HK1060866B - Process and apparatus for joining of synthetic materials at high welding speed - Google Patents

Description

The present invention relates to a process and device for joining plastic materials at high welding speed.

It is known to connect plastic materials by laser beams, in which the upper material facing the laser beam is beamed through it and at the contact point between the upper material transparent to the laser beam and the lower material impermeable to the laser beam, the two materials are heated and connected under pressure. The material transparent to the laser beam can be optically black in the visible wavelength range. It is also known to produce a linear laser beam, where a relative motion takes place between the materials and the laser beam during the welding process to produce the desired weld contour.

The accumulation of heat energy and the resulting temperature in the plastic depend on the energy dosage, such as energy density and irradiation time. Furthermore, the material property, such as thermal conductivity, is also important. The next step in the welding process is the phase transition between the solid state and the liquid state, which is then called the melting temperature. This temperature is shortened accordingly, but the energy saving is significantly reduced due to the individual heating efficiency of the plastic.

The endless film material can be used, for example, as part of a micromechanical component, sensors, actuators, etc., whereby the film material is also used as a means of transport for the component.

DD 84 474 A describes a device for continuous welding of thermoplastic films in which a rotating transparent quartz glass disc on which the films to be joined are welded overlapping and transported simultaneously through the disc is irradiated from the opposite side by focused beams of light so that the focal point of the beam of a light beam is in the weld zone of the films to be welded. This heats the films to a welding temperature and the pressure required for welding is generated by a spring-loaded androller press that either runs with or synchronizes with the rotating disc according to the throughput conditions. This device is used to produce a point-to-point heating.

DE 195 16 726 A1 shows a method for forming and closing a folding box with two opposite rolls, each of which is cut along the welded areas by a thermoplastic layer of plastic, which is welded together after or during a folding process by irradiation of infrared radiation and pressure application immediately afterwards.

The present invention is therefore based on the task of proposing a method for joining films at high welding speeds.

The present invention is based on the characteristics of the process and device claims, and the respective subclaims provide further advantages.

The method provides for the production of a longitudinal welding joint in which the material is continuously heated to the melting temperature in a preheating zone by laser beams and then melted into a melting zone. The third phase of the process zone, the cooling phase, is not covered by the laser beam. The invention provides for the desired higher welding speed by adjusting the dimension of the area covered by the laser beam.

The process area is linear, preferably at least partially produced by means of a collimated laser beam, the width of which can be adjusted by the corresponding optics.

It is important for the process that the linear laser beam, directed in the direction of movement, hits the contact surface throughout the process zone, and the base must therefore have at least one area corresponding to this length.

In order to provide additional energy for the welding process after the melting temperature has been reached, further training of the process makes it possible to provide a further high energy-density point laser beam after the linear radiation zone.

For temperature measurement, a pyrometer for IR temperature measurement can also be provided at this point, using the same optics for beam conduction for both the point laser beam and the IR measurement.

The materials are guided by two opposite rolls pressing against each other, whereby the laser beam is brought into the irradiation zone by a first roll which is permeable to the laser beam. This allows the appropriate advance of the films to be ensured. It is important that, as mentioned above, the contact surface is captured by the linear laser beam. This means that the first roll has a correspondingly large diameter.

In addition, as indicated at the beginning, it is important for the process that the materials are joined together under pressure.

The deformation of the second coil causes the two materials to be joined to be pressed together directly at the time of fusion with the appropriate pressure. The deformation of the second coil also inevitably causes a curvature of the two materials joined in accordance with the radius of the first transparent coil. As a result, it is necessary that the joined materials are then rolled up in this curvature direction during welding.

The transparent roller can be made of glass, transparent plastic, e.g. PMMA, or other suitable materials. To provide a laser beam of the desired width in the contact area, either a beam of the desired width can be produced by appropriate optics, or a radiation zone that is wider than the laser line can be produced by appropriate back-and-forth scanning at sufficient speed.

According to further training of the process, the first transparent coil is cleaned on the outer surface before contact with the materials in order to remove any adhering dirt particles originating from the materials so as not to interfere with the energy transfer through the coil required for the welding process, for example by mechanical and/or compressed air or vacuum brushes, electrical (antistatic coating) or other means appropriate to the particular application.

Another parameter important for an optimal connection is the application of the required pressure. To control this, the pressure can be determined by means of flat pressure sensors, which are commonly known and commonly used in the market, placed on the surface of the second roll.

To create a weld contour that differs from a normal linear shape, it is possible to arrange a mask on the transparent roll. Depending on the beam quality, this mask can be arranged inside or outside. A typical example of arranging a mask in such a way that it covers a certain area of the material to be welded when the roll is rotated is the production of a weld seam continuously interrupted in the direction of transport.

The device for joining endless materials consists of two oppositely pressing rollers, the first roll being made of a laser-permeable material and shaped like a tube, and the second roll being made of a material which is easily deformable on the surface. Furthermore, devices for producing at least one laser beam are placed in the first roll at the contact surface. These devices may be devices for generating the laser beam or re-directing devices to bring the laser beam generated outside the roll to the desired position. The outer roll is slightly deformed at least in the outer area by a rubber material made of the corresponding soft elasticity.

In accordance with a preferred training, an IR temperature measuring device is placed in the first roll, preferably trained to move relative to the measuring point, allowing the desired process phase to be checked and evaluated in a control and control device.

The devices for producing at least one laser beam shall produce a laser beam in the contact zone arranged in the direction of motion of the materials, preferably followed by a laser beam in the direction of motion of the linear laser beam.

The following illustrations give a detailed description of the invention: Figure 1the schematic representation of the temperature profile by means of a linear curtain-like laser beam on a surface;Figure 2the schematic representation of an arrangement with a linear laser beam and a point laser or pyrometer to measure temperature in the direction of motion;Figure 3the schematic representation of a device for connecting two plastic film paths; andFigure 4an enlarged schematic representation of the transparent roller and the counter roller with a reversing mirror.

Figure 1 shows a laser source 1 with a curtain-like collimated laser beam 2 which creates a linear radiation zone 5 on the plastic material 3. The radiation zone 5 has a width d and a length D which can be affected by the corresponding optics. The plastic material 3 is moved in an arrow direction at the speed v. In addition, the figure shows the temperature profile 4 with the temperature T over the path x. As can be seen from Figure 4 and line 4, the temperature in the material in the preheating zone I rises continuously and reaches the melting temperature Tm at the end. From there the melting zone II begins until the end of the radiation zone 5, whose length is denoted by D. After that the temperature in the cooling zone III drops. The total duration of the process is denoted by p.

In addition to the laser source 1, there may be either another laser source 7, and/or a pyrometer for IR measurement. This device has a rotating head point 8 which allows a freely definable movement along the material, so that each time a pyrometer is used, a point is heated or heated to the appropriate temperature without the optical elements being able to be moved in the same direction. The measurement can be carried out by inserting the pyrometer and the optical elements in the same direction and temperature can be measured by the pyrometer.

The diagram in Figure 3 shows the schematic arrangement of the individual elements in a device. In Figure 11 a laser source 11 is shown schematically in a transparent roll 17. This is done for example only, since here, in principle, and in practice also more feasibly, a reversing mirror 6 is used, as shown in Figure 4. The laser source 11 produces a curtain-like laser beam 12 which in the region 16 between the transparent roll 17 e.g. made of quartz glass or PMMA and the easily deformable roll 18 e.g. made of rubber elastic material, creates a linear radiation zone.The material is pushed forward by the drive rollers 25 and 26. The slightly deformable counterroller 18 is adjustable in terms of the pressure as shown in arrow 13. The interconnected sheets 13, 14 are slightly bent between the two rollers 17, 18 according to the curvature of the reel 17. As a result, the interconnected sheets 24 are carried along the reel 17 with the welding thread 15 and rolled up onto the reel 20 with the same curvature.that an appropriate length of the pressure area is available, which is longer than the radiation zone 16.

In the example, two materials are joined together, but in principle it is also possible to join three materials together, transferring the heat generated at the contact surface to the third film if the medium material is sufficiently thin.

In addition, a cleaning device in the form of a brush is also shown in Figure 19 in a schematic way. Furthermore, in a way which is not shown in the figure but which is easy to understand and implement for the professional, one or more masks may be provided in roll 17 to give a certain contour to the welding seam 15. In addition, 18 flat, non-shown pressure sensors may be provided on the outer edge of the second roll to control the pressure. It is also possible to provide roll 18 with a rubber elastic cover and to place the sensors under the cover.

With a laser power of 70 W, a welding speed of 400 mm per second can be achieved with a 15 mm welding line, and a 15 times slower welding speed with a point weld or a laser beam of the same width (1 mm) in the direction of motion.

Figure 4 shows the transparent reel 17 and the slightly deformable reel 18 in enlarged form, with a rear-view mirror 6 in reel 17 which redirects the laser beam from the light source to line 16.

Claims (12)

1. A process for joining endless polymer materials (13,14), in which by means of a laser beam (2,12) the upper material (13) is shone through by the laser beam (2,12) and, at the contact surface between the upper material (14), which is transparent to the laser beam, and the lower material, which is opaque to the laser beam, the two materials (13, 14) are melted and joined to each other under pressure, the laser beam (2,12) and the materials to be joined being moved relative to each other, wherein in order to produce a welded seam running in the longitudinal direction at the contact surface, a process zone (P) is provided, in which the material is heated continuously to the melting temperature (Tm) in a preheating zone (I) by means of laser beams and is subsequently melted in a melting zone (II), and wherein the materials are already pressed together in the area of the irradiation zone (D) of the laser beam (2,12), characterized in that the materials are guided through two contrarotating rollers (17, 18) that press against each other, the laser beam (2, 12) being brought into the irradiation zone by a first roller (17) that is transparent to the laser beam, there a linear process zone (P) is provided, and the second roller (18) is slightly deformed at the circumference by the first roller (17).
2. The process as claimed in claim 1, characterized in that the linear process zone (P) is produced, at least partly, by means of a curtain-like collimated laser beam (2).
3. The process as claimed in claim 2, characterized in that a following point-like laser beam is additionally provided in the melting zone (II).
4. The process as claimed in one of the preceding claims, characterized in that the joined materials are subsequently rolled up in the direction of curvature corresponding to the first roller (17).
5. The process as claimed in one of the preceding claims, characterized in that the first roller (17) is cleaned on the outer surface before making contact with the materials.
6. The process as claimed in one of the preceding claims, characterized in that the welding structure is influenced by means of a mask in the first roller.
7. The process as claimed in one of the preceding claims, characterized in that the contact pressure is determined by means of pressure sensors arranged on or in the area of the surface of the second roller (18).
8. The process as claimed in one of the preceding claims, characterized in that the temperature is measured by means of a pyrometer after the process zone (P).
9. An apparatus for joining polymer materials by means of a laser beam (12), which shines through the upper material (13) on account of the transparency of the latter and, at the contact surface with the lower material and a device for pressing the materials together, characterized in that in order to join endless materials, the latter are guided through two contrarotating rollers (17, 18) that press against each other, the first roller (17) being constructed from a material that is transparent to a laser beam and is tubular, and the second roller (18) being constructed from a material that can be deformed easily at the surface, and devices (11) for producing at least one linear laser beam (12) which is arranged in the direction of movement of the materials in the contact zone being arranged in the first roller (17).
10. The apparatus as claimed in claim 9, characterized in that a device (7) for the IR measurement of the temperature is arranged in the first roller (17), and is preferably designed such that it can be moved with regard to the measurement point.
11. The apparatus as claimed in claim 13, characterized in that the devices (11) produce a point-like laser beam after the linear laser beam in the direction of movement in the contact zone.
12. The apparatus as claimed in one of the preceding claims 9-11, characterized by a cleaning device (19) on the outer circumference of the first roller (17).