DE4225679A1 - Laser appts. for welding plastics parts of medical and laboratory filters - has low reject rate and uses same laser for both cutting and welding operations - Google Patents

Abstract

Appts. is claimed for welding plastics parts of medical and laboratory filter elements or systems, esp. for welding the housing upper and lower parts of a sterile one-way filter holder to a filter plate which is arranged, with bypass-tight filtrate spaces, between the housing parts and which is in the form of a surface filter, bulk filter or the like. The appts. includes (a) a manipulating device (29) which places the burr-free laser cut filter plates (2) directly into the filter element or between the housing upper and lower parts (30, 31) and/or which stacks the individual filter element parts to be welded; (b) a pressing device (32) which presses the filter element parts (30, 31) together; and (c) a laser unit (1) for welding the filter parts (30, 31) made of physiologically harmless PVC, polycarbonate, polysulphone, polypropylene or polyamide, the laser (4) and/or its focussing and welding optics (6, 7) being movable by a manipulation system (32, 9, 26, 27, 28) along the joint seam to be welded or along the axis of the optics and the laser emitting a laser beam of wavelength and power density corresponding to the transparency region of the plastics to be welded. Also claimed are a process for welding the plastics filter parts without burning, welding being carried out using laser radiation with low absorption and high penetration, energy coupling into the material vol. causing melting without destruction of the plastics and a medical and laboratory filter holder, made of thermoplastics, has join seams in the form of laser weld seams in longitudinally welded plastics walls of 0.5-2 mm thickness or with a joint seam depth of up to 2mm. ADVANTAGE - The appts. is inexpensive, since the same layer is used for both the cutting and welding operations, and the process has low reject rate.

Description

The present invention relates to a method and a system for welding individual plastics parts to filter elements or systems for medical and laboratory technology, especially for welding the Upper part of the housing and the lower part of a sterile Disposable filter holder, being between those to be welded Housings divide one that separates the filtrate spaces there Filter disc, which as a surface filter, depth filter or the like., bypass-tight is to be determined.

Such medical technology parts are usually made thermoplastic materials formed, whose So far, welding has usually been carried out using ultrasound Welding takes place. It applies plastic parts below various medical technology elements, for example for sterile ventilation and removal of liquids, for Filtration as well as for infusion and transfusion, in particular regarding the housing parts and the filter fabric and the  -Weld the membrane precisely and tightly together.

Since dimensional tolerances of 0.02-0.05 mm often do not exceed allowed to step, and an increased strength of the Joining seam is required, there are pinch seams there specially designed joining geometry, which Melt escaping during ultrasonic welding record so that no impurities or functional Malfunctions in the finished product due to the manufacturing process should be caused. In series production medicine technical plastic parts is a considerable ferti engineering effort necessary to meet the strict Regulations on sterile manufacturing and packaging and the high requirements regarding dimensional accuracy to comply with the parts. It must be permanent Quality control and a welding energy control take place, these plants using a microprocess control must be equipped.

An optimized energy flow must be ensured both too low and too high Welding energy to a reduced quality of ver bond line leads. Especially for sealing welds by thin-walled parts the joining area with a Squeezed seam. The installation of such But squeeze seam requires a high manufacturing technical effort in the manufacture of the joining parts. The Ultrasonic welding is disadvantageous in that than the parts to be welded through a large area the seam is coupled. With this welding process is a larger generator output and higher Amplitude necessary, so that there are high investment costs an ultrasonic welding machine. If the  Joined parts, in particular with regard to the installation of the squeeze not correctly constructed and manufactured to size there is a risk that the melt in the Joining zone is not actually embedded. she can to that extent spray out of the seam area in an uncontrolled manner. This results in an undefined welding behavior, low strength and poor reproducibility welded joint as well as poor Tightness.

In this respect, faulty ones very often occur in practice Welds due to incorrect joining geometry, due to raw material influences and lack of verification of manufacturing and processing conditions in the injection molded parts.

Perfect welding connections can be made with the Ultra Achieve sound welding only with dimensionally accurate molded parts. Such dimensional accuracy is only with injection molded parts possible within larger tolerances, so that Causes of incorrect welding. Based on these In practice, difficulties are monitored Weld seam quality and control of the welding machines with Microprocessors and process monitoring devices, which for example, when the performance falls below or exceeds interrupt the welding process when welding. Disturbances such as transformation piece, sonotrode, friction losses, dimensional tolerances of the molded parts and bad Coupling the sonotrode to the molded part can be done but not completely eliminate it.

Ultrasonic welding with a crimped seam in the joint compared to other welding processes  drive very high demands on the seam strength, where partially crystalline plastics such as polyamide weld are cash. There is also a gas and liquid at the seam tightness attainable.

However, ultrasonic welding is particularly important due to the high manufacturing costs for the Creation of the geometry of the joining seam, the required Control and monitoring devices for process monitoring, the required tight dimensional tolerances of the molded parts as well as the poor coupling of the sonotrode to the molded part of Disadvantage.

In this respect, the task of a procedure arises especially for the seam welding of plastic parts in the Medical and laboratory technology of the type mentioned at the beginning to improve and implement a facility to create this method so that the welding of the Plastic parts is easier and especially with a lower manufacturing outlay Joining zones results, with sufficient security of the Welding process occurs.

The expenditure on equipment for manufacturing laboratory and medicine technical parts should be reduced to the extent than partly the same through common manufacturing techniques Equipment for cutting plastic parts or Filter discs and for welding this plastic parts or to bypass-tightly enclose the filter disks should be usable in plastic filter holder. Despite the low manufacturing technology and equipment The filter elements and systems should also involve effort a small failure can be produced, so that at low overall manufacturing costs  more economical production results.

To solve this task is in a system for Welding plastic parts of filter elements or systems for the medical and laboratory technology of type mentioned at the outset in accordance with the characterizing part of the Main claim provided that the laser Cutting device beard and burr free with high cut edge quality cut filter discs directly over a Handling device in the filter elements or between the upper and lower parts of the sterile Disposable filter holder inserted and / or to each other welding individual parts of the filter elements on each other be arranged that also a pressing device is provided with which the parts of the filter elements are compressible and that in addition a laser processing system is used, which is now for Welding of the physiologically harmless art fabric, namely made of polyvinyl chloride, polycarbonate, Filters made of polypropylene, polysulfone or polyamide parts is used, the laser emitter and its sweat optics non-contact in a certain predefined Distance to the workpiece along the joint to be welded or this along its length along the welding optics is feasible via a handling system and with the using lasers laser beams with a wavelength and Intensity according to the permeability range of the welding plastic material is emitted.

In contrast to laser cutting, it applies to Laser welding to use laser radiation at which the penetration depth of the radiation in the order of magnitude Material thickness is (volume absorption). With a big one  The penetration depth is the absorption in the choose welding material so that for the present plastic material is still sufficient Transmittance depending on the absorption law speed of the material thickness, the intensity, the loading working speed and the temperature of the Material results.

For welding hollow cylinders or plate material with a wall thickness of 1 to 2 mm made of polyamide or polypropylene, an Nd: YAG laser with an output power of 50-100 watts at a processing speed of 10 cm / sec is preferably used according to claim 2. used. Although due to the wavelength of this laser there is a higher transmittance compared to a CO ₂ gas laser with a wavelength of 10.6 / µm, in principle a CO ₂ gas laser is also suitable for welding such plastic parts, the penetration depths of this laser radiation smaller and thus the thickness of the weldable materials is thinner. Especially with a CO ₂ - gas laser with which a welding of thermoplastics is to take place, in which a strong coupling of energy occurs due to the low melting temperatures of 100-300 ° C, laser welding must therefore be carried out at a lower processing speed, with heat build-up effects Avoid prolonged exposure to laser radiation so that no material decomposition or evaporation occurs. In this respect, when welding thicker pieces of material using CO ₂ gas laser radiation, it is necessary to adjust the machining parameters to avoid thermal decomposition. In this respect, monitoring of the temperature or the change in the material composition of the melt is provided.

By suitable setting of the local and temporal intensity distribution in the welding and cutting point, as well as the radiation intensity, the machining speed, the specified degree of absorption of the material, the material thickness and its optical deposition volume, the laser and machining parameters can be set such that at least at the production of thinner thermoplastic plastic parts (material thickness 1 to 2 mm) both CO ₂ gas lasers and suitably operated solid-state lasers in the form of the Nd: YAG laser or an Nd: glass laser can be used for welding as well as for cutting the plastic parts.

According to claim 9, the welding of Filter housing of the sterile disposable filter holder with the one there bypass-tight filter discs in one Laser processing station, which both for cutting the Filter discs made of web-shaped or curved filter fabric or filter membranes is suitable, as well as for ver welding the housing parts of the sterile disposable filter holder with bypass-tight inclusion of those to be created there Filter discs.

Advantageous embodiments of the system for welding of plastic parts for the medical and laboratory technology and the type of sweat to be used procedure result from the patent claims and the following description of Darge in the drawings presented embodiment of a system for welding Plastic parts.

The drawings show:

Fig. 1 A laser processing system for welding a filter housing upper part and a lower part of a disposable filter holder, with a filter disc inserted between them, and the structure of the laser processing system from a supply and processor part, a laser beam source and a welding head with infrared optics, which in 3 levels is adjustable, as well as a handling device for pressing the filter housing parts and for rotating these parts with the joint to be welded below the welding head;

Fig. 2 is a cross-sectional view of the welding head with its focus and optical processing system, showing the beam focusing and the supply of an inert, protective inert gas;

Fig. Both being effected 3 is a schematic representation of a laser cutting and laser welding usable focusing and processing optics, through the use of a mirror system with the rotatable deflecting mirrors the path control of the laser beam to cut out the filter disc and for applying the weld;

Fig. 4 is a schematic representation of the use of the laser processing system according to FIG. 1 for cutting round filters, in which the welding head of the system is now used as a cutting head and by means of its processing optics by laser beam melting from a membrane band guided over rollers, the filter disks can be cut out and can be transported to their packaging station via a lower conveyor belt that runs out to the side.

The laser processing system ( 1 ) shown in Fig. 1 is used there to weld an upper filter housing part ( 30 ) and a lower filter housing part ( 31 ) to a filter holder, these parts and the round filter ( 2 ) to be arranged between them being combined into one via a first handling device ( 29 ) second handling device ( 32 ) are transported.

The second handling device ( 32 ) is used to arrange the two filter housing parts ( 30 , 31 ) in such a way that they are arranged one above the other with their flange pieces forming a central circumferential sealing surface, the filter disc ( 2 ) with its radially outer circumferential peripheral regions being fixed there at the same time .

The two filter housing parts are connected by laser beam melting to the laser processing system ( 1 ), the welding head ( 5 ) of which is positioned at a suitable distance above the weld seam to be created, and the two filter housing parts are welded by rotating the joint to be welded underneath this welding head. The rotation is effected by the second handling device ( 32 ). In this respect, welding is achieved both by moving the infrared processing optics ( 6 , 7 ) and by moving the piece of material to be welded itself.

The welding head ( 5 ) is guided via an actuating unit which has three degrees of freedom in the form of a coordinate cutting machine. A linear unit ( 9 ) adjusts the welding head ( 5 ) in the x-direction, with two outer guide rails ( 26 , 27 ) perpendicular to the left and right, it can be moved in the z-direction and by the linear actuator ( 28 ) there is a movement perpendicular to these two planes in the y direction.

In this way, the welding head ( 5 ) with its focusing and processing optics ( 6 , 7 ) can be positioned at a suitable distance from the joint to be welded.

The laser processing system shown in Fig. 1 ( 1 ) consists of a power supply and processor part ( 3 ), a laser beam source ( 4 ), the laser welding head ( 5 ) and the focusing and processing optics arranged there ( 6 , 7 ).

The actuating device ( 8 ) for the welding head ( 5 ) can also be used as a coordinate cutting machine, so that filters ( 2 ) one after the other from a filter membrane web ( 11 ), which is moved discontinuously through an integrated transport system ( 10 ) via a cutting table ( 12 ) can be cut out in a row.

The laser beam source ( 4 ) serves both for welding the filter housing parts ( 30 , 31 ) and for cutting the round filter ( 2 ) according to FIG. 4. It is a CO ₂ gas laser with a wavelength of 10, 6 µm with an output beam power of 50 watts. When setting a focal point diameter of 1 mm, an ellipsoidal intensity distribution in the focal spot is a welding of the filter housing via a circumferential web axially projecting in the flange area with a web thickness of approx. 1 mm at a welding speed of 0.3 m / sec. possible. The welding is done by pressing the plastic parts. The laser power and / or intensity distribution in the focal spot is controlled by temperature detection so that the temperature of the melt does not exceed the decomposition temperature. If plastic walls with a greater material thickness are to be welded, an Nd: YAG laser is preferably used which, with the same performance data, has a greater depth of penetration with a lower surface absorption for the plastic materials to be welded. In this example, the filter housing parts consist of polypropylene or polycarbonate.

The laser beam fusion welding is carried out under protective gas, which can be introduced via the welding head ( 5 ) shown in FIG. 2 and can be guided onto the welding point coaxially with the laser beam. This protective gas prevents oxidation and discoloration of the plastic at the welding point.

The processing optics shown in the welding head consist of ZnSe lenses, of which the lower focusing lens ( 6 ) is shown. By means of these lenses, the laser beam can be expanded in a suitable manner and imaged on the joint to be welded with a different focal length. The shielding gas is supplied via an inflow opening ( 22 ) laterally below the focusing optics ( 6 ), the shielding gas exiting through an outlet opening together with the laser beam at the conically tapering tip of the welding head ( 5 ).

By welding the outer circumferential plastic it is at the same time bridges through laser beam melting possible the adjacent outer edge area of the inserted round filter with in the welded joint to involve. In this respect, an optimal seal this round filter with simultaneous contact pressure between the two circumferential flange surfaces of the filter upper part of the housing and the lower part of the filter housing.

If the welding with an Nd: YAG laser is to be carried out at high process speed, a focusing and processing optics ( 6 , 7 ) according to FIG. 3 is preferably used. In this case, the laser beam is guided outside using a scanning process around the arrangement of the two filter housing parts that is not to be rotated. Here, the (4) laser beam emitted from the solid-state laser (18) is mapped to the path control via a mirror system with inde pendently rotatable and tiltable deflecting mirrors (19,20) to be welded seam joint and is guided along this.

The deflection mirrors are preferably arranged in mutually perpendicular planes of rotation in order to simplify the beam guidance in accordance with the path coordinates stored in the process computer ( 3 ).

The cutting of the filter disks from the filter material web ( 11 ) is carried out using a CO ₂ gas laser with a wavelength of 10.6 µm with a focal spot of 0.1 to 0.5 mm in diameter and using a Gaussian energy distribution in the laser beam, the focal spot being set to the focus and the beam there to the only power density maximum with maximum intensity, in such a way that the round filters are also preferably cut by laser beam melting at a cutting speed of 10 to 100 m / min.

The energy is coupled in such a way that At least initially, there is surface absorption is present, so that due to the pronounced absorption maximums of plastics for a wavelength of 10.6 µm and the poor thermal conductivity of plastics melting of the plastic material on the outer cutting point and thus due to the high Radiation energy density of the sharply focused laser finally a cut across the entire material Strength.

According to Fig. 4, be cut into individual circular filter membrane filter web (11) is in this case from a supply roll to the plane of the cutting table (12) with a discontinuous feed, according to the filter moves forward disk diameter when adjacent slices across the width of the material web in a row, the filter ( 2 ) are cut out.

The rest of this cut material web is wound up as a waste belt ( 13 ) on a transport roller ( 14 ).

The material web ( 11 ) is guided on the cutting table ( 12 ) in such a way that the cut-out filter disks ( 2 ) from the filter material web () through an opening in this or a laterally extending gap between the cutting table and the upstream deflection roller ( 17 ). 11 ) fall out and are collected and transported to a packing station ( 15 ).

The cut filter disks ( 2 ) are transported to the packaging station ( 15 ) by an endless conveyor belt ( 16 ) arranged below the material web ( 11 ), onto which the filter disks ( 2 ) are cut after being cut out of the filter material web ( 11 ). fall.

Via the process computer ( 3 ) created in the power supply, both the welding and the cutting of the plastic and filter membrane parts were checked and controlled for the plug energy used during laser beam melting. The relationship between the laser output power P and the processing speed v is determined and regulated. Furthermore, for laser beam cutting in this process computer ( 3 ) control and control devices to maintain and control the exactly defined cutting path of the welding head ( 5 ) used as a cutting head. The distance between the focusing and processing optics ( 6 , 7 ) from the welding point and the intersection is automatically scanned using an automatic sensor system and automatically adjusted and kept constant by a capacitive height adjustment of the welding or cutting head ( 5 ).

It is there thanks to the laser beam fusion cutting possible, the round filter with a high cutting edge quality to cut, unlike conventional cutting punching process no fringes on the outer edge of the Filter disc result more. The filter edge is in this respect, beard and burr-free after laser cutting.

It is there thanks to the scanning method to be used possible filter discs with different diameters and cut different contours. Using of a mirror system it is by mere adjustment a larger or smaller deflection angle of the deflection mirror, which immediately before the one to be cut Workpiece is arranged, possible with this diameter to cut.

Due to the guidance of the processing optics ( 7 ) along the linear unit ( 9 ) and the mounting of the movable filter membrane web on the cutting table, low-vibration and precise guidance of the laser optics and membrane web is possible.

According to Fig. 3 there is a control section, in that a semitransparent mirror is arranged in the beam path of the laser, over which a suppression of the at edge quality for achieving a virtual dross-free section of the filter discs as well as a control of the reflectance of the laser beam during welding characterized is possible at an irregular cut edge or the reflected radiation portion to be welded. The processing optics and the setting of the laser parameters are adjusted via a discriminator when a threshold value of the reflected radiation is exceeded. In this respect, an optimal welding of the joint seam or an optimal cutout of the filter disc can then take place.

The reflectance serves as a measure for setting the laser parameters necessary for volume absorption. The The transmittance is measured immediately via a photodiode behind the welding point or Joining seam.

In laser fusion welding, the Trans Degree of mission of the laser radiation measured in that it It is important to choose the laser parameters such that a Welding without burning the plastic material takes place, the laser radiation a large depth of penetration in the material to be welded and thereby insofar as the absorption of laser radiation, in particular is low on the surface. So it's one Coupling of the laser radiation in the material volume with subsequent melting without destroying the plastic ensure.

To form the volume absorption of the laser radiation in the area of the joint to be welded, the regulation of the energy density and / or the intensity distribution of the laser radiation in the welding point is first carried out as a function of the reflection portion of the laser radiation resulting there in the welding point. This is then followed by a further regulation of the energy density and / or intensity distribution of the laser radiation in the welding point in order to set a sufficient size for the volume absorption and the welding depth or the penetration depth of the laser radiation as a function of the currently measured transmission degree behind the joint. The transmission is carried out via the diode ( 33 ) arranged there.

Furthermore, the energy density and / or intensity applies tity distribution in the focal spot or spot weld regulate that the temperature of the melt is not the Zer setting temperature of the plastic to be welded materials reached. In this respect, there is also a Temperature detection of the material surface and the Melt in the welding spot depending on this Temperature and the predetermined decomposition temperature of the Melt regulation of energy density and / or intensity distribution in the focal spot of the laser.

Claims (20)

1. System for welding plastic parts of filter elements or systems for medical and laboratory technology, in particular for welding the upper and lower housing parts of a sterile disposable filter holder with a parts between the housing and their filter spaces bypass-tight filter disk in the form of surface filters , depth filters, or the like. characterized in that a handling device (29) slices, the cutting device by a laser beard and burr-free cut filter (2) directly into the filter elements, and between the upper housing part and the housing lower part (30, 31) of the sterile disposable filter holder inserts and / or arranges the individual parts of the filter elements to be welded to one another, that a pressing device ( 32 ) is also provided, with which the assembled parts ( 30 , 31 ) of the filter elements can be pressed together and that a laser processing system ( 1 ) is also provided m welding the filter parts ( 30 , 31 ) provided from physiologically harmless plastic in the form of poly venyl chloride, polycarbonate, polypropylene, polysulfone or polyamide, the laser ( 4 ) and / or its focusing and welding optics ( 6 , 7 ) in Distance to the workpiece ( 30 , 31 ) along the joint to be welded or this along its length along the focusing and welding optics via a handling system ( 32 ; 9 , 26 , 27 , 28 ) is feasible and the laser ( 4 ) of the laser processing system ( 1 ) emits laser beams ( 18 ) with a wavelength and with a sufficient power density corresponding to the permeability range of the plastic material to be welded. 2. System for welding plastic parts according to claim 1, characterized in that the laser processing system is a continuously or quasi-continuously operated CO ₂ gas laser ( 4 ) or a solid-state laser operated in this way or in the form of a pulse in the form of an Nd: YAG laser or one Nd: glass laser. 3. System for welding plastic parts according to claim 1 or 2, characterized in that the laser ( 4 ) of the laser processing system ( 1 ) emit lasers ( 18 ) from a wavelength range of 190-11 000 nm and the distance of the weld from the laser is greater than the distance of the laser ( 4 ) from the point of maximum intensity of the focused laser beam, with an ellipsoidal intensity distribution of the laser radiation over the beam cross section resulting on the weld seam. 4. System for welding plastic parts after Claim 1, 2 or 3, characterized in that a solid-state laser with quality control is provided. 5. System for welding plastic parts according to claim 1 to 4, characterized in that in a laser processing system for welding with a CO ₂ gas laser ( 4 ) movable mirror systems are designed as flexible beam guidance and that for the flexible guidance of the beam of a Nd: YAG laser is a fiber optic with a flying infrared optics. 6. System for welding plastic parts according to one of claims 1 to 5, characterized in that the laser processing system ( 1 ) with a welding head ( 5 ), which has a processing and / or focusing optics ( 6 , 7 ), directly, or that their laser radiation can be guided around the plastic parts ( 30, 31 ) to be welded using a scan process along the intended weld seam. 7. System for welding plastic parts according to one of the claims 1 to 6, characterized in that for performing a welding process by means of laser beam melting, the arrangement of the welding optics ( 7 ) takes place within a tubular welding head ( 5 ), which extends to an outlet opening ( 21st ) tapers for the laser radiation and a lateral inflow opening ( 22 ) is created in the welding head at a distance from the outlet opening ( 21 ), through which an inert, inert gas blown coaxially to the laser beam onto the welding point can be supplied. 8. System for welding plastic parts according to one of the claims 1 to 7, characterized in that the laser processing system ( 1 ) has a process computer and a control unit with which the processing and beam parameters during welding can be adapted to the material properties of the plastic individual parts to be welded and adjustment according to the target values is possible. 9. System for welding plastic parts according to one of claims 1 to 8, characterized in that the laser processing system ( 1 ) in addition to welding the plastic parts ( 30 , 31 ) of a filter holder made of thermoplastic material also for cutting the bypass tightly to be arranged in the filter holder Filter disc ( 2 ) from a web or sheet-shaped filter fabric or membrane (11) is created. 10. System for welding plastic parts according to one of claims 1 to 9, characterized in that in the beam path of the processing optics ( 6 , 7 ) is arranged a semi-transparent mirror for the laser radiation and the radiation component reflected therefrom ( 24 ), via which a masking reflected, non-absorbed radiation components on a radiation meter ( 25 ). 11. Process for welding plastic parts of Filter elements or systems, especially for ver welding the upper part of the housing and the lower part of the housing a sterile disposable filter holder with inlet connection and Outlet connection as well as between the filtration rooms Plastic parts bypass-tight filter disks in Form of surface filters, depth filters and the like characterized in that for welding without burning the plastic material laser radiation is used, the absorption of which during Machining is low and the depth of penetration is large, with the energy coupling in the material volume closing melting without decomposing the plastic he follows. 12. Process for welding plastic parts according to Claim 11, characterized in that the radiation from an Nd: YAG laser is used, which a high depth of penetration with low surface absorption for the plastic parts to be welded. 13. Process for welding plastic parts according to  Claim 11 or 12, characterized in that the processing parameters of laser radiation during welding and the welding optics as well as their processing speed and laser output power to the material properties of the Plastic parts are adjusted so that a thermal Destruction of the plastic parts is avoided. 14. Process for welding plastic parts according to Claim 13, characterized in that via a temperature detection of the material surface and the Melt in the welding spot of the laser depending on this temperature and the decomposition temperature of the melt the energy density and / or intensity distribution in the Focal spot of the laser is controlled so that a Volume absorption in the weld spot forms and during the surface and volume absorption of laser radiation the decomposition temperature of the melt is not reached. 15. Process for welding plastic parts according to one of claims 11 to 14, characterized in that to form the volume absorption of the laser radiation in the Area of the seam to be welded depending on the portion of reflection resulting there in the welding spot the laser radiation and to set a sufficient size of the volume absorption and the welding depth or the penetration depth of the Laser radiation depending on the transmittance behind the seam the regulation of energy density and / or intensity ver division of the laser radiation at the welding point.   16. Process for welding plastic parts according to one of claims 11 to 15, characterized in that welding under pressure of the plastic parts on the Joined by laser beam melting under protective gas. 17. Process for welding plastic parts according to one of claims 11 to 16, characterized in that Plastic walls from 0.5 mm to 2 mm thick or with a Joint depth up to approx. 2 mm by compressing the Joining seams are welded lengthways by the laser radiation. 18. Process for welding plastic parts according to one of claims 10 to 17, characterized in that the walls of plastic parts made of polyvinyl chloride, Polycarbonate, polypropylene, polysulfone or polyamide Laser radiation are welded. 19. A method for welding plastic parts according to one of the claims 11 to 18, characterized in that the filter upper and lower filter parts of a disposable filter holder on their axially projecting connecting web, which extends around the outside in the flange region to be connected, with a web thickness of approx CO ₂ gas laser (10.6 µm) with an output power of 50 watts, a diameter of the focal spot in the welding spot of approx. 1 mm and with a welding speed of approx. 0.3 m / sec. be welded. 20. Filter holder made of a thermoplastic for Medical and laboratory technology, characterized in that Joining seams on longitudinally welded plastic walls by 0.5 mm to 2 mm thick or with a joint depth up to 2 mm are designed as a laser weld seam.