Method and apparatus for creating a flatbed screen print

Abstract

A method for producing a flatbed screen print on objects such as textiles, films, plastics, metallic, glass and / or wooden objects, paper, cardboard, etc., in which a liquid printing agent is applied to a printing fabric (1) and deposited as a defined layer of printing agent on the printing fabric (1) by means of a movable squeegee (6), and a force is exerted on the printing fabric (1) by means of a squeegee (5), causing it to deform elastically and bringing the defined layer of ink into contact with the object to be printed, characterized in that the squeegee (6) and the squeegee are moved together over the printing fabric (1) in their respective working positions, and a printing agent chamber (4) filled with the liquid printing agent is moved along with the squeegee (6) and the squeegee (5).that the liquid printing medium is supplied to the printing fabric (1) at an adjustable pressure via a chamber outlet (9) during the forward movement of the flood squeegee (6) and the printing squeegee (5), spatially in front of the flood squeegee (6) and the printing squeegee (5), that the outlet (9) of the printing medium chamber (4) can be controlled and closed, that the printing squeegee (5), which is spatially arranged behind the flood squeegee (6) with respect to the forward movement of the flood squeegee (6) and the printing squeegee (5), exerts the force on the printing fabric (1) during the forward movement of the flood squeegee (6) and the printing squeegee (5), and that the defined ink layer comes into contact with the object to be printed.

Description

[0001] The invention relates to a method for producing a flatbed screen print on objects such as textiles, films, plastics, metallic, glass and / or wooden objects, paper, cardboard, etc., in which a liquid printing agent is applied to a printing fabric and deposited as a defined layer of printing agent on the printing fabric by means of a movable squeegee, and a force is exerted on the printing fabric by means of a squeegee, whereby it is elastically deformed and the defined layer of ink comes into contact with the object to be printed.

[0002] Furthermore, the invention relates to a device for creating a flatbed screen print on objects according to the preamble of claim 12.

[0003] Methods for creating flatbed screen prints have been known for a very long time. In the conventional way, a stencil is made, and a specific amount of printing medium, often ink, is applied to this stencil. Using a squeegee, the printing medium can be evenly distributed across the surface of the screen with minimal pressure. Then, using a squeegee, the printing medium is transferred to the object to be printed, specifically to the areas where the mesh of the screen is open and not closed by a stencil. High-modulus screens, made of either special synthetic materials or very fine steel mesh, are used as stencil carriers.

[0004] The printing medium to be transferred has a certain viscosity so that it can be forced through the mesh of the printing fabric. This viscosity is conventionally adjusted using various solvents such as chlorinated hydrocarbons, distilled water, or similar substances. In the known method, the back-and-forth movement of the squeegee and pressure pad leads to an unwanted and uncontrollable evaporation rate of solvents. This makes it difficult to release untransferred printing medium from the mesh of the printing fabric, resulting in adhesion to the fabric that hinders accurate reproduction of the printed image. This also creates an excess of printing medium, leading to thickening. To dissolve this thickening, the printing medium is, for example,fed back into the printing process, which in turn leads to a change in the viscosity of the printing medium being processed, as old printing medium then mixes with fresh printing medium.

[0005] Conventional methods utilize a doctor blade traverse to which the flooding doctor blade and the pressure doctor blade are attached. Each blade is driven by a motor to perform forward and reverse movements. In this process, the pressure doctor blade is positioned in front of the flooding doctor blade when moving forward. At the start of a printing operation, the flooding doctor blade lowers onto the surface of the printing fabric while the pressure doctor blade is raised. With the flooding doctor blade positioned at the bottom and the pressure doctor blade at the top of the traverse, the flooding doctor blade moves from its starting position to its final operating position (forward movement). During this movement, the flooding doctor blade moves a bead of printing fluid as a rotating mass, depositing a defined layer of printing fluid onto the printing fabric. At the final operating position, the flooding doctor blade rises to its upper position, and the pressure doctor blade lowers.During the reverse movement from the end position to the starting position (reverse movement), a defined force is exerted on the printing fabric via the doctor blade, causing it to deform elastically and come into contact with the object to be printed. The bead of printing medium is also transported to the starting position in a fluid rotary motion. However, the static pressure of the doctor blade cleanly removes the printing form. The doctor blade then lifts to the upper position, allowing the process to begin again. The printing process requires both a forward and a reverse movement at a limited speed to ensure that all process parameters are maintained during both movements.

[0006] The doctor blade speed on modern flatbed machines is typically around 1 to 2 meters per second. During this movement, there is ample time for the solvent to evaporate. Due to the release of printing agent from the mesh, increasing the speed is hardly possible with conventional methods and machines. In many cases, cleaning the mesh requires the use of a chloride hydrocarbon, which an operator must pass over a cleaning device, such as a cleaning cloth. This exposes the operator to a significant amount of pollutants.

[0007] DE 11 205 001 680 T5 discloses a method and a device for screen printing, wherein the printing medium is introduced through an outlet from a printing medium chamber into a space bounded by two squeegees. DE 11 2012 004 675 discloses a screen printer and a screen printing method, with a squeegee head comprising a squeegee unit, wherein here too the printing medium is introduced through an outlet from a printing medium chamber into a space bounded by two squeegees.

[0008] The object of the present invention is to improve a method and a device of the type mentioned above, in particular also with the aim of increasing the speed of the printing process, also from the point of view of minimizing the time in which solvents contained in the printing medium can evaporate and with the further aim of avoiding or significantly reducing the filling of meshes of the printing medium fabric.

[0009] To solve this problem, the method of the type mentioned above provides that the flood squeegee and the printing squeegee are moved together over the printing fabric in their respective working positions, and that a pressure medium chamber filled with the liquid printing medium is moved along with the flood squeegee and the printing squeegee; that the liquid printing medium is supplied to the printing fabric at an adjustable pressure via a chamber outlet during the forward movement of the flood squeegee and the printing squeegee, spatially in front of the flood squeegee; that the outlet of the pressure medium chamber can be controlled and closed; that the printing squeegee, which is spatially arranged behind the flood squeegee with respect to the forward movement of the flood squeegee and the printing squeegee, exerts the force on the printing fabric during the forward movement of the flood squeegee and the printing squeegee, and that the defined ink layer comes into contact with the object to be printed.

[0010] In the method according to the invention, the flooding squeegee and the pressure squeegee are thus both in their working positions and in operation immediately after the start of the forward movement during the forward travel. The printing process begins, with the flooding squeegee and pressure squeegee arranged at a small distance from each other. The outlet of the pressure medium chamber is located upstream of the flooding squeegee, so that at the beginning of a printing process, the liquid pressure medium is initially supplied directly in front of the flooding squeegee. The method can be designed such that, upon commencement of the printing process, the outlet of the pressure medium chamber is opened by the movement of a closure element.The pressure squeegee is positioned immediately behind the flood squeegee, so that during further movement of the flood squeegee, the pressure squeegee, and the pressure medium chamber, the pressurized liquid printing medium continues to be supplied, distributed by the flood squeegee, and then forced directly behind it by the pressure squeegee into the mesh of the printing fabric and subsequently transferred to the object to be printed. For this purpose, the pressure squeegee, the flood squeegee, and the pressure medium chamber are preferably mounted on a common chamber squeegee traverse, forming a single chamber squeegee unit.

[0011] Overall, this allows for the creation of very fine screen layers. The solvents present in the printing medium have hardly any time to evaporate, which also prevents significant amounts of liquid flooding medium from remaining in the mesh of the printing fabric. The liquid printing medium can be fed into the printing medium chamber via an inlet line, with the amount supplied being controlled by a control unit via controlled valves and other supply devices.

[0012] It is particularly preferred if the pressure medium chamber has several adjacent but separate individual chambers and the pressure medium is supplied to the printing fabric via these individual chambers in a controllable manner, so that pressure medium quantities and other parameters can be influenced at different points in the printing fabric during the printing process. The individual chambers can be opened and closed separately.

[0013] It is particularly advantageous if the doctor blade is adjustable to different angular positions relative to the horizontal. The amount of liquid printing medium dispensed from the printing chamber or from the individual chambers can be controlled by changing the opening width of the outlet of the printing chamber or the individual chambers.

[0014] It is particularly advantageous to subject the liquid pressure medium introduced into the pressure chamber to ultrasonic waves. For this purpose, ultrasonic transducers can be attached to the pressure chamber or to the individual chambers. The ultrasonic waves prevent clumping within the pressure chamber, thus enabling the processing of thixotropic materials. The ultrasonic transducers can also be controlled via a higher-level control system, allowing the ultrasonic power to be varied.

[0015] The aforementioned method using ultrasound waves is also suitable for using allotropic graphene as a pressure medium. The allotropic graphene can be kept in solution in the pressure medium chamber using surfactants. As soon as the solution is no longer kinetically stimulated, the graphene could settle to the bottom and form graphite clumps, which is prevented by the ultrasound waves.

[0016] With this method, layer thicknesses of just a few micrometers can be created on objects to be printed in a very short time. A wide variety of applications for graphene-based printing on technical objects can be realized using a liquid, graphene-containing printing medium. The so-called color stability of the printing medium in this process is only a few milliseconds (distance between the outlet of the printing medium chamber and the point of contact of the squeegee). The graphene-containing solution can be kept in dynamic motion by the ultrasonic waves until it exits the mesh of the printing fabric upon release of the graphene-containing printing medium and is applied to the object to be printed. This creates an exceptionally homogeneous layer, resulting in a clean, new cross-linking of the graphene molecules. This flawless cross-linking reduces the surface tension in the printed layer.the graphene-containing printed image is reduced, which is advantageous for many applications of such a printed technical object, for example due to a lack of electrons during the discharge process of graphene-containing battery plates that have been printed according to the inventive method.

[0017] The inventive method allows for the saving of a significant amount of solvents that are conventionally used in printing media and that evaporate during the printing process, thus relieving the environment and contributing to the direct protection of operators.

[0018] Furthermore, the production speed can be increased by at least 30% compared to conventional methods, because the flooding and pressure process in the inventive method is essentially the forward movement. The reverse movement is a return stroke, during which the speed can be rapidly increased.

[0019] The inventive method also makes it possible to apply material with a lower viscosity than previously possible, since the pressure applied immediately after flooding prevents premature flow out of the ink channel. The shear forces required to release the material from the ink channel (mesh of the printing fabric) are significantly reduced.

[0020] A device capable of implementing the method according to the invention is specified in claim 12, with preferred embodiments of this device being specified in claims 13 to 20. Preferred improvements to the method specified in claim 1 are specified in claims 2 to 11.

[0021] For further explanation of the invention, reference is made to the following description and the drawing. The drawing shows: Fig. 1: a top view of an embodiment of a printed fabric with a chambered doctor blade traverse and a chambered doctor blade unit supported thereon; Fig. 2: a view according to section line II in Fig. 1; Fig. 3: a view of the section line I - I in Fig. 1 in the opposite direction; Fig. 4: a perspective view of the exemplary embodiment according to Fig. 1; Fig. 5: a front view of an embodiment of a chamber doctor blade unit; Fig. 6: a section view corresponding to the section line AA in Fig. 5; Fig. 7: Partially enlarged, showing the section of the chamber doctor blade unit according to section D in Fig. 6; Fig. 8: a front view of a single chamber (chamber segment) as part of a pressure medium chamber; Fig. 9: a top view of the embodiment according to Fig. 8; Fig. 10: a side view of the embodiment according to Fig. 8, and Fig. 11: a perspective view of the exemplary embodiment according to Fig. 8.

[0022] In principle, components that correspond in the drawing are provided with corresponding reference numbers.

[0023] The printing fabric 1 of a device for creating a flatbed screen print has a frame 1.1. A chambered doctor blade traverse 2 is movably driven by a main drive (not shown), which is to be moved back and forth (forward movement / backward movement) by the main drive, i.e., in the illustration of Fig. 1 from right to left and back from left to right into the respective end positions. A pressure medium chamber 4 is provided on the chamber doctor blade traverse 2, which in the illustrated embodiment consists of individual chambers 4.1, 4.2, 4.3 and 4.4. The construction of these individual chambers will be described separately with reference to the embodiments of the Fig. 8, Fig. 9, Fig. 10 to Fig. 11 as well Fig. 5 to Fig. Section 6 discusses this. A liquid printing medium is to be filled into these individual chambers 4.1 to 4.4 via a filling line 10. This can be solvent-based paints or, for example, solvent-based graphene.

[0024] The individual chambers can be pressurized via a pressure connection, allowing the pressurized pressure medium to be supplied to the base tissue 1. Furthermore, a pressure doctor blade 5 and a flood doctor blade 6 are provided, with the flood doctor blade 6 being located in Fig. 1 is not apparent, however in Fig. 2. The flood squeegee 6 is designed as a scraper with a scraping edge and does not need to touch the printing fabric, so that flooding takes place without contact.

[0025] The chamber doctor blade traverse 2, the pressure medium chamber 4 or the individual chambers 4.1 to 4.4 and the pressure doctor blade 5 and the flood doctor blade 6 together form the chamber doctor blade unit 7.

[0026] The pressure medium chamber 4 is arranged in a housing 8 and has an outlet 9 for the pressure medium, located in the immediate vicinity of the squeegee 6. Pressure medium can be supplied from a pressure medium chamber 11 via the line 10. The housing part 8 can be moved by a pneumatic cylinder 12, whereby the outlet 9 can be opened and closed by such a movement.

[0027] On the chambered doctor blade unit 7, the pressure squeegee 5 is arranged in a pressure squeegee holder 13, which in turn is attached to a lever 14 that can be pivoted to change the inclination of the pressure squeegee 5, so that it can not only be raised, but also set in different angular positions to the horizontal.

[0028] In the Fig. 8, Fig. 9, Fig. 10 to Fig.Figure 11 shows a more detailed view of individual chamber 4.1, which has a chamber cover 14 to seal the individual chamber 4.1 gas-tight. An inner receiving space 15 is provided within the individual chamber 4.1, which can be closed at its ends. Furthermore, the flood squeegee 6 is shown, which is height-adjustable and can be attached to each individual chamber 4.1, so that the flood squeegee 6 as a whole comprises the individual flood squeegees of the individual chambers 4.1 to 4.4. An opening in the chamber cover 14 is to be closed by means of a plug 16. A recess 17 or a projection 18 is provided on the respective end faces, so that the respective individual chambers 4.1 to 4.4 can be connected to each other by means of a tongue-and-groove joint.

[0029] Each of the individual chambers 4.1 to 4.4 is equipped with an ultrasonic transducer 19 on one of its side surfaces to emit ultrasonic waves onto the liquid pressure medium. A control unit may also be provided to control the wave frequency and the ultrasonic intensity (power) of the ultrasonic transducer 19.

Claims

[1] Method for producing a flatbed screen print on objects such as textiles, films, plastics, metallic, glass and / or wooden objects, paper, cardboard, etc., in which a liquid printing agent is applied to a printing fabric (1) and deposited as a defined layer of printing agent on the printing fabric (1) by means of a movable squeegee (6), and a force is exerted on the printing fabric (1) by means of a squeegee (5), causing it to be elastically deformed and the defined layer of ink to come into contact with the object to be printed, characterized by, that the flood squeegee (6) and the printing squeegee (5) are moved together over the printing fabric (1) in their respective working positions, and that a pressure medium chamber (4) filled with the liquid printing medium is moved along with the flood squeegee (6) and the printing squeegee (5), that the liquid printing medium is supplied to the printing fabric (1) at an adjustable pressure via a chamber outlet (9) during the forward movement of the flood squeegee (6) and the printing squeegee (5) spatially in front of the flood squeegee (6) and the printing squeegee (5), that the outlet (9) of the pressure medium chamber (4) can be controlled and closed, that the printing squeegee (5), which is arranged spatially behind the flood squeegee (6) with respect to the forward movement of the flood squeegee (6) and the printing squeegee (5), exerts the force on the printing fabric (1) during the forward movement of the flood squeegee (6) and the printing squeegee (5), and that the defined ink layer comes into contact with the object to be printed. [2] Method according to claim 1, characterized by, that the outlet (9) of the pressure medium chamber (4) can be closed via a movable housing (8). [3] Method according to claim 1 or 2, characterized by , that the liquid pressure medium can be supplied to the pressure medium chamber (4) in a controllable manner via an inlet line (10). [4] Method according to any one of claims 1 to 3, characterized by , that the pressure medium chamber (4) has several separate individual chambers (4.1, 4.2, 4.3, 4.4) arranged next to each other and that the pressure medium can be supplied to the pressure fabric (1) via these individual chambers (4.1, 4.2, 4.3, 4.4) in a controllable manner. [5] Method according to any one of claims 1 to 4, characterized by , that the liquid pressure medium is supplied to the pressure fabric (1) immediately in front of the flood squeegee (6) during the movement of the flood squeegee (6) and the pressure squeegee (5) in the direction of pressure movement. [6] Method according to claim 4, characterized by, that for a printing process individual chambers (4.1, 4.2, 4.3, 4.4) can be closed and opened separately. [7] Method according to any one of claims 1 to 6, characterized by , that the squeegee (5) is adjustable to different angular positions relative to the horizontal. [8] Method according to any one of claims 1 to 7, characterized by , that the amount of liquid pressure medium to be dispensed is controlled by a change in the opening width of the outlet (9) of the pressure medium chamber (4). [9] Method according to any one of the preceding claims, characterized by , that the liquid pressure medium introduced into the pressure medium chamber (4) is subjected to ultrasonic waves. [10] Method according to any one of the preceding claims, characterized by , that a liquid dye is used as the liquid printing medium. [11] Method according to claim 9, characterized by, that the allotrope graphene is used as the liquid pressure medium and that the graphene held in solution with surfactants is subjected to the ultrasound waves in the pressure medium chamber (4). [12] Device for producing a flatbed screen print on objects such as textiles, films, plastics, metallic, wooden, glass objects, paper, cardboard, and the like, with which a liquid printing medium is applied to a printing fabric (1) and which has a movable flood squeegee (6) and a printing squeegee (5), wherein a printing medium chamber (4) supported on a chamber squeegee traverse (2) and provided by a forward movement with an outlet (9) is provided, such that the flood squeegee (6) and the printing squeegee (5) are supported on the chamber squeegee traverse (2) and together form a chamber squeegee unit (7) which can be moved together from a starting position to a printing end position by a chamber squeegee drive, wherein the liquid printing medium in the printing medium chamber (4) can be pressurized to an adjustable pressure, characterized by, that the flood blade (6) and the pressure blade (5) are arranged one behind the other in the direction of the forward movement and behind the outlet (9) of the pressure medium chamber (4), wherein the outlet (9) of the pressure medium chamber (4) can be closed by a housing (8) and wherein a control unit is provided which controls the closing process of the outlet of the pressure medium chamber (4). [13] Device according to claim 12, characterized by , that the pressure medium chamber (4) is divided into several individual chambers (4.1, 4.2, 4.3, 4.4) with respective pressure medium outlets that can be closed independently of each other. [14] Device according to claim 12 or 13, characterized by , that a pneumatic cylinder (12) is provided for moving the closing movement of the housing (8) to close the outlet (9) of the pressure medium chamber (4). [15] Device according to claims 12 to 14, characterized by, that the flood blade (6) can be moved up and down and the pressure blade (5) is attached to a lever (14) so ​​that the pressure blade (5) is pivotably attached to the chamber blade unit (7). [16] Device according to any one of claims 12 to 15, characterized by , that the squeegee (5) is fixed by knurled screws, so that the adjustment of the template layer thickness of the printing medium according to motif, amount of ink and viscosity can be carried out individually via the knurled screws. [17] Device according to any one of claims 12 to 16, characterized by , that at least one ultrasonic transducer (19) is provided at the pressure medium chamber (4) for applying ultrasonic waves to the liquid pressure medium. [18] Device according to any one of claims 13 to 17, characterized by , that several individual ultrasonic transducers (19) are provided on individual chambers (4.1, 4.2, 4.3, 4.4) for applying ultrasonic waves to the liquid pressure medium. [19] Device according to any one of claims 12 to 18, characterized by , that the ultrasonic transmitter (19) is in operative communication with a control unit for controlling the operation of the ultrasonic transmitter (19). [20] Device according to any one of claims 12 to 19, characterized by , that the flood rake (6) is designed as a scraper with a scraping edge.

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