Patent Grant
10278237
The present invention relates to a method for producing a heating system on a 3D plastic window such as a car window of plastic, comprising an electric heat conductor structure consisting of at least two bus bars (principal heat conductors) and a grid line pattern with a plurality of grid lines (branch heat conductors).
DE 10 2008 015 853 A1 discloses a method for producing a heatable plastic window for motor vehicles with at least one plastic layer, wherein at least one heat conductor is printed onto the inner side of the plastic layer, preferably in a 3D screen-printing process. In this method, the plastic layer is made available in the form of a film, a sheet or an injection-moulded part. In order to print on the heat conductor, a monofilament polyester fabric is used as screen-printing fabric and an electrically conductive paste with metal particles, preferably silver particles, is used as screen-printing ink. After the heat conductor has been printed on, the plastic layer is heat-treated and/or deformed. The 3D screen-printing process is carried out on a curved surface on the inner side of the plastic layer, wherein two bus bars (principal heat conductors) are laterally arranged on the right and the left side of the plastic window and several grid lines (branch heat conductors), which are electrically connected to the two bus bars, horizontally extend essentially in a straight line and parallel to one another. The plastic layer of the plastic window is essentially made of polycarbonate, polymethylmethacrylate, polymethylmethacrylimide or cycloolefin copolymers.
Conventional screen-printing devices are suitable for printing plane objects such as, e.g., plane car window panes, wherein the strip conductors of a rear-window defroster are applied onto a plane car window pane, e.g., by means of screen printing. After the strip conductors have been printed on, the window pane is heated and bent while the ink printed on simultaneously cures.
A squeegee with an elastic application element and a holding device for screen-printing arbitrarily curved surfaces is disclosed in DE 103 44 023 B4, wherein the holding device is viewed over the width of the squeegee divided into several holding sections that can be moved relative to one another and a guide plate, which rests against the application element at least during the printing process, originates from each holding section. Due to the division into several holding sections that can be moved relative to one another, the squeegee can be adapted to differently curved surfaces of an object to be printed. The guide plates furthermore ensure a uniform pressure distribution over the pressing edge of the application element.
Furthermore, DE 103 62 093 B4 discloses a screen-printing method for printing curved surfaces with the following steps: reading in a surface contour of an object to be printed, storing the read-in surface structure in a central control unit, generating control commands by means of the control unit and aligning a printing unit during the printing process by means of actuators that are activated by the control commands as a function of the surface geometry of the object to be printed, as well as the position of the squeegees relative to the object to be printed, and thereby constantly holding a printing unit frame relative to the object to be printed during a printing motion of the squeegees in an imaginary contact line between squeegee and the object to be printed.
The present invention is based on the objective of realizing the series production of a heating system on a 3D plastic window such as a 3D car window of plastic in an exactly defined, flexible and cost-effective fashion.
In order to attain this objective, according to a first aspect of the invention, there is provided a method for producing a heating system on a 3D plastic window such as a car window of plastic, comprising an electric heat conductor structure consisting of at least two bus bars (principal heat conductors) and a grid line pattern with a plurality of grid lines (branch heat conductors), comprising
According to an embodiment, the silver paste used for applying the grid lines of the grid line pattern onto the 3D plastic window has a higher content of carbon particles than the silver paste used for printing the bus bars onto the 3D plastic window.
According to another embodiment, the step, in which the bus bars are applied onto the 3D plastic window, is offset in time referred to the step, in which the grid line pattern is applied onto the 3D plastic window.
In an embodiment, the step, in which the bus bars are applied onto the 3D plastic window, may also be carried out prior to the step, in which the grid line pattern is applied onto the 3D plastic window, or the step, in which the grid line pattern is applied onto the 3D plastic window, may be carried out prior to the step, in which the bus bars are applied onto the 3D plastic window.
In another embodiment, the grid line pattern may likewise be screen-printed onto the 3D plastic window by means of at least one displaceable squeegee. In addition, the bus bars may be applied onto the 3D the plastic window by means of at least one first displaceable squeegee and/or the grid lines of the grid line pattern may be applied by means of at least one second displaceable squeegee. However, the two bus bars and/or the grid lines of the grid line pattern may also be applied onto the 3D plastic window by means of one squeegee that prints in two directions and/or two squeegees that operate in different directions. Furthermore, the grid line pattern may be applied onto the 3D plastic window by means of dispensing or by utilizing a digital inkjet printer.
According to an embodiment, the two bus bars of the heat conductor structure are simultaneously applied on the left and on the right side of the 3D plastic window in the region of the grid line pattern due to the combination of a feed motion and a rotational motion of the at least one squeegee.
According to another embodiment, the screen-printing of the heat conductor structure consisting of the two bus bars and the grid lines overlapping these bus bars may be respectively carried out with one of two screens that are used offset in time, wherein the two bus bars are applied onto the 3D plastic window along the edges of the latter with the corresponding screen and with separately displaceable squeegees.
In an embodiment, the two screens, by means of which the heat conductor structure consisting of the bus bars and the grid lines overlapping these bus bars is screen-printed onto the 3D plastic window, are inserted into the upper unit of a screen-printing machine in succession.
In another embodiment, instead of using one screen for screen-printing the two bus bars of the heat conductor structure to be produced onto the 3D plastic window, it is also possible to use two screens with smaller dimensions, each of which is inserted into the upper unit of the screen-printing machine or guided by a robot or position-controlled for the respective application of one of the two bus bars.
According to an embodiment, the at least one displaceable squeegee used for applying the grid line pattern onto the 3D plastic window is a squeegee that prints in two directions and, starting at the beginning of the first grid line of the grid line pattern, prints the second electrically conductive paste onto the 3D plastic window in the feed direction such that the first grid line of the grid line pattern is formed, wherein the squeegee then carries out a rotational motion after it reaches the end of the first grid line of the grid line pattern referred to the feed direction and subsequently prints the second electrically conductive paste onto the 3D plastic window in the direction extending opposite to the feed direction such that the second grid line of the grid line pattern is formed, wherein this process is repeated until the complete grid line pattern is formed on the 3D plastic window.
According to a second aspect of the invention, the objective of the invention is also attained with a method for producing a heat conductor system on a 3D plastic window such as a car window of plastic, comprising an electric heat conductor structure consisting of at least two bus bars (principal heat conductors) and a grid line pattern with a plurality of grid lines (branch heat conductors), comprising
According to an embodiment, in this case, the screen-printing of the two bus bars and the grid line pattern with screen-printing ink in the form of the silver paste is carried out continuously by means of a displaceable squeegee capable of printing in opposite directions, wherein this squeegee prints the grid lines of the grid line pattern onto the 3D plastic window starting from the left or the right side with a respective rightward or leftward directed feed motion in a region with less curvature of the 3D plastic window for the grid line pattern, and wherein the feed motion of said squeegee respectively transforms into a rotational and pivoting motion and the squeegee continuously screen-prints one of the two respective bus bars onto the 3D plastic window such that it overlaps the grid lines of the applied grid line pattern in regions with more significant curvature of the 3D plastic window for the two bus bars.
According to another embodiment, instead of using the displaceable squeegee capable of printing in opposite directions, it would also be possible to use two squeegees that operate in different directions and the feed motions of which respectively need to be transformed into a rotational and the pivoting motion.
In an embodiment, after the respective application of the grid lines of the grid line pattern and/or one of the two bus bars, it is ensured that the electrically conductive paste printed onto the 3D plastic window can become touch-dry, preferably by means of self-drying, or is thermally cured by means of IR-radiation or heat transmission.
In another embodiment, the transformations from the feed motion of the at least one squeegee to the rotational and the pivoting motion or vice versa are preferably program-controlled. The two bus bars and the grid lines of the grid line pattern can be joined at the overlapping points by means of a conductive adhesive or by means of soldering.
The number of respective steps of three variations of the method according to the invention are compared below in table 1.
Table 1 shows that variation 1 with two-stage squeegee control requires thirteen steps due to the allowance for the edge regions of the 3D plastic window, wherein this number of steps corresponds to that of variation 3, in which the technology of screen-printing and dispensing is combined. However, if two different silver pastes should be used for the application of the bus bars and the grid lines in accordance with variation 2, the number of screen-printing steps increases to sixteen. In variation 3, in which the technology of screen-printing and dispensing is combined, the number of steps is not affected whether one or two silver pastes are used. In this context, only the logistics with respect to the supply of the two silver pastes are more elaborate.
Initial practical experiences showed that the expenditure of time for variation 1 lies in the range between 1.0 and 1.5 min. The expenditure of time for variation 2 increases to about 2 min due to the separate printing of bus bars and grid lines. The expenditure of time for variation 3, in contrast, is about 4 min due to the technology combination of screen-printing and dispensing. In this case, it should be planned to provide 3-4 more dispensing stations than screen-printing machines in order to achieve a coordinated process sequence.
The screen-printing of 3D components requires flexible screens with little prestress in the range of a few N/cm. Polyester monofilaments, as well as polyamide monofilaments, may be used in this case. Polyamide systems are usually very flexible and can be subjected to higher tensile stresses than polyester systems.
Mesh counts of 77-48 proved advantageous for 2D screen-printing on glass. In 3D screen-printing, the mesh counts represent another process parameter that must be adapted in dependence on the complexity of the component to be printed.
With respect to the setting of each screen on the frame, the prestress and homogeneity of the screen, as well as the adjusted angle of the pattern/heating system, are of importance.
The silver pastes used consist of commercially available silver pastes for polymer windows with different electric conductivity.
The size of the silver particles is decisive for the choice of a suitable screen. In this context, it should be observed that the mesh size of the chosen screen fabric is 3-times to 5-times larger than the particles to be printed.
Graduated viscosities require the addition of a solvent in order to lower the adjusted viscosity of the silver pastes. In this case, the solvent used may consist, e.g., of 2-octanol (98%).
The material to be printed may consist of polycarbonate or blend material with scratchproof paint and plasma layer or with scratchproof paint having anti-graffiti properties.
An exemplary parameter set of preferred printing parameters for the basic 3D component are shown below in table 2.
According to a third aspect of the present invention there is also provided a system for carrying out the method according to claim 1 or 9, comprising at least one supply station for cleaned 3D plastic windows, at least one screen-printing machine that is positioned on the outlet side of said supply station and respectively applies the electric heat conductor structure consisting of the two bus bars and the grid line pattern onto the supplied 3D plastic windows, a paternoster furnace that is arranged parallel to the at least one screen-printing machine, a robot station with at least one robot between the outlet of the screen-printing machine and the inlet of the paternoster furnace, wherein the 3D plastic windows with the electric heat conductor structure printed thereon by means of the screen-printing machine are picked up at the outlet of the latter and inserted into the paternoster furnace opposite to the previous processing direction in order to cure the electric conductor structure printed onto the 3D plastic windows, and a depositing station for the 3D plastic windows with cured electric heat conductor structure, which is arranged downstream of the outlet of the paternoster furnace.
Aspects of the present invention furthermore include the option of combining the technology of dispensing and of 3D screen-printing in the production of a heating system on a 3D plastic window such as a car window plastic. In this case, the advantages of the fast and robust screen-printing technique can be combined with the very flexible dispensing technology.
For this purpose, a dispensing unit is positioned between the robot station and the paternoster furnace in a system for carrying out the method according to claim 22, wherein the 3D plastic windows, onto which initially only the two respective bus bars of the electric heat conductor structure are printed in the at least one screen printing machine, are inserted into the inlet of said dispensing unit by means of the at least one robot of the robot station, wherein the grid lines of the grid line pattern are in the dispensing unit applied onto each of the 3D plastic windows inserted therein by means of dispensing such that they overlap the respective bus bars, and wherein the 3D plastic windows, which are respectively provided with the complete heat conductor structure, are picked up and transported to the inlet of the paternoster furnace by means of at least one conveyor belt or at least one additional robot that is respectively positioned between the outlet of the dispensing unit and the inlet of the paternoster furnace.
The invention is described below with reference to the drawings. In these drawings:
According to
If two displaceable squeegees 10 that operate in two different directions are used instead of the one displaceable squeegee 10 capable of printing in opposite directions, the leftward feed motion of the second squeegee 10 on the grid lines of the grid line pattern transforms during the second, oppositely directed step into the rotational and pivoting motion offset in time referred to the first squeegee 10 in order to end at the upper left edge of the 3D plastic window. The transformations from the feed motion of the at least one squeegee 10 to the rotational and pivoting motion or vice versa may respectively take place in a program-controlled fashion.
The two bus bars and the grid lines of the grid line pattern are then joined at the overlapping points by means of a conductive adhesive or by means of soldering.
After the respective application of the grid lines of the grid line pattern and/or one of the two bus bars, it is ensured that the electrically conductive paste printed onto the 3D plastic window 1 can become touch-dry, preferably by means of self-drying, or is thermally cured by means of IR-radiation or UV-radiation or by means of heat transmission.
It is important that the respective silver paste printed onto the 3D plastic window 1 is dried after each printing process such that the print pattern cannot smear or stick together. A short holding time of the respective printing process suffices for this purpose. However, the respective silver paste freshly printed onto the 3D plastic window may also be cured by means of heat transmission. UV-curable or IR-curable paste systems may be used as an alternative to thermal curing in order to promote a serial sequence of the printing process.
In this embodiment, the feed device 2 for the 3D plastic windows 1 and the screen-printing machine 3 arranged downstream thereof are positioned in the first processing line and the conveyor or robot unit 4, by means of which the 3D plastic windows 1 with the bus bars printed thereon are removed from the screen-printing machine 3 and inserted into the dispensing unit 12, is positioned between the outlet of the screen-printing machine and the inlet of the downstream dispensing unit 12. The robot system 4, by means of which the 3D plastic windows 1 provided with the electric heat conductor structure are removed from the dispensing unit 12 and placed into the drying furnace 5 in order to be cured, is positioned between the outlet of the dispensing unit 12 and the inlet of the drying furnace 5 arranged in the second processing line. In this case, the drying zone of the drying furnace 5 extends in the second processing line opposite to the transport direction of the first processing line, namely over a total length of 9 m. The depositing station 6, into which the 3D plastic windows 1 with the cured electric heat conductor system are placed, is arranged downstream of the outlet of the drying furnace 5.
It is to be understood that the embodiments of the invention disclosed are not limited to the particular structures, process steps, or materials disclosed herein, but are extended to equivalents thereof as would be recognized by those ordinarily skilled in the relevant arts. It should also be understood that terminology employed herein is used for the purpose of describing particular embodiments only and is not intended to be limiting.
Reference throughout this specification to one embodiment or an embodiment means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Where reference is made to a numerical value using a term such as, for example, about or substantially, the exact numerical value is also disclosed.
As used herein, a plurality of items, structural elements, compositional elements, and/or materials may be presented in a common list for convenience. However, these lists should be construed as though each member of the list is individually identified as a separate and unique member. Thus, no individual member of such list should be construed as a de facto equivalent of any other member of the same list solely based on their presentation in a common group without indications to the contrary. In addition, various embodiments and example of the present invention may be referred to herein along with alternatives for the various components thereof. It is understood that such embodiments, examples, and alternatives are not to be construed as de facto equivalents of one another, but are to be considered as separate and autonomous representations of the present invention.
Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided, such as examples of lengths, widths, shapes, etc., to provide a thorough understanding of embodiments of the invention. One skilled in the relevant art will recognize, however, that the invention can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the invention.
While the forgoing examples are illustrative of the principles of the present invention in one or more particular applications, it will be apparent to those of ordinary skill in the art that numerous modifications in form, usage and details of implementation can be made without the exercise of inventive faculty, and without departing from the principles and concepts of the invention. Accordingly, it is not intended that the invention be limited, except as by the claims set forth below.
The verbs “to comprise” and “to include” are used in this document as open limitations that neither exclude nor require the existence of also un-recited features. The features recited in depending claims are mutually freely combinable unless otherwise explicitly stated. Furthermore, it is to be understood that the use of “a” or “an”, that is, a singular form, throughout this document does not exclude a plurality.
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|---|---|---|---|
| 10 2015 008 838 | Jul 2015 | DE | national |
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| 20170006666 A1 | Jan 2017 | US |
