Coating module for coating a thin ink layer onto a ribbon

Abstract

A coating module for coating a thin layer of ink on a ribbon, comprising: a ribbon (5) with an inner and outer surface, a conveyor system with a support element (21) for holding and transporting the ribbon (20) on its inner surface, a squeeze roller (13) arranged in contact with the outer surface of the ribbon, the squeeze roller (13) having an outer layer (131) made of an elastic material, a reservoir assembly (11) designed to hold ink thereon and to supply said ink to the squeeze roller, and a pressure controller (COp) including an active element (14) for pushing the ribbon between the squeeze roller (13) and the support roller (21) along a coating zone (A).

Description

Technical Field

[0001] The present invention relates to a coating module for thin coatings using all kinds of inks, preferably for a thermal transfer printing device. The present invention also relates to a method of coating a ribbon with ink.

Background Art

[0002] In current solutions including thermal transfer printing devices, disposable pre-coated ribbons are used. One limitation of these solutions is the need to regularly replace the ribbon when the end of the ribbon is reached.

[0003] To cope with the disposal of such used ribbons and the remaining non-transferred ink, in an alternative class of thermal transfer printing devices, an endless ribbon is continuously coated while recovering non-printing ink and exposed to a thermal head.

[0004] Such a solution provides for reusing the remaining portion of the ink not used in the previous thermal transfer printing cycle and reducing the waste generated from the disposable ribbons of the printing device.

[0005] This imposes, among other steps, continuously coating the ribbon with fresh ink to ensure a uniform layer of ink on the ribbon during printing.

[0006] Also, European Patent No. 0412179 teaches an apparatus for re-inking a thermal transfer printer composed of an endless ribbon. The ink is transported by an ink roller having depressions on its circumferential surface and picks up the ink to coat the ribbon. In this solution, the surface of the ink roller is engraved: including a raster (or texture) surface structure. The depth of these cells (or circumscribed cavities) forming the depressions is several μm. A range of about 8 to 25 μm seems to be technically meaningful, and a cell depth of about 15 μm has proven to be particularly advantageous.

[0007] The first limitation of such a coating system is that the cavities impose a choice of particle size ranges within the ink. For example, if the particle size in the ink is larger than the size of the cavities, it is not possible to properly apply the complete distribution of particles within the ink. This solution does not allow for significant variability in the use of various inks.

[0008] The second limitation is that the aforementioned coating system cannot coat the ribbon with a constant thickness at a variable speed.

[0009] A third limitation of this device is that the circumferential surface needs to be cleaned regularly. In fact, such cavities can hold ink, and using the roller surface after several cycles can render it ineffective.

[0010] The fourth limitation is that some inks are not compatible with such coating systems because the ink is transported through the cavities of the ink roller. For example, inks containing colorant particles larger than the size of the cavities are not compatible with that ink roller. In fact, it is impossible to transport particles within the depressions of the ink roller's surface structure. This can also lead to undesirable localized non-uniformity of the ink during coating if the ink contains particles of several different sizes. [Prior art documents] [Patent Documents]

[0011] [Patent Document 1] European Patent No. 0412179 [Overview of the Initiative] [Problems that the invention aims to solve]

[0012] The present invention aims to provide methods and coating modules that circumvent these limitations. The present invention aims to provide a more agile and versatile coating module that enables coating and printing with a wide variety of inks. [Means for solving the problem]

[0013] The present invention relates to a coating module for variable-speed ribbon coating. The coating module comprises a conveyor system for holding and transporting ribbons; and a coater for coating the ribbons with molten ink. The coater includes a squeeze ink roller that carries the molten ink to a circumferential surface. The squeeze ink roller includes an outer layer made of an elastic material.

[0014] The coating module further includes a reservoir assembly designed to hold molten ink on it and to supply the molten ink to the coater. The coating module includes a pressure controller which includes an active element for pressing the squeeze ink roller against the conveyor system and changing the pressure applied to the ink between the squeeze ink roller and the ribbon supported by the conveyor system along the coating zone. The outer elastic material is intended to elastically deform relative to the conveyor system when the squeeze ink roller is pressed against the conveyor system.

[0015] According to one embodiment, the present invention relates to a coating module for variable-speed ribbon coating. The coating module includes a ribbon having an inner and outer surface, a conveyor system having a support element on the inner surface for holding and transporting the ribbon, a squeeze ink roller positioned in contact with the outer surface of the ribbon and having an outer layer made of an elastic material, a reservoir assembly designed to hold ink on it and supply the ink to the squeeze ink roller, and a pressure controller including an active element for pressing the ribbon between the squeeze ink roller and the support roller along a coating zone.

[0016] The advantage of the outer layer of a squeeze ink roller is that it allows for a thin coating of any type of ink on the ribbon. Advantageously, the coating module further enables such coatings when the ribbon is driven at low speeds (e.g., less than 1 m / s).

[0017] In one embodiment, both the surface of the squeeze-ink roller and the surface of the support roller that contacts the ribbon are smooth.

[0018] The advantage of a smooth surface is that less ink is supplied to the coating zone. Another advantage is that, in a plane perpendicular to the longitudinal axis of rotation of the squeeze ink roller or support roller, the stress profile applied to the ink between the squeeze ink roller and the ribbon along the coating zone exhibits a symmetrical bell-shaped or parabolic curve, at least in the central portion of the coating zone. This ensures that the applied stress remains above the threshold that allows for the coating of a thinner ink layer.

[0019] Such operation over a sufficient period of time favorably improves the control of the coating.

[0020] In one embodiment, the circumferential surface of the squeeze roller is smooth. In one embodiment, the circumferential surface of the support roller is smooth. In one embodiment, both the inner and outer surfaces of the ribbon are smooth.

[0021] In one embodiment, the arithmetic mean of the circumferential surface roughness profile of the squeeze-in roller is preferably less than 2 micrometers and less than 0.5 μm.

[0022] In one embodiment, the surface of the squeeze-in roller does not contain rasters with depressions or cavities greater than 5 μm in depth.

[0023] In one embodiment, the outer layer's elasticity, the surface of the squeeze ink roller, and the surface of the support roller are designed such that the stress applied to the ink along the coating zone in a plane perpendicular to the longitudinal axis of the support roller is monotonic on both sides of the maximum value.

[0024] In one embodiment, the pressure controller is configured to control the pressure between the squeeze ink roller and the conveyor system in order to deform the outer layer of the coating zone according to a predefined hardness.

[0025] In one embodiment, the pressure controller is configured to automatically adjust the pressure between the squeeze ink roller and the conveyor system in order to keep the thickness of the ink coated on the ribbon constant when the first speed is changed.

[0026] In one embodiment, the pressure controller is configured to automatically adjust the pressure between the squeeze ink roller and the conveyor system in order to change the thickness of the ink coated on the ribbon while keeping the first speed of the ribbon constant.

[0027] In one embodiment, the coating module includes a speed controller, and the speed controller includes a first motor for controlling the first speed of the ribbon and / or a second motor for controlling the second tangential speed of the squeeze ink roller.

[0028] In one embodiment, the speed controller is configured to automatically adjust the second speed in order to keep the thickness of the ink coated on the ribbon constant when the first speed is changed.

[0029] In one embodiment, the speed controller is configured to automatically adjust the second speed in order to change the thickness of the ink coated on the ribbon while keeping the first speed constant.

[0030] In one embodiment, the speed controller includes instructions to maintain the ratio of the first speed to the second speed within a predetermined range from 0 to 3, preferably between 0 and 0.85, or between 1.1 and 3.

[0031] In one embodiment, the conveyor system includes a conveyor belt for holding and transporting ribbons; the conveyor belt is held and transported by at least two rollers.

[0032] In one embodiment, the conveyor belt is held by rollers along the coating zone.

[0033] In one embodiment, the roller includes an outer surface made of a material that allows the conveyor belt to be driven by friction from the roller.

[0034] In one embodiment, the coater includes a reservoir for holding a thermally molten ink thereon, a reservoir in which a squeeze ink roller contacts the ink in the reservoir, and a coating module further including an ink controller for controlling the angle between the squeeze ink roller and the level of ink in the reservoir.

[0035] In one embodiment, an ink reservoir is positioned to collect excess ink compressed between the ink roller and the ribbon. In one embodiment, the coating module further includes a heater for heating the ink remaining on the ribbon. In one embodiment, the length of contact between the ink roller and the ribbon can be increased by deformation of the outer layer. In one embodiment, the coating module further includes a sensor for measuring the thickness of the ink layer coated on the ribbon.

[0036] The present invention further relates to a thermal transfer printing apparatus including a coating module according to the present invention. The ribbon is an endless ribbon, and the printing apparatus further includes a printhead and conveyor system designed to periodically hold and transport the ribbon from the coater to the printhead.

[0037] The present invention further relates to a method for coating a ribbon. The method includes providing a coating module according to the present invention, providing ink from a reservoir to a squeeze ink roller, transporting the ribbon along a path between a support roller and a squeeze ink roller, heating the ink in contact with both the squeeze ink roller and the ribbon, and applying pressure to the ink between the ribbon and the squeeze ink roller. [Brief explanation of the drawing]

[0038] [Figure 1A] This is a schematic diagram of a coating module according to one embodiment of the present invention. [Figure 1B] This is a schematic diagram of a coating module, including a conveyor belt for transporting ribbons. [Figure 2] This is a schematic diagram of the coating zone. [Figure 3] This is a schematic diagram of a coating module that includes an intermediate roller for transporting ink from the reservoir to the squeeze ink roller. [Figure 4] This is a schematic perspective view of a printing apparatus including a coating module according to one embodiment of the present invention. [Figure 5] This is a schematic diagram of a coating module according to another embodiment of the present invention, the reservoir including means for supplying ink to the circumferential surface of a squeeze ink roller. [Figure 6] This is another schematic diagram of a coating zone according to one embodiment of the present invention. [Figure 7] This graph shows the pressure profile of the ink along the coating zone on a plane perpendicular to the vertical axis of the squeeze ink roller or support roller. [Modes for carrying out the invention]

[0039] The coating module 10 includes a conveyor system 2. The conveyor system 2 is designed to hold and transport the ribbon 20. The conveyor system 2 preferably consists of rollers that directly or indirectly hold and transport the ribbon 20 along a predetermined path.

[0040] At least one of these rollers is a drive roller. The conveyor system 2 includes a motor that rotates the drive roller. The drive roller can control the speed of the ribbon 20.

[0041] (Squeeze Ink Roller) The coater module 10 is intended to coat the ribbon 20 with fused-to-metal ink 12. The coater 1 consists of a squeeze ink roller 13. The squeeze ink roller 13 is designed to transport the fused-to-metal ink 12 along its circumferential surface. The fused-to-metal ink 12 is transported or transferred from the circumferential surface of the squeeze ink roller 13 to the ribbon 20.

[0042] The squeeze ink roller 13 is mounted on a frame and rotates on its own to transport ink to the circumferential surface. In one embodiment, the squeeze ink roller 13 is cylindrical and mounted on the frame of the coating system so as to rotate about its longitudinal axis.

[0043] The squeeze-in roller 13 and the conveyor system are arranged such that the outer surface 51 of the ribbon 20 is in contact with the circumferential surface of the squeeze-in roller 13. It is desirable that the conveyor system includes support elements to support the inner surface of the portion of the ribbon that is in contact with the squeeze-in roller 13.

[0044] The contact between the circumferential surface of the squeeze ink roller 13 and the ribbon 20 creates a coating zone (and nip) where the heat-melted ink is squeezed between the ribbon 20 and the squeeze ink roller 13. The ink is optionally sheared and coated onto the ribbon 20.

[0045] (Support elements and coating zones) The "coating zone" may be defined by a surface or contact area between the ribbon 20 and the squeeze ink roller 13. More preferably, the "coating zone" may be defined by a portion of the circumferential surface of the squeeze ink roller 13 and a portion of the ribbon 20, where the ink layer on the ribbon 20 is mixed with the ink layer on the squeeze ink roller 13.

[0046] The conveyor system 2 has a support 21 for the ribbon 20 on its inner surface, at least along a portion of the coating zone A. By "inner surface," the surface opposite to the squeeze ink roller 13 and / or the surface of the ribbon 20 opposite to the surface of the ribbon 20 coated with ink by the squeeze ink roller 13 should be understood.

[0047] One of the advantages of this support is that it supports the ribbon 20 when the squeeze roller 13 is pressed against the conveyor system 2. When the squeeze roller 13 is pressed against the conveyor system 2 and / or against the support 21, the outer layer 131 made of elastic material undergoes elastic deformation.

[0048] The ribbon on the conveyor system 2 and the squeeze ink roller 13 are positioned to be in contact along the coating zone A, and the molten ink on the squeeze ink roller 13 is compressed between the circumferential surface of the squeeze ink roller 13 and the ribbon 20. The conveyor system 2 and the squeeze ink roller 13 are positioned to create sliding contact between the circumferential surface of the squeeze ink roller 13 and the ribbon 20. This contact is made in such a way that the molten ink can be transferred from the squeeze roller to the ribbon 20. The sliding contact may also be a coating contact.

[0049] In the first embodiment shown in Figures 1A and 1B, the conveyor system 2 includes rollers that support the ribbon 20 along the coating zone A. In the depicted embodiment, the support 21 is a support roller that holds and supports the ribbon 20. Preferably, the support roller 21 holds and supports the ribbon 20 along the coating zone A.

[0050] In one embodiment, the support roller 21 is cylindrical and mounted on the frame so as to rotate around its vertical axis.

[0051] One of the advantages of the support roller 21 is that it drives and / or ensures the movement of the ribbon 20 along the path within the coating zone A.

[0052] In another embodiment not shown, the support includes guides for guiding and supporting the ribbon 20 by its inner surface. The guides are preferably curved guides or partially rounded shape guides.

[0053] In the following description, the term “support roller” is used, but those skilled in the art will understand that this support roller also needs to be replaced with a support plate to support the ribbon within coating zone A. During transport, the ribbon slides along its length relative to the support plate.

[0054] In one embodiment, the coating zone includes an inlet A2 and an outlet A3. Both the inlet A2 and the outlet A3 are defined by the point where the ink 126 is pressed between the ribbon 20 and the squeeze ink roller 13. In one embodiment, the distance between A2 and A3 along a plane perpendicular to the longitudinal axis of the squeeze ink roller is referred to as the "length of the coating zone".

[0055] Figure 2 shows the coating zone of the coating module embodiment.

[0056] The support element 21 is preferably made of metal. One advantage of this metal is that it provides firm support to the squeeze roller, thereby squeezing the ink in the coating zone A.

[0057] (Squeeze Ink Roller outer layer and coating zone) The squeeze-in roller 13 may include an outer layer 131. Preferably, the outer layer 131 is elastically deformable. When the squeeze-in roller 13 comes into contact with the ribbon 20 and presses against the support element 21 of the conveyor system 2 that holds the ribbon, the outer layer 131 elastically deforms.

[0058] The advantage is that it increases the contact area between the circumferential surface of the squeeze ink roller 13 and the ribbon 20. As will be described later, increasing the time that the ink 126 is sheared in contact area A improves the uniformity of the transfer.

[0059] Another advantage is ensuring a level of shear rate to the ink 126 between the ribbon 20 and the squeeze ink roller 13 (i.e., within the nip). The shear applied between the squeeze ink roller 13 and the ribbon 20 allows for the transfer of molten ink from the squeeze ink roller 13 to the ribbon 20.

[0060] Another advantage is the formation of a nip within the coating zone. The coating zone comprises a nip corresponding to the ink layer between the outer layer of the squeeze ink roller and the ribbon 20. In one embodiment, coating zone A is defined by a region where the thickness of the ink within the nip between the outer layer of the squeeze roller and the ribbon 20 is substantially constant. Within the nip, the ink 126 is pressed against the outer surface of the ribbon 20, which is supported by the support roller 21 and the squeeze ink roller 13, thereby coating the surface of the ribbon with ink.

[0061] The ink 126 is squeezed and formed into a film through a nip during the transport of the endless ribbon. The nip can also be defined by a region in which the outer layer elastically deforms upon contact with the ribbon supported by the support roller 21.

[0062] In one embodiment, the outer layer 131 is made of elastomer or rubber. One advantage of elastomer is that it allows for high uniaxial compression, increasing the coating zone A between the circumferential surface of the squeeze ink roller 13 and the ribbon 20. As ink is added to the system, the presence of ink 126 within the nip further increases the length of the coating zone A. When a pressure threshold is reached, the thickness of the ink 126 within the nip reaches its limit, further increasing the length of the coating zone.

[0063] In the first embodiment, the circumferential surface of the squeeze ink roller 13 is formed by an outer layer 131. The molten ink is then transported by an elastic material. Another advantage of the outer layer 131 made of elastomer is that the elastomer has high wettability (degree of wetting), allowing the molten ink to maintain contact with the circumferential surface as a result of intermolecular interactions. The molten ink is driven by the wettability of the circumferential surface of the squeeze ink roller 13, depending on the polarity of the molten ink. In other words, due to intermolecular interactions, the molten ink 122 may temporarily adhere to the circumferential surface of the squeeze ink roller 13 or its outer layer 131.

[0064] The thickness of the outer layer 131 is preferably in the range of 1 mm to 8 mm, and more preferably in the range of 2 mm to 5 mm.

[0065] The outer layer 131 may contain an elastomer or may be made of an elastomer. Preferably, the outer layer is made of or contains rubber (natural rubber or synthetic rubber) such as EPDM rubber (for ethylene propylene diene monomer rubber). In one embodiment, the outer layer is made of or contains HNBR (for hydrogenated nitrile butadiene rubber). One advantage of HNBR is that it has higher thermal and chemical inertia or stability than other synthetic rubbers, improving the lifespan of the outer layer.

[0066] The hardness of the outer layer 131 should preferably be in the range of 30 to 90 on the Shore A scale.

[0067] It is desirable that the hardness of the outer surface of the support roller 21 is better than the hardness of the outer layer 131 of the squeeze-ink roller 13.

[0068] In another alternative embodiment, the squeeze ink roller comprises an outer film (not shown) arranged radially on the outer layer 131. The molten ink is then transported by the outer film. The outer film may be made of an elastomer or of any material that is flexible enough to follow the deformation of the outer layer 131 and has surface tension capable of transporting the molten ink over it. In this embodiment, the outer layer 131 may be positioned on its circumferential surface or around it.

[0069] The circumferential surface of the squeeze roller 13 is preferably not a textured surface. The circumferential surface of the squeeze roller is preferably a smooth surface. The circumferential surfaces of both the squeeze roller and the support roller are preferably smooth surfaces. In one embodiment, the inner and outer surfaces of the ribbon are smooth surfaces.

[0070] The term "smooth surface" must be understood as at least one of the following definitions.

[0071] The term "smooth surface" can be understood as a flat surface.

[0072] The term "smooth surface" can be understood as a surface that does not have any irregularities, creating individual pockets into which ink can be placed.

[0073] The term "smooth surface" can be understood as a surface that does not have a raster or textured surface structure.

[0074] The term "smooth surface" excludes surfaces consisting of multiple depressions designed to be filled with ink, as well as engraved or grooved surfaces. Therefore, the outer layer 131 does not consist of multiple depressions arranged (regularly or irregularly) along its surface.

[0075] In one embodiment, a “smooth surface” should be understood as a surface roughness Ra less than 2 micrometers, where Ra is defined by the arithmetic mean of the deviations from the mean line. A smooth surface roughness Ra is preferably less than 0.5 micrometers.

[0076] In one embodiment, the “smooth surface” should be understood as a surface that includes roughness consisting of cavities with a depth of 8 μm or less, preferably 2 μm or less, which yields better results.

[0077] A smooth surface advantageously allows the ink to be pressed between the ribbon and the outer surface of the squeeze ink roller, improving or influencing the shear stress and / or shear rate experienced by the ink.

[0078] The squeeze ink roller 13 may include a rigid core (also called a "rigid frame"). The outer layer 131 is arranged radially on or outside the rigid core. The rigid core has the advantage of providing rigid support to the outer layer 131 and increasing the squeezing of the ink in the coating zone A. In one embodiment, the circumferential surface of the rigid core is in contact with the outer layer 131. It is desirable that the circumferential surface of the rigid core includes a coating. The coating on the rigid core may have a wettability approximately equal to that of the material of the outer layer 131. One advantage is that ink transport is ensured even if a portion of the outer layer 131 is worn away. If holes are formed through the outer layer 131, the coating on the rigid core ensures wettability of the circumferential surface through the holes formed in the outer layer 131, ensuring ink transport on all circumferential surfaces of the squeeze ink roller. The lifespan of the coating module is then advantageously improved. Preferably, the rigid core is made of a material including metal or a metal alloy such as aluminum.

[0079] According to one embodiment, the squeeze-ink roller 13 is a drive roller. The coating module 10 may further include a motor for rotating the drive squeeze-ink roller 13 and a speed controller COs coupled to the motor. The speed controller COs can then control the rotational speed of the squeeze-ink roller 13. At least one battery or electric power supply may be implemented in the coating module 10 to power the first motor.

[0080] (Reservoir assembly and rollers) The coater module 10 includes a reservoir 11 (also called a reservoir assembly 11). In one embodiment, the reservoir 11 is for holding a molten ink 12 thereon.

[0081] In the first embodiment shown in Figures 1A and 1B, the squeeze ink roller 13 is for contacting the molten ink 12 in the reservoir 11 and transporting the ink to its circumferential surface. The squeeze ink roller 13 can be positioned at least partially within the reservoir 11. By rotation, the squeeze ink roller 13 transports the liquid ink from the reservoir 11 to the ribbon 20. In this embodiment, once the reservoir 11 is filled with ink, a portion of the squeeze ink roller is immersed in the molten ink 12. By rotating the squeeze ink roller 13, a layer of ink 122 is transported along the circumferential surface of the squeeze ink roller 13 toward the nip.

[0082] In the second alternative embodiment shown in Figure 3, the coating module 10 includes one or more intermediate rollers. One intermediate roller is positioned at least partially within the reservoir 11 to be in contact with the ink. One or more rollers transport the ink from the reservoir 11 to the circumferential surface of the squeeze ink roller 13.

[0083] The reservoir 11 may include a heating device for dissolving the ink. In one embodiment, the reservoir 11 may be coupled with a mixing element to maintain the ink in a predetermined physical state, such as temperature or viscosity. The reservoir 11 may be filled with solid ink or molten ink. The coating module 10 may include a device for automatically refilling the reservoir 11 with new ink and / or periodically adding new ink to the reservoir 11.

[0084] In one embodiment, the reservoir 11 is positioned to receive excess ink 125 from the coating zone A.

[0085] Other examples of reservoir assemblies are described below.

[0086] The coating module 10 includes a conveyor system 2. The conveyor system 2 is designed to hold and transport the ribbon 20. As shown in Figure 4, the conveyor system 2 preferably includes rollers 204 that directly or indirectly hold and transport the ribbon 20 along a predefined path. At least one of these rollers may be a drive roller. The drive roller of the conveyor system has a motor that controls the speed of the ribbon and is connected to a speed controller COs. The drive roller is preferably a support roller 21 of the conveyor system 2.

[0087] (Conveyor belt) In one embodiment shown in Figure 1A, the conveyor system 2 includes a conveyor belt 23. The conveyor belt 23 is designed and positioned to hold and transport the ribbon 20 along at least the coating zone A.

[0088] The conveyor belt 23 performs the same function as a continuous track that rotates the ribbon 20 in one direction. In one embodiment, the conveyor belt is an endless conveyor belt. The inner surface of the ribbon 20 is held by the outer surface of the conveyor belt 23. The conveyor belt may be supported and transported by rollers.

[0089] The conveyor belt 23 supports a portion of the ribbon 20 during its movement, reducing the tension along the ribbon 20. This supporting function of the conveyor belt 23 is intended to provide a better distribution of tension on the ribbon 20. The conveyor belt 23 offers greater design flexibility than rollers transporting the ribbon. The conveyor belt 23 can support the ribbon 20 over longer lengths. The tension driving the ribbon 20 can be obtained by the conveyor belt 23 instead of the ribbon 20 itself. Therefore, the tension of the conveyor belt 23 can be high in most cases, unlike the tension of the ribbon 20. Furthermore, using the conveyor belt 23 reduces the risk of wrinkles and slippage of the ribbon 20.

[0090] The conveyor belt 23 may include plastic bands arranged around at least two rollers, preferably at least three rollers. At least one of these rollers is a drive roller. In other embodiments, the conveyor belt 23 may be made of or constructed from any flexible material such as elastomer, thermosetting resin or thermosetting plastic such as polyimide, cork bands, or metal sheets such as stainless steel or titanium. In one preferred embodiment, the conveyor belt 23 is constructed from coated metal bands. The metal bands may be coated with a material that ensures adhesion or bonding to the ribbon 20. The coating preferably includes a plastic material, such as silicone. In such embodiments, the coating ensures adhesion to the ribbon 20 and softness to avoid degradation of the ribbon 20. The metal bands ensure the rigidity of the conveyor belt.

[0091] In one alternative embodiment shown in Figure 1B, the coating module does not have a conveyor belt. The ribbon is transported and supported by rollers 21 of the conveyor system.

[0092] In one embodiment, the support roller 21 of the conveyor system 2 includes an outer film of an elastic material. The thickness of the outer film of the support roller may be 2 cm or less, or 2 mm or less. The thickness of the outer film is preferably between 500 μm and 5000 μm, and more preferably between 2000 μm and 4000 μm. In one embodiment, the outer film of the support is made of EPDM rubber (in the case of ethylene propylene diene monomer rubber) or HNBR (in the case of hydrogenated nitrile butadiene rubber). In one embodiment, the outer film of the support is made of silicone rubber VMQ (for vinyl methyl silicone or vinyl ethyl silicone). One advantage of such silicone rubber is that VMQ can withstand a wide temperature range.

[0093] The outer film of the material can protect the conveyor belt 23 or ribbon 20 from frictional wear caused by the support, thereby advantageously extending the lifespan of the coating module 10.

[0094] (Pressure control) The coating module 10 further includes an active element 14. The active element 14 is designed to press the squeeze ink roller 13 against the support roller 21. Preferably, the squeeze ink roller 13 is pressed against a portion of the ribbon 20 supported by the support roller 21. One advantage is that the pressure deforms the outer layer 131, pressing the ink 126 in the nip against the ribbon 20.

[0095] This pressure allows the ink 126 to be squeezed between the circumferential surface of the squeeze ink roller 13 and the ribbon 20. Advantageously, both parameters can be combined: the pressure and the speed difference between the speed of the ribbon 20 and the tangential speed of the circumferential surface of the squeeze ink roller are advantageous in coating the outer surface of the ribbon 20 with a thin layer of ink.

[0096] One advantage is that the deformation of the outer layer 131 increases the contact zone in which the ink is squeezed between the squeeze ink roller 13 and the ribbon 20.

[0097] The coating module 10 further includes a pressure controller COp, which includes an active element 14 for actively pressing the squeeze roller against the support roller 21 and / or the support of the conveyor system 2. The pressure controller COp can control the force W applied to the squeeze roller 13 against the conveyor system 2 or the support 21 of the conveyor system 2, or vice versa.

[0098] The active element 14 can change the pressure applied to the ink between the squeeze ink roller 13 and the ribbon 20 or conveyor system 2 along the coating zone A.

[0099] The pressure controller COp controls the force W applied to the squeeze ink roller by controlling the active element 14. Controlling the pressure or shear applied to the ink 126 on the coating zone A is advantageous for controlling the thickness of the ink layer coated on the ribbon 20. Another advantage is that the thickness of the ink coated on the ribbon 20 can be kept constant when the speed of the ribbon 20 is changed.

[0100] The pressure controller COp can be configured to control the pressure that deforms the outer layer 131 within the coater zone according to a predetermined hardness or elasticity. The pressure controller COp can control the length of the nip or coating zone A. This length ensures that the circumferential surface of the squeeze ink roller 13 slides over the ribbon 20 within a predetermined time, thereby ensuring the transfer of ink from the squeeze ink roller 13 to the ribbon 20. In fact, higher pressure results in greater elastic deformation of the outer layer 131 and a longer coating zone A.

[0101] The pressure controller COp can be configured to automatically adjust the pressure between the squeeze roller 13 and the ribbon 20.

[0102] The pressure controller COp can be configured to automatically adjust the force W or pressure that changes the thickness of the ink coated on the ribbon 20 while keeping the ribbon speed constant. One advantage is that the thickness of the coated ink 123 can be changed without changing the speed of the ribbon 20 or the tangential speed of the ink roller.

[0103] In one embodiment, the active element 14 may include a linear slide. The squeeze-in roller 13 is mounted to move parallel to the linear slide, and the pressure controller COp can control the position of the squeeze-in roller 13 along the linear slide. The position of the squeeze-in roller 13 can be controlled by a motor, a spring element, or other means known to those skilled in the art to perform this function. Controlling the position of the squeeze-in roller 13 can control the force applied to the squeeze-in roller 13 relative to the support roller 21. Shortening the distance between the center of the squeeze-in roller 13 and the conveyor system 2 (e.g., the center C1 of the support roller 21) increases the force applied to the squeeze-in roller 13.

[0104] The support roller 21 functions as a stopper against the movement of the squeeze-ink roller 21.

[0105] The pressure applied to the ribbon 20 by the squeeze ink roller 13 favorably ensures a shear rate on the ink 126 in the coating zone as the circumferential surface of the squeeze ink roller 13 slides over the ribbon 20. The shear applied between the squeeze ink roller 13 and the ribbon 20 allows the molten ink to be transferred from the circumferential surface of the squeeze roller to the ribbon 20.

[0106] In another example, the active element includes magnetic means that apply force to the squeeze roller 13 in the direction of the conveyor system 2 or in the direction of the support of the conveyor system 2.

[0107] In another embodiment, the pressure controller COp and the active element control the force applied to the support 21 in the direction of the squeeze roller 13.

[0108] (Speed ​​control) In one embodiment, the coating module 10 includes a speed controller COs that operates various components of the coating module 10, including a squeeze ink roller 13 and drive rollers of the conveyor system 2.

[0109] The speed controller COs includes a motor for controlling a first speed U1 of the ribbon 20. As previously stated, it is preferable that the motor be configured to drive the rotation of the support roller 21 or another roller 204 of the conveyor system. The speed controller COs further includes a second motor for controlling the rotational speed of the squeeze-in roller 13. Controlling the rotational speed of the squeeze-in roller allows control of a second tangential speed U2 (also referred to herein as the second speed) of the squeeze-in roller 13. The "tangential speed of the squeeze-in roller" should be understood as the tangential speed of the squeeze-in roller 13 along its circumferential surface, preferably along the coating zone A.

[0110] One advantage is that the speeds of both the ribbon 20 and the squeeze ink roller 13 can be controlled, allowing for the creation of a shear rate in the ink 126 as desired. This shear rate directly depends on the ratio of the first speed U1 of the ribbon 20 to the second speed U2 of the squeeze ink roller 13. It also directly depends on the pressure applied to the ink being compressed between the ribbon 20 and the squeeze ink roller 13.

[0111] In one embodiment, the speed controller COs includes at least one pre-stored program.

[0112] The pre-storage program may include instructions to control the first speed U1 of the ribbon 20 and the tangential speed U2 of the squeeze-in roller 13 so that the speed U2 of the squeeze-in roller 13 is slower or faster than the speed U1 of the ribbon 20. The pre-storage program may also include instructions to maintain a constant ratio of the ribbon speed U1 to the tangential speed U2 of the squeeze-in roller 13.

[0113] The pre-stored program may include instructions to automatically adjust the tangential speed U2 of the squeeze ink roller 13 when the ribbon speed U1 is constant, thereby changing the thickness of the ink layer 124 coated on the ribbon 20. The coating module 10 according to this embodiment has the advantage of being able to change the thickness of the ink on the ribbon 20 at the same speed as the ribbon 20.

[0114] Preferably, the pre-stored program includes instructions to control a first speed U1 of the ribbon 20 so that it is approximately equal to the tangential speed U2 of the squeeze-in roller 13 when implemented by the speed controller COs.

[0115] When the first speed U1 and the tangential speed U2 of the squeeze in roller 13 are equal or approximately equal, damage to the roller is favorably reduced and the lifespan of the coating module is improved.

[0116] For clarity, the diagrams show the direction of rotation or translation, but not the direction vectors.

[0117] (Coating process) Next, the coating process according to the present invention will be described with reference to Figure 7.

[0118] The pressure applied to the ink within the coating zone depends on several factors, including the surface roughness of both the squeeze ink roller 13 and the support roller 21, and the elasticity of the outer layer 131 of the squeeze ink roller 13.

[0119] Because pressure W is applied between the two rollers 13 and 21, the pressure on the ink in coating zone A reaches its maximum value at point A1, which corresponds to the maximum pressure on the ink in the axis, passing through the center C1 of the support roller 21 and the center C2 of the squeeze ink roller 13.

[0120] In one embodiment, the force that generates the pressure W applied to the squeeze roller 13 by the pressure controller is in the range of 40 kPa to 500 kPa.

[0121] The center C1 is preferably defined by the vertical axis of rotation of the support roller 21. The center C2 is preferably defined by the vertical axis of rotation of the squeeze-in roller 13.

[0122] The surfaces of the squeeze ink roller 13 and / or support roller 21 are designed such that the pressure reaches its maximum at point A1, and such pressure applied to the ink on a plane perpendicular to the longitudinal axis of the support roller or squeeze ink roller is designed to be monotonous along the coating zone on both sides of point A1 of maximum pressure.

[0123] In one embodiment, the circumferential surface of the support element (e.g., support roller 21) is a previously defined smooth surface.

[0124] Preferably, from the inlet A2 to the outlet A3 of the coating zone A, the pressure or stress on the ink 126 increases monotonically due to the deformation of the outer layer 131 of the squeeze ink roller, reaching the point A1 of maximum pressure where the deformation of the outer layer 131 of the squeeze roller is maximum, and then decreasing monotonically until the outlet A3 of the coating zone A.

[0125] This pressure profile 141 is achieved by the roughness profiles of both the squeeze roller 13 and the support roller 21, as already described. One further advantage of the elastic outer layer of the squeeze roller is that the applied pressure flattens the outer layer, leading to the described pressure profile.

[0126] In fact, since neither the squeeze-in roller 13 nor the support roller 21 constitutes any recesses or cavities, the pressure profile increases or decreases monotonically up to the point of maximum pressure A1. This roughness avoids obtaining a profile that includes multiple maxima between the two cavities and multiple maxima in the center of each cavity.

[0127] Preferably, the inner surface 52 and outer surface 51 of the ribbon 5 may further include a roughness free of cavities or depressions for holding ink, and may include smooth surfaces as previously defined.

[0128] However, the Young's modulus of the ribbon 20 is much greater than that of the outer layer 131 of the squeeze-in roller 13. For example, the Young's modulus of the ribbon is in the range of 1 to 5 GPa, while the Young's modulus of the outer layer 131 is in the range of 1 to 10 MPa. Therefore, surface irregularities of the ribbon 20 are not a problem. The elasticity of the ribbon 20 allows the ribbon to be flattened within the coating zone.

[0129] Such a pressure profile 141, combined with temperature, contributes to a change in the behavior of the molten ink and is advantageous in reducing the viscosity of the ink.

[0130] In fact, ink exhibits shear-induced viscosity reduction; therefore, the higher the pressure applied to the ink, the lower its viscosity becomes.

[0131] The advantage of the elastic layer on the squeeze ink roller is that the pressure profile applied to the ink between the squeeze ink roller and the ribbon along the coating zone, in a plane perpendicular to the longitudinal axis of rotation of the squeeze ink roller, exhibits a symmetrical bell-shaped or parabolic curve, at least in the central portion of the coating zone A. Therefore, the applied pressure is maintained above a threshold sufficient to reduce the viscosity of the ink for a certain period of time. Reducing viscosity has the advantage of allowing for a thinner ink coating layer on the ribbon at the exit of the coating zone.

[0132] Such pressure applied to the ink 126 over a sufficient length D or time favorably improves coating control and enables coating in very thin layers smaller than 10 μm. Furthermore, this coating can also be performed when the ribbon is driven at low transport speeds of 1 m / s or less.

[0133] In one embodiment, viscosity can also be controlled by adjusting the temperature of the molten ink (as described later).

[0134] In one embodiment, the pressure on the ink can be increased by driving the first speed U1 at a speed different from the second speed U2.

[0135] (Temperature control) In one embodiment, the temperature of the ink transported by the squeeze ink roller 13 is controlled by a first heater. Preferably, the coating module 10 includes a heater for heating the ink on the squeeze ink roller 13. The heater can be positioned inside the squeeze ink roller 13 to heat the ink on its circumferential surface. Controlling the temperature of the ink on the squeeze roller ensures control of the viscosity of the ink on the coating zone A.

[0136] In one embodiment, the temperature of the ribbon 20 on the coating zone A is controlled by a second heater. Preferably, the conveyor system 2 includes a second heater that heats the ribbon from the inside, optionally via the conveyor belt 23. The heater can be located on a support element of the conveyor system 2, such as a support roller 21. Temperature control of the ribbon 20 allows control of the temperature of the ink squeezed between the ribbon 20 on the coating zone A and the squeeze ink roller 13. Optionally, the second heater can also be located along the path of an adjacent ribbon or near the coating zone A. This embodiment advantageously allows heating of the ribbon before it arrives at the coating zone A, improving temperature control of the ink squeezed in the coating zone A.

[0137] The heater advantageously allows for preheating of the support roller 21, the squeeze ink roller 13, and / or the endless ribbon.

[0138] As shown in Figure 5, the conveyor system 2 is positioned such that the ribbon 20 is supported by the support rollers 21 along an angle B that covers the coating zone A and the point of maximum pressure A1.

[0139] The ribbon 20 is supported by the support roller 21 along a distance from the first contact point with the support roller 21 to the point of maximum pressure A1 along an angle B1. Along this distance, the remaining ink 122 is heated by the support roller 21 as described above.

[0140] The ribbon 20 is supported by the support roller 21 until it separates from the support roller 21 along angle B2 from the point of maximum pressure. Along this distance, the layer of coated ink 124 is heated by the support roller via the ribbon 20. Heating the layer of coated ink after passing through coating zone A is advantageous in melting and maintaining the ink layer and improving the uniformity of the layer of coated ink 124.

[0141] Preferably, angle B1 is in the range of 10° to 90°.

[0142] Preferably, angle B2 is in the range of 10° to 90°.

[0143] The angle B1 directly depends on the relative position of the support roller 21 with respect to the front roller Y of the conveyor system 2 that supports the ribbon 20.

[0144] The angle B2 directly depends on the relative position of the support roller 21 with respect to the subsequent roller Z of the conveyor system 2 that supports the ribbon 20.

[0145] The terms “front roller” and “following roller” used herein should be understood as the nearest rollers of the conveyor system 2 that support the ribbon 20, before and after the support roller 21, respectively, depending on the direction of transport of the ribbon 20.

[0146] In one embodiment shown in Figure 4, the coating module 10 includes a thermal enclosure. The thermal enclosure may include an isolation wall 205. The thermal enclosure is positioned to thermally isolate the coating module 10. An opening can be controlled within the thermal enclosure for the ribbon 20 to pass through.

[0147] The thermal enclosure can improve temperature control of the ink 126 compressed or positioned between the ribbon 20 and the squeeze ink roller 13. This temperature control advantageously ensures uniform viscosity of the molten ink compressed in coating zone A, improving control of the thickness of the ink coated on the ribbon 20.

[0148] The heater controlling the temperature in this zone is preferably connected to controllers COs and COP. Temperature control is advantageous for controlling the viscosity of the molten ink 12 in coating zone A and improves coating control.

[0149] (Nip between rollers) The reservoir assembly may include any means designed and arranged to store molten or solid ink thereon and to supply the ink in a molten state to the circumferential surface of the squeeze ink roller.

[0150] Another embodiment of the coating module according to the present invention will be described below with reference to Figure 5.

[0151] In this embodiment, the reservoir assembly includes a device 111 for applying ink to the outer surface of the squeeze ink roller. In one embodiment, the device 111 may include a slot die device.

[0152] In one embodiment, contact between the squeeze ink roller 13 and the ribbon 20 supported by the support roller 21 provides an ink melt pool 61. The ink melt pool 61 is the excess amount of molten ink at the junction between the ribbon supported by the support roller 21 and the squeeze ink roller 13. In fact, if the amount of molten ink supplied to the coating zone (by both the molten ink 122 supplied by the squeeze ink roller 13 and the residual ink 123 supplied by the ribbon) is greater than the amount of ink (121, 124) coming out of the nip, the excess ink accumulates in the ink melt pool 61.

[0153] Creating such an ink melting pool 61 advantageously improves the quality of the coating. In fact, it can create an ink buffer volume and compensate for occasional fluctuations in the amount of ink supplied to the coating zone A, and furthermore, it advantageously promotes the melting of residual ink 123 in the ribbon 20 as the ink is submerged by the melted ink.

[0154] The nip contains ink in the coating zone between the squeeze ink roller and the support roller, and further includes an ink melting pool 61 that is fluidly connected to the ink in the coating zone.

[0155] Another advantage is that the speed of ribbon U1 can be rapidly accelerated without losing molten ink within the nip.

[0156] Such an ink melting pool 61 is common to all embodiments described herein and is not limited to this reservoir assembly.

[0157] In one embodiment, the reservoir assembly 11 further includes an ink sensor (not shown). The ink sensor is designed to detect when the level of molten ink in the ink melt pool 61 reaches a predetermined threshold. Preferably, the reservoir assembly 11 further includes an ink controller. The ink controller is configured to receive signals from the ink sensor, including data sensed by the ink sensor. The ink controller is configured to control the amount of ink 122 added to the ink melt pool 61 by the squeeze ink roller 13.

[0158] In one embodiment, the device 111 includes means for automatically adding new solid ink to the molten ink reservoir 11 when instructed by an ink sensor.

[0159] In another embodiment, the apparatus 111 includes means for melting a portion of the solid ink, and is arranged so that the melted ink is dropped onto the outer surface of the squeeze ink roller or into the ink melt pool 61. The dropping device may include means for automatically adding new melted ink to the ink melt pool 61 when instructed by an ink sensor.

[0160] This embodiment has the advantage that the amount of ink melted can be controlled to decrease or increase the ink level in the ink melting pool 61.

[0161] The second threshold preferably corresponds to an ink level higher than the level of molten ink in the ink melting pool 61 that corresponds to the first threshold.

[0162] The ink sensor may include a weight sensor. In another embodiment, the ink sensor includes an optical sensor. The optical sensor may include a light emitter and a receptor that receives light generated by the light emitter and reflected by the surface of the liquid ink in the reservoir. The optical ink sensor may be configured to determine the level of liquid ink in the reservoir by the time of flight of the detected light.

[0163] In another embodiment, the ink sensor includes at least two electrodes positioned to measure electrical conductivity. Preferably, one electrode is positioned to be partially immersed in the liquid ink in the ink melting pool 61, and at least one second electrode is positioned to be in contact with the liquid ink at a predetermined level of ink in the ink melting pool 61. Thus, the level of ink in the ink melting pool 61 depends on the electrical conductivity measured between the two electrodes. The ink sensor may include a plurality of second electrodes, each positioned to be in contact with the molten ink at another predetermined level of ink in the ink melting pool 61. Detection of electrical conductivity between the first and second electrodes advantageously means that the level of ink in the ink melting pool 61 has reached a predetermined threshold associated with this second electrode.

[0164] The ink sensor may also include a capacitive sensor that measures the level of ink in the ink melting pool 61. The ink controller may be associated with a memory connected to the ink controller. The memory, when executed by the controller, includes instructions that provide the controller to implement the described method.

[0165] The ink controller can be associated with memory. This memory is connected to the ink controller. When executed by the controller, this memory contains instructions that provide the controller to implement the described method.

[0166] In another embodiment, the reservoir assembly includes a container for holding elements of solid ink, and the reservoir assembly further includes means for transporting at least one element of solid ink from the container to the ink melting pool 61. As in the previous embodiment, the means for transporting the elements of solid ink can be controlled by an ink controller. In this way, when a sensor detects that the level of molten ink in the ink melting pool 61 has reached a predetermined threshold, the elements of solid ink are transported into the ink melting pool 61.

[0167] In another embodiment, the ink controller is configured to control the ink in the molten ink reservoir shown in Figures 1A and 1B, and to control the amount of new ink added to such reservoir.

[0168] (Printing device) In another aspect, the present invention relates to a thermal transfer printing apparatus including a coating module 10, as described herein. A thermal transfer printing apparatus according to one embodiment of the present invention is shown in Figure 4.

[0169] The printing apparatus may include a print head and a conveyor system 2 for transporting the ribbon 20 from the coater to the print head. Preferably, the conveyor system 2 periodically transports the printed ribbon 20 from the print head to the squeeze ink roller 13, as shown in Figure 4. The conveyor system may include a support roller 21 for the coating module and a plurality of rollers for holding and supporting the ribbon 20.

[0170] When the ribbon 20 comes into contact with the substrate 202 on which it is printed, some of the ink is transferred from the ribbon 20 to the substrate 202. The portion of the ribbon from which the ink has been partially removed during the transfer printing process is then transported back to the coater for repainting or re-inking.

[0171] In one embodiment, the data to be printed by the print head is received from memory. It is desirable that the data flow be ordered by a computer as a function of the printing speed. The data can be modified during the printing process while the ribbon 20 and the substrate 202 continue to move at the same speed.

[0172] In one example, a controller might receive commands from a control interface, such as instructions or settings for turning buttons on or off or for printing modes.

[0173] The printing apparatus 200 includes a print head 101. In one preferred embodiment, the print head 101 is a thermal transfer print head.

[0174] In the first mode, the print head contacts the inner surface of the ribbon 20, enabling thermal transfer of ink located on the outer surface of the ribbon 20. During this printing process, the outer surface of the ribbon 20 is in contact (preferably under pressure) with the substrate 202, transferring the ink on the substrate to be printed.

[0175] In the second mode, the print head 101 does not contact the ribbon 20. This mode may be activated when the printer is switched off or between two consecutive print sequences. Alternation between the first and second modes may be configured by the print mode.

[0176] At least one printing roller 203 can be used to transport the substrate 202 close to the ribbon 20. A thermal transfer print head 101 is preferably located close to the substrate 202 and is used to transfer a coating layer of ink 124 from the ribbon 20 to the substrate 202. The arrangement between the print head 101, ribbon 20, and substrate 202 can be ensured by mechanical components precisely set according to the desired printing accuracy. Several guides and position control components may be implemented to ensure a predetermined arrangement at least between the print head 101 and the ribbon 20.

[0177] The print roller 203 ensures sufficient pressure on the substrate 202 to keep it in contact with the ribbon 20 during the printing process. In this configuration, during the printing process, the ribbon 20 is maintained in a moving sandwich layer between the substrate 202 and the print head 101. The movement of the substrate 202 is in the same direction as the displacement direction of the ribbon 20 near the print head. This movement near the print head is preferably linear.

[0178] The ribbon 20 of the coating module 10 preferably forms a loop. In this configuration, residual ink 123 that was not used during the printing process is transported from the print head to the coating zone A and re-inked. Therefore, the same ribbon 20 is used continuously for transporting the printing ink and for transporting the residual ink to the first re-coating area after printing. This printing process is implemented to form a continuous loop process (i.e., a cyclical method) in which residual ink is automatically reused. This configuration allows for the reuse of ink that was not printed.

[0179] One advantage is to provide an autonomous printing device in which at least some, preferably 100% or substantially 100% of the ink is used, that is, in particular, ink is not lost during multiple cycles.

[0180] Ribbon 20 can be made from a variety of materials. Ideally, Ribbon 20 should be made from a material with high heat resistance, such as heat resistance up to 300°C, and high chemical resistance, such as resistance to alcohols, inks, solvents, and other chemicals. Polyimide is preferable for Ribbon 20, as it allows for use in temperatures within a range of [340°-380°] without deformation. Ribbon 20 may also be made from metal or a metal alloy such as titanium alloy.

[0181] Ribbon 20 should preferably be made of a material with a heat transfer coefficient exceeding 0.120 watts / meter-kelvin.

[0182] The thickness and composition of the ribbon material are designed to create heat transfer through the ribbon 20, enabling printing.

[0183] The thickness of the ribbon 20 is preferably less than 50 μm or 20 μm. This thickness advantageously allows for better heat conduction through the ribbon. The thickness of the ribbon 20 can be substantially between 0.5 μm and 50 μm, most preferably between 0.5 μm and 20 μm. In one example, the thickness of the ribbon 20 is selected in the range of [3-25 μm] or [5-10 μm].

[0184] Ribbon 20 is designed to hold molten ink on its outer surface. The outer surface of ribbon 20 is designed to hold ink on its surface.

[0185] For this purpose, the ribbon is a non-porous ribbon. It is desirable that the ribbon or its outer surface is sealed to the fluid. Even when the ribbon 20 is pressed between the squeeze ink roller 13 and the support roller 21, the composition of the ribbon 20 allows ink to penetrate into the volume of the ribbon 20. In another embodiment, the width of the ribbon is greater than the width of both the support roller and the squeeze ink roller. Therefore, during coating, the inner surface of the ribbon does not contain ink that is harmful to the print head.

[0186] In one embodiment, the ribbon does not include any fabric or cloth.

[0187] (Reservoir control) In the embodiments shown in Figures 1A and 1B, the amount of ink transported by the squeeze ink roller 13 depends on the angle between the circumferential surface of the squeeze ink roller 13 and the ink level in the reservoir 11. The coating module 10 preferably includes a level controller COi to control the angle between the level of the molten ink in the reservoir 11 and the circumferential surface of the squeeze ink roller 13. The level controller COi may include a device that automatically adds new ink to the reservoir 11 depending on the ink level and the angle formed between that level and the squeeze ink roller 13. In another embodiment, the level controller can control the position of the reservoir 11 relative to the squeeze ink roller 13. The angle between the circumferential surface of the intermediate roller and the ink level in the reservoir 11 should also be understood when the intermediate roller transports the molten ink from the reservoir 11 to the squeeze ink roller 13.

[0188] In one embodiment, the angle between the circumferential surface of the squeeze ink roller and the molten ink level in the reservoir 11 is defined by the angle between the horizontal axis and the tangent to the surface of the squeeze ink roller at the point of contact with the molten ink.

[0189] The speed controller COs, pressure controller COp, and / or level controller COi each contain hardware processors and software that control the speed of the ribbon 20 and the squeeze ink roller 13, and control the force applied to the squeeze ink roller 13 to squeeze the ink on the coating zone A, or control the ink level in the reservoir 11.

[0190] (operation) This section describes the operation of the coating module 10 in accordance with the above explanation.

[0191] In the first stage, the squeeze ink roller 13, which is in contact with the ribbon, transports some ink on its circumferential surface to the ribbon. The squeeze ink roller may be in contact with the molten ink in the reservoir 11, or it may be in contact with one or more intermediate rollers that transport the molten ink from the reservoir 11 to the circumferential surface of the squeeze ink roller 13.

[0192] In the second stage, the molten ink is transported to the coating zone A by the squeeze ink roller 13. Along the coating zone A, the tangential direction of movement of the squeeze ink roller 13 is substantially the same as the direction of movement of the ribbon. The ribbon 20 may be transported by the conveyor system 2 at a first speed U1 that is less than or greater than the tangential speed U2 of the squeeze ink roller 13. Preferably, the ribbon 20 may be transported by the conveyor system 2 at a first speed U1 that is equal to or approximately equal to the tangential speed U2 of the squeeze ink roller 13. Furthermore, a force is applied to the squeeze ink roller 13. This force is applied in the direction of the coating zone A or in the direction of the support roller 21 of the ribbon 20. Then, the thickness of the ink 126 in the coating zone A is squeezed and coated between the ribbon and the squeeze ink roller 13.

[0193] The difference in speed and / or pressure generates a shear force, which causes the ink to move from the squeeze ink roller 13 to the ribbon 20.

[0194] As shown in Figure 2, the squeeze ink roller 13 provides new ink 122 to the coating zone A. In one embodiment, residual ink 123 already present on the endless ribbon as residual ink from a previous printing operation is also provided to the coating zone by the ribbon 20. Due to the pressure profile on the nip, the ink is split between the ribbon 20 and the squeeze ink roller 13: a first portion of the ink 121 remains on the squeeze roller, and a second portion of the ink thinly coats the ribbon 20, forming a plain layer of ink 124 that spreads across the outer surface of the ribbon 20.

[0195] The thickness of the ink layer 123 coated on the ribbon 20 depends on the kinematic viscosity of the ink on the coating zone A, the rate of velocity variation between the ribbon velocity U1 and the tangential velocity U2 of the squeeze roller, the radius of curvature of the ribbon 20 along the coating zone A, and the force W applied to the squeeze roller.

[0196] In a preferred embodiment, the length of the coating zone when force is applied to the roller is at least 1 mm, preferably between 1 mm and 7 mm.

[0197] Therefore, the pressure controller COp and / or speed controller COs can adjust the rate of speed variation between the ribbon speed and the tangential speed of the squeeze roller in order to adjust the force applied to the squeeze roller and / or change the thickness of the ink coated on the ribbon.

[0198] If the coating module 10 is included in the thermal transfer printing apparatus, the portion of the ribbon 20 coated with ink 124 that has emerged from the coating zone A is transported to the print head by the conveyor system 2 for printing. During printing, some of the ink 124 is thermally transferred to the substrate, while the remaining untransferred ink remains on the ribbon 20.

[0199] The remaining unprinted ink 123 is then transported by the ribbon 20 to the coating zone A, where it is coated again, providing ink rejuvenation. In one embodiment, the remaining ink 123 on the ribbon 20 is heated between the print head and the coating zone A, preferably above its melting point. Heating the remaining ink 123 advantageously melts the ink, providing liquid ink to the ribbon on the coating zone A.

[0200] One advantage of the present invention is that it is possible to handle the thickness of the layer of ink 124 coated on the ribbon regardless of the amount of remaining ink 132 on the ribbon that reaches the coating zone A.

[0201] In one embodiment, excess ink 125 in coating zone A is returned to reservoir 11 during coating. One advantage is that all ink not printed on the substrate is reused, reducing ink loss.

[0202] The present invention has the advantage that the thickness of the ink layer 124 coated on the ribbon 20 can be controlled by adjusting the respective speed ratios of the ribbon and the squeeze ink roller 13, and / or by adjusting the pressure between the squeeze ink roller 13 and the ribbon on the coating zone A.

[0203] In one embodiment, the coating module includes at least one thickness sensor for measuring the thickness of the layer of ink 124 coated on the ribbon 20. The sensor may include an optical sensor or a camera. The thickness sensor may be connected to a speed controller COs and / or a pressure controller COp to provide information about the thickness of the layer of ink 124 coated on the ribbon 20. In one embodiment, the speed controller COs may adjust a first speed and / or a second speed U2 and / or the ratio of the first speed to the second speed U2 in accordance with the information provided by the thickness sensor. In one embodiment, the pressure controller COp may adjust the force applied in accordance with the information provided by the thickness sensor.

[0204] In one embodiment, the operation of the thermal transfer printing apparatus comprises two modes.

[0205] The first mode is a startup mode in which the ribbon is coated with a coater without performing the printing process, and the second mode is an operation mode in which the print head thermally transfers a portion of the ink on the ribbon onto the substrate.

[0206] The first mode operates when the thermal transfer printer is booted up, while the ribbon is not yet coated.

[0207] During the first mode, the coating module must reach its operating temperature before starting. The squeeze roller may be brought into contact with the ribbon. The speed of the ribbon and the tangential speed of the squeeze roller are increased to a predetermined fixed speed. During this increase, the squeeze roller "wets" with the molten ink, coating the ribbon with the molten ink. In one embodiment, the speed of the squeeze ink roller and the ribbon increase at approximately the same speed.

[0208] In one embodiment, at a fixed predetermined speed, the ratio of the ribbon speed to the tangential speed of the squeeze roller is fixed to a first predetermined ratio. In one embodiment, the first ratio is in the range of 0.95 to 1.05.

[0209] In the first mode, the force applied to the squeeze roller 13 is fixed to a first predetermined force. In one embodiment, the first predetermined force is in the range of 0.005 to 4N of the ribbon width.

[0210] In the first mode, no printing takes place. Therefore, when the ribbon completes one cycle and returns to coating zone A, all the ink coating the ribbon as it exits coating zone A remains. The purpose of the first mode is to "wet" the squeeze ink roller and ribbon with heat-melt ink.

[0211] Initially, because the ink temperature and viscosity are not stable, the first mode is executed until the amount of ink on the ribbon entering coating zone A is equal to the amount of ink on the ribbon exiting coating zone A.

[0212] In the second operating mode, the ribbon speed is adjusted to achieve the printing speed. The printing speed is faster than the predetermined startup speed. The operating ribbon speed is preferably in the range of 0.05 m / s to 10 m / s, and preferably in the range of 0.1 m / s to 5 m / s. Next, the tangential speed of the squeeze ink roller is adjusted over the transition time to obtain shear conditions favorable for coating.

[0213] In one embodiment, the ratio of the ribbon speed to the squeeze-in roller 13 speed is also adjusted to reach a second predetermined ratio. In one embodiment, the second predetermined ratio is in the range of 0 to 0, 85, or 1, 1 to 3. One advantage of such a predetermined speed ratio, including a configuration of ribbon speed different from the squeeze-roller speed, is that it can create a shear speed in the coating zone. Such a ratio enables the coating of the ribbon 20. In the second mode, the force applied to the squeeze-in roller 13 on the ribbon or support roller is fixed to a second predetermined force. In one embodiment, the second predetermined force is in the range of 0.005 N to 0.2 N per mm of ribbon width, or in the range of 0.1 N to 4 N per mm of ribbon width. The force directly changes the thickness of the outer layer 131 of the squeeze-in roller 13 due to its elasticity or flexibility. Subsequently, the angular velocity of the squeeze-in roller is controlled to reach a velocity tangential to the target (which also depends on the radius of the squeeze-in roller and the thickness of the outer layer).

[0214] In one embodiment, the level controller COi automatically adjusts the ink level on the reservoir 11 during the first mode by automatically supplying new ink to the reservoir 11. When entering the second mode, excess ink on the coating zone A is returned to the reservoir 11. The ink level must be controlled by the level controller COi. It is desirable that the level controller COi be equipped with a sensor for monitoring the ink level in the reservoir 11.

[0215] In one embodiment, the controller includes a pre-stored program that includes instructions for operating the coating module 10 according to a first mode and operating the coating module 10 according to a second mode. The coating module 10 may include automatically executing the first mode when the coating module 10 is started. In one embodiment, the controller automatically executes the second mode after a predetermined time has elapsed since executing the first mode. In another embodiment, the coating module 10 automatically executes the second mode when the stability of the coating is detected.

[0216] The term "ink" as used herein includes, but is not limited to, all types of coating materials.

[0217] In conclusion, the present invention and the embodiments described provide a coating module for coating ribbons. In contrast to other coating modules of the prior art, the particular structure of the coating module of the present invention allows for the uniform coating of thin ink layers (e.g., less than 10 μm) with any type of ink.

Claims

1. A ribbon having an inner surface (52) and an outer surface (51), wherein the outer surface is designed to hold ink on its surface, A conveyor system (2) including a support element (21) that holds the ribbon (20) on its inner surface (52) for transport, A squeeze roller (13) positioned in contact with the outer surface (51) of the ribbon, the squeeze roller (13) having an outer layer (131) made of an elastic material, A reservoir assembly (11) is provided thereon, which is designed to hold the ink and supply the ink to the squeeze ink roller. The system includes a pressure controller (COP) which includes an active element (14) for pressing the ribbon (20) between the squeeze roller (13) and the support element (21) along the coating zone (A), A coating module (10) for variable-speed ribbon coating is configured such that the pressure controller (COP) automatically adjusts the pressure (W) between the squeeze in roller (13) and the conveyor system (2) when the first speed (U1) of the ribbon is changed.

2. The coating module (10) according to claim 1, wherein the outer layer (131) of the squeeze ink roller (13) includes an elastomer.

3. The coating module (10) according to claim 1 or claim 2, wherein the outer surface of the ribbon is a flat surface without any cavities or depressions.

4. The coating module (10) according to claim 3, wherein the surface of the support element (21) and / or the squeeze ink roller (13) that contacts the ribbon (20) is a flat surface without cavities or depressions.

5. The coating module (10) according to any one of claims 1 to 4, wherein the arithmetic mean of the roughness profile of the circumferential surface of the squeeze roller (13) is less than 2 micrometers.

6. The coating module (10) according to any one of claims 1 to 4, wherein the surface of the squeeze ink roller does not contain rasters of depressions or cavities having a depth of more than 5 μm.

7. The coating module (10) according to claim 1, wherein the elasticity of the outer layer (131) of the surface of the squeeze ink roller (13) and the surface of the support element (21) is designed such that the stress applied to the ink (126) along a coating zone (A) in a plane perpendicular to the longitudinal axis of the support element (21) is symmetrical on both sides of the maximum value (A1).

8. The squeeze roller (13) comprises a rigid core, The coating module (10) according to any one of claims 1 to 7, wherein the outer layer (131) is arranged radially on the outside of the rigid core.

9. The coating module (10) according to claim 1, wherein the ribbon is made of polyimide.

10. The coating module (10) according to claim 1, wherein the pressure controller (COP), which includes communication means, is a means for receiving commands and is configured to automatically adjust the pressure (W) between the squeeze roller (13) and the conveyor system (2) when a command is received by the pressure controller (COP).

11. A coating module (10) according to any one of claims 1 to 10, comprising a speed controller (COs), wherein the speed controller (COs) comprises a first motor for controlling a first speed (U1) of the ribbon (20) and / or a second motor for controlling a second tangential speed (U2) of the squeeze in roller (13).

12. The coating module (10) according to claim 1, wherein the thickness of the outer layer is in the range of 1 mm to 8 mm.

13. The coating module (10) according to claim 1, wherein the hardness of the outer layer is in the range of 30 to 90 on the Shore A scale.

14. Furthermore, the coating module (10) according to claim 1 includes a heater for heating the ribbon (20) within the coating zone (A).

15. To provide a coating module (10) according to any one of claims 1 to 14, To provide the ink from the reservoir to the circumferential surface of the squeeze ink roller (13), Transporting the ribbon (20) along the path between the support element (21) and the squeeze roller (13), The ink (126) is heated by bringing it into contact with both the squeeze ink roller (13) and the ribbon (20), Applying pressure to the ink between the ribbon (21) and the squeeze ink roller (13), The pressure controller (COP) automatically adjusts the pressure (W) between the squeeze roller (13) and the conveyor system (2) when the first speed (U1) of the ribbon is changed. How to coat a ribbon containing [something].

16. The method further includes forming an ink melt pool (61) between the squeeze ink roller (13) and the ribbon (20), The method for coating a ribbon according to claim 15, wherein the ink melting pool (61) is formed at the entrance of the coating zone (A) at the joint between the ribbon (20) supported by the support element (21) and the squeeze ink roller (13).

17. A thermal transfer printing apparatus (200) comprising a coating module (10) according to any one of claims 1 to 14, The ribbon (20) is an endless ribbon, The printing apparatus further includes a thermal transfer printing apparatus (200) comprising a print head (101) and a conveyor system designed to hold and transport the ribbon (20) from the coating zone (A) to the print head (101) and from the print head (101) to the coating zone, and to recoat the ribbon.

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