DE102008020943A1 - Method for joining at least two transparent joining partners by means of laser transmission welding - Google Patents

Abstract

The invention relates to a method for joining at least two joining partners by means of laser transmission welding in which the at least two joining partners which are at least partially transparent for laser radiation are brought into mutual central or direct surface contact and include at least one common joining region, which is acted on by the laser beam, after the latter is at least partially passed through at least one joining partner, and is absorbed in the joining region to an extent, so that forms a melt in the joining region, which leads to solidification to a material bond between the two joining partners. The invention is characterized in that a joining region enclosed by at least two joining partners is provided, in which nanoparticles are contained which are capable of forming surface plasmons by way of light absorption, which lead to the heating of the nanoparticles and ultimately to the formation of enamel within the joining region.

Description

Technical area

The The invention relates to a method of joining at least two joining partners by means of laser transmission welding, in which the at least two for a laser radiation at least partially transparent joining partners in a mutual medium or immediate surface contact be brought and at least include a common joining area, the is acted upon by the laser beam after this by at least at least partially entered a joint partner is, and in the joining area to an extent is absorbed, so that in the joint area a melt training, which, after solidification to a material connection between the two Leads mating partners.

State of the art

To the integral connection of at least two mostly Polymer materials existing components or films is in common Practice the technique of laser transmission welding used in the at least one of the joining partners to be joined together from a transparent to the laser radiation polymer material exists, so that this of the laser beam largely harmless can be penetrated in transmission. Provision is hereby to that effect to meet that caused by light absorption heat input primarily in the joining plane of the respective cohesive has to be joined together. For this purpose, it is a material that significantly absorbs the laser light within a joining area comprising the joining plane to bring in between both joining partners.

The Absorber materials can either be in one of the two to be joined together or in the form of a superficial cloth job on the Surface of one or both to be joined together Joining partners, for example by means of a printing or spraying process be applied. The contact by surface contact both joining partners to be joined together Joining area is as explained above with laser light irradiated until a superficial melting of one or both join partners in the joining area, where the joining process can be supported thereby by the joining partners an additional on the Be exposed joint area oriented contact pressure.

typical Absorber materials used for laser transmission welding of transparent to the laser light thermoplastic Components are soot or dye particles, alone or in combination with an additional carrier particulate or molecularly applied to the surface of at least one joining partner become. Ideally, it is desirable that after completion of the welding process the absorber material contained within the joining area no haze or color changes the joining partner should cause. In a preferred manner Therefore, absorber materials are used, the laser radiation with absorb a wavelength in the infrared spectral range but transparent in the visible spectral range are. Absorber materials are also used for purposes of laser transmission welding used, which is thermally during the laser irradiation decompose and no longer visible after the welding process are.

All heretofore known absorber materials for this purpose the photon energy of the laser radiation either in the context of electronic To absorb band transitions or the laser beam inherent light energy is due to light scattering within the Joined joint area, a process of use particulate absorber materials, such as carbon black or silica occurs.

From the EP 0 159 169 For this purpose, a laser transmission welding process, in which two of synthetic resin material joining partners are welded together over a common joining region, of which a joining partner for the wavelength of the laser beam used is transparent and the other joining partner is offset at least at the contact surface to be joined with soot particles, the absorb the laser light passing through the transparent joining partner.

A similar process is the DE 44 32 081 A1 can be seen in which the each not transparent to the laser radiation joining partner consists of a thermoplastic material, which is as it is carbon black or nigrosine added for purposes of light absorption. Although nigrosine does not discolor the joining components of polymer material in the manner that is the case with the use of carbon black, nigrosine nevertheless has a significantly lower absorption in the near infrared range compared to carbon black. Thus, high laser light powers in the conventional laser wavelengths of 808, 940 and 1064 nm are required. In addition, nigrosine is toxic and, moreover, carcinogenic.

In addition to the use of carbon black as a laser light absorbing material for performing laser transmission welding process is from the publications EP 126 787 A1 such as DE 198 14 298 A1 also for the use of silicon oxide, but that at the usual laser wavelengths of 808, 940 and 1064 nm are not satis- satisfied lende absorption shows.

In contrast, in the WO 00/20157 proposed to use as laser beam absorbing materials dyes which are substantially transparent in the visible region of the spectrum, but have pronounced absorption properties in the infrared spectral range. Due to their lack of photostability or radiation resistance and especially because of the low thermal stability of such dyes are not suitable for direct incorporation into polymers to be welded together by conventional processing methods, such as extrusion, coextrusion, glass molding or injection molding. In addition, such dyes are chemically inert and also tend to migrate.

In the DE 10 2004 018 547 A1 discloses a method for welding-connecting plastic parts by means of laser radiation, in which at least one non-ionic, laser-resistant compound having a thermal resistance of at least 300 ° C. is selected as the material absorbing the laser radiation. For this purpose, polycyclic organic compounds, doped tin oxides and Hexaboride NeB ₆ of lanthanide and alkaline earth metals (Me) are selected, which are substantially non-absorbing in the visible region of the spectrum, however, in the infrared spectral region have pronounced absorption properties.

The absorber materials described above have a number of Disadvantages, for example, when mixing the absorber material in the polymer material of each joining partner involved a relatively large volume in the region of the weld influenced, so that the heat affected zone is not longitudinal a plane extends. When applying the absorber materials on the respective polymer surface of the respective joining partner the applied layer thicknesses are relatively large, d. H. they are in the micrometer range, especially as the dyes partially consist of micrometer sized crystalline particles and also from a surrounding auxiliary material on the surface to be fixed.

Presentation of the invention

Of the Invention is based on the object, a method for joining of at least two joining partners by means of laser transmission welding, in which the at least two for a laser radiation at least partially transparent joint partners in a mutual medium- or direct surface contact be brought and at least include a common joining area, the is acted upon by the laser beam after this by at least a joining partner at least partially passed is and absorbs in the joint area to an extent becomes, so that forms a melt in the joint area, which, after solidification, leads to a material bond between the two joining partners, in such a way that by the light-absorbing material influenced joining area as small as possible should be, so that the thermally treated joining area in training a weld as possible no or only slightly visible and material intrinsic Can cause irritation. In addition, supposedly the energy input to be deposited by laser beam for training a complete connection between the at least two joining partners are kept as low as possible.

The Solution of the problem underlying the invention is specified in claim 1. The concept of the invention advantageously further Features are the subject of the dependent claims and the other Description in particular with reference to possible Refer to exemplary embodiments.

The Solution-based method for joining at least two joining partners by means of laser transmission welding, in which the at least two for a laser radiation at least partially transparent joint partners in a mutual medium- or direct surface contact be brought and at least include a common joining area, the is acted upon by the laser beam after this by at least a joining partner at least partially passed is and absorbs in the joint area to an extent becomes, so that forms a melt in the joint area, after solidification to a material connection between the two joining partners leads, characterized by being one of at least Both joint partners included joining area is provided in which nanoparticles are contained in the way form the light absorption surface plasmons in capable of heating the nanoparticles and ultimately lead to the formation of enamel within the joint area.

The idea underlying the invention provides for the targeted use of special absorber materials for laser beam absorption at the location of the joining region, which show the physical effect of the plasmon excitation. These are collective oscillations of the conduction band electrons of metallic nanoparticles. Plasmon excitation is also referred to as surface plasmon, plasma resonance absorption, particle plasmon, or Mie plasmon. Basically, a collective oscillation of electrons within a nanoparticle is called a plasmon. The Plasmonenanregung becomes particularly with Nanopartikeln of metal len, their alloys as well as metal oxides observed. The excitation of plasmons can typically be observed in cases where the particle size of the light-exposed particles is small compared to the wavelength of light, ie in the case of the use of visible light or infrared light typical particle sizes of such nanoparticles are between a few nm to several 100 nm.

maximum Absorption effects in the context of the Plasmonenanregung takes place in those Cases where the wavelength of each incident Light coincides with the spectral position of the plasmon resonance of the nanoparticles. The spectral position of the plasmon resonance is of the material of the nanoparticles itself, from a medium surrounding the nanoparticles, usually one Polymer material, as well as the particle size and Particle shape of the nanoparticles dependent. Thus, it is possible by suitable choice and dimensioning of the above parameters to influence the position of the plasmon resonance in a suitable manner, to ensure the greatest possible overlap between the spectral position of the plasmon resonance and the wavelength of the laser light incident on the nanoparticles.

in the Pathways of plasmon excitation will heat and give the nanoparticles their heat locally to the matrix surrounding the nanoparticles from. Fall the spectral position of the plasmon resonance as well as the light wavelength the laser radiation largely together, so is to form a Melt a single layer of nanoparticles within the joining area sufficient, especially as nanoparticles by means of plasmon excitation light energy effective in vibrations and thus convert into heat capable of being directly within the joining area is delivered.

The laser-induced heating of the nanoparticles leads in addition to the developing melting of the nanoparticles surrounding Polymers also change size and shape of the nanoparticles due to coalescence and recrystallization processes, possibly also by Coulomb explosion. By the change of particle size as well as particle shape of the Nanoparticles cause a shift in the spectral position the plasmon resonance, by means of a suitable metrological Capture as an indication of a measure of incipient Is to be regarded melting process. For example, lies the plasmon resonance the nanoparticles in the visible spectral range, so can a color Change in the joining area within the itself forming weld, for example, using recorded a simple optical transmission measurement and accordingly be quantified. In this way, the changing ones allow Transmission values a quality assessment of the welding process, possibly even an online or inline monitoring the welding process.

A Particularly preferred expression of the arrangement within The nanoparticle to be provided in the joining region sees the Use of nanoparticles with a shape and size before, so that the nanoparticles through the interaction with the Laser radiation by way of the above cited coalescence and recrystallization to large particles with a size in the Convert micrometer range, causing the Plasmonenanregung stops and the forming weld in the joint area for visible light as almost completely transparent appears in appearance. Because in this case no plasmon excitation is more, is also no absorption maximum in the spectrum of visible light imperceptible. The relatively large particles in micrometer size cause only a scattering of light, causing the weld depending on the size and distance of the particles translucent until transparent acts.

For the application of nanoparticles within the joining area between the at least two joining partners, in principle can assume any component form, in particular also can be in foil form, are basically two different ways open. So can on the one hand the Nanoparticles as dissolved colloids within a solution and by means of a suitable wet coating method on the surface of at least one joining partner be applied. Another possibility sees a deposition of nanoparticles on the surface of at least one joining partner or, as the further remarks will show, on a carrier substrate by means of physical and / or chemical vapor deposition using vacuum technologies in front.

In the above-mentioned case of using wet coating methods, nanoparticles of different materials, preferably of gold, silver or copper or similar metals, metal alloys or metal oxides, having different particle sizes are commercially available which form a suspension in a liquid, for example in an organic solvent or a polymer solution. The suspension can be applied by brushing, spraying by means of a gravure printing method or an ink jet coating preferably on the surface of a joining partner, so that after drying of the so-called matrix liquid surrounding the suspended nanoparticles or by solution polymerization, a layer of substantially mutually isolated nanoparticles, the ever because they are separated by an organic solid medium. Such a layer formation is also known, for example, from the sol-gel technique to those skilled in the art. For the formation of plasmon excitations, it is particularly advantageous if the nanoparticles are embedded separately within the matrix layer embedding the nanoparticles. It is particularly preferred to produce the nanoparticle absorber layers that can be produced in this way with layer thicknesses of a few micrometers, preferably a maximum of 30 to 40 μm.

on the other hand However, nanoparticles can also be in the way of the aforementioned produce physical vapor deposition, such as by means of vacuum technical PVD process, thermal evaporation or sputtering, or by CVD methods, e.g. B. MOCVB organometallic chemical vapor deposition or by the combination of two this procedure.

So Most metals form during the vacuum engineering Deposition, for example, on a polymeric surface initially discontinuous island layers, where the size the nanoparticles by the amount of metal used in the metal evaporation or by a timely termination of the metal sputtering process can be targeted. In the context of such a vacuum coating method The nanoparticles grow directly on a polymeric surface a carrier substrate or a joining partner on. On the other hand, both individual components as well continuous films coated in this way with nanoparticles become. In particular, the shape and size can be the nanoparticles forming by deposition in the way of deposition thermal evaporation or sputtering by process parameters, such as process pressure, Substrate temperature and similar relevant, the evaporation process specifically set influencing process parameters. A decisive one Advantage of metallic nanoparticles as absorber material for the laser transmission welding is in the extremely high Effectiveness with which the nanoparticles through the Plasmonenresonanzanregung to convert absorbed light energy into heat energy and to deliver them directly to the polymer material surrounding the nanoparticles are able to. So it is perfectly sufficient by the thermal Vaporizing or sputtering deposited nanoparticles only in a layer isolated next to each other to arrange a sufficient Heat input, which is a melt of the nanoparticles surrounding polymer material causes.

About that In addition, in the context of vacuum vapor deposition or Sputtering masks are used, through which a deposition of the Nanoparticles on specifiable surface areas, for example. One Polymer surface can be applied, so that in this way ultimately any welding seam geometries, can be created in both the mm and the micron range. Of course it is also possible the deposition to make nanoparticles multilayered in this way also three-dimensional nanoparticle arrangements within the joining region to realize.

additionally for pure metal deposition, as described above, is also a combined deposition of metal and polymer material conceivable, For example by means of plasma polymerization or plasma sputtering. in this connection Both metal nanoparticles and polymer material on a Substrate surface deposited to form a thin polymer layer, which makes the nanoparticles matrix-like surrounds. It can by controlling the energy input Also layer produced and used as amorphous a-CH layers or so-called diamond-like carbon layers scarcely polymer properties demonstrate. Typical layer thicknesses of such hybrid layers, consisting of a polymer material and the nanoparticles are about 100 nm, but can also be made much thicker.

Also it is possible in a further embodiment the deposition of the metal nanoparticles by way of the above Combination of metal deposition and polymer deposition such so that the nanoparticle deposition exclusively on or under a thin polymer layer or polymer film or be applied spaced apart on both sides by the polymer film. For example, a polymer layer on the surface a joining partner deposited, on the further the Nanoparticles are applied, so the polymer layer is at suitable choice of the polymer used as a primer the respective joining partner, the different thermoplastic Polymers can exist. Are the nanoparticles in addition covered with a polymer layer, so the cover layer serve as a mechanical or chemical protective layer or accordingly be educated. In particular, the absorption behavior can be the individual nanoparticles and the associated plasmon resonance influenced by the material used, which is the nanoparticles surrounds like a matrix.

For example, it has been found that silver nanoparticles embedded in a thin polymer layer have better aging resistance as well as better adhesion to a corresponding polymer backing. In addition, due to only a very small layer thickness of the thus hybrid-shaped polymer layer, there are no disadvantages with the laser durchstrahlschweißen, whether in the context of the combination of two trained as foils joining partners or in the case of three-dimensional, designed as components joint partner. Particularly advantageous joining results could be achieved if the thin polymer layer containing or comprising the respective nanoparticles is selected from the same or a very similar material from which the two joining partners to be joined together also exist.

to Practical implementation of the solution according to Joining process, the surfaces of both Joining partner or at least the surface of a Joining partners are provided with nanoparticles. as it were Is it possible to have one between both joining partners? described above, enriched with nanoparticles or in the above manner combined with nanoparticles polymer layer to provide in the form of a so-called Schweißhilfsfolie. This can be done either by mere introduction between the two Join partners or by previous thermal Connect, preferably by means of lamination, with the surface at least one joining partner, in order in this way the following To simplify laser welding. The actual laser welding process, in which the joining area is specifically exposed to laser radiation and thereby melted, can advantageously supported by mutual compression of both joining partners become.

Also can the solution according to welding process to connect several join partners in such a way by several stacked superimposed, transparent to laser radiation, mostly of thermoplastic polymer materials existing joining partners, preferably in the form of films or components, are provided, between each of which the above described, nanoparticle-containing absorber materials introduced become. As the individual, each between two directly adjacent components introduced absorber layers are very thin, The laser beam from each absorber layer is not complete rather absorbs the individual joint areas successively, each with decreasing light output, due to the absorption occurring locally in each absorption layer, to penetrate. The individual transmitted by the laser beam in sequence Absorption layers are advantageously with different Absorbency is designed such that the upper absorption layers, penetrated by a largely unattenuated laser beam will have a lower absorption than those in the component or are arranged further down in the film stack. The respective Absorbency per absorption layer can be as above mentioned, through a series of measures individually be set, so for example by the choice of material, shape and size of the nanoparticles as well as by the Material choice of the polymer matrix surrounding the nanoparticles.

Also it is possible in a stack-shaped component assembly Joining areas with different absorption layers provide, each having different laser wavelengths absorb. This can be welded in a multiple Foil arrangement or at multiple times to be welded together Components individual joining areas independent of each other using different lasers, the light with different Emit wavelengths, be welded. hereby can structured welds, z. B. with interruptions for later filling processes within a multilayer structure.

With the solution according to the joining method The basis of laser transmission welding is a series connected by advantages. So it is possible in particular the absorption material layer to be provided within the joining area with very low layer thicknesses of 10 to 100 nm maximum 400 nm train, so the amount of foreign materials introduced - compared to the polymer material of the joining partners - between two join partners to be joined together low can be held. Due to the very high effectiveness, with which the irradiated laser energy in the joint area of the Nanoparticles absorbed and ultimately converted into heat can be, the polymer material of the joining partner in the particle environment is only locally heated and melted, whereby a very small heat affected zone is formed. The starting polymer of the respective joint partner is therefore only changed very locally, leaving one to cool down the welding seam accompanying internal material distortion very can be kept low.

By the possibility of adaptation of the plasmon resonance by the Material choice of nanoparticles and their size, Shape and arrangement as well as the material surrounding the nanoparticles to the wavelength of the laser radiation used in each case Laser systems are used in multiple technical fields already exist and are used, such as Neodymium YAG laser etc.

Depending on the intended use, it is possible to select the size and shape of the nanoparticles such that a color change in the welding region can be detected by interaction of the nanoparticles with the laser beam, for example with the aid of a spectrometer so that the quality of the image can be determined online by a transmission measurement forming weld joint can be determined. As part of a scheme, the laser power can be varied online to achieve the best possible welding result. Alternatively or in combination with the transmission measurement, it is also possible to carry out a reflection measurement at the location of the forming weld joint in order to carry out the quality check in the above sense.

Also allows the use of masks in the vacuum technology Deposition of the nanoparticles on the respective to be joined Surface of a joining partner or, as above described on a welding auxiliary foil the generation freely selectable weld geometries, so that individual curved or surface-expanded weld seam structures are feasible.

In the laser transmission welding method can be particularly advantageously used on transparent polymer films, for example for the Production of pneumatically stabilized membrane pads for Use roof and facade constructions. The welding the respective film can with the help of the solution according to Laser transmission welding process along individually spatially designed welds made be and not as previously only longitudinally straight running welds. Thus, that allows Solution-based joining process for architectural and design applications in Regarding the thickness, the patterning and crossovers of Weld seam geometries completely new design options.

The Solution-based method is already successful for joining two ETFE (ethylene tetrafluoroethylene copolymer) films each applied with thicknesses of 200 microns. Before the Applying the absorber layer were the respective film surfaces, which are brought into contact with each other, a corona treatment subjected. The following was by way of a plasma polymerization of Hexamethyldisilasan a kind of adhesion promoter layer with a layer thickness of 20 nm applied to by thermal evaporation of Gold the actual absorber layer in the form of gold nanoparticles was separated. As a protective layer are the gold nanoparticles by way of a further plasma polymerization with hexamethyldisilasan with a thickness of 20 nm has been coated.

The ETFE films contacted with each other were subsequently with an infrared laser at a wavelength of 808 nm irradiated, wherein the laser radiation from a on the absorber layer Focusing processing head emerged, at the same time the slides acted upon by a predeterminable pressing force. The used here Laser power was 25 watts.

in the Ways of a subsequent mechanical strength test the resulting weld could be shown that the tensile strength of at least half of the tensile strength corresponds to a thermal contact weld. Especially could be achieved a tensile strength, which is twice the Membrane voltage corresponds to the case of a foil pad internal pressure of 300 Pa occurs.

QUOTES INCLUDE IN THE DESCRIPTION

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Cited patent literature

• EP 0159169 [0006]
• - DE 4432081 A1 [0007]
• EP 126787 A1 [0008]
• - DE 19814298 A1 [0008]
• WO 00/20157 [0009]
• - DE 102004018547 A1 [0010]

Claims (19)

Method for joining at least two joining partners by means of laser transmission welding, in which the at least two joining partners which are at least partially transparent for laser radiation are brought into mutual central or direct surface contact and include at least one common joining area, which is acted upon by the laser beam, after it has passed through at least one Joining partner has at least partially passed through, and is absorbed in the joining region to a degree, so that forms a melt in the joining region, which leads to solidification to a material bond between the two joining partners, characterized in that provided by at least two joining partners joining area is contained in the nanoparticles, which are by way of light absorption surface plasmons capable of, which leads to the heating of the nanoparticles and ultimately to the formation of enamel within the joining region s. Method according to claim 1, characterized, that the nanoparticles are selected according to the following conditions become: - The nanoparticles have particle sizes which is smaller than the light wavelength of the light beam are, with the joining area is applied, and - the Nanoparticles have a plasmon resonance whose spectral Location with the light wavelength of the light beam at least partially overlapped. Method according to claim 2, characterized in that that the nanoparticles from the group of metals, their alloys and / or metal oxides. Method according to claim 3, characterized that as nanoparticles gold or silver is chosen. Method according to one of claims 1 to 4, characterized in that the nanoparticles containing Joining area is provided such that the nanoparticles single-layered or multi-layered or three-dimensionally distributed within be arranged of the joining area. Method according to one of claims 1 to 5, characterized in that the nanoparticles containing Joining area is provided such that the nanoparticles be arranged isolated within the joint area. Method according to one of claims 1 to 6, characterized in that the at least partially transparent Joining partners each consist of a polymer material, on or between them for surface contact surfaces provided or introduced the nanoparticles be made before the surface contact between two joining partners becomes. Method according to claim 7, characterized in that that the nanoparticles are prepared by a wet coating method, by physical vapor deposition or chemical vapor deposition on a surface of at least one joining partner be deposited. Method according to claim 7, characterized in that that the nanoparticles by means of a wet coating process or by physical or chemical vapor deposition deposited on at least one side on a carrier foil be, and that the carrier film between two joining partners is introduced. Method according to claim 9, characterized that provided with the nanoparticles carrier film to a surface of at least one joining partner is laminated. Method according to claim 8 or 9, characterized that as a wet coating process a two-dimensional order or a deposition of nanoparticles from a colloidal solution is selected, or that for the vapor deposition PVD-, (Evaporation, sputtering) or CVD method can be selected. Method according to claim 7, characterized in that that the nanoparticles in combination with a polymer deposition on a surface of at least one joining partner forming a polymer layer containing nanoparticles be deposited. Method according to one of claims 8 to 12, characterized in that the deposition of the nanoparticles the surface of at least one joining partner or takes place on the carrier film using a mask, by a predetermined area geometry for the surface area on which the nanoparticles are deposited be elected. Method according to one of claims 1 to 13, characterized in that at least three transparent joining partners are provided which include in a transmission direction of the laser beam at least two, each containing nanoparticles joining areas in pairs such that the at least two joining areas are penetrated by the laser beam successively , And that the nanoparticles are introduced according to type, number, arrangement shape and size in the respective joining region such that when exposed to the joining regions with the laser beam Surface plasmons are excited, which lead to the local melting of the joining areas. Method according to claim 14, characterized in that that the provision of the nanoparticles in the of the laser beam in Follow to enforced joining areas made in such a way is that at least one subsequent to be enforced by the laser beam Joining a greater degree of absorption has, as the already penetrated by the laser beam joining area. Method according to claim 14, characterized in that that the provision of the nanoparticles in the at least one laser beam in consequence to be enforced joining areas made in such a way that the spectral positions of the plasmon resonance of the nanoparticles, each contained in different joining areas are different from each other and that for surface plasmon excitation in the individual joint areas laser beams with different Wavelengths are used. Method according to one of claims 1 to 16, characterized in that as joining partner polymer films or thermoplastic films are used. Method according to one of claims 1 to 17, characterized in that during and / or after the Laserstrahlbeaufschlagung an optical transmission measurement or Reflection measurement performed at the joining area will be obtained at the readings that are a quality assessment the who adjusting in the way of laser transmission welding Joint connection are based. Method according to one of claims 1 to 18, characterized in that at least during Laserstrahlbeaufschlagung an optical transmission or reflection measurement at the joining area in which measured values are obtained which for online monitoring of the joining area Energy deposited by the laser beam can be used.