its width. This results in the fact that it is difficult for the ink to leave the cell or the channel, and finally ink residues accumulate and block the cell or channel. The anilox roller then needs to be cleaned. This is a tedious and hard work, which is also due to the fact that the cells and channels have a relatively large depth. In addition, the anilox rollers can easily be damaged during cleaning.

[0110] In anilox rollers according to the present invention this problem is less relevant. Since there is a larger absorption surface 20 for the ink, a smaller depth will be needed to transfer the appropriate amount of ink. In addition the restrictions are positioned at a relatively large distance from each other. This ensures that the transfer of the ink is relatively easy, so that it is more unlikely that an accumulation of ink in the anilox roller according to the present invention. An additional advantage of the relatively large distance between the constraints, and the relatively smaller depth of the anilox roller, is that the surface structure can be reached more easily for cleaning.

[0111] In one embodiment of the present invention, as shown in Figure 3b, winding channels 24 having uniform walls 25 are provided. It is relatively easy to create this embodiment. The winding channels may have a waveform, more specifically a sine wave, see Figure 4, where a succession by one shift in the first direction is alternated by a shift in the other direction. With reference to Figure 4, the walls have an upper part 32 and a bottom 31, where the walls have an amplitude a and where the walls oscillate around a baseline 30.

[0112] Preferably the baseline 30 of the sine is located parallel to the direction of rotation R of the anilox roller. The course of the meandering channel 24 follows a sine.

[0113] Due to the fact that in a preferred embodiment the amplitude of the wave is greater than the width of the channel, a channel with limited possibilities is obtained to extend or distribute the fluid received in the structure. In this application, the term free travel is used. Free travel refers to a radial expansion of any arbitrary point in the formed channel. In the sine channel shown, the free path is limited to a maximum of one wavelength. By limiting the radial or free distribution, it is possible for the ink to be absorbed into the channels on the outer side of the anilox roller. The limited distribution results in a decreased tension in the ink that is absorbed and distributed by the anilox roller when it is being used. The volume of the channel parts on the outer surface of the anilox roller is relatively large compared to the prior art volumes that are obtained using closed-cell grid models with a large line weft. With the anilox roller according to the present invention it is therefore possible to approximate and / or improve the properties of the large line weft of the anilox rollers.

[0114] However, the anilox roller model according to the present invention also has a limitation of direct extension. With this, it is also possible to apply the details on the substrate during printing. According to the state of the art, this was only possible using anilox rollers with a relatively small weft line. The anilox roller according to the present invention combines these two properties (heavy layer and small detail printing) and thus leads to a reduction in the amount of printing steps needed in the printing process.

[0115] The limitation on the extension is obtained due to the fact that wall portions 25 always create some limited channel part that are otherwise connected to each other by (indirect) connections. The channel parts according to the invention are limited due to the fact that the straight line distribution between the wall portions 25 is smaller than the curved or indirect distribution.

[0116] In the example in Figure 3b the wavelength is comparable to the grid size of the model. The grid size and the channel width are comparable. Preferably the wavelength is less than four times the grid size, preferably less than twice the grid size. Due to the fact that the grid size and wavelength are comparable, in fact every time a cell type model is obtained that is comparable to a honeycomb model according to the state of the art. According to the invention, however, these cells are connected in a limited way to each other and separate connections are formed because they eliminate closing wall parts.

[0117] The fluid can be distributed over a large part of the surface of the anilox roller if the path followed snakes over the surface.

[0118] The wavelength can be 80 µm for example, while the grid size is equal to about 30 µm. The anilox roller according to the present invention, having these dimensions, combines the properties of anilox rollers that have a larger or smaller line weft, that is, possibilities of heavy layers of ink (first operating mode) and detail printing (second operating mode ).

[0119] Figure 3b shows an embodiment, where two walls that are located next to each other are positioned at a distance from each other. The walls 26, 27 that are positioned next to each other have a distance d that is twice the amplitude a of the sine. The depressions 26 of a wall are introduced into the parts

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upper 27 of the neighboring wall. This embodiment ensures that the ink parts obtain a maximum free path. The structure / model prevents the mass to be absorbed between the wall parts from being easily spread, and more specifically that during the ink supply by the anilox roller a large mass of ink can be collected to be supplied. Curved connections between the channel parts are possible. With this, the increase mentioned above becomes possible, but only in a certain small amount. With this, relatively large volumes of mass can be transferred. Additionally it is possible, as shown in Figure 3c, to locate the channels and walls at the angle β with respect to the direction of rotation (or circumferential direction) R. Especially for printing heavy layers of ink this is an embodiment helpful

[0120] Figure 3d shows another embodiment, where different constraints 51, 52, 53, 55 are placed in such a way that a regular model is formed. The line-shaped restrictions 51, 52, 55 are positioned in a triangular shape, where the angles of the triangle are formed by cross-shaped restrictions 53. Between the cross-shaped restrictions 53 and the extremities of the restrictions in the form of line 51, 52, 55 there are breaks. An ink particle can freely flow between different parts of triangular channels 54. The free flow in a linear line of a straight line is limited. The walls form dams to restrict the spread of mass in the channel parts. In addition, the walls form dams against the accumulation or concentration of ink, for example when the ink is being supplied.

[0121] The restriction in the shape of the cross-shaped wall part 53 preferably has a size that blocks the flow of fluid along the part of the wall 51, but allows the deflection thereof, increasing the part of Wall 53 forms a larger barrier. The distance between one end of wall part 51 or 52 and therefore, the cross-shaped wall part does not change for that. The size of the connection part therefore remains the same.

[0122] The size of the connection part 49 is preferably equal to at least 10% of the length of the wall part 52. This is why the cell-shaped channel parts 47, 48 that are positioned on opposite sides of the wall part 52 have an open connection with each other. In addition two connections are formed between those parts in the form of a cell. In the first operating module it is relatively easy to obtain a relatively large ink droplet size due to the fact that both cell-shaped channel portions 47, 48 supply the ink.

[0123] The capacity of the cell-shaped channel parts 47, 48 is approximately equal to the relatively small drop size desired to print details and corresponds to the desired drop size to print details in the state of the art, such as for example 180 lines per centimeter of anilox rollers.

[0124] This model ensures that the ink can be well absorbed in the anilox roller, and that the ink can be properly supplied to the printing roller. Additionally, this embodiment ensures that the ink has sufficient freedom to flow, and yet that a film layer is present in the anilox roll.

[0125] Also, Figure 3b is an example of a winding channel since fluid flow is possible along a large part of the surface of the anilox roller, because the cell-shaped channel parts are connected each. Flowing along the wall parts 51, 52 the fluid is able to reach other channel parts in the form of a cell. Exactly this property ensures that the anilox roller is able to combine the printing properties of the first and second modes of operation.

[0126] The embodiments of the figures from 3 to 3d have a fluid distribution structure that is formed on the surface of the anilox roller, where the channels formed mainly have a similar depth. With this the size of the volume of fluid in the channels will not be locally disturbed and thus the fluid will remain more easily distributed on the external surface than in the prior art.

[0127] Fig. 3e shows another embodiment according to an aspect of the invention. The embodiment shown comprises a channel 301, which has wall parts 302, 302 '. Channel 301 has a width w2. The wall parts are positioned next to each other in a relatively parallel way of oscillation. In this way a sinus of the oscillating channel type is obtained. The wall parts are placed at a distance such as each other, that the upper part 351 and depressions 352 that are closer to the center of the channel 301, are spaced with an interval t. The interval suggests that a straight striped distribution of the fluid is possible. It has been found, however, that when the interval t is relatively small, this straight line distribution is avoided. The wall parts form restrictions that determine the thickness of the formed channel. The channels formed meander over the surface of the anilox roller.

[0128] The flow profile in the channel will be mainly the same in the different parts of the channel, which means that the flow profile will be the same in the parts of the channel that flow in different directions. However, the direction of the flow profile, and therefore the flow, will be different in neighboring channel parts. The flow has no chance of developing in a straight line, in the direction of rotation R. The walls guide the flow in such a way that the flow can only wind over the channel.

[0129] Preferably the interval t is small compared to the width w2 of the channel. Preferably the interval t is smaller than 10% of the width w2 of the channel, and even preferably smaller than 5% of the width of the channel.

[0130] Figure 3f shows an embodiment of a channel 401. The channel comprises saw-shaped walls 403, 403 '. In channel 401 the different parts of channel 405, 407, 409 are visible, each with its respective course 406, 408, 410. A course 408 of the part of channel 407 is positioned at an angle with respect to the course 406 of a

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neighboring channel part 405. In the embodiment shown the angle is approximately equal to 90 degrees, but it is also possible to use other angles. By positioning the channel parts at an angle with respect to each other, the straight striped distribution of fluid in the channel is avoided. On the other hand, a meandering flow in the channel 401 is possible. The walls 403, 403 'are positioned such that these walls guide the flow in a meandering way. The straight line distribution of the fluid is avoided by the walls.

[0131] Figure 3g shows a cross section of a channel 501 according to an embodiment of the invention. The bottom 503 of the channel is mainly flat. The walls 502, 502 'are mainly located perpendicular to the bottom 503. In this way a relatively large amount of fluid can be absorbed into the channel. Preferably the width of the channel is large with respect to the height of the channel. In this way a large volume of fluid can be absorbed into the channel, and in this way it is also possible to supply the amount of fluid in a relatively easy manner. There is only a relatively small amount of fluid that remains in the channel during substrate printing.

[0132] Additionally, it is possible that the embodiment shown in Figure 3g refers to a cell-shaped channel and a channel according to an aspect of the invention. The bottom of the cell and the bottom of the channel are mainly located at the same level. This improves the flow of fluid between cells through the channels. In this way the channels prevent congestion or upward pressure in the fluid. The upward pressure in the fluid may be the result of the bottom of the (connecting) channel being located at a level higher than the bottom of the cell.

[0133] Fig. 3h shows a channel 600 with parts of channel 601-605. Channel 600 is part of the fluid distribution structure for receiving, distributing to the anilox roller, as well as transferring the fluid to a subsequent printing roller. Channel 600 is arranged to distribute and guide the fluid over the fluid distribution structure. The winding channel 600 shown here forms a heavy layer printing unit in the fluid distribution structure. The channel 600 comprises a detail printing unit that is formed in the winding channel 600 by means of channel parts 601-605. Channel parts 601-605 have a convenient drop volume for detailed printing. Neighboring channel portions are positioned at an angle to each other to prevent the straight line distribution of the fluid in a course of the channel, while allowing a meandering distribution of the fluid in the channel 600.

[0134] Figure 4 shows in detail a restriction 33 according to an embodiment of the invention. In the embodiment shown in Figure 3b the amplitude of the wave is larger than the width between two walls. The wall itself has a size of approximately 1-4 micrometers. The channel according to Figure 3b has a width of between 10 and 150 micrometers, more preferably between 20 and 100 micrometers, and even more preferably between 30 and 80 micrometers. The wave can have an amplitude of at least about 50 micrometers. According to the invention an open structure is used to considerably reduce the size of the wall parts compared to the state of the art. This leads to another increase in the area available to receive ink and to transfer ink through the external surface of the anilox roller.

[0135] An open structure according to the invention can be characterized by larger surfaces of channel parts between wall parts that are formed on the outer surface of the anilox roller. The channel parts are connected to other large surface connections through connections that are provided between the wall parts. Although it is preferable to avoid a straight connection, it is possible to make a limited meandering connection.

[0136] The model according to the invention and more specifically the model according to Figure 3b reduces the amount of expansion that takes place in the anilox roller. Related to this is the fact that the parts of the channel and more specifically the channels are capable of having a mass, and more specifically of ink, with greater ease. The rotation of the anilox roller according to Figure 3b is mainly parallel to the base of the sine, and therefore the air from the open parts of the channel can be conducted outside the part of the channel by the relatively open structure according to the invention.

[0137] Of course the invention is not limited to sine wave channels. The channel and / or the walls can also have a sawtooth shape or any other repetitive model.

[0138] In an embodiment of the invention, the oscillating wall portions may show a phase difference from each other. In this way each time a stepped model of wall parts is obtained. With this it is also possible to obtain the advantages according to the present invention.

[0139] Figure 5 shows a schematic view of an apparatus for forming the structure of an anilox roller according to an embodiment of the invention. A laser 60 is used here. The laser is part of an engraving unit 61. The engraving unit is located along the longitudinal axis 62 of the anilox roller 63. The anilox roller 63 is only shown schematically. The figure is not drawn to scale. The engraving unit is placed in a frame (not shown), and the frame enables movement of the engraving unit along the anilox roller 63 according to arrow 62. Suitable guide means such as a guide path can be applied .

[0140] The anilox roller 63 is placed in a container that is supported by bearings and that is connected to the frame. In this way the anilox roller is capable of rotating around the longitudinal axis 62 according to arrow 64. The combination of both the rotation around the axis 62, and the movement along the axis 62 enables engraving machining of the entire external surface With the laser. The constructions for manufacturing, more specifically engraving of the anilox roller according to the state of the art using these movements, allows machining with accuracy less than 1

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micrometer. This, among others, allows wall parts according to the embodiments of the invention to be formed with a size smaller than 5 micrometers. The method allows the formation of channels on the surface of the anilox roller. The material of the channels evaporates, while the wall parts remain there.

[0141] The laser beam can be concentrated at a point 69 on the outer surface 70 of the anilox roller 63 by known optical guides 65-68, which in this embodiment are formed by four angular mirrors. In the position where the point is formed, a certain amount of heat is concentrated in such a way that the piece of material from the outer surface of the anilox roller will evaporate. This material may be a ceramic composition, such as a chromium oxide. One skilled in the art will be familiar with the different compositions and / or compounds.

[0142] By focusing the point it is possible to evaporate a part of the external surface of the anilox roller. In a preferred embodiment of the invention, a continuous laser 60 is used. Synchronizing the pulses of the laser with longitudinal and rotational movements is more continuous. More specifically, it is possible to form a continuous track of evaporated material on the anilox roller 63 using a continuous laser together with continuous movements of the roller and / or engraving unit, thus forming a channel. It is possible to form a continuous track at high speed. Speed is limited only by laser power:

[0143] In another embodiment of the invention, the beam 71 of the laser 60 is influenced by an optical guide in the path between the laser 60 and the point 69. The optical guide 72 can give force to a reciprocal movement 73 of the point on the surface to be engraved. As a result, the point repeatedly executes an identical movement, preferably at a continuous speed. This movement, with the rotation of the anilox roller, can lead to a continuous change of the location of the point. Preferably, reciprocal movement results in a deflection 73 of the point in a direction parallel to the longitudinal axis of the anilox roller. Such a change in combination with a continuous laser can for example be used to form a channel model according to fig. 3b

[0144] Preferably, the reciprocal movement is a sine wave type movement. The movement can be determined mechanically or electronically. In a preferred embodiment shown in Fig. 5, a combination of a crystal 74 is used on one side, and a voltage supplied by a power supply 75 on the other hand. The voltage is supplied to the crystal. The optical guide 72 and more specifically the crystal 74 will function as a generating device for the reciprocal movement of the laser point. A voltage is supplied to the crystal 74 to cause a change in the beam path, more specifically an eventual deflection of the point. The voltage supplied is, for example, repetitive, resulting in the movement of the point being also repetitive. A control unit 76 is, for example, provided in the electrical connection between the crystal 72 and the supply 75. The control unit is capable of adjusting the supplied voltage. The control unit can be connected to an external controller to synchronize the crystal voltage with the rotation 64 of the anilox roll 63 and the movement 62 along the anilox roll 63 of the engraving unit as a set.

[0145] The voltage change can be synchronized with the rotation of the anilox roller. The voltage change is for example characterized by parameters such as amplitude and frequency. These two parameters can be related to the amount of diversion and the repetition of reciprocal movement, respectively.

[0146] In the embodiment shown, for example, a tellurium dioxide crystal 74 can be used. The crystal functions as a baffle. By changing the voltage between 0 V and 10 V, the transmission properties of the crystal change. The mentioned crystal operates at 1064 nm.

[0147] Other embodiments of generating devices and optical guides are also possible. It is also possible to use a moving mirror. In another embodiment, an interference effect can be used to generate reciprocal movement of the point.

[0148] Another technique that is known to use such a wobble of a channel formed on an external surface is a technique for creating DVDs. The inventor is aware that a technique known in this technical field can be used to create such a model on an external surface.

[0149] Variations in the embodiments of the different profiles can be imagined, without deviating from the main notion of the invention. It should be clear that the invention is described using preferred embodiments. The invention is not limited to these embodiments.

Claims (17)

1. Anilox roller (5) for a printing apparatus for transferring fluid, such as ink, comprising a cylinder having a surface (100), where the surface comprises a distribution structure for receiving the fluid, distributing the fluid through a cylinder , and transfer the fluid, where said fluid distribution structure is 5 arranged to transfer in a first operational mode to print heavy layers of ink with a relatively large drop of fluid and in a second operational mode to print details with a relatively small drop of fluid by a combination of restrictions on the fluid distribution structure , characterized by the fact that The fluid distribution structure has a channel (24) formed on the surface to distribute the fluid over the fluid distribution structure, said channel (24) meanders on the surface, the waveform channel, more specifically a sine wave , and the channel would have a width of between 10 and 150 µm, preferably between 20 and 100 µm, and even more preferably between 30 and 80 µm. 2. Anilox roller according to claim 1, wherein the winding channel comprises channel parts that are connected to each other, said channel parts having a generally constant width.

3.

Anilox roller according to claim 1 or 2, wherein the meandering channel (24) has a wavelength less than 4 times the channel width, preferably less than 2 times the channel width.

Four.

Anilox roller according to any of the preceding claims, wherein the channel walls (25, 26, 27) of a winding channel (24) are generally positioned antisymmetrically with respect to a direction of course of the channel.

5.

Anilox roller according to claim 4, wherein the meandering channel (24) has an amplitude that is generally equal, preferably greater than the width of the channel.

6.

Anilox roller according to any of the preceding claims, wherein the fluid distribution structure for the second operational mode comprises channel parts (601-605) that are formed in the channel (24,

25 600) and are at least partially interconnected, said channel parts having a volume that allows the formation of relatively small fluid droplets to print details.

7.

Anilox roller according to claim 6, wherein connected channel parts (601-605) having a course direction are positioned such that the courses are at an angle with respect to each other to avoid a linear distribution of the fluid to be received in the channel parts, and allowing a meandering distribution of the fluid to be received in the channel (24, 600).

8.

Anilox roller according to claim 7, wherein the angle is at least 30 degrees, preferably at least 45 degrees, and more preferably at least 90 degrees.

9.

Anilox roller according to any of claims 6 to 8, wherein the meandering channel (24, 600) has

Channel parts (601-605) arranged so that it is impossible to create a straight line of connection between 35 different parts of the channel.

10.

Anilox roller according to any of the preceding claims, the channel (24, 600) having a free path of less than 150 µm, preferably less than 100 µm, more preferably less than 50 µm, the free path being defined as a distance in which a part of the ink can be moved in a radial random direction starting from a random point in a channel until it reaches a wall.

eleven.

Anilox roller according to any of the preceding claims, wherein the channel (24, 600) has a generally flat bottom with a generally equal channel depth, where the bottom has a substantially constant height level difference from the surface of the anilox roller .

12.

Anilox roller according to any preceding claim, wherein the walls of the channel (25, 26, 27) are

positioned from a location in the fluid distribution structure at a radial distance of at most 45 100 µm, preferably less than 80 µm.

13.

Anilox roller according to any of the preceding claims, wherein another channel is provided adjacent to the channel (24), that other channel having a course generally parallel to the channel.

14.

Anilox roller according to claim 12, wherein the walls (25, 26, 27) between the channel (24) and the other channel are less than 4 µm wide, preferably in the range of 1 to 3 µm.

fifteen.

Anilox roller according to any of the preceding claims, the restrictions having a width of less than 8 µm, preferably less than 5 µm, more preferably between 2 and 3 µm.

16.

Printing apparatus comprising a printing device having a supply for printing a substrate and an ink supply, wherein said printing device comprises an anilox roller (2) according to any of the preceding claims mounted on a support.

17.

Printing apparatus according to claim 16, wherein the printing apparatus is a flexographic apparatus.