Method for the Integral Bonding of Two Workpieces

Abstract

The invention relates to a method for the integral bonding of two workpieces made from different types of thermoplastic polymers with the help of a preferably thermoplastic polymer primer as bonding layer, comprising the following steps: providing a first workpiece made from a thermoplastic polymer having a first edge layer; providing a second workpiece made from a thermoplastic polymer having a second edge layer, said thermoplastic polymer being of a different type to the thermoplastic polymer of the first workpiece; preheating the first edge layer; applying the primer on the preheated first edge layer, wherein, during the application of the primer, the preheated first edge layer has a temperature in the range between the extrapolated onset of the glass transition temperature for amorphous plastics or the peak starting temperature of the melting region for partially crystalline plastics and the step starting temperature of the disintegration of the thermoplastic polymer of the first edge layer; bringing the first edge layer provided with the primer into contact with the second edge layer; and integral bonding of the first edge layer with the second edge layer.

Claims

1. A method for integrally bonding two workpieces made of dissimilar thermoplastic polymers using a thermoplastic polymer primer as a connecting layer, comprising: providing a first workpiece which is made of a thermoplastic polymer and comprises a first edge layer, providing a second workpiece which is made of a thermoplastic polymer and comprises a second layer, wherein the thermoplastic polymer is dissimilar with respect to the thermoplastic polymer of the first workpiece, preheating the first edge layer, applying the primer to the preheated first edge layer, wherein the preheated first edge layer, while the primer is being applied, has a temperature in the range between the extrapolated onset of the glass transition temperature for amorphous plastics materials or the initial peak temperature of the melting range for partially crystalline plastics materials and the initial stage temperature of the decomposition of the thermoplastic polymer of the first edge layer, bringing the first edge layer provided with the primer into contact with the second edge layer, integrally bonding the first edge layer to the second edge layer.

2. The method according to claim 1, wherein the first edge layer is preheated such that the temperature of the first edge layer is in the range between the extrapolated onset of the glass transition temperature for amorphous plastics materials or the initial peak temperature of the melting range for partially crystalline plastics materials and the initial stage temperature of the decomposition of the thermoplastic polymer of the first edge layer.

3. The method according to claim 1, comprising continuously recording the temperature of the first edge layer during the preheating and continuously controlling the preheating step based on the recorded temperature.

4. The method according to claim 1, wherein the preheated first edge layer, while the primer is being applied, has a temperature that is lower than the decomposition temperature of the primer.

5. The method according to claim 1, wherein the first edge layer is heated during the step of applying the primer to the first edge layer.

6. The method according to claim 1, comprising the step of pretreating the first edge layer by at least one of corona discharge, plasma arc, flame treatment, radiation treatment, chemical treatment and mechanical treatment of the first edge layer before the first edge layer is preheated.

7. The method according to claim 1, wherein during the preheating step a melt layer is produced in the first edge layer, the melt layer having a thickness in the range of from 0.05 mm to 6 mm.

8. The method according to claim 1, wherein a heating device is used for preheating the first edge layer, the first edge layer being preheated during relative movement between the first workpiece and the heating device in the range of from 10 mm/min to 100 m/min.

9. The method according to claim 1, wherein: the primer is applied to the first edge layer by a dosing device during relative movement between the first workpiece and the dosing device of from 10 mm/min to 100 m/min; and the first edge layer to which the primer is applied is heated by means of a heating device during relative movement between the first workpiece and the heating device before the primer is applied, the heating device simultaneously leading the dosing device or a nozzle of the dosing device in order to apply the primer in a time interval in the range of from 0.1-10 s.

10. The method according to claim 1, wherein a heating device is used for preheating the first edge layer, the spacing between the heating device during the preheating and the first edge layer being in a range of from 0.5 mm to 100 mm.

11. The method according to claim 1, wherein thickness of the applied primer is in the range of from 1 m to 5 mm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0091] By way of example, the invention is described using the following drawings, in which:

[0092] FIG. 1 is a sectional view through a first workpiece and a rear view of a coating unit for implementing a part of the method according to the invention,

[0093] FIG. 2 is a side view of the coating unit from FIG. 1 during the implementation of a part of the method according to the invention,

[0094] FIG. 3 is a side view of a welding device during the implementation of a part of the method according to the invention,

[0095] FIG. 4 is a side view of an alternative welding device during the implementation of a part of the method according to the invention.

[0096] FIG. 1 is a sectional view through a first workpiece 11 and a rear view of a coating unit 1 for implementing a part of the method according to the invention for integrally bonding the depicted first workpiece 11 with a second workpiece 21 (not shown), The two workpieces 11, 21 consist of dissimilar thermoplastic polymers.

[0097] The first workpiece 11 consists of a partially crystalline polyethylene comprising a first edge layer 12. This is understood to mean a surface region of the first workpiece 11 that is intended to be integrally bonded to the second workpiece 21 (not shown) and is thus arranged in the region of the subsequent bonding zone. The edge layer 12 can have any shape and size and is adapted to the particular use and of course to the second workpiece 21. The coating unit 1 comprises a dosing device 4 for applying a primer 13 and a heating device 2 for preheating, immediately before the primer 13 is applied, the first edge layer 12 of the workpiece 11 to which said primer is intended to be applied.

[0098] The heating device 2 comprises a heating unit 3 which faces the surface of the workpiece 11 to be preheated, in order to preheat the first edge layer 12. The heating unit 3 is the nozzle portion of a hot gas apparatus (not shown in more detail) from which hot gas for preheating the first edge layer 12 can flow towards said edge layer. In the present embodiment, the preheating time, i.e. the time for which the hot gas flows onto the edge layer, is in the region of from 1 s-120 s, the temperature of the hot gas preferably being in the range of from 300 C.-450 C.

[0099] In the embodiment shown, the first edge layer 12 is preheated in such a way and for such a time that the temperature of the first edge layer is in the range between the initial peak temperature (T.sub.ini,m) as the first limit and the initial stage temperature (T.sub.ini,z) of the decomposition as the second limit. The initial peak temperature (T.sub.ini,m) of the polyethylene used, for which the thermoplastic polymer is converted into a rubber-like to viscous melt, is 110 C. The initial stage temperature (T.sub.ini,z) of the polyethylene from which the chemical composition of the polyethylene is damaged and from which said polyethylene begins to decompose, is 260 C. The first edge layer 12 is preferably preheated such that and for such a time that the workpiece is itself deformed at most in the region of the edge layer 12.

[0100] In this case, the preheating is carried out by means of a relative movement of the heating device 2 and the workpiece 11. For this purpose, in the embodiment shown, the workpiece 11 is held in the application position shown by a robot arm (not shown), an additional multiaxial robot arm 9 being provided, on which said heating device 2 is mounted via a holding device 8 and by means of which the heating device 2 for preheating the first edge layer 12 can be moved relative to the workpiece 11 in a movement direction 10. In the embodiment shown, the feed rate of the heating device 2 relative to the workpiece 11 is in the range of from 10 mm/min-100 m/min. Alternatively or additionally, it is also conceivable for the workpiece 11 to be able to be moved relative to the coating device 1 in particular by means of the above-mentioned robot arm (not shown). In the embodiment shown, the spacing of the heating element 3 from the surface of the workpiece 11 is in the range of from 10 mm to 40 mm. All parameters are matched to one another and adapted to the material of the first substrate such that the workpiece 11 is melted by the heating element 3 in a preheated region 14 of the first edge layer 12, the melt layer thickness produced in the preheated region 14 being in the range of from 0.1 mm to 3 mm. The heating device 2 further comprises a pyrometer (not shown), in order to continuously record the temperature of the first edge layer during the preheating. A control unit (not shown) is also provided to allow the preheating to be controlled using the recorded value.

[0101] The dosing device 4 is also mounted on the robot arm 9 via said holding device 8. The dosing device 4 comprises an application nozzle 5 for applying the primer 13 to the edge layer 12 of the workpiece 11, the primer 13 being applied here too by means of a relative movement of the dosing device 4 and the workpiece 11. In this case, the dosing device 4 and in particular the application nozzle 5 are designed such that not only can different primers 13 be applied but also different types of application can be selected. The primer 13 can thus be applied as a bead or sprayed on; however, application by means of thin-jet spraying as shown is also conceivable via an application jet.

[0102] In addition, the arrangement of the heating device 2 and the dosing device 4 is selected such that the edge layer 12 to which the primer 13 is applied is preheated immediately before said primer 13 is applied. The coating unit 1 is thus arranged and is moved relative to the workpiece 11 in the movement direction 10 such that, during the preheating of the workpiece 11, the heating element 4 is at a constant spacing, within the above-mentioned spacing range of from 10 mm to 40 mm, away from the outer surface of the workpiece 11, i.e. the edge layer 12. In addition, the heating element 3 is selected such that and the coating unit 1 is moved at such a speed, preferably a constant speed, relative to the workpiece 11 in the movement direction 10 that the edge layer 12 is within the area of the heating element 3 that is effective for heating the application region only within a specific time period. In this case, the coating unit 1 is moved relative to the workpiece 11 (which is in this case stationary) at a feed rate in the range of from 10 mm/min-100 m/min. By means of the heating unit 3, the edge layer 12 of the workpiece 11 is thus directly preheated in order to achieve melting, the preheated region 14 having a melt layer thickness in the range of from 0.1 mm-3 mm. The primer 13 is subsequently applied to the preheated region 14, i.e. directly on the molten material. The spacing between the dosing device 4 and the heating device 2 on the holding device 8 and the speed of the coating unit 1 in the movement direction 10 are thus adjusted such that the heating device 2, or rather said region of the heating unit 3 that is effective for heating, simultaneously leads the dosing device 2 during the movement of the coating unit 1 in the movement direction 10 at a time interval in the range of from 0.1 s-10 s in this case. Cooling of the application region after the preheating can thus be prevented, meaning that the primer 13 can be applied when the temperature of the preheated region 14 of the edge layer 12 is still sufficient. The primer 13 is thus applied when the preheated region 14 is still in the preheated and preferably still in the molten state, which leads to an integral connection between the preheated region 14 and the primer 13.

[0103] FIG. 2 is a cut side view of the coating unit 1 from FIG. 1 during the implementation of a part of the method according to the invention. A cut side view of the first workpiece 11 comprising the first edge layer 12, said preheated region 14, in regions, and the primer 13 applied to the preheated region 14, can also be seen. It can also be seen that both the heating device 2 comprising the heating unit 3 and the dosing device 4 comprising the application nozzle 5 are fastened together to the multiaxial robot 9 via the holding device 8. Accordingly, the heating device 2 and the dosing device 4 are moved in the movement direction 10 as a unit, the heating device 2 and the dosing device 4 being rigidly secured relative to one another with respect to their position during the process in order to be able to maintain a defined spacing between the heating device 2 and the dosing device 4 during a relative movement between the coating unit 1 and the workpiece 11. In this case, the holding device 8 may be further designed so as to be able to allow said components to be secured for the process and such that the spacing between the heating device 2 and the dosing device 4 can be modified by means of a linear drive or similar mechanical aid, for example, in particular in order to adapt the coating unit 1 when the workpiece 11 is changed, for example, and to design said coating unit to be able to be used in a flexible manner.

[0104] Of course, as mentioned above, an alternative or additional movement of the workpiece, for example in a movement direction 15, is also possible. By means of the constant movement of the sealing unit 1 and the defined spacing between the heating device 2 and the dosing device 4, the primer 13 is applied, for example using the above-mentioned parameters, by means of the application stream 6 via the application nozzle 5 when the preheated region 14 is still in the preheated and preferably still in the molten state, which leads to an integral connection between the preheated region 14 and the primer 13.

[0105] FIG. 3 is another side view of a welding device 16 during the implementation of another part of the method according to the invention. FIG. 3 also shows the first workpiece 11 having the primer 13 on the first edge layer 12. The second workpiece 19 made of a thermoplastic polymer and comprising a second layer 20 can also be seen here. It should be noted that the thermoplastic polymer of the second workpiece 19 is dissimilar with respect to the first workpiece 11. In the embodiment shown, a polyester is used as the second workpiece 19. In this case, the second workpiece 19 is brought into contact with the first workpiece 11 such that the first edge layer 12 provided with the primer 13 is arranged directly opposite the second edge layer 20. The two edge layers 12, 20 are thus separated from one another by the primer 13 applied to the first edge layer 12. The two workpieces 11, 19 are fixed in their position relative to one another. This can be carried out by brackets (not shown), in order to prevent the workpieces 11, 19 from slipping. In the embodiment shown, the welding device 16 is designed as an ultrasonic welding device and comprises a sonotrode 22 and a counter bearing 23. The sonotrode 22 is powered via an ultrasonic generator (not shown) having an ultrasonic vibration in a frequency range of from 15 kHz to 40 kHz, for example. The spacing between the sonotrode 22 and the counter bearing 23 is variable, in order to be able to weld workpieces 11, 19 having different total thicknesses. The welding device 16 makes it possible to produce an integral bond between the first edge layer 12 provided with the primer 13 and the second edge layer 20. The welding is carried out in a clocked or continuous manner by means of a relative movement of the welding device 16 and the connected workpieces 11, 19. In the embodiment shown, the workpiece 11, together with the second workpiece 19 secured thereto, is again held in the application position shown by a robot arm (not shown), a second, multiaxial robot arm 18 being provided, on which said welding device 16 comprising the sonotrode 22 and the counter bearing 23 is mounted and by means of which the welding device 16 can be moved in a movement direction 10. In the embodiment shown, the feed rate of the welding device 16 relative to the workpieces 11, 19 is in the range of from 10 mm/min-100 m/min. Alternatively or additionally, it is also conceivable, however, for the workpieces 11, 19 to be able to be moved relative to the welding device 16 in particular by means of the above-mentioned robot arm (not shown). All parameters are matched to one another and the workpieces 11, 19 and the primer 13 are adapted to one another such that the first workpiece 11 in the region of the first edge layer 12 provided with the primer 13 and the second workpiece 19 in the region of the second edge layer 12 are melted directly or even indirectly by the welding device 16, which leads to an integral connection between the first edge layer 12 equipped with the primer 13 and the second edge layer 20. As an alternative to the welding device 16 designed as an ultrasonic welding device, in particular a device suitable for vibration welding and/or heated tool welding can also be used, in order to allow an integral bond to be produced between the first edge layer 12 provided with the primer 13 and the second edge layer 20.

[0106] FIG. 4 is a side view of an alternative welding device 16 during the implementation of the part of the method according to the invention that has already been described. In this case too, the second workpiece 19 is brought into contact with the first workpiece 11 such that the first edge layer 12 provided with the primer 13 is arranged directly opposite the second edge layer 20. In the embodiment shown, the second workpiece 19 is a bonding partner that is transparent to a laser beam and the first workpiece 11 equipped with the primer 13 is an absorbent bonding partner. The welding device 16 comprises a laser light source (not shown) and a focusing optics 17 for a laser beam 21, which is used to produce an integral bond between the first edge layer 12 provided with the primer 13 and the second edge layer 20. Alternatively, polychromatic light from at least one IR radiator may also be used instead of the laser light. An advantage of the laser light used in this case is that the heat affected zone is minimal and easily controllable, meaning that thermal damage to the immediate surroundings can be prevented. The irradiation of the edge layers 12, 20 and the primer 13 by the laser beam 21 is carried out by means of a relative movement of the welding device 16 and the connected workpieces 11, 19. In the embodiment shown, the workpiece 11, together with the second workpiece 19 secured thereto, is again held in the application position shown by a robot arm (not shown), a second, multiaxial robot arm 18 being provided, on which said welding device 16 is mounted and by means of which the welding device 16 for irradiating the second edge layer 20 and the first edge layer 12 equipped with the primer 13 can be moved in the movement direction 10. Here too, the feed rate of the welding device 16 relative to the workpiece 11 is again in the range of from 10 mm/min-100 m/min. Alternatively or additionally, a movement of the workpieces 11, 19 is again also conceivable here. All parameters are matched to one another and the workpieces 11, 19 and the primer 13 are adapted to one another such that both the first workpiece 11 in the region of the first edge layer 12 provided with the primer 13 and the second workpiece 19 in the region of the second edge layer 12 are melted directly or even indirectly by the laser beam 21, which leads to an integral connection between the first edge layer 12 equipped with the primer 13 and the second edge layer 20.

TABLE-US-00001 List of reference signs: 1 coating unit 2 heating device 3 heating unit 4 dosing device 5 application nozzle 6 application stream 8 holding device 9 robot arm 10 movement direction 11 workpiece 12 first edge layer 13 primer 14 preheated region 15 second movement direction 16 welding device 17 focusing optics 18 second robot arm 19 second workpiece 20 second edge layer 21 laser beam 22 sonotrode 23 counter bearing